Phosphinoferrocene ureas: Synthesis, structural characterization, and catalytic use in palladium-catalyzed cyanation of aryl bromides

DOI: 10.1021/acs.organomet.5b00197

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Organometallics p. 1942 - 1956 (2015)

Update date:2022-08-16

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Authors:

?koch, Karel

Císa?ová, Ivana

?těpni?ka, Petr

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Article abstract of DOI:10.1021/acs.organomet.5b00197

Phosphinoferrocene ureas Ph₂PfcCH₂NHCONR₂, where NR₂ = NH₂ (1a), NHMe (1b), NMe₂ (1c), NHCy (1d), and NHPh (1e); the analogous thiourea Ph₂PfcCH₂NHCSNHPh (1f); and the acetamido derivative Ph₂PfcCH₂NHCOMe (1g) (Cy = cyclohexyl, fc = ferrocene-1,1′-diyl) were prepared via three different approaches starting from Ph₂PfcCH₂NH₂·HCl (3·HCl) or Ph₂PfcCHO (4). The reactions of the representative ligand 1e with [PdCl₂(cod)] (cod = cycloocta-1,5-diene) afforded [PdCl(μ-Cl)(1e-κP)₂]₂ or [PdCl₂(1e-κP)₂]₂ depending on the metal-to-ligand stoichiometry, whereas those with [PdCl(η³-C₃H₅)]₂ and [PdCl(L^NC)]₂ produced the respective bridge cleavage products, [PdCl(η³-C₃H₅)(1e-κP)] and [PdCl(L^NC)(1e-κP)] (L^NC = [(2-dimethylamino-κN)methyl]phenyl-κC¹). Attempts to involve the polar pendant in coordination to the Pd(II) center were unsuccessful, indicating that the phosphinoferrocene ureas 1 bind Pd(II) preferentially as modified phosphines rather than bifunctional donors. When combined with palladium(II) acetate, the ligands give rise to active catalysts for Pd-catalyzed cyanation of aryl bromides with potassium hexacyanoferrate(II). Optimization experiments revealed that the best results are obtained in 50% aqueous dioxane with a catalyst generated from 1 mol % of palladium(II) acetate and 2 mol % of 1e in the presence of 1 equiv of Na₂CO₃ as the base and half molar equivalent of K₄[Fe(CN)₆]·3H₂O. Under such optimized conditions, bromobenzenes bearing electron-donating substituents are cyanated cleanly and rapidly, affording the nitriles in very good to excellent yields. In the case of substrates bearing electron-withdrawing groups, however, the cyanation is complicated by the hydrolysis of the formed nitriles to the respective amides, which reduces the yield of the desired primary product. Amine- and nitro-substituted substrates are cyanated only to a negligible extent, the former due to their metal-scavenging ability.

Full text of DOI:10.1021/acs.organomet.5b00197

Article

pubs.acs.org/Organometallics

Phosphinoferrocene Ureas: Synthesis, Structural Characterization,

and Catalytic Use in Palladium-Catalyzed Cyanation of Aryl Bromides

Karel Skoch, Ivana Císarova, and Petr Stepnicka*

Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, 128 40 Prague 2, Czech

Republic

S Supporting Information

A B S T R A C T : P h o s p h i n o f e r r o c e n e u r e a s

Ph PfcCH NHCONR , where NR = NH₂(1a), NHMe

(

1b), NMe (1c), NHCy (1d), and NHPh (1e); the analogous

thiourea Ph PfcCH NHCSNHPh (1f); and the acetamido

derivative Ph PfcCH NHCOMe (1g) (Cy = cyclohexyl, fc =

ferrocene-1,1′-diyl) were prepared via three diﬀerent ap-

proaches starting from Ph PfcCH NH ·HCl (3·HCl) or

Ph PfcCHO (4). The reactions of the representative ligand

e with [PdCl (cod)] (cod = cycloocta-1,5-diene) aﬀorded

[

PdCl(μ-Cl)(1e-κP) ] or [PdCl (1e-κP) ] depending on the

2 2 2 2 2

metal-to-ligand stoichiometry, whereas those with [PdCl(η -

C H )] and [PdCl(L )] produced the respective bridge cleavage products, [PdCl(η -C H )(1e-κP)] and [PdCl(L^N^C)(1e-

κP)] (L = [(2-dimethylamino-κN)methyl]phenyl-κC ). Attempts to involve the polar pendant in coordination to the Pd(II)

center were unsuccessful, indicating that the phosphinoferrocene ureas 1 bind Pd(II) preferentially as modiﬁed phosphines rather

than bifunctional donors. When combined with palladium(II) acetate, the ligands give rise to active catalysts for Pd-catalyzed

cyanation of aryl bromides with potassium hexacyanoferrate(II). Optimization experiments revealed that the best results are

obtained in 50% aqueous dioxane with a catalyst generated from 1 mol % of palladium(II) acetate and 2 mol % of 1e in the

presence of 1 equiv of Na CO as the base and half molar equivalent of K [Fe(CN) ]·3H O. Under such optimized conditions,

bromobenzenes bearing electron-donating substituents are cyanated cleanly and rapidly, aﬀording the nitriles in very good to

excellent yields. In the case of substrates bearing electron-withdrawing groups, however, the cyanation is complicated by the

hydrolysis of the formed nitriles to the respective amides, which reduces the yield of the desired primary product. Amine- and

nitro-substituted substrates are cyanated only to a negligible extent, the former due to their metal-scavenging ability.

INTRODUCTION

applications of urea-functionalized phosphinoferrocene donors

appear to be represented only by the preparation of urea- and

thiourea-modiﬁed BPPFA-type donors (C in Scheme 1; BPPFA

■

Modiﬁcation of phosphines via introduced functional groups

has been recognized as an eﬃcient route toward new tailored

ligands for coordination chemistry and catalysis. The latter ﬁeld,

in particular, advantageously capitalizes on the modiﬁcation of

pristine phosphine donors. For instance, phosphines modiﬁed

with highly polar moieties such as sulfonato, carboxyl, or

hydroxy groups have been successfully incorporated into

catalysts for organic reactions performed in less environ-

1,1′-bis(diphenylphosphino)-2-(1-dimethylaminoethyl)-

ferrocene ) and their applications in asymmetric catalytic

hydrogenations. In addition, our laboratory recently reported

the synthesis of phosphinoferrocene carboxamides bearing

7,8

extended urea-based pendants (D in Scheme 1) and their use in

Pd-catalyzed cross-coupling of arylboronic acids with acyl

chlorides to yield benzophenones. This situation markedly

contrasts with the numerous studies devoted to the electro-

chemical sensing properties of ferrocenyl- and ferrocenylmeth-

^m^eⁿ^t^a^l^l^y^d^e^m^aⁿ^dⁱⁿ^g^a^q^u^e^o^u^s^r^e^a^c^tⁱ^oⁿ^m^e^dⁱ^aⁱⁿ^c^l^u^dⁱⁿ^g^p^u^r^e1

water, homogeneous aqueous mixtures, and biphase mixtures.

The range of polar phosphine derivatives has been recently

yl-substituted ureas.

extended by those bearing urea substituents (A and B in

In this contribution, we report on the preparation,

coordination properties, and catalytic performance in the Pd-

catalyzed cyanation of aryl bromides of a new type of

phosphinoferrocene ureas (1 in Scheme 1). The urea moiety

Scheme 1). The presence of urea pendants in these donors has

been shown to be responsible for the formation of supra-

molecular assemblies via hydrogen bond interactions, which in

turn aﬀect their catalytic properties.

In the chemistry of phosphinoferrocene ligands, the urea

moiety has been used relatively scarcely, most often as a stable

in these functional hybrid ligands is attached to the ferrocene

scaﬀold via a methylene spacer, which increases conformational

and structurally deﬁned linking group in the preparation of

immobilized or water-soluble donors and conjugates of

Received: March 10, 2015

ferrocene with biologically relevant molecules. Genuine

XXXX American Chemical Society

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Scheme 1

Scheme 3. Synthesis of Phosphinoferrocene Ureas from in

Situ Generated Amine 3

ﬂexibility and enhances the ditopic nature of these polar

donors.

Nevertheless, because most of the starting amine hydrochloride

remained unreacted and could be isolated (57% of the starting

amine was recovered), the yield of 1a with respect to

unconsumed 3·HCl was very satisfactory (86%). It should be

noted that compound 1a is typically contaminated by traces of

the respective phosphine oxide (1aO), which cannot be

eﬃciently removed by chromatography or crystallization.

The second approach, method B, employed for the

preparation of trisubstituted urea 1c and the acetamido (i.e.,

non-urea) derivative 1g, which was included in the series of

prospective ligands for comparison, was also rather straightfor-

ward, making use of the reactions of amine 3 with the

corresponding acyl or carbamoyl chlorides (Scheme 3). As in

the previous case, free amine 3 was liberated in situ from its

hydrochloride by the action of triethylamine, which was used in

excess to also serve as a scavenger of the formed HCl. Even

these reactions proceeded satisfactorily and aﬀorded the

aforementioned products in isolated yields exceeding 90%.

The last alternative (method C, Scheme 4) relied on the

direct reaction of aldehyde 4 with the respective urea by

RESULTS AND DISCUSSION

■

Synthesis of Phosphinoferrocene Ureas. Three diﬀerent

methods were employed for the synthesis of phosphinoureas 1,

partly due to their exclusivity with respect to the substituents at

the terminal nitrogen atoms as well as for comparison of

diﬀerent preparative routes leading to this type of functionally

modiﬁed, polar phosphinoferrocene donors. The ﬁrst, perhaps

inevitable approach, method A, was based on the conventional

and widely applicable addition of amines across isocyanates.

The amine 3 required for this reaction was prepared by hydride

reduction of the known oxime 2 (Scheme 2), which is in turn

Scheme 2. Preparation of 3·HCl

Scheme 4. Preparation of Phosphinoferrocene Ureas by

Reductive Alkylation

accessible from 1′-(diphenylphosphino)ferrocene-1-carbalde-

hyde (4). The amine was advantageously isolated in the

form of stable and easy-to-handle hydrochloride (3·HCl),

which separates in reasonable yield from the solution of the

crude product upon addition of methanolic HCl. Contami-

nation of 3·HCl with the corresponding phosphine oxide,

which is otherwise diﬃcult to separate (e.g., by chromatog-

raphy), does not exceed 5% in this case.

Gratifyingly, the reaction of amine 3 generated in situ from

the hydrochloride and triethylamine proceeded in the

anticipated manner, leading to 1,3-disubstituted ureas 1d and

condensation and reduction of the presumed imine inter-

1e in very good isolated yields (Scheme 3). Not surprisingly,

mediates (reductive alkylation). This method was tested

mainly because it could possibly eliminate the two steps

required to convert 4 to 3. Thus, the reaction of 4 with N-

phenylurea performed in the presence of chlorotrimethylsilane

as the condensation agent and subsequent reduction with

this method could be successfully adopted for the synthesis of

thiourea 1f (yield: 94%). However, when applied to the

preparation of N-ferrocenylmethyl urea 1a by the action of

sodium cyanate on the amine, method A furnished a relatively

lower yield (37%) of the desired urea derivative, presumably

because of a low equilibrium concentration of HNCO as the

Li[AlH ] led to 1e in a good 82% yield. The choice of the

reducing agent proved to be crucial since a similar reaction with

active reagent in the presence of excess triethylamine.

Na[BH ] and simultaneous addition of acetic acid aﬀorded a

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was reduced directly to the corresponding alcohol (isolated

yields of 1b and the alcohol were 30% and 49%, respectively).

All newly prepared compounds were characterized by

multinuclear NMR and IR spectroscopy, electrospray ionization

(

ESI) mass spectrometry, and elemental analysis. In their H

NMR spectra, the compounds showed signals typical of the

phosphinoferrocenyl moiety, namely, a set of virtual multiplets

(

three triplets and one quartet) attributable to the unsym-

metrically 1,1′-disubstituted ferrocene moiety bearing one

phosphine substituent and a multiplet due to protons at the

PPh group. Corresponding signals were found in the

NMR spectra. Signals of the methylene linkers in 1a−e and 1g

were observed at δ around 4.0 and δ 38−39, whereas those

of 1f appeared shifted to lower ﬁelds (δ 4.34, δ 44.25).

NMR resonances of the CO units, another characteristic

feature in the NMR spectra, were observed at δ ca. 155−159

for ureas 1a−e, at δ 180.16 for thiourea 1f, and at δ 169.73

for the N-acetyl derivative 1g. Finally, the P NMR signals of

Figure 1. PLATON plot of cation 1 in the structure of 3·HCl showing

atom labeling and displacement ellipsoids at the 30% probability level.

Note: Atom numbering in molecule 2 is strictly analogous.

·HCl and 1a−g were found within the narrow range of δ −16

to −18 ppm.

The ESI mass spectra of ureas 1 displayed pseudomolecular

ions of the type [M + X] , where X = H, Na, and K. In contrast,

the mass spectrum of 3·HCl showed a strong signal attributable

product containing considerable amounts (approximately 30%)

to the [1′-(diphenylphosphino)ferrocenyl]methylium cation,

of the respective borane adduct, 1e·BH (δ 16.5). On the

Ph PfcCH , analogous to the stabilized [FcCH ] fragment

other hand, method C proved unsuitable for the preparation of

(

Fc = ferrocenyl) typically appearing in the mass spectra of

a because it mainly led to [1′-(diphenylphosphino)-

ferrocenylmethyl derivatives.

ferrocenyl]methanol (68% of this alcohol and only ca. 9%

In addition to characterization by various solution

techniques, the crystal structures of 3·HCl, 1a, 1e, and 1f

were determined by single-crystal X-ray diﬀraction analysis.

Compound 3·HCl (Figure 1 and Table 1) crystallizes with the

of 1a were isolated with Li[AlH ]) or yielded the desired

product 1a contaminated with the respective phosphine oxide

and borane adduct, only the latter of which could be eﬃciently

removed by crystallization (reaction with Na[BH ]; chroma-

symmetry of the monoclinic space group P2 /n and two

tography proved to be ineﬃcient in separating 1a, 1aO, and 1a·

BH₃).

On the other hand, method C becomes particularly

important when no isocyanate or carbamoyl chloride required

for the conventional additions or condensations is available or

at least reasonably accessible. In the present case, method C

was employed for the synthesis of N-methylurea 1b. Thus,

molecules per asymmetric unit. The two independent

molecules diﬀer only marginally, mainly in the mutual

orientation of the cyclopentadienyl rings (see τ angles in

Table 1 and the overlap in the Supporting Information, Figure

S1), and their geometric parameters are unexceptional. Hence,

the reason for their “multiplication” most likely lies in the

complexity of the hydrogen-bonded array in the crystal state.

Individual ions constituting the crystal structure of 3·HCl

assemble via charge-assisted N−H···Cl hydrogen bonds (N···Cl

= 3.054(4)−3.143(4) Å), forming inﬁnite columnar assemblies

oriented parallel to the crystallographic b-axis. The bulky

nonpolar phosphinoferrocenyl moieties are directed away from

the “central” polar domains and thus decorate the hydrogen-

bonded stacks on their exterior (Figure 2).

“reductive alkylation” of 4 with N-methylurea in the presence of

ClSiMe₃in THF−CH CO H followed by reduction by

Na[BH ] provided 1b in a 73% yield with less than 5%

contaminants (phosphine oxide and borane adduct; further

puriﬁcation could be achieved through recrystallization).

Similar reaction in the presence of Li[AlH ] as a more

energetic reducing agent aﬀorded a cleaner product but in a

lower yield because a considerable part of the starting aldehyde

Table 1. Selected Geometric Data for the Two Independent Cations in the Crystal Structure of 3·HCl (in Å and deg)

parameter

Fe−Cg1

Fe−Cg2

molecule 1

parameter

Fe−Cg1

Fe−Cg2

∠Cp1,Cp2

molecule 2

1.654(2)

1.651(2)

1.0(3)

1.655(2)

1.650(2)

1.5(3)

∠Cp1,Cp2

−156.8(4)

1.825(5)

1.846(5)

1.840(5)

1.482(6)

112.5(4)

−171.3(4)

1.821(5)

1.836(5)

1.844(5)

1.497(6)

111.4(4)

P1−C106

P1−C112

P1−C118

N1−C111

P2−C206

P2−C212

P2−C218

N2−C211

C201−C211−N2

C101−C111−N1

Deﬁnitions: Cp1 and Cp2 are the azoniamethyl- [C(101−105) and C(201−205) in molecules 1 and 2] and phosphine-substituted [C(106−110)

and C(206−210) in molecules 1 and 2] cyclopentadienyl rings, respectively. Cg1 and Cg2 are their respective centroids. τ represents the torsion

angle Cn01−Cg1−Cg2−Cn06, where n = 1 and 2 for molecules 1 and 2, respectively.

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Figure 3. (a) PLATON plot of the molecular structure of 1a.

Displacement ellipsoids enclose the 30% probability level. (b) Section

of the hydrogen-bonded chains in the structure of 1a. For clarity, only

the NH hydrogens are shown, and the phosphinoferrocenyl moieties

have been replaced with black squares.

Table 2. Selected Geometric Parameters for 1a, 1e, and 1f

(

in Å and deg)

parameter

1a (Y = O)

1e (Y = O)

1f (Y = S)

Fe−Cg1

Fe−Cg2

1.646(1)

1.639(1)

4.5(2)

1.6458(9)

1.6402(9)

2.6(1)

1.662(2)

1.656(2)

1.8(2)

∠

Cp1,Cp2

Figure 2. (a) Section of the hydrogen-bonded array in the structure of

−68.1(2)

1.805(2)

1.836(2)

1.829(2)

1.503(3)

1.454(3)

113.8(2)

1.354(3)

1.353(3)

n.a.

−90.0(1)

1.815(2)

1.840(2)

1.838(2)

1.504(3)

1.452(3)

112.0(2)

1.346(2)

1.376(2)

1.408(3)

1.238(2)

113.2(2)

157.7(3)

1.823(3)

1.838(4)

1.505(5)

1.452(5)

110.3(3)

1.344(5)

1.343(5)

1.434(5)

1.699(4)

117.0(3)

3·HCl. For convenience, the repeating unit is enclosed within a yellow

P−C6

P−C12

P−C18

C1−C11

C11−N1

C1−C11−N1

N1−C24

N2−C24

N2−C25

C24−Y

box. Only the NH hydrogens are shown, and the bulky

phosphinoferrocenyl moieties have been replaced with black circles

to avoid complicating the ﬁgure. (b) Projection of a single columnar

stack along the b-axis.

The molecular structure of 1a is depicted in Figure 3, and the

selected geometric parameters for all structurally characterized

phosphinoureas (i.e., 1a, 1e, and 1f) are compiled in Table 2.

Generally, the structural parameters determined for 1a fall into

9,20

1.241(2)

115.4(2)

the typical ranges.

The individual Fe−C distances vary

N1−C24−N2

slightly (2.020(3)−2.068(2) Å), which in turn results in tilting

of the cyclopentadienyl ring planes by ca. 5°. The cyclo-

pentadienyl rings assume an approximately synclinal eclipsed

Deﬁnitions: Cp1 and Cp2 are the CH - [C(1−5)] and phosphine-

substituted [C(6−10)] cyclopentadienyl rings, respectively. Cg1 and

Cg2 stand for the respective centroids. τ is the torsion angle C1−

Cg1−Cg2−C6. n.a. = not applicable.

(

ideal value: 72°) conformation, and the urea pendant is

directed below the ferrocene unit and takes part in

intermolecular interactions.

The individual molecules of 1a associate in a manner typical

for N,N′-disubtituted ureas by forming inﬁnite chains through

electron density map (see the Supporting Information, Figure

S2).

pairs of N−H···O hydrogen bonds between proximal

Although the molecules of 1e and 1f (Figure 4 and Table 2)

diﬀer “only” by the chalcogen atom in the urea pendant, their

structures are considerably dissimilar. The individual distances

and angles are quite unexceptional and, for 1e, compare well

with those determined for a calix[4]arene modiﬁed by two

NHCONH moieties, whose oxygen atoms behave as bifurcate

hydrogen bond acceptors. These hydrogen bonds thus

involve only hydrogen atoms in an anti position with respect

to the urea oxygen and are signiﬁcantly asymmetric (N1···O =

.212(3) Å; N2···O = 2.870(2) Å). The third NH proton

FcCH NHCONH− redox-active pendants (Fc = ferrocenyl).

available in 1a (H3N) does not take part in hydrogen bonding

The main diﬀerence lies in the molecular conformation and

solid-state assemblies the compounds constitute in their

crystals.

with any conventional acceptor. Nonetheless, it is positioned

appropriately for an interaction with the “residual” electron

density attributable to the lone pair of phosphorus, which

manifests itself as the most intense peak in the ﬁnal diﬀerence

The cyclopentadienyl rings in the molecules of 1e and 1f are

tilted by only 2.6(1)° and 1.8(2)°, respectively. They adopt

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via the relatively softer (weaker) N−H···S interactions (N2···S

3.335(3) Å) and make use of only one of the available NH

protons (N2−H2N, which is syn with respect to the sulfur

atom; see Figure S4 in the Supporting Information).

Preparation of Palladium(II) Complexes. The coordina-

tion properties of the phosphinoferrocene ureas were examined

in palladium(II) complexes using 1e as a representative ligand.

The experiments conﬁrmed that the compounds behave as

modiﬁed phosphines rather than as true bifunctional donors.

For instance, the reaction of 1e with [PdCl (cod)] (cod =

cycloocta-1,5-diene) at 1:1 molar ratio provided the

dipalladium(II) chloride-bridged complex 5 (δ 33.6; Scheme

). A similar reaction with two molar equivalents of 1e with

Scheme 5. Synthesis of Palladium(II) Complexes 5 and 6

Figure 4. PLATON plots of the molecular structures of (a) 1e and (b)

f. Displacement ellipsoids are scaled to the 30% probability level.

cod = cycloocta-1,5-diene.

diﬀerent mutual orientations, namely, an intermediate con-

formation between synclinal eclipsed and anticlinal staggered in

respect to Pd proved to be complicated due to unexpected side

reactions and required careful optimization to produce the bis-

e and a conformation close to ideal anticlinal eclipsed in 1f.

phosphine complex 6 (δ 16.5 ).

The reactions of 1e with dipalladium precursors [Pd(L^N^C)(μ-

Another substantial diﬀerence can be observed in the

arrangement of the urea pendants. Whereas the urea moiety

in 1e has both hydrocarbyl groups in syn positions with respect

to the oxygen of the central CO bond, the substituents at the

Cl)] and [Pd(η -C H )(μ-Cl)] also gave rise to the expected

“simple” phosphine complexes 7 and 8, both resulting via

cleavage of the chloride bridges in the starting Pd complexes

(Scheme 6). Repeated attempts to induce a chelate

NHC(S)NH assume syn (CH ) and anti (Ph) positions.

Together with reorientation of the entire urea pendant with

respect to the ferrocene units (cf. the C2/5−C1−C11−N1

angles 64.9(3)/−112.1(3)° for 1a, 17.6(3)/−165.1(2)° for 1e,

and −149.7(4)/34.8(5)° for 1f), this positioning directs the

phenyl ring closer to the ferrocene unit and results in twisting

of the terminal phenyl group with respect to the urea moiety, as

evidenced by the dihedral angles subtended by the phenyl and

the NC(E)N (E = O or S) planes being 24.8(1)° and 63.3(2)°

for 1e and 1f, respectively. (Note: The values of the C11−N1−

C24−N2 angles are higher than 175° in all three structures,

thereby ruling out any signiﬁcation torsion at the connecting

urea motifs.)

Scheme 6. Synthesis of Palladium(II) Complexes 7 and 8

The diﬀerent geometries of the urea pendants are clearly

associated with diﬀerences in the solid-state architecture.

Compound 1e forms the typical one-dimensional chain

coordination of 1e by removal of the Pd-bound chloride in 7

by either a soluble Ag(I) or Tl(I) salt (Ag[SbF ] and Tl[PF ])

23a

described by the C(4)[R (6)] descriptors

in graph set

or via an intramolecular replacement following deprotonation

of the NH group(s) with t-BuOK were unsuccessful, aﬀording

only complicated and easily decomposing reaction mixtures.

Although partly disordered, the molecular structures of 7·

2CHCl₃and 8 could be determined by X-ray diﬀraction

notation and observed as the main motif in the crystal

structure of 1a (see the Supporting Information, Figure S3;

N1···O = 3.053(2) Å, N2···O = 2.884(2) Å). In contrast, the

molecules of 1f associate into simple centrosymmetric dimers

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Figure 5. PLATON plot of the molecular structure of 7. The displacement ellipsoids are scaled to the 30% probability level. For clarity, only one

orientation of the disordered phenyl group is shown (for a complete drawing, see the Supporting Information). Selected geometric data (in Å and

deg): Pd−Cl 2.4160(9), Pd−P 2.2576(8), Pd−N(3) 2.153(3), Pd−C(31) 2.005(4), P−Pd−Cl 91.87(3), Cl−P−N3 90.28(8), N2−Pd−C31

81.9(1), C31−Pd−P 97.1(1).

analysis. The structures are presented in Figures 5 and 6,

respectively, along with relevant geometric parameters.

Ferrocene cyclopentadienyls in the structure of 7 are tilted by

as little as 0.5(2)° (Fe−Cg1 and Fe−Cg2 are 1.646(2) and

.647(2) Å, respectively) and assume a conformation near

anticlinal eclipsed (τ = 136.3(2)°, cf. ideal value: 144°). The

urea moiety is rotated by 68.5(2)° with respect to the plane of

the cyclopentadienyl ring C(1−5), forming a pair of N−H···Cl

hydrogen bridges toward chloride in a proximal, inversion-

related molecule of the complex (see the Supporting

Information, Figure S7; N1···Cl = 3.335(3) Å, N2···Cl =

.351(2) Å).

The η -allyl moiety in the structure of 8 is disordered over

two positions that are approximately related by reﬂection

through the plane constituted by the remaining ligands (i.e., the

{Pd, Cl, P} plane). The allyl unit intersects the latter plane at an

angle of 65.7(6)° (60.5(8)° for the less abundant orientation),

and the Pd−C distances gradually increase on going from C50

to C52, following the trend dictated by trans inﬂuence (P >

Cl). Similar structural features have been observed in the

structures of analogous (η -allyl)Pd(II) complexes with

0,31

phosphinoferrocene ligands.

Figure 6. PLATON plot of the molecular structure of 8 (30%

probability displacement ellipsoids) showing only the dominant

orientation of the π-allyl moiety and the N−H···Cl hydrogen bonds

as dashed lines (for a complete structural drawing, see the Supporting

Information, Figure S6). Coordination geometry parameters (in Å and

deg): Pd−Cl 2.3826(6), Pd−P 2.3013(6), Pd−C50 2.124(5), Pd−C51

Similarly to 7, the urea protons in 8 form hydrogen bridges

to the Pd-bound chloride, although within the same molecule

N1···Cl = 3.408(2) Å, N2···Cl = 3.380(2) Å). However,

because the N−H···Cl interactions are intramolecular, the urea

moiety is oriented nearly perpendicularly to the plane of its

parent cyclopentadienyl ring C(1−5) (dihedral angle: 89.8(1)°;

see Figure 6), and the ferrocene unit has a less open

conformation (τ = 99.5(2)°, N.B. the tilting is slightly higher:

(

.138(5), Pd−C52 2.221(7), Cl−Pd−P 95.35(2), P−Pd−C50

02.8(1), Cl−Pd−C52 94.6(2).

.4(1)°; Fe−Cg1/Cg2 = 1.657(1)/1.649(1) Å).

Pd-Catalyzed Cyanation of Aryl Bromides. In view of

The structure of solvated 7 corroborates the trans-P−N

relationship already deduced from the NMR parameters of the

the presence of the highly polar urea tags in the newly prepared

phosphinoferocene donors, we decided to evaluate their

catalytic potential in aqueous, Pd-catalyzed cyanation of aryl

CH NMe moiety, namely, the J_P_Cand J_P_Hcoupling

constants. The compound has the expected square-planar

coordination environment around the palladium center, which

is distorted due to the presence of a small metallacycle (the

Pd−C and Pd−N bonds are the shortest among the Pd-donor

distances, and the C−Pd−N angle is the most acute interligand

bromides leading to synthetically valued benzonitriles, using

potassium hexacyanoferrate(II) as an environmentally benign,

hydrolytically stable, and water-soluble cyanide source. For

the initial screening of the reaction conditions, we chose the

cyanation of 4-bromoanisole (9g), providing the corresponding

nitrile 10g and amide 11g as its hydrolytic side-product

9a,c,e,g

angle).

The ﬁve-membered palladium ring has an

envelope conformation with the nitrogen N3 at the tip position.

DOI: 10.1021/acs.organomet.5b00197

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Scheme 7). This reaction can be easily followed by H NMR

Article

(

On the basis of the results of the solvent screening

experiments, dioxane was chosen for further reaction tests as

an inexpensive aprotic solvent possessing favorable properties,

including a reasonably high boiling point and unlimited

miscibility with water. More detailed tests showed that

changing the water/dioxane ratio also signiﬁcantly aﬀects the

reaction course. For instance, whereas no coupling product was

obtained from reactions performed in pure and 80% dioxane

spectroscopy using the signals of the methoxy groups as

Scheme 7. Model Cyanation Reaction

(

Figure 8), the yield of 10g suddenly grew to 92% upon

characteristic markers. A catalyst generated in situ by mixing

palladium(II) acetate with two equivalents of ligand 1e was

used in most of the screening experiments.

Aiming at understanding the eﬀect of aqueous reaction media

,34

on the reaction course,

the possible inﬂuence of the solvent

was evaluated ﬁrst. The results presented graphically in Figure 7

Figure 8. Eﬀect of the composition of the water−dioxane mixture on

the yield of the coupling product 10g. For detailed conditions, see

caption of Figure 7

increasing the water content to 40 vol %. In accord with our

previous results, the best results were obtained in 40:60−

0:40 solvent mixtures (cf. 96% yield of 10g in 50% dioxane). A

further increase in the water content to 80% and 100%

markedly decreased the yield of the coupling product.

Consequently, a 1:1 dioxane−water mixture was employed as

the solvent for this particular reaction in all subsequent

experiments.

Figure 7. Eﬀect of the solvent on the yield of the coupling product

0g. Pure solvents (yellow bars) are compared with their 1:1 (by

volume) aqueous mixtures (blue bars). Conditions: substrate 9g (1.0

mmol), K CO₃(1.0 mmol), and K [Fe(CN) ]·3H O (0.5 mmol)

Experiments were also focused on the possible eﬀects of the

palladium source and the base. The evaluation of various

common palladium precursors at 1 mol % Pd loading (Table 3)

has indeed shown that the type of palladium precursor plays an

important role. The most satisfactory yields of the coupling

were reacted in the presence of in situ generated catalyst (1 mol % Pd,

mol % 1e; see Experimental Section) in the respective solvent (4

mL) at 100 °C for 3 h. NMR yields are given.

demonstrate that the yields of 10g achieved in an aqueous

mixture (solvent−water 1:1 by volume) were better than those

obtained in any tested pure organic solvent. This observation

likely reﬂects the solubility of the inorganic components in the

reaction mixture because the diﬀerence in the reaction outcome

was most pronounced for ethereal solvents such as (1,4-)

dioxane and 1,2-dimethoxyethane (DME) and for acetonitrile,

in which the polar reagents would be practically insoluble.

It is also noteworthy that the yield of the coupling product

obtained in pure water was lower than that in all other water−

organic solvent mixtures tested. Again, this result can be

accounted for by the solubility of the reaction components and

phase mixing phenomena. We observed that the addition of the

mixed solvent typically gave rise to a heterogeneous reaction

mixture (two liquid phases). However, this mixture was partly

or even fully homogenized upon heating to the reaction

temperature (100 °C), which in turn allowed for eﬃcient

interaction between the organic substrate, the catalyst, and the

Table 3. Survey of Various Pd Precursors in the Model

Coupling Reaction

Pd source

yield of 10g [%]

Pd source

[PdCl (cod)]

[PdCl

yield of 10g [%]

Pd(OAc)

]

[PdCl

(MeCN)

]

[PdCl(L^N^C)]

[PdCl(η -C

)]

Pd(O

CCF

)

[Pd

(dba)

]

^C^oⁿ^dⁱ^tⁱ^oⁿ^s^:^s^u^b^s^t^r^a^t^e⁹^g⁽¹^.⁰^m^m^o^l⁾^,^K^C^O3 (1.0 mmol), and

K [Fe(CN) ]·3H O (0.5 mmol) were reacted in the presence of in situ

generated catalyst (1 mol % Pd, 2 mol % 1e; see Experimental

Section) in dioxane−water (1:1, 4 mL) at 100 °C for 3 h. The yield

was determined by integration of H NMR spectra using mesitylene as

an internal standard. Pd:1e = 1:1. Reaction with 0.5 mol % Pd.

Reaction at 80 °C. Reaction at 60 °C. The catalyst was prepared in

methanol due to the insolubility of the starting Pd complex in

dichloromethane.

−

highly polar inorganic reagents (i.e., the base and CN source).

DOI: 10.1021/acs.organomet.5b00197

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

−

product (around 90%) were obtained with catalysts resulting

Table 5. Eﬀect of the Amount of CN Equivalents on the

Yield of Nitrile 10g

from simple palladium(II) carboxylates, viz., Pd(OAc) and

Pd(O CCF ) , at a Pd:1e ratio of 1:2. For practical reasons, the

3 2

amount of K [Fe(CN) ]·3H O [mmol]

CN equiv

yield of 10g [%]

former Pd(II) salt appears particularly attractive because it not

only gives rise to a highly active catalyst but is also relatively

inexpensive and readily available. Notably, catalysts generated

from other Pd(II) precursors as well as from [Pd (dba) ] as an

.00

.50

.33

.17

immediate source of Pd(0) performed signiﬁcantly worse.

Similarly, lowering the amount of the ligand to 1 equiv with

respect to palladium or decreasing the reaction temperature

Conditions: substrate 9g (1.0 mmol), Na

(1.0 mmol), and

varying amounts of K [Fe(CN) ]·3H O were reacted in the presence

of in situ generated catalyst (1 mol % Pd(OAc) , 2 mol % 1e; see

Experimental Section) in dioxane−water (1:1, 4 mL) at 100 °C for 3

h. The yield was determined by integration of H NMR spectra using

(

100 °C → 80 and 60 °C) considerably reduced the yield of

0g with the Pd(OAc) /1e catalyst.

The catalytic results achieved with diﬀerent bases are

presented in Table 4. Sodium and potassium carbonate

mesitylene as an internal standard.

Table 6. Catalytic Results Achieved with Diﬀerent Ligands

Table 4. Survey of Various Bases

ligand

yield of 10g [%]

ligand

yield of 10g [%]

base

yield of 10g [%]

base

yield of 10g [%]

Li CO₃

NaHCO₃

Na PO

Na CO₃

Na HPO

^F^c^P^P^h2

^K^C^O3

NaH PO

Conditions: substrate 9g (1.0 mmol), Na

K [Fe(CN) ]·3H O (0.5 mmol) were reacted in the presence of in situ

generated catalyst (1 mol % Pd(OAc) , 2 mol % ligand; see

Experimental Section) in dioxane−water (1:1, 4 mL) at 100 °C for

3 h. The yields were determined by integration of H NMR spectra

using mesitylene as an internal standard.

(1.0 mmol), and

K CO₃

NaOAc

NaOH

Cs CO₃

Conditions: substrate 9g (1.0 mmol), base (1.0 mmol unless speciﬁed

otherwise), and K [Fe(CN) ]·3H O (0.5 mmol) were reacted in the

presence of in situ generated catalyst (1 mol % Pd(OAc) , 2 mol % 1e;

see Experimental Section) in dioxane−water (1:1, 4 mL) at 100 °C for

h. The yield was determined by integration of H NMR spectra using

mesitylene as an internal standard. 0.5 mmol of base. 0.33 mmol of

more bulky and lipophilic substituents (phenyl and cyclohexyl),

with phenyl urea 1e being the most eﬃcient (92% of 10g).

Donors possessing urea substituents with relatively smaller

Na PO . Amide 11g (<5%) was also detected. Caution! (Partial)

hydrolysis to HCN likely occurs. Amide 11g (42%) also formed.

terminal substituents (NHMe and NMe ) as well as the

monosubstituted urea 3a furnished only ca. 50% yields of 10g,

whereas a further reduction of the polar pendants, such in the

acetylamino derivative 1g, caused the yield to decrease even

further.

aﬀorded comparable, very good yields (around 90%) when

employed in a 1:1 molar ratio with respect to the substrate 9g.

When the amount of these bases was reduced by half (i.e., to

one molar equivalent of alkali metal cation per 9g), the yields of

the coupling product decreased, although to diﬀerent extents,

to approximately half in the case of Na CO and by only 8%

The reaction performed in the absence of any supporting

ligand (i.e., employing only Pd(OAc) as the catalyst) did not

proceed in any appreciable extent under otherwise identical

conditions (results not tabulated), suggesting that the

supporting phosphine ligand represents a vital component of

the catalytic system (unlike many other cross-coupling

reactions). In addition, from the dependence of the reaction

yield on the structure of the phosphine ligands, it appears likely

that the urea moiety is also involved in the catalytic reaction,

e.g., by (temporary) coordination of the metal center or

through its solubility-tuning properties. The most indicative

signs are the dramatically diﬀerent performance of catalysts

based on the analogous phenyl-substituted urea and thiourea

ligands (1e vs 1f) and the fact that the catalyst based on FcPPh₂

as a P-monodentate donor produced a rather low yield of the

coupling product.

with K CO . Both the lighter (Li CO ) and the heavier

(

Cs CO ) congeners of these carbonates produced 10g in

2 3

lower yields, the former most likely due its relatively poor

solubility in the reaction system. Likewise, sodium hydrogen

carbonate as well as other bases tested (sodium phosphates,

sodium acetate, and sodium hydroxide) did not match the

results obtained for either simple carbonate from which the

common Na CO was selected as the most suitable for further

reactions because of its good performance and lower molar

weight (less material was needed).

To further minimize the amount of inorganic reagents

required for the cyanation reaction to proceed with good yields

and to limit the amount of waste produced, we have studied the

eﬀect of the amount of the cyanide source on the yield of the

coupling product. Unfortunately, the results presented in Table

As the last step, we studied the scope of the cyanation

reaction by altering the structure of the aryl bromide substrate

(Scheme 8). The results collected in Table 7 demonstrate that

the reaction proceeds satisfactorily with electron-rich, alkylated

substrates, despite moderate steric hindrance (see entries 1−5

indicate that the amount of K [Fe(CN) ]·3H O cannot be

4 6 2

reduced further below approximately 0.5 molar equivalents (i.e.,

−

equiv of CN ) with respect to 9g without reducing the yields

of the corresponding nitrile in the present case.

Having established the optimal reaction conditions in terms

of the reaction solvent, base, and palladium source, we turned

to studying the properties of individual phosphinoferrocene

ligands (Table 6). The best catalytic results showed catalysts

resulting from ligands equipped with urea moieties bearing

Scheme 8. General Scheme of the Cyanation Reaction

DOI: 10.1021/acs.organomet.5b00197

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Organometallics

Article

Table 7. Cyanation of Diﬀerent Aryl Bromides

did not improve the yield of 10p (isolated yield: 48%) because

of partial hydrolysis to the corresponding amide 11p (isolated

yield: 25%) and removal of the acetyl group resulting in the

formation of 4-aminobenzonitrile (10n; isolated yield: 16%).

The cyanation of 4-bromobenzoic acid (9q, entry 16) also

represents a notable example because the deprotonation of the

carboxyl group under the applied reaction conditions (2 equiv

of Na CO are used) activated the substrate, which was then

conversion (yield) after

4 h [%]

conversion to (yield

entry Ar in ArBr (9) of) 10 after 3 h [%]

2-MeC H (9a)

92 (89)

96 (90)

100 (94)

88 (84)

3-MeC H (9b)

4-MeC H (9c)

eﬃciently converted to the corresponding nitrile without any

⁴^-^t^-^B^u^C^H4

91 (84)

n.d. (9)

−

notable hydrolysis (COOH: −I and −M; COO : +I and +M).

(

9d)

2,4,6-Me C H

In addition to substituted bromobenzenes, we tested a few

other brominated arenes. Thus, 1-bromonaphthalene was fully

converted to the respective nitrile 10r over a period of 24 h,

whereas the isomeric 2-bromonaphthalene reacted to a similar

extent already within 3 h. The described procedure could also

be used to prepare 1-cyanopyrene (10t) and cyanoferrocene

(10u), in which case, however, extended reaction times were

required, and the latter product was isolated in only a modest

18% yield. In this case, however, 75% of the starting

bromoferrocene was recovered unchanged.

48 (n.d.)

100 (97)

(

9e)

4-PhC H (9f)

100 (96)

100 (92)

4-MeOC H₄

(

9g)

3,4-

98 (94)

62 (60)

(

MeO) C H

2 6 3

9h)

3,4-(OCH O)

C H (9i)

4-AcC H (9j)

9 (n.d.)

16 (15)

84 (82)

84 (80)

4-F CC H

18 (n.d.)

16 (n.d.)

In an attempt to further expand the scope of the reaction, we

also varied the halide substituent. Quite expectedly, 4-

iodoanisole reacted smoothly under the standard conditions

(

9k)

4-ClC H (9l)

25 (n.d.)

17 (14)

83 (80)

4-O NC H

(

1 mol % Pd, 3 h), aﬀording 10g in a 95% isolated yield, but no

(

9m)

reaction was observed with the less reactive chloride (i.e., 4-

chloroanisole). 4-Bromobenzyl bromide (9v) was not cyanated

either, being cleanly hydrolyzed under the reaction conditions

to 4-bromobenzyl alcohol (12; 100% conversion, 90% isolated

yield after 24 h).

4-H NC H

10 (n.d.)

60 (55)

10 (n.d.)

9 (n.d.)

50 (48)

(

9n)

4-Me NC H

(

9o)

4-AcNHC H

32 (25)

(

9p)

In is also noteworthy that analysis of the crude reaction

mixtures (i.e., prior to workup) typically revealed a character-

4-HO CC H

93 (84)

(

9q)

1-naphthyl (9r)

2-naphthyl (9s)

1-pyrenyl (9t)

Fc (9u)

18 (n.d.)

99 (94)

100 (94)

istic low-ﬁeld signal in the H NMR spectrum attributable to a

ligand decomposition product (δ_Hca. 8.7). To identify this

reaction product and, consequently, the fate of the phosphine

ligand, we prepared phosphine oxide 1eO by standard

hydrogen peroxide oxidation of the model ligand 1e. Indeed,

the NMR signals of authentic 1eO were identical to those

observed in the reaction mixtures, thereby conﬁrming that the

ligand undergoes oxidation during the reaction.

n.d. (79)

21 (18)

Conditions: substrate 9 (1.0 mmol), Na CO₃(1.0 mmol), and

K [Fe(CN) ]·3H O (0.5 mmol) were reacted in the presence of in situ

generated catalyst (1 mol % Pd(OAc) , 2 mol % 1e; see Experimental

Section) in dioxane−water (1:1, 4 mL) at 100 °C for 3 or 24 h.

NMR conversion (isolated yield in parentheses). These values are

averages of two independent runs. n.d. = not determined. 2 mmol of

Na CO were used. Nitrile 10n was also formed (conversion: 18%,

isolated yield: 16%).

CONCLUSION

■

This contribution describes the synthesis and catalytic

applications of a series of phosphinoferrocene donors modiﬁed

by various urea moieties, appended via a methylene linker.

These compounds were synthesized through three diﬀerent

methods, starting from either the newly prepared phosphino-

amine 3 (or rather its stable hydrochloride) or aldehyde 4. The

applicability of these methods was demonstrated to depend on

the urea pendant to be incorporated into the newly formed

molecule, namely, on the number and type of the substituents

at the nitrogen atoms.

in Table 7). The introduction of a methoxy group(s) or similar

substituents, whose +M eﬀect prevails over an −I eﬀect, does

not hamper the cyanation reaction (entries 7−9). On the other

hand, substrates bearing groups with a pronounced electron-

withdrawing character react less willingly, and the respective

nitriles as the primary products are activated toward hydrolysis

to the corresponding amides (see entries 10−12). The crystal

structures determined for two such amides, 11j and 11k, are

discussed in the Supporting Information.

The presence of the nitro group in the para position of the

benzene ring, exerting strong −M and −I eﬀects, practically

stopped the cyanation reaction, and substrate 9m thus

remained unchanged (entry 13). Aryl bromides bearing

amine substituents 9n and 9o (entries 14 and 15) also reacted

only sluggishly, albeit presumably due to the metal-scavenging

eﬀect of their donor substituents. This was corroborated by

cyanation of 4-bromoacetanilide (9p, entry 16), which

furnished nitrile 10p with 60% conversion (55% isolated

yield; entry 16) after 3 h. Extending the reaction time to 24 h

As exempliﬁed for the model ligand 1e, phosphinoferrocene

ureas 1 coordinate the Pd(II) ion as typical soft donors

(functionally modiﬁed phosphines) via their phosphine groups,

while the polar urea moieties remain available for the formation

of hydrogen-bonded assemblies in the solid state. When

combined with a suitable palladium source, these ligands give

rise to active catalysts for Pd-catalyzed cyanation of aryl

bromides with nontoxic K [Fe(CN) ]·3H O in aqueous

reaction media. Under the optimized conditions, the cyanation

reaction proceeds with very good to excellent yields for

bromoarenes devoid of other substituents and substrates

modiﬁed by electron-donating groups. In the case of

DOI: 10.1021/acs.organomet.5b00197

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Organometallics

Article

electron-poor substrates, the yield of cyanation product (the

nitrile) is typically reduced by subsequent hydrolysis upon the

action of the base present in the reaction mixture. Substrates

with amine substituents also pose some problems, presumably

because of their metal-scavenging eﬀect.

methanol and water (4 + 4 mL) was added, and the resultant solution

was stirred at room temperature overnight. Next, the mixture was

diluted with water (10 mL) and extracted with dichloromethane (2 ×

0 mL). The organic extracts were combined, washed with brine, dried

over anhydrous magnesium sulfate, and evaporated. Subsequent

chromatography over silica gel with dichloromethane−methanol

(10:1 v/v) led to the development of two orange bands. The ﬁrst

EXPERIMENTAL SECTION

Materials and Methods. The syntheses were performed under an

one contained the desired product 1a, which was isolated by

evaporation as an orange, readily crystallizing oil (75 mg, 37%).

Evaporation of the second band aﬀorded unreacted free amine (105

mg, 57%). Note: Isolated 1a is typically contaminated by traces of the

corresponding phosphine oxide, which cannot be removed by

crystallization. Increasing the amount of NaOCN to 5 equiv did not

improve the yield of 1a.

■

argon atmosphere using standard Schlenk techniques. Compounds

4, [PdCl (cod)], and [(L )Pd(μ-Cl)]₂were synthesized

according to procedures reported in the literature. Commercial N,N-

dimethylcarbamoyl chloride was distilled before use. Methanol,

dichloromethane, and tetrahydrofuran (HPLC grade) were dried

with a PureSolv MD5 solvent puriﬁcation system (Innovative

Technology). Other chemicals and solvents used for crystallizations

and during chromatography were used as received without any

additional puriﬁcation.

Attempted Preparation of 1a by Method C. Aldehyde 4 (398 mg,

.00 mmol) and urea (900 mg, 15 mmol) were mixed with THF (50

mL) and freshly distilled acetic acid (50 mL), and the resultant

mixture was cooled in an ice bath. Neat chlorotrimethylsilane (0.16

mL, 1.2 mmol) was added with stirring, and the stirring was continued

at room temperature for 3 h, during which time the color of the

reaction mixture changed from red to orange. The mixture was

NMR spectra were recorded at 25 °C on a Varian UNITY Inova

00 spectrometer operating at 399.95, 100.58, and 161.90 MHz for

H, C, and P, respectively. Chemical shifts (δ/ppm) are reported

recooled in ice, and Na[BH ] (189 mg, 5.0 mmol) was added in one

relative to internal tetramethylsilane ( H and C) or to external 85%

portion. After the addition, the reaction mixture was stirred at 0 °C for

H PO₄( P). In addition to the standard notation of signal

0 min and then at room temperature for another 2 h, whereupon it

multiplicity, vt and vq are used to denote virtual multiplets arising

turned yellow. The mixture was diluted with saturated aqueous

NaHCO₃(60 mL; Caution: gas evolution!) and extracted with

dichloromethane (40 mL). The organic layer was washed with

from the protons constituting the AA′BB′ and AA′BB′X spin systems

in the methylene- and PPh -substituted cyclopentadienyl rings,

respectively (fc = ferrocene-1,1′-diyl). IR spectra were recorded with

saturated aqueous NaHCO , water, and brine, dried over magnesium

a Thermo Nicolet Magna 6700 FTIR spectrometer over the range

−

sulfate, and evaporated with chromatography-grade silica gel.

Subsequent column chromatography of the crude preadsorbed

product over silica gel with dichloromethane−methanol (10:1) and

evaporation furnished an orange foam (353 mg), which was analyzed

as a mixture of 1a (approximately 80%), 1aO (approximately 10%),

00−4000 cm . Low-resolution ESI mass spectra were obtained with

an Esquire 3000 (Bruker) spectrometer. Elemental analyses were

determined with a PerkinElmer PE 2400 CHN analyzer. The amount

of residual solvents, typically present in amorphous products, was

veriﬁed by NMR analysis and taken into account during all subsequent

experiments.

and 1a·BH (10%). Crystallization from hot ethyl acetate−hexane

eﬃciently removes the borane adduct but not the phosphine oxide. A

Synthesis of 1′-(Diphenylphosphino)-1-(aminomethyl)ferrocene

Hydrochloride (3·HCl). Aldoxime 2 (250 mg, 0.61 mmol; mixture of

E- and Z-isomers) was dissolved in dry THF (15 mL), and the

similar reaction with Li[AlH ] (5.0 mmol) in THF (no acid added)

aﬀorded 1a in only 9% yield, the majority of the aldehyde being

converted to 1′-[(diphenylphoshino)ferrocenyl]methanol (isolated

yield: 68%). Crystals used for X-ray diﬀraction analysis were grown

from ethyl acetate−hexane.

solution was added dropwise to solid Li[AlH ] (115 mg, 3.0 mmol)

while stirring and cooling in an ice bath. The reaction mixture was

stirred at room temperature for 6 h and then recooled on ice and

quenched by sequential addition of water (0.55 mL) and 15% aqueous

NaOH (0.15 mL). After stirring for another 30 min, the resulting

heterogeneous mixture was ﬁltered through a pad of diatomaceous

earth (Celite). The ﬁltrate was diluted with diethyl ether (15 mL),

washed with brine (5 mL), dried over magnesium sulfate, and, after

removal of the drying agent, treated with methanolic HCl (0.81 mL of

a 0.75 M solution, 0.61 mmol). The separated product was ﬁltered oﬀ

and dried under vacuum to aﬀord hydrochloride 3·HCl as a yellow

solid (168 mg, 64%). Crystals for X-ray diﬀraction measurements were

grown from hot methanol−chloroform.

H NMR (CDCl ): δ 3.97 (d, J = 4.8 Hz, 2 H, CH ), 3.98 (vt, J′

1.8 Hz, 2 H, fc), 4.08 (vq, J′ = 1.8 Hz, 2 H, fc), 4.13 (vt, J′ = 1.9 Hz,

H, fc), 4.41 (vt, J′ = 1.8 Hz, 2 H, fc), 4.54 (br s, 2 H, NH ), 5.32 (br

13 1

s, 1 H, NH), 7.31−7.39 (m, 10 H, PPh

). C{ H} NMR (CDCl ): δ

39.21 (CH ), 68.86 (CH of fc), 69.01 (CH of fc), 71.46 (d, JPC = 3 Hz,

CH of fc), 73.27 (d, JPC = 15 Hz, CH of fc), 75.58 (C-P of fc), 86.86

ortho

para

(C-CH

of Ph), 133.40 (d, JPC = 19 Hz, CH

of fc), 128.28 (d, JPC = 7 Hz, CH

of Ph), 128.81 (CH

meta

ipso

of Ph), 138.04 (br s, C of

Ph), 158.47 (CO). P{ H} NMR (CDCl

): δ −16.1 (s). IR (Nujol,

−

cm ): 3355 br w, 3389 br w, 3322 br w, 3191 br m, 1738 w, 1644 br s,

1601 s, 1431 s, 1329 s, 1311 m, 1269 w, 1232 w, 1202 w, 1162 m, 1123

m, 1096 m, 1069 w, 1029 s, 998 w, 929 w, 888 w, 823 m, 781 w, 742 s,

696 s, 655 w, 571 m, 532 s, 488 s, 460 s, 436 m. ESI+ MS: m/z 443

H NMR (DMSO-d ): δ 3.55 (s, 2 H, CH ), 4.06 (vt, J′ = 1.9 Hz, 2

H, fc), 4.11 (vq, J′ = 1.9 Hz, 2 H, fc), 4.30 (vt, J = 1.9 Hz, 2 H, fc), 4.50

vt, J = 1.8 Hz, 2 H, fc), 7.29−7.41 (m, 10 H, Ph), 8.15 (br s, 3 H,

+ 13 1

(

NH ). C{ H} NMR (DMSO-d ): δ 37.73 (CH ), 69.48 (CH of fc),

([M + H] ), 465 ([M + Na] ), 481 ([M + K] ). Anal. Calcd for

C H23FeN OP·0.2AcOEt (459.9): C 64.77, H 5.39, N 6.09. Found: C

24 2

0.52 (CH of fc), 71.70 (d, J = 4 Hz, CH of fc), 73.11 (d, J_P_C= 15

Hz, CH of fc), 75.99 (d, J = 7 Hz, C-PPh of fc), 79.84 (C-CH of

64.62, H 5.25, N 5.94 (sample crystallized from ethyl acetate−hexane).

Synthesis of N-[1′-(Diphenylphosphino)ferrocenyl]-N′-methylur-

ea (1b). Method C. Aldehyde 4 (398 mg, 1.00 mmol) and N-

methylurea were dissolved in a mixture of dry THF (30 mL) and

acetic acid (60 mL). Chlorotrimethylsilane (0.15 mL, 1.2 mmol) was

added, causing an immediate change in color from the initial red to

deep orange. After stirring at room temperature for 3 h, the mixture

ortho

para

fc), 128.22 (d, J = 7 Hz, CH

32.94 (d, J = 20 Hz, CH

of PPh ), 128.58 (CH of PPh₂),

of PPh ), 138.44 (d, J = 10 Hz,

2 PC

meta

ipso

of PPh₂). P{ H} NMR (DMSO-d ): δ −17.7 (s). IR (Nujol,

cm ): ν 3068 m, 2635 w, 2559 w, 1594 w, 1562 w, 1309 w, 1241 w

−

max

162 m, 1104 m, 1026 m, 963 w, 911 w, 884 w, 827 s, 817 s, 746 s, 698

s, 633 w, 522 w, 503 s, 483 s, 452 m, 424 w, 412 w. ESI+ MS: m/z 383

(

[Ph PfcCH ] ). Anal. Calcd for C H ClFeNP·0.1CHCl (447.6): C

was cooled in an ice bath, and Na[BH ] (189 mg, 5.00 mmol) was

23 23

1.98, H 5.20, N 3.13. Found: C 61.78, H 5.07, N 3.02 (crystallized

added in one portion (the color of the reaction changed gradually to

yellow). The stirring was continued at 0 °C for 30 min and then at

room temperature overnight before quenching with water (100 mL,

eﬀervescence). The resultant mixture was extracted with dichloro-

methane (50 and 20 mL), and the combined organic layers were

washed twice with saturated aqueous NaHCO₃(Caution: gas

evolution!), water, and brine, dried over magnesium sulfate, and

sample).

Synthesis of N-[1′-(Diphenylphosphino)ferrocenyl]urea (1a).

Method A. Anhydrous triethylamine (1.0 mL, 7.2 mmol, 16 equiv)

was added to a suspension of 3·HCl (200 mg, 0.46 mol) in dry

methanol (15 mL), causing the solid hydrochloride to dissolve the

compound. Sodium cyanate (47 mg, 0.6 mmol, 1.5 equiv) dissolved in

DOI: 10.1021/acs.organomet.5b00197

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

evaporated. The crude product was puriﬁed by column chromatog-

raphy (silica gel, dichloromethane−methanol, 20:1 v/v). The major

band containing the product and some phosphine oxide was

evaporated, and the residue was puriﬁed again by chromatography

over silica gel using ethyl acetate as the eluent to aﬀord 1b as an

orange solid (335 mg, 73%).

H NMR (CDCl ): δ 1.06−1.20 (m, 3 H, CH of Cy), 1.29−1.41

(m, 2 H, CH of Cy), 1.54−1.61 (m, 1 H, CH of Cy), 1.64−1.72 (m,

2 H, CH of Cy), 1.90−1.98 (m, 2 H, CH of Cy), 3.59 (m, 1 H, CH

of Cy), 3.95 (d, J = 4.8 Hz, 2 H, CH NH), 3.97 (vt, J′ = 1.9 Hz, 2

H, fc), 4.06 (vq, J′ = 1.7 Hz, 2 H, fc), 4.12 (vt, J′ = 1.8 Hz, 2 H, fc),

4.39 (vt, J′ = 1.9 Hz, 2 H, fc), 4.64 (br d, J = 7.7 Hz, 1 H, NHCy),

A similar reaction with Li[AlH ] in THF (without added acetic

5.01 (br m, 1 H, CH NH), 7.30−7.39 (m, 10 H, Ph). C{ H} NMR

acid) yielded analytically pure 1b (30%) together with [1′-

(CDCl ): δ 24.87 (CH of Cy), 25.63 (CH of Cy), 33.94 (CH of

(

diphenylphoshino)ferrocenyl]methanol (49%). The second chroma-

Cy), 38.99 (CH NH), 48.94 (CH of Cy), 68.76 (CH of fc), 69.01

tography was not needed in this case.

(CH of fc), 71.40 (d, J_P_C= 4 Hz, CH of fc), 73.19 (d, J_P_C= 15 Hz, CH

H NMR (CDCl ): δ 2.80 (s, 3 H, CH ), 3.95 (br s, 2 H, CH ),

of fc), 75.55 (br s, C-P of fc), 87.53 (C-CH of fc), 128.25 (d, J = 7

ortho

para

.98 (vt, J′ = 1.9 Hz, 2 H, fc), 4.07 (vq, J′ = 1.8 Hz, 2 H, fc), 4.12 (vt, J′

Hz, CH

of Ph), 128.75 (CH of Ph), 133.39 (d, J = 19 Hz,

meta

ipso

1.8 Hz, 2 H, fc), 4.39 (vt, J′ = 1.8 Hz, 2 H, fc), 4.62 (br s, 1 H, NH),

of Ph), 138.09 (br d, J = 6 Hz, C of Ph), 157.37 (C

−1

.01 (br s, 1 H, NH), 7.30−7.38 (m, 10 H, PPh ). C{ H} NMR

O). P{ H} NMR (CDCl ): δ −16.4 (s). IR (Nujol, cm ): 3392 m,

(

CDCl ): δ 27.26 (CH ), 39.19 (CH ), 69.22 (CH of fc), 68.99 (CH

3264 br m, 3049 m, 1740 w, 1620 s, 1598 s, 1497 s, 1310 w, 1272 m,

1254 m, 1233 m, 1160 m, 1084 m, 1049 w, 1033 m, 1025 m, 921 w,

871 w, 842 w, 813 m, 750 s, 745 s, 700 s, 634 m, 528 w, 499 s, 484 s,

of fc), 71.42 (d, J = 4 Hz, CH of fc), 73.25 (J = 15 Hz, CH of fc),

5.60 (br s, C-CH of fc), 87.22 (C-P of fc), 128.26 (d, J = 7 Hz,

ortho

para

meta

of Ph), 128.76 (CH of Ph), 133.40 ( J = 19 Hz, CH of

461 w, 413 w. ESI+ MS: m/z 525 ([M + H] ), 547 ([M + Na] ), 563

([M + K] ). Anal. Calcd for C H FeN OP (524.4): C 68.71, H 6.34,

ipso

Ph), 138.20 (br s, C

of Ph), 158.71 (CO). P{ H} NMR

−

(

CDCl ): δ −16.1 (s). IR (Nujol, cm ): ν 3326 s, 3294 s, 3137 br

N 5.34. Found: C 68.51, H 6.29, N 5.22.

max

m, 3100 m, 3078 m, 3043 m, 1625 s, 1582 s, 1259 m, 1194 w, 1161 m,

Synthesis of N-[1′-(Diphenylphosphino)ferrocenyl]-N′-phenylur-

ea (1e). Method A. Anhydrous triethylamine (2.5 mL, 18 mmol) was

added to a suspension of 3·HCl (437 mg, 1.0 mmol) in

dichloromethane (35 mL), whereupon the hydrochloride dissolved

to yield a clear orange solution. After cooling in an ice bath, neat

phenyl isocyanate (86 μL, 1.1 mmol) was added, and the resulting

mixture was stirred at 0 °C for 15 min and then at room temperature

overnight. Next, the reaction mixture was diluted with water (20 mL),

and the organic layer was separated. The aqueous residue was

extracted with dichloromethane (10 mL), and the organic phases were

combined, washed with brine, dried over anhydrous magnesium

sulfate, and, ﬁnally, evaporated under vacuum. The crude product was

puriﬁed by ﬂash chromatography (silica gel, dichloromethane−

methanol, 20:1 v/v). The ﬁrst intense band was collected and

evaporated to aﬀord 1e, which was further crystallized from hot ethyl

acetate−hexane (approximately 1:1). Yield: 458 mg (88%), orange

microcrystalline solid.

089 w, 1059 w, 1038 m, 1025 m, 998 w, 923 w, 889 w, 831m, 807 s,

76 w, 794 s, 696 s, 667 m, 635 m, 570 w, 529 m, 496 s, 485 s, 453 m,

−1

22 w, 410 w cm . ESI+ MS: m/z 457 ([M + H] ), 479 ([M + Na] ),

95 ([M + K] ). Anal. Calcd for C H FeN OP·0.25AcOEt (478.3):

C 65.28, H 5.69, N 5.86. Found: C 65.19, H 5.44, N 5.91.

Synthesis of N-[1′-(Diphenylphosphino)ferrocenyl]-N′,N′-dime-

thylurea (1c). Method B. Anhydrous triethylamine (1.0 mmol, 7.2

mmol) was added to a suspension of 3·HCl (437 mg, 1.0 mmol) in dry

dichloromethane (20 mL). To the resulting clear orange solution was

introduced neat N,N-dimethylcarbamoyl chloride (0.10 mL, 1.1

mmol), and the resulting mixture was stirred at room temperature

overnight. The reaction was terminated by the addition of saturated

aqueous NaHCO₃solution (10 min). The organic phase was

separated, washed with water and brine, and dried. The product was

isolated by ﬂash column chromatography over silica gel with

dichloromethane−methanol (20:1 v/v) as the eluent and evaporation

under vacuum. Yield of 1c: 433 mg (92%), yellow solid foam.

Method C. Aldehyde 4 (199 mg, 0.50 mmol) and N-phenylurea

(136 mg, 1.0 mmol) were dissolved in anhydrous THF (20 mL), and

the solution was cooled on ice. Chlorotrimethylsilane (76 μL, 0.60

mmol) was added with stirring at 0 °C, and the reaction was continued

at room temperature for 30 min. The color of the reaction mixture

changed from deep red to orange, and a ﬁne precipitate formed. Then,

H NMR (CDCl ): δ 2.91 (s, 6 H, NMe ), 3.99 (br d, J = 3.8

Hz, 2 H, CH ), 4.01 (vt, J′ = 1.8 Hz, 2 H, fc), 4.08 (vq, J′ = 1.8 Hz, 2

H, fc), 4.13 (vt, J′ = 1.9 Hz, 2 H, fc), 4.36 (vt, J′ = 1.8 Hz, 2H, fc), 4.67

(

br s, 1 H, NH), 7.29−7.38 (m, 10 H, Ph). C{ H} NMR (CDCl ): δ

6.37 (NMe ), 37.77 (CH ), 69.06 (CH of fc), 69.15 (CH of fc),

2 2

1.33 (d, J_P_C= 4 Hz, CH of fc), 73.22 (d, J = 15 Hz, C-P of fc),

the reaction mixture was cooled again to 0 °C, and Li[AlH ] (57 mg,

ortho

7.14 (C-CH of fc), 128.18 (d, J = 7 Hz, CH

of Ph), 128.63

1.5 mmol) was added at once. Instant eﬀervescence and a change in

color to yellow were observed upon the addition. After the gas

evolution ceased (ca. 5 min), the reaction was terminated by a careful

addition of degassed water (0.3 mL) and 3 M NaOH (0.1 mL). The

cooling bath was removed, and the resultant mixture was stirred for 20

min at room temperature (to complete hydrolysis) and then ﬁltered

through a pad of Celite, eluting with diethyl ether. The yellow ﬁltrate

was washed with water (3×) and brine, dried over magnesium sulfate,

mixed with chromatography-grade silica gel, and, ﬁnally, evaporated

under reduced pressure. The preadsorbed crude product was

transferred to the top of a chromatographic column packed with

silica gel in ethyl acetate−hexane (1:3). Elution with the same solvent

mixture removed minor impurities. Changing the solvent to pure ethyl

acetate eluted the main yellow band due to 1e, which was collected

and evaporate to furnish pure 1e as an orange solid (212 mg, 82%).

A similar reaction of 4 (199 mg, 0.50 mmol), N-phenylurea (136

mg, 1.0 mmol), and chlorotrimethylsilane (76 μL, 0.6 mmol) in THF

para

meta

(

CH of Ph), 133.41 (d, J = 20 Hz, CH of Ph), 138.58 (d, J

PC PC

ipso

8 Hz, C of Ph). 158.11 (CO). One signal due to ferrocene CH

probably overlaps with the solvent resonance. P{ H} NMR

−

(

CDCl ): δ −16.5 (s). IR (Nujol, cm ): 3356 m, 3047 w, 1721 w,

630 s, 1585 w, 1533 s, 1339 m, 1239 m, 1220 w, 1162 w, 1088 w,

038 w, 1027 w, 831w, 812 w, 747 m, 699 m, 569 w, 500 m, 486 w,

49 w. ESI+ MS: m/z 471 ([M + H] ), 493 ([M + Na] ), 509 ([M +

K] ). Anal. Calcd for C H FeN OP·0.1CH Cl (478.8): C 65.47, H

.73, N 3.55. Found: C 65.48, H 5.77, N 5.62.

Synthesis of N-[1′-(Diphenylphosphino)ferrocenyl]-N′-cyclohex-

ylurea (1d). Method A. Hydrochloride 3·HCl (219 mg, 0.50 mmol)

and triethylamine (1.0 mmol, 7.2 mmol) were mixed in dry

dichloromethane (10 mL), producing a clear orange solution, which

was cooled on ice. Neat cyclohexyl isocyanate (10 μL, 0.55 mmol) was

introduced, and the reaction mixture was stirred at 0 °C for 15 min

and then at room temperature overnight. After the reaction was

quenched by addition of water (10 mL), the organic layer was

separated, and the aqueous residue was extracted with dichloro-

methane (3 × 10 mL). The combined organic phases were washed

with brine, dried over magnesium sulfate, and evaporated under

vacuum to aﬀord a crude product, which was puriﬁed by

chromatography (silica gel, dichloromethane−methanol, 10:1) and

then crystallized from hot ethyl acetate−hexane (approximately 1:3) to

aﬀord urea 1d as orange crystals (217 mg, 83%). Crystals suitable for

X-ray diﬀraction analysis were obtained from ethyl acetate−hexane.

(10 mL) and acetic acid (10 mL) with Na[BH ] (95 mg, 2.5 mmol) as

the reducing agent followed by aqueous workup provided 250 mg of a

solid product, which contained the desired product 1e strongly

contaminated by the respective borane adduct (1e·BH : approximately

30%) according to NMR analysis.

H NMR (CDCl ): δ 3.98 (vt, J′ = 1.9 Hz, 2 H, fc), 4.01 (d, J

4.9 Hz, 2 H, CH ), 4.04 (vq, J′ = 1.8 Hz, 2 H, fc), 4.13 (vt, J′ = 1.8 Hz,

2 H, fc), 4.35 (vt, J′ = 1.8 Hz, 2 H, fc), 5.53 (br s, 1 H, NH), 6.99 (br s,

1 H, NH), 7.02−7.06 (m, 1 H, Ph), 7.26−7.39 (m, 14 H, NHPh and

DOI: 10.1021/acs.organomet.5b00197

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

PPh ). ¹³C{ H} NMR (CDCl ): δ 38.80 (CH ), 68.87 (CH of fc),

1265 m, 1230 w, 1202 m, 1161 m, 1122 w, 1077 m, 1053 w, 1033 s,

1024 s, 929 w, 887 w, 864 w, 831 s, 738 s, 694 s, 634 w, 592 m, 569 w,

513 s, 484 s, 474 s, 453 m, 434 m, 413 w. ESI+ MS: m/z 462 ([M +

9.00 (CH of fc), 71.44 (d, J_P_C= 3 Hz, CH of fc), 73.17 (d, J = 14

ortho

Hz, CH of fc), 87.11 (C-CH of fc), 120.42 (CH

of NHPh),

of PPh ),

para

ortho

23.41 (CH of NHPh), 128.35 (d, J = 7 Hz, CH

H] ), 464 ([M + Na] ), 480 ([M + K] ). Anal. Calcd for

meta

28.91 (CH

of NHPh), 129.19 (CH of PPh ), 133.37 (d, J

C H FeNOP (441.3): C 68.04, H 5.48, N 3.17. Found: C 67.76,

ipso

25 24

meta

ipso

9 Hz, CH

of PPh ), 137.79 (br, C of PPh ), 138.87 (C of

H 5.36, N 2.90.

NPh), 155.40 (CO). Signal due to C-P of fc was not observed.

Synthesis of Phosphine Oxide 1eO. Compound 1e (40 mg, 77

μmol) was dissolved in acetone (6 mL), and the solution was cooled

on ice. Concentrated hydrogen peroxide (0.1 mL 30%) was added, and

the resulting mixture was stirred at 0 °C for 20 min. Then, the reaction

mixture was diluted with water (ca. 6 mL), and its volume was reduced

to half by evaporation under vacuum, whereupon the product

separated as a yellow solid. The latter was extracted into dichloro-

methane, and the extract was dried brieﬂy over anhydrous magnesium

sulfate and passed through a short silica gel column using

dichloromethane−methanol (10:1) as the eluent. Subsequent

evaporation aﬀorded phosphine oxide 1eO as a yellow-orange, glassy

solid. Yield: 40 mg, 97%.

−1

P{ H} NMR (CDCl ): δ − 16.3 (s). IR (Nujol, cm ): ν 3370 br

max

w, 3318 w, 3183 w, 3092 m, 1645 s, 1598 s, 1544 s, 1324 m, 1310 s,

250 s, 1189 w, 1159 m, 1089 w, 1051 w, 1025 w, 997 w, 912 w, 862

w, 839 s, 815 m, 756 s, 748 s, 698 s, 514 m, 493 s, 482 s, 451 m, 430 w.

ESI+ MS: m/z 519 ([M + H] ), 542 ([M + Na] ), 557 ([M + K] ).

Anal. Calcd for C H FeN OP (518.4): C 69.51, H 5.25, N 5.41.

Found: C 69.30, H 5.08, N 5.29.

Preparation of N-[1′-(Diphenylphosphino)ferrocenyl]-N′-phenyl-

thiourea (1f). Method A. Hydrochloride 3·HCl (437 mg, 1.0 mmol)

and dry triethylamine (2.5 mL, 18 mmol) were mixed in dry

dichloromethane (30 mL), and the resulting clear solution was cooled

on ice. Phenyl isothiocyanate (0.13 mL, 1.1 mmol) was added, and the

mixture was stirred at 0 °C for 15 min and then at room temperature

overnight. The reaction was terminated by addition of water (20 mL),

the organic phase was separated, and the aqueous residue was

extracted with dichloromethane (approximately10 mL). The com-

bined dichloromethane layer was washed with brine, dried with

magnesium sulfate, and evaporated under vacuum. The crude product

was puriﬁed by ﬂash chromatography (silica gel, dichloromethane−

methanol 50:1 v/v) and further crystallized from hot ethyl acetate−

hexane (1:1) to yield stoichiometric solvate 1f·AcOEt as yellow-orange

crystals (483 mg, 77%). Crystals of unsolvated 1f used for X-ray

H NMR (CDCl ): δ 3.93 (vt, J′ = 1.9 Hz, 2 H, fc), 4.08 (d, J

3.7 Hz, 2 H, CH ), 4.32 (vq, J′ = 1.8 Hz, 2 H, fc), 4.38 (vt, J′ = 1.9 Hz,

2 H, fc), 4.57 (vq, J′ = 1.8 Hz, 2 H, fc), 6.93 (tt, J′ = 7.4, 1.2 Hz, 1 H,

NPh), 7.22−7.28 (m, 2 H, NPh), 7.45−7.72 (m, 13 H, Ph and NH),

8.73 (br s, 1 H, NH). ¹³C{ H} NMR (CDCl ): δ 37.96 (CH ), 68.33

(CH of fc), 68.78 (CH of fc), 72.20 (d, J = 10 Hz, CH of fc), 72.30

ipso

(d, J = 117 Hz, C -P of fc), 72.69 (d, J = 13 Hz, CH of fc),

ortho

para

89.21 (C-CH of fc), 118.10 (CH

NHPh), 128.52 (d, J = 12 Hz, CH

NPh), 131.24 (d, J = 10 Hz, CH

of NHPh), 121.17 (CH of

ortho

meta

of PPh ), 128.69 (CH

meta

of PPh ), 132.08 (d, J = 3

Hz, CH of PPh ), 132.94 (d, J = 108 Hz, C of PPh ), 140.72

para

ipso

diﬀraction analysis were grown from ethyl acetate−hexane.

(C of NHPh), 156.47 (CO). P{ H} NMR (CDCl ): δ 32.8 (s).

H NMR (CDCl ): δ 3.88 (vq, J = 1.8 Hz, 2 H, fc), 4.01 (vt, J = 1.9

ESI+ MS: m/z 535 ([M + H] ), 557 ([M + Na] ), 573 ([M + K] ). IR

−

Hz, 2 H, fc), 4.04 (vt, J = 1.8 Hz, 2 H, fc), 4.07 (vt, J = 1.8, 2 H, fc),

(Nujol, cm ): ν 3329 br m, 3228 w, 3082 w, 1707 s, 1600 m, 1541

max

.34 (d, J = 4.9 Hz, 2 H, CH ), 6.27 (br s, 1 H, CH NH), (101

s, 1500 s, 1325 m, 1279 w, 1227 m, 1216 m, 1197 s, 1186 m, 1176 m,

1161 s, 1101 m, 1038 m, 997 w, 896 w, 871 w, 843 w, 754 s, 705 s, 696

s, 633 w, 571 s, 532 m, 507 m, 496 s, 483 m, 443 m. Anal. Calcd for

C H FeN O P·0.05CHCl (540.5): C 66.80, H 5.05, N 5.18. Found:

MHz): δ 44.25 (CH ), 68.53 (CH of fc), 69.45 (CH of fc), 71.02 (d, J

4 Hz, CH of fc), 73.08 (d, J = 14 Hz, CH of fc), 85.09 (C-CH of

ortho

para

fc), 125.77 (CH

of NHPh), 127.62 (CH of NHPh), 128.19 (d,

ortho

meta

J_P_C= 7 Hz, CH

of PPh ), 128.67 (CH

of NHPh), 130.25

C 66.59, H 5.03, N 4.99.

Preparation of [PdCl(1e-κP)(μ-Cl)]

(50 mg, 96 μmol) in dichloromethane (5 mL) was added to a solution

of [PdCl (cod)] (27.5 mg, 96 μmol) in the same solvent (1 mL). The

para

meta

(

CH of PPh ), 133.40 (d, J = 20 Hz, CH

of PPh ), 136.06

(5). A solution of phosphine 1e

ipso

(

of NHPh), 138.54 (d, J = 9 Hz, C of PPh ), 180.16 (C

S). The signal due to C-P of fc was not observed. P{ H} NMR

−1

(

CDCl ): δ − 16.7 (s). IR (Nujol, cm ): 3371 w, 3356 m, 3154 br m,

dark reaction mixture was stirred for 1 h and then ﬁltered through a

syringe ﬁlter (0.45 μm) into pentane (40 mL). The mixture was stored

at −18 °C overnight before the precipitated product was ﬁltered oﬀ,

washed with pentane, and dried under vacuum. Yield of 5: 66 mg

734 w 1588 w, 1515 s, 1316 m, 1300 m, 1261 m, 1240 m, 1192 w,

163 m, 1092 w, 1050 w, 1026 m, 970 w, 960 w, 844 w, 833 m, 754 s,

46 s, 699 w, 532 w, 493 m, 480 m, 458 w. ESI+ MS: m/z 535 ([M +

H] ), 557 ([M + Na] ), 573 ([M + K] ). Anal. Calcd for

(quant.), grayish solid.

C H FeN PS·AcOEt (622.5) C 65.59, H 5.67, N 4.50. Found: C

H NMR (CDCl

); 6.26 (br s, 1 H, NHCH

): δ 4.23, 4.53, 4.54, 4.64, and 4.93 (5× br s, 2 H,

6.00, H 5.42, N 4.50.

Preparation of 1′-(Diphenylphosphino)-1-[(acetylamino)methyl]-

fc and CH

), 6.95−7.00 (m, 1 H, Ph),

7.17−7.28 (m, 6 H, Ph), 7.35−7.41 (m, 3 H, Ph), 7.44−7.7.51 (m, 5

ferrocene (1g). Method B. Freshly distilled acetyl chloride (45 μL,

H, Ph), 7.94 (br s, 1 H, NHPh). C{ H} NMR (CDCl ): δ 38.83

0.63 mmol) was added to a solution of amine 3 generated in situ by

(CH ), 67.80 (d, J = 68 Hz, C-P of fc), 70.00 (CH of fc), 70.99

mixing 3·HCl (250 mg, 0.57 mmol) and triethylamine (0.7 mL, 5

mmol) in dry dichloromethane (10 mL). The reaction mixture was

stirred at room temperature overnight before quenching with 3 M HCl

(CH of fc), 73.32 (d, J_P_C= 9 Hz, CH of fc), 75.82 (d, J_P_C= 11 Hz, CH

para

of fc), 89.30 (C-CH of fc), 118.72 (CH of NHPh), 122.00 (CH of

NHPh), 128.58 (d, J = 63 Hz, C-P of PPh ), 128.15 (d, J = 13

para

(5 mL). The organic phase was separated and washed successively

Hz, CH of PPh ), 128.85 (CH of PPh ), 131.78 (CH of NHPh),

ipso

with 3 M HCl, 0.1 M NaOH, water, and brine (5 mL each), dried over

magnesium sulfate, and evaporated. The crude product was puriﬁed by

column chromatography over silica gel using dichloromethane−

methanol (5:1, v/v) as the eluent. Following evaporation under

vacuum, the product was isolated as a viscous, orange-brown oil (231

mg, 91%).

133.45 (d, J = 11 Hz, CH of PPh ), 139.76 (C of NHPh), 155.99

PC 2

(CO). P{ H} NMR (CDCl ): δ 33.6 (s). ESI+ MS: m/z 623

−1

([Pd(1e − H)] ), 659 ([Pd(1e)Cl] ). IR (Nujol, cm ): ν 3350 br

max

m, 3055 w, 1655 s, 1597 s, 1548 s, 1498 s, 1311 m, 1236 m, 1166 m,

1099 m, 1059 w, 1030 m, 999 w, 921 w, 896 w, 835 m, 748 s, 712 m,

692 s, 620 w, 548 m, 542 s, 478 s, 447 m. Anal. Calcd for

C H Cl Fe N O P Pd (1391.4): C 51.79, H 3.91, N 4.03. Found: C

H NMR (CDCl ): δ 2.03 (s, 3 H, CH ), 4.00−4.03 (m, 4 H, 2× fc

60 54

CH ), 4.07 (vq, J′ = 1.8 Hz, 2 H, fc), 4.11 (vt, J′ = 1.8 Hz, 2 H, fc),

51.66, H 3.86, N 3.85.

Preparation of [PdCl (1e-κP) ] (6). A dichloromethane solution of

.38 (vt, J′ = 1.8 Hz, 2 H, fc), 6.02 (br s, 1 H, NH), 7.30−7.39 (m, 10

13 1

H, Ph). C{ H} NMR (CDCl ): δ 22.23 (CH ), 38.51 (CH ), 69.14

[PdCl (cod)] (28.3 mg, 29 μmol in 2 mL) was added to a solution of

(

CH of fc), 69.24 (CH of fc), 71.50 (d, J_P_C= 4 Hz, 75.35 (br s, C-PPh₂

phosphine 1e (30 mg, 58 μmol) in the same solvent (3 mL). The

resulting red solution was stirred for 15 min, concentrated to

approximately one-half its original volume by evaporation under

vacuum, and precipitated by addition of pentane (20 mL). The

separated solid was ﬁltered oﬀ, washed with pentane, and dried under

vacuum. Yield of 6: 34 mg (96%), red solid. Note: The crude products

of fc), 71.53 (CH of fc), 73.34 (d, J_P_C= 14 Hz, CH of fc), 85.79 (C-

CH of fc), 128.29 (d, J = 7 Hz, CH of PPh ), 128.91 (CH of

PPh ), 133.40 (d, J = 19 Hz, CH

meta

para

ortho

ipso

of PPh ), 137.82 (br s, C of

PPh ), 169.73 (CO). P{ H} NMR (CDCl ): δ −16.3 (s). IR

−1

(

Nujol, cm ): 3279 br m, 1721 w, 1645 s, 1585 m, 1552 s, 1288 s,

DOI: 10.1021/acs.organomet.5b00197

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

contained traces of an unidentiﬁed impurity (diﬀerent from 5, 1e, and

5.4 Hz, 1 H, CH NH), 6.96 (m, 1 H, NPh), 7.24−7.29 (m, 2 H,

eO), which could be removed by precipitation of the concentrated

NHPh), 7.35−7.55 (m, 10 H, PPh ), 7.57−7.61 (m, 2 H, NPh), 8.45

reaction mixture with pentane.

(s, 1 H, NHPh). C{ H} NMR (CDCl ): δ 38.33 (CH NH), 61.12

H NMR (CDCl ): δ 4.04 (d, J = 4.3 Hz, 2 H, CH ), 4.37 (br s,

(d, J = 2 Hz,CH -allyl trans-Cl), 67.80 (CH of fc), 67.91 (CH of

PC 2

H, fc), 4.40 (br s, 2 H, fc), 4.47 (br s, 2 H, fc), 4.54 (br s, 2 H, fc),

fc), 69.08 (CH of fc), 69.22 (CH of fc), 71.92 (d, J = 7 Hz, CH of

.63 (br s, 1 H, CH NH), 6.94−6.98 (m, 1 H, Ph), 7.15−7.23 (m, 5

fc), 72.18 (d, J_P_C= 7 Hz, CH of fc), 73.45 (d, J = 48 Hz, C-P of fc),

H, Ph), 7.30−7.38 (m, 5 H, Ph), 7.55−7.62 (m, 4 H, 3× CH of Ph +

74.38 (d, J = 11 Hz, CH of fc), 74.78 (d, J_P_C= 13 Hz, CH of fc),

NHPh). ¹³C{ H} NMR (CDCl ): δ 38.81 (CH ), 69.34 (CH of fc),

81.16 (d, J = 31 Hz, CH -allyl trans-P), 89.49 (C-CH of fc), 118.34

0.41 (CH of fc), 71.70 (apparent t, J′ = 27 Hz, C-P of fc), 72.29

(CH-allyl meso; partly overlapped), 118.38 (CH of NHPh), 121.68

para

(

apparent t, J′ = 4 Hz, CH of fc), 75.86 (apparent t, J′ = 5 Hz, CH of

(CH of NHPh), 128.36 (d, J = 10 Hz, CH of PPh ), 128.80 (CH

para

fc), 88.41 (C-CH of fc), 119.94 (CH of NHPh), 122.86 (CH of

of NHPh), 130.32 (d, J = 2 Hz, CH of PPh ), 132.94 (d, J

11 Hz, CH of PPh ), 134.54 (dd, J = 45 Hz, 3 Hz, C of PPh₂),

ipso

NHPh), 127.87 (apparent t, J = 5 Hz, CH of PPh ), 128.90 (CH of

NHPh), 130.56 (CH of PPh ), 130.77 (apparent t, J = 25 Hz,

para

ipso

140.23 (C of NHPh), 155.95 (CO). P{ H} NMR (CDCl ): δ

ipso

−1

(

-P of PPh ), 134.04 (apparent t, J = 6 Hz, CH of PPh ), 139.02

16.4 (s). IR (Nujol, cm ): ν 3359 w, 3317 w, 3269 w, 3088 w, 3071

max

Cⁱ^p^s^oof NHPh) 155.62 (CO). P{ H} NMR (CDCl ): δ 16.4 (s).

w, 1688 s, 1595 m, 1544 s, 1310 m, 1269 w, 1233 m, 1167 w, 1097 w,

1054 w, 1024 w, 846 w, 824 w, 758 m, 744 m, 696 m, 626 w, 614 w,

ESI+ MS: m/z 519 ([1e + H] ), 623 ([Pd(1e − H)] ). ESI− MS: m/z

−

59 ([PdCl(1e − 2H)] ), 740 ([Pd(1e)Cl ] ), 1247 ([Pd(1e) Cl +

517 m, 503 w, 495 m, 462 w, 444 m. ESI+ MS: m/z 665 ([M − Cl] ).

−

−1

Cl] ). IR (Nujol, cm ): ν 3343 br m, 3053 w, 1652 s, 1598 s, 1552

s, 1498 s, 1311 m, 1236 m, 1164 m, 1099 m, 1058 w, 1029 m, 999 w,

Anal. Calcd for C H ClFeN OPPd·0.1CH Cl (709.8): C 56.01, H

max

33 32

4.57, N 3.95. Found: C 55.99, H 4.41, N 3.88.

20 w, 895 w, 833 m, 746 s, 692 s, 539 w, 509 m, 446 w. Anal. Calcd

Pd-Catalyzed Cyanation of Aryl Bromides. General Procedure. A

dry Schlenk tube was charged with the respective ligand (0.02 mmol)

and palladium complex (0.01 mmol). These solid educts were

dissolved in dichloromethane (2 mL), and the resulting solution was

stirred for 5 min before being evaporated under vacuum. Aryl bromide

(8, 1.0 mmol), K [Fe(CN) ]·3H O (212 mg, 0.50 mmol), and

for C H Cl Fe N O P Pd (1214.0): C 59.36, H 4.48, N 4.62. Found:

C 59.09, H 4.65, N 4.44.

Preparation of [PdCl(C H CH NMe -κ C ,N)(1e-κP)] (7). A solution

of ligand 1e (50 mg, 96 μmol) dissolved in dichloromethane (6 mL)

was added to [PdCl(L )] dissolved in the same solvent (2 mL). The

2 2

reaction mixture was stirred for 60 min and then evaporated under

vacuum to aﬀord 7 as a yellow solid. Yield: 76 mg (quant.). Crystals

suitable for X-ray diﬀraction analysis were obtained upon layering a

chloroform solution of the complex with hexane and slow

crystallization by liquid-phase diﬀusion.

anhydrous sodium carbonate (106 mg, 1.0 mmol) were introduced

successively, and the reaction vessel was ﬂushed with argon and sealed

with a rubber septum. Dioxane and degassed water (2 mL each) were

added, and the Schlenk tube was transferred to an oil bath preheated

to 100 °C, in which the reaction mixture was stirred for 3 or 24 h.

Next, the reaction mixture was cooled to room temperature and

diluted with ethyl acetate and water (5 mL each). The organic layer

was separated, and the aqueous residue was extracted with ethyl

acetate (3× 5 mL). The organic layers were combined, washed with

brine, dried over anhydrous magnesium sulfate, and evaporated to

aﬀord crude products, which were analyzed by NMR spectroscopy.

Pure products were isolated by column chromatography over silica gel

using ethyl acetate−hexane mixtures as the eluents (see the Supporting

Information). Details regarding the screening experiments are

presented in the text and tables above. Mesitylene (1.0 mmol) was

H NMR (CDCl ): δ 2.81 (d, J = 2.8 Hz, 6 H, NMe ), 4.12 (d,

³J_H_H= 2.2 Hz, 2 H, C H CH ), 4.18 (d, J_P_H= 4.8 Hz, 2 H,

Me NCH ), 4.29 (vt, J′ = 1.9 Hz, 2 H, fc), 4.41 (td, J′ = 1.9, 1.0 Hz, 2

H, fc), 4.49 (vq, J′ = 1.9 Hz, 2 H, fc), 4.58 (vt, J′ = 1.8 Hz, 2 H, fc),

.24 (ddd, J = 7.7 Hz, 6.5 Hz, 1.0 Hz, 1 H, C H ), 6.38 (m, 2 H, 1H of

C H and CH NH), 6.83 (td, J = 7.4, 1.1 Hz, 1 H, C H ), 6.94 (tt, J =

.4, 1.1 Hz, 1 H, NHPh), 7.01 (dd, J = 7.4, 1.5 Hz, 1 H, C H ), 7.21−

.25 (m, 2 H, Ph), 7.29−7.35 (m, 4 H, Ph), 7.39−7.44 (m, 2 H, Ph),

.49−7.55 (m, 6 H, Ph), 8.23 (s, 1 H, NHPh). C{ H} NMR

(

CDCl ): δ 38.79 (C H CH ), 50.14 (d, J = 3 Hz, N(CH ) ), 68.87

CH of fc), 69.91 (CH of fc), 72.32 (d, J_P_C= 7 Hz, CH of fc), 73.38

d, J = 3 Hz, C-PPh of fc), 73.73 (d, J = 60 Hz, Me NCH ),

3 5 4 2 PC 3 2

added to the reaction mixture as an internal standard for H NMR

analysis after the aqueous workup.

5.89 (d, J_P_C= 9 Hz, CH of fc), 89.05 (C-CH of fc), 118.49 (CH of

X-ray Crystallography. Diﬀraction data (±h ±k ±l, θmax = 26.0−

27.5°, completeness ≥99.5%) were collected at 150(2) K with a

Nonius Kappa CCD diﬀractometer equipped with an Apex II image

plate detector and Cryostream Cooler (Oxford Cryosystems) using

graphite-monochromatized Mo Kα radiation (λ = 0.710 73 Å). The

data were processed and corrected for absorption by methods included

in the diﬀractometer software. Parameters of the data collection,

structure solution, and reﬁnement are available in the Supporting

Information (Table S1).

para

NHPh), 121.83 (CH

of NHPh), 122.58 (CH of C H ), 123.94

6 4

(

CH of C H ), 125.04 (d, J = 6 Hz, CH of C H ), 128.01 (d, J

para

1 Hz, CH of PPh ), 128.77 (CH of NHPh), 130.68 (d, J = 2 Hz,

CH of C H ), 131.35 (d, J = 50 Hz, CH of PPh ), 134.33 (d, J =

ipso

2 Hz, CH of PPh ), 138.71 (d, J = 11 Hz, C of PPh ), 139.95

2 PC 2

ipso

(

of NHPh), 147.85 (d, J = 2 Hz, C-Pd of C H ), 151.91 (C-

PC 6 4

CH of C H ), 155.85 (CO). P{ H} NMR (CDCl ): δ 33.9 (s).

−1

IR (Nujol, cm ): ν 3379 w, 3344 w, 3314 w, 3280 m, 1698 s, 1601

max

m, 1579 w, 1548 s, 1499 s, 1318 m, 1233 m, 1210 m, 1162 w, 1097 w,

The structures were solved by direct methods (SHELXS97 ) and

032 w, 991 w, 839 w, 814 w, 738 m, 693 m, 654 w, 542 m, 522 w, 496

reﬁned by full-matrix least-squares routines based on F

w, 462 w, 443 w. ESI+ MS: m/z 758 ([M − Cl] ). Anal. Calcd for

C H ClFeN OPPd (794.4): C 58.96, H 4.95, N 5.29. Found: C

(SHELXL97 ). Unless speciﬁed otherwise, the non-hydrogen atoms

were reﬁned with anisotropic displacement parameters. The urea and

amide hydrogen atoms (NH) were typically located on the diﬀerence

8.81, H 4.90, N 5.05.

[

PdCl(η -C H )(1e-κP)] (8). A solution of ligand 1e (50 mg, 96

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

iso

μmol) in dichloromethane (6 mL) was added to a solution of

1.2U (N). Hydrogens residing on the carbon atoms as well as the

[

PdCl(η -C H )] (17.5 mg, 48 μmol) in the same solvent (2 mL).

NH₃protons in the structure of 3·HCl were included in their

The resulting solution was stirred for 60 min and then evaporated

under vacuum to aﬀord 8 as a glassy solid, which slowly crystallized.

Yield of 8·0.2CH Cl : 69 mg (quant.). Crystals suitable for X-ray

calculated positions and reﬁned similarly with U (H) set to

iso

1.5U (C) for the methyl groups and to 1.2U (C) for all other

CH moieties and the NH hydrogens. Further details regarding the

diﬀraction measurements were grown from ethyl acetate−hexane.

structure reﬁnement are as follows.

H NMR (CDCl ): δ 2.83 (d, J = 12.2 Hz, 1 H, CH -allyl trans-Cl),

The terminal phenyl group in the structure of 7·2CHCl₃is

disordered and was modeled over two positions. Carbon atoms in the

less abundant component (20%) were reﬁned isotropically, and the

hydrogen residing at the nitrogen N2 was placed into its calculated

position. Furthermore, the solvent molecules in the structure of 7·

.12 (d, J = 6.4 Hz, 1 H, CH -allyl trans-Cl), 3.74 (dd, J = 13.8, 9.8 Hz,

H, CH -allyl trans-P), 3.84 (m, 1 H, fc), 3.86 (m, 1 H, fc), 4.11 (dd,

J_H_H= 15.4, 5.1 Hz, 1 H, CH NH), 4.21 (dd, J = 15.4, 5.8 Hz, 1 H,

CH NH), 4.27 (br s, 1 H, fc), 4.38 (br s, 1 H, fc), 4.46−4.52 (m, 3 H,

fc), 4.63 (br s, 1 H, fc), 4.71 (td, J = 7.2, 1.7 Hz, 1 H, CH -allyl trans-

2CHCl were heavily disordered in structure voids and were thus

P), 5.57 (ddd, J = 18.9, 13.9, and 7.6 Hz, 1H, CH-allyl), 6.34 (t, J

modeled by PLATON/SQUEEZE. Finally, the η -allyl moiety in the

DOI: 10.1021/acs.organomet.5b00197

Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

crystal structure of 8 was disordered over two positions related

approximately by rotation along the axis connecting the center of

(Solvias AG, Switzerland). Diphosphine ligands for metal complexes.

International Patent WO 2001004131, 2001.

gravity of the allyl moiety and the Pd center, similarly to other

(5) Selected recent examples: (a) Simenel, A. A.; Morozova, E. A.;

Snegur, L. V.; Zykova, S. I.; Kachala, V. V.; Ostrovskaya, L. A.;

Bluchterova, N. V.; Fomina, M. M. Appl. Organomet. Chem. 2009, 23,

[

PdCl(η -C H )(L)]) complexes with D-type ligands (see Scheme

). The reﬁned occupancies of the contributing orientations were ca.

0:40.

19−224. (b) Lapic,

Organometallics 2008, 27, 726−735. (c) Kar

Orban, E.; Sohar, P.; Drahos, L.; Gal, E.; Csam

7, 2316−2329.

6) Hayashi, T.; Mise, T.; Fukushima, M.; Kagotani, M.; Nagashima,

J.; Pavlovic,

G.; Siebler, D.; Heinze, K.; Rapic,

olyi, B. I.; Bosze, S.;

pai, A. Molecules 2012,

All geometric calculations were carried out, and the diagrams were

obtained with the recent version of the PLATON program. The

numerical values were rounded with respect to their estimated

deviations (ESDs) given to one decimal place. Parameters pertaining

to atoms in constrained positions (mostly hydrogens) are presented

without ESDs.

(

N.; Hamada, Y.; Matsumoto, A.; Kawakami, S.; Konishi, M.;

Yamamoto, K.; Kumada, M. Bull. Chem. Soc. Jpn. 1980, 53, 1138−

151.

ASSOCIATED CONTENT

(

7) (a) Zhao, Q.; Li, S.; Huang, K.; Wang, R.; Zhang, X. Org. Lett.

013, 15, 4014−4017. (b) Zhao, Q.; Wen, J.; Tan, R.; Huang, T.;

Metola, P.; Wang, R.; Anslyn, E. V.; Zhang, X. Angew. Chem., Int. Ed.

014, 53, 8467−8470.

8) For structurally related, planar-chiral tertiary urea derivatives, see:

Metallinos, C.; John, J.; Zaifman, J.; Emberson, K. Adv. Synth. Catal.

012, 354, 602−606.

■

Supporting Information

Supporting Information for this article comprises additional

structural drawings and description of the crystal structure of

(

1j and 11k, a tabular summary of relevant crystallographic

data (Table S1), characterization data for the catalytic products

10, 11, and 12), and copies of the NMR spectra for the newly

(

9) Step

10) Solaro

33, 4131−4147.

(11) Selected reviews: (a) Beer, P. D.; Bayly, S. Top. Curr. Chem.

nick

a, P. Chem. Soc. Rev. 2012, 41, 4273−4305.

prepared compounds. The Supporting Information is available

free of charge on the ACS Publications website at DOI:

(

va,

́ ̌ ́ ̌

H.; Císarova, I.; Stepnicka, P. Organometallics 2014,

0.1021/acs.organomet.5b00197.

005, 255, 125−162. (b) Bayly, S.; Beer, P. D.; Chen, G. Z. In

AUTHOR INFORMATION

Ferrocenes: Ligands, Materials and Biomolecules; Step

nick

a, P., Ed.;

■

Wiley & Sons: Chichester, 2008; Part II − Materials, Molecular

Devices and Biomolecules, Chapter 8, pp 281−318. (c) Evans, N. H.;

Beer, P. D. Angew. Chem., Int. Ed. 2014, 53, 11716−11754. Further

recent examples: (d) Willener, Y.; Joly, K. M.; Moody, C. J.; Tucker, J.

H. R. J. Org. Chem. 2008, 73, 1225−1233. (e) Cormode, D. P.; Evans,

A. J.; Davis, J. J.; Beer, P. D. Dalton Trans. 2010, 6532−6541.

Corresponding Author

E-mail: stepnic@natur.cuni.cz.

Notes

The authors declare no competing ﬁnancial interest.

(

f) Evans, N. H.; Serpell, C. J.; Christensen, K. E.; Beer, P. D. Eur. J.

ACKNOWLEDGMENTS

■

Inorg. Chem. 2012, 939−944 and references therein. (g) Huang, X.;

The results reported in this paper were obtained with ﬁnancial

support from the Czech Science Foundation (project no. 13-

8890S) and the Grant Agency of Charles University in Prague

Wu, B.; Jia, C.; Hay, B. P.; Li, M.; Yang, X.-J. Chem.Eur. J. 2013, 19,

034−9041 and references therein.

(12) (a) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40,

(

project no. 108213). This article is dedicated to Professor

680−399. (b) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog.

Inorg. Chem. 1999, 48, 233−350. (c) Bader, A.; Lindner, E. Coord.

Chem. Rev. 1991, 108, 27−110.

Tamotsu Takahashi in honor of his 60th birthday.

(13) For examples of ferrocene phosphines bearing an additional

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(

DOI: 10.1021/acs.organomet.5b00197

Organometallics XXXX, XXX, XXX−XXX

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