Arylcalcium Iodides in Tetrahydropyran: Solution Stability in Comparison to Aryllithium Reagents

作者：Langer Jens; Koehler Mathias; Fischer Reinald; Duendar Feyza; Goerls Helmar; Westerhausen Matthias^*

来源：Organometallics, 2012, 31(17): 6172-6182.

DOI：10.1021/om300508w

Reduction of para-substituted iodobenzene in tetrahydropyran (THP) with finely dispersed calcium powder yields arylcalcium iodides of the type [(THP)(4)Ca(C6H4-4-R)I] with R = CH3 (1), Cl (2), Br (3), I (4), OCH3 (5). A 2-fold insertion of calcium into dihalobenzenes was not observed. The beta-naphthylcalcium iodide [(THP)(4)Ca(beta-Naph)I] (6) is also accessible by direct synthesis in THP. The durability of arylcalcium compounds in THP was studied in comparison to that in THF, and a slightly enhanced lifetime in THP at ambient temperature was observed. Furthermore, the relative reactivity and selectivity of 1 and its lithium counterpart [{(THP)(2)Li}(2)(mu-Tol)(mu-Br)] (7) in the reaction with THP and THF were studied. alpha-Metalation and subsequent cycloreversion was the major pathway observed for THF in both cases. In the degradation reaction induced by 7, several byproducts arising from carbolithiation and, surprisingly, from beta-metalation reactions were identified, while 1 was found to be more selective. The related [(THP)(2)Li(mu-Ph)](2) (9) was prepared and used to unambiguously identify some of the products. In order to verify the formation of benzyllithium as one of the byproducts, an authentic sample of [(dme)Li(mu-CH2Ph](2) (8) was prepared. In THP, an inversion of the relative reactivity of 1 and 7 was observed and the calcium compound was found to be more reactive than its lithium analogue. The crystal structures of 1-9 were determined by X-ray diffraction studies, and a trans arrangement of the anionic ligands due to electrostatic reasons was observed in case of the hexacoordinated calcium complexes.

• 出版日期2012-9-10