Carbon dioxide adducts

The in situ generation of the carbon dioxide adduct of an indole provides sufficient protection and activation of an indole for metalation at C-2 with r-butyl-lithium. The lithium reagent can be quenched with an electrophile, and quenching of the reaction with water releases the carbon dioxide. ... 

Abstract—The nature of the product of the reaction between an aminated silane and carbon dioxide was re-examined with the aid of simple model compounds, several amines, and several aminosilanes. Since the reaction products previously proposed include the amine bicarbonate and a carbamate derived from the amine, ammonium bicarbonate and ammonium carbamate were studied as models for the anions. Carbon dioxide adducts of neat model amines were prepared and studied. Results from a variety of techniques are summarized. Among the most useful was Fourier transform infrared (FTIR) spectroscopy of fluorolube mulls. FTIR spectra were distinctive and assignments characteristic of the two species were extracted from the spectral data. Comparisons of these assignments with the products of the reaction between carbon dioxide and various amines were made. The results indicate that alkylammonium carbamates are the principal product. Nuclear magnetic resonance (NMR) spectra in D20 indicated much dissociation and were not helpful in defining the products. 

Infrared spectra of amines and carbon dioxide adducts of amines... 

Figure 5. FTIR spectra of neat isopropylamine and its carbon dioxide adduct as a fluorolube mull.

Figure 6. Comparison of the FTIR spectra of the carbon dioxide adducts of isopropylamine, n-butylamine, and 1,4-diaminobutane as fluorolube mulls.

Figure 8. FTIR spectra of carbon dioxide adducts of 1 and Z-6020.

Figure 51 Meropenem, a secondary amine, reacts with sodium carbonate to form a carbon dioxide adduct.

Almarsson 6, Kaufman MJ, Stong JD, Wu Y, Mayr SM, Petrich MA, Williams MJ. Meropenem exists in equilibrium with a carbon dioxide adduct in bicarbonate solution. J Pharm Sci 1998 87 5. 

Interaction of the bis (carbon dioxide) adduct with various isocyanides affords new carbon dioxide complexes of composition trans, mer-Mo(C02) (CNR) (PMe3)3, (R=Me, i-Pr, t-Bu, C6H12, CH2C6H5), as shown in eq. 1. In no case has substitution of a second PMe3 or of a C02 ligands been observed. 

CH3)3N CH2CO2, the carbon dioxide adduct of the ylid, and may be expected to be stable. In an attempted preparation 11Q) of the boron trichloride adduct, an extremely unstable compound was isolated which had an nmr spectrum consistent with the expected adduct, but could not be purified. The BCI3 adduct of methylenetriphenylphosphorane is also unstable and cannot be purified 121>. 

Meropenem, a promising agent for combating resistant bacterial infections, is marketed as a powder blend of the crystalline drug and sodium carbonate. NMR spectra recorded for solution and solid state showed [51] that the carbonate in the formulation was the cause of a chemical modification of meropenem in solution. The C CPMAS spectrum of the reconstituted formulation showed the signal of bicarbonate at 159 ppm and a broader one, centered at 164 ppm of meropenem-C02 adduct. It is interesting that such a carbon dioxide adduct could be observed in the solid state, obtained after lyophilization. 

Another strategy to introduce both saturated and unsaturated NHCs to complex 6 was subsequently reported by Delaude and coworkers [57]. Stable, zwitterionic NHC carbon dioxide adducts were prepared via the deprotonation of imidazol(in)ium chloride with potassium bis(trimethylsilyl)amide, followed by reaction with CO2. In the presence of complex 6 in refluxing THF, these carbene precursors decomposed via the elimination of CO2, and the resulting ruthenium indenylidene complexes, featuring either an unsaturated or a... 

Kim Y-E, Lee Y. Formation of a nickel carbon dioxide adduct and its transformation mediated by a Lewis acid. Chem Commun. 2014 50 11458-11461. 

Carmona E, Hughes AK, Munoz MZ, O Hare DM, Perez PJ, Poveda ML (1991) Rotational isomerism and fluxional behavior of bis(carbon dioxide) adducts of molybdenum. J Am Chem Soc 113 9210-9218... 

Comparison of the free energy surface for the process in gas phase and supercritical CO2 revealed an increase in the free energy barrier for the bulk conditions (6.4 0.5 kcal mol in vacuum and 10.7 0.8 kcal mol in supercritical CO2). Analysis of the results for the reverse reaction showed that the change in entropy associated with the dissociation process is less important (increase less) in supercritical CO2 than in gas phase. This leads to a higher stabilization of the paUadium-carbon dioxide complex, pointing out that solvent effects have an important contribution to the stabilization of the palladium-carbon dioxide adduct. 

Electrocatalysis by transition metal complexes is elegantly illustrated by the work of DuBois and colleagues.2 In the absence of CO2, the palladium (II) complex undergoes two-electron reduction, but when CO2 is present, the one-electron reduction product binds CO2 (DMF as solvent) (Figure 5.9). With added acid, carbon monoxide is produced catalytically from carbon dioxide. This chemistry likely involves the protonated carbon dioxide adduct (hydroxycarbonyl complex) shown in Figures 5.9 and 5.10. Catalytic turnover numbers greater than 100 have been reported for this and related compounds. Some hydrogen is produced in parallel, evidently via a hydride complex. 

FIGURE 5.10 The protonated carbon dioxide adduct involved in reduction chemistry. 

The development of transition metal-free hydroelementation reactions has been a goal for the synthetic community for many years. As mentioned in the previous sections on Michael addition reactions, A-heterocyclic carbenes have been shown to be efficient catalysts for these addition reactions. One of the challenges that must be overcome when using these catalysts is the sensitivity of the catalysts to electrophiles. To circumvent this problem, carbon dioxide adducts have been synthesized and used as precatalysts for the phospha-Michael addition of secondary phosphine oxides to activated alkenes (Scheme 4.45) [96]. The success of this approach hinged on the observation that these adducts underwent cleavage in solution to generate the free carbene and carbon dioxide. The concentration of the free carbene was found to be dependent upon the solvent, and THF was found to be an effective solvent for the... 

---