Studies of complexes derived from 5-acetylamino-1,2-benzoquinone 2-oxime and related ligands
5-Acatylamino-l,2-benzoquinone 2-oxine [5-AcqoH] results from the direct nitrosation of 3-acatylaminophenol together with its isomer 3-acetylamino-l,4-benzoquinone 4-oxine [3-AcqoH]. The quinone oximic structure of the former has been indicated by i.r. and n.m.r. studies. In the case of 3-AcqoH this type of structure has been established by X-ray crystallography. Following a brief review of quinone oxinic complexes, a study of the synthesis, properties and structure of Cu(II), Ni(II), Co(III), and Mn(III) complexes of 5-AcqoH is presented. The complexes Ni(5-Acqo)2.nH2O (n = 2-6), Cu(5-Acqo)2, Co(5-Acqo)3, and Mn(5-Acqo)2, .H2O were prepared by the direct reaction of 5-AcqoH with the appropriate metal(II) chloride or by the nitrosation of 3-acetylaminophenol in the presence of the metal salt. Co(5-Acqo)3 was also prepared by the reaction of the ligand with Na3[Co(NO2)6]. The complex Na(Co(5-Acqo)2 (NO2)2 ], resulted from the nitrosation of Na3(Co(NO2)6] in the presence of 3-acetylaminophenol. Pyrolysis of Ni(5-Acqo)2.6H2O gave Ni(5-Acqo)2. The complexes Cu(5-Acqo)2 and Ni(5-Acqo)2.nH2O (n = 0, 2-6) reacted with pyridine and 2,2-dipyridyl to give adducts whereas the complexes of M(5-Acqo)3 (M = Co, Mn) showed no reaction with pyridine. Magnetochemical measurements, indicated that all complexes, [except Ni(5-Acqo)2], are magnetically dilute and hence monomeric. Ni(5-Acqo)2 complex has a subnormal magnetic moment due to association. The diamagnetism of Co(5-Acqo)3 and the low spin configuration of Mn(5-Acqo)3.H2O are indicative of the strong field character of the ligand. COSY, H- and C n.m.r. studies have shown that Co(5-Acqo)3 is a mixture of facial and meridial isomers. For all complexes i.r. studies indicate the involvement of the ring CO in bonding. Their electronic spectra show strong absorption in the u.v. region which tails into the visible but d - d transitions have been clearly Identified for Ni(5-Acqo)2.6H20 and Mn(5-Acqo)3 .H20. Reexamination of the reaction of several complexes of type M(Rqo)2 [M = Ni or Cu) with dimethyl acetylenedicarboxylate has confirmed the occurence of cycloaddition and the formation of oxazine. A metal-containing product, M(II)(butynedioate), and in some cases an additional organic product, l,4-benoxazin-2-one, have been isolated. Mechanistic appraisals for the 1,4-benoxazinone formation are presented and the structure of one has been elucidated by X-ray crystallography. The reaction of the new complex Cu(5-Acqo)2 with DMAD leads to analogous products. The reaction of the complexes M(l-nqo)2 [M = Cu, Ni) with methyl propiolate give the hydrated M(II)(propynoate)2 and oxazine.
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