Competition Studies of Oxidative Addition of Aryl Halides to the (PNP)Rh Fragment

Abstract

The (PNP)Rh fragment (2) can be conveniently accessed by dissociation of L from the four-coordinate complexes (PNP)Rh(L) (L = SPri2, 3; L = H2C═CHBut, 10), which contain the tridentate PNP pincer ligand (2-iPr2P-4-Me-C6H4)2N−. A new and a more straightforward synthesis of 10 is reported, yielding 65% of 10 based on RhCl3(H2O)x. A number of new aryl halide oxidation addition products (AHOAP) of the general formula (PNP)Rh(Ar)(Hal) (Hal = Cl, Br, I) have been synthesized through oxidative addition (OA) reactions of meta- and para-substituted aryl halides with 3 or 10. The rotation about the Rh−Caryl bond is restricted, resulting in rotamers for the meta-substituted aryls that are distinct on the NMR spectroscopy time scale. Reactions of some aryl halides containing a p-NO2 or p-CO2Me with 3 or 10 led to the observation of products of C−H OA that are ostensibly stabilized by coordination to the NO2 or CO2Me group. Analogous C−H OA products were observed for the halide-free nitrobenzene and ethyl benzoate, as...