Titanocene Borane σ-Complexes

Abstract

The chemistry of titanocene bisborane complexes Cp2Ti(HBcat‘)2 (1a−g) (HBcat‘ = catecholborane or a substitued catecholborane) and monoborane complexes Cp2Ti(HBcat‘)(L) (2−4) (L = PMe3, PhSiH3, or PhCCPh) is reported. These complexes are unusual σ-complexes. The B−H bond in the catecholborane of 1 acts as a two-electron-donor ligand. The 4-tert-butyl version 1a was studied in depth and underwent ligand substitution reactions with PMe3, CO, PhSiH3, and PhCCPh. The products of the reaction of 1a with PMe3 and PhSiH3 are the novel monoborane σ-complexes Cp2Ti(HBcat‘)(PMe3) (2a; HBcat‘ = HBO2C6H3-4-t-Bu) and Cp2Ti(HBcat‘)(PhSiH3) (3; HBcat‘ = HBO2C6H3-4-t-Bu), in which the catecholborane remains a two-electron-donating ligand. Reaction with CO formed Cp2Ti(CO)2. Reaction with PhCCPh formed Cp2Ti(HBcat‘)(PhCCPh) (4; HBcat‘ = HBO2C6H3-4-t-Bu), which was observed in solution and reductively eliminated the vinyl boronate ester (Ph)(Bcat‘)CC(Ph)(H). The rates for the reactions of 1a with these substrates showed a ...