[_The chemical, "BrCp2NbCl2", after a process to substitute one chlorine atom for a cyclopentadienyl group, forms "C5H5Nb(CH3)Cl"(3). Afterward, another substitution works, replacing another chlorine atom by a methyl group, thus becoming "C5H5Nb(CH3)2."(4)_
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[_化合物"BrCp2NbCl2"经过一步反应，将一个氯原子替换为环戊二烯基团，形成"C5H5Nb(CH3)Cl"(3)。随后，再次进行取代反应，将另一个氯原子替换为甲基，最终生成"C5H5Nb(CH3)2."(4)_ **请将内容改写为更加专业的格式。**
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