Anomalies in the polymerization kinetics of 4-dimethylaminostyrene initiated with trichloracetic acid in nitrobenzene

The relative permittivities (?_r²⁰) of 4-dimethylaminostyrene (I) and of 0.5–3.0 M solutions of N,N-dimethyl-4-toluidine (DMT) were measured in nitrobenzene (NB) and in a mixture of NB with diisopropyl ether (NB + E), the DMT solutions modelled those of I. An increase in [DMT] from 0.5 to 3.0 M caused a decrease in ?_r²⁰ from 32.3 to 18.3 in NB, while only from 20.8 to 18.3 in (NB + E) at fixed [NB]. The great difference between the ?_r²⁰ of 0.5 and 3.0 M DMT solutions in NB explains the previously observed drop in the percentage rate of polymerization (R_P) of I, in NB initiated with CCl₃COOH, with increasing [I]_o. In (NB + E) mixture with fixed [NB], the percentage R_P and the limiting viscosity number [ν] of polyl increase with increasing [I]_o. The observed dependences of both R_P (in Msec^?1) and [ν] on [I]₀ confirm the validity of the suggested polymerization scheme for I initiated with CCl₃COOH, and make possible determination of the characteristics of the elementary polymerization reactions.     

Novel binuclear rhodium complexes containing ketonic carbonyl and acetylene ligands

The reaction of trans-[RhCl(CO)(DPM)]₂ (DPM = Ph₂PCH₂PPh₂) with dimethylacetylenedicarboxylate (DMA) and hexafluoro-2-butyne (HFB) yield the novel species [Rh₂Cl₂(μ-CO)(μ-Acet)(DPM)₂] (Acet = DMA, HFB). The X-ray structure determination of the DMA derivative indicates that the complex has the acetylene molecule coordinated as a cis-dimetallated olefin and also contains a ketonic carbonyl ligand. The long Rh?Rh separation (3.3542(9) Å) suggests no metal—metal bond and the RhC(O)Rh angle (116.0(4)°) suggest sp² hybridization of the carbonyl carbon atom. Similarly the geometry at the acetylene ligand and the CC distance of the coordinated acetylene moiety (1.32(1) Å) are consistent with the dimetallated olefinic formulation. This represents the first reported characterization of a ketonic carbonyl complex outside the Ni triad. These novel complexes have also been formed by the direct insertion of the acetylene molecules into the formal RhRh bond in [Rh₂Cl₂(μ-CO)(DPM)₂].     

Steric interaction of solvation and sterically enhanced halogeno complexation of manganese(II), cobalt(II) and nickel(II) ions inN,N-dimethylacetamide

The complexation of manganese(II), cobalt(II) and nikel(II) with bromide ions has been studied in N,N-dimethylacetamide(DMA) by calorimetry and spectrophotometry. The formation of [MBr]⁺, [MBr₂] and [MBr₃]^– (M=Mn, Co, Ni) was revealed in all the metal systems. Interestingly, the complexation is significantly enhanced in DMA over N,N-dimethylformamide (DMF). This is unusual because physicochemical properties of DMA and DMF as solvent are similar. Furthermore, extracted electronic spectra of individual complexes of Ni^II suggested the presence of a geometry equilibrium, [NiBr(DMA)₅]⁺=[NiBr(DMA)₄]⁺+ DMA, in DMA. A similar geometry equilibrium is also suggested, [NiBr₂(DMA)₃]=[NiBr₂(DMA)₂]+DMA. Such geometry equilibria were not observed in DMF. With regard to cobalt(II), electronic spectra show the presence of the four-coordinated [CoBr(DMA)₃]⁺ complex in DMA, unlike the six-coordinated [CoBr(DMF)₅]⁺ one in DMF. These facts suggest that a specific strong steric interaction operates between coordinating solvent molecules, which plays a key role in the complexation behavior of the divalent transition metal ions in DMA.     

Photopolymerization of methyl methacrylate using triethylamine-nitrobenzene complex as photoinitiator

Photopolymerization of methyl methacrylate in bulk and in solution at 40° using triethylamine nitrobenzene (TEA-NB) complex as photoinitiator was studied kinetically. Initiator order x, given by the relation R_pα([TEA][NB])^x, was 0.28 for [TEA][NB] < 25 × 10 ^?8 mol² · l^?2; for higher values of [TEA][NB], x was practically zero. Monomer order was 1.1 in benzene and pyridine but much less than unity (0.65–0.70) in carbon tetrachloride and chloroform. Kinetic analysis indicated that the initiation process was monomer and solvent dependent. The halomethane solvents enhanced the polymerization rate through their active participation in the initiation or radical-generation steps. End-group analysis indicated incorporation of basic (amino) end-groups in the polymers. The kinetic non-ideality was explained on the basis of significant initiator-dependent termination through primary radicals or via degradative transfer to initiator.     

Chain transfer studies of alternating copolymerization

Dimethylaniline (DMA) induces chain transfer in the zinc bromide-complexed donor–acceptor polymerizations of styrene–acrylonitrile to form alternating copolymers. The Mayo plots are linear, but the rates decrease with increase in DMA and degradative chain transfer occurs. Although conventional free-radical transfer agents have negligible effect on the rates or molecular weights, a twentyfold reduction of molecular weight is obtained with DMA. Spectroscopic data indicate the formation of an equimolar complex of DMA and ZnBr₂, but the lowering of molecular weight is not attributable to the reduction of the effective ZnBr₂, concentration. A possible mechanism involving a competition between [ZnBr₂(DMA)₂] and [ZnBr₂,DMA,AN] is suggested.     

Silicon-phosphorus analogies : Participation of external nucleophiles to activated processes of racemization and hydrolysis of chlorophosphono derivatives

Kinetic and stereochemical studies show nucleophilic assistance by dimethylformamide (DMF), dimethylacetainide (DMA), hexamethylphosphotriamide (HMPT) and N-methylimidazole (NMI) in racemization and solvolysis of menthylchloro(phenyl)phosphonate, 1a, and O-ethylchloro(phenyl)thiophosphonate, 2. Similar orders of nucleophilic reactivity (Nu = NMI?HMPT>DMF>DMA), and identical rate-laws (v_rac=k [M-Cl] [Nu]² and v_H2O = k' [M-Cl] [H₂O] [Nu]) are consistent with a common mechanism, governed by entropy (?60 u.e< ΔS^≠<?40u.e). Analogies between reaction mechanisms at silicon and phosphorus are clearly evidenced. A two-step process, involving rate-determining attack on a pentacoordinate complex is discussed.     

Efficient and fast Heck vinylation of 2-bromo-6-methyl pyridines with methylacrylate. Application to the synthesis of 6-methyl cyclopenta[b]pyridinone

Heck vinylation of 2-bromo-6-methyl-3-substituted pyridines using η³-allylpalladium chloride dimer/P(o-Tol)₃ complex/toluene and dimethylacetamide (DMA) as co-solvent with methyl acrylate is reported. Electronic and steric effects were investigated engaging diversely 2-bromo-3,6-disubstituted pyridines. As application, a new synthesis of the 6-methyl cyclopenta[b]pyridinone building-block connecting Heck vinylation, alkene reduction and Dieckmann condensation is described.     

Crystal Engineering with the New Linker Tolanedisulfonic Acid (H2TDS): Helical Chains in Zn(TDS)(DMA)3, Linear Chains in Zn(TDS)(NMP)3, and Complex Anions in [HDMA]2[Zn(TDS)2(DMA)3](DMA)2

Reaction of 4,4′‐tolanedisulfonic acid, H₂TDS, with zinc hydroxide in dimethylacetamide, DMA, under solvothermal conditions led to the coordination polymer Zn(TDS)(DMA)₃ ( I ). In the crystal structure [trigonal, P3₂21, Z=3, a=1175.0(1) pm, c=1949.5(1) pm, R₁; wR₂ (I_o> 2σ(I_o))=0.0393; 0.0921] the disulfonate anions linked the Zn²⁺ ions into helical chains according to _∞¹[Zn(DMA)_3/1(TDS)_2/2] ( I ) causing the chirality of the compound. By using higher concentrations of H₂TDS in the starting mixture the compound [HDMA]₂[Zn(TDS)₂(DMA)₃](DMA)₂ ( II ) was formed. The structure [monoclinic, Cc, Z=4, a=1201.5(1) pm, b=1996.0(1) pm, c=2749.2(2) pm, β=101.897(2)°, R₁; wR₂ (I_o> 2σ(I_o))=0.0699; 0.2017] displayed the complex anion [Zn(TDS)₂(DMA)₃]^2? which was a perfect cut‐off of the helical chain in I . Charge compensation was achieved by protonated DMA molecules. If N‐methylpyrrolidone, NMP, was chosen as a solvent, the sulfonate Zn(TDS)(NMP)₃ ( III ) [monoclinic, I2/a, Z=4, a=1575.7(1) pm, b=1077.3(1) pm, c=1870.0(1) pm, β=101.189(9)°, R₁; wR₂ (I_o> 2σ(I_o))=0.0563; 0.1320] was obtained. Similarly to the findings for I , the formation of chains according to _∞¹[Zn(NMP)_3/1(TDS)_2/2] was observed. However, due to the more bulky NMP molecules these chains were no longer helical but straight instead.     

Triosmium clusters with bridging terpenic thioureato-like ligands

The reaction of acetone-4-(2-methoxy-phenyl)thiosemicarbazone with triosmium cluster Os₃(CO)₁₁(NCMe) results in the formation of the cluster with the μ₂ chelate-bridging ligand coordinated by S and N¹ atoms, which was studied by X-ray diffraction analysis. Reaction of (3aR, 3bR, 4aR, 5aS)-5a-hydroxy-3,4,4-trimethyl-3a,3b,4,4a,5,5a-hexahydrocyclopropa[3, 4]cyclopenta[1,2-c]pyrazole-1-carbothioic acid amide with Os₃(CO)₁₁(NCMe) gives rise to the complex with the bridging ligand coordinated by sulphur atom. Further transformation of the complex in hot benzene results in tautomeric rearrangement of the organic ligand and the cleavage of the pyrazolinol cycle to form an open chain tautomer. Unusual silica gel induced oxidative cleavage of the cyclopropane ring in the open chain derivative and epoxidation of cycloalcane C-C bond are observed on the air.     

Reaction of ferricytochrome c with the iron nitrosyl complex {Fe2[S(CH2)2NH3]2(NO)4}SO4 • 2.5H2O

By an example of cysteamine iron nitrosyl complex {Fe₂[S(CH₂)₂NH₃]₂(NO)₄}SO₄ ? 2.5H₂O (CAC) it was shown for the first time that the NO donor hydrolysis in the presence of ferricytochrome c (cyt c³⁺) affords the iron nitrosyl complex NO—cyt c³⁺. It was found that cyt c³⁺ can serve as a depot for NO evolved during the hydrolysis of CAC. In the presence of CAC, the rate of NO—cyt c³⁺ complex decomposition to NO and cyt c³⁺ depends on the molar ratio [cyt c³⁺]: [CAC] and at [cyt c³⁺]: [CAC] = 0.3 it was found to be lower than that in decomposition of CAC in the absence of cyt c³⁺. As a result, the total NO evolving process becomes 5.6 times more prolonged. The number of NO groups evolved from CAC can be determined by the reaction of CAC with cyt c³⁺ in the presence of ferricyanide: at most one NO group is evolved to a solution in the spontaneous hydrolysis of CAC (pH 7.0), and no less than three of them are evolved from oxidized CAC.     

Synthese und Charakterisierung von 2‐O‐funktionalisierten Ethylrhodoximen und ‐cobaloximen

Synthesis and Characterization of 2‐O‐Functionalized Ethylrhodoximes and ‐cobaloximes 2‐Hydroxyethylrhodoxime and ‐cobaloxime complexes L—[M]—CH₂CH₂OH (M = Rh, L = PPh₃, 1 ; M = Co, L = py, 2 ; abbr.: L—[M] = [M(dmgH)₂L] (dmgH₂ = dimethylglyoxime, L = axial base) were obtained by reaction of L—[M]^— (prepared by reduction of L—[M]—Cl with NaBH₄ in methanolic KOH) with BrCH₂CH₂OH. H₂O—[Rh]^—, prepared by reduction of H[RhCl₂(dmgH)₂] with NaBH₄ in methanolic KOH, reacted with BrCH₂CH₂OH followed by addition of pyridine yielding py—[Rh]—CH₂CH₂OH ( 3 ). Complexes 1 and 3 were found to react with (Me₃Si)₂NH forming 2‐(trimethylsilyloxy)ethylrhodoximes L—[Rh]—CH₂CH₂OSiMe₃ (L = PPh₃, 4 ; L = py, 5 ). Treatment of complex 1 with acetic anhydride resulted in formation of the 2‐(acet oxy)ethyl complex Ph₃P—[Rh]—CH₂CH₂OAc ( 6 ). All complexes 1 — 6 were isolated in good yields (55—71 %). Their identities were confirmed by NMR spectroscopic investigations ( 1 — 6 : ¹H, ¹³C; 1 , 4 , 6 : ³¹P) and for [Rh(CH₂CH₂OH)(dmgH)₂(PPh₃)]·CHCl₃·1/2H₂O ( 1 ·CHCl₃·1/2H₂O) and py—[Rh]—CH₂CH₂OSiMe₃ ( 5 ) by X‐ray diffraction analyses, too. In both molecules the rhodium atoms are distorted octahedrally coordinated with triphenylphosphine and the organo ligands (CH₂CH₂OH and CH₂CH₂OSiMe₃, respectively) in mutual trans position. Solutions of 1 in dmf decomposed within several weeks yielding a hydroxyrhodoxime complex “Ph₃P—[Rh]—OH”. X‐ray diffraction analysis exhibited that crystals of this complex have the composition [{Rh(dmg)(dmgH) (H₂O)(PPh₃)}₂]·4dmf ( 7 ) consisting of centrosymmetrical dimers. The rhodium atom is distorted octahedrally coordinated. Axial ligands are PPh₃ and H₂O. One of the two dimethylglyoximato ligands is doubly deprotonated. Thus, only one intramolecular O—H···O hydrogen bridge (O···O 2.447(9)Å) is formed in the equatorial plane. The other two oxygen atoms of dmgH^— and dmg^2—, respectively, act as hydrogen acceptors each forming a strong (intermolecular) O···H′—O′ hydrogen bridge to the H′₂O′ ligand of the other molecule (O···O′ 2.58(2)/2.57(2)Å).     

Are Sc—C and Sc—P Bonds Reactive in Scandium Phosphinoalkylidene Complex? Insights on a Versatile Reactivity

The peculiar electronic structure of scandium phosphinoalkylidene complex [LSc{C(SiMe₃)PPh₂}THF] (L=[MeC(NDIPP)CHC(NDIPP)Me]⁻), DIPP=2,6‐(ⁱPr)₂C₆H₃) leads to an interesting versatile reactivity, which is demonstrated both experimentally and computationally. The complex undergoes [2+2] cycloaddition reactions with alkynes, and easily activates various X—O bonds such as C—O of propylene oxide, N—O of 3,5‐dimethylisoxazole, B—O of pinacolborane and Si—O of triethoxysilane. These reactions occur on the Sc—C bond of the phosphinoalkylidene complex. Interestingly, the Sc—P bond can also be activated as the presence of a Sc—C—P three center π interaction in the complex allows performing C—F activation of 2,6‐difluoropyridine and 1,2 addition with imine or ketone. The complex also reacts with metal complexes, [(COD)RhCl]₂ and (Ph₃P)AuCl, to form structural intriguing heterobimetallic complexes.     

A novel supramolecular graft copolymer via cucurbit[8]uril-based complexation and its self-assembly

A novel supramolecular graft copolymer（SGP） composed of viologen-containing copolymer（P（DMA-co-diEV）） as the main chain and Np ended PNIPAM（Np-PN1PAm） as the grafts is prepared（DMA:N,N- dimethylacryamide,diEV:ethylviologen dimer,Np:naphthalene,PNIPAM:poly（N-isopropylacrylamide））. The grafting is based on the triple complexation among a host of cucurbit[8]uril（CB[8]）and two guests of diEV and Np,which is characterized by UV-vis spectra and ITC.Temperature sensitive property of PNIPAm moiety allows SGP to self-assemble into non-covalently connected micelle（NCCM） at high temperature. The micelles are sensitive to reducing agents,for example Na₂S₂O₃,which breaks the current inclusion complex pair and induces aggregation.     

[Phthalocyaninato(2–)]­antimony(III) chloride

The title antimony(III) complex, [Sb(C₃₂H₁₆N₈)]Cl or [SbPc]Cl (where Pc = C₃₂H₁₆N₈²⁻), has been obtained from the reaction of pure powdered antimony with 1,2-di­cyano­benzene under a stream of ICl vapour. The asymmetric unit of this complex consists of an [SbPc]⁺ cation and a Cl⁻ anion. The phthalocyaninate residue [SbPc]⁺ is not planar. The Sb atom lies 1.057 (3) Å from the plane defined by the four iso­indole N atoms. A combination of ionic and donor–acceptor interactions links the [SbPc]Cl mol­ecules to form centrosymmetric [(SbPc)Cl]₂ pseudo-dimers in the crystal. The Sb—Cl distances in the pseudo-dimer are not equivalent [3.043 (2) and 3.201 (2) Å]. The pseudo-dimers are weakly linked through Cl⃛H—C_benzo interactions to form a three-dimensional network. As a result of these interactions, the four Sn—N_isoindole bond lengths in the [SbPc]⁺ residue are not equivalent and the symmetry of the Sb—N core is only close to C_s.     

Solubility of <Emphasis Type="Italic">d</Emphasis>-Element Salts in Organic and Aqueous–Organic Solvents: VI.<Superscript>1</Superscript> Structure and Thermal Stability of Cadmium Iodide and Bromide Solvates with Dimethylacetamide and Dimethylformamide

Five solvates, [CdBr₂(DMF)] _n , [CdBr₂(DMA)] _n , [CdI²(DMF)] ⁿ , [Cd(DMF)₆][Cd₂I₆], and {[Cd(DMA)₆][Cd₅I₁₂] _n } _m , were isolated from the ternary systems CdX₂–L–H₂O (X = Br, I; L = N,N-dimethylacetamide, N,N-dimethylformamide) and characterized by the X-ray single crystal analysis. The structures of the first three solvates is similar to each other in structures and represent a one-dimensional polymer chain, the fourth solvate has the discrete structure containing [Cd(DMF)₆]²⁺ and [Cd₂I₆]^2– ions, and the fifth solvate contains discrete [Cd(DMA)₆]²⁺ cations and the polymer anionic fragment [Cd₅I₁₂] _n ^2n–.     

Petroporphyrins—III: Characterisation of a c32 aetioporphyrin from gilsonite as the bis[porphyrinato-mercury(II) acetato]mercury(II) complex. Origin and significance

A C₃₂ aetio porphyrin isolated from Gilsonite bitumen (ca. 60 × 10⁶yr) was assigned unambiguously as aetioporphyrin—III by ¹H NMR analysis of its bis[porphyrinato-mercury(II) acetato]mercury(II) complex and by comparison with an authentic sample. The occurrence of this compound provides the first direct evidence that the petroporphyrins of Gilsonite are the product of reductive degradation of naturally-occurring chlorophylls, and conversion of the chlorin to the porphyrin system.     

Crystal structure,electrochemical and photochemical studies of the trans-[Fe(cyclam)(NO)Cl]Cl2 complex (cyclam = 1,4,8,11-tetraazacyclotetradecane)

The trans-[Fe(cyclam)(NO)Cl]Cl₂ complex was synthesized by the reaction of cis-[Fe(cyclam)Cl₂]Cl with NO gas. The X-ray structure of the complex showed that the [Fe–NO] moiety is linear, consistent with the NO⁺ character of the nitric oxide ligand. This suggestion was reinforced by the IR data, which showed the νNO at 1888 cm⁻¹. The cyclic voltammogram of the trans-[Fe(cyclam)(NO)Cl]²⁺ complex presented three electrochemical processes at −0.70, 0.08 and 0.40 V versus Ag/AgCl. The first and last redox processes are centered at the NO ligand, whereas the second is characteristic of the generated aqua species, trans-[Fe(cyclam)Cl(H₂O)]²⁺. Upon irradiation at 330 nm, pH 3.4, the title complex releases the NO moiety with the concomitant generation of the trans-[Fe(cyclam)(H₂O)Cl]⁺ complex as suggested by electronic and IR spectroscopy as well as by cyclic voltammetry technique.     

Chemical relevance of the copper(II)—l-carnosine system in aqueous solution: A thermodynamic and spectrophotometric study

The copper(II)—l-carnosine (L⁻) system has been re-investigated in aqueous solution, at I = 0.1 mol dm⁻¹, different temperatures (5⩽t⩽45°C) and with metal to ligand ratios ranging from 3:1 to 1:3. Both potentiometry and visible spectrophotometry were employed. From an overall consideration of all experiments, [CuLH]²⁺, [CuL]⁺, [CuLH₋₁]°, [Cu₂L₂H₋₂]° and [Cu₂LH₋₁]²⁺ were recognized as the species which provide the best interpretation of experimental data. The complex formation constants, determined at different temperatures, allowed us to obtain reliable values of ΔH° and good estimates of ΔC°_p. From visible spectrophotometric measurements, carried out at different pH and metal to ligand ratios, it was possible to calculate the electronic spectrum of each complex formed in solution. A structure is also proposed for each species, on the basis of thermodynamic and spectral results.     

New routes to carbonyl complexes of general formula [RuCl2(CO)(S)(PPh3)2] (S = DMA,DMF, DMSO): crystal structure of [RuCl2(CO)(DMA)(PPh3)2] · 1/2CH2Cl2

The compound [RuCl₂(CO)(DMA)(PPh₃)₂] [DMA = dimethylacetamide] was obtained from [RuCl₃(PPh₃)₂-(DMA)] · DMA and CO in DMA. Orange crystals of [RuCl₂(CO)(DMA)(PPh₃)₂] · 1/2CH₂Cl₂ were isolated by slow evaporation of a CH₂Cl₂/DMA solution and its structure was determined by single crystal X-ray diffraction. The analogous compounds containing DMF and DMSO were obtained from the precursor ttt-[RuCl₂(CO)₂(PPh₃)₂]. Characterization of the other complexes is based on i.r. and n.m.r. spectroscopy, including ³¹P{¹H} data.     

A three‐dimensional framework in 2,2′‐biimidazolium bis(2,2′‐biimidazole‐κ2N,N′)bis(biphenyl‐2,4′‐dicarboxylato‐κO)manganese(II) hexahydrate

In the title salt, (C₆H₈N₄)[Mn(C₁₄H₈O₄)₂(C₆H₆N₄)₂]·6H₂O, the Mn^II atom lies on an inversion centre and is coordinated by four N atoms from two 2,2′‐biimidazole (biim) ligands and two O atoms from two biphenyl‐2,4′‐dicarboxylate (bpdc) anions to give a slightly distorted octahedral coordination, while the cation lies about another inversion centre. Adjacent [Mn(bpdc)₂(biim)₂]²⁻ anions are linked via two pairs of N—H...O hydrogen bonds, leading to an infinite chain along the [100] direction. The protonated [H₂biim]²⁺ moiety acts as a charge‐compensating cation and space‐filling structural subunit. It bridges two [Mn(bpdc)₂(biim)₂]²⁻ anions through two pairs of N—H...O hydrogen bonds, constructing two R₂²(9) rings, leading to a zigzag chain in the [2] direction, which gives rise to a ruffled set of [H₂biim]²⁺[Mn(bpdc)₂(biim)₂]²⁻ moieties in the [01] plane. The water molecules give rise to a chain structure in which O—H...O hydrogen bonds generate a chain of alternating four‐ and six‐membered water–oxygen R₄²(8) and R₆⁶(12) rings, each lying about independent inversion centres giving rise to a chain along the [100] direction. Within the water chain, the (H₂O)₆ water rings are hydrogen bonded to two O atoms from two [Mn(bpdc)₂(biim)₂]²⁻ anions, giving rise to a three‐dimensional framework.