Ansa [1]Trochrocenophanes and Their Related Unstrained 1,1‘-Disubstituted Counterparts: Synthesis and Electronic Structure

The heteroleptic sandwich complex [Cr(η5-C5H5)(η7-C7H7)] (trochrocene) was prepared by
subsequent treatment of CrCl3 with NaCp and Mg in the presence of cycloheptatriene in yields of 40%.
Selective dimetalation employing tBuLi/tmeda (N, N, N‘, N‘-tetramethylethylenediamine) afforded the highly
reactive species [Cr(η5-C5H4Li)(η7-C7H6Li)]·tmeda. An X-ray crystal-structure determination of its thf solvate
revealed a symmetrical, dimeric composition in the solid state, that is, a formula of [Cr(η5-C5H4Li)(η7-C7H6Li)]2·(thf)8, where the C5H4 moieties of both units are connected by two bridging lithium atoms. Addition of
different element dihalides to the dilithio precursor facilitated the isolation of ansa complexes with boron
and germanium in the bridging position. Structural characterization by X-ray diffraction studies on [Cr(η5-C5H4)-BN(SiMe3)2-(η7-C7H6)] and [Cr(η5-C5H4)-GeMe2-(η7-C7H6)] emphasized the strained character with
tilt angles of 23.87(13)° and 15.07(17)°, respectively. In contrast, the isolation of the appropriate
[1]stannatrochrocenophane failed because of the thermal lability of the resulting product. However, the
corresponding 1,1‘-disubstitued derivatives [Cr(η5-C5H4R)(η7-C7H6R)] (R = B(Cl)NiPr2, SiMe3, GeMe3, SnMe3)
were obtained by reverse addition of the dilithio precursor to an excess of the element (di)halide. The
unstrained nature was proven by a crystal structure analysis of the 1,1‘-diborylated species. The electronic
structure of these substituted trochrocene derivatives, as well as of the [2]bora and [n]sila congeners (n =
1, 2), was investigated by means of UV−vis spectroscopy and DFT methods. As a consequence of the
strong electronic influence of the B−N π-system on the LUMOs, the UV−vis studies revealed a
complementary correlation of the lowest energy band maxima as a function of molecular distortion for the
boron containing species on the one hand, and the boron-free compounds on the other hand. These trends
were reproduced fairly well by time dependent DFT calculations.

异构夹心型配合物[Cr(η5-C5H5)(η7-C7H7)]（托洛克烯）是通过在环庚三烯存在下，对CrCl3与NaCp和Mg进行后续处理，以40%的产率制备而成。采用tBuLi/tmeda（N，N，N‘，N‘-四甲基乙二胺）进行的选性双金属化反应，得到了高度活泼的物种[Cr(η5-C5H4Li)(η7-C7H6Li)]·tmeda。对其硫代甲烷合溶剂的X射线晶体结构测定揭示了其在固态中的对称二聚体结构，即[Cr(η5-C5H4Li)(η7-C7H6Li)]2·(thf)8的化学式，其中两个单元的C5H4部分通过两个桥连锂原子相连。向二锂前驱体中加入不同的元素二卤化物，促进了桥连位置具有硼和锗的环状配合物的分离。对[Cr(η5-C5H4)-BN(SiMe3)2-(η7-C7H6)]和[Cr(η5-C5H4)-GeMe2-(η7-C7H6)]的X射线衍射研究结构表征强调了其应变特性，分别具有23.87(13)°和15.07(17)°的倾斜角。然而，由于产物热不稳定，适当的[1]锡托洛克烯酚烷的分离未能成功。然而，通过将二锂前驱体反向加入过量的元素（二）卤化物，获得了相应的1,1‘-二取代衍生物[Cr(η5-C5H4R)(η7-C7H6R)]（R = B(Cl)NiPr2，SiMe3，GeMe3，SnMe3）。通过1,1‘-二硼化物种的晶体结构分析证实了其无应变性质。这些取代的托洛克烯衍生物的电子结构，以及[2]硼和[n]硅同系物（n = 1，2）的电子结构，通过紫外-可见光谱和DFT方法进行了研究。由于B−N π系统的强电子影响对LUMOs，紫外-可见光谱研究表明，硼含物种和硼无化合物在分子扭曲作为最低能量带最大值函数的互补相关性。这些趋势通过时间相关DFT计算得到了较好的重现。