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3
118.3 (C6), 118.5 (C8), 124.5 (C5), 125.2 (C7), 127.7 (C3),
129.4 (C8a). Mp: 265 °C (dec.). Anal. Calc. for
C15H14N4I2: C, 35.74; H, 2.80; N, 11.11; I, 50.35. Found:
C, 35.77; H, 2.90; N, 10.99; I, 50.18%. MS-ESI: m/
z = 377.1 [MꢀI]+.
CH2), 7.17 (d, JHH = 9.1 Hz, 2H, 8-H), 7.45 (s, 2H, 1-
H), 8.18 (d, JHH = 7.3 Hz, 2H, 5-H). 13C NMR (THF-
d8): d = 66.8 (CH2), 109.5 (C1), 111.7 (C6), 118.3 (C8),
3
122.5 (C7), 131.8 (C5), 132.3 (C8a), 209.5 (C3).
4.6. In situ generation of ethylenebis(imidazo[1,5-a]-
pyridine-3-ylidene) (4)
4.3. Synthesis of methylenebis(imidazo[1,5-a]pyridinium)-
dibromide (1b)
In a Young-NMR tube 25 mg (60 lmol) of the bisimi-
dazolium salt ethylenebis(imidazo[1,5-a]pyridinium)dibro-
mide (2) is dispersed in 0.5 ml of THF-d8. To the
suspension, 20 mg (0.18 mmol) of potassium-tert-butoxide
is added and the tube is gently shaken for a few minutes
until a dark solution can be obtained. 1H NMR
(500.13 MHz, THF-d8): d = 4.76 (s, 4H, CH2), 6.23 (dd,
In a sealed Schlenk tube 1.00 g (8.48 mmol) imidazo-
[1,5-a]pyridine and 296 ll (4.24 mmol) diiodoethane are
refluxed in 10 ml of toluene for a period of 70 h. The pre-
cipitated product is filtered off and washed three times with
5 ml of cold toluene. The residue is dried in vacuo to give
the product as an off-white solid. Yield: 18% (310 mg).
1H NMR (DMSO-d6): d = 7.23–7.34 (m, 4H, 7-H, 6-H),
3
3JHH = 7.3 Hz, JHH = 6.2 Hz, 2H, 6-H), 6.61 (dd,
3
3
7.37 (s, 2H, CH2), 7.95 (d, JHH = 9.1 Hz, 2H, 8-H), 8.58
3JHH = 9.3 Hz, JHH = 6.2 Hz, 2H, 7-H), 7.11 (s, 2H, 1-
3
4
3
(s, 2H, 1-H), 8.67 (dd, JHH = 7.0 Hz, JHH = 1.1 Hz, 2H,
5-H), 10.09 (s, 2H, 3-H). 13C NMR (DMSO-d6): d = 60.1
(CH2), 113.2 (C1), 118.3 (C6), 118.5 (C8), 124.5 (C5),
125.2 (C7), 127.8 (C3), 129.4 (C8a). Mp: 291 °C (dec.).
Anal. Calc. for C15H14Br2N4: C, 43.93; H, 3.44; N, 13.46.
Found: C, 43.69; H, 3.48; N, 13.46%. MS-ESI: m/
z = 331.2/229.2 [MꢀBr]+, 249.2 [MꢀH-2Br]+, 125.1
H), 7.16 (d, JHH = 9.3 Hz, 2H, 8-H), 8.16 (d,
3JHH = 7.3 Hz, 2H, 5-H). 13C NMR (THF-d8): d = 53.9
(CH2), 110.9 (C1), 111.2 (C6), 118.1 (C8), 121.8 (C7),
131.4 (C5), 131.7 (C8a), 208.2 (C3).
4.7. Synthesis of diiodo(methylenebis(imidazo[1,5-a]-
pyridine-3-ylidene))palladium(II) (5a)
[Mꢀ2Br]2+
.
1.00 g (1.97 mmol) methylenebis(imidazo[1,5-a]pyridi-
nium)diiodide (1a) and 441 mg (1.97 mmol) palladium(II)
acetate are dissolved in 13 ml DMSO to give a dark red
solution. This solution is heated to 80 °C and stirred over
night. The temperature is raised to 100 °C and the reaction
mixture stirred for another 2 h. The precipitate is filtered
and carefully recrystallised from DMSO in small portions
to give after drying (54%, 700 mg) of a yellow crystalline
material, which contains 1 equiv. of DMSO. The filtrate
is concentrated until a light brown precipitate is formed
which is filtered off and washed with 10 ml of acetonitrile,
ethylacetate and petroleum ether. After drying in vacuo for
a few days, the product (25%, 300 mg) can be obtained as a
light brown powder that is free of DMSO. Overall yield:
4.4. Synthesis of ethylenebis(imidazo[1,5-a]pyridinium)-
dibromide (2)
In a sealed Schlenk tube 1.00 g (8.50 mmol) imidazo-
[1,5-a]pyridine and 800 mg (4.30 mmol) 1,2-dibromoethane
are stirred in 17 ml of acetonitrile for a period of 20 h at
90 °C. Afterwards, the resulting suspension is filtered and
the white product washed three times with 10 ml of cold
acetonitrile and an additional 10 ml of n-pentane. After
drying in vacuo the imidazolium salt can be isolated as a
1
white solid. Yield: 44% (797 mg). H NMR (DMSO-d6):
3
d = 5.14 (s, 4H, CH2), 7.19 (t, JHH = 6.9 Hz, 2H, 6-H),
3
3
7.28 (dd, JHH = 6.9 Hz, JHH = 9.2 Hz, 2H, 7-H), 7.88
3
1
(d, JHH = 9.2 Hz, 2H, 8-H), 8.19 (s, 2H, 1-H), 8.64 (d,
79%. H NMR (DMSO-d6): d = 6.83–7.02 (m, 6H, 7-H,
3
3JHH = 6.9 Hz, 2H, 5-H), 9.69 (s, 2H, 3-H). 13C NMR
(DMSO-d6): d = 49.8 (CH2), 113.5 (C1), 117.5 (C6), 118.3
(C8), 124.3 (C5), 124.7 (C7), 127.0 (C3), 129.3 (C8a).
Mp: 279–282 °C (dec.). Anal. Calc. for C16H16N4Br2: C,
45.31; H, 3.80; N, 13.21. Found: C, 45.þ51; H, 3.90; N,
6-H, CH2, CH0 ), 7.59 (d, JHH = 9.2 Hz, 2H, 8-H), 8.21
2
3
(s, 2H, 1-H), 8.86 (d, JHH = 6.7 Hz, 2H, 5-H). 13C NMR
(DMSO-d6): d = 64.5 (CH2), 112.9 (C6), 113.2 (C1), 118.0
(C8), 123.5 (C7), 129.5 (C5), 130.5 (C8a), the signal C3
could not be detected. Mp: 304–306 °C (dec.). Anal. Calc.
for C15H12N4SOI2Pd: C, 29.74; H, 2.64; N, 8.16; I, 36.96.
Found: C, 29.86; H, 2.70; N, 8.11; I, 37.13%. MS-FAB:
m/z = 608.0 [M]+, 481.1 [MꢀI]+, 354.2 [Mꢀ2I]+.
13.24%. MS-ESI: m/z = 132.1 ½M ꢀ 2Brꢁ2
.
4.5. In situ generation of methylenebis(imidazo[1,5-a]-
pyridine-3-ylidene) (3)
4.8. Synthesis of dibromo(methylenebis(imidazo[1,5-a]-
pyridine-3-ylidene))palladium(II) (5b)
In a Young-NMR tube 30 mg (60 lmol) of the bisimi-
dazolium salt methylenebis(imidazo[1,5-a]pyridinium)diio-
dide (1a) is dispersed in 0.5 ml of THF-d8. To the
suspension, 20 mg (0.18 mmol) potassium-tert-butoxide is
added and the tube is gently shaken for a few minutes until
a dark solution can be obtained. 1H NMR (THF-d8):
d = 6.31–6.36 (m, 2H, 6-H), 6.60–6.65 (m, 4H, 7-H,
250 mg (610 lmol) methylenebis(imidazo[1,5-a]pyridi-
nium)dibromide (1b) and 140 mg (610 lmol) palladium(II)
acetate are dissolved in 4 ml of DMSO. The solution is
heated to 80 °C for 10 h, and then heated to 100 °C for
another 2 h. The grey precipitate which is formed upon