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

One-pot template condensation of CCl3C=N with ammonia on a metal source [MnCl2 center dot 4H(2)O, FeCl3 center dot 6H(2)O or Co(CH3COO)(2)center dot 4H(2)O] in DMSO led to the formation of tris(2,4-bis(trichloromethyl)-1,3,5-triazapentadienato)-M(III) complexes, [M(NH=C(CCl3)NC(CCl3)=-NH}(3)]center dot n(CH3)(2)SO [M = Mn, n = 1 (1); M = Fe, n = 2 (2); M = Co, n = 2 (3)1, 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 center dot center dot center dot Cl distances [3.178 (3) > 3.155 (2) > 3.133 (1) Al. Compounds 1-3 and the related di(triazapentadienato)-Cu(v) complex [Cu(NH=C(CCl3)NC(CCl3)=NH}2]center dot 2(CH3)(2)SO (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 x 10(3) after 1 h of low power (10 W) MW irradiation.

Solvent-free microwave-assisted peroxidative oxidation of alcohols catalyzed by Iron(III)-TEMPO catalytic systems

The iron(III) complexes [H(EtOH)][FeCl2(L)(2)] (1), [H(2)bipy](1/2)[FeCl2(L)(2)].DMF (2) and [FeCl2(L)(2,2'-bipy)] (3) (L = 3-amino-2-pyrazinecarboxylate; H(2)bipy = doubly protonated 4,4'-bipyridine; 2,2'-bipy = 2,2'-bipyridine, DMF = dimethylformamide) have been synthesized and fully characterized by IR, elemental and single-crystal X-ray diffraction analyses, as well as by electrochemical methods. Complexes 1 and 2 have similar mononuclear structures containing different guest molecules (protonated ethanol for 1 and doubly protonated 4,4'-bipyridine for 2) in their lattices, whereas the complex 3 has one 3-amino-2-pyrazinecarboxylate and a 2,2'-bipyridine ligand. They show a high catalytic activity for the low power (10 W) solvent-free microwave assisted peroxidative oxidation of 1-phenylethanol, leading, in the presence of TEMPO, to quantitative yields of acetophenone [TOFs up to 8.1 x 10(3) h(-1), (3)] after 1 h. Moreover, the catalysts are of easy recovery and reused, at least for four consecutive cycles, maintaining 83 % of the initial activity and concomitant rather high selectivity. 3-Amino-2-pyrazinecarboxylic acid is used to synthesize three new iron(III) complexes which act as heterogeneous catalysts for the solvent-free microwave-assisted peroxidative oxidation of 1-phenylethanol.