Four-Coordinate Dimethylgallium Compounds Vary in Stability toward Hydrolysis

Four-coordinate dimethylgallium complexes were prepared by the reaction of dimethylgallium 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 (CH 3 ) 2 Ga + unit from the Lewis base when exposed to 1000 equiv of water in acetone- d 6, determined by 1 H 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.