Dawei Yang

Ammonia formation by a thiolate-bridged diiron amide complex as a nitrogenase mimic

Although nitrogenase enzymes routinely convert molecular nitrogen into ammonia under ambient temperature and pressure, this reaction is currently carried out industrially using the Haber–Bosch process, which requires extreme temperatures and pressures to activate dinitrogen. Biological fixation occurs through dinitrogen and reduced NxHy species at multi-iron centres of compounds bearing sulfur ligands, but it is difficult to elucidate the mechanistic details and to obtain stable model intermediate complexes for further investigation. Metal-based synthetic models have been applied to reveal partial details, although most models involve a mononuclear system. Here, we report a diiron complex bridged by a bidentate thiolate ligand that can accommodate HN=NH. Following reductions and protonations, HN=NH is converted to NH3 through pivotal intermediate complexes bridged by N2H3– and NH2– species. Notably, the final ammonia release was effected with water as the proton source. Density functional theory calculations were carried out, and a pathway of biological nitrogen fixation is proposed. Although it is achieved routinely by nitrogenases, the conversion of molecular dinitrogen into ammonia under ambient conditions is proving difficult with synthetic systems. A thiolate-bridged diiron complex has now been developed that produces ammonia from coordinated N2H2 through a sequence of reduction and protonation reactions that may well mimic the biological nitrogen fixation.

Synthesis and Electrocatalytic Property of Diiron Hydride Complexes Derived from a Thiolate-Bridged Diiron Complex

Interaction of a diiron thiolate-bridged complex, [Cp*Fe(μ-η(2):η(4)-bdt)FeCp*] (1) (Cp* = η(5)-C5Me5; bdt = benzene-1,2-dithiolate) with a proton gives an Fe(III)Fe(III) hydride bridged complex, [Cp*Fe(μ-bdt)(μ-H)FeCp*][BF4] (3[BF4]). According to in situ variable temperature (1)H NMR studies, the formation of 3[BF4] was evidenced to occur through a stepwise pathway: protonation occurring at an iron center to produce terminal hydride [Cp*Fe(μ-bdt)(t-H)FeCp*][BF4] (2) and subsequent intramolecular isomerization to bridging hydride 3[BF4]. A one-electron reduction of 3[BF4] by CoCp2 affords a paramagnetic mixed-valent Fe(II)Fe(III) hydride complex, [Cp*Fe(μ-η(2):η(2)-bdt)(μ-H)FeCp*] (4). Further, studies on protonation processes of diruthenium and iron-ruthenium analogues of 1, [Cp*M1(μ-bdt)M2Cp*] (M1 = M2 = Ru, 5; M1 = Fe, M2 = Ru, 8), provide experimental evidence for terminal hydride species at these bdt systems. Importantly, diiron or diruthenium hydride bridged complexes 3[BF4], 7[BF4] and iron-ruthenium heterodinuclear complex 8[PF6] can realize electrocatalytic hydrogen evolution.

Highly β(Z)-Selective Hydrosilylation of Terminal Alkynes Catalyzed by Thiolate-Bridged Dirhodium Complexes

A series of novel monothiolate-bridged dirhodium complexes, [Cp*Rh(μ-SR)(μ-Cl)2RhCp*][BF4] {Cp* = η5-C5Me5, R = tertiary butyl ( tBu), 1a; R = ferrocenyl (Fc), 1b; R = adamantyl (Ad), 1c} were designed and successfully synthesized, which can smoothly facilitate highly regioselective and stereoselective hydrosilylation of terminal alkynes to afford β( Z) vinylsilanes with good functional group compatibility. Furthermore, the hydride bridged dirhodium complex [Cp*Rh(μ-S tBu)(μ-Cl)(μ-H)RhCp*][BF4] (5) as a potential intermediate was obtained by the reaction of 1a with excess HSiEt3.