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 aryn es form initially metallacyclobutenone species, which undergo further inser tion of CO to give five-membered metallacycles. The differences in regiosel ectivity observed for nickel or platinum have been investigated computation ally by DFT methods. Although both metals prefer insertion of the second CO via a five-coordinate mechanism, the formation of the five-membered nickel acycle is under thermodynamic control, leading to a symmetrical nickelacycl opentene-2,4-dione complex, whereas platinum yields the kinetically favoure d platinacyclopentene-2,3-dione complex. (C) 2000 Elsevier Science S.A. All rights reserved.