Selective formylation and methylation of amines using low pressure CO2 as a carbon source; mechanistic studies, time course and reaction scope.

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.

An operationally simple and atom-economical method for the E-selective preparation of enol ethers is described. A novel dicarbonyl(5-phenyldipyrrinato)rhodium complex, 2, was prepared in four synthetic steps, characterized by X-ray crystallography and NMR spectroscopy, and then investigated as a catalyst for the intermolecular hydroalkoxylation of terminal alkynes. Solvent and substrate studies were used to gain insight into the mechanism of the reaction. Cyclic voltammetry was also used to investigate the electronic properties of 2. The rhodium(I)-catalyzed intermolecular alkyne hydroalkoxylation reaction reported here mediates excellent substrate transformation with a high degree of E/Z selectivity which is opposite to that reported previously using alternative catalysts.

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