In situ Grignard metalation method (iGMM) for the preparation of alkynyl magnesium and calcium compounds

Metalation of Me 3 Si C C H with ethyl alkaline-earth metal halides yields the corresponding trimethylsilylethynyl compounds that show not only a Schlenk-type equilibrium but also increasing tendency to degrade with increasing radius of the metal. • The in situ generation of alkylcalcium halides is a powerful strategy to produce calciation reagents. • Contrary to Alkyl Mg X, organocalcium halides slowly convert to homoleptic CaR 2 and CaX 2 . • Bridging alkynyl ligands between Ca atoms are preferred compared to soft iodide ions. • The Schlenk equilibrium of alkynylmagnesium bromide shows characteristic thermodynamic parameters. In the in situ Grignard Metalation Method (iGMM), intermediately formed ethylmagnesium bromide as well as ethylcalcium and ethylstrontium iodide metalate trialkylsilylethyne in THF. For Me 3 Si C C MgBr ( 1a ) a temperature-dependent Schlenk equilibrium is operative and this heteroleptic compound coexists with the homoleptic congeners Mg(C C SiMe 3 ) 2 ( 1b ) and MgBr 2 . The reaction enthalpy ΔH and entropy ΔS adopt characteristic values. Initially formed Me 3 Si C C CaI ( 2a ) is quantitatively converted to the homoleptic compound Ca(C C SiMe 3 ) 2 ( 2b ) and CaI 2 . With increasing size of the alkaline-earth metal increasing amounts of the degradation product Me 3 Si C C SiMe 3 hamper isolation of analytically pure compounds of strontium and barium. The molecular structures of [(thf) 3 Mg(C C SiMe 3 ) 2 ] ( 1b ) and [(thf) 3 Ca(µ C C SiMe 3 )I] 2 ( 2a ) have been determined by single-crystal X-ray diffraction.