Planar bismuth triamides: a tunable platform for main group Lewis acidity and polymerization catalysis.

Geometric deformation in main group compounds can be used to elicit unique properties including strong Lewis acidity. Here we report on a family of planar bismuth(iii) complexes (cf. typically pyramidal structure for such compounds), which show a geometric Lewis acidity that can be further tuned by varying the steric and electronic features of the triamide ligand employed. The structural dynamism of the planar bismuth complexes was probed in both the solid and solution phase, revealing at least three distinct modes of intermolecular association. A modified Gutmann-Beckett method was used to assess their electrophilicity by employing trimethylphosphine sulfide in addition to triethylphosphine oxide as probes, providing insights into the preference for binding hard or soft substrates. Experimental binding studies were complemented by a computational assessment of the affinities and dissection of the latter into their intrinsic bond strength and deformation energy components. The results show comparable Lewis acidity to triarylboranes, with the added ability to bind two bases simultaneously, and reduced discrimination against soft substrates. We also study the catalytic efficacy of these complexes in the ring opening polymerization of cyclic esters ε-caprolactone and rac-lactide. The polymers obtained show excellent dispersity values and high molecular weights with low catalyst loadings used. The complexes retain their performance under industrially relevant conditions, suggesting they may be useful as less toxic alternatives to tin catalysts in the production of medical grade materials. Collectively, these results establish planar bismuth complexes as not only a novel neutral platform for main group Lewis acidity, but also a potentially valuable one for catalysis.

A Robust, Divalent, Phosphaza-bicyclo[2.2.2]octane Connector Provides Access to Cage-Dense Inorganic Polymers and Networks.

While polymers containing chain or ring motifs in their backbone are ubiquitous, those containing well-defined molecular cages are very rare and essentially unknown for the inorganic elements. We report that a rigid and dinucleophilic cage (PNSiMe3)2(NMe)6, which is chemically robust and accessible on a multi-gram scale from commercial precursors, serves as a linear and divalent connector that forms cage-dense inorganic materials. Reaction of the cage with various ditopic P(III) dihalide comonomers proceeded via Me3SiCl elimination to give high molecular weight (30 000-70 000 g mol-1), solution-processable polymers that form free-standing films. The end groups of the polymers could be tuned to engender orthogonal reactivity and form block copolymers. Networked cage-dense materials could be accessed by using PCl3 as a tritopic P(III) linker. Detailed mechanistic studies implicate a stepwise polycondensation that proceeds via phosphino-phosphonium ion intermediates, prior to Me3SiCl loss. Thus, metathesis between the dinucleophilic cage and polyhalides represents a general strategy to making cage-dense polymers, setting the stage for systematically understanding the consequences of the three-dimensional microstructure on macroscopic material properties.

(PNSiMe3 )4 (NMe)6 : A Robust Tetravalent Phosphaza-adamantane Scaffold for Molecular and Macromolecular Construction.

Tetraarylmethanes and adamantanes are important rigid covalent connectors that play a four-way scaffolding role in molecular and materials chemistry. We report the synthesis of a new tetravalent phosphaza-adamantane cage, (PNSiMe3 )4 (NMe)6 (2), that shows high thermal, air, and redox stability due to its geometry. It nevertheless participates in covalent four-fold functionalization reactions along its periphery. The combination of a robust core and reactive corona makes 2 a convenient inorganic scaffold upon which tetrahedral molecular and macromolecular chemistry can be constructed. This potential is demonstrated by the synthesis of a tetrakis(bis(phosphine)iminium) ion (in compound 3) and the first all P/N poly(phosphazene) network (5).

Access to thermally robust and abrasion resistant antimicrobial plastics: synthesis of UV-curable phosphonium small molecule coatings and extrudable additives.

The threat of antibiotic-resistant, biofilm-forming bacteria necessitates a preventative approach to combat the proliferation of robust, pathogenic strains on "high touch surfaces" in the food packaging, biomedical, and healthcare industries. The development of both biocide-releasing and tethered, immobilized biocide surface coatings has risen to meet this demand. While these surface coatings have demonstrated excellent antimicrobial efficacy, there are few examples of antimicrobial surfaces with long-term durability and performance. To this end, UV-curable phosphoniums bearing benzophenone anchors with either an alkyl, aryl, or fluoroalkyl group were synthesized and their efficacy as thermally stable antimicrobial additives in extruded plastics or as surface attached coatings probed. The surface topology and characteristics of these materials were studied to gain insight into the mechanism of their antimicrobial activity. Efficacy against both Gram negative and Gram positive bacteria as either a coating or additive showed compete reductions of the initial bacterial load. Crucially, the materials maintained the ability to kill biofilm-forming bacteria even after being subject to several cycles of abrasion.

Surface-attached sulfonamide containing quaternary ammonium antimicrobials for textiles and plastics.

With the risks associated with healthcare-associated infections and the rise of antibiotic resistant microorganisms, there is an important need to control the proliferation of these factors in hospitals, retirement homes and other institutions. This work explores the development and application of a novel class of sulfonamide-based quaternary ammonium antimicrobial coatings, anchored to commercially and clinically relevant material surfaces. Synthesized in high yields (60-97%), benzophenone-anchored antimicrobials were spray-coated and UV grafted onto plastic surfaces, while silane-anchored variants were adhered to select textiles via dip-coating. Surface modified samples were characterised by advancing contact angle, anionic dye staining, X-ray photoelectron spectroscopy and atomic force microscopy. After verifying coating quality through the above characterization methods, microbiological testing was performed on batch samples in conditions that simulate the natural inoculation of surfaces and objects (solid/air) and water containers (solid/liquid). Using the previously established Large Drop Inoculum (LDI) protocol at solid/air interfaces, all treated samples showed a full reduction (105-107 CFU) of viable Arthrobacter sp., S. aureus, and E. coli after 3 h of contact time. Additional testing of the walls of plastic LDPE vials treated with a UV-cured sulfonamide antimicrobial at a solid/liquid interface using the newly developed Large Reservoir Inoculum (LRI) protocol under static conditions revealed a complete kill (>106 reduction) of Gram-positive Arthrobacter sp., and a partial kill (>104 reduction) of Gram-negative E. coli within 24-48 h of contact.

UV-Curable Contact Active Benzophenone Terminated Quaternary Ammonium Antimicrobials for Applications in Polymer Plastics and Related Devices.

A series of UV active benzophenone ([C6H5COC6H4-O-(CH2)n-N+Me2R][X-]; 4, R = C12H25, n = 3, X- = Br-; 5a-c, R = C18H37, n = 3, X- = Cl-, Br-, I-; 6a-c, R = C18H37, n = 4, X- = Cl-, Br-, I-; 7a-c, R = C18H37, n = 6, X- = Cl-, Br-, I-) terminated C12 and C18 quaternary ammonium salts (QACs) were prepared by thermal or microwave-driven Menshutkin protocols of the appropriate benzophenone alkyl halide (1a-c, 2a-c, 3a-c) with the corresponding dodecyl- or octadecyl N,N-dimethylamine. All new compounds were characterized by NMR spectroscopy, HRMS spectrometry, and, in one instance (4), by single-crystal X-ray crystallography. Representative C12 and C18 benzophenone QACs were formulated into 1% (w/v) water or water/ethanol-based aerosol spray coatings and then UV-cured onto plastic substrates (polypropylene, polyethylene, polystyrene, polyvinyl chloride, and polyether ether ketone) with exposure to low to moderate doses of UV (20-30 J cm-2). Confirmation as to the presence of the coatings was detected by advancing water contact angle measurements, which revealed a more hydrophilic surface after coating. Further confirmation was gained by X-ray photoelectron spectroscopy analysis, time of flight secondary ion mass spectrometry, and bromophenol blue staining, all of which showed the presence of the attached quaternary ammonium molecule. Analysis of surfaces treated with the C18 benzophenone 5b by atomic force microscopy and surface profilometry revealed a coating thickness of ∼350 nm. The treated samples along with controls were then evaluated for their antimicrobial efficacy against Gram-positive (Arthrobacter sp., Listeria monocytogenes) and Gram-negative (Pseudomonas aeruginosa) bacteria at a solid/air interface using the large drop inoculum protocol; this technique gave no evidence for cell adhesion after a 3 h time frame. These antimicrobial materials show promise for their use as coatings on plastic biomedical devices with the aim of preventing biofilm formation and preventing the spread of hospital acquired infections.