An electron-excessive nitrosyl complex: reactivity of a ligand-centered radical leading to coordinated HNO

The reaction of RuHCl(CO)L-2 (L = (PPr3)-Pr-i) with NO initially forms a 1:1 adduct, shown by DFT calculations and EPR spectroscopy (including the RuD isotopomer) to contain a bent (angleRu-N-O = 143.9) nitrosyl where the majority of the spin density is on the nitrosyl nitrogen. This radical adduct transforms further to give equimolar RuCl(NO)(CO)L-2 and RuHCl(HNO)(CO)L-2, the latter with hydride trans to the nitroxyl ligand HN=O. This is the first observation of the synthesis of coordinated HNO from NO itself. DFT calculations lead to the proposal that this H-atom transfer is effected by free NO2. and the lifetime of RuHCl(HNO)(CO)L-2 is indeed qualitatively dependent on the presence of free NO.