A Structural, Theoretical and Coordinative Evaluation of the Bicyclic Guanidinate Dervived from 1,4,6-triazabicyclo[3.3.0]oct-4-ene

Partial deprotonation of the bicyclic guanidine 1,4,6-triazabicyclo[3.3.0]oct-4-ene (Htbo) is achieved using nBuLi. Isolation of the resulting lithium salts has resulted in the structural characterization of the mixed anion complex {[Li(tbo)( VIII)(tboH)]2} 1a (where VIII-H = 1-(2-aminoethyl)-2-imidazolidinethione) and the partially deprotonated salt Li6(tbo)6(Htbo)3, 1b. The neutral guanidine Htbo reacts cleanly with AlMe3 and ZnMe2 to afford the organometallic complexes [Al(tbo)Me2]2 [ 2]2, and Zn3(tbo)4Me2 ( 3). 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-pyrimido[1,2-a]pyrimidine). Results indicate that delocalization within the [tbo]- anion is restricted to the CN2 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.