Further Studies of the Isomeric 1,2,7- and 1,3,6-Re2Cl5(PMe3)3 Compounds

Mixed chloride/phosphine complexes of the dirhenium core. 10. Redox reactions of an edge-sharing dirhenium(III) non-metal-metal-bonded complex, Re(2)(mu-Cl)(2)Cl(4)(PMe(3))(4)

Reduction and oxidation reactions of the dirhenium(III) non-metal-metal-bonded edge-sharing complex, Re(2)(mu-Cl)(2)Cl(4)(PMe(3))(4) (1), have been studied. Several new mono- and dinuclear rhenium compounds have been isolated and structurally characterized in the course of this study. Reductions of 1 with 1 and 2 equiv of KC(8) result in an unusual face-sharing complex having an Re(2)(5+) core, Re(2)(mu-Cl)(3)Cl(2)(PMe(3))(4) (2), and a triply bonded Re(II) compound, 1,2,7,8-Re(2)Cl(4)(PMe(3))(4) (3), respectively. Two-electron reduction of 1 in the presence of tetrabutylammonium chloride affords a new triply bonded complex of the Re(2)(4+) core, [Bu(n)()(4)N][1,2,7-Re(2)Cl(5)(PMe(3))(3)] (4). Oxidation of 1 with NOBF(4) yields a Re(IV) mononuclear compound, trans-ReCl(4)(PMe(3))(2) (5). Two isomers of the monomeric Re(III) anion, [ReCl(4)(PMe(3))(2)](-) (6, 7), have been isolated as side products. The crystal structures of compounds 2 and 4-7 have been determined by X-ray crystallography. The Re-Re distance in the face-sharing complex 2 of 2.686(1) A is relatively short. The metal-metal bond length in anion 4 of 2.2354(7) A is consistent with the usual values for the triply bonded Re(2)(4+) core compounds. In addition, a cis arrangement of trimethylphosphine ligands in the starting material 1 is retained upon reduction in the dinuclear products 2-4.

Mixed Chloride/Amine Complexes of Dimolybdenum(II,II). 4. Rotational Isomers of Mo(2)Cl(4)(R-py)(4) (R-py = 4-Picoline, 3,5-Lutidine, and 4-tert-Butylpyridine)

The quadruply bonded dimolybdenum complexes with alkyl-substituted pyridines of the formula Mo(2)Cl(4)(R-py)(4) (R-py = 4-pic (4-methylpyridine) (1), 3,5-lut (3,5-dimethylpyridine) (2), and 4-Bu(t)-py (4-tert-butylpyridine) (3)) have been prepared. Nine different compounds, in which there are 11 independent molecules, have been obtained in crystalline form, and their crystal structures have been investigated by X-ray diffraction. Three types of geometric isomers which differ by the angle of internal rotation about the Mo-Mo axis have been recognized in these structures. The eclipsed structures 1-3a display pyridine ligands opposite to each other across the metal-metal bond and have a virtual symmetry D(2)(h)(). The noncentrosymmetric D(2)(d)() structures 1-3b have each pyridine ligand opposite to a Cl atom. The molecules 3c-f have a partially staggered D(2) geometry with N-Mo-Mo-N torsion angles ranging from 10.4 degrees to 25.2 degrees. As a result of this work it is now clear that Mo(2)Cl(4)(R-py)(4) compounds do not show a preference for D(2)(h)() conformation rather than D(2)(d)() conformation. In fact, they seem unusually unrestricted in their rotational conformation, and packing forces appear to have a major influence on the conformation adopted. Further clarification of this question will require spectroscopic study of solutions.

Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 5. Reduction or Disproportionation at the Re(2)(6+) Unit in Reactions with Tertiary Phosphines in Different Solvents

For reactions of the octachlorodirhenium anion, [Re(2)Cl(8)](2)(-), with tertiary phosphines PEt(3) and PPr(n)(3), the influence of solvent on the reaction pathway has been studied. It has been shown that in 1-propanol at room temperature the reaction leads to a one-electron reduction of the Re(2)(6+) core. The novel dirhenium(II,III) paramagnetic products of stoichiometries [Bu(n)(4)N][Re(2)Cl(6)(PEt(3))(2)] (1a) and Re(2)Cl(5)(PPr(n)(3))(3) (2a) have been isolated and characterized. In benzene a disproportionation process occurs resulting in mononuclear rhenium(IV) complexes ReCl(4)(PR(3))(2) (PR(3) = PEt(3) (1b) and PPr(n)(3) (2b)) in addition to 1a and 2a, respectively. The solid state structures of compounds 1a, 1b, 2a.0.25C(6)H(14), and 2b have been investigated by X-ray crystallography. The crystallographic parameters are as follows: for 1a, tetragonal space group P4(2)/m with a = 11.821(2) Å, c = 14.770(3) Å, and Z = 2; for 1b, monoclinic space group P2(1)/n with a = 8.0555(4) Å, b = 12.536(2) Å, c = 10.2041(6) Å, beta = 99.167(9) degrees, and Z = 2; for 2a.0.25C(6)H(14), monoclinic space group P2(1)/n with a = 11.7679(9) Å, b = 18.574(5) Å, c = 19.688(4) Å, beta = 93.37(2) degrees, and Z = 4; for 2b, monoclinic space group P2(1)/c with a = 8.219(2) Å, b = 11.210(1) Å, c = 14.331(3) Å, beta = 93.171(9) degrees, and Z = 2. It has also been found that the disproportionation process in benzene goes by way of an intermediate complex which is an initial product of interaction between the [Re(2)Cl(8)](2)(-) and the phosphine. In the case of the triethylphosphine ligand we formulate this complex as [Bu(n)(4)N][Re(2)Cl(7)(PEt(3))(3)] (1c).

Ligand Exchange or Reduction at Multiply Bonded Dimetal Units of Molybdenum and Rhenium by 2,6-Bis(diphenylphosphino)pyridine

Reaction of 2,6-bis(diphenylphosphino)pyridine (bdppp or (Ph(2)P)(2)Py)) with K(4)Mo(2)Cl(8) in refluxing methanol gives Mo(2)Cl(4)(bdppp)(2) (1) with retention of the quadruple Mo-Mo bond. However, the quadruply bonded octachlorodirhenate(III) anion, Re(2)Cl(8)(2)(-), reacts with bdppp under similar conditions to afford Re(2)Cl(4)(bdppp)(2) (2), which has a triply bonded dirhenium(II) core, Re(2)(4+). An intermediate species, [Bu(n)(4)N][Re(2)Cl(7)(bdppp)] (3), containing an Re(2)(6+) core and only one bridging bdppp ligand has also been isolated. The crystal structures of complexes 1-3 have been investigated by X-ray crystallography. In all cases the potentially tridentate bdppp acts as a bidentate ligand using one N and one of the P atoms, leaving the second phosphorus atom noncoordinated. The crystallographic parameters for these structures are as follows: Mo(2)Cl(4)(bdppp)(2).2CH(2)Cl(2) (1.2CH(2)Cl(2)), monoclinic space group P2(1)/c with a = 15.475(2) Å, b = 11.5958(7) Å, c = 16.7637 (6) Å, beta = 98.178(5) degrees, Z = 2; Re(2)Cl(4)(bdppp)(2) (2), monoclinic space group P2(1)/n with a = 16.173(2) Å, b = 11.285(1) Å, c = 28.771 (4) Å, beta = 96.17(1) degrees, Z = 4; [Bu(n)(4)N][Re(2)Cl(7)(bdppp)].CH(2)Cl(2) (3.CH(2)Cl(2)), triclinic space group P&onemacr; with a = 16.054(2) Å, b = 18.562(3) Å, c = 20.205 (6) Å, alpha = 89.71(2) degrees, beta = 73.21(1) degrees, gamma = 73.47(2) degrees, Z = 4.