Iridium(III, 0, and −I) Complexes Stabilized by 1,1‘-Bis(diphenylphosphino)ferrocene (dppf):  Synthesis and Characterization. Crystal Structures of [Na(THF)₅][Ir(dppf)₂]·THF and [Ir(dppf)₂]

Abstract

The iridium(I) complex stabilized by the organometallic ligand 1,1‘-bis(diphenylphosphino)ferrocene (dppf), [Ir(dppf)2]+, 1, undergoes a cyclometalation reaction in solution to give the iridium(III) hydride [IrH(dppf(−H))(dppf)]+, 2, which has been isolated and characterized by spectroscopic methods. The compound is the final product of the intramolecular oxidative addition of the ortho C−H bond of a phenyl substituent of the diphosphine and is formed through an intermediate hydride, which has also been spectroscopically characterized. 1 can be electrochemically reduced to the Ir(0) and Ir(−I) species, [Ir(dppf)2], 3, and [Ir(dppf)2]-, 4, respectively, in two reversible single-electron processes. These low-valent metal complexes have been obtained by chemical reduction of 1 with sodium naphthalenide in tetrahydrofuran solution and their crystal and molecular structures determined by single-crystal X-ray analyses. 3 crystallizes in the triclinic system, space group P1̄, with a = 13.019(4) Å, b = 13.765(6) Å, c = 15.549(5) Å, α = 93.74(3)°, β = 90.35(3)°, γ = 92.07(3)°, V = 2779(2) Å3, and Z = 2. Anionic complex 4 crystallizes as sodium-solvated salt [Na(THF)5][Ir(dppf)2]·THF, 4b, in which the sodium cation is surrounded by five molecules of THF in a slightly distorted trigonal-bipyramidal environment. 4b crystallizes in the monoclinic system, space group P21/n, with a = 13.325(3) Å, b = 23.976(5) Å, c = 26.774(7) Å, β = 98.77(2)°, V = 8454(4) Å3, and Z = 4. The coordination geometry around the metal in neutral d9 complex 3 is intermediate between the highly distorted square-planar geometry, found earlier in cationic d8 species 1, and the almost regular tetrahedral arrangement of the two diphosphines in the anionic d10 complex 4. Reduction of Ir(I) to Ir(0) and Ir(−I) causes a stepwise decrease of the Ir−P bond length of 0.04 Å (average) and 0.05 Å, respectively, with a concomitant increase of the bite angle of the diphosphine which ranges from 94.3° (average) in [Ir(dppf)2]+ to 102.3° in [Ir(dppf)2]-