AN UNUSUAL REACTION IN THE COURSE OF FISCHER CARBENE SYNTHESIS - PREPARATION AND STRUCTURE OF VINYLIDENEMOLYBDENUM COMPLEXES

The reaction of [(eta5-C5H5) (CO)2(NO)Mo] (1) with (phenylethynyl)lith ium and subsequently with methyl trifluoromethanesulfonate led in 43% yield to {(eta5-C5H5)(CO)(NO)Mo[=C=C(CH3)(Ph)]} (3a) as a 2:l mixture of rotamers (DELTAG(double dagger) = 20.5 (+/-0.3) kcal/mol). The anio nic intermediate [(eta5-C5H5)(CO)(NO)(R1CC)MO]Li (7) is trapped by the reaction with HCI or acetic anhydride which yields vinylidene complex es {(eta5-C5H5)(CO)(NO)-Mo[=C=C(CH3)(Ph)]} (5) and {(eta5-C5H5)(CO)(NO )-Mo[=C=C(COCH3)(Ph)]} (6) respectively. The X-ray analysis of {(eta5- C5H5)(CO)(NO)Mo[=C=C(CH3)(Ph)]} is reported.