Cyclometallated Pd(II) azido complexes containing 6-phenyl-2,2′- bipyridyl or 2-phenylpyridyl derivatives: Synthesis and reactivity toward organic isocyanides and isothiocyanates

Article abstract of DOI:10.1039/b411432a

Cyclometallated palladium(II) azido complexes containing C,N,N- or C,N-donor ligands, [Pd(N₃)L] (HL = 6-phenyl-2,2′-bipyridine or 2-phenylpyridyl derivatives), showed different reactivities toward organic isocyanides and isothiocyanates. In particular, aryl isocyanides (CN-Ar) underwent insertion into the orthometallated Pd-C bond on the phenyl moiety of the supporting ligand (L) in [Pd(N₃)L] or [Pd(N₃)(PR ₃)L] to selectively give carbodiimido {[Pd(N=C=N-Ar)L]}, imidoyl {[Pd(N₃)(-C=N-Ar)(PR₃)L]}, or imidoyl carbodiimido complexes {[Pd(N=C=N-Ar)(-C=N-Ar)L] or [Pd(N=C=N-Ar)(-C=N-Ar)(PR ₃)L]}, depending on reaction conditions. Interestingly, reactions of [Pd(N₃)(PR₃)L] with organic isothiocyanates gave unusual dinuclear complexes [(μ-SCN₄-R)PdL]₂, exhibiting the concurrent S- and N-coordinating thio-tetrazole bridge.

Full text of DOI:10.1039/b411432a

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F U L L P A P E R
Cyclometallated Pd(II) azido complexes containing 6-phenyl-2,2-
bipyridyl or 2-phenylpyridyl derivatives: synthesis and reactivity
toward organic isocyanides and isothiocyanates†
Yong-Joo Kim,*a Xiaohong Chang,a Jin-Taek Han,a Mi S. Limb and Soon W. Leeb
a
Department of Chemistry, Kangnung National University, Kangnung 210-702, Korea.
E-mail: yjkim@kangnung.ac.kr; Fax: + 82 + 33-647-1183; Tel: + 82 + 33-640-2308
Department of Chemistry, Sungkyunkwan University, Natural Science Campus,
b
Suwon 440-746, Korea
Received 26th July 2004, Accepted 22nd September 2004
First published as an Advance Article on the web 7th October 2004
Cyclometallated palladium(II) azido complexes containing C,N,N- or C,N-donor ligands, [Pd(N3)L] (HL = 6-
phenyl-2,2-bipyridine or 2-phenylpyridyl derivatives), showed different reactivities toward organic isocyanides and
isothiocyanates. In particular, aryl isocyanides (CN–Ar) underwent insertion into the orthometallated Pd–C bond
on the phenyl moiety of the supporting ligand (L) in [Pd(N3)L] or [Pd(N3)(PR3)L] to selectively give carbodiimido
{[Pd(NCN–Ar)L]}, imidoyl {[Pd(N3)(–CN–Ar)(PR3)L]}, or imidoyl carbodiimido complexes {[Pd(NCN–
Ar)(–CN–Ar)L] or [Pd(NCN–Ar)(–CN–Ar)(PR3)L]}, depending on reaction conditions. Interestingly,
reactions of [Pd(N3)(PR3)L] with organic isothiocyanates gave unusual dinuclear complexes [(l-SCN4–R)PdL]2,
exhibiting the concurrent S- and N-coordinating thio–tetrazole bridge.
Introduction
Cyclometallated Pd(II) or Pt(II) complexes containing C,N,N- or
C,N-donor ligands such as 6-phenyl-2,2-bipyridyl or 2-phenyl-
pyridyl are currently under intensive studies due to their intri-
guing photochemical or photophysical properties.1–7 For these
complexes, the intramolecular C–H activation of the involved
Chart 1
C,N,N- or C,N-donor ligands has been one of the most impor-
tant research topics.8–11 Considering rich studies on the photo-
chemical or photophysical properties and reactivity for these
systems, only a few cases have been reported regarding their
chemical properties.12–14 Furthermore, cyclometallated Pd(II)
or Pt(II) complexes containing pseudo-halogen ligands such as
an azido group have not been reported yet. The azido ligand in
transition-metal complexes is generally known to be photosen-
sitive, and therefore cyclometallated complexes containing that
ligand may have the potential to enhance their photochemical or
photophysical ability. In addition, the reactivity of those azido
complexes toward unsaturated organic molecules such as iso-
cyanides (CN–R) or isothiocyanates (SCN–R) is unknown.
Recently, we reported that group 10 metal azido complexes
having tertiary phosphines reacted with isocyanides or isothio-
cyanates to give the corresponding carbodiimido or tetrazole–
thiolato complexes depending on reaction conditions.15,16 As a
comparative study of these works, we examined the prepara-
tion and chemical properties of cyclometallated Pd(II) azido
complexes containing C,N,N- or C,N-donor ligands. Herein
we report the synthesis and structures of cyclometallated Pd(II)
azido complexes [Pd(N3)L] or [Pd(N3)(PR3)L], in which “L”
refers to a bipyridyl or pyridyl derivative acting as a C,N,N-
or C,N-donor ligand (see Chart 1), along with their reactivity
toward organic isocyanides or isothiocyanates.
of [Pd(Cl)L1] in DMF with excess NaN3 in MeOH at room
temperature as shown in eqn. (1). Formation of 1 was readily
confirmed by a characteristic stretching band at 2037 cm−1 due
to m(N3).
(1)
Our recent paper revealed that reactions of mono- or
bis(azido) Pd(II) complexes having tertiary phosphines
with 2,6-dimethylphenyl isocyanide gave Pd(II) complexes
containing an end-on carbodiimido group.15 On the basis
of these results, we employed the same synthetic strategy to
prepare new carbodiimido complexes. Reactions of 1 with
1 equiv. of aryl isocyanide (CN–Ar) at room temperature
afforded new Pd(II) complexes containing an aryl carbodiimido
group, [Pd(NCN–Ar)L1] (Ar = C6H3-2,6-Et2 (2) or, C6H3-
2,6-i-Pr2 (3) (eqn. (2)). Color, yields, and analytical data of
the complexes are listed in Table 1. The formation of the
products could also be readily confirmed by the IR spectrum,
which shows the disappearance of an asymmetric stretching
band m(N3) of the starting material and the appearance of a
new strong band at 2120 (for 2) or 2111 cm−1 (for 2) due to
the carbodiimido group (NCN) of the product. The same
reaction with 2 equiv. or more isocyanide gave a mixture of
three products whose NMR spectra indicate the presence of
a carbodiimido complex [Pd(NCN–Ar)L1], a new carbo-
diimido complex [Pd(NCN–Ar)(–CN–Ar)L1], and an
uncertain compound (probably an isocyanide-coordinated
Results and discussion
Preparation and reactions of cyclometallated Pd(II) azido
complex having C,N,N-donors
We have prepared a cyclometallated Pd(II) azido complex
[Pd(N3)L1] (HL1 = 6-phenyl-2,2-bipyridine) (1) by metathesis
† Electronic supplementary information (ESI) available: Spectroscopic
data. See http://www.rsc.org/suppdata/dt/b4/b411432a/
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 3 6 9 9 – 3 7 0 8
3 6 9 9

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Table 1 Color, yields and analytical data for 1–7 and 16–35
Analysesb (%)
C
Complex a
Color
Yield (%)
H
N
1, [Pd(N3)L1]
Yellow
Yellow
Orange
Orange
Green
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
95
78
35
77
66
59
72
78
41
86
70
95
88
85
45
74
82
66
36
55
74
66
37
44
39
56
71
50.21
(50.61)
63.29
(63.47)
61.18
(60.94)
66.80
(66.50)
54.46
(54.49)
53.57
(53.52)
50.20
(50.16)
44.40
(44.40)
51.70
(51.90)
45.63
(45.88)
49.73
(49.72)
52.61
(52.82)
52.41
(52.13)
52.37
(52.04)
56.99
(57.30)
58.23
(57.98)
59.64
(59.85)
61.45
(61.73)
54.77
(55.02)
63.08
(63.21)
58.96
(58.87)
64.53
(64.35)
46.32
(46.22)
47.54
(47.28)
44.52
(44.62)
43.26
(43.05)
50.50
(50.53)
2.85
(2.92)
4.75
(4.73)
5.09
(5.02)
4.73
(4.76)
4.38
(4.36)
4.17
(4.04)
3.38
(3.37)
4.54
(4.52)
6.31
(6.32)
4.83
(4.88)
5.86
(5.80)
4.72
(4.65)
7.33
(7.29)
5.67
(5.70)
6.22
(6.05)
6.44
(6.26)
6.88
(6.81)
5.71
(5.97)
5.49
(5.39)
6.07
(5.95)
6.84
(6.75)
6.34
(6.32)
3.67
(3.64)
4.59
(4.43)
3.82
(3.74)
3.97
(3.94)
5.77
(5.71)
18.31
(18.44)
10.86
(10.97)
9.60
(9.63)
11.26
(11.41)
18.05
(18.16)
18.56
(18.72)
17.52
(17.55)
14.60
(14.79)
12.09
(12.10)
14.44
(14.27)
12.79
(12.89)
12.19
(12.32)
10.21
(10.13)
10.36
(10.55)
12.01
(12.37)
11.91
(12.07)
11.08
(11.26)
10.67
(10.91)
13.14
(13.37)
8.69
(8.93)
6.77
(6.87)
7.32
(7.32)
16.76
(16.84)
15.93
(16.22)
17.21
(17.34)
15.11
(15.22)
11.24
(11.33)
2, [Pd(NCN–Ar)L1] (Ar = C6H3-2,6-Et2)
3, [Pd(NCN–Ar)L1] (Ar = C6H3-2,6-i-Pr2)
4, [Pd(NCN–Ar)(CN–Ar)L1] (Ar = C6H3-2,6-Me2)
5, [Pd(CN4-n-Bu)L1]
6, [Pd(CN4-i-Pr)L1]
7, [Pd(SCN4–CH2CHCH2)L1]
16, [Pd(N3)(PMe3)L2]
17, [Pd(N3)(P(n;-Pr)3)L2]
18, [Pd(N3)(PMe3)L3]
19, [Pd(N3)(PEt3)L3]
20, [Pd(N3)(PMe2Ph)L3]
21, [Pd(N3)(PEt3)2L3]
22, [Pd(N3)(PMe3)2L4]
23, [Pd(N3)(–CN–Ar)(PMe3)L2] (Ar = C6H3-2,6-i-Pr2)
24, [Pd(N3)(–CN–Ar)(PMe3)L3] (Ar = C6H3-2,6-i-Pr2)
25, [Pd(N3)(–CN–Ar)(PEt3)L3] (Ar = C6H3-2,6-i-Pr2)
26, [Pd(N3)(–CN–Ar)(PMe2Ph)L3] (Ar = C6H3-2,6-i-Pr2)
27, [Pd(N3)(–CN–Ar)(PMe3)L3] (Ar = C6H3-2,6-Me2)
28, [Pd(NCN–Ar)(CN–Ar)(PMe3)L3] (Ar = C6H3-2,6-Me2)
29, [Pd(NCN–Ar)(–CN–Ar)(Ph)(PMe3)2] (Ar = C6H3-2,6-Me2)
30, [Pd(NCN–Ar)(CN–Ar)(PMe3)2L4] (Ar = C6H3-2,6-Me2)
31, [(l-SCN4–CH2CHCH2)PdL3]2
32, [(l-SCN4-n-Bu)PdL3]2
33, [(l-SCN4–Et)PdL3]2
34, [(l-SCN4–i-Pr)PdL3]2
35, [Pd(SCN4–Et)(PMe3)2L4]
a HL1 = 6-Phenyl-2,2-bipyridine; HL2 = 2-phenylpyridine; HL3 = 2-(p-tolyl)pyridine; HL4 = 2,6-diphenylpyridine. b Calculated values are given in
parentheses.
complex). Isolation of pure compounds failed because of their
quite similar solubilities.
carbodiimido Pd(II) complex containing an imidoyl group,
[Pd(NCN–C6H3-2,6-Me2)(–CN–C6H3-2,6-Me2)L1] (4),
in 77% yield as shown in eqn. (3). The structure of complex
4 tells us that the incoming isocyanide has undergone both
insertion into the Pd–C bond and coupling with the azido
ligand to give a carbodiimido group during the reaction. The
formation of the imidoyl group by the isocyanide (CN–Ar)
insertion into the orthometallated Pd–C bond on the phenyl
moiety of a ligand is a rare example for the cyclometallated
complexes containing C,N,N-donor ligands. For a compari-
son, Che and co-workers recently reported that reactions of
[PtClL1] with isocyanides gave isocyanide-coordinated Pt(II)
complexes [Pt(CN–R)L1]+, indicating orthometallated Pt–C
bond remained intact.2
(2)
Fortunately, treatment of 1 with 2 equiv. of 2,6-dimethyl-
phenyl isocyanide at 60 °C for 3 h gave a new single
3 7 0 0
D a l t o n T r a n s . , 2 0 0 4 , 3 6 9 9 – 3 7 0 8

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(3)
Orange–red crystalline complex 4 was characterized by
spectroscopic and elemental analysis, and its molecular
structure was determined by X-ray crystallography. Its IR
spectrum of 4 shows a strong asymmetric band at 2161 cm−1
due to the m(NCN) group and a stretch band at 1622 cm−1
due to the m(CN) that is close to the values for known imidoyl
complexes.17 1H and 13C NMR spectra of 4 display two singlets
due to the symmetric methyl substituents of the 2,6-dimethyl-
phenyl group attached to the carbodiimido (NCN) or
imidoyl (CN) group. A singlet at 180 ppm in 13C{1H} NMR
corresponds to the carbon signal of the imidoyl (CN) group.
In contrast to the results for aryl isocyanides, reactions
of 1 with equimolar or excess alkyl isocyanides (n-BuNC
and i-PrNC) gave a totally different family of products,
C-coordinated tetrazolato Pd(II) complexes [Pd(CN4–R)L1]
(R = n-Bu (5) or i-Pr (6)), as pale green solids, as shown in
eqn. (4). Complexes 5 and 6 have been formed by the dipolar
cycloaddition of the isocyanide to the Pd–azido bond. The same
cycloaddition pattern could also be observed in the reaction of
1 and allyl isothiocyanate. Treating 1 with allyl isothiocyanate
led to the formation of a S-coordinated tetrazole–thiolato
Pd(II) complex 7, [Pd(SCN4–CH2CHCH2)L1], which was also
formed by the dipolar cycloaddition of isothiocyanate to the
Pd–azido bond.
Fig. 1 ORTEP drawing46 of 3 showing the atom-labeling scheme
and 50% probability thermal ellipsoids. Selected bond lengths (Å)
and angles (°): Pd1–N1 1.954(2), Pd1–C1 1.981(3), Pd1–N3 2.000(3),
Pd1–N2 2.129(3), N3–C17 1.172(4), N4–C17 1.255(4), N4–C18 1.412(4);
N1–Pd1–N3 178.1(1), C1–Pd1–N3 99.3(1), C17–N3–Pd1 148.1(3).
(4)
Figs. 1–3 show molecular structures of 3, 4 and 7, respectively.
Details on crystal data, intensity collection, and refinement
details are given in Table 2. Fig. 1 depicts the ORTEP drawing
of 3, which shows slightly distorted square-planar coordination,
consisting of two nitrogen atoms of the bipyridine group, one
orthometallated carbon atom, and one carbodiimido group.
The molecular structure clearly shows that the nitrogen atom
of the carbodiimido ligand (NCN–C6H3-2,6-Me2) is bonded
to the Pd center. The Pd–N bond distance (2.000(3) Å) of 3 is
very close to those (1.988–2.089(6) Å) previously found in Pd(II)
carbodiimido complexes.15,18
Interestingly, the ORTEP drawings of two isomers of 4 in
Fig. 2(A and B) show two crystallographically independent
molecules in an asymmetric unit, which explains the Z value
of 8 rather than 4. The two molecules are diasteromers to each
other, and the marked difference between them can be described
in terms of dihedral angles between the 2,6-dimethylphenyl
rings in each Pd coordination sphere: 17.3(4)° (around Pd1 in
Fig. 2 ORTEP drawing of 4: (a) Diastereomer 1, (b) Diastereomer 2.
Selected bond lengths (Å) and angles (°): Pd1–N4 1.965(7), Pd1–C17
1.971(7), Pd1–N2 2.023(6), Pd1–N1 2.144(6), Pd2–C51 1.968(8),
Pd2–N9 2.004(9), Pd2–N7 2.023(6), Pd2–N6 2.151(7); N4–Pd1–C17
94.2(3), N4–Pd1–N2 174.8(3), N4–Pd1–N1 96.9(3), C51–Pd2–N9
92.6(3), N9–Pd2–N7 175.8(3), N9–Pd2–N6 97.6(3), C26–N4–Pd1
168.3(8), C60–N9–Pd2 159.1(10).
diastereomer 1) and 85.4(3)° (around Pd2 in diastereomer 2).
The molecular structure of 4 clearly exhibits the presence of
imidoyl group formed by the CN–Ar insertion into the Pd–C
bond on the phenyl moiety of the supporting ligand.
D a l t o n T r a n s . , 2 0 0 4 , 3 6 9 9 – 3 7 0 8
3 7 0 1

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
3 7 0 2
D a l t o n T r a n s . , 2 0 0 4 , 3 6 9 9 – 3 7 0 8

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bis(phosphine) [Pd(N3)(PEt3)2L3] (21) as shown in eqn. (7).
However, complex 21 turns to a mixture of cyclometallated
complex, [Pd(N3)(PEt3)L3] (19) and itself by the dissocia-
tion of one PEt3 during recrystallization. On the other hand,
[Pd(Cl)L4]2 (HL4 = 2,6-diphenylpyridine) was completely
cleaved by 4 equiv. PMe3 to give [Pd(Cl)(PMe3)2L4] (15)
and then further treatment with excess NaN3 produced the
corresponding azido complex, [Pd(N3)(PMe3)2L4] (22) in 85%
yield. These azido complexes were characterized by spectro-
scopy and elemental analyses.
(5)
Fig. 3 ORTEP drawing of 7. Selected bond lengths (Å) and angles (°):
Pd1–N1 1.994(4), Pd1–C1 2.018(6), Pd1–N2 2.138(5), Pd1–S1 2.320(2),
S1–C17 1.711(6), N3–C17 1.357(8), N3–N4 1.363(7), N4–N5 1.277(7),
N5–N6 1.357(7), N6–C17 1.339(7); N1–Pd1–C1 81.4(2), N1–Pd1–N2
78.7(2), C1–Pd1–N2 160.1(2), N1–Pd1–S1 179.0(1), C1–Pd1–S1 99.7(2),
N2–Pd1–S1 100.3(2), C17–S1–Pd1 108.1(2).
(6)
Fig. 3 shows the ORTEP drawing of 7, which has square-
planar coordination containing two nitrogens and one carbon
on the cyclometallated plane and a thiolato ligand possessing
a five-membered (2-substituted) tetrazole ring. The tetra-
zole ring (CN4) is oriented perpendicularly to the molecular
plane. The bond length of the Pd–S bond (2.320(2) Å)
is close to that (2.342(7) Å) of a similar Pd(II) complex,
trans-[Pd(SCN4–CH2CHCH2)(PMe3)2] reported by our group.16
(7)
IR spectra show characteristic stretching bands at ca.
2030 cm−1 due to m(N3). As shown in Figs. 4 and 5, the molecular
structures of [Pd(N3)(PMe3)L2], (16) and [Pd(N3)(PMe3)L3]
Preparation of cyclometallated Pd(II) azido complexes having
C,N-donor and their reactivity toward isocyanides
By employing the same synthetic strategy for the prepara-
tion of the cyclometallated complex (1), which possesses the
C,N,N-donor ligand (L1), we could prepare the corresponding
cyclometallated Pd(II) azido complexes containing C,N-donor
ligands (2-phenylpyridine derivatives) and investigated their
reactivity toward isocyanides. Reactivity of these complexes
is initially expected to parallel that of complexes with
C,N,N-donor ligands.
Novel C,N-cyclometallated Pd(II) azido complexes, [Pd(N3)-
(PR3)L] (L = 2-phenylpyridine (HL2) or 2-(p-tolyl)pyridine
(HL3)), were obtained from the following procedures as shown
in eqns. (5) and (6). First, dinuclear chloro-bridged complexes
[Pd(Cl)L]2 were cleaved by 2 or 4 equiv. of PR3 (R = Me,
Et, etc.) to give mono(phosphine) [Pd(Cl)(PR3)L] (8–12)
or bis(phosphine) [PdCl(PR3)2L] complexes (13 and 14) as
shown in eqn. (5). Subsequent treatments of [Pd(Cl)(PR3)L]
with excess aqueous NaN3 produced the corresponding azido
complexes [Pd(N3)(PR3)L] (16–20) (eqn. (6)). In contrast,
reactions of [Pd(Cl)(PR3)2L3], where L3 is a monodentate
(C-coordinated) pyridyl ligand, with excess NaN3 gave a C,N-
cyclometallated mono(phosphine) [Pd(N3)(PMe3)L3] (18) or
Fig. 4 ORTEP drawing of 16. Selected bond lengths (Å) and angles
(°): Pd1–C1 2.018(2), Pd1–N4 2.086(2), Pd1–N1 2.115(2), Pd1–P1
2.2509(7), N1–N2 1.176(3), N2–N3 1.155(4); C1–Pd1–N4 81.17(10),
C1–Pd1–N1 170.86(10), N4–Pd1–N1 89.70(9), N4–Pd1–P1 174.76(6),
N1–Pd1–P1 92.26(8), N2–N1–Pd1 126.3(2), N3–N2–N1 177.3(3).
D a l t o n T r a n s . , 2 0 0 4 , 3 6 9 9 – 3 7 0 8
3 7 0 3

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starting materials. Interestingly, 1H NMR spectra of each
methyl group (–CH(CH3)2) in the 2,6-diisopropylarylimidoyl
group of complexes 23–26 display four doublets coupled with
the proton of the isopropyl group (–CH(CH3)2), which indicate
the magnetically inequivalent methyl groups in solution. By
contrast, the methyl groups in the 2,6-dimethylphenylimidoyl
group in complex 27 show only one signal, which suggests
somewhat relieved steric congestion around the methyl groups
relative to the 2,6-diisopropyl groups. The assignment of four
CH3 and two CH signals corresponding to the two isopropyl
groups of complexes 23–26 has been made by 1H–1H and
1H–13C COSY NMR methods. The spatial arrangement of
the isopropyl groups has been confirmed further by X-ray
structure determination. Fig. 6 shows the molecular structure of
[Pd(N3)(–CN–C6H3-2,6-i-Pr2)(PMe2Ph)L3] (26), which clearly
shows the imidoyl group formed by CN–Ar insertion into the
orthometallated Pd–C bond, as well as a terminal azido ligand.
This molecular structure also demonstrates sterically demand-
ing 2,6-diisopropyl phenyl fragments to restrict rotation about
the N–C bond to make the methyl substituents inequivalent in
1H NMR of that complex.
Fig. 5 ORTEP drawing of 18. Selected bond lengths (Å) and
angles (°): Pd1–C11 2.013(3), Pd1–N1 2.089(2), Pd1–N2 2.127(3),
Pd1–P1 2.2557(8), N2–N3 1.176(4), N3–N4 1.152(4); C11–Pd1–N1
80.96(10), C11–Pd1–N2 171.07(11), N1–Pd1–N2 90.14(10), C11–Pd1–
P1 96.96(8), N1–Pd1–P1 175.74(6), N2–Pd1–P1 91.97(9), N3–N2–Pd1
123.7(2), N4–N3–N2 176.4(3).
(18) were determined by X-ray crystallography. The ORTEP
drawings of the complexes show square-planar coordina-
tion conaining a C,N-coordinating ligand, one PMe3, and
an N3 ligand. The Pd–N (azido) bond lengths (2.115(2) Å
in 16 and 2.127(3) Å in 18) are close to that found for trans-
[Pd(N3)(tolyl)(PMe3)2] (2.119(5) Å).15
In order to compare the reactivity of orthometallated
Pd(II) azido complexes with the C,N,N-donor ligand (L1), we
examined reactions of the corresponding Pd(II) complexes with
the C,N-donor ligands {[Pd(N3)(PR3)L2] and [Pd(N3)(PR3)L3]}
with one equiv. or excess CN–Ar (Ar = C6H3-2,6-Me2 or C6H3-
2,6-i-Pr2) at room temperature.
Interestingly, those reactions exhibited the selective insertion
of the aryl isocyanide into the orthometallated Pd–C bond
to give imidoyl Pd(II) azido complexes, [Pd(N3)(–CN–
Ar)(PMe3)L2] (23) or [Pd(N3)(–CN–Ar)(PR3)L3] (24–27), as
shown in eqn. (8).
Fig. 6 ORTEP drawing of 26. Selected bond lengths (Å) and
angles (°): Pd1–C13 1.991(7), Pd1–N3 2.124(7), Pd1–N1 2.142(6), Pd1–
P1 2.248(2), P1–C27 1.800(9), N3–N4 1.154(9), N4–N5 1.154(10), N2–
C13 1.260(9), N2–C14, 1.416(9); C13–Pd1–N3 171.8(3), C13–Pd1–N1
84.1(3), N3–Pd1–N1 87.7(3), C13–Pd1–P1 96.9(2), N3–Pd1–P1 91.3(2),
N1–Pd1–P1 173.9(2), N3–N4–N5 175.8(9), N4–N3–Pd1 136.5(6),
N2–C13–Pd1 135.3(5).
Gently heating a mixture of [Pd(N3)(PR3)L3] (18) and 2 equiv.
of 2,6-dimethylphenyl isocyanide at 60 °C led to the formation
of a novel carbodiimido Pd(II) complex, [Pd(NCN–C6H3-
2,6-Me2)(–CN–C6H3-2,6-Me2)(PMe3)L3] (28), as shown in
eqn. (9). Formation of complex 28 was readily monitored by the
IR spectrum which shows the disappearance of an asymmetric
stretching band m(N3) at 2039 cm−1 and the appearance of a
new strong band at 2137 cm−1 due to the carbodiimido group
m(NCN) of the product. A signal at 194.0 ppm in 13C NMR
corresponding to the carbon atom of the imidoyl (CN–Ar)
group could be observed.
(8)
The azido ligand is well known to react readily with
isocyanides to give C-coordinated tetrazolato compounds
by the dipolar cycloaddition of the isocyanides into that
ligand.19–23 We also observed that the azido ligands in metal
phosphine complexes coupled with isocyanides to convert
to a carbodiimido (NCN–R) group or a tetrazolato ring
(CN4R) depending on the types of the isocyanides.15,22 However,
our present results (eqn. (8)) contrast with the previously
reported ones. Even with excess isocyanide, those reactions
gave the same complexes, indicating the azido ligand remained
intact. Although many studies on the isocyanide insertion for
organopalladium aryl complexes to form palladium imidoyl
compounds have been reported, the insertion of isocyanide
into the palladium aryl compounds containing pseudo-halogen
ligands has not been reported.17,24–34
IR spectra of imidoyl Pd(II) azido complexes 23–27 show a
stretch band at 2031–2038 cm−1 due to the m(N3), which is slightly
shifted to lower values compared to that (2040–2051 cm−1) of
(9)
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We have also examined the reactivity between aryl isocyanides
and the azido ligand in aryl palladium(II) azido complexes that
do not have the orthometallated Pd–C bond (eqns. (10) and
(11)). Previously, we reported that reactions of phenyl Pd(II)
azide with 1 equiv. of 2,6-dimethylphenyl isocyanide gave a
phenyl Pd(II) carbodiimido complex.15 In this work, similar
reactions of aryl Pd(II) azido complexes with 2 equiv. of aryl
isocyanide at room temperature smoothly afforded new imidoyl
Pd(II) carbodiimido complexes 29 and 30. Isolated complexes
were fully characterized by IR, NMR, and elemental analysis. In
addition, the molecular structure of complex 30 was determined
by X-ray crystallography. The ORTEP drawing of the complex
30 (Fig. 7) shows slightly distorted square-planar coordination
containing an aryl imidoyl group, two trans PMe3 ligands, and a
carbodiimido group bound to the metal center.
containing chelating phosphine ligands require more vigorous
conditions (longer reaction time or higher temperature) for
isocyanide interaction than the corresponding azido complexes
with monodentate phosphine ligands.15
Reactivity toward isothiocyanates (R–NCS)
In
a
recent work, we reported that reactions of
bis(azido)bis(phosphine) complexes of Pd(II) with various
organic isothiocyanates gave tetrazole–thiolato complexes of
Pd(II).16 In the present work, we decided to extend the scope of
such reactivity to other cyclometallated ligands such as C,N,N-
donor (L1) or C,N-donor ligands (L2–L4).
Treatments of [Pd(N3)(PR3)L3] (PR3 = PMe3 or PEt3) with
R–NCS (R = allyl, n-Bu, ethyl, or i-Pr) resulted in the
formation of unusual dinuclear Pd(II) complexes, [(l-SCN4–
R)PdL3]2 (31–34), in which the thio–tetrazole rings ((l-SCN4–R)
bridge two Pd metals through both S and N atoms as shown
in eqn. (12).
(10)
(12)
Dinuclear Pd(II) complexes 31–34 were obtained as yellow
crystals in 37–56% yields and characterized by IR, NMR, MS
(FAB), and elemental analyses. One (34) of the complexes was
structurally characterized by X-ray diffraction. Formation
of these complexes was readily confirmed by the disappear-
ance of m(N3) band at ca. 2030 cm−1 and m(P–C, PR3) band
at 950–1000 cm−1 of the starting materials. The assignment
for each proton and carbon of those complexes was made by
1H–13C COSY. The signal due to the carbon in the tetrazole
ring (CN4–R) of the complexes appears at 161–163 ppm. The
FAB (+) mass spectra of the complexes are consistent with the
formulas.
(11)
The molecular structure of a dinuclear compound 34 is shown
in Fig. 8. Each thio–tetrazole ligand bridges two palladium
metals through the nitrogen and sulfur atoms. Two equatorial
planes (plane 1: Pd1, S1, N1, N10, C11; plane 2: Pd2, S2, N5,
N6, C27) are relatively planar with the atomic displacements not
exceeding 0.0656 Å, and their dihedral angle is 15.0(2)°. Two
essentially planar thio–tetrazole ligands are twisted out of the
equatorial planes with dihedral angles of 76.1(2) or 69.3(2)°.
The Pd–Pd bond length (2.9704(6) Å) indicates a single bond
(the covalent radius of Pd is 1.380 Å). However, this bond
length is significantly longer than those (2.55–2.8 Å) of other
dinuclear complexes containing a Pd–Pd single bond, and this
bond lengthening can be attributed to the steric congestion
around the Pd atoms.35 The Pd–N (N-coordinated tetrazole
ring) bonds (Pd2–N5: 2.168(4) Å; Pd1–N10: 2.157(4) Å) are
significantly longer than those of the Pd–N (pyridine) bonds
(Pd2–N6: 2.062(4) Å; Pd1–N1 (2.056(4) Å). The former
Pd–N bond lengths are somewhat longer than those of other
Pd compounds, trans-[Pd(CN4–Ph)(PPh3)2] (2.01 Å),36 trans-
[PdMe(N3)(PMe3)2] (2.132(9) Å),22 and trans-[PdPh(NHPh)-
(PMe3)2] (2.116(13) Å).37 The Pd–S bond lengths (2.316(1) and
2.311(1) Å) are close to those found in mononuclear complexes
such as trans-[Pd(SCN4–CH2CHCH2)(PMe3)2] (2.342(7) Å),16
trans-[Pd(SCN4–Ph)(PMe3)2] (2.325(8) Å),16 and [Pd(SCN4–
Me)4]2− (2.332(1) and 2.339(1) Å).38 The most striking feature
Fig. 7 ORTEP drawing of 30. Selected bond lengths (Å) and angles
(°): Pd1–C16 2.011(2), Pd1–N1 2.125(2), Pd1–P1 2.3022(8), Pd1–P2
2.3650(8), N1–C7 1.173(4), N2–C7 1.265(4), N3–C16 1.267(3), N3–C17
1.412(3); C16–Pd1–N1 172.2(1), C16–Pd1–P1 90.51(7), N1–Pd1–P1
89.62(8), C16–Pd1–P2 94.08(7), N1–Pd1–P2 87.63(8), P1–Pd1–P2
165.84(3), C7–N1–Pd1 144.9(2), C7–N2–C8 128.0(3), C16–N3–C17
129.2(2), N1–C7–N2 169.9(4).
From a comparison of isocyanide reactivity toward cyclo-
metallated or non-cyclometallated Pd(II) azides (eqns. (8)–(11)),
we come to a conclusion that cyclometallated azido complexes
[Pd(N3)(PR3)L] (L = L2 or L3) containing 2-phenylpyridine or
2-(p-tolyl)pyridine, which is generally known as a hemilabile
ligand, are less reactive for isocyanide insertion or carbodiimido
formation than non-cyclometallated Pd(II) azido complexes
having tertiary phosphine ligands. These observations agree
with the previous report that late transition-metal azides
D a l t o n T r a n s . , 2 0 0 4 , 3 6 9 9 – 3 7 0 8
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of the molecular structure of compound 34 is a concurrent
S- and N-coordination of the thio–tetrazole ring to the metal.
Our recent paper revealed that reactions of bis(phosphine)
Ni(II), Pd(II), and Pt(II) azido complexes with organic isothio-
cyanates gave the selective formation of tetrazole–thiolato (S-
coordination) complexes.16 To our knowledge, dinuclear Pd(II)
complexes 31–34 represent the first structurally characterized
examples containing the concurrent S- and N-coordinating
thio–tetrazole ring, which has been formed by the dipolar
cycloaddition of an organic isothiocyanate (R–NCS) to the
palladium–azido bond.
mono(phosphine) Pd(II) complex possessing both a terminal
tetrazole–thiolato ring and a C,N-coordinated ligand, seems
to be too reactive to exist as a separate entity in our reaction
system.
(13)
In summary, we have prepared several cyclometallated azido
complexes, [Pd(N3)L] and [Pd(N3)(PR3)L], in which L refers to
6-phenyl-2,2-bipyridyl or 2-phenylpyridyl derivatives acting as
a C,N,N- or C,N-donor ligand. These complexes showed several
reactivities toward organic isocyanides and isothiocyanates.
Treatment of cyclometallated Pd(II) azido complexes with aryl
isocyanides (CN–Ar) resulted in the formation of carbodiimido
[Pd(NCN–Ar)L] or imidoyl (carbodiimido) [Pd(NCN–
Ar)(CN–Ar)L] complexes. In some cases, regioselectivity,
in which the isocyanide prefers insertion into the Pd–C bond
(that is, selective formation of imidoyl Pd(II) azido complexes,
[Pd(N3)(–CN–Ar)(PMe3)L]) over coupling with the azido
ligand, was observed, depending on reaction conditions. The
corresponding reactions with alkyl isocyanides (CN–R) and
allyl isothiocyanate (SCN–CH2CHCH2) produced tetrazolato
complexes {[Pd(CN4–R)L]} and a tetrazole–thiolato complex
{[Pd(SCN4–CH2CHCH2)L]}, respectively. In particular, with
organic isothiocyanates (R–NCS), we have observed the forma-
tion of dinuclear Pd compounds, in which the thio–tetrazolato
ligand bridges two Pd metals through both S and N atoms
with the concomitant formation of a Pd–Pd bond. On the
basis of reactivities observed in our study, that is, the selective
insertion and the dinuclear complex formation, we might come
to a conclusion the C,N-donor ligand system is more reactive
toward nucleophiles or electrophiles than the C,N,N-donor
ligand system.
Fig. 8 ORTEP drawing of 34. Selected bond lengths (Å) and angles
(°): Pd1–Pd2 2.9704(6), Pd1–N1 2.056(4), Pd1–N10 2.157(4), Pd1–S1
2.311(1), Pd2–N6 2.062(4), Pd2–N5 2.168(4), Pd2–S2 2.316(1), S1–C13
1.719(5), S2–C29 1.722(5); N1–Pd1–N10 95.2(2), N1–Pd1–S1 173.6(1),
N10–Pd1–S1 90.4(1), N1–Pd1–Pd2 95.6(1), N10–Pd1–Pd2 81.4(1),
S1–Pd1–Pd2 88.26(4), N6–Pd2–N5 97.5(2), C27–Pd2–S2 94.1(2),
N6–Pd2–S2 174.4(1), N5–Pd2–S2 87.1(1), N5–Pd2–Pd1 81.7(1),
S2–Pd2–Pd1 89.70(4).
One possible mechanism is shown in Scheme 1, which involves
an initial formation of a terminal tetrazole–thiolato Pd(II)
intermediate, followed by PR3 dissociation and the subsequent
dimerization to give the dinuclear products.
Experimental
General, materials and measurements
All manipulations of air-sensitive compounds were performed
under N2 or argon by standard Schlenk techniques.
Solvents were distilled from Na–benzophenone. The analytical
laboratories at Kangnung National University carried out
elemental analyses using CE instruments EA1110. IR spectra
were recorded on a Perkin Elmer BX spectrophotometer.
NMR (1H, 13C{1H}, and 31P{1H}) spectra were obtained on
a JEOL Lambda 300 MHz spectrometer. Chemical shifts
were referenced to internal Me4Si or to external 85% H3PO4.
Mass (FAB) spectra were obtained at Korea Basic Science
Institute (Seoul). [Pd(Cl)L1] (HL1 = 6-phenyl-2,2-bipyridine),
[Pd(Cl)L]2 (HL2 = 2-phenylpyridine; HL3 = 2-(p-tolyl)pyridine;
HL4 = 2,6-diphenylpyridine) were prepared by the literature
methods.39–43 2,6-Diethylphenyl isocyanide and 2,6-diisopropyl-
phenyl isocyanide were prepared as described in the literature.44
2-Phenylpyridine, 2-(p-tolyl)pyridine, and 2,6-diphenylpyridine
were used as supplied.
Scheme 1
In order to support the proposed mechanism, we decided
to isolate a mono(phosphine) Pd(II) complex possessing both
a terminal tetrazole–thiolato ring and a C,N-coordinated
ligand. The reactions of bis(phosphine) azido Pd(II) complexes
containing the C-coordinated ligand, [Pd(N3)(PEt3)2L3] (21) and
[Pd(N3)(PMe3)2L4] (22), with isopropyl (or ethyl) isothiocyanate
(R–NCS) were studied to examine whether to obtain such a
cyclometallated mono(phosphine) species [Pd(SCN4–R)(PR3)L]
formed by phosphine dissociation. In the former case, attempts
to obtain the desired product were unsuccessful because of the
formation of a mixture of both the tetrazole–thiolato and the
dinuclear compounds, presumably produced by the partial
dissociation of PEt3. On the other hand, in the case of complex
22, we could isolate the tetrazole–thiolato bis(phosphine) Pd(II)
complex, [Pd(SCN4–Et)(PMe3)2L4] (35), as shown in eqn. (13).
One possible explanation for the difference in the two cases
(L3 vs. L4) is the steric bulk of the pendent (or uncoordinated)
phenyl substituent of the ligand L4, which might hinder the
pyridyl nitrogen from coordinating to the Pd metal. These
results suggest that the proposed intermediate in Scheme 1, the
Preparations
[Pd(N3)L1] (HL1 = 6-phenyl-2,2-bipyridine) (1). To a Schlenk
flask containing [Pd(Cl)L] (0.482 g, 1.21 mmol) were added
DMF (55 ml) and a NaN3 solution (0.252 g, 3.63 mmol)
dissolved in methanol (10 ml) in that order. The initial orange
solution turned to a yellow suspension. After stirring for 4 h
3 7 0 6
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at room temperature, the solvent was reduced to half under
vacuum. The resulting solids were filtered off and washed with
H2O and ether to give yellow solids (0.437 g).
[Pd(N3)(P(n-Pr)3)L2] (17), [Pd(N3)(PMe3)L3] (18), [Pd(N3)-
(PEt3)L3] (19), [Pd(N3)(PMe2Ph)L3] (20), [Pd(N3)(PEt3)2L3] (21),
and [Pd(N3)(PMe3)2L4] (22) were similarly prepared.
Reactions of [Pd(N3)(PR3)L] (16–20) with CN–Ar (R = C6H3-
2,6-i-Pr2 or C6H3-2,6-Me2). To a Schlenk flask containing
[Pd(N3)(PMe3)L3], 18 (0.267 g, 0.68 mmol) were added CH2Cl2
(6 ml)and2,6-diisopropylphenylisocyanide(0.153g,0.81 mmol)
in that order. The initial yellow solution slowly turned to a dark
green solution. After stirring for 2 h at room temperature, the
solvent was completely evaporated under vacuum, and then
the resulting residue was solidified with hexane. The solids
were filtered off and washed with hexanes to give crude solids.
Recrystallization from CH2Cl2–hexane gave yellow crystals of
[Pd(N3)(–CN–C6H3-2,6-i-Pr2)(PMe3)L3] (24, 0.290 g).
Reactions of 1 with CN–Ar (Ar = C6H3-2,6-Et2, C6H3-2,6-i-
Pr2 or C6H3-2,6-Me2). To a Schlenk flask containing [Pd(N3)L1]
(0.070 g, 0.24 mmol) were added CH2Cl2 (10 ml) and 2,6-
diethylphenyl isocyanide (0.045 g, 0.29 mmol) in that order.
The initial suspension immediately turned to an orange homo-
geneous solution. After stirring for 10 h at room temperature, the
solvent was removed completely, and the resulting residue was
washed with hexane to give an orange powder. Recrystallization
from CH2Cl2–ether gave yellow crystals of [Pd(NCN–C6H3-
2,6-Et2)L1] (2, 0.096 g). Complex 3, [Pd(NCN–C6H3-2,6-i-
Pr2)L1], was similarly prepared (0.064 g).
[Pd(N3)(–CN–C6H3-2,6-i-Pr2)(PMe3)L2] (23), [Pd(N3)-
(–CN–C6H3-2,6-i-Pr2)(PEt3)L3] (25), [Pd(N3)(–CN–C6H3-
2,6-i-Pr2)(PMe2Ph)L3] (26) and [Pd(N3)(–CN–C6H3-2,6-Me2)-
(PMe3)L3] (27) were prepared in a similar way.
To a Schlenk flask containing [Pd(N3)L1] (0.153 g, 0.40 mmol)
were added CH2Cl2–THF (6:9 ml) and 2,6-dimethylphenyl iso-
cyanide (0.106 g, 0.80 mmol) in that order. The mixture was
heated at 60 °C for 3 h, and the initial yellow solution gradu-
ally turned to a homogeneous orange solution. The solvent
was then removed completely, and the resulting residue was
solidified with ether to give crude solids. Recrystallization from
CH2Cl2–ether gave yellow crystals of [Pd(NCN–C6H3-2,6-
Me2)(CN–C6H3-2,6-Me2)L1] (4, 0.191 g).
To a Schlenk flask containing [Pd(N3)L3] (0.253 g, 0.64 mmol)
were added THF (7 ml) and 2,6-dimethylphenyl isocyanide
(0.177 g, 1.35 mmol) in that order. The mixture was heated at
60 °C for 2 h, and the initial yellow suspension gradually turned
to a homogeneous brown solution. After stirring, the solvent
was then removed completely, and the resulting residue was
solidified with ether to give crude solids. Recrystallization from
CH2Cl2–hexane gave yellow crystals of [Pd(NCN–C6H3-2,6-
Me2)(CN–C6H3-2,6-Me2)L3] (28, 0.221 g).
Reactions of 1 with CN–R (R = n-Bu or i-Pr). To a Schlenk
flask containing [Pd(N3)L1] (0.143 g, 0.38 mmol) were added
CH2Cl2 (13 ml) and n-butyl isocyanide (0.063 g, 0.76 mmol)
in that order. The initial suspension immediately turned to a
yellow homogeneous solution. After stirring for 3 h at room
temperature, the solvent was removed completely, and the
resulting residue was washed with hexane to give yellow solids.
Recrystallization from CH2Cl2–hexane gave pale green crystals
of [Pd(CN4-n-Bu)L1] (5, 0.115 g).
Reactions of aryl Pd(II) azido complexes with 2,6-dimethyl-
phenyl isocyanide. To a Schlenk flask containing [Pd(N3)-
Ph(PMe3)2] (0.203 g, 0.54 mmol) were added CH2Cl2 (2 ml)
and 2,6-dimethylphenyl isocyanide (0.205 g, 1.13 mmol) in that
order. The initial colorless solution immediately turned to a pale
yellow solution with evolution of nitrogen. After stirring for 3 h
at room temperature, the solvent was completely evaporated
under vacuum and then the resulting residue was solidified with
diethyl ether. The solids were filtered off and washed with diethyl
ether to give crude solids. Recrystallization from CH2Cl2–hexane
gave pale yellow crystals of [Pd(NCN–C6H3-2,6-Me2)-
(–CN–C6H3-2,6-Me2)Ph(PMe3)2] (29, 0.245 g).
Complex [Pd(CN4-i-Pr)L1] was similarly prepared (6,
0.087 g).
Reaction of 1 with R–NCS (R = allyl). To a Schlenk
flask containing [Pd(N3)L] (0.124 g, 0.33 mmol) were added
CH2Cl2–THF (6:9 ml) and allyl isothiocyanate (0.065 g,
0.66 mmol) in that order. The mixture was heated at 60 °C for
24 h, and the resulting precipitates were filtered off and washed
with ether and hexane to give yellow solids of [Pd(SCN4–
CH2CHCH2)L1] (7, 0.114 g).
To a Schlenk flask containing [Pd(N3)(PMe3)2L4] (0.260 g,
0.49 mmol) were added CH2Cl2 (4 ml) and 2,6-dimethylphenyl
isocyanide (0.129 g, 0.98 mmol) in that order. The initial color-
less solution slowly turned to a green solution with evolution of
nitrogen. After stirring for 5 h at room temperature, the solvent
was completely evaporated under vacuum, and then the result-
ing residue was solidified with diethyl ether. The solids were
filtered off and washed with diethyl ether to give crude solids.
Recrystallization from CH2Cl2–hexane gave yellow crystals of
[Pd(NCN–C6H3-2,6-Me2)(–CN–C6H3-2,6-Me2)(PMe3)2L4]
(30, 0.248 g).
Cleavage of [Pd(Cl)L]2 (L = 2-phenylpyridine (HL2), 2-(p-
tolyl)pyridine (HL3), or 2,6-diphenylpyridine (HL4) by tertiary
phosphines (PMe3, PEt3, PMe2Ph or P(n-Pr)3). To a Schlenk
flask containing [Pd(Cl)L2]2 (0.454 g, 0.77 mmol) were added
CH2Cl2 (20 ml) and a 1 M THF (or 0.159 ml) solution of PMe3
(1.54 mmol) in that order. The yellow suspension turned to
a yellow homogeneous solution. After stirring for 1 h, the
mixture was evaporated to give pale green solids, which were
recrystallized from CH2Cl2–hexane to give pale green crystals of
[Pd(Cl)(PMe3)L2] (8, 0.488 g, 86%).
Reactions of [Pd(N3)(PMe3)L3] toward R–NCS
(R = allyl, n-Bu, Et or i-Pr). To a Schlenk flask containing
[Pd(N3)(PMe3)L3] (0.253 g, 0.64 mmol) were added CH2Cl2
(5 ml) and allyl isothiocyanate (0.125 cm3, 1.29 mmol) in that
order. After stirring for 24 h at room temperature, the solvent
was completely evaporated under vacuum, then the resulting
oily residue was solidified with hexane. The solids were filtered
off and washed with hexane (3 cm3 × 2) to give crude solids.
Recrystallization from CH2Cl2–hexane gave yellow crystals of
[(l-SCN4–CH2CHCH2)PdL3]2 (31, 0.200 g).
The formation of complexes 8–15 was confirmed by NMR
(1H, 13C{1H} and 31P{1H}) spectroscopy, and those complexes
were used for further reactions with NaN3 to give the corres-
ponding azido complexes 16–22 (see below).
[Pd(N3)(PR3)L] (PR3 = PMe3, P(n-Pr)3, PEt3, PMe2Ph)
(16–20), [Pd(N3)(PEt3)2L3] (21) and [Pd(N3)(PMe3)2L4] (22). To
a Schlenk flask containing [Pd(Cl)L2] (0.369 g, 0.99 mmol) were
added CH2Cl2 (3 ml) and NaN3 solution (0.129 g, 1.98 mmol)
dissolved in H2O (8 ml) in that order. The initial yellow solution
turned to a pale yellow suspension. After stirring for 18 h at
room temperature, the solvent was completely evaporated to
give pale yellow solids, which were extracted with CH2Cl2 to
give pale yellow solids. Recrystallization from CH2Cl2–hexane
gave pale yellow crystals of [Pd(N3)(PMe3)L2] (16, 0.293 g).
[(l-SCN4-n-Bu)PdL3]2 (32), [(l-SCN4–Et)PdL3]2 (33) and [(l-
SCN4–i-Pr)PdL3]2 (34) were similarly prepared. Complexes 31
and 33 were also obtained from the reactions of [Pd(N3)(PEt3)L3]
and the corresponding isothiocyanates and were identified by IR
and NMR (1H and 13C{1H}) spectra.
Reaction of [Pd(N3)(PMe3)2L4] with ethyl isothiocyanate.
To a Schlenk flask containing [Pd(N3)(PMe3)2L4] (0.251 g,
D a l t o n T r a n s . , 2 0 0 4 , 3 6 9 9 – 3 7 0 8
3 7 0 7

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0.47 mmol) were added CH2Cl2 (5 ml) and ethyl isothiocyanate
(0.083 cm3, 0.94 mmol) in that order. The initial colorless solu-
tion gradually turned to a pale yellow solution. After stirring for
24 h at room temperature, the solvent was completely evaporated
under vacuum, and then the resulting residue was solidified with
hexane. The solids were filtered off and washed with hexane to
give crude solids. Recrystallization from CH2Cl2–hexane gave
pale yellow crystals of [Pd(SCN4–Et)(PMe3)2L4] (35, 0.208 g).
X-Ray structure determination
X-Ray data of complexes 3, 4, 7, 16, 18, 26, and 30 were
collected with a Siemens P4 diffractometer equipped with a
Mo X-ray tube. Intensity data were corrected for absorption
with W-scan data. On the other hand, X-ray data of 34
were collected with the use of a Bruker CCD SMART
diffractometer, in which case absorption corrections were not
made. All calculations were carried out with the SHELX-97
programs.45 All structures were solved by direct methods. All
non-hydrogen atoms were refined anisotropically, except some
in complex 26 in which case the carbon and chlorine atoms in
the cocrystallized dichloromethane were extremely disordered
and refined isotropically. All hydrogen atoms were generated in
ideal positions and refined in a riding model, except for those
in the disordered dichloromethane in complex 26, which could
not be located.
CCDC reference numbers 245892–245899.
See http://www.rsc.org/suppdata/dt/b4/b411432a/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
This work was supported by Grant R05-2004-000-10149-0 from
the Basic Research Program of the Korea Science & Engineering
Foundation.
29 A. Albinati, P. S. Pregosin and R. Rüedi, Helv. Chim. Acta, 1985, 68,
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3 7 0 8
D a l t o n T r a n s . , 2 0 0 4 , 3 6 9 9 – 3 7 0 8