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-metalation in the sense that it is an intramolecular cyclometalation.^[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.

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, for example in the dihydrido diuranium complex [Cp*₃(η⁷-C₅Me₃(CH₂))U₂H₂]. In this complex the two methylene groups bind to different uranium centers.^[3] The tuck-over mode is binding of the Cp* methylene to a metal center elsewhere in the molecule rather than the one coordinated to that Cp* ligand.

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

^ ^a ^b Cloke, G. N.; Green, J. C.; Green, M. H.; Morley, C. P. (1985). "Metal Atom Synthesis and Photochemistry of Bis(η-pentamethylcyclopentadienyl)-tungsten Dihydride". Journal of the Chemical Society, Chemical Communications. 1985: 3430–3434. doi:10.1039/C39850000945.
^ Hartwig, J. F. (2010). Organotransition Metal Chemistry, from Bonding to Catalysis. New York, NY: University Science Books. ISBN 189138953X.^{[page needed]}
^ Montalvo, E.; Miller, K. A.; Ziller, J. W.; Evans, W. J. (2010). "Reactivity of Tuck-in and Tuck-over Uranium Metallocene Complexes". Organometallics. 29: 4159–4170. doi:10.1021/om1007538.
^ Sun, Y.; Rupert, E.; Spence, H.; Piers, W. E.; Parvez, M.; Yap, G. P. (1997). "Intramolecular Ion–Ion Interactions in Zwitterionic Metallocene Olefin Polymerization Catalysts Derived from "Tucked-In" Catalyst Precursors and the Highly Electrophilic Boranes". Journal of the American Chemical Society. 119: 5132–5143. doi:10.1021/ja970140h.

[Chem001Geoffrey-1] Cloke, G. N.; Green, J. C.; Green, M. H.; Morley, C. P. (1985). "Metal Atom Synthesis and Photochemistry of Bis(η-pentamethylcyclopentadienyl)-tungsten Dihydride". Journal of the Chemical Society, Chemical Communications. 1985: 3430–3434. doi:10.1039/C39850000945.

[2] Hartwig, J. F. (2010). Organotransition Metal Chemistry, from Bonding to Catalysis. New York, NY: University Science Books. ISBN 189138953X.^{[page needed]}

[3] Montalvo, E.; Miller, K. A.; Ziller, J. W.; Evans, W. J. (2010). "Reactivity of Tuck-in and Tuck-over Uranium Metallocene Complexes". Organometallics. 29: 4159–4170. doi:10.1021/om1007538.

[Chem003Sun-4] Sun, Y.; Rupert, E.; Spence, H.; Piers, W. E.; Parvez, M.; Yap, G. P. (1997). "Intramolecular Ion–Ion Interactions in Zwitterionic Metallocene Olefin Polymerization Catalysts Derived from "Tucked-In" Catalyst Precursors and the Highly Electrophilic Boranes". Journal of the American Chemical Society. 119: 5132–5143. doi:10.1021/ja970140h.

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