Regio- and Stereocontrolled Nucleophilic Addition Reactions of An Unsymmetrically Disbustituted Butadiene η4-Molybdenum Cationic Complex

The reactions of a new cationic complex, [Cp(CO)₂Mo(η⁴-2-methyl-3-SPh-C₄H₄)]⁺ PF^?₆ (3), with carbon, hydride, and nitrogen nucleophiles were found to give only the C-1 addition products in good yield. The X-ray crystal structures of two of the addition products 4a and 4e confirm the regio- and stereochemistry of the nucleophilic additions.     

Thermal and photochemical reactions of Fischer carbene complexes with trialkylsilyl-substituted alkynes

Thermal reaction of Fischer carbene complexes with triisopropylsilyl (TIPS) substituted alkynes in benzene afforded TIPS-substituted vinylketenes or 2-TIPS-substituted cyclobutenones as major products while photochemical reaction of Fischer carbene complexes with trimethylsilyl (TMS) substituted alkynes in acetonitrile afforded 3-TMS-substituted cyclobutenones.     

Transition metal carbene chemistry: Nucleophilic substitution reactions of imidazolide and benzimidazolide ions with Fischer carbene complexes in MeOH

Rate constants for the nucleophilic substitution reactions of imidazolide (IZ⁻) and benzimidazolide (BIZ⁻) ions with 4-Cr-Z and 5 in MeOH at 25 °C are reported and Hammett ρ values are evaluated to be 1.50 ± 0.10 and 1.51 ± 0.08 for 4-Cr-Z-IZ⁻ and 4-Cr-Z-BIZ⁻ reactions, respectively. The comparable reactivity and also almost identical ρ values for these reactions indicate that there is no difference in sensitivity towards electronic effects due to slightly bigger size of BIZ⁻ over IZ⁻ and bond formation at the transition states are equally progressed. The higher ρ values for these reactions compared to those with a wide range of nucleophiles may arise mainly due to lower polarity of the solvent MeOH which enhances the requirement for stabilization of the negative charge in the transition state by the Z-substituents.     

Reaction of α,β-unsaturated Fischer carbene complexes with allyl alkoxide

Optically enriched homo-binuclear Fischer chromium carbene complexes with planar chiral arene chromium complexes gave α-allyl β-arylpropionates up to 97% ee by reaction with allyl alkoxide and subsequent photo-oxidative demetalation. The chiral hetero-binuclear tungsten carbene complexes afforded anti α-allyl β-hydroxy β-arylpropionates as a major product up to 92/8 dr by the same reaction sequence. High diastereoselectivity in these reactions is contributed to the planar chirality of the arene chromium complex, even though the reaction was carried out under vigorous basic media. The reaction products, α-allyl β-arylpropionates were derived by 1,3-M(CO)₅ shift and subsequent [3,3]-sigmatropic rearrangement. Also, the corresponding chromium-uncomplexed α,β-unsaturated Fischer carbene complexes afforded α-allyl β-arylpropionates under the same conditions. Formation of β-allyl β-arylpropionates via 1,2-M(CO)₅ shift followed by [3,4]-sigmatropic rearrangement was not observed in both reactions of chromium-coordinated and the corresponding chromium-uncoordinated α,β-unsaturated Fischer carbene complexes with allyl alkoxide in the presence of base.     

Reactions of some ortho and para halogenated aromatic nitriles with ethylenediamine: selective synthesis of imidazolines

The reaction of ethylenediamine (EDA) with ortho and/or para halogenated benzonitriles did not lead to the imidazolines expected: a competitive aromatic nucleophilic substitution (S_NAr) was observed instead. The selective synthesis of these imidazolines was performed by nucleophilic addition of EDA to thiobenzamide derivatives. The difference in reactivity between the nitrile and thioamide derivatives was estimated by a frontier orbital approach at the RHF/6-31G** level which predicted a greater reactivity of substituted thiobenzamides towards the nucleophilic addition of EDA.     

Thermal properties of cyanatocopper(II) complexes with pyridine,bipyridine and phenanthroline

The thermal properties of cyanatocopper complexes with pyridine, bipyridine and phenanthroline are described in this paper. It was found that the thermal stabilities of the complexes were found to increase in the order pybipy2(NCS)₂ (L=pyridine and its methyl derivates) which are composed of the liberation of ligandsL and redox reactions of thiocyanate ligands with the central Cu(II) atom [1, 2]. The decomposition temperature of thiocyanate ligands depends on the properties of the ligandsL present in the coordination sphere. An analogous course of thermal decomposition was also observed for [Cu(bipy)₂(NCX)](NCX) (X=S or Se) [3]. For the phenanthroline complexes [Cu(phen)₂(NCX)₂] (X=S or Se) the thermal stability was found to increase significantly (by about 140C) and the decomposition stoichiometry was also changed [3].The present paper contains the results of thermoanalytical studies on bipyridine and phenanthroline cyanatocopper complexes, and a comparison of the thermal properties of pyridine cyanato and isothiocyanatocopper complexes.     

Addition Reactions of Me3SiCN with Aldehydes Catalyzed by Aluminum Complexes Containing in their Coordination Sphere O,S, and N Ligands

The reaction of one equivalent of LAlH₂ ( 1 ; L=HC(CMeNAr)₂, Ar=2,6‐iPr₂C₆H₃, β‐diketiminate ligand) with two equivalents of 2‐mercapto‐4,6‐dimethylpyrimidine hydrate resulted in LAl[(μ‐S)(m‐C₄N₂H)(CH₂)₂]₂ ( 2 ) in good yield. Similarly, when N‐2‐pyridylsalicylideneamine, N‐(2,6‐diisopropylphenyl)salicylaldimine, and ethyl 3‐amino‐4,5,6,7‐tetrahydrobenzo[b]thiophene‐2‐carboxylate were used as starting materials, the corresponding products LAl[(μ‐O)(o‐C₆H₄)CN(C₅NH₄)]₂ ( 3 ), LAlH[(μ‐O)(o‐C₄H₄)CN(2,6‐iPr₂C₆H₃)] ( 4 ), and LAl[(μ‐NH)(o‐C₈SH₈)(COOC₂H₅)]₂ ( 5 ) were isolated. Compounds 2 – 5 were characterized by ¹H and ¹³C NMR spectroscopy as well as by single‐crystal X‐ray structural analysis. Surprisingly, compounds 2 – 5 exhibit good catalytic activity in addition reactions of aldehydes with trimethylsilyl cyanide (TMSCN).     

Rigid pyridyl substituted NHC ligands,their Pd(0) complexes and their application in selective transfer semihydrogenation of alkynes

The synthesis of an air‐stable series of Pd⁰ complexes with unsymmetric bidentate N‐pyridine N‐heterocyclic carbene ligands has been described. The carbenes were generated by synthesis of the silver(I) complexes from the imidazolium salts, followed by transmetallation of the C‐N ligands to obtain the target electron‐rich zerovalent palladium compounds. The bidentate coordination behaviour of the ligands was confirmed by ¹H, ¹³C NMR and X‐ray spectroscopy. The complexes are active precatalysts for the selective transfer semihydrogenation of alkynes to Z‐alkenes, with selectivities up to 99%. Copyright © 2011 John Wiley & Sons, Ltd.     

Reactions on polymers with amine groups. V. Addition of pyridine and imidazole groups with acetylenecarboxylic acids

Unsaturated macromolecular carboxybetaines were obtained by reaction of poly(4-vinylpyridine) and poly(N-vinylimidazole) with propiolic acid. A kinetic model was presented for 4-methylpyridine. It consists of three coupled reactions: neutralization, addition which involves two molecules of acid and leads to a cation–anion pair structure, where the cation results from the addition of the amine nitrogen to the triple bond of acid, and an equilibrium reaction between the ion-pair structure and the betaine structure. The addition rate was found to be higher for poly(4-vinylpyridine) than for poly(N-vinylimidazole); it was also higher in water than in a water–methanol mixture. The reaction with acetylenedicarboxylic acid was carried out on poly(N-vinylimidazole), but the transformed units showed the structure that results from propiolic acid. The betaine products from 4-methylpyridine did not polymerize by radical initiation. The polymeric products show characteristics of photocrosslinking polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1615–1623, 1998     

Oxidative demetalation of Fischer alkoxy carbene complexes with stoichiometric pyridine N-oxide and NaBH4-promoted demetalation of Fischer iminocarbene complexes with sulfur and selenium

Oxidation of Fischer alkoxy carbene complexes were systematically investigated with stoichiometric pyridine N-oxide (PNO) under mild conditions, forming ester products in good to excellent yields from the corresponding monocarbene complexes. Fischer alkoxy biscarbene complexes efficiently underwent stepwise oxidative demetalation under controlled conditions, resulting in ester-monocarbene and diester products, respectively. This oxidation protocol has demonstrated a generally efficient method to oxidize Fischer alkoxy carbene complexes under mild conditions, providing a new route to novel monocarbene complexes from Fischer biscarbene complexes. In the presence of NaBH₄, reactions of Fischer iminocarbene complexes with elemental sulfur or selenium in ethanol at ambient temperature regioselectively afforded thione or selone complexes by insertion of a sulfur or selenium atom into the MC bonds in Fischer carbene complexes, and metal-free selone was also obtained. The molecular structures of the iminocarbene complexes and selone derivatives were confirmed by X-ray crystallographic study. The NaBH₄-promoted demetalation protocol suggests a potential new route to demetalate Fischer aminocarbene complexes.     

Palladium complexes of bidentate pyridine N‐heterocyclic carbenes: Optical resolution,antimicrobial and cytotoxicity studies

A series of bidentate pyridine‐functionalized palladium N‐heterocyclic carbene (Pd NHC) complexes with various wingtip substituents (R = methyl, phenyl and tert‐butyl) have been synthesized and evaluated for their potential biomedical applications as antimicrobials and antiproliferative drug candidates. The obtained Pd NHC complexes were applied in a standard broth microdilution assay for determination of their antimicrobial activities against thirteen strains of pathogenic microorganisms. In addition to that, cytotoxic activities of the Pd NHC complexes were also evaluated against three human cancer cell lines, namely breast (MCF‐7), colon (HCT116) and oral (H103) cancer cells, using a standard MTT assay. Upon coordination to palladium, the Pd NHC complexes show significant antimicrobial activities with minimum inhibitory concentrations in the micromolar range, and they are cytotoxic to the tested carcinomas with IC₅₀ ranging from 13 to 38 μM. Evidences for influence of both wingtip substituents and optical isomerism on the biological activities of the complexes have been found.     

Dinuclear titanium complexes with methylphenylsilylene bridge between cyclopentadienyl rings. Synthesis, characterization and reactivity towards ethylene

The new ansa-titanocene dichloride [{(SiMePh)(η⁵-C₅H₄)₂}TiCl₂] (1) was prepared by one pot reaction, whereas synthesis of its methylated analogue [{(SiMePh)(η⁵-C₅Me₄)₂}TiCl₂] (3) was performed in two steps with isolation of corresponding silane intermediate SiMePh(HC₅Me₄)₂ (2). The reaction of 1 and 3 with TiCl₄ afforded the dinuclear complexes [(SiMePh){(η⁵-C₅R₄)TiCl₃}₂] (R = H (4) and R = Me (5)). The catalysts formed from 4 and 5 after their activation with excess MAO exhibited a modest activity in ethylene polymerization. The polymer products consisted of high molar mass linear polyethylenes with a broad molar mass distribution. The presence of three paramagnetic titanium species in the mixture 4/MAO was revealed by EPR spectroscopy. All new prepared compounds 1-5 were characterized by multinuclear NMR, EI-MS, IR, and solid-state structures of 1, 3 and 5 were determined by X-ray single crystal diffraction.     

Spectral,crystallographic, theoretical and antibacterial studies of palladium(II)/platinum(II) complexes with unsymmetric diphosphine ylides

The reaction of α‐keto‐stabilized diphosphine ylides [Ph₂P(CH₂)_nPPh₂═C(H)C(O)C₆H₄‐p‐CN] (n = 1 (Y¹); n = 2 (Y²)) with dibromo(1,5‐cyclooctadiene) palladium(II)/platinum(II) complexes, [Pd/PtBr₂(cod)], in equimolar ratio gave the new cyclometalated Pd(II) and Pt(II) complexes [Br₂Pd(κ²‐Y¹)] ( 1 ), [Br₂Pt(κ²‐Y¹)] ( 2 ), [Br₂Pd(κ²‐Y²)] ( 3 ) and [Br₂Pt(κ²‐Y²)] ( 4 ). These compounds were screened in a search for novel antibacterial agents and characterized successfully using Fourier transfer infrared and NMR (¹H, ¹³C and ³¹P) spectroscopic methods. Also, the structures of complexes 1 and 2 were characterized using X‐ray crystallography. The results showed that the P,C‐chelated complexes 1 and 2 have structures consisting of five‐membered rings, while 3 and 4 have six‐membered rings, formed by coordination of the ligand through the phosphine group and the ylidic carbon atom to the metal centre. Also, a theoretical study of the structures of complexes 1 – 4 was conducted at the BP86/def2‐SVP level of theory. The nature of metal–ligand bonds in the complexes was investigated using energy decomposition analyses (EDA) and extended transition state combined with natural orbitals for chemical valence analyses. The results of EDA confirmed that the main portions of ΔE_int, about 57–58%, in the complexes are allocated to ΔE_elstat.     

Sequential catalytic process: synthesis of quinoline derivatives by AuCl3/CuBr-catalyzed three-component reaction of aldehydes, amines, and alkynes

A sequential catalytic process has been developed based on gold-catalyzed nucleophilic addition of terminal alkynes to imines, and gold-catalyzed intramolecular reaction of aromatic ring to alkynes. This one-pot reaction of aldehydes, amines, and alkynes gives quinoline derivatives in good yields.     

Reactions on polymers with amine groups. I. Reactions of vinylpridine polymers and of their model compounds with unsaturated carboxylic acids

The reactions of vinylpyridine polymers with α,β-unsaturated carboxylic acids such as acrylic, methacrylic, crotonic, itaconic, cinnamic, fumaric, and maleic acids were studied. It was found that, when reacted with acrylic, itaconic and fumaric acids. poly(4-vinylpyridine) gave macromolecular betaine products while with maleic acid, betaine as well as the corresponding salt was obtained. Poly(2-vinylpyridine) reacted with the same acids as poly(4-vinylpyridine) gave only the salts. No significant changes were observed with the two polymers when reacted with methacrylic, crotonic, and cinnamic acids. To attempt to rationalize these observations with the two macromolecular tertiary amines, the reactions of 4-methyl and 2-methylpyridines with the same carboxylic acids were investigated. The ¹H-NMR methodology was generally applied to elucidate the chemical structure obtained. © 1995 John Wiley & Sons, Inc.     

Synthesis of highly substituted benzene ring systems through three-component coupling of enyne imines,Fischer carbene complexes,and electron-deficient alkynes

Three-component coupling of Fischer carbene complexes, enyne aldehyde hydrazones, and electron-deficient alkynes leads to simple benzoate derivatives in a process involving the formation of an N-aminopyrrole derivative, Diels-Alder reaction, and nitrene extrusion. The products are readily converted into isoquinolones through reaction with primary amines. The reaction proceeds best with highly substituted and electron-rich pyrroles even though these are the sterically least favorable substrates, and this reactivity trend is supported by a computational study.     

Tricarbonylchromium complexes with phenalene. Synthesis, structure, and thermal rearrangements

The reaction of phenalene with Cr(CO)₃Py₃/BF₃·OEt₂ afforded a mixture of two isomeric complexes, tricarbonyl(6a,7-9,9a,9b-·⁶-phenalene)chromium (1) and tricarbonyl(3a,6a,9b,4-6-·⁶-phenalene)chromium (2). Deprotonation of the mixture of compounds1 and2 followed by treatment with MeI, BuⁿI, or D₂O gave complexesexo-1-R-1 (3–5: R=Me (3), Buⁿ (4), or D (5)). The molecular geometry of complex3 was established by X-ray structural analysis. Heating of complex5 in toluene or C₆F₆ at 90–110 °C resulted in redistribution of deuterium among positionsexo-1,endo-1, and 3 in the resulting complexes of types1 and2 via sigmatropic shifts of the H _exo and H _endo atoms in the nonaromatic ring as well asvia inter-ring migrations of the tricarbonylchromium group. In the case of3, the methyl label is distributed among positionsexo-1 and3 to form isomeric complexes with similar structures (exo-1-Me-2 (6), 3-Me-2 (7), and 3-Me-1 (8), respectively)via processes analogous to those observed in the case of isomerization of compound5 (except for migration of the H _exo atom). The mechanisms of these rearrangements are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1863–1880, October, 1997.     

Synthesis of (η-arene)(η-cyclopentadienyl) iron (II) complexes with heteroatom and carbonyl substituents Part II, Amino substituents

A variety of methods have been used in the synthesis of amino-substituted (η⁶-arene)(η⁵-cyclopentadienyl) iron(II) complexes. Conventional thermal ligand exchange of 2-fluoroaniline with ferrocene in the presence of Devarda’s alloy gave an Ullmann coupling product, 2,2′ diaminobiphenyl complex, whereas omitting metal powder gave the 2-fluorobenzene complex. Double S_NAr substitution of the 1,2-dichlorobenzene complex by dimethylamine is reported. Microwave-assisted S_NAr reactions have led to the development of a one-pot synthesis of N-arylaminoacids. Acetylation of amino-complexes is described and the product anilide complexes used in S_NAr displacements to form aminoanilide analogues. Hexamethyldisilazane was found to be an efficient aminating agent in the presence of alcohols or phenols in DMSO, leading to the synthesis of the (η⁶-1,2-diaminobenzene)(η⁵-Cp) iron(II) complex, the first (ArFeCp)⁺ species reported containing two primary amino groups.     

Transition metal complexes with heterocyclic analogs of fluorene. 1. Synthesis, structures, and haptotropic rearrangements of tricarbonylchromium complexes of dibenzothiophene

The complex formation of dibenzothiophene with chromium carbonyl complexes of the general formula L₃Cr(CO)₃ (L = Py, NH₃, or CO) afforded ⁶-C₁₂H₈SCr(CO)₃ (1). In the presence of tetramethylethylenediamine, complex 1 was selectively metallated with BuLi at position 4 of the coordinated ring to form ⁶-4-LiC₁₂H₈SCr(CO)₃ (2). In decane, the tricarbonylchromium group is reversibly and intramolecularly migrates from the unsubstituted to substituted ring due to the inter-ring haptotropic rearrangement (IRHR) at 130 °C for 100 h. In decane, the rate constant of IRHR was estimated experimentally by ¹H NMR spectroscopy and theoretically by the density functional theory (DFT).