Initial decarbonylation of $CpMoOs_3(CO)_{11}[\mu_3-\eta^2-C(O)CH_2Tol](1a)$ with $Me_3NO/MeCN$ follewed by reaction with dihydrogen gives the dihydride complex $CpMoOs_3(CO)_{10}(\mu-H)_2[\mu_3-\eta^2-C(O)CH_2Tol](2)$ in a quantitative yield. Thermolysis of 2 induces scission of the acyl C-O to offered the three isomeric hydrido - oxo - alkylidene compounds $CpMoOs_3(CO)_9(\mu-H)(\mu-O)(\mu-CHCH_2Tol)(3a-c)$. Complexes 3a,b are not chromatographically separable, and compound 3c is produced either by heating a mixture of 3a and 3b in toluene(100℃) or by treating with hydrochloric acid. Compounds 3a-c have been isolated as crystalline solids and have been characterized by spectroscopic(Infra Red, mass, $^1H$ and $^{13}$C NMR) data. The actual structure of 3c has been determined by a single crystal X-ray diffraction study. This clearly indicates that 3c is formed from anti isomers 3a,b by an apparent rotation of the μ-alkylidene carbon. The detailed mechanism concerning the acid - induced isomerization reaction was examined by a deuterium - labeling study. The result implies that a pathway for the formation of 3c by the acid involves protonation of an alkylidene carbon - metal bond of 3b to form a cationic alkyl species followed by rotation around a carbon - metal single bond and subsequent deprotonation. Thermal conversion of 3a,b to 3c has been examined by a deuterium - labeling study and a CO gas inhibition experiment. The result suggests that thermal rotation of the μ-alkylidene carbon be occurred by oxidative addition of the alkylidene carbon - hydrogen bond to form a dihydrido - alkylidyne species followed by reformation of the C-H bond from the opposite side.
