Diene Dissolution of the Heavier Alkaline Earth Metals

Alkaline and alkaline earth metals are efficiently activated in the presence of aromatic hydrocarbons (“potassium–naphthalene”, “magnesium–anthracene”) or (substituted) 1,3-dienes to produce well-defined organometallic complexes. In this study, mononuclear diene complexes of calcium, strontium, and barium have been synthesized by utilizing tailor-made 1,3-dienes. Complexes [M(2,3-dimethyl-1,4-ditolyl-1,3-butadiene)(thf)4] (M = Ca, Sr), [Ca(2,3-dimethyl-1,4-dinaphthyl-1,3-butadiene)(thf)4], and {Ba[2,3-dimethyl-1,4-bis(2,4-dimethylphenyl)-1,3-butadiene](thf)4} were isolated and fully characterized including X-ray structure analyses. Whereas the calcium– and strontium–dienes show an approximate metallacylo-3-pentene coordination, barium(II) as the largest nonradioactive metal(II) cation reveals metallacyclo-2,4-heptadiene bonding in the solid state. It is further shown that barium(II) can accommodate eight thf molecules as evidenced in the dicationic complex {[Ba(thf)8][B(C6F5)4]2}, obtained from the reaction of barium–diene with trityl borate.

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