N, N′-Dipp- o-phenylene-diamido Dianion: A Versatile Ligand for Main Group Metal-Metal-Bonded Compounds

Metal-metal-bonded compounds containing low-valent metal centers have attracted much attention because of their novel structure and reactivity, while the proper choice of ligands with suitable electronic and steric properties is the key to the synthesis of such species. Herein, we demonstrate that the ortho-phenylene-diamine (dipp-H2pda, H2L) ligand upon deprotonation to the dianion (dipp-pda2-) can effectively stabilize a series of E-E bonds, including group 12-15 elements Zn, Ga, Ge, and P. In particular, a Ge(I) compound in the digermylene form, [LGeI-GeIL]2-, has been isolated, which features the longest GeI-GeI bond (2.8774(4) Å) reported so far. The molecular and electronic structures of the compounds and their E-E bonding nature have been studied by X-ray diffraction, NMR or EPR and UV-vis spectroscopy, and computations.