Isolation and characterization of an unusually stable formamidinium-containing macrotricyclic complex of lithium ion formed during the synthesis of 14-thia-1,4,8,11-tetraaza-bicyclo[9,5,3]nonadecane

Abstract

Using 1,3-bis(chloroacetamido)propane (5) as the common intermediate, an efficient route is described to the stepwise syntheses of 1-thia-4,8-diazacyclodecane, [10]aneN2S (8), and the pentadentate macrobicycle 17-thia-1,4,8,11-tetraazabicyclo[9,5,3]-nonadecane (11). During the investigation of the condensation of (5) with (8), with Li2CO3 used as a base the Li+ cation is carried over as the complex of the dioxo intermediate (10) and survives further reduction. Prolonged contact of these complexes with CHCl3 during cyclisation and extraction (in the presence of Li2CO3 and NaOH, respectively), leads to the formation of the complex cation [Li(4)]2+ as a byproduct in which the cationic macrocycle (4), containing a formamidinium ring, is formed through bridging of the 1,11-nitrogens in the macrobicycle (11) by a -CH= group that is derived from CHCl3. This renders the cavity in (4) too small for the inclusion of transition metal ions. Reaction of the lithium cation [Li(4)]2+ with PdCl2 yielded the trimetallic salt [(Li(4)]-PdCl2-[(Li(4)])](ClO4)4 in which two [Li(4)]2+ ions are bridged by a PdCl2 unit through coordination of the pendant thioether donors. A crystal structure of this trimetallic salt confirms the formation of [Li(4)]2+. In contrast, if triethylamine is used as a base during the cyclisation reaction leading to the formation of (11) and contact with aqueous NaOH and CHCl3 during its isolation is minimized, the formation of (4) is prevented and the yield of (11) improved.Key words: macrobicycle synthesis, lithium, formamidinium, paaladium, complex.