High activity heterogeneous catalysts by plasma-enhanced chemical vapor deposition of volatile palladium complexes on biomorphic carbon

Article abstract of DOI:10.1016/j.crci.2018.04.008

Six new palladium complexes based on allyl and alkenolate ligands were synthesized and structurally characterized. Combination of delocalized allylic sp²-hybridized carbon centers and a strongly binding N?O chelating unit (e.g., 3,3,3-trifluoro(pyridin-2-yl)propen-2-ol) offered a promising combination of high volatility and thermal lability not commonly observed in noble metal precursors. Application of the new Pd compounds in thermal metal–organic and plasma-enhanced chemical vapor deposition demonstrated their clean and efficient decomposition pathways, which in conjunction with their intriguing air stability made them efficient precursors for Pd films and clusters. Plasma-enhanced chemical vapor deposition of the palladium compounds on biomorphic carbon used as a porous substrate with high surface area and interconnected channels delivered recyclable carbon-supported Pd catalysts (Pd@BioC), which showed excellent selectivity, stability, and recyclability in C–C coupling reactions.

Full text of DOI:10.1016/j.crci.2018.04.008

C. R. Chimie xxx (2018) 1e9
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Full paper/Memoire
High activity heterogeneous catalysts by plasma-enhanced
chemical vapor deposition of volatile palladium complexes on
biomorphic carbon
a
a
a
€
Lisa Czympiel , Michael Frank , Andreas Mettenborger ,
Sven-Martin Hühne b, Sanjay Mathur a
,
*
a Department of Chemistry, Institute of Inorganic Chemistry, University of Cologne, Greinstrasse 6, 50939 Cologne, Germany
b Institute of Inorganic Chemistry, University of Bonn, 53117 Bonn, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Six new palladium complexes based on allyl and alkenolate ligands were synthesized and
structurally characterized. Combination of delocalized allylic sp2-hybridized carbon cen-
ters and a strongly binding N^O chelating unit (e.g., 3,3,3-trifluoro(pyridin-2-yl)propen-2-
Received 14 November 2017
Accepted 5 April 2018
Available online xxxx
ol) offered
a promising combination of high volatility and thermal lability not
commonly observed in noble metal precursors. Application of the new Pd compounds in
thermal metaleorganic and plasma-enhanced chemical vapor deposition demonstrated
their clean and efficient decomposition pathways, which in conjunction with their
intriguing air stability made them efficient precursors for Pd films and clusters. Plasma-
enhanced chemical vapor deposition of the palladium compounds on biomorphic carbon
used as a porous substrate with high surface area and interconnected channels delivered
recyclable carbon-supported Pd catalysts (Pd@BioC), which showed excellent selectivity,
stability, and recyclability in CeC coupling reactions.
Keywords:
Pd precursor
PECVD
Solid-supported catalyst
BioC
© 2018 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
similar approach with heteroarylalkenols as N^O chelating
ligands [where N^O is 3,3,3-trifluoro(pyridin-2-yl)propen-
Achieving high atom economy in gas phase synthesis of
new materials demands precursor molecules with
adequate volatility and efficient ligand elimination during
thermal decomposition [1e7]. For the deposition of palla-
dium films often homoleptic acetylacetonate derivatives
have been reported, although the volatility of these com-
plexes is relatively low. One of the most promising pre-
cursors for the deposition of Pd films so far is the
heteroleptic cyclopentadienyl allyl palladium, which shows
a good volatility but only a limited stability [8e10]. For the
deposition of PdS, (allyl) palladium dithiocarbamates have
been used as precursors [11,12]. This study describes a
2-ol (H-PyTFP), 3,3,4,4,5,5,5-heptafluoro-1-(pyridin-2-yl)
penten-2-ol (H-PyHFP), 3,3,3-trifluoro(1,3-benzoxazol-2-
yl)propen-2-ol (H-BOTFP), 3,3,3-trifluoro(1,3-benzthiazol-
2-yl)propen-2-ol (H-BTTFP), 3,3,3-trifluoro(dimethyl-1,3-
thiazol-2-yl)propen-2-ol (H-DMTTFP), and 3,3,3-trifluoro
(dimethyl-1,3-oxazol-2-yl)propen-2-ol (H-DMOTFP)]. They
bind the metal center through an enolic oxygen as well as
the nitrogen atom of a heterocycle, resulting in stable six-
membered metallacycles. We have recently [1e7,13e19]
reported on the interplay of the electron-withdrawing
perfluoroalkyl units present in the alkenol backbone in
combination with the heterocycles that enhances the vapor
pressure of the metal complexes and at the same time re-
duces their moisture sensitivity because of the presence of
hydrophobic CeF units in the ligand skeleton. The
* Corresponding author.
E-mail address: sanjay.mathur@uni-koeln.de (S. Mathur).
https://doi.org/10.1016/j.crci.2018.04.008
1631-0748/© 2018 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: L. Czympiel, et al., High activity heterogeneous catalysts by plasma-enhanced chemical vapor
deposition of volatile palladium complexes on biomorphic carbon, Comptes Rendus Chimie (2018), https://doi.org/10.1016/
j.crci.2018.04.008

2
L. Czympiel et al. / C. R. Chimie xxx (2018) 1e9
combination of the stabilizing nature of these N^O chelating
ligands and the high reactivity of allyl palladium com-
pounds offers a promising strategy to highly volatile and
adequately stable precursors for the deposition of Pd films
(Fig. 1).
N^O ligand (Table 2). Complexes (PyTFP)Pd(
(BOTFP)Pd(
3-C3H5) (3), and (DMOTFP)Pd(
could be stored under ambient conditions for months
without decomposition, whereas (PyHFP)Pd(
3-C3H5) (2)
h
3-C3H5) (1),
h
3-C3H5) (6)
h
h
slowly decomposed under reductive elimination to
elemental palladium. In contrast, the thiazole derivatives
(BTTFP)Pd(h h
3-C3H5) (4) and (DMTTFP)Pd( 3-C3H5) (5) were
2. Results and discussion
only stable for a couple of hours and could not be sublimed
without decomposition.
2.1. Synthesis and characterization of palladium compounds
Considering the volatility of the complexes (Table 2),
only 1, 2, and 6 were investigated by thermogravimetric
analyses (TGA) (Fig. 5). The TGA profile of compounds 1 and
2 did not show a clear two-step or one-step decomposition,
indicating a concomitant loss of allyl and N^O ligands.
Nevertheless, the final residues of 32 wt % in compound 1
and 21 wt % in compound 2 relate to the calculated values
for elemental palladium (32 wtcalcd % for compound 1 and
24 wtcalcd % for compound 2) and indicate an efficient
conversion of precursor into the targeted solid-state phase.
The oxazole-derivative 6 showed a one-step decomposition
with a residue of 12 wt %, which is lower than the calcu-
lated residue of 30 wtcalcd % implying a partial sublimation
of the complex during the measurement.
By reacting the deprotonated N^O ligands with bis(h3
allyl)-di- -bromopalladium [20], the complexes (N^O)
Pd(
3-C3H5) (Fig. 2) were obtained in high yield and purity.
-
m
h
All complexes exist as yellow solids at room temperature
and were characterized by multinuclear NMR spectroscopy,
EIMS, and by single-crystal X-ray diffraction (XRD) analyses
for (PyHFP)Pd(h h
3-C3H5) (2), and (DMOTFP)Pd( 3-C3H5) (6).
Multinuclear NMR data (rt, CDCl3) of complexes 1e6
were recorded by a combination of 13Ce19F, 13Ce1H, and
1He1H correlation experiments. The 1H NMR spectra of all
six compounds showed one set of signals for the N^O ligands
and an ABCDX spin pattern for the protons of the allyl
group because of the asymmetrical nature of the N^O
Comparison of these results to thermal decompositions
(quantitative evaporation during TG/DTA measurements)
and sublimation temperatures (90e140 ꢀC/10ꢁ3 mbar) of
homoleptic Pd(N^O)2 compounds [14] validated our hypoth-
esis of enhancing the volatility and reducing the stability of
the complexes by a judicious choice of ligands. This choice
offers stability without hampering the thermal lability,
which is essential to initiate the fragmentation cascades
enabling the transformation of precursors into materials.
chelating ligands. The resonances of the protons syn (Hsyn
were observed at a lower field than the anti protons (Hanti
with reference to the central proton. In analogy to other p-
)
)
allyl complexes, characteristic coupling constants of 3J ~
7 Hz for Hanti and 3J ~ 12 Hz for Hsyn were found in all
complexes [21e23]. Inspection of the 1He1H NOESY spec-
trum revealed the presence of nuclear Overhauser effect
(NOE) contacts, which allowed defining the spatial rela-
tionship between the allyl and the protons present in the
N^O ligand unit (Fig. 3).
2.2. Plasma-enhanced chemical vapor deposition of Pd films
Complex 2 crystallized in the orthorhombic space group
Pbca (no. 61, Table 1) whereas 6 crystallized in the mono-
clinic space group P21/m (no. 11, Table 1) with a mirror
plane passing through the whole molecule (Fig. 4). The
central palladium atoms in complexes 2 and 6 displayed a
slightly distorted square planar arrangement of ligands,
with N^O ligands and one carbon atom of the allyl ligand
(C21 and C11) showing an almost ideal planarity. The car-
bon atoms trans to the nitrogen atoms lie slightly above
(0.16(1) Å (C23) and 0.42(2) Å (C9)) the plane, whereas the
central carbon atoms lie 0.43(1) Å (C22) and 0.46(1) Å (C10)
beneath the plane. The PdeO, PdeN, and PdeC distances
on silicon
Compound 6 was further used for chemical vapor
deposition (CVD) studies because of its superior sublima-
tion behavior when compared to compounds 1 and 2. For
the generation of palladium films, 6 was decomposed in a
plasma-enhanced chemical vapor deposition (PECVD)
process using argon as carrier and plasma gas. The XRD
patterns showed (Fig. 7a) the as-deposited films on silicon
substrates to be completely amorphous. The low deposition
temperature supplies an insufficient amount of energy for
diffusion and ordering processes resulting in amorphous
films. XPS measurements of the same films deposited with
changing plasma powers showed in all cases slight con-
taminations with carbon, oxygen, nitrogen, and fluorine
(Fig. 7 of Supplementary Information).
are in the range known for other h
3-allyl-palladium com-
plexes [24e28].
The thermal stability and volatility of the complexes was
found to vary significantly with respect to the coordinated
The exemplary high-resolution scan of
a sample
deposited at a plasma power of 75 W (Fig. 6) confirms the
presence of solely palladium(0) in the films; therefore, a
complete reduction in the metal ion during plasma pro-
cessing was achieved. When treating as-deposited amor-
phous films directly with a hydrogen plasma, the XRD
pattern shows an improved crystallinity of the films with
broad reflexes that correspond to pure elemental Pd. The
broadening of the relatively weak reflexes may be due to
remaining carbon contaminations in the coating, which
were not removed by the hydrogen plasma treatment.
Fig. 1. Schematic representation of ligand influence on the stability and
reactivity of heteroleptic allyl palladium alkenolates.
Please cite this article in press as: L. Czympiel, et al., High activity heterogeneous catalysts by plasma-enhanced chemical vapor
deposition of volatile palladium complexes on biomorphic carbon, Comptes Rendus Chimie (2018), https://doi.org/10.1016/
j.crci.2018.04.008

L. Czympiel et al. / C. R. Chimie xxx (2018) 1e9
3
Fig. 2. Synthetic approach to the heteroleptic (N^O)Pd(
h
3-C3H5) complexes and abbreviations used throughout the article.
Fig. 3. 1He1H NOESY spectrum of complex 6 in CDCl3 at room temperature (left) and structure of 6 with assignment of resonances in ppm (right).
Fig. 4. Molecular structure of 2 (a) and 6 (b) with atom labeling scheme. Thermal ellipsoids are drawn at the 50% probability level; all hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (ꢀ): (a) Pd1eO1 2.080(4), Pd1eN1 2.104(4), Pd1eC21 2.119(5), Pd1eC22 2.102(6), Pd1eC23 2.125(6),
O1ePd1eC23 97.5(2), O1ePd1eN1 91.98(17), C21ePd1eN1 102.2(2), C21ePd1eC23 68.3(3). (b) Pd1eN1 2.087(6), Pd1eO1 2.097(5), Pd1eC21 2.108(8), Pd1eC22
2.080(9), Pd1eC23 2.116(9), Pd2eN2 2.091(5), Pd2eO3 2.091(5), Pd2eC24 2.107(8), Pd2eC25 2.072(10), Pd2eC26 2.130(15); N1ePd1eO1 89.8(2), N1ePd1eC21
107.6(3), N1ePd1eC23 167.0(4), O1ePd1eC21 162.6(3), O1ePd1eC23 96.3(3), N2ePd2eO3 89.4(2), N2ePd2eC24 106.7(3), N2ePd2eC26 171.4(18),
O3ePd2eC24 163.9(3), O3ePd2eC26 95.7(3).
Please cite this article in press as: L. Czympiel, et al., High activity heterogeneous catalysts by plasma-enhanced chemical vapor
deposition of volatile palladium complexes on biomorphic carbon, Comptes Rendus Chimie (2018), https://doi.org/10.1016/
j.crci.2018.04.008

4
L. Czympiel et al. / C. R. Chimie xxx (2018) 1e9
Table 1
Selected crystallographic data and collection parameters for compounds 2 and 6.
Compound
2
6
Crystal system
Space group
Cell parameter
Orthorhombic
Pbca
a ¼ 7.4935(8) Å
b ¼ 19.155 (2) Å
c ¼ 20.405 (3) Å
8
Monoclinic
P21/m
a ¼ 11.149(3) Å
b ¼ 7.380(1) Å
c ¼ 16.526(4) Å
4
a
b
g
¼ 90ꢀ
¼ 90ꢀ
¼ 90ꢀ
a
b
g
¼ 90ꢀ
¼ 103.32(2)ꢀ
¼ 90ꢀ
Z
Total reflections
Unique reflections
3284
1726
5856
2815
R1, wR2 [I0> 2
s
(I)]
0.0466, 0.1303
0.0844, 0.1451
0.954
0.0336, 0.0615
0.0800, 0.0718
0.821
R1, wR2 [all data]
Goodness of fit (GOF)
CCDC
1061,689
1061,690
Table 2
Sublimation temperature and melting points of complexes 1e3 and 6.
to a plasma power of 100 W. At a power higher than 100 W,
the effect of Ar ion bombardment on the deposited layer
dominates over the decomposition of the precursor and
leads to an etching of the top surface of the palladium layer
instead of a further growth of the layer.
Compound
Melting point
Sublimation temperature
1
2
3
6
90 ꢀC
85 ꢀC/10ꢁꢁ33 mbar
65 ꢀC/10 mbar
Decomp.ꢁ3
70 ꢀC (decomp.)
135 ꢀC
90 ꢀC
65 ꢀC/10 mbar
2.3. Solid-supported Pd catalysts on BioC
After postannealing the films at 500 ꢀC under air, the
XRD pattern exhibits a dominant reflex at 34.1ꢀ and two
weak reflexes at 42.1ꢀ and 54.9ꢀ, which correspond to the
tetragonal PdO phase. When treating the PdO films with
hydrogen plasma, these reflexes disappear and two new
reflexes at 39.4 and 45.8ꢀ prove the formation of pure
elemental Pd, exhibiting relatively sharp signals.
To estimate the influence of used plasma power on film
thickness of as-deposited films, cross-sectional SEM images
were measured. The thicknesses of coatings depending on
the used plasma power are shown in Fig. 7b. With an
increasing plasma power, the film thickness increases from
97 nm (25 W) to a maximum of 262 nm (100 W), whereas a
further increase in plasma power then leads again to
thinner coatings. This trend in film thickness can be
explained by the growth-etching competition mechanism
[29]. The plasma process is dominated by the decomposi-
tion of precursor and therefore by the growth of the film up
A favored approach toward CeC coupling reactions is
based on the use of solid-supported nanostructures or
molecular complexes anchored on an inert support such as
carbon, zeolites, silicates, biopolymers, or metal oxides
(TiO2, Al2O3, etc.) [30e37]. In the scope of sustainability in
this study, carbonized wood, which is feedstock derived
from renewable resources and has a high surface to volume
ratio, has been applied as a support material. As has been
shown in previous studies the here used carbonized beech
wood (Fagus sylvatica) exhibits a porosity of 59.28 0.20
vol % [38]. The microstructure of the carbon scaffold retains
that of the original wood, consisting of interconnected
channels of bimodal size distribution (Fig. 8a) with larger
pores of 50 mm and smaller pores of 10 mm [39,40]. Because
of the high hydrophobicity of the material the often-used
wet chemical deposition of Pd particles on the substrates
is not applicable. Therefore, CVD was chosen to generate
solid-supported catalysts.
On the basis of the investigations of the Pd films on Si
substrates, the solid-supported Pd catalysts on carbonized
beech wood (Pd@BioC) [41] were generated by PECVD
processes with a plasma power of 75 W. The as-deposited
Pd nanostructures were then analyzed by TEM, EDX, and
ICP-MS measurements to evaluate the morphology and
composition of the deposits as well as the amount of
palladium on the porous scaffold. As can be seen in Fig. 8b,
spherical Pd nanoparticles (NPs) of 8.3 nm ( 1.0 nm) are
formed during the deposition. The average amount of Pd
NPs on the BioC was 0.02 wt %.
As a proof of concept, the Pd@BioC structures were
evaluated in established carbonecarbon cross-coupling
reactions to determine their catalytic activity and as a
comparison commercially available Pd on carbon (Sigma-
Aldrich) has been tested. The catalysts were reused in
catalytic reactions until no activity could be detected
anymore. The Heck reaction is well known to be promoted
by Pd NPs as the catalyst reservoir. Therefore, we decided
Fig. 5. TGA profiles of compounds 1, 2, and 6 measured under nitrogen
atmosphere with a heating rate of 10 ꢀC minꢁ1
.
Please cite this article in press as: L. Czympiel, et al., High activity heterogeneous catalysts by plasma-enhanced chemical vapor
deposition of volatile palladium complexes on biomorphic carbon, Comptes Rendus Chimie (2018), https://doi.org/10.1016/
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L. Czympiel et al. / C. R. Chimie xxx (2018) 1e9
5
present, because a change in size and morphology of the
particles during the reaction cannot be ruled out. In Fig. 9
the TON of recycling experiments in seven successive runs
are depicted. After each run catalyst material was
removed from the reaction vessel, washed with a 1:1
mixture of HOiPr and water, and reused with new
coupling substrates. In the first five runs the conversion
stays relatively stable between 39% and 47% before it
drops down to 32% in the sixth and finally to 0% in the
seventh cycle. ICP-MS measurements confirmed that this
drop of reactivity is on the one hand due to Pd leaching,
with only 0.02 mmol Pd left on the substrates after seven
catalysis cycles. On the other hand, SEM images of the
Pd@BioC after catalysis show nanoclusters that could
hamper the reactants to reach remaining catalytically
active Pd nanostructures supported on the BioC scaffold
(Fig. 8c). Nevertheless, the very low Pd loading of the
catalysts gives a total TON of 8767 in all runs. The com-
mercial Pd on carbon only gave a TON of 194. It was not
possible to recycle the catalysts at all, which only em-
phasizes the ease of recyclability of the presented
Pd@BioC catalyst.
Fig. 6. High-resolution XPS measurements of the film deposited at 75 W.
to couple 4-fluoroiodobenzene with n-butyl acrylate in
the presence of triethylamine and Pd@BioC (0.091
mmol
Pd content; 0.02 wt % Pd) at 100 ꢀC yielding butyl 4-
fluorocinnamate in 39% yield (turnover number (TON),
1435) in the first run, which was easily determined by in
situ 19F NMR spectroscopy (Fig. 9). Although, in nano-
catalysis, it is common to calculate TONs based on surface
atoms of NPs following the magic number methodology
[42], we decided to determine TONs based on all atoms
Even better results were achieved for the Suzuki
coupling of 4-fluoroiodobenzene with phenylboronic acid
in water. Potassium carbonate was added as a base and the
reaction was run with Pd@BioC (0.091 mmol Pd content;
Fig. 7. a) Grazing incidence XRD patterns of as-deposited, postannealed, and hydrogen plasma-treated films on Si substrates. All samples were deposited using a
plasma power of 75 W (reference patterns: Pd pdf 87-0641 (black), PdO pdf 75-0584 (red)). (b) Film thickness of as-deposited films estimated by cross-sectional
SEM depending on the plasma power used for film deposition.
Fig. 8. a) SEM image of a bare BioC scaffold (b) TEM image of as-deposited Pd NPs on BioC. (c) SEM image of a Pd@BioC catalyst after catalysis reactions
(nanoclusters colored in yellow).
Please cite this article in press as: L. Czympiel, et al., High activity heterogeneous catalysts by plasma-enhanced chemical vapor
deposition of volatile palladium complexes on biomorphic carbon, Comptes Rendus Chimie (2018), https://doi.org/10.1016/
j.crci.2018.04.008

6
L. Czympiel et al. / C. R. Chimie xxx (2018) 1e9
Fig. 9. TON of the recycling experiments in the Heck reaction.
0.02wt % Pd) at 100 ꢀC yielding 4-fluorobiphenyl in 99%
yield (TON, 5229) in the first run (Fig. 10). The catalyst stays
stable for the first 15 cycles with yields between 93% and
99% (TONs, 4912e5229). Between cycle 16 and 27 the yield
varies from 71% to 99% (TONs, 3750e5229) and then drops
down to 52% (TON, 2746) in the 28th run, 11% (TON, 581) in
the 29th, and finally no activity in the 30th run. The total
TON over 30 cycles reached 139,179, which is remarkably
high. As was the case in the Heck reaction, ICP-MS mea-
surements also showed a palladium leaching with only
3. Experimental section
All manipulations of air and moisture sensitive materials
were carried out under nitrogen using Stock-type all glass
assemblies. The ligands 3,3,3-trifluoro-1-(pyridin-2-yl)prop-
1-en-2-ol (H-PyTFP), 3,3,4,4,5,5,5-heptafluoro-1-(pyridin-2-
yl)pent-1-en-2-ol (H-PyHFP), 1-(dimethyl-1,3-oxazol-2-yl)-
3,3,3-trifluoropropen-1-ol (H-DMOTFP),1-(1,3-benzoxazol-2-
yl)-3,3,3-trifluoropropen-2-ol (H-BOTFP), 1-(1,3-benzthiazol-
2-yl)-3,3,3-trifluoropropen-2-ol (H-BTTFP), and 1-(dimethyl-
0.02
mmol Pd left on the substrates after the 30th cycle. It
1,3-thiazol-2-yl)-3,3,3-trifluoropropen-1-ol
(H-DMTTFP)
was not possible to determine the palladium leaching of
one cycle, because the amount of palladium was under the
detection level of the instrument. The commercial Pd on
carbon only reaches a TON of 450 and showed, under these
reaction conditions, all in all a lower reactivity than the
generated Pd@BioC catalyst.
Both CeC cross-coupling reactions demonstrate the
potential of the generated solid-supported catalysts. The
high surface to volume ratio and bimodal pore distribution
of the biomorphic carbon substrates serve well in allowing
a deposition of small Pd nanostructures throughout the
scaffold. These nanoclusters show a high catalytic activity
because of their small size, allowing one to run the Heck
and Suzuki reactions with a very low palladium loading.
Through the optimization of reaction conditions of the
catalytic reactions, along with pretreatment of the support
material to enhance the attachment of nanostructured Pd
to the wood, even better recyclability of the solid-
supported catalysts should be achievable.
were prepared following a procedure described by Kawase
et al. [43] As previously reported, the purification process was
improved by sublimation of the products instead of column
chromatography [1]. Bis(h m-bromopalladium was
3-allyl)-di-
prepared according to a published procedure [44]. The
wooden templates were prepared by carbonization of wood
(beech wood) at 1000 ꢀC in vacuo [41]. The commercial Pd on
carbon was bought from Sigma-Aldrich and used without
further purification.
Elemental analyses were performed using a HEKAtech
CHNS Euro EA 3000. Elemental analyses of the thiazole
derivatives (BTTFP)Pd(h -
3-C3H5) (4) and (DMTTFP)Pd(h3
C3H5) (5) were not possible because of their fast decom-
position. Mass spectra were obtained using a Finnigan MAT
95 (20 eV) in m/z (rel%). NMR spectra were recorded using a
Bruker Avance II spectrometer operating at 300 MHz,
chemical shifts are quoted in parts per million (ppm)
relative to TMS (1H and 13C) and CCl3F (19F). XRD patterns
were measured using an STOE-STADI MP vertical system
Fig. 10. TON of the recycling experiments in the Suzuki reaction.
Please cite this article in press as: L. Czympiel, et al., High activity heterogeneous catalysts by plasma-enhanced chemical vapor
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L. Czympiel et al. / C. R. Chimie xxx (2018) 1e9
7
working in grazing incident mode, using Cu Ka
{1H} NMR (75.1 MHz, 298 K, CDCl3)
d: 157.3 (C7), 154.9 (C1),
(
l
¼ 0.15406 nm) radiation. The film thickness and
154.9 (C5), 137.0 (C3), 124.9 (C4), 118.0 (C10), 117.8 (C2),
116.7 (C22), 111.7 (C8), 109.0 (C9), 95.2 (C6), 60.6 (C23), 56.4
morphology were analyzed by SEM (Nova Nano SEM 430
(FEI)) and TEM (Philips CM300 FEG/UT-STEM). TGA/DTA
measurements were performed using a TGA/DSC1 (Met-
tler-Toledo GmbH, Germany) apparatus. The ICP-MS mea-
surements were carried out by Mikroanalytik Labor Kolbe,
Mülheim an der Ruhr, Germany.
Data collection for X-ray structure elucidation was per-
formed using an STOE IPDS I/II diffractometer with graphite
monochromated Mo K
were corrected for Lorentz and polarization effects. A nu-
merical absorption correction based on crystal shape
optimization was applied for all data. The programs used in
this study are STOE's X-Area, including X-RED [45] and X-
Shape [46] for data reduction and absorption correction,
SIR-92 [47] and SHELXL-97 [48] for structure solution, and
SHELXL [48] and ShelXle [49] for structure refinement. The
hydrogen atoms were placed in idealized positions and
constrained to ride on their parent atom. The last cycles of
refinement included atomic positions for all atoms, aniso-
tropic thermal parameters for all non-hydrogen atoms, and
isotropic thermal parameters for all hydrogen atoms.
(C21). 19F NMR (282 MHz, 298 K, CDCl3)
d: ꢁ126.6 (s,
1JC,F ¼ 266 Hz, 2JC,F ¼ 32 Hz, F9, 2F),ꢁ117.2 (q, 4JF,F ¼ 9 Hz, F8,
2F),ꢁ80.5 (t, 4JF,F ¼ 9 Hz, F10, 3F). EIMS: 435 (80%, Mþ), 289
(40%, Mþ ꢁ PyHFP), 39 (8%, C3Hþ4 ). Elemental Anal. Calcd for
PdC13H10F7NO: C, 35.84; H, 2.31; N, 3.22. Found: C,ꢁ335.89; H,
ꢀ
2.70; N, 3.46. Sublimation temperature: 65 C/10 mbar.
a
radiation (0.71073 Å). The data
3.1.3. (BOTFP)Pd(h3eC3H5) (3)
Yield: 80% (0.18 g). 1H NMR (300 MHz, 298 K, CDCl3)
d:
7.46e7.41 (m, H5, 1H), 7.33e7.27 (m, H2/H3, 2H), 7.27e7.23
(m, H4, 1H), 5.81 (s, H8, 1H), 5.71e5.59 (m, H22, 1H), 4.38
(dd, J ¼ 6.9, 1.7 Hz, H23syn, 1H), 4.23 (dd, J ¼ 6.7, 1.7 Hz,
H21syn, 1H), 3.48 (d, J ¼ 12.5 Hz, H23anti, 1H), 2.99 (d,
J ¼ 11.6 Hz, H21anti, 1H). 13C{1H} NMR (75.1 MHz, 298 K,
CDCl3) d: 165.4 (C9), 164.8 (C7), 148.2 (C6), 141.2 (C1), 124.5
(C3), 123.4 (C4), 119.7 (C10), 116.5 (C2), 113.0 (C22), 110.5
(C5), 79.9 (C8), 66.2 (C23), 49.6 (C21). 19F NMR (282 MHz,
298 K, CDCl3)
d
: ꢁ73.8 (s, 1JC,F ¼ 283 Hz, 2JC,F ¼ 33 Hz). EIMS:
375 (100%, Mþ), 335 (12%, Mþ ꢁ C3H5), 306 (8%, Mþ ꢁ CF3),
229 (8%, BOTFPþ), 147 (20%, Mþ ꢁ BOTFP). Mp: 135 ꢀC
decomposition. Elemental Anal. Calcd for PdC13H10F3NO2:
C, 41.57; H, 2.68; N, 3.73. Found: C, 40.72; H, 2.87; N, 3.49.
Sublimation temperature: decomposition.
3.1. General synthesis of the organometallic precursor
To a stirred solution of 2 equiv of the N^O ligand in
acetone, 2 equiv of KOH in 1 mL of water was added. This
solution was stirred at ambient temperatures for 10 min. In
3.1.4. (BTTFP)Pd(h3eC3H5) (4)
Yield: 85% (0.20 g). 1H NMR (300 MHz, 298 K, CDCl3)
d:
10 mL CH2Cl2 1 equiv of bis(h m-bromopalladium
3-allyl)-di-
7.69 (d, J ¼ 7.9 Hz, H5, 1H), 7.65 (d, J ¼ 8.0 Hz, H2, 1H), 7.42
(t, J ¼ 8.4 Hz, H3, 1H), 7.30 (t, J ¼ 8.0 Hz, H4, 1H), 5.94 (s, H8,
1H), 5.69e5.57 (m, H22, 1H), 4.30 (d, J ¼ 6.5 Hz, H23syn, 1H),
was dissolved, added to the reaction mixture, and stirred
for 1 h at ambient temperatures. Excess solvent was
removed under reduced pressure and the products were
purified by sublimation.
4.06 (d, J ¼ 6.1 Hz, H21syn, 1H), 3.49 (d, J ¼ 12.4 Hz, H23anti
,
1H), 3.03 (d, J ¼ 11.7 Hz, H21anti, 1H). 13C{1H} NMR
(75.1 MHz, 298 K, CDCl3) d: 167.9 (C7), 160.4 (C9), 153.0
3.1.1. (PyTFP)Pd(h3eC3H5) (1)
(C1), 130.2 (C6), 126.3 (C3), 124.3 (C4), 121.1 (C5), 120.6 (C2),
119.8 (C10), 113.0 (C22), 88.3 (C8), 66.3 (C23), 51.9 (C21). 19
F
Yield: 95% (0.18 g). 1H NMR (300 MHz, 298 K, CDCl3)
d:
NMR (282 MHz, 298 K, CDCl3)
d
: ꢁ73.4 (s, 1JC,F ¼ 283 Hz,
8.41 (d, J ¼ 5.7 Hz, H1, 1H), 7.57 (d, J ¼ 8.4, 7.3, 1.7 Hz, H3,
1H), 7.08 (d, J ¼ 8.3 Hz, H4, 1H), 6.77 (t, J ¼ 7.2, 5.9, 1.4 Hz,
H2, 1H), 5.89e5.77 (m, H22, 1H), 5.63 (s, H6, 1H), 4.08 (dd,
2JC,F ¼ 32 Hz). EIMS: 391 (100%, Mþ), 355 (12%, Mþ ꢁ C3H5),
322 (8%, Mþ ꢁ CF3), 245 (40%, BTTFPþ), 176 (BTTFPþ ꢁ CF3),
147 (24%, Mþ ꢁ BTTFP). Mp: 87 ꢀC decomposition. Subli-
mation temperature: decomposition.
J ¼ 7.0, 2.0 Hz, H23syn, 1H), 3.44 (dd, J ¼ 6.8, 2.0 Hz, H21syn
1H), 3.24 (d, J ¼ 12.4 Hz, H23anti, 1H), 3.08 (d, J ¼ 11.8 Hz,
H21anti, 1H). 13C{1H} NMR (75.1 MHz, 298 K, CDCl3)
: 156.9
(C7), 155.1 (C1), 154.8 (C5), 137.4 (C3), 125.2 (C4), 120.6 (C8),
,
d
3.1.5. (DMTTFP)Pd(h3eC3H5) (5)
Yield: 73% (0.27 g). 1H NMR (300 MHz, CDCl3)
d: 5.81 (s,
118.1 (C2), 117.0 (C22), 93.7 (C6), 60.8 (C23), 57.0 (C21). 19
F
NMR (282 MHz, 298 K, CDCl3)
d
: ꢁ72.7 (s, 1JC,F ¼ 282 Hz,
H4, 1H), 5.63e5.51 (m, H22, 1H), 4.21 (d, J ¼ 6.9 Hz, H23syn
,
2JC,F ¼ 30 Hz). EIMS: 335 (100%, Mþ), 294 (8%, Mþꢁ C3H5),
266 (16%, Mþ ꢁ CF3), 228 (4%, Mþ ꢁ C3H5, ꢁ CF3), 197 (4%,
Mþ ꢁ COCF3, ꢁ C3H5), 147 (22%, Mþ ꢁ PyTFP). Elemental
Anal. Calcd for C11H10F3NOPd: C, 39.37; H, 3.00; N, 4.17.
Found: C, 39.62; H, 3.87; N, 4.47. Mp: 90 ꢀC. Sublimation
1H), 3.79 (d, J ¼ 6.6 Hz, H21syn, 1H), 3.38 (d, J ¼ 12.4 Hz,
H23anti, 1H), 2.83 (d, J ¼ 11.9 Hz, H21anti, 1H), 2.29 (s, 2-CH3,
3H), 2.22 (s, 1-CH3, 3H). 13C{1H} NMR (75,1 MHz, 298 K,
CDCl3) d: 164.1 (C3), 156.1 (C5), 147.2 (C2), 120.6 (C6), 120.2
(C1), 112.7 (C22), 87.9 (C4), 65.4 (C23), 52.3 (C21), 17.7 (1-
CH3), 12.3 (2-CH3). 19F NMR (282 MHz, 298 K, CDCl3)
d:
ꢁ3
ꢀ
temperature: 85 C/10 mbar.
ꢁ73.0 (s, 1JC,F ¼ 282 Hz, 2JC,F ¼ 31 Hz).
3.1.2. (PyHFP)Pd(h3eC3H5) (2)
3.1.6. (DMOTFP)Pd(h3eC3H5) (6)
Yield: 87% (0.21 g). 1H NMR (300 MHz, 298 K, CDCl3)
d:
Yield: 90% (0.18 g). 1H NMR (300 MHz, 298 K, CDCl3)
d:
8.40 (d, J ¼ 4.9 Hz, H1, 1H), 7.57 (t, J ¼ 8.3 Hz, H3, 1H), 7.08
(d, J ¼ 8.3 Hz, H4, 1H), 6.77 (t, J ¼ 7.2 Hz, H2, 1H), 5.87e5.74
(m, H22, 1H), 5.62 (s, H6, 1H), 4.00 (dd, J ¼ 7.0, 2.0 Hz,
H23syn, 1H), 3.42 (dd, J ¼ 6.8, 1.9 Hz, H21syn, 1H), 3.20 (d,
5.62 (s, H4, 1H), 5.62e5.49 (m, H22, 1H), 4.26 (dd, J ¼ 6.9,
2.2 Hz, H23syn, 1H), 3.90 (dd, J ¼ 6.6, 1.6 Hz, H21syn, 1H), 3.35
(d, J ¼ 12.5 Hz, H23anti, 1H), 2.81 (d, J ¼ 11.9 Hz, H21anti, 1H),
2.23 (s, 2-CH3, 3H), 1.99 (s, 1-CH3, 3H). 13C{1H} NMR
J ¼ 12.5 Hz, H23anti, 1H), 3.04 (d, J ¼ 11.8 Hz, H21anti, 1H). 13
C
Please cite this article in press as: L. Czympiel, et al., High activity heterogeneous catalysts by plasma-enhanced chemical vapor
deposition of volatile palladium complexes on biomorphic carbon, Comptes Rendus Chimie (2018), https://doi.org/10.1016/
j.crci.2018.04.008

8
L. Czympiel et al. / C. R. Chimie xxx (2018) 1e9
(75.1 MHz, 298 K, CDCl3)
d
: 160.8 (C5), 160.5 (C3), 139.8
10ꢁ3 mbar was used as a precursor for the formation of
palladium nanostructures in a PECVD process on both flat (Si)
and mesoporous (BioC) surfaces.
Palladium nanostructures embedded in porous BioC
scaffold showed high catalytic activity and recyclability for
Heck and Suzuki reactions, which is further emphasized by
the lower TON of commercially available Pd on carbon. In
combination with the total TON of 8767 (Heck) and 139,179
(Suzuki) under nonoptimized reaction conditions and an
excellent selectivity the potential of the presented sus-
tainable solid-supported catalysts could be demonstrated.
(C1),130.2 (C2),120.3 (C6),112.8 (C22), 80.6 (C4) 66.0 (C23),
50.8 (C21), 13.0 (1-CH3), 10.2 (2-CH3). 19F NMR (282 MHz,
298 K, CDCl3)
d
: ꢁ73.4 (s, 1JC,F ¼ 282 Hz, 2JC,F ¼ 32 Hz). EIMS:
353 (100%, Mþ), 313 (24%, Mþ
ꢁ
C3H5), 207 (20%,
DMOTFPþ), 138 (16%, DMOTFPþ ꢁ CF3), 39 (8%, C3Hþ4 ).
Elemental Anal. Calcd for C11H10F3NO2Pd: C, 39.37; H, 3.00;
ꢀ
N, 4.17. Found: C, 39.62; H, 3.87; N, 4.47. Mp: 90 C. Subli-
mation temperature: 65 C/10ꢁ3 mbar.
ꢀ
3.2. General procedure of the PECVD process
A weighed amount of precursor (100 mg) was transferred
into a stainless-steel precursor tank, which was connected to
the plasma reactor (plasma electronic) and heated to a tem-
perature of 100 ꢀC to provide a sufficient precursor flow.
Argon was used as carrier gas. All substrates were cleaned by
ultrasonification in distilled water and isopropanol and by Ar
sputtering using 20 sccm Ar and a plasma power of 50 W for
3 min. Silicon and carbon substrates, which were held at
room temperature during the deposition, were placed in the
reactor near the precursor inlet and the chamber was pum-
ped down to a basepressure of ca. 0.5 Pa before the precursor/
argon mixture and an additional amount of argon (20 sccm)
as reactive gas were introduced and the processes at variable
plasma powers (in a range of 25e150 W) were started. The
reaction time for each process was held constant at 1 h.
Acknowledgments
The authors gratefully acknowledge the University of
Cologne and the Regional Research Cluster Sustainable
Chemical Synthesis for financial support. The project
“Sustainable Chemical Synthesis (SusChemSys)” is cofi-
nanced by the European Regional Development Fund
(ERDF) and the state of North Rhine-Westphalia, Germany,
under the Operational Program “Regional Competitiveness
and Employment” 2007e2013. Thanks are also due to A.
ꢀ
ꢀ
Gutierrez-Pardo, J. Ramirez-Rico, and J.M. Fernandez (Uni-
versity of Sevilla) for providing the BioC substrates.
Appendix A. Supplementary data
Supplementary data related to this article can be found
at https://doi.org/10.1016/j.crci.2018.04.008.
3.3. CeC coupling reactions
3.3.1. Heck reaction
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mL,
m
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