Evaluating the kinetic indenyl effect of a π-thiaphentalenyl ancillary ligand

The magnitude of the “kinetic indenyl effect” for the π-thiapentalenyl ligand, isoelectronic heteroanalogue of the indenyl ligand, has been tested using the reaction between complex, Rh(η5-th)(CO)23 (th = 2-ethyl-5-methyl-cyclopenta[b]thienyl or thiapentalenyl) and PPh3 as a model process. Only moderate “kinetic indenyl effect” of the thiapentalenyl ligand was observed. The rational for such behavior was also supported by DFT computational correlation of ground and transition states for the reaction of carbonyl group substitution by a phosphine in the corresponding indenyl and thiapentalenyl rhodium complexes.