Synthesis and reactivity of HY zeolite-supported rhodium complexes.

摘要

The growing interest in the design of heterogeneous analogs of highly active and selective homogeneous catalysts prompted researchers to invest significant efforts in understanding of synthetic pathways, structure, and reactivity of supported single-site metal complexes.;Synthesis of catalytically active organometallic species on solid supports with properties resembling those of their homogeneous counterparts could offer the opportunities to perform efficiently the solution organic reactions by utilizing flow instead of batch reactors. In this regard, rhodium carbonyl complexes and their derivatives are viewed as very attractive candidates for heterogenization due to their extensive application as catalysts for variety of industrially important reactions.;We investigated structural properties of well-defined Rh carbonyl complexes attached to a HY zeolite framework and explored their reactivity. Our strategy was to prepare samples incorporating highly uniform and nearly molecular Rh(CO) 2 complexes anchored to a HY zeolite framework and to use the reactivity of the ligands in these complexes for the surface-mediated synthesis of important reaction intermediates. We developed a two-step pathway for the selective synthesis of well-defined and structurally uniform HY zeolite-supported Rh(CO)(H) x complexes under ambient conditions. The stability of these Rh(CO)(H) x species at elevated temperatures was addressed, as well as their surface chemistry in reactions with CO, C2H4, O2, and N2. Rh(CO)(H)x complexes were found to be catalytically active in both hydrogenation and dimerization of C2H4 at ambient conditions. While the role of the support was shown to be critical for the C-C bond formation reaction, it was possible to modify Rh coordination environment and suppress the dimerization pathway. Furthermore, it was revealed that zeolite-supported rhodium dicarbonyl complexes could be used as model catalysts to probe the structure sensitive character of the NO + CO reaction.