Substitution kinetics of biphenol at dichlorobis(acetylacetonato-O,O′)titanium(IV): Isolation,characterization, crystal structure and enhanced hydrolytic stability of the product bis(acetylacetonato-O,O′)(biphenyldiolato-O,O′)titanium(IV)

Novel bis(acetylacetonato-O,O′)(biphenyldiolato-O,O′)titanium(IV) is synthesized and characterized by X-ray crystallography and other physical methods. The kinetics of substitution of bidentate 2,2′-biphenyldiolato for the two monodentate Cl⁻ ligands in Ti(CH₃COCHCOCH₃)₂Cl₂ proceeds via a 7-coordinated transition state according to an associative mechanism. The Ti(CH₃COCHCOCH₃)₂biphen complex exhibits high hydrolytic stability.     

Asymmetric synthesis of (−)-(S,S)-homaline

The asymmetric synthesis of (−)-(S,S)-homaline was achieved in 8 steps from commercially available starting materials using the diastereoselective conjugate addition of the novel lithium amide reagent lithium (R)-N-(3-chloropropyl)-N-(α-methyl-p-methoxybenzyl)amide to methyl cinnamate to install the correct stereochemistry. Subsequent functional group manipulation of the resultant β-amino ester and Sb(OEt)₃-mediated macrolactamisation was followed by homodimerisation to give (−)-(S,S)-homaline in 18% overall yield, representing the first asymmetric, and by far the most efficient synthesis of this natural product reported to date.     

Preparation and ring-opening reactions of N,O-bis(diphenylphosphinyl) hydroxymethylaziridine (‘Di-Dpp’)

N,O-bis(diphenylphosphinyl)-2-(hydroxymethyl)aziridine (‘DiDpp’, 1) is efficiently prepared from 2-aminoethane-1,3-diol: this activated aziridine undergoes two sequential reactions with copper(I)-modified Grignard reagents, yielding α-branched N-Dpp amines in good yield.     

Synthesis and some reactions of bis(triphenylstannyl)carbodiimide, N′-(triphenylstannyl)-N′-tritylcarbodiimide,and (triphenylstannyl)cyanamide

Some methods for preparing bis(triphenylstannyl)carbodiimide (I), N-(triphenylstannyl)-N′-tritylcarbodiimide (II), and (triphenylstannyl)cyanamide are described. (I) was found to react with 1,3-disubstituted thioureas in refluxing acetonitrile or toluene to give bis(triphenyltin) sulfide and the corresponding N,N′-disubstituted-N″-cyanoguanidine. Some evidence for a diorganocarbodiimide intermediate in this reaction was found. The reaction of(I) with thiourea in refluxing acetonitrile was found to give bis(triphenyltin) sulfide,(triphenylstannyl)cyanamide and unchanged thiourea. The reaction of (I) with cyanamide gave (triphenylstannyl)cyanamide. (Triphenylstannyl)cyanamide was found to react with bis(triphenyltin) oxide in refluxing acetonitrile to give (I). (Triphenylstannyl)cyanamide was found to disproportionate in refluxing benzene to give (I) and dicyandiamide. (II) was found to be more hydrolytically stable than (I). The SnN bonds in both (I) and (II) were found to be readily cleaved by acetic acid. It was found that triphenyltin iodide and triphenyltin chloride can be conveniently prepared in good yield by the reaction of bis(triphenyltin) oxide with either calcium iodide or calcium chloride in refiuxing acetonitrile.     

Formal chromium–chromium triple bonds and bent rings in the binuclear cycloheptatrienylchromium carbonyls (C7H7)2Cr2(CO)n (n = 6, 5, 4, 3, 2, 1, 0): A density functional theory study

Binuclear cycloheptatrienylchromium carbonyls of the type (C₇H₇)₂Cr₂(CO)_n (n = 6, 5, 4, 3, 2, 1, 0) have been investigated by density functional theory. Energetically competitive structures with fully bonded heptahapto η⁷-C₇H₇ rings are not found for (C₇H₇)₂Cr₂(CO)_n structures having two or more carbonyl groups. This result stands in contrast to the related (C_nH_n)₂M₂(CO)_n (M = Mn, n = 6; M = Fe, n = 5; M = Co, n = 4) systems. Most of the predicted (C₇H₇)₂Cr₂(CO)_n structures have bent trihapto or pentahapto C₇H₇ rings and CrCr distances in the range 2.4–2.5 Å suggesting formal triple bonds. In some cases rearrangement of the heptagonal C₇H₇ ring to a tridentate cyclopropyldivinyl or tridentate bis(carbene)alkyl ligand is observed. In addition structures with CO insertion into the C₇H₇–Cr bond are predicted for (C₇H₇)₂Cr₂(CO)_n (n = 6, 4, 2). The global minima found for the (C₇H₇)₂Cr₂(CO)_n derivatives for n = 6, 5, and 4 are (η⁵-C₇H₇)(OC)₂CrCr(CO)₄(η¹-C₇H₇), (η³-C₇H₇)(OC)₂CrCr(CO)₃(η^2,1- C₇H₇), and (η⁵-C₇H₇)₂Cr₂(CO)₄, respectively. The global minima for (C₇H₇)₂Cr₂(CO)_n (n = 3, 2) have rearranged C₇H₇ groups. Singlet and triplet structures with heptahapto η⁷-C₇H₇ rings are found for the dimetallocenes (η⁷-C₇H₇)₂Cr₂(CO) and (η⁷-C₇H₇)₂Cr₂, with the singlet structures being of much lower energies in both cases.     

Ruthenium(III) complexes with N-(acetyl)-N′-(5-R-salicylidene)hydrazines: Syntheses,structures and properties

The reactions of 1 mol equiv. each of [Ru(PPh₃)₃Cl₂] and N-(acetyl)-N′-(5-R-salicylidene)hydrazines (H₂ahsR, R = H, OCH₃, Cl, Br and NO₂) in alcoholic media afford simultaneously two types of complexes having the general formulae [Ru(HahsR)(PPh₃)₂Cl₂] and [Ru(ahsR)(PPh₃)₂Cl]. The complexes have been characterized by elemental analysis, magnetic, spectroscopic and electrochemical measurements. Molecular structures of [Ru(HahsH)(PPh₃)₂Cl₂] and [Ru(ahsH)(PPh₃)₂Cl] have been confirmed by X-ray crystallography. In both species, the PPh₃ ligands are trans to each other. The bidentate HahsH⁻ coordinates to the metal ion via the O atom of the deprotonated amide and the imine–N atom in [Ru(HahsH)(PPh₃)₂Cl₂]. In HahsH⁻, the phenolic OH is involved in a strong intramolecular hydrogen bond with the uncoordinated amide N atom forming a seven-membered ring. In [Ru(ahsH)(PPh₃)₂Cl], the tridentate ahsH²⁻ binds to the metal ion via the deprotonated amide O, the imine N and the phenolate O atoms. In the electronic spectra, the green [Ru(HahsR)(PPh₃)₂Cl₂] and brown [Ru(ahsR)(PPh₃)₂Cl] complexes display several absorptions in the ranges 385–283 and 457–269 nm, respectively. Both complexes are low-spin and display rhombic EPR spectra in frozen solutions. Both types of complexes are redox active and display a quasi-reversible ruthenium(III) to ruthenium(II) reduction which is sensitive to the polar effect of the substituent on the chelating ligand. The reduction potentials are in the ranges −0.21 to −0.12 and −0.42 to −0.21 V (versus Ag/AgCl) for [Ru(HahsR)(PPh₃)₂Cl₂] and [Ru(ahsR)(PPh₃)₂Cl], respectively.     

Bis(1,10‐phenanthroline‐N,N′)(thiosulfato‐O,S)­nickel(II)–water–methanol (1/0.92/1.4) and bis(2,2′‐bi­pyridyl‐N,N′)(thiosulfato‐O,S)nickel(II)–water–methanol (1/2/0.55)

The title compounds, [Ni(S₂O₃)­(C₁₂H₈N₂)₂]·­0.92H₂O·­1.4CH₄O and [Ni(S₂O₃)­(C₁₀H₈N₂)₂]·­2H₂O·­0.55CH₄O, are monomeric, containing nickel(II) in a distorted octahedral coordination environment provided by the four N atoms of two bidentate bipy or phen groups and one S and one O atom from a chelating thio­sulfate anion. The crystals are highly unstable outside their mother liquors and are stabilized in solution by a not fully determined number of water and methanol solvate mol­ecules. The phenanthroline structure includes two independent moieties related by a non‐crystallographic inversion center. The thio­sulfate anions display the usual S—O lengthening found when the anion acts in a bidentate mode.     

Synthesis, photochemical, and electrochemical properties of naphthalene-1,4,5,8-tetracarboxylic acid-bis-(N,N′-bis-(2,2,4(2,4,4)-trimethylhexylpolyimide)) and poly(N,N′-bis-(2,2,4(2,4,4)-trimethyl-6-aminohexyl) 3,4,9,10-perylenetetracarboxdiimide)

Two new soluble polymers (naphthalene containing: TH-NPI, perylene containing: TH-PPI) have been synthesized via incorporation of branched chain substituent unit into their backbones. Because of existence of branched alkyl spacer, the polymers showed good solubility in common solvents such as chloroform without sacrificing their stability and caused a red shifted excimer-like emission. Their monomers (TH-NDI and TH-PDI) have been synthesized for comparison. The compounds are characterized by UV-vis, IR, MS, DSC, TGA, CV, GPC and viscosity measurements. Polymers TH-NPI and TH-PPI with inherent viscosities of 0.50 and 0.30 dL/g were obtained corresponding to their molecular weights 40,000 and 17,000 respectively. Thermogravimetric analysis (TGA) showed that TH-NDI, TH-NPI, TH-PDI and TH-PPI are thermally stable up to 380, 445, 512 and 515 °C respectively. The LUMO energy levels of these compounds are calculated as −3.66, −3.71, −3.62 and −3.61 eV respectively. The red-shifted (TH-NPI: 400-650 nm, TH-PPI: 535-800) excimer-like fluorescence in chloroform is attributed to the formation of ground state complexes probably due to intermolecular and intramolecular π-stackings of the polymers in solution. The fluorescence lifetimes, quantum yields and singlet-state energies are presented.     

Synthesis and characterisation of alkyl-N,N′-bis(salicylidene)ethylenediamino- and alkyl-N,N′-bis(salicylidene)-1,2-phenylenediaminogallium or indium complexes: crystal structure of methyl-N,N′-bis(salicylidene)-1,2-phenylenediaminoindium

The reaction of trialkylgallium or indium R₃M (M=In, Ga; R=Me, Et) with N,N′-ethylenebis(salicylideneimine) or 1,2-N,N′-phenylenebis(salicylideneimine) yields seven intramolecularly coordinated organogallium or organoindium complexes. Two hydroxyl protons in the ligands react with both trialkylindium and trimethylgallium, while one hydroxyl group reacts exclusively with triethylgallium. The complexes obtained have been fully characterised by elemental analysis, ¹H-NMR, IR and mass spectroscopy. The structure of methyl-N,N′-bis(salicylidene)-1,2-phenylenediaminoindium (1) has been determined by single-crystal X-ray analysis. The In atom is five coordinate in the structure. Fluorescence spectroscopy has shown that the maximum emission wavelength of 1 is 499 nm upon radiation by UV light.     

Reactivity of M(en)Cl2 (M = Pd/Pt,en = 1,2-diaminoethane) with N,N′-bis(salicylidene)-p-phenylenediamine: Binding with hexafluorobenzene

Schiff base N,N′-bis(salicylidene)-p-phenylenediamine (LH₂) complexed with Pt(en)Cl₂ and Pd(en)Cl₂ provided [Pt(en)L]₂ · 4PF₆ (1) and Pd(Salen) (2) (Salen = N,N′-bis(salicylidene)-ethylenediamine), respectively, which were characterized by their elemental analysis, spectroscopic data and X-ray data. A solid complex obtained by the reaction of hexafluorobenzene (hfb) with the representative complex 1 has been isolated and characterized as 3 (1 · hfb) using UV–Vis, NMR (¹H, ¹³C and ¹⁹F) data. A solid complex of hfb with a reported Zn-cyclophane 4 has also been prepared and characterized 5 (4 · hfb) for comparison with complex 3. The association of hfb with 1 and 4 has also been monitored using UV–Vis and luminescence data.     

Enantioselective synthesis of (2S,3′R,7′Z)-N-(3′-hydroxy-7′-tetradecenoyl)-homoserine lactone

A concise enantioselective total synthesis of (2S,3′R,7′Z)-N-(3′-hydroxy-7′-tetradecenoyl)-homoserine lactone is described. Key feature of this protocol is a catalytic asymmetric hydrogenation and a prophenol-zinc-catalyzed diazo addition to imine reaction as genesis of chirality. Moreover, flexibility is built in the synthesis to generate enantioenriched analogs using catalytic amount of enantioenriched C₂-symmetric ligands.     

Calorimetric determination of enthalpy changes for the proton ionization of glycine, N,N-bis(2-hyroxyethyl)glycine (“bicine”) and N-tris(hydroxymethyl)methylglycine (“tricine”) in water-methanol mixtures

Enthalpies for the two proton ionizations of glycine, N,N-bis(2-hyroxyethyl)glycine (“bicine”) and N-tris(hydroxymethyl)methylglycine (“tricine”) were obtained in water-methanol mixtures with methanol mole fraction (X_m) from 0 to 0.360. With increasing methanol the ionization enthalpy for the first proton (ΔH₁) of glycine increased from 4.4 to 9.4 kJ mol⁻¹ with a minimum of 4.1 kJ mol⁻¹ at X_m = 0.059. The ionization enthalpy of the second proton (ΔH₂) for glycine decreased from 46.3 to 38.1 kJ mol⁻¹. ΔH₁ of bicine increased from 3.5 to 7.6 kJ mol⁻¹ at X_m = 0.273 before dropping to 4.1 kJ mol⁻¹ at X_m = 0.360. ΔH₂ of bicine increased from 24.9 to 29.4 kJ mol⁻¹. For tricine, ΔH₁ increased from 6.7 to 9.8 kJ mol⁻¹ at X_m = 0.194 then dropped to 7.4 kJ mol⁻¹ at X_m = 0.360. ΔH₂ for tricine first dropped from 30.8 to 28.5 kJ mol⁻¹ at X_m = 0.059 before increasing to 33.3 kJ mol⁻¹ at X_m = 0.273. The solvent composition was selected so as to include the region of maximum structure enhancement of water by methanol. The results were interpreted in terms of solvent-solvent and solvent-solute interactions.     

On the reduced form of (imidazole-N)(N-salicylidene-alaninato-O,N,O′) copper(II)

The geometries of the (imidazole-N³)(N-salicylidene-alaninato-O,N,O′) copper(II) and of its anion as well as of six models of its neutral hydrogenated form with the additional hydrogen at oxygen or nitrogen sites modeling its reduced copper(I) form are optimized using the gaussian 98 program package at B3LYP/6-31G* level of theory. Energy data indicate the highest stability of the structures with additional hydrogen bonded to some of carboxyl oxygens with released (or significantly weakened) Cu–O(carboxyl) bond. Hydrogen atom is inserted into this bond in the second most stable model system (with ca. 1 kJ/mol higher energy).