Hidetoshi Ohta

Conversion of lignocellulose into renewable chemicals by heterogeneous catalysis

Conversion of lignocellulose into renewable chemicals and fuels has received great attention for building up sustainable societies. However, the utilisation of lignocellulose in the chemical industry has largely been limited to paper manufacturing because of the complicated chemical structure and persistent property of lignocellulose. Heterogeneous catalysis has the potential to selectively convert lignocellulosic biomass into various useful chemicals, and this methodology has rapidly progressed in the last several years. In this perspective article, we outline our recent approaches on the heterogeneous catalysis for this challenging subject with related literatures.

Hydrodeoxygenation of phenols as lignin models under acid-free conditions with carbon-supported platinum catalysts

Carbon-supported Pt catalysts are highly active and reusable for the aqueous-phase hydrodeoxygenation of phenols as lignin models without adding any acids. It is suggested that Pt/carbon facilitates the hydrogenation of phenols and the hydrogenolysis of the resulting cyclohexanols.

N-Heterocyclic carbene ligands bearing hydrophilic and/or hydrophobic chains: Rh(I) and Pd(II) complexes and their catalytic activity

A series of novel imidazolium salts bearing hydrophilic tetraethylene glycol (TEG) and/or hydrophobic long-chain alkyl (n-C12) functionalities, which are precursors for desired N-heterocyclic carbene (NHC) ligands, were synthesized and characterized. Rh(I)-NHC complexes were prepared in good yields by the silver carbene transfer method with NHC-Ag species derived from the imidazolium salts. The molecular structure of the Rh(I)-NHC complex having n-C12 chains has been determined by a single-crystal X-ray diffraction study and the complex is found to possess extended alkyl chains with anti conformations in the solid state. Hydrosilylation with the Rh(I) complexes and Suzuki-Miyaura coupling reactions with the Pd(II) complexes with these NHC ligands were carried out. In the latter case, the TEG moiety enhances catalytic activity considerably.

Pd-Catalyzed P–C Cross-Coupling Reactions for Versatile Triarylphosphine Synthesis

Practical and versatile syntheses of tertiary phosphine derivatives have been achieved by palladium-catalyzed deformylative P-C cross-coupling reactions of hydroxymethylphosphine derivatives. Sequential couplings of orthogonally protected precursors provide a simple and practical route toward a variety of tertiary phosphine derivatives having aryl substituents in any combination.

Highly Active Copper-Network Catalyst for the Direct Aldol Reaction

The development of a highly active solid-phase catechol-copper network catalyst for direct aldol reaction is described. The catalyst was prepared from an alkyl-chain-linked bis(catechol) and a copper(II) complex. The direct aldol reaction between carbonyl compounds (aldehydes and ketones) and methyl isocyanoacetate was carried out using 0.1-1 mol% [Cu] catalyst to give the corresponding oxazolines at yields of up to 99% and a trans/cis ratio of >99:1. The catalyst was reused with no loss of catalytic activity. A plausible reaction pathway is also described.

Synthesis and Photophysical Properties of λ5-Phosphinines as a Tunable Fluorophore

A practical synthesis of a variety of λ5-phosphinines, which show distinct fluorescence both in solution and solid state, is described. Both C4-selective electrophilic substitutions and the following conversions realized an easy preparation of a wide range of derivatives having several substituents for electronic modification, which provides the potential for fine-tuning of the photophysical properties.

CHAPTER 3:Noble-Metal Catalysts for Conversion of Lignocellulose under Hydrogen Pressure

Noble-metal catalysts are useful for the conversion of recalcitrant and highly oxygenated compounds derived from biomass, since they are remarkably active for the reduction reactions and more stable than base metals under harsh conditions. In this chapter, we show advances in research on the catalysis of noble metals through the hydrolytic hydrogenation and hydrodeoxygenation of lignocellulosic biomass and related compounds as representative reactions in the valorization of biomass. Analytical techniques using high-performance liquid chromatography and gas chromatography are also discussed.