Ligand Effects in the Synthesis of Ln2+ Complexes by Reduction of Tris(cyclopentadienyl) Precursors Including C–H Bond Activation of an Indenyl Anion

The tris­(cyclopentadienyl) yttrium
complexes Cp3Y­(THF),
CpMe3Y­(THF), Cp″3Y, Cp″2YCp, and Cp″2YCpMe [Cp = C5H5, CpMe = C5H4Me, Cp″ = C5H3(SiMe3)2] have been treated with potassium graphite in the presence
of 2.2.2-cryptand to search for more stable examples of complexes
featuring the recently discovered Y2+ ion first isolated
in [K­(18-crown-6)]­[Cp′3Y] and [K­(2.2.2-cryptand)]­[Cp′3Y], 1-Y (Cp′ = C5H4SiMe3). Reduction of the tris­(cyclopentadienyl)
complexes generates dark solutions like that of 1-Y, and the EPR spectra contain doublets with g values between 1.990 and 1.991 and hyperfine coupling constants
of 34–47 gauss that are consistent with the presence of Y2+. [K­(2.2.2-cryptand)]­[Cp″2YCp], 2-Y, was characterizable by X-ray crystallography. Reduction
of the Cp″3Gd, Cp″2GdCp, and Cp″2GdCpMe complexes containing the larger metal gadolinium
were also examined. In each case, dark solutions and EPR spectra like
that of [K­(2.2.2-cryptand)]­[Cp′3Gd], 1-Gd, were obtained, and [K­(2.2.2-cryptand)]­[Cp″2GdCp], 2-Gd, was crystallographically
characterizable. None of the new yttrium and gadolinium complexes
displayed greater stability than 1-Y and 1-Gd. Exploration of this reduction chemistry
with indenyl ligands did not give evidence for +2 complexes. The only
definitive information obtained from reductions of the CpIn3Ln (CpIn = C9H7, Ln
= Y, Ho, Dy) complexes was the X-ray crystal structure of {K­(2.2.2-cryptand)}2{[(C9H7)2Dy­(μ–η5:η1-C9H6)]2}, a complex containing the first example of the indenyl dianion,
(C9H6)2–, derived from C–H
bond activation of the (C9H7)1– monoanion. Density functional theory analysis of these results provides
an explanation for the observed hyperfine coupling constants in the
yttrium complexes and for the C–H bond activation observed
for the indenyl complex.

本研究对三环戊二烯基钇配合物Cp3Y-(THF)、CpMe3Y-(THF)、Cp″3Y、Cp″2YCp和Cp″2YCpMe [Cp = C5H5, CpMe = C5H4Me, Cp″ = C5H3(SiMe3)2] 进行了处理，以在2.2.2-立方烷存在下寻找更稳定的配合物实例，这些配合物以Y2+离子为特征，该离子首次在[K-(18-冠醚-6)]-[Cp′3Y]和[K-(2.2.2-立方烷)]-[Cp′3Y]，1-Y (Cp′ = C5H4SiMe3]中分离得到。三环戊二烯基配合物的还原产生了类似于1-Y的深色溶液，并且电子顺磁共振(EPR)光谱中出现了g值介于1.990和1.991之间、超精细耦合常数为34–47高斯的二重态，这些结果与Y2+的存在一致。[K-(2.2.2-立方烷)]-[Cp″2YCp]，2-Y，可通过X射线晶体学进行表征。含有较大金属镓的Cp″3Gd、Cp″2GdCp和Cp″2GdCpMe配合物的还原也被考察，每种情况下均获得了类似于[K-(2.2.2-立方烷)]-[Cp′3Gd]，1-Gd的深色溶液，并且[K-(2.2.2-立方烷)]-[Cp″2GdCp]，2-Gd可通过晶体学进行表征。新获得的钇和镓配合物中，没有一种比1-Y和1-Gd显示出更高的稳定性。使用 indenyl 配体进行此还原化学的探索并未提供+2配合物的证据。从CpIn3Ln (CpIn = C9H7, Ln = Y, Ho, Dy)配合物的还原中获得的唯一确切信息是{K-(2.2.2-立方烷)}2{[(C9H7)2Dy-μ-η5:η1-C9H6]2}的X射线晶体结构，这是一个含有首次发现的 indenyl 二阴离子(C9H6)2-的配合物，该阴离子由(C9H7)1-单阴离子通过C-H键活化生成。对这些结果的密度泛函理论分析解释了钇配合物中观察到的超精细耦合常数，以及 indenyl 配合物中观察到的C-H键活化。