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

Article abstract of DOI:10.1021/ic980455d

Reaction of 2,6-bis(diphenylphosphino)pyridine (bdppp or (Ph₂P)₂Py)) with K₄Mo₂Cl₈ in refluxing methanol gives Mo₂Cl₄(bdppp)₂ (1) with retention of the quadruple Mo-Mo bond. However, the quadruply bonded octachlorodirhenate(III) anion, Re₂Cl_82-, reacts with bdppp under similar conditions to afford Re₂Cl₄(bdppp)₂ (2), which has a triply bonded dirhenium(H) core, Re₂₄₊. An intermediate species, [Buⁿ₄N][Re₂Cl₇(bdppp)] (3), containing an Re₂₆₊ 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: Mo₂Cl₄(bdppp)₂·2CH₂Cl ₂ (1·2CH₂Cl₂), monoclinic space group P2₁/c with a = 15.475(2) A?, b = 11.5958(7) A?, c = 16.7637 (6) A?, β = 98.178(5)°, Z = 2; Re₂-Cl₄(bdppp)₂ (2), monoclinic space group P2₁/n with a = 16.173(2) A?, b = 11.285(1) A?, c = 28.771 (4) A?, β = 96.17(1)°, Z = 4; [Buⁿ₄N][Re₂Cl ₇(bdppp)]·CH₂Cl₂ (3·CH₂Cl₂), triclinic space group P1? with a = 16.054(2) A?, b = 18.562(3) A?, c = 20.205 (6) A?, a = 89.71(2)°, β = 73.21(1)°, γ = 73.47(2)°, Z = 4.