Facile Protocol for Water-Tolerant “Frustrated Lewis Pair”-Catalyzed Hydrogenation

Despite rapid advances in the field of metal-free, “frustrated Lewis pair” (FLP)-catalyzed hydrogenation, the need for strictly anhydrous reaction conditions has hampered wide-scale uptake of this methodology. Herein, we report that, despite the generally perceived moisture sensitivity of FLPs, 1,4-dioxane solutions of B(C6F5)3 actually show appreciable moisture tolerance and can catalyze hydrogenation of a range of weakly basic substrates without the need for rigorously inert conditions. In particular, reactions can be performed directly in commercially available nonanhydrous solvents without subsequent drying or use of internal desiccants

MECHANICAL DURABILITY OF 3D PRINTED FACIAL PROSTHESES COMPARED TO TRADITIONAL SILICONE POLYMER PROSTHESES

Purpose: To test the effect of natural and accelerated weathering conditions on the mechanical properties of 3D printed starch samples infiltrated with a maxillofacial silicone polymer. Materials and Methods: A total of 72 samples (dumbbell-shaped, trouserlegs samples, and hardness blocks) were manufactured from silicone polymer (SP) and starch printed and infiltrated silicone polymer (SPIS) according to industry standards (ASTM). Thus, they were set out to evaluate the key mechanical properties of the SPIS (tensile strength, tear strength, percentage elongation, and hardness test). Specimens were exposed to different natural weathering (outdoor, ambient, and dark environment for 4 months) and artificial weathering conditions (2 weeks exposure and 6 weeks exposure) were compared to those of pure silicone polymer (SP). One way analysis of variance ANOVA was used to test the results statistically. Results: Exposure to 4 month natural weathering conditions recorded a significant difference in tensile strength between the control group and the three test groups for SP samples (p<0.05). However, there was no significant differences between the three test groups (p>0.05).Tear strength statistical analysis showed a significant differences between the control group for the SP samples and the other three test samples (p<0.05). Furthermore, SPIS samples demonstrated a significant increase in tear strength of the indoor samples compared to the control samples and the outdoor samples (p<0.05). However, there was no significant difference (p>0.05) observed between the control values and the two other test groups. However, percentage elongation recorded no significant differences between the control group and the test groups for SP samples, or between the test samples in the same group (p>0.05). Percentage elongation for SPIS recorded non-significant differences (p>0.05) between the control values and the dark samples. However, when compared to the outdoor samples, there was a significant difference (p<0.05) between the control and the indoor samples. Hardness test also recorded significant differences (p<0.05) statistically between the control data and the test data for both SP and SPIS samples. Furthermore, artificial weathering condition was more detrimental and showed significant deterioration of some of the mechanical properties of both SP and SPIS specimens when they were exposed for 2 weeks and 6 weeks. Deterioration was more significant at six weeks exposure than 2 weeks when compared to non weathered control group. Conclusions The general properties of facial prostheses were affected non-significantly by exposure to four months natural weathering for both pure silicone polymer SP and starch printed infiltrated polymers SPIS. However, accelerated weathering conditions were significantly deteriorated for the silicone polymer infiltrated starch models SPIS

Synthesis, Photochemical, and Redox Properties of Gold(I) and Gold(III) Pincer Complexes Incorporating a 2,2′:6′,2″-Terpyridine Ligand Framework

Reaction of [Au(C6F5)(tht)] (tht = tetrahydrothiophene) with 2,2′:6′,2″-terpyridine (terpy) leads to complex [Au(C6F5)(η1-terpy)] (1). The chemical oxidation of complex (1) with 2 equiv of [N(C6H4Br-4)3](PF6) or using electrosynthetic techniques affords the Au(III) complex [Au(C6F5)(η3-terpy)](PF6)2 (2). The X-ray diffraction study of complex 2 reveals that the terpyridine acts as tridentate chelate ligand, which leads to a slightly distorted square-planar geometry. Complex 1 displays fluorescence in the solid state at 77 K due to a metal (gold) to ligand (terpy) charge transfer transition, whereas complex 2 displays fluorescence in acetonitrile due to excimer or exciplex formation. Time-dependent density functional theory calculations match the experimental absorption spectra of the synthesized complexes. In order to further probe the frontier orbitals of both complexes and study their redox behavior, each compound was separately characterized using cyclic voltammetry. The bulk electrolysis of a solution of complex 1 was analyzed by spectroscopic methods confirming the electrochemical synthesis of complex 2

Exploring structural and electronic effects in three isomers of tris{bis(trifluoromethyl)phenyl}borane: Towards the combined electrochemical-frustrated Lewis pair activation of H2

Three structural isomers of tris{bis(trifluoromethyl)phenyl}borane have been studied as the acidic com- ponent of frustrated Lewis pairs. While the 3,5-substituted isomer is already known to heterolytically cleave H2 to generate a bridging-hydride; ortho-substituents in the 2,4- and 2,5-isomers quench such reactivity through electron donation into the vacant boron pz orbital and steric blocking of the boron centre; as shown by electrochemical, structural and computational studies. Electrochemical studies of the corresponding borohydrides identify that the two-electron oxidation of terminal-hydrides occurs at more positive potentials than observed for [HB(C6F5)3]−, while the bridging-hydride oxidizes at a higher poten- tial still, comparable to that of free H2

Novel B(Ar')2(Ar'') hetero-tri(aryl)boranes: a systematic study of Lewis acidity

A series of homo- and hetero-tri(aryl)boranes incorporating pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl, and pentachlorophenyl groups, four of which are novel species, have been studied as the acidic component of frustrated Lewis pairs for the heterolytic cleavage of H2. Under mild conditions eight of these will cleave H2; the rate of cleavage depending on both the electrophilicity of the borane and the steric bulk around the boron atom. Electrochemical studies allow comparisons of the electrophilicity with spectroscopic measurements of Lewis acidity for different series of boranes. Discrepancies in the correlation between these two types of measurements, combined with structural characterisation of each borane, reveal that the twist of the aryl rings with respect to the boron-centred trigonal plane is significant from both a steric and electronic perspective, and is an important consideration in the design of tri(aryl)boranes as Lewis acids

“Janus” Calixarenes: Double-Sided Molecular Linkers for Facile, Multianchor Point, Multifunctional, Surface Modification

We herein report the synthesis of novel “Janus” calix[4]arenes bearing four “molecular tethering” functional groups on either the upper or lower rims of the calixarene. These enable facile multipoint covalent attachment to electrode surfaces with monolayer coverage. The other rim of the calixarenes bear either four azide or four ethynyl functional groups, which are easily modified by the copper(I)-catalyzed azide–alkyne cycloaddition reaction (CuAAC), either pre- or postsurface modification, enabling these conical, nanocavity reactor sites to be decorated with a wide range of substrates to impart desired chemical properties. Redox active species decorating the peripheral rim are shown to be electrically connected by the calixarene to the electrode surface in either “up” or “down” orientations of the calixarene

An Electrochemical Study of Frustrated Lewis Pairs: A Metal-free Route to Hydrogen Oxidation

[Image: see text] Frustrated Lewis pairs have found many applications in the heterolytic activation of H(2) and subsequent hydrogenation of small molecules through delivery of the resulting proton and hydride equivalents. Herein, we describe how H(2) can be preactivated using classical frustrated Lewis pair chemistry and combined with in situ nonaqueous electrochemical oxidation of the resulting borohydride. Our approach allows hydrogen to be cleanly converted into two protons and two electrons in situ, and reduces the potential (the required energetic driving force) for nonaqueous H(2) oxidation by 610 mV (117.7 kJ mol(–1)). This significant energy reduction opens routes to the development of nonaqueous hydrogen energy technology