Degradation of urea mediated by dinickel(II) complexes with the binucleating ligand N,N′-bis[2-(N,N-dimethyl)aminoethyl]-N,N′-dimethyl-1,3-diamino-2-hydroxypropane (HL)

Abstract

We have synthesized a new urea-coordinated dinickel(II) complex with a binucleating ligand, HL, which contains dimethylaminoethyl arms and a 2-hydroxytrimethylene bridge, [Ni2L(μ-Cl)(μ-urea)(urea)2](BPh4)2 (2), between its two chelating sites. Its structure as well as that of its parent complex [Ni2L(μ-Cl)2(CH3CN)2]BPh4·CH3CN (1) were studied by X-ray crystallography. In complex 2, one urea molecule was coordinated to each nickel(II) ion via the carbonyl oxygen atom, while another urea molecule bridged the two nickel(II) ions via the carbonyl oxygen atom acting as a bidentate ligand. Investigation of urea degradation mediated by complex 2 in a nitromethane/ethanol solution containing a small amount of water revealed the formation of a novel tetranuclear nickel(II) complex, [{Ni2L(μ-carbamato)}2(μ-NCO)2] (BPh4)2·(CH3NO2)4 (3). In complex 3, two dinuclear nickel(II) units containing two nickel(II) ions linked by carbamate ions were further bridged by isocyanate ions and by the carbamate ions acting as a tetradentate ligand. Formation of complex 3 was confirmed through another synthetic pathway via the tetranuclear nickel(II) complex [{Ni2L(μ-Cl)}2(μ-NCO)2](BPh4)2 (4). The carbamato nickel(II) complex 3, a urea-degradation product, was discovered for the first time. In addition, reaction of complex 2 with sodium t-butoxide afforded a rare ureato-coordinated tetranuclear nickel(II) complex [{Ni2L(μ-ureato)}2(μ-Cl)2](BPh4)2·(DMF)2 (5). Complex 3 also was obtained from degradation reactions involving complex 4 or 5.