Search

With the objective of gaining insight into the modulation of the reduction potential of the Ni(II / I) couple, we have synthesized two mononuclear nickel(II) complexes, NiLen (H2Len = N,N′-bis(3-methoxysalicylidene)-1,2-diamino-2-methylpropane) and NiLpn (H2Lpn = N,N′-bis(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane) of two N2O4 donor ligands and recorded their cyclic voltammograms. Both the nickel complexes show reversible reduction processes for the Ni(II / I) couple in acetonitrile solution but the reduction potential of NiLpn (E1/2 = −1.883 V) is 188 mV more positive than that of NiLen (E1/2 = −2.071 V). In the presence of redox inactive metal ions (Li+, Na+, K+, Mg2+, Ca2+ and Ba2+), the reduction potentials are shifted by 49–331 mV and 99–435 mV towards positive values compared to NiLen and NiLpn, respectively. The shift increases with the decrease of the pKa of the respective aqua-complexes of the metal ion but is poorly co-linear; however, better linearity is found when the shift of the mono- and bi-positive metal ion aqua complexes is plotted separately. Spectrophotometric titrations of these two nickel complexes with the guest metal ions in acetonitrile showed a well-anchored isosbestic point in all cases, confirming the adduct formation of NiLen and NiLpn with the metal ions. Structural analysis of single crystals, [(NiLen)Li(H2O)2]·ClO4 (1), [(NiLpn)Li(H2O)]·ClO4 (2), [(NiLpn)2Na]·BF4 (3) and [(NiLpn)2Ba(H2O)(ClO4)]·ClO4 (4), also corroborates the heterometallic adduct formation. The orbital energies of the optimised heterometallic adducts from which electron transfers originated were calculated in order to explain the observed reduction process. A strong linear connection between the calculated orbital energies and the experimental E1/2 values was observed. According to MEP and 2D vector field plots, the largest shift for divalent metal ions is most likely caused by the local electric field that they impose in addition to Lewis acidity. [ABSTRACT FROM AUTHOR]

The reactions of the frustrated Lewis pair (F5C2)2SbCH2P(tBu)2 with oxygen, sulphur, selenium and tellurium led to the mono-oxidation products (F5C2)2SbCH2P(E)(tBu)2 (E = O, S, Se, Te). Further oxidation of these chalcogen adducts with tetrachloro-ortho-benzoquinone (o-chloranil) gave (F5C2)2Sb(CH2)(μ-E)P(tBu)2·CatCl (CatCl = o-O2C6Cl4) with a central four-membered ring heterocycle for E = O, S, and Se. For E = Te the elimination of elemental tellurium led to an oxidation product with two equivalents of o-chloranil, (F5C2)2SbCH2P(tBu)2·2CatCl, which is also accessible by reaction of (F5C2)2SbCH2P(tBu)2 with o-chloranil. The synthesised compounds were characterised by NMR spectroscopy and X-ray structure analyses, and the structural properties were analysed in the light of the altered Lewis acidity due to the oxidation of the antimony atoms. [ABSTRACT FROM AUTHOR]

Flexible poly-Lewis acids (PLA) based on the tribenzotriquinacene (TBTQ) scaffold have been synthesised. Hydrosilylation of 4b,8b,12b-triallyltribenzotriquinacene and subsequent exchange of the chlorine substituents with weaker coordinating triflate groups afforded a novel triple silyl-functionalised PLA. By regioselective hydroboration of triallyl–TBTQ with various organoboranes, PLAs with different Lewis acidities were obtained. The synthesised PLAs were combined with neutral bases in host–guest experiments. DOSY NMR spectroscopy was performed to elucidate the complexation process in solution. These experiments revealed a highly dynamic interaction between the boron-functionalised PLA and triazine. However, the addition of one equivalent of tris(dimethylphosphino(methyl))phenylsilane led to the formation of a 1 : 1 adduct, which was confirmed by diffusion experiments. [ABSTRACT FROM AUTHOR]

In the present era, the fixation of atmospheric CO2 is of significant importance and plays a crucial role in maintaining the balance of carbon and energy flow within ecosystems. Generally, CO2 fixation is carried out by autotrophic organisms; however, the scientific community has paid substantial attention to execute this process in laboratory. In this report, we synthesized two carbonato-bridged trinuclear copper(II) complexes, [Cu3(L1)3(μ3-CO3)](ClO4)3 (1) and [Cu3(L2)3(μ3-CO3)](ClO4)3 (2) via atmospheric fixation of CO2 starting with Cu(ClO4)2·6H2O and easily accessible pyridine/pyrazine-based N4 donor Schiff base ligands L1 and L2, respectively. Under very similar reaction conditions, the ligand framework embedded with the phenolate moiety (HL3) fails to do so because of the reduction of the Lewis acidity of the metal center, inhibiting the formation of a reactive hydroxide bound copper(II) species, which is required for the fixation of atmospheric CO2. X-ray crystal structures display that carbonate-oxygen atoms bridge three copper(II) centers in μ3syn–anti disposition in 1 and 2, whereas [Cu(HL3)(ClO4)] (3) is a mononuclear complex. Interestingly, we also isolated an important intermediate of atmospheric CO2 fixation and structurally characterized it as an anti–anti μ2 carbonato-bridged dinuclear copper(II) complex, [Cu2(L2)2(μ2-CO3)](ClO4)2·MeOH (2-I), providing an in-depth understanding of CO2 fixation in these systems. Variable temperature magnetic susceptibility measurement suggests ferromagnetic interactions between the metal centers in both 1 and 2, and the results have been further supported by DFT calculations. The catalytic efficiency of our synthesized complexes 1–3 was checked by means of catechol oxidase and phenoxazinone synthase-like activities. While complexes 1 and 2 showed oxidase-like activity for aerobic oxidation of o-aminophenol and 3,5-di-tert-butylcatechol, complex 3 was found to be feebly active. ESI mass spectrometry revealed that the oxidation reaction proceeds through the formation of complex–substrate intermediations and was further substantiated by DFT calculations. Moreover, active catalysts 1 and 2 were effectively utilized for the base-free oxidation of benzylic alcohols in the presence of air as a green and sustainable oxidant and catalytic amount of TEMPO in acetonitrile. Various substituted benzylic alcohols smoothly converted to their corresponding aldehydes under very mild conditions and ambient temperature. The present catalytic protocol showcases its environmental sustainability by producing minimal waste. [ABSTRACT FROM AUTHOR]

Vinylidene rearrangement of alkynes is a well-established and powerful method for alkyne transformations, while use of borylalkynes has remained largely unexplored. This paper describes vinylidene rearrangements of internal borylalkynes using a cationic ruthenium complex. This rearrangement is applicable to alkynes with both tri-(B(pin), B(dan)) and tetracoordinate (B(mida)) boryl groups, and the reaction rate is dramatically affected by the Lewis acidity of the boryl group. Mechanistic study revealed that the rearrangement proceeds via 1,2-boryl migration regardless of the coordination number of the boron center. The migration mode was elucidated by theoretical calculations to indicate that the migration of the tricoordinate boryl groups is an electrophilic process in contrast to the previous vinylidene rearrangements of internal alkynes with two carbon substituents. [ABSTRACT FROM AUTHOR]

Hexadentate poly-Lewis acids (PLA) based on the bowl-shaped tribenzotriquinacene (TBTQ) have been synthesised. The introduction of three n-propyl groups into the benzhydrylic positions of the TBTQ backbone has significantly increased the solubility of the subsequently derived compounds. Semi-flexible PLAs containing boron and aluminium were obtained by hydrometallation of the corresponding 2,3,6,7,10,11-hexaalkynyl-TBTQ. Other rigid hexadentate PLAs were synthesised by stannylation of the corresponding alkyne units with Me3SnNMe2 followed by tin-element exchange reactions. The Lewis acidity of these PLAs was investigated in host–guest experiments with pyridine. Further experiments with bidentate bases showed correlations between their flexibility, their Lewis basicity and the complexation behaviour towards the synthesised PLAs. Addition of bis((dimethylphosphino)methyl)dimethylsilane (BisPhos) to solutions of the rigid alkynyl PLAs led to the formation of 3 : 1 adducts. Single crystal X-ray diffraction was used to further elucidate the host–guest connectivtiy. In addition, a sixfold pnictogen-bonding donor was synthesised by tin-antimony exchange. [ABSTRACT FROM AUTHOR]

This manuscript describes the syntheses, structures and magnetism of MnIII–CaII/SrII complexes which are compositionally relevant in the context of the oxygen evolving complex (OEC) of photosystem II (PS II). A series of trimetallic tetraoxo complexes containing redox-inactive metal ions CaII or SrII were synthesized using a tetranucleating ligand framework. The structural characteristics of these complexes, with the oxido ligands bridging the redox-inactive metals and the manganese centres, make them particularly relevant to biological and heterogeneous metal-oxido clusters. Electrochemical studies of these compounds show that the reduction potentials are highly dependent upon the Lewis acidity of the redox-inactive metal, identifying the chemical basis for the observed differences in electrochemistry. This correlation provides insights into the role of the CaII/SrII ion in modulating the redox potential of the OEC and of other redox-inactive ions in tuning the redox potentials of other metal-oxide electrocatalysts. Temperature dependent magnetic measurements have also been performed for the complexes. [ABSTRACT FROM AUTHOR]

This manuscript describes the syntheses, structures and magnetism of MnIII–CaII/SrII complexes which are compositionally relevant in the context of the oxygen evolving complex (OEC) of photosystem II (PS II). A series of trimetallic tetraoxo complexes containing redox-inactive metal ions CaII or SrII were synthesized using a tetranucleating ligand framework. The structural characteristics of these complexes, with the oxido ligands bridging the redox-inactive metals and the manganese centres, make them particularly relevant to biological and heterogeneous metal-oxido clusters. Electrochemical studies of these compounds show that the reduction potentials are highly dependent upon the Lewis acidity of the redox-inactive metal, identifying the chemical basis for the observed differences in electrochemistry. This correlation provides insights into the role of the CaII/SrII ion in modulating the redox potential of the OEC and of other redox-inactive ions in tuning the redox potentials of other metal-oxide electrocatalysts. Temperature dependent magnetic measurements have also been performed for the complexes. [ABSTRACT FROM AUTHOR]

Coordination chemistry and frustrated Lewis pair (FLP) chemistry have been most commonly studied using monodentate Lewis acids. In this paper, we examine the corresponding reactions employing the 1,1- and 1,2-bis-boranes, PhCH2CH(B(C6F5)2)21 and Me3SiCH(B(C6F5)2)CH2B(C6F5)22, respectively. Coordination of isocyanide to these species results in the formation of the products RCH(B(C6F5)2CNtBu)CH2(B(C6F5)2CNtBu) (R = Ph 3, Me3Si 4). The rearrangement of 1 to give the 1,2-bis-borane adduct 3 was probed and attributed to a donor-induced retrohydroboration and subsequent hydroboration. The analogous reaction of 1 is evident in efforts to use the Gutman–Beckett method to assess its Lewis acidity. However, in combination with tBu3P, bis-boranes 1 and 2 form FLPs and react with H2 to give [tBu3PH][PhCH2CH(B(C6F5)2)2(μ-H)] 5a and [tBu3PH][Me3SiCH(B(C6F5)2)CH2(B(C6F5)2)(μ-H)] 6, respectively. Reactions of 1 and 2 with various donors and PhCCH were shown to give deprotonation and addition products, depending on the nature of the base. However, in the case of 1, products resulting from retrohydroboration, and subsequent hydroboration are evident. Several of these alkyne products are crystallographically characterized. [ABSTRACT FROM AUTHOR]

A set of N-coordinated tellurium(II) compounds containing either C,N-chelating ligands CNR (where CN = 2-(RN＝CH)C6H4, R = tBu or Dipp; Dipp = 2,6-iPr2C6H3) or N,C,N pincer ligands NCNR (where NCN = 2,6-(RN＝CH)2C6H4, R = tBu or Dipp) were synthesized. In the case of C,N-chelated compounds, the reaction of CNDippLi with Te(dtc)2 (where dtc = Et2NCS2) in a 1 : 1 molar ratio smoothly provided the carbamate CNDippTe(dtc) which upon treatment with 2 eq. of HCl provided the chloride CNDippTeCl. In contrast, the analogous conversion of NCNRLi with Te(dtc)2 surprisingly furnished ionic bromides [NCNRTe]Br as a result of the exchange of dtc by Br coming from nBuBr present in the reaction mixture. Furthermore, the reaction of CNDippTeCl or [NCNRTe]Br with silver salts AgX (X = OTf or SbF6) provided the expected tellurenium cations [CNDippTe]SbF6 and [NCNRTe]X. To further increase the Lewis acidity of the central atom, the oxidation of selected compounds with 1 eq. of SO2Cl2 was examined yielding stable compounds [CNtBuTeCl2]X and [NCNtBuTeCl2]X. The oxidation of the Dipp substituted compounds proved to be more challenging and an excess of SO2Cl2 was necessary to obtain the oxidized products [CNDippTeCl2]SbF6 and [NCNDippTeCl2]SbF6, which could solely be characterized in solution. Compounds [CNtBuTeCl2]OTf and [NCNtBuTeCl2]OTf were shown to undergo a controlled hydrolysis to the corresponding telluroxanes. All compounds were studied by multinuclear NMR spectroscopy in solution and for selected compounds solid state 125Te NMR spectroscopy and single-crystal X-ray diffraction analysis were performed. The Lewis acidity of the studied cations was examined by the Gutmann–Beckett method using Et3PO as the probing agent. The Te–N chalcogen bonding situation of selected compounds has also been examined computationally by a set of real-space bonding indicators. [ABSTRACT FROM AUTHOR]

We present the synthesis and characterization of an Sb(III) monocation salt stabilized by a bulky bis(imino)dihydroacridanide pincer ligand. The Lewis acidity of the Sb cation is quantified using the Guttmann-Beckett method and confirmed by its reaction with 4-dimethylaminopyridine, which forms a Lewis acid–base adduct. This Sb cation exhibits catalytic activity in the cyanosilylation of arylketones. The electronic structure of the Sb cation as well as the mechanism of the catalytic transformation are explored by density functional theory computations. [ABSTRACT FROM AUTHOR]

It was first reported almost two decades ago that ligands with azo functions are capable of accepting electron(s) upon coordination to produce azo-anion radical complexes, thereby exhibiting redox non-innocence. Over the past two decades, there have been numerous reports of such complexes along with their structures and diverse characteristics. The ability of a coordinated azo function to accept one or more electron(s), thereby acting as an electron reservoir, is currently employed to carry out electron transfer catalysis since they can undergo redox transformation at mild potentials due to the presence of energetically accessible energy levels. The cooperative involvement of redox non-innocent ligand(s) containing an azo group and the coordinated metal centre can adjust and modulate the Lewis acidity of the latter through selective ligand-centred redox events, thereby manipulating the capacity of the metal centre to bind to the substrate. We have summarized the list of first row transition metal complexes of iron, cobalt, nickel, copper and zinc with redox non-innocent ligands incorporating an azo function that have been exploited as electron transfer catalysts to effectuate sustainable synthesis of a wide variety of useful chemicals. These include ketazines, pyrimidines, benzothiazole, benzoxazoles, N-acyl hydrazones, quinazoline-4(3)H-ones, C-3 alkylated indoles, N-alkylated anilines and N-alkylated heteroamines. The reaction pathways, as demonstrated by catalytic loops, reveal that the azo function of a coordinated ligand can act as an electron sink in the initial steps to bring about alcohol oxidation and thereafter, they serve as an electron pool to produce the final products either via HAT or PCET processes. [ABSTRACT FROM AUTHOR]

Reactions of tris(ortho-carboranyl)borane with Lewis bases reveals only small bases bind. The tremendous bulk and Lewis acidity is leveraged in frustrated Lewis pair Si–H cleavage with a wider range of Lewis bases and greater efficacy than B(C6F5)3. [ABSTRACT FROM AUTHOR]

Tricoordinate boron-incorporated π-conjugated systems are widely investigated as optoelectronic materials because of their unique p–π* orbital interactions and high Lewis acidity. Among them, thiophene-fused diborinines are characterized by moderate antiaromaticity and extended conjugation. In this work, we have developed two new dithienodiborinines with C2h and C2v symmetries, which exhibited completely different optical properties. The thiophene-fused diborinines synthesized in this study showed excellent fluorescence properties both in solution and in the solid state, with quantum yields of up to 95%. The high antiaromaticity enhanced the Lewis acidity of the boron centers, as proven by the large association constants with fluoride ion estimated from titration experiments. The high Lewis acidity and the superior luminescence property have enabled their application as fluorescent sensor materials for the detection of ammonia vapor. [ABSTRACT FROM AUTHOR]

Many complexes based on group 13 elements have been successfully applied as catalysts for the synthesis of cyclic carbonates from epoxides and CO2 and to date these have provided some of the most active catalysts developed. It is notable that most reports have focused on the use of aluminium-based compounds likely because of the well-established Lewis acidity of this element and its cost. In comparison, relatively little attention has been paid to the development of catalysts based on the heavier group 13 elements, despite their known Lewis acidic properties. This study describes the synthesis of aluminium, gallium and indium compounds supported by a readily prepared salphen ligand and explores both their comparative structures and also their potential as catalysts for the synthesis of cyclic carbonates. In addition, the halide ligand which forms a key part of the compound has been systematically varied and the effect of this change on the structure and catalytic activity is also discussed. It is demonstrated that the indium compounds are actually, and unexpectedly, the most active for cyclic carbonate synthesis, despite their lower Lewis acidity when compared to their aluminium congeners. The experimental observations from this work are fully supported by a Density Functional Theory (DFT) study, which provides important insights into the reasons as to why the indium catalyst with bromide, [InBr(salphen)], is most active. [ABSTRACT FROM AUTHOR]

The reactivity of biological or synthetic metalloenzymes is modulated in the presence of redox innocent Lewis acidic metal ions as they change the redox potential of the redox active metal ions present in the active site of metalloenzymes. To study this effect, we synthesised a mono-nuclear V(IV) complex (VOL, 1) with an N2O4 donor bicompartmental ligand, characterized it by single-crystal X-ray crystallography and recorded its cyclic voltammogram in acetonitrile. The CV revealed a reversible redox process for the V(IV)/V(V) couple. The potential of the V(IV)/V(V) couple shifted to a more positive value when equivalent amounts of Li+, Na+, K+, Mg2+, Ca2+ and Ba2+ ions were added separately to its acetonitrile solution, but the extent of shift for Li+ and Mg2+ was much less than that of the other metal ions. The guest metal ions except Li+ and Mg2+ were accommodated in the outer compartment of VOL as confirmed by IR and UV-Vis spectral analysis. Single-crystal structural analysis of [(VOL)KPF6]2, (1·K) and [(VOL)Ba (ClO4)2(H2O)]n, (1·Ba) also confirmed the hetero-metallic adduct formation. The correlation of the shift of the V(IV/V) redox potential with the Lewis acidity of respective metal ions deviated appreciably from linearity. DFT calculations suggest that the shift in potential is probably controlled by local electric fields induced by those ions, as indicated by 2D vector electric field maps. [ABSTRACT FROM AUTHOR]

The cycloaddition reaction of CO2 to epoxides is quite promising for CO2 capture and storage as well as the production of value-added fine chemicals. Herein, a novel atomically precise lead-doped titanium-oxide cluster with the formula Ti10Pb2O16(phen)4(Ac)12(DMF)2 (denoted as Ti10Pb2; phen = 1,10-phenanthroline; Ac = acetate; DMF = dimethylformamide) was synthesized through a facile solvothermal process, and is a molecular photocatalyst with surface-anchored main-group metal active sites. Its structure was characterized by single-crystal X-ray diffraction and other complementary techniques. Ti10Pb2 showed high photo-response and charge-separation efficiency under simulated sunlight irradiation. Ti10Pb2 was successfully used in the cycloaddition reaction of CO2 with epoxides under solvent-free conditions. While its catalytic activity due to the Lewis acidity was moderate, simulated solar light irradiation further enhanced the reaction rate, demonstrating the synergistic effect of photocatalysis and Lewis-acid thermocatalysis. [ABSTRACT FROM AUTHOR]

A series of fluorinated triaryl borates B(OArF)3 (ArF = 2-FC6H4, 3-FC6H4, 4-FC6H4, 2,4-F2C6H3, 3,5-F2C6H3, 2,3,4-F3C6H2, 2,4,6-F3C6H2, 3,4,5-F3C6H2) have been prepared and isolated from the reactions of the mono-, di-, or tri-fluorophenol with BCl3. The Lewis acidity of these borates has been determined by NMR spectroscopic and theoretical methods and compared to their well-established borane counterpart. [ABSTRACT FROM AUTHOR]

Pnictogen-mediated Lewis acidity is an emerging research subject in organic chemistry, supramolecular chemistry, etc. In contrast to the extensive studies on phosphorus and antimony, the diversity of arsenic-Lewis acids was quite limited. Herein, tetrachlorocatecholates of triarylarsines were newly synthesized. Their structures, electronic properties, and Lewis acidities were experimentally and computationally examined and compared with the corresponding phosphorus and antimony analogs. This is the first systematic study on the relationship between the structure and Lewis acidity of arsenic-mediated Lewis acids. [ABSTRACT FROM AUTHOR]

The synthesis of 1-silolyl and 1-germolyl triflates from the corresponding chlorides by salt metathesis reaction is reported. These covalent triflates are ideal starting materials for the preparation of ionic silolyl- and germolyl-imidazolium triflates by their reaction with N-heterocyclic carbenes. Similarily, ionic silolyl- and germolyl-oxophosphonium triflates are obtained by substitution of the triflate group by triethylphosphane oxide Et3PO. The analysis of their 31P NMR chemical shifts according to the Gutmann–Beckett method reveal the high Lewis acidity of the underlying silolyl and germolyl cations. Further analysis of structural and NMR parameters of the silolyl- and germolyl-imidazolium and oxophosphonium triflates indicates that these compounds are covalently bonded silole and germole derivatives with insignificant contributions from silolyl- or germolyl cations. Silolyl and germolyl triflates are however synthetic equivalents of these cations and might serve as a source for electrophilic silolyl and germolyl units. [ABSTRACT FROM AUTHOR]

Heterobimetallic Ln(III)–Pd(0) complexes (Ln = Y, Sm, Gd, Yb) featuring tetranuclear structures with COD as bridges were obtained via the metallation of tris(phosphinoamido) rare-earth metal complexes [Ph2PNAd]3Ln (Ad = adamantyl) with (COD)Pd(CH2SiMe3)2. Notably, the Sc(III)–Pd(0) complex possesses a C3-symmetry with a very short Sc–Pd bond length of 2.432(2) Å, while the tetranuclear complexes exhibited versatile structures both in solution and in the solid state. Reduction of the trivalent complex (Ph2PNAd)3Yb with one equivalent of KC8 in the presence of 18-c-6 afforded the divalent complex [(Ph2PNAd)3Yb][(18-c-6)K(THF)2], which was further reacted with (Ph3P)4Pd to form the first Yb(II)–Pd(0) complex. The Pd(0) → Yb dative interaction weakened significantly from Yb(III) to Yb(II) based on computational studies, which was attributed to the attenuated Lewis acidity of the Yb(II) center. Reactions of Ln(III)–Pd(0) complexes (Ln = Sc and Yb) with the disulfide PhSSPh showed that the Pd(0) center served as a two-electron donor while the reaction apparently occurred on the Ln(III) centers to form Ln(III)–Pd(0) bis-sulfide complexes. [ABSTRACT FROM AUTHOR]

The bidentate silicon-based Lewis acid, bis(dimethyl-(trifluoromethylsulfonyl)silylethyl)dimethylsilane, Me2Si[(CH2)2SiMe2OTf]2, was prepared in a two-step synthesis starting from dimethyldivinylsilane by hydrosilylation with dimethylchlorosilane and subsequent Lewis acidity enhancement of the terminal silicon atoms by substituting the chlorine with triflate groups using silver triflate. The potential of the resulting Me2Si[(CH2)2SiMe2OTf]2 for binding of Lewis basic guests was explored in reactions with monoand bifunctional aromatic nitrogen bases. A 1 : 2-adduct with pyridine and a 2 : 2-adduct with 4,4'-bipyridine was structurally characterised in the solid state. In solution, diffusion NMR spectroscopy revealed the existence of complex dynamic equilibria of oligomers which are formed by the host with bidentate guests. The size of the oligomers is significantly determined by the spatial arrangement of the docking sites within the guests and depends on the host-guest ratio. [ABSTRACT FROM AUTHOR]

The effective monitoring of water pollution and further purification are pressing yet challenging issues for guaranteeing the health of human beings and the stabilization of ecological systems. For this purpose, the development of efficient sensing and adsorption materials as a result of supramolecular interactions, including coordination and H-bonding etc., have been attracting increasing attention. With the aid of a coordination-driven self-assembly strategy, a new nonporous 2D CuII coordination network, [Cu2L(H2O)2]n (donated as CuCP), based on H4L, where H4L = 4-(4-(3,5-di-carboxy-pyridin-4-yl)phenyl)pyridine-2,6-dicarboxylic acid, was afforded hydrothermally. Structural analysis indicated that CuCP featured a wrinkled network similar to the ancient Chinese folding screens and constructed by the fully deprotonated ligand L4− with the coordination mode of bis(μ2-η1:η1:η2) and penta-coordinated Cu2+, which could be further upgraded to a supramolecular 3D framework as a result of the synergism of multiple C–H⋯O hydrogen bonds. The hydrostability of CuCP could be maintained within a wide pH range from 2 to 12 as verified by PXRD determination, endowing it with potential environmental applications. Thanks to the combination of the soft Lewis acidity of Cu2+ and its large conjugated structure, CuCP could be used as a turn-on fluorescence sensor for S2− and exhibited a different fluorescence response when Na2S, (NH4)2S or H2S were incorporated, even in actual water samples. The sensing mechanisms were disclosed in detail by the combination of experiments and density functional theory (DFT) calculations. Furthermore, CuCP was shown to be a selective and recoverable adsorbent with a maximum adsorption capacity of 379 mg g−1 in 60 minutes for methylene blue (MB). The adsorption mechanism could be a combination of π⋯π stacking, n⋯π interaction, aggregation effects and Soft and Hard Acid–Base theory (HSAB). The results presented herein open up new perspectives for CuII species in environmental applications. [ABSTRACT FROM AUTHOR]

The synthesis of a variety of bis(catecholato)germanes is reported. The Lewis acidity of the bis(catecholato)germanes was assessed using the experimental Gutmann–Beckett method and computational FIA and GEI methods. The oligomerization of alkenes using bis(catecholato)germanes demonstrates the use of these complexes in catalysis. The use of donor additives in the dimerization of α-methylstyrene resulted in selectivity control comparable to transition metal catalyst systems. [ABSTRACT FROM AUTHOR]

In this frontier article some peculiar characteristics of Zn(salen)-type Schiff-base complexes are reviewed. The paper is mainly focused on the most recent and relevant achievements on responsive supramolecular nanostructures and sensing properties, both of them related to the Lewis acidic character of the ZnII centre in these molecular species, providing an interpretation of these features. The sensing properties of Zn(salen)-type complexes mainly originate from optical spectroscopic changes associated with the formation of the adducts upon addition of a Lewis base (analyte), either by deaggregation of dimeric species or displacement of the solvent coordinated to the metal centre. In both cases the direct sensing is related either to the Lewis acidic character of the complex as well as to the Lewis basicity of the analyte. The formation of responsive nanostructures with fluorescent, and/or vapochromic, mechanochromic, and thermochromic characteristics is driven by non-mutual intermolecular Zn⋯O interactions, further stabilized by π–π stacking interactions and/or interdigitation of the alkyl side groups. The Lewis acidic character is not a prerogative of Zn(salen)-type complexes of tetradentate Schiff-bases. Many other classes of ZnII complexes can possess this property. A correct interpretation of their chemistry is certainly useful for further development of these classical coordination compounds as new molecular materials. [ABSTRACT FROM AUTHOR]

Selective separation of light hydrocarbons (LHs) and adsorption of volatile organic compounds (VOCs) remain expensive and complex scientific challenges in the petrochemical industry. Shape-selective adsorbent materials can cost-effectively face these demands. Two new porous, dynamic and amorphous metal–organic frameworks (MOFs), NEU-3 [= Zn(PMDA)(Py)2] and NEU-4 [= Fe(PMDA)(Py)2] are disclosed. These MOFs along with NEU-1c [= Zn(BPDI)(Py)2] and NEU-2 [= Fe(BPDI)(Py)2] display an electron-deficient pore surface due to predesigned π-electron-deficient ligands. They are unique smart guest-responsive materials owing to their π Lewis acidic pore surface and presumably their framework flexibility. A variety of effective adsorptions and adsorptive separations is achieved by using beds of NEU-1c, NEU-2, NEU-3 and NEU-4. Promising for further investigations into the petrochemical industry, NEU-4 shows ultrahigh benzene adsorption, recognition capability, selectivity for benzene over its analogues, and high stability and regenerability. [ABSTRACT FROM AUTHOR]

The kinetics of hydrolysis of dimethyl nitrophenyl phosphate (DMNP), a simulant of the nerve agent Soman, was studied and revealed transition metal salts as catalysts. The relative rates of DMNP hydrolysis by zirconium and hafnium chlorides are in accordance with their Lewis acidity. In situ conversion of zirconium chloride to zirconium oxy-hydroxide was identified as the key step. We propose a precursor-MOF activity relationship. [ABSTRACT FROM AUTHOR]

The crystal structure of [Al(tBu-salen)]2O·HCl shows major changes compared to that of [Al(tBu-salen)]2O. The additional proton is localized on the bridging oxygen atom, making the aluminium atoms more electron deficient. As a result, a water molecule coordinates to one of the aluminium atoms, which becomes six-coordinate. This pushes the salen ligand associated with the six-coordinate aluminium ion closer to the other salen ligand and results in the geometry around the five-coordinate aluminium atom becoming more trigonal bipyramidal. These results experimentally mirror the predications of DFT calculations on the interaction of [Al(tBu-salen)]2O and related complexes with carbon dioxide. Variable temperature NMR studies of protonated [Al(tBu-salen)]2O complexes revealed that the structures were dynamic and could be explained on the basis of an intramolecular rearrangement in which the non-salen substituent of a five-coordinate aluminium(tBu-salen) unit migrates from one face of a square based pyramidal structure to the other via the formation of structures with trigonal bipyramidal geometries. Protonated [Al(tBu-salen)]2O complexes were shown to have enhanced Lewis acidity relative to [Al(tBu-salen)]2O, coordinating to water, dioxane and 1,2-epoxyhexane. Coordinated epoxyhexane was activated towards ring-opening, to give various species which remained coordinated to the aluminium centers. The protonated [Al(tBu-salen)]2O complexes catalysed the synthesis of cyclic carbonates from epoxides and carbon dioxide both in the presence and absence of tetrabutylammonium bromide as a nucleophilic cocatalyst. The catalytic activity was principally determined by the nature of the nucleophilic species within the catalyst structure rather than by changes to the Lewis acidity of the metal centers. [ABSTRACT FROM AUTHOR]

The rare-earth elements (Ln = Sc, Y, La–Lu) are widely used in stoichiometric and catalytic carbonyl group transformations. Sufficient availability, non-toxicity, high oxophilicity, tunable ion size/Lewis acidity and enhanced ligand exchangeability have been major driving factors for their successful implementation. Routinely employed reagents for stoichiometric carbonyl group transformations are divalent ytterbium and samarium compounds (e.g., ketone reduction), bimetallic CeCl3/LiR (C–C coupling), or ceric ammonium nitrate CAN (cyclic ketone oxidation). Rare-earth-metal triflates, and in particular Sc(OTf)3, are prominent examples of Lewis acid catalysts for versatile use in organic synthesis (e.g., Aldol and Michael reactions). Moreover, Ln(II) and Ln(III) complexes efficiently catalyze the (co)polymerization of carbonyl group-containing monomers including lactones, lactides, acrylates, and carbon dioxide. Featuring the most notorious greenhouse gas, CO2 is currently assessed as a cheap, abundant, and non-toxic C1 building block. Ln(III) complexes are not only capable of efficient CO2 capture via reversible insertion but also of CO2 activation for catalytic conversions (copolymerization/cycloaddition with epoxides). This perspective focuses on structurally elucidated Ln complexes resulting from ketone or carbonyl derivative activation/insertion as well as carbon dioxide insertion products. The respective compounds will be sorted by structural motifs and, if applicable, details on reactivity and feasibility of catalytic reactions are presented. The article is subdivided in three parts: (i) donor and insertion products of ketones and aldehydes, (ii) redox-enhanced activation of carbonyl derivatives, and (iii) CO2 insertion/redox products and homogeneous catalytic conversion. [ABSTRACT FROM AUTHOR]

This perspective presents the design, synthesis and crystal structures of a large number of architectures constructed using assorted metalloligands of pyridine-2,6-dicarboxamide based ligands. The metalloligands offered various appended functional groups, whereas design strategies included varying both their position and number. A combination of these parameters resulted in the development of assorted architectures including discrete trinuclear and tetranuclear complexes as well as 1D/2D/3D coordination polymers. The metalloligand strategy not only assisted in the construction of ordered crystalline materials with varied dimensionalities but also judiciously allowed the incorporation of Lewis acidic and redox-active secondary metals in the resultant architectures. As a result, such designer architectures illustrated their noteworthy role both as homogenous and heterogeneous catalysts in different organic transformation reactions. [ABSTRACT FROM AUTHOR]

The synthesis and structural features of several families of unsolvated molecular complexes of the heavy alkaline earths (Ae = calcium, strontium and barium) supported by bis(phenolate)s or bis(fluoroalkoxide)s are described. These dianionic, multidentate ligands are built around diaza-macrocycles that contain either five or six N- and O-heteroatoms. Several of these complexes have been characterised by X-ray diffraction crystallography. A list of comparative features was drawn upon close examination of the molecular structures of these complexes. It highlights the subtle influences of the identity of the central Ae metal, denticity and nature -fluoroalkoxide vs. phenolate- of the anionic tethers in the ligands. All complexes are seven- or eight-coordinate. It is observed in particular that a decrease of the number of heteroatoms in the macrocyclic backbone of the ligand will be compensated by the establishment of intramolecular Ae⋯F interactions (accounting for ca. 3.8–6.4% of the pertaining coordination spheres according to bond valence sum analysis), dimerisation of the complex, or, in one case, solvent (thf) retention. Attempts to gauge the Lewis acidity in these series of complexes were carried out by three independent methods (Childs, Gutmann–Beckett and global electrophilicity index). However, conflicting results were obtained and no clear trend can be delineated, even if on the whole, these measurements concur to suggest relatively low Lewis acidity. [ABSTRACT FROM AUTHOR]

Two mixed-ligand metal–organic frameworks, [Zn2(BDHA)0.5(INA)3] (MOF-1: H2BDHA = benzene-1,4-dihydroxamic acid; HINA = isonicotinic acid) and [Co2(BDHA)0.5(INA)3(DMF)] (MOF-2), were solvothermally synthesized and fully characterized by single-crystal X-ray crystallography as well as N2, H2, and CO2 gas-sorption measurements. The results constitute the first detailed analysis of the bonding environment around the hydroxamates in such MOFs, which are simultaneously decorated with Lewis-basic sites from the hydroxamate moieties and metal sites predisposed for coordinative unsaturation. MOF-2 shows a desirably selective adsorption of CO2 relative to N2. [ABSTRACT FROM AUTHOR]

The basicity and acidity of solvent-treated layered double hydroxide (ST-LDHs) and their layered double oxides (ST-LDOs) have been fully studied using Hammett titration, in situ FTIR, CO2-TPD and NH3-TPD. Five solvents (ethanol, acetone, isopropanol, ethyl acetate and 1-hexanol) were selected to treat [Mg0.72Al0.28(OH)2](CO3)0.14 (Mg2.5Al-CO3 LDH) and compared with traditional LDH co-precipitated from water. The Brønsted basicity strength of the ST-LDHs and ST-LDOs increased but was accompanied by a decrease in basic site density. In addition, the Lewis acidity of ST-LDOs also changes significantly, with medium strength Lewis acid sites dissapearing after solvent treatment. We found that the CO2 capture capacity of solvent treated LDOs is 50% higher than that of traditional co-precipitated LDO sample. The ethanol treated LDO exhibited the highest CO2 uptake of 1.01 mmol g−1. The observed CO2 capture performance of the ST-LDOs correlates linearly with the ratio of total acid sites to total basic sites. [ABSTRACT FROM AUTHOR]

The 1,8-naphthalenediolate [1,8-O2C10H8] supported boronic and boric acid esters of general formula X-B(1,8-O2C10H8), where X = C6H5 (1a), C6F5 (2a), 3,4,5-F3-C6H2 (3a), 2,4,6-F3-C6H2 (4a), 2,6-F2-C6H3 (5a), 2,6-Cl2-C6H3 (6a), 2,4,6-Me3-C6H2 (7a), 2,6-(MeO)3-C6H3 (8a), Bun (9a), MeO (10a), OH (11a) and Cl (13a), were synthesized, NMR spectroscopically characterized, and the solid-state structures of 1a–5a, 8a and 10a determined by X-ray crystallography. The acceptor numbers of 1a–7a and 13a were determined and found to be similar to their catecholate analogues, R-Bcat, indicating similar Lewis acidities of these two classes of boronic acid esters. The reaction of B2(NMe2)4 with 1,8-naphthalenediol, followed by addition of HCl furnished the diboronic acid ester B2(1,8-O2C10H8)4 (16a) in ca. 70% yield. Cl-B(1,8-O2C10H8) (13a) was shown to react with O＝PEt3, DMAP, 1,10-phenanthroline and 2,2′-bipyridine, resp., to give the boronium salts [(Et3P＝O)2B(1,8-O2C10H8)]Cl (18a), [(DMAP)2B(1,8-O2C10H8)]Cl (22a), [(2,2′-bipyridine)B(1,8-O2C10H8)]Cl (23a) and [(1,10-phenanthroline)B(1,8-O2C10H8)]Cl (24a), which were characterized by NMR spectroscopy and X-ray crystallography. [ABSTRACT FROM AUTHOR]

Design and construction of stable adsorbents for efficient separation and purification of natural gas and C2H2 is fundamentally important in the chemical industry, and hierarchical cage-based MOFs are attractive in this regard due to their intrinsic structural advantages. In this work, a cage-based MOF (termed ZJNU-15) assembled from a tetranuclear Cu4O-based SBU and an amine-functionalized N,O-mixed donor ligand was solvothermally constructed. Single-crystal X-ray diffraction studies showed that the resulting MOF incorporates two different types of polyhedral cages in the entire network and bears incompatible open copper sites and uncoordinated amine groups immobilized in the pore surface. In view of its intriguing structural features, its gas adsorption properties with respect to C2 hydrocarbons, CO2, and CH4 were systematically investigated, revealing that it could achieve efficient removal of C2 hydrocarbons and CO2 from CH4 as well as separation of a binary C2H2–CO2 mixed gas, which is associated with natural gas and C2H2 separation and purification. At 298 K and 1 atm, for equimolar binary components, the IAST-predicted adsorption selectivities for C2 hydrocarbons over CH4 are above 17.7, while the CO2/CH4 and C2H2/CO2 adsorption selectivities are 5.0 and 4.4, respectively. Notably, stability studies showed that the framework maintained its structural integrity after being immersed in HCl/NaOH aqueous solutions within a pH range of 4–11 at ambient temperature for 24 h, indicating its good hydrolytic stability under harsh chemical conditions, which might lay a solid foundation for its practical applications. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of [Cu(Eind2-BPEP)][PF6] (2) (Eind2-BPEP = 2,6-bis(2-Eind-2-phosphaethenyl)pyridine, Eind = 1,1,3,3,5,5,7,7-octaethyl-1,2,3,5,6,7-hexahydro-s-indacen-4-yl), a three-coordinated Cu(I) complex bearing a PNP-pincer-type phosphaalkene ligand with bulky fused-ring Eind groups. The Gutmann–Beckett test revealed that complex 2 is highly Lewis acidic and comparable in strength to B(C6F5)3, which is a relatively strong Lewis acid. In addition, 2 is more Lewis acidic than [Cu(Mes*2-BPEP)][PF6] (3), the analogous complex with less-bulky Mes* instead of Eind groups. DFT calculations using model compounds revealed that the higher Lewis acidity of 2 compared to 3 is not due to the electronic effects of the ligand, but due to a reduction in the LUMO energy caused by the steric effect of the bulky Eind groups. When combined with a tertiary amine, the highly Lewis acidic and bulky 2 exhibits the reactivity of a frustrated Lewis pair (FLP) and can activate hydrogen and phenylacetylene. Complexes 2 and 3 were found to catalyze the hydrogenation and hydrosilylation of CO2 in the presence of DBU under relatively mild conditions. [ABSTRACT FROM AUTHOR]

Design and construction of stable adsorbents for efficient separation and purification of natural gas and C2H2 is fundamentally important in the chemical industry, and hierarchical cage-based MOFs are attractive in this regard due to their intrinsic structural advantages. In this work, a cage-based MOF (termed ZJNU-15) assembled from a tetranuclear Cu4O-based SBU and an amine-functionalized N,O-mixed donor ligand was solvothermally constructed. Single-crystal X-ray diffraction studies showed that the resulting MOF incorporates two different types of polyhedral cages in the entire network and bears incompatible open copper sites and uncoordinated amine groups immobilized in the pore surface. In view of its intriguing structural features, its gas adsorption properties with respect to C2 hydrocarbons, CO2, and CH4 were systematically investigated, revealing that it could achieve efficient removal of C2 hydrocarbons and CO2 from CH4 as well as separation of a binary C2H2–CO2 mixed gas, which is associated with natural gas and C2H2 separation and purification. At 298 K and 1 atm, for equimolar binary components, the IAST-predicted adsorption selectivities for C2 hydrocarbons over CH4 are above 17.7, while the CO2/CH4 and C2H2/CO2 adsorption selectivities are 5.0 and 4.4, respectively. Notably, stability studies showed that the framework maintained its structural integrity after being immersed in HCl/NaOH aqueous solutions within a pH range of 4–11 at ambient temperature for 24 h, indicating its good hydrolytic stability under harsh chemical conditions, which might lay a solid foundation for its practical applications. [ABSTRACT FROM AUTHOR]

The pentamethylcyclopentadienyl (Cp*) antimony(III) cations [Cp*2Sb][B(C6F5)4], [Cp2*Sb][OTf], [Cp*SbCl][B(C6F5)4] and [Cp*Sb][OTf]2 have been isolated and structurally characterised. [Cp*SbCl]+ forms dimers in the solid state via an intermolecular Sb–Cl interaction. Initial screening shows that [Cp*SbCl][B(C6F5)4] is significantly Lewis acidic and can catalyse the dimerisation of 1,1-diphenylethylene; [Cp2*Sb][B(C6F5)4] exhibits negligible Lewis acidity. Highly unstable [Cp*SbF][B(C6F5)4] could not be isolated, but stabilisation with the IMes ligand allowed isolation of [Cp*SbF(IMes)][B(C6F5)4]. Fluorodechlorination of CH2Cl2 and PhCCl3 was observed in the presence of crude [Cp*SbF][B(C6F5)4] in solution. A computational mechanistic investigation suggests that the latter proceeds via a carbocation intermediate. [ABSTRACT FROM AUTHOR]

FLPs, R2POBcat (R = tBu 1, Mes 2), are readily derived from the reactions of the corresponding phosphine oxides, nBuLi and ClBcat. Despite the poor Lewis acidity of boron, these species react with PhOH, CO2, CS2, PhNCO, MesCNO, O2, 9,10-phenanthrenedione, and diazomethanes to effect FLP addition reactions affording a series of heterocycles. The reaction of 1 with EtO2CCHN2 gives the bicyclic product, EtO2CCHN2(tBu2POBcat)2. High-level DFT calculations reveal that these cyclization processes proceed via 1,1-addition to the terminal N of diazomethane followed by 1,2-boron-migration affording the five membered rings. The reaction of the EtO2CCHN2 derivative with the second equivalent of FLP 1 is attributed to less steric demands. [ABSTRACT FROM AUTHOR]

The ring opening copolymerisation of CO2 and epoxides is a useful means to valorise waste emissions and to reduce pollution in polymer manufacturing. Heterodinuclear catalysts, particularly those of Zn(II)/Mg(II), have shown better performances than homodinuclear analogues in this reaction. As part of on-going efforts to better understand the catalytic synergy, this work describes a series of heterodinuclear complexes, combining Zn(II) with a metal from Group 13 (M = Al(III), Ga(III) or In(III)). The complexes are synthesised from a symmetrical macrocyclic ligand in high yields via sequential metalation steps and are the thermodynamic reaction products. The Zn(II)/Group 13 complexes are effective homogeneous catalysts for the ring opening copolymerisation (ROCOP) of cyclohexene oxide at 1 bar pressure of carbon dioxide, but all show inferior performances compared to the di-zinc analogue. The CO2 uptake into the polymer increases in the order Al(III) < Ga(III) < In(III) which is attributed to lower Lewis acidity heavier Group 13 homologues showing a reduced tendency to form ether linkages. Concurrently, polycarbonate activity increases down the Group 13 series consistent with weaker metal–oxygen bonds which show enhanced lability to insertion reactions. [ABSTRACT FROM AUTHOR]

Frustrated Lewis pairs (FLPs) featuring Lewis acid–base synergistic action have been recognized as one of the most powerful bifunctional catalytic systems. Each Lewis component, however, is usually composed of a single atom and hence lacks a cooperative effect. In this work, cluster FLPs (CFLPs) comprised of a triangularly Mo–Mo bonded Mo IV3 Lewis acidic cluster component and a Lewis basic SbIII partner in H[Sb III3 Mo IV3 Mo VI15 O55(OH)2py3] (1) have been developed. The more extensive cooperative actions both within Mo IV3 and between Mo IV3 and SbIII account for the excellent catalytic performance of 1, providing a new way of thinking for the designed synthesis of highly efficient FLP catalysts. [ABSTRACT FROM AUTHOR]

A metalloligand [CuL] (H2L = N-α-methylsalicylidene-N′-salicylidene-1,3-propanediamine) was reacted with a series (Li+, Na+, K+, Mg2+, Ca2+, Zn2+, Cd2+, Pr3+, Nd3+ and Sm3+) of redox-inactive metal ions (in excess) with different Lewis acidities in acetonitrile to form heterometallic complexes in situ. In the cases of K+ and Zn2+, single crystals were isolated from their respective solutions and solved. The complexes were found to be trinuclear with the phenoxido bridge between the redox-inactive metals and the copper center having closest equilibrium distance. In solution, some metal ions (Na+, K+, Mg2+ and Ca2+) formed predominantly 1 : 1 [CuL] : Mn+ adducts whereas others did not. Spectroscopic studies revealed that both the energy and intensity of the LMCT band of [CuL] at 363 nm were influenced by the Lewis acidity of the guest metal ions. The blue shift and the hypochromic shift of this band showed a linear dependence on the Lewis acidity of the corresponding redox-inactive metal ions only for 1 : 1 adducts. A combined EPR and d–d transition spectral analysis of these 1 : 1 adducts in acetonitrile at 298 K indicates that there is a change in the coordination geometry around Cu(II) on proximal cation binding of free [CuL]. The correlation of the half wave potential (E1/2) of the first oxidation of [CuL] with pKa of the corresponding metal(aqua)n+ ion as a measure of its Lewis acidity revealed that the potentials were linearly dependent for 1 : 1 adducts whereas in the case of the other metal ions an unexpected deviation from linearity was observed. An incremental addition of water to some of these mixtures revealed a decrease in the corresponding oxidation peak potential with a concomitant increase in the molar absorptivity. The molar absorptivities of different mixtures with their corresponding E1/2 values show a linear dependence with better correlation suggesting that the modulation of electron density around Cu(II) regulates the electrochemical oxidation of the metalloligand. [ABSTRACT FROM AUTHOR]

Due to their combined Lewis acidity and electron-donor capability, BII cations exhibit an interesting reactivity, which is almost unexplored so far. In this work, we compare the reduction in a dicationic diborane of a series of vicinal diones with different redox potentials, namely 3,5-di-tert-butylbenzoquinone, 3,4,5,6-tetrachlorobenzoquinone, 1,2-naphthalene-dione, 9,10-phenanthrene-dione, 2,2′-dichlorobenzil, benzil and 1,2-acenaphthylene-dione. The experimental work is complemented by quantum-chemical calculations, illuminating the electron-transfer step in the reactions. [ABSTRACT FROM AUTHOR]

The controlled assembly of early transition metals remains a challenging research target, especially with respect to the generation of heterometallic molecules and nanomaterials. In this study, metal chlorides of the early 4d/5d-transition-metals, i.e., ZrCl4, NbCl5, MoCl5, HfCl4, TaCl5, and WCl6, were stoichiometrically introduced into a tetraphenylmethane-core dendritic-phenylazomethine generation 4 dendrimer in the presence of an optimal amount of organic ligands such as pyridine and 3-chloropyridine. The coordinative interactions between the metal chlorides and the imines in the dendrimers indicated a positive correlation for the Lewis acidity of the metals. Moreover, it was clearly demonstrated for the first time that heterometallic assemblies of defined composition contain four kinds of early 4d/5d-transition-metals, such as TaV, NbV, MoV, and ZrIV, which was confirmed by UV-vis titration, XPS, and HAADF-STEM/EDS measurements. The results of this study should provide access to new routes to produce nanomaterials composed of heterometallic early 4d/5d-transition metals. [ABSTRACT FROM AUTHOR]

A porous Zr metal–organic framework, 1-PdBF4 [Zr6O4(OH)4(OAc)2.4{(PNNNP)Pd(MeCN)}2.4(BF4)2.4; PNNNP = 2,6-(HNPAr2)2C5H3N; Ar = p-C6H4CO2−], has been synthesized via postsynthetic oxidative I−/BF4− ligand exchange using NOBF4. 1-PdBF4 enjoys markedly superior catalytic activity and recyclability to its trifluoracetate-exchanged analogue, 1-PdTFA, for the intramolecular cyclization of o-alkynyl anilines and the carbonyl–ene cyclization of citronellal. Moreover, 1-PdBF4 demonstrates a rare example of pore selective catalysis for the cyclization of 2-ethynyl aniline. [ABSTRACT FROM AUTHOR]

A series of organoantimony(iii) halide complexes with a tetrahydrodibenzo[c,f][1,5]azastibocine framework were synthesized and employed as water tolerant Lewis acid catalysts. The results of a systematic structure–activity relationship study demonstrated that the strength of N→Sb donor–acceptor interaction could be synergistically modulated by tuning the properties of the nitrogen substituents and halogen atoms adjacent to the central antimony atom, and consequently resulted in distinct catalytic performances towards organic reactions such as Mannich, cross-condensation, cyclization–aromatization and epoxide aminolysis reaction. The fluorinated organoantimony(iii) derivatives were found to be more active than those of the chlorinated, brominated and iodinated analogues, owing to the use of an Sb–F moiety as a hydrogen bond acceptor. By comparison, the compound 6-cyclohexyl-12-fluoro-5,6,7,12-tetrahydrodibenzo[c,f][1,5] azastibocine (1d) is found to exhibit the highest catalytic activity, together with facile reusability in scale enlarged synthesis. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are crystalline porous solids with broad potential applications. So far, the successful construction of COFs has been limited to a few condensation reactions, and nearly all COFs were obtained by single-step synthesis based on predesigned linkers. Here, we report a general strategy in view of a one-pot cascade reaction to prepare both microporous and mesoporous fully π-conjugated pyrazine-linked COF materials (PZ-COFs). The obtained PZ-COFs show high chemical stability, large specific surface areas and promising H2, CH4 and CO2 uptake capacities. Furthermore, we demonstrate that manganese(ii)-incorporated PZ-COFs can act as excellent Lewis-acid catalysts for the cyanosilylation of aromatic aldehydes. This study not only provides a facile method to synthesize COFs required for multistep reactions but also expands the applications of COFs as promising catalysts. [ABSTRACT FROM AUTHOR]

We recently communicated (Angew. Chem. Int. Ed., 2018, 57, 5917–5920) the transmetallation of [6-Ph2P(O)-Ace-5-]2Hg (1) with Pb(OAc)4, which, after work-up with HCl in Et2O, provided the first aryl lead trichloride, 6-Ph2P(O)-Ace-5-PbCl3 (2), and 6-Ph2P(O)-Ace-5-HgCl (3). With LiCl, 1 forms a complex, [{[6-Ph2P(O)-Ace-5]2Hg}2Li]Cl (1a), that shows no reactivity towards Pb(OAc)4 anymore, which highlights the role of the intramolecularly coordinated P(O) functionality in transmetallation. In this work, we have broadened the scope of the transmetallation reagent by the reaction of 1 with SnCl4, SbCl3 and BiCl3 giving rise to the formation of 6-Ph2P(O)-Ace-5-SnCl3 (4), 6-Ph2P(O)-Ace-5-SbCl2 (5) and 6-Ph2P(O)-Ace-5-BiCl2 (6), respectively. The high Lewis acidity permits 4 and 5 to undergo complexation with THF, whereas no such complexes were formed with 2 and 6. The molecular structures of 1a, 3, 4, 4·THF, 5, 5·THF and 6 were established by X-ray crystallography. The different P–O distances of 2, 4, 4·THF, 5, 5·THF and 6, reflecting the relative strength of the P(O)…E coordination (E = Pb, Sn, Sb, Bi), were discussed. The nature of the P(O)…E interactions of 2, 4, 4·THF, 5, 5·THF and 6 was studied using a set of real-space bond indicators (RSBIs). [ABSTRACT FROM AUTHOR]

Cationic β-diketiminate Mg complexes with the bulky tBuBDI ligand and the weakly coordinating anion B(C6F5)4− have been prepared by the reaction of (tBuBDI)MgnBu with [Ph3C]+[B(C6F5)4]−; tBuBDI = CH[C(tBu)N-Dipp]2 and Dipp = 2,6-diisopropylphenyl. Their structures are compared to the previously reported cationic (MeBDI)Mg+ complexes; MeBDI = CH[C(Me)N-Dipp]2. Crystallization of [(tBuBDI)Mg]+[B(C6F5)4]− from chlorobenzene gave a unique (tBuBDI)Mg+·ClC6H5 cation with a rather short Mg…Cl and consequently long C–Cl bond. Crystallization from chlorobenzene/arene solvent mixtures gave (tBuBDI)Mg+·arene complexes (arene = benzene, toluene, m-xylene) but in the presence of mesitylene the chlorobenzene complex was formed. Due to the greater shielding of the metal, none of these complexes display Mg…(F5C6)4B− interactions. Crystal structures of the arene complexes show in all cases η2-coordination of the arene ligands. Ring slippage from a more favorable η2-coordination can be explained by the steric bulk of the tBuBDI ligand. The smaller arenes, benzene and toluene, also bind to (tBuBDI)Mg+ in bromobenzene solution. The Lewis acidity of these cationic Mg complexes was determined by the Gutmann–Beckett test. The acceptor number for (tBuBDI)Mg+ (AN = 76.0) is substantially higher than that estimated for (MeBDI)Mg+ (AN = 70.3). Calculation of the atomic NPA charges by DFT shows that the Mg2+ ion in (tBuBDI)Mg+ is slightly more positively charged than the metal in (MeBDI)Mg+, confirming its higher Lewis acidity. The lower benzene complexation energy calculated for (tBuBDI)Mg+versus (MeBDI)Mg+ is due to steric congestion of the metal in the (tBuBDI)Mg+ cation which allows only for Mg…(η1)C6H6 instead of Mg…(η6)C6H6 bonding. This ring slippage, however, results in a significant polarization of the electron density in the benzene ring, making it susceptible for nucleophilic attack. [ABSTRACT FROM AUTHOR]

A systematic study of the influence of the first coordination sphere over the reactivity and structure of metallo-β-lactamase (MβL) monozinc model complexes is reported. Three ZnII complexes with tripodal ligands forming the series [Zn(N-NNN)], [Zn(N-NNS)], and [Zn(N-NNO)] where N-NNX represents the tripodal donor atoms were investigated regarding their ability to mimic MβL. The tripodal series was inspired by MβL active sites in the respective subclasses, representing the (His, His, His) Zn1 site present in B1 and B3 subclasses, (His, His, Asp) present in the B3 subclass site and the thiolate present in B1 and B2 sites. The results were supported by electronic structure calculations. XAS analysis demonstrated that the ZnII electronic deficiency significantly changes in the order [Zn(N-NNS)] ＜ [Zn(N-NNN)] ＜ [Zn(N-NNO)]. This effect directly affects the reactivity over nitrocefin and amoxicillin, observed by the hydrolysis kinetics, which follows the same trend. NMR spectroscopy revealed the coordination of the carboxylic group in the substrate to the metal changes accordingly, affecting the hydrolysis kinetics. Our results also demonstrated that not only the Lewis acidity is changed by the ligand system but also the softness of the metal. [Zn(N-NNS)] is softened by the thiolate, promoting the ligand substitution reaction with solvents and favoring a secondary interaction with substrates, not observed for [Zn(N-NNO)]. XRD of the models reveals their similar geometric aspects in comparison to the crystal structure of GOB MβL. The present work demonstrates that the ZnII electronic details must be considered in the design of new MβL models that will further aid in the design of clinically useful inhibitors. [ABSTRACT FROM AUTHOR]