18-membered cyclic esters derived from glycolide and lactide: preparations, structures and coordination to sodium ions

From reactions between glycolide or lactide (4 equiv.) with 4-dimethylaminopyridine, DMAP (1 equiv.) and NaBPh(4) (1 equiv.) in benzene at 70 degrees C the cyclic ester adducts (CH(2)C(O)O)(6)NaBPh(4) and (CHMeC(O)O)(6)NaBPh(4) are formed respectively. The structures of the salts Na[(S,R,S,R,S,R)-(CH(3)CHC(O)O)(6)](2)BPh(4).CH(3)CN and (CH(2)C(O)O)(6)NaBPh(4).(CH(3)CN)(2) are reported. The cyclic esters were separated by chromatography and the structures of (CH(2)C(O)O)(6), (S,R,R,R,R,R)-(CHMeC(O)O)(6) and (S,S,R,R,R,R)-(CHMeC(O)O)(6) were determined. The (1)H and (13)C NMR data are reported for one of each of the six enantiomers of (CHMeC(O)O)(6) and the two meso isomers. The mechanism for the formation of these 18-membered rings is discussed in terms of an initial reaction between DMAP and NaBPh(4) in hot benzene that produces NaPh and DMAP:BPh(3) in the presence of the monomer lactide. The cyclic esters (CHMeC(O)O)(6) can also be obtained from the reaction between polylactide, PLA, in the presence of DMAP and NaBPh(4). The cyclic esters 3-methyl-1,4-dioxane-2,5-dione and 3,6,6-trimethyl-1,4-dioxane-2,5-dione undergo similar ring enlarging reactions to give cyclic 18-membered ring esters as determined by ESI-MS.     

Construction Of Two New 6‐connected Manganese(II) Metal Organic Frameworks via Isomeric Biphenyldicarboxylates Based on the Dinuclear Secondary Building Unit

Two coordination polymers, namely {[Mn(2,4′‐bpdc)(bimb)(H₂O)_0.5] · 0.5H₂O}_n ( 1 ) and [Mn(4,4′‐bpdc)(bimb)]_n · 2.5H₂O ( 2 ) [2,4′‐bpdc = biphenyl‐2,4′‐dicarboxylate, 4,4′‐bpdc = biphenyl‐4,4′‐dicarboxylate, and bimb = 1,4‐bis(1‐imidazol‐yl)‐2,5‐dimethyl benzene], were hydrothermally synthesized by reactions of manganese(II) salt with the rigid ligand 1,4‐bis(1‐imidazol‐yl)‐2,5‐dimethyl benzene and isomeric biphenyl dicarboxylate ligands. Complex 1 has an unusual 6‐connected three‐dimensional (3D) architecture with point symbol (4⁴.6¹¹). Complex 2 has also a 3D structure with two‐interpenetrated pcu topology with point symbol (4¹².6³). Structural comparisons show that the positions of the carboxylate groups in the ligand backbone play an important role in governing the structural topologies of these complexes.     

Synthesis and properties of azobenzocrown ethers with π-electron donor, or π-electron donor and π-electron acceptor group(s) on benzene ring(s)

New azobenzocrown ethers of differentiated size and with substituted benzene residues have been synthesized. These crown ethers possess π-electron donor, or π-electron donor-π-electron acceptor pair of functional group(s) in benzene ring(s) in the para position to azo-grouping. Their metal ion complexation abilities in solution were studied using UV-vis spectrophotometry. The X-ray structure of a 19-membered crown ether with 4-dimethylamino-4′-nitroazobenzene fragment has been solved.     

Novel design of 3,8-diazabicyclo[3.2.1]octane framework in oxidative sulfonamidation of 1,5-hexadiene

1,5-Hexadiene reacts with trifluoromethanesulfonamide in the oxidative system (t-BuOCl+NaI) to give trans-2,5-bis(iodomethyl)-1-(trifluoromethylsulfonyl)pyrrolidine 5 and 3,8-bis(trifluoromethylsulfonyl)-3,8-diazabicyclo[3.2.1]octane 6. With arenesulfonamides ArSO₂NH₂ (Ar=Ph, Tol), the reaction stops at the formation of the trans and cis isomers of 2,5-bis(iodomethyl)-1-(arenesulfonyl)pyrrolidine 7 and 8 (1:1). The cis isomers of 7 and 8 do not undergo cyclization to the corresponding 3,8-disubstituted 3,8-diazabicyclo[3.2.1]octanes. The reaction with triflamide represents the first example of one-pot two-step route to 3,8-diazabicyclo[3.2.1]octane system.     

Syntheses,structures and properties of copper(II) complexes with thiophene-2,5-dicarboxylic acid (H2Tda) and nitrogen-containing ligands

Five copper(II) complexes with thiophene-2,5-dicarboxylic acid (H₂Tda): Cu(Tda)(H₂O)⋅(H₂O)₂ (1), Cu(Tda)(im)₂⋅(H₂O) (2), Cu(Tda)(im)₄ (3), [Cu(Tda)(py)₂]_n (4) and [Cu(Tda)(bipy)(H₂O)]_n⋅n[Cu(Tda)(bipy)(H₂O)₂]⋅2nH₂O (5) (im=imidazole, py=pyridine and bipy=2,2′-bipyridine) have been synthesised and their spectroscopic and thermal properties investigated. Three of them (3, 4 and 5) are structurally characterised and the Cu atom is in five coordinate, distorted square pyramidal environments. The thiophene-2,5-dicarboxylate molecule is monodentate in 3 in which the molecular structure is stabilised by intermolecular hydrogen bonding involving two of the four non-coordinated nitrogen atoms of the imidazole ligands and carboxylate groups from adjacent Tda²⁻. In 4 the thiophene-2,5-dicarboxylate ion is bridging tridentate and bonded to three copper atoms to form a chain polymer with alternating 16-membered ring bridged by two Tda²⁻ and an 8-membered ring bridged by two carboxylates. Complex 5 comprises discrete [Cu(Tda)(bipy)(H₂O)₂] (5a), one dimensional zig–zag chain of [Cu(Tda)(bipy)(H₂O)]_n (5b) and water molecules of crystallization. The thiophene-2,5-dicarboxylate molecule is monodentate in 5a and involved in intermolecular stacking interactions with 2,2'-bipyridine rings, and bidentate in 5b to bridge [Cu(bipy)(H₂O)] to form a one dimensional zig–zag chain.     

Ruthenium(II) and iron(II) complexes of N-pyridyl substituted imidazolin-2-ylidenes

N-mesityl-N′-pyridyl-imidazolium chloride 1a and the corresponding bromide salt 1b have been deprotonated with NaH in THF giving the free N-heterocyclic carbene N-mesityl-N′-pyridyl-imidazolin-2-ylidene 2 in 80% yield (starting from 1a). Imidazolium salt 1a reacts with RuCl₃ · xH₂O to give a racemic mixture of dinuclear di-μ-chloro bridged ruthenium complexes [(κ²-2)₂Ru(μ-Cl)₂Ru(κ²-2)₂]²⁺ [3a]²⁺. The carbene carbon atoms as well as the halides are arranged in cis-positions to each other whereas the nitrogen atoms adopt a trans-configuration. The di-μ-bromo bridged derivative [(κ²-2)₂Ru(μ-Br)₂Ru(κ²-2)₂]²⁺ [3b]²⁺ was obtained from RuCl₃ · xH₂O and 1b. The bridging halide ligands can be removed by the reaction with silver or sodium salts of bidentate Lewis acids. Complex [3a]²⁺ reacts with silver pyridylcarboxylate to give a racemic mixture of the mononuclear complex [4]⁺. Reaction of [3a]²⁺ with the sodium salt of l-proline resulted in a diastereomeric mixture of complexes [5]⁺. The free N-heterocyclic carbene 2 reacts with [FeCl₂(PPh₃)₂] to give after anion exchange with NaBPh₄ cis/cis/trans coordinated [Fe(κ²-2)₂(MeCN)₂](BPh₄)₂ [6](BPh₄)₂. The molecular structures of [3b](PF₆)₂, [4]PF₆ and [6](BPh₄)₂ · H₂O are reported.     

Comparison of conventional and synchrotron X‐ray structure deter­minations of the adduct 1,2,4,5‐tetrahydroxybenzene–2,5‐dihydroxy‐1,4‐benzoquinone (1/1) and a conventional X‐ray structure determination of 1,2,4,5‐tetrahydroxybenzene monohydrate

The X‐ray structure of 1,2,4,5‐tetra­hydroxy­benzene (benzene‐1,2,4,5‐tetrol) monohydrate, C₆H₆O₄·H₂O, (I), reveals columns of 1,2,4,5‐tetra­hydroxy­benzene parallel to the b axis that are separated by 3.364 (12) and 3.453 (11) Å. Molecules in adjacent columns are tilted relative to each other by 27.78 (8)°. Water mol­ecules fill the channels between the columns and are involved in hydrogen‐bonding interactions with the 1,2,4,5‐tetra­hydroxy­benzene mol­ecules. The crystal structure of the adduct 1,2,4,5‐tetra­hydroxy­benzene–2,5‐di­hydroxy‐1,4‐benzo­quinone (1/1), C₆H₆O₄·C₆H₄O₄, (II), reveals alternating mol­ecules of 1,2,4,5‐tetra­hydroxy­benzene and 2,5‐di­hydroxy‐1,4‐benzo­quinone (both lying on inversion centers), and a zigzag hydrogen‐bonded network connecting mol­ecules in three dimensions. For compound (II), the conventional X‐ray determination, (IIa), is in very good agreement with the synchrotron X‐ray determination, (IIb). When differences in data collection temperatures are taken into account, even the displacement parameters are in very good agreement.     

Reactions of 2,5-pyrrolediylbis[N-(o-hydroxyphenylaldimine)] with some metal ions

The novel Schiff-base 2,5-pyrrolediylbis[N-(o-hydroxyphenylaldimine)] (SBH₂) has been synthesized by the condensation of 2,5-pyrroledicarboxaldehyde and o-amino-phenol. The reactions of the Schiff-base with several transition- and post-transition-metal ions have been investigated. The Schiff-base reacts as a tetradentate dianion without deprotonation of the pyrrole. The complexes M(SB)·nH₂O have been isolated and characterized with n = 1, 2 or 3; SB is the dianion of the Schiff-base; and M = divalent Mn, Co, Ni, Cu, Zn, Pd, Cd, Pb or UO₂. The binuclear complexes M(SB)MX₂ for M = Cu, X = NO₃, and M = Ni or Pd, X = Cl, have also been isolated.     

Fluorimetric determination of beryllium with 4-methyl-6-acetyl-7-hydroxycoumarin

Summary The acid dissociation constant of 4-methyl-6-acetyl-7-hydroxycoumarin, as determined by spectrophotometry was found to be K_a=9.77×10^–9. Beryllium reacts with this reagent to form a water-insoluble complex that can be extracted into benzene. The maximum wavelengths of the excitation and emission spectra of the beryllium complex in benzene are 403 and 465 nm, respectively. Beryllium can be determined in the range 0.0050.1 g per 10 ml benzene when extracted from the solution at pH 7.57.8 into benzene.     

The ligational behaviour of thiosemicarbazones and semicarbazones with tellurium(IV)—reactions with TeCl4

The reactions of thiosemicarbazones and semicarbazones of benzaldehyde, salicylaldehyde, acetophenone and 2-hydroxyacetophenone with TeCl₄ give the complexes LTeCl₄, (LH)TeCl₃ or (LH)Te₂Cl₇ (L = semicarbazone or thiosemicarbazone). The structural features of these tellurium derivatives are explored by IR, ¹H and ¹³C NMR, and conductance (in acetonitrile) measurements, and structures based on an octahedral arrangement of ligands around tellurium are proposed. The presence of facial and meridian isomers in equilibrium is indicated in some cases. The complexation occurs through S/O, the nitrogen of the > CN group and O⁻ (if present on benzene ring). The (LH)Te₂Cl₇ species seem to have chlorine bridged and octahedrally coordinated tellurium.     

Kinetic Study of the Substitution Reactions of Triphenylphosphine with Chlorobenzyl Chlorides,Dimethylbenzyl Chloride,and Methylbenzyl Bromides in Various Two-Phase Organic Solvent/Water Media

The kinetics of the substitution reactions of triphenylphosphine (TP) with chlorobenzyl chlorides (CBC), 2,5-dimethylbenzyl chloride (DMBC), and methylbenzyl bromides (MBB) in aprotic organic solvent was studied under the extraction by water. The effects of water, agitation, organic solvent, reactant, and temperature were investigated. These reactions take place via the S_N2 mechanism and exhibit large and negative entropy of activation. The order of relative activity of solvents is CHCl₃ > CH₂Cl₂ ? C₆H₆. In CHCl₃, the order of relative reactivity of benzyl chloride (BC), benzyl bromide (BB), CBC, DMBC, and MBB toward reaction with TP is 2-MBB > 4-MBB > 3-MBB > BB > DMBC > BC > 2-CBC > 4-CBC > 3-CBC. These reactions produce quantitatively benzyltriphenylphosphonium salts, which are useful for synthesizing Z-form isomers of stilbenes via the two-phase Wittig reaction.     

2D and 1D Coordination Polymers with the Ability for Inclusion of Guest Molecules: Nitrobenzene, Benzene, Alkoxysilanes

The complexation reactions of the electron rich, linear and bi-functional ligand, 9,10-bis(4-pyridyl)anthracene, with metal salts Cd(NO₃)₂, CdI₂, CoI₂ and CuI in the presence of guest molecules nitrobenzene, benzene and alkoxysilanes were studied. The single crystal analyses of the complexes reveal that an electron deficient guest molecule such as nitrobenzene consistently templated the open two-dimensional network with grid dimensions of ca. 15 × 15Å. On the other hand the presence of benzene or alkoxysilane templated1D-zigzag chains and/or 2D-grid layers. The crystal structures revealthe importance of host–guest interactions in tailoring the network architectures ofcoordination polymers.     

η-Arene complexes of ruthenium and osmium with pendant donor functionalities

Conversion of 4′-(2,5-dihydrophenyl)butanol or N-trifluoroacetyl-2,5-dihydrobenzylamine with MCl₃·n H₂O (M = Ru, Os) affords the corresponding dimeric η⁶-arene complexes in good to excellent yields. Under similar reaction conditions, the amine functionalized arene precursor 2,5-dihydrobenzylamine yields the corresponding Ru(II) complex. For osmium, HCl induced oxidation leads to formation of [OsCl₆]²⁻ salts. However, under optimized reaction conditions, conversion of the precursor 2,5-dihydrobenzylamine chloride results in clean formation of η⁶-arene Os(II) complex. X-ray structures of [(η⁶-benzyl ammonium)(dmso)RuCl₂] and (2,5-dihydrobenzyl ammonium)₄[OsCl₆]₂confirm the spectroscopic data. High stability towards air and acid as well as enhanced solubility in water is observed for all η⁶-arene complexes.     

Thermal and spectroscopic properties of light lanthanides (III) and sodium complexes of 2,5-pyridinedicarboxylic acid

Pyridine-2,5-dicarboxylic acid, known as isocinchomeric acid is one of six isomers containing two carboxylic groups. Light lanthanide (III) complexes with pyridine-2,5-dicarboxylic acid with general formula Ln₂L₃·nH₂O, where n = 8, 9, were obtained. Their thermal and spectroscopic properties were studied. Sodium salt was obtained as Na₂L·H₂O. Hydrated complexes of La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III) and Gd(III) are stable to 313–333 K, whereas Na₂L·H₂O is stable to about 333 K. Dehydration process for all compounds runs in one stage, next they decompose into appropriate lanthanide oxalates, oxocarbonates carbonates and finally to metal oxides. Bands of νCOOH vibrations at 1736 and 1728 cm⁻¹ disappear on complex spectra and ν_as and ν_s of COO⁻ groups appear thus indicating that complexation process took place.     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

Two novel 3-D coordination polymers based on isonicotinic acid: Syntheses, crystal structures and fluorescence

The hydrothermal reactions of isonicotinic acid (HIso) and metal salts yielded two novel 3-D coordination polymers {[Cu₄(Iso)₄(μ₃-O)₂(C₂H₅OH)₂]·2C₂H₅OH·C₂H₆N₄}_n (1), {[Cd(Iso)₂(H₂O)]·OHCCHO}_n (2), in which 1 was constructed from 32-membered rings and 3-D interpenetrating network of 2 from 42-membered rings. The fluorescent characterizations show the emissions at 565 nm for 1 and 440 nm for 2 possibly assigned to LMCT and IL, respectively.     

Deamination process in the formation of a copper(II) complex with glutamic acid and a new ligand derived from guanidinoacetic acid: Synthesis,characterization, and molecular modeling studies

A deamination process was observed after copper(II) complexation reaction with guanidinoacetic (Gaa) and glutamic acids (Glu), forming the binuclear copper(II) complex K₂Cu₂C₁₆H₂₃N₇O₁₂ · 1/2H₂O (1), which was characterized by elemental analysis (CHN), spectroscopy methods (IR and EPR), powder X-ray diffraction, thermogravimetric analysis (TGA), and mass spectrometry. A new ligand, namely biguanide-1,5-diethanoate (Bge) (C₆H₉N₅O₄), was formed during complexation, probably due to the reaction between two Gaa species and the consequent release of a significant amount of ammonia, thus, characterizing the deamination process. In complex 1, Bge behaved as a tetradentated ligand, using its oxygen and nitrogen atoms as coordinating sites to both Cu(II) ions. In addition, Glu has coordinated to Cu(II) through its α-N and O atoms. Theoretical calculations of the cis–cis, cis–trans, and trans–trans isomers of 1, considering three prototropic forms of the Bge ligand, were carried out using semi-empirical quantum mechanics (PM3/d). DFT (B3LYP and B3P86) calculations of complex 1, in which a hydrogen atom replaced the side chain of Glu, were also carried out using the 6-31G(d) basis set and the LanL2DZ effective core potential for the transition metal. Based on experimental and theoretical data, we concluded that the trans–trans isomer of the binuclear copper(II) complex 1 should be the most stable, although the occurrence of other isomers, even if in minor quantities, should not be disregarded.     

Effect of addition of trifluoroacetic acid on the photophysical properties and photoreactions of aromatic imides

The UV and IR spectra of N-methyl-1,8-naphthalimide in benzene showed a two-step consecutive complexation (hydrogen bond formation) with trifluoroacetic acid (TFA). The equilibrium constant K₁ for the first complexation in benzene was determined from the UV spectrum to be 48 M⁻¹. The fluorescence intensities of the imide in benzene were found to be remarkably enhanced by the addition of TFA. Furthermore, photochemical cyclobutane formation of the imide with styrene in benzene was enhanced by the addition of TFA. Enhancement of the fluorescence intensity and the photoreaction of the imide by complexation with TFA was explained by a decrease of the efficiency of the intersystem crossing from ¹(ππ^∗) to ³(nπ^∗), that results from an increase in the energy of the ³(nπ^∗) level due to the complexation.     

On the chemical resolution of the 87Rb+ (s0)/87Sr+ (s1) isobaric interference: a kinetic search for an optimum reagent

Room-temperature reactions of the atomic cations Sr⁺ and Rb⁺ have been surveyed systematically with a variety of gases using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients and product distributions have been measured in He buffer gas at 0.35 Torr and 295 K for reactions of Sr⁺ and Rb⁺ with CH₃F, CH₃Cl, N₂O, CO₂, CS₂, SF₆, D₂O and NH₃. Rb⁺ (s⁰) is seen to be quite inert with these molecules and reacts either slowly by molecule addition or not at all, while Sr⁺ (s¹) is much more reactive with all these 8 molecules, especially with CH₃F, CH₃Cl, N₂O and SF₆. Sr⁺ reacts with CH₃F and SF₆ by F-atom transfer, with CH₃Cl by Cl-atom transfer and with N₂O by O-atom transfer, and the reaction rate coefficients are all quite high, k ≥ 1.4 × 10⁻¹¹ cm³ molecules⁻¹ s⁻¹. The extreme differences in reactivity with CH₃F, SF₆, CH₃Cl and N₂O provide a chemical basis for the separation of isobaric interferences of ⁸⁷Rb⁺ and ⁸⁷Sr⁺ often encountered in ICP-MS. Among these four molecules, SF₆ exhibits the largest difference in reactivity, almost a factor of 10⁴, and so is identified as the kinetically recommended reagent for the chemical resolution of the isobaric interference of ⁸⁷Rb⁺ and ⁸⁷Sr⁺.     

Regio- and stereoselective reactions between cyclic Baylis-Hillman type adducts and N-nucleophiles and P-nucleophile

New important organic compounds multifunctionalized cyclic 6-membered and 7-membered allylic amines, azide and phosphonates have been obtained via regio- and diastereoselective reactions of cyclic Baylis-Hillman type adducts 1 with N-nucleophiles and P-nucleophile. We have found that the reactions proceed by S_N2 or S_N2′ processes exclusively, or by both processes simultaneously. The S_N2′ process occurs with anti stereochemistry.