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

Solution studies by H-1- and C-13-NMR, and IR spectroscopy of rhodium(I) complexes [Rh(mu(4)-nbd)(Tp(pAn))] (1), [Rh(eta(4)-cod)(Tp(pAn))] (2) and [Rh(CO)(2)(Tp(pAn))] (3) (nbd = 2,5-norbornadiene; cod = cycloocta-1,5-diene) have been performed. In all cases square planar complexes containing the Tp(pAn) ligand in a bidentate eta(2)-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 P2(1)/c) and 3 (monoclinic, space group P2(1)/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)(Tp(pAn))] (3) in a variety of solvents afforded the aryl hydride [Rh(H)(CO){HB(C3H2N2C6-H3OCH3)(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 [Rh(Cl)(CO){HB(C3H2N2C6-H3OCH3)(C3H2N2C6H4OCH3)(2)}] (5), which maintains the intramolecular ortho C-metal bond. Evolution of the hydride 3 to the chloro complex 5 in CDCl3 occurs through a hydrodechlorination process as deduced by monitoring the NMR spectra. Analysis of 2D NMR data (H-1-H-1 COSY, H-1-C-13 HMQC and H-1-C-13 HMBC) allowed the full identification of 4 and 5. (C) 2000 Elsevier Science S.A. All rights reserved.