Organometallics 1995, 14,3958-3962
3958
Synthesis of Half-Sandwich Iron Carboxyalkyls and Iron (Thiocarboxy)alkyls: Reaction of Cyclopentadienyldicarbonyliodoiron with 0- and S-Based Nucleophiles in the Presence of Triphenylphosphine Ling-Kang Liu,*l'J Uche B. Eke,*>$and M. Adediran Mesubis Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, ROC, Department of Chemistry, National Taiwan University, Taipei, Taiwan 10767, ROC, and Department of Chemistry, University of Zlorin, Ilorin, Nigeria Received April 18, 1995@ One equivalent of NaOMe is added to a n equimolar mixture of (q5-C5H5)Fe(C0)21(1) and PPh3 after the addition of a few drops of n-BuLi, to take advantage of the catalytic formation (3),which, upon formation, becomes the virtual reactant with of [(r5-C5H5)Fe(CO)z(PPh)3l+IOMe-. The OMe- reaction yields the methyl carboxylate (q5-C5H5)Fe(CO)(PPh)3C(0)OMe (8Me). A similar pattern is observed in the OPh-, SMe-, and SPh- reactions, resulting in (8Ph),(q5-C5Hs)Fe(CO)(PPh)3C(0)SMe (9Me), the derivatives (q5-C5H5)Fe(CO)(PPh)3C(0)OPh and (r5-C5H5)Fe(CO)(PPh)3C(O)SPh (9Ph),respectively. The metalloesters exist simultaneously in the molecular form (8R) and the ionic form E(q5-C5H5)Fe(C0)~(PPh)31+ OR- (10R; R = Me, Ph) in solutions of medium polarity (CHCl3, CHzC12, and MeCN), whereas the S analogs exist only in the ionic form. In CHC13, CHzC12, and MeCN solutions, the ratio of neutral 8Me to ionic lOMe is ca. (6.0-8.4):1,as judged from the NMR measurements. Nonetheless, the ratio of neutral 8Ph to ionic lOPh is ca. (0.17-0.25):l.
Introduction Transition-metal carboxylates and related derivatives are of great interest because they represent a series of proposed intermediates in metal carbonyl catalyzed water-gas shift reactions.' A number of years ago, Pettit et al. reported, among other derivatives, the preparation of ( T , W & H ~ ) F ~ ( C O ) ( P P ~ ~ ) C (by O )treating O M ~ the chlowith ride salt of the cation (175-C5H5)Fe(C0)2(PPh3)+ equimolar amounts of the base NaOMe (Scheme 1h2 Recently, Gibson et al. prepared the same compound by reacting the alkali-metal salts of (175-C5H5)Fe(CO)(PPh3)COz- with electrophilic methylating agents, e.g., Me1 and Me30BF4 (Scheme 2).3 We report in this note the synthesis of the similar species (175-C5H5)Fe(CO)(PPh3)C(0)Nu (Nu- = OMe-, OPh-, SMe-, SPh-) by reacting the neutral (qWsHs)Fe(CO)zIwith Nu- in the presence of PPh3, albeit initiated with a small amount of n-BuLi.
Scheme 1
9
l+Cl
l
BMe
Scheme 2 I
+Me30BF4 o c ~ p p h 3
- oc\\A'pph3
0' Na+
I
+ NaBF,
Fe
0
OMe
8Me
I- (3)under refluxing condition^.^ In our earlier studies, X = C1, Br, I) the reactions of (v5-C5H5)Fe(C0)2X(4X; and RLi (R = n-Bu, Me, i-Bu, Ph) in the presence of The 1:l mixture of (q5-C5H5)Fe(CO)zI(1) and PPh3, PPh3 at -78 "C effectively change the bonding mode of when stirred in THF at -78 "C,gives only (7,ACsHs)the ring from q5-C5H5to v ~ - R C ~ H It ~is. noted ~ that, Fe(CO)(PPh3)1(2) after several days, although in the literature it gives both 2 and [(r5-C5H5)Fe(C0)~(PPh3)1+ shortly after n-BuLi (1-2 drops) is introduced into a 1:l mixture of 1 and PPh3 in THF at -78 "C, the presence of a small amount of the cationic iron complex .' Academia Sinica. National Taiwan University. 3 and the dimer [(q5-C5H5)Fe(C0)&(5) is evident in the * University of Ilorin. IR spectrum.5b Stirring of this mixture for 2 h without Abstract published in Advance ACS Abstracts, July 15, 1995.
Results and Discussion
@
(1)( a ) Ford, P. C. Acc. Chem. Res. 1981, 14, 31. (b) Darensbourg, D. J.; Kudaroski, R. A. Adu. Organomet. Chem. 1983,22,129. (c) Ford, P. C.; Rokicki, A. Adu. Organomet. Chem. 1987,28, 139. (2) Grice, N.; Kao, S. S.; Pettit, R. J. Am. Chem. SOC.1979, 101, 1627. (3) la) Gibson, D.; Ong, T.-S. J . Am. Chem. SOC. 1987, 109, 7191. (b) Gibson, D.; Ong, T.-S.; Ye, M. Organometallics 1991, 10, 1811. (c) Gibson, D.; Franco, J. D.; Harris, M. T.; Ong, T.-S. Organometallics 1992, 11, 1993.
(4) (a)Pandey, V. N. Znorg. Chim. Acta 1977,22, L39 and references therein. (b) Alway, D. G.; Barnett, K. W. In Inorganic and Organometallic Photochemistry; Adv. Chem. Ser. 168; Wrighton, M. S., Ed.; American Chemical Society: Washington, DC, 1978; pp 115-131. (c) Zakrezewski, J. J. Organomet. Chem. 1991, 412, C23. (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. (c) Liu, L.-K.; Luh, L.-S.; Eke, U. B. Organometallics 1995, 14, 440.
0276-733319512314-3958$09.0010 0 1995 American Chemical Society
Organometallics, Vol. 14, No. 8, 1995 3959
Iron Carboxyalkyls and (Thiocarboxy)alkyls
Scheme 3
-
e,
oc,\\f\
oc
I
+ R'
+ PPh3
1
J
+ OPh'
___)
further addition of n-BuLi results in yellow precipitates of 3 (Scheme 3). The rationale here is that n-BuLi reduces 1 to the dimer 5 or to the radical (v5-C5H5)Fe(C0)z' t o act as a catalyst assisting the conversion of 1 and PPh3 to 3. The iron-centered radicals are exceedingly reactive species, dimerizing at near-diffusioncontrolled rates.6 The catalytic ability of dimer 5 has been demonstrated in the replacement reaction of CO or I- of 1 with ligands such as PPh3 and t-BuNC.' Stirring an equimolar mixture of 1, PPh3, and NaOMe in THF overnight has been found to result in the recovery of starting materials. Yet, under the experimental conditions employed in this note, the addition of NaOMe to a 1:l mixture of 1 and PPh3 follows the initiation by a few drops of n-BuLi, to take advantage of the catalytic formation of 3 that, upon formation, becomes the intermediate to react with OMe-. The nucleophile OMe- does not produce any detectable amounts of v4 species, different from the reaction (Scheme 3) of the lithiated C-based nucleophile R- with 1 in the presence of PPh3, which gives mainly (y4-ex0RC5H5)Fe(CO)zPPh3(7).5b Scheme 3 also shows the OMe- reaction in which the isolated product (80.391.7%), slowly decomposing in solution, is found to be the methyl carboxylate (v5-C5H5)Fe(CO)(PPh)3C(0)OMe (8Me) on the basis of spectroscopic data. In the literature, 8Me has been reported by Pettit et al. to be prepared from the reaction of the chloride salt of the cation [(v5-C5H5)Fe(C0)zPPh3I+ with equimolar NaOMe and by Gibson et al. to be prepared from the alkali-metal salts of (v5-C5H5)Fe(CO)PPh3(CO2)-with Me30BF4 or MeI. The preparation here involves the Pettit polarity in a modified way. With an initiation by a very small reacts amount of n-BuLi, the neutral (v5-C5H5)Fe(C0)21 with NaOMe in the presence of PPh3 to give an excellent yield of 8Me. The advantage here is that there is no (6)( a )Caspar, J . V.; Meyer, T. J . J.Am. Chem. SOC.1980,102,7794. (b) Moore, B. D.; Poliakoff, M.; Turner, J . J . J . Am. Chem. SOC. 1986, 108, 1819.(c) Dixon, A. J.; George, M. W.; Hughes, C.; Poliakoff, M.; Turner, J . J . J . Am. Chem. SOC.1992,114,1719.(d) Kuksis, T.; Baird, M. C. Organometallics 1994,13, 1551. (7)( a ) Coville, N.J.; Albers, M. 0.; Ashworth, T. V.; Singleton, E. J . Chem. Soc., Chem. Commun. 1981,408. (b) Coville, N. J.;Darling, E. A,; Hearn, A. W.; Johnston, P. J. Organomet. Chem. 1987,328,375.
oc'
7
e I
need to isolate the iodide salt [(v5-C5H5)Fe(C0)2PPh31+I-, effectively making the preparation a one-flask procedure. A very similar pattern is observed in the OPh-, SMe-, and SPh- reactions, resulting in the (BPh),(v5derivatives (v5-C5H5)Fe(CO)(PPh)3C(0)OPh C5H5)Fe(CO)(PPh)3C(O)SMe(9Me), and (v5-C5H5)Fe(CO)(PPh)3C(O)SPh(9Ph),respectively. The sequence of adding the small amount of n-BuLi is important, however. An attempt to mix 1:l:l 1,NaOMe, and PPh3 and then introduce 2-3 drops of n-BuLi into the mixture failed to produce 8Me.8 Table 1lists the recorded IR YCO stretching bands and NMR chemical shifts of 8R (R = Me, Ph) in CHCl3, CH2Clg, MeCN, and C6H6 and of 9R in CHC13. A relevant IR spectrum of 8Me in CHzClz is presented in Figure 1. The existence of two forms in CHzClz solution is clear, the same features being also found in CHC13 and MeCN solutions. The molecular metalloester (v5-C5H5)Fe(CO)(PPha)C(O)OMe@Me)has corresponding IR Y C O bands at 1940 (vs) and 1603 (s) cm-l and the ionic form [(v5-C5H5)Fe(CO)2PPh31+OMe(10Me) has IR vco bands at 2058 (m) and 2014 (m) cm-'. The complex 8Me in C6H6 exhibits in the IR spectrum YCO bands at 1939 (s) and 1600 (s) cm-', corresponding to the ester form only. No evidence of the ionic form lOMe could be found in the IR spectrum using C6H6 as solvent. Gibson et al. has reported the solid DRIFTS IR spectra of 8Me with YCO bands a t 1937 and 1594 Pettit et al. has reported for 8Me the existence of an ester in C6H6, Csz, and CHCl3 ( Y C O bands at 1935 and 1605 cm-l) and the existence of an ionic form in formamide (VCO bands at 2080 and 2030 cm-1).2 The cation [(v5-C5H5)Fe(C0)2(PPh3)1+with various counteranions shows characteristic Y C O bands at 2055 and 2010 cm-l (I-, KBr disk),4a 2055 ) , ~and ~ 2010 2058 and 2013 cm-l (I-, in C H ~ C ~ Z cm-l (PFe-, in CHC13),gand 2066-2070 and 2030-2033 cm-l (Cl-, BF4-, 0.5PtC162-, Nujol mulls).10 (8) In principle, the 1:l:l mixture of 1, PPh3, and NaOMe in THF should produce 8Me after addition of a small amount of n-BuLi. Due to the unavoidable presence of free MeOH, usually from the preparation of NaOMe, the third component (NaOMe) should be introduced after the n-BuLi initiation. Otherwise, the residual MeOH would likely block out the intended reaction.
Liu et al.
3960 Organometallics, Vol. 14, No. 8, 1995 Table 1. Recorded IFt YCO Bands, 'H NMR 6 Values, and slP NMR 6 Values for
(s5-CsHs)Fe(C0)(PPhs)C(O)Nua compd
solventb
8Me
CHzClz
IR
VCO,
cm-'
2058 w ,2014 w d 1940 vs, 1603 s
CHC13
2053 m, 2013 m
MeCN
2058 w ,2015 w
1941 vs, 1592 s 1937 w, 1617 vs 1939 vs, 1600 vs
CsH6
8Ph
CHzClz
2057 us, 2014 us 1952 m, 1602 w
CHC13
2055 s, 2014 s
MeCN
2055 us, 2013 us
1955 w, 1605 w 1952 m, 1626 w, br 1944 m, 1554 w, br
C6H6 9Me 9Ph
'H, b
3'P, 8
ratio"
7.40-7.62, 5.37, 3.43d 7.40-7.62,4.49,3.02 7.35-7.58, 5.46, 3.46 7.35-7.58, 4.47, 3.01 7.50-7.65, 5.29, 3.28 7.38-7.46,4.49,2.98 7.1-7.7, 4.34, 3.31
63.34d 79.58 61.78 77.29 67.14 82.88 78.51
Id
7.32-7.52, 5.31 7.32-7.52, 4.40 7.24-7.44, 5.35 7.24-7.44,4.31 7.40-7.57, 5.29 7.40-7.57, 4.51 7.40-7.93, 4.38
63.42 69.57 61.7 67.8 67.10 72.6 68.91
CHC13
2056 us, 2014 us
7.4-7.6, 5.47, 1.66
61.7
CHC13
2057 us, 2013 us
7.33-7.56, 5.47
61.78
6.5 1 8.4 1 6.0 1 0.25 1
0.17 1
0.21
M. Varying degrees of decomposition were observed in most a Conditions: [8Mel and [8Phl= ca. M; [9Mel and [9Phl= ca. of the solvents. For 'H and 31PNMR measurements, the corresponding D solvents were employed. Approximated by peak integration ratio in lH NMR and peak height ratio in 31PNMR; estimated error 20%. Data in italics correspond to the ionic forms.
The IR data suggest that 8Me in solution is in equilibrium (or in degradation). The interconversion between 8Me and lOMe in CHZC12 must be slower than s, the IR time scale.ll As the lH NMR data of 8Me in CDCl3, CDzClz, or CD3CN clearly reveal a ratio for 8Me t o lOMe of ca. (6.0-8.4):1, the exchange rate must be even slower than 10-1 s, the slow limit with (9) Treichel, P. M.; Shubkin, R. L.; Barnett, K. W.; Reichard, D. Inorg. Chem. 1966,5,1177. (10)Davison, A.; Green, M. L. H.; Wilkinson, G . J.Chem. SOC.1961, 3172. (11)Drago, R. S. Physical Methods in Chemistry; S a n d e r s : Philadelphia, PA, 1977.
NMR kinetic techniques.ll The lH NMR data of 8Me in C6D6 reveal no resonances assignable t o the ionic form, very reasonable if one takes into consideration of C6H6 a medium of low polarity that keeps the cation and anion from single iron carboxylate, if any, a close pair. Davies et al. reported that the base-promoted migration of carboxyalkyl ligands of (y5-CsH5)Fe(CO)(PPh&(O)OR (8R R = Me, i-Pr, t-Bu, 1-menthyl)from the Fe atom to the Cp ring is not stereospecific, the stereochemistry at Fe being scrambled.12 The racemization of the Fe center may be partially affected by the equilibrium between the achiral form, ionic 10R, and the chiral form, neutral 8R (Scheme 4).
Iron Carboxyalkyls and (Thiocarboxy)alkyls
Scheme 4
8Me (Nu=OMe) 8Ph (OPh)
lOMe (Nu=OMe) 10Ph (OPh)
The OPh- reaction results in a slowly decomposing 8Ph (45%),which has not been investigated previously in the literature. 8Ph exhibits in its IR spectra YCO bands attributed less to the molecular metalloester 8Ph (1952-1955 (m-w), 1602-1626 (w) cm-l) and more to the cation lOPh (2055-2057 (vs-SI, 2013-2014 (vs-s) cm-l) with CHC13, CH2C12, and MeCN as solvents (Table 1). An IR spectrum (YCO region) in CH2C12 is also presented in Figure 1. The solubility of 8Ph in CsHs is only sparse, and hence, the data from IR measurements are less reliable. Despite the solubility problem, the IR results suggest that only a very dilute concentration of molecular metalloester 8Ph is present in C6H6. The NMR data also indicate that there is a much smaller population of neutral 8Ph than that of ionic lOPh, the ratio being (0.17-0.25):1, which is the complete reverse of the NMR results for 8Me. Apparently, the anion OPh- is relatively much more stable than the anion OMe- because of a built-in aromatic system which effectively delocalizes the negative charge. It is not unreasonable that 8Ph in solution prefers an ionic form and 8Me a neutral form. The S analogs (r5-C5H5)Fe(CO)(PPh3)C(0)SR (9R;R = Me, Ph) are obtained similarly by dropwise addition of the nucleophile SMe- or SPh- t o the 1:l mixture of 1 and PPh3, shortly after the mixture has been treated with 1-2 drops of n-BuLi. The yields are 82.7%for 9Me and 45.0% for 9Ph, both exhibiting decomposition in solution. The solubility of the S analogs is much worse than that of the 0 analogs. 9Me and 9Ph are virtually insoluble in C6Hs. As indicated from the IR measurements shown in Table 1,9Me and 9Ph in solution show IR Y C O bands mostly of the ionic form (see Figure 1). With CDCl3 as solvent, 9Me exhibits in 'H NMR only resonances assignable to Ph, Cp, and Me protons and in 31PNMR a single peak due to a cationic species; 9Ph gives in lH NMR peaks for Ph and Cp and in 31PNMR one peak, also cationic in nature. In CHC13, CH2C12, or MeCN, the equilibrium between metalloester and oxide salt is such that for the methyl ester the majority is the metalloester BMe, with a (6.08.4):l ester to salt ratio and for the phenyl ester the majority is the oxide salt lOPh with a (0.17-0.25):l ester to salt ratio. On the other hand, the equilibria for the S analogs 9R favor only the thiolate salt, as judged from the spectroscopic evidence. PhOH is a stronger acid than MeOH, and thiols are even stronger acids than alcohols. The pKa values of the conjugated acids13 increase in the following order: PhSH < MeSH < PhOH < MeOH. The cation [($CsH5)Fe(CO)2PPh3If,if considered as a Lewis acid, (12) Abbot, S.; Baird, G. J.; Davies, S. G.; Dordor-Hedgecock, I. M.; Maberly, T.R.; Walker, J. C.; Warner, P. J. Organomet. Chem. 1985, 289, C13.
Organometallics, Vol. 14, No. 8, 1995 3961
would behave like a proton in the reaction with the conjugated bases. Therefore, 8Me is more in the metalloester form than BPh, as evidenced in the IR and NMR studies. That is, weak bases favor the ionic form and strong bases favor the ester. SMe- and SPh- are weaker bases than either OMe- or OPh-. Hence, it is not too surprising to see only ionic 9R forms (R = Me, Ph) are present in solution for the S analogs. Furthermore, considering a C-0 bond energy of 86 kcal/mol and a C-S bond energy of ca. 70 kcal/mol,14 the ionization process for 8R (Scheme 4, a C-0 bond cleavage) is also kinetically more difficult.
Experimental Section General Considerations. All manipulations were performed under an atmosphere of prepurified nitrogen with standard Schlenk techniques. All solvents were distilled from an appropriate drying agent.15 Infrared spectra were recorded in CHzClz using CaFz optics on a Perkin-Elmer 882 spectrophotometer. The 'H NMR and 13CNMR spectra were obtained on Bruker AC200/AC300 spectrometers, with chemical shifts reported in 6 values relative to the residual solvent resonance of CDC13 (lH, 7.24 ppm; 13C, 77.0 ppm). The 31P{1H)NMR spectra were obtained on Bruker AC200/AC300 spectrometers using 85% as an external standard (0.00 ppm). The melting points (uncorrected) were determined on a Yanaco MPL melting-point apparatus. Compound 1 was prepared according to the literature procedure.16 Other reagents were obtained from commercial sources (e.g. Aldrich, Merck) and used without further purification. Reaction of 1 and NaOMe in the Presence of PPh3. Compound 1 (1.216 g, 4 mmol) and PPh3 (1.049 g, 4 mmol) were dissolved in dry THF (100 mL) and cooled to -78 "C. On addition of 2-3 drops of n-BuLi, a yellow colloid was immediately observed. NaOMe (0.238 g, 4.4 mmol) in dry MeOH (5 mL) kept at -78 "C was added dropwise to the mixture from a pressure-equalizing dropping funnel. The mixture was stirred for 1h at -78 "C before being warmed with continued stirring for a further 2 h. The resultant clear yellow-light brown solution was reduced t o a small volume on a rotary evaporator. MeOH (10 mL) was added to the solution to precipitate golden yellow solids that were collected, washed with a small amount of cold water (5-10 mL), and repeatedly washed with diethyl ether (10mL x 3). Yield of 8Me: 1.51 g (80.3%).Alternatively in diethyl ether, the product could also be obtained by stirring the reactants as above. The product precipitated after 2-3 h and was collected and washed as described above. Yield: 1.70 g (91.7%). Mp: 112-114 "C. IR (CHZC12): vco 2058 s, 2014 s, 1940 v s , 1604 s cm-l. 31PNMR (CDC13): 6 77.3 major, 61.8 minor (s, respectively). 'H NMR (CDC13): 6 7.35-7.58 (m, 15 h, Ph), 5.47 minor, 4.47 major (b, respectively, 5H, Cp), 3.46 minor, 3.01 major (s, respectively, 3H, Me, the 6 3.46 peak with 0.5-0.6 MeOH in excess by integration). MS (FAB): m / z 439 (M+ - OMe). Anal. Calcd for C26H23Fe03P.0.5MeOH: C, 65.44; H, 5.19. Found: C, 65.41; H, 5.11. Reaction of 1 and NaOPh in the Presence of PPh3. Compound 1 (0.608 g, 2 mmol) and PPh3 (0.525 g, 2 mmol) were dissolved in dry THF (60.0 mL) and cooled to -78 "C. (13) (a) March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structures; McGraw-Hill: New York, 1968; pp 219-221. (b) Organicum: Practical Handbook of Organic Chemistry; Pergamon: Oxford, U.K., 1973; p 467. (c) Vollhardt, K. P. C. Organic Chemistry; Freeman: New York, 1987; p 339. (14) Purcell, K. F.; Kotz, J. C. Inorganic Chemistry; Saunders: Philadelphia, PA, 1977; Chapter 6. (15) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals; Pergamon: Oxford, U.K., 1981. (16) (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.
3962 Organometallics, Vol. 14, No. 8, 1995 On addition of a few drops (2-3) of n-BuLi, a n immediate cloudiness due to the yellow cationic [(r15-C5H5)Fe(C0)2PPh31+ species was observed. NaOPh (0.232 g, 2 mmol), freshly prepared from methanolic solutions of phenol and sodium hydroxide according to the method of Kornblum and Lurie," was taken up in dry MeOH (5.0 mL). After it was cooled to -78 "C, the solution was added dropwise to the stirred mixture of (v5-C5H5)Fe(C0)21and PPh3 over a period of 10 min. The mixture was then stirred for 1 h a t -78 "C before being warmed to room temperature and stirred for a further 2 h. After filtration on a bed of Celite, the resultant brown filtrate was reduced to a small volume on a rotary evaporator. Et20 (10.0 mL) was added to the solution to precipitate a brown solid material that was collected, washed with a small amount of cold water (5.0 mL), and repeatedly washed with Et20 (10.0 mL x 3). Yield of 8Ph: 0.48 g (45.0%). Mp: 150 "C dec. IR (CH2C12): YCO 2057 vs, 2014 vs, 1952 m, 1602 w cm-'. 31P NMR (CDC13): 6 67.8 minor, 61.8 major. 'H NMR (CDC13): d 7.24-7.44 (m, 20H, Ph), 5.35 major, 4.31 minor (s, respectively, 5H, Cp). MS (FAB): m l z 439 (M+ - OPh). Reaction of 1 and NaSMe in the Presence of PPhs. Compound 1 (1.216 g, 4 mmol) and PPh3 (1.049 g, 4 mmol) were dissolved in dry THF (100 mL) and cooled to -78 "C. The addition of a few drops of n-BuLi gave yellow colloids instantly in the stirred mixture when NaSMe (0.280 g, 4.4 mmol; freshly generated by refluxing equivalent amounts of Na and MeSSMe18 in THF for 1h), dissolved in THF (25 mL) and cooled to -78 "C, was added dropwise over a 15 min (17) Kornblum,
N.;Lurie, A. P. J.Am. Chem. Soc. 1959,81, 2705.
Liu et al. period. Stirred a t -78 "C for 1 h, the reaction mixture was then continuously stirred overnight a t room temperature under a stream of nitrogen. After the precipitate was filtered through a bed of Celite, the solvent was removed by rotary evaporation to obtain a dark paste that was shaken up in cold water (200 mL). The water layer was discarded. Diethyl ether (50 mL) was added t o the semiliquid residue t o precipitate slightly yellow solids which were filtered and washed with further amounts of ether. Yield of 9Me: 1.61 g (82.7%). Mp: 234 "C dec. IR (CH2C12): YCO 2057 vs, 2015 vs, 1598 vs cm-l. 31PNMR (CDC13): d 61.7. 'H NMR (CDC13): 6 7.36-7.57 (m, 15H, Ph), 5.47 (s, 5H, Cp), 1.66 (s, 3H, Me). MS (FAB): m l z 439 (M+ - SMe). Reaction of 1 and NaSPh in the Presence of PPhs. This procedure was carried out in a manner similar to that for the NaSMe analog. Yield of 9Ph: 0.99 g, (45.0%). Mp: '200 "C dec. IR (CH2C12): YCO 2057 vs, 2015 vs, 1735 m, 1585 vs cm-'. 31PNMR (CDC13): 6 61.8. 'H NMR (CDC13): d 7.377.57 (m, 20H, Ph), 5.47 (s, 5H, Cp). MS (FAB): m l z 439 (M+ - SPh).
Acknowledgment. We are obliged to Academia Sinica and the National Science Council of the ROC for financial support. OM9502805 (18) (a) Organicum: Practical Handbook of Organic Chemistry; Pergamon: Oxford, U.K., 1973; p 578. (b) Greene, T.W.; Wunts, P. G. P. Protective Groups in Organic Synthesis, 2nd ed.; Wiley: New York, 1991; p 302. ( c ) Lecher, H.Chem. Ber. 1915,48,254.
