Synthesis of Network Biobased Aliphatic Polyesters Exhibiting Better Tensile Properties than the Linear Polymers by ADMET Polymerization in the Presence of Glycerol Tris(undec-10-enoate).

Development of biobased aliphatic polyesters with better mechanical (tensile) properties in film has attracted considerable attention. This report presents the synthesis of soluble network biobased aliphatic polyesters by acyclic diene metathesis (ADMET) polymerization of bis(undec-10-enyl)isosorbide diester [M1, dianhydro-D-glucityl bis(undec-10-enoate)] in the presence of a tri-arm crosslinker [CL, glycerol tris(undec-10-enoate)] using a ruthenium-carbene catalyst, and subsequent olefin hydrogenation using RhCl(PPh3)3. The resultant polymers, after hydrogenation (expressed as HCP1) and prepared in the presence of 1.0 mol% CL, showed better tensile properties than the linear polymer (HP1) with similar molecular weight [tensile strength (elongation at break): 20.8 MPa (282%) in HP1 vs. 35.4 MPa (572%) in HCP1]. It turned out that the polymer films prepared by the addition of CL during the polymerization (expressed as a 2-step approach) showed better tensile properties. The resultant polymer film also shows better tensile properties than the conventional polyolefins such as linear high density polyethylene, polypropylene, and low density polyethylene.

Amorphous Elastomeric Ultra-High Molar Mass Polypropylene in High Yield by Half-Titanocene Catalysts.

Propylene polymerizations with different ketimide-modified half-titanocene catalysts, Cp'TiCl2(N=CtBu2) [Cp' = C5H5 (1), C5Me5 (2), Me3SiC5H4 (3)], with MAO as a cocatalyst, were investigated. The obtained polymers were studied in detail by determining their microstructure, molar masses, thermal, and mechanical properties. The Cp*-ketimide, (C5Me5)TiCl2(N=CtBu2) (2), exhibited higher catalytic activities than Cp'TiCl2(N=CtBu2) (1,3), yielding higher molar mass polymers, Mw up to 1400 Kg/mol. All the synthesized polypropylenes (PP) are atactic and highly regioregular, with predominant rrrr pentads, especially PP prepared with catalyst 1. Differential scanning calorimetry (DSC) established that the polymers are fully amorphous aPP, and no melting endotherm events are detected. Glass transition temperatures were detected between -2 and 2 °C. These polypropylenes have been established to be high-performance thermoplastic elastomers endowed with remarkably high ductility, and a tensile strain at break higher than 2000%.

Synthesis of High Molecular Weight Biobased Aliphatic Polyesters Exhibiting Tensile Properties Beyond Polyethylene.

Synthesis of high molecular weight polyesters prepared by acyclic diene metathesis (ADMET) polymerization of bis(undec-10-enoate) with isosorbide (M1), isomannide (M2), and 1,3-propanediol (M3) and the subsequent hydrogenation have been achieved by using a molybdenum-alkylidene catalyst. The resultant polymers (P1) prepared by the ADMET polymerization of M1 (in toluene at 25 °C) possessed high Mn values (Mn = 44400-49400 g/mol), and no significant differences in the Mn values and the PDI (Mw/Mn) values were observed in the samples after the hydrogenation. Both the tensile strength and the elongation at break in the hydrogenated polymers from M1 (HP1) increased upon increasing the molar mass, and the sample with an Mn value of 48200 exhibited better tensile properties (tensile strength of 39.7 MPa, elongation at break of 436%) than conventional polyethylene, polypropylene, as well as polyester containing C18 alkyl chains. The tensile properties were affected by the diol segment employed, whereas HP2 showed a similar property to HP1.

Analysis of Ethylene Copolymers with Long-Chain α-Olefins (1-Dodecene, 1-Tetradecene, 1-Hexadecene): A Transition between Main Chain Crystallization and Side Chain Crystallization.

A series of ethylene copolymers with long-chain α-olefins [LCAOs, 1-dodecene (DD), 1-tetradecene (TD), 1-hexadecene (HD)] and various LCAO contents were prepared, and their thermal properties, including effects of LCAO content and side chain length, were explored. The Cp*TiCl2(O-2,6- i Pr2-4-SiEt3-C6H2)-MAO catalyst system afforded rather high-molecular-weight copolymers with unimodal molecular weight distributions and uniform compositions (confirmed by DSC thermograms). In addition to the melting temperatures (T m values) corresponding to the so-called main chain crystallization (samples with low LCAO contents, the T m value decreased upon increasing the LCAO content) and the side chain crystallization [polymer samples with high LCAO contents, by intermolecular interaction of side chains as observed in poly(DD), poly(TD), and poly(HD)], the other T m value was observed, especially in poly(ethylene-co-HD)s (assumed to be due to co-crystallization of the branch and the main chain through an interaction of the main chain and the long side chains). The presence of another crystalline phase in poly(ethylene-co-HD)s was also suggested by a wide-angle X-ray diffraction (WAXD) analysis. These T m values in poly(ethylene-co-TD)s and poly(ethylene-co-DD)s with rather high TD or DD contents were affected by the heating conditions in the measurement of DSC thermograms (5 or 10 °C/min), suggesting that the driving force for formation of the crystal packing (observed as T m) is weak and affected by the alkyl side chain lengths.

Effect of Borate Cocatalysts toward Activity and Comonomer Incorporation in Ethylene Copolymerization by Half-Titanocene Catalysts in Methylcyclohexane.

Ethylene copolymerizations with 2-methyl-1-pentene, 1-dodecene (DD), vinylcyclohexane (VCH), [Me2Si(C5Me4)(N t Bu)]TiCl2 (1), Cp*TiMe2(O-2,6- i Pr2-4-RC6H2) [R = H (2), SiEt3 (3)]-borate, and [A(H)]+[BAr4]- [Ar = C6F5; A(H)+ = N+(H)Me(n-C18H37)2, N+(H)(CH2CF3)(n-C18H37)2, HO+(n-C14H29)2·O(n-C14H29)2, HO+(n-C16H33)2·O(n-C16H33)2; Ar = C10F7, A(H)+ = HO+(n-C14H29)2·O(n-C14H29)2 (B5), N+(H)(CH2CF3)(n-C18H37)2] catalyst systems conducted in methylcyclohexane (MCH) exhibited better comonomer incorporation than those conducted in toluene (in the presence of methylaluminoxane (MAO) or borate cocatalysts). The activity was affected by the borate cocatalyst and 1,3-B5 catalyst systems in MCH and showed the highest activity in the ethylene copolymerizations with VCH and DD.

Effect of para-Substituents in Ethylene Copolymerizations with 1-Decene, 1-Dodecene, and with 2-Methyl-1-Pentene Using Phenoxide Modified Half-Titanocenes-MAO Catalyst Systems.

Effect of para-substituents in the ethylene (E) copolymerization with 1-decene (DC), 1-dodecene (DD), and with 2-methyl-1-pentene (2M1P) using a series of Cp*TiCl2 (O-2,6-i Pr2 -4-R-C6 H2 ) [R=H (1), t Bu (2), Ph (3), CHPh2 (4), CPh3 (5), SiMe3 (6), SiEt3 (7), and newly prepared 4-t BuC6 H4 (8) and 3,5-Me2 C6 H3 (9)]-MAO catalyst systems has been studied. The activities in these copolymerization reactions were affected by the para-substituent, and the SiMe3 (6), SiEt3 (7) and 3,5-Me2 C6 H3 (9) analogues showed the higher activities at 50 °C in the E copolymerization reactions with DC (1.06-1.44×106  kg-polymer/mol-Ti⋅h), DD (1.04-1.88×106  kg-polymer/mol-Ti⋅h) than the others, whereas no significant differences were observed in the comonomer incorporations. Complexes 6 and 7 also showed the higher activities at 50 °C in the E/2M1P copolymerization, and the 2M1P incorporation was affected by the para-substituent and the polymerization temperature; complex 9 showed better 2M1P incorporation at 25 °C.

The Effect of SiMe3 and SiEt3 Para Substituents for High Activity and Introduction of a Hydroxy Group in Ethylene Copolymerization Catalyzed by Phenoxide-Modified Half-Titanocenes.

Remarkable effects of SiMe3 and SiEt3 para-substituents in the phenoxide-modified half-titanocenes, Cp*TiCl2 (O-2,6-i Pr2 -4-R-C6 H2 ) [R=SiMe3 (6), SiEt3 (7)], toward the catalytic activities in ethylene copolymerizations with 2-methyl-1-pentene, 1-decene, 1-dodecene and with 9-decen-1-ol (DC-OH) have been demonstrated. The activities by 6, 7 at 50 °C showed higher than those conducted at 25 °C in all cases in the presence of MAO cocatalyst. Efficient synthesis of high-molecular-weight (HMW) ethylene copolymers incorporating DC-OH (or 5-hexen-1-ol, HX-OH) has been attained in the copolymerization by 7, which showed better DC-OH (HX-OH) incorporation at 50 °C to afford the HMW copolymers, poly(ethylene-co-DC-OH)s, with high activities (activity 1.21-3.81×105  kg-polymer mol-1 -Ti h, Mn =6.55-10.0×104 , DC-OH 2.3-3.6 mol %).

Synthesis of Biobased Long-Chain Polyesters by Acyclic Diene Metathesis Polymerization and Tandem Hydrogenation and Depolymerization with Ethylene.

Acyclic diene metathesis (ADMET) polymerization of biobased α,ω-dienes of bis(undec-10-enoate) with diols (1,4-butanediol, isosorbide, isomannide, and 1,4-cyclohexanedimethanol) afforded high-molecular weight unsaturated polyesters, and subsequent tandem hydrogenation (H2 1.0 MPa, 50 °C, 3 h) gave the saturated polymers upon addition of a small amount of Al2O3 (1.0-1.7 wt %). Subsequent reaction of the unsaturated polymers with ethylene afforded the oligomers (by depolymerization and degradation).

Solution XANES and EXAFS analysis of active species of titanium, vanadium complex catalysts in ethylene polymerisation/dimerisation and syndiospecific styrene polymerisation.

Mechanistic studies in homogeneous catalysis through the solution transition metal K Edge XANES (X-ray absorption near-edge structure) and EXAFS (Extended X-ray absorption fine structure) analysis for vanadium and titanium complex catalysts for ethylene polymerisation/dimerization, and syndiospecific styrene polymerisation, including interpretation of the XANES spectra, have been introduced. The core excitation spectra of the complexes based on the time-dependent density functional theory (TD-DFT) can be used to interpret the Ti and V K-edge features and to extract information on the electronic structure from the XANES spectra. Theoretical calculations and experimental XAS analysis should have great potential for analysing the active species.

XAS Analysis of Reactions of (Arylimido)vanadium(V) Dichloride Complexes Containing Anionic NHC That Contains a Weakly Coordinating B(C6F5)3 Moiety (WCA-NHC) or Phenoxide Ligands with Al Alkyls: A Potential Ethylene Polymerization Catalyst with WCA-NHC Ligands.

(Arylimido)vanadium(V) dichloride complexes containing anionic N-heterocyclic carbene (NHC) ligands that contain weakly coordinating B(C6F5)3 moieties (WCA-NHC) of the type [V(NAr)Cl2(WCA-NHC-Ar')] (5, Ar = 2,6-Me2C6H3, Ar' = 2,6- i Pr2C6H3) showed significant catalytic activity for ethylene polymerization in the presence of Al cocatalysts (MAO and Al i Bu3); the activity by the 5-MAO catalyst (19 500 kg-PE/mol-V·h; TOF 11 600 min-1) is the highest among those reported using the other (imido)vanadium(V) complexes in the presence of MAO, and the 5-Al i Bu3 catalyst showed higher activity (66 000 kg-PE/mol-V·h; TOF 39 200 min-1). The V K-edge X-ray absorption near-edge structure (XANES) analyses (in toluene) strongly suggest the formation of certain vanadium(III) species by reduction with Al i Bu3 accompanying structural changes; the EXAFS analysis suggests the presence of the arylimido ligand and one V-Cl bond (2.34 ± 0.04 Å), which is longer than those [2.1901(8)-2.2462(8) Å] in the reported (imido)vanadium(V) complexes. The XANES analysis of [V(NAr)Cl2(OAr)] strongly suggests the formation of the other vanadium(III) species by reduction with Me2AlCl or Et2AlCl, and the EXAFS analysis suggests the presence of the arylimido ligand and two V-Cl bonds (2.45 ± 0.03 Å). The XANES spectra showed no significant changes in both the pre-edge peak(s) and the edge peak when these complexes were treated with MAO, suggesting that the basic geometry and the high oxidation state were preserved under these conditions.

Synthesis of new polyesters by acyclic diene metathesis polymerization of bio-based α,ω-dienes prepared from eugenol and castor oil (undecenoate).

Synthesis of new polyesters by acyclic diene metathesis (ADMET) polymerization of α,ω-diene, 4-allyl-2-methoxyphenyl 10-undecenoate (M1), prepared from bio-renewable eugenol and castor oil (undecenoate), have been demonstrated. Ruthenium-carbene (called second generation Grubbs) catalyst afforded polymers with unimodal molecular weight distributions (M n = 12 700, M w/M n = 1.85). The polymerization in the presence of a triarm cross-linker, 5-formylbenzene-1,2,3-triyl tris(undec-10-enoate), also afforded polymers with certain uniform network structures.

Synthesis and Structural Analysis of (Imido)vanadium Dichloride Complexes Containing 2-(2'-Benz-imidazolyl)pyridine Ligands: Effect of Al Cocatalyst for Efficient Ethylene (Co)polymerization.

(Imido)vanadium(V) dichloride complexes containing 2-(2'-benzimidazolyl)-6-methylpyridine ligand (L) of type V(NR)Cl2(L) [R = 1-adamantyl (Ad, 1), C6H5 (2), and 2,6-Me2C6H3 (3)] have been prepared, and their structures were determined by X-ray crystallography as distorted trigonal bipyramidal structures around vanadium. Reactions with ethylene using 1-3 in the presence of methylaluminoxane (MAO) afforded a mixture of oligomer and polymers, and the compositions were affected by the imido ligand employed. By contrast, 1-3 exhibited remarkable catalytic activities for ethylene polymerization in the presence of Me2AlCl; the phenylimido complex (2) exhibited the highest activity [80 100 kg-PE/mol-V·h turn over frequency (TOF, 2 850 000 h-1, 792 s-1)]. The ethylene copolymerizations with norbornene afforded ultrahigh-molecular-weight copolymers with uniform molecular weight distributions and compositions [e.g., M n = 1.71-2.66 × 106, M w/M n = 2.27-2.53]. On the basis of V nuclear magnetic resonance (51V NMR), electron spin resonance, and V K-edge X-ray absorption near-edge structure (XANES) spectra of the catalyst solution, the observed difference in the catalyst performance in the presence of (between) MAO and Me2AlCl cocatalyst should be due to the formation of different catalytically active species with different oxidation states. Apparent changes in the oxidation state were observed in the (especially in the NMR and XANES) spectra upon addition of Me2AlCl, whereas no significant changes in the spectra were observed in presence of MAO.

Ethylene polymerisation and ethylene/norbornene copolymerisation by using aryloxo-modified vanadium(V) complexes containing 2,6-difluoro-, dichloro-phenylimido complexes.

Aryloxo-modified vanadium(V) dichloride complexes containing a dichloro- or difluoro-phenylimido ligand of the type, V(N-2,6-X2C6H3)Cl2(O-2,6-R2C6H3) [X = Cl (1), F (2); R = Me (a), F (b)], showed remarkable catalytic activity in ethylene polymerisation and the copolymerisation with norbornene (NBE) in the presence of Et2AlCl; the activities were higher than that of V(N-2,6-Me2C6H3)Cl2(O-2,6-Me2C6H3) reported previously. Complex 1a is a suitable catalyst precursor in terms of not only the activity, but also synthesis of high molecular weight copolymers with both unimodal molecular weight distributions and uniform compositions.

Synthesis and structural analysis of (imido)vanadium(V) dichloride complexes containing imidazolin-2-iminato- and imidazolidin-2-iminato ligands, and their use as catalyst precursors for ethylene (co)polymerization.

A series of (imido)vanadium(V) dichloride complexes containing 1,3-imidazolin-2-iminato or 1,3-imidazolidin-2-iminato ligands of the type, V(NR')Cl2(L) [R' = 2,6-Me2C6H3, L = 1,3-R2(CHN)2C═N (1a-c,e) or 1,3-R2(CH2N)2C═N (2a-d), R = (t)Bu (a), 2,6-Me2C6H3 (b), 2,6-(i)Pr2C6H3 (c), C6H5 (d), 2,6-(Ph2CH)2-4-MeC6H2 (e); L = 1,3-(2,6-(i)Pr2C6H3)2(CHN)2C═N, R' = 1-adamantyl (Ad, 3c), C6H5 (4c); L = 1,3-(2,6-(i)Pr2C6H3)2(CH2N)2C═N, R' = Ad (5c)], were prepared and characterized. The molecular structures of 1a, 2a,c,d, 3c, 4c, and 5c were determined by X-ray crystallography. All complexes showed high catalytic activity for ethylene polymerization especially in the presence of Et2AlCl cocatalyst; the 2,6-R2C6H3 analogues (R = Me, (i)Pr; 1b,c, 2b,c) exhibited higher catalytic activities than the (t)Bu analogues (1a, 2a), which display rather unique (small) V-N-C(imido) bond angles in the solid state. A good correlation between the activity and the (51)V NMR chemical shift was found for the (arylimido)vanadium precatalysts (1a-c,e, 2a-d, and 4c). These complexes showed high catalytic activity for the copolymerization of ethylene with norbornene (NBE), affording ultrahigh molecular weight copolymers with uniform molecular weight distributions. The activities were affected by the imido ligand as well as by the substituents in the anionic ligand, and the 2,6-(i)Pr2C6H3 analogues (especially 2c and 4c) showed the higher activities. The complexes 2c and 4c also showed high activities with efficient comonomer incorporation for the ethylene copolymerization with 5-ethylidene-2-norbornene (ENB) in the presence of Et2AlCl; both the comonomer incorporation and the molecular weight in the resulting polymers were affected by the comonomer employed (NBE vs ENB).

Synthesis, structural analysis of the hetero-bimetallic complexes MMe[(O-2,4-tBu2C6H2-6-CH2)2(µ2-O-2,4-tBu2C6H2-6-CH2)N][Me2Al(µ2-OiPr)] [M = Zr, Hf] and their use in catalysis for ethylene polymerisation.

The synthesis and structural analysis of the hetero-bimetallic M-Al complexes MMe[(O-2,4-(t)Bu2C6H2-6-CH2)2(µ2-O-2,4-(t)Bu2C6H2-6-CH2)N][Me2Al(µ2-O(i)Pr)] [M = Zr, Hf], prepared from M(O(i)Pr)[{(O-2,4-(t)Bu2C6H2)-6-CH2}3N] by treating with 1.0 equiv. of AlMe3, have been explored: these complexes exhibited catalytic activities for ethylene polymerisation in n-octane in the presence of methylaluminoxane (MAO). The Zr-Al analogue showed high catalytic activities affording polymers with unimodal molecular weight distributions.

Synthesis and structural analysis of (imido)vanadium(V) complexes containing chelate (anilido)methyl-imine ligands: ligand effect in ethylene dimerization.

A series of (imido)vanadium dichlorido complexes containing chelate anionic donor ligands of the type, VCl2(L)(NR) [R = 1-adamantyl (Ad), L = 2-(2,6-Me2C6H3)NCH2(C9H6N) (2), 8-(2,6-Me2C6H3)NCH2(C9H6N) (3); L = 2-(2,6-R'2C6H3)NCH2(C5H4N), R = 2-MeC6H4, R' = Me (4a), (i)Pr (4b); L = 2-(2,6-Me2C6H3)NCH2(C5H4N), R = 4-MeC6H4 (5), 3,5-Me2C6H3 (6)], have been prepared and identified. The reactions with ethylene by 2,3 in the presence of methylaluminoxane (MAO) afforded a mixture of high molecular weight polyethylene and oligomers. Reactions with ethylene by VCl2[2-(2,6-R'2C6H3)NCH2(C5H4N)](NAd) (1a,b), 4-6 afforded 1-butene with high selectivities (>92%), and the activities by 4a,b are at the same level as those in 1a,b. The activities by 5,6 were lower than 4a,b and were at the same level of that by VCl2[2-(2,6-Me2C6H3)NCH2(C5H4N)](NPh). These results thus suggest that both the chelate anionic donor and the imido ligands play a role for both the activity and the selectivity.

Highly efficient dimerization of ethylene by (imido)vanadium complexes containing (2-anilidomethyl)pyridine ligands: notable ligand effect toward activity and selectivity.

(Imido)vanadium(V) complexes containing the (2-anilidomethyl)pyridine ligand, V(NR)Cl(2)[2-ArNCH(2)(C(5)H(4)N)] (R = 1-adamantyl (Ad), cyclohexyl (Cy), phenyl), exhibit remarkably high catalytic activities (e.g. TOF = 2 730 000 h(-1) (758 s(-1)) by V(NAd)Cl(2)[2-(2,6-Me(2)C(6)H(3))NCH(2)(C(5)H(4)N)) for ethylene dimerization in the presence of MAO, affording 1-butene exclusively (selectivity 90.4 to >99%). The steric bulk of the imido ligand plays an important role in the selectivity (polymerization vs dimerization), and the electronic nature directly affects the catalytic activity (activity: R = Ad > Cy > Ph).

Effect of aryloxo substituents in ethylene polymerisation by tris(pyrazolyl)borate titanium(IV) complexes containing aryloxo ligands of type, TpTiCl2(OAr).

Tris(pyrazolyl)borate titanium(IV) complexes containing aryloxo ligand of type, TpTiCl(2)(OAr) [Tp = HB(pyrazolyl)(3); Ar = 2-(i)PrC(6)H(4), C(6)F(5), 2,6-Ph(2)C(6)H(3)], have been prepared, identified, and the structures of TpTiCl(2)(OC(6)F(5)), TpTiCl(2)(O-2,6-Ph(2)C(6)H(3)) have been determined by X-ray crystallography. The 2-(i)PrC(6)H(4) analogue exhibits especially high catalytic activities for ethylene polymerisation in the presence of methylaluminoxane (MAO), and the activity by TpTiCl(2)(OAr) increased in the order: Ar = 2-(i)PrC(6)H(4) > Ph > C(6)F(5) >> 2,6-Ph(2)C(6)H(3) > 2,6-Me(2)C(6)H(3), 2,6-(i)Pr(2)C(6)H(3).

Synthesis and structural analysis of titanatranes bearing terminal substituted aryloxo ligands of the type [Ti(OAr){(O-2,4-Me2C6H2-6-CH2)2(OCH2CH2)N}]n (n = 1, 2): effect of aryloxo substituents in the ethylene polymerization.

A series of titanatranes containing both chelate bis(aryloxo)-(alkoxo)amine and the terminal aryloxo ligands of type [Ti(OAr)(L)](n) [n = 1 or 2, Ar = 2,6-Me(2)C(6)H(3) (1), 2,6-(i)Pr(2)C(6)H(3) (2), 2,6-Ph(2)C(6)H(3) (3), 2-FC(6)H(4) (4), 2,6-F(2)C(6)H(3) (5), C(6)F(5) (6); L = (O-2,4-Me(2)C(6)H(2)-6-CH(2))(2)(OCH(2)CH(2))N)] have been prepared, and their structures (1, 3-6) were determined by X-ray crystallography. The ortho-substituents in the terminal aryloxo ligand directly affect the structure in the solid state; the structures of 1-3 possessed monomeric form and fold a distorted trigonal bipyramidal geometry around Ti, whereas the structure of 4-6 were of dimeric form and fold a distorted octahedral around Ti bridged with oxygen in the alkoxo arm expressed as [Ti(OAr){(O-2,4-Me(2)C(6)H(2)-6-CH(2))(2)(mu(2)-OCH(2)CH(2))N)}](2). The Ti-O(Ar) bond distances and the Ti-O-C(Ar) bond angles are highly influenced by the terminal aryloxo substituents especially in the ortho-position. The 2,6-(i)Pr(2)C(6)H(3) analogue (2), the C(6)F(5) analogue (6), and the 2,6-Me(2)C(6)H(3) analogue (1) showed moderate/notable catalytic activities for ethylene polymerization in the presence of MAO especially at 80-100 degrees C, whereas both the 2,6-Ph(2)C(6)H(3) analogue (3) and 2-FC(6)H(4) analogue (4) showed the negligible catalytic activities, clearly indicating that the activity was strongly affected by the terminal aryloxo substituents especially in the ortho-position.

Synthesis and structural analysis of half-titanocenes containing eta(2)-pyrazolato ligands, and their use in catalysis for ethylene polymerization.

Cp*TiCl(2)(L) [L = C(3)H(3)N(2) (1), 3,5-Me(2)C(3)HN(2) (2) and 3,5-(i)Pr(2)C(3)HN(2) (3)], and Cp*Ti(C(3)H(3)N(2))(3) (4) were prepared in moderate yields by treating Cp*TiCl(3) with the pyrazoles in the presence of Et(3)N or with their corresponding lithium salts in Et(2)O. The structures of 1 and 2 determined by X-ray crystallography indicate that these complexes fold a distorted tetrahedral geometry around Ti, and the pyrazolato ligands coordinate to Ti with eta(2)-N,N'-coordination mode. In contrast, one of the pyrazolato ligand in 4 coordinates to Ti with eta(1)-N-bonding, whereas the other two ligands were bound to Ti with eta(2)-N,N'-fashion. The Cp analogues, CpTiCl(2)(L) [L = C(3)H(3)N(2) (5), 3,5-Me(2)C(3)HN(2) (6), 3,5-(i)Pr(2)C(3)HN(2) (7), and 3,5-Ph(2)C(3)HN(2) (8)], were also prepared by the reaction of CpTiCl(3) with the corresponding lithium salts in Et(2)O or n-hexane. The crystallographic analyses of 5 and 6 revealed that the pyrazolato ligands coordinate to Ti with eta(2)-N,N'-coordination mode. These complexes (1-3, 5-8) exhibited moderate catalytic activities for ethylene polymerization in the presence of methylaluminoxane (MAO), and the activities were highly affected by the substituent on the pyrazolato ligand employed. Complex 1 exhibited the highest activity affording polymer with uniform molecular weight distribution, suggesting that the polymerization proceeded with uniform catalytically active species. An increase in the steric bulk in the pyrazolato ligand led to a slight decrease in the activity by the Cp* analogues, whereas the activity by the Cp analogues increased upon increasing the steric bulk in the pyrazolato ligand employed.