REACTIONS OF 16-ELECTRON CP'M(NO)R2 COMPOUNDS [M = MO, W R = ALKYL, ARYL] WITH CARBON-MONOXIDE

This paper reports the reactions of 16-electron Cp'M(NO)R2 complexes [ Cp' = CP (eta5-C5H5), Cp (eta5-C5Me5); M = Mo, W; R = alkyl, aryl] wi th carbon monoxide. The reactions proceed in a stepwise fashion, and t heir outcomes are dependent on both the natures of Cp' and R and the e xperimental conditions employed. Thus, treatment of solutions of Cp'W( NO)R2 with CO under ambient conditions affords the corresponding 18-el ectron monoacyl species Cp'W(NO)-(eta2-C{O}R) (R) (Cp' = Cp, R = CH2C Me2Ph, p-tolyl; Cp' = Cp, R = CH2CMe2Ph, CH2CMe3, p-tolyl). An initial ly formed carbonyl adduct is isolable for CpW(NO)(p-tolyl)2 at-38-deg rees-C, but at higher temperatures it converts to CpW(NO)(eta2-C{O}-p -tolyl)(p-tolyl). The atom connectivity in CpW(NO)(eta2-C{O}CH2CMe2Ph) (CH2CMe2Ph) has been established by a single-crystal X-ray crystallog raphic analysis which was hampered by severe disorder. The cases havin g R = CH2Ar (Ar = C6H5, C6H4-4-Me) are unique in that exposure of the Cp'M(NO)(CH2Ar)2 complexes to CO does not produce isolable acyl alkyl complexes but rather leads to the reductive elimination of (ArCH2)2CO and formation of the well-known Cp'M(NO)(CO)2 compounds. Upon exposure to CO at higher pressures, only the (perhydrocyclopentadienyl)tungste n monoacyl alkyl complexes undergo insertion of a second equivalent of CO, thereby affording the novel bis(acyl) complexes CpW(NO)(C{O}alkyl )2, again probably via an initially formed carbonyl adduct. Such an ad duct is detectable by IR spectroscopy for CpW(NO)(eta2-C{O}-p-tolyl)( p-tolyl), but it only persists in an atmosphere of CO. The spectroscop ic properties of the CpW(NO)(C{O}alkyl)2 complexes are consistent with their being stereochemically nonrigid molecules having the instantane ous 18-electron molecular structures CpW(NO)(eta2-C{O}alkyl)(eta1-C{O} alkyl). A unified rationale of how steric and electronic factors influ ence the eventual outcomes of the carbonylation reactions is presented .