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

The synthesis of new Schrock-Osborn Rh(i) pre-catalysts with -substituted DPEphos ligands, [Rh(DPEphos-R)(NBD)][BAr ] [R = Me, OMe, Pr; Ar = 3,5-(CF)CH], is described. Along with the previously reported R = H variant, variable temperature H NMR spectroscopic and single-crystal X-ray diffraction studies show that these all have axial (C-H)⋯Rh anagostic interactions relative to the d 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-Pr)(NBD)][BAr ] addition of H results in a Rh(iii) Pr-C-H activated product, [Rh(κ,σ-P,O,P-DPEphos-Pr')(H)][BAr ]. This undergoes H/D exchange with D at the Pr groups, reacts with CO or NBD to return Rh(i) products, and reaction with HB·NMe/-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.