Rhodium complexes without bridging ligands

In the search for catalytically active species, heterobi-and polynuclear molecules containing both U(III) and a transition metal (palladium, platinum, rhodium, or ruthenium) strongly bonded in close proximity but without a direct metal-metal bond were synthesized. Difunctional bridging ligands like cyclopentadienylphosphido ligands were used to form such complexes. 

Finally, poly-NHC complexes of other metals have occasionally been employed as catalysts for hydrosilylations as well. The group of Hollis reported in 2012 on dinuclear rhodium(I) complexes with a bridging dicarbene ligand (structure 78, Fig. 26) as catalysts for the hydrosilylation of phenylacetylene with dimethylphenylsilane. Results were comparable to those previously obtained with platinum dicarbene complexes, which is in contrast to previous reports on Rh-catalyzed hydrosilylations, in which the Z-beta product is predominantly formed without production of the alpha isomer. 

---