Triphenylphosphine‑<i>m</i>‑sulfonate/Carbon Tetrabromide as an Efficient and Easily Recoverable Catalyst System for Friedel–Crafts Alkylation of Indoles with Carbonyl Compounds or Acetals

A solid complex, conveniently prepared from commercially available sodium triphenylphosphine-<i>m</i>-sulfonate (TPPMS) and carbon tetrabromide, can be used as an easily recoverable and reusable catalyst system for Friedel–Crafts alkylation of indoles with carbonyl compounds or acetals to produce bis­(indolyl)­alkane products (BIAs)