The problem of computation of vibrational molecular parameters in models of gas electron diffraction is discussed. Some peculiarities of the standard for these purposes Shrink program are analysed. ...An alternative code has been written to implement the well established Sipachev's first-order perturbation theory. It has been used for calculation of vibrational parameters of several molecules. Comparison of obtained results shows that the new program outperforms the available program Shrink in many aspects.
We reply to the comment by J.‐M. Mewes, A. Hansen and S. Grimme (MHG), who challenged the accuracy of our re value for the N⋅⋅⋅Te distance in (C6F5)Te(CH2)3NMe2 determined by gas electron diffraction ...(GED). We conclusively demonstrate that MHG′s quoted reference calculations are less accurate than they claim for solid state and gas phase. We show by higher level calculations, that we did not miss substantial contributions from open‐chain conformers. Refinements on simulated scattering data show that such contributions would have had only an almost negligible effect on re(N⋅⋅⋅Te). MHG suggested the use of a H0‐tuned GFN method for calculating vibrational corrections ra−re, but this did not change these values substantially. Alternative amplitude calculations using higher level analytic harmonic and numeric cubic force fields (PBE0‐D3BJ/def2‐TZVP) yield a GED value for re(N⋅⋅⋅Te)=2.852(25) Å that is well within the experimental error of our original value 2.918(31) Å but far from the 2.67(8) Å predicted by MHG. A now improved error estimation accounts for inaccuracies in the calculated auxiliary values. The gas/solid difference of the weak N⋅⋅⋅Te interaction is in a realistic range compared to other systems involving weak chemical interactions.
We reply to the comment which challenged the accuracy of our re value for the N⋅⋅⋅Te distance in (C6F5)Te(CH2)3NMe2 determined by gas electron diffraction. We show by higher level calculations, that we did not miss substantial contributions from open‐chain conformers.
The covalent diamantyl (C28H38) and oxadiamantyl (C26H34O2) dimers are stabilized by London dispersion attractions between the dimer moieties. Their solid-state and gas-phase structures were studied ...using a multitechnique approach, including single-crystal X-ray diffraction (XRD), gas-phase electron diffraction (GED), a combined GED/microwave (MW) spectroscopy study, and quantum chemical calculations. The inclusion of medium-range electron correlation as well as the London dispersion energy in density functional theory is essential to reproduce the experimental geometries. The conformational dynamics computed for C26H34O2 agree well with solution NMR data and help in the assignment of the gas-phase MW data to individual diastereomers. Both in the solid state and the gas phase the central C–C bond is of similar length for the diamantyl XRD, 1.642(2) Å; GED, 1.630(5) Å and the oxadiamantyl dimers XRD, 1.643(1) Å; GED, 1.632(9) Å; GED+MW, 1.632(5) Å, despite the presence of two oxygen atoms. Out of a larger series of quantum chemical computations, the best match with the experimental reference data is achieved with the PBEh-3c, PBE0-D3, PBE0, B3PW91-D3, and M06-2X approaches. This is the first gas-phase confirmation that the markedly elongated C–C bond is an intrinsic feature of the molecule and that crystal packing effects have only a minor influence.
Tris(perfluorotolyl)borane—A Boron Lewis Superacid Körte, Leif A.; Schwabedissen, Jan; Soffner, Marcel ...
Angewandte Chemie International Edition,
July 10, 2017, Letnik:
56, Številka:
29
Journal Article
Recenzirano
Odprti dostop
Tristetrafluoro‐4‐(trifluoromethyl)phenylborane (BTolF) was prepared by treating boron tribromide with tetrameric F3CC6F4‐CuI. The F3CC6F4‐CuI was generated from F3CC6F4MgBr and copper(I) bromide. ...Lewis acidities of BTolF evaluated by the Gutmann–Beckett method and calculated fluoride‐ion affinities are 9 and 10 %, respectively, higher than that of tris(pentafluorophenyl)borane (BCF) and even higher than that of SbF5. The molecular structures of BTolF and BCF were determined by gas‐phase electron diffraction, that of BTolF also by single‐crystal X‐ray diffraction.
Superacidic tristetrafluoro‐4‐(trifluoromethyl)phenylborane (BTolF) was prepared from BBr3 and F3CC6F4‐CuI. It is a stronger Lewis acid than tris(pentafluorophenyl)borane (BCF) and has a higher fluoride‐ion affinity than SbF5. The structures of BTolF and of the widely used BCF were determined by gas‐phase electron diffraction and reflect the different electronic situations.
We reply to the comment by J.‐M. Mewes, A. Hansen and S. Grimme (MHG), who challenged the accuracy of our re value for the N⋅⋅⋅Te distance in (C6F5)Te(CH2)3NMe2 determined by gas electron diffraction ...(GED). We conclusively demonstrate that MHG′s quoted reference calculations are less accurate than they claim for solid state and gas phase. We show by higher level calculations, that we did not miss substantial contributions from open‐chain conformers. Refinements on simulated scattering data show that such contributions would have had only an almost negligible effect on re(N⋅⋅⋅Te). MHG suggested the use of a H0‐tuned GFN method for calculating vibrational corrections ra−re, but this did not change these values substantially. Alternative amplitude calculations using higher level analytic harmonic and numeric cubic force fields (PBE0‐D3BJ/def2‐TZVP) yield a GED value for re(N⋅⋅⋅Te)=2.852(25) Å that is well within the experimental error of our original value 2.918(31) Å but far from the 2.67(8) Å predicted by MHG. A now improved error estimation accounts for inaccuracies in the calculated auxiliary values. The gas/solid difference of the weak N⋅⋅⋅Te interaction is in a realistic range compared to other systems involving weak chemical interactions.
We reply to the comment which challenged the accuracy of our re value for the N⋅⋅⋅Te distance in (C6F5)Te(CH2)3NMe2 determined by gas electron diffraction. We show by higher level calculations, that we did not miss substantial contributions from open‐chain conformers.
Herein, ring‐opening of mesoionic carbenes (iMICs) (iMIC=ArC{N(Dipp)}2C(SiMe3)C:) (Dipp=2,6‐iPr2C6H3, Ar=Ph, 4‐Me2NC6H4 or 4‐PhC6H4) based on an 1,3‐imidazole scaffold to yield N‐ethynylformimidamide ...(eFIM) derivatives as crystalline solids (eFIM={(Dipp)N=C(Ar)N(Dipp)}C≡CSiMe3) is reported. eFIMs are thermally stable under inert gas atmosphere and show moderate air stability (t1/2=3 h for Ar=Ph). eFIMs are excellent surrogates of iMICs, which generally have a limited shelf‐life, and readily undergo ring‐closing click reactions with a variety of main‐group as well as transition metal Lewis acids to form hitherto challenging iMIC‐compounds in good to excellent yields. In addition to the relevance of eFIMs in the synthesis of iMIC‐compounds, quantification of the stereoelectronic properties of a representative iMIC (Ar=Ph) by experimental and theoretical methods suggests remarkably σ‐donor property and steric profile of these new ligand sets.
Stable unmasked iMICs are extremely scarce and have limited shelf‐life. An unprecedented ring‐opening of iMICs to N‐ethynylformimidamides (eFIMs) has been reported. eFIMs are thermally stable under an inert atmosphere and show moderately air‐stability. They are excellent iMIC‐surrogates and readily undergo ring‐closing‐clicks with a variety of (non)metal Lewis acids, affording iMIC‐compounds (iMIC)M with zero waste and easy workup.
Cyclic organoalane compounds (ADCAr)AlH22 (ADCAr = ArC{(DippN)C}2; Dipp = 2,6‐iPr2C6H3; Ar = Ph or 4‐PhC6H4 (Bp)) based on anionic dicarbene (ADC) frameworks have been reported as crystalline solids. ...Treatments of Li(ADCAr) with LiAlH4 at room temperature afford (ADCAr)AlH22 with the concomitant release of LiH. Compounds (ADCAr)AlH22 are stable crystalline solids and are freely soluble in common organic solvents. They are annulated tricyclic compounds with an almost planar central C4Al2‐core embedded between two peripheral 1,3‐imidazole (C3N2) rings. At room temperature, (ADCPh)AlH22 readily reacts with CO2 to form two‐ and four‐fold hydroalumination products (ADCPh)AlH(OCHO)2 and (ADCPh)Al(OCHO)22, respectively. Further hydroalumination reactivity of (ADCPh)AlH22 has been shown with isocyanate (RNCO) and isothiocyanate (RNCS) species (R=alkyl or aryl group). All compounds have been characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction.
The carbocyclic aluminium hydrides (ADCAr)AlH22 are readily accessible as crystalline solids on treatment of anionic dicarbenes Li(ADCAr) with LiAlH4. Hydroalumination of CO2 (and other organic substrates) with (ADCPh)AlH22 has been shown to access (ADCPh)Al(OCH(O))22 (and other products).
We report the room temperature dimerization of carbon monoxide mediated by C4/C5‐vicinal anionic dicarbenes Li(ADC) (ADC = ArC{(Dipp)NC}2; Dipp = 2,6‐iPr2C6H3; Ar = Ph, DMP (4‐Me2NC6H4), Bp ...(4‐PhC6H4)) to yield (E)‐ethene‐1,2‐bis(olate) (i.e. −O−C=C−O− = COen) bridged mesoionic carbene (iMIC) lithium compounds COen‐(iMIC)Li2 (COen‐iMIC2 = ArC{(Dipp)NC}2(CO)2) in quantitative yields. COen‐(iMIC)Li2 are highly colored stable solids, exhibit a strikingly small HOMO–LUMO energy gap, and readily undergo 2e‐oxidations with selenium, CuCl (or CuCl2), and AgCl to afford the dinuclear compounds COon‐(iMIC)E2 (E = Se, CuCl, AgCl) featuring a 1,2‐dione bridged neutral bis‐iMIC (i.e. COon‐iMIC2 = ArC{(Dipp)NC}2(C=O)2). COen‐(iMIC)Li2 undergo redox‐neutral salt metathesis reactions with LiAlH4 and (Et2O)2BeBr2 and afford COen‐(iMIC)AlH22 and COen‐(iMIC)BeBr2, in which the dianionic COen‐moiety remains intact. All compounds have been characterized by NMR spectroscopy, mass spectrometry, and X‐ray diffraction. Stereoelectronic properties of COon‐iMIC2 are quantified by experimental and theoretical methods.
Direct room temperature dimerization of carbon monoxide by anionic dicarbenes Li(ADC) has been reported to quantitatively yield (E)‐ethene‐1,2‐bis(olate) bridged mesoionic carbene (iMIC) lithium compounds, COen‐(iMIC)Li2. They undergo 2e‐oxidation to afford 1,2‐dione bridged bis iMIC, COon‐(iMIC)2 containing compounds while redox neutral salt metatheses yield COen‐(iMIC)E2 compounds (E=main group species).
Carbocyclic aluminium halides (ADC)AlX22 (2‐X) (X=F, Cl, and I) based on an anionic dicarbene (ADC=PhC{N(Dipp)C}2, Dipp = 2,6‐iPr2C6H3) framework are prepared as crystalline solids by ...dehydrohalogenations of the alane (ADC)AlH22 (1). KC8 reduction of 2‐I affords the peri‐annulated Al(III) compound (ADCH)AlH2 (4) (ADCH=PhC{N(Dipp)C2(DippH)N}, DippH=2‐iPr,6‐(Me2C)C6H3)) as a colorless crystalline solid in 76 % yield. The formation of 4 suggests intramolecular insertion of the putative bis‐aluminylene species (ADC)Al2 (3) into the methine C−H bond of HCMe2 group. Calculations predict singlet ground state for 3, while the conversion of 3 into 4 is thermodynamically favored by 61 kcal/mol. Compounds 2‐F, 2‐Cl, 2‐I, and 4 have been characterized by NMR spectroscopy and their solid‐state molecular structures have been established by single crystal X‐ray diffraction.
KC8 reduction of 2‐I with a catalytic amount the NHC (IMe4) has been shown to afford the peri‐annulated compound 4 as a colorless crystalline solid. The formation of 4 suggests intramolecular insertion of the putative bis‐aluminylene 3 into the C−H bonds of HCMe2 groups. Calculations predict singlet ground state for 3 while the conversion of 3 into 4 is thermodynamically favored by 61 kcal/mol.
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