Synthesis and coordination chemistry of ferrocenyl-1,2,3-triazolyl ligands

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)degrees [0.7(3)degrees], and they are roughly eclipsed with a twist angle of 2.4(3)degrees [1.8(3)degrees). 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-d(6), 4 reversibly dissociates to regenerate 1, whose H-1 NMR spectrum is then observed. The 1H NMR study also shows that progressive addition of PdCl2 or [NCl2(NCR)(2)] (R = Me or Ph) to DMSO-d(6) 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 13 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.