The formation of overlooked compounds in the reaction of methyl amine with the diethyl ester of o-phenylenebis(oxamic acid) in MeOH

The treatment of the diethyl ester of o-phenylenebis(oxamic acid) (opbaH(2)Et(2)) with 2/3 of an equivalent of MeNH2 in MeOH does not result in the formation of the methyl ester of o-phenylene(N'-methyloxamide)(oxamic acid) (opooH(3)Me, 1) in pure state, as reported previously. The colourless crude material formed by this reaction was confirmed to be composed of 1 (89% content), the dimethyl ester of o-phenylenebis(oxamic acid) (opbaH(2)Me(2), 2, 6%), 1,4-dihydro-2,3-quinoxalinedione (3, 3%) and o-phenylenebis(N'-methyloxamide) (opboH(4)Me(2), 4, 1%), respectively. The identities of 1-4 have been verified by IR, H-1 and C-13 NMR spectroscopy as well as elemental analysis. In addition, the solid state structures of 1 and 2.2DMSO, respectively, were determined by single-crystal X-ray diffraction studies. Successive recrystallization of the crude material from MeOH and MeOH:THF (1:1), respectively, does not give pure 1, but a mixture of 1 and 2. It is shown further that out of this mixture pure bis(oxamato) complexes cannot be obtained, as previously reported. Instead, treatment of the mixture with Ni-II or Cu-II salts, followed by the addition of [(Bu4N)-Bu-n]OH, results in the formation of two mixtures of [(Bu4N)-Bu-n](2)[Ni(opba)] (5) and [(Bu4N)-Bu-n](2)[Ni(opooMe)] (6) as well as [(Bu4N)-Bu-n](2)[Cu(opba)] (7) and [(Bu4N)-Bu-n](2)[Cu(opooMe)] (8), respectively. The simultaneous formation of 5/6 and 7/8, respectively, has been verified by crystallization of the obtained mixtures and X-ray diffraction studies of the obtained single crystals. Co-crystallization of mixtures of 5/6 (99 mass%) and 7/8 (1 mass%), respectively, results in the formation of single-crystals of diamagnetically diluted 7 in the host lattice of 5 (7@5) accompanied by single-crystal formation of diamagnetically diluted 8 in the host lattice of 6 (8@6), as verified by EPR spectroscopy. It is finally shown that the ethyl ester of o-phenylene(N'-methyloxamide)(oxamic acid) (opooH(3)Et, 9), a homologue of 1, can be obtained in pure state by the treatment of opbaH(2)Et(2) with 5/6 of an equivalent of MeNH2 in EtOH.