Nachweis starker C – Sn-Hyperkonjugation über Kristallstruktur und NMR-Daten eines C-Stannylmethylenborans / Evidence for Strong C–Sn-Hyperconjugation by Crystal Structure and NMR Data of a C-Stannylmethyleneborane
Open Access
- 1 March 1990
- journal article
- Published by Walter de Gruyter GmbH in Zeitschrift für Naturforschung B
- Vol. 45 (3) , 290-298
- https://doi.org/10.1515/znb-1990-0304
Abstract
Strong C—Sn hyperconjugation in C-stannylmethyleneborane 3 is indicated by (1) a small B—sp2C—Sn bond angle (105.6°), (2) a long sp2C—Sn bond (216 pm), (3) a very short B=C double bond (131 pm), (4) a very small coupling constant 1J(119Sn-13C) = 125 Hz for the sp2C—Sn bond and (5) shielding of the boron atom of the B=C double bond by 20 ppm as compared to methyleneboranes without strong hyperconjugation. The boron atoms of the B=C double bond of 3 and related methyleneboranes act as π-donor and σ-acceptor, the substituents X at the carbon atom of the B=C double bond as π-acceptors and, through their C—X σ-bonds, as σ-donors. The partly bridged methyleneborane 3 closes the gap between unbridged and bridged methyleneboranes. Relationships to non-classical carbocations are pointed out.Keywords
This publication has 0 references indexed in Scilit: