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


Frei, Angelo; Sidler, David; Mokolokolo, Pennie; Braband, Henrik; Fox, Thomas; Spingler, Bernhard; Roodt, Andreas; Alberto, Roger (2016). Kinetics and Mechanism of CO Exchange infac-[MBr2(solvent)(CO)3]−(M = Re,99Tc). Inorganic Chemistry, 55(18):9352-9360.

Abstract

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 dimethylformamide and methanol. The two homologues exhibit surprisingly different chemical behavior. 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 second-order rate constant for the formation of [NEt4][ReBr2(CO)4], k1 = 0.039 ± 0.001 M–1 s–1 at 274 K. On the basis of variable-temperature NMR experiments, kinetic simulations, and density functional theory calculations, a complete model for the CO self-exchange, including all respective rate constants, is reported.

Abstract

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 dimethylformamide and methanol. The two homologues exhibit surprisingly different chemical behavior. 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 second-order rate constant for the formation of [NEt4][ReBr2(CO)4], k1 = 0.039 ± 0.001 M–1 s–1 at 274 K. On the basis of variable-temperature NMR experiments, kinetic simulations, and density functional theory calculations, a complete model for the CO self-exchange, including all respective rate constants, is reported.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2016
Deposited On:09 Feb 2017 12:49
Last Modified:09 Feb 2017 12:49
Publisher:American Chemical Society (ACS)
ISSN:0020-1669
Funders:SNF Project IZLSZ2_149029/1 within the SSAJRP program, South African National Research Foundation
Publisher DOI:https://doi.org/10.1021/acs.inorgchem.6b01503

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