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...

Poly(phenylene methylene) (PPM) exhibits pronounced blue fluorescence in solutions as well as in the solid state despite its non-p-conjugated nature. Optical spectroscopy was used to explore the characteristics and the physical origin of its unexpected optical properties, namely absorption in the 350-450 nm and photoluminescence in the 400-600 nm spectral regions. It is shown that PPM possesses two discrete optically active species, and a relatively long photoluminescence lifetime (>8 ns) in the solid-state. Given the evidence reported herein, p-stacking and aggregation/crystallization, as well as the formation of anthracene-related impurities, are excluded as the probable origins of the optical properties. Instead there is sufficient evidence that PPM supports homoconjugation, that is: p-orbital overlap across adjacent repeat units enabled by particular chain conformation(s), which is confirmed by DFT calculations. Furthermore, poly(2-methylphenylene methylene) and poly(2,4,6-trimethylphenylene methylene) -two derivatives of PPM -were synthesized and found to exhibit comparable spectroscopic properties, confirming the generality of the findings reported for PPM. Cyclic voltammetry measurements revealed the HOMO-LUMO gap to be 3.2-3.3 eV for all three polymers. This study illustrates a new approach to the design of light-emitting polymers possessing hitherto unknown optical properties.

Four dioxidomolybdenum­(VI) complexes of the general structure [MoO2L2] employing the S,N-bidentate ligands pyrimidine-2-thiolate (PymS, 1), pyridine-2-thiolate (PyS, 2), 4-methylpyridine-2-thiolate (4-MePyS, 3) and 6-methylpyridine-2-thiolate (6-MePyS, 4) were synthesized and characterized by spectroscopic means and single-crystal X-ray diffraction analysis (2–4). Complexes 1–4 were reacted with PPh3 and PMe3, respectively, to investigate their oxygen atom transfer (OAT) reactivity and catalytic applicability. Reduction with PPh3 leads to symmetric molybdenum­(V) dimers of the general structure [Mo2O3L4] (6–9). Kinetic studies showed that the OAT from [MoO2L2] to PPh3 is 5 times faster for the PymS system than for the PyS and 4-MePyS systems. The reaction of complexes 1–3 with PMe3 gives stable molybdenum­(IV) complexes of the structure [MoOL2(PMe3)2] (10–12), while reduction of [MoO2(6-MePyS)2] (4) yields [MoO­(6-MePyS)2(PMe3)] (13) with only one PMe3 coordinated to the metal center. The activity of complexes 1–4 in catalytic OAT reactions involving Me2SO and Ph2SO as oxygen donors and PPh3 as an oxygen acceptor has been investigated to assess the influence of the varied ligand frameworks on the OAT reaction rates. It was found that [MoO2(PymS)2] (1) and [MoO2(6-MePyS)2] (4) are similarly efficient catalysts, while complexes 2 and 3 are only moderately active. In the catalytic oxidation of PMe3 with Me2SO, complex 4 is the only efficient catalyst. Complexes 1–4 were also found to catalytically reduce NO3 – with PPh3, although their reactivity is inhibited by further reduced species such as NO, as exemplified by the formation of the nitrosyl complex [Mo­(NO)­(PymS)3] (14), which was identified by single-crystal X-ray diffraction analysis. Computed ΔG ⧧ values for the very first step of the OAT were found to be lower for complexes 1 and 4 than for 2 and 3, explaining the difference in catalytic reactivity between the two pairs and revealing the requirement for an electron-deficient ligand system.