Substituent Effects on Stoichiometric and Catalytic Cleavage of Carbon–Nitrogen Bonds in Aniline Derivatives by Ruthenium–Phosphine Complexes

Abstract

The reactivity of various o-acylaniline derivatives with ruthenium complexes was examined. The reaction of o-acylanilines with RuH2(CO)(PPh3)3 (1) or an activated ruthenium species formulated as “Ru(CO)(PPh3)3” (4) gave amido hydrido complexes 3 and aryl amido complexes 6 formed via N–H and C–N bond cleavage, respectively. Addition of olefins, such as vinylsilanes, accelerates the C–N bond cleavage. The aryl amido complexes 6 can provide the C–N arylation product upon treatment with arylboronates. The relative reactivity of o-acylanilines bearing various substituents was investigated by competition experiments, and it was found that electron-donating substituents increase the relative facileness of the C–N bond cleavage in both stoichiometric and catalytic reactions. The trend observed here is different from the one observed for the previously reported tantalum-mediated C–N bond cleavage.

Ruthenium‐Catalyzed Monoalkenylation of Aromatic Ketones by Cleavage of Carbon–Heteroatom Bonds with Unconventional Chemoselectivity

“…The lower reactivity of the bonds with better leaving groups is not commonly observed for bond‐cleavage reactions by oxidative addition. The reason for the observed trend is unclear, but it can be explained by considering that smaller, more‐electron‐donating groups coordinate to the metal center more easily to increase the chances of being cleaved by oxidative addition, as observed for our previously reported aromatic CN bond cleavage by a ruthenium center 6c…”

DFT Studies of Ru-Catalyzed C–O versus C–H Bond Functionalization of Aryl Ethers with Organoboronates

“…Further studies indicated that stronger C–N and C–O bonds can also be activated by the same method. In 2004, Kakiuchi et al reported the first ketone-directed Ru-catalyzed C–O bond functionalization (eq 3 ), , also using aryl Bneop as the nucleophile.…”

Direct Borylation of Tertiary Anilines via C–N Bond Activation

“…In this case, the oxidative transformation of tertiary anilines into N -arylamides was necessary, and the process to cleave aromatic C–N bonds was facilitated by the electron-withdrawing effect of the acyl group, and the π-extended aromatic ring containing substrates showed better reactivity (Scheme b). Kakiuchi and co-workers successfully applied a directing strategy into C–N bond activation to cleave aromatic C–N bonds of tertiary anilines via ruthenium-catalyzed Suzuki–Miyaura cross-coupling with the clear understanding of the catalytic mechanism . The introduction of the acyl group at ortho -position not only played a role as a directing group but also possibly activated the C–N bonds as an electron-withdrawing group (Scheme c).…”