A nickel phosphide nanoalloy catalyst for the C-3 alkylation of oxindoles with alcohols.

Although transition metal phosphides are well studied as electrocatalysts and hydrotreating catalysts, the application of metal phosphides in organic synthesis is rare, and cooperative catalysis between metal phosphides and supports remains unexplored. Herein, we report that a cerium dioxide-supported nickel phosphide nanoalloy (nano-NiP/CeO) efficiently promoted the C-3 alkylation of oxindoles with alcohols without any additives through the borrowing hydrogen methodology. Oxindoles were alkylated with various alcohols to provide the corresponding C-3 alkylated oxindoles in high yields. This is the first catalytic system for the C-3 alkylation of oxindoles with alcohols using a non-precious metal-based heterogeneous catalyst. The catalytic activity of nano-NiP/CeO was comparable to that reported for precious metal-based catalysts. Moreover, nano-NiP/CeO was easily recoverable and reusable without any significant loss of activity. Control experiments revealed that the NiP nanoalloy and the CeO support functioned cooperatively, leading to a high catalytic performance.