Novel CuII–MII–CuII (M = Cu or Ni) trinuclear and [Na I2Cu II6] hexanuclear complexes assembled by bi-compartmental ligands: syntheses, structures, magnetic and catalytic studies

Abstract

In the present work, two compartmental ligands H₂L¹ and H₂L² were in situ generated during the syntheses of new trinuclear complexes, [Cu₂Ni(L¹)(2,2′-bpy)₂(NO₃)₂][ClO₄]₂ (5), [Cu₃(L²)(NO₃)₂][ClO₄]₂ (6), and [Cu₃(L²)(NCS)₂(NO₃)]⁺ that co-crystallize in 7 with a [Cu₆(L²)₂Na₂(NO₃)₆(NCS)₄] unit to give the final molecular formula [Cu₆(L²)₂Na₂(NO₃)₆(NCS)₄][Cu₃(L²)(NCS)₂(NO₃)]₂(NO₃)₂·5H₂O (7). The magnetic property studies of 5–7 revealed weak Cu^II–Cu^II ferromagnetic interactions in compound 6 (J_Cu–Cu/k_B = +1.4(1) K) and 7 (J_Cu–Cu/k_B = +1.6) while in intranuclear Cu^II–Ni^II–Cu^II compound 5, the magnetic coupling between two Cu^II ions is switched off by the diamagnetic square planar Ni^II bridge. The catalytic epoxidation of two olefins, namely styrene and cyclooctene, by tert-BuOOH (TBHP) was also explored in the presence of a catalytic amount of 5, 6 or 7 in MeCN. For styrene oxidation, 5 exhibited ∼57% styrene epoxide selectively (conversion ∼37%) with a TON of about 925 along with benzaldehyde (∼43%), whereas 6 exhibited conversion up to ∼63% (TON ∼ 1575) with a good selectivity towards epoxide (∼71%). For compound 7, this conversion is more important (TON ∼ 8108) probably due to the presence of more active sites involved in the epoxidation. The concerted path was found to be operative for styrene oxidation while a radical path was suggested for the oxidation of cyclooctene.