An Electron-Excessive Nitrosyl Complex: Reactivity of a Ligand-Centered Radical Leading to Coordinated HNO

The reaction of RuHCl(CO)L2 (L = PiPr3) with NO initially forms
a 1:1 adduct, shown by DFT calculations and EPR spectroscopy
(including the RuD isotopomer) to contain a bent (∠Ru−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)L2 and RuHCl(HNO)(CO)L2, 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 NO, and the lifetime of RuHCl(HNO)(CO)L2 is
indeed qualitatively dependent on the presence of free NO.