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-dabqdiH(2)), [(thf)(2)Li(μ-dipp-dabqdi)Li(thf)(2)] (1) and (dme)(1.5)Na(μ-dipp-dabqdi)Na(dme)(1.5) (2, dme = 1,2-dimethoxyethane), have been synthesized by the reaction of dipp-dabqdiH(2) with Li(n)Bu or sodium metal. In addition, treatment of 1,2,4,5-tetrakis(2,6-diisopropylamino)benzene (dipp-tabH(4)) with potassium metal in dme afforded the complex [(dme)(2)K(μ-dipp-tabH(2))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 ZnCl(2) yielded the ion-contacted zinc complexes [(thf)(3)Li(μ-Cl)ClZn(μ-dipp-dabqdi)ZnCl(μ-Cl)Li(thf)(3)] (4), [(dme)(2)Li(μ-Cl)ClZn(μ-dippdabqdi)ZnCl(μ-Cl)Li(dme)(2)] (5), and [(dme)(2)Na(μ-Cl)(2)Zn(μ-dipp-dabqdi)Zn(μ-Cl)(2)Na(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.