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How to Predict Activation Barriers – Conformational Transformations of Compounds CH 3 C(CH 2 PPh 2 ) 3– n [CH 2 P( o Tol) 2 ] n Mo(CO) 3 ( n = 1–3): Force Field Calculations versus NMR Data
Author(s) -
Beyreuther Stefan,
Frick Axel,
Hunger Johannes,
Huttner Gottfried,
Antelmann Björn,
Schober Peter,
Soltek Rainer
Publication year - 2000
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/(sici)1099-0682(200004)2000:4<597::aid-ejic597>3.0.co;2-7
Subject(s) - chemistry , steric effects , force field (fiction) , field (mathematics) , hypersurface , activation energy , stereochemistry , computational chemistry , crystallography , physics , mathematical analysis , mathematics , quantum mechanics , pure mathematics
Tripod metal entities tripod M are sterically congested systems. The conformations adopted by compounds CH 3 C(CH 2 PPh 2 ) 3– n [CH 2 P( o Tol) 2 ] n Mo(CO) 3 ( n = 1: 1 , n = 2: 2 , n = 3: 3 ) will thus be largely determined by the repulsive forces acting in these molecules. The steric demand of the o ‐tolyl groups impedes their free rotation and enantiomerization processes referring to the compounds as a whole are sufficiently slow to permit their analysis by NMR techniques. Through a combination of line‐shape analysis, EXSY methods, and coalescence experiments, the Δ G ‡ values for these conformational enantiomerization processes have been determined as Δ G ‡ 298K = 54.3, 57.9, 65.5 kJ · mol –1 for compounds 1 , 2 , and 3 , respectively. By an exhaustive search on a force field generated hypersurface, activation energies of 53, 57 and 69 kJ · mol –1 have been calculated. Thus, the force field approach correctly reproduces the dependence of the activation energy on the degree of o ‐tolyl substitution. Moreover, the force field simulation also gives an insight into the individual microsteps of the enantiomerization pathways.