Search

Crystallizing molecules with long flexible chains is a challenge, making it difficult to perform X‐ray crystallography. Chaperones can assist in the crystallization of compounds that do not crystallize by themselves by producing solvate crystals that contain the analyte in their three‐dimensional lattices. Among the most versatile chaperones for liquid analytes are tetraaryladamantanes (TAAs), but the size of the compounds that can be encapsulated is limited, and attempts to surpass this limit with known TAAs were unsuccessful. Here we report that 1,3,5,7‐tetrakis(2‐fluoro‐4‐methoxyphenyl)adamantane (TFM) is a crystallization chaperone for acyclic molecules up to the molecular weight of phytyl acetate (338 g/mol). Encapsulation of such a large acyclic compound was achieved when the analyte was esterified and when a two‐step temperature protocol was used for crystallization. Exploratory work indicates that a drop to −20 °C allows for encapsulation of squalene (Mr 411 g/mol), albeit with positional disorder of the analyte. Our X‐ray crystal structures of solvates with flexible analytes shed light on how crystalline order can be imposed on large acyclic analytes. The new, fluorinated TAA gives access to crystal structures that were inaccessible thus far. [ABSTRACT FROM AUTHOR]

A new crystallization chaperone called TFM has been developed, which allows for the formation of X-ray diffraction-based crystal structures of liquid molecules that would otherwise be difficult to obtain. This chaperone acts like a glove that can fit molecules of various sizes, resulting in successful crystallization. The article also introduces a new temperature jump crystallization protocol. The cover graphic of the article displays the chaperone and the crystal lattice of the squalene solvate. [Extracted from the article]

The article discusses a new crystallization chaperone called TFM, which allows for the formation of X-ray diffraction-based crystal structures that would otherwise be impossible to obtain. The chaperone acts like a glove that fits many different sizes, enabling the crystallization of liquid molecules as a solvate. The article also introduces a new temperature jump crystallization protocol. The cover graphic of the article depicts the analytes and the chaperone, along with the crystal lattice of the squalene solvate. [Extracted from the article]

The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation‐state flexibility of the s‐block metals has long stood in the way of their participation in sophisticated π‐bonding arrangements, and truly antiaromatic systems containing s‐block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis‐base‐coordination chemistry. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The reactivity of a diruthenium tetrahydride complex towards three selected dihydroboranes was investigated. The use of [DurBH2] (Dur=2,3,5,6‐Me4C6H) and [(Me3Si)2NBH2] led to the formation of bridging borylene complexes of the form [(Cp*RuH)2BR] (Cp*=C5Me5; 1 a: R=Dur; 1 b: R=N(SiMe3)2) through oxidative addition of the B−H bonds with concomitant hydrogen liberation. Employing the more electron‐deficient dihydroborane [3,5‐(CF3)2‐C6H3BH2] led to the formation of an anionic complex bearing a tetraarylated chain of four boron atoms, namely Li(THF)4[(Cp*Ru)2B4H5(3,5‐(CF3)2C6H3)4] (4), through an unusual, incomplete threefold dehydrocoupling process. A comparative theoretical investigation of the bonding in a simplified model of 4 and the analogous complex nido‐[1,2(Cp*Ru)2(μ‐H)B4H9] (I) indicates that there appear to be no classical σ‐bonds between the boron atoms in complex I, whereas in the case of 4 the B4 chain better resembles a network of three B−B σ bonds, the central bond being significantly weaker than the other two. [ABSTRACT FROM AUTHOR]

A new pathway for the ring expansion reaction of antiaromatic boroles with organic azides is reported. While the reaction usually leads to 1,2‐azaborinines, it was diverted to the formation of a 1,2,3‐diazaborinine by changing the electronic characteristics of the reagents. The isolable azo‐azaborinine intermediate initially formed from the reaction of 1‐(2,3,4,5‐tetraphenylborolyl)ferrocene with 4‐azido‐N,N‐dimethylaniline gradually decomposed to a 1,2,3‐diazaborinine and benzonitrile. Both the spectroscopic properties and the reactivity of the heteroaromatic compound show analogies to pyridine, to which it is isoelectronic. Density functional theory (DFT) calculations provided insight into the mechanism of this unusual transformation. Nitrile & error: A new pathway for the ring expansion reaction of boroles with organic azides is presented, leading to a 1,2,3‐diazaborinine instead of the expected 1,2‐azaborinine. Mechanistic DFT calculations provided insight into the mechanism of formation of the BN2C3 heterocycle, and spectroscopic and reactivity studies demonstrated the analogies of the 1,2,3‐diazaborinine to pyridine. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A series of NHC-supported 1,2-dithienyldiborenes was synthesized from the corresponding (dihalo)thienylborane NHC precursors. NMR and UV/Vis spectroscopic data, as well as X-ray crystallographic analyses, were used to assess the electronic and steric influences on the B=B double bond of various NHCs and electron-donating substituents on the thienyl ligands. Crystallographic data showed that the degree of coplanarity of the diborene core and thienyl groups is highly dependent on the sterics of the substituents. Furthermore, any increase in the electron-donating ability of the substituents resulted in the destabilization of the HOMO and greater instability of the resulting diborenes. [ABSTRACT FROM AUTHOR]

Crystallizing molecules with long flexible chains is a challenge, making it difficult to perform X-ray crystallography. Chaperones can assist in the crystallization of compounds that do not crystallize by themselves by producing solvate crystals that contain the analyte in their three-dimensional lattices. Among the most versatile chaperones for liquid analytes are tetraaryladamantanes (TAAs), but the size of the compounds that can be encapsulated is limited, and attempts to surpass this limit with known TAAs were unsuccessful. Here we report that 1,3,5,7-tetrakis(2-fluoro-4-methoxyphenyl)adamantane (TFM) is a crystallization chaperone for acyclic molecules up to the molecular weight of phytyl acetate (338 g/mol). Encapsulation of such a large acyclic compound was achieved when the analyte was esterified and when a two-step temperature protocol was used for crystallization. Exploratory work indicates that a drop to -20 °C allows for encapsulation of squalene (Mr 411 g/mol), albeit with positional disorder of the analyte. Our X-ray crystal structures of solvates with flexible analytes shed light on how crystalline order can be imposed on large acyclic analytes. The new, fluorinated TAA gives access to crystal structures that were inaccessible thus far., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A series of chiral mechanochromic copper(I) cAAC (cAAC=cyclic (alkyl)(amino)carbene) complexes with a variety of amide ligands have been studied with regard to their photophysical and chiroptical properties to elucidate structure-property relationships for the design of efficient triplet exciton emitters exhibiting circularly polarized luminescence. Depending on the environment, which determines the excited state energies, either thermally activated delayed fluorescence (TADF) from 1/3 LLCT states or phosphorescence from 3 LLCT/LC states occurs. However, neither chiral moieties at the carbene nor at the carbazolate ligands provide detectable luminescence dissymmetries g lum . An exception is [Cu(phenoxazinyl)(cAAC)], showing orange to deep red TADF with λ max =601-715 nm in solution, powders and in PMMA. In this case, the amide ligand can undergo distortions in the excited state. This design motif leads to the first linear, non-aggregated CPL-active copper(I) complex with g lum of -3.4 ⋅ 10 -3 combined with a high radiative rate constant of 6.7 ⋅ 10 5  s -1 ., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The 2-aryl-3,4,5,6-tetraphenyl-1,2-azaborinines 1-EMe 3 and 2-EMe 3 (E=Si, Sn; aryl=Ph (1), Mes (=2,4,6-trimethylphenyl, 2)) were synthesized by ring-expansion of borole precursors with N 3 EMe 3 -derived nitrenes. Desilylative hydrolysis of 1- and 2-SiMe 3 yielded the corresponding N-protonated azaborinines, which were deprotonated with nBuLi or MN(SiMe 3 ) 2 (M=Na, K) to the corresponding group 1 salts, 1-M and 2-M. While the lithium salts crystallized as monomeric Lewis base adducts, the potassium salts formed coordination polymers or oligomers via intramolecular K⋅⋅⋅aryl π interactions. The reaction of 1-M or 2-M with CO 2 yielded N-carboxylate salts, which were derivatized by salt metathesis to methyl and silyl esters. Salt metathesis of 1-M or 2-M with methyl triflate, [Cp*BeCl] (Cp*=C 5 Me 5 ), BBr 2 Ar (Ar=Ph, Mes, 2-thienyl), ECl 3 (E=B, Al, Ga) and PX 3 (X=Cl, Br) afforded the respective group 2, 13 and 15 1,2-azaborinin-2-yl complexes. Salt metathesis of 1-K with BBr 3 resulted not only in N-borylation but also Ph-Br exchange between the endocyclic and exocyclic boron atoms. Solution 11 B NMR data suggest that the 1,2-azaborinin-2-yl ligand is similarly electron-withdrawing to a bromide. In the solid state the endocyclic bond length alternation and the twisting of the C 4 BN ring increase with the sterics of the substituents at the boron and nitrogen atoms, respectively. Regression analyses revealed that the downfield shift of the endocyclic 11 B NMR resonances is linearly correlated to both the degree of twisting of the C 4 BN ring and the tilt angle of the N-substituent. Calculations indicate that the 1,2-azaborinin-1-yl ligand has no sizeable π-donor ability and that the aromaticity of the ring can be subtly tuned by the electronics of the N-substituent., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation-state flexibility of the s-block metals has long stood in the way of their participation in sophisticated π-bonding arrangements, and truly antiaromatic systems containing s-block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis-base-coordination chemistry., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The reactivity of a diruthenium tetrahydride complex towards three selected dihydroboranes was investigated. The use of [DurBH 2 ] (Dur=2,3,5,6-Me 4 C 6 H) and [(Me 3 Si) 2 NBH 2 ] led to the formation of bridging borylene complexes of the form [(Cp*RuH) 2 BR] (Cp*=C 5 Me 5 ; 1 a: R=Dur; 1 b: R=N(SiMe 3 ) 2 ) through oxidative addition of the B-H bonds with concomitant hydrogen liberation. Employing the more electron-deficient dihydroborane [3,5-(CF 3 ) 2 -C 6 H 3 BH 2 ] led to the formation of an anionic complex bearing a tetraarylated chain of four boron atoms, namely Li(THF) 4 [(Cp*Ru) 2 B 4 H 5 (3,5-(CF 3 ) 2 C 6 H 3 ) 4 ] (4), through an unusual, incomplete threefold dehydrocoupling process. A comparative theoretical investigation of the bonding in a simplified model of 4 and the analogous complex nido-[1,2(Cp*Ru) 2 (μ-H)B 4 H 9 ] (I) indicates that there appear to be no classical σ-bonds between the boron atoms in complex I, whereas in the case of 4 the B 4 chain better resembles a network of three B-B σ bonds, the central bond being significantly weaker than the other two., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The steric and electronic properties of aryl substituents in monoaryl borohydrides (Li[ArBH 3 ]) and dihydroboranes were systematically varied and their reactions with [Ru(PCy 3 ) 2 HCl(H 2 )] (Cy: cyclohexyl) were studied, resulting in bis(σ)-borane or terminal borylene complexes of ruthenium. These variations allowed for the investigation of the factors involved in the activation of dihydroboranes in the synthesis of terminal borylene complexes. The complexes were studied by multinuclear NMR spectroscopy, mass spectrometry, X-ray diffraction analysis, and density functional theory (DFT) calculations. The experimental and computational results suggest that the ortho-substitution of the aryl groups is necessary for the formation of terminal borylene complexes., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of bis(σ)-borane complexes of Group 6 transition metals were prepared by direct dihydroborane coordination to the metal center. Reaction of [M(CO) 3 (PCy 3 ) 2 ] and two dihydroboranes [DurBH 2 ] and [(Me 3 Si) 2 NBH 2 ] (Dur=2,3,5,6-Me 4 C 6 H) yielded bis(σ)-borane complexes fac-[M(CO) 3 (PCy 3 ){η 2 -(H 2 BR)}] (R=Dur; 1: M=Cr, 2: M=W; R=N(SiMe 3 ) 2 ; 3: M=Cr, 4: M=W). In the case of molybdenum, we have isolated an arene complex (5) with [DurBH 2 ] in which the Dur group acts as a η 6 -bound ligand, and with [(Me 3 Si) 2 NBH 2 ] a similar bis(σ)-borane complex was isolated, cis,trans-[Mo(CO) 2 (PCy 3 ) 2 {η 2 -(H 2 BN(SiMe 3 ) 2 }] (6), with a different pattern of auxiliary ligands. The complexes were investigated by multinuclear NMR spectroscopy, mass spectrometry, X-ray diffraction analysis, and computational methods. Quantum theory of atoms in molecules (QTAIM) calculations demonstrated that the borane complexes may be described as pure bis(σ)-borane complexes rather than elongated or stretched examples given that the calculations do not show the presence of a ring-critical point (RCP) at the ring formed by the interactions of the B-H with metal center., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new pathway for the ring expansion reaction of antiaromatic boroles with organic azides is reported. While the reaction usually leads to 1,2-azaborinines, it was diverted to the formation of a 1,2,3-diazaborinine by changing the electronic characteristics of the reagents. The isolable azo-azaborinine intermediate initially formed from the reaction of 1-(2,3,4,5-tetraphenylborolyl)ferrocene with 4-azido-N,N-dimethylaniline gradually decomposed to a 1,2,3-diazaborinine and benzonitrile. Both the spectroscopic properties and the reactivity of the heteroaromatic compound show analogies to pyridine, to which it is isoelectronic. Density functional theory (DFT) calculations provided insight into the mechanism of this unusual transformation., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The reaction of a pentamethylcyclopentadienyl-substituted dialane with a variety of Lewis bases results in unexpected disproportionation of the dialane into Al I and Al III species. Use of a transition-metal Lewis base allows for the formation of metal-only Lewis pairs. Furthermore, the synthesis of a Lewis base bis-adduct was successful with the Lewis base 4-dimethylaminopyridine., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of NHC-supported 1,2-dithienyldiborenes was synthesized from the corresponding (dihalo)thienylborane NHC precursors. NMR and UV/Vis spectroscopic data, as well as X-ray crystallographic analyses, were used to assess the electronic and steric influences on the B=B double bond of various NHCs and electron-donating substituents on the thienyl ligands. Crystallographic data showed that the degree of coplanarity of the diborene core and thienyl groups is highly dependent on the sterics of the substituents. Furthermore, any increase in the electron-donating ability of the substituents resulted in the destabilization of the HOMO and greater instability of the resulting diborenes., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Boroles are important motifs within functional materials. With the aim to prepare a pinacolboryl-substituted derivative, the metallacycle transfer from corresponding zirconium and tin precursors has been explored. We show that the reaction of 1,1-dimethyl-2,3,4,5-tetrapinacolborylstannole with dichloro(phenyl)borane does not provide the desired borole, but instead a stannyl-substituted 1-chloroboracyclopent-3-ene. Spectroscopic and structural details of this highly functionalized boracycle indicate that intramolecular interactions between the tin and oxygen atoms of the boryl substituents may account for the unexpected outcome of the tin-boron exchange reaction., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)