Hua Fen Hsu

Catalytic reduction of hydrazine to ammonia by a mononuclear iron(II) complex on a tris(thiolato)phosphine platform

To provide the mechanistic information of nitrogenase at a molecular level, much effort has been made to develop synthetic metal complexes that have enzyme-like reactivity. Herein we obtain an iron(II) complex binding with a tris(thiolato)phosphine ligand, [P(Ph)4][Fe(PS3″)(CH3CN)] [1; PS3″ = P(C6H3-3-Me3Si-2-S)3(3-)] that catalyzes the reduction of hydrazine, an intermediate and a substrate of nitrogenase. The substrate- and product-bound adducts, [N(Bu)4][Fe(PS3″)(N2H4)] (2) and [N(Et)4][Fe(PS3″)(NH3)] (3), respectively, are also synthesized. This work provides the feasibility that the late stage of biological nitrogen fixation can be conducted at a single iron site with a sulfur-rich ligation environment.

Activation of dichloromethane by a V(III) thiolate complex: an example of S-based nucleophilic reactivity in an early transition metal thiolate

A V(III) thiolate complex activated C-Cl bond in dichloromethane via S-based nucleophilic attack. The reaction products, a V(III)-Cl species (major one) and a V(IV) binding to a CH(2) containing ligand (minor one) were obtained. The work demonstrates sulfur donors in the early-transition metal thiolates having strong nucleophilic characteristics.

Redox Interconversion of Non-Oxido Vanadium Complexes Accompanied by Acid–Base Chemistry of Thiol and Thiolate

The redox nature of the non-oxido vanadium sulfur center is associated with several biological systems such as vanadium nitrogenase, the reduction of vanadium ion in ascidians, and the function of amavadin, which is a vanadium(IV) natural product contained in Amanita mushrooms. But the related chemistry is less explored and understood compared to oxido vanadium species due to the oxophilic character of high valent vanadium ions. Herein, we present a class of non-oxido vanadium thiolate complexes, [VIII(PS2″SH)2]- (1) (PS2″SH = [P(C6H3-3-Me3Si-2-S)2(C6H3-3-Me3Si-2-SH)]2-), [VIV(PS3″)(PS2″SH)]- (2) (PS3″ = [P(C6H3-3-Me3Si-2-S)3]3-), [V(PS3″)2]- (3), [V(PS3″)(PS2″SH)] (4), and [VIV(PS3*)2]2- (5a) (PS3* = [P(C6H3-3-Ph-2-S)3]3-), and study their interconversion through the redox and acid-base reactions. Complex 1 consists of a six-coordinate octahedral vanadium center; complexes 2 and 4 are seven-coordinate with distorted capped trigonal prismatic geometry. Vanadium centers of 3 and 5a are both eight-coordinate; the former adopts ideal dodecahedral geometry, but the latter is better viewed as a distorted square antiprism. Complex 1 is oxidized to complex 2 and then to complex 3 with dioxygen. Each one-electron oxidation process is accompanied by the deprotonation of unbound thiol to bound thiolate. Complex 3 is also produced from complex 2 through stepwise addition of Fe(Cp)2+/n-BuLi, or in the reverse order. The formation of 2 from 3 is achieved in the order of adding Co(Cp)2 and acid or, as with the previous complex, inversely. Notably, the reduction of complex 2 to complex 1 accompanying the protonation of bound thiolate to unbound thiol only occurs with the presence of both Co(Cp)2 and acid, indicating a cooperative effect between the metal-centered reduction and bound thiolate protonation. The conversions among these complexes are observed with ESI-MS and UV-vis-NIR spectroscopies. The work demonstrates two-electron redox interconversion in these complexes mediated by transformations between unbound thiol and bound thiolate.

Reactivity of a Fe(III)-Bound Methoxide Supported with a Tris(thiolato)phosphine Ligand: Activation of C-Cl Bond in CH2Cl2 by Nucleophilic Attack of a Fe(III)-OCH3 Moiety

Two mononuclear nonheme Fe(III) complexes, [PPh4][Fe(III)(PS3″)(OCH3)] (1) and [PPh4][Fe(III)(PS3″)(Cl)] (2), supported by a tris(benzenethiolato)phosphine derivative PS3″ (PS3″ = P(C6H3-3-Me3Si-2-S)3(3-)) have been synthesized and characterized. The structures resolved from X-ray crystallography show that Fe(III) centers in both complexes adopt distorted trigonal-bipyramidal geometry with a methoxide or a chloride binding in the axial position. The magnetic data for both are consistent with intermediate-spin Fe(III) centers with a C3 symmetry (S = 3/2 ground state). The bound methoxide in 1 is labile and can be replaced by a CH3CN molecule. The forming Fe(III)-CH3CN species can be further reduced by cobaltcene quantitatively to a stable Fe(II)-CH3CN complex, [Fe(PS3″)(CH3CN)](-). One-electron oxidation of 2 by ferrocenium gave a Fe(IV) analogue, [Fe(IV)(PS3″)(Cl)]. Importantly, the Fe(III)-OCH3 moiety in complex 1 acts as a strong nucleophile that activates the C-Cl bond in CH2Cl2, leading to the formation of complex 2 quantitatively. Complex 1 also reacts with other electrophiles, benzyl chloride and benzyl bromide, to generate Fe(III)-X species (X = Cl or Br). The reactions were investigated and monitored by UV-vis-NIR, NMR, and ESI-MS spectroscopies.