Non-coordinating Research Articles

Catena-Poly[[[bis-(aceto-nitrile-κN)(4,4'-dimeth-oxy-2,2'-bi-pyridine-κ2 N,N')copper(II)]-μ-tri-fluoro-methane-sulfonato-κ2 O:O'] tri-fluoro-methane-sulfonate

The central copper(II) atom of the title salt, {[Cu(CF3SO3)(CH3CN)2(C12H12N2O2)](CF3SO3)} n or [[Cu(CH3CN)2(diOMe-bpy)(CF3SO3)](CF3SO3)] n where diOMe-bpy is 4,4'-dimeth-oxy-2,2'-bi-pyridine, C12H12N2O2, is sixfold coordin-ated by the N atoms of the chelating bi-pyridine ligand, the N atoms of two aceto-nitrile mol-ecules, and two tri-fluoro-methane-sulfonate O atoms in a tetra-gonally distorted octa-hedral shape. The formation of polymeric chains [Cu(CH3CN)2(diOMe-bpy)(CF3SO3)]+ n leaves voids for the non-coordinating tri-fluoro-methane-sulfonate anions that inter-act with the complex through weak hydrogen bonds. The presence of weakly coordinating ligands like aceto-nitrile and tri-fluoro-methane-sulfonate makes the title compound a convenient starting material for the synthesis of novel metal-organic frameworks.

Hexafluoroacetylacetonate (hfac) as ligand for pentamethylcyclopentadienyl (Cp*) rhodium and iridium complexes: Some surprising results, including an Ir3Na1O4 cubane structure

Attempts to prepare hexafluoroacetylacetonate (hfac) piano stool complexes of pentamethylcyclopentadienyl Cp* iridium and rhodium led to a surprising array of unexpected products. The desired complex, Cp*M(hfac)Cl, was obtained following the reaction of sodium hexafluoroacetylacetonate (hfacNa) with [Cp*MCl2]2 in dichloromethane. Variations of this synthetic method resulted in twelve unique crystallographically identified products, eleven of which contain the hfac ligand or a trifluoroacetylacetonate (TFA) ligand, either coordinated to the metal or as a non-coordinating anion. Five dinuclear Cp* iridium hydroxo-bridged products with various fluorinated non-coordinating anions were obtained. The most intriguing two complexes are trinuclear Cp*IrIII hydroxo-bridged clusters that have, at their core, an Ir3NaO4 cubane structure. Attempts to devise rational syntheses of the hydroxo-bridged cluster compounds were not successful. Generation of the TFA moieties likely occurred following degradation of Cp*Ir(hfac)Cl. The reaction between [Cp*MCl2]2 and 1,1,1-trifluoroacetylacetonate (tfac) proceeded as expected to give Cp*M(tfac)Cl with no observed side product formation, indicating that the metal-coordinated tfac moiety is significantly more stable than the metal-coordinated hfac moiety.

Synthesis and Characterization of Tetrakis(pentafluoroethyl)aluminate.

While perfluorinated aryl, aryloxy and alkoxy aluminum species are well‐established as weakly coordinating anions (WCAs), corresponding perfluoroalkyl aluminum derivatives are virtually unknown. Reaction of Si(C2F5)3CH3 with Li[AlH4] afforded the tetrakis(pentafluoroethyl)aluminate, [Al(C2F5)4]−. Several salts of the [Al(C2F5)4]− ion were synthesized and characterized by NMR spectroscopic methods, mass spectrometry, X‐ray diffraction studies and elemental analysis.

Tris(carbene) Stabilization of Monomeric Magnesium Cations: A Neutral, Nontethered Ligand Approach

Herein, we describe the syntheses and structural characterization of bis(carbene)- and tris(carbene)-stabilized organomagnesium cations. The reaction of the N-heterocyclic carbene (NHC) stabilized Grignard reagent (iPrNHC)2Mg(Me)(Br) (1) and Na[BArF4] (iPrNHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, ArF = 3,5-bis(trifluoromethyl)phenyl) in chlorobenzene yields exclusively the bis(NHC)-stabilized dication [{(iPrNHC)2Mg}2(μ-Me)2][(BArF4)2] (2). If the reaction is performed in ethereal or nonpolar arene solvents, 2 undergoes Schlenk-type rearrangements to tris(NHC)-stabilized cations [(iPrNHC)3Mg(Me)][BArF4] (3[BArF4]) and [(iPrNHC)3Mg(Br)][BArF4] (4[BArF4]). These monomeric cations 3[A] and 4[A] (A = BArF4, BPh4) can be independently prepared as single pure products in high yields using common hydrocarbon solvents. The electronic influence of tris(carbene) stabilization is further evidenced by an NHC-mediated ionization of magnesium bromide in the absence of abstraction reagents. The reaction between the sterically unencumbered 1,3,4,5-tetramethylimidazol-2-ylidene (MeNHC) ligand and (MeNHC)2MgBr2 (7) resulted in two geometrically unique cations of the type [(MeNHC)3MgBr][Br]: complex 8a bearing a weakly coordinating bromide anion resulting in a trigonal bipyramidal magnesium center, and complex 8b bearing a noncoordinating bromide anion where the magnesium atom resides in a tetrahedral coordination environment. All isolated complexes were characterized by NMR spectroscopy and single-crystal X-ray diffraction, and their bonding was investigated by density functional theory (DFT).

AuI-Catalyzed Hydroalkynylation of Haloalkynes.

The AuI-catalyzed reaction between terminal alkynes and aromatic haloalkynes proceeds through divergent pathways depending on the nature of the catalyst counteranion. Thus, cationic complexes containing strongly basic NHC ligands and noncoordinating anions such as BArF4 catalyze the cis haloalkynylation of the terminal alkyne, whereas introduction of a weakly basic triflate counteranion results in the stereoselective hydroalkynylation of the haloalkyne, yielding haloenyne products in good yields and complete trans selectivity. Experimental and computational studies suggest that the hydroalkynylation reaction takes place via nucleophilic attack of the terminal alkyne to the C2 carbon of the activated haloalkyne, assisted by a concerted proton abstraction by the triflate, and that the protodeauration is the turnover-limiting step, in agreement with an observed primary kinetic isotope effect.

Hydrogen Bonds with BF4− Anion as a Proton Acceptor

The BF4− anion is characterised by weak Lewis base properties; it is usually classified as a “non-coordinating anion”. The searches through the Cambridge Structural Database (CSD) were performed and it was found that the BF4− anion often occurs in crystal structures and it is involved in numerous intermolecular interactions; hydrogen bonds are the majority of them. The hydrogen bonds involving the BF4− anion as a proton acceptor are closer to linearity with the increase of the strength of interaction that is in line with the tendency known for other hydrogen bonds. However, even for short contacts between the proton and the Lewis base centre, slight deviations from linearity occur. The MP2/aug-cc-pVTZ calculations on the BF4−…HCN complex and on the BF4−…(HCN)4 cluster were also carried out to characterise corresponding C-H…F hydrogen bonds; such interactions often occur in crystal structures.

A Structurally Robust Chiral Borate Ion: Molecular Design, Synthesis, and Asymmetric Catalysis

AbstractCatalysis by chiral weakly‐coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non‐nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O‐tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins‐type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis.

Hungry for charge – how a beryllium scorpionate complex “eats” a weakly coordinating anion

Abstract We present the reaction of a tris(pyrazolyl) beryllium scorpionate (TpBe) complex with a weakly coordinating anion (WCA), which yields the heteroleptic complex TpBeOC(CF3)3 1 (TpBeOR F). The product 1 has been characterized by multinuclear NMR spectroscopy (1H, 9Be, 13C) and single-crystal X-ray diffraction (scXRD). Quantum chemical calculations (DFT, NPA, LOL) were performed to study the bonding nature in 1.

Weak Coordinating Carbonyl-Directed Rhodium(III)-Catalyzed C-H Activation at the C4-Position of Indole with Allyl Alcohols.

A weakly coordinating carbonyl-directed coupling of allyl alcohols at the C-4 position of indole derivatives under the C-H activation conditions catalyzed by Rh(III) is reported. This results in alkylation at the C-4 position of indole derivatives exclusively. The obtained product forms a tricyclic derivative under aldol reaction conditions, which can be a potential precursor for synthesizing a few alkaloid molecules such as ergot, hapalindole alkaloids, and related heterocyclic compounds.

Zinc(II) and Cadmium(II) complexes containing imidazole ring: Structural, spectroscopic, antibacterial, DFT calculations and Hirshfeld surface analysis

Two 2-D and 3-D supramolecular complexes [Zn(L)2](NO3)2·2CH3OH (1) and [Cd(L)2(NO3)2] (2) (L = 2-(4-imidazolyl)-4-methyl-1,2-quinazoline-N3-oxide) were synthesized and characterized by IR, UV–Vis, fluorescence spectroscopy and elemental analysis. X–ray crystallography reveals that 1 and 2 have 2:1 ligand-to-metal ratio. Zn(II) complex 1 had slightly distorted octahedral geometry with two non-coordinated nitrate anions and assembled into fishnet-like 2-D and even M-shape 3-D skeleton, while six-coordinated Cd(II) complex 2 had a distorted octahedral geometry included two coordinated nitrate anions and formed an infinite 2-D layered skeleton, and even a wavy 3-D supramolecular network. Furthermore, antimicrobial activities of all compounds were also investigated. Density Functional Theory (DFT) calculations were carried out to ascertain the optimum geometry structures of both complexes and the calculated HOMO and LUMO energies were presented. The electronic transitions and spectral character of complexes were discussed by TD-DFT calculations. Non-covalent interactions among both complexes were quantified using Hirshfeld surface analysis.

Role of Anions and Mixtures of Anions on the Thermochromism, Vapochromism, and Polymorph Formation of Luminescent Crystals of a Single Cation, [(C6H11NC)2Au

Noncoordinating anions, which generally play a subordinate role in coordination chemistry, alter the structure, the luminescence, as well as the thermochromic and vapochromic behaviors of salts of the two-coordinate cation, [(C6H11NC)2Au]+. Thus whereas the yellow polymorphs of [(C6H11NC)2Au](PF6) and [(C6H11NC)2Au](AsF6) contain single chains of cations and are vapochromic, yellow [(C6H11NC)2Au](SbF6) does not form the same polymorph and is not vapochromic but contains two distinct chains of cations connected through aurophilic interactions. Mixed crystals such as [(C6H11NC)2Au](PF6)0.50(AsF6)0.50 have been prepared by adding diethyl ether to a dichloromethane solution containing equimolar amounts of [(C6H11NC)2Au](PF6) and [(C6H11NC)2Au](AsF6). The initial (kinetic) product for the three combinations of anions ((PF6)-/(AsF6)-, (PF6)-/(SbF6)-, and (AsF6)-/(SbF6)-) was a precipitate of fine yellow needles with a green emission, which were gradually transformed at rates that depended on the anions present into colorless crystals with a blue emission. Whereas neither polymorph of [(C6H11NC)2Au](PF6) nor [(C6H11NC)2Au](SbF6) is thermochromic, the colorless mixed crystal [(C6H11NC)2Au](PF6)0.50(SbF6)0.50 is thermochromic and converts from blue-emitting to green-emitting at 87-95 °C. The temperature required to transform a crystal of the type [(C6H11NC)2Au](PF6)n(AsF6)1-n from colorless (blue-emitting) to yellow (green-emitting) increases as the fraction of hexafluorophosphate ion in the crystal increases. The yellow crystals of [(C6H11NC)2Au](PF6)0.75(AsF6)0.25, [(C6H11NC)2Au](PF6)0.50(AsF6)0.50, and [(C6H11NC)2Au](PF6)0.25(AsF6)0.75 are vapochromic, whereas the yellow crystals of [(C6H11NC)2Au](PF6)0.50(SbF6)0.50 and [(C6H11NC)2Au](AsF6)0.50(SbF6)0.50 are not.

Two heads are better than one: improving magnetic relaxation in the dysprosium metallocene upon dimerization by use of an exceptionally weakly-coordinating anion.

Partial metathesis between two weakly-coordinating anions in the archetypical dysprosium metallocene results in the first example of [BPh4]- as a bridging ligand in 4f metals, with a unique η2,η2:η2,η2-bridge. Magnetic susceptibility and relaxation dynamics studies along with ab initio calculations reveal improved slow relaxation of the magnetization in over its mononuclear congener, resulting in an energy barrier of 490 K/340 cm-1 and waist-restricted hysteresis up to 6.5 K.

Lewis acid-base synergistic catalysis of cationic halogen-bonding-donors with nucleophilic counter anions.

Cationic halogen-bonding-donors with little or non-coordinating counter anions have attracted great attention as new Lewis acid type organocatalysts. However, these anions cannot function as nucleophilic activation sites due to their low Lewis basicity. In this study, 1,3,4-triaryl-5-iodotriazolium iodides have been developed as bifunctional catalysts for simultaneous activation of nucleophiles and electrophiles. Computational and experimental studies indicated that the nucleophilicity of the counter anions plays an important role in achieving high catalytic efficiency for the cyanosilylation of aldehydes. In addition, the first report on carbon dioxide fixation by XB-donors is described.

Regioselective B(3,4)-H arylation of o-carboranes by weak amide coordination at room temperature.

Palladium-catalyzed regioselective di- or mono-arylation of o-carboranes was achieved using weakly coordinating amides at room temperature. Therefore, a series of B(3,4)-diarylated and B(3)-monoarylated o-carboranes anchored with valuable functional groups were accessed for the first time. This strategy provided an efficient approach for the selective activation of B(3,4)–H bonds for regioselective functionalizations of o-carboranes.

Bis{2,6-bis[(E)-(4-fluorobenzylimino)methyl]pyridine}nickel(II) dinitrate dihydrate

In the title hydrated salt, [Ni(C21H17F2N3)2](NO3)2·2H2O, the central NiII ion is coordinated by six N atoms from two tridentate chelating 2,6-bis[(E)-(4-fluorobenzylimino)methyl]pyridine ligands. While the central NiII ion is six-coordinate, its environment is distorted from an octahedral structure because of the unequal Ni—N distances. The Ni—N bond lengths vary from 1.8642 (14) to 2.2131 (15) Å, while the N—Ni—N angles range from 79.98 (6) to 104.44 (6)°. Three coordinating sites of each chelating agent are almost coplanar with respect to the pyridine ring, and two pyridine moieties are perpendicular to each other. Two non-coordinating nitrate anions within the asymmetric unit balance the charges of the central metal ion, and are linked with two crystal water molecules, forming a water–nitrate cyclic tetrameric unit [O...O = 2.813 (2) to 3.062 (2) Å]. In an isolated molecule, the fluorophenyl rings of one ligand are stacked with the central ring of the other ligand via π–π interactions, with the closest centroid-to-plane distances being 3.359 (6), 3.408 (5), 3.757 (6) and 3.659 (5) Å.

Strongly Coordinating Ligands To Form Weakly Coordinating Yet Functional Organometallic Anions.

Weakly coordinating anions (WCAs) are generally tailored to act as spectators with little or no function. Here we describe the implementation of strongly coordinating dianionic carboranyl N-heterocyclic carbenes (NHCs) to create organometallic -ate complexes of Au(I) that serve both as WCAs and functional catalysts. These organometallic WCAs can be utilized to form both heterobimetallic (Au(I)-/Ag(I)+; Au(I)-/Ir(I)+) and organometallic/main group ion pairs (Au(I)-/(CPh3+ or SiEt3+). Because parent unfunctionalized dianionic carboranyl NHC complex 3 is unstable in most solvents when paired with CPh3+, novel synthesis methodology was devised to create polyhalogenated carboranyl NHCs, which show superior stability toward electrophilic substitution and cyclometalation chemistry. Additionally, the WCAs containing polyhalogenated carboranyl NHCs are among the most active catalysts reported for the hydroamination of alkynes. This investigation has also produced the first examples of a low-coordinate Au(III) center with two cis accessible coordination sites and the first true dianionic carbene. These studies pave the way for the design of functional ion pairs that have the potential to participate in tandem or cooperative small-molecule activation and catalysis.

Antibacterial Activities of Transition Metal complexes of Mesocyclic Amidine 1,4-diazacycloheptane (DACH)

AbstractThe titled compound 1,4-diazacycloheptane have vibrational freedom which allows it to coordinate to metal through 1st and 4th positions. Copper (II) and Nickel (II) complexes of DACH were prepared and characterized through UV-Visible, FT-IR, elemental analyses, conductance, and magnetic susceptibilities and compared to the results published in Inorg. Chem., 8(3), 528 (1969). The prepared complexes bearing different coordinating or non-coordinating anions were screened against four different pathogenic bacterial strains to study anionic effect on antibacterial activity. The MIC values of all the compounds suggest that [Cu(DACH)2Br2] is almost inactive against the tested microbes except Staph aureus. Rest of the metal complexes are active at their respective MIC values.

Anion control in the complexation of cucurbit[6]uril with Cu(II) salts

Based on the coordination ability of SCN−, Cl− and NO3–, three coordination complexes, namely, (C36H36N24O12)·{Cu[(SCN)4(H3O)]}2·2(H3O)·35H2O (1), {(C36H36N24O12)·[CuCl(H2O)3]2}·2Cl·10H2O (2), {(C36H36N24O12)·Cu2(H2O)5}·2(NO3)·2Cl·7H2O (3), have been synthesized through the reaction of cucurbit[6]uril (Q[6]) with transition metal ion Cu(II) at different anion conditions. In the structure of complex 1, the thiocyanate anion preferentially coordinate with the Cu(II) ion, which disables the Cu(II) ion to coordinate directly with the Q[6]. For the complex 2, the chloride anion enhances the coordination ability of the Q[6] to the Cu(II) ion, resulting a coordination tube of Q[6] with Cu(II) ion. In the case of complex 3, in the presence of the noncoordinating nitrate anion, the Cu(II) ion coordinate directly with the Q[6], generating a discrete binuclear complex. These structures unequivocally indicate that the coordinative nature of the anions is the key factor controlling the complexation of Q[6] with Cu(II) ion.

Ruthenium(II)‐Catalyzed Homocoupling of Weakly Coordinating Sulfoxonium Ylides via C−H Activation/Annulations: Synthesis of Functionalized Isocoumarins

AbstractHomocoupling of weakly coordinating sulfoxonium ylides was accomplished via ruthenium (II) catalyzed C−H activation process. This strategy provides a convenient, efficient and step‐economic method to access 3‐substituted isocoumarins with good functional group tolerance. The sulfoxonium ylide acts both as the convenient aromatic substrate and the acylmethylation reagent in this transformation. Moreover, the products could be transformed to diverse valuable derivatives.magnified image

The synthesis and structure of pyridine-oxadiazole iridium complexes and catalytic applications: Non-coordinating-anion-tuned selective C[sbnd]N bond formation

Several novel pyridine-oxadiazole iridium complexes were synthesized and characterized through X-ray crystallography. The designed iridium complexes revealed surprisingly high catalytic activity in CN bondformation of amides and benzyl alcohols with the assistance of non-coordinating anions. In an attempt to achieve borrowing hydrogen reactions of amides with benzyl alcohols, N,N'-(phenylmethylene)dibenzamide products were unexpectedly isolated under non-coordinating anion conditions, whereas N-benzylbenzamide products were achieved in the absence of non-coordinating anions. The mechanism explorations excluded the possibility of "silver effect" (silver-assisted or bimetallic catalysis) and revealed that the reactivity of iridium catalyst was varied by non-coordinating anions. This work provided a convenient and useful methodology that allowed the iridium complex to be a chemoselective catalyst and demonstrated the first example of non-coordinating-anion-tuned selective CN bond formation