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

Abstract

Titanocene–bis(trimethylsilyl)ethyne complexes [Ti(η 5-C 5Me 4R) 2(η 2-Me 3SiCCSiMe 3)], where R=benzyl (Bz, 1a), phenyl (Ph, 1b) and p-fluorophenyl (FPh, 1c), thermolyse at 150–160°C to give products of double CH activation [Ti(η 5-C 5Me 4Bz){η 3:η 4-C 5Me 3(CH 2)(CHPh)}] ( 2a), [Ti(η 5-C 5Me 4Bz){η 3:η 4-C 5Me 2Bz(CH 2) 2}] ( 2a′), [Ti(η 5-C 5Me 4Ph){η 3:η 4-C 5Me 2Ph(CH 2) 2}] ( 2b), and [Ti(η 5-C 5Me 4FPh){η 3:η 4-C 5Me 2FPh(CH 2) 2}] ( 2c). In the presence of 2,2,7,7-tetramethylocta-3,5-diyne (TMOD) the thermolysis affords analogous doubly tucked-in compounds bearing one η 3:η 4-allyldiene and one η 5-C 5Me 4R ligand having TMOD attached by its C-3 and C-6 carbon 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 [TiCl 2{η 5-C 5Me 2Bz(CH 2CH( t-Bu)CHCHCH( t-Bu)CH 2)}(η 5-C 5Me 4Bz)] ( 4a) by a reaction with hydrogen chloride. Yields in both series of doubly tucked-in complexes decrease in the order of substituents: Bz≫Ph>FPh. Crystal structures of 1c, 2a, 2b, and 3b have been determined.