The reaction of (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid with carbodiimide reagents: Characterisation of the acid anhydride and urea products

Article abstract of DOI:10.1016/j.jorganchem.2008.07.042

Interaction of (S_p)-2-(diphenylphosphino)ferrocenecarboxylic acid [(S_p)-1] with N,N′-dicyclohexylcarbodiimide (DCC) and N-ethyl-N′-[3-(dimethylamino)propyl]carbodiimide (EDC) have been investigated in order to study the reacting system itself and to characterise side-products typically arising during the diimide-promoted condensation of acid (S_p)-1 with nucleophiles. The reaction between (S_p)-1 and DCC was found to give preferentially the respective urea derivative in the absence of a base, and (S_p)-2-(diphenylphosphino)ferrocenecarboxylic anhydride [(S_p,S_p)-3] when the same reaction was performed in the presence of 4-(dimethylamino)pyridine (DMAP). With EDC, the preference for a reaction pathway was less pronounced: whereas the reaction without the base afforded exclusively the corresponding urea, that in the presence of DMAP yielded a mixture of the urea and anhydride (S_p,S_p)-3.

Full text of DOI:10.1016/j.jorganchem.2008.07.042

Journal of Organometallic Chemistry 693 (2008) 3430–3434
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Journal of Organometallic Chemistry
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The reaction of (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid with
carbodiimide reagents: Characterisation of the acid anhydride and urea products
b
a,
ˇ a
ˇ
ˇ
ˇ
*
Martin Lamac , Josef Cvacka , Petr Štepnicka
a Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 12840 Prague 2, Czech Republic
b
ˇ
Institute of Organic Chemistry and Biochemistry, v.v.i., Academy of Sciences of the Czech Republic, Flemingovo námestí 2, 166 10 Prague 6, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Interaction of (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid [(Sp)-1] with N,N0-dicyclohexylcarbo-
diimide (DCC) and N-ethyl-N0-[3-(dimethylamino)propyl]carbodiimide (EDC) have been investigated in
order to study the reacting system itself and to characterise side-products typically arising during the dii-
mide-promoted condensation of acid (Sp)-1 with nucleophiles. The reaction between (Sp)-1 and DCC was
found to give preferentially the respective urea derivative in the absence of a base, and (Sp)-2-(diphenyl-
phosphino)ferrocenecarboxylic anhydride [(Sp,Sp)-3] when the same reaction was performed in the pres-
ence of 4-(dimethylamino)pyridine (DMAP). With EDC, the preference for a reaction pathway was less
pronounced: whereas the reaction without the base afforded exclusively the corresponding urea, that
in the presence of DMAP yielded a mixture of the urea and anhydride (Sp,Sp)-3.
Article history:
Received 4 June 2008
Received in revised form 21 July 2008
Accepted 28 July 2008
Available online 17 August 2008
Keywords:
Ferrocene
Carboxylic acids
Urea derivatives
Carbodiimide coupling
Phosphines
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Results
The research into ferrocene ligands represents an active re-
search area, which is continually stimulated by numerous practical
applications [1]. Aiming at new phosphinocarboxylic donors [2,3],
we [4] and others [5] have previously reported about the prepara-
tion of (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid, (Sp)-1,
via hydrolysis of the corresponding chiral oxazoline. Later, Breit
and Breuninger devised a practical synthesis of both enantiomers
of this acid based on ortho-directed lithiation of ferrocenecarbox-
ylic acid and subsequent resolution of racemic 1 via diastereoiso-
2.1. Reactivity studies
In order to study the reaction of acid (Sp)-1 with diimides we
performed a series of experiments with DCC and EDC in the pres-
ence and the absence of 4-(dimethylamino)pyridine (DMAP) as a
base. The reactions were performed similarly as described in Ref.
[6] – but without any nucleophile (alcohol or amine) added, and
proceeded reproducibly as indicated by repeated runs. Representa-
tive experiments are described in Section 4.
meric esters with
D
-glucose diacetonide [6]. Acid 1 has already
The reaction of (Sp)-1 with an excess of DCC (1.25 equiv.) affor-
ded
found manifold use in enantioselective catalysis: it was applied di-
rectly as a catalyst component [7], and also utilised as a chiral
building block in the preparation of chiral amidophosphine ligands
[5a,5b,7b,8] and an efficient chiral auxiliary [9].
In view of our continuing interest in the preparation of new
amide derivatives from (Sp)-1 [7b] as well as some related ferro-
cene phosphinocarboxylic acids [2] via diimide-promoted amide
coupling [10], we decided to optimise the amidation procedure
and possibly characterise any reaction by-products. In the present
study, we report the reactivity of the commonly used diimides,
N,N0-dicyclohexylcarbodiimide (DCC) and N-(3-dimethylamino-
propyl)-N0-ethylcarbodiimide (EDC), with (Sp)-1 both in the pres-
ence and the absence of a base.
N,N0-dicyclohexyl-N-[(Sp)-2-(diphenylphosphino)ferrocene-
carbonyl]urea [(Sp)-2a], slightly contaminated with anhydride
(Sp,Sp)-3 (ca. 5 mol.-% according to NMR spectra). The amount of
isolated (Sp)-2a corresponded to 87% yield. A similar reaction per-
formed in the presence of one molar equivalent of DMAP yielded
(Sp,Sp)-3 as the vastly dominating component in the product mix-
ture (94 mol.-%); the only other detectable product was (Sp)-2a. A
subsequent crystallisation of the mixture from ethyl acetate-pen-
tane removed the urea derivative, affording analytically pure
(Sp,Sp)-3 as an orange microcrystalline solid (see Scheme 1).
Replacing DCC with EDC did not basically change the reaction
course. First, the reaction between (Sp)-1 and EDC (2 molar equiv.)
gave exclusively N-[3-(dimethylamino)propyl]-N0-ethyl-N-[(Sp)-2-
(diphenylphosphino)ferrocenecarbonyl]urea [(Sp)-2b] in 91%
isolated yield. The isomeric product, N-[3-(dimethylamino)pro-
pyl]-N0-ethyl-N0-[(Sp)-2-(diphenylphosphino)ferrocenecarbonyl]urea
* Corresponding author. Fax: +420 221 951 253.
E-mail address: stepnic@natur.cuni.cz (P. Štepnicka).
ˇ
ˇ
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.07.042

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M. Lamac et al. / Journal of Organometallic Chemistry 693 (2008) 3430–3434
3431
CO H
2
PPh
2
Fe
(S )-1
p
1
R N
2
NR
C
(DMAP)
O
O
2
R
C
C
N
Fe
Fe
PPh
2
N
+
H
1
O
PPh
R
2
Fe
C
O
C
O
Fig. 1. Temperature dependence of amide proton chemical shift for urea (Sp)-2a.
The spectra were recorded on a 0.01 M CDCl3 solution and are referenced to
tetramethylsilane. Solid line shows least-square linear fit of the data.
PPh
2
(S )-2
p
(S ,S )-3
p p
1
2
R
R
dHðNHÞ ¼ ꢀ0:0056ð2ÞT þ 7:71ð6Þ ðr2 ¼ 0:993Þ:
The negative temperature coefficient,
indicates that the NH groups experience less hydrogen-bonding
at elevated temperatures while the magnitude of d/ T could be
Cy
(CH ) NMe Et
Cy
(S )-2a
p
(S )-2b
p
(S )-2b'
p
Dd/D
T = 5.6(2) ppb Kꢀ1
2 3
2
Et
(CH ) NMe
2 3
2
D
D
regarded as indicative of preferred formation of inter- rather than
intramolecular hydrogen bonds [13].
Scheme 1. The reaction of (Sp)-1 with diimides (DCC: R1/R2 = Cy/Cy, EDC: R1/
R2 = Et/(CH2)3NMe2; Cy = cyclohexyl).
In summary, the spectral data implicate that in CHCl3 and CDCl3
as poorly hydrogen-bonding solvents, intermolecular N–Hꢁ ꢁ ꢁO@C
hydrogen bonds are most probably the dominant interactions be-
tween the molecules of (Sp)-2a. This conclusion is in line with
the fact that all structurally characterised mono-acyl N,N0-dicyclo-
hexyl ureas [14] possess conformations unsuitable for the forma-
tion of intramolecular N–Hꢁ ꢁ ꢁO hydrogen bonds. Formation of an
intramolecularly stabilised structure such as I (Scheme 2) would
require a favourable donor–acceptor distance and orientation of
the NH and its more distant C@O bonds. Although the basic geo-
metric parameters are not strikingly unfavourable [15], none of
the structurally characterised compounds forms an intramolecular
Oꢁ ꢁ ꢁHN hydrogen bond in the solid state due to mutual rotation of
the {CON} planes forming the acyl-urea moiety. Such twisting is
typical also for ferrocenyl-substituted N,N0-dicyclohexyl ureas (II
in Scheme 2). The dihedral angles of the {CON} planes in (ferrocen-
ecarbonyl)ureas are as high as 86.3(3)° and 89(1)° in N-ferrocene-
carbonyl-N,N0-dicyclohexylurea (III; refcode OBAYIZ [16]) and
1,10-bis[(N,N0-dicyclohexylureido)carbonyl]ferrocene (IV; refcode
EBIXUJ [17]), respectively, whilst the 10-functionalised analogues
show lower rotations [cf. 61.1(3)° for N-[10-(N-cyclohexyl-
carbamoyl)ferrocenecarbonyl]-N,N0-dicyclohexylurea (V; refcode
CAPJAF [18]), and 39.6(3)° for N-[10-(acetylamino)ferrocenyl]-
N,N0-dicyclohexylurea (VI; refcode DADFAQ [19])].
[(Sp)-2b0], was not detected in the crude product. Second, the same
reaction of (Sp)-1 performed in the presence of DMAP afforded a
mixture whose subsequent chromatographic purification allowed
for isolation of anhydride (Sp,Sp)-3 contaminated by minor
amounts of its methanolysis product, methyl (Sp)-2-(diphenyl-
phosphino)ferrocenecarboxylate (Sp)-4 as the less polar compo-
nents, and the more polar (Sp)-2b as the major product (55%
isolated yield). Similarly to the previous case, the isomeric urea
(Sp)-2b0 was not detected.
2.2. Characterisation of the products
Urea (Sp)-2a displays two strong carbonyl stretching bands at
1698 and 1521 cmꢀ1 in its IR spectrum, while the 1H NMR spec-
trum comprises a complex multiplet due to cyclohexyl (Cy) groups,
signals attributable to 2-(diphenylphosphino)ferrocenyl group, and
a
CH-coupled doublet due to the amide proton at dH 6.05
(3JHH = 7.7 Hz). Likewise, the 13C{1H} NMR spectra of (Sp)-2a com-
bine two sets of Cy signals (five diastereotopic CH2 and one CH
per the ring) with the signals due to the phosphinoferrocenyl and
urea moieties. The C@O carbons resonate at dC 154.70 (NC(O)N)
and 171.24 (C(O)N), the latter as a doublet due to scalar coupling
with the proximal phosphorus atom (3JPC = 2 Hz). The observed
chemical shifts compare favourably with those reported for
FcC(O)N(Cy)C(O)NHCy (Fc = ferrocenyl) [11]. The 31P{1H} NMR
spectrum of (Sp)-2a displays a single resonance at dP ꢀ20.0, indi-
cating the presence of an unchanged diphenylphosphino group [4].
The spectral data provide also an insight into the nature of
‘molecular’ interactions of (Sp)-2a. For instance, the formation of
N–Hꢁ ꢁ ꢁacceptor hydrogen bonds is already indicated by IR spectra
H
Cy
Cy
Cy
O
C
N
C
HN
O
C
O
Y
O
N
ferrocenyl
Cy
that display a broad asymmetric m
NH band at ca. 3270 cmꢀ1 in Nu-
I
II
jol and at ca. 3425 cmꢀ1 when recorded on a 0.01 M solution in
CHCl3. In 1H NMR spectra, the position of the amide proton reso-
nance changes with the sample temperature [12], the parameters
showing a good linear correlation (Fig. 1):
Scheme 2. A hypothetic planar, hydrogen-bonded conformation (I) and the
conformation typically encountered in the crystal structures of compounds
featuring C(ferrocenyl)C(O)NACyCB(O)NHCy moiety (Cy = cyclohexyl) (II). For II, a
projection along the NAꢁ ꢁ ꢁCB line is shown.

ˇ
3432
M. Lamac et al. / Journal of Organometallic Chemistry 693 (2008) 3430–3434
O
O
R
N
R
N
rearrangement
Y
C
O
C
O
H
Y
N
N
H
(
S
)-2
p
R
R
N
R
Y
R
N
N
C
+
N
H
C
H
O
Y
O
C
O
(
Y
H
O
C
Y
H
C
O
C
O
NMe
O
S )-1
p
2
S )-5
p
(
Scheme 3. Selected 13C gHMBC (H ? C) and NOESY (H M H) correlations observed
in the NMR spectra of (Sp)-2b (Y stands for the (Sp)-2-(diphenylphosphino)ferroce-
nyl group).
(
S
,S
)-3
p
p
+
(
S )-1
p
R
N
R
N
Urea (Sp)-2b was isolated as a non-crystallising amorphous so-
lid, possessing a strong tendency to retain the reaction solvents. In
IR spectra, it exerts characteristic mC
C
O
6
@
bands (1706 and
o
1526 cmꢀ1) while its 1H NMR spectrum shows characteristic mul-
tiplets attributable to both aliphatic pendants and to the 1,2-disub-
stituted ferrocene framework. The 13C NMR spectrum of (Sp)-2b is
also consistent with the formulation. The C@O signals are observed
with the characteristic values, shifted to lower-fields than for (Sp)-
2a [dC 156.12 (NC(O)N), 173.33 (d, 3JPC = 3 Hz, CC(O)N)]. Finally, the
position of the 31P{1H} NMR resonance (dP ꢀ19.6) again indicates
that phosphine group remains unaffected during the reaction.
When combined with correlated 2D experiments, the NMR spectra
allowed to clearly distinguish between the two possible isomeric
forms [(Sp)-2b and (Sp)-2b0], the long-range H–C correlation (13C
gHMBC, Scheme 3) between the amide proton and the methylene
carbon of the ethyl group being of particular diagnostic
importance.
Scheme 4. Schematic depiction of the plausible reaction sequence (Y denotes the
(Sp)-2-(diphenylphosphino)ferrocenyl group).
However, the tautomerism of cyclic forms of EDC [11,23] or a pre-
ferred configuration of the O-acyl-urea intermediate may play
some role.
Finally, it is worth pointing out that the formation of the urea
derivatives (Sp)-2a/2b represents a competitive, non-productive
pathway in the synthesis of esters or amides from acid (Sp)-1. For-
tunately, it can be suppressed by a proper choice of the coupling
agent (diimide) and, particularly, by the presence of a nucleophilic
reaction partner, which usually reacts preferentially. The latter was
already demonstrated with the amidation of (Sp)-1 [7b] in case of
which no (Sp)-2b was detected in the reaction mixture.
At first sight, the 1H NMR spectra of anhydride (Sp,Sp)-3 do not
differ much from those of the parent acid (Sp)-1 (cf.
D
dH(C5H5) = 0.08 ppm, DdH(C5H3) 6 0.05 ppm) [4]. The differences
in the 13C NMR spectrum are more pronounced. Most significantly,
the C@O resonance of (Sp,Sp)-3 is observed as a phosphorus-cou-
pled doublet at dC 167.04, i.e. shifted by ca. 10 pm to higher field
as compared to the acid. In IR spectra, the presence of the carbo-
xanhydride moiety is reflected by a pair of strong bands attribut-
able to coupled C@O stretching vibrations at 1767 and
1713 cmꢀ1. Position of these bands corresponds with that reported
for ferrocenecarboxylic anhydride [20].
4. Experimental
4.1. General considerations
All syntheses were performed under an argon atmosphere and
with exclusion of direct daylight. Dichloromethane was dried over
anhydrous potassium carbonate and distilled from CaH2. Acid (Sp)-
1 was synthesised by the literature procedure [4]. Other chemicals
and solvents were used as received from commercial sources (Flu-
ka, Aldrich; solvents from Penta).
3. Discussion
NMR spectra were measured on a Varian UNITY Inova 400 spec-
trometer at 25 °C. Chemical shifts (d/ppm) are given relative to
internal tetramethylsilane (1H and 13C) or to an external 85% aque-
On the whole, the observed reactivity in the (Sp)-1–carbodiim-
ide systems is in accordance with the previous reports describing
the preparation of N,N0-diorganyl ureas from simple
[11,16,17,20a,20b] and functionalised [19,16] ferrocenecarboxylic
acids and N,N0-disubstituted carbodiimides. However, the exact
ous H3PO4 (
31P), all set to 0 ppm. Detailed assignment of the NMR
signals is based on COSY, NOESY, 13C gHSQC, and 13C gHMBC two-
dimensional spectra. IR spectra were recorded on an FT IR Nicolet
Magna 760 instrument in the range of 400–4000 cmꢀ1. Electro-
spray (ESI) mass spectra were recorded with a Waters Q-Tof Micro-
mass or a Thermo Scientific LTQ Orbitrap XL hybrid FT MS
spectrometer on methanol or methanol/CHCl3 solutions. Optical
rotations were determined with an automatic polarimeter Autopol
III (Rudolph Research) at room temperature.
product distribution (anhydride/urea) differs for
acid–diimide combination.
a particular
A tentative reaction sequence leading to (Sp)-2 is depicted in
Scheme 4 [21]. The reaction is probably initiated with addition of
the carboxylic acid across the diimide to give an O-acyl-urea (Sp)-
5. In the absence of a nucleophile (e.g., alcohol or amine), (Sp)-5
can only rearrange to give unreactive N-acyl-urea or react with an-
other molecule of the acid to give anhydride (Sp)-2 and urea 6.
Added DMAP (base) can change the reaction course (or at least fa-
vour one of the reaction pathways) via ‘‘activation” of the interme-
diate for the subsequent reaction yielding the anhydride, acting
probably as an acyl transfer agent [22]. The preferential formation
of (Sp)-2b over the isomeric product (Sp)-2b0 remains yet unclear.
4.2. The reaction of (Sp)-1 with DCC in the absence of a base
DCC (31 mg, 0.15 mmol) was added to a solution of (Sp)-1
(50 mg, 0.12 mmol) in dry dichloromethane (5 mL). The resulting
solution was stirred at room temperature overnight (20 h), filtered
(PTFE syringe filter, 0.45 lm pore size) and evaporated under

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M. Lamac et al. / Journal of Organometallic Chemistry 693 (2008) 3430–3434
3433
vacuum. Column chromatography on silica gel (hexane–diethyl
4.7. Analytical data for (Sp)-2b
ether 1:1) afforded the product (Sp)-2a (65 mg) contaminated with
a small amount of anhydride (Sp,Sp)-3 (ca. 5 mol.-% according to
NMR analysis).
1H NMR (CDCl3): d 1.14 (t, 3JHH = 7.3 Hz, 3H, CH2CH3), 1.60–1.80
(m, 2H, CH2CH2CH2), 2.23 (s, 3H, NMe2), 2.20–2.40 (m, 2H,
3
CH2NMe2), 3.21 (m, 2H, NHCH2CH3), 3.48 (dt, JHH = 7.6 Hz,
4.3. The reaction of (Sp)-1 with DCC in the presence of a base
2JHH = 14.2 Hz, 1H, NCH2CH2), 3.75 (ddd, 3JHH = 5.0 Hz, 3JHH = 8.0 Hz,
2JHH = 14.1 Hz, 1H, NCH2CH2), 3.92 (m, 1H, C5H3), 4.18 (s, 5H, C5H5),
4.39 (apparent t, J = 2.6 Hz, 1H, C5H3), 4.67 (m, 1H, C5H3), 7.22–7.58
The reaction was performed as above except that DMAP was
added to the reaction mixture. Thus, DCC (31 mg, 0.15 mmol)
was added to a solution of (Sp)-1 (50 mg, 0.12 mmol) and DMAP
(15 mg, 0.12 mmol) in dry dichloromethane (5 mL). After the reac-
tion mixture had been stirred at room temperature overnight
3
(m, 10H, PPh2), 8.94 (t, JHH = 5.3 Hz, 1H, NH). 13C{1H} NMR
(CDCl3): d 14.78 (CH2CH3), 26.24 (CH2CH2CH2), 35.30 (NHCH2CH3),
44.73 (NMe2 and NCH2CH2), 55.98 (CH2NMe2), 70.34 (CH of C5H3),
70.52 (d, JPC = 2.5 Hz, CH of C5H3), 71.39 (C5H5), 73.38 (d, JPC = 4 Hz,
CH of C5H3), 80.90 (d, JPC = 16 Hz, Cipso of C5H3), 85.20 (d,
(20 h), it was filtered (PTFE syringe filter, 0.45 lm pore size) and
3
evaporated under vacuum. Subsequent column chromatography
(silica gel, hexane–diethyl ether 1:1) and evaporation gave the
product (47 mg) which, according to NMR spectra, consisted of
anhydride (Sp,Sp)-3 (94 mol.-%) and a minor amount of (Sp)-2a.
Crystallisation of this mixture from ethyl acetate-pentane at
+4 °C afforded analytically pure (Sp,Sp)-3.
JPC = 17 Hz, Cipso of C5H3), 128.12, 128.20 (2ꢂ d, JPC = 7 Hz, CHm
of PPh2); 128.23, 129.02 (2ꢂ s, CHp of PPh2); 132.72, 134.80 (2ꢂ
d, 2JPC = 21 Hz, CHo of PPh2); 138.23, 139.09 (2ꢂ d, 1JPC = 13 Hz, Cipso
of PPh2); 156.12 (NC(O)N), 173.33 (d, 3JPC = 2.5 Hz, C(O)N). 31P{1H}
ꢀ1
~
NMR (CDCl3): d ꢀ19.6 (s). IR (RAS):
m=cm 3289, 3203 (m), 1706
(vs), 1570 (m), 1526 (s), 1435 (s), 1242 (s), 1202 (m), 1136 (s),
1002 (m), 963 (w), 823 (s), 761 (vs), 700 (vs). MS (ESI+): m/z 570
([M+H]+), 499 ([M+HꢀEtNCO]+), 397 ([(C5H5)Fe(C5H3)(PPh2)CO]+).
HR MS (ESI+) calcd. for C31H36N3O2P56Fe (M+) 569.1895, found
4.4. The reaction of (Sp)-1 with EDC in the absence of a base
EDC (31 mg, 0.2 mmol) was added to a solution of (Sp)-1 (41 mg,
0.1 mmol) in dry dichloromethane (4 mL). The resulting solution
was stirred at room temperature overnight (20 h) and then evapo-
rated under vacuum. The residue was purified by column chroma-
tography (silica gel, dichloromethane–methanol 10:1, gradually
increased to 5:1). Removal of the solvents under reduced pressure
gave pure urea (Sp)-2b. Yield: 52 mg (91%).
569.1902. [
a
]
D = ꢀ109° (c = 1.0, CHCl3).
4.8. Analytical data for (Sp,Sp)-3
1H NMR (CDCl3): d 3.84 (m, 1H, C5H3), 4.32 (s, 5H, C5H5), 4.49
(apparent t, J = 2.6 Hz, 1H, C5H3), 5.03 (m, 1H, C5H3), 7.15–7.55
(m, 10H, PPh2). 13C{1H} NMR (CDCl3): d 71.46 (C5H5), 72.78 (CH
of C5H3), 73.58 (d, JPC = 15 Hz, Cipso of C5H3), 74.99 (CH of C5H3),
76.50 (d, JPC = 5 Hz, CH of C5H3), 80.60 (d, JPC = 18 Hz, Cipso of
4.5. The reaction of (Sp)-1 with EDC in the presence of a base
3
C5H3), 128.10, 128.23 (2ꢂ d, JPC = 6 Hz, CHm of PPh2); 128.33,
2
EDC (78 mg, 0.50 mmol) was added to a solution of (Sp)-1
(104 mg, 0.25 mmol) and DMAP (30 mg, 0.25 mmol) in dry dichlo-
romethane (8 mL) and the resulting solution was stirred at room
temperature overnight (20 h). Then, the reaction mixture was
washed twice with saturated aqueous NaCl solution, the organic
layer was dried over MgSO4 and evaporated under vacuum. A sub-
sequent purification by column chromatography (silica gel, dichlo-
romethane–methanol 20:1, gradually increased to 5:1) afforded
two major bands. The first fraction (32 mg after evaporation) con-
tained mostly anhydride (Sp,Sp)-3 accompanied with a small
amount of methyl ester (Sp)-4 resulting by methanolysis of the
anhydride. Evaporation of the second band afforded urea (Sp)-2b
as a red oil, which solidifies when stored at 4 °C. Yield: 78 mg
(55%).
129.19 (2ꢂ s, CHp of PPh2); 132.19, 135.11 (2ꢂ d, JPC = 21 Hz,
1
CHo of PPh2); 137.98, 139.06 (2ꢂ d, JPC = 13 Hz, Cipso of PPh2);
3
167.04 (d, JPC = 4 Hz, C@O). 31P{1H} NMR (CDCl3): d ꢀ16.8 (s). IR
ꢀ1
~
(Nujol): m=cm 1767 (s), 1713 (m), 1435 (s), 1417 (w), 1317 (w),
1238 (s), 1166 (w), 1090 (s), 1042 (m), 1021 (vs), 956 (m), 742
(s), 697 (s), 501 (m). HR MS (ESI+) calcd. for C46H36NaO3P256Fe2
([M+Na]+) 833.0736, found 833.0728. [
a
]
D = ꢀ76° (c = 1.0, CHCl3).
4.9. Analytical data for (Sp)-4
1H NMR (CDCl3): d 3.69 (s, 3H, OCH3), 3.72 (m, 1H, C5H3), 4.21 (s,
5H, C5H5), 4.44 (m, 1H, C5H3), 5.05 (m, 1H, C5H3), 7.15–7.55 (m,
10H, PPh2). 31P{1H} NMR (CDCl3): d ꢀ16.4 (s). HR MS (ESI+) calcd.
for C24H21O2P56Fe (i.e., [M+H]+) 429.0707, found 429.0726. NMR
data are in agreement with those reported in Ref. [24].
4.6. Analytical data for (Sp)-2a
Acknowledgements
1H NMR (CDCl3): d 0.82–2.00 (m, 20H, Cy CH2), 3.53 (m, 1H,
NHCy CH), 3.89 (m, 1H, C5H3), 3.95 (tt, J = 3.6, 11.9 Hz, 1H, NCy
CH), 4.22 (s, 5H, C5H5), 4.33 (apparent t, J = 2.6 Hz, 1H, C5H3),
This work is a part of the long-term research projects supported
by the Ministry of Education, Youth and Sports of the Czech Repub-
lic (Project Nos. MSM0021620857 and LC06070).
3
4.73 (m, 1H, C5H3), 6.05 (d, JHH = 7.7 Hz, 1H, NH), 7.26–7.56 (m,
10H, PPh2). 13C{1H} NMR (CDCl3): d 24.96 (2 C), 25.30, 25.55,
26.23, 26.43, 30.09, 31.51, 32.52, 33.16 (10ꢂ CH2 of Cy); 49.89,
57.79 (2ꢂ CH of Cy); 69.72 (CH of C5H3), 70.00 (CH of C5H3),
71.58 (C5H5), 73.61 (d, JPC = 4 Hz, CH of C5H3), 82.40 (d, JPC = 16 Hz,
Cipso of C5H3), 83.89 (d, JPC = 15 Hz, Cipso of C5H3), 128.25, 128.31
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3
(2ꢂ d, JPC = 5 Hz, CHm of PPh2); 128.52, 128.91 (2ꢂ s, CHp of
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2
PPh2); 133.04, 134.47 (2ꢂ d, JPC = 21 Hz, CHo of PPh2); 138.05,
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1
139.91 (2ꢂ d, JPC = 15 Hz, Cipso of PPh2); 154.70 (NC(O)N), 171.24
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ꢀ1
~
m
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