Diiron bis‐cyclopentadienyl complexes as transfer hydrogenation catalysts: The key role of the bridging aminocarbyne ligand
Giulio Bresciani, Lorenzo Biancalana, Stefano Zacchini, Guido Pampaloni, Gianluca Ciancaleoni, Fabio Marchetti
Abstract
The catalytic activity of a series of diiron complexes based on the {Fe 2 Cp 2 (CO) x } core (x = 2–3) and containing a bridging aminocarbyne ligand was screened in transfer hydrogenation reaction of cyclohexanone from isopropanol. The series includes cationic tricarbonyl complexes, [1a – d]CF 3 SO 3 , and neutral derivatives obtained by substitution of one carbonyl with hydride ( 2a – c ), cyanide ( 3a – d ) or chloride ( 4a ) ligands. The novel compounds 2a – b , 3a – b and 4a were characterized by analytical and spectroscopic techniques, and the single crystal X‐ray structure of one isomer of 4a was determined. In general, diiron complexes exhibited a moderate activity in combination with potassium hydroxide; [Fe 2 Cp 2 (CN)(CO)(μ‐CO){μ‐CN (Me)(4‐C 6 H 4 OMe)}], 3a , emerged as the best catalyst, and the study of its activity was extended to a range of other ketones. DFT calculations suggest an unusual carbyne‐centred mechanism, and the better performance displayed by 3a is ascribable to the stabilizing effect provided by the cyanide co‐ligand, which is experimentally supported by IR analyses.