Synthesis and structure of a series of tungsten(II) and tungsten(VI) diynyl and diyndiyl complexes

Oxidation of the diynyl and diyndiyl complexes [W(C=CC=CH)(CO)3Cp*](1) and [{W(CO)3Cp*}2(mu-C=CC=C)](2) affords the corresponding dioxo compounds [W(C=CC=CH)(O)2Cp*](4) and [{W(O)2Cp*}2(mu-C=CC=C)](6)via oxo–peroxo intermediates. The molecular structures are consistent with a degree of mixing between the carbon orbitals of the C4(H) fragment and the d4, but not the d0, metal centres. A simple synthesis of the useful reagent WCl(CO)3Cp* is also described.