Structure of N,C,N-chelated organotin(IV) fluorides

The set of starting tri-, di- and monoorganotin(IV) halides containing N,C,N-chelating ligand (L^NCN = {1,3-[(CH₃)₂NCH₂]₂C₆H₃}⁻) has been prepared (1-5) and two compounds structurally characterized ([L^NCNPh₂Sn]⁺I₃⁻ (1c), L^NCNSnBr₃ (5)) in the solid state. These compounds were reacted with KF with 18-crown-6, NH₄F or L^CNnBu₂SnF to give derivatives containing fluorine atom(s). Triorganotin(IV) fluorides L^NCNMe₂SnF (2a) and L^NCNnBu₂SnF (3a) revealed monomeric structural arrangement with covalent Sn-F bond both in the coordinating and non-coordinating solvents, except the behaviour of 3a that was ionized in the methanol solution at low temperature. The products of fluorination of L^NCNSnPhCl₂ (4) and 5 were described by NMR in solution as the ionic hypervalent fluorostannates or the oligomeric species reacting with chloroform, methanol or moisture to zwitterionic monomeric stannate L^NCN(H)⁺SnF₄⁻ (5c), which was confirmed by XRD analysis in the solid state.     

Dioxomolybdenum(VI) complexes containing N-heterocyclic carbenes

Compound MoO₂Cl₂(THF)₂ reacts with two equivalents of 1,3-dialkyl substituted 4,5-dimethylimidazol-2-ylidenes to give the dioxomolybdenum(VI) complexes MoO₂Cl₂(L^R)₂ [R = Me (1), i-Pr (2)]. Treatment of MoO₂Cl₂(THF)₂ with one equivalent of the N-heterocyclic carbenes L^Me, L^i-Pr and ^C1L^n-Bu (L^Me = 1,3,4,5-tetramethylimidazol-2-ylidene, L^i-Pr = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, and ^C1L^n-Bu = 1,3-dibutyl-4,5-dichloroimidazol-2-ylidene) affords the monocarbene adducts MoO₂Cl₂(L^R) [R = Me (3), i-Pr (4)] and MoO₂Cl₂(^C1L^n-Bu) (5), respectively. Decomposition of complexes 1-5 affords a molybdenum oxychloride anion [Mo₂O₅Cl₄]²⁻ as an imidazolium salt.     

Syntheses and structures of zinc and tin(II) compounds with hemilabile N-silyl-tert-butylamido and N-silyl-p-tolylamido ligands that contain pendent tert-butoxy groups

Syntheses and solid-state structures of zinc and tin(II) compounds, containing the N-silyl-amide ligands (O^tBu)(NR)SiMe₂, R = ^tBu (L^tBu), or R = p-tolyl (L^pTol), are reported. The N-silyl amines were synthesized by modified published procedures from commercially available Me₂SiCl₂, ^tBuOH, and ^tBuNH₂, or p-Me-C₆H₄NH₂, respectively. Treatment of SnCl₂ with LiL^pTol furnished Sn(L^pTol)₂, which was X-ray structurally characterized and shown to contain two covalent Sn-N bonds and two asymmetrical O → Sn donor bonds. The single-crystal X-ray structure of Sn(L^tBu)₂ revealed a much more symmetrically-coordinated, pseudo-trigonal-bipyramidal tin atom. Aminolysis of diethylzinc with HL^pTol produced [EtZn(L^pTol)]₂, which crystallized as a centrosymmetric dimer, containing four-coordinate zinc atoms connected by bridging amides. Zinc dichloride, by contrast, reacted with two equivalents of LiL^tBu to produce the homoleptic, pseudo-spirocyclic Zn(L^tBu)₂.     

Preparation, spectroscopic properties of 1,4-di (N,N-diisopropylacetamido)-2,3(1H,4H)-quinoxalinedione (L) lanthanide complexes and the supramolecular structure of [Nd2L2(NO3)6(H2O)2]·H2O

The reaction of lanthanide nitrate with 1,4-di (N,N-diisopropylacetamido)-2,3(1H,4H)-quinoxalinedione (L) yields six novel Ln(III) complexes ([Ln₂L₂(NO₃)₆(H₂O)₂]·H₂O) which are characterized by elemental analysis, thermogravimetric analysis (TGA), conductivity measurements, IR, electronic and ¹H NMR spectroscopies. A new quinoxalinedione-based ligand is used as antenna ligand to sensitize the emission of lanthanide cations. The lowest triplet state energy level of the ligand in the nitrate complex matches better to the resonance level of Eu(III) and Sm(III) than Tb(III) and Dy(III) ion. The f-f fluorescence is induced in the Eu³⁺ and Sm³⁺ complexes by exciting into the π-π* absorptions of the ligand in the UV. Furthermore, the crystal structures of a novel binuclear complex [Nd₂L₂(NO₃)₆(H₂O)₂]·H₂O has been determined by single-crystal X-ray diffraction. The binuclear [Nd₂L₂(NO₃)₆(H₂O)₂]·H₂O complex units are linked by the intermolecular hydrogen bonds and π-π interactions to form a two-dimensional (2-D) layer supramolecule.     

Reactions of Ru(Cp) complexes with P(o-tolyl)3

Reaction of [Ru(Cp^∗)(CH₃CN)₃](PF₆) with P(o-tolyl)₃ affords [Ru(Cp^∗){(η⁶-o-tolyl)P(o-tolyl)₂}](PF₆) (4) in which the P-atom is not coordinated to the metal. The solid-state structure of 4 has been determined. A related reaction with P(p-tolyl)₃ reveals a small quantity [Ru(Cp^∗){(η⁶-p-tolyl)P(o-tolyl)₂}](PF₆), in solution, but mostly the expected bis-phosphine complex. Reaction of the Ru(IV) dication, [Ru(Cp^∗)(η³-PhCHCHCH₂)(DMF)₂](PF₆)₂, with P(o-tolyl)₃ gives a mixture of the phosphonium salt, C₆H₅CHCHCH₂P(o-tolyl)₃ (9) and the dication [Ru(Cp^∗) (η⁶-C₆H₅CHCHCH₂P(o-tolyl)₃)](PF₆)₂ (10). Salt 9 forms via attack of the P-atom on the allyl ligand. The latter product results from complexation of 9 via the phenyl group of the former allyl ligand. It would seem that the sterically demanding P(o-tolyl)₃ ligand is not readily compatible with the Ru(Cp^∗) fragment, in either the +2 or +4 oxidation state. Detailed NMR studies are reported.     

Two-stage formation of chloro (N-o-chlorobenzamido-meso-tetraphenylporphyrinato) zinc(II) methylene chloride solvate: Zn(N-NHCO(o-Cl)C6H4-tpp)Cl · CH2Cl2

The coordinating properties of N-o-chlorobenzamido-meso-tetraphenylporphyrin (N-NHCO(o-Cl)C₆H₄-Htpp; 11) have been investigated for the Zn²⁺ ion. Insertion of Zn results in the formation of the zinc complex Zn(N-NCO(o-Cl)C₆H₄-tpp)(MeOH) · MeOH (12 · MeOH). The diamagnetic 12 · MeOH can be transformed into the diamagnetic Zn(N-NHCO(o-Cl)C₆H₄-tpp)Cl · CH₂Cl₂ (13 · CH₂Cl₂) in a reaction with aqueous hydrogen chloride (2%). X-ray structures for 12 · MeOH and 13 · CH₂Cl₂ have been determined. The coordination sphere around the Zn²⁺ ion in 12 · MeOH is a distorted trigonal bipyramid with N(2), N(4) and O(2) lying in the equatorial plane, whereas for the Zn²⁺ ion in 13 · CH₂Cl₂, it is a square-based pyramid in which the apical site is occupied by the Cl(1) atom.     

Crystal structure and luminescence property of novel three-dimensional network of {Eu2(p-BDC)3(Phen)2(H2O)2}n

The single crystal of a supramolecule, {Eu₂(p-BDC)₃(Phen)₂(H₂O)₂}_n (p-BDC=1,4-benzenedicarboxylate), with characteristic luminescence of Eu³⁺ was obtained by means of soft chemistry. The crystal structure determination reveals that each Eu³⁺ ion is coordinated by five oxygen atoms of p-BDC anions, one oxygen atom from water molecule, and two nitrogen atoms of Phen, respectively, resulting in an eight-coordinated Eu³⁺ center and a distorted square antiprism coordination polyhedron. Four bridges, two carboxylates of μ₄-p-BDC and two of μ₃-p-BDC, connect two Eu atoms into a binuclear unit. Moreover, the μ₃-p-BDC integrates the binuclear building blocks at the direction of b axis and the μ₄-p-BDC polymerizes the structure roughly along the direction of the sum vector of axis b and c, respectively, forming two-dimensional layers. Hydrogen bonds between layers make the structure a three-dimensional network. The luminescence spectra measured under 77 K demonstrate the antenna effect of Phen and the ⁵D₁→⁵D₀ energy transfer path within Eu³⁺ ion. Both luminescence spectra and crystal structure lead to the conclusion that the local symmetry around the Eu³⁺ ion is C₁ and that more than one Eu³⁺ ion sites having slight environmental difference are present.     

Isoquinolin-1(2H)-ones and 1,6-naphthyridin-5(6H)-ones by an N-acylation-SNAr sequence

A new synthesis of 2,3-dialkyl-4-carbomethoxyisoquinolin-1(2H)-ones and 6,7-dialkyl-8-carbomethoxy-1,6-naphthyridin-5(6H)-ones is reported. The process involves treatment of a β-enaminoester with 2-fluoro-5-nitrobenzoyl chloride, 2-fluorobenzoyl chloride or 2-chloronicotinoyl chloride followed by heating in the presence of base. The conversion, which proceeds by an N-acylation-S_NAr reaction sequence, affords 50–86% yields when R¹ is n-alkyl but ≤30% yields when R¹ is α-branched.     

N-arylammonio- and N-pyridinium-substituted derivatives of dodecahydro-closo-dodecaborate(2-)

We report two methods for preparing N-arylammonio, N-pyridyl and N-arylamino dodecaborates: heating of the tetrabutylammonium salt of dodecahydro-closo-dodecaborate(2-) with aryl and pyridyl amines, or nucleophilic attack of [closo-B₁₂H₁₁NH₂]²⁻ on a strongly deactivated aromatic system. With aryl amines we obtained [1-closo-B₁₂H₁₁N(R¹)₂C₆H₅]⁻ (R¹ = H, CH₃). With 4-(dimethylamino)pyridine, [1-closo-(B₁₂H₁₁NC₅H₄)-4-N(CH₃)₂]⁻, with a bond between the boron and the pyridinium nitrogen, was obtained. A presumable mechanism for this kind of reactions is reported. By nucleophilic substitution, two products, [1-closo-(B₁₂H₁₁NHC₆H₃)-3,4-(CN)₂]²⁻ and [1-closo-(B₁₂H₁₁NHC₆H₂)-2-(NO₂)-4,5-(CN)₂]²⁻, were formed with 4-nitrophthalonitrile and 1-chloro-2,4-dinitrobenzene gave [1-closo-(B₁₂H₁₁NHC₆H₃)-2,4-(NO₂)₂]²⁻. For [1-closo-B₁₂H₁₁N(CH₃)₂C₆H₅]⁻ and [1-closo-(B₁₂H₁₁NHC₆H₃)-2,4-(NO₂)₂]²⁻ single crystal X-ray structures were obtained.     

Pd(PPh3)4-catalyzed direct ortho-fluorination of 2-arylbenzothiazoles with an electrophilic fluoride N-fluorobenzenesulfonimide (NFSI)

An efficient protocol was developed for regio-selective Pd-catalyzed direct ortho-fluorination of 2-arylbenzo[d]thiazoles using N-fluorobenzenesulfonimide (NFSI) as the F⁺ source, and l-proline as the crucial promoter. The present method offered a practical route to synthesize valuable fluorinated products, which are of potential importance in the pharmaceutical and agrochemical industries.     

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.     

Synthesis and structural characterization of a dichloro zinc complex of N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane: Application to ring opening polymerization of rac-lactide

A novel dichloro zinc complex (L¹)ZnCl₂, where L¹ is N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane, has been synthesized and characterized. The dimethyl derivatives, generated in situ from the well characterized dichloro zinc complexes (L¹)ZnCl₂ and (L²)ZnCl₂, where L² is N,N′-bis-(benzyl)-(R,R)-1,2-diaminocyclohexane, were employed as initiators for the ring opening polymerization (ROP) of rac-lactide (rac-LA). The complexes were found to be highly efficient initiators yielding the polylactide (PLA) with a narrow molecular weight distribution. The catalytic activity and heterotactic selectivity of the Zn(II) complexes were affected by the substituents on the phenyl groups of benzyl moieties in (R,R)-1,2-diaminocyclohexane. The dimethyl derivative of (L²)ZnCl₂ produced highly stereocontrolled PLA with P_r = 0.75 at −25 °C.     

Au(I) and Au(III) complexes of a sterically bulky benzimidazole-derived N-heterocyclic carbene

The reaction of [AuCl(SMe₂)] with in situ generated [AgCl(ⁱPr₂-bimy)] (ⁱPr₂-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene), which in turn was obtained by the reaction of Ag₂O with 1,3-diisopropylbenzimidazolium bromide (ⁱPr₂-bimyH⁺Br⁻, A), afforded the monocarbene Au(I) complex [AuCl(ⁱPr₂-bimy)] (1). Subsequent reaction of 1 and the ligand precursor ⁱPr₂-bimyH⁺BF₄⁻, (B) in acetone in the presence of K₂CO₃ yielded the bis(carbene) complex [Au(ⁱPr₂-bimy)₂]BF₄ (2) as a white powder in 80% yield. The oxidative addition of elemental iodine to complex 2 gave the bis(carbene) Au(III) complex trans-[AuI₂(ⁱPr₂-bimy)₂]BF₄ (3) as an orange-red powder in 92% yield. All complexes 1-3 have been fully characterized by multinuclear NMR spectroscopies, ESI mass spectrometry, elemental analysis, and X-ray single crystal diffraction. Complexes 1 and 2 adopt a linear geometry around metal centers as expected for d¹⁰ metals. The geometry around the Au(III) metal center in 3 is essentially square-planar with two carbene ligands in trans-position to each other. Complex 3 shows absorption and photoluminescence properties owing to a ligand to metal charge transfer.     

Coordination of N-methylpyrrolidone to iron(II)

The use of NMP (N-methylpyrrolidone) as a cosolvent has been shown to improve the yield of iron-catalyzed cross-coupling reactions, but surprisingly there are no iron complexes of NMP in the literature. This paper reports two novel NMP complexes of iron(II): Fe₃Cl₆(NMP)₈ and L^tBuFe(NMP)Cl (L^tBu = bulky β-diketiminate ligand). The X-ray crystal structure of Fe₃Cl₆(NMP)₈ shows an octahedral cation and two tetrahedral FeCl₃(NMP)⁻ anions. ¹H NMR spectra show that the NMP ligands are labile, exchanging rapidly on the NMR time scale. The β-diketiminate complex has a trigonal pyramidal geometry with the NMP in an axial position. The use of NMP improves the yield of the catalytic cross-coupling of methyl 4-chlorobenzoate and 1-hexylmagnesium bromide using these and other iron complexes as precatalysts.     

Complexes of N-thiophosphorylthiourea (EtO)2P(O)CH2C6H4-4-[NHC(S)NHP(S)(OiPr)2] with Zn(II), Cd(II), Co(II) and Cu(PPh3)(I)

Reaction of O,O’-diisopropylthiophosphoric acid isothiocyanate (iPrO)₂P(S)NCS with diethyl 4-aminobenzylphosphonate (EtO)₂P(O)CH₂C₆H₄-4-NH₂ leads to the new N-thiophosphorylated thiourea (EtO)₂P(O)CH₂C₆H₄-4-[NHC(S)NHP(S)(OiPr)₂] (HL). Reaction of the potassium salt of HL with Zn(II), Cd(II) and Co(II) in aqueous EtOH leads to complexes of formula M(L-S,S’)₂ (ML₂). Heteroligand copper(I) complex of HL and triphenylphosphine was prepared by the reaction of the potassium salt KL and Cu(PPh₃)₃I. Copper in complex Cu(PPh₃)L is bound by one PPh₃ and one SCNPS fragment of the chelating ligand. Compounds obtained were investigated by IR, UV–Vis, ¹H and ³¹P{¹H} NMR spectroscopy, and microanalysis. The structures of HL and Cu(PPh₃)L were investigated by single crystal X-ray diffraction analysis.     

Coordination to copper(II) strongly enhances the in vitro antimicrobial activity of pyridine-derived N(4)-tolyl thiosemicarbazones

Five copper(II) complexes with N(4)-ortho, N(4)-meta and N(4)-para-tolyl thiosemicarbazones derived from 2-formyl and 2-acetylpyridine were obtained and thoroughly characterized. The crystal structure of N(4)-meta-tolyl-2-acetylpyridine thiosemicarbazone (H2Ac4mT) was determined, as well as that of its copper(II) complex [Cu(2Ac4mT)Cl], which contains an anionic ligand and a chloride in the coordination sphere of the metal. The in vitro antimicrobial activities of all thiosemicarbazones and their copper(II) complexes were tested against Salmonella typhimurium and Candida albicans. Upon coordination a substantial decrease in the minimum inhibitory concentration, from 225 to 1478 μmol L⁻¹ for the thiosemicarbazones to 5–30 μmol L⁻¹ for the complexes was observe against the growth of Salmonella typhimurium and from 0.7–26 to 0.3–7 μmol L⁻¹ against the growth of C. albicans, suggesting that complexation to copper(II) could be an interesting strategy of dose reduction.     

Comparative XANES study on the two electron-doped high-Tc superconductor systems, (Sr,La)CuO2 and (Nd,Ce)2CuO4

Here we employ high-quality samples of (Sr_1−xLa_x)CuO₂ and (Nd_2−xCe_x)CuO₄ and XANES spectroscopy at O-K, Cu-L_2,3 and Ce-M_4,5 edges to gain comprehensive understanding of the electronic structure and doping in n-type high-T_c superconductors. Not only common but also slightly different features are revealed for the two systems. From O-K-edge spectra, the UHB is found essentially independent of the electron-doping level for both the systems, in line with our understanding that the doped electrons do not go to the O site in n-type copper-oxide superconductors. Another common observation is that the main Cu^II peak at the Cu-L₃ edge (due to transitions to the Cu^II-3d orbitals) systematically decreases in intensity upon electron doping, hence verifying the fact that the doped electrons go to the Cu site. The difference then between the two systems is that in (Sr_1−xLa_x)CuO₂ the weaker Cu^II peak due to transitions to the Cu^II-4s orbital depends on the degree of doping. Moreover, it was found that with increasing x, electron density increases much faster in (Sr_1−xLa_x)CuO₂ than in (Nd_2−xCe_x)CuO₄. This is a consequence of two phenomena: a tiny increase in oxygen content concomitant to the Ce^IV-for-Nd^III substitution and the somewhat lower Ce-valence value of +3.8 compared to the nominal tetravalent state.     

Photoluminescent behavior of SrB4O7:RE (RE=Sm and Eu) prepared by Pechini, combustion and ceramic methods

This work reports the preparation of system containing RE²⁺ ions (RE=Sm and Eu)-doped in SrB₄O₇ matrix by ceramic, Pechini and combustion methods. These compounds were prepared by reduction of RE³⁺ to RE²⁺ in air, which exhibit some different features according to the preparation method. Photoluminescent properties of these systems were investigated based on the emission and excitation spectral data. The emission spectra of SrB₄O₇:Eu²⁺ system prepared by combustion and Pechini methods are characterized by a broad band assigned to interconfigurational 4f⁶5d→4f⁷ transition, while SrB₄O₇:Sm²⁺ compound exhibit narrow emission bands arising from intraconfigurational-4f⁶ also shows ⁴G_5/2→⁶H_J′ transitions ( and ) arising from Sm³⁺ ion, transitions. SrB₄O₇:RE system prepared by combustion method presents emission bands from RE³⁺ ions as intense as that arising from RE²⁺, suggesting that the preparation route is not efficient for the reduction RE³⁺→RE²⁺ process. Emission quantum efficiency and radiative emission rates of Sm²⁺ ion are determined and discussed.     

Tri- and diorganostannates containing 2-(N,N-dimethylaminomethyl)phenyl ligand

The C,N-chelated tri and diorganotin(IV) chlorides react with both protic mineral acids and carboxylic acids. The nitrogen atom of the L^CN ligand (where L^CN is 2-(dimethylaminomethyl)phenyl) is thus quarternized - protonated and new Sn-X bond (X = Cl, Br, I or the remainder of the starting acid used) is simultaneously formed. The set of zwitterionic tri and diorganostannates containing protonated 2-(dimethylaminomethyl)phenyl-moiety was prepared and structurally characterized by multinuclear NMR spectroscopy and XRD techniques. In all these cases, the intramolecular N-H?X bond is present in the molecule. Despite the central tin atom remains five-coordinated (except for the [HL^CNH]⁺[(n-Bu)₂SnCl(NO₃)₂]⁻) and reveals a distorted trigonal bipyramidal geometry, the ¹¹⁹Sn NMR chemical shift values of these zwitterionic stannates are somewhat shifted to the higher field than corresponding starting C,N-chelated tri and diorganotin(IV) halides. Reactions of C,N-chelated organotin(IV) halides with various Lewis acids are also discussed.     

A novel P,S-heterodonor ligand and palladium(0) complex catalyzed Suzuki cross-coupling reaction

Axially dissymmetric P,S-heterodonor ligand L3 synthesized from BINOL is an effective promoter in the palladium(0)-catalyzed Suzuki cross-coupling reaction of phenylboronic acid with aryl bromides and iodide at 60-80 °C. On the basis of ¹³C and ³¹P NMR spectroscopic investigation and X-ray diffraction, it was revealed that N,N-dimethylthiocarbamate-phosphine ligand L3 might be a P,S-heterodonor bidentate ligand to palladium(0) center.