Multifunctionalization of synthetic polymer systems through self-assembly

A straightforward methodology towards the replacement of covalent strategies for the synthesis of multifunctional synthetic materials with a self-assembling strategy that employs multiple noncovalent recognition units to attach multiple functional molecules to a polymeric scaffold is outlined. Design requirements, advantages, and potential applications, as well as the possibility of rapid optimization of materials during the manufacturing process as a result of the parallel character of self-assembly, are presented. While still in its infancy, this novel methodology may overcome several shortcomings of current covalent multifunctionalization strategies and may yield highly complex materials that are extremely difficult or impossible to fabricate with current methods.     

An Ab Initio Molecular Orbital Theory and Density Functional Theory (DFT) Study of Conformers and Rotamers of 4-Substituted (Methyl, Hydroxymethyl, Methanoyl, Ethanoyl, Cyano, Fluoro, Chloro, Bromo, Acetoxy) Tetrahydro-2H-thiopyran-1,1-dioxides

The structures and energies of axial and equatorial conformers and rotamers of 4-substituted tetrahydro-2H-thiopyran-1,1-dioxides (tetrahydrothiopyran-1,1-dioxides, thiacyclohexane-1,1-dioxides, thiane-1,1-dioxides, and 1,1-dioxothianes; CH₃, CH₂OH, CHO, COCH₃, CN, F, Cl, Br, and OCOCH₃) were calculated using the hybrid density functionals B3LYP, B3P86, and B3PW91, as well as MP2 and the 6-31G(d), 6-31G(2d), 6-31G(3d), 6-31G(d,p), and 6-31+G(d) basis sets. MP2/6-31+G(d)/ /HF/6-31+G(d) [–G° = 1.73 kcal/mol], B3P86/6-31G(d) [–G° = 1.75 kcal/mol], and B3PW91/6-31G(d) [–G° = 1.85 kcal/mol] gave conformational free energy (G°) values at 180 K for 4-methyltetrahydro-2H-thiopyran-1,1-dioxide which were similar to the reported experimental values for methylcyclohexane (–G° = 1.80 kcal/mol), 4-methyltetrahydro-2H-thiopyran (–G° = 1.80 kcal/mol), and other 4-methyl-substituted heterocycles. All levels of theory showed that the conformational preferences of the 4-methanoyl (4-formyl), 4-ethanoyl (4-acetyl), and 4-cyano substituents were small. The HF calculations gave conformational free energy (G°) values for 4-chlorotetrahydro-2H-thiopyran-1,1dioxide which were closer to the experimental value than the MP2 and density functional methods. The best agreement with available experimental data for 4-bromotetrahydro-2H-thiopyran-1,1-dioxide was obtained from the HF/6-31G(2d), HF/6-31G(3d), and B3LYP/6-31G(2d) calculations, and, for 4-acetoxytetrahydro-2H-thiopyran-1,1-dioxide, from the HF/6–31G(3d) calculations. The conformational free energies (G°) and relative energies (E) of the conformers and rotamers have been compared with the correspondingly substituted cyclohexanes and tetrahydro-2H-thiopyrans and are discussed in terms of dipole–dipole (electrostatic) interactions and repulsive nonbonded interactions (steric) in the most stable axial and equatorial conformers. The axial S=O bond lengths are shorter than the equatorial S=O bond lengths and the C2–C3 bond lengths in the substituents with carbon-bonded to the ring are shorter than the C3–C4 and C4–C-5 bond lengths. In contrast, the C2–C3 bond lengths in the 4-halogen and 4-acetoxy substituents are longer than the C3–C4 and C4–C-5 bond lengths.     

Me2NN]Co(eta6-toluene): O=O, N=N, and O=N bond cleavage provides beta-diketiminato cobalt mu-oxo and imido complexes

The synthesis and structure of a novel beta-diketiminato Co(I) arene adduct [Me2NN]Co(eta6-toluene) (2) are described, that serves as a synthon to the reactive, "naked" 12-electron [Me2NN]Co fragment via loss of toluene in its reactions with dioxygen, organoazides, and a nitrosobenzene. Exposure of 2 to dioxygen in ether leads to {[Me2NN]Co}2(mu-O)2 (3), a rare example of a cobalt-oxo complex thermally stable at room temperature. The X-ray structure of 3 reveals a short Co-Co separation of 2.716(4) A and exhibits positional disorder for the bridging oxo groups; the predominant configuration contains oxygen atoms in square-planar sites with short Co-O distances (1.784(3) and 1.793(4) A). Reaction of 2 with organoazides N3R (R = 3,5-Me2C6H3 (Ar) or 1-adamantyl (Ad)) results in the formation of imido complexes whose structure depends on the nature of the azido substituent. The synthesis and structures of both {Me2NN]Co}2(mu-NAr)2 (4) with arylimido groups in tetrahedral bridging sites or the three-coordinate, 16-electron [Me2NN]CoNAd (5) are described. The X-ray structure of terminal imide 5 reveals a short Co-N bond distance (1.624(4) A) and only somewhat bent imido linkage (Co-N-C = 161.5(3) degrees ) consistent with a significant degree of multiple bond character. Complex 2 cleaves the O=N bond of the nitrosobenzene O=NAr (Ar = 3,5-Me2C6H3) to form the binuclear oxo-imido complex {[Me2NN]Co}2(mu-O)(mu-NAr) (6) that possesses a structure intermediate between square-planar 3 and tetrahedral 4 in which the [Me2NN]Co fragments are mutually orthogonal.     

Four-coordinate iron complexes bearing alpha-diimine ligands: efficient catalysts for atom transfer radical polymerisation (ATRP)

Four-coordinate iron(II) complexes bearing alpha-diimine ligands with alkyl substituents are shown to be efficient catalysts for the well-controlled atom transfer radical polymerisation of styrene; catalysts containing aryldiimine ligands support competitive beta-hydrogen chain transfer processes.     

Sulfonation and subsequent rections of ethylidene norbornane and dihydrodicyclopentadiene. The chemistry of some small molecule models for EPDM rubbers

Ionomers prepared by the sulfonation of EPDM rubbers have been the subject of considerable investigation with regard to their remarkable bulk and solution properties; however, relatively little is known about the chemistry of the sulfonation and the structure and subsequent reactions of the sulfonated intermediates. This article reports an effort to enlarge our understanding of sulfonate ionomers by examining the chemistry of small molecule analogs of the olefinic sites which are present in low concentrations in EPDMs. Ethylidene norbornane (ENBH) and dihydrodicyclopentadiene (DCPDH) were synthesized as models for EPDMs which use ethylidene norbornene and dicyclopentadiene as their respective termonomers. The sulfonated products from the two models were quite different, a sultone with a rearranged carbon skeleton being formed in the former case and a remarkable regiospecific sulfonic acid in the latter. Conditions necessary for hydrolysis and ammonolysis were established, the former proceeding essentially by a substitution mechanism, the latter via a retro-Wagner Meerwein elimination. Rate studies showed the importance of solvent effects in these sulfonation reactions which were attributed to a combination of site reactivity and acetylsulfate solubility. Mixed solvents were effective in improving reactivity while maintaining the solvency necessary for EPDM polymers. The results of this model study are being used as a guide in studies of EPDM polymers.     

Structure and dynamics of neutral beta-H agostic nickel alkyls: a combined experimental and theoretical study

Addition of BF(3).OEt(2) to ethereal solutions of the Ni(II) beta-diketiminates [Me(2)NN]Ni(R)(2,4-lutidine) (R = Et (1), Pr (2)) allows the isolation of the neutral beta-H agostic monoalkyls [Me(2)NN]Ni(R) (R = Et (3), Pr (4)). X-ray studies of primary alkyls 3 and 4a reveal acute Ni-C(alpha)-C(beta) angles with short Ni-C(beta) distances, indicating structures along the beta-H elimination pathway. Positional disorder of the alkyl group in the X-ray structure of 4 corresponds to partial (22%) occupancy by the secondary alkyl [Me(2)NN]Ni(CHMe(2)) (4b). Variable-temperature NMR spectra of 3 and 4 reveal fluxional behavior that result from beta-H elimination, in-plane rotation of the beta-CH(3) group, and a tetrahedral triplet structure for 3 that were investigated by density functional theory calculations at the Becke3LYP/6-31G level of theory without simplifications on the beta-diketiminate ancillary ligand. Calculations support low temperature NMR studies that identify the linear beta-H agostic propyl isomer 4a as the ground state with the branched beta-H agostic isomer 4b slightly higher in energy. NMR studies and calculations show that the beta-agostic 3 reluctantly coordinates ethene and that 3 is the ground state for this ethylene oligomerization catalyst. The thermodynamic isotope effect K(H)/K(D) = 1.3(2) measured for the loss of 2,4-lutidine from 1 to form beta-agostic 3 was also examined by DFT calculations.     

Autoxidation of 2-mercaptoethanol catalyzed by cobalt(II) phthalocyaninetetrasulfonate on colloidal particles

Cobalt(II) phthalocyaninetetrasulfonate (CoPcTS) is a highly active catalyst in aqueous media for the autoxidation of thiols to disulfides, and cationic polymers further enhance the activity. In this work we tested a variety of cationic polymer supports for the CoPcTS-catalyzed autoxidation of 2-mercaptoethanol in aqueous dispersions at 25°C. The order of activities is cationic polyelectrolytes > cationic polymer colloids > cationic colloidal silica > aqueous solution > ion exchange resins. Spectroscopic studies indicate that the high activity of the polyelectrolytes correlates with their ability to aggregate the CoPcTS. © 1992 John Wiley & Sons, Inc.     

Differential nephelauxetic reduction of the F2 and F4 Slater—Condon integrals

The sensitivity of the F₂ and F₄ Slater—Condon integrals to changes in the radial distribution due to covalency has been investigated for 3dⁿ cations using SCF atomic orbitals. It is demonstrated that either F₂ or F₄ may show the greater nephelauxetic effect, although the former is probably the more likely situation.     

A terminal Ni(III)-imide with diverse reactivity pathways

The synthesis and structure of the beta-diketiminato Ni(I) lutidine adducts [MexNN]Ni(2,4-lutidine) (x = 2 (2); x = 3 (3)) are described which serve as synthons to the "naked" 13-electron [MexNN]Ni fragments in reactions with N3Ad to give Ni-imido complexes. The singly bridged imide {[Me2NN]Ni}2(mu-NAd) (4) possesses short Ni-Ni (2.506(1) A) and Ni-N(imido) distances (1.732(4)-1.752(4) A). Steric modification of the beta-diketiminate ligand to include an additional methyl group in the N-aryl 4-position affords the Ni(III) terminal imide [Me3NN]Ni=NAd (8) isolated in 52% yield. The X-ray structure of terminal imide 8 reveals a contracted Ni-N(imido) bond distance (1.662(2) A) and an only somewhat bent imido linkage (Ni-N-C = 164.5(2) degrees ) consistent with a significant degree of multiple bond character. Frozen glass EPR studies of 5 indicate a rhombic environment in which one of the signals exhibits strong hyperfine coupling (A = 22 G) to the imido 14N (I = 1) nucleus. The terminal imide 5 undergoes complete imido group transfer to CO and CNBut to give AdNCO and AdNCNBut, respectively, as well as with PMe3 to afford AdN=PMe3. Exemplifying the radical character at the imido N atom, 5 adds to cobaltocene and abstracts a H atom from 1,4-cyclohexadiene to give the Ni(II)-amides [Me3NN]Ni-NAd(eta4-C5H5)CoCp (7) and [Me3NN]Ni-NHAd (8).     

Surface heterogeneity of polystyrene latex particles determined by dynamic force microscopy

Atomic force microscopy (AFM) was employed to characterize the surface chemistry distribution on individual polystyrene latex particles. The particles were obtained by surfactant-free emulsion polymerization and contained hydrophilic quaternary ammonium chloride, sodium sulfonate, or hydroxyethyl groups. The phase shift in dynamic force mode AFM is sensitive to charge/chemical interactions between an oscillating atomic force microscope tip and a sample surface. In this work, the phase imaging technique distinguished phase domains of 50-100 nm on the surfaces of dried latex particles in ambient air. The domains are attributed to the separation of ion-rich and ion-poor components of the polymer on the particle surface.