Kosuke Higashida

Semi-hydrogenation of alkynes was catalyzed by halide-bridged dinuclear iridium complexes, yielding (E)-alkenes with high selectivity. Mechanistic studies conducted with monohydride dinuclear species, dihydride mononuclear species, and trihydride dinuclear species led us to propose a mechanism involving dual cycles.

Abstract The silver‐catalyzed asymmetric aldol reaction of isocyanoacetic acid derivatives with aldehydes has been developed by employing a chiral prolinol‐phosphine as a hydrogen‐bond‐donating P,N,O ligand. DFT calculations indicated that the reaction proceeds in a stepwise manner, involving C−C bond forming carbonyl addition and subsequent enantioselectivity‐determining oxazoline ring formation. An O−H⋅⋅⋅O/ sp 3 ‐C−H⋅⋅⋅O two‐point hydrogen bond donated by the prolinol moiety of the ligand acti

A gold(I) complex bearing an imidazo[1,5-a]pyridin-3-ylidene ligand with a 2,2′-bipyridine moiety at the C5 position was prepared as a template for constructing heterobimetallic cooperative catalysts. In situ generated gold–zinc bimetallic systems enabled intermolecular nucleophilic anti-addition of O-nucleophiles such as carboxylic acids and phenols toward nonactivated internal alkynes. DFT calculations supported the proposed cooperative action of the cationic gold atom and the zinc salt site f

Abstract Dinuclear triply chloro‐bridged iridium(III) complexes bearing chiral diphosphine ligands catalyze the asymmetric hydrogenation of tosylamido‐substituted pyrazines to give the corresponding chiral tetrahydropyrazines with an amidine skeleton in high yield and with high enantioselectivity. Addition of N , N ‐dimethylanilinium bromide enhanced the catalytic activity of the iridium complexes and also increased the enantioselectivity of the products by trapping the hydrogenated amine produc

The asymmetric allylic alkylation (AAA) reaction using less reactive, stable allylic sources is challenging. We achieved a nickel(0)-catalyzed AAA reaction of β-dicarbonyl compounds under ambient conditions through unstrained C–C bond activation of 2-allylated 2-methylcyclohexane-1,3-dione derivatives to afford the corresponding quaternary chiral compounds in high yield with high enantioselectivity. The reaction proceeded almost irreversibly due to the low solubility of the side-product, 2-methy

A catalytic asymmetric intermolecular benzylic C–H amination was achieved under paddle-wheel diruthenium catalysis. A chiral diruthenium catalyst incorporating (S)-TPPTTL (tetraphenylphthaloyl-(S)-tert-leucine) ligand exhibited notable enantioselectivity, and aminated products were obtained with up to 99% ee. Unique chemoselectivity of the chiral diruthenium catalyst was also found for allylbenzene and alkyl-naphthalene substrates, demonstrating the complementary synthetic utility of chiral padd

We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes (1 a: (S)-BINAP; 1 b: (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex (1 c: (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determi

Abstract Silver complexes with 5‐(4‐ (tert ‐butyl)‐1 H ‐imidazol‐1‐yl)‐imidazo[1,5‐ a ]pyridin‐3‐ylidene ligands were synthesized as metal‐imidazole acid‐base cooperative catalysts. Single crystal XRD analysis revealed that the silver atom was located in the vicinity of the imidazole ring and that cationic silver complexes formed dimers through coordination between the silver metal and the imidazole pendant. These cationic silver complexes served as catalysts for cyclization of alkyne‐tethered c

Abstract Nickel-catalyzed reductive homocoupling of aryl ethers has been achieved with Mg(anthracene)(thf)3 as a readily available low-cost reductant. DFT calculations provided a rationale for the specific efficiency of the diorganomagnesium-type two-electron reducing agent. The calculations show that the dianionic anthracene-9,10-diyl ligand reduces the two aryl ether substrates, resulting in the homocoupling reaction through supply of electrons to the Ni-Mg bimetallic system to form organomagn

Seven-exo-dig hydrocarboxylation of nonactivated internal alkynes with conformationally flexible linker chains was achieved with cooperative gold-zinc catalysts composed of an imidazo[1,5-a]pyridinylidene ligand including a bipyridine coordination site at the C5 position. A proximity effect of the gold and zinc sites was essential for their high catalytic activity, in which the internal alkyne activated by the cationic gold species was attacked by the carboxylic acid deprotonated by the basic zi

As a dimetal-binding rigid scaffold, 2-(pyridin-2-yl)imidazo[1,5-b]pyridazine-7-ylidene was introduced. The scaffold was first converted into a meridional Au,N,N-tridentate ligand through binding of a Au(I)Cl moiety at the carbene center. The Au(I) center and the N,N-chelating moiety were expected to function as metallophilic and 4e-σ-donative interaction sites, respectively, in the binding of the second metal center. In this manner, various trinuclear heterobimetallic complexes were synthesized

A Ni-catalyzed cross-coupling reaction between aryl fluorides and dialkyl phosphonates [HP(O)(OR)₂] (R = secondary alkyl groups) in the presence of potassium <i>tert</i>-butoxide as a base is reported. The reaction converted various aryl fluorides into the corresponding aryl phosphonates even when electron-donating substituents were present on the aromatic ring. The combined experimental and computational studies suggested Ni-K⁺ cooperative action of a Ni(0) complex chelate

Monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands stand as novel candidates for asymmetric hydrogenation of non-functionalized olefins. The sterically hindered chiral diphosphine ligand, (S)-DTBM-SEGPHOS, made it possible to isolate the rhodium(III) complex as a mononuclear complex which was confirmed by XRD analysis and DOSY NMR analysis. The novel monohydride rhodium(III) complex showed much higher enantioselectivity than classical dihydride rhodium systems on asym

Abstract Hydrocarboxylation of methyl 2‐octynoate, a chemical commercially available at a low cost, with N ‐protected amino acids was developed with a gold‐zinc cooperative catalyst constructed with a 5‐[(2,2′‐bipyridin)‐5‐yl]imidazo[1,5‐ a ]pyridin‐3‐ylidene to prepare α‐methoxycarbonyl enol esters as acylating reagents. The α‐methoxycarbonyl enol esters were isolable through silica‐gel column chromatography and storable without precautions regarding moisture. Acylation of free amines with the