INTRA-MOLECULAR ISOMERIZATION OF AN OCTAHEDRAL COMPLEX - "BIS(TRI-N-BUTYLPHOSPHINE)MOLYBDENUM TETRACARBONYL

The cis ⇌ trans isomerization reaction of Mo(CO)4(P-n-Bu3)2 has been studied kinetically. The trans isomer was found to be slightly more stable than the cis isomer (ΔG ≈ -1 kcal) due to enhanced steric interactions in the cis isomeric form. This isomerization reaction is described as an intramolecular, nondissociative process on the basis of the lack of 13CO incorporation into either cis- or trans-Mo(CO)4(P-n-Bu3)2 or formation of Mo(CO)4(13CO)P-n-Bu3 during the rearrangement. A trigonal rotation mechanism is used to account for these observations. The activation energy for the cis → trans reaction was found to be ~ 5 kcal less than that observed for dissociative phosphine loss in closely related cis-Mo(CO)4L2 derivatives containing sterically more demanding phosphine ligands. Analogous observations were also made on the bis(triethyl-phosphine)molybdenum tetracarbonyl derivatives. © 1979, American Chemical Society. All rights reserved.