ZUR REAKTION VON METALL-KOORDINIERTEM KOHLENMONOXID MIT YLIDEN. VII. TRIMETHYLPHOSPHORANYLIDENMETHYL(TRIMETHYLSILOXY)CARBEN-KOMPLEXE VON CHROM, MOLYBDAEN UND WOLFRAM: AUFBAU EINER METALL-VINYL-EINHEIT DURCH C(CARBANION)-C(CARBEN)-?-WECHSELWIRKUNG UND PHOTOCHEMISCHE E/Z-ISOMERISIERUNG

Article abstract of DOI:10.1016/S0022-328X(00)87649-4

The treatment of the hexacarbonylmetal compounds M(CO)6 (M = Cr, Mo, W) with two equivalents Me3P=CH2 yields the phosphonium acylmetal-phosphorus ylides Me4P<(CO)5M=C(O)CH=PMe3> 1a-1c.Their reaction with Me3SiOSO2CF3 leads via O-silylation to formation of the neutral "siloxy-(ylidecarbene) complexes" (CO)5M=C(OSiMe3)-CH=PMe3 2a-2c, which are protonated by HX (X = Cl, CF3SO3) to give the thermolabile carbene complexes <(CO)5M=C(OSiMe3)H2CPMe3>X 3a, 3b. 1H, 13C NMR and IR data suggest, that delocalization of the ylidic charge to the carbene carbon generates a metal-coordinated vinyl group in the case of 2a-2c.In addition this fact is proved by the X-ray analysis of 2c, for which a C(ylide)-C(carbene) bond distance of 133 pm is found. 2a-2c are obtained as pure E-isomers but can be converted to the Z-isomers 2a'-2c' upon photolysis.