The geometries and bonding nature of interesting new tungsten η3-silaallyl/η3-vinylsilyl complex Cp(CO)2W(η3-H2SiCHCH2) (1) and tungsten vinyl silylene complex Cp(CO)2W(CHCH2)(SiH2) (2) and the conversion reaction of 1 to 2 were theoretically investigated with the density functional theory (DFT) and CCSD(T) methods, where 1 was adopted as a model of Cp*(CO)2W(η3-Me2SiCHCMe2). The nonbonding π orbital (φnπ) of the η3-H2SiCHCH2 group is similar to that of the η3-allyl group except that the Si p orbital more contributes to φnπ than the C p orbital. On the other hand, the π orbital (φπ) of the η3-H2SiCHCH2 group is considerably different from that of the η3-allyl group; the π-conjugation between the Si and C atoms is very weak, unlike that of the η3-allyl group in which π-conjugation is considerably strong. Thus, 1 can be understood to be a species between tungsten η3-vinylsilyl and tungsten η3-silaallyl complexes. From the geometry and frontier orbitals, 2 can be understood to be a tungsten vinyl silylene co...