Kouki Matsubara

A new aspect of nickel-catalyzed Grignard cross-coupling reactions: selective synthesis, structure, and catalytic behavior of a T-shape three-coordinate nickel(I) chloride bearing a bulky NHC ligand

Novel T-shape three-coordinate nickel(I) chlorides bearing an N-heterocyclic carbene ligand, NiCl(IPr)(2) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene), were isolated by a reaction of Ni(0)(NHC)(2) with aryl chlorides. This Ni(I) complex was shown to act as a catalyst in a cross-coupling reaction of aryl halides with phenylmagnesium chloride.

Chemistry of coordinatively unsaturated organoruthenium amidinates as entry to homogeneous catalysis

The chemistry of coordinatively unsaturated organoruthenium complexes is reviewed in this article. In particular, the subject is focused on neutral and cationic organoruthenium amidinates, which formally have 16 valence electrons and show signs of coordinative unsaturation. The ruthenium amidinates, ( 5 -C5Me5)Ru(-amidinate) (1), and their isoelectronic analogues, [( 6 -arene)Ru(-amidinate)] + (2), are synthesized and characterized; a possible stabilizing factor of the unsaturated metal center is weak coordination of -electrons in the amidinates ligands. Reactions of various two-electron donor ligands with 1 or 2 reveal the strong -donor property of 1 and Lewis acid nature of 2. One or two-electron redox processes of 1 in the reactions with organic halides are studied by isolation of the corresponding Ru(III) and Ru(IV) products; the results lead to their catalysis for the Tsuji–Trost reaction and the intramolecular Kharasch reaction. The treatment of 2 with trimethylsilyldiazomethane results in the formation of cationic amidinato-carbene complexes, which involve unusual reversible metal-to-carbon silyl group migration.

Copper-catalyzed facile carbon-carbon bond forming reactions at the α- position of α,α,γ-trichlorinated γ-lactams

Abstract Treatment of α,α,γ-trichlorinated γ-lactams with a catalytic amount of CuCl(bipyridine) complex resulted in facile activation of their carbon-chlorine bond at the α-position. Addition of the carbon moiety and the chlorine atom to olefins furnished the carbon-carbon bond forming reaction at the α-position of the carbonyl group. In certain trichlorinated γ-lactams including a carbon-carbon double bond at an appropriate position, intramolecular addition reactions took place to give bicyclic lactams. Sequential reactions consisting of the cyclization of N-allyl trichloroacetamides followed by the inter- or intramolecular carbon-carbon bond forming reactions at the α-position of the lactams were also achieved. Efficiency of the catalyst and reaction rate was dependent on the protecting group of the nitrogen atom of the γ-lactams; N-tosyl derivatives gave better results than the corresponding N-benzyl homologues. The molecular structure of the representative products revealed the stereochemical outcome of the reactions.

Structure‐activity relationship of indolicidin, a Trp‐rich antibacterial peptide

A series of Trp and Arg analogs of antibacterial indolicidin (Ind) was synthesized and the antimicrobial and hemolytic activities were investigated. [L9]Ind, [L11]Ind, [K8,L9]Ind and [K6, 8,L9]Ind showed desirable characteristics, exhibiting negligible hemolytic activity while keeping strong antibacterial activity. The results indicated that the Trp residue at position 11 essentially contributes to both activities and one can not be exchanged for the other, whereas the Trp residues at positions 4 and 9 play important roles in antimicrobial and hemolytic activities, respectively. The Trp residues at positions 6 and 8 play no important roles in biological activities. We then found that the retro analog of Ind showed higher antibacterial activity than Ind against both Gram‐positive and Gram‐negative bacteria but remarkably lower hemolytic activity than that of Ind. Copyright

Organoruthenium(ii) and (iii) amidinates, (η5-C5Me5)Ru(η-amidinate) and (η5-C5Me5)RuCl(η-amidinate), as unique redox catalysts for the intramolecular Kharasch reactions: Facile access to a pyrrolizidine alkaloid skeleton under mild conditionsElectronic supplementary information (ESI) available: representative experimental details and crystallographic data. See http://www.rsc.org/suppdata/cc/b2/b209369c/

A novel organoruthenium(III) amidinate, (eta5-C5Me5)RuCl(eta-iPrN=C(Me)NiPr) (2), has been prepared by oxidation of organoruthenium amidinate, (eta5-C5Me5)Ru(eta-iPrN=C-(Me)NiPr) (1), by organic chlorides; both 1 and 2 are found to be good catalysts for atom-transfer cyclization of N-allyltrichloroacetamides which are useful for successful preparation of a pyrrolizidine alkaloid skeleton under mild conditions.

C−F Bond-Cleavage Reactions of Fluoroalkanes with Magnesium Reagents and without Metal Catalysts

An unexpected C-F bond-cleavage reaction of unactivated fluoroalkanes with the well-known Grignard reagents without using metal catalysts has been discovered. For example, a reaction between 1-fluorooctane and phenyl magnesium chloride gave n-octylbenzene in moderate yield. This coupling reaction via the activation of an unactivated alkyl carbon-fluorine bond proceeds with phenylmagnesium chloride, whereas methylmagnesium chloride did not give the C-C cross-coupling product but rather a halogen exchange product.

Alkane activation on a multimetallic site

Trinuclear polyhydrido complex of ruthenium effectively activates alkanes to cleave C-H bonds in a selective manner due to cooperative action of the metal centers. The reaction of (Cp´Ru) 3 (m-H) 3 (m3 -H) 2 (1) (Cp´ = h5-C5Me5) with n-alkane at 170 °C leads to the formation of a trinuclear closo-ruthenacyclopentadiene complex as a result of a successive cleavage of six C-H bonds. Introduction of a m3-sulfido ligand into the Ru3 core of the trirutheniumpolyhydrido cluster significantly modifies the regioselectivity of the alkane C-H activation. Heating of a solution of (Cp´Ru) 3 (m3-S) (m-H) 3 (4) in alkane exclusively gives a trinuclear m3-alkylidyne complex via a selective C-H bond cleavage at the less-hindered terminus of alkane molecule.

Silane-induced ring-opening polymerization of 1,1,3,3-tetramethyl-2-oxa-1,3-disilacyclopentane catalyzed by a triruthenium cluster

Abstract The silane-induced ring-opening polymerization of a cyclic siloxane, 1,1,3,3-tetramethyl-2-oxa-1,3-disilacyclopentane (2), is catalyzed by a ruthenium cluster, (μ3,η2:η3:η5-acenapthylene)Ru3(CO)7 (1), to give poly(tetramethylsilethylenesiloxane) with Mn=6300–780,000 and Mw/Mn=1.5–3.0. The molecular weight of the polymer can be controlled by changing the concentration of the monomer solution. Addition of acetone results in formation of the polymer with Mn=4400, spectroscopic analysis of which reveals existence of a siloxy and an isopropoxy moieties at the end group.

Triarylation of η6-dihydronaphthalene-Cr(CO)3 complexes

With ease, η6-dihydronaphthalene tricarbonylchromium(0) complexes undergo a triple arylation with concomitant ring closure, when submitted to Heck reactions under ‘Jeffery conditions’.

Dinuclear Nickel(I) and Palladium(I) Complexes for Highly Active Transformations of Organic Compounds

In typical catalytic organic transformations, transition metals in catalytically active complexes are present in their most stable valence states, such as palladium(0) and (II). However, some dimeric monovalent metal complexes can be stabilized by auxiliary ligands to form diamagnetic compounds with metal–metal bonding interactions. These diamagnetic compounds can act as catalysts while retaining their dimeric forms, split homolytically or heterolytically into monomeric forms, which usually have high activity, or in contrast, become completely deactivated as catalysts. Recently, many studies using group 10 metal complexes containing nickel and palladium have demonstrated that under specific conditions, the active forms of these catalyst precursors are not mononuclear zerovalent complexes, but instead dinuclear monovalent metal complexes. In this mini-review, we have surveyed the preparation, reactivity, and the catalytic processes of dinuclear nickel(I) and palladium(I) complexes, focusing on mechanistic insights into the precatalyst activation systems and the structure and behavior of nickel and palladium intermediates.