Aminoazine-based unsymmetric multidentate ligands in Mn(ii and i) complexes and their application in hydrophosphination reactions

Abstract

Two aminoazine-based, non-palindromic, neutral ligands, L1 and L2, were synthesized. Ligand L1 was complexed with MnCl₂ and Mn(OAc)₂ to yield Mn(II) pincer complexes C1 and C2. Ligand L2 was reacted with Mn(CO)₅Br to form Mn(I) complex C3. The crystal structures of the three complexes C1, C2, and C3 were determined. In all three complexes, the ligands are in their neutral state. In the pincer complexes C1 and C2, the ligand adopts a hydrazone tautomeric state; however, in the bidentate complex C3, the azine tautomeric form of the ligand was observed. In addition, an intramolecular N–H–Br(Mn) bond was observed in C3 (the H4A–Br1 distance is 2.44(3) Å). These complexes were employed in the catalysis of hydrophosphination reactions with cinnamonitrile, cinnamaldehyde, benzylideneacetone, 2-vinylpyridine, styrene, and cyclohexenone. The mechanism of hydrophosphination reactions was explored through quantum chemical analysis, revealing that the ligands can exhibit hemilability and participate via nitrene–imide conversion during catalysis.