Arene Clusters Research Articles

Hetero- and Homointerlocked Metal-Organic Cages.

Interlocked molecular assemblies constitute a captivating ensemble of chemical topologies, comprising two or more separate components that exhibit remarkably intricate structures. The interlocked molecular assemblies are typically identical, and heterointerlocked systems that comprise structurally distinct assemblies remain unexplored. Here, we demonstrate that metal-templated synthesis can be exploited to afford not only a homointerlocked cage but also a heterointerlocked cage. Treatment of a carboxylated 2,9-dimethyl-1,10-phenanthroline (dmp) or Cu(I) bis-dmp linker with a Ni4-p-tert-butylsulfonylcalix[4]arene cluster affords noninterlocked octahedron and quadruply interlocked double cages consisting of two identical tetragonal pyramids, respectively. In contrast, when a mixture of dmp and Cu(I) bis-dmp linkers is used, a quadruply heterointerlocked cage is produced, consisting of a tetragonal pyramid and an octahedron. With photoredox-active [Cu(dmp)2]+ in the structures, both interlocked cages exhibit remarkable performance as photocatalysts for atom transfer radical addition (ATRA) reactions of trifluoromethanesulfonyl chloride with alkenes or oxo-azidations of vinyl arenes. These interlocked structures serve the dual purpose of stabilizing photocatalytically active components against deactivation and encapsulating substrates within the cavity, resulting in yields comparable to or even surpassing those of their molecular counterparts. This work thus provides a new strategy that combines metal templating and nontemplating approaches to design new types of interlocked assemblies with intriguing architectures and properties.

A Zn8 Double-Cavity Metallacalix[8]arene as Molecular Sieve to Realize Self-Cleaning Intramolecular Tandem Transformation of Li-S Chemistry.

Toward the well-explored lithium-sulfur (Li-S) catalytic chemistry, the slow adsorption-migration-conversion kinetics of lithium polysulfides on catalytic materials and Li2 S deposition-induced passivation of active sites limit the rapid and complete conversion of sulfur. Conceptively, molecular architectures can provide atom-precise models to understand the underlying active sites responsible for selective adsorption and conversion of LiPSs and Li2 S2 /Li2 S species. Here, an octanuclear Zn(II) (Zn8 ) cluster is presented, which features a metallacalix[8]arene with double cavities up and down the Zn8 ring. The central Zn8 ring and the specific double cavities with organic ligands of different electronegativity and bonding environments render active sites with variable steric hindrance and interaction toward the sulfur-borne species. An intramolecular tandem transformation mechanism is realized exclusively by Zn8 cluster, which promotes the self-cleaning of active sites and continuous electrochemical reaction. Notably, the external azo groups and internal Zn/O sites of Zn8 cluster in sequence stimulate the adsorption and conversion of long chain Li2 Sx (x≥ 4) and short chain Li2 S/Li2 S2 , contributing to remarkable rate performance and cycling stability. This work pioneers the application of metallacalix[n]arene clusters with atom-precise structure in Li-S batteries, and the proposed mechanism advances the molecule-level understanding of Li-S catalytic chemistry.

Permanent porous hydrogen-bonded frameworks with two types of Br\xf8nsted acid sites for heterogeneous asymmetric catalysis

The search for porous materials with strong Brønsted acid sites for challenging reactions has long been of significant interest, but it remains a formidable synthetic challenge. Here we demonstrate a cage extension strategy to construct chiral permanent porous hydrogen-bonded frameworks with strong Brønsted acid groups for heterogeneous asymmetric catalysis. We report the synthesis of two octahedral coordination cages using enantiopure 4,4’,6,6’-tetra(benzoate) ligand of 1,1’-spirobiindane-7,7’-phosphoric acid and Ni4/Co4-p-tert-butylsulfonylcalix[4]arene clusters. Intercage hydrogen-bonds and hydrophobic interactions between tert-butyl groups direct the hierarchical assembly of the cages into a permanent porous material. The chiral phosphoric acid-containing frameworks can be high efficient and recyclable heterogeneous Brønsted acid catalysts for asymmetric [3+2] coupling of indoles with quinone monoimine and Friedel-Crafts alkylations of indole with aryl aldimines. The afforded enantioselectivities (up to 99.9% ee) surpass those of the homogeneous counterparts and compare favorably with those of the most enantioselective homogeneous phosphoric acid catalysts reported to date.

Design and Assembly of a Chiral Metallosalen-Based Octahedral Coordination Cage for Supramolecular Asymmetric Catalysis.

Supramolecular containers featuring both high catalytic activity and high enantioselectivity represent a design challenge of practical importance. Herein, it is demonstrated that a chiral octahedral coordination cage can be constructed by using twelve enantiopure Mn(salen)-derived dicarboxylic acids as linear linkers and six Zn4 -p-tert-butylsulfonylcalix[4]arene clusters as tetravalent four-connected vertices. The porous cage features a large hydrophobic cavity (≈3944 Å3 ) decorated with catalytically active metallosalen species and is shown to be an efficient and recyclable asymmetric catalyst for the oxidative kinetic resolution of racemic secondary alcohols and the epoxidation of olefins with up to >99 % enantiomeric excess. The cage architecture not only prevents intermolecular deactivation and stabilizes the Mn(salen) catalysts but also encapsulates substrates and concentrates reactants in the cavity, resulting in enhanced reactivity and enantioselectivity relative to the free metallosalen catalyst.

Design and Assembly of a Chiral Metallosalen‐Based Octahedral Coordination Cage for Supramolecular Asymmetric Catalysis

AbstractSupramolecular containers featuring both high catalytic activity and high enantioselectivity represent a design challenge of practical importance. Herein, it is demonstrated that a chiral octahedral coordination cage can be constructed by using twelve enantiopure Mn(salen)‐derived dicarboxylic acids as linear linkers and six Zn4‐p‐tert‐butylsulfonylcalix[4]arene clusters as tetravalent four‐connected vertices. The porous cage features a large hydrophobic cavity (≈3944 Å3) decorated with catalytically active metallosalen species and is shown to be an efficient and recyclable asymmetric catalyst for the oxidative kinetic resolution of racemic secondary alcohols and the epoxidation of olefins with up to >99 % enantiomeric excess. The cage architecture not only prevents intermolecular deactivation and stabilizes the Mn(salen) catalysts but also encapsulates substrates and concentrates reactants in the cavity, resulting in enhanced reactivity and enantioselectivity relative to the free metallosalen catalyst.

On the formation of supramolecular systems in the adsorption of aromatic compounds at porous adsorbents

Competitive adsorption of anisole, benzaldehyde, benzoic acid, benzene, toluene, and phenol from dilute solutions in n-heptane at three chemically different porous adsorbents was studied by high-performance liquid chromatography (HPLC). The retention times of these compounds were used to calculate the equilibrium constants of the adsorption isotherms, the partition coefficients, and the Gibbs energy changes. The results obtained made it possible to estimate the Gibbs energy changes in the competitive adsorption of arenes leading to the formation of supramolecular surface compounds at cellulose and silica and the formation of arene clusters at the pyrocarbon surface from dilute solutions in n-heptane.

A novel one-dimensional coordination polymer capturing hydrated Co(II) cations

A novel one-dimensional (1D) coordination polymer built from tetracobalt(II)- p-sulfonatothiacalix[4]arene cluster units was prepared and characterized. Single crystal X-ray diffraction analyses reveal that each cavity of p-sulfonatothiacalix[4]arene in the polymer captures a hydrated cobalt(II) cation. The magnetic studies in the 2–300 K range show weak antiferromagnetic interactions between the four cobalt(II) centers.

Linked arene clusters: the interaction of tetracobalt nonacarbonyl with [2.2.2]paracyclophane

The thermolysis of [2.2.2]paracyclophane in the presence of an excess of [Co4(CO)12] yields three new arene clusters [{Co4(CO)9}n(C24H24)] (n = 1, 2 and 3): the molecular structures of the mono- and bis-cluster complexes have been established by single crystal X-ray diffraction while the tris-complex has been characterised by spectroscopy.

Linked arene clusters

The synthesis, isolation and characterisation of a number of [2n]cyclophane transition metal clusters with nuclearities ranging from four to twelve atoms is described. The primary objective of this work has been to prepare molecules composed of alternating cyclophane and cluster subunits which may be considered as precursors to novel organometallic polymer chains and networks. This aim has been achieved to a certain degree using the [2.2.2]paracyclophane ligand, which has been shown to interact with metal clusters (e.g. tetracobalt nonacarbonyl) via all three of its aromatic rings. Also, the dimerisation of a hexa- ruthenium-[2.2.2]paracyclophane complex has yielded a remarkable dodecanuclear bis-arene cluster which may form the basis for a novel linear polymeric chain containing only metal atoms in the backbone. We have also been able to demonstrate that the coordinated [2.2.2]paracyclophane unit is able to embrace metal ions such as GaI and AgI giving rise to a concomitant change in the observed IR spectrum of the attached cluster. This perspective highlights these areas of research and also examines the factors controlling coordination mode preferences of the [2n]cyclophane ligand and the central cluster nuclearity and geometry.

Synthesis and characterisation of hexa- and hepta-ruthenium carbido carbonyl clusters containing arenes derived from 1,1-diphenylethene

The three ruthenium arene clusters [Ru6C(CO)14(η6-PhCHMePh)] 1, [Ru6C(CO)14(η6-PhCCH2Ph)] 2 and [Ru7C(CO)14(µ3-κ∶η6∶η6-C6H4CH2C6H4)] 3 have been synthesized by reaction of 1,1-diphenylethene with triruthenium dodecacarbonyl in octane under reflux. Compound 1 is a 1,1-diphenylethene hexaruthenium carbido cluster (Ru6C) derivative wherein the organo-group, hydrogenated at the olefinic centre, is bound to the cluster by a single phenyl ring in an η6 manner. Compound 2 is a similar Ru6C derivative wherein the 1,1-diphenylethene ligand remains unsaturated, whilst the third, and minor, product is the first example of a metal carbonyl cluster chelated by a diphenyl ligand and is one of the few examples of an Ru7C ‘spiked’ octahedron. The subtle electronic effects of the Ru6C co-ordination in 2 have been probed by 1H NMR spectroscopy. The solid-state structures of both the hydrogenated derivative 1 and the Ru7C ‘spiked’ octahedral cluster 3 have been determined by single-crystal X-ray analysis. The supramolecular architecture of 3 has been examined in depth.

Effect of Ring Substituents on Formation Rates for Vanadium−Arene Clusters

Vanadium−arene complexes, Vn(arene)m (arene = benzene (C6H6), toluene (C6H5CH3), and fluorobenzene (C6H5F)), were synthesized by the reaction of laser-vaporized vanadium atoms with arene vapor. Both the analysis of the mass spectra and the measurements of their ionization energies indicate that both Vn(C6H5CH3)m and Vn(C6H5F)m clusters take a multiple-decker sandwich structure similar to the structure of Vn(C6H6)m clusters. The relative reactivity between benzene and toluene toward vanadium was also determined; toluene is 4 times as reactive as benzene for V1(C6H5CH3)1/V1(C6H6)1 production and 2 times for V1(C6H5CH3)2/V1(C6H6)2 production because of reactivity enhancement of the electron-donating ring substituent. In the case of the Vn(C6H5F)m cluster, it is found that the electron-withdrawing ring substituent of fluorobenzene results in much less reactivity than is observed for benzene and toluene.

Arene cluster compounds

The synthesis, isolation and characterisation of a wide and diverse range of arene clusters based on nuclearities of three to eight metal atoms are described. Their use as models for the chemisorption of benzene on the macromolecular surface are considered and matters relevant to the chemistry on the surface such as bonding type, mobility and reactivity discussed. Certain of these compounds readily undergo photoisomerisation to produce benzyne derivatives by cleavage of two C–H arene bonds. This process may be tuned by varying the nature of the other ligands present. In the solid many of the arene clusters exhibit strong arene–arene interactions which are ‘graphitic-like’ leading to the formation of chains, ribbons and snakes. Use of bridging bifunctional arenes such as [2.2]paracyclophane and PhCHCHCHCHCHCHPh leads to useful monomeric precursors to arene cluster polymers.

Thermolytic reaction of 1,4-diisopropenylbenzene with [Ru3(CO)12]: an arene ligand as a template for cluster formation

The reaction of [Ru3(CO)12] with 1,4-diisopropenylbenzene in refluxing octane led to the isolation of a series of clusters with nuclearities from 2 to 7: [Ru4(CO)10(C12H14)]1, [Ru3(CO)8(C12H12)]2, [Ru6H(CO)15(C12H11)]3, [Ru6H(CO)15(C12H13)]4, [Ru2(CO)6(C12H12)]5, [Ru7C(CO)16(C12H12)]6, [Ru3H(CO)9(C12H11)]7, [Ru5H(CO)14(C12H11)]8 and [Ru6C(CO)15(C11H10)]9. The molecular structures of 1 and the three metallacycle compounds 2–4 have been determined by X-ray crystallography. The hexaruthenium species 3 and 4 represent a new category of arene cluster. The six ruthenium atoms describe an edge-bridged tetrahedron with a ruthenium spike bound to the edge-bridging atom. The arene ligand acts as an eleven-electron donor via both σ and π bonds. The pathway of the reaction has been established and provides evidence for ligand-moderated modular cluster build-up in which the ligand acts as a template.

Synthesis, molecular and crystal structure of tetraruthenium butterfly arene clusters

A series of Ru4 butterfly cluster complexes have been synthesized and investigated by spectroscopic and diffraction methods. The solid-state structure of [Ru4(CO)12(µ4-η2 : η2-C6H8)]1 and of the two isomers of [Ru4(CO)9(µ4-η2 : η2-C6H8)(η6-C6H6)] with the benzene ring located on the butterfly hinge (2) or on the wingtip (3), have been characterized. The three complexes are monoclinic, 1: space group P21/c, a= 9.779(8), b= 22.163(14), c= 10.069(6)A, β= 90.23(9)°, Z= 4; 2: space group Cc, a= 10.010(3), b= 15.532(4), c= 15.384(4)A, β= 93.50(2)°, Z= 4; 3: space group P21/c, a= 16.655(3), b= 15.709(3), c= 17.831(4)A, β= 91.44(3)°, Z= 8. The molecular structures of the complexes have been investigated in relation with the respective crystal structure and, in the case of 2, compared with the polymorphic modification described previously.

Dynamics and molecular aggregation in crystalline [{M(C5H5)}3(µ3-η2: η2: η2-C6H5R)][M = Co, R = CH(Ph)Me, CH2CH2Ph or CHCHMe; M = Rh, R = H] clusters

The intermolecular aggregation in crystalline arene clusters of the type [{M(C5H5)}3(µ3-η2 : η2 : η2-C6H5R)][M = Co, R = CH(Ph)Me, CH2CH2Ph or CHCHMe; M = Rh, R = H] has been investigated by atom–atom packing potential-energy calculations and computer graphics. The ease of reorientation of the arene fragments and of the cyclopentadienyl ligands in the solid state has been investigated by calculating intramolecular and intermolecular potential-energy barriers. It has been shown that, except for the benzene ligand in [{Rh(C5H5)}3(µ3-η2 : η2 : η2-C6H6)], the facial arenes cannot undergo reorientation in the solid state, whereas the reorientational motion of the cyclopentadienyl ligands is under intramolecular control.

Electrophilic reactivity of arene carbonyl cluster complexes with the Ru6C core. Crystal and molecular structure of [Ru6C(CO)14(η6-C6H4Ph2-1,4)

Addition of LiPh to [Ru6C(CO)12(η6-C6H6)(µ-η2:η2-C6H8)], [Ru6C(CO)11(η6-C6H6)(µ3-η2:η2:η2-C6H6)] and [Ru6C(CO)14(η6-C6H6)], followed by treatment with [CPh3][BF4], has led to the substituted arene cluster complexes [Ru6C(CO)12(µ-η2:η2-C6H8)(η6-C6H5Ph)], [Ru6C(CO)11(µ3-η2:η2:η2-C6H6)(η6-C6H5-Ph)] and [Ru6C(CO)14(η6-C6H4Ph2-1,4)](structure established by X-ray crystallography).

Preparation, characterisation, molecular and crystal structure of the octaruthenium arene clusters [Ru8H4(CO)18(η6-arene)](arene = C6H6or C16H16)

Two octaruthenium arene clusters, [Ru8H4(CO)18(η-6-arene)](arene = C6H61 or C16H162), have been isolated from the thermolysis of [Ru3(CO)12] in octane, in the presence of cyclohexene (C6H10) or [2.2] paracyclophane (C16H16), respectively. Both compounds 1 and 2 have been characterised in the solid state by single-crystal X-ray diffraction and their molecular and crystal structures determined. The reaction of 2 with CO resulted in conversion to the carbido cluster [Ru6C(CO)14(µ3-η2:η2:η2-C16H16)] and [Ru3(CO)12] in quantitative amounts. Compound 1 did not react in the same way but yielded both [Ru4H4(CO)12] and [Ru4H2(CO)13].

Arene Clusters

Arene Clusters

Cluster build-up using the [Os(η6-C6H6)(MeCN)3]2+cation; synthesis and structural characterisation of some hexa- and hepta-nuclear arene-substituted clusters

Reactions of the cluster dianion [Os5(CO)15]2– with [Os(η6-C6H6)(MeCN)3]2+ and [Os(C6H5Me)(CF3SO3)2] provided [Os6(CO)15(η6-C6H6)]1 and [Os6(CO)15(η6-C6H5Me)]2, respectively, in good yield (≈45%). Reduction of the hexaosmium cluster [Os6(CO)18] with K–Ph2CO gave the cluster dianion [Os6(CO)17]2–3 in quantitative yield. When this dianion was treated with [Os(η6-C6H6)(MeCN)3]2+ the heptanuclear cluster [Os7(CO)17(η6-C6H6)]4 was obtained in fair yield, while the corresponding reaction with [Os(η6-C6H5Me)(CF3SO3)2] gave [Os7(CO)17(η6-C6H5Me)]5 in similar yield (ca. 25%). The four arene clusters have been characterised by spectroscopic techniques, and the molecular geometries of 1, 2 and 4 established by single-crystal X-ray diffraction techniques. In both 1 and 2 the metal framework geometry is best described as a bicapped tetrahedron. In 1 the η6-C6H6 ligand occupies a site on the central Os4 tetrahedron while in 2 in the η6-arene is co-ordinated to one of the capping Os atoms. The metal framework in 4 may be viewed as derived from a bicapped tetrahedron with the seventh metal capping one of the caps to give a chain of four fused tetrahedra. The η6-C6H6 ligand in 4 occupies a similar site to that found in 1.

Sequential synthesis of some tetraosmium–arene clusters

On activation with Me3NO the tetrahydrido-tetranuclear cluster [Os4(µ-H)4(CO)12]1 underwent reaction with cyclohexa-1,3-diene in CH2Cl2 under ambient conditions to give, as the major products, the four organometallic clusters [Os4(µ-H)3(CO)11(η3-C6H9)]2, [Os4(µ-H)2(CO)12(η2-C6H8)]3, [Os4(µ-H)2(CO)11(η4-C6H8)]4 and [Os4(µ-H)2(CO)10(η6-C6C6)]5. On heating in hexane, 3 is converted into 4 and subsequently 4 into 5. Compound 5 underwent further reaction with Me3NO in CH2Cl2 in the presence of cyclohexa-1,3-diene to produce [Os4(CO)9(η6-C6H6)(η4-C6H8)]6 and [Os4(µ-H)2(CO)8(η6-C6H6)(η4-C6H8)]7. Structural analyses of 4 and 7 by single-crystal X-ray diffraction have shown that the C6H8 ligand is bonded through two alkene bonds and that the benzene ligand in 7 is co-ordinated in an η6 fashion. In each case the ligands are bonded to single osmium atoms only. Compound 5 was also found to react with Me3NO in CH2Cl2 in the presence of benzene yielding [Os4(CO)8(η6-C6H6)2]8, whilst with either toluene or mesitylene it undergoes arene displacement to produce [OS4(µ-H)2(CO)10(η6-C6H5Me)]9 or [Os4(µ-H)2(CO)10(η6-C6H4Me2-1,3)]10 respectively.