Lewis acid promoted dehydration of amides to nitriles catalyzed by [PSiP]‐pincer iron hydrides

Abstract

The dehydration of primary amides to their corresponding nitriles using four [PSiP]‐pincer hydrido iron complexes 1–4 [(2‐Ph2PC6H4)2MeSiFe(H)(PMe3)2 (1), (2‐Ph2PC6H4)2HSiFe(H)(PMe3)2 (2), (2‐(iPr)2PC6H4)2HSiFe(H)(PMe3)2 (3) and (2‐(iPr)2PC6H4)2MeSiFe(H)(PMe3)2 (4)] as catalysts in the presence of (EtO)3SiH as dehydrating reagent was explored in the good to excellent yields. It was proved for the first time that Lewis acid could significantly promote this catalytic system under milder reaction conditions than other Lewis acid‐promoted system, such as shorter reaction time or lower reaction temperature. This is also the first example that dehydration of primary amides to nitriles was catalyzed by silyl hydrido iron complexes bearing [PSiP]‐pincer ligands with Lewis acid as additive. This catalytic system has good tolerance for many substituents. Among the four iron hydrides 1 is the best catalyst. The effects of substituents of the [PSiP]‐pincer ligands on the catalytic activity of the iron hydrides were discussed. A catalytic reaction mechanism was proposed. Complex 4 is a new iron complex and was fully characterized. The molecular structure of 4 was determined by single crystal X‐ray diffraction.

Syntheses and Structures of Gallyliron Complexes with Pyridine Ligands and Their Reactions with Methyl Acrylate

“…The 1 H NMR spectrum of 6a showed a singlet in the high-field region at −17.7 ppm assignable to Fe–H, two sets of signals corresponding to the inequivalent Mes groups, and four multiplets assignable to the pyridyl ligand, in addition to a singlet of the Cp* ligand. The signal corresponding to the hydride on the iron center was shifted to a higher magnetic field relative to those of Cp*­(OC)­(L)­FeH (L = CO and PMe 3 , −11 to −15 ppm), Cp*­(OC)­Fe­(SiR 3 ) 2 H (−11 to −14 ppm), , and Cp*Fe­(η 2 -H-ER 3 ) (E = Si and Ge, −12 to −14 ppm) and was comparable to that reported for Fe­(diphosphine)­(PR 3 ) 2 (SiR 3 )H (−14 to −19 ppm). , The IR spectrum showed one intense absorption band at 1918 cm –1 assignable to νCO. The absorption band was comparable to that of Cp*­(OC)­Fe­(LB)­(η 1 -aryl) (1903–1913 cm –1 , LB: Lewis base) …”

Progress in synthetic strategy and industrial preparation of aliphatic nitriles

“…表 2 芳香族酰胺脱水制备腈的4种催化体系 范围为67%~92%. 随后, Li等 [169] 发现在PSiP配位的甲 硅烷基氢化铁络合物催化体系中, 添加Lewis酸可以有 效地促进催化活性, 降低反应温度, 反应条件更温和.…”

“…Figure26 Fe or Co complexes catalyzed dehydration of primary amides to nitriles with (EtO) 3 SiH[167][168][169][170] (color online).…”

An Air-Stable N-Heterocyclic [PSiP] Pincer Iron Hydride and an Analogous Nitrogen Iron Hydride: Synthesis and Catalytic Dehydration of Primary Amides to Nitriles

“…This is similar to hydrido iron(II) catalyst. 17 Recently, we reported that the classical [PSiP]-pincer iron hydride (2-Ph 2 PC 6 H 4 ) 2 -MeSiFe(H)(PMe 3 ) 2 was an efficient catalyst to dehydration of primary amides with the assistance of Lewis acid at 40 °C for 40 h. 18 On the basis of the above research, we attempt to design novel [PSiP] pincer ligands to synthesize [PSiP] pincer iron hydrids, even iron nitrogen complexes, and to explore the catalytic activity of these complexes for dehydration of primary amides. Recently, we reported that the N-heterocyclic σ-silyl [PSiP] pincer ligand 1 could stabilize iron hydride 2 (Scheme 1).…”

“…This is similar to hydrido iron­(II) catalyst . Recently, we reported that the classical [PSiP]-pincer iron hydride (2-Ph 2 P C 6 H 4 ) 2 ­Me Si Fe­(H)­(PMe 3 ) 2 was an efficient catalyst to dehydration of primary amides with the assistance of Lewis acid at 40 °C for 40 h …”