Hydrido Iron Complexes Research Articles

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

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.

Synthesis and Catalytic Activity of Iron Hydride Ligated with Bidentate N-Heterocyclic Silylenes for Hydroboration of Carbonyl Compounds

We report the synthesis of a novel bidentate N-heterocyclic silylene (NHSi) ligand, N-(LSi:)-N-methyl-2-pyridinamine (1) (L = PhC(NtBu)2), and the first bischelate disilylene iron hydride, [(Si,N)(Si,C)Fe(H)(PMe3)] (2), and monosilylene iron hydride, [(Si,C)Fe(H)(PMe3)3] (2′), through Csp2–H activation of the NHSi ligand. Compounds 1 and 2 were fully characterized by spectroscopic methods and single-crystal X-ray diffraction analysis. Density functional theory calculations indicated the multiple-bond character of the Fe–Si bonds and the π back-donation from Fe(II) to the Si(II) center. Moreover, the strong donor character of ligand 1 enables 2 to act as an efficient catalyst for the hydroboration reaction of carbonyl compounds at room temperature. Chemoselective hydroboration is attained under these conditions. This might be the first example of hydroboration of ketones and aldehydes catalyzed by a silylene hydrido iron complex. A catalytic mechanism was suggested and partially experimentally verified.

Transfer hydrogenation of aldehydes catalyzed by silyl hydrido iron complexes bearing a [PSiP] pincer ligand.

The synthesis and characterization of a series of silyl hydrido iron complexes bearing a pincer-type [PSiP] ligand (2-R2PC6H4)2SiH2 (R = Ph (1) and iPr (5)) or (2-Ph2PC6H4)2SiMeH (2) were reported. Preligand 1 reacted with Fe(PMe3)4 to afford complex ((2-Ph2PC6H4)SiH)Fe(H)(PMe3)2 (3) in toluene, which was structurally characterized by X-ray diffraction. ((2-iPr2PC6H4)SiH)Fe(H)(PMe3) (6) could be obtained from the reaction of preligand 5 with Fe(PMe3)4 in toluene. Furthermore, complex ((2-iPr2PC6H4)Si(OMe))Fe(H)(PMe3) (7) was isolated by the reaction of complex 6 with 2 equiv. MeOH in THF. The molecular structure of complex 7 was also determined by single-crystal X-ray analysis. Complexes 3, 4, 6 and 7 showed good to excellent catalytic activity for transfer hydrogenation of aldehydes under mild conditions, using 2-propanol as both solvent and hydrogen donor. α,β-Unsaturated aldehydes could be selectively reduced to corresponding α,β-unsaturated alcohols. The catalytic activity of penta-coordinate complex 6 or 7 is stronger than that of hexa-coordinate complex 3 or 4.

Iron(II) hydrides bearing a tetradentate PSNP ligand

A new class of iron(II) hydrides based on a tetradentate PSNP ligand were synthesized and fully characterized. All the iron(II) complexes feature a folded PSNP ligand with cis reactive sites. The hydrido iron complex [2H(NCMe)](BF4) is capable of catalyzing aldehyde hydroboration by pinacolborane (HBpin) and with extremely high efficiency at room temperature. Aldehydes with various functional groups are compatible.

Synthesis of Iron Hydrides by Selective C–F/C–H Bond Activation in Fluoroarylimines and Their Applications in Catalytic Reduction Reactions

AbstractThe reactions of Fe(PMe3)4 with different 2,6‐diflurophenylarylimines 1–5 were explored. Fluoroarylimines 1–3, the aryl rings of which are substituted with electron‐withdrawing groups, reacted with Fe(PMe3)4 to afford the C–H activation products 6–8. However, if the aryl rings of the fluoroarylimines were substituted with electron‐donating groups, the iron hydrides 9 and 10 were obtained from the reactions of the fluoroarylimines with Fe(PMe3)4 through C–F bond activation. In a further study, silanes, especially triethoxysilane, were found to benefit the reactions and improve the yields of the hydridoiron complexes. The three‐component reaction of Fe(PMe3)4, a fluoroarylimine, and a silane could also be utilized in reactions involving 2,6‐(CH3)2C6H3–C(=NH)–2,6‐F2C6H3 (13) and 2,6‐F2C6H3–C(=NH)–C6F5 (16) to synthesize iron hydrides (15 and 18). The hydridoiron complexes could be utilized as efficient catalysts in the hydrosilylation of aldehydes and ketones. Furthermore, cinnamaldehydes were selectively reduced to the corresponding cinnamyl alcohols in high yields. The mechanism of the catalytic reduction reaction was studied extensively through operando IR spectroscopy.

Hydrosilylation of aldehydes and ketones catalyzed by hydrido iron complexes bearing imine ligands.

Two new hydrido iron complexes (2 and 4) were synthesized by the reactions of (4-methoxyphenyl)phenylketimine ((4-MeOPh)PhC=NH) with Fe(PMe3)4 or FeMe2(PMe3)4. The molecular structures of complexes 2 and 4 were confirmed by X-ray single crystal diffraction. Using hydrido iron complexes (1-4) as catalysts, the hydrosilylations of aldehydes and ketones were investigated. The four complexes were effective catalysts for this reduction reaction. Complex 1 among them is the best catalyst.

Selective activation of C–F and C–H bonds with iron complexes, the relevant mechanism study by DFT calculations and study on the chemical properties of hydrido iron complex

The reactions of (2,6-difluorophenyl)phenylmethanone (2,6-F(2)C(6)H(3)-C(=O)-C(6)H(5)) (1) and (2,6-difluorophenyl)phenylmethanimine (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(5)) (3) with Fe(PMe(3))(4) afforded different selective C-F/C-H bond activation products. The reaction of 1 with Fe(PMe(3))(4) gave rise to bis-chelate iron(II) complex [C(6)H(5)-C(=O)-3-FC(6)H(3))Fe(PMe(3))](2) (2) via C-F bond activation. The reaction of 3 with Fe(PMe(3))(4) delivered chelate hydrido iron(II) complex 2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(H)(PMe(3))(3) (4) through C-H bond activation. The DFT calculations show the detailed elementary steps of the mechanism of formation of hydrido complex 4 and indicate 4 is the kinetically preferred product. Complex 4 reacted with HCl, CH(3)Br and CH(3)I delivered the chelate iron halides (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(PMe(3))(3)X (X = Cl (5); Br (6); I (7)). A ligand (PMe(3)) replacement by CO of 4 was observed giving (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(H)(CO)(PMe(3))(2) (8). The chelate ligand exchange occurred through the reaction of 4 with salicylaldehydes. The reaction of 4 with Me(3)SiC[triple bond, length as m-dash]CH afforded (2,6-F(2)C(6)H(3)-C([double bond, length as m-dash]N)-C(6)H(5))Fe(C≡C-SiMe(3))(PMe(3))(3) (11). A reaction mechanism from 4 to 11 was discussed with the support of IR monitoring. The molecular structures of complexes 2, 4, 6, 7, 10 and 11 were determined by X-ray diffraction.

ChemInform Abstract: trans‐Selective Hydrogermylation of Alkynes Promoted by Methyliron and Bis(germyl)hydridoiron Complexes as a Catalyst Precursor.

AbstractTerminal and internal alkynes undergo a regio and stereoselective hydrogermylation in the presence of an iron methyl complex.

Trans-selective hydrogermylation of alkynes promoted by methyliron and bis(germyl)hydridoiron complexes as a catalyst precursor

Catalytic trans-selective hydrogermylation of terminal and internal alkynes was attained by a methyliron complex, CpFe(CO)(2)(Me), and a bis(germyl)hydridoiron(IV) complex as a catalyst precursor. The structures of (Z)-triphenyl-(2-phenylethenyl)germane and the bis(germyl)hydridoiron(IV) complexes CpFe(CO)(H)(GeR(3))(2) (R = Et, Ph) were confirmed by single crystal X-ray diffraction studies.

Activation of sp3 Carbon−Hydrogen Bonds by Cobalt and Iron Complexes and Subsequent C−C Bond Formation

The sp3 C−H bond activation induced by CoMe(PMe3)4 and FeMe2(PMe3)4 was investigated. C(sp3)-cyclometalated complexes, based on diphosphinito PCP ligand (Ph2POCH2)2CH2, Co{(Ph2POCH2)2CH}(PMe3)2 (1), and Fe{(Ph2POCH2)2MeC}(H)(PMe3)2 (2), were obtained under mild conditions. Iodomethane is oxidatively added to 1, affording Co{(Ph2POCH2)2CH}(PMe3)(Me)(I) (3). Monocarbonylation of the hydrido-iron complex 2 occurs with substitution of a trimethylphosphine ligand trans to the hydrido ligand, affording Fe{(Ph2POCH2)2MeC}(H)(CO)(PMe3) (4). The reaction of 2 with phenylacetylene delivered the demetalated new diphosphine ligand (Ph2POCH2)2CHCH3 (6) and bis(phenylethinyl)iron complex Fe(PhCC)2(PMe3)4 (5). The new complexes 1−4 were characterized by spectroscopic methods and by X-ray diffraction analysis.

Reactions of a Gallium-Bridged Diiron Complex with Alkyl Lithium, HCl, and Phosphines

Gallium-bridged diiron complex Cp*(dppe)FeGaFe(CO)4 (2, Cp* = η-C5Me5, dppe = Ph2CH2CH2PPh2) did not react with [PPN]Cl, DMAP (4-N,N-dimethylaminopyridine), and bpy (2,2′-bipyridine); however, reaction of 2 with HCl caused Ga−Fe(CO)4 bond fission to give Cp*(dppe)FeGaCl2 (4). The Ga−Fe(CO)4 bond cleavage also occurred by the reaction of 2 with RLi (R = Me, nBu) to afford Cp*(dppe)FeGaR2 (R = Me (5a), nBu (5b)). Irradiation of 2 in the presence of phosphine PR3 (R = OPh, Me, and OMe) gave Cp*(dppe)FeGaFe(CO)3L (L = P(OPh)3 (6a), PMe3 (6b), and P(OMe)3 (6c)) and Cp*(dppe)FeGaFe(CO)2L2 (L = PMe3 (7b) and P(OMe)3 (7c)) depending on the reaction conditions. Cleavage of the Cp*(dppe)Fe−Ga bond occurred by irradiation of 2 in the absence of PR3 to give hydridoiron complex Cp*(dppe)FeH (8) via abstraction of hydrogen from solvent. Structural investigation of 6a and 6b revealed that substitution of CO with an electron-releasing ligand PR3 caused shortening of the Ga−Fe(CO)3L bond and elongation of the Cp*(dppe)Fe−...

Selective hydrogenation of .alpha.,.beta.-unsaturated carbonyl compounds via hydridoiron complexes

Selective hydrogenation of .alpha.,.beta.-unsaturated carbonyl compounds via hydridoiron complexes