REACTIONS OF THE ELECTRON-RICH TRIPLY BONDED DIRHENIUM(II) COMPLEXES RE2X4-MU-DPPM)2 (X = CL, BR) WITH DIOXYGEN .1. MULTIELECTRON REDOX CHEMISTRY WITH PRESERVATION OF THE RE2X4(DPPM)2 UNIT

The dirhenium(II) complexes Re2X4(mu-dppm)2 (1a, X = Cl; 1b, X = Br; dppm = Ph2PCH2PPh2), which contain an electron-rich Re-Re triple bond, react with dioxygen in a variety of solvents to afford Re2(mu-O)(mu-X)(O)X3(mu-dppm)2 (2a, X = Cl; 2b, X = Br) and Re2(mu-O)(O)2X4(mu-dppm)2 (3a, X = Cl; 3b, X = Br) in which the Re2X4(mu-dppm)2 entity is preserved and net 4- and 6-electron oxidations of the dirhenium unit have occurred. The complexes of type 2, which are weakly paramagnetic and possess Knight-shifted NMR spectra, have edge-sharing bioctahedral structures as shown by a single-crystal X-ray structure determination on a crystal of composition Re2(mu-O)(mu-Cl)(O)Cl3(mu-dppm)2.(CH3)2CO (2a.(CH3)2CO). The structure solution was complicated by a disorder involving the terminal oxo ligand and the syn terminal chloro ligand on the adjacent Re atom. The Re ... Re distance is very long (3.363(2) angstrom). Crystal data for 2a.(CH3)2CO (+23-degrees-C): triclinic space group P1BAR (No. 2), a = 16.069(6) angstrom, b = 16.540(5) angstrom, c = 12.214(2) angstrom, alpha, = 109.18(2)-degrees, beta = 99.09(3)-degrees, gamma = 101.01(3)-degrees, V = 2923(2) angstrom3, and Z = 2. The structure was refined to R = 0.068 (R(w) = 0.082) for 6553 data with I > 3.0sigma(I). Complex 2a can be derivatized by reaction with isocyanide ligands (RNC; R = C6H3-2,6-Me2 (xylyl), CHMe2, CMe3, C6H11) and acetonitrile to give complexes of the type Re2(mu-O)(O)Cl4(mu-dppm)2(L) (4, L = RNC; 5, L = MeCN) which like 2a are weakly paramagnetic and have Knight-shifted NMR spectra. The structure of crystals of composition Re2(mu-O)(O)Cl4(mu-dppm)2(CNxyl).CH2Cl2.H2O(4a) has been established by X-ray crystallography. The structure is an unsymmetrical corner-sharing bioctahedron Cl3Re(mu-O)(mu-dppm)2Re(O)Cl(CNxyl), in which the rhenium centers can formally be represented as Re(III)-Re(V), i.e. Re(III)...O=Re(V)=O. Crystal data for 4a (+20-degrees-C): triclinic space group P1BAR (No. 2), a = 14.316(3) angstrom, b = 14.818(2) angstrom, c = 16.840(2) angstrom, alpha = 99.60(1)-degrees, beta = 106.38(1)-degrees, gamma = 97.26(1)-degrees, V = 3322(2) angstrom3 and Z = 2. The structure was refined to R = 0.056 (R(w) = 0.082) for 5978 data with I > 3.0sigma(I). The compounds of type 4 have been oxidized by [(eta5-C5H5)2Fe]PF6 to afford the mixed-valence paramagnetic complexes [Re2(mu-O)(O)Cl4(mu-dppm)(CNR)]PF6 (6; R = C6H3-2,6-Me2, CHMe2, CMe3). The dirhenium(V) complexes Re2(mu-O)(O)2X4(mu-dppm)2 (3), which are the final products of the oxygenation of 1 and 2, have a centrosymmetric corner-sharing bioctahedral structure. The structures of two different crystals of 3a (X = Cl), which contain either two molecules of lattice acetone (3a.(CH3)2CO) or two molecules of dichloromethane (3a.CH2Cl2), have been determined. Crystal data for 3a.(CH3)2CO (+23-degrees-C): triclinic space group P1BAR (No. 2), a = 11. 193(2) angstrom, b = 12.882(2) angstrom, c = 10.892(2) angstrom, alpha = 101.95(1)-degrees, beta = 113.30(1)-degrees, gamma = 75.52(1)-degrees, V = 1386.3(4) angstrom, and Z = 1. The structure was refined to R = 0.029 (R(w) = 0.058) for 4209 data with I > 3.0sigma(I). Crystal data for 3a.CH2Cl2 (+20-degrees-C): triclinic space group P1BAR (No. 2), a = 11.264(4) angstrom, b = 11.317(4) angstrom, c = 12.966(7) angstrom, alpha = 103.86(4)-degrees, beta = 104.24(4)-degrees, gamma = 113.54(3), V = 1358(3) angstrom3, and Z = 1. The structure was refined to R = 0.052 (R(w) = 0.072) for 3538 data with I > 3.0sigma(I).