Steric Selection of Anion Binding Sites by Organoantimony(V) Pnictogen Bond Donors: An Experimental and Computational Study.

Catecholatostiboranes have emerged as useful Lewis acids in several applications. To better understand the factors that control the properties of these species, we examined the Lewis acidities of (-CClO)Sb(-Tol) (, Tol = tolyl) and (-CClO)Sb(-Tol) (), two triarylcatecholatostiboranes that differ by the nature of the aryl substituent. Fluoride anion binding studies indicate that is more Lewis acidic than , a factor readily assigned to the steric crowding around antimony in the case of the -tolyl derivative.

Pnictogen Bonding at the Core of a Carbene-Stiborane-Gold Complex: Impact on Structure and Reactivity.

Our interest in the design of ambiphilic ligands and their coordination to gold has led us to synthesize an indazol-3-ylidene gold chloride complex functionalized at the 4-position of the indazole backbone by a stibine functionality. The antimony center of this new complex cleanly reacts with -chloranil to afford the corresponding stiborane derivative. Structural analysis indicates that the stiborane coordination environment is best described as a distorted square pyramid whose open face is oriented toward the gold center, allowing for the formation of a long donor-acceptor, or pnictogen, Au → Sb bonding interaction.

Rh → Sb Interactions Supported by Tris(8-quinolyl)antimony Ligands.

The ligands tris(8-quinolyl)stibine and tris(6-methyl-8-quinolyl)stibine have been synthesized and complexed to rhodium using (MeCN)RhCl. The resulting complexes feature an unusual [RhSb] core as a result of the formal insertion of the antimony center into one of the Rh-Cl bonds. Computational analysis using density functional theory (DFT) methods reveals that the resulting Rh-Sb σ bond is polarized toward the Rh atom, suggesting a description of this linkage as a Rh → Sb Z-type interaction.

Characterization of a Lewis adduct in its inner and outer forms.

The entrance channel of bimolecular reactions sometimes involves the formation of outer complexes as weakly bound, fleeting intermediates. Here, we characterize such an outer complex in a system that models the bimolecular, C-O bond-forming reaction of a phosphine oxide Lewis base with a carbenium Lewis acid. Crystallographic studies show that the C-O distance in the outer form exceeds that of the final or inner adduct by 1.

Bismuthenium Cations for the Transport of Chloride Anions via Pnictogen Bonding.

Our interest in the design of heavy pnictogen-based Lewis acids for anion trafficking across biological membrane mimics has led us to investigate trivalent bismuthenium cations as chloride anion transporters. Here, we describe two chlorodiarylbismuthines, elaborated on a peri-substituted naphthalene backbone and stabilized by an adjacent thio- or seleno-ether functionality that engages the bismuth center in a Ch→Bi interaction (Ch=chalcogen). These new derivatives are stable in aqueous environment and readiliy transport chloride anions across the membrane of phospholipid-based vesicles loaded with KCl.

Exploring the Effects of Se Basicity on a Te···Se Interaction Supported by a Rigid Indazolium Backbone.

With an interest in chalcogen bonding, we use a rigid indazolium backbone to install a formally zero-valent Se center next to a divalent Te center, allowing us to investigate the effects of oxidation of the Se center on the observed Te···Se interaction. Through spectroscopic and computational comparison of the Se(0) species with its Se(II) counterpart and their monochalcogen analogues, we experimentally and computationally investigate the effect of modulating Se basicity on the resulting Te···Se interaction. Comparison with well-studied naphthalene and acenaphthene variants indicates that the increased basicity of the Se(0) center allows for a comparably strong Te···Se interaction despite longer distances and a larger splay angle.

Tunable Pnictogen Bonding at the Service of Hydroxide Transport across Phospholipid Bilayers.

Our growing interest in the design of pnictogen-based strategies for anion transport has prompted an investigation into the properties of three simple triarylcatecholatostiboranes (-) of the general formula (-CClO)SbAr with Ar = Ph (), -tolyl (), and -xylyl () for the complexation and transport of hydroxide across phospholipid bilayers. A modified hydroxypyrene-1,3,6-trisulfonic acid (HPTS) assay carried out in artificial liposomes shows that and are potent hydroxide transporters while is inactive. These results indicate that the steric hindrance imposed by the three -xylyl groups prevents access by the hydroxide anion to the antimony center.

Synthesis of an Indazole/Indazolium Phosphine Ligand Scaffold and Its Application in Gold(I) Catalysis.

Advances in ligand development have allowed for the fine-tuning of gold catalysis. To contribute to this field, we designed an indazole phosphine ligand scaffold that allows facile introduction of cationic charge through methylation. With minimal changes to the structure upon methylation, we could assess the importance of the electronic effects of the insertion of a positive charge on the catalytic activity of the resulting gold(I) complex.

Are ArSbCl Species Lewis Acidic? Exploration of the Concept and Pnictogen Bond Catalysis Using a Geometrically Constrained Example.

As part of our investigations into the Lewis acidic behavior of antimony derivatives, we have decided to study the properties of 5-phenyl-5,5-dichloro-λ-dibenzostibole (), a dichlorostiborane with an antimony atom confined to a five-membered heterocycle. Our work shows that the resulting geometrical constraints elevate the Lewis acidity of the antimony atom, as confirmed by the crystal structure of -THF and the solution study of the interaction of with PhPO. The enhanced Lewis acidic properties of , which exceed those of simple dichlorostiboranes such as PhSbCl, also become manifest in pnictogen bonding catalysis experiments involving the reductions of imines with Hantzsch ester.

Double axial stabilization of a carbenium ion convergent PO → C tetrel bonding.

Our efforts in carbocation chemistry have led us to target examples of such species stabilized intramolecularly by tetrel bonding. Described here is an example of such a compound in which a triaryl carbenium is stabilized intramolecularly by two convergent PO → C interactions, as confirmed by structural studies. The formation of this new motif favorably impacts the reversibility of the first and second reduction of the carbenium center.

Pnictogen bonding at the service of gold catalysis: the case of a phosphinostiborane gold complex.

The search for alternative gold catalyst activators has led us to consider the design of platforms in which a phosphine gold chloride moiety could be activated formation of a pnictogen bond with a neighboring antimony unit. Here, we describe that such a system can be accessed from 4-(diphenylphosphino)-5-(diphenylstibino)-2,7-di--butyl-9,9-dimethylxanthene, by oxidation of the stibine with 3,5-di--butyl--benzoquinone and by coordination of an AuCl unit to the phosphine. This strategy affords a complex in which a Lewis acidic or pnictogen-bond donor catecholatostiborane unit flanks the adjacent gold chloride moiety.

Binding, Sensing, And Transporting Anions with Pnictogen Bonds: The Case of Organoantimony Lewis Acids.

Motivated by the discovery of main group Lewis acids that could compete or possibly outperform the ubiquitous organoboranes, several groups, including ours, have engaged in the chemistry of Lewis acidic organoantimony compounds as new platforms for anion capture, sensing, and transport. Principal to this approach are the intrinsically elevated Lewis acidic properties of antimony, which greatly favor the addition of halide anions to this group 15 element. The introduction of organic substituents to the antimony center and its oxidation from the + III to the + V state provide for tunable Lewis acidity and a breadth of applications in supramolecular chemistry and catalysis.

Analyzing Fluoride Binding by Group 15 Lewis Acids: Pnictogen Bonding in the Pentavalent State.

We report the results of a computational investigation into fluoride binding by a series of pentavalent pnictogen Lewis acids: pnictogen pentahalides (PnX), tetraphenyl pnictogeniums (PnPh), and triphenyl pnictogen tetrachlorocatecholates (PnPhCat). Activation strain and energy decomposition analyses of the Lewis adducts not only clearly delineate the electrostatic and orbital contributions to these acid-base interactions but also highlight the importance of Pauli repulsion and molecular flexibility in determining relative Lewis acidity among the pnictogens.

Four-Electron Reduction of O Using Distibines in the Presence of -Quinones.

This study, which aims to identify atypical platforms for the reduction of dioxygen, describes the reaction of O with two distibines, namely, 4,5-bis(diphenylstibino)-2,7-di--butyl-9,9-dimethylxanthene and 4,5-bis(diphenylstibino)-2,7-di--butyl-9,9-dimethyldihydroacridine, in the presence of an -quinone such as phenanthraquinone. The reaction proceeds by oxidation of the two antimony atoms to the + V state in concert with reductive cleavage of the O molecule. As confirmed by O labeling experiments, the two resulting oxo units combine with the -quinone to form an α,α,β,β-tetraolate ligand that bridges the two antimony(V) centers.

Transmembrane transport of fluoride studied by time-resolved emission spectroscopy.

Here we present a new method to monitor fluoride transmembrane transport into liposomes using a europium(III) complex. We take advantage of the long emission lifetime of this probe to measure the transport activity of a fluorescent transporter. The high sensitivity, selectivity, and versatility of the assay allowed us to study different types of fluoride transporters and unravel their mechanisms of action.

Placing gold on a π-surface: ligand design and impact on reactivity.

We describe a novel gold chloride complex supported by an ambiphilic phosphine/xanthylium ligand in which the AuCl moiety interacts with the π surface of the xanthylium unit as indicated by structural studies. Energy decomposition analyses carried out on a model system indicates the prevalence of non-covalent interactions in which the electrostatic and dispersion terms cumulatively dominate. The presence of these AuCl-π interactions correlates with the high catalytic activity of this complex in the cyclisation of 2-(phenylethynyl)phenylboronic acid, -propargyl--butylamide, and 2-allyl-2-(2-propynyl)malonate.

A cationic gold-fluorenyl complex with a dative Au → C bond: synthesis, structure, and carbophilic reactivity.

Aiming to study the interaction of gold with the highly Lewis acidic fluorenyl cation, we synthesised (-[PhP(CH)Flu)AuCl(tht)][BF] ([2][BF]) and (-PhP(CH)Flu)AuCl (3) (Flu = 9-fluorenyl) and found that the latter could be converted into [(-PhP(CH)Flu)AuCl] ([4]) upon treatment with NaBArF (BArF = B(3,5-CH(CF))). [4], which has been isolated as a chloride-bridged dimer, readily catalyses the cycloisomerisation of 2-allyl-2-(2-propynyl)malonate. Computational results show that [4] possesses a strong Au → C bond and readily activates enynes.

Augmenting metallobasicity to modulate gold hydrogen bonding.

We report the synthesis and characterization of two phosphine gold carbinol species designed to support intramolecular Au⋯H-O hydrogen bonding. Increasing the metallobasicity of gold through chloride to phenyl ligand substitution produced an observable increase in this hydrogen bond's strength which was analyzed experimentally and computationally.

Dipping Status, Ambulatory Blood Pressure Control, Cardiovascular Disease, and Kidney Disease Progression: A Multicenter Cohort Study of CKD.

Rationale & Objective: Ambulatory blood pressure (BP) monitoring allows concurrent evaluation of BP control and nocturnal BP dipping status, both related to adverse outcomes. However, few studies have assessed the prognostic role of combining information on dipping status and achieved ambulatory BP in patients with chronic kidney disease (CKD).

Study Design: Prospective observational cohort study.

Green-Light-Driven Reductive Elimination of Chlorine from a Carbene-Xanthylium Gold(III) Complex.

With the discovery of late transition metal platforms that support clean photoreductive halogen eliminations, we now describe an indazol-3-ylidene gold trichloride complex ([7] ) decorated at the 4-position by a xanthylium unit. This orange complex features a low energy band in the visible part of the spectrum, assigned to the charge transfer excitation of the indazol-3-ylidene/xanthylium donor/acceptor dyad. Green-light irradiation of this complex in the presence of a chlorine trap elicits the clean photoelimination of chlorine radicals, producing the corresponding gold(I) complex.

Spotlighting main group elements in polynuclear complexes.

François Gabbaï, Cameron Jones and Connie Lu introduce the themed collection on the topic of main group elements in polynuclear complexes.

Metal→Carbon Dative Bonding.

As part of our interest in unusual bonding situations, we are now targeting complexes featuring metal→carbon dative bonds. Here, we report on the formation of such linkages in a series of Group 10 complexes featuring a triarylphosphine ligand functionalized at the γ position by a carbenium ion. Through combined synthetic, spectroscopic, and computational studies, we show that the M→C interaction present in these complexes scales with the basicity of the donor, confirming its dative nature.

Fluoride anion complexation and transport using a stibonium cation stabilized by an intramolecular PO → Sb pnictogen bond.

We describe the synthesis of [-PhP(O)(CH)SbPh] ([2]), an intramolecularly base-stabilized stibonium Lewis acid which was obtained by reaction of [-PhP(CH)SbPh] with NOBF. This cation reacts with fluoride anions to afford the corresponding fluorostiborane -PhP(O)(CH)SbFPh, the structure of which indicates a strengthening of the PO → Sb interaction. When deployed in fluoride-containing POPC unilamellar vesicles, [2] behaves as a potent fluoride anion transporter whose activity greatly exceeds that of [PhSb].

Isolation and reactivity of a gold(I) hydroxytrifluoroborate complex stabilized by anion-π interactions.

A 9,9-dimethylxanthene-based ligand substituted at the 4- and 5-positions by a phosphine and a xanthylium unit, respectively, has been prepared and converted into an AuCl complex, the structure of which reveals an intramolecular Au-Cl⋯π interaction. This new ligand platform was also found to support the formation of an unprecedented hydroxytrifluoroborate derivative featuring a "hard/soft" mismatched Au-(OH)-BF motif. Despite its surprising stability, this gold hydroxytrifluoroborate complex is a remarkably potent carbophilic catalyst which readily activates alkynes, without activator.