Alkali Metal and Zinc Complexes of a Bridging 2,5-Diamino-1,4-Benzoquinonediimine Ligand

Two alkali metal complexes of a bridging 2,5-diamino-1,4-benzoquinonediimine
ligand (dipp-dabqdiH2), [(thf)2Li­(μ-dipp-dabqdi)­Li­(thf)2] (1) and [(dme)1.5Na­(μ-dipp-dabqdi)­Na­(dme)1.5]n (2, dme = 1,2-dimethoxyethane),
have been synthesized by the reaction of dipp-dabqdiH2 with
LinBu or sodium metal. In addition, treatment
of 1,2,4,5-tetrakis­(2,6-diisopropylamino)­benzene (dipp-tabH4) with potassium metal in dme afforded the complex [(dme)2K­(μ-dipp-tabH2)­K­(dme)2] (3). X-ray crystal diffraction analyses revealed that complexes 1 and 3 have dinuclear structures, while the
sodium complex 2 aggregates to a one-dimensional polymer
through bridging dme ligands. With increasing ion radius, the coordination
number of the alkali metal (Li, Na, and K) increases from four to
five to six, while the coordination geometry changes from distorted
tetrahedral to square pyramidal and further to octahedral in 1, 2, and 3, respectively. The salt
metathesis reactions of 1 and 2 with anhydrous
ZnCl2 yielded the ion-contacted zinc complexes [(thf)3Li­(μ-Cl)­ClZn­(μ-dipp-dabqdi)­ZnCl­(μ-Cl)­Li­(thf)3] (4), [(dme)2Li­(μ-Cl)­ClZn­(μ-dippdabqdi)­ZnCl­(μ-Cl)­Li­(dme)2] (5), and [(dme)2Na­(μ-Cl)2Zn­(μ-dipp-dabqdi)­Zn­(μ-Cl)2Na­(dme)2] (6), respectively. The ligand exists as the
dianionic form in compounds 1–6 upon
double deprotonation, and a complete electronic delocalization (except
for 3) of the quinonoid π-system is observed between
the metal centers over the two NCCCN
halves of the ligand. The electronic structures of the complexes were
studied by density functional theory (DFT) computations.