NO disproportionation by a {RhNO}⁹ pincer-type complex

The reactivity of the {RhNO}⁹ complex [Rh(PCP^tBu)(NO)] (1) with NO was studied. A disproportionation reaction takes place in which N₂O is released quantitatively, while the complex Rh(PCP^tBu)(NO)(NO₂) (2), with coordinated nitrite, is formed. The new complex 2 was fully characterized by multinuclear NMR techniques, IR and X-ray diffraction. The X-ray structure reveals a square pyramidal geometry with an N-bound nitro ligand trans to the C_ipso of the PCP ligand and a bent nitrosyl ligand in the apical position. IR measurement of released N₂O confirms that one equivalent forms for each molecule of 1. Infrared spectroscopic experiments with 1-¹⁵NO and ¹⁴NO suggest that the reaction occurs through the intermediacy of a dinitrosyl complex. In addition, DFT calculations were performed to provide more evidence on the structure of the intermediates and to support the observed reactivity.