Synthesis, structure and reactivity of NO+, NO• and NO-pincer PCN-Rh complexes

Abstract

Synthesis of a pincer-type linear nitrosyl complex [Rh(PtBu2CNEt2)(NO)]+ (3+ ) is described. The product and all intermediates involved were fully characterized by FTIR, NMR, cyclic voltammetry and X-ray crystallography. Attempts at obtaining (3+ ) from its chlorinated precursor Rh(PCN)(NO)Cl (2) revealed that a relative stabilization of this complex ion is introduced by the BArF− counteranion, as other counteranions – PF6 − , BF4 − and triflate- proved to coordinate to the metal center. Redox reactivity both of (3+ ) and of that of its five-coordinate derivatives (2) and [Rh(PCN)(NO)(CH3CN)]+ (4+ ) was found to distinguish itself from analogous PCP complexes due to a relative stabilization of higher oxidation states. Oxidation of these three complexes was studied by FTIR spectroelectrochemistry. Reduction of complex (3+ ) to yield a short-lived {RhNO} 9 species [Rh(PCN)(NO)]• (3• ) was also carried out. Complex (3• ) was proved able to activate carbon-halogen bonds in aryl halides, in much a similar way as that of its PCP analogue. Complex (3+ ) was also seen to establish a linear↔bent nitrosyl equilibrium upon addition of CO which could not be fully displaced with excess CO.