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Kinetics and Mechanism of CO Exchange in [MBr2(solvent)(CO)3]- (M=Re, 99Tc)

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2016
Author Frei Angelo,
Project Multi-functional Cyclopentadienyl and Carbonyl Complexes for Theranostic Applications
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Original article (peer-reviewed)

Journal Inorganic Chemistry
Volume (Issue) 55
Page(s) 9352 - 9360
Title of proceedings Inorganic Chemistry
DOI 10.1021/acs.inorgchem.6b01503


The self-exchange kinetics of CO ligands in the solvated forms of the commonly used complex [MBr3(CO)3]2- (M=Re, 99Tc) were investigated in-depth by 13C NMR spectroscopy in organic solvents such as DMF and MeOH. The two homologues exhibit a surprisingly different chemical behaviour. In the case of rhenium, the stable intermediate [NEt4][ReBr2(CO)4] was isolated and characterized by 13C NMR and IR spectroscopy as well as by single crystal X-ray diffraction. For technetium, no such intermediate could be identified. The activation parameters (ΔH = 110 ± 7 kJ mol-1 and ΔS = 127 ± 22 J mol-1 K-1) and the observed influences of different ligands and solvents suggest a dissociative-interchange-type mechanism with a 2nd order rate constant for the formation of [NEt4][ReBr2(CO)4] k1 = 0.039 ± 0.001 M 1 s 1 at 274 K. Based on variable temperature NMR experiments, kinetic simulations and DFT calculations, a complete model for the CO self-exchange including all respective rate constants is reported.