THE REDOX CHEMISTRY OF THE TRIPLY BONDED COMPOUNDS RE2X4(MU-DMPM)3 (X=CL OR BR - DMPM=ME2PCH2PME2) AND THE ISOLATION AND CHARACTERIZATION OF THE NITROSYL COMPLEX RE2CL5(MU-DMPM)2(NO)

The current literature on multiply bonded dirhenium complexes that contain the bis(dimethylphosphino)methane ligand (abbreviated dmpm) is reviewed. New procedures are described for the synthesis of the complex Re2Cl4(mu-dmpm)3. The analogous bromide and iodide complexes of stoichiometry Re2X4(mu-dmpm)3 have been prepared by the reactions of Re2Br4(mu-dppm)2 (dppm = Ph2PCH2PPh2) and Re2X4(PR3)4 (X = Br or I; R = Et or Pr(n)) with dmpm. The reactions of ReX4(mu-dmpm)3 (X = Cl or Br) with NOPF6 in dichloromethane give the paramagnetic species [Re2X4(mu-dmpm)3]PF6. The chloro complex reacts further with NOPF6 to afford the diamagnetic complex Re2Cl5(mu-dmpm)2(NO). This is the first triply bonded dimetal complex that contains a nitrosyl ligand and is stabilized to fission of the metal-metal bond. The identity of this complex has been confirmed by a single crystal X-ray structure determination. Crystal data at 20-degrees-C: orthorhombic space group Iba2 (No. 45), a = 14.278(3), b = 23.966(3), c = 13.880(3) angstrom, V= 4749(3) angstrom, Z = 8. The structure was refined by full matrix least-squares to R = 0.036 (R(w) = O.047) for 1427 data with I>3-sigma(I). The structure, which can be represented as Cl3Re(mu-dmpm)2ReCl2(NO), contains a terminally bound NO ligand and a cis, trans disposition of the pairs of phosphorus donor atoms at the two metal centers. The Re-Re bond distance is 2.379(1) angstrom.