MeLi Reactions with the Electrophile System of (η5-C5H5)Fe(CO)2I/P(OMe)3: The Roles of MeLi as Reductant, Nucleophile, and Base

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MeLi Reactions with the Electrophile System of

(

η

5

_-C

5

H

5

)Fe(CO)

2

I/P(OMe)

3

: The Roles of MeLi as

Reductant, Nucleophile, and Base

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_-C

5H5)Fe(CO)2I (1) and P(OMe)3. The addition of MeLi dropwise

without delay to the 1:1 mixture results in (η4_-exo-MeC

5H5)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_-C 5H4

-{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. Introduction

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_-C 5H5

)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)3substitution reactions, one for

the iodide and one for the CO ligand in sequence. Results and Discussion

The addition of MeLi dropwise to a 1:1 mixture of 1/P(OMe)3at -78 °C gives in 45% isolated yields the

ring-methylation product (η4_-exo-MeC

5H5)Fe(CO)2

P-(OMe)3(3), analogous to the reaction of MeLi with a 1:1

mixture of 1/PR3at -78 °C (where PR3is a phosphine).5

Thisη5_-C

5H5ring methylation changes the bonding of

the ring to metal fromη5_-C

5H5 toη4-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)3together 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_-C

5H5

)-Fe(CO)2X, with PPh3replacing halide X-.6The second

reaction is the nucleophilic addition of stoichiometric MeLi to the η5_-C

5H5 ring of 2 from an exo side to Fe.

The exo addition has been established for the similar complex (η4_-exo-MeC

5H5)Fe(CO)2PMePh27and (η4

-exo-MeC5H5)Fe(CO)2PPh38 by single-crystal X-ray

diffrac-tion.

As the 1:1 mixture of 1 and P(OMe)3gives the same

IRνCOfeatures 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 conversion to 2, which can be isolated as a PF6- salt

(2‚PF6) in 68% isolated yield if immediately

anion-exchanged in ca. 2 min (or in ca. 5 min for the (η5_-C

5H5)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 * To whom correspondence should be addressed at the Academia

Sinica.

†_{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) Julliard, 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.

(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.

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the well-known Arbuzov-like reaction9_{on standing for}

45 min and produces in 70% yields the phosphonate complex (η5_-C

5H5)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_-C

5H5)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_-C

5H5)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 theη5_-C

5H5ring of 4 but

could seemingly add at the CO ligand. On the basis of νCO1922, 1560 cm-1in the IR spectrum andδ 160.8 in 31_{P NMR detected from the mixture, a (}_η5_-C

5H5

)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 theη5_-C

5H5ring in (η5-C5H5)Fe(CO)2

P-(O)(OEt)2.13More studies with the metastable solution

of the (η5_-C

5H5)Fe(CO)C(O)Me{P(O)(OMe)2}-anion are

now underway.

The addition of 1 equiv of MeLi dropwise to a mixture of 1 and excess P(OMe)3at -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-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_-C

5H5

)-Fe(CO){P(OMe)3}2+ cation (5), could be isolated as a

PF6-salt (5‚PF6; 27%, not optimized)14whose

charac-terization data are consistent with those reported by Schuman15_{and Coville.}16_{The low yield of 5‚PF}

6here

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)3substitution for I-, as shown at the top

of Scheme 3, and the other is the P(OMe)3substitution

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_-C

5H5)Fe(CO)2I•- radical anion (1re), followed by a

dissociation of I-and the formation of the 17e (η5_-C 5H5

)-Fe(CO)2•radical, to which P(OMe)3is coordinated to give

the 19e (η5_-C

5H5)Fe(CO)2P(OMe)3•radical (2re), 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 1re. 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 (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_-C

5H5)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) Johnston, P.; Hutchings, G. J.; Denner, L.; Boeyens, J. C. A.; Coville, N. J. Organometallics 1987, 6, 1292.

Scheme 1

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which the formed (η5_-C

5H5)Fe(CO){P(OMe)3}2•radical

(5re) is also better than 2re as a reducing agent. In the literature, Tyler reported that the excess P(OEt)3

sub-stitution for CO in (η5_-C

5H5)Fe(CO)2{P(OEt)3}+is

cata-lyzed by the chemical reducing agent (η5_-C

5H5)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.

The Arbuzov-like reaction with 5 to give 6 is limited to just one P(OMe)3 and does not involve a second

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}3proceeds with only one P(OMe)3.19

(17) Goldman, A. S.; Tyler, D. R. Inorg. Chem. 1987, 26, 253.

(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.

(19) Ruther, T.; Englert, U.; Koelle, U. Inorg. Chem. 1998, 37, 4265.

Scheme 2

Scheme 3

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Also shown in Scheme 2, the 6 reaction with MeLi at -78 °C is the deprotonation and not the methylation of theη5_-C

5H5ring; i.e., MeLi works as a base rather than

a nucleophile. An intramolecular migration of the -P(O)(OMe)2group from Fe to theη5-C5H5ring follows,

effectively making the Fe anion instead of the C anion the site for a MeI quench to produce [η5_-C

5H4P{

(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-1for 4 and 1964 cm-1for 6. The higher IRνCOstretching 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 theη5_-C

5H5ring 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)3detects 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.

Experimental Section

General Considerations. 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 CH2Cl2using CaF2optics on a Perkin-Elmer 852

spectro-photometer. The1_{H NMR and}13_{C NMR spectra were obtained}

on Bruker AC200/AC300 spectrometers, with chemical shifts reported inδ values, downfield positive, relative to the residual solvent resonance of CDCl3(1Hδ 7.24,13Cδ 77.0). The31P

NMR spectra were obtained on Bruker AC200/AC300 spec-trometers using 85% H3PO4as an external standard (δ 0.00).

The melting points were determined on a Yanaco MPL melting-point apparatus and are uncorrected. (η5_-C

5H5

)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.

Synthesis of (η4_-exo-MeC

5H5)Fe(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): νCO1979 vs, 1916 vs cm-1.31_{P NMR (CDCl} 3): δ 189.5.1H NMR (CDCl3): δ 5.2 (b, 2H, -CHdCHCHMe-), 3.52 (d, 3_J PH ) 12 Hz, 9H, OMe), 2.80-2.79 (b, 3H, -CHdCHCHMe-), 0.41 (d,4_J PH) 6 Hz, 3H, Me).13_{C NMR (CDCl} 3): δ 217.5 (d,2JPC) 21.2 Hz,

CO), 81.1 (s, -CHdCHCHMe-), 57.7 (b, OMe), 51.3 (s, -CHd CHCHMe-), 51.2 (s, -CHdCHCHMe-), 28.5 (d,3_J

PC) 6.6

Hz, Me). MS (FAB): m/z 316 (M+_{). Anal. Calcd for C} 11H17

-FeO5P: C, 41.79; H, 5.43. Found: C, 41.72; H, 5.35.

Synthesis of [(η5_-C

5H5)Fe(CO)2P(OMe)3+][PF6-] (2‚PF6).

(η5_-C

5H5)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‚PF6(0.71 g, 68%). IR

(CH2Cl2): νCO2072, 2025 cm-1.1H NMR (CDCl3): δ 5.76 (s, 5H, Cp), 3.95 (d,3_J PH) 12 Hz, 9H, Me).31P NMR (acetone-d6): δ 160.8 (s, P(OMe)3), -145.0 (hep,1JPF) 706 Hz, PF6). (lit.10_{IR (CH} 2Cl2)νCO2073, 2032 cm-1;1H NMR (CDCl3)δ 5.64 (d,3_J PH) 1.1 Hz, 5H, Cp)). Synthesis of (η5_-C

5H5)Fe(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 CH2Cl2and 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

-Cl2): νCO 2040, 1990 cm-1.1H NMR (CDCl3): δ 4.99 (s, 5H, Cp), 3.51 (d,3_J PH ) 11.5 Hz, 6H, Me).31P NMR (CDCl3): δ 111.81.13_{C NMR (CDCl} 3): δ 210.86 (d,2JPC) 40.5 Hz, CO), 85.74 (Cp), 51.14 (d,2_J PC) 7.9 Hz, Me) (lit.11IR (CH2Cl2)νCO 2040, 1990 cm-1;1_{H NMR (CDCl} 3)δ 5.08 (d,3JPH) 1.8 Hz, 5H, Cp), 3.63 (d,3_J PH ) 11.0, 6H, Me);31P NMR (CDCl3)δ 109.2).

Reaction of 4 with 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 νCO1922, 1560 cm-1;31P NMRδ 160.8. After the solvent was

removed in vacuo, an air-sensitive and hygroscopic yellow solid was obtained that was resistant to purification nonetheless. (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. Johnson, E. C.; Winterton, N. Inorg. Chem. 1971, 10, 1673. (c) Inorg. Synth. 1971, 12, 36. (d) Inorg. Synth. 1963, 7, 110.

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Synthesis of [(η5_-C

5H5)Fe(CO){P(OMe)3}2+][PF6-] (5‚

PF6). (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‚ PF6(0.35 g, 0.65 mmol, 28%). IR (CH2Cl2): νCO 1999 cm-1 (lit.15,16_IR _ν CO 1993 cm-1).1H NMR (acetone-d6): δ 5.27 (s, 5H, Cp), 3.84 (d,3_J PH) 11.4 Hz, 18H, OMe) (lit.1H NMRδ 5.23 (Cp), 3.87 (OMe)). 31_{P NMR (acetone-d} 6): δ 168.5 (s,

P(OMe)3), -145 (hep,1JPF) 706 Hz, PF6) (lit.31P NMRδ 168.8

(P(OMe)3)).

Synthesis of (η5_-C

5H5)Fe(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)3were 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): νCO1964 cm-1(lit.22IR (KBr disk)νCO 1960 cm-1).1H NMR (CDCl3): δ 4.69 (s, 5H, Cp), 3.62 (d,3_J PH) 11.5 Hz, 9H, P(OMe)3), 3.46 (d,3JPH) 11.1 Hz, 6H, P(O)(OMe)2) (lit.1H NMR (CDCl3)δ 4.75 (s, 5H, Cp), 3.62 (dd, JPH) 11.7 Hz, 2.0 Hz, 9H, P(OMe)3), 3.46 (d, JPH) 11.2 Hz, 6H, P(O)(OMe)2)).31P NMR (CDCl3): δ 175.0 (d,2JPP)

139 Hz, P(OMe)3), 118.0 (d,2JPP) 139 Hz, PO(OMe)2) (lit.31P

NMR (CH2Cl2)δ 181.8 (d, JPP) 140.3 Hz, P(OMe)3), 124.9 (d, JPP) 140.3 Hz, P(O)(OMe)2)).13C NMR (CDCl3): δ 216.1 (dd, 2_J PC) 41.2 Hz,2JPC) 44.2 Hz, CO), 83.6 (s, Cp), 52.5 (d,2JPC ) 4.9 Hz, P(OMe)3), 50.0, 49.8 (d× 2,2JPC) 7.5 Hz, 8.4 Hz, P(O)(OMe)2). FAB MS: m/z 383 (M + 1)+. Synthesis of [η5_-C

5H4{P(O)(OMe)2}]Fe(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 CH2Cl2solution. The polarity of

the eluent increased from CH2Cl2to 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): νCO1939 cm-1.1H NMR (CDCl3): δ 4.85, 4.80, 4.64, 4.50 (br s_{× 4, 1H × 4, Cp), 3.77 (d,}3_J PH) 5.9 Hz, 6H, PO-(OMe)2), 3.56 (d,3JPH) 11.2 Hz, 9H, P(OMe)3), -0.04 (d,3JPH ) 4.0 Hz, 3H, FeMe).31_{P NMR (CDCl} 3): δ 188.7 (s, P(OMe)3), 23 (br, PO(OMe)2).13C NMR (CDCl3): δ 219.22 (d,2JPC) 50 Hz, CO), 95.06, 86.44, 85.34, 82.16 (d× 4, JPC) 14 Hz, Cp), 52.74 (br s, PO(OMe)2), 51.84 (d,3JPC) 4 Hz, P(OMe)3), -25.17 (d,2_J

PC) 33 Hz, FeMe). FAB MS: m/z 396 (M+). Anal. Calcd

for C12H22FeO7P2: C, 36.4; H, 5.6. Found: C, 36.6; H, 5.7.

Acknowledgment. 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.

OM981001R (22) Nakazawa, H.; Ichimura, S.; Nishihara, Y.; Miyoshi, K.;

Na-kashima, S.; Sakai, H. Organometallics 1998, 17, 5061.