Charging and deforming the pybox ligand: enantiomerically pure double helices and their interconversion

Reaction of pyrrole-2,5-biscarbonitrile (1) with an excess of (S)- or (R)-valinol in boiling chlorobenzene selectively yielded the two enantiomeric bis(oxazolinyl)pyrroles (S,S)-bis[2-(4,4'-diisopropyl-4,5-dihydrooxazolyl)]pyrrole ("S,S-iproxpH", 2 a) and (R,R)-bis[2-(4,4'-diisopropyl-4,5-dihydrooxazolyl)]pyrrole ("R,R-iproxpH", 2 b), respectively. Lithiation of 2 a and 2 b at -78 degrees C and reaction with an equimolar amount of [PdCl(2)(cod)] (cod=1,5-cyclooctadiene) gave the helical dinuclear palladium complexes (M)-[PdCl(S,S-iproxp)](2) (3 a) and (P)-[PdCl(S,S-iproxp)](2) (3 b) as well as (P)-[PdCl(R,R-iproxp)](2) (4 a) and (M)-[PdCl(R,R-iproxp)](2) (4 b). Reaction of a 1:1 mixture of lithiated 2 a and 2 b with an equimolar amount of [PdCl(2)(cod)] gave a mixture of the homochiral complexes 3 a,b and 4 a,b along with the racemic mixture of the heterochiral complex [Pd(2)Cl(2)(S,S-iproxp)(R,R-iproxp)] (5). The double helical structure as well as the absolute configuration of these neutral dinuclear palladium complexes was confirmed by X-ray diffraction studies of all five complexes. One of the oxazolyl units and the anionic pyrrolide occupy two coordination sites in an approximately square-planar ligand arrangement at the Pd centers whereas the second oxazolyl ring is twisted out of this plane and binds to the second metal center. The heterochiral complex 5 does not possess any element of molecular symmetry. The P-helical complexes 3 b and 4 a display a positive CD at 310 nm and a weaker negative CD at 350 nm, while the compounds possessing M-helicity have the corresponding mirror image CD spectra. Complexes 3 a and 4 a have an additional weak long wavelength CD feature between 380 and 420 nm which is absent in the spectra of 3 b and 4 b. Upon heating a solution of 3 b, interconversion to the diastereomer of opposite helicity 3 a sets in, for which a first-order rate law with respect to the concentration of the complex was established; activation parameters: DeltaH( not equal )=68 kJ mol(-1), DeltaS( not equal )=-99 J mol(-1) K(-1). A cross-over experiment monitored by (1)H NMR spectroscopy also gave the racemate of the mixed-ligand complex 5: (P)-[Pd(2)Cl(2)(S,S-iproxp)(R,R-iproxp)] and (M)-[Pd(2)Cl(2)(S,S-iproxp)(R,R-iproxp)] indicating an intermolecular exchange involving mononuclear [PdCl(iproxp)] complex fragments.     

Catalytic asymmetric hydrogenation of 2,3,5-trisubstituted pyrroles

Catalytic asymmetric hydrogenation of N-Boc-protected pyrroles proceeded with high enantioselectivity by using a ruthenium catalyst modified with a trans-chelating chiral bisphosphine PhTRAP. The ruthenium catalyst prepared from Ru(eta3-methallyl)2(cod) and (S,S)-(R,R)-PhTRAP in the presence of triethylamine was the most enantioselective for the asymmetric hydrogenation of methyl pyrrole-2-carboxylate, giving the desired (S)-proline derivative with 79% ee in 92% yield. Moreover, 2,3,5-trisubstituted pyrroles bearing a large substituent at the 5-position were hydrogenated with 93-99.7% ee. The asymmetric reduction of 4,5-dimethylpyrrole-2-carboxylate gave only all-cis isomer and created three chiral centers with high degree of stereocontrol in a single process. This is the first highly enantioselective reduction of pyrroles.     

Synthesis and polymerization of 2,5-dimethylene-2,5-dihydrothieno[3,2-b]thiophene derivatives: The structure and reactivity of quinonoid monomers

Novel 2,5-dimethylene-2,5-dihydrothieno[3,2-b]thiophene derivatives such as 2,5-bis[di(ethylthio)methylene]-2,5-dihydrothieno[3,2-b]thiophene ( 4b ) and 2,5-bis[cyano(ethylthio)methylene]-2,5-dihydrothieno[3,2-b]thiophene ( 4c ) were successfully synthesized as isolable crystals. Polymerization behavior of 2,5-bis(dicyanomethylene)-2,5-dihydrothieno[3,2-b]thiophene ( 4a ), 4b , and 4c was investigated. 4a , 4b , and 4c are not homopolymerizable with any initiators and also not copolymerizable with vinyl monomers such as styrene (St), methyl methacrylate, and acryronitrile except for an alternating copolymerization of 4a with St. 4a , 4b , and 4c did not copolymerize with 7,8-bis(butoxycarbonyl)-7,8-dicyanoquinodimethane (BCQ) as a highly conjugated comonomer and instead only homopolymer of BCQ was obtained, indicating that they are much less reactive than BCQ. To obtain the relative reactivity among 1c , 2c , and 4c , the rate of addition reaction of 2,2′-azobis(isobutyronitrile) (AIBN) with 4c was compared with those of AIBN with 7,8-bis(ethylthio)-7,8-dicyanoquinodimethane ( 1c ) and with 2,5-bis[cyano(ethylthio)methylene]-2,5-dihydrothiophene ( 2c ) by NMR spectroscopy and analyzed with the first-order kinetics. The relative reactivity among 1c , 2c , and 4c was found to be as follows: 1c > 4c > 2c . The relationship between structure and reactivity for the quinonoid compounds was discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3027–3039, 1999     

1,3-dialkyl- and 1,3-diaryl-3,4,5,6-tetrahydropyrimidin-2-ylidene rhodium(i) and palladium(II) complexes: synthesis, structure, and reactivity

The synthesis of novel 1,3-diaryl- and 1,3-dialkylpyrimidin-2-ylidene-based N-heterocyclic carbenes (NHCs) and their rhodium(i) and palladium(II) complexes is described. The rhodium compounds bromo(cod)[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene]rhodium (7), bromo(cod)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)rhodium (8) (cod=eta(4)-1,5-cyclooctadiene, mesityl=2,4,6-trimethylphenyl), chloro(cod)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)rhodium (9), and chloro(cod)[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene]rhodium (10) were prepared by reaction of [[Rh(cod)Cl](2)] with lithium tert-butoxide followed by addition of 1,3-dimesityl-3,4,5,6-tetrahydropyrimidinium bromide (3), 1,3-dimesityl-3,4,5,6-tetrahydropyrimidinium tetrafluoroborate (4), 1,3-di-2-propyl-3,4,5,6-tetrahydropyrimidinium bromide (6), and 1,3-di-2-propyl-3,4,5,6-tetrahydropyrimidinium tetrafluoroborate, respectively. Complex 7 crystallizes in the monoclinic space group P2(1)/n, and 8 in the monoclinic space group P2(1). Complexes 9 and 10 were used for the synthesis of the corresponding dicarbonyl complexes dicarbonylchloro(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)rhodium (11), and dicarbonylchloro[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene]rhodium (12). The wavenumbers nu(CO I)/nu(CO II) for 11 and 12 were used as a quantitative measure for the basicity of the NHC ligand. The values of 2062/1976 and 2063/1982 cm(-1), respectively, indicate that the new NHCs are among the most basic cyclic ligands reported so far. Compounds 3 and 6 were additionally converted to the corresponding cationic silver(i) bis-NHC complexes [Ag(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(2)]AgBr(2) (13) and [Ag[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene](2)]AgBr(2) (14), which were subsequently used in transmetalation reactions for the synthesis of the corresponding palladium(II) complexes Pd(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(2) (2+)(Ag(2)Br(2)Cl(4) (4-))(1/2) (15) and Pd[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene)(2)]Cl(2) (16). Complex 15 crystallizes in the monoclinic space group P2(1)/c, and 16 in the monoclinic space group C(2)/c. The catalytic activity of 15 and 16 in Heck-type reactions was studied in detail. Both compounds are highly active in the coupling of aliphatic and aromatic vinyl compounds with aryl bromides and chlorides with turnover numbers (TONs) up to 2000000. Stabilities of 15 and 16 under Heck-couplings conditions were correlated with their molecular structure. Finally, selected kinetic data for these couplings are presented.     

Synthesis and coordination chemistry of the first C2-chiral bisoxazine ligand

The ligand 2,5-bis(oxazinyl)-3,4-diethylpyrrole (4) was obtained in three reaction steps from the known pyrrole derivative 3,4-diethylpyrrole-2,5-dicarboxylic acid (1) which was first coupled with 2 molar equiv of (S)-1-benzoxy-3-butylamine to give the corresponding diamide 2 using dicyclohexylcarbodiimide and 1-hydroxybenzitriazole as coupling reagents. Subsequent hydrogenolysis of the benzyl ether functions yielded the dialcohol 3 which was cyclized in high yield after methylsulfonation and treatment with an excess of NaOH giving the target compound 2,5-bis[2-((S)-5-methyloxazinyl)]-3,4-diethylpyrrole (4). Lithiation of 4 by reaction with 1 molar equivalent of nBuLi at -78 degrees C and addition of [PdCl(2)(COD)] to the lithium pyrrolide cleanly gave the palladium complex 5 which was fully characterized. Complex 5 is unstable in solution and dimerizes to give a mixture of two diastereomeric helical dinuclear complexes, 6a and 6b, which cocrystallized in a 1:1 ratio to give X-ray quality single crystals. Both isomers possess virtual molecular 2-fold symmetry (though no crystallographic rotational symmetry), the molecular C(2)-axis being orthogonal to the Pd...Pd vector.     

Origin of enantioselectivity in palladium-catalyzed asymmetric allylic alkylation reactions using chiral N,N-ligands with different rigidity and flexibility

The chiral bidentate-N,N ligands, (S(a))-1, (S(a))-2, (S,S)-3 and (S,S)-4, were synthesized. They were shown to contain rigid 2-pyridinyl or 8-quinolinyl building blocks and the C(2)-symmetric chiral frameworks trans-2,5-dimethylpyrrolidinyl or (S)-(+)-2,2'-(2-azapropane-1,3-diyl)-1,1'-binaphthalene. In the (S(a))-2, and (S,S)-4 ligands pair, the 8-quinolinyl skeleton is directly bonded to the C(2)-symmetric chiral frameworks (S)-(+)-2,2'-(2-azapropane-1,3-diyl)-1,1'-binaphthalene or trans-2,5-dimethylpyrrolidinyl. This feature induces rigidity in this pair of ligands upon the N,N-framework. However, this does not occur for the (S(a))-1 and (S,S)-3 ligands, in which the presence of the -CH(2)- spacer between the frameworks bearing the nitrogen atom donors gives greater flexibility to the ligand. A further difference between the pairs of ligands is significant from the electronic properties of the chiral framework N-donor atom. The coordinating properties and the specific steric structural features of the (S(a))-1, (S(a))-2, (S,S)-3, and (S,S)-4 ligands are explained by their reactions with the [Pd(PhCN)(2)Cl(2)] and [Pd(eta(3)-PhCHCHCHPh)(mu-Cl)](2) substrates, in which the reported ligands form chelate complexes, with the exception of (S(a))-2, which failed to react with [Pd(eta(3)-PhCHCHCHPh)(mu-Cl)](2). The ligands were used in the palladium-allyl catalyzed substitution reaction of 1,3-diphenylallyl acetate with dimethylmalonate, with the best result being obtained using the (S(a))-1 ligand, giving the substitution product 2-(1,3-diphenylallyl)dimethylmalonate with an enantiomeric excess of 82% in the S form and a yield of 96%. The work demonstrates that in the presence of a steric ligand control, the electronic properties of the ligand donor atoms play a role though not significant in determining the enantioselectivity of palladium(II) catalyzed allylic substitution reactions. The results of the catalytic reaction do not provide a convincing explanation considering the coordinated chiral ligand features, as rigidity or flexibility and electronic properties of the N-donor atoms. A rationalization of the results is proposed on the basis of NMR studies and DFT calculation on the cationic complexes [Pd(eta(3)-PhCHCHCHPh)(N-N*)]CF(3)SO(3), (N-N* = (S(a))-1, 9; (S,S)-3, 10; (S,S)-4, 11).     

Synthesis of chiral hydroxyl phospholanes from D-mannitol and their use in asymmetric catalytic reactions

Chiral hydroxyl monophosphane 3 [(2S,3S,4S,5S)-3,4-dihydroxy-2, 5-dimethyl-1-phenylphospholane] and bisphospholanes 5a [1,2-bis[(2S, 3S,4S,5S)-3,4-dihydroxy-2,5-dimethylphospholanyl]benzene] and 5b [1, 2-bis[(2S,3S,4S,5S)-2,5-diethyl-3,4-dihydroxyphospholanyl]benzene] were synthesized from readily available D-mannitol in high yields. Strategies for protection and deprotection of OH-groups in the presence of phosphines have been explored. Rate acceleration in the Baylis-Hillman reaction was observed when a hydroxyl phosphine was used as the catalyst. Rhodium complexes with chiral bisphospholanes are highly enantioselective catalysts for the asymmetric hydrogenation of various kinds of functionalized olefins such as dehydroamino acid derivatives, itaconic acid derivatives, and enamides. An interesting feature of the hydroxyl phospholane system is that hydrogenation of some substrates can be carried out in water with >99% ee and 100% conversion (e.g., itaconic acid).     

(Fluoren-9-ylidene)methanedithiolato complexes of platinum: synthesis, reactivity, and luminescence

Platinum(II) complexes with (fluoren-9-ylidene)methanedithiolato and its 2,7-di-tert-butyl- and 2,7-dimethoxy-substituted analogues were obtained by reacting different chloroplatinum(II) precursors with the piperidinium dithioates (pipH)[(2,7-R2C12H6)CHCS2] [R = H (1a), t-Bu (1b), or OMe (1c)] in the presence of piperidine. The anionic complexes Q2[Pt{S(2)C=C(C12H6R(2)-2,7)}2] [R = H, (Pr(4)N)(2)2a; R = t-Bu, (Pr4N)(2)2b, (Et4N)(2)2b; R = OMe, (Pr4N)(2)2c] were prepared from PtCl(2), piperidine, the corresponding QCl salt, and 1a-c in molar ratio 1:2:2:2. In the absence of QCl, the complexes (pipH)(2)2b and [Pt(pip)(4)]2b were isolated depending on the PtCl(2):pip molar ratio. The neutral complexes [Pt{S2C=C(C12H6R(2)-2,7)L(2)] [L = PPh(3), R = H (3a), t-Bu (3b), OMe (3c); L = PEt(3), R = H (4a), t-Bu (4b), OMe (4c); L(2) = dbbpy, R = H (5a), t-Bu (5b), OMe (5c) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridyl)] were similarly prepared from the corresponding precursors [PtCl2L2] and 1a-c in the presence of piperidine. Oxidation of Q(2)2b with [FeCp2]PF6 afforded the mixed Pt(II)-Pt(IV) complex Q2[Pt2{S2C=C[C12H6(t-Bu)(2)-2,7]}4] (Q(2)6, Q = Et4N+, Pr4N+). The protonation of (Pr4N)(2)2b with 2 equiv of triflic acid gave the neutral dithioato complex [Pt2{S2CCH[C12H6(t-Bu)(2)-2,7]}4] (7). The same reaction in 1:1 molar ratio gave the mixed dithiolato/dithioato complex Pr4N[Pt{S2C=C[C12H6(t-Bu)(2)-2,7]}{S2CCH[C12H6(t-Bu)(2)-2,7]}] (Pr(4)N8) while the corresponding DMANH+ salt was obtained by treating 7 with 2 equiv of 1,8-bis(dimethylamino)naphthalene (DMAN). The crystal structures of 3b and 5c.CH2Cl2 have been solved by X-ray crystallography. All the platinum complexes are photoluminescent at 77 K in CH2Cl2 or KBr matrix, except for Q(2)6. Compounds 5a-c and Q8 show room-temperature luminescence in fluid solution. The electronic absorption and emission spectra of the dithiolato complexes reveal charge-transfer absorption and emission energies which are significantly lower than those of analogous platinum complexes with previously described 1,1-ethylenedithiolato ligands and in most cases compare well to those of 1,2-dithiolene complexes.     

旋光性聚{(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯}的合成与表征

设计、合成了一个带有横挂三联苯侧基的手性乙烯基单体——(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯,进行了普通自由基和原子转移自由基聚合反应.所得聚合物具有比单体低30°左右的比旋光度,且在侧基的紫外吸收处呈现明显不同于单体的Cotton效应,说明其主链可能形成了具有相反旋光方向的螺旋构象.在所研究范围内,聚合条件对聚合物的旋光度没有明显的影响.在分子量较小时,聚合物的比旋光度随着分子量的增加而降低,说明主链螺旋构象的贡献在增大,而当分子量达到一定值后,聚合物的比旋光度不再随分子量的增加而显著变化.     

(Perhalogenmethylthio)heterocyclen. XXI. Reaktionen halogenierter perhalogenmethylthiopyrrole: Salz- und radikalbildung,dimerisierung

2-Chloro-3,4,5-tris(trifluoromethylthio)pyrrole ( 2a ), 3-Chloro-2,4,5-tris(trifluoromethylthio)pyarrole ( 2b ) and 3,4-dichloro-2,5-bis(trifluromoethylthio)pyrrole ( 2c ) react with silver nitrate/silver acetate in good yield to give the corresponding N-silver salts 3a-c . Compound 2b forms with an aqueous potassium hydroxide solution the N-potassium salt 4 . Compounds 3a and 3b react with iodine to give the dimeers 2,2′-dichloro-3,3,′ 4,4′5,5′-hexakis(trifluoromethylthio)-2,2′-bi-2H-pyrrolyl ( 5a ) and 3,3′-dichloro-2,2′,4,4′,5,5′-hexakis(trifluoromethylthio)-2,2′-bi-2H-pyrrolyl ( 5b ). The dimers dissociate in solution to the corresponding pyrrolayl radicals. The esr and endor spectra of 3-chloro-2,4,5-tris(trifluoromethylthio)pyrrolyl were measured; coupling constants are given. For the newly prepared substances melting-points, ¹⁹F-nmr and ir spectroscopical data are provided.     

Enantiospecific syntheses of copper cubanes, double-stranded copper/palladium helicates, and a (dilithium)-dinickel coronate from enantiomerically pure bis-1,3-diketones--solid-state self-organization towards wirelike copper/palladium strands

Enantiomerically pure, vicinal diols 1 afforded in a two-step synthesis (etherification and subsequent Claisen condensation) chiral bis-1,3-diketones H(2)L((S,S)) (3 a-c) with different substitution patterns. Reaction of these C(2)-symmetric ligands with various transition-metal acetates in the presence of alkali ions generated distinct polynuclear aggregates 4-8 by diastereoselective self-assembly. Starting from copper(II) acetate monohydrate and depending on the ratio of transition-metal ion to alkali ion to ligand, chiral tetranuclear copper(II) cubanes (C,C,C,C)-[Cu(4)(L((S,S)))(2)(OMe)(4)] (4 a-c) or dinuclear copper(II) helicates (P)-[Cu(2)(L((S,S)))(2)] (5) could be synthesized with square-pyramidal and square-planar coordination geometry at the metal center. In analogy to the last case, with palladium(II) acetate double-stranded helical systems (P)-[Pd(2)(L((S,S)))(2)] (6,7) were accessible exhibiting a linear self-organization of ligand-isolated palladium filaments in the solid state with short inter- and intramolecular metal distances. Finally, the introduction of hexacoordinate nickel(II) in combination with lithium hydroxide monohydrate and chiral ligand H(2)L((S,S)) (3 a) allowed the isolation of enantiomerically pure dinuclear nickel(II) coronate [(LiMeOH)(2) subset{(Delta,Lambda)-Ni(2)(L((S,S)))(2)(OMe)(2)}] (8) with two lithium ions in the voids, defined by the oxygen donors in the ligand backbone. The high diastereoselectivity, induced by the chiral ligands, during the self-assembly process in the systems 4-8 could be exemplarily proven by circular dichroism spectroscopy for the synthesized enantiomers of the chiral copper(II) cubane 4 a and palladium(II) helicate 6.     

Coordination polymers from the self-assembly of silver(I) salts and two nonlinear aliphatic dinitrile ligands, cis-1,3-cyclopentanedicarbonitrile and cis-1,3-bis(cyanomethyl)cyclopentane: synthesis, structures, and photoluminescent properties

Six coordination polymers with aliphatic dinitrile ligands, {[Ag(cpdcn)2]ClO4}n (6a), {[Ag(cpdcn)2]PF6}n (6b), {[Ag(cpdcn)2]SbF6}n (6c, cpdcn = cis-1,3-cyclopentanedicarbonitrile), {[Ag(bcmcp)2] ClO4}n (7a), {[Ag(bcmcp)2]PF6}n (7b), {[Ag(bcmcp)2]SbF6}n, (7c, bcmcp = cis-1,3-bis(cyanomethyl)cyclopentane) have been synthesized and structurally characterized by IR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and X-ray crystallography. Both ligands used in this study are meso-compounds; while the ligand cpdcn is structurally rigid, the ligand bcmcp has greater conformational flexibility. X-ray crystallography has revealed that structures 6a-c consist of chiral 1D-polymers. The structure of complexes 7a and 7b are best described as a 2D chiral (4,4) square mesh with 3-fold parallel interpenetration. Surprisingly, complex 7c was characterized to be an achiral 1D coordination polymer. The synthesis of the ligands, IR spectra of the free and coordinated CN groups, DSC and TGA, and the photoluminescent properties of complexes 6a-c and 7a-c are also discussed.     

Variable coordination behaviour of pyrazole-containing N,P and N,P(O) ligands towards palladium(II)

Three bidentate, mixed-donor ligands based on a triphenylphosphine unit bearing a pyrazole group in the ortho-position of one phenyl ring have been synthesised; the N,P ligand [2-(3-pyrazolyl)phenyl]diphenylphosphine pzphos has been synthesised and transformed into new N,P(O) and N,P(S) derivatives, [2-(3-pyrazolyl)phenyl]diphenylphosphine oxide pzphos(O) and [2-(3-pyrazolyl)phenyl]diphenylphosphine sulfide pzphos(S), respectively. The coordination chemistry of pzphos and pzphos(O) towards palladium(II) has been investigated. Depending on the ligand to metal molar ratio employed in the reactions of palladium(II) with pzphos, either the 1 : 1 chelate [Pd(pzphos)Cl2] 1a or the 2 : 1 N,P chelate [Pd(pzphos)2]Cl2 1b was obtained. 1b contains two six-membered chelate rings in which the chlorides have been displaced from the inner coordination sphere of palladium. Exchange of the chloride anions in 1b for perchlorate anions was achieved using AgClO4 to give [Pd(pzphos)2][ClO4]2 1c. Reaction of pzphos(O) under the same conditions forms the 2 : 1 adduct [Pd(pzphos(O))2Cl2] 2b regardless of the metal to ligand ratio or the order of addition of reactants. Unlike the N,P chelate 1b, the N,P(O) ligands in complex 2b bind in a monodentate fashion through the N-donor atoms of the pyrazole rings. Abstraction of the chloro ligands in compound 2b using AgClO4 gave the 2 : 1 N,P(O) chelate [Pd{pzphos(O)}2][ClO4]2 2c, in which entropically unfavourable 7-membered chelate rings are formed. X-Ray diffraction has been used to confirm the solid-state structures of the pzphos(O) ligand and the complexes 1b, 1c, 2b and 2c.     

(Perhalogenmethylthio)heterocyclen. X. Säurekatalysierte Substitutionen an (Perchlorfluormethylthio)pyrrolen und deren agrobiologische Wirkung

(Perhalomethylthio)heterocycles. X

1 IX. Mitt.: s. [1].

. Acid-catalyzed substitutions on (perchlorofluoromethylthio)pyrroles and their agro-biological activities In the presence of C₄F₉SO₃H the (perhalomethylthio)pyrroles 1a–c react with Cl_3?nF_nCSCl (n = 1–3) to give mixtures of the 2,5- and 2,4-disubstituted pyrroles 2a–f and 3a–h . 2a and 3a react with CF₃SCl (catalyst CF₃SO₃H) yielding 2,3,5-tris (trifloromethylthio)pyrrole ( 4a ), which under similar conditions reacts further to give 2,3,4,5-tetrakis (trifluoromethylthio)pyrrole ( 5 ). As a by-product during the conversion of 3a to 4a 2,3,4-tris (trifluoromethylthio)pyrrole ( 4b ) is formed. The pyrroles 2a , 4a and 5 form the mercury salts 6a–c ; compound 5 yields also a silver salt 7 . The ¹H- and ¹⁹F-NMR. spectra are discussed and the agro-biological properties of the compounds investigated.     

Synthesis of 2‐(Selenophen‐2‐yl)pyrroles and Their Electropolymerization to Electrochromic Nanofilms

Bridging pyrrole and selenophene chemistries : Molecular assemblies have been developed that allow scrutiny of the electronic communication between pyrrole and selenophene nuclei. Divergent syntheses of 2‐(selenophen‐2‐yl)pyrroles and their N‐vinyl derivatives from available 2‐acylselenophenes and acetylenes in a one‐pot procedure have been devised (see scheme), which provide access to these exotic heterocyclic ensembles.

     

Highly selective addition of chiral,sulfonimidoyl substituted bis(allyl)titanium complexes to N-sulfonyl alpha-imino esters: asymmetric synthesis of gamma,delta-unsaturated alpha-amino acids bearing a chiral,electron-withdrawing nucleofuge at the delta-position

Selective addition of the chiral, sulfonimidoyl substituted bis(allyl)titanium complexes 5a-d, which are configurationally labile in regard to the Calpha-atoms, to N-toluenesulfonyl (Ts)-, N-2-trimethylsilylethanesulfonyl (SES)-, and N-tert-butylsulfonyl (Bus) alpha-imino ester (9a-c) in the presence of Ti(OiPr)(4) and ClTi(OiPr)(3) afforded with high regio- and diastereoselectivities in good yields the (syn, E)-configured beta-alkyl-gamma,delta-unsaturated alpha-amino acid derivatives 2a-g, which carry a chiral, electron-withdrawing nucleofuge at the delta-position and a cyclohexyl, an isopropyl, a phenyl, and a methyl group at the beta-position. Addition of the cyclic bis(allyl)titanium complex 14 to N-Bus alpha-imino ester 9c afforded with similar high regio- and diastereoselectivities the (E)- and (Z)-configured amino acid derivatives (E)-8 and (Z)-8. Reaction of complexes 5a-d with alpha-imino esters 9a-c in the presence of Ti(OiPr)(4) occurs stepwise to give first the mono(allyl)titanium complexes containing 2a-g as ligands, which react in the presence of ClTi(OiPr)(3) with a second molecule of 9a-c with formation of two molecules of 2a-g. Formation of (S,R,E)-configured homoallylic amines 2a-g entails Si,Re,E processes of alpha-imino esters 9a-c with the (R,R)-configured bis(allyl)titanium complexes (R,R)-5a-d and (R)-configured mono(allyl)titanium complexes (R)-17a-d, both of which are most likely in rapid equilibrium with their (S,S)-diastereomers and (S)-diastereomers, respectively. Interestingly, in the reaction of 5a-d with aldehydes, the (S,S)-configured complexes (S,S)-5a-d are the ones which react faster. Reaction of the N-titanated amino acid derivatives Ti-2a and Ti-2b with N-Ts alpha-imino ester 9a led to the highly diastereoselective formation of imidazolidinones 15a and 15b, respectively. Cleavage of the sulfonamide group of the N-Bus amino acid derivative 2d with CF(3)SO(3)H gave quantitatively the sulfonimidoyl functionalized amino acid H-2d. A Ni-catalyzed cross-coupling reaction of the amino acid derivative 2e with ZnPh(2) led to a substitution of the sulfonimidoyl group by a phenyl group and furnished the enantiomerically pure protected alpha-amino acid Bus-1. Two new N-sulfonyl alpha-imino esters, the SES and the Bus alpha-imino esters 9b and 9c, respectively, have been synthesized from the corresponding sulfonamides by the Kresze method in medium to good yields. The N-SES alpha-imino ester 9b and the N-Bus alpha-imino ester 9c should find many synthetic applications, in particular, in cases where the N-Ts alpha-imino ester 9a had been used before.     

Upper rim allyl- and arylazo-coupled calix[4]arenes as highly sensitive chromogenic sensors for Hg2+ ion

The syntheses and chromogenic properties of calix[4]arenes, carrying 5,17-bisallyl-11,23-bis(p-X-phenyl)azo 3a-c, 5,11,17-triallyl-23-(p-X-phenyl)azo 4a-c, and 5,17-bis(hydroxypropyl)-11,23-bis(p-X-phenyl)azo groups on the upper rims 5a,b, are described. Unexpectedly, UV/vis spectra of the very popular 4-(4-nitrophenyl)azophenol-coupled calix[4]arenes 3c and 4c did not show any shift in lambda(max) when 10 different metal perchlorates were added separately to the host in a methanol-chloroform (v/v = 1/399) cosolvent. In contrast, the absorption spectra of calix[4]arenes with either 4-methoxyphenylazo (3b-5b) or 4-phenylazo (3a-5a) on the upper rim showed substantial bathochromic shifts (Deltalambda = 128-162 nm) upon the addition of soft metal ions (such as Hg(2+), Cr(3+), and Cu(2+)). The 4-(4-methoxyphenyl)azophenol-coupled calix[4]arenes (the 3b-5b series) are found to be highly sensitive for mercury ion (Hg(2+)) among the 10 different metal ions screened. Strong interactions between Hg(2+) ion and the 4-(4-methoxyphenyl)azophenol(s) as well as the p-allyl groups are corroborated by the (1)H NMR studies of 3a,b.Hg(2+) complexes. Furthermore, Job's plots revealed 1:1 binding stoichiometry for all these p-allyl- and arylazo-coupled calix[4]arenes with transition metal ions, and Benesi-Hilderbrand plots were used for the determination of their association constants.     

Synthesis of substituted thieno[2,3‐bpyrroles

Thieno[2,3‐b]pyrroles can be synthesized through three steps: Gewald synthesis, alkylation, and Thorpe–Ziegler cyclization. Diethyl 3,6‐bis((ethoxycarbonyl)methyl)‐4‐amino‐6H‐thieno[2,3‐b]pyrrole‐2,5‐dicarboxylate ( 13 ) has been obtained by one‐pot method in DMF in good yield and high quality. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:236–238, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20290     

Easy formation of gold-like lustrous crystals with a high melting point from 1-aryl-2,5-bis[5-(tricyanoethenyl)-2-thienyl]pyrroles

A new class of π-conjugated organic compounds, 1-aryl-2,5-bis[5-(tricyanoethenyl)-2-thienyl]pyrroles that form gold-like lustrous crystals with a high melting point were obtained. The molecules in these crystals are arranged in a planar sheet to get close to each other via the intermolecular CH?N hydrogen bond between the cyano nitrogen and the hydrogen of the nearest thiophene or pyrrole ring, which makes the crystals sparingly soluble in common organic solvents.     

Special effects of ortho-isopropylphenyl groups. Diastereoisomerism in platinum(II) and palladium(II) complexes of helically chiral PAr3 ligands

The coordination chemistry of the four phosphines, P{C6H3(o-CH3)(p-Z)}3 where Z = H (1a) or OMe (1b) and P{C6H3(o-CHMe2)(p-Z)}3 Z = H (1c) or OMe (1d) with platinum(II) and palladium(II) is reported. Mononuclear complexes trans-[PdCl2L2](L = 1a,b) and trans-[PtCl2L2](L = 1a-c) have been prepared and the crystal structures of trans-[PdCl2(1b)2] and trans-[PtCl2(1c)2] as their dichloromethane solvates have been determined. The structures show that in these complexes, the ligands adopt g+ g+ a conformations. Examination of the Cambridge Structural Database confirms this to be one of only two conformer types that tri-o-tolylphosphines adopt and the only viable conformer in 4 and 6 coordinate complexes. The binuclear complexes trans-[Pd2Cl4L2](L = 1c,d) are formed even when an excess of the bulky 1c,d is used in the synthesis and the crystal structure of trans-[Pd2Cl4(1c)2] as its chloroform solvate is reported. Reaction of [PtCl2(NCBu(t))2] with 1b-d in refluxing toluene gave the cycloplatinated species [Pt2Cl2(L - H)2] where L - H is phosphine 1b-d deprotonated at one of the ortho-methyl carbon atoms. Variable temperature 31P and 1H NMR spectroscopy reveals that all the complexes reported are fluxional. The processes are analysed in terms of restricted P-C and P-M rotations that give rise to diastereoisomeric rotamers because of the helically chiral orientations of the aryl substituents. For the complexes of the bulky ligands 1c,d, rotation about the P-C bond is slow on the NMR timescale even up to 75 degrees C. The crystal structure of the cyclometallated complex [Pt2Cl2(1d - H)2] has been determined.