Systematic mixed-metal cluster synthesis. The preparation, structure, and spectroscopic properties of bis((diphenylphosphino)methyl)phenylarsine-bridged complexes containing nearly linear Rh3, RhIrRh, IrRhIr, and Ir3 chains

Article abstract of DOI:10.1021/om00141a001

Because metal ions prefer binding phosphorus rather than arsenic, reaction between bis((diphenylphosphino)methyl)phenylarsine (dpma) and Rh₂(CO)₄(μ-Cl)₂ or Ir(CO)₂Cl(p-toluidine) yields the 12-membered metallocycles Rh₂(μ-dpma)₂(CO)₂Cl₂ (1) or Ir₂(μ-dpma)₂(CO)₂Cl₂ (2) with uncoordinated arsenic atoms. Trinuclear complexes have been prepared by the addition of a metal ion to the central cavity of these metallocycles. For example, 1 reacts with Ir(CO)₂Cl(p-toluidine) in the presence of NaBPh₄ to yield [Rh₂Ir(μ-dpma)₂(CO)₃(μ-Cl)Cl][BPh ₄] with the RhIrRh sequence, and 2 reacts with Rh₂(μ-Cl)₂(CO)₄ and NaBPh₄ to form [Ir₂Rh(μ-dpma)₂(μ-CO)₂(CO) ₂(μ-Cl)Cl][BPh₄] with an IrRhIr chain. Infrared, electronic, and ³¹P and ¹³C NMR spectra of the complexes are reported. The NMR results show that the mixed-metal chains retain their identity under normal handling in solution at room temperature. [Rh₂Ir{μ-(C₆H₅)₂PCH ₂As(C₆H₅)CH₂P(C₆H ₅)₂}₂(CO)₃(μ-Cl)Cl][C(C ₆H₅)₄]·2.5CH₂Cl₂ crystallizes from dichloromethane/ethyl ether in the triclinic space group P1 (No. 2) with a = 12.618 (2) A?, b = 17.057 (5) A?, c = 22.545 (2) A?, α = 85.23 (2)°, β = 79.73 (2)°, and γ = 77.38 (2)° at 140 K. Least-squares refinement of 526 parameters using 7036 reflections yields R = 0.071 and R_w = 0.079. The complex consists of the RhIrRh chain bridged by trans-aligned dpma units. The carbonyl groups are all terminal, one bound to each metal. One chloride bridges one RhIr unit, and the other is a terminal ligand on the other rhodium. The nonbonded Rh?Ir separations are 3.154 (1) and 3.188 (1) A?, and the Rh-Ir-Rh angle is 156.3 (1)°. The electronic absorption spectra of this and related tricarbonyl complexes are analyzed in terms of a d_z2 → p_z transition.