5-Methyl-2-thienylcalcium iodide.

The reduction of 2-bromo- and 3-bromothiophene with calcium powder gives impure thienylcalcium complexes due to interference of various subsequent metalation and calcium-halogen exchange reactions as well as ether degradation. Therefore, calcium-iodine exchange succeeds via the reaction of trimethylsilylmethylcalcium halide with 3-iodothiophene in tetrahydrofuran at -78 °C in the presence of chloro-trimethylsilane, leading to the quantitative formation of 3-(trimethylsilyl)thiophene. The synthesis and isolation of a thienylcalcium halide, a heavy Grignard reagent with a thienyl group, is possible via the reduction of 2-iodo-5-methylthiophene with activated calcium in THF. Substitution of the thf ligands in 5-methyl-2-thienylcalcium iodide ([5-MeThien-2-Ca(thf)4I], 1) by dissolution in tetrahydropyran (THP) leads to the thp complex of 5-methyl-2-thienylcalcium iodide ([5-MeThien-2-Ca(thp)4I], 2). A low field shift of the calcium-bound carbon atom is characteristic of thienylcalcium complexes.