A [2 × 2] Cu4 molecular grid and a Mn5 cluster derived from a 1-(2-pyridyl)pyrazole based polytopic ligand – Synthesis, structure, magnetic properties and catalytic activity in the allylic oxidation of cyclohexene

The homoleptic [2 × 2] tetranuclear compound [Cu4(PyPzCAP)4](NO3)4·8H2O (1) and the pentanuclear Mn(II) cluster [Mn5(PyPzCAP)6](ClO4)4·4C6H6 (2) are self-assembled from the ditopic pro-ligand HPyPzCAP [(5-methyl-1-(pyridin-2-yl)-N′-[1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazide)]. Complex 1 is almost a square grid, and all the Cu(II) centers show a distorted octahedral environment with an N4O2 chromophore. Complex 2 has a pentanuclear core with a trigonal bipyramidal arrangement of the Mn(II) atoms. The axial Mn centers bear an N3O3 chromophore and the equatorial centers have an N4O2 distorted octahedral arrangement. Complex 1 shows a ferromagnetic exchange interaction (J = +4.62 cm−1 and g = 2.05), whereas 2 shows weak an antiferromagnetic interaction (J = −2.73 cm−1 and g = 2.02). Both complexes 1 and 2 catalyze the allylic oxidation of cyclohexene to cyclohex-2-ene-1-one with good selectivity and an excellent overall turnover number.

Graphical abstractThe homoleptic [2 × 2] tetranuclear compound [Cu4(PyPzCAP)4](NO3)4·8H2O (1) and the pentanuclear Mn(II) cluster [Mn5(PyPzCAP)6](ClO4)4·4C6H6 (2) are self-assembled from the ditopic pro-ligand HPyPzCAP. Complex 1 shows a ferromagnetic exchange interaction (J = +4.62 cm−1 and g = 2.05), whereas 2 shows a weak antiferromagnetic interaction (J = −2.73 cm−1 and g = 2.02). Both complexes 1 and 2 catalyze the allylic oxidation of cyclohexene to cyclohex-2-ene-1-one with good selectivity and an excellent overall turnover number.Figure optionsDownload full-size imageDownload as PowerPoint slide