SOLUTION BEHAVIOUR OF FIVE-COORDINATE PALLADIUM(II) COMPLEXES : ^1H NMR SPECTRAL EVIDENCES FOR THE COORDINATION SITE EXCHANGE OF 1,10-PHENANTHROLINE IN (TRIPHENYLPHOSPHINE)BIS (1,10-PHENANTHROLINE) PALLADIUM (II) TETRAFLUOROBORATE AND ITS 4,7-DIMETHYL AND

Abstract

Variable temperature ^1H NMR of [Pd(PPh_3) (4,7-R_2-phen)_2][BF_4]_2 (R=H, Me and Ph) has been obtained. The NMR spectra of the potentially five-coordinate complex support that at-40℃ the complex with R=Me is stereochemically rigid with an unusual trigonal bipyramidal structure (Tri. Bip) ; above-40℃ it behaves fluxional motion which appears to proceed via transition state of tetragonal pyramid (Tet. Py.) concurrently accompanying an oscillation of the apical phen. The intramolecular dynamic motion of the complex is explained by a coordinationsite exchange of the phen, and its G_273* for the twist motion from Tr. Bipy. To Tet. (that is, site exchange) was estimated approximately as to be 15.0 Kcal/mol for R=Ph and G_273* for R=Me was 13.9Kcal/mol.