Donor-acceptor interaction-mediated arrangement of hydrogen bonded dimers

The donor-acceptor interaction-driven supramolecular arrangement of a new series of quadruply hydrogen-bonded homo- and heterodimers have been investigated in chloroform with ¹H NMR and UV-Vis spectroscopy. Two kinds of structurally complementary monomers have been prepared. Monomers 3 and 4 are incorporated with one ureidopyrimidone unit and one electron deficient pyromellitic diimide (PDI) or naphthalene diimide (NDI) unit, respectively, monomers 5 and 6 are incorporated with two ureidopyrimidone units and one PDI or NDI unit, respectively, whereas monomers 7 and 8 consist of one electron rich bis-p-phenylene[34]crown-10 unit and one or two 2,7-diamido-1,6-naphthyridine units, respectively. Compounds 3 and 4 exist exclusively as homodimers, respectively. Adding 1 equiv. of 7 to the solution of 3·3 and 4·4 induced them to partially or fully dissociate to produce heterodimers 3·7 and 4·7 due to intermolecular donor-acceptor interaction and the formation of a new binding mode between the ureidopyrimidone of 3 or 4 and the 2,7-diamido-1,6-naphthyridine unit of 7. Both 5 and 6 exist as cyclic monomer and dimer in chloroform. Adding 1 equiv. of 8 to the solution of 5 or 6 in chloroform caused all the cyclic dimer and most of the cyclic monomer to de-cyclize to form new heterodimers 5·8 and 6·8, respectively. ¹H NMR and UV-vis study revealed that heterodimer 5·8 has a structure in which the PDI of 5 is not threaded through the cavity of the bis-p-phenylene[34]crown-10 unit of 8. In contrast, in addition to the heterodimer similar to 5·8, about 40% of heterodimer 6·8 is generated, in which the PDI of 6 is threaded through the cavity of the bis-p-phenylene[3]crown-10 unit of 8 due to the increased donor-acceptor interaction between NDI and bis-p-phenylene[34]crown-10. Steric hindrance and mismatching of the hydrogen bonding moiety play important roles in the arrangement of the new homo- and heterodimers.     

Self-assembly of a new series of quadruply hydrogen bonded heterotrimers driven by the donor-acceptor interaction

This paper describes the self-assembly of a new series of heterotrimers in chloroform-d by utilizing the cooperative interaction of hydrogen bonding and donor-acceptor interaction. Compounds 1 and 11, in which an 2-ureido-4[1H]-pyrimidinone unit is connected to 34-crown-10 or 36-crown-10, were used as donor monomer, and 2 and 19, in which an 2-ureido-4[1H]-pyrimidinone unit is connected to NDI, were used as acceptor monomer, while linear compound 4, which contains two diamido-1,8-naphthyridines, was used as template. A large tri-p-(t-butyl)phenylmethoxyl group was introduced to 19 in order to compare its assembling behavior with that of 2. Mixing 4 with dimer 1·2 caused 1·2 to fully decompose and to afford 55% of ‘in-in’-oriented heterotrimer 1·4·2. Adding 4 to the solution of 2·11 or 11·19 in chloroform-d also led to full dissociation of the dimers. However, in these systems the ‘in-in’-arranged heterotrimer 2·4·11 or 11·4·19 could be produced exclusively.     

Strapped porphyrin rosettes based on the melamine-cyanuric acid motif. Self-assembly and supramolecular recognition

This paper describes studies on the synthesis, self-assembly behavior, and complexing properties of several strapped porphyrin-incorporated melamine-cyanuric or melamine-barbiturate-based rosette supramolecules in chloroform-d. Strapped porpyrin cyanuric acid H₂1 and its Zn (II) complex Zn1 were designed and synthesized. Both H₂1 and Zn1 could combine melamine derivatives 11 or 12 to afford porphyrin rosettes, which are more stable than the model rosette initially reported by Whitesides due to the larger size of the porphyrin unit. The new porphyrin rosettes could efficiently complex tripyridyl derivative 13 through intermolecular, cooperative coordination between Zn (II) and pyridine. Two new pyridine-bearing barbiturates 18a and 18b were also synthesized. Mixing the identical amount of 18a or 18b with 11 or 12 in chloroform-d led to the formation of new isomeric rosettes as a result of different orientation of the pyridine unit of 18a or 18b in the rosettes. ¹H NMR study also revealed that porpyrin-bearing rosette Zn1₃·11₃ could complex pyridine-bearing rosette 11₃·18a₃, leading to the formation of new two-layer-typed supramolecular architectures.     

A facile approach for the synthesis of novel substituted 4H-chromenes and condensation reactions of 4H-chromenes leading to chromenopyrrolones and triazolylchromenopyrrolones

A facile method has been developed for the synthesis of 4H-chromene-3-carboxylates 3a–d by the nucleophilic substitution reaction of 2-hydroxy-2H-chromene-3-carboxylates 2a–d with triethylsilane in the presence of BF₃·O(C₂H₅)₂. Cyclocondensation of 4H-chromene-3-carboxylates 3a–d with benzylamines 4a–d afforded a series of 2,3-dihydrochromenopyrrolones 5a–p and with propargylamine afforded 2-propynyl-2,3-dihydrochromenopyrrolones 6a–d. Click reaction of 6a–d with benzyl azides 7a–d provided a series of 1H-1,2,3-triazolylmethyl-2,3-dihydrochromenopyrrolones 8a–p. Thus synthesized compounds 3a–d, 5a–p, 6a–d, and 8a–p are novel heterocyclic compounds and being reported for the first time.     

Solvophobically driven self-association of a butadiyne-bridged pyridine macrocycle

A butadiyne-bridged square-shaped pyridinophane 2b having ester groups derived from triethylene glycol monomethyl ether was prepared and its self-assembling properties were investigated to assess the repulsive dipole-dipole interaction in less polar solvent and solvophobic driving force in polar solvents. Concentration-dependent ¹H NMR spectra showed that whereas 2b did not self-assemble in chloroform-d, it did in polar solvents consisting of chloroform-d and methanol-d₄ (4:6 to 6:4) with increasing association constants with the increasing methanol-d₄ composition. Comparison of the free energies of association with those of the previously reported benzene macrocycle 1b indicates that solvophobically induced self-association of 2b is more promoted than 1b. The reasons for this difference are discussed from both enthalpy and entropy points of view.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Ring transformation of cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium ion to the corresponding pyrrole derivatives via troponeimine intermediates: photo-induced autorecycling oxidizing reactions of some amines

Ring transformation of 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]furan- 8(7H),10(9H)-dionylium tetrafluoroborate 4⁺·BF₄⁻ to 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrrole-8(7H),10(9H)-dionylium tetrafluoroborate 6a-d⁺·BF₄⁻ consists of the reaction of 4⁺·BF₄⁻ with amines and subsequent exchange of the counter-ion using aq. HBF₄. Reactions of 4⁺·BF₄⁻ with aniline and 4-substituted anilines afforded the corresponding pyrrole derivatives 6a-c⁺·BF₄⁻ directly in good yields. On the other hand, reaction of 4⁺·BF₄⁻ with benzylamine gave the troponeimine intermediate 9, which was not converted to 6d⁺·BF₄⁻ and reverted to 4⁺·BF₄⁻ by adding HBF₄; however, it was converted to 6d⁺·BF₄⁻ upon treatment with (COCl)₂ or SOCl₂, followed by exchange of the counter-ion. In a search for the characteristics of 9, inspection and comparison of the X-ray crystal analyses, NMR and UV-vis spectra, and CV measurement of 9 and N,N-disubstituted troponeimine derivatives 12 were carried out to suggest the remarkable structure of 12 having ionic C-O bonding between the imine-carbon atom and the oxygen atom of the barbituric acid moiety in the solid state. Thus, characteristics of 9 were ascribed to the sterically hindered and favorable conformation of N-protonated troponeimine intermediates. Furthermore, novel photo-induced oxidation reactions of a series of 4⁺·BF₄⁻, 5⁺·BF₄⁻, and 6a,e⁺·BF₄⁻ towards some amines under aerobic conditions were carried out to give the corresponding imines in 455-8362% yields [based on compounds 4⁺, 5⁺, and 6a,e⁺], suggesting the oxidation reaction occurs in an autorecycling process. Mechanistic aspects of the amine-oxidation reaction are also postulated.     

Regioselectivity in the 1,3-dipolar cycloaddition of adamantylidenefulvene and its modification by inclusion in cyclodextrins' solutions

The 1,3-dipolar cycloaddition of adamantylidenefulvene (1) with 2 equiv of nitrile oxides 2a-d gave 1/1 cycloadducts, 3a-d and 4a-d, as the major products, and four other 1/2 minor cycloadducts 5-8a,b. The ratios of 1/1 cycloadducts 3a-d to 4a-d in THF solution were about 1/1 in the four different nitrile oxides 2a-d studied and microwave was found to accelerate the reactions and enhance their yields. It is noteworthy that the regioselectivity of 3a/4a was enhanced to 71/29 in β-cyclodextrin (β-CD) aqueous solution compared to that of 40/60 in the absence of β-CD. The regioselectivity of 3b/4b was further enhanced to 99/1 when 4-tert-butylphenyl hydroximinoyl chloride (9b) was complexed with β-CD and then proceeded to react with 1; this is in sharp contrast with that of 33/67 in the absence of β-CD. The binding constant of 1·β-CD in acetone-d₆/D₂O (1/1) was determined to be 188±9 M⁻¹ by ¹H NMR titration experiments. The binding mode of 1·β-CD was further determined by ROESY experiment. Furthermore, molecular dynamic simulations were carried out to provide information of the complexation modes of 1·β-CD, 3a·β-CD, 4a·β-CD, 9a·β-CD, and 9b·β-CD. It was found that both steric and electrostatic effects play important roles in determining the regio- and stereochemistry of 1,3-dipolar cycloaddition of 1. Finally, β-CD is shown to serve as a chiral shift reagent to differentiate the enantiomers of 4a in ¹H NMR.     

Application and details of photoinduced oxidative cyclization of 5-(4′,9′-methanocycloundeca-2′,4′,6′,8′,10′-pentaenylidene)pyrimidine-2,4,6(1,3,5H)-triones and related compounds

As novel methodology for synthesizing the furan ring, a photoinduced oxidative cyclization of 5-(4′,9′-methanocycloundeca-2′,4′,6′,8′,10′-pentaenylidene)pyrimidine-2,4,6(1,3,5H)-triones (7a-c) and related compounds 9a-c was accomplished to give 5,10-methanocycloundeca[4,5]furo[2,3-d]pyrimidine-2,4(1,3H)-dionylium tetrafluoroborates (8a-c⁺·BF₄⁻) and related compounds 2a-c⁺·BF₄⁻, respectively. In the photoinduced oxidative cyclization, the molecular oxygen in air is used as oxidant and the reaction proceeds under mild conditions to give desired products without byproducts, and thus, it is interesting from the viewpoint of the green chemistry. On the reactions of the mono-substituted derivatives 7d,e and 9e,f, the selectivity of the photoinduced cyclizations were reversed as compared with those of the DDQ-promoted oxidative cyclizations. By the NMR monitoring of the reactions of 7a and deuterated compound 7a-D₂ under degassed conditions, the details of the reaction pathway were clarified and rationalized on the basis of the MO calculation by the 6-31G^∗ basis set of the MP2 levels as well.     

Syntheses,crystal structures,and magnetic and luminescent properties of a series of lanthanide coordination polymers with chelidamic acid ligand

A series of lanthanide(III) complexes with chelidamic acid ligand, [Ln(C₇H₂NO₅)·3H₂O]_n·nH₂O (Ln = La (1), Y (2), Sm (3), and Nd (4)), [Gd₂(C₇H₂NO₅)₃·4H₂O]_n·2nH₂O (5) and [Ce(C₇H₂NO₅)·1.5H₂O]_n (6), have been synthesized by hydrothermal method and structurally characterized by single-crystal X-ray diffraction. Complexes 1–4 are isostructural and possess 2D framework. Complex 5 contains two different Gd(III) ions linked through carboxylate group to form a 2D framework. Complex 6 exhibits a (4⁴) topology 2D network. The variable-temperature magnetic properties of 3 and 5 have been investigated. Furthermore, the photoluminescent properties of 1, 2, 3, and 5 at room temperature were also studied.     

Synthesis, coordination studies and redox properties of a novel ditertiary phosphine bearing two ferrocenyl groups

The new ferrocenyl substituted ditertiary phosphine {FcCH₂N(CH₂PPh₂)CH₂}₂ [Fc = (η⁵-C₅H₄)Fe(η⁵-C₅H₅)] (1) was prepared, in 72% yield, by Mannich based condensation of the known bis secondary amine {FcCH₂N(H)CH₂}₂ with 2 equiv. of Ph₂PCH₂OH in CH₃OH. Phosphine 1 readily coordinates to various transition-metal centres including Mo⁰, Ru^II, Rh^I, Pd^II, Pt^II and Au^I to afford the heterometallic complexes {RuCl₂(p-cym)}₂(1) (2), (AuCl)₂(1) (3), cis-PtCl₂(1) (4), cis-PdCl₂(1) (5), cis-Mo(CO)₄(1) (6), trans,trans-{Pd(CH₃)Cl(1)}₂ (7) and trans,trans-{Rh(CO)Cl(1)}₂ (8). In complexes 2, 3, 7 and 8 ligand 1 displays a P,P′-bridging mode whilst for 4-6 a P,P′-chelating mode is observed. All new compounds have been fully characterised by spectroscopic and analytical methods. Furthermore the structures of 1, 2 · 2CH₂Cl₂, 3 · CH₂Cl₂, 4 · CH₂Cl₂, 6 · 0.5CHCl₃ and 8 have been elucidated by single crystal X-ray crystallography. Electrochemical measurements have been undertaken, and their redox chemistry discussed, on both noncomplexed ligand 1 and representative compounds containing this new ditertiary phosphine.     

Synthesis, properties, and oxidizing function of 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates

Uracil-annulated heteroazulenes, 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates 7a,b·BF₄⁻, which are the isoelectronic compounds of 5-dezazaflavin, were synthesized. X-Ray crystal analysis and MO calculations were carried out to clarify the structural characteristics of 7a,b·BF₄⁻. The stability of cations 7a,b is expressed by the pK_R+ values which were determined spectrophotometrically to be 10.9 and 11.2, respectively. The electrochemical reduction of 7a,b exhibited high reduction potentials at −0.84 and −0.87 (V vs Ag/AgNO₃) upon cyclic voltammetry (CV). A good linear correlation between the pK_R+ values and reduction potentials (E1_red) of 7a,b·BF₄⁻ and reference compounds 4·BF₄⁻ and 5·BF₄⁻ was obtained. In a search of the reactivity, reactions of 7a,b·BF₄⁻ with some nucleophiles, hydride and diethylamine, were carried out to clarify that the introduction of nucleophiles to give regio-isomers is dependent on the nucleophile. The photo-induced oxidation reactions of 7a,b·BF₄⁻ toward some alcohols under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compounds 7a,b·BF₄⁻], suggesting the oxidizing function of 7a,b·BF₄⁻ toward alcohols in the autorecycling process.     

Syntheses, topological analyses and photoelectric properties of Ag(I)/Cu(I) metal-organic frameworks based on a tetradentate imidazolate ligand

A new tetradentate imidazolate ligand 1,1′,1″,1′′′-(2,2′,4,4′,6,6′-hexamethylbiphenyl-3,3′,5,5′-tetrayl)tetrakis(methylene)(1H-imidazole) (L) and four Ag(I)/Cu(I) coordination polymers, namely [(MCN)₃L]_n (1: M=Ag; 2: M=Cu), and [(MSCN)₂L]_n (3: M=Ag; 4: M=Cu) are described. All four new coordination polymers were fully characterized by infrared spectroscopy, elemental analysis and single-crystal X-ray diffraction. Compound 1 features a 3D supramolecular framework constructed by 1D chains through inter-chain Ag-N(CN) and inter-layer Ag-N(L) weak interactions with an uninodal 6⁶ topology. Complex 2 presents a 3D framework characterized by a tetranodal (3,4)-connected (3·4·5·10²·11)(3·4·5·6·7·9)(3·6·7)(6·10²) topology. Complexes 3 and 4 are isostructural, and both have a 3D network of trinodal 4-connected (4·8⁵)₂(4²·8²·10²)(4²·8⁴)₂ topology. The luminescent properties for these compounds in the solid state as well as the possible ferroelectric behavior of 1 are discussed.     

Preparation, coordination properties and catalytic use of 1′-(diphenylphosphanyl)-1-ferrocenecarboxamides bearing 2-hydroxyethyl pendant groups

Polar amido-phosphane ligands, viz 1-(diphenylphosphanyl)-1′-[N-(2-hydroxyethyl)carbamoyl]ferrocene (1) and 1-(diphenylphosphanyl)-1′-[N,N-bis(2-hydroxyethyl)carbamoyl]ferrocene (2) were synthesised from 1′-(diphenylphosphanyl)-1-ferrocenecarboxylic acid (Hdpf) by direct amide coupling or via Hdpf-pentafluorophenyl ester 3. Subsequent reactions of 1 and 2 with [PdCl₂(cod)] (cod = η²:η²-cyclocta-1,5-diene) gave the respective bis(phosphane) complexes trans-[PdCl₂L₂] (4, L = 1; 5, L = 2). Depending on the solvent used in their subsequent crystallisation (ethanol or chloroform), these complexes were isolated in several defined solvated forms. The structure determination for free ligands and their solvated complexes (4·2EtOH, 4·6CHCl₃, 5·2EtOH, and 5·4CHCl₃) revealed the dominating role of hydrogen bonding in their crystal assemblies, the nature and complexity of the formed hydrogen-bonded arrays strongly varying with the ligand structure (one vs. two 2-hydroxethyl chains), their number in the discrete species (free ligands vs. the complexes), and also with the solvate. Catalytic tests performed with 4 and 5 in Suzuki-Miyaura cross-coupling reaction showed that both complexes form active catalysts for the coupling of aryl bromides with phenylboronic acid in common polar organic solvents, in water and in toluene-water biphasic mixture. Yet, complex 4 gave rise to hydrolytically more stable catalyst, which could be used five times without any detectable loss of activity in the toluene/water system. Complex 4 was also successfully applied to the synthesis of biaryl anti-inflammatory drugs and their analogues in pure water and in the toluene-water mixture.     

Remarkable effect of hydrogen bonding between ring and axle components on deslipping reactions of rotaxanes

A series of rotaxanes 1·5, 2·5, 3·5, and 4·5 bearing a different substituent (X = NO₂, Br, H, and OMe, respectively) at para position on the phenol moiety of the ring component exhibit clear difference in deslipping behavior. The difference in the deslipping rates is consistent with the difference in intercomponent hydrogen bonding strength estimated from the O-H stretching vibration wavenumbers. The para substituent dictates the relative strength of the intra- and intermolecular hydrogen bonds. Thus the incorporation of an intramolecular hydrogen bond allows for tunability of the strength of the intercomponent interaction.     

Preparation and structures of 6- and 7-coordinate salen-type zirconium complexes and their catalytic properties for oligomerization of ethylene

A series of salen-type zirconium complexes of the general formula LZrCl₂ (L = N,N′-ethylenebis(salicylideneiminate), 3a; N,N′-ethylenebis(3,5-di-tert-butylsalicylideneiminate), 3b; N,N′-ethylenebis(5-methoxysalicylideneiminate), 3c; N,N′-ethylenebis(5-chlorosalicylideneiminate), 3d; N,N′-ethylenebis(5-nitrosalicylideneiminate), 3e; N,N′-o-phenylenebis(salicylideneiminate), 4a; N,N′-o-phenylenebis(3,5-di-tert-butylsalicylideneiminate), 4b; N,N′-o-phenylenebis(5-methoxysalicylideneiminate), 4c; N,N′-o-phenylenebis(5-chloro-salicylideneiminate), 4d) were prepared. The crystal structures of 6- and 7-coordinate zirconium complexes 4b and [4b · OCMe₂] were determined by X-ray crystallography, which reveals that a salen-type zirconium complex possesses a labile coordination site on the Zr center with a relatively stable framework and that the coordination and the dissociation of O-donor molecules occur readily at this site. The catalytic properties of 3(a-e) and 4(a-d) were studied for ethylene oligomerization in combination with Et₂AlCl as co-catalyst. Complex 3c featuring a methoxy-substituted salen ligand displayed higher activity than its analogous precursors having chloro and nitro groups as substituents. The catalytic reactions by 3(a-e) and 4(a-d) gave C₄-C₁₀ olefins and low-carbon linear α-olefins in good selectivity.     

Self-assembly of a novel series of hetero-duplexes driven by donor-acceptor interaction

The self-assembly of a novel series of donor-acceptor interaction-driven artificial hetero-duplexes in organic media has been described. Four linear compounds 1a-1d, bearing two to five electron rich 1,5-dioxynaphthalene units connected by the tetra(ethylene glycol) linker, respectively, have been prepared and used as donors, while eight compounds 2a-2d, 13-16, bearing one to four electron deficient pyromellitic diimide, 1,4,5,8-naphthalene-tetracarboxydiimide, or perylene-3,4,9,10-tetracarboxydiimide units, respectively, have been used as acceptors. The structure of the hetero-duplexes has been characterized by the ¹H NMR, UV-vis spectroscopy and vapor pressure osmometry. It is revealed that the binding stability of the duplexes vary greatly, depending on the length and structure of the monomers and also the solvent, and hetero-duplex 1d·2d displays a maximum association constant of ca. 1.0×10⁴ M⁻¹ in chloroform.     

One-pot synthesis of macrocyclic compounds possessing two cyclobutane rings by sequential inter- and intramolecular [2+2] photocycloaddition reactions

Sensitized photocycloaddition reactions of 6,6′-dimethyl-4,4′-[1,3-bis(methylenoxy)phenylene]-di-2-pyrone (1) with electron-poor α,ω-diolefins such as ethylene diacrylate (2a) and polyoxyethylene dimethacrylates (2b-d) afforded site- and stereoselective macrocyclic dioxatetralactones (3a-d) and (4b) having 18- to 25-membered rings across the C5-C6 and C5′-C6′ double bonds, or C5-C6 and C3′-C4′ double bonds in 1, respectively. Similar photoreactions of 1 with electron-rich α,ω-diolefins such as poly(ethylene glycol)divinyl ether (2e and 2f) afforded crown ether-type macrocyclic compounds (5e and 5f) having 18- and 21-membered rings across the C3-C4 and C3′-C4′ double bonds in 1, respectively. The stereochemical features of 3b, 5e-xx, and 5e-nn were determined by the X-ray crystal analysis. The reaction mechanism was inferred by MO methods.     

Cobalt(II), nickel(II) and copper(II) compounds derived from template reactions of enantiomerically pure 2-amino-thiazoles

Herein we report the syntheses and structural analyses of three coordination compounds Co(L)₂ (3), Ni(L)₂, (4) and Cu(L)₂ (5) (L = bis[(4R,5R)-4-methyl-5-phenyl-4,5-dihydro-thiazol-2-yl]-amine) prepared by template reactions from the optically active ligand (4R,5R)-4-methyl-5-phenyl-4,5-dihydro-thiazol-2-yl-amine (1) and CoCl₂·6H₂O, NiBr₂·3H₂O or Cu(OAc)₂·H₂O The template reactions involve the condensation of two molecules of thiazol-2-yl-amine and elimination of one NH₃. The resulting bidentate ligand coordinates to the metal ion through the imine nitrogen atoms forming a six-membered ring, presenting an electronic delocalization which averages the four M–N bond lengths. The distorted tetrahedral geometry of the metal atoms gives place to complex electronic spectra for compounds 3–5. A mixed ionic compound (6) formed by three cations (4S,5S)-3,4-dimethyl-5-phenyl-thiazolidin-2-ylidene ammonium, one dianion tris-(thiocyano)bromide cobaltate and one bromide, obtained from reaction of (4S,5S)-3,4-dimethyl-5-phenyl-thiazolidin-2-ylidene ammonium thiocyanate (2) and CoBr₂ is also described. Compounds 3–6 were characterized in the solid state by UV–Vis–NIR and IR spectroscopy, mass spectrometry and X-ray diffraction analyses. Metal···H–C, S···H–C interactions were observed in 3–6, whereas in 6, also Br···H–N, Br···H–C and Br···S, S···S short contacts were found.     

Metallacrown ethers with a symmetric bis(phosphite) ligand derived from 1,2-bis-(2-hydroxyethoxy)benzene: Synthesis, characterization and hydroformylation of styrene

To better understand the effects of ligand configuration on hydroformylation reactions carried out in the presence of LiBPh₄·3dme (dme = 1,2-dimethoxyethane), a conformationally restrained bis(phosphite) ligand derived from 1,2-bis-(2-hydroxyethoxy)benzene, {[(2,2′-O₂C₁₂H₈)P(C₂H₄O₂)]₂C₆H₄}, 1, has been prepared and its Rh(I) metallacrown ether complex has been evaluated as a catalyst for the hydroformylation of styrene. Both the activity and regioselectivity of the catalyst are sensitive to the amount of the LiBPh₄·3dme added with the activity decreasing by 16% and the regioselectivity for the iso increasing by 9% at a 8:1 LiBPh₄:Rh ratio.Model complexes for the octahedral, cis-Mo(CO)₄(1), 2, and square planar, cis-PtCl₂(1), 3, and cis-PdCl₂(1), 4, complexes in the catalytic cycle has been have been studied using multinuclear NMR spectroscopy and X-ray crystallography. Although the X-ray crystal structure of 2 suggests that the metallacrown ether ring could adopt a configuration capable of binding alkali metal cations, this does not appear to occur in a dichloromethane-d₂ solution of 2 because no shift in the ³¹P NMR resonance 2 is observed upon the addition of an excess of LiBPh₄·3dme. The ³¹P{¹H} NMR spectra of chloroform-d solutions of 2 (in the presence of a catalytic amount of HgCl₂) and of 4 and the X-ray crystal structures of the complexes indicate that the bis(phosphite) ligands are cis coordinated in these complexes in both the solution and in the solid state. This is particularly surprising for 4 because related PdCl₂{Ph₂P(CH₂CH₂O)_nCH₂CH₂PPh₂} (n = 3-5) complexes exhibit both cis-trans and monomer-oligomer equilibria in solution.