Bimetallic Paddlewheel-type Dirhodium(II,II) Acetate and Formamidinate Complexes: Synthesis, Structure, Electrochemistry, and Hydroformylation Activity

Classical hydroformylation catalysts use mononuclear rhodium(I) complexes as precursors; however, very few examples of bimetallic systems have been reported. Herein, we report fully substituted dirhodium(II,II) complexes (C1-C6) containing acetate and diphenylformamidinate bridging ligands (L1-L4). The structure and geometry around these paddlewheel-type, bimetallic cores were confirmed by single-crystal X-ray diffraction. The complexes C3-C6 show electrochemical redox reactions, with the expected reduction (Rh24+/3+) and two oxidation (Rh24+/5+ and Rh25+/6+) electron transfer processes. Furthermore, the bimetallic complexes were evaluated as catalyst precursors for the hydroformylation of 1-octene, with the acetate-containing complexes (C1 and C2) showing near quantitative conversion (>99%) of 1-octene, excellent activity and chemoselectivity toward aldehydes (>98%), with moderate regioselectivity toward linear products. Replacement of the acetate with diphenylformamidinate ligands (complexes C3-C6) yielded moderate-to-good chemoselectivity and regioselectivity, favoring linear aldehydes.