Abstract
Binuclear diphosphine-bridged complexes with the tridentate ligand 2-(bis(diphenylphosphino)methyl)pyridine, (Ph2P)2CHC5NH4 = PNP, have been prepared for rhodium and iridium. Two of the complexes, [Rh2(CO)2(PNP)2](P-F6) 2·C3H6O (1) and [Ir2(μ-CO)(CO)2(PNP)2](BF4) 2 (2), have been characterized by single-crystal X-ray diffraction. Complex 1 crystallizes in the orthorhombic space group Pbcn with Z = 4, a = 19.658 (7) Å, b = 18.528 (7) Å, c = 17.993 (6) Å, V = 6554 (7) Å3, and d = 1.553 g/cm3 while 2 crystallizes in the triclinic space group P1 with Z = 4, a = 16.387 (4) Å, b = 16.710 (6) Å, c = 24.710 (6) Å, α = 76.03 (2)°, β = 84.16 (2)°, γ = 75.37 (2)°, V = 6347 (4) Å3, and d = 1.638 g/cm3. Both complexes are of the diphosphine-bridged binuclear type with trans phosphorus atoms and with both pyridyl nitrogen atoms bonded to the metal atoms, giving five-membered PN chelate rings. The pyridyl nitrogen atoms are bonded to the metals on the same side of the binuclear complex. Complex 1 is of the face-to-face variety with a Rh⋯Rh separation of 3.054 (1) Å while 2 has a bridging CO ligand and approximate trigonal-bipyramidal geometry around each iridium atom. The Ir-Ir separation in 2 is 2.815 (1) Å and is consistent with the presence of an Ir-Ir bond. Complex 2 easily loses one CO ligand in solution, affording the iridium analogue of 1. Reactions of these complexes with nucleophiles such as halide and sulfide ions are described. Thus, 1 reacts with Cl- in acetone solution, giving the four-coordinate PN-bonded monomeric compound [Rh(Cl)(CO)(PNP)], which has a dangling phosphorus atom, whereas the analogous reaction with 2 gives the binuclear complex [Ir2(Cl)(CO)2(PNP)2]+, which has one bonded and one free pyridyl nitrogen atom. The reaction of 1 with S2- gives the binuclear sulfide-bridged A-frame complex [Rh2(μ-S)(CO)2(PNP)2], which has both pyridyl nitrogen atoms dangling. All of these complexes have been characterized by IR and 31P NMR spectroscopy, and their syntheses and properties are described.