Preagostic Rh−H Interactions and C−H Bond Functionalization: A Combined Experimental and Theoretical Investigation of Rhodium(I) Phosphinite Complexes

Three Rh−phosphinite complexes with the general structural formula [RhCl(i-Pr2POXy)(L)]2
(Xy = 2,3-xylyl; L = PPh3, PMe3, t-BuNC) were synthesized. Characterization of these
complexes using crystallographic and spectroscopic techniques revealed rare examples of
preagostic C−H···M interactions. 1H NMR chemical shielding calculations on a geometry-optimized model complex were used to provide a connection between the solution and solid-state data, which additionally supported assignment of the preagostic interaction. One of
these Rh−phosphinite complexes (L = PPh3) was used to catalyze the ortho alkylation of
phosphinites and phenols with an unactivated alkene. Finally, DFT calculations were used
to provide evidence for the involvement of the observed preagostic interaction in the
cyclometalation step of the catalytic cycle.