The geminal frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 (2) was prepared by reacting (F5C2)3SnCl with LiCH2P(tBu)2. It is neutral and contains an extremely electronegatively substituted, but ...relatively soft (hard–soft acid–base, HSAB) acidic tin function. Its FLP‐type reactivity was proven by reaction with a variety of small molecules (CO2, SO2, CS2, PhNCO, HCl, (Ph3P)AuCl). However, it shows no reaction in H/D scrambling experiments with H2/D2 mixtures and binds CO2 reversibly, as was observed by VT‐NMR spectroscopy. Compound 2 and all its adducts were completely characterized by means of multinuclear NMR spectroscopy, elemental analysis, and X‐ray diffraction experiments.
A soft binding site is provided by the tin atom in the intramolecular frustrated Lewis pair (F5C2)3SnCH2P(tBu)2, which forms adducts with a range of small molecules. The softer CS2 binds more strongly, whereas CO2 forms a weaker and reversibly bound adduct.
ConspectusThe structures of molecules can be different in different phases. Intermolecular forces, even those of weak noncovalent interactions (WNCIs), can lead to a preference for quite different ...conformations in the solid, the gas, and the liquid phases. WNCIs can cause variations in bond lengths, angles, and torsional angles. Since structure is a fundamental concept in chemistry, the knowledge of structural changes with phase is important to understand the source and effects of distorting contributions from WNCIs but also as a predictive tool for the design and stabilization of new bonding situations.X-ray crystallography is ubiquitous and now mostly straightforward to perform, but facilities for the determination of accurate gas-phase structure determination are rare, and gas-phase work is laborious and time-consuming. There are currently about 1.25 million crystal structures and more than 12 500 experimental gas-phase structures, but the intersection of the two data sets that can tell us about the structural differences of the same molecule in different phases is surprisingly small.In this Account, we describe several cases of WNCI-dominated systems for which accurate experimental structure determinations exist for both the gas phase and the solid state and, in one case, also for solution. The examples include aryl-aryl, aryl-alkyl, and alkyl-alkyl interactions; systems with chalcogen and halogen bonding; and fluorine-based interactions in arylboranes. We work out the role of WNCIs in stabilizing large, strained, or sterically overloaded molecules. We will show how flexible molecules will fold under the action of WNCIs when isolated in the gas and how they fold or unfold when they are embedded in an environment of neighbors in crystals. We will show how they can vary in strength when the substitution patterns in aryl groups are changed by different halogens and how intramolecular WNCIs, such as those forming rings, change when such systems experience additional intermolecular WNCIs.Overall, we hope that this Account will give the reader an idea of the type and magnitude of structural changes that can be expected from a free molecule in the gas phase or a single molecule calculated by quantum chemistry compared with one embedded in a crystal. This should define the limits of comparability and provide some predictive concepts of the distortions and variations to be expected.
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.
A Neutral Silicon/Phosphorus Frustrated Lewis Pair Waerder, Benedikt; Pieper, Martin; Körte, Leif A. ...
Angewandte Chemie (International ed.),
November 2, 2015, Letnik:
54, Številka:
45
Journal Article
Recenzirano
Frustrated Lewis pairs (FLPs) have a great potential for activation of small molecules. Most known FLP systems are based on boron or aluminum atoms as acid functions, few on zinc, and only two on ...boron‐isoelectronic silicenium cation systems. The first FLP system based on a neutral silane, (C2F5)3SiCH2P(tBu)2 (1), was prepared from (C2F5)3SiCl with C2F5 groups of very high electronegativity and LiCH2P(tBu)2. 1 is capable of cleaving hydrogen, and adds CO2 and SO2. Hydrogen splitting was confirmed by H/D scrambling reactions. The structures of 1, its CO2 and SO2 adducts, and a decomposition product with CO2 were elucidated by X‐ray diffraction.
Yes, Si can! The first neutral frustrated Lewis pair system based on silicon, (C2F5)3SiCH2P(tBu)2, was prepared from (C2F5)3SiCl and LiCH2P(tBu)2. This species binds CO2 and SO2 between its Lewis acidic and basic sites and cleaves dihydrogen (see structure with CO2: C gray, F green, O red, P magenta, Si orange).
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.
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.
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.
A bidentate boron Lewis acid based on 1,8‐diethynylanthracene has been studied in detail with respect to its adduct formation with diamines and diphosphanes of different linker lengths between the ...donor functions. A clear correlation between the linker length of the bifunctional base and the formation of 1 : 1 adducts, 1 : 2 adducts or oligomers was found. The adducts were characterized in solution by NMR titration experiments and structurally by X‐ray diffraction. In addition, adduct formation and competition experiments of the host system with ZR3 (Z=N, P; R=H, Me) demonstrated the generally higher stability of alkylphosphane adducts compared to alkylamine adducts with boron functions. The results provide a general insight into the adduct formation of bidentate Lewis acids with guests of different sizes as well as the differences in stability between borane‐amine and borane‐phosphane adducts.
The adduct formation of a bidentate boron Lewis acid with diamines and ‐phosphines with an increasing linker length was observed in solution by NMR experiments and in the solid state by X‐ray diffraction. This study offers insight into the selectivity of the host‐guest adduct formation of bidentate Lewis acids with host molecules of varying size.
Catechols occupy a unique role in the structural, bio-, and geochemistry of silicon. Although a wealth of knowledge exists on their hypercoordinate complexes, the structure of tetracoordinate ...bis(catecholato)silane, Si(catH)2 1, has been enigmatic since its first report in 1951. Indeed, the claim of a planar-tetracoordinated silicon in 1 triggered a prominent debate, which is unsettled to this day. Herewith, we present a comprehensive structural study on 1 and derivatives in the gas phase by electron diffraction, in a neon matrix by IR spectroscopy, in solution by diffusion NMR spectroscopy, and in the solid-state by X-ray diffraction and MAS NMR spectroscopy, complemented by high-level quantum-chemical computations. The compound exhibits unprecedented phase adaptation. In the gas phase, the monomeric bis(catecholato)silane is tetrahedral, but in the condensed phase, it is metastable toward oligomerization up to a degree controllable by the type of catechol, temperature, and concentration. For the first time, spectroscopic evidence is obtained for a rapid Si–O σ-bond metathesis reaction. Hence, this study sorts out a long-lasting debate and confirms dynamic covalent features for our Earth’s crust’s most abundant chemical bond.
Three 1,2‐diaryltetramethyldisilanes X5C6‐(SiMe2)2‐C6X5 with two C6H5, C6F5, or C6Cl5 groups were studied concerning the importance of London dispersion driven interactions between their aryl groups. ...They were prepared from 1,2‐dichlorotetramethyldisilane by salt elimination. Their structures were determined in the solid state by X‐ray diffraction and for free molecules by gas electron‐diffraction. The solid‐state structures of the fluorinated and chlorinated derivatives are dominated by aryl–aryl interactions. Unexpectedly, Cl5C6‐(SiMe2)2‐C6Cl5 exists exclusively as an eclipsed syn‐conformer in the gas phase with strongly distorted Si‐C6Cl5 units due to strong intramolecular interactions. In contrast, F5C6‐(SiMe2)2‐C6F5 reveals weaker interactions. The contributions to the total interaction energy were analyzed by SAPT calculations.
An eclipsed syn‐conformation is exclusively observed for Cl5C6‐(SiMe2)2‐C6Cl5 in the solid and gaseous phase with strongly distorted Si‐C6Cl5 units; it demonstrates the strikingly different ability of phenyl, pentafluorophenyl and pentachlorophenyl substituents to exert aryl–aryl stacking interactions (see figure).
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