Synthesis and Characterization of 1,2-Disubstituted Vinylsilanes and Their Geometric Differentiation with ³J(²⁹Si,¹H)-Coupling Constants. Application of a Novel Heteronuclear J-Resolved NMR Experiment

Abstract

The 3 J( 29 Si, 1 H)-coupling constants of a number of vinylsilanes have been accurately determined with the ACT-J-NMR experiment. For all investigated samples the values of the 3 J trans -coupling constants were found to be significantly larger than the corresponding values of the 3 J cis -coupling constants (8.8-20.5 Hz versus 3.1-11.9 Hz). Since substituent effects were characterized over a wide range, a conclusive assignment of the double-bond geometry of a particular vinylsilane by means of a single 3 J( 29 Si, 1 H)-coupling constant is now possible even though the ranges of the 3 J cis -and the 3 J trans -values overlap.

Exploratory Studies on the Synthesis of Unsymmetrically Substituted Diacetylenes Bearing Trialkoxysilyl Groups and Development of a Method for the Preparation of 1-Lithio-4-(2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undecanyl)-1,3-butadiyne: Synthetic and Mechanistic Aspects

“…A slight upfield shift (up to 10 ppm) might have been expected if structure 28 were present as a result of the interaction, due to geometrical constraints, between the oxygen lone pairs of the methoxy group and the silicon atom. , More convincing evidence for the existence of structure 27 was obtained by measuring the magnitude of the 3 J 29 Si 1 H coupling constant: 3.7 Hz. This value is close to that measured for 29 SiCCH ( cis ) in gem -(CH 3 ) 3 SiClCCH 2 , i.e., 4.36 Hz, and to those reported for other vinylsilanes. , 3 J 29 Si 1 H ( trans ) coupling constants are typically in the range 9−21 Hz. ,

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1,2-Palladasilacyclobutene: The Missing Link in the Pd-Catalyzed Annulation of Alkynes for the Silirene-to-Silole Transformation

“…The structure of 5′ was determined thanks to HRMS and multinuclear NMR analyses. In particular, the 3 J SiH coupling constant of 6.9 Hz indicates that the central olefin has retained its stereochemistry with the thienyl groups in the cis position …”

“…In particular, the 3 J SiH coupling constant of 6.9 Hz indicates that the central olefin has retained its stereochemistry with the thienyl groups in the cis position. 32 These results strongly support the involvement of a monophosphine-ligated 1,2-palladasilacyclobutene key intermediate in the palladium-catalyzed annulation reaction. With the objective of detecting intermediates derived from the palladacycle, the reaction between 6-PPh 3 and phenyl acetylene was monitored by NMR, at low temperature, in CD 2 Cl 2 .…”

Asymmetric Hydrosilylation of β-Silyl Styrenes Catalyzed by a Chiral Palladium Complex

“…Compound 1d (1.7 g) was prepared from the ethynylbenzene (1.02 g, 10.0 mmol) and the tert -butylchlorodimethylsilane (1.51 g, 10.0 mmol) by the procedure for the preparation of 1a , and the yield was 78% (from ethynylbenzene), known compound: R f = 0.79 (PE); 1 H NMR (CDCl 3 , 400 MHz): δ 7.47 (d, J = 7.6 Hz, 2H), 7.36 (t, J = 7.4 Hz, 2H), 7.27 (t, J = 7.2 Hz, 1H), 6.93 (d, J = 19.2 Hz, 1H), 6.52 (d, J = 19.2 Hz, 1H), 0.96 (s, 9H), 0.16 (s, 6H); 13 C { 1 H} NMR (CDCl 3 , 100 MHz, plus, APT): δ (up) 138.5, 16.8. δ (down) 144.9, 128.6, 128.0, 126.8, 126.4, 26.6, 5.9.…”