Four-coordinate dimethylgallium compounds vary in stability toward hydrolysis

Four-coordinate dimethylgallium complexes were prepared by the reaction of dimethyl- gallium hydroxide with bidentate Lewis bases and evaluated for their stability toward decomplexation in water, a key property in determining their potential usefulness as radiopharmaceuticals, particularly those targeted at specific receptor proteins. Model compounds from six structural classes, containing bidentate ligands with oxygen-oxygen, oxygen-nitrogen, and sulfur-nitrogen donor atoms, were prepared from the ligand and dimethylgallium hydroxide; they were characterized spectroscopically and, in two cases, by X-ray crystallography. The percentage decomplexation of the stable (CH3)(2)Ga+ unit from the Lewis base when exposed to 1000 equiv of water in acetone-d(6), determined by H-1 NMR, was used as a measure of the relative hydrolytic stability of each compound. Among the compounds we have investigated, the percent hydrolysis under these conditions ranged from 10% to 100%, the most hydrolytically stable compounds proving to be those based on an N-alkylsalicylaldimidate donor.