Syntheses and structures of doubly tucked-in titanocene complexes with tetramethyl(aryl)cyclopentadienyl ligands

Titanocene-bis(trimethylsilyl)ethyne complexes [Ti(eta (5)-C5Me4R)(2)(eta ( 2)-Me3SiC equivalent to CSiMe3)], where R = benzyl (Bz, 1a), phenyl (Ph 1b) and p-fluorophenyl (FPh, 1c), thermolyse at 150-160 degreesC to give produ cts of double C-H activation [Ti(eta (5)-C(5)Me(4)Bz){eta (3):eta (4)-C5Me3 (CH2)(CHPh)}] (2a), [Ti(eta (5)-C(5)Me(2)Bz){eta (3):eta (4)-C(5)Me(2)Bz(CH 2)(2)}] (2a'), [Ti(eta (5)-C5Me4Ph){eta (3):eta (4)-C5Me2Ph(CH2)(2)}] (2b), and [Ti(eta (5)-C5Me4FPh){eta (3):eta (4)-C5Me2FPh(CH2)(2)}] (2c). In the presence of 2,2,7,7-tetramethylocta-3,5-diyne (TMOD) the thermolysis afford s analogous doubly tucked-in compounds bearing one eta (3):eta (4)-allyldie ne and one eta (5)-C5Me4R ligand having TMOD attached by its C-3 and C-6 ca rbon atoms to the vicinal methylene groups adjacent to the substituent R (R = Bz (3a), Ph (3b), and FPh (3c)). Compound 3a is smoothly converted into air-stable titanocene dichloride [TiCl2{eta (5)-C(5)Me(2)Bz(CH2CH(t-Bu)CH=C HCH(t-Bu)CH2)}(eta (5)-C(5)Me(4)Bz)] (4a) by a reaction with hydrogen chlor ide. Yields in both series of doubly tucked-in complexes decrease in the or der of substituents: Bz >> Ph > FPh. Crystal structures of 1c, 2a, 2b and 3 b have been determined. (C) 2001 Elsevier Science B.V. All rights reserved.