Synthesis, structure, and formation mechanism of the halogen-bridged tricobalt clusters, [Co3CP3(mu(3)-CPh)(2)(mu-X)](+) (X = Cl, Br, and I)

摘要

Reactions of a benzylidyne-capped tricobalt cluster, [Co3Cp3(mu(3)-CPh)(2)] (1), with halogens (X-2 = Cl-2, Br-2, and I-2) in CH2Cl2 afforded halogen-adducts of 1. The structure of four isolated salts [Co3Cp3(mu(3)-CPh)(2)(mu-Cl)]PF6 . MeCN (2PF(6) . MeCN), [Co3Cp3(mu(3)-CPh)(2)(mu-Br)]SbF6 (3SbF(6)), [Co3Cp3(mu(3)-CPh)(2)(mu-I)]SbF6 . CH2Cl2 (4SbF(6) . CH2Cl2), and [Co3Cp3(mu(3)-CPh)(2)(mu-I)]I-3 (4I(3)) determined by X-ray diffraction can be regarded formally as halide-adducts of 1(2+). The halogen atom in each structure lies in the Co-3 plane. The halogen-bridged Co-Co edge was elongated (in 2PF(6) . MeCN = 2.6072(4), in 3SbF(6) = 2.6106(7), in 4SbF(6) . CH2Cl2 = 2.622(2), and in 4I(3)=2.6718(9) Angstrom), and the Co-Co distances that had no halogen-bridge remained unchanged from the Co-Co distance of 1 (2.382(8) Angstrom), (in 2PF(6)=2.4037(8) and 2.3948(7), in 3SbF(6)=2.3888(6) and 2.4017(7), in 4SbF(6) . CH2Cl2 = 2.393(2) and 2.388(1), and in 4I(3) = 2.397(1) and 2.3868(9) Angstrom). The UV-Vis absorption spectra of 2(+), 3(+), and 4(+) had characteristic absorption peaks at 796, 819, and 844 nm, respectively. Cyclic voltammograms of 2PF(6) in CH2Cl2 with 0.1 M (Bu4NPF6)-Bu-n as the supporting electrolyte showed a chemically reversible oxidation (at a potential of 0.75 V versus Fc/Fc(+)), and an irreversible reduction wave at -0.57 V. The irreversible reduction resulted in the recovery oft. The redox properties of 3+ and 4+ are very similar to that of 2(+). Cyclic voltammetry of 1 in 0.1 M (Bu4NCl)-Bu-n/MeCN indicates that the formation of 2(+) is a multi-step reaction. Initially, 1 is oxidized to 1(+), and then, 1(+) is coordinated by Cl- followed by immediate oxidation to 2(+). (C) 2003 Elsevier B.V. All rights reserved. [References: 24]