A CONVENIENT GENERAL-ROUTE TO A SERIES OF DIPHOSPHINE-BRIDGED HETEROBINUCLEAR COMPLEXES THAT CONTAIN RHODIUM AND STRUCTURES OF THE MIXED-VALENT COMPLEXES [RHMN(CO)4(PH2PCH2PPH2)2], [RHRE(CO)4(PH2PCH2PPH2)2]

A convenient route to a series of dppm-bridged complexes has been developed in which the chloride anion in [RhCl(dppm)2] is displaced by a metal carbonylate anion. This metathesis reaction is accompanied by unwinding of one or both of the chelating dppm groups to adopt a bridging arrangement and by loss of one carbonyl group. In the compounds [RhCo(CO)3(dppm)2], [RhMH(CO)3(dppm)2] (M = Fe, Ru, Os), [RhM(CO)4(dppm)2](M = Μη, Re), and [RhMH(CO)4(dppm)2](M = Cr, W), both diphosphines adopt a bridging arrangement, whereas in [RhFeCp(CO)(dppm)2] and [RhMoCp(CO)2(dppm)2] only one dppm group bridges the metals while one remains chelating on rhodium. The structures of [RhM(CO)4(dppm)2] (M = Mn (5), Re (6)) have been determined by X-ray methods. The coordination geometries at Mn and Re are not octahedral, but instead (ignoring the Rh atoms), the [M(CO)3L2] (L = one end of dppm unit) moieties have trigonal-bipyramidal geometries, suggesting that a M(-I) formulation is appropriate. This [M(CO)3L2]~ fragment then functions as a pseudohalide, forming a dative M-*Rh bond and giving the Rh center a square-planar arrangement consistent with a Rh(+I) formulation. The resulting M-Rh bond lengths are 2.8428 (8) Â (M = Mn) and 2.7919 (6) Â (M = Re). Compound 5 crystallizes in the triclinic space group PI with α = 10.897 (2) A, b = 11.046 (2) A, c = 11.700 (2) Α, α = 68.14 (1)°, β = 67.48 (1)°, γ = 87.69 (1)°, V = 1198.7 (4) A3, and Z = l and was refined to R = 0.054 and Rw = 0.082. Compound 6 crystallizes together with one THF molecule in the monoclinic space group P2Jc with α = 12.963 (4) A, b = 19.883 (3) A, c = 11.277 (2) k,ß-99.12 (2)°, V = 2870 (2) A3, and Ζ = 2 and was refined to R = 0.053 and fíw = 0.088. Both compounds occupy a crystallographic inversion center so the metal carbonyl fragments are disordered, although this disorder, in reality, is readily handled crystallographically, with only two carbonyl carbons having two sets of half-occupancy positions and each metal position being composed of one half-occupancy rhodium atom and one half-occupancy manganese or rhenium atom. © 1990, American Chemical Society. All rights reserved.