Formation of novel ansa-carborane-alkoxide complexes by carbonylation of (C5Me5)(η5-C2B9H11)TiMe

The reaction of Cp*(eta(5)-C2B9H11)TiMe (1, Cp* = C5Me5) with CO (0.5-1 atm) in toluene (-78 to 23 degrees C) yields a 1:4 mixture of Cp*(eta(5):eta(1)-8-CHMeO-C2B9H10)Ti (6) and Cp*(eta(5):eta(1)-4-CHMeO-C2B9H10)Ti (7), in ca. 90% total NMR yield. Complexes 6 and 7 both contain a linked carborane-alkoxide ligand but differ in the site of attachment of the -CHMeO-linker to the carborane cage. The linker is attached at the central boron of the C2B3 donor ring (B8) in 6 and to a lateral boron (B4 or B7) in 7. The anticipated acyl complex, Cp*(eta(5)-C2B9H11)TiC(=O)Me (8), was not observed. However, experiments with (CO)-C-13 show that the -BCHMeO- carbon atoms in 6 and 7 originate from the CO, which implies that 8 is formed first and rearranges to 6 or 7 by net insertion of the acyl carbon into a B-H bond. The molecular structures of 6 and Cp*(eta(5):eta(1)-4-CHMeO-C2B9H10)Ti(NCMe) (9) have been determined by X-ray crystallography.