Diphosphine capsules for transition-metal encapsulation

FULL PAPERS

DOI: 10.1002/asia.201100092

Diphosphine Capsules for Transition-Metal Encapsulation

Tehila S. Koblenz,^[a]Henk L. Dekker,^[b]Chris G. de Koster,^[b]

Piet W. N. M. van Leeuwen,^[a]and Joost N. H. Reek*^[a]

Abstract: Self-assembly and characteri-

ed part of the capsule with the transi-

tion metal located inside the capsule

and is not involved in the assembly

process. We present two approaches

for capsule assembly by mixing solu-

tions of the precharged building blocks

in methanol and mixing solutions of

the neutral building blocks in metha-

nol. The scope of the diphosphine cap-

sules and the metallodiphosphine cap-

zation of novel heterodimeric diphos-

phine capsules formed by multiple

ionic interactions and composed of one

tetracationic diphosphine ligand and

one complementary tetraanionic cal-

ix[4]arene are described. Encapsulation

of a palladium atom within a diphos-

phine capsule is achieved successfully

by using the metal complex of the

tetracationic diphosphine ligand for the

assembly process. In this templated ap-

proach to metal encapsulation, the

transition-metal complex is an integrat-

sules is easily extended by applying

tetracationic diphosphine ligands with

different backbones (ethylene, diphenyl

ether, and xanthene) and cationic bind-

ing motifs (p-C₆H₄-CH₂-ammonium, m-

C₆H₄-ammonium, and m-C₆H₄-guanidi-

nium). These tetracationic building

blocks with different flexibilities and

shapes readily associate into capsules

with the proper capsular structure, as is

Keywords: calixarenes · ionic inter-

1

indicated by H NMR spectroscopy, 1D

actions

· palladium · phosphine

NOESY, ESI-MS, and modeling stud-

ies.

ligands · supramolecular chemistry

Introduction

hosts enable their utilization as nanosized reactor vessels

(nanoreactors), and so far their use has been explored for

the stabilization of reactive intermediates, for organic trans-

formations, and for catalysis.^{[1a,b,g–r,2h,3h]}

Supramolecular capsules are composed of two or more, not

necessarily identical, building blocks programmed to self-as-

semble in solution into the desired structure.^[1a–f]The build-

ing blocks of the capsule have a similar size, complementary

functional groups, and associate by means of multiple rever-

sible noncovalent interactions such as hydrogen bonds,

metal–ligand, and ionic interactions.^[2–4]A wide variety of

homo- and heterocapsules based on functionalized calixar-

enes, resorcinarenes (cavitands), and other building blocks

have been reported. The encapsulation properties of these

Reports of capsules based on ionic interactions are in a

minority compared to the hydrogen-bonded capsules. Tim-

merman, Crego-Calama, and co-workers reported ionic-

based capsules that consisted of one tetrasulfonated calix[4]-

arene and one tetracationic Zn^IIporphyrinate (Fig-

ure 1a).^[4b,c,g]Schrader and co-workers studied ionic-based

capsules composed of one tetraanionic calix[4]arene and

one tetracationic calix[4]arene (Figure 1b).^[4a,g]Verboom

and co-workers reported ionic-based capsules constituted of

two tetracationic cavitands and four monovalent anions

(Figure 1c).^[4e]In contrast to hydrogen-bonded capsules,

ionic-based capsules are generally stable in polar solvents,

do not require an external guest (but contain solvent) as a

template for capsule formation, and undergo an exchange

process fast on the NMR spectroscopic timescale between

the free and capsule-bound building blocks.

[a] Dr. T. S. Koblenz, Prof. Dr. P. W. N. M. v. Leeuwen,

Prof. Dr. J. N. H. Reek

Homogeneous and Supramolecular Catalysis

Van’t Hoff Institute for Molecular Sciences

University of Amsterdam

Postbox 94720, 1090 GS Amsterdam (The Netherlands)

Fax : (+31)020-5255604

E-mail: J.N.H.Reek@uva.nl

Many reactions of interest require well-defined transition-

metal complexes as a catalyst, and the activity and selectivi-

ty of these catalysts are determined to a large extent by the

ligand associated with the metal. So far only a few supra-

molecular complexes have been reported in which the cata-

[b] H. L. Dekker, Prof. Dr. C. G. d. Koster

Mass Spectrometry of Biomacromolecules

Swammerdam Institute for Life Sciences

University of Amsterdam

Postbox 94720, 1090 GS Amsterdam (The Netherlands)

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Chem. Asian J. 2011, 6, 2444 – 2462

Figure 1. Supramolecular capsules based on ionic interactions and com-

posed of a calix[4]arene and a) a Zn^IIporphyrinate, b) two calix[4]arenes,

and c) two cavitands and four anions.

lytic potential of an encapsulated transition metal has been

explored. Raymond, Bergman, and co-workers encapsulated

cationic iridium and rhodium complexes inside the chiral

tetrahedral coordination cage [M⁴L₆]^12Àthrough nondirec-

tional noncovalent bonds (Figure 2a). Encapsulation of the

catalyst resulted in substrate selectivity on the basis of size

Figure 2. Encapsulated transition-metal catalysts within a) a tetrahedral

coordination cage [M⁴L₆]^12Àand b) a hemispherical ligand-template cap-

sule.

and shape in the C H bond activation of aldehydes and the

the capsule and it is not involved in the assembly process.^[3-

À

isomerization of allylic alcohols.^[3j,6a,b]Reek and co-workers

introduced a templated approach for the encapsulation of li-

gands and their metal complexes, in which the template li-

gands have a bifunctional character in that they coordinate

to the active metal center and function as a template for the

capsule formation.^[5,6c–j]Pyridylphosphines are successful

template ligands as the nitrogen atoms of the pyridyl groups

selectively coordinate to Zn^II–porphyrins or Zn^II–salphens,

thereby resulting in a hemispherical ligand–template capsule

around the transition metal (Figure 2b). Such encapsulated

rhodium complexes were shown to have unusual reactivity

and selectivity in the hydroformylation of terminal and in-

ternal alkenes.

Hence, the encapsulated metal is still available for cata

j,6a–h]

lytic transformations. Transition-metal complexes that con-

tain diphosphine ligands represent an important class of

catalysts, and changes in ligand structure have important

We have previously communicated an ionic-based capsule

composed of a tetracationic xantphos-type diphosphine and

a tetraanionic calix[4]arene.^[5]Encapsulation of a palladium

atom within this capsule is achieved by using the metal com-

plex of the tetracationic diphosphine ligand for the assembly

process (Figure 3). In this templated approach to metal en-

capsulation, the transition-metal complex is an integrated

part of the capsule with the transition metal located inside

Figure 3. Encapsulation of a palladium species within an ionic-based cap-

sule composed of a Pd(diphosphine) complex and a calix[4]arene: molec-

ular and modeled structures.

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J. N. H. Reek et al.

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consequences for their application in catalysis.^[7]In that re-

spect, we were interested if the structure of the bidentate

ligand has a large influence on the formation of the capsule.

Here, we report diphosphine capsules based on a tetracat-

ionic diphosphine and a tetraanionic calix[4]arene. To show

the versatility of the diphosphine capsules, we used various

tetracationic diphosphines with different backbones (ethyl-

ene, diphenyl ether, and xanthene) and different binding

motifs (p-C₆H₄-CH₂-ammonium, m-C₆H₄-ammonium, and

m-C₆H₄-guanidinium). In addition, we report the formation

and characterization of the metallodiphosphine capsules

based on palladium complexes of the tetracationic diphos-

phines.

methyldiphenyl ether was carried out as reported by van

Leeuwen and co-workers.^[10]First, the bis-diethylamino

phosphane was prepared by lithiation of the 4,4’-dimethyldi-

phenyl ether backbone and a subsequent reaction with ClP-

AHCTUNTGRENGUN(N NEt₂)₂. Next, the bis-dichlorophosphine compound was

prepared by reaction with HCl. Reaction of the bis-dichloro-

phosphine with the lithiated product of p-bromobenzyldie-

thylamine gave the tetrakis(p-diethylbenzylamine)-DPE-

phos b in 60% yield (Scheme 1b). Tetrakis(p-diethylbenzyl-

amine)-xantphos c was previously reported by van Leeuwen

and co-workers and was used in the rhodium-catalyzed hy-

droformylation reaction in which the rhodium complex of

the amphiphilic ligand c was recycled by extraction into an

acidic aqueous phase.^[8a]We have developed an improved

synthetic route towards c, which involves only two steps in-

stead of five, with an overall yield of 50% (Scheme 1c). The

diphosphonite was prepared by lithiation of the xanthene

Results and Discussion

Capsules Based on Cationic Diphosphines: Backbone

Variation

backbone and a subsequent reaction with ClPACTHNUTRGNEUNG

(OEt)₂.^[8b–d]

Reaction of the diphosphonite with the lithiated product of

p-bromobenzyldiethylamine gave the tetrakis(p-diethylben-

zylamine) xantphos c.^[11]

Selective N-protonation of tetrakis(p-diethylbenzyl

amine)-diphosphines a, b, and c in diethyl ether resulted in

the corresponding tetrakis(p-diethylbenzylammonium)-di-

phosphine ligands A-HCl, B-HCl, and C-HCl (Scheme 2).^[5]

The electronic effect of the ammonium groups of A-HCl, B-

We set out to study capsules composed of tetracationic di-

phosphines and tetraanionic calix[4]arenes.^[5]The tetracat-

ionic diphosphines used here have different shapes and flex-

ibility properties as a result of their different backbones,

that is, ethylene (dppe), diphenyl ether (DPEphos), and

xanthene (xantphos).

Synthesis

The cationic charges on the di-

phosphine ligands were creat-

ed by functionalizing the four

phenyl groups on the phospho-

rus atoms. The tetrakis-ammo-

nium diphosphine ligands A,

B, and C were prepared from

the corresponding tetrakis-

amine precursors a, b, and c.

Tetrakis(p-diethylbenzyla-

mine)-dppe a, tetrakis(p-dieth-

ylbenzylamine)-DPEphos

b,

and tetrakis(p-diethylbenzyl

amine)-xantphos c were pre-

pared by the reaction of the

lithiated product of p-bromo-

benzyldiethylamine with

a

phosphorus electrophile, that

is, the corresponding bis-di-

chlorophosphines or diphos-

phonite (Scheme 1).^[8]Reac-

tion of the commercially avail-

able 1,2-bis(dichlorophosphi-

no)ethane with the lithiated

product of p-bromobenzyldie-

thylamine gave the tetrakis(p-

diethylbenzylamine)-dppe a in

60% yield (Scheme 1a).^[9]The

synthesis of the precursor 2,2’-

bis(dichlorophosphino)-4,4’-di-

Scheme 1. Synthesis of tetrakis(p-diethylbenzylamine)diphosphines of a) the dppe-type a, b) DPEphos-type b,

and c) and xantphos-type c.

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Diphosphine Capsules

NaCl salt. The second approach

involved mixing of the neutral

building blocks: for example,

tetraamine diphosphine a and

tetrasulfonic acid calix[4]arene

2-SO₃H to give capsule (A)·2

(Scheme 4b). Capsules (B)·2

and (C)·2 were prepared in a

similar fashion. Upon mixing

solutions of the neutral building

Scheme 2. Selective N-protonation of a, b, and c to give the tetrakis(p-diethylbenzylammonium)diphosphines

A-HCl, B-HCl, and C-HCl.

HCl, and C-HCl on the phosphorus atoms is negligible be-

cause of the presence of the benzylic methylene spacer.

Indeed, ³¹P{¹H} NMR spectroscopic data confirm that the

phosphines are barely affected by the electron-withdrawing

ammonium groups (see Scheme 2).^[8a,11]

The tetraanionic building block tetrasulfonatocalix[4]ar-

ene tetrasodium salt 2-SO₃Na was prepared according to a

literature procedure and was subsequently acidified to give

the tetrasulfonic acid calix[4]arene 2-SO₃H (Scheme 3).^[4b,12]

blocks in methanol, the tetrasulfonic acid calix[4]arene

quantitatively protonated the tetraamine diphosphines.^[4f,h]

The charged building blocks assemble into capsules (A)·2,

(B)·2, and (C)·2 without salt formation as a side product.

Capsules are more stable, that is, they have a higher associa-

tion constant, when no salt is present in solution.^[13]Still, in

both approaches the capsules are in equilibrium with their

charged and/or neutral building blocks. All diphosphine-

based capsules appeared to be soluble and stable in metha-

nol, as will be clear from the evidence presented in the next

section.

Scheme 3. Acidification of tetrasulfonatocalix[4]arene tetrasodium salt 2-

SO₃Na to give the tetrasulfonic acid calix[4]arene 2-SO₃H.

During the synthesis of the tetrasodium salt, we did not suc-

ceed in isolating the corresponding tetraacid prior to neu-

tralization. Fortunately, exchange of the sodium cations of

2-SO₃Na with protons was easily achieved with the strongly

acidic Amberlyst 15 ion-exchange resin to give 2-SO₃H. All

new compounds described here have been characterized by

NMR spectroscopy and mass spectrometry (see the Experi-

mental Section).

Self-Assembly

The heterodimeric diphosphine capsules A·2, B·2, and C·2

consist of the tetracationic diphosphines A, B, and C, and

the complementary tetraanionic calix[4]arene 2. Self-assem-

bly of these ionic-based capsules was achieved simply by

mixing solutions of the corresponding building blocks in

methanol. Capsule formation was evidenced by NMR spec-

troscopy and mass spectrometry. We have developed two

approaches for capsule assembly. The first approach involves

mixing of the precharged building blocks: for example, tet-

raammonium diphosphine A-HCl and tetrasulfonatocalix[4]-

Scheme 4. Self-assembly of capsules A·2, B·2, and C·2 by the use of

a) precharged and b) neutral building blocks.

Characterization

The evidence for the formation of the diphosphine-based

capsules A·2 and B·2, composed of dppe- and DPEphos-

type ligands A and B, is similar to that obtained for capsule

C·2 based on the xantphos-type ligand C, which was previ-

ously reported.^[5]As can be seen in Figure 4 and Table 1, the

¹H NMR spectra of capsules A·2, B·2, and C·2 in CD₃OD

show sharp resonances and large upfield shifts for the dieth-

arene tetrasodium salt 2-SO₃Na to give capsule

ACHTUNGTRENN(UNG A-HCl)·2

(Scheme 4a). Capsules (B-HCl)·2 and (C-HCl)·2 were pre-

A

ACHTUNGTRENNUNG

pared in a similar fashion. All the capsules were instantane-

ously formed upon mixing methanol solutions of the build-

ing blocks and contain four equivalents of the corresponding

⁺A

ylammoniummethyl substituents, CH₂NH CTHNUGTREN(NUG CH₂CH₃)₂with

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J. N. H. Reek et al.

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phine ligands and the tetrasulfonatocalix[4]arene fit well to

form stable capsules at low concentrations. The titration

curve fitted to a 1:1 binding model, which is in line with the

1:1 stoichiometry of the capsules. As can be seen in

Figure 4, a single set of proton resonances for the free and

associated building blocks was observed for capsules self-as-

sembled from charged or neutral building blocks. This indi-

cates a fast exchange process on the NMR spectroscopic

timescale between the building blocks that are in the mono-

meric form (free) and those in the capsular form (bound).

Consequently, the lower symmetry of the capsules compared

to the calix[4]arene 2 (C_4v) and possible changes in ligand

conformation upon capsule formation are not apparent in

Figure 4. ¹H NMR spectra in CD₃OD at 208C. Top: A-HCl (dppe);

middle: capsule ACHTUNGTRENNUNG(A-HCl)·2 (A/2=2:3, [A]=2 mm); bottom: 2-SO₃Na.

Asterisks indicate solvent signals.

1

the H NMR spectra.^[4b]

The 1D NOESY spectra of the heterodimeric capsules

A·2 and B·2 in CD₃OD display

significant negative intermolec-

ular NOE contacts between the

⁺A

Table 1. Upfield shifts (Dd) for the CH₂NH CTHNUGTRNE(NGU CH₂CH₃)₂protons of the diphosphine capsules with respect to

the corresponding free diphosphines A-HCl, B-HCl, and C-HCl; the association constants (K) and the Gibbs

free energy of the corresponding diphosphine capsules (DG).

⁺A

NH CTHNUGTENR(UNG CH₂CH₃)₂protons of the

(CH₂CH₃)^[a,b][ppm] Dd

(CH₂N)^[a,b][ppm] K^[a][m^À1

]

DG^[c][kJmol^À1

]

diphosphines A and B and the

aromatic protons of 2 upon se-

lective saturation of the methyl

protons of A and B (Figure 6).

This illustrates that the aryl

Capsule

Dd

dppe:

ACHTUNGTRENNUNG

0.46

0.42

0.43

0.31

0.32

0.33

0.15

0.20

0.25

3ꢁ10⁴

8ꢁ10⁴

6ꢁ10⁴

25.5

28.0

27.3

ACHTUNGTRENNUNG

substituents of the diphosphines

ACHTUNGTRENNUNG

and the upper rim of the cal-

ix[4]arene are facing one anoth-

er to form the typical dimeric

[a] Measured in CD₃OD at 298 K. [b] ACTHNUTRGNEU(GN A-C)/2=1:3, capsules assembled from the pre-charged building blocks.

[c] Gibbs free energy calculated according to DG=ÀRTlnK.

1:1 capsular structure. The neg-

respect to those of the corresponding free diphosphines A,

B, and C. The chemical shifts of the other protons are less

affected (Dd<0.20 ppm). The upfield shifts point to partial

inclusion of the diethylammoniummethyl substituents inside

the hydrophobic cavity of the capsules.^[4c,5]

ative NOE enhancements observed for the capsules confirm

their large size.^[14]Additional evidence for capsule formation

and their stabilities in the gas phase was obtained by elec-

trospray ionization mass spectrometry (ESI-MS).^[15]The

ESI-MS spectra of capsules A·2 and B·2 in CH₃OH show

prominent ion peaks of the capsules at m/z 908.95 for

[A·2+2Na]²⁺and at m/z 981.99 for [B·2+H+Na]²⁺

(Figure 7). All the ion peaks of the capsule correspond to

1:1 complexes and no ion peaks for higher aggregates were

detected. The assignment of the ion peaks of the capsule is

¹H NMR spectroscopic titrations were carried out in

CD₃OD (298 K) and provided stability constants of K_A·2

=

3ꢁ10⁴m^À1, K_B·2=8ꢁ10⁴m^À1, and K_C·2=6ꢁ10⁴m^À1for capsu-

les ACHTUNGTRENNUNG(A-HCl)·2, ACHTUNGTRENNUNG(B-HCl)·2, and CAHTNUGTREN(GUNN C-HCl)·2, respectively

(Table 1 and Figure 5).^[5]The high association constants

found for the diphosphine capsules confirm that the diphos-

Figure 5. The ¹H NMR spectroscopic titration data fitted with a 1:1 bind-

ing model for B-HCl (DPEphos) with 2-SO₃Na in CD₃OD at 298 K.

Data points represent the absolute upfield shifts (Dd_B) of CH₂NH⁺

A

Figure 6. 1D NOESY spectrum of capsule A·2 in CD₃OD (inset: spec-

~

&

*

(

) CH₂CH₃, ( ) CH₂CH₃, and ( ) CH₂N.

trum enlargement).

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Diphosphine Capsules

À

that only rotation around the two P C_xanthenebonds is possi-

ble. The diphenyl ether backbone of the DPEphos-type di-

phosphine B has a size similar to that of the xanthene back-

bone of C, but it is flexible because it can rotate around its

À

ether functionality and P C_backbonebonds (Scheme 5b). The

ethylene backbone of the dppe-type diphosphine A results

in a slightly smaller diphosphine compared to B and C and

is flexible because it can rotate around three bonds

(Scheme 5a). The diphosphines A and B are less preorgan-

ized for capsule formation compared to C because they

have no concave structure and their four cationic benzylic

groups are pointing in different directions. Nevertheless, the

modeled structure of capsules A·2 and B·2 show that the di-

phosphines and the calix[4]arene are complementary and

that the capsules have a defined and proper capsular struc-

ture (Scheme 5). The high association constants of capsules

Figure 7. ESI-MS spectrum of capsule

sured isotope pattern).

ACHTUNGRTENUN(NG B-HCl)·2 in CH₃OH (inset: mea-

(A-HCl)·2 and

(B-HCl)·2 (K_A·2=3ꢁ10⁴m^À1, DG_A·2

ACHTUNGTERNNUNG =

25.5 kJmol^À1and K_B·2=8ꢁ10⁴m^À1, DG_B·2=28.0 kJmol^À1) re-

flect their stability. The flexibility of A and B allows them to

adopt the optimal conformation needed to form a stable

capsule. The expected larger entropy loss for A and B rela-

tive to C does not lead to a major difference in DG.

The rigid and concave calix[4]arene 2 fixes the flexible di-

phosphines A and B into the proper conformation needed

to form a stable capsule. During this fixation, the diphos-

phine is frozen in its rotation around a few bonds. Hence,

only one of the two building blocks needs to be rigid to

form a stable capsule with a defined and proper capsular

structure.^[16b,c]The fine-tuning needed to reach a proper cap-

sular structure is achieved for all the diphosphine capsules

by introducing flexibilities at the periphery of the ligand,

in agreement with the ESI-MS/MS collision-induced dissoci-

ation experiments, upon which the isolated ion peak of the

capsule (partly) disappeared and product ion peaks ap-

peared that correspond to the capsule building blocks.

These MS/MS experiments reveal the gas-phase stability of

the capsule.

Structure

Successful formation of stable supramolecular capsules with

proper capsular structures requires their building blocks to

be preorganized, that is, thoroughly programmed for the

self-assembly process. In general, the building blocks should

have comparable sizes, complimentary shapes, and function-

al groups, and contain the proper balance between flexibili-

ty/rigidity.^[4a,h,16a,b]Self-assembly of the heterodimeric capsu-

les A·2, B·2, and C·2 is primarily driven by the formation of

multiple intermolecular ionic interactions between the cat-

ionic diphosphine and the anionic calix[4]arene. The three

diphosphines contain the same p-diethylbenzylammonium

groups but have different backbones: ethylene A, diphenyl

ether B, and xanthene C. The molecular size of the diphos-

phines is quite similar to that of concave rigid calix[4]arene

2. On the other hand, their shape and conformational rigidi-

ty varies, which allows us to have a closer look at the influ-

ence of the preorganization properties of the building

blocks on the structure and stability of the capsule. The

xantphos-type diphosphine C has a rigid xanthene back-

À

that is, rotation of the P Ar and Ar CH₂bonds. The mod-

eled structures of A and A·2 show that in both the free and

bound state the phosphines are in trans conformation, with

a C₂symmetry of A (Scheme 5a). We have also noticed that

the free electron pairs on the phosphorus atoms of A·2 are

pointing away from the capsule, whereas the free electron

pairs on the phosphorus atoms of B·2 and C·2 are pointing

toward the capsule interior. Clearly, to form a metallodi-

phosphine capsule, diphosphine capsule A·2 will have to un-

dergo another conformational change.

Capsules Based on Cationic Diphosphines: Binding Motif

Variation

À

bone, two parallel P C_xanthenebonds, and four cationic ben-

The tetracationic diphosphines studied so far contain a CH₂-

ammonium group at the para position of the phosphorus

aryl groups. In this section we describe tetracationic xant-

phos-type diphosphines with ammonium and guanidinium

groups attached directly to the meta position of the phos-

phorus aryl groups.

zylic groups that are pointing in the same direction, that is,

below the ligand plane, as can be seen in the modeled struc-

ture (PM3 level) of C (Scheme 5c). Consequently, C has a

defined concave structure and is preorganized for capsule

formation. The modeled structure of capsule C·2 shows that

the two building blocks are complementary and that the

Synthesis

capsule has

a defined and proper capsular structure

(Scheme 5c). The high association constant of capsule

(C-

The tetrakis(m-aniline)-xantphos ligand d was prepared by

the reaction of the commercially available Grignard reagent

3-[bis(trimethylsilyl)amino]phenylmagnesium chloride with

2,7-di-tert-butyl-4,5-bis(dichlorophosphino)-9,9-dimethylxan-

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Scheme 5. Self-assembly of diphosphine capsules a) A·2, b) B·2, and c) C·2: modeled and molecular structures.

thene, synthesized from the corresponding bis(diethylami-

no)phosphonitoxanthene, in 25% yield (Scheme 6a).^[17]This

reaction requires the use of a dichlorophosphine as the

phosphorus electrophile because a diphosphonite is not suf-

ficiently electrophilic to react with the Grignard reagent,

which in turn is less nucleophilic than the organolithium

compounds. To our surprise, the N-protecting trimethylsilyl

groups were removed during the workup procedure, which

involved an excess amount of diethylamine, hence no meth-

anolysis step was required.^[9a]In a subsequent step, the tet-

rakis(m-aniline)-xantphos d ligand was selectively N-proton-

ated by HCl in diethyl ether to yield the corresponding tet-

rakis(m-anilinium)-xantphos D-HCl in a quantitative yield

(Scheme 6b).

Stelzer and co-workers previously reported the synthesis

of 4,5-bisACTHNUTRGENUG[N bis(m-N,N-dimethylguanidiniumphenyl)phosphi-

À

no]-9,9-dimethylxanthene by palladium-catalyzed P C cou-

pling of m-iodophenylguanidine with the corresponding

highly toxic, diprimary phosphine.^[18]We prepared tetrak-

is(m-N,N-dimethylguanidiniumphenyl)-xantphos E-HCl in

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Chem. Asian J. 2011, 6, 2444 – 2462

Diphosphine Capsules

in [D₆]DMSO. The upfield

shifts point to partial inclusion

of the guanidinium moiety

inside the hydrophobic cavity

of the capsule. A single set of

proton resonances for the free

and bound building blocks was

observed for capsules D·2 and

E·2. This indicates a fast ex-

change process on the NMR

spectroscopic timescale be-

tween the building blocks that

are in the monomeric form

(free) and those that are part of

the capsule (bound). The ESI-

MS spectra of capsules D·2 and

E·2 in CH₃OH show prominent

ion peaks of the capsules at, for

example, m/z 914.98

for

[D·2+2Na]²⁺and at m/z 711.07

for [E·2+3Na]³⁺(Figure 8).

These results support capsule

formation and demonstrate

their stability in the gas phase.

Capsule

stability

against

bases and acids is important for

their further applications in cat-

alysis, and therefore a few pre-

liminary NMR spectroscopic

experiments were performed.

The addition of cesium carbon-

ate (20 equiv) to a methanol so-

lution of capsule C·2 resulted in

the precipitation of the calix[4]-

arene 2 and deprotonation of

the ammonium-based diphos-

Scheme 6. Synthesis of a) tetrakis(m-aniline)-xantphos d as well as b) tetrakis(m-anilinium)-xantphos D-HCl

and tetrakis(m-guanidiniumphenyl)-xantphos E-HCl.

89% yield by treating tetrakis(m-anilinium)-xantphos

D-HCl with an excess amount of dimethylcyanamide

(Scheme 6b). The electronic effect of the cationic groups of

D-HCl and E-HCl on the phosphorus atoms is negligible as

is suggested by their similar ³¹P NMR spectroscopic chemi-

cal shifts (see Scheme 6b).

phine C. We assume that the cesium cation is encapsulated

within the calix[4]arene.^[19]A similar experiment using cap-

sule E·2 also resulted in the precipitation of 2, but the guani-

Self-Assembly and Characterization

Self-assembly of capsules D·2 and E·2 was achieved by

mixing methanol or dimethyl sulfoxide (DMSO) solutions

of the corresponding precharged building blocks. The

¹H NMR spectra of the xantphos-anilinium-based capsule

D·2 in CD₃OD and [D₆]DMSO show sharp resonances. In

contrast to, for example, capsule C·2, no significant upfield

shifts are observed upon capsule formation (Ddꢀ0.07 ppm)

because no side chains are present in D that change their

environment by filling the capsule. The xantphos-guanidini-

um-based capsule E·2 shows sharp resonances and signifi-

cant upfield shifts for the guanidinium substituents, with re-

spect to those of the corresponding free diphosphine E:

Figure 8. ESI-MS spectrum of capsule

sured isotope pattern).

ACHTUNGRTENUN(NG E-HCl)·2 in CH₃OH (inset: mea-

Dd(NACHTUNGTRENNUNG(CH₃)₂)=0.51 ppm in CD₃OD and Dd(NH)=0.55 ppm

Chem. Asian J. 2011, 6, 2444 – 2462

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2451

J. N. H. Reek et al.

FULL PAPERS

dinium-based diphosphine E remained protonated. This is in

line with the strong basicity of guanidine. Upon addition of

p-toluenesulfonic acid (20 equiv) to capsule E·2 no precipi-

tation appeared, but judging from the NMR spectra we con-

t.^{[4a,h,16a,b,20]}Unlike the diethylammonium-xantphos ligand C,

the xantphos-anilinium ligand D lacks alkyl substituents on

the ammonium groups and still forms a capsule. Hence, the

presence of side chains is not a prerequisite for capsule for-

mation.

clude that the presence of an acid slightly destabilizes the

+

ionic capsule: Dd(N

(CH₃)₂

)

decreased from 0.51 to

The planar Y-shaped guanidinium group, [NHCACTHNGUTERNNUG

(NH₂)₂]⁺,

0.42 ppm.

is known for its ability to form directed hydrogen bonds as

well as nondirected ionic interactions, that is, ionic-hydrogen

bonds, with, for example, complementary oxoanions such as

Structure

The four positive charges of the xantphos-anilinium ligand

D are located directly at the meta position of the phospho-

rus aryl groups. The modeled structure (PM3 level) of cap-

sule D·2 shows a highly symmetrical capsular structure with

the four aryl groups situated perpendicular to the capsule

equator (Figure 9a). In addition, the ammonium groups are

pointing down; each one is situated between two sulfonato

groups of the calix[4]arene and interacts with both sulfonato

groups. According to molecular modeling studies, moving

the ammonium groups from the meta to the para position is

less favorable because the corresponding capsule enforces a

twist in the phosphorus aryl groups. Introducing a methylene

spacer between the aryl ring and the cationic group does

result in stable capsules, as was shown for capsule C·2.

Hence, a careful design of the building blocks is importan-

carboxylates.^[4c,21a]The four [NHC (NMe₂)]⁺guanidini-

ACTHNGUTERN(NUG NH₂)ACHTUNGTRENNUNG

um groups of the xantphos-guanidinium ligand E are located

directly on the meta position of the phosphorus aryl groups.

The modeled structure of capsule E·2 shows that each guani-

dinium group is located between two sulfonato groups of

the calix[4]arene and interacts with both sulfonato groups

(Figure 9b).^[2c,21b,c]As a result of the large size of the guani-

dinium groups, capsule E·2 is less symmetrical than capsule

D·2.

Encapsulation of a Palladium Species

Encapsulation of a transition metal within capsules A·2 and

B·2 was achieved by using palladium dichloride complexes

that contain tetracationic ligands, cis-[PdCl₂(A)] (1A) and

cis-[PdCl₂(B)] (1B).

Synthesis

Palladium dichloride complexes cis-[PdCl₂(a)] (1a) and cis-

[PdCl₂(b)] (1b), which contain the tetraamine diphosphine

ligands a (dppe) and b (DPEphos), were prepared in a

straightforward manner by the reaction of the metal precur-

sor [PdCl₂ACTHNUTRGNEUG(N cod)] (cod=1,5-cyclooctadiene) with the corre-

sponding tetraamine diphosphine in dichloromethane

(Scheme 7).^[10,22]The two palladium complexes were stable

in common organic solvents such as chloroform and acetoni-

trile, but 1b was unstable in methanol and decomposed rap-

idly—as is also evident from a color change from yellow to

deep brown-purple. Phosphorus NMR spectroscopy displays

at least four multiplets at d=À8.0, 15.7, 20.1, and 29.7 ppm.

The deep brown-purple color suggests that Pd^Iclusters are

formed, probably due to the basic amine groups of the

ligand and methanol.^[23]Pd^IIand base in methanol will gen-

erate palladium methoxy species, which give palladium hy-

drides through b-hydrogen elimination. The latter with base

gives Pd⁰, which dimerizes with Pd^IIto give strongly colored

dimers (or trimers).

The positive charges on the tetraamine diphosphine li-

gands of 1a and 1b are created by N-quaternization by pro-

tonation or methylation. Selective N-protonation of 1a and

1b was achieved by a reaction with p-toluenesulfonic acid

(PTSA) to give 1ACTHNUGRTENNUG(A-HOTs) and 1ACHTUNTGREN(NUNG B-HOTs), respectively

(Scheme 8a). N-Methylation is preferred over N-protona-

tion because an acidic proton is more labile than an alky-

lammonium group, and also oxidative addition of HX to the

metal can take place. Selective N-methylation of 1a and 1b

was achieved by a reaction with methyl triflate to yield the

Figure 9. Modeled and molecular structures of diphosphine capsules

a) D·2 and b) E·2. The NH hydrogen atoms are visible.

tetracationic-diphosphine

palladium

complexes

1ACHTUNGTRENNUNG(A-

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Diphosphine Capsules

mixing solutions of the neutral

building blocks [(tetraamine di-

phosphine)PdCl₂] complex (1a

or 1b) in methanol or dichlo

romethane and tetrasulfonic

acid

calix[4]arene

2-SO₃H

(Scheme 9b). After protonation

of the tetraamine diphosphine

by the acidic calix[4]arene, the

now charged building blocks

self-assembled into capsules

1(A)·2 or 1(B)·2, respectively,

without salt formation. The

salt-free palladium capsules

1(A)·2 and 1(B)·2 hardly dis-

solved in methanol, unlike the

palladium capsules assembled

from the precharged building

blocks. Addition of 5–10%

Scheme 7. Synthesis of [(tetraamine diphosphine)PdCl₂] complexes a) 1a and b) 1b.

AHCTUNGTRENGN(UN v/v) of the cosolvents dichloro-

methane or water did result in

better solubility of the capsules.

The four equivalents of salt and

the NMe⁺groups of capsules

1

(A-MeOTf)·2

and

1ACHTUNGTRENNUNG(B-

MeOTf)·2 probably facilitate

capsule solubility in methanol

relative to the salt-free capsules

Scheme 8. Selective N-quaternization of the [(tetraamine diphosphine)PdCl₂] complexes 1a and 1b by a) tol- 1(A)·2 and 1(B)·2.

uenesulfonic acid and b) methyl triflate to give the [(tetraammonium diphosphine)PdCl₂] complexes 1A and

Characterization

1B.

The ¹H NMR spectra of the

palladium–diphosphine capsules

MeOTf) and 1

G

1A·2 and 1B·2 show upfield shifts for the diethylammo-

niummethyl substituents, CH₂N

respect to those of the corresponding free palladium com-

estingly, after protection of the amines of 1b by N-quaterni-

⁺A

ACHTUTGNERN(NGU H/CH₃) HCTUNGTRNE(NUGN CH₂CH₃)₂, with

zation, the palladium complexes

MeOTf) were stable in metha-

nol, in contrast to their neutral

(i.e., basic) analogue 1b.

Self-Assembly

Self-assembly of the metallodi-

phosphine capsules was ob-

served upon mixing solutions of

the precharged building blocks

in methanol: [(tetraammonium

diphosphine)PdCl₂]

for example, 1(A-MeOTf), and

tetrasulfonatocalix[4]arene tet-

rasodium salt 2-SO₃Na

(Scheme 9a). The palladium

capsules (A-MeOTf)·2 and

(B-MeOTf)·2 were formed in-

complex,

ACHTUNGTRENNUNG

1ACHTUNGTRENNUNG

stantaneously and contain four

equivalents of the correspond-

ing NaOTf salt. Capsule forma-

Scheme 9. Self-assembly of palladium–diphosphine capsules 1A·2 and 1B·2 by the use of a) precharged and

tion was also accomplished by b) neutral building blocks (schematic picture).

Chem. Asian J. 2011, 6, 2444 – 2462

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2453

J. N. H. Reek et al.

FULL PAPERS

plexes 1A or 1B, respectively: Dd

Dd(CH₂CH₃)₂=0.16–0.23, Dd(CH₂N)=0.06–0.12, and Dd-

(NCH₃)=0.07–0.13 ppm (Figures 10 and 11). The upfield

(CH₂CH₃)₂=0.33–0.37,

A single set of proton resonances for the free and bound

building blocks was observed in the temperature window 0–

608C for all the ionic-based palladium capsules. Variable-

temperature ¹H NMR spectra of the palladium capsules

show line broadening at 208C, in particular for the palladi-

um building blocks, and sharper resonances at higher tem-

peratures (40 and 608C; Figure 10).^[16b]The observed line

broadening indicates that the phosphorus substituents of the

rigid palladium complex are not equivalent anymore upon

capsule formation because they experience different envi-

ronments. At higher temperatures, the exchange process be-

tween the free and bound building blocks and the bond-ro-

tation rates are faster, thereby resulting in sharper NMR

spectra. The phosphorus chemical shifts of 1A and 1B in

their capsular form 1A·2 and 1B·2 did not exhibit a note-

worthy shift compared to the monomeric form (Ddꢀ

0.8 ppm), thus indicating that the cis geometry around the

phosphorus atoms did not change.^[24]Additional support for

the formation of the palladium capsules 1A·2 and 1B·2

comes from Jobꢂs plot analysis of titration experiments car-

ried out in CD₃OD at 608C (at 208C, the proton signals

were too broad to be accurately determined). The observed

maximum at a mole fraction of 0.5 proves the 1:1 stoichiom-

E

ACHTUNGTRENNUNG

shifts point to partial inclusion of the diethylammonium-

Figure 10. ¹H NMR spectra of palladium capsule 1(A)·2 self-assembled

from neutral building blocks: a) 1ACHTNUGRTENUNG(A-HOTs) in CD₃OD at 208C; b) cap-

sule 1(A)·2 in CD₃OD/D₂O (90:10 v/v) at 208C, [1A]=[2]=2 mm;

c) capsule 1(A)·2 at 408C; and d) 2-SO₃Na in CD₃OD at 208C. Asterisks

indicate solvent signals.

etry between 1

ACHUTNGTRENG(NU A-MeOTf) and 2-SO₃Na, and between 1ACHTUNGTRENNUNG(B-

MeOTf) and 2-SO₃Na (Figure 12).

Figure 11. ¹H NMR spectra of palladium capsule 1

sembled from precharged building blocks in CD₃OD: a) 1

208C; b) capsule 1(B-MeOTf)·2 at 608C, [1B]=2 mm, [2]=4 mm; and

(B-MeOTf)·2 self-as-

(B-MeOTf) at

Figure 12. Job plot for 1

ACHTUNGTRENNUN(G A-MeOTf) with calix 2-SO₃Na (Y=(Dd_1A)ꢁ

(mol fraction 1A)) in CD₃OD at 608C. Data points represent the abso-

AHCTUNGTRENNUNG

⁺A

lute upfield shifts (Dd_1A) of CH₂NH CTHUNGTRNE(NUG CH₂CH₃)₂protons of 1A·2 relative

ACHTUNGTRENNUNG

~

&

to the chemical shifts of free 1A: ( ) CH₂CH₃, ( ) CH₂CH₃.

c) 2-SO₃Na at 208C. Asterisks indicate solvent signals.

methyl substituents inside the hydrophobic cavity of the cap-

sule. The observed upfield shifts of the palladium capsules

1A·2 and 1B·2 are smaller than those of the diphosphine

capsules A·2 and B·2 and of the previously reported palladi-

Just like the guanidinium-based capsule E·2, NMR spec-

troscopic studies show that addition of cesium carbonate

(20 equiv) to a solution of the palladium capsule 1

MeOTf)·2 in methanol results in precipitation of calix[4]ar-

ene 2, whereas the N-methylated palladium complex 1(A-

MeOTf) remains intact. Upon addition of p-toluenesulfonic

acid (20 equiv) to 1(A-MeOTf)·2 no precipitation appears,

ACHTUNGTRENNUNG(A-

um

capsule

[Pd

N

(Dd-

A

Dd

E

N

ACHTUNGTRENNUNG

0.17 ppm).^[5]Even though the size of Dd depends on the

exact nature of the metal complex, our observations indicate

that the conformational rigid cis-PdCl₂complexes 1A and

1B experience less side-chain encapsulation and fit less well

onto calix[4]arene than the corresponding free ligands. In

addition, because the capsule is also occupied by the palladi-

um dichloride species, less space is available to accommo-

date side chains.

AHCTUNGTRENNUNG

but, judging from the NMR spectroscopic studies, the pres-

ence of an acid destabilizes the ionic-based capsule: Dd of

+

N

(CH₂CH₃)₂decreased from 0.35 to 0.09 ppm at 608C.

The ESI-MS spectra confirm the formation of the palladi-

um capsules 1A·2 and 1B·2. Prominent doubly and triply

charged ion peaks are observed for the capsules in CH₃OH

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Chem. Asian J. 2011, 6, 2444 – 2462

Diphosphine Capsules

at m/z 957.30 for [1(A)·2ÀCl+H]²⁺, at m/z 652.60 for [1

G

thereby indicating that the palladium capsules do not encap-

sulate counterions. The absence of the counterions also indi-

cates that the palladium complexes prefer to associate with

one calix[4]arene rather than with one to three triflate coun-

terions.^[13]

MeOTf)·2-2Cl+Na]³⁺, at m/z 1023.37 for [1(B)·2À2Cl]²⁺

and at m/z 701.28 for [1ACHTUGNTRENNNUG

ures 13 and 14). The charge on the capsules is created by

the loss of one or two chloride ligands from the palladium

complex and/or by addition of protons or sodium cations

from the solution. All the ion peaks of the capsule corre-

spond to 1:1 complexes, and no ion peaks for higher aggre-

gates were detected. Comparison of the measured isotope

patterns of the capsules with the calculated ones confirms

the elemental composition and charge state. The palladium

dichloride complexes contain a tetracationic diphosphine

and four triflate counterions. Interestingly, the ESI-MS spec-

tra of the palladium complexes show that one to three out

of their four triflate counterions remain attached to the am-

monium groups during the ionization process. Examples are

Structure

After characterizing the metallodiphosphine capsules 1A·2

and 1B·2, we studied their capsular structures by molecular

modeling (PM3 level). The modeled structures of the d⁸pal-

ladium complexes 1A and 1B, which contain the dppe- and

DPEphos-type ligands, show that they both adopt a square-

planar geometry with the diphosphine ligand chelated in a

cis fashion (Scheme 10). The four aryl groups of 1A point in

a slightly more uniform direction than the aryl groups of

1B, that is, they are better preorganized for capsule forma-

ion peaks at m/z 694.21 for [1

at m/z 778.22 for [1

(B-MeOTf)ÀClÀOTf]²⁺. None of the

ion peaks of the palladium capsules contains counterions,

N

tion. The reported X-ray structures of related [Pd

ACHTUNGTRENNUNG(dppe)]

A

and [Pd(DPEphos)] complexes illustrate that the relative

ACHTUNGTRENNUNG

spatial arrangement of the four aryl groups and the diphenyl

ether backbone can vary to some extent.^{[10a,17b,22,25a,b]}The re-

semblance between the modeled structure and the related

X-ray structures is better for 1A than for 1B. The palladium

complexes 1A and 1B might be rigid compared to their cor-

responding free ligands, but they can still rotate around

À

some bonds, that is, around the Pd P, P Ar, and Ar CH₂

bonds, and around the diphenyl ether backbone (Figure 15).

Figure 15. Possible bond rotations in the Pd complexes 1A and 1B.

Figure 13. ESI-MS spectrum of a palladium capsule 1ACTHUNRTGNEUNG(A-MeOTf)·2 self-

assembled of precharged building blocks (insets: measured isotope pat-

terns).

In this way, they can adopt the proper conformation needed

for capsule self-assembly. We assume that the transition-

metal complexes will adopt higher-energy conformations

only if the energy gain achieved upon capsule formation will

compensate the energy loss. The modeled structures of the

palladium capsules 1A·2 and 1B·2 illustrate that the capsu-

les have a proper capsular structure with the two chloride li-

gands pointing into the interior of the capsule. Noteworthy,

À

the calculated bite angles (P Pd P) of 1A and 1B are com-

parable to the literature values and do not change signifi-

cantly upon capsule formation (Table 2).

Conclusion

We have demonstrated that the scope of capsules based on

functionalized diphosphine ligands or metal complexes

thereof can easily be extended. These capsules are formed

by ionic interactions and are composed of a tetracationic di-

phosphine ligand and a complementary tetraanionic calix[4]-

arene. Encapsulation of a transition metal within the capsu-

Figure 14. ESI-MS spectrum of a palladium capsule 1(B)·2 self-assembled

of neutral building blocks (insets: measured isotope patterns).

Chem. Asian J. 2011, 6, 2444 – 2462

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2455

J. N. H. Reek et al.

FULL PAPERS

Scheme 10. Self-assembly of metallodiphosphine capsules a) 1A·2 and b) 1B·2: modeled and molecular structures.

wise. Solvents were dried and distilled under nitrogen prior to use. Dieth-

yl ether, THF, hexanes, and pentane were distilled from sodium/benzo-

phenone. N,N,N’,N’-Tetramethylethylenediamine (TMEDA) was distilled

from sodium. Dichloromethane, methanol, and acetonitrile were distilled

from CaH₂. Deuterated solvents were distilled from the appropriate

drying agents. Unless stated otherwise, all chemicals were obtained from

commercial suppliers and used as received. Bis(N,N-diethylamino)chloro-

phosphine,^[26](4-bromobenzyl)diethylamine,^[11]and 5,11,17,23-tetrakis(sul-

À

Table 2. Bite angles (P Pd P) for the Pd complexes 1A and 1B, the Pd

capsules 1A·2 and 1B·2, and related Pd complexes.

À

P Pd P

1A

1A·2

[Pd

868 (calcd)

1B

1B·2

1078 (calcd)

1118 (calcd)

(dppe)Cl₂]^[25a]868 (X-ray)

[PdACTHUNGETRNNUG

(DPEphos)Cl₂]^[25c]1018 (X-ray)

E

858 (70–958) [PdCAHTUNGTRENNUNG

fonato)-25,26,27,28-tetrakis(2-ethoxyethoxy)calix[4]arene

tetrasodium

salt 2-SO₃Na^[4b]were synthesized according to reported procedures.

NMR spectra were recorded with Varian Inova 500, Bruker Avance

DRX 300, and Varian Mercury 300 NMR spectrometers. Chemical shifts

are given relative to TMS (¹H and ¹³C NMR spectroscopy), 85% H₃PO₄

(³¹P NMR spectroscopy), and Cl₃CF (¹⁹F NMR spectroscopy). Chemical

shifts are given in ppm. 1D NOESY measurements (1D transient NOE)

(flexibility range)

(calcd)

(flexibility range)

ACHTUNGTRENNUNG

les is achieved successfully by self-assembly of a transition-

metal complex that contains a tetracationic ligand and a tet-

raanionic calix[4]arene. Diphosphine ligands with different

flexibilities and shapes (i.e., different backbones and cation-

ic binding motifs) assembled into (metallo)capsules with the

were carried out with

a double-pulsed field-gradient spin echo

(DPFGSE) excitation. Elemental analyses were performed at the H.

Kolbe Mikroanalytisches laboratory in Mꢃlheim (Germany). High-reso-

lution fast atom bombardment mass spectrometry (HRMS FAB) meas-

urements were carried out with a JEOL JMS SX/SX 102A at the Depart-

ment of Mass Spectrometry at the University of Amsterdam. Electro-

spray ionization mass spectrometry (ESI-MS) measurements were carried

out with a Q-TOF (Micromass, Waters, Whyttenshawe, UK) mass spec-

trometer equipped with a Z-spray orthogonal nanoelectrospray source,

using Econo Tips (New Objective, Woburn, MA) to create an offline

nanospray, at the Department of Mass Spectrometry of Biomacromole-

cules at the University of Amsterdam. Molecular modeling calculations

1

proper capsular structure, as is indicated by H NMR spec-

troscopy, 1D NOESY, ESI-MS, and modeling studies. This

approach to metal encapsulation opens up new opportuni-

ties to control the activity, stability, and selectivity of the po-

tential homogeneous catalysts.

were performed with Spartan 04V1.0.3 software on the semiempirical

Experimental Section

À

PM3 level. Abbreviations used: Me-p-C₆H₄SO₃^À=OTs^À, CF₃SO₃

=

OTf^À, and cod=1,5-cyclooctadiene. The [PdCl₂(b)] and [PdCl₂(B)] com-

plexes that contain the DPEphos-type ligand give broad carbon resonan-

ces in their ¹³C NMR spectra and therefore could not be characterized by

carbon NMR spectroscopy.

General Remarks

All reactions were carried out under a dry, inert atmosphere of purified

nitrogen or argon using standard Schlenk techniques unless stated other-

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Chem. Asian J. 2011, 6, 2444 – 2462

Diphosphine Capsules

1,2-Bis

(bis{p-[(diethylamino)methyl]phenyl}phosphino)ethane (a)

ing pink reaction mixture was stirred for another 30 min at À458C. After

cooling the resulting pale orange reaction mixture to À658C, a solution

of 2,2’-bis(dichlorophosphino)-4,4’-dimethyldiphenyl ether (2.28 g,

5.69 mmol) in THF (20 mL) was added in 30 min. The resulting green re-

action mixture was allowed to warm to room temperature overnight. The

orange reaction mixture was hydrolyzed with degassed water (3 mL), and

the solvent was removed in vacuo. Subsequently, the yellow viscous oil

was dissolved in diethyl ether and washed with degassed water. The or-

ganic layer was separated, and the aqueous layer was extracted with di-

ethyl ether. The combined organic layers were dried with MgSO₄, and

the solvent was removed in vacuo. The resulting yellow viscous oil was

purified by column chromatography (silica gel, 97–45% hexanes, 0–50%

EtOAc, 3–5% NEt₃). Product b was obtained as a white solid (3.12 g,

3.43 mmol, 60%). ¹H NMR (300 MHz, CDCl₃, 293 K): d=7.19 (d, J=

7.6 Hz, 8H; PC₆H₄), 7.18–7.07 (m, 8H; PC₆H₄), 6.87 (d, J=8.1 Hz, 2H;

OC₆H₃), 6.56 (brs, 2H; OC₆H₃), 6.44–6.40 (m, 2H; OC₆H₃), 3.51 (s, 8H;

CH₂N), 2.47 (q, J=6.9 Hz, 16H; CH₂CH₃), 2.09 (s, 6H; CH₃), 0.99 ppm

(t, J=7.2 Hz, 24H; CH₂CH₃); ¹³C{¹H} NMR (76 MHz, CDCl₃, 293 K):

d=157.8 (brs; Cq, C_Ar), 140.5 (s; Cq, C_Ar), 135.5 (s; Cq, C_Ar), 134.6 (s;

Cq, C_Ar), 134.3 (s; CH, OC₆H₃), 134.0 (s; CH, PC₆H₄), 132.8 (s; Cq, C_Ar),

131.0 (s; CH, OC₆H₃), 129.2 (s; CH, PC₆H₄), 118.1 (s; CH, OC₆H₃), 57.7

(s; CH₂N), 47.1 (s; CH₂CH₃), 21.2 (s; CH₃), 12.2 ppm (s; CH₂CH₃);

³¹P{¹H} NMR (121.5 MHz, CDCl₃, 293 K): d=À16.4 (s); HRMS (FAB+

): m/z calcd for [C₅₈H₇₆ON₄P₂+H]⁺: 907.5573; found: 907.5588; elemental

analysis calcd (%) for C₅₈H₇₆N₄OP₂: C 76.79, H 8.44, N 6.18; found: C

76.67, H 8.40, N 6.11.

n-Butyllithium (2.5m in hexanes, 15.09 mL, 37.72 mmol) was added to

THF (100 mL) at 08C, and the solution was further cooled to À658C. A

yellow solution of (4-bromobenzyl)diethylamine (9.14 g, 37.72 mmol) in

THF (40 mL) was added to the n-butyllithium solution in 1 h. The result-

ing pink reaction mixture was stirred for another 30 min at À458C. After

cooling the resulting yellow reaction mixture to À658C, a solution of 1,2-

bis(dichlorophosphino)ethane (1.99 g, 8.57 mmol) in THF (30 mL) was

added in 30 min. The resulting green reaction mixture was allowed to

warm to room temperature overnight. The yellow reaction mixture was

hydrolyzed with degassed water (3 mL), and the solvent was removed in

vacuo. Subsequently, the yellow viscous oil was dissolved in diethyl ether

and washed with degassed water. The organic layer was separated, and

the aqueous layer was extracted with diethyl ether. The combined organ-

ic layers were dried with MgSO₄, and the solvent was removed in vacuo.

The resulting yellow viscous oil was purified by column chromatography

(silica gel, 95–65% petroleum ether (PE) 40/60, 0–30% EtOAc, 5%

NEt₃). Product a was obtained as a white solid (3.80 g, 5.14 mmol, 60%).

¹H NMR (300 MHz, CDCl₃, 293 K): d=7.25 (s, 16H; PC₆H₄), 3.52 (s,

8H; CH₂N), 2.48 (q, J=7.0 Hz, 16H; CH₂CH₃), 2.02 (t, J=3.8 Hz, 4H;

CH₂CH₂), 1.01 ppm (t, J=7.1 Hz, 24H; CH₂CH₃); ¹³C{¹H} NMR

(76 MHz, CDCl₃, 293 K): d=141.1 (s; Cq, PC₆H₄), 136.6 (s; Cq, PC₆H₄),

133.0 (s; CH, PC₆H₄), 129.3 (s; CH, PC₆H₄), 57.6 (s; CH₂N), 47.1 (s;

CH₂CH₃), 24.4 (s; CH₂CH₂), 12.1 ppm (s; CH₂CH₃); ³¹P{¹H} NMR

(121.5 MHz, CDCl₃, 293 K): d=À12.7 ppm (s); HRMS (FAB+): m/z

calcd for [C₄₆H₆₈N₄P₂+H]⁺: 739.4998; found: 739.4990.

4,5-Bis(diethoxyphosphonito)-9,9-dimethylxanthene^[12]

2,2’-[Bis(bis-diethylamino)phosphonito]-4,4’-dimethyldiphenyl ether^[10]

A yellow solution of 9,9-dimethylxanthene (10.17 g, 48.36 mmol) and

TMEDA (21.89 mL, 145.08 mmol) in diethyl ether (120 mL) was cooled

to 08C. Next, n-butyllithium (2.5m in hexanes, 46.43 mL, 116.06 mmol)

was added dropwise, and the reaction mixture was stirred overnight. The

resulting dark red solution was cooled to À788C, and a solution of dieth-

yl chlorophosphite (18.07 mL, 125.74 mmol) in diethyl ether (120 mL)

was added dropwise. The reaction mixture was allowed to warm to room

temperature and was stirred overnight. The solvent was evaporated in

vacuo to give a yellow oil. The salts were extracted by adding dichloro-

methane (100 mL) and degassed water (100 mL) to the crude product.

After vigorous stirring, the organic layer was washed twice with degassed

water and dried over MgSO₄. Evaporation of the solvent resulted in 4,5-

A solution of p-tolyl ether (5.10 g, 25.72 mmol) and TMEDA (8.54 mL

56.59 mmol) in hexanes (20 mL) was stirred and cooled to À458C, there-

by giving a white suspension. Subsequently n-butyllithium (2.5m in hex-

anes, 22.64 mL, 56.59 mmol) was added dropwise and the reaction mix-

ture was allowed to warm to room temperature overnight, which resulted

in a yellow suspension. The dilithio salt was isolated from excess amounts

of n-butyllithium by leaving the salt to precipitate at À208C for 7 h and

subsequently removing the orange supernatant liquid with a syringe (this

step is not necessary). Subsequently, a solution of bis(diethylamino)chlor-

ophosphine (11.38 g, 54.01 mmol) in hexanes/diethyl ether (40 mL, 1:1)

was stirred and cooled to À788C. The off-white dilithio salt was dissolved

in diethyl ether (40 mL) and was slowly added to the solution of ClP-

bis(diethoxyphosphino)-9,9-dimethylxanthene as

(21.13 g, 46.91 mmol, 97%). H NMR (300 MHz, CDCl₃, 293 K): d=7.60

(d, J=7.4 Hz, 2H; H₃), 7.43 (d, J=7.6 Hz, 2H; H₁), 7.11 (t, J=7.4 Hz,

a yellow sticky oil

ACHTUNGTRENNUNG(NEt₂)₂with a Teflon cannula. The reaction mixture was allowed to

1

warm to room temperature overnight. The salts were filtered off from

the yellow solution and washed twice with diethyl ether. Evaporation of

the solvents in vacuo yielded 2,2’-[bis(bis-diethylamino)phosphonito]-4,4’-

2H; H₂), 3.94 (dm, 8H; OCH₂CH₃), 1.59 (s, 6H; CACHTUNTRGNEUNG(CH₃)₂), 1.25 ppm (t,

J=7.1 Hz, 12H; OCH₂CH₃); ¹³C{¹H} NMR (76 MHz, CDCl₃, 293 K): d=

152.4 (brt; C^4a), 130.1 (s; Cq, C_Ar), 129.1 (s; CH, C_Ar), 128.7 (s; Cq, C_Ar),

128.2 (s; CH, C_Ar), 123.4 (s; CH, C_Ar), 63.3 (s; CH₂CH₃), 34.4 (s; C-

dimethyldiphenyl ether as

a

yellow oil. ³¹P{¹H} NMR (121.5 MHz,

293 K): d=93.53 ppm (s).

A

CACTHNGUTERNNUG

(CH₃)₂), 17.7 ppm (s; CH₂CH₃); ³¹P{¹H} NMR

2,2’-Bis(dichlorophosphino)-4,4’-dimethyldiphenyl ether^[10]

A

solution of 2,2’-[bis(bis-diethylamino)phosphonito]-4,4’-dimethyldi-

4,5-Bis(bis{p-[(diethylamino)methyl]phenyl}phosphino)-9,9-

ACHTUNGTRENNUNG

phenyl ether in hexanes (600 mL) was stirred and cooled down to

À788C. HCl gas was bubbled into the reaction mixture over 1.5 h, which

resulted immediately in large amounts of white precipitation. Subse-

quently, the reaction mixture was allowed to warm to room temperature.

The salts were filtered off and washed with diethyl ether (100 mL). Evap-

oration of the solvents resulted in a white powder. Crystallization from

hexanes (35 mL) at À208C yielded 2,2’-bis(dichlorophosphino)-4,4’-dime-

thyldiphenyl ether as an off-white powder (52%, 5.34 g, 13.35 mmol).

¹H NMR (500 MHz, CDCl₃, 293 K): d=7.85 (brs, 2H; H_Ar), 7.30 (dd, J=

1.5 Hz, J=8.5 Hz, 2H; H_Ar), 6.81 (dt, J=3.0 Hz, J=8.5 Hz, 2H; H_Ar),

2.44 ppm (s, 6H; CH₃); ³¹P{¹H} NMR (202 MHz, CDCl₃, 293 K): d=

159.12 ppm (s).

dimethylxanthene (c)

n-Butyllithium (2.5m in hexanes, 12.88 mL, 32.20 mmol) was added to

THF (100 mL) at 08C, and the solution was further cooled to À658C. A

yellow solution of (4-bromobenzyl)diethylamine (7.80 g, 32.20 mmol) in

THF (35 mL) was added to the n-butyllithium solution in 1 h. The result-

ing pink reaction mixture was stirred for another 30 min at À458C. After

cooling the resulting orange reaction mixture to À658C, a solution of 4,5-

bis(diethoxyphosphino)-9,9-dimethylxanthene (2.90 g, 6.44 mmol) in THF

(25 mL) was added in 30 min. The resulting green reaction mixture was

allowed to warm to room temperature overnight. The pale orange reac-

tion mixture was hydrolyzed with degassed water (3 mL), and the solvent

was removed in vacuo. Subsequently, the yellow viscous oil was dissolved

in diethyl ether and washed with degassed water. The organic layer was

separated, and the aqueous layer was extracted with diethyl ether. The

combined organic layers were dried with MgSO₄, and the solvent was re-

moved in vacuo. The resulting dark-orange viscous oil was purified by

column chromatography (silica gel, 97–67% hexanes, 0–30% EtOAc,

2,2’-BisACHTUNGTRENNUNG(bis{p-[(diethylamino)methyl]phenyl}phosphino)-4,4’-

dimethyldiphenyl ether (b)

n-Butyllithium (2.5m in hexanes, 11.39 mL, 24.47 mmol) was added to

THF (75 mL) at 08C, and the solution was further cooled to À658C. A

yellow solution of (4-bromobenzyl)diethylamine (6.89 g, 28.47 mmol) in

THF (30 mL) was added to the n-butyllithium solution in 1 h. The result-

3% NEt₃). The product

c was obtained as a white solid (3.02 g,

Chem. Asian J. 2011, 6, 2444 – 2462

ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org

2457

J. N. H. Reek et al.

FULL PAPERS

3.25 mmol, 51%). ¹H NMR (300 MHz, CDCl₃, 293 K): d=7.34 (d, J=

7.8 Hz, 2H; H₃), 7.17 (d, J=7.8 Hz, 8H; PC₆H₄), 7.16–7.08 (m, 8H;

PC₆H₄), 6.90 (t, J=7.6 Hz, 2H; H₂), 6.52 (d, J=7.6 Hz, 2H; H₁), 3.51 (s,

methylxanthene (16.50 g, 34.35 mmol) in THF (250 mL) at À708C. After

stirring the pink suspension for 2 h at À708C, a solution of bis(diethyla-

mino)chlorophosphine (14.48 mL, 68.71 mmol) in THF (40 mL) was

added dropwise at À708C. The reaction mixture was allowed to warm to

room temperature overnight, which resulted in a clear yellow solution.

The solvents were removed in vacuo, and the residue was dissolved in

hexanes (80 mL). The precipitated salts were removed from the solution

by filtration. Evaporation of the solvents in vacuo yielded 2,7-di-tert-

8H; CH₂N), 2.49 (q, J=7.1 Hz, 16H; CH₂CH₃), 1.61 (s, 6H; CACTHNUTRGNEUNG(CH₃)₂),

1.01 ppm (t, J=7.1 Hz, 24H; CH₂CH₃); ¹³C{¹H} NMR (76 MHz, CDCl₃,

293 K): d=152.6 (brt; C^4a), 140.3 (s; Cq, C_Ar), 136.1 (s; Cq, C_Ar), 134.3

(s; CH, PC₆H₄), 132.4 (s; C₁), 130.1 (s; Cq, C_Ar), 129.1 (s; CH, PC₆H₄),

126.6 (s; C₃), 123.5 (s; C₂), 57.7 (s; CH₂N), 47.1 (s; CH₂CH₃), 34.8 (s; C-

A

C

A

butyl-4,5-bisACHTUNRGTNEG[NU bis(diethylamino)phosphonito]-9,9-dimethylxanthene as a

(122 MHz, CDCl₃, 293 K): d=À18.3 ppm (s); HRMS (FAB+): m/z

calcd for [C₅₉H₇₆ON₄P₂Cl₄+H]⁺: 919.5573; found: 919.5574; elemental

analysis calcd (%) for C₅₉H₇₆N₄OP₂: C 77.09, H 8.33, N 6.10; found: C

76.88, H 8.39, N 5.96.

yellow powder (22.87 g, 34.09 mmol, 99%). ¹H NMR (300 MHz, CDCl₃,

293 K): d=7.33 (brs, 2H; PC₆H₂), 7.26 (brs, 2H; PC₆H₂), 3.15–2.93 (m,

16H; CH₂CH₃), 1.57 (s, 6H; CACTHNUGTRENN(UG CH₃)₂), 1.31 (s, 18H; CAHCTUNGTREN(NUGN CH₃)₃), 0.99 ppm

(t, J=6.9 Hz, 24H; CH₂CH₃); ¹³C{¹H} NMR (75 MHz, CDCl₃, 293 K):

d=149.0 (brs; Cq, C_Ar), 144.1 (s; Cq, C_Ar), 129.4 (s; Cq, C_Ar), 128.8 (s;

Cq, C_Ar), 127.4 (s; CH, C_Ar), 122.6 (s; CH, C_Ar), 43.4 (brs; NCH₂CH₃),

1,2-BisACHTUNGTRENNUNG(bis{p-[(diethylammonium

chloride)methyl]phenyl}phosphino)ethane (A-HCl)

34.9 (s; CCATHGNUTRENU(NNG CH₃)₃), 34.7 (s; CACHTUNGTREN(GUN CH₃)₂), 33.4 (s; CACHTNUREGTGNN(UN CH₃)₃), 32.0 (s; CACHTUNGTRENNUNG(CH₃)₂),

14.9 ppm (s; NCH₂CH₃); ³¹P{¹H} NMR (121.5 MHz, CDCl₃, 293 K): d=

A 2m solution of HCl in diethyl ether (0.50 mL, 1.00 mmol) was added

dropwise to a solution of a (85 mg, 114 mmol) in diethyl ether (10 mL),

upon which a white precipitation appeared. After stirring for 30 min, the

volatiles were removed in vacuo and A-HCl was obtained as a white

powder in quantitative yield. ¹H NMR (300 MHz, CD₃OD, 293 K): d=

7.64 (d, J=7.9 Hz, 8H; PC₆H₄), 7.46 (m, 8H; PC₆H₄), 4.40 (s, 8H;

CH₂N), 3.31–3.15 (m, 16H; CH₂CH₃), 2.18 (t, J=4.3 Hz, 4H; CH₂CH₂),

1.38 ppm (t, J=7.3 Hz, 24H; CH₂CH₃); ¹³C{¹H} NMR (75 MHz, CD₃OD,

293 K): d=139.5 (brs; Cq, PC₆H₄), 133.2 (t, J=9.3 Hz; CH, PC₆H₄),

131.1 (t, J=3.3 Hz; CH, PC₆H₄), 130.7 (s; Cq, PC₆H₄), 55.3 (s; CH₂N),

46.7 (s; CH₂CH₃), 46.6 (s; CH₂CH₃), 23.0 (brs; CH₂CH₂), 7.7 ppm (s;

CH₂CH₃); ³¹P{¹H} NMR (121.5 MHz, CD₃OD, 293 K): d=À12.7 ppm (s);

HRMS (FAB+): m/z calcd for [C₄₆H₇₂N₄P₂Cl₄À2HÀ3Cl]⁺: 775.4764;

found: 775.4777.

93.1 ppm (s).

2,7-Di-tert-butyl-4,5-bis(dichlorophosphino)-9,9-dimethylxanthene^[17b]

A solution of distilled phosphorus trichloride (29.97 mL, 343.5 mmol) in

diethyl ether (100 mL) was added to a solution of 2,7-di-tert-butyl-4,5-bis-

[bis(diethylamino)phosphonito]-9,9-dimethylxanthene

(22.87 g,

34.09 mmol, 99%) in diethyl ether (200 mL) at 08C. The reaction mixture

was allowed to warm to room temperature overnight. Next, the reaction

mixture was heated at reflux (508C) for 20 h. After cooling to room tem-

perature, the solvents were evaporated in vacuo, and the product was

crystallized from hexanes (120 mL) at À208C. After the solvents were re-

moved and the product was dried in vacuo, 2,7-di-tert-butyl-4,5-bis(di-

chlorophosphino)-9,9-dimethylxanthene was obtained as an off-white

powder (12.70 g, 24.23 mmol, 70%). ¹H NMR (300 MHz, CDCl₃, 293 K):

2,2’-BisACHTUNGTRENNUNG(bis{p-[(diethylammonium chloride)methyl]phenyl}phosphino)-

4,4’-dimethyldiphenyl ether (B-HCl)

d=7.90 (brs, 2H; PC₆H₂), 7.58 (brs, 2H; PC₆H₂), 1.66 (s, 6H; C

1.36 ppm (s, 18H; C

(CH₃)₃); ¹³C{¹H} NMR (75 MHz, CDCl₃, 293 K): d=

149.0 (t, J=13.5; Cq, C_Ar), 147.7 (s; Cq, C_Ar), 129.9 (s; Cq, C_Ar), 128.1 (s;

CH, C_Ar), 127.2 (s; Cq, C_Ar), 126.5 (s; CH, C_Ar), 35.6 (s; C(CH₃)₃), 35.0

(s; C(CH₃)₂), 32.8 (s; C(CH₃)₃), 31.9 ppm (s; C

(CH₃)₂); ³¹P{¹H} NMR

(121.5 MHz, CDCl₃, 293 K): d=161.6 ppm (s).

ACHTUNGTRENNUNG(CH₃)₂),

AHCTUNGTRENNUNG

This compound was prepared similarly to A-HCl, starting from b.

¹H NMR (300 MHz, CD₃OD, 293 K): d=7.62 (d, J=7.3 Hz, 8H; PC₆H₄),

7.37–7.22 (m, 8H; PC₆H₄), 7.11 (d, J=7.9 Hz, 2H; OC₆H₃), 6.66 (d, J=

4.3 Hz, 2H; OC₆H₃), 6.56–6.50 (m, 2H; OC₆H₃), 4.41 (s, 8H; CH₂N),

3.31–3.12 (m, 16H; CH₂CH₃), 2.16 (s, 6H; CH₃), 1.37 ppm (brt, 24H;

CH₂CH₃); ¹³C{¹H} NMR (75 MHz, CD₃OD, 293 K): d=156.9 (brs; Cq,

C_Ar), 138.5 (brs; Cq, C_Ar), 134.4 (s; CH, C_Ar), 134.1 (s; CH, C_Ar), 133.1 (s;

Cq, C_Ar), 131.4 (s; Cq, C_Ar), 130.9 (brs; CH, C_Ar), 130.4 (s; CH, C_Ar),

AHCTUNGTRENNUNG

G

ACHTUNGTRENNUNG

2,7-Di-tert-butyl-4,5-bisACTHUNRTGNEUNG[bis(3-aminophenyl)phosphino]-9,9-

dimethylxanthene (d)

The solution of 2,7-di-tert-butyl-4,5-bis(dichlorophosphino)-9,9-dimethyl-

xanthene (3.95 g, 7.57 mmol) in THF (60 mL) was added slowly to 1.0m

THF solution of 3-[N,N-bis(trimethylsilyl)amino]phenylmagnesium chlo-

ride (37.83 mL, 37.83 mmol) at À258C. The resulting yellow reaction mix-

ture was allowed to warm to room temperature overnight. The reaction

mixture was hydrolyzed with degassed water (5 mL), and the solvent was

removed in vacuo. Next, to receive the crude product as a powder, it was

dissolved in dichloromethane, and the solvent was removed in vacuo.

Subsequently, the product was extracted and N-deprotected by solid–

liquid extraction with diethylamine (4ꢁ, 250 mL, 30 min, filtration over a

glass filter (Por 4)). The product d was purified by column chromatogra-

phy (basic alumina, dichloromethane/methanol, 95:5 then 80:20). The

product was obtained as an orange powder (1.40 g, 1.86 mmol, 25%).

¹H NMR (300 MHz, CDCl₃, 293 K): d=7.31 (brs, 2H; PC₆H₂), 6.97 (t,

J=7.3 Hz, 4H; PC₆H₄), 6.66 (brs, 2H; PC₆H₂), 6.64–6.49 (m, 12H;

126.6 (brs; Cq,

C_Ar), 117.7 (s; CH, C_Ar), 55.4 (s; CH₂N), 46.7 (s;

CH₂CH₃), 46.6 (s; CH₂CH₃), 19.4 (s; CH₃), 7.7 ppm (brs; CH₂CH₃);

³¹P{¹H} NMR (121.5 MHz, CD₃OD, 293 K): d=À15.3 ppm (s); HRMS

(FAB+): m/z calcd for [C₅₈H₈₀ON₄P₂Cl₄À2HÀ3Cl]⁺: 943.5339; found:

943.5336.

4,5-BisACHTUNGTRENNUNG(bis{p-[(diethylammonium chloride)methyl]phenyl}phosphino)-9,9-

dimethylxanthene (C-HCl)

This compound was prepared similarly to A-HCl, starting from c.

¹H NMR (500 MHz, CD₃OD, 293 K): d=7.59 (d, J=8.1 Hz, 10H; H₃

+

PC₆H₄), 7.33–7.30 (m, 8H; PC₆H₄), 7.03 (t, J=7.7 Hz, 2H; H₂), 6.48 (d,

J=7.6 Hz, 2H; H₁), 4.40 (s, 8H; CH₂N), 3.29–3.19 (m, 16H; CH₂CH₃),

1.68 (s, 6H; CCH₃), 1.38 ppm (dt, J=3.0 and 7.5 Hz, 24H; CH₂CH₃);

¹H NMR (500 MHz, CDCl₃, 293 K): d=12.12 ppm (s, 4H; NH⁺);

¹³C{¹H} NMR (126 MHz, CD₃OD, 293 K): d=153.2 (t, J=9.6 Hz; CO),

140.6 (t, J=7.2 Hz), 136.0 (t, J=10.9 Hz), 132.8 (s; C₁), 132.4 (t; J=

3.2 Hz), 131.9 (s), 131.6 (s), 129.0 (s), 125.4 (t, J=8.9 Hz), 125.2 (s; C₂),

57.0 (s; CH₂N), 48.3 (s; CH₂CH₃), 48.2 (s; CH₂CH₃), 35.7 (s; CCH₃), 32.7

(s; CCH₃), 9.3 (s; CH₂CH₃), 9.2 ppm (s; CH₂CH₃); ³¹P{¹H} NMR

(202 MHz, CD₃OD, 293 K): d=À16.8 ppm (s); ³¹P{¹H} NMR (202 MHz,

[D₆]DMSO, 293 K): d=À17.8 ppm (s); HRMS (FAB+): m/z calcd for

[C₅₉H₈₀ON₄P₂Cl₄À4ClÀ3H]⁺: 919.5573; found: 919.5573.

PC₆H₄), 3.52 (brs, 8H; NH₂), 1.62 (s, 6H; C

AHCTUNGTRENNUNG

ACHTUGNTRENUN(GN CH₃)₂), 1.10 ppm (s, 18H; C-

(CH₃)₃); ¹³C{¹H} NMR (75 MHz, CDCl₃, 293 K): d=151.2 (brt; Cq, C_Ar),

146.3 (t, J=4.1 Hz; Cq, C_Ar), 145.4 (s; Cq, C_Ar), 139.3 (t, J=6.2 Hz; Cq,

C_Ar), 130.0 (s; CH, PC₆H₂), 129.9 (s; Cq, C_Ar), 129.2 (s; Cq, C_Ar), 129.0 (s;

CH, PC₆H₄), 124.7 (t, J=8.8 Hz; CH, PC₆H₄), 123.2 (s; CH, PC₆H₂),

121.2 (t, J=11.0 Hz; CH, PC₆H₄), 115.5 (s, CH; PC₆H₄), 35.2 (s; C-

AHCNUTETGRGNN(UN CH₃)₂), 34.9 (s; CACHTUNGTRNEG(UN CH₃)₃), 32.5 (s; CAHCTNUGERTGN(NNU CH₃)₂), 31.8 ppm (s; CACHTUNGTRENNUNG(CH₃)₃);

³¹P{¹H} NMR (121.5 MHz, CDCl₃, 293 K): d=À15.1 ppm (s); HRMS

(FAB+): m/z calcd for [C₄₇H₅₂ON₄P₂+H]⁺: 751.3695; found: 751.3678.

2,7-Di-tert-butyl-4,5-bis

dimethylxanthene^[17b]

ACHTUNGTRENNUNG[bis(diethylamino)phosphonito]-9,9-

A solution of n-butyllithium (2.5m in hexanes, 27.48 mL, 68.71 mmol)

was added dropwise to a solution of 2,7-di-tert-butyl-4,5-dibromo-9,9-di-

2458

www.chemasianj.org

ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Asian J. 2011, 6, 2444 – 2462

Diphosphine Capsules

2,7-Di-tert-butyl-4,5-bis

9,9-dimethylxanthene (D-HCl)

{bis[(3-ammonium chloride)phenyl]phosphino}-

mixture was stirred for 1 h at room temperature. Next, the solvent was

evaporated, and pentane was added to the solid precipitate. After evapo-

ration of the solvent in vacuo, the product 1ACTHNUTRGNE(UNG A-HOTs) was obtained as a

A 2m solution of HCl in diethyl ether (3.20 mL, 6.40 mmol) was added

dropwise to a solution of d (600.7 mg, 800.0 mmol) in dichloromethane

(20 mL), upon which a fine pink precipitation appeared. After stirring

for 30 min, the volatiles were removed in vacuo, and D-HCl was obtained

as a pink powder in quantitative yield. ¹H NMR (300 MHz, CD₃OD,

293 K): d=7.60–7.47 (m, 6H; PC₆H₂+PC₆H₄), 7.41 (d, J=7.4 Hz, 4H;

PC₆H₄), 7.31 (brt, J=7.3 Hz, 4H; PC₆H₄), 7.24 (s, 4H; PC₆H₄), 6.38 (s,

yellow powder in quantitative yield. ¹H NMR (300 MHz, CD₃OD,

293 K): d=8.06–7.93 (m, 8H; PC₆H₄), 7.69 (d, J=6.8 Hz, 8H; PC₆H₄),

7.64 (d, J=7.9 Hz, 8H; OTs^À), 7.21 (d, J=7.9 Hz, 8H; OTs^À), 4.38 (s,

8H; CH₂N), 3.29–3.05 (m, 16H; CH₂CH₃), 2.89–2.72 (m, 4H; CH₂CH₂),

2.32 (s, 12H; CH₃, OTs^À), 1.29 ppm (t, J=6.9 Hz, 24H; CH₂CH₃);

¹³C{¹H} NMR (75 MHz, CD₃OD, 293 K): d=142.2 (s; OTs^À), 140.6 (s;

OTs^À), 134.4 (brs), 131.6 (brs), 129.8 (s), 129.1 (s), 128.7 (s; OTs^À), 125.6

(s; OTs^À), 55.1 (s; CH₂N), 46.9 (s; CH₂CH₃), 28.0 (brs; CH₂CH₂), 20.1 (s;

CH₃, OTs^À), 7.7 ppm (s; CH₂CH₃); ³¹P{¹H} NMR (121.5 MHz, CD₃OD,

293 K): d=68.3 ppm (s); HRMS (FAB+): m/z calcd for

[C₇₄H₁₀₀Cl₂N₄O₁₂P₂PdS₄ÀC₂₈H₃₂S₄O₁₂Cl]⁺: 879.3656; found: 879.3665;

ESI-MS: (m/z, CH₃OH) calcd for [C₇₄H₁₀₀Cl₂N₄O₁₂P₂PdS₄ÀC₁₄H₁₄S₂O₆]²⁺

: 630.20; found: 630.21.

2H; PC₆H₂), 1.68 (s, 6H;

CACHTUGNTRENNU(G CH₃)₂), 1.08 ppm (s, 18H; CACHTNUGTREN(NUNG CH₃)₃);

¹³C{¹H} NMR (75 MHz, CD₃OD, 293 K): d=146.4, 139.3, 134.5, 134.3,

131.1, 130.1, 129.3, 128.3, 127.7, 127.2, 124.8, 123.6, 34.5, 34.1, 31.7,

30.3 ppm; ³¹P{¹H} NMR (121.5 MHz, CD₃OD, 293 K): d=À13.7 ppm (s);

HRMS (FAB+): m/z calcd for [C₄₇H₅₆Cl₄N₄OP₂À3HÀ4Cl]⁺: 751.3695;

found: 751.3687.

2,7-Di-tert-butyl-4,5-bisACHTUNGTRENNUNG{bis[(3-N,N-dimethylguanidinium

chloride)phenyl]phosphino}-9,9-dimethylxanthene (E-HCl)

cis-[PdCl₂ACTHNUGTRENNUG(B-HOTs)] (1ACHTUNGTNER(NUGN B-HOTs))

p-Toluenesulfonic acid monohydrate (18.0 mg, 94.4 mmol) was added to a

solution of 1b (25.6 mg, 23.6 mmol) in dichloromethane (3 mL). The reac-

tion mixture was stirred for 2 h at room temperature. Next, the solvent

was evaporated, and pentane was added to the solid precipitate. After

An orange suspension of D-HCl (300 mg, 269 mmol) in degassed dime-

thylcyanamide (48.9 mL, 6.00 mmol) was heated at 1108C for 24 h. Subse-

quently, the clear brown solution was cooled to room temperature, upon

which a fine brown precipitation appeared. After washing the precipita-

tion with diethyl ether (4ꢁ10 mL), the product E-HCl was obtained as

an orange powder (314 mg, 267 mmol, 89%). ¹H NMR (300 MHz,

CD₃OD, 293 K): d=7.56 (d, J=2.1 Hz, 2H; PC₆H₂), 7.47 (t, J=7.8 Hz,

4H; PC₆H₄), 7.30 (d, J=6.6 Hz, 4H; PC₆H₄), 7.20 (brt, 4H; PC₆H₄), 7.12

(brs, 4H; PC₆H₄), 6.60 (q, J=2.4 Hz, 2H; PC₆H₂), 3.07 (s, 24H; N-

evaporation of the solvent in vacuo, the product 1ACHTUNTRGNEU(GN B-HOTs) was ob-

tained as an orange powder in quantitative yield. ¹H NMR (300 MHz,

CD₃OD, 293 K): d=7.66 (d, J=8.3 Hz, 8H; OTs^À), 7.60 (m, 16H;

PC₆H₄), 7.30 (d, J=8.3 Hz, 2H; OC₆H₃), 7.20 (d, J=7.9 Hz, 8H; OTs^À),

6.95 (m, 2H; OC₆H₃), 6.50 (d, J=10.0 Hz, 2H; OC₆H₃), 4.36 (dd, J=

13.3 Hz and 18.8 Hz, 8H; CH₂N), 3.31–3.03 (m, 16H; CH₂CH₃), 2.32 (s,

12H; CH₃, OTs^À), 2.05 (s, 6H; CH₃), 1.28 ppm (t, J=7.3 Hz, 24H;

CH₂CH₃); ³¹P{¹H} NMR (121.5 MHz, CD₃OD, 293 K): d=20.3 ppm (s);

HRMS (FAB+): m/z calcd for [C₈₆H₁₀₈Cl₂N₄O₁₃P₂PdS₄ÀC₂₈H₃₂S₄O₁₂Cl]⁺:

1047.4235; found: 1047.4226; ESI-MS: (m/z, CH₃OH) calcd for

[C₈₆H₁₀₈Cl₂N₄O₁₃P₂PdS₄ÀC₁₄H₁₄S₂O₆Cl]³⁺: 464.49; found: 464.48.

A

C

E

CACHTNGUTERNNU(G CH₃)₃);

¹³C{¹H} NMR (75 MHz, CD₃OD, 293 K): d=155.9 (s; Cq, CN₃), 149.7

(brs; Cq, C_Ar), 146.1 (s; Cq, C_Ar), 138.8 (t, J=7.0 Hz; Cq, C_Ar), 136.7 (t,

J=3.7 Hz; Cq, C_Ar), 132.1 (t, J=10.7 Hz; CH, C_Ar), 129.7 (brs; CH, C_Ar),

129.4 (s; Cq, C_Ar), 129.0 (brt; CH, C_Ar), 128.7 (s; CH, C_Ar), 124.5 (s; CH,

C_Ar), 124.1 (s; CH, C_Ar), 37.9 (s; NMe₂), 34.6 (s; C

ACHTUGNTRENN(UNG CH₃)₂), 34.2 (s; C-

G

CG

CN

cis-[PdCl₂ACTHUGNRTENNU(G A-MeOTf)] (1ACHTUNGTNER(NUNG A-MeOTf))

(121.5 MHz, CD₃OD, 293 K): d=À14.5 ppm (s); HRMS (FAB+): m/z

calcd for [C₅₉H₈₀ON₁₂P₂Cl₄À3HÀ4Cl]⁺: 1031.5819; found: 1031.5829.

three times with 20 mL pentane

Methyl trifluoromethanesulfonate (0.34 mL, 3.00 mmol) was added drop-

wise to a solution of 1a (0.46 g, 0.50 mmol) in dichloromethane (20 mL),

which resulted in some orange precipitation. The reaction mixture was

stirred for 2 h at room temperature. Next, the solution was concentrated

to 2 mL, and diethyl ether (10 mL) was added, which resulted in more

precipitation. The supernatant was removed, and the crude product was

cis-[PdCl₂(a)] (1a)

A solution of dppe-p-C₆H₄-CH₂NEt₂a (0.915 g, 1.24 mmol) in dichloro-

methane (15 mL) was added to a solution of [(cod)PdCl₂] (0.354 g,

1.24 mmol) in dichloromethane (20 mL). The pale yellow reaction mix-

ture was stirred for 1 h at room temperature. Subsequently, the solvent

was evaporated and the precipitate was washed thoroughly with pentane

(3ꢁ20 ml) and dried in vacuo. The product 1a was obtained as a pale

yellow powder (1.10 g, 1.20 mmol, 97%). ¹H NMR (300 MHz, CDCl₃,

293 K): d=7.83–7.71 (m, 8H; PC₆H₄), 7.42 (d, J=8.0 Hz, 8H; PC₆H₄),

3.56 (s, 8H; CH₂N), 2.50 (q, J=7.2 Hz, 16H; CH₂CH₃), 2.44–2.30 (m,

4H; CH₂CH₂), 1.01 ppm (t, J=7.1 Hz, 24H; CH₂CH₃); ¹³C{¹H} NMR

(75 MHz, CDCl₃, 293 K): d=145.6 (s; Cq, PC₆H₄), 133.9 (s; CH, PC₆H₄),

129.7 (s; CH, PC₆H₄), 126.2 (s; Cq, PC₆H₄), 57.7 (s; CH₂N), 47.4 (s;

CH₂CH₃), 28.9 (brs; CH₂CH₂), 12.2 ppm (s; CH₂CH₃); ³¹P{¹H} NMR

(121.5 MHz, CDCl₃, 293 K): d=64.4 ppm (s); HRMS (FAB+): m/z

calcd for [C₄₆H₆₈Cl₂N₄P₂PdÀCl]⁺: 879.3656; found: 879.3637.

washed twice with diethyl ether and dried in vacuo. The product 1ACHTUNGTRENNUNG(A-

MeOTf) was obtained as an off-white fine powder (0.75 g, 0.48 mmol,

96%). ¹H NMR (300 MHz, CD₃OD, 293 K): d=8.10–7.97 (m, 8H;

PC₆H₄), 7.75 (d, J=7.0 Hz, 8H; PC₆H₄), 4.56 (s, 8H; CH₂N), 3.39 (m,

16H; CH₂CH₃), 2.95 (s, 12H; NCH₃), 2.96–2.78 (m, 4H; CH₂CH₂),

1.41 ppm (t, J=7.2 Hz, 24H; CH₂CH₃); ¹³C{¹H} NMR (75 MHz, CD₃OD,

293 K): d=133.9 (brs), 132.1 (s), 130.3 (s), 129.6 (s), 120.5 (q, J=319 Hz;

CF₃), 63.6 (s; NCH₃), 55.9 (s; CH₂N), 46.0 (s; CH₂CH₃), 27.8 (brs;

CH₂CH₂), 6.9 ppm (s; CH₂CH₃); ³¹P{¹H} NMR (121.5 MHz, CD₃OD,

293 K): d=69.3 ppm (s); ¹⁹F NMR (282 MHz, CD₃OD, 293 K): d=

À77.8 ppm

(s);

HRMS

(FAB+):

m/z

calcd

for

[C₅₄H₈₀Cl₂F₁₂N₄O₁₂P₂PdS₄ÀCF₃SO₃]⁺: 1423.2832; found: 1423.2822.

cis-[PdCl

₂ACHUTGTNRENN(GU B-MeOTf)] (1ACHTUNGTRENN(UGN B-MeOTf))

This compound was prepared similarly to 1CATHNUGTREN(NUG A-MeOTf). The product was

cis-[PdCl₂(b)] (1b)

obtained as an ochre fine powder (92%). ¹H NMR (300 MHz, CD₃OD,

293 K): d=7.74–7.61 (m, 16H; PC₆H₄), 7.33 (d, J=8.3 Hz, 2H; OC₆H₃),

7.03–6.95 (m, 2H; OC₆H₃), 6.58 (d, J=10.5 Hz, 2H; OC₆H₃), 4.53 (dd,

J=12.9 Hz and 24.2 Hz, 8H; CH₂N), 3.75–3.50 (m, 16H; CH₂CH₃), 2.93

(s, 12H; NCH₃), 2.07 (s, 12H; CH₃), 1.40 ppm (t, J=6.7 Hz, 24H;

CH₂CH₃); ³¹P{¹H} NMR (121.5 MHz, CD₃OD, 293 K): d=21.2 ppm (s);

¹⁹F NMR (282 MHz, CD₃OD, 293 K): d=À80.4 ppm (s); HRMS (FAB+

): m/z calcd for [C₆₆H₈₈Cl₂F₁₂N₄O₁₃P₂PdS₄ÀCF₃SO₃]⁺: 1591.3411; found:

1591.3403.

This compound was prepared similarly to 1a. The product was obtained

as an orange powder (98%). ¹H NMR (300 MHz, CDCl₃, 293 K): d=

7.54–7.41 (m, 8H; PC₆H₄), 7.30–7.14 (m, 8H; PC₆H₄), 7.06 (d, J=7.7 Hz,

2H; OC₆H₃), 6.86–6.78 (m, 2H; OC₆H₃), 6.46 (d, J=9.2 Hz, 2H; OC₆H₃),

3.52 (s, 8H; CH₂N), 2.48 (q, J=7.4 Hz, 16H; CH₂CH₃), 2.00 (s, 6H;

CH₃), 1.00 ppm (t, J=7.0 Hz, 24H; CH₂CH₃); ³¹P{¹H} NMR (121.5 MHz,

CDCl₃, 293 K): d=19.2 ppm (s); HRMS (FAB+): m/z calcd for

[C₅₈H₇₆Cl₂N₄OP₂PdÀCl]⁺: 1047.4235; found: 1047.4235.

cis-[PdCl₂ACHTUNGTRENNUNG(A-HOTs)] (1ACHTUNGTRENNUNG(A-HOTs))

p-Toluenesulfonic acid monohydrate (29.6 mg, 155.4 mmol) was added to

a solution of 1a (35.6 mg, 38.9 mmol) in methanol (3 mL). The reaction

Chem. Asian J. 2011, 6, 2444 – 2462

ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org

2459

J. N. H. Reek et al.

FULL PAPERS

5,11,17,23-Tetrakis(sulfonic acid)-25,26,27,28-tetrakis(2-

ethoxyethoxy)calix[4]arene (2-SO₃H)

of capsule 1(B)·2 was done in dichloromethane because of the instability

of 1b in methanol. After the capsule was formed, the capsule was stable

and soluble in MeOH/CH₂Cl₂or MeOH/H₂O mixtures.

The strongly acidic Amberlyst 15 ion-exchange resin (3.6 g; macroreticu-

lar resin with sulfonic acid functionality) was added to a white suspension

of tetrasulfonatocalix[4]arene tetrasodium salt 2-SO₃Na (2.02 g,

1.80 mmol) in methanol (35 mL). The reaction mixture was stirred for 1 h

at room temperature. Subsequently, the clear pale yellow solution was fil-

tered, and upon evaporation of the solvent in vacuo, the product 2-SO₃H

was obtained as a brown sticky solid in quantitative yield. ¹H NMR

(300 MHz, CD₃OD, 293 K): d=7.38 (s, 8H; H_Ar), 4.74 (d, J=12.8 Hz,

4H; CHH’), 4.31 (t, J=5.0 Hz, 8H; OCH₂CH₂), 3.91 (t, J=5.0 Hz, 8H;

OCH₂CH₂), 3.56 (q, J=7.0 Hz, 8H; OCH₂CH₃), 3.39 (d, J=12.9 Hz, 4H;

CHH’), 1.22 ppm (t, J=7.0 Hz, 12H; OCH₂CH₃); ¹H NMR (300 MHz,

CD₂Cl₂, 293 K): d=11.0 ppm (brs, SO₃H); ¹³C{¹H} NMR (75 MHz,

CD₃OD, 293 K): d=158.8 (s; Cq, C_Ar), 136.7 (s; Cq, C_Ar), 135.0 (s; Cq,

C_Ar), 126.4 (s; CH, C_Ar), 73.8 (s; CH₂), 69.6 (s; CH₂), 66.3 (s; CH₂), 30.8

(s; ArCH₂Ar), 14.8 ppm (s; CH₃).

NMR Spectroscopic Characterization of the Capsules

+

Upfield shifts (Dd_H) of the CH₂N

G

)

N

bound PP or Pd(PP) building blocks upon capsule formation are given,

with respect to those of the corresponding free building blocks (for cap-

sules assembled from neutral building blocks, Dd_His calculated with re-

spect to the corresponding protonated building blocks; Table 3). Some of

the proton resonances were not visible because they overlap with other

signals or are very broad, or because of H–D exchange with CD₃OD.

Capsule

ACHTUNGTRENNUNG

formation (Dd_Hꢀ0.07 ppm). Capsule

A

ACHTUNGTRENNUNG

0.51 ppm in CD₃OD and Dd(NH)=0.55 ppm in [D₆]DMSO. The phos-

phorus chemical shifts of the diphosphines A–E and the Pd–diphosphines

1A and 1B in their capsular form did not exhibit a noteworthy shift com-

pared to the monomeric form (Ddꢀ0.8 ppm).

General Procedure for the Self-

Assembly of the Diphosphine Capsules

by the Using Precharged Building

Blocks

+

Table 3. Observed upfield shifts (DdH) of the CH₂N

G

)

E

Capsule

(A-HCl)·2^[b]

(B-HCl)·2^[b]

PP/2 Dd

N

(CH₂CH₃) [ppm] Dd

G

ACHTUNGTRENNUNG

Capsule self-assembly was done in

situ. Equimolar methanol solutions of

the tetracationic diphosphine (A-HCl

or B-HCl or C-HCl) and the tetraa-

nionic calix[4]arene 2-SO₃Na were

mixed at room temperature, thereby

resulting in the immediate formation

T

1:3

1:1

1:2

1:1

0.15

0.20

0.25

0.18

0.22

0.27

0.06

n.o.

–

AHCTUNGTRENNUNG

A

(A)·2^[b]

(B)·2^[b]

(C)·2^[b]

–

1

(A-MeOTf)·2^[c]

0.13

0.10

–

of the corresponding capsule

HCl)·2, (B-HCl)·2, and (C-HCl)·2 re-

spectively). Self-assembly of capsules

(D-HCl)·2 and (E-HCl)·2 was done in

a similar way.

(ACTHNGUTRENNU(G A-

1(A)·2^[d]

1(B)·2^[d]

0.11

0.12

A

ACHTUNGTRENNUNG

–

A

ACHTUNGTRENNUNG

[a] [PP] or [Pd(PP)]=2 mm; n.o.=not observed. [b] In CD₃OD, at 208C. [c] In CD₃OD at 608C. [d] In

CD₃OD/D₂O (8:2 mol%) at 408C.

General Procedure for the Self-

Assembly of the Diphosphine Capsules

by the Use of Neutral Building Blocks

Job Plot

Equimolar solutions (2 mm) of 1(PP) and 2-SO₃Na in CD₃OD were pre-

A methanol solution of the tetraacidic calix[4]arene 2-SO₃H (1 equiv)

was slowly added to a methanol solution of the tetraamine diphosphine

(a or b or c; 1 equiv). The solution was stirred for 30 min at room tem-

perature, and subsequently the solvent was evaporated, thereby resulting

in the corresponding capsule ((A)·2, (B)·2, and (C)·2 respectively).

pared and mixed in various ratios. In this way the total concentration of

1(PP) and 2 was kept constant at 2 mm and only the 1(PP)/2 ratio was

varied. ¹H NMR spectra of the mixtures were recorded at 608C, and the

chemical shifts of 1(PP) were analyzed by Jobꢂs method of continuous

variation, that is, a plot of the capsule concentration as a function of the

mole fraction of 2,^[27]1(PP)=1

¹H NMR Spectroscopic Titrations

ACHTUGTNREN(UNG A-MeOTf), or 1ACHTUNGTRENN(UGN B-MeOTf).

General Procedure for the Self-Assembly of Pd Capsules by Using

Precharged Building Blocks

Capsule self-assembly was done in situ. Equimolar methanol solutions of

the palladium tetracationic-diphosphine complex (1ACTHNUTRGENN(UG A-MeOTf) or 1ACHTUTGNREN(NUGN B-

MeOTf)) and the tetraanionic calix[4]arene 2-SO₃Na were mixed at

room temperature, thereby resulting in the immediate formation of the

The ¹H NMR spectroscopic titrations of 2-SO₃Na with A-HCl and of 2-

SO₃Na with B-HCl were measured in CD₃OD at 298 K under inert con-

ditions. Because of solubility reasons the concentration of 2 was kept

constant and low in all the samples (1 mm), whereas the concentrations

of A-HCl and B-HCl were varied from 0 to 3 mm. The chemical shifts of

corresponding capsule (1ACTHUNTGRNENUG(A-MeOTf)·2 and 1ACHTUGNTREN(NUGN B-MeOTf)·2, respectively).

⁺A

the diphosphine protons CH₂NH CTHUNGTREN(UNNG CH₂CH₃)₂of ACHTUNTRGEG(NNUN A-HCl)·2 and ACHTUNGTRENNUNG(B-

Self-Assembly of Pd Capsules by Using Neutral Building Blocks (Capsule

HCl)·2, relative to the chemical shifts of A-HCl and B-HCl, respectively,

were followed and fitted to a 1:1 binding model by using a least-squares

fitting procedure.^[21b]The association constants K for a single run were

calculated as the mean of the values obtained for each of the followed di-

phosphine signals, weighted by the observed changes in chemicals

shift.^[28]The association constants from different runs were then aver-

1(A)·2)

An equimolar solution of tetraacidic calix[4]arene 2-SO₃H (1 equiv) in

methanol was slowly added to a methanol solution of 1a (1 equiv), upon

which some precipitation appeared. The reaction mixture was stirred for

30 min at room temperature, and subsequently the solvent was evaporat-

ed, thereby resulting in capsule 1(A)·2.

aged. The association constant found for capsule

ACHTUNGTRNEN(NUG A-HCl)·2 is K_A·2=3ꢁ

10⁴m^À1and for capsule (B-HCl)·2 is K_B·2=8ꢁ10⁴m^À1. Lines in the titra-

AHCTUNGTRENNUNG

Self-Assembly of Pd Capsules by the Use of Neutral Building Blocks

(Capsule 1(B)·2)

tion curves are best-fit curves calculated by nonlinear regression.

ESI-MS Measurements

An equimolar solution of tetraacidic calix[4]arene 2-SO₃H (1 equiv) in

dichloromethane was slowly added to a solution of 1b (1 equiv) in di-

chloromethane, upon which precipitation appeared. The reaction mixture

was stirred for 30 min at room temperature, and subsequently the solvent

was evaporated, thereby resulting in capsule 1(B)·2. Note: self-assembly

Samples of the capsules (PP/calix=1:1–1:3) with initial concentrations of

100–250 mm were diluted in MeOH to a final concentration of 1%. Com-

parison of the measured isotope patterns of the capsules with the calcu-

lated ones confirm their elemental composition and charge state. The ion

2460

www.chemasianj.org

ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Asian J. 2011, 6, 2444 – 2462

Diphosphine Capsules

peaks of the capsules correspond to 1:1 complexes, and no ion peaks for

higher aggregates were detected. From the survey MS spectra, individual

candidate ions were selected for collision-induced dissociation (CID)

MS/MS with Argon as collision gas. The assignment of the ion peaks of

the capsule is confirmed by CID experiments: upon collision-induced dis-

sociation of the ion peaks of the capsule, product peaks appeared that

correspond to the building blocks of the capsule. The reported m/z

values correspond to the 100% ion peak (isotope with the highest inten-

Fujita, Science 2006 , 312 , 25 1 –2 54; p) H. Ito, T. Kusukawa, M.

Fujita, Chem. Lett. 2000, 29, 598–599; q) M. Yoshizawa, T. Kusuka-

wa, M. Fujita, S. Sakamoto, K. Yamaguchi, J. Am. Chem. Soc. 2001 ,

123 , 1045 4 –1 0459; r) Y. Nishioka, T. Yamaguchi, M. Kawano, M.

Fujita, J. Am. Chem. Soc. 2008 , 130 , 816 0 –8 161.

[2] Capsules based on hydrogen bonds: a) S. K. Kçrner, F. C. Tucci,

D. M. Rudkevich, T. Heinz, J. Rebek, Jr., Chem. Eur. J. 2000 , 6 ,

18 7 –1 95; b) D. Ajami, J. Rebek, Jr., Proc. Natl. Acad. Sci. USA

2007 , 104 , 1600 0 –1 6003; c) R. K. Castellano, B. H. Kim, J. Re-

bek, Jr., J. Am. Chem. Soc. 1997 , 119 , 1267 1 –1 2672; d) M. Bolte, I.

Thondorf, V. Boehmer, V. Rudzevich, Y. Rudzevich, CrystEng-

Comm 2008, 10, 270–272; e) D. Ajami, M. P. Schramm, A. Volonter-

io, J. Rebek, Jr., Angew. Chem. 2007 , 119 , 24 6 –2 48; Angew. Chem.

Int. Ed. 2007 , 46 , 24 2 –2 44; f) S. Ma, D. M. Rudkevich, J. Rebek, Jr.,

J. Am. Chem. Soc. 1998 , 120 , 497 7 –4 981; g) A. Shivanyuk, J. Re-

bek, Jr., Chem. Commun. 2001 , 242 4 –2 425; h) J. Kang, J. Santama-

ria, G. Hilmersson, J. Rebek, Jr., J. Am. Chem. Soc. 1998 , 120 ,

738 9 –7 390; i) J. L. Atwood, L. J. Barbour, A. Jerga, Proc. Natl.

Acad. Sci. USA 2002 , 99 , 483 7 –4 841.

[3] Capsules based on metal–ligand bonds: a) F. Fochi, P. Jacopozzi, E.

Wegelius, K. Rissanen, P. Cozzini, E. Marastoni, E. Fisicaro, P.

Manini, R. Fokkens, E. Dalcanale, J. Am. Chem. Soc. 2001 , 123 ,

753 9 –7 552; b) M. Fujita, M. Tominaga, A. Hori, B. Therrien, Acc.

Chem. Res. 2005 , 38 , 36 9 –3 78; c) K. Suzuki, J. Iida, S. Sato, M.

Kawano, M. Fujita, Angew. Chem. 2008 , 120 , 586 4 –5 866; Angew.

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sity). Capsule

calcd for [A·2+2Na]²⁺: 908.85; found: 908.95; calcd for [A·2+Na+H]²⁺

897.86; found: 897.93; calcd for [A·2+2H]²⁺: 886.37; found: 886.42. Cap-

ACHTUNGTRENNUNG(A-HCl)·2 (C₉₀H₁₂₄N₄O₂₀P₂S₄): ESI-MS (CH₃OH): m/z:

:

sule ACHTUNGTRENNUNG(B-HCl)·2 (C₁₀₂H₁₃₂N₄O₂₁P₂S₄): ESI-MS (CH₃OH): m/z: calcd for

[B·2+H+Na]²⁺: 981.89; found: 981.99; calcd for [B·2+2H]²⁺: 970.90;

found: 970.97; calcd for [B·2+2H+Na]³⁺: 654.93; found: 654.99; calcd

for [B·2+3H]³⁺

:

647.60; found: 647.66. Capsule

ACHTUNGTRENN(UNG C-HCl)·2

(C₁₀₃H₁₃₂N₄O₂₁P₂S₄): ESI-MS (CH₃OH): m/z: calcd for [C·2+3H]³⁺

:

651.265; found: 651.263; calcd for [C·2+2H+1Na]³⁺: 658.593; found:

658.602; calcd for [C·2+1H+2Na]³⁺: 665.920; found: 665.921; calcd for

[C·2+3Na]³⁺: 673.247; found: 673.251; calcd for [C·2+2H]²⁺: 976.394;

found: 976.354; calcd for [C·2+1H+1Na]²⁺: 987.385; found: 987.327;

calcd for [C·2+2Na]²⁺

:

998.375; found: 998.325. Capsule

(C₉₁H₁₀₈N₄O₂₁P₂S₄): ESI-MS (CH₃OH): m/z: calcd for [D·2+2Na]²⁺

914.78; found: 914.98; calcd for [D·2+Na+H]²⁺: 903.79; found: 903.99;

calcd for [D·2+2H]²⁺

892.80; found: 893.00. Capsule (E-HCl)·2

(C₁₀₃H₁₃₂N₁₂O₂₁P₂S₄): ESI-MS (CH₃OH): m/z: calcd for [E·2+2Na]²⁺

1054.89; found: 1055.13; calcd for [E·2+Na+H]²⁺

1043.90; found:

ACHTUNGTRENN(UNG D-HCl)·2

:

ACHTUNGTRENNUNG

:

1044.11; calcd for [E·2+2H]²⁺

: 1032.91; found: 1033.16; calcd for

[E·2+3Na]³⁺: 710.92; found: 711.07; calcd for [E·2+2Na+H]³⁺: 703.60;

found: 703.77; calcd for [E·2+Na+2H]³⁺: 696.27; found: 696.44. Capsule

1ACHTUNGTRENNUNG(A-MeOTf)·2 (C₉₄H₁₃₂N₄O₂₀P₂PdS₄Cl₂): ESI-MS (CH₃OH): m/z: calcd

for [1

G

:

967.34; found: 967.38; calcd for [1

652.56; found: 652.60; calcd for [1

645.23; found: 645.24. Capsule 1(A)·2

ACHTUNGTRENNUNG

MeOTf)·2À2Cl+Na]³⁺

:

ACHTUNGTRENNUNG

MeOTf)·2À2Cl+H]³⁺

(C₉₀H₁₂₄Cl₂N₄O₂₀P₂PdS₄):

ESI-MS

(CH₃OH):

m/z:

calcd

for

[1(A)·2ÀCl+H]²⁺

:

938.31; found: 938.31; calcd for [1(A)·2À2Cl+H]³⁺

: 625.88; found:

625.88. Capsule

(CH₃OH): m/z: calcd for [1

713.26; calcd for [1

A

: 713.24; found:

sule 1(B)·2 (C₁₀₂H₁₃₂N₄O₂₁P₂PdS₄Cl₂): ESI-MS (CH₃OH): m/z: calcd for

[1(B)·2ÀCl+H]²⁺: 1041.33; found: 1041.36; calcd for [1(B)·2À2Cl]²⁺

:

1023.34; found: 1023.37; calcd for [1(B)·2ÀCl+2H]³⁺: 694.55; found:

694.58; calcd for [1(B)·2À2Cl+H]³⁺: 682.56; found: 682.58.

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Received: January 31, 2011

Published online: June 9, 2011

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Chem. Asian J. 2011, 6, 2444 – 2462

Article Doi

Diphosphine capsules for transition-metal encapsulation

DOI: 10.1002/asia.201100092

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