RATES AND ACTIVATION PARAMETERS FOR SOLVENT EXCHANGE WITH (1+) (M = RhIII OR IrIII, R = CYCLOHEXYL OR PHENYL) CATIONS

Article abstract of DOI:10.1039/DT9810001481

Using ₁H n.m.r. line-broadening and, where possible, stopped-flow Fourier-transform n.m.r., rates and activation parameters have been determined for solvent exchange with complexes of the type (1+) (M = Rh_III or Ir_III; R = phenyl, solvent = MeCN or Me2CO; R = cyclohexyl, solvent = MeCN) in <₂H²>-dichloromethane solution.In all cases the co-ordinated solvent molecules are in trans positions with respect to the hydride ligands, and at 298 K the various complexes have rate constans for solvent exchange (k¹) which differ almost by a factor of 10₇; k¹(Rh) > k¹(Ir) because for analogous species ΔH<*>(Rh) < ΔH<*>(Ir), and the acetone solvates are much more labile than the acetonitrile complexes because of lower ΔH<*> values.Values of ΔS<*> are significantly positive (8-32 J K_-1mol_-1 when M = Rh_III, 25-30 J K_-1mol_-1 when M= Ir_III) in line with a dissociative, D mechanism.Hydrogen-1 n.m.r. spectra of (1+) and (1+) ions (L = MeOH, MeCN, pyridine, styrene, or cyclo-octene) are reported and compared.

Full text of DOI:10.1039/DT9810001481

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