Diiron bis‐cyclopentadienyl complexes as transfer hydrogenation catalysts: The key role of the bridging aminocarbyne ligand

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.

Diiron Aminocarbyne Complexes with NCE− Ligands (E = O, S, Se)

“…Formation of cis/trans mixtures is believed to be consequent to rotation around the Fe–Fe bond (Adams–Cotton mechanism) [ 68 , 69 ], which is operative during the nitrile substitution process. In the majority of the cases, trans isomers based on the Fe 2 Cp 2 (CO) x (x = 2, 3) scaffold are kinetic and less thermodynamically favored products, which might be observed due to a combination of electronic and steric effects [ 36 , 37 , 39 , 70 ]. In the case of 4a and 5a , stability studies revealed that the trans to cis route was not viable in boiling THF solution, whereas formation of cyanide complexes was observed (vide infra).…”

Synthesis and studies of aqueous-stable diruthenium aminocarbyne complexes uncovered an N-indolyl derivative as a prospective anticancer agent

“…These unprecedented 13 C{ 1 H} NMR data allow us to observe a peculiar upfield shift of the resonances of the [M 2 (CO) 2 (μ-CO){μ-CN}] core on going from Fe to Ru (μ-CO and μ-CN: −22/26 ppm, t-CO: −12 ppm). 26,52 The structures of [2ad]CF 3 SO 3 and [2g]CF 3 SO 3 were ascertained by X-ray diffraction on single crystals (Fig. 1 and Table 1).…”

Construction of Two-Faced (Hetero)hydrocarbyl Diiron Complexes Mediated by the Interplay of Ligands

“…The latter values fall within the interval of C–N bonds in bridging aminocarbyne complexes (Scheme ). , …”

“…The latter values fall within the interval of C−N bonds in bridging aminocarbyne complexes (Scheme 4). 20,71 The NMR spectra of [3a−b]CF 3 SO 3 show the presence of two isomers in solution, one of them being largely predominant. Based on the DFT outcomes, it is probable that such pairs of isomers differ in the orientation of the substituents on the aminocarbyne moiety (E and Z isomers).…”