organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

, a tuck-in complex usually refers to derivatives of

Cp* ligand 1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic diene with the formula C5Me5H (Me = CH3). 1,2,3,4,5-Pentamethylcyclopentadiene is the precursor to the ligand ''1,2,3,4,5-pentamethylcyclopentadienyl'', which is often denoted Cp* (C5Me5) and read ...

s 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. Although most "tucked-in" complexes are derived from Cp* ligands, other pi-bonded rings undergo similar reactions. Tuck-inMLHGtung

Scope and bonding

The "tuck-in" process is related to ortho-metalation in the sense that it is an intramolecular cyclometalation. Tuck-in complexes derived from Cp* ligands are derivatives of tetramethyl

fulvene Fulvene (pentafulvene) is a hydrocarbon with the formula (CH=CH)2C=CH2. It is a prototype of a cross-conjugated hydrocarbon. Fulvene is rarely encountered, but substituted derivatives (fulvenes) are numerous. They are mainly of interest as ligand ...

, 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. FulveneCmpxs

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: :(C₅Me₅)₂WH₂ → (C₅Me₅)(''η''⁶-C₅Me₄CH₂)WH + H₂ The second dehydrogenation step affords a double tuck-in complex: :(C₅Me₅)(''η''⁶-C₅Me₄CH₂)WH → (C₅Me₅)(''η''⁷-C₅Me₃(CH₂)₂)W + H₂ In

organouranium chemistry Organouranium chemistry is the science exploring the properties, structure and reactivity of organouranium compounds, which are organometallic compounds containing a carbon to uranium chemical bond. The field is of some importance to the nuclear ...

, both tuck-in and tuck-over complexes are recognized, for example in the dihydrido diuranium complex p*₃(''η''⁷-C₅Me₃(CH₂))U₂H₂ In this complex the two methylene groups bind to different uranium centers. 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 acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

s 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.

References

{{reflist Organometallic chemistry