ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 36, Number 6
JKCSEZ 36(6)
December 20, 1992 

The conformations of several carbene-olefin-transition metal complexes[(CO)4M-(CHX)olefin] (X: OCH3, NHCH3, SCH3, M: C, Mo, W) have been studied by means of Extend Huckel calculations. In the case of d6 transition metal octahedral complexes, it is shown that the two main factors which determine the optimal conformation are metal-to-ligand back-donation and direct ligand-ligand interaction at the metal, but the ligand-ligand interaction dominates the situation for a metal that is coordinated to π acceptor ligands and to π donor group on the carbene. The relative amounts of both factors depend strongly on the electronic nature of the ligands at the metal. The greater electron donating ability of nitrogen stabilizes amino-substituted carbene complexes compared with their alkoxyl substituted analogues. This interaction is optimal when the π systems of the carbene and olefin are coplanar. The introduction of the π donor group on the carbene carbon increases also the importance of the ligand-ligand interaction.