Oligomerisation and telomerisation of buta-1,3-diene catalysed by bis-(η-cyclo-octa-1,5-diene)-palladium and -platinum

Abstract

The [Pd(cod)₂]-catalysed reaction of buta-1,3-diene with secondary amines (morpholine, piperidine, diethylamine, or dimethylamine) affords octa-2,7-dienylamines, the highest yields being obtained with the cyclic amines. However, treatment of buta-1,3-diene with acetic acid-diethylamine in the presence of [Pd(cod)₂](cod = cyclo-octa-1,5-diene) affords an improved yield of the diethylamine C₈ adduct. The addition of 1 mol of PPh₃ per mol of Pd has only a small effect on the above reactions. The addition of acetic acid to buta-1,3-diene is catalysed by [Pd(cod)₂] to give octa-2,7-dienyl acetate and 1-vinylhex-5-enyl acetate in the ratio of 4 : 1. The [Pd(cod)₂]-catalysed reaction of isoprene with morpholine affords as the major product the tail-to-tail amine adduct. The specificity of this reaction is improved by the addition of 1 mol of PPh₃. The system [Pd(cod)₂]–PPh₃ catalyses the addition of acetaldehyde to buta-1,3-diene to form 2-methyl-3,6-divinyltetrahydropyran. With phenyl isocyanate, piperidones are formed. Reaction of buta-1,3-diene with morpholine in the presence of [Pt(cod)₂] gives only octa-1,3,6-triene; however, addition of the co-catalyst Al(OPr^t)₃ or Al(OBu^t)₃ leads to the formation of the octadienylamine adducts. Telomerisation of buta-1,3-diene with acetic acid catalysed by [Pt(cod)₂] gives selectively octa-2,7-dienyl acetate. Possible mechanisms for these reactions are discussed.