Allyl Calcium Compounds: Synthesis and Structure of Bis(η3-1-alkenyl)calcium

Allyl calcium compounds of different chain lengths [Ca(R)(2)(THF)(x)] (x = 0.15-0.25 (1-Ca, 3-Ca), 0.25-0.75 (2-Ca)) were synthesized by salt metathesis of CaI2 with allylpotassium reagents [K(R)] (R = n-butenyl (1-K), isobutenyl (2-K), n-hexenyl (3-K)), prepared from the corresponding alpha-olefin and Schlosser base. The new calcium derivatives were obtained in nearly quantitative yields. 1-Ca and 2-Ca could be crystallized as triglyme adducts (triglyme: tris(ethylene glycol)dimethyl ether) and structurally characterized by single-crystal X-ray diffraction. All potassium precursors [K(R)] were also isolated and characterized by H-1 and C-13 NMR spectroscopy. The solution properties in THF are in agreement with an eta(3)-coordination mode of the allyl moiety for all isolated compounds. For the potassium reagents 1-K and 3-K, endo/exo equilibrium distributions of > 99:< 1 and 85:15 were observed, whereas for the calcium compounds 1-Ca and 3-Ca, distributions of 60:40 and 42:58 were found at 25 degrees C, respectively. This distribution pattern is discussed in the context of the behavior found for alkali metal analogues.