Rotational barriers and mechanisms of rotation in triene chromiumtricarbonyls and pi-allyl rheniumtetracarbonyls

A series of Cycloheptatrienechromiumtricarbonyls, either substituted at the seven position, or bridged at the one and six positions, has been examined using 13C dynamic NMR (DNMR) techniques. The rotational barriers for seven complexes with 7-substituents have been determined quantitatively via total line shape analysis (LSA). In addition, semi-quantitative calculations set an upper limit for three 1,6-bridged complexes as well as troponechromiUmtricarbonyl. The relative magnitudes in every case follow the earlier theoretical predictions, which are derived from a fragment molecular orbital treatment of the proposed mechanism, which couples the rotation process to the well known cycloheptatriene-norcaradiene equilibrium. [...]