A straight forward in situ preparation of NHC-substituted phosphapalladacycles

Article abstract of DOI:10.1016/j.jorganchem.2006.01.018

A new simple technique for the preparation of NHC-substituted phosphapalladacycles is reported by using phosphapalladacycle acetate precursors and azolium tetrafluoroborate salts in DMSO. The one-pot synthesis avoids multi-step reactions employing free ca

Full text of DOI:10.1016/j.jorganchem.2006.01.018

Journal of Organometallic Chemistry 691 (2006) 2403–2408
www.elsevier.com/locate/jorganchem
A straight forward in situ preparation of NHC-substituted
q
phosphapalladacycles
*
Guido D. Frey, Jan Schutz, Wolfgang A. Herrmann
¨
Department Chemie, Lehrstuhl fu¨r Anorganische Chemie, Technische Universita¨t Mu¨nchen, Lichtenbergstraße 4, D-85747 Garching, Germany
Received 26 September 2005; received in revised form 9 January 2006; accepted 11 January 2006
Available online 21 February 2006
Abstract
A new simple technique for the preparation of NHC-substituted phosphapalladacycles is reported by using phosphapalladacycle ace-
tate precursors and azolium tetrafluoroborate salts in DMSO. The one-pot synthesis avoids multi-step reactions employing free carbenes.
With this technique, NHC-substituted phosphapalladacycles were thus obtained that are not accessible via the free carbene route.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Carbenes; Phosphapalladacycle; Palladium; NHCs; In situ method
1. Introduction
oxide reacts at elevated temperature with azolium salts
via deprotonation [6,10–13]. This route is particularly use-
ful in cases where the metal acetates are easily available and
where the corresponding free carbenes are not available.
Palladacycles are among the most active catalyst systems
for CC-coupling reactions. Palladium(II) complexes con-
taining a cyclopalladated (di-o-tolylphosphino)benzyl frag-
ment were first characterized by Shaw [1], Mason [2], Aleya
[3], and Heck [4]. They were also intensely investigated in
our group [5,6], and from this work they promised to be
excellent catalysts in CC-coupling reactions. As a matter
of fact these catalysts exhibit high air-, moisture-, and ther-
mal stability (up to 250 °C) for processes such as Heck- and
Suzuki-catalysis [7]. Recently we presented a new class of
phosphapalladacycles, the N-heterocyclic carbene (NHC)
substituted phosphapalladacycles [8]. The latter combine
the advantageous stability of phosphapalladacycles with
the high r-donor strength and steric demand of N-hetero-
cyclic carbenes [9].
2. Results and discussion
First we tried to react an azolium chloride salt (2a) with
the acetate-bridged phosphapalladacycle dimer 1a in
DMSO at temperatures between 70 and 120 °C. However,
only a substitution of the anion occurs and the chloride
bridged phosphapalladacycle 1b was obtained as product
(Scheme 1) [14].
In order to avoid halogen scrambling during the reac-
tion, the phosphapalladacycle acetate was reacted with
azolium salts bearing weak coordinating anions like BF4ꢀ
or PFꢀ6 . However, an additional base is necessary for the
deprotonation of the azolium salts. In this case sodium ace-
tate showed the best performance, because it does not com-
pete in carbene complex formation (Scheme 2). When
stronger bases are applied, such as KOtBu, the palladacy-
cle precursor decomposes [15].
It is now possible to synthesize NHC-complexes without
isolation of the free carbene when metal acetates are used
as starting material. Palladium(II) acetate in dimethylsulf-
q
N-Heterocyclic carbenes, part 43. For part 42 see Ref. [22].
Corresponding author. Tel.: +49 89 289 13080; fax: +49 89 289 13473.
A temperature dependency was observed for the
reactions of the different azolium salts with the phospha-
palladacycles. Best results were obtained at reaction
*
E-mail address: lit@arthur.anorg.chemie.tu-muenchen.de (W.A. Herr-
mann).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.01.018

2404
G.D. Frey et al. / Journal of Organometallic Chemistry 691 (2006) 2403–2408
t-Bu
OAc
N
Pd
P
N
o-Tol t-Bu
+ Cl-
t-Bu
t-Bu
Ac
O
N
1
3
Pd
+
/
2
2
P
N
o-Tol
t-Bu
t-Bu
Cl
1a
2a
Pd
2
P
o-Tol
t-Bu
1b
Scheme 1. Attempt for the preparation of complex 3.
Ac
O
Fig. 1. Complexes 8–11.
OAc
-
+ NaOAc
+ [NHC-H]+BF4
1
Pd
Pd
/
2
2
P
DMSO
- HOAc
- NaBF4
P
NHC
Ac
O
R1R2
R1 R2
+ BF4
-
OAc
Pd
+ KOt-Bu
1
Pd
+
/
2
N
2
N
N
P
DMSO
- HOt-Bu
- KBF4
P
-
R1
R2
[NHC-H]+BF4
N
o-Tol
t-Bu
o-Tol t-Bu
1a = o-Tol t-Bu
1c = o-Tol o-Tol
1c = o-Tol o-Tol
4
8
9
1a
12
13
5
Scheme 3. Synthesis of complex 13.
2d
10
-
+ BF4
O
N
-
+ BF4
N
-
+ BF4
amide (DMAc). With this solvent no or very small yields
were obtained in such reactions.
N
Cl
N
O
N
N
To form a bridged biscarbene palladacycle, we used
a,a0-bis(1-isopropyl-triazolium)m-xylole ditetrafluorobo-
rate (7b) as the azolium salt, prepared according to Scheme
4. The counter ion chloride in salt 7a was exchanged to
BFꢀ4 to form 7b. This salt was used to synthesize 11
(Fig. 1), in a similar way to the preparation route shown
in Scheme 2.
If the steric bulkiness at the nitrogens in 1,3-position of
the azolium salt is increased, such as in adamantyl-, or tert-
butyl-groups, no reaction occurs with this method. For
highly sterical hindered carbene ligands, the recently pub-
lished free carbene route [8] is the best way to synthesize
the corresponding NHC-substituted phosphapalladacycles.
Via the free carbene route the mono substituted complex
3 and the biscarbene substituted complex 14 (Scheme 5)
were synthesized. It depends on the sterical hindrance of
the carbene ligand if one or two of them coordinate to
the metal center, as recently published [8].
N
N
N
N
4
2d
5
Scheme 2. In situ method for the preparation of complexes 8–10.
temperatures between 75 and 90 °C [13]. At higher temper-
atures, palladium black is formed at lower product yields.
With this preparation technique it was possible to
synthesize the first dimethyl-purine-8-ylidene palladium
complex 8 (Fig. 1), by reaction of 6-chloro-7,9-dimethylpu-
rinium tetrafluoroborate (4) with palladacycle 1a (Scheme
2).
A 1,3,7,9-tetramethylxanthine-8-ylidene substituted
complex 9 was received by reaction of azolium salt 5 with
complex 1c, analogous complex 10 was obtained. After
completion of the reactions the solvent was removed
in vacuo and afterwards the product was extracted in each
case with toluene from the residue, to obtain light yellow or
colourless products.
If less acidic azolium salts, such as 1,3-diisopropyl-
3,4,5,6-tetrahydropyrimidin-1-ium tetrafluoroborate (12)
are applied, the basicity of sodium acetate is not high
enough to form the corresponding carbene complex (13)
(Scheme 3). In this case we used a stronger base such as
KOtBu at reduced temperature, and accepted a decreased
yield because of partly decomposition of the phosphapalla-
dacycle due to the stronger base.
2+ 2 Cl-
Cl
Cl
N
N
N
N
N
N
N
N
N
7a
NH4BF4
6
NaOMe
MeOH
-
2+ 2 BF4
N
N
N
N
N
N
N
NH
Br
N
7b
To avoid hardly removable DMSO as solvent we tried
to use another high polar solvent such as dimethylacet-
Scheme 4. Preparation of ligand 7b.

G.D. Frey et al. / Journal of Organometallic Chemistry 691 (2006) 2403–2408
2405
borate (2d) [16], 6-chloro-7,9-dimethylpurinium tetra-
fluoroborate (4) [17], 1,3,7,9-tetramethylxanthinium
tetrafluoroborate (5) [18], 1-isopropyl-4,5-dihydro-1H-
1,2,4-triazole (6) [19] and 3,4,5,6-tetrahydro-1,3-bis(isopro-
pyl)pyrimidinium tetrafluoroborate (12) [20] were prepared
1
according to the literature. H, 13C and 31P NMR spectra
were recorded on a JEOL-JMX-GX 270 or 400 MHz spec-
trometer at room temperature and referenced to the resid-
ual 1H and 13C signals of the solvents or 85% H3PO4 as an
external standard (31P). NMR multiplicities are abbrevi-
ated as follows: s, singulet; d, doublet; t, triplet; sept., sep-
tet; m, multiplet; br., broad signal. Coupling constants J
are given in Hz. Elemental analyses were carried out by
Scheme 5. Complexes synthesized via the free carbene route.
Table 1
the Microanalytical Laboratory at the TU Munchen. Mass
¨
13C NMR carbene signals of the new complexes
spectra were performed at the TU Munchen Mass Spec-
¨
trometry Laboratory on a Finnigan MAT 90 spectrometer
using the CI or FAB technique.
13
Complex
C
carbene
(ppm)
3
8
178.3, 176.9
185.5
9
189.3, 187.2
182.3
180.5
200.6, 200.4
177.6, 177.4
3.2. a,a0-Bis(1-isopropyl-triazolium)m-xylole dichloride
(7a)
10
11
13a
14
a
In a high pressure tube 946 mg (8.52 mmol) 1-isopropyl-
4,5-dihydro-1H-1,2,4-triazole 6 and 720 mg (6.52 mmol)
a,a0-dichlor-m-xylole in 5 ml THF at 130 °C were heated
for 80 h. The suspension was filtered and washed three
times with 15 ml diethyl ether. Yield: 865 mg (2.18 mmol,
Small amounts of a biscarbene-substituted complex was obtained with
a chemical shift in 13C NMR for the carbene of 199.3 ppm.
For the complexes 3, 8–11, 14 the 13C NMR signals of
the carbene carbon are in the standard range of 176–
190 ppm for imidazolin-2-ylidene and triazolin-2-ylidene
complexes (Table 1). Complex 13 shows with 200 ppm
for the carbene signal a slightly higher downfield shift
because of the stronger r-donor effect of this carbene.
The complexes 3, 9 and 13 show two carbene signals in
the 13C NMR spectra, because of the possible cis/trans con-
figuration of the NHC-ligand to the phosphorous. A differ-
entiation of the carbene signals in complex 8 and 10 could
not be obtained in the 13C NMR spectra, but the 31P NMR
spectra show two signals for the phosphorous, and gives a
first hint that these complexes also form cis/trans species.
In complex 11 the two carbenes should have different
chemical shifts, but only one signal could be obtained. As
expected the 31P NMR spectra show only one signal,
because no cis/trans isomerization is possible. Contrary
to complex 11 for the biscarbene complex 14 two carbene
signals were obtained in the 13C NMR spectra. Only one
signal in the 31P NMR spectra was observed for the same
reason as in complex 11. In the 13C NMR spectra most
1
53%). H NMR (400 MHz, d6-DMSO): d = 10.87 (2H, s,
CHNCHNCH2), 9.54 (2H, s, NCHNCH2), 7.94 (1H, s,
Ar), 7.60–7.50 (3H, m, Ar), 5.57 (4H, s, CH2), 4.82 (2H,
3
3
hept., JHH = 6.4 Hz, CH(CH3)2), 1.51 (12H, d, JHH
=
6.4 Hz, CH3). 13C{1H} NMR (100.5 MHz, d6-DMSO):
d = 144.5 (CH3NCHNCH2), 141.7 (NCHNCH2), 134.5,
129.8, 129.7, 129.6 (Ar), 55.3 (CH(CH3)2), 50.1 (CH2),
21.2 (CH3).
3.3. a,a0-Bis(1-isopropyl-triazolium)m-xylole
ditetrafluoroborate (7b)
Five hundred milligrams (4.77 mmol) of ammoniumte-
trafluroroborate was dissolved in 5 ml water and added
to a solution of 600 mg (1.51 mmol) a,a0-bis(1-isopropyl-
triazolium)m-xylole dichloride 7a in 5 ml water. The solu-
tion was stirred for 15 min at room temperature. The pre-
cipitate was filtered and washed twice with 4 ml water and
once with 20 ml diethyl ether. Yield: 400 mg (0.97 mmol,
1
2
1
complexes show JPC (>16 Hz) and JPC (5–16 Hz) cou-
pling constants for the carbons bonded directly to phos-
phorous and bonded not across the palladium center.
69%). H NMR (400 MHz, d6-DMSO): d = 10.18 (2H, s,
CHNCHNCH2), 9.22 (2H, s, NCHNCH2), 7.58 (1H, s,
Ar), 7.53 (3H, s, Ar), 5.49 (4H, s, CH2), 4.79 (2H, hept.,
3
3JHH = 6.4 Hz, CH(CH3)2), 1.51 (12H, d, JHH = 6.6 Hz,
CH3). 13C{1H} NMR (100.5 MHz, d6-DMSO): d = 143.8
(CHNCHNCH2), 140.7 (NCHNCH2), 133.5 (CH2C, Ar),
129.3 (Ar), 128.9 (CH2CCHCH), 128.5 (Ar), 54.7
(CH(CH3)2), 49.6 (CH2), 20.5 (CH3). MS (FAB) m/z (%):
413.0 (87, [M+]), 325.0 (100, [M2+]). Anal. Calc. for
C18H26N6B2F8 (500.05): C, 43.23; H, 5.24; N, 16.81.
Found: C, 43.00; H, 5.10; N, 17.15%.
3. Experimental section
3.1. General comments
The precursors 1a and 1c [5i], 1,3-di-tert-butylimidazo-
lin-2-ylidene (2b), 1,3-di-cyclohexylimidazolin-2-ylidene
(2c), 1-diphenylbenzyl-3-methylimidazolium tetrafluoro-

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G.D. Frey et al. / Journal of Organometallic Chemistry 691 (2006) 2403–2408
3.4. Trans-di(l-chloro)-bis[o-(tert-butyl-o-
tolylphosphino)benzyl]dipalladium(II) (1b) [21]
(0.72 mmol) sodium acetate and 260 mg (0.30 mmol)
trans-di(l-acetato)-bis[o-(tert-butyl-o-tolylphosphino)ben-
zyl]dipalladium(II) 1a are suspended in 5 ml DMSO and
heated for 2 h at 70 °C. All volatile compounds were
removed in vacuo and the residue was extracted three times
with 4 ml toluene. After removal of the solvent a yellow
precipitate was obtained. Yield: 215 mg (0.33 mmol,
55%). 1H NMR (270 MHz, C6D6): d = 8.32 (1H, s,
NCHN), 7.35–6.60 (12H, m, Ar), 3.93 (3H, s, NCH3),
3.88 (3H, s, NCH3), 2.90 (3H, s, CO2CH3), 2.76 (2H, s,
CH2), 2.08 (3H, s, CCH3), 1.39 (9H, m, C(CH3)3).
13C{1H} NMR (100.5 MHz, C6D6): d = 185.5 (br. NCN),
172.8 (CO2CH3), 151.3, 149.8 (NCHN, CCl), 132.6,
132.5, 131.8, 131.4, 130.4, 129.9, 128.7, 128.5, 128.3,
127.5, 127.3, 125.4, 125.1, 125.0, 67.5 (CH2), 34.8
(C(CH3)3), 30.6 (NCH3), 28.7 (d, JPC = 6.1 Hz, CH3, t-
Bu), 28.4 (br., C(CH3)3), 27.8 (NCH3), 22.9 (CH3 of P-o-
tol), 20.7 (CO2CH3). 31P{1H} NMR (161.8 MHz,
C6H5CH3): d = 54.0 (s), 53.8 (s) (cis/trans = 75/25). MS
(FAB) m/z: 558 [M+ꢀOAc], 375 [M+ꢀ(OAc + carbene)].
A solution of 106 mg (0.49 mmol) 1,3-di-tert-butylimi-
dazolium chloride 2a and 200 mg (0.22 mmol) trans-di(l-
acetato)-bis[o-(tert-butyl-o-tolylphosphino)benzyl]dipalla-
dium(II) 1a were suspended in 10 ml DMSO and heated for
2 h at 120 °C. After 20 min a white solid precipitates. The
precipitate was filtered and washed with 5 ml DMSO,
5 ml THF, 5 ml toluene, and 5 ml n-hexane. The solid is
extremely insoluble in commonly used solvents. Yield:
182 mg (0.22 mmol, 99.6%). 1H NMR (400 MHz, d7-
DMF): d = 8.02 (1H, s), 7.31 (2H, s), 7.25 (2H, s), 7.15
3
(1H, s), 7.01 (1H, s), 6.82 (1H, t, JHH = 7.8 Hz), 3.36
(2H, br. s, CH2), 2.40 (3H, s, CH3,Tol), 1.53 (9H, d,
3JPH = 14.9 Hz, C(CH3)3). 13C{1H} NMR (100.5 MHz,
d7-DMF): d = 135.4, 134.7, 134.6, 134.1, 134.0, 132.5,
130.8, 130.0, 128.5, 125.3 (Ar), 67.9 (C(CH3)3), 41.2
(CH2), 25.8 (C(CH3)3), 23.0 (CH3). 31P{1H} NMR
(161.8 MHz, (CD3)2SO): d = 63.0. 31P{1H} NMR (161.8
MHz, d7-DMF): d = 63.2.
3.7. Acetato(1,3,7,9-tetramethylxanthine-8-ylidene)-
[o-(di-o-tolylphosphino)benzyl]palladium(II) (9)
3.5. Acetato(1,3-di-tert-butylimidazolin-2-ylidene)[o-(tert-
butyl-o-tolylphosphino)benzyl]palladium(II) (3)
Two hundred and eight milligrams (0.70 mmol) of
1,3,7,9-tetramethylxanthinium tetrafluoroborate 5, 63 mg
(0.77 mmol) sodium acetate and 300 mg (0.32 mmol)
trans-di(l-acetato)-bis[o-(di-o-tolylphosphino)benzyl]dipal-
ladium(II) 1c were suspended in 5 ml DMSO and heated
for 2 h at 80 °C. All volatile compounds were removed
in vacuo and the residue was extracted three times with
4 ml toluene. After removal of the solvent a yellow precip-
To a solution of 300 mg (0.34 mmol) trans-di(l-acetato)-
bis[o-(tert-butyl-o-tolylphosphino)benzyl]dipalladium(II)
1a dissolved in 10 ml toluene, 123 mg (0.68 mmol) 1,3-di-
tert-butylimidazolin-2-ylidene 2b in 10 ml toluene was
added at ꢀ90 °C. The combined solution was stirred at
room temperature for 3 h. Afterwards the solvent was
removed in vacuo and the residue was extracted three times
with 5 ml n-hexane. The solvent was removed in vacuo, to
obtain a yellow product. The product can be recrystallized
1
itate was obtained. Yield: 268 mg (0.40 mmol, 62%). H
NMR (270 MHz, C6D6): d = 7.44–6.60 (12H, m, Ar),
4.29 (3H, s, NCH3), 4.07 (3H, s, NCH3), 3.76 (3H, s,
NCH3), 3.16 (3H, s, NCH3), 3.14 (3H, s, CO2CH3), 2.11
(2H, s, CH2), 1.76 (3H, s, CCH3). 13C{1H} NMR
(67.8 MHz, C6D6): d = 189.3 (br. NCN), 187.2 (br.
NCN), 176.3 (CO2CH3), 159.5 (CO), 159.0 (CO), 143.0
from
a n-hexane/n-pentane solution. Yield: 280 mg
1
(0.45 mmol, 66%). H NMR (400 MHz, C6D6): d = 7.67
(2H, t, JHH = 7.6 Hz), 7.06 (2H, t, JHH = 7.2 Hz), 6.97
(2H, d, JHH = 6.4 Hz), 6.92 (2H, m), 6.77 (2H, d,
3
3
3
3JHH = 17.2 Hz, NCHCHN), 3.14 (2H, s, CH2), 2.07(3H,
s, CH3), 1.84 (9H, s, CH3), 1.76 (9H, s, CH3), 1.50(3H, s,
CO2CH3), 1.47 (9H, s, CH3). 13C{1H} NMR (100.5 MHz,
C6D6): d = 178.3 (NCN), 176.9 (NCN), 174.2 (CO2CH3),
161.2 (d, J = 42.0 Hz), 143.4 (d, J = 14.6 Hz), 136.3,
135.9, 134.5, 132.4, 131.9 (d, J = 6.8 Hz), 130.8 (d,
J = 23.8 Hz), 130.3, 129.7, 125.0 (d, J = 5.3 Hz), 124.2 (d,
J = 5.4 Hz), 118.1 (d, J = 20.0 Hz), 58.9 (C(CH3)3), 58.3
(C(CH3)3), 34.7 (d, J = 17.6 Hz, CH2), 31.7 (d, J =
20.7 Hz, C(CH3)3), 28.2 (d, J = 5.4 Hz, C(CH3)3), 25.9
(CH3), 23.9 (CO2CH3). 31P{1H} NMR (161.8 MHz,
C6D6): d = 46.9 (s), 45.0 (s), (Intensity = 1: 14.8). MS
(FAB) m/z (%): 374.5 (8, [M+]), 180 (100, [carbene]).
2
(d, JPC = 15.6 Hz, ipso-C of P-o-tol), 140.7 (NCCN),
2
139.2 (d, JPC = 15.2 Hz, ipso-C of P-o-tol), 134.5, 133.8,
2
132.8 (br.), 131.8 (Ar), 131.6 (d, JPC = 7.8 Hz, ipso-C of
P-o-tol), 130.9, 130.3 (br.), 129.1 (Ar), 125.7 (d,
2JPC = 6.2 Hz, p-C of P-o-tol), 125.4 (Ar), 109.1 (NCCN),
67.6 (CH2), 38.6 (NCH3), 36.5 (NCH3), 30.5 (NCH3), 27.7
(NCH3), 22.6, 22.4 (CH3 of P-o-tol), 17.6 (CO2CH3).
31P{1H} NMR (109.1 MHz, C6H5CH3): d = 29.1 (s). MS
(FAB) m/z: 617 [M+ꢀOAc], 409 [M+ꢀ(OAc + carbene)],
209 [carbene]. Anal. Calc. for C32H35N4O4PPd (677.03):
C, 56.77; H, 5.21; N, 8.28. Found: C, 56.86; H, 5.31; N,
8.33%.
3.6. Acetato(6-chloro-7,9-dimethylpurine-8-ylidene)-
[o-(tert-butyl-o-tolylphosphino)benzyl]palladium(II) (8)
3.8. Acetato(1-diphenylmethyl-3-methylimidazolin-2-
ylidene)[o-(di-o-tolylphosphino)benzyl]palladium(II) (10)
One hundred and eighty six milligrams (0.69 mmol) of 6-
chloro-7,9-dimethylpurinium tetrafluoroborate 4, 59 mg
Two hundred milligrams (0.21 mmol) of trans-di(l-ace-
tato)-bis[o-(di-o-tolylphosphino)-benzyl]dipalladium(II)

G.D. Frey et al. / Journal of Organometallic Chemistry 691 (2006) 2403–2408
2407
1c, 60 mg (0.73 mmol) sodium acetate and 150 mg
3.10. Acetato[3,4,5,6-tetrahydro-1,3-bis(1-methylethyl)-
pyrimidine-2-ylidene][o-(tert-butyl-o-
tolylphosphino)benzyl]palladium(II) (13)
(0.45 mmol) 1-diphenylbenzyl-3-methylimidazolium tetra-
fluoroborate 2d were suspended in 6 ml DMSO and heated
for 2 h at 90 °C. All volatile compounds were removed in
vacuo and the residue was extracted three times with 4 ml
toluene. After removal of the solvent a yellow compound
Two hundred and fifty milligrams (0.29 mmol) of trans-
di(l-acetato)-bis[o-(tert-butyl-o-tolylphosphino)benzyl]-
dipalladium(II) 1a, 65 mg (0.58 mmol) potassium-tert-
butylate and 160 mg (0.63 mmol) 3,4,5,6-tetrahydro-1,3-
bis(1-methylethyl)pyrimidinium tetrafluoroborate 12 were
combined in 5 ml DMSO at room temperature. The solu-
tion was heated up slowly to 80 °C and reacted for further
2 h, while the color changed from white to brown. The sol-
vent was removed in vacuo and the residue was extracted
three times with 4 ml toluene. After the solvent was
removed in vacuo a yellow solid was obtained, containing
1
was obtained. Yield: 116 mg (0.16 mmol, 38%). H NMR
(400 MHz, C6D6): d = 7.52 (2H, br.), 7.43 (2H, br.),
3
7.21–6.84 (18H, m), 6.71 (1H, t, JHH = 7.6 Hz, CH),
6.25 (2H, br. NCHCHN), 3.78 (2H, s, PdCH2), 3.47 (3H,
s, NCH3), 3.04 (3H, s, CH3), 2.89 (3H, s, CH3), 2.02 (3H,
s, CO2CH3). 13C{1H} NMR (67.8 MHz, C6D6): d = 182.3
(NCN), 175.5 (CO2CH3), 160.2 (d, J = 36.8 Hz), 143.4,
140.7, 140.1, 137.7, 137.2, 132.9, 132.6, 131.7, 130.0,
129.3, 128.8, 125.6, 121.4 (d, NCHCHN,J = 20.2 Hz),
67.5 (NCH), 40.8 (NCH3), 37.9 (CH2), 22.7, 21.4 (CH3),
18.0 (CO2CH3). 31P{1H} NMR (161 MHz, C6D5CD3):
d = 28.5 (s), 27.5 (s), (Intensity = 1: 1). 31P{1H} NMR
(161.8 MHz, (CD3)2SO): d = 28.0 (s). 31P{1H} NMR
(161.8 MHz, d8-THF): d = 28.4 (s), 27.9 (s), (Intensity = 1:
1). MS (FAB) m/z (%): 656.5 (60, [M+]), 408.6 (14,
[Pd + PC7H6(C7H7)2]), 352.6 (21, [Pd + carbene]), 246.8
(100, [carbene]). Anal. Calc. for C40H39N2O2PPd
(717.14): C, 66.99; H, 5.48; N, 3.91. Found: C, 67.21; H,
5.38; N, 3.97%.
1
three isomers. Yield: 73 mg (0.12 mmol, 21%). H NMR
(400 MHz, (CD3)2SO): d = 8.06 (1H, s), 7.32 (1H, s),
3
7.24–7.18 (4H, m), 7.11 (1H, d, JHH = 4.9 Hz), 6.94 (1H,
3
m), 3.71 (2H, sept., JHH = 7.4 Hz, CH(CH3)2), 3.34 (2H,
s, CH2Pd), 3.06 (4H, m, NCH2), 2.26 (2H, m, CH2), 2.03
(3H, s, CH3), 1.80 (3H, s, CH3), 1.39 (12H, d,
3
3JHH = 13.5 Hz, CH(CH3)2), 1.11 (9H, d, JPH = 6.2 Hz,
C(CH3)3). 13C{1H} NMR (100.5 MHz, (CD3)2SO):
d = 200.6 (NC1N), 200.4 (NC2N), 199.3 (NC3N), 175.5
(br. s, CO2CH3), 172.9 (s, CO2CH3), 162.7 (C1Aryl), 162.2
(C2Aryl), 162.1 (CA3ryl), 159.6 (d, JPC = 37.4 Hz, C3), 158.4
(d, JPC = 28.2 Hz, C2), 159.6 (d, JPC = 27.4 Hz, C1),
142.5 (d, J = 14.4 Hz), 142.2 (d, J = 11.4 Hz), 137.3,
134.1, 132.3, 131.9, 131.7 (d, J = 5.3 Hz), 131.6 (d,
J = 7.6 Hz), 131.1 (d, J = 8.4 Hz), 130.4, 130.3, 130.0 (d,
JPC = 8.4 Hz), 129.3, 128.9, 128.2, 128.0 (d, J = 10.7 Hz),
3.9. a,a0-Bis(1-isopropyl-4,5-dihydro-1H-1,2,4-triazolin-5-
ylidene)-m-xylole[o-(di-o-tolylphosphino)benzyl]-
palladium(II)acetate (11)
Two hundred and thirty three milligrams (0.59 mmol) of
a,a0-bis(1-isopropyl-1,2,4-triazolium)m-xylole ditetrafluo-
roborate 7b, 53 mg (0.65 mmol) sodium acetate and
250 mg (0.27 mmol) trans-di(l-acetato)-bis[o-(di-o-toly-
lphosphino)benzyl]dipalladium(II) 1c were suspended in
5 ml DMSO and heated for 2 h at 80 °C. All volatile com-
pounds were removed in vacuo and the residue was
extracted three times with 4 ml toluene. After removal of
the solvent a white precipitate was obtained. Yield:
291 mg (0.37 mmol, 68%). 1H NMR (270 MHz, C6D6):
d = 9.01 (2H, s, NCHN), 7.28–6.73 (16H, m, Ar), 5.36
(4H, br. NCH2), 4.88 (2H, br. (CH3)2CH), 3.04 (3H, s,
CO2CH3), 2.40 (2H, s, PdCH2), 2.12 (6H, s, CCH3), 1.35
(12H, br. (CH3)2CH). 13C{1H} NMR (67.8 MHz, C6D6):
d = 180.5 (br. NCN), 175.8 (CO2CH3), 144.5 (NCHN),
127.7 (d, JPC = 6.1 Hz), 125.3, 124.9, 124.4 (d, JPC
=
5.3 Hz, CAryl), 57.3, 57.1 (CH(CH3)2), 48.9 (C(CH3)3),
40.4 (NCH2), 37.6 (C3H2Pd), 37.3 (C1H2Pd), 37.2
(C2H2Pd), 27.9 (br. CO2CH3), 21.7 (CH2CH2CH2), 19.9,
19.7 (CH3,Tol). 31P{1H} NMR (109.1 MHz, (CD3)2SO):
d = 52.4 (s), 50.5, 50.4 (cis/trans). MS (FAB) m/z (%):
542.6 (46, [M+ꢀOAc]), 374.6 (60), 270.8 (12, [Pd +
carbene]), 166.9 (100, [carbene]).
3.11. Bis(1,3-di-cyclohexylimidazolin-2-ylidene)[o-(tert-
butyl-o-tolylphosphino)benzyl]palladium(II)acetate (14)
To a solution of 300 mg (0.34 mmol) trans-di(l-acetato)-
bis[o-(tert-butyl-o-tolylphosphino)benzyl]dipalladium(II)
(1a) dissolved in 15 ml toluene a solution of 200 mg
(0.86 mmol) 1,3-di-cyclohexylimidazolin-2-ylidene 2c in
10 ml n-hexane was added at ꢀ90 °C. After the solution
was concentrated in vacuo to 15 ml and stirred for 12 h
at room temperature, a white solid precipitated. The solu-
tion was filtered off and the precipitate was washed twice
with 5 ml toluene. Yield: 545 mg (0.61 mmol, 88%). 1H
NMR (270 MHz, (CD3)2SO): d = 7.99 (1H, m), 7.85 (1H,
2
143.0 (d, JPC = 15.6 Hz, ipso-C of P-o-tol), 140.7
2
(NCCN), 139.2 (d, JPC = 15.2 Hz, ipso-C of P-o-tol),
134.5, 133.8, 132.8 (br.), 131.8 (Ar), 131.6 (d,
2JPC = 7.8 Hz, ipso-C of P-o-tol), 130.9, 130.3 (br.), 129.1
2
(Ar), 125.7 (d, JPC = 6.2 Hz, p-C of P-o-tol), 125.4 (Ar),
109.1 (NCCN), 67.6 (PdCH2), 54.9 (NCH2), 52.0
((CH3)2CH), 22.9, 22.5, 22.2, 20.9 (CH3 of P-o-tol,
CO2CH3 and ((CH3)2CH)). 31P{1H} NMR (109.1 MHz,
C6H5CH3): d = 28.8 (s). MS (FAB) m/z: 734 [M+], 691
[M+ꢀt-Bu]. Anal. Calc. for C41H47N6O2PPd (793.24): C,
62.08; H, 5.97; N, 10.59. Found: C, 61.96; H, 6.02; N,
10.47%.
3
s), 7.65 (1H, m), 7.59 (1H; s), 7.41 (2H, t, JHH = 3.6 Hz),
3
7.31 (2H, d, JHH = 2.1 Hz), 7.09 (2H, m), 6.81 (2H, t,
3JHH = 7.4 Hz), 4.70 (4H, m, NCHCy), 3.30 (2H, m,
CH2), 2.02 (3H, s, CO2CH3), 2.28–1.15 (43H, m), 1.35

2408
G.D. Frey et al. / Journal of Organometallic Chemistry 691 (2006) 2403–2408
3
¨
[6] W.A. Herrmann, C.-P. Reisinger, K. Ofele, C. Broßmer, M. Beller,
H. Fischer, J. Mol. Catal. A 108 (1996) 51.
(9H, JPH = 14.7 Hz, C(CH3)3), 1.09–0.88 (m, n-hexane).
13C{1H} NMR (100.5 MHz, (CD3)2SO): d = 177.6
[7] (a) J. Dupont, M. Pfeffer, J. Spencer, Eur. J. Inorg. Chem. (2001)
1917;
(NCN), 177.4 (NCN), 174.4 (CO2CH3), 158.3 (d, JPC
=
32.7 Hz, CAryl), 142.7 (d, JPC = 14.0 Hz, CAryl), 133.2,
132.9, 132.0, 130.9, 130.4, 129.1, 128.2, 127.9, 126.2 (d,
JPC = 7.8 Hz, CAryl), 125.3 (d, JPC = 5.7 Hz, CAryl), 120.8,
120.4, 120.0, 119.3 (NCHCHN), 60.1, 58.9, 58.4, 58.0
(CHCy), 55.2 (C(CH3)3), 35.5, 35.0, 34.5, 34.4, 34.1, 34.1,
33.7, 33.0 (CH2), 31.7, 31.5, 30.9, 30.7 (CH2), 25.9
(CO2CH3), 24.1 (C(CH3)), 22.0 (d, JPC = 11.4 Hz,
CH3,Tol). 31P{1H} NMR (161.8 MHz, (CD3)2SO):
d = 49.3 (s). 31P{1H} NMR (161.8 MHz, THF): d = 48.3
(s). MS (FAB) m/z (%): 839.0 (14, [M+]), 606.9 (52,
[M+ꢀ[OAc + carbene]]), 570.0 (7, [Pd + 2*carbene]),
334.9 (8, [Pd + carbene]), 233.1 (100, [carbene]).
(b) A. Zapf, M. Beller, Top. Catal. 19 (2002) 101;
(c) A.F. Littke, G.C. Fu, Angew. Chem. 114 (2002) 4350;
Angew. Chem., Int. Ed. 41 (2002) 4176;
(d) W.A. Herrmann, second ed., in: B. Cornils, W.A. Herrmann
(Eds.), Applied Homogeneous Catalysis with Organometallic Com-
pounds, vol. 1, Wiley-VCH, Weinheim, 2002, p. 591;
(e) W.A. Herrmann, second ed., in: B. Cornils, W.A. Herrmann
(Eds.), Applied Homogeneous Catalysis with Organometallic Com-
pounds, vol. 2, Wiley-VCH, Weinheim, 2002, p. 775;
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Acknowledgement
¨
Helpful suggestions by Dr. K. Ofele are gratefully
acknowledged.
Angew. Chem., Int. Ed. 34 (1995) 2371;
(b) W.A. Herrmann, M. Elison, J. Fischer, C. Ko¨cher, G.R.J. Artus,
Chem. Eur. J. 2 (1996) 772;
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