Hydrodehalogenation of alkyl halides catalyzed by a trichloroniobium complex with a redox active α-diimine ligand.

A high-valent d niobium(v) complex, (α-diimine)NbCl (1), bearing a dianionic redox-active α-diimine ligand served as a catalyst for a hydrodehalogenation reaction of alkyl halides in the presence of PhSiH. During the catalytic reaction, the redox-active α-diimine ligand allowed the complex to reversibly release and accept one-electron through switching its coordination mode between a dianionic folded form and a monoanionic planar one.

Nickel-catalyzed cyanation of aryl halides and triflates using acetonitrile C-CN bond cleavage assisted by 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine.

We developed a non-toxic cyanation reaction of various aryl halides and triflates in acetonitrile using a catalyst system of [Ni(MeCN)](BF), 1,10-phenanthroline, and 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine (-Me-DHP). -Me-DHP was found to function as a reductant for generating nickel(0) species and a silylation reagent to achieve the catalytic cyanation C-CN bond cleavage.

Metathesis cleavage of an N[double bond, length as m-dash]N bond in benzo[c]cinnolines and azobenzenes by triply-bonded ditungsten complexes.

A metathesis reaction of a W[triple bond, length as m-dash]W bond and an N[double bond, length as m-dash]N bond was observed by reacting a W-W triply-bonded W(iii)2 complex, (tBuO)3W[triple bond, length as m-dash]W(OtBu)3 (1), with benzo[c]cinnoline derivatives to form biphenyl-linked dinuclear (imido)tungsten complexes 2-4. When azobenzene was used as the substrate, a trans to cis isomerization induced by blue-LED light was essential prior to the metathesis cleavage of the N[double bond, length as m-dash]N bond by the W[triple bond, length as m-dash]W bond of (Me2N)2(TfO)W[triple bond, length as m-dash]W(OTf)(NMe2)2 (6), affording the corresponding imido-bridged dinuclear tungsten complexes 7-9.

Tantallacyclopentadiene as a unique metal-containing diene ligand coordinated to nickel for preparing tantalum-nickel heterobimetallic complexes.

A mononuclear tantallacyclopentadiene complex, TaCl(CHtBu) (3), serves as a unique ligand to nickel: the addition of Ni(COD) to 3 selectively afforded heterobimetallic Ta-Ni complex 4. The cyclooctadiene ligand bound to the nickel center in complex 4 was readily substituted by monodentate and bidentate phosphine ligands, such as dimethylphenylphosphine, 1,2-bis(diphenylphosphino)ethane, and 1,2-bis(diethylphosphino)ethane, to give the corresponding phosphine complexes 5, 6a, and 6b. We also examined a ligand substitution reaction with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) to produce the corresponding Ta-Ni complex 7.

Mechanistic understanding of alkyne cyclotrimerization on mononuclear and dinuclear scaffolds: [4 + 2] cycloaddition of the third alkyne onto metallacyclopentadienes and dimetallacyclopentadienes.

Cyclotrimerization of alkynes catalyzed by transition metal complexes is a straightforward synthetic method for constructing a benzene skeleton in organic synthesis. Not only mononuclear complexes, but also multinuclear complexes act as catalysts for alkyne cyclotrimerization, and their reaction mechanisms have been intensively investigated toward developing highly efficient and regio- and chemo-selective catalysts. In this review, we summarize stoichiometric and catalytic alkyne coupling reactions on mononuclear and dinuclear scaffolds in relation to the reaction mechanism of alkyne cyclotrimerization, including our recent mechanistic approaches using dinuclear tantalum motifs.

Cerium-Complex-Catalyzed Oxidation of Arylmethanols under Atmospheric Pressure of Dioxygen and Its Mechanism through a Side-On μ-Peroxo Dicerium(IV) Complex.

A new Ce(IV) complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)2-2-O)2}(NO3)2] (1), bearing a dianionic pentadentate ligand with an N3O2 donor set, has been prepared by treating (NH4)2Ce(NO3)6 with the sodium salt of ligand L1. Complex 1 in the presence of TEMPO and 4 Å molecular sieves (MS4 A) has been found to serve as a catalyst for the oxidation of arylmethanols using dioxygen as an oxidant. We propose an oxidation mechanism based on the isolation and reactivity study of a trivalent cerium complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)2-2-O)2}(NO3)(THF)] (2), its side-on μ-O2 adduct [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)2-2-O)2}(NO3)]2(μ-η(2):η(2)-O2) (3), and the hydroxo-bridged Ce(IV) complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)2-2-O)2}(NO3)]2(μ-OH)2 (4) as key intermediates during the catalytic cycle.

2,2'-Bipyridyl formation from 2-arylpyridines through bimetallic diyttrium intermediate.

An alkylyttrium complex supported by an ,'-bis(2,6-diisopropylphenyl)ethylenediamido ligand, (ArNCHCHNAr)Y(CHSiMe)(THF) (, Ar = 2,6- PrCH), activated an -phenyl C-H bond of 2-phenylpyridine () to form a (2-pyridylphenyl)yttrium complex () containing a five-membered metallacycle. Subsequently, a unique C(sp)-C(sp) coupling of 2-phenylpyridine proceeded through a bimetallic yttrium intermediate, derived from an intramolecular shift of the yttrium center to an -position of the pyridine ring in , to yield a bimetallic yttrium complex () bridged by two-electron reduced 6,6'-diphenyl-2,2'-bipyridyl. Aryl substituents at the -position of the pyridine ring were key in order to destabilize the μ,κ-(C,N)-pyridyldiyttrium intermediate prior to the C(sp)-C(sp) bond formation.

Cerium(IV) Hexanuclear Clusters from Cerium(III) Precursors: Molecular Models for Oxidative Growth of Ceria Nanoparticles.

Reactions of cerium(III) nitrate, Ce(NO3 )3 ⋅6 H2 O, with different carboxylic acids, such as pivalic acid, benzoic acid, and 4-methoxybenzoic acid, in the presence of a tridentate N,N,N-donor ligand, diethylenetriamine (L(1) ), under aerobic conditions yielded the corresponding cerium hexamers Ce6 O8 (O2 CtBu)8 (L(1) )4 (1), Ce6 O8 (O2 CC6 H5 )8 (L(1) )4 (2), and Ce6 O8 (O2 CC6 H4 -4-OCH3 )8 (L(1) )4 (3). Hexamers 1, 2, and 3 contain the same octahedral Ce(IV) 6 O8 core, in which all interstitial oxygen atoms are connected by μ3 -oxo bridging ligands. In contrast, treatment of the Ce(IV) precursor (NH4 )2 Ce(NO3 )6 (CAN) with pivalic acid and the ligand L(1) under the same conditions afforded Ce6 O4 (OH)4 (O2 CtBu)12 (L(1) )2 (4), exhibiting a deformed octahedral Ce(IV) 6 O4 (OH)4 core containing μ3 -oxo and μ3 -hydroxo moieties in defined positions.

Mixed-ligand complexes of paddlewheel dinuclear molybdenum as hydrodehalogenation catalysts for polyhaloalkanes.

We developed a hydrodehalogenation reaction of polyhaloalkanes catalyzed by paddlewheel dimolybdenum complexes in combination with 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (MBTCD) as a non-toxic H-atom source as well as a salt-free reductant. A mixed-ligated dimolybdenum complex Mo(OAc)[CH(NAr)] (, Ar = 4-MeOCH) having two acetates and two amidinates exhibited high catalytic activity in the presence of BuNCl, in which [ BuN][Mo{CH(NAr)}Cl] (), derived by treating with ClSiMe and BuNCl, was generated as a catalytically-active species in the hydrodehalogenation. All reaction processes, oxidation and reduction of the dimolybdenum complex, were clarified by control experiments, and the oxidized product, [ BuN][Mo{CH(NAr)}Cl] (), was characterized by EPR and X-ray diffraction studies.

Organomagnesium-catalyzed isomerization of terminal alkynes to allenes and internal alkynes.

Organomagnesium complexes 2 were synthesized from N,N-dialkylamineimine ligands 1 and dibenzylmagnesium by benzylation of the imine moiety. 3-Aryl-1-propynes reacted with 2 to form the corresponding tetraalkynyl complexes, which acted as catalysts for the transformation of these terminal alkynes into allenes and further to internal alkynes under mild conditions. To the best of our knowledge, this example is the first of an organomagnesium-catalyzed isomerization of alkynes.