Reactivity of Rh(I) homobimetallic complexes & the synthesis & reactivity of heterobimetallic complexes containing Rh(I), Ir(I), Ir(III), Au(I), Ru(II)

Bimetallic catalysts, both homo- and heterobimetallic, can exhibit unique cooperative properties such as enhanced reaction rates and selectivities in comparison to their monometallic counterparts. The degree of intermetallic cooperativity achieved using bimetallic complexes can be dependent on the distance between the metal pairs. Heterobimetallic complexes, which contain two different metal centres, are of particular interest due to their ability to promote two or more different transformations in one pot. We have been able to use the principle of bimetallic cooperativity to enhance the efficiency of Rh(I) bis(pyrazol-1-yl)methane (bpm) catalysts for the dihydroalkoxylation of alkyne diols. To determine the optimal spatial relationship between the two metal centres we synthesised a series of homobimetallic Rh(I) bpm complexes supported on rigid, semi-rigid and flexible bridging scaffolds and tested them as catalysts for the dihydroalkoxylation reaction. We were also interested in the catalysis of two step reactions using heterobimetallic complexes, and synthesised a series of heteroditopic ligands that contain two distinct binding pockets including the bidentate bis(pyrazol-1-yl)methane (bpm) ligand as well as a monodentate N-heterocyclic carbene (NHC) donor. The coordination chemistry of the bitopic ligands with Au(I), Rh(I), Ir(I) and Ir(III) is described. The derivitisation of the monodentate NHC motif of the bitopic ligand with benzyl triazole was also investigated and subsequent complexation with Ru(II), Rh(I) and Ir(I) is also described. The complexes were investigated as catalysts for sequential transformations such as dihydroalkoxylation and hydroamination/hydrosilylation reactions.