The Cu-catalyzed three-component reaction between quinolines, diazo compounds, and alkenes has been established for direct construction of indolizine derivatives via quinolinium ylides. This methodology is distinguished by the use of a commercially inexpensive catalyst and readily available starting materials, wide substrate scope, and operational simplicity.

In this letter, an unprecedented cross-coupling reaction between copper carbene and nitroso radical has been developed. This radical-carbene coupling reaction (RCC reaction) offers a novel approach for the preparation of various isoxazolines, which features the construction of C–C, C–O, and C═N bonds in a one-pot process. The synthetic utility of our method is further enhanced by its mild reaction conditions, wide substrate scope, and simple procedures.

A series of ionic iron(III) complexes of general formula [HLn][FeX4] (HL1 = 1,3-dibenzylbenzimidazolium cation, X = Cl, 1; HL1, X = Br, 2; HL2 = 1,3-dibutylbenzimidazolium cation, X = Br, 3; HL3 = 1,3-bis(diphenylmethyl)benzimidazolium cation, X = Br, 4) were easily prepared in high yields by the direct reaction of FeX3 with 1 equiv. of [HLn]X under mild conditions. All of them were characterized using elemental analysis, Raman spectroscopy and electrospray ionization mass spectrometry, and X-ray crystallography for 1 and 4. In the presence of magnesium turnings and LiCl, these air- and moisture-insensitive complexes showed high catalytic activities in direct cross-couplings of aryl phosphates with primary and secondary alkyl bromides with broad substrate scope, wherein complex 4 was the most effective.

•A novel method for the synthesis of ionic iron(III) complexes.•First general and efficient iron-catalyzed esterification of allylic sp3 C–H bonds.•A new method for synthesis of allylic esters.The first general and efficient iron-catalyzed esterification of allylic sp3 C–H bonds with carboxylic acids using ionic iron(III) complexes (1–4) as a catalyst and DTBP (DTBP = di-tert-butyl peroxide) as an oxidant is achieved. A variety of allylic esters were synthesized in good to excellent yields using the ionic iron(III) complex 2 as a catalyst in a 5 mol% loading. This reaction is characterized by its high efficiency, broad substrate scope with excellent steric hindrance tolerance and good functional group compatibility.Download high-res image (106KB)Download full-size image

The first iron-catalyzed esterification of the primary benzylic C–H bonds with carboxylic acids using di-tert-butyl peroxide as an oxidant is achieved by novel ionic iron(III) complexes containing an imidazolinium cation. The use of well-defined, air-stable, and available iron(III) complex in a 5 mol % loading and readily available starting materials with a broad generality and outstanding sterically hindered tolerance renders this methodology a useful alternative to other protocols that are typically employed for the synthesis of benzyl esters.

The first nickel-catalyzed, magnesium-mediated reductive cross-coupling between benzyl chlorides and aryl chlorides or fluorides is reported. A variety of diarylmethanes can be prepared in good to excellent yields in a one-pot manner using easy-to-access mixed PPh3/NHC Ni(II) complexes of Ni(PPh3)(NHC)Br2 (NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, IPr, 1a; 1,3-di-tert-butylimidazol-2-ylidene, ItBu, 1b) as catalyst precursors. Activation of polychloroarenes or chemoselective cross-coupling based on the difference in catalytic activity between 1a and 1b is used to construct oligo-diarylmethane motifs.

An efficient one-pot intermolecular reductive cross-coupling of unactivated primary and secondary alkyl chlorides bearing β-hydrogens with aryl bromides is described. A combination of magnesium turnings and a catalytic amount of the commercially available iron(III) complex Fe(PPh3)2Cl3 was used, and the conditions were also successfully extended to an intramolecular reaction for the first time. Both types of cross-coupling reactions proceed under mild conditions, involving the in situ generation of aryl Grignard reagents, and show good applicability to a variety of readily available unactivated alkyl chlorides, which have previously been challenging substrates in iron-catalyzed reductive cross-coupling reactions.

•A novel ionic iron(III) complex has been prepared.•Iron-catalyzed the direct sp3 C–H bond amidation of N,N-dimethylanilines.•A new method for synthesis of N-substituted aromatic and aliphatic amides.A new imino-functionalized imidazolium salt, 1-[1-(2,6-diisopropylphenylimino)ethyl]-3-benzylimidazolium chloride ([HL]Cl,), was designed and used to prepare a novel ionic iron(III) complex [HL][FeCl4] (2). Complex 2 was an efficient and easy-to-use catalyst for the direct sp3 C–H bond amidation of N,N-dimethylanilines, affording a wide variety of N-substituted aromatic or aliphatic amides in moderate to good yields. This reaction is the first example of iron-catalyzed intermolecular amidation of unactivated sp3 C–H bonds of tertiary amines by aromatic or aliphatic amides under mild reaction conditions.

New methods for the preparation of mixed NHC/phosphine Ni(II) complexes have been developed. It was shown that the quaternary ammonium cation in the easily available Ni(II) complexes [NEt4][Ni(PPh3)X3] (X = Cl and Br) can act as a good leaving group in reactions of [NEt4][Ni(PPh3)X3] with the bulky ItBu (ItBu = 1,3-ditertbutylimidazol-2-ylidene) or IPr [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] ligand, resulting in the corresponding mixed NHC/PPh3 Ni(II) complexes Ni(PPh3)(ItBu)X2 (X = Cl, 1; X = Br, 2) or Ni(PPh3)(IPr)Br2 (3) in high yields. The PPh3 ligand in these obtained mixed NHC/PPh3 Ni(II) complexes can be easily substituted by a more electron-donating phosphine ligand, i.e., PCy3, resulting in the corresponding mixed NHC/PCy3 Ni(II) complexes Ni(PCy3)(ItBu)Br2 (4) and Ni(PCy3)(IPr)Br2 (5) in high yields. The crystal structures of these Ni(II) complexes have been characterized, which revealed a trans disposition of the NHC ligand to the phosphine ligand. The catalytic behaviors of them on varying the carbene ligand (ItBu vs IPr) as well as the phosphine ligand (PPh3 vs PCy3) were investigated in the cross-coupling of aryl Grignard reagents with a wide range of electrophiles. In addition to a significant synergic effect on their catalytic activities, high selectivity for the activation and transformation of C–Cl, C–F and C–O bonds was achieved based on the rational structural design. Complex 2 showed the highest catalytic activity for the cross-coupling of aryl chlorides and fluorides with aryl Grignard reagents, but exhibit little activity for the cross-coupling of aryl methyl ethers with aryl Grignard reagents. On contrast, complex 4 showed great potential for the aryl methyl ethers involved cross-coupling reactions, although its reactivity for the activation of the C–X bond is very poor. The difference in catalytic activity between 2 and 4 has been successfully employed to construct oligoarenes by selective cross-coupling reactions.

A novel phenol-linked bis(imidazolium) salt, H3LCl2 (L = O-4-C(CH3)3-C6H2-2,6-di[CH2{C(NCHCHNAr)}]2, Ar = 2,6-diisopropylphenyl, 1), was designed and used to prepare an ionic iron(III) complex [H2L][FeCl4] (2). Complex 2 was a highly efficient catalyst for aryl Grignard cross-coupling of alkyl chlorides bearing β-hydrogens. Furthermore, complex 2 was reusable and could be reused in at least eight times without significant loss in catalytic activity.

Novel ionic Ni(II) complexes of general formula [R2im][Ni(PPh3)Cl3] (R2im = 1,3-bis(2,6-diisopropylphenyl)imidazolium cation, IPrim, 1a; R2im = 1,3-diisopropylimidazolium cation, iPrim, 2a) were easily prepared in high yields by the direct reaction of Ni(PPh3)2Cl2 with 1 equiv. of N,N′-dihydrocarbylimidazolium salt, [R2im]Cl. Their bromide analogs [R2im][Ni(PPh3)Br3] (R2im = IPrim, 1b; R2im = iPrim, 2b) were synthesized by the same reaction in the presence of excess NaBr. The reaction of Ni(DME)Cl2 (DME = 1,2-dimethoxyethane) with 2 equiv. of [IPrim]Cl led to the formation of the complex [IPrim]2[NiCl4] (3) in an almost quantitative yield. All these complexes were characterized by elemental analysis, electrospray ionization mass spectrometry (ESI-MS), and 1H NMR spectroscopy; X-ray crystallography was performed for 1a, 1b, 2a, and 2b. A catalytic study of the cross-coupling reactions of aryl Grignard reagents with aryl halides revealed that complexes 1a and 1b possessed the highest activities. In comparison, complexes 2a, 2b, 3, and the related biscarbene Ni(II) complex Ni(IPr)2Cl2 [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] exhibited moderate activities; the least active complexes were Ni(PPh3)2Cl2 and [NEt4][Ni(PPh3)Cl3].

A novel bis(phenol)-functionalized benzimidazolium salt, 1,3-bis(3,5-di-tert-butyl-2-hydroxybenzyl)benzimidazolium chloride (H3LCl, 1), was designed and used to prepare ionic iron(III) complexes of the type [H3L][FeX4] (X = Cl, 2; X = Br, 3). Both 2 and 3 were characterized by elemental analysis, Raman spectroscopy, electrospray ionization mass spectrometry and X-ray crystallography. The catalytic performances of 2 and 3 in cross-coupling reactions using aryl Grignard reagents with primary and secondary alkyl halides bearing β-hydrogens were studied. This analysis shows that complex 2 has good potential for alkyl chloride-mediated coupling. In comparison, complex 3 showed slightly lower catalytic activity. After decanting the product contained in the ethereal layer, complex 2 could be recycled at least eight times without significant loss of catalytic activity.

A series of iron(III)-containing imidazolium salts of the general formula [DRim][FeX4] (R = 2,6-diisopropylphenyl, IPr, X = Cl, 1; R = IPr, X = Br, 2; R = tertbutyl, tBu, X = Cl, 3; R = isopropyl, iPr, X = Cl, 4; R = benzyl, Bn, X = Cl, 5; R = Bn, X = Br, 6) have been prepared in high yields via reactions of anhydrous ferric halides with equivalent of the corresponding N,N-dihydrocarby-limidazolium halides, where 2–6 are novel ones. All of the complexes were characterized by elemental analysis, Raman spectroscopy, electrospray ionization mass spectroscopy, and X-ray crystallography for 1 and 2. All of them were non-hygroscopic and air-stable, with four of them existing as solids (1–4) and two as liquids (5 and 6) at room temperature. A preliminary catalytic study on the coupling of 4-tolylmagnesium bromide with cyclohexyl bromide revealed that 1 and 3 possessed the highest activity. In comparison, 2, 4 and 5 exhibited moderate activity and the least active complex was 6.

A series of Fe(III)-containing imidazolium-based ionic liquids containing ether substituents, including [C3OMim][FeCl4] (1, [C3OMim] = 1-(2-methoxyethyl)-3-methylimidazolium), [C3OiPim][FeCl4] (2, [C3OiPim] = 1-isopropyl-3-(2-methoxyethyl) imidazolium), [C3OBim][FeCl4] (3, [C3OBim] = 1-butyl-3-(2-methoxyethyl)imidazolium), [(C3O)2im][FeCl4] (4, [(C3O)2im] = 1,3-bis(2-methoxyethyl)imidazolium), [C3OMim][FeBr4] (5) and [(C3O)2im][FeBr4] (6), were prepared and characterized by elemental analysis, Raman spectroscopy and electrospray ionization mass spectrometry. The catalytic performances of 1–6 and related Fe(III)-based catalysts in the cross-coupling of aryl Grignard reagents with alkyl halides bearing β-hydrogens were studied, revealing that mono(ether) functionality improves the catalytic activity and that bis(ether) functionality improves the reusability. After simply decanting the product contained in the ethereal layer, complex 4, which containing bis(ether)-functionalized imidazolium cation, could be successfully recycled seven times.

A series of bis(phenol)-functionalized imidazolium salts, 1,3-bis(4,6-di-R1-2-hydroxybenzyl)-2-R2-4,5-di-R3-imidazolium chlorides H3LnCl (R1 = tBu, R2 = R3 = H, H3L1Cl, 1; R1 = CH3, R2 = R3 = H, H3L2Cl, 2; R1 = tBu, R2 = H, R3 = Cl, H3L3Cl, 3; R1 = tBu, R2 = CH3, R3 = H, H3L4Cl, 4), were used to produce a novel series of ionic iron(III) complexes [H3Ln][FeX4] (n = 1, X = Cl, 5; n = 2, X = Cl, 6; n = 3, X = Cl, 7; n = 4, X = Cl, 8; n = 1, X = Br, 9; n = 3, X = Br, 10). All of the complexes were characterized by Raman spectroscopy and electrospray ionization mass spectrometry. Elemental analysis and X-ray crystallography were also used. All of the complexes were non-hygroscopic and air-stable, with five of them existing as solids (5, 7–10) and one as an oil (6) at room temperature. A preliminary catalytic study on the cross-coupling reactions of aryl Grignard reagents with primary and secondary alkyl halides bearing β-hydrogens, revealed that all of the ionic iron(III) complexes exhibited good to excellent catalytic activity. Complexes 5, 6 and 8 exhibited optimal activity, whereas 7, 9 and 10 showed only moderate activity. Furthermore, by simply decanting the cross-coupling product in the ether layer, complexes 5 and 6 could be reused in at least seven successive runs without significant loss in catalytic activity.

1,3-Bis(2,6-diisopropylphenyl)imidazolium chloride, [DIPrim]Cl, was used to produce a novel iron(III)-containing imidazolium salt [DIPrim][FeCl4], which included a N,N-diarylimidazolium cation (R = 2,6-diisopropylphenyl), [DIPrim]+, and tetrachloroferrate(III) anion, [FeCl4]−. This compound was an effective and easy-to-use catalyst for the cross-coupling of aryl Grignard reagents with primary and secondary alkyl halides bearing β-hydrogens. After simply decanting the cross-coupling product in the ether layer, [DIPrim][FeCl4] could be reused in at least four successive runs without significant loss of catalytic activity.

Ni(II) dihalides bearing two different or identical NHC ligands have been prepared via a controlled indene elimination synthesis, and the former product provides a new route for the design of biscarbene Ni(II)-based catalysts. The indene elimination reaction of the indenynickel(II) complex (1-H-Ind)Ni(NHC)X (Ind = indenyl) with one equiv. of a distinct imidazolium salt at 100 °C afforded the first example of Ni(II) dihalides bearing two different NHC ligands, i.e., Ni(iPr)(IPr)X2 [iPr = 1,3-diisopropylimidazol-2-ylidene, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), X = Cl, 1; X = Br, 2] and Ni(iPr)(IMes)Br2 [IMes = 1,3-bis(mesityl)imidazol-2-ylidene, 3]. Alternatively, complexes 1–3 can be synthesized using a bis-indenyl Ni(II) complex (1-H-Ind)2Ni as starting materials via a step-by-step indene elimination at different reaction temperatures. The direct reaction of (1-R-Ind)2Ni (R = H or Me) with two equiv. of imidazolium salts at 100 °C afforded Ni(II) dihalides bearing two identical NHC ligands, i.e., Ni(iPr)X2 (X = Cl, 4; X = Br, 5) and Ni(IPr)Cl2 (6). All of these complexes were characterized by elemental analysis, NMR spectroscopy and X-ray crystallography for complexes 1–5. The two identical or different NHC ligands in complexes 1–6 changed the coordination sphere of the nickel center from a typical square-planar geometry to a slightly tetrahedral array. A preliminary catalytic study on the cross-coupling reactions of aryl Grignard reagents with aryl halides revealed that complexes 1 and 2 possess the highest activity. In comparison, complexes 3 and 6 exhibited moderate activity and the least active complexes were 4 and 5.

The reaction of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with one equivalent of a novel imidazolium salt of iron(II), [FeBr3(C4H8O)](HIPr)·C4H8O (1), afforded the anionic iron(II) complex bearing an N-heterocyclic carbene ligand [Fe(IPr)Br3](HIPr)·C7H8 (2), which shows extremely high activity in comparison with the other iron(II)-based precatalysts in the cross-coupling reaction of 4-tolylmagnesium bromide with cyclohexyl bromide.

Yttrium complexes stabilized by a diaminobis(phenolate) ligand were synthesized and their catalytic behavior was explored. Reaction of YCl3 with 1 equiv of LNa2 [L= Me2NCH2CH2N{CH2-(2-O-C6H2-tBu2-3, 5)}2] gave the yttrium chloride LYCl(THF) (1) in 92% yield. Complex 1 can be used as starting material to prepare the yttrium amido derivative. Complex 1 reacted with 1 equiv of LiNPh2 in THF to afford the expected yttrium amido complex LYNPh2 (2) in high yield. Both of complexes 1 and 2 have been well detected by elemental analysis, NMR spectra and single-crystal X-ray analysis. It was found that complex 2 can efficiently initiate the ring-opening polymerization of L-lactide and ɛ-caprolactone, and a controlled manner is observed in the former case.

The reaction of anhydrous FeBr2 with two equivalents of anionic N-heterocyclic carbene (NaL1 and NaL2), which are generated in situ by the reaction of the corresponding salt [4-R-C6H4COCH2{CH-(NCHCHNiPr)}Br] (R = OCH3, H2L1Br, 1; R = F, H2L2Br, 2) with two equivalents of NaN(SiMe3)2, affords bis-ligand Fe(II) complexes of L12Fe (3) and L22Fe (4) in high yield, respectively. Attempt to synthesize mono-ligand Fe(II) bromide by the 1:1 molar ratio of NaL to FeBr2 is unsuccessful, and the same complexes of 3 and 4 were obtained. Both 3 and 4 have been depicted by elemental analysis and X-ray structure determination. Preliminary studies show that both 3 and 4 can be used as single-component catalyst for the ring-opening polymerization of ɛ-caprolactone, and the catalytic activity of 3 is higher than that of 4.

A novel family of ionic iron(II) complexes of the general formula [HL][Fe(PR′3)X3] (HL = 1,3-bis(2,6-diisopropylphenyl)imidazolium cation, HIPr, R′ = Ph, X = Cl, 2; HL = HIPr, R′ = Cy, X = Cl, 3; HL = HIPr, R′ = Ph, X = Br, 4; HL = HIPr, R′ = Cy, X = Br, 5; HL = 1,3-bis(2,4,6-trimethylphenyl)imidazolium cation, HIMes, R′ = Cy, X = Br, 6) was easily prepared via a stepwise approach in 88%–92% yields. In addition, an ionic iron(II) complex, [HIPr][Fe(C4H8O)Cl3] (1), has been isolated from the reaction of FeCl2(THF)1.5 with one equiv. of [HIPr]Cl in 90% yield and it can further react with one equiv. of PPh3 or PCy3, affording the corresponding target iron(II) complex 2 or 3, respectively. All these complexes were characterized by elemental analysis, electrospray ionization mass spectrometry (ESI-MS), 1H NMR spectroscopy and X-ray crystallography. These air-insensitive complexes 2–6 showed high catalytic activities in the cross-coupling of aryl phosphates with primary and secondary alkyl Grignard reagents with a broad substrate scope, wherein [HIPr][Fe(PCy3)Br3] (5) was the most effective. Complex 5 also catalyzes the reductive cross-coupling of aryl phosphates with unactivated alkyl bromides in the presence of magnesium turnings and LiCl, as well as the corresponding one-pot acylation/cross-coupling sequence under mild conditions.

Novel ionic Ni(II) complexes of general formula [R2im][Ni(PPh3)Cl3] (R2im = 1,3-bis(2,6-diisopropylphenyl)imidazolium cation, IPrim, 1a; R2im = 1,3-diisopropylimidazolium cation, iPrim, 2a) were easily prepared in high yields by the direct reaction of Ni(PPh3)2Cl2 with 1 equiv. of N,N′-dihydrocarbylimidazolium salt, [R2im]Cl. Their bromide analogs [R2im][Ni(PPh3)Br3] (R2im = IPrim, 1b; R2im = iPrim, 2b) were synthesized by the same reaction in the presence of excess NaBr. The reaction of Ni(DME)Cl2 (DME = 1,2-dimethoxyethane) with 2 equiv. of [IPrim]Cl led to the formation of the complex [IPrim]2[NiCl4] (3) in an almost quantitative yield. All these complexes were characterized by elemental analysis, electrospray ionization mass spectrometry (ESI-MS), and 1H NMR spectroscopy; X-ray crystallography was performed for 1a, 1b, 2a, and 2b. A catalytic study of the cross-coupling reactions of aryl Grignard reagents with aryl halides revealed that complexes 1a and 1b possessed the highest activities. In comparison, complexes 2a, 2b, 3, and the related biscarbene Ni(II) complex Ni(IPr)2Cl2 [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] exhibited moderate activities; the least active complexes were Ni(PPh3)2Cl2 and [NEt4][Ni(PPh3)Cl3].

Ni(II) dihalides bearing two different or identical NHC ligands have been prepared via a controlled indene elimination synthesis, and the former product provides a new route for the design of biscarbene Ni(II)-based catalysts. The indene elimination reaction of the indenynickel(II) complex (1-H-Ind)Ni(NHC)X (Ind = indenyl) with one equiv. of a distinct imidazolium salt at 100 °C afforded the first example of Ni(II) dihalides bearing two different NHC ligands, i.e., Ni(iPr)(IPr)X2 [iPr = 1,3-diisopropylimidazol-2-ylidene, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), X = Cl, 1; X = Br, 2] and Ni(iPr)(IMes)Br2 [IMes = 1,3-bis(mesityl)imidazol-2-ylidene, 3]. Alternatively, complexes 1–3 can be synthesized using a bis-indenyl Ni(II) complex (1-H-Ind)2Ni as starting materials via a step-by-step indene elimination at different reaction temperatures. The direct reaction of (1-R-Ind)2Ni (R = H or Me) with two equiv. of imidazolium salts at 100 °C afforded Ni(II) dihalides bearing two identical NHC ligands, i.e., Ni(iPr)X2 (X = Cl, 4; X = Br, 5) and Ni(IPr)Cl2 (6). All of these complexes were characterized by elemental analysis, NMR spectroscopy and X-ray crystallography for complexes 1–5. The two identical or different NHC ligands in complexes 1–6 changed the coordination sphere of the nickel center from a typical square-planar geometry to a slightly tetrahedral array. A preliminary catalytic study on the cross-coupling reactions of aryl Grignard reagents with aryl halides revealed that complexes 1 and 2 possess the highest activity. In comparison, complexes 3 and 6 exhibited moderate activity and the least active complexes were 4 and 5.

A series of bis(phenol)-functionalized imidazolium salts, 1,3-bis(4,6-di-R1-2-hydroxybenzyl)-2-R2-4,5-di-R3-imidazolium chlorides H3LnCl (R1 = tBu, R2 = R3 = H, H3L1Cl, 1; R1 = CH3, R2 = R3 = H, H3L2Cl, 2; R1 = tBu, R2 = H, R3 = Cl, H3L3Cl, 3; R1 = tBu, R2 = CH3, R3 = H, H3L4Cl, 4), were used to produce a novel series of ionic iron(III) complexes [H3Ln][FeX4] (n = 1, X = Cl, 5; n = 2, X = Cl, 6; n = 3, X = Cl, 7; n = 4, X = Cl, 8; n = 1, X = Br, 9; n = 3, X = Br, 10). All of the complexes were characterized by Raman spectroscopy and electrospray ionization mass spectrometry. Elemental analysis and X-ray crystallography were also used. All of the complexes were non-hygroscopic and air-stable, with five of them existing as solids (5, 7–10) and one as an oil (6) at room temperature. A preliminary catalytic study on the cross-coupling reactions of aryl Grignard reagents with primary and secondary alkyl halides bearing β-hydrogens, revealed that all of the ionic iron(III) complexes exhibited good to excellent catalytic activity. Complexes 5, 6 and 8 exhibited optimal activity, whereas 7, 9 and 10 showed only moderate activity. Furthermore, by simply decanting the cross-coupling product in the ether layer, complexes 5 and 6 could be reused in at least seven successive runs without significant loss in catalytic activity.

An efficient one-pot intermolecular reductive cross-coupling of unactivated primary and secondary alkyl chlorides bearing β-hydrogens with aryl bromides is described. A combination of magnesium turnings and a catalytic amount of the commercially available iron(III) complex Fe(PPh3)2Cl3 was used, and the conditions were also successfully extended to an intramolecular reaction for the first time. Both types of cross-coupling reactions proceed under mild conditions, involving the in situ generation of aryl Grignard reagents, and show good applicability to a variety of readily available unactivated alkyl chlorides, which have previously been challenging substrates in iron-catalyzed reductive cross-coupling reactions.

A novel bis(phenol)-functionalized benzimidazolium salt, 1,3-bis(3,5-di-tert-butyl-2-hydroxybenzyl)benzimidazolium chloride (H3LCl, 1), was designed and used to prepare ionic iron(III) complexes of the type [H3L][FeX4] (X = Cl, 2; X = Br, 3). Both 2 and 3 were characterized by elemental analysis, Raman spectroscopy, electrospray ionization mass spectrometry and X-ray crystallography. The catalytic performances of 2 and 3 in cross-coupling reactions using aryl Grignard reagents with primary and secondary alkyl halides bearing β-hydrogens were studied. This analysis shows that complex 2 has good potential for alkyl chloride-mediated coupling. In comparison, complex 3 showed slightly lower catalytic activity. After decanting the product contained in the ethereal layer, complex 2 could be recycled at least eight times without significant loss of catalytic activity.