Post-Grignard Reagents: Influence of the Coligands L on the Molecular Structures of Phenylcalcium Iodides [(L)(n)Ca(R)I] and Calcium Diiodides[(L)(n)CaI2]

Iodide is a very soft and large anion and as such its extreme ability to be polarized leads to a flat energy surface with respect to the variation of the Ca-I distances in [(L)(n)CaI2] and [(L)(n)Ca(R)I]. The influence of the donor strength and the bulkiness of the neutral coligands L on the Ca-I distances is studied. The base adducts of calcium diiodide can be isolated after the addition of L to CaI2 or from the Schlenk equilibrium after the direct synthesis of calcium powder with aryl iodides. As L the ethers diethyl ether (Et2O), tetrahydrofuran (thf), tetrahydropyran (thp), 1,2-dimethoxyethane (dme), I 8-crown-6 (18C6), bis(methoxyethyl)ether (diglyme), and amines tetramethylethylenediamine (tmeda), and hexamethyltriethylenetetramine (hmteta) are studied yielding the adducts [(thp)(4)Ca(Ph)I] (1a), Rthf)(4)Ca(Ph)I] (1b), [(dme)(2)(tht)Ca(Ph)I] (1c), [(18C6)Ca(Ph)I] (Id), and [(tmeda)(2)Ca(Ph)I] (1e), as well as [(thp)(4)CaI2] (2a), [(thf)(4)CaI2] (2b), [(Et2O)(4)CaI2] (2c), [(diglyme)(thf)(2)CaI2] (2d), [(diglyme)(dme)CaI2 k(2e), [(dme)(2)(thf)CaI2] (2f), [(18C6)CaI2] (2g), [(tmeda)(2)CaI2] (2h), and [(hmteta)CaI2] (2i). For comparison reasons, [(thf)(4)Ca(Ph)Br] (3a), [(thP)(4)CaBr2] (4a), [(thf)(4)CaBr2] (4b), and (dme)(2)(AcOH)CaBr2] (4c) with AcOH being acetic acid are included as well. The comparison shows that the coordination number of calcium itself only plays an insignificant role whereas bulkiness and donor strength of L represent the key influences.