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.