For a series of α and β substituted haloethanes and haloethenes, gas-phase experiments and computational modeling have been used to characterize their nucleophilic substitution and elimination reactions. Despite being less thermodynamically favorable, the vinylic eliminations have rate constants and computed barriers that are similar to those of analogous aliphatic eliminations. This is the result of the vinylic systems shifting to more E1(cb)-like transition states and exploiting the inherent greater acidity of vinylic hydrogens. In general, the α-substituents have a greater impact on the S(N)2 pathways and stabilize the transition states via field and polarizability effects. Substantial stabilization is also provided to the E2 transition states by the α-substituents, but they have surprisingly little impact on the geometries of the transition states of either pathway. The β-substituents generally lead to a strong bias toward elimination and greatly affect the synchronicity of the elimination (more E1(cb)-like) as well as its location on the reaction coordinate (early). The experimental and computational data are in good accord, and the full data set provides a comprehensive picture of substituent effects on solvent-free S(N)2 and E2 processes.

A series of ligated gold(I) carbenes (where the ligand is Ph 3 P, Me 2 S, or an N-heterocyclic carbene, NHC) were formed in the gas phase by a variety of methods. Gold(I) benzylidenes could be formed using Chen's method of dissociating an appropriate phosphorus ylide precursor. The resulting carbene undergoes an addition reaction with olefins to give an adduct. The adduct undergoes a second gas-phase reaction with an olefin, where presumably a cyclopropanation product is displaced by the second olefin molecule. Both steps in the process were analyzed with linear free energy relationships (i.e., Hammett plots). Under collision-induced dissociation conditions, the adduct undergoes competing processes: (1) dissociation of the cyclopropanation product to give ligated gold(I) species and (2) metathesis to give a more stable gold(I) carbene. Attempts to form less stable gold(I) carbenes in the gas phase by Chen's approach or by reactions of diazo species with the ligated gold(I) cations were not successfulprocesses other than carbene formation are preferred or the desired carbene, after formation, rearranges rapidly to a more stable species. In accord with other recent work, the data suggest that coordination to a ligated gold(I) cation in the gas phase may not offer sufficient stabilization to carbenes to prevent competition from rearrangement processes.

A novel approach is used to synthesize a stable, ligated copper(I) carbene in the gas phase that is capable of typical metal carbenoid chemistry. However, it is shown that copper(I) carbenes generally undergo rapid unimolecular rearrangements including insertions into copper-ligand bonds and Wolff rearrangements. The results indicate that most copper(I) carbenes are inherently unstable and would not be viable intermediates in condensed-phase applications; an alternative intermediate that is less prone to rearrangements is required. Computational data suggest that ylides formed by the complexation of the carbene with solvent or other weak nucleophiles are viable intermediates in the reactions of copper(I) carbenes.

The gold­(I)-induced rearrangements of a variety of propargyl derivatives (ethers, acetals, acetates, and carbonates) were explored in the gas phase with experiments in an ion-trap mass spectrometer as well as with computations at the M06/QZVP level. In accord with condensed-phase studies, it appears that propargyl ethers and acetals prefer 1,3-migrations to give allenes with the release of aldehydes. With propargyl acetates, we show that the preferred path is also a 1,3-migration of the acetate to give an allene species, but that a 1,2-migration to give a gold­(I) carbene species is competitive. However, with the kinetic window of our gas-phase instrumentation, only systems that can be locked into a gold­(I) carbene structure give carbenoid chemistry. Finally, we found that propargyl carbonates react with gold­(I) species and release CO2 in the gas phase; the likely pathway involves sequential 1,3-migrations, leading to a propargyl ether. Overall, the results highlight the dynamic nature of gold­(I)-induced rearrangements and the competition between 1,2-migrations, 1,3-migrations, and the bridged intermediates that link them.

It is demonstrated that a cationic iridium(III) dichloride phenanthroline complex is capable of C-H activation and H/D exchange. It can cleave benzylic and unactivated secondary C-H bonds, but exhibits unique selectivity when compared to similar systems that have been studied in the condensed phase. Gas-phase rate constants and kinetic isotope effects are reported for a variety of substrates and the analysis is supported by DFT calculations at the M06/QZVP level.