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Catalytic hydrosilylations of various N-heterocycles mediated by silylium ion and electrophilic borane catalysts are reported. The reactions proceed via intermediate silylquinolinium ions that give...

Reactions of carbene complex [Cp(IPr)Ru(pyr)2][BF4] (6, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with excess acetonitrile and LiCl in THF afford complexes [Cp(IPr)Ru(NCCH3)2][PF6] (7) and Cp(IPr)RuCl (8), respectively. Complex 8 was characterized by NMR and X-ray diffraction analysis. Addition of hydrosilanes to 8 results in silane σ-complexes Cp(IPr)Ru(η2-HSiR3)Cl (4), which were characterized by NMR and X-ray studies of Cp(IPr)Ru(η2-HSiMeCl2)Cl (4b) and Cp(IPr)Ru(η2-H3SiPh)Cl (4d). The hydrogen–silicon coupling constants of complexes 4 show an unusual trend in that the J(H–Si) values increase from the less-chlorinated complex Cp(IPr)Ru(η2-HSiMe2Cl)Cl (4c) to the trichloro derivative Cp(IPr)Ru(η2-HSiCl3)Cl (4a). Reaction of Cp(IPr)RuCl (8) with two equivalents of HSiCl3 gave the ruthenate complex [IPrH]+[CpRuCl(H) (SiCl3)2]−, characterized by NMR and X-ray study. Addition of hydrosilanes to the cationic complex [Cp(IPr)Ru(NCCH3)2][BArF4] (9) furnished very unstable cationic silane σ-comple...

In the presence of KOBut, N-heterocyclic carbene-supported half-sandwich complex [Cp(IPr)Ru(pyr)2][PF6] (3) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) catalyzes transfer hydrogenation (TH) of nitriles, activated N-heterocycles, olefins, and conjugated olefins in isopropanol at the catalyst loading of 0.5%. The TH of nitriles leads to imines, produced as a result of coupling of the initially formed amines with acetone (produced from isopropanol), and showed good chemoselectivity. Reduction of N-heterocycles occurs for activated polycyclic substrates (e.g., quinoline) and takes place exclusively in the heterocycle. The TH also works well for linear and cyclic olefins but fails for trisubstituted substrates. However, the C═C bond of α,β-unsaturated esters, amides, and acids is easily reduced even for trisubstituted species, such as isovaleriates. Mechanistic studies suggest that the active species in these catalytic reactions is the trihydride Cp(IPr)RuH3 (5), which can catalyze these reactions...

Oxidative addition of very robust C–F and C–O bonds has been accomplished in reactions of the aluminum(I) compound NacNacAl (1, NacNac = [ArNC(Me)CHC(Me)NAr]− and Ar = 2,6-Pri2C6H3) with fluoroarenes, fluoroalkanes, and ethers. Similar to the transition metals, the ease of aryl C–F oxidative addition decreases as the degree of fluorination diminishes on the aromatic substrate. As well, kinetic studies on the addition of 1,2,3,4-tetrafluorobenzene to compound 1 revealed a second-order reaction characterized by a very negative entropy of activation (ΔS⧧ = −113.6(3) J/K·mol), consistent with a transition metal-like oxidative addition process.

Interaction of copper chlorides with radicals is a key step of single electron transfer reactions and is responsible for high selectivity of copper-catalyzed radical processes. In the present article reactions of binuclear copper(II) chlorides with methyl radical were studied in the scope of density functional theory. The results of quantum-chemical calculations of potential energy surfaces allow proposing that there are at least two reasons for the lower activity of binuclear complexes Cu2Cl62– in comparison with CuCl42–. First, the radicals react with binuclear chlorocuprates via an atom transfer mechanism through an activation barrier, in contrast to the barrierless character of such reactions with partition of CuCl42–. Second, only in the systems with binuclear copper chloro complexes may an alternative path of spontaneous formation of chloroorganocuprates be realized. These intermediates may be dormant species in radical reactions.

The ruthenium complex [Cp(iPr3P)Ru(NCCH3)2]+ (1) catalyzes the regioselective hydrosilylation of pyridines to 1,4-dihydropyridines. Substitution in the 3- and 5-positions is tolerated, whereas pyridines with substituents in the 2-, 4-, and 6-positions are not reduced. Reduction of functionalized pyridines having keto and ester substituents results in a mixture of products. N-Silyl-1,4-dihydropyridine reacts with ketones and aldehydes to give products of N–Si addition across the C═O bond. Hydrosilylation of pyridine in acetone results quantitatively in the addition product PhMe2SiO–CMe2–NC5H6, which decomposes in hexane to give the parent dihydropyridine HNC5H6. The phenanthroline complex [Cp(phen)Ru(NCCH3)2]+ (10) catalyzes regioselective 1,4-reduction of phenanthroline by a 3–4-fold excess of silane/water or silane/alcohol mixtures. The Cp* analogue [Cp*(phen)Ru(NCCH3)2]+ (9) catalyzes 1,4-regioselective monohydrosilylation of phenanthroline, quinoline, acridine, and 1,3,5-triazine and the 1,2-reduction ...

A novel type of reaction of lanthanide hydrido complexes with C60 is described. The hydride anion of complex [{(Me3Si)2NC(NCy)2}2Lu(μ-H)]2 reduces C60 (1:2 molar ratio, toluene, 20 °C) to the radical anion, and the reaction results in the formation of ionic complex [{(Me3Si)2NC(NCy)2}2Lu(Et2O)+](C60−•). At low temperature (below ∼120 K) reversible dimerization of radical anions C60−• occurs and affords the complex [{(Me3Si)2NC(NCy)2}2Lu(Et2O)+]2[(C60−)2]·2(C7H8)·(Et2O) with the diamagnetic σ-bonded (C60−)2 dianion.

Reactions of a new imido phosphido complex, Cp2Nb(═NBut)(PPh2) (1), with olefin complexes of rhodium afford two types of compounds. With [(μ-Cl)Rh(C2H4)2]2, an imido/phosphido-bridged complex, Cp(Cl)Nb(μ-NBut)(μ-PPh2)RhCp (2), characterized by NMR and X-ray diffraction, was prepared. Formation of 2 represents a rare example of a Cp/Cl exchange reaction in organometallic chemistry. When 1 reacts with [(μ-Cl)Rh(COD)]2, the target phosphido-bridged bimetallic complex Cp2Nb(═NBut)(μ-PPh2)Rh(Cl)(COD) (4) is formed. The structure of this product was established by NMR and an X-ray diffraction study. Both 2 and 4 are catalyst precursors for hydrosilylation of benzaldehyde and acetophenone. The activity of the neutral complex 4 exceeds that of the cation [Cp2Nb(NBut)(PPh2)Rh(COD)]+ derived from 4 by chloride anion abstraction.

Intramolecular sp3-hybridized C−H activation of novel yttrium alkyl and hydrido complexes supported by bulky aminopyridinato ligands derived from deprotonated 2,6-(diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]amine (Ap‘-H) is reported. Reaction of YCl3 with a 2-fold molar excess of Ap‘K in THF afforded complex [Ap‘2YCl(thf)] (1). Alkylation of 1 with an equimolar amount of LiCH2SiMe3 in hexane allowed isolation of the alkylyttrium derivative [Ap‘2YCH2SiMe3(thf)] (2) in 65% yield. Unexpectedly treatment of complex 2 with PhSiH3 (toluene, 20 °C) afforded the product of intramolecular sp3-hybridized C−H bond activation, Ap‘(Ap‘-H)Y(THF) (3). Most likely a hydrid species is formed in the course of this reaction, which undergoes rapid C−H activation since 3 is formed from 2 directly about 500 times slower than in the presence of 1 equiv of PhSiH3. Molecular structures of complexes 2 and 3 have been confirmed by X-ray crystal structure analysis.

Four families of silyl hydride complexes of rhodium in the formal oxidation state +5 were investigated by means of DFT calculations, supplemented by the calculation of Mayer bond indices and Si−H coupling constants. In each case some degree of interligand Si−H interaction has been found. In the compounds CpRh(SiMe3)2H2 (1), CpRh(SiMe3)3H (2), CpRh(SiMe3)2(SiEt3)H (3), and [Cp(Me3P)Rh(SiMe3)2H]+ (4) the hydride(s) interact(s) with both silyl ligands. Relaxed potential energy scans indicate that the potential energy surface is extremely flat. It takes only 1 kcal·mol-1 to compress the Si−H bond from 2.3 A to 2.0 A in 1, and 2 kcal·mol-1 to compress the Si−H distance from 1.990 A to 1.70 A in complex 2. ONIOM calculations of the compound CpRh(SiMe3)3H and optimization of the lowest energy conformers of complex CpRh(SiMe3)2(SiEt3)H show that their geometries are largely determined by steric effects. Increasing steric hindrance promotes Si−H interactions because they result in longer Rh−Si bond lengths, leadin...

The reactions of a series of half-sandwich trihydrides of ruthenium, Cp*(R3P)Ru(H)3 (R3P = Pri3P, Pri2MeP, PriMe2P, PhMe2P), with a family of chlorosilanes (ClSiHMe2, Cl2SiHMe, Cl3SiH) have been st...

The Cp ring is found to exert a primarily electronic effect on the strength of Si−H interaction in silane σ-complexes Cp(Pri3P)RuCl(η2-HSiClR2). Complexation of chlorosilanes HSiClR2 is supported by an additional RuCl···SiCl interaction.

The reactions of the bis(alkyl) complexes [Ap*Ln(CH2SiMe3)2(thf)] (Ln = Y, Lu) with both PhSiH3 and H2 result in selective assembly of the novel trinuclear rare-earth alkyl hydrido clusters [(Ap*Ln...

The first asymmetric bis(silyl) niobocene hydrides Cp2Nb(SiHMe2)H(SiXMe2) (2: X = F (a), Cl (b), Br (c), I (d)), having interligand interactions Nb−H···Si−X, were prepared by selective halogenation of the Si−H bond in Cp2Nb(SiHMe2)2H. X-ray studies of 2b,c and a combined X-ray/neutron diffraction study of 2b establish a slightly stronger interaction of the niobium-bound hydride with the halosilyl ligand.

Ph2PCl easily inserts into the Ta-H bond of Cp2TaH3 affording an ionic complex [Cp2TaH2(HPPh2)]Cl (4). This species was deprotonated to give the first phosphido-substituted tantalocene complex Cp2TaH2PPh2 (5), which was characterized by NMR spectroscopy and X-ray crystallography. Thermal decomposition of 5 as well as its reaction with HPPh2 was studied. © 1995 American Chemical Society.

Reactions of niobocene hydrides with halogermanes present a new effective method for the synthesis of mono(germyl)- and bis(germyl)niobocenes. Chlorodemethylation of Cp2NbH(GeMe3)2 under the action...

Reactions of the imido complex Cp(ArN)Ta(PMe 3) 2 (1, Ar = 2,6-diisopropylphenyl) with silanes afford the silyl hydrides Cp(ArN)Ta(PMe 3)(H)(SiR nCl 3-n) (2b-e) and Cp(ArN)Ta(PMe 3)(H)(SiPhMeH) (2a) as the first kinetic products. However, the hydride compounds Cp(ArN)Ta(PMe 3)(H)(SiR nCl 3-n) are metastable and, first, rearrange in the presence of phosphine to the chlorides Cp(ArN)Ta(PMe 3)(Cl)(SiHR nCl 2-n) (5) and then decompose to Cp(ArN)Ta(PMe 3)(Cl)(H) (4) and eventually to Cp(ArN)Ta(PMe 3)Cl 2 (3). Complexes with a smaller Ar' substituent at nitrogen (Ar′ = 2,6-dimethylphenyl) react faster, as do more Lewis acidic silanes. The occurrence of interligand hypervalent interactions in the tantalum complexes Cp(ArN)Ta(PMe 3)(H)(SiR nCl 3-n) has been revealed by X-ray structure analysis, DFT calculations, and the experimental determination of the sign of the coupling constant J(Si-H). The J(Si-H) was found to be negative for Cp(ArN)Ta(PMe 3)(H)(SiMe nCl 3-n) (J(Si-H) = -40 Hz for n = 1; J(Si-H) = -50 Hz for n = 0), indicative of the presence of Si-H bonding, but positive for Cp(ArN)Ta(PMe 3)(H)(SiMeHPh) (J(Si-H) = +14 Hz), suggesting the absence of direct Si-H interactions. A DFT study of the mechanism of silane coupling with the model imido complex Cp(MeN)Ta(PMe 3) 2 established the feasibility of the direct addition of silanes HSiMe nCl 3-n (n = 1-3) to the imido group to give the adduct Cp(MeN{→SiR 3-H})Ta(PMe 3) 2, as previously found in the related niobium chemistry. © 2008 American Chemical Society.

29Si NMR, photoelectron spectroscopy (PES), and DFT calculations provided apparently contradictory descriptions of the bonding situation in Cp(CO)2Mn(HSiCl3), because measurement of a large J(Si-H)...