Abstract: The invention provides a method for manufacturing or preparing neutral, low molecular weight 99mTc-labeled and 186Re-labeled carbohydrate complexes with an improved radiochemical yield from a simple functionalized sugar, such as glucosamine. In particular the synthesis relies on single ligand transfer (SLT) or double ligand transfer (DLT) reactions for converting a ferrocene compound into a rhenium or technetium tricarbonyl complex. The ferrocene compound may be linked to a sugar through various functional groups including, for example, thio, amino and alcohol functionalities to provide a wide range of radiolabeled sugar complexes that include both water soluble and relatively water insoluble compounds.