Light‐induced NO release from iron‐nitrosyl‐thiolato complex: The role of noncovalent thiol/thioether

Four low‐spin {FeNO}6 complexes, [Fe(NO)(PS2)(PS2H)] (1, PS2H2 = bis(2‐dimercaptophenyl)phenylphosphine) with a pendant thiol, [Fe(NO)(PS2)(PS2CH3)] (2) bearing a pendant thioether, and [Fe(NO)(PS2)(RPS)] (RH, 4a; RTMS, 4b) without the noncovalent thiol/thioether group are spectroscopically and structurally characterized. In comparisons of the νNO, absorption energy in UV/vis spectra and structural parameters from single X‐ray diffraction studies, the four iron‐nitrosyl‐thiolato compounds share similarity in electronic structure. Complex 1 with a pendant thiol leads to NO and HNO production upon exposure to the light. Photolysis of 2 bearing a pendant thioether only affords NO. Effective detection of HNO or NO from 1 or 2 is achieved by the employment of [MnIII(TMSPS3)(DABCO)]. In contrast, 4a and 4b show inertness toward visible‐light stimulus. Photolysis and having pendant thiol/thioether group play key roles in NO production from these iron‐nitrosyl‐thiolato complexes, that is, the Fe‐NO bond is weakened by exposure to light and the noncovalent SH of 1 or SCH3 of 2 can serve as an incoming ligand to interact with Fe atom, resulting in a transient with intramolecular [RS⋅⋅⋅Fe⋅⋅⋅NO] interaction (RH and CH3) which could facilitate NO dissociation. The noncovalent sulfur plays significant roles in Fe‐NO bond cleavage upon exposure to visible light, leading to production of NO and HNO (RH), and only formation of NO (RCH3).