Allylpalladium(II) histidylidene complexes and their application in Z-selective transfer semihydrogenation of alkynes

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DOI:10.1002/ejic.201403104

Allylpalladium(II) Histidylidene Complexes and Their

Application in Z-Selective Transfer Semihydrogenation of

Alkynes

[

a]

[b]

[a]

Ruben M. Drost, Daniël L. J. Broere, Jorin Hoogenboom,

[a]

[c]

[b]

Simone N. de Baan, Martin Lutz, B. de Bruin, and

[

a]

C. J. Elsevier*

Keywords: Homogeneous catalysis / Palladium / Carbenes / Hydrogenation / Reduction / Alkynes

We have studied the use of amino acid histidine as a

precursor for N-heterocyclic carbene (NHC) ligands. This

natural amino acid possesses an imidazole substituent, which

makes it an interesting NHC precursor that contains both an

acid and an amino functionality. These functionalities may

be used for further tuning of NHC complexes. We have

developed routes for the synthesis of symmetric and dissym-

metric alkyl, benzyl, and aryl-substituted histidinium salts.

Subsequently, the corresponding Ag and Pd histidylidenes

were synthesized and the palladium complexes were tested

in the Z-selective transfer semihydrogenation of alkynes.

Histidylidene palladium complexes that contain additional

donor functionalities were found to display good selectivities.

The best catalytic results were obtained with a Pd-histidylid-

ene complex that contains two picolyl functional groups.

Introduction

ethylorthoformate, and (V) reacting formamidines with di-

[

1,10–13]

electrophiles, which provides an imidazolidine.

Syn-

N-Heterocyclic carbenes (NHCs) have found application

in functional materials, transition-metal catalysis, organo-

catalysis, bioorganometallic chemistry, and organometallic

thesis of backbone-functionalized NHCs through these

[14–16]

routes is less trivial.

Nevertheless, alternative strategies

toward these compounds would lead to a wider versatility

in NHC ligands and options for the fine-tuning of catalyst

reactivity. This makes development of such strategies

[

1–8]

chemistry.

The development of imidazolium salts, NHC

ligands, and methodologies that allow further modification

of these compounds would have a great impact on their

applications.

Imidazolium and imidazolinium salts are the most

common NHC precursors and they also form the basis of

[15]

desirable.

Applying readily available backbone functionalized imid-

azoles as starting materials for NHC ligands may circum-

vent laborious or challenging synthetic procedures; there-

fore, the use of the naturally occurring amino acid histidine

is an appealing strategy. Both the amine and acid functional

groups of histidine can be functionalized by using well-

[1,9]

many types of ionic liquids.

Imidazoles and their

derivatives possess four sites for functionalization: the wing

tips and the backbone of the imidazole. These compounds

can be synthesized through five archetypal routes:

[

17–21]

established chemistry.

Histidine can be converted into

(

I) multicomponent synthesis of imidazolium compounds,

II) multicomponent synthesis of a substituted imidazole

a histidinium salt through a methodology that is similar to

Route III described above. This allows the synthesis of

NHC precursors that possess four handles for further func-

tionalization (Scheme 1), which makes histidylidenes very

versatile ligands. An additional reason why histidine is an

interesting precursor for NHC ligands is that it is present

in many biological molecules. Hence, the development of

histidine as a precursor for NHC ligands is also relevant for

and its subsequent functionalization, (III) two-step func-

tionalization of imidazole (derivatives), (IV) synthesis of a

diamine compound and subsequent ring-closure with tri-

[

a] Molecular Inorganic Chemistry, Van ’t Hoff Institute for

Molecular Sciences, University of Amsterdam,

Science Park 904, 1090 GD Amsterdam, the Netherlands

E-mail: c.j.elsevier@uva.nl

[

22,23]

bioinorganic and bioorganometallic applications.

http://hims.uva.nl/research/research-groups/content/molecular-

inorganic-chemistry/molecular-inorganic-chemistry.html

b] Homogeneous Catalysis, Van ’t Hoff Institute for Molecular

Sciences, University of Amsterdam,

Science Park 904, 1090 GD Amsterdam, The Netherlands

c] Crystal and Structural Chemistry, Utrecht University,

Padualaan 8, 3584 CH Utrecht, The Netherlands

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejic.201403104.

Histidylidenes, NHCs that are derived from histidine,

[

[24]

have only recently been explored by Erker et al.

and by

[

25–28]

Albrecht et al.

The alkylation of histidine was also re-

[29,30]

ported in studies toward chiral ionic liquids.

The publi-

cations by Albrecht et al. and several other publications

show that NHCs, histidylidenes, and other NHCs derived

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the development of NHC-based catalysts with improved

selectivity for transfer semihydrogenation. To this end, we

studied the influence of the histidylidene substitution

pattern on the selectivity.

Results and Discussion

Scheme 1. Histidine as a starting material for NHCs.

Synthesis of Histidinium Salts

from natural compounds^[³¹^–³⁵^]are highly interesting com-

One of the reasons for our interest in histidine as a pre-

cursor for NHC complexes is that it provides four handles

for functionalization: the two nitrogen atoms of the imid-

azolyl, the amino, and the acid group (Scheme 2). The

amine and the acid group are protected to allow the selec-

tive synthesis of the histidinium salts. We chose protecting

groups that can be removed selectively so that both the free

acid and amine histidylidenes can be obtained. This design

allows the incorporation of histidylidenes in, for instance,

catalyst heterogenization or synthetic biomolecular

pounds for bioorganometallic applications.^[

4,36]

For in-

stance, amino acid derived Au and Ag-NHC compounds

[

37–39]

have been demonstrated to possess antitumor activity.

Until now, only histidylidenes bearing simple alkyl wing-

tip substituents have been reported. The wing tips of the

NHC are important for the fine-tuning of the catalytic

performance of the transition-metal complex. A wider

variation in these precursors should increase the applica-

bility of these compounds. Therefore, we set out to expand

the synthetic methodologies for relevant precursors of

histidylidene transition-metal catalysts. We investigated

methodologies that allow the synthesis of symmetric and

dissymmetric alkyl-, benzyl-, and aryl-substituted histidin-

ium salts. Subsequently, the newly developed ligand precur-

[51]

scaffolds.

The carboxylic acid group was protected in the form of

a methyl ester, which can be removed under basic condi-

tions. We chose a tert-butyloxycarbonyl (Boc) group for the

protection of the amine. This group affords a carbamate

that is unreactive under basic conditions, but may be

cleaved by trifluoroacetic acid (TFA) or a 4 m solution of

HCl in an organic solvent. Boc-protection of the histidine

methyl ester is performed in a two-step reaction, which

I

II

sors were applied in the synthesis of Ag and Pd histidylid-

ene complexes. The catalytic properties of the palladium

complexes in the Z-selective transfer semihydrogenation of

alkynes were also investigated.^[

40–46]

The semihydrogenation of alkynes is one of the most

reliable methods with which to selectively synthesize Z-alk-

[19]

affords precursor 1 (Scheme 2).

We then employed three routes to synthesize histidinium

salts: 1) Direct benzylation of Boc-protected histidine;

[

41,47]

enes,

which are part of many biologically and pharma-

ceutically active compounds. The alkenes are produced

2) the cyclic urea route; and 3) the arylation of Boc-pro-

both as bulk and as specialty compounds.^[

41,48–50]

For labo-

tected histidine.

ratory-scale synthetic purposes, the transfer semihydrogen-

ation is a more practical methodology because it circum-

vents the use of hydrogen gas by using a hydrogen donor

molecule. Most often the donor is ammonium formate. In

transfer semihydrogenation, the chemoselectivity of the cat-

Direct Benzylation

The direct benzylation of protected histidine (Scheme 3)

alyst is a key aspect because many side products may be 1 provides symmetrically substituted benzyl functionalized

formed such as the corresponding E-alkene and alkene mi- imidazolium bromides. When benzyl (Bn) bromide was

gration products as well as the corresponding alkane, which used (Z = CH), compound 2 was obtained in quantitative

is the product of further reduction of those alkenes. The yield. When picolyl (Pic) bromide was used (Z = N), forma-

substitution of NHC catalysts has a pronounced influence tion of several side products was observed by TLC analysis.

on the selectivity of the transfer semihydrogenation reac- Column chromatography allowed isolation of the pure

[

40]

1

tion. Therefore, the extended possibilities for functionali- product 3 in a decent yield of 80%. The H NMR spectra

zation and the ease of access to histidylidenes may lead to show two separate A-B systems for the diastereotopic benz-

Scheme 2. Boc-histidine methyl ester, as precursor for the synthesis of the histidinium salts.

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ylic CH₂protons, indicating that these protons are not which is the protection group we chose in the design of

equivalent on the NMR timescale.

the general synthetic route (Scheme 3). A disadvantage of

applying tBuOH as a ring-opening reagent is its poor nu-

cleophilicity, which is the cause of the low yields. The report

by Brégeon shows that the yields could be improved by

using less sterically hindered alcohols, such as methanol.^[

Therefore, the overall yields may be improved by a minor

synthetic variation, if the deprotection of the amine is not

required. Compounds 9 and 10 (Table 1) can then be alkyl-

30]

2

ated, once more, with another electrophile (R -X) to afford

histidinium salts.

Scheme 3. Synthesis of symmetrically substituted benzylic histidin-

ium bromides.

Table 1. Histidines and histidinium salts synthesized through the

cyclic urea route.

The Cyclic Urea Approach

_R1

_R2

X

Yield [%]

6

7

8

9

Bn

Pic

iPr

Bn

Pic

Bn

Pic

Ͼ99

72

0

30

25

Ͼ99

68

0

Subsequently, we employed the cyclic urea approach,

which allows the synthesis of dissymmetrically substituted

histidinium salts and further tuning of the properties of the

NHC metal complex. This is not straightforward because 10

histidine has two tautomeric forms, which means that the 11

Me

Pic

iPr

Me

I

Br

I

12

13

14

δ- and the ε-nitrogen of the imidazole possess both imine

and amine character (compound 4, Scheme 5).^[There-

fore, mixtures of regioisomers are obtained when the imid-

azole is reacted with one equivalent of an electrophile. To

obtain the desired dissymmetrically substituted histidinium

salts, we applied a route based on the report by Hodges and

20]

I

58

By using this cyclic urea route, we synthesized 6 and 7,

1

R -functionalized imidazoles 9 and 10, and histidinium

salts 11–14. However, we were unable to functionalize both

the urea and the R -substituted imidazole compounds with

[

17]

[30]

Chivikas,

Scheme 4).

and was improved by Brégeon et al.

1

(

isopropyl iodide (entries 3 and 8).

Chan–Lam–Evans Arylation and Subsequent

Quaternization

A synthetic route to NHC ligands that have an aryl sub-

stitution on the wingtips is also highly desirable because

many NHC compounds bearing aryl substituents display

[

1,3]

the best reactivities in catalytic applications.

This is also

true for our model reaction: the semihydrogenation of alk-

[

40,52]

ynes towards Z-alkenes.

Several methods have been de-

veloped for the arylation of imidazoles; for instance, the

[

53]

[54]

Ullman

and Buchwald

coupling reactions. These

methodologies have been applied in the arylation of imid-

[

55,56]

[57]

azoles with aryl halides,

boronic acids,

aryllead(IV) reagents, aryl-

[

58,59]

[60]

and trifluoroaryl borates. Despite the

tautomeric equilibrium of imidazoles, several N-arylation

reactions were reported to have good chemoselectivities to-

ward the ε-nitrogen atom of backbone-functionalized imid-

[

55,57]

azoles.

cal and may not be compatible with more functionalized

However, some of these methods are unpracti-

Scheme 4. The cyclic urea route toward dissymmetrically substi-

tuted histidinium salts.

[

61,62]

histidine imidazoles.

The Chan–Lam–Evans reaction

This cyclic urea route induces regioselectivity because with aryl boronic acids is an alternative reaction that oper-

only the six-membered cyclic urea 5 can be formed. The ates under very mild conditions (Scheme 5).^[

63,64]

The re-

second nitrogen atom can then be functionalized selectively gioselective N-arylation of a benzyl carbamate-protected

1

through nucleophilic substitution. Subsequently, the R - histidine methyl ester with 4-methoxyphenylboronic acid

[

64]

functionalized urea compounds can be ring-opened by reac- gave yields of less than 10%.

However, the improved

tion with an alcohol, which liberates the δ-nitrogen atom of Chan–Lam–Evans method developed by Campagne and

the imidazole, and provides a carbamate-protected amine. co-workers gave yields of up to 31% of the desired com-

The use of tBuOH affords the Boc-protected histidine, pound. We adapted this protocol by performing the reac-

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Scheme 5. Application of the Chan–Lam–Evans method to synthesize aryl-functionalized histidinium salts.

tion at room temperature and extending the reaction times. formed silver-NHC complex, which is driven by the precipi-

With these adjustments, we were able to obtain the para- tation of a silver halide. The application of TFA in the Boc-

methoxyphenyl 15 and mesityl 16 and N-arylated products deprotection step may cause scrambling of the counterions

in satisfactory yields of 84 and 61%, respectively.

of the imidazolium salt, which could give rise to issues later

Subsequently, these two aryl-functionalized histidines 15 on in the synthesis during the transmetalation step. There-

2

and 16 were alkylated with a range of electrophiles (R - fore, the application of HCl in dioxane is preferred over

X), which afforded another set of histidinium salts 17–20 TFA. An excess of HCl is used, therefore, anion metathesis

(Table 2). This method proved to be reliable and gave access takes place concurrently with deprotection, yielding prod-

to a wide variety of histidylidene precursors. Histidinium ucts with only chloride anions. In the case of simple histidi-

salts 19 and 20 were obtained in reasonable to good yields, nium salts, which do not contain additional basic function-

and were synthesized through the reaction of histidine 16 alities, the dicationic HCl salts are obtained. If additional

with a Pic or lutidyl (Lut) bromide, which appears to de- basic functionalities are present in the compound (for in-

compose during the reaction causing the decrease in stance picolyl moieties), tri- or tetracationic HCl salts are

[

65]

yield. NMR spectroscopy and mass spectrometry suggest obtained (Scheme 6 and Table 3).

that the decomposition product also gives rise to trans-

esterification of 16 and its product histidinium salts.

Table 2. N-Arylation of histidine precursor 1 and its subsequent

alkylation to give aryl-substituted histidinium salts.

Ar

R²

X

Yield [%]

15

16

17

18

19

20

p-OMePh

Mes

p-OMePh

Mes

–

Me

Pic

Lut

–

I

Br

84

61

Ͼ99

51

Scheme 6. Boc-Deprotection of histidinium salts.

Table 3. Yields for Boc-deprotection.

80

_R1

_R2

Yield [%]

2

1

2

3

4

5

Bn

Pic

Mes

Bn

Ͼ99

92

Me

Pic

Me

Histidinium Deprotection

After the development of the three routes for the synthe-

sis of a variety of histidinium salts, we studied an approach

for the deprotection of the amine and acid group. In the

initial design, the protection groups were chosen in such a

way that the amine and/or the acid functionality could be

deprotected selectively. In this way, the free amine or acid

compound could be prepared from a common precursor.

Deprotection may be performed either after the synthesis

of the histidinium salt, or after the synthesis of the histidyli-

dene metal complex. NHCs generally lead to the formation

of highly stable compounds. However, a wide range of tran-

sition-metal complexes and precursors may not be stable

under the conditions that are used in the deprotection step.

Therefore, deprotection of the desired functionality before

complexation to the metal was considered desirable.

Saponification of the methyl ester of 17 was performed

by stirring the compound in a solution of MeOH with

0 equiv. LiOH, which provided 26. TLC analysis showed

1

full conversion of the starting material and, after workup,

1

H NMR spectroscopic analysis showed the presence of the

imidazolium proton as well as the complete disappearance

of the characteristic methyl ester signal (Scheme 7).

Scheme 7. Methyl ester deprotection of 17.

Boc-deprotection of an amino acid is a common syn-

thetic procedure in organic chemistry. It is usually per-

formed with TFA, or a 4 m solution of HCl in dioxane. In

general, the synthesis of the desired NHC transition-metal

I

Synthesis of Ag -Histidylidenes

After development of the methods for the synthesis of

complexes often involves a transmetalation step with a pre- the histidinium salts, we investigated the generation of Ag^I

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II

carbenes with silver oxide. The silver carbenes may sub- Synthesis of Pd -Histidylidenes

sequently be employed as carbene transfer agents to obtain

I

From these Ag carbenes, we performed transmetalation

the desired Pd histidylidene precatalysts. Our preference for

this methodology was based on two factors: firstly, trans-

metalation from silver to the target precursor is a highly

reliable and commonly applied method to obtain NHC

complexes for a wide range of transition metals. This makes

II

3

with [Pd (η -allyl)Cl] to obtain the histidylidene analogues

2

II

3

of [Pd (NHC)(η -allyl)Cl] complexes, which are highly

stable, readily synthesized, and are good precatalysts for

several reactions such as cross-coupling,

[

68–72]

and cyclo-

[

73]

propanation,

as well as the Z-selective semihydrogen-

the synthesis of the silver carbenes also relevant for other

[

74]

ation of alkynes (Scheme 9).

possible transition-metal compounds.^[

1,66]

Secondly, this

methodology is very mild and highly tolerant towards a

variety of functionalities that are present in the histidinium

[

67]

I

salts.

Ag NHCs are generally synthesized by the reaction of

an imidazolium salt with silver(I) oxide, which functions as

a base as well as a complexing agent. We synthesized a wide

I

range of Ag histidylidenes by stirring the ligand with

Scheme 9. Synthesis of Pd histidylidenes through transmetalation

from their Ag histidylidene precursors.

0

.55 equiv. Ag O under inert conditions and with the ex-

2

I

clusion of light (Scheme 8 and Table 4). The silver carbene

I

is represented as an [Ag (NHC)(halido)] complex. However,

With this method, we successfully synthesized a variety

I

a multitude of [Ag NHC] coordination compounds may be of compounds (Table 5), for which we observed several

[

66,67]

formed.

For simplicity, this representation was chosen. noteworthy properties. In previous studies, we found that

H NMR spectroscopic analysis shows the absence of the the presence of hemilabile donors has a positive effect on

imidazolium proton, and signals were observed in the ¹³

the catalytic performance as well as on the stability of the

NMR spectrum around 180 ppm, which is a value that is complexes.

1

C

[

52,74,75]

For the described ligands, we find that

typical for a silver carbene. For the Boc-protected histidin- the presence of a hemilabile picolyl or lutidyl group is also

ium salts, good to excellent yields were obtained for a range beneficial for the synthesis of the Pd complexes. Complexes

1

2

of R - and R -substituents (compounds 27–32; Table 4).

36, 37 and 38 could be purified by column chromatography.

This is in contrast to compounds 35 and 39, which do not

possess a hemilabile moiety, and decomposed during col-

umn chromatography forming [Pd(allyl)Cl] and a cationic

2

+

–

bis-NHC [Pd(histidylidene) (allyl)] Cl complex 41 (Fig-

2

ure 1). Similar complexes have been obtained with nonco-

[

76,77]

ordinating counterions.

II

Table 5. Synthesized Pd (allyl) histidylidenes.

I

Scheme 8. Synthesis of Ag histidylidenes.

R¹

R²

R³

Yield [%]

3

5

Bn

Pic

Mes

p-OMePh

Bn

Pic

Lut

Me

Bn

Boc

H

41

53

Ͼ99

93

0

31

I

36

Table 4. Synthesized Ag histidylidenes.

3

7

R¹

R²

R³

X

Yield [%]

38

3

9

0

27

28

29

30

31

32

33

34

Bn

Pic

Bn

Pic

Boc

H

Br

I

95

85

80

78

86

89

96

22

4

p-OMePh Me

Mes

Bn

Me

Lut

Bn

I

Br

Cl

Mes

Me

H

Complexes 27 and 29 display a high stability and can

be stored as a solid for several weeks; they also tolerate

manipulations in air. We also synthesized free-amine ana-

logues 33 and 34. Their precursors are ammonium chloride

salts of the histidinium salts. An ammonium proton is more

acidic than a histidinium proton. Therefore, we applied an

Figure 1. Cationic bis-NHC [Pd(histidylidene)

1.

2

(allyl)]Cl complex

4

The stability of complexes 37 and 38, possessing hemi-

extra half equivalent of Ag O as a base in the synthesis of labile groups, is not surprising. We previously reported a

2

3

3 and 34 (Table 4). The presence of the free amine, which wide variety of highly stable NHCs bearing a triazole group

[

74]

is a better ligand for silver than a carbamate, does not seem as a secondary donor.

The instability of complexes not

to interfere in the synthesis of 33.

bearing a hemilabile donor and concomitant formation of

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bis-histidylidene complexes is unexpected. In fact, similar

NHC analogues that are not functionalized on the back-

bone could be isolated by column chromatography without

[

46,78]

decomposition.

The difference between those species

and those described here is that the NHC complexes with-

out backbone functionalization bear an N-mesityl substitu-

ent. Possibly, the extra bulk of the mesityl group provides

additional stabilization through steric protection. In this

case, the incorporation of large (aryl) wingtips seems to be

important for the stability of these compounds. Therefore,

the Chan–Lam–Evans approach, which allows the intro-

duction aryl functionalities on the wingtips of the NHC,

may be particularly relevant.

We investigated the viability of using Boc-deprotection

II

of Pd histidylidene complexes to obtain free amine species.

Subjecting compound 35 to a solution with TFA resulted

in decomposition of the complex. However, free amine Pd

histidylidenes such as 40 can be synthesized through the Hydrogen atoms, nitrate anion, and solvent molecules are omitted

previously developed route that uses free amine histidinium for clarity. Only one of two independent molecules is displayed.

II

Figure 3. ORTEP representation of the cationic Pd histidylidene

II

3

η -allyl complex 42. Ellipsoids are drawn at 50% probability.

The disorder of the allyl ligand is not shown.

salts as ligand precursors (Scheme 9, Table 5).

We studied the structure of the histidylidenes further

with X-ray crystallography. X-ray quality crystals were ob- Table 6. Selected bond lengths and angles of 42 and 43.^[⁷⁴^]

tained through slow vapor diffusion of cyclohexane into a

solution of 38 in tetrahydrofuran (THF) in the presence of

nitric acid. This gave crystals of complex 42 that had a non-

coordinating nitrate counterion (Figure 2).

₄₃[74]

Entry Bond lengths [Å]

42

1

2

3

4

5

Pd–NHC

Pd–N

Pd–Cβ

Pd–Cγ

Pd–Cα

2.015(5)/1.999(5)

2.135(4)/2.148(5)

2.226(6)/2.111(7)

2.139(10)/2.101(13)

2.102(5)/2.221(7)

2.044(3)

2.098(2)

2.186(4)

2.163(7)

2.111(5)

Entry Angle [°]

42

43^[⁷⁴^]

6

7

8

NHC–Pd–N

NHC–Pd–Cα

N–Pd–Cβ

85.31(16)/84.53(17)

100.0(2)/166.1(3)

106.4(2)/176.0(3)

86.42(11)

103.05(15)

101.94(11)

Figure 2. Complexes 42 and 43.

We compared the structure of 42 to the previously re-

[

74]

ported complex 43

(Figure 3, Table 6). These structures

The crystal structure contains cocrystalized cyclohexane

and THF solvent molecules, some of which were heavily

II

3

are similar, cationic, square planar [Pd (NHC)(η -allyl)] bi-

dentate complexes that possess a noncoordinating counter-

ion. The Pd–NHC and the Pd–N distances are significantly

longer for 42 (Table 6 entries 1 and 2). The CPK model of

disordered and were treated as diffuse electron density by

_u_s_i_n_g_t_h_e_S_Q_U_E_E_Z_E_a_l_g_o_r_i_t_h_m_._[79] The absolute structure

determination using Bijvoet pairs showed that the overall

4

2 suggests a steric interaction between the methyl of the

lutidyl donor and the allyl ligand, and an interaction be-

tween the allyl ligand and the mesityl wingtip substituent

see the Supporting Information, SI3). We attribute the dif-

ferences in bond lengths to this steric congestion around

the Pd center. The large Boc-group may also contribute to

the steric crowding around the Pd center.

crystal structure is enantiopure, as indicated by the Flack

_p_a_r_a_m_e_t_e_r_[_x₌_–₀_.₀₂₍₂₎_][93] (see Exp. Sect.). The asymmet-

ric unit of the enatiopure crystal contains two independent

Pd molecules. The chiral carbon of the amino acid moiety

of both of these molecules is in the S-configuration (Fig-

ure 3). However, the metallacycles of these molecules are

inverted with respect to each other (see the Supporting In-

formation, SI2). The chirality of the starting material is

thus retained in the crystal that was measured. This may

indicate that, as for the similar method developed by

(

Transfer Semihydrogenation

Albrecht et al., the synthetic route reported herein leads

Subsequently, we tested complexes 35–38 as well as 44

to optically pure compounds.^[Further inspection of the and 45

27]

[46]

in the transfer semihydrogenation of 1-phenyl-1-

3

crystal structure shows that the η -coordinated allyl ligand propyne toward Z-1-phenyl-1-propene (Scheme 10).

was disordered and it was refined with a disorder model.

We evaluated the influence of the (protected) amino acid

This is in line with previous observations that there is no functionality, and the hemilabile donors on the reaction

preference for either orientation of the allyl group. The ob- with this set of precatalysts (Table 7). The performance of

served bond lengths and geometry of 42 are normal for this 35–38 was put into context by comparison with the pre-

type of compound (Figure 3, Table 6).^[

69,80,81]

viously discussed complexes 44 and 45.

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FULL PAPER

Scheme 10. Investigated precatalysts in the Z-selective transfer semihydrogenation of 1-phenyl-1-propyne.

Table 7. The results of the Z-selective transfer semihydrogenation which are notoriously difficult, has been improved. By care-

of 1-phenyl-1-propyne.^[

a]

ful selection of the protection groups, both the protected

_C_a_t_._T_O_F₁₅_%_[b]

_Z_-_y_i_e_l_d_[_%_][c]

_Z_-_s_e_l[d]

and selectively deprotected amino acid functionalities can

be obtained. This allows facile access to a range of com-

pounds via a single synthetic intermediate and provides a

histidylidene precursor with four handles for the adaptation

of its catalyst systems as well as implementation of these

ligands in complex systems. These ligands are, therefore,

interesting intermediates for the heterogenization of this

type of compound and for their implementation in biocon-

Time to FC

[h]^[

e]

(conv) [%]

[g]

3

4

5

6

7

8

4

5

9.6

12

7.2

18

38

8.5

38

80

91

68

88

61

94 (40)

95 (84)^[

92 (Ͼ99)_[

68 (Ͻ99)

92 (97)^[

94 (64)

f]

10.3^[^h^]

28

f]

[h]

18

f]

5.6

_Ͼ_Ͼ₂₄_h[

g]

[

(

a] Reaction conditions: catalyst (1 mol-%), 1-phenyl-1-propyne

2.7 mmol), 70 °C. [b] In molsubs/molcat·h. [c] GC-yield for the Z-

alkene. [d] Selectivity toward the Z-alkene in% ([response factor

[

4]

I

II

3

jugates. We have synthesized a variety of Ag and Pd (η -

allyl) histidylidenes and investigated the activities of the pal-

corrected GC area of Z-alkene]/[response factor corrected GC area ladium complexes in the Z-selective transfer semihydrogen-

of the total products]·100%) at the corresponding conversion, given

ation of an alkyne. We found that the substitution pattern

of the ligand, and especially the presence of hemilabile

groups, has significant effects on the reactivity of these

compounds. Moreover, the presence of a mesityl substituent

on the wingtips seems important for successful catalysis.

in parentheses. [e] Time to reach full conversion of the substrate.

[f] Strong over-reduction and isomerization of the Z-alkene product

was observed after full substrate conversion. [g] Reaction was

stopped after 24 h. [h] Extrapolated time to full conversion.

Compounds 35, 36, and 38 give over-reduction and iso-

merization of the product Z-alkene after full consumption

of the substrate. This was also observed for compounds 44

and 45. However, other systems were reported that do not

display further conversion of the product Z-alk-

Experimental Section

General: Complex synthesis was performed by using Schlenk

techniques under an atmosphere of dry nitrogen. Synthesis of the

histidinium salts was performed in air, unless stated otherwise.

When anhydrous solvents were used, these were prepared according

[

40,46,82–86]

ene.

The substitution on the histidylidene ligand

seems to be crucial for the performance of the catalyst. In-

corporation of an aryl wingtip substituent on the ligand

seems not only beneficial for the synthesis of these histidyl-

[87]

3

to standard procedures and distilled prior to use. [Pd(η -C

3 5

H )-

Cl] , triethylamine, formic acid, and potassium tert-butoxide were

2

purchased from Sigma–Aldrich. Compound 6 was synthesized

idene complexes, but also for their catalytic performance. according to the procedure reported by Jain et al.^[NMR spectra

20]

The bisbenzylic compound 35 loses activity during the reac- were recorded with Bruker AV 400 MHz, Bruker DRX 300, Bruker

tion, most likely due to catalyst decomposition.

DRX 500 MHz, or Varian Mercury 300 MHz spectrometers. High-

resolution mass spectra were recorded with a JEOL JMS SX/

SX102A four-sector mass spectrometer; mass samples were loaded

in a matrix solution (3-nitrobenzyl alcohol) onto a stainless steel

probe and bombarded with xenon atoms with an energy of 3 keV.

Conclusions

We have developed versatile and robust methodologies During the high-resolution FAB-MS measurements a resolving

for the synthesis of symmetrically and dissymmetrically power of 10 000 (10% valley definition) was used.

functionalized histidylidene ligand precursors. Especially, 1,3-Dibenzyl-4-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-oxo-

3

the methodology for arylation of histidine imidazoles, propyl}-1H-imidazol-3-ium Bromide (2): NaHCO (188 mg,

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FULL PAPER

2

.23 mmol) was added to a stirred solution of 1 (547 mg,

.03 mmol) and benzyl bromide (725 μL, 6.09 mmol) in MeCN a white solid. H NMR (400 MHz, CDCl

2

Et O (2ϫ 100 mL) and dried in vacuo to afford 5 (2.8 g, 72%) as

1

3

): δ = 8.15 (d, J = 0.5 Hz,

(

20 mL). The suspension was stirred and heated to reflux for 22 h,

1 H, NCHN), 6.88 (d, J = 0.9 Hz, 1 H, Im-bb), 6.47 (br. s, 1 H,

NH), 4.37 (dd, J = 8.4, 5.4 Hz, 1 H, α-CH), 3.81 (s, 3 H, OMe),

3.38 (ddd, J = 15.7, 5.3, 1.0 Hz, 1 H, β-CHH), 3.15 (ddd, J = 15.7,

8.7, 1.3 Hz, 1 H, β-CHH) ppm.

after which, TLC analysis (KMnO indicator; CH Cl /MeOH, 9:1)

showed full consumption of 1. The reaction mixture was filtered

and volatiles were removed by rotary evaporation. The crude prod-

4

2

uct was dissolved in a minimal amount of CH

wise to vigorously stirred Et O (200 mL). The white precipitate was

filtered off, washed with Et O, and dissolved in CH Cl . All vola-

tiles were removed to afford the title compound (1.1 g, Ͼ99%) as

2 2

Cl and added drop-

7

-(Methoxycarbonyl)-5-oxo-2-(pyridin-2-ylmethyl)-5,6,7,8-tetra-

2

hydroimidazol-[1,5-c]pyrimidin-2-ium Bromide (7): 2-(Bromometh-

yl)pyridine hydrobromide (142 mg, 0.56 mmol) was neutralized

with saturated aqueous NaHCO

bromomethylpyridine was extracted with Et

Organic fractions were combined, dried with anhydrous MgSO

2

1

3

solution. The liberated 2-

a white foam. H NMR (400 MHz CD

NCHN), 7.52–7.38 (m, 10 H, Ar), 7.13 (br. s, 1 H, Im-bb), 5.75 (d,

J = 6.1 Hz, 1 H, NH), 5.56 (dd, J = 50.1, 15.2 Hz, 2 H, NCH Ar),

Ar), 4.46 (br. s, 1 H, α-CH),

), 3.13 (ddd, J = 15.9, 5.1, 0.7 Hz, 1 H, β-CHH),

.04 (ddd, J = 16.0, 7.8, 0.7 Hz, 1 H, β-CHH), 1.41 [s, 9 H,

2 2

Cl ): δ = 10.62 (s, 1 H,

2

O (4 ϫ 15 mL).

4

2

and filtered. The solution was concentrated to approximately 3 mL

then added to a stirred solution of 5 (142 mg, 0.56 mmol) in MeCN

5

3

.52 (dd, J = 20.4, 14.6 Hz, 1 H, NCH

2

.68 (s, 3 H, OCH

3

(

5 mL). The diethyl ether was removed in vacuo and the reaction

_]_p_p_m_.1 C NMR (75 MHz CD

3

mixture was stirred for 5 d at room temperature and subsequently

overnight at 50 °C, after which TLC analysis showed the absence

of 5. Volatiles were removed under reduced pressure and the crude

product was dissolved in a minimal amount of CH

dropwise to vigorously stirred Et O (25 mL). The orange precipi-

tate was filtered off, washed with Et O, and dissolved in CH Cl

All volatiles were removed in vacuo, affording the title compound

C(CH

OMe)], 155.7 [CO(OtBu)], 137.4 (NCHN), 133.6 [Im-bb(C

33.3 (C ), 132.3 (C ), 129.6 (ArCH), 129.6 [Ar(CH)], 129.4

3

)

3

2

Cl

2

): δ = 171.2 [CO-

(

1

q

)],

q

2 2

Cl and added

[

(

Ar(CH)], 129.2 [Ar(CH)], 128.5 [Ar(CH)], 120.9 [Im-bb(CH)], 80.5

2

C(CH

3

)

3

], 53.3 (NCH

2

Ph), 53.0 (α-CH), 52.3 (OMe), 51.3

], 26.8 (β-CH ) ppm. MS (FAB-TOF):

23 4

H O N 450.2387; found 450.2397.

2

.

NCH Ph), 28.3 [C(CH

2

3

)

3

+

2

m/z calcd. for C26

1

(

3

136 mg, 72%) as an orange solid. H NMR (400 MHz, CD CN):

4

-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1,3-bis-

δ = 9.43 (d, J = 1.6 Hz, 1 H, NCHN), 8.58 (dd, J = 4.8, 4.0 Hz, 1

H, Py-H2), 8.00 (br. s, 1 H, NH), 7.87 (dt, J = 7.6, 2.0 Hz, 1 H,

Py-H4), 7.55 (d, J = 7.6 Hz, Py-H5), 7.44–7.42 (m, 3 H, Im-bb, Py-

(

pyridin-2-ylmethyl)-1H-imidazol-3-ium Bromide (3): NaHCO

439 mg, 4.98 mmol) was added to a stirred suspension of 1

134 mg, 0.50 mmol) and 2-(bromomethyl)pyridine hydrobromide

264 mg, 1.05 mmol) in MeCN (10 mL) and the suspension was

3

H3), 5.57 (dd, J = 18.1, 16.0 Hz, 2 H, NCH

H, α-CH), 3.73 (s, 3 H, OCH ), 3.38 (d, J = 5.2 Hz, 2 H, β-

) ppm. C NMR (101 MHz, CD CN): δ = 171.0 [CO(OMe)],

53.2 [Py(C )], 150.8 [Py(CH)], 145.1 [N(CO)N], 138.6 (Ar), 136.0

Ar), 129.6 (Ar), 125.0 (Ar), 124.3 (Ar), 120.8 (Ar), 118.3 (Ar), 55.1

α-CH), 53.9 (NCH Py), 52.6 (OMe), 22.8 (β-CH ) ppm. HRMS

FAB): m/z calcd. for C14 287.1139; found 287.1142.

2

Py), 4.60–4.56 (m, 1

3

stirred and heated to reflux for 16 h, after which, TLC analysis

silica; KMnO indicator; CH Cl /MeOH, 9:1) showed full con-

13

CH

1

(

2

3

(

4

2

q

sumption of 1. The reaction mixture was filtered and volatiles were

removed by rotary evaporation. The crude product was dissolved

2

in a minimal amount of CH

ously stirred Et O (100 mL). The light-brown precipitate was fil-

tered off, washed with Et O, and dissolved in CH Cl . The mixture

was concentrated and purified by column chromatography

CH Cl /MeOH, 95:5Ǟ9:1) to afford 3 (219 mg, 80%) as a light-

brown foam. H NMR (400 MHz, CD

.1 Hz, 1 H, NCHN), 8.62–8.50 (m, 2 H, Py-H2, Py-H2Ј), 7.78

ddd, J = 15.9, 7.7, 1.8 Hz, 2 H, Py-H4, Py-H4Ј), 7.68 (t, J =

.8 Hz, 2 H, Py-H3, Py-H3Ј), 7.47 (s, 1 H, Im-bb), 7.34–7.30 (m,

Py-H5, Py-H5Ј), 5.99 (d, J = 6.5 Hz, 1 H, NH), 5.68 (dd, J = 66.3,

2

Cl

2

and was added dropwise to vigor-

+

15 3 4

H O N

2

Methyl 2-[(tert-Butoxycarbonyl)amino]-3-[1-(pyridin-2-ylmethyl)-

H-imidazol-4-yl]propanoate (10): The method was adapted from

2

1

[17]

Hodges et al. DIPEA (65 μL, 0.39 mmol) was added to a suspen-

sion of 7 (130 mg, 0.35 mmol) in anhydrous tBuOH (2.5 mL) under

an argon atmosphere. The reaction mixture was stirred overnight

at 85 °C. Volatiles were evaporated and the residue was dissolved in

CH

washed with brine (10 mL), dried with MgSO

to give a brown oil. The oil was impregnated on silica and purified

by column chromatography (CH Cl /MeOH/acetone, 95:5:10) to

afford 10 (44 mg, 35 %) as a brown oil. H NMR (400 MHz,

(

2

1

2

Cl ): δ = 10.52 (d, J =

1

(

8

2

Cl

2

(20 mL). The solution was washed with H

2

O (2ϫ10 mL),

4

and concentrated

1

5

5.5 Hz, 2 H, NCH

.7 Hz, 1 H, α-CH), 3.70 (s, 2 H), 3.27 (dd, J = 14.6, 4.2 Hz, 1 H,

2 2

Py), 5.60 (s, 2 H, NCH Py), 4.53 (d, J =

2

1

β-CHH), 3.22 (dd, J = 15.3, 6.4 Hz, 1 H, β-CHH), 1.37 [s, 9 H,

_]_p_p_m_.1 C NMR (126 MHz, CD

3

CDCl ): δ = 8.56 (m, 1 H, Py-H2), 7.65 (dt, J = 8.0, 2.0 Hz, 1 H,

Py-H4), 7.49 (d, J = 1.2 Hz, NCHN), 7.26–7.22 (m, 1 H, Py-H3),

C(CH

3

)

3

2

Cl

2

): δ = 171.6 [CO-

3

(OMe)], 155.9 [CO(OtBu)], 153.4 (Py-C6, Py-C6Ј), 150.5 (Py-C2),

6

.89 (d, J = 7.6 Hz, 2 H, Py-H5), 6.73 (s, 1 H, Im-bb), 5.90 (d, J

8.0 Hz, 1 H, NH), 5.15 (s, 2 H, NCH Py), 4.55–4.51 (m, 1 H, α-

CH), 3.64 (s, 3 H, OMe), 3.02 (dd, J = 16.1, 5.2 Hz, 1 H, β-CHH),

.99 (dd, J = 14.4, 4.8 Hz, 1 H, β-CHH), 1.41 [s, 9 H,

1

50.4 (Py-C2Ј), 138.9 (NCHN), 138.0 (Py-C4), 138.0 (Py-C4Ј),

32.7 [Im-bb(C )], 124.4 [Py(CH)], 124.3 [Py(CH)], 124.0 [Py(CH)],

23.8 [Py(CH)], 121.6 [Im-bb(CH)], 80.7 [C(CH ], 54.9

Py), 53.3 (NCH Py), 53.0 (α-CH), 52.4 (OMe), 28.6,

7.1 ppm. MS (FAB-TOF): m/z calcd. for C24

=

2

q

3 3

)

2

(

NCH

2

1

3

+

3 3 3

C(CH ) ] ppm. C NMR (101 MHz, CDCl ): δ = 172.7 [CO-

2

H

30

O

4

N

5

452.2298;

(

[

(

OMe)], 156.2 [CO(OtBu)], 155.7 (Py-C6), 149.8 (Py-C2), 138.3

Im-bb(C )], 137.6 (NCHN), 137.4 (Py-C4), 123.1 (Py-C5), 121.2

Py-C3), 117.2 [Im-bb(CH)], 79.7 [C(CH ], 53.7 (α-CH), 52.6

NCH Py), 52.2 (OMe), 30.5 (β-CH ), 28.5 [C(CH ] ppm. MS

FAB-TOF): m/z calcd. for C18 361.1870; found

61.1875.

found 452.2294.

q

Methyl 5-Oxo-5,6,7,8-tetrahydroimidazo[1,5-c]pyrimidine-7-carb-

oxylate (5): A method adapted from Hodges et al. was applied.^[

l-Histidine methyl ester dihydrochloride (5.0 g, 20.7 mmol) and

3 3

)

17]

2

3 3

)

+

25 4 4

H O N

1,1-carbonyldiimidazole (3.68 g, 22.7 mmol) were heated at 85 °C

3

under vigorous mechanical stirring for 45 min. The slurry was

cooled to ambient temperature and the reaction was quenched with

Methyl 3-(1-Benzyl-1H-imidazol-4-yl)-2-[(tert-butoxycarbonyl)-

amino]propanoate (9): The title compound was obtained as

H

2

O (5 mL). After 45 min stirring, the suspension was extracted

with CH Cl (10ϫ 20 mL, each checked by TLC for content). Or-

ganic fractions were combined, dried with MgSO and concen-

[

17]

2

described for 10 and was previously reported by Hodges et al.

1

4

3

H NMR (400 MHz CDCl ): δ = 7.42 (d, J = 8.2 Hz, 1 H, NCHN),

trated by rotary evaporation. The crude product was washed with

7.35–7.25 (m, 3 H, Ar), 7.08 (d, J = 6.7 Hz, 2 H, o-Ar), 6.62 (s, 1

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2

H, Im-bb), 5.94 (d, J = 8.2 Hz, 1 H, NH), 5.01 (s, 2 H, NCH Ar), (s, 3 H, OMe), 3.26 (dd, J = 15.7, 5.2 Hz, 1 H, β-CHH), 3.15 (dd,

1

3

4

5

1

.54–4.46 (m, 1 H, α-CH), 3.60 (s, 3 H, OMe), 3.04 (A-B, J = 14.8, J = 15.8, 7.2 Hz, 1 H, β-CHH), 1.37 [s, 9 H, C(CH

.5 Hz, 1 H, β-CHH), 2.95 (dd, J = 14.6, 4.8 Hz, 1 H, β-CHH), NMR (101 MHz, CDCl ): δ = 170.7 [CO(OMe)], 152.3 (Py-C6),

.40 [s, 9 H, C(CH ] ppm. 150.0 (Py-C2), 137.9 (Py-C4), 131.2 [Im-bb(C )], 124.2 (Py-C5),

], 54.1 (NCH Py),

3

)

3

] ppm.

C

3

)

3

q

1

5

24.1 (Py-C3), 121.2 [Im-bb(CH)], 80.9 [C(CH

3

)

3

2

1

-Benzyl-4-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-

3.3 (α-CH), 52.3 (OMe), 34.6 (NMe), 28.3 [C(CH ], 26.7 (β-

) ppm. MS (FAB-TOF): m/z calcd. for C19H O N 375.2032;

2 27 4 4

3 3

)

oxopropyl}-3-methyl-1H-imidazol-3-ium Iodide (11): This com-

+

CH

pound was previously reported by Nakamura et al.^[Methyliodide

88]

found 375.2037.

(

25 μL, 0.39 mmol) was added to a stirred solution of 6 (48 mg,

.13 mmol) in MeCN (3 mL). The mixture was stirred and heated

to reflux overnight, then volatiles were evaporated and the crude

product was dissolved in a minimal amount of CH Cl . The mix-

ture was added dropwise to vigorously stirred Et O (50 mL). The

white precipitate was collected by filtration, washed with Et O and

dissolved in CH Cl . All volatiles were removed in vacuo, which

0

Methyl 2-[(tert-Butoxycarbonyl)amino]-3-[1-(4-methoxyphenyl)-1H-

imidazol-4-yl]propanoate (15): To a stirred solution of 1 (0.103 g,

0.382 mmol), NaOAc (0.094 g, 1.15 mmol), and Cu(OAc) ·H O

2 2

(7.62 mg, 0.0382 mmol) in MeOH (2 mL), 4-methoxyphenylbor-

onic acid (0.174 g, 1.15 mmol) was added. The mixture was stirred

at 20 °C for 26 h and concentrated in vacuo. The residue was dis-

2

1

afforded the title compound (84 mg Ͼ99%) as a white foam. H solved in CH

NMR (400 MHz, CDCl ): δ = 10.01 [s, 1 H, (NCHN)], 7.54–7.42 (10 mL), dried with MgSO

m, 2 H, o-Ar), 7.42–7.35 (m, 3 H, Ar), 7.11 (s, 1 H, Im-bb), 5.62 umn chromatography of the residue (silica; EtOAc/n-hexane, 1:4)

d, J = 6.6 Hz, 1 H, NH), 5.45 (dd, J = 18.4, 14.5 Hz, 2 H, afforded the title product (120 mg, 0.320 mmol, 84%) as a yellow

2

Cl

2

(35 mL), washed with H

2

O (10 mL) and brine

3

4

, and concentrated in vacuo. Flash col-

(

1

NCH

.71 (s, 3 H, OMe), 3.22 (dd, J = 15.8, 5.2 Hz, 1 H, β-CHH), 3.14 7.21 (m, 2 H, Ar), 7.05–6.89 (m, 3 H, Ar, Im-bb), 5.91 (d, J =

dd, J = 15.8, 7.7 Hz, 1 H, β-CHH), 1.35 [s, 9 H, C(CH ]. 8.2 Hz, 1 H, NH), 4.66–4.50 (m, 1 H, α-CH), 3.83 (s, 3 H, OMe),

.72 (s, 3 H, OMe), 3.11 (m, 2 H, β-CH ), 1.43 (s, 9 H, CH ) ppm.

2

Ar), 4.51 (d, J = 5.5 Hz, 1 H, α-CH), 3.94 (s, 3 H, NMe),

3

oil. H NMR (300 MHz, CDCl ): δ = 7.66 (s, 1 H, NCHN), 7.29–

3

(

3 3

)

3

2

3

-Benzyl-5-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-

13

3

C NMR (101 MHz, CDCl ): δ = 172.57 [CO(OMe)], 158.84 (p-

Ar), 155.61 [CO(OtBu)], 138.31 (NCHN), 135.49 (Im-bb), 130.51

oxopropyl}-1-(pyridin-2-ylmethyl)-1H-imidazol-3-ium Bromide (12):

2

-(Bromomethyl)pyridine hydrobromide (76 mg) was neutralized

with saturated aqueous NaHCO solution. The liberated 2-bro-

momethylpyridine was extracted with Et O (4ϫ 15 mL) and the

organic fractions were combined, dried with anhydrous MgSO

(

5

2

i-Ar), 122.91 (Ar), 116.28 (Im-bb), 114.87 (Ar), 79.64 [C(CH

3

)

3

],

),

3

5.59 (Ar-OMe), 53.49 (α-CH), 52.25 [CO(OMe)], 30.27 (β-CH

8.34 [C(CH

2

3

)

3

] ppm. MS (FAB-TOF): m/z calcd. for

4

,

+

C

19

H

26

N

3

O

5

376.1872; found 376.1869.

and filtered. The solution was concentrated to approximately 3 mL

and then added to a stirred solution of 9 (97 mg, 0.27 mmol) in

MeCN (5 mL). The Et O was removed in vacuo and the mixture

2

Methyl 2-[(tert-Butoxycarbonyl)amino]-3-(1-mesityl-1H-imidazol-4-

yl)propanoate (16): To a stirred solution of 1 (0.092 g, 0.342 mmol),

2 2

was heated at 50 °C for 5 d, after which, TLC analysis showed the NaOAc (0.080 g, 1.02 mmol), and Cu(OAc) ·H O (6.8 mg,

absence of 9. Volatiles were evaporated in vacuo and the crude

product was purified by column chromatography on a silica column

0.0342 mmol) in MeOH (2 mL), 2,4,6-trimethylphenylboronic acid

(0.166 g, 1.01 mmol) was added. The mixture was stirred at 20 °C

for 6 d in an open air vessel. The mixture was dried over 6 d and

(

CH

as a white foam. H NMR (400 MHz, CD

NCHN), 8.51 (d, J = 4.4 Hz, 1 H, Py-H2), 7.76 (td, J = 7.7, 1.8 Hz, with H

2 2

Cl /MeOH, 95:5) to afford the title compound (101 mg, 71%)

1

2

Cl

2

): δ = 10.30 (s, 1 H, the green residue was then dissolved in CH

2

Cl

2

(35 mL), washed

and con-

2

O (10 mL) and brine (5 mL), dried with MgSO

4

1

H, Py-H4), 7.67 (d, J = 7.8 Hz, 1 H, Py-H5), 7.51–7.36 (m, 5 H,

centrated in vacuo. Flash column chromatography of the residue

Ar), 7.33–7.19 (m, 2 H, Ar), 6.22 (d, J = 7.0 Hz, 1 H, NH), 5.83

(silica; EtOAc/n-hexane, 1:4) gave the title compound (80 mg,

1

(

d, J = 15.6 Hz, 1 H, NCHHPy), 5.67 (d, J = 15.6 Hz, 1 H, 0.206 mmol, 61%) as a yellow oil. H NMR (300 MHz, CDCl

3

): δ

NCHHPy), 5.46 (s, 2 H, NCH

2

Ph), 4.48 (d, J = 6.4 Hz, 1 H, α- = 7.33 (s, 1 H, NCHN), 6.94 (s, 2 H, Mes), 6.64 (s, 1 H, Im-bb),

), 1.34 [s, 9 H, 6.03 (d, J = 8.5 Hz, 1 H, NH), 4.78–4.54 (m, 1 H, α-CH), 3.67 (s,

): δ = 170.9 [CO- 3 H, OMe), 3.12 (m, 2 H, β-CH ), 2.32 [s, 3 H, p-Mes(Me)], 1.96

OMe)], 155.4 [CO(OtBu)], 152.2 (Py-C6), 149.6 (Py-C2), 137.5 [d, J = 8.7 Hz, 6 H, o-Mes(Me)], 1.43 {s, 9 H, [C(CH

Py-C4), 132.8 (C ), 132.2 (C ), 129.1 [Ar(CH)], 128.7 [Ar(CH)], NMR (101 MHz, CDCl ): δ = 172.53 [CO(OMe)], 155.54 [CO-

23.7 [Ar(CH)], 123.1 [Ar(CH)], 119.9 [Im-bb(CH)], 80.1 [C(CH (OtBu)], 138.89, 137.39, 137.22 (NCHN), 135.30 (o-Ar), 135.18 (o-

], 53.1 (Im-CH -Ar), 52.6 (α-CH), 52.1 (OMe), 51.4 (Im-CH -Ar), Ar), 132.89 (i-Ar), 128.82 (m-Ar), 117.55 [Im-bb(CH)], 79.62

], 26.2 (β-CH ) ppm. MS (FAB-TOF): m/z calcd. for [C(CH ], 53.48 (α-CH), 52.29 (OMe), 30.05 (β-CH ), 28.22

451.2340; found 451.2351. [C(CH ], 21.06 [Mes(p-Me)], 17.27 [Mes(o-Me)], 14.14 [Mes(o-

CH), 3.64 (s, 3 H, OCH

3 2

), 3.26–3.14 (m, 2 H, β-CH

C(CH

3

)

3

] ppm. ¹³C NMR (101 MHz, CDCl

3

2

1

3

(

3

)

3

]} ppm.

C

q

3

1

3

)

3

2

C

8.0 [C(CH

3

)

3

+

2

3

)

3 3

3

2

25

H

31

O

4

N

4

+

3 4

Me)] ppm. MS (FAB-TOF): m/z calcd. for C21H30N O 388.2236;

found 388.2234.

5

-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-

methyl-3-(pyridin-2-ylmethyl)-1H-imidazol-3-ium Iodide (14): Meth-

yliodide (21 μL, 0.33 mmol) was added to a stirred solution of 10 4-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-p-

(

40 mg, 0.11 mmol) in MeCN (2 mL). The mixture was stirred and

heated to reflux overnight. Volatiles were evaporated and the crude

product was dissolved in a minimal amount of CH Cl and added

dropwise to vigorously stirred Et O (50 mL). The white precipitate

was filtered off, washed with Et O and dissolved in CH Cl . All

volatiles were removed in vacuo to give the title compound (32 mg,

methoxyphenyl-3-methyl-1H-imidazol-3-ium Iodide (17): To a

stirred solution of 15 (0.530 g, 1.41 mmol) in MeCN (12 mL),

methyliodide (0.44 mL, 7.06 mmol) was added. The mixture was

stirred and heated to reflux for 6 h, then concentrated in vacuo to

2

give the title compound (0.729 g, 1.41 mmol, 99%) as a yellow so-

1

lid. H NMR (300 MHz, CDCl

3

): δ = 10.22 (s, 1 H, NCHN), 7.65

1

5

1

8%) as a white foam. H NMR (400 MHz, CDCl

H, NCHN), 8.54–8.52 (m, 1 H, Py-H2), 7.82–7.70 (m, 2 H, Py- 2 H, Ar), 5.71 (d, J = 7.3 Hz, 1 H, NH), 4.66 (s, 1 H, α-CH), 4.12

(s, 3 H, NMe), 3.86 (s, 3 H, OMe), 3.83 (s, 3 H, OMe), 3.46–3.07

3

): δ = 10.10 (s,

(d, J = 8.9 Hz, 2 H, Ar), 7.46 (s, 1 H, Im-bb), 7.04 (d, J = 8.9 Hz,

H4, Py-H5), 7.40 (s, 1 H, Im-bb), 7.33–7.26 (m, 1 H, Py-H3), 5.63

dd, J = 20.5, 14.7 Hz, 2 H, NCH Py), 5.54 (d, J = 7.0 Hz, 1 H,

1

3

(

2

2 3 3

(m, 2 H, β-CH ), 1.41 [s, 9 H, C(CH ) ] ppm. C NMR (75 MHz,

NH), 4.55 (d, J = 5.3 Hz, 1 H, α-CH), 3.94 (s, 3 H, NCH

3

), 3.76

CDCl

3

): δ = 170.68 [CO(OMe)], 160.80 (Ar), 155.47 [CO(OtBu)],

Eur. J. Inorg. Chem. 0000, 0–0

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FULL PAPER

1

35.40 (NCHN), 132.30, 127.33, 123.51 [Ar(CH)], 119.15 [Im- 6.06–5.95 (A-B system, 2 H, NCH

bb(CH)], 115.52 [Ar(CH)], 80.92 [C(CH ], 55.79 [p-Ar(OMe)],

3.24 (α-CH), 51.95 [CO(OMe)], 34.77 (NMe), 28.21 [C(CH ], Lut(Me)], 2.35 [s, 3 H, Mes(p-CH

6.90 (β-CH ) ppm. MS (FAB-TOF): m/z calcd. for C20

90.2029; found 390.2029.

2

Py), 4.63 (br. s, 1 H, α-CH),

3

)

3

3.73 (s, 3 H, OMe), 3.39–3.30 (m, 2 H, β-CH

2

), 2.44 [s, 3 H,

5

2

3

)

O

3

)], 2.12 [s, 3 H, Mes(o-Me)] 2.1

+

13

2

H

25

N

3

5

[s, 3 H, Mes(o-Me)], 1.37 [s, 9 H, C(CH

(126 MHz, CD Cl ): δ = 171.6 [CO(OMe)], 159.4 (Py-C6), 155.9

CO(OtBu)], 152.7 (Py-C2), 141.4 (Ar), 139.4 (Ar), 137.9 (Ar),

3 3

) ] ppm. C NMR

2

[

1

4

-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-mes-

35.0 (Ar), 133.5 (Ar), 131.7 (Ar), 130.1 (Ar), 123.4 (Ar), 122.4

], 53.0 (NCH Py), 52.7 (α-CH), 52.1

], 26.6 (β-CH ), 24.3 [Lut(CH )], 21.1

ityl-3-methyl-1H-imidazol-3-ium Iodide (18): To a stirred solution of

(

Ar), 120.3 (Ar), 80.1 [C(CH

OMe), 28.5 [C(CH

3

)

3

2

16 (0.500 g, 1.29 mmol) in MeCN (12 mL), methyliodide (0.40 mL,

3

)

3

2

3

6.45 mmol) was added. The mixture was heated to reflux overnight

[

Mes(p-Me)], 17.7 [Mes(o-Me)] ppm. MS (FAB-TOF): m/z calcd.

and then concentrated in vacuo to give the title compound (0.686 g,

+

for C28

37 4 4

H O N 493.2808; found 493.2818.

1

.29 mmol, Ͼ99%) as a yellow solid. H NMR (300 MHz, CDCl

δ = 9.79 (s, 1 H, NCHN), 7.05 (s, 1 H, Im-bb), 6.98 (s, 2 H, Ar),

.64 (d, J = 7.4 Hz, 1 H, NH), 4.65 (s, 1 H, α-CH), 4.23 (s, 3 H,

NMe), 3.79 (s, 3 H, OMe), 3.6–3.4 (m, 2 H, β-CH ), 2.33 (s, 3 H,

_]_p_p_m_.1 C NMR

MeAr), 2.09 (s, 6 H, MeAr), 1.39 [s, 9 H, (CH

101 MHz, CD OD): δ = 170.93 [CO(OMe)], 156.15 [CO(OtBu)],

40.90, 137.27 (NCN), 134.28, 132.90, 130.90, 129.16 (ArH), 122.0

Im-bb(CH)], 79.56 [C(CH ], 51.99, 51.80 (OMe/α-CH), 33.61

NMe), 27.17 {[C(CH ]}, 25.85 (β-CH ), 19.67 [Mes(Me)], 16.25

Mes(Me)], 16.22 [Mes(Me)] ppm. MS (FAB-TOF): m/z calcd. for

3

):

4-(2-Ammonio-3-methoxy-3-oxopropyl)-1,3-dibenzyl-1H-imidazol-3-

ium Chloride Hydrochloride (21): Compound 2 (265 mg, 0.5 mmol)

was dissolved in 5 mL of a 4.0 m HCl solution in dioxane. The

reaction mixture was stirred overnight at room temperature. Vola-

tiles were removed in vacuo and the residue was stripped with

MeOH (3ϫ 10 mL). The crude product was dissolved in a small

amount of MeOH and was added dropwise to vigorously stirred

5

2

3

3 3

)

(

1

[

(

3

3 3

)

Et

0 min and then filtered. The residue was washed with Et

dissolved in MeOH. The mixture was concentrated and stripped

with CH Cl to give the title compound (239 mg, Ͼ99%) as a yel-

-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-mes- low foam. H NMR (400 MHz CD OD): δ = 9.16 (s, 1 H, NCHN),

ityl-3-(pyridin-2-ylmethyl)-1H-imidazol-3-ium Bromide (19): To a 7.66 (s, 1 H, Im-bb), 7.50–7.35 (m, 10 H, Ar), 5.51 (s, 2 H,

solution of 2-(bromomethyl)pyridine hydrobromide (0.234 g, NCH Ph), 5.44 (s, 2 H, NCH Ph), 4.23 (s, 1 H, α-CH), 3.72 (s, 3

.927 mmol) in cold H O (10 mL), a saturated aqueous solution of H, OMe), 3.40–3.18 (m, 2 H, β-CH

Na CO (10 mL) was added dropwise. The liberated 2- CD OD): δ = 169.1 [CO(OMe)], 135.0 [Ar(C

bromomethyl)pyridine was extracted into Et O (3 ϫ 10 mL) at 130.9 [Im-bb(C )], 130.8 [Ar(CH)], 130.6 [Ar(CH)], 130.5 [Ar(CH)],

and filtered. The filtrate was concentrated 130.5 [Ar(CH)], 130.2 [Ar(CH)], 129.6 [Ar(CH)], 124.2 [Im-

bb(CH)], 55.0 (Im-CH -Ph), 54.6 (α-CH), 52.6 (Im-CH -Ph), 52.3

(OMe), 26.0 (β-CH ) ppm. MS (FAB-TOF): m/z calcd. for

351.1936; found 351.1946.

-(2-Ammonio-3-methoxy-3-oxopropyl)-3-benzyl-1-methyl-1H-imid-

azol-3-ium Chloride Hydrochloride (22): Prepared as described for

2

O (100 mL). The resulting white suspension was stirred for

3

)

3

2

3

2

O and

[

+

22 32 3 4

C H N O 402.2393; found 402.2389.

2

1

4

3

2

1

3

0

2

) ppm. C NMR (100 MHz

)], 134.4 [Ar(C )],

2

3

q

(

0

2

q

°C, dried with MgSO

4

to ca. 2 mL and added to a solution of 16 (0.116 g, 0.299 mmol) in

MeCN (8.5 mL) at 0 °C. The ether was removed under reduced

pressure and the resulting solution was warmed to room tempera-

ture. Molecular sieves (4 Å) were added after 2 h, and the mixture

was stirred for 7 d. The molecular sieves were removed by filtration,

2

+

21 25 2 3

C H O N

5

then Et

2

O was added to the filtrate, which caused the precipitation

1

2

(

1, yield 81%; red solid. H NMR (400 MHz, CD

s, 1 H, NCHN), 7.61 (s, 1 H, Im-bb), 7.50–7.38 (m, 5 H, Ar), 5.42

s, 2 H, NCH Ph), 4.48 (t, J = 7.1 Hz, 1 H, α-CH), 3.91 (s, 3 H,

3

OD): δ = 9.08

of a red solid. The organic layer was collected and concentrated in

vacuo to give the title compound (86 mg, 0.154 mmol, 51%) as a

yellow oil. H NMR (400 MHz, CDCl

2

1

3

): δ = 9.88 (s, 1 H, NCHN),

NMe), 3.79 (s, 3 H, OMe), 3.46 (dd, J = 16.1, 7.2 Hz, 1 H, β-

8

.53 (d, J = 4.1 Hz, 1 H, Pyr), 7.92 (d, J = 7.7 Hz, 1 H, Pyr), 7.85

t, J = 7.5 Hz, 1 H, Pyr), 7.36 (m, 1 H, Pyr), 7.12 (s, 1 H, Im-bb),

.98 (s, 2 H, Mes), 6.18 (A-B system, 2 H, Im-CH -Pyr), 4.64–4.63

m, 1 H, NH), 3.75 (s, 3 H, OMe), 3.39 (d, J = 6.6 Hz, 2 H, β-

CH ), 2.33 [s, 3 H, Mes(Me)], 2.09 [s, 3 H, Mes(Me)], 2.06 [s 3

H, Mes(Me)], 1.39 {s, 9 H, [C(CH

]} ppm. ¹³C NMR (101 MHz,

CDCl ): δ = 170.87 [CO(OMe)], 160.08 (Pyr), 159.69 (Py), 155.47

CO(OtBu)], 151.86, 148.74, 141.10 (Ar), 138.59 (Ar), 138.25 (Ar),

13

CHH), 3.37 (dd, J = 16.6, 7.1 Hz, 1 H, β-CHH) ppm. C NMR

(

6

(

[

101 MHz, CD

Ar(C )], 131.0 [Im-bb(C

Ar(CH)], 123.2 [Im-bb(CH)], 54.4 (NCH

α-OMe), 34.9 (NCH ), 25.4 (β-CH ) ppm. HRMS (FAB): m/z

calcd. for C15 Cl 345.1011; found 345.0983.

-{[5-(2-Ammonio-3-methoxy-3-oxopropyl)-1H-imidazol-3-ium-3-

3

OD): δ = 169.2 [CO(OMe)], 138.6 (NCHN), 134.9

)], 130.4 [Ar(CH)], 130.4 [Ar(CH)], 130.0

Ph), 54.3 (α-CH), 52.2

2

q

2

(

3

2

3

)

3

2+

H

21

O

2

N

3

2

3

2

[

yl]methyl}-1,3-bispyridin-1-ium Chloride Dihydrochloride (23): Pre-

134.21 (Ar), 134.12 (Ar), 132.80 (Ar), 130.55 (Ar), 129.65 (Ar),

124.08 (Ar), 124.03 (Ar), 120.87 (Ar), 80.44 {[C(CH ]}, 52.85,

52.16, 50.84, 28.11 {[C(CH ]}, 26.63 (β-CH ), 20.97 [Mes(Me)],

17.39 [Mes(Me)] ppm. MS (FAB-TOF): m/z calcd. for

pared as described for 21. Quantitative yield (99%); off-white foam.

H NMR (400 MHz CD OD): δ = 9.62 (s, 1 H, NCHN), 8.93 (d,

3

)

3

1

3

)

3

2

J = 5.3 Hz, 1 H, Py-H2), 8.87 (d, J = 5.1 Hz, 1 H, Py-H2Ј), 8.65

(

t, J = 7.6 Hz, 1 H, Py-H4), 8.51 (t, J = 7.5 Hz, 1 H, Py-H4Ј), 8.23

d, J = 7.8 Hz, 1 H, Py-H5), 8.13–8.02 (m, 3 H, Py-H5Ј, Im-bb,

+

C

27

H

36

N

4

O

4

480.2731; found 480.2737.

Py-H3), 8.00–7.92 (m, 1 H, Py-H3Ј), 6.09 (s, 2 H, NCH

s, 2 H, NCH PyЈ), 4.62 (t, J = 6.4 Hz, 1 H, α-CH), 3.85 (s, 3 H,

OMe), 3.57 (dd, J = 16.8, 6.5 Hz, 1 H, β-CHH), 3.45 (dd, J = 16.3,

2

Py), 6.07

5

-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-3-mes-

(

2

ityl-1-[(6-methylpyridin-2-yl)methyl]-1H-imidazol-3-ium Bromide

20): Compound 16 (410 mg, 1.06 mmol) and 2-(bromomethyl)-6-

methylpyridine (236 mg, 1.27 mmol) were dissolved in MeCN

20 mL). The mixture was heated to reflux for 72 h, after which,

(

1

3

7.0 Hz, 1 H, β-CHH) ppm. C NMR (75 MHz CD OD): δ = 169.0

[

CO(OMe)], 149.9 (Py-C6), 149.5 (Py-C6Ј), 148.0 [Py(CH)], 146.6

Py(CH)], 146.1 [Py(CH)], 144.7 (PyCH), 141.3 [Py(CH)], 132.1

(

TLC analysis showed the full conversion of 16. All volatiles were

removed in vacuo and the crude product was purified by column

Im-bb(C

Im-bb(CH)], 54.4 (NCH

q

)], 128.3 [Py(CH)], 127.8 [Py(CH)], 127.4 [Py(CH)], 124.6

Py), 52.2 (NCH PyЈ), 51.3 (α-CH), 25.5

chromatography (silica;CH

compound (527 mg, 87 %) as an off-white foam. H NMR

400 MHz, CD Cl ): δ = 9.87 (s, 1 H, NCHN), 7.67 (t, J = 7.7 Hz,

H, Py-H4), 7.54 (d, J = 7.7 Hz, 1 H, Py-H3), 7.18–7.12 (m, 2 H,

Im-bb, Py-H5), 7.05 (s, 2 H, Mes), 6.10 (d, J = 7.7 Hz, 1 H, NH), ium-3-yl]methyl}pyridin-1-ium Chloride Hydrochloride (24): Pre-

2

Cl /MeOH, 95:5 to 9:1) to give the title

2

3

+

1

(β-CH ) ppm. MS (FAB-TOF): m/z calcd. for C19^H O N

3

2

24

2

5

54.1914; found 354.1928.

(

1

2

2-{[5-(2-Ammonio-3-methoxy-3-oxopropyl)-1-methyl-1H-imidazol-3-

Eur. J. Inorg. Chem. 0000, 0–0

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Job/Unit: I43104

/KAP1

Date: 28-01-15 15:33:33

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FULL PAPER

1

pared as described for 23. Quantitative yield; red solid. H NMR

(

(1-Benzyl-4-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-

oxopropyl}-3-(pyridin-2-ylmethyl)-1H-imidazol-2-(3H)-ylidene)-

3

400 MHz, CD OD): δ = 9.23 (s, 1 H, NCHN), 8.80 (d, J = 5.1 Hz,

1

H, Py-H2), 8.41 (t, J = 7.8 Hz, 1 H, Py-H4), 7.95 (d, J = 7.8 Hz, silver(I) Bromide (28): The title compound was prepared as de-

H, Py-H5), 7.90–7.84 (m, 1 H, Py-H3), 7.79 (s, 1 H, Im-bb), 5.85 scribed for 27. The compound was obtained as a mixture of species,

-Py), 4.53 (t, J = 7.0 Hz, 1 H, α-CH), 3.97 (s, 3 H, which are presumably coordination oligomers. The compounds

NMe), 3.87 (s, 3 H, OMe), 3.54 (dd, J = 16.2, 6.4 Hz, 1 H, β- were applied in the transmetalation reactions and gave the desired

(s, 2 H, Im-CH

2

1

3

1

CHH), 3.38 (dd, J = 16.3, 7.6 Hz, 1 H, β-CHH) ppm. C NMR Pd complex in good yields. H NMR (400 MHz, CD

2

Cl

OD): δ = 169.1 [CO(OMe)], 150.4 (Py-C6), 147.1 (d, J = 2.9 Hz, 1 H, Py-H2), 8.42 (d, J = 3.8 Hz, 0.5 H, Py-H2Ј),

Py-C2), 145.3 (Py-C4), 131.6 [Im-bb(C )], 127.9 (Py-C5), 127.6 7.68 (t, J = 7.0 Hz, 1 H, Py-H4), 7.55 (t, J = 7.6 Hz, 0.5 H, Py-

Py-C3), 124.0 [Im-bb(CH)], 54.4 (α-CH), 52.2 (OMe), 51.5 H4Ј), 7.38–7.08 (m, 12 H, Ar), 6.89 (s, 0.5 H, Im-bbЈ), 6.86 (s, 1

NCH Py), 35.1 (NMe), 25.4 (β-CH ) ppm. H, Im-bb), 6.02 (s, 1 H, NH), 5.41 (m, 3 H, NCH Ar), 5.21 (s, 2

H, NCH Ar), 5.13 (s, 1 H, NCH ArЈ), 4.64 (s, 0.5 H, α-CH), 4.46

2

): δ = 8.55

(

101 MHz, CD

3

q

2

4

-(2-Ammonio-3-methoxy-3-oxopropyl)-1-mesityl-3-methyl-1H-imid-

2

(

s, 1 H, α-CHЈ), 3.63 (s, 3 H, OMe), 3.47 (s, 1.5 H, OMeЈ), 3.14

azol-3-ium Chloride Hydrochloride (25): Prepared as described for

1

(dd, J = 15.8, 4.8 Hz, 1 H, β-CHH), 3.04 (dd, J = 15.9, 8.3 Hz, 1

2

1, yield 92%; off-white foam. H NMR (400 MHz, CD

.17 (s, 1 H, NCHN), 7.70 (s, 1 H, Im-bb), 7.13 (s, 2 H, Mes), 4.61

), 3.86 (s, 3 H, OMe),

), 2.36 [s, 3 H, Mes(p-Me)], 2.11 [s, 6 H,

OD): δ = 167.85 [CO(-

OMe)], 141.20 (Mes), 138.16 (NCN), 134.43, 130.94, 130.37, 129.30

Mes(CH)], 123.23 [Im-bb(CH)], 52.86 (OMe), 50.75 (α-CH), 33.67

NMe), 24.10 (β-CH ), 19.70 [Mes(Me)], 16.14 [Mes(Me)] ppm.

MS (FAB-TOF): m/z calcd. for C17

3

OD): δ =

H, β-CHH), 2.87–2.61 (m, 1 H, β-CH Ј), 1.37 [s, 9 H, C(CH ],

Ј] ppm. C NMR (101 MHz, CDCl ): δ =

70.88 [CO(O tBu)], 155.37, 152.20, 149.58, 137.50, 132.82, 132.15,

2

3 3

)

9

1

3

1

.26 [s, 4.5 H, C(CH

3

)

3

(t, J = 6.6 Hz, 1 H, α-CH), 4.04 (s, 3 H,NCH

3

.60–3.40 (m, 2 H, β-CH

2

13

129.14, 128.73, 123.65, 123.08, 119.84 [Im-bb(CH)], 80.07

C(CH ], 53.09 (α-CH ), 52.60 (Im-CH -Ar), 52.07 (Im-CH -Ar),

1.35 (OMe), 27.99 [C(CH ], 26.21 (β-CH ) ppm ( C NCN sig-

na l wa s no t ob s er ved ). HRM S ( FAB): m/z cal cd. for

Mes(o-Me)] ppm. C NMR (75 MHz, CD

3

[

5

3

)

3

2

1

3

)

3

2

[

(

2

1

09

+

50 60 8 8

C H O N Ag 1009.3582; found 1009.3591.

H

24DN

3

O

2

304.2010; found

304.2025.

(

4-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1,3-bis-

4

-{2-[(tert-Butoxycarbonyl)amino]-3-carboxylate}-1-p-methoxy-

(pyridin-2-ylmethyl)-1H-imidazol-2-(3H)-ylidene)silver(I) Bromide

(29): Prepared as described for compound 27, yield 80%; white

phenyl-3-methyl-1H-imidazol-3-ium Iodide (26): Compound 17

1

(0.125 g, 0.24 mmol) was dissolved in methanol (20 mL), then H

2

O

foam. H NMR (400 MHz, CD Cl ): δ = 8.56 (d, J = 3.6 Hz, 2 H,

2

(

2 mL) and LiOH (60 mg, 2.4 mmol) were added. The solution was

Py-H2, Py-H2Ј), 7.83–7.63 (m, 2 H, Py-H4, Py-H4Ј), 7.36 (d, J =

7.6 Hz, 1 H, Py-H5), 7.32–7.19 (m, 4 H, Py), 7.02 (s, 1 H, Im-bb),

5.93 (d, J = 7.4 Hz, 1 H, NH), 5.42 (AB system, J = 28.7, 15.9 Hz,

2 H, NCH Py), 5.35 (s, 2 H, NCH PyЈ), 4.51 (s, 1 H, α-CH), 3.68

stirred overnight, after which TLC analysis showed the disappear-

ance of the starting material. The solvent was removed in vacuo

and the obtained yellow oil was stripped twice with methanol. The

2

crude product was further purified by column chromatography (sil-

(s, 3 H, OMe), 3.17 (dd, J = 15.8, 4.9 Hz, 1 H, β-CHH), 3.06 (dd,

1

13

ica; CH

2

Cl

2

/MeOH, 9:1) to give the product (0.08 g, 65%). H J = 15.9, 8.0 Hz, 1 H, β-CHH), 1.37 [s, 9 H, C(CH ) ] ppm.

C

3

NMR (400 MHz, CD

3

OD): δ = 9.36 (s, 1 H, NCHN), 7.72 (s, 1 H,

2 2

NMR (126 MHz, CD Cl ): δ = 184.4 (NCN), 171.9 [CO(OMe)],

Im-bb), 7.62 (d, J = 8.9 Hz, 2 H, Ar), 7.16 (d, J = 9.0 Hz, 2 H, 156.0 (Py-C6), 155.9 (Py-C6Ј), 155.7 [CO(OtBu)], 150.2 (Py-C2, Py-

Ar), 4.36–4.11 (m, 1 H, α-CH), 4.00 (s, 3 H, NMe), 3.89 (s, 3 H, C2Ј), 137.8 (Py-C4), 137.6 (Py-C4Ј), 131.4 [Im-bb(C )], 123.7

q

1

3

OMe), 3.11 (m, 2 H, β-CH

2

), 1.39 [s, 9 H, C(CH

3

)

3

] ppm.

C

[Py(CH)], 123.6 [Py(CH)], 122.9 [Py(CH)], 122.9 [Py(CH)], 120.5

–

NMR (101 MHz, MeOD): δ = 174.72 (COO ), 160.71 (Ar), 157.87 [Im-bb(CH)], 80.5 [C(CH ) ], 57.8 (NCH Py), 54.4 (α-CH), 52.8

3

2

(

1

5

Ar), 155.99 [CO(OtBu)], 133.53 (NCHN), 127.77 [Im-bb(C

q

)],

3 3 2

(OMe), 28.5 [C(CH ) ], 27.7 (β-CH ) ppm. MS (FAB-TOF): m/z

1

07

+

23.03 (Ar), 119.43 [Im-bb(CH)], 114.91 (Ar), 79.01 [C(CH

4.90 (Ar-OMe), 48.38 (α-CH), 33.10 (NMe), 27.36 (β-CH ), 27.17

] ppm. MS (FAB-TOF): m/z calcd. for C19 24DLiN

83.2012; found 383.2287.

3 3

) ], calcd. for C H O N Ag 558.1270; found 558.1269.

2

4

29

4

5

2

+

(4-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-(4-

methoxyphenyl)-3-methyl-1H-imidazol-3-ium-2-yl)silver(I) Iodide

[C(CH

3

)

3

H

3 5

O

3

1

(

30): The title compound was prepared as described for 27. The H

(

1,3-Dibenzyl-4-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-

13

spectrum was very broad and the C spectrum showed double

peaks, probably due to coordination oligomers, or multiple coordi-

nation modes of the histidylidene to the silver. The compound was

oxopropyl}-1H-imidazol-2-(3H)-ylidene)silver(I) Bromide (27):

Compound 2 (223 mg, 0.42 mmol) was dried azeotropically by co-

evaporation with toluene (3ϫ 3 mL). Ag

and 4 Å molecular sieves were added and the Schlenk flask was

purged with argon twice. CH Cl (10 mL) was added and the mix-

ture was stirred overnight at room temperature with exclusion of

light. The mixture was filtered through a pad of Celite in air and

the residue was washed with CH

removed in vacuo to afford the title compound (203 mg, 96%) as

an off-white foam. H NMR (400 MHz CD

1

H, NCH

(

2

O (54 mg, 0.23 mmol),

1

used as obtained, and yielded the corresponding Pd-compound. H

NMR (400 MHz, CD

2

Cl

2

): δ = 7.47 (d, J = 8.8 Hz, 2 H, Ar), 7.12

2

(

s, 1 H, Im-bb), 6.96 (d, J = 8.8 Hz, 2 H, Ar), 5.50 (s, 1 H, NH),

4.63 (s, 1 H, α-CH), 3.89 (s, 3 H, NMe), 3.86 (s, 3 H,OMe), 3.80

(

s, 3 H,OMe), 3.29 (AB-M system dd, J = 10.8, 4.8 Hz, 1 H, β-

CH ), 3.12 (AB-M system dd, J = 8.0, 7.6 Hz, 1 H, β-CH ), 1.41

): δ = 180.87

NCN), 171.31 [CO(OMe)], 159.60, 155.30 [CO(OtBu)], 137.82,

33.17, 132.92, 130.80, 128.82, 128.01, 125.09 [Ar(CH)], 125.00

Ar(CH)], 120.38 [Im-bb(CH)], 120.19 [Im-bb(CH)], 114.44

Ar(CH)], 114.21 [Ar(CH)], 79.80 [C(CH ], 77.94 [C(CH ],

5.50 (Ar-OMe), 52.53 (CH ), 52.22 (CH ), 36.35 (NMe), 36.29

NMe), 28.05 [C(CH ], 27.86 [C(CH ], 27.35 (β-CH

) ppm. MS (FAB-TOF) calculated for C40

2 2

Cl (10 mL). All volatiles were

2

13

[

(

1

3 3 2 2

s, 9 H, C(CH ) ] ppm. C NMR (101 MHz, CD Cl

1

2

Cl

2

): δ = 7.48–7.08 (m,

Ph), 5.33 (s, 2

2

PhЈ), 5.07 (s, 1 H, NH), 4.42 (m, 1 H, α-CH), 2.90–2.84

0 H, Ar), 6.82 (s, 1 H, Im-bb), 5.47 (s, 2 H, NCH

2

[

m, 1 H, β-CHH), 2.67–2.61 (m, 1 H, β-CHH), 1.32 [d, J = 48.6 Hz,

3

)

3

3 3

)

9

H, C(CH

3

)

3

] ppm. ¹³C NMR (75 MHz CD

2

Cl

2

): δ = 183.2 (Ag-

)], 136.2

)], 129.4 (ArCH), 128.9 [Ar(CH)], 128.6

Ar(CH)], 128.1 [Ar(CH)], 127.1 [Ar(CH)], 120.4 [Im-bb(CH)], 80.7

C(CH ], 56.2 (NCH Ph), 53.4 (NCH PhЈ), 52.9 (α-CH), 52.8

OMe), 28.3 (β-CH ), 28.0 [C(CH ] ppm. MS (FAB-TOF): m/z Bis(4-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-

calcd. for C52

5

3

C), 171.5 [CO(OMe)], 155.4 [CO(OtBu)], 136.2 [Ar(C

q

(

3

)

3

)

3

2

), 27.15 (β-

[

Ar(C

q

)], 130.9 [Im-bb(C

q

107

+

CH

2

H

54

N

6

O

10 Ag

887.2949, found 887.2964.

3

)

3

2

(

2

3 3

)

109

+

H

62

O

8

N

6

Ag 1007.3677; found 1007.3674.

mesityl-3-methyl-1H-imidazol-2-ylidene)silver(I) Silver(I) Diiodide

Eur. J. Inorg. Chem. 0000, 0–0

11

Job/Unit: I43104

/KAP1

Date: 28-01-15 15:33:33

Pages: 16

www.eurjic.org

FULL PAPER

(

31): Prepared as described for 27, yield 86%; yellow foam. ¹

NMR (400 MHz, CD Cl ): δ = 7.01 (s, 2 H, Ar), 6.79 (s, 1 H, Im-

bb), 5.33 (d, J = 7.4 Hz, 1 H, NH), 4.64 (m, 1 H, α-CH), 3.87 (s,

H

20.79 (Mes), 17.41 (Mes) ppm. MS (FAB-TOF): m/z calcd. for

1

09

+

2

C

34

H

46 AgN

6 4

O 711.2628; found 711.2634.

(

1,3-Dibenzyl-4-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-

3

5

H, Me), 3.78 (s, 3 H, Me), 3.12 (AB-M system, dd, J = 15.7,

oxopropyl}-1H-imidazol-2-(3H)-ylidene)allylpalladium(II) Chloride

(35): A solution of 28 (223 mg. 0.35 mmol) in CH Cl (11 mL) was

added dropwise to a stirred solution of [Pd(allyl)Cl] (64 mg,

.175 mmol) in CH Cl (5.5 mL). The mixture was stirred for 1 h

at room temperature, then filtered through a pad of Celite in air

and the residue was rinsed with CH Cl (10 mL). Volatiles were

evaporated and the crude product was purified by selective precipi-

tation of the impurity by gradual cooling of a CH Cl /pentane

solution to give the title compound (90 mg, 41%) as an off-white

.1 Hz, 1 H,α-CH), 2.38 (s, 3 H, Mes), 1.96 (d, J = 4.2 Hz, 6 H,

_]_p_p_m_.1 C NMR (400 MHz, CD

3

2

Mes), 1.44 [s, 9 H, C(CH

3

)

3

2

Cl

2

):

2

δ = 183.80 (NCN), 171.19 [CO(OMe)], 154.97 [CO(OtBu)], 138.89,

35.43, 134.84, 130.19, 128.93, 120.57 [Im-bb(CH)], 80.03

0

2

1

[

(

C(CH

3

)

3

], 52.71 (OMe), 52.50 (α-CH), 36.73 (NMe), 27.90

], 27.52 (β-CH ), 20.80 (Mes), 17.52 (Mes), 17.49

2

3

2

1

07

+

Mes) ppm. MS (FAB-TOF): m/z calcd. for C44

11.3677; found 911.3693.

H

62

N

6

O

8

Ag

2

9

1

(

4-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-mes- solid. H NMR (400 MHz, CD

ityl-3-[(6-methylpyridin-2-yl)methyl]-1H-imidazol-2-(3H)-ylidene)- 7.23–7.18 (m, 2 H, Ar), 6.82 (s, 1 H, Im-bb), 5.63–5.34 (m, 4 H,

silver(I) Bromide (32): Prepared as described for 27, yield 89%; yel- NCH Ph), 5.12–5.00 (m, 2 H, NH, allyl), 4.39 (br. s, 1 H, α-CH),

2 2

Cl ): δ = 7.39–7.26 (m, 8 H, Ar),

2

1

low foam. H NMR (400 MHz, CD

1

2

Cl

2

): δ = 7.61 (t, J = 7.7 Hz,

4.08 (dd, J = 7.5, 2.1 Hz, 1 H, allyl), 3.62 (s, 3 H, OMe), 3.12 (br.

s, 1 H, allyl), 3.02 (d, J = 13.1 Hz, 1 H, allyl), 2.98–2.87 (m, 1 H,

H, Py-H4), 7.27–7.02 (m, 2 H, Py-H3, Py-H5), 6.99 (s, 2 H, Mes),

6

.82 (s, 1 H, Im-bb), 5.81 (d, J = 6.1 Hz, 1 H, NH), 5.4 (br. s, 2 H, β-CHH), 2.84–2.71 (m, 1 H, β-CHH), 1.93 (d, J = 12.0 Hz, 1 H,

1

3

NCH

2

Py), 4.59 (d, J = 5.1 Hz, 1 H, α-CH), 3.69 (s, 3 H, OMe),

allyl), 1.38 [br. s, 9 H, C(CH

Cl ): δ = 182.7 (NCN), 171.8 [CO(OMe)], 155.3 [CO(OtBu)],

137.2 [Ar(C )], 137.1 [Ar(C )], 130.6 [Ar(CH)], 129.1 [Ar(CH)],

128.4 [Ar(CH)], 128.3 [Ar(CH)], 128.3 [Ar(CH)], 128.1 [Ar(CH)],

): δ = 185.2 (NCN), 127.3 [Ar(CH)], 120.3 [Im-bb(CH)], 115.1 (allyl), 80.5 [C(CH ],

71.9 [CO(OMe)], 159.7 (Py-C6), 155.7 [CO(OtBu)], 155.4 (Py-C2), 71.7 (allyl), 55.1 (NCH Ph), 52.9 (α-CH), 52.6 (OMe), 52.4 (allyl),

40.1 (Ar), 138.0 (Ar), 136.4 (Ar), 135.5 (Ar), 135.5 (Ar), 131.6 28.3 [C(CH ], 28.1 (β-CH ) ppm. MS (FAB-TOF): m/z calcd. for

Pd 596.1741; found 596.1743.

3 3

) ] ppm. C NMR (101 MHz,

3

1

.21 (dd, J = 15.9, 5.1 Hz, 1 H, β-CHH), 3.14 (dd, J = 15.9, 7.3 Hz, CD

H, β-CHH), 2.50 [s, 3 H, Lut(CH )], 2.34 [s, 3 H, Mes(p-Me)],

.98 [s, 3 H, Mes(o-Me)], 1.97 [s, 3 H, Mes(p-Me)Ј], 1.36 [s, 9 H,

] ppm. ¹³C NMR (126 MHz, CD

Cl

2

3

q

C(CH

1

3

)

3

2

3 3

)

2

3

)

3

2

+

(

8

[

ArC), 129.9 (Ar), 128.7 (Ar), 123.3 (Ar), 121.7 (Ar), 119.3 (Ar),

0.8 [C(CH ], 54.7 (NCH Py), 53.6 (α-CH), 53.0 (OMe), 28.6

C(CH ], 28.2 (β-CH ), 24.6 [Lut(Me)], 21.4 [Mes(p-Me)], 17.9

M e s ( o - M e ) ] p p m . M S ( FA B - T O F ) : m / z c a l c d . f o r

29 36 4 3

C H O N

3

)

3

2

(

1-Benzyl-4-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-

3

)

3

2

oxopropyl}-3-(pyridin-2-ylmethyl)-1H-imidazol-2-(3H)-ylidene)allyl-

palladium(II) Chloride (36): A solution of 29 (95 mg, 0.15 mmol) in

107

+

C

28

H

36

O

4

N

4

Ag [M – Br] 599.1787; found 599.1766.

CH

(allyl)Cl]

stirred for 24 h at room temperature, then filtered through a pad

of Celite in air and the residue was washed with CH Cl (5 mL).

O (125 mg, 0.54 mmol) and molecular sieves were Volatiles were evaporated, and the crude product was purified by

added, then the Schlenk flask was purged twice and placed under column chromatography (silica; CH Cl to CH Cl /MeOH, 9:1) to

an argon atmosphere. CH Cl (10 mL) was added and the mixture give the title compound (70 mg, 74%) as an off-white foam. H

NMR (400 MHz, CD Cl ): δ = 8.63 (d, J = 4.4 Hz, 1 H, Py-H2),

7.84–7.67 (m, 2 H, Ar), 7.40–7.19 (m, 6 H, Ar), 6.81 (s, 1 H, Im-

bb), 6.56 (br. s, 1 H, NH), 5.73–5.47 (m, 2 H, NCH Py), 5.30 (s, 2

H, NCH Ph), 5.5.21–5.14 (m, 1 H, allyl), 4.45 (dd, J = 13.1, 7.3 Hz,

1 H, α-CH), 4.13 (d, J = 7.6 Hz, 1 H, allyl), 3.65 (s, 3 H, OMe),

3.16 (dd, J = 14.7, 10.0 Hz, 2 H, β-CH ), 3.01 (br. s, 2 H, 2ϫallyl),

2.0 (br. s, 1 H, allyl), 1.36 [s, 9 H, C(CH

(101 MHz, CD Cl ): δ = 180.9 (NCN), 172.0 [CO(OMe)], 156.1

(Py-C6), 155.9 [CO(OtBu)], 151.4 (Py-C2), 138.2 (Py-C4), 136.8

): δ = 181.9 (NCN), 174.9 [Ar(C )], 131.9 [Im-bb(C )], 129.1 [Ar(CH)], 128.5 [Ar(CH)], 128.0

), 132.3 [Im-bb(C )], 129.6 [Ar(CH)], 124.6 (Py-C5), 123.8 (Py-C3), 119.7 [Im-bb(CH)], 116.8

Ar(CH)], 129.5 [Ar(CH)], 129.0 [Ar(CH)], 128.7 [Ar(CH)], 128.3 (allyl), 80.0 [C(CH ], 72.7 (allyl), 55.2 (NCH Py), 53.7 (α-CH),

Ar(CH)], 127.2 [Ar(CH)], 120.6 [Im-bb(CH)], 56.4 (NCH Ph), 52.8 (NCH Ph), 52.7 (OCH ), 48.6 (allyl), 28.4 [C(CH ], 27.2 (β-

4.2 (NCH PhЈ), 53.7 (α-CH), 52.5 (OMe), 30.2 (β-CH ) ppm. MS CH ) ppm. MS (FAB-TOF): m/z calcd. for C28

FAB-TOF): m/z calcd. for C21 351.1947; found 597.1693; found 597.1697.

51.1946.

2

Cl

2

(3 mL) was added dropwise to a stirred solution of [Pd-

[

(

0

(

4-(2-Amino-3-methoxy-3-oxopropyl)-1,3-dibenzyl-1H-imidazol-2-

3H)-ylidene]silver(I) Chloride (33): Compound 21 (183 mg,

.43 mmol) was dried azeotropically by coevaporation with toluene

3ϫ 3 mL). Ag

2

(23 mg, 0.075 mmol) in CH Cl (2 mL). The mixture was

2

1

2

was stirred overnight at room temperature with exclusion of light.

The mixture was filtered through a pad of Celite in air and the

2

residue was washed with CH

2

Cl

2

(10 mL). All volatiles were re-

2

moved in vacuo to give the title compound (203 mg, 96%) as an

2

1

off-white foam. H NMR (400 MHz CD

H, Ar), 7.18–7.12 (m, 2 H, Ar), 6.91 (s, 1 H, Im-bb), 5.43 (s, 2 H,

NCH Ph), 5.30 (s, 2 H, NCH PhЈ), 3.59 (s, 3 H, OMe), 3.52–3.40

m, 1 H, α-CH), 2.84 (dd, J = 15.6, 5.2 Hz, 1 H, β-CHH), 2.61 (dd,

J = 15.6, 7.8 Hz, 1 H, β-CHH), 1.43 (d, J = 7.2 Hz, 2 H,

NH Cl

) ppm. ¹³C NMR (126 MHz CD

CO(OMe)], 136.6 [Ar(C )], 136.5 (Ar-C

2 2

Cl ): δ = 7.45–7.24 (m, 8

2

1

3

2

3 3

) ] ppm. C NMR

(

2

q

[

q

3

)

3

2

3

3 3

)

+

5

(

2

35 4 4

H O N Pd

+

25 3 2

H N O

3

(

4-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1,3-bis-

Bis[4-(2-amino-3-methoxy-3-oxopropyl)-1-mesityl-3-methyl-imid-

(pyridin-2-ylmethyl)-1H-imidazol-2-(3H)-ylidene)allylpalladium(II)

azol-2-ylidene]silver(I) Silver(I) Dichloride (34): Prepared as de-

scribed for 33, yield 27 mg (22%); off-white hygroscopic solid. H white foam. H NMR (400 MHz, CD

Chloride (37): Prepared as described for 36, yield quantitative; off-

1

2

Cl

2

): δ = 8.62 (d, J = 4.4 Hz,

NMR (400 MHz, CD

bb), 3.91 (s, 3 H, OMe), 3.81 (s, 1 H, α-CH), 3.73 (s, 3 H, NMe),

.05 (ddd, J = 52.6, 15.5, 6.4 Hz, 2 H, β-CH

Me)], 2.01 [s, 6 H, Mes(o-Me)], 1.63 (s, 2 H, NH

75 MHz, CDCl ): δ = 181.20 (NCN), 174.48 [CO(OMe)], 139.36, NCH

35.65, 134.88, 131.00, 129.17 [Ar(CH)], 120.70 [Im-bb(CH)], 53.80 CH), 4.19 (d, J = 7.6 Hz, 1 H, allyl), 3.27 (d, J = 13.6 Hz, 1 H,

OMe/α-CH), 52.14 (OMe/α-CH), 36.55 (NCH ), 29.64 (β-CH ), allyl), 3.23–3.04 (m, 3 H, β-CH , allyl), 2.1 (br. s, 1 H, allyl), 1.34

2

Cl

2

): δ = 7.03 (s, 2 H, Ar), 6.87 (s, 1 H, Im-

1 H, Py-H2), 8.59 (d, J = 4.9 Hz, 1 H, Py-H2Ј), 7.89–7.68 (m, 2 H,

Py-H4, Py-H4Ј), 7.64 (d, J = 7.5 Hz, 1 H, Py-H5), 7.41 (d, J =

3

2

), 2.38 [s, 3 H, Mes(p- 7.6 Hz, 1 H, Py-H5Ј), 7.34–7.24 (m, 2 H, Py-H3, Py-H3Ј), 7.17 (s,

) ppm. ¹³C NMR 1 H, Im-bb), 6.56 (d, J = 6.7 Hz, 1 H, NH), 5.66–5.54 (m, 4 H,

Py), 5.31–5.19 (m, 1 H, allyl), 4.44 (d, J = 4.9 Hz, 1 H, α-

2

(

3

2

1

(

3

2

Eur. J. Inorg. Chem. 0000, 0–0

12

Job/Unit: I43104

/KAP1

Date: 28-01-15 15:33:33

Pages: 16

www.eurjic.org

FULL PAPER

[

(

s, 9 H, C(CH

3

)

3

] ppm. ¹³C NMR (126 MHz, CD

2

Cl

2

): δ = 182.6

H, allyl), 1.42 [s, 18 H, CO(OtBu)] ppm. ¹³C NMR (101 MHz,

Cl ): δ = 175.90 (NCN), 171.52 [CO(OMe)], 159.44 (p-Ar),

)], 130.79 (i-Ar), 125.83 (m-

)], 123.8 (Py-CH), 123.8 (Py-CH), 123.5 Ar), 121.40 [Im-bb(CH)], 118.00 (allyl), 114.13 (o-Ar), 79.34

Py-CH), 123.4 (Py-CH), 120.7 [Im-bb(CH)], 116.4 (allyl), 80.5 [C(CH ], 58.45 (allyl), 55.57 (Ar-OMe), 52.25 {α-CH/

], 72.8 (allyl), 57.1 (NCH Py), 53.5 (α-CH), 52.8 (OMe), [CO(OMe)]}, 51.90 [α-CH/CO(OMe)], 34.78 (NMe), 27.84

8.7 (allyl), 28.6 [C(CH ], 27.8 (β-CH ) ppm. MS (FAB-TOF): [C(CH ], 26.57 (β-CH ) ppm. MS (ESI-Coldspray): m/z calcd. for

Pd 598.1646; found 598.1646.

10ClPd⁺960.3016; found 960.3029.

Pd-C), 172.2 [CO(OMe)], 156.8 (Py-C6), 156.7 (Py-C6Ј), 155.8 CD

2

[CO(OtBu)], 150.7 (Py-C2), 150.4 (Py-C2Ј), 137.7 (Py-C4), 137.6 155.43 [CO(OtBu)], 133.13 [Im-bb(C

q

(

Py-C4Ј), 131.8 [Im-bb(C

q

3 3

)

[C(CH

3

)

3

2

4

3

)

3

2

3

)

3

2

+

m/z calcd. for C27

H

34

O

4

N

5

43 59 6

C H N O

(

4-{2-[(tert-Butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-mes- Catalytic Transfer Semihydrogenation of Alkynes: A Radleys’

ityl-3-[(6-methylpyridin-2-yl)methyl]-1H-imidazol-2-(3H)-ylidene)all- twelve-place reaction station with integrated heating and cooling

ylpalladium(II) Chloride (38): Prepared as described for 36, yield setup was used for all catalytic experiments. Samples were taken at

): δ = 7.61 (t, J regular time intervals by filtering aliquots of the reaction mixture

7.5 Hz, 1 H, Py-H4), 7.40 (br. s, 1 H, Py-H5), 7.12 (d, J = 7.6 Hz, over short silica pads and eluting with CH Cl . Samples were ana-

H, Py-H3), 6.94 (br. s, 2 H, Mes), 6.84 (br. s, 1 H, Im-bb), 6.79 lyzed with a Thermo Scientific Trace GC Ultra equipped with an

Py), 4.66 (br. s, 1 H, allyl), R-Rxi 5ms column (30 m, ID 0.25 mm) and quantified by using

1

9

2 2

3%; off-white foam. H NMR (400 MHz, CD Cl

=

1

2

(

s, 1 H, NH), 5.83–5.40 (m, 2 H, NCH

2

4

3

6

2

.62–4.45 (m, 1 H, α-CH), 3.90 (d, J = 7.2 Hz, 1 H, allyl), 3.73 (s,

H, OMe), 3.43 (d, J = 4.1 Hz, 1 H, allyl), 3.37 (dd, J = 16.1,

.1 Hz, 1 H, β-CHH), 3.22 (dd, J = 14.9, 2.7 Hz, 1 H, β-CHH), with a Bruker 400 MHz spectrometer.

3

.80–2.59 (m, 2 H, 2ϫallyl), 2.54 (s, 3 H, Py-CH ), 2.31 [s, 3 H,

the response factor corrected GC-area in respect to the internal

standard. Samples were further analyzed by NMR spectroscopy

General Procedure: A stock solution was prepared by adding in

their respective order: acetonitrile (320 mL, 250.3 g), 1-phenyl-1-

propyne (6.4 g, 55 mmol), p-xylene (internal standard, 5.68 g,

Mes(p-Me)], 2.23–1.93 [m, 6 H, Mes(o-Me)], 1.31 [s, 9 H,

C(CH ) Cl ): δ = 184.1 (NCN),

_]_p_p_m_.1 C NMR (126 MHz, CD

3

3 3 2 2

172.1 [CO(OMe)], 159.3 (Py-C6), 156.9 (Py-C2), 155.9 [CO(OtBu)],

5

(

4 mmol), triethylamine (27.00 g, 267 mmol), and formic acid

11.48 g, 267 mmol), and the solution was saturated with nitrogen

gas by gently bubbling N for 20 min. An aliquot (20 mL) was

139.4 (Ar), 137.5 (Ar), 137.1 (Ar), 136.2 (Ar), 135.8 (Ar), 131.8

(

1

Ar), 129.4 (Ar), 129.3 (Ar), 122.7 (Ar), 121.2 (Ar), 120.8 (Ar),

15.1 (allyl), 80.2 [C(CH ], 71.3 (allyl), 54.1 (NCH Py), 52.9 (α-

CH), 52.8 (OMe), 48.9 (allyl), 28.5 [C(CH ], 27.9 (β-CH

2

3

)

3

2

taken from the stock solution by using a syringe and added to one

of the twelve reaction vessels. The exact amount of added stock

solution was determined by weighing; for this reason, molar and

weight percentages were applied to determine quantities and fur-

ther calculations. The Radleys’ station was heated to 70 °C, after

which the appropriate amount of catalyst was added in aluminum

weighing trays. Reaction rates were determined by taking the first

order derivative of the conversion at 15%.

3

)

3

2

), 24.7

[

3

Lut(CH )], 21.3 [Mes(p-Me)], 18.5 [Mes(o-Me)], 18.2 [Mes(o-

+

CH

6

3

)] ppm. MS (FAB-TOF): m/z calcd. for C31

H

41

O

4

N

4

Pd

93.2163; found 639.2174.

[

4-(2-Amino-3-methoxy-3-oxopropyl)-1,3-dibenzyl-1H-imidazol-2-

(3H)-ylidene]allylpalladium(II) Chloride (40): Prepared as described

1

for 36, yield 31%. H NMR (400 MHz, CD

2

Cl

H, Ar), 7.19 (d, J = 7.1 Hz, 2 H, Ar), 6.88 (s, 1 H, Im-bb), 5.64–

.33 (m, 4 H, NCH Ph), 5.13–5.02 (m, 1 H, allyl), 4.07 (dd, J =

.5, 1.6 Hz, 1 H, allyl), 3.60 (s, 3 H, OMe), 3.45 (d, J = 5.7 Hz, 1

2

): δ = 7.42–7.26 (m,

8

5

7

X-ray Crystal Structure Determination of 42: C31

12 0.5 C O, disordered solvent; Fw = 780.21*; pale-brown

block; 0.40ϫ0.18ϫ0.11 mm ; monoclinic; P2

4.5823(3), b = 14.2173(4), c = 20.5565(4) Å, β = 103.670(1)°; V =

41 4 4

H N O Pd 0.5

2

C

6

H

4 8

H

3

1

(no. 4); a =

H, α-CH), 3.08–3.02 (m, 2 H, 2 ϫ allyl), 2.89–2.80 (m, 1 H, β-

CHH), 2.63–2.56 (m, 1 H, β-CHH), 1.92 (d, J = 11.9 Hz, 1 H,

allyl), 1.4 (br. s, 2 H, NH

=

1

3

–1

₎_p_p_m_.1 C NMR (101 MHz, CD

3

x

4141.06(16) Å ; Z = 4; D = 1.251 g/cm *; μ = 0.50 mm *; * de-

2

Cl

)], 137.3 [Ar(C

)], 129.1 [Ar(CH)], 129.1 [Ar(CH)], 128.3 [Ar(CH)],

28.3 [Ar(CH)], 128.0 [Ar(CH)], 127.3 [Ar(CH)], 120.4 [Im-

Ph), 52.5 (α-CH),

) ppm. MS (FAB-TOF): m/z

Pd 496.1216; found 496.1221.

2

): δ

rived values do not contain the contribution of the disordered sol-

vent molecules. 74792 Reflections were measured with a Bruker

Kappa ApexII diffractometer with sealed tube and Triumph mono-

chromator (λ = 0.71073 Å) at a temperature of 150(2) K up to a

182.4 (NCN), 175.0 [CO(OMe)], 137.4 [Ar(C

q

)],

31.7 [Im-bb(C

q

bb(CH)], 115.2 (allyl), 71.9 (allyl), 55.1 (NCH

2.4 (OMe), 49.3 (allyl), 30.2 (β-CH

2

–

1

resolution of (sin θ/λ)max = 0.65 Å . Intensity integration was per-

formed with the software Eval15.^[Multiscan absorption correc-

tion and scaling was performed with SADABS^[(correction range

0.65–0.75). 19045 Reflections were unique (Rint = 0.026), of which

16710 were observed [IϾ2σ(I)]. The structure was solved by using

5

2

89]

+

28 2 3

calcd. for C24H O N

90]

Bis(4-{2-[(tert-butoxycarbonyl)amino]-3-methoxy-3-oxopropyl}-1-

mesityl-3-methyl-1H-imidazol(3H)-2-ylidene)allylpalladium(II)

[91]

Chloride (41): A solution of 30 (0.288 g, 0.46 mmol) in CH

2

Cl

5 mL) was added dropwise to a stirred solution of [Pd(allyl)Cl]

0.168 g, 0.46 mmol) in CH Cl

2

the program SHELXT. Least-squares refinement was performed

with SHELXL-2013^[against F of all reflections. Because of the

large shifts of the structure along the polar b-axis, the y-coordinate

of Pd1 was fixed in the refinement. All other non-hydrogen atoms

were refined freely with anisotropic displacement parameters. The

coordinated allyl groups, one of the noncoordinated nitrate ions,

and the cyclohexane molecule were refined with disordered models.

92]

2

(

2

(5 mL). The solution was stirred

for 1 h, then the mixture was filtered through a pad of Celite in air,

which was rinsed with additional CH Cl (5 mL). The volatiles

were removed in vacuo to give a yellow foamy solid. The compound

contained an excess of the Pd precursor. The crude product was

2

3

purified by column chromatography [CH

2

Cl

2

to CH

2

Cl

2

/MeOH

The crystal structure additionally contains voids (526 Å /unit cell),

(

95:5), to CH Cl /MeOH (9:1)]. The fractions containing the prod-

2

filled with disordered cyclohexane and THF solvent molecules.

Their contribution to the structure factors was secured by back-

uct were combined. The solution was concentrated on a rotavap

apparatus, and the remaining solvent was removed in vacuo to give

the product (0.162 g, 0.17 mmol, 36%) as a light-yellow foamy so-

lid. H NMR (400 MHz, CD

6

4

Fourier transformation using the SQUEEZE algorithm of

PLATON,^[

79]

resulting in 161 electrons/unit cell. All hydrogen

1

2

Cl

2

): δ = 7.16 (s, 2 H, Im-bb), 7.05–

atoms were introduced in calculated positions and refined with a

riding model. 1011 Parameters were refined with 292 restraints con-

.90 (m, 8 H, Ar), 6.35 (s, 2 H, NH), 5.34–5.20 (m, 1 H, allyl),

.55–4.36 (m, 2 H, α-CH), 3.96–3.86 (m, 10 H, allyl, OMe), 3.78 cerning the disordered moieties. R /wR [IϾ2σ(I)]: 0.0401/0.1029;

1 2

2

(s, 6 H, OMe), 3.24–2.94 (m, 10 H, β-CH , NMe), 2.71–2.50 (m, 2

R

1

/wR

2

[all refl.]: 0.0492/0.1085; S = 1.037. The absolute structure

Eur. J. Inorg. Chem. 0000, 0–0

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Job/Unit: I43104

/KAP1

Date: 28-01-15 15:33:33

Pages: 16

www.eurjic.org

FULL PAPER

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Received: November 19, 2014

Published Online: ᭿

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FULL PAPER

NHC Complexes

R. M. Drost, D. L. J. Broere,

J. Hoogenboom, S. N. de Baan, M. Lutz,

B. de Bruin, C. J. Elsevier* ............. 1–16

From an amino acid to versatile ligands

and catalysts. Synthetic routes to histidin-

ium salts and Ag and Pd histidylidenes

were developed. The Pd-histidylidenes were

subsequently investigated in the transfer

semihydrogenation of alkynes to Z-alkenes

I

II

Allylpalladium(II) Histidylidene Com-

plexes and Their Application in Z-Selective

Transfer Semihydrogenation of Alkynes

Keywords: Homogeneous catalysis / Palla-

dium / Carbenes / Hydrogenation / Re-

duction / Alkynes

Eur. J. Inorg. Chem. 0000, 0–0

16

Article Doi

Allylpalladium(II) histidylidene complexes and their application in Z-selective transfer semihydrogenation of alkynes

DOI: 10.1002/ejic.201403104

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Authors:

Article abstract of DOI:10.1002/ejic.201403104

Full text of DOI:10.1002/ejic.201403104

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