Novel hepta-coordinated molybdenum(ii) and tungsten(ii) carbene complexes by oxidative decarbonylation of Mo(0) and W(0) carbene complexes

C,O-Chelated tetracarbonyl[o-methoxyphenyl(methoxy)- carbene] complexes of molybdenum(0) and tungsten(0) react with tin tetrahalides SnX4 (X = Cl, Br, I) by oxidative decarbonylation and incorporation of two halides to form novel chelated hepta-coordinated Fischer-type tricarbonyl- (bishalogeno)carbene molybdenum(II) and tungsten(II) complexes