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The cobalt center in HCo(CO)4 exchanges with those in Co2(CO)g through a facile hydride ligand transfer reaction which has been studied by 59Co NMR line-shape analysis over the temperature range of 80 to 200 °C and total system pressures up to 370 atm in supercritical carbon dioxide. The lifetime of the cobalt center in HCo(CO)4 varies from 2 ms at 80 °C to 10 ns at 200 °C, exhibiting an activation energy of 15.3 ± 0.4 kcal/mol. The hydride ligand transfer process is highly specific for the HCo(CO)4 and Co2(CO)g complexes. Thus, neither Co4(CO)i2 nor MnCo(CO)g exhibit measurable chemical exchange line broadening in the 59Co NMR spectra within solutions where the resonances for HCo(CO)4 and Co2(CO)g coalesce. In addition, the full peak widths at half-height (W\¡i) for the hydride, dihydrogen, and water resonances vary by less than 3 Hz in the NMR spectra, while the line widths (IVi/2) for the HCo(CO)4 and Co2(CO)g resonances broaden by more than 15 000 Hz in the 59Co NMR spectra. A similar hydride ligand transfer reaction exchanges the hydride moieties in HCo(CO)4 and HMn(CO)s. This latter heterometallic hydride ligand transfer reaction has been investigated by *H NMR line-width analysis over the temperature range of 110 to 190 °C at two initial carbon monoxide concentrations, 1.39 and 4.13 M. The lifetime of the hydride moiety on the manganese center in the heterometallic hydride ligand transfer reaction between HCo(CO)4 and HMn(CO)s is independent of the carbon monoxide pressure and exhibits an activation energy of 19 ± 1 kcal/mol. The 55Mn NMR spectra indicate no measurable exchange (less than 30 transfers per second) between the manganese centers in HMn-(CO)5, MnCo(CO)g, and Mn2(CO)i0 under the same reaction conditions, where the hydride moieties in HMn(CO)5 and HCo(CO)4 are undergoing facile exchange (greater than 104 transfers per second) as evident in the *H NMR spectra. This lack of measurable exchange between the manganese centers in fíMn(CO)s, MnCo(CO)g, and Mn2-(CO)io is inconsistent with an oxidative addition reaction mechanism for the heterometallic hydride ligand transfer reaction. Alternatively, the kinetics of these hydride ligand transfer reactions are interpreted in terms of a hydrogen atom transfer reaction mechanism involving *Co(CO)4 and "Mn(CO)5 radicals. Thus, the degenerate hydrogen atom transfer reaction between HCo(CO)4 and *Co(CO)4 proceeds with activation parameters of AH* = 5.5 ± 0.6 kcal/mol and AS* = -16 ± 1 cal/(K-mol), while the endothermic hydrogen atom transfer from manganese in HMn(CO)5 to cobalt in "Co(CO)4 exhibits an activation enthalpy of 10 ± 1 kcal/mol. In addition, the kinetics for the ligand exchange reaction between the coordinated carbonyl groups in Co2(CO)g and free carbon monoxide has been studied in mesitylene solvent by 13C NMR line-shape analysis over the temperature range of 100 to 180 °C under 8.2 M of carbon monoxide.In this temperature range, the free carbon monoxide ligand exhibits a strongly temperature-dependent chemical shift in the presence of Co2(CO)g. T...

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The reversible electrochemical process (insertion/extraction) of lithium ions in graphitic carbon was monitored in situ for the first time by 7Li nuclear magnetic resonance (NMR) spectroscopy using a novel NMR apparatus. The compression coin cell battery imager is a simple device that combines the functions of an electrochemical cell and an NMR detector. A series of 7Li NMR spectra obtained for a blend of spherical and flaky disordered graphitic carbon particles revealed two distinct chemical shift signatures for the lithium ions that were inserted and extracted in the first electrochemical cycle. The lithium signal at ~50 ppm is consistent with the interplane sites for lithium ions on the sixfold axis between two stacked aromatic carbon rings aligned in registry. The second predominant lithium signal at ~12 ppm occurs in the chemical shift region reported for high-stage lithiated graphite and a dispersion of lithium-ion sites found in disordered carbon matrices. In addition, we observed chemical shift signatures similar to those assigned to Li-7 nuclei in lithium oxide, lithium carbonate, lithium alkyls, and lithium alkoxides that occur near 0 ppm and represent lithium nuclei that are irreversibly bound in the electrode/electrolyte interphase. An increase in intensity in the spectral region that is normally associated with irreversibly bound lithium was observed during the first discharge cycle, as anticipated. However, the same peaks in the spectrum unexpectedly diminished during the subsequent charge cycle, suggesting that the interphase between the carbon electrode and the electrolyte is built up over several cycles.