A structural, theoretical and coordinative evaluation of the bicyclic guanidinate derived from 1,4,6-triazabicyclo[3.3.0]oct-4-ene

Partial deprotonation of the bicyclic guanidine 1,4,6-triazabicyclo3.3.0]oct-4-ene (Htbo) is achieved using (n)BuLi. Isolation of the resulting lithium salts has resulted in the structural characterization of the mixed anion complex {Li(tbo)()(tboH)](2)}(infinity) (where -H = 1-(2-aminoethyl)-2-imidazolidinethione) and the partially deprotonated salt Li(6)(tbo)(6)(Htbo)(3), . The neutral guanidine Htbo reacts cleanly with AlMe(3) and ZnMe(2) to afford the organometallic complexes Al(tbo)Me(2)](2) ](2), and Zn(3)(tbo)(4)Me(2) (). Structural characterization of these compounds enables comparison between the {5:5}-bicyclic system, tbo](-), and the previously reported {6:6}-bicyclic system, hpp](-) (where hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido1,2-a]pyrimidine). Results indicate that delocalization within the tbo](-) anion is restricted to the CN(2) amidinate component, with retention of electron density in the non-bonding nitrogen lone-pair. These conclusions are supported by a DFT analysis of the neutral guanidines, Htbo and hppH.