Stabilization and Destabilization of the Ru−CO Bond During the 2,2′-Bipyridin-6-onato (bpyO)-Localized Redox Reaction of [Ru(terpy)(bpyO)(CO)](PF6)

✍ Scribed by Takashi Tomon; Take-aki Koizumi; Koji Tanaka

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 217 KB
• Volume: 2005
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/ejic.200400522

✦ Synopsis

Abstract

Two stereoisomers of Ru(terpy)(bpyO)(CO) ([1]^+^ and [2]^+^; terpy = 2,2′:6′,2′′‐terpyridine, bpyO = 2,2′‐bipyridin‐6‐onato) were prepared. The pyridonato moiety in the bpyO ligand of [1]^+^ and [2]^+^ is located trans and cis, respectively, to CO. Treatment of [1]^+^ and [2]^+^ with HPF~6~ produced [1H]^2+^ and [2H]^2+^, both of which contain bpyOH (bpyOH = 6‐hydroxy‐2,2′‐bipyridine). The difference in the p__K__~a~ values of [1H]^2+^ (3.5) and [2H]^2+^ (3.9) reflects the stronger electronic interaction between CO and the pyridonato moiety in the bpyO ligand in the trans position compared with that in the cis position. The molecular structures of 1, 2·H~2~O and 2H~2~·2H~2~O were determined by X‐ray structure analyses. [1]^+^ and [2]^+^ undergo one, reversible reduction at E~1/2~ = −1.65 V and −1.51 V, respectively, and one irreversible reduction at E~p,c~ = −2.07 and E~p,c~ = −2.13 V, respectively. Both reductions are assigned to redox reactions localized at the terpy and bpyO ligands. Irreversible reduction of [1]^0^ results from reductive cleavage of the Ru−CO bond of [1]^−^. On the other hand, a two‐electron oxidation of [2]^−^ almost regenerates [2]^+^ because of the depression of the reductive Ru−CO bond cleavage of [2]^−^ due to cyclometalation formed by an attack of oxygen of bpyO to the carbon of the Ru−CO bond. An unusually large shift of the ν(C≡O) band on going from [2]^0^ (1950 cm^−1^) to [2]^−^ (1587 cm^−1^) also supports a reversible cyclometalation driven by the bpyO‐localized redox reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)