The ability to produce polymer nanocomposites, which comprise a percolating, three-dimensional network of well-individualized nanofibers, is important to maximize the reinforcing effect of the nanofibers. While microcrystalline cellulose (MCC) has been previously shown to improve the mechanical properties of polymer composites, the formation of fibrous percolating networks within the nanocomposites has been stifled. Through the utilization of a template approach, nanocomposites based on an ethylene oxide/epichlorohydrin copolymer and nanowhiskers isolated from MCC were produced that display the maximum mechanical reinforcement predicted by the percolation model.

Addition of two or more equivalents of LiPPhH to [N3N]MCl ([N3N]3- = [(Me3SiNCH2CH2)3N]3-; M = Mo or W) produced [N3N]M⋮P complexes via intermediate [N3N]M(PPhH) complexes. The reaction between [N3N]MoCl and 2 equiv of LiAsPhH in the absence of light gave a mixture of [N3N]Mo⋮As (∼30% yield) and [N3N]MoPh. [N3N]Mo⋮N and [N3N]W⋮N were both prepared via decomposition of intermediate azide complexes. Tungsten nitrido, phosphido, or arsenido complexes react readily with methyl triflate in toluene to give the cationic methyl imido, methyl phosphinidene, and methyl arsinidene complexes, respectively. Addition of methyl triflate or trimethylsilyl triflate to [N3N]Mo⋮N yields the cationic imido complexes {[N3N]MoNMe}OTf and {[N3N]MoNSiMe3}OTf, respectively, but {[N3N]Mo=PMe}OTf is not stable in solution at room temperature for more than 1−2 h. The reaction between “[Rh(CO)2(CH3CN)2]PF6” and 2 equiv of [N3N]Mo⋮P or [N3N]W⋮P gave red, crystalline adducts that contain two [N3N]M⋮P “ligands”, e.g., [Rh{[N3N]W⋮P}2(CO)(CH3CN)]+, while red, crystalline [Rh{[N3N]W⋮As}2(CO)(CH3CN)]PF6 could be prepared by an analogous route. {[N3N]MoNSiMe3}OTf could be reduced to “19-electron” [N3N]MoNSiMe3, while addition of MeMgCl to {[N3N]MoNSiMe3}OTf or {[N3N]MoNMe}OTf yielded complexes of the type [N3N]Mo(NR)(Me). The complex in which R = Me was unstable with respect to loss of methane and formation of the iminato complex, [N3N]Mo(NCH2). Both [N3NF]W(PPhH) and [N3NF]Mo(PPhH) ([N3NF]3- = [(C6F5NCH2CH2)3N]3-) could be prepared readily, but all attempts to prepare [N3NF]W⋮P failed. X-ray studies of [N3N]W⋮P, [N3N]Mo(PPhH), [N3N]Mo⋮As, {[N3N]WAsMe}OTf, [Rh{[N3N]W⋮P}2(CO)(CH3CN)]+, and [N3N]Mo=NSiMe3 are presented and discussed.

A variety of paramagnetic molybdenum complexes, [N 3 N]MoR ([N 3 N] 3-) [(Me 3 SiNCH 2 CH 2 ) 3 N] 3-; R ) Me, Et, Bu, CH 2 Ph, CH 2 SiMe 3 , CH 2 CMe 3 , cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclopentenyl, phenyl), have been prepared from [N 3 N]MoCl. The several that have been examined all follow Curie-Weiss S ) 1 behavior with a magnetic moment in the solid state between 2.4 and 2.9 µ Β down to 50 K. Below ∼50 K the effective moments undergo a sharp decrease as a consequence of what are proposed to be a combination of spin-orbit coupling and zero field splitting effects. NMR spectra are temperature dependent as a consequence of "locking" of the backbone into one C 3 -symmetric conformation and as a consequence of Curie-Weiss behavior. The cyclopentyl and cyclohexyl complexes show another type of temperature-dependent fluxional behavior that can be ascribed to a rapid and reversible R-elimination process. For the cyclopentyl complex the rate constant for R-elimination is ∼10 3 s -1 at room temperature, while the rate constant for R-elimination for the cyclohexyl complex is estimated to be ∼200 s -1 at room temperature. An isotope effect for R-elimination for the cyclohexyl complex was found to be ∼3 at 337 K. Several of the alkyl complexes decompose between 50 and 120°C. Of the complexes that contain linear alkyls, only [N 3 N]Mo(CH 2 CMe 3 ) decomposes cleanly (but slowly) by R,R-dehydrogenation to give [N 3 N]MotCCMe 3 . [N 3 N]MoMe is by far the most stable of the alkyl complexes; no [N 3 N]MotCH can be detected upon attempted thermolysis at 120°C. Other decompositions of linear alkyl complexes are complicated by competing reactions, including -hydride elimination. -Hydride elimination (to give [N 3 N]MoH) is the sole mode of decomposition of the cyclopentyl and cyclohexyl complexes; the former decomposes at a rate calculated to be approximately 10× that of the latter at 298 K. -Hydride elimination in [N 3 N]Mo(cyclopentyl) to give (unobservable) [N 3 N]Mo(cyclopentene)-(H) has been shown to be 6-7 orders of magnitude slower than R-hydride elimination to give (unobservable) [N 3 N]-Mo(cyclopentylidene)(H). [N 3 N]Mo(cyclopropyl) evolves ethylene in a first-order process upon being heated to give [N 3 N]MotCH, while [N 3 N]Mo(cyclobutyl) is converted into [N 3 N]MotCCH 2 CH 2 CH 3 . [N 3 N]MoH decomposes slowly and reversibly at 100°C to yield molecular hydrogen and [(Me 3 SiNCH 2 CH 2 ) 2 NCH 2 CH 2 SiMe 2 CH 2 ]Mo ([bitN 3 N]Mo). X-ray structures of [N 3 N]Mo(triflate), [N 3 N]MoMe, [N 3 N]Mo(cyclohexyl), and [bitN 3 N]Moshow that the degree of twist of the TMS groups away from an "upright" position correlates with the size of the ligand in the apical pocket and that steric congestion in the cyclohexyl complex is significantly greater than in the methyl complex. Relief of steric strain in the ground state in molecules of this general type to give a less crowded alkylidene hydride intermediate is proposed to be an important feature of the high rate of R-elimination relative to -elimination in se...

The synthesis of a variety of tungsten alkyl complexes of the type [N3N]WR ([N3N]3- = [(Me3SiNCH2CH2)3N]3-; R = Me, Et, Bu, CH2Ph, CH2SiMe3, CH2CMe3, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclopentenyl) was attempted by alkylation of [N3N]WCl complexes. Only the methyl, phenyl, and cyclopentenyl complexes could be isolated. The susceptibility of the [N3N]WR complexes is similar to that of [N3N]WCl; the effective moment is depressed as a consequence of a combination of spin−orbit effects and low-symmetry ligand-field components that result in zero-field splitting of the d2 ground-state spin triplet. No linear alkyl complexes could be observed as a consequence of α,α-dehydrogenation to give molecular hydrogen and alkylidyne complexes, [N3N]W⋮CR‘. [N3N]W(cyclopropyl) evolves ethylene in a first-order process to give [N3N]W⋮CH, while [N3N]W(cyclobutyl) is converted into the 1-tungstacyclopentene complex, [N3N]W(CHCH2CH2CH2), as confirmed in an X-ray study. [N3N]W(CHCH2CH2CH2) decomposes readily in a first-order manner to give [N3N]W⋮CCH2CH2CH3. An attempt to prepare [N3N]W(cyclopentyl) led to formation of [N3N]W(cyclopentylidene)(H), as confirmed in an X-ray study. NMR studies suggest that [N3N]W(cyclopentylidene)(H) is in equilibrium with [N3N]W(cyclopentyl) where ΔH° = 11.8(6) kcal mol-1 and ΔS° = 33(2) eu or K eq ≈ 0.1 at 46 °C. From these and other data it is concluded that the rate constant for α elimination in [N3N]M(cyclopentyl) is approximately the same for Mo and W. The [N3N]W(cyclopentenyl) complex is unstable, decomposing to give a complex containing a “bent imido” ligand, [(Me3SiNCH2CH2)2(NCH2CH2)N]W(1-(trimethylsilyl)cyclopentene), as confirmed in an X-ray study.

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Various catalysts for the polymerization of carbodiimide have been investigated. In early studies, anionic polymerization techniques were employed, but the products obtained were low molecular weight oligomers. More recently, a living route using titanium(IV) complexes as initiators has been employed and the high molecular weight polymers obtained exhibit a well-ordered helical, extendedchain conformation. However, the titanium complexes are sensitive to high temperatures and the presence of oxygen or water. Herein, we report that more robust catalysts based on copper(I) and copper(II) complexes also initiate living carbodiimide polymerizations. The tolerance of these complexes to impurities is illustrated by the fact that they cleanly initiate the polymerization of carbodiimides under air and oxygen. They are even active in the presence of water, but both molecular weights and yields tend to be lower than in dry solvents. It has been shown that the catalytic activity of a copper(II) amidinato complex is almost equal that of reported titanium(IV) initiators. Analysis of these systems by gel permeation chromatography-light scattering measurements (GPC-LS) and preliminary kinetic analysis suggest this system to be living.

We report the results of Magic Angle Spinning (MAS) 13C and static 2H NMR studies of the dynamics of the methyl groups coordinated to tungsten in [WCp*Me4][PF6] (Cp* = η5-C5Me5). The temperature-dependent broadening of the axial methyl 13C line can be ascribed to interference between 1H decoupling and methyl motion when the motional rate and decoupling nutation frequency are comparable. This proposal is consistent with the absence of broadening in the 2H labeled compound and the motional rate constants inferred from 2H NMR lineshape and T 1 studies, which range from 107 s-1 at 25 °C to 103 s-1 at −125 °C. The measured barrier to axial methyl hopping (26 kJ/mol) is among the highest reported to date. An X-ray crystal study of [W(η5-C5Me4Et)Me4][PF6] reveals no evidence (in terms of the core geometry) for an agostic interaction in either the axial methyl group or the equatorial methyl groups.

Here we demonstrate a novel technique for the fabrication of porous polymer membranes via vapor phase polymerization. Vapor phase processing allows for control over the chemical functionality of the membranes and eliminates solubility requirements and surface tension effects. Porous polymer membranes are formed by concurrent deposition of solid monomer and polymerization, which is achieved by increasing the partial pressure of the monomer above its saturation pressure and decreasing the substrate temperature below the freezing point of the monomer. The membranes exhibit dual-scale porosity, where the large-scale pores form during the deposition and the small-scale pores form upon sublimation of the solid monomer. We demonstrate that the growth rate and pore size of the membrane can be controlled by varying the reactor parameters, including deposition time, monomer partial pressure, and substrate temperature. Stimuli-responsive poly(methacrylic acid) and poly(N-isopropylacrylamide) membranes were fabricated to show the generality of the process. Furthermore, the ability to make copolymer membranes was demonstrated using ethylene glycol diacrylate as a cross-linking agent. Our ability to produce tailored polymer membranes with chemically diverse compositions has potential applications in separations and biosensing.