Synthesis, structure, and temperature-dependent dynamics of neutral palladium allyl complexes of annulated diaminocarbenes and their catalytic application for C-C and C-N bond formation reactions

Article abstract of DOI:10.1021/om1000327

Imidazolinium salts 7,9-bis(2,4,6-trimethylphenyl)-6b,9a- dihydroacenaphtho[1,2-d]imidazolinium tetrafluoroborate and 7,9-bis(2,6- diisopropylphenyl)-6b,9a-dihydroacenaphtho[1,2-d]imidazolinium tetrafluoroborate, designated as [(BIAN-SIMes)(H)]BF₄ (3a) and [(BIAN-SIPr)(H)]BF₄ (3b), respectively, have been prepared and structurally characterized. The molecular structure of 3a shows the presence of a bifurcated hydrogen bond between the tetrafluoroborate anions and the central imidazolinium proton (-NCHN-). The palladium(II) complexes (η³- C₃H₅)Pd(BIAN-SIMes)Cl (5a) and (η³-C ₃H₅)Pd(BIAN-SIPr)Cl (5b) have been synthesized. The temperature-dependent NMR behavior of σ-bonded palladium(II) complex 5b was studied. The crystal structure of 5b shows a localized single and double bond between the allyl ligand. The catalytic activities of the palladium(II) complexes 5a and 5b have been evaluated for Suzuki-type C-C coupling and for room-temperature C-N bond formation using aryl halides.

Full text of DOI:10.1021/om1000327

4858 Organometallics 2010, 29, 4858–4870
DOI: 10.1021/om1000327
Synthesis, Structure, and Temperature-Dependent Dynamics of Neutral
Palladium Allyl Complexes of Annulated Diaminocarbenes and Their
Catalytic Application for C-C and C-N Bond Formation Reactions†
Sarim Dastgir,*,‡,§ Karl S. Coleman,^ Andrew R. Cowley,‡ and Malcolm L. H. Green*,‡
‡Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QR, U.K., and
^Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, U.K. §Present address:
Department of Chemistry, York University, 4700 Keele St., Toronto, ON, M3J 2Z3, Canada. Tel: þ1 416
736 2100, ext. 77720. Fax: þ1 416 736 5936
Received January 11, 2010
Imidazolinium salts 7,9-bis(2,4,6-trimethylphenyl)-6b,9a-dihydroacenaphtho[1,2-d]imidazolinium
tetrafluoroborate and 7,9-bis(2,6-diisopropylphenyl)-6b,9a-dihydroacenaphtho[1,2-d]imidazolinium
tetrafluoroborate, designated as [(BIAN-SIMes)(H)]BF4 (3a) and [(BIAN-SIPr)(H)]BF4 (3b), respec-
tively, have been prepared and structurally characterized. The molecular structure of 3a shows the
presence of a bifurcated hydrogen bond between the tetrafluoroborate anions and the central
imidazolinium proton (-NCHN-). The palladium(II) complexes (η3-C3H5)Pd(BIAN-SIMes)Cl
(5a) and (η3-C3H5)Pd(BIAN-SIPr)Cl (5b) have been synthesized. The temperature-dependent NMR
behavior of σ-bonded palladium(II) complex 5b was studied. The crystal structure of 5b shows a
localized single and double bond between the allyl ligand. The catalytic activities of the palladium(II)
complexes 5a and 5b have been evaluated for Suzuki-type C-C coupling and for room-temperature
C-N bond formation using aryl halides.
Introduction
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discussed extensively in recent literature.10-14 The strong
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reductive elimination and to degradative cleavage during
catalytic reactions;12,13,15 however, their reductive elimina-
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catalysts for a wide range of organic transformations,
including metathesis17,18 and cross-coupling reactions.19-22
Unlike phosphines,23 the steric and electronic tunability of
Almost two decades after the pioneering work by Wanzlick
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2
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† Part of the Dietmar Seyferth Festschrift.
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*Corresponding authors. Tel: þ44 (0) 1865 272600. Fax: þ44 (0) 1865
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Published on Web 05/13/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 21, 2010 4859
Scheme 2. Synthesis of (η3-C3H5)Pd(BIAN-SIAr)Cl Complexesa
Figure 1. Stable acenaphthylene-annulated diamino carbene
ligands.
Scheme 1. Synthesis of Imidazolium Salts
a (i) KOtBu/THF, -78 ꢀC (3a); (ii) nBuLi/pentane, -78 ꢀC (3b); (iii)
[(η3-C3H5)Pd(μ-Cl)]2/THF, -78 ꢀC (10 min) to room temperature (3 h).
In our studies of the organometallic chemistry of NHCs,8,33-38
we have recently described the first stable acenaphthylene-
annulated backbone (C4-C5) diamino carbene ligand39
(Figure 1) and its coordination with rhodium(I) and iridium-
(I). The presence of substantial steric bulk located away from
the coordination site could modify the coordination behavior
of these ligands and thereby provide the opportunity for
catalyst fine-tuning. Here we report the synthesis of ligand
precursors [(BIAN-SIMes)(H)]BF4 (3a) and [(BIAN-SIPr)-
(H)]BF4 (3b) (Scheme 1) and their coordination to palladium
using [Pd(η3-C3H5)(μ-Cl)]2, Scheme 2. The variable-tempera-
ture dynamics for the corresponding palladium allyl com-
plexes and their catalytic behavior for Suzuki-type C-C
coupling and room-temperature C-N bond formation using
aryl halides have also been investigated.
NHCs is more restricted due to their confined architectures.
Studies on the annulated backbone (C4-C5)-substituted
NHCs have demonstrated that the stability24-29 and the
σ-donating ability of NHCs vary substantially with a
change in the substituent (π-donor/acceptor) attached to
the imidazole ring and may be used as a tool for the fine-
tuning of the electronic properties.30-32 A range of annu-
lated NHC complexes have been synthesized by in situ
trapping of the carbene with suitable metal precursors,
but the corresponding NHCs were not isolated, presum-
ably due to the more ubiquitous dimerization of saturated
carbenes to produce enetetramines.24,26-28
Results and Discussion
Synthesis and Characterization of the Imidazolinium Salts
[(BIAN-SIMes)(H)]BF4 (3a) and [(BIAN-SIPr)(H)]BF4 (3b).
Our investigation of the synthesis of imidazolinium salts
[(BIAN-SIMes)(H)]BF4 (3a) and [(BIAN-SIPr)(H)]BF4 (3b)
started with the synthesis of bis(aryl)acenaphthenequinone-
diimine Ar-BIAN, where Ar = 2,4,6-trimethylphenyl (1a)40
and 2,6-diisopropylphenyl (1b).41 The reduction of Ar-BIAN
with LiAlH4 produced (1R,2S)-N,N-bis(aryl)-1,2-dihydro-
acenaphthylene-1,2-diamine, which on cyclization with triethyl
orthoformate in the presence NH4BF4 and an acid catalyst
gave the imidazolinium salts 3a and 3b as off-white solids in
good yields (60-75%), Scheme 1. The imidazolinium salts 3a
and 3b were characterized by elemental analysis, mass spectro-
metry (ESþ), single-crystal X-ray diffraction analysis, and 1H
and 13C NMR studies using gCOSY, HMBC, HMQC, DEPT,
and TOCSY experiments.
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As expected, the 1H NMR (CDCl3) spectrum of imidazo-
linium salt 3a shows the presence of one set of three char-
acteristic resonances for the mesityl CH3 protons at δ 2.60,
2.34, and 1.42, while the mesityl m-CH protons appeared as a
set of two broad singlets at δ 7.09 and 6.87, respectively. On
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1
the other hand, the H NMR (CDCl3) spectrum of imida-
zolinium salt 3b showed a typical AX2 spectrum as two sets
of four doublets for the isopropyl CH3 protons at δ 1.55
(3J = 6.6 Hz), 1.34 (3J = 6.6 Hz), 0.89 (3J = 6.7 Hz), and
0.72 (3J = 6.6 Hz), respectively, whereas the isopropyl
methine protons were observed as a set of two septets at δ
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Fukuda, Y. Eur. J. Inorg. Chem. 2001, 10, 2641–2646.

4860 Organometallics, Vol. 29, No. 21, 2010
Dastgir et al.
Figure 2. ORTEP diagram of the molecular structure of [(BIAN-SIMes)(H)]BF4 (3a) at 40% probability (a). Solvent molecule and
BF4 anion have been removed for clarity. (b) A bifurcated hydrogen bond between two neighboring BF4 anions is shown. (Solvent
molecules and the backbone naphthyl group have been removed for clarity.)
3.43 (3J = 6.7 Hz) and 1.94 (3J = 6.6 Hz), respectively. The
N-2,6-diisopropylphenyl m-CH on either side of the imida-
zole ring appeared as a set of two doublets of doublets at
δ 7.42 (3J = 7.4 Hz, 4J = 1.4 Hz) and 7.20 (3J = 7.6 Hz, 4J =
1.4 Hz), and the p-CH appeared as a triplet at δ 7.48 (3J =
6.7 Hz). This peak pattern suggests the hindered rotation
around the N-aromatic bonds on either side of imidazole
rings. The backbone (-NCHCHN-) protons appear as
singlets at δ 6.61 (3a) and 6.67 (3b), respectively, and the
central imidazolinium (-NCHN-) proton shows the char-
acteristic downfield resonance at δ 8.19 (3a) and 8.18 (3b),
respectively. In the 13C NMR spectrum the central imidazo-
linium carbon (-NCN-) shows a resonance at δ 157.1
(3a) and 156.3 (3b), respectively. The (-NCCN-) carbons
appeared as singlets at δ 70.6 (3a) and 72.6 (3b), respectively.
1
Full H and 13C{1H} assignments for imidazolium salts 3a
and 3b are detailed in the Experimental Section and are
comparable with data reported for similar compounds.42,43
Structural Study. To establish the molecular structure for
the imidazolinium salts 3a and 3b, a single-crystal diffraction
analysis was performed on a crystal grown by layering of
pentane onto a saturated dichloromethane solution. The
ORTEP views of the molecular structures of imidazolinium
salts are shown in Figures 2 (3a) and 3 (3b), and crystal data
are summarized in Table 1 in the Supporting Information.
A comparison of the selected bond lengths and angles for
imidazolinium salts 3a and 3b along with the related struc-
tural parameters for 1,3-dimesitylimidazolinium chloride44
Figure 3. ORTEP diagram of the molecular structure of
[(BIAN-SIPr)(H)]BF4 (3b) at 40% probability (solvent molecule
has been removed for clarity).
are given in Table 1. The X-ray diffraction analyses for
imidazolinium salts 3a and 3b reveal that the cations lie on
a site with no crystallographic symmetry, but have an
approximate local mirror plane. In the molecular structure
of imidazolinium salts, the average C1-N1(2) and N1(2)-C2(3)
bond lengths for 3a and 3b are on the same order as observed
for the [(SIMes)(H)]Cl.44 Due to ring strain and the presence
of the bulky naphthyl group at the backbone, the consider-
ably longer C2-C3 bond lengths of 1.560(4) A, 3a, and
1.567(3) A, 3b, and the N1(2)-C(aromatic) length of 1.442(4) A,
(42) Arduengo, A. J., III; Krafczyk, R.; Schmutzler, R.; Craig, H. A.;
Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55,
14523–14534.
€
€ €
€
€
(43) Turkmen, H.; S-hin, O.; Buyukgungor, O.; C-etinkaya, B. Eur.
J. Inorg. Chem. 2006, 4915–4921.
(44) Arduengo, A. J., III; Goerlich, J. R.; Marshall, W. J. J. Am.
Chem. Soc. 1995, 117, 11027–11028.

Article
Organometallics, Vol. 29, No. 21, 2010 4861
˚
Table 1. Comparison of the Selected Bond Lengths (A) and Angles (ꢀ) for Imidazolinium Salts 3a and 3b with Reported Data
property
[(BIAN-SIMes)(H)]BF4, 3aa [(BIAN-SIPr)(H)]BF4, 3ba
BIAN-SIMes, 4ab
(η3-C3H5)Pd(BIAN-SIPr)Cl, 5b
[(SIMes)(H)]Clc
Bond Lengths
C1-N1(2)
N1(2)-C2(3)
C2-C3
1.315(4), 1.313(4)
1.496(4), 1.494(4)
1.560(4)
1.313(3), 1.317(3)
1.497(3), 1.490(3)
1.567(3)
1.348(2), 1.346(2)
1.491(2), 1.496(2)
1.558(2)
1.344(3), 1.350(3)
1.484(3), 1.492(3)
1.555(4)
1.327(5), 1.310(5)
1.498(6), 1.487(6)
1.518(7)
N1(2)-C(aromatic)
1.442(4), 1.442(4)
1.446(3), 1.440(3)
1.434(2), 1.435(2)
1.447(3), 1.442(3)
1.432(5), 1.437(6)
Hydrogen Bond Lengths
H1-F3
H1-F4
H1-F1
2.383
2.426
2.198
Bond Angles (θ)
N1-C1-N2
113.8(3)
114.0(2)
106.09(14)
108.4(2)
113.1(4)
C1-N1(2)-C2(3)
N1(2)-C2(3)-C3(2)
C1-N1(2)-Cmes
N1(2)-C2(3)-C4(8)
110.7(2), 110.7(2)
102.3(2), 102.5(2)
126.9(2), 127.9(2)
113.2(2), 112.5(2)
110.5(2), 110.81(19)
102.31(18), 102.32(18)
125.8(2), 126.8(2)
114.3(2), 113.3(8)
115.51(14),115.37(14)
101.51(13),101.43(13)
124.01(14), 123.18(14)
113.97(14), 114.30(14)
112.9(2),112.9(2)
102.6(2),100.9(2)
129.1(2), 125.8(2)
117.2(2), 116.2(3)
109.7(4), 110.6(4)
103.0(4), 103.3(4)
127.0(4), 126.2(4)
Torsion Angle (θ)
N1-C2-C3-N2
0.68
2.42
1.97
12.9
a This work. b Reference 39. c Reference 44.
3a, and 1.443(3) A, 3b, were observed. The N1-C1-N2 bond
angles of 113.8(3)ꢀ and 114.0(2)ꢀ observed for 3a and 3b are on
the same order as found for [(SIMes)(H)]Cl,44 but significantly
larger than the corresponding bond angle of 108.7(4)ꢀ ob-
served for [(IMes)(H)]Cl.42 The significantly larger
N1-C2-C4 and N2-C3-C8 bond angles of 114.3(2)ꢀ and
113.32(18)o observed for 3b are due to the greater interaction
of the bulky, more hindered isopropyl groups with the
naphthyl group attached at the backbone, Table 1. This is
further supported by the larger torsion angle of 2.42ꢀ, 3b,
when compared with 0.68ꢀ observed for 3a. The angles
between the best planes of the dihydroimidazole ring and
the naphthyl group are 62.7ꢀ, 3a, and 59.5ꢀ, 3b, respectively.
The angle between the best planes of the dihydroimidazole
ring andthe phenyl ringsC15-C14-C19 and C24-C23-C28 are
78.6ꢀ and 72.2ꢀ, 3a, and 79.7ꢀ and 80.6ꢀ, 3b, respectively.
It is also noteworthy that the CH group of the imidazolinium
ion, 3a, Figure 2, and two F atoms of the neighboring anion
change to the imidazolium architecture has a dramatic effect on
the clean generation of the corresponding imidazolin-2-ylidene.39
1
NMR Studies. The H NMR spectrum for the palladium
complex 5a (room temperature) shows the formation of only
one diasteromer, and the assignments were made with the help
of COSY, TOCSY ROESY, and 1H-13C HMQC NMR
experiments, along with the chemical shift data reported for
the related NHC complexes.45 For palladium complex 5a, the
1H NMR spectrum shows five distinct and well-defined reso-
nances for allylic protons, typical of an ABCDX-type spin
system. The strong σ-donor properties and greater trans influ-
ence of the carbene ligand compared with the chloride ligand
causes the allylic carbon atom trans to carbene to be weakly
bonded, consequently causing the asymmetry in the allylic
bonding. The central allylic CH proton (H2) appears as a
complex multiplet at δ 4.68, whereas the allylic CH2 protons
pseudo-trans to carbene appear at δ 3.71 (dd, 3J = 7.5 Hz, 2J =
1.8 Hz, syn in relation to H2) and δ 2.62 (d, 3J = 13.8 Hz, anti
in relation to H2), and the CH2 protons pseudo-trans to chloride
resonate at δ 3.16 (d, 3J = 6.7 Hz, syn in relation to H2) and δ
1.71 (d, 3J = 11.8 Hz, anti in relation to H2), respectively. The
1H NMR spectrum of 5a also shows five resonances (δ 2.69
(3H), 2.66 (3H), 2.27 (6H), 1.53 (3H), and 1.38 (3H), re-
spectively) for the mesityl CH3 protons and a set of four broad
resonances at δ 7.02, 7.01 6.79, and 6.82 for the mesityl m-CH
protons, which suggests that the mesityl ring protons are in a
slightly different chemical environment with a restricted rota-
tion around the N-mesityl bonds on either side of the imidazole
ring. The backbone protons (-NCHCHN-) resonate upfield
at δ 6.09 (d, J = 9.3 Hz) and 6.07 for palladium complex 5a,
when compared with δ 6.61 observed for imidazolinium salt 3a.
The 1H NMR (room temperature, 291 K) of (η3-C3H5)Pd-
(BIAN-SIPr)Cl, 5b, shows the absence of one set of the char-
acteristic resonances for isopropyl-CH3, naphthyl-CH, and
m-CH protons of the 2,6-diisopropylphenyl ring and a set of
resonances for the allyl-CH2 protons. The broad resonance
observed for the backbone (-NCHCHN-), isopropyl-CH
appear to have some interactions: C1 F3 3.149(3) A with
3 3 3
symmetry operator 1/2-x, 1/2þy, 1/2-z, C1 F4 2.899(3) A,
3 3 3
respectively. Consequently the CH group projects between these
F atoms, and this may be considered as a bifurcated hydrogen
bond due to the H1 F3 bond length of 2.383 A and H1 F4
3 3 3
3 3 3
bond length of 2.426 A. In contrast to the imidazolinium salt
[(BIAN-H2IMes)(H)]BF4, 3a, the CH group of the imidazole
ring in [(BIAN-H2IPr)(H)]BF4, 3b, forms a hydrogen bond only
to one of the F atoms of the anion: H1 F1 bond length of 2.198
3 3 3
A. The remaining bond lengths and angles are unexceptional and
lie within the range expected. Complete details of the single-
crystal X-ray analysis are given in the Supporting Information.
Synthesis and Characterization of the Palladium Complexes
(η3-C3H5)Pd(BIAN-SIMes)Cl (5a) and (η3-C3H5)Pd(BIAN-
SIPr)Cl (5b). The palladium(II) complexes 5a and 5b were
synthesized by the reaction of the free carbenes with [(η3-C3H5)Pd-
(μ-Cl)]2 in THF at -78 ꢀC, Scheme 2. After the workup palla-
dium(II) complexes 5a and 5b were isolated as air-stable crystal-
line solids. It is important to mention here that the deprotonation
of imidazolinium salts 3a and 3b is very much dependent on the
choice of an appropriate solvent as well as the base, since a slight
(45) Filipuzzi, S.; Pregosin, P. S.; Albinati, A.; Rizzato, S. Organo-
metallics 2008, 27, 437–444, and references therein..

4862 Organometallics, Vol. 29, No. 21, 2010
Dastgir et al.
Figure 4. Selected 1H VT-NMR spectra in the allylic region of (η3-C3H5)Pd(BIAN-SIPr)Cl, 5b.
Figure 5. Selected 1H VT-NMR spectra in the aromatic region of (η3-C3H5)Pd(BIAN-H2IPr)Cl, 5b.
protons further suggests a dynamic fluxional behavior in the
molecule. Complete freezing of the fluxional process was
achieved at 233 K, and at this temperature assignment of the
1H NMR data was made with the help of gCOSY, TOCSY,
ROESY, and 1H-13C HMQC NMR spectroscopy. The 1H
VT-NMR spectrum in the high-field region is shown in
Figure 4, and that in the aromatic region, in Figure 5. They
further show the formation of only one diasteromer over a
temperature range. The diisopropyl-CH3 and methine (CH)
protons resonate as a set of eight doublets, δ 1.50 (d, 3H, J =
6.2 Hz), 1.48 (d, 3H, J = 6.2 Hz), 1.40 (d, 3H, J = 6.8 Hz),
1.29 (d, 3H, J = 6.8 Hz), 0.86 (d, 3H, J = 6.7 Hz, iPr-C39H3),
0.82 (d, 3H, J = 6.7 Hz), 0.30 (d, 3H, J = 6.7 Hz), and 0.08
(d, 3H, J = 6.7 Hz), and a set of four septets, δ 3.99-3.91 (m,
1H), 3.84 (sept, 1H, J = 6.6 Hz), 2.58 (sept, 1H, J = 6.7 Hz),
and 1.97 (sept, 1H, J = 6.7 Hz), at 233 K, respectively,
suggesting that all the diisopropyl methyl and diisopropyl
methine protons are inequivalent. Upon warming the NMR
sample, the resonances started to broaden and then coalesce
to a set of four sharp doublets and a set of two broad septets
at 333 K for the diisopropyl methyl and methine protons,
respectively. At 233 K the resonance corresponding to the
naphthyl-CH protons appears as a set of four doublets
at δ 7.73 (d, 2H, J = 8.3 Hz), 7.72 (d, 2H, J = 8.3 Hz),
6.81 (d, 3J = 6.8 Hz), and 6.36 (d, 3J = 6.9 Hz) and
a complex multiplet at δ 7.41-7.29, respectively, whereas a
set of m-CH protons shows two doublets of doublets at δ 7.02
(dd, 3J = 6.9 Hz, 4J = 2.2 Hz) and 7.06 (dd, 3J = 6.9 Hz,
4J
= 2.2 Hz), respectively. The backbone protons
(-NCHCHN-) resonate upfield at δ 6.23 as a singlet from
291 to 333 K, whereas two doublets δ 6.13 (d, 3J = 10 Hz)
and 6.24 (d, J = 6.8 Hz) were observed at 233 K. This
3
reflects a high degree of asymmetry in the molecule at 333 K
due to the hindered rotation around N-aromatic bond and
the asymmetrically bonded allylic ligand (vide infra). The 1H
VT-NMR spectra also reveal that a set of resonances arising
from the naphthyl-CH protons coalesce to one broad doub-
let δ 6.62 (d, 3J = 6.8 Hz) at 333 K, suggesting a free rota-
tion around the Pd-NHC bond. Similar behaviors were
observed for the other set of naphthyl-CH, a set of m-CH
for either side of the imidazole ring, and backbone
(-NCHCHN-) protons. This dynamic behavior reflects
the presence of a free rotation around the Pd-NHC bond.
The molecular structure of 5b, Figure 10, shows that
the mean plane passing through the imidazole ring is
almost perpendicular (83.12ꢀ) to the plane that is com-
posed of NHC-C, palladium, allylic C38, C40, and chloride
ligands. Due to a bulky naphthyl group at the backbone
(-NCHCHN-), a twist in the imidazole ring was also
observed (vide infra), which in turn puts the aromatic rings
on the either side of the imidazole ring in a slightly
different environment. In principle, one should expect
four nonequivalent diisopropyl groups and consequently
four nonequivalent isopropyl methine protons. Whereas
the observed peak pattern in the 1H and 13C NMR
spectrum at 233 K suggests that all the diisopropyl methyl,

Article
Organometallics, Vol. 29, No. 21, 2010 4863
Figure 6. Slice of the 1H-13C HMQC (500 MHz, CDCl3, 233 K) correlation for 5b.
diisopropyl methine, and the N-aromatic ring protons/
carbons are indeed nonequivalent due to restricted rota-
tion around the N-diisopropylphenyl bonds on either side
of the imidazole ring and asymmetrically bonded allyl
ligand, consequently, all the naphthyl ring CH protons
are also inequivalent (vide supra).
chemical shift values observed for the allylic protons in (η3-
C3H5)Pd(BIAN-SIMes)Cl (5a) and (η3-C3H5)Pd(BIAN-
SIPr)Cl (5b) are consistent with the chemical shift values
reported for related (η3-C3H5)Pd(NHC)Cl complexes. Because
of the strong σ-donor properties of NHC ligands, the selective
opening of the allyl ligand trans to the NHC was expected
exclusively on the grounds of the greater trans influence of the
NHC ligand, when compared with the chloride ligand. As
expected, upon warming the NMR sample, the allylic CH2
(pseudo-trans to chloride) resonances started to broaden, and
at 291 K they have completely disappeared into the baseline,
whereas the resonances arising from the allylic CH2 protons
pseudo-trans to NHC remain sharp throughout. Complete
coalescence for the allylic CH2 pseudo-trans to chloride ligands
was not observed due to the temperature limitation of the
solvent. This kind of dynamic behavior is consistent with the
selective η3-η1 opening of the allyl ligand under electronic
control, followed by the rotation around the C-C bond, and
then isomerization to η1-η3 to re-form the allyl ligand.-
(Scheme 3). Such selective η3-η1 exchange processes are very
well recognized for the chiral phosphine bidentate ligand sys-
tems due to their enhanced steric and electronic effects.46,51-61
The 1H-1H ROESY NMR spectra, Figures 8 and 9, at 233 K,
further show a selective exchange for the isopropyl methyl,
and methine protons. Furthermore, the observed exchange
crossprocess for the backbone (-NCHCHN-), naphthylCH
and the diisopropylphenyl m-CH protons on either side of
the imidazole ring strongly confirms a free rotation around
the Pd-NHC bond and a hindered rotation around the
N-aromatic bond on either side of the imidazole ring; similar
behaviors were also observed previously.46,47
A section of the 1H VT-NMR spectrum in the allylic
region, Figure 4, shows a typical ABCDX-type spin system
for the allylic protons45,48-50 at 233 K. Given the greater
trans influence of the NHC group when compared with the
chloride ligand, the positions of allylic CH2 protons pseudo-
trans to the NHC ligand were unambiguously assigned with
the aid of 1H-13C HMBC and 1H-13C HMQC experiments.
1
A section of the H-13C HMQC experiment is shown in
Figure 6. The allylic CH2 protons pseudo-trans to NHC
appeared as a doublet at δ 3.92 (3J = 7.2 Hz, H1s, syn in
relation to H2) and 2.71 (3J = 13.5 Hz, H1a, anti in relation to
H2), while the corresponding protons pseudo-trans to chlo-
ride ligands appeared as doublets at δ 2.97 (3J = 6.7 Hz, H3s)
and 1.15 (3J = 12.2 Hz, H3a) at 233 K, respectively. The
(51) Albinati, A.; Kunz, R.; Ammann, C. J.; Pregosin, P. S. Organo-
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(52) Gogoll, A.; Ornebro, J.; Grennberg, H.; Backvall, J.-E. J. Am.
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Albinati, A.; Rizzato, S. Organometallics 2005, 24, 1306–1314.
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2006, 17, 1853–1858.
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(48) Powell, J.; Shaw, B. L. J. Chem. Soc. A 1967, 11, 1839–1851.
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Chem. 1989, 370, 407–419.

4864 Organometallics, Vol. 29, No. 21, 2010
Scheme 3. η3-η1-η3 Isomerisation Process for Palladium Allyl Complex 5b
Dastgir et al.
The π to σ equilibrium is well documented for Pd(η3-C3H5)-
(L1)(L2) complexes, where L1 and L2 = chloride, PPh3, P(OPh)3,
DMSO, pyridine, and bidentate phosphine ligands. This is
followed by temperature-dependent selective syn to anti inter-
change of the allylic protons, which usually takes place through
the η3-η1-η3 interconversion process under electronic or steric
control45,48-50,52-61 (Scheme 3).
by slow diffusion of pentane into a saturated dichloro-
methane solution. Two (alterable) ORTEP views of the
molecule 5b are shown in Figure 10, and the crystal data
are summarized in Table 1 in the Supporting Information.
The absolute configuration of the palladium complex 5b,
determined by X-ray analysis, reveals that the palladium
has a distorted square-planar geometry, as expected for
the palladium allyl complexes, but interestingly the Flack
enantiopole parameter64 gives a value of -0.06(3), suggest-
ing the crystal consists of a single enantiomer despite the
achiral nature of the complex. The geometry of the allyl
ligand was interpreted with extreme caution in view of its
disordered nature. It was also observed that the allyl group
is bonded in an asymmetric mode; the C38-C39 and C39-C40
bond lengths are 1.321(8) and 1.549(9) A, respectively, which
indicates that the formal single and double bonds are par-
tially localized. All attempts to enforce a symmetric geo-
metry on the allyl ligand during refinement worsened the
agreement with the X-ray data. Hydrogen atoms on the
carbene ligand were positioned geometrically after each
cycle, but it was not possible to locate the allyl hydrogen
atoms unambiguously in the Fourier maps, as no appro-
priate prototype structure was available; therefore, they
could not be positioned geometrically and are omitted from
the model. They were, however, included in the calculation of
the molecular formula, molecular weights, etc. The three-
term Chebychev polynomial weighting scheme was then
applied, and refinements converged satisfactory to give
R = 0.0330 and Rw = 0.0327.
The carbene ligand is present in a plane normal to the
plane of the molecule that comprises Pd, C(carbene), Cl,
and two terminal carbon atoms of the allyl ligand. The
Pd-C(carbene) and Pd-Cl bond lengths are 2.044(3) and
2.3715(3) A, respectively, and consistent with the reported
datafor (η3-C3H5)Pd(NHC)Clcomplexes,62,65 whereNHC=
SIMes, SIPr. The Pd-C38, Pd-C39, and Pd-C40 bond lengths
are 2.204(6), 2.165(4), and 2.121(6) A, respectively. Due to the
large aromatic system at the C2-C3 bond, no large torsion
angles for the palladium complex was expected, but to our
surprise, upon coordination with palladium, a twist appears
in the backbone, Figure 10, producing a torsion angle of
12.92ꢀ, which is approximately 10ꢀ greater than that observed
for imidazolinium salt 3b. In the molecular structure of
The section of ROESY NMR (233 K) spectrum in the
allylic region for palladium complex 5b is given in Figure 8.
To our surprise, the 1H-1H ROESY NMR spectrum shows
selective exchange peaks only for the carbene ligand, whereas
the peaks arising from the corresponding allyl interconver-
sion process (synfanti and antifsyn) for the protons trans to
the chloride ligand (labeled H3) are canceled out by a strong
overlapping NOE peak. However, the only observed cross-
peaks are the TOCSY breakthrough peak caused by J-coupling
between the H1a, H3s, and H3a, respectively. Furthermore, the
dynamic NMR behavior observed over 233 to 333 K (Figure 4)
for the allyl ligand and NHC ligand and the absence of the
1
corresponding exchange cross-peaks in the H-1H ROESY
NMR for the protons pseudo-trans to the NHC ligand (labeled
H1) strongly suggest the selective η3-η1-η3 isomerization
process is operative under electronic control. Therefore, after
the selective η3-η1-η3 isomerization process, the protons
labeled H1 (pseudo-trans to NHC) find themselves in the same
environment, and this may be considered as synfsyn and
antifanti exchange processes. This is also further supported
by the X-ray diffraction studies (vide infra), confirming that the
allyl ligand is bound in the asymmetric fashion, with localized
single and double bonds within the allyl ligand, Figure 7c.
In the 13C{1H} NMR spectrum the Pd-C(carbene) reso-
nance is shifted to lower frequency at δ 210.6 (5a) and 213.4
(5b) when compared with imidazolin-2-ylidene δ 247.3 (4a)
and 241.9 (4b);39 this characteristic upfield shift is sympto-
matic of the coordination of saturated NHC with transfer of
the electron density to the metal center and consistent with
previously reported NHC palladium complexes.45,62,63 Full
1H and 13C assignments are given in the Experimental
Section.
X-ray Crystal Structure of (η3-C3H5)Pd(BIAN-SIPr)Cl,
5b. Single crystals suitable for X-ray diffraction were grown
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Organometallics 2004, 23, 1629–1635.

Article
Organometallics, Vol. 29, No. 21, 2010 4865
Figure 7. Allyl bonding mode for palladium complex 5b.
Figure 8. Section of the 1H-1H ROESY NMR (500 MHz,
CDCl3, 233 K) spectrum (negative phase) in the allylic region
for 5b, showing exchange (*) and the TOCSY cross-peaks.
Figure 9. Section of the 1H-1H ROESY NMR (500 MHz,
CDCl3, 233 K) spectrum (negative phase) in the aromatic region
for 5b, showing exchange (*) cross-peaks.
Figure 10. ORTEP diagram of the molecular structure of 5b at 40% probability. Hydrogen atoms, minor orientation of the allyl group,
and 2,6-diisopropylphenyl groups (structure on right) have been omitted for clarity.
imidazolinium salts the average C1-N1(2) and N1(2)-C2(3)
bond lengths of 1.347 and 1.488 A are slightly larger than the
corresponding bond lengths observed for imidazolinium salt
3b, which are indicative of the loss of electron density from the
C1-N1(2) bonds. The smaller N1-C1-N2 bond angle of
108.4(2)ꢀ when compared with 3b is also due to the loss of

4866 Organometallics, Vol. 29, No. 21, 2010
Dastgir et al.
˚
Table 2. Comparison of Selected Bond Lengths(A) and
Angles (deg)
Scheme 4. Catalytic Cycle for Suzuki-Miyaura and Buch-
wald-Hartwig Coupling Reactions
(η3-C3H5)Pd-
(BIAN-SIPr)Cl, 5b
(η3-C3H5)Pd-
property
(SIPr)Cla
Bond Lengths
Pd-C(carbene)
Pd-Cl
Pd-C(trans to NHC)
Pd-C39
2.044(3)
2.042(5)
2.3715(8)
2.204(6)
2.165(4)
2.376(14)
2.211(6)
2.124(7)
Pd-C(trans to chloride)
C38-C39
2.121(6)
1.321(8)
1.549(9)
1.344(3), 1.350(3)
1.484(3), 1.492(3)
1.555(4)
2.098(6)
1.304(1)
1.407(9)
1.344(7), 1.346(6)
1.489(7)
1.516(9)
C39-C40
C1-N1(2)
N1(2)-C2(3)
C2-C3
Bond Angle (θ)
108.4(2)
N1-C1-N2
108.19(4)
19.8(6)
Torsion Angle (θ)
12.9
N1-C2-C3-N2
a Reference 65.
with the help of a suitable base, and then a monoligated
Pd(0) species takes part in three discrete catalytic steps such
as oxidative-addition, transmetalation, and then reductive-
elimination to give the coupled product and regenerated
Pd(0) species for the next catalytic cycle. The catalytic cycle
suggests that a strong σ-donor ligand is needed for a facile
oxidative addition, whereas a sterically bulky ligand is required
for the reductive elimination step.27,75,76 However, a recent
mechanistic study by Fu et al. has shown that a bulky, steri-
cally demanding ligand can have adverse effects on the oxida-
tive-addition step;72 therefore, for a highly active catalyst
a delicate balance between the electronic and steric bulk is
required.
The structure and electronic properties of the palladium
complexes 5a and 5b appear to fulfill all the requirements
for good catalysts in these cross-coupling reactions and
proved to be thermally robust for C-C coupling reactions
of activated and deactivated aryl halides with boronic
acids, Table 3, and also for C-N bond formation with
morpholine and N-methylaniline, Table 4. Our initial at-
tempts using K2CO3 or Cs2CO3 failed to activate the catalyst.
However, the Suzuki coupling reactions were then success-
fully performed using KOtBu in 1,4-dioxane at 80 ꢀC, unless
otherwise stated. In some cases up to 5% homocoupling of the
boronic acid substrate was observed as a side reaction (entries
2 and 5, Table 3). The optimum conversion of 90-96% was
obtained for highly deactivated and hindered aryl bromides,
2,3,5,6-tetrafluorobromobenzene, and bromomesitylene
(entries 4 and 5, Table 3). More than 99% conversions were
obtained for hindered boronic acid using activated and deac-
tivated aryl chlorides.
electron density from C1-N1(2) bonds but of the same order as
observed for the corresponding rhodium(I) and iridium(I)
complexes.39 The significantly larger N1-C2-C4 and N2-
C3-C8 bond angles of 117.2(2)ꢀ and 116.2(3)ꢀ observed for
5b are due to the greater interaction of bulky, more hindered
isopropyl groups and further supported by the larger torsion
angle of 12.9ꢀ when compared with 2.42ꢀ observed for 3b. The
angle between the best planes of the dihydroimidazole ring and
the naphthyl group is 56.56ꢀ, whereas the angles between the
best planes of the dihydroimidazole ring and the phenyl rings
C15-C14-C19 and C31-C26-C27 are 65.19ꢀ and 82.28ꢀ, re-
spectively. The angle between the mean plane passing through
the imidazole ring and the plane composed of C1-Cl1-
C38-C40 is 83.15ꢀ. A comparison of the selected crystal data
for 5b with the related palladium complex (η3-C3H5)Pd-
(SIPr)Cl is given in Table 2. Complete details of the single-
crystal X-ray analysis are given in the Supporting Information.
Catalytic Cross-Coupling Reactions. The Suzuki-Miyaura
reaction,66 the coupling of ArB(OH)2 (Ar = phenyl or sub-
stituted aromatic groups) with aryl, vinyl, or alkyl halides,
offers a mild, versatile, and dominant methodology for the
construction of C-C bonds.22 The popularity of the Suzu-
ki-Miyaura reaction is due to the easy accessibility of a
wide variety of air- and moisture-stable reactants that are
nontoxic. In recent years, palladium N-heterocyclic carbene
metal complexes have emerged as a new class of catalysts for
cross-coupling reactions.67-74 The catalytic cycle, Scheme 4,
first involves the in situ reduction of Pd(II) complex to Pd(0)
The first tin-free palladium-catalyzed carbon-nitrogen
bond (aryl amination) formation was independently re-
ported by Hartwig et al.77,78 and Buchwald et al.79,80 in
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Article
Organometallics, Vol. 29, No. 21, 2010 4867
Table 3. Palladium-Catalyzed Suzuki Coupling Reaction of Activated and Deactivated Aryl Halided
a Average of two runs. b 5% biphenyl was observed. c Isolated yield in parentheses. d Standard conditions: 0.75 mmol of boronic acid, 0.5 mmol of
aryl halide, 1.0 mmol of Cs2CO3, 1% Pd, 4.0 mL of dioxane, 80 ꢀC.
Table 4. Palladium-Catalyzed Aryl Amination Reaction of Activated and Deactivated Aryl Halided
a Average of two runs. b Isolated yields. c Reaction was carried out at 50 ꢀC. d Standard conditions: 1.2 mmol of amine, 1.0 mmol of aryl halide,
1.5 mmol of KOtBu, 1% Pd, 4.0 mL of dioxane, room temperature.
1995, and thereafter Yamamoto et al.81 and Hartwig et al.21
have developed general methodologies for carbon-nitrogen
bond formation reactions in small molecules. The catalytic
cycle for palladium(II)-catalyzed aryl amination reactions
also involves in situ formation of monoligated Pd(0) spe-
cies. The representative catalytic cycle for the Suzuki and
Buchwald-Hartwig coupling is shown in Scheme 4. The
aryl amination reactions were performed using KOtBu
in 1,4-dioxane at room temperature, except entry 2, Table 4,
which was heated to 50 ꢀC. The catalytic system using
palladium complex 5b can couple the deactivated aryl
(81) Yamamoto, T.; Nishiyama, M.; Koie, Y. Tetrahedron Lett. 1998,
39, 2367–2370.

4868 Organometallics, Vol. 29, No. 21, 2010
Dastgir et al.
bromide in less than 10 min (entry 3, Table 4), while
hindered and deactivated bromomesitylene was coupled
in 85% yield (entry 6, Table 4). Activated and deactivated
aryl chlorides can be coupled in more than 95% yields at
room temperature.
38.4 mmol) was suspended in acetonitrile (150 mL) and heated under
reflux (80 ꢀC) for 60 min. Acetic acid (65 mL) was then added, and
heating was continued until the acenaphthenequinone had comple-
tely dissolved. To this hot solution was added 2,6-diisopropylphe-
nylaniline, 92% (16.0 g, 89.9 mmol), with the help of a dropping
funnel over a period of 30 min, and the solution was heated under
reflux for a further 5 h and then cooled to room temperature. The
resulting orange-yellow solid was then filtered, washed with pentane
Conclusion
(3 ꢀ 20 mL), and dried in air. Yield: 18.1 g, 94%. The 1H and 13
C
We have described a novel family of monodentate bulky
backbone annulated imidazolinium ligand precursors and their
corresponding palladium(II) carbene complexes. A bifurcated
hydrogen bond between BF4 anions and imidazolinium pro-
tons (-NCHN-) was observed for [(BIAN-SIMes)(H)]BF4,
3a. Furthermore the palladium complex (η3-C3H5)Pd(BIAN-
SIPr)Cl, 5b, showed a selective temperature-dependent, elec-
tronically controlled η3-η1-η3 exchange of the allyl ligand.
The crystal structure of (η3-C3H5)Pd(BIAN-SIPr)Cl, 5b,
represents a rare example in which a localized single and
double bond within the allyl ligand was observed. The
palladium(II) complexes show high activity in Suzuki-type
C-C and Buchwald-Hartwig-type C-N cross-coupling
reactions of activated and deactivated aryl halides.
NMR spectra were consistent with the reported data.41
Synthesis of Bis[N,N0-(2,4,6-trimethylphenyl)amino]acenaphthene
(2a). To a suspension of LiAlH4 (0.23 g, 6.1 mmol) in diethyl ether
(30 mL) was added dropwise a solution of bis[N,N0-(2,4,6-tri-
methylphenyl)imino]acenaphthene, 1a (3.4 g, 8.1 mmol), in diethyl
ether (40 mL) at 0 ꢀC, and the mixture was stirred for 1 h. The
reaction mixture was warmed to room temperature, stirred for an
additional 3 h, and then quenched with 10% HCl solution in water.
The product was extracted in CH2Cl2 (3 ꢀ 15 mL), dried, and
purified by flash chromatography using CH2Cl2/pentane (70:30) to
1
give an orange-yellow solid. Yield: 2.9 g, 85%. The H and 13C
NMR spectra were consistent with the reported data.43
SynthesisofBis[N,N0-(2,6-diisopropylphenyl)amino]acenaphthene
(2b). To a suspension of LiAlH4 (0.20 g, 5.3 mmol) in diethyl ether
(60 mL) was dropwise added a diethyl ether (40 mL) solution of
bis[N,N0-(2,6-diisopropylphenyl)imino]acenaphthene, 1b (3.6 g,
7.19 mmol), at 0 ꢀC, and the mixture was stirred for 1 h. The
reaction mixture was warmed to room temperature and stirred for
an additional 3 h and then quenched with a 10% HCl solution. The
product was extracted in CH2Cl2 (3 ꢀ 15 mL), dried, and then
purified by flash chromatography using CH2Cl2/pentane (70:30) to
Experimental Section
General Procedures. All manipulations were performed under
dinitrogen using standard Schlenk vessel techniques or an inert
atmosphere glovebox. All solvents were dried by passage through an
alumina column under a positive pressure of dinitrogen and deoxy-
genated by bubbling dry dinitrogen through the dried solvents for
20 min before use. NMR spectra were recorded on either a Varian
Unity Plus 500 (1H at 500 MHz, 13C at 125.7 MHz) or a Varian
Mercury 300 (1H at 300 MHz, 13C at 75.5 MHz) spectrometer at
room temperature unless otherwise stated. The spectra were refer-
enced internally relative to the residual protio-solvent (1H) and
solvent (13C) resonances, and chemical shifts were reported with
respect to δ = 0 for tetramethylsilane. Electrospray mass spectra
were recorded in acetonitrile on a Micromass LC TOF spectrometer.
Microanalyses were performed by the microanalytical laboratory
of the Inorganic Chemistry Laboratory, University of Oxford. Gas
chromatographs were recorded using a Perkin-Elmer XL 1100
instrument with a Perkin-Elmer NCI 900 Network Chromatography
Interface using a fused silica, nonpolar SGE column 25QC2/BP1 1.0.
All reagents were purchased from Aldrich; metal precursors were
from Johnson-Matthey and were used as received unless otherwise
stated. The reagents BIAN-SIMes,39 BIAN-SIPr,39 and [Pd(η3-
C3H5)(μ-Cl)]282 were prepared using published procedures. The base
KOtBu was sublimed and kept in the inert atmosphere glovebox.
Synthesis of Bis[N,N0-(2,4,6-trimethylphenyl)imino]acenaphthene
(1a). The compound bis[N,N0-(2,4,6-trimethylphenyl)imino]-
acenaphthene was prepared using a modified method from that
published by El-Ayaan et al.40 Acenaphthenequinone (3.0 g, 16.5
mmol) was suspended in acetonitrile (100 mL) and heated under
reflux (80ꢀC) for 60 min. Aceticacid (30mL) was then added, and
heating was continued until the acenaphthenequinone had com-
pletely dissolved. To this hot solution was added 2,4,6-trimethy-
laniline (4.8 g, 35.5mmol) using a droppingfunnel over the period
of 20 min. The resulting solution was heated under reflux for
another 3 h and cooled to room temperature. The precipitated
orange-red solid was filtered, washed with pentane (3 ꢀ 10 mL),
and dried in air. Yield: 6.5 g, 95%. The 1H and 13C NMR spectra
were consistent with the reported data.40
1
give an orange-yellow solid. Yield: 3.1 g, 86%. The H and 13C
NMR spectra were consistent with the reported data.83
Synthesis of 7,9-Bis(2,4,6-trimethylphenyl)-6b,9a-dihydro-
acenaphtho[1,2-d]imidazolinium Tetrafluoroborate (3a). To a
one-neckflask(250mL) fittedwithafractionaldistillationcolumn
was added a solution of bis[N,N0-(2,4,6-trimethylphenyl)amino]-
acenaphthene, 2a (1.5 g, 3.5 mmol), in triethyl orthoformate (30 mL)
and ammonium tetrafluoroborate (0.38 g, 3.5 mmol). The
reaction mixture was heated at 135 ꢀC with constant stirring
for 3 h with the distillation of ethanol, during which time the
color of the reaction mixture turned yellow-brown from the
original yellow solution with the precipitation of an oily black
solid. The reaction was cooled to room temperature, and the
solid was separated by decanting the brown solution. The
crude product was dissolved in CH2Cl2 (10 mL), filtered, and
precipitated with diethyl ether (20 mL). The resulting brown
solid was then filtered and washed with ice-cold diethyl ether/
THF (40:60) (3 ꢀ 10 mL) to give an off-white solid, which was
dried under vacuum. Yield: 1.1 g, 61%. Crystals suitable for
diffraction study were grown by layering of pentane onto a
saturated dichloromethane solution.
1H NMR (300 MHz, 291.6 K, CDCl3): δ 8.19 (s, 1H,
-NCHN-), 7.89 (d, 2H, J = 8.2 Hz, naphthyl ring CH), 7.42
(t, 2H, J =7.1Hz, naphthyl ring CH), 7.08 (s,2H, mesityl m-CH),
7.03 (d, 2H, J = 7.1 Hz, naphthyl ring CH), 6.87 (s, 2H, mesityl
m-CH), 6.6 (s, 2H, -NCHCHN-), 2.60 (s, 6H, mesityl-CH3),
2.34 (s, 6H, mesityl-CH3), 1.42 (s, 6H, mesityl-CH3). 13C NMR
(75.5 MHz, 293 K, CDCl3): δ 157.1 (s, C(-NCN-)), 128.8, 131.8,
135.6, 135.9, 136.1, 137.3, 140.8 (s, C(quaternary naphthyl and mesityl)),
130.1, 130.8 (s, m-C(mesityl)H), 122.3, 126.8, 128.7 (s, C(naphthyl)H),
70.6 (s, C(-NCCN-)), 17.8, 18.3, 21.3 (s, C(mesityl)H3). MS (ESþ,
CH3CN): m/z = 431.07 [M - BF4]þ (100%). Anal. Found (calcd):
C 71.76 (71.82); H 5.98 (6.03); N 5.32 (5.40).
Synthesis of 7,9-Bis(2,6-diisopropylphenyl)-6b,9a-dihydro-
acenaphtho[1,2-d]imidazolinium Tetrafluoroborate (3b). To a
one-neck flask (250 mL) fitted with a fractional distillation
Synthesis of Bis[N,N0-(2,6-diisopropylphenyl)imino]acenaphthene
(1b). The compound bis[N,N0-(2,6-diisopropylphenyl)imino]-
acenaphthene was prepared using a modified method from that
published by Paulovicova et al.41 Acenaphthenequinone (7.0 g,
(83) Ishizaki, K.; Komuro, K.; Kato, H.; Suzuki, H. Production
method of phenylsilane in the presence of diamine and transition metal
catalyst. 2003277388, 20020325, 2003.
(82) Tatsuno, Y.; Yoshida, T.; Otsuka, S. Inorg. Syn. 1990, 28, 343.

Article
Organometallics, Vol. 29, No. 21, 2010 4869
column was added a solution of bis[N,N0-(2,6-diisopropylphe-
nyl)amino]acenaphthene (2b) (3.9 g, 7.7 mmol) in triethyl ortho-
formate (60 mL) and ammonium tetrafluoroborate (0.81 g, 7.7
mmol). The reaction mixture was heated at 135 ꢀC with constant
stirring for 3 h with the distillation of ethanol, during which time
the color of the reaction mixture turned brown from the original
yellow solution with the precipitation of an oily black solid. The
reaction was cooled to room temperature, and the solid was
separated by decanting the brown solution. The crude product
was dissolved in CH2Cl2 (10 mL), filtered, and precipitated with
diethyl ether (20 mL). The resulting brown solid was then filtered
and washed with ice-cold diethyl ether/THF (40:60) (3 ꢀ 20 mL)
to give an off-white solid, which was dried under vacuum.
Yield: 3.4 g, 74%. Crystals suitable for diffraction study were
grown by layering of pentane onto a saturated dichloromethane
solution.
(4b) (0.88 g, 1.72 mmol) in THF (5.0 mL). The reaction mixture
was stirred for 10 min, gradually warmed to room temperature,
and stirred for 3 h. The reaction mixture was filtered, and the
pale yellow solution was evaporated to reduce the total volume
to 2 mL. Addition of pentane (10 mL) gave the product as an
off-white solid. This was washed with pentane (3 ꢀ 5 mL) and
dried under vacuum. Yield: 0.87 g, 76%.
1H NMR (500 MHz, 293 K, CDCl3):δ8.18 (s, 1H, -NCHN-),
7.89 (d, 2H, J = 8.3 Hz, naphthyl ring CH), 7.53 (t, 2H, J =
7.8 Hz, naphthyl CH), 7.48 (d, 2H, J = 7.4 Hz, p-CH), 7.45
(dd, 2H, J = 7.4 Hz, J = 1.4 Hz, m-CH), 7.23 (dd, 2H, J = 7.6 Hz,
J = 1.4 Hz, m-CH), 6.92 (d, 2H, J = 7.1 Hz, naphthyl ring CH),
6.67 (s, 2H, -NCHCHN-), 3.43 (sept, 2H, J = 6.8 Hz, iPr-CH),
1.94 (sept, 2H, J = 6.6 Hz, iPr-CH), 1.55 (d, 6H, J = 6.6 Hz, iPr-
CH3), 1.34 (d, 6H, J = 6.6 Hz, iPr-CH3), 0.89 (d, 6H, J = 6.7 Hz,
iPr-CH3), 0.72 (d, 6H, J = 6.6 Hz, iPr-CH3). 13C{1H} NMR (125.7
MHz, 293 K, CDCl3): 156.3 (s, C(-NCN-)), 127.8, 131.9, 135.5,
136.9, 146.5, 147.2 (s, C(quaternary naphthyl and 2,6-diisopropylphenyl)),
131.7 (s, p-CH), 128.5, 127.1, (s, C(naphthyl)H), 125.7, 124.7 (s,
m-CH), 122.8 (s, C(naphthyl)H), 72.9 (s, C(-NCCN-)), 29.5, 29.0 (s,
C(iPr)H), 26.7, 25.1, 23.9, 22.3 (s, C(iPr)H3). MS (ESþ, CH3CN):
m/z = 515.43 [M - BF4]þ (100%). Anal. Found (calcd): C 72.91
(73.75); H 7.20 (7.19); N 4.69 (4.65).
1H NMR (500 MHz, 233 K, CDCl3): δ 7.73 (d, 2H, J = 8.3 Hz,
naphthyl C11H), 7.73 (d, 2H, J = 8.3 Hz, naphthyl C9H),
7.41-7.29 (m, 6H, p-C19H, m-C18H, m-C33H, p-C34H, naphthyl
C8H, naphthyl C12H), 7.08 (dd, 1H, J = 6.9 Hz, J = 2.2 Hz,
m-C35H), 7.02 (dd, 1H, J = 6.9 Hz, J = 2.2 Hz, m-C19H), 6.81 (d,
1H, J = 6.81 Hz, naphthyl-C13H), 6.36 (d, 1H, J = 6.9 Hz,
naphthyl-C7H), 6.24 (d, 1H, J = 10.0 Hz, -NC4HCHN-), 6.13
(d, 1H, J = 10.0 Hz, -NCHC5HN-), 4.75-4.57 (m, 1H, allyl
C29H), 3.99-3.91 (m, 2H, iPr-C23H, allyl C30Hs), 3.84 (sept, 1H,
J = 6.6 Hz, iPr-C41H), 2.97 (d, 1H, J = 6.7 Hz, allyl C28Hs), 2.71
(d, 1H, J = 13.5 Hz, allyl C30Ha), 2.58 (sept, 1H, J = 6.7 Hz, iPr-
C38H), 1.97 (sept, 1H, J = 6.7 Hz, iPr-C26H), 1.50 (d, 3H, J =
6.2 Hz, iPr-C24H3), 1.48 (d, 3H, J = 6.2 Hz, iPr-C42H3), 1.40 (d,
3H, J = 6.8 Hz, iPr-C22H3), 1.29 (d, 3H, J = 6.8 Hz, iPr-C40H3),
1.15 (d, 1H, J = 12.2 Hz, allyl C28Ha), 0.86 (d, 3H, J = 6.7 Hz,
iPr-C39H3), 0.82 (d, 3H, J = 6.7 Hz, iPr-C27H3), 0.30 (d, 3H, J =
6.7 Hz, iPr-C37H3), 0.08 (d, 3H, J = 6.7 Hz, iPr-C25H3). 13C{1H}
NMR (125.7 MHz, 233 K, CDCl3): δ 213.4 (s, C1), 148.5 (s, C17),
147.9 (s, C21), 146.7 (s, C36), 146.4 (s, C32), 138.4 (s, C6), 137.5 (s,
C14), 136.9 (s, C15), 134.5 (s, C31), 134.4 (s, C17), 131.1(s, C10),
128.9 (s, C19), 128.4 (s, C34), 128.1 (s, C12), 127.9 (s, C8), 125.9 (s,
C11), 125.5(s, C9), 125.3 (s, C33), 124.6 (s, C18), 124.3(s, C35) 124.0
(s, C20), 122.3 (s, C13), 122.2 (s, C7), 114.6 (s, C29), 72.2 (s,
C30),72.1 (s, C4) 71.9 (s, C5), 53.8 (s, C28), 29.2 (s, C41), 28.7 (s,
C23), 28.2 (s, C26), 27.9 (s, C38), 26.8 (s, C22), 25.9 (s, C40), 24.9 (s,
C39), 24.9 (s, C27), 24.5 (s, C24), 24.4 (s, C42), 24.1 (s, C25), 23.9 (s,
C37). MS (ESþ, CHCN): m/z = 661.48 [M - Cl]þ (100%). Anal.
Found (calcd): C 69.01 (68.86); H 6.68 (6.76); N 3.93 (4.02).
Catalytic Studies. Typical Suzuki Coupling Procedure. A small
Schlenk vessel was charged with aryl halide (0.5 mmol), boronic acid
(0.75 mmol), KOtBu (1.0 mmol), and 4.0 mL of 1,4-dioxane in a
glovebox. The catalyst (1.0 mol %) solution in 1,4-dioxane (0.25 mL)
was added through the Suba seal, and the mixture was stirred at
room temperature for 5 min. The catalytic mixture was then stirred at
80 ꢀC for the indicated period of time (Table 3). The GC was
calibrated with the authenticated samples of the coupled product,
and the progress of the reaction was monitored by GC. The GC
conversions were optimized in each case and reported as an average
of two GC runs. For isolation of the products, the contents of the
Schlenk vessel were mixed with silica gel and evaporated. The
product/silica gel mixture was placed on the top of the flash
chromatography column and eluted with a mixture of pentane and
diethyl ether (90:10) (Table 3, entry 5). The product was analyzed by
NMR, and the data were compared with the literature.84
Synthesis of (η3-Allyl)Pd(BIAN-SIMes)Cl (5a). To a stirred
solution of [Pd(η3-C3H5)(μ-Cl)]2 (0.2 g, 0.55 mmol) in THF
(5.0 mL) at -78 ꢀC was added dropwise a solution of BIAN-
SIMes (4a) (0.49 g, 1.14 mmol) in THF (5.0 mL). The reac-
tion mixture was stirred for 10 min and then gradually warmed
to room temperature and stirred for an additional 3 h. The
mixture was then filtered, and the pale yellow solution was
evaporated to reduce the total volume to 2 mL. Addition of
pentane (10 mL) gave an orange-yellow solid, which was
filtered, washed with ice-cold diethyl ether/pentane (20:80)
(5 mL) and pentane (2 ꢀ 5 mL), and dried under vacuum. Yield:
0.49 g, 73%.
1H NMR (500 MHz, 293 K, CDCl3): δ 7.81 (d, 1H, J = 8.2 Hz,
naphthyl ring CH), 7.80 (d, 1H, J = 8.1 Hz, naphthyl ring CH),
7.43 (dt, 2H, J = 8.3 Hz, J = 1.7 Hz, naphthyl ring CH), 7.04 (s,
1H, mesityl m-CH), 7.03 (s, 1H, mesityl m-CH), 6.89 (d, 1H, J =
7.2 Hz, naphthyl ring CH), 6.85 (d, 1H, J = 7.2 Hz, naphthyl ring
CH), 6.83 (s, 1H, mesityl m-CH), 6.81 (s, 1H, mesityl m-CH), 6.10
(d, 1H, J = 9.3 Hz, -NCHCHN-), 6.09 (d, 1H, J = 9.2 Hz,
-NCHCHN-), 4.76-4.66 (m, 1H, allyl H), 3.74 (dd, 1H, J =
7.5 Hz, J = 1.8 Hz, allyl C(pseudo-trans to NHC) Hs), 3.18 (d, 1H, J =
6.9 Hz, allyl C(pseudo-trans to Cl)Hs), 2.71 (s, 3H, mesityl-CH3),
2.67 (s, 3H, mesityl-CH3), 2.65 (d, 1H, J = 13.4 Hz, allyl allyl
C(pseudo-trans to NHC)Ha), 2.30 (s, 6H, mesityl-CH3), 1.73 (d, 1H,
J = 12.0 Hz, allyl(pseudo-trans to Cl)Ha), 1.60 (s, 3H, mesityl-CH3),
1.40 (s, 3H, mesityl-CH3). 13C{1H} NMR (75.5 MHz, 293 K,
CD2Cl2): δ 210.6 (s, C(Pd-carbene)), 139.9,139.2, 138.2, 138.0, 137.7,
137.1, 136.8, 136.7, 136.4, 134.6, 131.6, (s, C(quaternary naphthyl) and
C(quaternary mesityl)), 128.3, 129.2, 129.3, 129.6(s, C(mesityl)H), 121.5,
121.8, 125.4, 125.5, 128.0 (s, C(naphtyl)H), 114.5 (s, allyl CH), 71.6
(s, allyl C(trans to Carbene)H2), 71.1 (s, C(-NCHCHN-)), 51.5 (s, allyl
C(trans to chloride)H2), 20.9 (s, C(mesityl)H3), 18.7, 18.9, 19.0 (br s,
C(mesityl)H3).MS(ESþ,CHCN):m/z= 618.43 [M - Cl þ CH3CN]þ
(100%), 577.21 [M - Cl]þ (50%). Anal. Found (calcd): C 66.39
(66.56); H 5.81 (5.75); N 4.43 (4.57).
Typical C-N Coupling Procedures. A small Schlenk vessel was
charged with aryl halide (1.0 mmol), amine (1.2 mmol), KOtBu
(1.5 mmol), and 4.0 mL of 1,4-dioxane in a glovebox. The catalyst
(1.0 mol %) solution in 1,4-dioxane was added through the Suba
Synthesis of (η3-Allyl)Pd(BIAN-SIPr)Cl (5b). To a stirred
solution of [Pd(η3-C3H5)(μ-Cl)]2 (0.3 g, 0.82 mmol) in THF
(10 mL) at -78 ꢀC was added dropwise a solution of BIAN-SIPr
(84) Wei, Y.; Kan, J.; Wang, M.; Su, W.; Hong, M. Org. Lett. 2009,
11, 3346–3349.

4870 Organometallics, Vol. 29, No. 21, 2010
Dastgir et al.
seal, andthe mixture wasstirred forthe indicated period oftime at
room temperature, unless otherwise stated (Table 4). The gas
chromatograph was calibrated with the authenticated samples of
the coupled product, and the progress of the reaction was
monitored by GC. The GC conversions were optimized in each
case and reported as an average of two GC runs. For isolation of
the products, the contents of the Schlenk vessel were quenched
with an aqueous solution of NH4Cl and extracted in CH2Cl2. The
organic fractions were mixed with silica gel and evaporated. The
product/silica gel mixture was placed on the top of the flash
chromatography column, and the product was purified by flash
chromatography. The isolated products were analyzed by NMR,
and the data were compared with the literature values.85
of Science and Technology (MOST) and Lady Margaret
Hall, University of Oxford, for graduate funding (S.D.).
Special thanks to Dr. Nick Rees, Inorganic Chemistry
Laboratory, Department of Chemistry, University of
Oxford, for his help in the NMR studies and useful
discussions, and Dr. David J. Watkin for helpful dis-
cussions on crystallography. S.D. thanks Dr. Howard
Hunter, Department of Chemistry, York University,
Toronto, Canada, for his help in reprocessing the NMR
data.
Supporting Information Available: Crystallographic data (CIF)
and a tablecontaining a summary ofcrystaldataare available free
of charge via the Internet at http://pubs.acs.org. The structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre with CCDC reference numbers
714509 (3a), 714510 (3b), and 714511 (5b).
Acknowledgment. We thank the Royal Society for a
University Research Fellowship (K.S.C.) and the Ministry
(85) Viciu, M. S.; Kissling, R. M.; Stevens, E. D.; Nolan, S. P. Org.
Lett. 2002, 4, 2229–2231.