Directed C-H activation with heterogeneous nano-sized palladium and homogeneous rhodium catalysts

Abstract

Metal nanoparticles as heterogeneous catalysts have been limited to serve low-valent metal surfaces, although high-valent metal chemistry covers a wide range of homogeneous catalytic reactions. We reported that high-valent Pd(IV) clusters efficiently promotes directed C-H halogenation reactions. In addition, Pd nanoparticles by the adjustment of oxidation states provide both high-valent Pd(IV) and low-valent Pd(0) species within one system, and thus a tandem reaction of C-H halogenation and cross coupling such as C-N, C-C, and C-S bond formation is successfully established.

[$Rh(III)Cp^\ast$]-catalyzed directed C-H bromination and iodination reaction of 2-aryl isoquinolines/pyridines is highly efficient to provide atropisomeric biaryl compounds. Among several reported C-H bond halogenation methods, the combination of [$Rh(III)Cp^\ast Cl_2]_Cl2/AgSbF_6$, N-halosuccinimide, and pivalic acid in 1,2-dichloroethane is found to be the only effective catalytic system to provide atropisomeric 2’-halogenated 2-aryl isoquinolines/pyridines.

We have demonstrated that the directed C-H hydroxylation and arylation reaction catalyzed by [$Rh(III)Cp\ast Cl_2]_2/AgF$ is highly efficient to provide hydroxylated aromatics (phenols) and atropisomeric biaryl compounds. This transformation is successfully applied for C-H hydroxylation by $H_2O$ and C-H arylation by $PhI(OPiv)_2$ to provide excellent reactivity and broad substrate scopes in good to excellent yields. This hydroxylation provides a green and economic method to synthetize a variety of substituted hydroxylated aromatics (phenols).