Novel 1,2,3-triazolyl phosphine with a pyridyl functionality: synthesis, coinage metal complexes, photophysical studies and Cu(i) catalyzed C–O coupling of phenols with aryl bromides

Abstract

This manuscript describes the synthesis and coinage metal complexes of pyridine appended 1,2,3-triazolyl-phosphine [2-{(C₆H₄N)(C₂(PPh₂)N₃C₆H₅)}] (1), photophysical studies and their catalytic application. The reactions of 1 with copper salts afforded dimeric complexes [{Cu(μ₂-X)}₂{2-(C₆H₄N)(C₂(PPh₂)N₃C₆H₅)}₂] (2, X = Cl; 3, X = Br; and 4, X = I). The crystal structure indicates that the Cu⋯Cu distance in 4 (2.694 Å) is significantly shorter than that in complexes 3 (3.0387 Å) and 2 (3.104 Å), indicating strong cuprophilic interactions which is also supported by NBO calculations, signifying the involvement of 3d_z² orbitals from each Cu atom contributing to the bonding interaction. The fluorescence studies on complexes 2–4 carried out in the solid state showed broad emission bands around 560 nm on excitation at λ_ex = 420 nm. Complex 4 on treatment with two equivalents of 1,10-phenanthroline yielded a mononuclear complex 5 which showed almost complete quenching of fluorescence in the solid state, clearly indicating that the emissive properties of 4 are mainly due to the Cu⋯Cu interaction, along with (M + X)LCT. The reactions of 1 with silver salts led to the isolation of dimeric complexes [{Ag(μ₂-X)}₂{2-(C₆H₄N)(C₂(PPh₂)N₃C₆H₅)}₂] (6, X = Cl; 7, X = Br; and 8, X = I) in good yield. The reaction between 1 and [AuCl(SMe₂)] yielded [{AuCl}{2-(C₆H₄N)(C₂(PPh₂)N₃C₆H₅)}] (9). The molecular structures of 2–5 and 7–9 were confirmed by single crystal X-ray analysis. The complex 4 is found to be an excellent catalyst for C–O coupling under mild conditions.