FORMAMIDINATE COMPLEXES OF DIRHENIUM, RE2N+, CORES WITH N = 4, 5, AND 6

Re2(DMF)4Cl2 (1) has been prepared by the reaction of molten HDFM (di-p-tolylformamidine) and Re2(OAc)4Cl2. The accessibility of the quadruply bridged dinuclear derivatives with both formal charges 5+ and 4+ on the dirhenium cores is suggested by the CV measurement of this complex, which shows reversible and quasireversible one-electron reductions at -780 and -1050 mV, respectively (vs Ag/AgCl). Re2(DFM)4CI has been isolated from the reaction between 1 and 1 equiv of Na/Hg, as a purple crystalline material (2). The reduction of either 2 with 1 equiv of Na/Hg or 1 with 2 equiv of Na/Hg results in Re2(DFM)4 (3). Orange Re2(DFM)4Cl2 Crystallizes with three benzene molecules (1) in the space group C2/m with a = 15.631 (5) angstrom, b = 24.307 (8) angstrom, c = 11.879 (4) angstrom, beta = 129.73 (2)-degrees, V = 3471 (2) angstrom3, and Z = 2, and also with two dichloromethane molecules (4) in the space group P2(1)/c with a = 10.703 (2) angstrom b = 27.825 (5) angstrom, c = 10.472 (1) angstrom, beta = 96.06 (1)-degrees V = 3101 (1) angstrom3, and Z = 2. Dark purple Re2(DFM)4.C6H6 (3) crystallizes in the space group P4/n with a = 13.252 (3) angstrom, c = 17.440 (4) angstrom, V = 3063 (1) angstrom3, and Z = 2. Red Re2)DFM)4(OMe)2.3C6H6 (5) crystallizes in the space group P1BAR with a = 12.047 (3) angstrom, b = 15.433 (3) angstrom, c = 10.824 (2) angstrom, alpha = 95.45 (2)-degrees, beta = 104.37 (2)-degrees, gamma = 67.15 (2)-degrees, V = 1796 (1) angstrom3, and Z = 1. The Re-Re bond lengths found are 2.2759 (3), 2.344 (2), 2.2705 (5), and 2.3045 (2) angstrom for 1, 3,4, and 5, respectively. SCF-X-alpha calculations were performed on model complexes and reveal that while both compounds 1 and 5 assume a classic quadruple bond configuration sigma-2-pi-4-delta-2 the addition of two electrons results in a novel triple bond configuration sigma-2-pi-4-delta-2-pi-*2 for compound 3. The electronic spectra have also been assigned in accordance with the results of the MO calculations.