The reduction of oxalic amidines with metallic lithium. Preparation of lithiated bisamides [R2N(RR1N)C:C(NRR1)NR2]Li2 and their use as intermediates in a novel synthesis of tetraaminoethenes.
Redn. of the 1,4-diaza-1,3-butadiene substructure of hexasubstituted oxalic amidines with Li metal yields the new Li diamides [R2N(RR1N)C:C(NRR1)NR2]Li2 [R = Ph; R1 = Me; R2 = 4-MeC6H4 (I) and R = R1 = Et; R2 = 2,4,6-Me3C6H2]. Subsequent reaction of I with various electrophiles gives the corresponding tetraaminoethenes R2R3N(RR1N)C:C(NRR1)NR2R4 [R3 = R4 = Me; R3R4 = -(CH2)3-] and the acylated derivs. II and III, resp. The 1st SET step in this reaction is the formation of monolithium radical anions, which were detected by EPR spectroscopy. The second electron transfer leads to the deeply colored dianions. In the case of I [cis-I.3 Et2O], the x-ray crystal structure reveals the cisoid arrangement of the bidental ligand and 3 mols. of Et2O which are located in a 2:1 fashion in the first coordination sphere of Li+. The NMR 2D-1H,6Li-HOESY-investigations of I in [D10]Et2O/Et2O (8:1) show Li+ contacts to the H atoms of the ether mols. and to the ortho-H atoms of the aryl moieties. Results of semiempirical calcns. are throughout in acceptable agreement with the exptl. data and explain the unusual coordination pattern of Li+ in the Li diamides.
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