In the context of slowly chemically exchanging systems, we show how the same theory may be applied to the analysis of 2D NOESY data and 1D selective perturbation data. Both an iterative and a noniterative method may be used to analyze the same NOESY data and yield relaxation rates and exchange rate coefficients. In application to the intramolecular rearrangement of [Re3(μ-H)4(CO)9NCMe]−, the use of 13C experimental NOESY data yields rate coefficients which support a concerted mechanism for the rearrangement, the first step of which is the dissociation of the acetonitrile ligand. The temperature dependence of the kinetics gives an activation energy of 63.1 ± 17.1 kJ mol−1 for the process. The 13C relaxation is shown to be dominated by scalar coupling of the second kind to the quadrupolar rhenium. In the analysis of the 1 D selective perturbation 1H data, using an iterative method, a nonzero value for the 1H-1H cross-relaxation rate (σ) means that it is not possible to obtain a reliable value for the exchange rate coefficients. The 1H relaxation of the hydride ligands is dominated by dipole-dipole interactions with the rhenium nuclei.

Quantitative Analysis of 1- and 2-dimensional Magnetisation Transfer Experiments and the Mechanism of Rearrangement of [Re3(m-H)4(CO)9(NCMe)]

MOLINARI, Henriette;
1988

Abstract

In the context of slowly chemically exchanging systems, we show how the same theory may be applied to the analysis of 2D NOESY data and 1D selective perturbation data. Both an iterative and a noniterative method may be used to analyze the same NOESY data and yield relaxation rates and exchange rate coefficients. In application to the intramolecular rearrangement of [Re3(μ-H)4(CO)9NCMe]−, the use of 13C experimental NOESY data yields rate coefficients which support a concerted mechanism for the rearrangement, the first step of which is the dissociation of the acetonitrile ligand. The temperature dependence of the kinetics gives an activation energy of 63.1 ± 17.1 kJ mol−1 for the process. The 13C relaxation is shown to be dominated by scalar coupling of the second kind to the quadrupolar rhenium. In the analysis of the 1 D selective perturbation 1H data, using an iterative method, a nonzero value for the 1H-1H cross-relaxation rate (σ) means that it is not possible to obtain a reliable value for the exchange rate coefficients. The 1H relaxation of the hydride ligands is dominated by dipole-dipole interactions with the rhenium nuclei.
NMR chemical exchange relaxation matrix kinetics
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11562/15597
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