Synthesis and reactivity of a nickel(ii) thioperoxide complex: demonstration of sulfide-mediated N(2)O reduction

The thiohyponitrite ([SNNO](2–)) complex, [K(18-crown-6)][L(tBu)Ni(II)(κ(2)-SNNO)] (L(tBu) = {(2,6-(i)Pr(2)C(6)H(3))NC((t)Bu)}(2)CH), extrudes N(2) under mild heating to yield [K(18-crown-6)][L(tBu)Ni(II)(η(2)-SO)] (1), along with minor products [K(18-crown-6)][L(tBu)Ni(II)(η(2)-OSSO)] (2) and [K(18-crown-6)][L(tBu)Ni(II)(η(2)-S(2))] (3). Subsequent reaction of 1 with carbon monoxide (CO) results in the formation of [K(18-crown-6)][L(tBu)Ni(II)(η(2)-SCO)] (4), [K(18-crown-6)][L(tBu)Ni(II)(S,O:κ(2)-SCO(2))] (5), [K(18-crown-6)][L(tBu)Ni(II)(κ(2)-CO(3))] (6), carbonyl sulfide (COS) (7), and [K(18-crown-6)][L(tBu)Ni(II)(S(2)CO)] (8). To rationalize the formation of these products we propose that 1 first reacts with CO to form [K(18-crown-6)][L(tBu)Ni(II)(S)] (I) and CO(2), via O-atom abstraction. Subsequently, complex I reacts with CO or CO(2) to form 4 and 5, respectively. Similarly, the formation of complex 6 and COS can be rationalized by the reaction of 1 with CO(2) to form a putative Ni(ii) monothiopercarbonate, [K(18-crown-6)][L(tBu)Ni(II)(κ(2)-SOCO(2))] (11). The Ni(ii) monothiopercarbonate subsequently transfers a S-atom to CO to form COS and [K(18-crown-6)][L(tBu)Ni(II)(κ(2)-CO(3))] (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(tBu)Ni(II)(κ(2)-SNNO)] to 1 and then I, which represents the formal reduction of N(2)O by CO.