Isotope-induced chemical shifts (2)Delta B-10/11(Si-29) in alkenylsilanes containing three- and four-coordinate boron. A new tool for studying weak intramolecular boron-element bonds

摘要

Numerous alkenylsilanes with silyl and boryl groups in cis -positions at the C=C bond were studied for the first time by Si-29 NMR with regard to isotope-induced chemical shifts Delta(10/11)B(Si-29). Such effects are transmitted across an Si-X-B bridge (X=H, OR, SR, Cl) most efficiently if the interactions in this bridge are weak. In the absence of an Si-X-B bridge, (3)Delta(10/11)B(Si-29) effects were not observed. In such cases, where, depending on the substituents, both weak and strong B-X bonding are possible, the (2)Delta(10/11)B(Si-29) effects were readily observed only for weak B-X interactions (except for X=Cl), whereas for strong B-X bonding the effects were small or not detectable. Thus, the (2)Delta(10/11)B(Si-29) values provide another tool for probing weak interactions which are not clearly reflected by other NMR data. Copyright (C) 2002 John Wiley Sons, Ltd. [References: 47]