Synthesis and structure of two lithium terphenyls and a “halide rich” terphenyl lithium species

The syntheses and characterization of two new terphenyl iodides 2,6-(2,3,4,5,6-Me₅C₆)₂C₆H₃I (Ar^Pmp₂I) and (Ar^Dbp₂I) are described. Treatment of these with LiBuⁿ or LiBu^t afforded their lithium salts Ar^Pmp₂Li]₂ (2), Ar^Dbp₂{Li(OEt₂)}₂I (3), and Ar^Dbp₂Li]₂ (4), which were spectroscopically characterized. The X-ray crystal structures of 2 and the “halide-rich” species 3 as well as that of the previously known 2,6-(2,6-Me₂C₆H₃)₂C₆H₃Li]₂ (i.e. Ar^Xyl₂Li]₂, 1) were determined. The structures of both 1 and 2 are dimers in which the lithiums bridge the ipso carbons of the central aryl ring of each terphenyl ligand and also interact with the ipso carbons of the flanking aryl rings. The structure of 3 is a rare example of a structurally characterized “halide rich” organolithium complex and has a monomeric arrangement in which two ether-coordinated lithiums are bridged by an ipso-carbon of the central aryl ring as well as an iodine atom.