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Nuclear magnetic resonance studies in coordination chemistry V. Kinetic studies of exchange reactions involving 1,5-cyclooctadiene complexes of rhodium(I)

1968; Elsevier BV; Volume: 14; Issue: 1 Linguagem: Inglês

10.1016/s0022-328x(00)92655-x

1872-8561

Kees Vrieze, H. C. Volger, A.P. Praat,

Coordination Chemistry and Organometallics

NMR studies showed that the signals of the non-equivalent olefinic protons of the diene complexes (diene) RhCl(L) and (diene) IrCl(L) (diene = 1,5-cyclooctadiene, bicyclo [2.2.1] hepta-2,5-diene and L = PR3, AsR3 or SbR3 with R = aryl or substituted aryl or alkyl) broaden and eventually coalesce to one signal when the temperature of the CDCl3 solutions is raised. Kinetic studies on the monomeric complexes (COD)RhCl(L) (COD 1,5-cyclooctadiene; L = AsPh3, PPh3) showed that this coalescence is caused by monomer-monomer reactions. If, however, ligand L is also present, fast ligand exchange reactions are observed. If along with (COD)RhCl(L) the dimer [(COD)RhCl]2 is present, the olefinic signals of both complexes coalesce. For L = AsPh3 the kinetic behaviour is explained by a reaction between an active intermediate “(COD)RhCl(AsPh3)” and [(COD)RhCl]2, while L = PPh3 reactions occur between (COD)RhCl(PPh3) and the monomeric species (COD)RhCl formed from the dissociation of the dimer. Finally, it is shown that addition of Cl− to (COD)RhCl(AsPh3) also results in the coalescence of the olefinic signals. The chloride effect upon (COD)RhCl(PPh3) is negligible.