SYNTHESIS AND CHARACTERIZATION OF NEW ALKYL-CARBON DIOXIDE COMPOUNDS AND THE FIRST NEUTRAL ACYL-CARBONYL NIOBOCENE COMPLEXES

The olefin-hydride complexes Cp-2'Nb(H)(eta(2)-RHC=CH2) (Cp' = eta(5)- C5H4SiMe3; R = H (3), C6H5 (4, endo isomer)) were prepared by the alky lation reactions of [Cp-2'NbCl](2) (1) with the appropriate Grignard r eagents RMgX (R = CH2CH3, CH2CH2C6H5) followed by a stereoselective be ta-elimination from the intermediate alkyl complexes Cp-2'Nb(CH2CH2R). Complexes Cp-2'Nb(H)(eta(2)-RHC=CH2) (R = C6H4CH3 (5), C6H4OCH3 (6)) were prepared as a mixture of endo and exo isomers by reaction of Cp-2 'NbH3 (2) with the corresponding olefin. Furthermore, reactions of CO with 3 and 4, and the reactions of CO2 with 3-6, afforded the alkylnio bocene complexes Cp-2'Nb(CO)R (R = CH2CH3 (7), CH2CH2C6H5 (8)) Cp-2'Nb (eta(2)-CO2)(R) (R = CH2CH3 (9)), CH2CH2C6H5 (10), CH2CH2C6H4CH3 (11), CH2CH2C6H4OCH3 (12)). The reactivity of 9 and 10 toward the strong Le wis acid B(C6F5)(3) was also studied; in a first step the adducts Cp-2 'Nb(eta(2)-CO2-B(C6F5)(3))(CH2CH2R) (R = H (13), C6H5 (14)) were forme d and subsequently evolved to give the oxo-alkyl complexes Cp-2'Nb(O-B (C6F5)(3))(CH2CH2R) (R = H (15), C6H5 (16)) with the loss of CO. Final ly, reactions of 3 and 4 with CO under appropriate conditions gave the neutral acylniobocene complexes Cp-2'Nb(CO)(eta(1)-C(O)CH2CH2R) (R = H (17), C6H5 (18)), which were alternatively prepared from the reactio ns of 7 and 8 with CO. The different complexes were characterized by s pectroscopic methods.