AN ARYLLITHIUM COMPLEX WITH INTRAMOLECULAR COORDINATION OF AN O-DIAMINE SUBSTITUENT - X-RAY AND SOLUTION NMR STRUCTURES OF DIMERIC [LI(C6H4(CH2N(ME)CH2CH2NME2)-2)]2

The reaction of 2-bromobenzyl bromide, BrC6H4(CH2Br)-2, with HN(Me)CH2CH2NMe2 affords the diamine BrC6H4(CH2N(Me)CH2CH2NMe2)-2 (1). This o-diamine aryl bromide reacts quantitatively with n-BuLi to give [Li{C6H4(CH2N(Me)CH2CH2NMe2)-2-C,N,N'}]2 (2), which exists as a dimer in benzene (cryoscopy). The structure of 2 in the solid state was determined by X-ray crystallography: space group P2(1)/c with a = 15.7740(13) angstrom, b = 10.6866(8) angstrom, c = 18.205(2) angstrom, beta = 124.928(9)-degrees, Z = 4, R = 0.066, and R(w) = 0.045 for 1276 observed reflections. In the dimeric structure each lithium atom has a distorted-tetrahedral geometry consisting of coordination by two nitrogens of one ortho substituent and the two C(ipso) carbons of the aryl rings. Each C(ipso) is three-center-two-electron bonded to two lithium atoms with characteristics acute Li-C-Li angles of 66.3(4) and 66.6(5)-degrees and a Li...Li distance of 2.444-(15) angstrom. H-1, C-13, and Li-7 NMR spectroscopy of 2 in benzene-d6 reveal that both nitrogen donor atoms of one ligand coordinate to the same lithium center and that each dimeric molecule (as in the solid state) is one of two enantiomeric pairs in which the two central nitrogen atoms of the o-diamine substituents both have the same absolute configuration.