Thomas A. Zevaco

Synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by an easy-to-handle ionic iron(III) complex

We report the successful utilization of monometallic, ionic iron(II)- and iron(III)-N2O2-ligand-systems as highly active homogeneous catalysts for the conversion of CO2 with different epoxides to cyclic carbonates. The catalytic tests were performed using propylene oxide (PO) and a range of nine substituted epoxides. Terminal monosubstituted oxides react quantitatively.

Chemical synthesis of 13C labeled anti-HIV nucleosides as mass-internal standards

Abstract Synthesis of [ 13 C 5 ]-labeled anti-HIV nucleosides, e.g. d4T, ddI, ddA, is described. The methodology used has been optimized due to the very high cost of the starting compound. The key step of this approach was the stereoselective dehomologation of 1,2:5,6-di- O -isopropylidene-3-oxo-α- d -glucofuranose ( 2 ) with periodic acid and sodium borohydride, which gave optically pure ribose derivative as the exclusive product. Nucleoside derivatives 6a – c were obtained from ribosylation of 5 with persilylated nucleobases under Vorbruggen conditions. Deoxygenation of 9a – c under Corey-Winter conditions afforded the desired labeled nucleoside analogues 12a – c .

New air-stable zinc complexes formed from cyanoacrylate- and methylenemalonate-based [N2O2]-ligands and their role as catalysts in epoxide–CO2 coupling

The synthesis of a range of zinc complexes based on ligands displaying an N2O2-framework with cyanoacrylate and/or malonate functionality is presented. Some complexes could be examined via X-ray diffraction on single crystals, giving interesting insights into the structures of these zinc compounds, some of them building coordination polymers. The zinc complexes are highly active in the catalytic conversion of propylene oxide with CO2 to afford propylene carbonate. The study of this class of complexes leads to reactivity trends showing that ligands with aromatic diamino linkers and malonate fragments display the highest catalytic activity under mild conditions.

Aluminium triisopropoxide: An inexpensive and easy-to-handle catalyst of the copolymerisation of cyclohexene oxide with CO2

Aluminium triisopropoxide, a versatile and cheap oligomeric Lewis acid catalyst, easily reacts with carbon dioxide to build complex oligomeric aluminium alkoxo-alkylcarbonato compounds. A first series of experiments with cyclohexene oxide and CO2 showed that the catalyst is highly active in the copolymerisation with carbon dioxide and that a satisfactory carbon dioxide insertion takes place when the reaction is run at temperatures between 50 and 80 °C and pressures around 100 bar CO2. High yields of polyether-carbonates can be obtained (up to 1000 g of copolymer per g aluminium) with molecular weight up to 11 000 g mol−1 and a better selectivity of the CO2-insertion than other aluminium trialkoxides (carbonate to ether linkages ratio: 1 to 3). On the basis of 27Al-NMR spectra it can be seen that the high reactivity of the catalyst is due to a rearrangement of the stable tetrameric aluminium isopropoxide in a more reactive oligomer and, most likely, during the copolymerisation, to a further fragmentation into reactive monomeric species.

Synthesis, spectral and structural characterization of the zinc car☐ylate [Zn(2-quinolinecar☐ylato)2(1-methylimidazole)2]

Abstract Reaction of an aqueous suspension of zinc oxide with 2-quinolinecar☐ylic acid afforded, after recrystallization from a 1-methylimidazole/ acetonitrile solution, crystals of the anhydrous car☐ylate [Zn(2-quinolinecar☐ylato)2 (1-methylimidazole)2]. 1 [Zn(C10H6NO2)2 (C4H6N2)2], monoclinic, space group P21/n, a = 9.052(1), b = 9.626(1), c = 14.771(2)A, β = 105.48(1)°, V = 1240.4(3)A3, Z = 2. The zinc atom is hexacoordinated, located at an inversion center and exhibits a slightly distorted octahedral geometry. The Zn-equatorial ligand distances are 2.057(2)Afor Zn O and 2.244(2)Afor Zn N. The Zn N distance for the apical imidazole ligands is 2.144(2)A.

Study of different copper(I) catalysts for the "click chemistry" approach to carbanucleosides

We compare herein the scope of three copper (I) catalysts on the synthesis of various 1,4-disubstitued-1,2,3-triazolo-carbanucleosides through a microwave (and thermic) assisted Huisgen 1,3-dipolar cycloaddition. The tetrakis(acetonitrile)copper hexafluorophosphate ([Cu(CH 3 CN)4]PF 6 ), the imidazoline(mesythyl)copper bromide (Imes)CuBr, and the copper/copper sulfate Cu(0)/CuSO 4 (II) mixture have been chosen for this study. Their influence in a catalytic amount will be analyzed according to the substituent of the alkyne, the solvent, or the heating method.

Alkyl-substituted 2,6-dioxadiazolylpyridines as selective extractants for trivalent actinides

Abstract2,6-di(3-alkyl-1,2,4-oxadiazol-5-yl)pyridines, 2,6-di(5-alkyl-1,3,4-oxadiazol-2-yl)pyridines, and 2,6-di(5-alkyl-1,2,4-oxadiazol-3-yl)pyridines were synthesized and tested for their americium(III)-europium(III) selectivity by liquid-liquid extraction. 0.02M solutions of the compounds extract americium(III) 2-bromohexanoates as monosolvates, AmA3B, from solutions of pH 2, with an americium(III)-europium(III) separation factor of up to 23. Decreasing the alkyl chain length (butyl < ethyl < methyl) or the polarity of the diluent (chlorobenzene < toluene < tert.-butyl benzene) increased both americium(III) distribution ratio and americium(III)-europium(III) separation factor.

New Phosphacyclic Molecules and Their Application aS Flame Retardants for Epoxy Resins

Abstract 9,10-Dihydro-9,10-oxa-10-phosphaphenanthrene-10-oxide (DOPO) has been commercialized as a gas phase active flame retardant. Its P‒H bond allows its reactive incorporation into epoxy resins and formation of new additives via Michael-like addition. To better understand of the role of radicals in the flame retardant mechanism, 9,10-dihydro-9-aza-10-phosphaphenanthrene-10-oxide (DAPO) and 9,10-dihydro-9,10-oxa-10-phosphaphenanthrene-10-sulfide (DOPS) were synthesized. DAPO was found to undergo unprecedented tautomerism for a P(V) cycle. The detailed synthetic approach and spectroscopic characterization of DAPO and the flame retardant behavior of DAPO and DOPS will be discussed.

Synthesis of a novel heterocyclic ring system: 2-thia-3,5,6,7,9-pentaazabenz[cd]azulenes

Abstract Derivatives of 6,9-dihydro- and 6,7,8,9-tetrahydro-2-thia-3,5,6,7,9-pentaazabenz[cd]azulenes representing a new heterocyclic system have been prepared by the cyclocondensation reaction of ethyl 5-amino-4-(1-methylhydrazino)-2-methylthiothieno[2,3-d]-pyrimidine-6-carboxylate with ethyl orthoformate and various aldehydes.

Spectral Assignment of Phenanthrene Derivatives Based on 6H-Dibenzo[C,E][1,2] Oxaphosphinine 6-Oxide by NMR and Quantum Chemical Calculations

Abstract Organophosphorus compounds such as 6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide (DOPO, 1) and its derivatives are important and versatile compounds for a broad field of applications. However, a thorough spectral assignment is often subordinate to its chemical properties. This article presents and unambiguously attributes the 1H and 13C NMR spectra of DOPO (1), selected products yielded from the Atherton–Todd reaction (2–4), DOPO-HQ (5) as well as sulfur derivatives (6–7) via a set of 1D- and 2D-NMR experiments. The complex P-C and P-H coupling patterns are discussed and compared with the derivatives possessing different chemical environments around the phosphorus atom. In addition, we compared our results with density functional theory calculations. Even though the prediction of NMR data of organophosphorus compounds via molecular modeling is limited, this study presents a method that yields good results for this class of heterocycles. This knowledge should help to quickly assign NMR spectroscopic data of other DOPO (1) derivatives and can be extrapolated to organophosphorus compounds in general. Supplemental materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: NMR Spectra of Compounds 1-7 (Figures S1 - S15). GRAPHICAL ABSTRACT