Metallocenes of the alkaline earth metals and their carbene complexes

Abstract

Abstract Novel alkaline earth metallocenes with various cyclopentadienyl ligands and their carbene adducts with 1,3-di-iso-propyl-4,5-dimethylimidazol-2-ylidene (iPr-carbene) are described. The syntheses of the magnesocenes (C5Me4H)2Mg (1), (C5Me4tBu)2Mg (2), and (C5H3-1-(SiMe3)-3-tBu)2Mg (3) were carried out by reaction of the corresponding cyclopentadiene with dibutylmagnesium. The calcocenes (C5Me4H)2(NH3)2Ca (6), (C5Me4H)2(NH3)(THF)Ca (7) and the barocene (C5Me4tBu)2(THF)2Ba (13) were prepaired by reaction of calcium and barium, respectively, with the corresponding cyclopentadienes. Refluxing 7 in THF–toluene yielded the ammonia-free complex (C5Me4H)2(THF)Ca (8). Metathesis reaction of (C5Me4iPr)Na with CaI2 gave the calcocene (C5Me4iPr)2(THF)Ca (9). (C5Me4tBu)2(py)2Ba (14) results from dissolving 13 in pyridine. 1,3-Di-iso-propyl-4,5-dimethylimidazol-2-ylidene reacted with 1, 3, 7, 8, 13, and (C5Me5)2(THF)2Sr in toluene or THF to give the air- and moisture-sensitive adducts (C5Me4H)2(iPr-carbene)Mg (4), (C5H3-1-(SiMe3)-3-tBu)2(iPr-carbene)Mg (5), (C5Me4H)2(iPr-carbene)Ca (10), (C5Me4iPr)2(iPr-carbene)Ca (11), (C5Me5)2(iPr-carbene)Sr (12), and (C5Me4tBu)2(iPr-carbene)Ba (15). The novel compounds have been characterized by elemental analysis, mass spectrometry and NMR spectroscopy as well as the X-ray structures of the metallocenes (1, 2, 6, 9, 13) and the carbene adducts (4, 10, 11, 12, 15).