Synthesis, characterization, and thermochemistry of (η1-C13H9)MN(CO)5 and (η5-C13H9)MN(CO)3

Article abstract of DOI:10.1021/om020013g

Reaction of LiC₁₃H₉ with Mn(CO)₅Br at -78 °C gave (η¹-C₁₃H₉)Mn(CO)₅, 2. Thermal rearrangement of 2 yielded (η⁵-C₁₃H₉)Mn(CO)₃, 1, 9, 9′

Full text of DOI:10.1021/om020013g

2006
Organometallics 2002, 21, 2006-2009
Notes
Syn th esis, Ch a r a cter iza tion , a n d Th er m och em istr y of
(η1-C13H9)Mn (CO)5 a n d (η5-C13H9)Mn (CO)3
Andreas Decken,* Andrew J . MacKay, Martin J . Brown, and Frank Bottomley
Department of Chemistry, University of New Brunswick, P.O. Box 45222,
Fredericton, New Brunswick, E3B 6E2, Canada
Received J anuary 7, 2002
Summary: Reaction of LiC13H9 with Mn(CO)5Br at -78
°C gave (η1-C13H9)Mn(CO)5, 2. Thermal rearrangement
of 2 yielded (η5-C13H9)Mn(CO)3, 1, 9,9′-bifluorene, 3, and
Mn2(CO)10, 4. The product distribution was controlled
by the electron donor capacity of the reaction medium.
The crystal structures of 1 and 2 have been determined.
Resu lts
King and Efraty isolated 1, in 11% yield, by reacting
sodium fluorenide with Mn(CO)5Br in refluxing THF.7
We found that 1 can be prepared at room temperature
by addition of a solution of Mn(CO)5Br in THF to C13H9-
Li, generated in situ in THF. Orange complex 1 was
produced in 30% yield, together with 9,9′-bifluorene
(10%), fluorene (15%), and Mn2(CO)10 (20%). All spec-
troscopic data for 1 were in accord with that previously
published.2,3 Compound 1 was also identified by X-ray
diffraction (Figure 1). At room temperature, there was
no detectable intermediate in the reaction, but at -78
°C, yellow (η1-C13H9)Mn(CO)5, 2, was isolated in 59%
yield. Compound 2 was characterized by 1H and 13C
NMR and IR spectroscopies, mass spectrometry, el-
emental analysis, and X-ray crystallography (Figure 2).
It was moderately air and moisture sensitive, but could
be stored under an inert atmosphere at -23 °C for
several weeks.
In tr od u ction
Haptotropic rearrangements in metal complexes of
fluorenide (C13H9-) have attracted considerable inter-
est.1-6 The most thorough investigations have centered
on manganese carbonyl complexes of fluorene and
fluorenide, e.g., (η5-C13H9)Mn(CO)3, 1. Two methods for
the preparation of 1 have been developed: (1) via
haptotropic inter-ring rearrangement;2,3 (2) reaction of
the fluorenide anion with manganese carbonyl halides.7-9
The pathway for haptotropic rearrangements has been
established,10,11 but the pathway of the reaction of
fluorenide with Mn(CO)5Br is poorly understood. The
reaction could proceed by formation of (η1-C13H9)Mn-
(CO)5, 2, with subsequent loss of two carbonyl ligands
to give the final product, (η5-C13H9)Mn(CO)3, 1. How-
ever, η1-fluorenyl complexes have not been detected as
intermediates in the synthesis of 1, even though such
complexes of fluorenyl and related ring systems are well
known.4,5,11 This prompted us to investigate the reaction
between fluorenide and Mn(CO)5Br and to explore the
intermediacy of (η1-C13H9)Mn(CO)5, 2, in the synthesis
of 1.
Refluxing 2 in THF for 30 min resulted in a gradual
color change from yellow to dark orange. The products
were identified as (η5-C13H9)Mn(CO)3, 1, obtained in
80% yield, 9,9′-bifluorene, 3, and Mn2(CO)10, 4, each in
20% yield. The conversion of 2 into 1, 3, and 4 was
achieved in a variety of solvents and in the solid state
(see Supporting Information). Under inert and dry
atmospheres compounds 1, 3, and 4 were the only
products, accounting for complete mass balance; 3 and
* Corresponding author. E-mail: adecken@unb.ca.
(1) J ohnson, J . W.; Treichel, P. M. J . Am. Chem. Soc. 1977, 99, 1427.
(2) Treichel, P. M.; J ohnson, J . W. J . Chem. Soc., Chem. Commun.
1976, 688.
(3) Treichel, P. M.; J ohnson, J . W. Inorg. Chem. 1977, 16, 749.
(4) J i, L.-N.; Rerek, M. E.; Basolo, F. Organometallics 1984, 3, 740.
(5) Biagioni, R. N.; Lorkovic, I. M.; Skelton, J .; Hartung, J . B.
Organometallics 1990, 9, 547.
(7) King, R. B.; Efraty. A. J . Organomet. Chem. 1970, 23, 527.
(8) Kolobova, N. E.; Zolanovich, V. I.; Lobanova, I. A. Izv. Akad.
Nauk. SSSR, Ser. Khim. 1980, 1651.
(9) Yarmolenko, A. I.; Kukharenko, S. V.; Novikova, L. N.; Ustynyuk,
N. A.; Dolgushin, F. M.; Yanovsky, A. I.; Struchkov, Yu. T,; Kraftaeva,
T. A.; Oprunenko, Yu. F.; Strelets, V. V. Izv. Akad. Nauk., Ser. Khim.
1996, 45, 199.
(10) Albright, T. A.; Hofmann, P.; Hoffmann, R.; Lillya, C. P.;
Dobosh, P. A. J . Am. Chem. Soc. 1983, 105, 3396.
(11) Decken, A.; Rigby, S. S.; Girard, L.; Bain, A. D.; McGlinchey,
M. J . Organometallics 1997, 16, 1308.
(6) Ustynyuk, N. A.; Pomazanova, N. A.; Novikova, L. N.; Kravtsov,
D. N.; Ustynyuk, Yu. A. Izv. Akad. Nauk SSSR, Sr. Khim. 1986, 7,
1688.
10.1021/om020013g CCC: $22.00 © 2002 American Chemical Society
Publication on Web 04/04/2002

Notes
Organometallics, Vol. 21, No. 9, 2002 2007
rahydrofuran12 were used as solvents. There was no
spectroscopic evidence for the formation of acyl com-
plexes in donor solvents.13 No reaction occurred between
bifluorene, 3, and Mn2(CO)10, 4, nor between (η5-C13H9)-
Mn(CO)3, 1, and CO (10 atm).
The indenyl analogue of 1, (η5-C9H7)Mn(CO)3, 5, was
prepared from C9H7Li and Mn(CO)5Br in THF at -78
°C in 30% yield, together with 3,3′-biindene (14%),
indene (13%), and Mn2(CO)10 (29%); no (η1-C9H7)Mn-
(CO)5, 6, was observed.
Discu ssion
Our results are different from thermochemical and
photochemical reactions of other RMn(CO)5 (R ) CH3,
C2H5, Ph, CH2Ph, CR′HCHdCH2), (C13H9)Mn(CO)3-
(PR′′3)2, (C15H9)Mn(CO)3(PR′′3)2, and (C13H9)Re(CO)5
complexes. (η1-C13H9)Re(CO)5 gave exclusively (η5-C13H9)-
Re(CO)3 at 127 °C in methylcyclohexane,14 but the
reaction was much slower than that of 2. Degradation
of (η1-C13H9)Re(CO)5 was also concentration dependent
and reversible under CO (1 atm). In contrast, thermoly-
sis of 2 was independent of concentration and irrevers-
ible. The different chemical behavior of 2 and (η1-
C13H9)Re(CO)5 is explained by much stronger Re-ligand
bonds, preventing CO loss at ambient temperatures and
homolytic cleavage of the fluorenyl-Re bond under the
thermochemical conditions employed by Wrighton and
co-workers. A difference in bond enthalpies was deter-
mined for the related CH3M(CO)5 complexes (CH3-Re
) 199 kJ mol-1; CH3-Mn ) 115 kJ mol-1; Re-CO )
185 kJ mol-1; Mn-CO ) 98 kJ mol-1),15 and a similar
trend is expected for the fluorenyl complexes. Heating
(η1-C3H4R′)Mn(CO)5 (R′ ) H, CH3) gave the allylic
complexes (η3-C3H4R′)Mn(CO)4,16 but there was no
formation of 4 or the appropriate organic products.
Heating (η1-C15H9)Mn(CO)3(PEt3)2 gave only intractable
decomposition products,11 and heating (η1-C13H9)Mn-
(CO)3(PEt3)2 resulted exclusively in cleavage of the
fluorenyl-Mn bond. Photochemical reactions of RMn-
(CO)5 (R ) CH3, C2H5, Ph, and CH2Ph) gave Mn2(CO)10,
4, R-R, and R-H.17,18
Our results show conclusively that two, competing,
irreversible and monomolecular pathways lead from 2
to 1 or 3/4: (1) loss of CO, promoted by coordination of
electron donors, followed by haptotropic rearrangement
to give 1, or (2) homolytic cleavage of the Mn-C(9) bond,
followed by recombination of the resulting radicals to
give 3 and 4. The production of Mn(CO)5 and C13H9
radicals was proven by trapping them with benzylbro-
mide and O2, respectively, giving Mn(CO)5Br and C13H8O.
In the rearrangement of 2 f 1, the first step must be
loss of a carbonyl ligand to give 7 (Scheme 1). Compound
7 can convert to 8 by addition of an electron donor or to
F igu r e 1. View of 1, thermal ellipsoids at the 30%
probability level.
F igu r e 2. View of 2, thermal ellipsoids at the 30%
probability level.
4 were always produced in equimolar amounts. The
reaction was much slower at 23 °C in THF, resulting in
60% yield of 1 after 5 days. A 60% yield was also
obtained in the nonpolar solvent hexane after reflux for
30 min, and a 37% yield was obtained at 23 °C after 5
days. The yield of 1 was not influenced by water and
was only slightly reduced under CO (1 atm), but only 3
and 4 were obtained under 10 atm of CO. The yield of
1 decreased to 51% under O2 (1 atm), and fluorenone
(8%) and fluorene (10%) were isolated as well as 3 (19%).
Addition of benzylbromide to the reaction mixture
decreased the yield of 1 only slightly, but produced Mn-
(CO)5Br instead of Mn2(CO)10. The conversion of 2 into
1, 3, and 4 proceeded at the same rate in the dark and
was concentration independent in the range 0.02-
0.00022 M. Thermolysis of 2, generated in situ from Mn-
(CO)5Br and C13H9Li in THF, gave a higher yield of 1
than prepurified 2. Addition of Mn2(CO)10, fluorene, or
bifluorene had no effect on product yields or distribution,
but addition of MX (M ) Li, Na, NEt4; X ) Cl, Br)
greatly increased the yield of 1. For example, at room
temperature in THF, 2 gave 1 in 23% yield after 24 h,
increasing to 61% upon addition of LiBr. NaBPh4 did
not increase the yield of 1. The yields of 1 were slightly
reduced when the sterically hindered THF derivatives
2,5-dimethyltetrahydrofuran and 2,2,5,5-tetramethyltet-
(12) Wax, M. J .; Bergman, R. G. J . Am. Chem. Soc. 1981, 103, 7028.
(13) Bent, T. L.; Cotton, J . D. Organometallics 1991, 10, 3156.
(14) Young, K. M.; Miller, T. M.; Wrighton, M. S. J . Am. Chem. Soc.
1990, 112, 1529.
(15) Connor, J . A. Thermochemical Studies of Organo-Transition
Metal Carbonyls and Related Compounds. In Topics in Current
Chemistry; Boschke, F. L., Ed.; Springer-Verlag: Berlin, 1977; Vol. 71,
72.
(16) McClennan, W. R.; Hoehn, H. H.; Cripps, H. N.; Muetterties,
E. L.; Howk, B. W. J . Am. Chem. Soc. 1961, 83, 1601.
(17) Young, K. M.; Wrighton, M. S. J . Am. Chem. Soc. 1990, 112,
157.
(18) Gismondi, T. E.; Rausch, M. D. J . Organomet. Chem. 1985, 284,
59.

2008 Organometallics, Vol. 21, No. 9, 2002
Notes
Sch em e 1
tion of electron donors and/or haptotropic rearrange-
ment which cannot be attained for RMn(CO)5 (R ) alkyl,
aryl) complexes. The pathways via intermediates 7-12
are also highly unlikely for (η1-C13H9)Mn(CO)3(PEt3)2
and (η1-C15H9)Mn(CO)3(PEt3)2 due to the steric bulk of
the phosphine groups and the increased strength of the
Mn-CO bond. Competitive Mn-C(9) or Mn-CO cleav-
age in 2 implies similar activation barriers for both
processes. This is supported by the similar dissociation
enthalpies for alkyl-Mn (115 kJ mol-1) and Mn-CO
(98 kJ mol-1) bonds.15 The thermochemical behavior of
(η1-C13H9)Mn(CO)5, 2, is unprecedented. The analogous
indenyl complex, (η1-C9H7)Mn(CO)5, 6, is unknown.
However, we prepared (η5-C9H7)Mn(CO)3, 5, by reaction
of Mn(CO)5Br with C9H7Li and isolated 3,3′-biindene
and Mn2(CO)10 as major side products and conclude that
the formation of 1 and 5 follow similar pathways. The
relative stability of 2 in comparison to 6 is due to the
unfavorable loss of local aromaticity in the six-mem-
bered rings in (η5-C13H9)Mn(CO)3. This effect is reduced
for the indenyl ligand because of the lower degree of
benzannelation.
In conclusion, we have synthesized (η1-C13H9)Mn-
(CO)5, 2, and converted 2 to (η5-C13H9)Mn(CO)3, 1, under
a variety of reaction conditions. Generation of 1 is in
competition with the formation of 9,9′-bifluorene, 3, and
Mn2(CO)10, 4, and the product distribution is controlled
by the donor capacity of the medium.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were carried out
under an atmosphere of argon utilizing standard Schlenk
techniques. Solvents were dried and distilled according to
standard procedures.20 1H and 13C NMR spectra were recorded
on a Varian Unity 400 spectrometer at 399.99 and 100.6 MHz,
respectively. Chemical shifts were referenced to residual
solvent signals. IR spectra were recorded as KBr pellets on a
Perkin-Elmer 1600 FT-IR spectrometer. Mass spectra were
obtained on a Kratos MS-50 spectrometer. Unless otherwise
stated, all reagents were obtained from commercial suppliers
and used without further purification. Mn(CO)5Br was pre-
pared by a literature procedure.21 Flash column chromatog-
raphy was carried out using Merck silica gel (330-400 mesh).
Elemental analyses were preformed by Galbraith Laboratories,
Knoxville, TN.
(η5-C13H9)Mn (CO)3, 1, was prepared using a modified
literature procedure.7 N-Butyllithium (0.8 cm3, 1.6 M in
hexanes, 1.28 mmol) was added dropwise to a solution of
fluorene (0.158 g, 0.952 mmol) in THF (5 cm3) at -78 °C. The
reaction mixture was allowed to warm to room temperature,
and Mn(CO)5Br (0.258 g, 0.939 mmol) in THF (10 cm3) was
added dropwise; the resultant mixture was stirred overnight.
The solvents were removed under vacuum and the product
purified by flash column chromatography using hexane to give
1 as an orange solid. Yield: 0.086 g, 0.284 mmol, 30%. Flash
column chromatography using hexane as eluent also yielded
9,9′-bifluorene (0.018 g, 0.05 mmol), fluorene (0.025 g, 0.151
mmol), and Mn2(CO)10 (0.040 g, 0.103 mmol). Unreacted Mn-
(CO)5Br (0.032 g, 0.115 mmol) was obtained with CH2Cl2. IR
and NMR spectral data of 1 matched that of the literature.2,3
MS (EI, m/z (%), assignment): 304 (29) {C16H9MnO3}+
{(C13H9)Mn(CO)3}+; 276 (30) {C15H9MnO2}+ {(C13H9)Mn-
(CO)2}+; 248 (45) {C14H9MnO}+ {(C13H9)Mn(CO)}+; 220 (84)
{C13H9Mn}+; 165 (100) {C13H9}+.
11 by haptotropic rearrangement. Loss of CO from 8 or
11 would result in 9 or 12, respectively, from which 10
and the final product 1 are obtained via haptotropic
rearrangement. The evidence suggests that the path-
ways via 8/9 and 11/12 are in competition. The pathway
via 11 and 12 occurs in the solid state and in noncoor-
dinating solvents. The increased yield of 1 in coordinat-
ing solvents and in the presence of strong electron
donors such as X- (X ) Br, Cl) is evidence for the
rearrangement via 8 and 9. Decreased yields of 1 upon
replacement of THF by sterically demanding analogues
further corroborates ligand coordination. The most
likely irreversible step is the transformation of 12 to 1.
Competition between CO loss and homolytic cleavage
of the R-Mn bond has not been observed previously in
reactions of RMn(CO)5. The formation of 1, 3, and 4 at
lower temperatures than for comparable systems must
be due to low reactivities and high stabilities of the
intermediates. It has been shown that rate constants
for trapping the fluorenyl radical are significantly lower
than for alkyl and aryl radicals.19 The low reactivity of
the fluorenyl radical facilitates the formation of 3, which
is competing with regeneration of 2. Carbonyl loss from
2 can be accomplished under very mild conditions
because the intermediates can be stabilized by coordina-
(20) Perrin, D. D.; Armarego, W. L. F., Perrin, D. R. Purification of
Laboratory Chemicals; Pergamon Press: New York, 1980.
(21) Abel, E. W.; Wilkinson, G. J . Chem. Soc. 1959, 1501.
(19) Arends, I. W. C. E.; Mulder, P.; Clark, K. B.; Wayner, D. D. M.
J . Phys. Chem. 1995, 99, 8182.

Notes
(η1-C13H9)Mn (CO)5, 2. N-Butyllithium (1.70 cm3, 1.6 M in
Organometallics, Vol. 21, No. 9, 2002 2009
(η5-C9H7)Mn (CO)3, 5. The preparation was carried out
analogously to that of 2. N-Butyllithium (1.70 cm3, 1.6 M in
hexanes, 2.72 mmol), indene (0.25 cm3, 0.248 g, 2.14 mmol),
and Mn(CO)5Br (0.543 g, 1.98 mmol) gave 5 as a yellow solid.
Yield: 0.148 g, 0.583 mmol, 30%. IR and NMR spectral data
of 5 matched that of the literature.7 Flash column chromatog-
raphy using hexane as eluent also yielded 3,3′-biindene (0.031
g, 0.135 mmol), indene (0.030 g, 0.259 mmol), and Mn2(CO)10
(0.114 g, 0.292 mmol). Unreacted Mn(CO)5Br (0.041 g, 0.149
mmol) was obtained with CH2Cl2.
hexanes, 2.72 mmol) was added dropwise to a solution of
fluorene (0.346 g, 2.08 mmol) in THF (8 cm3) at -78 °C and
the reaction mixture stirred for 1 h at -78 °C. Mn(CO)5Br
(0.586 g, 2.13 mmol) in THF (16 cm3) was cooled to -78 °C
and added to the fluorenyllithium solution dropwise at -78
°C. The resulting reaction mixture was stirred for 2 h at -78
°C. Hexane (100 cm3) was added, and the solvents were
removed under vacuum. The product was purified by flash
column chromatography using hexane to yield 2 as a yellow
solid. Yield: 0.440 g, 1.22 mmol, 59%. Anal. Found: C, 59.48;
H, 2.39. Anal. Calcd for C18H9MnO5: C, 60.02; H, 2.53. Mp:
115 °C (dec). 1H NMR (acetone-d6 solution): δ 7.96 (d, 6.0 Hz,
2H); 7.70 (d, 6.8 Hz, 2H); 7.28 (m, 4H); 4.62 (s, 1H). 13C NMR
(benzene-d6 solution): δ 210.5 (CO); 157.5; 136.4; 126.5; 124.5;
122.4; 120.9; 30.8 (C-9). IR (KBr disk): νCO 2106 (m-s); 2010
(s); 1988 (s) cm-1. MS (EI, m/z (%), assignment): 360 (0.9)
Ack n ow led gm en t. Dr. Larry Calhoun (UNB) is
thanked for assistance with the NMR experiments, Mr.
Gilles Vautour (UNB) for mass spectrometry, and
Austin Chen and Dr. Cathleen M. Crudden (UNB) for
assistance with high-pressure experiments. We are
grateful to the Natural Sciences and Engineering Re-
search Council of Canada for financial support of this
work.
{C18H9MnO5}+ {(C13H9)Mn(CO)5}+; 332 (17) {C17H9MnO4}+
+
{(C13H9)Mn(CO)4}+; 330 (45) {C26H18
}
{(C13H9)2}+; 304 (42)
{C16H9MnO3}+ {(C13H9)Mn(CO)3}+; 276 (53) {C15H9MnO2}+
{(C13H9)Mn(CO)2}+; 248 (59) {C14H9MnO}+ {(C13H9)Mn(CO)}+;
220 (64) {C13H9Mn}+; 165 (79) {(C13H9)}+.
Th er m a l Rea r r a n gem en t of (η1-C13H9)Mn (CO)5, 2. (η1-
13H9)Mn(CO)5 (0.036 g, 0.1 mmol) in solvent (5 cm3) was
Su p p or tin g In for m a tion Ava ila ble: Tables of the reac-
tion conditions for the rearrangement 2 f 1, crystallographic
data, atomic coordinates, interatomic distances and angles,
anisotropic displacement parameters, and hydrogen atom
coordinates. This material is available free of charge via the
Internet at http://pubs.acs.org.
C
reacted according to the conditions indicated in Table 1
(Supporting Information). The solvent was removed at ambient
temperatures under vacuum, the remaining solid dissolved in
CDCl3 (2 cm3), and the ratio of 1:3 established by 1H NMR.
Flash column chromatography with hexane as eluent was used
to separate all products with the exception of Mn(CO)5Br,
which was obtained with CH2Cl2.
OM020013G