TY - JOUR
T1 - Ortho-aryl substituted DPEphos ligands
T2 - rhodium complexes featuring C-H anagostic interactions and B-H agostic bonds
AU - Race, James J.
AU - Burnage, Arron L.
AU - Boyd, Timothy M.
AU - Heyam, Alex
AU - Martínez-Martínez, Antonio J.
AU - Macgregor, Stuart A.
AU - Weller, Andrew S.
N1 - Funding Information:
The EPSRC (M024210) and SCG Chemicals Ltd. Oxford and Heriot-Watt Universities and the EPSRC for studentship support to J. J. R., T. M. B. and A. L. B., and Professors Simon Duckett (York), Michael Willis (Oxford) and Odile Eisenstein (Montpellier) for useful discussions.
Publisher Copyright:
© The Royal Society of Chemistry 2021.
PY - 2021/7/7
Y1 - 2021/7/7
N2 - The synthesis of new Schrock-Osborn Rh(i) pre-catalysts withortho-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 temperature1H NMR spectroscopic and single-crystal X-ray diffraction studies show that these all have axial (C-H)⋯Rh anagostic interactions relative to the d8pseudo 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 H2results 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 D2at theiPr 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.
AB - The synthesis of new Schrock-Osborn Rh(i) pre-catalysts withortho-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 temperature1H NMR spectroscopic and single-crystal X-ray diffraction studies show that these all have axial (C-H)⋯Rh anagostic interactions relative to the d8pseudo 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 H2results 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 D2at theiPr 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.
UR - http://www.scopus.com/inward/record.url?scp=85109085662&partnerID=8YFLogxK
U2 - 10.1039/d1sc01430g
DO - 10.1039/d1sc01430g
M3 - Article
C2 - 34257884
AN - SCOPUS:85109085662
SN - 2041-6520
VL - 12
SP - 8832
EP - 8843
JO - Chemical Science
JF - Chemical Science
IS - 25
ER -