Synthesis and Coordination Chemistry of Ferrocenyl-1,2,3-triazolyl Ligands

Abstract

“Click” reactions between ethynylferrocene and mono-, bis-, and tris-azido aromatic derivatives yielded mono-, bis-, and tris-1,2,3-ferrocenyltriazoles (1, 2, and 3, respectively) as orange crystals. The X-ray crystal structure of the monoferrocenyltriazole compound 1 was solved with two nearly identical molecules within the asymmetric unit. In both molecules, the two Cp rings make a tilt angle of 2.1(3)° [0.7(3)°], and they are roughly eclipsed with a twist angle of 2.4(3)° [1.8(3)°]. Reaction of 1 with [PdCl₂(PhCN)₂] in dimethylsulfoxide (DMSO) yielded orange crystals of [PdCl₂L₂] (4; L = 1), for which the X-ray crystal structure shows trans coordination to the nitrogen atom close to the ferrocene substitution. The Pd atom is located on an inversion center and displays a nearly perfect square planar environment. In DMSO-d₆, 4 reversibly dissociates to regenerate 1, whose ¹H NMR spectrum is then observed. The ¹H NMR study also shows that progressive addition of PdCl₂ or [PdCl₂(NCR)₂] (R = Me or Ph) to DMSO-d₆ solutions of 1 reversibly leads to the formation of 4 and the addition of excess Pd^II is necessary to lead to the complete disappearance of the signals of 1. The cyclic voltammograms of 1, 2, and 3 show the reversible oxidation wave of the ferrocenyl group, and that of 4 shows that this wave appears with increased intensity tentatively attributable to redox-catalyzed oxidation.