Reduction of Nitrite in an Iron(II)-Nitrito Compound by Thiols and Selenol Produces Dinitrosyl Iron Complexes via an {FeNO}<sup>7</sup> Intermediate
Soumik Karmakar, Suman Patra, Ritapravo Halder, Suchismita Karmakar, Amit Majumdar
Abstract
Reaction of an Fe(II) complex, [Fe(6-COO – -tpa)] 1+ ( 1 ), with PhE – and NO 2 – produced [Fe(6-COO – -tpa)(EPh)] (E = S, 2a; Se, 3 ) and [Fe(6-COO – -tpa) ( κ 2 - O,O′-NO 2 )] ( 4 ), respectively (6-COOH-tpa is bis(2-pyridylmethyl)(6-carboxyl-2-pyridylmethyl)amine). Treatment of 4 with 2 equiv of PhEH (E = S, Se) produced NO in ∼40% yields, respectively, along with 1 and the DNICs, [Fe(EPh) 2 (NO) 2 ] 1– (E = S, Se). Treatment of 4 with excess PhEH produced NO in similar yields, while 4 was converted to the same DNICs and 2a / 3 (instead of 1 ). The DNICs have been proposed to be generated via the reaction of PhE – with an in situ generated, unstable {FeNO} 7 intermediate, [Fe(6-COO – -tpa)(NO)] 1+ ( 6 ), which has also been synthesized separately. Compound 6 reacts with PhS – to generate [Fe(SPh) 2 (NO) 2 ] 1–, thus supporting the proposed reaction pathway. Finally, while the treatment of two unique compounds, featuring inbuilt proton sources, [Fe(6-COO – -tpa)(S-C 6 H 4 - p -COOH)] ( 7 ) and [Fe(6-COO – -tpa)(S-C 6 H 4 - o -OH)] ( 8 ), with 0.5 and 1 equiv of NO 2 – could produce NO only in 8–26% yields, treatment of 4 with HS-C 6 H 4 - p -COOH and HS-C 6 H 4 - o -OH produced NO in much higher yields (65–77%). The combined results delineated the importance of coordination of NO 2 – for the proton-assisted reduction of NO 2 – to generate NO.