A new class of stable, saturated N-heterocyclic carbenes with N-naphthyl substituents: Synthesis, dynamic behavior, and catalytic potential

Article abstract of DOI:10.1002/ejic.200900010

A new family of easily accessible and stable imidazolin-2-ylidenes has been synthesized, where the side chains are comprised of substituted naphthyl units. This generates C2- symmetric (anti) and Cs-symmetric (syn) atropisomers. The interconversion betwee

Full text of DOI:10.1002/ejic.200900010

FULL PAPER
DOI: 10.1002/ejic.200900010
A New Class of Stable, Saturated N-Heterocyclic Carbenes with N-Naphthyl
Substituents: Synthesis, Dynamic Behavior, and Catalytic Potential
Ludovic Vieille-Petit,[a] Xinjun Luan,[a] Ronaldo Mariz,[a] Sascha Blumentritt,[a]
Anthony Linden,[a] and Reto Dorta*[a]
Keywords: Carbenes / Atropisomerism / Interconversion / Amination / Carbenoids
A new family of easily accessible and stable imidazolin-2-
ylidenes has been synthesized, where the side chains are
comprised of substituted naphthyl units. This generates C2-
symmetric (anti) and Cs-symmetric (syn) atropisomers. The
interconversion between the isomers is studied in detail both
for the N-heterocyclic carbene salts and the free carbenes
through variable-temperature 1H NMR spectroscopic stud-
ies; activation free energies are calculated and can be linked
to the substitution pattern of the naphthyl moieties. Palla-
dium complexes comprising the new N-heterocyclic carb-
enes are synthesized and preliminary data show that these
compounds behave well as precatalysts in the Buchwald–
Hartwig amination reaction of aryl bromides and aryl chlo-
rides.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
as the substituents at the nitrogen atoms need to be very
bulky. The demarcation line separating stable from unstable
carbenes may be established and lies somewhere between
tBu/iPr for N-alkyl substituents and Mes/Ph for aromatic
side chains.[8–10]
Introduction
Almost 30 years have elapsed between the proposal of
stable N-heterocyclic carbenes (NHCs)[1] and the prepara-
tion of the first member of this class of compounds by Ard-
uengo et al.[2] The isolation and characterization of the first
stable and crystalline imidazol-2-ylidene A[2] and the satu-
rated imidazolidin-2-ylidene derivative B[3] have sparked re-
newed interest in the chemistry of carbenes. To a large ex-
tent, research efforts in this area have been stimulated by
the fact that NHCs can serve as ligand entities for transi-
tion-metal catalysts and often show increased stability and
reactivity relative to their phosphane analogues.[4,5]
Among the NHC ligand architectures that behave well in
catalysis, 2,4,6-mesityl- and 2,6-isopropylphenyl-substituted
imidazol-2-ylidenes (IMes and IPr, respectively) and their
saturated imidazolidin-2-ylidene counterparts (SIMes and
SIPr) are by far the most versatile and reactive when used
as bulky monodentate ligands and remain the only ligands
representing a truly viable alternative to monodentate phos-
phanes. Presumably, the perpendicular arrangement of the
aryl side chains, combined with the steric bulk on the aro-
matic rings, leads to a situation where these ligands confer
stability to unsaturated, reactive metal centers during catal-
ysis and where decomposition of the catalyst through un-
wanted metal–ligand interactions is rarely observed.
Recent work in our laboratory has led to the synthesis of
promising members of a new family of stable, saturated
NHCs that incorporate bulky naphthyl side chains.[11] The
introduction of the naphthyl moieties generates atropisom-
eric ligands with C2-symmetric (anti) and Cs-symmetric
(syn) conformations (Scheme 1).[12] When used in catalysis,
these systems seem to present versatility comparable to the
reference systems SIMes and SIPr and show excellent cata-
lytic activities, especially with one of the three ligands syn-
thesized, which incorporates isopropyl groups at the C-2
and C-7 positions of the naphthyl side chains.
Whereas dozens of structural variations of NHCs A and
B exist nowadays, the overwhelming majority incorporate
the unsaturated central N-heterocycle of A. The reason for
this lies in the surprisingly different stabilities of unsatu-
rated and saturated NHCs. Whereas dimerization of aro-
matically stabilized carbenes of type A is thermodynami-
cally unfavorable even for small N-substituents like R =
Me[6] and has only been observed for a special case of a
covalently tethered bis-carbene,[7] formation of the enetetra-
mine dimer of derivatives of B occurs readily. This renders
saturated NHCs considerably less amenable to catalysis and
restricts access to stable modifications of this ligand class,
Following up on these preliminary data, we now report
the synthesis of several new members of stable, saturated
NHC structures that incorporate naphthyl side chains with
different substitution patterns. We show that their chemical
[a] Organisch-chemisches Institut, Universität Zürich,
Winterthurerstrasse 190, 8057 Zürich, Switzerland
E-mail: dorta@oci.uzh.ch
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FULL PAPER
Scheme 1. Imidazolin-2-ylidenes with phenyl (left) and naphthyl (right) side chains.
behavior is similar and present a comparative study on their enediamine in the presence of Pd(dba)2, (Ϯ)-BINAP, and
fluxional behavior. Further, the new ligands are used to syn- NaOtBu, diamines 2a–g were obtained as pure products af-
thesize new palladium complexes that are subsequently ter chromatographic workup. Finally, ring closing of 2a–g
tested as precatalysts in the Buchwald–Hartwig amination with triethyl orthoformate in the presence of NH4BF4 by
reaction of aromatic bromides and chlorides.
following an adapted synthetic procedure[15] afforded the
corresponding imidazolinium salts 3a–g in good yields and
high purity (Scheme 2).
Results and Discussion
As a result of the presence of the alkyl substituents at C-
2 of their naphthyl moieties, the (2)-SIMeNap·HBF4 (3b),
(2,7)-SIMeNap·HBF4 (3c), (2)-SIPrNap·HBF4 (3d), (2,6)-
SIPrNap·HBF4 (3e), (2,7)-SIPrNap·HBF4 (3f), and (2)-
SICyNap·HBF4 (3g) salts were obtained as a mixture of C2-
(anti) and Cs-symmetric (syn) atropisomers, whereas
SINap·HBF4 (3a) adopts only one conformation. At room
Synthesis and Characterization of N,NЈ-Binaphthyl-
Substituted Imidazolinium Salts
Saturated NHCs with symmetrically substituted aro-
matic side chains are normally prepared from the reaction
of triethyl orthoformate with the corresponding diamine,
which in turn is either accessible through a condensation
and reduction sequence starting from the corresponding
aromatic amine,[9b,13] or through a palladium-catalyzed
double C–N coupling of the aromatic bromide with ethyl-
ene diamine.[14] In our case, this latter reaction sequence
appeared more straightforward when starting from alkyl-
substituted naphthalene derivatives. Indeed, under opti-
mized reaction conditions, the initial bromination turned
out to be very selective for the C-1 position of the naphthyl
derivatives, giving rise to expected isomers 1c–g with selec-
tivities of at least 80%. In some cases, small amounts of
other brominated products were present, but these were
conveniently eliminated through purification by column
chromatography in the next step of the synthetic procedure.
After a double Buchwald–Hartwig coupling with ethyl-
1
temperature ([D6]DMSO), the H NMR spectra of 3c, 3d,
3e, and 3f exhibit two distinct singlets in the region 9.6–
9.5 ppm with an approximate ratio of 1.1:0.9, which corre-
spond to the resonance of the imidazolinium protons. In
the case of (2)-SICyNap·HBF4 (3g), the presence of the
bulky 2-cyclohexyl substituent significantly favors one of
the two isomers, and the 1H NMR spectrum shows two
singlets centered at 9.56 and 9.64 ppm in a ratio of 3:1.
1
Finally, the H NMR spectrum of 3b in [D6]DMSO gives
only one broad signal for the imidazolinium proton
(9.47 ppm), but the presence of both isomers can be de-
duced from the presence of two signals for the aromatic H8
protons of the naphthyl moieties (8.36 and 8.17 ppm).
In order to obtain more information on the dynamic be-
havior of the NHC salts, variable-temperature (VT) 1H
Scheme 2. Synthesis of N,NЈ-binaphthyl-substituted imidazolinium salts. Reaction conditions: (i) Br2, CH2Cl2, 0 °C; (ii) ethylenediamine,
Pd(dba)2, (Ϯ)-BINAP, NaOtBu, toluene, 100 °C; (iii) NH4BF4, HCO2H (cat.), HC(OEt)3, 100 °C.
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A New Class of Stable, Saturated NHCs with N-Naphthyl Substituents
NMR spectroscopic studies were performed. Figure 1 sche- crease in fluxionality is caused by the increased size of the
matically represents the rotation around the C–N bonds C-2 substituents on the naphthyl moieties (isopropyl and
and the hydrogen atoms likely to be affected by the rotation cyclohexyl vs. methyl).
(bold).[16]
Full characterization of these new imidazolinium salts
includes single-crystal X-ray structure analysis of (2)-
SIMeNap·HBF4 (3b) and (2)-SICyNap·HBF4 (3g). For 3b,
the crystals measured correspond to the Cs-symmetric (syn)
species, whereas those of 3g show the C2-symmetric (anti)
isomer (Figure 3).
Figure 1. Schematic representation of the interconversion between
the atropisomers of the imidazolinium salts.
1
First, VT H NMR spectra of SINap·HBF4 (3a) were
measured in [D6]acetone in the temperature range 183–
303 K. Only one set of signals was observed for the whole
temperature range, suggesting that the naphthyl substitu-
ents rotate freely even at low temperature (183 K). In the
case of (2)-SIMeNap·HBF4 (3b), the spectra were recorded
in the temperature range 300–400 K in [D6]DMSO. The re-
sults showed coalescence of the aromatic H8 protons (8.17
and 8.36 ppm at room temperature) at 370 K, and above
380 K the backbone protons of the N-heterocycle appear
as broad singlets, indicating fast interconversion. Note that
the ease of rotation is almost unaffected by the introduction
of the 7-methyl group, as the coalescence temperatures for
(2)-SIMeNap·HBF4 (3b) and (2,7)-SIMeNap·HBF4 (3c) are
almost identical. In the case of 3c, the coalescence can be
also observed for the imidazolinium proton, as its 1H NMR
spectrum shows two distinct singlets (8.05 and 8.10 ppm) at
room temperature and only one signal at 370 K.
Figure 3. ORTEP views (50% probability ellipsoids) of 3b (left) and
3g (right). Hydrogen atoms (except for backbone and imidazolin-
–
ium hydrogen atoms) and counterions (BF4 ) are omitted for clar-
ity.
Synthesis of N,NЈ-Binaphthyl-Substituted NHCs
Deprotonation of imidazolinium salts 3b–g with NaH
and a catalytic amount of potassium tert-butoxide led to
the clean formation of free, monomeric carbenes 4b–g in
high yields. However, attempts to deprotonate SINap·HBF4
(3a) with NaH/KOtBu, KH/DMSO, or KHMDS invariably
led to immediate formation of a bright orange solution con-
taining the dimer SINap=SINap (4a) as the sole observable
product (Scheme 3).
1
Contrary to 3b and 3c, the VT H NMR spectra of (2)-
SIPrNap·HBF4 (3d), (2,6)-SIPrNap·HBF4 (3e), (2,7)-
SIPrNap·HBF4 (3f), and (2)-SICyNap·HBF4 (3g) revealed
a static behavior, with no detectable line-shape modifica-
tions up to 400 K. As an example, Figure 2 shows the spec-
tra of (2)-SICyNap·HBF4 (3g) measured in [D6]DMSO in
the temperature range 300–400 K. Undoubtedly, the de-
Scheme 3. Deprotonation of imidazolinium salts 3a–g.
1
According to the H and 13C NMR spectra, deproton-
ated products 4a–c adopt one conformation at 300 K. In
the case of dimer 4a, this implies that only one of the pos-
sible regioisomers is formed. For monomers (2)-SIMeNap
(4b) and (2,7)-SIMeNap (4c), the results suggest that depro-
tonation of the imidazolinium salts leads to a situation
where the naphthyl side chains are able to freely rotate due
to the removal of the imidazolinium proton. Finally, exami-
nation of (2)-SIPrNap (4d), (2,6)-SIPrNap (4e), (2,7)-
SIPrNap (4f), and (2)-SICyNap (4g) by 1H NMR spec-
troscopy at 300 K revealed two sets of signals correspond-
ing to the presence of two isomers in an approximate ratio
of 1.1:0.9 in the case of 4d–f and 3:1 in the case of 4g. Thus,
removal of the imidazolinium proton does not seem to alter
the initial syn/anti ratio of the isomers, and we can therefore
assume that a sufficiently high barrier to rotation between
Figure 2. VT 1H NMR spectra (400 MHz, [D6]DMSO) of (2)-
SICyNap·HBF4 (3g).
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the C2- and Cs-conformations exists and no interconversion
occurs during the deprotonation step. A straightforward ex-
perimental way to test this hypothesis comes from analysis
of the nuclear Overhauser effects (2D NOESY NMR) be-
tween the respective isomers (Figure 4) and confirms our
assumption for 3f/4f and 3g/4g. The major isomer in both
cases is represented by the anti conformer (C2 symmetry).
This in turn means that the respective orientation of the
side chains and the ratio between anti and syn isomers is
determined during the ring-closing reaction leading to the
NHC salts.
Figure 6. VT 1H NMR spectra (400 MHz, [D8]toluene) of (2)-
SIPrNap (4d).
Figure 4. NOE signals expected for the C2-symmetric conforma-
tion.
In order to evaluate the effect of the removal of the
NHC–H bond on the dynamic behavior of carbenes 4b–g,
1
VT H NMR studies were performed (Figure 5).
Figure 5. Schematic representation of the interconversion between
the atropisomers of the free carbenes (hydrogen atoms affected by
the rotation represented in bold).
As noted above, fast interconversion of the two confor-
mations in (2)-SIMeNap (4b) and (2,7)-SIMeNap (4c) at
room temperature leads to the observation of a single signal
for the H8 protons (8.18 ppm for 4b and 8.02 ppm for 4c
in [D8]toluene). Lowering the temperature showed gradual
broadening of these signals with decoalescence at 273 K
and 293 K for 4b and 4c, respectively. In the case of (2)-
SIPrNap (4d), (2,6)-SIPrNap (4e), (2,7)-SIPrNap (4f), and
(2)-SICyNap (4g), two sets of signals were observed at
Figure 7. VT 1H NMR spectra (400 MHz, [D8]toluene) of (2)-
SICyNap (4g).
A comparison of bond lengths and angles with the only
300 K and fully attributed to the anti and syn forms. By two other crystallographically characterized saturated
raising the temperature, coalescence of the signals corre- NHCs, namely, Arduengo’s SIMes,[3] and Denk’s SItBu,[9a]
sponding to the resonance of the H8 protons was achieved reveals a similar bonding situation for 4c, 4d, and 4f. The
at 330 (4d and 4e), 360 (4f), and 340 K (4g). At 370 K, the N–C–N angles [104.8(2)° for 4c, 104.5(2)° for 4f and
signal appeared as a sharp doublet in all cases (Figures 6 104.8(1)° for 4d] are almost identical to that for SIMes
and 7).
[104.7(3)°] but slightly smaller than that in SItBu
The identities of enetetramine 4a and free NHCs 4c, 4d, [106.44(9)°]. A closer inspection of the planarity of the cen-
and 4f were unambiguously established by single-crystal X- tral N-heterocycle shows that different degrees of distortion
ray structure analyses (Figure 8). The analyzed crystals of exist in these saturated NHCs. Whereas the backbone car-
both (2,7)-SIMeNap (4c) and (2)-SIPrNap (4d) correspond bon atoms in 4d, SIMes, and SItBu deviate measurably
to the syn form, whereas (2,7)-SIPrNap (4f) shows its C2- from the plane of the other three ring atoms, the N-hetero-
symmetric (anti) conformer.[17]
cycles in 4c and 4f are almost perfectly planar.
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A New Class of Stable, Saturated NHCs with N-Naphthyl Substituents
Figure 8. ORTEP views (50% probability ellipsoids) of 4a (top, left), 4c (top, right), 4d (bottom, left), and 4f (bottom, right). Hydrogen
atoms (except for backbone hydrogens) are omitted for clarity.
Activation Free Energies
enes. Furthermore, the values calculated for the rotational
barrier of free carbenes 4d–g validate our experimental con-
clusion that we have drawn above and clearly indicates that
the respective symmetry (C2 or Cs) is maintained in these
structures at room temperature.
From the VT NMR analyses performed above, we calcu-
lated activation free energies for the interconversion of both
imidazolinium salts and free carbenes by using complete
line-shape analysis,[18] which gave the corresponding ∆G‡
values (Table 1). The coalescence temperatures were calcu-
lated from the Gutowsky–Holm equation (kc = π∆ν/21/2).
Assuming the transmission coefficient, κ, to be unity, the
free energy activation (∆G‡) was calculated from the Eyring
equation (∆G‡ = RTc[lnTc – lnkc + 23.76]).[19]
Catalytic Studies: Pd-Catalyzed Buchwald–Hartwig
Amination
Pioneering work by Nolan et al. has shown that NHC-
It is evident from the data that the rotational barriers modified allyl–Pd catalysts are extremely active systems in
decrease in the order 3d–g Ͼ 3c Ͼ 3b Ͼ 3a for the imid- various cross-coupling reaction protocols.[20] We previously
azolinium salts and 4d–g Ͼ 4c Ͼ 4b for the free carbenes. demonstrated that the corresponding complexes incorporat-
These trends can be directly associated with the steric de- ing ligands 4b, 4c, and 4f showed very similar activity to
mand of the naphthyl side chains. More specifically, the size the reference SIMes/SIPr modified systems.[11] We wanted
of the substituents at C-2 of the naphthyl moieties affect therefore to establish how the new ligands reported here,
∆G‡ and limit the rotation about the C–N bonds. Surpris- namely, 4d, 4e, and 4g, would behave in palladium-cata-
ingly, introduction of the cyclohexyl substituent at C-2 lyzed reactions and chose the Buchwald–Hartwig coupling
(Table 1, Entry 13) does not affect the rotational barrier of both aryl bromides and aryl chlorides as the benchmark
more than the introduction of an isopropyl substituent catalytic transformation. At the same time and to see
(Table 1, Entry 10). Overall, ∆G‡ decreases by roughly whether a modification of the precatalyst structure would
20 kJmol–1 when removing the carbenic proton, that is, give a similar increase in reactivity as observed by Nolan et
when going from the imidazolinium salts to the free carb- al.,[20d] we decided to incorporate the cinnamyl fragment
Table 1. Values of Tc and ∆G‡ for 3a–g (imidazolinium salts) and 4b–g (free carbenes).
Entry
Compound
Solvent
Tc (K)
∆G‡ (kJmol–1)
∆G‡ (kcalmol–1)
1
2
3
4
5
6
7
8
SINap·HBF4 (3a)
[D6]acetone
[D6]DMSO
C2D2Cl4
Ͻ183
Ͻ44.1
74.6
75.5
Ͼ89.9
Ͼ89.9
Ͼ89.9
Ͼ89.9
56.9
59.8
80.6
80.4
82.6
Ͻ10.5
17.8
18.0
Ͼ21.5
Ͼ21.5
Ͼ21.5
Ͼ21.5
13.6
14.3
19.2
19.2
19.7
(2)-SIMeNap·HBF4 (3b)
(2,7)-SIMeNap·HBF4 (3c)
(2)-SIPrNap·HBF4 (3d)
(2,6)-SIPrNap·HBF4 (3e)
(2,7)-SIPrNap·HBF4 (3f)
(2)-SICyNap·HBF4 (3g)
(2)-SIMeNap (4b)
370 (H8)
353 (Him
Ͼ410
Ͼ410
)
[D6]DMSO
[D6]DMSO
[D6]DMSO
[D6]DMSO
[D8]toluene
[D8]toluene
[D8]toluene
[D8]toluene
[D8]toluene
[D8]toluene
Ͼ410
Ͼ410
273 (H8)
293 (H8)
350 (H8)
350 (H8)
360 (H8)
350 (H8)
9
(2,7)-SIMeNap (4c)
(2)-SIPrNap (4d)
10
11
12
13
(2,6)-SIPrNap (4e)
(2,7)-SIPrNap (4f)
(2)-SICyNap (4g)
80.6
19.2
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FULL PAPER
(instead of allyl) into the precatalyst structure. Thus, ad- catalysts showing complete conversions at a catalyst loading
dition of [Pd(cinnamyl)Cl]2 to NHC salts 3d, 3e, and 3g in of 1 mol-% and a reaction temperature of 80 °C. Second,
the presence of KOtBu gave high yields of syn/anti mixtures among our complexes, [{(2)-SICyNap}Pd(cinnamyl)Cl]
of complexes [{(2)-SIPrNap}Pd(cinnamyl)Cl] (5d), [{(2,6)- (5g), containing the most sterically demanding substituent
SIPrNap}Pd(cinnamyl)Cl] (5e), and [{(2)-SICyNap}- at C-2, shows the best catalytic performance in all tested
Pd(cinnamyl)Cl] (5g) (Scheme 4). The new complexes were reactions. However, 5d, 5e, and 5g present clearly lower
1
fully characterized by H and 13C NMR spectroscopy and catalytic activities relative to that of reference catalytic sys-
high-resolution mass spectrometry. As expected, the tem 6, which is able to efficiently transform all substrates
syn/anti ratios of the NHC precursors were maintained in studied at room temperature. Furthermore, we should note
the complexes.
that 5d, 5e, and 5g are not more active than our previously
reported [{(2,7)-SIPrNap}Pd(allyl)Cl].[11] Whether this me-
ans that the somewhat different architecture of our naphth-
yl-substituted NHCs (as compared to SIPr/IPr) makes them
insensitive to changes to the allyl moiety of the palladium
precatalyst is not clear at present. Combining the data gath-
ered in Table 2 with our earlier studies[11] indicates that
whereas increased steric bulk at the 2-position of the naph-
thyl side chains translates into overall higher activity, the
substitution pattern on the second naphthyl ring (C-6, C-7)
also plays a role in the catalytic performance of these palla-
dium complexes.
Scheme 4. Synthesis of complexes with general formula [(NHC)-
Pd(cinnamyl)Cl].
The results of the catalytic reactions are summarized in
Table 2 and compared to [(SIPr)Pd(cinnamyl)Cl] (6).[20d]
The following conclusion can be drawn from these prelimi-
nary studies. Firstly, precatalysts 5d, 5e, and 5g are active
Conclusions
The present work extends our previous results on the
synthesis of a new class of saturated NHC ligands with
naphthyl-derived side chains. Both imidazolinium salts and
free carbene species were obtained in a straightforward
manner and in good overall yield and high purity. The dy-
namic behavior of the salts and carbenes, that is, their in-
terconversion between C2-symmetric and Cs-symmetric
conformations, was studied by VT NMR experiments and
shows that the decrease in fluxionality is caused by the in-
creased size of the substituents at C-2 of the naphthyl moie-
ties (cyclohexyl and isopropyl vs. methyl). Steric considera-
tions also played an important role in the catalytic activity
of the palladium complexes derived from these new ligands.
In representative Buchwald–Hartwig amination reactions,
we identified the most bulky new NHC ligand as being su-
perior to the other two NHC–Pd precatalysts tested.
Table 2. Buchwald–Hartwig coupling reactions catalyzed by 5d, 5e,
and 5g.
Experimental Section
General Information: All manipulations were routinely carried out
under an inert atmosphere of nitrogen by using Schlenk techniques
or glove boxes (Mecaplex or Innovative Technology). Solvents were
purged with argon and collected after passage through alumina
columns in a solvent purification system (Innovative Technology).
Deuterated NMR solvents were purchased from Armar Chemicals,
degassed by purging with nitrogen, and dried with activated molec-
ular sieves of appropriate size. NMR spectra were recorded with
Bruker ARX-300, AV2–400, and AV-500 spectrometers and treated
with MestReC. Mass spectra were recorded by the analytical ser-
vices of the Chemistry Department of the University of Zurich.
GC analyses of catalytic products were carried out with a Trace
GC 2000 equipped with an FID detector. The column used was a
30-m ZB-5 capillary column with 0.25-mm inner diameter and
0.25-µm film thickness. Flow rate = 1.5 mLmin–1 for He carrier
[a] Yield determined by GC against internal standard. [b] Data
taken from ref.[20d]
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A New Class of Stable, Saturated NHCs with N-Naphthyl Substituents
gas. Crystals were mounted on a glass fiber for low-temperature X-
in triethyl orthoformate (40 mL) and a few drops of formic acid
ray structure determinations. All measurements were made with a were added. The solution was heated at 100 °C for 4 h. During
Nonius Kappa CCD area-detector diffractometer by using graph- the reaction, ethanol was regularly removed from the solution by
ite-monochromated Mo-Kα radiation (λ = 0.71073 Å) and an Ox-
applying a slight vacuum for a few second. The resulting white
ford Cryosystems Cryostream 700 cooler. CCDC-715132 (for 3g) precipitate was filtered, washed with diethyl ether, and extracted
and -715133 (for 4d) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. Crystallographic data for 3b, 4a, 4c, and 4f
can be found in the Supporting Information of ref.[11] 2-Cyclohex-
ylnaphthalene was prepared according to a published method.[21]
Synthesis of compounds 1c, 1f, 2a–c, 2f, 3a–c, 3f, 4a–c, and 4f was
reported elsewhere.[11] [Pd(cinnamyl)Cl]2 was synthesized following
with CH2Cl2 to remove the excess amount of NH4BF4. After evap-
oration and drying in vacuo, 3d was obtained as a white powder.
1
Yield: 1.12 g (72%). H NMR (400 MHz, [D6]DMSO): δ = 9.62 (s,
0.55 H, N-CH=N of the major isomer), 9.58 (s, 0.45 H, N-CH=N
of the minor isomer), 8.38–7.68 (series of m, 12 H, Har), 4.82 [m,
3
4 H, N(CH2)2N], 3.64 [sept., J = 6.9 Hz, 0.9 H, Ar-CH(CH3)2 of
the minor isomer], 3.41 [sept., 3J = 6.7 Hz, 1.1 H, Ar-CH(CH3)2
of the major isomer], 1.51, 1.47, 1.34, 1.32 [series of d, 12 H, Ar-
CH(CH3)2] ppm. 13C{1H} NMR (100 MHz, [D6]DMSO): δ =
161.5, 161.3 (N-CH=N), 144.4, 144.0, 132.3, 132.2, 130.9, 129.2,
129.1, 128.5, 128.4, 128.35, 128.3, 127.1, 127.0, 126.7, 126.6, 124.3,
124.2, 122.0, 121.3 (Har), 53.6, 53.5 [N(CH2)2N], 28.5, 28.3 [Ar-
CH(CH3)2], 24.0, 23.2, 23.0 [Ar-CH(CH3)2] ppm. HRMS (ESI):
a
published procedure.[22] 2-Isopropylnaphthalene and 2,6-di-
isopropylnaphthalene were purchased from TCI Laboratory Chem-
icals and used without further purification.
1-Bromo-2-isopropylnaphthalene (1d): To a solution of 2-isopropyl-
naphthalene (30 g, 176 mmol) dissolved in CH2Cl2 (250 mL) and
cooled to 0 °C was added a solution of Br2 (28.13 g, 9.04 mL,
176 mmol) in CH2Cl2 (200 mL) dropwise over 90 min. The solution
was then stirred for 1 h at room temperature. Subsequently, the
reaction mixture was quenched by the addition of an aqueous solu-
tion of NaOH. After decantation, the orange organic phase was
separated, washed with water, and dried with anhydrous MgSO4.
After filtration and concentration, the resulting yellow oil was sub-
jected to a short silica gel plug (cyclohexane). The expected product
was isolated as a light yellow liquid containing about 10% of a
secondary brominated isomer and trace amounts of starting mate-
rial. The material was used without further purification for the con-
tinuation of the experiments. Yield: 40.05 g (91%). 1H NMR
+
calcd. for C29H31N2 [M]+ 407.2487; found 407.2491.
1,3-Bis(2-isopropylnaphthalen-1-yl)imidazolin-2-ylidene [(2)-SIPr-
Nap] (4d): A suspension of NaH (60% dispersion in mineral oil,
67 mg, 1.675 mmol) and KOtBu (10 mg, 0.089 mmol) in THF
(10 mL) was added to a suspension of 3d (750 mg, 1.516 mmol) in
THF (10 mL), and the mixture was stirred at room temperature for
24 h. The resulting yellow solution was filtered trough Celite, and
the solvents were evaporated to dryness. After triturating with pen-
tane, evaporation, and drying in vacuo, 4d was obtained as a fine
yellowish powder. Yield: 602 mg (98%). Crystals suitable for X-ray
structure analysis were obtained by slow evaporation of a solution
of 4d in diethyl ether. M.p. 158–159 °C. 1H NMR (400 MHz,
(400 MHz, CDCl3): δ = 8.34 (m, 1 H, Har), 7.79 (m, 2 H, Har), 7.57 C6D6): δ = 8.27 (d, J = 8.4 Hz, 1.10 H, Har of the major isomer),
(m, 1 H, Har), 7.46 (m, 2 H, Har), 3.78 [sept., 3J = 6.9 Hz, 1 H, Ar- 8.19 (d, J = 8.3 Hz, 0.90 H, Har of the minor isomer), 7.70–7.27
CH(CH3)2], 1.33 [d, 3J = 6.9 Hz, 6 H, Ar-CH(CH3)2] ppm. 13C{1H} (series of m, 10 H, Har), 3.78–3.35 [m, 6 H, N(CH2)2N and Ar-
NMR (100 MHz, CDCl3): δ = 145.1, 133.2, 132.5, 127.9, 127.8,
CH(CH3)2], 1.44–1.32 [series of four d, 12 H, Ar-CH(CH3)2] ppm.
127.7, 127.2, 125.7, 124.1, 123.1 (Car), 33.8 [Ar-CH(CH3)2], 22.8 13C{1H} NMR (100 MHz, [D8]toluene): δ = 246.2, 246.0 (N-C-N),
[Ar-CH(CH3)2] ppm. HRMS (EI): calcd. for C13H13Br 248.0201; 143.8, 143.7, 136.8, 133.6, 132.4, 132.3, 128.4, 128.2, 126.7, 126.6,
found 248.0200.
125.5, 124.3, 124.0, 123.8 (Car), 53.6 [N(CH2)2N], 29.1, 29.0 [Ar-
CH(CH3)2], 24.7, 24.6, 23.5 [Ar-CH(CH3)2] ppm.
N,NЈ-Bis(2-isopropylnaphthalen-1-yl)ethane-1,2-diamine (2d): In a
glove box, a mixture of Pd2(dba)3 (261.4 mg, 0.285 mmol), (Ϯ)-
1-Bromo-2,6-diisopropylnaphthalene (1e): To a solution of 2,6-di-
BINAP (357.8 mg, 0.575 mmol), and NaOtBu (1.651 g, isopropylnaphthalene (37.4 g, 176 mmol) dissolved in CH2Cl2
17.178 mmol) in toluene (50 mL) was stirred for a few minutes. (250 mL) and cooled to 0 °C was added a solution of Br2 (28.13 g,
Then, a solution of 1d (3 g, 12.036 mmol) in toluene (30 mL) was
added. Finally, ethylenediamine (383 µL, 5.729 mmol) was added.
The volume of toluene was adjusted to 150 mL. The resulted dark
red solution was heated at 100 °C for 20 h, subsequently cooled to
room temperature, and filtered through a silica gel/Celite plug to
remove insoluble residues. The filtrate was washed with CH2Cl2
until the eluent became colorless. After concentration in vacuo, the
residue was subjected to column chromatography on silica gel (hex-
ane/CH2Cl2, 10:1 to 1:1). Product 2d was isolated from the last
9.04 mL, 176 mmol) in CH2Cl2 (200 mL) dropwise over a period
of 1 h. The solution was then stirred for 1 h at room temperature
and subsequently quenched by the addition of an aqueous solution
of NaOH. After decantation, the orange organic phase was sepa-
rated, washed with water, and dried with anhydrous MgSO4. After
filtration and concentration, the resulting yellow oil was subjected
to a silica gel plug (hexane). The expected product contained about
15% of a secondary brominated isomer. Yield: 45.61 g (89%). This
starting material was used without further purification for the con-
tinuation of the experiments. 1H NMR (400 MHz, CDCl3): δ =
1
fraction as a yellow oil. Yield: 1.52 g (66%). H NMR (400 MHz,
CDCl3): δ = 8.27 (m, 2 H, Har), 7.82 (m, 2 H, Har), 7.62 (m, 2 H, 8.31 (m, 1 H, Har), 7.76 (m, 1 H, Har), 7.62 (m, 1 H, Har), 7.51 (m,
Har), 7.46 (m, 6 H, Har), 3.97 (br., 2 H, NH), 3.53 [sept., 3J = 1 H, Har), 7.43 (m, 1 H, Har), 3.79 [sept., 3J = 6.9 Hz, 1 H, Ar-
3
3
6.8 Hz, 2 H, Ar-CH(CH3)2], 3.48 [s, 4 H, N(CH2)2N], 1.34 [d, J = CH(CH3)2], 3.11 [sept., J = 6.9 Hz, 1 H, Ar-CH(CH3)2], 1.38 [d,
6.8 Hz, 12 H, Ar-CH(CH3)2] ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 140.7, 137.2, 133.2, 129.4, 128.3, 125.6, 125.1, 124.2,
123.8, 123.3 (Car), 52.0 [N(CH2)2N], 27.8 [Ar-CH(CH3)2], 23.9 [Ar-
3J = 6.9 Hz, 6 H, Ar-CH(CH3)2], 1.35 [d, 3J = 6.9 Hz, 6 H, Ar-
CH(CH3)2] ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 146.3,
144.2, 133.4, 131.2, 127.7, 127.6, 127.1, 124.2, 124.1, 122.9 (Car),
33.9, 33.7 [Ar-CH(CH3)2], 23.9, 22.9 [Ar-CH(CH3)2] ppm. HRMS
(EI): calcd. for C16H19Br 290.0670; found 290.0668.
CH(CH3)2] ppm. HRMS (ESI): calcd. for C28H33N2 [M + H]+
+
397.2644; found 397.2642.
1,3-Bis(2-isopropylnaphthalen-1-yl)imidazolinium Tetrafluoroborate
N,NЈ-Bis(2,6-diisopropylnaphthalen-1-yl)ethane-1,2-diamine (2e): In
a glove box, a mixture of Pd2(dba)3 (261.4 mg, 0.285 mmol), (Ϯ)-
BINAP (357.8 mg, 0.575 mmol), and NaOtBu (1.651 g,
[(2)-SIPrNap·HBF4] (3d):
A mixture of diamine 2d (1.25 g,
3.152 mmol) and NH4BF4 (429.6 mg, 4.098 mmol) was dissolved
Eur. J. Inorg. Chem. 2009, 1861–1870
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1867

L. Vieille-Petit, X. Luan, R. Mariz, S. Blumentritt, A. Linden, R. Dorta
FULL PAPER
17.178 mmol) in toluene (50 mL) was stirred for a few minutes.
Then, a solution of 1e (3.5 g, 12.022 mmol) in toluene (30 mL) was
added. Finally, ethylenediamine (383 µL, 5.729 mmol) was added.
The volume of toluene was adjusted to 150 mL. The resulting dark
red solution was heated at 100 °C for 20 h, subsequently cooled to
room temperature, and filtered through silica gel/Celite to remove
the insoluble materials. The filtrate was washed with CH2Cl2 until
the eluent became colorless. After concentration in vacuo, the resi-
due was subjected to column chromatography on silica gel (hexane/
CH2Cl2, 10:1 to 1:1). Product 2e was isolated from the last fraction
as a yellowish oil. Yield: 1.81 g (66%). 1H NMR (400 MHz,
CDCl3): δ = 8.27 (d, J = 8.8 Hz, 2 H, Har), 7.68 (m, 2 H, Har), 7.61
(d, J = 8.8 Hz, 2 H, Har), 7.45 (m, 4 H, Har), 3.89 (br., 2 H, NH),
3.57 [sept., 3J = 6.8 Hz, 2 H, Ar-CH(CH3)2], 3.52 [s, 4 H, N(CH2)2-
N], 3.12 [sept., 3J = 6.8 Hz, 2 H, Ar-CH(CH3)2], 1.40 [d, 3J =
1-Bromo-2-cyclohexylnaphthalene (1g): To a solution of 2-cyclohex-
ylnaphthalene (3.70 g, 17.6 mmol) dissolved in CH2Cl2 (100 mL)
and cooled to 0 °C was added a solution of Br2 (3.63 g, 22.7 mmol)
in CH2Cl2 (100 mL) dropwise over 30 min. The solution was stirred
for 1 h at room temperature and subsequently quenched by the
addition of an aqueous solution of NaOH (200 mL). After decan-
tation, the orange organic phase was separated, washed with water,
and dried with anhydrous MgSO4. After concentration, filtration
through a plug of silica gel (hexane) and drying in vacuo, pure 1g
was obtained as a yellow liquid. Yield: 5.01 g (91%). 1H NMR
(500 MHz, CDCl3): δ = 8.37 (m, 1 H, Har), 7.80 (m, 2 H, Har), 7.59
(m, 1 H, Har), 7.48 (m, 2 H, Har), 3.40 (m, 1 H, HCy), 1.91 (m, 5
H, HCy), 1.53 (m, 4 H, HCy), 1.34 (m, 1 H, HCy) ppm. 13C{1H}
NMR (125 MHz, CDCl3): δ = 144.4, 133.5, 132.8, 128.1, 128.0,
127.9, 127.4, 126.0, 125.2, 123.6 (Car), 44.6, 33.4, 27.1, 26.5 (CCy
)
6.8 Hz, 12 H, Ar-CH(CH3)2], 1.38 [d, 3J = 6.8 Hz, 12 H, Ar- ppm. HRMS (EI): calcd. for C16H17Br 288.0514; found 288.0514.
CH(CH3)2] ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 145.5,
140.7, 136.3, 133.4, 127.9, 125.4, 124.5, 124.2, 123.5, 123.3 (Car),
N,NЈ-Bis(2-cyclohexylnaphthalen-1-yl)ethane-1,2-diamine (2g): In a
glove box, a mixture of Pd(dba)2 (442 mg, 0.769 mmol), (Ϯ)-BI-
52.0 [N(CH2)2N], 34.0 [Ar-CH(CH3)2], 27.7 [Ar-CH(CH3)2], 23.95
NAP (483 mg, 0.776 mmol), and NaOtBu (2.217 g, 23.067 mmol)
[Ar-CH(CH3)2], 23.9 [Ar-CH(CH3)2] ppm. HRMS (EI): calcd. for
in toluene (50 mL) was stirred for a few minutes. Then, a solution
C34H44N2Na 503.3402; found 503.3408.
of 1g (4.7 g, 16.252 mmol) in toluene (30 mL) was added. Finally,
ethylenediamine (414 µL, 7.685 mmol) was added. The volume of
toluene was adjusted to 150 mL. The resulting dark red solution
was heated at 100 °C for 20 h, cooled to room temperature, and
1,3-Bis(2,6-diisopropylnaphthalen-1-yl)imidazolinium Tetrafluorobo-
rate [(2,6)-SIPrNap·HBF4] (3e): A mixture of diamine 2e (1.17 g,
2.434 mmol) and NH4BF4 (306 mg, 2.919 mmol) was dissolved in
filtered through silica gel/Celite to remove the insoluble materials.
triethyl orthoformate (30 mL) and a few drops of formic acid were
The filtrate was washed with CH2Cl2 until the eluent became color-
added. The solution was heated at 100 °C for 4 h. During the reac-
tion, ethanol was regularly removed from the solution by applying
less. After concentration in vacuo, the residue was subjected to col-
umn chromatography on silica gel (hexane/CH2Cl2, 10:1 to 1:1).
a slight vacuum for a few seconds. The resulting white precipitate
The last fraction was collected and concentrated, and the residue
was filtered, washed with diethyl ether, and then with water (to
was recrystallized from pentane to give 2g as a yellowish solid.
remove the excess amount of NH4BF4). After drying in vacuo for
1
Yield: 2.50 g (68%). H NMR (400 MHz, CDCl3): δ = 8.25 (m, 2
2 d, 3e was obtained as a white powder. Yield: 1.09 g (77%). 1H
H, Har), 7.79 (m, 2 H, Har), 7.57 (m, 2 H, Har), 7.42 (m, 6 H, Har),
NMR (300 MHz, [D6]DMSO): δ = 9.58 (s, 0.55 H, N-CH=N of
3.93 (br., 2 H, NH), 3.13 (m, 2 H, HCy), 1.86–1.26 (m, 20 H, HCy
)
the major isomer), 9.55 (s, 0.45 H, N-CH=N of the minor isomer),
8.28–7.71 (series of m, 10 H, Har), 4.81 [m, 4 H, N(CH2)2N], 3.61
[sept., 3J = 6.8 Hz, 0.9 H, Ar-CH(CH3)2 of the minor isomer], 3.38
[sept., 3J = 6.9 Hz, 1.1 H, Ar-CH(CH3)2 of the major isomer], 3.16
[m, 2 H, Ar-CH(CH3)2], 1.52–1.32 [m, 24 H, Ar-CH(CH3)2] ppm.
13C{1H} NMR (125 MHz, [D6]DMSO): δ = 161.4, 161.2 (N-
CH=N), 146.9, 143.4, 143.0, 132.6, 132.5, 130.6, 128.1, 128.0,
127.8, 127.7, 127.0, 126.9, 124.6, 124.5, 124.2, 124.1, 122.1, 121.4
(Car), 53.6, 53.5 [N(CH2)2N], 33.3, 28.4, 28.2 [Ar-CH(CH3)2], 24.1,
24.0, 23.7, 23.6, 23.55, 23.5, 23.2, 22.9 [Ar-CH(CH3)2] ppm. HRMS
ppm. 13C{1H} NMR (100 MHz, CDCl3): δ = 141.3, 136.8, 133.4,
129.7, 128.5, 125.8, 125.3, 123.9, 123.5 (Car), 52.4 [N(CH2)2N],
39.1, 34.5, 27.4, 36.4 (CCy) ppm. HRMS (ESI): calcd. for
C34H40N2Na 499.3089; found 499.3091.
1,3-Bis(2-cyclohexylnaphthalen-1-yl)imidazolinium Tetrafluorobo-
rate [(2)-SICyNap·HBF4] (3g): A mixture of diamine 2g (2.00 g,
4.195 mmol) and NH4BF4 (440 mg, 4.197 mmol) was dissolved in
triethyl orthoformate (45 mL) and a few drops of formic acid were
added. The solution was heated at 100 °C for 4 h. During the reac-
tion, ethanol was regularly removed by applying a slight vacuum
for a few seconds. The resulting white precipitate was filtered,
washed, redissolved in a mixture of acetone/CH2Cl2 (9:1, 60 mL),
and precipitated by the addition of a mixture Et2O/pentane (1:1).
After drying in vacuo, 3g was obtained as white powder. Yield:
+
(ESI): calcd. for C35H43N2 [M]+ 491.3426; found 491.3422.
1,3-Bis(2,6-diisopropylnaphthalen-1-yl)imidazolin-2-ylidene [(2,6)-
SIPrNap] (4e): In a glove box, a suspension of NaH (60% disper-
sion in mineral oil, 45 mg, 1.125 mmol) and KOtBu (7 mg,
0.062 mmol) in THF (10 mL) was added to a suspension of 3e
(576 mg, 0.995 mmol) in THF (10 mL) and stirred at room tem-
perature for 24 h. The resulting yellow solution was filtered through
Celite, and the solvents were evaporated to dryness. The residue
was dissolved in ether and again filtered through Celite. After evap-
oration and drying in vacuo, 4e was obtained as a fine yellowish
powder. Yield: 470 mg (96%). M.p. 155–156 °C. 1H NMR
(400 MHz, C6D6): δ = 8.28 (d, J = 8.5 Hz, 1.10 H, Har of the major
isomer), 8.19 (d, J = 8.3 Hz, 0.90 H, Har of the minor isomer),
7.71–7.40 (series of m, 8 H, Har), 3.85–3.43 [m, 6 H, N(CH2)2N
1
1.89 g (78%). H NMR (400 MHz, [D6]DMSO): δ = 9.64 (s, 0.25
H, N-CH=N, minor isomer), 9.56 (s, 0.75 H, N-CH=N, major iso-
mer), 8.24–7.69 (series of m, 12 H, Har), 5.03–4.68 [m, 4 H, N(CH2)2-
N], 3.07 (m, 1.5 H, cyclohexyl-CH, major isomer), 2.93 (m, 0.5
H, cyclohexyl-CH, minor isomer), 1.99–1.36 (m, 20 H, HCy) ppm.
13C{1H} NMR (100 MHz, [D6]DMSO): δ = 161.9, 161.3 (N-
CH=N), 143.2, 142.8, 132.3, 132.2, 130.8, 130.7, 129.1, 129.0,
128.5, 128.45, 128.4, 128.2, 127.2, 127.1, 126.7, 126.6, 125.1, 125.0,
121.6, 121.4 (Car), 54.8 [N(CH2)2N], 53.5 [N(CH2)2N], 33.9, 33.1,
32.3, 26.2, 26.1, 26.0, 25.3, 25.2 (CCy) ppm. HRMS (ESI): calcd.
for C35H39N2 [M]+ 487.3113; found 487.3110.
3
and Ar-CH(CH3)2], 2.91 [sept., J = 6.8 Hz, 2 H, Ar-CH(CH3)2],
1.48–1.25 [m, 24 H, Ar-CH(CH3)2] ppm. 13C{1H} NMR
(100 MHz, [D8]toluene): δ = 246.0, 245.9 (N-C-N), 145.8, 143.0,
142.9, 136.9, 134.0, 131.1, 131.0, 126.4, 126.3, 124.8, 124.3, 124.2,
1,3-Bis(2-cyclohexylnaphthalen-1-yl)imidazolin-2-ylidene [(2)-SICy-
Nap] (4g): In a glove box, a suspension of NaH (60% dispersion
124.1 (Car), 53.6 [N(CH2)2N], 34.4, 29.1, 29.0 [Ar-CH(CH3)2], 24.8, in mineral oil, 61 mg, 1.525 mmol) and KOtBu (7 mg, 0.062 mmol)
24.7, 24.1, 24.0, 23.7, 23.6 [Ar-CH(CH3)2] ppm. in THF (40 mL) was added to a suspension of 3g (800 mg,
1868
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1861–1870

A New Class of Stable, Saturated NHCs with N-Naphthyl Substituents
1.392 mmol) in THF (40 mL) and stirred at room temperature for
24 h. The resulting yellow solution was filtered through Celite, and
the solvents were evaporated to dryness. After triturating with pen-
tane, evaporation, and drying in vacuo, 4g was obtained as a fine
off-white powder. Yield: 640 mg (95%). M.p. 169–171 °C. 1H NMR
(400 MHz, C6D6): δ = 8.36 (d, J = 8.3 Hz, 0.5 H, H8, minor iso-
mer), 8.27 (d, J = 8.3 Hz, 1.5 H, H8, major isomer), 7.72–7.26
(mixture of isomers) was obtained from the major fraction as a
pale-yellow powder. Yield: 310 g (93%). 1H NMR (400 MHz,
CDCl3): δ = 8.16–6.67 (series of m, 17 H), 4.96 (m, 0.25 H), 4.41–
3.23 (series of m, 6 H), 2.95–2.39 (series of m, 1.5 H), 2.21–1.26
(series of m, 21.5 H), 0.89 (m, 0.5 H), 0.72 (m, 0.25 H) ppm.
13C{1H} NMR (100 MHz, CDCl3): δ = 214.3, 213.9, 212.1, 145.2,
145.1, 144.4, 144.3, 139.2, 138.6, 134.4, 134.3, 134.3, 134.1, 133.9,
(series of m, 10 H, Har), 3.73–3.31 [m, 6 H, N(CH2)2N and cyclo- 133.6, 133.4, 133.3, 131.5, 131.4, 129.5, 129.4, 129.3, 129.0, 128.6,
hexyl-CH], 2.31–1.22 (series of m, 20 H, cyclohexyl-CH2) ppm. 128.5, 128.4, 128.3, 128.1, 127.6, 127.4, 127.2, 127.1, 127.0, 126.9,
13C{1H} NMR (100 MHz, C6D6): δ = 245.6 (N-C-N), 143.3, 142.8, 126.6, 126.5, 126.3, 126.2, 126.1, 126.0, 125.9, 125.8, 125.1, 125.0,
137.1, 137.0, 133.8, 133.7, 132.5, 128.6, 128.1, 127.9, 127.4, 126.9,
126.6, 125.6, 125.5, 125.4, 124.2, 124.0 (Car), 54.0, 53.7 [N(CH2)2-
124.0, 110.1, 109.9, 90.4, 90.2, 88.3, 87.8, 51.2, 49.6, 48.0, 47.2,
40.3, 40.1, 40.0, 37.0, 36.9, 36.8, 36.5, 34.8, 33.7, 33.3, 33.2, 32.9,
N], 40.1, 39.8, 34.7, 34.6, 34.4, 34.0, 30.2, 28.0, 27.8, 27.5, 26.7, 28.2, 28.1, 28.0, 27.4, 27.3, 27.2, 27.0, 26.9, 26.8, 22.9, 14.4 ppm.
+
26.6 (CCy) ppm.
HRMS (ESI): calcd. for C44H47104PdN2 [M – Cl]+ 707.2779;
found 707.2785.
{[(2)-SIPrNap]Pd(cinnamyl)Cl} (5d): In a glove box, a 20-mL vial
was charged with (2)-SIPrNap·HBF4 (3d; 200 mg, 0.404 mmol),
[Pd(cinnamyl)Cl]2 (100 mg, 0.190 mmol), KOtBu (45 mg,
0.404 mmol), and THF (10 mL). The reaction mixture was stirred
at room temperature for 16 h and subsequently filtered through a
mixture of silica gel/Celite, and the filter was washed with hexane/
EtOAc (1:1). After evaporation, the residue was subjected to col-
umn chromatography on silica gel (hexane/EtOAc, 2:1). Product 5d
(mixture of isomers) was obtained from the major fraction as a
pale-yellow powder. Yield: 330 mg (94%). 1H NMR (300 MHz,
CD2Cl2): δ = 8.17–6.70 (series of m, 17 H), 4.93 (m, 0.25 H), 4.40–
4.19 (m, 4.75 H), 3.98–3.61 (m, 3 H), 2.71 (m, 1 H), 1.58–1.32
(series of m, 12 H), 1.28–1.15 (m, 1.2 H), 0.91–0.75 (m, 0.8 H)
ppm. 13C{1H} NMR (100 MHz, CD2Cl2): δ = 215.2, 146.2, 145.3,
139.1, 138.6, 134.1, 134.0, 133.8, 133.7, 133.5, 131.4, 131.3, 129.8,
129.7, 129.6, 129.1, 128.6, 128.5, 128.4, 127.5, 127.4, 127.2, 127.1,
126.9, 126.7, 126.3, 126.2, 126.1, 125.5, 125.3, 125.0, 124.8, 123.9,
110.1, 110.0, 90.2, 88.2, 87.9, 49.6, 48.6, 47.7, 34.7, 29.3, 26.0, 25.9,
25.8, 25.7, 24.0, 23.6, 22.9, 14.4 ppm. HRMS (ESI): calcd. for
Buchwald–Hartwig Cross-Coupling Reactions (General Procedure):
In a glove box, to a vial closed with a screw cap fitted with a
septum and equipped with a magnetic stir bar was sequentially
added the catalyst (1 mol-%), KOtBu (124 mg, 1.1 mmol), DME
(1 mL), and dodecane (216 µL, 1 mmol). The mixture was then
stirred at room temperature. After 5 min, the aryl chloride
(1 mmol) and the amine (1.1 mmol) were injected. If the reaction
was carried out at 80 °C, the aryl chloride and the amine were
injected outside the glove box. The reaction was monitored by gas
chromatography.
Buchwald–Hartwig Cross-Coupling Reactions at Low Catalyst
Loading: In a glove box, the catalyst (0.01 mmol) was dissolved in
DME (10 mL), providing catalyst solution A. To another vial
closed with a screw cap fitted with a septum and equipped with a
magnetic stir bar was sequentially added potassium KOtBu
(124 mg, 1.1 mmol), catalyst solution A (1 mL, 0.1 mol-%), and do-
decane (216 µL, 1 mmol). The mixture was then stirred at room
temperature. After 5 min, the aryl chloride (1 mmol) and the amine
(1.1 mmol) were injected. The reaction was monitored by gas
chromatography.
C38H39104PdN2 [M – Cl]+ 627.2153; found 627.2161.
+
{[(2,6)-SIPrNap]Pd(cinnamyl)Cl} (5e): In the glove box, a 20-mL
vial was charged with (2,6)-SIPrNap·HBF4 (3e; 100 mg,
0.173 mmol), [Pd(cinnamyl)Cl]2 (43 mg, 0.082 mmol), KOtBu
(20 mg, 0.173 mmol), and THF (8 mL). The reaction mixture was
stirred at room temperature for 16 h and subsequently filtered
through a mixture of silica gel/Celite, and the filter was washed
with hexane/EtOAc (1:1). After evaporation, the residue was sub-
jected to column chromatography on silica gel (hexane/EtOAc,
2:1). Product 5e (mixture of isomers) was obtained from the major
Acknowledgments
R.D. holds an Alfred Werner Assistant Professorship and thanks
the foundation for generous financial support. L.V.-P. acknowl-
edges the Legerlotz Foundation for a fellowship. X.L. thanks the
University of Zurich (Drittmittelkredit) for support. We thank
Prof. Jay S. Siegel and LPF (Labor für Prozessforschung, OCI) for
the generous donation of 2,7-dimethylnaphthalene and Prof. Luigi
Cavallo for his suggestion for the graphical abstract.
1
fraction as a pale-yellow powder. Yield: 180 mg (97%). H NMR
(400 MHz, CDCl3): δ = 8.06–6.72 (series of m, 15 H), 4.35–3.66
(series of m, 8.5 H), 3.16 (m, 2 H), 2.73–2.63 (m, 1 H), 1.62–1.31
(series of m, 24 H), 0.90 (m, 0.5 H) ppm. 13C{1H} NMR
(100 MHz, CDCl3): δ = 214.4, 146.2, 146.0, 144.8, 144.6, 138.4,
133.4, 133.2, 133.1, 133.0, 129.3, 129.2, 129.1, 128.9, 128.8, 128.7,
128.0, 127.9, 127.6, 127.3, 127.0, 126.9, 126.7, 126.3, 126.2, 126.0,
124.9, 124.8, 124.7, 124.3, 124.1, 123.3, 109.6, 87.2, 53.9, 53.7, 53.4,
49.2, 34.0, 28.5, 25.6, 25.5, 24.1, 23.8, 23.7, 23.2, 22.3 ppm. HRMS
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Eur. J. Inorg. Chem. 2009, 1861–1870
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1869

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Received: January 5, 2009
Published Online: March 12, 2009
1870
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 1861–1870