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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. Although most "tucked-in" complexes are derived from Cp* ligands, other pi-bonded rings undergo similar reactions.
Contents
Scope and bonding
The "tuck-in" process is related to ortho-metallation in the sense that it is an intramolecular cyclometallation. 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:
(C5Me5)2WH2 → (C5Me5)(η6-C5Me4CH2)WH + H2The second dehydrogenation step affords a "double tuck-in" complex:
(C5Me5)(η6-C5Me4CH2)WH → (C5Me5)(η7-C5Me3(CH2)2)W + H2In 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.
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.