Metal-metal interactions in binuclear complexes. Structural characterization of isomers resulting from apparent internal oxidative addition of a platinum-chlorine bond to a rhodium(I) center

Article abstract of DOI:10.1021/om00127a024

The face-to-face complex trans-Rh(CO)Cl(μ-Ph₂AsCH₂PPh₂) ₂-cis-PtCl₂, 1, isomerizes to trans-Rh-(CO)Cl₂(μ-Ph₂AsCH₂PPh ₂)₂-trans-PtCl upon heating in chloroform or upon treatment with a small amount of Ph₂AsCH₂PPh₂. Metathesis of 1 with iodide produces trans-Rh(CO)I₂(μ-Ph₂AsCH₂PPh ₂)₂-trans-PtI, and the bromo analogue has been prepared similarly. trans-Rh(CO)Cl₂(μ-Ph₂AsCH₂PPh ₂)₂-trans-PtCl·2CH₂Cl₂, 2, crystallizes in the monoclinic space group P2₁/c with a = 17.563 (4) A?, b = 14.995 (4) A?, c = 21.338 (4) A?, β = 105.90 (2)°, V = 5404 (2) A?³, and Z = 4, at 140 K. The structure was refined to a conventional R value of 0.051 using 6017 unique reflections and 334 parameters. trans-Rh(CO)I₂(μ-Ph₂AsCH₂PPh ₂)₂-trans-PtI-CH₂Cl ₂·2CHCl₃, 4, crystallizes in the orthorhombic space group Pbca with a = 17.808 (8) A?, b = 19.488 (8) A?, c = 35.228 (15) A?, V = 12225.6 (9) A?³, and Z = 8 at 140 K. The structure was refined to a conventional R value of 0.092 using 5001 unique data and 344 parameters. Both structures are similar with a six-coordinate rhodium atom (ligands: two As, CO, two Cl or two I, Pt) and a four-coordinate platinum (ligands two P, Rh, Cl or I) joined by a Pt-Rh bond (2.692 (1) A? in 2 and 2.737 (3) A? in 4). The carbonyl group in both complexes displays a subtle tilting toward the platinum atom. This results in a significant lowering (20-40 cm^-1) of the carbonyl stretching frequency.