Kinetic study of the dynamic behavior of [M(C6F5)X(OPPy(n)Ph(3-n))] (M=Pd,Pt; X=C6F5, halide; n=1-3): Activation parameters for the restricted rotation about the M-aryl bond and for the Py associative exchange

The behavior in CDCl3 of complexes of the type [M(C6F5)X(OPPy(n)Ph(3-n))] (M = Pd, Pt; X = C6F5; halide; n = 1-3) has been studied by F-19 and H-1 NMR spectroscopy. For the nonplanar N,N-chelating ligands with n = 2, 3, two processes have been observed and their activation parameters, Delta G(double dagger), Delta H-double dagger, and Delta S-double dagger, have been determined, using magnetization transfer (NIT) or line-shape analysis methods. The rotation of the C6F5 groups about the M-C-ipso bond occurs in the square-planar species without dissociation, and its rate depends on the size of the coordinated atom X, in the order C6F5 > Cl > Br > I. The rotation for the last three is very slow and is detected only by MT. With OPPy(3) the occurrence of associative exchange of free and coordinated Py groups is observed (studied only for X = C6F5, CI), the rate depending on M and X in the order Pd > Pt and Cl > C6F5. Only for [Pd(C6F5)Cl(OPPy(3))] is this rate faster than the C6F5 rotation, producing the effect of an apparent rotation with anomalously low activation parameters. The structures of two complexes, [Pd(C6F5)Br(OPPy(2)Ph)] and [Pd(C6F5)(2)(OPPy(2)Ph)], have been studied by X-ray diffraction.