Photo‐/Electroinduced Irreversible Isomerization of 2,2’‐Azobispyridine Ligands in Arene Ruthenium(II) Complexes

Abstract

Novel arene RuII complexes containing 2,2’‐azobispyridine ligands were synthesized and characterized by using 1H and 13C NMR spectroscopy, UV/vis spectroscopy, electrochemistry, DFT calculations and single‐crystal X‐ray diffraction. Z‐configured complexes featuring unprecedented seven‐membered chelate rings involving the nitrogen atom of both pyridines were isolated and were shown to undergo irreversible isomerization to the corresponding E‐configured five‐membered chelate complexes in response to light or electrochemical stimulus.

Light‐Promoted Basic Nitrogen Unmasking in Arene Ruthenium Complexes Derived from Z‐Configured 2,2′‐Azobispyridine

“…The spectrum of Z ‐ 1 (obtained as previously reported [5] ) in MeCN displays a strong absorption band at 275 nm and a weaker broad one around 445 nm (n→π* character, see Tables 1 and S2). These bands are conserved in Z ‐ 2 and Z ‐ 3 (see synthesis below), at around 255 nm and 438 nm, while an additional weak shoulder peak appears at 345–350 nm due to the participation of the N ‐dialkylamino groups in π→π* transitions (Tables 1 and S2).…”

“…Their analysis by XRD confirmed our previous conclusions (based on DFT computations) about the preferred coordination geometry of (arene)‐Ru II complexes bearing Z ‐configured 2,2’‐azobispyridine ligands (Figure 2). [5] As indicated by the X‐ray structure, this coordination pattern induced an increase in the Ru−N bond lengths by ca . 0.1 Å and decreased the Ru‐centroid distance by 0.04 Å, as compared to E ‐ 8 (Table 3).…”

“…Photophysical studies were performed on compounds 2 and 3 and compared with those of structurally related 2,2’‐azobispyridine 1 , [5] which lacks the N ‐dialkylamino moieties (Scheme 2). The absorption spectrum of E ‐ 1 in MeCN shows a typical pattern for azobenzene derivatives, with a sharp strong band at 310 nm and a weak broad one centered around 450 nm, assigned to π→π* and n→π* transitions, respectively (Figure 1).…”

“…The target 7‐membered chelate complexes Z ‐ 10 – 13 and their related 5‐membered counterparts E ‐ 6 – 9 were obtained following a procedure adapted from our previously reported route (Scheme 4). [5] The E and Z isomers of 2/3 were independently reacted with the para ‐cymene ( p ‐cym) or hexamethylbenzene (hmbz) chlororuthenium dimers in CH 2 Cl 2 at rt followed by counter‐ion exchange with NH 4 PF 6 . All complexes were obtained in yields greater than 73 %.…”

Iron complexes of bridging azo ligands in aqueous solution: changes in the thermal switching mechanism on coordination and oxidation state of metal centres

“…14 These reactions normally produce photochemically inactive mono-and dinuclear-cyclometalated derivatives. [15][16][17][18][19][20] Nevertheless, functionalisation of the phenyl rings of these derivatives with different donor groups has also been conducted, with the aim of having a photoactive dangling azo moiety coordinatively attached to a transition metal. [21][22][23][24][25][26][27] The possible implication of these appended photoswitches in biologically relevant interactions has also been reported.…”