Regioselective Rhodium‐Catalyzed 1,2‐Hydroboration of Pyridines and Quinolines Enabled by the Tris(8‐quinolinyl)phosphite Ligand**

Abstract

A Rh(I) complex [κ2P,N‐{P(OQuin)3}RhCl(PPh3)] (1) bearing the P,N ligand tris(8‐quinolinyl)phosphite, P(OQuin)3, has been synthesized and structurally characterized. The molecular structure of complex 1 confirms the ability of P(OQuin)3 to act as a chelate ligand. Reactivity studies of 1 reveal that the triphenylphosphine ligand can be replaced by an 8‐quinolyl ligand of P(OQuin)3 or PCy3. In addition, the Rh(III) complex [RhCl2{OP(OQuin)2}] (3), resulting from treating 1 with wet CDCl3 under air, was characterized by X‐ray diffraction analysis. Complex 1 is a highly active catalyst for the 1,2‐regioselective hydroboration of pyridines and quinolines, affording 1,2‐dihydropyridines (1,2‐DHP) and 1,2‐dihydroquinolines (1,2‐DHQ) in high yield (up to >95%) and with turnover numbers (TONs) of up to 130. The system tolerates a variety of substrates of different electronic and steric nature. Further advantages of this system in comparison with other transition‐metal‐based hydroboration catalysts are the low catalyst loading without requirement of base or other additives.