Poly(<i>p</i>‑phenylenediethynylene phosphine)s and Related π‑Conjugated Phosphine–Diyne Polymers: Synthesis, Characterization and Photophysical Properties

Despite the considerable synthetic challenge, polymers that incorporate phosphorus atoms within or adjacent to a π-conjugated backbone framework are of interest due to the ability to modulate the photophysical properties of the polymer based on the chemical environment at phosphorus. We report the synthesis and characterization of poly­(<i>p</i>-phenylenediethlynylene phosphine)­s, <b>1a</b>–<b>1e</b>, a new class of σ–π conjugated polymer. Polymers <b>1a</b>–<b>1e</b> were prepared by a Ni-catalyzed coupling of dialkynes with phenyldichlorophosphine in the presence of excess triethylamine and have molecular weights (<i>M</i>_w) up to 12,000 g mol^–1 (vs. polystyrene). While the polymers <b>1b</b>–<b>1e</b> are nonfluorescent, blue fluorescence is observed upon oxidation of the phosphorus centers (Φ_soln = 0.12–0.28). Polymers <b>1b</b>·O–<b>1e</b>·O also exhibit yellow/green fluorescence in the solid state (Φ_solid = 0.04–0.08). These results introduce a fascinating new class of main group-containing macromolecule and lay the groundwork for their utilization in sensory applications and/or their incorporation into optoelectrical devices

A C‑Pyrenyl Poly(methylenephosphine): Oxidation “Turns On” Blue Photoluminescence in Solution and the Solid State

A C-pyrenyl poly­(methylenephosphine) (<i>M</i>_n = 4800, <i>Đ</i> = 1.56) was synthesized from the anionic polymerization of a P-mesityl phosphaalkene. The phosphine oxide polymer exhibits blue fluorescence in solution (λ_max 379, 400 nm, λ_onset 560 nm; Φ = 0.05) and blue-green fluorescence in the solid state at room temperature (λ_max 460 nm, Φ = 0.07). In contrast, unoxidized polymer displays only a weak emission in solution and no emission in the solid state. Fluorescence studies of partially oxidized polymers (50, 75, 83% oxidation) indicate that “turn on” emission occurs only at very high degrees of oxidation (near 100%). We conclude that even a small number of unoxidized phosphine moieties within the partially oxidized polymer intramolecularly quench the fluorescence

High-selectivity palladium catalysts for the partial hydrogenation of alkynes by gas-phase cluster deposition onto oxide powders

<p>The selective hydrogenation of alkynes is an important reaction in the synthesis of fine and bulk chemicals. We show that the synthesis of metal nanoparticles in the gas phase, followed by deposition onto conventional support powders results in materials that perform as well as those made by typical methods for making catalysts (impregnation, deposition). The nature of the active sites in these catalysts is explored.</p