Synthesis and reactivity of a nickel(ii) thioperoxide complex: demonstration of sulfide-mediated N2O reduction.

The thiohyponitrite ([SNNO]2-) complex, [K(18-crown-6)][L tBuNiII(κ2-SNNO)] (L tBu = {(2,6-iPr2C6H3)NC( t Bu)}2CH), extrudes N2 under mild heating to yield [K(18-crown-6)][L tBuNiII(η2-SO)] (1), along with minor products [K(18-crown-6)][L tBuNiII(η2-OSSO)] (2) and [K(18-crown-6)][L tBuNiII(η2-S2)] (3). Subsequent reaction of 1 with carbon monoxide (CO) results in the formation of [K(18-crown-6)][L tBuNiII(η2-SCO)] (4), [K(18-crown-6)][L tBuNiII(S,O:κ2-SCO2)] (5), [K(18-crown-6)][L tBuNiII(κ2-CO3)] (6), carbonyl sulfide (COS) (7), and [K(18-crown-6)][L tBuNiII(S2CO)] (8). To rationalize the formation of these products we propose that 1 first reacts with CO to form [K(18-crown-6)][L tBuNiII(S)] (I) and CO2, via O-atom abstraction. Subsequently, complex I reacts with CO or CO2 to form 4 and 5, respectively. Similarly, the formation of complex 6 and COS can be rationalized by the reaction of 1 with CO2 to form a putative Ni(ii) monothiopercarbonate, [K(18-crown-6)][L tBuNiII(κ2-SOCO2)] (11). The Ni(ii) monothiopercarbonate subsequently transfers a S-atom to CO to form COS and [K(18-crown-6)][L tBuNiII(κ2-CO3)] (6). Finally, the formation of 8 can be rationalized by the reaction of COS with I. Critically, the observation of complexes 4 and 5 in the reaction mixture reveals the stepwise conversion of [K(18-crown-6)][L tBuNiII(κ2-SNNO)] to 1 and then I, which represents the formal reduction of N2O by CO.