ELECTRON-TRANSFER REACTIONS OF RE(CO)(5) - ATOM-TRANSFER-CONCERTED MECHANISM VS BIMETALLIC INTERMEDIATE FORMATION

Flash photochemically generated Re(CO)(5) reacts with halide complexes , Cu(Me(4)[14]-1,3,8,10-tetraeneN(4))X(+), Cu(Me(2)pyo[l4]trieneN(4))X (+), and Ni(Me(2)pyo[l4]trieneN(4))X(+) (X = Cl, Br, I) and ion pairs, [Co(bipy)(3)(3+), X(-)]. The rate constants for the electron transfer s have values, k approximate to 10(9) M(-1) s(-1), close to expectatio ns for processes with diffusion-controlled rates. Reaction intermediat es, probably bimetallic species, were detected in electron-transfer re actions of Re(CO)(5) with Cu(Me(6)[14]dieneN(4))X(+), (X = Cl, Br, I). In the absence of the halides X(-), the electron-transfer reactions b etween Re(CO)(5) and these complexes are slow, k < 10(6) M(-1) s(-1). The results are discussed in terms of inner-sphere pathways, namely an atom-transfer-concerted mechanism. The mediation of bimetallic interm ediates in the electron transfer is also considered.