Bis[μ-bis-(2,6-diiso-propyl-phen-yl) phosphato-κ2 O: O']bis-[(2,2'-bi-pyridine-κ2 N, N')lithium] toluene disolvate and its catalytic activity in ring-opening polymerization of ∊-caprolactone and l-dilactide

Abstract

The solvated centrosymmmtric title compound, [Li₂(C₂₄H₃₄O₄P)₂(C₁₀H₈N₂)₂]·2C₇H₈, was formed in the reaction between {Li[(2,6-ⁱPr₂C₆H₃-O)₂POO](MeOH)₃}(MeOH) and 2,2'-bi-pyridine (bipy) in toluene. The structure has monoclinic (P2₁/n) symmetry at 120 K and the asymmetric unit consists of half a complex mol-ecule and one mol-ecule of toluene solvent. The diaryl phosphate ligand demonstrates a μ-κO:κO'-bridging coordination mode and the 2,2'-bi-pyridine ligand is chelating to the Li⁺ cation, generating a distorted tetra-hedral LiN₂O₂ coordination polyhedron. The complex exhibits a unique dimeric Li₂O₄P₂ core. One isopropyl group is disordered over two orientations in a 0.621 (4):0.379 (4) ratio. In the crystal, weak C-H⋯O and C-H⋯π inter-actions help to consolidate the packing. Catalytic systems based on the title complex and on the closely related complex {Li[(2,6-ⁱPr₂C₆H₃-O)₂POO](MeOH)₃}(MeOH) display activity in the ring-opening polymerization of ∊-caprolactone and l-dilactide.

Keywords: bi­pyridine; coordination compound; crystal structure; cyclic esters; diaryl phosphate; lithium; ring-opening polymerization.