Synthesis and Catalytic Use of Polar Phosphinoferrocene Amidosulfonates Bearing Bulky Substituents at the Ferrocene Backbone

Petr Vos á hlo, L é a Radal, Marine Labonde, Ivana C í saro

Article

Synthesis and Catalytic Use of Polar Phosphinoferrocene

Amidosulfonates Bearing Bulky Substituents at the Ferrocene

Backbone

v á , Julien Roger, Nadine Pirio,

Jean-Cyrille Hierso,* and Petr Stepnicka*

̌ ̌

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sı Supporting Information

ABSTRACT: Anionic phosphinoferrocene amidosulfonates bear-

ing sterically demanding tert-butyl substituents in positions 3 and

(

′ of the ferrocene scaﬀold, viz. rac-(Et NH)[Fe(η -tBuC H PR )-

η -tBuC H C(O)NHCH SO )] (R = phenyl, cyclohexyl), were

5 3 2 3

synthesized by amidation of the corresponding

phosphinocarboxylic acids, [Fe(η -tBuC H PR )(η -

tBuC H CO H)]. These ditopic polar phosphinoferrocenes and

their non-tert-butylated analogues have been used as ligands to

prepare zwitterionic (η -allyl)palladium(II) complexes [Pd(η -

C H ){Fe(η -R′C H PR )(η -R′C H C(O)NHCH SO )}] (R′ =

H, tBu; R = Ph, Cy). Depending on the isolation procedure and

crystallization conditions, some complexes were isolated in two isomeric forms which diﬀered in the coordination of the

amidosulfonate pendant group, where either amide or sulfonated oxygen ligated the Pd(II) center. The preference for coordination

of the amide or sulfonate oxygen atoms has been explained by the interplay of electrostatic and solvation eﬀects and further

supported by DFT calculations. The (η -allyl)Pd complexes have been applied as deﬁned precatalysts for Pd-catalyzed C−H

arylation of an unprotected indole with aryl iodides in polar solvents. Under the optimized reaction conditions at 100 °C in water,

C2-arylation proceeded selectively with various aryl iodides to produce the respective 2-arylindoles in acceptable yields at a low

catalyst loading (1 mol % Pd) and in the absence of any phase transfer agent. The catalyst possessing tert-butyl groups at the

ferrocene core and an electron-rich dicyclohexylphosphino group exhibited the best catalytic performance.

INTRODUCTION

producing the functional amidophosphine ligands 1 (Scheme

■

, left; R = Ph, Cy). These coupling reactions proceed with

good to excellent yields, employ stable, safe, and readily

accessible starting materials, and typically produce pure

crystalline products. Utilizing this approach, we synthesized

several phosphinoferrocene amidosulfonates, which proved to

Homogeneous catalysis by transition-metal complexes relies on

the development of suitable supporting ligands. Phosphines

are particularly attractive due to their tunable steric and

electronic properties that can be used to control the course of

catalytic processes by means of substituent modiﬁcation and

by incorporation of additional functional groups. The

be useful ligands for catalytic reactions in aqueous systems.

introduction of polar hydrophilic substituents into the ligands

is of particular practical importance, as it allows for the transfer

of catalytic reactions from purely organic solvents to more

Scheme 1. Phosphinoferrocene Amidosulfonates 1 and 2

innocuous aqueous media. Although numerous polar groups

have been used as solubilizing moieties for phosphine ligands

(

e.g., charged ammonium, guanidinium, and carboxylate

fragments), sulfonated phosphines remain the most successful

ligands for aqueous catalysis. However, their practical success

is partially compromised by the challenging synthesis, as

synthetic methods for introducing phosphine and sulfonate

moieties are often incompatible due to the sensitivity of the

Received: April 21, 2021

Published: June 4, 2021

phosphine groups toward oxidation.

To alleviate these problems, we have recently devised an

alternative approach based on amide coupling reactions

between phosphinocarboxylic acids and aminosulfonic acids,

2021 American Chemical Society

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Notably, even a single amidosulfonate tag was suﬃcient to

was achieved by treating acids 5^P^hand 5^C^ysuccessively with 1-

hydroxybenztriazole (HOBt), 1-ethyl-3-[3-(dimethylamino)-

propyl]carbodiimide (EDC), and aminomethanesulfonic acid

overcome the hydrophobicity of phosphinoferrocene ligands,

which limits their applications in aqueous catalysis.

In this paper, we report the synthesis of new phosphino-

in triethylamine/acetonitrile. This procedure furnished better

yields of the coupling products, typically a ca. 95% yield after

chromatography, than the method used previously to prepare

ferrocene amidosulfonate ligands 2 containing bulky tert-butyl

substituents at the ferrocene scaﬀold (Scheme 1, right; R = Ph,

Cy). We have already shown that the introduction of sterically

demanding tert-butyl substituents to the ferrocene scaﬀold

hinders rotation of the ferrocene cyclopentadienyls, thereby

1 , in which the starting acids were converted to

pentaﬂuorophenyl esters that were subsequently reacted with

aminomethanesulfonic acid and triethylamine.

resulting in sterically locked conformations. Such conforma-

Amide 2 was also synthesized in its P-protected form

tions are beneﬁcial for catalysis, partially because of

(Scheme 2), 2 ·BH . In this case, the amidation was

preorganized strong interactions between the donor atoms.

performed with the protected acid 5 ·BH , obtained from

The aliphatic substituents also increase electron density at the

ferrocene unit and at the attached phosphorus atom and

provide steric protection for the phosphine moiety and the

ligated, catalytically active metal center. Furthermore, aliphatic

substituents render the phosphinoferrocene fragment more

hydrophobic and can direct the ligated metal centers toward

the organic components of the reaction system, typically the

organic reagents. The hydrophilic amidosulfonate tags, mean-

4 ·BH . Deprotection was achieved by heating 2 ·BH in

3 3

freshly distilled morpholine (65 °C/16 h), providing 2 in

66% yield after chromatography and crystallization. Although

this route employs air-stable and easier to handle protected

intermediates, it provides a lower overall yield of 2 in

comparison to the shorter route, making use of unprotected

intermediates (13% vs 38%).

Compounds 2 and 2 were puriﬁed by chromatography

and crystallization from ethyl acetate, which removed minor

amounts of the respective phosphine oxides. The compounds

are orange crystalline materials and are stable over extended

periods, especially when they are stored under an inert

atmosphere. In solution, they undergo slow oxidation under

ambient conditions.

4c,14

while, can stabilize dispersions formed in water.

In this

study, the eﬀect of the additional auxiliary substituents was

investigated in the challenging Pd-catalyzed C−H arylation of

unprotected indoles performed in water, using Pd-allyl

complexes stabilized with ligands 1 and 2 as the precatalysts.

The polar ferrocenes 2 and 2^C^yand all reaction

intermediates were characterized by NMR and IR spectrosco-

py, ESI mass spectrometry, and elemental analysis. The solid-

RESULTS AND DISCUSSION

■

Synthesis of Polar Phosphinoferrocenes and Their

η -Allyl)palladium Complexes. The synthesis of planar-

chiral but racemic phosphinoferrocene amidosulfonates 2 ,

(

state structures of 2 and 2 ·BH were determined by single-

crystal X-ray diﬀraction analysis (Figure 1 and Table 1 ;

additional structural diagrams are available as Supporting

Information ).

where R = Ph or cyclohexyl (Cy), was performed analogously

to the synthesis of compounds 1 lacking the tert-butyl

substituents (Scheme 2). The respective starting materials,

The molecular structure of 2 (Figure 1) is similar to the

phosphinocarboxylic acids 5 , were obtained in two steps by

6,9c

structures of 1 and 1 reported previously. It comprises a

regular ferrocene moiety, showing similar Fe−C distances and

negligible tilting. The functional substituents at positions 1 and

sequential lithiation/functionalization of racemic 1,1′-dibro-

mo-3,3′-di-tert-butylferrocene (3) via phosphine-bromides

. Subsequent amidation producing compounds 2 and 2

′ depart by 20° from an eclipsed arrangement. The amide

moiety is rotated by 16.5(3)° with respect to its bonding

cyclopentadienyl ring so that the nitrogen atom is inclined

toward the ferrocene unit. In the crystal, the ions constituting

Scheme 2. Synthesis of Phosphinoferrocenes 2 (R = Ph,

Cy)

the structure of 2 assemble into closed arrays (Figure 1).

Speciﬁcally, two amidosulfonate anions forming an enatiomeric

pair are linked into dimers located around crystallographic

inversion centers by pairs of N1−H1N···O3 hydrogen bonds,

and these dimers further serve as H-bond acceptors for two

adjacent Et NH cations, with the latter acting as bifurcated H-

bond donors (N2−H2N···O2/N2−H2N···O4).

Compound 2 ·BH crystallizes with two structurally

independent but essentially identical molecules (see the

Supporting Information). Its molecular structure is similar to

that of 2 . However, the ferrocene units adopt a more opened

conformation (i.e., their substituents are more distant; see τ

angles in Table 1), and the amide planes depart more from an

arrangement coplanar with their parent cyclopentadienyl ring

(

dihedral angles 34.0(6)/35.5(6)°; in this case, the nitrogen

atoms are diverted from the ferrocene unit). The crystal

assembly of 2 ·BH is virtually identical with that of 2 .

To examine the catalytic properties of 1 and 2 , we used

these hydrophilic ligands to prepare zwitterionic Pd(allyl)

complexes applicable as deﬁned precatalysts (Scheme 3).

Cy 9c

Abbreviations: HOBt, 1-hydroxybenzotriazole; EDC, 1-ethyl-3-[3-

Following the procedure used to prepare 6 , we ﬁrst

dimethylamino)propyl]carbodiimide.

reacted the ligands with [Pd(μ-Cl)(η -C H )] to give the

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Scheme 3. Synthesis of Allylpalladium(II) Complexes 6

and 7^R

The ligands bearing dicyclohexylphosphine groups produced

complexes 6 (reported compound ) and 7 , wherein the

amide oxygen completed the coordination sphere of Pd(II)

(

N.B.: for 7 , the same product resulted upon crystallization

from CHCl /hexane and CH Cl + methanol/hexane).

Conversely, depending on the crystallization conditions,

complex 6 was isolated in two coordinative isomeric forms,

Figure 1. (top) View of the amidosulfonate anion in the structure of

and (bottom) simpliﬁed packing diagram for the same compound.

where either the amide oxygen or the sulfonate oxygen

Hydrogen bond parameters: N1···O3 = 3.289(3) Å, N2···O2 =

.096(3) Å, and N2···O4 = 2.794(3) Å. Note: only one position of

coordinated to palladium (henceforth distinguished as 6 -C

the disordered atom C37 is shown for clarity.

and 6 -S). Whereas 6 -C containing a smaller and more rigid

P,O-chelate ring was reproducibly obtained from the CH Cl +

methanol/hexane mixture, the isomeric complex 6 -S

featuring a charge-supported O→Pd interaction resulted

Table 1. Selected Distances (Å) and Angles (deg) for 2^P^h

and 2 ·BH

from crystallization with the CHCl /hexane mixture. Appa-

₂Ph

₂Cy·BH (mol 1/mol 2)

param

rently, polar solvents that better solvate the charged sulfonate

Fe−C (range)

2.045(2)−

2.037(5)−2.081(4)/2.033(5)−

group favor the formation of 6 -C, whereas using a less polar

.080(2)

2.085(4)

solvent mixture leads to the preferential formation of 6 -S.

tilt

1.3(1)

4.2(3)/3.9(3)

The analogous complex featuring 2 was isolated only as a

19.9(2)

1.227(3)

1.361(3)

54.5(3)/−55.2(3)

1.226(6)/1.227(6)

1.360(6)/1.363(6)

123.6(5)/123.4(5)

-S isomer when either a CHCl /ethyl acetate mixture or a

C11O1

CH Cl + methanol/hexane mixture was used for crystal-

C11−N1

lization. The complexes were structurally authenticated by

spectroscopic methods and by an X-ray diﬀraction analysis

(vide infra).

N1−C11O1 122.9(2)

S1−O

1.442(2)−

.461(2)

1.453(4)−1.464(3)/1.449(3)−

1.464(3)

C32−S1

1.804(2)

1.792(4)/1.797(4)

The formation of isomers diﬀering in the coordination of the

pendant amidosulfonate moiety was analyzed by DFT. In

particular, the diﬀerences in the Gibbs energy of the C- and S-

isomers, ΔG = G − G , at 298 K (Table 2) suggested that the

Deﬁnitions: tilt is the dihedral angle between the least-squares

cyclopentadienyl planes; τ stands for the torsion angle C1−Cg1−

Cg2−C6, where Cg1 and Cg2 denote the centroids of the

cyclopentadienyl rings C(1−5) and C(6−10), respectively. Data

for two structurally independent molecules. Further parameters: P1−

Table 2. Gibbs Energy Diﬀerences Computed in CHCl and

B1= 1.919(6)/1.924(6) Å.

Methanol (PCM) between the S- and C-Isomers of 6 , 7 ,

and 7

ΔG = G_S²⁹⁸− G_C(kcal mol⁻¹

298

)

nonisolated phosphine complexes [PdCl(η -C H )(L-κP)] (L

complex

vacuum

CHCl₃

methanol

1 , 2 ), which were treated with Ag[BF ] to remove the Pd-

−12.83

−14.09

2.84

−4.60

−6.19

4.05

0.028

−1.46

8.87

bound halide. The resulting zwitterionic complexes were less

water soluble than the original phosphinoferrocenes. This was

advantageously used during their puriﬁcation: the partitioning

of the crude product between CH Cl and water removed

Et NH)[BF ], and the subsequent ﬂash chromatography and

crystallization furnished pure complexes 6 and 7 as air-stable

Diﬀerences in Gibbs free energies at 298 K. A negative ΔG value

(

3 4

indicates that the S-isomer is energetically favored over the C-isomer;

see the Experimental Section for details. Full computational data are

available in the Supporting Information .

solids.

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.5CHCl are displayed in Figure 2 ; the structures of solvated

Article

isomer with the sulfonate-bound amidophosphine ligand is

Table 3. Selected Distances (Å) and Angles (deg) for 6 -C·

favored for 7 in both CHCl and methanol. Conversely, the

CH Cl ·MeOH and 6 -S·1.5CHCl

C-isomer is preferred for 7 , in line with the experimental

6^P^h-C (Y = O1)

6^P^h-S (Y = O2)

2.3189(7)

param

Pd1−P1

Pd1−Y

results. For complex 6 , both isomers can be isolated

2.3086(7)

2.123(2)

depending on the crystallization conditions. The calculations

2.165(1)

96.16(3)

2.024(2)−2.065(2)

4.3(1)

favored the 6 -S isomer in CHCl as the less polar solvent and

P1−Pd−Y

Fe1−C

tilt

101.11(6)

2.018(3)−2.075(3)

5.0(2)

revealed a slight preference for the 6 -C isomer in methanol,

again in accordance with the experimental observations.

Although the PCM approach used for modeling the solvation

eﬀects has limitations for properly accounting for H-bonding

interactions, which seem to stabilize the C-isomers via

solvation of the uncoordinated sulfonate moiety, our DFT

results are consistent with the general experimental trends.

Consistent with the solid-state results, the solution NMR

59.3(2)

49.4(1)

C11O1

1.257(3)

1.336(4)

1.232(2)

1.357(2)

122.6(2)

1.478(1)/1.451(1)/

1.449(1)

C11−N1

N1−C11O1 120.4(2)

S1−O2/3/4 1.443(2)/1.466(2)/

.448(3)

spectra of 6 and 7 displayed markedly broad signals with a

signiﬁcant temperature dependence. This indicated a net

ﬂuxionality of the complexes in solution, attributed to ligand

shuttling (amide vs sulfonate coordination) and rotation of the

Pd-bound allyl moiety. FTIR spectra of the isomeric complexes

were quite similar, diﬀering mostly in band intensities.

Nonetheless, some diagnostic diﬀerences could be observed

in the region of carbon stretching modes (see Figure S1).

Parameters are deﬁned as for the free ligand; see footnote to Table 1.

(

Pd1···O1 = 2.888(1) Å; the angle between the Pd1···O1

interconnection and the {Pd1,P1,O2} plane is 77.88(5)°),

pointing to a possible “axial” interaction. No such contact is

detected in the structure of 6 -C, where the shortest

intramolecular distances between Pd1 and sulfonate oxygen

atoms exceed 5 Å. The allyl moiety in both structures is

disordered over two positions that are approximately mirror

images with respect to the {Pd1,On,P1} plane (n = 1, 2).

Catalytic Experiments. Arylindoles are recurring motifs in

biologically active molecules and pharmaceuticals. They have

been prepared traditionally using cross-coupling strategies.

The structures of 6 -C·CH Cl ·MeOH and 6 -S·

However, the development of direct C−H arylation, while

challenging because of the intrinsic strength of this bond,

allows direct functionalization of indoles, thus enabling the

simple synthesis of aryl-substituted indoles in a more atom-

economical process. We used this reaction to assess the

properties of palladium catalysts supported by polar ligands 1

and 2 (Scheme 4).

Scheme 4. Direct C−H Arylation of Unprotected Indoles

using Allylpalladium Complexes 6 and 7

Figure 2. Views of the complex molecules in the structures of 6 -C·

CH Cl ·MeOH and 6 -S·1.5CHCl .

7^P^hand 7^C^yare reported in the Supporting Information, which

also provides additional structural diagrams. As stated above,

-C·CH Cl ·MeOH and 6 -S·1.5CHCl diﬀer in coordina-

2 2 3

tion of the amidosulfonate moiety. When the molecular

structures of 6 -C and 6 -S are compared (Table 3),

diﬀerences in the conformation of the 1,1′-disubstituted

ferrocene units can be observed, with the pendant functions

approximately 10° closer in 6 -S. Twisting of the amide

moiety in 6 -C facilitates coordination of the amide oxygen

O1, while in 6 -S, it brings the sulfonate group in the vicinity

The arylation of unprotected indole 8 was performed in

of the palladium atom (the dihedral angles of the amide plane

water using complexes 6 and 7 as the deﬁned precatalysts

and various para-substituted iodoarenes as the arylating agents.

Bromoarenes were found to be unreactive during preliminary

reaction tests. The initial studies were conducted using 1 mol

and ring C(1−5) are 21.6(3)° for 6 -C and 8.8(2)° in the

opposite sense for 6 -S). In addition, coordination of O2

requires rotation of the sulfonate group along the pivotal C32−

S1 bond. Despite these structural changes, the arrangements of

the amidosulfonate chain remain similar (cf. the torsion angles

% of 7 for the reaction between 8 and 4-ﬂuoro-1-

iodobenzene (9a, Scheme 4). As shown in Table 4, the

arylation proceeded with a high selectivity, producing nearly

exclusively (>99%) C2-arylated product 10a. We, however,

take note of the challenges associated with this coupling

reaction under biphasic conditions (see the Experimental

Section) since, despite our eﬀorts, the best yields of arylated

C11−N1−C32−S1 of 99.0(3)° in 6 -C and 95.4(2)° in 6 -

S). The diﬀerence in the ligand bite angles, P1−Pd1−O1 vs

P1−Pd1−O2, is also small (ca. 5°).

Another notable feature is the positioning of the amide

oxygen O1 above the palladium atom in the molecule of 6 -S

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Table 4. Screening of Conditions for the Pd-Catalyzed

Table 5. Palladium-Catalyzed C2−H Arylation of Indole

Indole C2−H Arylation Yielding 2(4-Fluorophenyl)indole

using Substituted Iodoarenes 9b−g

(

10a)

entry

catalyst

solvent

toluene

DMF

base

yield of 10a (%)

(1%)

(3%)

(5%)

(1%)

KHCO₃

AcOH

ethylene carbonate

MeOC H

^K^H^C^O3

entry

catalyst

[PdCl(C H )]

R′

OMe

product

yield (%)

KHCO₃

10b

10c

10d

10e

10f

EtOH

tert-amyl alcohol

dioxane

KHCO₃

K CO

[PdCl(C H )] /PPh

[PdCl(C H )] /PCy HBF

₆Ph

dioxane/H O

H O

KOAc

Conditions: 0.5 mmol of 8, 0.6 mmol of 9a, 1.5 mmol of base, 2 mL

of solvent at 100 °C for 24 h. Yields are from standardized H NMR

spectra and duplicate experiments. MeOC H denotes methyl

cyclopentyl ether. 1:1 (v:v) mixture. Partial loss of selectivity was

^C^F3

observed with the formation of ca. 5% of the C3-arylated isomer.

10g

For conditions, see Table 3. The yields are from standardized H

NMR spectra and duplicate experiments. A loss of selectivity was

observed with the formation of ca. 10% of arylated C3 isomer.

indoles were limited to ca. 50%. As anticipated, the solvent

played a crucial role. The use of classical organic solvents such

as toluene, DMF, AcOH, and dioxane (Table 4, entries 1−3

and 8) or alcohols (entries 6 and 7) and their more innocuous

alternatives (ethylene carbonate and methyl cyclopentyl ether,

entries 4 and 5) provided less than 5% conversion. We

observed a 20% conversion using a 1:1 mixture of dioxane and

water, albeit with a slight loss of selectivity (entry 9).

Pleasingly, the use of pure water resulted in a better conversion

of 25% and full selectivity (entry 10). Gradually increasing the

Considering these results, we utilized the most active catalyst

7^C^yin reaction tests employing iodoarenes 9d−g with diﬀerent

substituents. Thus, compounds 10d,e, incorporating the 4-

methoxyphenyl and 4-(triﬂuoromethyl)phenyl moieties, re-

spectively, were obtained in 47% and 40% yields (entries 12

and 13). The reaction of unsubstituted iodobenzene 9f

proceeded with a lower conversion (36% of 10f, entry 14),

whereas arylation with its electron-poor cyano derivative 9g

amount of catalyst 7 up to 5 mol % (entries 11 and 12)

allowed us to improve this yield to 40% while the C2 selectivity

(

15% of 10g, entry 15) was more diﬃcult. Surprisingly, catalyst

was conserved. Various bases other than KHCO were also

showed a higher eﬃciency for electron-rich iodoarenes,

tested, albeit with detrimental eﬀects on either selectivity or

22b

which is rather unusual. Increasing the reaction time and the

amount of catalysts had only marginal eﬀects on the yield of

the arylation product.

conversion, as illustrated for K CO and KOAc (entries 13 and

4).

On the basis of these results, we used water as the solvent

and KHCO as the base for subsequent experiments aimed at

CONCLUSION

comparing the activity (at 1 mol %) of palladium complexes 6

■

and 7 in the coupling of 8 with functionalized iodoarenes 9b−

In this paper, we have described the synthesis of two new

phosphinoferrocene ligands possessing hydrophilic amidosul-

fonate pendants and tert-butyl substituents that limit the

overall molecular mobility. Together with their analogues,

which lack the tert-butyl substituents, these compounds were

used to prepare zwitterionic (η -allyl)Pd complexes. The

formation of isomers diﬀering in the coordination of the

pendant amidosulfonate was noted, controlled by crystalliza-

tion conditions. This behavior, conﬁrmed by the results of

g to give arylindoles 10b−g (Table 5). When the simple

allylpalladium(II) complex [PdCl(η -C H ) ] in the absence

5 2 2

of any ligand (entry 1) or with the “classical” tertiary

phosphine ligands PPh and in situ deprotected PCy (entries

and 3) was used, the arylation of 8 using 4-bromo-1-

iodobenzene (9b) occurred only marginally. A comparison of

the results achieved with palladium complexes stabilized by the

polar phosphinoferrocene amidosulfonate ligands with (7 ) or

without (6 ) the tBu groups revealed that the activity

DFT calculations, underlines the hybrid nature of ligands 1

practically doubled when tBu groups were present (entries

and 2 , wherein the soft phosphine moiety forms a stronger

−7). The presence of dicyclohexylphosphino groups was also

bond to Pd(II) in comparison to the hard oxygen donors,

which in turn results in ﬂuxional coordination. As deﬁned

precatalysts, the allylpalladium complexes mediate direct C−H

arylation of indole with aryl iodides. Of note is the fairly low

catalyst amount (1 mol %), high C2 selectivity, and the

absence of the use of an additional phase-transfer agent in this

catalytic system.

beneﬁcial, and complex 7 provided 10b in the best, albeit still

modest, yield of 19%. This general trend was conﬁrmed for the

reactions producing p-tolyl derivative 10c, since 7 provided a

8% yield of this arylindole (entry 11), while 7 achieved only

a 31% yield (entry 10), and the non-tert-butylated counterparts

and 6 were found to be ineﬀective (entries 8 and 9).

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temperature for 30 min. Then, the reaction mixture was diluted with

dichloromethane (5 mL) and concentrated under reduced pressure.

The oily residue was diluted by degassed CH Cl /MeOH (20/1) and

transferred onto the top of a silica gel column packed with the same

solvent. The ﬁrst, minor, yellow band was discarded, and the

EXPERIMENTAL SECTION

■

Materials and Methods. All reactions were performed under an

argon or nitrogen atmosphere by using standard Schlenk techniques.

Ph 15 Cy

Racemic 1,1′-dibromo-3,3′-di-tert-butylferrocene (3), 4 , 4 ·BH ,

Ph 16 Ph

Cy9c

Cy·BH , 5 , 1 , and 1

were prepared as previously reported.

following, major, red band was collected and evaporated to aﬀord acid

Anhydrous THF and dichloromethane were obtained from a Puresolv

MD5 solvent puriﬁcation system. Solvents used for chromatography

and crystallizations were of reagent grade and were employed without

additional puriﬁcation. NMR spectra were recorded at 25 °C on

Varian UNITY Inova 400 and Bruker Avance 500 and 600

spectrometers. Chemical shifts (δ/ppm) are given relative to internal

tetramethylsilane or, alternatively, to residual signals of the deuterated

as a red-orange solid. Yield: 326 mg (74%).

H NMR (400 MHz, DMSO-d ): δ 12.07 (br s, 1 H, COOH), 4.59

(

br s, 1 H, Cp), 4.35 (br s, 1 H, Cp), 4.21 (br s, 1 H, Cp), 4.09 (br s,

H, Cp), 4.05 (br s, 1 H, Cp), 3.88 (br s, 1 H, Cp), 1.95−1.53 (br m,

2 H, Cy), 1.38−0.76 (br m, 10 H, Cy), 1.22 (s, 9 H, tBu), 1.20 (s, 9

H, tBu) ppm. C{ H} NMR (101 MHz, DMSO-d ): δ 172.16

(

ipso

COOH), 104.67 (C -tBu of Cp), 104.20 (d, J = 3 Hz, C -tBu of

solvents ( H and C NMR) and to external 85% aqueous H PO ( P

ipso

Cp), 77.41 (d, J = 21 Hz, C -P of Cp), 71.46 (C -COOH of Cp),

1.01 (br s, CH of Cp), 70.07 (CH of Cp), 69.99 (d, J ≈ 14 Hz, CH

of Cp), 69.09 (CH of Cp), 68.00 (CH of Cp), 67.70 (CH of Cp),

2.84 (d, J = 13 Hz, Cy), 32.79 (d, J = 13 Hz, Cy), 31.54 (d, J = 3 Hz,

NMR). FTIR spectra were recorded on a Nicolet 6700 spectrometer

−

in the range of 400−4000 cm . ESI mass spectra were obtained with

a Bruker Compact Q-TOF spectrometer. Elemental analyses were

performed using a PerkinElmer PE 2400 CHN analyzer or a Thermo

Electron Flash EA 1112 Series instrument.

ipso

CH of tBu), 31.26 (CH of tBu), 31.03 (C of tBu), 30.89 (C of

tBu), 30.40 (2 × Cy), 30.27 (d, J = 8 Hz, Cy), 29.96 (d, J = 13 Hz,

Synthesis of 4 . Under an argon atmosphere, racemic 1,1′-

Cy), 26.79 (Cy), 26.69 (2 × Cy), 26.60 (Cy), 26.19 (Cy), 26.06 (Cy)

dibromo-3,3′-di-tert-butylferrocene (3; 0.912 g, 2.0 mmol) was

dissolved in dry THF (10 mL) in an oven-dried, two-necked reaction

ﬂask equipped with a stirring bar and an argon inlet. The solution was

cooled with an acetone/liquid nitrogen bath to approximately −80 °C

before n-butyllithium (0.80 mL of 2.5 M in hexanes, 2.0 mmol) was

introduced, whereupon the initially yellow solution turned orange-red.

The mixture was stirred and cooled for 30 min, and then neat ClPCy₂

ppm. P{ H} NMR (162 MHz, DMSO-d ): δ −10.2 (s) ppm. The

signal due to the corresponding phosphine oxide appears at δ 45.2

(

s). FTIR (ATR diamond): ν_m_a_x2957 m, 2918 m, 2850 m, 1666 vs

CO), 1489 m, 1479 m, 1464 m, 1446 m, 1390 w, 1366 m, 1339 w,

313 m, 1263 s, 1173 m, 1070 w, 1039 m, 1022 w, 996 w, 968 m, 939

m, 917 m, 885 w, 852 m, 827 m, 818 m, 783 w, 753 m, 676 w, 630 w,

614 m, 564 m, 532 m, 512 m, 499 s, 479 m, 441 m cm . Anal. Calcd

−1

(

0.49 mL, 2.2 mmol) was added dropwise. The resulting mixture was

for C H FePO (538.5): C, 69.14; H, 8.80. Found: C, 69.05; H,

stirred at −80 °C for another 30 min and then gradually warmed to

room temperature over 90 min. The crude reaction mixture was

concentrated under reduced pressure, and the red oily residue was

partitioned between dichloromethane and water (10 mL each). The

organic phase was washed with brine, dried over magnesium sulfate,

and evaporated, leaving an orange oil, which was taken up with

degassed pentane and transferred onto the top of a silica gel column

packed in the same solvent. The ﬁrst yellow band, removed by

pentane and containing mostly bromo- and 1,1′-dibromo-3,3′-di-tert-

butylferrocene (80 mg), was discarded, and the second major orange

band eluted by degassed pentane/dichloromethane (4/1) was

.60. ESI-MS: m/z 539 ([M + H] ).

Synthesis of 2 . Under argon, acid 5 (524.2 mg, 1.0 mmol)

and 1-hydroxybenzotriazole (HOBt) (162.1 mg, 1.2 mmol) were

suspended in a mixture of dry acetonitrile (19 mL) and triethylamine

(

1.3 mL). The mixture was cooled in an ice bath and treated with neat

N-(3-(dimethylamino)propyl)-N′-ethylcarbodiimide (EDC; 0.2 mL,

.2 mmol). After the mixture was stirred at 4 °C for 30 min, solid

aminomethanesulfonic acid (888.0 mg, 8.0 mmol) was added, and

this mixture was stirred at room temperature for 24 h. Then, it was

ﬁltered using a 0.45 μm PTFE syringe ﬁlter and evaporated. The

obtained crude product was puriﬁed by chromatography over a silica

gel column using dichloromethane/methanol/triethylamine (90/9/1)

as the eluent. The second band was collected and evaporated to give

collected and evaporated, providing pure 4 as a yellow-orange

foam. Yield: 828 mg (72%).

H NMR (500 MHz, CDCl ): δ 4.29 (dd, J = 2.4, 1.3 Hz, 1 H,

compound 2 as an orange solid. Yield: 686.3 mg (95%). Single

Cp), 4.15−4.13 (m, 1 H, Cp), 4.12 (t, J = 1.5 Hz, 1 H, Cp), 4.03 (dd,

J = 2.4, 1.5 Hz, 1 H, Cp), 3.92 (dd, J = 2.5, 1.5 Hz, 1 H, Cp), 3.79 (q,

J = 1.4 Hz, 1 H, Cp), 2.00−1.63 (br m, 12 H, Cy), 1.41−0.99 (br m,

crystals were obtained from CH Cl /AcOEt.

H NMR (400 MHz, CD Cl ): δ 9.86 (br s, 1 H, HNEt ), 7.63−

7.55 (m, 2 H, Ph), 7.40−7.35 (m, 3 H, Ph), 7.27−7.16 (m, 5 H, Ph),

0 H, Cy), 1.27 (s, 9 H, tBu), 1.22 (s, 9 H, tBu) ppm. C{ H} NMR

6.59 (m, 1 H, NHCO), 4.66 (dd, J = 13.4, 8.1 Hz, 1 H, CH ), 4.58

ipso

(

126 MHz, CDCl ): δ 105.06 (d, J = 2 Hz, C -tBu of Cp), 101.20

(dd, J = 2.6, 1.4 Hz, 1 H, Cp), 4.37 (t, J = 1.5 Hz, 1 H, Cp), 4.20 (dd,

J = 2.4, 1.5 Hz, 1 H, Cp), 4.18 (dd, J = 2.6, 1.5 Hz, 1 H, Cp), 4.15 (dt,

ipso

-tBu of Cp), 78.83 (d, J = 19 Hz, C -P of Cp), 78.71 (C

Br), 73.10 (d, J = 14 Hz, CH of Cp), 72.73 (d, J = 7 Hz, CH of Cp),

0.06 (CH of Cp), 69.45 (d, J = 2 Hz, CH of Cp), 68.56 (CH of Cp),

4.58 (CH of Cp), 33.86 (d, J = 13 Hz, Cy), 33.38 (d, J = 12 Hz, Cy),

J = 2.8, 1.5 Hz, 1 H, Cp), 4.14 (dd, J = 13.4, 4.8 Hz, 1 H, CH ), 3.95

(dt, J = 2.6, 1.3 Hz, 1 H, Cp), 3.07 (dq, J = 7.2, 3.2 Hz, 6 H,

CH CH N), 1.27 (t, J = 1.3 Hz, 9 H, CH CH N),1.27 (s, 9 H, tBu),

ipso

1.83 (d, J = 2 Hz, CH of tBu), 31.78 (CH of tBu), 31.68 (C of

0.99 (s, 9 H, tBu) ppm. C{ H} NMR (101 MHz, CD Cl ): δ 170.0

2 2

ipso

tBu), 31.56 (C of tBu), 30.95 (Cy), 30.81 (d, J = 14 Hz, Cy), 30.71

d, J = 10 Hz, Cy), 30.70 (Cy), 30.48 (d, J = 10 Hz, Cy), 27.57 (d, J =

(CONH), 141.0 (d, J = 12 Hz, C of Ph), 138.1 (d, J = 10 Hz,

PC PC

ipso

(

of Ph), 135.5 (d, J = 22 Hz, CH of Ph), 132.7 (d, J = 19 Hz, CH

para

1 Hz, Cy), 27.50 (d, J = 10 Hz, Cy), 27.47 (Cy), 26.75 (Cy), 26.63

of Ph), 129.7 (CH of Ph), 128.9 (d, J = 8 Hz, CH of Ph), 128.6 (d,

J = 6 Hz, CH of Ph), 128.4 (CH of Ph), 107.3 (d, J = 6 Hz, C

tBu of Cp), 105.6 (C -tBu of Cp), 76.1 (d, J = 7 Hz, C -P of

Cp), 75.5 (C -CONH of Cp), 73.6 (d, J = 25 Hz, CH of Cp), 71.7

Cy) ppm. ³¹P{ H} NMR (202 MHz, CDCl ): δ −8.8 (s) ppm. FTIR

para

ipso

ATR diamond): ν_m_a_x2953 m, 2917 vs, 2847 s, 1480 m, 1461 m,

ipso

446 m, 1381 m, 1358 m, 1297 w, 1276 m, 1197 w, 1174 m, 1074 w,

045 m, 1022 w, 997 w, 917 s, 902, w, 879 s, 843 s, 801 m, 747 w, 675

(CH of Cp), 69.7 (CH of Cp), 69.05 (CH of Cp), 68.95 (CH of Cp),

w, 630 w, 594 w, 550 w, 530 w, 514 s, 497 vs, 478 s, 445 m, 429 m

67.2 (d, J = 3 Hz, CH of Cp), 56.1 (CH SO ), 46.5 (CH CH N),

−

ipso

cm . Anal. Calcd for C H BrFeP (573.4): C, 62.84; H, 8.09.

31.7 (CH of tBu), 31.5 (CH of tBu), 31.2 (C of tBu), 30.7 (C of

Found: C, 63.09; H, 7.92. ESI-MS: m/z 573 ([M + H] ).

tBu), 8.8 (CH CH N) ppm. P{ H} NMR (162 MHz, CD Cl ): δ

Synthesis of 5 . Compound 4 (0.470 g, 0.82 mmol) was

dissolved in dry THF (10 mL) under an argon atmosphere. The

solution was cooled in an acetone/liquid nitrogen bath to −80 °C,

and n-butyllithium (0.56 mL of 1.6 M in hexanes, 0.90 mmol) was

added with continuous stirring. The yellow solution turned orange-

red after the addition. The resulting mixture was stirred at −80 °C for

an additional 30 min before a stream of carbon dioxide was passed

through the mixture, ﬁrst at −80 °C for 2.5 h and then at room

−18.4 (s) ppm. FTIR (Nujol): ν 3335 w (N−H), 3051 m (N−H),

max

2720 w, 2688 w, 2525 w, 2360 w, 2342 w, 1717 w, 1656 s (CO),

1585 w, 1569 w, 1532 m, 1316 w, 1299 w, 1262 m, 1212 m, 1175 m

(SO), 1153 m (P−C), 1104 w, 1087 w, 1079 w, 1071 w, 1036 s

(SO), 971 w (P−C), 930 w, 918 w, 907 w, 895 w, 876 w, 864 w,

849 w, 830 w, 813 w, 766 w, 751 m, 743 m, 699 m, 675 w, 669 w, 626

w, 607 m, 539 m, 530 m, 514 m, 497 m, 479 m, 464 w, 442 m, 424 m,

−

411 m cm . Anal. Calcd for C H N PO FeS (720.28): C, 63.33; H,

939

Organometallics 2021, 40, 1934−1944

Organometallics

Article

.41; N, 3.89. Found: C, 63.03; H, 7.15; N, 4.05. ESI-MS: m/z 618

(Cⁱ^p^s^o-CONH of Cp), 72.44 (d, J = 5 Hz, CH of Cp), 70.96 (d, J = 7

−

ipso

([M − HNEt ] ).

Hz, CH of Cp), 70.50 (d, J = 55 Hz, C -P of Cp), 69.93 (CH of

Synthesis of 2 . An oven-dried, two-necked ﬂask equipped with

Cp), 69.48 (CH of Cp), 69.06 (CH of Cp), 66.81 (CH of Cp), 56.17

an argon inlet and stirring bar was charged with the acid 5 (619 mg,

.15 mmol) and HOBt (212 mg, 1.38 mmol), ﬂushed with argon, and

(CH SO ), 46.51 (CH CH N), 33.51 (d, J = 10 Hz, Cy), 33.18 (d, J

ipso

= 10 Hz, Cy), 32.20 (CH of tBu), 31.75 (CH of tBu), 31.17 (C of

tBu), 31.03 (C of tBu), 28.19 (Cy), 28.14 (Cy), 27.95 (Cy), 27.84

ipso

sealed. The solids were dissolved by adding dry acetonitrile (20 mL)

and degassed triethylamine (8 mL). The solution was cooled on ice,

before neat EDC (0.24 mL, 1.38 mmol) was introduced, followed by

solid aminomethanesulfonic acid (1.022 g, 9.20 mmol). The reaction

mixture was stirred at room temperature for 24 h and then

evaporated. The solid residue was taken up with a dichloro-

methane/methanol/triethylamine (95/4/1) mixture and transferred

onto the top of a silica gel column. Elution with the same solvent

mixture led to the development of a pale orange band, which was

discarded, and a major orange band, which was collected and

evaporated. The oily residue was dissolved in hot ethyl acetate (5 mL)

and crystallized by cooling to 4 °C. The separated orange crystalline

(Cy), 27.40 (d, J = 11 Hz, Cy), 27.39 (Cy), 27.27 (Cy), 27.21 (d, J ≈

12 Hz, Cy), 26.52 (Cy), 26.47 (Cy), 9.27 (CH CH N) ppm. P{ H}

NMR (162 MHz, CD Cl ): δ 25.2 (br s) ppm. FTIR (Nujol): ν

max

3412 m, 2377 m (borane), 2274 w, 1648 m (CO), 1540 m, 1263 m,

202 m, 1178 m, 1062 m, 1038 m, 972 w, 931 w, 920 w, 903 w, 890

w, 853 w, 822 w, 755 w, 722 w, 670 w, 616 w, 596 w, 519 w, 473 w,

−

(

35 w cm . Anal. Calcd for C H N BFePO S (746.7): C, 61.13; H,

38 68 2 4

.18; N, 3.75. Found: C, 61.07; H, 9.35; N, 3.35. ESI-MS: m/z 644

[M − HNEt ] ).

Deprotection of 2 ·BH . Compound 2 ·BH (691 mg, 1.0

mmol) was dissolved in morpholine (7 mL). The mixture was

solid was isolated by suction and dried under vacuum. Yield of 2 :

degassed by three freeze−pump−thaw cycles and then heated at 65

596 mg (71%).

C for 16 h before evaporation under reduced pressure. The oily

H NMR (400 MHz, DMSO-d ): δ 9.29 (br s, 1 H, HNEt ), 7.74

residue was transferred onto the top of a silica gel column packed in

degassed CH Cl /MeOH/Et N (100/5/5). A single orange band was

(

dd, J = 7.7, 5.0 Hz, 1 H, NHCO), 4.86 (dd, J = 2.6, 1.4 Hz, 1 H, Cp),

.55 (t, J = 1.5 Hz, 1 H, Cp), 4.26 (dd, J = 13.0, 7.6 Hz, 1 H,

eluted with degassed CH Cl /MeOH (20/1) and evaporated. The

CHSO ), 4.22 (dd, J = 2.5, 1.6 Hz, 1 H, Cp), 4.15−4.13 (m, 1 H,

Cp), 4.00 (dd, J = 2.5, 1.6 Hz, 1 H, Cp), 3.84 (q, J = 1.5 Hz, 1 H, Cp),

gummy residue was crystallized from hot ethyl acetate (ca. 5 mL) to

produce 2 as an orange-red microcrystalline solid (487 mg, 66%).

.79 (dd, J = 13.0, 4.9 Hz, 1 H, CHSO ), 3.08 (q, J = 7.3 Hz, 6 H,

Synthesis of 6 . Solid [Pd(μ-Cl)(η -C H )] (18.3 mg, 0.05

CH CH N), 2.10−2.20 (m, 1 H, Cy), 1.95−0.85 (m, 20 H, Cy), 1.21

mmol) and 1 (60.9 mg, 0.10 mmol) were dissolved in dry

dichloromethane (5 mL). After the mixture was stirred for 30 min, a

solution of silver(I) tetraﬂuoroborate (19.4 mg, 0.10 mmol) in

MeOH (1 mL) was added, causing immediate separation of an oﬀ-

white precipitate (AgCl) and a color change from orange to orange-

brown. The resulting mixture was stirred for 1 h and ﬁltered through a

plug of Dicalite ﬁlter aid. The ﬁltrate was evaporated and the residue

redissolved in dichloromethane (5 mL). The solution was washed

three times with distilled water (5 mL each) to remove Et NH[BF ],

(s, 9 H, tBu), 1.18 (t, J = 7.3 Hz, 9 H, CH CH N), 1.17 (s, 9 H, tBu),

3 2

.68−0.55 (m, 1 H, Cy) ppm. C{ H} NMR (101 MHz, DMSO-d ):

ipso

δ 168.45 (CONH), 104.46 (d, J = 4 Hz, C -tBu of Cp), 103.76

ipso

-tBu of Cp), 76.11 (d, J = 20 Hz, C -P of Cp), 75.59 (C

CONH of Cp), 70.39 (d, J = 20 Hz, CH of Cp), 69.46 (CH of Cp),

9.30 (CH of Cp), 68.72 (CH of Cp), 67.50 (CH of Cp), 66.29 (CH

of Cp), 55.50 (CH SO ), 45.65 (CH CH N), 33.28 (d, J = 15 Hz,

Cy), 32.38 (d, J = 12 Hz, Cy), 31.79 (d, J = 3 Hz, CH of tBu), 31.55

ipso

of tBu), 31.50 (CH of tBu), 31.37 (C of tBu), 30.73 (d, J =

dried over magnesium sulfate, and evaporated. The residue was taken

7 Hz, Cy), 30.38 (Cy), 30.29 (Cy), 29.38 (d, J = 10.5 Hz, Cy), 28.69

up with dichloromethane/methanol (20/1) and ﬁltered through a pad

(br s, Cy), 27.01 (d, J = 4 Hz, Cy), 26.89 (d, J = 5 Hz, Cy), 26.69 (d, J

of silica gel to provide pure 6 as an orange solid after evaporation.

8 Hz, Cy), 26.62 (d, J = 6 Hz, Cy), 26.21 (Cy), 26.10 (Cy), 8.57

Crystallization by liquid-phase diﬀusion of pentane into a solution of

(

CH CH N) ppm. P{ H} NMR (162 MHz, DMSO-d ): δ −10.0

the complex in CH Cl /MeOH (20/1) gave orange crystals. Yield: 54

(

s) ppm. The signal of the respective phosphine oxide is observed at

mg (82%). Crystals used for X-ray diﬀraction analysis were grown

from chloroform/pentane.

δ_P45.2 (s). FTIR (ATR diamond): ν_m_a_x3345 w, 3082 w, 2915 m,

848 m, 2696 w, 1651 m (CO), 1522 m, 1484 m, 1449 m, 390 w,

363 w, 1313 w, 1256 m, 1233 m, 1209 m, 1163 s, 1075 w, 1035 s,

69 w, 930 w, 919 w, 897 w, 848 m, 814 w, 791 w, 772 w, 750 w, 669

H NMR (400 MHz, CDCl , 25 °C): δ 7.49−7.36 (m, 10 H, Ph),

.32 (t, J = 6.7 Hz, 1 H, NH), 5.78 (qi, J = 9.9 Hz, 1 H, C H ), 5.60−

−

5.00 (very br s, 1 H, C H ), 5.00−4.30 (br s, 2 H of Cp and 1 H of

w, 598 m, 532 m, 519 m, 487 m, 441 w cm . Anal. Calcd for

C H N FeO PS (732.8): C, 62.28; H, 8.94; N, 3.82. Found: C,

C H ), 4.84 (t, J = 1.9 Hz, 2 H, Cp), 4.49 (br s, 2 H, Cp), 4.21 (t, J =

−

1.9 Hz, 2 H, Cp), 3.60−2.60 (very br s, 2 H, C H or CH ) ppm. H

1.90; H, 8.68; N, 3.65. ESI-MS: m/z 630 ([M − HNEt ] ).

Cy Cy

NMR (400 MHz, CDCl , 50 °C): δ 7.51−7.36 (m, 10 H, Ph), 7.06 (t,

Synthesis of 2 ·BH . Compound 2 ·BH was prepared

J = 6.7 Hz, 1 H, NH), 5.76 (qi, J = 9.9 Hz, 1 H, C H ), 4.75 (t, J = 1.9

similarly, starting from 5 ·BH (1.10 g, 2.0 mmol) and HOBt

Hz, 2 H, Cp), 4.68 (br s, 2 H, C H or Cp), 4.66 (br s, 2 H, C H or

(

0.324 g, 2.4 mmol) in dry acetonitrile (38 mL) and triethylamine

2.6 mL). The suspension was cooled in an ice bath and treated with

Cp), 4.51 (br t, J = 1.8 Hz, 2 H, Cp), 4.35−3.09 (br s, 2 H, C H or

CH ), 4.19 (t, J = 1.9 Hz, 2 H, Cp) ppm. At both temperatures,

neat EDC (0.40 mL, 2.4 mmol). The mixture was stirred at 0 °C for

signals due to two hydrogen atoms of C H and/or CH SO were not

0 min, and aminomethanesulfonic acid (1.78 g, 16.0 mmol) was

observed due to extensive broadening. P{ H} NMR (161 MHz,

CDCl , 25 °C): δ 14.8 (s) ppm. FTIR of 6 -C (DRIFTS, KBr): ν

312 w, 3233 w, 3088 w, 1641 m, 1596 m, 1541 m, 1480 w, 1436 m,

402 w, 1387 w, 1314 w, 1257 m, 1228 m, 1220 m, 1185 m, 1154 s,

099 w, 1074 w, 1044 m, 1035 w, 963 w, 912 w, 897 w, 844 w, 828 w,

51 m, 694 m, 611 m, 541 w, 532 m, 516 s, 490 m, 469 m, 450 m

added. The resultant mixture was stirred at room temperature for 24 h

and ﬁltered through a 0.45 μm PTFE syringe ﬁlter, and the ﬁltrate was

evaporated. The crude product was puriﬁed by chromatography over

silica gel and eluted with a dichloromethane/methanol/triethylamine

max

mixture (90/9/1). The main second band was collected and

evaporated, leaving 2 ·BH as an orange solid. Yield: 1.42 g

−

cm . FTIR of 6 -S (DRIFTS, KBr): ν 3319 s, 3116 w, 300 w,

(95%). Single crystals were obtained from CH Cl /AcOEt.

max

H NMR (400 MHz, CD Cl ): δ 6.62−6.58 (m, 1 H, NH), 4.75

3085 w, 3057 m, 2955 m, 2871 w, 1641 s, 1586 w, 1538 m, 1532 m,

1481 w, 1456 w, 1435 m, 1402 w, 1388 w, 1379 w, 1363 w, 1312 m,

1258 s, 1214 m, 1155 vs, 1099 m, 1074 w, 1058 w, 1027 m, 1019 m,

911 w, 892 w, 869 w, 857 w, 823 w, 817 w, 747 m, 705 m, 694 m, 668

w, 626 w, 613 m, 590 w, 583 w, 552 w, 541 w, 528 m, 514 m, 494 m,

(dd, J = 2.6, 1.4 Hz, 1 H, Cp), 4.67 (t, J = 1.5 Hz, 1 H, Cp), 4.58 (dd,

J = 13.5, 7.5 Hz, 1 H, CH ), 4.40−4.37 (m, 1 H, Cp), 4.35 (dd, J =

.6, 1.6 Hz, 1 H, Cp), 4.31−4.29 (m, 1 H, Cp), 4.23 (dd, J = 13.5, 5.5

Hz, 1 H, CH ), 4.10 (q, J = 1.5 Hz, 1 H, Cp), 3.90−3.35 (very br s,

−

H, NH of HNEt ), 3.01 (q, J = 7.3 Hz, 6 H, CH CH N), 1.99−1.61

480 w, 469 m, 451 w, 439 m, 430 w cm . Anal. Calcd for

26NFeO Cl (679.28): C, 48.27; H, 3.95; N, 2.06.

(

m, 12 H, Cy), 1.45−0.98 (m, 12 H, Cy), 1.29 (s, 9 H, tBu), 1.26 (s, 9

PPdS·0.3CH

H, tBu), 1.25 (t, J = 7.3 Hz, 9 H, CH CH N), 0.85−0.12 (m, 3 H,

BH ) ppm. C{ H} NMR (101 MHz, CD Cl ): δ 169.88 (CONH),

Found: C, 48.34; H, 4.03; N, 2.12. The amount of clathrated solvent

was veriﬁed by NMR analysis (δ 5.30). HR ESI-MS calc. for

ipso

06.84 (d, J = 6 Hz, C -tBu of Cp), 106.61 (C -tBu of Cp), 76.05

C H NNaPO FeSPd ([M + Na] ): 675.9597, found: 675.9613.

940

Organometallics 2021, 40, 1934−1944

Organometallics

Article

Synthesis of 6 . Compound 6 was prepared similarly, using

1.23 (s, 9 H, tBu), 2.20−0.64 (m, 21 H, Cy) ppm. Two signals with

[

Pd(μ-Cl)(η -C H )] (17.5 mg, 0.048 mmol) and 1 (59.5 mg,

integral intensities corresponding to two hydrogen atoms at C H

.096 mmol) in dry dichloromethane (5 mL) and Ag[BF ] (18.7 mg,

were not observed due to broadening. H NMR (400 MHz, CDCl ,

.096 mmol) in MeOH (1 mL). Puriﬁcation and crystallization as

50 °C): δ 6.74 (br d, J = 10.7 Hz, 1 H, NH), 5.67 (qi, J = 9.9 Hz, 1 H,

described above produced 6 as an orange crystalline solid. Yield: 51

mg (80%).

C H ), 5.28 (dt, J = 2.8, 1.5 Hz, 1 H, Cp), 5.12 (dd, J = 13.6, 10.6 Hz,

1 H, C H ), 4.80−4.04 (very br s, 1 H, C H ), 4.75 (dd, J = 2.7, 1.4

H NMR (400 MHz, CDCl , 25 °C): δ 7.87 (t, J = 6.7 Hz, 1 H,

Hz, 1 H, Cp), 4.72 (t, J = 1.6 Hz, 1 H, Cp), 4.30 (dd, J = 2.7, 1.8 Hz,

1 H, Cp), 4.23 (dt, J = 2.5, 1.2 Hz, 1 H, Cp), 4.14 (dd, J = 2.5, 1.6 Hz,

1 H, Cp), 4.04−3.31 (very br s, 1 H, C H ) 3.94 (dd, J = 13.5, 2.9 Hz,

NH), 5.71 (qi, J = 9.9 Hz, 1 H, C H ), 4.96 (br m, 2 H, Cp), 4.74 (br

m, 2 H, Cp), 4.62 (br d, J = 6.6 Hz, 2 H, CH ), 4.53 (br m, 2 H, Cp),

.41 (br m, 2 H, Cp). 4.00−3.20 (very br s, 2 H, C H ), 3.20−2.50

1 H, C H ), 3.48 (br s, 2 H, CH SO ), 2.66−2.57 (m, 1 H, Cy),

(

very br s, 2 H, C H ), 2.09−1.65 (m, 11 H, Cy), 1.41−1.09 (m, 11

2.24−0.70 (m, 21 H, Cy), 1.34 (s, 9 H, tBu), 1.24 (s, 9 H, tBu) ppm.

H, Cy) ppm. P{ H} NMR (161 MHz, CDCl , 25 °C): δ 27.3 (s)

P{ H} NMR (161 MHz, CDCl , 25 °C): δ 27.2 (br s) ppm. FTIR

ppm. The data agree with those found in the literature.

(DRIFTS, KBr): ν_m_a_x3599 w, 3450 w, 3240 m, 3102 w, 3062 w, 2958

Synthesis of 7 . The solids [Pd(μ-Cl)(η -C H )] (56.0 mg,

m, 2930 s, 2853 m, 1644 w, 1574 s, 1484 w, 1456 m, 1448 m, 1407 w,

.15 mmol) and 2 (216.2 mg, 0.30 mmol) were dissolved in dry

389 w, 1365 m, 1332 m, 1290 w, 1271 m, 1223 m, 1197 m, 1178 s,

155 m, 1114 w, 1092 w, 1038 m, 1007 w, 966 w, 918 w, 907 w, 890

dichloromethane (10 mL). After the mixture was stirred for 30 min, a

solution of Ag[BF ] (59.6 mg, 0.30 mmol) in MeOH (1.5 mL) was

w, 855 w, 831 w, 813 w, 771 w, 746 m, 679 w, 616 m, 592 w, 539 w,

added, resulting in the separation of an oﬀ-white solid (AgCl) and a

color change from orange to orange-brown. The resulting mixture was

stirred for 1 h and ﬁltered through a cotton plug. The ﬁltrate was

evaporated and redissolved in dichloromethane (10 mL). The

solution was washed three times with 10 mL of distilled water to

remove Et NH[BF ], dried over magnesium sulfate, and evaporated.

The residue was dissolved in dichloromethane/methanol (20/1) and

ﬁltered through a pad of silica gel. The ﬁltrate was evaporated, and the

residue was crystallized by dissolving in dichloromethane/methanol

−1

25 m, 508 m, 493 m, 478 w cm . Anal. Calcd for

C H NFeO PPdS·0.3CH Cl (803.6): C, 52.76; H, 6.85; N, 1.74.

Found: C, 52.85; H, 6.84; N, 1.56. The amount of residual solvent

was conﬁrmed by NMR analysis (δ 5.30). HR ESI-MS: calcd for

C H NNaPO FeSPd ([M + Na] ) 800.17876, found 800.18026.

Catalytic Experiments. In air, the preformed catalyst 7 or 6 (1

mol % based on indole) was placed into a Schlenk tube equipped with

a stirring bar, followed by indole (58.6 mg, 0.50 mmol) and KHCO₃

as the base (150 mg, 1.50 mmol; 3 equiv). Solid iodoarenes (0.60

mmol, 1.2 equiv) were added at this stage before deoxygenating the

solid mixture through three vacuum/argon cycles. Liquid iodoarenes

were added by syringe after deoxygenation. Next, 2 mL of degassed

water (bubbled for 30 min with argon) was added and the Schlenk

tube was transferred into a preheated oil bath (100 ± 2 °C) and

stirred for 24 h. All reactions were clearly biphasic, potentially limiting

the mass transfer, which was also the limitation for the conversion.

The reaction was terminated by cooling to room temperature and

adding dichloromethane (5 mL). The organic phase was separated,

and the water phase was washed two times using 5 mL of

dichloromethane. The combined organic phases were dried over

(

20/1, 5 mL) and layering with pentane (ca. 15 mL). The crystals,

which separated for several days, were ﬁltered oﬀ and dried under

vacuum to give 7 as an orange crystalline solid. Yield: 196 mg

(85%).

H NMR (400 MHz, CDCl , 25 °C): δ 7.84−7.75 (m, 2 H, Ph),

.53−7.47 (m, 3 H, Ph), 7.37−7.24 (m, 3 H, Ph), 7.06−6.98 (m, 2 H,

Ph), 6.62 (dd, J = 10.8, 2.2 Hz, 1 H, NH), 5.79 (br s, 1 H, C H ),

.63 (br s, 1 H, Cp), 5.30 (dd, J = 13.6, 11.0 Hz, 1 H, C H ), 4.77 (br

3 5

s, 1 H, Cp), 4.71 (dd, J = 2.7, 1.4 Hz, 1 H, Cp), 4.27 (dd, J = 2.6, 1.8

Hz, 1 H, Cp), 4.17 (dd, J = 2.5, 1.6 Hz, 1 H, Cp), 4.10−2.50 (very br

s, 1 H, C H or CH SO ), 3.97 (dd, J = 13.7, 2.6 Hz, 1 H, C H ), 3.72

(

td, J = 2.1, 1.4 Hz, 1 H, Cp), 1.37 (s, 9 H, tBu), 0.82 (s, 9 H, tBu)

MgSO and evaporated after ﬁltration. The resulting crude products

ppm. H NMR (400 MHz, CDCl , 50 °C): δ 7.84−7.77 (m, 2 H, Ph),

were dissolved in DMSO-d and analyzed by NMR spectroscopy.

.51−7.47 (m, 3 H, Ph), 7.36−7.24 (m, 3 H, Ph), 7.06−6.99 (m, 2 H,

X-ray Crystallography. Full-sphere diﬀraction data (±h,±k,±l,

Ph), 6.54 (dd, J = 11.1, 2.1 Hz, 1 H, NH), 5.78 (qi, J = 9.8 Hz, 1 H,

C H ), 5.64 (dt, J = 3.0, 1.5 Hz, 1 H, Cp), 5.27 (dd, J = 13.6, 10.9 Hz,

θ_m_a_x= 27.5°) were collected with a Bruker D8 VENTURE Kappa Duo

diﬀractometer equipped with a Cryostream Cooler (Oxford

H, C H ), 4.75 (br s, 1 H, Cp), 4.70 (dd, J = 2.8, 1.4 Hz, 1 H, Cp),

3 5

Cryosystems) using Cu Kα (λ = 1.54178 Å; only for 2 ·BH ) or

.25 (dd, J = 2.7, 1.7 Hz, 1 H, Cp), 4.16 (dd, J = 2.5, 1.6 Hz, 1 H,

Mo Kα (λ = 0.71073 Å; all other compounds) radiation. The

Cp), 3.95 (dd, J = 13.6, 2.6 Hz, 1 H, C H ), 3.73 (td, J = 2.2, 1.4 Hz,

structures were obtained using direct methods (SHELXT, recent

H, Cp), 4.40−3.22 (very br s, 1 H, C H or CH SO ), 1.37 (s, 9 H,

version ) and subsequently reﬁned by full-matrix least squares based

tBu), 0.83 (s, 9 H, tBu) ppm. At both temperatures, the signals of

three hydrogen atoms from C H₅and CH SO could not be

on F (SHELXL-2017 ). Non-hydrogen atoms were reﬁned with

anisotropic displacement parameters. Amide NH (except for 6 -C·

unequivocally identiﬁed due to extensive broadening. P{ H} NMR

161 MHz, CDCl , 25 °C): δ 14.2 (s) ppm. FTIR (DRIFTS, KBr):

CH Cl ·MeOH) and BH hydrogens were identiﬁed on the diﬀerence

(

electron density maps and reﬁned as riding atoms with U (H) set to

ν_m_a_x3504 w, 3441 w, 3339 w, 3097 w, 3058 w, 2963 m, 2905 w, 2867

w, 1643 m, 1526 m, 1482 m, 1459 w, 1435 m, 1400 w, 1365 m, 1314

w, 1270 m, 1258 s, 1214 w, 1179 m, 1150 vs, 1097 w, 1080 w, 1013

m, 973 w, 920 w, 856 w, 824 w, 750 m, 728 w, 704 w, 697 s, 616 w,

iso

^.²^Ueq of their bonding atom. Hydrogen atoms in the CH groups

were placed in their theoretical positions and reﬁned similarly.

Particular details are as follows.

−

Compound 2 ·BH crystallized as a three-component, non-

588 w, 560 w, 539 m, 524 m, 509 s, 493 m, 481 m, 440 w cm . Anal.

merohedral twin. The reﬁned contributions of the three domains

Calcd for C H NFeO PPdS·0.8CH Cl (833.96): C, 51.56; H, 5.27;

N, 1.68. Found: C, 51.42; H, 5.43; N, 1.72. The amount of residual

solvent was conﬁrmed by NMR analysis (δ 5.30). HR ESI-MS: calcd

for C H FeNNaO PPdS ([M + Na] ) 788.08486, found 788.08674.

were approximately 0.661:0.214:0.125. In the structure of 2 , one

ethyl substituent of the Et NH cation had to be reﬁned over two

positions due to disorder. Similarly, the allyl moieties in all Pd(η -

Synthesis of 7 . Compound 7 was prepared in an analogous

allyl) complexes reported here were disordered and had to be

manner starting from 2 (219.9 mg, 0.30 mmol). Crystallization by

modeled over two positions, rotated approximately 180° along the

dissolving the crude product in dichloromethane/methanol (20/1, 3

Pd−allyl axis. The solvent molecules in the structure of 7 ·

mL) and layering with pentane (10 mL) provided 7^C^yas an orange-

0.125CH Cl ·0.875 MeOH occupy the same space and were reﬁned

2 2

red crystalline solid. Yield: 194 mg (83%).

so that their occupancies summed up to 1. Finally, the solvent

H NMR (400 MHz, CDCl , 25 °C): δ 6.99 (br s, 1 H, NH), 5.70

molecules in the structures of 6 -C·CH

2 2

Cl ·MeOH and 6 -S·

(

qi, J = 9.5 Hz, 1 H, C H ), 5.26 (dt, J = 2.8, 1.5 Hz, 1 H, Cp), 5.13

dd, J = 13.6, 10.5 Hz, 1 H, C H ), 4.80 (br s, 1 H, Cp), 4.73 (br s, 1

1.5CHCl were disordered within structural voids and could not be

satisfactorily incorporated in the structure model. Therefore, their

contribution to the overall scattering was eliminated using PLATON

H, Cp), 4.32 (dd, J = 2.7, 1.8 Hz, 1 H, Cp), 4.24 (br s, 1 H, Cp), 4.14

(dd, J = 2.4, 1.6 Hz, 1 H, Cp), 3.97 (dd, J = 13.6, 2.0 Hz, 1 H, C H ),

SQUEEZE. The removed electron density was in good agreement

.49 (br s, 2 H, CH SO ), 2.68−2.58 (m, 1 H, Cy), 1.33 (s, 9 H, tBu),

with the expected value (106 electrons for 6 -C·CH Cl ·MeOH with

941

Organometallics 2021, 40, 1934−1944

Organometallics

orcid.org/0000-0002-4964-366X

Article

20 expected, and 696 electrons for 6 -S·1.5CHCl with 696

Julien Roger − Institut de Chimie Moléculaire de l’Université

de Bourgogne (ICMUB) UMR CNRS 6302, Université

Bourgogne Franche-Comté (UBFC), 21078 Dijon, France;

Nadine Pirio − Institut de Chimie Moléculaire de l’Université

de Bourgogne (ICMUB) UMR CNRS 6302, Université

Bourgogne Franche-Comté (UBFC), 21078 Dijon, France

electrons expected).

Selected crystallographic data and reﬁnement parameters are

available in Table S1 in the Supporting Information. All geometric

data and structural diagrams were obtained using a recent version of

the PLATON program. The numerical values were rounded to one

decimal place with respect to their estimated standard deviations

(

ESDs). Parameters pertaining to atoms in geometrically constrained

positions (hydrogens) are given without ESDs.

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.organomet.1c00244

DFT Calculations. Density functional theory calculations were

performed using Gaussian 16, revision C.01. The reported energies

correspond to Gibbs free energies obtained after full geometry

optimizations, starting from atomic coordinates determined by X-ray

diﬀraction analysis where possible (the more populated orientation of

the π-coordinated allyl group was used), using the PBE0 density

Notes

The authors declare no competing ﬁnancial interest.

functional combined with the Stuttgart−Dresden core potential

ACKNOWLEDGMENTS

■

for Fe and Pd and the Jul-cc-pVDZ basis set for the remaining

atoms. The solvent eﬀects were approximated using the polarized

This article is dedicated to Professor Pierre H. Dixneuf in

recognition of his outstanding contributions to organometallic

chemistry and catalysis. This work was supported by the

Charles University Research Centre Programme (project

UNCE/SCI/014). Computational resources were provided

by the project “e-Infrastruktura CZ” (e-INFRA LM2018140)

falling within the scheme Projects of Large Research,

Development and Innovations Infrastructures. P.V. also thanks

the Foundation of Faculty of Science, Charles University, for

supporting his stay in Dijon. In Dijon, this work was supported

by the ANR-PRC 2016 programme (ALCATRAS, ANR-16-

CE07-0001-01), the CNRS, Université de Bourgogne, Conseil

Régional de Bourgogne through the plan d’actions régional

pour l’innovation (PARI), and the fonds européen de

développement regional (FEDER). The authors also thank

Dr. R. Gyepes from the Department of Inorganic Chemistry,

Faculty of Science, Charles University, for valuable suggestions

regarding DFT computations. Thanks are also due to Dr. H.

Cattey from Institut de Chimie Moléculaire de l’Université de

Bourgogne, Université Bourgogne Franche-Comté, for com-

plementary crystallographic measurements.

continuum model (PCM). Cartesian coordinates of the DFT-

optimized structures are available in the Supporting Information.

ASSOCIATED CONTENT

sı Supporting Information

■

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.organomet.1c00244.

FTIR spectra of 6 -C and 6 -S, additional structural

data and structure diagrams, summary of relevant

crystallographic parameters, and NMR spectra (PDF )

Cartesian coordinates of the DFT optimized structures

(XYZ )

Accession Codes

CCDC 2077801 −2077807 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.

REFERENCES

■

AUTHOR INFORMATION

■

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