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 a nd H-1 NMR spectroscopy. For the nonplanar N,N-chelating ligands with n = 2, 3, two processes have been observed and their activation parame ters, Delta G(double dagger), Delta H-double dagger, and Delta S-doubl e 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 dissociatio n, 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 associativ e 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 tha n the C6F5 rotation, producing the effect of an apparent rotation with anomalously low activation parameters. The structures of two complexe s, [Pd(C6F5)Br(OPPy(2)Ph)] and [Pd(C6F5)(2)(OPPy(2)Ph)], have been stu died by X-ray diffraction.