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

Titanocene–bis(trimethylsilyl)ethyne complexes [Ti(η5-C5Me4R)2(η2-Me3SiCCSiMe3)], 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(η5-C5Me4Bz){η3:η4-C5Me3(CH2)(CHPh)}] (2a), [Ti(η5-C5Me4Bz){η3:η4-C5Me2Bz(CH2)2}] (2a′), [Ti(η5-C5Me4Ph){η3:η4-C5Me2Ph(CH2)2}] (2b), and [Ti(η5-C5Me4FPh){η3:η4-C5Me2FPh(CH2)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 η3:η4-allyldiene and one η5-C5Me4R 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 [TiCl2{η5-C5Me2Bz(CH2CH(t-Bu)CHCHCH(t-Bu)CH2)}(η5-C5Me4Bz)] (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.