Coordination of the sulfur-bridged dialkoxide ligands {OCR 2 CH 2 SCH 2 CR 2 O} 2 - ({OSOR} 2 -, R = Me, p -tolyl) on titanium and zirconium centers has been studied. A variety of complexes having one or two ancillary {OSO Me } 2 - ligands, viz., M(OR) 2 {OSO Me } (M = Zr, OR = O t Bu, 4; M = Ti, OR = O i Pr, 5 ), M{OSO Me } 2 (M = Zr, 6; Ti, 7 ), Zr(CH 2 Ph) 2 {OSO Me } ( 8 ), and MCl 2 {OSO Me }(THF) n (M = Zr, n = 0, 9; n = 1, 10; n = 2, 11; M = Ti, n = 0, 12; n = 2, 13 ), have been prepared in good yields by alcohol or alkane elimination from {OSO Me }H 2 ( 1a ) or by salt metathesis routes from alkali metal salts M{OSO Me } (M = K, 2a; M = Li, in situ-generated). Coordination of the p -tolyl-substituted ligand by these and other routes proved to be much more difficult, and only TiCl 2 {OSO tol } ( 14 ) was obtained. Crystallographic studies showed that dichloro complexes 11 and 13 and bis-ligand complex 7 adopt in the solid state mononuclear structures with no bonding interaction between the sulfur atom and metal centers. The crystal structure of 4 contains two independent dinuclear molecules that interconvert formally by exchange of t BuO and chelating {OSO Me } ligands between terminal and bridging modes and feature normal Zr−S bonds. NMR data for 4 and 12 are consistent with dinuclear C 1 -symmetric structures in toluene solution, while dibenzyl complex 8 has a mononuclear structure. Variable-temperature NMR studies combined with line-shape analysis established that the fluxional behavior of 8 results from the exchange between η 2 / η 1 -benzyl ligands (Δ H ⧧ = 10.6 ± 1 kcal·mol - 1; Δ S ⧧ = −2.7 ± 2 cal·mol - 1 ·K - 1 ). Abstraction of one benzyl ligand of 4 with 1 equiv of [Ph 3 C][B(C 6 F 5 ) 4 ] or B(C 6 F 5 ) 3 proceeds cleanly to give the corresponding thermally unstable, ionic species [Zr(CH 2 Ph){OSO Me }] + [BX(C 6 F 5 ) 3 ] - (X = C 6 F 5, 15; CH 2 Ph, 16 ), which have been characterized by 1 H, 11 B, 13 C, and 19 F NMR spectroscopy and show C s symmetry in solution. The decomposition of 16 proceeds via C 6 F 5 /benzyl exchange from Zr to B and generates the stable [Zr(C 6 F 5 ){OSO Me }] + [η 6 -(PhCH 2 )B(CH 2 Ph)(C 6 F 5 ) 2 ] - ( 17 ). Cationic species in situ-generated from Zr chloro complexes and MAO are highly active but very unstable ethylene polymerization catalysts.
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Lavanant et al. (2005) studied this question.