Reduction of RuVI(N) to RuIII-NH3 by Cysteine in Aqueous Solution
The reduction of metal nitride to ammonia is a key step in biological and chemical nitrogen fixation. We report herein the facile reduction of a ruthenium(VI) nitride complex [(L)RuVI(N)(OH2)]+ (1, L = N,N′-bis(salicylidene)- o-cyclohexyldiamine dianion) to [(L)RuIII(NH3)(OH2)]+ by Lcysteine (Cys), an ubiquitous biological reductant, in aqueous solution. At pH 1.0−5.3, the reaction has the following stoichiometry: [(L)RuVI(N)(OH2)]+ + 3HSCH2CH(NH3)CO2 → [(L)RuIII(NH3)(OH2)]+ + 1.5(SCH2CH(NH3)CO2)2. Kinetic studies show that at pH 1 the reaction consists of two phases, while at pH 5 there are three distinct phases. For all phases the rate law is rate = k2[Cys]. Studies on the effects of acidity indicate that both HSCH2CH(NH3 +)CO2 – and −SCH2CH(NH3 +)CO2 − are kinetically active species. At pH 1, the reaction is proposed to go through [(L)- RuIV(NHSCH2CHNH3CO2H)(OH2)]2+ (2a), [(L)RuIII(NH2SCH2CHNH3CO2H)(OH2)]2+ (3), and [(L)RuIV(NH2)(OH2)]+ (4) intermediates. On the other hand, at pH around 5, the proposed intermediates are [(L)RuIV(NHSCH2CHNH3CO2)- (OH2)]+ (2b) and [(L)RuIV(NH2)(OH2)]+ (4). The intermediate ruthenium(IV) sulfilamido species, [(L)- RuIV(NHSCH2CHNH3CO2H)(OH2)]2+ (2a) and the final ruthenium(III) ammine species, [(L)RuIII(NH3)(MeOH)]+ (5) (where H2O was replaced by MeOH) have been isolated and characterized by various spectroscopic methods.
Qian, W.,Man, W.,Lam, W.,Yiu, S.,Tse, M.,& Lau, T. (2018). Reduction of RuVI(N) to RuIII-NH3 by Cysteine in Aqueous Solution. Inorganic Chemistry, 57 (10), 5850-5858. http://dx.doi.org/10.1021/acs.inorgchem.8b00238