Design of cationic mixed phosphine/n-heterocyclic carbene palladium(ii) π Allyl complexes as monoligated phosphine Pd(0) precatalysts: Synthesis, structural studies, catalysis, and reactivity

Article abstract of DOI:10.1021/om8008052

Compounds of general formula [Pd(L)(NHC)(L′)]BF₄ (where L = allyl or crotyl, NHC = tetrameth-ylimidazolin-2-ylidene (tmiy) or l,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene (dipdmiy), and L′ = tertiary phosphine) have been prepared from the parent [Pd(L)Cl(NHC)(L′)] complexes and fully characterized. A perpendicular orientation of the NHC is observed in the solid state (X-ray) and in solution (NOESY). The crystal structures of these complexes reveal the double-bond character of the allyl trans to the phosphine ligand; for example, [Pd(η³-C ₃H₅)(tmiy)(PPh₃)]BF₄ (4d) displays C-C distances of 1.198 A (trans to P) and 1.374 A (trans to the NHC). The NHC-Pd-allyl precatalysts are thought to generate monoligated phosphine-Pd(0) active species by reductive elimination of 2-allylimidazolium following η³-η¹ isomerization of the allyl group. This was observed in the case of [Pd(η³-C₃H ₅)(tmiy)(PCy₃)]BF₄ (4b), which successfully catalyzed the coupling of imidazolium salts with ethylene. The intriguing reactivity of 4b with Phi, yielding 2-phenylimidazolium selectively, is also reported.

Full text of DOI:10.1021/om8008052

Organometallics 2008, 27, 6507–6520
6507
Design of Cationic Mixed Phosphine/N-Heterocyclic Carbene
Palladium(II) π-Allyl Complexes as Monoligated Phosphine Pd(0)
Precatalysts: Synthesis, Structural Studies, Catalysis, and Reactivity
Adrien T. Normand, Andreas Stasch, Li-Ling Ooi, and Kingsley J. Cavell*
School of Chemistry, Main Building, Cardiff UniVersity, Park Place, Cardiff, Wales, U.K., CF10 3AT
ReceiVed August 19, 2008
Compounds of general formula [Pd(L)(NHC)(L′)]BF4 (where L ) allyl or crotyl, NHC ) tetrameth-
ylimidazolin-2-ylidene (tmiy) or 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene (dipdmiy), and L′ )
tertiary phosphine) have been prepared from the parent [Pd(L)Cl(NHC)(L′)] complexes and fully
characterized. A perpendicular orientation of the NHC is observed in the solid state (X-ray) and in solution
(NOESY). The crystal structures of these complexes reveal the double-bond character of the allyl trans
to the phosphine ligand; for example, [Pd(η3-C3H5)(tmiy)(PPh3)]BF4 (4d) displays C-C distances of
1.198 Å (trans to P) and 1.374 Å (trans to the NHC). The NHC-Pd-allyl precatalysts are thought to
generate monoligated phosphine-Pd(0) active species by reductive elimination of 2-allylimidazolium
following η3-η1 isomerization of the allyl group. This was observed in the case of [Pd(η3-
C3H5)(tmiy)(PCy3)]BF4 (4b), which successfully catalyzed the coupling of imidazolium salts with ethylene.
The intriguing reactivity of 4b with PhI, yielding 2-phenylimidazolium selectively, is also reported.
Scheme 1. η3-η1-η3 Rearrangement in Pd(II) Complexes
Introduction
Palladium(II) π-allyl complexes have attracted considerable
attention over the years,1-9 mainly due to their reactivity toward
nucleophiles, which makes those complexes excellent catalysts
for the so-called Tsuji-Trost allylic alkylation.10-23 Transition
metal allyl complexes can exist in two coordination modes, η1
(anionic, 2e donor ligand) and η3 (mixed, 4e ligand). An
interesting feature of Pd-allyl complexes is their tendency to
undergo η3-η1-η3 rearrangements (Scheme 1):
This behavior can be observed directly by NOESY spectrosco-
py.9,15,18,24-28 Allyl decoordination occurs under steric or
electronic control and may happen exclusively trans to either
L1 or L2. It is then followed by rotation around either the Pd-C
or the C-C bond of the allyl.9,16,17,25,26
Upon switching from η3 to η1 coordination, the allyl ligand
is analogous to a σ-alkyl group, and the decomposition of Pd(II)-
alkyl-NHC (NHC) N-heterocyclic carbene) complexes by
reductive elimination is well documented.29-36 Thus, it was
anticipated that a Pd(II)-allyl-NHC complex (1, Scheme 2)
containing a tertiary phosphine ligand could reductively elimi-
nate 2-propenylimidazolium to yield 2, a “monoligated”37
phosphine-Pd(0) complex. Monoligated Pd(0) species are
believed to be active catalysts in a number of Pd-catalyzed
* Corresponding author. E-mail: cavellkj@cf.ac.uk.
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2008 American Chemical Society
Publication on Web 11/11/2008

6508 Organometallics, Vol. 27, No. 24, 2008
Normand et al.
Suzuki-Miyaura and Buchwald-Hartwig coupling.47,48,54-58
Nolan and Beller also reported the use of such complexes in
butadiene telomerization,40,55 and a number of donor-function-
alized NHC Pd-allyl compounds have been applied to allylic
alkylation, either as preformed59,60 or in situ59,61,62 catalysts.
Other examples have been reported by Porschke,7,8 Pregosin,9
and Li63 (structural studies) and Wang (Suzuki coupling).64
When we initiated our studies on compounds of type 1, there
was no reported example of mixed phosphine-NHC cationic
Pd(II) complexes. Since then, Danopoulos,65 Jarvo,66 and
Visentin67 have reported related complexes in which the
phosphine and the NHC form a chelate ring, thus preventing
reductive elimination of 2-allylimidazolium.33 In addition Ro-
land68 and Liu69 have now reported in situ catalysts probably
involving a complex of type 1.
Scheme 2.
Hypothetical Reductive Elimination of
2-Propenylimidazolium from a Pd-π-allyl Complex Following
Η3-η1 Rearrangement
In this paper we present a general synthetic route for a new
family of Pd-allyl complexes containing both a phosphine and
a carbene ligand, and we report some aspects of their solid-
state and solution structures investigated by X-ray diffraction
and 2D NMR (HSQC and NOESY). A range of complexes with
a variety of different phosphines, carbenes, and allylic groups
have been investigated. Since all previously reported examples
of Pd-NHC-π-allyl complexes were found to be stable toward
reductive elimination of 2-allylimidazolium, a consequential
target of this study was to attempt to determine if our compounds
showed evidence of η3-η1-η3 rearrangement. Preliminary
investigations relating to the catalytic activity of mixed ligand
complex [Pd(η3-C3H5)(tmiy)(PCy3)]BF4 (4b) in the Pd-catalyzed
coupling of azolium salts with olefins have demonstrated the
formation of L-Pd(0) active species via the reductive elimination
of 2-propenylimidazolium following ethylene-promoted η3-η1
allyl isomerization. Novel studies, aimed at trapping L-Pd(0)
with PhI, yielded the clean formation of 2-phenylimidazolium,
highlighting the interesting reactivity of these mixed-ligand
systems.
reactions, and the design of precatalysts able to effectively
generate “Pd(0)-L” is currently an active research area.38-53
NHC-containing Pd(II) π-allyl complexes have been known
for some time. They have mainly been developed by Nolan as
cross-coupling catalysts, showing excellent catalytic activity in
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Monoligated Phosphine Pd(0) Precatalysts
Organometallics, Vol. 27, No. 24, 2008 6509
Scheme 4. Synthesis of [Pd(π-allyl)Cl(NHC)]
Scheme 3. Possible Routes for the Synthesis of Compounds
of General Formula [Pd(π-allyl)(NHC)(L)]BF4
Scheme 5. Initial Attempted Synthesis of [Pd(π-allyl)(NH-
C)(L)]BF4 from [Pd(π-allyl)Cl(NHC)]
The intermediate chloro complexes have previously been
isolated as air-stable solids for a variety of phosphines and
carbenes.1,7,55,70 With this general scheme as a guide, a range
of ligands (allyl, NHC, and phosphine) were identified (Figure
1).
Surprisingly, it was not possible to obtain complexes
7a-9a pure, as the reactions invariably resulted in a mixture
of products.77 Nolan47 and others7,8,62 have used a similar
procedure to prepare compounds with bulky NHCs. However,
in our case, the NHCs are both less bulky and more basic,
which might account for the multiple side reactions we
observed.
The NHCs investigated in this study were selected because
of their low steric bulk compared to IMes or IPr. This feature
was expected to increase the propensity of the final Pd(II) π-allyl
complexes to reductively eliminate 2-allylimidazolium salt.34
A range of commercially available phosphines with a variety
of stereoelectronic properties were also selected. Tolman’s
electronic (ν) and cone angle (θ) parameters for phosphines are
useful descriptors of their properties.71 From Tolman’s param-
eters PEt3 is the least bulky of the selected ligands, while PCy3
is the bulkiest. The phosphines PPh3 and PCy3, which are widely
used in catalysis,38,72-75 are the least and the most electron-
donating ligands, respectively.76
The synthesis of the desired mixed-ligand, cationic com-
plexes from complexes 4a-6a was then attempted (Sch-
eme 5).
Initial attempts to generate the desired compounds used
AgBF4 in the presence of the selected phosphine (Scheme
5). This led to ligand scrambling, generating unwanted bis-
carbene cationic complexes78 that could not be readily
separated from the mixed phosphine-carbene complexes. A
few reports have previously appeared in the literature on the
unexpected reactivity of silver carbene transfer agents.
Porschke reported the synthesis of NHC-Pd π-allyl complexes
Following route A, compounds 4a, 5a, and 6a were obtained
as air-stable yellow solids slowly decomposing over time at
room temperature (Scheme 4; 6a and 5a are stable over weeks
in the solid state, whereas 4a decomposes to Pd black in one
week).
-
containing weakly coordinating ligands such as BF4 and
TfO- from the corresponding chloro precursors.8 The authors
also found that the NHC in the chloro complexes reacted
with an excess of Ag(I) salt to give [Ag(NHC)(Y)] (where
Y ) BF4). The steric bulk of the NHCs employed in their
study apparently prevented the formation of cationic bis-
carbene complexes, but it is likely that in the present work
the formation of a silver-NHC complex would be followed
by carbene transfer to Pd.
(70) DiRenzo, G. M.; White, P. S.; Brookhart, M. J. Am. Chem. Soc.
1996, 118, 6225–6234.
(71) Tolman, C. A. Chem. ReV. 1977, 77, 313–348.
(72) Hills, I. D.; Netherton, M. R.; Fu, G. C. Angew. Chem., Int. Ed.
2003, 42, 5749–5752.
(73) Netherton, M. R.; Fu, G. C. Org. Lett. 2001, 3, 4295–4298.
(74) Kudo, N.; Perseghini, M.; Fu, G. C. Angew. Chem., Int. Ed. 2006,
45, 1282–1284.
(75) Netherton, M. R.; Dai, C.; Neuschutz, K.; Fu, G. C. J. Am. Chem.
Soc. 2001, 123, 10099–10100.
(76) A Tolman map of the ligands in this work can be found in the
Supporting Information.
(77) However, an impure sample of 7a was successfully recrystallized
from DCM/hexane on a small scale, and crystals suitable for X-ray
diffraction were obtained.
(78) Identified on the basis of 1H and 31P NMR spectroscopy and ESI-
MS.
Figure 1. Selected ligands.

6510 Organometallics, Vol. 27, No. 24, 2008
Normand et al.
Figure 2. Compounds of general formula [Pd(π-allyl)(NHC)(PR3)]BF4 obtained in this study.
Scheme 6. Synthesis of [Pd(π-allyl)Cl(PCy3)]
Subsequently, using NaBF4 instead of AgBF4 to abstract the
halide afforded the desired cationic compounds 4b-6d (Figure
2) in reasonable yields, without generating any of the biscarbene
Figure 3. Designation of H and C atoms in compounds of general
formula [Pd(π-allyl)(NHC)(PR3)]BF4.
complex.79
Thus, route A is a robust synthetic procedure for a wide range
of phosphine ligands. Route B, which would theoretically allow
for more diversity in the NHC (once a particular phosphine has
been introduced, e.g., PCy3), turned out to be impractical for
several reasons, notably the enhanced reactivity of NHCs toward
[Pd(π-allyl)Cl(PCy3)] complexes 1a-3a, which were obtained
by a modification of existing procedures,70,80 Scheme 6, and
the lower lability of the chloro ligand (necessitating the use of
AgBF4, which in turns lead to NHC scrambling). In all cases
multiple side products were obtained, rendering the purification
extremely difficult. We could obtain only complex 2b (R1) Me,
R2 ) H, NHC ) tmiy, PR3 ) PCy3, Figure 2) using this route.
Atoms in the target cationic compounds are designated
according to Figure 3. In the case of neutral compounds of
general formula [Pd(η3-C3H5)Cl(L)], the carbon atom trans to
Cl is referred to as CCl, and the carbon atom trans to L is referred
to as CL.
Figure 4. POV-Ray projections of neutral complexes 4a and 7a.82
tions of representative compounds are presented in Figures 4
and 5. Selected bond lengths and angles are presented in Tables
1-4. (Most of the X-ray data, for neutral compounds 2a-7a,
are presented in the Supporting Information, in Tables S1-S8,
where CIF files and POV-Ray projections can also be found.)
The more compact parent allyl group η3-C3H5 is disordered
(disorder was refined anisotropically), with the notable exception
of 4a. The crotyl ligand in 2a is also disordered (refined
anisotropically). The unit cells of two complexes bearing a tmiy
ligand (2b and 4b) contain two independent molecules. Least-
square planes were calculated for the allyl ligand,83 the mean
X-ray Diffraction Studies. For the majority of neutral and
cationic compounds, crystals suitable for X-ray diffraction were
grown by slow evaporation of CH2Cl2 solutions of the com-
plexes into hexane, or diffusion of Et2O into THF solutions of
the compounds.81 The structures of these crystals were eluci-
dated by single-crystal X-ray diffraction, and POV-Ray projec-
(79) The synthesis of known [Pd(η3-C3H5)(PCy3)2]BF4 from 5a was also
attempted, but the reaction mainly yielded tricyclohexylphosphonium allyl
cation and almost no desired compound. This is most probably the result
of nucleophilic attack of free PCy3 onto the allyl ligand and indicates that
NHC ligands are probably far better at labilizing the chloro ligand (and
slow down the nucleophilic attack on the allyl).
(80) Reference deleted in revision.
(81) Some compounds did not crystallize; others gave thin microcrystals
unsuitable for X-ray crystallography.
(82) Solvent molecules as well as hydrogen atoms and, in the case of
cationic complexes, BF4 anions have been omitted from these projections
for clarity. Thermal ellipsoids are drawn at the 50% probability level.
(83) Comprising the three carbon atoms coordinated to Pd.

Monoligated Phosphine Pd(0) Precatalysts
Organometallics, Vol. 27, No. 24, 2008 6511
As expected, there are noticeable differences in the geometries
of neutral [Pd(π-allyl)Cl(L)] complexes and their cationic [Pd(π-
allyl)(L)(L′)] counterparts, although both families show a
number of common features. For example, Pd-CNHC distances
(2.04 Å on average, Tables 1 and 2), N1-CNHC, N2-CNHC (1.35
Å on average Tables 1 and 3) and angles N1-CNHC-N2 (105.5°
on average, Tables S4 and S8) are almost equal within standard
deviation limits. On the other hand, Pd-PR3 distances are
shorter for cationic complexess2.31 Å on average (Table 2),
compared to 2.37 Å average for neutral complexes (Table
1)sindicating that phosphine coordination is predominantly
affected by the nature (neutral or cationic) of the Pd complex,
perhaps to compensate for the lower electronic density on Pd.
The main structural features of the cationic complexes are
as follows:
Figure 5. POV-Ray projections of cationic complexes 4d and 5b.
coordination plane,84 and the NHC ring.85 Interplanar angles
Φ1 (carbene twist angle) and Φ2 between those planes were
calculated, as shown in Figure 6.86
Neutral complexes generally display little variation in their
geometries. The main structural features of these compounds
are as follows:
• A pseudo-square-planar geometry with Cl-Pd-L angles
around 90°. Only 7a differs significantly from this arrangement,
with a Cl-Pd-L angle of 105.2° (Table S3).
• A Φ2 value of about 65° with respect to the coordination
plane, and the plane of the three carbon atoms of the allyl group
forming a CCl-Cmeso-CL angle of 120° on average (Table S4,
in the Supporting Information).
• A roughly perpendicular orientation of the NHC with respect
to the coordination plane, most probably to minimize steric
interactions. This tendency increases both with the size of the
NHC and with that of the π-allyl. Thus, Φ1 values range from
60.1(1)° (4a) to 89.2(1)° (7a) (Table S4).87
• Distances between Pd and the NHC ligands are much shorter
than distances between Pd and the phosphines (on average 2.04
Å versu 2.30 Å, Table 1), reflecting the higher covalent radius
of phosphorus (1.07 Å) compared to that of carbon (0.73 Å)88
and the stronger metal-NHC bond.
• Distances between Pd and the carbon atom trans to the NHC
or the phosphine (Pd-CL ) 2.20 Å on average for NHCs and
2.19 Å for PCy3) are longer than distances between Pd and the
carbon atom trans to Cl (Pd-CX), owing to the strong electron-
donating ability of NHCs and PCy3. Likewise, the allyl C-C
bond trans to L (L) NHC or PCy3) is shorter than the C-C
bond trans to Cl in any given complex (Table 1). This can be
rationalized by considering that the allyl H2C-CH moiety trans
to a strong σ-donor ligand such as PCy3 or an NHC should be
more olefin-like (i.e., better π acceptor) than an allyl trans to a
weaker donor such as Cl.
• Finally, there is no significant variation in the C-N bond
distance of NHCs, with an average value of 1.35 Å (Table S2).
This parameter is expected to vary depending on the degree of
back-donation from Pd to the NHC (more back-donation should
decrease the “push” mesomeric effect in the NHC and lengthen
the C-N distance); therefore, it seems that all complexes display
a similar level of back-donation.
• A pseudo-square-planar geometry, with a narrower Cp-Pd--
Cc value (66° on average, Table S7) compared to the three other
angles around Pd.
• A Φ2 angle of just above 65° is generally observed (Table
4), with the notable exceptions of 5b (59.8°) and 4d (39.5°).
• As observed for neutral complexes, CX-Cmeso-CL angles
are close to 120° on average (Table 4). Some structures (4d,
138.3°; 5b, 131.3°; and 5c, 127.8°) deviate significantly from
this value. There is no apparent trend in these values (although
the crotyl group displays a narrower angle than the allyl).
• Compared to neutral complexes, the perpendicular orienta-
tion of the NHC ligand is even more pronounced at 85° on
average for Φ1, most probably to accommodate the larger
phosphine ligand. This geometry is likely to be the one adopted
in solution, as indicated by NOESY studies (Vide infra).
Complex 4d displays a reduced value for Φ1, at 71.5°, probably
a result of reduced congestion within the complex.
• In the cationic complexes C-C bonds trans to NHCs
(CC-Cmeso) are longer than C-C bonds trans to phosphines
(CP-Cmeso); see Table 3. This does not seem to be due to purely
electronic reasons, since CP-Cmeso is shorter in 4d (1.198 Å)
than in 4e (1.247 Å), despite PBz3 being a stronger donor than
PPh3. A cis steric effect cannot be invoked either, since
CC-Cmeso is longer in 4b (1.426 Å) than in 4d (1.374 Å), despite
the bulkier nature of PCy3 compared to PPh3. A more subtle
interplay of factors is probably responsible; nevertheless it is
interesting to note that it confers a marked double-bond character
to the part of the allyl trans to the phosphine ligand.
• Finally, Pd-CC distances appear to correlate well with the
cone angle (θ) of the phosphine ligand, highlighting the steric
influence of the phosphine. For example, Pd-CC distances
decrease in the order PCy3 (θ ) 170°), PBz3 (θ ) 165°), and
PPh3 (θ ) 145°) for complexes 4b (2.220 Å), 4e (2.181 Å),
and 4d (2.168 Å).
Solution Structure. The assignment of chemical shifts for
[Pd(π-allyl)(NHC)(PR3)]BF4 complexes was obtained in part
by the combination of 1D 1H, 13C, and 31P NMR spectroscopy.
Relevant chemical shifts are presented in Tables 5 and 6. Atoms
are designated according to Figure 3, as previously indicated.
3
2
The presence of a phosphine ligand leads to JHP and JCP
coupling in H and {1H}13C spectra for hydrogen and carbon
1
(84) Comprising Pd and the four atoms sitting at the corners of the
pseudo-square.
(85) Comprising the three carbon and two nitrogen atoms of the
imidazolin-2-ylidene ring.
(86) These angles were calculated with the PLATON suite of programs
using the LSPL and CALC GEOM commands.
(87) Cl is relatively small, but the fact that smaller NHCs significantly
deviate from this orientation points to a steric rather than electronic
preference.
atoms trans to P. This feature of phosphine-containing Pd(II)
π-allyl complexes has been reported previously.1 In addition,
3JHH coupling between Hmeso and Hanti allows the complete
assignment of chemical shifts of carbon and hydrogen atoms
in π-allyl ligands.
Overall, there is no clear-cut correlation between Tolman
parameters (θ and ν) of the phosphine ligands and NMR
chemical shifts in the cationic complexes. In particular, 13C
(88) Cordero, B.; Go´mez, V.; Platero-Prats, A. E.; Reve´s, M.; Echeverr´ıa,
J.; Cremades, E.; Barraga´n, F.; Alvarez, S. Dalton Trans. 2008, 2832–2838.

6512 Organometallics, Vol. 27, No. 24, 2008
Normand et al.
Table 1. Selected Bond Distances (Å) for Neutral Complexes of General Formula [Pd(π-allyl)Cl(L)]
allyl ) η3-C4H7
L ) PCy3
2a
allyl ) η3-C9H9
L ) PCy3
3a
allyl ) η3-C3H5
L ) tmiy
4a
allyl ) η3-C3H5
L ) dipdmiy
5a
allyl ) η3-C9H9
L ) dipdmiy
7a
Pd-L
2.302(1)
2.362(1)
2.177(7)
2.121(12)
2.110(7)
1.404(14)
1.367(14)
2.299(1)
2.373(1)
2.320(2)
2.161(2)
2.107(2)
1.419(3)
1.386(3)
2.046(3)
2.399(1)
2.200(3)
2.131(3)
2.107(3)
1.401(5)
1.349(5)
2.042(4)
2.375(1)
2.199(5)
2.140(8)
2.097(4)
1.469(11)
1.236(10)
2.043(2)
2.370(1)
2.202(2)
2.148(2)
2.130(2)
1.429(3)
1.386(3)
Pd-Cl
Pd-CL
Pd-Cmeso
Pd-CCl
CCl-Cmeso
CL-Cmeso
Figure 6. Least-squares planes calculated to determine acute angles Φ1 and Φ2 between the carbene ring (blue) or the allyl group (black)
and the mean coordination plane (gold).
Table 2. Bond Distances (Å) around Pd for Complexes of General Formula [Pd(π-allyl)(NHC)(PR3)]BF4
compound
Pd-CNHC
Pd-P
Pd-Cc
Pd-Cmeso
Pd-CP
[Pd(η3-C3H5)(tmiy)(PCy3)]+4b
[Pd(η3-C3H5)(tmiy)(PPh3)]+ 4d
[Pdη3-C3H5)(tmiy)(PBz3)]+ 4e
[Pd(η3-C3H5)(dipdmiy)(PCy3)]+ 5b
[Pd(η3-C3H5)(dipdmiy)P(Ar)3]+ 5ca
[Pd(η3-C4H7)(tmiy)(PCy3)]+ 2b
[Pd(η3-C4H7)(dipdmiy)(PCy3)]+ 6b
[Pd(η3-C4H7)(dipdmiy)(PEt3)]+ 6d
2.035(3)
2.056(3)
2.057(3)
2.062(2)
2.050(5)
2.045(2)
2.054(6)
2.047(6)
2.328(1)
2.308(1)
2.307(1)
2.317(1)
2.300(1)
2.315(1)
2.319(2)
2.297(2)
2.220(10)
2.168(4)
2.181(4)
2.182(3)
2.165(6)
2.176(2)
2.185(6)
2.153(7)
2.163(6)
2.177(14)
2.151(10)
2.131(7)
2.099(10)
2.180(2)
2.168(7)
2.141(7)
2.197(12)
2.167(6)
2.181(4)
2.178(3)
2.147(6)
2.167(3)
2.155(7)
2.158(8)
a Ar ) p-C6H4OCH3.
Table 3. Other Bond Distance (Å) for Complexes of General Formula [Pd(π-allyl)(NHC)(PR3)]BF4
compound
CP-Cmeso
CC-Cmeso
N1-CNHC
N2-CNHC
[Pd(η3-C3H5)(tmiy)(PCy3)]+ 4b
[Pd(η3-C3H5)(tmiy)(PPh3)]+ 4d
[Pd(η3-C3H5)(tmiy)(PBz3)]+ 4e
[Pd(η3-C3H5)(dipdmiy)(PCy3)]+ 5b
[Pd(η3-C3H5)(dipdmiy)P(Ar)3]+ 5ca
[Pd(η3-C4H7)(tmiy)(PCy3)]+ 2b
[Pd(η3-C4H7)(dipdmiy)(PCy3)]+ 6b
[Pd(η3-C4H7)(dipdmiy)(PEt3)]+ 6d
1.403(11)
1.198(16)
1.247(13)
1.297(8)
1.275(14)
1.405(4)
1.426(10)
1.374(16)
1.524(14)
1.382(8)
1.421(14)
1.410(3)
1.353(4)
1.351(5)
1.336(5)
1.349(3)
1.346(6)
1.356(3)
1.363(9)
1.379(8)
1.354(4)
1.355(4)
1.351(4)
1.353(3)
1.348(6)
1.351(3)
1.367(8)
1.334(9)
1.385(10)
1.394(10)
1.397(10)
1.382(11)
a Ar ) p-C6H4OCH3.
Table 4. Other Angles (deg) for Complexes of General Formula [Pd(π-allyl)(NHC)(PR3)]BF4
compound
Cp-Cmeso-Cc
N1-CNHC-N2
Φ1
Φ2
[Pd(η3-C3H5)(tmiy)(PCy3)]+ 4b
[Pd(η3-C3H5)(tmiy)(PPh3)]+ 4d
[Pd(η3-C3H5)(tmiy)(PBz3)]+ 4e
[Pd(η3-C3H5)(dipdmiy)(PCy3)]+ 5b
[Pd(η3-C3H5)(dipdmiy)P(Ar)3]+ 5ca
[Pd(η3-C4H7)(tmiy)(PCy3)]+ 2b
[Pd(η3-C4H7)(dipdmiy)(PCy3)]+ 6b
[Pd(η3-C4H7)(dipdmiy)(PEt3)]+ 6d
121.3(1)
138.3(1)
120.7(9)
131.3(6)
127.8(1)
117.1(2)
118.2(6)
118.2(7)
104.8(3)
104.2(3)
106.0(3)
105.7(2)
105.7(4)
104.5(2)
104.6(6)
104.8(5)
89.6(2)
71.5(2)
83.3(2)
80.0(1)
84.2(2)
83.3(1)
80.6(3)
84.3(3)
68.5(1)
39.5(2)
69.0(12)
59.8(7)
65.3(1)
68.5(3)
67.4(8)
68.6(8)
a Ar ) p-C6H4OCH3.
NMR shifts of the coordinating carbon of the NHC are relatively
insensitive to the nature of the phosphine, ranging from 170.8
ppm (5c) to 174.3 ppm (6b). Also, 31P NMR shifts do not vary
significantly with changes in the allyl or NHC ligands, although
marked differences are observed between different phosphines
(e.g., the chemical shifts for PCy3 complexes range from 41.39
ppm (5b) to 43.17 ppm (2b), whereas those for PPh3 complexes
range from 19.99 ppm (5d) to 22.36 (4d)). Interestingly,
however, the chemical shift of the π-allyl carbon atom trans to
the NHC (Table 7) is quite sensitive to which phosphine is
present, ranging from 60.8 ppm (5b) to 69.9 ppm (5c), while
the chemical shifts of the carbon atom trans to PR3 ranges only
from 64.8 ppm (6c) to 67.1 ppm (5e), suggesting that the impact
of the phosphine is largely steric rather than electronic. However,

Monoligated Phosphine Pd(0) Precatalysts
Organometallics, Vol. 27, No. 24, 2008 6513
1
Table 5. Selected H NMR Shifts (δ in ppm) for
discrepancies between observed and expected catalytic activity
(based on Tolman parameters).89
[Pd(π-allyl)(NHC)(PR3)]BF4 Complexes (in d2-DCM)
compound
R1
Hsp
Hsc
3.87
Hap (JHP in Hz)
Hac
2.49
We note that CH3 groups on the N-iPr wingtips of dipdmiy
(or those attached to the carbene ring) are nonequivalent, an
observation that can be explained by the absence of free rotation
around the Pd-CNHC bond caused by the presence of phosphine
cis to the carbene. Therefore, NOESY experiments were carried
out in order to assign the chemical shifts of the nonequivalent
carbene hydrogens. Work by Pregosin has shown that NOESY
can be successfully applied to Pd(II) π-allyl complexes to gain
structural information, and they observed chemical exchange
occurring at the allyl ligand.6,9,16,18,24-26,28 An elegant example
of the application of NOESY to the observation of dynamic
allyl exchange in a chiral bis-phosphine complex is shown in
Figure 7. Diastereoisomers A and B are both present in solution,
and negative-phase cross-peaks between these compounds reveal
selective exchange between allyl hydrogens trans to PPh2, (i.e.,
decoordination occurs under steric control exclusively cis to the
bulky PCy2 moiety).
2b
4b
4c
4d
4e
4f
5b
5c
5d
5e
6b
6c
6d
CH3 1.77 3.84
2.59 (8.8)
2.80 (8.9)
3.06 (NA)
3.00 (10.3)
H 5.24
H 5.58
H 5.52
H 4.99
H 5.31
H 5.20
H 5.53
H 5.50
H 5.28
4.07
4.29
4.22
3.94
4.12
4.10
3.99
3.92
2.58
2.91
2.85
2.08
2.66
2.58
2.87
2.84
2.65
2.47
3.04-3.14a 2.65 (10.3)
3.93
2.83 (9.4)
4.09-4.15a 4.09-4.15a 2.72 (8.8)
4.22-4.30a 3.76
2.98 (8.8)
2.94 (9.9)
2.75 (9.5)
4.21
4.13
3.71
3.90
CH3 1.74 3.87-3.91a 3.87-3.91a 2.62 (8.8)
CH3 1.87 3.86
CH3 1.75 3.90
3.43
3.63
2.77-2.85 (NA)b 2.77-2.85
2.63 (9.5) 2.52
a Overlap with other peaks. b Overlap with Hac prevented the deter-
mination of JHP
.
Table 6. Selected 13C and 31P NMR Shifts (δ in ppm) for
[Pd(π-allyl)(NHC)(PR3)]BF4 Complexes (in d2-DCM)
Cmeso
CP
CNHC
compound (JCP in Hz) (JCP in Hz)
CC
(JCP in Hz)
P
X-ray diffraction studies (Vide supra) show that NHCs adopt
a roughly perpendicular orientation with respect to the coordina-
tion plane in the solid state. It was thus interesting to confirm
this preference in solution. The NOESY spectra of complexes
bearing either a phosphine with alkyl substituents or a more
compact NHC (dmiy, tmiy) did not show any cross-peak
between the phosphine and the NHC, thus precluding absolute
assignment of NMR signals. However, complexes 5c, 5d, and
6c, which bear a dipdmiy ligand and a phosphine ligand with
aromatic substituents, were investigated. Atoms in 5c, 5d, and
6c are designated as shown in Figure 8.
2b
4b
4c
4d
4e
4f
5b
5c
5d
5e
6b
6c
6d
134.1 (4.0)
119.9 (4.5)
121.6 (5.5)
121.4 (5.5)
121.2 (6.0)
121.1 (5.0)
119.4 (4.0)
121.0 (6.0)
120.8 (5.0)
120.6 (5.0)
133.7 (4.0)
135.6 (5.0)
135.0 (5.0)
66.1 (29.0)
66.5 (28.0)
65.8 (31.0)
65.2 (31.0)
66.0 (30.0)
66.1 (29.0)
66.7 (28.0)
66.2 (31.0)
65.7 (31.0)
67.1 (30.0)
66.8 (29.0)
64.8 (32.0)
66.5 (31.0)
61.2
174.2 (16.0) 43.17
61.3a 173.2 (16.0) 42.01
68.9
68.1
64.5
61.7
60.8
171.9 (17.0) 26.25
172.8 (21.5) 22.36
171.8 (2.0)
26.09
172.4 (19.0) 20.41
173.4 (15.0) 41.39
69.9a 170.8 (19.0) 23.88
69.1
61.5
60.9
68.8
61.3
171.3 (17.0) 19.99
171.2 (19.0) 20.41
174.3 (16.0) 42.40
171.2 (18.0) 21.89
172.2 (19.0) 21.59
a A very small P-C coupling was seen in the 13C NMR spectrum.
NHC ligands can be divided into four quadrants: above and
under the coordination plane (a and u), toward or away from
palladium (in and out). Hydrogens on the allyl are assigned as
before, and phosphine hydrogens are designated according to
their position relative to the phosphorus atom (ortho, o; meta,
m; para, p).
Scheme 7. Direct Coupling of Azolium Salts with Olefins
Using Ni or Pd Catalysts
Figure 9 shows the NOESY spectrum obtained for 6c. The
cross-peaks are circled and numbered from 1 to 23. Tables
summarizing the data can be found in the Supporting Informa-
tion together with the full spectra for 5c, 5d, and 6c.
The relative u/a assignment of NMR signals for 6c (Table
S11) is given by cross-peaks 6, 7, 19, and 23 between u protons
(Hu, Hiu, Houtu, Hinu). Absolute assignment stems from key
interligand cross-peaks 1 (protons in and Ho), 9 (Hsp/Houta), 14
(Hap/Houtu), 21 (Houta/crotyl CH3), and 20 (Hina/crotyl CH3). Ho
interacts with both in methyls, indicating that dipdmiy retains
a roughly perpendicular orientation in solution.
the fact that 5b (containing PCy3) and 5e (PEt3) have very
similar chemical shifts for Cc indicates that steric effects alone
cannot explain the range of chemical shifts.
It has previously been suggested that the 13C NMR chemical
shift of π-allyl ligands is an indicator of electrophilicity, with
downfield carbons being more electrophilic.1 We find that for
complexes with trialkylphosphines (2b, 4b, 4e, 4f, 5b, 5e, 6b,
and 6d), the CC carbon trans to the NHC is upfield compared
to the CP carbon trans to the phosphine (61.0 ppm compared to
66.5 ppm on average, Table 6), indicating that CP is the more
electrophilic carbon. This pattern is reversed for phosphines with
aromatic substituents (4c, 4d, 5c, 5d, and 6c), and CC (69 ppm
on average) is downfield compared to CP (65.5 ppm on average).
Complex 4e, bearing benzyl groups, falls nicely between these
extremes (64.5 ppm for CC and 66.0 ppm for CP). These
observations could be important for ligand design in allylic
alkylation, since enantioselectivity has been shown to arise from
electronic discrimination in the case of P,N ligands.21,23 It is
also evident that trying to define phosphines by their Tolman
parameters alone and relating these features to catalytic activity
is not reliable. Studies by Orpen have previously shown
Complexes 5c and 5d (Tables S9 and S10) have essentially
the same NOESY pattern as 6c. The only significant differences
are the absence of cross-peaks between R1 (Hmeso) and Hina and
Houta, as a consequence of replacing CH3 by H, and the absence
of cross-peaks between Ho and Hina and between Hsp and Houta
.
Finally, HSQC spectra (see Supporting Information) allow
1
correlation of H and 13C NMR chemical shifts. Thus, the
combination of HSQC and phase-sensitive NOESY allows
1
complete H and 13C NMR assignments for 5c, 5d, and 6c.
As mentioned above, NOESY can be applied to the observa-
tion of chemical exchange. However, only extremely weak
cross-peaks for the allyl ligand are observed here; therefore, it
is difficult to draw any definitive conclusions on possible allyl
(89) Clarke, M. L.; Ellis, D.; Mason, K. L.; Orpen, A. G.; Pringle, P. G.;
Wingad, R. L.; Zaher, D. A.; Baker, R. T. Dalton Trans. 2005, 1294–1300.

6514 Organometallics, Vol. 27, No. 24, 2008
Normand et al.
Figure 7. Dynamic behavior of a π-allyl bis-phosphine Pd(II) complex observed by NOESY.25
activity. Thus, it appears that the activity of 4b arises from its
unique design, rather than its cationic nature or the specific
presence of the allyl ligand. This, in turn, suggests that this
complex may act as a source of monoligated PCy3-Pd(0),
possibly via reductive elimination of the NHC.
To probe this concept more thoroughly, and to shed more
light on the activation of 4b, we undertook a series of
experiments aimed at detecting the possible products resulting
from reductive elimination (i.e., 2-propenylimidazolium and the
PCy3-Pd(0) fragment). Thus, 4b was heated to 80 °C in DMF
for 5 h in the presence of phenyl iodide and ethylene and in the
absence of additive (Scheme 8). Reaction mixtures were
analyzed by H and 31P NMR and low-resolution ESI-MS.
1
Figure 8. Naming of atoms for complexes studied by NOESY.
ESI-MS analysis of the products from heating 4b alone
(without added reactants) confirmed the presence, albeit at trace
levels, of 2-propenylimidazolium.95 However, experiments
conducted in the presence of ethylene and phenyl iodide lead
to very different outcomes. In the presence of ethylene, the
solution turned brown very quickly and some Pd black was
observed. The 31P NMR was unchanged, although there was
isomerization.90 On the other hand, the absence of allyl exchange
in these complexes would be contrary to recent findings by
Pregosin et al. on [Pd(η3-C3H5)(X)(IPr)] complexes (X ) Cl,
Br, I, NCO, SCN, CN, OAc, OTf), wherein (except where X
) SCN or CN) allyl exchange was found to occur by selective
decoordination trans to X (i.e., under electronic control).
Compared to our experimental conditions (298 K, in CD2Cl2,
300 ms evolution time), Pregosin et al. used a substantially
longer evolution period (800 ms), which may account for the
different results. More detailed studies (e.g., investigating more
coordinating solvents such as d7-DMF or d3-MeCN, using higher
temperatures or longer evolution periods) are clearly warranted.
As physical measurements were inconclusive, indirect chemi-
cal methods were used to probe the likelihood of η3-η1-η3
isomerization and, hence, the validity of our approach to
generate monoligated Pd(0).
Catalysis and Reactivity. In the course of our studies on
the Ni-catalyzed coupling of azolium salts with olefins (Scheme
7),91-93 we also investigated a Pd-catalyzed version. It was
anticipated that Pd catalysts would provide better functional
group tolerance than their Ni counterparts, thus possibly
broadening the scope of this reaction.94
Screening in situ catalysts using Pd(dba)2 and various
phosphine and NHC ligands revealed that PCy3 was uniquely
effective in the catalysis (Table S12). Importantly, the use of a
2.1 PCy3/Pd ratio instead of 1.1 strongly inhibits catalyst activity,
pointing to a monoligated PCy3-Pd(0) catalyst. Therefore, the
use of 4b as a well-defined precatalyst was investigated.
The results in Table 7 clearly demonstrate that 4b is a more
effective catalyst than Pd(dba)2/PCy3 mixtures. Notably, com-
plexes 1a and 7a, which lack an NHC ligand, do not show any
1
significant background noise, but H NMR revealed a new set
of weak peaks (see Experimental Section), consistent with the
presence of about 10-15% of 2-propenylimidazolium salt. ESI-
MS showed two main sets of peaks corresponding to unreacted
4b and 2-propenylimidazolium salt. A likely explanation for
these observations is that ethylene coordination promoted the
conversion of the η3-allyl group into a η1-bonding mode, leading
to 2-propenylimidazolium salt elimination. Thus, the presence
of an olefin appears to favor the activation of 4b, indicating
the potential of this family of complexes in Pd-catalyzed
reactions, such as telomerization40,96 or the Heck reaction.97,98
Finally, in an attempt to trap the PCy3-Pd(0) fragment,
generated by thermal activation of 4b, we added PhI to the
system. Unexpectedly, the reaction generated 2-phenylimida-
zolium and tricyclohexylphosphine palladium allyl iodide (4g)
almost quantitatively. Complex 4g was prepared separately and
1
its identity confirmed by H and 31P NMR. The presence of
previously reported 2-phenyltetramethylimidazolium99 was also
1
confirmed by H NMR and ESI-MS (see Supporting Informa-
tion). The reaction is very clean, and on first consideration
appears to proceed via a Pd(II)/Pd(IV) sequence. However,
preliminary studies indicate that reaction occurs through the
activation of small amounts of 4b, via reductive elimination,
giving Pd(0), to which oxidative addition of PhI occurs; this is
(95) ESI-MS of 4b does not show the presence of 2-propenyltetram-
ethylimidazolium in the absence of heating; therefore its presence cannot
be attributed to MS-induced reductive elimination.
(96) Nielsen, D. J.; Cavell, K. J., Pd-NHC Complexes as Catalysts in
Telomerization and Aryl Amination Reactions. In N-Heterocyclic Carbenes
in Synthesis; Nolan, S. P., Ed.; Wiley-VCH Verlag GmbH & Co.: Weinheim,
2006; pp 73-102.
(97) Farina, V. AdV. Synth. Catal. 2004, 346, 1553–1582.
(98) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009–
3066.
(90) Some peaks are visible depending on the zoom applied to the
spectra, but they disappear when all the circled peaks are visible.
(91) Normand, A. T.; Yen, S. K.; Huynh, H. V.; Hor, T. S. A.; Cavell,
K. J. Organometallics 2008, 27, 3153–3160.
(92) Normand, A. T.; Hawkes, K. J.; Clement, N. D.; Cavell, K. J.;
Yates, B. F. Organometallics 2007, 26, 5352–5363.
(93) Clement, N. D.; Cavell, K. J. Angew. Chem., Int. Ed. 2004, 43,
3845–3847.
(94) Eventually, we did not find any benefit in using Pd catalysts. In
particular, isomerizable and/or electron-withdrawing olefins did not react.
(99) McGuinness, D. S.; Cavell, K. J.; Skelton, B. W.; White, A. H.
Organometallics 1999, 18, 1596–1605.

Monoligated Phosphine Pd(0) Precatalysts
Organometallics, Vol. 27, No. 24, 2008 6515
Figure 9. NOESY spectrum of 6c.
Table 7. Selected Results for the Pd-Catalyzed Alkylation of
[pmim]Br with Ethylenea
quite restricted, owing to the variable stability of the [Pd(π-
allyl)Cl(NHC)] templates. The structure of a number of these
compounds was investigated by X-ray crystallography and
NOESY, indicating that the carbene ligand adopts a roughly
perpendicular orientation with respect to the coordination plane,
both in solution and in the solid state. These compounds may
generate monoligated phosphine-Pd(0), as demonstrated in the
case of 4b. This complex was found to undergo reductive
elimination of 2-propenylimidazolium in the presence of eth-
ylene, and this activation process appears to be responsible for
the catalytic activity of 4b in the coupling of imidazolium salts
with ethylene. Finally, some intriguing reactivity was observed
in the case of compound 4b, notably its reaction with phenyl
iodide. Reductive elimination yielded 2-phenylimidazolium,
following a sequence probably involving monoligated Pd(0).
entry
catalyst
conv (%)
1
2
3
4
Pd(dba)2/PCy3 1:1
26
0
0
[Pd(η3-C3H5)Cl(PCy3)] 1a
[Pd(η3-C3H5)(MeCN)(PCy3)]BF4 7a
[Pd(η3-C3H5)(dmiy)(PCy3)]BF4 4b
81
a Reagents and conditions: 1-propyl-3-methylimidazolium bromide,
[pmim]Br, 0.73 mmol, [Pd] 5 mol %, DMF 3 mL, C2H4 1 bar, 80 °C,
24 h. Based on the average of two runs.
then followed by ligand exchange between the resulting Pd-
aryl species and 4b, yielding iodo complex 4g and a Pd-NHC-
aryl species that eventually undergoes reductive elimination to
form phenylimidazolium and Pd(0). Such Pd-based ligand
exchange processes are well documented,36,99-101 although they
are often overlooked in favor of mechanisms involving Pd(IV)
intermediates.102 The results of more detailed experimental and
DFT investigations are ongoing and will be reported in a
subsequent publication.
Experimental Section
General Procedures. All manipulations involving air-sensitive
compounds were performed under argon atmosphere, using standard
Schlenk line techniques or in a nitrogen atmosphere MBraun
UNILAB glovebox with less than 1 ppm water and O2 (where free
NHCs, phosphines, and Pd π-allyl dimers were stored). Solvents
were dried using appropriate drying agents (CaH2 for CH2Cl2,
sodium/benzophenone for THF, Et2O, and hexane). The following
compounds were prepared according to literature procedures:
[Ag(dmiy)2]2Ag4I6,103 tmiy and dipdmiy.104 [Pd(η3-C3H5)Cl]2,
[Pd(η3-C4H7)Cl]2, and [Pd(η3-C3H4C6H5)Cl]2 were prepared using
a slight modification of known literature procedures (using non-
degassed H2O as solvent and no carbon monoxide).4 NMR spectra
were recorded at 298 K on a Bruker Avance 500 MHz with a
multinuclear gradient probe. Chemical shift values are given relative
to residual solvent peak,105 i.e., for CD2Cl2 5.23 ppm for 1H NMR
and 54.00 ppm for 13C NMR. 31P chemical shifts are given relative
to H3PO4 (capillary tube filled with an aqueous solution of H3PO4
Conclusion
A new family of cationic [Pd(π-allyl)(NHC)(PR3)]BF4 com-
plexes containing an NHC, a π-bound allyl ligand, and a tertiary
phosphine has been reported. The range of phosphines that can
be incorporated into this type of complex appears to be virtually
unlimited. By contrast, the choice of allyl and NHC ligands is
(100) Ozawa, F.; Hidaka, T.; Yamamoto, T.; Yamamoto, A. J. Orga-
nomet. Chem. 1987, 330, 253–263.
(101) Ozawa, F.; Fujimori, M.; Yamamoto, T.; Yamamoto, A. Orga-
nometallics 1986, 5, 2144–2149.
(102) Cardenas, D. J.; Martin-Matute, B.; Echavarren, A. M. J. Am.
Chem. Soc. 2006, 128, 5033–5040.
(103) Chen, W.; Liu, F. J. Organomet. Chem. 2003, 673, 5–12.
(104) Kuhn, N.; Kratz, T. Synthesis 1993, 561–562.
(105) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997,
62, 7512–7515.

6516 Organometallics, Vol. 27, No. 24, 2008
Normand et al.
Scheme 8. Reactivity Studies on 4b
in CD2Cl2). NOESY spectra were recorded in degassed CD2Cl2 with
a gradient duration of 300 ms. ESI-MS were perfomed on a Waters
LCT Premier XE instrument, with a source temperature of 80 °C,
a desolvation temperature of 200 °C, a capillary voltage of 3500
V, and a cone voltage of 100 V. X-ray diffraction data were
obtained on a Kappa Nonius CCD diffractometer equipped with
an Oxford cryogenic system to maintain the crystals at 150 K.
Structure solution and refinement were performed by Dr. Andreas
Stasch and Dr. Li-Ling Ooi at Cardiff University. Microanalyses
were performed by Warwick Analytical Services.
Procedure for the Studies of the Activation of 4b. 4b (10 mg,
0.016 mmol) was dissolved in 1 mL of DMF. The appropriate
reagent was added (e.g., phenyl iodide, 2 equiv), and the reaction
mixture was heated to 80 °C under Ar or ethylene (1 bar). After
5 h, the solvent was removed in Vacuo, and the crude reaction
mixture was analyzed by 1H and 31P NMR spectroscopy and ESI-
MS. The reaction with ethylene yielded 10-15% (2-propenyl)-
tetramethylimidazolium tetrafluoroborate: 1H NMR (CD2Cl2, 500.13
MHz, 298 K): δ (ppm) 5.84 (m, 1H, CHCH2), 5.15 (d, 1H, CHCHH
(Z), 3J ) 12.5 Hz), 5.15 (d, 1H, CHCHH (E), 3J ) 17.2 Hz), 3.89
(m, 2H, CH2), 3.71 (s, 6H, NCH3), 2.23 (s, 6H, CCH3). ESIpos-MS
(MeCN): [M]+ found 165.1 (calc 165.14).
solid. The solid was rinsed with hexane. The collected mass was
986 mg (81%) and found identical to literature.70
Tricyclohexylphosphinepalladium cinnamyl chloride, 3a. Tri-
cyclohexylphosphine (PCy3; 832 mg, 2.97 mmol, 1.03 equiv) was
dissolved in 10 mL of DCM. This solution was canulated over 5
min to a solution of [Pd(η3-C4H6C6H5)Cl]2 (750 mg, 1.45 mmol,
0.5 equiv) in 10 mL of DCM. The solution became paler. When
the addition was complete, the solution was stirred 30 min,
evaporated under reduced pressure, and triturated with hexane to
afford a yellow solid. The solid was rinsed with hexane. The
collected mass was 1186 mg (75%) and found identical to
literature.70
Tetramethylimidazolin-2-ylidenepalladium Allyl Chloride,
4a. Tetramethylimidazolin-2-ylidene (tmiy; 182 mg, 1.47 mmol,
2.1 equiv) was dissolved in 5 mL of THF. This solution was
syringed into a 5 mL THF suspension of [Pd(η3-C3H5)Cl]2 (256
mg, 0.70 mmol, 1 equiv) at -10 °C. The resulting brown solution
was warmed to 0 °C for about 15 min. It was then cooled to -70
°C. A yellow precipitate formed, the solution was filtered out, and
the solid was rinsed with 4 mL of a 1:1 mixture of THF and Et2O.
The collected mass was 280 mg (62%) and slowly degrades at room
temperature, precluding microanalysis and ESI-MS. 1H NMR
(CD2Cl2, 500.13 MHz, 298 K): δ (ppm) 5.35 (m, 1H, Hmeso
overlapping with solvent signal), 4.13 (d, 1H, Hsyn trans to Cl,
3JHsynHmeso) 7.7 Hz), 3.66 (s, 6H, NCH3), 3.37(d, 1H, Hsyn trans to
tmiy, 3JHsynHmeso) 6.6 Hz), 3.20 (d, 1H, Hanti trans to Cl, 3JHantiHmeso
Procedure for the Pd-Catalyzed Coupling of Ethylene and
[pmim]Br. A 60 mL Young’s Schlenk tube was charged with the
Pd catalyst (0.037 mmol, 5 mol %), or Pd(dba)2 (0.037 mmol, 5
mol %) and PCy3 (0.040 mmol, 5.5 mol %), and the substrate (0.73
mmol, 1 equiv) in a glovebox. DMF was then syringed under a
flow of ethylene into the reaction vessel. and the orange-yellow
solution was heated to 80 °C. The vessel was then pressurized with
1 bar of ethylene and closed. The solution was stirred for 24 h.
The solvent was then removed in Vacuo and the residue dissolved
3
) 13.6 Hz), 2.42 (d, 1H, Hanti trans to tmiy, JHantiHmeso ) 11.7
Hz), 2.10 (s, 6H, carbene CH3). 13C NMR (CD2Cl2, 125.76 MHz,
298 K): δ (ppm) 176.09 (s, PdC), 125.33 (s, NC), 114.61 (s, Cmeso),
71.52 (s, Cterm anti to Cl), 47.23 (s, Cterm anti to tmiy), 35.18 (s,
NCH3), 8.91 (s, carbene CH3).
1
1,3-Diisopropyl-4,5-dimethylimidazolin-2-ylidenepalladium Al-
lyl Chloride, 5a. 1,3-Diisopropyl-4,5-dimethylimidazolin-2-ylidene
(dipdmiy; 260 mg, 1.40 mmol, 2.05 equiv) was dissolved in 2.5
mL of THF. This solution was syringed into a 2.5 mL THF
suspension of [Pd(η3-C3H5)Cl]2 (250 mg, 0.68 mmol, 1 equiv) at
-70 °C. The yellow solution was stirred for 25 min, then warmed
to room temperature and evaporated. The residue was triturated
with a 1:1 mixture of Et2O and hexane, filtered through a sintered
glass filter, and vaccuum-dried. The collected mass was 456 mg
(91%), yellow solid, decomposes over time at room temperature
(hence making microanalysis impossible). This compound was
previously described in a patent but no analytical data were
reported.106 1H NMR (CD2Cl2, 500.13 MHz, 298 K): δ (ppm)
5.25-5.35 (two overlapping m overlapping with residual solvent
peak, 2H, isopropyl CH and Hmeso), 4.85 (m, 1H, isopropyl CH),
in d6-DMSO and submitted for H NMR spectroscopy.
Tricyclohexylphosphinepalladium Allyl Chloride, 1a. Tricy-
clohexylphosphine (PCy3; 767 mg, 2.73 mmol, 1 equiv) was
dissolved in 20 mL of DCM. This solution was canulated over 5
min to a solution of [Pd(η3-C3H5)Cl]2 (500 mg, 1.37 mmol, 0.5
equiv) in 20 mL of DCM. The solution became paler. When the
addition was complete, the solution was stirred 30 min, evaporated
under reduced pressure, and triturated with hexane to afford a yellow
solid. The solid was rinsed with hexane. The collected mass was
1.02 g (81%). and found identical to literature.70
Tricyclohexylphosphinepalladium Crotyl Chloride, 2a. Tri-
cyclohexylphosphine (PCy3; 712 mg, 2.54 mmol, 1.0 equiv) was
dissolved in 5 mL of DCM. This solution was canulated over 5
min to a solution of [Pd(η3-C4H7)Cl]2 (500 mg, 1.37 mmol, 0.5
equiv) in 5 mL of DCM. The solution became paler. When the
addition was complete, the solution was stirred 10 min, evaporated
under reduced pressure, and triturated with hexane to afford a yellow
(106) Tinkl, M.; Hafner, A. WO 9947474, 1999.

Monoligated Phosphine Pd(0) Precatalysts
Organometallics, Vol. 27, No. 24, 2008 6517
3
4.07 (d, Hsyn trans to Cl, JHsynHmeso) 7.5 Hz), 3.34 (d, 1H, Hsyn
(calcd 565.2903, dev: 1.6 ppm). Anal. Calcd for C29H52N2PPdBF4
(MW ) 652.93): C, 53.35; H, 8.03; N, 4.29; P, 4.74. Found: C,
52.89; H, 7.95; N, 4.17; P, 5.00.
3
trans to tmiy, JHsynHmeso) 6.6 Hz), 3.18 (d, 1H, Hanti trans to Cl,
3JHantiHmeso)13.6 Hz), 2.33 (d, 1H, Hanti trans to tmiy, 3JHantiHmeso
)
11.7 Hz), 2.12-2.20 (two overlapping s, 6H, carbene CH3),
1.40-1.60 (two overlapping m, 12H, isopropyl CH3). 13C NMR
(CD2Cl2, 125.76 MHz, 298 K): δ (ppm) 176.00 (s, PdC, 126.24 (s,
NC), 125.62 (s, NC), 114.28 (s, Cmeso), 70.83 (s, Cterm anti to Cl),
54.32 (s, isopropyl CH), 53.07 (s, isopropyl CH), 48.23 (s, Cterm
anti to tmiy), 22.88 (s, isopropyl CH3), 22.61 (s, isopropyl CH3),
10.50 (s, carbene CH3), 10.33 (s, carbene CH3). Anal. Calcd for
C14H25N2ClPd (MW ) 363.24): C, 46.40; H, 6.96; N, 7.73. Found:
C, 45.79; H, 6.82; N, 7.55.
Tricyclohexylphosphine Tetramethylimidazolin-2-ylidenepal-
ladium Allyl Tetrafluoroborate, 4b. A mixture of tetramethylimi-
dazolin-2-ylidenepalladium allyl chloride (4a; 230 mg, 1.07 mmol,
1.0 equiv) and sodium tetrafluoroborate (334 mg, 3.21 mmol, 3.0
equiv) was suspended in 2.5 mL of DCM. Tricyclohexylphosphine
(329 mg, 1.17 mmol, 1.1 equiv) was added as a 2.5 mL solution in
DCM over 5 min. The reaction mixture was stirred at room
temperature for 3 h, then filtered through Celite, and the solution
was evaporated and triturated with Et2O. The resulting brown-red
powder was further purified by successive washes with small
amounts of hot THF to yield a white powder. The collected mass
was 230 mg. A further 115 mg was obtained from the THF liquors
(combined yield 47%). 1H NMR (CD2Cl2, 500.13 MHz, 298 K): δ
(ppm) 5.24 (m overlapping with solvent signal, 1H, Hmeso), 4.10
(overlapped m, 1H, Hsyn trans to tmiy), 4.07 (overlapped m, 1H,
1,3-Diisopropyl-4,5-dimethylimidazolin-2-ylidenepalladium
Crotyl Chloride, 6a. 1,3-Diisopropyl-4,5-dimethylimidazolin-2-
ylidene (dipdmiy; 191 mg, 1.03 mmol, 2.05 equiv) was dissolved
in 2 mL of THF. This solution was syringed into a 4 mL THF
suspension of [Pd(η3-C4H7)Cl]2 (162 mg, 0.41 mmol, 1 equiv) at
-55 °C. The yellow solution was stirred for 30 min, then warmed
to room temperature and evaporated. The residue was triturated
with a 1:1 mixture of Et2O and hexane, filtered through a sintered
glass filter, and vaccuum-dried. The collected mass was 237 mg
(75%), yellow solid, slowly degrades at room temperature. 1H NMR
(CD2Cl2, 500.13 MHz, 298 K): δ (ppm) 5.26 (m, 1H, isopropyl
CH), 5.00 (m, 1H, isopropyl CH), 3.87 (d, Hsyn trans to Cl, 4JHsynHsyn
) 2.9 Hz), 3.15 (m, 1H, Hsyn trans to tmiy), 3.04 (s, 1H, Hanti trans
H
syn trans to PCy3), 3.47 (s, 3H, NCH3), 3.30 (s, 3H, NCH3), 2.80
3
(dd, 1H, Hanti trans to PCy3, JHantiHmeso ) 13.8 Hz, JPHanti ) 8.9
Hz), 2.58 (d, 1H, Hanti trans to tmiy, JHantiHmeso ) 13.2 Hz), 2.09
3
(s, 3H, carbene CH3), 2.07 (s, 3H, carbene CH3), 1.80 (m, 3H,
PCH), 1.60-1.75 (m, 15H, PCy3 cyclohexyl), 1.00-1.23 (m, 15H,
PCy3 cyclohexyl). Signals were assigned on the basis of a gs-HSQC
experiment. A gs-COSY experiment showed coupling between
Hmeso and both Hsyn, but it was impossible to resolve the spectrum
in order to obtain coupling constants. 13C NMR (CD2Cl2, 125.76
MHz, 298 K): δ (ppm) 173.15 (d, PdC, JPC ) 16.3 Hz), 127.95 (s,
NC), 127.74 (s, NC), 119.88 (d, Cmeso, JPC) 4.5 Hz), 66.50 (d,
2
to Cl), 2.26 (d, 1H, Hanti trans to tmiy, JHantiHsyn ) 0.9 Hz),
2.18-2.17 (two overlapping s, 6H, carbene CH3), 1.97 (s, 3H, crotyl
CH3), 1.40-1.60 (two overlapping m, 12H, isopropyl CH3). 13C
NMR (CD2Cl2, 125.76 MHz, 298 K): δ (ppm) 176.89 (s, PdC),
126.07 (s, NC), 125.58 (s, NC), 113.16 (s, Cmeso), 88.78 (s, Cterm
anti to Cl), 54.32 (s, isopropyl CH), 53.07 (s, isopropyl CH), 43.57
(s, Cterm anti to tmiy), 23.16 (s, isopropyl CH3), 22.86 (s, isopropyl
CH3), 22.63 (s, isopropyl CH3), 22.40 (s, isopropyl CH3), 17.31 (s,
crotyl CH3), 10.55 (s, carbene CH3), 10.36 (s, carbene CH3). High-
resolution ESIpos-MS (MeCN): [M - Cl + MeCN]+ found 382.1479
(calc 382.1474, dev: 1.3 ppm). Anal. Calcd for C15H27N2ClPd (MW
) 377.26): C, 48.53; H, 7.52; N, 7.99. Found: C, 47.86; H, 7.24
N, 7.45.
Cterm trans to PCy3, JPC ) 27.9 Hz), 61.28 (s, Cterm trans to tmiy),
36.85 (d, PCH, JPC ) 18.9 Hz), 36.26 (s, NCH3), 36.01 (s, NCH3),
30.94 (s, CH2), 30.64 (s, CH2), 27.95 (s, CH2), 27.86 (s, CH2), 26.65
(s, CH2), 9.43 (s, carbene CH3), 9.37 (s, carbene CH3). 31P{1H}
NMR (CD2Cl2, 202.46 MHz, 298 K): δ (ppm) 42.88. High-
resolution ESIpos-MS (MeCN): found 551.2729 (calcd 551.2746,
dev: -3.2 ppm). Anal. Calcd for C28H50N2PPdBF4 (MW ) 638.28):
C, 52.64; H, 7.89; N, 4.39. Found: C, 52.78; H, 7.78; N, 4.15.
Triphenylphosphine Tetramethylimidazolin-2-ylidenepalla-
dium Allyl Tetrafluoroborate, 4c. A mixture of tetramethylimi-
dazolin-2-ylidenepalladium allyl chloride (4a; 125 mg, 0.41 mmol,
1.0 equiv) and sodium tetrafluoroborate (131 mg, 1.27 mmol, 3.0
equiv) was suspended in 2.5 mL of DCM. Triphenylphosphine (113
mg, 0.43 mmol, 1.1 equiv) was added as a 2.5 mL solution in DCM
over 5 min. The reaction mixture turned from pink to yellow to
orange. It was stirred at room temperature for 2.5 h, then filtered
through Celite, evaporated, and purified by trituration with THF,
followed by successive washes with small amounts of hot THF.
Tricyclohexylphosphine Tetramethylimidazolin-2-ylidene Pal-
ladium Crotyl Tetrafluoroborate, 2b. A mixture of tricyclohexy-
lpalladium crotyl chloride 2a (442 mg, 0.93 mmol, 1.0 equiv) and
silver tetrafluoroborate (189 mg, 0.93 mmol, 1.0 equiv) was
suspended in 4.0 mL of THF in a Schlenk tube under argon.
Tetramethylimidazolin-2-ylidene (1115 mg, 0.93 mmol, 1.0 equiv)
was added as a 4 mL solution in THF over 1 min. The reaction
mixture was stirred at room temperature for 1 h, then evaporated,
taken in DCM, filtered through Celite, evaporated, and triturated
with Et2O. The resulting powder was taken in hot THF and filtered,
and the solution was evaporated and triturated with Et2O to afford
a white powder. The collected mass was 150 mg (25%). 1H NMR
(CD2Cl2, 500.13 MHz, 298 K): δ (ppm) 3.87 (m, 1H, Hsyn trans to
tmiy), 3.84 (m, 1H, Hsyn trans to PCy3), 3.46 (s, 3H, NCH3), 3.32
(s, 3H, NCH3), 2.59 (d, 1H, Hanti trans to PCy3, JPHanti ) 8.8 Hz),
2.49 (s, 1H, Hanti trans to tmiy), 2.08 (s, 3H, carbene CH3), 2.07
(s, 3H, carbene CH3), 1.77 (overlapped s, 3H, crotyl CH3),
1.59-1.83 (overlapped m, 18H, PCy3 cyclohexyl), 1.47 (d, 3H,
1
The collected mass was 108 mg (42%), white powder. H NMR
(CD2Cl2, 500.13 MHz, 298 K): δ (ppm) 7.39-7.44 (m, 3H, Harom
para to P), 7.28-7.34 (m, 6H, Harom meta to P), 7.06-7.12 (m,
6H, Harom ortho to P), 5.58 (m, 1H, Hmeso), 4.29 (m, 1H, Hsyn trans
3
to PPh3), 3.99 (d, 1H, Hsyn trans to tmiy, JHsynHmeso ) 7.3 Hz),
3.09 (s, 3H, NCH3), 3.06 (m overlapping with NCH3 signal, 1H,
H
anti trans to PPh3), 2.95 (s, 3H, NCH3), 2.91 (d, 1H, Hanti trans to
3
tmiy, JHantiHmeso ) 13.2 Hz), 1.90 (s, 6H, carbene CH3). Signals
were assigned on the basis of gs-HSQC and gs-NOESY experiments
(Supporting Information). 13C NMR (CD2Cl2, 125.76 MHz, 298
K): δ (ppm) 171.90 (d, PdC, JPC ) 16.8 Hz), 133.79 (d, Carom ortho
to P, JPC ) 13.0 Hz), 132.12 (d, PCarom, JPC ) 43.9 Hz), 131.67 (d,
3
3
isopropyl CH3, JHH ) 7.2 Hz), 1.41 (d, 3H, isopropyl CH3, JHH
) 7.2 Hz), 1.00-1.24 (overlapped m, 15H, PCy3 cyclohexyl). 13
C
NMR (CD2Cl2, 125.03 MHz): δ (ppm) 174.18 (d, PdC, JPC ) 16.0
Hz), 134.11 (s, Cmeso, JPC ) 4.0 Hz), 127.85 (s, NC), 127.74 (s,
NC), 66.05 (d, Cterm trans to PCy3, JPC ) 28.9 Hz), 61.22 (s, Cterm
trans to tmiy), 36.71 (d, PCH, JPC ) 18.9 Hz), 36.31 (s, NCH3),
36.29 (s, NCH3), 31.06 (s, CH2), 30.74 (s, CH2), 27.99 (d, CH2,
Carom para to P, JPC ) 3.0 Hz), 129.52 (d, Carom meta to P, JPC
11.0 Hz), 127.78 (s, NC), 127.62 (s, NC), 121.59 (d, Cmeso, JPC
)
)
5.5 Hz), 68.88 (d, Cterm trans to tmiy), 65.84 (s, Cterm trans to PPh3,
JPC ) 30.9 Hz), 35.39 (s, NCH3), 35.24 (s, NCH3), 9.29 (s, carbene
CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz, 298 K): δ (ppm) 26.12.
High-resolution ESIpos-MS (MeCN): found 531.1332 (calcd 531.1343
dev: -2.1 ppm). Anal. Calcd for C28H32N2PPdBF4 (MW ) 620.14):
C, 54.18; H, 5.20; N, 4.52. Found: C, 54.01; H, 5.11; N, 4.34.
JCP) 2.0 Hz), 27.91 (d, CH2, JCP ) 3.0 Hz), 26.72 (d, CH2, JCP
)
2.0 Hz), 24.32 (s, crotyl CH3), 9.44 (s, carbene CH3), 9.41 (s,
carbene CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz, 298 K): δ
(ppm) 43.04. High-resolution ESIpos-MS (MeCN): found 565.2912

6518 Organometallics, Vol. 27, No. 24, 2008
Normand et al.
Tris(4-methoxyphenyl)phosphine Tetramethylimidazolin-2-
ylidenepalladium allyl Tetrafluoroborate, 4d. A mixture of
tetramethylimidazolin-2-ylidenepalladium allyl chloride (1a; 125
mg, 0.41 mmol, 1.0 equiv) and sodium tetrafluoroborate (131 mg,
1.27 mmol, 3.0 equiv) was suspended in 2.5 mL of DCM. Tris(4-
methoxyphenyl)phosphine (140 mg, 0.43 mmol, 1.1 equiv) was
added as a 2.5 mL solution in DCM over 5 min. No change of
color was observed. The reaction mixture was stirred at room
temperature for 2.5 h, then filtered through Celite, evaporated, and
purified by trituration with Et2O, then 3:1 Et2O/THF mixtures to
give a yellow oil, turning back to a powder after drying and
triturating with Et2O. The collected mass was 145 mg (50%), yellow
powder, soluble in THF. 1H NMR (CD2Cl2, 500.13 MHz, 298 K):
δ (ppm) 6.93-6.98 (m, 6H, Harom), 6.77-6.81 (m, 6H, Harom), 5.52
(m, 1H, Hmeso), 4.22 (m, 1H, Hsyn trans to P(C6H4OMe)3), 3.92 (d,
1.0 equiv) and sodium tetrafluoroborate (142 mg, 1.37 mmol, 3.0
equiv) was suspended in 3.0 mL of DCM. Triethylphosphine (d )
0.81, 70 µL, 0.48 mmol, 1.05 equiv) was added neat by microsy-
ringe over 2 min. The reaction mixture was stirred at room
temperature for 3 h, then filtered through Celite, evaporated, and
purified by trituration with hexane, followed by trituration in 1:3
mixtures of THF/Et2O (forms an oil, which turned back into
powdery material after drying and triturating with hexane). The
product is a yellow-green powder, soluble in THF, and forms an
oil when washed with Et2O. The collected mass was 111 mg (51%).
1H NMR (CD2Cl2, 500.13 MHz, 298 K): δ (ppm) 5.31 (m, 1H,
H
meso), 4.12 (m, 1H, Hsyn trans to PEt3), 3.93 (d, 1H, Hsyn trans to
tmiy, 3JHsynHmeso ) 7.5 Hz), 3.46 (s, 3H, NCH3), 3.29 (s, 3H, NCH3),
3
2.83 (dd, Hanti trans to PEt3, JHantiHmeso ) 13.7 Hz, JPHanti ) 9.4
Hz), 2.66 (d, 1H, Hanti trans to tmiy, JHantiHmeso ) 13.4 Hz), 2.08
3
3
1H, Hsyn trans to tmiy, JHsynHmeso ) 7.3 Hz), 3.72 (s, 9H, OCH3),
(s, 3H, CCH3), 2.06 (s, 3H, carbene CH3), 1.61 (m, 6H, PCH2),
0.94 (m, 9H, CH3). 13C NMR (CD2Cl2, 125.76 MHz, 298 K): δ
(ppm) 172.39 (d, PdC, JPC ) 18.9 Hz), 127.73 (s, NC), 127.54 (s,
NC), 121.13 (d, Cmeso, JPCmeso ) 5.0 Hz), 66.13 (s, Cterm trans to
PEt3, JPC ) 28.9 Hz), 61.72 (d, Cterm trans to tmiy), 35.82 (s, NCH3),
35.59 (s, NCH3), 19.10 (d, PCH2, JPC ) 24.9 Hz), 9.37 (s, carbene
CH3), 8.53 (s, CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz, 298
K): δ (ppm) 21.38. High-resolution ESIpos-MS (MeCN): found
389.1328 (calcd 389.1338 dev: -2.6 ppm). Anal. Calcd for
C16H32N2PPdBF4 (MW ) 476.14): C, 40.32; H, 6.77; N, 5.88; P,
6.51. Found: C, 39.91; H, 6.70; N, 5.91; P, 6.25.
3.10 (s, 3H, NCH3), 3.00 (dd, 1H, Hanti trans to P(C6H4OMe)3,
3JHantiHmeso ) 13.5 Hz, JPHsyn ) 10.3 Hz), 2.95 (s, 3H, NCH3), 2.85
3
(d, 1H, Hanti trans to tmiy, JHantiHmeso ) 13.4 Hz), 1.90 (s, 6H,
carbene CH3). Signals were assigned on the basis of gs-HSQC and
gs-NOESY experiments (Supporting Information). 13C NMR
(CD2Cl2, 125.76 MHz, 298 K): δ (ppm) 172.84 (d, PdC, JPC
21.3 Hz), 162.40 (d, CaromO, JPC ) 2.0 Hz), 135.21 (d, Carom, JPC
)
) 15.0 Hz), 127.56 (s, NC), 127.40 (s, NC), 123.57 (d, PC, JPC
48.9 Hz), 121.35 (d, Cmeso, JPC ) 5.5 Hz), 115.00 (d, Carom, JPC
)
)
11.5 Hz), 68.08 (s, Cterm trans to tmiy), 65.23 (d, Cterm trans to
P(C6H4OMe)3, JPC ) 31.4 Hz), 56.05 (s, OCH3), 35.44 (s, NCH3),
35.27 (s, NCH3), 9.33 (s, carbene CH3). 31P{1H} NMR (CD2Cl2,
202.46 MHz, 298 K): δ (ppm) 22.23. High-resolution ESIpos-MS
(MeCN): found 621.1632 (calcd 621.1660 dev: -4.5 ppm). Anal.
Calcd for C31H38N2O3PPdBF4 (MW ) 710.17): C, 52.38; H, 5.39;
N, 3.99. Found: C, 51.00; H, 5.27; N, 4.09. These values are not
satisfactory due to the solubility of 4d in THF, causing minor
impurities to remain in the sample.
Tricyclohexylphosphine 1,3-Diisopropyl-4,5-dimethylimida-
zolin-2-ylidenepalladium Allyl Tetrafluoroborate, 5b. A mixture
of 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidenepalladium allyl
chloride (5a, 249 mg, 0.67 mmol, 1.0 equiv) and sodium tetrafluo-
roborate (214 mg, 2.06 mmol, 3.0 equiv) was suspended in 3 mL
of DCM. Tricyclohexylphosphine (212 mg, 0.75 mmol, 1.1 equiv)
was added as a 3 mL solution in DCM over 5 min. The reaction
mixture was stirred at room temperature for 4.5 h, then filtered
through Celite, evaporated, and triturated with Et2O. The resulting
powder was taken in hot THF and cooled to -80 °C for 30 min.
The resulting precipitate was filtered, rinsed with Et2O, and dried
under vacuum. The collected mass was 160 mg (35%), white
powder. 1H NMR (CD2Cl2, 500.13 MHz, 298 K): δ (ppm) 5.20 (m
overlapping with solvent signal, 1H, Hmeso), 4.61 (m, 1H, isopropyl
CH), 4.36 (m, 1H, isopropyl CH), 4.09-4.15 (two overlapped m,
2H, Hsyn trans to dipdmiy and PCy3), 2.72 (dd, 1H, Hanti trans to
Tribenzylphosphine Tetramethylimidazolin-2-ylidenepalla-
dium Allyl Tetrafluoroborate, 4e. A mixture of tetramethylimi-
dazolin-2-ylidenepalladium allyl chloride (4a; 125 mg, 0.41 mmol,
1.0 equiv) and sodium tetrafluoroborate (131 mg, 1.27 mmol, 3.0
equiv) was suspended in 2.5 mL of DCM. Tribenzylphosphine (131
mg, 0.43 mmol, 1.1 equiv) was added as a 2.5 mL solution in DCM
over 5 min. The reaction mixture turned from pink to yellow. It
was stirred at room temperature for 2.5 h, then filtered through
Celite, evaporated, and purified by trituration with THF, followed
by successive washes with small amounts of hot THF. The collected
mass was 167 mg (62%), white powder. 1H NMR (CD2Cl2, 500.13
MHz, 298 K): δ (ppm) 7.21-7.25 (m, 9H, Harom), 6.96-7.00 (m,
6H, Harom), 4.99 (m, 1H, Hmeso), 3.94 (m, 1H, Hsyn trans to PBz3),
3.04-3.14 (two overlapping m, 7H, PCH2 and Hsyn trans to tmiy),
3.02 (s, 3H, NCH3), 2.82 (s, 3H, NCH3), 2.65 (dd, Hanti trans to
3
PCy3, JHantiHmeso ) 13.5 Hz, JPHanti ) 8.8 Hz), 2.58 (d, 1H, Hanti
3
trans to tmiy, JHantiHmeso ) 13.2 Hz), 2.18 (s, 3H, carbene CH3),
2.15 (s, 3H, carbene CH3), 1.86 (m, 3H, PCH), 1.61-1.75 (m, 15H,
3
PCy3 cyclohexyl), 1.49 (d, 3H, isopropyl CH3, JHH ) 7.2 Hz),
1.39 (d, 3H, isopropyl CH3, 3JHH ) 7.2 Hz), 1.30 (d, 3H, isopropyl
CH3, 3 JHH ) 7.0 Hz), 1.24 (overlapped d, 3H, isopropyl CH3, 3JHH
) 7.0 Hz), 1.02-1.30 (overlapped m, 9H, PCy3 cyclohexyl). Signals
were assigned on the basis of gs-NOESY and gs-HSQC experiments
(Supporting Information). 13C NMR (CD2Cl2, 125.76 MHz, 298
K): δ (ppm) 173.35 (d, PdC, JPC ) 15.0 Hz), 128.37 (s, NC), 128.02
(s, NC), 119.37 (d, Cmeso, JPC ) 4.0 Hz), 66.72 (d, Cterm trans to
PCy3, JPC ) 27.9 Hz), 60.79 (s, Cterm trans to tmiy), 55.16 (s,
isopropyl CH), 54.71 (s, isopropyl CH), 36.57 (d, PCH, JPC ) 18.9
Hz), 30.81 (s, CH2), 30.64 (s, CH2), 30.56 (s, CH2), 27.94 (s, CH2),
27.92 (s, CH2),), 27.85 (s, CH2), 27.84 (s, CH2), 26.58 (s, CH2),
23.23 (s, isopropyl CH3), 22.82 (s, isopropyl CH3), 21.71 (s,
isopropyl CH3), 21.51 (s, isopropyl CH3), 10.92
(s, carbene CH3), 10.90 (s, carbene CH3). 31P{1H} NMR (CD2Cl2,
202.46 MHz, 298 K): δ (ppm) 41.26. High-resolution ESIpos-MS
(MeCN): found 605.3354 (calcd 605.3378, dev: -4.0 ppm). Anal.
Calcd for C32H58N2PPdBF4 (MW ) 638.28): C, 55.30; H, 8.41; N,
4.03. Found: C, 55.10; H, 8.30; N, 3.94.
3
PBz3, JHantiHmeso ) 13.3 Hz, JPHanti ) 10.3 Hz), 2.08 (d, 1H, Hanti
trans to tmiy, 3JHantiHmeso ) 13.4 Hz), 1.98 (s, 3H, CCH3), 1.97 (s,
3H, CCH3). Signals were assigned on the basis of gs-HSQC and
gs-NOESY experiments (Supporting Information). 13C NMR
(CD2Cl2, 125.76 MHz, 298 K): δ (ppm) 171.83 (d, PdC, JPC
19.9 Hz), 134.59 (d, Carom, JPC ) 3.0 Hz), 130.28 (d, Carom, JPC
5.0 Hz), 129.46 (d, Carom, JPC ) 2.0 Hz), 127.87 (d, Carom, JPC
)
)
)
3.0 Hz), 127.77 (s, NC), 127.58 (s, NC), 121.21 (d, Cmeso, JPCmeso
) 6.0 Hz), 66.01 (s, Cterm trans to PBz3, JPC ) 29.9 Hz), 64.45 (d,
Cterm trans to tmiy), 35.42 (d, PCH2, JPC ) 17.0 Hz), 35.27 (s,
NCH3), 34.99 (s, NCH3), 9.36 (s, carbene CH3), 9.34 (s, carbene
CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz, 298 K): δ (ppm) 25.96.
High-resolution ESIpos-MS (MeCN): found 575.1779 (calcd 575.1807
dev: -4.9 ppm) Anal. Calcd for C31H38N2PPdBF4 (MW ) 662.18):
C, 56.18; H, 5.78; N, 4.23. Found: C, 56.05; H, 5.76; N, 4.20.
Triethylphosphine Tetramethylimidazolin-2-ylidenepalladi-
um Allyl Tetrafluoroborate, 4f. A mixture of tetramethylimida-
zolin-2-ylidenepalladium allyl chloride (4a; 140 mg, 0.46 mmol,
Triphenylphosphine 1,3-Diisopropyl-4,5-dimethylimidazolin-
2-ylidenepalladium Allyl Tetrafluoroborate, 5c. A mixture of 1,3-
diisopropyl-4,5-dimethylimidazolin-2-ylidenepalladium allyl chlo-

Monoligated Phosphine Pd(0) Precatalysts
Organometallics, Vol. 27, No. 24, 2008 6519
ride (5a, 200 mg, 0.54 mmol, 1.0 equiv) and sodium tetrafluoroborate
(169 mg, 1.63 mmol, 3.0 equiv) was suspended in 3 mL of DCM.
Triphenylphosphine (150 mg, 0.57 mmol, 1.1 equiv) was added as
a 3.0 mL solution in DCM over 3 min. The reaction mixture was
stirred at room temperature for 2.5 h, then filtered through Celite,
evaporated, and purified by trituration with Et2O, a 3:1 mixture of
Et2O/THF, and finally with THF. The collected mass was 262 mg
resolution ESIpos-MS (MeCN): found 679.2287 (calcd 679.2281 dev:
0.9 ppm). Anal. Calcd for C35H46N2O3PPdBF4 (MW ) 738.23):
C, 54.81; H, 6.05; N, 3.66; P, 4.04. Found: C, 54.66; H, 6.00; N,
3.60; P, 3.97.
Triethylphosphine 1,3-Diisopropyl-4,5-dimethylimidazolin-
2-ylidenepalladium Allyl Tetrafluoroborate, 5e. A mixture of 1,3-
diisopropyl-4,5-dimethylimidazolin-2-ylidenepalladium allyl chlo-
ride (5a; 250 mg, 0.69 mmol, 1.0 equiv) and sodium tetrafluoroborate
(214 mg, 2.06 mmol, 3.0 equiv) was suspended in 5 mL of DCM.
Triethylphosphine (d ) 0.81, 105 µL, 0.72 mmol, 1.05 equiv) was
added neat by microsyringe over 2 min. The reaction mixture was
stirred at room temperature for 3 h, then filtered through Celite,
evaporated, and purified by trituration with Et2O. The collected mass
was 193 mg (53%), yellow-green powder. 1H NMR (CD2Cl2, 500.13
MHz, 298 K): δ (ppm) 5.28 (m, 1H, Hmeso), 4.58 (m, 1H, isopropyl
CH), 4.31 (m, 1H, isopropyl CH), 4.13 (m, 1H, Hsyn trans to PEt3),
3.90 (d, 1H, Hsyn trans to dipdmiy, 3JHsynHmeso ) 6.9 Hz), 2.75 (dd,
1
(71%), white powder. H NMR (CD2Cl2, 500.13 MHz, 298 K): δ
(ppm) 7.39-7.44 (m, 3H, Harom para to P), 7.28-7.34 (m, 6H,
Harom meta to P), 6.94-7.00 (m, 6H, Harom ortho to P), 5.53 (m,
1H, Hmeso), 4.57 (m, 1H, isopropyl CH), 4.22-4.30 (two overlapped
m, 2H, isopropyl CH and Hsyn trans to PPh3), 3.76 (dm, 1H, Hsyn
3
trans to tmiy, JHsynHmeso ) 7.3 Hz), 2.98 (dd, 1H, Hanti trans to
3
PPh3, JHantiHmeso ) 13.4 Hz, JPHanti ) 9.9 Hz), 2.87 (d, 1H, Hanti
trans to tmiy, 3JHantiHmeso ) 13.4 Hz), 2.10 (s, 3H, CCH3), 2.09 (s,
3
3H, CCH3), 1.25 (d, 3H, isopropyl CH3, JHH ) 7.0 Hz), 1.13 (d,
3
3H, isopropyl CH3, JHH ) 7.0 Hz), 0.74 (d, 3H, isopropyl CH3,
3JHH ) 7.2 Hz), 0.72 (d, 3H, isopropyl CH3, 3JHH ) 7.2 Hz). Signals
were assigned on the basis of gs-NOESY and gsHSQC experiments
(Supporting Information). 13C NMR (CD2Cl2, 125.76 MHz, 298
K): δ (ppm) 170.75 (d, PdC, JPC ) 18.9 Hz), 133.81 (d, Carom, JPC
H
anti trans to PEt3, 3JHantiHmeso ) 13.0 Hz, JPHanti ) 9.5 Hz), 2.65 (d,
1H, Hanti trans to tmiy, 3JHantiHmeso ) 13.2 Hz), 2.17 (s, 3H, carbene
CH3), 2.14 (s, 3H, carbene CH3), 1.65 (m, 6H, PCH2), 1.45 (d, 3H,
isopropyl CH3, 3JHH ) 7.3 Hz), 1.34 (overlapped d, 3H, isopropyl
CH3, 3JHH ) 6.9 Hz), 1.33 (overlapped d, 3H, isopropyl CH3, 3JHH
) 13.0 Hz), 132.10 (d, PCarom, JPC ) 42.9 Hz), 131.72 (d, Carom
,
3
JPC ) 2.0 Hz), 129.66 (d, Carom, JPC ) 11.0 Hz), 128.50 (s, NC),
127.95 (s, NC), 121.02 (d, Cmeso, JPC ) 6.0 Hz), 69.87 (d, Cterm
trans to dipdmiy, JPC ) 2.0 Hz), 66.17 (d, Cterm trans to PPh3, JPC
) 30.9 Hz), 55.47 (s, isopropyl CH), 54.46 (s, isopropyl CH), 22.84
(s, isopropyl CH3), 22.59 (s, isopropyl CH3), 21.09 (s, isopropyl
CH3), 20.90 (s, isopropyl CH3), 10.62 (s, carbene CH3), 10.52 (s,
carbene CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz, 298 K): δ
(ppm) 23.75. High-resolution ESIpos-MS (MeCN): found 587.1948
(calcd 587.1969 dev: -3.6 ppm). Anal. Calcd for C32H40N2PPdBF4
(MW ) 676.20): C, 56.79; H, 5.96; N, 4.14; P, 4.58. Found: C,
55.89; H, 6.03; N, 3.78; P, 4.36.
) 6.9 Hz), 1.25 (d, 3H, isopropyl CH3, JHH ) 7.3 Hz) 0.95 (m,
9H, PEt3 CH3). 13C NMR (CD2Cl2, 125.76 MHz, 298 K): δ (ppm)
171.24 (d, PdC, JPC ) 18.9 Hz), 128.22 (s, NC), 127.58 (s, NC),
120.64 (d, Cmeso, JPCmeso ) 5.0 Hz), 67.09 (s, Cterm trans to PEt3,
JPC ) 29.9 Hz), 61.49 (d, Cterm trans to dipdmiy), 55.13 (s, isopropyl
CH), 54.16 (s, isopropyl CH), 22.76 (s, isopropyl CH3), 22.55 (s,
isopropyl CH3), 22.16 (s, isopropyl CH3), 19.41 (d, PCH2, JPC
)
24.9 Hz), 10.75 (s, carbene CH3), 10.66 (s, carbene CH3), 8.57 (s,
PEt3 CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz, 298 K): δ (ppm)
20.28. High-resolution ESIpos-MS (MeCN): found 445.1945 (calcd
445.1964 dev: -4.3 ppm). Anal. Calcd for C20H40N2PPdBF4 (MW
) 532.20): C, 45.10; H, 7.57; N, 5.26; P, 5.82. Found: C, 44.77;
H, 7.56; N, 5.19; P, 6.10.
Tris(4-methoxyphenyl)phosphine 1,3-Diisopropyl-4,5-dimeth-
ylimidazolin-2-ylidenepalladium Allyl Tetrafluoroborate, 5d. A
mixture of 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidenepalla-
dium allyl chloride (5a, 250 mg, 0.69 mmol, 1.0 equiv) and sodium
tetrafluoroborate (214 mg, 2.06 mmol, 3.0 equiv) was suspended
in 5 mL of DCM. Tris(4-methoxyphenyl)phosphine (255 mg, 0.78
mmol, 1.05 equiv) was added as a 5 mL solution in DCM over 1
min. The reaction mixture turned from yellow to colorless and
finally to orange (after 30 min). It was stirred at room temperature
for 5 h, then filtered through Celite, evaporated, and purified by
trituration with Et2O, followed by washing with hot THF. The
collected mass was 290 mg (56%), white powder. 1H NMR
(CD2Cl2, 500.13 MHz, 298 K): δ (ppm) 6.83-6.90 (m, 6H, Harom
ortho to P), 6.79-6.83 (m, 6H, Harom meta to P), 5.50 (m, 1H,
Tricyclohexylphosphine 1,3-Diisopropyl-4,5-dimethylimida-
zolin-2-ylidenepalladium Crotyl Tetrafluoroborate, 6b. A mix-
ture of 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidenepalladium
crotyl chloride (6a; 136 mg, 0.36 mmol, 1.0 equiv) and sodium
tetrafluoroborate (112 mg, 1.08 mmol, 3.0 equiv) was suspended
in 2.5 mL of DCM. Tricyclohexylphosphine (106 mg, 0.38 mmol,
1.08 equiv) was added as a 2.5 mL solution in DCM over 15 min.
The yellow reaction mixture turned pale. It was stirred at room
temperature for 2.5 h, then filtered through Celite, evaporated, and
purified by trituration with Et2O, then a 3:1 mixture of Et2O/THF.
1
The collected mass was 140 mg (60%), white powder. H NMR
(CD2Cl2, 500.13 MHz, 298 K): δ (ppm) 4.64 (m, 1H, isopropyl
CH), 4.38 (m, 1H, isopropyl CH), 3.87-3.91 (two overlapped m,
2H, Hsyn trans to dipdmiy and PCy3), 2.62 (d, 1H, Hanti trans to
PCy3, JPHanti) 8.8 Hz), 2.47 (s, 1H, Hanti trans to tmiy), 2.17 (s,
3H, carbene CH3), 2.16 (s, 3H, carbene CH3), 1.83 (m, 3H, PCH),
1.74 (overlapped s, 3H, crotyl CH3), 1.60-1.79 (overlapped m,
H
meso), 4.60 (m, 1H, isopropyl CH), 4.30 (m, 2H, isopropyl
CH), 4.21 (m, 1H, Hsyn trans to P(C6H4OMe)3), 3.74 (s, 9H, OCH3),
3.71 (overlapped m, 1H, Hsyn trans to dipdmiy), 2.94 (dd, 1H, Hanti
3
trans to P(C6H4OMe)3, JHantiHmeso ) 13.5 Hz, JPHanti ) 9.9 Hz),
3
2.84 (d, 1H, Hanti trans to tmiy, JHantiHmeso ) 13.4 Hz), 2.12 (s,
3
3H, carbene CH3), 2.10 (s, 3H, carbene CH3), 1.27 (d, 3H, isopropyl
CH3, 3JHH ) 7.2 Hz), 1.15 (d, 3H, isopropyl CH3, 3JHH ) 7.0 Hz),
0.82 (d, 3H, isopropyl CH3, 3JHH ) 7.2 Hz), 0.78 (d, 3H, isopropyl
15H, PCy3 cyclohexyl), 1.47 (d, 3H, isopropyl CH3, JHH ) 7.2
3
Hz), 1.41 (d, 3H, isopropyl CH3, JHH ) 7.2 Hz), 1.29
(overlapped d, 3H, isopropyl CH3, 3JHH ) 5.5 Hz), 1.27 (overlapped
3
3
CH3, JHH ) 7.0 Hz). Signals were assigned on the basis of gs-
d, 3H, isopropyl CH3, JHH ) 5.5 Hz), 1.02-1.32 (overlapped m,
HSQC and gNOESY experiments (Supporting Information). 13C
9H, PCy3 cyclohexyl). 13C NMR (CD2Cl2, 125.76 MHz, 298 K): δ
(ppm) 174.27 (d, PdC, JPC ) 16.0 Hz), 133.66 (d, Cmeso, JPC ) 4.0
Hz), 128.10 (s, NC), 128.03 (s, NC), 66.83 (d, Cterm trans to PCy3,
JPC ) 28.9 Hz), 60.91 (s, Cterm trans to tmiy), 55.08 (s, isopropyl
CH), 54.77 (s, isopropyl CH), 36.37 (d, PCH, JPC ) 18.0 Hz), 30.79
(s, CH2), 30.58 (s, CH2), 27.92 (d, CH2, JCP ) 3.0 Hz), 27.83 (d,
CH2, JCP ) 3.0 Hz), 26.61 (s, CH2), 23.63 (s, crotyl CH3), 23.14
(s, isopropyl CH3), 22.94 (s, isopropyl CH3), 21.60 (s, isopropyl
CH3), 21.44 (s, isopropyl CH3), 10.93 (s, carbene CH3), 10.87 (s,
carbene CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz, 298 K): δ
(ppm) 42.27. High-resolution ESIpos-MS (MeCN): found 619.3504
NMR (CD2Cl2, 125.76 MHz, 298 K): δ (ppm) 171.32 (d, PdC, JPC
) 17.0 Hz), 162.40 (bs, CaromO), 135.23 (d, Carom ortho to P, JPC
15.0 Hz), 128.39 (s, NC), 127.81 (s, NC), 123.65 (d, PC, JPC
)
)
48.9 Hz), 120.78 (d, Cmeso, JPC ) 5.0 Hz), 115.16 (d, Carom meta to
P, JPC ) 11.0 Hz), 69.08 (s, Cterm trans to tmiy), 65.68 (d, Cterm
trans to P(C6H4OMe)3, JPC ) 30.9 Hz), 56.05 (s, OCH3), 55.43 (s,
isopropyl CH), 54.38 (s, isopropyl CH), 22.86 (s, isopropyl CH3),
22.63 (s, isopropyl CH3), 21.24 (s, isopropyl CH3), 21.06 (s,
isopropyl CH3), 10.68 (s, carbene CH3), 10.59 (s, carbene CH3).
31P{1H} NMR (CD2Cl2, 202.46 MHz, 298 K): δ (ppm) 19.86. High-

6520 Organometallics, Vol. 27, No. 24, 2008
Normand et al.
(calcd 619.3534, dev: -4.8 ppm). Anal. Calcd for C33H60N2PPdBF4
(MW ) 709.04): C, 55.90; H, 8.53; N, 3.95; P, 4.37. Found: C,
55.64; H, 8.57; N, 3.88; P, 4.46.
CH3), 22.70 (s, isopropyl CH3), 22.52 (s, isopropyl CH3), 22.15
(s, isopropyl CH3), 22.06 (s, isopropyl CH3), 19.36 (d, PCH2,
JPC ) 24.9 Hz), 10.81 (s, carbene CH3), 10.77 (s, carbene CH3),
8.66 (s, PEt3 CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz, 298
K): δ (ppm) 21.46. High-resolution ESIpos-MS (MeCN): found
457.2110 (calcd 457.2126 dev: -3.5 ppm). Anal. Calcd for
C21H42N2PPdBF4 (MW ) 546.21): C, 46.13; H, 7.74; N, 5.12;
P, 5.66. Found: C, 45.99; H, 7.76; N, 4.97; P, 5.66.
Tris(4-methoxyphenyl)phosphine 1,3-Diisopropyl-4,5-dimeth-
ylimidazolin-2-ylidenepalladium Crotyl Tetrafluoroborate, 6c.
A mixture of 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene-
palladium crotyl chloride (6a; 190 mg, 0.50 mmol, 1.0 equiv)
and sodium tetrafluoroborate (165 mg, 1.57 mmol, 3.0 equiv)
was suspended in 5 mL of DCM. Tris(4-methoxyphenyl)phos-
phine (172 mg, 0.53 mmol, 1.05 equiv) was added as a 2 mL
solution in DCM over 5 min. The reaction mixture gradually
turned from a paler to a darker yellow. It was stirred at room
temperature for 3 h, then filtered through Celite, evaporated,
and purified by trituration with Et2O, followed by a 2:1 mixture
of Et2O/THF. The collected mass was 258 mg (65%), white
powder. 1H NMR (CD2Cl2, 500.13 MHz, 298 K): δ (ppm)
6.78-6.85 (m, 6H, Harom meta to P), 6.85-6.92 (m, 6H, Harom
ortho to P), 4.60 (m, 1H, isopropyl CH), 4.35 (m, 2H, isopropyl
CH), 3.96 (m, 1H, Hsyn trans to P(C6H4OMe)3), 3.74 (s, 9H,
OCH3), 3.43 (bs, 1H, Hsyn trans to dipdmiy), 2.77-2.85
(overlapped dd and s, 2H, Hanti trans to P(C6H4OMe)3 and
Tricyclohexylphosphinepalladium Allyl Iodide, 4g. Tricyclo-
hexylphosphinepalladium allyl chloride (1a; 144 mg, 0.31 mmol,
1.0 equiv) and sodium iodide (466 mg, 3.11 mmol, 10 equiv) were
suspended in 5 mL of DCM for 18 h. The reaction mixture was
filtered through Celite and evaporated, and the residue was triturated
in hexane to afford the title compound as a yellow powder (112
mg 65%). This compound was reported in a patent but no analytical
data were given.107 1H NMR (CD2Cl2, 500.13 MHz, 298 K): δ
(ppm) 5.16 (m, 1H, Hmeso), 4.53 (m, 1H, Hsyn trans to PCy3, 3.91
(m, 1H, Hsyn trans to I), 3.12 (dd, 1H, Hanti trans to PCy3, 3JHantiHmeso
) 13.5 Hz, JPHanti ) 9.0 Hz), 2.75 (d, 1H, Hanti trans to I, 3JHantiHmeso
) 12.3 Hz), 2.15 (m, 3H, PCH), 1.13-1.87 (m, 30H, PCy3
cyclohexyl). 13C NMR (CD2Cl2, 125.76 MHz, 298 K): δ (ppm)
115.27 (d, Cmeso, JPC ) 5.0 Hz), 75.66 (d, Cterm trans to PCy3, JPC
) 29.9 Hz), 60.64 (d, Cterm trans to I, JPC ) 2.0 Hz), 36.01 (d,
PCH, JPC ) 18.9 Hz), 30.87 (s, CH2), 28.10 (d, CH2, JPC ) 3.0
Hz), 28.01 (d, CH2, JPC ) 3.0 Hz), 26.93 (s, CH2). 31P{1H} NMR
(CD2Cl2, 202.46 MHz, 298 K): δ (ppm) 39.68. High-resolution
ESIpos-MS (MeCN): [M - I + MeCN]+ found 466.1994 (calcd
466.2017, dev: -4.9 ppm). Anal. Calcd for C21H38PPdI (MW )
554.82): C, 45.46; H, 6.90; P, 5.58. Found: C, 45.21; H, 6.85; P,
5.86.
dipdmiy), 2.13 (s, 3H, carbene CH3), 2.11 (s, 3H, carbene CH3),
3
1.87 (s, 3H, crotyl CH3), 1.26 (d, 3H, isopropyl CH3, JHH
)
3
6.9 Hz), 1.20 (d, 3H, isopropyl CH3, JHH ) 6.9 Hz), 0.84 (d,
3H, isopropyl CH3, 3JHH ) 6.9 Hz), 0.75 (d, 3H, isopropyl CH3,
3JHH ) 7.3 Hz). Signals were assigned on the basis of gs-HSQC
and gs-NOESY experiments (Supporting Information). 13C NMR
(CD2Cl2, 125.76 MHz, 298 K): δ (ppm) 171.21 (d, PdC, JPC
)
18.0 Hz), 162.37 (s, CaromO), 135.62 (d, Cmeso, JPC ) 5.0 Hz),
135.18 (d, Carom, JPC ) 15.0 Hz), 128.06 (s, NC), 127.96 (s,
NC), 123.65 (d, PC, JPC ) 46.9 Hz), 115.10 (d, Carom, JPC
)
Tricycloxexylphosphine Acetonitrilepalladium Allyl Tetraflu-
oroborate, 7a. AgBF4 (42 mg, 0.22 mmol, 1 equiv) and [Pd(η3-
C3H5)(Cl)(PCy3)] (1a; 100 mg, 0.22 mmol, 1 equiv) were stirred
in dry acetonitrile (5 mL) under argon for 1 h. The suspension was
then filtered through Celite, and the filtrate was concentrated to
about 1 mL by evaporation. Dry Et2O was then added to precipitate
the product, and the resulting powder was dried under vacuum.
The collected mass was 111 mg (91%). 1H NMR (CD2Cl2, 500.13
MHz, 298 K): δ (ppm) 5.51 (m, 1H, Hmeso), 4.95 (m, 1H, Hsyn trans
11.0 Hz), 68.76 (s, Cterm trans to dipdmiy), 64.83 (d, Cterm trans
to P(C6H4OMe)3, JPC ) 31.9 Hz), 56.04 (s, OCH3), 55.21 (s,
isopropyl CH), 54.91 (s, isopropyl CH), 24.07 (s, crotyl CH3),
22.75 (s, isopropyl CH3), 22.57 (s, isopropyl CH3), 21.07 (s,
isopropyl CH3), 20.88 (s, isopropyl CH3), 10.69 (s, carbene CH3),
10.64 (s, carbene CH3). 31P{1H} NMR (CD2Cl2, 202.46 MHz,
298 K): δ (ppm) 21.76. High-resolution ESIpos-MS (MeCN):
found 693.2451 (calcd 693.2437 dev: 2.0 ppm). Anal. Calcd for
C35H46N2O3PPdBF4 (MW ) 738.23): C, 55.37; H, 6.20; N, 3.59.
Found: C, 54.94; H, 6.34; N, 3.55.
3
to PCy3), 3.70 (dd, 1H, Hanti trans to PCy3, JHantiHmeso ) 14.4 Hz,
JPHanti ) 8.4 Hz), 3.48 (m, 1H, Hsyn trans to MeCN), 2.69 (d, 1H,
3
Triethylphosphine 1,3-Diisopropyl-4,5-dimethylimidazolin-
2-ylidenepalladium Crotyl Tetrafluoroborate, 6d. A mixture of
1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidenepalladium cro-
tyl chloride (6a; 200 mg, 0.53 mmol, 1.0 equiv) and sodium
tetrafluoroborate (165 mg, 1.57 mmol, 3.0 equiv) was suspended
in 5 mL of DCM. Triethylphosphine (d ) 0.81, 81 µL, 0.56
mmol, 1.05 equiv) was added neat by microsyringe over 5 min.
The color of the yellow reaction mixture gradually faded away.
It was stirred at room temperature for 3 h, then filtered through
Celite, evaporated, and purified by trituration with Et2O. A
solution of the compound in hot THF was layered with hexane
followed by cooling to -80 °C. The collected mass was 197
mg (68%), gray powder. 1H NMR (CD2Cl2, 400.13 MHz): δ
(ppm) 4.57 (m, 1H, isopropyl CH), 4.32 (m, 1H, isopropyl CH),
3.90 (m, 1H, Hsyn trans to PEt3), 3.63 (m, 1H, Hsyn trans to
dipdmiy), 2.63 (d, Hanti trans to PEt3, JPHanti ) 9.5 Hz), 2.52 (s,
1H, Hanti trans to tmiy), 2.16 (s, 3H, carbene CH3), 2.15 (s, 3H,
carbene CH3), 1.75 (s, 3H, crotyl CH3), 1.63 (m, 6H, PCH2),
Hanti trans to MeCN, JHantiHmeso ) 11.8 Hz), 2.34 (s, 3H, MeCN),
1.86-1.96 (m, 3H, PCH), 1.12-1.85 (m, 30H, PCy3 cyclohexyl).
13C NMR (CD2Cl2, 125.76 MHz, 298 K): δ (ppm) 120.51 (bs,
Cmeso), 84.71 (d, Cterm trans to PCy3, JPC ) 21.9 Hz), 52.36 (s,
Cterm trans to MeCN), 35.32 (d,, PCH, JPC ) 18.9 Hz), 30.85(s,
CH2), 30.70 (s, CH2), 28.07 (d, CH2, JPC ) 2.0 Hz), 27.99 (d, CH2,
JPC ) 2.0 Hz), 26.72 (s, CH2), 3.57 (s, MeCN CH3). The signal for
the carbon atom of CN in acetonitrile was not seen.
Acknowledgment. We thank EPSRC for funding and
Johnson Matthey for a loan of Pd salts. We thank Dr. Robert
Jenkins and Mr. Robin Hicks (Cardiff University) for ESI-
MS analysis, and Dr. D. J. Beetstra (Cardiff University) for
advice on X-ray diffraction and solving one of the X-ray
structures.
Supporting Information Available: Tables of X-ray data
collection information, atom coordinates and thermal parameters,
bond lengths and angles, together with CIF data, for 2a, 2b, 3a,
4a-e, 4g, 5a-c, 6b, 6d, and 7a. NOESY and HSQC spectra and
summary tables for 5b, 5c, and 6c. This material is available free
of charge via the Internet at http://pubs.acs.org.
3
1.43 (d, 3H, isopropyl CH3, JHH ) 7.0 Hz), 1.37 (overlapped
3
d, 3H, isopropyl CH3, JHH ) 7.0 Hz), 1.32 (d, 3H, isopropyl
3
3
CH3, JHH ) 7.0 Hz), 1.28 (d, 3H, isopropyl CH3, JHH ) 7.0
Hz) 0.95 (m, 9H, PEt3 CH3). 13C NMR (CD2Cl2, 125.03 MHz):
δ (ppm) 172.21 (d, PdC, JPC ) 18.9 Hz), 134.99 (d, Cmeso, JPCmeso
) 5.0 Hz), 127.96 (s, NC), 127.76 (s, NC), 66.47 (s, Cterm trans
to PEt3, JPC ) 30.9 Hz), 61.34 (d, Cterm trans to dipdmiy),
55.05(s, isopropyl CH), 54.59 (s, isopropyl CH), 24.19 (s, crotyl
OM8008052
(107) Tinkl, M.; Hafner, A. WO 2001016057, 2001.