Search

The μ3-η2-iminoacyl-μ3-hexylidyne complex, [(Cp*Ru)3(μ3-CC5H11)(μ3-η2-HN═CMe)(μ-H)] (2a) (Cp* = η5-C5Me5), was prepared by the reaction of the μ3-η2:η2(⊥)-hexyne complex, [{Cp*Ru(μ-H)}3(μ3-η2:η2-nB...

Studies on the deactivation mechanism of the reaction of N,N-dialkylamides with TMDS catalyzed by Vaska’s complex, IrCl(CO)(PPh3)2 (1a), triggered the discovery of highly active Ir-PPh3 catalysts: photochemically activated 1a and thermally activated IrCl(PPh3)3 (8). Both catalysts showed excellent activity toward the selective conversion of a variety of N,N-dialkyl-, N-alkyl-N-aryl-, and N,N-diarylamides to the corresponding enamines with low catalyst loadings. The 14-electron species “ClIr(PPh3)2”, which is stabilized by solvents or reactants in the actual catalytic reactions, could be involved in the catalysis, which produces “HIr(PPh3)2” and “SiIr(PPh3)2” (Si = Me2HSiOMe2Si−) species in the catalytic cycle. An in situ generation method for the “ClIrL2” species was established by simply mixing [IrCl(η4-COD)]2 with PPh3 or other phosphorus ligands, which realized the facile large-scale syntheses of enamines.

A triruthenium complex containing μ3-η2(||)-benzyne and μ3-sulfido ligands, [(Cp*Ru)3(μ3-S){μ3-η2(||)-C6H4}(μ-H)] (2), was synthesized by the reaction of [(Cp*Ru)3(μ3-S)(μ-H)3] (1) with benzene. Although 2 was stable toward oxygen and water, two-electron oxidation of 2 with a Ag(I) salt in the presence of water afforded the dicationic μ-hydroxo complex [(Cp*Ru)3(μ3-S){μ3-η2(||)-C6H4}(μ-OH)]2+ (3). Treatment of 3 with amine resulted in the deprotonation of the μ-hydroxo ligand, and an unsaturated monocationic complex, [(Cp*Ru)3(μ3-S)(μ3-OC6H4-κO,κC)]+ (4), which possesses a μ3-cyclohexadienonediyl ligand, was formed via reductive C–O bond formation between the μ3-benzyne and transient μ-oxo ligands. Phenol was extruded from the Ru3 cluster upon the hydrogenation of 4 via the formation of a μ3-phenoxo complex, [(Cp*Ru)3(μ3-S){μ3-OPh}(μ-H)]+ (5). The cyclic voltammogram of 2 shows two reversible one-electron redox waves, and a dicationic μ3-benzyne complex, [(Cp*Ru)3(μ3-S){μ3-η2:η2(⊥)-C6H4}(μ-H)]2+(8), was s...

Palladium-catalyzed reactions of dodecamethylcyclohexasilane [(SiMe2)6] (1) with alkynes led to efficient preparation of 1,1,4,4-tetramethyl-1,4-disilacyclohexadienes (3). The reactions were best catalyzed by Pd(0) species generated from Pd2(dba)3·CHCl3 and 1-isocyanoadamantane (AdNC). Terminal and internal alkynes bearing aryl and alkyl substituents could be used as substrates, and the reaction allowed gram-scale preparation of 3. A dimethylsilylene (Me2Si:) species, generated by activation of Si–Si bonds in 1 by Pd(0) species, was involved in the reaction mechanism. The DFT calculations suggest that oxidative addition of Si–Si bonds in 1 to Pd(CNAd)2 species is followed by extrusion of a Me2Si═Pd(CNAd) intermediate. Reaction of the resulting palladium-coordinated silylene with an alkyne forms a silacyclopropene, which dimerizes to give 3. The extrusion is accompanied by ring contraction of 1 to generate (SiMe2)5, which also contributes to formation of 3 and (SiMe2)4 by the Pd(0)-catalyzed reaction with ...

High functional group compatibility of iridium-catalyzed synthesis of enamines from amides and 1,1,3,3-tetramethyldisiloxane (TMDS) realized facile access of a series of donor (D)-π-acceptor (A)-conjugated enamines, in which enamine behaves as a donor functional group. The amide precursors containing reducible functional groups, such as halogen, carbonyl, and nitro groups, underwent reaction with TMDS to give the corresponding enamines in high yields. In most cases, chemoselective hydrosilane reduction of the amide group occurred while other reducible groups remained intact. Absorption and emission properties including solvatochromic behavior for the resulting D-π-A-conjugated enamines were determined using UV-visible and fluorescent spectra, which provided an understanding of the donor properties of the CH═CHNPh

Iridium-catalyzed hydrosilylation of amides with 1,1,3,3-tetramethyldisiloxane (TMDS) allows access to silylhemiaminals, which are often spontaneously converted to aldenamines. Iridium(I) phosphine species generated from IrCl(CO)(PPh3)2, IrCl(PPh3)3, or a mixture of [IrCl(COD)]2 and phosphorous ligands showed high catalytic activity for this reaction protocol, which demonstrated remarkable compatibility toward other reducible functional groups such as ketone and ester groups. This reaction enables the synthesis of π-conjugate enamines having hole-transport properties by appropriate selection of the iridium catalyst. Easy access to silyl hemiaminals and enamined stimulated other research groups to discover new reductive C–C bond-forming reactions to transform amides to amine derivatives, which can be applied to the synthesis of complex alkaloid molecules.

The appropriate design of a ligand (L) in IrCl(CO)(L)2 (4) realized the efficient synthesis of π-conjugated enamines possessing hole-transport properties. The iridium complex with electron-withdrawing phosphorus ligands catalyzed the hydrosilylation of amides to the corresponding silylhemiaminals, which were transformed to the enamines by heat or by treatment with acids. High catalytic efficiency (TON > 10,000) was achieved, which made it possible for the residual iridium in the enamine product to be below 20 ppb.

The mechanisms associated with the hydrogenation of alkenes catalyzed by the iron complex Fe(cis-CO)2{o-(SiMe2)2C6H4}2(H)2 (1) were investigated by DFT calculations. The complex 1 has a structure in which the iron center is bonded to four silicon atoms and two hydrides. Secondary Si···H···Si interactions were also observed. The exchange of a 1,2-bis(dimethylsilyl)benzene ligand with ethylene and hydrogen gives a disilaferracycle bearing η2-(CH2═CH2) and η2-H2 ligands. The catalytic cycle initiated from the disilaferracycle involves cleavage of a H–H linkage assisted by an Fe–Si bond to form Fe–H and η1-(H–Si) moieties (step 1), hydrogen migration from the Fe–H group to the η2-(CH2═CH2) ligand which accomplishes the insertion of ethylene into the Fe–H bond (step 2), and reaction of the resulting β-agostic ethyl moiety with the η2-(H–Si) group to form ethane on the iron atom (step 3). The octahedral geometry of 1 as well as the presence of π-acidic CO ligands and Fe–Si σ-bonds contributes to all of the cata...

A triruthenium complex containing μ3-η2(∥)-ethyne and μ3-methylidyne ligands, (CpRu)3{μ3-η2(∥)-HC≡CH}(μ3-CH)(μ-H)2 (2a), was synthesized via the treatment of {Cp*Ru(μ-H)}3(μ3-H)2 (3) (Cp* = η5-C5Me5) with propene. In the low-temperature region, VT 1H NMR spectra showed that complex 2a is in equilibrium with a nonclassical μ3-vinyl complex, (CpRu)3(μ3-η2:η2-HC═CH2)(μ3-CH)(μ-H) (5a), which features an interaction between one of the β-vinyl protons and a Ru center. The presence of the unusual 3c-2e interaction of the β-C–H bond of the vinyl group is strongly supported by the small JC–H value (98 Hz) found for the β-carbon as well as the small JH–H value for the α-vinyl proton. Treatment of the equilibrated mixture of phenyl-substituted complexes (CpRu)3{μ3-η2(∥)-HC≡CPh}(μ3-CH)(μ-H)2 (2b) and (CpRu)3(μ3-η2:η2-HC═CHPh)(μ3-CH)(μ-H) (5b) with tBuNC afforded a μ-styryl complex, (CpRu)3(μ-η2-HC═CHPh)(μ3-CH)(μ-tBuNC)(μ-H) (6), while analogous treatment of 2a and 5a resulted in the formation of μ3-dimetalloallyl com...