A Family of Titanium Complexes with Catechol Ligands: Structural Investigation and Catalytic Application

• Published in: European journal of inorganic chemistry 2016-11, Vol.2016 (33), p.5215-5221
• Main Authors: Bazhenova, Tamara A., Kovaleva, Nadezhda V., Shilov, Gennady V., Petrova, Galina N., Kuznetsov, Denis A.
• Format: Article
• Language: English
• Subjects: Acetylene; Bridging; Catalysis; Catalysts; Catechol; Coordination compounds; Ligands; Methyl alcohol; O ligands; Reduction; Titanium
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201600804

Four new titanium catecholate complexes – [Ti2(Cat)2(CatH)2(OCH3)2(CH3OH)2] (1; Cat = C6H4O22–), [Ti2(4tBuCat)4(CH3OH)2]·2CH3OH (2·2CH3OH; 4tBuCat = [4‐t‐C4H9‐C6H3O2]2–), [Ti(Cat)2(dmf)2] (3; dmf = N,N‐dimethylformamide), and [Na(dme)Ti(Cat)3]2[Na(dme)CH3OH]2 (4; dme = 1,2‐dimethoxyethane) – have been obtained by treatment of Ti(OCH3)4 with catechols in methanol and structurally characterized. Complex 3 is the first example of a neutral mononuclear titanium catecholate containing more than one catechol molecule per titanium atom. Complexes 1 and 2 are neutral dimers in the solid state, each with a catechol/Ti ratio equal to 2 and featuring one of the catechol ligands bridging two titanium centres in a singly bridging chelate µ2‐(O,O′,O′) mode. The other catechol molecule is either a terminal bidentate chelating ligand (complex 2) or a Ti monodentate ligand (complex 1). Complex 4 is a heterometallic aryloxide complex with a tetrameric [{Na(dme)Ti(Cat)3)2]2– (Ti2Na2) core as an anionic moiety and Na ions, solvated by methanol and dme ligands – [{Na(dme)(CH3OH)}2]2+ – as a cationic counterpart. Each Ti centre in 4 is octahedrally coordinated by three catechol ligands, demonstrating three distinct types of bridging modality. It was shown that 1–4 effectively catalyze the selective homogeneous hydrogenation of acetylene to ethylene. Various kinetic relationships were determined and analyzed, enabling a reaction pathway for this catalytic reaction to be proposed. A series of titanium(+4) catecholate complexes with different architectures has been synthesized and structurally characterized. The investigated compounds demonstrated excellent activity as catalysts for C2H2 → C2H4 conversion, representing a rare example of selective hydrogenation of acetylene catalyzed by a non‐precious metal.