Directed tridentate Lewis acids based on the 1,3,5‐trisilacyclohexane skeleton with three ethynyl groups CH2Si(Me)(C2H)3 were synthesised and functionalised by hydroboration with HB(C6F5)2, yielding ...the ethenylborane {CH2Si(Me)C2H2B(C6F5)2}3, and by metalation with gallium and indium organyls affording {CH2Si(Me)C2M(R)2}3 (M=Ga, In, R=Me, Et). In the synthesis of the backbone the influence of substituents (MeO, EtO and iPrO groups at Si) on the orientation of the methyl group was studied with the aim to increase the abundance of the all‐cis isomer. New compounds were identified by elemental analyses, multi‐nuclear NMR spectroscopy and in some cases by IR spectroscopy. Crystal structures were obtained for cis‐trans‐CH2Si(Me)(Cl)3, all‐cis‐CH2Si(Me)(H)3, all‐cis‐CH2Si(Me)(C2H)3, cis‐trans‐CH2Si(Me)(C2H)3 and all‐cis‐CH2Si(Me)(C2SiMe3)3. A gas‐phase electron diffraction experiment for all‐cis‐CH2Si(Me)(C2H)3 provides information on the relative stabilities of the all‐equatorial and all‐axial form; the first is preferred in both solid and gas phase. The gallium‐based Lewis acid {CH2Si(Me)C2Ga(Et)2}3 was reacted with a tridentate Lewis base (1,3,5‐trimethyl‐1,3,5‐triazacyclohexane) in an NMR titration experiment. The generated host–guest complexes involved in the equilibria during this reaction were identified by DOSY NMR spectroscopy by comparing measured diffusion coefficients with those of the suitable reference compounds of same size and shape.
Directed tridentate Lewis acids with 1,3,5‐triethynyl‐1,3,5‐trisilacyclohexane skeletons and three boron‐, gallium‐ or indium‐based acid functions have been synthesised and tested in host–guest chemistry experiments in a dynamic system in solution; the picture shows the scaffold in its unsubstituted form with equatorially orientated ethynyl groups.
9‐Br‐closo‐1,2‐C2B10H11 has been prepared and its gas‐phase structure has been examined by means of gas electron diffraction. The structure of the carbaborane core is similar to the structure of the ...parent compound, which is of C2v symmetry. A DFT‐based search for the corresponding reaction pathway of the bromination of closo‐1,2‐C2B10H12 revealed that the catalytic amount of aluminum reduces the barrier of the initial attack of the bromination agent toward the negatively charged part of the icosahedral carbaborane, i. e., the first transition state, from about 40 to about 27 kcalmol‐1. The Br−Br bond is weakened by an intermediate binding to the large π‐hole on the aluminum atom of AlBr3, which is the driving force for the AlBr3‐catalyzed bromination.
Al helps: A sample of 9‐Br‐closo‐1,2‐C2B10H11 was prepared and was successfully diffracted with electrons in order to determine its gas‐phase molecular structure. Computational examinations of the different reaction pathways of the bromination were carried out and AlBr3, serving as a catalyst, was found to be decisive for the bromination to occur.
Carbaboranes 1,2‐(EH)2‐closo‐1,2‐C2B10H10 (E=S, Se) were prepared, in the case of E=Se for the first time. Their semi‐experimental equilibrium molecular structures were established by the concerted ...use of quantum‐chemical calculations and gas electron diffraction. A method was developed and implemented to quantify the contribution of experimental data to each refined structural parameter. The accuracy of the experimental structures and those calculated at the MP2 level of theory were gauged by comparison of experimental 11B NMR chemical shifts with quantum‐chemically computed values; the inclusion of electron correlation (GIAO‐MP2) provided superior results. For the purpose of geometrical prediction, the remaining group 16 elements were considered, and the icosahedral structures for E=O and Te were also computed; for E=O the same theoretical approach was used as for E=S, and for E=Te a description similar to that for E=Se was employed.
Hydrochalcogeno carbaboranes: Icosahedral carbaboranes with thiol and selenol groups were prepared and their structures determined by gas electron diffraction augmented by ab initio calculated data (see figure). A method for quantifying the experimental contribution to the structural parameters was developed and tested. Comparison of NMR chemical shifts in solution with quantum‐chemically calculated values allowed further structural information to be retrieved.
Wir berichten über die Dimerisierung von Kohlenmonoxid bei Raumtemperatur mittels anionischer C4/C5‐Dicarbene Li(ADC) (ADC = ArC{(Dipp)NC}2; Dipp = 2,6‐iPr2C6H3; Ar = Ph, DMP (4‐Me2NC6H4), Bp ...(4‐PhC6H4)), wobei (E)‐Ethen‐1,2‐bis(olat) (d. h. −O−C=C−O− = COen) verbrückte mesoionische Carben (iMIC)‐Lithiumverbindungen COen‐(iMIC)Li2 (COen‐iMIC2 = ArC{(Dipp)NC}2(CO)2) in quantitativer Ausbeute isoliert wurden. COen‐(iMIC)Li2 sind farbliche, stabile Feststoffe und weisen eine bemerkenswert kleine HOMO–LUMO‐Energielücke auf. Sie untergehen mit Selen, CuCl (oder CuCl2) und AgCl 2e‐Oxidationen, um die dinuklearen Verbindungen COon‐(iMIC)E2 (E = Se, CuCl, AgCl) mit einem 1,2‐Dion‐verbrückten neutralen Bis‐iMIC (d. h. COon‐iMIC2 = ArC{(Dipp)NC}2(C=O)2) zu erzeugen. COen‐(iMIC)Li2 reagieren mit LiAlH4 und (Et2O)2BeBr2 durch redoxneutrale Salzmetathesereaktion zu COen‐(iMIC)AlH22 und COen‐(iMIC)BeBr2, bei denen die dianionische COen‐Brücke erhalten bleibt. Alle Verbindungen wurden mittels NMR‐Spektroskopie, Massenspektrometrie und Röntgenbeugung charakterisiert. Die stereoelektronischen Eigenschaften von COon‐iMIC2 wurden durch experimentelle und theoretische Methoden quantifiziert.
Die direkte Dimerisierung von Kohlenmonoxid bei Raumtemperatur durch anionische Dicarbene Li(ADC) liefert quantitativ (E)‐Ethen‐1,2‐bis(olat)‐verbrückte mesoionische Carben (iMIC)‐Lithiumverbindungen, COen‐(iMIC)Li2. Sie gehen eine 2e‐Oxidation ein, um 1,2‐dionverbrückte Bis‐iMIC, COon‐(iMIC)2‐haltigen Verbindungen zu erhalten, während redoxneutrale Salzmetathesen zu COen‐(iMIC)E2‐Verbindungen führen (E = Hauptgruppenelement‐Spezies).
Abstract Ein zweizähniges Pniktogenbrücken‐Wirtsystem auf der Basis von 1,8‐Diethinylanthracen wurde mittels einer selektiven Zinn‐Antimon‐Austauschreaktion hergestellt und auf seine Fähigkeit ...untersucht, als Lewis‐saure Wirtskomponente für die Komplexierung von Lewis‐basischen oder anionischen Gästen zu fungieren. In dieser Arbeit wurde mit der C≡C−Sb(C 2 F 5 ) 2 ‐Gruppe eine neuartige Akzeptorfunktion etabliert, mit der das Potenzial von Antimon(III)‐Funktionen als Vertreter der kaum erforschten Pniktogenbrücken‐Donatoren untersucht werden kann. Die Akzeptorfähigkeit dieses teilfluorierten Wirtsystems wurde gegenüber Halogenidanionen (Cl − , Br − , I − ), Dimethylchalkogeniden Me 2 Y (Y = O, S, Se, Te) und Stickstoffheterozyklen (Pyridin, Pyrimidin) untersucht. Einblicke in das Adduktbildungsverhalten sowie die Bindungssituation solcher E⋅⋅⋅Sb−C F ‐Einheiten wurden in Lösung mittels NMR‐Spektroskopie, im festen Zustand durch Röntgenbeugung, durch Elementaranalysen sowie durch rechnerische Methoden (DFT, QTAIM, IQA) gewonnen.
After numerous attempts over the last seven decades to obtain a structure for the simple, highly symmetric molecule tetranitromethane (C(NO2)4, TNM) that is consistent with results from diffraction ...experiments and spectroscopic analysis, the structure has now been determined in the gas phase and the solid state. For the gas phase, a new approach based on a four‐dimensional dynamic model for describing the correlated torsional dynamics of the four C−NO2 units was necessary to describe the experimental gas‐phase electron diffraction intensities. A model describing a highly disordered high‐temperature crystalline phase was also established, and the structure of an ordered low‐temperature phase was determined by X‐ray diffraction. TNM is a prime example of molecular flexibility, bringing structural methods to the limits of their applicability.
Highly dynamic is the structural behavior of tetranitromethane, C(NO2)4. After more than half a century of investigations, its structure in the gas phase was solved through the development and application of a new approach for the dynamic modeling of electron diffraction data while the refinement of single‐crystal X‐ray diffraction data has now been successful for two phases.
A number of measures to increase the quality of data recorded with an improved Balzers Eldigraph KD-G2 gas-phase electron diffractometer are discussed. The beam-stop has been decoupled from the ...sector enabling us recording the current of the primary beam and scattered electrons during the experiment. Different beam-stops were tested for use in the present setup. Modifications of the nozzle tip of an earlier described medium temperature nozzle are reported. The measures lead to reduced exposure times and reduced amount of sample necessary for complete data collection.
The refrigerant trans‐1,3,3,3‐tetrafluoropropene (HFO‐1234ze) is used as a replacement for former cooling agents that have been phased‐out due to their global warming potential or ozone depleting ...potential. Although it is used on a large scale, only a few vibrational data and no structural data of HFO‐1234ze are known. We report structure determinations based on low‐temperature single‐crystal X‐ray diffraction data as well as gas‐phase diffraction data of HFO‐1234ze and HFO‐1234yf (2,3,3,3‐tetrafluoropropene). Furthermore, vibrational spectra of HFO‐1234ze in all phases are described. The results are discussed together with quantum‐chemical calculations on the PBE0/cc‐pVTZ level of theory. Combustion experiments of HFO‐1234ze show carbonyl difluoride, carbon dioxide and hydrogen fluoride to be the main combustion products.
The structures of two tetrafluoropropenes have been elucidated in the solid state and in the gas phase. Combustion experiments prove the flammability of the refrigerant HFO‐1234ze and the formation of hazardous gases.
(C2F5)2PNEt2 represents an excellent starting material for the selective synthesis of bis(pentafluoroethyl)phosphane derivatives. The moderately air‐sensitive aminophosphane is accessible on a ...multi‐gram scale by treating Cl2PNEt2 with C2F5Li. Treatment with gaseous HCl or HBr yielded the corresponding phosphane halides (C2F5)2PCl and the so far unknown (C2F5)2PBr in good yields. The hitherto unknown (C2F5)2PF was obtained by treating (C2F5)2PBr with excess antimony trifluoride. Treatment of (C2F5)2PCl with Bu3SnH led to the quantitative formation of (C2F5)2PH. Deprotonation formally yielded the (C2F5)2P– anion in a form that was stabilized by coordination to mercury ions to form the complex Hg{P(C2F5)2}2(dppe). An improved high‐yielding synthesis of (C2F5)2POH was achieved by treating (C2F5)2PNEt2 with p‐toluenesulfonic acid. The gas‐phase structures of (C2F5)2PH and (C2F5)2POH were determined by electron diffraction. The vibrational corrections employed in the data analysis of the diffraction data were derived from molecular dynamics calculations. Both compounds exist in the gas phase mostly as C1‐symmetric cis,cis conformers with regard the orientation of the C2F5 groups relative to the functional groups H and OH. The presence of a second conformer at ambient temperature is likely in both cases. The refined amounts of dominant conformers are 94(6) and 85(6) % for (C2F5)2PH and (C2F5)2POH, respectively. The conformational behaviour was further explored by potential energy surface scans based on DFT calculations. Important experimental structural parameters for the most stable conformers are re(P–C)average = 1.884(3) Å for (C2F5)2PH and re(P–C)average = 1.894(4) Å and re(P–O) = 1.582(3) Å for (C2F5)2POH. The different coordination properties of (C2F5)3P, (C2F5)2POH, (CF3)3P and (CF3)2POH were evaluated by complex formation with Ni(CO)4: the maximum achievable number of CO ligands substituted by (C2F5)3P is 1, by (C2F5)2POH is 2, by (CF3)3P is 3 and by the smallest ligand (CF3)2POH is 4.
New synthetic routes to a series of bis(pentafluoroethyl)phosphanes have been developed and the structures of two of them, (C2F5)2PH and the phosphinous acid (C2F5)2POH, were studied by gas electron diffraction, making use of molecular dynamics calculations to support data analysis in an improved approach.
In diesem Artikel berichten wir über die Synthese, Charakterisierung und Reaktivitätsstudien des ersten zyklischen C2As2‐Diradikaloids {(IPr)CAs}2 (6) (IPr = C{N(Dipp)CH}2; Dipp = 2,6‐iPr2C6H3). Die ...Umsetzung von (IPr)CH2 (1) mit AsCl3 ergibt das Lewis‐Addukt {(IPr)CH2}AsCl3 (2). Verbindung 2 geht schrittweise eine Dehydrochlorierung ein, die über {(IPr)CH}AsCl2 (3) zu {(IPr)CAsCl}2 (5 a) oder {(IPr)CAs}2ClOTf (5 b) führt. Die Reduktion von 5 a (oder 5 b) mit Magnesiumspänen ergibt 6 als roten kristallinen Feststoff in 90 %iger Ausbeute. Verbindung 6, die einen planaren C2As2‐Ring aufweist, ist diamagnetisch und zeigt gut aufgelöste NMR‐Signale. DFT‐Berechnungen zeigen einen Singulett‐Grundzustand für 6 mit einer kleinen Singulett‐Triplett‐Energielücke von 8.7 kcal mol−1. Der diradikalische Charakter von 6 beträgt 20% (CASSCF, Complete Active Space Self Consistent Field) und 28% (DFT). Die Reaktionen von 6 mit (PhSe)2 bzw. Fe2(CO)9 führen zur Bildung von {(IPr)CAs(SePh)}2 (7) bzw. {(IPr)CAs}2Fe(CO)4 (8).
Das C2As2‐zyklische Diradikaloid 6 wurde als roter kristalliner Feststoff durch 2e‐Reduktion von 5 a isoliert. Berechnungen deuten auf einen Singulett‐Grundzustand für 6 hin, der um 0.34 kcal mol−1 höher ist als der der Broken‐Symmetry offenschaligen Singulett‐Lösung. Das HOMO von 6 befindet sich an den Arsenatomen und ist transannulär antibindend, während das LUMO transannulär bindend ist und sich über das C2As2C2‐Gerüst erstreckt. Reaktivitätsstudien von 6 werden mit (PhSe)2 und Fe2(CO)9 gezeigt.
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