Metal-free catalysis of the reductive amination of aldehydes using a phosphonium-doped porous aromatic framework

The development of metal-free, recyclable, and efficient catalysts for the reductive amination of aldehydes is extremely promising for the preparation of amines in synthetic organic chemistry. In this study, OTf@PAF-180, a porous aromatic framework (PAF) containing rich Lewis acidic phosphonium centers and triflate (-OTf) counter anions, was prepared via Yamamoto-type Ullmann cross-coupling of tris(4-bromophenyl)phosphane and subsequent treatment with methyl triflate (MeOTf). It showed high performance in catalyzing the reductive amination of aldehydes using dimethylphenylsilane (PhMe2SiH) as the hydride source, and a variety of amines have been prepared in this way with good to excellent yields. As a metal-free heterogeneous catalyst, OTf@PAF-180 also exhibited excellent recyclability and retained high catalytic activity after five consecutive cycles. The high activity, recyclability and stability of OTf@PAF-180 make it a promising novel heterogeneous catalyst for organic synthesis.