Kinetic Study of the Dynamic Behavior of [M(C 6 F 5 )X(OPPy n Ph 3- n )] (M = Pd, Pt; X = C 6 F 5 , Halide; n = 1−3): Activation Parameters for the Restricted Rotation about the M−Aryl Bond and for the Py Associative Exchange

The behavior in CDCl 3 of complexes of the type [M(C 6 F 5 )X(OPPy n Ph 3 - n )] (M = Pd, Pt; X = C 6 F 5; halide; n = 1−3) has been studied by 19 F and 1 H NMR spectroscopy. For the nonplanar N,N-chelating ligands with n = 2, 3, two processes have been observed and their activation parameters, Δ G ⧧, Δ H ⧧, and Δ S ⧧, have been determined, using magnetization transfer (MT) or line-shape analysis methods. The rotation of the C 6 F 5 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 C 6 F 5 > 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 = C 6 F 5, Cl), the rate depending on M and X in the order Pd > Pt and Cl > C 6 F 5 . Only for [Pd(C 6 F 5 )Cl(OPPy 3 )] is this rate faster than the C 6 F 5 rotation, producing the effect of an apparent rotation with anomalously low activation parameters. The structures of two complexes, [Pd(C 6 F 5 )Br(OPPy 2 Ph)] and [Pd(C 6 F 5 ) 2 (OPPy 2 Ph)], have been studied by X-ray diffraction.