Carbon−Oxygen and Carbon−Hydrogen Bond Cleavage Reactions of <i>ortho</i>-Substituted Phenols by Ruthenium(II) Complexes

Treatment of Ru(η4-1,5-COD)(η6-1,3,5-COT) (1) (COD = cyclooctadiene (C8H12)) with a monosubstituted phenol HOC6H4(R1-2) (R1 = OMe, CHO, CO2Me) in the presence of PMe3 gives corresponding oxaruthenacycle complexes formulated as cis-Ru[OC6H4(R1-2)](PMe3)4 [R1 = O (2a), CO (2b), CO2 (2d)] accompanied by the C−O or C−H bond cleavage of the ortho substituents. Similar treatments of 1/PMe3 with 2,6-disubstituted phenols HOC6H3(R1-2)(R2-6) (R1 = OMe, CO2Me, CHO, Me; R2 = OMe, Me) also proceed to give cis-Ru[OC6H3(R1-2)(R2-6)](PMe3)4 [R1 = O, R2 = OMe (2e); R1 = O, R2 = Me (2f); R1 = CO2, R2 = OMe (2g); R1 = CO2, R2 = Me (2h); R1 = CO, R2 = OMe (2i); R1 = CO, R2 = Me (2j)]. On the basis of the reaction profiles monitored by NMR spectroscopy, a mechanism involving a cationic η5-cyclooctadienylruthenium(II) intermediate, [Ru(η5-C8H11)(PMe3)3][OAr] (11), followed by the carbon−heteroatom bond cleavage is proposed.