Syntheses and Crystal Structures of Simple Dibenzylcalcium Complexes:  Useful Reagents in the Preparation of Calcium Compounds

Synthetic routes to dibenzylcalcium or para-substituted dibenzylcalcium complexes are described. Crystal structures of trans-(p-tBu-benzyl)<INF>2</INF>Ca·(THF)<INF>4</INF> and cis-(benzyl)<INF>2</INF>Ca·(THF)<INF>4</INF> show similar Ca−C and Ca−O bond distances. The observation of different geometries (cis/trans) is explained by packing effects (DFT methods calculate less than 2 kcal/mol energy difference between cis- and trans-geometries). The strongly basic dibenzylcalcium complexes are useful precursors in calcium chemistry. Triphenylmethane was deprotonated, and the highly symmetric structure of [Ph<INF>3</INF>C^-]<INF>2</INF>[Ca²⁺·(THF)<INF>6</INF>] is discussed.