Electrochemical reduction properties of A-frame compounds and crystal structure of Pd-2(dppm)(2)(Me)(2)(Br)(+) dimer

摘要

Two series of A-frame complexes, [Pd-2(dppm)(2)(R)(2)(mu-X)](+) (R = Me and X = Cl, Br, I, H; R = Mes and X = Br, I), were investigated by cyclic voltammetry (CV). The 2-electron reduction potentials for the first series increase from I (-1.10), Br (-1.17), Cl (-1.25) to H (-1.65 V versus SCE, in CHCl3) as well as in the second series; Br (-1.35) and I (-1.38 V versus SCE, in THF). The nature of the LUMO where the electron reduction takes place is qualitatively addressed by DFT on the corresponding model complexes [Pd-2(H2PCH2PH2)(2)(R)(2)(mu-X)](+). The LUMO and (LUMO + 1) of the halide derivatives exhibit the presence of Pd d(x2-y2) atomic orbitals interacting in an anti-bonding fashion with the n-donor orbitals of X-, P, and Me-, explaining in part the observed reactivity upon reduction. The X-ray structure of [Pd-2(dPPM)(2)(Me)(2)(mu-Br)](+) compound exhibits the typical A-frame structure with a Pd center dot center dot center dot Pd non-bonding distance of 3.036(1) angstrom, and long Pd-Br bonds of 2.5623(5) and 2.5793(5) angstrom. 2005 Elsevier B.V. All rights reserved.