The Pt-BO bonding nature and the formation reaction of the experimentally reported platinum(II) oxoboryl complex, simplified to PtBr(BO)(PMe3)(2), were theoretically investigated with the density functional theory method. The BO- ligand was quantitatively demonstrated to have extremely strong sigma-donation but very weak d(pi)-electron-accepting abilities. Therefore, it exhibits a strong trans influence. The formation reaction occurs through a four-center transition state, in which the B delta+- Br delta- polarization and the Br -> Si and O p(pi) -> B p(pi) charge-transfer interactions play key roles. The Gibbs activation energy (Delta G degrees(double dagger)) and Gibbs reaction energy (Delta G degrees) of the formation reaction are 32.2 and -6.1 kcal/mol, respectively. The electron-donating bulky phosphine ligand is found to be favorable for lowering both Delta G degrees(double dagger) and Delta G degrees. In addition, the metal effect is examined with the nickel and palladium analogues and MBrCl[BBr(OSiMe3)]-(CO)(PR3)(2) (M = Ir and Rh). By a comparison of the Delta G degrees(double dagger) and Delta G degrees values, the M-BO (M = Ni, Pd, Ir, and Rh) bonding nature, and the interaction energy between [MBrCl(CO)(PR3)(2)](+) and BO- with those of the platinum system, MBrCl(BO)(CO)(PR3)(2) (M = Ir and Rh) is predicted to be a good candidate for a stable oxoboryl complex.