Rhodium complexes with hydrotris(3-p-anisylpyrazol-1-yl)borate ligand TppAn. Intramolecular CH bond activation and dehydro-chlorination processes

Solution studies by 1H- and 13C-NMR, and IR spectroscopy of rhodium(I) complexes [Rh(η4-nbd)(TppAn)] (1), [Rh(η4-cod)(TppAn)] (2) and [Rh(CO)2(TppAn)] (3) (nbd=2,5-norbornadiene; cod=cycloocta-1,5-diene) have been performed. In all cases square planar complexes containing the TppAn ligand in a bidentate η2-bonded form were observed. Compounds 2 and 3 exist as mixtures of two isomers with the third uncoordinated pyrazolyl ring occupying an equatorial position (form A) or an axial position (form B), but in complex 1 only form B is present. X-ray crystallography proved that complexes 1 and 3 are also tetracoordinated in solid state: 1 (monoclinic, space group P21/c) and 3 (monoclinic, space group P21/c), whose structures correspond to two different B forms, their difference lying in the disposition of the axial pyrazolyl group. Photochemical irradiation of [Rh(CO)2(TppAn)] (3) in a variety of solvents afforded the aryl hydride [R6H3OCH3)(C3H2N2C6H4OCH3)2}] (4) by intramolecular cyclometallation involving an ortho CH bond of one p-anisyl substituent. Functionalization of the hydride 4 by chlorinated solvents resulted in the chloro complex [R6H3OCH3)(C3H2N2C6H4OCH3)2}] (5), which maintains the intramolecular ortho Cmetal bond. Evolution of the hydride 4 to the chloro complex 5 in CDCl3 occurs through a hydrodechlorination process as deduced by monitoring the NMR spectra. Analysis of 2D NMR data (1H–1H COSY, 1H–13C HMQC and 1H–13C HMBC) allowed the full identification of 4 and 5.