Thiol-Assisted Stepwise Reduction of Nitrite to Nitric Oxide to Nitrous Oxide by a Cobalt(II)-ONO Compound Featuring the Intermediary of Highly Reducing Cobalt(II)-Thiolate Compounds

A detailed study of the stepwise reduction of nitrite (NO 2 – ) to nitric oxide (NO) to nitrous oxide (N 2 O) by a Co(II)-ONO compound is presented. Reactions of [Co II (6-COO – -tpa)] 1+ ( 1 ) and [Co III (6-COO – -tpa)(DMF)] 2+ ( 2 ) with NO 2 – produced [Co II (6-COO – -tpa)(ONO)] ( 3 ) and [Co III (6-COO – -tpa)(NO 2 )] 1+ ( 4 ), respectively. Complex 4 reacts with thiols at −35 °C to produce [Co III (6-COO – -tpa)(SR)] 1+ (R = Ph, 5a; p –F-C 6 H 4, 5b ), while the same reaction at RT generated NO (48–58%) along with 1 . On the other hand, compound 3 reacts with thiols to generate NO (20–24%) along with [Co II (6-COO – -tpa)(SR)] (R = Ph, 6a; p –F-C 6 H 4, 6b ) and 1 . Interestingly, mechanistic investigation revealed that the in situ generated, highly reducing ( E 1/2 = −0.73 V to −0.75 V vs Cp 2 Fe + /Cp 2 Fe), Co(II)-thiolate compounds, 6a and 6b, reduced the in situ generated NO further to N 2 O. Analytically pure samples of 6a and 6b demonstrated the direct reduction of NO to N 2 O in excellent yields (82–89%), which were improved further to 91–97% upon use of MeCOOH and (TMS)(OTf). Finally, based on IR spectroscopic analysis of the NO reduction reactions, a probable mechanism for the reduction of NO to N 2 O involving the generation of a {Co(NO) 2 } 10 species has been proposed.