Formation of chiral ionic liquids and imidazol-2-ylidene metal complexes from the proteinogenic aminoacid l-histidine

Article abstract of DOI:10.1016/j.jorganchem.2005.07.115

Treatment of the amino acid derivative Bz-His-OMe with excess n-propyl bromide gave the corresponding histidinium salt [Bz-His(n-propyl) ₂-OMe⁺Br^-]. It features a melting point of 39 °C and may serve as a useful readily av

Full text of DOI:10.1016/j.jorganchem.2005.07.115

Journal of Organometallic Chemistry 690 (2005) 5959–5972
www.elsevier.com/locate/jorganchem
Formation of chiral ionic liquids and imidazol-2-ylidene metal
complexes from the proteinogenic aminoacid L-histidine
1
*
Frithjof Hannig, Gerald Kehr, Roland Fro¨hlich , Gerhard Erker
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40, 48149 Mu¨nster, Germany
Received 5 July 2005; accepted 25 July 2005
Available online 22 September 2005
Abstract
Treatment of the amino acid derivative Bz-His-OMe with excess n-propyl bromide gave the corresponding histidinium salt [Bz-His(n-
propyl)2-OMe+Brꢀ]. It features a melting point of 39 ꢀC and may serve as a useful readily available optically active ionic liquid. Its
subsequent treatment with silver oxide gave the corresponding L-histidine derived chiral N-heterocyclic carbene complex [‘‘(car-
bene)2Ag Æ AgBr2’’]. Transmetallation by treatment with Pd(CH3CN)2Cl2 or [Rh(cod)Cl]2 led to the formation of the respective chiral
late metal imidazol-2-ylidene complexes [‘‘(carbene)2PdCl2’’] and [‘‘(carbene)RhCl(cod)’’], respectively. Four diastereomers of the square
planar palladium system were observed. Due to the additional chirality center in the L-histidine-derived ‘‘Arduengo-carbene ligand’’ two
diastereomers of the rhodium carbene complex were formed.
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Imidazolium salts; Arduengo-carbenes; Metal complexes; Bio-organometallic chemistry; Chiral ionic liquid
1. Introduction
surprisingly few examples that were derived from amino
acids [4–6].
N-Alkylated imidazolium salts (1) and imidazol-2-ylid-
enes (2) are chemically related [1]. The latter are usually
derived from the former by a deprotonation reaction at
carbon atom C2 of the heterocyclic ring system. Exam-
ples of both systems have found extensive use in organic
synthesis, in organometallic chemistry and catalysis. Suit-
ably substituted imidazolium salts (1) that are associated
with the right counteranions have served as ionic liquids,
which represent a class of very polar reaction media that
is finding a rapidly increasing current interest [2]. The
neutral stable carbenes 2 have found extensive use as
strong r-donating ligands in metal complex synthesis
and in catalysis [3]. From both the families of the com-
pounds 1 and 2 a limited number of enantiomerically en-
riched chiral variants has become known, among them
We have developed synthetic pathways to chiral deriv-
atives of 1 based on L-histidine and found that some
such systems featuring rather low melting points have a
potential to serve as useful ionic liquids. Subsequent
deprotonation makes L-histidine derived chiral imidazol-
2-ylidene derivatives or their respective metal complexes
available. Several examples that illustrate this synthetic
development will be presented and discussed in this
account.
*
Corresponding author. Tel.: +49 251 83 33221; fax: +49 251 8336503.
E-mail address: erker@uni-muenster.de (G. Erker).
X-ray crystal structure analyses.
1
0022-328X/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.115

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F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
2. Results and discussion
2.1. Formation of L-histidine-derived imidazolium salts: new
optically active ionic liquids
For this study, L-histidine (3) was O-protected by ester
formation (methyl or ethyl ester) and then N-benzoyl
(Bz) or N-tert-butoxycarbonyl (Boc) protected to give the
starting materials 4 (see Scheme 1). Treatment with excess
Meerweinꢀs reagent ½Et3OþBFꢀꢁ ð5Þ resulted in N- as well
4
as O-alkylation [7]. Starting from Bz-His-OMe (4a) [8] we
obtained a mixture of compounds (including transesterifi-
cation products) from which the main component (7a)
was isolated by chromatography and characterized by X-
ray diffraction. The reaction of 4b (R = C2H5) with 5 was
less complicated. It gave a mixture of 6b and 7b, from
which the N,N,O-tri-alkylated product 7b was isolated in
43%. The imino-ester 7b was also characterized by X-ray
diffraction (see Fig. 1). Unfortunately, the products 7 were
obtained racemized from these reactions. Apparently,
(reversible) deprotonation at Ca of these histidine deriva-
tives occurs too fast under the applied reaction conditions
[9] to make these routes useful and, consequently, a differ-
ent synthetic pathway was subsequently followed.
The problem was solved by treatment of Bz-His-OMe
(4a) with n-propylbromide in acetonitrile. The N-selective
di-alkylation [10] required 60 h at 65 ꢀC to go to comple-
tion. Product isolation was facilitated by the high water
solubility of 8. It was isolated on a 150 g scale in >70%
yield. The [Bz-His(n-propyl)2-OMe+Brꢀ] salt 8 was charac-
terized by X-ray diffraction (see Fig. 2). The 1H NMR spec-
trum of 8 shows the typical pairs of resonances for the two
positionally differentiated n-propyl groups. The 2-H reso-
nance of the imidazolium subunit is monitored at typical
d 9.62 (see Scheme 2).
Fig. 1. A view of the molecular structure of rac-7b (R = C2H5). Selected
bond lengths (A) and angles (ꢀ): N1–C2 1.331(6), N1–C5 1.370(6), N1–
˚
C11 1.497(6), C2–N3 1.327(6), N3–C4 1.392(6), N3–C31 1.481(6), C4–C5
1.344(6), C4–C6 1.485(7), C6–C7 1.524(6), C7–C8 1.520(6), C8–O81
1.192(6), C8–O82 1.316(6), C7–N9 1.469(5), N9–C10 1.266(5), C10–O10
1.364(5); C2–N1–C5 108.1(4), C2–N1–C11 125.7(5), C5–N1–C11 126.1(4),
N1–C2–N3 108.3(4), C2–N3–C4 109.4(4), C2–N3–C31 125.6(4), C4–N3–
C31 124.9(4), N3–C4–C5 105.2(4), C5–C4–C6 129.6(4), N3–C4–C6
125.0(4), N1–C5–C4 108.9(4), C4–C6–C7 112.0(4), C6–C7–C8 111.2(4),
C6–C7–N9 108.6(4), C8–C7–N9 106.8(4), C7–N9–C10 119.5(4), N9–C10–
O10 119.9(4).
Ionic liquids have per definition a melting point below
100 ꢀC [2]. The new histidinium salt 8a exhibits mp
39 ꢀC. It is optically active ([a]20(589) = ꢀ34 (CHCl3)). A
test has shown that the ionic liquid 8a does not lose its opti-
cal activity even if heated for 6 h at 110 ꢀC in a two phase
system with toluene. First, orientating experiments have
shown that 8a has typical features that may make it a
Fig. 2. Molecular structure of the L-histidine-derived chiral ionic liquid
˚
8a. Selected bond lengths (A) and angles (ꢀ) for molecule A: N1–C2
1.320(6), N1–C5 1.387(6), N1–C11 1.478(6), C2–N3 1.337(6), N3–C4
1.402(5), N3–C31 1.470(6), C4–C5 1.347(6), C4–C6 1.492(5), C6–C7
1.524(5), C7–C8 1.538(6), C8–O81 1.194(5), C8–O82 1.328(5), C7–N9
1.459(6), N9–C10 1.334(6), C10–O10 1.228(5); C2–N1–C5 108.5(4), C2–
N1–C11 125.1(4), C5–N1–C11 126.4(4), N1–C2–N3 109.1(4), C2–N3–C4
108.2(4), C2–N3–C31 124.1(4), C4–N3–C31 127.7(4), N3–C4–C5 106.2(4),
C5–C4–C6 133.2(4), N3–C4–C6 120.6(4), N1–C5–C4 107.9(4), C4–C6–C7
111.8(3), C6–C7–C8 110.7(3), C6–C7–N9 112.3(3), C8–C7–N9 111.8(4),
C7–N9–C10 121.3(4), N9–C10–O10 121.0(4).
Scheme 1.

F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
5961
Scheme 4.
were followed, one involving the isolated Ag-carbene com-
plexes 11 as reagents for the transmetallation step; alterna-
tively, the systems 11 were in situ generated from the
corresponding histidinium salts by treatment with silver
oxide, and then Pd(CH3CN)2Cl2 was added to effect the
transmetallation. The formation of both the (car-
bene)2PdCl2 products 12a (Bz) and 12b (Boc) was practi-
cally quantitative. These two products were isolated in
>90% (12a) or >80% (12b) yield, respectively. Optical activ-
ity is retained through the transmetallation step from Ag to
Pd. However, in each case a mixture of four stereoisomers
was formed. This was evident from a splitting of many of
the NMR signals of these compounds into sets of four sig-
nals resulting from the presence of these isomers (e.g., the
12a: C2 13C NMR resonance: d 170.2, 169.99, 169.83,
169.77). We assume that we have here observed two pairs
of cis- and trans-L2PdCl2. These are characterized by a
syn- or anti-arrangement at the substituents at carbon atom
C4 of the imidazol-2-ylidene ring in a situation where
the heterocyclic ligand plane and the major plane of the
square-planar L2PdCl2 framework are orthogonal and the
rotation around the (imidazol-2-ylidene)–C2–Pd vector is
frozen on the NMR time scale [15]. Although this can safely
be assumed we have prepared an achiral closely related
model system to support this likely interpretation.
For this purpose we alkylated 4-methylimidazol with n-
propylbromide/NaHCO3. The resulting imidazolium salt
[16] was then deprotonated by treatment with silver oxide
in dichloromethane and the resulting 4-methyl-imidazol-
2-ylidene ligand system transmetallated to palladium. The
resulting (carbene)2PdCl2 system 13 can again form a set
of four isomers (cis–syn-, cis–anti, trans–syn- and trans–
anti-13). A near to equimolar mixture of these four isomers
was actually formed, as is evident from the observation of
the respective ‘‘quadrupletts’’ of NMR signals (e.g., imi-
dazol-2-ylidene C2 13C NMR resonances at d 169.03,
169.00, 168.74 and 168.72). Heating of a sample of the four
13 isomers in d2-tetrachlorethane showed the coalescence
to the two pairs of C4 13C NMR (d 129.31, 129.28,
129.20, 129.17) to a single pair of such signals (cis-13/
trans-13) at ca. 90 ꢀC, which emphasizes the rather large
rotational barrier around the carbene–C2–Pd vector in
these complexes (13) and their related chiral analogues 12
(see above) (see Scheme 6).
Scheme 2.
useful compound for ionic liquid applications. The hydro-
xyalkylation of a-naphthol with ethylpyruvate, catalyzed
by the Lewis acid CpZrCl3 (6 mol%) [11], was successfully
carried out in a 1:2 mixture of [Bz-His(n-propyl)2-
OMe+Brꢀ] (8a)/CH2Cl2 [12] at room temperature. Unfor-
tunately, the isolated product (10, 60% yield) was racemic
(Scheme 3).
Treatment of 4a with iso-propyl iodide under the typical
reaction conditions gave 9a in excellent yield (see Scheme
2). The salt 9a features a melting point of mp 55 ꢀC. It,
thus, may potentially serve as a chiral ionic liquid as well.
We have similarly dialkylated the imidazol core of the re-
lated Boc-His-OMe starting materials to give the products
8b and 9b, respectively (see Scheme 4).
2.2. Histidine-based (imidazol-2-ylidene)metal complexes
The deprotonation at C2 of the imidazolium unit of the
[Bz-His(n-propyl)2-OMe+Brꢀ] salt 8a was effected by treat-
ment with 0.5 molar equivalents of Ag2O in dichlorometh-
ane [13] (in the presence of molecular sieves to remove the
water that was formed in this reaction). The histidine-
derived ‘‘Arduengo-carbene’’ complex 11a was formed
and isolated in close to quantitative yield. The formation
of the carbene complex system is evident by the marked
shift of the C2 13C NMR resonance [14] from d 135.7
(8a) to d 180.3 for the (carbene)2Ag Æ AgBr2 complex 11a.
The [(carbene)2Ag+] subunit was identified by HR ESI
MS, featuring a characteristic isotopic pattern (see Section
4). Complex 11a was obtained optically active, as shown by
its optical rotation. The Boc-protected analogue (8b) reacts
analogously with silver oxide to yield 11b [d (C2): 181.2]
(see Scheme 5).
The (carbene)2Ag Æ AgBr2 complexes 11a and 11b were
used as reagents for the transfer of the chiral imidazol-2-yli-
dende ligands to transition metals [15,16]. Two procedures
Single crystals of the trans–anti-13 isomer that were sui-
ted for an X-ray crystal structure determination were ob-
tained from dichloromethane. The structure of the
complex is distorted square planar. The two halide ligands
Scheme 3.

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F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
Scheme 5.
Br
H3C
H3C
H3C
N
N
N
N
N
Br
H
PdCl2
2
NaHCO3
CH3CN
1. Ag2O
2. Pd(CH3CN)2Cl2
CH2Cl2
N
H
cis-syn - 13
12
cis-anti - 13
trans-syn - 13
trans-anti - 13
Scheme 6.
˚
(70% Cl and 30% Br because of some halide exchange) are
in trans-positions as are the imidazol-2-ylidene ligand (see
Fig. 3). The planes of the ‘‘Arduengo-carbene’’ ligands
are oriented normal to the central N2X2Pd plane.
The C2–Pd bond length amounts to 2.047(5) A, which is
in a typical range [17]. In this general arrangement the
methyl groups at C4 of the carbene ligands could be ori-
ented on the same (syn) or different faces (anti) relative to
˚
Fig. 3. Two views of the molecular structure of the trans-anti-13 isomer. Selected bond lengths (A) and angles (ꢀ):Pd–C2 2.047(5), Pd–Cl 2.311(14), Pd-Br
2.384(15), N1–C2 1.351(6), N1–C5 1.381(7), N1–C11 1.465(8), C2–N3 1.327(6), N3–C4 1.401(7), N3–C31 1.437(7), C4–C5 1.292(8), C4–C41 1.521(9);
Cl–Pd–Cl* 180.0(5), Cl–Pd–C2 90.3(3), Pd–C2–N1 127.7(4), Pd–C2–N3 127.5(4), C2–N1–C5 110.1(5), C2–N1–C11 124.6(5), C5–N1–C11 125.3(5), N1–
C2–N3 104.8(4), C2–N3–C4 110.4(5), C2–N3–C31 122.7(4), C4–N3–C31 126.9(5), N3–C4–C5 106.9(5), C5–C4–C41 131.0(6), N3–C4–C41 122.1(5), N1–
C5–C4 107.8(5).

F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
5963
Scheme 7.
the central plane. In this structure they are anti-oriented at
the trans-L2PdX2 framework.
may become useful solvents, reagents or catalysts in reac-
tions proceeding with transfer of their chirality features.
We have also prepared two rhodium complexes of the L-
histidine-derived carbene ligands. For that purpose the
(carbene)2Ag Æ AgBr2 reagents 11a,b (see above) were each
treated with [Rh(cod)Cl]2 (14) [18]. Transmetallation gave
the (carbene)RhCl(cod) complexes 15a (Bz) and 15b
(Boc) in 65% and 73% yield, respectively. Each of the com-
plexes was obtained as a ca. 1:0.8 mixture of two diastere-
oisomers. This became evident by the observation of the
respective pairs of e.g., the carbene C2 13C NMR reso-
nances of the isomers 15a-A (d 183.04) and 15a-B (d
182.98) each with a 1J(Rh,C) coupling constant of ca.
51.5 Hz.
One may assume a distorted square planar geometry of
the complexes 15 with the carbene ligand plane oriented
normal to the major complex framework plane and a hin-
dered rotation around the carbene ligand C2-Rh vector
[19]. This orientations results in the presence of an element
of axial chirality inside the framework. Together with the
additional chirality center in the side chain of the L-histi-
dine derived unsymmetrically substituted imidazol-2-yli-
dene ligand this gives rise to the occurrence of pairs of
diastereomers of the compound 15, as it is experimentally
observed.
4. Experimental
4.1. General information
Solvents were dried and distilled under argon prior to
use or purified by a chromatographic solvent purification
system. Organometallic reactions were carried out under
argon using Schlenk-type glassware or in a glovebox. For
additional general information, including a list of instru-
ments used for spectroscopic and physical characterization
of the compounds see [20]. X-ray crystal structure analyses
were done using Enraf Nonius CAD4 and Nonius Kappa-
CCD diffractometers. For the programs used see [21].
Bz-His-OMe was synthesized according to the literature
procedures [7]. NMR assignments were mostly secured by
additional 2D NMR measurements.
4.2. Synthesis of rac-7a
A solution of Meerweinꢀs reagent ½Et3OþBFꢀꢁ (15.7 g,
4
82.8 mmol) in dichloromethane was slowly added via syr-
inge pump to a solution of the sodium salt of N-(a)-ben-
zoyl-L-histidine methyl ester [Na(Bz-His-OMe)] (8.15 g,
27.6 mmol) in 50 ml of CH2Cl2 over 4 h at ambient temper-
ature. After stirring overnight, the NaBF4 precipitate was
filtered off and the solvent removed in vacuo. The compo-
nents of the mixture were separated by column chromatog-
raphy (silicagel, CH2Cl2/MeOH/NH3: 75/10/1 rac-7a:
Rf = 0.18). The trialkylated product was obtained in 26%
yield (3.2 g). mp 124 ꢀC (DSC). 1H NMR (600 MHz,
298 K, CD3OD): d = 8.83 (s, 1H, 2-H); 7.52 (m, 1H, p-
Ph); 7.44 (m, 2H, m-Ph); 7.31 (s, 1H, 5-H); 7.16 (m, 2H,
o-Ph); 4.31 (m, 1H, 10-H); 4.26 (m, 1H, 7-H); 4.21 (m,
2H, 1.1-H); 4.20 (m, 1H, 100-H); 4.05 (m, 1H, 3.1-H);
3.94 (m, 1H, 3.10-H); 3.67 (s, 3H, O–CH3); 3.18 (ddd,
4J(H,H) = 0.6 Hz, 3J(H,H) = 4.6 Hz, 2J(H,H) = 15.4 Hz,
A consequence of this structure is that all four carbons
of each pair of cod C@C double bonds become different.
Consequently, sets of four cod C@C 13C NMR signals were
observed of each of the diastereomers 15a-A and 15a-B (A:
d 98.14, 97.74, 68.82, 68.08; B: d 98.14, 97.78, 68.72, 67.97)
(see Scheme 7).
3. Conclusion
This study has shown that L-histidine derived imidazo-
lium salts, some of which have the potential to serve as
useful chiral ionic liquids, and their related chiral imi-
dazol-2-ylidene ligands and their metal complexes are
readily available by the synthetic routes described in this
article. It will be investigated if derivatives of such systems
4
3
1H, 6-H); 3.11 (ddd, J(H,H) = 0.6 Hz, J(H,H) = 8.2 Hz,

5964
F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
3
2J(H,H) = 15.4 Hz, 1H, 60-H); 1.50 (t, J(H,H) = 7.4 Hz,
27.7 (CH2, C6); 14.9 (CH3, C10); 15.1 (CH3, C13); 14.2
(CH3, C3.2); 14.1 (CH3, C1.2). HR-MS (C21H30BF4N3O3,
MW = 459.29) (ESI, m/z): calcd. þ 372.2287; found:
3
3H, 1.2-H); 1.34 (t, J(H,H) = 7.2 Hz, 3H, 3.2-H); 1.31 (t,
3J(H,H) = 7.1 Hz, 3H, 11-H). 13C{1H} NMR (150 MHz,
298 K, CD3OD): d = 173.1 (C, C8); 166.9 (C, C9); 135.9
(C, C2); 133.3 (C, C4); 133.0 (C, i-Ph); 131.1 (CH, p-Ph);
129.8 (CH, m-Ph); 128.5 (CH, o-Ph); 121.7 (CH, C5);
63.3 (CH2, C10); 62.0 (CH, C7); 53.0 (CH3, O–CH3); 45.9
(CH2, C1.1); 43.3 (CH2, C3.1); 28.3 (CH2, C6); 15.6 (CH3,
372.2258 [C21H30N3O3]+ ½M ꢀ BF4 ꢁ . IR (KBr): m ¼
ꢀ
~
3474 ðwÞ, 3165 (s), 3135 (s), 3100 (w), 2978 (s), 2943 (s),
2908 (s), 1734 (s), 1661 (s), 1600 (s), 1483 (s), 1443 (s),
1365 (s), 1287 (s), 1174 (s), 1061 (br), 856 (w), 774 (s),
713 (s), 657 (w), 522 (w). [a]20 (k) = ꢀ1.5 (589), ꢀ1.6
(578), ꢀ1.8 (546), ꢀ3.1 (436) (c = 11.0, EtOH).
C
1.2); 15.0 (CH3, C3.2); 14.6 (CH3, C11). HR-MS
(C20H28BF4N3O3, MW = 445.26) (ESI, m/z): calcd.
358.2131; found: 358.2123 [C20H28N3O3]+ ½M ꢀ BF4ꢀꢁþ.
4.5. X-ray crystal structure analysis of rac-7b
~
IR (KBr): m ¼ 3487 ðbrÞ, 3174 (w), 3135 (w), 3104 (vw),
2978 (w), 2943 (vw), 2904 (vw), 1748 (vs), 1648 (s), 1604
(w), 1556 (w), 1452 (w), 1374 (w), 1283 (s), 1204 (s), 1169
(s), 1060 (br), 1000 (w), 852 (w), 783 (w), 709 (w), 652
(w), 522 (w). [a]20 (k) = 0 (589), 0 (578), 0 (546), 0 (436),
0 (365) (c = 8.1, CHCl3).
Formula C21H30N3O3 Æ BF4, MW = 459.29, colourless
˚
crystal 0.30 · 0.20 · 0.03 mm, a = 8.709(2) A, b = 9.245
˚
˚
(2) A, c = 17.049(3) A, a = 84.30(2)ꢀ, b = 81.44(1)ꢀ, c =
3
˚
62.97(2)ꢀ, V = 1208.4(4) A ,
q , l =
calc = 1.262 g cmꢀ3
8.89 cmꢀ1, empirical absorption correction via w scan data
(0.776 6 T 6 0.974), Z = 2, triclinic, space group
ꢀ
˚
4.3. X-ray crystal structure analysis of rac-7a
P1 ðNo. 2Þ, k = 1.54178 A, T = 223 K, x/2h scans, 4385
ꢀ1
˚
reflections collected (+h, k, l), [(sinh)/k] = 0.59 A
,
Formula C20H28N3O3 Æ BF4, MW = 445.26, colourless
4085 independent (Rint = 0.041) and 1920 observed reflec-
tions [I P 2r(I)], 331 refined parameters, R = 0.072,
wR2 = 0.254, maximum (minimum) residual electron den-
˚
crystal 0.60 · 0.40 · 0.15 mm, a = 8.715(1) A, b = 9.389
˚
˚
(1) A, c = 31.953(1) A, a = 81.61(1)ꢀ, b = 89.98(1)ꢀ,
c = 62.54(1)ꢀ, V = 2288.5(4) A , qcalc = 1.292 g cmꢀ3, l =
sity 0.35 (ꢀ0.24) e Aꢀ3, hydrogen atoms calculated and re-
3
˚
˚
1.08 cmꢀ1, no absorption correction (0.938 6 T 6 0.984),
fined as riding atoms, due to crystal size and form
diffracting power was low.
ꢀ
˚
Z = 4, triclinic, space group P1 ðNo. 2Þ, k = 0.71073 A,
T = 198 K, x and / scans, 13336 reflections collected
ꢀ1
( h, k, l), [(sinh)/k] = 0.59 A
,
7899 independent
4.6. Synthesis of [Bz-His(n-propyl)2-OMe+Brꢀ] (8a)
˚
(Rint = 0.032) and 5251 observed reflections [I P 2r(I)],
659 refined parameters, R = 0.064, wR2 = 0.169, maximum
Compound [Bz-His-OMe] (4a) (133.6 g, 0.49 mol) and
164.7 g (1.69 mol, 4 equiv.) of NaHCO3 were suspended
in 1.2 l acetonitrile. 1-Bromopropane (600 ml, 12.3 mol,
25 equiv.) were slowly added and the suspension was stir-
red under argon for 60 h at 65 ꢀC. The end of the reaction
was monitored by 1H NMR of samples taken. The mixture
was allowed to cool to room temperature, filtered and the
solvent removed in vacuo. The residue was dissolved in
water (500 ml) and extracted with 400 ml of CHCl3. The
aqueous phase was stripped in vacuo and the product 8a
dried. The organic phase was extracted with water
(3 · 150 ml). The water was removed and the product dried
in vacuo. The product 8a is hygroscopic. Combined yield
154.1 g (72%), mp 39 ꢀC (DSC). Anal. Calc. for
C20H28BrN3O3 (MW = 437.36): C, 54.80; H, 6.44; N,
9.59. Found: C, 54.33; H, 6.44; N, 9.62%. 1H NMR
(600 MHz, 298 K, CDCl3): d = 9.62 (s, 1H, 2-H); 8.77 (d,
3J(H,H) = 7.8 Hz, 1H, N–H); 8.03 (m, 2H, o-Ph); 7.55 (s,
1H, 5-H); 7.43 (m, 1H, p-Ph); 7.35 (m, 2H, m-Ph); 4.94
(m, 1H, 7-H); 4.20 (m, 1H, 3.1-H); 4.10 (m, 1H, 3.10-H);
4.06 (m, 2H, 1.1-H); 3.71 (m, 1H, 6-H); 3.71 (s, 3H, O–
CH3); 3.32 (dd, 3J(H,H) = 4.1 Hz, 2J(H,H) = 16.0 Hz,
1H, 60-H); 1.87 (m, 2H, 3.2-H); 1.75 (m, 2H, 1.2-H); 0.91
(t, 3J(H,H) = 7.3 Hz, 3H, 3.3-H); 0.77 (t, 3J(H,H) =
7.3 Hz, 3H, 1.3-H). 13C{1H} NMR (150 MHz, 298 K,
CDCl3): d = 170.8 (C, C8); 167.5 (C, C9); 135.7 (C, C2);
132.6 (C, i-Ph); 132.0 (CH, p-Ph); 132.0 (C, C4); 128.4
(CH, m-Ph); 127.8 (CH, o-Ph); 120.5 (CH, C5); 52.9
ꢀ3
˚
(minimum) residual electron density 0.42 (ꢀ0.28) e A
,
hydrogen atoms calculated and refined as riding atoms, an-
ions heavily disordered and refined with split positions.
4.4. Preparation of rac-7b
The reaction of [Na(Bz-His-OEt)] (4.6 g, 14.87 mmol)
with ½Et3OþBFꢀꢁ (9.89 g, 52.1 mmol) was carried out anal-
4
ogously as the reaction described above. The product
rac-7b was isolated in 30% yield (2.08 g) after column chro-
matography (Rf = 0.14, silica gel, CH2Cl2/MeOH/NH3:
1
75/10/1). mp 122 ꢀC (DSC). H NMR (400 MHz, 298 K,
CDCl3): d = 8.93 (s, 1H, 2-H); 7.60 (m, 1H, p-Ph); 7.42
(m, 2H, m-Ph); 7.17 (m, 2H, o-Ph); 6.96 (s, 1H, 5-H);
4.3–4.1 (m, 8H, 1.1, 3.1, 9-H, 12-H); 4.02 (d,
3J(H,H) = 7.6 Hz, 1H, 7-H); 3.03 (m, 1H, 6-H); 1.49,
3
1.48 (t, J(H,H) = 7.2 Hz, each 3H (double bond isomers),
13-H); 1.40 (t, 3J(H,H) = 7.2 Hz, 3H, 10-H); 1.31 (t,
3J(H,H) = 7.2 Hz, 2· 3H (double bond isomers), 1.2-H);
3
1.23 (t, J(H,H) = 6.8 Hz, 2· 3H (double bond isomers),
3.2-H). 13C{1H} NMR (100 MHz, 298 K, CDCl3):
d = 170.9 (C, C8); 165.5 (C, C11); 132.9 (C, C4); 132.8 (C,
i-Ph); 135.3 (CH, C2); 131.9, 131.4 (each CH (double bond
isomers), p-Ph); 130.1, 129.5 (each CH (double bond iso-
mers), m-Ph); 128.8, 128.3 (each CH (double bond iso-
mers), o-Ph) 119.5 (CH, C5); 61.7 (CH2, C12); 60.6 (CH2,
C9); 62.3 (CH, C7); 42.5 (CH2, C1.1); 45.1 (CH2, C3.1);

F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
5965
0
(CH3, O–CH3); 48.8 (CH2, C3.1); 51.3 (CH2, C1.1); 51.0
(CH, C7); 23.32 (CH2, C1.2); 23.27 (CH2, C3.2); 25.3
(CH2, C6); 10.8 (CH3, C3.3); 10.5 (CH3, C1.3). MS
52.5 (CH, C7); 53.4 (CH3, O–CH3); 26.8 (CH2, C6 ); 23.6
(CH3, C3.2); 23.2 (CH3, C3.2ꢀ); 23.0 (CH3, C1.2); 23.0
(CH3, C1.2ꢀ). MS ꢀ(+C20H28IN3O3, MW = 438,36) (ESI,
~
(C20H28BrN3O3, MW = 437.36) (ESI, m/z): 358.4
m/z): 358.4 [M ꢀ I ] . IR (KBr): m ¼ 2978 ðwÞ, 1743 (s),
ꢀ +
~
[M ꢀ Br ] . IR (KBr): m ¼ 3208 ðbrÞ, 2965 (br), 2874
1648 (vs), 1600 (w), 1526 (vs), 1483 (w), 1439 (w), 1296
(w), 1183 (w), 1130 (w), 804 (w), 717 (w), 687 (w), 643
(w). [a]20 (k) = ꢀ5.7 (589), ꢀ5.8 (578), ꢀ6.9 (546), ꢀ12.8
(436), ꢀ23.0 (365) (c = 13.35, MeOH).
(vs), 2352 (vw), 1748 (vs), 1656 (vs), 1600 (w), 1535 (vs),
1487 (s), 1443 (w), 1339 (s), 1304 (s), 1174 (s), 1087 (w),
1035 (w), 991 (w), 870 (w), 804 (w), 717 (s), 696 (s), 648
(w). [a]20 (k) = ꢀ34 (589), ꢀ36 (578), ꢀ41 (546), ꢀ75
(436), ꢀ132 (365) (c = 9.9, CHCl3). [a]20 (k) = ꢀ16.6
(589), ꢀ17.4 (578), ꢀ20.0 (546), ꢀ36.9 (436), ꢀ66.2 (365)
(c = 10.2, MeOH).
4.9. Preparation of [Boc-His(n-propyl)2-OMe+Brꢀ] (8b)
Analogously as described above Boc-His-OMe (4c)
(2.98 g, 11.1 mmol) was reacted with 25.4 ml n-propyl
bromide (271 mmol) in the presence of 3.75 g (44.6 mmol)
of NaHCO3 in acetonitrile (8 d, 65 ꢀC) to yield 4.46 g
(92%) of 8b after the usual aqueous workup, mp 198 ꢀC
(decomp., DSC). Anal. Calc. for C18H32BrN3O4 Æ
1/2H2O (MW = 452.37): C, 47.79; H, 7.58; N, 9.29. Found:
4.7. X-ray crystal structure analysis of 8a
Formula C20H28N3O3Br, MW = 438.36, colourless crys-
˚
tal 0.20 · 0.15 · 0.06 mm, a = 11.920(1) A, b = 13.670
3
˚
˚
˚
(1) A, c = 14.317(1) Aꢀ, b = 111.31(1)ꢀ, V = 2173.4(3) A ,
1
q
calc = 1.340 g cmꢀ3, l = 19.15 cmꢀ1, empirical absorption
C, 48.36; H, 7.47; N, 9.37%. H NMR (600 MHz, 298 K,
correction (0.701 6 T 6 0.894), Z = 4, monoclinic, space
CD3OD): d = 9.21 (s, 1H, 2-H); 7.55 (s, 1H, 5-H); 7.24
(ABMX, 3J(H,H) = 9.4 Hz, 1H, N–H); 4.52 (ABMX,
˚
group P21 (No. 4), k = 0.71073 A, T = 198 K, x and /
2
scans, 14951 reflections collected ( h, k, l), [(sinh)/
3J(H,H) = 4.9 Hz, J(H,H) = 9.4 Hz, 1H, 7-H); 4.23 (m,
k] = 0.66 Aꢀ1, 9584 independent (Rint = 0.039) and 7394
2H, 3.1-H); 4.23 (m, 2H, 1.1-H); 3.77 (s, 3H, O–CH3);
˚
3
2
observed reflections [I P 2 (I)], 501 refined parameters,
R = 0.050, wR2 = 0.108, Flack parameter 0.001(9), maxi-
mum (minimum) residual electron density 0.51 (ꢀ0.49)
3.33 (ABMX, J(H,H) = 4.9 Hz, J(H,H) = 15.8 Hz, 1H,
3
2
6-H); 3.17 (ABMX, J(H,H) = 9.4 Hz, J(H,H) = 15.8 Hz,
1H, 60-H); 1.94 (m, 2H, 3.2-H); 1.94 (m, 2H, 1.2-H); 1.41
(s, 9H, C(CH3)3); 1.02 (t, J(H,H) = 7.5 Hz, 3H, 3.3-H);
e Aꢀ3, hydrogen atoms calculated and refined as riding
˚
3
atoms.
0.96 (t, 3J(H,H) = 7.5 Hz, 3H, 1.3-H). 13C{1H} NMR
(150 MHz, 298 K, CD3OD): d = 172.4 (C, C8); 157.5 (C,
C9); 132.9 (C, C4); 137.0 (C, C2); 121.9 (CH, C5); 80.8
(C, C(CH3)3); 53.5 (CH3, O–CH3); 53.3 (CH, C7); 49.6
(CH2, C3.1); 52.3 (CH2, C1.1); 26.8 (CH2, C6); 28.5
(CH3, C(CH3)3); 24.4 (CH2, C3.2); 24.2 (CH2, C1.2); 11.1
(CH3, C3.3); 11.0 (CH3, C1.3). HR-MS (C18H32BrN3O4,
MW = 434.37) (ESI, m/z): calcꢀ.: + 354.2393; found:
4.8. Preparation of [Bz-His(iso-propyl)2-OMe+Iꢀ] (9a)
In
a
Schlenk flask [Bz-His-OMe] (4a) (1.00 g,
3.66 mmol) and 1.20 g (14.0 mmol, 4 equiv.) NaHCO3 were
suspended in dry acetonitrile. iso-Propyliodide (9.15 ml,
92.0 mmol, 25 equiv.) was added and the mixture was re-
fluxed at 65 ꢀC for 3 d with stirring. After cooling the mix-
ture was filtered. Solvent was removed in vacuo. The
residue was dissolved in chloroform (30 ml) and extracted
with water (5 · 10 ml). Water was removed in vacuo and
the hygroscopic product dried. Yield of 9a: 1.69 g (95%),
mp 55 ꢀC (DSC). Anal. Calc. for C20H28IN3O3
(MW = 438.36): C, 49.49; H, 5.81; N, 8.66. Found: C,
49.23; H, 5.66; N, 8.60%. 1H NMR (600 MHz, 298 K,
CD3OD): d = 9.15 (d, 4J(H,H) = 1.7 Hz 1H, 2-H); 7.83
(m, 2H, o-Ph); 7.56 (m, 1H, p-Ph); 7.56 (s, 1H, 5-H); 7.47
354.2392 [C18H32N3O4]+ [M ꢀ Br ] . IR (KBr): m ¼
~
3235 ðbrÞ, 3130 (s), 2965 (br), 2874 (s), 1748 (vs), 1700
(vs), 1608 (w), 1565 (s), 1513 (vs), 1452 (s), 1365 (s),
1256 (s), 1169 (s), 1048 (s), 1013 (s), 861 (w), 791 (w),
648 (w), 626 (w), 465 (w). [a]20 (k) = ꢀ15.6 (589), ꢀ16.1
(578), ꢀ18.4 (546), ꢀ32.0 (436), ꢀ52.2 (365) (c = 10.65,
MeOH).
4.10. Preparation of [Boc-His(iso-propyl)2-OMe+Iꢀ] (9b)
3
(m, 2H, m-Ph); 5.03 (d, J(H,H) = 5.0 Hz, 1H, 7-H); 4.74
Analogously as described above the reaction of 2.00 g
(7.43 mmol) of Boc-His-OMe (4c) with 16.8 ml
(58.2 mmol) of iso-propyl iodide and 2.50 g (29.8 mmol)
of NaHCO3 gave 2.47 g (69%) of 9b, mp 55 ꢀC (DSC).
1H NMR (600 MHz, 298 K, CD3OD): d = 9.27 (d,4J-
(H,H) = 1.6 Hz, 1H, 2-H); 7.58 (s, 1H, 5-H); 4.72 (sep.,
3J(H,H) = 6.8 Hz, 1H, 1.1-H); 4.69 (sep., 3J(H,H) =
(sep., 3J(H,H) = 6.8 Hz, 1H, 3.1-H); 4.60 (sep.,
3J(H,H) = 6.8 Hz, 1H, 1.1-H); 3.80 (s, 3H, O–CH3); 3.51
3
2
(dd, J(H,H) = 5.0 Hz, J(H,H) = 16.0 Hz, 1H, 6-H); 3.32
(dd, 3J(H,H) = 10.1 Hz, J(H,H) = 16.0 Hz, 1H, 60-H);
2
1.64 (d, 3J(H,H) = 6.8 Hz, 3H, 3.2-H); 1.56 (d,
3J(H,H) = 6.8 Hz, 3H, 3.20-H); 1.48 (d, J(H,H) = 6.8 Hz,
3
3
3
3H, 1.2-H); 1.46 (d, J(H,H) = 6.8 Hz, 3H, 1.20-H).
6.7 Hz, 1H, 3.1-H); 4.54 (ABX, J(H,H) = 5.0 Hz, 1H, 7-
13C{1H} NMR (150 MHz, 298 K, CD3OD): d = 172.0 (C,
C8); 169.9 (C, C9); 134.4 (C, i-Ph); 134.0 (C, C2); 133.3
(CH, p-Ph); 132.6 (C, C4); 129.7 (CH, m-Ph); 128.5 (CH,
o-Ph); 119.8 (CH, C5); 54.7 (CH, C1.1); 51.9 (CH, C3.1);
H); 3.77 (s, 3H, O–CH3); 3.36 (ABX, J(H,H) = 5.0 Hz,
3
2J(H,H) = 15.8 Hz, 1H, 6-H); 3.16 (ABX, 3J(H,H) =
2
3
9.7 Hz, J(H,H) = 15.8 Hz, 1H, 60-H); 1.63 (d, J(H,H) =
3
6.7 Hz, 3H, 3.2-H); 1.62 (d, J(H,H) = 6.7 Hz, 3H, 3.20-H);

5966
F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
3
3
1.58 (d, J(H,H) = 6.7 Hz, 3H, 1.2-H); 1.58 (d, J(H,H) =
6.7 Hz, 3H, 1.20-H); 1.41 (s, 9H, C(CH3)3). 13C{1H}
NMR (150 MHz, 298 K, CD3OD): d = 172.4 (C, C8);
157.6 (C, C9); 133.9 (C, C2); 132.6 (C, C4); 119.7 (CH,
C5); 80.9 (C, C(CH3)3); 54.6 (CH, C3.1); 51.8 (CH, C1.1);
53.5 (CH, C7); 53.3 (CH3, O–CH3); 28.7 (CH3, C(CH3)3);
4.97 (m, 1H, 7-H); 4.08 (m, 1H, 3.1-H); 4.01 (m, 1H, 3.1-
H0); 3.93 (m, 2H, 1.1-H); 3.71 (s, 3H, O–CH3); 3.44 (dd,
2
3J(H,H) = 9.2 Hz, J(H,H) = 16.1 Hz, 1H, 6-H); 3.29 (dd,
2
3J(H,H) = 4.7 Hz, J(H,H) = 16.1 Hz, 1H, 6-H0); 1.81 (m,
2H, 3.2-H); 1.72 (m, 2H, 1.2-H); 0.92 (t, 3J(H,H) = 7.5 Hz,
3H, 3.3-H); 0.79 (t, 3J(H,H) = 7.4 Hz, 3H, 1.3-H). 13C{1H}
NMR (150 MHz, 298 K, CD2Cl2): d = 180.0 (C, C2);
171.3 (C, C8); 167.1 (C, C9); 133.6 (C, i-Ph); 133.4 (C,
C4); 132.0 (CH, p-Ph); 128.6 (CH, m-Ph); 127.7 (CH, o-Ph);
119.8 (CH, C5); 53.5 (CH2, C1.1); 52.5 (CH3, O–CH3);
51.5 (CH, C7); 50.5 (CH2, C3.1); 26.3 (CH2, C6); 25.1
(CH2, C3.2); 24.6 (CH2, C1.2); 10.7 (CH3, C1.3); 11.0 (CH3,
0
27.2 (CH2, C6); 23.6 (CH3, C3.2); 23.4 (CH3, C3.2 ); 23.2
(CH3, C1.2); 23.1 (CH3, C1.2 ). HR-MS (C18H32IN3O4,
MW = 481.37): calc.: 354.2393; found: 354.2405
½C18H32N3O4 ꢁ [M ꢀ I ] . IR (KBr): m ¼ 3421 ðvwÞ, 3061
(vs), 2982 (vs), 2312 (vw), 1743 (w), 1704 (w), 1496 (w),
1439 (w), 1365 (w), 1156 (w), 896 (w), 778 (s), 717 (s),
461 (s). [a]20 (k) = ꢀ13.3 (589), ꢀ14.0 (578), ꢀ15.9 (546),
ꢀ27.7 (436), ꢀ44.7 (365) (c = 10.4, CH3OH).
0
þ
ꢀ +
~
C3.3). HR-MS (C40H54Ag2Br2N6O6, MW = 1090.44)
(ESI, LM [CHCl3/CH3CN], m/z): calc.: 821.3150/
822.3181/823.3154/ 824.3181/825.3208; found: 821.3125/
4.11. Reaction of 8a with silver oxide, preparation of 11a:
general procedure
822.3165/823.3134/824.3143/825.3153
[C40H54AgN6O6]
+
~
[M ꢀ AgBr2] . IR (KBr): m ¼ 3856 ðwÞ, 3752 (w), 3350
(br), 2965 (s), 2931 (s), 2878 (w), 2365 (vw), 2339 (vw),
1739 (vs), 1660 (vs), 1526 (s), 1491 (w), 1456 (w), 1339
(w), 1226 (w), 1196 (w), 1091 (vw), 1022 (vw), 804 (w),
717 (w). [a]20 (k) = +13.9 (589), +16.8 (578), +20.6 (546),
+35.0 (436), +54.3 (365) (c = 10.5, CHCl3) (see Fig. 4).
Ag2O (0.52 molar equiv.) are added to a solution of the
respective histidinium salt in abs. dichloromethane at room
temperature. The mixture is then stirred in the dark for 2 h.
The solution is then decanted from the precipitate. Solvent
is removed in vacuo and the product dried in vacuo. In
some reactions activated molecular sieves were added to re-
move the reaction water. In this case the mixture was not
stirred but only shaken to avoid mechanical decomposition
of the mol. sieve pellets.
4.12. Reaction of 9a with silver oxide, preparation of 11b
According to the general procedure, 1.01 g (2.33 mmol)
of 9a was treated with 0.32 g (1.38 mmol) of Ag2O to give
1.20 g (96%) of 11b, mp 173 ꢀC (DSC). Anal. Calc. for
C36H62Ag2Br2N6O8 (MW = 1082.46): C, 39.94; H, 5.77;
According to this procedure, 2.00 g (2.29 mmol) of 8a
were reacted with 0.63 g (2.71 mmol) of Ag2O to give
1.98 g (97%) of 11a, mp 57 ꢀC, decomp.: 182 ꢀC (DSC).
Anal. Calc. for C40H54Ag2Br2N6O6 (MW = 1090.44): C,
44.06; H, 4.99; N, 7.71. Found: C, 45.21; H, 5.03; N,
7.76%. 1H NMR (600 MHz, 298 K, CD2Cl2): d = 7.94
(m, 2H, o-Ph); 7.46 (m, 1H, p-Ph); 7.37 (m, 2H, m-Ph);
1
N, 7.76. Found: C, 40.47; H, 5.76; N, 7.71%. H NMR
(600 MHz, 298 K, CD2Cl2): d = 6.86 (s, 1H, 5-H); 5.43
(d, 3J(H,H) = 7.1 Hz, 1H, N–H); 4.55 (d, 3J(H,H) =
5.6 Hz, 1H, 7-H); 4.05 (m, 1H, 3.1-H); 4.02 (m, 1H, 1.1-
H); 4.00 (m, 1H, 3.10-H); 3.74 (s, 3H, O–CH3); 3.16 (dd,
3
2
7.12 (s, 1H, 5-H); 7.10 (d, J(H,H) = 3.7 Hz, 1H, N–H);
3J(H,H) = 5.6 Hz, J(H,H) = 16.0 Hz, 1H, 6-H); 3.00 (dd,
Fig. 4. Measured (top) and calculated (bottom) ESI HRMS of 11a (i.e., C40H54AgN6O6, [M ꢀ AgBr2]+, left) and 11b (i.e., C36H62AgN6O8, [M ꢀ AgBr2]+,
right).

F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
5967
2
3J(H,H) = 7.6 Hz, J(H,H) = 16.0 Hz 1H, 60-H); 1.82
3J(H,H) = 7.5 Hz, 3H, 3.3 or 1.3 (III, IV)-H); 0.92 (2· t,
3J(H,H) = 7.5 Hz, each 3H, 3.3 or 1.3 (III, IV)-H).
13C{1H} NMR (150 MHz, 298 K, CDCl3): d = 171.38 (C,
(m, 2H, 1.2-H); 1.81 (m, 2H, 3.2-H); 1.41 (s, 9H,
3
C(CH3)3); 0.95 (t, J(H,H) = 7.3 Hz, 3H, 3.3-H); 0.91 (t,
3J(H,H) = 7.3 Hz, 3H, 1.3-H). 13C{1H} NMR (150 MHz,
298 K, CD2Cl2): d = 181.2 (C, C2); 171.7 (C, C8); 155.5
(C, C9); 129.9 (C, C4); 119.4 (CH, C5); 80.6 (C, C(CH3)3);
52.9 (CH, C7); 54.1 (CH2, C1.1); 53.0 (CH3, O–CH3); 51.0
(CH2, C3.1); 27.8 (CH2, C6); 28.3 (CH3, C(CH3)3); 25.5
(CH2, C3.2); 25.0 (CH2, C1.2); 11.3 (CH3, C3.3); 11.2 (CH3,
C
8(I + II)); 170.02 (C, C2(I)); 169.99 (C, C2(II)); 169.83,
169.77, (C, C2(isomers)); 167.27 (C, C9(I + II)); 167.20 (C,
9(isomer)); 133.10 (C, i-Ph(I + II)); 131.96 (CH, p-
C
Ph(I + II)); 128.60 (CH, m-Ph(I + II)); 128.40, 128.31,
128.29 (C, C4(isomers)); 128.19 (C, C4(I)); 128.17 (C, C4(II));
127.09 (CH, o-Ph(I + II)); 119.13, 118.73, 118.70, 118.59,
118.57 (CH, C5(isomers)); 118.56 (CH, C5(II)); 118.44 (CH,
C1.3). HR-MS (C36H62Ag2Br2N6O8, MW = 1082.46) (ESI,
LM [CHCl3/CH3CN], m/z): calc.: 813.3675/814.3705/
815.3677/816.3705/817.3731; found: 813.3640/814.3684/
C
5(I)); 52.92 (CH3, O–CH3(II)); 52.90 (CH3, O–CH3(I));
52.42, 52.39, 52.37, 52.33 (CH2, C1.1(isomers)); 52.26 (CH2,
1.1(II)); 52.22 (CH2, C1.1(I)); 51.61, 51.57 (CH, C7(isomers));
815.3641/816.3678/817.33697
[C36H62AgN6O8]
[M ꢀ
C
+
~
AgBr2] . IR (KBr): m ¼ 3387 ðbrÞ, 3113 (w), 2965 (s),
2930 (s), 2869 (w), 1752 (s), 1717 (vs), 1617 (w), 1517 (w),
1456 (s), 1365 (s), 1252 (s), 1161 (vs), 1056 (w), 1017 (w),
861 (vw), 783 (w), 639 (w), 461 (w). [a]20 (k) = +25.8
(589), +27.2 (578), +31.1 (546), +55.3 (436), +94.2 (365)
(c = 10.9, CHCl3).
51.50 (CH, C7(I + II)); 49.29, 49.18 (CH, C3.1(isomers));
49.04 (CH, C3.1(I + II)); 26.77 (br, CH2, C6(isomers)); 26.73
(CH2, C6(I + II)); 24.66 (CH2, C3.2(I)); 24.59 (CH2, C3.2(II));
24.43, 24.38 (CH2, C1.2(isomers)); 24.26 (CH2, C1.2(I));,
24.14 (CH2, C1.2(II)); 24.07, 23.97 (CH2, C1.2(isomers));
11.39 (CH3, C3.3(II)); 11.37 (CH3, C3.3(I)); 11.29 (CH3,
C1.3(I)); 11.27 (CH3, C1.3(II)). HR-MS (C40H54Cl2N6O6Pd,
4.13. Preparation of the palladium complexes: general
procedure
MW = 892.22) (ESI, LM[CHCl3/CH3CN], m/z): calc.:
853.2829/854.2843/855.2834/8562844/857.2827/858.2853/
859.2832/860.2857/861.2839; found: 853.2827/854.2769/
855.2789/856.2811/857.2780/858.2789/859.2799/860.2823/
861.2843 [C40H54ClN6O6Pd]+ [M ꢀ Clꢀ]+. IR (KBr):
Silver oxide (0.52 g molar equiv.) ware added to a solu-
tion of the respective histidinium salt in dichloromethane.
The mixture is stirred in the dark for 1 h at ambient tem-
perature. Then 0.50 molar equiv. of Pd(CH3CN)2Cl2 in
abs. CH2Cl2 is added and the mixture again stirred for
1 h at room temperature. Silver halide is precipitated dur-
ing this time and the solution decanted from the precipi-
tate. Solvent was removed in vacuo and the product
dried in vacuo.
~
m ¼ 3321 ðbrÞ, 3121 (w), 3056 (w), 2961 (s), 2930 (s),
2874 (w), 1743 (vs), 1647 (vs), 1535 (s), 1465 (w), 1426
(w), 1343 (w), 1269 (w), 1217 (w), 1100 (w), 1022 (s), 809
(s), 713 (s), 683 (s). [a]20 (k) = +34 (589), +36 (578), +41
(546), +74 (436) (c = 10.25, CHCl3) (see Fig. 5).
4.13.2. Preparation of 12b
According to the general procedure, 1.26 g (2.61 mmol)
of 9a was treated with Ag2O (0.39 g, 1.70 mmol) and then
Pd(CH3CN)2Cl2 (0.26 g, 1.45 mmol) to yield 1.90 g (82%)
of 12b, mp 62 ꢀC (DSC). The NMR analysis revealed the
presence of four diastereoisomers (I–IV). 1H NMR
(600 MHz, 298 K, CDCl3): d = 6.65, 6.65, 6.64 (s, 1H,
5(II–IV)-H); 6.63 (s, 1H, 5(I)-H); 5.11 (d, 3J(H,H) =
8.1 Hz, 1H, N–H); 4.55 (m, 1H, 7-H); 4.41 (m, 2H, 1.1-
H); 4.33 (m, 2H, 3.1-H) 4.33 (m, isomers of 1.1 or
4.13.1. Reaction of in situ generated 11a with Pd(CH3CN)2-
Cl2: preparation of 12a
The carbene silver complex 11a was in situ generated by
treatment of 8a (2.00 g, 4.58 mmol) with 0.62 g (2.68 mmol)
of Ag2O in dichloromethane, as described in the general
procedure, followed by the reaction with 0.59 g
(2.28 mmol) of Pd(CH3CN)2Cl2 to yield 3.51 g (86%) of
complex 12a, mp 80 ꢀC (DSC). The NMR analysis revealed
the presence of four diastereoisomers (I–IV). 1H NMR
(600 MHz, 298 K, CDCl3): d = 7.74 (m, 2H, o-Ph(I + II));
7.46 (m, 1H, p-Ph(I + II)); 7.39 (m, 2H, m-Ph(I + II); 6.86
3
3.1-H); 3.70 (s, 3H, O–Me); 3.02 (dd, J(H,H) = 4.5 Hz,
2J(H-H) = 15.8 Hz, 1H, 6(I)-H); 2.91 (dd, 3J(H,H) =
2
6.8 Hz, J(H,H) = 15.8 Hz, 1H, 6(I)-H0); 2.10 (m, 2H,
3
3
(d, J(H,H) = 7.4 Hz, 1H, N–H(III)); 6.85 (d, J(H,H) =
3.2-H); 2.03 (m, 2H, 1.2-H); 1.40 (s, 9H, C(CH3)3(I));
3
3
7.6 Hz, 1H, N–H(I)); 6.82 (d, J(H,H) = 7.7 Hz, 1H, N–
1.39, 1.37 (s, 9H, C(CH3)3(isomers)); 1.03 (t, J(H,H) =
H(II + IV)); 6.65 (s, 1H, 5(III)-H); 6.64 (s, 1H, 5(I)-H);
6.63 (s, 1H, 5(II)-H); 5.01 (m, 1H, 7(I)-H); 5.00 (m, 1H,
7(II)-H); 4.46–4.30 (m, each 1H, 3.1(I–IV)-H); 4.39–4.31
(m, each 2H, 1.1(I–IV)-H); 4.27–3.19 (m, each 1H, 3.10(I–
IV)-H); 3.72 (s, 3H, O–CH3(I + II)); 3.71, 3.70 (s, 3H, O–
CH3(III + IV)); 3.16 (m, each 2H, 6(I–IV)-H); 2.14–1.95
(m, each 2H, 3.2(I–IV)-H and 3.2(I–IV)-H0); 1.00 (t,
3J(H,H) = 7.3 Hz, 3H, 3.3(I)-H); 0.99 (t, 3J(H,H) = 7.3 Hz,
7.0 Hz, 3H, 1.3(I)-H); 1.05, 1.03, 1.02 (each t,
3J(H,H) = 6.6–7.7 Hz, each 3H, 1.3-H(isomers)); 0.99
3
(t, J(H,H) = 7.3 Hz, 3H, 3.3(I)-H); 1.01, 1.00, 0.98 (each
t, 3J(H,H) = 6.6–7.7 Hz, each 3H, 3.3-H(isomers)). 13C-
{1H} NMR (150 MHz, 298 K, CHCl3): d = 171.7 (C, C8);
169.84, 169.82 (I), 169.60, 169.58, 169.20, 169.17 (C, C2);
155.0 (C, C9); 128.57, 128.53, 128.44, 128.42, 128.31 (I),
128.28 (C, C4); 118.56, 118.42, 118.28 (I), 118.15 (CH,
C5); 80.43 (C, C(CH3)3); 52.81 (CH3, O–Me(I)); 52.80
(CH3, O–Me(II)) 52.58, 52.52, 52.48, 52.46, 52.42, 52.41,
52.33, 52.28 (I) (CH2, C1.1); 51.90, 51.85 (CH, C7); 49.40,
3
3H, 3.3(II)-H); 0.97 (t, J(H,H) = 7.6 Hz, 3H, 1.3(II)-H);
0.96 (t, 3J(H,H) = 7.5 Hz, 3H, 1.3(I)-H); 0.94 (t,
3J(H,H) = 7.5 Hz, 3H, 3.3 or 1.3 (III, IV)-H); 0.93 (t,

5968
F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
Fig. 5. Experimental (top) and calculated (bottom) ESI HRMS of 12a (i.e., C40H54ClN6O6Pd+, [M ꢀ Cl]+, left) and 12b (i.e., C36H62ClN6O8Pd+,
[M ꢀ Cl]+, right).
49.38, 49.25 (I), 49.10 (CH2, C3.1); 28.1 (CH3, C(CH3)3);
27.56, 27.51 (I) (CH2, C6); 24.60, 24.54, 24.38, 24.33 (I),
24.22 (I), 24.14, 24.04, 23.96, 23.87 (CH2, C1.2 and C3.2);
11.48 (CH3, C3.3); 11.39 (CH3, C1.3). HR-MS (C36-
H62Cl2N6O8Pd, MW = 884.24) (ESI, LM [CHCl3/
CH3CN], m/z): calc.: 845.3353/846.3367/847.3357/
848.3367/849.3350/850.3377/851.3355/852.3381/853.3361;
found: 854.3346/846.3339/847.3344/848.3331/849.333316/
129.20 (C, C4(I)); 129.17 (C, C4(II)); 118.30 (CH, C5(III));
118.18 (CH, C5(IV + I)); 118.06 (CH, C5(II)); 52.57 (CH2,
C
1.1(III)); 52.53 (CH2, C1.1(IV)); 52.42 (CH2, C1.1(I)); 52.39
(CH2, C1.1(II)); 49.51 (CH2, C3.1(III + b)); 49.37 (CH2,
3.1(I)); 49.36 (CH2, C3.1(II)); 24.79 (CH2, C1.2(III)); 24.74
C
(CH2, C1.2(IV)); 24.74 (CH2, C1.2(I)); 24.64 (CH2, C1.2(II));
24.58 (CH2, C3.2(I)); 24.56 (CH2, C3.2(II)); 24.54 (CH2,
C3.2(III)); 24.47 (CH2, C3.2(IV)); 11.93 (CH3, C3.3(II)); 11.93
850.3364/851.3336/852.3353/853.3378 [C36H62ClN6O8Pd]+
(CH3, C3.3(III)); 11.93 (CH3, C3.3(IV)); 11.93 (CH3, C1.3(II));
11.93 (CH3, C1.3(III)); 11.93 (CH3, C1.3(IV)); 11.93 (CH3,
C1.3(I)); 11.93 (CH3, C3.3(I)); 9.96 (CH3, C6(III)); 9.94
ꢀ +
~
[M ꢀ Cl ] . IR (KBr): m ¼ 3369 ðbrÞ, 3121 (w), 2961 (s),
2930 (s), 2878 (w), 1752 (vs), 1704 (vs), 1517 (w), 1461
(w), 1417 (w), 1365 (s), 1265 (s), 1165 (vs), 1061 (w), 1017
(s), 856 (w), 796 (s). [a]20 (k) = +34 (589), +36 (578), +41
(546), +74 (436) (c = 10.5, CHCl3).
(CH3, C6(IV)); 9.92 (CH3, C6(I)); 9.90 (CH3, C6(II)). At
383 K only two isomers (cis-13/trans-13) are monitored
by NMR (I/II): 1H NMR (600 MHz, 383 K, C2D2Cl4):
d = 6.51 (d,4J(H,H) = 1.0 Hz, 1H, 5(II)-H); 6.50
(d,4J(H,H) = 1.0 Hz, 1H, 5(I)-H); 4.38 (m, each 2H,
1.1(I + II)-H); 4.36 (m, each 2H, 3.1(I + II)-H); 2.12 (s,
3H, 6(II)-H); 2.12 (s, 3H, 6(I)-H); 2.06 (m, each 2H,
3.2(I + II)-H); 2.05 (m, each 2H, 1.2(I + II)-H); 1.06 (t,
3H, 3.3(II)-H); 1.05 (t, 3H, 3.3(I)-H); 1.02 (t, 3H, 1.3(I)-
H); 1.02 (t, 3H, 1.3(II)-H). 13C{1H} NMR (150 MHz,
383 K, C2D2Cl4): d = 170.41 (C, C2(I)); 170.09 (C, C2(II));
129.21 (C, C4(II)); 129.08 (C, C4(I)); 117.95 (CH, C5(II));
117.95 (CH, C5(I)); 52.63 (CH2, C1.1(II)); 52.48 (CH2,
4.14. Synthesis of the palladium complexes 13
Analogously to the general procedure, 500 mg
(2.02 mmol) of 1,3-di-n-propyl-4-methylimidazolium bro-
mide was dissolved in 100 ml of CH2Cl2 and then reacted
with Ag2O (244 mg, 1.05 mmol) in the presence of 0.7 g
activated molecular sieves. Subsequent transmetallation
was carried out by adding
a solution of 262 mg
(1.01 mmol) of Pd(CH3CN)2Cl2 in 50 ml dichloromethane.
After 1 h a precipitate was removed by filtration and the
solvent removed in vacuo. The yellow crystalline solid
was dried in vacuo to yield 0.85 g (83%) of 13 as a mixture
of four isomers (I–IV), mp 221 ꢀC (DSC). 1H NMR
(600 MHz, 298 K, C2D2Cl4): d = 6.50 (m, each 1H,
5(III)-H); 6.49 (m, each 1H, 5(IV,I + b)-H); 4.26 (m, 2H,
1.1(III)-H); 4.24 (m, 2H, 3.1(III + b)-H); 2.07 (s, 3H,
6(III)-H); 2.04 (m, 2H, 3.2(I)-H); 1.97 (m, 2H, 1.2(III)-
H); 0.99 (m, 3H, 3.3(I)-H); 0.95 (m, 3H, 1.3(I)-H).
13C{1H} NMR (150 MHz, 298 K, C2D2Cl4): d 13C =
169.03 (C, C2(I)); 169.00 (C, C2(II)); 168.74 (C, C2(III));
168.72 (C, C2(IV)); 129.32 (C, C4(III)); 129.28 (C, C4(IV));
C1.1(I)); 49.61 (CH2, C3.1(II)); 49.46 (CH2, C3.1(I)); 24.47
(CH2, C1.2(I)); 24.28 (CH2, C3.2(II)); 24.28 (CH2, C1.2(II));
24.11 (CH2, C3.2(I)); 11.55 (CH3, C3.3(II)); 11.55 (CH3,
C1.3(I)); 11.53 (CH3, C3.3(I)); 11.53 (CH3, C1.3(II)); 9.62
(CH3, C6(II)); 9.59 (CH3, C6(I)). HR-MS (C20H36Cl2N4Pd,
MW = 509.85) (ESI, LM [CHCl3/CH3CN], m/z): calc.:
471.1663/472.1676/473.1663/474.1668/475.1656/476.1685/
477.1659/478.1688/479.1654; found: 471.1669/472.1667/
473.1666/474.1659/475.1657/476.1670/477.1664/478.1764/
479.1759 [C20H36ClN4Pd]+ [M ꢀ Clꢀ]+. IR (KBr):
~
m ¼ 3113 ðsÞ, 2961 (s), 2926 (s), 2878 (s), 2369 (vw), 2343
(vw), 1617 (vw), 1469 (s), 1417 (s), 1365 (w), 1343 (w),

F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
5969
1234 (w), 1187 (s), 1126 (w), 909 (w), 826 (w), 778 (w), 748
(w), 713 (w), 622 (w).
54.86; H, 6.58; N, 6.85. Found: C, 54.65; H, 6.32; N,
6.57%. 1H NMR (600 MHz, 298 K, CD2Cl2): d = 7.78
(m, 2H, o-Ph(II)); 7.72 (m, 2H, o-Ph(I)); 7.54 (m, 1H, p-
Ph(II)); 7.53 (m, 1H, p-Ph(I)); 7.45 (m, 2H, m-Ph(I)); 7.45
(m, 2H, m-Ph(II)); 6.82 (d, 3J(H,H) = 7.45 Hz, 1H, N–
4.15. X-ray crystal structure analysis of complex
trans-anti-13
3
H(II)); 6.77 (d, J(H,H) = 7.45 Hz, 1H, N–H(I)); 6.72 (s,
Formula C20H36N4Br0.56Cl1.44Pd, MW = 534.73, yellow
1H, 5(II)-H); 6.68 (s, 1H, 5(I)-H); 5.00 (m, 1H, 7(II)-H);
4.97 (m, 1H, 7(I)-H); 4.92 (m, 1H, COD@CH(II)); 4.92
(m, 1H, COD@CH(I)); 4.85 (m, 1H, COD@CH(II)); 4.85
(m, 1H, COD@CH(I)); 4.57 (m, 1H, 3.1(I)); 4.50 (m, 1H,
3.1(II)-H); 4.36 (m, 2H, 1.1(II)-H); 4.36 (m, 2H, 1.1(I)-
H); 4.31 (m, 1H, 3.10(II)-H); 4.21 (m, 1H, 3.10(I)-H); 3.77
(s, 3H, OCH3(I)-H); 3.72 (s, 3H, OCH3(II)-H); 3.26 (m,
1H, COD@CH(I)); 3.26 (m, 1H, COD@CH(II)); 3.24
(dd, 3J(H,H) = 5.2 Hz, 2J(H,H) = 16.0 Hz, 1H, 6(I)-H);
3.20 (m, 1H, COD@CH(II)); 3.20 (m, 1H, COD@CH(I));
3.18 (dd, (H,H) = 6.5 Hz, 2J(H,H) = 16.0 Hz 1H, 6(II)-
H); 3.13 (dd, 3J(H,H) = 6.5 Hz, 2J(H,H) = 16.0 Hz, 1H,
˚
crystal 0.15 · 0.10 · 0.06 mm, a = 8.215(1) A, b = 10.329
3
˚
˚
˚
(1) A, c = 14.858(1) Aꢀ, b = 92.27(1)ꢀ, V = 1259.8(2) A ,
q
calc = 1.410 g cmꢀ3, l = 17.89 cmꢀ1, empirical absorption
correction (0.775 6 T 6 0.900), Z = 2, monoclinic, space
˚
group P21/c (No. 14), k = 0.71073 A, T = 198 K, x and
/ scans, 8429 reflections collected ( h, k, l), [(sinh)/
k] = 0.66 Aꢀ1, 2005 independent (Rint = 0.042) and 2021
˚
observed reflections [I P 2r(I)], 137 refined parameters,
R = 0.049, wR2 = 0.141, chlorine site occupied with 28%
bromine, maximum (minimum) residual electron density
0.84 (ꢀ0.40) e Aꢀ3, hydrogen atoms calculated and refined
˚
3
2
as riding atoms. Single crystals of this single diastereomer
were obtained from dichloromethane (see Fig. 6).
60(II)-H); 3.06 (dd, J(H,H) = 7.7 Hz, J(H,H) = 16.0 Hz,
1H, 60(I)-H); 2.42, 1.96 (m, 2H, COD–CH2(I)); 2.42, 1.96
(m, 2H, COD–CH2(II)); 2.38, 1.96 (m, 2H, COD–
CH2(I)); 2.38, 1.96 (m, 2H, COD–CH2(II)); 2.36, 1.89 (m,
2H, COD–CH2(II)); 2.36, 1.89 (m, 2H, COD–CH2(I));
2.31, 1.89 (m, 2H, COD–CH2(I)); 2.31, 1.88 (m, 2H,
COD–CH2(II)); 2.13 (m, 2H, 3.2(I)-H); 1.77 (m, 2H,
1.2(II)-H); 1.77 (m, 2H, 1.2(I)-H); 1.77 (m, 2H, 3.2(II)-
H); 1.06 (m, 3H, 3.3(I)-H); 1.06 (m, 3H, 3.3(II)-H); 1.00
(t, 3J(H,H) = 7.45 Hz, 3H, 1.3(I)-H); 0.95 (t, 3J(H,H) =
7.65 Hz, 3H, 1.3(II)-H). 13C{1H} NMR (150 MHz,
298 K, CD2Cl2): d = 183.04 (C, C2(I),1J(Rh,C) = 51.4 Hz);
4.16. Preparation of the carbene rhodium complexes
15a(A,B)
In a Schlenk flask the solid histidinium salt 8a (0.53 g,
1.22 mmol) and 0.14 g (0.63 mmol) of Ag2O plus ca.
0.75 g of activated molecular sieves were mixed. Dichloro-
methane (60 ml) was added and the mixture was mechani-
cally shaken for 4 h. Then a solution containing 301 mg
(0.61 mmol) of [Rh(cod)Cl]2 in 15 ml methylene chloride
was added and the mixture shaken for 16 h. The solution
was decanted from the Ag halide precipitate. Solvent was
removed in vacuo and the yellow-orange colored product
dried in vacuo to yield 0.51 g (65%) of 15a as a 1:0.8 mix-
ture of two diastereoisomers (I, II), mp 72 ꢀC (DSC). Anal.
Calc. for C28H39ClN3O3Rh + 1/2H2O (MW = 613.00): C,
182.98 (C, C2(II),
1J(Rh,C) = 51.7 Hz); 171.89 (C, C8(I));
171.86 (C, C8(II)); 167.17 (C, C9(II)); 167.17 (C, C9(I));
133.91 (C, II-Ph(I)); 133.86 (C, II-Ph(II)); 132.30 (CH, p-
Ph(II)); 132.29 (CH, p-Ph(I)); 129.18 (C, C4(II)); 129.12
(C, C4(I)); 129.00 (CH, m-Ph(II)); 128.97 (CH, m-Ph(I));
127.5 (CH, o-Ph(II)); 127.3 (CH, o-Ph(I)); 118.68 (CH,
Fig. 6. Experimental (top) and calculated (bottom) ESI HRMS of 13 (i.e., C20H36ClN4Pd+ [M ꢀ Cl]+, left) and 15a (i.e., C28H39H3O3Ru+, [M ꢀ Cl]+,
right).

5970
F. Hannig et al. / Journal of Organometallic Chemistry 690 (2005) 5959–5972
3
C5(II)); 118.66 (CH, C5(I)); 98.14 (CH, COD@CH(II),
1.12 (s, 9H, C(CH3)3(I)); 0.80 (t, J(H,H) = 7.4 Hz, 3H,
1J(Rh,C) = 7.0 Hz); 98.14 (CH, COD@CH(I), J(Rh,C) =
3.3(I)-H); 0.79 (t, 3J(H,H) = 7.4 Hz, 3H, 3.3(II)-H); 0.74 (t,
3J(H,H) = 7.5 Hz, 3H, 1.3(II)-H); 0.73 (t, 3J(H,H) = 7.4 Hz
3H, 1.3(I)-H). 13C{1H} NMR (150 MHz, 298 K, CD3CN):
d = 182.53 (C, C2(II)); 182.16 (C, C2(I)); 172.65 (C, C8(II));
172.59 (C, C8I)); 156.30 (C, C9(II)); 156.23 (C, C9(I)); 130.62
(C, C4(II)); 130.4 (C, C4(I)); 119.77 (CH, C5(I)); 119.57 (CH,
1
7.0 Hz); 97.78 (CH, COD@CH(II), 1J(Rh,C) = 6.2 Hz);
1
97.74 (CH, COD@CH(I), J(Rh,C) = 6.8 Hz); 68.82 (CH,
COD@CH(I), 1J(Rh,C) = 14.6 Hz); 68.72 (CH, COD@
CH(II), 1J(Rh,C) = 15.0 Hz); 68.03 (CH, COD@CH(I),
1J(Rh,C) = 14.3 Hz); 67.97 (CH, COD@CH(II), 1J(Rh,
C) = 14.9 Hz); 53.2 (CH3, OCH3(I)); 53.0 (CH3,
OCH3(II)); 52.84 (CH2, C1.1(II)); 52.79 (CH2, C1.1(I)); 52.0
(CH, C7(II)); 51.8 (CH, C7(I)); 50.45 (CH2, C3.1(I)); 50.43
(CH2, C3.1(II)); 33.62 (CH2, COD–CH2(I)); 33.59 (CH2,
COD–CH2(II)); 32.89 (CH2, COD–CH2(II)); 32.84 (CH2,
COD–CH2(I)); 29.59 (CH2, COD–CH2(I)); 29.54
(CH2, COD–CH2(II)); 28.90 (CH2, COD–CH2(II)); 28.80
C
5(II)); 98.07 (CH, COD@CH(I), 1J(Rh,C) = 5.5 Hz);
98.01 (CH, COD@CH(II), 1J(Rh,C) = 5.9 Hz); 97.75 (CH,
COD@CH(I)); 97.70 (CH, COD@CH(II)); 80.27 (C,
C(CH3)3); 80.16 (C, C(CH3)3); 69.60 (CH, COD@CH(II));
69.60 (CH, COD@CH(I)); 68.85 (CH, COD@CH(II));
68.85 (CH, COD@CH(I)); 53.60 (CH, C7(I)); 53.60 (CH,
C
7(II)); 53.12 (CH3, O–CH3(I)); 53.11 (CH2, C1.1(II)); 53.09
(CH2, C1.1(I)); 53.09 (CH3, O–CH3(II)); 50.68 (CH2,
3.1(I)); 50.63 (CH2, C3.1(II)); 33.83 (CH2, COD–CH2(II));
33.79 (CH2, COD–CH2(I)); 33.19 (CH2, COD–CH2(I));
33.16 (CH2, COD–CH2(II)); 29.88 (CH2, COD–CH2(I));
29.86 (CH2, COD–CH2(II)); 29.21 (CH2, COD–CH2(II));
29.19 (CH2, COD–CH2(I)); 28.45 (CH3, C(CH3)3); 28.44
(CH3, C(CH3)3); 27.63 (CH2, C6(II)); 27.45 (CH2, C6(I));
25.17 (CH2, C3.2(II)); 25.13 (CH2, C3.2(I)); 24.79 (CH2,
0
(CH2, COD–CH2(I)); 27.73 (CH2, C6 (II)); 27.73 (CH2,
C6(II)); 27.72 (CH2, C6(I)); 25.0 (CH2, C3.2(II)); 24.9 (CH2,
C3.2(I)); 24.5 (CH2, C1.2(II)); 24.4 (CH2, C1.2(I)); 11.8 (CH,
C3.3(I)); 11.7 (CH, C3.3(II)); 11.54 (CH3, C1.3(I)); 11.50
C
(CH3, C1.3(II)). HR-MS (C28H39ClN3O3Rh, MW = 603.99)
(ESI, LM [CHCl3/CH3CN], m/z): calc.: 568.2041/
569.2073/570.2102; found:ꢀ +568.1996/569.2025/570.2050
[C28H39N3-O3Rh]+ [M ꢀ Cl ] . IR (KBr): m ¼ 3400 ðbrÞ,
~
2965 (s), 2926 (s), 2874 (s), 2826 (w), 2374 (w), 2348 (w),
1739 (s), 1648 (s), 1526 (s), 1491 (w), 1400 (w), 1026 (w),
800 (w), 709 (w), 687 (w). [a]20 (k) = +2.1 (589), +2.1
(578), +3.0 (546) (c = 10.35, CHCl3).
C1.2(I)); 24.78 (CH2, C1.2(II)); 11.77 (CH3, C3.3(I)); 11.73
(CH3, C3.3(II)); 11.63 (CH3, C1.3(I)); 11.61 (CH3, C1.3(II)).
HR-MS (C26H43ClN3O4Rh, MW = 584.00) (ESI, LM
[CHCl3/CH3CN], m/z): calc.: 564.2303/565.2335/566.2363;
found: 564.2252/565.2282/566.2301 [C26H43N3O4Rh]+
ꢀ +
~
4.17. Preparation of 15b(A,B)
[M ꢀ Cl ] . IR (KBr): m ¼ 3434 ðbrÞ, 2965 (s), 2930 (s),
2869 (s), 2826 (s), 1752 (s), 1704 (s), 1517 (w), 1365 (w),
1252 (w), 1161 (s), 1056 (w), 1026 (w), 996 (w), 961 (w), 865
(w), 813 (w), 478 (w). [a]20 (k) = +16.4 (589), +17.3 (578),
+19.8 (546) (c = 5.1, CHCl3).
Analogously as described above the reaction of 0.20 g
(0.46 mmol) of 8b with 63 mg (0.24 mmol) of Ag2O and
0.28 g (0.23 mmol) of [Rh(cod)Cl]2 in a total volume of
100 ml of dichloromethane gave 196 mg (73%) of the prod-
uct 15b as a mixture (1:0.8) of two diastereoisomers (I, II),
5. Supplementary data
1
mp 49 ꢀC decomp.: 236 ꢀC (DSC). H NMR (600 MHz,
298 K, CD3CN): d = 6.65 (s, 1H, 5(II)-H); 6.53 (s, 1H,
CCDC 276235, 276236, 276237, and 277073 contain the
supplementary crystallographic data for this paper. These
data can be obtained free of charge at www.ccdc.cam.
ac.uk/conts/retrieving.html [or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (internat.) +44 1223 336 033, e-mail:
deposit@ccdc.cam.ac.uk].
3
5(I)-H); 5.49 (d, J(H,H) = 7.7 Hz, 1H, N–H(II)); 5.43 (d,
3J(H,H) = 8.4 Hz, 1H, N–H(I)); 4.61 (m, 1H, COD@
CH(I)); 4.61 (m, 1H, COD@CH(II)); 4.55 (m, 1H, COD@
CH(I)); 4.54 (m, 1H, COD@CH(II)); 4.39 (m, 1H, 3.1(II)-
H); 4.37 (m, 1H, 3.1(I)-H); 4.19 (m, 2H, 1.1(I)-H); 4.13 (m,
1H, 7(I)-H); 4.07 (m, 1H, 7(II)-H); 4.03 (m, 2H, 1.1(II)-H);
3.91 (m, 1H, 3.1(II0)-H); 3.87 (m, 1H, 3.10(I)-H); 3.44 (s,
3H, OCH3(I)); 3.40 (s, 3H, OCH3(II)); 3.05 (m, 1H, COD@
CH(II)); 3.04 (m, 1H, COD@CH(I)); 3.00 (m, 1H, COD@
Acknowledgements
3
CH(II)); 3.00 (m, 1H, COD@CH(I)); 2.81 (dd, J(H,H) =
Financial support by the Deutsche Forschungsgemeins-
chaft and the Fonds der Chemischen Industrie is gratefully
acknowledged.
4.9 Hz, 2J(H,H) = 15.8 Hz, 1H, 6(II)-H); 2.78 (dd,
3J(H,H) = 4.6 Hz, 2J(H,H) = 15.8 Hz, 1H, 6(I)-H); 2.65
2
(dd, 3J(H,H) = 9.1 Hz, J(H,H) = 15.8 Hz, 1H, 60(I)-H);
2.62 (dd, 3J(H,H) = 9.3 Hz, 2J(H,H) = 15.8 Hz, 1H, 60(II)-
H); 2.15, 1.55 (m, 2H, COD–CH2(I)); 2.15, 1.55 (m, 2H,
COD–CH2(II)); 2.15, 1.53 (m, 2H, COD–CH2(II)); 2.15,
1.53 (m, 2H, COD–CH2(I)); 2.14, 1.55 (m, 2H, COD–
CH2(II)); 2.14, 1.55 (m, 2H, COD–CH2(I)); 2.14, 1.53 (m,
2H, COD–CH2(I)); 2.14, 1.53 (m, 2H, COD–CH2(II)); 1.87
(m, 2H, 3.2(I)-H); 1.70 (m, 2H, 1.2(I)-H); 1.57 (m, 2H,
1.2(II)-H); 1.51 (m, 2H, 3.2(II)-H); 1.14 (s, 9H, C(CH3)3(II));
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