Theoretical and experimental studies on stability, bonding and isolation of elusive bis-(dichloro-aluminium) oxides supported by donor-base ligands

Abstract

Herein, we depict the stability, and bonding studies of bis-(dichloro-aluminium) oxides Cl₂Al–O–AlCl₂ supported by a pair of homo-/hetero-leptic donor base ligands L, L′ [L, L′ = cyclic alkyl(amino) carbene (cAAC^Me; 1); N-heterocyclic carbene (NHC^Me; 2); di-amido carbene (DAC^Me; 3); L = cAAC^Me, L′ = NHC^Me; (4)] with a general formula (L)Al(Cl)₂–O–Al(Cl)₂(L′) (1–4) by NBO, QTAIM and EDA-NOCV analyses. Theoretical calculations suggest that 1–4 possess favorable interaction energies (ΔE_int), and bond dissociation energies between L/L′, and Al(Cl)₂–O–Al(Cl)₂ fragments via the formation of two dative L→Al bonds [1 > 4 > 2 > 3]. This trend is rationalized by the σ-donor ability of the ligands L/L′. Moreover, we depict the first successful solid-state isolation of the colorless compound (cAAC)Al(Cl)₂–O–Al(Cl)₂(cAAC) (1′) by reacting cAAC and AlCl₃ in the presence of a controlled amount of H₂O, where two equiv. of cAAC is being utilized as the base. 1′ has been structurally characterized by single-crystal X-ray diffraction, and further studied by NMR spectroscopy.