MeLi reactions with the electrophile system of (η5-C5H5)Fe(CO)2I/P(OMe) 3: The roles of MeLi as reductant, nucleophile, and base

Article abstract of DOI:10.1021/om981001r

The three roles of MeLi-nucleophile, base and reductant-could be revealed by the electrophile system of (η⁵-C₅H₅)Fe(CO)₂I (1) and P(OMe)₃. The addition of MeLi dropwise without delay to the 1:1 mixture results in (η4-exo-MeC₅H₅)Fe(CO)₂P(OMe)₃ (3), where MeLi is a reductant at the first stage and then a nucleophile at the second stage. On the other hand, the addition of a catalytic amount of MeLi to the mixture of 1 and excess P(OMe)₃, followed by the MeLi/MeI sequence after a delay time, results in the formation of [η⁵-C₅H_4- {P(O)(OMe)₂}]-Fe(CO){P(OMe)₃}Me (7), where MeLi is a reductant at the initial stage and a base at the latter stage.

Full text of DOI:10.1021/om981001r

1154
Organometallics 1999, 18, 1154-1158
MeLi Rea ction s w ith th e Electr op h ile System of
(η5-C5H5)F e(CO)2I/P (OMe)3: Th e Roles of MeLi a s
Red u cta n t, Nu cleop h ile, a n d Ba se
Ling-Kang Liu,*,†,‡ Yi-Hsien Liao,† and Uche B. Eke†,§
Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan 11529, ROC,
Department of Chemistry, National Taiwan University, Taipei, Taiwan 10767, ROC,
and Department of Chemistry, University of Ilorin, Ilorin, Nigeria
Received December 8, 1998
The three roles of MeLisnucleophile, base and reductantscould be revealed by the
electrophile system of (η5-C5H5)Fe(CO)2I (1) and P(OMe)3. The addition of MeLi dropwise
without delay to the 1:1 mixture results in (η4-exo-MeC5H5)Fe(CO)2P(OMe)3 (3), where MeLi
is a reductant at the first stage and then a nucleophile at the second stage. On the other
hand, the addition of a catalytic amount of MeLi to the mixture of 1 and excess P(OMe)3,
followed by the MeLi/MeI sequence after a delay time, results in the formation of [η5-C5H4-
{P(O)(OMe)2}]-Fe(CO){P(OMe)3}Me (7), where MeLi is a reductant at the initial stage and
a base at the latter stage.
In tr od u ction
(OMe)3 (3), analogous to the reaction of MeLi with a 1:1
mixture of 1/PR3 at -78 °C (where PR3 is a phosphine).5
This η5-C5H5 ring methylation changes the bonding of
the ring to metal from η5-C5H5 to η4-exo-MeC5H5 and
the oxidation state of Fe from +2 to 0; i.e., the aroma-
ticity of the ring is lost. The facile formation of 3 from
1, P(OMe)3, and MeLi is the sum of two sequential
reactions, as shown in Scheme 1. The first reaction is
an ETC initiated by the initial, small amount of MeLi,
bringing 1 and P(OMe)3 together to form [(η5-C5H5)Fe-
(CO)2P(OMe)3+][I-] (2‚I) (vide infra). Such an ETC
pathway initiated by a strong reductant has been
established for the substitution reaction of (η5-C5H5)-
Fe(CO)2X, with PPh3 replacing halide X-.6 The second
reaction is the nucleophilic addition of stoichiometric
MeLi to the η5-C5H5 ring of 2 from an exo side to Fe.
The exo addition has been established for the similar
A lithiated reagent serves as a nucleophile and a
base.1 Occasionally, the lithiated reagent works as a
reductant.2 In this paper, we report these various roles
of MeLi3 in its reaction with a mixture of (η5-C5H5)Fe-
(CO)2I (1) and P(OMe)3. Depending upon the molar ratio
of 1/P(OMe)3 and the delay time, MeLi acts as a
reductant and then a nucleophile or as a reductant and
then a base. In the latter case, for the first time electron-
transfer chain catalysis (ETC)4 of two levels has been
observed on the P(OMe)3 substitution reactions, one for
the iodide and one for the CO ligand in sequence.
Resu lts a n d Discu ssion
The addition of MeLi dropwise to a 1:1 mixture of
1/P(OMe)3 at -78 °C gives in 45% isolated yields the
ring-methylation product (η4-exo-MeC5H5)Fe(CO)2P-
7
complex (η4-exo-MeC5H5)Fe(CO)2PMePh2 and (η4-exo-
8
MeC5H5)Fe(CO)2PPh3 by single-crystal X-ray diffrac-
tion.
* To whom correspondence should be addressed at the Academia
Sinica.
As the 1:1 mixture of 1 and P(OMe)3 gives the same
IR νCO features as 1 alone, compound 1 does not interact
with P(OMe)3 at -78 °C. Only after the addition of a
few drops of MeLi does the mixture reveal a rapid
† Academia Sinica.
‡ National Taiwan University.
§ University of Ilorin.
(1) (a) Fieser; L. F.; Fieser, M. Reagents for Organic Synthesis;
Wiley: New York, 1967; Vol. 1, p 686. (b) Wakefield, B. J . In
Comprehensive Organometallic Chemistry: The Synthesis, Reactions
and Structures of Organometallic Compounds; Wilkinson, G., Stone,
F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 7,
Chapter 44. (c) Wakefield, B. J . Organolithium Methods; Academic
Press: London, 1988. (d) Elschenbroich, Ch.; Salzer, A. Organometal-
lics: A Concise Introduction; VCH: Weinheim, Germany, 1989; pp 28-
34.
(2) RLi compounds are known to be able to function as reducing
agents: (a) Ashby, E. C.; Pham, T. N.; Park, B. Tetrahedron Lett. 1985,
26, 4691. (b) Yamataka, H.; Fujimura, N.; Kawafuji, Y.; Hanafusa, T.
J . Am. Chem. Soc. 1987, 109, 4305. (c) Treichel, P. M.; Shubkin, R. L.
Inorg. Chem. 1967, 6, 1328. (d) Darensbourg, M. Y. J . Organomet.
Chem. 1972, 38, 133.
(3) Paquette, L. A., Ed. Encyclopedia of Reagents for Organic
Synthesis; Wiley: New York, 1995; Vol. 5, pp 3530-3532.
(4) Reviews for electron-transfer chain catalysis: (a) J ulliard, M.;
Chanon, M. Chem. Rev. 1983, 83, 425. (b) Astruc, D. Electron Transfer
and Radical Process in Transition-Metal Chemistry; VCH: New York,
1995; Chapter 6.
-
conversion to 2, which can be isolated as a PF6 salt
(2‚P F 6) in 68% isolated yield if immediately anion-
exchanged in ca. 2 min (or in ca. 5 min for the
(η5-C5H5)Fe(CO)2Cl reaction) after introduction of a few
drops of MeLi to the mixture. The delay time between
the introduction of initial catalytic MeLi to the mixture
and the addition of stoichiometric MeLi is an important
factor, because the rapidly formed 2‚I will proceed with
(5) (a) Luh, L.-S.; Liu, L.-K. Bull. Inst. Chem., Acad. Sin. 1994, 41,
39. (b) Liu, L.-K.; Luh, L.-S. Organometallics 1994, 13, 2816.
(6) Gipson, S. L.; Liu, L.-K.; Soliz, R. V. J . Organomet. Chem. 1995,
526, 393.
(7) Liu, L.-K.; Luh, L.-S.; Eke, U. B. Organometallics 1995, 14, 440.
(8) Liu, L.-K.; Luh, L.-S.; Chao, P.-C.; Fu, Y.-T. Bull. Inst. Chem.,
Acad. Sin. 1995, 42, 1.
10.1021/om981001r CCC: $18.00 © 1999 American Chemical Society
Publication on Web 03/02/1999

MeLi as Reductant, Nucleophile, and Base
Organometallics, Vol. 18, No. 7, 1999 1155
Sch em e 1
the well-known Arbuzov-like reaction9 on standing for
45 min and produces in 70% yields the phosphonate
complex (η5-C5H5)Fe(CO)2P(O)(OMe)2 (4) when the solu-
tion is warmed from -78 °C to room temperature, also
presented in Scheme 1. In the literature, the prepara-
tion of 4 from (η5-C5H5)Fe(CO)2X (X ) Cl, I) and
P(OMe)3 requires a long stirring at reflux or at room
temperature with a large quantity of byproducts (η5-
C5H5)Fe(CO){P(OMe)3}{P(O)(OMe)2} (6) and (η5-C5H5)-
Fe(CO){P(OMe)3}X.10 Compound 4 could also be pre-
pared from the treatment of [(η5-C5H5)Fe(CO)2{P-
(NC4H8)(OMe)2}+][Cl-] with KOH.11 Thus, the proce-
dure employing a catalytic amount of MeLi improves
the method of preparation in that the reaction is at a
low temperature, requires a short time, and gives a high
yield. MeLi could not add at the η5-C5H5 ring of 4 but
could seemingly add at the CO ligand. On the basis of
νCO 1922, 1560 cm-1 in the IR spectrum and δ 160.8 in
31P NMR detected from the mixture, a (η5-C5H5)Fe-
(CO)C(O)Me{P(O)(OMe)2}- anion has been assumed,
which is resistant to our attempted isolation, however.12
Employing LDA, which is just a base and not a nucleo-
phile at all, Nakazawa observed a -P(O)(OEt)2 migra-
tion from Fe to the η5-C5H5 ring in (η5-C5H5)Fe(CO)2P-
(O)(OEt)2.13 More studies with the metastable solution
of the (η5-C5H5)Fe(CO)C(O)Me{P(O)(OMe)2}- anion are
now underway.
bling of CO gas could be observed. After 2 h, the
phosphite-phosphonate complex 6 could be isolated in
92% yield (Scheme 2). An intermediate, the (η5-C5H5)-
+
Fe(CO){P(OMe)3}2 cation (5), could be isolated as a
-
PF6 salt (5‚P F 6; 27%, not optimized)14 whose charac-
terization data are consistent with those reported by
Schuman15 and Coville.16 The low yield of 5‚P F 6 here
is due to the decomposition of the cationic complex
during workup. Cation 5 then proceeds with the Arbu-
zov-like reaction. It is clear that prior to the Arbuzov-
like reaction, there are two levels of ETC reactions: one
is the P(OMe)3 substitution for I-, as shown at the top
of Scheme 3, and the other is the P(OMe)3 substitution
for CO, as shown at the bottom of Scheme 3. The former
ETC is initiated by a few drops of MeLi at -78 °C, and
the latter is a continuation, requiring a slightly higher
temperature, in addition to the second equivalent of
P(OMe)3. Due to trace MeLi, it is believed that an
electron transfer occurs from MeLi to 1 to give the 19e
(η5-C5H5)Fe(CO)2I•- radical anion (1r e), followed by a
dissociation of I- and the formation of the 17e (η5-C5H5)-
Fe(CO)2• radical, to which P(OMe)3 is coordinated to give
the 19e (η5-C5H5)Fe(CO)2P(OMe)3• radical (2r e), which
reduces another molecule of 1 and is itself oxidized to 2
(see Scheme 3, a 17e-19e mechanism). This process
goes on in cycles until all the I- ions are replaced by
P(OMe)3. The driving force is believed to be the elec-
tronegative iodine taking away the negative charge to
dissociate from 1r e. When the temperature is increased
from -78 °C to between -60 and -40 °C, the catalytic
electron allows a rapid ligand exchange of free P(OMe)3
with the ligands in 2. The P(OMe)3 substitution for
P(OMe)3 may be kinetically more favored but gives
products that are the same as the reactants. The
P(OMe)3 substitution for CO may be kinetically less
favored, but the release of CO to the gaseous phase
serves as a driving force for the second level of ETC, in
The addition of 1 equiv of MeLi dropwise to a mixture
of 1 and excess P(OMe)3 at -78 °C produces the same 3
as the addition to a 1:1 mixture of 1/P(OMe)3 at -78
°C. However, when the mixture of 1 and excess P(OMe)3
at -78 °C is treated with just a few drops of MeLi and
then allowed to return to room temperature, the bub-
(9) Brill, T. B.; Landon, S. J . Chem. Rev. 1984, 84, 577.
(10) (a) Haines, R. J .; du Preez, A. L.; Marais, I. L. J . Organomet.
Chem. 1970, 24, C26. (b) Haines, R. J .; du Preez, A. L.; Marais, I. L.
J . Organomet. Chem. 1971, 28, 405. (c) Brown, D. A.; Lyons, H. J .;
Manning, A. R. Inorg. Chim. Acta 1970, 4, 428.
(11) Nakazawa, H.; Kubo, K.; Tanisaki, K.; Kawamura, K.; Miyoshi,
K. Inorg. Chim. Acta 1994, 222, 123.
(12) Prof. H. Nakazawa had reached the same results and conclu-
sion: Nakazawa, H. Personal communication.
(13) Nakazawa, H.; Sone, M.; Miyoshi, K. Organometallics 1989, 8,
1564.
(14) (η5-C5H5)Fe(CO)2Cl works better than 1 in producing 2: the
chloride is a weaker nucleophile than the iodide.
(15) Schumann, H. J . Organomet. Chem. 1985, 293, 75.
(16) J ohnston, P.; Hutchings, G. J .; Denner, L.; Boeyens, J . C. A.;
Coville, N. J . Organometallics 1987, 6, 1292.

1156 Organometallics, Vol. 18, No. 7, 1999
Liu et al.
Sch em e 2
Sch em e 3
•
which the formed (η5-C5H5)Fe(CO){P(OMe)3}2 radical
(5r e) is also better than 2r e as a reducing agent. In the
literature, Tyler reported that the excess P(OEt)3 sub-
stitution for CO in (η5-C5H5)Fe(CO)2{P(OEt)3}+ is cata-
lyzed by the chemical reducing agent (η5-C5H5)2Co.17
The last CO is not activated in the 17e-19e mechanism
at room temperature and is rationalized from the IR
νCO stretching frequenciessthat of 5 (1999 cm-1) is
shifted toward low enough wavenumbers from those of
2 (2072, 2025 cm-1), the former having a much stronger
Fe-C(CO) bond.
P(OMe)3, partially because the phosphonium structure
which assists the I- counterattack is much higher in
energy for 6. Attempts to bring about a further Arbuzov-
like reaction of 6 in the same sense by using extra NH4I
was unsuccessful in the present case. In the literature,
excess iodide had furnished bis- and tris(phosphonate)
complexes of a variety of transition-metal moieties.18
Koelle reported that the Arbuzov-like reaction of (η5-
C5Me5)Ru{P(OMe)3}3 proceeds with only one P(OMe)3.19
(18) (a) Werner, H.; Feser, R. Z. Allg. Anorg. Chem. 1979, 485, 309.
(b) Klaeui, W.; Otto, H.; Eberspach, W.; Buchholz, E. Chem. Ber. 1982,
115, 1922. (c) Schubert, U.; Werner, R.; Zinner, L.; Werner, H. J .
Organomet. Chem. 1983, 253, 363. (d) Klaeui, W.; Buchholz, E. Inorg.
Chem. 1988, 27, 3500.
The Arbuzov-like reaction with 5 to give 6 is limited
to just one P(OMe)3 and does not involve a second
(17) Goldman, A. S.; Tyler, D. R. Inorg. Chem. 1987, 26, 253.
(19) Ruther, T.; Englert, U.; Koelle, U. Inorg. Chem. 1998, 37, 4265.

MeLi as Reductant, Nucleophile, and Base
Organometallics, Vol. 18, No. 7, 1999 1157
Syn th esis of (η4-exo-MeC5H5)F e(CO)2P (OMe)3 (3). Com-
pound 1 (1.519 g, 5.0 mmol) and P(OMe)3 (0.60 mL, 0.621 g,
5.0 mmol) were taken up in dry THF (90 mL), and the solution
was chilled to -78 °C. Excess MeLi (5.0 mL, 15% ether
solution) in ether (30 mL) maintained at -78 °C was added
dropwise to the stirred mixture over a period of 15 min. The
stirring was continued at -78 °C for 1 h before the mixture
was warmed gradually to room temperature and continuously
stirred for another 1 h. The reaction mixture was filtered
through a glass frit containing a short column of alumina to
obtain a clear yellow solution. The solvent was then removed
by rotary evaporation. The resultant oily concentrates were
packed on a column of nonactivated alumina by dry packing
and then eluted with 10% ethyl acetate in hexane. Only one
yellow band separated on the column. The fraction was
collected, and after solvent removal, the resultant yellow oil
was frozen in liquid nitrogen for 1 h to obtain yellow solids of
3 (0.711 g, 44.9%). Mp: 38-39 °C. IR (CH2Cl2): νCO 1979 vs,
Also shown in Scheme 2, the 6 reaction with MeLi at
-78 °C is the deprotonation and not the methylation of
the η5-C5H5 ring; i.e., MeLi works as a base rather than
a nucleophile. An intramolecular migration of the
-P(O)(OMe)2 group from Fe to the η5-C5H5 ring follows,
effectively making the Fe anion instead of the C anion
the site for a MeI quench to produce [η5-C5H4P{(O)-
(OMe)2}]Fe(CO){P(OMe)3}Me (7; 89%). Nakazawa re-
ported the -P(O)Ph2 group migration in (η5-C5H5)Fe-
(CO){P(OMe)Ph2}{P(O)Ph2} employing a LDA/MeI
sequence.13
The difference in MeLi reactions toward 4 and 6 could
be rationalized by the Fe back-bonding to CO ligands,
as revealed from the IR νCO stretching frequenciess
2040, 1990 cm-1 for 4 and 1964 cm-1 for 6. The higher
IR νCO stretching frequencies associated with 4 suggest
that there is less back-bonding and hence there is more
positive charge on the CO carbon atoms, in favor of
receiving MeLi as a nucleophile. Compound 6, on the
other hand, has more back-bonding from Fe and hence
has less positive charge on the CO carbon atom,
disfavoring the reception of MeLi at the CO site. MeLi
works as a base as a consequence. The fact that MeLi
attacks one of the CO sites in 4 and the η5-C5H5 ring in
6 could be attributed to a steric affect as well.
Overall 7 could be prepared in one flask, starting from
a mixture of 1 and excess P(OMe)3, plus trace MeLi as
an initiator at -78 °C. With evolution time, temperature
increase, and decrease, and then the MeLi/MeI se-
quence, the reaction gives 7 in yields comparable to the
stepwise operation. The MeI produced at the Arbuzov-
like reaction stage could be removed under vacuum for
use as a quencher in the end or simply destroyed with
extra MeLi during deprotonation in the MeLi/MeI
sequence.
In summary, a mixture of 1 and P(OMe)3 detects the
three roles of MeLi. The addition of MeLi dropwise
without delay to the 1:1 mixture results in 3, where
MeLi is both a reductant and a nucleophile. On the
other hand, the addition of a catalytic amount of MeLi
to the mixture of 1 and excess P(OMe)3, with a delay
time applied before the MeLi/MeI sequence, results in
7, where MeLi is both a reductant and a base.
1916 vs cm-1
.
31P NMR (CDCl3): δ 189.5. 1H NMR (CDCl3): δ
3
5.2 (b, 2H, -CHdCHCHMe-), 3.52 (d, J PH ) 12 Hz, 9H,
4
OMe), 2.80-2.79 (b, 3H, -CHdCHCHMe-), 0.41 (d, J PH ) 6
2
Hz, 3H, Me). 13C NMR (CDCl3): δ 217.5 (d, J PC ) 21.2 Hz,
CO), 81.1 (s, -CHdCHCHMe-), 57.7 (b, OMe), 51.3 (s, -CHd
3
CHCHMe-), 51.2 (s, -CHdCHCHMe-), 28.5 (d, J PC ) 6.6
Hz, Me). MS (FAB): m/z 316 (M+). Anal. Calcd for C11H17
-
FeO5P: C, 41.79; H, 5.43. Found: C, 41.72; H, 5.35.
Syn th esis of [(η5-C5H5)F e(CO)2P (OMe)3+][P F 6-] (2‚P F 6).
(η5-C5H5)Fe(CO)2Cl (0.50 g, 2.35 mmol) and P(OMe)3 (0.29 g,
2.35 mmol) were dissolved in THF (50 mL) and the solution
was maintained at -78 °C. A few drops of MeLi in ether were
added to the solution, resulting in a yellow precipitate in 5
min. NH4PF6 (0.38 g, 2.35 mmol) was then added to the
suspension. After 30 min, the temperature of the mixture was
slowly raised to room temperature over ca. 1 h. After filtration,
the filtrate was removed in vacuo. The yellow residue was
extracted with CH2Cl2 (30 mL) and reprecipitated on dilution
with hexane to give yellow crystals of 2‚P F 6 (0.71 g, 68%). IR
(CH2Cl2): νCO 2072, 2025 cm-1
.
1H NMR (CDCl3): δ 5.76 (s,
3
5H, Cp), 3.95 (d, J PH ) 12 Hz, 9H, Me). 31P NMR (acetone-
1
d6): δ 160.8 (s, P(OMe)3), -145.0 (hep, J PF ) 706 Hz, PF6).
(lit.10 IR (CH2Cl2) νCO 2073, 2032 cm-1; 1H NMR (CDCl3) δ 5.64
3
(d, J PH ) 1.1 Hz, 5H, Cp)).
Syn th esis of (η5-C5H5)F e(CO)2P (O)(OMe)2 (4). Com-
pound 1 (0.51 g, 1.7 mmol) was mixed with P(OMe)3 (0.21 g,
1.7 mmol) in THF (30 mL) at -78 °C. A few drops of MeLi in
ether were then added to the solution. After about 2 min, a
pale yellow precipitate formed that slowly disappeared to
finally give a yellow solution when the temperature was raised
from -78 °C to room temperature over a period of 45 min.
The solvent was removed in vacuo. The yellow oily residue
was dissolved in minimum amount of CH2Cl2 and transferred
to a silica gel column made up with CH2Cl2. A yellow band,
obtained on elution with CH2Cl2, was a mixture of 3 and (η5-
C5H5)Fe(CO)2Me (70 mg). The second yellow band, collected
on elution with 1:1 acetone/MeOH, gave after the solvent
removal yellow solids of 4 (0.35 g, 1.2 mmol, 70%). IR (CH2-
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were per-
formed under an atmosphere of prepurified nitrogen with
standard Schlenk techniques. All solvents were distilled from
an appropriate drying agent.20 Infrared spectra were recorded
in CH2Cl2 using CaF2 optics on a Perkin-Elmer 852 spectro-
photometer. The 1H NMR and 13C NMR spectra were obtained
on Bruker AC200/AC300 spectrometers, with chemical shifts
reported in δ values, downfield positive, relative to the residual
solvent resonance of CDCl3 (1H δ 7.24, 13C δ 77.0). The 31P
NMR spectra were obtained on Bruker AC200/AC300 spec-
trometers using 85% H3PO4 as an external standard (δ 0.00).
Cl2): νCO 2040, 1990 cm-1
.
1H NMR (CDCl3): δ 4.99 (s, 5H,
3
Cp), 3.51 (d, J PH ) 11.5 Hz, 6H, Me). 31P NMR (CDCl3): δ
111.81. 13C NMR (CDCl3): δ 210.86 (d, J PC ) 40.5 Hz, CO),
2
2
85.74 (Cp), 51.14 (d, J PC ) 7.9 Hz, Me) (lit.11 IR (CH2Cl2) νCO
1
3
2040, 1990 cm-1; H NMR (CDCl3) δ 5.08 (d, J PH ) 1.8 Hz,
3
5H, Cp), 3.63 (d, J PH ) 11.0, 6H, Me); 31P NMR (CDCl3) δ
The melting points were determined on
a Yanaco MPL
melting-point apparatus and are uncorrected. (η5-C5H5)Fe-
(CO)2X (X ) Cl, I) was prepared according to the literature
procedure.21 Other reagents were obtained from commercial
sources and used without further purification.
109.2).
Rea ction of 4 w ith MeLi. Compound 4 (0.30 g, 1.05 mmol)
was suspended in THF (30 mL) at -78 °C. MeLi in THF/
cumene (1:9) solution (1.2 mL × 1 M) was added dropwise to
the mixture. The temperature of the mixture was slowly raised
to room temperature for 30 min to give a yellow solution: IR
(20) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals; Pergamon Press: Oxford, U.K., 1981.
(21) (a) Dombek, B. D.; Angelici, R. J . Inorg. Chim. Acta 1973, 7,
345. (b) Meyer, T. J . J ohnson, E. C.; Winterton, N. Inorg. Chem. 1971,
10, 1673. (c) Inorg. Synth. 1971, 12, 36. (d) Inorg. Synth. 1963, 7, 110.
νCO 1922, 1560 cm-1 31P NMR δ 160.8. After the solvent was
;
removed in vacuo, an air-sensitive and hygroscopic yellow solid
was obtained that was resistant to purification nonetheless.

1158 Organometallics, Vol. 18, No. 7, 1999
Liu et al.
2
Syn th esis of [(η5-C5H5)F e(CO){P (OMe)3}2+][P F 6-] (5‚
P F 6). (η5-C5H5)Fe(CO)2Cl (0.5 g, 2.35 mmol) and P(OMe)3 (0.7
mL, 5.92 mmol) were dissolved in THF (35 mL) at -78 °C. A
few drops of MeLi (1.4 M in ether, ca. 3 drops) were added to
the mixture. A yellow precipitate formed in 2 min at -78 °C.
The reaction mixture was stirred for another 10 min at -40
°C until the bubbling ceased. Following addition of NH4PF6
(0.42 g, 3.33 mmol), the reaction mixture was stirred for
another 30 min at room temperature. The volatiles were
removed in vacuo to give a yellow solid. After two precipita-
tions from MeOH/H2O and CH2Cl2/hexane, a yellow oil was
obtained. Removal of the solvents gave a yellow solid of 5‚
P F 6 (0.35 g, 0.65 mmol, 28%). IR (CH2Cl2): νCO 1999 cm-1
(lit.15,16 IR νCO 1993 cm-1). 1H NMR (acetone-d6): δ 5.27 (s,
Hz, 6H, P(O)(OMe)2)). 31P NMR (CDCl3): δ 175.0 (d, J PP
)
139 Hz, P(OMe)3), 118.0 (d, 2J PP ) 139 Hz, PO(OMe)2) (lit. 31
P
NMR (CH2Cl2) δ 181.8 (d, J PP ) 140.3 Hz, P(OMe)3), 124.9 (d,
J PP ) 140.3 Hz, P(O)(OMe)2)). 13C NMR (CDCl3): δ 216.1 (dd,
2J PC ) 41.2 Hz, J PC ) 44.2 Hz, CO), 83.6 (s, Cp), 52.5 (d, J PC
2
2
2
) 4.9 Hz, P(OMe)3), 50.0, 49.8 (d × 2, J PC ) 7.5 Hz, 8.4 Hz,
P(O)(OMe)2). FAB MS: m/z 383 (M + 1)+.
Syn th esis of [η5-C5H4{P (O)(OMe)2}]F e(CO){P (OMe)3}-
Me (7). Compound 6 (0.70 g, 1.83 mmol) was dissolved in THF
(40 mL) at -78 °C. MeLi in THF/cumene (1:9) (1.0 M × 3.5
mL, 3.50 mmol) was added dropwise to the solution, which
was maintained at -78 °C for 30 min, at which point the color
changed from yellow to orange-red. MeI (0.2 mL, 3.2 mmol)
was then added via a syringe to the solution before the
temperature was slowly raised from -78 °C to room temper-
ature. The color returned to yellow. Upon removal of the
solvents and the volatiles, the yellow residue dissolved in a
minimum volume of THF was transferred to the top of a silica
gel column made up with a CH2Cl2 solution. The polarity of
the eluent increased from CH2Cl2 to 30% acetone in CH2Cl2.
A major yellow fraction was collected which, upon removal of
solvents, gave a yellow oil of 7 (0.64 g, 1.62 mmol, 89%). IR
(CH2Cl2): νCO 1939 cm-1. 1H NMR (CDCl3): δ 4.85, 4.80, 4.64,
3
5H, Cp), 3.84 (d, J PH ) 11.4 Hz, 18H, OMe) (lit. 1H NMR δ
5.23 (Cp), 3.87 (OMe)). 31P NMR (acetone-d6): δ 168.5 (s,
P(OMe)3), -145 (hep, 1J PF ) 706 Hz, PF6) (lit. 31P NMR δ 168.8
(P(OMe)3)).
Syn th esis of (η5-C5H5)F e(CO){P (OMe)3}{P (O)(OMe)2}
(6). Compound 1 (0.60 g, 1.97 mmol) and P(OMe)3 (0.6 mL,
5.07 mmol) were dissolved in THF (40 mL) at -78 °C. A few
drops of MeLi (1.4 M in ether) were added to the reaction
mixture. Initially a yellow precipitate formed that was followed
by gas evolving from solution when the reaction temperature
was raised from -78 °C to room temperature. The reaction
carried on at room temperature for another 2 h until all the
precipitate redissolved to give a clear yellow solution. The
solvents together with excess P(OMe)3 were then removed in
vacuo. The resultant yellow residue was dissolved in acetone
(10 mL) and transferred to the top of a silica gel column. The
polarity of the eluent was slowly increased from acetone to
30% methanol in acetone. A major yellow band was collected
which, after removal of the solvents, gave a yellow oil of 6 (0.70
g, 1.83 mmol; 92%). IR (THF): νCO 1964 cm-1 (lit.22 IR (KBr
disk) νCO 1960 cm-1). 1H NMR (CDCl3): δ 4.69 (s, 5H, Cp),
3.62 (d, 3J PH ) 11.5 Hz, 9H, P(OMe)3), 3.46 (d, 3J PH ) 11.1 Hz,
6H, P(O)(OMe)2) (lit. 1H NMR (CDCl3) δ 4.75 (s, 5H, Cp), 3.62
(dd, J PH ) 11.7 Hz, 2.0 Hz, 9H, P(OMe)3), 3.46 (d, J PH ) 11.2
3
4.50 (br s × 4, 1H × 4, Cp), 3.77 (d, J PH ) 5.9 Hz, 6H, PO-
(OMe)2), 3.56 (d, 3J PH ) 11.2 Hz, 9H, P(OMe)3), -0.04 (d, 3J PH
) 4.0 Hz, 3H, FeMe). 31P NMR (CDCl3): δ 188.7 (s, P(OMe)3),
23 (br, PO(OMe)2). 13C NMR (CDCl3): δ 219.22 (d, J PC ) 50
2
Hz, CO), 95.06, 86.44, 85.34, 82.16 (d × 4, J PC ) 14 Hz, Cp),
52.74 (br s, PO(OMe)2), 51.84 (d, 3J PC ) 4 Hz, P(OMe)3), -25.17
(d, J PC ) 33 Hz, FeMe). FAB MS: m/z 396 (M+). Anal. Calcd
2
for C12H22FeO7P2: C, 36.4; H, 5.6. Found: C, 36.6; H, 5.7.
Ack n ow led gm en t. The authors thank Academia
Sinica and the National Science Council of the ROC for
the financial support. Y.-H.L. is grateful to the NSC for
a postdoctoral fellowship.
(22) Nakazawa, H.; Ichimura, S.; Nishihara, Y.; Miyoshi, K.; Na-
kashima, S.; Sakai, H. Organometallics 1998, 17, 5061.
OM981001R