Transition metal induced derivatisations resulting in novel coordination behaviour of bis(oxamato) ligands

Abstract

Two mononuclear bis(oxamato) complexes with the formula [ⁿBu₄N]₂[M(2,3-acbo)] (M = Ni (2), Cu (3), with acbo = anthra-9,10-chinone-2,3-bis(oxamato) have been synthesized starting from symmetric diethyl N,N′-anthra-9,10-chinone-2,3-bis(oxamate) (1, 2,3-acboH₂Et₂). The crystal structures of 2 and 3 have been determined, verifying that the transition metal ions are η⁴(κ²N,κ²O) coordinated by the [2,3-acbo]⁴⁻ ligands. Using the asymmetric diethyl N,N′-anthra-9,10-chinone-1,2-bis(oxamate) (4, 1,2-acboH₂Et₂) leads, under otherwise identical reaction conditions, to the novel bis(oxamato) complex [ⁿBu₄N]₂[Ni(1,2-acbo)] (5) whereby in the case of Cu(II) the derivate [ⁿBu₄N]₂[Cu(aibo)₂] (6) (aibo = anthra[1,2-d]-(imidazole-2-carboxylato)-6,11-dione) has been obtained. The crystal structures of 5 and 6 have been determined, displaying that the Ni(II) ion of 5 is η⁴(κ²N,κ²O) coordinated by the [1,2-acbo]⁴⁻ ligand. The Cu(II) ion of 6 is coordinated by two [aibo]²⁻ ligands, giving rise to an approximately square-planar trans-bis(aibo-N,O) arrangement. Using the symmetric diethyl N,N′-4,5-dinitro-o-phenylene-bis(oxamate) (7, niboH₂Et₂), possessing strongly electron withdrawing NO₂-groups, leads under otherwise identical reaction conditions to the bis(oxamato) complex [ⁿBu₄N]₂[Ni(nibo)] (8), whereby in the case of Cu(II) the derivate [ⁿBu₄N]₂[Cu(niqo)₂] (9) (niqo = 7,8-dinitro-2,3-quinoxalinedionato) has been obtained. The crystal structures of 8 and 9 have been determined, ensuring that the Ni(II) ion of 8 is η⁴(κ²N,κ²O) coordinated by the [nibo]⁴⁻ ligand. The Cu(II) ion of 9 is coordinated by four oxygen atoms of two [niqo]²⁻ ligands, giving rise to an approximately square-planar coordination geometry.