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  • 1
    ISSN: 0009-2940
    Keywords: Rhodium(I) phosphane complexes ; 14-Electron intermediates ; MO theory, applied ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(di-tert-butylphosphanyl)methane Complexes of Rhodium: Geometry, Electronic Structure, and Derivatives of the 14-Electron Fragment [Rh(dtbpm)Cl]. Molecular Structure of Rh(dtbpm)Cl(PMe3)14-Electron fragments [M(PR3)2X] (M = Rh, Ir, X = halogen etc.) are considered to be an important class of highly reactive, coordinatively unsaturated intermediates in many metal-induced stoichiometric or catalytic transformations of organic substrates. As available theoretical data suggest a slightly preferred T-shaped groundstate geometry with a less symmetric cis rather than the usually implied trans phosphane arrangement for such tricoordinate d8-ML3-type systems with monodentate phosphanes PR3, the chemistry of η2-diphosphanylmethane complexes of rhodium with four-membered RhPCP-chelate rings and thus with enforced cis phosphane coordination and anomalously small cis P - Rh - P angles has been studied by theory and by experiment. MO calculations (EH) have been performed both for the model 14-electron system [Rh(dhpm)Cl] (dhpm = diphosphanylmethane, H2P - CH2 - PH2) and for the experimentally accessible fragment [Rh(dhbpm)Cl], where dtbpm is bis(di-tert-butylphosphanyl)-methane, (tBu)2P - CH2 - P(tBu)2. The electronic and geometric structure of these species is described. Employing the unusual ligand dtbpm, tailor-made for stabilizing mononuclear η2- and destabilizing dinuclear μ-diphosphanylmethane coordination, the chloro-bridged dimer [Rh(dtbpm)Cl]2, has been synthesized. In agreement with steric and electronic considerations, its chemistry is dominated by a facile dissociation to monomeric (presumably solvent coordinated) fragments [Rh(dtbpm)Cl], even in benzene, as suggested by molecular mass determinations. Accordingly, by using [Rh(dtbpm)Cl]2 as a starting material, a series of sterically very congested but nevertheless mononuclear, square-planar complexes Rh(dtbpm)Cl(L) (L = CO, PMe3, PPh3, PCy3, pyridine, acrylonitrile) with chelating dtbpm could be readily prepared and fully characterized. The relative stability of these potential alternative precursors of a [Rh(dtbpm)Cl] intermediate towards dissociation of ligands L is reported. The molecular structure of Rh(dtbpm)Cl(PMe3) as the first representative of this class of compounds has been determined by X-ray crystallography.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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