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Dynamic Behaviour of Tris(2‐methylallyl)chromium − NMR and DFT Results
Author(s) -
Blom Richard,
Swang Ole
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(20022)2002:2<411::aid-ejic411>3.0.co;2-s
Subject(s) - chemistry , chromium , intramolecular force , conformational isomerism , activation energy , toluene , paramagnetism , spectral line , nmr spectra database , atmospheric temperature range , proton nmr , tris , stereochemistry , crystallography , thermodynamics , organic chemistry , molecule , biochemistry , physics , quantum mechanics , astronomy
Abstract The variable‐temperature 1 H NMR spectra of paramagnetic (2‐Me‐allyl) 3 Cr in [D 8 ]toluene were recorded in the temperature range from 243 to 323 K. The changes observed in the spectra are interpreted in terms of intramolecular dynamic behaviour. Line‐shape analyses gave an entropy of activation Δ H ‡ of 40(5) kJ/mol, and an entropy of activation Δ S ‡ of −31(4) J/mol·K for the observed transformation. This corresponds to a free energy of activation Δ G ‡ of 49(6) kJ/mol at 300 K. Different possible mechanisms were investigated by DFT. The presence of two different conformers, which were converted into each other by rotation of one allyl ligand around the allyl−chromium axis, may explain the observations.