Syntheses and Crystal Structures of Simple Dibenzylcalcium Complexes: Useful Reagents in the Preparation of Calcium Compounds.
Prepn. and structure of para-substituted dibenzylcalcium THF complexes are described. Transmetalation of ArCH2K with CaI2 in THF afforded octahedral calcium complexes, (ArCH2)Ca(THF)4 (Ar = Ph, 4-tBuC6H4, 4-Me3SiC6H4). Reaction of (PhCH2)2Ca(THF)4 with Ph3CH gave calcium salt of the carbanion, [Ph3C-]2[Ca(THF)4]2+ which highly sym. structure is discussed. Crystal structures of trans-[(4-tBuC6H4CH2)2Ca(THF)4] and cis-[(PhCH2)2Ca(THF)4] show similar Ca-C and Ca-O bond distances. The cis-trans isomerism of calcium complexes is explained by packing effects, since DFT calcn. of the energy of the cis/trans-isomers gave less than 2 kcal/mol difference between cis- and trans-geometries. The strongly basic dibenzylcalcium complexes are useful precursors in calcium chem.
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