Dirhodium paddlewheels have seen extensive application in a range of reactions involving a metal carbenoid intermediate. This carbenoid intermediate is generated in situ from the reaction of a diazo compound with the rhodium complex, and contains an electrophilic carbon predominantly stabilized by the rhodium metal and the substituents of the diazo precursor. When reactive diazo precursors are employed, such as acceptor diazo compounds (Fig 1a), an increase in diazo dimerization and a decrease in stereoselectivity is observed. The problem has been circumvented by modifying the diazo substrate to a more stabilized species, where the diazo carbon is flanked by an electron donating and electron withdrawing group. While this strategy has led to higher stereoselectivity, methods of stabilization using the rhodium complex has been relatively underdeveloped. By controlling stability through the rhodium complex, diazo compounds previously considered too reactive may be viable options.<br/>Our research is focused on axial site modification of dirhodium complexes; wherein the coordinating atom can donate electron density through the Rh-Rh bond. Added electron density should stabilize the electrophilic carbon of the carbenoid intermediate. This work focuses on the synthesis of a dirhodium paddlewheel complex containing an oxazolidinone bridging ligand, with a thioether tether that is capable of axial coordination (Fig 1b). This catalyst was applied to C-H insertion, N-H insertion, and epoxidation reactions utilizing acceptor/acceptor and donor diazo compounds.

Stabilization of dirhodium paddlewheel carbenoids through tethered axial coordination

255th National Meeting (2018)

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