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

Abstract

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 CaI 2 with allylpotassium reagents [K(R)] (R = n-butenyl (1-K), isobutenyl (2-K), n-hexenyl (3-K)), prepared from the corresponding R-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 1 H and 13 C NMR spectroscopy. The solution properties in THF are in agreement with an η 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 °C, respectively. This distribution pattern is discussed in the context of the behavior found for alkali metal analogues.

Nucleophilic Aromatic Substitution at Benzene with Powerful Strontium Hydride and Alkyl Complexes

“…In contrast, heavier group 2 metal reagents remained elusive for at least a century . Organocalcium chemistry is slowly awakening but recent developments mainly include syntheses of benzyl, aryl, allyl, or silylated methyl compounds. The much more potent unsubstituted alkyl metal complexes were a long sought after goal in alkaline‐earth metal chemistry, and this quest has only very recently been realized …”

Structurally Defined Allyl Compounds of Main Group Metals: Coordination and Reactivity

“…In contrast to its lighter magnesium homologue, bis(allyl)calcium shows η 3 coordination of the allyl ligands in the presence of donor ligands in solution and in the solid state (Figure 5 a). 57 In allylcalcium compounds with unsymmetrically substituted allyl ligands (butenyl or hexenyl), unsymmetric η 3 coordination is observed in the solid state 58 . 13 C NMR spectroscopic data for these compounds hint at a similar bonding situation in solution.…”

“…Recently, the same reactivity pattern has been observed for allyl compounds of the alkaline earth metals Ca–Ba, by using iodine as the oxidizing agent (Table 2). 57a, 58, 62 The reactions proceed instantaneously and quantitatively. When unsymmetrically substituted allyl ligands are used, formation of the coupling products with the sterically demanding substituents in the terminal positions is favored (Table 2, entries 3 and 4).…”

CH Activation of Isobutylene Using Frustrated Lewis Pairs: Aluminum and Boron σ‐Allyl Complexes

“…Whereas a number of recent reports have described early main-group allyl metal compounds, [9,19] as well as allyl aluminum compounds, [11c, 20] the compound described above is, to the best of our knowledge, the first example of an isolable allyl species that is derived from facile CÀH activation. It should be noted that C À H activation of alkynes by FLPs has been previously reported.…”