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Our undergraduate research group has long focused on the preparation and investigation of electron-deficient analogs of the perimidinespirohexadienone (PSHD) family of photochromic molecular switches for potential application as "photochromic photooxidants" for gating sensitivity to photoinduced charge transfer. We previously reported the photochemistry of two closely related and more reducible quinazolinespirohexadienones (QSHDs), wherein the naphthalene of the PSHD is replaced with a quinoline. In the present work, we report our investigation of the electrochemistry of these asymmetric QSHDs. In addition to the short wavelength and photochromic long-wavelength isomers, we have found that a second, distinct long-wavelength isomer is produced electrochemically. This different long-wavelength isomer arises from a difference in the regiochemistry of spirocyclic ring-opening. The structures of both long-wavelength isomers were ascertained by cyclic voltammetry and 1 H NMR analyses, in concert with computational modeling. These results are compared to those for the symmetric parent PSHD, which due to symmetry possesses only a single possible regioisomer upon either electrochemical or photochemical ring-opening. Density functional theory calculations of bond lengths, bond orders, and molecular orbitals allow the rationalization of this differential photochromic vs electrochromic behavior of the QSHDs. 

Non‐heme high‐spin (hs) {FeNO}⁸complexes have been proposed as important intermediates towards N₂O formation in flavodiiron NO reductases (FNORs). Many hs‐{FeNO}⁸complexes disproportionate by forming dinitrosyl iron complexes (DNICs), but the mechanism of this reaction is not understood. While investigating this process, we isolated a new type of non‐heme iron nitrosyl complex that is stabilized by an unexpected spin‐state change. Upon reduction of the hs‐{FeNO}⁷complex, [Fe(TPA)(NO)(OTf)](OTf) (1), the N‐O stretching band vanishes, but no sign of DNIC or N₂O formation is observed. Instead, the dimer, [Fe₂(TPA)₂(NO)₂](OTf)₂(2) could be isolated and structurally characterized. We propose that2is formed from dimerization of the hs‐{FeNO}⁸intermediate, followed by a spin state change of the iron centers to low‐spin (ls), and speculate that2models intermediates in hs‐{FeNO}⁸complexes that precede the disproportionation reaction.

 

Non‐heme high‐spin (hs) {FeNO}⁸complexes have been proposed as important intermediates towards N₂O formation in flavodiiron NO reductases (FNORs). Many hs‐{FeNO}⁸complexes disproportionate by forming dinitrosyl iron complexes (DNICs), but the mechanism of this reaction is not understood. While investigating this process, we isolated a new type of non‐heme iron nitrosyl complex that is stabilized by an unexpected spin‐state change. Upon reduction of the hs‐{FeNO}⁷complex, [Fe(TPA)(NO)(OTf)](OTf) (1), the N‐O stretching band vanishes, but no sign of DNIC or N₂O formation is observed. Instead, the dimer, [Fe₂(TPA)₂(NO)₂](OTf)₂(2) could be isolated and structurally characterized. We propose that2is formed from dimerization of the hs‐{FeNO}⁸intermediate, followed by a spin state change of the iron centers to low‐spin (ls), and speculate that2models intermediates in hs‐{FeNO}⁸complexes that precede the disproportionation reaction.