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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.