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 ~( t Bu) Ni ~(II) (κ ~(2) -SNNO)] (L ~( t Bu) = {(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 ~( t Bu) Ni ~(II) (η ~(2) -SO)] ( 1 ), along with minor products [K(18-crown-6)][L ~( t Bu) Ni ~(II) (η ~(2) -OSSO)] ( 2 ) and [K(18-crown-6)][L ~( t Bu) 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 ~( t Bu) Ni ~(II) (η ~(2) -SCO)] ( 4 ), [K(18-crown-6)][L ~( t Bu) Ni ~(II) ( S , O :κ ~(2) -SCO _(2) )] ( 5 ), [K(18-crown-6)][L ~( t Bu) Ni ~(II) (κ ~(2) -CO _(3) )] ( 6 ), carbonyl sulfide (COS) ( 7 ), and [K(18-crown-6)][L ~( t Bu) 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 ~( t Bu) 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 ~( t Bu) 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 ~( t Bu) 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 ~( t Bu) Ni ~(II) (κ ~(2) -SNNO)] to 1 and then I , which represents the formal reduction of N _(2) O by CO.