Effect of Metal Doping on the Catalytic Activity of MoS2: Access to High-Spin Co (III) Species In Situ toward the Synthesis of Bisindolylmethanes and a Study of Their Bioactivity

Nanomaterials such as transition metal dichalcogenides (TMDs) have emerged as sustainable and promising catalytic agents in synthetic chemistry. Doping of the TMDs with a transition metal activates the basal plane/edge. However, such systems have not been explored much for catalytic applications, including the generation of suitable or essential reactive intermediates, to date. Herein, by using a suitable amalgamation of nanomaterial-mediated photocatalysis, we have explored this possibility of accessing the unstable Co (III) species with higher Lewis acidity. Taking the synthesis of bisindolylmethanes as the model reaction, the stable Co (II)-doped MoS₂ was used as the catalyst. The enhanced activity of the material in the presence of light was attributed to the in situ conversion of Co (II) to the short-lived and Lewis acidic Co (III) via electron transfer to the Mo center. The performance of the material surpasses that of the commercial Co complexes, validating our hypothesis and providing access to several bisindolylmethane derivatives. In contrast to most of the known Lewis acids, the material could retain its activity in subsequent runs. Further, the as-prepared bisindolylmethanes exhibited bacteriostatic/bactericidal effects against MRSA and were found to be compatible with the mammalian cell environment. Thus, the protocol highlights the potential of heterogeneous nanomaterial-mediated synthetic routes for the fabrication of biologically important molecules in a single step and further expands the utility of photomediated strategies for the in situ access of the otherwise unstable and uncommon Co (III) species, which can be conceptually extended to other transformations as well.