Synthesis and Reactivity of Bis(η5:η1‑pentafulvene)zirconium Complexes

Here we present the first synthetic route to bis­(η5:η1-pentafulvene)zirconium complexes as well as investigations of several consecutive reactions. Sodium amalgam reduction of ZrCl4 in the presence of a bulky substituted pentafulvene in THF leads to the formation of [η5:η1-C5H4CR2]2Zr­(THF) (2a, R = p-tol; 2b, R = Ph). The molecular structure of 2a has been determined by single-crystal X-ray diffraction and exhibits an unusually large Zr–Cexo distance (2.708(2) Å) caused by the bulky substituents at the exocyclic carbon, which allows THF coordination. The reaction of 2a with H-acidic compounds such as hydrogen chloride, amines, and water were examined: addition of HCl leads to the dichloride complex [η5-C5H4-CH­(p-tol)2]2ZrCl2 (3) and treatment of 2a with p-methylaniline forms the bis-amide complex [η5-C5H4-CH­(p-tol)2]2Zr­(NH-p-tol)2 (4), whereas addition of the sterically more demanding dicyclohexylamine furnishes the monoamide complex [η5:η1-C5H4C­(p-tol)2]­[η5-C5H4-CH­(p-tol)2]­Zr­(NCy2) (5). The cyclotrimeric compound {[η5-C5H4-CH­(p-tol)2]2Zr­(μ-O)}3 (6) is obtained by reaction of 2a with water. Moreover, insertion reactions of CX multiple bonds (X = N, O) into the Zr–Cexo(Fv) bond of 2a result in the formation of the zirconacycles [η5:η1-C5H4-C­(p-tol)2-C­(C6H4Cl)N−]2Zr (7), [η5:η1-C5H4-C­(p-tol)2-MeC4H6N−]2Zr (8), and [η5:η1-C5H4-C­(p-tol)2-C­(Ph)2O−]2Zr (9). Finally, 2a is a valuable agent for the activation of molecular hydrogen under ambient conditions. In this regard, only one pentafulvene ligand per zirconium atom is protonated and the dinuclear zirconium hydride complex {[η5:η1-C5H4C­(p-tol)2]­[η5-C5H4-CH­(p-tol)2]­Zr­(μ-H)}2 (10) is isolated. All compounds were confirmed by single-crystal X-ray diffraction and NMR spectroscopic measurements.

本工作首次报道了双(η⁵:η¹-戊富烯（pentafulvene）)锆配合物的合成路线，并对其系列连续转化反应开展了系统研究。在大位阻取代戊富烯存在下，于四氢呋喃（THF）中经钠汞齐还原四氯化锆（ZrCl₄），可得到配合物[η⁵:η¹-C₅H₄=CR₂]₂Zr(THF)（2a，R = 对甲苯基（p-tol）；2b，R = 苯基（Ph））。通过单晶X射线衍射测定了配合物2a的分子结构，其展现出异常大的Zr-外环碳（Zr–Cexo）键长（2.708(2) Å），该现象源于外环碳上的大位阻取代基，同时也为四氢呋喃配位提供了空间条件。研究了配合物2a与含氢酸性化合物（如氯化氢、胺类和水）的反应：加入氯化氢可生成二氯化物配合物[η⁵-C₅H₄-CH(p-tol)₂]₂ZrCl₂（3）；与对甲基苯胺反应则得到双酰胺配合物[η⁵-C₅H₄-CH(p-tol)₂]₂Zr(NH-p-tol)₂（4）；而改用空间位阻更大的二环己基胺时，仅生成单酰胺配合物[η⁵:η¹-C₅H₄=C(p-tol)₂][η⁵-C₅H₄-CH(p-tol)₂]Zr(NCy₂)（5）。配合物2a与水反应可得到环三聚体{[η⁵-C₅H₄-CH(p-tol)₂]₂Zr(μ-O)}₃（6）。此外，考察了CX多重键（X = N、O）在2a的Zr–Cexo(Fv)键中的插入反应，成功得到三类锆杂环配合物：[η⁵:η¹-C₅H₄-C(p-tol)₂-C(C₆H₄Cl)=N−]₂Zr（7）、[η⁵:η¹-C₅H₄-C(p-tol)₂-MeC₄H₆N−]₂Zr（8）以及[η⁵:η¹-C₅H₄-C(p-tol)₂-C(Ph)₂O−]₂Zr（9）。最后，配合物2a可作为常温常压下活化分子氢的高效试剂：此时每个锆原子仅结合一个质子化的戊富烯配体，最终分离得到双核氢化锆配合物{[η⁵:η¹-C₅H₄=C(p-tol)₂][η⁵-C₅H₄-CH(p-tol)₂]Zr(μ-H)}₂（10）。所有目标化合物均通过单晶X射线衍射与核磁共振波谱（NMR）表征得以确认。