Dioxomolybdenum(VI) Complexes with Salicylamide Ligands: Synthesis, Structure, and Catalysis in the Epoxidation of Olefins under Eco-Friendly Conditions

Racemization Pathway for MoO2(acac)2 Favored over Ray-Dutt, Bailar, and Conte-Hippler Twists

Chiral cis-MoO₂(acac)₂ racemizes via four pathways that agree with and extend upon Muetterties' topological analysis for dynamic MX₂(chel)₂ complexes. Textbook Ray-Dutt and Bailar twists are the least favored with barriers of 27.5 and 28.7 kcal/mol, respectively. Rotating both acac ligands of the Bailar structure by 90° gives the lower Conte-Hippler twist (20.0 kcal/mol), which represents a valley-ridge inflection that invokes the trans isomer. The most favorable is a new twist that was found by 90° rotation of only one acac ligand of the Bailar structure. The gas-phase barrier of 17.4 kcal/mol for this Dhimba-Muller-Lammertsma twist further decreases upon inclusion of the effects of solvents to 16.3 kcal/mol (benzene), 16.2 kcal/mol (toluene), and 15.4 kcal/mol (chloroform), which are in excellent agreement with the reported experimental values.

Bis(2,4-dioxopentan-3-ido-κ2 O,O′)dioxidomolybdenum(VI): a redetermination

The crystal structure of cis-[MoO₂(acac)₂] has been redetermined at 100 K, providing a more precise description of the structure including hydrogen atoms and inter­molecular contacts.

The title compound, [Mo(C₅H₇O₂)₂O₂] or cis-[MoO₂(acac)₂] (acac is acetyl­acetonate), contains a molybdenum(VI) atom coordinated by two acetyl­acetonate ligands and two doubly bonded oxido ligands in a distorted octa­hedral shape. The mol­ecule is chiral and the asymmetric unit contains two independent mol­ecules (one Δ, one Λ). Extensive C—H⋯O contacts are present throughout the structure. Data were collected at 100 K, providing higher precision of unit-cell parameters and atomic positions than previous determinations [Kamenar et al. (1973 ▸). Cryst. Struct. Commun.2, 41–44.; Krasochka et al. (1975). Zh. Strukt. Khim.16, 696–698].