On the preparation of bimetallic Rh-Co hydroformylation catalysts from [Rh(CO)2Cl]2 and cobalt carbonyls on the surface of SiO2

The preparation of bimetallic Rh-Co catalysts from [Rh(CO)(2)Cl](2) and cobalt carbonyls (Co-2(CO)(8) and Co-4(CO)(12)) on the surface of SiO2 has been investigated by IR spectroscopy and the ethylene hydroformylation reaction. The reaction of Co-2(CO)(8) with [Rh(CO)(2)Cl](2) (Rh:Co = 1:3.5 atomic ratio) yields spontaneously and promptly RhCo3(CO)(12) on the surface. The RhCo3(CO)(12) thus synthesized is characterized by in situ IR monitoring and extraction from the surface into n-hexane. This chemistry parallels that in solution. In n-hexane solution, the reaction proceeds very slowly and is complete after approximately 1 d. The results show that the surface of SiO2 exerts an unusual promoting effect on this organometallic synthesis. When Co-2(CO)(8) is replaced by Co-4(CO)(12), no reaction takes place either in solution or on the surface. However, a bimetallic Rh-Co catalyst may efficiently result from ([Rh(CO)(2)Cl](2) + Co-4(CO)(12))/SiO2 (Rh:Co = 1.3 atomic ratio) by thermal treatment under a reducing atmosphere. In particular, (Rh+ + Co2+)/SiO2 (Rh:Co = 1 :3 atomic ratio) derived from [Rh(CO)(2)Cl](2) and Co-4(CO)(12) likewise may be efficiently transformed to bimetallic Rh-Co clusters or particles under an ethylene hydroformylation atmosphere at 423 K. All the catalysts derived from [Rh(CO)(2)Cl](2) and cobalt carbonyls in this work have catalytic performances close to those of RhCo3(CO)(12)/SiO2 in ethylene hydroformylation.