Bis(isothiocyanato)bis(phosphine) complexes of group 10 metals: Reactivity toward organic isocyanides

Article abstract of DOI:10.1039/b508134c

Treatment of Ni(NCS)₂(PMe₂Ph)₂ with organic isocyanides CN-R gave five-coordinate isocyanide Ni(II) complexes, Ni(CN-R)(NCS)₂(PMe₂Ph)₂ (R = C ₆H₃-2,6-Me₂ (1

Full text of DOI:10.1039/b508134c

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F U L L P A P E R
Bis(isothiocyanato)bis(phosphine) complexes of group 10 metals:
reactivity toward organic isocyanides†
Xiaohong Chang,a Kyung-Eun Lee,a Sang Il Jeon,a Yong-Joo Kim,*a H.-K. Leeb and
Soon W. Leeb
a Department of Chemistry, Kangnung National University, Kangnung, 210-702, Korea
b Department of Chemistry, Sungkyunkwan University, Natural Science Campus, Suwon,
440-746, Korea. E-mail: yjkim@kangnung.ac.kr; Fax: Int + 82 + 33-647-1183;
Tel: Int + 82 + 33-640-2308
Received 9th June 2005, Accepted 15th August 2005
First published as an Advance Article on the web 8th September 2005
Treatment of Ni(NCS)2(PMe2Ph)2 with organic isocyanides CN–R gave five-coordinate isocyanide Ni(II) complexes,
Ni(CN–R)(NCS)2(PMe2Ph)2 (R = C6H3-2,6-Me2 (1), t-Bu (2)). Interestingly, the corresponding reaction of
Ni(NCS)2(P(n-Pr)3)2 with 2 equiv. of CN-t-Bu gave an unusual compound, which exists as an ion pair of the trigonal
bipyramidal cation [Ni(P(n-Pr)3)2(CN-t-Bu)3]2+ (3) and the dinuclear NCS-bridged anion [Ni(1,3–l-NCS)(NCS)3]2
2−
(4). In contrast, Pd(NCS)2(P(n-Pr)3)2 underwent substitution with 2 equiv. of CN-t-Bu to give the four-coordinate
mono(isocyanide) Pd(II) complex Pd(NCS)(SCN)(CN-t-Bu)(P(n-Pr)3) (5) via phosphine dissociation. Reactions
of M(NCS)2L2 (M = Pd, Pt; L = PMe3, PEt3, PMePh2, P(n-Pr)3) with two equiv. of CN–R (R = t-Bu, i-Pr,
C6H3-2,6-Me2) gave the corresponding bis(isocyanide) complexes [M(CN–R)2(PR3)2](SCN)2 (7–13), except for
Pd(NCS)2(PEt3)2 that reacted with CN–Rꢀ (Rꢀ = i-Pr, C6H3-2,6-Me2) and produced the mono(isocyanide) Pd(II)
complexes [Pd(CN–Rꢀ)(SCN)(PEt3)2](SCN) (14 and 15). Finally, treatment of M(NCS)2(PMe3)2 (M = Ni, Pd, Pt)
with sterically bulky isocyanide CN–C6H3-2,6-i-Pr2 gave various products, (16–18) depending on the identity of the
metal.
several possible products by adduct formation or substitution
Introduction
(Scheme 1). In addition, we tried to examine their reactivity
The isothiocyanato (or thiocyanato) ligand in late transition-
toward organic halides (RX), which might lead to the for-
metal complexes, which belongs to pseudo-halide ligands such
mation of (1) metal–NCSR complexes by electrophilic attack
as azide (N3) or isocyanate (NCO), has long been an interesting
of the halide at the NCS sulfur atom or (2) metal alkyls
subject due to its various coordination modes: S- or N-
by oxidative-addition of the alkyl halides. We herein report
coordination or bridging coordination through both S and N
the reactivity of bis(isothiocyanato)bis(phosphine) complexes
atoms.1–3 Most of the isothiocyanato (or thiocyanato) complexes
of group 10 metals toward organic isocyanides and alkyl
of late transition metals are typically prepared from metal
halides.
halides and alkali metal isothiocyanates such as KSCN and
NaSCN by metathesis in alcohol or aqueous media. Unfor-
tunately, these reactions frequently give unwanted linkage iso-
mers. For example, treating bis(dihalo)bis(phosphine or amine)
metal complexes (MX2(PR3)2 or MX2(NR3)2) with KSCN or
NaSCN gives various isomers such as M(NCS)2L2, M(SCN)2L2,
and M(NCS)(SCN)L2.4–16 Recently, we have reported the prepa-
ration of isothiocyanato complexes of group 10 metals from
bis(azido)bis(phosphine) complexes [M(N3)2(PR3)2] (M = Ni,
Pd, Pt) and (CH3)3Si–NCS by replacing the N3 ligands with the
Scheme 1
NCS group.17
Although many studies of the formation of late transition-
metal isothiocyanato complexes and their coordination be-
haviour including linkage isomerization have been reported,
studies of their reactivity toward electrophiles or nucleophiles
Results and discussion
are relatively rare.18,19 In particular, chemical reactivity to-
Reactions of bis(isothiocyanato) Ni(II) complexes with
isocyanides
ward small molecules such as isocyanides has not been
reported yet. Recently, we reported the formation of the
adduct [Ni(NCS)2(PMe3)2]·(CN-t-Bu)2 from the reaction of
the bis(isothiocyanato) nickel complex [Ni(NCS)2(PMe3)2] with
CN-t-Bu.17 Unfortunately, we failed to determine the structure
of this adduct due to its poor crystal quality. These results
led us to decide to systematically investigate the reactivity
of the isothiocyanato complexes of a nickel triad (group 10
metals) toward various organic isocyanides, which might form
In this work, all starting materials M(NCS)2L2 (M = Ni,
Pd, Pt; L = tertiary or chelating phosphines) were obtained
from the reaction of bis(azido) metal complexes M(N3)2L2
with Me3Si–NCS using our previous methods.17 In preparing
bis(isothiocyanato) complexes, compared with the conventional
metathesis using KSCN (or NaSCN), these methods appear
to have the advantage of suppressing the formation of linkage
isomers.
Treating the bis(isothiocyanato) Ni(II) complex Ni(NCS)2L2
with 2 equiv. of isocyanides (CN–C6H3-2,6-Me2 and CN-t-Bu)
† Electronic supplementary information (ESI) available: NMR data for
all complexes. See http://dx.doi.org/10.1039/b508134c
3 7 2 2
D a l t o n T r a n s . , 2 0 0 5 , 3 7 2 2 – 3 7 3 1
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 5
©

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gave the mono(isocyanide) Ni(II) complexes, Ni(NCS)2(CN–
R)L2, as shown in eqn (1)
square planar complexes, [Ni(R–NC)(NCS)(PMe2Ph](SCN), or
partial ionization in solution may occur.
The ORTEP drawing of compound 1 with the atom-
numbering scheme is shown in Fig. 1. Crystallographic data
and bonding parameters are given in Table 2. The coordination
sphere of Ni can be described as a trigonal bipyramid (TBP),
with two isothiocyanato ligands and one 2,6-dimethylphenyl
(1)
These reactions proceed smoothly at room temperature. Com-
plexes 1 and 2 were isolated as brown crystals and characterized
by spectroscopy and elemental analysis (see the supporting
information and Table 1). The molecular structure of 1 was
determined by X-ray diffraction. IR spectra of the complexes
show a sharp absorption band at 2135 (for 1) and 2186 cm−1
(for 2) due to the C≡N group of the isocyanide ligand and one
broad band at 2072 cm−1 (for 1) and two sharp bands at 2093 and
2078 cm−1 (for 2), whereas those of the starting material display
a single absorption band at 2091 cm−1 corresponding to the ter-
1
minal NCS ligands. 13C{ H} NMR spectra display a signal at ca.
130 ppm corresponding to the NCS carbon atom, but the CN–
R carbon atom signals are not observed, probably because of
their too weak intensities. A singlet in the 31P{ H} NMR spectra
1
of both complexes strongly supports the formation of a single
product Ni(NCS)2(CN–R)(PMe2Ph)2, indicating the absence of
linkage isomers at least in solution. Unexpectedly, proposed
neutral TBP Ni complexes (1, 2 and 18) indicate somewhat
molar conductance in methanol solution, which are less than
those data of the ionic Pd(II) or Pt(II) complexes as shown in
Table 1. Considering these conductivities, the formation of ionic
Fig. 1 ORTEP drawing66 of 1 showing the atom-labelling scheme
˚
and 50% probability thermal ellipsoids. Selected bond lengths (A)
and angles (◦): Ni1–C1 1.773(9), Ni1–N2 1.899(9), Ni1–N3 2.097(9),
Ni1–P1 2.2084(18), S1–C18 1.608(12), S2–C19 1.605(11), N1–C1
1.163(9), N1–C2 1.405(10), N2–C18 1.130(11), N3–C19 1.142(11);
C1–Ni1–N2 147.3(4), C1–Ni1–N3 114.6(4), N2–Ni1–N3 98.0(4),
C1–Ni1–P1 88.38(6), N2–Ni1–P1 92.23(7), N3–Ni1–P1 89.21(7),
C1–N1–C2 178.8(10), C18–N2–Ni1 172.8(9), C19–N3–Ni1 158.8(10).
Table 1 Colors, yields, analytical data and molar conductances
Analysesb
Complex
Color
Yield (%)
90
C (%)
H (%)
N (%)
Molar conductancec
1, Ni(NCS)2(CN–R)(PMe2Ph)2
(R = C6H3-2,6-Me2)
Brown
Brown
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
Yellow
White
55.99
(55.69)
52.04
(51.70)
45.72
(45.44)
41.59
(41.24)
40.31
(39.96)
57.61
(57.83)
37.34
(37.46)
62.54
(62.40)
42.93
(43.03
47.02
(47.46)
51.31
(51.05)
41.39
(40.95)
47.04
(46.82)
54.24
(54.50)
49.13
(48.73)
49.35
5.45
(5.37)
6.11
(5.85)
7.15
(7.12)
6.67
(6.49)
6.83
(6.71)
5.69
(5.62)
6.58
(6.29)
5.22
(5.01)
5.04
(5.00)
6.07
(5.97)
6.99
(6.76)
7.09
(7.06)
6.81
(6.66)
7.20
(6.99)
6.49
(6.25)
7.07
7.20
(7.22)
7.92
(7.86)
9.80
(9.76)
8.92
(9.02)
10.32
(10.36)
6.84
(7.10)
10.87
(10.92)
6.26
(6.33)
7.70
(7.72)
6.77
(6.92)
6.34
(6.27)
7.86
(7.96)
6.97
(7.12)
7.24
(7.48)
6.50
(6.69)
8.31
(8.17)
3.76
(3.87)
56
59
2, Ni(NCS)2(CN-t-Bu)(PMe2Ph)2
85
3·4 [Ni(P(n-Pr)3)2(CN-t-Bu)3]·
[Ni(1,3-l-NCS)(NCS)3]2
5, Pd(NCS)(SCN)(CN-t-Bu)(P(n-Pr)3)
30
106
4
95
7, [Pd(CN-t-Bu)2(PMe3)2](SCN)2
8, [Pd(CN-t-Bu)2(PMePh2)2](SCN)2
9, [Pd(CN-i-Pr)2(PMe3)2](SCN)2
94
90
88
80
68
113
85
10, [Pd(CN–R)2(PMePh2)2](SCN)2
(R = C6H3-2,6-Me2)
82
11, [Pt(CN–R)2(PMe3)2](SCN)2
(R = C6H3-2,6-Me2)
68
114
98
12, [Pt(CN–R)2(PEt3)2](SCN)2
(R = C6H3-2,6-Me2)
52
13, [Pt(CN–R)2(P(n-Pr)3)2](SCN)2
(R = C6H3-2,6-Me2)
Yellow
Yellow
Yellow
Orange
Yellow
Brown
White
89
95
14, [Pd(CN–R)(SCN)(PEt3)2](SCN)
(R = i-Pr)
90
85
15, [Pd(CN–R)(SCN)(PEt3)2](SCN)
(R = C6H3-2,6-Me2)
80
84
16, [Pd(CN–Ar)2(PMe3)2](SCN)2
(Ar = C6H3-2,6-i-Pr2)
79
84
17, [Pt(CN–Ar)2(PMe3)2](SCN)2
(Ar = C6H3-2,6-i-Pr2)
56
89
18, Ni(CN–Ar)(NCS)2(PMe3)2
(Ar = C6H3-2,6-i-Pr2)
91
36
(49.04)
36.13
(36.51)
(6.86)
6.91
(6.68)
19a, [Pt(depe)2](SCN)2
72
181
a depe = 1,2-bis(diethylphosphino)ethane. b Calculated values are given in parentheses. c In MeOH solution at 25 ◦C, 10−3 M. Units: X−1cm2 mol−1
.
D a l t o n T r a n s . , 2 0 0 5 , 3 7 2 2 – 3 7 3 1
3 7 2 3

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3 7 2 4
D a l t o n T r a n s . , 2 0 0 5 , 3 7 2 2 – 3 7 3 1

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isocyanide ligand at equatorial sites. All isothiocyanate atoms,
cyanide atoms, and the nickel atom lie on the crystallographic
mirror plane, which is coincident with the molecular plane.
Strangely, one isothiocyanato ligand (N3–C19–S2) is coordi-
nated to the Ni atom in a strongly bent manner with the Ni–N–C
bond angle of 158.8(10)◦. Two absorption bands for complex 2
may arise from this bent Ni–NCS and the other linear Ni–NCS
˚
linkage. The Ni–C (CNR) bond length (1.773(9) A) is close to
˚
that (1.787(3) A) of [Ni(triphos)(CN-xylyl)], but it is shorter than
20–29
˚
those (1.81–1.92 A) found for other isocyanide Ni complexes,
indicating a somewhat strong coordination of CN–R to the Ni
center.
Earlier works by Ibers and co-workers suggested the TBP
Ni(II) complex Ni(CN)2(PMe2Ph)3 to have two cyano ligands
at axial sites and three phosphine ligands at equatorial sites.30
However, as shown in Fig. 1, complex 1 has a distorted TBP
geometry with two phosphine ligands at axial sites and one
cyano and two isothiocyanato (NCS) ligands at equatorial sites.
This ligand arrangement in complex 1 probably arises from the
sterically demanding 2,6-dimethylphenyl isocyanide ligand that
prefers to occupy the sterically less hindered equatorial sites.
The formation of five-coordinate TBP Ni(II) complexes
containing an isocyanide group has been proposed by several
research groups.23,26,31 Although several isocyanide Ni com-
plexes have been reported, trigonal bipyramidal Ni-isocyanide
complexes have never been structurally characterized by X-ray
diffraction. Moreover, those Ni complexes have been frequently
proposed as intermediates or precursors in catalytic processes of
isocyanide polymerization and olefin polymerization.24,26,31
Interestingly, treating Ni(NCS)2[P(n-Pr)3]2 with two equiv. of
t-Bu isocyanide gave an unusual compound, which exists as an
ion pair of the trigonal bipyramidal cation [Ni(P(n-Pr)3)2(CN-
t-Bu)3]2+ (3) and the dinuclear NCS-bridged anion [Ni(1,3-l-
Fig. 2 ORTEP drawing66 of (3)·(4)·CH2Cl2: Fig. 2A, [Ni(P(n-Pr)3)2-
2−
(CN-t-Bu)3]2+
;
Fig. 2B, [Ni(1,3-l-NCS)(NCS)3]2
.
Selected bond
◦
˚
lengths (A) and angles ( ): Ni1–C1 1.868(10), Ni1–C11 1.870(9),
Ni1–C6 1.879(9), Ni1–P2 2.227(2), Ni1–P1 2.239(2) Ni2–N7 1.980(10),
Ni2–N6 1.984(11), Ni2–N5 1.997(9), Ni2–N4 2.025(10), N2–S1
2.414(3); C1–Ni1–C11 120.9(4), C1–Ni1–C6 119.1(4), C11–Ni1–C6
120.0(3), P2–Ni1–P1 179.7(11), N7–Ni2–N6 105.3(4), N7–Ni2–N5
93.9(4), N6–Ni2–N5 92.9(4), N7–Ni2–N4 93.8(5), N6–Ni2–N4 91.2(5),
N5–Ni2–N4 170.0(4), N7–Ni2–S1 122.1(3), N5–Ni2–S1 83.2(3).
2−
NCS)(NCS)3]2 (4) (eqn (2)). The formulation of this ion pair
was determined on the basis of conductivity, magnetic moment,
and NMR data of the compound. The conductivity value (106
KM) for the mixture at 25 ◦C in methanol is close to those values
(80–114 KM) for the ionic Pd(II) or Pt(II) complexes (Table 1)
and is definitely much higher than those of neutral TBP Ni(II)
complexes 1 and 2. This observation strongly indicates that the
mixture exists as an ion pair rather than two independent neutral
species. In addition, the effective magnetic moment (leff) of the
compound at room temperature is 2.71 lB, which is quite close
to the spin-only value (2.83 lB) for two unpaired electrons and
is consistent with a trigonal bipyramidal d8 Ni(II) complex.
Considering these conductivity and magnetic moment values
together, every nickel in this compound attains an 18-electron
configuration, regardless of different oxidation states (+2 in the
dicationic species 3 and +3 in the dianionic species 4).
(Fig. 2B) is a unique dinuclear Ni(III)-isothiocyanate species with
˚
no supporting ligands. The Ni–N bond lengths (1.98–2.03 A)
˚
are close to those (1.90–2.10 A) found for other dinuclear Ni(II)
complexes containing bridging NCS ligands,32–39 and therefore
bond lengths do not seem to be a clear criterion for the
assignment of the oxidation state of the Ni metals in the mixture
of 3 and 4. Most dinuclear Ni(II) complexes having bridging
NCS ligands contain octahedral or distorted octahedral Ni
moieties, but examples of dinuclear pseudo-TBP Ni complexes
with bridging NCS ligands are rare and unusual.
Numerous reports on the dinuclear or trinuclear Ni com-
plexes having chelating amines or 1,3-bridging NCS groups
have appeared.32–47 In addition, the molecular structure of the
dinuclear l-NCS-bridged Pt-phosphine (P(n-Pr)3) complex was
previously reported.48 To our best knowledge, complex 4 is the
first example of a homoleptic and dinuclear Ni–NCS complex
without any supporting ligands such as phosphines or amines.
(2)
The IR spectrum of the compound shows a sharp band at
2168 cm−1 due to the C≡N group of CN–R and one strong band
at 2074 cm−1 due to the terminal and bridging NCS groups. The
molecular structure of the compound clearly demonstrated the
existence of two different molecules. Fig. 2A shows a PLUTO
drawing of compound 3 that has a typical TBP structure, and
Fig. 2B shows an ORTEP drawing of compound 4 that has a
dinuclear structure with pseudo-TBP nickel(III) centers bridged
by the NCS ligands. The reason why we presented the PLUTO
drawing for compound 3 is the extreme difficultly in labelling
carbon atoms in the t-Bu groups. As shown in Fig. 2A, three
isocyanides (CN-t-Bu) form an equatorial plane of the TBP
geometry of a dicationic species 3. The Ni–C bond lengths
Reactions of bis(isothiocyanato) Pd(II) and Pt(II) complexes with
isocyanides
The bis(isothiocyanato)bis(phosphine) complex Pd(NCS)2(P(n-
Pr)3)2 reacted with 2 equiv. of CN-t-Bu to give the 4-coordinate
mono(isocyanide) Pd(II) complex Pd(NCS)(SCN)(CN-t-Bu)-
(P(n-Pr)3) (5) by the replacement of phosphine with CN-t-Bu
(eqn (3).
˚
(1.868(10)–1.879(9) A) of 3 are within the range of values
found for other isocyanide Ni(II) complexes.23–29 The dianion 4
(3)
D a l t o n T r a n s . , 2 0 0 5 , 3 7 2 2 – 3 7 3 1
3 7 2 5

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The IR spectrum of 5 shows a strong band at 2218 cm−1 due
to the CN–R and two bands at 2096 and 2064 cm−1 assignable
1
to the two terminal NCS or SCN groups. The 1H, 13C{ H}, and
1
31P{ H} NMR spectra of the complex are consistent with the
proposed formulation. The molecular structure of complex 5
gives concrete evidence for the formation of an isocyanide Pd(II)
complex (Fig. 3). Fig. 3 clearly shows two distinct coordination
modes (or a linkage isomerism) of the two NCS ligands, a N-
bound NCS trans to the isocyanide and a S-bound NCS trans to
the phosphine. On the basis of the hard-soft acid–base concept,
anti-symbiosis appears to work in complex 5 in which the hard
atom (the NCS nitrogen) prefers to bind to the metal trans to
the hard atom (the isocyanide carbon) and the soft atom (the
NCS sulfur) trans to the soft atom (the phosphine phosphorus).
Fig. 4 ORTEP drawing66 of Pd(NCS)2L2·Pd(SCN)2L2 (L = P(n-Pr)3).
◦
˚
Selected bond lengths (A) and angles ( ): Pd1–N1 1.983(3), S1–C1
1.612(4), N1–C1 1.130(5), Pd2–S2 2.3371(10), S2–C11 1.647(6), N2–C11
1.148(6); C1–N1–Pd1 176.5(3), N1–C1–S1 179.8(4), S2–Pd2–P2
92.93(4), C11–S2–Pd2 99.80(18), N2–C11–S2 176.7(6).
characterized by spectroscopy (IR, 1H-,◦13C{ H}-, and 31P{ H}-
NMR). The conductivity (98 KM at 25 C in MeOH) supports
complex 6 existing as an ionic compound in solution rather
than the neutral adduct [Pd(NCS)2(P(n-Pr)3)2]·2(CN-i-Pr). The
IR spectrum of 6 shows a strong band at 2224 cm−1 due to
the CN–R and two bands at 2096 and 2052 cm−1 due to the
NCS or SCN groups. However, several recrystallizations of 6
in CH2Cl2/ether/hexane resulted in the loss of the isocyanide
ligand (similar isocyanide dissociation was also observed, as
shown in eqn (7)) and caused it to go back to the starting
material.
1
1
Fig. 3 ORTEP drawing66 of 5. Selected bond lengths (A) and angles
˚
To further examine the effects of supporting ligands (phos-
phines) and attacking isocyanides, we have carried out the
reactions of Pd(NCS)2L2 (L = PMe3, PMePh2) with 2 equiv.
of CN–R (R = t-Bu, i-Pr, C6H3-2,6-Me2) as shown in eqn (4).
(◦): Pd1–C12 1.917(6), Pd1–N1 1.995(6), Pd1–P1 2.2860(12), Pd1–S2
2.3824(14), S1–C10 1.607(6), S2–C11 1.656(8), N1–C10 1.138(9),
N2–C11 1.148(9), N3–C12 1.143(9); C12–Pd1–N1 178.8(3), P1–Pd1–S2
175.28(6), C11–S2–Pd1 107.7(2), C10–N1–Pd1 167.7(6), N1–C10–S1
179.2(6), N2–C11–S2 175.7(6), N3–C12–Pd1 178.0(5).
The above result (eqn (3)) is quite different from the case for
the nickel analogue (Ni(NCS)2(P(n-Pr)3)2) (eqn (2)), which reacts
with CN-t-Bu to give a TBP Ni(II) complex and a homoleptic
isothiocyanato Ni(III) complex. In order to gain more insight
into the linkage isomerization, we have characterized the
starting material. The H and 31P{ H} NMR spectra of the
starting material Pd(NCS)2(P(n-Pr)3)2 revealed the presence of
three linkage isomers of Pd(NCS)2L2, Pd(NCS)(SCN)L2, and
Pd(SCN)2L2 (in the ratio of 0.51 : 1.00 : 0.28 based on the
1
1
(4)
These reactions gave a series of the ionic bis(isocyanide) Pd(II)
complexes [Pd(CN–R)2(PR3)2](SCN)2 (7–10), in which the SCN
groups lie outside the coordination sphere as counterions. The
products were obtained as yellow solids in 80–94% yields. The
IR spectra of the complexes display a strong band at 2190–
2229 cm−1 due to the isocyanide ligand and another strong
band at 2047–2070 cm−1 due to the SCN ions. The integration
1
integration ratio by 31P{ H} NMR). This phenomenon agrees
with that found for ((PhCH2)3P)2Pd(NCS)2 prepared from a
Pd(II) dichloride complex and KSCN.5 By repeated recrystal-
lizations of the starting material, X-ray quality crystals could be
obtained. Interestingly, its molecular structure clearly exhibited
two linkage isomers (Fig. 4): Pd(NCS)2L2 and Pd(SCN)2L2
(L = P(n-Pr)3). The two independent Pd atoms in these isomers
both lie on inversion centers. It should be mentioned that the
corresponding Ni complex Ni(NCS)2(P(n-Pr)3)2 does not show
linkage isomerism both in the solid state and in solution.
Many studies of the linkage isomerization of thiocyanato
phosphine Pd(II) complexes have been reported, which has been
attributed to various factors such as electronic or steric factors
of ligands and medium effects.4–10 Particularly, Balch and co-
workers showed the linkage isomerization for thiocyanato Pd(II)
complexes having chelating phosphine ligands by spectroscopy
and X-ray diffraction.4 We believe that the formation of 5
via phosphine dissociation is probably a direct consequence
of the presence of the linkage isomers in the starting material
Pd(NCS)2(P(n-Pr)3)2.
1
ratios in the H NMR spectra of the complexes are consistent
with the proposed structure. A singlet in the 31P{ H} NMR
1
spectra of the complexes suggests a symmetric orientation of the
ligands. The molecular structure of 8 clearly demonstrates the
formation of the ionic bis(isocyanide) Pd(II) complex [Pd(CN-t-
Bu)2(PMePh2)2](SCN)2, which shows a square planar geometry
with trans isocyanides and trans phopshines, together with
two SCN− counterions (Fig. 5). Many isocyanide Pd(I) or
Pd(II) complexes with halides (Cl, Br) or pseudo halides (PF6,
SbF6, B(C6H5)4, ClO4, OAc, OTf) have been reported.49–60
Some of them are unstable in the solid state or in solution at
room temperature and often lose the isocyanide(s). Our Pd(II)
complexes 7–10 (in eqn (4)) exhibit a relatively high stability
both in the solid state and in solution. For instance, several
repeated recrystallizations do not bring about the loss of the
isocyanide ligand, indicating a relatively strong coordination of
the isocyanide to the metal center.
When Pd(NCS)2(P(n-Pr)3)2 was treated with 2 equiv. of
CN-i-Pr at room temperature, the ionic bis(isocyanide) Pd(II)
complex {Pd[P(n-Pr)3]2(CN-i-Pr)2}(NCS)2 (6) was obtained and
3 7 2 6
D a l t o n T r a n s . , 2 0 0 5 , 3 7 2 2 – 3 7 3 1

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Fig. 6 ORTEP drawing 66 of 11. Selected bond lengths (A) and angles
˚
(◦): Pt1–C1 1.899(15), Pt1–C10 1.997(12), Pt1–P1 2.345(3), Pt1–P2
2.316(3), S1–C25 1.56(2), S2–C26 1.70(3), N3–C25 1.14(3), N4–C26
1.06(3); C1–Pt1–C10 177.1(5), C1–Pt1–P1 89.8(3), C10–Pt1–P1 88.2(3),
C1–Pt1–P2 90.5(3), C10–Pt1–P2 91.4(3), P1–Pt1–P2 176.21(11).
66
˚
Fig. 5 ORTEP drawing of 8. Selected bond lengths (A) and angles
(◦): Pd1–C27 1.987(5), Pd1–C32 1.987(5), Pd1–P1 2.3596(14), Pd1–P2
2.3590(14), S1–C37 1.544(12), S2–C38 1.657(9), N3–C37 1.063(18),
N4–C38 1.154(10); C27–Pd1–C32 169.7(2), C27–Pd1–P1 86.67(14),
C32–Pd1–P1 93.46(15), C27–Pd1–P2 90.69(14), C32–Pd1–P2 87.27(15),
P1–Pd1–P2 169.12(5).
Consistent with our expectation, treatments of
Pt(NCS)2(PR3)2 (R = Me, Et, n-Pr) with 2 equiv. of CN–
Ar (Ar = C6H3-2,6-Me2) also gave the bis(isocyanide) Pt(II)
complexes [Pt(CN–Ar)2(PR3)2](SCN)2 (11–13) in 52–89% yields
(eqn (5)).
(5)
66
˚
of 12. Selected bond lengths (A) and
Fig. 7 ORTEP drawing
The IR spectra of the complexes 11–13 show one C≡N
stretching band at 2189–2194 cm−1 and one SCN stretching
band at 2048–2052 cm−1. Molecular structures of the cationic
parts of 11 and 12 clearly show a square planar geometry, with
trans phosphines and trans isocyanides as well as two SCN−
counterions (Figs. 6 and 7). This type of coordination was
previously observed for the other Pt(II) complexes of [Pt(CN–
R)2L2]X2 (L = PR3; X = BF4, PF6, Cl).61–63 In contrast, the cor-
responding reactions of Pd(NCS)2(PEt3)2 with 2 equiv. of CN–R
produced totally different products, the ionic mono(isocyanide)
Pd(II) complexes [Pd(CN–R)(SCN)(PEt3)2](SCN) (R = i-Pr
(14), C6H3-2,6-Me2 (15)) (eqn (6)).
angles (◦): Pt1–C1 1.927(7), Pt1–C10 1.955(7), Pt1–P1 2.3468(17),
Pt1–P2 2.3575(18), S1–C31 1.646(12), N3–C31 1.130(13), S2–C32
1.677(18), N4–C32 0.880(19); C1–Pt1–C10 173.9(3), C1–Pt1–P1 90.4(2),
C10–Pt1–P1 88.4(2), C1–Pt1–P2 88.4(2), C10–Pt1–P2 91.59(19),
P1–Pt1–P2 167.99(7).
As shown in eqns (4)–(6), reactions of M(NCS)2(PR3)2 (M =
Pd or Pt) with 2 equiv. of isocyanide led to the formation of
mono(isocyanide) or bis(isocyanide) metal complexes, depend-
ing on the supporting ligands, isocyanides, and metal center.
These results prompted us to perform a comparative study of
bis(isothiocyanato)bis(trimethylphosphine) complexes of group
10 metals M(NCS)2(PMe3)2, which have the same ligand set,
toward the identical isocyanide CN–Ar (Ar = C6H3-2,6-i-Pr2)
(eqns (7)–(9)).
Pd(NCS)2(PMe3)2 reacted with 2 equiv. of 2,6-diisopropyl
phenyl isocyanide CN–Ar (Ar = C6H3-2,6-i-Pr2) gave the
bis(isocyanide) Pd(II) complex [Pd(CN–Ar)2(PMe3)2](SCN)2
(16), which was isolated as an orange solid and characterized
by spectroscopy and elemental analysis (eqn (7)). However,
repeated crystallizations of 16 from CH2Cl2/hexane caused the
isocyanide dissociation and it went back to the starting material,
suggesting that the steric congestion is due to the 2,6-diisopropyl
groups in the CN–Ar ligand.
(6)
Complexes 14 and 15 were isolated as yellow solids and
characterized by spectroscopy (IR, NMR), analytical data and
conductivities. IR spectra of the complexes display one C≡N
stretching band at 2249 (for 14) or 2196 (for 15) cm−1 and two
strong SCN bands at 2114 and 2057 (for 14) cm−1 or 2106
and 2056 (for 15) cm−1. The IR absorption bands of the S-
bound and N-bound NCS ligands in Pd complexes are known
to appear at 2130–2100 cm−1 and below 2100 cm−1, respectively.4
Although the poor crystal quality of the products prevented us
from their structural characterization by X-ray diffraction, the
conductivity data as shown in Table 1 support the formation of
ionic four-coordinate square planar complexes.
(7)
D a l t o n T r a n s . , 2 0 0 5 , 3 7 2 2 – 3 7 3 1
3 7 2 7

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(19) in 91% yield as shown in eqn (11). Three absorption bands
due to the terminal NCS or SCN groups appear at 2125, 2098,
and 2056 cm−1 in the starting material Pt(NCS)2(depe), whereas
only a single band appears at 2052 cm−1 in the product (complex
19). A single signal with satellites (JPtP = 2124 Hz) in the 31P{ H}
1
NMR of 19 strongly supports its high symmetry. The molecular
structure of 19 (Fig. 8) clearly illustrates a symmetric square
planar geometry, with the Pt atom on the crystallographic
inversion center. The asymmetric unit of 19 consists of two
halves of the formula unit with the other two halves generated by
crystallographic inversion. The NCS− ions are not coordinated
to the Pt metal and act as counterions.
(8)
(9)
We also examined the corresponding reactions of the Pt
and Ni analogues M(NCS)2(PMe3)2 (M = Ni, Pt) with the
isocyanide. Treating Pt(NCS)2(PMe3)2 with 2 equiv. of 2,6-
diisopropyl phenyl isocyanide produced the bis(isocyanide)
Pt(II) complex [Pt(CN–Ar)2(PMe3)2](SCN)2 (17) as shown in eqn
(8), in which the isocyanide dissociation did not occur. Isolated
complexes 16 and 17 show two strong absorption bands at 2196
(C≡N) and 2055 (SCN) cm−1 (for 16) and at 2195 (C≡N) and
2059 (SCN) cm−1 (for 17), respectively. These IR data are well
consistent with those for the bis(isocyanide) Pd(II) and Pt(II)
complexes shown in eqns (4) and (5).
(10)
(11)
In contrast, the corresponding reaction of Ni(NCS)2(PMe3)2
with 2 equiv. of 2,6-diisopropyl phenyl isocyanide resulted in the
formation of the mono(isocyanide) 5-coordinate Ni(II) complex
[Ni(CN–Ar)(NCS)2(PMe3)2] (18) (eqn (9)). Complex 18 was
obtained as a brown solid in 91% yield. The IR spectrum of
18 also displays a stretching band at 2163 cm−1 due to C≡N
and two strong bands at 2102 and 2047 cm−1 due to NCS of the
complex and suggests a distorted TBP geometry. In addition,
1
1
other spectral (1H, 31P{ H}, and 13C{ H} NMR) and analytical
data strongly support the coordination of one isocyanide to
the Ni metal. The present data indicate that the reactivity of
group 10 metal bis(isothiocyanato) complexes M(NCS)2(PMe3)2
toward CN–C6H3-2,6-i-Pr2 depends primarily on the identity of
the metal. However, we cannot underestimate the role of the
steric bulk of the isocyanide due to the isopropyl groups on the
phenyl ring.
Properties of the group 10 bis(isothiocyanato) complexes with a
chelating phosphine
We carried out reactions of the metal isothiocyanates with a
chelating phosphine M(NCS)2L2 (M = Pd, Pt; L–L (depe) =
Et2PCH2CH2PEt2) with CN–R, but the isocyanide coordination
or any other adduct formation was not observed. Thus, we
further examined the reactivity of these bis(isothiocyanato) com-
Fig. 8 ORTEP drawing66 of 19. Selected bond lengths (A) and angles
˚
=
plexes toward organic halides such as allyl halides (CH2 CH–
(◦): Pt1–P2 2.3370(18), Pt1–P1 2.3446(17), Pt2–P3 2.3342(19), Pt2–P4
2.3475(18); P2#1–Pt1–P2 180.0, P2–Pt1–P1#1 84.41(6), P2–Pt1–P1
95.59(6), P1#1–Pt1–P1 180.0, P3–Pt2–P4 84.09(7). Symmetry trans-
formations used to generate equivalent atoms: #1 = −x, −y + 1,
−z + 1.
CH2X; X = Br, I) and MeI.
Treatments of Pd(NCS)2(P(n-Pr)3)2 and Ni(NCS)2(PMe2Ph)2
with excess MeI and allyl iodide do not give any oxidative–
addition products or metal-NCSR complexes as shown in
Scheme 1. However, reactions of Pt(NCS)2(depe) with excess
allyl halides slowly proceeded to give the corresponding metal
=
dihalo complexes as well as allyl isothiocyanate (CH2 CH–
In summary, we have examined the reactivity bis(isothio-
cyanato)bis(phosphine) complexes of group 10 metals toward
organic isocyanides. These complexes did not undergo cycload-
dition with the isocyanides to give heterocyclic compounds. In-
stead, various unusual compounds were formed, depending on
the isocyanide or supporting ligands. For Pd(II) and Pt(II) isoth-
iocyanates, the mono(isocyanide) or bis(isocyanide) M(II) com-
plexes, [M(CNR)(SCN)(NCS)L], [M(CNR)(SCN)L2](SCN),
and [M(CNR)2L2](SCN)2, were formed. Crystallographic data
of several complexes clearly revealed the square planar ge-
ometry of the cationic parts of these complexes and the
existence of SCN− counterions. In particular, reactions of
bis(isothiocyanato)Ni(II) complexes with organic isocyanides
CH2–NCS), as shown in eqn (10), but other possible com-
pounds such as oxidative–addition products were not observed.
Interestingly, the GC–MS spectrum of the isolated allyl isoth-
iocyanate revealed it to be a mixture of two linkage isomers,
=
allyl isothiocyanate (CH2 CHCH2–NCS) and allyl thiocyanate
(CH2 CHCH2–SCN). This linkage isomerism is believed to
=
arise from the linkage isomerism in the starting materials. Inte-
gration ratios in 31P{ H} NMR spectra gave a strong clue to the
1
presence of three linkage isomers, Pt(NCS)2L2, Pt(SCN)2L2, and
Pt(NCS)(SCN)L2, in the ratio of 1.00 : 0.77 : 0.84. Furthermore,
the reaction of Pt(NCS)2(depe) with depe in the mole ratio of 1 : 1
at room temperature slowly proceeded to give [Pt(depe)2](SCN)2
3 7 2 8
D a l t o n T r a n s . , 2 0 0 5 , 3 7 2 2 – 3 7 3 1

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produced trigonal bipyramidal mono(isocyanide) Ni(II) com-
plexes, which may be presumed to be a catalytic intermediate or
precursor proposed in Ni-catalyzed isocyanide polymerization
and olefin polymerization.
reaction mixture for 18 h, the mixture was evaporated to give a
crude solid, which was crystallized from CH2Cl2/hexane to give
a yellow solid, [Pd(CN-t-Bu)2(PMe3)2](SCN)2 (7, 0.384 g).
Complexes 8–10 were prepared analogously.
Experimental
Reactions of Pt(NCS)2(PR3)2 (PR3 = PMe3, PEt3, P(n-Pr)3)
with CN–C6H3-2,6-Me2
All manipulations of air-sensitive compounds were performed
under N2 or Ar by Schlenk line techniques. Solvents were
distilled from Na-benzophenone. The analytical laboratories
at Basic Science Institute of Korea and Kangnung National
University carried out elemental analyses. IR spectra were
recorded on a Perkin Elmer BX spectrophotometer. NMR
To a CH2Cl2 (5 cm3) suspension containing Pt(NCS)2(PMe3)2
(0.199 g, 0.43 mmol) was added CN–C6H3-2,6-Me2 (0.113 g,
0.86 mmol). The initial suspension instantly turned to a pale
yellow solution. After stirring the reaction mixture for 18 h, the
mixture was evaporated to give a crude solid. Recrystallization
from CH2Cl2/diethyl ether gave yellow crystals of [Pt(CN–C6H3-
2,6-Me2)2(PMe3)2](SCN)2 (11, 0.212 g)
1
1
(1H, 13C{ H} and 31P{ H}) spectra were obtained on a JEOL
Lamda 300 MHz spectrometer. Chemical shifts were referenced
to internal Me4Si and to external 85% H3PO4. Conductivity
data were obtained on a TPS 2100 conductivity bridge at
25 ◦C. Magnetic susceptibilities were measured with a Johnson
Matthey MK–I magnetic balance, and magnetic moments were
calculated from the equation leff = 2.828(vMT)1/2. M(NCS)2L2
(M = Ni, Pd, Pt; L = PMe3, PEt3, PMe2Ph, PMePh2, P(n-Pr)3,
and depe = Et2PCH2CH2PEt2) were prepared by the literature
method.17 2,6-Diisopropylphenyl isocyanide was prepared as
described in the literature64 and CN–C6H3-2,6-Me2, CN-t-Bu
and CN-i-Pr were purchased.
Complexes 12 and 13 were prepared analogously.
Reactions of Pd(NCS)2(PEt3)2 with CN-i-Pr and CN–Ar (Ar =
C6H3-2,6-Me2)
To a CH2Cl2 (8 cm3) solution containing Pd(NCS)2(PEt3)2,
(0.249 g, 0.54 mmol) was added CN-i-Pr (0.099 cm3, 1.09 mmol)
at room temperature. After stirring the reaction mixture for
18 h, the solvent was removed, and the resulting residues were
solidified with diethyl ether to give a pale yellow solid, [Pd(CN–
R)(SCN)(PEt3)2](SCN) (R = i-Pr (14, 0.259 g).
Reactions of Ni(NCS)2(PMe2Ph)2 with isocyanides
(CN–C6H3-2,6-Me2 and CN-t-Bu)
Complex 15 was prepared analogously.
To a Schlenk flask containing Ni(NCS)2(PMe2Ph)2 (0.362 g,
0.80 mmol) were added sequentially CH2Cl2 (5 cm3) and 2,6-
dimethylphenyl isocyanide (0.210 g, 1.60 mmol). After stirring
the reaction mixture at room temperature for 18 h, the sol-
vent was removed completely, and the resulting residues were
solidified with diethyl ether and CH2Cl2 (3 : 1) to give a crys-
talline brown solid. Recrystallization from CH2Cl2/ether gave
dark red crystals of Ni(NCS)2(CN–C6H3-2,6-Me2)(PMe2Ph)2 (1,
0.422 g)
Reactions of M(NCS)2(PMe3)2 (M = Pd, Pt, Ni) with
CN–C6H3-2,6-i-Pr2
To a CH2Cl2 (10 cm3) suspension containing Pd(NCS)2(PMe3)2
(0.241 g, 0.64 mmol) was added CN–C6H3-2,6-i-Pr2 (0.268 cm3,
1.41 mmol). The initial suspension instantly turned to an orange
solution. After stirring the reaction mixture for 18 h, the
mixture was evaporated to give a crude solid, which was washed
with hexane. Recrystallization from CH2Cl2/hexane gave a
yellow solid, [Pd(CN–Ar)2(PMe3)2](SCN)2 (16, 0.381 g). Several
crystallizations from CH2Cl2/hexane caused the formation of
Pd(NCS)2(PMe3)2.
Complex 2 was prepared analogously.
Reaction of Ni(NCS)2(P(n-Pr)3)2 with CN-t-Bu
Complexes 17 and 18 were prepared analogously.
To a Schlenk flask containing Ni(NCS)2(P(n-Pr)3)2 (0.294 g,
0.59 mmol) were added CH2Cl2 (4 cm3) and CN-t-Bu (0.134 cm3,
1.18 mmol). After stirring the reaction mixture at room tempera-
ture for 18 h, the solvent was removed, and the resulting residues
were solidified with diethyl ether to give a yellow solid, [Ni(CN-
t-Bu)2(P(n-Pr)3)2](SCN)2(0.260 g). Repeated crystallization of
[Ni(CN-t-Bu)2(P(n-Pr)3)2](SCN)2 from (diethyl ether)/CH2Cl2
gave a greenish yellow solid, [Ni(P(n-Pr)3)2(CN-t-Bu)3]2+[Ni(1,3-
Reactions of Pt(NCS)2(depe) with allyl bromide, allyl iodide,
and depe
To a CH2Cl2 (3 cm3) solution containing Pt(NCS)2(depe)
(0.347 g, 0.67 mmol) was added allyl bromide (0.811 g,
6.70 mmol). After stirring the reaction mixture for 18 h, the
solvent was evaporated, and the resulting residues were solidified
with diethyl ether to give a white solid, PtBr2(depe). The solid
was filtered, washed with diethyl ether and dried under vacuum
(0.352 g, 94%). The collected filtrate was analyzed by GC and
GC–MS. Reaction of Pt(NCS)2(depe) with allyl iodide was
analogously carried out.
2−
l-NCS)(NCS)3]2 (0.181 g).
Reactions of Pd(NCS)2(P(n-Pr)3)2 with CN-t-Bu and CN-i-Pr
To a Schlenk flask containing Pd(NCS)2(P(n-Pr)3)2 (0.201 g,
0.37 mmol) were added CH2Cl2 (2 cm3) and CN-t-Bu (0.088 cm3,
0.78 mmol). The initial pale yellow solution slowly turned
to a yellow solution. After stirring the reaction mixture for
18 h, the solvent was removed, and the resulting residues were
solidified with diethyl ether. Recrystallization from diethyl ether
gave yellow crystals of Pd(NCS)(SCN)(CN-t-Bu)(P(n-Pr)3) (5,
0.304 g).
To a CH2Cl2 (3 cm3) suspension containing Pt(NCS)2(depe)
(0.169 g, 0.33 mmol) was added depe (0.074 g, 0.36 mmol). The
initial suspension instantly turned to a colorless solution. After
stirring the reaction mixture for 5 h, the mixture was evaporated
to give a white solid, which was crystallized from CH2Cl2/hexane
to give white crystals of [Pt(depe)2](SCN)2 (19, 0.170 g).
Complex 6, {Pd(CN-i-Pr)2[P(n-Pr)3]2}(SCN)2 was similarly
prepared according to the procedure described above.
X-Ray structure determination
All X-ray data were collected with a Siemens P4 diffractometer
equipped with a Mo X-ray tube. Intensity data were empirically
corrected for absorption with w-scan data. All calculations were
carried out with the use of SHELXTL programs.65 All structures
were solved by direct methods. Unless otherwise stated, all non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were generated in ideal positions and refined in a riding mode.
Reactions of Pd(NCS)2(PR3)2 (PR3 = PMe3, PPh2Me) with
CN-t-Bu, CN-i-Pr and CN–C6H3-2,6-Me2
To a CH2Cl2 (20 cm3) suspension containing Pd(NCS)2(PMe3)2
(0.284 g, 0.76 mmol) was added CN-t-Bu (0.180 cm3,
1.59 mmol). The initial suspension instantly turned to a yellow
solution, and then precipitation occurred. After stirring the
D a l t o n T r a n s . , 2 0 0 5 , 3 7 2 2 – 3 7 3 1
3 7 2 9

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For compound 12, six carbon atoms (C25–C30) in one phos-
phine ligand showed extreme structural disorder and therefore
were refined isotropically. For the same reason, the atoms (N2,
C22, S2) in one of the NCS counterions for compound 19
were also refined isotropically. Details on crystal data, intensity
collection, and refinement details are given in Table 2.
CCDC reference numbers 275741–275748.
29 D. Wilhekm, E. Wenschuh, U. Baumeister and H. Hartung, Z. Anorg.
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Acknowledgements
This work was supported by Grant R05–2004–000–10149–0
from the Korea Research Foundation. We thank Professor Shin-
Geol Kang for obtaining the magnetic moments.
˙
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Sawka-Dobrowolska, Inorg. Chem., 2002, 41, 1771.
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