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A series of nickel complexes containing α-iminocarboxamide, η¹-benzyl, and PMe3 ligands were synthesized to identify structural features of neutral Ni complexes that are employed in ethylene polymerization and ethylene/functionalized norbornene copolymerizations. Variations in steric bulk on aryl substituents in the α-iminocarboxamide framework were used to probe N,N- versus N,O-binding modes. When the steric bulk is sufficiently large, as in [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-κ²N,O]Ni(η¹-CH2Ph)(PMe3) (1), [N-(2,6-diethylphenyl)-2-(2,6-diethylphenylimino)propanamidato-κ²N,O](η¹-CH2Ph)(PMe3)nickel (2), and [N-(2,6-methyl-isopropylphenyl)-2-(2,6-methylisopropylphenylimino)propanamidato-κ²N,O](η¹-CH2Ph)(PMe3)nickel (3), one observes N,O-binding. In the case of [N-(2,6-dimethylphenyl)-2-(2,6-dimethylphenylimino)propanamidato]((η¹-CH2Ph)(PMe3)nickel (4), both, N,O- and N,N-bound modes can be obtained and isolated; the N,N structure is the thermodynamic product. N,N products are observed with smaller ligands, as in [N-phenyl-2-(2,6-diisopropylphenylimino)propanamidato-κ²N,N](η¹-CH2Ph)(PMe3)nickel (5) and [N-(2,6-diisopropylphenyl)-2-(phenylimino)propanamidato-κ²N,N](η¹-CH2Ph)(PMe3)nickel (6). Ethylene polymerization, upon activation with Ni(COD)2, is observed only with the N,O-bound species. NMR spectroscopy shows that addition of Ni(COD)2 to 5 and 6 results in removal of the phosphine and the formation of an η³-benzyl fragment. Furthermore, the phosphine-free complex [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamidato-κ²N,N](η³-CH2Ph)nickel (7) is also inactive toward ethylene polymerization. These observations suggest that ethylene polymerization is preferentially initiated by nickel complexes with N,O-bound α-iminocarboxamide ligands.

Four generations of phenylenefluorene (1F)- and phenylenebis(fluorene) (2F)-terminated polyamidoamine (PAMAM) dendrimers were synthesized by coupling activated esters with commercially available PAMAM precursors. Treatment of Boc-terminated pendant groups on the optically active units with 3 M HCl in dioxane yields cationic water-soluble dendrimers. Fluorescence resonance energy transfer (FRET) experiments with the cationic dendrimers as the donor and double stranded DNA containing a fluorescein label as the acceptor reveal cooperative optical behavior.

Methods for real-time, high-sensitivity polynucleotide detection are of vast scientific and economic importance. Homogeneous biosensor assays that take advantage of the collective response of water-soluble conjugated polymers and the self-assembly characteristic of aqueous polyelectrolytes have shown potential for improvements over small molecule methods. Cationic polythiophenes transduce oligonucleotide hybridization into a colorimetric output based on conformational changes of the polymer upon interaction with single-stranded DNAs or double-stranded DNAs. Cationic poly(fluorene-co-phenylene) materials serve as donors in fluorescence energy-transfer assays which display signal amplification. Signal transduction in aqueous media is controlled by specific electrostatic interactions.

Ring closing of 1,5-hexadiene with [(C6H5)2PC6H4C(O−B(C6F5)3)O-κ²P,O]Ni(η³-CH2C6H5) gives methylenecyclopentane. The reaction with 1,4-pentadiene provides 20% cyclopentene.

The homopolymerization and the copolymerization of ethylene with functionalized 5-norbornen-2-yl derivatives by the nickel catalyst system L(ⁱPr2)Ni(η¹-CH2Ph)(PMe3) (1) [L = N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide] and Ni(COD)2 (bis(1,5-cyclooctadiene)nickel) produces polymers with high molecular weights and narrow molecular weight distributions. A typical ethylene polymerization reaction proceeds under 100 psi of ethylene and at 20 °C, using 1 (0.34 mM) and Ni(COD)2 (0.83 mM). Likewise, under similar conditions, the copolymerization of ethylene with 5-norbornen-2-yl acetate (3) (0.15 M) for 90 min by 1 (0.67 mM) and Ni(COD)2 (1.67 mM) produced a high molecular weight functionalized polyethylene bearing ester functionalities. 5-Norbornen-2-ol (0.15 M) underwent a similar copolymerization with ethylene for 20 min to yield a hydroxy-functionalized polyethylene. Narrow molecular weight distributions, coupled with the increase of polymer molar mass with time, are consistent with a quasi-living polymerization process in the case of ethylene homopolymerization and ethylene copolymerization with 3.

Boratabenzene complexes of the type [C5H5B-R]2ZrCl2 are activated by methylaluminoxane (MAO) to form catalyst mixtures that polymerize (R = dialkylamino) or oligomerize (R = alkyl, alkoxy) ethylene. The selectivity for specific olefin products is influenced by the exocyclic substituent on the boratabenzene ring. When [C5H5B-OEt]2ZrCl2(1)/MAO is exposed to 1 atm of ethylene, α-olefins are produced in greater than 99% purity, while [C5H5B-Me]2ZrCl2(4)/MAO/C2H4 gives a mixture of α-olefins, internal olefins, and vinylidenes. Other catalysts, such as [C5H5B-OCH2Ph]2ZrCl2(2)/MAO and [C5H5B-OCy]2ZrCl2(3)/MAO, oligomerize ethylene with selectivities for α-olefin production that are between those of 1/MAO and 4/MAO. The isomerization and dimerization of 1-decene by 1−4 with MAO agree well with the ethylene data. More selective catalysts (1/MAO) exhibit slow rates of isomerization, while less selective catalysts (4/MAO) rapidly convert 1-decene to 2-decene and 2-octyl-1-dodecene. The presence of boron in the ancillary ligands of these catalyst mixtures allows their reaction chemistry to be examined using ¹¹B NMR spectroscopy. Signals are observed at 35 and 42 ppm for 1/MAO and 4/MAO, respectively. These signals remain unchanged over a 3 h period. For 2/MAO the initial resonance at 35 ppm diminishes with time and gives rise to a signal at 42 ppm. Two new zirconium complexes, [C5H5B-OMe]2ZrCl2(5)/MAO and [C5H5B-OCMe3]2ZrCl2(6)/MAO, were synthesized to further examine steric effects. With 5/MAO, no exchange was observed. A rapid exchange of exocyclic substituent occurs for 6/MAO. Ethylene oligomerization and 1-decene isomerization reactions with 5/MAO and 6/MAO support these observations. Different commercially available samples of MAO were also compared.

Resonance Raman intensities of the push−pull chromophore 4-(dimethylamino)-4‘-nitrostilbene (DANS) have been measured in dichloromethane, acetonitrile, and methanol at excitation wavelengths spanning its strong visible charge-transfer absorption band. The effects of inserting a paracyclophane moiety between the donor and the acceptor are investigated by performing similar measurements on a second molecule, PCP−DANS, which consists of p-dihexylaminostilbene and p-nitrostilbene moieties attached through their unsubstituted rings by a paracyclophane linker. The Raman excitation profiles and absorption spectra are simulated using time-dependent wave packet propagation techniques to determine reorganization energies along the Raman-active normal coordinates. Excitation to the nominal charge-transfer state generates a much greater change in geometry in the vicinity of the nitro acceptor group in DANS than in PCP−DANS, while the geometry changes around the dialkylamino donor end are similar. Comparison with other push−pull chromophores coupled with the results of ZINDO electronic structure calculations both suggest that the transition in DANS is well-described as an intramolecular charge-transfer transition, whereas the transition in PCP−DANS has less charge-transfer character.

The products obtained with the system {[(ArN&dbd;C(Me))2C5H3N]FeCl2}/MAO (Ar = 2-C6H4(Et)) (1) and the ones obtained by the use of 1 in conjunction with Me2SiInd2ZrCl2/MAO (2) or EtInd2ZrCl2/MAO (3) were completely characterized by ¹H NMR and ¹³C NMR. Catalyst 1 gives mainly linear α-olefins of molecular weights close to 2000 g/mol and a low amount of alkanes. The use of 1 with 2 or 3 using only ethylene as monomer gives branched polyethylene with ethyl, butyl, and mainly long branches. Some amount of unreacted α-olefin was also found in some cases, especially in reactions where a high ratio Fe to Zr was used.

The synthesis, characterization, and reactivity toward ethylene of pyridinecarboxamidato complexes of nickel are reported. These compounds are isoelectronic to α-iminocarboxamidato complexes, which are useful ethylene polymerization catalysts. Addition of a benzene solution containing N-phenyl-2-pyridinecarboxamide and B(C6F5)3 to bis(methallyl)nickel results in the formation of [N-phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ²N,N]Ni(η³-CH2CMeCH2) (3) in 93% yield. A similar procedure using N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamide provides [N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ²N,N]Ni(η³-CH2CMeCH2) (4) in 92% yield. The solid-state structures of 3 and 4 were determined by X-ray diffraction techniques. The intramolecular metrical parameters are consistent with substantial partial positive charge at the nickel atom. Deprotonation of N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamide in THF with KH, followed by addition to Ni(η³-CH2C6H5)Cl(PMe3) and subsequent treatment with 2 equiv of B(C6F5)3, produces [N-(2,6-diisopropyl)phenyl-2-pyridinecarboxamidatotris(pentafluorophenyl)borate-κ²N,N]Ni(η³-CH2C6H5) (5). Compound 5 is obtained as a mixture of isomers. Deprotonation of N-(2,6-diisopropylphenyl)-6-triisopropylsilyl-2-pyridinecarboxamide, followed by addition to Ni(η³-CH2C6H5)Cl(PMe3), gives a product (7) which lacks a benzyl fragment. An X-ray diffraction study shows that metalation of one of the isopropyl groups and loss of the benzyl ligand takes place. The reactivity of 3, 4, 5, and 7 toward ethylene is presented. Considerably more activity is obtained with 5, probably as a result of faster initiation. The pyridine ligand leaves an open quadrant adjacent to nickel. As a result, the molecular weight of the product is not high.

The crystal structures of tiny crystallites (micron to submicron in size) of tetrakis(4,4‘-(2,2-diphenylvinyl)-1,1‘-biphenyl)methane (C(DPVBi)4) have been investigated by using a combination of transmission electron microscopy (TEM) and X-ray powder diffraction techniques. The crystal structure of as-synthesized C(DPVBi)4 is hexagonal. The lattice parameters are a = 2.068 nm and c = 2.194 nm with possible space group P&sixmacr;. After C(DPVBi)4 was annealed up to 280 °C, the crystal structure converted to a different hexagonal structure with lattice parameters:  a = 2.102 nm and c = 3.370 nm. The possible space group is P6/m. The two hexagonal structures correspond to different packing of the individual molecules, which may result in different bulk optical and electronic properties.

Addition of ethylene to mixtures of Cp*CrMe2(PMe3) (1) and excess methylaluminoxane (MAO), followed by aqueous workup of the resulting solutions, results in the formation of a distribution of odd-carbon alkanes. When B(C6F5)3 is added to 1, followed by THF, one obtains dark crystals. A single-crystal X-ray diffraction study revealed that the product of the reaction is [Cp*CrMe(PMe3)(THF)][MeB(C6F5)3] (2). Polyethylene is obtained when using 1 and 2 equiv of B(C6F5)3. The reaction of ethylene with a mixture of 1 + 2 B(C6F5)3 + 380 “AlMe3” produces a distribution of odd-carbon alkanes. If triethylaluminum is used, instead of trimethylaluminum, the product is a distribution of even-carbon alkanes. The product distribution shifts to lower molecular weight product, and lower activities are attained with increasing triethylaluminum concentration. Use of more dichoromethane instead of toluene or hexane increases the ethylene consumption. Triisobutylaluminum and trioctylaluminum result in considerably lower activities. A mechanism for the oligomerization of ethylene involving fast transmetalation reactions between chromium and aluminum is proposed.

The synthesis of low-density polyethylene from ethylene as the only monomer feed has been investigated as an alternative route to branched polyethylene and to obtain new materials with different properties, avoiding the need to feed 1-alkenes into the polymerization process. The details of the evaluation of two combination catalyst systems based on single site catalysts are discussed. The {[(2-ArN&dbd;C(Me))2C5H3N]FeCl2} (Ar = 2-C6H4(Et)) compound, designated as catalyst 1, oligomerizes ethylene to produce linear α-olefins with high selectivity, and Me2SiInd2ZrCl2 (2) or EtInd2ZrCl2 (3) are used as catalysts that incorporate the α-olefins in the polymer. For catalyst 1 in the presence of methylaluminoxane (MAO) and ethylene, a wide range of α-olefin products were found, both soluble and insoluble. Also, tandem catalyst combinations 1 and 2 or 1 and 3 in the presence of ethylene alone can readily produce branched polyethylene with levels of 1−4 branches per 100 units of ethylene. A change in activity was found for variations in the Fe/Zr ratio for both systems, with lower activity but higher frequency of branching in the polymer backbone for catalyst 2. The final product obtained by the 1/3/MAO systems, however, shows a more homogeneous structure as determined by DSC and GPC.

Quenching of the photoluminescence from a water-soluble conjugated macromolecule, poly[5-methoxy-2-(4-sulfobutoxy)-1,4-phenylenevinylene], by neutral 4,4‘-dipyridyl and by six bipyridinium derivatives with different charges was studied. For the neutral quenchers, the linear Stern−Volmer constant (Ksv) was (1−2) × 10⁵ M^-1. For the charged quenchers, Ksv increases when the charge on the quencher is increased, from (1−3) × 10⁶ M^-1 for singly charged quenchers to 2 × 10⁷ M^-1 for bipyridinium derivatives with charge +2 and +4, consistent with static quenching via the formation of a complex between the positively charged polymer and the positively charged quencher. A modified Stern−Volmer equation, including the sphere-of-action contribution, is used to discuss the upward curvature observed in the Stern−Volmer plots at higher concentrations.

The electronic delocalization between chromophores in the solid is an important parameter to optimize when designing organic materials for optoelectronic applications. The [2.2]paracyclophane framework allows for the synthesis of well-defined, nonfluxional molecules that bring together two chromophores into close proximity. From the photophysical properties of these molecules we can examine how the chromophore conjugation length, their relative orientation, and the regiochemistry of contact affects the electronic delocalization between the two subunits.

In contrast to the reactivity observed with the isoelectronic cyclopentadienyl salts, the reaction of CrCl3(THF)3 with boratabenzene anions results in the formation of Cr(II) complexes. Thus, addition of Li(C5H5B−Me) to CrCl3(THF)3 in THF gives (C5H5B−Me)2Cr (3). Similarly, Li(C5H5B−NMe2) and CrCl3(THF)3 yield (C5H5B−NMe2)2Cr (4), while Li(C5H5B−Ph) and CrCl3(THF)3 provide (C5H5B−Ph)2Cr (5). Compounds 3−5 were characterized by single-crystal X-ray diffraction studies, and all possess typical sandwich structures. The reaction of borabenzene−ligand adducts with suitable Cr(III) starting materials provides boratabenzene−Cr(III) complexes. Addition of C5H5B−PMe3 (Bb-PMe3) to MeCrCl2(THF)3 in benzene gives (C5H5B−Me)CrCl2(PMe3) (6) in low yield. Treatment of MeCrCl2(THF)3 with the pyridine adduct of borabenzene, C5H5B−NC5H5 (Bb-Py), does not work effectively. The composition of one of the products from this reaction, the binuclear dimer [(C5H5B−Me)CrClMe]2 (7), indicates Me/Cl redistribution processes. Treatment of CrCl3(THF)3 with 3 equivalents MeMgBr in THF, followed by addition of Bb-Py gives (C5H5B−Me)CrMe2(Py) (8). Similarly, Ph3Cr(THF)3 and Bb-Py afford (C5H5B−Ph)CrPh2(Py) (9). Compound 8 with the well-defined activators B(C6F5)3 and [Ph3C][B(C6F5)4] can polymerize ethylene with activities competitive with those of (C5H5B−Me)CrMe2(PMe3)/B(C6F5)3 (2/B(C6F5)3) and Cp*CrMe2(PMe3)/B(C6F5)3. Methylaluminoxane (MAO) can also be used as an activator with the complexes containing a coordinated phosphine. The pyridine counterparts fail to give polymerization catalysts with MAO.

A combination of powder and single-crystal X-ray diffraction techniques were used to probe the generality of phenyl−perfluorophenyl stacking among a small library of 1,4-distyrylbenzene derivatives. The specific derivatives in the present study are 1,4-bis-(4-dimethylaminostyryl)benzene (DMADSB), 1,4-distyrylbenzene (DSB), 1,4-di(1-cyano-2-phenylethenyl)benzene(CNDSB), 1,4-di(1-cyano-2-(4-methylphenyl)ethenyl)benzene (MeCNDSB) 1,4-bis(styryl)-2,5-difluorobenzene (2Fc), 1,4-bis(4-fluorostyryl)-2,5-difluorobenzene (2Fc2Ft), 1,4-bis(pentaflourostyryl)benzene (10Ft), and 1,4-bis(pentafluorostyryl)-2,5-difluorobenzene (2Fc10Ft). Electrostatic distribution diagrams aid in assessing the likelihood of success in pair formation. Powder diffraction provides a means to determine both positive and negative results for binary phase formation. Four new structures are presented and discussed including (DSB/2Fc10Ft), (DMADSB/2Fc10Ft), (CNDSB/2Fc10Ft), and (MeCNDSB/2Fc10Ft). Single-crystal diffraction work confirms that the resulting lattices contain alternating layers of fluorinated and unfluorinated DSB derivatives arranged in a cofacial fashion with multiple H···F interactions between stacks. Differential scanning calorimetry is reported on (DSB/2Fc10Ft), (CNDSB/2Fc10Ft), (MeCNDSB/2Fc10Ft), and their components.

Quenching of the photoluminescence (PL) emission from conjugated macromolecules by charge transfer to cationic electron acceptors is studied by changing the ion concentration in buffered aqueous solutions, by changing the concentration of acceptors, and by varying the temperature. A weakly bound complex is formed (in water) between polyanionic conjugated macromolecules and cationic electron acceptors with Coulomb binding energy ~150 meV. The mean distance between the polymer^(-) and quencher⁽⁺⁾ was estimated as 10 Å, consistent with the effective charge-transfer distance. At high quencher concentrations, quenching by acceptors within the sphere-of-action becomes important; a modified Stern−Volmer equation is used to estimate the radius (~400 Å). High-temperature studies of concentrated quencher solutions independently indicate a crossover from static quenching to sphere-of-action quenching with a radius ~400 Å. Since the radius is comparable to the radius of gyration of the macromolecule, the high molecular weight of the conjugated polymer enhances the quenching.

A range of 1,4-distyrylbenzene derivatives were synthesized and characterized by single-crystal X-ray diffraction to investigate the effects of substitution on the resulting crystal lattices. Molecules in this report include 1,4-bis(2,2-diphenylethenyl)benzene (1), 1,4-bis(1-cyano-2,2-diphenylethenyl)benzene (2), 1,4-bis(1-cyano-2-phenylethenyl)benzene (3) 1,4-bis(2,5-dimethoxystyryl)benzene (4), 1,4-bis(3,5-dimethoxystyryl)benzene (5), 2,5-difluoro-1-(pentafluorostyryl)-4-(4-tert-butylstyryl)benzene (6), and 1,4-bis(4-nitrostyryl)benzene·2DMF (7). The lattice of each is described and contrasted in light of distyrylbenzene derivatives previously reported. The results of thermal analysis by differential scanning calorimetry are included to further examine the effect of substitution on crystal properties.

The reaction of 6,6-dimethylfulvene with M(CH2Ph)4 (M = Zr, Hf) in benzene gives [η⁵-C5H4(CMe2CH2Ph)]M(CH2Ph)3 (1, M = Zr; 2, M = Hf) without any observable byproducts. A similar reaction for M = Ti is not observed. The single-crystal X-ray study of 1 shows a three-legged piano-stool geometry with an η²-bound benzyl ligand. A second equivalent of 6,6-dimethylfulvene does not react with either 1 or 2. The bulkier 6,6-diphenyfulvene only reacts cleanly with the more Lewis acidic Hf(CH2Ph)4 to give [η⁵-C5H4(CPh2CH2Ph)]Hf(CH2Ph)3 (3). Using the tetraamido complexes M(NMe2)4 and 6,6-dimethylfulvene, one obtains dimethylamine and [η⁵-C5H4(CMeCH2)]M(NMe2)3 (4 for M = Zr) in good yield. These products are formally derived from the deprotonation of a fulvene methyl group and subsequent coordination of the resulting 2-propenylcyclopentadienyl fragment. Reaction of 4 and 6,6-dimethylfulvene affords the bent metallocene [η⁵-C5H4(CMeCH2)]2Zr(NMe2)2 (5). Excess 8,8-dimethylbenzofulvene and M(NMe2)4 provides exclusively the product with only one coordinated indene.

A series of bis(vinylthienyl)silane monomers were prepared by reaction of 2 equiv of (vinylthienyl)lithium or (vinylthienyl)magnesium bromide with different dichlorosilicon dialkyls. The monomers react with the Schrock initiator Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)2 (Ar = 2,6-diisopropylphenyl), via the acyclic diene metathesis polymerization (ADMET) mechanism, to give poly(silanyl−dithienylethene) derivatives in excellent yield. GPC data suggest that the resulting polymers have short repeat sequences. Interchromophore cooperativity is evident, as a low energy emission, for polymer structures that have smaller side groups. This phenomenon is similar to the chromophore cooperativity observed in polymers containing stilbene fragments along the backbone.

This communication shows that it is possible to activate nickel complexes containing the α-iminoenamide ligand using B(C6F5)3 or Al(C6F5)3 to generate catalysts that polymerize ethylene. The polymerization of ethylene using these novel compounds is discussed. The novel activation method is confirmed by the X-ray crystallography studies of the methallyl analogs.