Follow-Up Study of -C to -C Thermally or Photochemically Induced Isomerization of Terpyridine Adducts of Cycloruthenated 2-Aryl-2'-pyridine Compounds.

The mechanism of isomerization of the known 2-phenyl,pyridine () derivatives [Ru(-κC,N) (MeCNN)()]PF, , to [Ru(-κC,N)(MeCNC)()]PF ( = 2,2';6',2″-terpyridine), , at temperatures >50 °C has been investigated both by H NMR spectroscopy and by DFT calculations. The photoisomerization of to by UV light occurred also quantitatively in MeCN after 20 h at room temperature. A similar behavior to that of could be established for the related compound [Ru(3-acridine-2'-CHN-κC,N)(MeCNN)(2,2';6',2″-terpyridine)]PF, (acridine = dibenzo[,]pyridine or 2,3-benzoquinoline), that was obtained from the reaction between [Ru(3-acridine-2'-CHN-κC,N) (MeCN)]PF, , and in MeOH/MeCN at 60 °C for 24 h. Similar to , the isomerization of to [Ru(3-acridine-2'-CHN-κC,N)(MeCNC) ()]PF, , could be induced thermally (48 h at 60 °C in pure MeOH) or photochemically under UV radiation in MeCN at room temperature. A compound closely related to but in which MeCN was replaced by HO was described earlier (Tanaka et al. , 51, 5386-539). The presence of water on this compound had a dramatic effect as far as the coordination of was concerned as its isomerization to a compound related to (in which HO instead of MeCN is coordinated to Ru) occurred indeed photochemically via irradiation with visible light.