Exploring the nitrosyl-approach: “Re(CO)2(NO)”- and “Tc(CO)2(NO)”-complexes provide new pathways for bioorganometallic chemistry

Nitrosylation reactions are rare in the context of low valent Re(I)- and Tc(I)-tricarbonyl complexes so far. We herein describe a method for the conversion of a “M(CO)3-moiety” (M = Re, Tc) into a dicarbonyl-nitrosyl moiety “M(CO)2NO”, the synthesis of important precursor complexes and intermediates and possible applications for this new kind of Re- and Tc-chemistry. The behavior of the complex [ReCl3(CO)2(NO)]− in water was studied in detail and compared to that of [ReCl3(CO)3]2−. Contrary to the conversion of [ReCl3(CO)3]2− to the mixed aquo-carbonyl complex [Re(OH2)3(CO)3]+ in water, one chloride remains initially bound to the metal center in the dicarbonyl-nitrosyl complex, making [ReCl(OH2)2(CO)2(NO)]+ the main species for further reactions. In this context, we isolated and characterized the complex [Re(μ3-O)(CO)2(NO)]4. Examples of complexes with different bi- and tridentate ligands based on ReCl3(CO)2(NO)]− are discussed. For the development of potential new radiopharmaceuticals we also adapted the nitrosylation technique to the n.c.a. level with 99mTc. [99mTc(OH2)3(CO)3]+ served as starting material to form a 99mTc(CO)2(NO)-core. Labelling reactions with ligands such as iminodiacetic acid (IDA), nitrilotriacetic acid (NTA) and diethylenetriamine pentaacetic acid (DTPA) were performed, resulting in the complexes [99mTc(IDA)(CO)2(NO)], [99mTc(NTA)(CO)2(NO)] and [99mTc(DTPA)(CO)2(NO)]. In this way, the “nitrosyl-approach” adds a new and challenging synthetic tool to the already established organometallic chemistry of Re- and Tc-tricarbonyl complexes.