Unusual Hydrogenation Reactivities of a Thiolate-Bridged Dicobalt μ-Nitride Featuring a Bent {Co III -N-Co III } Core.

Transition metal nitrides have received considerable attention owing to their crucial roles in nitrogen fixation and nitrogen atom transfer reactions. Compared to the early and middle transition metals, it is much more challenging to access late transition metal nitrides, especially cobalt in group 9. So far, only a handful of cobalt nitrides have been reported; consequently, their hydrogenation reactivity is largely unexplored. Herein, we present a structurally and spectroscopically well-characterized thiolate-bridged dicobalt μ-nitride [Cp*Co III (μ-SAd)(μ-N)Co III Cp*] ( 2 ) featuring a bent {Co III (μ-N)Co III } core. Remarkably, complex 2 can realize not only direct hydrogenation of nitride to amide but also stepwise N-H bond formation from nitride to ammonia. Specifically, 2 can facilely activate dihydrogen (H 2 ) at mild conditions to generate a dicobalt μ-amide [Cp*Co II (μ-SAd)(μ-NH 2 )Co II Cp*] ( 4 ) via an unusual mechanism of two-electron oxidation of H 2 as proposed by computational studies; in the presence of protons (H + ) and electrons, nitride 2 can convert to dicobalt μ-imide [Cp*Co III (μ-SAd)(μ-NH)Co III Cp*][BPh 4 ] ( 3[BPh 4 ] ) and to Co II Co II μ-amide 4 , and finally release ammonia. In contrast to 2 , the only other structurally characterized dicobalt μ-nitride Na(THF) 4 {[( ket guan)Co III (N 3 )] 2 (μ-N)} ( ket guan = [( t Bu 2 CN)C(NDipp) 2 ] - , Dipp = 2,6-diisopropylphenyl) ( e ) that possesses a linear {Co III (μ-N)Co III } moiety cannot directly react with H 2 or H + . Further in-depth electronic structure analyses shed light on how the varying geometries of the {Co III (μ-N)Co III } moieties in 2 and e , bent vs linear, impart their disparate reactivities.