2,6-Bis(benzimidazol-2-yl)pyridine complexes of group 14 elements

Variants of the 2,6-bis(benzimidazol-2-yl)pyridine ligand are used to synthesize novel group 14 complexes of germanium and tin. The salts are characterized by X-ray crystallography, NMR, UV-vis, and the Lewis acidity of some examples are probed.

2,6-Bis(benzimidazol-2-yl)pyridines as more electron-rich and sterically accessible alternatives to 2,6-bis(imino)pyridine for group 13 coordination chemistry

2,6-bis(benzimidazol-2-yl)pyridines are more electron-rich yet more sterically open ligands for monovalent and trivalent group 13 elements than bis(imino)pyridines.

Tris(benzoimidazol)amine (L) complexes of pnictogen(iii) and pnictogen(v) cations and assessment of the [LP]3+/[LPF2]3+ redox couple

A series of cationic complexes involving a pnictogen(iii) (Pn = P, As, Sb) centre and the tetradentate ligand tris((1-ethyl-benzoimidazol-2-yl)methyl)amine (BIMEt3) have been synthesized and comprehensively characterized. Oxidation of [P(BIMEt3)]3+ with XeF2 provides access to [PF2(BIMEt3)]3+ representing the first structurally characterized example of a phosphorus(v) centred trication.

Pyridine, thiophosphine, and selenophosphine complexes of the phenylphosphine dication

Compounds of the generic formula [PhPL][OTf]2 with L = bipyridine (bipy) and 4,4′-di(tert-butyl)-2,2′-bipyridine (Bbipy) and [PhPL2][OTf]2 with L = 4-dimethylaminopyridine (dmap), tricyclohexyl-thiophosphine, and tricyclohexyl-selenophosphine have been prepared by the reaction of dichlorophenylphosphine with two equivalents of trimethylsilyl triflate and the respective ligand. The new complexes of the phenylphosphine dication with this variety of ligands expands the scope of coordination complexes involving phosphorus as an acceptor.

Reversible Oxidative Se-Se Coupling of Phosphine Selenides by Ph3 Sb(OTf)2

Salts of diphosphoniumdiselenide dications ([R₃ PSeSePR₃ ][OTf]₂ ) have been isolated from reactions of trialkylphosphine selenides with triphenylantimony bistriflate. The redox process is speculated to proceed via a cationic coordination complex [Ph₃ SbL₂ ][OTf]₂ (L=Me₃ PSe, iPr₃ PSe), which is also formed in the reaction of [R₃ PSeSePR₃ ][OTf]₂ with Ph₃ Sb. The observations indicate that the reductive elimination of [R₃ PSeSePR₃ ]²⁺ from [Ph₃ Sb(SePR₃ )₂ ]²⁺ is reversible through the oxidative addition of [R₃ PSeSePR₃ ]²⁺ to Ph₃ Sb.

Oxidation of a germanium(ii) dication to access cationic germanium(iv) fluorides

Herein we describe the synthesis and characterization of the tris(1-ethyl-benzoimidazol-2-ylmethyl)amine (BIMEt₃ = L) complex of Ge(ii)²⁺ and its oxidation with XeF₂ to access the cationic germanium fluorides [LGeF₂][OTf]₂ and [LGeF(OTf)][OTf]₂.

Synthesis, characterization and mass-spectrometric analysis of [LSn(IV)F4−x]x+ salts [L = tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine, x = 1–4]

A series of cationic tin fluoride complexes has been synthesized by successive fluoride abstraction from SnF₄ with TMSOTf in the presence of the tetradentate nitrogen donor BIMEt₃.

[GaX2(dmpe)2][GaX4] (X = Cl, Br, I): a synthetic, solid state, and computational study

Derivatives of [GaX2(dmpe)2][GaX4] (X = Cl,Br, I) were prepared and characterized. The salts contain a cation involving two diphosphine ligands bound to GaX2+, imposing a pseudo-octahedral geometry at gallium. A variety of possible structural alternatives for the equimolar combination of GaX3 and dmpe have been computationally modelled and shown to be energetically similar to the observed cations, indicating potential fluxionality in the system, and are in agreement with spectroscopic characterization.

Tris(2-pyridyl)phosphine as a versatile ligand for pnictogen acceptors

We report cationic complexes of arsenic and antimony with the tris(2-pyridyl)phosphine ligand. Chloride ion abstraction from the main group halide using TMSOTf in presence of the ligand gives [P(Pyr)₃Pn][OTf]₃, in which the trication adopts a Janus Head type complex with a C_3v symmetric cage structure and two apical lone pairs.

Cationic 2,2′-bipyridine complexes of germanium(ii) and tin(ii)

Tetrel analogues of transition metal complexes.

Bond fission in monocationic frameworks: diverse fragmentation pathways for phosphinophosphonium cations

A series of phosphinophosphonium cations ([R2PPMe3]+; R = Me, Et, i Pr, t Bu, Cy, Ph and N i Pr2) have been prepared and examined by collision-induced dissociation (CID) to determine the fragmentation pathways accessible to these prototypical catena-phosphorus cations in the gas-phase. Experimental evidence for fission of P-P and P-E (E = P, C) bonds, and β-hydride elimination has been obtained. Comparison of appearance potentials for the P-P bond dissociation fragments [R2P]+ (P-P heterolysis) and [PMe3]+˙ (P-P homolysis) shows that heterolytic P-P cleavage is more sensitive than P-P homolysis towards changes in substitution at the trivalent phosphorus center. The facility of β-hydride elimination increases with the steric bulk of R in [R2PPMe3]+. A density functional theory (DFT) study modelling these observed processes in gas-phase, counterion- and solvent-free conditions, to mimic the mass spectrometric environment, was performed for derivatives of [R2PPMe3]+ (R = Me, Et, i Pr, t Bu, Ph and N i Pr2), showing good agreement with experimental trends. The unusual observation of both homolytic and heterolytic cleavage pathways for the P-P and P-C bonds reveals new insight into the fundamental aspects of bonding in monocations and undermines the use of simplistic bonding models.

Complexes of trimethylsilyl trifluoromethanesulfonate with nitrogen, oxygen, and phosphorus donors

The Lewis acceptor chemistry of Me3SiOTf with p-block Lewis bases has been explored and a library of complexes has been characterized by spectroscopic and, where possible, crystallographic methods. Compounds with the generic formula [Me3Si(L)][OTf] (L = 4-dmap, pyr, imz, OPMe3, OPCy3, OPPh3, OpyrMe, dmso, PMe3) were isolated from 1:1 mixtures of Me3SiOTf and the respective ligand in CH2Cl2. Characterization by NMR spectroscopy confirmed the solution stability of all but [Me3Si(PMe3)][OTf], with indications that the latter dissociates into PMe3 and Me3SiOTf. Solid-state structures of [Me3Si(4-dmap)][OTf], [Me3Si(pyr)][OTf], [Me3Si(OPCy3)][OTf], [Me3Si(OPPh3)][OTf], [Me3Si(OpyrMe)][OTf], and [Me3Si(PMe3)][OTf] were elucidated by single crystal X-ray diffraction, confirming the envisaged ionic formulations resulting from the displacement of the OTf anion from the silicon center of Me3SiOTf by the incoming ligand. Mixtures of Me3SiOTf with other related donors, including ChPPh3 (Ch = S or Se), NEt3, SMe2, PPh3, 2,2′-bipy, or Me2CO, show no evidence of reaction under ambient conditions, reflecting the lower basicity and (or) greater steric encumbrance of these ligands. Reactions of Me3SiOTf with bis-donor ligands yielded complexes of the generic formulae [Me3Si(L–L)SiMe3][OTf]2 (L–L = 4,4′-bipy, tmeda, dmpe) and [Me3Si(L–L)][OTf] (L–L = 4,4′-bipy, tmeda, dmpe). The tmeda and dmpe complexes, however, were found to dissociate in solution, with complexes only prevailing in the solid phase. X-ray diffraction studies of [Me3Si(4,4′-bipy)SiMe3][OTf]2 and [Me3Si(dmpe)SiMe3][OTf]2 confirmed the expected connectivities and ionic formulations, with Si–ligand bond lengths comparable to those observed in [Me3Si(pyr)][OTf] and [Me3Si(PMe3)][OTf], respectively.

2-Phosphino-1,3-diphosphonium ions

A series of 2-phosphino-1,3-diphosphonium trifluoromethanesulfonate salts has been prepared and comprehensively characterized. The compounds represent rare examples of salts containing triphosphorus dications and establish important structural and spectroscopic parameters and trends for catenated phosphorus chains.

Correction: Bipyridine complexes of E3+ (E = P, As, Sb, Bi): strong Lewis acids, sources of E(OTf)3 and synthons for EI and EV cations

Correction for ‘Bipyridine complexes of E³⁺ (E = P, As, Sb, Bi): strong Lewis acids, sources of E(OTf)₃ and synthons for E^I and E^V cations’ by Saurabh S. Chitnis et al., Chem. Sci., 2015, 6, 6545–6555.

Distinction between coordination and phosphine ligand oxidation: interactions of di- and triphosphines with Pn3+ (Pn = P, As, Sb, Bi)

Hard and soft acceptors react differently towards phosphine donors, defining a range of phosphine coordination chemistry outcomes for p-block elements.

Bipyridine complexes of E3+ (E = P, As, Sb, Bi): strong Lewis acids, sources of E(OTf)3 and synthons for EI and EV cations

Triflate salts of trications [(bipy)₂E]³⁺ ([6E][OTf]₃) and [(tbbipy)₂E]³⁺ ([6′E][OTf]₃) (bipy = 2,2′-bipyridine, tbbipy = 4,4′-di-^tbutyl-2,2′-bipyridine; E = P, As, Sb, Bi) have been synthesized and comprehensively characterized.

Triflate salts of trications [(bipy)₂E]³⁺ ([6E][OTf]₃) and [(tbbipy)₂E]³⁺ ([6′E][OTf]₃) (bipy = 2,2′-bipyridine, tbbipy = 4,4′-di-^tbutyl-2,2′-bipyridine; E = P, As, Sb, Bi) have been synthesized and comprehensively characterized. The unique molecular and electronic structures of this new class of complexes involving pnictogen Lewis acids has been assessed in the solid, solution and gas phases to reveal systematic variations in metric parameters, ligand lability and charge concentration. While the Lewis acidity of E³⁺ has the trend E = Bi < Sb < As < P as determined by gas-phase calculations and ¹H NMR spectroscopy, the Lewis acidity of [6E]³⁺ has the trend E = P < As < Sb < Bi according to gas-phase calculations. Derivatives of [6′E][OTf]₃ (E = P, As) are latent sources of E(OTf)₃ as demonstrated by their reactions with dmap, which give the corresponding derivatives of [(dmap)₃E][OTf]₃. The highly oxidizing nature of P(OTf)₃ and As(OTf)₃ is evidenced in reactions of [6′E][OTf]₃ (E = P, As) with phosphines, which give E^I-containing monocations [(R₃P)₂E]¹⁺ and oxidatively coupled dications [R₃PPR₃]²⁺, illustrating new P–P and P–As bond forming strategies. Cations [6′E]³⁺ (E = P, As) are C–H bond activating agents that dehydrogenate 1,4-cyclohexadiene, with higher activity observed for E = P. Combinations of [6′E]³⁺ and ^tBu₃P activate H₂ and D₂ under mild conditions, evidencing frustrated Lewis pair activity. Oxidation of [6′P][OTf]₃ with SO₂Cl₂ gives [(tbbipy)₂PCl₂][OTf]₃, containing a P^V-trication, but there is no evidence of the analogous reaction with [6′As][OTf]₃. The observations highlight new directions in the chemistry of highly charged cations and reveal a rich reactivity for p-block triflates E(OTf)₃, which can be accessed through derivatives of [6E][OTf]₃ and [6′E][OTf]₃.

Establishing the Coordination Chemistry of Antimony(V) Cations: Systematic Assessment of Ph4 Sb(OTf) and Ph3 Sb(OTf)2 as Lewis Acceptors

The coordination chemistry of the stiboranes Ph4 Sb(OTf) (1 a, OTf = OSO2 CF3 ) and Ph3 Sb(OTf)2 (3) with Lewis bases has been investigated. The significant steric encumbrance of the Sb center in 1 a precludes interaction with most ligands, but the relatively low steric demands of 4-methylpyridine-N-oxide (OPyrMe) and OPMe3 enabled the characterization of [Ph4 Sb(OPyrMe)][OTf] (2 a) and [Ph4 Sb(OPMe3 )][OTf] (2 b), rare examples of structurally characterized complexes of stibonium acceptors. In contrast, 3 was found to engage a variety of Lewis bases, forming stable isolable complexes of the form [Ph3 Sb(donor)2 ][OTf]2 [donor=OPMe3 (6 a), OPCy3 (6 b, Cy=cyclohexyl), OPPh3 (6 c), OPyrMe (6 d)], [Ph3 Sb(dmap)2 (OTf)][OTf] (6 e, dmap=4-(dimethylamino)pyridine) and [Ph3 Sb(donor)(OTf)][OTf] [donor=1,10-phenanthroline (7 a) or 2,2'-bipy (7 b, bipy=bipyridine)]. These compounds exhibit significant structural diversity in the solid-state, and undergo ligand exchange reactions in line with their assignment as coordination complexes. Compound 3 did not form stable complexes with phosphine donors, with reactions instead leading to redox processes yielding SbPh3 and products of phosphine oxidation.

Synthesis and reactivity of cyclo-tetra(stibinophosphonium) tetracations: redox and coordination chemistry of phosphine-antimony complexes

Reductive elimination of [R3PPR3]2+, [11(R)]2+, from the highly electrophilic SbIII centres in [(R3P)3Sb]3+, [8(R)]3+, gives SbI containing cations [(R3P)Sb]1+, [9(R)]1+, which assemble into frameworks identified as cyclo-tetra(stibinophosphonium) tetracations, [(R3P)4Sb4]4+, [10(R)]4+. A phosphine catalyzed mechanism is proposed for conversion of fluoroantimony complexes [(R3P)2SbF]2+, [7(R)]2+, to [10(R)]4+, and the characterization of key intermediates is presented. The results constitute evidence of a novel ligand activation pathway for phosphines in the coordination sphere of hard, electron deficient acceptors. Characterization of the associated reactants and products supports earlier, albeit less definitive, detection of analogous phosphine ligand activation in CuIII and TlIII complexes, demonstrating that these prototypical ligands can behave simultaneously as reducing agents and σ donors towards a variety of hard acceptors. The reactivity of the parent cyclo-tetra(stibinophosphonium) tetracation, [10(Me)]4+, is directed by high charge concentration and strong polarization of the P-Sb bonds. The former explains the observed facility for reductive elimination to yield elemental antimony and the latter enabled activation of P-Cl and P-H bonds to give phosphinophosphonium cations, [Me3PPR'2]1+, including the first example of an H-phosphinophosphonium, [(Me3P)P(H)R']1+, and 2-phosphino-1,3-diphosphonium cations, [(Me3P)2PR']2+. Exchange of a phosphine ligand in [10(Me)]4+ with [nacnac]1- gives [(Me3P)3Sb4(nacnac)]3+, [15(Me)]3+, and with dmap gives [(Me3P)3Sb4(dmap)]4+, [16]4+. The lability of P-Sb or Sb-Sb interactions in [10(Me)]4+ has also been illustrated by characterization of heteroleptically substituted derivatives featuring PMe3 and PEt3 ligands.

Phosphine chalcogenide complexes of antimony(III) halides

Three series of phosphine chalcogenide complexes of the antimony(III) halides SbX3 (X = F, Cl, Br, or I) have been synthesized and characterized by spectroscopic and crystallographic methods. Complexes of the generic formulae (Cy3PO)SbX3 (X = F (1a), Cl (1b), or Br (1c)), (Cy3PO)2SbX3 (X = F (2a), Cl (2b), or Br (2c)), and (Cy3PS)SbX3 (X = Cl (3b), Br (3c), or I (3d)) were synthesized via the treatment of solutions of SbX3 with OPCy3 and SPCy3, respectively. Derivatives of (Cy3PO)SbX3 were characterized by single crystal X-ray diffraction for 1a and 1b and crystallize as dimers through symmetry related intermolecular Sb–X interactions, providing the first structurally characterized examples of this class of complex. Derivatives of (Cy3PS)SbX3 (3b–3c) adopt analogous dimeric structures in the solid state. The solid-state structure of (Cy3PO)2SbCl3 (2b) is consistent with the previously reported structures of bis-phosphine oxide complexes of antimony(III), with a square pyramidal Sb center and cis-configured OPCy3 ligands. The phosphine chalcogenide complexes of SbX3 display configurations that are consistent with the perceived trans-labilizing properties of the ligands/substituents.

The discovery of potent agonists for GPR88, an orphan GPCR, for the potential treatment of CNS disorders

Modulating GPR88 activity is suggested to have therapeutic utility in the treatment of CNS disorders, such as schizophrenia. This Letter will describe the discovery and SAR development of a class of potent GPR88 agonists.

Design, synthesis, and evaluation of phenylglycinols and phenyl amines as agonists of GPR88

Small molecule modulators of GPR88 activity (agonists, antagonists, or modulators) are of interest as potential agents for the treatment of a variety of psychiatric disorders including schizophrenia. A series of phenylglycinol and phenylamine analogs have been prepared and evaluated for their GPR88 agonist activity and pharmacokinetic (PK) properties.

Phosphine complexes of lone pair bearing Lewis acceptors

An overview of the synthesis, structures and reaction chemistry of coordination complexes featuring an acceptor with at least one lone pair and at least one phosphine donor is presented. One or more examples of complexes have been structurally-characterized for the majority of p-block elements but few are known for most elements. The unusual condition of a p-block element centre accommodating a lone pair of electrons and offering a low energy LUMO gives the element centre the potential to behave as both a Lewis acid and a Lewis Base. The structural diversity and reactivity of the phosphine complexes highlights new directions in main group chemistry and by comparison with transition metal coordination chemistry, the featured complexes demonstrate significant configurational and stereochemical flexibility. Ligand exchange, oxidation and reduction chemistry at the lone pair bearing acceptor centre reveals unusual reactivity and an interesting class of ligands and inorganic reagents, with new possibilities for catalysis or small molecule activation.

Integrating High-Content Analysis into a Multiplexed Screening Approach to Identify and Characterize GPCR Agonists

G protein–coupled receptors (GPCRs) are one of the most popular and proven target classes for therapeutic intervention. The increased appreciation for allosteric modulation, receptor oligomerization, and biased agonism has led to the development of new assay platforms that seek to capitalize on these aspects of GPCR biology. High-content screening is particularly well suited for GPCR drug discovery given the ability to image and quantify changes in multiple cellular parameters, to resolve subcellular structures, and to monitor events within a physiologically relevant environment. Focusing on the sphingosine-1-phosphate (S1P1) receptor, we evaluated the utility of high-content approaches in hit identification efforts by developing and applying assays to monitor β-arrestin translocation, GPCR internalization, and GPCR recycling kinetics. Using these approaches in combination with more traditional GPCR screening assays, we identified compounds whose unique pharmacological profiles would have gone unnoticed if using a single platform. In addition, we identified a compound that induces an atypical pattern of β-arrestin translocation and GPCR recycling kinetics. Our results highlight the value of high-content imaging in GPCR drug discovery efforts and emphasize the value of a multiassay approach to study pharmacological properties of compounds of interest.

Coordination complexes of bismuth triflates with tetrahydrofuran and diphosphine ligands

The reaction of CH3OSO2CF3 (MeOTf) with BiBr3 in tetrahydrofuran (THF) yields (THF)2BiBr2(OTf) (1), which is converted to (dmpe)BiBr2(OTf) (2Br) upon displacement of the THF ligands with bis(dimethylphosphino)ethane (dmpe). The chloride derivatives (dmpe)BiCl2(OTf) (2Cl) and (dmpe)BiCl(OTf)2 (3) are obtained from the reaction of BiCl3 and dmpe with 1 and 2 equiv of Me3SiOSO2CF3 (TMSOTf), respectively. The complexes readily decompose in solution to give elemental bismuth and a mixture of products. The solid-state structures reveal dimeric units bridged by both triflate O-S-O interactions and weak Bi-X-Bi interactions (X = Cl, Br). Comparison of the solid-state structures illustrates that both cis and trans configurations of halides are possible in complexes of the form L2BiX2(OTf), depending upon the denticity of the ligand. The experimentally observed configurations are consistent with minima calculated at the MP2 level for the triflate-free cations in the gas phase. Examination of the MP2-calculated electronic structure of 3 reveals the presence of low-lying π-type orbitals that may result in Z-type ligand activity. However, the attempted coordination of 3 with the electron-rich metal center in K2PdCl4, via metal-to-ligand back-donation, leads instead to halide abstraction, giving [(dmpe)2Pd][(CH3CN)2Bi2Cl6(OTf)2] (8). The anion in 8 consists of two octahedral bismuth environments bridged along one edge by two triflate anions. The results illustrate new coordination chemistry for bismuth.

Phosphenium-Insertion and Chloronium-Addition Reactions Involving the cyclo-Phosphanes (t-BuP)n (n=3, 4)

The transfer of a Ph2P+-moiety provided by Ph2PCl and chloronium-addition with PCl5 or PhICl2 to the cyclo-phosphanes (t-BuP)n (n = 3 (4), 4 (5)) were investigated. The reactions strongly depend on the presence of GaCl3 or Me3SiOTf as a halide abstracting reagent. The reaction of 4 with Ph2PCl and GaCl3 quantitatively yields cation [Ph2P(t-BuP)3]+ (6+) as a GaCl4–-salt. Using Me3SiOTf as a halide abstracting reagent leads to the ring expansion of (t-BuP)3 (4) to tetrameric (t-BuP)4 (5) and cation 6+ is only formed as a minor product. Chloronium addition employing the PCl5/GaCl3 or PhICl2/Me3SiOTf systems as Cl+-sources to 4 gives complex reaction mixtures. In contrast, the Cl+-addition to 5 gives cation [Cl(t-BuP)4]+ (8+) quantitatively when the system PCl5/GaCl3 is used. Utilising PhICl2 in the presence of Me3SiOTf gives t-BuPCl2 as the main product.

P-P Menschutkin preparation of prototypical phosphinophosphonium salts

Reactions of Me(3)P with alkyl- or arylchlorophosphines yield phosphinophosphonium salts in quantitative yields, demonstrating a Menschutkin P-P methodology that has potentially broad application for element-element bond formation.