Reactions of palladium(II) and platinum(II) bis(azido) complexes with isocyanides: Synthesis and structural characterization of palladium(II) and platinum(II) complexes containing carbodiimido (or bis(carbodiimido)) and bis(tetrazolato) ligands

Article abstract of DOI:10.1039/b103916b

Bis(azido)palladium(II) complexes Pd(N₃)₂L₂ (L = PMe₃, PMe₂Ph, PEt₃, PMePh₂) reacted with two equivalents of 2,6-dimethylphenyl isocyanide to give the Pd(II) complexes, trans-Pd[CN₄(R)](N=C=N-R)L₂ (R = 2,6-Me₂C₆H₃, L = PMe₃, 1; PMe₂Ph, 2; PEt₃, 3; PMePh₂, 4) containing a carbodiimido ligand and a C-coordinated 5-membered tetrazolato ligand. X-Ray structures of 1 and 2 identified the formation of palladium(II) complexes with a carbodiimido group, in which a nitrogen of the linear N=C=N moiety is bonded to the metal center, and with a tetrazolato ring formed via 1,3-dipolar cycloaddition of the isocyanide to the coordinated azido bond. Heating the isolated complexes 1 and 3 at 60 °C for 5 h converted them into the bis(carbodiimido)palladium(n) complexes, trans-Pd[N=C=N R]₂L₂ (R = 2,6-Me₂C₆H₃, L = PMe₃, 5; PEt₃, 6). The reactions of 2,6-dimethylphenyl isocyanide with Pd(N₃)₂L₂ (L = PMe₃, PEt₃) also gave the same complexes directly. Reaction of Pd(N₃)₂(dppe) with 2,6-dimethylphenyl isocyanide also caused the formation of the bis(carbodiimido) complex Pd[N=C=N-2,6-Me₂C₆H₃]₂(dppe), 7 in 75% yield. However, reactions of M(N₃)₂(PMe₃)₂ (M = Pd or Pt) with tert-butyl isocyanide resulted in the formation of bis(tetrazolato) compounds, M[CN₄(R)]₂(PMe₃)₂ (R = tert-butyl, M = Pd, 8; Pt, 9) by the cycloaddition of isocyanide to the coordinated azido bond. The same reactions with other isocyanides such as cyclohexyl and n-butyl isocyanides afforded bis(tetrazolato) complexes, trans-M[CN₄(R)]₂L₂ (M = Pd, R = C₆H₁₁, L = PMe₃: 10_anti,syn; M = Pd, R = n-Bu, L = PMe₃: 11_anti,syn; M = Pt, R = n-Bu, L = PMe₃: 12_anti,syn; M = Pt, R = n-Bu, L = PEt₃: 13_anti,syn), which show a mixture of syn and anti isomers in solution. Molecular structures of 11_anti, 12_anti, and 13_syn have been determined by X-ray crystallography.

Full text of DOI:10.1039/b103916b

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Reactions of palladium(II) and platinum(II) bis(azido) complexes
with isocyanides: synthesis and structural characterization of
palladium(II) and platinum(II) complexes containing carbodiimido
(or bis(carbodiimido)) and bis(tetrazolato) ligands
Yong-Joo Kim,*a Yong-Su Kwak,a Young-Seon Jooa and Soon-W. Leeb
a Department of Chemistry, Kangnung National University, Kangnung 210-702, Korea.
E-mail: yjkim@knusun-kangnung.ac.kr
b Department of Chemistry, Sung Kyun Kwan University, Natural Science Campus,
Suwon 440-746, Korea
Received 1st May 2001, Accepted 22nd October 2001
First published as an Advance Article on the web 14th December 2001
Bis(azido)palladium() complexes Pd(N3)2L2 (L = PMe3, PMe2Ph, PEt3, PMePh2) reacted with two equivalents of
2,6-dimethylphenyl isocyanide to give the Pd() complexes, trans-Pd[CN (R)](N᎐C᎐N–R)L (R = 2,6-Me C H ,
᎐ ᎐
4
2
2
6
3
L = PMe3, 1; PMe2Ph, 2; PEt3, 3; PMePh2, 4) containing a carbodiimido ligand and a C-coordinated 5-membered
tetrazolato ligand. X-Ray structures of 1 and 2 identified the formation of palladium() complexes with a
carbodiimido group, in which a nitrogen of the linear N᎐C᎐N moiety is bonded to the metal center, and with a
᎐ ᎐
tetrazolato ring formed via 1,3-dipolar cycloaddition of the isocyanide to the coordinated azido bond. Heating the
isolated complexes 1 and 3 at 60 ЊC for 5 h converted them into the bis(carbodiimido)palladium() complexes,
trans-Pd[N᎐C᎐N–R] L (R = 2,6-Me C H , L = PMe , 5; PEt , 6). The reactions of 2,6-dimethylphenyl isocyanide
᎐ ᎐
2
2
2
6
3
3
3
with Pd(N3)2L2 (L = PMe3, PEt3) also gave the same complexes directly. Reaction of Pd(N3)2(dppe) with
2,6-dimethylphenyl isocyanide also caused the formation of the bis(carbodiimido) complex Pd[N᎐C᎐N–2,6-
᎐ ᎐
Me2C6H3]2(dppe), 7 in 75% yield. However, reactions of M(N3)2(PMe3)2 (M = Pd or Pt) with tert-butyl isocyanide
resulted in the formation of bis(tetrazolato) compounds, M[CN4(R)]2(PMe3)2 (R = tert-butyl, M = Pd, 8; Pt, 9) by
the cycloaddition of isocyanide to the coordinated azido bond. The same reactions with other isocyanides such as
cyclohexyl and n-butyl isocyanides afforded bis(tetrazolato) complexes, trans-M[CN4(R)]2L2 (M = Pd, R = C6H11,
L = PMe3: 10anti,syn; M = Pd, R = n-Bu, L = PMe3: 11anti,syn; M = Pt, R = n-Bu, L = PMe3: 12anti,syn; M = Pt, R = n-Bu,
L = PEt3: 13anti,syn), which show a mixture of syn and anti isomers in solution. Molecular structures of 11anti, 12anti
,
and 13syn have been determined by X-ray crystallography.
carbodiimides with metal complexes3 and from oxidative
addition of the carbodiimides to metal () or () complexes.4–7
Werner and coworkers8 and Hessell and Jones9 have pre-
pared η2-carbodiimido complexes (type IV) of Rh and Co from
the reaction of an organic azide and a metal-bound isocyanide,
while Fisher and coworkers10a reported the formation of a type
I complex from the reaction of isocyanide-bound complex
[(CO)5CrCN(C2H5)2][BF4] with [N(C4H9)4]N3. In particular,
Lewis and coworkers11 reported a unique method for prepar-
ing the terminally bound carbodiimido complex [Os3(CO)10-
{Au(PEt3)}(NCNPh)] from the reaction of [Os3(CO)10{Au-
(PEt3)}(NCO)] with PhNPPh3. In the early seventies Beck and
coworkers12 first observed the presence of a type I complex
from the thermolysis of AsPh4[Au(CN4CH2C6H5)4].
Recently we obtained type I carbodiimido palladium()
complexes from the reactions of arylpalladium() azido com-
plexes with 2,6-dimethylphenyl isocyanide.13 These results sug-
gested the possibility of conversion reactions of 2,6-dimethyl-
phenyl isocyanide with coordinated azides to give general
group 10 carbodiimido complexes. In an attempt to isolate
various carbodiimido complexes we studied the reactions of
palladium() and platinum() bis(azido) complexes with 2,6-
dimethylphenyl isocyanide as well as other organic isocyan-
ides. Earlier work by Beck and coworkers12 showed that
similar reactions of Pd()- and Pt()-bis(azido) complexes with
various isocyanides gave bis(tetrazolato) complexes, but the
Introduction
Transition metal complexes containing a carbodiimido ligand,
in which the nitrogen of the linear N᎐C᎐N ligand is directly
᎐ ᎐
bound to the metal, are considered to be potential catalysts for
polymerization and/or precursors for metal nitrides and metal
carbonitrides.1 Despite their potential usefulness as catalysts
and precursors, synthetic routes towards these complexes
remain relatively unexplored. Currently, early transition metal
or main group carbodiimido complexes are prepared by trans-
metallation of metal halides with trialkyltin (or silicon) carbo-
diimides,1,2 but to date detailed synthetic methods for late
transition metal carbodiimido complexes (type I and II) con-
taining a linear N᎐C᎐N moiety with a metal–nitrogen bond
have not been reported. However, the σ-bond formation (type
III) through the nitrogen lone pair or π-coordination (type IV)
᎐ ᎐
via the C᎐N bond of organic carbodiimides (R–N᎐C᎐N–R) is
᎐
᎐ ᎐
relatively well-known as shown in Scheme 1. These complexes
(type III and IV) are prepared from direct reactions of organic
Scheme 1
144
J. Chem. Soc., Dalton Trans., 2002, 144–151
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b103916b

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Table 1 Color, yields and analytical data of 1–13
Analysesb
C (%)
Complexa
Color
Yield(%)
H (%)
N(%)
1 Pd[CN4(R)](N᎐C᎐N–R)(PMe3)2
Pale yellow
Pale yellow
Pale yellow
Yellow
Yellow
Yellow
Orange
White
White
White
White
79
57
88
63
89
74
75
79
71
86
85
92
62
49.92 (49.96)
58.34 (58.25)
54.85 (54.50)
63.96 (64.04)
52.28 (52.51)
56.91 (56.91)
66.43 (66.46)
37.96 (37.76)
32.38 (32.16)
42.51 (42.82)
37.79 (37.76)
32.07 (32.16)
38.99 (38.76)
6.19 (6.29)
5.82 (5.75)
7.41 (7.32)
5.43 (5.37)
6.62 (6.61)
7.72 (7.64)
5.31 (5.32)
7.21 (7.13)
6.12 (6.07)
7.17 (7.19)
7.14 (7.13)
6.07 (6.07)
7.20 (7.10)
14.31 (14.57)
11.42 (11.99)
12.73 (12.71)
10.24 (10.18)
10.04 (10.21)
8.66 (8.85)
᎐
᎐
2 Pd[CN4(R)](N᎐C᎐N–R)(PMe2Ph)2
᎐
᎐
3 Pd[CN4(R)](N᎐C᎐N–R)(PEt3)2
᎐
᎐
4 Pd[CN4(R)](N᎐C᎐N–R)(PMePh2)2
᎐
᎐
5 Pd[N᎐C᎐N–R]2(PMe3)2
᎐
᎐
6 Pd[N᎐C᎐N–R]2(PEt3)2
᎐
᎐
7 Pd[N᎐C᎐N–R]2(dppe)2
6.81 (7.04)
᎐
᎐
8 Pd[CN4(tert-butyl)]2(PMe3)2
9 Pt[CN4(tert-butyl)]2(PMe3)2
10 Pd[CN4(cyclohexyl)]2(PMe3)2
11 Pd[CN4(n-butyl)]2(PMe3)2
12 Pt[CN4(n-butyl)]2(PMe3)2
13 Pt[CN4(n-butyl)]2(PEt3)2
22.39 (22.02)
18.94 (18.75)
19.59 (19.98)
21.78 (22.02)
18.59 (18.75)
16.40 (16.44)
White
White
a In complexes 1–7 R = 2,6-Me2C6H3. b Calculated values are given in parentheses.
formation of carbodiimido or bis(carbodiimido) complexes by
those reactions was unexplored.
broad triplet at δ 157–158 which is assigned to the tetrazolato
carbon coordinated to the metal center. The carbon signals of
the NCN group are observed in the δ 130 region with a weak
intensity.
Molecular structures of 1 and 2 were determined by X-ray
diffraction. Selected bond lengths and angles and crystallo-
graphic data are given in Tables 3 and 4. Figs. 1 and 2 show the
In this work we report the unusual formation of several new
complexes such as palladium() carbodiimido or bis(carbodi-
imido) complexes as well as palladium() and platinum()
complexes containing bis(tetrazolato) ligands, whose structures
were determined by X-ray diffraction studies.
Results and discussion
In a recent paper13 we reported that reactions of arylpal-
ladium() azido complexes with 2,6-dimethylphenyl isocyanide
give arylpalladium() carbodiimido complexes, formulated as
ArPd(N᎐C᎐N-2,6-Me -C H )(PMe ) . Based on that result, we
᎐ ᎐
2
6
3
3 2
conducted the reactions of various bis(azido)palladium()
complexes Pd(N3)2L2 (L = PMe3, PMe2Ph, PEt3, PMePh2) with
two equivalents of 2,6-dimethylphenyl isocyanide.
The reactions at room temperature afforded Pd() com-
plexes containing a carbodiimido ligand (N᎐C᎐N) and a C-
᎐ ᎐
coordinated tetrazolato ring, trans-Pd[CN (R)](N᎐C᎐N–R)L
᎐ ᎐
4
2
(R = 2,6-Me2C6H3, L = PMe3, 1; PMe2Ph, 2; PEt3, 3; PMePh2,
4) as shown in eqn. (1).
Addition of the isocyanide to a solution of the azido com-
plex caused immediate evolution of nitrogen gas and the reac-
tion was monitored easily by the IR spectra which showed
disappearance of an asymmetric stretching band ν(N3) at ca.
2030 cmϪ1 and appearance of a new strong band at 2140–2170
Fig. 1 ORTEP drawing34 of 1 showing the atom-labeling scheme and
50% probability thermal ellipsoids.
cmϪ1 due to the carbodiimido group ν(N᎐C᎐N) of the products.
ORTEP drawings of the complexes, trans-Pd[CN (R)](N᎐C᎐
᎐ ᎐
᎐ ᎐
4
The reactions occurred cleanly and gave no other possible
products such as bis(tetrazolato) complexes, Pd[CN4(R)]2L2
N–R)L2 (R = 2,6-Me2C6H3, L = PMe3, PMe2Ph), which have a
slightly distorted square-planar coordination, containing two
phosphines, a carbodiimido group, and a tetrazolato ring. The
carbodiimido ligand and tetrazolato rings are at mutually trans
positions. The ORTEP drawings clearly show that the nitrogen
of the carbodiimido ligand is bonded to the Pd center and
that the five-membered tetrazolato ring is coordinated to Pd
through the carbon. The tetrazolato ligand is essentially planar,
and the 2,6-dimethylphenyl ring bonded to the tetrazolato ring
is twisted out of the tetrazolato ring with a dihedral angle of
(R = 2,6-Me C H ), or bis(carbodiimido) complexes, Pd[N᎐C᎐
᎐ ᎐
2
3
N–R]2L2 (R = 62,6-Me2C6H3). Complexes 1–4 were isolated as
pale yellow crystals and characterized by IR and NMR spectra
1
as well as elemental analyses (see Tables 1 and 2). H NMR
signals in the range of 1.00–1.67 ppm of complexes 1–4 indicate
the presence of tertiary alkyl phosphines. The 31P{1H} NMR
spectra show a singlet which is consistent with the proposed
trans structure. The 13C{1H} NMR spectra of 1–4 each show a
(1)
J. Chem. Soc., Dalton Trans., 2002, 144–151
145

Table 2 NMR and IR data of the complexes (δ, J/Hz)
1H NMRa
Complex PR3 (R = Me or Et)
Others
13C{1H}b
31P{1H}c
ν(NCN)d/cmϪ1
1
2
1.17 (t, 18 H, J = 4)
2.26 (s, 6H, CH3), 2.32 (s, 6H, CH3), 6.69–6.73 (m, 1H), 6.91–6.93
(m, 2H), 7.21–7.34 (m, 3H)
1.77 (br s, 6H, CH3), 2.13 (br s, 6H, CH3), 6.65–6.71 (m, 1H), 6.84–
6.87 (m, 2H), 6.98–7.01 (m, 2H), 7.11–7.19 (m, 1H), 7.24–7.36 (m,
6H), 7.46–7.52 (m, 4H)
13.8 (t, J = 16), 19.3, 20.3 (t, J = 1), 120.3, 127.8, 129.3, 129.4, 130.0 Ϫ12.2
(br, NCN), 134.9, 135.4, 143.4, 157.9 (J = 9.8, CN4)
19.1, 19.6 (t, J = 1), 120.1, 127.7, 128.7, 128.8, 128.9, 129.2, 130.5,
130.8, 130.9, 131.0, 132.6, 135.2, 143.3 (t, J = 1), 157.1 (br, CN4)
2140
2170
1.45 (br, 12H)
Ϫ4.0
3
4
1.00 (q, 18H), 1.50 (br, 12H)
1.67 (t, 6H, J = 4)
2.31 (s, 12H, CH3), 6.69–6.71 (m, 1H), 6.89–6.92 (m, 2H), 7.18–7.28
(m, 4H)
1.59 (s, 6H, CH3), 1.68 (s, 6H, CH3), 6.50–6.68 (m, 4H), 6.93–6.96
(m, 2H), 7.18–7.50 (m, 20H)
7.92, 15.1 (t, J = 14), 19.1, 20.6, 119.9, 127.6, 129.1, 129.4, 129.6 (br,
NCN), 131.0, 135.1, 135.6, 143.8, 156.8 (br, CN4)
12.7 (t, J = 16), 18.8, 19.2, 119.4, 127.2, 128.6, 128.7, 129.1 130.4,
130.8, 131.9, 132.8, 135.4, 143.3, 157.4 (br t, CN4)
12.8 (t, J = 15), 19.2, 120.9, 127.8, 131.1, 131.3 (NCN), 142.6 (br)
7.89, 14.1 (t, J = 13), 19.0, 120.6, 127.7, 130.7 (NCN), 131.0, 142.9 (t,
J = 1)
25.6, 27.7 (d, J = 15), 28.1 (d, J = 15), 119.6, 126.6, 127.3, 127.5,
129.2, 129.1, 129.3, 129.5, 131.6, 132.3, 133.1, 133.2, 133.5, 133.6,
143.3
18.4
2129
2128
6.29
5
6
1.44 (t, 18H, J = 4)
2.33 (s, 12H, CH3), 6.75 (m, 2H, Ph), 6.92 (m, 4H, Ph)
Ϫ10.4
20.6
2091
2081
1.67 (br, 18H), 1.77 (m, 12H) 2.31 (s, 12H, CH3), 6.72 (m, 2H, Ph), 6.93 (m, 4H, Ph)
7
2.35 (br s, 2H), 2.43 (br s, 2H) 2.05 (br s, 12H, CH3), 6.55–6.60 (m, 2H), 6.73–6.75 (m, 4H), 7.35–
7.51 (m, 12H), 7.70–7.77 (m, 8H)
61.5
2090
8
9
1.08 (t, 18H, J = 4)
1.85 (s, 18H, CH3)
1.18 (t, 18H, J = 4, JPt–H = 32) 1.88 (s, 18H, CH3)
14.4 (t, J = 16), 31.2, 57.8, 161.8 (br, CN4)
Ϫ15.1
Ϫ20.8
(JPt–P = 1297)
Ϫ14.7
Ϫ15.4
Ϫ14.9
14.2 (t, J = 19), 31.2, 58.2, 157.1 (br, CN4)
10anti,syn
11anti,syn
1.10 (br, 18H)
1.09 (br, 18H)
1.28 (br, 6H, –CH2), 1.85–2.23 (m, 14H, –CH2), 4.49 (m, 2H, –CH)
anti: 14.6 (t, J = 16), 25.5, 26.0, 34.1, 59.4, 165.6 (br t)
syn: 15.0 (t, J = 16), 25.1, 26.0, 33.9, 58.3, 165.4 (br, CN4)
1.05 (br t, 6H, CH3), 1.53 (m, 4H, –CH2), 2.01 (m, 4H, –CH2), 4.38 anti: 13.6, 14.4 (t, J = 17), 20.2, 32.1, 48.3, 166.4 (t, J = 14, CN4)
(m, 4H, –CH)
syn: 13.5, 14.1 (t, J = 16), 20.0, 32.5, 48.2, 166.4 (t, J = 14, CN4)
1.04 (t, 6H, CH3), 1.53 (m, 4H, CH2), 1.98 (m, 4H, CH2), 4.36 (m, anti: 13.8, 14.2 (t, J = 13), 20.4, 32.1, 48.3, 162.5 (t, J = 12, CN4)
4H, –CH2)
Ϫ13.9
Ϫ19.4,
JPt–P = 2311
Ϫ18.8,
JPt–P = 2316
9.67,
JPt–P = 2351
9.45,
12anti,syn
1.17 (t, 6H, J = 7)
syn: 13.7, 14.1 (t, J = 19), 20.2, 32.5, 48.2, 162.5 (t, J = 12, CN4)
13anti,syn
1.05 (m, 18H), 1.39 (m, 12H) 1.55 (m, 4H, CH2), 2.07 (m, 4H, CH2), 4.36 (m, 4H, CH2)
anti: 7.60, 13.7, 14.5 (t, J = 17), 20.5, 31.8, 46.6, 162.7 (t, J = 8, CN4)
syn: 7.66, 13.7, 14.8 (t, J = 17), 20.5, 31.7, 48.5, 162.7 (t, J = 8, CN4)
JPt–P = 2338
a Obtained in CDCl3 at 25 ЊC. Peak positions were referenced to internal SiMe4. b Obtained in CDCl3 at 25 ЊC. Peak positions were referenced to internal SiMe4. c Obtained in CDCl3 at 25 ЊC. Peak positions were
referenced to external 85% H3PO4. Abbreviations: t, triplet; br, broad; br s, broad singlet; q, quartet; m, multiplet. d KBr.

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64.4(2) (for 1) or 64.9(3)Њ (for 2). Complexes 1 and 2 show quite
similar structures, but the 2,6-C6H3Me2 groups on the carbodi-
imido ligand across the molecular plane of the complexes show
an approximately syn (for 1) or anti (for 2) conformation. Also,
the orientation of the phosphine groups in each complex takes
a staggered (for 1) or an eclipsed (for 2) conformation.
The carbodiimido group in each complex is approximately
linear (NCN: 169.7(6)Њ and 171.4(10)Њ). The Pd–N distances
(2.030(5) Å and 1.988(8) Å) of the carbodiimido ligand in com-
Table 3 Selected bond distances (Å) and bond angles (Њ) in 1 and 2
1
2
Pd1–C1
Pd1–N5
Pd1–P1
Pd1–P2
N1–C1
N1–N2
N2–N3
N3–N4
N4–C1
N5–C10
N6–C10
2.006(5)
2.030(5)
2.318(1)
2.336(2)
1.363(7)
1.384(6)
1.292(8)
1.363(7)
1.325(7)
1.156(7)
1.235(8)
Pd1–C26
Pd1–N1
Pd1–P1
Pd1–P2
N3–C26
N3–N4
N4–N5
N5–N6
N6–C26
N1–C17
N2–C17
1.969(9)
1.988(8)
2.334(2)
2.329(2)
1.352(11)
1.393(10)
1.309(11)
1.350(11)
1.367(11)
1.150(11)
1.274(11)
Fig. 2 ORTEP drawing of 2 showing the atom-labeling scheme and
50% probability thermal ellipsoids.
pounds 1 and 2 are comparable with that (2.087(3) Å) found in
trans-PdPh(N᎐C᎐N-2,6-Me C H )(PMe ) .13 However, these
᎐ ᎐
2
6
3
3 2
bonds are somewhat shorter than those found in palladium
azide, trans-Pd(C6H4-p-Me)(N3)(PMe3)2 (2.114(3) Å)13 as well
as palladium amide, trans-PdPh(NHPh)(PMe3)2 (2.116(13)
Å),14 indicating a partial π-bonding in the Pd–N bond. The
Pd–N (1.988(8) Å) and Pd–C (1.969(9) Å) bond distances in 2
are shorter than those of 1 (2.030(5) Å and 2.006(5) Å) and
C1–Pd1–N5
C1–Pd1–P1
C1–Pd1–P2
N5–Pd1–P1
N5–Pd1–P2
P1–Pd1–P2
C1–N1–N2
N3–N2–N1
N2–N3–N4
C1–N4–N3
C10–N5–Pd1
C10–N6–C11
N4–C1–N1
N5–C10–N6
175.6(2)
95.9(1)
87.3(2)
87.0(2)
90.2(2)
172.72(6)
108.3(5)
105.6(5)
111.6(5)
107.0(5)
158.2(5)
132.7(6)
107.4(5)
169.7(6)
C26–Pd1–N1
C26–Pd1–P1
C26–Pd1–P2
N1–Pd1–P1
N1–Pd1–P2
P2–Pd1–P1
C26–N3–N4
N5–N4–N3
N4–N5–N6
N5–N6–C26
C17–N1–Pd1
C17–N2–C18
N3–C26–N6
N1–C17–N2
175.5(3)
98.9(2)
89.0(3)
85.7(2)
86.5(2)
171.54(8)
110.1(8)
106.4(9)
109.0(9)
110.2(8)
168.9(8)
131.9(8)
104.1(8)
171.4(10)
those (2.087(3) Å and 2.014(3) Å) in trans-PdPh(N᎐C᎐N-2,6-
᎐ ᎐
Me2C6H3)(PMe3)2, suggesting a weaker coordination of PMe2-
Ph compared with PMe3. Interestingly, the bond distances
between the nitrogen bound to the metal and center carbon in
the carbodiimido groups of 1 (N5–C10) and 2 (N1–C17) are
1.156(7) Å and 1.150(11) Å, respectively, which are very close to
15
᎐
the general C᎐N bond length (1.16 Å), whereas the other
᎐
nitrogen–carbon bond distances are 1.235(8) Å (N6–C10 in 1)
Table 4 X-Ray data collection and structure refinement for 1, 2, 11, 12 and 13
1
2
11
12
13
Formula
M
C24H36N6P2Pd
576.93
293(2)
0.48 × 0.40 × 0.32
Monoclinic
P21
C34H40N6P2Pd
701.06
293(2)
0.60 × 0.46 × 0.07
Orthorhombic
Pbca
C16H36N8P2Pd
508.87
294(2)
0.30 × 0.40 × 0.44
Monoclinic
P21/n
C16H36N8P2Pt
597.56
296(2)
0.58 × 0.10 × 0.06
Monoclinic
P21/n
C22H48N8P2Pt
681.71
294(2)
0.10 × 0.20 × 0.50
Triclinic
¯
P1
Temperature/K
Crystal size/mm3
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
9.078(2)
11.772(3)
13.628(4)
—
109.12(2)
—
1375.9(6)
2
1.393
10.064(1)
16.446(3)
40.816(5)
—
—
—
6756(2)
8
1.379
6.376(1)
15.657(1)
12.671(2)
—
92.422(9)
—
1263.7(2)
2
1.337
6.369(1)
15.643(1)
12.686(1)
—
92.50(1)
—
1262.6(2)
2
1.572
10.153(2)
11.872(2)
12.910(2)
94.864(9)
102.154(8)
93.323(9)
1511.1(4)
2
β/Њ
γ/Њ
V/Å3
Z
dcal/g cmϪ3
1.498
4.773
µ/mmϪ1
0.813
0.677
0.877
5.700
F(000)
T min
T max
596
2896
528
592
688
0.3360
0.3895
2704
2538
2469
298
0.330
Ϫ0.406
1.032
0.5032
0.5230
5827
5827
3044
389
1.279
Ϫ1.165
1.012
0.2274
0.2768
2399
2192
2009
125
0.621
Ϫ0.379
1.015
0.0322
0.0545
2382
2174
1607
125
0.890
Ϫ0.682
1.133
0.2766
0.4086
5584
5261
4784
307
1.178
Ϫ1.078
1.036
No. of reflns measured
No. of unique reflns
No. of reflns with I > 2σ(I )
No. of parameters refined
Max., in ∆ρ/e ÅϪ3
Min., in ∆ρ/e ÅϪ3
GOF on F 2
R
wR2
0.0275
0.0724
0.0285
0.0734
0.0669
0.1344
0.1502
0.1717
0.0282
0.0760
0.0308
0.0784
0.0311
0.0705
0.0478
0.0788
0.0295
0.0719
0.0349
0.0745
a
R (all data)
wR2 a (all data)
2
a wR2 = Σ[w(Fo2 Ϫ Fc2)2]/Σ[w(Fo )2]1/2
.
J. Chem. Soc., Dalton Trans., 2002, 144–151
147

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(2)
and 1.274(11) Å (N2–C17 in 2), suggesting a double bond
character. These asymmetric NCN linkages are similar to
those found in the early transition metal complexes such as
Cp2Ti(NCNPh)2 1 and (CO)5CrNCN(C2H5)2.10
tion of Pd(N3)2(dppe) with two equivalents of 2,6-dimethyl-
phenyl isocyanide under the same conditions. The reaction
gave a bis(carbodiimido) complex, Pd[N᎐C᎐N–2,6-Me C H ] -
᎐ ᎐
2
6
3 2
(dppe), 7 in 75% yield as shown in eqn. (4). However, in
this instance the reaction can also occur slowly at room
temperature.
We carried out similar reactions of bis(azido) Pd() and Pt()
complexes with tert-butyl and cyclohexyl isocyanides in CH2Cl2
as shown in eqn. (5).
As shown in eqn. (1), the formation of the carbodiimide
group using the isocyanide seems to involve initial formation of
the C-coordinated bis(tetrazolato) ligand. One of the tetra-
zolato rings then eliminates a molecule of N2 to give the prod-
uct. Another possibility to be considered in the formation of
the tetrazolato ring involves the prior dissociation of the azido
anion. This is followed by isocyanide coordination to the metal
center and then nucleophilic attack by the azide anion.12,16 The
carbodiimido formation from Pd(N3)2(PMePh2)2 with the iso-
cyanide is slower than that from Pd(N3)2(PMe3)2 or Pd(N-
3)2(PEt3)2, probably because of weaker basicity or steric effects
of PMePh2 compared with PMe3 and PEt3. Although we could
not provide conclusive information on the formation of the
carbodiimido complexes, electronic or steric effects of phos-
phines seem to operate on the formation of carbodiimido com-
plexes. In order to gain insight into the mechanism of the
carbodiimide group we have carried out the following reaction,
as shown in eqn. (2).
(5)
The reactions (eqn. (5)) did not give the expected carbodi-
imido complexes but bis(tetrazolato) Pd() and Pt() com-
plexes with C-coordinated tetrazolato rings through 1,3-dipolar
cycloaddition of the isocyanide into the coordinated azido
bond in high yields. Earlier work by Beck and coworkers12
showed that the azido complexes M(N3)2(PPh3)2 (M = Pd, Pt)
react with excess amounts of alkyl isocyanide to give complexes
[Ph3P(R–NC)M(CN4R)2] (R = C6H11, C6H5CH2, C6H5) in
which one phosphine has been replaced by an isocyanide. How-
ever, in our case, reactions (eqn. (5)) do not give any isocyanide-
adduct complexes. Complexes 8–10 are characterized by IR,
NMR, and elemental analyses (see Tables 1 and 2). The
13C{1H} NMR spectra in the complexes exhibit a triplet or
a broad singlet at δ 162.0–166.4 with a coupling with two
magnetically equivalent phosphorus atoms, indicating C-
coordination of the tetrazolato ring to the metal center. The
31P{1H} spectra of the complexes also support the proposed
trans structure. Interestingly, the 13C{1H} and 31P{1H} spectra
of 10 apparently show the presence of syn and anti-isomers
according to the orientation of substitutents on the tetrazolato
ring. The 13C{1H} NMR spectrum of 10 exhibits eight signals
due to the cyclohexyl group substituted on the tetrazolato ring
as anti and syn species and also shows two triplets due to the
corresponding PMe3 with virtual coupling. The 31P{1H} spec-
trum also shows two singlets due to anti and syn species. The
relative abundance ratio of the isomers (anti/syn), illustrated by
the 31P{1H} spectrum, is 1 : 0.79. In contrast, no other isomers
of complexes 8 and 9 are observed because rotation of the Pd–
C (or Pt–C) bond in the C-coordinated tetrazolato ring for syn
Gently heating a solution of trans-Pd[CN (R)](N᎐C᎐N–R)-
L2 (R = 2,6-Me2C6H3, L = PMe3, PEt3) at 60 ЊC for 5 h in
THF–CH2Cl2 (3 : 1 ratio) caused the formation of the bis(car-
᎐ ᎐
4
bodiimido) complexes, trans-Pd[N᎐C᎐N–R] L (R = 2,6-Me -
᎐ ᎐
2
2
2
C6H3, L = PMe3, 5; PEt3, 6). The bis(carbodiimido) complexes 5
and 6 were obtained as yellow crystalline solids and were fully
1
characterized by elemental analysis and IR, H, 31P{1H}, and
13C{1H} NMR spectroscopy. IR spectra of the complexes show
a characteristic band (νN᎐C᎐N) at 2091 and 2081 cmϪ1, for 5 and 6,
respectively, which are sl᎐ig᎐htly shifted to a lower frequency than
1
that of the starting materials. Also, the two H NMR signals
due to the inequivalent methyl substituents of the starting
materials are changed to a singlet with a correct integration
ratio. The 13C{1H} and 31P{1H} NMR spectra of the complexes
are consistent with the proposed symmetrical structure.
Direct reaction of Pd(N3)2L2 (L = PMe3, PEt3) with 2,6-
dimethylphenyl isocyanide at 60 ЊC for 5 h caused the formation
of the same bis(carbodiimido) complexes trans-Pd[N᎐C᎐N–
᎐ ᎐
R]2L2 (R = 2,6-Me2C6H3, L = PMe3, 5; PEt3, 6) in high yields, as
shown in eqn. (3).
(3)
1
The obtained complexes were identified with IR, H, and
31P{1H} NMR spectroscopy. We have also attempted the reac-
(4)
148
J. Chem. Soc., Dalton Trans., 2002, 144–151

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(6)
and anti isomer formation might be influenced by the steric
hindrance of the substituents on the tetrazolato ring.
It is well known that the cycloaddition of organic nitriles to
coordinated azides produces N-coordinated tetrazolato com-
pounds containing several linkage isomers formed by the N(1)
or N(2)-coordination to one of the nitrogen atoms on the tetra-
zolato ring.17–27 In contrast, similar studies on the cycloaddition
of organic isocyanides with coordinated azides to form the
C-coordinated tetrazolato compounds are rarer than those of
N-tetrazolato compounds, because there is no such linkage
isomer in the metal–carbon bond formation.28,29 Moreover,
there is only one example concerning a C-coordinated tetra-
zolato compound, [Au(CN4R)4]Ϫ (R = i-C3H7)30 which is struc-
turally characterized and suggests an anti and syn conformation
of the substituent attached to the tetrazolato ring in the
molecule. In order to obtain more detailed information about
the conformation of the C-coordinated tetrazolato compounds
in the solution and solid state we chose the following cyclo-
addition using n-butyl isocyanide as shown in eqn. (6).
These reactions occur rapidly to give bis(tetrazolato) Pd()
and Pt() complexes, 11–13 as white solids in high yields. The
13C{1H} NMR spectra of the complexes show a triplet (J =
8–14 Hz) at δ 162.5–166.4 due to the carbon of the C-
coordinated tetrazolato ring. Four pairs of singlets and two
triplets with very close chemical shifts, which are assigned to the
corresponding n-butyl carbons and PMe3 as anti and syn iso-
mers, are also observed. Also, each of the two singlets in the
31P{1H} NMR spectra of the complexes indicates a mixture
of the syn and anti conformers with the trans structure. All
spectroscopic data support the presence of the syn and anti
conformers in solution at room temperature. The relative ratios
of the isomers (anti/syn) in the complexes 11–13 are 1.0/0.72,
1.0/0.64 and 1.0/0.27, respectively, which are measured by inte-
gration of the peaks in the 31P{1H} NMR spectra. The higher
abundance of the anti isomer rather than the syn isomer may be
explained by a sterically favorable geometry which minimizes
steric repulsion between the two phosphine ligands and two
n-butyl groups attached to the tetrazolato ring in the solution.
The molecular structures of 11–13 have been determined by
X-ray crystallography. The ORTEP drawings of these com-
plexes with the atom-numbering scheme are shown in Figs. 3–5,
respectively. Selected bond lengths and angles are listed in Table
5. Compounds 11 and 12 are isostructural. The molecular
structures of 11 and 12 clearly indicate that the two tetrazolato
rings are mutually trans and oriented perpendicular to the
coordination plane containing the two PMe3 groups and the
two carbons (C4 and C4A). The central metal lies on the crys-
tallographic inversion point, by which the n-butyl substituents
attached to the tetrazolato rings are oriented in the opposite
direction (anti orientation). In contrast, the n-butyl groups
attached to the tetrazolato ring in 13 indicate a syn orientation
in spite of the expected steric repulsion between the n-butyl
substituents and the two PEt3 groups. Thus, the P1–Pt–P2
(167.88(5)Њ) fragment of 13 is severely bent compared with the
linear fragments of P1–Pd–P1A (180.0(0)Њ) in 11 and P1–Pt–
Fig. 3 ORTEP drawing of 11 showing the atom-labeling scheme and
50% probability thermal ellipsoids. Symmetry-equivalent atoms
(denoted by an A) are generated by the crystallographic inversion
center located at the Pd1 atom.
Fig. 4 ORTEP drawing of 12 showing the atom-labeling scheme and
50% probability thermal ellipsoids. Symmetry-equivalent atoms
(denoted by an A) are generated by the crystallographic inversion
center.
P1A (180.0(8)Њ) in 12. The C-coordinated tetrazolato ring of
complexes 11–13 is nearly planar. Bond distances (C–N and
N–N) in the tetrazolato rings lie in the range 1.280–1.389 Å,
indicating a slight π-electron localization in the tetrazolato
ring. This deviation is relatively larger than that in similar
N-coordinated counterparts such as trans-(Ph3P)2Pd(N4C-
C6H5)2 (1.300–1.347 Å)18 and cis-(PhMe2P)2Pd(N4C-CH3)2
(1.296–1.366 Å and 1.327–1.351 Å).31 In this work, we have
J. Chem. Soc., Dalton Trans., 2002, 144–151
149

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Table 5 Selected bond distances (Å) and bond angles (Њ) in 11–13
11
12
13
Pd1–C4
Pd1–P1
N1–C4
N1–N2
N2–N3
N3–N4
N4–C4
2.034(3)
2.3072(6)
1.350(4)
1.352(3)
1.280(4)
1.365(4)
1.331(4)
Pt1–C4
Pt1–P1
N1–C4
N1–N2
N2–N3
N3–N4
N4–C4
2.033(6)
2.304(2)
1.340(8)
1.341(8)
1.294(9)
1.389(8)
1.338(8)
Pt–C18
Pt–P2
N1–N2
N2–N3
N4–C13
N5–N6
N7–N8
2.033(5)
2.303(1)
1.345(8)
1.275(9)
1.327(7)
1.362(7)
1.360(7)
Pt–C13
Pt–P1
N1–C13
N3–N4
N5–C18
N6–N7
N8–C18
2.056(5)
2.307(1)
1.356(7)
1.379(8)
1.338(7)
1.280(8)
1.334(7)
C4–Pd1–P1
C4–N1–N2
N3–N2–N1
N2–N3–N4
C4–N4–N3
N4–C4–N1
N4–C4–Pd1
N1–C4–Pd1
91.84(8)
109.6(3)
106.2(2)
111.0(3)
106.8(3)
106.4(2)
126.3(2)
127.2(2)
C4–Pt1–P1
C4–N1–N2
N3–N2–N1
N2–N3–N4
C4–N4–N3
N4–C4–N1
N4–C4–Pt1
N1–C4–Pt1
91.7(2)
111.0(6)
106.2(6)
110.1(6)
106.2(6)
106.5(6)
125.3(5)
128.2(5)
C18–Pt–C13
C18–Pt–P2
C18–Pt–P1
P2–Pt–P1
N2–N1–C13
N3–N2–N1
N2–N3–N4
C13–N4–N3
178.82(16)
90.82(12)
91.84(12)
167.88(5)
109.7(6)
106.5(5)
111.0(5)
106.2(5)
C18–N5–N6
N7–N6–N5
N6–N7–N8
C18–N8–N7
N4–C13–N1
N8–C18–N5
107.4(5)
110.8(5)
105.6(5)
110.7(5)
106.6(5)
105.6(4)
Experimental
General, materials and measurements
All manipulations of air-sensitive compounds were performed
under an N2 or argon atmosphere using standard Schlenk tech-
niques. Solvents were distilled from Na-benzophenone. The
analytical laboratories at the Basic Science Institute of Korea
and at Kangnung National University carried out elemental
analyses. IR spectra were recorded on Hitachi 270-30 and
Perkin-Elmer BX spectrophotometers. NMR (1H, 13C{1H} and
31P{1H}) spectra were obtained on Bruker-300 and -500 MHz
and on JEOL Lamda 300 MHz spectrometers. Chemical shifts
were referenced to an internal Me4Si standard and to an
external 85% H3PO4 standard. Pd(N3)2L2 (L = PMe3, PEt3,
PMePh2, PMe2Ph, dppe) and Pt(N3)2L2 (L = PMe3, PEt3) were
prepared from ligand exchange reactions of Pd(N3)2(tmeda)32
(tmeda = N,N,NЈ,NЈ-tetramethylethylenediamine) and Pt(N3)2-
(COD)32 (COD = 1,5-cyclooctadiene) with corresponding
tertiary or chelated phosphine ligands, respectively.
Preparations
Fig. 5 ORTEP drawing of 13 showing the atom-labeling scheme and
50% probability thermal ellipsoids.
Complexes 1–4. To a Schlenk flask containing Pd(N3)2-
(PMe3)2 (0.138 g, 0.40 mmol) were added CH2Cl2 (5 cm3) and
2,6-dimethylphenyl isocyanide (0.106 g, 0.81 mmol) in that
order. The initial yellow solution immediately turned to pale
yellow with evolution of nitrogen. After stirring for 3 h at room
temperature, the reaction mixture was fully evaporated under
vacuum and then the resulting solid was washed with hexane.
Recrystallization from CH2Cl2–hexane gave pale yellow crystals
confirmed the existence of the stereoisomers of bis(tetrazolato)
complexes. To the best of our knowledge, this is the first
example of the isolation of syn–anti conformers of the
tetrazolato–transition metal complexes in the solid state.
In this work, we have shown that bis(azido)palladium()
complexes react with 2,6-dimethylphenyl isocyanide to give
unique palladium() complexes, trans-Pd[CN (R)](N᎐C᎐N–R)-
᎐ ᎐
4
of trans-Pd[CN (R)](N᎐C᎐N–R)(PMe ) (R = 2,6-Me C H ), 1
᎐ ᎐
4
3
2
2
6
3
L2 (R = 2,6-Me2C6H3, L = tertiary phosphine) containing
a carbodiimido and a tetrazolato ligand. We have also found
that heating the palladium() complexes at 60 ЊC results in
formation of the bis(carbodiimido)palladium() complexes,
(0.183 g).
Complexes 2, 3, and 4 were analogously prepared.
Complexes 5 and 6. Complex 1 (0.101 g, 0.18 mmol) was
dissolved in a 3 : 2 mixture of THF–CH2Cl2 (5 cm3). The mix-
ture was heated at 60 ЊC for 5 h. The initial yellow solution
slowly turned to orange. After stirring, the solvent was removed
completely, and the resulting residue was solidified with ether
and hexane as a yellow powder. Recrystallization from CH2Cl2–
trans-Pd[N᎐C᎐N–R] L (R = 2,6-Me C H , L = tertiary phos-
᎐ ᎐
2
2
2
6
3
phine). Thus, we have demonstrated that the direct reaction of
bis(azido)palladium() complexes with 2,6-dimethylphenyl
isocyanide results in the formation of bis(carbodiimido)pal-
ladium() complexes with phosphine ligands. These results
provide an efficient preparation for the bis(carbodiimido)pal-
ladium() complex. Although several transition metal com-
pounds of π-coordinated (η2) carbodiimide are known, those
mono or bis(carbodiimido) compounds of group 10 metals
hexane gave yellow crystals of trans-Pd[N᎐C᎐N–R] (PMe )
᎐ ᎐
3 2
2
(R = 2,6-Me2C6H3), 5 (0.085 g).
Complex 6 was analogously prepared from complex 3.
Complexes 5–7 were prepared independently from the reac-
tions of bis(azido) complexes Pd(N3)2(PMe3)2, Pd(N3)2(PEt3)2
and Pd(N3)2(dppe), respectively, with 2,6-dimethylphenyl iso-
cyanide under the conditions described above.
with a linear N᎐C᎐N moiety have not been reported. Among
᎐ ᎐
the amido-type ligands, the carbodiimido ligands are sterically
less hindered around the metal center and thus may have
a potent possibility for the polymerization of carbodiimido
ligands. The functionality of the complexes having a mono or
bis(carbodiimido) group seems to be of interest as reaction
intermediate in synthetic organic reactions catalyzed by group
10 metals.
Complexes 8–10. To a Schlenk flask containing Pd(N3)2-
(PMe3)2 (0.343 g, 1.00 mmol) were added CH2Cl2 (15 cm3) and
tert-butyl isocyanide (0.238 cm3, 2.10 mmol) in that order. The
150
J. Chem. Soc., Dalton Trans., 2002, 144–151

View Article Online
7 D. S. Glueck, F. J. Holland and R. G. Bergman, J. Am. Chem. Soc.,
1989, 111, 2719.
initial yellow solution immediately turned colorless. After stir-
ring for 1 h at room temperature, the reaction mixture was fully
evaporated under vacuum and then the resulting solid was
washed with hexane (10 cm3). Recrystallization from CH2Cl2–
hexane gave white crystals of trans-Pd[CN4(tert-butyl)]2(PMe3)2,
8 (0.401 g).
8 H. Werner, G. Hörlin and N. Mahr, J. Organomet. Chem., 1998, 551,
367; G. Hörlin, N. Mahr and H. Werner, Organometallics, 1993, 12,
1775.
9 E. T. Hessell and W. D. Jones, Organometallics, 1992, 11, 1496.
10 (a) E. O. Fisher, W. Kleine, U. Schubert and D. Neugebauer,
J. Organomet. Chem., 1978, 149, C40; (b) v. U. Schubert, D.
Neugebauer and P. Fridrich, Acta Crystallogr., Sect. B, 1978, 34,
2293.
Complexes 9 and 10 were analogously prepared.
Complexes 11–13. To a Schlenk flask containing Pd(N3)2-
(PMe3)2 (0.364 g, 1.06 mmol) were added CH2Cl2 (30 cm3) and
n-butyl isocyanide (0.234 cm3, 2.23 mmol) in that order. The
initial yellow solution immediately turned colorless. After
stirring for 1 h at room temperature, the reaction mixture was
fully evaporated under vacuum and then the resulting solid was
washed with hexane (3 × 3 cm3). Recrystallization from
CH2Cl2–hexane gave white crystals of trans-Pd[CN4(n-butyl)]2-
(PMe3)2, 11 (0.459 g).
11 K. Burgess, B. F. G. Johnson and J. Lewis, J. Chem. Soc., Dalton
Trans., 1983, 1179.
12 W. Beck, K. Burger and W. P. Fehlhammer, Chem. Ber., 1971, 104,
1816.
13 Y.-J. Kim, Y.-S. Kwak and S.-W. Lee, J. Organomet. Chem., 2000,
603, 152.
14 L. A. Villanueva, K. A. Abboud and J. M. Boncella,
Organometallics, 1994, 13, 3921.
15 J. E. Huheey, E. A. Keitter and R. L. Keitter, Inorganic Chemistry,
Harper Collins, New York, 4th edn., 1993, Appendix, Table E1.
16 P. M. Treichel, W. J. Knebel and R. W. Hess, J. Am. Chem. Soc.,
1971, 93, 5424.
Complexes 12 and 13 were analogously prepared.
17 W. Beck and W. P. Fehlhammer, Angew. Chem., Int. Ed. Engl., 1967,
6, 169; W. Beck, M. Bander, W. P. Fehlhammer, P. Pöllmann and
H. Schachl, J. Inorg. Nucl. Chem. Lett., 1968, 4, 143; W. Beck, W. P.
Fehlhammer, P. Pöllmann and H. Schachl, Chem. Ber., 1969, 102,
1976; W. Beck, W. P. Fehlhammer, H. Bock and M. Bauder, Chem.
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X-Ray structure determination
All X-ray data were collected using a Siemens P4 diffractometer
equipped with a Mo X-ray tube and a graphite crystal mono-
chromator. The orientation matrix and unit cell parameters
were determined by least-squares analyses of the setting angles
of 25–36 reflections in the range 10.0Њ < 2θ < 25.0Њ. Intensity
data were corrected for Lorentz and polarization effects. Decay
corrections were also made. The intensity data were empirically
corrected for absorption with Ψ-scan data. All calculations
were carried out using the SHELX-97 programs.33 The struc-
tures were solved by direct methods and refined by full-matrix
least-squares calculations of F 2 values, initially with isotropic
and finally anisotropic temperature factors for all non-hydrogen
atoms. All hydrogen atoms were located in the difference
Fourier maps and refined isotropically. The crystal data and
details of the structure refinement of 1, 2, 11, 12, and 13 are
summarized in Table 4.
CCDC reference numbers 167462–167466.
See http://www.rsc.org/suppdata/dt/b1/b103916b/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
This work was supported by the Korea Research Foundation
Grant (KRF-2000-041-D00157).
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