Chemical bonding in transition metal complexes with beryllium ligands [(PMe_3)_2M-BeCl_2], [(PMe_3) _2M-BeClMe], and [(PMe_3)_2M-BeMe_2] (M = Ni, Pd, Pt)

摘要

The equilibrium geometries and bond dissociation energies of the 14 valence electron (VE) complexes [(PMe_3)_2M-BeCl_2], [(PMe_3)_2M-BeClMe], and [(PMe_3) _2M-BeMe_2] 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 BeX_2 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.