Well-defined Aryl-FeII complexes in cross-coupling and C?H activation processes

Communication

Well-Deﬁned Aryl-Fe Complexes in Cross-Coupling and C−H

Activation Processes

Carla Magall ó n, Oriol Planas, Steven Rold á n-G ó mez, Josep M. Luis, Anna Company,* and Xavi Ribas*

Cite This: Organometallics 2021, 40, 1195 −1200

Read Online

ACCESS

Metrics & More

Article Recommendations

sı Supporting Information

ABSTRACT: Herein we explore the intrinsic organometallic

reactivity of iron embedded in a tetradentate N C macrocyclic

ligand scaﬀold that allows the stabilization of aryl-Fe species, which

are key intermediates in Fe-catalyzed cross-coupling and C−H

functionalization processes. This study covers C−H activation

reactions using

L and FeCl , biaryl C−C coupling product

formation through reaction with Grignard reagents, and cross-

coupling reactions using L_B_ror L_B_rin combination with

Fe (CO) . Synthesis under light irradiation and moderate heating

(

50 °C) aﬀords the aryl-Fe complexes [Fe (Br)( L)(CO)]

Me II H H

1 ) and [Fe ( L)(CO) ]Br (1 ). Exhaustive spectroscopic

characterization of these rare low-spin diamagnetic species,

including their crystal structures, allowed the investigation of their intrinsic reactivity.

rganoiron species have been invoked for a long time in

aminoquinoline (AQ) directing group, but actual spectroscopic

35,36

cross-coupling transformations and C−H functionaliza-

data on this compound were not reported.

This lack of

tion reactions for the formation of C−C products. Early in the

mechanistic understanding stems from the metastable

character of organoiron species together with their multiple

geometries and oxidation and spin states. Recently Neidig

reported a series of insightful publications in which the

combination of advanced spectroscopic techniques such as

970s, Kochi reported that simple FeCl could catalyze the

methylation of haloalkenes with the use of alkyl Grignard

reagents. Since then, many reports using cheap and nontoxic

iron-based catalysts have appeared, highlighting the use of N-

−6

methylpyrrolidine (NMP) as an additive.

More recently,

ligands or N-heterocyclic

ligands to tune the reactivity of the in situ

be a successful strategy to identify catalytically relevant

ssbauer spectroscopy and X-ray crystallography proved to

−9

the use of bisphosphine

0−13

37−39

carbene

organoiron species.

formed organoiron species has allowed the development of a

Moreover, there are very few examples of key low-spin aryl-

variety of cross-coupling C−C bond forming transforma-

Fe species stemming from C−H metalation in DG-bearing

4−22

tions.

Many iron-catalyzed C−H functionalization proto-

substrates. One of them was recently trapped by Neidig at very

low temperatures using noncyclic substrates with an amide-

cols have also ﬂourished in the past decade involving C −H

and C −H activation, C−C bond forming reactions being the

triazole bidentate directing group (Scheme 1b). Another

3−25

vast majority,

although some examples of C−X bond

species was reported by Ackermann featuring a cyclometalated

formation (X = N, B, Si, O, halides) have also been reported.

low-spin aryl-Fe -hydride species ligated with a ketone DG and

In the past decade, important advances in understanding the

mechanism of these reactions relied on trapping relevant aryl

three PMe ligands. With regard to well-deﬁned systems

featuring aryl-halide oxidative addition processes, Nishiyama

18,27−31

or alkyl organoiron intermediate species.

the particular case of aryl-Fe species bearing directing groups

DG) attached to the substrate, detection of the organo-

However, in

reported a low-spin aryl-Fe complex using a bisoxazoline aryl-

Br pincer ligand and Fe (CO) . Recently, Fout described

(

the synthesis of an aryl-Fe -hydride stabilized within a

bis(carbene) pincer CCC ligand, but no reactivity of the

metallic species involved in cross-coupling or C−H activation

catalysis has been quite elusive for a long time, and only scarce

spectroscopic characterization has been reported. Either

Received: February 19, 2021

Published: March 9, 2021

oxidative addition at Fe or σ-bond metathesis at Fe has

been proposed to lead to the formation of aryl-Fe species

2,33

(

Scheme 1a).

Concerted metalation−deprotonation

CMD) by Fe has also been proposed in some cases.

Nakamura postulated a cyclometalated iron species as the

active intermediate in an arene-containing substrate using the

2021 American Chemical Society

195

Organometallics 2021, 40, 1195−1200

Organometallics

analogues ( L , R = H, Me, t Bu; Figure 2 a) and reacted them

Communication

Scheme 1. Relevant Examples of Iron-Mediated C−H

Activation: (a) σ-Bond Metathesis at Fe and Oxidative

Addition at Fe , (b) Low-Spin Aryl-Fe Trapped at Low

Temperature, and (c) Reactivity of Well-Deﬁned Aryl-Fe

Species formed via C−H Activation or Cross-Coupling to

Undergo C−C Coupling (This Work)

Figure 1. (a) Synthesis of the Fe^I^Icomplex 1·Cl and subsequent

reactivity with PhMgBr to obtain the biaryl C−C coupling product

(

L ). (b) Crystal structures of 1·Cl and 1·Br (ellipsoids set at

Ph 2 2

50% probability and H atoms removed for clarity, except for inner

Ar−H).

temperature (−78 °C) for 1 h and warming up the mixture

to room temperature for an additional 2 h, we obtained a 66%

yield of the C −C biaryl coupling product ( L ) after

workup under aerobic conditions (Figure 1a). The product

was fully characterized by NMR and HR-ESI-MS (see the

Supporting Information ). Despite no organoiron species

derived from C−H activation could be isolated, the

intermediacy of an aryl-iron species is clearly inferred by the

obtained coupling product. Whether C−H activation proceeds

via σ-bond metathesis or concerted metalation−deprotonation

32−34,50

(

CMD) at the iron(II) center is diﬃcult to establish.

This prompted us to attempt another synthetic strategy to

stabilize and isolate relevant aryl-iron species via aryl-halide

aryl-Fe was reported. An alternative strategy to get access to

oxidative addition at Fe . Thus, we prepared aryl-Br ligand

well-deﬁned aryl-Fe species consists of the use of macrocyclic

aryl-X and aryl-H model substrates capable of stabilizing

otherwise very reactive species. These size-tunable macrocyclic

model substrates have been used by our group and others to

III 44

III 45

II 46

stabilize square-planar aryl-Cu , aryl-Ag , and aryl-Ni ,

as well as octahedral aryl-Co^I^I^I⁴⁷and aryl-Mn species.

III

Following this strategy, herein we report the reactivity of well-

deﬁned octahedral aryl-Fe^I^Ispecies and their C−C cross-

coupling reactivity with ArMgX reagents (Scheme 1c).

The model arene substrate L was exposed to FeCl in

CH CN to obtain the coordination complex [Fe (Cl) ( L )]

(

1·Cl ) in 86% yield, which was isolated as a yellowish

crystalline solid (Figure 1a). Paramagnetic H NMR spectros-

copy clearly indicated a high-spin Fe species, which was

conﬁrmed by X-ray crystallography (Figure 1b). The Fe

center featured a pentacoordinated distorted-square-pyramidal

geometry (τ = 0.46) with long Fe−N distances (>2.1 Å).

Noticeably, the sixth coordination site was occupied by an

interaction with the inner aromatic C−H bond of L _H , which

conformed to an incipient C -H···Fe interaction (Figure S59).

The analogous structure with bromides as counterions was also

Figure 2. (a) Experimental conditions for the synthesis of 1^t^B^u, 1^M^e

obtained (1·Br , τ = 0.46; Figure 1b and Figure S60).

and 1 via aryl-Br oxidative addition at Fe . (b) Crystal structures of

These structures suggested that an octahedral geometry

and 1 (monocation shown) (ellipsoids set at 50% probability

featuring an organometallic aryl−Fe bond was feasible,

and H atoms removed for clarity). Selected bond distances (Å): for

provided the C −H activation could be executed. At this

1 , Fe−C 1.925(2), Fe−N 1.928(2), Fe−N9 2.030(2), Fe−N18

aryl

point we explored the reactivity of the complex 1·Cl with

2.034(2), Fe−C20 1.837(3), Fe−C22 1.759(3); for 1 , Fe−C

aryl

PhMgBr Grignard reagent, seeking for a biaryl coupling

product. By performing the reaction in THF at low

1.904(3), Fe−N 1.935(3), Fe−N12 2.095(3), Fe−N22 2.102(3),

Fe−Br 2.571(2), Fe−C3 1.785(4).

196

Organometallics 2021, 40, 1195−1200

Organometallics

mechanistic proposals are outlined in Figure 4 a for the

Communication

with Fe (CO) . In the case of ^M^eL_B_r, upon overnight

examples.

26,53

Despite cryo-MS analysis at −40 °C of the

photoirradiation (254 nm) at 50 °C, the oxidative addition

aryl-Fe product was obtained. The compound [Fe (Br)-

L)(CO)] (1 , Figure 2a) was characterized as a low-spin

Fe species and displayed diamagnetic NMR spectra (Figures

S19 −S23 ), which was directly related to the coordination of

the strong-ﬁeld carbonyl ligand. The crystal structure of 1

conﬁrmed a distorted-octahedral structure of the Fe center,

mixture immediately after exposure to O , the decay was so fast

that only the ﬁnal coupling product L _P _h was detected as a

single peak in the mass spectrum (Figure S2b). Moreover,

when the crude mixture containing [Fe ( L)(Ph)] was

quenched with HCl prior to air exposure, L_Hwas solely

obtained (85%) with no signs of biaryl coupling. Finally, since

1,2- dichloroisobutane (DCIB) is generally used as an oxidant

in Fe-catalyzed C−H activations, the addition of 2 equiv of

DCIB under N to the green species [Fe ( L)(Ph)] aﬀorded

L_P_hin 45% yield, a value slightly lower than that with O₂

exposure (66%) (section 7.3 in the Supporting Information).

Interestingly, DCIB addition at the beginning of the reaction

only aﬀorded a 9% yield of L_P_h, suggesting that oxidation to

Fe at the initial stages is detrimental to the observed

chemistry. In line with the latter, catalytic attempts have been

unfruitful.

On the basis of all these experimental observations, feasible

(

II Me

featuring a short Fe−aryl bond (1.904(3) Å) and a long Fe−Br

bond (2.571(2) Å) trans to the aryl moiety, with a CO ligand

completing the coordination sphere (Figure 2b). This trans

disposition indicated that the reaction must entail an aryl-Br

oxidative addition concomitant with a cis to trans rearrange-

II Me

1,52

II H

ment.

(

Indeed, the analogous [Fe ( L)(CO) ]Br complex

III

1 ) featured two CO ligands coordinated to the Fe center

and a noncoordinating Br anion, clearly indicating that Br

and CO ligands can easily exchange. Indeed, the trans eﬀect of

the aryl moiety is visualized by a longer Fe−CO bond trans to

the aryl (1.837(3) Å) compared to the Fe−CO bond trans to

the pyridine (1.759(3) Å). To evaluate the electronic eﬀects of

the tertiary amines, we also prepared the analogous complex

−

II tBu

tBu

[

Fe ( L)(CO) ]Br (1 ) (Figure 2a), which was charac-

terized by NMR and HR-ESI-MS.

At this point, we centered our eﬀorts on investigating the

intrinsic reactivity of [Fe (Br)( L)(CO)] (1 ) as a

reference compound for well-deﬁned low-spin aryl-Fe species.

In order to determine whether this species could be involved in

the reaction of the complex 1·Cl with the Grignard reagent,

we reacted 1 with PhMgBr under experimental conditions

and workup analogous to those described above for 1·Cl ,

obtaining a relevant 38% yield of the

product (Figure

COPh

, top). NMR and HR-ESI-MS conﬁrmed the nature of the

Figure 3. Synthesis of ^M^e

COPh

from well-deﬁned aryl-Fe (top) and

synthesis of L-CO from L_B_rvia 2 (CO) in an unprecedented

amine-to-amide transformation (bottom).

_F_i_g_u_r_e₄_.₍_a₎_P_r_o_p_o_s_e_d_m_e_c_h_a_n_i_s_m_f_o_r_t_h_e_s_y_n_t_h_e_s_i_s_o_fMeL_P_h_v_i_a_F_eII_-

mediated C−H activation. (b) Proposed mechanism for the synthesis

II Me

via the reaction of 1 with PhMgBr (E-1 and E-2

coupling product, which stemmed from a putative [Fe ( L)-

(

COPh

quintuplet DFT optimized structures shown as insets; see the

Supporting Information).

Ph)(CO)] (1 -Ph) followed by a CO migratory insertion

and reductive elimination to form the aryl−COPh bond in

COPh

It is worth noting here that the products ^M^eL_P_h(derived

synthesis of ^M^eLPh and in Figure 4b for the synthesis of

from 1·Cl ) and L_C_O_P_h(derived from 1 ) are obtained

LCOPh. The reaction of 1·Cl with PhMgBr (Figure 4a)

II Me

presumably via exposure of [Fe ( L)(Ph)] and [Fe ( L)-

Ph)(CO)] to O (or air) and a subsequent acid/base workup.

aﬀords species A, which undergoes C−H activation, presum-

ably via σ-bond metathesis, to give species B. A second

equivalent of the Grignard reagent generates species C, which

(

An evident change in color (UV−vis monitoring, Figures S1

and S2 ) from dark green to reddish brown was observed upon

contact with air, suggesting an oxidation to an Fe species that

triggered the C−C reductive elimination, as reported in other

undergoes oxidative reductive elimination via C upon

III

exposure to O . With regard to the reactivity of 1 with

−

PhMgBr (Figure 4b), ﬁrst the Br ligand is exchanged by Ph

197

Organometallics 2021, 40, 1195−1200

Organometallics

The Supporting Information is available free of charge at

Communication

to aﬀord D, and then a CO migratory insertion occurs to give

E-1 or E-2. Both species would form the ﬁnal product L_C_O_P_h

others in the design of improved Fe-catalyzed bond forming

transformations.

via reductive elimination. To discern between the two

possibilities, the crude compound was treated with HCl(aq)

prior to air exposure, and ^M^e^LH ^w^a^s^o^b^t^aⁱⁿ^e^d^a^s^t^h^e^p^r^o^d^u^c^tⁱⁿ

ASSOCIATED CONTENT

sı Supporting Information

https://pubs.acs.org/doi/10.1021/acs.organomet.1c00100.

■

5% yield. This supports the idea that E-1 is the most plausible

intermediate, which is backed by DFT studies (Gibbs energies

with respect to D are 6.19 kcal/mol for E-1 and 9.72 kcal/mol

for E-2; Figure 4b and the Supporting Information).

Spectroscopic characterization of all compounds,

crystallographic data for 1·Cl , 1·Br , 1 , and 1 , and

DFT results for D, E-1, and E-2 (PDF )

Accession Codes

CCDC 2046155−2046158 contain the supplementary crys-

tallographic data for this paper. These data can be obtained

free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by

emailing data_request@ccdc.cam.ac.uk, or by contacting The

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

While exploring the reactivity of L_B_rwith Fe(CO) , we

2 2

also performed the reaction under thermal conditions (100

C) instead of via photoirradiation (Figure 3, bottom).

Strikingly, the nature of the low-spin Fe complex 2 (CO)

obtained after 24 h was completely unexpected. A detailed

diamagnetic 1D/2D NMR and FT-IR characterization

concluded that a formal CO insertion occurred by amine to

amide conversion at a pyridine-benzylic position, still holding

the organoiron aryl-Fe moiety: i.e., [Fe (Br)( L-CO)-

(

CO) ] (2 (CO)) (Figure 3). C NMR integration of the

coordinated CO signal and the lack of a HR-ESI-MS peak

AUTHOR INFORMATION

Corresponding Authors

−

■

clearly points toward the coordination of two CO and one Br

_l_i_g_a_n_d_t_o_t_h_e_F_eII center, leaving the amide moiety

Anna Company − Institut de Química Computacional i

Catalisi (IQCC) and Departament de Química, Universitat

uncoordinated. The amide moiety was corroborated upon

protodemetalation, aﬀording L-CO as the resulting macro-

de Girona, Girona E-17003, Catalonia, Spain; orcid.org/

000-0003-4845-4418 ; Email: anna.company@udg.edu

Xavi Ribas − Institut de Química Computacional i Catalisi

IQCC) and Departament de Química, Universitat de

Girona, Girona E-17003, Catalonia, Spain; orcid.org/

000-0002-2850-4409 ; Email: xavi.ribas@udg.edu

cyclic compound (see the Supporting Information for

characterization). To our knowledge, carbonylation into the

ligand backbone to transform a tertiary amine to a tertiary

amide is unprecedented and is reminiscent of an unreported

(

inverse Curtius-like rearrangement. Although it is not the

same transformation, Cantat recently reported the iron-

catalyzed amine to amide transformation of an N,N-

dimethylaniline substrate by taking advantage of the acylation

Authors

Carla Magallón − Institut de Química Computacional i

Catalisi (IQCC) and Departament de Química, Universitat

de Girona, Girona E-17003, Catalonia, Spain

Oriol Planas − Institut de Química Computacional i Catal

IQCC) and Departament de Química, Universitat de

Girona, Girona E-17003, Catalonia, Spain; orcid.org/

000-0003-2038-2678

Steven Roldán-Gómez − Institut de Química Computacional i

Catalisi (IQCC) and Departament de Química, Universitat

de Girona, Girona E-17003, Catalonia, Spain

Josep M. Luis − Institut de Química Computacional i Catal

IQCC) and Departament de Química, Universitat de

Girona, Girona E-17003, Catalonia, Spain; orcid.org/

000-0002-2880-8680

of a tertiary amine followed by the extrusion of Me as MeI.

Also, the participation of Fe in Curtius-like rearrangements has

only a few precedents, such as the work from Xia, forming

isi

isocyanates from hydroxamates through an Fe -nitrenoid

(

complex.

In order to gain insight into the mechanism of this

unprecedented reactivity, the well-deﬁned 1^M^ecomplex was

heated under a CO atmosphere (1 bar). The reaction was

monitored by H NMR, and formation of 2 (CO) was

observed (14%) just after 2 h, together with the starting 1

and protodemetalation byproduct ( L ), thus suggesting that

aryl-Br oxidative addition at Fe takes place prior to the amine

isi

(

to amide conversion. Also, the nature of the tertiary amine is

tBu

crucial, since a tBu-N-substituted ligand ( L ) did not

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.organomet.1c00100

undergo the amine to amide transformation, whereas L_B_r

_a_ﬀ_o_r_d_e_dHL-CO_Hin a sluggish manner (section 8 in the

Supporting Information).

In conclusion, model macrocyclic aryl-Fe species have been

Notes

The authors declare no competing ﬁnancial interest.

studied in detail by taking advantage of the stabilizing eﬀect

imposed by the macrocyclic N C-type ligands L (X = H, Me;

ACKNOWLEDGMENTS

Y = H, Br). The system aﬀords the C−C biaryl cross-coupling

■

products through C−H activation at a Fe complex using

We acknowledge ﬁnancial support from the MINECO-Spain

for projects PID2019-104498GB-I00 to X.R., PID2019-

106699GB-I00 to A.C., and PGC2018-098212-B-C22 to

J.M.L. The Generalitat de Catalunya is also acknowledged

for projects 2017SGR264 and 2017SGR39. We thank the UdG

for a IFUdG Ph.D. grant to C.M. and the MINECO for an FPI

grant to S.R.-G. We also thank COST Action CHAOS

(CA15106). X.R. and A.C. are thankful for an ICREA

ArMgX reagents and the phenylcarbonylation cross-coupling

products when well-deﬁned aryl-Fe species are used, featuring

C−C coupling with Grignard reagents, concomitantly with CO

insertion. Furthermore, the overstabilized 1^M^especies under-

goes at high temperatures an unprecedented CO insertion−

carbonylation into the tertiary amine ligand backbone,

rendering a tertiary amide quantitatively. Such model aryl-

Fe complexes provide a neat mechanistic picture for C−H

Academia award. The authors are grateful to STR-UdG for

technical support.

arylation and cross-coupling reactions that should inspire

198

Organometallics 2021, 40, 1195−1200

Organometallics

Communication

21) Piontek, A.; Bisz, E.; Szostak, M. Iron-Catalyzed Cross-

REFERENCES

■

Couplings in the Synthesis of Pharmaceuticals: In Pursuit of

1) Tamura, M.; Kochi, J. Iron catalysis in the reaction of grignard

Sustainability. Angew. Chem., Int. Ed. 2018, 57 , 11116 −11128.

reagents with alkyl halides. J. Organomet. Chem. 1971 , 31 , 289 −309.

(22) Lubken, D.; Saxarra, M.; Kalesse, M. Tris(acetylacetonato)

3) Cahiez, G.; Avedissian, H. Highly Stereo- and Chemoselective

2) Tamura, M.; Kochi, J. K. Vinylation of Grignard reagents.

Catalysis by iron. J. Am. Chem. Soc. 1971 , 93 , 1487 −1489.

Iron(III): Recent Developments and Synthetic Applications. Synthesis

019, 51, 161−177.

23) Ilies, L.; Asako, S.; Nakamura, E. Iron-Catalyzed Stereospecific

Iron-Catalyzed Alkenylation of Organomagnesium Compounds.

Synthesis 1998, 1998, 1199−1205.

4) Sears, J. D.; Munoz, S. B., III; Daifuku, S. L.; Shaps, A. A.;

Carpenter, S. H.; Brennessel, W. W.; Neidig, M. L. The Effect of β -

Hydrogen Atoms on Iron Speciation in Cross-Couplings with Simple

Iron Salts and Alkyl Grignard Reagents. Angew. Chem., Int. Ed. 2019,

Activation of Olefinic C −H Bonds with Grignard Reagent for

Synthesis of Substituted Olefins. J. Am. Chem. Soc. 2011, 133, 7672−

(

675.

24) Shang, R.; Ilies, L.; Asako, S.; Nakamura, E. Iron-Catalyzed

C(sp2)−H Bond Functionalization with Organoboron Compounds. J.

Am. Chem. Soc. 2014, 136, 14349−14352.

(25) Ilies, L.; Ichikawa, S.; Asako, S.; Matsubara, T.; Nakamura, E.

8, 2769−2773.

5) Gärtner, D.; Stein, A. L.; Grupe, S.; Arp, J.; Jacobi von Wangelin,

Iron-Catalyzed Directed Alkylation of Alkenes and Arenes with

A. Iron-Catalyzed Cross-Coupling of Alkenyl Acetates. Angew. Chem.,

Int. Ed. 2015, 54, 10545−10549.

6) Cahiez, G.; Duplais, C.; Moyeux, A. Iron-Catalyzed Alkylation of

Alkenyl Grignard Reagents. Org. Lett. 2007, 9, 3253−3254.

7) Hatakeyama, T.; Hashimoto, T.; Kondo, Y.; Fujiwara, Y.; Seike,

Alkylzinc Halides. Adv. Synth. Catal. 2015 , 357 , 2175 −2179.

26) Shang, R.; Ilies, L.; Nakamura, E. Iron-Catalyzed C −H Bond

(27) Furstner, A. Iron Catalysis in Organic Synthesis: A Critical

Activation. Chem. Rev. 2017 , 117 , 9086 −9139.

(

Assessment of What It Takes To Make This Base Metal a

H.; Takaya, H.; Tamada, Y.; Ono, T.; Nakamura, M. Iron-Catalyzed

Multitasking Champion. ACS Cent. Sci. 2016 , 2 , 778 −789.

Suzuki −Miyaura Coupling of Alkyl Halides. J. Am. Chem. Soc. 2010,

(28) Bauer, I.; Knölker, H.-J. Iron Catalysis in Organic Synthesis.

8) Hatakeyama, T.; Okada, Y.; Yoshimoto, Y.; Nakamura, M.

32, 10674−10676.

Chem. Rev. 2015, 115, 3170−3387.

(29) Bedford, R. B.; Brenner, P. B.; Carter, E.; Cogswell, P. M.;

Tuning Chemoselectivity in Iron-Catalyzed Sonogashira-Type Re-

actions Using a Bisphosphine Ligand with Peripheral Steric Bulk:

Selective Alkynylation of Nonactivated Alkyl Halides. Angew. Chem.,

Int. Ed. 2011, 50, 10973−10976.

Haddow, M. F.; Harvey, J. N.; Murphy, D. M.; Nunn, J.; Woodall, C.

H. TMEDA in Iron-Catalyzed Kumada Coupling: Amine Adduct

versus Homoleptic “ate ” Complex Formation. Angew. Chem., Int. Ed.

30) Liu, Y.; Xiao, J.; Wang, L.; Song, Y.; Deng, L. Carbon −Carbon

014, 53, 1804−1808.

(

9) Hatakeyama, T.; Hashimoto, T.; Kathriarachchi, K. K. A. D. S.;

Zenmyo, T.; Seike, H.; Nakamura, M. Iron-Catalyzed Alkyl −Alkyl

Bond Formation Reactivity of a Four-Coordinate NHC-Supported

Iron(II) Phenyl Compound. Organometallics 2015 , 34 , 599 −605.

Organoferrate. Organometallics 2017, 36, 499−501.

Activation of Imines by Trimethylphosphine-Supported Iron

Complexes and Their Reactivities. Organometallics 2009, 28, 2300−

2310.

(33) Shi, Y.; Li, M.; Hu, Q.; Li, X.; Sun, H. C −Cl Bond Activation of

ortho-Chlorinated Imine with Iron Complexes in Low Oxidation

States. Organometallics 2009, 28, 2206 −2210.

(34) Wunderlich, S. H.; Knochel, P. Preparation of Functionalized

Aryl Iron(II) Compounds and a Nickel-Catalyzed Cross-Coupling

with Alkyl Halides. Angew. Chem., Int. Ed. 2009 , 48 , 9717 −9720.

(35) Asako, S.; Ilies, L.; Nakamura, E. Iron-Catalyzed Ortho-

Allylation of Aromatic Carboxamides with Allyl Ethers. J. Am. Chem.

Soc. 2013, 135, 17755−17757.

Suzuki −Miyaura Coupling. Angew. Chem., Int. Ed. 2012, 51, 8834−

(

837.

31) Zhurkin, F. E.; Wodrich, M. D.; Hu, X. A Monometallic Iron(I)

10) Bedford, R. B.; Betham, M.; Bruce, D. W.; Danopoulos, A. A.;

Frost, R. M.; Hird, M. Iron −Phosphine, − Phosphite, − Arsine, and −

Carbene Catalysts for the Coupling of Primary and Secondary Alkyl

Halides with Aryl Grignard Reagents. J. Org. Chem. 2006, 71, 1104−

32) Camadanli, S.; Beck, R.; Flörke, U.; Klein, H.-F. C −H

11) Ghorai, S. K.; Jin, M.; Hatakeyama, T.; Nakamura, M. Cross-

110.

Coupling of Non-activated Chloroalkanes with Aryl Grignard

Reagents in the Presence of Iron/N-Heterocyclic Carbene Catalysts.

Org. Lett. 2012, 14, 1066−1069.

12) Guisán-Ceinos, M.; Tato, F.; Bunuel, E.; Calle, P.; Cárdenas, D.

J. Fe-catalysed Kumada-type alkyl −alkyl cross-coupling. Evidence for

the intermediacy of Fe(i) complexes. Chem. Sci. 2013 , 4 , 1098 −1104.

13) Hatakeyama, T.; Nakamura, M. Iron-Catalyzed Selective Biaryl

Coupling: Remarkable Suppression of Homocoupling by the Fluoride

Anion. J. Am. Chem. Soc. 2007, 129, 9844−9845.

14) Dongol, K. G.; Koh, H.; Sau, M.; Chai, C. L. L. Iron-Catalysed

(36) Matsubara, T.; Asako, S.; Ilies, L.; Nakamura, E. Synthesis of

Anthranilic Acid Derivatives through Iron-Catalyzed Ortho Amina-

tion of Aromatic Carboxamides with N-Chloroamines. J. Am. Chem.

Soc. 2014, 136, 646−649.

sp3 −sp3 Cross-Coupling Reactions of Unactivated Alkyl Halides with

Alkyl Grignard Reagents. Adv. Synth. Catal. 2007 , 349 , 1015 −1018.

15) Jin, M.; Adak, L.; Nakamura, M. Iron-Catalyzed Enantiose-

(37) Daifuku, S. L.; Al-Afyouni, M. H.; Snyder, B. E. R.; Kneebone,

lective Cross-Coupling Reactions of α -Chloroesters with Aryl

Grignard Reagents. J. Am. Chem. Soc. 2015 , 137 , 7128 −7134.

J. L.; Neidig, M. L. A Combined Mossbauer, Magnetic Circular

Dichroism, and Density Functional Theory Approach for Iron Cross-

Coupling Catalysis: Electronic Structure, In Situ Formation, and

Reactivity of Iron-Mesityl-Bisphosphines. J. Am. Chem. Soc. 2014, 136,

9132−9143.

16) Chua, Y.-Y.; Duong, H. A. Selective Kumada biaryl cross-

coupling reaction enabled by an iron(iii) alkoxide −N-heterocyclic

carbene catalyst system. Chem. Commun. 2014, 50, 8424−8427.

(17) O’Brien, H. M.; Manzotti, M.; Abrams, R. D.; Elorriaga, D.;

(38) Neidig, M. L.; Carpenter, S. H.; Curran, D. J.; DeMuth, J. C.;

Fleischauer, V. E.; Iannuzzi, T. E.; Neate, P. G. N.; Sears, J. D.;

Wolford, N. J. Development and Evolution of Mechanistic Under-

standing in Iron-Catalyzed Cross-Coupling. Acc. Chem. Res. 2019, 52,

140−150.

(39) Neate, P. G. N.; Greenhalgh, M. D.; Brennessel, W. W.;

Thomas, S. P.; Neidig, M. L. Mechanism of the Bis(imino)pyridine-

Iron-Catalyzed Hydromagnesiation of Styrene Derivatives. J. Am.

Chem. Soc. 2019, 141, 10099−10108.

(40) Boddie, T. E.; Carpenter, S. H.; Baker, T. M.; DeMuth, J. C.;

Cera, G.; Brennessel, W. W.; Ackermann, L.; Neidig, M. L.

Identification and Reactivity of Cyclometalated Iron(II) Intermedi-

Sparkes, H. A.; Davis, S. A.; Bedford, R. B. Iron-catalysed substrate-

directed Suzuki biaryl cross-coupling. Nat. Catal. 2018, 1, 429−437.

(18) Przyojski, J. A.; Veggeberg, K. P.; Arman, H. D.; Tonzetich, Z.

J. Mechanistic Studies of Catalytic Carbon −Carbon Cross-Coupling

by Well-Defined Iron NHC Complexes. ACS Catal. 2015, 5, 5938−

946.

19) Sherry, B. D.; Fu

Catalyzed Cross Coupling. Acc. Chem. Res. 2008, 41, 1500−1511.

20) Nakamura, E.; Hatakeyama, T.; Ito, S.; Ishizuka, K.; Ilies, L.;

rstner, A. The Promise and Challenge of Iron-

(

Nakamura, M., Iron-Catalyzed Cross-Coupling Reactions. In Organic

Reactions; Wiley: 2014; Vol. 83, pp 1−210.

199

Organometallics 2021, 40, 1195−1200

Organometallics

(41) Messinis, A. M.; Finger, L. H.; Hu, L.; Ackermann, L. Allenes

Communication

ates in Triazole-Directed Iron-Catalyzed C −H Activation. J. Am.

Chem. Soc. 2019, 141, 12338−12345.

for Versatile Iron-Catalyzed C −H Activation by Weak O-Coordina-

tion: Mechanistic Insights by Kinetics, Intermediate Isolation, and

Computation. J. Am. Chem. Soc. 2020, 142, 13102 −13111.

(42) Hosokawa, S.; Ito, J.-i.; Nishiyama, H. A Chiral Iron Complex

Containing a Bis(oxazolinyl)phenyl Ligand: Preparation and Asym-

metric Hydrosilylation of Ketones. Organometallics 2010, 29, 5773−

775.

(

43) Jackson, B. J.; Najera, D. C.; Matson, E. M.; Woods, T. J.;

Bertke, J. A.; Fout, A. R. Synthesis and Characterization of

DIPPCCC)Fe Complexes: A Zwitterionic Metalation Method and

CO2 Reactivity. Organometallics 2019, 38, 2943−2952.

44) Casitas, A.; King, A. E.; Parella, T.; Costas, M.; Stahl, S. S.;

Ribas, X. Direct Observation of CuI/CuIII Redox Steps Relevant to

Ullmann-Type Coupling Reactions. Chem. Sci. 2010, 1, 326−330.

(

45) Font, M.; Acuna-Parés, F.; Parella, T.; Serra, J.; Luis, J. M.;

Lloret-Fillol, J.; Costas, M.; Ribas, X. Direct observation of two-

electron Ag(I)/Ag(III) redox cycles in coupling catalysis. Nat.

Commun. 2014, 5, 4373.

(

46) Rovira, M.; Roldán-Gómez, S.; Martin-Diaconescu, V.;

Whiteoak, C. J.; Company, A.; Luis, J. M.; Ribas, X. Trifluoromethy-

lation of a Well-Defined Square-Planar Aryl-NiII Complex involving

NiIII/CF3. and NiIV −CF3 Intermediate Species. Chem. - Eur. J.

(

017, 23, 11662−11668.

47) Planas, O.; Roldán-Gómez, S.; Martin-Diaconescu, V.; Parella,

T.; Luis, J. M.; Company, A.; Ribas, X. Carboxylate-Assisted

Formation of Aryl-Co(III) Masked-Carbenes in Cobalt-Catalyzed

C −H Functionalization with Diazo Esters. J. Am. Chem. Soc. 2017,

(

39, 14649−14655.

48) Sarbajna, A.; He, Y.-T.; Dinh, M. H.; Gladkovskaya, O.;

Rahaman, S. M. W.; Karimata, A.; Khaskin, E.; Lapointe, S.; Fayzullin,

R. R.; Khusnutdinova, J. R. Aryl −X Bond-Forming Reductive

Elimination from High-Valent Mn −Aryl Complexes. Organometallics

49) Addison, A. W.; Rao, T. N.; Reedijk, J.; Van Rijn, J.; Verschoor,

019, 38, 4409−4419.

G. C. Synthesis, structure, and spectroscopic properties of copper(II)

compounds containing nitrogen-sulfur donor ligands: the crystal and

molecular structure of aqua[1,7-bis(N-methylbenzimidazol-2 ′-yl)-2,6-

dithiaheptane]copper(II) perchlorate. J. Chem. Soc., Dalton Trans.

50) Beck, R.; Sun, H.; Li, X.; Camadanli, S.; Klein, H.-F.

984, 7, 1349−46.

Cyclometalation of Thiobenzophenones with Mononuclear Methyl-

iron and -cobalt Complexes. Eur. J. Inorg. Chem. 2008, 2008, 3253−

51) Tolman, C. A.; Ittel, S. D.; English, A. D.; Jesson, J. P. The

257.

chemistry of 2-naphthyl bis[bis(dimethylphosphino)ethane] hydride

complexes of iron, ruthenium, and osmium. 1. Characterization and

reactions with hydrogen and Lewis base ligands. J. Am. Chem. Soc.

52) Tolman, C. A.; Ittel, S. D.; English, A. D.; Jesson, J. P.

978, 100, 4080−4089.

Chemistry of 2-naphthyl bis[bis(dimethylphosphino)ethane] hydride

complexes of iron, ruthenium, and osmium. 3. Cleavage of sp2

carbon-hydrogen bonds. J. Am. Chem. Soc. 1979, 101, 1742−1751.

(53) Yoshikai, N.; Matsumoto, A.; Norinder, J.; Nakamura, E. Iron-

Catalyzed Direct Arylation of Aryl Pyridines and Imines Using

Oxygen as an Oxidant. Synlett 2010, 2010, 313−316.

54) Ghosh, A. K.; Sarkar, A.; Brindisi, M. The Curtius

rearrangement: mechanistic insight and recent applications in natural

product syntheses. Org. Biomol. Chem. 2018, 16, 2006−2027.

(55) Nasr Allah, T.; Savourey, S.; Berthet, J.-C.; Nicolas, E.; Cantat,

T. Carbonylation of C −N Bonds in Tertiary Amines Catalyzed by

Low-Valent Iron Catalysts. Angew. Chem., Int. Ed. 2019, 58, 10884−

56) Li, D.; Wu, T.; Liang, K.; Xia, C. Curtius-like Rearrangement of

0887.

an Iron −Nitrenoid Complex and Application in Biomimetic Synthesis

of Bisindolylmethanes. Org. Lett. 2016, 18, 2228−2231.

200