Synthesis and structures of alkynylchlorocyclotriphosphazenes and their cluster-forming reactions with octacarbonyldicobalt

Article abstract of DOI:10.3987/COM-08-S(F)96

Cyclotriphosphazenes having p-tolylethynyl and chloro substituents N ₃P₃C≡C(p-Tol)_n,Cl_6-n (1a: n = 2, 1b: n = 4; p-Tol = p-tolyl) were synthesized by the reaction of hexachlorocyclotriphosphazene (NPC1₂

Full text of DOI:10.3987/COM-08-S(F)96

HETEROCYCLES, Vol. 77, No. 2, 2009
1171
HETEROCYCLES, Vol. 77, No. 2, 2009, pp. 1171 - 1183. © The Japan Institute of Heterocyclic Chemistry
Received, 5th August, 2008, Accepted, 12th September, 2009, Published online, 18th September, 2008
DOI: 10.3987/COM-08-S(F)96
SYNTHESIS AND STRUCTURES OF
ALKYNYLCHLOROCYCLOTRIPHOSPHAZENES AND THEIR
CLUSTER-FORMING REACTIONS WITH
OCTACARBONYLDICOBALT†
Takashi Komuro, Kenichi Mori, and Hiromi Tobita*
Department of Chemistry, Graduate School of Science, Tohoku University,
Aoba-ku, Sendai 980-8578, Japan. E-mail: tobita@m.tains.tohoku.ac.jp
† Dedication to Professor Emeritus Keiichiro Fukumoto on the occasion of his 75th
birthday
Abstract – Cyclotriphosphazenes having p-tolylethynyl and chloro substituents
N3P3{CC(p-Tol)}nCl6–n (1a: n = 2, 1b: n = 4; p-Tol = p-tolyl) were synthesized
by the reaction of hexachlorocyclotriphosphazene (NPCl2)3 with 2 equiv of
LiCC(p-Tol) in THF. 1a and 1b were characterized by spectroscopic methods
and elemental analyses. The reactions of 1a and 1b with octacarbonyldicobalt
Co2(CO)8 produced cobalt clusters containing tetrahedral C2Co2(CO)6(p-Tol)
cluster units; namely, tetranuclear cluster N3P3{C2Co2(CO)6(p-Tol)}2Cl4 (2) and
hexanuclear cluster N3P3{C2Co2(CO)6(p-Tol)}3{CC(p-Tol)}Cl2 (3). Crystal
structures of 1a and 2 were determined by X-ray crystallography.
INTRODUCTION
Functionalized cyclotriphosphazenes are attractive for their application to a multi-site-coordination ligand
in coordination and organometallic chemistry.1 Cyclotriphosphazenes (NPX2)3 have six exocyclic
substituents X on the three phosphorus atoms (Chart 1) and can be tailored by functionalization of the
substituents X with coordinating groups to construct multi-site-coordination ligands. For example,
cyclotriphosphazene ligands having N-donor substituents such as pyrazolyl, pyridyloxy, and amino
groups have been extensively investigated in coordination chemistry of transition metals.1 One of the
unique features of the cyclotriphosphazene ligands is their potential utility as bridging ligands for the
synthesis of multinuclear metal complexes.
Since an alkynyl group acts as a ligand to form organometallic complexes by coordination of the CC
bond to transition metals, we have aimed at the synthesis of cyclotriphosphazenes having plural alkynyl

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HETEROCYCLES, Vol. 77, No. 2, 2009
groups. Although the synthesis of several alkynyl-substituted cyclotriphosphazenes2–5 and their reactivity
toward cobalt and iron complexes2,5–9 have been investigated, cyclotriphosphazenes having more than two
alkynyl substituents have not yet been synthesized. To prepare cyclotriphosphazenes having different
numbers of alkynyl groups, we have used
a
salt elimination reaction between
hexachlorocyclotriphosphazene (NPCl2)3 and alkynyllithium. As the closely related works, Chivers2 and
Allen et al.4,5 have reported the reactions of hexafluorocyclotriphosphazene (NPF2)3 with alkynyllithium
reagents LiCCR
(R
=
Ph, SiMe3, Me, n-Bu) giving mono- and disubstituted
alkynylfluorocyclotriphosphazenes N3P3(CCR)nF6–n (n = 1, 2). Hexachlorocyclotriphosphazene (NPCl2)3
is thought to be a more convenient starting material compared to the fluoride analog (NPF2)3, since the
latter is a volatile liquid and is usually derived from (NPCl2)3.10 However, to the best of our knowledge,
the reaction of (NPCl2)3 with alkynyllithium has not been used for P–C(alkynyl) bond formation,11
probably because the reaction of (NPCl2)3 with organolithium reagents usually results in a complicated
mixture accompanied by the ring cleavage of the cyclotriphosphazene moiety.2,12 Herein, we describe the
synthesis of alkynylchlorocyclotriphosphazenes having two or four p-tolylethynyl groups by the reaction
between (NPCl2)3 and p-tolylethynyllithium. We also describe the reactions of the
alkynylchlorocyclotriphosphazenes with octacarbonyldicobalt that give tetra- and hexanuclear cobalt
clusters.
X
X
P
N
N
N
P
P
X
X
X
X
Chart 1. Cyclotriphosphazenes (NPX2)3 (X = various substituents).
RESULTS AND DISCUSSION
Preparation of alkynylchlorocyclotriphosphazenes 1a and 1b
Treatment of hexachlorocyclotriphosphazene (NPCl2)3 with 2 equiv of LiCC(p-Tol) in THF gave a
mixture containing bis(p-tolylethynyl)tetrachlorocyclotriphosphazene N3P3{CC(p-Tol)}2Cl4 (1a) and
tetrakis(p-tolylethynyl)dichlorocyclotriphosphazene N3P3{CC(p-Tol)}4Cl2 (1b) in ca. 6 : 1 molar ratio
(eq. 1).13 Compounds 1a and 1b in the mixture were separated by silica gel flash chromatography14 and
isolated in 54 and 5% yields, respectively. 1a and 1b are both one of the geminal isomers, which contain
only P{CC(p-Tol)}2 and PCl2 moieties but no P{CC(p-Tol)}Cl moieties.15,16 In the 31P{1H} NMR
spectrum of the reaction mixture, no signals were observed for cyclotriphosphazenes having a
P{CC(p-Tol)}Cl moiety, i.e., non-geminal isomers of 1a and 1b as well as mono- or trisubstituted
cyclotriphosphazenes (vide infra). It has been reported that the reaction of (NPF2)3 with 2 equiv of
LiCCPh
in
diethylether
afforded
the
geminal
isomer
of

HETEROCYCLES, Vol. 77, No. 2, 2009
1173
bis(phenylethynyl)tetrafluorocyclotriphosphazene N3P3(CCPh)2F4 almost selectively,2,4 but, in this case,
formation of a small amount of non-geminal isomers was also observed.4
p-Tol
p-Tol
p-Tol
p-Tol
C
C
C
C
C
C
Cl Cl
P
C C
P
P
N
P
N
P
N
P
N
N
N
P
(1)
+
2
+
p-Tol
C
C
Li
P
P
Cl
Cl
Cl
Cl
C
C
THF
Cl
Cl
Cl
Cl
Cl
Cl
N
N
N
C
p-Tol
C
1a
1b
p-Tol
Compounds 1a and 1b were characterized by spectoroscopic methods (NMR, IR, and MS) and elemental
1
13
analyses. In the H and C{1H} NMR spectroscopy, 1a and 1b show only one set of the signals for the
p-tolylethynyl groups. This indicates that all the p-tolyl groups in 1a and also in 1b are equivalent. The
31P{1H} NMR spectrum of 1a exhibits a doublet and a triplet signal. The doublet signal appears at 19.3
ppm and, since the chemical shift is comparable to that of (NPCl2)3 (20.5 ppm), it is assignable to the
chloro-substituted phosphorus atoms. The triplet signal at –32.1 ppm is assignable to the
p-tolylethynyl-substituted phosphorus atom, and the chemical shift is similar to that for the geminal
isomer of N3P3(CCPh)2F4 (–23.2 ppm).4 Therefore, the replacement of chloro groups in (NPCl2)3 by
p-tolylethynyl groups results in the considerable upfield shift by 52.6 ppm of the 31P signal in 1a.
Similarly, the 31P{1H} NMR spectrum of 1b shows a doublet signal (–31.9 ppm) of the
p-tolylethynyl-substituted phosphorus atoms and a triplet signal (18.9 ppm) of the chloro-substituted
phosphorus atom. Since the 31P{1H} NMR spectrum of (phenylethynyl)pentafluorocyclotriphosphazene
N3P3(CCPh)F5 shows the signal of the phosphorus atom in the P(CCPh)F moiety at 6.0 ppm,4 similar
chemical
shifts
are
expected
for
those
in
P{CC(p-Tol)}Cl
moieties
of
(p-tolylethynyl)chlorocyclotriphosphazenes, if any. However, in the 31P{1H} NMR spectrum of the
reaction mixture as well as those of 1a and 1b, there are no signals in the region between 15 and –25 ppm.
This suggests that neither non-geminal isomers of 1a and 1b nor mono- or trisubstituted
cyclotriphosphazenes were obtained as mentioned above. These NMR observations are consistent with
the geminal configuration of 1a and 1b. The IR spectra of 1a and 1b exhibit a CC stretching band at
2179 (1a) and 2177 (1b) cm–1.
The crystal structure of 1a was unequivocally determined by X-ray crystallography (Figure 1, Table 1).
The N3P3 ring is puckered in a chair-type geometry: P1 and N2 deviate from the mean plane of P2, P3,
N1, and N3 by 0.37 and –0.28 Å, respectively. The P–N bonds for the p-tolylethynyl-substituted
phosphorus atom P1 [P1–N1: 1.6128(17) Å, P1–N3: 1.6088(17) Å] are longer than the other P–N bonds
for the chloro-substituted phosphorus atoms P2 and P3 [1.5644(17)–1.5877(17) Å] that are close to those
in (NPCl2)3 [av. 1.581(3) Å].17 This elongation is attributable to the electron donation of the alkynyl

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HETEROCYCLES, Vol. 77, No. 2, 2009
groups to the phosphorus atom P1 as also observed in several mono- and diorgano-substituted
cyclotriphosphazenes.18,19 The N1–P1–N3 angle [115.13(9)°] is narrower than the other N–P–N angles
[av. 119.17(9)°]. Similar reduction of the corresponding N–P–N angles was observed in geminally
substituted dialkyl- or diarylcyclotriphosphazenes N3P3R2Cl4 (R = alkyl, aryl).19 We could not get single
crystals of 1b suitable for a full X-ray structure analysis, but a tentative analysis using a low-quality
crystal of 1b revealed a N3P3 ring structure containing four p-tolylethynyl and two chloro groups bonded
geminally to phosphorus atoms.
Figure 1. Crystal structure of 1a. Thermal ellipsoids are drawn at the 50% probability level, and all
hydrogen atoms are omitted for clarity.
Table 1. Selected bond distances (Å) and angles (°) in 1a.
P1–N1
P2–N2
P1–C1
P2–Cl2
C1–C2
1.6128(17)
1.5857(17)
1.731(2)
2.0193(8)
1.196(3)
P1–N3
P3–N2
P1–C10
P3–Cl3
C10–C11
1.6088(17)
1.5877(17)
1.741(2)
1.9792(8)
1.202(3)
P2–N1
P3–N3
P2–Cl1
P3–Cl4
1.5644(17)
1.5735(17)
1.9823(8)
2.0179(9)
N1–P1–N3
P1–N1–P2
C1–P1–C10
P1–C1–C2
115.13(9)
119.62(10)
105.35(10)
170.39(19)
N1–P2–N2
P2–N2–P3
Cl1–P2–Cl2
P1–C10–C11
119.10(9)
117.65(10)
100.76(3)
167.83(19)
N2–P3–N3
P1–N3–P3
Cl3–P3–Cl4
119.24(9)
118.03(10)
101.16(3)
To prepare more highly substituted cyclotriphosphazenes with p-tolylethynyl groups, the reaction of
(NPCl2)3 with ca. 6 equiv of LiCC(p-Tol) was investigated. But, the reaction resulted in a complicated
mixture. The 31P{1H} NMR spectrum of the reaction mixture shows only one sharp singlet signal at –31.3
ppm with weak intensity accompanied by unresolved broad signals in the region between –40 and 30 ppm.
The chemical shift of the singlet signal is comparable to those for the p-tolylethynyl-substituted

HETEROCYCLES, Vol. 77, No. 2, 2009
1175
phosphorus atoms in 1a and 1b, and thus the signal would be assignable to
hexakis(p-tolylethynyl)cyclotriphosphazene N3P3{CC(p-Tol)}6 (1c). However, the content of 1c in the
mixture is considerably low, and the isolation of the pure form of 1c has been unsuccessful (see
Experimental section). Undesired reactions, e.g., ring cleavage of cyclotriphosphazene,2,12 may have
predominantly occurred to form unidentified products.
Reactions of the ligand precursors 1a and 1b with Co2(CO)8
To estimate the ability of (p-tolylethynyl)cyclotriphosphazenes 1a and 1b as multidentate ligands, we
investigated the reactions of 1a and 1b with octacarbonyldicobalt, which is well known to react with an
alkyne molecule to give a Co2C2 cluster. Thus, the reaction of 1a with 2 equiv of Co2(CO)8 in toluene at
room temperature produced a tetranuclear cobalt cluster N3P3{C2Co2(CO)6(p-Tol)}2Cl4 (2) in 94% yield
(eq. 2). The structure of 2 was elucidated by spectroscopy (NMR, IR, and MS), elemental analysis, and
X-ray crystallography (vide infra). The 31P{1H} NMR spectrum of 2 shows two inequivalent signals: one
doublet at 17.0 ppm assigned to the chloro-substituted phosphorus atoms and one triplet at 26.6 ppm
assigned to the p-tolylethynyl-substituted phosphorus atom. The chemical shift of the latter signal is
similar to that for the alkynyl-substituted phosphorus atom in the geminal isomer of tetranuclear cobalt
cluster N3P3{C2Co2(CO)6(Ph)}2F4 (32.5 ppm).8 In comparison of the 31P resonances of 2 with those of 1a,
the former signal of PCl2’s is slightly (2.3 ppm) upfield shifted, while the latter signal is significantly
downfield shifted by 58.7 ppm due to the coordination of the alkynyl substituents to cobalt. The coupling
constant between the inequivalent phosphorus atoms (2JPP = 8.1 Hz) is considerably decreased compared
to 1a (2JPP = 45 Hz). Similar decrease of the P–P coupling constant has also been observed by conversion
of N3P3(CCPh)2F4 (2JPP = 91.1 Hz) to cluster N3P3{C2Co2(CO)6(Ph)}2F4 (2JPP = 50.1 Hz).4,8 In the IR
spectrum of 2, the CC stretching band observed in 1a (2179 cm−1) disappeared and a new band
assignable to the C–C stretching of Co2C2 cluster units appeared at 1576 cm−1.
p-Tol
p-Tol
(OC)3Co
C
C
Co(CO)3
2 Co2(CO)8
C
C
(OC)3Co
Co(CO)3
1a
(2)
P
N
P
N
P
toluene
Cl
Cl
Cl
Cl
N
2
The X-ray structure analysis of the tetranuclear cobalt cluster 2 confirmed the molecular structure
consisting of a N3P3 6-membered ring and two Co2C2 tetrahedral cluster units (Figure 2, Table 2). This is
the first detailed report on the crystal structure analysis of bis(hexacarbonyldicobalt) complexes of
dialkynylcyclotriphosphazenes. The N3P3 ring is slightly puckered: P2 and N2 deviate from the

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HETEROCYCLES, Vol. 77, No. 2, 2009
least-squares plane of P1, P3, N1, and N3 by 0.16 and 0.27 Å, respectively. The N3P3-ring distortion seen
in the P–N bonds and N–P–N angles are similar to that in 1a. Thus, the P1–N1 and P1–N3 bonds [av.
1.616(2) Å] are longer than the other P–N bonds [av. 1.573(2) Å], and the N1–P1–N3 angle [115.16(9)°]
is narrower than the other N–P–N angles [av. 119.6(1)°]. The considerable decrease of the s-character in
the alkynyl CC bonds in 2 compared to the corresponding free ligand 1a leads to the geometric changes
in the P–CC moieties as follows: longer P1–C bond distances in 2 [av. 1.776(2) Å] compared to those in
1a [av. 1.736(2) Å], narrower P1–C1–C2 and P1–C16–C17 angles in 2 [av. 144.4(2)°] compared to the
corresponding P–C–C angles in 1a [av. 169.1(2)°], and elongation of the alkynyl C–C bonds by ca. 0.15
Å from 1a to 2. The wider C1–P1–C16 angle [109.18(10)°] compared to the corresponding angle in 1a
[C1–P1–C10: 105.35(10)°] reflects the larger steric repulsion between the Co2C2 units in 2.
Figure 2. Crystal structure of 2. Thermal ellipsoids are drawn at the 50% probability level, and all
hydrogen atoms are omitted for clarity.
Table 2. Selected bond distances (Å) and angles (°) in 2.
Co1–Co2
Co1–C2
Co3–C16
Co4–C17
P1–N1
P2–N2
P1–C1
P2–Cl2
2.4590(7)
1.985(2)
1.961(2)
1.971(2)
1.6129(18)
1.582(2)
1.773(2)
2.0032(10)
Co3–Co4
Co2–C1
Co3–C17
C1–C2
P1–N3
P3–N2
2.4672(7)
1.962(2)
1.969(2)
1.346(3)
1.6184(18)
1.579(2)
1.779(2)
2.0146(10)
Co1–C1
Co2–C2
Co4–C16
C16–C17
P2–N1
P3–N3
P2–Cl1
P3–Cl4
1.992(2)
1.964(2)
1.982(2)
1.347(3)
1.5648(18)
1.5678(18)
1.9999(10)
1.9925(11)
P1–C16
P3–Cl3
N1–P1–N3
P1–N1–P2
C1–P1–C16
P1–C1–C2
115.16(9)
122.57(11)
109.18(10)
145.55(18)
N1–P2–N2
P2–N2–P3
Cl1–P2–Cl2
P1–C16–C17
119.60(10)
119.29(12)
100.37(4)
143.30(17)
N2–P3–N3
P1–N3–P3
Cl3–P3–Cl4
119.51(10)
121.92(11)
99.87(4)

HETEROCYCLES, Vol. 77, No. 2, 2009
1177
The reaction of 1b with excess Co2(CO)8 (ca. 5 equiv) in C6D6 at room temperature in a sealed NMR tube
1
was monitored by H NMR spectroscopy. The spectroscopic analysis of the final reaction mixture
indicates the formation of hexanuclear cluster having an unreacted p-tolylethynyl group
N3P3{C2Co2(CO)6(p-Tol)}3{CC(p-Tol)}Cl2 (3) as a major product in 88% NMR yield (eq. 3).20 No
signals assignable to octanuclear cluster N3P3{C2Co2(CO)6(p-Tol)}4Cl2, in which all the four alkynyl
groups are coordinated to cobalt atoms, have observed. The incomplete reaction is probably due to the
steric hindrance in cluster 3 that prevents further complexation of a Co2(CO)6 fragment with the
1
remaining p-tolylethynyl group. The H NMR spectrum of product 3 shows four inequivalent methyl
signals of the p-tolylethynyl groups with 1 : 1 : 1 : 1 intensity ratio. The 31P{1H} NMR spectrum of 3
exhibits three inequivalent signals of the phosphrous atoms in the N3P3 ring at 1.1, 17.7, and 24.1 ppm.
31
Comparing the P NMR chemical shifts of 3 with those in 2 (PCl2: 17.0 ppm, P{C2Co2(CO)6(p-Tol)}2:
26.6 ppm), the signals at 17.7 and 24.1 ppm can be assigned to the phosphorus atoms in the PCl2 and
P{C2Co2(CO)6(p-Tol)}2 moieties, respectively. The third signal at 1.1 ppm is assignable to the
phosphorus atom in the partially complexed P{C2Co2(CO)6(p-Tol)}{CC(p-Tol)} moiety, which is
downfield shifted by 33 ppm compared to the signal (–31.9 ppm) of the p-tolylethynyl-substituted
phosphorus atoms in 1b. The analogous 32 ppm downfield-shift by coordination of one alkynyl group on
cyclotriphosphazene to
a
Co2(CO)6 fragment has been reported for the reaction of
(phenylethynyl)pentafluorocyclotriphosphazene
N3P3(CCPh)F5 with Co2(CO)8 to give
N3P3{C2Co2(CO)6(Ph)}F5.8 In the high-resolution electrospray mass spectrometry of the reaction mixture,
the peak (m/z = 1545.5847) assignable to the Na+ adduct of the parent molecule was observed when NaI
was added to the sample. The IR spectrum of the reaction mixture shows four terminal CO stretching
bands of 3 in the range of 2033−2100 cm−1. These observations support the structural characterization of
3. Since the C6D6 or toluene solution of product 3 is thermally unstable under nitrogen atmosphere at
room temperature, we have not succeeded in isolation of 3 from the reaction mixture in a synthetic-scale
experiment. This makes the further characterization of 3 difficult. The thermal lability would be caused
by the facile dissociation of CO ligands in 3. This was supported by the experimental result that the
decomposition of 3 in toluene solution was accelerated under reduced pressure.
Cl Cl
Co(CO)3
Co(CO)3
P
(OC)3Co
N
P
N
P
Co(CO)3
C
C
excess Co2(CO)8
C6D6
C
C
N
C
1b
(3)
p-Tol
C
C
p-Tol
p-Tol
C
(OC)3Co
p-Tol
Co
(CO)3
3

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HETEROCYCLES, Vol. 77, No. 2, 2009
CONCLUSION
We synthesized (p-tolylethynyl)chlorocyclotriphosphazenes 1a and 1b by the salt elimination reaction
between (NPCl2)3 and LiCC(p-Tol). The products were isolated in pure form and characterized. The
capability of 1a and 1b as multidentate ligands was confirmed by their reactions with Co2(CO)8, where
tetra- and hexanuclear cobalt clusters 2 and 3 were obtained from 1a and 1b, respectively. It is worth
noting that 1b is the first example of the cyclotriphosphazene having four alkynyl groups and, of course,
the hexanuclear structure of the cobalt cluster 3 is unprecedented. Our ongoing works are (1) exploration
of a high-yield synthesis of hexaalkynylcyclotriphosphazene 1c, (2) isolation and full-characterization of
hexanuclear cobalt cluster 3, and (3) investigation of the reactions of p-tolylethynyl-substituted
phosphazenes 1a and 1b with other transition-metal complexes that provide different multinuclear
clusters.
EXPERIMENTAL
General Procedures
All manipulations of air- and moisture-sensitive compounds were carried out under an inert atmosphere in
a N2-filled glovebox or using standard high-vacuum-line and Schlenk techniques. CDCl3 was dried and
vacuum-transferred from CaH2, and then stored under nitrogen over 4 Å molecular sieves. Hexane and
toluene were dried over sodium/benzophenone and distilled before use. Dehydrated THF was purchased
from Kanto Chemical Co., Inc. and used without further purification. Hexachlorocyclotriphosphazene
(NPCl2)3 was recystallized with hot hexane. 4-Ethynyltoluene (Kanto Chemical) was dried over CaH2 and
distilled prior to use. Octacarbonyldicobalt Co2(CO)8 (Kanto Chemical) was purchased and used as
received. Flash chromatography14 was performed using silica gel 60N (Kanto Chemical, 40-50 m,
spherical, neutral) or activated alumina (Wako Pure Chemicals Industries, Ltd., 45 m). 1H, 13C{1H}, and
31P{1H} NMR spectra were recorded on a Bruker AVANCE-300 Fourier transform spectrometer, and
chemical shifts were reported in parts per million. The residual proton (C6D5H: 7.15 ppm, CHCl3: 7.24
ppm) and the carbon (C6D6: 128.0 ppm, CDCl3: 77.0 ppm) resonances of deuterated solvents were used
as internal references for 1H and 13C resonances, respectively. Aromatic carbon or proton is abbreviated to
ArC or ArH. 31P{1H} NMR chemical shifts were referenced to 85% H3PO4 as an external standard.
Infrared spectra were recorded using a HORIBA FT-730 spectrometer. High-resolution mass spectra
(HRMS) were collected on a Bruker Daltonics APEX-(III) spectrometer operating in the electrospray
ionization (ESI) mode, when NaI was added to the sample. Elemental analyses were carried out using a
Yanaco MT-6 and a Yanaco HNS-15/HSU-20 microanalyzers. Mass spectrometric analyses and
elemental analyses were performed at the Research and Analytical Center for Giant Molecules, Tohoku
University.

HETEROCYCLES, Vol. 77, No. 2, 2009
1179
Synthesis of N3P3{CC(p-Tol)}2Cl4 (1a) and N3P3{CC(p-Tol)}4Cl2 (1b)
A THF/hexane solution of p-tolylethynyllithium LiCC(p-Tol) was prepared as follows: To a solution of
4-ethynyltoluene (1.165 g, 10.03 mmol) in THF (30 mL) was slowly added n-BuLi (1.52 M in hexane,
7.5 mL, 11 mmol) via a syringe at ca. −90 °C, and then the mixture was stirred for 1 h at this temperature.
To this solution of LiCC(p-Tol) was added dropwise a solution of (NPCl2)3 (1.742 g, 5.011 mmol) in
THF (40 mL) at −80 °C for 15 min. The yellow reaction mixture was allowed to warm up to room
temperature. The reaction was monitored by 31P{1H} NMR spectroscopy until the relative intensity of
signals became constant. After stirring at room temperature overnight, the dark-brown solution was
evaporated under vacuum. The dark-brown residue was extracted three times with toluene (25, 7.5, 7.5
mL), and the extracts were centrifuged. The supernatants were combined and evaporated. The residue was
separated by flash chromatography on silica gel (eluent: toluene/hexane 1 : 1), and three fractions were
obtained. Evaporation of the first colorless fraction gave a colorless solid, and then recrystallization of the
solid from toluene gave colorless crystals of 1a in 54% yield (1.37 g, 2.71 mmol). From the second
yellow fraction, an unidentified yellow oil (0.047 g) was obtained. From the third fraction, pale-yellow
crystals of 1b (0.180 g, 0.270 mmol) were obtained in 5% yield. The fourth fraction was obtained by
elution with THF and was evaporated to give unidentified products as a brown oil (0.765 g).
Data for 1a: 1H NMR (300 MHz, CDCl3):  2.37 (s, 3H, CH3), 7.18 (d, 2H, 3JHH = 8.0 Hz, ArH), 7.49 (d,
2H, 3JHH = 8.0 Hz, ArH). 31P{1H} NMR (121.5 MHz, CDCl3):  –32.1 (t, 2JPP = 45 Hz, P{CC(p-Tol)}2),
19.3 (d, 2JPP = 45 Hz, PCl2). 13C{1H} NMR (75.5 MHz, CDCl3):  22.2 (s, CH3), 83.0 (dt, 1JCP = 279 Hz,
2
4
3
3JCP = 7.6 Hz, CC(p-Tol)), 102.8 (dt, JCP = 54 Hz, JCP ~ 2 Hz, CC(p-Tol)), 116.4 (d, JCP = 5.3 Hz,
4
ArC-ipso), 129.7 (s, ArC-meta), 133.1 (d, JCP = 2.0 Hz, ArC-ortho), 142.3 (s, ArC-para). IR
(KBr-pellet): 2179 (s, CC), 1604 (w), 1508 (w), 1228 (s, NP), 1196 (s, NP), 874 (m), 816 (w), 611 (m),
565 (m), 519 (m), 463 (m), 424 (m) cm–1. HRMS (ESI): m/z calcd for C18H14Cl4N3P3Na: 527.9047,
found: 527.9046 [M+Na]+. Anal. Calcd (%) for C18H14Cl4N3P3: C, 42.63; H, 2.78; N, 8.29; Cl, 27.97.
Found: C, 42.59; H, 2.97; N, 8.18; Cl, 27.66.
Data for 1b: 1H NMR (300 MHz, CDCl3):  2.35 (s, 3H, CH3), 7.11 (d, 2H, 3JHH = 8.0 Hz, ArH), 7.45 (d,
2H, 3JHH = 8.0 Hz, ArH). 31P{1H} NMR (121.5 MHz, CDCl3):  –31.9 (d, 2JPP = 41 Hz, P{CC(p-Tol)}2),
18.9 (t, 2JPP = 41 Hz, PCl2). 13C{1H} NMR (75.5 MHz, CDCl3):  21.7 (s, CH3), 84.4 (ddd, 1JCP = 275 Hz,
3JCP = 7.8, 0.9 Hz, CC(p-Tol)), 99.9–101.3 (m, CC(p-Tol)), 116.8 (virtual t, JCP = 2.6 Hz, ArC-ipso),
129.2 (s, ArC-meta), 132.7 (s, ArC-ortho), 141.2 (s, ArC-para). IR (KBr-pellet): 2177 (s, CC), 1604 (w),
1508 (w), 1190 (s, NP), 1174 (s, NP), 868 (m), 839 (w), 814 (m), 781 (w), 768 (w), 611 (m), 573 (m),
563 (m), 546 (m), 538 (m), 474 (m), 459 (m) cm–1. HRMS (ESI): m/z calcd for C36H28Cl2N3P3Na:
688.0765, found: 688.0768 [M+Na]+. Anal. Calcd (%) for C36H28Cl2N3P3: C, 64.88; H, 4.23; N, 6.31; Cl,

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HETEROCYCLES, Vol. 77, No. 2, 2009
10.63. Found: C, 64.53; H, 4.53; N, 6.22; Cl, 10.38.
The reaction of (NPCl2)3 with ca. 6 equiv of LiCC(p-Tol)
A solution of p-tolylethynyllithium LiCC(p-Tol) was prepared by slow addition of n-BuLi (1.57 M in
hexane, 14 mL, 22 mmol) to a solution of 4-ethynyltoluene (2.36 g, 20.3 mmol) in THF (18 mL) at 0 °C
followed by stirring of the mixture for 1 h. The mixture was allowed to warm to room temperature, and a
solution of (NPCl2)3 (1.16 g, 3.34 mmol) in THF (5 mL) was added dropwise to the mixture over 30 min.
After stirring for 3.5 h at room temperature, the reaction was quenched by adding methanol (3.5 mL) at
0 °C. Evaporation of volatiles under vacuum gave a dark-brown oil (5.79 g). The residual oil was
extracted with toluene (65 mL), and the extract was centrifuged. After the supernatant was concentrated
under vacuum, the dark-brown residue (2.96 g) was separated by flash chromatography on alumina
(eluent: THF/toluene 1 : 300). Evaporation of the second fraction gave a yellow oil, and then trituration
and washing of the solid with hexane yielded
a
yellow powder containing
hexakis(p-tolylethynyl)cyclotriphosphazene N3P3{CC(p-Tol)}6 (1c) as a major component (0.020 g).
Attempt to isolate pure 1c from the yellow powder was unsuccessful.
Data assignable to 1c in the yellow powder: 1H NMR (300 MHz, CDCl3):  2.33 (s, 3 H, CH3), 7.06 (d, 2
H, 3JHH = 8.1 Hz, ArH), 7.42 (d, 2 H, JHH = 8.1 Hz, ArH). 31P{1H} NMR (121.5 MHz, CDCl3):  –31.3
3
(s, P{CC(p-Tol)}2).
Synthesis of N3P3{C2Co2(CO)6(p-Tol)}2Cl4 (2)
A solution of 1a (0.469 g, 0.925 mmol) in toluene (12 mL) was added to a solution of Co2(CO)8 (0.704 g,
2.06 mmol) in toluene (12 mL) with stirring. After stirring the mixture for 40 min at room temperature,
volatiles were removed under vacuum. The dark-red residue was dissolved in a mixture of CH2Cl2 (8 mL)
and hexane (4 mL). Cooling of the solution at −30 °C afforded dark-red crystals as the first crop (0.747 g,
0.692 mmol). Concentration and cooling of the mother liquor at −30 °C gave the second crop (0.194 g,
0.180 mmol). Total yield: 94%.
Data for 2: 1H NMR (300 MHz, CDCl3):  2.31 (s, 3 H, CH3), 7.00 (d, 2 H, 3JHH = 8.0 Hz, ArH), 7.48 (d,
3
31
2
2 H, JHH = 8.0 Hz, ArH). P{1H} NMR (121.5 MHz, CDCl3):  17.0 (d, JPP = 8.1 Hz, PCl2), 26.6 (t,
2JPP = 8.1 Hz, P{C2Co2(CO)6(p-Tol)}2). 13C{1H} NMR (75.5 MHz, CDCl3):  21.5 (s, Me), 76.8 (dt, 1JCP
3
= 149 Hz, JCP ~ 4 Hz, C−C(p-Tol)), 100.6 (s, C−C(p-Tol)), 129.6 (s, ArC), 130.1 (s, ArC), 133.4 (s,
ArC), 138.9 (s, ArC), 197.8 (br s, CO). IR (KBr-pellet): 2102 (m, CO), 2094 (m, CO), 2063 (s, CO),
2044 (s, CO), 2027 (s, CO), 2015 (s, CO), 2008 (m, CO), 1576 (w, C−C), 1491 (w), 1209 (m, NP), 1186
(m, NP), 582 (m), 569 (w), 511 (m), 492 (w) cm–1. HRMS (ESI): m/z calcd for C30H14O12Cl4N3P3Co4Na:
1099.5765, found: 1099.5759 [M+Na]+. Anal. Calcd (%) for C30H14O12Cl4N3P3Co4: C, 33.40; H, 1.38; N,
3.89; Cl, 13.14. Found: C, 32.99; H, 1.38; N, 3.80; Cl, 12.89.
Monitoring the reaction of 1b with excess (ca. 5 equiv) Co2(CO)8

HETEROCYCLES, Vol. 77, No. 2, 2009
1181
An NMR tube with a J. Young valve (5 mm o.d.) was charged with 1b (5 mg, 8 mol), (C5H5)2Fe (less
1
than 1 mg) as an internal standard, and C6D6 (0.46 mL). After measuring a H NMR spectrum of the
solution to determine the intensity ratio of 1b to (C5H5)2Fe, the solution was transferred to a Pyrex NMR
tube, and then the washing of the J. Young NMR tube with C6D6 (ca. 0.1 mL) was added. Co2(CO)8 (13
mg, 38 mol) was then added to the Pyrex NMR tube, and the C6D6 (ca. 0.1 mL) washing of the beaker
and funnel, which had been used for weighing and transferring Co2(CO)8, was also added. After the Pyrex
NMR tube was flame-sealed under vacuum, the mixture was allowed to stand at room temperature for 22
1
h. During that time, the reaction was monitored by H and 31P{1H} NMR spectroscopy, showing the
formation of N3P3{C2Co2(CO)6(p-Tol)}3{CC(p-Tol)}Cl2 (3) in 88% NMR yield. Then the tube was
opened, and the HRMS and IR spectrum of 3 in the C6D6 solution were measured.
Data for 3: 1H NMR (300 MHz, C6D6):  1.86 (s, 3 H, CH3), 1.96 (s, 3 H, CH3), 1.98 (s, 3 H, CH3), 2.03
(s, 3 H, CH3), 6.77 (d, 2 H, 3JHH = 8.0 Hz, ArH), 6.85 (d, 2 H, 3JHH = 8.3 Hz, ArH), 6.95 (d, 2 H, 3JHH
=
3
8.3 Hz, ArH), 6.97 (d, 2 H, 3JHH = 8.6 Hz, ArH), 7.57 (d, 2 H, JHH = 8.0 Hz, ArH), 7.85 (d, 2 H, 3JHH
=
8.6 Hz, ArH), 7.88 (d, 2 H, 3JHH = 8.3 Hz, ArH), 7.93 (d, 2 H, 3JHH = 8.3 Hz, ArH). 31P{1H} NMR (121.5
MHz, C6D6):  1.1 (dd, 2JPP = 6.1 Hz, 2JPP = 12.6 Hz, P{C2Co2(CO)6(p-Tol)}{CC(p-Tol)}), 17.7 (t, 2JPP
2
2
= 12.6 Hz, PCl2), 24.1 (dd, JPP = 6.1 Hz, JPP = 12.6 Hz, P{C2Co2(CO)6(p-Tol)}2). IR (C6D6): 2100 (w,
CO), 2092 (w, CO), 2069 (s, CO), 2033 (s, CO) cm–1. HRMS (ESI): m/z calcd for
C54H28O18Cl2N3P3Co6Na: 1545.5842, found: 1545.5847 [M+Na]+.
X-Ray crystal structure determination
X-Ray quality single crystals of 1a were obtained by recrystallization from toluene as colorless blocks
and those of 2 from CH2Cl2/hexane as dark-red blocks. Intensity data for the analysis were collected on a
Rigaku Saturn CCD diffractometer with graphite-monochromated Mo K radiation ( = 0.71070 Å)
under a cold nitrogen stream (T = 173 K). Numerical absorption corrections were applied to the data. The
structures were solved by direct method using the SHELXS-97 program21 for 1a or the Patterson method
using the DIRDIF-99 program22 for 2 and refined by full matrix least-squares techniques on all F2 data
with SHELXL-97.21 Anisotropic refinement was applied to all non-hydrogen atoms, and all the hydrogen
atoms were put at calculated positions. CCDC-700217 (1a) and 700218 (2) contain the supplementary
crystallographic data for this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Crystallographic data for 1a: C18H14Cl4N3P3, M = 507.03, monoclinic, space group P21/n (no. 14), a =
10.623(3) Å, b = 17.038(5) Å, c = 12.194(4) Å,  = 90.4320(13)°, V = 2207.0(12) Å3, Z = 4, Dcalc = 1.526
g cm−3, (Mo−K) = 0.76 mm−1, 15524 reflections measured, 4783 unique (Rint = 0.040), R1 = 0.044 and
wR2 = 0.082 (all data).
Crystallographic data for 2: C30H14Cl4Co4N3O12P3, M = 1078.87, triclinic, space group P-1 (no. 2), a =

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HETEROCYCLES, Vol. 77, No. 2, 2009
9.050(3) Å, b = 11.436(4) Å, c = 20.122(6) Å,  = 74.483(8)°,  = 79.287(9)°,  = 88.179(10)°, V =
1971.4(11) Å3, Z = 2, Dcalc = 1.818 g cm−3, (Mo−K) = 2.11 mm−1, 14183 reflections measured, 8395
unique (Rint = 0.030), R1 = 0.036 and wR2 = 0.066 (all data).
ACKNOWLEDGEMENTS
This work was supported by 2007 Research Grants from the Science and Technology Foundation of
Japan (JSTF).
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