Steric vs Electronic Effects in the Structure of Heteroatom (S and O) Substituted Free and Metal (Cr and W) Complexed Carbenes.

DIEGO M. ANDRADA; MARTIN E. ZOLOFF MICHOFF; ISRAEL FERNANADEZ; ALEJANDRO M. GRANADOS; MIGUEL ANGEL SIERRA

Americal Chemical Society

Lugar: Washington; Año: 2007 vol. 26 p. 5854 - 5854

FT computational energies for free alkoxy- and thio-substitued free carbenes correlate withexperimental steric data (Taft parameters) showing the importance of the steric volume at the expense ofthe electronic interaction in determining the conformation of free carbenes 1-14. The shorter C-O bonddistances in the alkoxy derivatives render alkoxycarbene more sensitive to steric effects than thiocarbenes.This strong dependence of the conformation with the steric hindrance is not applicable to metal-complexedcarbenes. Thio-substituted carbene complexes exist exclusively as syn-isomers due to the combinationof an interaction of the sulfur lone pair with two CO ligands and the steric repulsion with the ?CO-wall?.The stronger Ccarbene-S bond compared to Ccarbene-O is responsible for the increased syn-anti rotationbarrier observed for the alkylthio-substituted metal carbene complexes compared to their oxygen analogues.The differences of po