FURTHER-STUDIES ON THE REACTIVITY OF COMPLEXES OF THE TYPE CIS-RE2(MU-O2CR)2X2(MU-DPPM)2 - THE STRUCTURAL CHARACTERIZATION OF CIS-RE2(MU-O2CCH3)2(NCBH3)2(MU-DPPM)2 AND [RE2CL3(MU-DPPM)2(1,2-C6H4(CN)2)2]PF6

The reactions of cis-Re2(O2CC2H5)2Cl2(dppm)2 (dppm = Ph2PCH2PPh2) with the nitriles RCN (R = CH3 or C2H5) in the presence of HBF4. Et2O or HPF6 (aq.) afford salts of the cis-[Re2Cl2(dppm)2(NCR)4]2+ cations. Studies on the reactivity of cis-[Re2Cl2(dppm)2(NCC2H5)4](PF6)2 with CO in acetone show that the mixed carbonyl-nitrile complexes [Re2Cl3(dppm)2(CO)2(NCC2H5)]PF6 and Re2Cl3(dppm)2(CO)2(NCC2H5) are the major products; these reactions involve the displacement of nitrile by CO and the uptake of Cl- through the sacrifice of a portion of the starting dirhenium complex. Attempts to grow crystals of cis-[Re2Cl2(dppm)2(NCC2H5)4](PF6)2 led to its conversion to [Re2Cl3(dppm)2(NCC2H5)2]PF6. The related complex [Re2Cl3(dppm)2(1,2-C6H4(CN)2)2]PF6 has been prepared by the reaction of Re2Cl4(dppm)2 with 1,2-C6H4(CN)2 and KPF6 in acetone, and its structure established by X-ray crystallography. The crystallographic data are as follows: orthorhombic space group P2(1)2(1)2(1), a = 18.242(6), b = 19.197(6), c = 19.789(6) angstrom, V = 6929(7) angstrom3 and Z = 4. The structure was refined to R = 0.081 (R(w) = 0.098) for 3511 data with I > 3.0-sigma-(I). The structure, which can be represented as [Cl2Re(mu-dppm)2ReCl(1,2-C6H4(CN)2)2]PF6, contains monodentate 1,2-C6H4(CN)2 ligands and possesses a staggered rotational geometry. The Re-Re bond length is 2.265(1) angstrom. The reaction of cis-Re2(O2CCH3)2Cl2(dppm)2 with NaBH3CN in THF gives cis-Re2(O2CCH3)2(NCBH3)2(dppm)2, in which the structure of the parent complex is retained but with N-bound cyanotrihydroborato ligands in place of the axially bound chlorides. The crystallographic data for cis-Re2(O2CCH3)2(NCBH3)2(dppm)2.CH2Cl2 are as follows: orthorhombic space group Pbca, a = 18.072(2), b = 19.982(2), c = 31.795(6) angstrom, V = 11481(5) angstrom3 and Z = 8. The structure was refined to R = 0.035 (R(w) = 0.045) for 4613 data with I > 3.0-sigma-(I). The Re-Re bond distance in this complex is 2.2938(7) angstrom.