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

Abstract

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