Synthesis and structures of π-allylpalladium(II) complexes containing bis(1,2,4-triazol-5-ylidene-1-yl)borate ligands. An unusual tetrahedral palladium complex

Article abstract of DOI:10.1016/j.jorganchem.2011.09.003

Four air stable, neutral π-allylpalladium(II) complexes containing bis(1,2,4-triazol-5-ylidene-1-yl)borate ligands [H₂B(RBTz) ₂Pd(π-allyl)] (R = ⁿBu, 2a; ^tBu, 2b; 2,6-diisopropylphenyl, 2c; cyclohexyl, 2d) have

Full text of DOI:10.1016/j.jorganchem.2011.09.003

Journal of Organometallic Chemistry 696 (2011) 3800e3806
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and structures of p-allylpalladium(II) complexes containing
bis(1,2,4-triazol-5-ylidene-1-yl)borate ligands. An unusual tetrahedral palladium
complex
,
b
Wei-Feng Xua, Xiao-Wei Lia, Yi-Zhi Lia, Xue-Tai Chena , Zi-Ling Xue
*
a State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing University,
Nanjing 210093, People’s Republic of China
b Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Four air stable, neutral
ligands [H2B(RBTz)2Pd(
p
p
-allylpalladium(II) complexes containing bis(1,2,4-triazol-5-ylidene-1-yl)borate
-allyl)] (R ¼ nBu, 2a; tBu, 2b; 2,6-diisopropylphenyl, 2c; cyclohexyl, 2d) have
Received 31 March 2011
Received in revised form
26 August 2011
been prepared and characterized. The molecular structures of 2c and 2d have been confirmed by single-
crystal X-ray diffraction. To our surprise, the coordination geometry about the palladium atom in 2d is
distorted tetrahedron, in which the allyl group is nearly perpendicular to the plane defined by the Pd and
the carbene C atoms. To our knowledge, such configuration has not been reported for a four-coordinated
palladium allyl complex.
Accepted 1 September 2011
Keywords:
N-Heterocyclic carbene
Palladium
Ó 2011 Elsevier B.V. All rights reserved.
Allyl
Tetrahedral Pd(II) complex
1. Introduction
[46,47], Pd(II) [46], Pt(II) [46], and Au(I) [46], Ca(II) [48], Sr(II) [48],
Ni(II) [49], Rh(I) and Ir(I) [50], have been prepared. The studies on
N-Heterocyclic carbenes (NHC) have been actively studied, since
Arduengo and coworkers isolated and characterized the first stable
NHC in 1991 [1]. It has been well documented that metal-NHC
complexes have broad applications in homogeneous catalysis
[2e6]. Among transition metal complexes containing N-heterocyclic
carbene ligands, Pd-NHC complexes have attracted particular atten-
tion mainly due to their excellent catalytic performances in the CeC
cross-coupling reactions [7e15]. Several types of well defined Pd(II)e
bis(1,2,4-triazol-5-ylidene-1-yl)borate are relatively limited. Santini
et al. reported the synthesis of dinuclear silver(I) and gold(I)
complexes with bis(1,2,4-triazol-5-ylidene-1-yl)borate [51]. No
palladium complex with bis(1,2,4-triazol-5-ylidene-1-yl)borate has
been reported. Hereinwe report the synthesis and characterization of
four neutral
p-allylpalladium(II) complexes (2a-2d) containing
bis(1,2,4-triazol-5-ylidene-1-yl)borate ligands.
NHC complexes such as
allyl)X] [16e20], solvent-coordinated
[(NHC)Pd(solvent)( -allyl)] [21e24],
p
-allylpalladium complexes [(NHC)Pd(
-allylpalladium complexes
and -allylpalladium
p-
p
p
p
complexes with donor-functionalized NHC have been reported
[20,25e31]. Bis(pyrazolyl)borate (Bp)ligand (A) hasbeenwidely used
in coordination and organometallic chemistry [32e45]. Its NHC
analogues, which exhibit the framework of the Bp and the novel
strong electronic donicity of the NHC, have attracted some attention.
So far two types of such bidentate NHC ligands such as bis(imidazol-
2-ylidene-1-yl)borate (BIm) (B) and bis(1,2,4-triazol-5-ylidene-1-yl)
borate [H2B(RBTz)2, C] are known. Several metal complexes with
bis(imidazol-2-ylidene-1-yl)borate ligands, including those of Li(I)
2. Results and discussion
2.1. Synthesis and characterization
4-(n-Butyl)-1,2,4-triazole,
4-(tert-butyl)-1,2,4-triazole,
4-
cyclohexyl-1,2,4-triazole, and 4-(2,6-diisopropylphenyl)-1,2,4-
triazole were synthesized by the literature procedures [52]. The
* Corresponding author. Tel.: þ86 25 83597147; fax: þ86 25 83314502.
E-mail addresses: xtchen@nju.edu.cn, xtchen@netra.nju.edu.cn (X.-T. Chen).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.09.003

W.-F. Xu et al. / Journal of Organometallic Chemistry 696 (2011) 3800e3806
3801
bidentate NHC ligand precursors 1a-1d were synthesized with
nearly quantitative yields by the reaction of alkyl or aryl-1,2,4-
triazole with a boride solution, which was obtained from the
treatment of 1.0 eq of Me3N:BH3 in toluene with 0.5 eq of I2
(Scheme 1).
Transmetalation from Ag-NHC complexes has been shown to be
an efficient method for the preparation of NHC complexes of transi-
tion metals [53,54]. Here, a two-step process was used to prepare the
In addition, their chemical shift difference is very small. Thus their
mutual coupling in an AB pattern as well as the coupling by the two
b
-H atoms in N-CHAHBeCH2eCH2eCH3 lead to a complex 1H NMR
spectrum for the diastereotopic CHAHB atoms, as shown in the
insert in Fig. 2. The effect of the pro-chiral NHC ring on the two -H
atoms is much smaller. In addition, the chemical environment
b
between
a
-HA and HB atoms is small so that, to the
b
-H atoms,
a
-HA
and HB atoms are close to being identical. The 1H peak of
b-H atoms
p
-allylpalladium(II) complexes. The first step involves deprotonation
in 2a is thus a quintet (Supplementary material).
of the imidazolium salts with Ag2O to form the Ag-NHC species.
Although these complexes could be isolated [51], we used the Ag-
NHC complexes in situ. The [H2B(RTz)2Pd(p-allyl)] complexes 2a-2d
were prepared by the reactions of the Ag-NHC complexes with [Pd(
allyl)Cl]2 at room temperature in good yields (Scheme 1).
The new complexes 2a-2d were isolated as white and air stable
solids. They are insoluble in nonpolar solvents such as diethyl ether,
hexane, or toluene, but soluble in polar organic solvents such as
CH2Cl2, DMF, CH3CN, DMSO, and acetone.
The new complexes were characterized by elemental analysis
and 1H, 13C and 11B NMR spectroscopies. 1H and 13C NMR spectra of
2a-2d are given in supplementary materials. Compared with the
ligand precursors, the 1H resonances of the 3H-triazolium protons at
9e10 ppm have disappeared in 2a-2d, indicating the formation of
the carbene carbon atoms that coordinate to the palladium atoms.
The formation of the metal complexes is also evident from the
distinctive Pd-13Ccarbene peak, appearing in the range 168e177 ppm
for 2a-2d. These signals are in the typical range for Pd-triazolylidene
complexes [51,55e57].
The 1H and 13C NMR spectra of the tBu analog 2b show that there
are two isomers (Fig. 3). Two sets of peaks, one for each isomer,
were observed at room temperature. The allyl ligand in both
isomers show features similar to those of 2a, 2c, and 2d discussed
earlier (Fig. 1 and Table 1). It is not clear what these isomers are.
Attempts to obtain the X-ray quality crystals of 2b were unsuc-
cessful. Without its crystal structure(s), we speculate that these two
isomers are square planar and tetrahedral, and their interchange
(or the rotation of allyl ligand in solution) is probably restricted by
p-
t
the bulky Bu groups in 2b.
The 1H and 13C NMR spectra of 2,6-diisopropylphenyl analog 2c
give one resonance each for the 3-H-triazole (8.06 ppm), triazole
(143.20 ppm), and the Ccarbene atoms (174.27 ppm), indicating that
there is a reflection plane (mirror) through the Pd and B atoms
(Fig. 4) and perpendicular to the plane defined by the Pd, C1 and C3
atoms (Fig. 5), as discussed in detail later in the crystal structure of
2c. The NMR peaks of the allyl group (Supplementary material and
Table 1) are also consistent with the presence of the mirror
symmetry. The peaks of the isopropyl groups in 2c (Fig. 4) show
there are two eCH- and four methyl groups. There is an accidental
degeneracy of two methyl peaks at 2.084 ppm in the 1H NMR
spectrum. A structure consistent with the NMR observations is
given in Fig. 4. This is a crowded molecule, as its structure in Fig. 5
demonstrates later, and the rotation of the isopropyl groups is
limited, resulting in four methyl resonances.
Three 1H NMR signals with a ratio of 2:2:1 and two 13C NMR
signals were observed for the allylic groups in 2a (insert in Fig. 1),
square planar 2c and tetrahedral 2d. This is consistent with
symmetric allyl ligands (CH2CHCHꢀ2 ), leading to two equivalent CH2
groups in the allyl ligands. As in the reported allyl ligands in, e.g.,
asymmetric allyl Pd NHC complexes by Li and coworkers [27], the
two H atoms in the CH2 groups are in the syn and anti configura-
tions with respect to the H atom in the CH group in the allyl ligands
(Table 1). The assignment of the Hsyn and Hanti atoms in 2a, 2c, and
2d was based on comparison with those in other reported allyl Pd
NHC complexes [27]. The peak of the syn H atoms is downfield from
that of the anti atoms. The JH-H couplings between the CH and Hsyn
and Hanti atoms are 6.5e7.5 and 13.0 Hz, respectively. Similar
couplings were also observed in chloroethene (ClHC ¼ CH2, Scheme
2), where Jac and Jbc ¼ 7.0 and 14.6 Hz, respectively (Fig. 1) [58].
As shown in Table 1, the chemical shifts of 1H NMR peaks of the
alkyl ligand in tetrahedral 2d is downfield shifted from those of
square planar 2c. The separation of the syn and anti peaks in 2d
(1.21 ppm) is larger than that (0.60 ppm) in 2c. The 13C NMR
chemical shifts in both complexes are similar (Table 1).
2.2. Molecular structures of 2c and 2d
Crystals of 2c$1/2H2O and 2d$1/2CH2Cl2 were obtained by slow
evaporation of their dichloromethane solutions. The structures
were determined by single-crystal X-ray diffraction. Molecular
structures of 2c and 2d are shown in Figs. 5 and 6, respectively.
Crystallographic data for 2c$1/2H2O and 2d$1/2CH2Cl2 are pre-
sented in Table 2. Selected bond distances and angles are given in
Table 2. There are two crystallographically independent molecules
in the crystal structure of 2c$1/2H2O. Bond distances and angles of
the two molecules are similar, and those of one molecule are listed
in Table 3.
The coordination geometry around the Pd atom in 2c is dis-
torted square planar with two carbene carbons and two peripheral
allyl carbon atoms. Here the coordinated allyl ligand is considered
bidentate. The two substituent phenyl rings are almost perpen-
dicular to the corresponding triazolyl rings with the dihedral angle
of 75.8(7)ꢁ and 76.6(4)ꢁ, respectively. The two triazolyl rings have
a dihedral angle of 145.8(5)ꢁ. The dihedral angle of the plane of C1-
The a
-H atoms in the nBu (NeCH2eCH2eCH2eCH3) groups in
2a are diastereotopic, as shown in the Newman projection in Fig. 2.
Pd-C3 and the plane of C17-Pd-C19 is 4.6(5)ꢁ, indicating that the
allyl group is almost parallel to the plane of C1-Pd-C3.
p-
The coordination geometry about the Pd atom in 2d is distorted
tetrahedron with two carbene carbons and two terminal allyl
carbons. In 2d, the two triazolyl rings have a dihedral angle of
131.4(4)ꢁ. The dihedral angle of the plane of C1-Pd-C3 and the plane
of C17-Pd-C19 is 70.0(1)ꢁ, indicating that the
p-allyl group is almost
perpendicular to the plane of C1-Pd-C3, in sharp contrast to the
nearly planar geometry around the Pd atom in 2c. To our knowledge,
such distorted tetrahedral configuration in 2d has not been reported
for a four-coordinated allyl palladium complex. The difference
Scheme 1. Synthesis of precursors 1a-1d and NHC-Pd(II) complexes 2a-d.

3802
W.-F. Xu et al. / Journal of Organometallic Chemistry 696 (2011) 3800e3806
Fig. 1. Hsyn and Hanti atoms in the symmetric allyl ligands in 2a-d, in comparison to CH2]CHCl. Insert: 1H NMR spectrum of the allyl ligand in 2a.
between the coordination modes of the
p
-allyl ligands in 2c and 2d
(60 mL) was slowly added I2 (2.08 g, 8.04 mmol). The reaction
mixture was stirred at room temperature for 1 h. Alkyl or aryl 1,2,4-
triazole (32.9 mmol) was added to the yellow solution and refluxed
for 24 h. After filtration, the solvent was decanted and the residue
was washed with hexane, Et2O and toluene (20 mL ꢂ 2) each. The
white oily solid was heated to 80 ꢁC under vacuum for several
hours. The pure product was obtained from recrystallization in hot
ethanol.
may be attributed to the larger steric effect by the cyclohexyl groups
in 2d. Chen et al. have examined the steric effects of the substutuents
on the structures of the Ni and Pd NHC complexes, in which bulky
substitutents induced distortion (steric pressure) [59,60].
The Pd-Ccarbene bond lengths of 2.064(6) Å and 2.050(6) Å in 2c
and 2.080(7) Å and 2.137(7) Å in 2d are in the range of the reported
values [25e31]. Due to the chelating effect, the bite angles of C1-
Pd1-C3 are 89.1(3)ꢁ in 2c and 90.5(2)ꢁ in 2d. The bond distances
1a (5.505 g, 85.8% yield). 1H NMR (500 MHz, J in Hz, CDCl3)
of
h
3 coordination of the allyl group and the palladium center in 2c
d
9.84 (s, 2H, 5-H-triazole), 8.61 (s, 2H, 3-H-triazole), 4.37 (t, J ¼ 7.5,
and 2d are comparable to those reported [19,25e31].
4H, NCH2CH2), 3.55 (b, B-H), 1.93 (quintet, J ¼ 7.5, 4H, NCH2CH2),
1.39 (sextuple, J ¼ 7.5, 4H, CH2CH3), 0.95 (t, J ¼ 7.5 Hz, 6H, CH3). 13
C
NMR (125 MHz, CDCl3)
d 144.98 (5-C-triazole), 144.05 (3-C-tri-
3. Experimental
azole), 47.61 (nBu), 31.94 (nBu), 19.48 (nBu), 13.41 (nBu). 11B NMR
(160 MHz, CDCl3)
ꢀ4.44 (s, 1B). Elemental analysis (%) calcd. for
d
3.1. Instruments and reagents
C
12H24BIN6: C, 36.95; H, 6.20; N, 21.54; found: C, 36.91, H, 6.32, N,
21.39. MS (ESI): calcd. for C12H24BIN6 m/z 263.22 ([M ꢀ I]þ),
All the reagents were purchased from Aldrich or Acros and used
without further purification. All solvents were distilled prior to use.
The starting materials 4-(n-butyl)-4H-1,2,4-triazole, 4-(tert-butyl)-
4H-1,2,4-triazole ,4-(2,6-diisopropylphenyl)-4H-1,2,4-triazole, and
4-cyclohexyl-4H-1,2,4-triazole were prepared by the literature
procedure [52]. Elemental analyses were performed in an Ele-
mentar Vario ELIII elemental analyzer. NMR measurements were
obtained in DMSO-d6 and CDCl3 on a Bruker AM-500 spectrometer.
Chemical shifts for 1H, and 13C NMR are given in parts per million
relative to Me4Si while chemical shifts for 11B NMR is relative to
observed 263.17.
1b (5.781 g, 90.1% yield). 1H NMR (500 MHz, CDCl3)
d
10.19 (s,
2H, 5-H-triazole), 8.31 (s, 2H, 3-H-triazole), 4.1e3.3 (b, B-H), 1.78 (s,
18H, CMe3). 13C NMR (125 MHz, CDCl3)
145.78 (5-C-triazole),
144.65 (3-C-triazole), 61.40 (CMe3), 30.15 (CMe3). 11B NMR
(160 MHz, CDCl3)
ꢀ4.40 (s, 1B). Elemental analysis (%) calcd. for
d
d
C
12H24BIN6: C, 36.95; H, 6.20; N, 21.54; found: C, 36.75, H, 6.12, N,
21.34. MS (ESI): calcd. for C12H24BIN6 m/z 263.22 ([M ꢀ I]þ),
observed 263.25.
1c (7.235 g, 73.5% yield). 1H NMR (500 MHz, J in Hz, DMSO-d6)
external Et2O-BF3 (
APEX II FTICR Mass Spectrometer (Bruker-Franzen).
d
11B ¼ 0). ESI mass spectra were recorded on an
d
10.46 (s, 2H, 5-H-triazole), 9.58 (s, 2H, 3-H-triazole), 7.66 (t,
J ¼ 8.0, 2H, C6H3), 7.48 (d, J ¼ 8.0, 4H, C6H3), 4.0e3.2 (b, B-H), 2.21
(m, J ¼ 6.5, 4H, CHMe2), 1.11 (dd, 3J ¼ 19, 5J ¼ 7.0 Hz, 24H, CHMe2).
3.2. Preparation of 1a-1d
13C NMR (125 MHz, CDCl3)
d 148.79 (C6H3), 147.42 (C6H3), 145.58 (5-
C-triazole), 144.95 (3-C-triazole), 132.40 (C6H3), 127.82 (C6H3),
125.07 (C6H3), 124.43 (C6H3), 28.67 (CHMe2), 24.19 (CHMe2), 23.87
The general procedure for synthesis of 1a, 1b, 1c and 1d is given
here. To a solution of Me3N:BH3 (1.2 g, 16.45 mmol) in toluene
Table 1
NMR chemical shifts of the allyl ligands in 2c and 2d (J in Hz).
Complexes
1H NMR
CH
Hsyn
Hanti
2a
5.23 (m)
5.28 (m)
5.27 (m)
4.44 (m)
5.18 (m)
4.00 (d), JH-Hsyn ¼ 7.5
3.76 (d), JH-Hsyn ¼ 7.5
3.92 (d), JH-Hsyn ¼ 7.5
2.33 (d), JH-Hsyn ¼ 7.5
3.84 (d), JH-Hsyn ¼ 6.5
2.71 (d), JH-Hanti ¼ 13.0
2.79 (d), JH-Hanti ¼ 13.0
2.59 (d), JH-Hanti ¼ 13.0
1.73 (d), JH-Hanti ¼ 13.0
2.63 (d), JH-Hanti ¼ 13.0
2b-1
2b-2
2c
2d
{1H}-13C NMR
CH
CH2
56.2
58.9
59.6
57.9
57.8
2a
118.3
114.9
118.1
117.0
118.3
2b-1
2b-2
2c
2d
Fig. 2. Diastereotopic a
-H atoms in the nBu groups in 2a.

W.-F. Xu et al. / Journal of Organometallic Chemistry 696 (2011) 3800e3806
3803
Fig. 3. 1H and 13C NMR spectra of 2b, showing two isomers. The B-H peak is not shown.
Fig. 4. A possible structure of 2c showing four inequivalent methyl groups. Inserts: 1H (A) and 13C (B) NMR peaks the eCHMe2 groups in 2c.

3804
W.-F. Xu et al. / Journal of Organometallic Chemistry 696 (2011) 3800e3806
Fig. 5. Molecular structure and atom numbering scheme for 2c (with 30% probability ellipsoids). Hydrogen atoms and solvent molecule are omitted for clarity.
(CHMe2). 11B NMR (160 MHz, CDCl3)
moisture-sensitive to conduct its elemental analysis. MS (ESI):
calcd. for C28H40BIN6 m/z 471.34 ([M ꢀ I]þ), observed 471.42.
1d (6.444 g, yield 92.8%). 1H NMR (500 MHz, J in Hz, CDCl3)
d
ꢀ4.95 (s, 1B). 1c was too
2a (0.360 g, yield 88.1%). 1H NMR (500 MHz, J in Hz, CDCl3) 7.96
(s, 2H, 3-H-triazole), 5.23 (m, J ¼ 7.5, 1H, CH in allyl), 4.08 (m, J ¼ 7.5,
4H, NCH2CH2CH2CH3), 4.00 (d, J ¼ 7.5, 2H, CHsyn in allyl), 3.7 (b, B-
H), 2.71 (d, J ¼ 13, 2H, CHanti in allyl), 1.74 (quintet, J ¼ ca. 7.5, 4H,
NCH2CH2CH2CH3), 1.31 (sextuple, J ¼ 7.5, 4H, NCH2CH2CH2CH3),
d
9.90 (s, 2H, 5-H-triazole), 8.62 (s, 2H, 3-H-triazole), 4.46 (t, 2H, CH
in Cy), 3.9e3.1 (b, B-H), 2.26e1.27 (10H, CH2 in Cy). 13C NMR
(125 MHz, CDCl3) 144.40 (5-C-triazole), 142.39 (3-C-triazole),
0.91 (t, J ¼ 7.5, 6H, CH3). 13C NMR (125 MHz, CDCl3)
d 175.1 (Ccarbene),
d
140.8 (triazole), 118.3 (CH in allyl), 56.2 (CH2 in allyl), 47.3 (nBu),
57.36 (CH in Cy), 33.30 (CH2 in Cy), 32.77 (CH2 in Cy), 26.02 (CH2 in
33.2 (nBu), 19.4 (nBu), 13.3 (nBu). 11B NMR (160 MHz, CDCl3)
d
ꢀ2.20
Cy), 24.92 (CH2 in Cy), 24.66 (CH2 in Cy). 11B NMR (160 MHz, CDCl3)
(broad). Elemental analysis (%) calcd. for C15H27BN6Pd: C, 44.09; H,
6.66; N, 20.57; found: C, 44.07, H, 6.74, N, 20.78.
d
ꢀ4.45 (s, 1B). Elemental analysis (%) calcd. for C16H28BIN6: C,
43.46; H, 6.38; N, 19.01; found: C, 43.26, H, 6.31, N, 19.07. MS (ESI):
2b-1 and 2b-2 (0.382 g, yield 93.5%). 2b-1: 1H NMR (500 MHz, J
in Hz, CDCl3) 8.03 (s, 1H, 3-H-triazole), 5.28 (m, J ¼ 7.5, 1H, CH in
allyl), 3.76 (d, J ¼ 7.5, 2H, CHsyn in allyl), 2.79 (d, J ¼ 7.5, 2H, CHanti in
calcd. for C16H28BIN6 m/z 315.25 ([M ꢀ I]þ), observed 315.33.
allyl), 1.60 (s, 9H, CMe3). 13C NMR (125 MHz, CDCl3)
d 176.3 (Ccar-
3.3. Preparation of 2a-2d
bene), 139.1 (triazole), 114.9 (CH in allyl), 58.9 (CH2 allyl), 56.1
(CMe3), 30.9 (CMe3). 2b-2 1H NMR (500 MHz, J in Hz, CDCl3) 8.00 (s,
1H, 3-H-triazole), 5.27 (m, J ¼ 7.5,1H, CH in allyl), 3.92 (d, J ¼ 7.5, 2H,
CHsyn in allyl), 4.0e3.2 (b, B-H), 2.59 (d, J ¼ 7.5, 2H, CHanti in allyl),
1.67 (s, 9H, CMe3). 13C NMR (125 MHz, CDCl3) 176.1 (Ccarbene), 138.7
(triazole), 118.1 (CH in allyl), 59.6 (CH2 in allyl), 56.1 (CMe3), 31.2
A mixture of 1a-1d (1 mmol) and Ag2O (1.1 mmol) was stirred in
CH2Cl2 (20 mL) at room temperature for 12 h. Then [Pd(p-allyl)Cl]2
(0.5 mmol) was added and stirred for 2 h. The mixture was filtrated.
The colorless filtrate was concentrated under vacuum and the
residue was purified by chromatography on silica gel. Elution with
CH2Cl2/CH3OH (20:1) afforded the separation of a colorless portion.
Removing the solvent gave the desired products as white solids.
Recrystallization from acetone or CH2Cl2 gave the pure products
suitable for elemental analysis and crystals for X-ray diffraction (for
2c and 2d).
(CMe3). 11B NMR (160 MHz, CDCl3)
d
ꢀ2.24 (broad for both 2b-1 and
2b-2). Elemental analysis (%) calcd. for C15H27BN6Pd: C, 44.09; H,
6.66; N, 20.57; found: C, 44.01, H, 6.86, N, 20.67.
2c (0.533 g, yield 86.5%). 1H NMR (500 MHz, J in Hz, CDCl3) 8.06
(s, 2H, 3-H-triazole), 7.49 (t, J ¼ 8.0, 2H, C6H3), 7.26 (d, J ¼ 8.0, 4H,
Fig. 6. Molecular structure and atom numbering scheme for 2d (with 30% probability ellipsoids). Hydrogen atoms and solvent molecule are omitted for clarity.

W.-F. Xu et al. / Journal of Organometallic Chemistry 696 (2011) 3800e3806
3805
J ¼ 13.0, 2H, CHanti in allyl), 2.00e1.12 (10H, CH2 in Cy). 13C NMR
Table 2
Crystallographic data for 2c$1/2H2O and 2d$1/2CH2Cl2.
(125 MHz, CDCl3)
d 174.5 (Ccarbene), 138.3 (triazole), 118.3 (CH in
allyl), 57.8 (CH2 in allyl), 56.3 (CH in Cy), 34.6e24.9 (CH2 in Cy). 11
NMR (160 MHz, CDCl3)
calcd. for C19H31BN6Pd: C, 49.53; H, 6.78; N, 18.24; found: C, 49.47,
H, 6.71, N, 18.17.
B
2c$1/2H2O
2d$1/2CH2Cl2
d
ꢀ2.28 (broad). Elemental analysis (%)
Empirical formula
Formula weight
T (K)
C62H88B2N12OPd2
1251.86
291(2)
0.28 ꢂ 0.22 ꢂ 0.20
monoclinic
P2(1)/c
22.612(6)
17.292(5)
18.352(5)
90.00
C39H66B2Cl2N12Pd2
1008.36
291(2)
0.28 ꢂ 0.24 ꢂ 0.22
monoclinic
C2
24.831(5)
9.0502(17)
11.503(2)
90.00
104.416(3)
90.00
2503.7(8)
2
1.338
0.864
Crystal size (mm3)
Crystal system
Space group
a (Å)
3.4. X-ray crystallography
b (Å)
c (Å)
A suitable single crystal of 2c$1/2H2O or 2d$1/2CH2Cl2 was
mounted on the top of glass fibers for X-ray structure analysis.
Diffraction data were collected on a Bruker SMART APEX CCD
diffractometer with graphite-monochromatized Mo Ka radiation
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
111.221(4)
90.00
6689(3)
Volume (Å3)
(
l
¼ 0.71073 Å) at room temperature and corrected for absorption
Z
4
using SADABS program [61]. The structures were solved by direct
methods and refined on F2 against all reflections by full-matrix
least-squares methods with SHELXTL program [62]. Anisotropy
thermal parameters were assigned to all non-hydrogen atoms.
Dcalc (g/cm3)
1.243
0.584
2616
1.52e26.00
ꢀ27 ꢃ h ꢃ 15
ꢀ21 ꢃ k ꢃ 21
ꢀ21 ꢃ l ꢃ 22
35571/13040
0.0562
Absorption coefficient (mmꢀ1
F(000)
)
1040
q
Range for data collection (ꢁ)
1.69e25.99
ꢀ30 ꢃ h ꢃ 30
ꢀ11 ꢃ k ꢃ 10
ꢀ14 ꢃ l ꢃ 11
6939/4253
0.0346
Index ranges
4. Conclusions
Reflections collected/unique
R(int)
Completeness to
Max. and min. transmission
Data/restraints/parameters
GOF
Four air stable，neutral p-allylpalladium(II) complexes 2a-2d
q
¼ 26.00 (%)
99.2
99.4
have been prepared and characterized. The molecular structures
of 2c and 2d have been confirmed by single-crystal X-ray
diffraction. To our surprise, the coordination geometry about the
palladium atom in 2d is distorted tetrahedron, in which the allyl
group is nearly perpendicular to the plane defined by the Pd and
the carbene C atoms. To our knowledge, such configuration has
0.892 and 0.861
13040/0/737
1.043
R1 ¼ 0.0486
wR2 ¼ 0.0870
R1 ¼ 0.0975
wR2 ¼ 0.0947
1.297 and ꢀ0.583
0.8327 and 0.7940
4253/1/271
1.076
R1 ¼ 0.0499
wR2 ¼ 0.1329
R1 ¼ 0.0571
wR2 ¼ 0.1366
0.625 and ꢀ0.609
Final R indices [I > 2
s
(I)]a
R indices (all data)
not been reported for
complex.
a four-coordinated palladium allyl
Largest differences in peak
and hole (e Åꢀ3
)
a
2
R1
¼
S
jjFoj
ꢀ
jFcjj/SjFoj; wR2
¼
[Sw(jFoj
ꢀ
jFcj)2/SwjFoj ]1/2
;
GOF ¼ [Sw(jFoj ꢀ jFcj)2/(noꢀnv)]1/2
.
Acknowledgment
We are grateful for the financial support from the National Basic
Research Program of China (No. 2007CB925102 to XTC), Natural
Science Grant of China (Nos. 21071078 and 21021062 to XTC), and
the U.S. National Science Foundation (CHE-1012173 to ZLX).
C6H3), 4.44 (m, J ¼ 7.0, 1H, CH in allyl), 4.4e3.8 (b, B-H), 2.50
[quintet, J ¼ 7.0, 2H, CHMe2], 2.38 (quintet, J ¼ 7.0, 2H, CHMe2), 2.33
(d, J ¼ 6.5, 2H, CHsyn in allyl),1.73 (d, J ¼ 13.0, 2H, CHanti in allyl),1.09
(d, J ¼ 7.0, 6H, CHMe2), 1.08 (d, J ¼ 6.5, 6H, CHMe2), 1.05 (d, J ¼ 6.5,
6H, CHMe2), 1.02 (d, J ¼ 6.5, 6H, CHMe2). 13C NMR (125 MHz, CDCl3)
Supplementary material
d
174.3 (Ccarbene), 146.4 (C6H3), 146.2 (C6H3), 143.2 (triazole), 134.2
(C6H3), 130.3 (C6H3), 123.9 (C6H3), 123.8 (C6H3), 117.0 (CH in allyl),
57.9 (CH2 in allyl), 28.1 (CHMe2), 28.0 (CHMe2), 25.2 (CHMe2), 24.8
(CHMe2), 23.1 (CHMe2), 23.0 (CHMe2). 11B NMR (160 MHz, CDCl3)
CCDC 818081-818082 contain the supplementary crystallo-
graphic data for 2c and 2d. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif. Catalytic studies are given in
Supplementary material.
d
ꢀ2.32 (broad). Elemental analysis (%) calcd. for C31H43BN6Pd: C,
60.35; H, 7.03; N, 13.62; found: C, 60.25, H, 6.93, N, 13.66.
2d (0.339 g, yield 73.7%). 1H NMR (500 MHz, J in Hz, CDCl3) 7.94
(s, 2H, 3-H-triazole), 5.18 (m, J ¼ 7.5, 1H, CH in allyl), 4.19 (m, 2H, CH
in Cy), 3.84 (d, J ¼ 6.5, 2H, CHsyn in allyl), 4.0e3.3 (b, B-H), 2.63 (d,
Appendix A. Supplementary material
Supplementary material associated with this article can be found,
in the online version, at doi:10.1016/j.jorganchem.2011.09.003.
Table 3
Selected bond distances (Å) and angles (ꢁ) in 2c and 2d.
2c
References
Pd(1)eC(1)
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2.080(7)
2.137(7)
2.108(7)
2.245(7)
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Pd(1)eC(19)
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110.4(3)
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