Synthesis and characterization of η2-C60 and μ3-η2,η2,η2-C 60 triosmium cluster complexes

Article abstract of DOI:10.1021/om970689p

Various η²-C₆₀ and μ₃-η²,η²,η²-C ₆₀ triosmium carbonyl cluster complexes Os₃(CO)₁₁(η²-C₆₀) (1), Os₃(CO)₁₀(NCMe)(η²-C₆₀) (2), Os₃(CO)₁₀(PPh₃)(η₂-C ₆₀) (3), Os₃(CO)₉(PR₃)₂(η ²-C₆₀) (4, R = Ph; 5, R = Me), Os₃(CO)₉(μ₃-η₂,η ₂,η₂-C₆₀) (6), and Os₃(CO)₈(PMe₃)(μ₃-η ²,η²,η²-C₆₀) (7) have been isolated as crystalline solids and characterized by spectroscopic (IR, MS, and ¹H, ³¹P, and ¹³C NMR) and analytical data. The molecular structure of complex 1 has been determined by a single-crystal X-ray diffraction study. The structure of 1 is derived from that of Os₃(CO)₁₂ by replacing an equatorial carbonyl ligand with an η²-C₆₀ ligand coordinated through a 6-6 ring fusion. The structural assignment of 2-7 is made on the basis of spectroscopic results. Compound 2 exists as two isomers in solution in a ratio of 2:1 (2a: 2b). VT ¹³C NMR spectra of 2a and 5 indicate that both complexes undergo similar fluxional processes of restricted equilibration of in-plane equatorial C₆₀ and carbonyl ligands via a triply bridged intermediate with identical values of ΔG_c^? = 12.7 ± 0.1 kcal/mol. Thermolysis of 2 in refluxing chlorobenzene affords Os₃(CO)₉(μ₃-η²,η ²,η²-C₆₀) (6) in 23percent yield, which can be alternatively prepared in 32percent yield from the reaction of Os₃(CO)₁₀(NCMe)₂ (2 equiv) and C₆₀ (1 equiv). Decarbonylation of 6 with Me₃NO/MeCN reagent in the presence of excess PMe₃ gives Os₃(CO)₈(PMe₃)(μ₃-η ²,η²,η²-C₆₀) (7) in a quantitative yield. VT ¹³C NMR spectra of both 6 and 7 reveal a localized-3-fold rotation of carbonyl and phosphine ligands on each osmium center.

Full text of DOI:10.1021/om970689p

Organometallics 1998, 17, 227-236
227
Syn th esis a n d Ch a r a cter iza tion of η2-C60 a n d
µ3-η2,η2,η2-C60 Tr iosm iu m Clu ster Com p lexes
J oon T. Park,*,† Hyunjoon Song,† J eong-J u Cho,† Mee-Kyung Chung,†
J in-Ho Lee,‡ and Il-Hwan Suh‡
Department of Chemistry, Korea Advanced Institute of Science and Technology,
Taejon 305-701, Korea, and Department of Physics, Chungnam National University,
Taejon 305-701, Korea
Received August 7, 1997X
Various η2-C60 and µ3-η2,η2,η2-C60 triosmium carbonyl cluster complexes Os3(CO)11(η2-C60)
(1), Os3(CO)10(NCMe)(η2-C60) (2), Os3(CO)10(PPh3)(η2-C60) (3), Os3(CO)9(PR3)2(η2-C60) (4, R )
Ph; 5, R ) Me), Os3(CO)9(µ3-η2,η2,η2-C60) (6), and Os3(CO)8(PMe3)(µ3-η2,η2,η2-C60) (7) have
1
been isolated as crystalline solids and characterized by spectroscopic (IR, MS, and H, 31P,
and 13C NMR) and analytical data. The molecular structure of complex 1 has been
determined by a single-crystal X-ray diffraction study. The structure of 1 is derived from
that of Os3(CO)12 by replacing an equatorial carbonyl ligand with an η2-C60 ligand coordinated
through a 6-6 ring fusion. The structural assignment of 2-7 is made on the basis of
spectroscopic results. Compound 2 exists as two isomers in solution in a ratio of 2:1 (2a :
2b). VT 13C NMR spectra of 2a and 5 indicate that both complexes undergo similar fluxional
processes of restricted equilibration of in-plane equatorial C60 and carbonyl ligands via a
q
triply bridged intermediate with identical values of ∆Gc ) 12.7 ( 0.1 kcal/mol. Thermolysis
of 2 in refluxing chlorobenzene affords Os3(CO)9(µ3-η2,η2,η2-C60) (6) in 23% yield, which can
be alternatively prepared in 32% yield from the reaction of Os3(CO)10(NCMe)2 (2 equiv) and
C60 (1 equiv). Decarbonylation of 6 with Me3NO/MeCN reagent in the presence of excess
PMe3 gives Os3(CO)8(PMe3)(µ3-η2,η2,η2-C60) (7) in a quantitative yield. VT 13C NMR spectra
of both 6 and 7 reveal a localized-3-fold rotation of carbonyl and phosphine ligands on each
osmium center.
In tr od u ction
sequent development in metal-C60 π-complex chemistry
has led to the synthesis of µ-η2,η2-C60 complexes, (µ-
η2,η2-C60)[Ir2Cl2(1,5-COD)2]27 and (µ-η2,η2-C60)Cp′2Ru2(µ-
Cl)2 (Cp′ ) η5-C5Me5),8 in which the metal atoms occupy
the adjacent π-bonds of a six-membered ring of C60 like
diene complexes. We set out to investigate complexes
of C60 with transition metal clusters with the expecta-
tion of seeing new bonding modes, physical properties,
fluxionality, or reactivities of C60 in these complexes by
cooperative interactions of the metal centers. We have
prepared various C60-triosmium carbonyl cluster com-
plexes, Os3(CO)11(η2-C60) (1), Os3(CO)10(NCMe)(η2-C60)
(2), Os3(CO)10(PPh3)(η2-C60) (3), Os3(CO)9(PR3)2(η2-C60)
(4, R ) Ph; 5, R ) Me), Os3(CO)9(µ3-η2,η2,η2-C60) (6), and
The organometallic chemistry of C60 has attracted
much attention1 concerning the effect of metal coordina-
tion on the properties of C60 since the discovery2 and
macroscopic synthesis3 of C60. The first structurally
characterized complex, (C60)(OsO4)(4-tBuC5H4N)2, an
osmate ester with C-O-Os bonds, was reported by
Hawkins and co-workers.4 However, the first example
with a direct metal-C60 bond, (η2-C60)Pt(PPh3)2, was
reported by Fagan et al.5 Numerous reports of other
metal-coordinated C60 complexes have included those
of Ta, Mo, W, Fe, Ru, Co, Rh, Ir, Ni, and Pd, in which
all the mononuclear metals are bound in an η2-fashion
at the 6-6 ring fusion.6 The C60 ligand in these
complexes acts as an electronegative alkene.1a,6j Sub-
(6) (a) Balch, A. L.; Catalano, V. J .; Lee, J . W. Inorg, Chem. 1991,
30, 3980. (b) Koefod, R. S.; Hudgens, M. F.; Shapley, J . R. J . Am. Chem.
Soc. 1991, 113, 8957. (c) Chase, B.; Fagan, P. J . J . Am. Chem. Soc.
1992, 114, 2252. (d) Balch, A. L.; Catalano, V. J .; Lee, J . W.; Olmstead,
M. M. J . Am. Chem. Soc. 1992, 114, 5455. (e) Balch, A. L.; Lee, J . W.;
Noll, B. C.; Olmstead, M. M. Inorg. Chem. 1993, 32, 3577. (f) Bashilov,
V. V.; Petrovskii, P. V.; Sokolov, V. I.; Lindeman, S. V.; Guzey, I. A.;
Struchkov, Y. T. Organometallics 1993, 12, 991. (g) Douthwaite, R.
E.; Green, M. L. H.; Stephens, A. H. H.; Turner, J . F. C. J . Chem. Soc.,
Chem. Commun. 1993, 1522. (h) Balch, A. L.; Lee, J . W.; Noll, B. C.;
Olmstead, M. M. Inorg. Chem. 1994, 33, 5238. (i) Rasinkangas, M.;
Pakkanen, T. T.; Pakkanen, T. A. J . Organomet. Chem. 1994, 476, C6.
(j) Shapley, J . R.; Du, Y.; Hsu, H.-F; Way, J . J . Proc. Electrochem. Soc.
1994, 94, 1255. (k) Green, M. L. H.; Stephens, A. H. H. J . Chem. Soc.,
Chem. Commun. 1997, 793.
* To whom correspondence should be addressed. E-mail:
jtpark@sorak.kaist.ac.kr. Fax: +82-42-869-2810.
† Korea Advanced Institute of Science and Technology.
‡ Chungnam National University.
X Abstract published in Advance ACS Abstracts, December 15, 1997.
(1) (a) Bowser, J . R. Adv. Organomet. Chem. 1994, 36, 57. (b) Fagan,
P. J .; Calabrese, J . C.; Malone, B. Acc. Chem. Res. 1992, 25, 134. (c)
Hirsch, A. The Chemistry of the Fullerenes; Thieme: Stuttgart, 1994.
(2) Kroto, H. W.; Heath, J . R.; O’Brien, S. C.; Curl, R. F.; Smalley,
R. E. Nature 1985, 318, 162.
(3) Kra¨tschmer, W.; Lamb, L. D.; Fostiropoulos, K.; Huffman, D. R.
Nature 1990, 347, 354.
(4) Hawkins, J . M.; Meyer, A.; Lewis, T. A.; Loren, S.; Hollander,
F. J . Science 1991, 252, 312.
(7) Rasinkangas, M.; Pakkanen, T. T.; Pakkanen, T. A.; Ahlgre´n,
M.; Rouvinen, J . J . Am. Chem. Soc. 1993, 115, 4901.
(8) Mavunkal, I. J .; Chi, Y.; Peng, S.-M.; Lee, G.-H. Organometallics
1995, 14, 4454.
(5) Fagan, P. J .; Calabrese, J . C.; Malone, B. Science 1991, 252, 1160.
S0276-7333(97)00689-4 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/01/1998

228 Organometallics, Vol. 17, No. 2, 1998
Ch a r t 1. Str u ctu r es of 1-7
Park et al.
(99.8%, Gold grade, Hoechst AG) was used without further
purification. Anhydrous trimethylamine N-oxide (mp 225-
230 °C) was obtained from Me3NO‚2H2O (98%, Aldrich Chemi-
cal Ltd.) by sublimation (3 times) at 90-100 °C under vacuum.
Os3(CO)11(NCMe),12 Os3(CO)11(PR3),12 and Os3(CO)10(PR3)2 (R
) Ph, Me)13 were prepared by literature methods. Carbon-13
(*C) CO-enriched complexes were prepared by using Os3-
(*CO)1214 (ca. 50% enrichment). Preparative thin-layer plates
were prepared from silica gel GF254 (type 60, E. Merck).
Infrared spectra were obtained on a Bomem MB-100 FT-IR
spectrometer. 1H NMR (300 MHz), 13C NMR (75 or 151 MHz),
and 31P NMR (122 MHz) spectra were recorded on either a
Bruker AM-300 or DMX-600 spectrometer. FAB positive-ion
mass spectra (FAB+) were obtained by the staff of the Korea
Basic Science Center. All m/ z values are referenced to 192Os.
Elemental analyses were provided by the staff of the Agency
for Defense Development.
P r ep a r a tion of Os3(CO)11(η2-C60) (1). A toluene solution
(30 mL) of Os3(CO)11(NCMe) (20.0 mg, 0.0217 mmol) and C60
(20.0 mg, 0.0278 mmol) was heated at 80 °C for 5 min to give
a dark brown solution. The solvent was evaporated and the
residue was purified by preparative TLC (toluene:hexane, 1:2)
at -15 °C to afford compound 1 (18.4 mg, 0.0115 mmol, 53%,
Rf ) 0.7) as a black microcrystalline solid. IR (CH2Cl2) ν(CO)
2122 (m), 2074 (s), 2059 (m), 2038 (vs), 2016 (m), 2006 (m),
1990 (w) cm-1 13C NMR (toluene-d8, 298 K) δ 183.3 (2 CO),
;
182.9 (2 CO), 181.7 (2 CO), 172.0 (1 CO), 171.9 (1 CO), 170.3
(1 CO), 168.8 (1 CO), 168.5 (1 CO); MS (FAB+) m/ z 1604 (M+).
Anal. Calcd for C78H8O11Os3 (1‚toluene): C, 55.39; H, 0.48.
Found: C, 55.33; H, 0.35.
P r ep a r a tion of Os3(CO)10(NCMe)(η2-C60) (2). A dichlo-
romethane (20 mL)-acetonitrile (3 mL) solution of Os3(CO)11-
(NCMe) (20.0 mg, 0.0217 mmol) was treated with an acetoni-
trile solution (3 mL) of anhydrous Me3NO (1.7 mg, 0.023 mmol)
at room temperature for 30 min. After evaporation of the
solvent in vacuo, a toluene (30 mL) solution of C60 (20.0 mg,
0.0278 mmol) was added to the residue. The resulting solution
was heated at 80 °C for 30 min to give a dark green solution.
The solvent was evaporated, and the residue was purified by
preparative TLC (toluene:hexane, 1:1) at -15 °C to afford a
mixture of two isomeric compounds 2 (27.3 mg, 0.0169 mmol,
78%, Rf ) 0.5) as a black solid. IR (CH2Cl2) ν(CO) 2110 (m),
2101 (w), 2064 (s), 2055 (m), 2032 (s), 2018 (vs), 1988 (m), 1958
(w) cm-1; 1H NMR (CDCl3, 298 K) δ 3.02 (s, 3H, CH3CN, 2a ),
2.85 (s, 3H, CH3CN, 2b), [2a ]:[2b] ) 2:1; 13C NMR (CD2Cl2,
193 K) δ 187-183 (4 CO), 181.6, 176.9, 174.6, 173.3, 170.0,
169.2 (CO’s of major isomer 2a from an isomeric mixture); MS
(FAB+) m/ z 1617 (M+). Anal. Calcd for C72H3O10NOs3: C,
53.63; H, 0.19. Found: C, 53.81; H, 0.18.
Os3(CO)8(PMe3)(µ3-η2,η2,η2-C60) (7), both η2-C60 (1-5)
and µ3-η2,η2,η2-C60 (6 and 7) triosmium complexes.
Transition metal cluster-bound C60 complexes were
unknown prior to this work. The first arene-like
complex of C60, Ru3(CO)9(µ3-η2,η2,η2-C60),9 however, has
been recently prepared from the reaction of Ru3(CO)12
and C60 in hexane under reflux for 2 days in a very low
(4%) yield by Shapley and co-workers during our
investigation. In preliminary forms, we have reported
the synthesis and characterization of complexes 1, 2, 3,
and 4.10 Electrochemical studies of 1, 3, and 4 have
revealed the first example of C60-mediated electron
transfer to the metal center.11 Since then, we have
completed the structural characterization of 1 and
fluxional processes of 2 and 5. Furthermore, reactivity
studies of 2 have resulted in high-yield syntheses of µ3-
η2,η2,η2-C60 triosmium complexes, 6 and 7. Herein we
report the preparation and characterization of trios-
mium cluster derivatives of C60, 1-7, as shown in Chart
1.
In ter con ver sion of 1 a n d 2. 1 f 2: Compound 1 (10.0
mg, 0.0063 mmol) was dissolved in a mixture of toluene (20
mL) and acetonitrile (3 mL). The solution was cooled to -50
°C, and an acetonitrile solution (3 mL) of anhydrous Me3NO
(0.5 mg, 0.007 mmol) was added dropwise. The reaction
mixture was allowed to warm to room temperature for 2 h.
Evaporation of the solvent and purification by preparative TLC
(toluene:hexane, 1:1) at -15 °C gave compound 2 (9.1 mg,
0.0056 mmol, 90%). 2 f 1: Carbon monoxide was bubbled
with a gas dispersion tube through a toluene solution (20 mL)
of compound 2 (10.0 mg, 0.0062 mmol) at room temperature
for 2 h. The solvent was evaporated, and the residue was
purified by preparative TLC (toluene:hexane, 1:2) at -15 °C
to give compound 1 (9.4 mg, 0.0059 mmol, 95%).
Exp er im en ta l Section
P r ep a r a tion of Os3(CO)10(P P h 3)(η2-C60) (3). A dichlo-
romethane (20 mL)-acetonitrile (3 mL) solution of Os3(CO)11-
Gen er a l Com m en ts. All reactions were carried out under
a nitrogen atmosphere with the use of standard Schlenk
techniques. Solvents were appropriately dried before use. C60
(12) J ohnson, B. F. G.; Lewis, J .; Pippard, D. A. J . Chem. Soc.,
Dalton Trans. 1981, 407.
(13) Tachikawa, M.; Shapley, J . R. J . Organomet. Chem. 1977, 124,
C19.
(9) Hsu, H.-F.; Shapley, J . R. J . Am. Chem. Soc. 1996, 118, 9192.
(10) Park, J . T.; Cho, J .-J .; Song, H. J . Chem. Soc., Chem. Commun.
1995, 15.
(11) Park, J . T.; Cho, J .-J .; Song, H.; J un, C.-S.; Son, Y.; Kwak, J .
Inorg. Chem. 1997, 36, 2698.
(14) Clauss, A. D.; Tachikawa, M.; Shapley, J . R.; Pierpont, C. G.
Inorg. Chem. 1981, 20, 1528.

Synthesis of Triosmium Cluster Complexes
Organometallics, Vol. 17, No. 2, 1998 229
(PPh3) (20.0 mg, 0.0175 mmol) was treated with an acetonitrile
solution (3 mL) of anhydrous Me3NO (1.5 mg, 0.020 mmol) at
room temperature for 30 min. After evaporation of the solvent
in vacuo, a toluene solution (30 mL) of C60 (16.4 mg, 0.0228
mmol) was added to the residue. The solution was stirred at
room temperature for 4 h to give a green solution. The solvent
was evaporated, and the residue was purified by preparative
TLC (toluene:hexane, 1:1) at -15 °C to afford compound 3 (26.7
mg, 0.0146 mmol, 83%, Rf ) 0.8) as a black microcrystalline
solid. IR (CH2Cl2) ν(CO) 2099 (m), 2051 (m), 2034 (m), 2017
(vs), 1993 (m), 1975 (sh) cm-1; MS (FAB+) m/ z 1838 (M+).
Anal. Calcd for C88H15O10POs3: C, 57.64; H, 0.82. Found: C,
56.77; H, 0.90.
Con ver sion of 2 to 3. Compound 2 (10.0 mg, 0.0062 mmol)
was dissolved in toluene (20 mL), and then PPh3 (3.3 mg, 0.013
mmol) was added. The reaction mixture was stirred for 1 h
at room temperature, and the solvent was evaporated. Puri-
fication by preparative TLC (toluene:hexane, 1:1) at -15 °C
afforded compound 3 (10.9 mg, 0.0059 mmol, 96%).
preparative TLC (CS2) to give compound 6 (13.7 mg, 0.00888
mmol, 32%, Rf ) 0.8) as a reddish-brown solid. IR (CS2) ν-
(CO) 2081 (s), 2046 (vs), 2016 (m), 2002 (m), 1983 (sh) cm-1
;
13C NMR (CS2/ext. CD2Cl2, 298 K) δ 176.1 (s, 9 CO); MS (FAB+)
m/ z 1548 (M+). Anal. Calcd for C69O9Os3:C, 53.70. Found:
C, 53.94.
Th er m olysis of 2. A chlorobenzene solution (20 mL) of
compound 2 (10.0 mg, 0.0062 mmol) was heated at reflux for
1 h. After evaporation of the solvent in vacuo, the residue was
purified by preparative TLC (CS2) to afford compound 6 (2.2
mg, 0.0014 mmol, 23%).
P r ep a r a tion of Os3(CO)8(P Me3)(µ3-η2,η2,η2-C60) (7). Os3-
(CO)11(PMe3) (50.0 mg, 0.0524 mmol) was dissolved in a
mixture of dichloromethane (30 mL) and acetonitrile (5 mL).
An acetonitrile solution (3 mL) of anhydrous Me3NO (4.3 mg,
0.057 mmol) was added dropwise at room temperature. After
evaporation of the solvent in vacuo, the residue was dissolved
in chlorobenzene (5 mL). The solution was added dropwise to
a refluxing chlorobenzene solution of C60 (20.0 mg, 0.0278
mmol, 0.5 equiv), and the reaction mixture was stirred for 90
min. The solvent was evaporated, and the residue was purified
by preparative TLC (CS2) to give compound 7 (6.2 mg, 0.00390
mmol, 14%, Rf ) 0.5) as a black solid. IR (CS2) ν(CO) 2064
(vs), 2032 (s), 2010 (s), 1998 (m), 1984 (m), 1960 (w), 1946(w)
P r ep a r a tion of Os3(CO)9(P R3)2(η2-C60) (R ) P h (4), Me
(5)). A dichloromethane (20 mL)-acetonitrile (3 mL) solution
of Os3(CO)10(PPh3)2 (20.0 mg, 0.0145 mmol) was treated with
an acetonitrile solution (3 mL) of anhydrous Me3NO (1.2 mg,
0.016 mmol) at room temperature for 30 min. After evapora-
tion of the solvent in vacuo, the residue was dissolved in
toluene (30 mL) containing C60 (13.6 mg, 0.0189 mmol). The
resulting solution was stirred at room temperature for 4 h to
give a blue-green solution. The solvent was evaporated and
the residue was purified by preparative TLC (toluene:hexane,
1:1) at -15 °C to produce compound 4 (19.5 mg, 0.00945 mmol,
65%, Rf ) 0.5) as a black solid. The reaction of Os3(CO)10-
(PMe3)2 (20.0 mg, 0.0199 mmol) with anhydrous Me3NO (1.6
mg, 0.022 mmol) followed by treatment with C60 (18.7 mg,
0.0259 mmol) was carried out following a procedure similar
to that for 4. Evaporation of the solvent and purification by
preparative TLC (toluene:hexane, 2:1) at -15 °C produced
compound 5 (16.6 mg, 0.00979 mmol, 49%, Rf ) 0.6) as a black
solid. Compound 4: IR (CH2Cl2) ν(CO) 2109 (w), 2083 (w),
2072 (w), 2051 (m), 2017 (s), 1999 (vs), 1964 (m), 1941 (sh)
1
2
cm-1; H NMR (CS2/C6D6, 298 K) δ 1.71 (d, J PH ) 10.0 Hz,
9H); 31P{1H} NMR (CS2/C6D6, 298 K) δ -47.4 (s); 13C NMR
2
(C6D4Cl2, 298 K) δ 185.4 (d, J PC ) 5.9 Hz, 2 CO), 178.5 (s, 6
CO); MS (FAB+) m/ z 1596 (M+). Anal. Calcd for C71H9O8-
POs3:C, 53.59; H, 0.57. Found: C, 53.14; H, 0.38.
Con ver sion of 6 to 7. Meth od 1: Compound 6 (20.0 mg,
0.0130 mmol) was dissolved in chlorobenzene (20 mL), and an
excess amount (0.006 mL, 0.06 mmol) of PMe3 was added. The
resulting mixture was heated to reflux for 5 h. The solvent
was evaporated, and the residue was purified by preparative
TLC (CS2) to afford compound 7 (8.8 mg, 0.0055 mmol, 43%).
Meth od 2: Compound 6 (20.0 mg, 0.0130 mmol) was dissolved
in chlorobenzene (20 mL), and an excess amount of PMe3 was
added. The solution was cooled to -20 °C, and an acetonitrile
solution (3 mL) of anhydrous Me3NO (1.0 mg, 0.013 mmol) was
added dropwise. The reaction mixture was allowed to warm
to room temperature for 1 h. The solvent was evaporated, and
the residue was purified by preparative TLC (CS2) to afford
compound 7 (19.8 mg, 0.0124 mmol, 96%).
cm-1
;
MS (FAB+) m/ z 2072 (M+). Anal. Calcd for
C
105H30O9P2Os3: C, 60.99; H, 1.46. Found: C, 59.67; H, 1.46.
Compound 5: IR (CH2Cl2) ν(CO) 2069 (m), 2016 (sh), 2007 (s),
1990 (vs), 1966 (sh), 1954 (s) cm-1; 1H NMR (CD2Cl2, 298 K) δ
2
2.04 (d, J PH ) 10.3 Hz, 18H); 31P{1H} NMR (CD2Cl2, 213 K)
X-r a y Str u ctu r e Deter m in a tion for 1‚CH2Cl2. Crystals
of 1 suitable for an X-ray analysis were obtained by slow
recrystallization from a mixed solvent of toluene, dichlo-
romethane, and hexane at -20 °C. An opaque dark crystal
with approximate dimensions of 0.26 × 0.40 × 0.03 mm was
mounted and aligned on a CAD4 diffractometer. Details of
the relevant crystallographic data are given in Table 1. The
accurate cell parameters were refined from setting angles of
25 reflections with 11.39° < θ < 13.91°, and intensity data for
4054 independent reflections in the range 0 e h e 17, 0 e k e
15, 0 e l e 32 were collected using graphite-monochromated
Mo KR radiation and the ω/2θ scan mode, ω-scan width ) (0.8
+ 0.35 tan θ)°, θmax ) 25°. One orientation reflection was
checked every 300 reflections, and three standard reflections
were monitored every 3 h. The intensity variation was less
than 1.4% during data collection, and thus, the decay correc-
tion was not applied to the data. All data were corrected for
Lp and absorption factors: the maximum and minimum
transmission factors were 1.00 and 0.65 with an average of
0.83. Data collection, cell refinement, and data reduction were
performed by SDP.15 Consistent with the observed values of
the cell parameters and observed symmetries in reflection
intensities, the unit cell was determined to be orthorhombic.
The observed extinctions (0kl, k + l ) odd; and hk0, h ) odd)
permitted only two space groups; the noncentrosymmetric
δ -49.29 (s), -50.87 (s); 13C{1H} NMR (CD2Cl2, 213 K) δ 194.8
(2J CP ) 7.2 Hz, 2 CO), 194.5 (2J CP ) 8.1 Hz, 2 CO), 185.4 (2
CO), 181.6 (1 CO), 180.6 (1 CO), 178.3 (1 CO); 13C{1H} NMR
(CD2Cl2, 298 K) δ 161.3, 147.6, 146.9, 145.8, 145.7, 145.3,
145.2, 145.1, 144.8, 144.2, 144.1, 143.3, 142.9, 142.7, 142.3,
141.4 (16 C60 signals), 56.5 (C60 sp3 carbon), 22.6, 22.2 (br,
P(CH3)3); MS (FAB+) m/ z 1700 (M+). Anal. Calcd for
C
75H18O9P2Os3:C, 53.13; H, 1.07. Found: C, 53.41; H, 1.33.
Con ver sion of 3 to 4. Compound 3 (10.0 mg, 0.0055 mmol)
was dissolved in toluene (20 mL), and PPh3 (2.9 mg, 0.011
mmol) was added. The solution was cooled to -50 °C, and a
solution of anhydrous Me3NO (0.5 mg, 0.007 mmol) in aceto-
nitrile (3 mL) was added dropwise. The mixture was allowed
to warm to room temperature for 2 h. The solvent was
evaporated, and the residue was purified by preparative TLC
(toluene:hexane, 1:1) at -15 °C to afford compound 4 (10.3
mg, 0.0050 mmol, 91%).
P r ep a r a tion of Os3(CO)9(µ3-η2,η2,η2-C60) (6). To a dichlo-
romethane (30 mL) and acetonitrile (5 mL) solution of Os3-
(CO)11(NCMe) (50.0 mg, 0.0544 mmol) was added an acetoni-
trile solution (3 mL) of anhydrous Me3NO (4.5 mg, 0.060 mmol)
dropwise at room temperature. After evaporation of the
solvent in vacuo, the residue was dissolved in chlorobenzene
(5 mL). The solution was added dropwise to a refluxing
chlorobenzene solution of C60 (20.0 mg, 0.0278 mmol, 0.5
equiv), and the reaction mixture was stirred for 90 min. The
solvent was evaporated, and the residue was purified by
(15) Structure Determination Package; Enraf-Nonius: The Nether-
lands, 1985.

230 Organometallics, Vol. 17, No. 2, 1998
Park et al.
Sch em e 1. Syn th esis of η2-C60 Com p lexesa
Ta ble 1. Cr ysta l a n d Str u ctu r e Deter m in a tion
Da ta for 1‚CH2Cl2
formula
fw
cryst syst
space group
a, Å
C71O11Os3‚CH2Cl2
1684.31
orthorhombic
Pnma
13.879(2)
12.034(1)
27.468(2)
4587.7(8)
4
b, Å
c, Å
V, Å3
Z
D
calcd, Mg m-3
2.439
temp, K
294
λ (Mo KR), Å
0.710 69
8.55
0.65-1.00
5449
4054
2885
0.064
0.154
µ, mm-1
transmission factors
no. of rflns measd
no. of unique rflns
no. of rflns (Fo > 4σ(Fo))
a
Rf
b
Rw
a
b
2
Rf ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) [∑ω(|Fo| - |Fc|)2/∑ω|Fo| ]1/2
.
group Pna21 (No. 33) and the centrosymmetric group Pnma
(No. 62).16 Both possible assignments were tested. Whereas
least-squares refinement was processed well in Pnma, no
satisfactory refinement was obtained in Pna21 (indeed, un-
satisfactory thermal parameters and geometric parameters
and high R values were consistently observed in this case).
Thus Pnma is strongly indicated as a space group for 1. The
structure was determined using the direct-method procedure
of the SHELX86 program,17 which revealed one osmium atom
occupied a special position (4c) of space group Pnma. The
other two osmium atoms, which are at the general position,
synthesis of 1-5 are summarized in Scheme 1. Oxida-
tive decarbonylation by Me3NO in the presence of the
weak-field ligand MeCN has been used extensively in
the activation of Os3(CO)12 and affords the labile deriva-
tives Os3(CO)12-n(NCMe)n (n ) 1, 2), which are versatile
starting materials for the synthesis of many triosmium
cluster complexes.12,13 Complexes 1 and 2 have been
prepared upon brief heating (5 min for 1, 30 min for 2)
of Os3(CO)11(NCMe) and Os3(CO)10(NCMe)2 with C60 in
toluene at 80 °C, respectively, by substitution of a
weakly coordinated MeCN ligand with C60. Longer
periods of heating resulted in extensive decomposition
and gave lower yields for both 1 and 2. The phosphine-
substituted complexes, 3-5, have been prepared after
initial treatment of the corresponding starting material
with Me3NO/MeCN reagent and subsequent reaction
with C60 at room temperature. Complexes 1 and 2 are
interconvertible either by decarbonylation of 1 with Me3-
NO/MeCN reagent or by exposure of 2 to CO gas (1
atm). Complex 2 reacts with PPh3 to afford 3, which
undergoes further reaction with PPh3 to produce 4 upon
decarbonylation with Me3NO. All these transformations
(1 h 2 f 3 f 4) proceed in quantitative yields.
Complexes 2-5 are soluble in dichloromethane and
1-5 in aromatic solvents to form either brown (1) or
green (2-5) solutions, but they are insoluble in pentane
and hexane. The formulations of 1-5 are supported by
elemental analysis and by the molecular-ion (M+) mul-
tiplet in the FAB+ mass spectrum (MS) of each com-
pound. The M+ multiplet of 1-5 perfectly matches the
calculated pattern (the highest peak in the M+ multiplet
(m/ z, found, calcd), 1 (1600, 1600), 2 (1613, 1613), 3
(1834, 1834), 4 (2068, 2068), and 5 (1696, 1696)). The
presence of MeCN ligand in 2 was confirmed by obser-
vation of the highest peak at 1616 (2 + 3) in the MS of
the deuterated derivative of 2, Os3(CO)10(CD3CN)(η2-
C60).
1
are disordered at two positions, related by a (x, /4, z) mirror
plane, with half-occupancy (see Supporting Information). The
rest of the atoms in 1 were located from difference Fourier
maps. The crystallographic mirror plane passes through the
molecule so that six atoms of the three carbonyl groups, four
atoms of the C60 ligand, and the carbon and one chlorine atom
of the CH2Cl2 solvate molecule are located on the mirror plane.
Six carbonyl groups of the Os3(CO)11 moiety are disordered at
the opposite side of the mirror plane with half-occupancy. The
chlorine atom located on the mirror plane is split into two
positions with an occupancy factor of 0.25, while the other
chlorine atom occupies two general positions related by the
mirror plane with half-occupancy. The whole structure was
refined by full-matrix least-squares techniques on F2. Of the
58 atoms present in the asymmetric unit, 46 were refined with
anisotropic thermal parameters and the remaining 12 atoms
were given isotropic thermal parameters (see Supporting
Information). For all computations, the SHELX93 package18
was used and the function minimized was ∑ω(|Fo| - |Fc|)2, with
ω ) 1/[σ2(Fo2) + (0.1123P)2], where P ) (Fo2 + 2Fc2)/3. Neutral
atomic scattering factors were used with Os (f′ and f′′),
corrected for anomalous dispersion. The number of param-
eters refined was 431. Hydrogen atoms for the CH2Cl2 solvate
molecule were not located. Final reliability factors for 2885
unique observed reflections [Fo > 4σ(Fo)] were RF ) 0.064, Rw
) 0.154, with (∆/σ)max ) 0.102, ∆Fmax/∆Fmin ) 2.434/-1.301 e/Å3
in final ∆F map and S ) 0.982.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of η2-C60 Com -
p lexes 1-5. Details of the reaction conditions for the
(16) International Tables for Crystallography; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1992; Vol. A.
(17) Sheldrick, G. M. SHELX86, Program for Crystal Structure
Solution; University of Go¨ttingen: Go¨ttingen, Germany, 1985.
(18) Sheldrick, G. M. SHELX93, Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
The definitive structural assignment of 1-5 (see
Chart 1) is made on the basis of spectroscopic data (1H
and 13C NMR and IR). The IR spectrum of 1 is identical

Synthesis of Triosmium Cluster Complexes
Organometallics, Vol. 17, No. 2, 1998 231
to that of Os3(CO)11(PPh3),19 and the IR spectra of 3 and
4 (5) are similar to those of Os3(CO)10(PPh3)220 and Os3-
(CO)9(PPh3)3,21 except that the IR bands of C60 com-
plexes are shifted to higher energies by ca. 20 cm-1
compared to those of the corresponding phosphine
derivative, reflecting the electron-withdrawing nature
of the C60 ligand. Phosphine substitution for CO in Os3-
(CO)12 invariably occurs at an equatorial site.22 These
results indicate that compounds 1, 3, and 4 (5) are
isostructural with the respective phosphine-substituted
complex, Os3(CO)12-n(PPh3)n (n ) 1-3), and thus the
C
60 moiety occupies an equatorial site as shown in Chart
1. Furthermore, the limiting low-temperature 13C NMR
(CO region) of 1* (ca. 50% 13CO-enriched) reveals eight
resonances at δ 183.3, 182.9, 181.7, 172.0, 171.9, 170.3,
168.8, and 168.5 with an intensity ratio of 2:2:2:1:1:1:
1:1. The three lower-field resonances with higher
intensities are considered to be due to three sets of the
six axial carbonyl ligands, and the rest of the resonances
are attributed to the five inequivalent equatorial car-
bonyl ligands.23 These data are entirely consistent with
the crystal structure of 1 (vide infra), with η2-C60
occupying an equatorial position at an osmium center.
The 13C signals for the C60 moiety are too weak to be
detected. The 1H NMR spectrum of 2 shows two
singlets due to the coordinated MeCN at δ 3.02 (2a ) and
2.85 (2b) in a ratio of 2:1, indicating that 2 exists as
two isomers. Upon addition of CD3CN, the two reso-
nances for 2a and 2b slowly (2 h) lose intensity at room
temperature and are replaced by a sharp singlet at δ
1.98 due to free MeCN, which is consistent with facile
displacement of the coordinated MeCN by the deuter-
ated solvent. In compound 2, the MeCN ligand may be
coordinated at an axial site of an osmium atom, as
shown in all known acetonitrile derivatives of triosmium
clusters.24 The limiting low-temperature 13C NMR (CO
region) of 2* shows two sets of 10 resonances due to 2a
and 2b in an intensity ratio of 2:1. Major isomer 2a is
considered to have a structure with an axial MeCN and
a bulky equatorial C60 ligand coordinated at the same
osmium atom, which is strongly supported by both the
crystal structure of Os3(CO)10(NCMe)(dmfu) (8) (dmfu
) MeO2C(H)CdC(H)CO2Me)25 and the fluxional behav-
ior of 2a (vide infra). The dimethylfumarate ligand is
known to have a similar electron-withdrawing property
to that of C60.6j The crystal structure of an isomer
obtained from an isomeric mixture of 8 indicated that
the axial MeCN and equatorial dmfu ligands were
coordinated at the same metal center,25 which was
assumed to be isostructural with 2a . The only struc-
tural possibility of minor isomer 2b is a structure that
axial MeCN and equatorial C60 ligands are bonded to
each adjacent osmium atom. This structure may pro-
duce two isomers due to two inequivalent equatorial
sites for C60. We, however, observed only one isomer
F igu r e 1. Molecular geometry and atomic-labeling scheme
for 1. Labels for primed atoms of C60 are omitted for clarity.
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) a n d
Esd ’s for 1‚CH2Cl2
(A) Metal-Metal Distances
Os(1)-Os(2)
(1)Os(2)-Os(3)
2.891(1)
2.851(2)
Os(1)-Os(3)
2.897(1)
(B) Metal-Carbon (Carbonyl) Distances
Os(1)-C(100)
Os(1)-C(200)
Os(2)-C(202)
Os(3)-C(300)
Os(3)-C(302)
1.89(2)
1.97(3)
1.93(5)
1.93(3)
1.93(3)
Os(1)-C(101)
Os(2)-C(201)
Os(2)-C(203)
Os(3)-C(301)
Os(3)-C(303)
1.94(1)
1.86
1.94(4)
1.96(3)
1.99(3)
(C) Carbon-Oxygen (Carbonyl) Distances
C(100)-O(100)
C(100)-O(200)
C(202)-O(202)
C(300)-O(300)
C(302)-O(302)
1.12(3)
1.14(3)
1.16(6)
1.11(3)
1.13(4)
C(101)-O(101)
C(201)-O(201)
C(203)-O(203)
C(301)-O(301)
C(303)-O(303)
1.13(2)
1.24(4)
1.17(4)
1.11(4)
1.10(3)
(D) Metal-Carbon (C60) Distances
2.21(2) Os(1)-C(2)
Os(1)-C(1)
2.26(2)
(E) Distances within the C60 Ligand
C(1)-C(2)
C(2)-C(3)
1.42(3)
1.48(2)
C(1)-C(18)
C(10)-C(11)
1.45(2)
1.36(3)
1
for 2b in both the H and 13C NMR spectra (down to
193 K), which may be explained by a fast exchange of
the C60 ligand between the two inequivalent equatorial
sites in the temperature range. It seems that the
electron-withdrawing nature of the C60 ligand favors the
structure of 2a , which has C60 and the donor MeCN
ligands bonded to the same metal center, and also
accounts for the observation that the methyl proton
resonance of 2a (δ 3.02) is more downfield than that of
2b (δ 2.85).
Cr ysta l Str u ctu r e of 1‚CH2Cl2. The crystal con-
tains a disordered arrangement of discrete Os3(CO)11(η2-
C60)‚CH2Cl2 molecules, which are mutually separated
by normal van der Waals distances. The CH2Cl2 solvate
molecule does not enter into any significant interactions
with molecule 1. The overall molecular geometry and
the atomic-labeling scheme are illustrated in Figure 1.
Interatomic distances and angles are listed in Tables 2
and 3, respectively.
(19) Bruce, M. I.; Liddell, M. J .; Hughes, C. A.; Skelton, B. W.; White,
A. H. J . Organomet. Chem. 1988, 347, 157.
The molecular structure of 1 is derived from that of
Os3(CO)12 by replacing an equatorial carbonyl group on
the Os(1) atom with the C60 ligand. The two osmium
atoms (2, 3) and six carbonyl ligands (201, 202, 203, 301,
302, 303), however, are disordered out of the crystal-
lographic mirror plane, which includes the Os(1) atom,
four C60 carbon (1, 2, 10, 11) atoms, and three equatorial
carbonyl (100, 200, 300) groups, and bisects the C60
ligand and the Os(2)-Os(3) bond. The primed atoms
(20) Bruce, M. I.; Liddell, M. J .; Hughes, C. A.; Patrick, J . M.;
Skelton, B. W.; White, A. H. J . Organomet. Chem. 1988, 347, 181.
(21) Bruce, M. I.; Liddell, M. J .; Shawkataly, O.; Hughes, C. A.;
Skelton, B. W.; White, A. H. J . Organomet. Chem. 1988, 347, 207.
(22) Deeming, A. J . Adv. Organomet. Chem. 1986, 26, 1.
(23) J ohnson, B. F. G.; Lewis, J .; Reichert, B. E.; Schropp, K. T. J .
Chem. Soc., Dalton Trans. 1976, 1403.
(24) Dawson, P. A.; J ohnson, B. F. G.; Lewis, J .; Puga, J .; Raithby,
P. R.; Rosales, M. J . J . Chem. Soc., Dalton Trans. 1982, 233.
(25) Park, J . T.; Song, H. Manuscript in preparation.

232 Organometallics, Vol. 17, No. 2, 1998
Park et al.
Ta ble 3. Selected In ter a tom ic An gles (d eg) a n d
Esd ’s for 1‚CH2Cl2
(A) Intermetallic Angles
Os(1)-Os(2)-Os(3) 59.03(4) Os(1)-Os(2)-Os(3) 60.59(4)
(B) M-M-CO Angles
Os(2)-Os(1)-C(100) 123.8(8) Os(3)-Os(1)-C(100) 139.0(6)
Os(2)-Os(1)-C(101)
89.8(5) Os(3)-Os(1)-C(101)
77.7(4)
92.9(8)
94(1)
Os(1)-Os(2)-C(200) 149.7(6) Os(3)-Os(2)-C(200)
Os(1)-Os(2)-C(201) 78(1) Os(3)-Os(2)-C(201)
Os(1)-Os(2)-C(202) 103(1)
Os(1)-Os(2)-C(203) 95(1)
Os(1)-Os(3)-C(300) 152.4(5) Os(2)-Os(3)-C(300)
Os(3)-Os(2)-C(202) 161(1)
Os(3)-Os(2)-C(203)
81(1)
97.5(9)
96(1)
Os(1)-Os(3)-C(301)
Os(1)-Os(3)-C(302)
Os(1)-Os(3)-C(303)
79.4(9) Os(2)-Os(3)-C(301)
3(9)
Os(2)-Os(3)-C(302) 160.5(9)
96.0(9) Os(2)-Os(3)-C(303)
81(1)
(C) Os-C-O and C-Os-C Angles
Os(1)-C(100)-O(100) 171(2)
Os(2)-C(200)-O(200) 165(1)
Os(2)-C(202)-O(202) 177(3)
Os(3)-C(300)-O(300) 166(1)
Os(3)-C(302)-O(302) 171(3)
Os(1)-C(101)-O(101) 176(1)
Os(2)-C(201)-O(201) 169(4)
Os(2)-C(203)-O(203) 173(3)
Os(3)-C(301)-O(301) 177(3)
Os(3)-C(303)-O(303) 175(3)
92.7(4) C(200)-Os(2)-C(201) 91(1)
C(100)-Os(1)-C(101)
C(200)-Os(2)-C(202) 105(1)
C(200)-Os(2)-C(203)
95(1)
C(201)-Os(2)-C(202)
C(202)-Os(2)-C(203)
91(1)
92(1)
C(201)-Os(2)-C(203) 172(2)
C(300)-Os(3)-C(301)
C(300)-Os(3)-C(303)
88(1)
97(1)
C(300)-Os(3)-C(302) 102(1)
C(301)-Os(3)-C(302)
C(302)-Os(3)-C(303)
89(1)
93(1)
C(301)-Os(3)-C(303) 175(1)
(D) Angles Involving C(1) and C(2)
C(1)-Os(1)-C(2)
Os(2)-Os(1)-C(1)
Os(3)-Os(1)-C(1)
Os(1)-C(1)-C(18)
C(18)-C(1)-C(2)
C(18)-C(1)-C(18)′
37.1(7)
166.6(3)
132.7(4)
121.1(9)
119(1)
Os(1)-C(1)-C(2)
Os(2)-Os(1)-C(2)
Os(3)-Os(1)-C(2)
Os(1)-C(2)-C(3)
C(3)-C(2)-C(1)
C(3)-C(2)-C(3)′
73(1)
151.2(4)
96.3(5)
91(1)
122(1)
104(2)
F igu r e 2. VT 13C NMR spectra (75 MHz, CO region, CD2-
Cl2) of 2*. Resonances marked with b are from 2a and those
with 4 are from 2b.
103(2)
are the symmetry mates of the unprimed atoms, and
each mate occupies the opposite side of the mirror plane
with half-occupancy. The Os(2)-Os(3) bond in the Os3
triangle is slightly shorter (ca. 0.05 Å) than the other
two Os-Os bonds. The average Os-Os distance for 1
(2.879(1) Å) is similar to that for Os3(CO)12 (2.877(3)
Å).26 The C60 moiety is bound to the Os(1) atom in an
η2 fashion through a 6-6 ring fusion, as found in other
η2-C60 transition metal complexes.6 The dihedral angle
between Os(1)-C(1)-C(2) and Os3 triangles is 19(1)°,
and the carbonyl ligands on each osmium atom also
reveal significant distortion. Both distortions are,
presumably, due to a steric conjestion between the C60
and the adjacent equatorial carbonyl (302) ligand. The
Os-C(C60) bond distances are Os(1)-C(1) ) 2.21(2) Å
and Os(1)-C(2) ) 2.26(2) Å, which are comparable to
the values (2.15(3), 2.22(3) Å) of Os-C(alkene) bonds
found in Os3(CO)10(PEt3)[CF3(H)CdC(H)CF3].27 The
C(1)-C(2) bond length is 1.42(2) Å, and this bond is
elongated due to the metal-to-C60 π-back-donation com-
pared with 1.38(2) Å for an unperturbed (6, 6)-bond. We
note here that the following C-C distances of C60
directly bonded to the metal center have been observed
in η2-C60 complexes: 1.45(3) Å in Pd(PPh3)2(η2-C60),6f
1.48(1) Å in RhH(CO)(PPh3)2(η2-C60),6e 1.49(2) Å in {Ir-
(CO)Cl(PEt3)2}2C60,6h 1.50(1) Å in W(CO)3(diphos)(η2-
C60),6j 1.50(3) Å in Pt(PPh3)2(η2-C60),5 1.51(2) Å in
{Ir(CO)Cl(PMe3)2}2C60,6h and 1.53(3) Å in Ir(CO)Cl-
(PPh3)2(η2-C60).6a The C(1)-C(2) bond of 1, therefore,
is the shortest value observed in these complexes,
implying that the π-back-donation in 1 may be signifi-
cantly suppressed by strong π-acid carbonyl ligands on
the osmium atoms. The C60 moiety shows the same
distortion of pulling the C(1) and C(2) atoms away from
the C60 surface as that seen in other complexes: the
angles between the C(1) and C(2) axis and the planes
described by C(2)-C(3)-C(3)′ and C(1)-C(18)-C(18)′
are 40(2)° and 39(2)°, respectively, but such angles in
free C60 are known to be 31°.1b
All other features of the molecular geometry are
within the expected range. The average C-C bond
length at the junction of the 5,6 ring is 1.45(2) Å and
that at the junction of the 6,6 ring is 1.38(2) Å.
Individual Os-CO distances range from 1.86(3) to 1.99-
(3) Å, C-O bond lengths range from 1.10(3) to 1.24(4)
Å, and Os-C-O angles are in the range 165(1)-177-
(3)°.
F lu xion a l P r ocesses of 2 a n d 5. The molecular
dynamics of 2 and 5 have been examined by variable-
temperature (VT) 13C NMR spectroscopy using *CO-
enriched samples, 2* and 5*. The limiting low-temper-
ature 13C NMR spectrum of 2* at 193 K (Figure 2, CO
region) reveals two sets of 10 resonances attributed to
unsymmetrical structures of 2a (denoted as b) and 2b
(4) in an intensity ratio of 2:1. Superimposed [AB]
patterns for the eight inequivalent trans axial carbonyls
for 2a and 2b are observed in the range of ca. 187-183
ppm, which is consistent with earlier observations that
the resonances of axial carbonyls appear at lower field
than those of equatorial carbonyls.28 The carbonyl
(26) Churchill, M. R.; DeBore, B. G. Inorg. Chem. 1977, 16, 878.
(27) Dawoodi, Z.; Mays, M. J .; Raithby, P. R. J . Chem. Soc., Chem.
Commun. 1980, 641.
(28) (a) Gladfelter, W. L.; Geoffroy, G. L. Inorg. Chem. 1980, 19,
2579. (b) Park, J . T.; Cho, J .-J .; Chun, K.-M.; Yun, S.-S.; Kim, S. Bull.
Korean Chem. Soc. 1993, 14, 137.

Synthesis of Triosmium Cluster Complexes
Organometallics, Vol. 17, No. 2, 1998 233
Sch em e 2
equilibration in 2a is clearly observable between 193
and 298 K. As shown in the spectrum at 298 K, the
four complex axial carbonyl resonances become two
resonances, the two pairs (δ 176.9, 174.6 and 173.3,
170.0) of equatorial carbonyls are averaged and the two
carbonyl signals (δ 181.6, 169.2) are unaffected.
These spectral changes can be interpreted in terms
of restricted in-plane cyclic motions of equatorial C60 and
carbonyl ligands, as shown in Scheme 2. Three equato-
rial carbonyls (d, f, and h) swing into bridging positions
and move on to new osmium atoms and reform the all-
terminal carbonyl structure, while the C60 ligand swings
to the adjacent equatorial site on the same metal atom.
This process generates a triply bridged Cs-symmetric
intermediate (see I in Scheme 2) and thus leads to
pairwise equilibration of the four axial carbonyls a/a′
and b/b′ and the four equatorial carbonyls d/h and e/g.
However, axial carbonyl c and equatorial carbonyl f on
the mirror plane of the intermediate are not affected
by this rearrangement. Equatorial carbonyl f retains
its trans relationship through the Os-Os bond to the
equatorial C60 ligand even after the rearrangement.
Therefore, the unique axial carbonyl c is assigned to the
next lowest signal at δ 181.6, and the equatorial
carbonyl f is assigned to the unaffected higher field
resonance at δ 169.2. The free energy of activation
(∆Gc ) 12.7 ( 0.1 kcal/mol) has been obtained29 from
q
a coalescence of the two carbonyl resonances (δ 176.9
and 174.6) at 273 K for the fluxional process of 2a . A
similar fluxional process has been previously observed
for the norbonadiene complex Os3(CO)10(η2,η2-C7H8)
with an axial-equatorial-substituted structure (∆Gq )
9.7 kcal/mol).30 The solution dynamics of minor isomer
2b could not be interpreted because of relatively low-
intensity signals and overlap of the 2b resonances with
2a resonances.
The restricted equilibration of in-plane equatorial C60
and carbonyl ligands via a triply bridged intermediate
for 2a is further supported by the solution-dynamics
studies on 5. The VT 13C NMR spectra of 5* are
illustrated in Figure 3. The limiting low-temperature
spectrum at 213 K reveals six carbonyl resonances at δ
194.8 (2J CP ) 7.2 Hz), 194.5 (2J CP ) 8.1 Hz), 185.4, 181.6,
180.6, and 178.3 with relative intensities of 2:2:2:1:1:1,
which is consistent with the structure of a pseudo-C3-
symmetry shown in Scheme 3. The two lowest field
resonances with C-P couplings and an intensity of 2
F igu r e 3. VT 13C NMR spectra (75 MHz, CO region, CD2-
Cl2) of 5*.
are assigned to the two pairs of axial carbonyls, a and
b, on the two osmium atoms coordinated with phosphine
ligands.23 The resonance at δ 185.4 with an intensity
of 2 is assigned to the two equivalent axial carbonyls,
c, on the osmium atom coordinated with the C60 ligand.
The remaining three resonances with intensities of 1
are due to three inequivalent carbonyls, d, e, and f. As
the temperature increases, the two low-field doublets
at δ 194.8 and 194.5 broaden and merge into a single
peak and the two high-field resonances at δ 181.6 and
178.3 broaden and coalesce at 298 K while the two
resonances at δ 185.4 and 180.6 are virtually unaffected.
These observations can also be rationalized by the same
fluxional process as that for 2a . The process, via a C2v
intermediate shown in Scheme 3, leads to pairwise
equilibration among the four axial carbonyls a/b and
between the equatorial carbonyls d/f. However, the two
axial carbonyls c and the equatorial carbonyl e are not
affected by the process. Note that the two inequivalent
PMe3 ligands become equivalent by the rearrangement.
The 31P{1H} NMR spectrum of 5 shows two resonances
(29) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic Press:
London, 1982, p.96.
(30) Tachikawa, M.; Richter, S. I.; Shapley, J . R. J . Organomet.
Chem. 1977, 128. C9.

234 Organometallics, Vol. 17, No. 2, 1998
Park et al.
Sch em e 3
Sch em e 4
Sch em e 5. Syn th esis of µ3-η2,η2,η2-C60 Com p lexesa
at δ -49.3 and -50.9 at 213 K, which coalesce at 273
K. The line shape analysis29 of the 31P resonances gives
q
∆Gc ) 12.7 ( 0.1 kcal/mol for the fluxional process of
5. It is interesting to observe identical ∆Gcq values for
the similar fluxional processes of 2a and 5, strongly
suggesting that similar mechanisms operate in both
complexes.
We were able to obtain 13C NMR spectrum of the C60
moiety with the most soluble complex, 5, among the C60-
triosmium cluster complexes (see Experimental Sec-
tion). The spectrum at room temperature shows a 17-
line C2v symmetry pattern, which can be explained
either by the intermediate of C2v symmetry (see II in
Scheme 3) for the fluxional process of 5 or by free
rotation about the metal-C60 bond. Previous studies
on fluxional processes of the C60 moiety revealed C60-
metal bond axis rotation for M(CO)4(η2-C60) (M ) Fe,
Ru)6g and migration of the metal fragment over the
surface of C60 for Pd(PR3)2(η2-C60) (R3 ) Me2Ph, MePh2,
(OMe)3)31 by VT 13C NMR spectroscopy. A recent report
by Green and co-workers on M(NO)(PPh3)2(η2-C60) (M
) Co, Rh)6k showed the presence of a C60-metal moiety
rotation at low temperatures and a migration process
at high temperatures.
removing the weak-field MeCN ligand. The reaction
resulted in extensive decomposition of 2 and did not
produce any isolable products. However, thermolysis
of 2 at a higher temperature in refluxing chlorobenzene
(134 °C) unexpectedly affords Os3(CO)9(µ3-η2,η2,η2-C60)
(6) in 23% yield by loss of both the acetonitrile and a
carbonyl ligand (see Scheme 5). A better yield (32%)
has been obtained from an alternative reaction of Os3-
(CO)10(NCMe)2 (2 equiv) and C60 (1 equiv). The reaction
of 6 with either CO (1 atm) or PMe3 has been carried
out in refluxing chlorobenzene to prepare a µ-η2,η2-C60
complex by addition of a 2-electron-donor ligand to 6.
The former reaction gives only the starting material
back, but the latter reaction produces Os3(CO)8(PMe3)-
(µ3-η2,η2,η2-C60) (7) in 43% yield by substitution of a
carbonyl ligand with PMe3 instead of the expected
addition of PMe3 to 6. Complex 7 can be prepared either
in a quantitative yield by initial decarbonylation of 6
with Me3NO/MeCN reagent under mild conditions (-20
°C to room temperature) or in 14% yield by a similar
decarbonylation of Os3(CO)11(PMe3) (2 equiv) and sub-
sequent thermolysis with C60 (1 equiv) in refluxing
chlorobenzene. We have not been successful in the
preparation of the µ-η2,η2-C60 complex as of yet.
Syn th esis a n d Ch a r a cter iza tion of µ3-η2,η2,η2-C60
Com p lexes, 6 a n d 7. We are interested in reversible
interconversions of η2-C60, µ-η2,η2-C60, and µ3-η2,η2,η2-
C60 ligands on a triosmium cluster framework (see
Scheme 4). Successive loss of a carbonyl ligand from
η2-C60 complex will give µ-η2,η2-C60 and µ3-η2,η2,η2-C60
complexes in turn, and the corresponding reverse path-
ways may render reversibility to these reactions.
Thermolysis of 2 in refluxing toluene (110 °C) has
been attempted to prepare a µ-η2,η2-C60 complex by
(31) (a) Nagashima, H.; Yamaguchi, H.; Kato, Y.; Saito, Y.; Haga,
M.; Itoh, K. Chem. Lett. 1993, 2153. (b) Nagashima, H.; Kato, Y.;
Yamaguchi, H.; Kimura, E.; Kawanishi, T.; Kato, M.; Saito, Y.; Haga,
M.; Itoh, K. Chem. Lett. 1994, 1207.
(32) J ohnson, B. F. G.; Lewis, J .; Martinelli, M.; Wright, A. H.;
Braga, D.; Grepioni, F. J . Chem. Soc., Chem. Commun. 1990, 364.

Synthesis of Triosmium Cluster Complexes
Organometallics, Vol. 17, No. 2, 1998 235
Ta ble 4. Com p a r ison of IR Sp ectr a betw een µ3-η2,η2,η2-C60 a n d Ar en e Com p lexes
complex
νCO (cm-1
)
solvent
ref
Ru3(CO)9(µ3-η2,η2,η2-C60
)
2078s, 2045vs, 2012m, 1985sh
2071m, 2027vs, 1996s, 1976sh
2081s, 2046vs, 2016m, 2002m, 1983sh
2076m, 2030vs, 1999m, 1978m, 1951sh
2064vs, 2032s, 2010s, 1998m, 1984m, 1960w, 1946w
2057s, 2018vs, 1991s, 1975m, 1962sh, 1943w, 1920w
CS2
CH2Cl2
CS2
CH2Cl2
CS2
CH2Cl2
9
32
Ru3(CO)9(µ3-η2,η2,η2-C6H6)
Os3(CO)9(µ3-η2,η2,η2-C60), 6
Os3(CO)9(µ3-η2,η2,η2-C6H6)
this work
33
this work
33
Os3(CO)8(PMe3)(µ3-η2,η2,η2-C60), 7
Os3(CO)8(PPh3)(µ3-η2,η2,η2-C6H6)
Complexes 6 and 7 are sparingly soluble in toluene
and more soluble in carbon disulfide and 1,2-dichlo-
robenzene to form either a brown (6) or greenish-brown
(7) solution. Formulations of both complexes are es-
tablished by elemental analysis and by FAB+ MS
spectroscopy. The M+ multiplet of 6 and 7 completely
matches the calculated pattern: the highest peaks in
the M+ multiplet (m/ z, found, calcd) for 6 are 1544, 1544
and 7 are 1592, 1592. The carbonyl regions of the IR
spectra for 6 and 7 are similar in pattern to those
reported for face-capping arene complexes,33 Os3(CO)9-
(µ3-η2,η2,η2-C6H6) and Os3(CO)8(PPh3)(µ3-η2,η2,η2-C6H6)
(see Table 4), whose structures are derived from re-
placement of three axial carbonyls at a triosmium face
and the capping of µ3-η2,η2,η2-C6H6 ligand. Shapley and
co-workers recently reported the structural character-
ization of Ru3(CO)9(µ3-η2,η2,η2-C60)9 and {Ru3(CO)9}x(µ3-
η2,η2,η2-C70) (x ) 1, 2),34 which verify arene-like coor-
dination of the C60 ligand to the open face of a
triruthenium cluster. An extra band is observed for C60
and arene triosmium complexes compared to the cor-
responding triruthenium complexes, as shown in Table
4. The shift of the IR bands for C60 complexes to higher
energies is consistently revealed in these complexes due
to the electron-withdrawing nature of the C60 ligand.
The structural correspondence between C60 and arene
complexes are indicated by the close similarities of the
IR spectra.
F igu r e 4. (a) 13C NMR spectrum (151 MHz, CO region,
298 K, CS2/ext.CD2Cl2) of 6*. (b) 13C NMR spectrum (151
MHz, CO region, CS2/C6D6) of 7*. The inset is from the 13C-
{31P} NMR spectrum.
The 13C NMR spectrum of 6* at 298 K (Figure 4a)
reveals a single resonance at δ 176.1 for the nine
carbonyls, which implies the presence of a fast localized
3-fold rotation of three carbonyl groups on each atom.
The arene analogue Os3(CO)9(µ3-η2,η2,η2-C6H6),33 how-
ever, has two resonances at δ 175.86 (6 CO) and 175.82
(3 CO) for the six equatorial and three axial carbonyl
ligands, although they are very close in chemical shifts.
The single carbonyl resonance of 6* became slightly
broad at 188 K but was not resolved. A single-crystal
X-ray diffraction study has previously revealed equato-
rial coordination of triphenylphosphine in Os3(CO)8-
(PPh3)(µ3-η2,η2,η2-C6H6),33 which appears to be isostruc-
tural with compound 7. The 13C NMR spectrum of 7 at
298 K (Figure 4b) shows two resonances at δ 185.4 (d,
2J PC ) 5.9 Hz) and 178.5 in a 1:3 ratio, whose general
features are very similar to that of the arene analogue
with two peaks at δ 183.96 (d, 2J PC ) 8.0 Hz, 2 CO) and
177.39 (s, 6 CO). The P-C coupling in 7 was verified
by obtaining a 13C{31P} NMR spectrum (see the inset
of Figure 4). A fast localized 3-fold rotation of three
ligands at each osmium center seems to occur in 7 also.
The phosphine-substituted osmium center in 7 may
undergo a restricted 3-fold rotation proposed by Pomer-
oy and co-workers,35 without requiring the bulky phos-
phine ligand to enter an axial site. In any case, the
resonance at δ 185.4 with a P-C coupling and that at
δ 178.5 can be assigned to the two carbonyl ligands on
the osmium atom coordinated with PMe3 and the six
carbonyl groups on the other two osmium atoms,
respectively. The two resonances only become broad at
a low temperature of 188 K.
Con clu d in g Rem a r k s
The present work provides the first examples of
transition metal cluster-bound C60 complexes, 1-7,
although the only C60-metal cluster complex, Ru3(CO)9-
(µ3-η2,η2,η2-C60),9 has appeared in the literature after
our preliminary communication.10 As expected, the C60
ligand in 1-5 invariably occupies an equatorial position
similar to bulky ligands, such as phosphines and alk-
enes, and acts as an electron-withdrawing entity evi-
denced by high-energy ν(CO) bands in 1-7. The
shortest C-C bond length (1.42 Å in 1) of C60 directly
bonded to the metal center among all known η2-C60
complexes, however, implies that the metal-to-C60 π-back-
donation is significantly suppressed by the strong π-acid
carbonyl ligands on the osmium atoms. This fact is
further supported by our previous observation11 that
C60-mediated electron transfer to the metal center
(33) Gallop, M. A.; Gomez-Sal, M. P.; Housecroft, C. E.; J ohnson,
B. F. G.; Lewis, J .; Owen, S. M.; Raithby, P. R.; Wright, A. H. J . Am.
Chem. Soc. 1992, 114, 2502.
(34) Hsu, H.-F.; Wilson, S. R.; Shapley, J . R. J . Chem. Soc., Chem.
Commun. 1997, 1125.
(35) Alex, R. F.; Pomeroy, R. K. Organometallics 1987, 6, 2437.

236 Organometallics, Vol. 17, No. 2, 1998
Park et al.
occurs in the electrochemical pathways of 1, 3, and 4.
A η6-C60 ligand has only been observed in trimetallic
ruthenium and osmium (6 and 7) cluster complexes.
These results suggest that a metal triangle provides for
effective overlap of metal d orbitals with C60 pπ-orbitals,
which is known to be oriented at angle of ca. 10°36 away
from the perpendicular face of the six-membered ring
of C60. Nevertheless formation of µ-η2,η2-C60 complexes
eluded our observation. There are three possible flux-
ional processes proposed for Os3(CO)12 and its deriva-
tives: (1) axial-equatorial ligand exchange between two
metal centers through an intermediate like the solid
structure of Fe3(CO)12, (2) equatorial ligand exchange
among three metal centers via a triply bridged inter-
mediate, and (3) axial-equatorial ligand exchange
through a localized 3-fold rotation of ligands on each
metal center. Both complexes 2a and 5 have shown a
fluxional process (∆Gc ) 12.7 ( 0.1 kcal/mol) of the
restricted pathway of (2) due to the presence of MeCN
and C60 ligands, which cannot commonly bridge. Com-
plexes 6 and 7 appear to undergo the fluxional pathway
(3) of a facile 3-fold rotation on each osmium atom, even
down to a very low temperature (188 K).
q
Ack n ow led gm en t. We are grateful to the Korea
Advanced Institute of Science and Technology for fi-
nancial support of this research.
Su p p or tin g In for m a tion Ava ila ble: Figures of disor-
dered molecular geometry and the packing diagram and tables
of atomic coordinates and equivalent isotropic displacement
parameters, anisotropic displacement parameters, and com-
plete bond lengths and angles for complex 1 (11 pages).
Ordering information is given on any current masthead page.
(36) (a) Haddon, R. C. Acc. Chem. Res. 1988, 21, 243. (b) Haddon,
R. C. Science 1993, 261, 1545.
OM970689P