Halogen-bonded tris(2,4-bis(trichloromethyl)-1,3,5-triazapentadienato)-M(iii) [M = Mn, Fe, Co] complexes and their catalytic activity in the peroxidative oxidation of 1-phenylethanol to acetophenone

Abstract

One-pot template condensation of CCl₃CN with ammonia on a metal source [MnCl₂·4H₂O, FeCl₃·6H₂O or Co(CH₃COO)₂·4H₂O] in DMSO led to the formation of tris{2,4-bis(trichloromethyl)-1,3,5-triazapentadienato}-M(III) complexes, [M{NHC(CCl₃)NC(CCl₃)NH}₃]·n(CH₃)₂SO [M = Mn, n = 1 (1); M = Fe, n = 2 (2); M = Co, n = 2 (3)], which were characterized using elemental analysis, and IR, ESI-MS and single-crystal X-ray analysis. The role of inter- and intramolecular non-covalent halogen and hydrogen bonds in the synthesis of 1–3 is discussed. It is shown that the crystal ionic radii of the metal ions [68.5 (Co) < 69 (Fe) < 72 (Mn), pm] are related to the corresponding Cl⋯Cl distances [3.178 (3) > 3.155 (2) > 3.133 (1) Å]. Compounds 1–3 and the related di(triazapentadienato)-Cu(II) complex [Cu{NHC(CCl₃)NC(CCl₃)NH}₂]·2(CH₃)₂SO (4) act as catalyst precursors for the additive-free microwave (MW) assisted homogeneous oxidation of 1-phenylethanol with tert-butylhydroperoxide (TBHP), leading to the formation of acetophenone with yields up to 99% and TONs up to 5.0 × 10³ after 1 h of low power (10 W) MW irradiation.