Over several years, our research team has contributed to ligand design for metal-catalyzed stereoselective transformations. This has been achieved with the synthesis and application to organic transformations of interest of an array of structurally diverse P-containing ligands. These range from highly modular enantiopure phosphine–phosphite ligands to supramolecularly regulated enantioselective phosphorus-based catalysts. Our research in supramolecular interactions has also led to the discovery of an unprecedented halogen-bonded rhodium-catalyst.

The role of the counterion in metal-catalyzed reactions can be crucial as this often-unconsidered component of the catalyst can modify the performance of the catalyst and influence the reaction rate and/or selectivity of the transformation under study. Herein, we disclose the effects of counterion variation in cationic halogen bond-assembled Rh(I) catalysts in the hydroboration reaction of terminal alkynes, which leads to rather elusive branched (or internal) hydroboration products. Our studies showed that the higher the coordination ability of the counterion, the higher the activity and selectivity toward the hydroboration products. This observation was demonstrated by catalytic and spectroscopic (NMR, IR and X-ray) studies. An array of structurally diverse alkynes was efficiently transformed into the corresponding hydroboration products employing the highest performing catalyst XBphos-Rh-OTf. The practicality of our synthetic method was demonstrated by developing one-pot hydroboration/Csp2-Csp2 coupling processes.