Synthesis and selectivity in the formation of cyclophosphazene-derived 1,3-cyclohexadienes from reactions of RCpCo(COD) [R = MeOC(O)] with alkynes and alkenes

Article abstract of DOI:10.1021/ic7024507

The first examples of mono and bisfluorophosphazene derived [η⁵-cyclopentadienyl] [η⁴-1,3-cyclohexadiene] cobalt complexes have been prepared along with the sandwich compound [η⁵-carbomethoxycyclopentadienyl] [η⁴-1,3- bis(pentafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene] cobalt and acetylene trimerized products from the reactions of [η⁵-MeOC(O) C₅H₄]Co[COD], PhC≡CP₃N₃F ₅ and phenylacetylene in the presence or absence of an additional cycloalkene or indene. Formation of these mono and bis fluorophosphazene derived cobalt cyclohexadiene complexes provide experimental evidence for a metallacyclopentadiene pathway for cyclohexadiene formation in CpCo catalyzed reactions. Selectivity is also observed in the formation of bisfluorophosphazene derived cyclohexadienes which stems from the fact that two P₃N ₃F₅ units cannot be accommodated on vicinal carbon atoms of a carbacycle or metallacycle. Interestingly, reactions of (β-phenylethynyl)pentafluorobenzene with [η⁵-MeOC(O)C ₅H₄]Co[COD] in the presence and absence of external cycloalkene under identical reaction conditions yielded only the cis and trans isomers of the metallocene [η⁵-MeOC(O)C₅H ₄]Co[η⁴-C₄Ph₂(C ₆F₅)₂] along with alkyne trimerized product indicating that the selectivity in cyclohexadiene formation is governed more by steric than electronic factors. All the new compounds were characterized by ¹H, ¹³C, ³¹P, and ¹⁹F NMR as well as mass spectrometry and elemental analysis. Mono and bispentafluorocyclotriphosphazene derived [η⁵-cyclopentadienyl] [η⁴-1,3-cyclohexadiene] cobalt complexes and [η⁵- carbomethoxycyclopentadienyl] [η⁴-bis(1,3-pentafluorophenyl)-2,4- diphenylcyclobutadiene] cobalt have also been structurally characterized by single crystal X-ray analysis.

Full text of DOI:10.1021/ic7024507

Inorg. Chem. 2008, 47, 3433-3441
Synthesis and Selectivity in the Formation of
Cyclophosphazene-Derived 1,3-Cyclohexadienes from Reactions of
RCpCo(COD) [R ) MeOC(O)] with Alkynes and Alkenes
Muthiah Senthil Kumar, Ram Prakash Gupta, and Anil J. Elias*
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India
Received December 19, 2007
5
4
The first examples of mono and bisfluorophosphazene derived [η -cyclopentadienyl] [η -1,3-cyclohexadiene] cobalt
5
4
complexes have been prepared along with the sandwich compound [η -carbomethoxycyclopentadienyl] [η -1,3-
bis(pentafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene] cobalt and acetylene trimerized products from the
5
reactions of [η -MeOC(O)C5H4]Co[COD], PhCt CP3N3F5 and phenylacetylene in the presence or absence of an
additional cycloalkene or indene. Formation of these mono and bis fluorophosphazene derived cobalt cyclohexadiene
complexes provide experimental evidence for a metallacyclopentadiene pathway for cyclohexadiene formation in
CpCo catalyzed reactions. Selectivity is also observed in the formation of bisfluorophosphazene derived
cyclohexadienes which stems from the fact that two P3N3F5 units cannot be accommodated on vicinal carbon
5
atoms of a carbacycle or metallacycle. Interestingly, reactions of (ꢀ-phenylethynyl)pentafluorobenzene with [η -
MeOC(O)C5H4]Co[COD] in the presence and absence of external cycloalkene under identical reaction conditions
5
4
yielded only the cis and trans isomers of the metallocene [η -MeOC(O)C5H4]Co[η -C4Ph2(C6F5)2] along with alkyne
trimerized product indicating that the selectivity in cyclohexadiene formation is governed more by steric than electronic
1
factors. All the new compounds were characterized by H, 13C, 31P, and 19F NMR as well as mass spectrometry
5
4
and elemental analysis. Mono and bispentafluorocyclotriphosphazene derived [η -cyclopentadienyl] [η -1,3-
5
4
cyclohexadiene] cobalt complexes and [η -carbomethoxycyclopentadienyl] [η -bis(1,3-pentafluorophenyl)-2,4-
diphenylcyclobutadiene] cobalt have also been structurally characterized by single crystal X-ray analysis.
Introduction
and exploring the versatility in the reactions of difunctional
reagents with the phosphorus-halogen bonds of the hetero-
cycle.7 Among the reactions of difunctional reagents with
cyclophosphazenes, those leading to spiro and ansa substitu-
Interest in halogenated cyclophosphazenes stems not only
from a host of potential applications but also from the
uniqueness of structurally diverse derivatives resulting from
their reactions. While the applications include their proven
use as monomers for realizing phosphazene based polymers,1
stable cores for realizing dendrimers,2 ionic liquids,3 as well
as multidendate4and multianionic5 ligands, studies on reac-
tivity have been mainly centered on integrating chirality6
(3) (a) Omotowa, B. A.; Phillips, B. S.; Zabinski, J. S.; Shreeve, J. M.
Inorg. Chem. 2004, 43, 5466–5471. (b) Muralidharan, K.; Omotowa,
B. A.; Twamley, B.; Piekarski, C.; Shreeve, J. M. Chem. Commun.
2005, 5193–5195.
(4) (a) Chandrasekhar, V.; Thilagar, P.; Krishnan, V.; Bickley, J. F.;
Steiner, A. Cryst. Growth Des. 2007, 7, 668–675. (b) Chandrasekhar,
V.; Pandian, B. M.; Azhakar, R. Inorg. Chem. 2006, 45, 3510–3518.
(c) Chandrasekhar, V.; Nagendran, S. Chem. Soc. ReV. 2001, 30, 193–
203. (d) Chandrasekhar, V.; Krishnan, V.; Steiner, A.; Bickley, J. F.
Inorg. Chem. 2004, 43, 166–172. (e) Chandrasekhar, V.; Senthil
Andavan, G. T.; Nagendran, S.; Krishnan, V.; Azhakar, R.; Butcher,
R. J. Organometallics. 2003, 22, 976–986.
* To whom correspondence should be addressed. E-mail: eliasanil@
gmail.com.
(1) (a) Chandrasekhar, V. Inorganic and Organometallic Polymers;
Springer-Verlag: Berlin, Heidelberg, 2005; p 82. (b) Chandrasekhar,
V.; Krishnan, V. AdV. Inorg. Chem. 2002, 53, 159–211. (c) Allcock,
H. R., Chemistry and applications of polyphosphazene; Wiley Inter-
science: NJ, 2003; p 1.
(5) (a) Boomishankar, R.; Joanne, L.; Jean-Baptiste, G.; Neil, L. C.; John,
B.; Richard, B. L.; Yaroslav, Z. K.; Steiner, A. Chem. Commun. 2007,
5152–5154. (b) Benson, M. A.; Zacchini, S.; Boomishankar, R.; Chan,
Y.; Steiner, A. Inorg. Chem. 2007, 46, 7097–7108. (c) Richards, P. I.;
Boomishankar, R.; Steiner, A. J. Organomet. Chem. 2007, 692, 2773–
2779. (d) Richards, P. I.; Steiner, A. Inorg. Chem. 2005, 44, 275–
281. (e) Richards, P. I.; Steiner, A. Inorg. Chem. 2004, 43, 2810–
2817.
(2) (a) Gritte, L.; Paupot, M.; Marchand, P.; Maroval, A.; Turrin, C.-D.;
Rolland, O.; Metivier, P.; Bacquet, G.; Fournie, J.-J.; Caminade, A.-
M.; Paupout, R.; Majoral, J.-P. Angew. Chem., Int. Ed. 2007, 46, 2523–
2526. (b) Schneider, R.; Köllner, C.; Weber, I.; Togni, A. Chem.
Commun 1999, 2415–2416.
10.1021/ic7024507 CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 8, 2008 3433
Published on Web 02/27/2008

Kumar et al.
tion have been explored in detail.8 However, very few
attempts have been made to explore and understand the
formation of bridged or multiphosphazenyl assemblies having
sodium benzophenone ketyl under a nitrogen atmosphere and were
used. (ꢀ-Phenylethynyl)pentafluorocyclotriphosphazene,11 [η5-car-
bomethoxycyclopentadienyl] [η4-cyclooctadiene] cobalt,13 and (ꢀ-
phenylethynyl)pentafluorobenzene14 were prepared according to
literature procedures.
6d 9
,
reactive P-X bonds
which are potential precursors for
realizing phosphazene based condensation polymers, den-
drimers, and multidendate ligands.
Instrumentation. 1H, 13C{1H}, 31P{1H} and 19F{1H} NMR
spectra were recorded on a Bruker Spectrospin DPX-300 NMR
spectrometer at 300, 75.47, 121, and 282 MHz respectively. IR
spectra in the range 4000–250 cm-1 were recorded on a Nicolet
Protége 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 electrospray ionization (ESI)
mode using a JEOL SX 102/DA-6000 mass spectrometer.
X-ray Crystallography. Suitable crystals of compounds 1, 6,
and 7 were obtained by slow evaporation of their saturated solutions
in pentane, and compound 8 was recrystallized from an ethylacetate/
hexane solvent mixture. X-ray diffraction studies of crystals
mounted on a capillary were carried out on a BRUKER AXS
SMART-APEX diffractometer equipped with a CCD area detector
(KR ) 0.71073 Å; monochromator, graphite).15a Frames were
collected at T ) 298 K by ω, ꢁ, and 2θ-rotations with full quadrant
data collection strategy (four domains each with 600 frames) at
10s per frame with SMART.15b The measured intensities were
reduced to F2 and corrected for absorption with SADABS.15b
Structure solution, refinement, and data output were carried out with
the SHELXTL package by direct methods.15c Nonhydrogen 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.15d For compound
6, because of poor crystal quality, we have omitted the higher 2θ
reflections.
Use of organocobalt reagents in realizing multiphosphaze-
nyl assemblies were initially reported by Allen and co-
workers in a conference paper using the phosphazene derived
alkyne, PhCt CP3N3F5 and cobalt carbonyls.10 Reaction of
fluorophosphazene derived alkynes with Co2(CO)8 and
CpCo(CO)2 had resulted in the formation of novel phosp-
hazene derived cobalt carbonyls and cyclobutadiene com-
plexes.11 We have recently shown in a detailed study
that the reactions of PhCt CP3N3F5 with [η5-MeOC(O)-
C5H4]Co(PPh3)2 differ considerably from its reactions with
CpCo(CO)2 and result in the formation of metallacycles as
well.12 In this paper, we report the first reactions of [η5-
MeOC(O)C5H4]Co[η4-COD] [where COD ) 1,5-cyclooc-
tadiene] with PhCt CP3N3F5 along with cycloalkenes or
indene, which has resulted in the formation of the first
examples of mono and bis fluorophosphazene derived
cyclohexadiene complexes of cobalt with an interesting
product selectivity. The study also addressess the mechanism
of cyclohexadiene formation using CpCo based reagents and
provides experimental evidence for a metallacyclopentadiene
pathway for the same.
Experimental Section
Reaction of (ꢀ-Phenylethynyl)pentafluorocyclotriphosphazene,
1,5-Cyclooctadiene, and Phenylacetylene with [η5-Carbomethox-
ycyclopentadienyl] [η4-cyclooctadiene] Cobalt. A solution con-
taining 0.20 g (0.6 mmol) of [η5-carbomethoxycyclopentadienyl]
[η4-cyclooctadiene] cobalt, 0.46 g (1.3 mmol) of (ꢀ-phenylethy-
nyl)pentafluorocyclotriphosphazene, 0.07 g (0.6 mmol) of pheny-
lacetylene, and 0.24 g (1.8 mmol) of 1,5-cyclooctadiene in 20 mL
of xylene was refluxed for 33 h. The reaction was monitored by
thin layer chromatography. After completion of the reaction, all
solvents were evaporated off, and the remaining crude product was
chromatographed through a silica gel column using a hexane/
ethylacetate mixture as the eluent. The first fraction that came out
while using pure hexane as the eluent was identified as a mixture
of 1,3,5- and 1,2,4-triphenylbenzene (3 and 4).16 The second fraction
that came out with 2% ethylacetate/hexane mixture as a viscous
liquid was identified and characterized as mono(pentafluorocyclo-
triphosphazenyl) triphenyl benzene (5). Yield: 0.08 g (44%). IR
(ν, cm-1): 1266 vs (P ) N), 1073 w, 1020 w, 940 s, and 823 s
(P-F). 1H NMR: δ 6.89–7.94 [m, 17H, -PhH]. 31P{1H} NMR: δ
General Methods. All manipulations of compounds were carried
out using standard Schlenk techniques under a nitrogen atmosphere.
Tetrahydrofuran, xylene, and toluene were freshly distilled from
(6) (a) Carriedo, G. A.; Alonso, G. F. J.; Elipe, G. P.; Brillas, E.; Julia,
L. Org. Lett. 2001, 3, 1625–1628. (b) Carriedo, G. A.; Alonso, G. F. J.;
Garcia-Alvarez, J. L.; Pappalardo, G. C.; Punzo, F.; Rossi, P. Eur.
J. Inorg. Chem. 2003, 13, 2413–2418. (c) Carriedo, G. A.; Crochet,
P.; Alonso, G. F. J.; Gimeno, J.; Persa-Soto, A. Eur. J. Inorg. Chem.
2004, 18, 3668–3674. (d) Coles, S. J.; Davies, D. B.; Eaton, R. J.;
Hursthouse, M. B.; Kilic, A.; Shaw, R. A.; Uslu, A. Dalton Trans.
2006, 130, 2–1312.
(7) (a) Bilge, S.; Demiriz, S.; Okumus, A.; Kilic, Z.; Tercan, B.; Hokelek,
T.; Buyukgungor, O. Inorg. Chem. 2006, 45, 8755–8767. (b) Ilter,
E. E.; Asmafiliz, N.; Kilic, Z.; Isiklan, M.; Hokelek, T.; Caylak, N.;
Sahin, E. Inorg. Chem. 2007, 46, 9931–9944. (c) Uslu, A.; Coles,
S. J.; Davies, D. B.; Eaton, R. J.; Hursthouse, M. B.; Kilic, A.; Shaw,
R. A. Eur. J. Inorg. Chem. 2005, 6, 1042–1047. (d) Coles, S. J.;
Davies, D. B.; Eaton, R. J.; Hursthouse, M. B.; Kilic, A.; Shaw, R. A.;
Uslu, A. Eur. J. Org. Chem. 2004, 9, 1881–1886.
(8) (a) Muralidharan, K.; Elias, A. J. Inorg. Chem. 2003, 42, 7535–7543.
(b) Muralidharan, K.; Venugopalan, P.; Elias, A. J. Inorg. Chem. 2003,
42, 3176–3182. (c) Muralidharan, K.; Reddy, N. D.; Elias, A. J. Inorg.
Chem. 2000, 39, 3988–3994. (d) Muralidharan, K.; Elias, A. J. Inorg.
Chem. Commun. 2003, 6, 584–588.
1
1
7.62 [tm, JP-F ) 885 Hz, -PF2], 33.43 [tm, JP-F ) 980 Hz,
1
-PF(C)]. 19F{1H} NMR: δ -90.62 [dm, JP-F ) 880 Hz, -PF2],
(9) (a) Benson, M. A.; Boomishankar, R.; Wright, D. S.; Steiner, A. J.
Organomet. Chem. 2007, 692, 2768–2772. (b) Ainscough, E. W.;
Brodie, A. M.; Depree, C. V. Dalton Trans. 1999, 4123–4124. (c)
Vij, A.; Geib, S. J.; Kirchmeier, R. L.; Shreeve, J. M. Inorg. Chem.
1996, 35, 2915–2929. (d) Keat, R.; Rycroft, D. S.; Miller, V. R.;
Schmulbach, C. D.; Shaw, R. A. Phosphorus, Sulfur Silicon Relat.
Elem. 1981, 10, 121–122.
-85.58 [dm, 1JP-F ) 887 Hz, -PF2], -75.34 [d, 1JP-F ) 981 Hz,
(13) Wakatsuki, Y.; Yamazaki, H. Bull. Chem. Soc. Jpn. 1985, 58, 2715–
2716.
(14) Yadong, Z.; Jianxun, W. J. Fluorine Chem. 1990, 47, 533–535.
(15) (a) SMART: Bruker Molecular Analysis Research Tools, Version 5.618;
Bruker Analytical X-ray Systems: 2000. (b) Sheldrick G. M. SAINT-
NT, Version 6.04; Bruker Analytical X-ray Systems: 2001. (c)
Sheldrick,G. M. SHELXTL-NT, Version 6.10; Bruker Analytical X-ray
Systems: 2000. (d) Klaus, B. Diamond, Version 1.2c; University of
Bonn: Germany, 1999.
(10) Allen, C. W.; Malik, P.; Bridges, A.; Desorcie, J.; Pellon, B.
Phosphorus, Sulfur Silicon Relat. Elem. 1990, 49–50, 433–436.
(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) Kumar, M. S.; Upreti, S.; Elias, A. J. Inorg. Chem. 2006, 45, 7835–
7842.
(16) Farnetti, E.; Marsich, N. J. Organomet. Chem. 2004, 689, 14–17.
3434 Inorganic Chemistry, Vol. 47, No. 8, 2008

Formation of Cyclophosphazene-DeriWed 1,3-Cyclohexadienes
Scheme 1
-PF(C)]. MS (ESI) [m/e (species)]: 534 [M - 1]+. Anal. Calcd
for C24H17F5N3P3: C, 53.85; H, 3.20; N, 7.85. Found: C, 53.78; H,
3.04; N, 7.46.
solvents were evaporated off. The remaining crude product was
chromatographed through a silica gel column using hexane/
ethylacetate mixture as the eluent. The cyclohexadiene complex
[η5-carbomethoxycyclopentadiene] [η4-3,6-bis(pentafluorocyclot-
riphosphazene)-4,5-diphenyl-endo-tetracyclo[6.5.1.0.2,709,13] trideca-
3,6,10-triene] cobalt (6) came out as the second fraction while using
2% ethylacetate/hexane mixture. Yield: 0.18 g (36%). Mp: 200–205
°C. IR (ν, cm-1): 1721 s (CdO), 1265 vs (PdN), 1145 w, 938 s
The red fraction that came out next using a 4% ethylacetate/
hexane mixture was identified as [η5-carbomethoxycyclopentadiene]
[η4-1-mono(pentafluorocyclotriphosphazene)-2,3-diphenyl-
4a,5,6,9,10,10a-hexahydro[8]annulene] cobalt (1) Yield: 0.13 g
(27%). Mp: 165–170 °C. IR (ν, cm-1): 1713 s (CdO), 1272 vs
1
1
(PdN), 1146 w, 926 s and 828 s (P-F). H NMR: δ 0.88-1.25
and 828 s (P-F). H NMR: δ 0.85 [d, 1H], 1.09 [d, 1H], 1.34 [d,
[m, 3H, -CH2], 1.51 [m, 4H, -CH2], 2.4 [m, 4H, -CH2], 3.82 [s,
3H, -COOCH3], 4.28 [s, 1H, -CpH], 4.60 [s, 1H, -CpH], 4.89
[s, 1H, -CpH], 5.12 [s, 1H, -CpH], 5.56-5.74 [m, 2H, -olefinic
H], 7.35-7.41 [m, 6H, -PhH), 7.62–7.84 [m, 4H, -PhH]. 13C{1H}
NMR: δ 25.18, 28.63, 30.48, 30.92, 31.99, 50.26 [saturated
cyclooctene C], 51.68 [-CH3], 83.33, 87.29, 90.11 [C5 ring C],
126.60, 128.33, 128.59, 128.83, 130.90, 144.12 [Ar C, olefinic C],
1H], 1.47 [d, 1H], 2.26 [m, 2H], 2.28 [m, 1H], 2.33 [m, 1H], 2.40
[m, 1H], 2.98 [m, 1H], 3.89 [s, 3H], 5.46 [m, 1H], 5.61 [d, 2H],
5.82 [d, 1H], 5.90 [d, 2H], 7.18–7.57 [m, 10H]. 13C{1H} NMR: δ
26.92, 31.90, 34.44, 40.62, 41.45, 44.19, 44.94, 45.91, 52.52, 76.59
[saturated dicyclopentene C], 51.94 [-CH3], 85.80, 88.42, 88.62
[-C5 ring C], 127.60, 128.19, 128.27, 128.57, 129.14, 129.86,
131.29, 131.94, 132.45, 132.51, 133.01 [ArC, olefinic C], 166.23
[-C)O]. 31P{1H} NMR: δ 7.25 [tm, 1JP-F ) 949 Hz, -PF2], 44.88
1
167.14 [-C)O]. 31P{1H} NMR: δ 7.51 [tm, JP-F ) 879 Hz,
1
-PF2], 45.27 [dm, JP-F ) 968 Hz, -PF(C)]. 19F{1H} NMR: δ
1
[dm, JP-F ) 961 Hz, -PF(C)]. 19F{1H} NMR: δ -70.45 [dm,
-92.5 (dm, 1JP-F ) 882 Hz, -PF2), -87.34 (dm, 1JP-F ) 884 Hz,
1
1JP-F ) 941 Hz, -PF2], -65.55 [dm, JP-F ) 945 Hz, -PF2],
1
1
1
-PF2), -76.55 [d, JP-F ) 970 Hz, -PF(C)]. MS (ESI) [m/e
-64.87 [dm, JP-F ) 953 Hz, -PF2], -53.75 [dm, JP-F ) 956
Hz, -PF(C)]. MS (ESI) [m/e (species)]: 977 [M + 1]+. Anal. Calcd
for C33H29CoF10N6O2P6: C, 40.59; H, 2.99; N, 8.61. Found: C,
40.65; H, 2.91; N, 8.54. The third red fraction that came at 6%
ethylacetate/hexane mixture was identified as the sandwich com-
pound 2 with 15% yield.
(species)]: 723 [M+]. Anal. Calcd for C31H30CoF5N3O2P3: C, 51.47;
H, 4.18; N, 5.81. Found: C, 51.21; H, 3.98; N, 5.69. The fourth
red fraction that came at 6% ethylacetate/hexane mixture was
identified as [η5-carbomethoxycyclopentadienyl] [η4-1,3-bis(pen-
tafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene] cobalt
(2) in 21% yield. The identity of 2 was confirmed by comparing
its 1H, 13C, 31P, and 19F NMR and IR spectral data to reported data
in the literature.12
Reaction of (ꢀ-Phenylethynyl)pentafluorocyclotriphosphazene
and Indene with [η5-Carbomethoxycyclopentadienyl] [η4-cy-
clooctadiene] Cobalt. A solution containing 0.50 g (1.7 mmol) of
[η5-carbomethoxycyclopentadienyl] [η4-cyclooctadiene] cobalt, 1.14 g
(3.4 mmol) of (ꢀ-phenylethynyl)pentafluorocyclotriphosphazene,
and 0.58 g (5.1 mmol) of indene in 20 mL of xylene was refluxed
for 24 h. The reaction was followed by thin layer chromatography,
and after completion of the reaction, all solvents were evaporated
off. The remaining crude product was chromatographed through a
silica gel column using hexane/ethylacetate mixture as the eluent.
Unreacted starting materials were removed by passing pure hexane
through the column. The cyclohexadiene complex, [η5-carbomethox-
ycyclopentadiene] [η4-1,4-bis(pentafluorocyclotriphosphazene)-9,9a-
dihydro-4aH-fluorene] (7) came out as the third fraction while using
2% ethylacetate/hexane mixture as the eluent. Yield: 0.64 g (40%).
Mp:146–148 °C. IR (ν, cm-1): 1720 s (CdO), 1621 (CdC), 1265
Reaction of (ꢀ-Phenylethynyl)pentafluorocyclotriphosphazene
and Dicyclopentadiene with [η5-Carbomethoxycyclopentadi-
enyl] [η4-cyclooctadiene] Cobalt. A solution of 0.15 g (0.5 mmol)
of [η5-carbomethoxycyclopentadienyl] [η4-cyclooctadiene] cobalt,
0.34 g (1.0 mmol) of (ꢀ-phenylethynyl)pentafluorocyclotriphospha-
zene, and 0.20 g (1.5 mmol) of dicyclopentadiene in 20 mL of
xylene was refluxed for 24 h. The reaction was followed up by
thin layer chromatography and after completion of the reaction, all
1
vs (PdN), 936 s and 831s (P-F). H NMR: δ 3.07 [m, 1H], 3.35
[m, 1H], 3.54 [m, 1H], 3.91 [s, 3H, -C(O)OCH3], 4.07 [m, 1H],
5.53 [s, 2H, CpH], 6.05 [s, 2H, CpH], 6.72, 7.08–7.24, 7.36–7.50,
7.83 [m, 14H, ArH]. 13C NMR: δ 27.53, 29.71, 38.91 [aliphatic
C], 52.15 [-CH3], 85.82, 86.66, 89.08 [C5 ring C], 124.32, 126.22,
126.87, 127.44, 127.57, 128.04, 128.08, 128.15, 128.59, 128.69,
129.93, 132.24, 141.44, 141.56 [Ar C, olefinic C], 166.19 [-CO].
31P{1H} NMR: δ 6.87 [tm, JP-F ) 949 Hz, -PF2], 45.27 [dm,
1
1JP-F ) 960 Hz, -PF(C)]. 19F{1H} NMR: δ -70.57 [dm, 1JP-F
)
940 Hz, -PF2], -65.45 [dm, 1JP-F ) 937 Hz, -PF2], -64.34 [dm,
1
1JP-F ) 955 Hz, -PF2], -54.32 [dm, JP-F ) 950 Hz], -51.30
1
(dm, JP-F ) 970 Hz). MS (ESI) [m/e (species)]: 961 [M + 1]+.
Figure 1. Molecular structure of compound 1 (H atoms are omitted for
clarity).
Anal. Calcd for C32H25CoF10N6O2P6: C, 40.02; H, 2.62; N, 8.75.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3435

Kumar et al.
Scheme 2
Scheme 3
Scheme 4
Scheme 5
Found: C, 39.39; H, 2.42; N, 8.62. The fourth red fraction which
came at 6% ethylacetate/hexane mixture was identified as the
sandwich compound 2 with 18% yield.
literature.17 The sandwich compound [η5-carbomethoxycyclopen-
tadienyl] [η4-bis(1,3-pentafluorophenyl)-2,4-diphenylcyclobutadi-
ene] cobalt (8) came out as the second fraction while using 4%
ethylacetate/hexane mixture as the eluent and was further purified
by crystallization. Yield: 0.25 g (50%). Mp: 210–215 °C. IR (ν,
Reaction of (ꢀ-Phenylethynyl)pentafluorobenzene and Dicy-
clopentadiene with [η5-Carbomethoxycyclopentadienyl] [η4-
cyclooctadiene] Cobalt. A solution of 0.20 g (0.6 mmol) of [η5-
carbomethoxycyclopentadienyl] [η4-cyclooctadiene] cobalt, 0.37 g
(1.3 mmol) of (ꢀ-phenylethynyl)pentafluorobenzene and 0.23 g (1.8
mmol) of dicyclopentadiene in 20 mL of xylene was refluxed for
24 h. The reaction was followed up by thin layer chromatography,
and after completion of the reaction, all solvents were evaporated
off. The remaining crude product was chromatographed through a
silica gel column using hexane/ethylacetate mixture as the eluent.
Unreacted starting materials were removed by passing pure hexane
through the column. 1,3,5-tris(pentafluorophenyl)-2,4,6-triphenyl-
benzene (10) came out as the first fraction while using pure hexane
as the eluent, which was confirmed by comparing the values of
1H, 13C NMR and IR spectral data with the values reported in the
1
cm-1): 1704 vs (CdO), 1287 vs (CsF). H NMR: δ 3.34 [s, 3H,
-COOCH3], 4.94 [s, 2H, -CpH], 5.48 [s, 2H, -CpH], 6.99–7.31
[m, 10H, PhH]. 13C{1H} NMR: δ 51.35 [-CH3], 62.14, 76.43 [C4
ring C], 84.89, 86.46, 88.09 [-CpC], 126.26, 127.42, 128.36,
134.70, 142.45 [PhC], 165.65 [sCdO]. 19F{1H} NMR: δ -161.30
(m), -153.95 (m), -130.92 (m). MS (ESI) [m/e (species)]: 718
[M+]; Anal. Calcd for C35H17CoF10O2: C, 58.51; H, 2.39. Found:
C, 58.34; H, 2.01.
[η5-carbomethoxycyclopentadienyl] [η4-bis(1,4-pentafluorophe-
nyl)-2,3-diphenylcyclobutadiene] cobalt (9) which could not be
purified fully because of contamination of 8 was identified by
1
spectral data. Yield: 11%. H NMR: δ 3.42 [s, 3H, -COOCH3],
4.96 [s, 2H, -CpH], 5.33 [s, 2H, -CpH], 6.84–7.54 [m, 10H, PhH].
(17) Yang, J.; Verkade, J. G. Organometallics, 2000, 19, 893–900.
3436 Inorganic Chemistry, Vol. 47, No. 8, 2008

Formation of Cyclophosphazene-DeriWed 1,3-Cyclohexadienes
Table 1. Selected Bond Lengths and Bond Angles of Compound 1
Bond Lengths (Å)
Co1-C3
Co1-C10
Co1-C11
P1-C8
2.075(5)
1.979(5)
2.081(6)
1.773(4)
1.523(4)
1.597(4)
1.554(7)
Co1-C8
Co1-C9
C11-C24
P1-F1
2.034(4)
1.966(4)
1.532(5)
1.547(3)
1.524(4)
1.566(5)
1.592(4)
P3-F5
P3-F4
P1-N1
P3-N2
P2-N2
P1-N3
Bond Angles (deg)
Co1-C9-C12
Co1-C8-P1
C5-Co1-C9
C29-C30-C31
128.49(17)
Co1-C11-C18
C3-Co1–11
C5-Co1–10
118.73(16)
115.30(9)
128.49(10)
116.14(12)
109.76(9)
117.77(20)
Table 2. Selected Bond Lengths and Bond Angles of Compound 6
Figure 2. Molecular structure of compound 6 (H atoms are omitted for
clarity).
Bond Lengths (Å)
Co1-C3
Co1-C10
P4-F6
C13-C20
P1-N1
P4-N6
2.064(8)
2.024(7)
1.548(5)
1.527(13)
1.581(6)
1.589(8)
Co1-C8
P4-C8
P5-F7
C16-C17
P4-N4
P5-N5
2.059(8)
1.781 (7)
1.524(10)
1.405(19)
1.586(7)
1.550(9)
Bond Angles (deg)
Co1-C8-P4
C18-C19–C21
N1-P1-N3
C11-P1-F1
119.57(39)
109.98(63)
114.16(34)
101.30(3)
Co1-C10-C28
P4-C8-C9
F2-P2-F3
133.73 (52)
118.71(53)
97.69(32)
Table 3. Selected Bond Lengths and Bond Angles of Compound 7
Bond Lengths (Å)
Co1-C3
C2-O2
C19-P4
P1-F1
2.124(5)
1.185(7)
1.779(4)
1.547(4)
1.484(9)
Co1-C6
C2-O1
C9-P1
P1-N1
2.069(4)
1.317(6)
1.792(4)
1.569(4)
C11-C12
Bond Angles (deg)
132.77(26)
Co1-C20-C27
C9-P1-F1
C3-Co1-C20
125.00(15)
114.25(20)
115.85(33)
99.97(19)
125.09(47)
116.38(31)
N1-P1-N3
C9-C10-C11
O2-C2-O1
Figure 3. Molecular structure of compound 7 (H atoms are omitted for
clarity).
C17-C18-C19
in the 2:1:1 molar ratio gave the novel cobalt cyclohexadiene
complex [η5-carbomethoxycyclopentadiene] [η4-1-mono-
(pentafluorocyclotriphosphazene)-2,3-diphenyl-4a,5,6,9,10,10a-
hexahydro[8]annulene] cobalt 1 along with the sandwich
compound [η5-carbomethoxycyclopentadienyl] [η4-1,3-bis(pen-
tafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene] co-
balt (2),12 in addition to alkyne trimerized products, 1,3,5-
Ph3C6H3 (3), 1,2,4-Ph3C6H3 (4), 16 and [C6H2(P3N3F5)(Ph)3]
(5) (Scheme 1). The nature of compound 1 indicates an
unprecedented participation of the 1,5-cyclooctadiene present
in CpCo(COD) in a [2 + 2 + 2] cycloaddition leading to
the formation of a cyclohexadiene complex. Compound 1,
which has been structurally characterized, is also the first
example of a phosphazene derived CpCo complexed cyclo-
hexadiene (Figure 1). Such compounds are potential precur-
sors for a host of novel phosphazene derived aryl and
cyclohexadiene compounds which can be obtained by
removal of the RCpCo fragment.18
Figure 4. Molecular structure of compound 8 (H atoms are omitted for
clarity).
19F{1H} NMR: δ -161.92 (m), -154.67 (m), -131.93 (m). MS
(ESI) [m/e (species)]: 719 [M + 1]+.
Results and Discussion
While exploring the reactions of PhCt CP3N3F5 with
RCpCo(COD), the inadvertent presence of phenylacetylene
in the reaction mixture was found to give traces of a unique
phosphazene derived cyclohexadiene compound. This ob-
servation initiated our study on the reactions of RCpCo-
(COD) with a combination of alkynes and cycloalkenes. A
reaction of PhCt CP3N3F5 and phenylacetylene with [η5-
carbomethoxycyclopentadienyl] [η4-cyclooctadiene] cobalt
The [2 + 2 + 2] cyclooligomerization of alkynes and
alkenes using CpCo based catalysts has been known as an
elegant method for the preparation of 1,3-cyclohexadiene
derivatives, often with chemo-, regio-, and stereo-selectiv-
ity.19 While several mechanisms have been proposed for the
(18) Macomber, D. W.; Verma, A. G.; Rogers, R. D. Organometallics,
1988, 7, 1241–1253.
Inorganic Chemistry, Vol. 47, No. 8, 2008 3437

Kumar et al.
mented in the literature.24 The second involves a mechanism
in which the COD falls off completely from the complex
and is replaced by two molecules of alkyne which undergo
oxidative coupling to form a cobaltacyclopentadiene inter-
mediate B (Scheme 2; route 2). Complexation of another
molecule of the alkyne on the cobalt center of A or
complexation of COD on B in η2 mode followed by insertion
and reductive elimination can result in the CpCo(η4-
cyclohexadiene) compound 1.
To identify between these two possible mechanisms, we
have carried out the same reaction under identical reaction
conditions; however, after adding an additional amount (1
mole) of 1,5-cyclooctadiene. Interestingly, the reaction
resulted in the formation of same set of products but with
different yields, and the yield of RCpCo(η4-cyclohexadiene)
compound 1 increased from 8 to 18%. Further, an increase
in yield of compound 1 (up to 27%) was observed by
increasing the amount of 1,5-cyclooctadiene added to 3
moles. This indicates that the COD which took part in the
reaction need not be the one complexed to the metal, and
for a purely intramolecular pathway involving a metallacy-
clopentene intermediate, the yield of compound 1 should not
have increased.
Further to confirm the evidence of the metallacyclopen-
tadiene pathway for the formation of 1,3-cyclohexadiene
complexes, two reactions of PhCt CP3N3F5 with [η5-car-
bomethoxycyclopentadienyl] [η4-cyclooctadiene] cobalt were
carried out with additional alkenes; one by adding 3 moles
of dicyclopentadiene and other by adding 3 moles of indene
instead of 1,5-cyclooctadiene (Schemes 3 and 4). Interest-
ingly, both the reactions resulted in the formation of RCpCo-
complexed cyclohexadienes 6 and 7 having two phosphaze-
nyl units adjacent to the added cycloalkene units. Both
reactions also yielded compound 2, the cyclobutadiene
sandwich compound having the phosphazene units trans to
each other. A reaction of PhCt CP3N3F5 and phenylacetylene
with MeOC(O)C5H4Co(COD) in the presence of 3 moles of
dicyclopentadiene also gave compounds 2 and 6 in addition
to the alkyne trimerized products, and formation of 1 was
not observed in the same. The absence of compound 1 and
the incorporation of dicyclopentadiene or indene in the
cyclohexadiene unit in these reactions clearly indicates an
intermolecular cobaltacyclopentadiene pathway for the for-
mation of cyclohexadiene complexes (Scheme 2; route 2).
To determine if there is any specific role of pentafluoro-
phosphazenyl (N3P3F5) units in forming the RCpCo stabilized
cyclohexadiene complex, we have carried out reactions of
PhCt CC6F5 with the [η5-carbomethoxycyclopentadienyl]
[η4-cyclooctadiene] cobalt complex in the absence of external
alkene as well as in the presence of dicyclopentadiene. These
reactions were undertaken as C6F5 is closest to N3P3F5 when
Table 4. Selected Bond Lengths and Bond Angles of Compound 8
Bond Lengths (Å)
Co1-C3
C2-O2
C10-C23
C24-F3
2.038(3)
1.186(5)
1.466(4)
1.336(4)
Co1-C8
C2-O1
C9-C18
C17-F4
1.983(3)
1.337(5)
1.475(5)
1.332(4)
Bond Angles (deg)
Co1-C10-C23
C3-Co1-C11
127.68(20)
123.78(12)
Co1-C9-C18
Co1-C11-C29
130.82(23)
131.76(22)
formation of CpCo complexed 1,3-cyclohexadienes, all of
them begin with a sequential displacement of the ligands
bound to the CpCoL2 complex by alkyne or alkene units.20
For successive steps, theoretical studies reported on the
reactions provide two possible pathways involving metalla-
cycles, one involving a metallacyclopentene and the other a
metallacyclopentadiene. The former is expected to form by
the sequential complexation of one alkyne and one alkene
unit displacing the ligands already present in the cobalt
complex followed by an oxidative coupling. The latter is
envisaged in a similar way but by the oxidative coupling of
two alkyne units coordinated to the cobalt center.21
The possibility of formation of both these intermediates
is supported by structurally characterized examples in the
literature for iridium22 and cobalt23 based metallacyclo-
pentenes and metallacyclopentadienes. Wakatsuki, Yamazaki,
and co-workers using carefully planned reactions have also
shown that triphenylphosphine ligated cobaltacyclopenta-
dienes and cobaltacyclopentenes on reaction with alkenes
or alkynes, respectively, can lead to the formation of
CpCo(η4-cyclohexadiene) complexes.23 However, recent
theoretical studies by Gandon et al. has shown that out of
the two pathways, the formation of a metallacyclopentadiene
intermediate is energetically more favored (about 10 kcal/
mol) than the metallacyclopentene intermediate.21 In this
context, we were interested to see the type of mechanism
involved in the reaction of PhCt CP3N3F5 with RCpCo-
(COD) and an alkene.
The formation of 1 can be explained by two possible
mechanisms. The first, a shorter route, involves association
of one mole of alkyne to the cobalt center by changing the
coordination of the complexed cyclooctadiene from an η4
to η2 mode followed by an oxidative coupling of the η2 bound
COD and the alkyne leading to a metallacyclopentene
intermediate A (Scheme 2; route 1). The presence of η2
bound 1,5-COD transition metal complexes is well docu-
(19) (a) Schore, N. E. Chem. ReV. 1988, 88, 1081–1119. (b) Gandon, V.;
Leboeuf, D.; Amslinger, S.; Vollhardt, K. P. C. Angew. Chem., Int.
Ed. 2005, 44, 7114–7118. (c) Vollhardt, K. P.C. Angew. Chem., Int.
Ed. Engl. 1984, 23, 539–556. (d) Eichberg, M. J.; Dorta, R. L.;
Grotjahn, D. B.; Lamottke, K.; Schmidt, M.; Vollhardt, K. P. C. J. Am.
Chem. Soc. 2001, 123, 9324–9337.
(20) (a) Lautens, M.; Klute, W.; Tam, W. Chem. ReV. 1991, 96, 49–92.
(b) Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. L. Chem. ReV.
1996, 96, 635–662. (c) Saito, S.; Yamamoto, Y. Chem. ReV. 2000,
100, 2901–2916. (d) Gevorgyan, V.; Radhakrishnan, U.; Takeda, A.;
Rubina, M.; Rubin, M.; Yamamoto, Y. J. Org. Chem. 2001, 66, 2835–
2841. (e) Gandon, V.; Aubert, C.; Malacria, M. Curr. Org. Chem.
2005, 9, 1699–1712.
(23) (a) Wakatsuki, Y.; Katsuyuki, A.; Yamazaki, H. J. Am. Chem. Soc.
1979, 101, 1123–1130. (b) Wakatsuki, Y.; Katsuyuki, A.; Yamazaki,
H. J. Am. Chem. Soc. 1974, 94, 5284–5285. (c) Wakatsuki, Y.;
Yamazaki, H. J. Organomet. Chem. 1977, 139, 169–177. (d) Wakat-
suki, Y.; Kuramitsu, T.; Yamazaki, H. Tetrahedron Lett. 1974, 51,
4549–4552.
(21) Gandon, V.; Agenet, N.; Vollhardt, K. P. C.; Malacria, M.; Aubert,
C. J. Am. Chem. Soc. 2006, 128, 8509–8520.
(22) (a) O’Connor, J. M.; Closson, A.; Gantzel, P. J. Am. Chem. Soc. 2002,
124, 2434–2435. (b) Martin, M.; Sola, E.; Torres, O.; Plou, P.; Oro,
L. A. Organometallics, 2003, 22, 5406–5417.
(24) (a) Martin, M.; Sola, E.; Torres, O.; Plou, P.; Oro, L. A. Organome-
tallics, 2003, 22, 5406–5417. (b) Guiu, E.; Claver, C.´; Castillon, S.
J. Organomet. Chem. 2004, 689, 1911–1918.
3438 Inorganic Chemistry, Vol. 47, No. 8, 2008

Formation of Cyclophosphazene-DeriWed 1,3-Cyclohexadienes
Table 5. X-ray Crystallographic Data for Compounds 1, 6, 7, and 8
1
6
7
8
empirical formula
fw
space group
a (Å)
b (Å)
c (Å)
C31H30CoF5N3O2P3
723.42
P1
C33H29CoF10N6O2P6O2
976.37
P2(1)/n
17.9726(19)
11.8081(12)
19.162(2)
101.704(2)
101.704(2)
90
C32H25CoF10N6O2P6
960.33
P1
C35H17CoF10O2
718.43
Pbca
20.620(4)
10.9120(18)
25.222(4)
90
j
j
10.830(3)
11.497(3)
12.943(3)
88.369(4)
88.369(4)
89.931(4)
1540.2(7)
2
9.2110(14)
12.6795(19)
17.506(3)
78.019(2)
78.019(2)
74.057(2)
1885.1(5)
2
R (deg)
ꢀ (deg)
90
90
γ (deg)
V (Å3)
3982.1(7)
4
5675.1(16)
8
Z
T (K)
298(2)
298(2)
298(2)
298(2)
λ (Å)
0.71073
1.560
0.779
1.65-25.50
0.0399, 0.1116
0.71073
1.629
0.760
1.42-21.00
0.0783, 0.1701
0.71073
1.692
0.801
1.21–25.17
0.0587, 0.1507
0.71073
1.682
0.705
1.61-25.50
0.0533, 0.1263
Fcalcd (g/cm3)
µ (mm-1)
θ range
R1a, wR2b (I > 2σ(I))
a R1 ) Σ|Fo| - |Fc||/Σ|Fo|; wR2 ) {[ Σ(|Fo|2 - |Fc|2)2]}1/2
b
rings, respectively, which are similar to that of other CpCo
stabilized cyclobutadiene complexes.12 In compound 1, the
phosphazene ring is present on the adjacent carbon atom of
the added cycloalkene moiety, and the mean plane containing
the phosphazene ring makes an angle of 66.52(57)° with the
mean plane containing the atoms C7, C8, C9, and C10 of
the cyclohexadiene unit. In compounds 6 and 7, the two
phosphazene rings are present on the carbon atoms adjacent
to the alkene moieties. While in compound 6 the two
phosphazene rings make angles of 71.16(92) and 68.64(43)°,
respectively, with the mean plane containing the four carbon
atoms C8, C9, C10, and C11 of the cyclohexadiene ring, in
compound 7 the two phosphazene units are oriented at angles
of 67.14(21) and 85.79(61)° with respect to the mean plane
containing the atoms C8, C9, C19, and C20 of the cyclo-
hexadiene ring. In compound 6, the two phosphazene rings
are eclipsed with respect to each other while in compound 7
the phosphazene rings are present in a skew conformation.
The CpCo fragment of compound 6 is oriented on the
opposite side of the bridging methano moiety of the
dicyclopentene group. The six membered ring which contains
the atoms C8, C9, C10, C11, C12, and C21 and the five
membered ring containing the atoms C14, C15, C16, C17,
and C18 are cis fused with the dicyclopentene system in
compound 6. The cis fused orientation of the five and six
membered rings is similar to the orientation observed in the
analogous tetraphenyl CpCo (η4-1,3-cyclohexadiene) com-
plex.18 In compound 8, the two phenyl rings are oriented at
angles of 59.42(61) and 43.07(21)° with respect to the plane
containing the cyclobutadiene ring, and the two pentafluo-
rophenyl rings are oriented at angles of 30.01(91) and
35.52(21)° with respect to the plane containing the cyclob-
utadiene ring.
Figure 5. Three possible isomers of bisfluorophosphazene derived cyclo-
hexadiene complexes.
electronic factors are considered. Interestingly, the reactions
resulted in the formation the cis and trans C6F5 substituted
cyclobutadiene RCpCo complexes, [η5-carbomethoxycyclo-
pentadienyl] [η4-bis(1,3-pentafluorophenyl)-2,4-diphenylcy-
clobutadiene] cobalt (8) [η5-carbomethoxycyclopentadienyl]
[η4-bis(1,2-pentafluorophenyl)-3,4-diphenylcyclobutadi-
ene] cobalt (9) along with a trimerized product (Scheme 5).
The above reaction did not yield any pentafluorophenyl
substituted cyclohexadiene complexes analogous to com-
pounds 1, 6, and 7, and unlike the reactions involving
PhCt CP3N3F5, it resulted also in the formation of sandwich
compound 9 in which the two pentaflurophenyl moieties are
present in the vicinal carbon atoms of the cyclobutadiene
moiety. This difference in the nature of product formation
between the alkynes PhCt CC6F5 and PhCt CP3N3F5 sug-
gests that, more than electronic factors, steric factors are
involved in the formation of cyclohexadiene complexes.
X-ray Crystal Structures of Compounds 1, 6, 7, and 8.
The X-ray crystal structures of compounds 1, 6, 7, and 8
are given in Figures 1-4, respectively (Tables 1-5). In
compounds 1, 6, and 7, the cyclopentadiene ligand is coor-
dinated in an η5 mode, and the cyclohexadiene ring coor-
dinated in an η4 mode with the cobalt atom. In compounds
1, 6, and 7, the cobalt atom is at a distance in the range of
1.695(2) to 1.708(1) Å with the centroids of the cyclopen-
tadienyl rings, whereas the distance between the cobalt atom
and the centroids of the four atoms of the cyclohexadiene
ring which form the η4-coordination are in the range of
1.592(2) to 1.600(l) Å. Unlike compounds 1, 6, and 7, where
there are differences in distances of Co- η5-Cp centroids and
Co- η4-C centroids, in compound 8 the cobalt atom makes
comparable distances of 1.680(9) and 1.688(9) Å with the
centroids of the cyclopentadienyl and the cyclobutadiene
Spectral Studies on Compounds 1 and 3. All the new
compounds prepared are stable to air and moisture and were
analyzed by IR, multinuclear (1H, 13C, 31P and 19F) NMR,
and mass spectra. The 31P NMR of compound 1 gave a signal
at 7.51 ppm which corresponds to the -PF2 groups, and the
signal at 45.27 ppm is due to the -PF group. The 19F NMR
spectra of compound 1 gave two different signals for the
-PF2 fluorines (-92.5 and -87.34 ppm) because of the
Inorganic Chemistry, Vol. 47, No. 8, 2008 3439

Kumar et al.
Scheme 6
diastereotopic nature of the fluorine atoms attached to
the same phosphorus atom. Similarly, the 31P NMR of
compounds 6 and 7 gave two signals in the expected
multiplicity for the -PF2 and the -PF groups. Compared to
1, the 19F NMR spectra of both compounds 6 and 7 were
complex in nature, but they showed similarity to reported
examples of bis(pentafluorocyclotriphosphazene) derived
cobaltametallacycles.12 Both compounds gave three different
signals for the -PF2 groups which can be attributed to the
diastereotopic nature of fluorines, an observation common
in many bis(pentafluorocyclotriphosphazene) derived cobalt
complexes.12 While compound 6 gave only one doublet at
-53.75 ppm for the -PF groups, compound 7 gave two
different doublets at -54.32 and at -51.30 ppm for the -PF
groups indicating that the orientations of the pentafluorocy-
clotriphosphazene moieties in compounds 6 and 7 are
different. This observation can be related to the fact that from
their crystal structures it is observed that in compound 6 the
two phosphazene units are eclipsed while in compound 7
they are present in a skew conformation with respect to each
other.
Selectivity and Mechanistic Considerations. The forma-
tion of bis pentafluorocyclotriphosphazene derived cyclo-
hexadiene complexes 6 and 7 shows an interesting selectivity.
As shown in Figure 5, there exists a possibility of forming
three isomers a, b, and c for compounds 6 and 7. Out of
these three possible isomers, only isomer a is found to form;
in this isomer the two fluorophosphazene units are present
on the carbon atoms which are adjacent to the added
dicyclopentadiene or indene moiety.
first step, 2 moles of PhCt CP3N3F5 displace the cyclooc-
tadiene present in [η5-carbomethoxycyclopentadienyl] [η4-
cyclooctadiene] cobalt complex, and the two alkynes can
coordinate with the cobalt center in two different orientations
(a and b). These can undergo oxidative coupling leading to
the metallacycle intermediates c, d, and g. The intermediate
a, in principle, can form two different metallacyclopentadiene
complexes (c and d) but the possibility of formation of the
intermediate c is restricted as it would result in two
pentafluorophosphazenyl moieties present on vicinal carbon
atoms of the metallacycle. The intermediate d, in the presence
of an external cycloalkene undergoes a [4 + 2] cycloaddition
leading to the formation of the hexadiene complex (f). The
possibility of formation of the cyclobutadiene complex (e)
from (d) is not favored, as it would force two fluorophos-
phazene units to be present on vicinal carbon atoms of the
cyclobutadiene unit, which is contrary to the experimental
results obtained from all the above reactions. Further, the
intermediate b can undergo oxidative coupling to form the
metallacyclopentadiene intermediate (g), which in turn can
readily convert to the more stable trans fluorophosphazene
substituted cyclobutadiene complex (h) which obeys the 18
electron rule as well. In a previous work, the metallacyles d
and g in their PPh3 stabilized form have been isolated and
structurally characterized, which further supports the pro-
posed mechanism.12 It is also of interest to note that the same
reaction did not yield the PPh3 stabilized metallacycle c,
supporting our contention that two fluorophosphazenyl units
are not accommodated on vicinal carbon atoms of a carba-
cycle or metallacycle.
This selectivity of product formation can be explained
using the following reaction mechanism (Scheme 6). In the
The fact that the reactions of PhCt CC6F5 with RCpCo-
(COD) did not give any cyclohexadiene complexes and also
3440 Inorganic Chemistry, Vol. 47, No. 8, 2008

Formation of Cyclophosphazene-DeriWed 1,3-Cyclohexadienes
resulted in cis and trans C6F5 substituted cyclobutadiene
RCpCo complexes indicates that the metallacycle analogues
of c and d having C6F5 units are able to convert readily to
the cis substituted cyclobutadiene complex similar to e. This
indicates that unlike N3P3F5, there is no difficulty for two
C6F5 units to be present on vicinal carbon atoms of a
carbacycle or metallacycle, and although electronically
similar, the steric features of N3P3F5 and C6F5 are signifi-
cantly different. This is further confirmed by reported
examples of multi pentafluorophenyl substituted aryl and
cycloalkyl compounds having two pentafluorophenyl groups
on adjacent carbon atoms.25
factors more than electronic factors, and unlike pentafluo-
rophenyl units, there is difficulty in accommodating two
N3P3F5 units on vicinal carbon atoms of a carbacycle or
metallacycle.
The reactions have also contributed to the understanding
of the mechanism of cobalt based [2 + 2 + 2] cycloaddition
reactions of two alkynes and one alkene. Although two
pathways are possible for the formation of cyclohexadiene
complexes, namely, through a metallacyclopentene or a
metallacyclopentadiene, calculations based on recent theo-
retical studies have predicted the metallacyclopentadiene
pathaway as energetically more feasible. While previous
experimental studies have shown that both cobaltacyclopen-
tene and cobaltacyclopentadiene can be precursors for CpCo
complexed cyclohexadienes, formation of phosphazene based
cyclohexadienes in this study support a cobaltacyclopenta-
diene intermediate, which is in agreement with the energy
calculations. The bispentafluorocyclotriphosphazene based
compounds synthesized in this study can also be precursors
for novel cyclohexadiene and aryl bridged fluorophosphazene
compounds.
Conclusions
In conclusion, we report the first examples of mono and
bis pentafluorocyclotriphosphazene derived [η5-carbomethox-
ycyclopentadienyl] [η4-1,3-cyclohexadiene] cobalt complexes
from the reactions of MeOC(O)CpCo(COD), PhCt
CP3N3F5 along with other alkynes or cyclic alkenes. These
cobalt based cyclohexadiene complexes can be used as
precursors for a host of aryl and cyclohexadiene derived
cyclophosphazenes. Although structural isomers are possible,
the reactions are found to be selective in nature, resulting in
only one isomer of the cyclohexadiene complex having
fluorophosphazene moieties attached to the carbon atoms
adjacent to the added alkene or indene unit. The reactions
also yielded only the trans [η5-carbomethoxycyclopentadi-
enyl] [η4-bis(1,3-pentafluorocyclotriphosphazenyl)-2,4-diphe-
nylcyclobutadiene] cobalt metallocene 2. The comparison of
the above reactions with the (ꢀ-phenylethynyl)pentafluo-
robenzene indicates that the selectivity observed in the
formation of the cyclohexadiene complexes is due to steric
Acknowledgment. The authors thank Department of
Science and Technology (DST) [SR/S1/IC-31/2007] and
Council of Scientific and Industrial Research (CSIR) India,
[01(2054) 06/ EMR-II] for financial assistance in the form
of research grants. We acknowledge DST-FIST and IITD
for funding of the single crystal X-ray diffraction facility at
IIT Delhi. Thanks are due to SAIF, CDRI, Lucknow for mass
spectral and analytical measurements. M.S.K. thanks CSIR
India for a senior research fellowship.
Supporting Information Available: Crystallographic informa-
tion files (CIF) for compounds 1, 6, 7, and 8 (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
(25) (a) Kosynkin, D.; Bockman, T. M.; Kochi, J. K. J. Am. Chem. Soc.
1997, 119, 4846–4855. (b) Kobrina, L. S.; Salenko, V. L.; Yakobson,
G. G. J. Fluorine Chem. 1976, 8, 193–207. (c) Thornberry, M. P.;
Slebodnick, C.; Deck, P. A.; Fronczek, F. R. Organometallics, 2000,
19, 5352–5369.
IC7024507
Inorganic Chemistry, Vol. 47, No. 8, 2008 3441