Use of Stille-type cross-coupling as a route to oligopyridylimines

Article abstract of DOI:10.1016/j.tet.2005.09.137

The new tin reagents, 2-(n-Bu₃Sn)-6-{C(R)OCH₂CH ₂O}-C₅H₃N, (R=H a, Me b), have been employed in Stille-type cross-coupling reactions with a range of oligopyridylbromides generating, following a facile deprotection step, a series of formyl- and acetyl-functionalised oligopyridines. Condensation reactions with 2,6-diisopropylaniline has allowed access to families of novel sterically bulky multidentate N,N,N,N (tetradentate), N,N,N,N,N (pentadentate), N,N,N,N,N,N (sexidentate) and N,N,N,N,N,N,N (heptadentate) nitrogen donor ligands. This work represents a straightforward and rapid synthetic route for the preparation of oligopyridylimines, which are expected to act as useful components for the self-assembly of polymetallic complexes.

Full text of DOI:10.1016/j.tet.2005.09.137

Tetrahedron 62 (2006) 79–89
Use of Stille-type cross-coupling as a route to oligopyridylimines
Yohan D. M. Champouret, Rajinder K. Chaggar, Ishaq Dadhiwala, John Fawcett
*
and Gregory A. Solan
Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK
Received 2 August 2005; revised 14 September 2005; accepted 29 September 2005
Available online 25 October 2005
Abstract—The new tin reagents, 2-(n-Bu Sn)-6-{C(R)OCH CH O}-C H N, (RZH a, Me b), have been employed in Stille-type cross-
3
2
2
5 3
coupling reactions with a range of oligopyridylbromides generating, following a facile deprotection step, a series of formyl- and acetyl-
functionalised oligopyridines. Condensation reactions with 2,6-diisopropylaniline has allowed access to families of novel sterically bulky
multidentate N,N,N,N (tetradentate), N,N,N,N,N (pentadentate), N,N,N,N,N,N (sexidentate) and N,N,N,N,N,N,N (heptadentate) nitrogen
donor ligands. This work represents a straightforward and rapid synthetic route for the preparation of oligopyridylimines, which are expected
to act as useful components for the self-assembly of polymetallic complexes.
q 2005 Elsevier Ltd. All rights reserved.
1
1–13
1. Introduction
for olefin polymerisation catalysts.
Notably, in the latter
case an appreciation of the steric properties of the arylimino
N-substituent has been paramount in the development of the
area.
The chemistry of 2,6-oligopyridines, C H N(C H N) C -
3
H N (nZ1–7), has been widely developed in recent years
4
5
4
5
n 5
due, in the main, to its connection with supramolecular
chemistry, in which the ligand in combination with a
suitable metal ion can self-assemble to form helical or grid-
like superstructures. In the same way, it would be
anticipated that the structurally related 2,6-oligopyridyl-
Herein, we introduce a simple general strategy for preparing
a wide variety of new multitopic nitrogen donor oligo-
pyridylimines ligands containing either one or two sterically
demanding aryl-aldimino [–C(H)]NAr] or aryl-ketimino
[–C(Me)]NAr] end-groups. The ligand synthesis proceeds
via the synthesis of formyl- and acetyl-functionalised
oligopyridines (using Stille-type coupling methodologies )
which can be readily converted to their aryl-imine
counterparts.
1–4
0
0
imines, C H N(C H N) CR]NR or R N]RC(C H N) -
5
4
5
3
n
5
3
m
0
0
CR]NR (m or nR1; RZH or hydrocarbyl; R Z
hydrocarbyl), in which the pyridyl chain is terminated by
either one or two imino units, could be employed to develop
a similar chemistry. Moreover, the presence of a
1
4
0
functionalisable imino-substituent (R or R ) would offer a
convenient method of modifying both the electronic and
steric properties of the ligand manifold. However, an
absence of suitable synthetic protocols has meant the
chemistry of the higher members (m or nR2) of the
2
. Results and discussion
2
.1. Synthesis of 2-(n-Bu Sn)-6-{C(R)OCH CH O}-
3
C H N (RZH a, Me b)
2
2
5
–10
oligopyridylimine family is not nearly as well developed.
5
3
5
,8
Nevertheless, multistep procedures have been carried out
that have allowed access to bis(imino)bipyridine (mZ2) and
bis(imino)terpyridine (mZ3) compounds and indeed their
capacity to form double helicate structures has been
recognised. In stark contrast, the lower members of the
family, that is, bis(imino)pyridine (mZ1), have been widely
used in coordination chemistry and more recently as supports
The tin reagents, 2-(n-Bu Sn)-6-{C(R)OCH CH O}-
3
2
2
C H N (RZH a, Me b), can be prepared in good overall
5
3
yield in two steps from 2-bromo-6-formylpyridine and
2-bromo-6-acetylpyridine, respectively (Scheme 1). Firstly,
the protected ketal derivatives 2-Br-6-{C(R)OCH CH O}-
8
,9
2
2
C H N (RZH, Me) can be prepared by reaction of
5
3
2
with ethane-1,2-diol under azeotropic reflux in benzene.
-bromo-6-formylpyridine and 2-bromo-6-acetylpyridine
1
5
Keywords: Stille-type; Cross-coupling; Oligopyridylimines; Nitrogen
donor.
Secondly, treatment of 2-Br-6-{C(R)OCH CH O}-C H N
2
2
5 3
*
Corresponding author. Tel.: C44 116 252 2096; fax: C44 116 252 3789;
e-mail: gas8@leicester.ac.uk
(RZH, Me) with n-BuLi at K100 8C in diethylether
followed by reaction of the lithiated intermediates with
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.09.137

80
Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
15
2 2 3 2
Scheme 1. Reagents and conditions: (i) (CH OH) , cat. p-TsOH, benzene, reflux; (ii) n-BuLi, ClSn(n-Bu) , Et O, K100 8C.
tributyltin chloride affords air stable a and b in good yield.
Notably, the reactions can be readily scaled-up allowing
access to up to 30 g of the tin reagents.
2,6-diisopropylaniline as both reactant and solvent (method
B) at elevated temperatures over short time periods. All the
1
new compounds have been characterised by H NMR,
13
C
NMR, IR spectroscopy and ESI mass spectrometry (see
Section 4).
2.2. Stille-type reaction of a and b with
oligopyridylbromides
The molecular structures of 6b, 8a and 9a are depicted in
Figures 1–3; selected bond distances and angles are listed in
Table 3. Each structure consists of a chain of 2,6-linked
pyridine rings (three for 6a and 6b; four for 9a) containing
either one (6a) or two (8a and 9a) 2,6-diisopropylphenyl-
substituted imino groups as the chain-ends. In each
compound a mutually transoid conformation of the nitrogen
atoms is observed throughout the imine–pyridine backbone
as has been observed for the structurally related 2,6-
Stille-type cross-coupling reactions of a or b were carried
out with a range of oligopyridylbromides in toluene at
elevated temperature in the presence of catalytic quantities
of Pd(PPh3)4 (loadings between 6–8 mol%) to yield,
following acid-mediated deprotection, the formyl- and
acetyl-oligopyridines 1–5, respectively (Table 1). All the
1
13
new compounds have been characterised by H, C NMR,
IR spectroscopy and ESI mass spectrometry (see Section 4).
1
8
oligopyridines. The C–N bond lengths of the imine groups
˚
range from 1.256(2) to 1.275(4) A and are consistent with
The IR spectra for 1–5 showed characteristic absorption
K1
bands for their carbonyl functionalities (ca. 1705 cm
while molecular ion peaks were revealed in their ESI mass
)
double bond character. While the pyridine and imine groups
in 6a are essentially coplanar some twisting is evident
within the backbone of 8a [tors.: N(3)–C(19)–C(18)–N(2)
14.08], which is even more noticeable in 9a [tors.: N(2)–
C(18)–C(19)–N(3) 28.98]. For all three structures the 2,6-
diisopropylphenyl rings are inclined essentially
orthogonally to the plane of the adjacent pyridyl-imine
units.
1
spectra. In the C { H} NMR spectra, the carbonyl carbon
3
1
atoms were seen in the range d 193.8 and 200.4 with the
CH]O and CMe]O protons being seen at ca. d 10.1 (1a,
1
a, 3a, 4a) and d 2.8 (1b, 2b, 3b, 4b) in their H NMR
2
spectra, respectively.
The overall yields obtained for the combination of both the
coupling reaction and the acid deprotection are generally
good (O60%) but start to decrease as the pyridyl chain
length is increased (Table 1). This observation can be, in
part, attributed to the reduction in solubility of the higher
members of the carbonyl-containing oligopyridines in the
organic solvents employed, which is particularly significant
in the case of the diformyl-substituted quartepyridine 4a
where the yield drops to 45%. Moreover, we have not been
able to isolate the diformylquinquepyridine (5a) despite
being able to characterise the protected form. It is
noteworthy that alternative procedures for compounds
Compounds 6–10 gave molecular ion peaks in their mass
spectra and IR spectroscopy showed characteristic absorp-
K1
tion bands for their imino functionalities (ca. 1635 cm ).
1
In the H NMR spectra, the aldimine compounds (6a, 7a,
8a, 9a) gave singlets at ca. d 8.1 consistent with the presence
of CH]N protons while the CMe]N protons could be seen
at ca. d 2.2 for the ketimine compounds (6b, 7b, 8b, 9b,
10b).
It is noteworthy that the introduction of the 2,6-diiso-
propylphenyl group to the oligopyridyl chain not only
changes the steric and electronic attributes of the
compounds but significantly also enhances the solubility
of the longer chain members of the series. For example, 9a
is highly soluble in chlorinated solvents while the
corresponding formyl precursor 4a is scarcely soluble.
16
17
5
1
a, 1b and 3a have been previously reported although
no spectroscopic data was included for 1b; the yields
described here are higher or comparable with the previous
reports.
2
2
.3. Condensation reaction of carbonyl compounds with
,6-diisopropylaniline
Treatment of 1–5 with 2,6-diisopropylaniline in the
presence of a catalytic amount of acid (glacial acetic or
formic acid) gave the imine compounds 6–10 (see Table 2)
as pale yellow or white solids in moderate to good yield.
The aldimine compounds (6a, 7a, 8a, 9a) were most
conveniently prepared by carrying out the reaction in
ethanol at 50 8C overnight (method A) while the ketimine
compounds (6b, 7b, 8b, 9b, 10b) could be prepared by using
3. Conclusions
In summary, we have described a straightforward and
efficient synthesis for a broad range of formyl- and acetyl-
oligopyridines via a palladium-mediated Stille-type cross-
coupling approach. Their subsequent condensation
reactions with 2,6-diisopropylaniline have allowed access
to several novel families of sterically encumbered

Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
81
Table 1. Synthesis of formyl- and acetyl-functionalised oligopyridines via Stille-type cross-coupling of a or b with oligopyridylbromides
a
Entry
1
Tin reagent
R-Br
Deprotected product
Yield (%)
b
a
60
1
a
2
b
62
1
b
a
3
4
a
70
75
2
b
2b
3a
3b
4a
4b
c
5
6
7
8
9
a
b
a
b
b
80
75
45
72
50
d
5
b
a
Isolated yields from both steps.
b
c
d
See Ref. 16 for an alternative procedure.
See Ref. 5 for an alternative procedure.
Note 5a proved too insoluble.

82
Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
Table 2. Condensation reactions of 1–5 with 2,6-diisopropylaniline
Entry
Method
A
R-C(R)]O
Oligopyridylimine product
Yield
a
(
%)
10
45
1
a
6
a
11
B
50
1
b
a
6
b
1
2
3
A
B
50
60
2
7
a
1
2
b
7
b
1
4
5
A
B
65
60
3
3
a
8
a
1
b
8
b
16
17
18
A
B
B
50
58
45
4a
4b
5b
9
a
9
b
1
0b
a
Isolated yields.

Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
83
Figure 1. Molecular structures of 6b including a partial atom numbering scheme. All hydrogen atoms have been omitted for clarity.
Figure 2. Molecular structures of 8a including a partial atom numbering scheme. All hydrogen atoms apart from H13 and H29 have been omitted for clarity.
Figure 3. Molecular structures of 9a including a partial atom numbering scheme. All hydrogen atoms apart from H13 have been omitted for clarity.
˚
Table 3. Selected bond distances (A) and angles (8) for 6b, 8a and 9a
6b
8a
9a
N(1)–C(14)
N(1)–C(12)
C(13)–C(14)
C(14)–C(15)
C(19)–C(20)
C(24)–C(25)
1.275(4)
1.434(4)
1.493(4)
1.495(4)
1.484(4)
1.484(4)
N(1)–C(13)
N(5)–C(29)
C(28)–C(29)
C(18)–C(19)
C(23)–C(24)
C(13)–C(14)
1.256(2)
1.260(2)
1.470(2)
1.488(2)
1.487(2)
1.472(2)
N(1)–C(13)
C(1)–N(1)
C(18)–C(19)
C(23)–C(23A)
C(13)–C(14)
1.265(6)
1.437(6)
1.489(7)
1.514(12)
1.478(7)
C(14)–N(1)–C(12)
N(1)–C(14)–C(13)
121.1(3)
125.0(3)
C(13)–N(1)–C(12)
C(29)–N(5)–C(30)
119.64(14)
117.84(14)
C(1)–N(1)–C(13)
N(1)–C(13)–C(14)
120.7(5)
120.7(6)
multidentate oligopyridylimines. The coordination chem-
istry of these new ligand types will be explored elsewhere.
standard Schlenk techniques. Solvents were distilled under
nitrogen from appropriate drying agents and degassed prior
1
9
to use. The infrared spectra were recorded on a Perkin-
Elmer Spectrum One FT-IR spectrometer on solid samples.
The electrospray ionisation (ESI) and the fast atom
bombardment (FAB) mass spectra were recorded using a
micromass Quattra LC mass spectrometer and a Kratos
Concept spectrometer with chloroform or NBA as the
matrix, respectively. High resolution FAB mass spectra
were recorded on Kratos Concept spectrometer (xenon gas,
4
. Experimental
4
.1. General
All reactions, unless otherwise stated, were carried out
under an atmosphere of dry, oxygen-free nitrogen, using

84
Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
1 13
kV) with NBA as matrix. H and C NMR spectra were
3
3
7
JH–HZ8.5 Hz, 6H, CH ), 1.25 (app. sex, JH–HZ7 Hz,
2
recorded on a Bruker ARX spectrometer (250 or 300 MHz);
chemical shifts (ppm) are referred to the residual protic
solvent peaks; coupling constants are in Hertz (Hz). Melting
points (mp) were measured on a Gallenkamp melting point
apparatus (model MFB-595) in open capillary tubes and
were uncorrected. Elemental analyses were performed at the
Department of Chemistry, University of North London by
Dr. Boyer.
6H, CH ), 1.49 (m, 6H, CH ), 1.70 (s, 3H, CH ), 3.6–4.0 (m,
2
2
3
3
4H, CH ), 7.2–7.3 (m, 2H, Py-H), 7.41 (app. t, JH–HZ7.6 Hz,
2
1
1H, Py-H). C { H} NMR (75 MHz, CDCl ): d 10.0 (CH ),
3
1
3
3
13.6 (CH ), 24.4 (CH ), 27.9 (CH ), 28.0 (CH ), 65.0 (CH ),
2
2
2
2
3
109.2, 118.9 (Py), 131.4 (Py), 133.6 (Py), 160.4 (Py), 173.5
(Py). IR (cm ): 2955, 2923, 1569, 1556, 1463, 1411, 1376,
K1
1192, 1099, 1042, 947, 872, 800, 752, 690, 661. FABMS:
m/z 452 [MCH ( Sn)] . HRMS (FAB): calcd for
1
16
C
1
16
C
Sn)] 452.19235, found
C H NO Sn [MCH
2
(
1
38
2
The reagents, 2,6-diisopropylaniline, tributyltinchloride,
452.19242.
2
,6-dibromopyridine and n-BuLi were purchased from
Aldrich Chemical Co. and used without further purification.
4.3. Stille-type cross-coupling reactions
1
5
The compounds, 6-bromo-2-(1,3-dioxolan-2-yl)pyridine,
6
kis(triphenylphosphine)palladium(0),
1
-bromo-2-(2-methyl-1,3-dioxolan-2-yl)pyridine, tetra-
5
0
0
00
0
4.3.1. Formyl-2,2 :6 ,2 -terpyridine (1a). 6-Bromo-2,2 -
bipyridine (0.971 g, 4.13 mmol), a (1.99 g, 4.54 mmol,
1.1 equiv) and tetrakis(triphenylphosphine)palladium(0)
(0.286 g, 0.25 mmol, 0.06 equiv) were loaded in a Schlenk
2
0
0
6-bromo-2,2 -
2
1
0
dibromo-2,2 -bipyridine and 6,6 -dibromo-2,2 ;6 ,2 -ter-
0
00
00
22
0
6,6 -
bipyridine,
6-bromo-2,2 ;6 ,2 -terpyridine,
0
0
23
0
00
2
4
pyridine were prepared according to previously reported
procedures. All other chemicals were obtained com-
mercially and used without further purification.
tube under N and the contents stirred in dry toluene (30 ml)
2
for 72 h at 90 8C. After removal of the solvent under
reduced pressure, the reaction mixture was stirred overnight
at 60 8C in 4 M HCl (20 ml), cooled to room temperature
4
4
.2. Synthesis of tin reagents
and carefully neutralised by addition of 2 M NaHCO . The
3
suspension was extracted with CHCl (3!30 ml) and the
3
.2.1. 6-Tributylstannyl-2-(1,3-dioxolan-2-yl)pyridine
organic phase separated, washed with water (3!30 ml),
brine (1!40 ml) and dried over magnesium sulphate.
Following filtration, the solvent was removed under reduced
pressure and the crude product crystallised from ethanol at
K30 8C. The resulting precipitate was collected by filtration
to afford 1a (0.647 g, 60%) as a pale yellow solid. The
(
a). Under an atmosphere of nitrogen, 6-bromo-2-(1,3-
dioxolan-2-yl)pyridine (16.02 g, 69.65 mmol) was dis-
solved in anhydrous diethyl ether (160 ml) and cooled to
K100 8C. n-BuLi (43.5 ml, 69.65 mmol, 1 equiv, 1.6 M in
hexanes) was added dropwise over 15 min. After stirring the
mixture for 10 min, the solution was warmed to K78 8C and
stirred for a further 30 min. The solution was re-cooled to
K100 8C before addition of freshly distilled tributyl-
tinchloride (20.4 ml, 76.62 mmol, 1.1 equiv). The solution
was stirred for 1 h at K100 8C, allowed to warm to room
temperature and left to stir overnight. The resulting mixture
was filtered through Celite and washed with dichloro-
methane. The reaction mixture was concentrated under
reduced pressure to give a brown/black oil. The resulting oil
was distilled (Kugelrohr, 210 8C/0.1 mmHg) to afford
1
melting point and H NMR spectroscopic data of 1a were
1
6a 13
1
C { H}
consistent with the data previously reported.
NMR (62.5 MHz, CDCl ): d 121.6 (Py), 121.9 (Py), 122.0
3
(Py), 124.1 (Py), 124.3 (Py), 125.6 (Py), 137.3 (Py), 138.5
(Py), 138.8 (Py), 147.1 (Py), 149.6 (Py), 152.6 (Py), 154.1
(Py), 156.0 (Py), 156.4 (Py), 194.2 (C]O). IR (cm ) 1725
K1
C
(C]O). ESIMS: m/z 262 [MCH] .
0
0
00
4.3.2. 6-Acetyl-2,2 :6 ,2 -terpyridine (1b). A similar
procedure to that described for 1a was followed, using
6-bromo-2,2 -bipyridine (0.971 g, 4.13 mmol), b (2.06 g,
0
6
9
-tributylstannyl-2-(1,3-dioxolan-2-yl)pyridine (28.0 g,
2%) as a clear brown oil. H NMR (300 MHz, CDCl ): d
1
4.54 mmol, 1.1 equiv) and tetrakis(triphenylphosphine)-
palladium(0) (0.286 g, 0.25 mmol, 0.06 equiv). The product
was crystallised from ethanol at K30 8C and collected by
3
3
3
0
.94 (t, J Z7.3 Hz, 9H, CH ), 1.17 (dd, JH–HZ8.2 Hz,
H–H 3
3
3
JH–HZ8.5 Hz, 6H, CH ), 1.38 (app. sex, JH–HZ7 Hz, 6H,
2
CH ), 1.63 (m, 6H, CH ), 4.1–4.3 (m, 4H, CH ), 5.91 (s, 1H,
filtration to afford 1b (0.704 g, 62%) as a pale yellow solid.
Mp: 185–187 8C. H NMR (250 MHz, CDCl ): d 2.79 (s,
2
2
2
3
1
CH), 7.3–7.5 (m, 2H, Py-H), 7.57 (app. t, JH–HZ7.6 Hz,
3
1
H, Py-H). C { H} NMR (75 MHz, CDCl ): d 10.1 (CH ),
3
1
1
3H, CH
CZO), 7.27 (m, 1H, Py-H), 7.78 (m, 1H, Py-H),
3
3
3
2
1
3.7 (CH ), 27.3 (CH ), 28.0 (CH ), 65.6 (CH ), 104.8
2
7.87 (m, 1H, Py-H), 7.98 (m, 1H, Py-H), 8.38 (dd, JH–H
Z
3
2
2
4
(
(
CH), 118.9 (Py), 132.4 (Py), 133.1 (Py), 157.3 (Py), 173.5
Py). IR (cm ): 2955, 2922, 1575, 1557, 1463, 1411, 1340,
8.0 Hz, JH–HZ2.8 Hz, 1H, Py-H) 8.41 (m, 1H, Py-H), 8.51
K1
3 4
(dd,
J
H–HZ7.5 Hz,
JH–HZ2.6 Hz, 1H, Py-H), 8.56
3
3
1
123, 1093, 960, 944, 794, 665. FABMS: m/z 438 [MCH
Sn)] . HRMS (FAB): calcd for C H NO Sn [MC
(d, JH–HZ7.4 Hz, Py-H), 8.64 (d, JH–H H = 7.5 Hz, 1H,
1
16 C 116
2
C
3
4
(
H] 438.17670, found 438.17663.
Py-H), d 8.76 (dd, J Z7.7 Hz, JH–HZ2.5 Hz, 1H,
H–H
13 1
0
36
2
Py-H) C { H} NMR (62.5 MHz, CDCl ): d 24.8
3
(
CH C]O), 120.0 (Py), 120.1 (Py), 120.4 (Py), 120.5
3
4
.2.2. Synthesis of 6-tributylstannyl-2-(2-methyl-1,3-
(Py), 122.8 (Py), 122.9 (Py), 135.9 (Py), 136.7 (Py), 137.0
(Py), 148.2 (Py), 151.9 (Py), 153.5 (Py), 154.4 (Py), 154.5
(Py), 155.9 (Py), 199.4 (C]O). IR (cm ) 1700 (C]O),
dioxolan-2-yl)pyridine (b). A similar procedure to that
described for a was followed, using 6-bromo-2-(2-methyl-
K1
1
,3-dioxolan-2-yl)pyridine (16.99 g, 69.65 mmol) as the
protected ketal derivative. The resulting oil was distilled
Kugelrohr, 230 8C/0.1 mmHg) to afford 6-tributylstannyl-
-(2-methyl-1,3-dioxolan-2-yl)pyridine (27.64 g, 88%) as a
1564, 1426, 1078, 790, 748, 668. ESIMS: m/z 276
[MCH] . HRMS (FAB): calcd for C H N O
C
1
7
14
3
C
[MCH] 276.11369, found 276.11364.
(
2
1
0
0
00 00 000
clear brown oil. H NMR (300 MHz, CDCl ): d 0.79 (t,
3
4.3.3. 6-Formyl-2,2 :6 ,2 :6 ,2 -quaterpyridine (2a). A
similar procedure to that described for 1a was followed,
3
3
JH–HZ7.3 Hz, 9H, CH ), 1.02 (dd, JH–HZ8.2 Hz,
3

Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
85
0
0
00
C
740. ESIMS: m/z 318 [MCH] . Anal. Calcd for
using 6-bromo-2,2 :6 ,2 -terpyridine (1.28 g, 4.13 mmol), a
2.00 g, 4.54 mmol, 1.1 equiv) and tetrakis(triphenyl-
phosphine)palladium(0) (0.286 g, 0.25 mmol, 0.06 equiv).
(
C H N O : C, 71.92; H, 4.73; N, 13.25. Found C,
1
9 15 3 2
72.00; H, 4.82; N, 13.15.
The product was crystallised from ethanol at K30 8C and
collected by filtration to afford 2a (0.977 g, 70%) as a
000
4a). 2,6 -Dibromo-2,2 -bipyridine (1.42 g, 4.52 mmol), a
(
phosphine)palladium(0) (0.417 g, 0.36 mmol, 0.08 equiv)
0
0
00 00 000
4
(
.3.7. 6,6 -Diformyl-2,2 :6 ,2 :6 ,2 -quaterpyridine
1
white solid. Mp: 210–213 8C. H NMR (300 MHz, CDCl ):
0
4.38 g, 9.95 mmol, 2.2 equiv) and tetrakis(triphenyl-
00
3
3
d 7.2–7.3 (m, 1H, Py-H), 7.82 (ddd, JH–HZ7.9, 7.9 Hz,
JH–HZ1.7 Hz, 1H, Py-H), 7.9–8.0 (m, 4H, Py-H), 8.43 (dd,
JH–HZ7.9 Hz, J Z1.2 Hz, 1H, Py-H), 8.5–8.7 (m, 5H,
4
3
4
H–H
were loaded in a Schlenk tube under N and the contents
2
3
4
Py-H), 8.85 (dd, J Z7.6 Hz, JH–HZ1.7 Hz, 1H, Py-H),
H–H
stirred in dry toluene (35 ml) for 72 h at 100 8C. After
removal of the solvent under reduced pressure, the reaction
mixture was stirred overnight at 60 8C in 4 M HCl (20 ml),
cooled to room temperature and carefully neutralised by
addition of 2 M NaHCO . The suspension was extracted
3
with CHCl (3!30 ml) and the organic phase separated,
3
washed with water (3!30 ml), brine (1!40 ml) and dried
over magnesium sulphate. Following filtration, the solvent
was removed under reduced pressure and the crude product
recrystallised from ethanol at K30 8C. The resulting
1
3
1
0.18 (s, 1H, HC]O). C { H} NMR (75 MHz, CDCl ): d
1
1
1
1
1
3
21.0 (Py), 121.2 (Py), 121.5 (Py), 121.7 (Py), 123.8 (Py),
25.3 (Py), 136.9 (Py), 137.9 (Py), 138.0 (Py), 149.2 (Py),
93.8 (HC]O). IR (cm ) 1715 (C]O), 1564, 1427, 1260,
076, 799, 774, 683. ESIMS: m/z 339 [MCH] . HRMS
FAB): calcd for C H N O [MCH] 339.12471, found
21 15 4
K1
C
C
(
3
39.12549.
.3.4. 6-Acetyl-2,2 :6 ,2 :6 ,2 -quaterpyridine (2b). A
similar procedure to that described for 1a was followed,
0
0
00 00 000
4
precipitate was collected by filtration to afford 4a
0
0
00
using 6-bromo-2,2 :6 ,2 -terpyridine (1.50 g, 4.82 mmol), b
2.410 g, 5.30 mmol, 1.1 equiv) and tetrakis(triphenyl-
phosphine)palladium(0) (0.334 g, 0.29 mmol, 0.06 equiv).
1
(
0.746 g, 45%) as a white solid. Mp: 202–204 8C.
H
NMR (300 MHz, CDCl ): d 7.9–8.1 (m, 6H, Py-H), 8.60
(
3
3
4
(
dd, J Z7.9 Hz, JH–HZ1.7 Hz, 2H, Py-H), 8.67 (dd,
JH–HZ7.9 Hz, JH–HZ1.7 Hz, 2H, Py-H), 8.85 (dd,
H–H
The product was crystallised from ethanol at K30 8C and
collected by filtration to afford 2b (1.270 g, 75%) as a white
3
3
4
4
JH–HZ7.9 Hz, JH–HZ1.7 Hz, 2H, Py-H), 10.13 (s, 1H,
1
solid. Mp: 215–217 8C. H NMR (300 MHz, CDCl ): d 2.81
13
HC]O). C { H} NMR (75 MHz, CDCl ): poor quality
1
3
3
(
s, 3H, CH C]O), 7.2–7.3 (m, 1H, Py-H), 7.82 (dd,
3
K1
spectrum (compound too insoluble). IR (cm ): 1721
3
4
JH–HZ7.9 Hz, J Z1.7 Hz, 1H, Py-H), 7.9–8.0 (m, 4H,
H–H
(
C]O), 1565, 1429, 1348, 1259, 1213, 992, 878, 786,
3
4
Py-H), 8.43 (dd, J Z7.9 Hz, JH–HZ0.9 Hz, 1H, Py-H),
C
66. EIMS: m/z 367 [MCH] .
H–H
6
3
4
8
8
1
.54 (dd, J Z7.9 Hz, J Z1.7 Hz, 1H, Py-H), 8.5–
H–H H–H
3 4
.7 (m, 4H, Py-H), 8.80 (dd, J Z7.6 Hz, JH–HZ1.2,
H–H
0
00
0
0
00 00 000
A similar procedure to that described for 4a was followed,
1
H, Py-H). C { H} NMR (75 MHz, CDCl ): d 25.9
3
1
4.3.8. 6,6 -Diacetyl-2,2 :6 ,2 :6 ,2 -quaterpyridine (4b).
3
(
CH C]O), 121.1 (Py), 121.5 (Py), 123.9 (Py), 124.4 (Py),
3
0
00
using 2,6 -dibromo-2,2 -bipyridine (1.32 g, 4.20 mmol), a
(4.19 g, 9.24 mmol, 2.2 equiv) and tetrakis(triphenyl-
phosphine)palladium(0) (0.388 g, 0.34 mmol, 0.08 equiv).
The product was crystallised from ethanol at K30 8C and
1
1
1
36.9 (Py), 137.8 (Py), 137.9 (Py), 149.2 (Py), 154.5 (Py),
K1
55.5 (Py), 200.4 (CH C]O). IR (cm ) 1697 (C]O),
562, 1426, 1352, 1267, 1109, 1075, 992, 804, 775, 740.
3
C
ESIMS: m/z 353 [MCH] . HRMS (FAB): calcd for
C H N O [MCH] 353.14024, found 353.14016.
C
collected by filtration to afford 4b (1.19 g, 72%) as a white
solid. Mp: 242–244 8C. H NMR (300 MHz, CDCl ): d 2.81
2
2
17
4
1
3
3
0
0
0
0
00
(s, 6H, CH ), 7.95 (dd, J Z7.6, 7.6 Hz, 2H, Py-H), 7.99
3
H–H
4
.3.5. 6,6 -Diformyl-2,2 :6 ,2 -terpyridine (3a). A similar
3
3
(
dd,
J
Z7.9, 7.9 Hz, 2H, Py-H), 8.04 (dd, 3JH–H
Z
Z
Z
Z
H–H
4
procedure to that described for 1a was followed, using 2,6-
dibromopyridine (1.10 g, 4.65 mmol), (4.50 g,
0.23 mmol, 2.2 equiv) and tetrakis(triphenylphosphine)-
7
7
7
7
.6 Hz, JH–HZ1.2 Hz, 2H, Py-H), 8.55 (dd, 3JH–H
a
4
.9 Hz, JH–HZ1.2 Hz, 2H, Py-H), 8.65 (dd, 3JH–H
1
4
.6 Hz, JH–HZ1.2 Hz, 2H, Py-H), 8.80 (dd, JH–H
palladium(0) (0.429 g, 0.37 mmol, 0.08 equiv). The product
was crystallised from ethanol at K30 8C and collected by
4
13
1
.9 Hz, JH–HZ1.2 Hz, 2H, Py-H).
C { H} NMR
1
filtration to afford 3a (1.08 g, 80%) as a white solid. The H
(75 MHz, CDCl ): d 25.8 (CH ), 121.2 (Py), 121.5 (Py),
3 3
1
and C NMR spectroscopic data of 3a were consistent with
3
121.6 (Py), 124.4 (Py), 137.8 (Py), 137.9 (Py), 153.0 (Py),
154.6 (Py), 155.4 (Py), 155.5 (Py), 200.3 (C]O). IR (cm
K
5
those previously reported.
1
): 1697 (C]O), 1565, 1429, 1355, 1293, 1269, 1112, 1066,
992, 952, 792, 740. ESIMS: m/z 395 [MCH] . HRMS
C
0
0
0
0
00
4
.3.6. 6,6 -Diacetyl-2,2 :6 ,2 -terpyridine (3b). A similar
procedure to that described for 1a was followed, using 2,6-
dibromopyridine (1.21 g, 5.12 mmol), (5.11 g,
1.26 mmol, 2.2 equiv) and tetrakis(triphenylphosphine)-
C
FAB): calcd for C H N O [MCH] 395.15094, found
(
24 19 4 2
395.15080.
b
1
0000
4.3.9. Attempted synthesis of 6,6 -diformyl-
palladium(0) (0.473 g, 0.41 mmol, 0.08 equiv). The product
was crystallised from ethanol at K30 8C and collected by
0 0 00 00 000 000 0000
2,2 :6 ,2 :6 ,2 :6 :2 -quinquepyridine (5a). A similar
00
procedure to that described for 4a was followed, using 2,6 -
filtration to afford 3b (1.22 g, 75%) as a white solid. Mp:
1
1
92–194 8C. H NMR (300 MHz, CDCl ): d 2.85 (s, 6H,
0
0
00
dibromo-2,2 :6 ,2 -terpyridine (1.64 g, 4.20 mmol), a
(4.07 g, 9.24 mmol, 2.2 equiv) and tetrakis(triphenyl-
phosphine)palladium(0) (0.388 g, 0.34 mmol, 0.08 equiv).
Following the deprotection step and subsequent neutralis-
ation, the resultant suspension was insoluble in the
chlorinated solvents employed for the extraction and could
not be isolated and characterised.
3
3
CH ), 7.8–8.1 (m, 5H, Py-H), 8.51 (d, JH–HZ7.9 Hz, 2H,
3
3
4
Py-H), 8.75 (dd, J Z7.9 Hz, JH–HZ1.7 Hz, 2H, Py-H).
H–H
1
C { H} NMR (75 MHz, CDCl ): d 24.7 (CH ), 120.4 (Py),
1
3
3
3
1
1
20.6 (Py), 123.3 (Py), 136.7 (Py), 137.0 (Py), 151.9 (Py),
53.6 (Py), 154.2 (Py), 199.2 (C]O). IR (cm ): 1697
K1
(
C]O), 1577, 1429, 1349, 1268, 1111, 1071, 992, 951, 793,

86
Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
0
pyridine (5b). A similar procedure to that described for
000
0
0
00 00 000 000 0000
C
m/z 421 [MCH] . HRMS (FAB): calcd for C H N [MC
28 29 4
4
.3.10. 6,6 -Diacetyl-2,2 :6 ,2 :6 ,2 :6 :2 -quinque-
C
H] 421.23922, found 421.23936.
0
.65 mmol), a (4.64 g, 10.23 mmol, 2.2 equiv) and tetra-
0
0
0
00
4
a, using 2,6 -dibromo-2,2 :6 ,2 -terpyridine (1.82 g,
0
0
00
4
4.4.2. 6-Iminoacetyl-2,2 :6 ,2 -terpyridine (2,6-diisopro-
pylanil) (6b). The procedure outlined in method B was
followed, using 1b (0.300 g, 1.09 mmol) in 2,6-diisopro-
pylaniline (3.00 g, 10.90 mmol, 10 equiv). The product was
recrystallised from a dichloromethane–hexane (1/9) mixture
at room temperature and the resulting precipitate was
filtered, washed with hexane and dried under reduced
pressure to afford 6b (0.237 g, 50%) as a pale yellow solid.
Crystals suitable for the X-ray determination were grown by
kis(triphenylphosphine)palladium(0) (0.430 g, 0.37 mmol,
.08 equiv). The product was crystallised from ethanol at
0
K30 8C. The resulting precipitate was collected by filtration
to afford 5b (1.030 g, 50%) as a white solid. Mp: O260 8C.
1
H NMR (300 MHz, CDCl ): d 2.81 (s, 6H, CH C]O),
3
3
4
3
7
1
.9–8.1 (m, 7H, Py-H), 8.55 (dd, J Z7.9 Hz, JH–HZ
H–H
3
.2 Hz, 2H, Py-H), 8.64 (d, JH–HZ7.9 Hz, 2H, Py-H), 8.69
3
4
(
dd, J Z7.9 Hz, J Z0.9 Hz, 2H, Py-H), 8.81 (dd,
H–H H–H
4 13 1
3
JH–HZ7.9 Hz, JH–HZ1.2 Hz, 2H, Py-H). C { H} NMR
75 MHz, CDCl ): poor quality spectrum (compound too
insoluble). IR (cm ): 1705 (C]O), 1562, 1465, 1426,
slow cooling of a hot n-BuOH solution containing 6b. Mp:
242–245 8C. H NMR (300 MHz, CDCl ): d 1.10 (d,
1
(
3
3
K1
3
JH–HZ6.7 Hz, 12H, CH(Me) ), 2.28 (s, 3H, CH C]N),
2
3
1
4
360, 1269, 1108, 1076, 992, 805, 788, 742. ESIMS: m/z
72 [MCH] .
2.81 (sept, 2H, CH(Me) ), 7.0–7.2 (m, 3H, Ar-H), 7.2–7.3
2
C
3
(m, 1H, Py-H), 7.7–7.9 (m, 1H, Py-H), 7.91 (dd, JH–HZ7.9,
3
7
.9 Hz, 2H, Py-H), 8.35 (d, J Z7.9 Hz, 1H, Py-H), 8.42
H–H
3
3
4
.4. Synthesis of the imino-substituted oligopyridines
(d, JH–HZ7.9 Hz, 1H, Py-H), 8.53 (d, JH–HZ7.9 Hz, 1H,
Py-H), 8.59 (d, JH–HZ7.9 Hz, 1H, Py-H), 8.67 (m, 2H, Py-
H). C { H} NMR (75 MHz, CDCl ): d 16.3 (CH C]N),
3 3
3
1
3
1
Method A. The monoformyl- or diformyl-substituted
oligopyridine was suspended in absolute ethanol and 2,6-
diisopropylaniline (1.1 or 2.2 equiv) introduced along with a
catalytic amount of glacial acetic acid. The mixture was
stirred and heated vigourously at 50 8C for 18 h. The
solution was cooled and the resulting precipitate collected
by filtration and washed with ethanol.
21.9 (CH ), 22.2 (CH ), 27.3 (CH), 120.1 (Py), 120.2 (Py),
3
3
121.0 (Py), 122.5 (Ar), 122.8 (Ar), 134.8 (Py), 136.3 (Py),
136.8 (Py), 142.0 (Ar), 148.1 (Py), 154.4 (Py), 154.5 (Py),
155.1 (Py), 155.9 (Py), 166.1 (C]N). IR (cm ) 2952,
K1
1630 (C]N), 1562, 1422, 1360, 1263, 1075, 990, 777, 744.
ESIMS: m/z 435 [MCH] . HRMS (FAB): calcd for
C
C
C H N [MCH] 435.25490, found 435.25487.
2
9 31 4
Method B. The monoacetyl- or diacetyl-substituted oligo-
pyridine was suspended in an excess of 2,6-diisopropyl-
aniline (10 equiv) and stirred for 15 min at 160 8C on a
heating mantle. A catalytic amount of formic acid was
added, and the reaction mixture was stirred for an additional
0
0
00 00 000
4.4.3. 6-Iminoformyl-2,2 :6 ,2 :6 ,2 -quaterpyridine
(2,6-diisopropylanil) (7a). The procedure outlined in
method A was followed, using 2a (0.836 g, 2.48 mmol)
and 2,6-diisopropylaniline (0.483 g, 2.73 mmol, 1.1 equiv)
in ethanol (15 ml). The residue was recrystallised from a
dichloromethane–hexane (1/9) mixture at room temperature
and the resulting precipitate was filtered, washed with
hexane and dried under reduced pressure to afford 7a
20 min at this temperature. Following removal of the excess
2,6-diisopropylaniline under reduced pressure (130 8C,
0.5 mmHg), the resulting brown residue was stirred in
ethanol at room temperature and the resultant precipitate
filtered and washed with ethanol.
1
(0.616 g, 50%) as a pale yellow solid. Mp: O260 8C. H
NMR (300 MHz, CDCl ): d 1.17 (d, JH–HZ7 Hz, 12H,
), 2.95 (sept, 2H, CH(Me)
Ar-H), 7.2–7.3 (m, 1H, Py-H), 7.81 (dd, JH–HZ7.9, 7.6 Hz,
1H, Py-H), 7.9–8.0 (m, 3H, Py-H), 8.27 (d, JH–HZ7.6 Hz,
1H, Py-H), 8.37 (s, 1H, HC]N), 8.43 (d, JH–HZ7.9 Hz,
1H, Py-H), 8.52 (d, JH–HZ7.9 Hz, 1H, Py-H), 8.5–8.7 (m,
4H, Py-H), 8.72 (d, JH–HZ7.9 Hz, 1H, Py-H). C { H}
NMR (75 MHz, CDCl ): d 23.5 (CH ), 28.0 (CH), 121.1
3
3
0
0
00
4
.4.1. 6-Iminoformyl-2,2 :6 ,2 -terpyridine (2,6-diiso-
CH(Me)
2
2
)3, 7.0–7.2 (m, 3H,
propylanil) (6a). The procedure outlined in method A
was followed, using 1a (0.630 g, 2.41 mmol) and 2,6-
diisopropylaniline (0.483 g, 2.73 mmol, 1.1 equiv) in
ethanol (15 ml). The residue was crystallised from a
dichloromethane–hexane (1/9) mixture at room temperature
and the resulting precipitate filtered, washed with hexane
3
3
3
3
13
1
3
3
and dried under reduced pressure to afford 6a (0.453 g,
4
(Py), 121.2 (Py), 122.7 (Py), 123.1 (Py), 123.8 (Ar), 124.4
(Ar), 136.9 (Py), 137.3 (Ar), 137.6 (Py), 137.9 (Py), 149.2
(Py), 153.9 (Py), 154.8 (Py), 155.4 (Py), 156.2 (Py), 155.1
1
5%) as a pale yellow solid. Mp: 223–225 8C. H NMR
3
(
CH(Me) ), 2.94 (sept, 2H, CH(Me) ), 7.0–7.2 (m, 3H, Ar-
250 MHz, CDCl ): d 1.14 (d, JH–HZ7 Hz, 12H,
3
K1
(Py), 163.5 (C]N). IR (cm ): 2959, 1636 (C]N), 1565,
1425, 1263, 1181, 1077, 991, 772. ESIMS: m/z 498 [MC
2
2
H), 7.2–7.3 (m, 1H, Py-H), 7.7–7.8 (m, 1H, Py-H), 7.90 (dd,
3
3
3
C
H] . HRMS (FAB): calcd for
JH–HZ7.9 Hz, JH–HZ7.6 Hz, 1H, Py-H), 7.93 (dd,
C
33
H
32
N
5
[MC
3
C
H] 498.26577, found 498.26570.
JH–HZ7.9, 7.6 Hz, 1H, Py-H), 8.26 (d, JH–HZ7.9 Hz,
H, Py-H), 8.37 (s, 1H, HC]N), 8.41 (d, JH–HZ7.9 Hz,
H, Py-H), 8.49 (d, JH–HZ7.6 Hz, 1H, Py-H), 8.56 (d,
JH–HZ8.2 Hz, 1H, Py-H), 8.63 (m, 1H, Py-H), 8.67 (d,
3
1
3
0
0
00 00 000
1
4.4.4. 6-Iminoacetyl-2,2 :6 ,2 :6 ,2 -quaterpyridine
(2,6-diisopropylanil) (7b). The procedure outlined in
method B was followed, using 2b (1.50 g, 4.44 mmol) and
2,6-diisopropylaniline (7.86 g, 44.40 mmol, 10 equiv). The
residue was crystallised from a dichloromethane–hexane
(1/9) mixture at room temperature and the resulting
precipitate filtered, washed with hexane and dried under
3
3
13
1
JH–HZ7.9 Hz, 1H, Py-H). C { H} NMR (75 MHz,
CDCl ): d 22.4 (CH ), 26.8 (CH), 120.0 (Py), 120.1 (Py),
3
3
1
1
1
1
1
20.2 (Py), 121.6 (Ar), 122.0 (Ar), 122.8 (Py), 123.4 (Py),
35.9 (Py), 136.2 (Py), 136.5 (Py), 136.9 (Py), 147.5 (Py),
48.1 (Py), 152.8 (Py), 153.8 (Py), 154.4 (Py), 155.1 (Py),
62.4 (C]N). IR (cm ): 2952, 1629 (C]N), 1577, 1562,
422, 1263, 1180, 1104, 1076, 990, 856, 775, 758. FABMS:
K1
reduced pressure to afford 7b (0.629 g, 60%) as a pale
1
yellow solid. Mp: O260 8C. H NMR (300 MHz, CDCl ): d
3

Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
87
3
1
CH C]N), 2.71 (sept, 2H, CH(Me) ), 7.0–7.2 (m, 3H,
.10 (d, JH–HZ6.7 Hz, 12H, CH(Me) ), 2.28 (s, 3H,
1642 (C]N), 1563, 1430, 1362, 1256, 1184, 1108, 800,
784, 760. ESIMS: m/z 636 [MCH] . Anal. Calcd for
2
C
3
2
Ar-H), 7.2–7.3 (m, 1H, Py-H), 7.8–7.9 (m, 1H, Py-H), 7.91
(
(C H N ): C, 81.26; H, 7.72; N, 11.02. Found C, 81.16; H,
3 49 5
7.86; N, 10.92.
4
3
3
dd, J Z7.9, 7.9 Hz, 2H, Py-H), 8.35 (d, JH–HZ7.9 Hz,
H–H
3
1
H, Py-H), 8.42 (d, J Z7.9 Hz, 1H, Py-H), 8.53 (d,
H–H
3
3
000
0
0
00 00 000
JH–HZ7.9 Hz, 1H, Py-H), 8.59 (d, JH–HZ7.9 Hz, 1H, Py-
4.4.7. 6,6 -Bis-(iminoformyl)-2,2 :6 ,2 :6 ,2 -quater-
pyridine-bis-(2,6-diisopropylanil) (9a). The procedure
outlined in method A was followed, using 4a (0.875 g,
2.05 mmol) and 2,6-diisopropylaniline (0.798 g,
4.51 mmol, 2.2 equiv) in ethanol (12 ml). The residue was
recrystallised from a dichloromethane–hexane (1/9) mixture
at room temperature and the resulting precipitate filtered,
washed with hexane and dried under reduced pressure to
afford 9a (0.701 g, 50%) as a white solid. Crystals
suitable for the X-ray determination were grown by slow
1
H), 8.67 (m, 2H, Py-H). C { H} NMR (75 MHz, CDCl ):
3
1
3
d 16.3 (s, CH C]N), 21.9 (CH ), 22.2 (CH ), 27.3 (CH),
3
3
3
1
1
1
1
1
20.1 (Py), 120.2 (Py), 121.0 (Py), 122.0 (Py), 122.5 (Ar),
22.8 (Ar), 134.8 (Py), 135.9 (Py), 136.3 (Ar), 136.7 (Py),
36.9 (Py), 148.1 (Py), 154.2 (Py), 154.4 (Py), 154.6 (Py),
K1
66.1 (C]N). IR (cm ): 2950, 1634 (C]N), 1562, 1425,
362, 1292, 1269, 1188, 1111, 1080, 991, 807, 759, 684.
C
ESIMS: m/z 512 [MCH] . HRMS (FAB): calcd for
C H N [MCH] 512.28142, found 512.28155.
C
3
4 34 5
evaporation of a dichloromethane solution containing 9a.
0
2,6-diisopropylanil) (8a). The procedure outlined in
0
0
0
00
1
4
(
.4.5. 6,6 -Bis-(iminoformyl)-2,2 :6 ,2 -terpyridine-bis-
Mp: O260 8C. H NMR (300 MHz, CDCl
3
): d 1.14 (d,
) ), 2.90 (sept, 4H,
3 2
3
J
H–HZ6.7 Hz, 24H, CH(CH
3
method A was followed, using 3a (1.031 g, 3.57 mmol)
and 2,6-diisopropylaniline (1.390 g, 7.85 mmol, 2.2 equiv)
in ethanol (25 ml). The residue was recrystallised from a
dichloromethane–hexane (1/9) mixture at room temperature
and the resulting precipitate filtered, washed with hexane
and dried under reduced pressure to afford 8a (1.411 g,
CH(CH ), 7.0–7.2 (m, 6H, Ar-H), 7.95 (app. t, JH–HZ
3
)
2
3
7.9, 7.9 Hz, 4H, Py-H), 8.27 (d, JH–HZ7.3 Hz, 2H, Py-H),
8.63 (s, 2H, HC]N), 8.52 (d, JH–HZ7.3 Hz, 2H, Py-H),
8.64 (dd, JH–HZ7.9 Hz, JH–HZ0.9 Hz, 2H, Py-H), 8.72
(d, JH–HZ7.9 Hz, 2H, Py-H). C { H} NMR (75 MHz,
CDCl ): d 23.5 (CH ), 28.0 (CH), 121.1 (Py), 121.2 (Py),
3
3
4
3
13
1
3
3
65%) as a pale yellow solid. Crystals suitable for the X-ray
determination were grown by slow evaporation of a
dichloromethane solution containing 8a. Mp: 220–222 8C.
121.4 (Py), 122.7 (Ar), 123.1 (Ar), 134.5 (Ar), 137.3 (Py),
137.6 (Py), 137.9 (Py), 148.6 (Ar), 154.0 (Py), 154.9 (Py),
155.5 (Py), 156.2 (Py), 163.5 (C]N). IR (cm ): 2960,
K1
1
3
H NMR (300 MHz, CDCl ): d 1.14 (d, JH–HZ7 Hz, 24H,
1644 (C]N), 1566, 1456, 1427, 1321, 1262, 1108, 1098,
1076, 990, 885, 794, 768, 743, 692. FABMS: m/z 685 [MC
3
CH(Me) ), 2.92 (sept, 4H, CH(Me) ), 7.0–7.2 (m, 6H,
2
2
3
C
H] . HRMS (FAB): calcd for
Ar-H), 7.91 (app. t, J Z7.6, 7.6 Hz, 1H, Py-H), 7.96
C
46
H
49
N
6
[MC
H–H
3
3
C
H] 685.40190, found 685.40187.
(
7
app. t, J Z7.9, 7.9 Hz, 2H, Py-H), 8.29 (d, JH–HZ
H–H
3
.6 Hz, 2H, Py-H), 8.36 (s, 2H, HC]N), 8.52 (d, JH–HZ
3
00
0
0
00 00 000
7
.9 Hz, 2H, Py-H) and 8.71 (d, JH–HZ7.6 Hz, 2H, Py-H).
4.4.8. 6,6 -Bis-(iminoacetyl)-2,2 :6 ,2 :6 ,2 -quaterpyri-
dine-bis-(2,6-diisopropylanil) (9b). The procedure out-
lined in method B was followed, using 4b (0.854 g,
2.17 mmol) and 2,6-diisopropylaniline (3.84 g, 21.7 mmol,
10 equiv). The residue was recrystallised from a dichloro-
methane–hexane (1/9) mixture at room temperature and the
resulting precipitate was filtered, washed with hexane and
1
3
1
C { H} NMR (75 MHz, CDCl ): d 23.5 (CH ), 28.0 (CH),
21.1 (Py), 121.4 (Py), 122.7 (Py), 122.8 (Py), 123.1 (Ar),
3
3
1
1
1
1
24.5 (Ar), 137.3 (Py), 137.6 (Py), 148.6 (Ar), 154.0 (Ar),
55.0 (Py), 156.1 (Py), 163.5 (C]N). IR (cm ): 2952,
648 (C]N), 1563, 1434, 1361, 1190, 1115, 795, 786, 760.
ESIMS: m/z 608 [MCH] . HRMS (FAB): calcd for
C H N H [MCH] 608.37532, found 608.37532.
K1
C
C
C
4
1
45
5
dried under vacuum to afford 9b (0.896 g, 58%) as a white
1
Anal. Calcd for (C H N $0.5H O): C, 79.87; H, 7.46;
2
solid. Mp: O260 8C. H NMR (300 MHz, CDCl ): d 1.16
4
1
45
5
3
3
N, 11.36. Found C, 79.62; H, 7.63; N, 10.81.
(d, J Z6.7 Hz, 24H, CH(Me) ), 2.30 (s, 6H, CH C]N),
H–H
2
3
2
J
.78 (sept, 4H, CH(Me) ), 7.0–7.1 (m, 6H, Ar-H), 7.93 (dd,
H–HZ7.9,
2
0
0
0
2,6-diisopropylanil) (8b). The procedure outlined in
0
00
3
3
4
(
.4.6. 6,6 -Bis-(iminoacetyl)-2,2 :6 ,2 -terpyridine-bis-
H–HZ7.9, 7.9 Hz, 2H, Py-H), 7.97 (dd,
J
3
7.9 Hz, 2H, Py-H), 8.36 (d, JH–HZ7.9 Hz, 2H, Py-H),
8.56 (d, JH–HZ7.9 Hz, 2H, Py-H), 8.66 (d, JH–HZ7.9 Hz,
3
3
method B was followed, using 3b (1.050 g, 3.31 mmol)
and 2,6-diisopropylaniline (5.86 g, 33.10 mmol, 10 equiv).
The residue was recrystallised from a dichloromethane–
hexane (1/9) mixture at room temperature and the resulting
precipitate filtered, washed with hexane and dried under
vacuum to afford 8b (1.263 g, 60%) as a pale yellow solid.
Mp: 252–254 8C. H NMR (300 MHz, CDCl ): d 1.11 (d,
JH–HZ6.7 Hz, 24H, CH(Me) ), 2.29 (s, 6H, CH C]N),
3 13 1
2H, Py-H), 8.72 (d, JH–HZ7.9 Hz, 2H, Py-H). C { H}
NMR (75 MHz, CDCl ): d 17.3 (CH C]N), 22.9 (CH ),
23.3 (CH ), 28.3 (CH), 121.1 (Py), 121.2 (Py), 122.0 (Py),
123.0 (Ar), 123.6 (Ar), 135.9 (Ar), 137.4 (Py), 137.8 (Py),
146.6 (Ar), 155.0 (Py), 155.3 (Py), 155.5 (Py), 155.7 (Py),
167.1 (C]N). IR (cm ): 2959, 1646, 1565, 1458, 1429,
1363, 1261, 1192, 1111, 1080, 1042, 991, 860, 764, 740,
686. ESIMS: m/z 713 [MCH] . Anal. Calcd for
(C48H N ): C, 80.90; H, 7.30; N, 11.80. Found C, 80.63;
52 6
3
3
3
3
1
K1
3
3
2
3
C
2
.72 (sept, 4H, CH(Me) ), 7.00–7.14 (m, 6H, Ar-H), 7.91
2
3
3
(
app. t, J Z7.9, 7.9 Hz, 1H, Py-H), 7.92 (app. t, JH–HZ
H–H
3
4
7
0
.9, 7.9 Hz, 2H, Py-H), 8.37 (dd, J Z7.9 Hz, JH–HZ
.9 Hz, 2H, Py-H), 8.54 (d, J Z7.9 Hz, 2H, Py-H), 8.71
(dd, J Z7.9 Hz, JH–HZ0.9 Hz, 2H, Py-H). C { H}
NMR (75 MHz, CDCl ): d 16.3 (CH C]N), 21.9 (CH ),
H, 7.40; N, 11.66.
H–H
3
H–H
3
4
13
1
0000
0
0
00 00 000 000 0000
4.4.9. 6,6 -Bis-(iminoformyl)-2,2 :6 ,2 :6 ,2 :6 ,2 -
quinquepyridine-bis-(2,6-diisopropylanil) (10b). The
procedure outlined in method B was followed, using 5b
(0.645 g, 1.42 mmol) and 2,6-diisopropylaniline (2.51 g,
14.20 mmol, 10 equiv). The residue was recrystallised from
a dichloromethane–hexane (1/9) mixture at room
H–H
3
3
3
2
1
1
1
2.2 (CH ), 27.3 (CH), 120.0 (Py), 120.3 (Py), 121.0 (Py),
3
22.0 (Ar), 122.6 (Ar), 134.8 (Ar), 136.3 (Py), 136.8 (Py),
45.5 (Py), 136.3 (Py), 136.8 (Py), 145.4 (Ar), 154.0 (Py),
54.2 (Py), 154.6 (Py), 166.1 (C]N). IR (cm ): 2955,
K1

88
Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
temperature and the resulting precipitate filtered, washed
with hexane and dried under vacuum to afford 10b (0.504 g,
CCDC reference numbers 279915–279917 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 Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ;
fax: (internet) C44 1223 336 033; e-mail: deposit@ccdc.
cam.ac.uk].
1
4
5%) as a white solid. Mp: O260 8C. H NMR (300 MHz,
3
CDCl ): d 1.11 (d, J Z7.1 Hz, 12H, CH(Me) ), 2.31 (s,
3
H–H
2
6
7
7
H, CH ), 2.74 (sept, 4H, CH(Me) ), 7.0–7.2 (m, 6H, Ar-H),
3 2
3
3
.94 (dd, J Z7.9, 7.9 Hz, 2H, Py-H), 7.97 (dd, JH–HZ
H–H
3
.9, 7.9 Hz, 2H, Py-H), 8.02 (dd, J Z7.9, 7.9 Hz, 1H,
H–H
3
3
Py-H), 8.38 (d, J Z7.9 Hz, 2H, Py-H), 8.56 (d, JH–HZ
H–H
3
7
.9 Hz, 2H, Py-H), 8.67 (d, J Z7.9 Hz, 2H, Py-H), 8.68
H–H
3 3
(
d, J Z7.9 Hz, 2H, Py-H), 8.73 (d, JH–HZ7.9 Hz, 2H,
Acknowledgements
H–H
1
Py-H). C { H} NMR (75 MHz, CDCl ): d 16.3 (CH), 21.9
3
1
3
(
1
1
CH ), 22.2 (CH ), 27.3 (CH C]O), 120.0 (Py), 120.2 (Py),
3
We thank the University of Leicester for financial
assistance. ExxonMobil Chemical are also thanked for an
Undergraduate summer Bursary (to I.D.). Johnson Matthey
PLC are thanked for their loan of palladium chloride.
3
3
21.0 (Py), 122.0 (Ar), 122.5 (Ar), 134.8 (Py), 136.3 (Py),
36.8 (Py), 145.5 (Ar), 154.0 (Py), 154.3 (s, Py), 154.5 (s,
K1
Py), 154.6 (Py), 167.1 (C]N). IR (cm ): 2960, 1643
(
7
calcd for C H N [MCH] 790.45979, found 790.45972.
C]N), 1565, 1425, 1363, 1262, 1241, 1110, 1066, 935,
C
00, 743, 687. FABMS: m/z 790 [MCH] . HRMS (FAB):
C
5
3 56 7
References and notes
4
.5. Crystallography
1
. Constable, E. C. Metals and Ligand Reactivity; VCH:
Weinheim, 1996.
Data for 6b, 8a and 9a were collected on a Bruker APEX
000 CCD diffractometer. Details of data collection,
2
2. Constable, E. C.; Carlin, K. D. Progress in Inorganic
Chemistry; Wiley: New York, 1994; p 67.
refinement and crystal data are listed in Table 4. The data
were corrected for Lorentz and polarisation effects and
empirical absorption corrections applied. Structure solution
3. Lehn, J. M. Supramolecular Chemistry, Concepts and
Perspectives; VCH: Weinheim, 1995.
2
by Patterson methods and structure refinement on F
employed SHELXTL version 6.10. Hydrogen atoms
4. Piguet, C.; Bernardinelli, G.; Hopfgartner, G. Chem. Rev.
1997, 97, 2005.
2
5
˚
were included in calculated positions (C–HZ0.96 A) riding
on the bonded atom with isotropic displacement parameters
5. (a) El-ghayoury, A.; Ziessel, R. J. Org. Chem. 2000, 65, 7757.
(b) El-ghayoury, A.; Ziessel, R. Tetrahedron Lett. 1998, 39,
4473. (c) Hicks, R. G.; Koivisto, B. D.; Lemaire, M. T. Org.
Lett. 2004, 6, 1887.
set to 1.5 U (C) for methyl H atoms and 1.2 U (C) for all
eq
eq
other H atoms. All non H atoms were refined with
anisotropic displacement parameters. In the case of 9a, the
small crystals were weak diffractors; the data was refined
with full matrix and anisotropic parameters resulting in a
poor ratio of observed data:parameter (4.5:1).
6. Ziessel, R.; Douce, L.; El-ghayoury, A.; Harriman, A.;
Skoulios, A. Angew. Chem., Int. Ed. 2000, 39, 1489.
7. El-ghayoury, A.; Douce, L.; Skoulios, A.; Ziessel, R. Angew.
Chem., Int. Ed. 1998, 37, 2205.
Table 4. Crystallographic and data processing parameters for 6b, 8a and 9a
Complex
6b
8a
9a
Formula
M
C
434.57
0.59!0.38!0.18
200(2)
29
H
30
N
4
C
41
H
45
N
5
$CDCl
3
46 48 6
C H N
684.90
728.19
0.37!0.32!0.25
160(2)
Monoclinic
P2(1)/n
14.2131(9)
20.9441(13)
14.3123(9)
—
112.2860(10)
—
3942.2(4)
4
1.225
1536
0.268
30,472
7739
0.0240
0/477
3
Crystal size (mm )
Temperature (K)
Crystal system
Space group
0.22!0.15!0.03
150(2)
Monoclinic
P2(1)/c
11.445(15)
11.289(14)
15.38(2)
—
98.12(3)
—
1967(4)
2
1.156
732
0.069
13,854
3454
0.4098
0/239
Triclinic
P bar 1
8.851(4)
11.016(5)
12.976(5)
97.48(3)
102.49(4)
93.17(4)
1220.2(9)
2
1.183
464
0.071
4373
4233
0.0791
0/298
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
U (A )
Z
K3
D
F(000)
c
(Mg m
)
K1
m(Mo K
Reflections collected
a
)(mm
)
Independent reflections
R
int
Restraints/parameters
Final R indices (IO2s(I))
All data
R
R
1
Z0.0674, wR
Z0.1446, wR
2
Z0.1579
Z0.1983
R
R
1
Z0.0444, wR
Z0.0574, wR
2
2
Z0.1257
Z0.1305
R
R
1
Z0.0969, wR
Z0.2716, wR
2
Z0.1450
Z0.2079
1
2
1
1
2
2
Goodness of fit on F (all data)
1.023
1.086
0.860
1
2
2 2
2 2
⁄
2
K1
2
2
˚
Data in common: graphite-monochromated Mo K
a
radiation, lZ0.71073 A; R
)]/3, where a is a constant adjusted by the program; goodness of fitZ[S(F
and p the number of parameters.
1
ZSkF
o
jKjF
c
k/SjF j, wR
o
2 o c o o
Z[Sw(F KF ) /Sw(F ) ] , w Z[s (F ) C
2
2
2
2
2 1/2
KF )2/(nKp)] where n is the number of reflections
o c
(
aP) ], PZ[max(F
o
,0)C2(F
c

Y. D. M. Champouret et al. / Tetrahedron 62 (2006) 79–89
89
8
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16. (a) Potts, K. T.; Usifer, D. A.; Guadalupe, A.; Abruna, H. D.
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Takakazu, N.; Nishiwaki, K.; Wakabayashi, S.; Oae, S.;
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18. Potts, K. T.; Cheysen Raiford, K. A.; Keshavarz-K, M. J. Am.
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1
0. Britovsek, G. J. P.; Baugh, S. P. D.; Hoarau, O.; Gibson, V. C.;
Wass, D. F.; White, A. J. P.; Williams, D. J. Inorg. Chim. Acta
2
003, 345, 279.
1. Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J.; McTavish, S. J.; Solan, G. A.;
White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 849.
2. Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120,
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Chemicals, 4th ed; Butterworth Heinemann: 1996.
20. Tellier, F.; Sauvetre, R.; Normant, J.-F. J. Organomet. Chem.
1985, 292, 2.
1
1
7
143.
3. For reviews see, (a) Gibson, V. C.; Spitzmesser, S. K. Chem.
Rev. 2003, 103, 283. (b) Britovsek, G. J. P.; Gibson, V. C.;
Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (c) Ittel,
S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
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1986, 51, 850.
1
169. (d) Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 534.
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122, 12174.
1
1
4. (a) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (b)
Espinet, P.; Echavarren, A. M. Angew. Chem., Int. Ed. 2004,
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8, 939.
43, 4707.
5. (a) Heirtzler, F. R.; Neuburger, M.; Zehnder, M.; Constable,
E. C. Liebigs Ann. Recl. 1997, 2971. (b) Constable, E. C.;
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