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In this communication, we demonstrate a novel approach to prepare a discrete dimer of chiral phthalocyanine (Pc) by exploiting the flexible molecular geometry of helicenes, which enables structural interlocking and strong aggregation tendency of Pcs. Synthesized [7]helicene-Pc hybrid molecular structure, zinc-[7]helicenocyanine (Zn-7HPc), exclusively forms a stable dimeric pair consisting of two homochiral molecules. The dimerization constants were estimated to be as high as 8.96×10\(^6\) M\(^{−1}\) and 3.42×107 M\(^{−1}\) in THF and DMSO, respectively, indicating remarkable stability of dimer. In addition, Zn\(^{-7}\)HPc exhibited chiral self-sorting behavior, which resulted in preferential formation of a homochiral dimer also in the racemic sample. Two phthalocyanine subunits in the dimeric form strongly communicate with each other as revealed by a large comproportionation constant and observation of an IV-CT band for the thermodynamically stable mixed-valence state.
Phosphines are important ligands in homogenous catalysis and have been crucial for many advances, such as in cross-coupling, hydrofunctionalization, or hydrogenation reactions. Herein we report the synthesis and application of a novel class of phosphines bearing ylide substituents. These phosphines are easily accessible via different synthetic routes from commercially available starting materials. Owing to the extra donation from the ylide group to the phosphorus center the ligands are unusually electron-rich and can thus function as strong electron donors. The donor capacity surpasses that of commonly used phosphines and carbenes and can easily be tuned by changing the substitution pattern at the ylidic carbon atom. The huge potential of ylide-functionalized phosphines in catalysis is demonstrated by their use in gold catalysis. Excellent performance at low catalyst loadings under mild reaction conditions is thus seen in different types of transformations.
A series of diorgano(bismuth)chalcogenides, [Bi(di‐aryl)EPh], has been synthesised and fully characterised (E=S, Se, Te). These molecular bismuth complexes have been exploited in homogeneous photochemically‐induced radical catalysis, using the coupling of silanes with TEMPO as a model reaction (TEMPO=(tetramethyl‐piperidin‐1‐yl)‐oxyl). Their catalytic properties are complementary or superior to those of known catalysts for these coupling reactions. Catalytically competent intermediates of the reaction have been identified. Applied analytical techniques include NMR, UV/Vis, and EPR spectroscopy, mass spectrometry, single‐crystal X‐ray diffraction analysis, and (TD)‐DFT calculations.
π-Conjugated oligomers and polymers with tricoordinate boron centers incorporated into the main chain have attracted considerable attention as the interaction of the vacant p orbital on boron with an adjacent π system of the chain leads to conjugated materials with intriguing optical and electronic properties. This enables applicability in organic electronics and optoelectronics (OLEDs, OFETs, photovoltaics) or as sensory materials.
The potential of our B–C coupling protocol using metal-free catalytic Si/B exchange condensation is demonstrated by the synthesis of a series of π-conjugated monodisperse (het)aryl oligoboranes. Variation of the (het)aryl moieties allowed for tunability of the optoelectronic properties of the materials. Additionally, catalytic C–C cross-coupling strategies were applied to synthesize oligofuryl-based mono- and bisboranes, as well as polymers. These studies led to very robust and highly emissive compounds (f up to 97 %), which allow for tuning of their emission color from blue to orange. Furthermore, this work includes investigations of reaction routes to a kinetically stabilized tetraoxaporphyrinogen.
Being a key aspect of this work, a full investigation of the mechanism of the catalytic Si/B exchange was carried out. Additionally, this work presents the use of borenium cations to perform B–C coupling via intermolecular electrophilic borylation. Similar to the Si/B exchange, this route is capable of giving access to diaryl(bromo)boranes.
A series of photoactivatable CO‐releasing molecules (PhotoCORMs) was prepared from manganese pentacarbonyl bromide and 1H‐benzimidazol‐2‐ylmethyl‐(N‐phenyl)amine ligands (L) bearing different electron‐donating and electron‐withdrawing groups R = H, 4‐CH\(_3\), 4‐OCH\(_3\), 4‐Cl, 4‐NO\(_2\), 2‐, 3‐, and 4‐COOCH\(_3\) on the phenyl substituent to give octahedral manganese(I) complexes of the general formula [MnBr(CO)\(_3\)(L)]. Aerated DMSO solutions of the compounds are stable in the dark for 16 h with no CO release. However, the compounds rapidly release CO upon illumination at 412–525 nm, depending on the substitution pattern. Its influence on the photophysical and photochemical properties was systematically explored using UV/Vis spectroscopy and CO release measurements with a commercial gas sensor system. In the nitro‐substituted compound, the electronically excited state switched from benzimidazole‐ to phenyl‐centered, leading to a markedly different photochemical behavior of this visible‐light activated PhotoCORM.
Crystals of the R, S diastereoisomer of [Cp(CO)\(_2\)-FeSiCH\(_3\)F]\(_2\)O are monoclinic, space group ndc (No. 14), with a = 846.0(3) [836.4(1»), b = 768.0(3) [757.1(1»), c = 1548.5(4) [1522.3(2)] pm, {3 = 97.34(3t [97.47(3t] at 300 K [120 K] with Z = 2. Even at 120 K the Si-O-Si fragment is found to be strictly linear due to crystallographically imposed symmetry. To explain the unusual electron distribution derived from the X-ray data collected, several types of possible disorders are discussed, none of which leads to a satisfying explanation. Retaining the Ci symmetry (linear Si-O-Si fragment in the final model) the important bond lengths are Fe-Si 226.7(1) [226.5(1)] pm, Si-F 160.9(2) [161.8(2)] pm, Si-O 160.3(1) [161.1(1)] pm, Si-C 185.0(3) [185.6(3)] pm. The electronic features of this compound were probed via molecular orbital calculations of the extended Hiickel type. It was found that the lone pairs on the siloxane oxygen were tipped away from cylindrical symmetry. The tipping was directed toward the fluorine substituents on the silicon atoms and away from the CpFe(CO)\(_2\) units. A pertubational approach was utilized to rationalize this effect.
Cyclic diboranes(4) based on a chelating monoanionic, benzylphosphine linker were prepared by boron-silicon exchange between arylsilanes and B\(_2\)Br\(_4\). Coordination of Lewis bases to the remaining sp\(^2\) boron atom yielded unsymmetrical sp\(^3\)-sp\(^3\) diboranes, which were reduced with KC\(_8\) to their corresponding trans-diborenes. These compounds were studied by a combination of spectroscopic methods, X-ray diffraction and DFT calculations. PMe\(_3\)-stabilized diborene 6 was found to undergo thermal rearrangement to gem- diborene 8. DFT calculations on 8 reveal a polar boron-boron bond, and indicate that the compound is best described as a borylborylene.
Room temperature hydrogenation of an SIDep-stabilized diboryne (SIDep = 1,3-bis(diethylphenyl)-4,5-dihydroimidazol-2-ylidene) and a CAAC-supported diboracumulene (CAAC = 1-(2,6- diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) provided the first selective route to the corresponding 1,2-dihydrodiborenes. DFT calculations showed an overall exothermic (ΔG = 19.4 kcal mol\(^{-1}\) two-step asynchronous H\(_2\) addition mechanism proceeding via a bridging hydride.
The diorgano(bismuth)alcoholate [Bi((C\(_{6}\)H\(_{4}\)CH\(_{2}\))\(_{2}\)S)OPh] (1-OPh) has been synthesized and fully characterized. Stoichiometric reactions, UV/Vis spectroscopy, and (TD-)DFT calculations suggest its susceptibility to homolytic and heterolytic Bi−O bond cleavage under given reaction conditions. Using the dehydrocoupling of silanes with either TEMPO or phenol as model reactions, the catalytic competency of 1-OPh has been investigated (TEMPO=(tetramethyl-piperidin-1-yl)-oxyl). Different reaction pathways can deliberately be addressed by applying photochemical or thermal reaction conditions and by choosing radical or closed-shell substrates (TEMPO vs. phenol). Applied analytical techniques include NMR, UV/Vis, and EPR spectroscopy, mass spectrometry, single-crystal X-ray diffraction analysis, and (TD)-DFT calculations.
Twisted boron-based biradicals featuring unsaturated C\(_2\)R\(_2\) (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C\(_2\)R\(_2\)-bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.
Whereas the reduction of N-heterocyclic carbene (NHC)-stabilised cymantrenyldibromoboranes, (NHC)BBr\(_2\)Cym, in benzene results in formation of the corresponding diborenes (NHC)\(_2\)B\(_2\)Cym\(_2\), a change of solvent to THF yields a borylene of the form (NHC)\(_2\)BCym, stabilised through its boratafulvene resonance form.
TUCAN is a canonical serialization format that is independent of domain-specific concepts of structure and bonding. The atomic number is the only chemical feature that is used to derive the TUCAN format. Other than that, the format is solely based on the molecular topology. Validation is reported on a manually curated test set of molecules as well as a library of non-chemical graphs. The serialization procedure generates a canonical “tuple-style” output which is bidirectional, allowing the TUCAN string to serve as both identifier and descriptor. Use of the Python NetworkX graph library facilitated a compact and easily extensible implementation.
Fluoride abstraction from different types of transition metal fluoride complexes [L\(_n\)MF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C\(_2\)F\(_5\))\(_3\)PF\(_2\) to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C\(_2\)F\(_5\))\(_3\)PF\(_3\)]\(^-\)) is reported. (C\(_2\)F\(_5\))\(_3\)PF\(_2\) reacted with trans-[Ni(iPr\(_2\)Im)\(_2\)(Ar\(^F\))F] (iPr2Im=1,3-diisopropylimidazolin-2-ylidene; Ar\(^F\)=C\(_6\)F\(_5\), 1 a; 4-CF\(_3\)-C\(_6\)F\(_4\), 1 b; 4-C\(_6\)F\(_5\)-C\(_6\)F\(_4\), 1 c) through fluoride transfer to form the complex salts trans-[Ni(iPr\(_2\)Im)\(_2\)(solv)(Ar\(^F\))]FAP (2 a-c[solv]; solv=Et\(_2\)O, CH\(_2\)Cl\(_2\), THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh\(_3\), solvent coordination was suppressed and the complexes trans-[Ni(iPr\(_2\)Im)\(_2\)(PPh\(_3\))(C\(_6\)F\(_5\))]FAP (trans-2 a[PPh\(_3\)]) and cis-[Ni(iPr\(_2\)Im)\(_2\)(Dipp\(_2\)Im)(C\(_6\)F\(_5\))]FAP (cis-2 a[Dipp\(_2\)Im]) (Dipp\(_2\)Im=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were isolated. Fluoride abstraction from [(Dipp\(_2\)Im)CuF] (3) in CH\(_2\)Cl\(_2\) or 1,2-difluorobenzene led to the isolation of [{(Dipp\(_2\)Im)Cu}\(_2\)]\(^2\)\(^+\)2 FAP\(^-\) (4). Subsequent reaction of 4 with PPh\(_3\) and different carbenes resulted in the complexes [(Dipp\(_2\)Im)Cu(LB)]FAP (5 a–e, LB=Lewis base). In the presence of C6Me6, fluoride transfer afforded [(Dipp\(_2\)Im)Cu(C\(_6\)Me\(_6\))]FAP (5 f), which serves as a source of [(Dipp\(_2\)Im)Cu)]\(^+\). Fluoride abstraction of [Cp\(_2\)TiF\(_2\)] (7) resulted in the formation of dinuclear [FCp\(_2\)Ti(μ-F)TiCp\(_2\)F]FAP (8) (Cp=η\(^5\)-C\(_5\)H\(_5\)) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand.
The synthesis and characterization of Lewis acid/base adducts between tris(pentafluoroethyl)difluorophosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) and selected N-heterocyclic carbenes (NHCs) R\(_{2}\)Im (1,3-di-organyl-imidazolin-2-ylidene) and phosphines are reported. For NHCs with small alkyl substituents at nitrogen (R=Me, nPr, iPr) the adducts NHC ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) (2 a–h) were isolated. The reaction with the sterically more demanding NHCs Dipp\(_{2}\)Im (1,3-bis-(2,6-di-iso-propylphenyl)-imidazolin-2-ylidene) (1 i) and tBu\(_{2}\)Im (1,3-di-tert-butyl-imidazolin-2-ylidene) (1 j) afforded the aNHC adducts 3 i and 3 j (a denotes “abnormal” NHC coordination via a backbone carbon atom). The use of tBuMeIm (1-tert-butyl-3-methyl-imidazolin-2-ylidene) (1 m) led to partial decomposition of the NHC and formation of the salt [tBuMeIm−H][MeIm ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)] (4 m). The phosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) forms adducts with PMe\(_{3}\) but does not react with PPh\(_{3}\) or PCy\(_{3}\). The mer-cis isomer of literature-known Me\(_{3}\)P ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) (5 a) was structurally characterized. Mixtures of the phosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) and the sterically encumbered NHCs tBu\(_{2}\)Im, Dipp\(_{2}\)Im, and Dipp\(_{2}\)Im\(^{H2}\) (1,3-bis-(2,6-di-iso-propylphenyl)-imidazolidin-2-ylidene) (1 k) showed properties of FLPs (Frustrated Lewis Pairs) as these mixtures were able to open the ring of THF (tetrahydrofuran) to yield NHC−(CH\(_{2}\))\(_{4}\)O−PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) 6 i–k. Furthermore, the deprotonation of the weak C−H acids CH\(_{3}\)CN, acetone, and ethyl acetate was achieved, which led to the formation of the corresponding imidazolium salts and the phosphates [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(CH\(_{2}\)CN)]\(^{-}\) (7), [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(OC(=CH\(_{2}\))CH\(_{3}\))]\(^{-}\) (8) and [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(CH\(_{2}\)CO\(_{2}\)Et)]\(^{-}\) (9).
Treatment of an anionic dimanganaborylene complex ([{Cp(CO)\(_2\)Mn}\(_2\)B]\(^-\)) with coinage metal cations stabilized by a very weakly coordinating Lewis base (SMe\(_2\)) led to the coordination of the incoming metal and subsequent displacement of dimethylsulfide in the formation of hexametalladiborides featuring planar four-membered M\(_2\)B\(_2\) cores (M = Cu, Au) comparable to transition metal clusters constructed around four-membered rings composed solely of coinage metals. The analogies between compounds consisting of B\(_2\)M\(_2\) units and M\(_4\) (M = Cu, Au) units speak to the often overlooked metalloid nature of boron. Treatment of one of these compounds (M = Cu) with a Lewis-basic metal fragment (Pt(PCy\(_3\))\(_2\)) led to the formation of a tetrametallaboride featuring two manganese, one copper and one platinum atom, all bound to boron in a geometry not yet seen for this kind of compound. Computational examination suggests that this geometry is the result of d\(^{10}\)-d\(^{10}\) dispersion interactions between the copper and platinum fragments.
The 1‐methyl‐3‐(tricyanoborane)imidazolin‐2‐ylidenate anion (2) was obtained in high yield by deprotonation of the B(CN)3‐methylimidazole adduct 1. Regarding charge and stereo‐electronic properties, anion 2 closes the gap between well‐known neutral NHCs and the ditopic dianionic NHC, the 1,3‐bis(tricyanoborane)imidazolin‐2‐ylidenate dianion (IIb). The influence of the number of N‐bonded tricyanoborane moieties on the σ‐donating and π‐accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2, IIb, and 1,3‐dimethylimidazolin‐2‐ylidene (IMe, IIa). Therefore NHC 2, which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO)\(_{4}\)] yielding alkylated imidazoles 3 and 4, the anionic selenium adduct 5, and the anionic nickel tricarbonyl complex 8, respectively. The results of this study prove that charge, number of coordination sites, buried volume (%V\(_{bur}\)) and σ‐donor and π‐acceptor abilities of NHCs can be effectively fine‐tuned via the number of tricyanoborane substituents.
Novel dyes were prepared by simple “click CuAAC” attachment of a triarylborane–alkyne to the azide side chain of an amino acid yielding triarylborane dye 1 which was conjugated with pyrene (dye 2) forming a triarylborane–pyrene FRET pair. In contrast to previous cationic triarylboranes, the novel neutral dyes interact only with proteins, while their affinity to DNA/RNA is completely abolished. Both the reference triarylborane amino acid and triarylborane–pyrene conjugate bind to BSA and the hDPP III enzyme with high affinities, exhibiting a strong (up to 100-fold) fluorescence increase, whereby the triarylborane–pyrene conjugate additionally retained FRET upon binding to the protein. Furthermore, the triarylborane dyes, upon binding to the hDPP III enzyme, did not impair its enzymatic activity under a wide range of experimental conditions, thus being the first non-covalent fluorimetric markers for hDPP III, also applicable during enzymatic reactions with hDPP III substrates.
The reductive coupling of an NHC-stabilized aryldibromoborane yields a mixture of trans- and cis-diborenes in which the aryl groups are coplanar with the diborene core. Under dilute reduction conditions two diastereomers of a borirane-borane intermediate are isolated, which upon further reduction give rise to the aforementioned diborene mixture. DFT calculations suggest a mechanism proceeding via nucleophilic attack of a dicoordinate borylene intermediate on the aryl ring and subsequent intramolecular B-B bond formation.
We report a transition metal‐free, regio‐ and stereo‐selective, phosphine‐catalyzed method for the trans hydroboration of 1,3‐diynes with pinacolborane that affords (E)‐1‐boryl‐1,3‐enynes. The reaction proceeds with excellent selectivity for boron addition to the external carbon of the 1,3‐diyne framework as unambiguously established by NMR and X‐ray crystallographic studies. The reaction displays a broad substrate scope including unsymmetrical diynes to generate products in high yield (up to 95 %). Experimental and theoretical studies suggest that phosphine attack on the alkyne is a key process in the catalytic cycle.
Organoboron compounds, such as benzyl-, allyl-, allenyl-, vinyl-, and 2-boryl allyl-boronates, have been synthesized via metal-catalyzed borylations of sp3 C-O and C-H bonds. Thus, Cu-catalyzed borylations of alcohols and their derivatives provide benzyl-, allyl-, allenyl-, vinyl-, and 2-boryl allyl-boronates via nucleophilic substitution. The employment of Ti(OiPr)4 turns the OH moiety into a good leaving group (‘OTi’). The products of Pd-catalyzed oxidative borylations of allylic C-H bonds of alkenes were isolated and purified, and their application in the one-pot synthesis of stereodefined homoallyl alcohols was also investigated. Chapter 2 presents a copper-catalyzed synthesis of benzyl-, allyl-, and allenyl-boronates from benzylic, allylic, and propargylic alcohols, respectively, employing a commercially available catalyst precursor, [Cu(CH3CN)4]2+[BF4-]2, and Xantphos as the ligand. The borylation of benzylic alcohols was carried out at 100 oC with 5-10 mol % [Cu(CH3CN)4]2+[BF4-]2, which afforded benzylic boronates in 32%-95% yields. With 10 mol % [Cu(CH3CN)4]2+[BF4-]2, allylic boronates were provided in 53%-89% yields from the borylation of allylic alcohols at 60 or 100 oC. Secondary allylboronates were prepared in 72%-84% yields from the borylation of primary allylic alcohols, which also suggests that a nucleophilic substitution pathway is involved in this reaction. Allenylboronates were also synthesized in 72%-89% yields from the borylation of propargylic alcohols at 40 or 60 oC. This methodology can be extended to borylation of benzylic and allylic acetates. This protocol exhibits broad reaction scope (40 examples) and high efficiency (up to 95% yield) under mild conditions, including the preparation of secondary allylic boronates. Preliminary mechanistic studies suggest that nucleophilic substitution is involved in this reaction. Chapter 3 reports an efficient methodology for the synthesis of vinyl-, allyl-, and (E)-2-boryl allylboronates from propargylic alcohols via copper-catalyzed borylation reactions under mild conditions. In the presence of a commercially available catalyst precursor (Cu(OAc)2 or Cu(acac)2) and ligand (Xantphos), the reaction affords the desired products in up to 92% yield with a broad substrate scope (43 examples). Vinylboronates were synthesized in 50%-83% yields via Cu-catalyzed hydroboration of mono-substituted propargylic alcohols. With 1,1-disubstituted propargylic alcohols as the starting materials and Cu(OAc)2 as the catalyst precursor, a variety of allylboronates were synthesized in 44%-83% yields. The (E)-2-boryl allylboronates were synthesized in 54%-92% yields via the Cu-catalyzed diboration of propargylic alcohols. The stereoselectivity is different from the Pd(dba)2-catalyzed diboration of allenes that provided (Z)-2-boryl allylboronates predominantly. The isolation of an allenyl boronate as the reaction intermediate suggests that an SN2’-type reaction, followed by borylcupration, is involved in the mechanism of the diboration of propargylic alcohols. In chapter 4, a Pd-catalyzed allylic C-H borylation of alkenes is reported. The transformation exhibits high regioselectivity with a variety of linear alkenes, employing a Pd-pincer complex as the catalyst precursor, and the allylic boronate products were isolated and purified. This protocol can also be extended to one-pot carbonyl allylation reactions to provide homoallyl alcohols efficiently. An interesting mechanistic feature is that the reaction proceeds via a Pd(II)/Pd(IV) catalytic cycle. Formation of the Pd(IV) intermediate occurs by a unique combination of an NCNpincer complex and application of F-TEDA-BF4 as the oxidant. An important novelty of the present C-H borylation reaction is that all allyl-Bpin products can be isolated with usually high yields. This is probably a consequence of the application of the NCN-pincer complex as catalyst, which selectively catalyzes C-B bond formation avoiding subsequent C-B bond cleavage based side-reactions
A novel protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones. Control experiments and DFT calculations indicate that both the ortho-F substituents on the polyfluorophenyl boronates and the counterion K\(^+\) in the carbonate base are critical. The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields. Intriguing structural features involving O−H⋅⋅⋅O and O−H⋅⋅⋅N hydrogen bonding, as well as arene-perfluoroarene interactions, in this series of racemic polyfluoroaryl carbinols have also been addressed.
The reaction of aryl‐ and amino(dihydro)boranes with dibora[2]ferrocenophane 1 leads to the formation 1,3‐trans ‐dihydrotriboranes by formal hydrogenation and insertion of a borylene unit into the B=B bond. The aryltriborane derivatives undergo reversible photoisomerization to the cis ‐1,2‐μ‐H‐3‐hydrotriboranes, while hydride abstraction affords cationic triboranes, which represent the first doubly base‐stabilized B3H4\(^+\) analogues.
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.
1 We studied the effect of temperature on the binding to rat heart \(M_2\) muscarinic receptors of antagonists related to the carbon/silicon pairs pridinol/sila-pridinol and diphenidol/sila-diphenidol (including three germanium compounds) and six structurally related pairs of enantiomers [(R)- and (S)-procyclidine, (R)- and (S)-trihexyphenidyl, (R)- and (S)-tricyclamol, (R)- and (S)-trihexyphenidyl methiodide, (R)- and (S)-hexahydro-diphenidol and (R)- and (S)-hexbutinol]. Binding affinities were determined in competition experiments using \([^3H]\)-N-methyl-scopolamine chloride as radioligand. The reference drugs were scopolamine and N-methyl-scopolamine bromide.
2 The affinity of the antagonists either increased or decreased with temperature, van 't Hoff plots were linear in the 278–310°K temperature range. Binding of all antagonists was entropy driven. Enthalpy changes varied from large negative values (down to \(−29 kJ mol^{−1}\)) to large positive values (up to \(+ 30 kJ mol^{−1}\)).
3 (R)-configurated drugs had a 10 to 100 fold greater affinity for \(M_2\) receptors than the corresponding (S)-enantiomers. Enthalpy and entropy changes of the respective enantiomers were different but no consistent pattern was observed.
4 When silanols \((R_3SiOH)\) were compared to carbinols \((R_3COH)\), the affinity increase caused by C/Si exchange varied between 3 and 10 fold for achiral drugs but was negligible in the case of chiral drugs. Silanols induced more favourable enthalpy and less favourable entropy changes than the corresponding carbinols when binding. Organogermanium compounds \((R_4Ge)\) when compared to their silicon counterparts (R4Si) showed no significant difference in affinity as well as in enthalpy and entropy changes.
5 Exchange of a cyclohexyl by a phenyl moiety was associated with an increase or a decrease in drug affinity (depending on the absolute configuration in the case of chiral drugs) and generally also with a more favourable enthalpy change and a less favourable entropy change of drug binding.
6 Replacement of a pyrrolidino by a piperidino group and increasing the length of the alkylene chain bridging the amino group and the central carbon or silicon atom were associated with either an increase or a decrease of entropy and enthalpy changes of drug binding. However, there was no clear correlation between these structural variations and the thermodynamic effects.
7 Taken together, these results suggest that hydrogen bond-forming OH groups and, to a lesser extent, polarizable phenyl groups contribute significantly to the thermodynamics of interactions between these classes of muscarinic antagonists and \(M_2\) muscarinic receptors.
Direct Heteroarylation Polymerization (DHAP) is becoming a valuable alternative to classical polymerization methods being used to synthesize π-conjugated polymers for organic electronics applications. In previous work, we showed that theoretical calculations on activation energy (Ea) of the C–H bonds were helpful to rationalize and predict the selectivity of the DHAP. For readers’ convenience, we have gathered in this work all our previous theoretical calculations on Ea and performed new ones. Those theoretical calculations cover now most of the widely utilized electron-rich and electron-poor moieties studied in organic electronics like dithienyl-diketopyrrolopyrrole (DT-DPP) derivatives. Theoretical calculations reported herein show strong modulation of the Ea of C–H bond on DT-DPP when a bromine atom or strong electron withdrawing groups (such as fluorine or nitrile) are added to the thienyl moiety. Based on those theoretical calculations, new cyanated dithienyl-diketopyrrolopyrrole (CNDT-DPP) monomers and copolymers were prepared by DHAP and their electro-optical properties were compared with their non-fluorinated and fluorinated analogues.
A series of tetracationic bis-triarylborane dyes, differing in the aromatic linker connecting two dicationic triarylborane moieties, showed very high submicromolar affinities toward ds-DNA and ds-RNA. The linker strongly influenced the emissive properties of triarylborane cations and controlled the fluorimetric response of dyes. The fluorene-analog shows the most selective fluorescence response between AT-DNA, GC-DNA, and AU-RNA, the pyrene-analog’s emission is non-selectively enhanced by all DNA/RNA, and the dithienyl-diketopyrrolopyrrole analog’s emission is strongly quenched upon DNA/RNA binding. The emission properties of the biphenyl-analog were not applicable, but the compound showed specific induced circular dichroism (ICD) signals only for AT-sequence-containing ds-DNAs, whereas the pyrene-analog ICD signals were specific for AT-DNA with respect to GC-DNA, and also recognized AU-RNA by giving a different ICD pattern from that observed upon interaction with AT-DNA. The fluorene- and dithienyl-diketopyrrolopyrrole analogs were ICD-signal silent. Thus, fine-tuning of the aromatic linker properties connecting two triarylborane dications can be used for the dual sensing (fluorimetric and CD) of various ds-DNA/RNA secondary structures, depending on the steric properties of the DNA/RNA grooves.
The theoretical work presented in this thesis is concerned with the highest possible oxidation states of the 5d transition metal row. Based on a validation study of several DFT functionals against accurate coupled-cluster CCSD(T) methods we will present calculations on a series of new high oxidation state HgIV species. Quantum-chemical calculations have also been applied to various fluoro complexes of gold in oxidation states +V through +VII to evaluate the previously claimed existence of AuF7. The calculations indicate clearly that the oxidation state (+V), e.g., in [AuF5]2, remains the highest well-established gold oxidation state. Further calculations on iridium in oxidation state (+VII) show that IrF7 and IrOF5 are viable synthetic targets, whereas higher oxidation states of iridium appear to be unlikely. Structures and stabilities of several osmium fluorides and oxyfluorides were also studied in this thesis. It is shown that homoleptic fluorides all the way up to OsF8 may exist. Combining the results of the most accurate quantum-chemical predictions of this thesis and of the most reliable experimental studies, we observe a revised trend of the highest oxidation states of the 5d transition metal row. From lanthanum (+III) to osmium (+VIII), there is a linear increase of the highest oxidation states with increasing atomic number. Thereafter, we observe a linear descent from osmium (+VIII) to mercury (+IV). We will also present a short outlook to the transition metals of the 3d and 4d row and their highest reachable oxidation states.
Two different chromophores, namely a dipolar and an octupolar system, were prepared and their linear and nonlinear optical properties as well as their bioimaging capabilities were compared. Both contain triphenylamine as the donor and a triarylborane as the acceptor, the latter modified with cationic trimethylammonio groups to provide solubility in aqueous media. The octupolar system exhibits a much higher two‐photon brightness, and also better cell viability and enhanced selectivity for lysosomes compared with the dipolar chromophore. Furthermore, both dyes were applied in two‐photon excited fluorescence (TPEF) live‐cell imaging.
Two different chromophores, namely a dipolar and an octupolar system, were prepared and their linear and nonlinear optical properties as well as their bioimaging capabilities were compared. Both contain triphenylamine as the donor and a triarylborane as the acceptor, the latter modified with cationic trimethylammonio groups to provide solubility in aqueous media. The octupolar system exhibits a much higher two‐photon brightness, and also better cell viability and enhanced selectivity for lysosomes compared with the dipolar chromophore. Furthermore, both dyes were applied in two‐photon excited fluorescence (TPEF) live‐cell imaging.
The dimethylbismuth cation: entry into dative Bi-Bi bonding and unconventional methyl exchange
(2021)
The dimethyl bismuth cation, [BiMe\(_2\)(SbF\(_6\))], has been isolated and characterized. Reaction with BiMe\(_3\) allows access to the first compound featuring Bi→Bi donor–acceptor bonding. In solution, dynamic behavior with methyl exchange via an unusual S\(_E\)2 mechanism is observed, underlining the unique properties of bismuth species as soft Lewis acids with the ability to undergo reversible Bi−C bond cleavage.
Tetraiododiborane(4) (B\(_2\)I\(_4\)) is a Polymer based on sp\(^3\) Boron in the Solid State
(2020)
Herein we present the first solid‐state structures of tetraiododiborane(4) (B\(_2\)I\(_4\)), which was long believed to exist in all phases as discrete molecules with planar, tricoordinate boron atoms, like the lighter tetrahalodiboranes(4) B\(_2\)F\(_4\), B\(_2\)Cl\(_4\), and B\(_2\)Br\(_4\). Single‐crystal X‐ray diffraction, solid‐state NMR, and IR measurements indicate that B\(_2\)I\(_4\) in fact exists as two different polymeric forms in the solid state, both of which feature boron atoms in tetrahedral environments. DFT calculations are used to simulate the IR spectra of the solution and solid‐state structures, and these are compared with the experimental spectra.
The development of complexes featuring low-valent, multiply bonded metal centers is an exciting field with several potential applications. In this work, we describe the design principles and extensive computational investigation of new organometallic platforms featuring the elusive manganese-manganese bond stabilized by experimentally realized N-heterocyclic carbenes (NHCs). By using DFT computations benchmarked against multireference calculations, as well as MO- and VB-based bonding analyses, we could disentangle the various electronic and structural effects contributing to the thermodynamic and kinetic stability, as well as the experimental feasibility, of the systems. In particular, we explored the nature of the metal-carbene interaction and the role of the ancillary η\(^{6}\) coordination to the generation of Mn\(_{2}\) systems featuring ultrashort metal-metal bonds, closed-shell singlet multiplicities, and positive adiabatic singlet-triplet gaps. Our analysis identifies two distinct classes of viable synthetic targets, whose electrostructural properties are thoroughly investigated.
This theses deals with the syntheses and the coordination behaviour of polyimidosulfur anions like S(NR)32–, S(NR)42–, RS(NR)2– or RS(NR)3–, the nitrogen analogues of the well known oxo-anions SO32–, SO42–, RSO2– and RSO3–. The first aim was the synthesis of a triimidosulfite with three different NR-substituents, a so called asymmetrical triimidosulfite. In all reactions, that have been carried out to obtain a triimidosulfite with three (or two) different residues at nitrogen, the final product was always the dilithium sulfide adduct. The syntheses of chiral alkylenediimidosulfites was successful. Similar to Corey’s S-ylides (R2(O)S+––CR2) and Wittig’s phosphonium ylides (R3P+––CR2) these molecules contain a positively charged sulfur atom next to a carbanionic centre. The structures of the alkylenediimidosulfites are not influenced by the different substituents at nitrogen and carbon, respectively. In each case a doublecubic structure is received. The first members of a completely new class of compounds were synthesised: the aryl-bis-(diimidosulfinates). In this compounds two SN2 units are connected via a heteroaromatic linker, containing a potential donor centre in metal coordination. They represent, like the known alkyldiimidosulfinates, dipodal monoanionic ligands. In the field of sulfur (VI) chemistry the syntheses of aryltriimidosulfonates were successful. Hitherto it was believed, that only spatial less demanding lithium organics could be added to a S=N double bond in S(NtBu)3. This assumption was confirmed by the fact that methyl- and phenylacetylene-triimidosulfonate were the only known alkylsulfonates. Nevertheless, the addition of several lithiumheteroarenes to sulfurtriimide worked without difficulties. If the shape of the nucleophile permits to slot in between the NtBu substituents and to approach the electrophilic sulfur in the sulfurtriimide from the side rather than in an orthogonal angle, the addition reaction works smoothly. Although the steric demand of the tris(tert.-butyl)triimidosulfonate unit is very high, the synthesis of thiophene-bis-(triimidosulfonate) worked. The sulfonate moieties function as dipodal ligands.