Reactivity of 2-(Diphenylphosphino)pyridine toward Complexes Containing the Quadruply Bonded Re26+ Core: Ortho Metalation and Redox Chemistry

Article abstract of DOI:10.1021/ja00317a026

The quadruply bonded dirhenium(III) complexes (n-Bu4N)2Re2Cl8 and Re2Cl6(PR3)2 (R = Et or n-Bu) react in methanol with 2-(diphenylphosphino)pyridine (Ph2Ppy) to afford complexes that are derivatives of the triply bonded dirhenium(II) core, Re₂⁴⁺.The complex Re2Cl4(Ph2Ppy)3 (I) is formed initially and is found to eliminate HCl to give the ortho-metalated complex Re2Cl3(Ph2Ppy)2<(C6H5)(C6H4)Ppy> (II), the first example of a reaction of this type occurring at a metal-metal multiple bond of the M2L8 type.Both chloride and hexafluorophosphate salts of the ²⁺ dication (III) have been isolated (Cl^-, IIIa; PF6^-, IIIb); III constitutes a rare example of a multiply bonded dimetal unit complexed by four neutral bridging ligands. Cl2 can be converted to either I or II under certain conditions.When acetone is used as the solvent, then Re2Cl6(PR3)2 reacts with Ph2Ppy to give Re2Cl4(Ph2Ppy)2(PR3) (R = Et, IVa; R = n-Bu, IVb), whereas with acetonitrile as the solvent, Ph2Ppy converts (n-Bu4N)2Re2Cl8 to the dirhenium(III) complex Re2(μ-Cl)2(μ-Ph2Ppy)2Cl4; i.e., substitution occurs but without concomitant reduction.The complexes II, IIIb, and IVa have been structurally characterized by X-ray crystallography.Compound II crystallizes in space group P2₁/n with a = 12.160 (6) Angstroem, b = 21.418 (7) Angstroem, c = 18.464 (2) Angstroem, β = 99.04 (3)^o, and Z = 4.Complex IIIb forms crystals in space group P2₁/c with a = 24.316 (3) Angstroem, b = 12.101 (2) Angstroem, c = 27.070 (3) Angstroem, β = 105.670 (9)^o, and Z = 4.Two acetone molecules per dimer unit are also present in the lattice.Compound IVa crystallizes in space group P1 with a = 10.683 (2) Angstroem, b = 20.033 (5) Angstroem, c = 10.544 (3) Angstroem, α = 102.29 (3)^o, β = 107.69 (2)^o. γ = 94.19 (2)^o, and Z = 2.