Mild oxidative functionalization of alkanes and alcohols catalyzed by new mono- and dicopper(II) aminopolyalcoholates

• Published in: Journal of molecular catalysis. A, Chemical Vol. 350; no. 1; pp. 26 - 34
• Main Authors: Kirillov, Alexander M., Kirillova, Marina V., Shul’pina, Lidia S., Figiel, Paweł J., Gruenwald, Katrin R., Guedes da Silva, M. Fátima C., Haukka, Matti, Pombeiro, Armando J.L., Shul’pin, Georgiy B.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-11-2011; Elsevier
• Subjects: Carboxylation; Copper complexes; C–H activation; Homogeneous catalysis; N,O ligands; Oxidation; Carboxylation; C–H activation; Oxidation; Homogeneous catalysis; Copper complexes; N,O ligands
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2011.08.028

New mono- and dicopper(II) complexes bearing aminopolyalcoholate N,O-ligands have been easily self-assembled and shown to act as versatile homogeneous catalysts for the oxygenation of alkanes and alcohols as well as the hydrocarboxylation of different alkanes, under mild conditions.
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► Synthesis and X-ray crystal structures of mono- and dicopper(II) complexes. ► Homogeneous oxidation catalysts. ► Oxidation of alkanes and alcohols by
t-BuOOH. ► Cu-catalyzed transformation of cyclic and linear C
n
alkanes to C
n+1
carboxylic acids.
The new mono- and dicopper(II) complexes [Cu(H
3L
1)(NCS)] (
1) and [Cu
2(μ-HL
2)
2(NCS)
2] (
2) were easily self-assembled from Cu(CH
3COO)
2·H
2O, NaNCS, NaOH and N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (H
4L
1) or N-ethyldiethanolamine (H
2L
2), respectively. They were fully characterized by IR spectroscopy, ESI-MS(±), elemental and single-crystal X-ray diffraction analyses, and applied as homogeneous catalysts for (i) the oxidation of alkanes by
t-BuOOH in air to alkyl peroxides, alcohols and ketones, and in turn the oxidation of alcohols to ketones, and (ii) the single-pot aqueous medium hydrocarboxylation, by CO, H
2O and K
2S
2O
8, of various linear and cyclic C
n
(
n
=
5–8) alkanes into the corresponding C
n+1
carboxylic acids. Compound
1 was significantly more active in the oxygenation of alkanes and oxidation of alcohols, allowing to achieve 18% yield (TON
=
800) of oxygenates in the oxidation of cyclohexane, and 78% yield (TON
=
780) of cyclohexanone in the oxidation of cyclohexanol. In alkane hydrocarboxylations,
1 and
2 exhibited comparable activities with the total yields (based on alkane) of carboxylic acids attaining 39%. The selectivity parameters for oxidative transformations were measured and discussed, supporting free-radical mechanisms.