Reaction of phenylhydrazones with bis(π-allyl)-nickel and -palladium complexes

Abstract

The reactions of 2 mol of butadiene and 1 mol of the phenylhydrazones of acetaldehyde, propionaldehyde, acetone, and butanone in the presence of nickel and palladium complexes have been shown to yield a series of two isomeric azo-compounds. In the presence of the latter complexes N-octadienylated phenylhydrazones were also formed and the ratio of products varied with the anion of the palladium salt and the nature of the added organophosphorus ligand. With tetrakis(triphenylphosphine)palladium, formation of the azo-adducts was predominant, whereas exclusive alkylation was found in the presence of PdCl₂–PPh₃ and Pd(NO₃)₂–PPh₃. The results of the palladium-complex catalysed reactions have been discussed in terms of the σ–π character of the bis(π-allyl)palladium intermediates and their reactivity towards electrophilic and nucleophilic reagents. A system containing bis(cyclo-octa-1,5-diene)triphenylphosphinenickel at room temperature gave higher yields than an analogous system in which αω-octadienediylnickel was produced in situ from a nickel(II) salt and tri-isobutylaluminium. This has been shown to be due to the preferred decomposition of one of the isomeric azo-compounds.