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)CH2 CH2NMe2 affords the diamine BrC6H4(CH2N(Me)CH2CH2NMe2)-2 (1). This o-d iamine 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 benze ne (cryoscopy). The structure of 2 in the solid state was determined b y X-ray crystallography: space group P2(1)/c with a = 15.7740(13) angs trom, 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 refle ctions. In the dimeric structure each lithium atom has a distorted-tet rahedral geometry consisting of coordination by two nitrogens of one o rtho 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 c haracteristics 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 sp ectroscopy of 2 in benzene-d6 reveal that both nitrogen donor atoms of one ligand coordinate to the same lithium center and that each dimeri c molecule (as in the solid state) is one of two enantiomeric pairs in which the two central nitrogen atoms of the o-diamine substituents bo th have the same absolute configuration.