Formation of a rhodium(II) monohydrido complex derived from wilkinson's complex RhCl(PPh3)3 in the interlamellar spaces of montmorillonite and catalytic hydrogenation of cyclohexene
1991; Elsevier BV; Volume: 10; Issue: 23-24 Linguagem: Inglês
10.1016/s0277-5387(00)86174-4
ISSN1873-3719
AutoresM.M.Taqui Khán, S. A. Samad, Mohammed Rafiq H. Siddiqui, Hari C. Bajaj, G. Ramachandraiah,
Tópico(s)Asymmetric Hydrogenation and Catalysis
ResumoThe interaction of molecular hydrogen with [Rh(PPh3)3]+ (1a) “immobilized” in the interlamellar spaces of montmorillonite resulted in the formation of a monohydrido complex, [RhIIH(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 ΔH0 and ΔS0 corresponding to the formation of the monohydrido species were found to be 18 kcal mol−1 and 61 e.u., respectively. The activation enthalpy, ΔH‡, and entropy, ΔS‡, for the hydrogenation of cyclohexene by the RhII—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.
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