How to synthesize a constrained geometry catalyst (CGC) – A survey

The Influence of t-Butyl and Cyclododecyl Substitution on Ethylene/1-Hexene Copolymerization Using Ansa-Fluorenylamidodimethyltitanium Derivatives

In the present study, copolymerization of ethylene and 1-hexene was conducted with a series of ansa-fluorenylamidodimethyltitanium complexes, including [t-BuNSiMe₂Flu]TiMe₂ (complex 1), [cyclododecylNSiMe₂Flu]TiMe₂ (complex 2) and [t-BuNSiMe₂(2,7-t-Bu₂Flu)]TiMe₂ (complex 3), activated by MMAO. The effect of these catalysts on catalytic behavior, namely activity, molecular weight and monomer reactivity ratios, has been investigated. The results showed that all of them acted by a single site polymerization mechanism and the molecular weight distribution is independent of catalyst structure. Based on the study, it revealed that the introduction of a t-butyl at the 2,7 position on the fluorenyl ligand is able to enhance both catalytic activity and copolymer molecular weight more than introducing a cyclododecyl on the amine, which is probably associated with the electronic effect exerted by the t-butyl substituent. The comonomer incorporation content was controllable over a wide range by adjusting the comonomer feed ratio. Moreover, referring to monomer reactivity ratio exploration, it seems that the substitution on the ansa-fluorenylamidodimethyltitanium complex tends to hinder the insertion of 1-hexene into the polymer chain, leading to the highest 1-hexene content for traditional complex 1.

Half-titanocenes for precise olefin polymerisation: effects of ligand substituents and some mechanistic aspects

Selected examples concerning effects of both cyclopentadienyl fragment (Cp') and anionic donor ligand (Y) in nonbridged modified half-titanocenes of the type, Cp'TiX(2)(Y) (X = halogen, alkyl), as new type of olefin polymerisation catalysts have been reviewed. These complexes displayed unique characteristics not only for ethylene (co)polymerisation but also for syndiospecific styrene polymerisation, ethylene/styrene copolymerisation; precise fine tuning of the ligand substituents plays an important role for the successful (co)polymerisation; a different mechanistic consideration for the syndiospecific styrene polymerisation, which can explain the copolymerisation behaviour in this catalysis, has also been introduced.

The potassium hydride mediated trimerization of imines

A novel reaction, the potassium hydride mediated synthesis of fulvenes, is described. The synthesis utilizes N-aryl imines as an inexpensive starting material affording novel substituted aminofulvenes. It is proposed that the presence of the metalated enamine as well as the imine (ratio 2 : 1) leads to the formation of an initial dimerization and a transient trimerization product, which cyclizes, giving rise to the aminofulvene.

Titanium "constrained geometry" complexes with pendant arene groups

The synthesis of the proligands C(5)Me(4)HSiMe(2)N(H)R) (R = CMe(2)Ph 1, 2-C(6)H(4)Ph 2) was accomplished via a straightforward salt metathesis reaction of the appropriate lithium amide and ClSiMe(2)(C(5)Me(5)H). Generation of the dilithio salt and reaction with TiCl(3)·(THF)(3) followed by oxidation gave C(5)Me(4)SiMe(2)N(C(6)H(4)Ph)TiCl(2) (3) in low yield. In contrast, deprotonation of 1 and 2 and reaction with (Me(2)N)(2)TiCl(2) afforded C(5)Me(4)(SiMe(2)NR)Ti(NMe(2))(2) (R = CMe(2)Ph 4, 2-C(6)H(4)Ph 5), respectively, in good yields Treatment with MeI gave the analogs C(5)Me(4)(SiMe(2)NR)TiI(2) (R = CMe(2)Ph 6, 2-C(6)H(4)Ph 7). Reduction of 7 with potassium graphite afforded C(5)Me(4)(SiMe(2)NC(6)H(4)Ph)Ti 8. Treatment of 6 and 7 with MeMgBr afforded C(5)Me(4)(SiMe(2)NR)TiMe(2) (R = CMe(2)Ph 9, 2-C(6)H(4)Ph 10). Complexes 9 and 10 in combination with the activator [Ph(3)C][B(C(6)F(5))(4)] catalyzed the polymerization of styrene and ethylene. Copolymerization was also investigated. While the catalyst derived from 10 showed poor activity, compound 9 showed markedly higher activity than 10 and (C(5)Me(4))SiMe(2)(NtBu)]TiMe(2).

Preparation of half-metallocenes of thiophene-fused and tetrahydroquinoline-linked cyclopentadienyl ligands for ethylene/α-olefin copolymerization

Directed ortho-lithiation of the lithium carbamates generated from tetrahydroquinoline or tetrahydroquinaldine enables one-step preparation of thiophene-fused and tetrahydroquinoline-linked cyclopentadienes [2-R(1)-3-R(2)-4,5-dimethyl-6-(2-R(3)-2,3,4,5-tetrahydroquinolin-8-yl)-4H-cyclopenta[b]thiophene (R(1), R(2), R(3) = H or methyl)], from which titanium(iv) and zirconium(iv) complexes are prepared. The molecular structures of Me(2)Ti-complexes (12, R(1) = R(2) = Me, R(3) = H; 14, R(1) = R(2) = R(3) = Me) and Cl(2)Zr-complex (17, R(1) = R(2) = Me, R(3) = H) are determined by X-ray crystallography. The Me(2)Ti-complexes, 14 and 15 (R(1) = R(3) = Me, R(2) = H) show excellent activities (62 and 54 × 10(6) g/molTi·h) in ethylene/1-octene copolymerization, even when activated with small amount of MAO (Al/Ti = 1000).

The amido-bridged zirconocene's reactivity and catalytic behavior for ethylene polymerization

Reaction of the amido-bridged zirconium complex (CpSiMe(2)NSiMe(2)Cp)ZrCH(3) (1) (Cp = C(5)H(4)) with half an equivalent of B(C(6)F(5))(3) or Ph(3)CB(C(6)F(5))(4) afforded the binuclear zirconium complexes [(CpSiMe(2)NSiMe(2)Cp)Zr)(2)(mu-CH(3))][RB(C(6)F(5))(3)] (2a, R = CH(3), 2b, R = C(6)F(5)) with a methyl group as the bridge between the two zirconium atoms. In the presence of one equivalent of B(C(6)F(5))(3) or Ph(3)C(C(6)F(5))(4), 1 was transformed to the zwitterionic complexes [(CpSiMe(2)NSiMe(2)Cp)Zr][RB(C(6)F(5))(3)] (3a, R = CH(3), 3b, R = C(6)F(5)) which are free of a metal-bound sigma-alkyl ligand. 2b is stable with Me(3)Al while 3b combined with Me(3)Al to form a hetero-binuclear complex [(CpSiMe(2)NSiMe(2)Cp)Zr(mu-CH(3))]Al(CH(3))(2)][B(C(6)F(5))(4)] (4) as shown by NMR spectroscopy at room temperature. Treatment of 2a or 3a with an excess of Me(3)Al led to (CpSiMe(2)NSiMe(2)Cp)Zr(C(6)F(5)) (5) through a group exchange process. 2b, 3a and 5 have been characterized by X-ray diffraction studies. 2b, 2b, 3a and 3b were highly active catalysts for ethylene polymerization and copolymerization with 1-octene in the presence of trialkylaluminium, but the binuclear zirconium complexes (2a and 2b) showed higher activities than their mononuclear counterparts 3a and 3b. Polymerization activities varied with the trialkylaluminiums and increased with the trialkylaluminium concentration applied in the system. The product existed mainly in the form of Al(PE)(3) with polymeric chains, and its molecular weight and distribution were greatly influenced by the type and amount of trialkylaluminium applied in the catalytic system.

Half-titanocenes containing anionic ancillary donor ligands as promising new catalysts for precise olefin polymerisation

Recent efforts concerning nonbridged half-titanocenes containing anionic donor ligand of the type, Cp'TiX(2)(Y) [Cp' = cyclopentadienyl group; X = halogen, alkyl; Y = anionic ancillary donor ligands such as aryloxo, ketimide etc.], as new types of olefin polymerisation catalysts have been reviewed. It has been demonstrated that these complexes displayed unique characteristics especially for ethylene copolymerisation affording new polymers by efficient incorporation of bulky olefins (so called "traditionally unreactive" monomers in transition metal catalysed coordination polymerisation), that have not been attained by the ordinary catalysts.