Switchable C‐ and N‐Bound Isomers of Transition‐Metal Cyanocarbanions: Synthesis and Interconversions of Cyclopentadienyl Ruthenium Complexes of Phenylsulfonylacetonitrile Anions

Abstract

The synthesis, structure, and dynamic behavior of bistable C- and N-bound isomers of transition-metal cyanocarbanions are described. A series of C-bound cyclopentadienyl (Cp) ruthenium phosphane complexes, [Ru{CH(CN)SO2Ph}(Cp)L1L2] (3), and their N-bound isomers, [Ru+(Cp)(NCCH(-)SO2Ph)L1L2] (4), were prepared by treating [RuCl(Cp)(PR3)2] with the sodium salt of phenylsulfonylacetonitrile and performing ligand-exchange reactions with the resulting compounds. Structural characterization by X-ray diffraction indicates that the cyanocarbanion moiety of 3 has an alpha-metalated structure, whereas that of 4 has a zwitterionic, end-on structure. Heating these complexes in aprotic solvents gives rise to irreversible linkage isomerization between C- and N-bound isomers, in which the relative thermal stabilities vary greatly depending on the steric and electronic nature of the ligands. Mechanistic studies of N-to-C isomerization revealed that the reaction proceeds irreversibly in a unimolecular manner without the formation of coordinatively unsaturated species. A metal-sliding process, which occurs over the -C-C triple chemical bond N pi-conjugated surface of the cyanocarbanion moiety, was suggested by results from kinetic studies and density functional theory (DFT) calculations. C-to-N isomerizations proceed by the above-mentioned intramolecular process, with a temperature-dependent contribution from the formation and cleavage of mu2-C,N coordination dimers [{Ru{CH(CN)SO2Ph}(Cp)(PPh3)}2] (15 and 16).

A Robust Nickel Catalyst for Cyanomethylation of Aldehydes: Activation of Acetonitrile under Base‐Free Conditions

“…The group of Naota has shown that ruthenium cyanomethyl complexes undergo interconversion between C‐bound and N‐bound isomers through sliding the metal along the cyanomethyl ligand skeleton 16a. Ritleng, Chetcuti, and co‐workers have proposed a similar isomerization process which converts [Cp(NHC)NiNCCH 2 ] to [Cp(NHC)NiCH 2 CN] 16b,c.…”

Chemoselective Catalytic Conjugate Addition of Alcohols over Amines

“…[11] The nucleophilic addition of copper alkoxide to acrylonitrile (1 a) then proceeded to afford the Cor N-bound copper intermediate. [21][22][23] Subsequent protonation occurred with the OH proton to give amino ether 7 with the concomitant generation of copper(I) alkoxide.…”

Chemoselective Catalytic Conjugate Addition of Alcohols over Amines

“…The combined use of copper(I) complex with Brønsted base generated the actual catalytic species copper(I) alkoxide (Table 1, entry 8) 11. The nucleophilic addition of copper alkoxide to acrylonitrile ( 1 a ) then proceeded to afford the C‐ or N‐bound copper intermediate 21–23. Subsequent protonation occurred with the OH proton to give amino ether 7 with the concomitant generation of copper(I) alkoxide.…”