Accurate Rate Constants for Chemical Exchange from Improved Weighted Linear-Least-Squares Analysis of Multiple 1D-EXSY Data

Stereochemical Nonrigidity of Organometallic Complexes

“…There have also been extensive studies of a η 4 -diene rotation and rotamers that can be observed in complexes of dienes. In Cp complexes, the orientation relative to the Cp ligand gives rise to endo and exo isomers, for example, (57) and (58), the interconversion of which can be observed by DNMR.…”

“…This is the method by which nonrigidity or fluxionality is generally detected Fluxional molecule: a stereochemically nonrigid molecule in which all interconverting structures are equivalent Stereochemically nonrigid compound: a compound that undergoes intramolecular rearrangements at rates that affect the NMR line shapes in generally accessible temperature ranges Stereodynamics: dynamics associated with interconversion of stereoisomers or conformers Abbreviations DNMR = dynamic NMR; T c = coalescence temperature; T I = temperature at which initial broadening occurs in a DNMR spectrum; T LL = low temperature at which broadening is no longer observed in a DNMR spectrum (usually 5 -10 • C below T I ); T 1 = spin -lattice relaxation time; EXSY = 2D NMR method for evaluating exchange sites and rates; PSEXSY = phase-sensitive EXSY; HMQC = Indirect method for observing NMR of low abundance nuclei, such as 15 N, 57 Fe, 13 C, and so on, using the coupling to a sensitive nucleus, often 1 H; NOESY = Nuclear Overhauser Effect Spectroscopy, a 2D NMR method for assignment of resonances based on proximity; SIT = Spin Inversion Transfer; sp = square pyramidal; tbp = trigonal bipyramidal; Tp = hydrido(trispyrazolylborate); Tp = hydridotris(3,5-dimethylpyrazolylborate).…”

Dynamic NMR: combined use of 1D selective EXSY and complete lineshape analysis of spectra subjected to reference deconvolution and linear prediction or the maximum entropy method

“…Multiple 1D selective inversion experiments 39 or multiple 1D-EXSY experiments 40 are also termed '1D-EXSY.' Accurate rate constants are obtained using weighted linear-least-squares analysis of the data.…”

Stereochemical Nonrigidity of Organometallic Complexes

“…This is the method by which nonrigidity or fluxionality is generally detected Fluxional molecule: a stereochemically nonrigid molecule in which all interconverting structures are equivalent Stereochemically nonrigid compound: a compound that undergoes intramolecular rearrangements at rates that affect the NMR line shapes in generally accessible temperature ranges Stereodynamics: dynamics associated with interconversion of stereoisomers or conformers Abbreviations DNMR = dynamic NMR; T c = coalescence temperature; T I = temperature at which initial broadening occurs in a DNMR spectrum; T LL = low temperature at which broadening is no longer observed in a DNMR spectrum (usually 5 -10 • C below T I ); T 1 = spin -lattice relaxation time; EXSY = 2D NMR method for evaluating exchange sites and rates; PSEXSY = phase-sensitive EXSY; HMQC = Indirect method for observing NMR of low abundance nuclei, such as 15 N, 57 Fe, 13 C, and so on, using the coupling to a sensitive nucleus, often 1 H; NOESY = Nuclear Overhauser Effect Spectroscopy, a 2D NMR method for assignment of resonances based on proximity; SIT = Spin Inversion Transfer; sp = square pyramidal; tbp = trigonal bipyramidal; Tp = hydrido(trispyrazolylborate); Tp = hydridotris(3,5-dimethylpyrazolylborate).…”

“…The intensities versus time are fitted to exponentials and the rates can be derived from them. 35,36,57 This approach was used in earlier studies of organometallics for observation of hydrides exchanging with carbenes and vinyls. 58,59 A recent study of ring inversion provides an example of its application including experimental parameters.…”