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Three new complexes of the Rh24+unit, each containing phosphine and chloride ligands in addition to, or totally replacing, carboxylato ligands, are described. These have all been accessed by employing Me3SiCl to remove carboxyl groups from the starting materials, thus allowing each of them to be replaced by a combination of Cl and a phosphorus atom. Compound 1, Rh2Cl2(02CCH3)2(dppm)2-2CH3CN, prepared by reaction of Rh2(02CCH3)4with 2 equiv of Me3SiCl in the presence of dppm, crystallizes in the monoclinic space group P2x/c with unit cell dimensions a - 14.599 (2) A, b = 15.395 (2) A, c = 24.614 (4) A, jg = 103.63 (1), V = 5376 (3) A3, and Z = 4. The structure was refined to least-squares residuals of R = 0.0443, Rw= 0.0552, and quality-of-fit = 1.58. The molecules occupy general positions in the unit cell, and each one consists of a dirhodium unit bridged by two cisoid acetate groups and by two dppm ligands, with chloride ions in the axial positions. The asymmetric unit also contains two molecules of CH3CN as interstitial solvent. Compound 2, Rh2Cl4(dppm)23CH3CN.H20, was prepared by the action of Me3SiCl on 1 or by the addition of 4 equiv of Me3SiCl to a mixture of Rh2(02CCH3)4and dppm in refluxing benzene. Orange-red crystals of 2 were isolated from a CH2C12-CH3CN solution and belong to the orthorhombic space group Pc2xn with a = 9.379 (5) A, b = 22.65 (1) A, c = 27.31 (1) A, V = 5803 (4) A3, and Z = 4. Molecules of 2 exhibit a novel geometry consisting of two square pyramids that share an edge. Two cis bridging chloride ligands occupy the positions of the shared basal edge, four phosphorus atoms of the cis dppm ligands define the additional edges of the square plane, and a terminal chloride ligand on each Rh atom occupies an apex position. This is an unprecendented arrangement of ligands for a M2X4(L-L)2 compound; a possible reason for it will be discussed. The structure was refined to R = 0.064, Rw~ 0.080, and quality-of-fit = 1.41. R^C^dmpm^KQHs^PCQH^-CT^C^ (3) was isolated from the reaction of Rh2(02CCH3)2(Ph2PC6H4)22CH3C00H, Me3SiCl, and dmpm in THF. Red monoclinic crystals of 3 were grown from CH2Cl2-hexane, space group P21/cwith a = 11.268 (2) A, b = 24.834 (3) A, c = 17.589 (5) A, = 99.14 (2), V= 4859 (3) A3, Z = 4. The new compound is comprised of two cis bridging o-(Ph2P)C6H4 groups in a head-to-tail arrangement and two cis dmpm ligands that also span the Rh2unit. The coordination sphere is completed by two axial chloride ligands. After final refinement the residuals were R = 0.0641, Rw= 0.0742, and the quality-of-fit = 1.43. The Rh-Rh distances in 1, 2, and 3 are 2.622 (1), 2.523 (2), and 2.770 (3) A, respectively, values which are significantly longer than nearly all previously reported Rh-Rh single bond distances. This point is discussed along with other pertinent structural details. In addition to X-ray studies, the new compounds were characterized by elemental analysis, infrared and electronic spectroscopy, and cyclic voltammetry. 1987, American Chemical Society. All rights reserved.
Journal of the American Chemical Society
author list (cited authors)
Cotton, F. A., Dunbar, K. R., & Verbruggen, M. G.