Coordination Behavior of Calcocene and Its Use as a Synthon for Heteroleptic Organocalcium Compounds

The insoluble calcocene Ca(η5-C5H5)2 readily dissolves after addition of Lewis bases. Monodentate donor solvents such as tetrahydrofuran (thf), pyridine (py), and tetrahydropyran (thp) form complexes of the type [(L)2CaCp2] (L = thf (1), py (2), thp (4)). Bidentate Lewis bases such as 1,2-bis(dimethylamino)ethane (tmeda) and 1,2-dimethoxyethane (dme) act as chelating ligands in complexes of the type [(L)CaCp2] (L = tmeda (3), dme (5)). Multidentate ethers of the type MeO−(CH2CH2O)n−Me (n = 2, diglyme; n = 3, triglyme; n = 4, tetraglyme) bind in all cases as tridentate Lewis bases of the type [(η3-L)CaCp2] (L = diglyme (6), triglyme (7), tetraglyme (8)), but the formation of [(L)CaCp]+ cations with these ethers or even with crown ethers was not observed. However, partial hydrolysis of 1 releases one Cp ligand, and from this reaction mixture crystalline [(15C5)CaCp]+[(thf)CaCp3]− (9) precipitates in the presence of 15-crown-5 (15C5). Calcocene behaves as a pseudohalide complex of calcium, and the reaction of 1 or 5 with phenyllithium in the presence of DME yields heteroleptic [(dme)(η5-Cp)Ca(μ-Ph)]2 (10), which forms a dimer with bridging phenyl groups in the solid state. Especially this last reaction offers an expansion of organocalcium chemistry.不溶性二茂钙（calcocene）Ca(η⁵-环戊二烯基)₂（Ca(η⁵-C₅H₅)₂）在添加路易斯碱后可迅速溶解。单齿给体溶剂如四氢呋喃（tetrahydrofuran，THF）、吡啶（pyridine，Py）及四氢吡喃（tetrahydropyran，THP）可形成[(L)₂CaCp₂]型配合物（其中L为溶剂配体，对应L=THF（1）、Py（2）、THP（4），Cp为环戊二烯基（cyclopentadienyl）的通用简写）。双齿路易斯碱如1,2-双(二甲氨基)乙烷（1,2-bis(dimethylamino)ethane，TMEDA）与1,2-二甲氧基乙烷（1,2-dimethoxyethane，DME）可作为螯合配体，生成[(L)CaCp₂]型配合物（L=TMEDA（3）、DME（5））。通式为MeO-(CH₂CH₂O)ₙ-Me的多齿醚（n=2时为二甘醇二甲醚（diglyme）；n=3时为三甘醇二甲醚（triglyme）；n=4时为四甘醇二甲醚（tetraglyme））在所有反应中均以三齿路易斯碱形式配位，得到[(η³-L)CaCp₂]型配合物（L=diglyme（6）、triglyme（7）、tetraglyme（8）），但未观察到此类醚甚至冠醚与体系形成[(L)CaCp]⁺阳离子的情况。不过，对配合物1进行部分水解可释放一个Cp配体，当反应体系中存在15-冠-5（15-crown-5，15C5）时，会从该反应混合液中析出结晶态的[(15C5)CaCp]⁺[(THF)CaCp₃]⁻（9）。二茂钙可被视作钙的类卤化物配合物，将配合物1或5与苯基锂在DME存在下反应，可得到杂配型配合物[(DME)(η⁵-Cp)Ca(μ-苯基)]₂（10），该配合物在固态下通过桥连苯基形成二聚体。尤为重要的是，上述最后一例反应为有机钙化学的研究提供了新的拓展方向。