Formation of Trichlorosilyl‐Substituted Carbon‐Centered Stable Radicals through the Use of π‐Accepting Carbenes

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Silicon difluoride (SiF ) is highly unstable at room temperature and condenses at this temperature rapidly to a polymeric material of unknown structure. Therefore, the isolation of a stable monomeric silicon difluoride species is a challenging task. The cyclic alkyl(amino) carbene (cAAC) coordinated silicon difluoride was isolated as (cAAC) SiF (2), synthesized from the reduction of cAAC-SiF (1) by using two equivalents of KC in the presence of one equivalent of cAAC. In the solid state, compound 2 is stable at room temperature for a long time under inert conditions. The reduction of compound 1 in the presence of one equivalent KC resulted in the first stable silicon trifluoride monoradical (cAAC)SiF (3).

supporting

confidence: 66%

“…The melting point of 3 (71 8C) is significantly lower compared witht hat of the SiCl 3 analogue (cAAC)SiCl 3 (114 to 118 8C). [13] The UV/Vis spectrum of 3 in hexane showed absorption bandsa t3 27, 287, and 274 nm. Due to the radicaln ature of 3,t he 1 HNMR Scheme1.Synthesis of precursor 1.…”

mentioning

confidence: 95%

A Route to Base Coordinate Silicon Difluoride and the Silicon Trifluoride Radical

Sinhababu

Kundu

Paesch

et al. 2018

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“…2 SiCl 2 and (cAAC . )SiCl 3 ] possess more than one polymorph . Recently, it has been observed that the (cAAC) 2 Pd 0 complex displays a crystalochromism effect.…”

Section: Methodsmentioning

confidence: 99%

Two Structurally Characterized Conformational Isomers with Different C−P Bonds

Roy

Mondal

Kundu

et al. 2017

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The cyclic alkyl(amino) carbene (cAAC) bonded chlorophosphinidene (cAAC)PÀCl (2/2')w as isolated from the direct reaction between cAAC and phosphorus trichloride (PCl 3 ). Compound 2/2' has been characterizedb y NMR spectroscopy and mass spectrometry. 31 PNMR investigations [d % 160 ppm (major) and d % 130 ppm (minor)] reveal that there are two different Pe nvironments of the PÀCl unit. X-ray single-crystal determinations uggests ac o-crystallization of two conformational isomers of (cAAC)PÀCl (2/2'); the major compound possessing ac AACÀPCl unit with C cAAC ÀP1 .75 .T his CÀPb ond length is very close to that of (NHC) 2 P 2 [NHC = N-heterocyclic carbene].T he residual density can be interpreted as ac onformational isomer with as horter C cAAC ÀPb ond similar to an on-conjugated phosphaalkene [RÀP=CR 2 ]. Our study shows an unprecedented example of two conformational isomersw ith different C carbene Àelementb onds. Additionally,B r( 3c/3c'), I( 4c/4c'), and H( 5c/5c')a nalogues [(Me 2 -cAAC)PÀX; X= Br (3), I( 4), H( 5)] of 2c/2c'[(Me 2 -cAAC)PÀCl] were also synthesized and characterized by NMR spectroscopy suggesting similare quilibrium in solution. The unique property of cAAC and the required electronegativity of the X( X= Cl, Br,I ,a nd H) atom play ac rucial role for the existence of the two isomersw hichw ere further studied by theoretical calculations.Since the synthetic reports of stable and isolable singlet Nheterocyclic carbenes (NHCs) in 1988 by Bertrand et al. [1] and in 1991 by Arduengo et al., [2] syntheses and characterization of severals table carbenes have been reported. [3] The use of carbenes has brought numerousb reakthroughs in the field of homogenous catalysis [4] and NHCs have been utilized as strong s-donors in different fields of chemistry. [5] The carbene carbon atom of an NHC is bound to two s-withdrawing and p-donating nitrogen atoms. [5] Consequently,t he accumulationo fe lectron density in the p z -orbital of the carbenec arbon atom is reasonably high leading to the weak p-accepting property of NHC. [6] Theoretical studies as well as experimental evidence have shown that non-negligible p-back-donation occurs in the bondingb etween NHCs and transition metals. [7] The syntheses of cyclic alkyl(amino)c arbenes (cAACs) [8] were reported in 2005 by Bertrande tal. One s-withdrawing and p-donating nitrogen atom of an NHC is replaced by a s-donating quaternary carbon atom in cAAC leading to al ower lying LUMO. cAACs are superior ligands for the stabilization of various unstable chemicals pecies, [9] radicals, [10] and elements in their different oxidation states [11] due to their stronger p-accepting properties. This is energetically advantageous for acceptance of pback donation from the element bound to the carbene carbon atom (C cAAC )o fc AAC (see the Supporting Information). [3b, 12, 13] The electronic properties of C cAAC and the accumulation of electron densities on the elements (E) are very important since they control the chemical behavior of the cAAC-containing compo...

“…Severali nvestigations have shown that XCW fitting allows not only to obtain reliable charge density distributions, but also to determine physical properties of materials [126][127][128][129] (e.g.,n on-linear opticalp roperties) and to consistently capture electronc orrelation, [130] polarization and crystal fielde ffects. Other ongoing studies also focus on the capability of the method in capturing relativistic effects [34] and in reliably determining experimental spin densities for interesting open-shell systems, such as the cyclic alkylaminocarbene radicalc AAC-SiCl 3 , [131] for which preliminaryr esults are available.…”

Section: Wavefunction-based Refinementmentioning

confidence: 99%

Quantum Crystallography: Current Developments and Future Perspectives

Genoni

Bučinský

Claiser

et al. 2018

Self Cite

127

114

Crystallography and quantum mechanics have always been tightly connected because reliable quantum mechanical models are needed to determine crystal structures. Due to this natural synergy, nowadays accurate distributions of electrons in space can be obtained from diffraction and scattering experiments. In the original definition of quantum crystallography (QCr) given by Massa, Karle and Huang, direct extraction of wavefunctions or density matrices from measured intensities of reflections or, conversely, ad hoc quantum mechanical calculations to enhance the accuracy of the crystallographic refinement are implicated. Nevertheless, many other active and emerging research areas involving quantum mechanics and scattering experiments are not covered by the original definition although they enable to observe and explain quantum phenomena as accurately and successfully as the original strategies. Therefore, we give an overview over current research that is related to a broader notion of QCr, and discuss options how QCr can evolve to become a complete and independent domain of natural sciences. The goal of this paper is to initiate discussions around QCr, but not to find a final definition of the field.