REACTIONS OF LOW-COORDINATE TRANSITION-METAL AMIDES WITH SECONDARY PHOSPHANES AND ARSANES - SYNTHESIS, STRUCTURAL, AND SPECTROSCOPIC STUDIES OF [M(N(SIME3)2)(MU-PMES2)]2 (M = MN, FE), [MN(N(SIME3)2)(MU-ASMES2)]2, AND MES2ASASMES2

The reactions of the transition-metal amides M[N(SiMe3)2]2 (M = Mn, Fe) with dimesitylphosphane or dimesitylarsane, HPMes2 or HAsMes2, (Mes = 2,4,6-Me3C6H2) have been investigated. For the reactions involving 1 or 2 equiv of HPMes2, the major products are the dimers [M{N(SiMe3)2}(mu-PMes2)]2 (M = Mn (1), Fe (2)). These complexes feature three-coordinate metals with phosphide bridges and terminal amide groups. A similar product, [Mn{N(SiMe3)2}(mu-AsMes2)]2 (3), is obtained from the reaction between Mn[N(SiMe3)2]2 and either 1 or 2 equiv of HAsMes2. When Fe[N(SiMe3)2]2 is treated with 1 or 2 equiv of HAsMes2, however, tetramesityldiarsane, Mes2AsAsMes2, (4), is formed. The X-ray crystal structures of 1-4 were determined by X-ray crystallography. The metal complexes were further characterized by electronic absorption spectroscopy and magnetic data. Variable-temperature H-1 NMR spectroscopy of 1 and 4 is also reported. Crystal data with Mo K-alpha (lambda = 0.71069 angstrom) radiation at 130 K: 1, [Mn{N(SiMe3)2}(mu-PMes2)]2, C48H80Mn2N2P2Si4, a = 20.480 (14) angstrom, b = 11.808 (14) angstrom, c = 23.331 (9) angstrom, beta = 106.39 (4)degrees, Z = 4, monoclinic, space group P21/c, R = 0.053; 2, [Fe{N(SiMe3)2}(mu-PMes2)]2, C48H80Fe2N2P2Si4, a = 12.459 (3) angstrom, b = 19.438 (6) angstrom. c = 24.794 (6) angstrom, alpha = 67.43 (2)degrees, beta = 84.78 (2)degrees, gamma = 80.68 (2)degrees, Z = 4, triclinic, space group P1BAR, R = 0.099; 3, [Mn{N(SiMe3)2}(mu-AsMes2)]2, C48H80As2Mn2N2Si4, a = 20.549 (8) angstrom, b = 11.801 (6) angstrom, c = 23.467 (10) angstrom, beta = 106.01 (3)degrees, Z = 4, monoclinic, space group P2(1)/c, R = 0.070; 4, Mes2AsAsMes2, C36H44As2, a = 8.857 (2) angstrom, c = 39.715 (14) angstrom, Z = 4, tetragonal, space group P4(3)2(1)2, R = 0.072.