Novel multitopic diphos-type ligands

Article abstract of DOI:10.1016/j.jorganchem.2010.04.028

Seven novel imidazole and thiazole derivatives of diphos-type ligands are presented. They are of the general structure R₂P(CH₂) ₂PR₂, where R is imidazol-2-yl (1), 1-methylimidazol-2-yl (2), 1-methylbenzimidazol-2-yl (3), 1-methylimidazol-5-yl (4), 2-isopropylimidazol-4(5)-yl (5), thiazol-2-yl (6), benzothiazol-2-yl (7), thiazol-4-yl (8) or thiazol-5-yl (9). Syntheses involved direct metallation or halogen-metal exchange reactions. Their solubility, especially in aqueous solution, is strongly dependent on the nature of the substituents as is their partition coefficient log D. The crystal structures of compounds 2, 3, 7a and 9 as well as the structure of the rhodium complex [(2)₂Rh ₂Cl₂]Cl₂ (10) have been determined.

Full text of DOI:10.1016/j.jorganchem.2010.04.028

Journal of Organometallic Chemistry 695 (2010) 1891e1897
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Novel multitopic diphos-type ligands.
,
a
a
a
b,1
Peter C. Kunz a , Corinna Wetzel , Melanie Bongartz , Anna Louisa Noffke , Bernhard Spingler
*
a Heinrich-Heine Universität, Institut für Anorganische Chemie und Strukturchemie I, Düsseldorf, Universitätsstrasse 1, D-40225 Düsseldorf, Germany
b Anorganisch-Chemisches Institut, Universität Zürich-Irchel, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
Seven novel imidazole and thiazole derivatives of diphos-type ligands are presented. They are of the
general structure R2P(CH2)2PR2, where R is imidazol-2-yl (1), 1-methylimidazol-2-yl (2), 1-methyl-
benzimidazol-2-yl (3), 1-methylimidazol-5-yl (4), 2-isopropylimidazol-4(5)-yl (5), thiazol-2-yl (6),
benzothiazol-2-yl (7), thiazol-4-yl (8) or thiazol-5-yl (9). Syntheses involved direct metallation or
halogenemetal exchange reactions. Their solubility, especially in aqueous solution, is strongly dependent
on the nature of the substituents as is their partition coefficient log D. The crystal structures of
compounds 2, 3, 7a and 9 as well as the structure of the rhodium complex [(2)2Rh2Cl2]Cl2 (10) have been
determined.
Received 11 February 2010
Received in revised form
19 April 2010
Accepted 22 April 2010
Available online 29 April 2010
Keywords:
Phosphane ligands
Nitrogen heterocycles
Imidazoles
Ó 2010 Elsevier B.V. All rights reserved.
Thiazoles
1. Introduction
hydrophilicity/hydrophobicity profile, as this determines both their
pharmacokinetic and pharmacodynamics. For example, clinical
Undoubtedly, diphosphane ligands play a key role in homoge-
nous catalysis. The rare amino acid L-DOPA is synthesised using the
rhodium(I) complex [Rh{(R,R)-DiPAMP}(cod)]BF4 of the chiral
diphosphane (R,R)-DiPAMP for which Knowles received the Nobel
price in 2001. Especially the development of chiral diphosphanes
such as DIOP, Norphos and Chiraphos or P-stereogenic ligands as
DiPAMP or BisP* has been pursued due to their abilities to induce
high enantioselectivities [1,2]. For the use in biphasic catalysis,
water-soluble diphosphanes were developed. Usually these have
charged functional groups as carboxylato, sulfonato or phospho-
nato groups or quaternary ammonium groups. But still, compared
to the wide variety of diphosphanes used in catalysis, water-soluble
diphosphanes are scarce. Beside the importance of phosphanes in
catalysis, phosphane complexes in medicinal chemistry gain more
trials on [(dppe)2Au]Cl were hampered by high hepato- and car-
diotoxicity related to the highly hydrophobic nature of this complex
[5,6]. To circumvent the lipophilicity related side effects, more
hydrophilic diphos complexes have to be developed and one
approach is to replace the phenyl rings of dppe by pyridine [7e11].
We have developed imidazole-based water-soluble phosphane
ligands for application as enzyme models and for biomedical
applications in the past [12,13]. Based upon our previous findings,
we herein report on synthetic routes towards diverse imidazolyl as
well as thiazolyl substituted diphosphane ligands, which should
exhibit similar properties concerning their use in biological media.
To evaluate the new ligands exact hydrophilicity/hydrophobicity
profile, their n-octanol/water partition coefficients at pH ¼ 7.4 were
determined.
and more attention; For example the Ru(II) complex [(h
6-p-cym-
ene)RuCl2(pta)] of the water-soluble pta ligand (pta ¼ 1,3,5-triaza-
7-phosphatricyclo[3.3.1.1]decane) has been reported to exhibit
antibacterial activity [3] and the gold(I) complex [(dppe)2Au]Cl
exhibits antitumor activity in different cell lines [4]. For the use in
biomedical applications the (di)phosphane ligands and their
complexes have to fulfil certain demands. Not only do they need
2. Results and discussion
Symmetrical diphosphanes of the diphos-type R2P(CH2)2PR2
were prepared by reaction of bis(dichlorophosphino)ethane with
nucleophiles. The starting material bis(dichlorophosphino)ethane
was prepared from ethylene, phosphorus trichloride and white
phosphorus in an steel autoclave according to the high-pressure
procedure of Chatt [14]. While it has been reported, that after
several runs the autoclave begins to deteriorate [15], we observed
corrosion especially of the needle-valves.
to be water-soluble, but have to exhibit
a finely adjusted
* Corresponding author. Tel.: þ49 211 8112873; fax: þ49 211 811287.
E-mail address: peter.kunz@uni-duesseldorf.de (P.C. Kunz).
Ligands 2 and 6 were synthesised according procedures for
tris(N-methylimidazol-2-yl)phosphane
1
X-ray structural analysis.
and
tris(thiazol-2-yl)
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.04.028

1892
P.C. Kunz et al. / Journal of Organometallic Chemistry 695 (2010) 1891e1897
Table 2
phosphane by Moore and Whitesides [16]. For the preparation of 2
bis(dichlorophosphino)ethane was treated with 1-methyl-2-
trimethylsilylimidazole. After lithiation of either N-methyl-
benzimidazole or thiazole and the following reaction with bis
(dichlorophosphino)ethane ligands 3 and 6, respectively, were
obtained in good yields, whereas the reaction of 2-bromothiazole
with n-butyl lithium did not yield the desired product.
Ligands 1 and 5 were prepared starting from the corresponding
diethoxymethyl-protected imidazoles [17,18], which were lithiated
using n-butyl lithium and tert-butyl lithium respectively. The
lithiated species were reacted with bis(dichlorophosphino)ethane
to obtain the DEM-protected ligands. Direct deprotection was
achieved by refluxing the products in a 10:1 mixture of acetone/
water, from which the analytically pure ligands precipitated upon
cooling.
13C{1H} chemical shifts (
d
/ppm) of diphos-type ligands.
13C{1H})/ppm
eC2H4e Other signals
Ligand
R
d (
1
2
Imidazol-2-yl
1-Methylimidazol-2-yl 21.7
22.6
124.9, 143.1
35.0 (NCH3), 127.1 (C5),
129.5 (C4), 144.1
3
4
5
6
7
1-Methyl-
benzimidazol-2-yl
1-Methylimidazol-5-yl 22.4
21.0
29.5, 109.9, 120.5, 122.8,
123.8, 161.3
32.8 (NCH3), 124.4 (C2),
137.3 (C4), 142.3 (C5)
20.5 (CH3), 48 (CH), 130.1
(C4(5)), 153.7 (C5(4)), 157.7 (C2).
123.8 (C4/5), 145.6 (C4/5),
167.9 (C2)
2-Isopropylimidazol-
4(5)-yl
Thiazol-2-yl
28.2
25.7
25.0
Benzothiazol-2-yl
121.8, 124.0, 126.0, 126.5,
137.3, 155.0
For the synthesis of 4, which is a regioisomer of 2, a different
approach had to be taken. Prior to forming the PeC bonds a halo-
genemetal exchange was carried out [19]. Therefore, 5-bromo-
1-methylimidazole was reacted in dichloromethane with ethyl
magnesium bromide and the resulting Grignard component reac-
ted with bis(dichlorophosphino)ethane to give ligand 4. The three
isomeric thiazole ligands 6, 8 and 9 were prepared in a similar
manner. Ligand 6 was prepared by direct lithiation of thiazole,
where as ligands 8 and 9 were prepared via metalehalogen
exchange of the corresponding 4- and 5-bromothiazole. The
benzimidazole ligand 3 and the benzothiazole ligand 7 have been
reported previously by Richards and Al-Dulaymmi in the prepara-
tion of different metal complexes. However, the syntheses of the
ligands were not mentioned and the ligands themselves not
characterised [20e22].
8
9
Thiazol-4-yl
Thiazol-5-yl
25.4
28.5
122.3 (C2), 128.0 (C5), 168.2 (C4)
132.5 (C5), 151.0 (C4), 159.0 (C2)
In the case of the reactions to the three isomeric thiazole ligands
different reaction products were obtained, as can be easily seen
from the different resonances in the 31P{1H} NMR spectra. The
unambiguous assignment to the thiazol-2-yl, 4-yl and 5-yl ligands
6, 8 and 9 was not possible based upon the spectroscopic data, as
during the course of the reaction isomerisation of the metallated
thiazole moieties might have occurred [23,24]. The final assign-
ment of the 2-, 4- and 5-yl isomers to 6, 8 and 9 was achieved by
determination of the solid-state structure of 6 and 9. However, the
data of the structure of 6 was not sufficient for publication but
clearly shows the 2-yl connectivity.
Compounds 1e9 are potent chelating ligands as can be already
seen in the MALDI mass spectra of these ligands. Besides the
molecular ion and characteristic fragments, copper complexes are
observed. The source of the copper is unknown, but seems to be the
probe slit of the mass spectrometer. All ligands were characterised
by 1H, 13C{1H} and 31P{1H} NMR spectroscopy (data summarised in
Tables 1 and 2). Structural assignments were achieved with the
help of a combination of 2D NMR experiments and by comparison
of 1H NMR data with those reported previously for analogous
phosphanes. The signal of the protons of the ethylene bridge
appears as a deceptively simple triplet [21] in the region of 2.1 to
3.1 ppm (Table 1).
2.1. Hydrophilic/hydrophobic balance
The partition coefficients of the compounds were determined
using the shake-flask method (Table 3). The coefficients of the
highly hydrophobic benzylated compounds 3 and 7 could not be
determined by this method. As expected, compound 5 with the
isopropyl groups shows the lowest hydrophilicity of the imidazolyl
based compounds. Interestingly, both N-methylated imidazolyl
compounds (2 and 4) seem to be more hydrophilic than 1 which
bears no alkyl groups at the nitrogen atoms. Presumably, 1 can form
hydrogen bonds towards solvent molecules e.g. n-octanol and these
solvates are than more lipophilic than the structure of 1 might
suggest. The log D7.4 values for the three isomeric 2-, 4- and 5-yl
thiazoles 6, 8 and 9 are within the range of 0.6e1.0 and therefore
are less hydrophilic than the isomeric imidazols 2 and 4.
The signals of the methylene bridge in the 13C{1H} NMR spectra
are split due to the coupling with the two phosphorous atoms. For
each carbon atom a second order system AA’X results. Furthermore,
for the CH carbon atoms in the thiazole ring of 6 and the CH carbon
atoms in the benzothiazole substituents in 7 assignments of
specific signals could not be accomplished on the basis of H,C-COSY,
HMBC and HMQC NMR and thus remain ambiguous.
In order to validate the log D values determined by UV/Vis
spectroscopy we measured the partition coefficient of a sample of 2
by 31P NMR spectroscopy. Compound 2 was dissolved in n-octanol/
PBS buffer and both phases were measured using a glass inlet tube
with PPh3 as internal standard. To ensure that no nuclear
Table 1
31P{1H} and 1H chemical shifts (
d
/ppm) of diphos-type ligands.
31P{1H})/ (1H)/ppm
eC2H4e Other signals
Table 3
Ligand
R
d
(
d
Log D7.4 values and standard deviation determined via the shake-flask method.
ppm
Ligand
R
log D7.4 (exp.)
1
2
3
Imidazol-2-yl
1-Methylimidazol-2-yl
1-Methyl-benzimidazol-2-yl ꢀ45
ꢀ50
ꢀ54
2.30
2.62
3.09
7.22
3.63, 7.12, 7.26
3.72, 7.16e7.31,
7.63e7.75
7.09, 7.56
1.28, 3.04, 7.00
7.58, 8.06
7.30e7.59, 7.78e
7.85, 8.02e8.10
7.44
1
2
3
4
5
6
7
8
9
Imidazol-2-yl
0.19 ꢁ 0.07
ꢀ0.73 ꢁ 0.03
n.d.
ꢀ0.02 ꢁ 0.05
0.85 ꢁ 0.04
0.73 ꢁ 0.01
n.d.
1-Methylimidazol-2-yl
1-Methyl-benzimidazol-2-yl
1-Methylimidazol-5-yl
2-Isopropylimidazol-4(5)-yl
Thiazol-2-yl
Benzothiazol-2-yl
Thiazol-4-yl
Thiazol-5-yl
4
5
6
7
1-Methylimidazol-5-yl
ꢀ73
2.20
2.03
2.73
3.01
2-Isopropylimidazol-4(5)-yl ꢀ63
Thiazol-2-yl
ꢀ20
ꢀ15
Benzothiazol-2-yl
0.61 ꢁ 0.05
8
9
Thiazol-4-yl
Thiazol-5-yl
ꢀ19
ꢀ52
2.64
2.15
0.97 ꢁ 0.07
8.04, 9.01
n.d. not determined due to low solubility in water and/or n-octanol.

P.C. Kunz et al. / Journal of Organometallic Chemistry 695 (2010) 1891e1897
1893
Overhauser effect was observed we used standard inverse gated
decoupling and additional delay time of 10 s for complete relaxa-
tion of the nuclei. Here, the log D value was determined to
ꢀ0.76 ꢁ 0.06 which is in good agreement with the value deter-
mined by UV/Vis spectroscopy.
of the donor atoms in the azole substituents these ligands should
display a plethora of coordination modes. The availability of these
ligands should be useful for investigation of new organometallic
reagents for use in aqueous and biphasic catalysis as well as in
bioorganometallic chemistry(Scheme 1).
2.2. Solid state structures
4. Experimental section
Crystals for X-ray analysis were grown by vapour diffusion.
During the crystallisation process 7 was oxidised to the corre-
sponding diphosphane dioxide 7a. The crystallographic data for 2,
3, 9 and 7a are summarised in Table 4. Tables with all angles and
bond lengths can be found in the supporting information. The
metric parameters are within the range found in diphos ligands
[24,25]. In all structures, the asymmetric unit contains only half of
the corresponding ligand. The other half is either generated by a 42
symmetry element (for 2) or an inversion centre (for all other
structures), respectively (Fig. 1e5).
The reaction of 2 with [{(CO)2RhCl}2] in chloroform did not yield
a ligand-stabilized rhodium carbonyl complex, as was seen by the
missing carbonyl bands in the IR spectrum. Oxidation occurred to
a binuclear rhodium(II) complex of the composition [(2)2Rh2Cl2]Cl2
(10). We were able to obtain red crystals of 10 as solvate (Fig. 6). In
the cation, each rhodium carries a ligand 2 chelating through the
phosphorus atoms, and a imidazolyl group from each phosphorus
ligates the second rhodium through nitrogen, to give a ‘Double-
A-Frame’ geometry and the RheRh distance of 2.6626(3) Å is within
the range associated with a RheRh single-bond. Such a ‘Double-
A-Frame’ geometry is also observed in analogues compounds of 7
[20,22].
Compounds 1-diethoxymethylimidazol [18], 1-diethoxymethyl-
2-isopropylimidazole [17], 1-methyl-2-trimethylsilyimidazole and
bis(dichlorphosphino)ethane [14] were prepared according to the
literature procedures. All preparations were carried out in Schlenk
tubes under an atmosphere of dry nitrogen using anhydrous
solvents purified according to standard procedures. All chemicals
were used as purchased. NMR spectra were recorded on a Bruker
DRX 200 or Bruker DRX 500 spectrometer. The 1H and 13C NMR
spectra were calibrated against the residual proton signals and
the carbon signals of the solvents as internal references ([D1]
chloroform: dH ¼ 7.24 ppm and dC ¼ 77.0 ppm; [D4]methanol:
dH ¼ 3.31 ppm and dC ¼ 49.1 ppm) while the 31P{1H} NMR spectra
were referenced to external 85% H3PO4. Infrared spectra were
recorded with a Bruker IFS 66 FT-IR spectrometer. Time-of-flight
mass spectra were recorded on a Bruker Ultraflex TOF, ESI mass
spectra on an ion-trap mass spectrometer Finnigan LCQ Deca and EI
mass spectra on a GC/MS-system Thermo Finnigan Trace DSQ.
4.1. Synthesis of bis(diimidazol-2-ylphosphino)ethane, 2-dimpe (1)
A solution of n-butyl lithium in hexane (1.6 M, 15 mL, 24 mmol)
was added drop-wise to a solution of 3.7 g (22 mmol) of 1-dieth-
oxymethylimidazole in diethyl ether (300 mL) at ꢀ78 ꢂC. The
reaction mixture was stirred at e40 ꢂC for 1 h and at ambient
temperature for 2 h. The reaction mixture was cooled to e78 ꢂC and
bis(dichlorophosphino)ethane (1.00 g, 4.31 mmol) was added. The
reaction mixture was stirred at ambient temperature over night.
The precipitate was removed by filtration and the filtrate was
concentrated in vacuo. The resulting orange oil was dissolved in
3. Conclusion
We presented a variety of isomeric new imidazole and thiazole
based bisphosphanes are accessible. The hydrophilic/hydrophobic
balance of such diphos-type ligands can be addressed by the nature
and the connectivity of the azole substituents. Due to the topology
Table 4
Crystallographic data for compounds 2, 3, 7a$(C5H10)2, 9 and 10$C4H8O$½C2H5OH.
2
3
7a$(C5H10
)
9
10$C4H8O$½C2H5OH
2
Formula
C
18H24N8P2
C34H32N8P2
614.62
C40H40N4O2P2S4
798.94
C14H12N4P2S4
426.46
C46H70Cl4N16O3P4Rh2
1366.68
M (g molꢀ1
)
414.39
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Tetragonal
P42
12.5078(3)
12.5078(3)
6.7689(2)
Monoclinic
P21/c
9.0807(2)
10.4579(2)
15.9180(3)
Triclinic
Pꢀ1
Triclinic
Pꢀ1
Monoclinic
C2/c
25.3183(3)
16.88021(16)
13.51874(12)
9.7003(3)
10.3399(2)
10.6682(3)
98.5494(19)
108.157(2)
97.012(2)
989.17(4)
1
5.6563(6)
8.4971(9)
10.1074(9)
104.719(8)
102.660(8)
93.637(8)
454.75(8)
1
a
b
g
(ꢂ)
(ꢂ)
(ꢂ)
91.494(2)
102.903(1)
V (Å3)
1058.96(5)
2
1.300
1511.14(5)
2
1.351
5631.7(1)
4
1.612
Z
dcalc (g cmꢀ3
)
1.341
0.362
0.41 ꢃ 0.30 ꢃ 0.25
colourless prism
27475
7535/0.0229
6021
100.0%/33.14ꢂ
0.9150/0.8727
235 /0
1.064
0.0447/0.1353
0.0555/0.1400
1.557
0.703
0.36 ꢃ 0.14 ꢃ 0.05
colourless plate
10020
2758/0.0298
2098
100.0%/30.50ꢂ
0.9657 /0.8587
109/0
1.027
0.0372/0.0932
0.0572/0.0983
Linear absorption coefficient (mmꢀ1
)
0.226
0.184
0.946
Crystal size (mm3)
0.19 ꢃ 0.14 ꢃ 0.06
colourless plate
6350
2164/0.0489
1369
99.7%/26.37ꢂ
0.9865/0.9451
129/1
0.62 ꢃ 0.25 ꢃ 0.19
colourless prism
19990
5749/0.0311
3779
99.9%/33.14ꢂ
0.9659/0.8955
203/0
0.37 ꢃ 0.32 ꢃ 0.25
light pink block
63619
10732/0.0307
8491
100.0%/33.14ꢂ
0.7981/0.7803
338/12
Crystal description
Measured reflections
Unique reflections/Rint
Observed reflections
Completeness to theta
Max. and min. transmission
Refined parameters /restraints
GooF
0.962
0.966
0.0579/0.1397
0.0945/0.1534
1.069
0.0373/0.1122
0.0509/0.1172
R1(F) /wR2 (F2) [I>2
s(I)]
0.0598/0.1220
0.1074/0.1334
ꢀ0.1(2)
R1(F) /wR2 (F2) (all data)
Flack parameter
Largest diff. peak and hole (e Åꢀ3
)
0.680/ꢀ0.202
0.611/ꢀ0.221
0.785/ꢀ0.452
0.720/ꢀ0.289
1.142/ꢀ0.724

1894
P.C. Kunz et al. / Journal of Organometallic Chemistry 695 (2010) 1891e1897
Fig. 1. Azole-based diphosphane ligands 1e9.
CHCl3 (200 mL) and 2 mL of ammonia solution added. The organic
phase was collected and all volatiles were removed in vacuo. The
oily residue was dissolved in 100 mL acetone/water (10:1) and
stirred at ambient temperature for 72 h. After cooling in an ice bath,
the resulting precipitate was collected by filtration and dried in
vacuo. Yield 0.97 g (63%). 1H-NMR (200 MHz, 296 K, MeOD-d4):
7.12 (s, 4 H, H4), 7.26 (s, 4 H, H5). 13C{1H}-NMR (125 MHz, 296 K,
MeOD-d4):
/ppm ¼ 21.7 ((CH2)2), 35.0 (NCH3),127.1 (C5),129.5 (C4),
d
144.1 (C2). 31P{1H}-NMR (81 MHz, 296 K, MeOD-d4):
d
/ppm ¼ ꢀ54
(s). ESIþ (MeOH): m/z ¼ 333.3 [M-imNMe]þ, 415.3 [MþH]þ, 437.4
[MþNa]þ. C18H24N8P2 2H2O (450.41): calcd. C 48.0, N 6.3, H 24.9;
found C 48.1, H 6.0, N 24.3.
d
/ppm ¼ 2.30 (t, 4 H, (CH2)2), 7.22 (s, 8 H, Him). 1H-NMR (500 MHz,
296 K, dmso-d6):
d
/ppm ¼ 2.20 (t, 4 H, (CH2)2), 7.20e7.25 (m, 8 H,
4.3. Synthesis of bis(di-1-methylbenzimidazol-2-ylphosphino)
Him), 12.57 (s, 4 H, NH). 13C{1H}-NMR (125 MHz, 296 K, dmso-d6):
ethane, 2-dbimpeNMe (3)
d
/ppm ¼ 22.6 ((CH2)2),124.9 (broad, C2),143.1 (C4, C5). 31P{1H}-NMR
(81 MHz, 296 K, MeOD-d4):
d
/ppm ¼ ꢀ50 (s). 31P{1H}-NMR
A solution of n-butyl lithium in hexane (1.6 M, 6.3 mL) was
added drop-wise to a solution of 1-methylbenzimidazol (1.44 g) in
toluene at e78 ꢂC. The reaction mixture was stirred for 2 h and then
bis(dichlorophosphino)ethane (500 mg, 0.32 mL) was added, the
solution stirred for another hour at e78 ꢂC and over night at
ambient temperature. Concentrated ammonia solution (5 mL) was
added, the phases separated and the organic layer dried over
Na2SO4. The volatiles were removed in vacuo to yield a slightly
yellow solid, which was crystallised from methanol/toluene. Yield
(81 MHz, 296 K, dmso-d6):
d
/ppm ¼ ꢀ49 (s). EI MS (Pt, 210 ꢂC): m/z
(%) ¼ 68 (100) ([C3H4N2]þ), 222 (4.7) ([M-2im]þ), 290 (1.3)
([M-im]þ), 358 (0.4) ([M]þ). C14H16N8P2 CH3OH H2O (408.13): calcd.
C 45.1, H 5.3, N 28.1; found C 45.4, H 5.4, N 28.5.
4.2. Synthesis of bis(di-1-methylimidazol-2-ylphosphino)ethane,
2-dimpeNMe (2)
(80%). 1H-NMR (200 MHz, 296 K, CDCl3):
(CH2)2), 3.72 (s, 12H, NCH3), 7.16e7.31 (m, 12H, bzim), 7.63e7.75 (m,
4H, bzim). 13C{1H}-NMR (125 MHz, 296 K, CDCl3):
/ppm ¼ 21.0,
29.5, 109.9, 120.5, 122.8, 123.8, 161.3. 31P{1H}-NMR (81 MHz, 296 K,
CDCl3):
/ppm ¼ e45 (s). MALDI TOF (DIT, CHCl3): m/z ¼ 483.1
d
/ppm ¼ 3.09 (t, 4H,
Bis(dichlorophosphino)ethane (635 mg, 2.74 mmol) was added
drop-wise to 2.1 g (14 mmol) of neat 1-methyl-2-trimethylsilyli-
midazole at 0 ꢂC. The reaction mixture was stirred for 14 h at
ambient temperature. All volatiles were removed in vacuo. The
residue was washed several times with n-hexane and dried in
vacuo to yield 0.73 g (76%) of a white solid. 1H-NMR (200 MHz,
d
d
296 K, MeOD-d4):
d/ppm ¼ 2.62 (t, 4 H, (CH2)2), 3.63 (s, 12 H, NMe),
Fig. 2. Molecular structure of 2. The displacement ellipsoids are shown on a 50% level
Fig. 3. Molecular structure of 3. The displacement ellipsoids are shown on a 50% level
and hydrogen atoms are omitted for clarity.
and hydrogen atoms are omitted for clarity.

P.C. Kunz et al. / Journal of Organometallic Chemistry 695 (2010) 1891e1897
1895
Fig. 4. Molecular structure of the dioxide of 7 (7a). The displacement ellipsoids are
shown on a 50% level. Hydrogen atoms and solvent molecules are omitted for clarity.
Fig. 6. Molecular structure of 10$C4H8O$½C2H5OH. Displacement ellipsoids are shown
on a 50% level. The counter-ions, solvent molecules and hydrogen atoms are omitted
for clarity.
[M-C8H7N2]þ, 615.2 [M]þ, 647.2 [MþO]þ, 677.9 [MþCu]þ.
C34H32N8P2 6MeOH (806.88): calcd. C 59.5, H 6.9, N 13.9; found C
59.9, H 6.3, N 13.5.
{1H}-NMR (125 MHz, 296 K, CDCl3):
(NCH3), 124.4 (C5), 137.3 (C4), 142.3 (C2). 31P{1H}-NMR (81 MHz,
d
/ppm ¼ 22.4 ((CH2)2), 32.8
4.4. Synthesis of bis(di-1-methylimidazol-5-ylphosphino)ethane,
5-dimpeNMe (4)
296 K, CDCl3):
d
/ppm ¼ e73 (s). MALDI TOF (DIT, CHCl3):
m/z ¼ 415.0 [MþH]þ, 431.0 [MþOþH]þ. C18H24N8P2 2MeOH H2O
(450.41): calcd. C 48.4, H 6.9, N 22.6; found C 48.1, H 6.3, N 22.3.
To a solution of 5-bromo-1-methylimidazole (2.13 g, 13.2 mmol)
in 20 mL of dichloromethane 4.4 mL of ethylmagnesium bromide in
diethyl ether (3.0 M, 4.4 mL, 13.2 mmol) were added at ambient
temperature. The solution was stirred for 1 h at ambient temper-
ature, then bis(dichlorophosphino)ethane (0.4 mL, 2.6 mmol) in
dichloromethane (10 mL) was added drop-wise. The suspension
was stirred over night, then a brine solution (5 mL) added and the
organic layer extracted with bidistilled water (3 ꢃ 10 mL) and dried
over Na2SO4. After filtration and evaporation the residue was
stirred in n-hexane, the white precipitate isolated by filtration and
dissolved in methanol. After filtration, n-hexane was added to the
clear filtrate and the precipitate dried in vacuo to yield 0.57 g (62%)
4.5. Synthesis of bis(di-2-isopropylimidazol-4(5)-ylphosphino)
ethane, 4-dimpeiPr (5)
To 1-diethoxymethyl-2-isopropylimidazol (2.3 g, 11 mmol) in
thf (100 mL) was added tert-butyl lithium in hexane (1.6 M, 6.9 mL,
11 mmol) at e78 ꢂC. The solution was stirred at e78 ꢂC for 1 h and
then bis(dichlorophosphino)ethane (500 mg, 0.32 mL, 2.2 mmol)
added. The reaction mixture was stirred over night at ambient
temperature, ammonia solution (3 mL) added and concentrated in
vacuo to 20 mL. Dichloromethane (100 mL) was added and the
organic phase extracted with brine. The organic layer was sepa-
rated, all volatiles removed in vacuo, 100 mL acetone/water (10:1)
added and the solution stirred at ambient temperature over night.
The resulting white precipitate was filtered, washed with acetone
and dried in vacuo to yield 0.48 g (42%) of the product. 1H-NMR
of a white solid. 1H-NMR (500 MHz, 296 K, CDCl3):
4H, (CH2)2), 3.51 (s, 12H, NMe), 7.09 (s, 4 H, H4), 7.56 (s, 4H, H2). 13
d/ppm ¼ 2.20 (t,
C
(200 MHz, 296 K, MeOD-d4):
d
/ppm ¼ 1.28 (d, J ¼ 7.0 Hz, 24H, CH
(CH3)2), 2.03 (t, 4 H, (CH2)2), 3.04 (sept., J ¼ 7.0 Hz, 4H, CH(CH3)2),
7.00 (s, 4H, H4(5)). 13C{1H}-NMR (125 MHz, 296 K, MeOD-d4):
d
/ppm ¼ 20.5 (CH3), 28.2 (CH2), 48 (CH), 130.1 (C4(5)), 153.7 (C5(4)),
157.7 (C2). 31P{1H}-NMR (81 MHz, 296 K, MeOD-d4):
d
/ppm ¼ ꢀ63
(s). ESIþ (MeOH): m/z ¼ 417.5 [M-imiPr]þ, 527.5 [MþH]þ.
C26H40N8P2 1/2C3H6O 3/2H2O (582.32): calcd. C 56.7, H 8.0, N 19.2;
found C 56.4, H 7.6, N 19.6.
4.6. Synthesis of bis(dithiazol-2-ylphosphino)ethane, 2-dthiape (6)
A solution of thiazole (930 mg, 0.78 mL) in 100 mL of toluene
was cooled to e78 ꢂC and 6.3 mL n-butyl lithium in hexanes (1.6 M)
were added. The solution was stirred at e78 ꢂC for 2 h and then bis
(dichlorophosphino)ethane (500 mg, 0.32 mL, 2.2 mmol) was
added, the solution stirred for another hour at e78 ꢂC and over
night at ambient temperature. Concentrated ammonia solution
(5 mL) was added, the phases separated and the organic layer dried
over Na2SO4. The volatiles were removed in vacuo to yield a slightly
Fig. 5. Molecular structure of 9. The displacement ellipsoids are shown on a 50% level
and hydrogen atoms are omitted for clarity.

1896
P.C. Kunz et al. / Journal of Organometallic Chemistry 695 (2010) 1891e1897
Scheme 1. Reaction conditions for the preparation of the different 1,2-bis(diazoylphosphino)ethanes 1e9: i) neat 1-methyl-2-TMS-imidazole; ii) 1. DEM-imidazole, n-BuLi, thf, ꢀ78
ꢂC, 2. H2O/acetone; iii) 1-methylbenzimidazole, n-BuLi, thf, ꢀ78 ꢂC; iv) 5-bromoimidazole, EtMgBr, CH2Cl2; v) 1-DEM-2-isopropylimidazole, n-BuLi, thf, ꢀ78 ꢂC, 2. H2O/acetone; vi)
thiazole, n-BuLi, thf, ꢀ78 ꢂC; vii) benzothiazole, n-BuLi, thf, ꢀ78 ꢂC; viii) benzothiazole, n-BuLi, thf, ꢀ78 ꢂC; viii) 4-bromothiazole, EtMgBr, CH2Cl2; ix) 5-bromothiazole, EtMgBr,
CH2Cl2.
yellow solid. After solution in methanol, the product was precipi-
tated upon addition of diethyl ether and dried in vacuo to yield
0.58 g (62%) of a white solid. 1H-NMR (200 MHz, 296 K, CDCl3):
diethyl ether (3.0 M, 2.03 mL, 6.1 mmol) was added. The solution
was stirred for 1.5 h at ambient temperature, then bis(dichlor-
ophosphino)ethane (0.2 mL, 1.3 mmol) in dichloromethane (10 mL)
was added drop wise and the suspension stirred over night. The
mixture was quenched by addition of conc. ammonia (25%, 5 mL)
and brine (10 mL). The organic solvents were removed in vacuo, the
precipitate was removed by filtration, washed with bidistilled
water and diethyl ether and the off-white solid dried in vacuo. The
solid was dissolved in dichloromethane (50 mL), died over Na2SO4,
and after filtration and concentration in vacuo the product was
precipitated upon addition of diethyl ether. Yield 0.36 g (65%). 1H-
d
/ppm ¼ 2.73 (t, 4H, (CH2)2), 7.58 (d, 4H, J ¼ 3.0 Hz, H4/5), 8.06
(d, 4H, J ¼ 3.0 Hz, H4/5). 13C{1H}-NMR (125 MHz, 296 K, CDCl3):
d
/ppm ¼ 25.7 ((CH2)2), 123.8 (C4/5), 145.6 (C4/5), 167.9 (C2). 31P{1H}-
NMR (81 MHz, 296 K, CDCl3):
d
/ppm ¼ ꢀ23 (s). ESIþ (MeOH):
m/z ¼ 342.3 [M-C3H2NS]þ, 427.1 [MþH]þ, 449.3 [MþNa]þ.
C14H12N4P2S4 CH3OH (457.97): calcd. C 39.3, H 3.5, N 12.2; found C
39.2, H 3.3, N 11.9.
NMR (200 MHz, 296 K, CDCl3):
d
/ppm ¼ 2.64 (t, 4 H, (CH2)2), 7.44
4.7. Synthesis of bis(dibenzothiazol-2-yl)ethane,2-dbthiape (7)
(m, 4H). 13C{1H}-NMR (125 MHz, 296 K, CDCl3):
d/ppm ¼ 25.4
((CH2)2), 122.3 (C2), 128.0 (C5), 168.2 (C4). 31P{1H}-NMR (81 MHz,
Benzothiazole (1.13 mL, 10.0 mmol) in thf (100 mL were treated
with n-butyl lithium (1.6 M in hexane, 6.3 mL, 10.0 mmol) at
e78 ꢂC. The deep red solution was stirred at e78 ꢂC for 90 min and
then bis(dichlorophosphino)ethane (500 mg, 0.32 mL, 2.2 mmol)
was added, the solution stirred for another hour at e78 ꢂC and over
night at ambient temperature. Ammonia solution was added
(20 mL), stirred and the suspension concentrated to about 80 mL in
vacuo. The precipitate was filtered, washed with water (100 mL)
and ethyl ether (100 mL) and dried in vacuo. Yield 1.09 g (78%).
296 K, CDCl3):
d
/ppm ¼ ꢀ19 (s). EI MS (Pt, 200 ꢂC): m/z (%) ¼ 426
(10.6) [M]þ. C14H12N4P2S4 3.5CHCl3 (838.65): calcd. C 24.9, H 1.9, N
6.6; found C 25.2, H 1.7, N 6.9.
4.9. Synthesis of bis(dithiazol-5-ylphosphino)ethane, 5-dthiape (9)
To
a solution of 5-bromothiazole (0.96 g, 5.7 mmol) in
dichloromethane (100 mL) a solution of ethylmagnesium bromide
in diethyl ether (3.0 M, 2.01 mL, 5.7 mmol) was added. The solution
was stirred for 1.5 h at ambient temperature, then bis(dichlor-
ophosphino)ethane (0.27 g, 1.2 mmol) in dichloromethane (10 mL)
was added drop-wise and the suspension stirred over night. The
mixture was quenched by addition of conc. ammonia (25%, 5 mL).
The mixture was filtered through a plug of Celite, the organic layer
extracted with bidistilled water and the aqueous layer with
dichloromethane. The combined organic layers were dried over
Na2SO4, and after filtration and all volatiles were removed in vacuo.
The product was washed with bidistilled water and diethyl ether
and dried in vacuo. Yield 0.35 g (58%). 1H-NMR (200 MHz, 296 K,
1H-NMR (200 MHz, 296 K, CDCl3):
7.30e7.59 (m, 8H), 7.78e7.85 (m, 4H), 8.02e8.10 (m, 4H). 13C{1H}-
NMR (125 MHz, 296 K, CDCl3):
/ppm ¼ 25.0, 121.8, 124.0, 126.0,
d
/ppm ¼ 3.01 (t, 4H, (CH2)2),
d
126.5, 137.3, 155.0. 31P{1H}-NMR (81 MHz, 296 K, CDCl3):
d
/ppm ¼ ꢀ15 (s). MALDI TOF (DIT, CHCl3): m/z ¼ 626.9 [M]þ, 642.0
[MþO]þ, 658.9 [Mþ2OþH]þ, 688.9 [MþCu]þ. C30H20N4P2S4 H2O
(644.01): calcd. C 55.9, H 3.4, N 8.7; found C 56.1, H 3.4, N 8.6.
4.8. Synthesis of bis(dithiazol-4-ylphosphino)ethane, 4-dthiape (8)
To a solution of 4-bromothiazole (1 g, 6 mmol) in dichloro-
methane (200 mL) a solution of ethylmagnesium bromide in
CDCl3):
d
/ppm ¼ 2.15 (t, 4 H, (CH2)2), 8.04 (m, 4H), 9.01 (s, 4H). 13
C

P.C. Kunz et al. / Journal of Organometallic Chemistry 695 (2010) 1891e1897
1897
{1H}-NMR (125 MHz, 296 K, CDCl3):
d
/ppm ¼ 28.5 ((CH2)2), 132.5
least-squares methods on F2 with SHELXL-97 [28]. The structures
were checked for higher symmetry with help of the program Platon
[29]. A disordered THF molecule was found in 10$C4H8O$½C2H5OH,
the two orientations were refined with a ratio of 6:4. In addition
a half occupied ethanol molecule near a centre of inversion was
found. In both cases, appropriate restraints were applied.
(C5), 151.0 (C4), 159.0 (C2). 31P{1H}-NMR (81 MHz, 296 K, CDCl3):
d
/ppm ¼ ꢀ52 (s). EI MS (Pt, 210 ꢂC): m/z (%) ¼ 426 (2.4) [M]þ.
C14H12N4P2S4 H2O (443.95): calcd. C 37.8, H 3.2, N 12.6; found C
38.2, H 3.3, N 12.1.
4.10. Synthesis of [(2)2Rh2Cl2]Cl2 (10)
Appendix. Supporting material
[{(CO)2RhCl}2] (30 mg, 77
mmol) was added to a solution of 2
(63.9 mg, 154 mol) in CHCl3. The solution was stirred at ambient
m
Supplementary information associated with this article could be
found online, at doi:10.1016/j.jorganchem.2010.04.028
temperature for 1.5 h. The volume was concentrated to one third,
then n-hexane added. The resulting red precipitate was removed by
centrifugation, washed with n-hexane and dried in vacuo. Yield
19 mg, 21%. Crystals were grown form EtOH/thf. 1H NMR (200 MHz,
References
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7.76 (s, 4H, Him). 13C{1H} NMR (125 MHz, 296 K, MeOD-d4):
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