An agostic interaction in W(CO)(5)(cyclo-C3H6) is investigated using a hybrid density functional theory (B3LYP) with ECPs (LanL2DZ) on W and 6-311 +G(2d,p) on C, O, and H atoms. The structure with the minimum energy is confirmed on the basis of the reproducibility of the characteristic frequency shifts in the C-O stretching region observed by a time-resolved infrared absorption spectroscopy on the coordination Of cyclo-C3H6 to "naked" W(CO)(5). The C-H bond is found to coordinate to the W atom in n(2)-form with the bond enthalpy of 5.5 kcal mol(-1).