Synthesis of Cyclopentadienyl Rhodium Catalysts by Co-Cyclization of Two Different Alkynes

Cyclopentadienyl rhodium complexes (C5R5)RhLx are widely used as homogeneous catalysts. Herein we report the synthesis of such complexes with structurally diverse cyclopentadienyl ligands in one step directly from alkynes. Specifically, reactions of bulky terminal alkynes (tert-butylacetylene or trimethylsilylacetylene) with activated internal alkynes (ethyl 2-butynoate or dimethyl acetylenedicarboxylate) and [(cod)RhCl]2 produce either cyclopentadienyl or pentalene-type complexes (L)Rh(cod) in 60-95% yields. Oxidation of these Rh(I) complexes with halogens afforded the corresponding Rh(III) derivatives [(L)RhHal2]2 which can catalyze C-H activation of phenylhydroxamate giving products with varying regioselectivity depending on the substituents in pi-ligands.