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

摘要

The thiohyponitrite ([SNNO]^2–) complex, [K(18-crown-6)][L^tBuNi^II(κ²-SNNO)] (L^tBu = {(2,6-ⁱPr2C6H3)NC(^tBu)}2CH), extrudes N2 under mild heating to yield [K(18-crown-6)][L^tBuNi^II(η²-SO)] (>1), along with minor products [K(18-crown-6)][L^tBuNi^II(η²-OSSO)] (>2) and [K(18-crown-6)][L^tBuNi^II(η²-S2)] (>3). Subsequent reaction of >1 with carbon monoxide (CO) results in the formation of [K(18-crown-6)][L^tBuNi^II(η²-SCO)] (>4), [K(18-crown-6)][L^tBuNi^II(S,O:κ²-SCO2)] (>5), [K(18-crown-6)][L^tBuNi^II(κ²-CO3)] (>6), carbonyl sulfide (COS) (>7), and [K(18-crown-6)][L^tBuNi^II(S2CO)] (>8). To rationalize the formation of these products we propose that >1 first reacts with CO to form [K(18-crown-6)][L^tBuNi^II(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^tBuNi^II(κ²-SOCO2)] (>11). The Ni(ii) monothiopercarbonate subsequently transfers a S-atom to CO to form COS and [K(18-crown-6)][L^tBuNi^II(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^tBuNi^II(κ²-SNNO)] to >1 and then >I, which represents the formal reduction of N2O by CO.