Triphenylsiloxide is one of the most successful ancillary ligands for Mo­(VI)-alkyne metathesis catalysts. It was proposed that flexible siloxide ligands allow Mo–O–Si bond angles to modulate the electrophilicity of MoC and thereby promote the catalysis. Introduction of a siloxide podand ligand allowed elucidation of the effect of ligand flexibility and Mo–O–Si angles on the electrophilicity of MoC. It also allowed for the isolation of a rare metallatetrahedrane of Mo­(VI) which was found to be dynamic in solution.

The intermediacy of metallacyclobutadienes as part of a [2 + 2]/retro-[2 + 2] cycloaddition-based mechanism is a well-established paradigm in alkyne metathesis with alternative species viewed as off-cycle decomposition products that interfere with efficient product formation. Recent work has shown that the exclusive intermediate isolated from a siloxide podand-supported molybdenum-based catalyst was not the expected metallacyclobutadiene but instead a dynamic metallatetrahedrane. Despite their paucity in the chemical literature, theoretical work has shown these species to be thermodynamically more stable as well as having modest barriers for cycloaddition. Consequentially, we report the synthesis of a library of group VI alkylidynes as well as the roles metal identity, ligand flexibility, secondary coordination sphere, and substrate identity all have on isolable intermediates. Furthermore, we report the disparities in catalyst competency as a function of ligand sterics and metal choice. Dispersion-corrected DFT calculations are used to shed light on the mechanism and role of ligand and metal on the intermediacy of metallacyclobutadiene and metallatetrahedrane as well as their implications to alkyne metathesis.

Asymmetric allylic fluorination has proven to be a robust and efficient methodology with potential applications for the development of pharmaceuticals and practical synthesis for 18F-radio­labeling. A combined computational (dispersion-corrected DFT) and experimental approach was taken to interrogate the mechanism of the diene-ligated, iridium-catalyzed regio- and enantio­selective allylic fluorination. Our group has shown that, in the presence of an iridium­(I) catalyst and nucleo­philic fluoride source (Et3N·3HF), allylic trichloro­acet­imidates undergo rapid fluoride substitution to generate allylic fluoride products with excellent levels of branched-to-linear ratios. Mechanistic studies reveal the crucial role of the trichloro­acet­imidate as a potent leaving group and ligand to enable conversion of racemic allylic trichloro­acet­imidates to the corresponding enantio­enriched allylic fluorides, via a dynamic kinetic asymmetric transformation (DYKAT), in the presence of the chiral bicyclo­[3.3.0]­octadiene-ligated iridium catalyst.

A regioselective, nickel-catalyzed photoredox allylation of secondary, benzyl, and α-alkoxy radical precursors is disclosed. Through this manifold, a variety of linear allylic alcohols and allylated monosaccharides are accessible in high yields under mild reaction conditions. Quantum mechanical calculations [DFT and DLPNO-CCSD(T)] support the mechanistic hypothesis of a Ni(0) to Ni(II) oxidative addition pathway followed by radical addition and inner-sphere allylation.

Hydrogen bonding is a key molecular interaction in biological processes, drug delivery, and catalysis. This report describes a high throughput UV-Vis spectroscopic method to measure hydrogen bonding capacity using a pyrazinone sensor. This colormetric sensor reversibly binds to a hydrogen bond donor, resulting in a blue shift as additional equivalents of donor are added. Titration with excess equivalents of donor is used to determine the binding coefficient, ln(K eq ). Over 100 titrations were performed for a variety of bio-logically relevant compounds. This data enabled development a multiple linear regression model that is capable of predicting 95 % of ln(K eq ) values within 1 unit, allowing for the estimation of hydrogen bonding affinity from a single measurement. To show the effectiveness of the single point measurements, hydrogen bond strengths were obtained for a set of carboxylic acid bioisosteres. The values from the single point measurements were validated with full titrations.