Alkali-Metal Sandwich Complexes of a 1,2-Diaza-3,5-diborolyl Ligand Featuring η1, η2, η3, and η4 Coordination Modes

The ring closure of 1,2-diisopropylhydrazine and 1,1-bis(phenylchloroboryl)ethane produced a heterocyclic compound with a CB2N2 framework. Deprotonation of this precursor yielded 1,2-diisopropyl-4-methyl-3,5-diphenyl-1,2-diaza-3,5-diborolyl, a cyclopentadienyl analogue containing only one carbon atom in the ring skeleton. Lithium, sodium, and potassium salts of the new ligand have been prepared and characterized. The structures of both monomeric and polymeric sodium metallocenes, as well as the structures of polymeric potassium metallocenes incorporating the new heterocycle, have been determined by single-crystal X-ray diffractometry. These structures reveal not only many similarities but also significant differences in the coordination behavior of the new ligand compared with that of the carbon-based analogue.