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
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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.
Small‐ to medium‐sized clusters occur in various areas of chemistry, for example, as active species of heterogeneous catalysis or as transient intermediates during chemical vapor deposition. The ...manipulation of stable representatives is mostly limited to the stabilizing ligand periphery, virtually excluding the systematic variation of the property‐determining cluster scaffold. We now report the deliberate expansion of a stable unsaturated silicon cluster from six to seven and finally eight vertices. The consecutive application of lithium/naphthalene as the reducing agent and decamethylsilicocene as the electrophilic source of silicon results in the expansion of the core by precisely one atom with the potential of infinite repetition.
A stable unsaturated Si6R6 cluster was consecutively expanded to the stable neutral and anionic clusters Si7R6, Si7R5−, and Si8R6. Key to this method is the use of decamethylsilicocene (Cp*2Si) as the electrophile with Cp*− as the leaving group.
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).
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.
Difluorothiophosphoryl isocyanate, F2P(S)NCO was characterized with UV/vis, NMR, IR (gas and Ar‐matrix), and Raman (liquid) spectroscopy. Its molecular structure was also established by means of gas ...electron diffraction (GED) and single crystal X‐ray diffraction (XRD) in the gas phase and solid state, respectively. The analysis of the spectroscopic data and molecular structures is complemented by extensive quantum‐chemical calculations. Theoretically, the Cs symmetric syn‐conformer is predicted to be the most stable conformation. Rotation about the P−N bond requires about 9 kJ mol−1 and the predicted existence of an anti‐conformer is dependent on the quantum‐chemical method used. This syn‐orientation of the isocyanate group is the only one found in the gas phase and contained likewise in the crystal. The overall molecular structure is very similar in gas and solid, despite in the solid state the molecules arrange through intramolecular O⋅⋅⋅F contacts into layers, which are further interconnected by S⋅⋅⋅N, S⋅⋅⋅C and C⋅⋅⋅F contacts. Additionally, the photodecomposition of F2P(S)NCO to form CO, F2P(S)N, and F2PNCO is observed in the solid Ar‐matrix.
All about isocyanates: Difluorothiophosphoryl isocyanate, F2P(S)NCO, was investigated using an experimental multimethod approach in the gaseous, liquid and solid state to elucidate its structure, vibrational behaviour and photodecomposition: spectroscopy (UV/Vis, NMR, IR, Raman) and gas electron as well as single‐crystal X‐ray diffraction and in addition quantum‐chemical calculations.
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.
Di-
tert
-butyldiphosphatetrahedrane (
t
BuCP)
2
(
1
) is a mixed carbon- and phosphorus-based tetrahedral molecule, isolobal to white phosphorus (P
4
). However, despite the fundamental significance ...and well-explored reactivity of the latter molecule, the precise structure of the free (
t
BuCP)
2
molecule (
1
) and a detailed analysis of its electronic properties have remained elusive. Here, single-crystal X-ray structure determination of
1
at low temperature confirms the tetrahedral structure. Furthermore, quantum chemical calculations confirm that
1
is isolobal to P
4
and shows a strong largely isotropic diamagnetic response in the magnetic field and thus pronounced spherical aromaticity. A spectroscopic and computational study on the photochemical reactivity reveals that diphosphatetrahedrane
1
readily dimerises to the ladderane-type phosphaalkyne tetramer (
t
BuCP)
4
(
2
) under irradiation with UV light. With sufficient thermal activation energy, the dimerisation proceeds also in the dark. In both cases, an isomerisation to a 1,2-diphosphacyclobutadiene
1′
is the first step. This intermediate subsequently undergoes a 2 + 2 cycloaddition with a second 1,2-diphosphacyclobutadiene molecule to form
2
. The 1,2-diphosphacyclobutadiene intermediate
1′
can be trapped chemically by
N
-methylmaleimide as an alternative 2 + 2 cycloaddition partner.
Crystallographic and quantum chemical studies reveal a close relationship of (
t
BuCP)
2
with P
4
. Photochemical transformations proceed
via
the 1,2-diphosphacyclobutadiene isomer, which dimerises to give (
t
BuCP)
4
in the absence of a trap.
Di-
-butyldiphosphatetrahedrane (
BuCP)
(1) is a mixed carbon- and phosphorus-based tetrahedral molecule, isolobal to white phosphorus (P
). However, despite the fundamental significance and ...well-explored reactivity of the latter molecule, the precise structure of the free (
BuCP)
molecule (1) and a detailed analysis of its electronic properties have remained elusive. Here, single-crystal X-ray structure determination of 1 at low temperature confirms the tetrahedral structure. Furthermore, quantum chemical calculations confirm that 1 is isolobal to P
and shows a strong largely isotropic diamagnetic response in the magnetic field and thus pronounced spherical aromaticity. A spectroscopic and computational study on the photochemical reactivity reveals that diphosphatetrahedrane 1 readily dimerises to the ladderane-type phosphaalkyne tetramer (
BuCP)
(2) under irradiation with UV light. With sufficient thermal activation energy, the dimerisation proceeds also in the dark. In both cases, an isomerisation to a 1,2-diphosphacyclobutadiene 1' is the first step. This intermediate subsequently undergoes a 2 + 2 cycloaddition with a second 1,2-diphosphacyclobutadiene molecule to form 2. The 1,2-diphosphacyclobutadiene intermediate 1' can be trapped chemically by
-methylmaleimide as an alternative 2 + 2 cycloaddition partner.
The reactivity of the frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 (1) was investigated with respect to the activation of elemental hydrogen. The reaction of 1 at elevated hydrogen pressure ...afforded the intramolecular phosphonium stannate(II) (F5C2)2SnCH2PH(tBu)2 (3). It was characterized by means of multinuclear NMR spectroscopy and single crystal X‐ray diffraction. NMR experiments with the two isotopologues H2 and D2 showed it to be formed via an H2 adduct (F5C2)3HSnCH2PH(tBu)2 (2) and the subsequent formal reductive elimination of pentafluoroethane; this is supported by DFT calculations. Parahydrogen‐induced polarization experiments revealed the formation of a second product of the reaction of 1 with H2, HP(tBu)2MeSn(C2F5)3 (4), in 1H NMR spectra, whereas 2 was not detected due to its transient nature.
Hydrogen splitting and two pathways of reductive elimination were found by reacting H2 with an intramolecular Sn/P frustrated Lewis pair; quantum‐chemical calculations and high‐pressure NMR experiments indicate an neutral and zwitterionic phosphonium stannate(II) as the energetically favored product of reaction.
An improved synthesis of the simplest nitric acid ester, methyl nitrate, and a new synthesis of fluoromethyl nitrate use the metathesis of the corresponding iodomethanes with silver nitrate. Both ...compounds were identified by spectroscopy and the structures determined for in situ grown crystals by X‐ray diffraction as well as in the gas phase by electron diffraction. Fluorination leads to structures with shorter C−O and N−O bonds, has an energetically destabilizing effect and increases friction sensitivity, but decreases detonation performance.
Six centuries after the discovery of the simplest nitric acid ester, methyl nitrate (H3CONO2), experimental solid‐state and gas‐phase structures as well as energetic properties are compared with those of the new monofluorine‐substituted analogue, fluoromethyl nitrate (FH2CONO2).
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