Follow-Up Study of Trans -C to Cis -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 ( phpy ) derivatives [Ru( phpy -κC,N) (MeCN -trans- N)( terpy )]PF 6 , 2 , to [Ru( phpy -κC,N)(MeCN -trans- C)( terpy )]PF 6 ( terpy = 2,2';6',2″-terpyridine), 3 , at temperatures >50 °C has been investigated both by 1 H NMR spectroscopy and by DFT calculations. The photoisomerization of 2 to 3 by UV light occurred also quantitatively in MeCN after 20 h at room temperature. A similar behavior to that of 2 could be established for the related compound [Ru(3-acridine-2'-C 5 H 4 N-κC,N)(MeCN -trans- N)(2,2';6',2″-terpyridine)]PF 6 , 6 (acridine = dibenzo[ b , e ]pyridine or 2,3-benzoquinoline), that was obtained from the reaction between [Ru(3-acridine-2'-C 5 H 4 N-κC,N) (MeCN) 4 ]PF 6 , 4 , and terpy in MeOH/MeCN at 60 °C for 24 h. Similar to 2 , the isomerization of 6 to [Ru(3-acridine-2'-C 5 H 4 N-κC,N)(MeCN -trans- C) ( terpy )]PF 6 , 7 , 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 7 but in which MeCN was replaced by H 2 O was described earlier (Tanaka et al. Inorg. Chem. 2012 , 51, 5386-539). The presence of water on this compound had a dramatic effect as far as the coordination of terpy was concerned as its isomerization to a compound related to 6 (in which H 2 O instead of MeCN is coordinated to Ru) occurred indeed photochemically via irradiation with visible light.