Formation of Novel ansa-Carborane−Alkoxide Complexes by Carbonylation of (C5Me5)(η5-C2B9H11)TiMe

The reaction of Cp*(η 5 -C 2 B 9 H 11 )TiMe ( 1, Cp* = C 5 Me 5 ) with CO (0.5−1 atm) in toluene (−78 to 23 °C) yields a 1:4 mixture of Cp*(η 5:η 1 -8-CHMeO-C 2 B 9 H 10 )Ti ( 6 ) and Cp*(η 5:η 1 -4-CHMeO-C 2 B 9 H 10 )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 C 2 B 3 donor ring (B8) in 6 and to a lateral boron (B4 or B7) in 7 . The anticipated acyl complex, Cp*(η 5 -C 2 B 9 H 11 )TiC( O)Me ( 8 ), was not observed. However, experiments with 13 CO show that the −B C HMeO− 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*(η 5:η 1 -4-CHMeO-C 2 B 9 H 10 )Ti(NCMe) ( 9 ) have been determined by X-ray crystallography.