B−C Bond Cleavage of BAr_FAnion Upon Oxidation of Rhodium(I) with AgBAr_F. Phosphinite Rhodium(I), Rhodium(II), and Rhodium(III) Pincer Complexes

Abstract

A rare case of BArF anion cleavage (BArF− = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) by a metal complex is described. Reaction of the Rh(I) dinitrogen complexes 5a,b and 6a,b, based on the phosphinite pincer ligands {C6H4[OP(tBu)2]2} (2), with 2 equiv of AgBArF at room temperature resulted in B−C bond cleavage of one of the BArF anions and aryl transfer to afford the Rh(III) aryl complexes 7 and 8, respectively. The X-ray structure of 8 revealed a square-pyramidal geometry with a coordinated acetone molecule. The aryl transfer occurred as a result of electrophilic attack by unsaturated Rh(III) on one of the aryl rings of the BArF anion. Utilizing different solvents yielded the same product, except when CH3CN was used, in which case one-electron oxidation took place, yielding complex 9. Treatment of 6a,b with 1 equiv of AgX (X = BArF, BF4, PF6) resulted in a one-electron oxidation to yield the paramagnetic Rh(II) complexes 9−11, respectively. Complex 11 was characterized by X-ray diffraction, revealing a mononuclear square-planar Rh(II) complex.