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

Abstract

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 [ReCl 3(CO) 2(NO)] − in water was studied in detail and compared to that of [ReCl 3(CO) 3] 2−. Contrary to the conversion of [ReCl 3(CO) 3] 2− to the mixed aquo-carbonyl complex [Re(OH 2) 3(CO) 3] + in water, one chloride remains initially bound to the metal center in the dicarbonyl-nitrosyl complex, making [ReCl(OH 2) 2(CO) 2(NO)] + the main species for further reactions. In this context, we isolated and characterized the complex [Re(μ 3-O)(CO) 2(NO)] 4. Examples of complexes with different bi- and tridentate ligands based on ReCl 3(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(OH 2) 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.