Details

Autor(en) / Beteiligte

• Álvarez-Ruiz, Elena
• Sancho, Ignacio
• Navarro, Marta
• Fernández, Israel
• Santamaría, Cristina
• Hernán-Gómez, Alberto

Titel

A Mixed-Valence Ti(II)/Ti(III) Inverted Sandwich Compound as a Regioselective Catalyst for the Uncommon 1,3,5-Alkyne Cyclotrimerization

Ist Teil von

• Inorganic chemistry, 2024-05, Vol.63 (19), p.8642-8653

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2024

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The synthesis, structure, and catalytic activity of a Ti­(II)/Ti­(III) inverted sandwich compound are presented in this study. Synthesis of the arene-bridged dititanium compound begins with the preparation of the titanium­(IV) precursor [TiCl2(MesPDA)­(thf)2] (MesPDA = N,N′-bis­(2,4,6-trimethylphenyl)-o-phenylenediamide) (2). The reduction of 2 with sodium metal results in species [{Ti­(MesPDA)­(thf)}2(μ-Cl)3{Na}] (3) in oxidation state III. To achieve the lower oxidation state II, 2 undergoes reduction through alkylation with lithium cyclopentyl. This alkylation approach triggers a cascade of reactions, including β-hydride abstraction/elimination, hydrogen evolution, and chemical reduction, to generate the Ti­(II)/Ti­(III) compound [Li­(thf)4]­[(TiMesPDA)2(μ–η6: η6-C6H6)] (4). X-ray and EPR characterization confirms the mixed-valence states of the titanium species. Compound 4 catalyzes a mild, efficient, and regiospecific cyclotrimerization of alkynes to form 1,3,5-substituted arenes. Kinetic data support a mechanism involving a binuclear titanium arene compound, similar to compound 4, as the resting state. The active catalyst promotes the oxidative coupling of two alkynes in the rate-limiting step, followed by a rapid [4 + 2] cycloaddition to form the arene product. Computational analysis of the resting state for the cycloaddition of trimethylsilylacetylene indicates a thermodynamic preference for stabilizing the 1,3,5-arene within the space between the two [TiMesPDA] fragments, consistent with the observed regioselectivity.