Ru(II)–Pd(II) dinuclear complexes of di(pyridin-2-yl)amino-substituted 1,10-phenanthrolines: synthesis, characterization and application for catalysis

Abstract

Dinuclear complexes bearing Ru(II) photoactive center are of interest for the development of efficient dual catalysts for many photocatalyzed reactions. Ditopic polypyrine ligands – bis(pyridine-2-yl)amino-1,10-phenanthrolines – containing additional coordination site (bis(pyridine-2-yl)amine, dpa) at positions 3, 4 or 5 of 1,10-phenanthroline core (Phen-3NPy2, Phen-4NPy2 and Phen-5NPy2) were synthesized. They were used as bridging ligands to obtain dinuclear complexes of composition [(bpy)2Ru(Phen-NPy2)PdCl2](PF6)2 (Ru(Phen-NPy2)Pd) via stepvise comlexing in good yields. Ru(II) is coordinated to 1,10-phenanthroline in these complexes, while Pd(II) is bound to dpa chelating moiety, which was established by NMR spectroscopy and X-ray single crystal analysis. The influence of the position of dpa in phenanthroline ring on the structural, optical and electrochemical properties of Ru(Phen-NPy2)Pd complexes was studied. The complexes possess photoluminescence in argon-saturated MeCN solution with maxima in the range of 615–625 nm, emission quantum yields range from 0.11 to 0.15 for Ru(Phen-NPy2) complexes and from 0.018 to 0.026 for dinucear Ru(Phen-NPy2)Pd complexes. All the complexes have high extinction coefficients in the range of 370–470 nm, efficiently absorb visible light and can be used as photocatalysts. The Ru2+/3+ potential in Ru(Phen-NPy2)Pd complexes showed no significant dependence on dpa position, while Pd2+/0 reduction potential was quite lower for Ru(Phen-3NPy2)Pd and Ru(Phen-NPy2)Pd, than for Ru(Phen-NPy2)Pd (–0.57V and –0.72V vs Ag/AgCl, KCl(sat), respectively). The behaviour of the complexes was studied in Сu-free Sonogashira coupling under blue LED (12 W) irradiation. The reaction proceeds three times faster when Ru(Phen-4NPy2)Pd and Ru(Phen-3NPy2)Pd are used as catalysts precursors than in the case of mixed catalytic system Ru(bpy)3(PF6)2/(RNPy2)PdCl2.

Hybrid Catalysts in Photoredox Arylation of Sodium Arylsulfinates

“…The coordination mode was supported by the NMR spectroscopy (Figures S7-S10) and briefly discussed in the Supporting Information. [16] The extinction coefficients of the complexes in the visible region of the spectrum do not differ significantly from those of standard photocatalysts based on Ru(II) or Ir(III) (Figure S11, Table S6). The Ni complexation does not lead to significant change in UV-vis spectrum and emission quenching (Figure S12).…”

“…[10,15] We have previously shown that the bonding of Ru(II) and Pd(II) using ditopic ligand based on 1,10-phenanthroline and di(pyridin-2yl)amine leads to a significant increase of the efficiency of such photoactivated precatalysts in Cufree Sonogashira coupling compared to a mixed system. [16] It is worth noting that no examples of the use of binuclear complexes in the reaction between aryl halides and sodium arylsulfinates under visible light have been described in the literature.…”