Ruthenium-catalyzed O-allylation of phenols from allylic chlorides via cationic [Cp*(η3-allyl)(MeCN)RuX][PF6] complexes

The [Cp*(MeCN)(3)Ru(II)][PF6] complex is an efficient catalyst precursor for the O-allylation of phenols with allylic chlorides in the presence of K2CO3 under mild conditions. This ruthenium precursor affords branched allyl aryl ethers according to a regioselective reaction, which contrasts with the uncatalyzed nucleophilic substitution from the same substrates. Stable (eta(3)-allyl)Ru(IV) cationic complexes resulting from the reaction of [Cp*(MeCN),Ru][PF6] with allylic halides were identified as intermediate catalytic species. An X-ray structure determination of the complex [Cp*(MeCHCHCH2)(MeCN)RuBr] [PF6] disclosed an (endo-trans-MeCHCHCH2) allylic ligand. The structural information obtained from the study of Cp*(allyl)Ru(IV) complexes indicated that electronic effects at the coordinated allylic ligand likely account for the better regioselectivity obtained from cinnamyl chloride as compared to aliphatic allylic chlorides.