Synthesis and reactions of the carbene complexes [M(SnPh3)(CO)2{=C(OEt)Ph}L] (M=Mo or W ; L=η-C5H5, η-C5Me5 or indenyl), [M(SnPh3)(CO)2{=C(OEt)Me}(η-C5H5)] (M=Mo or W) and [MI(CO)2{=C(OEt)R}(η-C5H5)] (M=Mo or W, R=Me or Ph). X-ray crystal structures of [Mo(SnPh3)(CO)2{=C(OEt)Ph}(η-C5Me5)] and [WI(CO)2{=C(OEt)Ph}(η-C5H5)]