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

Abstract

Stable [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.

Progress towards Bioorthogonal Catalysis with Organometallic Compounds

“…[14] These catalysts ([CpRu(PA)(h 3 -allyl)]PF 6 , [Cp*Ru(QA)(h 3 -allyl)]PF 6 , and [Cp*Ru(PA)(h 3 -allyl)]PF 6 ) were found to exceed most complexes tested so far in our laboratory, although could not reach the high catalytic activity of Ru2 (Table 1). We believe that the reduced reactivity of the Cp* complexes is due to steric hindrance by the five methyl groups [15] and that the fast deactivation rate of the pyridine complexes is a consequence of the electronic properties of the bidentate ligand-particularly its p-accepting ability. [16] We therefore hypothesized that an even higher catalytic activity for the quinoline complexes could be attained once the p backbonding of the bidentate ligand was reduced.…”

Ruthenium(IV) Complexes Featuring P,O‐Chelating Ligands: Regioselective Substitution Directly from Allylic Alcohols

“…[13] As observed in most ruth- enium(IV) complexes bearing an unsymmetrical allylic ligand, the distance from the ruthenium center to the substituted carbon atom of the allylic ligand is longer than that to the terminal CH 2 group, leading to a distorted p-allyl ligand coordination. [15] Whereas the half-chair conformation of the six-membered metallacycle was found to be exo for B, the structure of C revealed an endo conformation. [15] Whereas the half-chair conformation of the six-membered metallacycle was found to be exo for B, the structure of C revealed an endo conformation.…”

Ruthenium‐Catalyzed Cascade N‐ and C(3)‐Dialkylation of Cyclic Amines with Alcohols Involving Hydrogen Autotransfer Processes

“…[16] Herein, we report an unprecedented N-and C(3)-dialkylation of unactivated cyclic amines in the presence of new ruthenium precatalysts based on phos-A C H T U N G T R E N N U N G phinosulfonate ligands acting as P,O chelates, involving the borrowing hydrogen methodology. During the course of our studies on the applications of N,O-and P,O-chelating ligands in ruthenium-catalyzedreactions, [17] we synthesized in good yields the new A C H T U N G T R E N N U N G (arene)ruthenium(II) complexes A and B featuring phosphinobenzenesulfonate ligands 1a and 1b starting from [RuA C H T U N G T R E N N U N G (p-cymene)Cl 2 ] 2 (Scheme 1). Crystal struc-tures of these complexes revealed that the phosphinosulfonate coordinates as a bidentate ligand through the phosphine and one oxygen atom (Figure 1).…”