Chemical bonding in transition metal complexes with beryllium ligands [(PMe₃)₂M-BeCl₂], [(PMe₃) ₂M-BeClMe], and [(PMe₃)₂M-BeMe₂] (M = Ni, Pd, Pt)

The equilibrium geometries and bond dissociation energies of the 14 valence electron (VE) complexes [(PMe₃)₂M-BeCl₂], [(PMe₃)₂M-BeClMe], and [(PMe₃) ₂M-BeMe₂] with M = Ni, Pd, and Pt have been calculated using density functional theory at the BP86/TZ2P level. The nature of the M-Be bond was analyzed with the NBO charge decomposition analysis and the EDA energy decomposition analysis. The theoretical results predict the equilibrium structures with a T-shaped geometry at the transition metal where the PMe ₃ ligands are in the axial positions. The calculated bond dissociation energies show that the M-E bond strengths are in the range of donor-acceptor complexes of divalent beryllium compounds with ammonia. The bond strength decreases when the substituent at beryllium changes from Cl to CH ₃. The NBO analysis shows a negative charge at the BeX₂ fragment, which indicates a net charge flow from the transition metal fragment to the beryllium fragment. The energy decomposition analysis of the M-Be bonds suggests two donor-acceptor bonds with σ and π symmetry where the transition metal fragment is a double donor with respect to the beryllium ligand. The π component of the [Ni]→BeXX′ donation is much smaller than the σ component.