Substituent exchange reactions of silylium ions can be steered in opposite directions. The judicious choice of the hydrosilane and the counteranion enables the selective formation of either triaryl- or trialkylsilylium ions.

Palladium-catalyzed cross-couplings of secondary alkyls are promising tools for the stereoselective formation of carbon−carbon bonds. We report a computational mechanistic study of the stereoselective Suzuki coupling between (S)-2chloropropanenitrile and phenylboronic acid, following a recent experimental report on related α-cyanohydrin triflates (J. Am. Chem. Soc. 2010Soc. , 132, 2524. Added Lewis base helps accelerate S N 2 oxidative addition, leading to the experimentally observed inversion of configuration. Undesired β-hydride elimination side reactions are reduced by the activating cyano group's inductive effects, by cyano-Pd II coordination, and by excess boronic acid. The catalyst ligand's trans influence and steric bulk also affect the rate of β-hydride elimination, suggesting design rules for alkyl cross-coupling ligands.

The Suzuki–Miyaura cross-coupling reaction is an important route to forming carbon–carbon bonds. Suzuki coupling of secondary alkyls containing β-hydrogens is challenging, due in part to a competing and undesired β-hydride elimination. We perform density functional electronic structure calculations on model compounds to study the selectivity of Suzuki coupling of secondary alkyl boranes. Results indicate that the rate and selectivity of the desired reductive elimination are strongly influenced by how the reactants and ligand interact with a coordinatively unsaturated PdII intermediate. Agostic interactions between PdII and reactant β-hydrogens provide facile routes to β-hydride elimination, while coordination of electron-donating reactant groups to PdII slows the reductive elimination. The bulky ligands used in typical Suzuki couplings, such as the SPhos dialkylbiarylphosphine, appear to block both types of undesired interaction while stabilizing the reductive elimination transition state.

The palladium-catalyzed conversion of (bio)pentenoic acid isomers (PEAs) occurs with high activity and selectivity to adipic acid (ADA) in the presence of the diphosphine ligand L 2 = 1,2-bis[(di-tert-butyl)phosphinomethyl]benzene (DTBPX) and an acid cocatalyst. Using density functional theory (DFT) calculations, we show that the active catalyst ([L 2 Pd II -H] + ) isomerizes the PEAs to their equilibrium mixture, from which selective carbonylation and hydrolysis results in the ADA product. Hydrolysis is the rate-limiting and also selectivity-determining step, consisting of two parts, hydration and "product release". After the separation of ADA from Pd(0), the product is in a hydrate form. The conversion of this Pd(0) species to the active catalyst occurs quickly with an acid cocatalyst. This conclusion is also supported by the experimental finding that a moderate acidity increases the overall reaction rate. The bulky P substituents in the DTBPX ligand largely prevent chelation of the pending COOH moiety of PEAs, thus allowing the same high regioselectivity as is obtainable with unfunctionalized long-chain alkenes. We also modeled the CO insertion into the chelate complexes and confirmed an increase of more than 50 kJ mol −1 in the barrier for their conversion.