The generation of a metallocene-fused imidazol-2-ylidene and its mercury complex
The generation of a metallocene-fused imidazol-2-ylidene and its mercury complex
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DOI：
10.1002/anie.200502814
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Marshall, WJ
中科院分区：
文献类型：
--
作者：
Arduengo, AJ;Tapu, D;Marshall, WJ
咪唑鎓盐和咪唑-2-硫酮已被广泛用作合成稳定的咪唑-2-亚基的前体。 [1]我们最近报道了第一个直接环状咪唑环戊二烯两性离子 (1) 及其二茂铁基双（硫酮）衍生物 (2) 的成功合成方法。 [2]这些结构为一类新的茂金属稠合咪唑-2-亚基提供了一个入口。这种卡宾的新结构允许通过 σ 和 π 键的组合将两个或多个金属中心掺入分子中，并通过环状配体紧密耦合。钌茂 3 是一种黄色固体，熔点为 240–2428℃，由 1 和 [Cp* Ru (CH3CN) 3]-[CF3SO3]（Cp* Ru 转移源；Cp*= 五甲基环戊二烯基；[3] 方案 1）生产，产率为 91%。通过从 THF 中重结晶生长出适合 X 射线晶体学测量的 3 单晶（选定的键长和角度在表 1 中给出）。 3 的 3D 结构由图 1 中的 KANVAS [4] 绘图描绘。钌茂 3 在三斜空间群 P1 中结晶，两个 π 配体（1 和 Cp*）以 η5 方式与钌中心结合。两个环戊二烯基配体的平面基本平行（φ=1.138）并采用重叠构象。 1 中 RuÀC（环）的平均长度为 219.78 (4) pm，略长于 RuÀCp*（环）的平均长度 218.08 (4) pm。这个微小的差异与两性离子更广泛的 π 离域一致。 112.7 (3) 8 的 N1-C2-N3 角比 1 中的 N1-C2-N3 角大 2.338，也比典型咪唑鎓离子中的 N1-C2-N3 角大。 [5] 1与铬的金属化可以通过用三(乙腈)三羰基铬(0)处理1来完成。半夹心铬配合物 4 几乎是定量产率（方案 1），为橙色固体，熔点为 286-2888C。配合物 4 不溶于非极性或卤化溶剂，但微溶于乙腈，易溶于二甲亚砜 (DMSO)。 4的分子结构通过X射线晶体学研究确定。通过将石油醚缓慢扩散到4的乙腈饱和溶液中来生长优质晶体。 4 的 X 射线晶体结构如图 2 中的 KANVAS [4] 图所示，4 中选定的键长和角度列于表 1。化合物 4 在单斜空间群 P21/n 中结晶。铬原子与环戊二烯基环进行 η5 配位，平均 CrÀC（环）长度为 221.84 pm。 CrÀCO 和 CÀO 的平均长度分别为 181.5 pm 和 117.3 pm。通过 3 或 4 的去质子化在溶液中生成游离、稳定的卡宾已被证明是有问题的。这些卡宾可能太富电子（亲核）而无法容易分离，或者原位生成的卡宾能够与络合物中的其他亲电子中心（例如钌、铬或羰基中心）反应。然而，在亲电子试剂（金属或主族元素）存在下产生卡宾可以分离各种卡宾加合物。
Imidazolium salts and imidazol-2-thiones have been widely used as precursors for the synthesis of stable imidazol-2-ylidene.[1] We recently reported successful methodologies for the synthesis of the first directly annulated imidazolium cyclopentadienide zwitterion (1) and its ferrocenyl bis-(thione) derivative (2).[2] These structures provide an entry into a new class of metallocene-fused imidazole-2-ylidenes. This new architecture for carbenes allows the incorporation of two or more metal centers into a molecule through a combination of σ and π bonding that is tightly coupled through the annulated ligand. The ruthenocene 3, a yellow solid that melts at 240–2428C, was produced in 91% yield from 1 and [Cp* Ru (CH3CN) 3]-[CF3SO3](a Cp* Ru transfer source; Cp*= pentamethyl cyclopentadienyl;[3] Scheme 1). A single crystal of 3 suitable for X-ray crystallographic measurements was grown by recrystallization from THF (selected bond lengths and angles are given in Table 1). The 3D structure of 3 is depicted by the KANVAS [4] drawing in Figure1. Ruthenocene 3 crystallizes in the triclinic space group P1, and the two πligands (1 and Cp*) are bound to the ruthenium center in a η5-fashion. The planes of the two cyclopentadienyl ligands are essentially parallel (φ= 1.138) and adopt an eclipsed conformation. The average RuÀC (ring) length of 219.78 (4) pm in 1 is slightly longer than the average RuÀCp*(ring) length of 218.08 (4) pm. This small difference is consistent with the more extensive π delocalization of the zwitterion. The N1-C2-N3 angle of 112.7 (3) 8 is 2.338 greater than that found in 1 and also larger than those found in typical imidazolium ions.[5] Metalation of 1 with chromium can be accomplished by treatment of 1 with tris (acetonitrile) tricarbonylchromium (0). The half-sandwich chromium complex 4 was obtained in almost quantitative yield (Scheme 1) as an orange solid which melts at 286–2888C. Complex 4 is not soluble in nonpolar or halogenated solvents, but it is sparingly soluble in acetonitrile and readily soluble in dimethyl sulfoxide (DMSO). The molecular structure of 4 was determined by X-ray crystallographic studies. Quality crystals were grown by slow diffusion of petroleum ether into a saturated solution of 4 in acetonitrile. The X-ray crystal structure of 4 is illustrated by the KANVAS [4] drawing in Figure2, and selected bond lengths and angles in 4 are presented in Table 1. Compound 4 crystallizes in the monoclinic space group P21/n. The chromium atom is η5-coordinated to the cyclopentadienyl ring with an average CrÀC (ring) length of 221.84 pm. The average CrÀCO and CÀO lengths are 181.5 and 117.3 pm, respectively.Generation of the free, stable carbenes in solution by deprotonation of 3 or 4 has proved problematic. These carbenes may be too electron-rich (nucleophilic) to allow easy isolation, or alternatively the insitu generated carbene is capable of reaction with the other electrophilic centers in the complex (eg, ruthenium, chromium, or carbonyl centers). Carbene generation in the presence of electrophiles (metals or main-group elements) has, however, allowed the isolation of various carbene adducts.