Jingping Qu

Development of Tartaric Acid Derived Chiral Guanidines and Their Application to Catalytic Enantioselective α-Hydroxylation of β-Dicarbonyl Compounds

A novel library of chiral guanidines featuring a tartaric acid skeleton was developed from diethyl l-tartrate. These guanidines are easily accessed with tunable steric and electronic properties. The utilities of the guanidines were highlighted by their ability to catalyze the α-hydroxylation of β-ketoesters and β-diketones with remarkable efficiency and excellent enantioselectivity.

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.

An Organocatalytic Asymmetric Friedel–Crafts Addition/Fluorination Sequence: Construction of Oxindole–Pyrazolone Conjugates Bearing Vicinal Tetrasubstituted Stereocenters

A highly efficient and practical one-pot sequential process, consisting of an organocatalytic enantioselective Friedel-Crafts-type addition of 4-nonsubstituted pyrazolones to isatin-derived N-Boc ketimines and a subsequent diastereoselective fluorination of the pyrazolone moiety, is developed. This reaction sequence delivers novel oxindole-pyrazolone adducts featuring vicinal tetrasubstituted stereocenters with a 0.5 mol % catalyst loading in high yield with excellent enantio- and diastereocontrol. Notably, chloro, bromo, and thioether functionalities can be readily incorporated, rendering a broad diversity of the product.

Nitrogenase Model Complexes [Cp*Fe(μ-SR1)2(μ-η2-R2N═NH)FeCp*] (R1 = Me, Et; R2 = Me, Ph; Cp* = η5-C5Me5): Synthesis, Structure, and Catalytic N−N Bond Cleavage of Hydrazines on Diiron Centers

The reactions of [Cp*Fe(mu-SR1)3FeCp*] (Cp* = eta5-C5Me5; R1 = Et, Me) with 1.5 equiv R2NHNH2 (R2 = Ph, Me) give the mu-eta2-diazene diiron thiolate-bridged complexes [Cp*Fe(mu-SR1)2(mu-eta2-R2N NH)FeCp*], along with the formation of PhNH2 and NH3. These mu-eta2-diazene diiron thiolate-bridged complexes exhibit excellent catalytic N-N bond cleavage of hydrazines under ambient conditions.

Unusual Thiolate-Bridged Diiron Clusters Bearing the cis-HN═NH Ligand and Their Reactivities with Terminal Alkynes

A series of well-defined thiolate-bridged diiron clusters bearing the cis-HN═NH ligand, [Cp(†)Fe(μ-SEt)(2)(μ-η(1):η(1)-HN═NH)FeCp(†)][PF(6)] (Cp(†) = η(5)-C(5)Me(4)H or η(5)-C(5)Me(5)), are successfully prepared in high yields and fully characterized by spectroscopy and X-ray crystallography. Under moderate conditions, these new Fe/S clusters exhibit high activity, not only for the catalytic cleavage of the N-N bond of hydrazines but also for the activation and coupling of terminal alkynes.

Synthesis of trifluoromethyl ketones via tandem Claisen condensation and retro-Claisen C-C bond-cleavage reaction.

A highly efficient, operationally simple approach to trifluoromethyl ketones has been developed that builds on the use of a tandem process involving Claisen condensation and retro-Claisen C-C bond cleavage reaction. Enolizable alkyl phenyl ketones were found to react readily with ethyl trifuoroacetate under the promotion of NaH to afford trifluoroacetic ester/ketone exchange products, trifluoromethyl ketones, which were quite different from the general Claisen condensation products, β-diketones. This procedure uses readily available starting materials and can be extended to the preparation of perfluoroalkyl ketones in excellent yield.

Asymmetric chlorination of 4-substituted pyrazolones catalyzed by natural cinchona alkaloid

A natural quinidine-catalyzed asymmetric chlorination of 4-substituted pyrazolones is developed, affording products with a quaternary chiral chlorine-attached carbon centre in high yield with excellent enantioselectivity. The low catalyst loading (1 mol%), broad substrate scope, and facile and valuable transformation of the product highlight the practical utility of this process.

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.

Friedel–Crafts-Type Allylation of Nitrogen-Containing Aromatic Compounds with Allylic Alcohols Catalyzed by a [Mo3S4Pd(η3-allyl)] Cluster

With the direct use of allylic alcohols as allylating agents, the Friedel-Crafts-type allylic alkylation of nitrogen-containing aromatic compounds catalyzed by a [Mo(3)S(4)Pd(η(3)-allyl)] cluster is achieved. With a 3 mol % catalyst loading in acetonitrile at reflux or 60 °C, a variety of N,N-dialkylanilines and indoles reacted smoothly with allylic alcohols to afford the Friedel-Crafts-type allylation products in good to excellent yields with high levels of regioselectivity.

FeCl2-catalyzed hydroboration of aryl alkenes with bis(pinacolato)diboron

The first ligand-free ferrous chloride catalyzed anti-Markovnikov hydroboration of un-activated aryl alkenes with bis(pinacolato)diboron (B2pin2) has been reported. The reactions proceeded smoothly with high regioselectivity for a large range of aryl alkenes with wide functional-group compatibility and low catalyst loading under mild conditions.