Intramolecular thermolytic C-H activation processes. Solid-state structural characterization of a mononuclear η6-Me4C5CH2 zirconium complex and a mechanistic study of its formation from (Me5C5)2Zr(C6H5) 2

Laurel E. Schock, Carolyn P. Brock, Tobin J Marks

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Abstract

The complex Cp′2Zr(C6H5)2 (1, Cp′ = η5-Me5C5) undergoes unimolecular thermolysis in solution (ΔH‡ = 22.5 (3) kcal/mol, ΔS‡ = -11.8 (3) eu) to yield the ring-metalated complex Cp′Zr(C6H5)(Me4C5CH 2) (2) and benzene. Complex 2 crystallizes in the monoclinic space group P21/c with four molecules in a unit cell of dimensions a = 13.550 (2) Å, b = 9.651 (2) Å, c = 17.613 (3) Å, and β = 94.94 (1)° at 0°C. Least-squares refinement led to a value for the conventional R index (on F) of 0.043 for 2594 reflections having 2θMoKα <55° and I > 3σ(7). The molecular structure of 2 consists of η5-Cp′ and η6-Me4C5CH2 ligands in a distorted "bent sandwich" Cp′2ZrX2 configuration (∠ring centroid-Zr-ring centroid = 143.6 (3)°) with the X groups being an unexceptional phenyl ligand (Zr-C = 2.285 (5) Å) and a metalated cyclopentadienyl methyl group (Zr-C = 2.388 (7) Å). The latter carbon atom is displaced 0.88 Å (37°) from the C5 mean plane in the direction of the zirconium atom and is bonded to the C5 ring at a C-C distance of 1.468 (9) Å. The zirconium atom is displaced slightly from the center of the methyl-metalated C5 ring toward the metalated carbon atom. It appears that the η6 ligand has little fulvene character and that a metalated σ,η5-Cp′ bonding description is more appropriate. Labeling and kinetic studies with Cp′2Zr(C6D5)2 show that thermolysis occurs via rate-limiting phenyl ortho hydrogen atom abstraction (kH/kD = 6-5 (10) at 70°C) to yield a benzene/ortho phenylene intermediate which can be trapped with ethylene. Benzene elimination is followed by hydrogen atom abstraction from a Cp′ ligand to yield 2.

Original languageEnglish
Pages (from-to)232-241
Number of pages10
JournalOrganometallics
Volume6
Issue number2
Publication statusPublished - 1987

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

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