used as received. NMR spectra were obtained on a Bruker Avance
AMX 400 or 500. The chemical shifts are given as dimensionless
d values and are frequency referenced relative to the peak for
SiCH3ax). 13C NMR (CDCl3, 125 MHz, 298 K): d 247.55 (1C, s,
NCN), 134.27 (1C, s, m-CH), 131.21 (1C, s, m-CH), 129.03 (1C, s,
m-CH), 128.49 (1C, s, m-CH), 59.64 (4C, s, HC CH2), 55.76
(2C, s, NCH2), 54.21 (2C, s, HC CH2), 25.49 (1C, s, NCH2CH2),
20.34 (2C, s, p-CH3), 18.57 (2C, s, o-CH3), 18.30 (2C, s, o-CH3),
0.00 (2C, s, SiCH3eq), -2.41 (2C, s, SiCH3ax). LRMS (ES): m/z
626.18 (M+ - H) – C36H48N2OSi2Pd requires 627.24). Anal. Calcd
for C36H48N2OSi2Pd.3H20: C, 58.32; H, 7.34; N, 3.78. Found: C,
58.66; H, 7.08; N, 3.96.
1
TMS for H and 13C. Coupling constants J are given in hertz
as positive values regardless of their real individual signs. The
multiplicity of the signals is indicated as “s”, “d”, “t” or “m”
for singlet, doublet, triplet or multiplet, respectively. Mass spectra
were obtained in electrospray (ES) mode unless otherwise reported
on a Waters Q-Tof micromass spectrometer. GC-MS data was
obtained on an Agilent Technologies 6890 N GC system with an
Agilent Technologies 5973 inert MS detector with MSD.
General Heck coupling procedure
A 2-neck round bottom flask was charged with 4-bromoaceto-
phenone (0.996 g, 5 mmol) and sodium acetate (0.406 g,
5.6 mmol) then degassed by successive vacuum-nitrogen cycles.
N-N¢-dimethylacetamide (10 ml) was injected followed by n-butyl
acrylate (0.705 g, 6 mmol) and decane (0.711 g, 5 mmol) (internal
standard). The reaction mixture was equilibrated to 120 ◦C for 1 h
followed by the addition of 0.1 mol % of the appropriate palladium
(0) complex. 0.5 ml samples were taken every 30 min and prepared
for GC-MS analysis by washing with 5% HCl (5 ml) and extraction
with HPLC DCM (2.5 ml).
General procedure for the synthesis of halide salts
A mixture of 1 mmol of amidine, 0.5 mmol of K2CO3 and 1.2 mmol
of dihalide in 25 ml of acetonitrile is heated under reflux. At the
end of the reaction, the volatiles are removed in vacuo, the residue
dissolved in dichloromethane and diethyl ether is slowly added
until the product began to crystallise.4
General procedure for the synthesis of palladium (0) dvtms
complexes
Complex 15 was prepared according to the literature;9 the
synthesis and analytical data for complexes 8 and 12 are reported
below, see ESI† for all other new compounds.
Identification of the Heck coupling product
(n-butyl-(E)-4-formylcinnamate)
The general synthetic procedure for complexes 8–14 is as
follows: The expanded ring NHC halide salt (3.16 mmol) was
loaded into a flame dried Schlenk and dried under vacuum for
30 min prior to being suspended in dry toluene (20 ml) and tBuOK
(4.24 mmol) added quickly in one portion. The reaction mixture
was stirred at room temperature for 2 h generating the free carbene
which was transferred to a flame dried Schlenk via a cannula.
The Pd(dvtms) solution (3.16 mmol (8.2% Pd)) was added to the
free carbene solution resulting in a yellow to dark brown colour
change. The solution was stirred overnight at room temperature
yielding a light brown suspension, which was washed in n-pentane
furnishing the desired complex.
The Heck coupling product was isolated by vacuum distillation.
The stereochemistry of the product was determined by 1H NMR
based upon characteristic olefinic coupling constants. The two
3
protons in the b-(E) isomer are mutually trans with typical JHH
coupling constants of between 18 and 20 Hz whereas the two
3
protons in the b-(Z) isomer are mutually cis with typical JHH
coupling constants of between 12 and 16 Hz. The molecular
weights of coupled products were determined by the molecular ion
peaks present in the GC-MS analysis. GC-MS data was obtained
via an internal standard method of quantification on an Agilent
Technologies 6890 N GC system with an Agilent Technologies
5973 inert MS detector with MSD. Column: Agilent 190915-433
capillary, 0.25 mm ¥ 30 m ¥ 0.25 mm.
1,3-Bis-(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydro-pyrimidin-1-
ium palladium (divinyltetramethyldisiloxane) 8. Yield: 41.56%
(0.67 g). 1H NMR (CDCl3, 400 MHz, 298K): d 6.69 (4H, s, m-CH),
3.34 (4H, t, 3JHH = 5.7, NCH2), 2.65 (2H, t, 3JHH = 4.7, NCH2CH2),
2.31 (12H, s, o-CH3), 2.22 (6H, s, p-CH3), 2.13 (4H, d, 3JHH = 10.1,
Acknowledgements
We would like to acknowledge the Engineering and Physical
Sciences Research Council (EPSRC) for their financial support
and the Cardiff Catalysis Institute for JJD’s PhD studentship.
3
HC CH2), 1.79 (2H, t, JHH = 12.4, HC CH2), 0.00 (6H, s,
SiCH3eq), -0.82 (6H, s, SiCH3ax). 13C NMR (CDCl3, 125 MHz,
298 K): d 230.38 (1C, s, NCN), 131.40 (2C, s, m-CH), 130.87 (2C, s,
m-CH), 60.92 (2C, s, HC CH2), 58.63 (2C, s, NCH2), 48.35 (2C, s,
HC CH2), 23.86 (4C, s, o-CH3), 22.90 (1C, s, NCH2CH2), 20.43
(2C, s, p-CH3), 3.65 (2C, s, SiCH3eq), 0.00 (2C, s, SiCH3ax). LRMS
(ES): m/z 549.15 (M + 3MeCN – dvtms) – C28H37N5Pd requires
549.21). Anal. Calcd for C30H47N2OSi2Pd: C, 58.75; H, 7.56; N,
4.57. Found: C, 57.91; H, 7.72; N, 4.47.
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3
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9134 | Dalton Trans., 2011, 40, 9131–9135
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