Metal- and Ligand-Centered Reactivity of <i>meta</i>-Carboranyl-Backbone Pincer Complexes of Rhodium

We report the synthesis of the chelating phosphinite-arm carboranyl POBOP-H (POBOP = 1,7-OP­(<i>i</i>-Pr)₂-<i>m</i>-carboranyl) ligand precursor, preparation of its rhodium complexes, and their reactivity in oxidative addition/reductive elimination reactions. The oxidative addition of iodobenzene to the low-valent (POBOP)­Rh­(PPh₃) resulted in the selective formation of the 16-electron complex (POBOP)­Rh­(Ph)­(I), featuring a highly strained exohedral rhodium–boron bond. The complex (POBOP)­Rh­(Ph)­(I) is the first example of a B-carboranyl aryl metal complex, which is a proposed intermediate in metal-promoted B–C coupling reactions. The complex (POBOP)­Rh­(Ph)­(I) was selectively and directly converted, in the presence of acetonitrile, to (POB­(BPh)­OP)­Rh­(H)­(I)­(CH₃CN) (POB­(BPh)­OP = 1,7-OP­(<i>i</i>-Pr)₂-2-Ph-<i>m</i>-carboranyl) through unprecedented cascade reductive elimination of the phenyl-<i>B</i>-carboranyl and the oxidative addition of a vicinal B–H bond of the boron cluster to the metal center, exhibiting both metal- and cluster-centered reactivity