The electronic structures of the Bbt(Br)E=M(PCy3)(2) (E = C, Si, Ge, Sn, Pb and M = Pt, Pd) complexes and their potential energy surfaces for the formation and water addition reactions were studied using density functional theory (B3LYP/LANL2DZ). The theoretical evidence suggests that the bonding character of the E=M double bond between the six valence-electron Bbt(Br)E: species and the 14 valence-electron (PCy3)(2)M complexes has a predominantly high s-character. That is, on the basis of the NBO, this theoretical study indicates that the sigma-donation from the E element to the M atom prevails. Also, theoretical computations suggest that the relative reactivity decreases in the order: Bbt(Br)C=M(PCy3)(2) > Bbt(Br)Si=M(PCy3)(2) > Bbt(Br)Ge=M(PCy3)(2) > Bbt(Br)Sn=M(PCy3)(2) > Bbt(Br)Pb=M(PCy3)(2), irrespective of whether M = Pt or M = Pd is chosen. Namely, the greater the atomic weight of the group 14 atom (E), the larger is the atomic radius of E and the more stable is its Bbt(Br)E=M(PCy3)(2) doubly bonded species toward chemical reactions. The computational results show good agreement with the available experimental observations. The theoretical results obtained predictions to be made. Pd in this work allow a number of