CARBONYLATION OF THE ALKYL-COMPOUNDS [U(ETA-C(5)H(4)R)(3)R'] AND REARRANGEMENT OF THE ACYL DERIVATIVES [U(ETA-C(5)H(4)R)(3)-(ETA(2)-COR')] INTO C(6)H(4)RR' - INFLUENCE OF R AND R' (ME, PR-I OR BU(T)) AND ROLE OF THE SOLVENT (BENZENE OR TETRAHYDROFURAN)

Carbonylation of the alkyl compounds [U(eta-C(5)H(4)R(3)R'] 1 into the acyl derivatives [U(eta-C(5)H(4)R)(3)(eta(2)COR')] 2 exhibited pseudo first-order kinetics (pCO = 1 atm). The rate constants were dependent on R, following the order Bu(t) < Pr-i < Me < H and varied with R' in the unusual order Pr-i < Me < Bu(t) < Bu(n); for [U(eta-C5H5)(3)R'], k(Bu(n)) = 2k(Bu(t)) = 4k(Pr-i). The rates were similar in benzene and in tetrahydrofuran. These results suggest that the migratory insertio n of CO into the metal-carbon bond is not the rate-determining step. T he rearrangement of the acyl complexes 2 afforded the alkylbenzene mol ecules C(6)H(4)RR', resulting from ring enlargement of a C(5)H(4)R lig and by incorporation of the CR' fragment. This reaction exhibited firs t-order kinetics. Whatever the solvent, the rate constants were found to depend markedly on R', increasing in the order Bu(t) < Pr-i < Bu(n) < Me. In benzene, the rates varied with R in the sequence H < Me < Pr -i < Bu(t) whereas the opposite trend was observed in tetrahydrofuran. For a given solvent, the relative proportions of meta- and para-isome rs of C(6)H(4)RR' were practically constant, whatever R and R'. These facts are best explained by a mechanism which involves a cyclopropyl i ntermediate resulting from addition of the oxycarbene group to the cyc lopentadienyl ligand.