2
D. Meyer, T. Strassner / Journal of Organometallic Chemistry xxx (2014) 1e4
Fig. 2. Biscarbene catalyst 8 [18,19]
Scheme 1. CH-activation of methane.
started with 500 rpm when the final temperature is reached. After a
reaction time of 17 h, stirring and heating are stopped and the re-
action mixture is cooled to room temperature. The autoclave is
depressurized and the reaction mixture analyzed by gas chroma-
tography with an Agilent 6850 Series II Networked GC, equipped
obtained on a Bruker AC 300 P (1H: 300.1 MHz, 13C: 75.5 MHz) or
a Bruker DRX 500 (1H: 499.8 MHz, 13C: 125.8 MHz) at 298 K.
Shifts
d are given in ppm; coupling constants J in Hz. Elemental
analyses were performed by the microanalytical laboratory of our
institute using an EuroVector EA-3000 Elemental Analyzer.
Melting and decomposition points were determined with a
Wagner&Munz PolyTherm A melting point apparatus and are
uncorrected.
with an FID detector and a MachereyeNagel Optima-210-0.25
column (30 m ꢂ 0.25 mm). Quantification of the trifluoroacetic acid
methyl ester is done by adding 25 L of benzene to 1.00 mL of the
reaction mixture after the reaction as an external standard and
injection of this mixture into the GC. All GC measurements are
repeated four times; given values are averaged over all measure-
ments. The turnover number (TON) is defined as (mol product)/
(mol Pd).
mm
m
Synthesis of the metal complex 11
9 (0.38 g; 1.5 mmol) is suspended together with Ag2O (0.35 g;
1.5 mmol) in 30 mL dichloromethane and 30 mL ethanol. The
mixture is stirred at room temperature under exclusion of light for
3 h. Chloro(methyl)(cyclooctadiene)palladium(II) [53] (0.40 g;
1.5 mmol) is added and stirring is continued for additional 12 h. The
suspension formed is filtered over a celite pad and the resulting
solution is reduced in vacuo to 5 mL. The product is precipitated by
addition of diethyl ether. Recrystallization from dichloromethane/
methanol/diethyl ether gives the product as a white solid (0.21 g,
21%). M.p. 178 ꢀC (decomp.). Anal. Calcd for C20H30N8Cl2Pd2: C
36.05, H 4.54, N 16.82. Found: C 35.61, H 4.58, N 16.97.Mass spec-
trum (ESI): m/z [M ꢁ Cl]þ 631.0, 633.0, 629.0, [M ꢁ 2Cl þ OAc]þ
655.0, 653.1, 657.1. 1H NMR (300 MHz, DMSO-d6, ppm): ꢁ0.13 (s,
6H, PdeCH3), 3.90 (s, 12H, NeCH3), 6.25 (d, J ¼ 13.1 Hz, 2H, CH2),
7.37 (d, J ¼ 1.7 Hz, 4H, NCH), 7.53 (d, J ¼ 13.1 Hz, 2H, CH2), 7.81 (d,
J ¼ 1.7 Hz, 4H, NCH). 13C NMR (75.5 MHz, DMSO-d6, ppm): ꢁ13.4
(PdeCH3), 36.9 (NeCH3), 62.3 (CH2),120.4 (NCH),123.1 (NCH),184.3
(NCN).
Structure determination of compound 11
Preliminary examination and data collection were carried out on
an area detecting system (Kappa-CCD; Nonius, FR590) using
graphite monochromated Mo K
a
radiation (
l
¼ 0.71073 Å) with an
Oxford Cryosystems cooling system at the window of a sealed fine-
focus X-ray tube. The reflections were integrated. Raw data were
corrected for Lorentz, polarization, decay and absorption effects.
The absorption correction was applied using SADABS [54]. After
merging the independent reflections were used for all calculations.
The structure was solved by a combination of direct methods
[55,56] and difference Fourier syntheses [57]. All non-hydrogen
atom positions were refined with anisotropic displacement pa-
rameters. Hydrogen atoms were placed in ideal positions using the
SHELXL riding model. Full-matrix least-squares refinements were
carried out by minimizing Sw(Fo2 ꢁ Fc2)2 with the SHELXL-97
weighting scheme and stopped at shift/err < 0.001. Neutral-atom
scattering factors for all atoms and anomalous dispersion correc-
tions for the non-hydrogen atoms were taken from International
Tables for Crystallography [58]. All calculations were performed
with the programs COLLECT [59], DIRAX [60], EVALCCD [61], SIR92
[55], SADABS [54], PLATON [62,63] and the SHELXL-97 and
SHELXL2013 packages [57,64,65]. For the visualization ORTEP-III
[66] was used. One disordered Solvent molecule was removed us-
ing the PLATON SQUEEZE procedure.
Methane activation
The reaction was conducted in a 160 mL Hastelloy C-2000 Parr
autoclave in the presence of palladium catalyst 11 (0.084 mmol)
and K2S2O8 (16.8 mmol) in a mixture of trifluoroacetic acid and its
anhydride (32 mL/24 mL). The reaction vessel is pressurized with
30 bar of methane and heated to 90 ꢀC. A gas injection stirrer is
Fig. 1. Methyl palladium complexes with biscarbene ligands prepared by Douthwaite (1, 2) [42], Hofmann (3) [50], Danopoulos (4) [51], Slaughter (5,6) [26] and Alcalde (7).[35]
j.jorganchem.2014.09.022