Simultaneous Functionalization of Carbon Surfaces with Rhodium and Iridium Organometallic Complexes: Hybrid Bimetallic Catalysts for Hydroamination

Abstract

Carbon-based surfaces were explored here for the synthesis of heterometallic surface-bound catalysts. This takes advantage of catalytic enhancements found using bimetallic catalysts relative to monometallic analogues, as well as the advantages of heterogeneous catalysts over homogeneous catalysts. To achieve this, two organometallic cations with different metal centers, oxidation states, and coligands, [Rh(N,N′)(CO)2]+ and [Ir(N,N′)Cp*Cl]+ (N,N′ = pyrazolyltriazolylmethane ligands), were simultaneously immobilized onto the surface of carbon materials (carbon black and reduced graphene oxide). The relative concentration of the rhodium and iridium cations in the synthetic media was varied allowing for different metal ratios on the carbon surfaces. The composition of the complexes bound to the surfaces was confirmed using XPS which revealed the relative ratios of the iridium and the rhodium species on the surface, agreeing well with the values obtained by MP-AES. The materials were further characterized by N2 absorption. The qualitative distribution of rhodium and iridium ions on the carbon surfaces was determined by STEM-EDX, revealing a uniform distribution of both complexes on the carbon surfaces. The efficiency of the materials as catalysts for intramolecular hydroamination was investigated. The data acquired demonstrated that the optimized ratio of rhodium and iridium on the carbon black material led to more effective catalysts than their monometallic counterparts. Having both complexes on the same carbon black surface presented an improvement in the catalytic activity compared to the complexes immobilized on separate particles.