Bonding energy analysis in cationic borylene complexes of palladium and platinum: A theoretical study

Abstract

Quantum chemical calculations at DFT/BP86/TZ2P have been carried out for cationic metal borylene complexes of palladium and platinum trans-[X(PMe3)2M(BR)]+ (X=Cl, Br, I; M=Pd, Pt; R=Mesityl, Xylyl, Ph, NMe2). The bonding analysis was carried out with charge decomposition and energy decomposition analysis. The calculated geometry of the platinum borylene complex trans-[Br(PMe3)2Pt(BMes)]+ is in excellent agreement with the experimental structural data for trans-[Br(PCy3)2Pt(BMes)]+. Pauling bond order of the optimized structures shows that the M–B bonds in these complexes have multiple M–B bond character, which is also supported by the performed energy decomposition analysis. The orbital interactions between the metal and boron arise mainly from M←BR σ donation. In all complexes, the π bonding contribution to the orbital interactions is relatively small. The bonding analysis clearly shows that the platinum borylene complexes [X(PMe3)2Pt(BR)]+ are more strongly stabilized by Pt–BR interactions than the platinum borylene complexes [X(PMe3)2Pd(BR)]+ which is probably the reason the complex platinum borylene complexes [X(PCy3)2Pt(BMes)]+ could become isolated. The contributions of the electrostatic interaction terms ΔEelstat in the MBR bonding are significantly larger in all borylene complexes than the covalent bonding ΔEorb term. Thus, the MBR bond in the studied cationic borylene complexes of palladium and platinum has a greater degree of ionic character. The larger gap between HOMOs of metal fragments [X(PMe3)2M)]+ and LUMO of BNMe2 allow relatively weak [X(PMe3)2M]+→BNMe2 π-back bonding.