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

In this article, we present the serendipitous synthesis of the unknown Re(I) complex [(OPPh 3 )Re(NO) 2 Cl 3 ] (3) that we obtained reacting the Re(V) complex trans -[(PPh 3 ) 2 ReOCl 3 ] (1) with NO gas in presence of CH 3 COOH. We found that 3 reacts with 1,3-bis (2,4,6-trimethylphenyl)-1,3-dihydro-2 H -imidazol-2-ylidene (IMes) to yield a stable oximate-Re(III) complex [(OPPh 3 )Re(NO)(ONIMes)Cl 3 ] (4). We speculate that the IMes reacts with a bent NO, because the DFT calculations excluded the formation of both dimeric and η 2 -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.