Synthesis and structural characterization of mixed carbene-carboxylate complexes of palladium(II)

Mixed carbene-carboxylate complexes of Palladium(II) have been prepared by reacting {1,1^′-dimethyl-3,3^′-methylenediimidazoline-2,2^′-diylidene} palladium(II) diiodide (1) [Angew. Chem. 107 (1995) 2602; Angew. Chem. Int. Ed. Engl. 34 (1995) 2371; J. Organomet. Chem. 557 (1998) 93] with AgO₂CR, where R=CF₃, CF₂CF₃ and CF₂CF₂CF₃. In this manner, {1,1^′-dimethyl-3,3^′-methylenediimidazoline-2,2^′-diylidene} palladium(II) bis(trifluo-roacetate) (2), {1,1^′-dimethyl-3,3^′-methylenediimidazoline-2,2^′-diylidene} palladium(II) bis(pentafluoropropionate) (3) and {1,1^′-dimethyl-3,3^′-methylenediimidazoline-2,2^′-diylidene} palladium(II) bis(heptafluorobutyrate) (4) were obtained. All three complexes were fully characterized by ¹H-, ¹³C- and ¹⁹F NMR spectroscopy as well as ESI mass spectrometry. X-ray crystal structure analyses of complexes 3 and 4 reveal mononuclear species with a square planar metal center coordinated by a cis-chelating dicarbene and two monodentate carboxylate ligands. The results show that the introduction of a cis-chelating N,N-heterocyclic carbene ligand stabilizes the palladium-carboxylate moiety effectively.     

Synthesis of a new bidentate ferrocenyl N-heterocyclic carbene ligand precursor and the palladium (II) complex trans-[PdCl2(CfcC)], where (CfcC) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene

A new ferrocenyl-N-heterocyclic carbene ligand precursor 1,1′-bis[(1-tert-butylimidazolium)-3-methyl]ferrocene dichloride has been synthesised and structurally characterised. The imidazolium salt was readily deprotonated in situ with KN(SiMe₃)₂ and reacted with [PdCl₂ (cod)] to afford the structurally characterised palladium (II) complex trans-[PdCl₂(C^∧fc^∧C)], where (cod) = 1,5-cyclooctadiene and (C^∧fc^∧C) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene.     

Acyclic tertiary diamines and 1,4,7,10-tetraazacyclododecane with fluorine-containing β-diketones: Leading to low melting ionic adducts

N,N,N′,N′-Tetramethylmethanediamine (1a), N,N,N′,N′-tetramethylethanediamine (1b), N,N,N′,N′-tetramethyl-1,3-propanediamine (1c), and N,N,N′,N′-tetramethyl-1,6-hexanediamine (1d) were reacted at 25 °C with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2a), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (2b), 2-thenoyltrifluoroacetone (2c), and 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (2d) to form the ionic adducts 3-18. 1,4,7,10-Tetraazacyclododecane (1e) reacted at 25 °C with β-diketones (2a-d) and 1,1,1-trifluoro-2,4-pentanedione (2e) to give ionic solids 19-23 in good yields. Some of the products are liquid at 25 °C and are thermally stable over long liquid ranges as determined by thermal gravimetric analyses. Single-crystal X-ray structure determinations show that compounds 9 and 21 crystallize in the monoclinic space groups P2(1)/c and P2(1)/n, respectively. All the new compounds were characterized by ¹H, ¹⁹F and ¹³C NMR, electrospray MS and/or elemental analyses.     

Guests inducing p-sulfonatocalix[4]arenes into nanocapsule and layer structure

Reaction of sodium p-sulfonatocalix[4]arene and TbCl₃ in the presence of 2,2′-bipyridine-N,N′-dioxide (bpdo) gives the 2:1 supramolecular nanocapsule [[Tb(bpdo)₂·4H₂O]³⁺?{p-sulfonatocalix[4]arene⁴⁻}₂], which further interacts with the [Tb(bpdo)₄]³⁺ through charge-assisted π-stacking interactions forming a channel structure 1. In further investigation, we tried to use the terpyridine-1,1′,1′-trisoxide (tpto) instead of bpdo. Although we failed to isolate a supramolecular capsules based on the tpto, lanthanide and p-sulfonatocalix[4]arene, a layer structure derived from p-sulfonatocalix[4]arene with an unusual [Cu(tpto)₂]²⁺ incorporation into the cavity of the calixarene and an outside [Cu(tpto)₂]²⁺ balancing the charge, has been obtained. Fluorescence spectra show clearly that compound 1 possesses the luminescence characteristics of Tb³⁺ and the ligand bpdo can sensitize Tb³⁺ ion. Gas sorption experiment shows the channel structure 1 has highly selective gas sorption properties for water and methanol.     

A novel 4.6 5-connected metal-organic framework with strong fluorescent emission constructed by m-thioacetatebenzoic acid

A novel uninodal 5-connected metal-organic framework (MOF), [Cd₂L₂(4,4′-bipy)_3/2(H₂O)₂]_n (H₂L=m-thioacetatebenzoic acid and 4,4′-bipy=4,4′-bipyridine), was prepared under hydrothermal condition. It features an unusual brick-wall shape layer by 4,4′-bipy, which consists of right- and left-handed helical chains arrayed alternatively and finally expands by L^2- to a rare 5-connected nov (4⁴.6⁶) topology network. Photoluminescence study reveals that it displays intense structure-related fluorescent emission bands (λ_ex=355 nm) at 450 nm in the solid state at room temperature.     

New soluble aromatic polyamides containing ether linkages and laterally attached p-terphenyls

Two series of new polyamides containing flexible ether linkages and laterally attached side rods (3a-i and 4a-i) were synthesized from 2^′,5^′-bis(4-aminophenoxy)-[1,1^′;4^′,1^″]terphenyl (1a) and 2^′,5^′-bis(4-amino-2-trifluoromethylphenoxy)-[1,1^′;4^′,1^″]terphenyl (1b), respectively, with various aromatic dicarboxylic acids by the direct phosphorylation polycondensation. The polymers were produced with high yields and moderate to high inherent viscosities (0.41-0.97 dl/g) that corresponded to weight-average molecular weights (by size exclusion chromatography) of 47,000-65,000. Except for some polyamides that derived from rigid diacids, the obtained polyamides were readily soluble in aprotic polar solvents, such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc), and could afford flexible and tough films via solvent casting. The polymer films cast from DMAc solutions possessed tensile strengths of 85-106 MPa and initial moduli of 1.82-2.96 GPa. These polyamides showed glass-transition temperatures (T_g) in the range of 206-263 °C (by DSC) and softening temperatures (T_s) in the range of 211-253 °C (by TMA). Decomposition temperatures (T_d) for 10% weight loss all occurred above 400 °C (by TGA) in both nitrogen and air atmospheres. The polyamides 4a-i derived from trifluoromethyl-substituted diamine 1b generally showed a higher solubility, T_g and T_s but lower thermal stability as compared to the analogous polyamides 3a-i based on diamine 1a.     

Simultaneous measurement of trace monoadenosine and diadenosine monophosphate in biomimicking prebiotic synthesis using high-performance liquid chromatography with ultraviolet detection and electrospray ionization mass spectrometry characterization

The method for simultaneous separation and determination of trace monoadenosine and diadenosine monophosphate (i.e. 2′-AMP, 3′-AMP, 5′-AMP and 3′-5′ ApA) in biomimicking prebiotic synthesis was developed using high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection and electrospray ionization mass spectrometry (ESI-MS) identification. The separation was performed on a Supelco C₁₈ column with a gradient elution (solvent A: 10 mM NH₄Ac aqueous solution; solvent B: MeOH). The flow rate was set at 1.0 ml/min. The quantitative determination was achieved by HPLC with UV detection at 260 nm. The linearity ranged from 0.5 to 100 μg/ml for each nucleotide. The limits of detection (LODs) for the four nucleotides were less than 0.30 μg/ml. The recovery ranged from 95.2 to 100.7%. The intra-day relative standard deviations (RSDs) of the retention times were between 0.7 and 1.1%. Both full-scan ESI-MS and -MS² for the four nucleotides under both positive and negative polarity were carried out and the possible cleavage pathways of them were depicted. The specific ions, [AMP + H]⁺ at m/z 348 and [ApA + H]⁺ at m/z 597, were chosen to characterize the four nucleotides in biomimicking prebiotic synthesis between N-(O,O-diisopropyl) phosphoryl amino acid (Dipp-aa) and adenosine. Using the proposed HPLC/UV/ESI-MS method, the concentration of 2′-AMP, 3′-AMP, 5′-AMP and 3′-5′ ApA in the biomimicking prebiotic synthesis samples were determined.     

Diastereoselective synthesis of 1-alkyl-2,4,6-trioxoperhydropyrimidine-5-spiro-3′-(1′,2′,3′,4′-tetrahydroquinolines)

Knoevenagel products formed by the condensation of N-monoalkyl barbituric acids with o-tert-amino benzaldehydes undergo tert-amino effect reactions (T-reactions) yielding 1-alkyl-2,4,6-trioxoperhydropyrimidine-5-spiro-3′-(1′,2′,3′,4′-tetrahydroquinoline) derivatives as a mixture of (S^∗,S^∗)- and (S^∗,R^∗)-diastereomers. Mostly, the major diastereomer has the S^∗,S^∗-configuration. According to X-ray diffraction data in the solid form and NOE data in solution, diastereoselectivity of the T-reactions can be associated with the structure of the Knoevenagel products whose conformation is fixed by the strong intramolecular C-H?π interaction.     

Effect of 5-Me substituent(s) on the catalytic activity of palladium(II) 2,2-bipyridine complexes in CO/4-tert-butylstyrene copolymerization

The coordination of two 5-substituted-2,2^′-bipyridines L (L¹=5-methyl-2,2^′-bipyridine, L²=5,5^′-dimethyl-2,2^′-bipyridine) to palladium was studied. The neutral complexes [Pd(L)Cl₂] and [Pd(L)(Me)Cl], and the cationic complexes obtained after chlorine abstraction [Pd(L)₂][BAr^′₄]₂ and [Pd(L)(Me)(NCMe)][BAr^′₄] (Ar^′=3,5-(CF₃)₂-C₆H₃), respectively, were isolated and characterized by NMR and FAB mass spectroscopy. The complex [Pd(L²)(L³)][BAr^′₄]₂ (L³=2,2^′-bipyridine) bearing different ligands, was prepared for comparison purposes. The activity of the monocationic and dicationic complexes as catalytic precursors in the CO/4-tert-butylstyrene copolymerization was compared with that of related well-known catalysts containing the unsubstituted 2,2^′-bipyridine as nitrogen ligand, to evaluate the influence of the substituents in 5- and 5,5^′-position. The presence of one or two substituents on the nitrogen ligand has a positive effect on productivity using both types of precursors. No influence was observed on the polymer properties in terms of molecular weight and tacticity. Analysis of the reactivity of the methyl-palladium complexes towards carbon monoxide shows further differences depending on the nitrogen ligand.     

Syntheses and evaluation of fluorinated benzothiazole anilines as potential tracers for β-amyloid plaques in Alzheimer's disease

[¹¹C]2-(4′-(Methylamino)phenyl)-6-hydroxybenzothiazole ([¹¹C]PIB) is a most potential PET tracer for detecting the β-amyloid plaques in Alzheimer's disease. Here the syntheses of three fluorinated PIB, namely 2-(4′-(methylamino)phenyl)-6-fluoroethoxybenzothiazole (O-FEt-PIB), 2-(4′-(methylamino)phenyl)-6-fluoro-benzothiazole (F-N-Me) and 2-(4′-(dimethylamino)phenyl)-6-fluorobenzo-thiazole (F-N,N-Me), and the radiosynthesis of one corresponding ¹⁸F-labeled PIB compound, [¹⁸F]O-FEt-PIB, as well as their in vitro/in vivo biological characters were reported. The structures of the products were confirmed by IR, ¹H NMR, EI/ESI-MS, elemental analysis and HRMS techniques. The radiolabeled product was characterized by radio-TLC and radio-HPLC and purified by semi-preparative radio-HPLC. The suitable biological characters showed these tracers were potential to be developed as probes for detecting β-amyloid plaques in Alzheimer's disease.     

Synthesis and characterization of bis[dicarboxylatotetraorganodistannoxane] units involving 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids: An investigation of structures by X-ray diffraction, NMR, electrospray ionisation MS and assessment of in vitro cytotoxicity

Reactions of 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids (LHH′, where the aryl group is an R-substituted phenyl ring such that for L¹HH′: R = H; L²HH′: R = 2′-CH₃; L³HH′: R = 3′-CH₃; L⁴HH′: R = 4′-CH₃; L⁵HH′: R = 4′-Cl; L⁶HH′: R = 4′-Br) with ⁿBu₂SnO in a 1:1 molar ratio yielded complexes of composition {[ⁿBu₂Sn(LH)]₂O}₂. The complexes have been characterized by ¹H, ¹³C, ¹¹⁹Sn NMR, ESI-MS, IR and ^119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The crystal structures of {[ⁿBu₂Sn(L¹H)]₂O}₂ (1), {[ⁿBu₂Sn(L⁴H)]₂O}₂ (4), {[ⁿBu₂Sn(L⁵H)]₂O}₂ (5) and {[ⁿBu₂Sn(L⁶H)]₂O}₂ (6) were determined. The compounds are centrosymmetric tetranuclear bis(dicarboxylatotetrabutyldistannoxane) complexes containing a planar Sn₄O₂ core in which two μ₃-oxo O-atoms connect an Sn₂O₂ ring to two exocyclic Sn-atoms. The four carboxylate ligands display two different modes of coordination where both modes involve bridging of two structurally distinct Sn-atoms. The solution structures were confirmed by ¹¹⁹Sn NMR spectroscopy by observing two tin resonances in compounds 1, and 4-6. The observed difference between the two tin resonances was about 3 ppm while the differences in ¹³C resonances were even smaller. Compounds {[ⁿBu₂Sn(L²H)]₂O}₂ (2) and {[ⁿBu₂Sn(L³H)]₂O}₂ (3) undergo a very complex exchange processes in deuteriochloroform solution. The in vitro cytotoxic activity of compounds 1 and 4 against WIDR, M19 MEL, A498, IGROV, H226, MCF7 and EVSA-T human tumour cell lines is reported.     

4-Ketoantheraxanthin, a novel carotenoid produced by the combination of the bacterial enzyme β-carotene ketolase CrtW and endogenous carotenoid biosynthetic enzymes in higher plants

Higher plants do not ordinarily possess ketocarotenoids due to the absence of a carotenoid ketolase enzyme. We expressed genes coding for marine-bacterial enzymes β-carotene ketolase (CrtW) and β-carotene hydroxylase (CrtZ) in tobacco plants (Nicotiana tabacum) by transplastomic engineering. A novel carotenoid, 4-ketoantheraxanthin, was isolated from the leaves of the tobacco transformants. The structure of 4-ketoantheraxanthin was determined to be (3S,3′S,5′R,6′S)-5′,6′-epoxy-3,3′-dihydroxy-β,β-caroten-4-one by analysis of the MS, NMR, and CD data. This carotenoid was considered to be synthesized by a 4-ketolation reaction by CrtW of antheraxanthin that had been synthesized by the endogenous carotenoid biosynthetic enzymes present in higher plants and CrtZ. 4-Ketoantheraxanthin was also shown to have potent antioxidative activity against a ¹O₂ suppression model.     

A new class of aromatic polybenzoxazoles containing ortho-phenylenedioxy groups

A series of poly(o-hydroxy amide)s having both ether and ortho-catenated phenylene unit in the main chain were synthesized via the low-temperature solution polycondensation of 4,4^′-(1,2-phenylenedioxy)dibenzoyl chloride and 4,4^′-(4-tert-butyl-1,2-phenylenedioxy)dibenzoyl chloride with three bis(o-aminophenol)s including 4,4^′-diamino-3,3^′-dihydroxybiphenyl, 3,3^′-diamino-4,4^′-dihydroxybiphenyl, and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. The poly(o-hydroxy amide)s exhibited inherent viscosities in the range of 0.23-0.96 dl/g. Most of the poly(o-hydroxy amide)s were soluble in polar organic solvents such as N,N-dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP) and could afford flexible and tough films by solution casting. Subsequent thermal cyclodehydration of the poly(o-hydroxy amide)s afforded polybenzoxazoles. However, the polybenzoxazoles were organic-insoluble except for those with the hexafluoroisopropylidene group. The polybenzoxazoles exhibited glass-transition temperatures (T_g) in the range of 200-232 °C by DSC and softening temperatures (T_s) of 250-256 °C by thermomechanical analysis. Thermogravimetric analyses indicated that most polybenzoxazoles were stable up to 500 °C in air or nitrogen. The 10% weight loss temperatures were recorded in the ranges of 546-606 °C in air and 574-631 °C in nitrogen.     

Di-n-octyltin(IV) complexes with 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acid: Syntheses and assessment of solid state structures by Sn Mössbauer and X-ray diffraction and further insight into the solution structures using electrospray ionization MS, Sn NMR and variable temperature NMR spectroscopy

Reactions of 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids (LHH′, where the aryl group is an R-substituted phenyl ring such that for L¹HH′: X = H; L²HH′: X=2′-OCH₃; L³HH′: X = 3′-CH₃; L⁴HH′: X = 4′-CH₃; L⁵HH′:X = 4′-Cl) with ⁿOct₂SnO in 2:1 and 1:1 molar ratios have been investigated. Two types of complexes, ⁿOct₂Sn(LH)₂ and {[ⁿOct₂Sn(LH)]₂O}₂, were isolated and they have been characterized by ¹H, ¹³C, ¹¹⁹Sn NMR, ESI-MS, IR and ^119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The crystal structures of ⁿOct₂Sn(L¹H)₂ (1), {[ⁿOct₂Sn(L²H)]₂O}₂ (3) and {[ⁿOct₂Sn(L³H)]₂O}₂(4) were determined. The mononuclear complex 1 was found to adopt a skew-trapezoidal bipyramidal arrangement around the tin atom while 3 and 4 are centrosymmetric tetranuclear bis(dicarboxylatotetrabutyldistannoxane) complexes containing a planar Sn₄O₂ core in which two μ₃-oxo O-atoms connect an Sn₂O₂ ring to two exocyclic Sn-atoms. The solution structures were confirmed by ¹¹⁹Sn NMR spectroscopy by observing one tin resonance in compound 1 and two tin resonances in {[ⁿOct₂Sn(L⁵H)]₂O}₂ (5). {[ⁿOct₂Sn(L²H)]₂O}₂ (3) and {[ⁿOct₂Sn(L³H)]₂O}₂ (4) undergo very complex exchange processes in deuteriochloroform solution, which has been confirmed by variable temperature ¹H NMR spectroscopy. The cleavage of the most labile bond in the molecule was studied by ESI mass spectrometry.     

Convenient synthesis of N-isobutyryl-2′-O-methyl guanosine by efficient alkylation of O-trimethylsilylethyl-3′,5′-di-tert-butylsilanediyl guanosine

We present a novel route for the synthesis of N²-isobutyryl-2′-O-methyl guanosine, introducing 3′,5′-di-tert-butylsilyl and O⁶-trimethylsilylethyl groups as efficient protections during the 2′-O-methylation step with NaH/CH₃I. These protections were then removed simultaneously in a single step with TBAF. The eight-step synthesis is easy to perform, employing convenient commercially available reagents; crude mixtures are of satisfying purity, so only three chromatography purifications were required. Title compound was obtained in 25% overall yield from guanosine.     

Highly diastereoselective chemoenzymatic synthesis of (2′R)- and (2′S)-2′-deoxy[2′-H]guanosines

In an effort to develop an efficient synthetic method of highly diastereoselective (2′R)- and (2′S)-2′-deoxy[2′-²H]guanosines, chemoenzymatic conversion was investigated. The synthesis of (2′R > 98% de)-2′-deoxy[2′-²H]guanosine was achieved by biological transdeoxyribosylation using (2′R > 98% de)-2′-deoxy[2′-²H]uridine, 2,6-diaminopurine, and Enterobacter aerogenes AJ-11125, followed by treatment with adenosine deaminase. (2′S > 98% de)-2′-Deoxy[2′-²H]guanosine was synthesized from (2′S > 98% de)-2′-deoxy[2′-²H]uridine and 2,6-diaminopurine using thymidine phosphorylase and purine nucleoside phosphorylase instead of E. aerogenes AJ-11125.     

Stereoselective synthesis of an ansa-zirconocene in a spirane scaffold

Methodology is described for the preparation of a rigid C₂-bridged zirconocene catalyst system where the C₂-bridge is embedded in a spirane scaffold. The ligand was prepared from 3,4-dihydro-2H-fluoren-1(9H)-one. Initially, the oxo group was converted into a spirocyclobutanone function. Further conversion to a fulvene was followed by regio- and stereoselective saturation to provide the ligand cis-2-(cyclopentadienyl)-1′,2′,3′,4′-tetrahydro-9H-spiro[cyclobutane-1,1′-fluorene]. The ligand was dilithiated and reacted with zirconium tetrachloride to provide the corresponding (η⁵-cyclopentadienyl)-spiro[cyclobutane-1,1′-(η⁵-fluorenyl)]zirconium dichloride complex. The structure of the zirconocene dichloride has been established by crystal X-ray analysis.     

Highly efficient and selective biocatalytic acylation studies on triazolylsugars

Different acid anhydrides (of C₂ to C₇ aliphatic fatty acids and benzoic acid) have been used to study the selective acylation of primary/secondary hydroxyl groups in 2-phenyl-4-(d-threo-1′,2′,3′-trihydroxypropyl)-2H-1,2,3-triazole, 2-phenyl-4-(d-erythro-1′,2′,3′-trihydroxypropyl)-2H-1,2,3-triazole, 2-phenyl-4-(d-arabino-1′,2′,3′,4′-tetrahydroxybutyl)-2H-1,2,3-triazole and 2-phenyl-4-(d-lyxo-1′,2′,3′,4′-tetrahydroxybutyl)-2H-1,2,3-triazole in the presence of Candida antarctica lipase B in diisopropyl ether. Among the different acid anhydrides, butanoic anhydride was found to be the most efficient acylating agent (for butanoylation); for acetylation, vinyl acetate gave the best results. The reactions with both these acylating agents were highly selective and efficient yielding exclusively the monoacylated products in 95-99% yields in 1-5 h.     

Synthesis and characterization of isomeric 4- and 8-(σ-CHCHPh)-closo-ruthenacarboranes with η:η-phosphacarbocyclic ligand

Reactions of [3,3-(PPh₃)₂-3-Cl-3-H-3,1,2-closo-RuC₂B₉H₁₁] (1) and its exo-nido isomer [exo-5,6,10-{Ru(Ph₃P)₂Cl}-5,6,10-(μ-H)₃-10-H-7,8-nido-C₂B₉H₈] (2) with NH₄PF₆ in methanol or ethanol solution followed by heating in the presence of an excess of phenylacetylene (3) affords a mixture of two isomeric closo species [3,3-{(1′-3′-η³):(5′,6′-η²)-ortho-C₆H₄PPh₂CHC(Ph)CHCHPh}-8-(σ-CHCHPh)-3,1,2-closo-RuC₂B₉H₁₀] (4) and [3,3-{(1′-3′-η³):(5′,6′-η²)-ortho-C₆H₄PPh₂CHC(Ph)CHCHPh}-4-(σ-CHCHPh)-3,1,2-closo-RuC₂B₉H₁₀] (5) in which boron vertexes in β- and α-sites with respect to the cage carbons bear the (E)-CHCHPh group. The X-ray diffraction study of 4 together with the multinuclear NMR data for 4 and 5 revealed that such an unusual η³:η²-phosphacarbocyclic ligand in both isomeric complexes is formed by specific insertion of the initially metal-bound PPh₃ group into the chain of two alkyne molecules coupled in a “head-to-tail” fashion around the metal vertex.     

Rapid synthesis of optically active poly(amide-imide)s by direct polycondensation of aromatic dicarboxylic acid with aromatic diamines

4,4^′-(Hexafluoroisopropylidene)-N,N^′-bis(phthaloyl-l-leucine-p-amidobenzoic acid) (2) was prepared from the reaction of 4,4^′-(hexafluoroisopropylidene)-N,N^′-bis(phthaloyl-l-leucine) diacid chloride with p-aminobenzoic acid. The direct polycondensation reaction of monomer (2) with p-phenylenediamine (2a), 4,4^′-diaminodiphenylsulfone (2b), 2,4-diaminotoluene (2c), 2,6-diaminopyridine (2d), m-phenylene diamine (2e), benzidine (2f), 4,4^′-diaminodiphenylether (2g) and 4,4^′-diaminodiphenyl methane (2h) was carried out in a medium consisting of triphenyl phosphite, N-methyl-2-pyrolidone, pyridine, and calcium chloride. The homogeneous mixture was heated at 220 °C for 1 min under nitrogen. The resulting poly(amide-imide)s (PAIs) having inherent viscosities 0.27-0.78 dl/g were obtained in high yield and are optically active and thermally stable. All of the above polymers were fully characterized by IR spectroscopy, elemental analyses and specific rotation. Some structural characterization and physical properties of this new optically active PAIs are reported.