Bimetallic Rhodium Complexes: Precatalyst Activation-Triggered Bimetallic Enhancement for the Hydrosilylation Transformation

Abstract

To explore how to access bimetallic catalysts that can outperform their monometallic analogues, a set of mono- and bimetallic NHC/phosphine (NHC = N-heterocyclic carbene)-ligated rhodium(I) complexes were designed, synthesized, and characterized. The complexes were used as catalysts for the intermolecular hydrosilylation of diphenylacetylene. All four catalysts displayed significantly faster catalytic rates than the related complexes reported previously containing NHC/pyrazolyl donor ligands. The bimetallic catalyst design led to enhanced catalytic activity over the monometallic analogue. The data revealed that the degree of bimetallic enhancement was highly dependent on the reaction conditions, coligands used, and the substrate addition order. The catalytic trends, in combination with mechanistic studies using individual substrates and density functional theory calculations, exposed that the bimetallic benefits were strongly linked to the catalyst activation procedure.

A highly active and chemoselective homobimetallic ruthenium catalyst for one-pot reductive amination in water

“…[45][46][47][48] The improved efficiency of a bimetallic catalyst compared to its monometallic analog can be ascribed to cooperative interactions between the two metals and any possible electronic communication through bridging organic ligands. 49,50 Bimetallic catalysts can be of two types, viz. homobimetallic (same metals) and heterobimetallic (different metals).…”

“…substitution reactions. 55,56 For example, Pernik and coworkers 49 have shown that a bimetallic rhodium complex is more active than a monometallic catalyst for hydrosilylation. Similarly, a dinuclear nickel catalyst that is significantly more active than its mononuclear counterpart in alkyne hydrosilylation was reported by Uyeda and co-workers.…”

“…These include hydroformylation, 46,48 hydroelementation of alkynes, 51 disproportionation of formic acid to methanol, 52 hydroamination, 53 cycloisomerisation, 54 and propargylic reduction and substitution reactions. 55,56 For example, Pernik and co-workers 49 have shown that a bimetallic rhodium complex is more active than a monometallic catalyst for hydrosilylation. Similarly, a dinuclear nickel catalyst that is significantly more active than its mononuclear counterpart in alkyne hydrosilylation was reported by Uyeda and co-workers.…”

Microwave-Assisted Transfer Hydrogenation of Carbonyl and ­Nitro Compounds Using Bimetallic Ru(II) Cymene Complexes

“…8,[13][14][15][16][17][18] Uyeda and coworkers have reported a bimetallic nickel complex containing a direct Ni-Ni bond promoting hydrosilylation of olefins with a broad substrate scope. 19 Similarly, a Rh(I) NHC/phosphine bimetallic complex, reported by Pernik and co-workers in 2023, effectively catalyses intermolecular hydrosilylation of alkyne with high selectivity, 20 displaying significant superiority over mono-rhodium catalysts with NHC-pyrazole donors. 20 Similarly, binuclear indium catalysts exhibited high catalytic activity for the ring-opening polymerization of lactide to form poly(lactic acid) at room temperature.…”

“…19 Similarly, a Rh(I) NHC/phosphine bimetallic complex, reported by Pernik and co-workers in 2023, effectively catalyses intermolecular hydrosilylation of alkyne with high selectivity, 20 displaying significant superiority over mono-rhodium catalysts with NHC-pyrazole donors. 20 Similarly, binuclear indium catalysts exhibited high catalytic activity for the ring-opening polymerization of lactide to form poly(lactic acid) at room temperature. 21 Both bimetallic cobalt and ruthenium N-heterocyclic carbene complexes have been reported to promote the oxidation of water.…”