Issue 25, 2021

Ortho-aryl substituted DPEphos ligands: rhodium complexes featuring C–H anagostic interactions and B–H agostic bonds

Abstract

The synthesis of new Schrock–Osborn Rh(I) pre-catalysts with ortho-substituted DPEphos ligands, [Rh(DPEphos-R)(NBD)][BArF4] [R = Me, OMe, iPr; ArF = 3,5-(CF3)2C6H3], is described. Along with the previously reported R = H variant, variable temperature 1H NMR spectroscopic and single-crystal X-ray diffraction studies show that these all have axial (C–H)⋯Rh anagostic interactions relative to the d8 pseudo square planar metal centres, that also result in corresponding downfield chemical shifts. Analysis by NBO, QTAIM and NCI methods shows these to be only very weak C–H⋯Rh bonding interactions, the magnitudes of which do not correlate with the observed chemical shifts. Instead, as informed by Scherer's approach, it is the topological positioning of the C–H bond with regard to the metal centre that is important. For [Rh(DPEphos–iPr)(NBD)][BArF4] addition of H2 results in a Rh(III) iPr–C–H activated product, [Rh(κ3,σ-P,O,P-DPEphos-iPr′)(H)][BArF4]. This undergoes H/D exchange with D2 at the iPr groups, reacts with CO or NBD to return Rh(I) products, and reaction with H3B·NMe3/tert-butylethene results in a dehydrogenative borylation to form a complex that shows both a non-classical B–H⋯Rh 3c-2e agostic bond and a C–H⋯Rh anagostic interaction at the same metal centre.

Graphical abstract: Ortho-aryl substituted DPEphos ligands: rhodium complexes featuring C–H anagostic interactions and B–H agostic bonds

Supplementary files

Article information

Article type
Edge Article
Submitted
11 Mar 2021
Accepted
24 May 2021
First published
25 May 2021
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2021,12, 8832-8843

Ortho-aryl substituted DPEphos ligands: rhodium complexes featuring C–H anagostic interactions and B–H agostic bonds

J. J. Race, A. L. Burnage, T. M. Boyd, A. Heyam, A. J. Martínez-Martínez, S. A. Macgregor and A. S. Weller, Chem. Sci., 2021, 12, 8832 DOI: 10.1039/D1SC01430G

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