The synthesis and structure of lithium derivatives of the sterically encumbered β-diketiminate ligand [{(2,6-Pri2H3C6)N(CH3)C}2CH]−, and a modified synthesis of the aminoimine precursor

Abstract

The reaction of the β-aminoimine compound (2,6-Prⁱ₂H₃C₆)NC(CH₃)CHC(CH₃)N(C₆H₃-2,6-Prⁱ₂)H (1, Dipp₂nacnacH; Dipp = C₆H₃-2,6-Prⁱ₂) with n-BuLi in diethyl ether or tetrahydrofuran afforded the solvates Dipp₂nacnacLi(Et₂O) (2) and Dipp₂nacnacLi(THF) (3), respectively, which crystallized as monomers featuring the Li⁺ ions in a distorted trigonal planar environment and an essentially planar arrangement for the LiN₂C₃ ring. The lithiation of 1, in the absence of a donor solvent, afforded a Dipp₂nacnacLi product that crystallized in two different types of associated structures, 4a and 4b. In the dimer 4a, the Li⁺ ion is coordinated to the two nitrogens of the Dipp₂nacnac ligand, and it is associated by coordination of lithium to a carbon of the Dipp ring of the other Dipp₂nacnac unit of the dimer. In the dodecamer 4b, the asymmetric unit consists of a chain of six LiDipp₂nacnac units associated by interactions of the Li⁺ ions with one or two carbons from a Dipp ring of the next molecule in the chain. The hexamer is linked to an identical one (generated through an inversion center) by Li⁺–Dipp interactions involving the first and third lithium atoms from each hexamer, thereby generating an overall dodecameric structure of a type that was previously unknown for lithium salts. An improved yield synthesis for 1 was also developed.