Synthesis and characterization of novel fluorophosphazene-derived cobaltacyclopentadienyl metallacycles: Reagents for assembly of aryl-bridged fluorophosphazenes

Article abstract of DOI:10.1021/ic0609204

Reaction of (β-phenylethynyl)pentafluorocyclotriphosphazene, F ₅P₃N₃C≡CPh, with in situ generated η⁵-(MeOC(O)C₅H₄)Co(PPh₃) ₂ resulted in the formation of two isomers of cobaltacyclopentadienylmetallacycles, (η⁵- carbomethoxycyclopentadienyl)(triphenylphosphine)-2,5- bis(pentafluorocyclotriphosphazenyl)-3,4-diphenyl cobaltacyclopentadiene (1) and (η⁵-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,4- bis(pentafluorocyclotriphosphazenyl)-3,5-diphenyl cobaltacyclopentadiene (2), along with the sandwich compound [η⁵- carbomethoxycyclopentadienyl]-[η⁴-1,3- bis(pentafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene]cobalt (3). Formation of cobaltacyclopentadienylmetallacycles or cyclobutadienylmetallocene having two fluorophosphazene units on vicinal carbon atoms of the rings was not observed in this reaction. Reaction of 1 with diphenylacetylene resulted in the formation of a novel aryl-bridged fluorophosphazene, 1,4- bis(pentafluorocyclotriphosphazenyl)-2,3,5,6-tetraphenyl benzene (4), and the conversion of cobaltametallacycle to the sandwich compound, [η⁵- (MeOC(O)C₅H₄]Co(η⁴-C₄Ph ₄) (5). Reaction of 1 with phenylacetylene resulted in the formation of aryl-bridged fluorophosphazene, 1,4-bis(pentafluorophosphazenyl)-2,3,5,- triphenyl benzene (6). New compounds 1-4 were structurally characterized. In compound 1, the two fluorophosphazene units were oriented in gauche form with respect to each other. However, in compounds 2 and 3, they were eclipsed to each other, and in compound 4, they were oriented anti to each other.

Full text of DOI:10.1021/ic0609204

Inorg. Chem. 2006, 45, 7835−7842
Synthesis and Characterization of Novel Fluorophosphazene-Derived
Cobaltacyclopentadienyl Metallacycles: Reagents for Assembly of
Aryl-Bridged Fluorophosphazenes
Muthiah Senthil Kumar, Shailesh Upreti, and Anil J. Elias*
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas,
New Delhi 110 016, India
Received May 26, 2006
Reaction of (
(O)C5H4)Co(PPh3)2 resulted in the formation of two isomers of cobaltacyclopentadienylmetallacycles,
carbomethoxycyclopentadienyl)(triphenylphosphine)-2,5-bis(pentafluorocyclotriphosphazenyl)-3,4-diphenyl cobalta-
cyclopentadiene (1) and (
5-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,4-bis(pentafluorocyclotriphosphazenyl)-
3,5-diphenyl cobaltacyclopentadiene (2), along with the sandwich compound [
5-carbomethoxycyclopentadienyl]-
4-1,3-bis(pentafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene]cobalt (3). Formation of cobaltacyclopentadienyl-
â
-phenylethynyl)pentafluorocyclotriphosphazene, F5P3N3C
≡
CPh, with in situ generated η
5-(MeOC-
(
η5
-
η
η
[η
metallacycles or cyclobutadienylmetallocene having two fluorophosphazene units on vicinal carbon atoms of the
rings was not observed in this reaction. Reaction of 1 with diphenylacetylene resulted in the formation of a novel
aryl-bridged fluorophosphazene, 1,4-bis(pentafluorocyclotriphosphazenyl)
conversion of cobaltametallacycle to the sandwich compound, [
5-(MeOC(O)C5H4]Co(
with phenylacetylene resulted in the formation of aryl-bridged fluorophosphazene, 1,4-bis(pentafluorophosphazenyl)
2,3,5,-triphenyl benzene (6). New compounds 1 4 were structurally characterized. In compound 1, the two
−
2,3,5,6-tetraphenyl benzene (4), and the
η
η
4-C4Ph4) (5). Reaction of 1
−
−
fluorophosphazene units were oriented in gauche form with respect to each other. However, in compounds 2 and
3, they were eclipsed to each other, and in compound 4, they were oriented anti to each other.
Introduction
well-known trimeric phosphazenes, N3P3Cl6 and N3P3F6,
differ significantly in their stability, volatility, and reactivity,6
and the latter has been the more favored molecule for making
organometallic derivatives of phosphazenes because of lesser
complexity in its reactions, resulting from the higher stability
of the P-F bonds. Reported examples of organometallic
fluorophosphazene compounds mostly include metallocenyl
Cyclic phosphazenes continue to attract considerable
interest not only from the perspective of being precursors
for phosphazene-based polymers 1 but also for a host of other
applications. Recent reports indicate their potential as useful
molecules for synthesizing ionic liquids and high-energy-
density materials,2 as highly stable cores for the design of
dendrimers and air-stable inclusion adducts,3 and as nodal
ligands in coordination compounds and polymers.4,5 The two
7
8
derivatives with Cp-P3N3F5 or Ph-P3N3F5 bonds, such
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* To whom correspondence should be addressed. E-mail: eliasanil@
gmail.com.
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10.1021/ic0609204 CCC: $33.50
Published on Web 08/22/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 19, 2006 7835

Kumar et al.
as ferrocenyl or bisbenzene chromium derivatives, molecules
with a direct metal-P3N3F5 bond,9 or those having a spacer
between a cyclopentadienyl and phosphazene moiety.10 Allen
and co-workers have recently shown that pentafluorophos-
phazenyl-substituted acetylenes such as F5P3N3CtCPh can
be interesting reagents for the synthesis of novel fluorophos-
phazene-derived clusters by their reactions with metal
carbonyls such as Co2(CO)8 and Fe2(CO)9.11 In a related
preliminary communication, they have also shown that
reactions of the half-sandwich compound, CpCo(CO)2, with
F5P3N3CtCPh results in a novel fluorophosphazene-
substituted cyclobutadiene cobalt sandwich compound, along
with a few other phosphazene-derived molecules.12
η5-(MeOC(O)C5H4)Co(PPh3)2 with fluorophosphazene-de-
rived acetylenes to see the possibility of making bisfluoro-
phosphazene-derived cobaltametallacycles. The facts that the
bisphosphine complex η5-(MeOC(O)C5H4)Co(PPh3)2, unlike
the carbonyl complex, can be prepared in situ starting with
the inexpensive Co(PPh3)3Cl and that the ester moiety on
the cyclopentadienyl group has the potential for further
conversion to useful functional groups were added attractions
in pursuing this reaction. Herein, we report the results of
our studies on the reactions of (MeOC(O)C5H4)Co(PPh3)2
with F5P3N3CtCPh.
Experimental Section
It has been observed that reactions of the half-sandwich
compound CpCo(CO)2 with disubstituted acetylenes differ
significantly when compared to that of phosphine complex
CpCo(PPh3)2.13,14 Whereas the former, without exception,
results in metallocenes with η5-cyclopentadienyl-η4-cyclo-
butadiene groups, the latter has also been found to form PPh3
stabilized cobaltacyclopentadiene metallacycles, depending
upon the reaction conditions and nature of substituents on
the alkyne.15,16 These cobaltametallocycles are potential
precursors for making novel acetylene-trimerized aryl com-
pounds as well as [η5-Cp]Co[η4-R4C4] metallocenes.
Our interest in this chemistry stems from our previous
work in the synthesis and transformations of bridged and
ansa-substituted fluorinated phosphazenes with dialkoxy
substituents.6c,6d,10a In our search for novel examples of
bridged phosphazenes and ways to synthesize them, we were
keen to explore the reactions of the half-sandwich compound
General Methods. All manipulations of the complexes
were carried out using standard Schlenk techniques under a
nitrogen atmosphere. Tetrahydrofuran, xylene, and toluene
were freshly distilled from sodium benzophenone ketyl under
a nitrogen atmosphere and used. Sodium salt of car-
bomethoxycyclopentadiene,14 tris(triphenylphosphine)cobalt
chloride,17 and (â-phenylethynyl) pentafluorocyclotriphos-
phazene12 were prepared according to literature procedures.
Diphenyl acetylene, Dimethyl carbonate, and triphenylphos-
phine (Aldrich) were used as such.
Instrumentation. 1H and 13C {1H} spectra were recorded
on a Bruker Spectrospin DPX-300 NMR spectrometer at 300
and 75.47 MHz, respectively. 31P{1H} and 19F{1H} NMR
spectra were recorded on a Bruker Spectrospin DPX-400
NMR spectrometer at 161 and 376 MHz, respectively. IR
spectra in the range 4000-250 cm-1 were recorded on a
Nicolet Prote´ge 460 FT-IR spectrometer as KBr pellets.
Elemental analyses were carried out on a Carlo Erba CHNSO
1108 elemental analyzer. Mass spectra were recorded in the
FAB mode using a JEOL SX 102/DA-6000 mass spectrom-
eter.
X-ray Crystallography. Suitable crystals of compounds
1-4 were obtained by slow evaporation of their saturated
solutions in ethyl acetate/hexane solvent mixtures. X-ray
diffraction studies of crystals mounted on a capillary were
carried out on a BRUKER AXS SMART-APEX diffract-
ometer equipped with CCD area detector (KR ) 0.71073 Å,
graphite monochromator).18a Frames were collected at T )
298 K for compounds 1, 3, and 4 and at 100 K for compound
2 by ω, φ, and 2θ rotation with full quadrant data collection
strategy (four domains each with 600 frames) at 10 s per
frame with SAINT.18b The measured intensities were reduced
to F2 and corrected for absorption with SADABS.18b
Structure solution and refinement were carried out with the
SHELXTL package by direct methods.18c Non-hydrogen
atoms were refined anisotropically. All hydrogen atoms were
included in idealized positions, and a riding model was used
for the refinement. Images were created with the program
Diamond.18d For compound 1, some of the observed intensi-
(7) (a) Allcock, H. R.; Desorcie, J. L.; Riding, G. H. Polyhedron 1987,
6, 119-157. (b) Allcock, H. R.; Lavin, K. D.; Riding, G. H.; Suszko,
P. R.; Whittle, R. R. J. Am. Chem. Soc. 1984, 106, 2337-2347. (c)
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5, 2153-2154. (b) Allcock, H. R.; Dembek, A. A.; Bennet, J. L.;
Manners, I.; Parvez, M. Organometallics 1991, 10, 1865-1874.
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1983, 195, 1321-1327. (b) Allcock, H. R.; Greigger, P. P.; Wagner,
L. J. Inorg. Chem. 1981, 20, 716-722. (c) Greigger, P. P.; Allcock,
H. R. J. Am. Chem. Soc. 1979, 101, 2492-2493.
(10) (a) Muralidharan, K.; Elias, A. J. Inorg. Chem. 2003, 42, 7535-7543.
(b) Herberhold, M.; Hofmann, A.; Milius, W. Z. Anorg. Allg. Chem.
1997, 623, 1599-1608. (c) Nataro, C.; Myer, C. N.; Cleaver, W. M.;
Allen, C. W. J. Organomet. Chem. 2001, 637-639, 284-290.
(11) (a) Bahadur, M.; Allen, C. W.; Geiger, W. E.; Bridges, A. Can. J.
Chem. 2002, 80, 1393-1397. (b) Allen, C. W. Bahadur, M. J. Inorg.
Organomet. Polym. 1998, 8, 23-31.
(12) Allen, C. W.; Malik, P.; Bridges, A.; Desorcie, J.; Pellon, B.
Phosphorus, Sulfur Silicon Relat. Elem. 1990, 49-50, 433-436.
(13) (a) Varela, J. A.; Saa, C. Chem ReV. 2003, 103, 3787-3801. (b)
MacFarland, D. K.; Gorodetzer, R. J. Chem. Educ. 2005, 82, 109-
110. (c) Rausch, M. D.; Genetti, R. A. J. Org. Chem. 1970, 35, 3888-
3897. (d) Rausch, M.; D. Pure Appl. Chem. 1972, 30, 523-538.
(14) Stevens, A. M.; Richards, C. J. Organometallics 1999, 18, 1346-
1348.
(15) Goswami, A.; Meier, C.-J.; Pritzkow, H.; Siebert, W. Eur. J. Inorg.
Chem. 2004, 13, 2635-2645. (b) Schaefer, C.; Gleiter.; Rominger, F.
Organometallics 2004, 23, 2225-2227. (c) Laskoski, M.; Morton, J.
G. M.; Smith, M. D.; Bunz, U. H. F. Chem. Commun. 2001, 24, 2590-
2591.
(16) Wakatsuki, Y.; Nomura, O.; Kitaura, K.; Morokuma K.; Yamazaki,
H. J. Am. Chem. Soc. 1983, 105, 1907-1912. (b) Yasafuku, K.;
Yamazaki, H. J. Organomet. Chem. 1977, 127, 197-207. (c) Yam-
azaki, H.; Wakatsuki, Y. J. Organomet. Chem. 1977, 132, 157-167.
(17) Wakatsuki, Y.; Yamazaki, H. Inorg. Synth. 1989, 26, 189-200.
(18) (a) SMART: Bruker Molecular Analysis Research Tools, version 5.618;
Bruker Analytical X-ray Systems: Madison, WI, 2000. (b) Sheldrick,
G. M. SAINT-NT, version 6.04; Bruker Analytical X-ray Systems:
Madison, WI, 2001. (c) Sheldrick, G. M. SHELXTL-NT, version 6.10;
Bruker Analytical X-ray Systems: Madison, WI, 2000. (d) Klaus, B.
DIAMOND, version 1.2c; University of Bonn: Bonn, Germany, 1999.
7836 Inorganic Chemistry, Vol. 45, No. 19, 2006

Fluorophosphazene-DeriWed Cobaltcyclopentadienyl Metallacycles
1
ties were anomalously large because of contributions from
overlapping reflections of another minor component. The
imperfection in the crystal and room temperature data
collection has possibly resulted in relatively high values of
residual factors and standard uncertainties in compound 1.
The ester group present in the cyclopentadienyl ring of 2
shows disorder, and O1, O2, C1, and C2 atoms occupied
two crystallographically independent positions that could be
located from the additional residual electron density observed
in the difference map. The site occupancy factors were
refined with the help of free variable PART instruction.18c
Refinement of the site occupancy factors for the disordered
atoms O1, O2, C1, and C2 gave the values 0.54 (2), 0.57-
(4), 0.56(3), and 0.57(5), respectively. These factors were
thereafter fixed at 0.55. The occupancy factor of the other
possible set of positions (O1D, O2D, C1D, and C2D) was
0.45. Hydrogen atoms were fixed to the terminal disordered
carbon atoms C1 and C1D in idealized positions with site
occupancy factors 0.55 and 0.45, respectively, and a riding
model was used for the refinement.
31P{1H} NMR: δ 6.72 [tm, JP-F ) 935 Hz, PF2], 37.33
[dm, JP-F ) 946 Hz, PF(C)], 51.16 [s, PPh3]. 19F{1H}
1
1
NMR: δ -73.12 [dm, 4F, JP-F ) 940 Hz, PF2], -67.45
[dm, 4F, 1JP-F ) 940 Hz, PF2], -41.35 [dt, 2F, 1JP-F ) 950
Hz, PF(C)]. MS (FAB) [m/e (species)]: 1105 [M]+, 1104
+
[M - 1]+, 844 [(3) + 1]+, 812 [M - CH3O]+, 263 [PPh3
+ 1], 181 [COOCH3CpCo]+. Anal. Calcd for C42H35-
CoF10N6O2P7: C, 44.98; H, 3.15; N, 7.49. Found: C, 44.90;
H, 3.17; N, 7.43.
The fifth fraction, which came out of the column at 3%
ethyl acetate in hexane, was analyzed and identified as (η5-
MeOC(O)C5H4)(PPh3)Co[2,5-(N3P3F5)2-3,4-(C6H5)2] (2).
Yield: 0.16 g, 20%. Mp: 150-152 °C. IR (ν, cm-1): 1717s
(CdO), 1252vs (PdN), 1089w, 1000w, 936s (P-F), 851s
1
(P-F), 825s (P-F). H NMR: δ 3.57 [s, 3H, COOCH3],
4.65 [s, 1H, CpH], 5.09 [s, 1H, CpH], 5.27 [s, 1H, CpH],
5.52 [s, 1H, CpH], 6.53-6.55 [m, 2H, C4Co ring Ph H],
7.09-7.26 [m, 8H, C4Co ring Ph H], 7.27-8.06 [m, 15H,
PPh3 H]. 13C{1H} NMR: δ 53.15 [CH3], 85.06, 86.91 [C4-
Co ring C], 92.84, 98.73, 99.73 [CpC], 127.32, 127.41,
128.23, 128.32, 128.62, 128.72, 129.03, 130.80, 131.21,
134.27 [PhC], 166.04 [-CdO]. 31P{1H} NMR: δ 7.36 [tm,
1JP-F ) 910 Hz, PF2], 19.09 [dm, 1JP-F ) 1002 Hz, PF(C)],
Preparation of 1-3. A solution of (â-phenylethynyl)-
pentafluorocyclotriphosphazene (2.00 g, 6.04 mmol) and
(PPh3)3CoCl (2.67 g, 3.00 mmol) in 35 mL of toluene was
added to a stirred solution of a sodium salt of carbomethoxy
cyclopentadiene (0.44 g, 3.00 mmol) in 10 mL of THF. The
mixture was stirred at room temperature for 15 min before
being refluxed for 24 h. Afterward, all solvents were removed
under vacuum; the resulting crude product was chromato-
graphed on a silica gel column and eluted with hexane to
remove triphenylphosphine and triphenylphosphine oxide as
the first and second fractions. The third fraction, which came
out of the column at 2% ethyl acetate in hexane, was found
to be (η5-MeOC(O)C5H4)Co[1,3-(N3P3F5)2-2,4-(C6H5)2] (3).
Yield: 0.07 g, 15%. Mp: 84 °C. IR (ν, cm-1): 1720s (Cd
O), 1267vs (PdN), 1062w, 1014w, 950s (P-F), 866s (P-
F), 823s (P-F). 1H NMR (CDCl3): δ 3.37 [s, 3H, COOCH3],
5.20 [s, 2H, CpH], 5.73 [s, 2H, CpH], 7.34-7.43 [m, 6H,
PhH), 7.49-7.51 [m, 4H, -PhH].13C{1H} NMR: δ 51.98
[CH3], 84.71, 86.92 [C4 ring C], 87.83, 98.30, 99.27 [CpC],
125.22, 128.21, 129.15, 133.83 [PhC], 167.24 [-CdO]. 31P-
{1H} NMR: δ 9.90 [tm, 1JP-F ) 921 Hz, -PF2], 32.44 [tm,
1JP-F ) 980 Hz, -PF(C)]. 19F{1H} NMR: δ -69.21 [dm,
4F, 1JP-F ) 930 Hz, PF2], -70.70 [dm, 4F, 1JP-F ) 924 Hz,
1
35.81 [dm, JP-F ) 945 Hz, PF(C)], 43.81 [s, PPh3].
19F{1H} NMR: δ -72.99 [dm, 4F, JP-F ) 899 Hz,
1
1
PF2], -69.25 to -65.07 [m, 4F, JP-F ) 915 Hz, PF2],
-53.24 [dt, 1F, JP-F ) 1000 Hz, PF(C)], -40.67 [dt,
1
1
1F, JP-F ) 939 Hz, PF(C)]. MS (FAB) [m/e (species)]:
1105 [M]+, 1104 [M - 1]+, 843 [3]+, 812 [M - CH3O]+,
+
263 [PPh3 + 1], 181 [COOCH3CpCo]+. Anal. Calcd for
C42H35CoF10N6O2P7: C, 44.98; H, 3.15; N, 7.49. Found: C,
44.93; H, 3.10; N, 7.41.
Preparation of 4. A solution of 1 (0.29 g, 0.26 mmol)
and diphenyl acetylene (0.14 g, 0.78 mmol) in 20 mL of
xylene was refluxed for 24 h. During the course of the
reaction, the color of the solution changed from dark red to
brown. After completion of the reaction, the solvent was
evaporated off by applying a vacuum, and the crude product
mixture was chromatographed through a silica gel column
using a ethyl acetate/hexane mixture as the eluant. With pure
hexane as eluant, PPh3 was removed; at 2% ethyl acetate in
hexane, a colorless compound came out. All solvents were
removed from the fraction by a vacuum. The compound
crystallized by slow cooling of a saturated solution in ethyl
acetate and was characterized as [{1,4-(N3P3F5)2-2,3,5,6-
(C6H5)4}C6] (4). Yield: 0.12 g, 54%. Mp: 215-220 °C. IR
(ν, cm-1): 1256 vs (PdN), 1077 w, 1014 w, 935 s (P-F),
1
PF2] -47.89 [d, 2F, JP-F ) 970 Hz, PF(C)]. MS (FAB)
[m/e (species)]: 843 [M]+, 812 [M - CH3O]+, 181 [COOCH3-
CpCo]+. Anal. Calcd for C25H27CoF10N6O2P6: C, 34.19; H,
3.10; N, 9.57. Found: C, 34.13; H, 3.05; N, 9.50.
Compound (η5-MeOC(O)C5H4)(PPh3)Co[2,5-(N3P3F5)2-
3,4-(C6H5)2] (1) came as the fourth fraction, using 2.5% ethyl
acetate in hexane as the eluant. Yield: 0.34 g, 11%. Mp:
198-200 °C. IR (ν, cm-1): 1725s (CdO), 1269vs (PdN),
1091w, 1001w, 928s (P-F), 825s (P-F). 1H NMR: δ 3.27
[s, 3H, COOCH3], 5.31 [s, 2H, CpH], 5.7 [s, 2H, CpH],
6.73-6.80 [m, 4H, C4Co ring Ph H], 7.39-7.41 [m, 6H,
C4Co ring Ph H], 7.48-7.57 [m, 15H, PPh3 H]. 13C{1H}
NMR: δ 52.47 [CH3], 85.13, 86.82 [C4Co ring C], 90.11,
93.75, 93.89 [CpC], 126.72, 126.94, 127.39, 127.83 127.95,
129.45, 134.52, 130.03, 134.52, 141.17 [PhC], 170 [CdO].
859 s (P-F), and 828 s (P-F) H NMR: δ 6.97-6.99 [m,
1
8H, PhH], 7.08-7.15 [m, 12H, PhH].13C{1H} NMR: δ
127.40 [m-PhC], 127.64 [p-PhC], 130.41 [o-PhC], 137.56
[ipso-PhC], 142.86 [PhC], 146.70 [PhC]. 31P{1H} NMR: δ
6.96 [tm, JP-F ) 911 Hz, -PF2], 31.24 [dm, JP-F )1004
Hz, -PF(C)]. 19F{1H} NMR: δ -73.12 [dm, 4F, JP-F
)
913 Hz, -PF2], -66.45 [dm, 4F, JP-F ) 913 Hz, -PF2],
-45.15 [d, 2F, JP-F ) 1003 Hz, -PF(C)]. MS (FAB) [m/e
(species)]: 840 [M]+; Anal. Calcd for C30H20F10N6P6: C,
42.88; H, 2.40; N, 10.00. Found: C, 42.83; H, 2.35; N, 9.94.
The second fraction, which came out at 5% ethyl acetate in
Inorganic Chemistry, Vol. 45, No. 19, 2006 7837

Kumar et al.
Scheme 1
Scheme 2
Scheme 3
hexane, was crystallized and identified as [η5-(MeOC(O)-
2.08; N, 10.92. On increasing the polarity of the solvent
mixture to 2% ethyl acetate in hexane, a colorless compound
was isolated that was identified as 1,3,5-triphenylbenzene.19
1
C5H4]Co(η4-C4Ph4) (5). Melting point, H NMR, and IR
spectral data of this compound were found to agree well with
the reported values for the same (yield: 0.12 g, 25%).14
Preparation of 6. A solution of 1 (0.16 g, 0.14 mmol)
and phenylacetylene (0.04 g, 0.42 mmol) in 20 mL of xylene
was refluxed for 8 h. After completion of the reaction, the
solvent was evaporated by applying vacuum, and the crude
product was chromatographed on a silica gel column using
an ethyl acetate/hexane mixture as the eluant. Compound
[{1,4-(N3P3F5)2-2,3,5-(C6H5)3}C6] (6) came out, along with
PPh3, while using pure hexane as the eluant and was purified
further by fractional crystallization. Yield: 0.06 g, 54%.
Mp: 65 °C. IR (ν, cm-1): 2924m (Ar C-H), 1267vs (Pd
N), 1071w, 1017w, 930w (P-F), 834s (P-F).1H NMR: δ
6.59-8.45 (m, ArH). 13C{1H} NMR: δ 121.93, 122.30,
126.07, 127.62, 128.30, 128.52, 129.21, 129.41, 130.40,
132.45, 138.94, 141.33 [PhC]. 31P{1H} NMR: δ 7.42 [tm,
1JP-F ) 941 Hz, -PF2], 31.02 [dm, 1JP-F ) 1000, -PF(C)],
Results and Discussion
Reaction of (â-phenylethynyl)pentafluorocyclotriphospha-
zene with in situ generated (η5-(MeOC(O)C5H4)Co(PPh3)2
resulted in three new compounds, 1-3 (Scheme 1). Com-
pounds 1 and 2 are two isomers of fluorophosphazene-
derived cobaltacyclopentadiene metallacycles, and compound
3 is a metallocene with a η4-cyclobutadiene unit with trans
arrangement of two fluorophosphazene units. It is of interest
to note that although the cis-fluorophosphazene-substituted
cyclobutadienylmetallocene or the metallacycle having both
phosphazenyl units on vicinal carbons, (η5-carbomethoxy-
cyclopentadienyl)(triphenylphosphine)-3,4-bis(pentafluoro-
cyclotriphosphazenyl)-2,5-diphenyl cobaltacyclopentadiene,
can be expected as products, they were not isolated from
these reactions. The reactions of (â-phenylethynyl)pentafluo-
rocyclotriphosphazene, sodium carbomethoxycyclopentadi-
ene, and tris(triphenylphosphine)cobalt chloride were carried
out in two different molar ratios, namely 1.5:1:1 and 2:1:1.
1
29.53 [dm, JP-F )1003 Hz, -PF(C)]. 19F{1H} NMR δ
-73.00 [dm, 4F, 1JP-F ) 939, -PF2], -67.25 [dm, 4F, 1JP-F
1
) 940 Hz, -PF2], -58.16 [d, 1F, JP-F ) 1005 Hz, -PF-
1
(C)], -47.64 [d, 1F, JP-F ) 997 Hz, -PF(C)]. MS (FAB)
[m/e (species)]: 765 [M + 1]+. Anal. Calcd for C24H16N6-
(19) Williams, A. C.; Sheffels, P.; Sheehan, D.; Livinghouse, T. Organo-
metallics 1989, 8, 1566-1567.
P6F10: C, 37.72; H, 2.11; N, 11.00. Found: C, 37.67; H,
7838 Inorganic Chemistry, Vol. 45, No. 19, 2006

Fluorophosphazene-DeriWed Cobaltcyclopentadienyl Metallacycles
Table 1. Selected Bond Lengths and Bond Angles of Compound 1
Bond Lengths (Å)
Co(1)-C(3)
Co(1)-P(1)
Co(1)-C(8)
P(5)-C(11)
P(2)-N(3)
P(3)-N(2)
P(3)-F(2)
P(5)-F(6)
P(7)-F(9)
2.074 (6)
2.219(4)
1.988(6)
1.587(6)
1.775(8)
1.554(7)
1.530(6)
1.548(6)
1.520(6)
Co(1)-C(5)
Co(1)-C(11)
P(2)-F(1)
P(2)-C(8)
P(2)-N(1)
P(3)-F(3)
P(3)-N(1)
P(5)-N(6)
2.130(9)
1.955(7)
1.775(8)
1.552(6)
1.584(7)
1.530(6)
1.553(7)
1.591(6)
Bond Angles (deg)
92.64 (17) P(1)-Co(1)-C(11)
P(1)-Co(1)-C(8)
93.30(17)
118.03(47)
137.14(40)
120.17(51)
C(10)-C(11)-P(5) 119.57(43)
C(9)-C(8)-P(2)
P(3)-N(2)-P(4)
P(6)-N(5)-P(7)
N(3)-P(2)-N(1)
N(6)-P(5)-N(4)
114.57(30)
115.23(32)
Table 2. Selected Bond Lengths and Bond Angles of compound 2
Bond Lengths (Å)
Co(1)-C(3)
Co(1)-P(1)
Co(1)-C(8)
P(5)-C(10)
P(3)-N(2)
P(4)-F(4)
P(3)-F(2)
P(5)-F(6)
P(7)-F(10)
2.073(3)
2.217(1)
1.960 (3)
1.786(2)
1.567(2)
1.538(2)
1.536(2)
1.549(2)
1.524(2)
Co(1)-C(5)
Co(1)-C(11)
P(2)-C(8)
P(4)-N(2)
P(2)-N(1)
P(4)-F(5)
P(3)-F(3)
P(6)-F(7)
P(7)-F(9)
2.155(3)
1.951(5)
1.769(3)
1.566(3)
1.599(3)
1.529(2)
1.530(2)
1.538(2)
1.531(2)
Bond Angles (deg)
P(1)-Co(1)-C(8)
C(11)-C(10)-P(5)
N(1)-P(2)-N(3)
N(6)-P(5)-N(4)
F(7)-P(6)-F(8)
F(9)-P(7)-F(10)
F(2)-P(3)-F(3)
95.43(15)
124.82(23)
115.64(12)
115.46(12)
97.26(10)
97.89(13)
97.83(11)
P(1)-Co(1)-C(11)
C(9)-C(10)-P(5)
P(3)-N(2)-P(4)
P(7)-N(5)-P(6)
F(6)-P(5)-C(10)
F(1)-P(2)-C(8)
F(4)-P(4)-F(5)
95.58(7)
119.77(17)
119.09(15)
119.50(16)
104.73(10)
103.67(10)
97.36(10)
Figure 1. 31P NMR spectra of compounds 1 and 2.
Table 3. . Selected Bond Lengths and Bond Angles of Compound 3
Bond Lengths (Å)
Co(1)-C(3)
Co(1)-C(11)
P(4)-C(10)
C(2)-O(1)
P(1)-N(1)
P(1)-N(3)
P(5)-N(5)
P(5)-N(4)
P(4)-F(6)
2.058 (5)
1.958 (5)
1.744 (10)
1.334(7)
1.581(4)
1.583(4)
1.561(4)
1.544(4)
1.537(3)
Co(1)-C(5)
Co(1)-C(8)
P(1)-C(8)
C(2)-O(2)
P(2)-N(1)
P(3)-F(4)
P(5)-F(7)
P(4)-N(6)
2.053 (5)
1.968 (5)
1.734 (4)
1.202(7)
1.548(4)
1.517(4)
1.518(4)
1.577(4)
Figure 2. Thermal ellipsoid view of compound 1 with 30% probability
factor (hydrogen atoms and the phenyl groups attached to the triphenylphos-
phine moiety have been omitted for clarity).
Bond Angles (deg)
135.34 (36) C(9)-C(8)-P(1)
141.95 (31) N(1)-P(1)-N(3)
C(12)-C(9)-C(8)
C(9)-C(10)-P(4)
F(1)-P(1)-C(8)
141.68 (31)
115.62(20)
However, no significant changes in the yields of the products
were observed. The relative yields of 1-3 were found to
vary with a change in reaction time. Reactions carried out
under reflux conditions in toluene for 24 h gave yields of
11, 20, and 15%, respectively, whereas refluxing for 48 h
gave 10, 15, and 10% yields of 1-3, respectively. A reaction
carried out for 7 h in refluxing toluene gave the same
compounds 1-3 in lower yields (11, 6, and 4%, respectively)
in addition to a red viscous liquid that was obtained at the
end of the column with a polar solvent mixture as eluant.
This viscous liquid was found to disappear when the reaction
period was increased to 48 h. Analysis of this liquid by mass
spectral and 31 P NMR studies suggests a possible intermedi-
ate with one or two phosphines replaced by (â-phenylethy-
nyl)pentafluorocyclotriphosphazene. The projected overall
low yields of products in these reactions are a result of the
fact that the reactive reagent η5-(MeOC(O)C5H4)Co(PPh3)2
generated in situ is formed in only around 50% yield as
104.20(18)
C(10)-P(4)-F(6) 104.40(17)
N(6)-P(4)-N(4) 116.28(20)
C(18)-C(11)-C(10) 133.21(36)
P(6)-N(5)-(P(5)
120.03(24)
Table 4. Selected Bond Lengths and Bond Angles of Compound 4
Bond Lengths (Å)
P(1)-C(1)
P(1)-N(1)
P(3)-F(5)
P(2)-F(2)
P(1)-N(3)
1.810(2)
1.576(2)
1.517(7)
1.512(7)
1.581(9)
C(2)-C(3)
P(2)-F(3)
P(3)-F(4)
1.495(3)
1.522(8)
1.519(2)
Bond Angles (deg)
C(1)-C(2)-C(3)
C(1)-P(1)-F(1)
P(2)-N(2)-P(3)
122.10(17)
103.35(8)
119.71(14)
C(2)-C(1)-P(1)
N(1)-P(1)-N(3)
P(1)-C(1)-C(2)
118.34(14)
116.46(11)
118.34(14)
observed from separate studies. In addition to compounds
1-3, Ph3P and Ph3PO were also separated from the reaction
mixture. No examples of alkyne-trimerized products were
isolated from these reactions.
Inorganic Chemistry, Vol. 45, No. 19, 2006 7839

Kumar et al.
Table 5. X-ray Crystallographic Data for Compounds 1-4
1
2
3
4
empirical formula
fw
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
C41H32CoF10N6O2P7
1106.45
P1
C41H32CoF10N6O2P7
1106.45
P1
C23H17CoF10N6O2P6
844.18
P21/c
7.3106(11)
22.024(3)
19.681(3)
90
94.876(3)
90
C30H20F10N6P6
840.34
Pbca
13.352(1)
13.708(1)
18.695(6)
90
90
90
3422.0(5)
4
10.563(3)
11.418(3)
20.883(5)
82.733(5)
76.226(4)
72.190(5)
2325.1(11)
2
11.7729(8)
12.2864(9)
16.5497(12)
84.5950(10)
85.9960(10)
70.9650(10)
2251.0(3)
2
3157.2(8)
4
T (K)
λ (Å)
298(2)
0.71073
1.580
0.694
100(2)
0.71073
1.632
0.717
298(2)
0.71073
1.776
0.943
0.0480, 0.0985
298(2)
0.71073
1.631
0.403
0.0395, 0.1121
F
calcd (g/cm3)
µ (mm-1
R1a, wR2b (I > 2σ (I))
)
0.0848, 0.1925
0.0352, 0.0949
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR ) {[∑(|Fo| |Fc| )2]}1/2
.
This reaction differs considerably when compared to the
reaction of CpCo(CO)2 with (â-phenylethynyl)pentafluoro-
cyclotriphosphazene, which, although it gave (η5-cyclopen-
tadienyl)-[η4-1, 3-bis(pentafluorocyclotriphosphazenyl)-2,
4-diphenylcyclobutadiene]cobalt, did not result in the forma-
tion of any cobaltametallacycle compounds.12 Further, under
similar reaction conditions, the reaction of diphenylacetylene
with η5-(MeOC(O)C5H4)Co(PPh3)2 gave exclusively (η5-
(MeOC(O)C5H4)Co(η4-C4Ph4).14 The cobaltametallacycles 1
and 2 have enhanced thermal stability compared to tetrakis
pentafluorophenyl and tetraphenyl analogues. Whereas com-
pounds 1 and 2 are stable as such in refluxing toluene, the
tetrakis(pentafluorophenyl) cobaltametallacycle is stable only
in refluxing benzene; tetraphenyl cobaltametallacycle con-
verts to the metallocene, [η5-CpCo(η4-C4Ph4)], in refluxing
benzene.13c,20
CpCo(PPh3)2.23 The reaction indicates a wider scope is
possible for such reactions in realizing a variety of novel
aryl- and heteroaryl-bridged fluorophosphazenes by varying
substituents on the reactants (Scheme 3).
Spectral Studies on Compounds 1-6. The 1H NMR spec-
trum of compound 2 differs considerably from the 1H NMR
spectra of compounds 1 and 3. Whereas the four protons
present in the cyclopentadienyl ring gave only two different
signals in the case of compounds 1 and 3, for compound 2,
four different signals for these protons (δ, 4.65, 5.09, 5.27,
and 5.52 ppm) were observed, which indicated the lesser
symmetry of molecule 2. In addition, the chemical shift
values of the phenyl ring protons were shifted downfield in
comparison to compounds 1 and 3. In case of compound 2,
the two PF moieties are present in different environments
and hence have different chemical shifts in their 31P and 19
F
Although described as being model compounds for
condensation polymerization reactions of cyclophosphazenes,
the bridged derivatives of cyclophosphazenes are some of
the most difficult to obtain.21 Becuase of the multiplicity and
reactivity of the phosphorus-halogen bonds, reactions car-
ried out to prepare such derivatives often result in polym-
erized products. A few examples of alkoxy-bridged cyclo-
phosphazenes are known in the literature and some of these
have been found to undergo a bridged-to-spiro transformation
in the presence of catalysts.22 By carrying out a reaction of
the cobaltametallacycle 1 with diphenylacetylene, we have
been able to prepare, in reasonably good yields, aryl-bridged
fluorophosphazenes with pentafluorophosphazenyl units para-
substituted on the aryl ring. The 1,4-bisfluorophosphazene-
substituted aryl derivative 4 is the first example of an aryl-
bridged phosphazene molecule (Scheme 2). The cobalta-
metallacycle was found to convert to the highly stable
sandwich compound [η5-(MeOC(O)C5H4]Co(η4-C4Ph4)] (5).14
A reaction similar to that of 1 with phenyl acetylene gave
the 1,4-disubstituted compound 6 with one phenyl group less
than in 4. This reaction also resulted in a phenylacetylene
trimerized product, which is in agreement with the observa-
tion of trimerization of 2-ethynylpyridine in its reaction with
NMR spectra. For the 31P NMR spectrum of compound 2, the
signal at 19.09 ppm is due to the PF(C) group that is away
from the metal center and the signal at 35.81 ppm is due to
the PF(C) group that is nearer to the metal center, whereas
the 31P NMR spectrum of compound 1 gave only one signal
at 37.33 ppm for both the PF(C) groups (Figure 1). The pres-
ence of triphenylphosphine on 1 and 2 makes the 13C NMR
of these compounds complex especially for the phenyl groups
compared to compounds 3 and 4. 19F NMR spectra of all
compounds gave two sets of doublet of multiplets at different
chemical shifts for the PF2 groups (1JP-F ∼ 900-1000 Hz)
due to the diasterotopic nature of the fluorine atoms of the
N3P3F5 units. Compound 2 gave two different signals for
two -PF(C) groups, both as doublets at -53.24 and -40.67
ppm indicating its less symmetric nature compared to
compound 1. The -PF2 groups of compound 2 were also
observed as a complex multiplet in the range -69.25 to
-65.07. However for all compounds the 31P NMR spectra
were much simpler and gave the expected number of signals
which were assigned to the PF(C) and PF2 groups.
(21) Chandrasekhar, V.; Muralidhara, M. G. R.; Selvaraj, I. I. Heterocycles
1990, 31, 2231-2266.
(22) Vij, A.; Geib, S. J.; Kirchmeier, R. L.; Shreeve, J. M. Inorg. Chem.
1996, 35, 2915-2929 and references therein.
(20) (a) Gastinger, R. G.; Rausch, M. D.; Sullivan D. A.; Palenik G. J. J.
Am. Chem. Soc. 1975, 98, 719-723. (b) Nakamura, A.; Hagihara, N.
Bull Chem. Soc. Jpn. 1961, 34, 452-458.
(23) Wakatsuki, Y.; Yoshimura, H.; Yamazaki, H. J. Organomet. Chem.
1989, 366, 215-221.
7840 Inorganic Chemistry, Vol. 45, No. 19, 2006

Fluorophosphazene-DeriWed Cobaltcyclopentadienyl Metallacycles
Figure 4. Thermal ellipsoid view of compound 3 with 30% probability
factor (hydrogen atoms have been omitted for clarity).
Figure 3. Thermal ellipsoid view of compound 2 with 30% probability
factor (hydrogen atoms and the phenyl groups attached to the triphenylphos-
phine moiety have been omitted for clarity).
spectra compared to the latter. The two phosphazene units
which are present in the metallacycle are eclipsed to each
other, which is in contrast to the relative orientation of two
phosphazene units in compound 1. The ester group present
in the cyclopentadienyl ring of compound 2 shows disorder
and the atoms O1, O2, C1 and C2 were occupying two
crystallographically independent positions. The site oc-
cupancy factors of these atoms were refined and these factors
were fixed at 0.55.
In compound 3, the cyclobutadiene contains two pen-
tafluorophosphazene units are trans to each other (Figure 4).
Unlike compound 2, which showed two different bond
distances for the P-F bonds, compound 3 has almost equal
bond distances for the P-F bonds [P(1)-F(1) 1.538 (3) Å
and P(4)-F(6) 1.537(3) Å] which are closer to the metal
center. Further the P-F groups of both the phosphazene
moieties are involved in weak intramolecular C-H...F
interaction with one of the phenyl rings (C(13)-H(13)...
F(1) 2.389(5) and C(17)-H(17)...F(6) 2.369(3) Å). These
distances are in good agreement with the values reported
for weak C-H...F interactions.10a This weak interaction is
probably making one of the phenyl rings to be in the plane
of the cyclobutadiene ring. The other phenyl ring which does
not involve in any weak interactions lies almost perpendicular
to the plane of the cyclobutadiene ring. The two phosphazene
units present in the cyclobutadiene ring are eclipsed to each
other at a particular orientation.
The molecular structure of compound 4 is given in the
Figure 5. Compound 4 is the first example of a structurally
characterized aryl bridged cyclophosphazene. The four phen-
yl groups are oriented at an angle to the central aryl ring
while the two phosphazene units are anti to each other. The
mean plane containing two opposite phenyl rings makes an
angle of 64.82° with the plane of the central benzene ring.
Similarly the mean plane containing the other two phenyl
rings makes an angle of 66.48° with the plane of the central
benzene ring. The two phosphazene units are anti to each
other and the closest P-F bonds to the central aryl ring
makes a torsional angle of 150.92°. The fluorine atoms of
Compound 6 gave two different signals for two -PF
groups, both as doublets at -58.16 and -47.64 ppm, which
was similar to the spectral pattern shown by compound 2.
Further the -PF2 groups showed two signals at -73.00 and
another at -67.25 ppm. The difference in the 19F NMR of
compounds 4 and 6 showed that the orientations of the
phosphazene moieties in compound 6 are not the same as
that of compound 4, and suggests a possible conformation
where the two phosphazene units are eclipsed to each other,
similar to compound 2. However, in the absence of suitable
crystals for structure determination, structural features of
compound 6 could not be confirmed.
X-ray crystal structures of compounds 1-4. The crystal
structure of compound1 is given in Figure 2. The cobalt
triphenylphosphine bond distance [Co(1)-P(1) 2.219(4) Å,
Table 1] was shorter than the values of 2.327 (4), and 2.339
(1) Å24 found in cobaloxime complexes, and 2.234 Å in
1-(η5-cyclopentadienyl)-1,3-bis(pentafluorophosphazenyl)-
2,4-bis(phenyl)cobalt complex.20 The two C-P distances
connecting the fluorophosphazene units to the metallacycle
are found to be same [1.775(8) Å]. The P-F bond distances
[P(2)-F(1) 1.552(6) and P(5)-F(6) 1.548(6) Å] which are
directly attached to the carbon atom of metallacycle were
found to be longer than the P-F bond distances which are
away from the metal center [P(3)-F(3) 1.530(6) and P(6)-
F(7) 1.533(7) Å]. The two phosphazene units present in the
metallacycle were oriented in the gauche form with respect
to each other. Selected bond angles and bond distances for
compounds 1-4 are given in Tables 1-4, respectively.
Molecular structure of compound 2 differs from 1 in such
a way that one of the pentafluorophosphazene units and one
phenyl group exchanged their positions to make an arrange-
ment having two phosphazene units and two phenyl rings
occupying alternate positions in the metallocyclic ring (Figure
3). It is interesting to note that the distance of the P-F bond
closer to the metal atom [P(5)-F(6) 1.549(2) Å] is slightly
shorter than the distance of P-F bond which is away from
the cobalt atom [P(2)-F(1) 1.558(2) Å], which confirms the
upfield shift of the former in the 31P NMR and 19F NMR
(24) (a) Bruckner, S.; Randacclo, L. J. Chem. Soc., Dalton Trans. 1974,
1017-1021. (b) Adams. W. W.; Lenhert, P. G. Acta Crystallogr., Sect.
B 1973, 29, 2412-2414.
Inorganic Chemistry, Vol. 45, No. 19, 2006 7841

Kumar et al.
(Figure 7). None of the compounds isolated and characterized
in this study has two fluorophosphazene units present on
vicinal carbon atoms of four, five and six-membered carbo
or metallacyclic rings. The phosphazene units present in
compounds 2 and 3 are eclipsing with each other. In the
case of compounds 1, the phosphazene units are gauche to
each other, and in compound 4 the orientations of the
phosphazene units are anti to each other. In the case of
compounds 2 and 3, the mean planes containing the two
phosphazene units intersect each other at an angle of 52.28°
and 63.66° respectively. For compound 1 the angle between
the two planes is 80.99°. The number and chemical shifts
of signals obtained in the 31P and 19F NMR spectra of
compounds 1-4 reflects these differences in the orientations
of phosphazene groups and indicates further the stability of
the structure in solution phase as well.
Figure 5. Thermal ellipsoid view of compound 4 with 30% probability
factor (hydrogen atoms have been omitted for clarity). Atoms labeled with
the suffix A were generated by the symmetry code (1 - x, -y, 1 - z).
Conclusions
In conclusion, we report the synthesis and characterization
of two novel fluorophosphazene derived cobaltocyclopen-
tadienylmetallacycles, and also provide a hitherto unknown
synthetic route for making aryl bridged fluorinated cyclo-
phosphazenes by the reaction of the metallacycles with
substituted acetylenes. The PPh3 stabilized metallacycles are
prepared by the reaction of (â-phenylethynyl) pentafluoro-
cyclotriphosphazene, F5P3N3C≡CPh with in situ generated
η5- (MeOC(O)C5H4)Co(PPh3)2. This reaction also gives a
cyclobutadienyl cobaltametallocene having two fluorophos-
phazenyl groups trans to each other on the cyclobutadiene
ring. Quite interestingly, structural studies indicate that com-
pounds having two fluorophosphazene moieties on vicinal
carbon atoms of four, five and six membered carbocyclic
rings have not been formed in these reactions thus indicating
selectivity in product formation. This may possibly be due
the steric bulkiness of the phosphazene molecules. The
metallocyclic compounds, metallocenyl compound and the
aryl bridged fluorophosphazene compounds considerably
differ in their spectral and structural properties and these have
been compared. The method described for making bridged
phosphazenes shows potential for making a host of aryl and
heteroaryl fluorophosphazene derivatives, which can them-
selves, be precursors for a host of new molecules.
Figure 6. Molecular structure 4 showing weak intermolecular C-H‚‚‚F
interactions.
Acknowledgment. The authors thank the Department of
Science and Technology (DST) of India and the Council of
Scientific and Industrial Research (CSIR) of India for
financial assistance in the form of research grants to A.J.E.
and IIT Delhi for an equipment grant. We thank DST-FIST
and IITD for funding of the single crystal X-ray diffraction
facility at IIT Delhi. The authors thank Dr. N. Kurur and
Prof. A. Ramanan, Department of Chemistry, IIT Delhi, for
their help in recording multinuclear NMR and analyzing
X-ray crystallographic data. We thank SAIF, CDRI, Luc-
know, for providing mass spectral and analytical data.
Figure 7. Molecular structures of compounds 1-4 showing orientations
of the phosphazene moieties with respect to the central ring (other parts of
the molecules have been omitted for clarity).
the phosphazene units are involved in weak intermolec-
ular C-H...F interaction with the phenyl rings of the
neighboring molecules [C(13)-H(13)...F(3) 2.652(2) Å]
resulting in a two-dimensional layer type supramolecular
assembly (Figure 6).
A comparison of the orientations of the two phosphazene
moieties in compounds 1-4 shows interesting features
Supporting Information Available: Crystallographic informa-
tion files (CIF) for compounds 1-4. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC0609204
7842 Inorganic Chemistry, Vol. 45, No. 19, 2006