The synthesis and structure of lithium derivatives of the sterically encumbered beta-diketiminate ligand [{(2,6-(Pr2H3C6)-H-i)N(CH3)C}(2)CH](-), and a modified synthesis of the aminoimine precursor

Abstract

The reaction of the beta -aminoimine compound (2,6-(Pr2H3C6)-H-i)NC(CH3)CHC(CH3)N(C6H3-2,6-Pr-2(i))H (1, Dipp(2)nacnacH; Dipp = C6H3-2,6-Pri2) with n-BuLi in diethyl ether or tetrahydrofuran afforded the solvates Dipp(2)nacnacLi(Et2O) (2) and Dipp(2)nacnacLi(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 Dipp(2)nacnacLi 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 Dipp(2)nacnac ligand, and it is associated by coordination of lithium to a carbon of the Dipp ring of the other Dipp(2)nacnac unit of the dimer. In the dodecamer 4b, the asymmetric unit consists of a chain of six LiDipp(2)nacnac 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 rst 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.