Encapsulated alkaline-earth metallocenes. Synthesis, solution behavior, and solid-state structures of bis(tetraisopropylcyclopentadienyl)calcium and -barium, [(C3H7)4C5H]2Ca and [(C3H7)4C5H]2Ba

Reaction of 2 equiv of KCp 4i (Cp 4i =(C 3 H 7 ) 4 C 5 H)with CaI 2 in diethyl ether or BaI 2 in THF produces the metallocenes (Cp 4i ) 2 Ca and (Cp 4i ) 2 Ba. The calcium metallocene (Cp 4i ) 2 Ca displays a remarkable degree of air stability and can be handled in dry air for several minutes without decomposition. It displays virtually no tendency to form adducts in solution with ethers or aromatic amines. The barium metallocene is the most volatile known organobarium compound, subliming at 90 o C and 0.01 Torr. These physical properties of the metallocenes are most likely related to the ability of the isopropyl groups of the Cp 4i rings to interlock, forming «cages» around the metal centers. DNMR experiments have provided evidence for hindered rotation in the complexes, either around the ring-C-CHMe 2 bonds or around the metal-ring centroid axis, with energies of activation of ΔG + ≤11.1 kcal mol −1 in (Cp 4i ) 2 Ca and 11.1 (±0.5) kcal mol −1 in (Cp 4i ) 2 Ba