The reaction of rhenium nitrosyl with a sterically hindered NHC-carbene

Abstract

In this article, we present the serendipitous synthesis of the unknown Re(I) complex [(OPPh₃)Re(NO)₂Cl₃] (3) that we obtained reacting the Re(V) complex trans-[(PPh₃)₂ReOCl₃] (1) with NO gas in presence of CH₃COOH. We found that 3 reacts with 1,3-bis (2,4,6-trimethylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene (IMes) to yield a stable oximate—Re(III) complex [(OPPh₃)Re(NO)(ONIMes)Cl₃] (4). We speculate that the IMes reacts with a bent NO, because the DFT calculations excluded the formation of both dimeric and η²–NO complexes in solution. The reactivity of the NO toward the carbene is probably due to an internal fluxional process in which the NO passes from linear to bent, triggered by the π-electrons given by the three chlorides to the Re through the mesomeric effect.