Binding N2, N2H2, N2H4, and NH3 to Transition-Metal Sulfur Sites: Modeling Potential Intermediates of Biological N2 Fixation

In the quest for low‐molecular‐weight metal sulfur complexes that bind nitrogenase‐relevant small molecules and can serve as model complexes for nitrogenase, compounds with the [Ru(PiPr3)(‘N2Me2S2’)] fragment were found (‘N2Me2S2’2−=1,2‐ethanediamine‐N,N′‐dimethyl‐N,N′‐bis(2‐benzenethiolate)2−). This fragment enabled the synthesis of a first series of chiral metal sulfur complexes, [Ru(L)(PiPr3)(‘N2Me2S2’)] with L=N2, N2H2, N2H4, and NH3, that meet the biological constraint of forming under mild conditions. The reaction of [Ru(NCCH3)(PiPr3)(‘N2Me2S2’)] (1) with NH3 gave the ammonia complex [Ru(NH3)(PiPr3)(‘N2Me2S2’)] (4), which readily exchanged NH3 for N2 to yield the mononuclear dinitrogen complex [Ru(N2)(PiPr3)(‘N2Me2S2’)] (2) in almost quantitative yield. Complex 2, obtained by this new efficient synthesis, was the starting material for the synthesis of dinuclear (R,R)‐ and (S,S)‐[μ‐N2{Ru(PiPr3)(‘N2Me2S2’)}2] ((R,R)‐/(S,S)‐3). (Both 2 and 3 have been reported previously.) The as‐yet inexplicable behavior of complex 3 to form also the R,S isomer in solution has been revealed by DFT calculations and 2D NMR spectroscopy studies. The reaction of 1 or 2 with anhydrous hydrazine yielded the hydrazine complex [Ru(N2H4)(PiPr3)(‘N2Me2S2’)] (6), which is a highly reactive intermediate. Disproportionation of 6 resulted in the formation of mononuclear diazene complexes, the ammonia complex 4, and finally the dinuclear diazene complex [μ‐N2H2{Ru(PiPr3)(‘N2Me2S2’)}2] (5). Dinuclear complex 5 could also be obtained directly in an independent synthesis from 1 and N2H2, which was generated in situ by acidolysis of K2N2(CO2)2. Treatment of 6 with CH2Cl2, however, formed a chloromethylated diazene species [{Ru(PiPr3)(‘N2Me2S2’)}‐μ‐N2H2{Ru(Cl)(‘N2Me2S2CH2Cl’)}] (9) (‘N2Me2S2CH2Cl’2− =1,2‐ethanediamine‐N,N′‐dimethyl‐N‐(2‐benzenethiolate)1−‐N′‐(2‐benzenechloromethylthioether)1−]. The molecular structures of 4, 5, and 9 were determined by X‐ray crystal structure analysis, and the labile N2H4 complex 6 was characterized by NMR spectroscopy. Fixated on complexes: In the search to find model complexes for biological N2 fixation, a first series of chiral metal sulfur complexes, [Ru(L)(PiPr3)(‘N2Me2S2’)] with L=N2, N2H2, N2H4, and NH3 (2), that meets the biological constraint of forming under mild conditions is reported. Dinuclear complexes such as 1 were also synthesized and studied. ‘N2Me2S2’2−=1,2‐ethanediamine‐N,N′‐dimethyl‐N,N′‐bis(2‐benzenethiolate)2−.