C-13 NUCLEAR MAGNETIC-RESONANCE STUDY OF RHODIUM(I) AND RHODIUM(III) AND IRIDIUM(I) AND IRIDIUM(III) COMPLEXES CONTAINING CHELATING UNSATURATED TERTIARY PHOSPHINES AND ARSINES

A 13C NMR spectral analysis of Rh and Ir olefin complexes containing tertiary unsaturated phosphines has been carried out. The analysis included the square-planar complexes RhX(BDPH), X = CI or Br, RhCl(BDAH), and IrCl(BDPH); the trigonal-bipyramidal complexes [RhX(DBP)]2, X = CI or Br, Rh(CO)X(DBP), X = CI, Br or I, Ir(CO)X(DBP), X = CI, Br, or I, RhX(TBP), X = CI, Br, or I, IrCl(TBP), RhX(TPP), X = CI or Br, and IrCl(TPP); and the octahedral complexes Rh(XY)Cl(BDPH), XY = Cl2 or Br2, and Ir(XY)Cl(BDPH), XY = Cl2, H2, or HC1, where BDH = trans-1, 6-bis(diphenylphosphino)hex-3-ene, (C6H5)2PCH2CH2CH=CHCH2CH2P(C6H5)2, DBP = dibut-3-enylphenylphosphine, (C6H5)P(CH2CH2CH=CH2)2, TBP = tribut-3-enylphosphine, P(CH2CH2CH=CH2)3 and TPP = tripent-4-enyl)phosphine, P(CH2CH2CH2CH=CH2)3. The coordination-induced shift of the olefin A5(C) has been shown to be dependent on the stereochemistry of the metal complex and the oxidation state of the metal and reflects the relative amount of electron density at the metal center available for back-bonding to the olefin, as predicted by the Dewar-Chatt-Duncanson model of metal-olefin bonding. The 103Rh-13C coupling constants to the olefinic carbons support the above trends. Variable-temperature 13C NMR spectra have shown that the olefin in the complexes RhCl(TBP) and RhBr(TBP) undergoes a rotation (albeit small) about the rhodium-olefin bond, whereas in Rhl(TBP) variable-temperature spectra have shown an equilibrium between coordinated and uncoordinated olefin. © 1979, American Chemical Society. All rights reserved.