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Theoretical Study on the Transition-Metal Oxoboryl Complex: M–BO Bonding Nature, Mechanism of the Formation Reaction, and Prediction of a New Oxoboryl Complex

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journal contribution
posted on 16.04.2012 by Guixiang Zeng, Shigeyoshi Sakaki
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 σ-donation but very weak dπ-electron-accepting abilities. Therefore, it exhibits a strong trans influence. The formation reaction occurs through a four-center transition state, in which the Bδ+–Brδ− polarization and the Br → Si and O pπ → B pπ charge-transfer interactions play key roles. The Gibbs activation energy (ΔG°) and Gibbs reaction energy (ΔG°) 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 ΔG° and ΔG°. 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 ΔG° and ΔG° 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.