Triel Bonds between BH3/C5H4BX and M(MDA)2 (X = H, CN, F, CH3, NH2; M = Ni, Pd, Pt, MDA = Enolated Malondialdehyde) and Group 10 Transition Metal Electron Donors

A systematic theoretical study was conducted on the triel bonds (TrB) within the BH₃∙∙∙M(MDA)₂ and C₅H₄BX∙∙∙M(MDA)₂ (M = Ni, Pd, Pt, X = H, CN, F, CH₃, NH₂, MDA = enolated malondialdehyde) complexes, with BH₃ and C₅H₄BX acting as the electron acceptors and the square-coordinated M(MDA)₂ acting as the electron donor. The interaction energies of these systems range between -4.71 and -33.18 kcal/mol. The larger the transition metal center M, the greater the enhancement of the TrB, with σ-hole TrBs found to be stronger than π-hole TrBs. In the σ-hole TrB complex, an electron-withdrawing substituent on the C opposite to the B atom enhances the TrB, while an electron-donating substituent has little effect on the strength of TrB in the Pd and Pt complexes but enhances the TrB in the Ni-containing complexes. The van der Waals interaction plays an important role in stabilizing these binary systems, and its contribution diminishes with increasing M size. The orbital effect within these systems is largely due to charge transfer from the d_z² orbital of M into the empty p_z orbital of B.