Polymer-supported N-heterocyclic carbene-iron(III) catalyst and its application to dehydration of fructose into 5-hydroxymethyl-2-furfural

Disarming the alkoxide trap to access a practical FeCl3 system for borrowing-hydrogen N-alkylation

Disarming the alkoxide trap using an in situ reduction strategy to access a practical FeCl3 and N-heterocyclic carbene system for borrowing-hydrogen N-alkylation.

Earth-abundant 3d-transition-metal catalysts for lignocellulosic biomass conversion

Transformation of biomass to chemicals and fuels is a long-term goal in both science and industry. However, high cost is one of the major obstacles to the industrialization of this sustainable technology. Thus, developing catalysts with high activity and low-cost is of great importance for biomass conversion. The last two decades have witnessed the increasing achievement of the use of earth-abundant 3d-transition-metals in catalysis due to their low-cost, high efficiency and excellent stability. Here, we aim to review the fast development and recent advances of 3d-metal-based catalysts including Cu, Fe, Co, Ni and Mn in lignocellulosic biomass conversion. Moreover, present research trends and invigorating perspectives on future development are given.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Sugar dehydration to 5-hydroxymethylfurfural in mixtures of water/[Bmim]Cl catalyzed by iron sulfate

Stabilization effect of [Bmim]Cl on HMF is demonstrated, which can suppress the rehydration and polymerization side-reactions and enhance HMF yield.

Poly(styrene)-supported N-heterocyclic carbene coordinated iron chloride as a catalyst for delayed polyurethane polymerization

An advanced organometallic catalyst based on N-heterocyclic carbene (NHC) coordinated FeCl3 has been synthesized and used to control the reaction rate in polyurethane (PUR) polymerization. The imidazolium (Im)-based NHC was functionalized on the surface of the supporting material of bead-type chloromethyl polystyrene (PS) resin. The PS-Im-FeCl3 catalyst was synthesized through the coordination reaction between Im and FeCl3. The successful formation, functional groups, structure, and geometry of the PS-Im-FeCl3 catalysts were confirmed by Fourier transform infrared and X-ray photoelectron spectroscopy techniques. A thin layer of Im was observed to be coated uniformly on the PS bead surface and FeCl3 nanoparticles were observed to cover the coating layer homogeneously, as determined by field-emission scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy measurements. The PUR polymerization reaction was investigated through viscosity measurements and non-isothermal activation energy calculations by differential scanning calorimetry analysis. Based on the viscosity measurements, delayed PUR polymerization was achieved using the PS-Im-FeCl3 catalyst system. The highest viscosity (6000 cP) was achieved without any catalyst, with triphenylene bismuth, and with the PS-Im-FeCl3 catalyst after 23, 5, and 25 h of reaction time, respectively. Furthermore, the calculated activation energies (E a) were 27.92 and 36.35 kJ mol-1 for the no-catalyst and the PS-Im-FeCl3 systems, respectively. Thus, the viscosity measurements and DSC analyses confirm that the PS-Im-FeCl3 catalyst considerably increases the PUR reaction time. The Im-FeCl3 catalyst supported by CMPS can control the reaction rate in PUR synthesis because of its high activity. Thus, the PS-Im-FeCl3 catalyst can be used as a curing retardant in the PUR industry.

High-Oxidation-State 3d Metal (Ti-Cu) Complexes with N-Heterocyclic Carbene Ligation

High-oxidation-state 3d metal species have found a wide range of applications in modern synthetic chemistry and materials science. They are also implicated as key reactive species in biological reactions. These applications have thus prompted explorations of their formation, structure, and properties. While the traditional wisdom regarding these species was gained mainly from complexes supported by nitrogen- and oxygen-donor ligands, recent studies with N-heterocyclic carbenes (NHCs), which are widely used for the preparation of low-oxidation-state transition metal complexes in organometallic chemistry, have led to the preparation of a large variety of isolable high-oxidation-state 3d metal complexes with NHC ligation. Since the first report in this area in the 1990s, isolable complexes of this type have been reported for titanium(IV), vanadium(IV,V), chromium(IV,V), manganese(IV,V), iron(III,IV,V), cobalt(III,IV,V), nickel(IV), and copper(II). With the aim of providing an overview of this intriguing field, this Review summarizes our current understanding of the synthetic methods, structure and spectroscopic features, reactivity, and catalytic applications of high-oxidation-state 3d metal NHC complexes of titanium to copper. In addition to this progress, factors affecting the stability and reactivity of high-oxidation-state 3d metal NHC species are also presented, as well as perspectives on future efforts.

Starbon/High-Amylose Corn Starch-Supported N-Heterocyclic Carbene-Iron(III) Catalyst for Conversion of Fructose into 5-Hydroxymethylfurfural

Iron-N-heterocyclic carbene complexes (Fe-NHCs) have come to prominence because of their applicability in diverse catalytic reactions, ranging from C-C cross-coupling and C-X bond formation to substitution, reduction, polymerization, and dehydration reactions. The detailed synthesis, characterization, and application of novel heterogeneous Fe-NHC catalysts immobilized on mesoporous expanded high-amylose corn starch (HACS) and Starbon 350 (S350) for facile fructose conversion into 5-hydroxymethylfurfural (HMF) is reported. Both catalyst types showed good performance for the dehydration of fructose to HMF when the reaction was tested at 100 °C with varying time (10 min, 20 min, 0.5 h, 1 h, 3 h and 6 h). For Fe-NHC/S350, the highest HMF yield was 81.7 % (t=0.5 h), with a TOF of 169 h^-1 , fructose conversion of 95 %, and HMF selectivity of 85.7 %, whereas for Fe-NHC/expanded HACS, the highest yield was 86 % (t=0.5 h), with a TOF of 206 h^-1 , fructose conversion of 87 %, and HMF selectivity of 99 %. Iron loadings of 0.26 and 0.30 mmol g^-1 were achieved for Fe-NHC/expanded starch and Fe-NHC/S350, respectively.