Mechanistic studies on the reductive cyclooligomerisation of CO by U(III) mixed sandwich complexes; the molecular structure of [(U(eta-C8H6{Si(i)Pr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta1-C2O2).

The stoichiometric reaction of 1 equiv of CO with [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)] affords the linear diuranium ynediolate complex [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta1-C2O2) which does not react with further CO to give the deltate derivative [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta2-C3O3). Spectroscopic and computational studies suggest a plausible mechanism for the formation of the deltate complex, in which a "zig-zag" diuranium ynediolate species is the key intermediate.