Stereochemical aspects of the cycloaddition reaction products of the coordinated azide in palladium complexes [Pd(N---N---S)(N₃)]

Abstract

Cycloaddition reactions of coordinated azide in the palladium(II) complexes [PdL(N₃)] (L=L¹---L³; HL₁ = methyl 2-(2-aminoethyl)amino)cyclopent-1-enedithiocarboxylate, HL² = methyl 2-((2-dimethylamino)ethyl)amino)cyclopent-1-enedithiocarboxylate, HL³ = methyl 2-((2-diethylamino)ethyl)amino)cyclopent-1-enedithiocarboxylate)) with nitriles, alkynes, alkenes, PhNCS and CS₂ have been investigated. In all the cases the products obtained are of the type [PdL-(heterocycle)^-]. The tetrazolates obtained by reacting [PdL(N₃)] with nitriles give rise to syn-N(1)-, anti-N(1)- and N(2)-bound isomers, whose relative abundances have been determined from ¹H NMR spectra. The relative abundance of the N(2)-bound species increases with electron-withdrawing substituents on the tetrazolates. The triazolato and triazolinato complexes obtained from alkynes and alkenes, repectively exist only as the N(2) isomer. The rate constants for the reaction of [PdL(N₃)] with aromatic nitriles show a strong dependence on σ_p (Hammett parameters) of the substituent. The reaction rate also depends upon the steric influences of the substituents attached to the terminal nitrogen atom of L and decreases in the order: [PdL¹(N3)]> [PdL²(N₃)]>[PdL³(N₃)].