Chapter 2 Applications of Silicon–Carbon Coupling Constants

Blechta, Vratislav

doi:10.1016/s0066-4103(09)06702-7

Cited by 8 publications

(4 citation statements)

References 193 publications

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“…It seems that at the constant sp 3 hybridization of the carbon the substituent electronegativity becomes a leading factor determining the 1 J ( 13 C, 79 Br) value. The importance of the substituent negativity for other 1 J spin–spin couplings was documented many times. − The carbon–bromine coupling constant determined here for 2 differs somewhat from the value 136 Hz, reported in ref . On the other hand, the value | 1 J ( 13 C, 79 Br)| = 266 Hz determined for bromoacetylene, | 1 J ( 13 C, 79 Br)| = 241(17) Hz for phenylacetylene, and | 1 J ( 13 C, 79 Br)| = 264(9) Hz for bromoethynyltrimethylsilane are similar to the value determined for the compound 3 .…”

Section: Discussionsupporting

confidence: 37%

Scalar Relaxation of the Second Kind. A Potential Source of Information on the Dynamics of Molecular Movements. 4. Molecules with Collinear C–H and C–Br Bonds

et al. 2014

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Continuing studies based on measurements of the nuclear spin relaxation rates running via the SC2 mechanism (scalar relaxation of the second kind), we present in this work the results obtained for three molecules: 9-bromotriptycene, 1,3,5-tribromobenzene, and 1-(2-bromoethynyl)-4-ethynylbenzene in which C-Br bond and one of C-H bonds are collinear. Separation of saturation-recovery or inversion-recovery curves of (13)C NMR signals of bromine-bonded carbons in the investigated compounds on two components has provided the longitudinal SC2 relaxation rates of these carbons in (79)Br- and (81)Br-containing isotopomers. These data have enabled experimental determination of the bromine-carbon spin-spin coupling constants and relaxation rates of quadrupole bromine nuclei, hardly accessible by direct measurements. At the same time the rotational diffusion parameters describing the reorientation of the C-Br vectors have been determined for the investigated molecules on the basis of the dipolar relaxation of protonated carbons. These diffusion parameters are crucial for interpretation of the bromine relaxation rates. The values of the indirect (1)J((13)C,(79)Br) coupling constants, magnetic shielding of carbon nuclei and quadrupole coupling constants of bromines, determined for the investigated compounds, have been compared with the results of the theoretical calculations which take into account relativistic effects. The origin of some divergences between the results obtained by different methods has been discussed.

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Section: Discussionsupporting

confidence: 37%

Scalar Relaxation of the Second Kind. A Potential Source of Information on the Dynamics of Molecular Movements. 4. Molecules with Collinear C–H and C–Br Bonds

et al. 2014

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“…The 13 C NMR spectrum of 1 in D 6 -benzene displays two characteristic signals for the Si-bonded C isocyanide and C NHC atoms at δ = 197.9 and 210.8 ppm, respectively, which both appear at considerably higher frequency than those of 2 [B(Ar F ) 4 ] (δ( C NR) = 167.7 ppm; δ(C NHC ) = 183.7 ppm). Both signals are flanked by a pair of Si satellites, yielding quite small 1 J (Si,C CNR ) and 1 J (Si,C NHC ) coupling constants of 9.5 and 27 Hz, respectively (SI, Figure S14) . The strong deshielding of the C isocyanide signal appears to be a common feature of compounds with pronounced azaallene structure. ,,, The 29 Si{ 1 H} spectrum of 1 displays a distinctive, high-field shifted signal at δ = −141.8 ppm.…”

Section: Resultsmentioning

confidence: 98%

(NHC)Si═C═N–R: A Two-Coordinated Si⁰-Isocyanide Compound as Si(NHC) Transfer Reagent

et al. 2021

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Experimental and theoretical studies are reported of the first two-coordinated Si 0 -isocyanide compound (SIDipp)Si CN−Ar Mes (1: SIDipp (NHC) = C[N(Dipp)CH 2 ] 2 , Ar Mes = 2,6dimesitylphenyl), supported by an N-heterocyclic carbene (NHC). A Si atom economic two-step synthesis of 1 involves a 2e reduction of the isocyanide-stabilized silyliumylidene salt [SiBr(CNAr Mes )-(SIDipp)][B(Ar F ) 4 ] (2[B(Ar F ) 4 ], Ar F = B(C 6 H 3 -3,5-(CF 3 ) 2 ) 4 ) with KC 8 . 2[B(Ar F ) 4 ] was obtained from SiBr 2 (SIDipp) after bromide abstraction with an equimolar mixture of Na[B(Ar F ) 4 ] and Ar Mes NC. Exact adherence to the stoichiometry is crucial in the latter reaction, since 2[B(Ar F ) 4 ] reacts with SiBr 2 (SIDipp) via isocyanide exchange to afford the disilicon(II) salt [Si 2 Br 3 (SIDipp) 2 )][B(Ar F ) 4 ] (3[B(Ar F ) 4 ]), the reaction leading to an equilibrium that favors 3[B(Ar F ) 4 ] (K eq (298 K) = 10.6, ΔH°= −10.6 kJ mol −1 ; ΔS°= −16.0 J mol −1 K −1 ). 3[B(Ar F ) 4 ] was obtained selectively from the 2:1 reaction of SiBr 2 (SIDipp) with Na[B(Ar F ) 4 ] and fully characterized. Detailed studies of 1 reveal an intriguing structure featuring a planar C NHC −Si−C−N skeleton with a V-shaped geometry at the dicoordinated Si 0 center, a slightly bent SiCN core, a C NHC −Si−C CNR 3c-2e out of plane π-bond (HOMO), and an anticlinal conformation of the SIDipp and Ar Mes substituents leading to axial chirality and the presence of two enantiomers, (R a )-1 and (S a )-1. Compound 1 displays structural dynamics in solution, rapidly interconverting the enantiomers. The silacumulene 1 is a potent Si(SIDipp) transfer agent as demonstrated by the synthesis and full characterization of the NHC-supported germasilyne (Z)-(SIDipp)(Cl)SiGeAr Mes (4) from 1 and Ge(Ar Mes )Cl.

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“…For their interpretation and comparison with calculated coupling constants, knowledge of their signs is essential. In view of the absence of 4 J( 29 Si-O-Si-C-1 H)) coupling constants, none of the currently available methods for sign determination [39] is suitable for oligomethylsiloxanes or oligophenylsiloxanes studied here. While we are developing such methods, the few oligosiloxanes containing Si-H bond lend themselves (thanks to small 3 J( 29 Si-O-Si-1 H) coupling) to standard 2D heteronuclear correlations that produce E.COSY pattern with its tilt indicating the relative signs of the coupling constants.…”

Section: Signs Of 2 J( 29 Si-o-29 Si) Couplingsmentioning

confidence: 99%

Geminal²J(²⁹Si‐O‐²⁹Si) couplings in oligosiloxanes and their relation to direct¹J(²⁹Si‐¹³C) couplings

Kurfürst¹,

Blechta²,

Schraml³

2011

Magnetic Reson in Chemistry

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Absolute values of (79) geminal (2)J((29) Si-O-(29)Si) couplings were measured in an extensive series of (55) unstrained siloxanes dissolved in chloroform-d. Signs of (2)J((29)Si-O-(29)Si) in some (9) silicon hydrides were determined relative to (1)J((29)Si-(1)H) which are known to be negative. It is supposed that positive sign of the (2)J((29)Si-O-(29)Si) coupling found in all studied hydrides is common to all siloxanes. Theoretical calculations for simple model compounds failed to reproduce this sign and so their predictions of bond length and angle dependences cannot be taken as reliable. Useful empirical correlations were found between the (2)J((29)Si-O-(29)Si) couplings on one side and the total number m of oxygen atoms bonded to the silicon atoms, sum of (29)Si chemical shifts or product of (1)J((29)Si-(13)C) couplings on the other side. The significance of these correlations is briefly discussed.

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Chapter 2 Applications of Silicon–Carbon Coupling Constants

Cited by 8 publications

References 193 publications

Scalar Relaxation of the Second Kind. A Potential Source of Information on the Dynamics of Molecular Movements. 4. Molecules with Collinear C–H and C–Br Bonds

Scalar Relaxation of the Second Kind. A Potential Source of Information on the Dynamics of Molecular Movements. 4. Molecules with Collinear C–H and C–Br Bonds

(NHC)Si═C═N–R: A Two-Coordinated Si⁰-Isocyanide Compound as Si(NHC) Transfer Reagent

Geminal²J(²⁹Si‐O‐²⁹Si) couplings in oligosiloxanes and their relation to direct¹J(²⁹Si‐¹³C) couplings

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Chapter 2 Applications of Silicon–Carbon Coupling Constants

Cited by 8 publications

References 193 publications

Scalar Relaxation of the Second Kind. A Potential Source of Information on the Dynamics of Molecular Movements. 4. Molecules with Collinear C–H and C–Br Bonds

Scalar Relaxation of the Second Kind. A Potential Source of Information on the Dynamics of Molecular Movements. 4. Molecules with Collinear C–H and C–Br Bonds

(NHC)Si═C═N–R: A Two-Coordinated Si0-Isocyanide Compound as Si(NHC) Transfer Reagent

Geminal2J(29Si‐O‐29Si) couplings in oligosiloxanes and their relation to direct1J(29Si‐13C) couplings

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(NHC)Si═C═N–R: A Two-Coordinated Si⁰-Isocyanide Compound as Si(NHC) Transfer Reagent

Geminal²J(²⁹Si‐O‐²⁹Si) couplings in oligosiloxanes and their relation to direct¹J(²⁹Si‐¹³C) couplings