Mechanism of Reduction of Bound Nitrite to Ammonia

Electrochemical experiments on the oxidation of [(tpy)(bpy)M(NH₃)]²⁺(M = Ru, Os; tpy = 2,2’,2”-terpyridine; bpy = 2,2’-bipyridine) and reduction of [(tpy)(bpy)M(NO₂)]⁺ have given insight into the mechanistic details of how bound nitrite is converted into ammonia. A critical feature is acid-base interconversion to the nitrosyl form, [(tpy)(bpy)M(NO)]³⁺, which undergoes a series of stepwise, one-electron reductions. Direct experimental evidence has been obtained for a series of intermediates that can be formulated as [(tpy)(bpy)M^IV(NH)]²⁺, [(tpy)(bpy)M^v(N)]²⁺ or [(tpy)(bpy)M^II(NH₂O)]²⁺, [(tpy)(bpy)M^II(NHO)]²⁺, and [(tpy)(bpy)M_II(NO*)]²⁺.