Intramolecular alkoxide-tethered permethyltitanocene(III) complexes - synthesis and crystal structure
Abstract
Singly tucked-in titanocene [Ti(III)(eta(5)-C5Me5)(eta(5):eta(1)-C5Me4CH2)] (1) reacted readily with di-tert-butyl ketone and 2,4,6-trimethylacetophenone to give permethyltitanocene derivatives [Ti( III)(eta(5)-C5Me5){eta(5)-C5Me4CH2C(t-Bu)(2)O-kappa O}] (2) and [(Ti(III)(eta(5)-C5Me5){eta(5)-C5Me4CH2CMe(C6H2Me3)O-kappa O}] (3) with the tetramethylcyclopentadienyl ring tethered to the titanium atom by ethoxy group disubstituted at C-alpha. Crystal structures of 2 and 3 showed that the Ti-O bond is only slightly inclined to the tethered cyclopentadienyl ligand, and the bulky mesityl or tert-butyl substituents did not impose an observable steric hindrance into molecules of 2 and 3.
Whereas the Ti-O bond lengths in 2 and 3 do not significantly differ, a higher wavenumber of the 1a(1) -> b(2) electronic transition for 2 (7326 cm(-1)) compared with that for 3 (6666 cm(-1)) indicates a more efficient oxygen-to-titanium pi-electron back donation in 2.