Aleš Růžička

The Dominant Role of Chalcogen Bonding in the Crystal Packing of 2D/3D Aromatics

The chalcogen bond is a nonclassical σ-hole-based noncovalent interaction with emerging applications in medicinal chemistry and material science. It is found in organic compounds, including 2D aromatics, but has so far never been observed in 3D aromatic inorganic boron hydrides. Thiaboranes, harboring a sulfur heteroatom in the icosahedral cage, are candidates for the formation of chalcogen bonds. The phenyl-substituted thiaborane, synthesized and crystalized in this study, forms sulfur⋅⋅⋅π type chalcogen bonds. Quantum chemical analysis revealed that these interactions are considerably stronger than both in their organic counterparts and in the known halogen bond. The reason is the existence of a highly positive σ-hole on the positively charged sulfur atom. This discovery expands the possibilities of applying substituted boron clusters in crystal engineering and drug design.

Solution and cross-polarization/magic angle spinning NMR investigation of intramolecular coordination SnN in some organotin(IV) C,N-chelates

Abstract An intramolecular donor/acceptor SnN bonding connection in a set of triphenyl- and diphenyl-(halogeno)tin(IV) C,N-chelates, Ph2XSnL, where Ph=C6H5, X=Ph, Cl or Br and L1=2-(dimethylaminomethyl)phenyl-, C6H4(CH2NMe2)-2, and L2=2,6-bis[(dimethylaminomethyl)phenyl]-, C6H3(CH2NMe2)2-2,6, respectively, was studied by 119Sn, 15N, 13C and 1H NMR spectroscopy in solution of non-coordinating solvent (CDCl3) and by 119Sn cross-polarization/magic angle spinning NMR techniques in the solid-state. The existence of SnN coordination bonds was confirmed in studied compounds and their strengths were evaluated through the values of NMR spectra parameters of nuclei directly involved in SnN connection, namely by characteristic changes of chemical shifts δ(119Sn) and δ(15N) and values of J(119Sn, 13C) and J(119Sn, 15N) coupling constants. The set was extended by compound [2,6-C6H3(CH2NMe2)2]PhSnCl2 (5a), that is the decomposition product of compound [2,6-C6H3(CH2NMe2)2]Ph2SnCl (5). This 5a was characterized by NMR spectroscopy and its structure was estimated by X-ray diffraction techniques.

Monomeric Organoantimony(I) and Organobismuth(I) Compounds Stabilized by an NCN Chelating Ligand: Syntheses and Structures

The synthesis and structure of compounds containing multiple bonds between heavier Group 15 (Sb, Bi) elements, or analogous low-valent compounds with the central atom in the formal oxidation state + 1, have been among the most exciting targets in the chemistry of main-group elements. However, these compounds are often very unstable under normal conditions. The introduction of sufficiently large substituents is necessary for kinetic stabilization of such reactive species. Utilizing very effective and bulky ligands, such as 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl, or various m-terphenyl ligands, allowed isolation of stable heavier-element dipnictenes RMMR (M = Sb, Bi). Related ligands are able to stabilize unsymmetric compounds, where two different heavier Group 15 elements are connected. Using less stericaly crowded ligands, such as bis(trimethylsilyl)methyl resulted in formation of various cluster compounds, and coordination of a transition metal was necessary for stabilization of the RMMR fragment. Nevertheless, monomeric compounds of the type RM (stibinidenes or bismuthinidenes) have not been isolated in the condensed phase to date, although the existence of such compounds with two lone pairs for bismuth has been predicted based on relativistic effects. We and others have recently demonstrated that using of so-called NCN pincer-type ligand, [2,6bis(dimethylamino)methyl]phenyl (denoted as Ar hereafter), is an alternative to sterically overcrowded ligands for stabilization of low-valent antimony and bismuth compounds and the terminal ArSb=E (E = S, Se, Te) bonds. In view of this fact, it was believed that using of even more rigid and more sterically demanding NCN pincer ligand may lead to a stabilization of monomeric RM species (stibinidenes or bismuthinidenes) by combination of thermodynamical and kinetic influence of the ligand. Herein, we present the syntheses and structures of unprecedented monomeric stibinidene and bismuthinidene by taking advantage of using of 2,6-bis[N-(2’,6’-dimethylphenyl)ketimino]phenyl (denoted as L hereafter; Scheme 1).

Cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), its properties and initiation reactivity

Using the (15)N NMR chemical shifts of nitrogen atoms in nitramino groups of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (bicyclo-HMX or BCHMX) and additional 10 nitramines, we have assessed its reactivity in detonation, under the influence of impact, and by action of electric spark. It is stated that the thermal stability of BCHMX is higher than that of 1,3,5-trinitro-1,3,5-triazinane (RDX). The longest NN bond in the BCHMX molecule (1.412(4)A) is the cause for its higher impact reactivity, which is at the level of that of penterythritol tetranitrate (PETN). In the experimentally determined detonation velocity, BCMX can be slightly better performing than RDX. From the standpoint of friction sensitivity, BCHMX is similar to 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Attention was also focused on the solubility-temperature dependence of BCHMX in acetone, acetonitrile, ethyl acetate, dimethyl sulfoxide, tetrahydrofurane, and nitromethane. X-ray crystallographic study of BCHMX (C(4)H(6)N(8)O(8), M(r)=294.17), has been carried out at the temperature of 150K with the following results: a=8.5430(8), b=6.9480(6), c=8.7780(8)A, alpha=90.0(7) degrees , beta=102.452(11) degrees , gamma=90.0(9) degrees , V=508.777(8)A(3), Z=2, D(x)=1.920 g cm(-3), lambda(Mo Ka)=0.71073A, micro=0.169 cm(-1), F(000)=856, final R=0.0414 for 1254 independent observed reflections. In the BCHMX crystal there were found more short contacts in the molecular crystal of BCHMX data of Gilardi creating extensive supramolecular architecture.

Synthesis of hexahelicene and 1-methoxyhexahelicene via cycloisomerization of biphenylyl-naphthalene derivatives.

The new approach provides nonphotochemical syntheses of helicenes based on the easy, convergent, and modular assembly of key biphenylyl-naphthalenes and their platinum-catalyzed double cycloisomerization. This sequence of reactions provides a synthetic route to helicenes in two steps from simply accessible building blocks. Furthermore, the method enables the introduction of substituents into the hexahelicene skeleton. The strategy developed is exemplified by the synthesis of 6,10-dimethylhexahelicene and 1-methoxy-6,10-dimethylhexahelicene.

Ferrocene-Donor and 4,5-Dicyanoimidazole-Acceptor Moieties in Charge-Transfer Chromophores with π Linkers Tailored for Second-Order Nonlinear Optics

A series of new nonlinear optical chromophores (1-15) that were comprised of ferrocene-donor and 4,5-dicyanoimidazole-acceptor moieties and various π linkers of different length were synthesized. Support for the presence of significant DA interactions in these NLO-phores was obtained from the evaluation of the quinoid character of the 1,4-phenylene moieties and their electronic absorption spectra, which featured intense high-energy (HE) bands that were accompanied by less-intense low-energy (LE) bands. The redox behavior of these compounds was investigated by cyclic voltammetry (CV) and by rotating-disc voltammetry (RDV); their electrochemical gaps decreased steadily from 2.64 to 2.09 V. In addition to the experimentally obtained data, DFT calculations of their absorption spectra, HOMO/LUMO levels, and second-order polarizabilities (β) (-2ω,ω,ω) were performed. A structure-property relationship study that was performed by systematically altering the π linker revealed that the intramolecular charge-transfer and nonlinear optical properties of these inorganic-organic hybrid D-π-A systems (1-15) were primarily affected by: 1) The presence of olefinic/acetylenic subunits; 2) the length of the π linker; and 3) the spatial arrangement (planarity) of the π linker.

Intramolecularly Coordinated Tin(II) Selenide and Triseleneoxostannonic Acid Anhydride

Understanding the nature of chemical bonding remains a central focus of fundamental research, and one of the valuable methods for the increasing of the understanding of intramolecular binding forces is the investigation of compounds containing multiple bonds between heavier Group 14 elements of the type RE ER (where E= group elements Si, Ge, Sn, and Pb). Recent studies of these heavier Group 14 element analogues of alkynes revealed essential structural differences between alkynes, RC CR, and their heavier Group 14 analogues, RE ER (E=Si, Ge, Sn, Pb) and opened debate as to whether the Group 14 analogue compounds exhibit a true triple bond (A), a double bond (B), or a single bond whose geometry is strongly trans-bent (C) (see Scheme 1). The presence of rather bulky substituents such as a variety of substituted aryl and silyl groups afforded the synthesis of RE ER that possess multiple bonds. The presence of a multiple bond was proposed by the UV/Vis absorptions, molecular orbital (MO) calculations, and also by the reactivity studies on these molecules. All these experiments afforded insights into the nature of the E E triple bonds. Scission of the Si Si or Ge Ge triple bond was observed by the addition of an olefin 9, 22–27] and most recently, Power and coworkers nicely outlined the cleavage of the Sn Sn multiple bond in the distannyne [ArSnSnAr] (Ar=C6H3-2,6-(C6H32,6-iPr2)2) by complexation with two molecules of either ethylene or norbornadiene or by cyclic polyolefinic molecules. 29] Moreover, the latest study dealing with the reactivity of [ArSnSnAr] with cyclooctatetraene (cot) showed the powerful reducing character of the tin(I) compound towards neutral cot. Recently, we have shown that the use of intramolecularly coordinating built-in N,C,N-coordinating pincer-type ligands is an alternative concept for the synthesis and stabilization of the reactive distannyne [({2,6-(Me2NCH2)2C6H3}Sn)2] (1). This compound showed, however, Sn Sn single bond character with a central tin atom in the oxidation state + I. We have, therefore, concentrated on the redox-type reaction of compound 1 instead of cycloadditions of the olefins. In the course of a systematic studies on the metal-type redox reactivity of 1 we present here the reaction of 1 with Se as the oxidizing agent and show that the reaction results in the two-step oxidation of the tin(I) atom along with complete cleavage of the Sn Sn bond to give a new organotin(II) selenide [({2,6-(Me2NCH2)2C6H3}Sn)2Se] (2) in the first step of the oxidation (Scheme 2). This compound is unprecedented and there is no report on well-defined selenides of low-valent Group 14 elements. Preparation of organotin(IV) selenide [({2,6-(Me2NCH2)2C6H3}Sn(Se))2Se] (3), the first example of an intramolecularly coordinated triseleneoxostannonic acid anhydride, as the final product of the oxidation of 1 by Se is reported as well (Scheme 2). Compound 3 contains two terminal Sn Se bonds and represents a new [a] M. Bouška, Dr. L. Dost l, Dr. A. Růžička, Dr. R. Jambor Department of General and Inorganic Chemistry Faculty of Chemical Technology University of Pardubice Čs legi 565, 53210, Pardubice (Czech Republic) E-mail : roman.jambor@upce.cz [b] Dr. F. de Proft Eenheid Algemene Chemie (ALGC) Vrije Universiteit Brussel (VUB) Pleinlaan 2, 1050 Brussels, (Belgium) [c] Prof. A. Lyčka Research Institute for Organic Chemistry VUOS a.s. 532 10, Pardubice, (Czech Republic) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201002641. Scheme 1. Canonical formulas for compounds of the type REER.

Oxidation of intramolecularly coordinated distannyne by S8: from tin(I) to tin(IV) polysulfide via tin(II) sulfide.

The investigation of heavier Group 14 element analogues of alkynes of the type (RE)2 (where E=Si, Ge, Sn, or Pb) is of current interest. These studies showed that the presence of rather bulky substituents such as a variety of substituted aryl and silyl groups allowed the synthesis of RE ER, which possess multiple bonds. The studies dealing with the reactivity of the RE ER multiple bonds showed scission of the Si Si or Ge Ge triple bond by the addition of an olefin, and most recently, Power and coworkers nicely outlined the cleavage of the Sn Sn multiple bond in the distannyne [ArSnSnAr] (Ar=C6H3-2,6-(C6H32,6-iPr2)2) by complexation with two molecules of either ethylene or norbornadiene. Moreover, the latest study dealing with the reactivity of [ArSnSnAr] with cyclooctatetraene (cot) showed the powerful reducing character of the tin(I) compound towards neutral cot. The reactivity studies of [ArSnSnAr] towards N2O also showed the reducing character of the Sn species, yielding the organotin(II) oxide [ArSnOSnAr] as the final product. Recently, the single-bonded dimeric species [{SiACHTUNGTRENNUNG(NtBu)2CPh}2] and [({2,6-(Me2NCH2)2C6H3}Sn)2] (1), as the first example of an Sn N intramolecularly coordinated distannyne containing a built-in N,C,N-pincer-type ligand, were reported as well. The redox reaction of [{Si ACHTUNGTRENNUNG(NtBu)2CPh}2] with N2O showed the reducing character of the Si I species, and led to the production of the well-defined [R4Si4O6] compound (R= (NtBu)2CPh) with a double-decker structure. [8]

Dimers of N‐Heterocyclic Carbene Copper, Silver, and Gold Halides: Probing Metallophilic Interactions through Electron Density Based Concepts

Homobimetallic metallophilic interactions between copper, silver, and gold-based [(NHC)MX]-type complexes (NHC=N-heterocyclic carbene, i.e, 1,3,4-trimethyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene; X=F, Cl, Br, I) were investigated by means of ab initio interaction energies, Ziegler-Rauk-type energy-decomposition analysis, the natural orbital for chemical valence (NOCV) framework, and the noncovalent interaction (NCI) index. It was found that the dimers of these complexes predominantly adopt a head-to-tail arrangement with typical M⋅⋅⋅M distance of 3.04-3.64 Å, in good agreement with the experimental X-ray structure determined for [{(NHC)AuCl}2 ], which has an Au⋅⋅⋅Au distance of 3.33 Å. The interaction energies between silver- and gold-based monomers are calculated to be about -25 kcal mol(-1) , whereas that for the Cu congener is significantly lower (-19.7 kcal mol(-1) ). With the inclusion of thermal and solvent contributions, both of which are destabilizing, by about 15 and 8 kcal mol(-1) , respectively, an equilibrium process is predicted for the formation of dimer complexes. Energy-decomposition analysis revealed a dominant electrostatic contribution to the interaction energy, besides significantly stabilizing dispersion and orbital interactions. This electrostatic contribution is rationalized by NHC(δ(+) )⋅⋅⋅halogen(δ(-) ) interactions between monomers, as demonstrated by electrostatic potentials and derived charges. The dominant NOCV orbital indicates weakening of the π backdonation in the monomers on dimer formation, whereas the second most dominant NOCV represents an electron-density deformation according to the formation of a very weak M⋅⋅⋅M bond. One of the characteristic signals found in the reduced density gradient versus electron density diagram corresponds to the noncovalent interactions between the metal centers of the monomers in the NCI plots, which is the manifestation of metallophilic interaction.

Tetrylenes chelated by hybrid amido-amino ligand: derivatives of 2-[(N,N-dimethylamino)methyl]aniline.

Reaction of 2-[(dimethylamino)methyl]aniline with butyllithium, followed by conversion with trimethylsilyl, triphenylsilyl, triphenylgermyl, trimethylstannyl, or tri-n-butylstannyl chloride, gives the corresponding substituted aniline. These compounds were further deprotonated by butyllithium and reacted with germanium, tin, and lead dichlorides, respectively, in both stoichiometric ratios 2:1 and 1:1, providing the target homo- ([2-(Me(2)NCH(2))C(6)H(4)(YR(3))N](2)M) and heteroleptic ([2-(Me(2)NCH(2))C(6)H(4)(YR(3))N]MCl) germylenes and stannylenes, where M = Ge, Sn, Y = Si, Ge, and R = Me, Ph. Unlike all of these cases, the heteroleptic plumbylene can only be obtained with this reaction when the amide is substituted by a trimethylsilyl moiety. Anilines substituted by trimethyltin or tri-n-butyltin moieties gave transmetalation products after the second deprotonation by butyllithium. The trimethyltin-substituted stannylenes could likewise not be obtained by hexamethyldisilazane elimination of (trimethylstannyl)-2-[(dimethylamino)methyl]aniline with 0.5 mol equiv of either bis[bis(trimethylsilyl)amido]tin or {bis[bis(trimethylsilyl)amido]tin chloride}. Products of these reactions are heterocubanes with compositions {[2-(Me(2)NCH(2))C(6)H(4)N]Sn}(4) and [2-(Me(2)NCH(2))C(6)H(4)N](2)(μ(2)-SnMe(2))(2), respectively, and Me(4)Sn or Me(3)SnCl. The structures of trimethylsilyl- and triphenylgermyl-substituted germylenes, stannylenes, and plumbylenes, as well as a number of their precursors, in the crystalline state, were investigated by X-ray diffraction and NMR spectroscopy in solution. Density functional theory methods were used for evaluation of the structures of several compounds.