Issue 45, 2020

Origin of the 29Si NMR chemical shift in R3Si–X and relationship to the formation of silylium (R3Si+) ions

Abstract

The origin in deshielding of 29Si NMR chemical shifts in R3Si–X, where X = H, OMe, Cl, OTf, [CH6B11X6], toluene, and OX (OX = surface oxygen), as well as iPr3Si+ and Mes3Si+ were studied using DFT methods. At the M06-L/6-31G(d,p) level of theory the geometry optimized structures agree well with those obtained experimentally. The trends in 29Si NMR chemical shift also reproduce experimental trends; iPr3Si–H has the most shielded 29Si NMR chemical shift and free iPr3Si+ or isolable Mes3Si+ have the most deshielded 29Si NMR chemical shift. Natural localized molecular orbital (NLMO) analysis of the contributions to paramagnetic shielding (σp) in these compounds shows that Si–R (R = alkyl, H) bonding orbitals are the major contributors to deshielding in this series. The Si–R bonding orbitals are coupled to the empty p-orbital in iPr3Si+ or Mes3Si+, or to the Image ID:d0dt02099k-t1.gif orbital in R3Si–X. This trend also applies to surface bound R3Si–OX. This model also explains chemical shift trends in recently isolated tBu2SiH2+, tBuSiH2+, and SiH3+ that show more shielded 29Si NMR signals than R3Si+ species. There is no correlation between isotropic 29Si NMR chemical shift and charge at silicon.

Graphical abstract: Origin of the 29Si NMR chemical shift in R3Si–X and relationship to the formation of silylium (R3Si+) ions

Supplementary files

Article information

Article type
Paper
Submitted
12 јун. 2020
Accepted
30 јул. 2020
First published
31 јул. 2020

Dalton Trans., 2020,49, 16453-16463

Author version available

Origin of the 29Si NMR chemical shift in R3Si–X and relationship to the formation of silylium (R3Si+) ions

W. Huynh and M. P. Conley, Dalton Trans., 2020, 49, 16453 DOI: 10.1039/D0DT02099K

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements