M(CO)2(NO)]2+, a new core in bioorganometallic chemistry: model complexes of [Re(CO)2(NO)]2+ and [99mTc(CO)2(NO)]2+

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In this study selected bidentate (L2) and tridentate (L3) ligands were coordinated to the Re(I) or Tc(I) core [M(CO)2(NO)]2+ resulting in complexes of the general formula fac-[MX(L2)(CO)2(NO)] and fac-[M(L3)(CO)2(NO)] (M=Re or Tc; X=Br or Cl). The complexes were obtained directly from the reaction of [M(CO)2(NO)]2+ with the ligand or indirectly by first reacting the ligand with [M(CO)3]+ and subsequent nitrosylation with [NO][BF4] or [NO][HSO4]. Most of the reactions were performed with cold rhenium on a macroscopic level before the conditions were adapted to the n.c.a. level with technetium (99mTc). Chloride, bromide and nitrate were used as monodentate ligands, picolinic acid (PIC) as a bidentate ligand and histidine (HIS), iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) as tridentate ligands. We synthesised and describe the dinuclear complex [ReCl(μ-Cl)(CO)2(NO)]2 and the mononuclear complexes [NEt4][ReCl3(CO)2(NO)], [NEt4][ReBr3(CO)2(NO)], [ReBr(PIC)(CO)2(NO)], [NMe4][Re(NO3)3(CO)2(NO)], [Re(HIS)(CO)2(NO)][BF4], [99Tc(HIS)(CO)2(NO)][BF4], [99mTc(IDA)(CO)2 (NO)] and [99mTc(NTA)(CO)2(NO)]. The chemical and physical characteristics of the Re and Tc–dicarbonyl–nitrosyl complexes differ significantly from those of the corresponding tricarbonyl compounds.