Mono- and dilithiation of primary amine/secondary amine mixtures: Transamination, solvation, and cocomplexation

Addition of 1 equiv of N,N,2,2-tetramethylpropanediamine (4) to 1 equiv of either lithium dibenzylamide (1) or lithium 2,2,6,6-tetramethylpiperidide (2) results in the exclusive formation of the primary amide [{Me2NCH2CMe2CH2N(H)Li}(6)] (5). Compound 5 was determined to be a prismatic hexamer in the solid state, with each lithium, being tetracoordinated by binding to three amido anions and one chelating dimethylamino unit. In contrast, when 1 equiv of 4 is added to lithium hexamethyldisilazide (3), the sole product isolated from solution was the primary amine solvate [{Me3Si)(2)NLi . H2NCH2CMe2CH2NMe2}(2)] (6). Similarly, reaction of 1 equiv of 1,3-diaminopropane with 3 gave the solvate [{(Me3Si)(2)NLi . H2NCH2CH2CH2NH2}(2)] (12), Crystallographic analyses of 6 and 12 revealed dimeric aggregation, with each amine eta(1)-bonding to a metal center through the primary amine group. Addition of 1 equiv of (BuLi)-Li-n to the amine/amide mixtures resulted in lithiation of the remaining amine to yield the mixed-anion aggregates t(1.5)(2)](9), [(2.5)(2)] (10),and [(3.5)(2)] (11). These compounds adopt similar solid-state structures which can be regarded as four-rung ladders formed by the association of two mixed-anion heterodimers. Each metal center of the ladders is three-coordinate, either by bridging three amido nitrogens or by coordinating to two amido nitrogens and to one chelating dimethylamino unit.