A DFT Comparison of C-C Reductive Coupling from Terminal Cyanido and Cyaphido Complexes of Nickel.

The density functional theory study of the thermal C-C reductive coupling from terminal cyanido and hypothetical cyaphido complexes of [Ni(dmpe)] (dmpe = 1,2-bis(dimethylphosphino)ethane) revealed the key reaction intermediate in the reductive C-CP coupling being a σ-CC complex unlike an η-aryl complex in the Ni C-CN system, as already observed in our previous studies. The reaction in THF is endothermic by 4.9 kcal/mol for cyanido with a 32.

-Fluoro or Effect? Oxidative Addition of Zerovalent Nickel into the C-CN Bond of Substituted Benzonitriles.

A recent study of the oxidative addition of zerovalent Ni to the C-CN bond of F-substituted benzonitriles showed significantly increased stabilization of the C-CN oxidative addition products with -F groups (-6.6 kcal/mol per -F) compared to -F groups (-1.8 kcal/mol per -F).

Enantioselective palladium(0)-catalyzed Nazarov-type cyclization.

A Pd(0)-catalyzed asymmetric Nazarov-type cyclization is described. The optimized ligand for the reaction incorporates a weakly coordinating pyridine ring into a TADDOL-derived phosphoramidite (TADDOL=α,α,α,α-tetraaryl-1,3-dioxolane-4,5-dimethanol). The reaction leads to the formation of cyclopentenones as single diastereoisomers that incorporate two contiguous asymmetric centers, one tertiary and one an all-carbon-atom quaternary stereocenter, in high yield and optical purity.

Palladium-Catalyzed C8-Selective C-H Arylation of Quinoline -Oxides: Insights into the Electronic, Steric and Solvation Effects on the Site-Selectivity by Mechanistic and DFT Computational Studies.

We report herein a palladium-catalyzed C-H arylation of quinoline -oxides that proceeds with high selectivity in favor of the C8-isomer. This site-selectivity is unusual for palladium, since all of the hitherto described methods of palladium-catalyzed C-H functionalization of quinoline -oxides are highly C2-selective. The reaction exhibits a broad synthetic scope with respect to quinoline -oxides and iodoarenes and can be significantly accelerated to sub-hour reaction times under microwave irradiation.

Rapid ether and alcohol C-O bond hydrogenolysis catalyzed by tandem high-valent metal triflate + supported Pd catalysts.

The thermodynamically leveraged conversion of ethers and alcohols to saturated hydrocarbons is achieved efficiently with low loadings of homogeneous M(OTf)n + heterogeneous Pd tandem catalysts (M = transition metal; OTf = triflate; n = 4). For example, Hf(OTf)4 mediates rapid endothermic ether ⇌ alcohol and alcohol ⇌ alkene equilibria, while Pd/C catalyzes the subsequent, exothermic alkene hydrogenation. The relative C-O cleavage rates scale as 3° > 2° > 1°.

Etheric C-O bond hydrogenolysis using a tandem lanthanide triflate/supported palladium nanoparticle catalyst system.

Selective hydrogenolysis of cyclic and linear ether C-O bonds is accomplished by a tandem catalytic system consisting of lanthanide triflates and sinter-resistant supported palladium nanoparticles in an ionic liquid. The lanthanide triflates catalyze endothermic dehydroalkoxylation, while the palladium nanoparticles hydrogenate the resulting intermediate alkenols to afford saturated alkanols with high overall selectivity. The catalytic C-O hydrogenolysis is shown to have significant scope, and the C-O bond cleavage is turnover-limiting.

Synthesis, characterization, and catalytic properties of new electrophilic iridium(III) complexes containing the (R)-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl ligand.

The oxidative addition of MeI to the Ir(I) square-planar complex IrI(CO)((R)-(+)-BINAP) where (R)-(+)-BINAP = (R)-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl)) results in the formation of two diastereomers in a 2:1 ratio of the Ir(III) oxidative addition product IrI(2)(CO)(Me)((R)-(+)-BINAP) (4a and 4b) in a 85% overall yield. Upon iodide abstraction from the diastereomeric mixture with 2 equiv of AgSbF(6) in the presence of diethyl isopropylidene malonate (DIM), two diastereomers of the dicationic complex [Ir(CO)(Me)(DIM)((R)-(+)-BINAP)][SbF(6)](2) (5) are formed in a 90% yield with a ratio of 9:1. One diastereomer of the diiodide complex 4 and one diastereomer of the dicationic complex 5 have been characterized by X-ray diffraction.

A highly reactive dicationic iridium(III) catalyst for the polarized Nazarov cyclization reaction.

[Image: see text] Pushing the Nazarov Envelope A new electrophilic complex [IrBr(CO)(diethylisopropylidene malonate)(()-(+)-BINAP)](SbF) () exhibits unusual activity in the catalysis of polarized Nazarov cyclization. Aryl vinyl ketones that show poor reactivity with well-known catalysts such as [Ir(CH)(CO)(1,2-diiodobenzene)(dppe)](B(Ar)) (), Sc(OTf) + LiClO and Cu(ClO), can be cyclized with + AgSbF (1:1) under mild conditions with concurrent AgBr precipitation.

Understanding selectivity in the oxidative addition of the carbon-sulfur bonds of 2-cyanothiophene to Pt(0).

The reaction of 2-cyanothiophene with a zerovalent platinum bisalkylphosphine fragment yields two thiaplatinacycles derived from the cleavage of the substituted and unsubstituted C-S bonds. While cleavage away from the cyano group is preferred kinetically, cleavage adjacent to the cyano group is preferred thermodynamically. Density functional theory using B3LYP level of theory on a model of this system is consistent with experimental results in that the transition state energy leading to the formation of the kinetically favored C-S bond cleavage product is lower by 5.

Diastereoselective oxidative addition of dihydrogen to IrI(CO)((R)-BINAP) and [Ir(CO)2((R)-BINAP)][SbF6].

Two chiral iridium(I) (R)-BINAP complexes, IrI(CO)((R)-BINAP) (1) and [Ir(CO)2((R)-BINAP)][SbF6] (2), have been synthesized and characterized, and their reactivity with dihydrogen has been studied. Complex 1 is formed on the addition of (R)-BINAP to [Bu4N][IrI2(CO)2] in toluene, and 2 is generated by the addition of AgSbF6 to a solution of 1 in dichloromethane under CO. A structure determination of complex 2 confirms a square planar coordination geometry, while that of 1 reveals a significant tetrahedral distortion from the expected planar coordination.

Highly diastereoselective oxidative addition of methyl iodide to a chiral square-planar complex.

Oxidative addition of methyl iodide to the chiral square-planar complex IrI(CO)(duphos) shows a high level of diastereoselectivity. The basis for the diastereoselectivity of the reaction is best explained based on the crystal structure of IrI(CO)(duphos) in which methyl iodide approach across the two faces is differentiated by the chiral ligand.