Chiral pyridine imidazolines from C1-symmetric diamines: Synthesis, arene ruthenium complexes and application as asymmetric catalysis for Diels-Alder reactions

Article abstract of DOI:10.1016/j.jorganchem.2006.04.028

Condensation of mono N-substituted chiral ethylenediamines and pyridine-2-methoxyimidate gives new chiral pyridine imidazolines (1a-c). These react with [RuCl₂(mes)]₂ (mes = 1,3,5-trimethyl benzene) in the presence of NaSbF₆ to give complexes [RuCl(L)(mes)][SbF₆] (5a-c) which after treatment with AgSbF₆ are enantioselective catalysts for the Diels-Alder reaction of methacrolein and cyclopentadiene. The imidazoline catalysts are less selective than the corresponding oxazoline ones. Compounds 1a, 5b and 5c have been characterised by X-ray crystallography.

Full text of DOI:10.1016/j.jorganchem.2006.04.028

Journal of Organometallic Chemistry 691 (2006) 3445–3450
www.elsevier.com/locate/jorganchem
Chiral pyridine imidazolines from C1-symmetric diamines:
Synthesis, arene ruthenium complexes and application
as asymmetric catalysis for Diels-Alder reactions
*
Adam J. Davenport, David L. Davies , John Fawcett, David R. Russell
Department of Chemistry, University of Leicester, Leicester LE1 7RH, United Kingdom
Received 7 February 2006; accepted 21 April 2006
Available online 29 April 2006
Abstract
Condensation of mono N-substituted chiral ethylenediamines and pyridine-2-methoxyimidate gives new chiral pyridine imidazolines
(1a–c). These react with [RuCl2(mes)]2 (mes = 1,3,5-trimethyl benzene) in the presence of NaSbF6 to give complexes [RuCl(L)-
(mes)][SbF6] (5a–c) which after treatment with AgSbF6 are enantioselective catalysts for the Diels-Alder reaction of methacrolein and
cyclopentadiene. The imidazoline catalysts are less selective than the corresponding oxazoline ones. Compounds 1a, 5b and 5c have been
characterised by X-ray crystallography.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Chiral; Half-sandwich; Imidazoline; Asymmetric catalysis
1. Introduction
sponding pyridine oxazoline complex with a 4-phenyl sub-
stituent is also not a very effective catalyst in this reaction
[8]. In order to synthesise more active imidazoline catalysts
for this reaction we targeted ligands with an alkyl or benzyl
substituent in the 4-position of the imidazoline.
Our previous route to pyridine imidazolines (pymim)
involved condensation of the C2-symmetric 1,2-diphenyl-
ethylenediamine with pyridine-2-methoxyimidate and then
functionalisation of one nitrogen atom (Scheme 1) [7]. We
were concerned that direct reaction of a C1-symmetric
diamine may lead to two isomeric pyridine imidazolines 1
with the chiral centre adjacent to the imine nitrogen (A,
desired) or adjacent to the amine nitrogen (B, expected to
give less chiral induction). Hence our strategy was to make
suitably mono-N-substituted chiral diamines 2 with the ste-
reogenic centre adjacent to the primary nitrogen that
should react to give imidazolines 1 (only isomer A).
Over the last 15 or so years certain classes of ligands have
become established as being particularly useful in asymmet-
ric catalysis. One such class is oxazolines, particularly
bis(oxazolines) and phosphino-oxazolines [1]. More recently
the related heterocycles, imidazolines, have attracted some
attention for their use in asymmetric catalysis [2–7]. Imidaz-
olines offer the potential advantage of tuning the electronic
properties of the ligand by substitution at the Nꢀ1 position.
Indeed such electronic tuning of enantioselectivity has been
observed in the addition of diethylzinc to aldehydes with
hydroxyalkyl imidazolines [5] and in intramolecular Heck
reactions with phosphine imidazolines [6].
We have previously reported the preparation of a chiral
pyridine imidazoline derived from 1,2-diphenylethylenedi-
amine [7]. The resultant arene ruthenium complex was
not a very good catalyst for the Diels-Alder reaction of
methacrolein and cyclopentadiene; however, the corre-
2. Results and discussion
*
Our approach to diamines 2 involved the regioselective
Corresponding author.
E-mail address: dld3@le.ac.uk (D.L. Davies).
ring-opening of chiral aziridines with primary amines. This
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.04.028

3446
A.J. Davenport et al. / Journal of Organometallic Chemistry 691 (2006) 3445–3450
Scheme 1.
method has been used previously to produce C3-symmetric
tripodal tetra-amines [9]. Initial attempts used mesyl and
nosyl protected aziridines made from L-valinol [9]. Ring
opening proceeded as expected with the desired regioselec-
tivity, however deprotection of these proved difficult.
Hence, the use of a diphenylphosphonoyl protecting group
that is more readily cleaved was investigated (Scheme 2).
Chiral aziridines 3, (R = iPr, Bn) were synthesised follow-
ing the method of Sweeney et al. [10]. Regioselective nucle-
ophilic ring opening was achieved with R1NH2 (R1 = tBu,
nBu, Ph), by heating to reflux in methanol, to form pro-
tected diamines 4, which were deprotected by bubbling
dry HCl gas through CH2Cl2/ether solutions to yield
hydrochloride salts from which diamines 2 are easily liber-
ated by treatment with base.
The new ligands, 1a–c, were easily synthesised in high
yield by reaction of diamines 2 with pyridine-2-methoxyim-
idate (Scheme 2). Using this procedure the ligands are suf-
ficiently pure for complexation and do not require
chromatography which is necessary if pyridine imidazo-
lines are prepared by Lewis acid catalysed condensation
of 2-cyanopyridine with the diamine [3,4]. Ligand 1a was
Fig. 1. Ortep drawing of 1a, showing the atom labelling scheme.
Displacement ellipsoids are shown at the 50% level. Selected bond
˚
distances (A) and bond angles (ꢁ): N(1)–C(5) 1.467(2), N(1)–C(6) 1.381(2),
N(2)–C(6) 1.282(2), N(3)–C(7) 1.344(2), N(3)–C(8) 1.337(3), N(2)–C(4)
1.481(3) and C(6)–N(1)–C(12) 128.2(2), C(6)–N(1)–C(5) 107.4(2), C(5)–
N(1)–C(12) 119.9(2).
characterised by X-ray crystallography and the structure
with selected bond lengths and bond angles are shown in
˚
Fig. 1. The N(1)–C(6) bond [1.381(2) A] is only slightly
longer than the N(3)–C(7) and N(3)–C(8) distances [aver-
˚
age 1.341(3) A] in the pyridine ring, being considerably
shorter than the formal single bonds N(2)–C(4) and
˚
N(1)–C(5) [average 1.474(3) A], suggesting some delocali-
sation in the imidazoline ring. The sum of the bond angles
at N(1) is 355.5ꢁ also consistent with sp2 rather than sp3
hybridisation at N(1).
Half-sandwich complexes [RuCl{(S)4R-pymimNR1}-
(mes)]SbF6 (5a–c) were synthesised from [RuCl2(mes)]2 by
treatment with 2 equiv. of ligand 1a–c and NaSbF6, in
1
refluxing MeOH. The complexes were characterised by H
NMR spectroscopy, mass spectrometry and microanalysis
and by X-ray diffraction for 5b and 5c. In 5a–c, both the
metal centre and the pyridine imidazoline ligands are chiral
so a mixture of diastereomers is possible as found for anal-
ogous pyridine oxazoline complexes reported previously
[8].
1
The H NMR spectra in CD2Cl2 of crude reaction mix-
tures containing 5a–c each contained a single set of well-
resolved signals, with no trace of a second isomer as
found previously for the corresponding pyridine oxazoline
complexes [8].
Recrystallisation from CH2Cl2/ether gave crystals of 5b
and 5c suitable for X-ray diffraction. The X-ray structures
of the cations of 5b and 5c are shown in Figs. 2 and 3,
respectively, with selected bond distances and angles in
Table 1. The ruthenium atoms have a pseudooctahedral
geometry with the arene occupying three adjacent sites of
the octahedron. The imidazolines are coordinated such
Scheme 2. (i) R1NH2; (ii) HCl(g); (iii) pyridine-2-methoxyimidate;
(iv) [RuCl2(mes)]2/NaSbF6.

A.J. Davenport et al. / Journal of Organometallic Chemistry 691 (2006) 3445–3450
3447
Table 1
Selected bond lengths (A) and bond angles (ꢁ) for complexes 5b and 5c
˚
5b 5c
Ru–N(1)
Ru–N(2)
Ru–Cl
N(1)–C(1)
N(1)–C(5)
N(2)–C(8)
N(2)–C(6)
N(3)–C(6)
N(3)–C(7)
C(5)–C(6)
2.112(5) 2.098(8)
2.073(5)
2.406(2)
1.339(8)
1.356(8)
1.473(7)
1.282(7)
1.359(8)
1.465(8)
1.468(8)
2.057(9)
2.394(3)
1.33(2)
1.373(14)
1.471(13)
1.306(13)
1.362(14)
1.481(14)
1.48(2)
N(1)–Ru–N(2)
75.55(18)
74.9(3)
of 5c the phenyl ring of the benzyl substituent is orientated
anti and perpendicular to the mesitylene ring, reducing
unfavourable interactions with both the mesitylene and
chloride ligand. The Ru–N(2)im distance is shorter than
Ru–N(1)py, in each complex possibly due to the greater
electron donating ability of the imidazoline ring. Similar
features are seen for palladium and rhodium pyridine imi-
dazoline complexes [4], whereas in arene ruthenium pyri-
dine oxazoline complexes the Ru–Npy and Ru–Nox bond
lengths are usually statistically the same [8,11]. In each of
Fig. 2. Ortep drawing of the cation of 5b, showing the atom labelling
scheme. Displacement ellipsoids are shown at the 50% level. H atoms are
omitted for clarity.
˚
5b and 5c, the N(3)–C(6) distance [average 1.361(11) A] is
statistically the same as the N(1)–C(1) and N(1)–C(5) dis-
tances in the pyridine ring, being only slightly longer than
the formal double bond N(2)–C(6) distance [average
˚
1.294(10) A] and considerably shorter than the formal sin-
˚
gle bonds N(2)–C(8) [average 1.472(10) A] implying a
degree of delocalisation across the amidine N(2)–C(6)–
N(3) fragment as discussed for the free ligand 1a above
and as found previously for pyridine imidazoline com-
plexes [4,7]. Consistent with this, the sum of the angles
around N(3) is 359.5(10)ꢁ in 5c, though it is slightly less,
346.6(6)ꢁ in 5b. Thus 5b and 5c are structurally similar to
the corresponding pyridine oxazoline complexes confirm-
ing that the steric requirements of imidazolines are similar
to those of the related oxazolines. This is also consistent
with the similar diastereoselectivity observed for forma-
tion of these R-pymim complexes and the corresponding
R-pymox ones. Hence, the substituent on N(3) can com-
municate electronically with the metal centre but has
minimal steric impact. In the case of 5c the steric effect of
Fig. 3. Ortep drawing of the cation of 5c, showing the atom labelling
scheme. Displacement ellipsoids are shown at the 50% level. H atoms are
omitted for clarity.
t
the Bu leads to an increased torsion angle [N(1)–C(5)–
that the isopropyl or benzyl substituent adjacent to the
imine nitrogen is on the same side as the chloride rather
than the arene; as found in related pyridine oxazoline com-
plexes [8,11]. After dissolution of crystals of 5b or 5c in
C(6)–N(2)] of 16.8ꢁ between the pyridine and imidazoline
n
rings compared to that of 11.0ꢁ in the Bu complex 5b.
In the recent years there has been particular interest in
using chiral late-transition-metal complexes as catalysts
for Diels-Alder reactions since such complexes show less
water-sensitivity than the more common titanium, alumin-
ium or boron catalysts [12]. Cationic arene ruthenium
complexes with P,N or P,O bidentate ligands [13], bisox-
azolines [14] and pyridine oxazolines [8,11] have all been
successfully used as asymmetric catalysts for Diels-Alder
reactions.
1
CD2Cl2 at low temperature and recording the H NMR
spectra each complex showed only a single diastereomer,
which is presumed to be the same as that in the solid-state
in each case. A phase-sensitive NOESY spectrum of 5a
recorded at 253 K confirmed that the same isomer is also
present in this case.
As mentioned previously, both complexes have the imi-
dazoline substituent pointing towards chloride. In the case

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A.J. Davenport et al. / Journal of Organometallic Chemistry 691 (2006) 3445–3450
Table 2
Enantioselective Diels-Alder reaction of methacrolein or bromoacrolein with cyclopentadiene catalysed by [RuCl(L)(mes)] (L = pymim, pymox) after
a
treatment with AgSbF6
catalyst
CHO
+
R
R
CHO
R
CHO
R = Me, Br
exo
endo
Entry
Complex
R
NR1
Dienophile
Yield
exo:endo
E.e. (%)
1
2
3
4
5
6
7
8
a
5a
5b
5c
6
iPr
iPr
Bn
iPr
iPr
iPr
Bn
iPr
Ph
Methacrolein
Methacrolein
Methacrolein
Methacrolein
Bromoacrolein
Bromoacrolein
Bromoacrolein
Bromoacrolein
45
87
48
72
45
92
50
0
93:7
95:5
93:7
95:5
83:17
93:7
90:10
26
58
19
75
10
50
3
nBu
tBu
5a
5b
5c
6
Ph
nBu
tBu
Reactions at 0 ꢁC for 72 h, with 2 mol% catalyst formed in situ except entry 4 only 4 h.
Treatment of 5a–c with AgSbF6 generates dications
[Ru(solvent)(R-pymim)(mes)]2+ which can catalyse the
Diels-Alder reaction between methacrolein or bromoacro-
lein and cyclopentadiene. Results for these and the related
cation [Ru(solvent)(iPr-pymox)(mes)]2+ (6) [8] are shown in
Table 2. The effect of differing electronic properties of the
NR1 group can be seen by comparing entries 1 and 5
(NPh) with entries 2 and 6 (NnBu) for the R = iPr catalysts.
of the major exo product is consistent with the imidazoline
substituent shielding the Si face of the coordinated methac-
rolein leading to attack of cyclopentadiene at the Re face as
we have discussed previously for the ruthenium pyridyloxaz-
oline complexes [8].
In conclusion, imidazolines are structurally similar to
oxazolines but are more basic therefore giving less Lewis
acidic complexes than corresponding oxazolines. Hence,
imidazolines are stronger donors than oxazolines and this
difference can be fine tuned by substitution on the amine
nitrogen of the imidazoline. The ability to tune the Lewis
acidity of half-sandwich complexes whilst maintaining their
gross geometrical features may prove beneficial for their
use in asymmetric catalysis [5–7].
n
With the Bu group the catalyst gives good enantioselec-
tion (58% and 50% e.e.) and exo:endo selectivity (95:5
and 93:7) with either methacrolein or bromoacrolein as
dienophile. In comparison, the selectivities are dramatically
reduced (26% and 10% e.e.) and (93:7 and 83:17 exo:endo),
for the comparable reactions with R1 = Ph, suggesting an
element of electronic control is possible, by selecting an
electron donating (nBu) or withdrawing (Ph) group. It
should be noted that the exo:endo ratio 83:17 (entry 5) is
similar to that of the thermal reaction, indicating complex
5a is a poor catalyst for the reaction of bromoacrolein and
CpH. Substituting R = iPr with Bn, lowers the enantiose-
lectivity of both reactions from 58% to 19% e.e. for meth-
acrolein and from 50% to 3% e.e. for bromoacrolein.
Reduced selectivity with a benzyl-substituent in place of
an isopropyl is consistent with the results from pyridine
oxazoline [8] and salicyloxazoline-containing [15] catalysts.
The imidazoline complexes are less active and selective
than the analogous oxazoline complexes [11] for the meth-
acrolein/CpH reaction (compare entries 1 and 2 versus
entry 4), but they are more active for the bromoacrolein/
CpH reaction (compare entries 5 and 6 versus entry 8),
indeed the oxazoline complexes do not catalyse this reaction.
Kundig has previously noted that strong Lewis acids may
fail as catalysts for bromoacrolein reactions due to abstrac-
tion of the bromide by the catalyst [16]. In the reaction with
methacrolein the major product was identified as (1R,
2S,4R)-2-methylbicyclo-[2.2.1]hept-5-ene-2-carbaldehyde,
by comparison of the sign of the optical rotation and the GC
behaviour of the acetal formed from (2R,4R)-pentanediol
with the literature values [17]. The absolute configuration
3. Experimental
Petroleum ether and diethyl ether were dried by reflux-
ing over purple sodium/benzophenone under nitrogen,
whilst dichloromethane was purified by refluxing over cal-
cium hydride and acetone from calcium sulphate. The reac-
tions described were carried out under nitrogen; however,
once isolated as pure solids the compounds are air-stable
and precautions for their storage are unnecessary. 1H
NMR spectra were obtained using Bruker 250, 300 and
400 MHz spectrometers in CD2Cl2 unless stated otherwise,
chemical shifts were recorded in ppm (referenced to tetra-
methylsilane or residual protons in the NMR solvent).
FAB mass spectra were obtained on a Kratos concept mass
spectrometer using an NOBA matrix. Microanalyses were
performed by Butterworth laboratories Ltd., Middlesex.
Bromoacrolein [18], and [RuCl2(mes)]2 [19] were prepared
using the literature procedures.
3.1. Preparation of pyridine imidazolines 1
A
mixture of pyridine-carboxyimidate (303 mg,
2.22 mmol), the appropriate diamine (2.22 mmol) and

A.J. Davenport et al. / Journal of Organometallic Chemistry 691 (2006) 3445–3450
3449
CHCl3 (1 cm3) was stirred overnight at 60 ꢁC. The solvent
was evaporated and the residue dissolved in CH2Cl2 and
then washed with three 15 cm3 portions of water. The
aqueous layers were extracted with dichloromethane
(40 cm3) and the combined organic layers were dried over
MgSO4 and evaporated to give an off-white solid. The pur-
ity of the solids was checked by NMR spectroscopy and the
ligands were used without further characterisation.
An orange/brown coloured solution was obtained, which
was evaporated and the crude residue was dissolved in
CH2Cl2. Filtration through celite gave a red solution,
which was evaporated to afford 5b (181 mg, 91%). Calc.
for C24H35ClF6N3RuSb: C, 39.07; H, 4.78; N, 5.70. Found:
C, 38.18; H, 4.46; N, 5.23%. 1H NMR d 0.73 (d, 3H, J 6.5,
MeCHMe0), 0.97 (d, 3H, J 7.5, MeCHMe0), 0.98 (t, 3H, J
7.5, nBu–CH3), 1.42 (m, 2H, CH2–nBu), 1.64 (m, 2H,
CH2–nBu), 2.24 (m, 1H, MeCHMe0) 2.25 (s, 9H, C6Me3),
3.35 (m, 1H, NCH0), 3.81 (dd, 1H, J 10, 5.5, NCH), 3.94
(m, 2H, NCH2–nBu), 4.62 (m, 1H, NCH), 5.30 (s, 3H,
C6Me3), 7.63 (t, 1H, J 6.5, Py-5-H), 7.78 (d, 1H, J 8, Py-
3-H), 8.00 (t, 1H, J 8, Py-4-H), 9.17 (d, 1H, J 5.5, Py-6-
H). MS (FAB+): m/z 502 [M]+, 467 [MꢀCl].
[RuCl(1a)(mes)][SbF6] (5a). A solution of 1a (20 mg,
0.08 mmol) and NaSbF6 (20 mg, 0.08 mmol) in MeOH
(10 cm3) was added to [RuCl2(mes)]2 (22 mg, 0.04 mmol)
and the resulting suspension was heated to reflux for 2 h.
An orange/brown coloured solution was obtained, which
was evaporated and the crude residue was dissolved in
CH2Cl2. Filtration through celite gave a red solution,
which was evaporated to afford 5a (54 mg, 95%). Calc.
for C26H31ClF6N3RuSb(0.5CH2Cl2): C, 39.77; H, 4.03;
[RuCl(1c)(mes)][SbF6] (5c). A solution of 1c (50 mg,
0.17 mmol) and NaSbF6 (46 mg, 0.17 mmol) in MeOH
(10 cm3) was added to [RuCl2(mes)]2 (50 mg, 0.09 mmol)
and the resulting suspension was heated to reflux for 2 h.
An orange/brown coloured solution was obtained, which
was evaporated and the crude residue was dissolved in
CH2Cl2. Filtration through celite gave a red solution,
which was evaporated to afford 5c (127 mg, 94%). Calc.
for C28H35ClF6N3RuSb: C, 42.79; H, 4.49; N, 5.35. Found:
1
N, 5.25. Found: C, 40.04; H, 4.00; N, 5.24%. H NMR d
0.87 (d, 3H, J 7, MeCHMe0), 0.97 (d, 3H, J 6.5, MeCH
Me0), 2.25 (s, 9H, C6Me3), 2.25 (m, 1H, MeCHMe0), 3.93
(dd, 1H, J 10, 5, NCHH0), 4.54 (t, 1H, J 10, NCHH),
4.76 (m, 1H, NCH), 5.36 (s, 3H, C6Me3), 6.87 (d, 1H, J
7.5, Py-3-H), 7.02 (d, 1H, J 7, N–Ph), 7.39 (m, 2H, N–
Ph), 7.51 (m, 1H, Py-5-H), 7.56 (m, 2H, N–Ph), 7.65 (dt,
1H, J 1.5, 8, Py-4-H), 9.15 (d, 1H, J 5, Py-6-H). MS
(FAB+): m/z 522 [M]+, 487 [MꢀCl].
1
C, 42.60; H, 4.39; N, 5.21%. H NMR d 1.48 (s, 9H, N–
But), 2.32 (s, 9H, C6Me3), 2.67 (dd, 1H, J 14.5, 10.5,
CHH0Ph), 3.44 (dd, 1H, J 14.5, 4, CHH0Ph), 3.68 (dd,
1H, J 11, 7.5, NCH0), 4.01 (dd, 1H, J 11, 10, NCH), 4.79
(ddd, 1H, {J = 10.5, 10, 7.5 Hz}, NCH), 5.37 (s, 3H,
C6Me3), 7.32 (m, 5H, Ph), 7.68 (dt, 1H, J 1.5, 5.5, Py-5-
H), 8.01 (dt, 1H, J 7.0, 1.5, Py-4-H), 8.15 (d, 1H, J 8.0,
[RuCl(1b)(mes)][SbF6] (5b). A solution of 1b (66 mg,
0.27 mmol) and NaSbF6 (70 mg, 0.27 mmol) in MeOH
(10 cm3) was added to [RuCl2(mes)]2 (78 mg, 0.13 mmol)
and the resulting suspension was heated to reflux for 2 h.
Table 3
Crystallographic data for complexes 1a, 5b and 5c
1a
5b
5c
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
265.35
200(2)
Orthorhombic
P212121
17H19N3
C24H35ClF6N3RuSb
737.82
200(2)
Orthorhombic
P212121
9.083(1)
C28H35ClF6N3RuSb
785.86
200(2)
Orthorhombic
P212121
8.0067(13)
˚
a (A)
7.744(2)
11.060(2)
˚
b (A)
15.031(4)
17.323(2)
˚
c (A)
16.926(3)
1449.8(5)
20.902(3)
2853.8(8)
22.141(3)
3071.0(7)
3
˚
U (A )
Z
4
4
4
Density (calculated) (Mg mꢀ3
Absorption coefficient (mmꢀ1
F(000)
)
)
1.216
0.073
568
1.717
1.966
1464
1.700
1.517
1560
Crystal size (mm)
H range (ꢁ)
0.56 · 0.31 · 0.27
2.20–25.01
0 6 h 6 9, ꢀ13 6 k 6 1,
ꢀ1 6 l 6 20
1761
0.51 · 0.42 · 0.37
1.95–48.03
ꢀ19 6 h 6 1, ꢀ21 6 k 6 0,
ꢀ29 6 l 6 11
5453
0.74 · 0.30 · 0.17
2.18–27.00
0 6 h 6 9, ꢀ1 6 k 6 22,
ꢀ1 6 l 6 28
3920
Index ranges
Reflections collected
Independent reflections [Rint
Data/restraints/parameters
Goodness-of-fit, F2
]
1692 [0.0140]
1692/0/182
1.089
5249 [0.0185]
5249/0/361
1.033
3854 [0.0485]
3854/0/362
1.008
Final R indices [I > 2r(I)]
R indices (all data)
Absolute structure parameter
Largest difference in peak and hole (e A
R1 = 0.0317, wR2 = 0.0687
R1 = 0.0407, wR2 = 0.0729
ꢀ8(3)
R1 = 0.0421, wR2 = 0.0847
R1 = 0.0652, wR2 = 0.0943
ꢀ0.07(4)
R1 = 0.0542, wR2 = 0.1340
R1 = 0.0724, wR2 = 0.1621
ꢀ0.01(7)
ꢀ3
˚
)
0.129 and ꢀ0.111
1.051 and ꢀ0.960
1.051 and ꢀ1.616

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A.J. Davenport et al. / Journal of Organometallic Chemistry 691 (2006) 3445–3450
Py-3-H), 9.18 (d, 1H, J 5.5, Py-6-H). MS (ES+): m/z
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1
colourless oil. The exo:endo ratio was determined by H
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1
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with (2R,4R)-pentanediol [17].
Acknowledgements
We thank the EPSRC (A.J.D.) for a studentship and
Johnson Matthey for a loan of RuCl3.
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Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2006.04.028.