Efficient covalent capping of carbon and gold with TEMPO for catalysis and spin writing

International audienceCovalent immobilization of TEMPO at carbon and gold via an aliphatic -(CH(2))(6)- linker was achieved via cathodic grafting of a diamagnetic precursor, tetramethylpiperidine, with subsequent >NH to >NO oxidation to give TEMPO-capped paramagnetic interfaces (Γ(TEMPO) = 5.2 × 10(-10) mol cm(-2)); catalytic and spin switching potential of the thus prepared systems was demonstrated

Molecular Design of Silicon-Containing Diazenes: Absorbance of E and Z Isomers in the Near-Infrared Region

International audienceThe effective use of photochromic systems based on azo compounds in a number of applications, especially biomedical and pharmacological ones, is impeded by the unresolved problem of their E⇆Z isomerization in the near-IR region, NIR (780-1400 nm). We have demonstrated at the TD-DFT, STEOM-DLPNO-CCSD and CASSCF-NEVPT2 levels of theory that the presence of a silylated diazene core -Si-N=N-Si- with three-, tetra- or five-coordinated silicon atoms practically guarantees the absorption of the E and Z forms of such derivatives in NIR and the amazing (185-400 nm) separation of their first absorption bands. In particular, the maximum λ(1) of the first n→π* band of the E isomer of azosilabenzene ASiB is at ∼1030 nm, while for the Z isomer λ(1) ≅1340 nm. Based on the found bistable azo compounds (ASiB, bis(silyl)- SiD and bis(silatranyl)- SaD diazenes) and their derivatives with E and Z absorption in NIR, unique photoswitches can be created for a number of applications, in particular, for photothermal therapy

Isomer-selective dative bond O -> M (M = Si, Ge) for designing new photochromic hemi-indigo systems

International audienceNew photochromic systems MY2X-HI (M = Si, Ge) were designed (at the DFT level of theory) by replacing the hydrogen atom in the nitrogen of the pyrrole ring of hemi-indigo, HI, with silyl- or germyl-substituents. The E isomers of MY2X-HI contain a dative bond O -> M (pentacoordinated atom M) both in the ground S-0 and in the excited S-1 states. This leads to a significant difference in the absorption and fluorescence maxima (lambda(fl) - lambda(abs)) of the Z and E forms of hypervalent hemi-indigos; this difference is more than twice that of the parent HI. There is a trend to increasing separation of first pi ->pi* absorption bands of the E and Z isomers of MY2X-HI with the increase in their relative stability. (C) 2021 Published by Elsevier B.V

Hypervalent benzophenones

International audienceBenzophenones (BPs) of the type 2-R-BP and 2,2'-R-BP, carrying silicon-or germanium-containing substituents R (R = EY2X; E = Si, Ge; Y = H, Me, F, Cl; X = H, F, Cl, OTf) at one or at two ortho-positions of the arene rings, were theoretically designed. Among 26 compounds considered, only 10 monosubstituted 2-R-BP and 5 bis-substituted 2,2'-R-BP (in hexane and DMSO solutions) belong to the first examples of hypervalent benzophenones. In these "true" chelates, the length of the O -> E dative contact (which has a covalent component, according to the AIM analysis) is in the range of 2.0-2.4 angstrom, and the degree of pentacoordination of E is higher than 40%. In these compounds, a significant planarization of the benzophenone part occurs, compared to the initial BP. The TD-DFT calculations suggest the UV spectral properties of the hypervalent BPs to differ fundamentally from those of BP. For the "true" chelates 2-R-BP and 2,2'-R-BP, there is a well pronounced trend of a change of the coordination O -> E contact strength along with the difference between the wavelengths of their first high-intensity band and the pi pi* band of the unsubstituted BP. (c) 2018 Elsevier B.V. All rights reserved

Crystal Structure of New 1-Phenyl-Substituted Tribenzsilatranes

International audienceThe family of practically requested "common" silatrane derivatives of triethanolamine X-Si(OCH2CH2)(3)N, 1, was enlarged with the first representatives of 3,4,6,7,10,11-tribenzo-2,8,9trioxa-5aza-1-silatricyclo(3.3.3.0<^>1,5<^>)undecanes X-Si(O-para-R-C6H3)(3)N, tribenzsilatranes 2 (R = H (a), Me (b), F (c)), carrying the substituent R in the side aromatic rings. These compounds were prepared via the transesterification of phenyl trimethoxysilane with the corresponding triphenol amines and studied using XRD and DFT calculations. These derivatives of 1-X-(4-R-2,2',2 ''-nitrilotriphenoxy)silane are expected to have, as their parent "common" silatranes 1, diverse biological and pharma activities. A common characteristic feature of the molecular structures of both 1 and 2 is the presence of an intramolecular dative bond N -> Si whose existence is evidenced by geometric and quantum topological (AIM) criteria. In the crystals, the length of this bond (d(SiN)) is noticeably longer in tribenzsilatranes than in 1. The results of DFT B3PW91/6-311++G(d,p) calculations suggest the reason for this to be the more rigid nature of the potential functions of the N -> Si bond deformation in 2 compared to 1. The relative degree of "softness"/"hardness" of the potential functions can be assessed from the difference in the calculated values of dSiN in isolated molecules 1 and 2a-c and in their crystals

Electrochemical Oxidation and Radical Cations of Structurally Non-rigid Hypervalent Silatranes: Theoretical and Experimental Studies

International audienceUsing 18 silatranes XSi(OCH CH ) N (1) as examples, the potentials of electrochemical oxidation E of the hypervalent compounds of Si were calculated for the first time at the ab initio and DFT levels. The experimental peak potentials E (acetonitrile) show an excellent agreement (MAE=0.03) with the MP2//B3PW91 calculated E (C-PCM). Radical cations of 1 reveal a stretch isomerism of the N→Si dative bond. Localization of the spin density (SD) on the substituent X and the short (s) coordination contact Si⋅⋅⋅N (d 3.0 Å), the four-coordinate Si and the SD localized on the silatrane nitrogen atom N . The vertical model of adiabatic ionization (1→1 or 1→1 ) was developed. It allows, in accordance with an original experimental test (electrooxidation of 1 in the presence of ferrocene), a reliable prediction of the most probable pathways of the silatrane oxidation. The reliable relationships of E (1) with the strength characteristics of the dative contact N→Si were revealed

Analysis of the Hypersensitivity of the ²⁹Si NMR Chemical Shift of the Pentacoordinate Silicon Compounds to the Temperature Effect. <i>N</i>‑(Silylmethyl)acetamides

Theoretical investigation of the phenomenon of hypersensitivity of the ²⁹Si NMR chemical shift, δ, in the pentacoordinate silicon compounds to the temperature effect has been performed by the example of <i>N</i>-(silylmethyl)­acetamides MeC­(O)­NMeCH₂SiX₃ (X = Me, <b>1</b>; OMe, <b>2</b>; F, <b>3</b>) and MeC­(O)­NMeCH₂SiMe₂F (<b>4</b>) with the use of experimental dynamic NMR (DNMR) ²⁹Si data. It is based on the following: (i) the analysis of the potential energy surface of molecules <b>1</b>–<b>4</b> in polar solvents and the energetics of interconversion between their possible isomeric forms; (ii) the calculations of δ at different temperatures taking into account the dependence of the dielectric constant (ε) of the medium on <i>T</i>, and (iii) the isolation of dynamic, geometrical, and polar contributions to the temperature drift of δ. The results obtained allowed us to give a consistent explanation of the DNMR ²⁹Si spectra of acetamides <b>1</b>–<b>4</b> and to elucidate the nature of an unusual effect of <i>T</i> on δ

C_Ar–H···O Hydrogen Bonds in Substituted Isobenzofuranone Derivatives: Geometric, Topological, and NMR Characterization

Substituted isobenzofuranone derivatives <b>1a</b>–<b>3a</b> and bindone <b>4</b> are characterized by the presence of an intramolecular C_Ar–H···O hydrogen bond in the crystal (X-ray), solution (¹H NMR and specific and nonspecific IEF-PCM solvation model combined with MP2 and B3LYP methods), and gas (MP2 and B3LYP) phases. According to geometric and AIM criteria, the C_Ar–H···O interaction weakens in <b>1a</b>–<b>3a</b> (independent of substituent nature) and in <b>4</b> with the change in media in the following order: gas phase > CHCl₃ solution > DMSO solution > crystal. The maximum value of hydrogen bond energy is 4.6 kcal/mol for <b>1a</b>–<b>3a</b> and 5.6 kcal/mol for <b>4</b>. Both in crystals and in solutions, hydrogen bond strength increases in the order <b>1a</b> < <b>2a</b> < <b>3a</b> with the rising electronegativity of the ring substituents (H < OMe < Cl). The best method for calculating ¹H NMR chemical shifts (δ^calcd – δ^expl < 0.7 ppm) of hydrogen bonded and nonbonded protons in <b>1a</b>–<b>3a</b> and <b>1b</b>–<b>3b</b> (isomers without hydrogen bonds) is the GIAO method at the B3LYP level with the 6-31G** and 6-311G** basis sets. For the C–H moiety involved in the hydrogen bond, the increase of the spin–spin coupling constant ¹<i>J</i>(¹³C–¹H) by about 7.5 Hz is in good agreement with calculations for C–H bond shortening and for blue shifts of C–H stretching vibrations (by 55–75 cm^–1)

C_Ar–H···O Hydrogen Bonds in Substituted Isobenzofuranone Derivatives: Geometric, Topological, and NMR Characterization

Substituted isobenzofuranone derivatives <b>1a</b>–<b>3a</b> and bindone <b>4</b> are characterized by the presence of an intramolecular C_Ar–H···O hydrogen bond in the crystal (X-ray), solution (¹H NMR and specific and nonspecific IEF-PCM solvation model combined with MP2 and B3LYP methods), and gas (MP2 and B3LYP) phases. According to geometric and AIM criteria, the C_Ar–H···O interaction weakens in <b>1a</b>–<b>3a</b> (independent of substituent nature) and in <b>4</b> with the change in media in the following order: gas phase > CHCl₃ solution > DMSO solution > crystal. The maximum value of hydrogen bond energy is 4.6 kcal/mol for <b>1a</b>–<b>3a</b> and 5.6 kcal/mol for <b>4</b>. Both in crystals and in solutions, hydrogen bond strength increases in the order <b>1a</b> < <b>2a</b> < <b>3a</b> with the rising electronegativity of the ring substituents (H < OMe < Cl). The best method for calculating ¹H NMR chemical shifts (δ^calcd – δ^expl < 0.7 ppm) of hydrogen bonded and nonbonded protons in <b>1a</b>–<b>3a</b> and <b>1b</b>–<b>3b</b> (isomers without hydrogen bonds) is the GIAO method at the B3LYP level with the 6-31G** and 6-311G** basis sets. For the C–H moiety involved in the hydrogen bond, the increase of the spin–spin coupling constant ¹<i>J</i>(¹³C–¹H) by about 7.5 Hz is in good agreement with calculations for C–H bond shortening and for blue shifts of C–H stretching vibrations (by 55–75 cm^–1)