Norbornene bidentate ligands: coordination chemistry and enantioselective catalytic applications

Article abstract of DOI:10.1002/ejic.200900879

N- and P-donor derivatives have been prepared by functionalization of a readily available norbomene precursor. Palladium, catalytic systems containing these new ligands were applied in allylic substitution, and yielded high, activities and excellent enantioselectivities for the allylic alkylation and amination reactions (ee up to 97%). A full coordination analysis of the catalytic precursors including modelling studies was also carried, out.

Full text of DOI:10.1002/ejic.200900879

FULL PAPER
DOI: 10.1002/ejic.200900879
Norbornene Bidentate Ligands: Coordination Chemistry and Enantioselective
Catalytic Applications
Fernando Fernández,[a,b] Aitor Gual,[c] Carmen Claver,[c] Sergio Castillón,[c]
Guillermo Muller,[a] and Montserrat Gómez*[b]
Keywords: Palladium / Norbornene ligands / Enantioselectivity / N ligands / Allylic compounds
N- and P-donor derivatives have been prepared by function-
alization of a readily available norbornene precursor. Palla-
dium catalytic systems containing these new ligands were
applied in allylic substitution, and yielded high activities and
excellent enantioselectivities for the allylic alkylation and
amination reactions (ee up to 97%). A full coordination
analysis of the catalytic precursors including modelling stud-
ies was also carried out.
mer (pyridine and related aromatic heterocycles[10] or ox-
azoline derivatives[11]) is the most largely applied in enantio-
selective reactions. As is known, P-donor fragments are in-
cluded in the main part of classical homogeneous catalysis,
ligands such as phosphanes and phosphites, but also phos-
phinites, phosphonites and phosphoramidites.[12] After the
successful results obtained with diphosphites derived from
(2R,4R)-pentanediol by Union Carbide in the 1990s,[13] di-
phosphites derived from different backbones were designed,
in particular those with the xylofuranose skeleton described
by van Leeuwen.[4a,4b] In the last few years, we have also
reported the synthesis of diphosphites derived from rigid
backbones, such as ribofuranose and glucofuranose,[4c,14]
and also from 9,10-dihydroanthracene,[5c] obtaining excel-
lent selectivities (ee Ͼ 97%) and activities (TOF Ͼ
22000 h–1) for the Pd-catalyzed allylic substitution.[15] These
diphosphites have also found remarkable application in
styrene hydroformylation (ee Ͼ 50%).[4,5c,14]
Introduction
The creation of an asymmetric environment around a
metallic centre in order to accommodate the partners of an
organic transformation allows enantioselectivity induction
in catalytic processes.[1,2] A classical approach to get this
goal is the use of enantiomerically pure ligands containing
donor atoms (mainly nitrogen and phosphorus) with a de-
fined symmetry.[3] The rigidity of the backbone is one of
the key aspects to take into account in the design of chiral
ligands. Furanose,[4] 9,10-dihydroanthracene[5] or imide[5a]
backbones are significant examples that contain donor moi-
eties that lead to excellent asymmetric inductions in several
processes. Keeping this idea in mind, we have developed a
new family of ligands containing a polycyclic backbone de-
rived from the norbonene carboxylic anhydride. Although
similar compounds have been widely used as substrates in
ring opening metathesis polymerization (ROMP) reac-
tions,[6] only one study that involves the use of related li-
gands (derived from bicyclo[2.2.2]-2-octene) in V-catalyzed
asymmetric epoxidation of homoallylic alcohols has thus
far been reported.[7] We have been interested in N- and P-
donor ligands because these derivatives, in particular, give
excellent enantioselectivies in allylic substitutions catalyzed
by palladium.[8] With regard to the nature of the nitrogen
atom, ligands containing both sp2 (imines) and sp3 (amines)
hybridized nitrogen moieties have been explored;[9] the for-
Herein we report the synthesis of new ligands derived
from endo-norborn-5-ene-2,3-dicarboxylic anhydride (Fig-
ure 1) and their application in Pd-catalyzed enantioselective
allylic substitution reactions. The coordination chemistry of
the new amine and phosphite ligands has been studied both
in solution and in the solid state.
Results and Discussion
[a] Departament de Química Inorgànica, Universitat de Barcelona,
Martí i Franquès, 1-11, 08028 Barcelona, Spain
[b] Laboratoire Hétérochimie Fondamentale et Appliquée, UMR
CNRS 5069, Université Paul Sabatier,
Synthesis of Ligands
N,N- and P,P-donor ligands with a norbornene scaffold
were developed (Figure 1). Bis(amines) 3 and 4 were pre-
pared following a two-step synthetic procedure based on
our previously reported methodology (Schemes 1 and 2).[16]
In the first step, bis(imides) 1 and 2 were prepared by con-
densation of the anhydride with the appropriate primary
bis(amine) in toluene at reflux,[17] by using a Dean–Stark
118, route de Narbonne, 31120 Toulouse Cedex 9, France
Fax: +33-5-61558204
E-mail: gomez@chimie.ups-tlse.fr
[c] Departament de Química Física i Química Inorgànica i Quím-
ica Analítica i Química Orgànica, Universitat Rovira i Virgili,
c/Marcel.lí Domingo, s/n, 43007 Tarragona, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900879.
758
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Norbornene Ligands: Coordination Chemistry and Enantioselective Catalysis
Figure 1. New N- and P-donor ligands containing a norbornene scaffold.
Scheme 1. Synthesis of imides 1 and 2 starting from endo-carbic anhydride.
system to eliminate the water formed (Scheme 1). When the
more sterically hindered (1R,2R)-1,2-diphenylethylenedi-
amine was used, a mixture of the mono(imide) and the cor-
responding amido acid only was recovered.
Figure 2. View of the molecular structure of 1. Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å]: N1–C1 = 1.455;
N1–C2 = 1.390; N1–C3 = 1.385; O1–C2 = 1.208; O2–C3 = 1.214.
Selected torsion angles [°]: O1–C2–N1–C3 = 179.3; N1–C2–C4–C5
= 2.7.
Scheme 2. Synthesis of bis(amines) 3 and 4 from the corresponding
imides.
1
For 2, the VT H NMR study in solution (323–223 K)
evidences the presence of two isomers below room tempera-
ture in a ratio of 4:3 (Figure S1 in the Supporting Infor-
The bis(amines) 3 and 4 were obtained by standard re- mation), presumably resulting from the rotation around the
duction of the carbonyl groups with LiAlH4, from the iso- C*–N bond; this result is in agreement with the modelling
lated bis(imides) (Scheme 2).[18]
study carried out (Figure 3). This rotation is more sterically
An X-ray diffraction study carried out on monocrystals hindered for the corresponding bis(amine) 4 than for the
of compound 1 reveals a centrosymmetric structure that corresponding imide 2, mainly because of the pyramidali-
presents a quasi-planar five-membered heterocycle. The zation of the nitrogen atom after reduction of the carbonyl
short N1–C2 and N1–C3 bond lengths (ca. 1.39 Å) relative groups (Figure 3). Actually, the 1H NMR spectra of 4
to the N1–C1 distance (1.45 Å) points to an electronic delo- shows only the presence of one species in the temperature
calization between the nitrogen and the close carbonyl range studied (298–223 K) (Figure S2 in the Supporting In-
groups (Figure 2).
formation).
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759

F. Fernández, A. Gual, C. Claver, S. Castillón, G. Muller, M. Gómez
FULL PAPER
Scheme 3. Synthesis of the chiral diphosphite 5 from the corresponding diol.
Figure 4. Modelled structures (by PM3 methodology) of both iso-
mers of ligand 5 (their relative formation enthalpies are in paren-
theses). Hydrogen atoms are omitted for clarity.
Enantioselective Catalytic Reactions
The allylic alkylation of racemic substrate rac-I with di-
methyl malonate under basic conditions (BSA/KOAc) was
performed, which involved in situ catalyst formation by re-
action of [Pd(η3-C3H5)Cl]2 and the corresponding ligand
(3–6, Scheme 4). Unlike other catalytic systems containing
nonchiral bis(amines), 3 and 6 gave good conversions after
2 h (Entries 1 and 2, Table 1); the catalyst containing the
bulkier and more rigid chiral bis(amine) 4 was inactive (En-
try 3, Table 1). In contrast, Pd/5 gave nearly total conver-
sion of the substrate after 30 min of reaction (Entries 4 and
5, Table 1), with an excellent asymmetric induction [ee =
97% (S) for II]. This system was also very active in allylic
amination with benzylamine as the nucleophile; 80% con-
version of rac-I was observed in 1 h with an ee of 95%
(R) for III (Entries 6 and 7, Table 1). However, the allylic
Figure 3. Modelled structures (by PM3 methodology) of both iso-
mers of compounds 2 and 4 (their relative formation enthalpies are
in parentheses). Only selected hydrogen atoms are shown.
A bidentate P-donor ligand was also synthesized by func-
tionalization of the alcohol groups integrated in an op-
tically pure imide–norbornene precursor.[16] Thus, diphos-
phite 5 was isolated following our previously reported
methodology (Scheme 3).[5c] The diol was treated with the
appropriate phosphorochloridite (prepared in situ by stan-
dard procedures[19]) to give 5 in a good yield (71%).
This ligand shows two isomers in solution in a ratio of
1
3:1 (for the H and 31P spectra, see Figure S3 in the Sup-
porting Information). In order to understand the origin of
these conformers, a modelling study (PM3 semiempirical
level) was carried out. These isomers probably arise because
of the relative position of both substituents on the C
stereocentres (Figure 4). No interconversion was observed
in solution, which is in agreement with the important differ-
ence in their relative calculated enthalpies (∆E = 3.9 kcal/
mol) and with the calculated rotation barrier around the
corresponding C–N bond (ca. 3 kcal/mol).
Scheme 4. Allylic substitution catalyzed by palladium systems con-
taining ligands 3–6.
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Norbornene Ligands: Coordination Chemistry and Enantioselective Catalysis
Scheme 5. Regioselective allylic alkylation catalyzed by palladium systems containing ligands 3, 5 and 6.
alkylation of the less hindered cyclohexenyl allylic acetate tive in the catalytic processes studied (Scheme 6). Therefore
rac-IV catalyzed by Pd/5 led to a low asymmetric induction, we prepared the palladium allylic complexes Pd5 and Pd6
ee up to 17% (S) (Entries 8 and 9, Table 1).
containing the chiral diphosphite 5, which led to excellent
enantioselectivies in the alkylation and amination reactions,
and the bis(amine) 6, which gave the highest activity in the
allylic alkylation of substrate rac-I and a high regioselectiv-
ity towards the linear isomer in the alkylation of cinnamyl
acetate The complexes were fully characterized by conven-
tional techniques (see Experimental Section). The results of
the elemental analysis and the mass spectrometry and IR
spectroscopy studies are in agreement with the formation of
ionic complexes with the formula [Pd(η3-1,3-Ph2–C3H3)(κ2-
X,X-L)]PF6 (where X = P or N and L = 5 or 6, respec-
tively), proposed in Scheme 6.
Table 1. Palladium-catalyzed allylic substitution with ligands 3–6.[a]
Entry
L
Sub-
strate
NuH[b] Time
[h]
Conv.
[%][c]
ee
l/b
[%][d] ratio[c]
1
3
6
4
5
5
5
5
5
5
5
3
6
rac-I
rac-I
rac-I
rac-I
rac-I
rac-I
rac-I
DMM 2
DMM 2
DMM 4
DMM 0.25
DMM 0.5
BnNH2 0.25
BnNH2 1
64
100
0
–
–
–
–
–
–
–
–
–
–
–
2
3[e]
4
76
95
35
80
34
99
96
92
98
97(S)
97(S)
95(R)
95(R)
9(S)
17(S)
–
5
6
7
8
rac-IV DMM 0.5
rac-IV DMM 2
VI
VI
VI
9
–
10
11
12
DMM 0.5
DMM 1
DMM 1
7:1
Ͼ9:1
Ͼ9:1
–
–
[a] Catalytic conditions for alkylation: [Pd(η3-C3H5)Cl]2/L/sub-
strate/DMM/BSA = 1:2.5:100:300:300, CH2Cl2, room tempera-
ture.; for amination: [Pd(η3-C3H5)Cl]2/L/substrate/BnNH2
=
1:2.5:100:300, CH2Cl2, room temperature. [b] NuH = dimethyl-
malonate (DMM) using BSA and a catalytic amount of KOAc as
a base; NuH = benzylamine (BnNH2). [c] Determined by 1H NMR
spectroscopy. [d] Determined by HPLC for II and III and by GC
for V. The absolute configuration of the substituted product deter-
mined by optical rotation is given in parentheses: for II and III,
see ref.[25]; for V, see ref.[26] [e] When Pd/4 = 1:2.5, 7% conversion
was obtained after 4 h of reaction.
Scheme 6. Synthesis of Pd5 and Pd6 complexes.
1H and 31P spectra at variable temperatures were re-
corded for Pd5. The 31P NMR spectrum at room tempera-
ture shows broad signals in the region ca. 125–135 ppm. At
lower temperatures, two groups of signals can be distin-
guished (ca. 134 and 124 ppm); each of these groups exhibit
several signals, probably resulting from the presence of sev-
eral isomers (Figure 5). At 233 K, a 31P-31P COSY experi-
ment was recorded in order to observe the correlations be-
tween both groups of signals, but, unfortunately, no signals
In order to evaluate the regio- and enantioselectivity, we
studied the reactivity of the Pd/5 catalytic system in the
allylic alkylation of cinnamyl acetate (Scheme 5). Unfortu-
nately, this catalytic system principally favoured the forma-
tion of the linear regioisomer (l/b = 7:1, Entry 10, Table 1).
The use of the achiral bis(amine) ligands 3 and 6[16] im-
proves this regioselectivity and exclusively gives the linear
isomer (Entries 11 and 12, Table 1). No reactivity differ-
ences were observed when preformed complex Pd6 (see be-
low) was used as a catalytic precursor.
Bis(amine) ligands 3, 4 and 6 were also used in the Ru-
catalyzed asymmetric hydrogen transfer reaction of aceto-
phenone by using 2-propanol in the presence of potassium
tert-butoxide as the hydrogen source. Ru/bis(amine) systems
were moderately active, but unfortunately Ru/4 did not in-
duce enantioselectivity (see Supporting Information for
catalytic results and experimental details).
1
were observed. The H NMR spectra show a complicated
pattern, and it is difficult to assign the different signals to
the different isomers involved in solution (Figure S4 in the
Supporting Information). These observations evidence the
formation of several isomers in solution, which arise from
the ligand conformers (see above) and the allyl isomers.
1
With regard to Pd6, the H and 13C NMR spectra at
room temperature proves the presence of two isomers in
solution in a ratio of ca. 7:1 (Figure S5 in the Supporting
Information). The complex shows three sources of plausible
isomerism. One of them is the relative position of the bicy-
cle moiety of the bis(amine) in relation to the phenyl group
of the allyl ligand (isomers A and B or C and D in
Scheme 7). Another arrangement that can lead to different
isomers is the relative position of the central allylic carbon
Coordination Chemistry
We have carried out a coordination chemistry study in- atom in relation to the PdNNЈ coordination plane (isomers
volving the ligands which were active and/or enantioselec- A and C or B and D in Scheme 7); A and C, and B and D
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761

F. Fernández, A. Gual, C. Claver, S. Castillón, G. Muller, M. Gómez
FULL PAPER
Scheme 7. Possible isomers of Pd6 (only the cation is shown) de-
pending on the relative position of the bicycle group of the bis-
(amine) and the allyl ligands.
Figure 5. VT 31P NMR spectra (150–110 ppm region, 161 MHz,
CD2Cl2) for Pd5. At –145.5 ppm, a septet assigned to the hexafluo-
rophosphate anion is observed.
We were also interested in the study of the coordination
of the symmetrical bis(amines) 3 and 4 with ruthenium. Ac-
tually, Ru3 was obtained in a good yield (63%) from the
Ru dimer [RuCl2(p-cymene)]2 in the presence of 3. However,
attempts to isolate the corresponding complex containing
the chiral bis(amine) 4 were unsuccessful, probably because
of the steric hindrance around the metal centre upon coor-
dination (see Supporting Information for characterization
and experimental details).
represent two couples of enantiomers. The third arrange-
ment comes from the relative syn or anti position of the
phenyl groups in the allyl fragment; taking into account
that the syn arrangement corresponds to the most stable
conformation and that the 2D NOESY NMR spectrum
does not exhibit exchange signals between the two isomers
observed in solution, we can propose that the π–σ–π in-
terconversion did not take place and consequently only
syn/syn isomers are observed.
Conclusions
In summary, new N-donor (3 and 4) and P-donor (5)
Therefore the two isomers observed by NMR spec- ligands containing a norbornene backbone were synthe-
troscopy must arise as a result of the relative position of sized, and their catalytic applications in Pd-catalyzed allylic
the bicycle. The X-ray diffraction analysis of monocrystals substitution reactions were examined. For the more active
obtained by slow evaporation of a chloroform solution and selective systems, a coordination chemistry study was
shows a structural disorder with 88.7% occupancy for the carried out both in the solid state and in solution by means
isomer A and 11.3% for B (Figure 6). Both molecules show of NMR spectroscopy. A full discussion about the different
a slightly distorted square-planar arrangement around the isomers observed in solution was considered including
palladium atom (dihedral angle between N1PdN2 and modelling approaches. The chiral diphosphite 5 gave excel-
C20Pd1C22 is ca. 11°, Figure 6). The five-membered lent asymmetric induction in allylic alkylation (97% ee) and
metallacycle adopts a half-chair conformation.
amination (95% ee). With respect to the bidentate N,N-do-
Figure 6. ORTEP diagrams of Pd6 corresponding to the isomers A and B. Their enantiomers and hydrogen atoms are omitted for clarity.
Selected bond lengths [Å]: Pd1–C20 = 2.171; Pd1–C22 = 2.174; Pd1–C21 = 2.134; Pd1–N1 = 2.160; Pd1–N2 = 2.148. Selected bond
angles [°]: C20–Pd1–C22 = 67.65; N1–Pd1–N2 = 84.09; C20–C21–C22 = 118.3.
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Norbornene Ligands: Coordination Chemistry and Enantioselective Catalysis
and consecutively washed with 1  H2SO4 (3ϫ20 cm3) and water
nor ligands 3 and 6, the palladium systems were active in
allylic alkylation. The palladium systems were highly re-
gioselective towards the linear isomer (l/b Ͼ 9:1) in the al-
lylic alkylation of cinnamyl acetate. However, the chiral bis-
(amine) 4 was not active in allylic alkylation, probably be-
cause of its steric hindrance to give metallacycle. A prelimi-
nary study involving the Ru systems did not induce enantio-
selectivity in the hydrogen transfer of acetophenone.
(3ϫ20 cm3). The aqueous phases were extracted with 10 cm3 of
CH2Cl2. The combined organic extracts were dried with anhydrous
Na2SO4 and filtered. The filtrate was concentrated to dryness un-
der reduced pressure, to give the corresponding bis(imide). Bis-
(imide) 1: White solid. Yield: 2.13 g (99%). White crystals suitable
for the structural resolution by X-ray diffraction were grown by
slow evaporation of a solution of this product in water. IR (KBr
pellet): ν = 2997, 2956, 1703 (CO), 1395, 1339, 1162, 1127, 1029,
˜
874, 843, 781, 720, 613 cm–1. 1H NMR (400 MHz, CDCl3): δ =
1.51 (d, J = 8.8 Hz, 2 H, 2ϫCHHЈbridge), 1.71 (dt, J = 1.6 and
8.8 Hz, 2 H, 2ϫCHHЈbridge), 3.23 (dd, J = 1.6 and 3.2 Hz, 4 H, 4ϫ
CHolefinCHCH2bridge), 3.34 (m, 4 H, 4ϫCHCON), 3.47 (s, 4 H,
2ϫCONCH2), 6.05 (t, J = 1.8 Hz, 4 H, 4ϫCHolefin) ppm. 13C
NMR (100 MHz, CDCl3): δ = 36.5 (2ϫCONCH2), 44.8 (4ϫ
CHolefinCHCH2bridge), 46.1 (4ϫCHCON), 52.4 (2ϫCH2bridge),
134.6 (4ϫCHolefin), 177.8 (4ϫCO) ppm. MS (EI): calcd. for
C20H20N2O4 [M]+ 352.1; found 352.0. C20H20N2O4 (352.1): calcd.
C 68.2, H 5.7, N 8.0; found C 67.7, H 5.8, N 7.9. Bis(imide) 2:
White solid obtained after crystallization of the original brown oil
Experimental Section
General Remarks: Compounds were prepared under a purified ni-
trogen atmosphere by using standard Schlenk and vacuum-line
techniques. Organic solvents were purified by standard procedures
and distilled under nitrogen. Unless stated otherwise, all reactants
and reagents were purchased commercially and used without fur-
ther purification. Syntheses of the PdII dimer,[20] substrates rac-I[21]
and rac-IV,[22] endo-N-[(1S,2S)-1,3-dihydroxy-1-phenylprop-2-yl]bi-
cyclo[2.2.1]hept-5-ene-2,3-dicarboximide and ligand 6[16] are de-
scribed elsewhere. 1H, 13C{1H} and 31P{1H} NMR spectra were
recorded on Varian Mercury 400 and Bruker Advance 500 spec-
trometers equipped with a CryoFlowProbe. Chemical shifts are re-
25
in hexane/CH2Cl2 (5:1). Yield: 1.62 g (65%). [α]D = –13.1 (c 1.0,
CHCl ). IR (KBr pellet): ν = 2990, 2941, 2871, 1702 (CO), 1376,
˜
3
1337, 1257, 1187, 1124, 1044, 845, 752, 725, 662, 626 cm–1. 1H
NMR (40 MHz, CDCl3): Isomer A (66%): δ = 1.32 (bs t,
2ϫCONCHCHHЈ,
2ϫCONCHCH2CHHЈ,
2ϫCHHЈbridge), 1.64–1.74 (bs, s, 2ϫCONCHCHHЈ, 2 H), 1.68
(d, 8.4 Hz, H, 2ϫCHHЈbridge), 2.06 (br. s, H,
2ϫCONCHCH2CHHЈ), 3.10 (bs, s, 4 H, 4ϫCHCON), 3.34 (bs,
s, H, 4ϫCHolefinCHCH2bridge), 4.61 (bs, s, H,
J
=
10.2 Hz,
2
H), 1.44–1.50 (bs, s,
2
H), 1.47 (d,
J
=
8.4 Hz, H,
2
ported in ppm relative to external standards (SiMe4 for 1H and 13
C
and 85% H3PO4 for 31P), and coupling constants are given in Hz.
IR spectra were carried out on pellets of dispersed samples of the
corresponding compounds in KBr and were obtained on a FTIR
Nicolet Nexus 5700 spectrometer. MS spectra were recorded with
a Hewlett–Packard 5989A instrument with an electron energy of
70 eV (EI), with a ThermoFinnigan TRACE DSQ mass spectrome-
ter with an electron energy of 70 eV, and ammonia as reactant gas
(CI), or with a LC/MSD-TOF mass spectrometer (HR-ES). Ele-
mental analyses were carried out at the Servei dЈAnàlisi Elemental
of the Universitat de Barcelona or the Servei dЈAnàlisi Química of
the Universitat Rovira i Virgili, in both cases by using an Eager
1108 instrument. Optical rotations were measured on a Perkin–
Elmer 241MC polarimeter at room temperature. GC routine analy-
ses were carried out by using an Agilent 6890N chromatograph
(30 mϫ0.32 mm HP5 column), while enantioselectivities in prod-
uct V were also analyzed by GC on a Hewlett–Packard 5890 chro-
matograph (30 mϫ0.25 mm capillary Chiraldex B-DM column),
both of them with a FID detector. Enantiomeric excesses in prod-
ucts II and III were determined by HPLC by using a Waters 717
Plus autosampler chromatograph with a Waters 996 multidiode ar-
ray detector fitted with a Chiralcel OD-H chiral column [eluent:
hexane/2-propanol (95:5)] for II or a Alliance 2695 chromatograph
with PDA-UV detector fitted with a Chiralcel OJ-H column [elu-
ent: hexane/2-propanol (95:5)] for III. Modelling studies were per-
formed with the SPARTANЈ06 software.[27]
J
=
2
2
4
2
2ϫCONCHCH2), 6.04 (bs, s, 4 H, 4ϫCHolefin). Isomer B (34%):
1.32 (bs, t, 2ϫCONCHCHHЈ, J = 10.2 Hz, 2 H), 1.47 (d, J =
8.4 Hz,
2ϫCONCHCH2CHHЈ),
2
H, 2ϫCHHЈbridge), 1.61 (bs, s,
1.64–1.74 (bs, s,
2
H,
H,
2
2ϫCONCHCHHЈ), 1.68 (d, J = 8.4 Hz, 2 H, 2ϫCHHЈbridge),
1.86 (bs, s, 2 H, 2ϫCONCHCH2CHHЈ), 3.10 (bs, s, 2 H,
2ϫCHCON), 3.16 (bs, s, 2 H, 2ϫCHЈCON), 3.34 (bs, s, 4 H,
4ϫCHolefinCHCH2bridge), 4.80 (bs, s, 2 H, 2ϫCONCHCH2),
5.89 (bs, s, 2 H, 2ϫCHolefin), 6.04 (bs, s, 2 H, 2ϫCHЈolefin) ppm.
13C NMR (100 MHz, CDCl3): δ = 24.7 (2ϫCONCHCH2), 28.9
(bs, 2ϫCONCHCH2CH2), 45.1 (2ϫCHolefinCHCH2bridge), 45.3
(2ϫCHolefinCЈHCH2bridge),
45.4
(2ϫCHCON),
45.5
(2ϫCЈHCON), 49.8–50.1 (bs, 2ϫCONCHCH2), 52.0–52.4 (bs,
2ϫCH2bridge), 133.7–135.1 (bs, 4ϫCHolefin), 176.8–177.5
(4ϫCO) ppm. MS (CI, NH3): calcd. for [M + H]+ 407.2; found
407.6. C24H26N2O4·H2O: calcd. C 67.9, H 6.7, N 6.6; found C 68.2,
H 6.6, N, 6.5.
Bis(endo-4-azatricyclo[5.2.1.02,6]dec-8-enes) 3 and 4: A solution of
the corresponding bis(imide) (2.84 mmol) in THF (75 cm3) was co-
oled to 0 °C, and lithium tetrahydridoaluminate (2.15 g,
56.75 mmol) was then slowly added. The resulting grey suspension
was heated at reflux for 48–72 h and then cooled to 0 °C. Ethyl
ether (30 cm3) and a saturated aqueous solution of Na2SO4 were
poured into the reaction mixture. The aqueous solution was added
very slowly and stopped when effervescence was no longer ob-
served. The white gel thus obtained was filtered through Celite, and
the resulting colourless solution was washed several times with a
mixture CH2Cl2/MeOH (9:1). The organic layer was washed with
water (3ϫ30 cm3), dried with anhydrous Na2SO4 and filtered, and
the solvent evaporated under reduced pressure to give the corre-
sponding product. Bis(amine) 3: White solid. Yield: 717 mg (85%).
Synthesis of Ligands
Bis(endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide)s 1 and 2: endo-
Norborn-5-ene-2,3-dicarboxylic anhydride (2.00 g, 12.18 mmol)
was dissolved in toluene (50 cm3) under vigorous stirring. The cor-
responding diamine (6.13 mmol) was then slowly added, which lead
to a white suspension. The mixture was heated at reflux and stirred
for 120 h with continuous extraction of water (by means of a Dean–
Stark apparatus). After cooling to room temperature, the solution
formed was concentrated under reduced pressure to render a yel-
lowish solid, which was subsequently dissolved in CH2Cl2 (30 cm3)
IR (KBr pellet): ν = 3059, 2965, 2930, 2865, 2804, 1475, 1336, 1252,
˜
1137, 903, 872, 815, 796, 735 cm–1. 1H NMR (400 MHz, CDCl3): δ
Eur. J. Inorg. Chem. 2010, 758–766
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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763

F. Fernández, A. Gual, C. Claver, S. Castillón, G. Muller, M. Gómez
FULL PAPER
= 1.55 (d, J = 8.0 Hz, 2 H, 2ϫCHHЈbridge), 1.67 (d, J = 8.0 Hz, Synthesis of Complexes
2 H, 2ϫCHHЈbridge), 1.78–1.81 (m, 4 H, 4ϫCHCHHЈN), 2.40
[endo-N-[(1S,2S)-1,3-Bis(3,3Ј,5,5Ј-tetrakis(tert-butyl)biphenyl-2,2Ј-di-
(s, 4 H, 2ϫCHCH2NCH2), 2.76 (bs, s, 4 H, 4ϫCHolefinCHCH2-
bridge), 2.83–2.90 (m, 4 H, 4ϫCHCHHЈN), 2.89 (bs, s, 4 H,
4ϫCHCH2N), 6.09 (bs, s, 4 H, 4ϫCHolefin) ppm. 13C NMR
(100 MHz, CDCl3): δ = 44.7 (4ϫCHolefinCHCH2bridge), 46.7
(4ϫCHCH2N), 54.0 (2ϫCH2bridge), 55.1 (4ϫCHCH2NCH2),
57.3 (4ϫCHCH2N), 137.5 (4ϫCHolefin) ppm. MS [HR-ES(+)]:
calcd. for [M + H]+ 297.2331; found 297.2337. Bis(amine) 4: White
solid obtained after crystallization of the original brown paste by
slow evaporation of a solution of the product in 40 cm3 hexane.
ylphosphito)-1-phenylprop-2-yl]bicyclo[2.2.1]hept-5-ene-2,3-dicarb-
oximide](η3-1,3-diphenylallyl)palladium(II) Hexafluorophosphate
(Pd5): Di-µ-chlorobis[(η3-1,3-diphenylallyl)palladium(II)] (22 mg,
33.3ϫ10–3 mmol) and ligand 5 (76 mg, 63.4 ϫ10–3 mmol) were
combined in CH2Cl2 (20 cm3), and the resulting yellow solution
was stirred at room temperature for 6 h. Ammonium hexafluoro-
phosphate (33 mg, 0.20 mmol) was then added, and the mixture
was stirred at room temperature for a further 18 h. The brownish
suspension obtained was then filtered through Celite to eliminate
Pd0 and gave a yellow solution. The solvent was then evaporated
under reduced pressure, and the yellow foam obtained was recrys-
tallized from a hexane/CH2Cl2 mixture (3:1) at 4 °C. The solid
formed was separated upon filtration and washed with freshly dis-
tilled hexane. The product was thus obtained in the form of yellow
25
Yield: 408 mg (41%). [α]D = +10.5 (c 0.2, CHCl3). IR (KBr pel-
let): ν = 2964, 2934, 2788, 1456, 1439, 1383, 1343, 1260, 1091, 1014,
˜
802, 735 cm–1. 1H NMR (400 MHz, CDCl3): δ = 1.23 (bs, d,
2ϫNCHCHHЈ, J = 4.4 Hz, 2 H), 1.28 (bs, d, J = 14.8 Hz, 2 H,
2ϫNCHCH2CHHЈ), 1.43–1.46 (bs, s, 2 H, 2ϫNCHCHHЈ), 1.44
(d, J = 7.6 Hz, 2 H, 2ϫCHHЈbridge), 1.54 (d, J = 7.6 Hz, 2 H,
2ϫCHHЈbridge), 1.64 (bs, s, 2 H, 2ϫNCHCH2CHHЈ), 2.02 (bs,
s, 2 H, 2ϫNCHCH2), 2.10 (bs, s, 4 H, 4ϫCHCHHЈN), 2.53 (bs,
s, 4 H, 4 ϫCHolefinCHCH2bridge), 2.78 (s, 8 H, 4ϫCHCH2N and
4ϫCHCHHЈN), 6.11 (bs, s, 4 H, 4ϫCHolefin) ppm. 13C NMR
crystals. Yield: 47 mg (45%). IR (KBr pellet): ν = 3445, 2961, 2871,
˜
–
1715, 1456, 1393, 1224, 1200, 1121, 1077, 1048, 885, 842 (PF6 ),
619, 556 cm–1. MS [HR-ES(+)]: calcd. for [M]+ 1488.6735; found
1488.6745. C89H110F6NO8P3Pd (1633.7): calcd. C 65.4, H 6.8, N
0.9; found C 64.4, H 6.9, N 0.9.
(100 MHz, CDCl3):
(2ϫNCHCH2CH2), 45.7 (2ϫCHolefinCHCH2bridge), 45.7
(2ϫCHolefinCЈHCH2bridge), 45.9 (4ϫCHCH2N), 53.0
δ
=
21.0
(2ϫNCHCH2), 24.8
[endo-N-(2-(NЈ,NЈ-Dimethylamino)ethyl)-4-azatricyclo[5.2.1.02,6]dec-
8-ene](η3-1,3-diphenylallyl)palladium(II) Hexafluorophosphate (Pd6):
Di-µ-chlorobis[(η3-1,3-diphenylallyl)palladium(II)] (122 mg, 0.18
mmol) and ligand 6 (75 mg, 0.36 mmol) were combined in CH2Cl2
(20 cm3), and the resulting yellow solution was stirred at room tem-
perature for 2 h. Ammonium hexafluorophosphate (178 mg,
1.09 mmol) was then added, and the mixture was stirred at room
temperature for a further 22 h. The orange solution obtained was
then washed with deoxygenated water (6ϫ10 cm3) under nitrogen
atmosphere, and the aqueous phases were extracted with freshly
distilled CH2Cl2 (10 cm3). After the combined organic extracts
were dried with anhydrous Na2SO4 and filtered, the solvent was
evaporated under reduced pressure. The resulting yellow foam ob-
tained was treated with distilled ethyl ether (3ϫ5 cm3), and the
solvent was evaporated under vacuum, which led to a pale yellow
solid product. Yield: 112 mg (47%). Yellow crystals suitable for the
structural resolution by X-ray diffraction were grown by slow evap-
(4ϫCHCH2N), 54.5 (2ϫCH2bridge), 62.9 (2ϫNCHCH2), 136.6
(4ϫCHolefin) ppm. MS [HR-ES(+)]: calcd. for [M + H]+ 351.2800;
found 351.2804.
endo-N-[(1S,2S)-1,3-Bis(3,3Ј,5,5Ј-tetrakis(tert-butyl)biphenyl-2,2Ј-di-
ylphosphito)-1-phenylprop-2-yl]bicyclo[2.2.1]hept-5-ene-2,3-dicarb-
oximide (5): A solution of endo-N-[(1S,2S)-1,3-dihydroxy-1-phen-
ylprop-2-yl]bicyclo[2.2.1]hept-5-ene-2,3-dicarboximide (313 mg,
1.00 mmol), previously azeotropically dried with toluene
(3ϫ1 cm3), in dry and degassed toluene (10 cm3) and cooled to
0 °C, was slowly added to a solution of phosphorochloridite
(2.10 mmol), synthesized in situ by standard procedures,[4a,19b] in
dry and degassed pyridine (1.5 cm3). The resulting mixture was
stirred overnight allowing the temperature to rise to room tempera-
ture. The pyridinium salts were then removed upon filtration, and
the solution was concentrated to dryness under reduced pressure.
The white foam thus obtained was purified by flash column
chromatography under nitrogen by using toluene as the eluent to
give the desired product as a white solid. Yield: 832 mg (71%). IR
oration of a solution of this product in CHCl . IR (KBr pellet): ν
˜
3
–
= 3429, 2967, 2927, 1649, 1493, 1459, 1260, 1097, 1024, 835 (PF6 ),
696, 666, 556 cm–1. H NMR (40 MHz, CDCl3): Isomer A (88%):
1
δ = 1.49 (d, J = 8.8 Hz, 1 H, CHHЈbridge), 1.52 (dd, J = 8.8 and
11.6 Hz, 1 H, CHCHHЈN), 1.60 (dt, J = 1.8 and 8.0 Hz, 1 H,
CHHЈbridge), 1.72 (s, 3 H, NCH3), 2.13 (dd, J = 9.6 and 12.4 Hz,
(KBr pellet): ν = 3445, 2961, 1708, 1456, 1436, 1396, 1360, 1227,
˜
1091, 994, 878, 802, 782, 699 cm–1. 31P NMR (162 MHz, CDCl3):
Isomer A (74%): δ = 134.4, 146.9 ppm; Isomer B (26%): δ = 132.8,
146.7 ppm. 1H NMR (40 MHz, CDCl3): Isomer A (74%): δ = 1.42–
1.56 [m, 74 H, 8 ϫ C(CH3)3 and CH2bridge], 3.23 (bs, s, 2 H,
2ϫCHolefinCHCH2bridge), 3.27 (bs, s, 2 H, 2ϫCHCON), 3.44 (bs,
s, 1 H, CONCHCHHЈ), 4.13 (bs, s, 1 H, CONCHCHHЈ), 4.58 (dt,
J = 4.4 and 10.4 Hz, 1 H, CONCH), 5.47 (pt, J = 9.8 Hz, 1 H,
CONCHCHPh), 5.95 (bs, s, 1 H, CHolefin), 6.00 (bs, s, 1 H,
CHЈolefin), 7.16–7.54 (m, 13 H, H Ar) ppm. 13C NMR (10 MHz,
CDCl3): Isomer A (74%): δ = 31.1 [C(CH3)3], 31.4 [C(CH3)3], 31.7
[3 ϫ C(CH3)3], 31.8 [2 ϫ C(CH3)3], 31.9 [C(CH3)3], 34.7 [2 ϫ
C(CH3)3], 34.8 [2 ϫ C(CH3)3], 35.4 [2 ϫ C(CH3)3], 35.5 [2 ϫ
C(CH3)3], 44.6 (CHolefinCHCH2bridge), 44.7 (CHolefinCЈHCH2-
bridge), 45.2 (CHCON), 45.3 (CЈHCON), 51.7 (CH2bridge), 57.0
(CONCH), 59.6 (CONCHCH2), 72.0 (CONCHCHPh), 124.1–
146.5 (C Ar) ppm. MS [HR-ES(+)]: calcd. for [M + Na]+
1212.6587; found 1212.6584; calcd. for [M + K]+ 1228.6326; found
1228.6325. C74H97NO8P2 (1228.6): calcd. C 74.7, H 8.2, N 1.2;
found C 74.5, H 8.3, N 1.3.
1
H, CHCHHЈN), 2.51 [bs, s, 5 H, CHolefinCHCH2bridge,
CHHЈN(CH3)2 and NCHЈ3], 2.57–2.63 [m, 3 H, CHolefinCHЈCH2-
bridge, NCHHЈCH2 and CHHЈN(CH3)2], 2.69–2.87 (m, 4 H,
2ϫCHCH2N, CHCHHЈN and NCHHЈCH2), 3.40 (dd, J = 1.5,
7.1 and 12.3 Hz, 1 H, CHCHHЈN), 4.59 (d, J = 11.6 Hz, 1 H,
Hanti), 4.64 (d, J = 12.0 Hz, 1 H, HЈanti), 5.00 (dd, J = 3.2 and
5.6 Hz, 1 H, CHolefin), 5.40 (dd, J = 2.8 and 5.6 Hz, 1 H, CHЈolefin),
6.16 (t, J = 11.6 Hz, 1 H, Hcentral), 7.35–7.59 (m, 10 H, H Ar) ppm.
13C NMR (10 MHz, CDCl3): Isomer
A (88%): δ = 43.2
(CHolefinCHCH2bridge), 43.9 (CHolefinCЈHCH2bridge), 44.3
(CHCH2N), 45.2 (CЈHCH2N), 48.7 (NCH3), 49.2 (NCЈH3), 55.3
(CH2bridge), 57.0 (NCH2CH2), 58.2 (CHCH2N), 61.0
(CHCЈH2N), 61.6 (NCH2CH2), 77.0 (Cterminal), 77.9 (CЈterminal),
109.7 (Ccentral), 128.4–130.2 (C Ar), 135.4 (CHolefin), 136.0
(CЈHolefin), 136.9 (CH-C Ar), 138.0 (CH-CЈ Ar) ppm. MS [HR-
ES(+)]: calcd. for [M]+ 505.1829; found 505.1852.
Palladium-Catalyzed Allylic Substitution Reactions: Di-µ-chlo-
robis[(η3-allyl)palladium(II)] (3.7 mg, 0.01 mmol) and the corre-
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Eur. J. Inorg. Chem. 2010, 758–766

Norbornene Ligands: Coordination Chemistry and Enantioselective Catalysis
sponding ligand (0.025 mmol) were dissolved in CH2Cl2 (1 cm3),
and the resulting yellow solution was stirred at room temperature
for 0.5 (ligand 5) or 2 h (ligands 3, 4 and 6). The corresponding
allylic acetate (1.00 mmol, 252 mg of rac-I, 140 mg of rac-IV or
157 mg of VI), the nucleophile (3.00 mmol, 396 mg dimethyl ma-
lonate {DMM} or 107 mg benzylamine), N,O-bis(trimethylsilyl)-
acetamide, BSA (610 mg, 3.00 mmol), each dissolved in CH2Cl2
(1 cm3) and a catalytic amount of potassium acetate were then con-
secutively added. When benzylamine was used as the nucleophile
no extra base (BSA/KOAc) was added. The reaction mixture was
stirred at room temperature, and the reaction was monitored by
TLC (SiO2; hexane/ethyl acetate, 3:1). Ethyl ether (10 cm3) was
added to stop the reaction, and the yellow suspension was filtered
through Celite and washed with a 10% aqueous solution of NH4Cl
(3ϫ10 cm3) and water (3ϫ10 cm3). The organic layer was dried
with anhydrous Na2SO4 and filtered, and the solvent was evapo-
rated under reduced pressure to give a yellow oil.
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diffractometer operating at 173 K and that of complex Pd6 by
using a Bruker APEX-II CCD diffractometer at 100 K, with graph-
ite-monochromatized Mo-Kα radiation (λ = 0.71073 Å). Both
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=
10.7757(14) Å, b = 8.4143(11) Å, c = 9.5586(19) Å, β =
103.631(2)°, 2, crystal size
842.27(19) Å3,
0.1ϫ0.4ϫ0.4 mm, 4804 reflections collected (1714 independent,
Rint = 0.0310), GOF = 1.021, R1 [IϾ2σ(I)] = 0.0448 and wR2
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V
=
Z
=
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=
0.0914, R1[all data] = 0.0721 and wR2 = 0.1025, largest diff. peak
and hole: 0.177 and –0.169 eÅ–3. Selected data for Pd6:
C29H36Cl3F6N2PPd, M = 770.32, monoclinic, space group P21/c,
a = 9.5990(3) Å, b = 33.4444(10) Å, c = 10.8901(4) Å, β =
114.589(2)°,
V
=
3179.04(18) Å3,
Z
=
4, crystal size
0.12ϫ0.12ϫ0.11 mm, 70251 reflections collected (7593 indepen-
dent, Rint = 0.034), GOF = 1.311, R1 [IϾ2σ(I)] = 0.0456 and wR2
= 0.1017, R1 [all data] = 0.0564 and wR2 = 0.1059, largest diff.
peak and hole: 2.699 and –0.989 eÅ–3. CCDC-739813 (for 1) and
CCDC-739814 (for Pd6) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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Supporting Information (see footnote on the first page of this arti-
cle): The results of the coordination chemistry and the catalytic
reactivity of the ruthenium systems containing norbornene ligands
are presented. NMR spectra of compounds 5 and Pd6 and vari-
able-temperature NMR spectra of compounds 2, 4 and Pd5 are
also given.
[18]
[19]
Acknowledgments
[20]
The authors wish to thank the Université Paul Sabatier, CNRS,
Ministerio de Educación
y Ciencia (CTQ2007-61058/BQU,
CTQ2007-62288/BQU, Consolider Ingenio 2010 and CSD2006-
0003) and Generalitat de Catalunya for financial support. A. Gual
thanks the Ministerio de Educación y Ciencia for a predoctoral
fellowship (AP2005-1263). The authors also thank Dr. Antonio L.
Llamas-Saiz and Prof. Heinz Gornitzka for their helpful contri-
bution with the crystal structures.
[21]
[22]
[23]
B. Åkermark, E. M. Larsson, J. D. Oslob, J. Org. Chem. 1994,
59, 5729–5733.
SHELXS-97: G. M. Sheldrick, Acta Crystallogr., Sect. A 1990,
46, 467–473.
Eur. J. Inorg. Chem. 2010, 758–766
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www.eurjic.org
765

F. Fernández, A. Gual, C. Claver, S. Castillón, G. Muller, M. Gómez
FULL PAPER
[24] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Göttingen 1997.
[25] U. U. Leutenegger, G. Umbricht, C. Fahrni, P. V. Matt, A.
Pfaltz, Tetrahedron 1992, 48, 2143–2156.
[26] L. Xiao, W. Weissensteiner, K. Mereiter, M. Widhalm, J. Org.
Chem. 2002, 67, 2206–2214.
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SPARTANЈ06 for Windows and Linux, Wavefunction, Inc., Irv-
ine, CA, USA.
Received: September 4, 2009
Published Online: January 12, 2010
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Eur. J. Inorg. Chem. 2010, 758–766