Heterobimetallic copper(I) complexes bearing both 1,1′-bis(diphenylphosphino)ferrocene and functionalized 3-(2′-pyridyl)-1,2,4-triazole

A new series of cationic and neutral heterobimetallic Cu(i) complexes bearing both 1,1′-bis(diphenylphosphino)ferrocene and functional 3-(2′-pyridyl)-1,2,4-triazole have been synthesized. They all show a highly distorted tetrahedral P₂N₂ geometry around Cu(I), in which functional 3-(2′-pyridyl)-1,2,4-triazole adopts either mono-anionic η²(N1,N2) or neutral η2(N1,N2) or η²(N1,N4) bonding mode, depending on the substituent and NH ↔ N⁻ conversion of 1,2,4-triazole. All these Cu(I) complexes are air-stable in both solution and solid states, and isomerization is only observed in solution for the cationic complex with a bulky tert-butyl group, as evidenced by ¹H and ³¹P NMR studies. All these 1,2,4-triazole-based complexes show a relatively weak and broadened low-energy absorption band, attributed to the charge-transfer transitions, as suggested by time-dependent density functional theory (TDDFT) calculations, which is more influenced by the NH ↔ N⁻ conversion of 1,2,4-triazole relative to the variation of their substituents. Since the charge-transfer excited state is quenched by a photoinduced intramolecular energy transfer from the {Cu(N^N)(PP)} moiety to the ferrocene, as supported by the lowered oxidation potential of the ferrocene in comparison to the Cu(I) center, these dppf-based Cu(I) complexes all show no detectable emission in solution and solid states at room temperature and at 77 K.