One metal is enough: A nickel complex reduces nitrate anions to nitrogen gas

A stepwise reduction sequence from nitrate to dinitrogen gas at a single nickel center was discovered. A PNP nickel scaffold (PNP - = N[2-P i Pr 2 -4-Me-C 6 H 3 ] 2 ) emerged as a universal platform for the deoxygenation of NO x substrates. In these reactions carbon monoxide acts as the oxygen acceptor and forms CO 2 to provide the necessary chemical driving force. Whereas the first two oxygens are removed from the Ni-nitrate and Ni-nitrite complexes with CO, the deoxygenation of NO requires a disproportionation reaction with another NO molecule to form NO 2 and N 2 O. The final deoxygenation of nitrous oxide is accomplished by the Ni-NO complex and generates N 2 and Ni-NO 2 in a relatively slow, but clean reaction. This sequence of reactions is the first example of the complete denitrification of nitrate at a single metal-site and suggests a new paradigm of connecting CO and NO x as an effective reaction pair for NO x removal. © The Royal Society of Chemistry 2019