REACTIONS OF RE2CL4(DPPM)2 WITH CARBON-MONOXIDE THAT PROCEED WITH RETENTION OF THE METAL METAL BOND - SYNTHESIS OF RE2CL4(DPPM)2(CO)N (N = 1,2) AND THE STRUCTURAL CHARACTERIZATION OF CL2RE(MU-CL)(MU-CO)(MU-DPPM)2RECL(CO)
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The triply bonded dirhenium(II) complex Re2Cl4(dppm)2(dppm = bis(diphenylphosphino)methane) reacts with carbon monoxide to give the carbonyl complexes Re2Cl4(dppm)2(CO)n(n = 1 or 2). These results provide for the first time evidence as to the nature of the intermediates that are formed in the cleavage of the electron-rich metal-metal triple bond (242*2configuration) by -acceptor ligands. The neutral complex, Cl2Re(-Cl)(-CO)(-dppm)2ReCl(CO), which has been characterized by X-ray diffraction, crystallizes in the monoclinic system, space group C2/c, with a = 22.877 (6) , b = 11.044 (3) , c = 22.726 (5) , = 123.02 (2), V= 4814 (4) 3, and Z = 4. The crystal structure was refined to residuals of R = 0.0298, Rw= 0.0285, and quality-of-fit - 1.043. The Re-Re bond distance is 2.584 (1) A, and the molecule comprises a pair of distorted, edge-sharing octahedra. The bridging and terminal Cl and CO ligand sites are disordered in a well-defined manner. A comparison of the spectroscopic properties (IR, and 1H, 31P{1H} and 13C[1H] NMR) of the dicarbonyl complex with those of its 13CO labeled analogue accord with the structure found in the solid state, although 31P{1H} and 13C{1H} NMR spectroscopy show that there is a fluxional process that renders the carbonyl ligands equivalent between room temperature and ca. -20 C. The monocarbonyl has been shown by IR spectroscopy to exist as a mixture of two isomers both in the solid state and in solution. The NMR spectral properties of this complex (1H, 31P{1H}, and 13C{1H} are consistent with an A-frame A-frame fluxionality that keeps the CO ligand bound to a single rhenium atom only. 1985, American Chemical Society. All rights reserved.
