Theoretical investigation of the formation of five-membered metallacycles by reaction of CO with metallacyclobutenones: differences between Ni and Pt

Reactions of CO with nickel or platinum complexes of cyclic alkynes or arynes form initially metallacyclobutenone species, which undergo further insertion of CO to give five-membered metallacycles. The differences in regioselectivity observed for nickel or platinum have been investigated computationally by DFT methods. Although both metals prefer insertion of the second CO via a five-coordinate mechanism, the formation of the five-membered nickelacycle is under thermodynamic control, leading to a symmetrical nickelacyclopentene-2,4-dione complex, whereas platinum yields the kinetically favoured platinacyclopentene-2,3-dione complex. (C) 2000 Elsevier Science S.A. All rights reserved.