REACTIONS OF THE A-FRAME-LIKE MONOCARBONYL COMPLEXES RE2(ETA-X)(ETA-DPPM)2X3(CO) (X = CL OR BR-DPPM = PH2PCH2PPH2) WITH TRIMETHYLPHOSPHINE AND TRIALKYLPHOSPHITE LIGANDS - THE STRUCTURAL CHARACTERIZATION OF [RE2(ETA-CL)(ETA-CO)(ETA-DPPM)2CL2(PME3)2]CL

The 1:1 carbonyl adduct Re2Cl4(dppm)2(CO) reacts with PMe3 in CH2Cl2 at room temperature to afford the green diamagnetic complex [Re2Cl3(dppm)2(CO)(PMe3)2]Cl. When similar reactions are carried out in the presence of NaBPh4 or TlPF6, with THF or CH2Cl2 as the reaction solvents, respectively, the salts [Re2Cl3(dppm)2(CO)(PMe3)2]X (X = BPh4 or PF6) are produced. Similar procedures have been used to prepare the bromo-derivative [Re2Br3(dppm)2(CO)(PMe3)2]PF6, and the phosphite complexes {Re2Cl3(dppm)2(CO)[P(OR)3]2}PF6 (R = Me or Et). IR spectroscopy shows that the CO ligand is bridging the two metal centres (ν(CO) ca 1635 cm-1 for the PMe3 complexes and ca 1680 cm-1 for the P(OR)3 derivatives). This conclusion has been confirmed by a crystal structure determination on [Re2Cl3(dppm)2(CO)(PMe3)2]Cl·1/2CH2Cl2. The crystallographic data are as follows: triclinic space group P1̄, a = 13.261(1), b = 19.246(2), c = 11.860(2) Å, α = 97.57(1), β = 98.98(1), γ = 79.08(1)°, V = 2919(1) Å3 and Z = 2. The structure was refined to R = 0.043 (Rw = 0.056) for 5949 data with I > 3.0σ(I). The dirhenium cation has the structure of an edge-shared bioctahedron with virtual C2ν symmetry. There is a trans disposition of bridging dppm ligands. The equatorial plane contains a bridging carbonyl and a bridging chloride ligand. The three chloride ligands are in an all-cis arrangement to one another on one side of this plane; the two PMe3 ligands are cis to the μ-CO ligand. The ReRe distance is 2.602(1) Å. © 1990.