Maurizio Peruzzini

CO2 absorption by aqueous NH3 solutions : speciation of ammonium carbamate, bicarbonate and carbonate by a 13C NMR study

The absorption of CO2 in aqueous NH3 solutions occurs with high efficiency and loading capacity at room temperature and atmospheric pressure producing the ammonium salts of bicarbonate (HCO3−), carbonate (CO32−), and carbamate (NH2CO2−) anions. 13C NMR spectroscopy at room temperature has been proven to be a simple and reliable method to investigate the speciation in solution of these three ionic species. Fast equilibration of HCO3−/CO32− anions results in a single NMR peak whose chemical shift depends on the relative concentration of the two species. A method has been developed to correlate the chemical shift of this carbon resonance to the ratio of the two anionic species. Integration of the carbamate carbon peak provided the relative amount of this species with respect to HCO3−/CO32− pair. No other species was detected in solution by 13C NMR, and no solid compounds separated out under our experimental conditions. Finally, the relative amount of HCO3−, CO32−, and NH2CO2− in solution have been correlated to the molar ratio between free ammonia in solution and absorbed CO2.

Coordination chemistry and functionalization of white phosphorus via transition metal complexes

The chemistry of phosphorus is nowadays rivaling that of carbon in terms of complexity and diversity. This tutorial review highlights the state-of-the-art in the field of metal-mediated activation and functionalization of white phosphorus. Particular attention is given to an illustration of the coordination abilities of the intact molecule as well as the disaggregating and reaggregating metal-mediated processes resulting in different polyphosphorus ligands from P(1) to P(12). The metal-promoted P-C and P-H bond forming processes are also reviewed showing that an ecoefficient catalytic protocol for transforming P(4) into high value organophosphorus compounds is a concrete possibility for chemical companies. This tutorial review deals with the activation and functionalization of white phosphorus in the coordination sphere of transition metal complexes. Particular attention is given to the coordination abilities of the intact molecule as well as to the disaggregating and reaggregating metal-mediated processes yielding various polyphosphorus ligands from P(1) to P(12). The metal-promoted processes for P-C and P-H bond formation are also reviewed showing that an ecoefficient catalytic protocol for transforming P(4) into high value organophosphorus compounds offers good opportunities for chemical companies.

Ammonia-Borane and Amine-Borane Dehydrogenation Mediated by Complex Metal Hydrides.

This review is a comprehensive survey of the last 10 years of research on ammonia-borane and amine-borane dehydrogenation mediated by complex metal hydrides (CMHs), within the broader context of chemical hydrogen storage. The review also collects those cases where CMHs are the catalyst spent form or its resting state. Highlights on the reaction mechanism (strictly dependent on the CMH of choice) and the catalysts efficiency (in terms of equivalents of H2 produced and relative reaction rates) are provided throughout the discussion.

A 13C NMR study of the carbon dioxide absorption and desorption equilibria by aqueous 2-aminoethanol and N-methyl-substituted 2-aminoethanol

The 13C NMR experimental study presented investigates the absorption of CO2 by a series of primary, secondary and tertiary alkanolamines in aqueous solution. The absorption experiments were made at room temperature with four different amine concentrations in the range 0.167–0.667 M (1.01–5.88 wt%). As inferred by 13C NMR spectral analysis, the formation of carbamate increases with increasing amine concentration following the order secondary amine < primary amine. Moreover, it has been shown that carbamate reduces the CO2 absorption efficiency. A considerable physical absorption (10–20%) contributes to the loading capacity of the amines and partially compensates for the yield of chemical capture, which turned out to be poorer than was expected theoretically. Quite unexpectedly, carbamate was also produced by an endothermic reaction during the thermal CO2 desorption process which regenerated the amines (primary and secondary amines). In the case of the secondary amine 2-(methylamino)ethanol (MMEA), the amount of carbamate at the end of the desorption process is greater than the amount found at the end of the absorption step, thus reducing the desorption efficiency of the secondary amine in comparison to both primary and tertiary amines. Five cycles of absorption–desorption tests were carried out to verify the feasibility of regenerated amines for reuse. Our results indicate that absorption efficiency and loading capacity of the regenerated amine solutions remain essentially constant during the second to the fifth absorption–desorption experiments, but they both decrease slightly when compared to the initial amine.

Metal-mediated degradation and reaggregation of white phosphorus

A critical survey of the coordination chemistry of white phosphorus illustrating the metal-mediated degradation of the P4 tetrahedron is presented. The underlying principles to account for the activation and stepwise fragmentation of this molecule in the presence of transition metal complexes are presented with emphasis given to mechanistic aspects. A collection of 31P-NMR spectral data for the known polyphosphorus Px compounds (x ≤ 4) is also presented and briefly commented.

Amine-Templated Polymeric Lanthanide Formates: Synthesis, Characterization, and Applications in Luminescence and Magnetism

The novel polymeric formates of general formula [(Fmd)Ln(III)(HCOO)(4)](∞) (Fmd(+) = NH(2)-CH(+)-NH(2); Ln = Eu (1), Gd (2), Tb (3), Dy (4)] were synthesized through solvothermal methods in formamide solutions. The compounds are isotructural; they crystallize in the orthorhombic C222(1) chiral space group. The coordination geometry at the metal centers is square antiprismatic (coordination number eight), with each formate ligand bridging adjacent lanthanide ions. The overall negative three-dimensional (3D) framework charge is balanced by the formamidinium cations sitting inside the channels along the a axis, forming extensive N-H···O hydrogen bonding with the surrounding cage. All the compounds have been characterized through single-crystal/powder X-ray diffraction, IR spectroscopy, and TG-MS analysis. Finally, their luminescence and magnetic properties have been assessed, leading to remarkable emission intensities, especially for the Tb(III) compound (Φ = 0.83), with corresponding lifetime decays in the micro (Dy) and millisecond (Tb, Eu) time scale. A weak but sizable antiferromagnetic interaction has been observed for the Gd(III) derivative.

Synthesis and Characterization of Terminal [Re(XCO)(CO)2(triphos)] (X=N, P): Isocyanate versus Phosphaethynolate Complexes

The terminal rhenium(I) phosphaethynolate complex [Re(PCO)(CO)(2)(triphos)] has been prepared in a salt metathesis reaction from Na(OCP) and [Re(OTf)(CO)(2)(triphos)]. The analogous isocyanato complex [Re(NCO)(CO)(2)(triphos)] has been likewise prepared for comparison. The structure of both complexes was elucidated by X-ray diffraction studies. While the isocyanato complex is linear, the phosphaethynolate complex is strongly bent around the pnictogen center. Computations including natural bond orbital (NBO) theory, natural resonance theory (NRT), and natural population analysis (NPA) indicate that the isocyanato complex can be viewed as a classic Werner-type complex, that is, with an electrostatic interaction between the Re(I) and the NCO group. The phosphaethynolate complex [Re(P=C=O)(CO)(2)(triphos)] is best described as a metallaphosphaketene with a Re(I)-phosphorus bond of highly covalent character.

Continuous cycles of CO2 absorption and amine regeneration with aqueous alkanolamines: a comparison of the efficiency between pure and blended DEA, MDEA and AMP solutions by 13C NMR spectroscopy

This experimental study describes the performances of CO2 capture by aqueous solutions of pure alkanolamines (0.667, 1.33 and 2.00 M) 2,2′-iminodiethanol (DEA), N-methyl-2,2′-iminodiethanol (MDEA) and 2-amino-2-methy-1-propanol (AMP). The behaviour of some alkanolamine blends (2.00 M) has been also considered. In these experiments the CO2-loaded and the regenerated amine solutions were continuously circulated in a closed system between the absorber (set at 293 K) and the desorber (set at 363, 373 and 363–388 K). The absorption efficiency of the single amines at equilibrium is between 69 and 81% according to the desorber temperature and to the amine concentration. The CO2-amine reaction equilibria have been investigated by 13C NMR spectroscopy, which established the regeneration efficiency and the loading capacity for each single amine experiment. AMP displays the greatest absorption efficiency and MDEA the greatest regeneration efficiency at any amine concentration and desorber temperature. Blended AMP-MDEA and AMP-DEA systems (1/2 and 2/1 molar ratios) significantly enhance the absorption efficiency (in the range 7–14%) with respect to single amines under identical operating conditions. AMP-MDEA blends display better performances than AMP-DEA due to the lower efficiency of DEA carbamate in both CO2 absorption and amine regeneration. Owing to a higher thermal stability, AMP and MDEA solutions surpass DEA, as no degradation product has been detected by 13C NMR analysis after heating AMP and MDEA solutions at 403 K up to fourteen days.

Reactivity of the [ReNR]3+ and [ReN]2+ cores toward bis(diphenylphosphino)amine and its derivatives. Synthesis and crystal structures

The complexes fac-[Re(NMe)Cl3{NH(PPh2)2-P,P′}]1, [ReNCl{NH(PPh2)2-P,P′}2]X (X = Cl 2 or BPh42a), [Re(NMe) Cl2{N(XPPh2)2-X,X′}(PPh3)](X = 0 3, S 4 or Se 8), [Re(NMe)Cl{N(XPPh2)2-X,X′}2](X = S 5 or Se 9), [ReNCl{N(SPPh2)2-S,S′}(PPh3)]6, [ReN{N(XPPh2)2-X,X′)2](X = S 7 or Se 10) and trans-[ReOCl2{N(OPPh2)2-O,O′}(AsPh3)]11 were obtained by treatment of [Re(NMe)Cl3(PPh3)2], [ReNCl2(PPh3)2] or [ReOCl3(AsPh3)2] with the appropriate ligand under different experimental conditions. The structures of complexes 1, 2a and 6 were determined by X-ray crystallography. In 1 and 2a the Re atom is six-co-ordinate in a distorted octahedral configuration, whereas in 6 the Re atom is five-co-ordinate square pyramidal with the N atom in the apical position.

From greenhouse gas to feedstock: formation of ammonium carbamate from CO2 and NH3 in organic solvents and its catalytic conversion into urea under mild conditions

The capture of carbon dioxide by ammonia in both aqueous and non-aqueous solutions was investigated at atmospheric pressure and 273 K under different operating conditions. The CO2 capture is fast and efficient ranging between 78 and 99%, depending on both the NH3 concentration and the solvent nature. The precipitation of solid mixtures of ammonium bicarbonate, ammonium carbonate and ammonium carbamate occurred in ethanol–water solution. Selective precipitation of ammonium carbamate was achieved by reacting gaseous CO2 and NH3 in anhydrous ethanol, 1-propanol or N,N-dimethylformamide (DMF) in a flow reactor that operates in continuous. In the second step of the process, the pure ammonium carbamate is used to produce urea with good yield (up to 54% on carbamate basis) at 393–413 K in the presence of inexpensive Cu(II) and Zn(II) catalysts. The yield of urea depends on several factors including the catalyst, the reaction temperature and the reaction time. Identification and quantification of urea in the reaction mixtures was obtained by analysis of its 13C NMR spectrum. A preliminary mechanistic interpretation of the catalytic reaction is also briefly presented and commented.