Reduction of buta-1,3-diene by the hexacyanodinickelate(I) anion

The kinetics of the reaction of buta-1,3-diene with an aqueous solution of sodium hexacyanodinickelate(I) and the subsequent formation of butenes have been studied at 25° and at an ionic strength of 1·1. The kinetics of the removal of butadiene show that the slow step in complex formation is reaction (i), in which ki= 1·4 ± 0·1 l mol–1 s–1. The kinetics of the formation of the butenes are interpreted in terms of the rate-controlling reduction of two Ni2(CN)64–+ C4H6→(π-C4H6)Ni2(CN)64–(i), cyano-nickel intermediates, π1 and π2, containing a π-1-methylallyl ligand and a π-buta-1,3-diene ligand respectively. The two intermediates react by kinetically distinct paths yielding predominantly trans-but-2-ene, (π1), and cis-but-2-ene, (π2). The presence of a π-1-methylallylnickel complex in the reaction mixture has been confirmed by n.m.r. spectroscopy.