A [2 x 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 x 2] tetranuclear compound [Cu-4(PyPzCAF)(4)](NO3)(4)center dot 8H(2)O (1) and the pentanuclear Mn(II) cluster [Mn-5(PyPzCAP)(6)](ClO4)(4)center dot 4C(6)N(6) (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. (c) 2013 Elsevier Ltd. All rights reserved.