Photoinduced NO and HNO Production from Mononuclear {FeNO}~6 Complex Bearing a Pendant Thiol

摘要

Light triggers the formation of HNO from a metal- nitrosyl species, facilitated by an intramolecular pendant thiol proton. Two {FeNO}~6 complexes (the Enemark-Felthan nota- tion), [Fe(NO)(~(TMS)PS2)(~(TMS)PS2H)] (1,~(TMS)PS2H_2 = 2,2'- dimercapto-3,3'-bis(trimethylsilyl)diphenyl)phenylphosphine; H is a dissociable proton) with a pendant thiol and [Fe(NO)- (~(TMS)PS2)(~(TMS)PS2CH_3)] (2) bearing a pendant thioether, are spectroscopically and structurally characterized. Both complexes are highly sensitive to visible light. Upon photolysis, complex 2 undergoes NO dissociation to yield a mononuclear Fe(Ⅲ) complex, [Fe(~(TMS)PS2)(~(TMS)PS2CH_3)] (3). In contrast, the pendant SH of 1 can act as a trap for the departing NO radical upon irradiation, resulting in the formation of an intermediate A with an intramolecular [SH...ON-Fe] interaction. As suggested by computational results (density functional theory), the NO stretching frequency (ν_(NO)) is sensitive to the intramolecular interaction between the pendant ligand and the iron-bound NO, and a shift of ν_(NO) from 1833 (1) to 1823 cm~(-1) (A) is observed experimentally. Subsequent photolysis of the intermediate A results in HNO production and a thiyl group that then coordinates to the Fe center for the formation of [Fe(~(TMS)PS2)_2] (4). In contrast with the common acid-base coupling pathway, the HNO is not voluntarily yielded from 1 but rather is generated by the photopromoted pathway. The photogenerated HNO can further react with [Mn~Ⅲ(~(TMS)PS3)(DABCO)] (~(TMS)PS3H_3 = (2,2′2″-trimercapto-3,3′,3″- tris(trimethylsilyl)triphenylphosphine; DABCO = 1,4-diazabicyclo[2.2.2]octane) in organic media to yield anionic [Mn(NO)- (~(TMS)PS3)]~- (5~-) with a {MnNO}~6 electronic configuration, whereas [Mn~Ⅲ(~(TMS)PS3)(DABCO)] reacts with NO gas for the formation of a {MnNO}~5 species, [Mn(NO)(~(TMS)PS3)] (6). Effective differentiation of the formation of HNO from complex 1 with the pendant SH versus NO from 2 with the pendant SMe is achieved by the employment of [Mn~Ⅲ(~(TMS)PS3)(DABCO)].