Half-sandwich Titanium Complexes Research Articles

Ethylene/Propylene Copolymerization and Their Terpolymerization with 5-Ethylidene-2-norbornene over Catalytic Systems Based on Half-Sandwich Titanium Complexes with Organoaluminum and Organoboron Activators

Ethylene/Propylene Copolymerization and Their Terpolymerization with 5-Ethylidene-2-norbornene over Catalytic Systems Based on Half-Sandwich Titanium Complexes with Organoaluminum and Organoboron Activators

Development and future prospects of selective organometallic compounds as anticancer drug candidates exhibiting novel modes of action

Organometallic complexes have widely been used for the treatment of various diseases viz., malaria, arthritis, syphilis, pernicious anemia, tuberculosis and particular in cancers. Recent decades have witnessed an upsurging interest in the application of organometallic compounds to treat various phenotypes of cancers with multiple etiologies. The unique and exceptional properties of organometallic compounds, intermediate between classical inorganic and organic materials provide new insight in the progress of inorganic medicinal chemistry. Herein, we have selectively focused on various organometallic sandwich and half-sandwich complexes of ruthenium (Ru), titanium (Ti), gold (Au) and iron (Fe) exhibiting promising activity towards a panel of cancer cell lines and resistant cancer cell lines. These complexes exhibit novel mechanisms of drug action through incorporation of outer-sphere recognition of molecular targets and controlled activation features based on ligand substitution along with monometallic and heterometallic redox processes. Furthermore, they are usually found to be uncharged or neutral possessing metals in a low oxidation state, exhibit kinetic stability, relative lipophilicity and are amenable to a host of various chemical transformations. This review mainly sheds light on the successful advancement of organometallic complexes as anticancer drug aspirants in relation to their versatile structural chemistry and innovative mechanisms of action targeting nucleic acids, several enzymes viz; thioredoxin reductases (Thrx), EGFR, transferrin, cathepsin B, topoisomerases etc.

Synthesis, structure, spectral properties and theoretical studies of two half-sandwich titanium-complexes with adamantoxy ligands

Two novel half-sandwich Ti complexes, both incorporating two adamantoxy (OAd) ligands coordinated to their central atoms were synthesized. The complexes were characterized by 1H, 13C, 19F NMR, EI-MS and IR spectroscopy and by single-crystal X-ray diffraction. In both complexes, the coordination environment is pseudo-tetrahedral and is assembled of two O-coordinated adamantoxy and one η5-coordinated permethylcyclopentadienyl ligand. The fourth ligand in complex 1 is a methyl group coordinated through a regular σ-bond, whereas in complex 2 the same coordination site is occupied by the methyl group of the balancing (C6F5)3BMeˉ anion. DFT computations complemented with NBO analyses of 2 have unveiled, that in addition to the electrostatic interactions occurring between the half-sandwich titanocene moiety and the anionic ligand, delocalization of one methyl CH bond into the available acceptor orbital on the central atom takes place. AIM analyses of 2 have revealed the presence of a Bond Critical Point between the metal atom and the anionic methyl group. These results prove foundation for the description of 2 as a zwitterionic complex coupled with a concurrent Ti⋯CH agostic interaction in its molecule. The comparison of 2 with its analogous complex equipped with two Ot-Bu ligands instead of both OAd has suggested only a minor change in the extent of the agostic interaction, despite significant geometric differences between the two complexes.

Synthesis of polystyrene-block-poly(iso-butyl vinyl ether) by dinuclear half-metallocene catalyst and atom transfer radical polymerization

The synthesis of polystyrene-block-poly(iso-butyl vinyl ether) by using the combination of metallocene catalyst and atom transfer radical polymerization (ATRP) has been tried. This synthetic method takes advantages of both metallocene catalyst to form stereoregular polymer with high activity and ATRP with the controlled molecular weights and low polydispersity. The recent dinuclear half-sandwich complexes of titanium with xylene bridge, [Ti(η5-cyclopentadienyl)Cl2L]2-ortho, meta-[CH2-C6H4-CH2] (L = Cl, L = O-2,6-iPr2C6H3 ) were successfully synthesized. These catalysts were characterized by 1H NMR, 13C NMR and elemental analysis. Copolymers have been characterized by using gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). The collected copolymers have got narrow molecular weight distribution (≤1.8) and the improvement of stereoregularity (racemo dyads, r, are from 45 % to 56 %).

Synthesis, structures of half-sandwich titanium complexes with bulky aryloxide ligand and their catalytic performance for olefin polymerization

Three bulky cyclopentadienyltitanium aryloxide complexes, [Ti(η5-C5Me4Ar)(O-2,6-tBu2C6H3)Cl2], (Ar=C6H5 (4), 4-iPrC6H4 (5), 4-Me3SiC6H4 (6)) have been synthesized from reaction of the corresponding cyclopentadienyltitanium trichloride derivatives with 1 equiv of LiO-2,6-tBu2C6H3. These half-sandwich complexes 4–6 have been characterized by 1H and 13C NMR spectroscopy. The molecular structure of complexes 4 and 6 has been determined by single-crystal X-ray diffraction studies. When activated with iBu3Al and Ph3C+B(C6F5)4−, complexes 4–6 exhibits reasonable catalytic activity for ethylene polymerization, producing moderate molecular weight polyethylenes.

Half-sandwich titanium complexes with β-oxodithioester ligands

The reaction of CpTiCl3 with HLx [HLx = methyl 3-(4′-X-phenyl)-3-hydroxy-2-propenedithioate ligands; X = H(1), Me(2), OMe(3), Cl(4), Br(5)] in the presence of NEt3 yielded the corresponding half-sandwich complexes TiCpCl2(Lx) [X = H(6), Me(7), OMe(8), Cl(9), Br(10)]. Compounds 1–10 were characterized by elemental analyses, infrared, 1H and 13C NMR spectroscopy and EI mass spectrometry, while ligands 1,3–5 and complexes 6–10 were also characterized by single-crystal X-ray diffraction studies. The structural arrangements observed in 1,3–5 include an intramolecular O–H⋯S hydrogen bond. The metal center in 6–10 exhibits a square pyramidal geometry by means of the O∩S coordination mode of ligands, which led to the racemic form of the A, C enantiomers, associated by an inversion center.

Highly selective trimerization of ethylene with half-sandwich cyclopentadienyl and indenyl titanium complexes bearing pendant thienyl group

A series of half-sandwich titanium complexes bearing thienyl group [Cp(Ind)-bridge-thienyl]TiCl3 (CS1–CS10) have been synthesized and show high selective ethylene trimerizaion to 1-hexene. The molecular structure of CS8 [Ind-C(cyclo-C5H10)-(5-Me-thienyl)]TiCl3 was confirmed by X-ray. No intramolecular coordination interaction between the sulfur atom on the thienyl group and the titanium center could be observed in the solid state of these complexes. After activated with MAO, the complexes can effectively catalyze ethylene trimerization. For [Cp-bridge-thienyl]TiCl3/MAO system, the best productivity is obtained at 30°C; increasing the bulk of the substituent on the 5-position of the thienyl can improve the productivity for 1-hexene. CS6 [Cp-C(cyclo-C5H10)-(5-SiMe3-thienyl)]TiCl3 upon with MAO can make a productivity of 553kg/(molTi-h) and 1-hexene selectivity of 86% at 30°C, 0.5MPa ethylene pressure. For [Ind-bridge-thienyl] TiCl3/MAO system, catalysts have more active and more tolerant of temperature comparing to corresponding Cp complexes. For example, CS8 can make the productivity of 697kg/(molTi-h) and 1-hexene selectivity of 95% at 80°C, 0.5MPa ethylene.

New Titanium(IV) Complexes with 2-Cyclopentadienylbenzylamido Ligands: Synthesis, Characterization, and Catalytic Properties for Ethylene Polymerization and Copolymerization with 1-Hexene

A series of new half-sandwich titanium(IV) complexes chelated with 2-(tetramethylcyclopentadienyl)benzylamido ligands, 2-Me4CpC6H4CH2(R)NTiCl2 (R = iPr (1), Cy (2), nPr (3), 4-MePh (4)), have been ...

Effect of ligand substituents in olefin polymerisation by half-sandwich titanium complexes containing monoanionic iminoimidazolidide ligands–MAO catalyst systems

Various half-sandwich titanium complexes containing iminoimidazolidide ligands, CpTiCl(2)[1,3-R(2)(CH(2)N)(2)C=N] (1a-d) [R = Ph (a), 2,6-Me(2)C(6)H(3) (b), cyclohexyl (c), (t)Bu (d)], have been employed as the catalyst precursors for ethylene polymerisation, syndiospecific styrene polymerisation, and copolymerisation of ethylene with 1-hexene in the presence of MAO cocatalyst; 1d showed the highest catalytic activity for ethylene polymerisation whereas 1b showed the highest activity for syndiospecific styrene polymerisation.

Syntheses, reactions, and ethylene polymerization of half-sandwich titanium complexes containing salicylbenzoxazole and salicylbenzothiazole ligands

Half-sandwich titanium salicylbenzoxazole complexes CpTiLCl(2) 2a-2c [L = R-2-(benzo[d]xazol-2-yl)phenol (R = H (2a), R = 6-CH(3) (2b), R = 4-CH(3)-6-(t)Bu (2c)] and salicylbenzothiazole complexes CpTiLCl(2) 2d-2g [L = R-2-(benzo[d]thiazol-2-yl)phenol (R = H (2d), R = 6-CH(3) (2e), R = 6-(t)Bu (2f), R = 4-Cl (2g)] were synthesized by the reaction of CpTiCl(3) with the sodium salts of their corresponding precursors. Complexes 2a-2g were fully characterized by (1)H and (13)C NMR spectra and elemental analyses. The molecular structures of 2a and 2b were determined by single crystal X-ray diffraction methods. When activated by excess methylaluminoxane (MAO) these half-sandwich titanium complexes showed moderate to high activities for ethylene polymerization and produced high molecular weight polyethylenes. The half-sandwich titanium salicylbenzoxazole complexes (2a-2c) exhibited higher activities, of up to 1.23 × 10(6) g PE mol Ti(-1) h(-1) for the 2b/MAO system, than those of their analogues, half-sandwich titanium salicylbenzothiazole complexes (2d-2g).

Preparation of new dinuclear half-titanocene complexes with ortho- and meta-xylene linkages and investigation of styrene polymerization

Half-titanocene is well-known as an excellent catalyst for the preparation of SPS (syndiotactic polystyrene) when activated with methylaluminoxane (MAO). Dinuclear half-sandwich complexes of titanium bearing a xylene bridge, (TiCl 2L ) 2{(μ-η 5, η 5-C 5H 4-ortho-(CH 2–C 6H 4–CH 2)C 5H 4} , ( 4 (L = Cl), 7 (L = O-2,6- iPr 2C 6H 3)) and (TiCl 2L ) 2{(μ-η 5, η 5-C 5H 4-meta-(CH 2–C 6H 4–CH 2)C 5H 4} ( 5 (L = Cl), 8(L = O-2,6- iPr 2C 6H 3)), have been successfully synthesized and introduced for styrene polymerization. The catalysts were characterized by 1H- and 13C NMR, and elemental analysis. These catalysts were found to be effective in forming SPS in combination with MAO. The activities of the catalysts with rigid ortho- and meta-xylene bridges were higher than those of catalysts with flexible pentamethylene bridges. The catalytic activity of four dinuclear half-titanocenes increased in the order of 4 < 5 < 7 < 8. This result displays that the meta-xylene bridged catalyst is more active than the ortho-xylene bridged and that the aryloxo group at the titanium center is more effective at promoting catalyst activity compared to the chloride group at the titanium center. Temperature and ratio of [Al]:[Ti] had significant effects on catalytic activity. Polymerizations were conducted at three different temperatures (25, 40, and 70 °C) with variation in the [Al]:[Ti] ratio from 2000 to 4000. It was observed that activity of the catalysts increased with increasing temperature, as well as higher [Al]:[Ti]. Different xylene linkage patterns ( ortho and meta) were recognized to be a principal factor leading to the characteristics of the dinuclear catalyst due to its different spatial arrangement, causing dissimilar intramolecular interactions between the two active sites.

Synthesis, characterization, and catalytic activities in syndiospecific polymerization of styrene for half-sandwich titanium complexes with non-Cp tridentate dianionic ligands MeN(CH 2CR 2O −) 2

New half-titanocenes, Cp ∗TiCl[(OCR 2CH 2)NMe(CH 2CR ′ 2O)] [R,R′ = H ( 1), R,R′ = Me, H, ( 2), R,R′ = Me ( 3)], were prepared from Cp ∗TiCl 3 ( 4) with the corresponding alcohols in the presence of triethylamine. X-ray analysis shows that 1 has slightly distorted trigonal bipyramidal geometry around Ti. These complexes exhibited moderate catalytic activities for syndiospecific styrene polymerization in the presence of MAO and the activity increased in the order: 2 > 1 > 4 > 3 (at 50 °C), 1 > 2 > 4 > 3 (at 70 °C and 90 °C).

Synthesis, structures, and catalytic properties for ethylene polymerization of bridged [η 5,η 1-C 5H 4CHPhArO]TiCl 2 complexes

A number of bridged half-sandwich titanium complexes [η 5:η 1-2-C 5H 4CHPh-4-R 1-6-R 2C 6H 2O]TiCl 2 [R 1 = H ( 5), Me ( 6), t Bu ( 7, 8); R 2 = H ( 6, 7), t Bu ( 5, 8)] were synthesized from the reaction of their corresponding trimethylsilyl substituted ligand precursors 2-Me 3SiC 5H 4CHPh-4-R 1-6-R 2C 6H 2OSiMe 3 [R 1 = H ( 1), Me ( 2), t Bu ( 3, 4); R 2 = H ( 2, 3), t Bu ( 1, 4)] with TiCl 4 in hexane. All new complexes were characterized by 1H and 13C NMR spectroscopy. Molecular structures of complexes 5 and 8 were determined by single crystal X-ray diffraction analysis. Upon activation with Al i Bu 3/Ph 3CB (C 6F 5) 4, complexes 5– 8 exhibit reasonable catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing polyethylene and poly(ethylene-co-1-hexene) with moderate molecular weights.

Synthesis, Characterization, and Ethylene Polymerization of Group IV Metal Complexes with Mono-Cp and Tridentate Aryloxide or Arylsulfide Ligands

Half-sandwich titanium and zirconium complexes with tridentate dianionic aryloxide or arylsulfide ligands [R-2-{(2-XC6H4)NCH}C6H2O]2- ([XNOR]2-, R = H, X = O (L1); R = 4-Me-6-But (R‘), X = O (L2); R = H, X = S (L3); R = 4-Me-6-But (R‘), X = S (L4)) have been prepared. Reactions of CpMCl3 (M = Ti, Zr) with sodium salts of the aryloxide or arylsulfide ligands (L1−L4) afford CpTi[XNOR]Cl [R = H, X = O (1); R = 4-Me-6-But (R‘), X = O (2); R = H, X = S (3); R = 4-Me-6-But (R‘), X = S (4)] and CpZr[ONOR]Cl [R = H (5)], respectively. Complexes 1−5 were characterized by IR and 1H NMR spectra and elemental analyses, and their molecular structures have been determined by X-ray diffraction methods. The coordination properties of these complexes have been investigated in the solid state and compared to related systems. When activated by excess methylaluminoxane (MAO), these complexes can be used as catalysts for ethylene polymerization and exhibited moderate activities. The activities of arylsulfide complexes 3 and 4 are higher than those of their analogues, aryloxide complexes 1 and 2, and zirconium complex 5 is much more active than titanium complexes 1−4.

Synthesis, structures and catalytic properties of stable oxo-bridged half-sandwich titanium complexes

Hydrolysis of 1,2-diphenyl-4-R-cyclopentadienyl titanium trichloride (R = Me ( 1), n-Bu ( 2)) affords the corresponding oxo-bridged monocyclopentadienyl titanium compounds (1,2-Ph 2-4-R-CpTiCl 2) 2(μ-O) (R = Me ( 3), n-Bu ( 4)), new dinuclear species. The molecular structures of complexes 3 and 4 have been confirmed by single-crystal X-ray diffraction. Both complexes have been characterized by elemental analysis, 1H and 13C NMR spectroscopy. When activated with Al( i Bu) 3 and Ph 3 C + B ( C 6 F 5 ) 4 - , complexes 3 and 4 show reasonable catalytic activity for ethylene polymerization, producing polyethylenes with moderate molecular weights, and upon activation with methylaluminoxane (MAO), complexes 3 and 4 exhibit high catalytic activity and syndiospecificity for the polymerization of styrene.

Styrene polymerization with half-sandwich titanium complexes bearing pendent cyclo-alkenyl groups

A new series of substituted half-sandwich titanium complexes bearing bridged cyclo-alkenyl groups [η 5-C 5H 4–(bridge)–(cyclo-alkenyl)]TiCl 3 have been synthesized and characterized. All the titanium complexes display considerable catalytic activity towards the polymerization of styrene in the presence of methylaluminoxane (MAO), yielding atactic-rich polystyrene. Experimental results indicate that there might be an interaction between the double bond and the titanium center, which was reflected by 1H NMR spectrum and polymerization behavior. As compared with the size of cyclo-alkenyl ring, the bridging unit plays a crucial role in reactivity and stereoselectivity of styrene polymerization.

Synthesis and styrene polymerization properties of dinuclear half-titanocene complexes with xylene linkage

The new dinuclear half-sandwich complexes of titanium with xylene bridge, [Ti(η 5-cyclopentadienyl)Cl 2L] 2[CH 2–C 6H 4–CH 2] (L = Cl ( 3), L = O-2,6- iPr 2C 6H 3 ( 4), L = N(SiMe 3)(2,6-Me 2C 6H 3) ( 5)), have been synthesized. The complexes 4 and 5 have been prepared by the reaction of the complex 3 with the corresponding lithium salts of aryloxy and anilide. Structure of these complexes has been characterized by 1H and 13C NMR. The change of substituent from chloride, 3, to anilide, 5, at titanium resulted in chemical shift change of cyclopentadienyl protons from 6.92 and 6.79 to 6.13 and 5.95 ppm probably due to the positive electron density delivery from the anilide group. It was found that all three half-titanocenes were effective catalyst for the generation of SPS (syndiotactic polystyrene). Xylene bridged dinuclear catalyst ( 4) with aryloxy substituent exhibited very high activity (458 kg of SPS/(mol of [Ti])h), at 40 °C, whereas the analogous hexamethylene bridged dinuclear half-titanocene catalyst ( 7) showed a lower activity (80.7 kg of SPS/(mol of [Ti])h) under the same conditions. While the catalyst 3 was the most active catalyst among three complexes less than 40 °C the catalyst 5 exhibited the highest activity at 70 °C. Xylene linkage was suggested to be too stiff to permit any kind of intramolecular interaction between two active centers. Lack of steric disturbance due to the rigidity of the xylene bridge might give rise to the similar properties of dinuclear metallocene to the corresponding mononuclear metallocene to result in not only the facile coordination of monomer at the active center to lead high activity but also the easier β-H elimination comparing to the dinuclear catalysts with the flexible bridge to result in the formation of lower molecular weight polymer.

Styrene polymerization with half-sandwich titanium complexes bearing pendent alkenyl groups: From atactic to syndiotactic

A new series of substituted half-sandwich titanium complexes bearing bridged alkenyl groups [ η 5-C 5H 4-(bridge)-(alkenyl)]TiCl 3 have been synthesized and characterized. All the titanium complexes display considerable catalytic activity towards the polymerization of styrene in the presence of methylaluminoxane (MAO). Bridging unit between the cyclopentadienyl moiety and the allyl groups plays a crucial role in reactivity and stereoselectivity of styrene polymerization. By modification of the bridging unit, the syndioselectivity of the polymer can be tailor-made, providing a new guideline to design catalyst for polymers having desired properties.

Cyclopentadienyl titanium hydroxylaminato complexes as highly active catalysts for the polymerization of propylene

Half sandwich complexes of titanium bearing eta1 or eta2 bound nitroxide ligands are highly active catalysts for the polymerisation of propylene to high molecular weight atactic poly(propylene).

Synthesis of monoalkoxy- and trialkoxy-substituted half-sandwich titanium complexes PhCH2CpTiCl3-n (OR)n (n = 1 or 3) as catalysts for syndiotactic styrene polymerization

Two new series of various substituted half-sandwich titanium complexes PhCH2CpTiCl2(OR) (R = Et (1), iPr (2), tBu (3), cyclohexyl (4), benzyl (5)) and PhCH2CpTi(OR)3 (R = Et (6), iPr (7), tBu (8), cyclohexyl (9), benzyl (10)) were prepared from PhCH2CpTiCl3 with lithium alkoxide or alcohol in the presence of triethylamine. All complexes were well characterized by 1H NMR, MS, infrared spectroscopy and elemental analysis or high-resolution MS. Complexes 1–5 have two conformations, which were confirmed by temperature-dependent NMR. All complexes were tested as catalyst precursors for the syndiotactic polymerization of styrene. The syndiotactic polystyrene obtained exhibits low molecular weight (Mw = 2.78 × 104) and narrow molecular weight distribution (Mw/Mn = 1.50). The different alkoxy ligands affected the activities slightly. The existence of the additional phenyl group on the cyclopentadienyl ligand stabilized the active species more effectively, which was reflected by the activities and syndiotacticities of all complexes, and even at high temperature the activities still kept high. The effects of Al/Ti and time on the syndiotactic styrene polymerization by complex 1 were investigated. Copyright © 2005 John Wiley & Sons, Ltd.