The artificial sweeteners, saccharin (Hsac) in its anionic form (sac-) and acesulfame (ace-) are capable of forming a number of complexes with a variety of metal ions. With multiple donor atoms, the saccharinate anion exhibits a wide range of coordination motifs including monodentate, bidentate, and multiple bridging modes. The coordination chemistry of acesulfamate is less well-studied with only a handful of known metal complexes. In these complexes, acesulfamate primarily bonds to the metal via the imino nitrogen. We are currently exploring the chemistry of dirhodium saccharinate and acesulfamate complexes in the expectation that the presence of the neighboring sulfonyl group may impart unusual electronic behavior to the dimetal center compared to other dirhodium species. Such ligands are also attractive based on their FDA approval for human consumption status which could ease approval of anti-tumor dirhodium complexes bearing these ligands. Reaction of rhodium acetate with excess saccharin in refluxing toluene resulted in the formation of Rh2(sac)4 in good yield. The reaction is in part driven by the removal of acetic acid through azeotropic distillation with toluene. The analogous acesulfamate complex, Rh2(ace)4, has been prepared by ligand exchange with Rh2(O2CCH3)4 in the presence of excess potassium acesulfamate. Single crystals of Rh2(sac)4(dmf)2 and Rh2(sac)4(dmso)2 have been obtained by slow evaporation of dmf and dmso solutions of Rh2(sac)4. X-ray diffraction studies reveal that Rh2(sac)4(solv)2 adopt the expected paddlewheel geometry typical of other tetra-bridged dirhodium(II,II) complexes. Rh2(ace)4(MeCN)2 was also found to adopt two different tetra-bridged head-to-tail isomers. Partially solvated bis-bridged acesulfamate and sacharinate complexes with the formula [Rh2(sac)2(solv)6]2+ and [Rh2(ace)2(solv)6]2+ (solv = MeCN, DMF) were prepared through acidification of the mixed ligand complexes Rh2(sac)2(OAc)2 and Rh2(ace)2(OAc)2 in the appropriate coordinating solvent. Details of the syntheses, structures, and spectroscopic properties of these new dirhodium(II,II) complexes will be presented.

Metal-Metal bonded complexes supported by artificial sweeteners: Tetra and bis saccharinate and acesulfamate complexes of dirhodium(II,II)

2019 Spring National Meeting

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