Photochemical and Chemical Oxidation of α-Dimine−Dithiolene Metal Complexes: Insight into the Role of the Metal Atom

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Abstract
[Pd(bpy)(bdt)], 2 (bpy = 2,2'-bipyridine, bdt = 1,2-benzenedithiolate), was prepared in good yield by the reaction of bdtNa2 with [(bpy)PdCl2] in DMSO. The analogous nickel complex, 1, was prepared in a similar reaction using MeOH/CH2Cl2 and [(bpy)NiCl2.dmf]2. Both 1 (a = 7.9920(1) A, b = 11.4385(1) A, c = 16.1415(1) A, beta = 103.327(1) degrees, V = 1435.86(2) A3, Z = 4) and 2 (a = 8.1631(5) A, b = 11.4379(7) A, c = 16.2475(10) A, beta = 103.7010(10) degrees, V = 1473.84(12) A3, Z = 4) crystallize in the monoclinic space group P2(1)/c and are isostructural with their previously reported platinum analogue. In accord with the results observed for platinum but not nickel, photochemical oxidation of 2 in DMF provides the monosulfinate complex [Pd(bpy)(bdtO2)], 4, along with a minor amount of the corresponding disulfinate [Pd(bpy)(bdtO4)], 5, while chemical oxidation yields only the latter. 4 cocrystallizes with 5 in the monoclinic space group P2(1)/c (a = 8.026(3) A, b = 14.600(6) A, c = 13.371(3) A, beta = 101.80(3) degrees, V = 1533.8(9) A3, Z = 4) as does pure 5 (a = 8.5611(9) A, b = 14.4586(15) A, c = 13.3677(14) A, beta = 108.122(2) degrees, V = 1572.6(3) A3, Z = 4). Comparison of spectroscopic and electrochemical properties of the three complexes, [M(bpy)(bdt)], yields the following ordering for the energy of the HOMO: Pd < Ni < Pt. The observed reactivity patterns and the electronic data suggest that the "anomalous" reactivity of 1 be attributed to the greater relative flexibility of the coordination geometry for nickel(II) complexes rather than electronic differences such as the energies of the frontier orbitals.