Synthesis and Spectroscopic Properties of Arylcalcium Halides

The direct synthesis of activated calcium with aryl halides in tetrahydrofuran (THF) gave the following
compounds of the type RCaX in fair to good yields:  [MesCaI(THF)4] (1), [(p-tolyl)CaI(THF)4] (2),
[PhCaI(THF)4] (3), and [PhCaBr(THF)4] (5). All of these “heavy Grignard reagents” contain a calcium
atom in a slightly distorted octahedral environment. They must be handled at low temperatures in order
to avoid ether cleavage reactions. The Ca−C bond lengths vary between 2.556(5) Å (3) and 2.583(3) Å
(5). The thermal stability is enhanced when the coordination number of calcium is increased. The calcium
in the seven-coordinate complex [PhCaI(THF)(DME)2] (4) has a distorted-pentagonal-bipyramidical
configuration. This complex is thermally more stable and can be handled at 0 °C. The larger coordination
number results in a longer Ca−C bond of 2.621(5) Å.