Thermal and spectroscopic study of dialkyl [ α-(4-benzeneazoanilino)- N-benzyl] phosphates and their palladium (II) halide complexes

Abstract

The mode of thermal decomposition of diethyl and dibutyl esters of [ α-(4-benzeneazoanilino)- N-benzyl] phosphonic acid and their palladium (II) dihalide adducts, Pd(L) 2X 2 (L = organophosphorous ligand; X = Cl, Br), as well as cyclopalladated complexes, [Pd(L-H)Cl] 2, have been investigated by thermal (TG, DTA) and spectroscopic (IR, FAB-mass) analyses. Thermal decomposition of the complexes takes place through a multistep process, the first step being a dehalogenation along with deesterification, followed by a complex pyrolysis that leads to a mixture of Pd and P 2O 5. All complexes are anhydrous, and on the basis of their initial decomposition temperatures, the thermal stability follows the order of Pd(L) 2Cl 2 < Pd(L) 2Br 2 < [Pd(L-H)Cl] 2. The mass spectrometric data indicate differences in the gas-phase fragmentation pathways between the two types of metal complex and a scheme for their thermal decomposition is proposed. In the adducts the main fragmentation routes consist off sequential losses of HCl giving arise to the mono- and bis-orthometallated species. The primary decomposition step in the cyclometallated complexes is shown to be the loss of Cl. In both derivatives these processes are in competition with the loss of the phosphate ester group.