η 3-Allyl complexes of the type [M(η 3-allyl)(L 2)] + (M Pd; allyl = 1-MeC 3H 4; L 2 = 1,5-C 8H 12, 2MeCN; allyl = C 3H 5: L 2 = 1,5-C 8H 12, 2PPh 3, 2P(C 6H 11) 3, 2MeCN; allyl = 2-MeC 3H 4; L 2 = 1,5-C 8H 12, 2MeCN, 2PPh 3; M Pt; allyl = C 3H 5; L 2 = 2PPh 3, 2P- (C 6H 11) 3) are reduced by H − and by cathodic electron transfer. In both cases the nature of the reduction products is determined by the coordination properties of L 2, elemental metal appearing when L 2 = 1,5-C 8H 12 or 2MeCN, and ML 2 species being formed in other cases. The reduction potentials are related to the stabilities of the starting complexes, and a parallel is dxawn with nucleophilic attack on η 3-allyl complexes of d 8 transition metal ions. The one-electron demand for electrochemical reduction and loss of the allyl group to form 1,5-hexadienes agree with the proposed reaction mechanism in which elimination of the allyl radical is proposed.