Since the pioneering by Karl Ziegler and Giulio Natta in the early 1950's on the polymerization of simple olefins, there has been intense interest in the application of early transition metal catalysts for the selective polymerization of inexpensive olefins. Following to Ziegler-Natta catalysts , metallocene catalysts were discovered in the late 1980's and resulted in numerous industrial processes for improving the properties of polyolefinic materials along with performance parameters. This field has been remarkably renewed with the use of catalysts based on early transition metals metallocene . Development of new catalysts with transition metals has played a substantial role in the fast-growing polyolefins industry. Improvement of new, better performing, less costly polyolefins has often been a result of catalyst development. However, polymerization processes of olefins, beside the requirement of higher activity catalyst to control the particle size, particle size distribution, and morphology of the resultant polyolefin are quite important. In the other words, success in these developments requires an appropriate integration of catalyst selections with reactor type and process parameters [3-5].
As is well-known, most polyolefinic materials are produced using transition metal- catalyzed olefin polymerization technology. While the multisited heterogeneous Ziegler–Natta catalysts represented by MgCl2-supported TiCl4 catalysts currently dominate the market, molecular catalysts (single-site catalysts) represented by group 4 metallocene catalysts and constrained geometry catalysts (CGCs) are gaining an increasing presence in the market (Figure 1) [4-9].
As DFT (Density Functional Theory) calculations performed on a model metallocene catalyst H2SiCp2ZrMe+ for ethylene polymerization (Figure 2) suggested that ethylene polymerization is a process that involves intense electron exchange between a ligand and a metal . Accordingly and following the great success of the metallocene catalysts, significant efforts have been directed toward the discovery and application of new, highly active, single-site catalysts (post-metallocene catalysts) [10,11].
These research efforts have led to the introduction of quite a few high-activity single-site catalysts based on both early and late transition metal complexes with various ligand environments [12-18]. In association with appropriate cocatalysts, many of these catalysts show ethylene polymerization activities that are superior or comparable to those seen with early group 4 transition metals metallocene catalysts. These post-metallocene catalysts can produce a wide array of distinctive polymers (e.g., hyper-branched PEs, ethylene–methyl acrylate copolymers, monodisperse poly(1-hexene)s, and block copolymers based on α-olefins), many of which were inaccessible using metallocene catalysts [3,16-24].
Since the ligand structure has a central role in determining the activity as well as the stereospecifity of these types of catalysts, and as shown in Figure 2, flexible electronic nature of a ligand is a key requirement for achieving high activity, the research based on the ligand oriented catalyst design concept has resulted in the discovery of a number of highly active catalysts for the polymerization of ethylene, which include: phenoxy-imine ligand early transition metal complexes (FI catalysts), pyrrolide-imine ligand group 4 transition metal complexes (PI catalysts), indolide-imine ligand Ti complexes (II catalysts), phenoxy-imine ligand group 4 transition metal complexes (IF catalysts), phenoxy-ether ligand Ti complexes (FE catalysts), imine-pyridine ligand late transition metal complexes (IP catalysts), and tris(pyrazolyl) borate ligand Ta complexes (PB catalysts) (Figure 3) [20,26-30].
In particular, bis(phenoxy-imine) group 4 metal catalysts, developed by Fujita [19–21] caused a new revolution in the field of catalytic olefin polymerization. These complex catalysts exhibit unique characteristics for production of new polymers that are not prepared by conventional Ziegler–Natta catalysts, as well as by ordinary metallocene-type catalysts . The key feature of these complexes is the incorporation of nonsymmetric bidenate or tridentates ligands that possess electronically flexible properties (e.g., phenoxy–cyclopentadienyl, phenoxy–imine, phenoxy–ether, phenoxy–pyridine, pyrrolide–imine, and indolide–imine). These complexes can typically combine with appropriate cocatalysts to form highly active catalysts for the polymerization of ethylene. Among these new complexes, bis(phenoxy–imine) early transition metal complexes (named FI Catalysts) are particularly versatile for olefin polymerization when activated (Figure 4) [20,21].
Although a large number of families of high-performance single-site catalysts have been developed thus far, improvements in some aspects of catalytic performance (e.g., temperature stability, precise control of chain transfer, comonomer sequence distribution control, precise control of polymer stereochemistry, and the ability to incorporate sterically encumbered monomers and polar monomers) are still required to achieve both greater control over polymer microstructures and extension of generic polyolefinic materials by introducing new monomer combinations .
2. Characteristics of FI catalysts
In 1997, researchers at Mitsui Chemicals introduced phenoxy–imine [O-N] ligand early transition metal complexes (now known as FI catalysts) for the controlled polymerization and copolymerization of olefinic monomers . Depending on the ligand design, the catalysts show different behaviors in ethylene and propylene polymerization, and the ligands strongly influence catalyst parameters such as activity, polymerization mechanism, and polymer properties including molecular weight. Extensively, FI catalysts, can polymerized ethylene with high efficiency, independent of the transition metals that are employed (Ti, Zr, Hf, etc.), showing the notable ability of phenoxy–imine ligands for efficient ethylene insertion.
The electronically flexible nature of the phenoxy–imine ligands may be responsible for these superior results. FI catalysts have the following structural and electronic features resulting in unique polymerization catalysis as well as formation of distinctive polymers [31-34].
2.1. Structure of FI catalysts
Since an FI catalyst contains two bidentate nonsymmetric phenoxy-imine ligands, it can potentially display five isomers from a to e (Figure 5) arising from the coordination modes of ligands in an octahedral configuration. X-ray analysis has established that, in the solid state, an FI catalyst normally exists as the isomer a, meaning, it has a
When FI catalysts possess extremely bulky groups on the imine-Ns (
In the other words, among the five possible isomers (Figure 5), the crystallographically determined structures of FI catalysts, adopt a configuration in which the shortest M-O bonds (M = group 4 transition metal) are positioned
As discussed, an important feature of these complexes is that the chlorines occupy mutually
Nevertheless, the DFT calculations suggest that the Zr–N bonds that lie on the same plane as the polymerization sites expand and shrink according to the reaction coordinate of the ethylene insertion (2.23–2.34 Å), while the Zr–O bond length remains virtually unchanged (Figure 7). From studying these results, we believe that this variable Zr–N bond length (which facilitates a smooth and flexible electron exchange between the metal and the ligands) and the
In general, FI ligands can be obtained in practically quantitative yields by the Schiff-base condensation of
These phenol derivatives and amines are easily synthesized, and thus have a rich inventory of commercially available compounds. Therefore, FI catalysts have a wide range of catalyst design possibilities, which is the most important feature of FI catalysts.
As a result of this feature, FI catalysts have enormous and diverse ligand structures with a wide variety of substituents, including O, S, N, P and halogen-based functional groups. This enormous structural diversity of FI catalysts has given rise to unprecedented olefin polymerization catalysis and unique polymer formation [34,35,37].
2.2. Electronic characteristics of FI catalysts
In general, the discovery of new olefin polymerization catalysts seems to be a time-intensive, trial-and-error process, with no guarantee of success. However, theoretical calculations on ethylene polymerization with a metallocene catalyst have provided clues about how to design highly active catalysts. Polymerization olefin catalyst components has been depicted in Figure 8 including a metal, ligand(s), a growing polymer chain, a coordinated olefin, and a cocatalyst [40-42].
As can bee seen in Figure 8, FI catalysts are heteroatom [O-, N] coordinated early transition metal complexes, which makes FI catalysts different from group 4 transition metals metallocene catalysts that possess cyclopentadienyl (Cp) carbanion-based ligands. Because of the coordination of heteroatom-based [O-,N] ligands that are more electron withdrawing than Cp carbanion-based ligands, the catalytically active species originating from FI catalysts possess a highly electrophilic nature relative to the active species derived from group 4 transition metals metallocene catalysts .
As explained before, DFT calculations using a cationic metallocene complex (H2SiCp2ZrMe+) as a model suggest that olefin polymerization is a process that involves intense electron exchange between a ligand and a metal. Since all transition metals (even Mn and Fe) potentially possess the capability of olefin insertion, it is believed that ligands with an electronically flexible nature are a prime requisite for achieving high activity. Therefore, the combination of a transition metal and electronically flexible ligand(s) can yield a highly active olefin polymerization catalyst. Electronically flexible ligands typically possess well-balanced electron donating and withdrawing properties, indicated by a small energy gap between HOMO (the highest occupied molecular orbital) and LUMO (the lowest unoccupied molecular orbital). Therefore, they are capable of receiving electrons from the coordinating olefin through the metal atom and of releasing electrons whenever required to expedite the olefin insertion process. As a result, it can be realized that it is the ligands that play the predominant role in polymerization catalysis among the typical components of the catalyst, and that electronically flexible ligands combined with transition metals form high-activity catalysts when activated as long as the potentially active species possesses an appropriate electron deficiency (10- to 16-electron species) as well as a pair of available
FI catalysts have another distinctive feature verses metallocenes, that is, M-ligand bonding characteristics. The presence of FI ligands with heteroatom donors renders the complex more electrophilic, a requirement for an active olefin polymerization catalyst, as supported by DFT calculations, which demonstrated that the Mulliken charge at the metal center (in au) in three cationic species increases in the following order, (C5H5)2TiMe+ < CGC (Me2Si(C5Me4)-(
Furthermore, DFT calculation revealed that anionic phenoxy-imine chelate ligand possess a smaller energy gap between HOMO and LUMO than a Cp ligand (C5H5-) and thus presumably display electronically more flexible properties than the Cp ligand (Figure 10) . Small energy gap between HOMO and LUMO represents well-balanced electron-donating and withdrawing properties which are anticipated to expedite ethylene polymerization process .
According to the ligand-oriented catalyst design concept, Fujita and co-workers were designed transition metal complexes incorporating nonsymmetric and electronically flexible ligands as candidates for high-activity catalysts . These complexes were examined as catalysts for the polymerization of ethylene with MAO as the cocatalyst at 25 °C under atmospheric pressure. As a result, a number of complexes were found to be highly active catalysts for the polymerization of ethylene. Polymerization results indicate that phenoxy–imine ligands can produce highly active catalysts when attached to a variety of transition metals, supporting the idea that ligands play the predominant role in polymerization catalysis and that electronically flexible ligands can engender highly active catalysts. A remarkable feature of phenoxy–imine ligated early transition metal complexes is that they possess ligands that can be readily tailored synthetically from both an electronic and steric point of view, and thus possess a wide range of possibilities in terms of catalyst design [39-41].
3. Catalytic properties of FI Catalysts for ethylene polymerization
One of the unique characteristics of FI catalysts, due to its flexible structure, is that the minor change in the structure of the FI catalysts leads to the major changes in activities as well as molecular weight and other characteristics of the resulting polymer. The flexibility refers to the simple Schiff base condensation of the aniline and salicylaldehyde derivatives which can produce a wide range of phenoxy–imine ligands. As depicted in Fig. 11, FI catalysts can be synthesized by treating the phenoxy-imine ligands and transition metal halids to furnish FI catalysts (Figure 11) .
3.1. Influence of alkyl substitutions on the catalyst behavior
Ethylene polymerization revealed that FI catalyst requires steric bulk ortho to the phenoxy-O in order to exhibit high ethylene polymerization activity [42,43]. The steric bulk is thought to afford steric protection toward the anionic phenoxy-O donors from coordination with Lewis acidic compounds such as MAO or from another molecule of the catalytically active cationic species, which are supposed to be highly electrophilic, and the inducement of effective ion separation between the cationic active species and an anionic cocatalyst, resulting in enhanced catalytic activity . Moreover, Cavallo and co-workers  have proposed a site-inversion mechanism that can explain the unexpected syndiospecificity exhibited by the Ti-based FI complexes with
Ethylene polymerization via FI catalysts has been shown that the increase in the steric bulk of the R1 substituent resulted in the marked enhancement in both the catalytic activity and the product molecular weight . The increase in the catalytic activity as a result of introducing sterically-hindered substituent at the R1 position may be attributed to the fact that the steric bulk of the R1 substituent plays an essential role in the ion separation between the cationic active species and the anionic cocatalyst. The effective ion separation will provide more space for polymerization and, in addition, enhances the degree of unsaturation associated with the catalytically active cationic species. On the other hand, the increase in the product molecular weight may be ascribed to the fact that the steric congestion exerted by the R1 substituent diminishes the rate of chain termination .
For instance, FI catalyst bearing a hydrogen at the R1 position (R2 = R3 = H) gave polyethylene with an
The steric bulk of the R2 substituent also has a significant influence on the catalytic performance of the complexes but differently compared with the R1 substituent . A Ti-based FI catalyst bearing a methyl at the R2 position demonstrated an activity of 301 kg-PE/mol-cat h and gave polyethylene with
Eventually, the substituent at the R3 position exercised an effect on both the catalytic activity and the product molecular weight but not significantly, presumably because of the location of the R3 position being far from the polymerization center [48,49].
Not only catalyst activity is affected by substitutions, but even thermal stability of the catalyst can be affected by electronic aspects of the substitutions. For instance, the introduction of an electrondonating methoxy group
4. Polymerization of higher α-olefin with FI catalyst
Catalyst systems based on bis(phenoxy-imine) complexes of Ti(IV), Zr(IV) and MAO are effective catalysts for polymerization of ethylene and propylene [19,33,34,38,50,51-54]. Detailed 13C NMR analysis of end-groups in polypropylene prepared with several catalysts of this type showed unusual chemical and regio-effects [52,55].
Phenoxy-imine ligands in complexes contain alkyl substituents in the 2nd and the 4th positions of their phenyl rings, they produce moderately syndiospecific catalysts [55,56]. Detailed investigations of the Ti and Zr complexes with the same ligands showed a surprising difference in the chemistry of polymerization reactions.
Active centers of the highest stereospecificity are produced when the aryl group attached to the nitrogen atom in the phenoxyimine ligand is C6F5 (Figure 3) and the phenyl group attached to the oxygen atom carries bulky t-Bu or SiMe substituents in the ortho position to the C–O bond. The [rrrr] content in polypropylene produced with these complexes at 0–20 0C can reach 0.95–0.96 corresponding to a very high probability of syndiotactic linking, ~0.99 [55-58]. However, a replacement of these substituents with two bromine or two iodin atoms changes the regiocontrol to primary and the stereocontrol to moderately isospecific, the [mm] values of polypropylene prepared at 0 0C increases from 0.17 for dialkyl-substituted complexes to 0.73 for diiodo-substituted complexes .
Bis(phenoxy-imine) complexes of Ti(IV) and Zr(IV) combined with MAO or with common organoaluminum compounds form effective catalysts for polymerization of ethylene, 1-alkenes, and for ethylene/1-alkene copolymerization. The productivity of catalyst systems containing the Ti complexes and MAO in ethylene polymerization reactions at 25–75 0C can reach 2,000–4,000 kg/mol Ti. h [34,52,55,59-61].
Bis(phenoxy-imine) complexes of Ti (IV) containing C6F5 groups attached to the N atom in each bidentate ligand form catalyst systems with very low chain transfer rates. They copolymerize ethylene with propylene and higher 1-alkenes under living-chain conditions (Mw/Mn = 1.07–1.19) at temperatures as high as 500C [52,55,62,63] and they are suitable for the synthesis of alkene block-copolymers. These catalysts were employed for the synthesis of various alkene diblock- and triblock-copolymers [48,52,55,63].
Polypropylene produced with combinations of the aldimine Ti complexes and MAO or AlR3-[Ph3C]+ [B(C6F5)4]- as cocatalysts under moderate conditions also has a very narrow molecular weight distribution [52,55,61,62]. The stereospecificity of catalyst systems based on bis(phenoxy-imine) complexes depends on the type of substituents in the ligands (substituents R in Fig. 11). When R = H or Me, the catalysts produce polypropylene with a predominantly syndiotactic structure. However, complexes of the same type bearing two bromine or two iodine atoms in the 2nd and the 4th positions of the phenyl groups produce moderately isotactic polypropylene with [mm] from ~0.5 to 0.73, depending on reaction temperature, and the dichloro-substituted complex produces atactic polypropylene .
Bis(phenoxy-imine) complexes of Ti(IV) activated with ion-forming cocatalysts instead of MAO, such as Ali-Bu3-[CPh3]+ [B(C6F5)4]- are efficient single-center catalysts for polymerization of higher 1-alkenes, 1-hexene, 1-octene, 1-decene, and 4-methyl-1-pentene. The catalysts have very high activity and produce regioand stereo-irregular polymers with very high molecular weights, <1.4×106 .
The Zr bis(phenoxy-imine) complex was used for the synthesis of an ethylene/1-octene copolymer with a low 1-octene content, and a complex of Hf with a tridentate ligand was used for the synthesis of an ethylene/1-octene copolymer with a high 1-octene content.
The flexibility of the FI catalysts allows for the making of new polymers which are difficult or impossible to prepare using group 4 metallocene catalysts. For example, it is possible to prepare low molecular weight (Mv ~103) polyethylene or poly(ethylene-copropylene) with olefinic end groups, ultra-high molecular weight polyethylene or poly(ethylene-co-propylene), high molecular weight poly(1-hexene) with atactic structures including frequent regioerrors, monodisperse poly(ethylene-co-propylene) with various propylene contents, and a number of polyolefin block copolymers [e.g., polyethylene-b-poly(ethylene-co-propylene), syndiotactic polypropylene-b-poly-(ethylene-co-propylene), polyethylene-b-poly(ethylene-co-propylene)-b-syndiotactic polypropylene. These unique polymers are predictable to possess novel material properties and uses .
5. Living polymerization with FI catalyst
The synthesize polymers with completely defined structures is a goal. Living polymerization is known to control some elements like as degree of polymerization, chain-end structures, stereochemistry, especially molecular weight and chain-end structures of polymer. Although there have been a number of transition metal catalysts which can polymerize ethylene or α-olefins in a living fashion [66-68] there are few catalysts that are useful for both ethylene and α-olefins. Besides, most catalysts require a low polymerization temperature, usually below room temperature, to suppress chain termination and therefore exhibit low activities and insufficient polymer molecular weights. The titanium FI catalyst bearing a perfluorophenyl group as R (Figure 12) with MAO exhibited living polymerization with ethylene even at 50 0C to afford high molecular-weight polymer (Mw=424×103) having a narrow molecular weight distribution (Mw/Mn=1.13). This catalyst exhibits living polymerization behavior over a wide range of temperature .
There is a clear difference in polymerization results depending on the fluorine substitution patterns. First of all, living polymerizations proceed only when at least one fluorine is located in the 2,6-positions of R-phenyl group (Figure 12). Second, the activity of living systems is considerably lower than that of non-living systems. Finally, the activity increases with the number of fluorine atoms in both living and non-living systems. It is reasonable that electron-withdrawing fluorines enhance the electrophilicity and consequently the reactivity of the active centers. The ortho-fluorine substituent effect represents a novel strategy for the design of a new transition metal complex for living olefin polymerization .
Interestingly, a titanium FI catalyst having a chlorine at the 2-position of the R-phenyl group instead of fluorine, bis[N-(3-t-butylsalicylidene)-2-chloroanilinato]titanium(IV) dichloride, also promoted ethylene polymerization at 25 0C to produce polyethylene having a narrow molecular weight distribution (Mw/Mn=1.23), implying that the interaction with β-hydrogen is potentially achieved by any substituent possessing lone-pair electrons. Propylene polymerization with the above complex (Figure 12) at room temperature also turned out to be living and produced polypropylene with a controlled molecular weight, a narrow molecular weight distribution (Mw/Mn=1.07-1.14), and surprisingly high syndiotacticity (rr=87%, 98%) .
Mitani et al, introduce a Ti-FI catalyst having fluorine- and trimethylsilyl-containing ligands, which polymerizes propylene above room temperature to form highly syndiotactic monodisperse PPs with extremely high
Kinetic studies of ethylene polymerization reactions  and propylene polymerization reactions  with FI catalysts demonstrated that all features typical for living-chain reactions are present when these reactions are carried out at 250C. The catalyst activity remains constant for over 1 hour in the ethylene polymerization reactions and for 3 hours in the propylene polymerization reactions and it very slowly decreases after that. The molecular weight increases with reaction time in a nearly linear manner in the same time ranges, and the molecular weight distributions of the polymers remain narrow, Mw/Mn =1.07-1.10. The value of the propagation rate constant for ethylene polymerization reaction at 250C was ~1,400–1,900 M-1.s-1, it is comparable to the same value in metallocene catalysis .
The syndiospecific polymerization of propylene with this types of catalyst also exhibits kinetic features of living-chain polymerization reactions [52,55]. Both the polymer yield and the molecular weight of polypropylene produced at 0 0C increase nearly proportionally to the reaction time, and the molecular weight distribution of the polymer remains narrow (Mw/Mn =1.08–1.11) . Kinetic parameters of the propylene polymerization reactions at 0-25 0C are: kp = 0.05–0.06 M-1.s-1, [C]/[Ti] = 0.4–0.6% [52,71]. However, when the same complex contains 3,5-difluoro-substituted benzene rings, chain transfer reactions occur much more readily and the polymer has the typical molecular weight distribution characteristics of a material synthesized with a single-center catalyst, Mw/Mn ~2.5 .
Polymerization reactions with Ti diamide-based catalysts: Low-temperature propylene polymerization reactions with a Ti diamide complex LTiMe2 activated with MMAO or with silica- and alumina-supported MMAO give an interesting example of long-term living-chain reactions. These catalysts are very stable kinetically at 0 0C and the Mn value of the produced polymers increases with time in a linear manner for over 30 minutes resulting in the formation of atactic polymers of a very high molecular weight, with Mn ~1.5×106. The kp value for the homogeneous catalyst system is ~5 M-1.s-1 at 0 0C and when MMAO is supported on silica (this step increases the acidity of Al atoms in MMAO), the kp value increases to ~20 M-1.s-1 [72,73].
6. Modification of the FI catalysts
Fujita group at Mitsui Chemicals discovered the fluorinated Ti–FI catalysts that can promote unprecedented living ethylene and propylene polymerization, resulting in the formation of functionalized polymers and block copolymers from ethylene, propylene, and higher α-olefins . Coates  and Sakuma  reported that fluorinated Ti–FI catalysts are capable of mediating the highly controlled, thermally robust living polymerization of ethylene and propylene. Electronic attractive interaction between a fluorinated phenoxy-imine ligand and a growing polymer chain has significant effects on the catalytic properties of Ti–FI catalysts [59,74,75]. Additionally, the presence of electron withdrawing fluoro substituents on aniline is considered to be highly beneficial for increasing the catalyst activity. Ishii and coworkers described that introduction of electron-withdrawing F atoms on the ligand structure results in an increase in metal–carbon reactivity leading to reduced activation energy for ethylene insertion .
Although the catalytic behavior of ethylene and propylene polymerization, as well as ethylene–propylene copolymerization, using fluorinated Ti–FI complexes are extensively described in literature [77-79], but less attention has been paid to the fluorinated Zr–FI complexes. Recently, Zohuri and coworkers have reported the catalytic properties of a fluorinated Zr–FI catalyst in ethylene polymerization (Figure 13) .
The synthesized catalyst could produce polyethylene with high molecular weight (Mv=1.39 ×106) which is surprisingly higher in comparison with the similar non-fluorinated FI catalysts [33,42] indicating the dramatic electronic effect of
Additionally, a highly active Zr-based FI catalyst of bis[N-(3,5-dicumylsalicylidene)cyclohexyl-aminato]zirconium(IV) dichloride has been synthesized and used for polymerization of ethylene by Zohuri et al . The synthesized catalyst by changing the phenyl group on the imine nitrogen of FI catalyst (Fig. 11, R2) to a cyclohexyl group exhibited enhanced activity, may be due to the electron-donating effects of an aliphatic group at the R2 position. The prepared FI catalyst displayed a very high activity of about 3.2×106 g PE/mmol Zr. h in ethylene polymerization at the monomer pressure of 3 bars. Despite such high activity, this catalyst showed a short lifetime .
Some complexes with ligands based on naphthalene carbaldehydes having a hydroxy group in the ortho position with respect to the aldehyde group were described [81,82], but no data on their catalytic activity were given. Ahmadjo and coworkers  used 2-hydroxynaphtaldehyde instead of salicylaldehyde for the preparation of naphthoxy-imines as ligands and three FI-like Zr-based catalysts, Bis[1-[(phenylimino)methyl]-2-naphtholato]zirconium(IV) dichloride (1), Bis[1-[(mesitylimino)methyl]-2-naphtholato] zirconium(IV) dichloride (2) and Bis[1-[(2,6-diisopropylphenyl)imino] methyl-2-naphtholato]zirconium(IV) dichloride (3) were prepared by changing the ligand from salicylaldehyde imine ligand, to 2-hydroxynaphthalene-1-carbaldehyde imine ligand and used for polymerization of ethylene (Figure 14) . It has been reported that introducing the sterically bulky isopropyl groups enhances molecular weight of the resulting polymer through destabilization of β–agostic interaction due to the steric repulsion between β–hydrogen of the growing polymer and isopropyl leading to decrease the β–H elimination .
The transition state for β-hydride elimination requires the overlapping of a σ C-H orbital with an empty d orbital of the metal, and the two carbon adjacent to the metal and β-hydrogen must be on the same plane containing the metal between the two phenoxy-imine kelates. Therefore, the energy of the conformation needed for β-hydride elimination increases with increase of steric hindrance around the metal [83,84]. In the catalyst containing bulky isopropyl group phenyl ring on the N (Figure 14), it seems that β-carbon of polymer chain is not easily accommodated in the plane because of the steric interaction between naphthoxy-imine ligands of the catalyst and β-H of the growing polymer chain (Figure 15). It can be concluded that the sterically bulky substituents on the aniline ring of the naphthoxy-imine ligands cause a strong suppression of the both β-hydride elimination and β-hydride transfer to monomer leading to increase the molecular weight of the resulted polymer .
Plurality of the fused aromatic rings on the N atom of the imine in the catalyst structure affected the polymerization activity and molecular weight of the resulting polymer as well. It has been reported that changing of ligand from FI-type single aryl substituted on the N atom of imine to further aromatic fused rings, enhances the steric hindrance of the catalyst which resulted in diminishing the catalyst activity in comparison with FI catalysts including single aryl substituted on the N. However, this replacement could increase the molecular weight of the polymer obtained. It is presumable that rigidity of the catalyst structure, sterically causes low β-hydride transfer through destabilization of β–agostic interaction. The Mv values of the obtained polymer using the catalyst containing naphtholato group were higher than the obtained polymer using the catalyst containing anilinato group (Fig. 15). The increase in Mv values is referred to the steric repulsion between a β-hydrogen of growing polymer and aromatic fused rings on the imine-N which could diminish β-hydride elimination through destabilization of β–agostic interaction [53,85].
Furthermore, Damavandi et al. showed that polydispersity can remarkably increase with time which reveals that the system starts to deviate from pure living behavior . Although a linear dependence between the polymerization time and the molecular weight was observed indicating for living behavior, but the polydispersity was broadened with the time (Figure 17). The reason can be that either the catalyst is not truly living over the full polymerization time or that the single-site system turns into a multi-site system due to heterogenization of the system. This phenomenon could be comparable with self-immobilization of single site catalysts that has been a subject of interest . Similar result has been reported already by Ivanchev et. al . The capture and blocking of active sites by the grown polymer after a certain polymerization time have been suggested.
Also, Sandaroos and coworkers reported the synthesis and structure of novel Ti complex having a pair of chelating aminotropone [O–N] ligand . Experimental as well as theoretical studies show that the active species derived from bis(aminotropone) Ti catalyst normally possess higher electrophilicity nature compared with those produced using bis(phenoxyimine) Ti complexes (Ti–FI catalysts) (Figure 18) .
Ahmadjo et al.  Studied ethylene polymerization using FI catalysts in the presence of different amount of hydrogen. They reported that the polymerization activity can be increased with increasing the hydrogen concentration due to the fast hydrogenation of sterically more hindered and less reactive intermediates such as those resulting from 2,1-insertions (Figure 19) .
Isomerization is possible when the polymer chain at the Zr center undergoes β-hydride elimination forming an intermediate of olefin hydride complex and the olefin reinserts in a 2,1-manner into the Zr–hydride bond before insertion of the next monomer takes place. Consequently, methyl branches are formed (Figure 19). The new Zr-C bond is expected to be more hindered and less reactive for further monomer insertion which can be reactivated by hydrogen. As it is shown in Figure 19, in the presence of hydrogen, a dihydrogen complex is formed in the first step. This intermediate can subsequently form a hydride cation and a saturated alkyl chain, which is ejected from the active site. A new ethylene monomer can be inserted into the hydride cation structure and a new polymer chain starts to grow .
Additionally, 2,1-reinsertion of short olefin branches, terminated by β-H elimination which are still capable to be coordinated to the active centers, is probable. As it is shown in Figure 19, in the presence of hydrogen, the resulting sterically more hindered and less reactive intermediate undergoes fast hydrogenation to form hydrid cation which is susceptible to start new ethylene polymerization. However, it has been suggested that the catalyst structure limits the hydrogen role during the polymerization specifically in the latest ligand-oriented catalysts .
7. Immobilizing polymerization catalysts
The cocatalysts for bis(phenoxy-imine)Zr and Ti complexes are generally MAO (methylaluminoxane),
Up to now, several highly active transition metal complexes including metallocenes with MgCl2-based activator catalyst systems, often introduced as MgCl2-supported catalyst systems, have been reported [90,91]. These catalyst systems normally give polymers with broad molecular weight distributions.
MgCl2 may work as an activator for the bis(phenoxy-imine)Ti complexes since these complexes possess O and N heteroatoms in the ligands, which are capable of electronically interacting with MgCl2. Thus, researcher decided to investigate MgCl2 as an activator for the bis(phenoxy-imine)Ti complexes in the hope of developing high performance catalysts based on these complexes [73,92].
At first dealcoholysis of a MgCl2
The complexes with MgCl2
It is of great significance that the activities obtained using MgCl2
Moreover, Bis(phenoxy-imine) V complex in association with MgCl2/RmAl(OR)n demonstrate high activities at elevated temperatures (75 0C, 65.1 kg-PE/(mmol-cat h), atmospheric ethylene pressure) and a thermally robust single-site V-based olefin polymerization catalysts. All of the V compounds with MgCl2/EtmAl(OR)n provided very high molecular weight PEs (Mv > 5,000,000) for which we are unable to determine the molecular weights and molecular weight distributions using GPC analyses. All of the polyethylenes formed from the MgCl2/RmAl(OR)n systems display good polymer morphology, indicating that complexes are heterogenized on the surface of the MgCl2/RmAl(OR)n. These results suggest that MgCl2/RmAl(OR)n not only works as an excellent cocatalyst, but is also a good support for phenoxy-imine ligated V complexes .
Xu et al reported Bis(phenoxy-imine) zirconium catalyst, bis-[
Ethylene polymerization by titanium complex having two phenoxy-imine with different supports and solvents has been investigated by Srijumnong et al . The catalytic activity depended on supports used, and especially on the types of solvent medium. For the supported system, catalytic activities decreased in the following order: TiO2 >TiO2-SiO2 > SiO2. This can be attributed to the strong interaction of the TiO2 with dried MMAO (dMMAO) and the larger amount of dMMAO present on the TiO2 than other supports.
Zhang et al. reported self-immobilized titanium and zirconium complexes with allyloxy substituted phenoxy-imine ligands as well as their catalytic performance for ethylene polymerization. The results of ethylene polymerization showed that the self-immobilized titanium (IV( and zirconium (IV) catalysts kept high activity for ethylene polymerization. SEM showed the immobilization effect could greatly improve the morphology of polymer particles to afford micron-granula polyolefin as supported catalysts. Polymer produced by self-immobilized catalysts had broader molecular weight distribution (3.5–19.2), while polymer produced by titanium and zirconium complexes free from allyloxy groups had very narrow molecular weight distribution (<3.0) in most case .
Brinzingger H. H. Fisher D. Mulhaupt R. Rieger R. Waymouth R. M. 1995Stereospecific Olefin Polymerization with Chiral Metallocene Catalysts. Angew. Chem. Int. Eng. 34 1143 1170
Kaminsky W. 1999Metalorganic Catalysts for Synthesis and Polymerization. Springer-Verlag, Heidelberg.
Zohuri G. H. Damavandi S. Sandaroos R. Ahmadjo S. 2011Ethylene Polymerization Using Fluorinated FI Zr-Based Catalyst. Polym. Bull. 66 1051 1062
Kaminsky W. 2005in Handbook of Polymer Synthesis, 2nd ed. Kricheldorf H, Nuyken O, Swift G, Eds. Marcel Dekker, New York, 1 73
Kuran W. 2001Principles of Coordination Polymerization, Wiley, New York.
Moor EP, 2003Polypropylene Handbook, Hanser; Munich, Germany.
Resconi L. Cavallo L. Fait A. Piemontesi F. 2000Selectivity in Propene Polymerization with Metallocene Catalysts. Chem. Rev. 100 1253 1345
Wang B. 2006Ansa-Metallocene Polymerization Catalysts: Effects of the Bridges on the Catalytic Activities. Coord. Chem. Rev. 250 242 258
Irwin LJ, Miller SA 2007Catalyst System for High Activity and Stereoselectivity in the Homopolymerization and Copolymerization of Olefins. U.S. Patent 7214749.
Yoshida Y. Matsui S. Fujita T. 2010FI Catalysts: Unique Olefin Polymerization Catalysis for Formation of Value-added Olefin-based Materials. Journal of the Japan Petroleum Institute, 53: (3), 111-129.
Kaminsky W. 2004The Discovery of Metallocene Catalysts and Their Present State of the Art. J Polym. Sci. Part A. 42 3911 3921
Gibson VC, Spitzmesser SK 2003Advances in Non-Metallocene Olefin Polymerization Ccatalysis. Chem. Rev. 103 283 315
Britovsek GJP, Gibson VC, Wass DF 1999The Search for New-Generation Olefin Polymerization Catalysts: Life Beyond Metallocenes. Angew. Chem. Int. Ed. 38 428 447
Baumann R. Davis W. M. Schrock R. R. 1997Synthesis of Titanium and Zirconium Complexes that Contain the Tridentate Diamido Ligand, [((t-Bu-d6)N-o-C6H4)2O]2- ([NON]2-) and the Living Polymerization of 1-Hexene by Activated [NON]ZrMe2. J. Am. Chem. Soc. 119 3830 3831
Nomura K. Sagara A. Imanishi Y. 2002Olefin Polymerization and Ring-Opening Metathesis Polymerization of Norbornene by (Arylimido)(Aryloxo)Vanadium(V) Complexes of the Type VX2(NAr)(OAr¢). Remarkable Effect of Aluminum Cocatalyst for the Coordination and Insertion and Ring-Opening Metathesis Polymerization. Macromolecules 35 1583 1590
Johnson L. K. Killian C. M. Brookhart M. 1995New Pd(II)- and Ni(II)-Based Catalysts for Polymerization of Ethylene and α-Olefins. J. Am. Chem. Soc. 117 6414 6415
Quijada R. Rojas R. Bazan G. Komon Z. J. A. Mauler R. S. Galland G. B. 2001Synthesis of Branched Polyethylene from Ethylene by Tandem Action of Iron and Zirconium Single Site Catalysts. Macromolecules 34 2411 2417
Azoulay JD, Bazan GC, Galland GB 2010Microstructural Characterization of Poly(1-hexene) Obtained Using a Nickel R-Keto-β-diimine Initiator. Macromolecules 43 2794 2800
Terao H. Ishii S. Mitani M. Tanaka H. Fujita T. 2008Ethylene/Polar Monomer Copolymerization Behavior of Bis(phenoxy-imine)Ti Complexes: Formation of Polar Monomer Copolymers. J. Am. Chem. Soc. 130 17636 17637
Suzuki Y. Terao H. Fujita T. 2003Recent Advances in Phenoxy-Based Catalysts for Olefin Polymerization. Bull. Chem. Soc. Jpn. 76 1493 1517
Furuyama R. Saito J. Ishii S. I. Mitani M. Tohi Y. Makio H. Matsukawa N. Tanaka H. Fujita T. 2003Ethylene and Propylene Polymerization Behavior of a Series of Bis(Phenoxy-imine)Titanium Complexes. J. Mol. Cat. A. 200 31 42
Mecking S. Johnson L. K. Wang L. Brookhart M. 1998Mechanistic Studies of the Palladium-Catalyzed Copolymerization of Ethylene and α-Olefins with Methyl acrylate. Journal of the American Chemical Society, 120 5 888 899
Liu W. Malinoski J. M. Brookhart M. 2002Ethylene Polymerization and Ethylene/Methyl 10-undecenoate Copolymerization Using nickel(II) and Palladium(II) Complexes Derived from a Bulky P,O Chelating Ligand. Organometallics, 21 14 2836 2838
Sun J. Shan Y. Xu Y. Cui Y. Schumann H. Hummert M. 2004Novel Cyclohexyl-Substituted salicylaldiminato-Nickel(II) Complex as a Catalyst for Ethylene Homopolymerization and Copolymerization. J. Polym. Sci. Part A, Polym. Chem. 42 23 6071 6080
Matsugi T. Matsui S. Kojoh S. Takagi Y. Inoue Y. Nakano T. Fujita T. Kashiwa N. 2002New Titanium Complexes Bearing Two Indolide−Imine Chelate Ligands for the Polymerization of Ethylene. Macromolecules, 35 4880 4887
Yoshida Y. Mohri J. Ishii S. Mitani M. Saito J. Matsui S. Makio H. Nakano T. Tanaka H. Onda M. Yamamoto Y. Mizuno A. Fujita T. 2004Living Copolymerization of Ethylene with Norbornene Catalyzed by Bis(Pyrrolide−Imine) Titanium Complexes with MAO. J. Am. Chem. Soc. 126 12023 12032
Suzuki Y. Inoue Y. Tanaka H. Fujita T. 2004Phenoxyether Ligated Ti Complexes for the Polymerization of Ethylene. Macromol. Rapid Commun. 25 493 497
Suzuki Y. Tanaka H. Oshiki T. Takai K. Fujita T. 2006Titanium and Zirconium Complexes with Non-Salicylaldimine-Type Imine-Phenoxy Chelate Ligands: Syntheses, Structures, and Ethylene-Polymerization Behavior. Chem. Asian J. 1 878 887
Matsugi T. Fujita T. 2008High-Performance Olefin Polymerization Catalysts Discovered on the Basis of a New Catalyst Design Concept. Chem. Soc. Rev. 37 1264 1277
Fujita T. Tohi Y. Mitani M. Matsui S. Saito J. Nitabaru M. Sugi K. Makio H. Tsutsui T. 1998Olefin Polymerization Catalysts, Transition Metal Compounds, Processes for Olefin Polymerization, and Alpha-Olefin/Conjugated Diene Copolymers. EP Patent 0874005.
Matsugi T. Fujita T. 2008High Performance Olefin Polymerization Catalysts Discovered on the Basis of a New Catalyst Design Concept, Chem. Soc. Rev. 37 1266 1277
Tohi Y. Nakano T. Makio H. Matsui S. Fujita T. Yamaguchi T. 2004Polyethylenes Having Well-Defined Bimodal Molecular Weight Distributions Formed with Bis(phenoxy-imine) Zr Complexes, Macromol. Chem. Phys. 205 1179 1183
Matsui S. Mitani M. Saito J. Tohi Y. Makio H. Matsukawa N. Takagi Y. Tsuru K. Nitabaru M. Nakano T. Tanaka H. Kashiwa N. Fujita T. 2001J. Am. Chem. Soc. A Family of Zirconium Complexes Having Two Phenoxy−Imine Chelate Ligands for Olefin Polymerization, 123 6847 6856
Tohi Y. Makio H. Matsui S. Onda M. Fujita T. 2003Polyethylenes with Uni-, Bi-, and Trimodal Molecular Weight Distributions Produced with a Single Bis(phenoxy−imine)zirconium Complex. Macromole. 36 523 525
Strauch J. Warren T. H. Erker G. Fröhlich R. Saarenketo P. 2000Formation and Structural Properties of Salicylaldiminato Complexes of Zirconium and Titanium. Inorg. Chim. Acta. 300-302: 810-821.
Johnson, AL, Davidson MG, Lunn MD, Mahon MF 2006Synthesis, Isolation and Structural Investigation of Schiff-Base Alkoxytitanium Complexes: Steric Limitations of Ligand Coordination. Eur. J. Inorg. Chem. 15 3088 3098
Pärssinen A. Luhtanen T. Klinga M. Pakkanen T. Leskelä M. Repo T. 2007Alkylphenyl-Substituted Bis(salicylaldiminato) Titanium Catalysts in Ethene Polymerization. Organometallics, 26 3690 3698
Mitani M. Saito J. Ishii S. Nakayama Y. Makio H. Matsukawa N. Matsui S. Mohri J. Furuyama R. Terao H. Bando H. Tanaka H. Fujita T. 2004FI Catalysts: New Olefin Polymerization Catalysts for the Creation of Value-Added Polymers. Chem. Rec. 4 137 158
Makio H. Fujita T. 2009Development and Application of FI Catalysts for Olefin Polymerization: Unique Catalysis and Distinctive Polymer Formation. Acc. Chem. Res. 42: (10) 1532-1544.
Chen E. Y. X. Marks T. J. 2000Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure-Activity Relationships. Chem. Rev. 100 1391 1434
Matsui S. Mitani M. Saito J. Tohi Y. Makio H. Tanaka H. Fujita T. 1999Post-Metallocenes: a New Bis(Salicylaldiminato) Zirconium Complex for Ethylene Polymerization. Chem. Lett. 28 1263 1264
Mitani M. Nakano T. Fujita T. 2003Unprecedented Living Olefin Polymerization Derived from an Attractive Interaction Between a Ligand and a Growing Polymer Chain. Chem. Eur. J. 9:(11) 2396-2403.
Makio H. Fujita T. 2005Propene Polymerization with Bis(phenoxy-imine) Group 4 Transition Metal Complexes. Bull. Chem. Soc. Jpn. 78 52 66
Yoshida Y. Matsui S. Fujita T. 2005Bis(pyrrolideimine) Ti Complexes with MAO: a New Family of High Performance Catalysts for Olefin Polymerization. J. Organometal. Chem. 690 4382 4397
Milano G. Cavallo L. Guerra G. 2002Site Chirality as a Messenger in Chain-End Stereocontrolled Propene Polymerization. J. Am. Chem. Soc. 124 13368 13369
Furuyama R. Saito J. Ishii S. I. Mitani M. Matsui S. Tohi Y. Makio H. Matsukawa N. Tanaka H. Fujita T. 2003Ethylene and Propylene Polymerization Behavior of a Series of Bis(phenoxy-imine)Titanium Complexes. J. Mol. Cat. A: Chem. 200 31 42
Matsui S. Mitani M. Saito J. Matsukawa N. Tanaka H. Nakano T. Fujita T. 2000Post-Metallocenes: Catalytic Perfomance of New Bis(salicylaldiminato) Zirconium Complexes for Ethylene Polymerization. Chem. Lett. 5 554 555
Fujita T. Coates G. W. 2002Synthesis and Characterization of Alternating and Multiblock Copolymers From Ethylene and Cyclopentene Macromolecules, 35 9640 9647
Matsui S. Fujita T. 2001FI Catalysts: Super Active New Ethylene Polymerization Catalysts. Catal Today, 66 63 73
Ittel S. D. Johnson L. K. Brookhart M. 2000Late-Metal Catalysts for Ethylene Homo-and copolymerization. Chem. Rev. 100 1169 1203
Rieger B. Saunders Baugh. L. Kacker S. Striegler S. (eds 2003Late Transition Metal Polymerization Catalysis. Wiley-VCH, Weinheim.
Tian J. Hustad P. D. Coates G. W. 2001A New Catalyst for Highly Syndiospecific Living Olefin Polymerization Homopolymers and Block Copolymers from Ethylene and Propylene. J. Am. Chem. Soc. 123 5134 5135
Ahmadjo S. Zohuri G. H. Damavandi S. Sandaroos R. 2010Comparative Ethylene Polymerization Using FI-like Zirconium Based Catalysts, Reac. Kinet. Mech. Cat. 101 429 442
Liu D. Wang S. Wang H. Chen W. 2006Trialkylaluminums: Efficient Cocatalysts for Bis(phenoxy-imine)Zirconium Complexes in Ethylene Polymerization, J. Mol. Catal. A: Chem. 246 53 58
Hustad P. D. Tian J. Coates G. W. 2002J. Am. Chem. Soc. Mechanism of Propylene Insertion Using Bis(phenoxyimine)-Based Titanium Catalysts: An Unusual Secondary Insertion of Propylene in a Group IV Catalyst System. 124 3614 3621
Busico V. Cipullo R. Cutillo F. Friederichs N. Ronca S. Wang B. 2003Improving the Performance of Methylalumoxane: A Facile and Efficient Method to Trap “Free” Trimethylaluminum, J. Am. Chem. Soc. 125 12402 12403
Lamberti M. Pappalardo D. Mazzeo M. Pellecchia C. 2004Effects of the Reaction Conditions on the Syndiospecific Polymerization of Propene Promoted by Bis(phenoxyimine) Titanium Catalysts Macromol. Chem. Phys. 205 486 491
Mazzeo M. Strianese M. Santoriello I. Pellecchia C. 2006Phenoxyaldimine and Phenoxyketimine Titanium Complexes in Propene Polymerization. A Different Effect of o-Phenoxy Halide Substituents. Macromolecules, 39 7812 7820
Saito J. Mitani M. Mohri J. Ishii S. Yoshida Y. Matsugi T. Kojoh S. Kashiwa N. Fujita T. 2001Highly Syndio Specific Living Polymerization of Propylene Using a Titanium Complex Having Two Phenoxy-imine Chelate Ligands. Chem. Lett. 30 576 582
Arriola DJ, Carnahan EM, Hustad PD, Kuhlman RL, Wenzel TT 2006Catalytic Production of Olefin Block Copolymers via Chain Shuttling Polymerization. Science, 312 714 719
Lamberti M. Pappalardo D. Zambelli A. Pellecchia C. 2002Syndiospecific Polymerization of Propene Promoted by Bis(salicylaldiminato)Titanium Catalysts: Regiochemistry of Monomer Insertion and Polymerization Mechanism. Macromolecules, 35 658 663
Mitani M. Furuyama R. Mohri J. I. Saito J. Ishii S. Terao H. Nakano T. Tanaka H. Fujita T. 2003Syndiospecific Living Propylene Polymerization Catalyzed by Titanium Complexes Having Fluorine-Containing Phenoxy−imine Chelate Ligands. J. Am. Chem. Soc. 125 4293 4305
Furuyama R. Mitani M. Mohri J. I. Mori R. Tanaka H. Fujita T. 2005Ethylene/Higher α-Olefin Copolymerization Behavior of Fluorinated Bis(phenoxy−imine)titanium Complexes with Methylalumoxane: Synthesis of New Polyethylene-based Block Copolymers, Macromolecules, 38 1546 1552
Saito J. Suzuki Y. Makio H. Tanaka H. Onda M. Fujita T. 2006Polymerization of Higher α-Olefins with a Bis(Phenoxyimine)Ti Complex/i-Bu3Al/Ph3CB(C6F5)4: Formation of Stereo- and Regioirregular High Molecular Weight Polymers with High Efficiency. Macromolecules, 39 4023 4031
Makio H. Kashiwa N. Fujita T. 2002FI Catalysts: a New Family of High Performance Catalysts for Olefin Polymerization. Adv. Synth. Catal. 34 477 493
Matsugi T. Matsui S. Kojoh S. Takagi Y. Inoue Y. Fujita T. Kashiwa N. 2001New Titanium Complexes Having Two Indolide-Imine Chelate Ligands for Living Ethylene Polymerization. Chem. Lett. 30 566 577
Gottfried A. C. Brookhart M. 2001Living Polymerization of Ethylene Using Pd(II) α-diimine Catalysts, Macromolecules, 34 1140 1142
Tshuva E. Y. Goldberg I. Kol M. 2000Isospecific Living Polymerization of 1-Hexene by a Readily Available Nonmetallocene C2 Symmetrical Zirconium Catalyst. J. Am. Chem. Soc. 122 10706 10707
Mitani M. Furuyama R. Mohri J. Saito J. Ishii S. Terao H. Kashiwa N. Fujita T. 2002Fluorine- and Trimethylsilyl-Containing Phenoxy−Imine Ti Complex for Highly Syndiotactic Living Polypropylenes with Extremely High Melting Temperatures. J. Am. Chem. Soc. 124 7888 7889
Mitani M. Mohri J. Yoshida Y. Saito J. Ishii S. Tsuru K. Matsui S. Furuyama R. Nakano T. Tanaka H. Kohoj S. Matsugi T. Kashiwa N. Fujita T. 2002Living Polymerization of Ethylene Catalyzed by Titanium Complexes Having Fluorine-Containing Phenoxy−imine Chelate Ligands. J. Am. Chem. Soc. 124 3327 3366
Zambelli A. Longo P. Pellecchia C. Grassi A. 1987Beta-Hydrogen Aabstraction and Regiospecific Insertion in Syndiotactic Polymerization of Styrene. Macromolecules, 20 2035 2037
Hagimoto H. Shiono T. Ikeda T. 2004Supporting Effects of Methylaluminoxane on the Living Polymerization of Propylene with a Chelating (diamide)dimethyltitanium Complex. Macromol. Chem. Phys. 205 19 26
Nakayama Y. Bando H. Sonobe Y. Fujita T. 2004Olefin Polymerization Behavior of Bis(phenoxy-imine) Zr, Ti, and V Complexes with MgCl2-Based Cocatalysts, J. Mol. Catal. A. 213 141 150
Coates G. W. Tian J. Hustad P. D. 2003Bis(salicylaldiminato)Titanium Complex Catalysts, Highly Syndiotactic Polypropylene by a Chain-end Control Mechanism, Block Copolymers Containing this. US Patent 6562930.
Sakuma A. MS Weiser Fujita. T. 2007Living Olefin Polymerization and Block Copolymer Formation with FI Catalyst. Polym. J. 39 3 193 207
Ishii S. I. Saito J. Mitani M. Mohri J. I. Matsukawa N. Tohi Y. Matsui S. Kashiwa N. Fujita T. 2002Highly Active Ethylene Polymerization Catalysts Based on Titanium Complexes Having Two Phenoxyimine Chelate Ligand. J. Macromol. Catal. 179 11 16
Nakayama Y. Saito J. Bando H. Fujita T. 2005Propylene Polymerization Behavior of Fluorinated Bis(Phenoxy-imine) Ti Complexes with an MgCl2-Based Compound (MgCl2-Supported Ti-Based Catalysts). Macromol. Chem. Phys. 206 1847 1852
Ishii S. I. Furuyama R. Matsukawa N. Saito J. Mitani M. Tanaka H. Fujita T. 2003Ethylene and Ethylene/Propylene Polymerization Behavior of Bis(Phenoxy-imine) Zr and Hf Complexes with Perfluorophenyl Substituents. Macromol. Rapid. Commun. 24 452 456
Yasunori Y. Shigekazu M. Terunori F. 2005Bis(pyrrolide-imine) Ti Complexes with MAO: A New Family of High Performance Catalysts for Olefin Polymerization. J. Organometal. Chem. 690 4382 4397
Zohuri G. H. Damavandi S. Sandaroos R. Ahmadjo S. 2010Highly Active FI Catalyst of Bis[N-( 3 5dicumylsalicylidene)cyclohexylaminato] Zirconium(IV) Dichloride for Polymerization of Ethylene, Iran Polym. J. 19:(9) 679-687.
Fujita T. Tohi Y. Mitani M. Matsui S. Saito J. Nitabaru M. Sugi K. Makio H. Tsutsui T. 2005Olefin Polymerization Catalysts, Transition Metal Compounds, Processes for Olefin Polymerization, and α-Olefin/Conjugated Diene Copolymers. US Patent 6875718.
Oleinik II, Oleinik IV, Ivanchev SS 2008Design of Schiff Base-Like Postmetallocene Catalytic Systems for Polymerization of Olefins: VIII. Synthesis of N-(o-cycloalkylphenyl) 2Hydroxynaphthalene-1-Carbaldehyde imines. Russ. J. Org. Chem. 44:(1) 103-106.
Burger BJ, Thompson ME, Cottor WD, Barcaw JE 1990Ethylene Insertion and Beta.-hydrogen Elimination for Permethylscandocene Alkyl Complexes. A Study of the Chain Propagation and Termination Steps in Ziegler-Natta Polymerization of Ethylene. J. Am. Chem. Soc. 112 1566 1577
Bordwell F. MJ Bausch 1983Methyl Effects on the Basicities of Cyclopentadienide and Indenide Ions and on the Chemistry of Their Transition Metal Complexes. J. Am. Chem. Soc. 105 6188 6189
Damavandi S. Galland G. B. Zohuri G. H. Sandaroos R. 2011FI Zr-type Catalysts for Ethylene Polymerization. J. Polym. Res. 18 1059 1065
Zhang J. Wang X. Jin G. X. 2006Polymerized Metallocene Catalysts and Late Transition Metal Catalysts for Ethylene Polymerization. Coord. Chem. Rev. 250 95 109
Ivanchev SS, Trunov VA, Rybakov VB, Albov DV, Rogozin DG 2005Dik Phys Chem 404:165.
Sandaroos R. Damavandi S. Nazif A. Goharjoo M. Mohammadi A. 2011Highly Efficient Bis(aminotropone) Ti Catalyst for Ethylene Polymerization. Chinese Chemical Letters, 22 213 216
Nakayama Y. Bando H. Sonobe Y. Fujita T. 2004Development of Single-site New Olefin Polymerization Catalyst Ssystems Using MgCl2-Based Activators: MAO-Free MgCl2-Supported FI Catalyst Systems. Chem. Soc. Japan, 77 617 625
Soga K. Uozumi T. Saito M. Shiono T. 1994Structure of Polypropylene and Poly(ethylene-co-propylene) Produced with an Alumina-Supported CpTiCl3/Common Alkylaluminium Catalyst System. Macromol. Chem. Phys. 195 1503 1515
Satyanarayana G. Sivaram S. 1993An Unusually Stable Supported Bis(cyclopentadienyl)titanium dichloride-trialkylaluminum Catalyst System for Ethylene Polymerization. Macromolecules, 26 4712 4714
Nakayama Y. Bando H. Sonobe Y. Kaneko H. Kashiwa N. Fujita T. 2003New Olefin Polymerization Catalyst Systems Comprised of Bis(Phenoxy-imine) Titanium Complexes and MgCl2-Based Activators. J. Cat. 21 171 175
Hedden D. Marks T. J. 1988CH3)5C5]2Th(CH3)2 Surface Chemistry and Catalysis. Direct NMR Spectroscopic Observation of Surface Alkylation and Ethylene Insertion/Polymerization on MgCl2, J. Am. Chem. Soc. 110 1647 1649
Xu R. Liu D. Wang S. Wang N. Mao B. 2007Preparation of Spherical MgCl2-Supported Bis(Phenoxy-imine) Zirconium Complex for Ethylene Polymerization. J. Mol. Catal. A. 263 86 92
Srijumnonga S. Suttipitakwong P. Jongsomjita B. Praserthdama P. 2008Effect of Supports and Solvents on Ethylene Polymerization with Titanium Complex Consisting of Phenoxy-imine Ligands/dMMAO Catalytic System. J. Mol. Catal. A. 29 1 7
Zhang D. Jin G. 2004Self-immobilized Titanium and Zirconium Catalysts with Phenoxy-imine Ligands for Ethylene Polymerization. X-ray Crystal Structure of Bis(N-(3-t-butylsalicylidene)-4’-allyloxyanilinato) Zirconium (IV) dichloride. Applied Catalysis A: General, 262 85 91