Conformational properties of ethyl- and 2,2,2-trifluoroethyl thionitrites, (CX3CH2SNO, X = H and F)

The simple 2,2,2-trifluoroethyl thionitrite molecule, CF3CH2SNO, has been prepared in good yield for the first time using CF3CH2SH and NOCl in slight excess. The vapor pressure of the red-brown compound CF3CH2SNO follows, in the temperature range between 226 and 268 K, the equation log p = 12.0-3881/T (p/bar, T/K), and its extrapolated boiling point reaches 51 °C. Its structural and conformational properties have been compared with the ethyl thionitrite analogue, CH3CH2SNO. The FTIR spectra of the vapor of both thionitrites show the presence of bands with well-defined contours, allowing for a detailed conformational analysis and vibrational assignment on the basis of a normal coordinate analysis. The conformational space of both thionitrite derivatives has also been studied by using the DFT and MP2(full) level of theory with extended basis sets [6-311+G(2df) and cc-pVTZ]. The overall evaluation of the experimental and theoretical results suggests the existence of a mixture of two conformers at room temperature. The relative abundance of the most stable syn form (N=O double bond syn with respect to the C-S single bond) has been estimated to be ca. 79 and 75% for CF3CH2SNO and CH3CH2SNO, respectively.Centro de Química Inorgánic

Aryl-Aryl Interactions in (aryl-perhalogenated) 1,2-Diaryldisilanes.

Mitzel NW, Linnemannstöns M, Schwabedissen J, Neumann B, Stammler H-G, Berger R. Aryl-Aryl Interactions in (aryl-perhalogenated) 1,2-Diaryldisilanes. Chemistry. 2020;26(10):2169-2173.Three 1,2-diaryltetramethyldisilanes X5C6-(SiMe2)2-C6X5 with two C6H5, C6F5 or C6Cl5 groups were studied concerning the im-por-tan-ce of London dispersion driven interactions between their aryl groups. They were prepared from 1,2-di-chlo-rotetra-methyl-disi-la-ne by salt elimination. Their structures were determi-ned in the solid state by X-ray diffraction and for free molecules by gas elec-tron-diffraction. The solid-state struc-tures of the fluori-nated and chlo-rinated derivatives are domi-na-ted by aryl-aryl inter-actions. Unex-pectedly, Cl5C6-(SiMe2)2-C6Cl5 exists exclusive-ly as eclipsed syn-conformer in the gas phase with strongly distor-ted Si-C6Cl5 units due to strong intramo-le-cular interactions. In contrast, F5C6-(SiMe2)2-C6F5 reveals wea-ker inter-actions. The contributions to the total interaction energy was analyzed by SAPT calculations. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Spectroscopic Properties, Conformation and Structure of Difluorothiophosphoryl Isocyanate in the Gaseous and Solid Phase

Schwabedissen J, Trapp PC, Stammler H-G, et al. Spectroscopic Properties, Conformation and Structure of Difluorothiophosphoryl Isocyanate in the Gaseous and Solid Phase. ChemistryOpen. 2020;9(9):913-920.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

The experimental gas-phase structures of 1,3,5-trisilylbenzene and hexasilylbenzene and the theoretical structures of all benzenes with three or more silyl substituents

The structures of 1,3,5-trisilylbenzene and hexasilylbenzene in the gas phase have been determined by electron diffraction, and that of 1,3,5-trisilylbenzene by X-ray crystallography. The structures of three trisilylbenzene isomers, three tetrasilylbenzenes, pentasilylbenzene and hexasilylbenzene have been computed, ab initio and using Density Functional Theory, at levels up to MP2/6-31G*. The primary effect of silyl substituents is to narrow the ring angle at the substituted carbon atoms. Steric interactions between silyl groups on neighbouring carbon atoms lead first to displacement of these groups away from one another, and then to displacement out of the ring plane, with alternate groups moving to opposite sides of the ring. In the extreme example, hexasilylbenzene, the SiCCSi dihedral angle is 17.8(8)°

M e t hylsi lyl hyd roxylami nes: Preparative, Spectroscopic and Ab initio Studiest

Methylsilylhydroxylamines [ (MeH,Si),NOMe, (MeH,Si) MeNOMe, Me,NOSiH,Me] have been prepared from bromo(methy1)silane and the corresponding methylhydroxylamines in the presence of an auxiliary base (triethylamine or N,N,N',N'-tetramethylethylenediamine). The compounds were studied by N M R spectroscopy of all elements present ( l H , 13C, 15N, 170, 29Si). The magnitude of the one-bond coupling constants 1J('5N29Si) is interpreted in terms of the hybridization associated with the pyramidal co-ordination of nitrogen, a unique structural feature in Si/N chemistry. Ab initiu studies confirmed these structural predictions. Singly silylated hydroxylamines have been shown to be more strongly pyramidal than doubly silylated ones. Calculations on the model compound (H,Si),NOMe gave a barrier to inversion at nitrogen of 9.7 kcal mol-'. This inversion is accompanied by a partial rotation around the N-0 bond. The has a planar co-ordination at the nitrogen atom, has been maintained ever since, and during the last 40 years the structures of a large number of silylamines have been determined.2 As a general rule it was derived from these results that all compounds with doubly and triply silylated nitrogen atoms exhibit a planar geometry at n i t r~g e n .~ Only for a few monosilylated amines deviations from a planar arrangement of the nitrogen substituents occur, but with significant variations for the gas phase and the solid state. p,d, B~n d i n g ,~ formerly the most widespread hypothesis to explain this and other unique properties of silylamines, like low basicity at nitrogen and short Si-N bonds, was shown to be rather insignificant, and p,. interactions (negative hyperconjugation, anomeric effect) and an electrostatic repulsion model ' have since been introduced as more meaningful approaches. Compounds with a wide variety of substituents at the silicon part of the molecules have been structurally studied, but the variations of nitrogen substituents have been limited to silylated hydrazines some of which were presented in previous papers from this laboratory.8 For this class of Si/N compounds with nitrogen in its oxidation state -11, planarity at nitrogen induced by silyl substituents appears to be also well established.' As a continuation of these studies we have now investigated silylated hydroxylamines bearing oxygen as a very electronegative substituent at nitrogen in its oxidation state -I. In this context we recently reported the unique structure of 0-methyl-N,N-bis(ptolylsily1)hydroxylamine 1, oneofonly a few doubly N-silylated compounds with a pyramidal co-ordination sphere at nitrogen. ' ' t Non-SI unit employed: cal = 4.184 J. 1 As a follow-up to this work, and as a part of our current search for new single-source feedstock precursors for chemical vapour deposition ' (CVD) of silicon nitride and oxynitride films, ' we are now examining low-molecular-weight silylhydroxylamines with low carbon contents and high volatilities. These small molecules should also allow a direct comparison of experimental data with the results of more sophisticated theoretical calculations of structure and bonding. Results and Discussion Preparation of Methylsilylhydroxy1amines.-Since compounds with silyl groups H,Si are generally pyrophoric, methylsilyl groups, the organosilyl groups with the lowest carbon content, were chosen for this study. Bromo(methy1)silane is a powerful silylating agent for N H and OH functions and reacts with 0-methyl, N,O-dimethyl-and N,N-dimethylhydroxylamine in the presence of triethylamine to give the silylated hydroxylamines 2,3 and 4, respectively (Scheme 1). The compounds have low boiling points (97, 61 and 58 "C, respectively), and separation from the solvents and from the excess of triethylamine is difficult. These complications can be overcome by a solvent-free reaction mode and by using N,N,N',N'-tetramethylethylenediamine (tmen) as the dehydrohalogenating agent. The advantage of tmen is its dibasic nature. Since both di-and mono-protonated tmen salts are non-volatile

Regiochemical Control in Triptycene Formation-An Exercise in Subtle Balancing Multiple Factors

Lamm J-H, Vishnevskiy Y, Ziemann E, Neumann B, Stammler H-G, Mitzel NW. Regiochemical Control in Triptycene Formation-An Exercise in Subtle Balancing Multiple Factors. ChemistryOpen. 2018;7(1):111-114.Reactions between 1,8-dichloroanthracenes with substituents in position 10 and ortho-chloroaryne afford mixtures of 1,8,13- (syn) and 1,8,16-trichlorotriptycenes (anti). The syn/anti ratio is dependent on these substituents. Electropositive substituents like SiMe3 and GeMe3 lead to preferred formation of the syn-isomer, whereas CMe3 groups exclusively afford the anti-isomer. Different quantum chemical calculations including location of transition states give conflicting results, but indicate the importance of dispersion forces for an at least qualitative prediction of results. The syn-trichlorotriptycenes with SiMe3 and GeMe3 substituents were characterized by using NMR spectroscopy, mass spectrometry, and X-ray diffraction experiments. Triptycene represents one of a few rigid organic frameworks of D3h symmetry without any (Lewis-basic) heteroatoms. It was first synthesized by Bartlett et al. in 1942 using a multi-step procedure starting from anthracene and p-benzoquinone.[1] In 1956, Wittig and Ludwig reported a more efficient access to triptycene in one step from anthracene by reacting it with in situ-formed benzyne.[2] The symmetry and rigidity of triptycene have inspired a plethora of applications in fundamental and applied chemical research.[3-5] Substituted triptycenes are widely used, for example, as building blocks for fluorescent or non-fluorescent organic macromolecules, polymers, and liquid crystals,[3, 6] as rigid spacers in several Pd complexes used for cross coupling reactions,[7] as devices in molecular machines,[8] in crystal engineering processes,[9, 10] and as a basis for the design of highly porous organic materials with numerous applications.[11] Although the chemistry of triptycenes and their functionalization is generally in an advanced state, the 1,8,13-trisubstitution motif remains a challenge for synthesis. However, exactly this pattern is interesting to introduce three functionalities oriented in the same direction. We try to make use of such 1,8,13-trisubstituted triptycenes (also called syn-triptycenes) as rigid organic frameworks for constructing directed polydentate Lewis acids,[12, 13] but many other applications might be envisioned. syn-Triptycenes can be obtained through Diels–Alder reactions of 1,8-disubstituted anthracenes with ortho-functionalized arynes, a protocol introduced by Rogers and Averill in 1986.[14] The drawback of this method is that the corresponding anti-trisubstituted 1,8,16-isomer is always formed as the main product when, for example, Cl-functionalized anthracenes and arynes are used.[12, 14] In 2010, we reported attempts to increase the syn/anti ratio by making use of the steric interference of the (bulky) anthracene substituent at C-10 with the chlorine atom of the chloroaryne (Scheme 1). We expected this strategy to provide an increased formation of the syn-isomer. However, the steric influence of the C-10 substituent turned out to be minimal, whereas the electronic properties are dominant;[12] of all substituents tested, the biggest R=C(CH3)3 led to the formation of 100 % anti-isomer, despite the formation of an extremely deformed product by mutual repulsion of the Cl and R substituents, as indicated in Scheme 1 b

Influence of Antipodally Coupled Iodine and Carbon Atoms on the Cage Structure of 9,12-I2-closo-1,2-C2B10H10 : An Electron Diffraction and Computational Study

Because of the comparable electron scattering abilities of carbon and boron, the electron diffraction structure of the C2v-symmetric molecule closo-1,2-C2B10H12 (1), one of the building blocks of boron cluster chemistry, is not as accurate as it could be. On that basis, we have prepared the known diiodo derivative of 1, 9,12-I2-closo-1,2-C2B10H10 (2), which has the same point-group symmetry as 1 but in which the presence of iodine atoms, with their much stronger ability to scatter electrons, ensures much better structural characterization of the C2B10 icosahedral core. Furthermore, the influence on the C2B10 geometry in 2 of the antipodally positioned iodine substituents with respect to both carbon atoms has been examined using the concerted application of gas electron diffraction and quantum chemical calculations at the MP2 and density functional theory (DFT) levels. The experimental and computed molecular geometries are in good overall agreement. Molecular dynamics simulations used to obtain vibrational parameters, which are needed for analyzing the electron diffraction data, have been performed for the first time for this class of compound. According to DFT calculations at the ZORA-SO/BP86 level, the 11B chemical shifts of the boron atoms to which the iodine substituents are bonded are dominated by spin-orbit coupling. Magnetically induced currents within 2 have been calculated and compared to those for [B12H12]2-, the latter adopting a regular icosahedral structure with Ih point-group symmetry. Similar total current strengths are found but with a certain anisotropy, suggesting that spherical aromaticity is present; electron delocalization in the plane of the hetero atoms in 2 is slightly hindered compared to that for [B12H12]2-, presumably because of the departure from ideal icosahedral symmetry

Synthesis and structures of simple (silylmethyl)(methyl)ethers

Mitzel NW. Synthesis and structures of simple (silylmethyl)(methyl)ethers. ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES. 2003;58(8):759-763.The compound Cl3SiCH2OCH3 was prepared by reacting ClCH2OCH3 with the Cl3SiH/NEt3 reagent. H3SiCH2OCH3 and F3SiCH2OCH3 were synthesized from Cl3SiCH2OCH3 by reduction with LiAlH4 and by fluorination with SbF3, respectively. The crystal structures of the low-melting compounds H3SiCH2OCH3 and F3SiCH2OCH3 were determined by X-ray diffraction of in situ grown crystals. Both compounds do not show any observable beta-donor-acceptor interactions, but behave structurally like usual dialkylethers or silanes, as is obvious from the structural parameters in H3SiCH2OCH3 (<SiCO 108.4(3)-109.4(3)&DEG;, <COC 111.0(4)-111.6(4)degrees) and in F3SiCH2OCH3 (< SiCO 107.1 (1), <COC 111.2(2)degrees). Earlier postulates of Si...O interactions in compounds with SiCO units could thus not be confirmed on a structural basis

The molecular structure of dichloro(dimethylamino)phosphine

Mitzel NW. The molecular structure of dichloro(dimethylamino)phosphine. JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS. 1998;(19):3239-3242.The solid state structure of the low-melting compound Cl2P-NMe2 was determined by X-ray diffraction using an in situ grown single crystal. Two independent molecules in the asymmetric unit have very similar geometries with planar co-ordination at their nitrogen atoms and the C2NP unit almost coinciding with the approximate molecular plane of symmetry. According to ab initio calculations up to the MP2/6-311G** level of theory the structure in the solid state corresponds to a transition state of inversion of the nitrogen pyramid, which is about 3.1 kJ mol(-1) higher in energy than the ground state. The calculated ground state is of C-1 symmetry with a gauche arrangement of the NMe2 group. Both conformations of Cl2P-NMe2 are at variance to that determined by gas-phase electron diffraction in 1966, with a planar Me2NP group being oriented perpendicular to the plane of symmetry. The calculations predict the latter structure not to be a stationary point on the potential hypersurface. The preference for the C-s structure of Cl2P-NMe2 in the crystal can be rationalised by the molecular dipole moments which are larger for the C-s structure than for the C-1 ground state. The results are discussed in comparison to the structure of F2P-NMe2 which was determined earlier in the gaseous and solid state, also with different geometries. New ab initio calculations for F2P-NMe2 are provided favouring C-1 symmetry, but showing the molecule to have a very small barrier to inversion of the nitrogen centre if any

On the 70th birthday of Hubert Schmidbaur

Mitzel NW. On the 70th birthday of Hubert Schmidbaur. ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES. 2004;59(11-12):1181-1184