ROTATIONAL BARRIERS IN TRIMETHYLENEMETHANE FE(CO)2L COMPLEXES - A DENSITY-FUNCTIONAL STUDY

Density functional calculations have been carried out on the staggered (1a) and eclipsed (1b) conformations of {eta4-C(CH2)3 Fe(CO)2L with L = CO, PF3, and PH3. The calculations provide fully optimized structur es for 1a and 1b. Barriers of rotation, DELTAE(b), for the trimethylen emethane ligand around the Fe-C 3-fold axis connecting the staggered e quilibrium structures 1a were calculated to be 78 kJ/mol (L = CO), 81 kJ/mol (L = PH3), and 79 kJ/mol (L = PF3), where lb represents the tra nsition state for the rotation process. The present calculations indic ate that DELTAE(b) is nearly the same for CO and phosphines. A decompo sition of DELTAE(b) into steric and electronic factors revealed that s teric factors contribute to the barrier whereas electronic factors red uce DELTAE(b).