Novel [Ruthenium(substituted‐tetramethylcyclopentadiene) (2‐quinolinecarboxylato)(allyl)] Hexafluorophosphate Complexes as Efficient Catalysts for Highly Regioselective Nucleophilic Substitution of Aliphatic Allylic Substrates

Abstract

AbstractStable [ruthenium(R‐substituted‐tetramethylcyclopentadiene)(2‐quinolinecarboxylato)(1‐R′‐substituted‐allyl) hexafluorophosphate (R=Me, R′=H, Me, n‐Pr, Ph; R=t‐Bu, R′=Me) and [ruthenium(pentamethylcyclopentadiene)(2‐quinolinecarboxylato)(1‐n‐propylallyl)] tetrafluoroborate (4′a), as allylruthenium(IV) complexes, have been synthesized in one step, starting from [ruthenium(R‐substituted‐tetramethylcyclopentadiene)tris(acetonitrile) hexafluorophosphate or tetrafluoroborate complexes, quinaldic acid, and allylic alcohols. Single stereoisomers are obtained and the X‐ray single crystal structure determinations of 3b (R=t‐Bu, R′=Me) and 4′a allow one to specify the preferred arrangement. Complexes 3a (R=R′=Me) and 3b are involved as precatalysts favoring the formation of branched products in regioselective nucleophilic allylic substitution reactions, starting from ethyl 2‐(E)‐hexen‐1‐yl carbonate and chlorohexene as unsymmetrical aliphatic allylic substrates. Phenols, dimethyl malonate, and primary (aniline) and secondary (pyrrolidine, piperidine) amines have been used as nucleophiles under mild basic conditions. For the first time, the regioselectivity in favor of the branched product obtained from purely aliphatic allylic substrates is close to the high regioselectivity previously reached starting from cinnamyl‐type substrates in the presence of ruthenium catalysts.