Tuck-in complex

In organometallic chemistry, a tuck-In complex usually refers to derivatives of Cp* ligands wherein a methyl group is deprotonated and the resulting methylene attaches to the metal. The C5-CH2-M angle is acute. The term "tucked-in" was coined to describe derivatives of organotungsten complexes.[1] Although most "tucked-in" complexes are derived from Cp* ligands, other pi-bonded rings undergo similar reactions.

Double tuck-in derivative of decamethyltungstocene.

Scope and bonding

The "tuck-in" process is related to ortho-metallation in the sense that it is an intramolecular cyclometallation.[2] Tuck-in complexes derived from Cp* ligands are derivatives of tetramethylfulvene, sometimes abbreviated Me4Fv. A variety of complexes are known for Me4Fv and related ligands. In these complexes, the Fv can serve as a 4-electron or as a 6-electron ligand.

η4- and η6-fulvene complexes.

Examples

The original example proceeded via sequential loss of two equivalents of H2 from decamethyltungstocene dihydride, Cp*2WH2. The first dehydrogenation step affords a simple tuck-in complex:[1]

(C5Me5)2WH2 → (C5Me5)(η6-C5Me4CH2)WH + H2

The second dehydrogenation step affords a "double tuck-in" complex:

(C5Me5)(η6-C5Me4CH2)WH → (C5Me5)(η7-C5Me3(CH2)2)W + H2

In organouranium chemistry, both tuck-in and tuck-over complexes are recognized, e.g. in the dihydrido diuranium complex [Cp*3(η7-C5Me3(CH2))U2H2]. In this complex the two methylene groups bind to different uranium centers.[3]

Reactions

Tuck-in complexes retain nucleophilicity at the methylene carbon. They can be activated by Lewis acids to generate active catalysts for use in Ziegler-Natta catalysis. The Lewis acid attaches to the CH2 group, exposing a vacant site on the electrophilic Zr(IV) centre.[4]

References

  1. 1 2 Cloke, G. N.; Green, J. C.; Green, M. H.; and Morley, C. P. "Metal Atom Synthesis and Photochemistry of Bis(q-pentamethylcyclopentadienyl)-tungsten Dihydride" J. Chem. Soc, Chem. Communication 1985 3430-3434. doi:10.1039/C39850000945
  2. ↑ Hartwig, J. F. Organotransition Metal Chemistry, from Bonding to Catalysis; University Science Books: New York, 2010. ISBN 189138953X
  3. ↑ Elizabeth Montalvo , Kevin A. Miller , Joseph W. Ziller, William J. Evans "Reactivity of Tuck-in and Tuck-over Uranium Metallocene Complexes" Organometallics, 2010, vol. 29, pp 4159–4170. doi:10.1021/om1007538
  4. ↑ Sun, Y.; Rupert, E.; Spence, H.; Piers, W. E.; Parvez, M.; and Yap, G. P. "Intramolecular Ion-Ion Interactions in Zwitterionic Metallocene Olefin Polymerization Catalysts Derived from "Tucked-In" Catalyst Precursors and the Highly Electrophilic Boranes" J. Am. Chem. Soc. 1997, vol. 119, pp 5132–5143. doi:10.1021/ja970140h
This article is issued from Wikipedia - version of the Wednesday, November 26, 2014. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.