LEWIS-ACID-PROMOTED DECARBONYLATION OF COORDINATED CARBON-DIOXIDE - REACTIONS OF (ETA-5-MEC5H4)2NB(ETA-2-CO2)CH2SIME3 WITH LEWIS-ACIDS

The interaction of Cp'2Nb(eta-2-CO2)CH2SiMe3 (1; Cp' = eta-5-MeC5H4) with several Lewis acids has been studied and found to result in facile decarbonylation of 1; the Nb-containing products depend markedly on the Lewis acid partner. Reaction of 1 with LiPF6 or BF3.Et2O causes both decarbonylation and deoxygenation, producing [Cp'2Nb(F)CH2SiMe3]Z [Z = PF6- (3), BF4- (6)], which have been characterized spectroscopically and (for 3) by X-ray diffraction; 3 is also produced in the reaction of the oxo derivative Cp'2Nb(O)CH2SiMe3 (2) with LiPF6 or BF3.Et2O. 1 reacts with ZnCl2 first to form an adduct, Cp'2Nb(CO)2CH2SiMe3.ZnCl2 (7), which based on IR and NMR data appears to have a novel mu-CO2 unit bridging Nb and Zn. Complex 7 is unstable, decomposing with CO loss to form [Cp'2Nb(CH2SiMe3)O.ZnCl2]2 (8), an adduct of ZnCl2 with the oxo species 2, which has been characterized crystallographically; 8 is also produced from 2 and ZnCl2. Reaction of 1 with HgCl2 rapidly produces an incompletely characterized product 10, which has been both decarbonylated and dealkylated. Although CdCl2 does not react with 1 under comparable conditions, Me3SiCl reacts rapidly with 1 to produce Cp'2Nb(O)Cl (11), resulting from decarbonylation and dealkylation; the structure of 11 has been established by X-ray diffraction.