Syntheses, and optical, fluorescence, and nonlinear optical characterization of phosphine-substituted terthiophenes

Earlier studies of phosphine-substituted terthiophenes have demonstrated that some of these materials exhibit nonlinear absorption at 532 nm. However, this wavelength is significantly removed from the linear absorption maxima of the complexes, suggesting that better nonlinear absorption might be observed at wavelengths closer to the linear absorption maxima. To investigate this possibility, a library of compounds has been prepared either by varying the group attached to the nonbonding pair of electrons on the phosphorus atoms of 5,5'-bis(diphenylphosphino)-2,2':5',2'-terthiophene (PT(3)P), or by introducing additional substituents on the 5'-position of 5-(diphenylphosphino)-2,2':5',2'-terthiophene (PT(3)). All these compounds have been characterized using multinuclear NMR, UV-vis, and fluorescence spectroscopy. The compounds are strongly fluorescent, and both the fluorescence wavelength and the intensity depend upon the thiophene substituents. The nonlinear optical properties have also been evaluated at various wavelengths in the blue region. Each compound exhibits reverse saturable absorption, and the intensity of the reverse saturable absorption at a particular wavelength depends on the chemical structure of the compound.     

A ROMP-derived, polymer-supported chiral Schrock catalyst for enantioselective ring-closing olefin metathesis

A permanently polymer-immobilised version of Schrock's molybdenum catalyst was realised via polymerisation of chiral 5,5'-bis(norborn-5-ene-2-ylmethyleneoxymethyl)-3,3'-di-tert-butyl-6,6'-dimethylbiphen-2,2'-diol followed by reaction with the catalyst precursor Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OSO2CF3)2(CH3OCH2CH2OCH3); using this 5-, 6- and 7-membered heterocycles were synthesised via ring-closing metathesis (RCM) from (pro-)chiral substrates in high yields and ee with short reaction times; the catalyst shows low loss of molybdenum during RCM, and was easily separated and recycled.     

Highly fluorescent solid-state asymmetric spirosilabifluorene derivatives

A series of four asymmetrically aryl-substituted 9,9'-spiro-9-silabifluorene (SSF) derivatives, 2,2'-di-tert-butyl-7,7'-diphenyl-9,9'-spiro-9-silabifluorene (PhSSF), 2,2'-di-tert-butyl-7,7'-dipyridin-2-yl-9,9'-spiro-9-silabifluorene (PySSF), 2,2'-di-tert-butyl-7,7'-dibiphenyl-4-yl-9,9'-spiro-9-silabifluorene (BPhSSF), and 2,2'-di-tert-butyl-7,7'-bis(2',2' '-bipyridin-6-yl)-9,9'-spiro-9-silabifluorene (BPySSF) are prepared through the cyclization of the corresponding 2,2'-dilithiobiphenyls with silicon tetrachloride. These novel spiro-linked silacyclopentadienes (siloles) form transparent and stable amorphous films with relatively high glass transition temperatures (T(g) = 203-228 degrees C). The absorbance spectrum of each compound shows a significant bathochromic shift relative to that of the corresponding carbon analogue as a result of the effective sigma-pi conjugation between the sigma orbital of the exocyclic Si-C bond and the pi orbital of the oligoarylene fragment. Solid-state films exhibit intense violet-blue emission (lambda(PL) = 398-415 nm) with high absolute photoluminescence quantum yields (phi(PL) = 30-55%).     

Fluorocarbon-modified organic semiconductors: molecular architecture, electronic, and crystal structure tuning of arene- versus fluoroarene-thiophene oligomer thin-film properties

We present here the systematic synthesis and comparative physicochemical characterization of a series of regiochemically varied and core size extension-modulated arene(perfluoroarene)-thiophene oligomers. The molecules investigated are: 5,5'-diphenyl-2,2':5',2':5',2'-quaterthiophene (1), 5,5'-bis[1-[4-(thien-2-yl)phenyl]]-2,2'-dithiophene (2), 4,4'-bis[5-(2,2'-dithiophenyl)]-biphenyl (3), 5,5'-diperfluorophenyl-2,2':5',2':5',2'-quaterthiophene (4), 5,5'-bis[1-[4-(thien-2-yl)perfluorophenyl]]-2,2'-dithiophene (5), 4,4'-bis[5-(2,2'-dithiophenyl)]-perfluorobiphenyl (6), 5,5'-diperfluorophenyl-2,2':5',2'-tertthiophene (7), 5,5'-diperfluorophenyl-2,2'-dihiophene (8), and 5,5-diperfluorophenylthiophene (9). Trends in optical absorption and emission parameters, molecular structures as defined by single-crystal X-ray diffraction, as well as electrochemical redox processes are described. The morphologies and microstructures of the vapor-deposited films grown over a range of growth temperatures have also been characterized. Field-effect transistor (FET) measurements demonstrate that all of these materials are FET-active and, depending on the molecular architecture, exhibit comparably good p- or n-type mobility when optimum film microstructural order is achieved. A very large n-channel mobility of approximately 0.5 cm2/Vs with I(on)/I(off) ratios > 10(8) is achieved for films of 4.     

Rhodium-catalyzed linear cross-trimerization of two different alkynes with an alkene and two different alkenes with an alkyne

Crossing paths with rhodium: A cationic Rh(I)/H(8)-BINAP complex has been found to catalyze the linear cross-trimerization of terminal alkynes, acetylenedicarboxylates, and acrylamides to give substituted trienes. The asymmetric linear cross-trimerization, giving substituted chiral dienes, has also been achieved by using monosubstituted alkenes and (R)-BINAP instead of terminal alkynes and H(8)-BINAP (see scheme; H(8)-BINAP = 2,2'-bis(diphenylphosphino)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl; BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl]).     

Synthesis and characterization of new biphenolate and binaphtholate rare-Earth-metal amido complexes: catalysts for asymmetric olefin hydroamination/cyclization

Monomeric diolate amido yttrium complexes [Y[diolate][N(SiHMe(2))(2)](thf)(2)] can be prepared in good yield by treating [Y[N(SiHMe(2))(2)](3)(thf)(2)] with either 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diol (H(2)(Biphen)), 3,3'-bis(2,4,6-triisopropylphenyl)-2,2'-dihydroxy-1,1'-dinaphthyl (H(2)(Trip(2)BINO)) or 3,3'-bis(2,6-diisopropylphenyl)-2,2'-dihydroxy-1,1'-dinaphthyl (H(2)(Dip(2)BINO)) in racemic and enantiopure form. The racemic complex [Y(biphen)[N(SiHMe(2))(2)](thf)(2)] dimerizes upon heating to give the heterochiral complex (R,S)-[Y(biphen)[N(SiHMe(2))(2)](thf)](2). The corresponding dimeric heterochiral lanthanum complex was the sole product in the reaction of H(2)(Biphen) with [La[N(SiHMe(2))(2)](3)(thf)(2)]. Single-crystal X-ray diffraction of both dimeric complexes revealed that the two Ln(biphen)[N(SiHMe(2))(2)](thf) fragments are connected through bridging phenolate groups of the biphenolate ligands. The two different phenolate groups undergo an intramolecular exchange process in solution leading to their equivalence on the NMR timescale. All complexes were active catalysts for the hydroamination/cyclization of aminoalkynes and aminoalkenes at elevated temperature, with [Y((R)-dip(2)bino)[N(SiHMe(2))(2)](thf)(2)] being the most active one giving enantioselectivities of up to 57 % ee. Kinetic resolution of 2-aminohex-5-ene proceeded with this catalyst with 6.4:1 trans selectivity to give 2,5-dimethylpyrrolidine with a k(rel) of 2.6.     

Thiophene-functionalized isoindigo dyes bearing electron donor substituents with absorptions approaching the near infrared region

A series of six new, highly soluble N,N'-dialkylated isoindigo derivatives bearing different electron donating thiophene units at the 6,6'-positions were synthesized by Stille cross-coupling reaction. The optical and electrochemical properties of these dyes were studied by UV-vis spectroscopy and cyclic voltammetry, revealing a good tunability of their electronic properties by peripheral substituents with amino groups leading to strong absorption reaching the NIR region. The DFT calculations of the frontier molecular orbitals of these dyes corroborate the observed substituent effect on absorption and redox properties.     

Unusual frequency dispersion effects of the nonlinear optical response in highly conjugated (polypyridyl)metal-(porphinato)zinc(II) chromophores

The syntheses and electrooptic properties of a new family of nonlinear optical chromophores are reported. These species feature an ethyne-elaborated, highly polarizable porphyrinic component and metal polypyridyl complexes that serve as integral donor and acceptor elements. Examples of this structural motif include ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Ru-PZn); osmium(II) [5-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2'-terpyridine)(2+) bis-hexafluorophosphate (Os-PZn); ruthenium(II) [5-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phen-yl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Ru-PZn-A); osmium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Os-PZn-A); and ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))osmium(II)-15-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-10,20-bis (2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-bis(2,2';6',2'-terpyridine)(4+) tetrakis-hexafluorophosphate (Ru-PZn-Os). The frequency dependence of the dynamic hyperpolarizability of these compounds was determined from hyperRayleigh light scattering (HRS) measurements carried out at fundamental incident irradiation wavelengths (lambda(inc)) of 800, 1064, and 1300 nm. These data show that (i) coupled oscillator photophysics and metal-mediated cross-coupling can be exploited to elaborate high beta(0) supermolecules that exhibit significant excited-state electronic communication between their respective pigment building blocks; (ii) high-stability metal polypyridyl compounds constitute an attractive alternative to electron releasing dialkyl- and diarylamino groups, the most commonly used donor moieties in a wide range of established nonlinear optical dyes; (iii) this design strategy enables ready elaboration of chromophores having extraordinarily large dynamic hyperpolarizabilities (beta(lambda) values) at telecommunication relevant wavelengths; and (iv) porphyrin B- and Q-state-derived static hyperpolarizabilities (beta(0) values) can be designed to have the same or opposite sign in these species, thus providing a new means to regulate the magnitude of lambda(inc)-specific dynamic hyperpolarizabilities.     

Extreme electronic modulation of the cofacial porphyrin structural motif

The synthesis, electrochemistry, and optical spectroscopy of an extensive series of cofacial bis[(porphinato)zinc(II)] compounds are reported. These species were synthesized using sequential palladium-catalyzed cross-coupling and cobalt-mediated [2+2+2] cycloaddition reactions. This modular methodology enables facile control of the nature of macrocycle-to-macrocycle connectivity and allows unprecedented modulation of the redox properties of face-to-face porphyrin species. We report the synthesis of 5,6-bis[(5',5'-10',20'-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (1), 5,6-bis[(2'-5',10',15',20'-tetraphenylporphinato)zinc(II)]indane (2), 5-([2'-5',10',15',20'-tetraphenylporphinato]zinc(II))-6-[(5"-10',20'-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (3), 5-([2'-5',10',15',20'-tetrakis(trifluoromethyl)porphinato]zinc(II))-6-[(5' '-10' ',20' '-bis[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (4), 5-(2'-5',10',15',20'-[tetrakis(trifluoromethyl)porphinato]zinc(II))-6-[(2'-5',10',15',20'-tetraphenylporphinato)zinc(II)]indane (5), 5,6-bis([2'-5',15'-diphenyl-10',20'-(trifluoromethyl)porphinato]zinc(II))indane (6), and 5,6-bis([2'-5',10',15',20'-tetrakis(trifluoromethyl)porphinato]zinc(II))indane (7); 4-7 define the first examples of cofacial bis[(porphinato)metal] compounds in which sigma-electron-withdrawing perfluoroalkyl groups serve as macrocycle substituents, while 2, 6, and 7 constitute the first such structures that possess a beta-to-beta linkage topology. Cyclic voltammetric studies show that the electrochemically determined HOMO and LUMO energy levels of these cofacial bis(porphinato) complexes can be lowered by 780 and 945 mV, respectively, relative to the archetypal members of this class of compounds; importantly, these orbital energy levels can be modulated over well-defined increments throughout these wide potentiometric domains. Analyses of these cofacial bis[(porphinato)metal] potentiometric data, in terms of the absolute and relative frontier orbital energies of their constituent [porphinato]zinc(II) building blocks, as well as the nature of macrocycle-to-macrocycle connectivity, provide predictive electronic structural models that rationalize the redox behavior of these species.     

Bidirectional racemic synthesis of the biologically active quinone cardinalin 3

Readily available 2,2',6,6'-tetramethoxy-1,1'-biphenyl was transformed in 14 synthetic steps into the natural product cardinalin 3 using a bidirectional approach. One of the key steps was the formation of the cis-1,3-dimethylnaphtho[2,3-c]pyran ring. (+/-)-1,1'-[6,6'-Diallyl-5,5'-bis(benzyloxy)-1,1',3,3'-tetramethoxy-2,2'-binaphthalene-7,7'-diyl]diethanol was treated with O(2) in the presence of CuCl(2) and catalytic PdCl(2) to afford 5,5'-bis(benzyloxy)-7,7',9,9'-tetramethoxy-1,1',3,3'-tetramethyl-1H,1'H-8,8'-bibenzo[g]isochromene. Hydrogenation of this compound afforded 7,7',9,9'-tetramethoxy-cis-1,3-cis-1',3'-tetramethyl-3,3',4,4'-tetrahydro-1H,1'H-8,8'-bibenzo[g]isochromene-5,5'-diol in quantitative yield, which was converted in 3 steps to cardinalin 3.     

Density matrix analysis, simulation, and measurements of electronic absorption and fluorescence spectra of spirobifluorenes

The linear absorption and fluorescence spectra as well as the oscillator strengths of 2,2',7,7'-tetraphenyl-9,9'-spirobifluorene (A), 2,2',7,7'-tetrakis(biphenyl-4-yl)-9,9'-spirobifluorene (B), and 2,2',7,7'-tetrakis(9,9'-spirobifluoren-2-yl)-9,9'-spirobifluorene (C) are calculated on the basis of the collective electronic oscillator (CEO) approach of Mukamel et al. (see, e.g., Chem. Rev. 2002, 102, 3171). The graphical visualization and quantitative characterization of CEO modes allows one to extract the real-space distribution of electronic excitations of the molecules under study. Effects of the lengthening and branching of the oligophenylene segments have been analyzed. The influence of the lowest excited (S1) vs ground-state (S0) geometry changes on the CEO modes is investigated and related to the geometry changes of the molecular parts. The obtained theoretical results are in good agreement with experimental trends observed in absorption and fluorescence data.     

Tuning the gas phase redox properties of copper(II) ternary complexes of terpyridines to control the formation of nucleobase radical cations

Electrospray ionization (ESI) tandem mass spectrometry (MS/MS) of ternary copper(II) complexes of [Cu(terpyX)(M)]2+ (where terpyX = is a substituted 2,2':6',2'-terpyridine ligand; M = the nucleobases: adenine, guanine, thymine and cytosine) was examined as a means of forming radical cations of nucleobases in the gas phase. The following substituents were examined: 4'-NMe2-2,2':6',6'-terpyridine; 4'-OH-2,2':6',6'-terpyridine; 4'-F-2,2':6',6'-terpyridine; 2,2':6',6'-terpyridine; 4'-Cl-2,2':6',6'-terpyridine; 4'-Br-2,2':6',6'-terpyridine; 4'-CO2H-2,2':6',6'-terpyridine; 4'-NO2-2,2':6',6'-terpyridine and 6,6'-dibromo-2',2:6',2'-terpyridine. Each of the ternary complexes [Cu(terpyX)(M)]2+ was mass selected and subjected to collision induced dissociation (CID) in a quadrupole ion trap. The types of fragmentation reactions observed for these complexes depend on the nature of the substituent on the terpyridine ligand, while the yields of the radical cations of the nucleobases follow the order of their ionization energies (IEs): G (lowest IE) > A > C > T (highest IE). In general, radical cation formation is favoured for electron withdrawing substituents (e.g. NO2) while loss of the neutral nucleobase is favoured for electron donating substituents (e.g. NMe2). Loss of the protonated nucleobase is a major fragmentation pathway for the OH substituted terpyridine system, consistent with its ability to bind to a metal centre as a deprotonated ligand. Crystal structure determinations of (6,6'-dibromo-2',2:6',2'-terpyridine)bis(nitrato)copper(II) and diaqua(4'-oxo-2,2':6',6'-terpyridine)copper(II) nitrate monohydrate were performed and correlated with the ESI results.     

Blue emitting 3π-2spiro terfluorene-indenofluorene isomers: a structure-properties relationship study

Two novel terfluorenyl derivatives, 2,2',7,7'-tetrakis(9,9-dioctyl-9H-fluoren-2-yl)dispiro[fluorene-9,11'-indeno-(2,1-a)-fluorene-12',9'-fluorene] ((2,1-a)-DST-IF) and 2,2',7,7'-tetrakis(9,9-dioctyl-9H-fluoren-2-yl)dispiro- [fluorene-9,6'-indeno-(1,2-b)-fluorene-12',9'-fluorene] ((1,2-b)-DST-IF) have been synthesized by two different synthetic approaches. These terfluorenyl derivatives possess a different central indenofluorene core, namely (2,1-a)-indenofluorene or (1,2-b)-indenofluorene, which imposes two distinct geometry profiles, and different structural environments for the terfluorenyl fluorophores that translates into drastically different optical and electrochemical properties for (2,1-a)-DST-IF and (1,2-b)-DST-IF. These properties have been carefully studied through a combined experimental and theoretical approach. The (2,1-a)-DST-IF isomer has been successfully used as emitting layer in a blue single-layer small-molecule organic light-emitting diode (SMOLED) and appears as the first example of a blue emission arising from intramolecular terfluorenyl excimers. Regarding the importance of terfluorenyl derivatives in organic electronics, the present structure-properties relationship study, may open new avenues in the design of efficient blue fluorophores.     

Asymmetric polymerization of aromatic isocyanates with optically active anionic initiators

The asymmetric anionic polymerization of o-, m-, and p-methylphenyl isocyanates, p-methoxyphenyl isocyanate, p-chlorophenyl isocyanate, 2,6- and 3,4-dimethylphenyl isocyanates, and 1-naphthyl isocyanate was carried out using chiral anionic initiators such as the lithium salts of (?) -menthol, (?) -(2-methoxymethyl) pyrrolidine, and (+) -1-(2-pyrrolidinylmethyl) pyrrolidine. Although o-methylphenyl isocyanate gave an insoluble polymer and 2,6-dimethylphenyl isocyanate afforded no polymer, the other monomers gave soluble polymers, which showed optical activity due to the prevailing helicity of the polymer chain induced by chiral initiator residues attached to the α-end of the polymer chain. The molecular mechanics conformational calculation for a tetramer of m-methylphenyl isocyanate supported the helical conformation of the main chain. The optical rotation of the polymers depended significantly on temperature. © 1994 John Wiley & Sons, Inc.     

Synthesis and catalytic activity of group 5 metal amides with chiral biaryldiamine-based ligands

A new series of group 5 metal amides have been prepared from the reaction between V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) and chiral ligands, (R)-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (1H(2)), (R)-5,5',6,6',7,7',8,8'-octahydro-2,2'-bis(mesitoylamino)-1,1'-binaphthyl (2H(2)), (R)-6,6'-dimethyl-2,2'-bis(mesitoylamino)-1,1'-biphenyl (3H(2)), (R)-2,2'-bis(mesitylenesulfonylamino)-6,6'-dimethyl-1,1'-biphenyl (4H(2)), (R)-2,2'-bis(diphenylthiophosphoramino)-1,1'-binaphthyl (5H(2)), (R)-2,2'-bis[(3-tert-butyl-2-hydroxybenzylidene)amino]-6,6'-dimethyl-1,1'-biphenyl (6H(2)), (R)-2,2'-bis[(3,5-di-tert-butyl-2-hydroxybenzylidene)amino]-6,6'-dimethyl-1,1'-biphenyl (7H(2)), (R)-2,2'-bis[(3-tert-butyl-2-hydroxybenzylidene)amino]-1,1'-binaphthyl (8H(2)), (S)-2-(mesitoylamino)-2'-(dimethylamino)-1,1'-binaphthyl (9H), and (R)-2-(mesitoylamino)-2'-(dimethylamino)-6,6'-dimethyl-1,1'-biphenyl (10H), which are derived from (R) or (S)-2,2'-diamino-1,1'-binaphthyl, and (R)-2,2'-diamino-6,6'-dimethyl-1,1'-biphenyl, respectively. Treatment of V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) with 1 equiv of C(2)-symmetric amidate ligands 1H(2), 2H(2), 3H(2), 4H(2), and 5H(2), or Schiff base ligands 6H(2), 7H(2) and 8H(2) at room temperature gives, after recrystallization from a benzene, toluene or n-hexane solution, the vanadium amides (1)V(NMe(2))(2) (11), (2)V(NMe(2))(2) (14), (3)V(NMe(2))(2) (17), (5)V(NMe(2))(2) (22), (6)V(NMe(2))(2) (23) and (7)V(NMe(2))(2) (24), and niobium amides (1)Nb(NMe(2))(3) (12), (2)Nb(NMe(2))(3) (15), (3)Nb(NMe(2))(3) (18), (4)Nb(NMe(2))(3) (20) and [2-(3-Me(3)C-2-O-C(6)H(3)CHN)-2'-(N)-C(20)H(12)][2-(Me(2)N)(2)CH-6-CMe(3)-C(6)H(3)O]NbNMe(2)·C(7)H(8) (25·C(7)H(8)), and tantalum amides (1)Ta(NMe(2))(3) (13), (2)Ta(NMe(2))(3) (16), (3)Ta(NMe(2))(3) (19) and (4)Ta(NMe(2))(3) (21) respectively, in good yields. Reaction of V(NMe(2))(4) or M(NMe(2))(5) (M = Nb, Ta) with 2 equiv of C(1)-symmetric amidate ligands 9H or 10H at room temperature gives, after recrystallization from a toluene or n-hexane solution, the chiral bis-ligated vanadium amides (9)(2)V(NMe(2))(2)·3C(7)H(8) (27·3C(7)H(8)) and (10)V(NMe(2))(2) (28), and chiral bis-ligated metallaaziridine complexes (10)(2)M(NMe(2))(η(2)-CH(2)NMe) (M = Nb (29), Ta (30)) respectively, in good yields. The niobium and tantalum amidate complexes are stable in a toluene solution at or below 160 °C, while the vanadium amidate complexes degrade via diemthylamino group elimination at this temperature. For example, heating the complex (2)V(NMe(2))(2) (14) in toluene at 160 °C for four days leads to the isolation of the complex [(2)V](2)(μ-NMe(2))(2) (26) in 58% yield. These new complexes have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 12, 13, and 15-30 have further been confirmed by X-ray diffraction analyses. The vanadium amides are active chiral catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to good yields with good ee values (up to 80%), and the tantalum amides are outstanding chiral catalysts for the hydroaminoalkylation, giving chiral secondary amines in good yields with excellent ee values (up to 93%).     

Polyhydroxyoligothiophenes. 2. Hydrogen-Bonding-Oriented Solid State Conformation of 3,3'-Bis(2-hydroxyethyl)-2,2'-bithiophene and Regioselective Synthesis of the Corresponding Head-to-Head/Tail-to-Tail Quater- and Sexithiophene

This paper reports the X-ray structure of 3,3'-bis(2-hydroxyethyl)-2,2'-bithiophene (1), which is the building block for the synthesis of head-to-head/tail-to-tail 2-hydroxyethyl-substituted oligothiophenes. Contrary to all the bithiophenes reported so far, 1 exhibits a noncoplanar anti conformation and an inter-ring twist angle (67.5 degrees ) which is the largest ever measured for adjacent rings of alpha-conjugated oligothiophenes. This unusual conformation appears to be dictated by intermolecular hydrogen-bonding interactions involving the OH groups, which bind the molecule in close packed layers. The paper also describes the regioselective synthesis of the dimer and the trimer of 1, namely of 3,3',4",3"'-tetrakis(2-hydroxyethyl)-2,2':5',2":5",2"'-quaterthiophene (3c) and of 3,3',4",3"',4",3"'-hexakis(2-hydroxyethyl)-2,2':5',2":5",2"':5"',2":5",2"'-sexithiophene (4b). 3c And 4b were obtained through palladium(0)-catalyzed coupling of the mono- and distannanes of the tetrahydropyranyl derivative of 1 with the appropriate monobromo compound (Stille's reaction). Finally, the paper reports force-field calculations which suggest that the low lambda(max) values measured for 1, 3c, and 4b are also the result of intramolecular hydrogen-bonding interactions which favor highly twisted conformations in solution.     

Catalytic homologation of vinyltributylstannane to allyltributylstannane by Mo(IV) complexes in the presence of ethylene

We have found that CH2=CHSnBu3 is converted into CH2=CHCH2SnBu3 catalytically in the presence of Mo(IV) olefin complexes such as Mo(NAr)(CH2CH2)[biphen] (where Ar = 2,6-i-Pr2C6H3 and [biphen]2- = 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate). The proposed mechanism involves formation of a metalacyclopentane (MC4) complex from ethylene and CH2=CHSnBu3, "contraction" of this MC4 complex to a metalacyclobutane (MC3) complex, and finally metathesis of the MC3 complex to give CH2=CHCH2SnBu3 and Mo(NAr)(CH2)[biphen]. These new findings suggest (inter alia) that contraction of an MC4 ring to an MC3 ring may be a much more common mode of decomposition of metalacyclopentane rings in d0 complexes than previously believed.     

Alkylidene and metalacyclic complexes of tungsten that contain a chiral biphenoxide ligand. synthesis,asymmetric ring-closing metathesis,and mechanistic investigations

Two complexes that contain the racemic or enantiomerically pure (S) form of the 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diolate (Biphen(2-)) ligand, W(NAr)(CHCMe(2)Ph)(Biphen) (2a) and W(NAr')(CHCMe(2)Ph)(Biphen) (2b) (Ar = 2,6-i-Pr(2)C(6)H(3); Ar' = 2,6-Me(2)C(6)H(3)), were prepared and shown to be viable catalysts for several representative ring-closing reactions to give products in good yields in most cases and high % ee in asymmetric reactions. Exploration of the reaction between 2a and a stoichiometric amount of one desymmetrization substrate allowed two intermediate tungstacyclobutane complexes to be observed, in addition to the final and quite stable tungstacyclobutane complex formed in a reaction between the ring-closed product and a tungsten methylene complex. Reactions involving (13)C labeled ethylene allowed for the observation of an unsubstituted tungstacyclobutane complex, an ethylene complex, an unsubstituted tungstacyclopentane complex, and a heterochiral dimeric form of a methylene complex. The tungstacyclopentane complex was found to catalyze the dimerization of ethylene to 1-butene slowly.     

Remarkable steric effects and influence of monodentate axial ligands l on the spin-crossover properties of trans-[FeII(N4 ligand)L] complexes

Iron(II) complexes obtained from tetradentate, rigid, linear N4 ligands have been investigated to appraise the influence of steric effects and the impact of trans-coordinated anions on the spin-transition behavior. As expected, the well-designed ligands embrace the metal center, resulting in octahedral iron(II) complexes where the basal plane is fully occupied by the pyridine/pyrazole N4 ligand, while anions or solvent molecules are exclusively axially coordinated. Precursor complexes, namely, [Fe(bpzbpy)(MeOH)2](BF4)2 (where bpzbpy symbolizes the ligand 6,6'-bis(N-pyrazolylmethyl)-2,2'-bipyridine) and [Fe(mbpzbpy)(MeOH)2](BF4)2 (where mbpzbpy symbolizes the ligand 6,6'-bis(3,5-dimethyl-N-pyrazolmethyl)-2,2'-bipyridine), have been used for the in situ preparation of a series of structural analogues via the exchange of the weakly coordinated trans methanol molecules by various anions, such as thiocyanate, selenocyanate, or dicyanamide. The magnetic properties of all seven iron(II) compounds thus obtained have been investigated. Two iron(II) complexes, i.e., [Fe(bpzbpy)(NCS)2] and [Fe(bpzbpy)(NCSe)2], exhibit gradual spin-crossover (SCO) properties typical of isolated mononuclear species with weak cooperative interaction. These two SCO materials have been studied by M?ssbauer spectroscopy, and the light-induced excited spin state trapping effect has been investigated, revealing the possibility to induce the spin-transition both by temperature variation and by light irradiation. A correlation between steric/anion effect and SCO behavior is suggested.     

Use of reversed-phase high-performance liquid chromatography-diode array detection for complete separation of 2,4,6-trinitrotoluene metabolites and EPA Method 8330 explosives: influence of temperature and an ion-pair reagent

Explosives such as 2,4,6-trinitrotoluene (TNT), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are widely distributed environmental contaminants. Complete chromatographic separation is necessary in order to accurately determine and quantify explosives and their degradation products in environmental samples and in (bio)transformation studies. The present study describes a RP-HPLC method with diode array detection using a LC-8 guard column, a Supelcosil LC-8 chromatographic column, and a gradient elution system. This gradient method is capable of baseline separating the most commonly observed explosives and TNT transformation metabolites including 2,4,6-triaminotoluene (TAT) in a single run. The TNT metabolites separated were 2-hydroxylamino-4,6-dinitrotoluene, 4-hydroxylamino-2,6-dinitrotoluene, 2,4-dihydroxylamino-6-nitrotoluene, 4,4',6,6'-tetranitro-2,2'-azoxytoluene, 2,2',6,6'-tetranitro-4,4'-azoxytoluene, 4,4',6,6'-tetranitro-2,2'-azotoluene, 2,2',6,6'-tetranitro-4,4'-azotoluene, 2-amino-4,6-dinitrotoluene, 4-amino-2, 6-dinitrotoluene, 2,6-diamino-4-nitrotoluene, 2,4-diamino-6-nitrotoluene, and TAT. The same gradient method at a different column temperature can also be used to baseline separate the explosives targeted in the Environmental Protection Agency (EPA) Method 8330 with approximately 22% reduction in total run time and 48% decrease in solvent consumption compared to previously published methods. Good separation was also obtained when all TNT metabolites and EPA Method 8330 compounds (a total of 23 compounds) were analyzed together; only 2,6-DANT and HMX co-eluted in this case. The influence of temperature (35-55 degrees C) and the use of an ion-pair reagent on the chromatographic resolution and retention were investigated. Temperature was identified as the key parameter for optimal baseline separation. Increased temperature resulted in shorter retention times and better peak resolution especially for the aminoaromatics investigated. The use of an ion-pair reagent (octanesulfonic acid) generally resulted in longer retention times for compounds containing amine functional groups, more baseline noise, and decreased peak resolution.