FORMATION OF A RHODIUM(II) MONOHYDRIDO COMPLEX DERIVED FROM WILKINSON COMPLEX RHCL(PPH3)3 IN THE INTERLAMELLAR SPACES OF MONTMORILLONITE AND CATALYTIC-HYDROGENATION OF CYCLOHEXENE

The interaction of molecular hydrogen with [Rh(PPh3)3]+ (1a) "immobilized" in the interlamellar spaces of montmorillonite resulted in the formation of a monohydrido complex, [Rh(II)H(PPh3)3] (2a), characterized by electrochemical data of the clay-loaded electrode, IR, EPR and hydrogen absorption studies. Heterogenized homogeneous catalytic hydrogenation of cyclohexene catalysed by 1a was investigated in the temperature range 283-313 K. The order of reaction with respect to cyclohexene and hydrogen concentration is fractional and first order with respect to catalyst concentration. Thermodynamic parameters DELTA-H0 and DELTA-S0 corresponding to the formation of the monohydrido species were found to be 18 kcal mol-1 and 61 e.u., respectively. The activation enthalpy, DELTA-H double-ended dagger, and entropy, DELTA-S double-ended dagger, for the hydrogenation of cyclohexene by the Rh(II)-H complex in clay are more negative by about 2 kcal mol-1 and 7 e.u. compared to Wilkinson's catalyst, RhCl(PPh3)3 (1), in homogeneous solution.