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*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

170 Scopus citations

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)(Me4C5CH2) (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 2θMoKa < 55° and I > 3σ(I). The molecular structure of 2 consists of η6-Cpʹ and η6-Me4C5CH2ligands in a distorted “bent sandwich” Cpʹ2ZrX2configuration (⁁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 C5mean plane in the direction of the zirconium atom and is bonded to the C5ring at a C-C distance of 1.468 (9) Å. The zirconium atom is displaced slightly from the center of the methyl-metalated C5ring toward the metalated carbon atom. It appears that the η6ligand has little fulvene character and that a metalated σ,η5-Cpʹ bonding description is more appropriate. Labeling and kinetic studies with Cpʹ2Zr(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 (US)
Pages (from-to)232-241
Number of pages10
JournalOrganometallics
Volume6
Issue number2
DOIs
StatePublished - Feb 1 1987

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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