Hetero‐ ansa ‐Bridged Main Group Metallocenes — a Structural and NMR Study

1,2-Bis(dimethylamino)-1,2-di-9-fluorenyldiborane(4) (1) is doubly metallated with group 1 and 2 metals to yield metal 1,2-bis(dimethylamino)-1,2-di-9-fluorenyldiborate(4) 2-Li to 2-Ba. The conformations of these compounds in solution are investigated by NMR spectroscopy, and the solid-state structures of 2-Li · 5 THF, 2-K · 4 THF, 2-K · 2 DME, and 2-Ca · 2 THF are determined by X-ray diffraction. All four structures can be described as main group metallocenes. The potassium derivatives form contact ion pairs, leading to polymeric chain-like structures. In contrast, 2-Li · 5 THF exhibits the rare combination of a contact ion pair with a solventseparated ion pair, giving the monomeric structure [Li(THF)4][(fl2B2(NMe2)2)Li · THF]. 2-Ca · 2 THF, which is also monomeric, adapts a severely distorted geometry.