Preparation, structure, and reactivity of a (pentamethylcyclopentadienyl)titanium dimer bridged by oxygen and tetramethylmethylenecyclopentadienyl

Article abstract of DOI:10.1021/om00122a021

The reaction between Cp*₂Ti (Cp* = η⁵-C₅(CH₃)₅) and N₂O in toluene affords [(Cp*Ti)₂-μ-(η¹:η⁵-C ₅(CH₃)₄CH₂)(μ-O)₂] (I). The structure of the product was determined by X-ray diffraction; it crystallizes in the orthorhombic space group Pnma with a = 10.650 (5) A?, b = 15.283 (3) A?, c = 17.064 (8) A?, and Z = 4. The structure was refined to R = 0.048 and R_w = 0.052 for 256 parameters and 1226 observed reflections. The molecule consists of two (η⁵-C₅(CH₃)₅)Ti units bridged unsymmetrically by two oxygen atoms (Ti(1)-O = 1.961 (3) A? and Ti(2)-O = 1.787 (3) A?) and an η¹:η⁵-C₅(CH₃) ₄CH₂ ligand (η¹ to Ti(2) and η⁵ to Ti(1)). The bond distances are in agreement with the description of the C₅(CH₃)₄CH₂ bridge as a truly methylenic η¹:η⁵ ligand and not as an η²:η⁴ olefinic ligand. The Ti(2)-CH₂ distance is 2.178 (6) A?; all other C-C and Ti-C distances are normal for Cp*Ti units. The methylenic description of C₅(CH₃)₄CH₂ is supported by NMR (δ(CH₂) 50.4 in the ¹³C spectrum) and IR (ν(C-H) 2960, 2900, and 2850 cm^-1) spectroscopies and also explains the remarkable stability of I (no reaction with H₂, CO, or C₂H₄) since both titanium atoms are Ti(IV). With HCl, I gives Cp*₂TiCl₂ and Cp*TiCl₃.