Synthesis, X-ray, and NMR Studies on Palladium BINAP Complexes Containing Oxazolidinone and Acetylacetonate Anions

Abstract

A series of monocationic palladium BINAP complexes, [Pd(rac-BINAP)(an oxazolidinone anion)][X] and [Pd(rac-BINAP)(an acetylacetonate anion)][X] (X = a, CF3SO3-; b, BF4-) (9−13), have been synthesized and characterized. A dicationic intermediate, pertinent to the Pd-catalyzed hydroamination reaction, arising from the reaction of the bis-aquo complex [Pd(H2O)2(rac-BINAP)]2(CF3SO3)2 and 1 equiv of an oxazolidinone, has been characterized via low-temperature NMR studies. The structures of the complexes [Pd(rac-BINAP)(CH3−C(O)−C(CH3)−C(O)−CH3)](BF4), 12b, and [Pd(μ-OH)(rac-BINAP)]2(CF3SO3)2 have been determined by X-ray diffraction. The solid-state structures of two separate forms of the BF4- salt 12b were obtained. One form of the salt can be thought of as a tight ion pair, whereas the second form contains a dichloromethane solvent molecule, packed in approximately a fifth coordination position together with a relatively remote BF4- anion. These structures represent a rare example where both ion pairing and strong solvation could be individually characterized. PGSE diffusion coefficients (D values) were measured for both the CF3SO3- and BF4- salts of 9−13 in CD2Cl2. In addition, D values were obtained for the CF3SO3- salts in THF and CDCl3 solutions. The amount of ion pairing decreases in the sequence CDCl3 > THF > CD2Cl2. The 1H,19F-HOESY spectra for the salts in CDCl3 suggest that the CF3SO3- is approaching the positive metal and phosphorus centers via a pathway that brings it closest to the P-phenyl groups but remote from the chelating anion