Search

In this study, a variety of new triiron complexes were obtained by nucleophilic additions to vinyliminium ligands bridging between a diiron core and a ferrocene skeleton, and the reaction outcomes were elucidated using DFT calculations.

The μ-(amino)alkylidyne complex [Fe2Cp2(CO)2(μ-CO){μ-CNMe(CH2CHCH2)}]CF3SO3, [1]CF3SO3, reacted with NBu4CN in dichloromethane affording the μ-(cyano)(amino)alkylidene [Fe2Cp2(CO)2(μ-CO){μ-C(CN)N(Me)(CH2CHCH2)}], 2, in 91% yield. Decarbonylation of 2 by using Me3NO in acetone at room temperature yielded [Fe2Cp2(CO)(μ-CO){μ-κ3C-C(CN)N(Me)(CH2CHCH2)}], 3, containing a multidentate alkylidene-alkene ligand occupying both a bridging site and a terminal site, in admixture with the μ-(amino)alkylidyne cyanide product [Fe2Cp2(CN)(CO)(μ-CO){μ-CN(Me)(CH2CHCH2)}], 4. The reaction of the μ-(amino)alkylidyne imine complex [Fe2Cp2(CO)(μ-CO)(NHCPh2){μ-CN(Me)(CH2CHCH2)}]CF3SO3, [7]CF3SO3, with NBu4CN gave 3 with an optimized yield of 75% via imine elimination. According to DFT calculations, 3 is less stable than its geometric isomer 4 by 13.4 kcal mol-1 and quantitative conversion to 4 was achieved by refluxing a THF solution of 3 for 2 hours. No replacement of alkene coordination occurred upon treating 3 with CO or PPh3. The previously unknown compounds 2, 3, 4 and [7]CF3SO3 were fully characterized by analytical and spectroscopic techniques and the structure of 3 was elucidated by single crystal X-ray diffraction.

Diiron vinyliminium complexes constitute a large family of organometallics displaying a promising anticancer potential. The complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(R3)C(R4)CN(R1)(R2)}]CF3SO3 (2a-c, 4a-d) were synthesized, assessed for their behavior in aqueous solutions (D2O solubility, Log Pow, stability in D2O/Me2SO-d6 mixture at 37°C over 48 h) and investigated for their antiproliferative activity against A2780 and A2780cisR ovarian cancer cell lines and the nontumoral one Balb/3T3 clone A31. Cytotoxicity data collected for 50 vinyliminium complexes were correlated with the structural properties (i.e. the different R1–R4 substituents) using the partial least squares methodology. A clear positive correlation emerged between the octanol–water partition coefficient and the relative antiproliferative activity on ovarian cancer cell lines, both of which appear as uncorrelated to the cancer cell selectivity. However, the different effects played by the R1–R4 substituents allow tracing guidelines for the development of novel, more effective compounds. Based on these results, three additional complexes (4p-r) were designed, synthesized and biologically investigated, revealing their ability to hamper thioredoxin reductase enzyme and to induce cancer cell production of reactive oxygen species.

Catalysts are involved in a number of established and emerging chemical processes as well as in environmental remediation and energy conversion. Nanoparticles (NPs) can offer several advantages over some conventional catalysts, such as higher efficiency and selectivity. Nowadays, versatile and scalable nanocatalysts that combine activity and stability are still lacking. Here, we report a comprehensive investigation on the production and characterization of hybrid nano-architectures bringing a partial or total bare surface together with their catalytic efficiency evaluation on, as a proof-of-concept, the formic acid decomposition reaction. In this regard, formic acid (FA) is a convenient and safe hydrogen carrier with appealing features for mobile applications, fuel cells technologies, petrochemical processes and energetic applications. Thus, the design of robust catalysts for FA dehydrogenation is strongly demanded. Due to this, we produced and evaluated nano-architectures with various equilibrium between the size-increase of the active part and the barer catalytic surface. Overall, this work paves the way for the development of new approaches for green energy storage and safe delivery.

The room temperature reactions with internal alkynes, RCCR, of the μ-allenyl acetonitrile complex [Ru

The development of sustainable synthetic routes to access valuable oxazolidinones via CO2 fixation is an active research area, and the aziridine/carbon dioxide coupling has aroused a considerable interest. This reaction is featured by a high activation barrier, so to require a catalytic system, and may present some other critical issues. Here, we describe the straightforward gram-scale synthesis of a series of 5-​aryl-​2-oxazolidinones at ambient temperature and atmospheric CO2 pressure, in the absence of any catalyst/co-catalyst. The key to this innovative procedure consists in the direct transfer of the pre-formed amine/CO2 adduct (carbamate) to common aziridine precursors (dimethylsulfonium salts), replacing the classical sequential addition of amine (intermediate isolation of aziridine) and then CO2. The reaction mechanism has been investigated by NMR studies and DFT calculations applied to model cases.

The room temperature reactions with internal alkynes, RCCR, of the mu-allenyl acetonitrile complex [Ru2Cp2(CO)(2)(NCMe){mu-eta(1):eta(2) -(CH)-H-1=C-2=(CMe2)-Me-3}]BF4 (1-NCMe), freshly prepared from the tricarbonyl precursor [Ru2Cp2(CO)(3){mu-eta(1):eta(2) -(CH)-H-1=C-2=(CMe2)-Me-3}]BF4, 1, proceeded with alkyne insertion into ruthenium-allenyl bond and allenyl-CO coupling, affording compounds [Ru2Cp2(CO2{mu-eta(2):eta(5)-C(R)C(R)(CHC2)-H-1((CMe)-Me-3=CH2)C(OH))}]BF4 (R = Ph, 2; R = CO2Me, 3; R = CO2Et, 4) in 83-94% yields. Deprotonation of 2-4 by triethylamine gave [Ru2Cp2(CO)(2){mu-eta(2):eta(5)-C(R)C(R)CHC(CMe=CH2)C(O)}] (R = Ph, 5; R = CO2Me, 6; R = CO2Et, 7) in 75-88% yields, and 2-4 could be recovered upon HBF4 center dot Et2O addition to 5-7. All the products, 2-7, were fully characterized by elemental analysis, IR and multinuclear NMR spectroscopy. The structure of 2 was ascertained by single crystal X-ray diffraction and investigated by DFT calculations, revealing a six-membered ruthenacycle with Shannon aromaticity index in line with related compounds. The formation of ruthenium-coordinated ruthenabenzenes from a preexistent diruthenium scaffold is a versatile but underdeveloped approach exploiting cooperative effects typical of a dimetallic core.

Dimetallic complexes are suitable platforms for the assembly of small molecular units, and the reactivity of bridging alkenyl ligands has been widely investigated to model C-C bond forming processes. Here, we report the unusual coupling of an alkenyl ligand, bridging coordinated on a diruthenium scaffold, with a series of alkynes, revealing two possible outcomes. The diruthenium complex [Ru2Cp2(Cl)(CO)(mu-CO) {mu-eta(1):eta(2)-C(Ph)=CH(Ph)}], 2, was prepared in two steps from [Ru2Cp2(CO)(2)(mu-CO){mu-eta(1):eta(2)-C(Ph)=CH (Ph)}]BF4, [1]BF4, in 69% yield. Then, the reaction of 2 with C-2(CO2Me)(2), promoted by AgCF3SO3 in dichloromethane, afforded in 51% yield the complex [Ru2Cp2(CO)(2){mu-eta(3):eta(2)-C(Ph)CH(Ph)C(CO2Me)C (CO2Me)}]CF3SO3, [3]CF3SO3, containing a ruthenacyclopentene-based hydrocarbyl ligand. On the other hand, 2 reacted with other alkynes and AgX salts to give the butadienyl complexes [Ru2Cp2(CO)(2){mu-eta(3):eta(2)-C(R)CH(R')C(Ph)C(Ph)}]X (R = R' = H, [4]BF4; R = R' = Me, [5]CF3SO3; R = R' = Ph, [6]CF3SO3; R = Ph, R' = H, [7]CF3SO3), in 42-56% yields. All products were characterized by IR and NMR spectroscopy, and by single crystal X-ray diffraction in the cases of 2, [3]CF3SO3 and [6]BF4. DFT calculations highlighted the higher stability of [4-7](+)- like structures with respect to the corresponding [3](+)-like isomers. It is presumable that [3](+)-like isomers initially form as kinetic intermediates, then undergo H-migration which is disfavoured in the presence of carboxylato substituents on the alkyne. Such hypothesis was supported by the computational optimization of the transition states for H-migration in the cases of R = R' = H and R = R' = CO2Me.

We report a screening study aimed to assess for the first time the air- and water-stability and the biological potential of simple metal-carbamates. These molecular metallic species are based on elements belonging to the groups 4–5, 7–9 and 11, and tin, and are easily available from inexpensive reagents. Complexes [Ag(O2CNEt2)] (13-Ag) and [Au(O2CNMe2)(PPh3)] (14-Au) resulted substantially stable in aqueous media and exhibited a potent in vitro cytotoxicity. Especially 13-Ag revealed a significant selectivity against the A549 lung adenocarcinoma and the A2780 ovarian cancer cell lines with respect to the noncancerous HEK293 cell line. Generation of ROS (reactive oxygen species) and mitochondrial membrane depolarization were recognized for 13-Ag and 14-Au; notwithstanding, the cell death mechanism is different in the two cases: apoptosis and cell cycle arrest in G0/G1 phase for 13-Ag; necroptosis and cell cycle arrest in S phase for 14-Au. Both 13-Ag and 14-Au are endowed with antibacterial activity, which is relatively stronger for 13-Ag towards Gram negative and for 14-Au towards Gram positive strains, respectively., La Caixa Foundation (LCF/PR/PR12/11070003), Consejería de Educación-Junta de Castilla y León-FEDER Funds (BU305P18), Ministerio de Ciencia, Innovación y Universidades (RTI2018-102040-B-100) and the University of Pisa (PRA_2020_39).

The reactions of the diiron aminocarbyne complexes [Fe2Cp2(NCMe)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, 1aNCMe; R = Cy, 1bNCMe), freshly prepared from the tricarbonyl precursors 1a–b, with primary amines containing an additional function (i.e., alcohol or ether) proceeded with the replacement of the labile acetonitrile ligand and formation of [Fe2Cp2(NH2CH2CH2OR’)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, R’ = H, 2a; R = Cy, R’ = H, 2b; R = Cy, R’ = Me, 2c) in 81–95% yields. The diiron-oxazolidinone conjugate [Fe2Cp2(NH2OX)(CO)(μ-CO){μ-CN(Me)2}]CF3SO3, 3, was prepared from 1a, 3-(2-aminoethyl)-5-phenyloxazolidin-2-one (NH2OX) and Me3NO, and finally isolated in 96% yield. In contrast, the one pot reactions of 1a-b with NHEt2 in the presence of Me3NO gave the unstable [Fe2Cp2(NHEt2)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, 4a; R = Cy, 4b) as unclean products. All diiron complexes were characterized by analytical and spectroscopic techniques; moreover, the behavior of 2a–c and 3 in aqueous media was ascertained.

Nitriles (N≡CR) are ubiquitous in coordination chemistry, yet literature studies on metal–nitrile bonding based on a multi-technique approach are rare. We selected an easily-available di-organoiron framework, containing both π-acceptor (CO, aminocarbyne) and donor (Cp = η5−C5H5) ligands, as a suitable system to provide a comprehensive description of the iron–nitrile bond. Thus, the new nitrile (2–12)CF3SO3 and the related imine/amine complexes (8–9)CF3SO3 were synthesized in 58–83% yields from the respective tris-carbonyl precursors (1a–d)CF3SO3, using the TMNO strategy (TMNO = trimethylamine-N-oxide). The products were fully characterized by elemental analysis, IR (solution and solid state) and multinuclear NMR spectroscopy. In addition, the structures of (2)CF3SO3, (3)CF3SO3, (5)CF3SO3 and (11)CF3SO3 were ascertained by single crystal X-ray diffraction. Salient spectroscopic data of the nitrile complexes are coherent with the scale of electron-donor power of the R substituents; otherwise, this scale does not match the degree of Fe → N π-back-donation and the Fe–N bond energies, which were elucidated in (2–7)CF3SO3 by DFT calculations.

Transition metal carbamates constitute a class of compounds with unique properties, however their catalytic potential has been sparingly explored so far. The easily available silver N,N-dimethylcarbamate, Ag(O2CNMe2), worked as a catalyst in the carboxylation reaction of terminal alkynes with CO2 at atmospheric pressure. Different reaction parameters (solvent, base, temperature, time and the amount of catalyst) were investigated in order to establish the optimal conditions.

The catalytic potential of a large series of easily available metal carbamates (based on thirteen different non-precious metal elements) was explored for the first time in the coupling reaction between 2-aryl-aziridines and carbon dioxide, working under solventless and ambient conditions and using tetraalkylammonium halides as co-catalysts. The straightforward synthesis of novel [NbCl3(O2CNEt2)2], NbCl, and [NbBr3(O2CNEt2)2], NbBr, is reported. The niobium complex NbCl, in combination with NBu4I, emerged as the best catalyst of the overall series to convert aziridines with small N-alkyl substituents into the corresponding 5-aryl-oxazolidin-2-ones.

The catalytic potential of ammonium halide salts was explored in the coupling reaction of a model aziridine with carbon dioxide, highlighting the superior activity of [NH2Et2]I. Then, working at room temperature, atmospheric CO2 pressure and in the absence of solvent, the [NH2Et2]I-catalyzed synthesis of a series of 5-aryl-2-oxazolidinones was accomplished in good to high yields and excellent selectivity, from 2-aryl-aziridines with N-methyl or N-ethyl groups. NMR studies and DFT calculations outlined the pivotal role of both the diethylammonium cation and the iodide anion. The proposed method represents a convenient choice for obtaining a limited number of valuable molecules for which more complex and more expensive catalytic systems have been reported even in recent years.

The simple and cost-effective compound [Ag(O2CNEt2)], in combination with PPh3, works as an effective catalytic precursor in the carboxylation of propargyl alcohols at ambient temperature and atmospheric CO2 pressure, and in most cases under solventless conditions. The silver carbamate revealed a better performance than commercial silver oxide, Ag2O, and allowed to obtain a series of α-alkylidene cyclic carbonates in high yields.

J. Stix proved that a curve of positive genus over $$\mathbb {Q}$$ Q which maps to a non-trivial Brauer–Severi variety satisfies the section conjecture. We prove that, if X is a curve of positive genus over a number field k and the Weil restriction $$R_{k/\mathbb {Q}}X$$ R k / Q X admits a rational map to a non-trivial Brauer–Severi variety, then X satisfies the section conjecture. As a consequence, if X maps to a Brauer–Severi variety P such that the corestriction $${\text {cor}}_{k/\mathbb {Q}}([P])\in {\text {Br}}(\mathbb {Q})$$ cor k / Q ( [ P ] ) ∈ Br ( Q ) is non-trivial, then X satisfies the section conjecture.

The catalytic potential of a large series of easily available metal carbamates (based on thirteen different non-precious metal elements) was explored for the first time in the coupling reaction between 2-aryl-aziridines and carbon dioxide, working under solventless and ambient conditions and using tetraalkylammonium halides as co-catalysts. The straightforward synthesis of novel [NbCl3(O2CNEt2)2], NbCl, and [NbBr3(O2CNEt2)2], NbBr, is reported. The niobium complex NbCl, in combination with NBu4I, emerged as the best catalyst of the overall series to convert aziridines with small N-alkyl substituents into the corresponding 5-aryl-oxazolidin-2-ones.

Grothendieck gave two forms of his "main conjecture of anabelian geometry", i.e. the section conjecture and the hom conjecture. He stated that these two forms are equivalent and that if they hold for hyperbolic curves then they hold for elementary anabelian varieties too. We state a stronger form of Grothendieck's conjecture (equivalent in the case of curves) and prove that Grothendieck's statements hold for our form of the conjecture. We work with DM stacks, rather than schemes. If $X$ is a DM stack over a field $k\subseteq\mathbb{C}$ finitely generated over $\mathbb{Q}$, we prove that whether $X$ satisfies the conjecture or not depends only on $X_{\mathbb{C}}$. We prove that the section conjecture for hyperbolic orbicurves stated by Borne and Emsalem follows from the conjecture for hyperbolic curves., Comment: arXiv admin note: text overlap with arXiv:1801.05758

The oxidation of the sulfide function promoted by a variety of vanadium compounds has been largely explored, whereas the use of homogeneous catalytic systems based on the heavier group 5 metals remains less explored. We report the use of easily available niobium and tantalum carbamates, i.e. [M(O2CNMe2)5] (M = Nb, 1; M = Ta, 2), [Nb(O2CNMe2)4], 3, [NbO(O2CNEt2)3], 4, and [NbCl3(O2CNEt2)2], 5, as effective catalysts for the conversion of a series of alkyl aryl and aromatic sulfides into the corresponding sulfones. NMR investigations on the performant niobium catalyst 4 unexpectedly revealed the substantial stability of this compound in the protic catalytic environment, and a plausible catalytic cycle was obtained by DFT studies. The two active catalytic species, i.e. 4 and its minor mono-methoxide derivative, presumably interconvert to each other exploiting the versatile coordination of the carbamato ligand.

Carbonation of natural α-amino acids in water and subsequent cyclization with (2-bromo-1-arylethyl)dimethylsulfonium bromides led selectively to a family of 2-oxazolidinonyl derivatives, which were isolated without the needing of purification. Analogous conjugation of the 2-oxazolidinone skeleton with amino acids was previously realized by complicated and narrow-scope routes, whereby the amino acid core is built stepwise. Deprotonation of some of the products afforded the corresponding water-soluble carboxylates, while a straightforward, proof of concept esterification reaction of the carboxylic acid group yielded a menthol-alanine-oxazolidinone conjugate.

Gold nanomaterials have been recognized as considerably active and effective catalysts toward several industrial and environmentally relevant reactions, among which are hydrocarbon selective oxidation, CO oxidation and propylene epoxidation. Engineered nanomaterials may be able to suppress some of the more severe issues that block their industrial applicability, such as recyclability, catalytic activity reduction during time due to sintering effects or leakage of the active material. In this regard, the composition of hybrid nanomaterials comprising encapsulated ultrasmall gold nanoparticles, also called ultrasmall-in-nano, will broaden and enhance their potential catalytic applications by including synergic features. Here, we report a systematic investigation on the design and production of optimized titania-decorated gold nano-architectures together with their efficiency evaluation on both formic acid (thermo/photo-induced) decomposition and cyclic carbonates formation by carbon dioxide fixation for carbon capture and storage technology. This work paves the way for the next development of ultrasmall-in-nano catalysts bearing an early–late transition metal combination for sustainable processes.

The development of sustainable synthetic routes to access valuable oxazolidinones via CO

Following a related review dating back to 2003, the present review discusses in detail the various synthetic, structural and reactivity aspects of metal species containing one or more carbamato ligands, representing a large family of compounds across all the periodic table. A preliminary overview is provided on the reactivity of carbon dioxide with amines, and emphasis is given to recent findings concerning applications in various fields.

Thermally stable amidinium/guanidinium N,N-dialkylcarbamates, including vacuum stable compounds, have been prepared, and then isolated in the solid state, by reaction of tetramethylguanidine (TMG) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with secondary amines under atmospheric pressure of CO2. The same method has been successfully applied to α-amino acids, thus the corresponding carbamates of sarcosine, L-proline and L-phenylalanine have been obtained. All the products are highly moisture sensitive, and have been characterized by analytical and spectroscopic (IR, multinuclear NMR) techniques.

A. Vistoli observed that, if Grothendieck's section conjecture is true and $X$ is a smooth hyperbolic curve over a field finitely generated over $\mathbb{Q}$, then $\underline{\pi}_{1}(X)$ should somehow have essential dimension $1$. We prove that an infinite, pro-finite \'etale group scheme always has infinite essential dimension. We introduce a variant of essential dimension, the fce dimension $\operatorname{fced} G$ of a pro-finite group scheme $G$, which naturally coincides with $\operatorname{ed} G$ if $G$ is finite but has a better behaviour in the pro-finite case. Grothendieck's section conjecture implies $\operatorname{fced}\underline{\pi}_{1}(X)=\dim X=1$ for $X$ as above. We prove that, if $A$ is an abelian variety over a field finitely generated over $\mathbb{Q}$, then $\operatorname{fced}\underline{\pi}_{1}(A)=\operatorname{fced} TA=\dim A$., Comment: Simplified proofs and stronger results in the new version

Easily available and inexpensive Fe

A series of previously reported homoleptic and non-homoleptic N,N-dialkylcarbamates of a range of non precious metals and N,N-dialkylcarbamate of Al(III) were investigated as easily available and inexpensive catalysts in the solventless synthesis of propylene carbonate (PC) from propylene oxide (PO) and CO2. By operating at atmospheric CO2 pressure at ambient temperature, excellent results were achieved using Ti(O2CNEt2)4, Al(O2CNR2)3 (R = Et, iPr), Cu(O2CNEt2)2 and Sn(O2CNEt2)4, in combination with NBu4X (X = Br or Cl) as a co-catalyst. The reactions of MCl2(O2CNEt2)2 (M = Ti, Zr) with amorphous silica were straightforward through partial release of both chlorido and carbamato ligands, and readily afforded solid materials which were characterized by ICP-OES and EDS analyses, coupled to SEM. These heterogeneous catalytic systems revealed less efficient than the homogeneous counterparts.

The authors report the first modification of ionic liquids with metal carbamates. A selection of homoleptic N,N-dialkylcarbamates of group 4 and 5 metals, M(O2CNR2)n, were dissolved in bis(trifluoromethylsulfonyl)imide-based ionic liquids, i.e. [bmim][Tf2N] and [P(oct)4][Tf2N], at 293 K. The resulting solutions were characterized by means of IR, UV and NMR spectroscopy, and the data were compared to those of the respective metal compounds. Notably, the dissolution process did not proceed with the release of any of the original carbamato ligands, thus preserving the intact coordination frame around the metal centre. The solvation process of Ti(O2CNiPr2)4, as a model species, in [bmim][Tf2N] was rationalized by DFT calculations. As a comparative study, solutions of NbF5 and MCl5 (M = Nb, Ta) in [bmim][Tf2N] were also investigated, revealing the possible occurrence of solvent anion coordination to the metal centres.

The vanadium(V) amido-carbamato derivatives VO(NR2)(O2CNR2)2(R = Me, 1; Et, 2) are obtained by the reaction of VOCl3with preformed carbamato species (ammonium or sodium carbamates). The synthesis of an ionic ammonium chlorido-amide of WVI, 3, is performed using WOCl4and diethylamine as precursors. Moreover, the reactivity of 3 with CO2is investigated. Mixed WVIchlorido-carbamato compounds, 4 and 5, are obtained by the reaction of WOCl4with stoichiometric amounts of sodium diethylcarbamate. All of the products are characterized by analytical and spectroscopic methods (IR spectroscopy, multinuclear NMR spectroscopy) and by X-ray diffraction in the cases of 3 and 4. DFT calculations are useful to elucidate the structures of the compounds and to give insight into the various reaction pathways. The combination of 2 or 5 with amorphous silica gives solid materials, which are characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and energy dispersive X-ray spectroscopy (EDS) coupled to scanning electron microscopy (SEM).

The pentafluorides of niobium and tantalum reacted with benzophenone (Ph2CO), (2-diphenylphosphino)phenol (DPPPh) and 4-fluorobenzonitrile affording adducts corresponding to the asymmetric (Ph2CO and DPPPh) and symmetric (4-fluorobenzonitrile) cleavage of the tetranuclear structure of MF5. The products were characterized by elemental analysis, IR and multinuclear NMR spectroscopy. A selection of Ta(V) complexes was investigated in the attempt to obtain tantalum tetrafluoride derivatives, which are almost unknown in the literature. The reactions with cobaltocene in dichloromethane afforded unidentified paramagnetic materials and [CoCp2][TaF6], characterized by X-ray diffraction.

Easily available and inexpensive FeIII carbamates were employed in the solvent-free synthesis of a series of cyclic carbonates from epoxides and CO2 at room temperature and atmospheric pressure, in the presence of a cocatalyst. Different experimental conditions (type and concentration of catalyst and cocatalyst, as well as reaction time) were investigated: Fe(O2 CNEt2 )3 and NBu4 Br acted as the best catalyst/cocatalyst combination, allowing the formation of propylene carbonate and 1,2-butylene carbonate with quantitative yield and selectivity in 24 h. According to NMR and DFT studies, the reaction proceeds with the dynamic trapping of carbon dioxide as a carbamato ligand.

Background Donation of returned medicines is a debated health policy issue as it is discouraged by WHO, but accepted in some countries. Methods Lessons learned from a donation programme of returned medicines carried out in Europe were documented. Results The donation programme we reviewed followed a strict protocol for collection, sorting and distribution of returned drugs, in order to avoid the major limitations associated with unused medicine donations. Over a period of 3 years, 23 145 boxes of medicines were donated to 14 organizations operating in Europe, Africa and Latin America. Conclusions The donations covered about one-third of the volume of medicines used by beneficiary organizations. The programme helped to decrease expenditure by both patients and health facilities.

The reactivity of MoCl5 with α-amino acids was investigated for the first time by choosing CH2Cl2 as the reaction medium. The interaction of MoCl5 with l-proline proceeded with Cl/O interchange and led to the formation of [NH2(CH2)3CHC(O)Cl][MoOCl4], 1, in 63% yield. The reactions of MoCl5 with l-phenylalanine, sarcosine, N,N-dimethylglycine and N,N-dimethyl-l-phenylalanine afforded the α-amino-acylchloride complexes MoOCl3[O[double bond, length as m-dash]C(Cl)CH(R)N(R')(R'')] (R = CH2Ph, R' = R'' = H, 2a; R = R' = H, R'' = Me, 2b; R = H, R' = R'' = Me, 2c R = CH2Ph, R' = R'' = Me, 2d), in ca. 70% yields. According to DFT studies, 2a,d are mononuclear Mo(v) octahedral complexes bearing a N,O-coordinated α-amino-acylchloride ligand. The presumed species formed during the first stages of the MoCl5/l-phenylalanine interaction were DFT-elucidated, thus the calculated Gibbs free energy profile for the multi-step reaction of MoCl5 with l-phenylalanine was traced. [NH3CH(CH2Ph)C(O)Cl][MoOCl4], 3, acting as an intermediate in the course of the formation of 2a, was isolated by combination of [NH3CH(CH2Ph)C(O)Cl][Cl] with MoOCl3.

Solid-state, thermally stable tetramethylguanidinium N,N-diethylcarbamate [TMGH][O2CNEt2] was prepared from tetramethylguanidine (TMG), N,N-diethylamine and carbon dioxide (1 atm). The reaction of [TMGH][O2CNEt2] with TiCl4 in toluene afforded [TMGH]2[TiCl6] and TiCl2(O2CNEt2)2. The tetrachlorides of titanium, zirconium and hafnium were effectively converted into the respective mixed dichloride-dicarbamates, MCl2(O2CNEt2)2, by the reaction with either silver diethylcarbamate or the corresponding homoleptic metal N,N-diethylcarbamate, M(O2CNEt2)4. The titanium and hafnium derivatives are trinuclear in the solid state according to X-ray diffraction analysis (M = Ti) and DFT calculations (M = Hf). Instead, ZrCl2(O2CNEt2)4 was obtained as a mixture of two isomers presumably holding dinuclear and trinuclear structures, according to DFT calculations. Difluoride-dicarbamate TiF2(O2CNEt2)4 was prepared in a similar way as the homologous Cl-compound. All the products were characterized by analytical and spectroscopic methods, and by X-ray diffraction in the cases of [TMGH]2[TiCl6] and Ti3Cl6(μ-O2CNEt2)6. The complex Hf4Cl4(O)2(O2CNEt2)6[O(CH2)3CHO]2 was isolated in low yield in crystalline form from a thf solution of HfCl2(O2CNEt2)2, and then X-ray characterized.