Magnesium Dihalide Promoted Addition of Grignard Reagents to the Cyclopentadienyl Rings of Tungstenocene Dichloride

Article abstract of DOI:10.1021/ja00201a022

Some Grignard reagents, including CH2=CHCH2MgCl, CH2=C(CH3)CH2MgCl, and PhCH2MgCl, add to a cyclopentadienyl ring of (2) to give the ring-substituted hydrochlorides (3), (4), and (5).These reactions are promoted by the addition of MgCl2, which is essential for the reproducible synthesis of 3, 4, or 5 in good yield.Grignards which react at the metal to give bis-alkyls , including CH3MgCl and (CH3)3SiCH2MgCl, were unaffected by added MgCl2.The hydrochlorides 3, 4, and 5 can be converted to the corresponding dichlorides (6), (7), and (8) by reaction with CCl4.Further reaction of 6 with CH2=CHCH2MgCl in the presence of added MgCl2 leads to substitution of the second cyclopentadienyl ligand and formation of (10).It is proposed that added magnesium dihalides promote Grignard addition to cyclopentadienyl rings of 2 by complexation of an intermediate cyclopentadiene complex.The presence of a double halide bridge in an adduct such as 4-C5H4CH2CH=CH2)(η-C5H5)Cl(μ-Cl)(μ-Br)MgBr> would account for the otherwise surprising observation that reaction of 2 with CH2=CHCH2MgBr leads to predominant (64percent) formation of the hydrobromide (11), with the hydrochloride 3 as a minor (7percent) product.