Ph(2)PPy replacement of the 1,5-COD ligand in the sulfido-capped cluster Fe-2(CO)(6)(mu(3)-S)(2)Pt(1,5-COD). X-ray diffraction structure and redox behavior of Fe-2(CO)(6)(mu(3)-S)(2)Pt(Ph(2)PPy)(2)

The replacement of the 1,5-cyclooctadiene (COD) ligand in the cluster Fe-2(CO)(6)(mu(3)-S)(2)Pt(1,5-COD) (1) with the pyridylphosphine ligand Ph(2)PPy (2.0 equiv; occurs readily at room temperature to give the phosphine-substituted cluster Fe-2(CO)(6)(mu 3-S)(2)Pt(Ph(2)PPy)(2) (2). Cluster 2 was isolated by preparative chromatography and characterized in solution by IR and P-31 NMR spectroscopy. The solid-state structure was established by X-ray diffraction analysis. Fe-2(CO)(6)(mu(3)-S)(2)Pt(Ph(2)PPy)(2) crystallizes in the monoclinic space group C-2/c, a = 19.8781(5) Angstrom, b = 13.4603(3) Angstrom, c = 16.3304(4) Angstrom, beta = 108.828(2) degrees, V = 4135.6(2) Angstrom(3), Z = 4, d(calc) = 1.711 g cm(-3); R = 0.0232, R(w) = 0.0258 for 2212 observed reflections with I > 3 sigma(1). The X-ray structure confirms the square planar geometry at the platinum center and coordination of the phosphorus centers to the platinum center in cluster 2, The arachno polyhedral shape adopted by cluster 2 is not consistent with PSEP theory, with the deviation from PSEP theory being attributed to the strong propensity for the platinum center in 2 to maintain a square planar geometry. Cyclic voltammetric studies in CH2Cl2 indicate that 2 undergoes a reversible, one-election oxidation at E(1/2) = 0.39 V. The composition and energy of the HOMO and LUMO levels in the model cluster Fe-2(CO)(6)(mu(3)-S)(2)Pt(PH3)(2) have been determined by carrying out extended Huckel molecular orbital calculations, and the data are discussed with respect to the observed electrochemistry.