A Mononitrosyl Diiron(II) Compound Catalyzes the Reduction of Nitrite to Nitric Oxide

A diiron(II) compound, [Fe₂(HPTP)(NCS)₃(DMF)] (<b>1</b>), mediated the direct reduction of nitrite (NO₂^-) to nitric oxide (NO) in 100% yield and allowed the generation of a mononitrosyl diiron(II) compound, [Fe₂(HPTP)(NCS)₃(NO)] (<b>2</b>). Compound <b>2</b> is a rare [Fe^II{FeNO}⁷] species, which featured Fe-N and N-O distances of 1.768(4) Å and 1.142(5) Å, respectively, <Fe-N-O angle of 158.2(4)°, ν_NO = 1765 cm^-1, EPR signal centered at <<i>g</i>> = 2.00 characteristic of an <i>S</i> = 1/2 ground state, and released NO to regenerate <b>1</b> within 36 h in DMF. Interestingly, <b>2</b> could also reduce NO₂^- to NO in 100% yield, and thus the formation of <b>2</b> did not inhibit the quantitative reduction of NO₂^- to NO by <b>1</b>. It was also observed that the redox reaction of PhS^- with the Fe(III) centers, generated after the reduction of NO₂^- to NO, to regenerate <b>1</b> and PhS-SPh was much more facile than the reaction of the in situ generated <b>2</b> with PhS^- to produce the dinitrosyl iron complex (DNIC), [Fe(SPh)₂(NO)₂]^1-. The reduction of NO₂^- to NO by <b>1</b> and <b>2</b> has been made catalytic with a TON of 20 and 16, respectively. Compound <b>2</b> is the only [Fe^II{FeNO}⁷] compound that can catalyze the reduction of NO₂^- to NO.