The transition state of metal carboxylate mediated C–H activation is associated with carbon–metal bond formation supported by electron-poor carboxylates.

Accurate bond dissociation energies for large molecules are difficult to obtain by either experimental or computational methods. The former methods are hampered by a range of physical and practical limitations in gas-phase measurement techniques, while the latter require incorporation of multiple approximations whose impact on accuracy may not always be clear. When internal benchmarks are not available, one hopes that experiment and theory can mutually support each other. A recent report found, however, a large discrepancy between gas-phase bond dissociation energies, measured mass spectrometrically, and the corresponding quantities computed using density functional theory (DFT)-D3 and DLPNO-CCSD(T) methods. With the widespread application of these computational methods to large molecular systems, the discrepancy needs to be resolved. We report a series of experimental studies that validate the mass spectrometric methods from small to large ions and find that bond dissociation energies extracted from threshold collision-induced dissociation experiments on large ions do indeed behave correctly. The implications for the computational studies are discussed.

Cryogenic ion vibrational predissociation (CIVP) spectroscopy of a gas-phase molecular torsion balance to probe London dispersion forces in large molecules.

Copper(II) acetate is frequently used as a catalyst for bondforming reactions in organic synthesis. Unlike aqueous solutions, in which complete heterolysis to CuOAc + (aq) and AcO -(aq) prevails at low concentrations, it is clear that copper(II) acetate shows a large degree of aggregation in typical organic solvents. Here, the speciation behavior of Cu(OAc) 2 in organic solvents is probed by electrospray ionization mass spectrometry (ESI-MS), which reveals an extensive clustering of copper acetate species to form ions of the general composition [Cu n (X) 2n-1 ] + and [Cu n (X) 2n+1 ] -(X = OAc and [a]

We present the design of the newly constructed cryogenic Fourier-transform ion cyclotron resonance (FT-ICR) ion trap for infrared ion spectroscopy. Trapped ions are collisionally cooled by the pulsed introduction of buffer gas into the cell. Using different buffer gases and cell temperatures, we record action spectra of weakly bound neutral gas-analyte complexes with an IR laser source. We show for the first time that ion-He complexes can be observed in an ICR cell at temperatures around 4 K. We compare the experimental vibrational spectra of Ag(PPh) obtained by tagging with different neutral gases: He, Ne, Ar, H, and N to computed vibrational spectra. Furthermore, the conditions necessary for the formation of neutral tags within an ICR ion trap are studied.

The reaction mechanism of a tandem conjugate addition/α-alkylation of enals leading to functionalized cyclopentanes catalyzed by O-trimethylsilyldiphenylprolinol was investigated by mass spectrometry, NMR spectroscopy, and DFT calculations. We have shown that the high stereoselectivity of the reaction depends on the energy discrimination between the two stereoisomers formed by the condensation of the α,β-unsaturated aldehyde (cinnamaldehyde) and the catalyst. The stereoselectivity of this step depends on the solvent used. The experimental activation barriers were determined to be E(a) = 25 ± 7 kJ mol(-1) (Arrhenius equation), ΔH(‡) = 23 ± 7 kJ mol(-1), and ΔG(‡) = 101 ± 9 kJ mol(-1) (Eyring equation).

Electrospray ionization mass spectrometry (ESI-MS) is becoming an important tool for mechanistic studies in organic and organometallic chemistry. It allows investigation of reaction mixtures including monitoring of reactants, products, and intermediates, studying properties of the intermediates and their reactivity. Studying the reactive species in the gas phase can be advantageously combined with theoretical calculations. This review is focused on ESI-MS studies of copper-catalyzed reactions. Possible effects of the electrospray process on the transfer of the copper complexes to the gas phase are discussed. The plethora of mass spectrometric approaches is demonstrated on copper mediated C-H activations, cross coupling reactions, rearrangements, organocuprate chemistry, and other examples.

Rapidly developing mid-infrared quantum cascade laser (QCL) technology gives easy access to broadly tunable mid-IR laser radiation at a modest cost. Despite several applications of QCL in the industry, its usage for spectroscopic investigation of synthetically relevant organic compounds has been limited. Here we report the application of an external cavity, continuous wave, mid-IR QCL to cryogenic ion vibrational predissociation spectroscopy (CIVP) to analyze a set of large organic molecules, organometallic complexes, and isotopically labeled compounds. The obtained spectra of test molecules are characterized by high signal-to-noise ratio and low FWHM-values, allowing the assignment of two compounds with just a few wavenumbers difference. Data generated by cw-QCL and spectra produced by another standard Nd:YAG DFG system are compared and discussed.