DFT Investigation of the Mechanism of Phosphine-Thioether Isomerization in the Triosmium Cluster Os₃(CO)₁₀(Ph₂PCH₂CH₂SMe): Migratory Preference for the Formation of an Edge-Bridged Thioether versus a Phosphine Moiety

Abstract

The rearrangement of the phosphine-thioether ligand in 1,2-(P eq,S eq)-Os3(CO)10(Ph2PCH2CH2SMe) to 1,1-(P eq,S ax)-Os3(CO)10(Ph2PCH2CH2SMe) was investigated by electronic structure calculations. The chelated isomer lies 2.5 kcal/mol lower in energy than its bridged counterpart, and the barrier computed for the mechanism is in agreement with the results from our earlier experimental study. Phosphine-thioether isomerization occurs via three distinct steps that involve the migration of the CO and SMe groups in a plane that is perpendicular to the trimetallic core. One of the intermediates on the reaction surface corresponds to the 50e cluster Os3(CO)9(μ-CO)­(μ-Ph2PCH2CH2SMe), whose edge-bridging thioether moiety functions as a 4e donor ligand. Alternative mechanisms involving ligand dissociation/association and merry-go-round sequences are energetically prohibitive.

Polyhedral Flexibility in the Sulfido-Capped Cluster H2Ru3(CO)9(μ3-S) on Reaction with 2-(Diphenylphosphino)thioanisole (PS) and Reversible Tripodal Rotation of the Chelated PS Ligand in H2Ru3(CO)7(κ2-PS)(μ3-S)

“…The bridged cluster Os 3 (CO) 10 (μ-PS′) is formed as a kinetic product of substitution that undergoes a slow, nondissociative isomerization to the thermodynamically favored chelated cluster Os 3 (CO) 10 (κ 2 -PS′) (Scheme ). Here the thiomethyl moiety promotes an in-plane migration of ligands about the Os–Os bond by changing from a 2e to 4e donor that enables the coordination of adjacent metal centers. Other reports on the reaction of PS, PSP, and PSSP donors with metal clusters have since appeared, but the total number of examples is small compared to the mononuclear studies published to date.…”

“…Syntheses and Characterization of H 2 Ru 3 (CO) 7 (κ 2 -PS)(μ 3 -S). Treatment of an equimolar mixture of H 2 Ru 3 (CO) 9 (μ 3 -S) (1) and 2-(diphenylphosphino)thioanisole (PS) with Me 3 NO (2 equiv) in CH 2 Cl 2 at room temperature gives a pair of diastereomers that possess a chelated PS ligand and exhibit the formula H 2 Ru 3 (CO) 7 (κ 2 -PS)(μ 3 -S) (2). NMR analysis after 1 h confirms the presence of an 8:1 mixture of products.…”