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Anion carriers are developed for their potential biological applications, including antibacterial properties. However, only a few fluoride carriers have been reported and no reliable spectroscopic method exists for the study of fluoride transport in liposomes. Here we present the use of an encapsulated europium(III) complex to monitor fluoride transport. We take advantage of the long emission lifetime of this probe to use time-resolved emission spectroscopy to study fluoride transport by a fluorescent phosphonium borane. Furthermore, the high sensitivity, selectivity, and versatility of the assay allowed us to study different types of fluoride transporters and unravel their mechanisms of action. This revealed the phosphonium borane and the bambusuril to be active as F-/Cl- antiporters, and the antimony-based compound to be a more efficient OH-/Cl- antiporter, while demonstrating the power of lanthanide probes for studying anion transport.

A complex in which a gold atom interacts with a highly Lewis acidic fluorenyl cation via an Au → C+ interaction has been synthesised and evaluated as a carbophilic catalyst.

As part of our interest in the chemistry of late transition metal complexes bearing cationic antimony ligands, we have investigated the reaction of ((o-(Ph2P)C6H4)3)SbClPtCl (1) with H2O2 and found...

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph2 P)C6 H4 )2 GeIV Cl2 ]PtII Cl2 and [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtIII Cl3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtI Cl with quantum yields of 1.7 % and 3.2 % for the GeIV -PtII and GeIII -PtIII isomers, respectively. Conversion of the GeIV -PtII isomer into the platinum germyl complex is a rare example of a light-induced transition-metal/main-group-element bond-forming process. Finally, transient-absorption-spectroscopy studies carried out on the GeIII -PtIII isomer point to a ligand arene-Cl. charge-transfer complex as an intermediate.

Our long-standing interest in atypical bonding situations has recently led us to target complexes in which a metallobasic gold(I) center is hydrogen-bonded to a nearby OH functionality. Here, we report on the synthesis and characterization of two neutral gold(I) indazol-3-ylidene complexes bearing a carbinol or silanol group at the 4-position. As indicated by X-ray diffraction, 1H NMR spectroscopy, IR spectroscopy, and extensive computational modeling, the OH group of these derivatives is engaged in a bona fide Au···H-O interaction. In addition to shedding light on an elusive bonding situation, these results also indicate that increasing the acidity of the OH functionality is not necessarily beneficial to the stability of the Au(I)···H-O interaction.

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.

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]

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–μ(OH)–BF3 motif. Despite its surprising stability, this gold hydroxytrifluoroborate complex is a remarkably potent carbophilic catalyst which readily activates alkynes, without activator.

As part of our efforts in the chemistry of main group platforms that support anion sensing and transport, we are now reporting the synthesis of anitmony-based bidentate Lewis acids featuring the o-C6F4 backbone. These compounds can be easily accessed by reaction of the newly synthesized o-C6F4(SbPh2)2 (5) with o-chloranil or octafluorophenanthra-9,10-quinone, affording the corresponding distiboranes 6 and 7 of general formula o-C6F4(SbPh2(diolate))2 with diolate = tetrachlorocatecholate for 6 and octafluorophenanthrene-9,10-diolate for 7, respectively. While 6 is very poorly soluble, its octafluorophenanthrene-9,10-diolate analog 7 readily dissolves in CH2Cl2 and undergoes swift conversion into the corresponding fluoride chelate complex [7-μ2-F]- which has been isolated as a [nBu4N]+ salt. The o-C6H4 analog of 7, referred to as 8, has also been prepared. Although less Lewis acidic than 7, 8 also forms a very stable fluoride chelate complex ([8-μ2-F]-). Altogether, our experiental results, coupled with computational analyses and fluoride anion affinity calculations, show that 7 and 8 are some of the strongest antimony-based fluoride anion chelators prepared to date. Another notable aspect of this work concerns the use of the octafluorophenanthrene-9,10-diolate ligand and its ablity to impart advantageous solubility and Lewis acidity properties.

We describe the synthesis of [o-Ph2P(O)(C6H4)SbPh3]+ ([2]+), an intramolecularly base-stabilized stibonium Lewis acid which was obtained by reaction of [o-Ph2P(C6H4)SbPh3]+ with NOBF4. This cation reacts with fluoride anions to afford the corresponding fluorostiborane o-Ph2P(O)(C6H4)SbFPh3, the structure of which indicates a strengthening of the PO → Sb interaction. When deployed in fluoride-containing POPC unilamellar vesicles, [2]+ behaves as a potent fluoride anion transporter whose activity greatly exceeds that of [Ph4Sb]+.

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

The phosphino‐stibine ligands (o‐PPh2C6H4)2SbR [R = o‐PPh2C6H4 (L1), Ph (L2), Cl (L3)] were incorporated into tungsten and molybdenum carbonyl complexes leading to the formation of cis‐[W(CO)4{(o‐PPh2C6H4)2SbR}] [R = o‐PPh2C6H4 (1), Ph (2), Cl (3)], fac‐[W(CO)3{(o‐PPh2C6H4)3Sb}] (4), fac‐[W(CO)3{(o‐PPh2C6H4)2SbCl}] (5), fac‐[(W(CO)3{(o‐PPh2C6H4)2Sb})2] (6), fac‐[Mo(CO)3{(o‐PPh2C6H4)2SbR}] [R = o‐PPh2C6H4 (7), Ph (8), Cl (9)]. Compounds 1 and 4 were allowed to react with MX salts with M = Cu, Ag, Au and X = Cl–, [PF6]–, respectively. These reactions yielded cis‐[W(CO)4{(o‐PPh2C6H4)3Sb}{MCl}] [M = Cu (10), Ag (11)], cis‐[W(CO)4{(o‐PPh2C6H4)2Sb}{AuCl(o‐PPh2C6H4)}{AuCl}] (12) cis‐[(W(CO)4{(o‐PPh2C6H4)2Sb})2AuCl] (13), cis‐[W(CO)3(μ‐CO){(o‐PPh2C6H4)3Sb}{Cu}][PF6] (14), cis‐[W(CO)4{(o‐PPh2C6H4)3Sb}{AgMeCN}][PF6] (15), cis‐[W(CO)4{(o‐PPh2C6H4)3Sb}{Au}][PF6] (16) cis‐[W(CO)2(μ‐CO){(o‐PPh2C6H4)3Sb}{Cu2(μ‐Cl)2}] (17), fac‐[W(CO)3{(o‐PPh2C6H4)3Sb}{AuCl}] (18), and fac‐[W(CO)2(μ‐CO){(o‐PPh2C6H4)3Sb}{ML}][PF6] [M = Cu, L = MeCN (19), M = Ag, L = MeCN (20), M = Au (21)]. Complexes 10–21 all show metal‐metal distances below the sum of the corresponding van der Waals radii. The proximity of the two metal centers is especially significant in 19–21, indicating the presence of metal‐metal bonding.

With the view of developing electrophilic late-transition-metal catalysts, we have now synthesized [(o-(Ph2P)C6H4)2Sb(OTf)2]Pt(OTf) (2) and [(o-(iPr2P)C6H4)2Sb(OTf)2]Pt(OTf) (4) by treatment of the...

With the view of developing selective transmembrane anion transporters, a series of phosphonium boranes of general formula [p-RPh2 P(C6 H4 )BMes2 ]+ have been synthesized and evaluated. The results demonstrate that variation of the R group appended to the phosphorus atom informs the lipophilicity of these compounds, their Lewis acidity, as well as their transport activity. Anion transport experiments in POPC-based large unilamellar vesicles show that these main-group cations are highly selective for the fluoride anion, which is transported more than 20 times faster than the chloride anion. Finally, this work shows that the anion transport properties of these compounds are extremely sensitive to the steric crowding about the boron atom, pointing to the crucial involvement of the Group 13 element as the anion binding site.

Our interests in the chemistry of atypical main group Lewis acids have led us to devise strategies that augment the affinity of chalcogen-bond donors for anionic guests. In this study, we describe the oxidative methylation of diaryltellurides as one such strategy along with its application to the synthesis of [Mes(C6F5)TeMe]+ and [(C6F5)2TeMe]+ starting from Mes(C6F5)Te and (C6F5)2Te, respectively. These new telluronium cations have been evaluated for their ability to complex and transport chloride anions across phospholipid bilayers. These studies show that, when compared to their neutral Te(ii) precursors, these Te(iv) cations display both higher Lewis acidity and transport activity. The positive attributes of these telluronium cations, which originate from a lowering of the tellurium-centered σ* orbitals and a deepening of the associated σ-holes, demonstrate that the redox state of the main group element provides a convenient handle over its chalcogen-bonding properties., The oxidative alkylation of diorganotellurides enhances the chalcogen-bond donor properties of the tellurium center, an effect manifested in the enhanced chloride anion affinity and transport properties of the resulting telluronium cations.

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

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph

Controlling the reactivity of transition metal complexes by positioning non-innocent functionalities around the catalytic pocket is a concept that has led to significant advances in catalysis. Here we describe our efforts toward the synthesis of dicationic phosphine gold complexes of general formula [(o-Ph2P(C6H4)Carb)Au(tht)]2+ decorated by a carbenium moiety (Carb) positioned in the immediate vicinity of the gold center. While the most acidic examples of such compounds have limited stability, the dicationic complexes with Carb+ = 9-N-methylacridinium and Carb+ = [C(ArN)2]+ (ArN = p-(C6H4)NMe2) are active as catalysts for the cycloisomerization of N-propargyl-4-fluorobenzamide, a substrate chosen to benchmark reactivity. The dicationic complex [(o-Ph2P(C6H4)C(ArN)2)Au(tht)]2+, which also promotes hydroarylation and enyne cyclization reactions, displays a higher catalytic activity than its acridinium analog, indicating that the electrophilic reactivity of these complexes scales with the Lewis acidity of the carbenium moiety. These results support the role of the carbenium unit as a non-innocent functionality which can readily enhance the activity of the adjacent metal center. Finally, we also describe our efforts toward the generation and isolation of free γ-cationic phosphines of general formula [(o-Ph2P(C6H4)Carb)]+. While cyclization into phosphonium species is observed for Carb+ = [C(ArN)2]+, [C(Ph)(ArN)]+, and 9-xanthylium, [(o-Ph2P(C6H4)-9-N-methylacridinium)]+ can be isolated as an air stable, biphilic derivative with uncompromised Lewis acidic and basic properties., This work describes the synthesis of carbenium-based, γ-cationic phosphines and their coordination to Au(i) cations , leading to carbophilic catalysts whose activity is enhanced by the ligand-enforced convergence of the positively charged moieties.

Our interest in the chemistry of tunable chalcogen and pnictogen bond donors as Lewis acidic platforms for the complexation and transport of anions has led us to investigate examples of such compounds that can be activated by redox events. Here, we describe the synthesis of [o-MePhS(C6H4)SbPh3]2+ ([3]2+) and [o-MePhS(C6H4)Sb(p-Tol)3]2+ ([4]2+), two dicationic stibonium/sulfonium bifunctional Lewis acids which were obtained by methylation of the phenylthioether derivatives [o-PhS(C6H4)SbPh3]+ ([1]+) and [o-PhS(C6H4)Sb(p-Tol)3]+ ([2]+), respectively. An evaluation of the chloride anion transport properties of these derivatives using chloride-loaded POPC unilamellar vesicles shows that the activity of the monocations [1]+ and [2]+ greatly exceeds that of the dications [3]2+ and [4]2+, a phenomenon that we assign to the higher lipophilicity of the monocationic compounds. Harnessing this large transport activity differential, we show that [4]2+ can be used as a prechloridophore that is readily activated by reduction of the sulfonium moiety. Indeed, [4]2+ reacts with GSH to afford [2]+ as an active transporter. This activation, which has been monitored in aqueous solution, can also be carried out in situ, in the presence of the chloride-loaded POPC unilamellar vesicles., We describe a sulfonium/stibonium dication that behaves as a preanionophore activatable by glutathione (GSH). Indeed, this dication is reduced by GSH to yield a thioether/stibonium monocation that readily transports Cl− across phospholipid membranes.

Telluronium cations have long been known to engage their counteranions via secondary interactions. Yet, this property has rarely been exploited for anion binding. Motivated by such an application, we have now synthesized a bis-telluronium dication ([3]2+) that was obtained as a tetrafluoroborate salt by reaction of 2,7-di-tert-butyl-9,9-dimethylxanthene-4,5-diboronic acid with phenoxatellurine difluoride and BF3·OEt2. As confirmed by the formation of Te-(μ-BF4)-Te bridges in the structure of [3][BF4]2, [3]2+ functions as a bidentate Lewis acid toward anions. [3][BF4]2 has also been converted into the more exposed [3][BArF24]2 ([BArF24]- = [B(3,5-(CF3)2C6H3)4]-). The latter, which readily ionizes Ph3CCl, displays a chloride anion binding constant that exceeds that of a monofunctional model compound by almost 4 orders of magnitude. The unique properties of this new bis-telluronium dication are further highlighted by its ability to activate Ph3PAuCl and cis-(Ph3P)2PtCl2, leading to catalytic systems highly active in the cycloisomerization of propargylamide or enyne substrates.

As part of our efforts in the chemistry of main group platforms that support anion sensing and transport, we are now reporting the synthesis of anitmony-based bidentate Lewis acids featuring the o-C6F4 backbone. These compounds can be easily accessed by reaction of the newly synthesized o-C6F4(SbPh2)2 (5) with o-chloranil or octafluorophenanthra-9,10-quinone, affording the corresponding distiboranes 6 and 7 of general formula o-C6F4(SbPh2(diolate))2 with diolate = tetrachlorocatecholate for 6 and octafluorophenanthrene-9,10-diolate for 7, respectively. While 6 is very poorly soluble, its octafluorophenanthrene-9,10-diolate analog 7 readily dissolves in CH2Cl2 and undergoes swift conversion into the corresponding fluoride chelate complex [7-μ2-F]- which has been isolated as a [nBu4N]+ salt. The o-C6H4 analog of 7, referred to as 8, has also been prepared. Although less Lewis acidic than 7, 8 also forms a very stable fluoride chelate complex ([8-μ2-F]-). Altogether, our experiental results, coupled with computational analyses and fluoride anion affinity calculations, show that 7 and 8 are some of the strongest antimony-based fluoride anion chelators prepared to date. Another notable aspect of this work concerns the use of the octafluorophenanthrene-9,10-diolate ligand and its ablity to impart advantageous solubility and Lewis acidity properties.

Over the past decade, the chemistry of σ-accepting or Z-type ligands based on main group elements has drawn renewed attention because of the realization that their interaction with a transition metal (M) could be used to control the reactivity of the metal center. In this article, we describe several conceptual models that have been developed to understand the properties of main group-based Z-type ligands. We also explain how these models can be applied to the design of new coordination platforms where the electron-accepting properties of the Z-type ligand can be adjusted via postsynthetic transformations occurring at the main group element. Last, we show that the M → Z interaction and its tunable nature offer unique opportunities in the domain of ligand-controlled organometallic catalysis.

We describe the synthesis and properties of a series of sulfonium boranes featuring a dimesitylboryl unit and a dimethylsulfonium or methylphenyl sulfonium moiety connected by an ortho- or para-phenylene linker. Acid-base and fluoride anion tritration experiments carried out in aqueous media indicate that [o-(Mes2B)C6H4(SMePh)]+ is the most Lewis acidic derivative. Structural and computational analysis indicate that the favorable properties of this cationic borane derive from the proximity of the sulfonium and boryl units which enhances the Coulombic stabilization of the ensuing zwitterions o-(Mes2XB)C6H4(SMePh) with X = OH or F. Another important factor is the overall hydrophobicity of the sulfonium borane which, we propose, promotes anion desolvation, a factor also favoring B-X bond formation. Finally, the crystal structure of o-(Mes2FB)C6H4(SMePh) shows that the zwitterion is further stabilized by formation of a B F→S chelate motif.

Intermetallics are atomically ordered crystalline compounds containing two or more main group and transition metals. In addition to their rich crystal chemistry, intermetallics display unique properties of interest for a variety of applications, including superconductivity, hydrogen storage, and catalysis. Because of the presence of metals with a wide range of reduction potentials, the controlled synthesis of intermetallics can be difficult. Recently, soft chemical syntheses such as the modified polyol and ship-in-a-bottle methods have helped advance the preparation of these materials. However, phase-segregated products and complex multistep syntheses remain common. Here, we demonstrate the use of heterobimetallic single-source precursors for the synthesis of 10-15 and 11-15 binary intermetallics. The coordination environment of the precursor, as well as the exact temperature used play a critical role in determining the crystalline intermetallic phase that is produced, highlighting the potential versatility of this approach in the synthesis of a variety of compounds. Furthermore, we show that a recently developed novel plasma-processing technique is successful in removing the surface graphitic carbon observed in some of the prepared compounds. This new single-source precursor approach is a powerful addition to the synthesis of atomically ordered intermetallic compounds and will help facilitate their further study and development for future applications.

Bifunctional Lewis acidic group 15 compounds have emerged as appealing platforms for anion sensing and organocatalysis. As part of our interest in the chemistry of these compounds, we have now compared the catalytic properties of [o-(MePPh2)C6H4SbPh2]+ ([3]+), [o-(PPh2)C6H4SbPh3]+ ([4]+), [o-(MePPh2)C6H4SbPh3]2+ ([5]2+), and [o-C6H4(SbMePh2)2]2+ ([6]2+) using the transfer hydrogenation of 2-phenyl-quinoline and 3-bromoquinoline with a Hantzsch ester benchmark reactions. This study, which also involved an evaluation of the catalytic properties of [Ph4Sb]+ and [Ph3MeP]+, shows that antimony cations are generally more active than their phosphorus counterparts and neutral stiboranes. Our results also demonstrate that dicationic systems such as [6]2+ are superior activators.

Two boranes, 1-(dimesitylboryl)anthracene (1) and 1,8-bis(dimesitylboryl)anthracene (2), have been synthesized with the spectrophysical properties showing how the inclusion of one or two boron atoms progressively perturbs the π-system of the anthracene backbone. This perturbation is caused by conjugation of the anthracene-π* orbital with the vacant p-orbital on boron. Additionally, both 1 and 2 have a high affinity for fluoride and cyanide anions which are complexed in a 1 : 1 guest-host ratio. The mono-borane 1 is particularly well-suited for cyanide binding, displaying a binding constant of 3 × 107 in THF. Furthermore, as a result of their unique electronic structures, these boranes display a fluorescence response to fluoride anion characterized by a blue shift in the case of 1 and a red shift in the case of 2.

Our efforts in the chemistry of gold complexes featuring ambiphilic phosphine-carbenium L/Z-type ligand have led us to consider the reduction of the carbenium moiety as a means to modulate the gold-carbenium interaction present in these complexes. Here, we show that the one-electron reduction of [( o -Ph 2 P(C 6 H 4 )Acr)AuCl] + (Acr = 9- N -methylacridinium) produces a neutral stable radical, the structure of which shows a marked increase in the Au - Acr distance. Related structural changes are observed for the phosphine oxide analog [( o -Ph 2 P(O)(C 6 H 4 )Acr] + , the reduction of which also interferes with the P=O - carbenium interaction. These structural effects, driven by a reduction-induced change in the electrostatic potential profile of the compounds, show that the charge and accepting properties of the carbenium unit can be modulated. These results highlight the redox-noninnocence of carbenium Z-type ligand, a feature that can be exploited to induce specific conformational changes.

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

The development of catalysts for the oxygen reduction reaction is a coveted objective of relevance to energy research. This study describes a metal-free approach to catalyzing the reduction of O2 into H2O2, based on the use of redox-active carbenium species. The most active catalysts uncovered by these studies are the bifunctional dications 1,8-bis(xanthylium)-biphenylene ([3]2+) and 4,5-bis(xanthylium)-9,9-dimethylxanthene ([4]2+) which promote the reaction when in the presence of decamethylferrocene and methanesulfonic acid. Electrochemical studies carried out with [4]2+ suggest the intermediacy of an organic peroxide that, upon protonation, converts back into the starting dication while also releasing H2O2. Kinetic studies point to the second protonation event as being rate-determining.

Our interest in the chemistry of antimony derivatives has led us to investigate the synthesis and properties of 4-(diphenylstibino)-2,2′-bipyridine (LSbPh2). This new ligand, which could be obtained by reaction of 4-lithio-2,2′-bipyridine with Ph2SbCl, was treated with Pt(CH3CN)2Cl2 to afford the platinum complex LSbPh2PtCl2 (1). Interestingly, the latter reacts with PhICl2 to afford LSbCl2Ph2PtCl2 (2), a complex in which the peripheral stibine moiety has been converted into a dichlorostiborane. Complexes 1 and 2 have both been fully characterized. Computational, UV–vis, and cyclic voltammetry studies show that oxidation of the antimony atom leads to a lowering of the bipy-centered LUMO, indicating that 2 is more electron deficient than 1. A congruent picture emerges from reactivity studies, which show that 2 is a more active catalyst for the hydroarylation of ethyl propiolate by mesitylene.

As part of our interest in the chemistry of polydentate Lewis acids as hosts for diatomic molecules, we have investigated the synthesis and coordination chemistry of bidentate boranes that feature a large boron–boron separation. In this paper, we describe the synthesis of a new example of such a diborane, namely 1,8-bis(dimesitylboryl)triptycene (2) and compare its properties to those of the recently reported 1,8-bis(dimesitylboryl)biphenylene (1). These comparative studies reveal that these two diboranes feature some important differences. As indicated by cyclic voltammetry, 1 is more electron deficient than 2; it also adopts a more compact and rigid structure with a boron–boron separation (4.566(5) A) shorter by ∼1 A than that in 2 (5.559(4) A). These differences appear to dictate the coordination behaviour of these two compounds. While 2 remains inert toward hydrazine, we observed that 1 forms a very stable μ(1,2) hydrazine complex which can also be obtained by phase transfer upon layering a solution of 1 with a dilute aqueous hydrazine solution. The stability of this complex is further reflected by its lack of reaction with benzaldehyde at room temperature. We have also investigated the behaviour of 1 and 2 toward anions. In MeOH/CHCl3 (1/1 vol) both compounds selectively bind cyanide to form the corresponding μ(1,2) chelate complexes with a B–CN–B bridge at their cores. Competition experiments in protic media show that the anionic cyanide complex formed by 1 is the most stable, with no evidence of decomplexation even in the presence of (C6F5)3B.

A series of triarylmethylstibonium Lewis acids of general formula [Ph2MeSb-(p-(C6H4))-FLUO]+ bearing a peripheral electron-rich fluorophore (FLUO = 10H-phenoxazine ([3a]+), diphenylamine ([3b]+), and 9H-carbazole ([3c]+)) have been synthesized and investigated for the fluorescence turn-on sensing of fluoride anions. Treatment of the stibonium cations with fluoride anions leads to the corresponding fluorostiboranes (3a-F–3c-F). While the stibonium cations are almost nonemissive, the fluorostiboranes display fluorophore-centered emissions arising from the corresponding π–π* excited state. The carbazole-containing derivative [3c]+ exhibits the most intense fluorescence turn-on response. It also displays a high binding constant (K > 107 M–1) in MeCN and shows compatibility with protic media such as MeOH (K = 950(±50) M–1). Computational studies aimed at identifying the origin of the turn-on response show that the excited state of the stibonium cations is best described as charge transfer in nature with the π ...

Borinic acids have typically not been considered as hydrogen bond donor groups in molecular recognition. Described herein is a bifunctional borane/borinic acid derivative (2) in which the two functionalities are connected by a 1,8-biphenylenediyl backbone. Anion binding studies reveal that 2 readily binds a fluoride anion by formation of a unique B-F⋅⋅⋅H-O-B hydrogen bond. This hydrogen bond is characterized by a short H-F distance of 1.79(3) A and a large coupling constant (1 JHF ) of 57.2 Hz. The magnitude of this interaction, which has also been investigated computationally, augments the fluoride anion binding properties of 2, thus making it compatible with aqueous environments.

As part of our efforts toward the discovery of new late transition metal catalysts, we synthesized [(o-(Ph2P)C6H4)2(o-C6Cl4O2)SbPh)Au]+ (3+) and [(o-(iPr2P)C6H4)2(o-C6Cl4O2)SbPh)Au]+ (4+), two cationic bis(phosphino)gold stiborane complexes, which were isolated as their hexafluorophosphate salts and fully characterized. Structural and computational studies indicate that the cores of these two complexes are almost structurally and electronically identical. Despite these similarities, these two complexes exhibit different catalytic activities in the hydroamination of phenylacetylene using anilines or in the cyclization of N-(prop-2-yn-1-yl)benzamide. Indeed, whereas 3+ catalyzes both reactions, we found that 4+ is inactive. The data collected on these two complexes suggest that the origin of this contrasting behavior is steric, rather than electronic, with the relatively bulky iPr2P ancillary ligands blocking access to the reactive gold center.

Two cyclometalated ruthenium polypyridyl complexes bearing novel Sb(III)- and Sb(V)-substituted phenylpyridine ligands have been synthesized and their photophysical and electrochemical properties studied. The influence of a strongly electron-withdrawing and Lewis acidic Sb(V) substituent on the cyclometalating ligand resulted in marked changes in the absorption spectrum and electrochemical profile of the complex. These effects have been utilized as a strategy for anion sensing, in which coordination of fluoride or cyanide anions at the Sb(V) substituent can be observed both spectroscopically and electrochemically.

The characterization of a naphthalene diimide (NDI) radical anion is presented. Its properties allow a reliable comparison point for other systems involving the NDI radical anion, such as systems claimed to perform the oxidation of the fluoride anion. In addition to reiterating the obvious thermodynamic objections to such an unlikely oxidation, we present several observations that show that the fluoride anion does not act as a one-electron reducing agent toward the NDI investigated in this work.

Our interest in anion-responsive materials has led us to investigate the synthesis and properties of derivatives featuring a Lewis acidic antimony(V) moiety integrated within the π-conjugated structure of a 1λ5-stibaindole (or 1λ5-benzostibole). Starting from an organozirconium reagent, 1,2,3-tris(phenyl)-1-stibaindole (1) was first synthesized and subsequently allowed to react with o-chloranil and 3,5-di-tert-butyl-o-benzoquinone to afford the corresponding catecholato-1λ5-stibaindole derivatives 2 and 3, respectively, as a result of oxidative addition of the o-benzoquinone reagent to the antimony center. Conversion of 1 into 2 and 3 lowers the energy of the antimony-based σ* orbital, thus promoting its conjugation with the π* orbital of the heterocyclic chromophore. As a result of this σ*−π* conjugation, 2 and 3 experience a narrowing of the π–π* energy gap leading to a red shift of the corresponding UV–vis absorption band. This σ*−π* conjugation can be turned off by addition of a fluoride anion, which ...

As part of our ongoing interest in main group species that support the photoreductive elimination of halogens, we have synthesized [Cl3SbVPdIICl2(o-dppp)2] (o-dppp = o-(Ph2P)C6H4), a palladium dichloride complex featuring a Lewis acidic trichlorostiborane moiety positioned within the ligand architecture. Upon UV irradiation, this complex undergoes a clean photoreductive chlorine elimination reaction which produces [Cl2SbIVPdICl(o-dppp)2], a complex with a covalent Sb–Pd bond. This transformation illustrates the viability of antimony as an element from which a halogen can be photoeliminated; it also shows that a metal halide can be photolytically coupled with a main group halide to generate a metal-element bond.

As part of our fundamental interest in the chemistry of main-group Lewis acids, we have decided to target stibonium cations whose Lewis acidity is enhanced by the presence of a halogen substituent directly bound to antimony. Starting from Ph3Sb(OTf)2 (1) and Mes3Sb(OTf)2 (2), we successfully prepared the triflate derivatives Ph3SbF(OTf) (3) and Mes3SbF(OTf) (4). We also synthesized the hexachloroantimonate salt of [Mes3SbCl]+ (6), an analogue of the known [Ph3SbCl][SbCl6] (5). The structures of these complexes have been investigated experimentally as well as computationally using density functional theory methods. While direct interaction is observed between the anion and the stibonium center in compounds 3–5, compound 6 exists as an ionic solid with the four-coordinate [Mes3SbCl]+ cation separated from the [SbCl6]− anion. The structural difference observed between the two hexachloroantimonate derivatives 5 and 6 is ascribed to the increased steric protection provided by the larger mesityl substituents. T...

As part of our interest in the coordination chemistry of heavy Group 14 elements, we have synthesized complexes of general formula [(o-(Ph2P)C6H4)2SnClPh]AuX (X = Cl (2-Cl), X = Br (2-Br), and X = I (2-I)) in which the chlorostanane unit acts as a σ-acceptor ligand toward gold. The existence of a Au → Sn dative bond is evidenced by a trigonal bipyramidal geometry about the tin atom as well as a distorted square planar geometry about the gold center. While the measured Au–Sn bond distances are crystallographically indistinguishable in this series, theoretical investigations reveal that the strength of the Au → Sn interaction increases in the order 2-I

N-Heterocyclic carbene boron trifluoride (NHC-BF3) conjugates were successfully radiofluorinated by SnCl4-promoted 18F–19F isotopic exchange reaction in one labelling step. This method afforded in vivo stable PET agents that efficiently bound to targeted tumours yielding PET images with good tumour-to-background contrast.

We describe the synthesis of a BODIPY dye substituted with a Lewis acidic antimony(v) moiety. This compound, which has been fully characterized, shows a high affinity for small anions including fluoride and cyanide, the complexation of which elicits a fluorescence turn-on response.