Synthesis, structure, theoretical studies, and Ligand exchange reactions of monomeric, T-shaped arylpalladium(II) halide complexes with an additional, weak agostic interaction

A series of monomeric arylpalladium(II) complexes LPd(Ph)X (L = 1-AdPtBu2, PtBu3, or Ph5FcPtBu2 (Q-phos); X = Br, I, OTf) containing a single phosphine ligand have been prepared. Oxidative addition of aryl bromide or aryl iodide to bis-ligated palladium(0) complexes of bulky, trialkylphosphines or to Pd(dba)2 (dba = dibenzylidene acetone) in the presence of 1 equiv of phosphine produced the corresponding arylpalladium(II) complexes in good yields. In contrast, oxidative addition of phenyl chloride to the bis-ligated palladium(0) complexes did not produce arylpalladium(II) complexes. The oxidative addition of phenyl triflate to PdL2 (L = 1-AdPtBu2, PtBu3, or Q-phos) also did not form arylpalladium(II) complexes. The reaction of silver triflate with (1-AdPtBu2)Pd(Ph)Br furnished the corresponding arylpalladium(II) triflate in good yield. The oxidative addition of phenyl bromide and iodide to Pd(Q-phos)2 was faster than oxidative addition to Pd(1-AdPtBu2)2 or Pd(PtBu3)2. Several of the arylpalladium complexes were characterized by X-ray diffraction. All of the arylpalladium(II) complexes are T-shaped monomers. The phenyl ligand, which has the largest trans influence, is located trans to the open coordination site. The complexes appear to be stabilized by a weak agostic interaction of the metal with a ligand C-H bond positioned at the fourth-coordination site of the palladium center. The strength of the Pd.H bond, as assessed by tools of density functional theory, depended upon the donating properties of the ancillary ligands on palladium.     

Eine mikromethode der flammen-atomabsorptions- und emissionsspektrometrie (platinschlaufen-methode)—II: Die bestimmung von As,Bi, Cd,Hg, Pb,Sb, Se,Te, Tl,Zn/Li,Na, K,Cs, Sr,Ba

This paper described the continuation of the work of Part I dealing with a microanalytical method in which the sample is introduced into a flame using an electrically heated platinum loop. This device is used in connection with an atomic absorption (AA) spectrometer. The detection limits are one to two orders of magnitude better than those of conventional flame AAS. The reproducibility depends on the element and is in general 3–5% (relative standard deviation) for concentrations in the $\text{ng}\text{ml}$ range. The platinum loop method can be also applied for flame emission analysis of small amounts of sample or the determination of low concentrations (alkalis). This application gives access to determinations in the lower ng or the pg range (detection limit of lithium: 0.6 pg).     

Influence of the correlation,aggregation, and solvation on ab initio computed Li-C,Li-N,and Li-Li NMR coupling constants

The (1)J and (3)J(C-Li), (1)J(N-Li), and (2)J(Li-Li) NMR coupling constants have been calculated for various homogeneous and heterogeneous aggregates of methyllithium and lithium dimethylamide at the HF and MP2 levels of calculation. Ethereal solvation has also been taken into account either through a continuum model or through the explicit introduction of Me(2)O molecules. The results obtained are in good general agreement with the experimental data available for methyllithium itself or model alkyllithiums and supports the empirical rule proposed by Bauer, Winchester, and Schleyer to evaluate (1)J(C-Li) provided that calculations include solvent and/or aggregation effects.     

Auration, argentation, and mercuration reactions of an iridaphosphirene

The reactions of the iridaphosphirene complex [Ir{=C(tBu)P(Cy)}(CO)(PPh3)2] (Cy = cyclohexyl) with either [AuCl(tht)] (tht = tetrahydrothiophene) or AgCl result in the products [Ir{=C(tBu)P[M(Cl)](Cy)}(CO)(PPh3)2], M = Au or Ag. The aurated product can additionally be obtained on reaction of the iridaphosphirene with [AuCl(CNtBu)], via loss of the isocyanide ligand. Treatment of [Ir{=C(tBu)P(Cy)}(CO)(PPh3)2] with [AuCl(PPh3)] in the presence of silver triflate leads to the isolation of the salt, [Ir{=C(tBu)P[Au(PPh3)](Cy)}(CO)(PPh3)2][SO3CF3]. Reaction of the iridaphosphirene with PhHgCl in the absence or presence of silver triflate affords the mercurated species [Ir{=C(tBu)P[Hg(Ph)](Cy)}(CO)(PPh3)2]X, X = Cl or CF3SO3, respectively. The former exhibits a weakly mercury-coordinated chloride ion. The X-ray crystal structures of all of the complexes are described.     

New and efficient syntheses of alpha-iodo-alpha,alpha-difluoro- and beta-iodo-alpha,alpha,beta,beta-tetrafluorocarboxylic acid derivatives as useful building blocks for making functional fluoro compounds

Perfluoroolefins reacted with I-Cl and ClSO(3)H under mild conditions to give R(F)CFICF(2)OSO(2)Cl, which could be readily converted into various alpha-iodo-perfluorocarboxylic acid derivatives or telomerized with tetrafluoroethylene to I(CF(2)CF(2))(n)()OSO(2)Cl. Ring-opening reaction of perfluoroalkoxypentafluorocyclopropane with iodine at 240 degrees C produced ICF(2)CF(2)COF, which was quenched by alcohol, water, or NH(3) to give beta-iodo-alpha,alpha,beta,beta-tetrafluorocarboxylic acid derivatives. These functional fluorinated iodides can be used as building blocks for making selectively fluorinated compounds.     

Solubility of phosphonium ionic liquid in alcohols, benzene, and alkylbenzenes

The (solid + liquid) phase equilibria and (liquid + liquid) phase equilibria of binary mixtures containing quaternary phosphonium salt-tetrabutylphosphonium methanesulfonate and alcohols or alkylbenzenes were investigated. The systems {[(CH(3)CH(2)CH(2)CH(2))4P][CH(3)SO(3)] + 1-butanol, or 1-hexanol, 1-octanol, 1-decanol, or 1-dodecanol} and {[(CH(3)CH(2)CH(2)CH(2))4P][CH(3)SO(3)] + benzene, or toluene, ethylbenzene, or propylbenzene} have been measured by a dynamic method at a wide range of temperatures from 220 to 386 K. Solid-liquid equilibria with immiscibility in the liquid phase were detected with the aromatic hydrocarbons ethylbenzene and propylbenzene. The basic thermodynamic properties of pure ionic liquid--the melting point, enthalpy of fusion, enthalpy of solid-solid-phase transition, and glass transition--have been determined by differential scanning calorimetry. The experimental data of systems with alcohols were correlated by means of the UNIQUAC ASM and NRTL1 equations and of systems with alkylbenzenes with Wilson and NRTL equations utilizing parameters derived from the (solid + liquid) equilibrium. The root-mean-square deviations of the solubility temperatures for all calculated data are dependent upon the particular system and the particular equation used.     

Boron dipyrromethene analogs with phenyl, styryl, and ethynylphenyl substituents: synthesis, photophysics, electrochemistry, and quantum-chemical calculations

Seven fluorescent boradiazaindacene-based compounds with one or two phenyl, ethenylphenyl, and ethynylphenyl substituents at the 3- (or 3,5-) position(s) were synthesized via palladium-catalyzed coupling reactions with the appropriate 3,5-dichloroBODIPY derivative. The effect of the various substituents at the 3- (or 3,5-) position(s) on the spectroscopic and photophysical properties were studied as a function of solvent by means of UV/vis absorption, steady-state, and time-resolved fluorometry, and theoretical modeling. The emission maxima of the symmetrically 3,5-disubstituted dyes are shifted to longer wavelengths (by 30 to 60 nm) relative to the related asymmetrically 3,5-disubstituted ones. Introduction of styryl substituents causes the largest red shift in both the absorption and emission spectra. BODIPY derivatives with ethynylaryl groups also shift the spectral maxima to longer wavelengths compared to aryl-substituted ones but to a lesser degree than the styryl compounds. The quantum-chemical calculations confirm these trends and provide a rationale for the spectral shifts induced by substitution. The fluorescence quantum yields of the ethenylaryl and ethynylaryl analogs are significantly higher that those of the aryl-substituted dyes. The 3,5-diethynylaryl dye has the highest fluorescence quantum yield (approximately 1.0) and longest lifetime (around 6.5 ns) among the BODIPY dyes studied. The differences in the photophysical properties of the dyes are also reflected in their electrochemical properties where the symmetrically 3,5-disubstituted dyes display much lower oxidation potentials when compared to their asymmetric counterparts.     

Oligodentate P,N ligands: N,N,N',N'-tetrakis(diphenylphosphanyl)-1,3-diaminobenzene complexes of rhodium, nickel and palladium

The oligodentate P,N ligand N,N,N',N'-tetrakis(diphenylphosphanyl)-1,3-diaminobenzene reacts with two equivalents of [{Rh(mu-Cl)(COD)}(2)], [NiBr(2)(DME)] or [PdCl(2)(NCMe)(2)](COD = 1,5-cyclooctadiene, DME = dimethoxyethane) in dichloromethane to give the tetranuclear complex [1,3-{cis-Rh(COD)(mu-Cl)(2)Rh(PPh(2))(2)N}(2)C(6)H(4)](1) or the dinuclear complexes [1,3-{cis-NiBr(2)(PPh(2))(2)N}(2)C(6)H(4)](2) and [1,3-{cis-PdCl(2)(PPh(2))(2)N}(2)C(6)H(4)](3), respectively. Compounds 1-3 were characterised by NMR ((1)H, (13)C, (31)P) and IR spectroscopy. The molecular structure of 2 and 3 shows the formation of a bis-chelate complex with M-P-N-P four-membered rings (M = Pd, Ni). An N,N,N',N'-tetrakis(diphenylphosphanyl)-1,3-diaminobenzene/Pd(OAc)(2) mixture was used for the copolymerisation of carbon monoxide with ethene or ethylidenenorbornene. Compound 1 was employed as catalyst in the hydrogenation of styrene.     

Electrochemistry, spectroelectrochemistry, chloride binding, and O2 catalytic reactions of free-base porphyrin-cobalt corrole dyads

Three face-to-face linked porphyrin-corrole dyads were investigated as to their electrochemistry, spectroelectrochemistry, and chloride-binding properties in dichloromethane or benzonitrile. The same three compounds were also investigated as to their ability to catalyze the electroreduction of dioxygen in aqueous 1 M HClO4 or HCl when adsorbed on a graphite electrode. The characterized compounds are represented as (PCY)H2Co, where P = a porphyrin dianion; C = a corrole trianion; and Y = a biphenylenyl, 9,9-dimethylxanthenyl, or anthracenyl spacer, which links the two macrocycles in a face-to-face arrangement. An axial binding of one or two Cl- ligands to the cobalt center of the corrole is observed for singly and doubly oxidized (PCY)H2Co, with the exact stoichiometry of the reaction depending upon the spacer size and the concentration of Cl- added to solution. No Cl- binding occurs for the neutral or reduced forms of the dyad, which contrasts with what is seen for the monocorrole, (Me4Ph5Cor)Co, where a single Cl- ligand is added to the Co(III) corrole in PhCN. The Co(III) form of the corrole in (PCY)H2Co also appears to be the catalytically active species in the electroreduction of dioxygen, which occurs at potentials associated with the Co(IV)/Co(III) reaction, that is, 0.35 V in 1 M HClO4 as compared to 0.31-0.42 V for the same three dyads in PhCN and 0.1 M TBAP. The potential for the catalytic electroreduction of O2 in HCl shifts negatively by 60 to 70 mV as compared to E(1/2) values in 1 M HClO4, consistent with the binding of Cl- to the Co(IV) form of the corrole and its rapid dissociation after electroreduction to Co(III) at the electrode surface.     

Computation of methodology-independent single-ion solvation properties from molecular simulations. III. Correction terms for the solvation free energies, enthalpies, entropies, heat capacities, volumes, compressibilities, and expansivities of solvated ions

The raw single-ion solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions (finite or periodic system, system or box size) and treatment of electrostatic interactions (Coulombic, lattice-sum, or cutoff-based) used during these simulations. However, as shown by Kastenholz and Hu?nenberger [J. Chem. Phys. 124, 224501 (2006)], correction terms can be derived for the effects of: (A) an incorrect solvent polarization around the ion and an incomplete or/and inexact interaction of the ion with the polarized solvent due to the use of an approximate (not strictly Coulombic) electrostatic scheme; (B) the finite-size or artificial periodicity of the simulated system; (C) an improper summation scheme to evaluate the potential at the ion site, and the possible presence of a polarized air-liquid interface or of a constraint of vanishing average electrostatic potential in the simulated system; and (D) an inaccurate dielectric permittivity of the employed solvent model. Comparison with standard experimental data also requires the inclusion of appropriate cavity-formation and standard-state correction terms. In the present study, this correction scheme is extended by: (i) providing simple approximate analytical expressions (empirically-fitted) for the correction terms that were evaluated numerically in the above scheme (continuum-electrostatics calculations); (ii) providing correction terms for derivative thermodynamic single-ion solvation properties (and corresponding partial molar variables in solution), namely, the enthalpy, entropy, isobaric heat capacity, volume, isothermal compressibility, and isobaric expansivity (including appropriate standard-state correction terms). The ability of the correction scheme to produce methodology-independent single-ion solvation free energies based on atomistic simulations is tested in the case of Na(+) hydration, and the nature and magnitude of the correction terms for derivative thermodynamic properties is assessed numerically.     

The exchange reaction of tetramethyl-diphosphine, -diarsine, -distibine and -dibismuthine

Tetramethyldiphosphine and tetramethyldiarsine undergo an exchange reaction to give (dimethylarsino)dimethylphosphine. The equilibrium constant at 25°C in benzene is found to be 0.26. Similarly, mixtures of tetramethyldistibine with tetramethyldiarsine or tetramethyldibismuthine are partially converted to (dimethylarsino)dimethylstibine or (dimethylbismuthino)dimethylstibine, respectively. The thermochromic arsinostibine, 1-(2,5-dimethylarsolo)-2,5-dimethylstibole, has been prepared by a similar reaction.     

Syntheses,structures, and dynamic behavior of chiral racemic organoantimony and -bismuth compounds RR'SbCl,RR'BiCl,and RR'SbM [R = 2-(Me2NCH2)C6H4, R' = CH(Me3Si)2, M = H,Li, Na

RR'SbCl (1) and RR'BiCl (2) [R = 2-(Me(2)NCH(2))C(6)H(4), R' = CH(Me(3)Si)(2)] form by the reaction of R'ECl(2) (E = Sb, Bi) with RLi. The reaction of 1 with LiAlH(4) and metalation with n-BuLi gives RR'SbH (3) and RR'SbLi.2THF (4) (THF = tetrahydrofuran). Transmetalation of 4 with sodium tert-butoxide in the presence of TMEDA (TMEDA = tetramethylethylenediamine) leads to RR'SbNa.TMEDA (5). Structural analyses by (1)H NMR in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO with a variation of the temperature (1, 2, 4, and 5) and by single-crystal X-ray diffraction (1, 2, 4, and 5) revealed the intramolecular coordination of the pendant Me(2)N group on the pnicogen centers in 1 and 2 and on Li or Na in 4 or 5. The variable-temperature (1)H NMR spectra of the hydride 3 in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO show that the pyramidal configuration on antimony is stable up to 100 degrees C, whereas inversion at the nitrogen is not prevented by internal coordination even at -80 degrees C. The crystals of 1, 2, 4, and 5 consist of discrete molecules with the Sb and Bi atoms in an approximately Psi-trigonal-bipyramidal environment in the cases of 1 and 2 and in a pyramidal environment in the cases of 4 and 5. Crystal data for 1: triclinic, space group Ponemacr;, a = 7.243(4) A, b = 10.373(3) A, c = 15.396(5) A, alpha = 79.88 degrees, beta = 78.27 degrees, gamma = 71.480(10) degrees, V = 1066.2(7) A(3), Z = 2, R = 0.0614. 2: monoclinic, space group P2(1)/n, a = 10.665(2) A, b = 14.241(2) A, c = 14.058(2) A, beta = 90.100(10) degrees, V = 2135.1(6) A(3), Z = 4, R = 0.049. 4: monoclinic, space group P2(1)/n, a = 11.552(2) A, b = 16.518(3) A, c = 15.971(5) A, beta = 96.11(2) degrees, V = 3030.2(12) A(3), Z = 4, R = 0.0595. 5: monoclinic, space group P2(1)/n, a = 9.797(2) A, b = 24.991(5) A, c = 14.348(3) A, beta = 94.98(3) degrees, V = 3499.66(12) A(3), Z = 4, R = 0.0571. The dissociation of the intramolecular N-pnicogen bond and inversion at the nitrogen occurs when solutions of 1 or 2 in C(6)D(6) or C(6)D(5)CD(3) are heated above 25 or 30 degrees C. 1 and 3-5 are stable with respect to inversion of the configuration at the antimony in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO up to 160 degrees C. Bismuth inversion, probably via the edge mechanism, is observed in solutions of 2 in (CD(3))(2)SO at 45 degrees C but not in C(6)D(5)CD(3) below 125 degrees C.     

New layered materials: syntheses, structures, and optical and magnetic properties of CsGdZnSe3, CsZrCuSe3, CsUCuSe3, and BaGdCuSe3

Four new quaternary selenides CsGdZnSe3, CsZrCuSe3, CsUCuSe3, and BaGdCuSe3 have been synthesized with the use of traditional high-temperature solid-state experimental methods. These compounds are isostructural with KZrCuS3, crystallizing with four formula units in the orthorhombic space group Cmcm. Cell constants (A) at 153 K are CsGdZnSe3 4.1684(7), 15.765(3), 11.0089(18); CsZrCuSe3 3.903(2), 15.841(10), 10.215(6); CsUCuSe3 4.1443(7), 15.786(3), 10.7188(18); and BaGdCuSe3 4.1839(6), 13.8935(19), 10.6692(15). The structure of these ALnMSe3 compounds (A = Cs, Ba; Ln = Zr, Gd, U; M = Cu, Zn) is composed of 2 to infinity [LnMSe3(n-)] (n = 1, 2) layers separated by A atoms. The Ln atom is octahedrally coordinated to six Se atoms, the M atom is tetrahedrally coordinated to four Se atoms, and the A atom is coordinated to a bicapped trigonal prism of eight Se atoms. Because there are no Se-Se bonds in the structure, the oxidation state of A is 1+ (Cs) or 2+ (Ba), that of Ln is 3+ (Gd) or 4+ (Zr, U), and that of M is 1+ (Cu) or 2+ (Zn). CsGdZnSe3 and BaGdCuSe3, which are paramagnetic, obey the Curie-Weiss law and have effective magnetic moments of 7.87(6) and 7.85(5) muB for Gd(3+), in good agreement with the theoretical value of 7.94 muB. Optical transitions at 1.88 and 2.92 eV for CsGdZnSe3 and 1.96 eV for BaGdCuSe3 were deduced from diffuse reflectance spectra.     

Crystalline metal (Li, Mg, Ca, Sr, Ba, Sn, Pb) complexes of the new chelating N,N'-dianionic [1,2-N(R)C6H4(CH2NR)](2-) ligand (R = SiMe3, CH2Bu(t))

2-Aminomethylaniline was converted into the N,N'-bis(pivaloyl) (1) or -bis(trimethylsilyl) (2) derivative, using 2 Bu(t)C(O)Cl or 2 Me(3)SiCl (≡ RCl), respectively, with 2 NEt(3), or for 2 from successively using 2 LiBu(n) and 2 RCl. N,N'-Bis(neopentyl)-2-(aminomethyl)aniline (3) was prepared by LiAlH(4) reduction of 1. From 2 or 3 and 2 LiBu(n), the appropriate dilitiodiamide {2-[{N(Li)R}C(6)H(4){CH(2)N(Li)R}(L)](2) (L absent, 4a; or L = THF, 4b) or the N,N'-bis(neopentyl) analogue (5) of 4a was prepared. Treatment of 4a with 2 Bu(t)NC, 2 (2,6-Me(2)C(6)H(3)NC) or 2 Bu(t)CN (≡ L') furnished the corresponding adduct [2-N{Li(L')R}C(6)H(4){CH(2)N(Li)R}] (4c, 4d or 4e, respectively), whereas 4b with 2 PhCN afforded [2-{N(Li)R}C(6)H(4){CH(2)C(Ph) = NLi(NCPh)}] (6). The dimeric bis(amido)stannylene [Sn{N(R)C(6)H(4)(CH(2)NR)-1,2}](2) (7) was obtained from 4a and [Sn(μ-Cl)NR(2)](2), while the N,N'-bis(neopentyl) analogue 8 of 7 was similarly derived from [Sn(μ-Cl)NR(2)](2) and 5. Reaction of two equivalents of the diamine 2 with Pb(NR(2))(2) yielded 9, the lead homologue of 7. Oxidative addition of sulfur to 7 led to the dimeric bis(diamido)tin sulfide 10. Treatment of 2 successively with 'MgBu(2)' in C(5)H(12) and THF gave [Mg{N(R)C(6)H(4)(CH(2)NR)}(THF)](2) (11a), which by displacement of its THF by an equivalent portion of Bu(t)CN or PhCN produced [Mg{N(R)C(6)H(4)(CH(2)NR)}(CNR')(n)] [R' = Bu(t), n = 1 (11b); R' = Ph, n = 2 (11c)]. The Ca (12), Sr (13) or Ba (14) analogues of the Mg compound 11a were isolated from 2 and either the appropriate compound M(NR(2))(2) (M = Ca, Sr, Ba), or successively 2 LiBu(n) and 2 M(OTos)(2). The new compounds 1-14 were characterized by microanalysis (C, H, N; not for 1, 2, 3, 5), solution NMR spectra, ν(max) (C≡N) (IR for 4c, 4d, 4e, 6, 11b, 11c), selected EI-MS peaks (for 1, 2, 3, 7, 8, 9, 10), and single crystal X-ray diffraction (for 4a, 4b, 11a).     

Synthesis of Novel Chromene,Pyridine, Pyrazole,Pyrimidine, and Imidazole Derivatives via One‐pot Multicomponent Reaction

New series of chromenes 2 – 4 , pyridines 5 – 8 , and pyranopyrazoles 9a,b were synthesized via one‐pot multicomponent reaction of 4‐tosyloxybenzaldehyde ( 1 ) and malononitrile with phenols, amines or hydrazines, and ethyl acetoacetate, respectively. Compound 9a was reacted with acetic anhydride, formic acid, or formamide to afford N ‐acetyl derivative 10 and pyrazolopyranopyrimidines 11 – 13 , respectively. Imidazole derivatives 14 and 15a – d were obtained by multicomponent reaction between compound 1 with ammonium acetate and benzil or aromatic amines in (1:2:1) or (1:1:1:1) ratio, respectively. The structures of new compounds were elucidated by elemental and spectral analyses.     

Novel thiophene-based cycloruthenated compounds: synthesis, characterization, and reactivity

The reactions between a series of thiophene-based imines with [(η(6)-C(6)H(6))RuCl(μ-Cl)](2), in a basic medium, and in MeCN give a family of ruthenacycles of stoichiometry [Ru(C^N)(NCMe)(4)]PF(6) (C^N = orthometalated thiopheneimine). In these species, the C-H activation process is produced in most cases at the thiophene ring. When two C-H bonds are competing (thiophene vs aryl), the cyclometalation can be driven regioselectively to the thiophene unit or to the aryl ring as a function of the location of the iminic C=N bond. Cyclometalation can also be oriented to positions 2 or 3 of the thiophene depending on the situation of the imine in the heterocycle (3 or 2, respectively). In all studied cases, the η(6)-C(6)H(6) ligand was substituted by acetonitrile. The X-ray structures of two representative complexes have been determined. These thiophene-based metallacycles react with iodine under very mild conditions affording, after hydrolysis, substituted 3-iodo-2-formyl(benzo)thiophenes or substituted 2-iodo-3-formyl(benzo)thiophenes, as a function of the organometallic precursor.     

Virtual libraries of tetrapyrrole macrocycles. Combinatorics, isomers, product distributions, and data mining

A software program (PorphyrinViLiGe) has been developed to enumerate the type and relative amounts of substituted tetrapyrrole macrocycles in a virtual library formed by one of four different classes of reactions. The classes include (1) 4-fold reaction of n disubstituted heterocycles (e.g., pyrroles or diiminoisoindolines) to form β-substituted porphyrins, β-substituted tetraazaporphyrins, or α- or β-substituted phthalocyanines; (2) combination of m aminoketones and n diones to form m × n pyrroles, which upon 4-fold reaction give β-substituted porphyrins; (3) derivatization of an 8-point tetrapyrrole scaffold with n reagents, and (4) 4-fold reaction of n aldehydes and pyrrole to form meso-substituted porphyrins. The program accommodates variable ratios of reactants, reversible or irreversible reaction (reaction classes 1 and 2), and degenerate modes of formation. Po?lya's theorem (for enumeration of cyclic entities) has also been implemented and provides validation for reaction classes 3 and 4. The output includes the number and identity of distinct reaction-accessible substituent combinations, the number and identity of isomers thereof, and the theoretical mass spectrum. Provisions for data mining enable assessment of the number of products having a chosen pattern of substituents. Examples include derivatization of an octa-substituted phthalocyanine with eight reagents to afford a library of 2,099,728 members (yet only 6435 distinct substituent combinations) and reversible reaction of six distinct disubstituted pyrroles to afford 2649 members (yet only 126 distinct substituent combinations). In general, libraries of substituted tetrapyrrole macrocycles occupy a synthetically accessible region of chemical space that is rich in isomers (>99% or 95% for the two examples, respectively).     

Synthesis of novel thiazoles bearing hydrazine,thiosemicarbazide, thiazole,and thiazolidinone moieties

Thiazolecarboxylate esters (I) and (II) react with hydrazine hydrate to give the acid hydrazides (III) and (IV), which then react with KSCN and PhNCS to give high yields of the thiosemicarbazides (V)-(VIII). Cyclocondensation of the thiosemicarbazide (V) with 3-phenyl-3-chloro-2-oxopropionic acid derivatives gives compounds with two thiazole moieties (IX)-(XIV). The reaction of the phenylthiosemicarbazides (VII) and (VIII) with chloroacetyl chloride and (or) chloroacetic acid affords the thiazolidinonethiazoles (XV) and (XVI).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2832–2836, December, 1991.     

Odd-numbered Fe(III) complexes: synthesis, molecular structure, reactivity, and magnetic properties

Three isostructural disklike heptanuclear FeIII compounds of the general formula [FeIII7(mu3-O)3(L)3(mu-O2CCMe3)6(eta1-O2CCMe3)3(H2O)3], where L represents a di- or triethanolamine moiety, display a three-blade propeller topology, with the central Fe atom representing the axle or axis of the propeller. This motif corresponds to the theoretical model of a frustrated Heisenberg star, which is one of the very few solvable models in the area of frustrated quantum-spin systems and can, furthermore, be converted to an octanuclear cage for the case where L is triethanolamine to give [FeIII8(mu4O)3(mu4-tea)(teaH)3(O2CCMe3)6(N3)3].1/2MeCN.1/2H2O or [FeIII8(mu4O)3(mu4-tea)(teaH)3(O2CCMe3)6(SCN)3].2MeCN when treated with excess NaN3 or NH4SCN, respectively. The core structure is formally derived from that of the heptanuclear compounds by the replacement of the three aqua ligands by an {Fe(tea)} moiety, so that the 3-fold axis of the propeller is now defined by two central FeIII atoms. Magnetic studies on two of the heptanulcear compounds established unequivocally S = 5/2 spin ground state for these complexes, consistent with overall antiferromagnetic interactions between the constituent FeIII ions.     

First principles study of the ignition mechanism for hypergolic bipropellants: N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N',N'-tetramethylmethylenediamine (TMMDA) with nitric acid

We report quantum mechanics calculations (B3LYP flavor of density functional theory) to determine the chemical reaction mechanism underlying the hypergolic reaction of pure HNO(3) with N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N',N'-tetramethylmethylenediamine (TMMDA). TMEDA and TMMDA are dimethyl amines linked by two CH(2) groups or one CH(2) group, respectively, but ignite very differently with HNO(3). We explain this dramatic difference in terms of the role that N lone-pair electrons play in activating adjacent chemical bonds. We identify two key atomistic level factors that affect the ignition delay: (1) The exothermicity for formation of the dinitrate salt from TMEDA or TMMDA. With only a single CH(2) group between basic amines, the diprotonation of TMMDA results in much stronger electrostatic repulsion, reducing the heat of dinitrate salt formation by 6.3 kcal/mol. (2) The reaction of NO(2) with TMEDA or TMMDA, which is the step that releases the heat and reactive species required to propagate the reaction. Two factors of TMEDA promote the kinetics by providing routes with low barriers to oxidize the C: (a) formation of a stable intermediate with a C-C double bond and (b) the lower bond energy for breaking the C-C single bond (by 18 kcal/mol comparing to alkane) between two amines. Both factors would decrease the ignition delay for TMEDA versus TMMDA. The same factors also explain the shorter ignition delay of 1,4-dimethylpiperazine (DMPipZ) versus 1,3,5-trimethylhexahydro-1,3,5-triazine (TMTZ). These results indicate that TMEDA and DMPipZ are excellent green replacements for hydrazines as the fuel in bipropellants.