Concerted aryl-sulfur reductive elimination from PNP pincer-supported Co(iii) and subsequent Co(i)/Co(iii) comproportionation

Abstract

This report discloses a combined experimental and computational study aimed at understanding C–S reductive elimination from Co(III) supported by a diarylamido/bis(phosphine) PNP pincer ligand. Divalent (PNP)Co-aryl complexes could be easily oxidized to five-coordinate Co(III) derivatives, and anion metathesis provided five-coordinate (PNP)Co(Ar)(SAr′) complexes of Co(III). In contrast to their previously described (POCOP)Co(Ar)(SAr′) analogs, but similarly to the (PNP)Rh(Ar)(SAr′) and (POCOP)Rh(Ar)(SAr′) analogs, (PNP)Co(Ar)(SAr′) undergo C–S reductive elimination with the formation of the desired diarylsulfide product ArSAr′. DFT studies and experimental observations are consistent with a concerted process. However, in contrast to the Rh analogs, the immediate product of such reductive elimination, the unobserved Co(I) complex (PNP)Co, un-dergoes rapid comproportionation with the (PNP)Co(Ar)(SAr′) starting material to give Co(II) compounds (PNP)Co–Ar and (PNP)Co-SAr′.