(q5-C5H5)Mo(C0)3(q1-CHzCOONS) - American Chemical Society

Jun 15, 1995 - and [(q5-C5H5)Mo(C0)3(q1-CHzCOONS)]. (-NS = N-Succinimidyl). Bouchra El Mouatassim,' Hani Elamouri,*>+ Jacqueline Vaissermann,$ ...
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Organometallics 1995, 14, 3296-3302

3296

Comparative Study of the Structures and Reactivity of the mCyclopentadieny1-Bonded and Metal-Bonded Succinimidyl Ester Complexes (Metal = Mo, Fe): X-ray Molecular Structures of [(q5-C&€&OONS)Mo(C0)3Me] and [(q5-C5H5)Mo(C0)3(q1-CHzCOONS)] (-NS = N-Succinimidyl) Bouchra El Mouatassim,' Hani Elamouri,*>+ Jacqueline Vaissermann,$ and GBrard Jaouen*l+ Ecole Nationale Sup6rieure de Chimie de Paris, URA CNRS 403, 11, rue Pierre et Marie Curie, 75231 Paris Cedex 05, France, and Universitk Pierre et Marie Curie, Place Jussieu, 75231 Paris Cedex 05, France Received March 3, 1995@

The activated ester compounds [(r5-C5H4COONS)Mo(CO)3Mel (5) and [(q5-C5H4COONS)Fe(C0)zMeI (6) were obtained by treatment of the novel organometallic carboxylic acid complexes [(q5-C5H4COOH)Mo(CO)3Mel(2) and [(q5-CjH4COOH)Fe(CO)~Mel (4) with Nhydroxysuccinimide in THF in the presence of DCC (dicyclohexylcarbodiimide)or with DSC (disuccinimidyl carbonate) in CH3CN in the presence of pyridine. These activated ester complexes were identified spectroscopically, and in addition, the X-ray molecular structure of 5 was determined. Compound 5 crystallizes in the triclinic space group Pi:a = 8.684(4) A, b = 12.764(8) A, c = 16.522(10) A, a = 65.13(4)", /3 = 72.52(4)", y = 71.34(4)", V = 1544.6 A3,2 = 4. Similarly, the metal-activated ester complex [(r5-C5H5)Mo(C0)3(r1-CH~COONS)] (7) was obtained by treatment of the dimer [CpzMoz(C0)6]with N a g followed by addition of 2 equiv of ClCHZCOONS in THF; in this compound the ester unit is bonded directly to the metal center rather than to the n-bonded cyclopentadienyl. Complex 7 was characterized by spectroscopic methods, and its molecular structure was ascertained by X-ray crystallography which showed that it belongs to the well-known carbon-bound molybdenum (7) crystallizes 2-oxaalkyl (r'-enolate) category. Complex [(q5-CjHj)Mo(COh(q1-CHzC0ONS)1 in the monoclinic space group C2h: a = 19.484(2) A, b = 11.393(2) A, c = 13.694(2) A, /3 = 98.91(2)", V = 3000 Hi3, 2 = 8. The reactivity of n-bonded activated ester complexes 5 and 6 with ISiMe3 gave respectively the iodo derivatives [(q5-C5H&OONS)Mo(CO)31](9) and (10) as deep red microcrystalline solids. The reactivity of the [(~5-C5H&OONS)Fe(CO)~Il n-bonded activated ester complexes 5 and 6 and that of the metal-bonded activated ester 7 with amino esters are presented and discussed.

Introduction Recently, there has been considerable interest toward the synthesis of organometallic synthons which form stable conjugates with amino acids and proteins.' An important objective is their potential use as labeling agents: the introduction of such species helps to bring about the crystallization of the corresponding adduct and hence its identification by X-ray analysis.2 Such perspective has been demonstrated with success, particularly with amino acids and nucleotides; for instance, the stable conjugates [Cp*Ir(glycine)land [Cp*(phenyl~

~~

~

~~

' Ecole Nationale Superieure de

Chimie de Paris. Universitb Pierre et Marie Curie. Abstract published in Advance ACS Abstracts, June 15, 1995. (1)(a) Laurie, S. H. Amino Acids, Peptides and Proteins. In Comprehensive Coordination Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, England, 1987;Vol. 2,p 739. (b)Jaouen, G.; VessiBres, A.; Butler, I. S. Acc. Chem. Res. 1993,26, 361 and references therein. (c)Sloop, F. V.; Brown, G. M.; Sachleben, R. A.; Garrity, M. L.; Elbert, J. E.; Jacobson, K. B. New J . Chem. 1994,18, 317. td) Craver, J. A.; Fates, B.; Kane-Maguire, L. A. P. J. Chem. Soc., Chem. Commun. 1993, 928. (e)Anson, C. E.; Creaser, C. S.; Egyed, 0.;Fey, M. A.; Stephenson, G. R. J . Chem. SOC.,Chem. Commun. 1994, 39. rf, Lavastre, I.; Besancon, J.; Brossier, P.; Moise, C. Appl. Organomet. Chem. 1991.5, @

143.

0276-7333l95/2314-3296$09.00/0

glycine)] have been isolated and identified by X-ray determination.2b An interesting class of synthons are r,15-cyclopentadienyl metallocarbonyl complexes, where the x-bonded cyclopentadienyl is attached to an activated N-succinimidyl ester function. Such species have been used for the selective labeling of amino acids in peptide chains and proved to be a valuable method to assay the number of such amino acids which are exposed and available for r e a ~ t i o n . ~The ~ , ~metal-carbonyl bands absorb in the range of 1900-2100 cm-l, where biological molecules are transparent. Hence the labeling of proteins by these complexes can be achieved by monitoring the metallocarbonyl bands using FT infrared techniques. In this paper we report on the syntheses of the novel N-succinimidyl ester complexes [(r,15-C5H4COONS)Mo( 2 )(a)Elamouri, H.; Gruselle, M.; Vaissermann, J.; McGlinchey, M. J.; Jaouen, G. J . Organomet. Chem. 1995, 485, 79. tbl Grotjahn, D. B.; Groy, T. L. J . Am. Chem. SOC. 1994, 116, 6969. (cj Beck, W.; Kramer, R. Angew. Chem., Int. Ed. Engl. 1991,30, 1467. (3)tal Wang, Z.;Roe, B. A,; Nicholas, K. M.; White, R. L. J.Am. Chem. SOC.1993, 115, 4399. tb) Salmain, M.; Gunn, M.; Gorfti, A,; Top, S.; Jaouen, G. Bioconjugate Chem. 1993,4, 425.

0 1995 American Chemical Society

Succinimidyl Ester Complexes

Organometallics, Vol. 14, No. 7, 1995 3297

Scheme l a

Soc. 1980, 102, 1196. (b)Hart, W. P.; Rausch, M. D. J . Organomet.

lowed by addition of dry ice (Con) and acidification with acqueous HC1 solution (Scheme 1). Although the preparation of the iron derivative 4 was attained without difficulties,the molybdenum derivative [(q5-CfiCOOH)Mo(C0)sMeI (2), reported for the first time, could only be obtained by avoiding its recrystallization in basic medium. A brief communication has already been reported concerning their synthesis and their pk, values.' The lH-NMR spectra of 2 and 4 show a pair of triplets in the area (5-6 ppm) characteristic of a functionalized x-bonded cyclopentadienyl ring; there is also a singlet peak at 0.44and 0.25 ppm attributed to the metal-bonded methyl groups of 2 and 4, respectively. The organic carbonyl stretching absorptions in these compounds are shifted to a lower frequency when compared to organic carboxylic acids, and they absorb at 1680 cm-l for 2 and 1676 cm-l for 4. When the carboxylic acid complex [(q5-C5H4COOH)Fe(COhMeI(4)was treated with N-hydroxysuccinimide in the presence of DCC (dicyclohexylcarbodiimide) in THF solution (see Scheme 11, the succinimidyl ester derivative [(q5-C5H4COONS)Fe(CO)zMe1 (6) was isolated in 62% yield. Similarly, the analogous molybdenum derivative [(q5-C5H4COONS)Mo(C0)3Mel (5)was obtained but in a low yield. We have found that 5 can be prepared in 57% yield by treatment of [(q5-C5H4COOH)Mo(C0)3Mel(2) with DSC (disuccinimidyl carbonate) in CH3CN in the presence of pyridine. In general the iron compounds 4 and 6 exhibit higher stabilities in solution than the molybdenum derivatives 2 and 5. The structures of these activated ester complexes were proposed on the basis of spectroscopic data as well as X-ray analysis carried out on [(q5-C5H4COONS)Mo(C0)3Mel(5)(vide infra). The 'H-NMR spectra of complexes 5 and 6 show a pair of triplets characteristic of these functionalized rc-complexed Cp rings which appear in the area 5-6.2 ppm and a singlet attributed to the N-succinimidyl fragment around 2.8-2.9 ppm; finally, the methyl group attached to the metal center appears as a singlet upfield in the range 0.4-0.6 ppm. The organic carbonyls of 5 and 6 show three strong stretching vibrations in the area of 1730-1812 cm-'. X-ray Molecular Structure of (;t15-C5H4COONS)Mo(C0)sMe (5). Suitable crystals for X-ray analysis were obtained from cooling a solution of 5 in an ether/ hexane mixture. The unit cell contains two independent molecules (a) and (b) (see Figure 1). A view of molecule a is shown in Figure 2; the unit cell was found to be triclinic Pi, and crystallographic data collection parameters and selected bond lengths and angles are listed in Tables 1-3. The complex exhibits four-legged piano stool geometry (vide infra);the carbonyls and the methyl group serve as legs. The structure shows also that the plane containing the succinimidyl moiety is almost orthogonal to that of the Cp ring with 8 = 82" (a) and 85" (b). The Mo-Cpcentroidbond distance is 2.02 (a) and 2.01A (b)and compares well to that of (q5-C5H4COMe)Mo(C0)aMewith an MO-CPcentroid bond distance of 2-01 A reported by Rausch et a1.8 The activated ester complexes 5 and 6 react with excess ISiMe3 in THF for 16 h at T = 60 "C to give

Chem. 1988,355,455. ( 5 ) Macomber, D. W.; Rausch, M. D. J.Organomet. Chem. 1983,258, 331. (6)Orlova, T.Yu.;Setkina, V. N.; Kursanov, D. N. J. Organomet. Chem. 1984,267,309.

( 7 ) El Mouatassim, B.; Elamouri, H.; Salmain, M.: Jaouen, G. J. Organomet. Chem. 1994,479, Cl8. (8) Rodgers, R. D.; Atwood, J. L.; Rausch, M. D.; Macomber, D. W. J . Cryst. Spectrosc. Res. 1990,20, 555.

M = Mo.L = CO.n = 2. ( 2 )

M

= Fe. L = CO.n = I . ( 4 )

M = Mo. L = co. II = 2: (5) M = Fe. L = CO.n = I:(6)

Reagents and conditions: (i) (a)THF, s-BuLi (1.7 equiv), -78 "C, 15 min, (b)THF, dry ice (excess), -30 "C, 10 min, (c) HC1 (lo%),THF, room temperature; (ii)CH&N, DSC (1equiv), pyridine (1equiv), room temperature.

(C0)3Mel(5)and [(q5-C5H4COONS)Fe(CO)zMe[(6)from their organometallic carboxylic acids [(q5-C5H4COOH)Mo(C0)sMeI (2) and [(q5-C5H4COOH)Fe(CO)zMe1(4). The molecular structure of 5 has been ascertained by X-ray analysis; furthermore the reactivity of these new succinimidyl ester complexes with ISiMe3 and with various amino esters are reported. On the other hand we have also prepared the metal-activated ester complex [(q5-C5H5)Mo(C0)3(q1-CH~COONS)1 (7), where the ester unit is bonded directly to the metal center rather than to the n-bonded cyclopentadienyl. The molecular structure of 7 was identified by X-ray analysis. Finally, the structure and the reactivity of the latter complex are compared t o those of [(q5-C5H4COONS)Mo(C0)3Me1 (5) and [(q5-C5H4COONS(Fe(CO)zMe1 (6).

Results and Discussion Synthesis and NMR Characterization. The cornerstone for the preparation of these functionalized q5cyclopentadienyl metallocarbonyl complexes 5 and 6 is the synthesis of the parent organometallic carboxylic acids [(q5-C5H4COOH)Mo(CO)3Mel(2) and [(q5-C5H4COOH)Fe(C0)2Mel (4). The latter reacts either with NHS (N-hydroxysuccinimide) in the presence of DCC (dicyclohexylcarbodiimide)or with DSC (disuccinimidyl carbonate) in the presence of pyridine to give the target compounds (Scheme 1). Rausch et al. have prepared the organometallic carboxylic acid complexes (q5-C5H4COOH)ML,(M = Co, W) by saponification of the corresponding ester derivatives with aqueous potassium hydroxide in methanol, followed by acidification with hydrochloric acid;4however, the previous experimental conditions have been shown to be unsuccessful for preparing the compound [(q5C5H&OOH)Mo(C0)3Mel(2);the authors attributed this behavior to the instability of 2 in basic m e d i ~ m .We ~ also note that complexes of the type [(q5-C5H4COOH)Fe(C0)zRI (R= -Ph; -CpMn(CO)s) have been reported but using a different synthetic procedure.6 In our case, the organometallic acid complexes [(q5C~H~COOH)MO(CO)~M~I (2) and [(q5-C5H&OOH)Fe(C0)zMeI (4) were prepared in good yields, 62% and 63%, respectively, by treatment of [(q5-C5H5)Mo(C0)3Me] (1)and [(q5-C5H5)Fe(CO)zMel(3) with s-BuLi fol(4)(a)Hart, W. P.; Macomber, D. W.; Rausch, M. D. J . Am. Chem.

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Organometallics, Vol. 14, No. 7, 1995

Table 1. Crystallographic Data for

[(q5-C5H4COONS)Mo(CO)~Mel (5)

chemical formula fw cryst syst space group

z

a,A

b, A

C,

A

a,deg P, deg I , deg

v, A3

F(OO0) g(calcd1, g ~ m - ~ u(Mo Ka)cm-l diffractometer monochromator radiation (A, i, temp, "C scan type scan range 0, deg 20 range, deg no. of refctn collcd no. of reflctn used (criteria) R RWa

Figure 1. Unit cell of 5 showing two independent molecules (a) and (b).

abs corr secondary ext weighting scheme rms (shiftiesd)(last ref) Is params

C14H1107NMo 401.18 t ric1inic

pi 4 8.684(4) 12.764(8) 16.522( 10) 65.13(4) 72.52(4) 7 1.34(41 1544.6 800 1.72 8.61

Philips PWllOO graphite Mo Ka (0.710 70) 20 W i m

+

1.1 0.34 tan 0 4-50 5395 4323(Z > 3dZ)) 0.0253 0.0269 min 0.85, max 1.15 51 x

unit weights 0.34 484

a R, = [x,W,(F, - Fc)2/z,WlFa211'2. Difabs. Walker, N.; Stuart, D. Acta Crystallogr. 1983,A39, 159.

01121

Figure 2. Molecular structure and atom labeling for [(q5C5H4COONS)Mo(CO)~Mel (5). respectively the iodo derivatives [(v5-CsH4COONS)Mo(C0)311(9)and [(v5-C5H4COONS)Fe(CO)zIl(10) as deep red microcrystals. The infrared data were the most informative, which show a higher wavenumber shift for the metal-carbonyl bands of 30-40 cm-l; this is due to the presence of the electron-withdrawing iodo atom which is bonded t o the metal center instead of the methyl group. The IH-NMR spectra of these complexes show the usual pair of triplets but appearing slightly downfield relative to the parent molecules 5 and 6 in the area 5.2-6.6 ppm as well as the singlet attributed to the succinimidyl moiety; we also note the disappearance of the singlet signals in the 0.4-0.6 ppm range characteristic of the metal-bonded methyl groups. On the other hand we have prepared another type of metal-activated ester, in which the ester unit bonded directly t o the metal center and not to the cyclopentadienyl fragment. The main objective of this work is to

compare the reactivity and the stability of both systems toward amino acids labeling. Thus [(v5-C5H5)Mo(C0)3(q1CHzCOONSIl(7) was obtained as the major product in 45% yield by a one-pot reaction from the cleavage of the dimer [CpzMoz(CO)61with N a g followed by addition of 2 equiv of ClCHzCOONS in THF (Scheme 2). We have also isolated a minor compound as an orange material; attempts to identify this unstable species have been so far unsuccessful, since its transforms to the starting material [Cp~Moz(CO)6l.Similar results were obtained by Bailey, Winter and co-workers, when [CpMo(C0)3l[Nal prepared in situ, was treated with 2 equiv of BrCHzCHzCHzBrin THF. The authors obtained the expected alkyl derivative C~MO(CO)~CHZCHZCH~B~, as well as an unstable orange compound, which transforms t o give the starting material [CpzMo~(C0)61.~ It is worth mentioning that preparation of tungsten complexes by and molybdenum 2-oxaallyl(y1-(C)-enolate) the above procedure has been well investigated by King, Green, and co-workers.1° Recently, a detailed and improved synthesis of such complexes as well as their reactivity have been reported by Bergman, Heathcock, and co-workers;" in general the authors observed the formation of only one product in 50-80% yield, but we are not aware of any previous example in the literature in which the enolate ester complex possesses an Nsuccinimidyl fragment. (9)Adams, H.;Bailey, N. A.; Winter, M. J. J . Chem. Soc., Dalton Trans. 1984.273. (10)ia) King, R. B.; Bisnette, M. B.; Fronzaylia, A. J . Organomet. Chem. 1966,5,341. ( b ) Ariyarante, J. K. P.; Bierrum, A. M.; Green, M. L. H.; Ishaq, M.; Prout, C. K.; Swainwick, M. G . J . Chem. SOC.A 1969, 1309. ic) Hillis, J.; Ishaq, M.; Gorewit, B.; Tsutsui, M. J . Organomet. Chem. 1976,116,91. ( 11 1 ( a )Doney, J. J.; Bergman, R. G.; Heathcock, C. H. J . Am. Chem. SOC.1985,107, 3724. tb) Burkhardt, E. R.; Doney, J. J.; Bergman, R. G.; Heathcock, C. H. J . Am. Chem. SOC.1987,109, 2022.

Succinimidyl Ester Complexes

Organometallics, Vol. 14, No. 7, 1995 3299

Table 2. Collection Parameters for

[(q6-C~H&OONS)Mo(C0)3Mel (5) atom

xla

0.19459(3 0.0020(3) -0.1707(3 1 -0.2908(4) 0.1502(4) 0.5257(4) 0.2248(5) 0.1505(4) -0.0538(4) -0.0737(4) -0.2037(5) -0.2275(5) -0.0872(5) 0.0237(5) -0.0199(4) -0.0824(4) -0.0034(4) 0.1063(5) 0.0970(4) 0.4048(5) 0.2142(5) 0.1634( 5) 0.4001(6)

(362) C(63) C(64)

-0.33644(3) 0.0639(3) 0.1808(3) 0.1507(5) 0.3266(5) -0.4290(4) -0.2285(4) -0.7217(3) 0.2105(4) 0.0682(4) 0.2405(5) 0.4029(6) 0.4643(5j 0.3330(5) -0.0821(4) -0.2026(4) -0.3 167(5) -0.2706(51 -0.1245(4) -0.3946(5 j -0.2691(4) -0.5804(4) -0.3961(5)

Yfb

Molecule a 0.23280(2) 0.2072(2) 0.3597(2) 0.2029(3) 0.3745(3) 0.1399(3j 0.4683(3) 0.3998(3) 0.2708(3) 0.2665(3) 0.2649(3) 0.3503(4) 0.4148(3) 0.3565(3) 0.1959(3) 0.2273(3) 0.1382(3) 0.0504(3) 0.0849(31 0.1753(4) 0.3837(4) 0.3397(3) 0.1892(4) Molecule b 0.90997(3) 0.6570(2) 0.8115(2) 0.7042(4 1 0.4999(3) 1.1876(2) 0.9476(3) 0.9590(3) 0.6067(3) 0.7655(3) 0.6318(4) 0.5512(4) 0.4861(4) 0.5270(3) 0.8062(31 0.7404(3) 0.8114(4) 0.9212(3) 0.9170(3) 1.0869(3) 0.9363(3) 0.9413(3) 0.7603(4)

zfc

U(eq),.&z

0.52333(2) 0.7825(2) 0.6950(2j 0.9092(2) 0.7799(2j 0.4087(3) 0.5264(2) 0.3248(2) 0.8404(2) 0.7063(2) 0.8999(2) 0.9454(3) 0.8967(3) 0.8311(3) 0.6482(2) 0.5693(2) 0.5321(2) 0.5884(3 0.6599(2) 0.4506(3) 0.5227(3) 0.3974(3) 0.6016(3)

0.0315 0.0446 0.0505 0.0579 0.0676 0.0774 0.0763 0.0638 0.0438 0.0375 0.0420 0.0535 0.0502 0.0453 0.0356 0.0396 0.0407 0.0413 0.0380 0.0512 0.0506 0.0441 0.0660

0.84385(2) 0.8316(2) 0.7896(2) 0.6439(3) 0.9114(2) 0.7602(2) 0.6373(2) 0.8726(2) 0.7855(2) 0.8309(2) 0.6929(3) 0.6738(3) 0.7626(3) 0.8318(3) 0.8897(2) 0.9521(2) 0.9991(21 0.9666(2) 0.8999(2) 0.7900(3) 0.7127(2) 0.8610(2) 0.8218(3)

0.0309 0.0484 0.0462 0.0902 0.0703 0.0618 0.0624 0.0603 0.0422 0.0354 0.0554 0.0577 0.0573 0.0429 0.0337 0.0395 0.0445 0.0418 0.0377 0.0429 0.0411 0.0414 0.0540

The metal-activated ester complex [(q5-C5H5)Mo(C0)3(q1-CH2COONS)1(7) was obtained as light yellow crystals and was identified spectroscopically; in addition, the X-ray molecular structure was determined. X-rayMolecular Structure of (q5-C5Hs)Mo(CO)s(qWH2COONS) (7). Recrystallization of 7 from ether/ hexane gave a sample suitable for an X-ray crystallographic diffraction study. Figure 3 shows a view of [(q5-C5H5)Mo(C0)3(q1-CH2C00NS)1 (71, and crystallographic data collection parameters and selected bond lengths and angles are listed in Tables 4-6. Complex [(r5-C5H~)Mo(C0)3(r1-CH2COONS)I (7) displays a piano stool structure well-known for halfsandwich complexes with Cp as the seat and the four legs occupied by the carbonyl ligands and the ql-(C)enolate unit. The carbonyl oxygen is not coordinated to the metal center, similar to that observed for the methyl ester enolate derivative (q5-C5H5)W(C0)3(q1CH2COOMe)or the more recently reported structure of (q5-C5H5)W(C0)3(r1-CH2COOEt). The term "enolate" as applied to compounds such as 7 and the interaction between carbon-metal bonding electrons and the car-

Table 3. Selected Intramolecular Distances (A) and Angles (deg) for [(~s-C~H&OONS)Mo(CO)~el (5a,b) Mol-C6 Mol-CS Mol-C7 Mol-C9 Mol-CP" Mol-Cl2 Mol-C14

Distances 2.320(3) M051-C61 m05 1-C62 2.338(3) 2.310(3) M051-C63 2.389(3) m05 1-C64 2.02 1.98314) c1-01 2.305(4) c1-02

M051-C56 M051-C57 M051-C58 M051-c59 Mo51-C60 Mo51-CF C6-C7 C7-C8 C8-C9 C9-ClO C6-C10 C56-C57 C57-C58 C58-C59 C59-C60 C56-C60

2.345(3) 2.370(3) 2.367(4) 2.335(3) 2.335(3) 2.01 1.413(5) 1.406(5) 1.416(5) 1.398(5) 1.43015) 1.431(5) 1.401(5) 1.417(5) 1.412(5) 1.412(5)

C7-Mol -C6 C8-Mol-C7 C9-Mol-C7 ClO-Mol-CG CIO-Mol-C8 C11-Mol -C10 C12-Mol-C7 C12-Mol-C9 C14-Mol-C7 C12-Mol-Cl1 C13-Mol-C7 C13-Mol-C9 C13-Mol -C 11 C14-Mol-Cll C14-Mol-Cl2 C14-Mol-Cl3 C13-Mol-Cl2 a

2.000(4) 1.976(4) 1.980(4) 2.321(4)

01-N1

1.403(4) 1.194(4) 1.390(4)

C56-C51 C51-051 (31-052 051-N51

1.466(5) 1.392(4) 1.182(4) 1.385(4)

Angles 35.5(1) C6-C1-02 35.2(1) (31-01-02 58.2(1) C1-01-N1 35.4(1) C56-M051-C64 57.8(1) C59-M051-C60 114.9(1j C12-Mo-C 13 107.5(2) C57-M051-C59 154.8(1) C57-M051-C63 C60-M051-C62 105.5(2) C58-M051-C62 91.6(1) C60-M051-C64

127.2(3) 122.6(3) 110.7(3) 98.3(1) 35.2(1) 78.1(1) 58.2(1) 118.0(1) 111.3(1) 155.3(1) 133.2(1)

118.8(1)

78.6(2) 73.2(2) 72.2(2) 132.4(2) 79.6(2)

CP is the centroid of the cyclopentadienyl ring plane.

Scheme 2"

(7)

Reagents and conditions: (iii) THF, N a g , 2h, room temperature; (iv)THF, ClCH2COONS (1equiv), -78 "C, 5 min, then 1 h a t room temperature.

bony1 x-orbital have been invoked previously by Bergman, Heathcock, and co-workers on the basis of spectroscopic and crystallographic data.11b In this regard, we feel, in our case, that such an interaction is also valid; for instance, the carbonyl absorptions for complex 7 are shifted toward lower energy when compared to those of the isomer 5 where the ester unit is attached to the x-Cp ligand. Confirmation of this interaction is displayed by the structure of 7 in the solid state where the (C-0)-C bond (1.46 A) is shorter than the normal ester value of 1.48-1.51 A, although the -C=O bond

El Mouatassim et al.

3300 Organometallics, Vol. 14, No. 7, 1995

Table 5. Collection Parameters for

[(~6-C~)M~(CO)s(t'-CH~COONS)1 (7) atom

a2

Ci121

Figure 3. Molecular structure and atom labeling for [(r5-

C~H~)MO(CO)~(~~-CH~COONS)I (7). Table 4. Crystallographic Data for [(45-CsHs)M~(CO)s(~'-CHzCOONS)1 (7) chemical formula fw cryst syst space group

C14H1107mO 401.18 monoclinic

a,A b, A

19.484(2) 11.393(2) 13.694(2) 98.91(2) 3000 1600 1.79 8.92 Philips PWllOO graphite Mo Ka (0.710 70) 20 w120 1.0 0.34 tan 0 4-57 3801 2946 (I > 3dI)) 0.027 0.029 min 0.88, max 1.11 99.9 x 10-6 unit weights 0.10 243

z

C,

A

A deg

v, A3

F(000) p(calcd), g - ~ m - ~ p(Mo Ka)cm-l diffractometer monochromator radiation (A,A) temp, "C scan type scan range 0, deg 20 range, deg no. of reflctn collected no. of reflctn used (criteria) R RW"

abs c o d secondary ext weighting scheme rms (shift/esd)(last re0 Is params

CWC 8

+

a R, = [X.,W.,(F, - Fc)2/ztWtFo2]1'2.Difabs. Walker, N.; Stuart, D. Acta Crystallogr. 1983,A39, 159.

distance is 1.194 A, typical of a carbonyl function. We also note that the plane of the N-succinimidyl unit forms an angle 8 = 54" with that of the n-bonded cyclopentadienyl ligand; this value is smaller than that observed in 5 (vide supra). "he MO-Cpcentroid bond distance is 1.99 A, slightly shorter than that of its isomer 5 and comparable to that reported for the tun sten enolate ($CsH5)W(C0)3(v1-CH&OOEt) (1.998 1; further, the (C-01-02 bond distance is 1.42 A, longer than that in 5 (C=O)-Ol (a) 1.40 A and -(b) 1.39 A. Although there were no differences in the bond lengths of the N-succinimidyl unit between 5 and 7 in the solid state, their behaviors in solution, in particular their reactivity toward amino esters, showed stark contrast. Reactivity of 5-7 with Benzylamine and Various Amino Esters. We have studied the reactivity of the above organometallic species with p-alanine ethyl ester, amphetamine, and benzylamine. The labeling of amino esters by our organometallic N-succinimidyl esters is described by Scheme 3. Complex [(~5-CsH&OONS)Mo(CO)3Mel (5) reacted with p-alanine ethyl ester in THF to give the conjugate

I

rla

vlb

0.16001(1) 0.3549(1) 0.3131(1) 0.3231(1) 0.4433(1) 0.2761(1) 0.0783(2) 0.0974(1) 0.3705(1) 0.2483( 1) 0.3101(1) 0.3700(2) 0.4393(2) 0.4785(2) 0.4322(2 0.2353(2) 0.1082(2) 0.1218(2) 0.1858(2) 0.1652(2) 0.0954(2) 0.0733(2) 0.1297(2) 0.261(2) 0.231(2) 0.224(2) 0.192(2) 0.075(2) 0.027(2) 0.134(2) 0.569(2) 0.040(2) 0.486(2) 0.526(2)

0.04854(2) 0.0131(2) -0.1138(2) 0.0786(2) -0.2209(2) 0.1745(2) 0.1908(3) -0.1516(2) -0.0841(2) -0.0928(3) -0.0550(3) 0.0105(3) 0.0072(4) -0.0961(3) -0.1452(3) 0.1269(3) 0.1396(3) -0.0789(3) 0.1230(3) 0.0067(3) -0.0048(4) 0.1056(4) 0.1854(3) -0.102(3) -0.169(3) 0.148(3) -0.060(3) -0.073(3) 0.122(3) 0.267(4) 0.004(3) 0.411(3) -0.159(3) -0.073(3)

ZIC

0.08387(2) 0.0977(2) -0.0239(2) -0.1494(2) 0.0157(2) 0.2319(2) 0.2248(2) 0.2004(2) -0.0663(2) 0.1065(2) 0.0670(2) -0.1302(2) -0.1660(3) -0.1135(3) -0.0452(2) 0.1783(2) 0.1730(3) 0.1599(2) -0.0647(3) -0.0838(2) -0.0698(2) -0.0418(3) -0.0394(3) 0.173(3) 0.078(3) -0.069(3) -0.104(3) -0.076(3) -0.028(3) -0.025(3) 0.228(3) 0.150(3) -0.157(3) -0.076(3)

U(eq),

U(iso),

A2

A2

0.0302 0.0442 0.0381 0.0544 0.0563 0.0554 0.0716 0.0548 0.0363 0.0315 0.0316 0.0403 0.0463 0.0429 0.0382 0.0395 0.0496 0.0377 0.0438 0.0420 0.0455 0.0451 0.0473 0.057(3) 0.057(3) 0.057(3) 0.057(3) 0.057(3) 0.057(3) 0.057(3) 0.057(3) 0.057(3) 0.057(3) 0.057(3)

Table 6. Selected Intramolecular Distances (A) and Angles (deg) for

[(p5-C5H5)Mo(CO)s(~'-CH~COONS)1 (7) Distances 2.330(3) C6-04 1.197(4) 2.363(3) N1-C3 1.387(4) 2.358(3) C3-03 1.198(4) 2.310(3) c3-c4 1.507(4) 2.307(3) c4-c5 1.521(5) C5-C6 1.505(4) Mo-C1 2.341(3) C1-C2 1.461(4) Mo-C11 2.008(3) c2-01 1.194(3) Mo-Cl2 1.992(4) c2-02 1.422(3) Mo-Cl3 1.997(3) 02-N1 1.380(3) Mo-CP' 1.99 Nl-C6 1.381(4) Angles C1-Mo-C 11 76.8(1) Mo-Cl-C2 112.3(2) C1-Mo-C 12 135.1(1) Cl-C2-01 131.3(3) C1-Mo-C 13 75.9(1) C2-02-N1 113.4(2) Cll-Mo-Cl2 76.3(1) Nl-C6-04 124.6(3) Cll-Mo-Cl3 106.4(1) Nl-C3-03 124.9(3) C12-Mo-Cl3 78.1(1) a CP is the centroid of the cyclopentadienyl ring plane. Mo-Cl4 Mo-C15 Mo-Cl6 Mo-C17 Mo-C18

Scheme 3

0

j ,

[ M] =

Me(CO),Mo, Me(CO),Fe

Ho-N 0

adduct [(~5-C~H4CONH(CH2)~COOEt)Mo(C0)~Mel (11) as yellow microcrystalline solids in 36% yield. We have found that the Fe derivative 6 is more stable than its

Succinimidyl Ester Complexes

Mo analog 5 and particularly in basic medium (vide supra); thus 6 reacted with benzylamine and amphetamine to give the amide counterpart complexes [(a5C~&CONHCHZP~)F~(CO)ZM~I (12)and [(q5-C5&CONHC(H)(Me)CHzPh)Fe(CO)zMeI(13)in 25% and 32% yields respectively, while [(q5-C~I&COONS)Mo(C0)3Me] (5) failed to give any stable product, instead decomposing during the reaction course. On the other hand the N-succinimidyl enolate derivative [(q5-C5H5)Mo(C0)3(q1-CH2COONS)l (7) was inactive toward amino acid labeling. Thus treatment of 7 with &alanine ethyl ester in THF for 2 days failed to give any defined product; only decomposition of the starting material was noticed. It should be mentioned that the analogous Fe-activated succinimidyl ester [(q5-C5H5)Fe(C0)2(q1-COONS)1(8) requires 1 week to react with amino acids. This difference in reactivity between the two families, for instance qWp-bonded activated ester complexes and metal-bonded ester complexes, could be related to the enolate character of the latter complexes. As pointed out in this work and previously in the literature for the enolate species, there is an association of the metal (M-C) with the oxaallyl unit whereby the carbon-metal bonding electrons interact with the carbonyl n-orbital; we feel that this interaction influences their reactivity. In this respect we also note that the pk, values of the parent acid molecules of the type (q5C5H5)M(CO)n(CH2COOH) (M = Mo, n = 3; M = Fe, n = 2) are in the range 8.2-8.71°b and are weaker acids than those of (q5-C5H&OOH)M(CO),Me(M = Mo, n = 3 (2); M = Fe, n = 2 (5))with pk, values of 4 - 4 ~ 5 ,and ~ hence are less reactive. In general the previous trend remains valid also for the corresponding N-succinimidyl esters; therefore the activated ester complexes, for instance (q5C5H&OONS)M(CO),Me (M = Mo, n = 3 (3);M = Fe, n = 2 (6)) should be more reactive toward the additionelimination reaction that took place during the labeling process of amino acids. We are currently pursuing our research toward the labeling of proteins by the above complexes and also to enhance the stability of 5 by changing the ancillary ligands around the metal center.

Organometallics, Vol. 14, No. 7, 1995 3301

dropwise to a solution of CpMo(C0)sMe(1)( 2 mmol, 500 mg) in 50 mL of THF a t -80 "C. The mixture was left under stirring for 30 min, then an excess of dry ice (COZ)was added, and the resulting mixture was stirred for further 15 min, while the temperature was kept at -80 "C. The reaction mixture was allowed to reach room temperature, followed by acidification with 8 mL of 10% HC1 solution. The organometallic carboxylic acid2 was extracted with 15 mL of CHzC12 and then dried over MgS04, filtered, and evaporated to dryness under vacuum; the yellow powder was washed with pentane to remove starting material 1. Further purification was attained when the product was dissolved in acetone and the solution filtered through Celite. The solvent was removed under vacuum, and recrystallization from CHCldpentane gave a yellow microcrystalline solid. Yield: 550 mg, 61%. IR, vlcm-l (KBr): M-CO 2025,1950,1917;C-0 1680. 'H-NMR ((CD3)z= 2.5 Hz, 2H, -CsH4), 5.68 (t, JH-H = 2.5 CO): d 5.90 (t, JH-H Hz, 2H, -C5H4), 0.44 (s,3H,-CHsJ. 13C-NMR((CD3)zCO): 6 239,227 (M-CO), 165.40 (C=O), 99.33,96.15, 95.99 (-C5H4), -19.60 (-CHs). Anal. Calcd for CloHsOsMo: C, 39.47; H, 2.63. Found: C, 38.81; H, 2.61. Synthesis of [(q5-C~&COOH)Fe(CO)&el (4). A THF solution ofs-BuLi (1.69mmol, 1 mL) was added dropwise to a solution of CpFe(C0)zMe(3)(600 mg, 1.69 mmol) in 50 mL of THF at T = -80 "C. The reaction mixture was stirred for 20 min, then an excess of solid CO2 was added, and the resulting mixture was stirred for a further 15 minutes. The system was allowed to reach room temperature, and the mixture was acidified by 10 mL of 10% HC1 and then extracted with 10 mL of CH2C12. The organic phase was hydrolyzed with 20% Na2C03 and acidified with 15 mL of 5% HC1; then the organic phase was again extracted with 10 mL of CH2C12. The solvent was removed under vacuum, and the product was recrystallized from acetonelpentane. Yield: 62%, 380 mg. IR, vlcm-l (KBr): M-CO 2012,1951: C=0,1676. 'H-NMR ((CD&CO): d 5.43 (t, JH-H= 2.5 Hz, 2H, -CjH4), 5.13 (br, 2H, -C5H4), 0.25 (s, 3H,CH3). 13C-NMR ((CD3)2CO):d 216.75 (M-CO), 166.22 (C-O), 91.50, 87.96, 85.96 (-C5H4), -21.41 (-CH3). Anal. Calcd for CgHa04Fe: C, 45.69; H, 3.39. Found: C, 45.69; H, 3.47. Synthesis of [(q5-C~H.&OONS)Mo(CO)sMel(5). A solution of DSC (0.33 mmol, 84 mg) and pyridine (0.33 mmol, 26 pLj in 2 mL of CH3CN was added dropwise to a solution of 2 (100 mg, 0.33 mmol) in 10 mL of CHsCN, and the reaction was stirred for 18 h; then the solvent was removed under vacuum, and the product was eluted on silica gel using CHC13 as eluent. The solvent was removed under vacuum to give a yellow microcrystalline solid. Yield: 74 mg, 57%. IR, vlcm-' Experimental Section (KBr): M-CO 2028, 1936, C-0 1802, 1769, 1736. 'H-NMR ((CD3)zCO): d 6.10 (t, JH-H= 2.5 Hz, 2H, -C5H4), 5.83 (t,JH-H General Procedures. All manipulations were carried out = 2.5 Hz, 2H, -C5H4), 2.92 (s,4H, -CHz-CHz-, -NSj, 0.55 under argon atmosphere using Shlenck techniques. Solvents (s,3H, CH3). 13C-NMR((CDs)2CO):d 235.71, 223.15 (M-CO), were purified and dired prior to use by conventional distillation 166.76, 160.38 (C=O), 95.94, 94.60, 90.47 (-C5H4), 25.50 techniques. All reagents obtained from commercial sources (-CHz-CHz-, -NS), -19.36 (-CH3). Anal. Calcd for C14Hllwere used without further purification, and [Nal[CpM0(C0)31~~ 0,NMo: C, 41.89; H, 2.74; N, 3.49. Found: C, 41.98; H, 2.58; and [Na1[CpFe(C0)21l3were prepared according to published N, 3.59. procedures. 'H- and 13C-NMRwere recorded on a Bruker AM Synthesis of [(q5-C~H&OONS)Fe(CO)&el (6). N-Hy250 MHz instrument. 'H-NMR chemical shifts are reported droxysuccinimide (NHS) (49 mg, 0.42 mmol) was added to a in parts per million referenced to the residual solvent proton yellow solution of 4 (100 mg, 0.42 mmol) in 10 mL of THF, in resonance. Infrared spectra were obtained on a FT Bomem the presence of dicyclohexylcarbodiimide(DCC) (88 mg, 0.42 Michelson 100 spectrometer from samples prepared either on mmolj, and the mixture was stirred for 10 h. The solution KBr disks or in CHzC12 solutions. All absorptions are exwas filtered through Celite, and the residue was chromatopressed in wavenumbers (cm-l). Elemental analyses were graphed on silica gel and eluted with acetone, hexane (10:3) performed by the Microanalytical Laboratory of the CNRS of to give a yellow band which afforded yellow-orange crystals the University of Paris VI. of6. Yield: 86 mg, 61%. IR, vlcm-' (KBr): M-CO 2024,1970, Synthesis on [(q5-C&COOH)Mo(CO)&le] (2). A soluC-0 1811, 1780, 1738. 'H-NMR (CDCln): d 5.50 (t, JH-H = tion of s-BuLi (3.45 mmol, 1.8 mL) in hexane was added 2.0 Hz, 2H, -C5H4), 5.03 (t,JH-H = 2.0 Hz, 2H, -C5H4), 2.89 (s, 4H, -CHs-CHz-, -NS), 0.46 (s, 3H, CHs). 13C-NMR 112) ( a ) Ellis, J. E. J. Orgunomet. Chem. 1976,86, 1. cbJ Patil, H. ((CDaJ2CO):d 213.76 (M-CO), 168.58, 160.70, 91.44, 85.10, R. H.; Graham, W. A. G . Inorg. Chem. 1966,5,1401. rc) Hayter, R. G. 78.15 (-C5H4), 25.29 (-CHn-CHs-, -NS), -20.70 (-CHs). Znorg. Chem. 1963, 2, 1031. Anal. Calcd for C13H110aFe: C, 46.87; H, 3.30; N, 4.21. 113) Zhen,Y.Q.;Feighery, W. G.; Lai, C. K.; Atwood, J.D.J . Am. Found: C, 47.22; H, 3.42; N, 4.12. Chem. SOC.1989,111, 7832.

3302

Organometallics, Vol. 14, No. 7, 1995

El Mouatassim et al.

Synthesis of [(tlj-CsH4CONHCHzPh)Fe(CO)zMe] (12). Synthesis of [(~3-C~Hs)Mo(CO)~(~1'-CH~COONS)1 (7). A A solution of benzylamine ( 16 +L, 0.15 mmol) in 2 mL of THF solution of [CpMo(CO)& (500 mg, 1.02 mmol) in 30 mL of THF was cleaved by 10% NaHg amalgam, and after 1 h the yellow was added dropwise to a solution of 6 (50 mg, 0.15 mmol) in 4 mL of THF, and the mixture was stirred for 10 h. Then solvent solution of [Na][CpMo(CO)3]was filtered into a Schlenk tube was removed, and the residue was chromatographed on a silica kept under argon. To this mixture was added dropwise a solution of ClCHZCOONS (2 mmol, 383 mg) in 12 mL of THF gel column and eluted with toluene/acetone i1 O : l ) to give a yellow band which afforded yellow crystals of 12. Yield: 12 while the temperature was kept a t -78 "C. The mixture was stirred for 1h a t -78 "C, and then the mixture was filtered to mg, 25%. IR, v/cm-l (KBri: NH 3289, M-CO 2001, 19461, CON 1636, 1555. 'H-NMR ((CDdzCO): b 7.32-7.45 (m, 5H, remove the precipitate salt, followed by evaporation to dryness using the vacuum line. The residue was then eluted on silica = 2.0 Hz, 2H, -C5H4), 5.06 it, JH-H phenyl Hs), 5.53 (t, JH-H gel using etherhexane (5/1), the yellow band was collected, = 2.0 Hz, 2H, -CjH4), 4.52 (d, JH-H = 6.0 Hz, 2H, -N-CHZj, and the solvent mixture was concentrated under vacuum. 0.24 (s, 3H, Fe-CHd. Upon cooling overnight a t -20 "C, yellow crystals were Synthesis of [(r15-CsH4CONHC(H)(Me)CH2Ph)Fe(CO)2obtained. Yield: 200 mg, 45%. IR, dcm-' (KBr): M-CO 2031, Me] (13). This compound was prepared in a fashion similar 1965,1954,1927, C-0 1791,1731. 'H-NMR ((CDC13): b 5.54 to that of 12 using an equimolar concentration of 6 and (s, 5H, -C5H5), 2.82 (s,4H, -CH*-CHz-, -NS), 1.92 (s,2H, amphetamine. The product was separated on silica gel plates using etherhexane ( 1 0 5 ) as eluent, which afforded a yellow -CHz-). 13C-NMR ((CD3)zCO): b 228.24 (M-CO), 177.16, microcrystalline solid of 13. Yield: 32%. IR, vicm-' (CHC13): 171.39 (C=O), 95.36 (-CsH*), 26.23 (-CHz-CH2-, -NS), -9.51 (-CHz-). Anal. Calcd for C14H110,NMo: C, 41.89; H, M-CO 2016,1960, CON 1658,1519. 'H-NMR ((CD3)zCO): b 7.26-7.20 (m, 5H, phenyl Hs), 5.60 (t, 2H, -C5H4), 5.10 (t, 2.74; N, 3.49. Found: C, 41.71; H, 2.82; N, 3.47. 2H, -C5H4), 4.29 im, l H , -CH,,j, 2.94 (m, l H , -CHAHB),2.53 Synthesis of [(q5-C&COONS)Mo(CO)J1(9). The preparation of 9 was performed, following the synthetic procedure im, l H , -CHAHB), 1.20 id, 3H, -Me), 0.18 (s, 3H, Fe-CH3). Structure Determination of [(rf-CfiCOONS)Mo(CO)sdescribed by Rausch et al. for the compound [(t15-C5H4COOMe)W(C0)31].5 A solution of ISiMe3 (70 pL, 0.5 mmol) Me1 (5) and of [(t15-C5H~)Mo(CO)s(i1-CH2COONS)] (7). Single crystals were grown from cooling a hexane solution of was added to a solution of [(q6-C5H4COONS)MoiCO)3Me](5) (100 mg, 0.25 mmol) in 15 mL of CHsCN, and the reaction [(q5-C5H4COONS)Mo(CO)3Mel (5) and from etherhexane for mixture was stirred at T = 60 "C for 16 h. At this stage the [(~5C~H~)MoiC0)~i~1-CH~COONS)l (7). Crystallographic data for 5 and 7 are collected in Tables 1 and 4, respectively. solvent was removed and the residue was eluted on silica gel using toluene/acetone (10:3) as eluent. Compound 9 was Accurate cell dimensions and orientation matrices were obtained by least-squares refinement of 25 accurately centered obtained as a deep red microcrystalline solid. Yield: 58 mg, reflections on a Nonius CAD4 diffractometer equipped with 45%. IR, v/cm-' (KBr): M-CO 2050,1973, C=O 1803,1769, 1737. 'H-NMR ((CD3)zCO): b 6.42 (t, JH-H = 2.5 Hz, 2H, graphite-monochromated Mo K a radiation. No significant variations were observed in the two check reflections during = 2.5 Hz, 2H, -C5H4), 2.92 is, 4H, -C5H4), 6.19 it, JH-H data collection. The data were corrected for Lorentz and -CHz-CHz-, -NS). 13C-NMR((CD3)2COi: d 237, 230, 223 polarization effects; an empirical absorption correction (DI(M-CO), 174.31, 165.32 (C=O), 105.68, 101.28,96.04 (-C5H4), FA13S)14was applied. Computations were performed by using 30.79 (-CHz-CHz-, -NS). Synthesis of [(t,r5-CfiCOONS)Fe(CO)21](10). This comCRYSTALS'5 modified locally for a Microvax I1 Computer.16 The structures were resolved by direct methods (SHELXS)17 pound was prepared in a fashion similar to that of 9; thus a n excess of ISiMe4 was added dropwise at room temperature to and refined by full-matrix least squares with anisotropic thermal parameters for all non-hydrogen atoms. All hydrogen a solution of 6 (100 mg, 0.3 mmol) in 10 mL of CHsCN. Then the mixture was stirred for 24 h while the temperature was atoms were then located on a difference Fourier map and their kept at 60 "C. At this stage the reaction was stopped and the coordinates refined with a n isotropic thermal parameter. The excess of ISiMe3 was hydrolyzed followed by extraction with structures of [ig5-CjH4COONS)Mo(CO)~Mel (5) and [($CHzClz. The organic phase was concentrated under vacuum, CjH5)Mo(C0)3(q1-CH~COONS)l (7) were refined to R = 0.0253, and the residue was chromatographed on silica gel and eluted R, = 0.0269 and R = 0.027, R, = 0.029, respectively, with with toluene/acetone i10:8) t o give a brown-red microcrystaluse of 4323 and 2946 reflections of 484 and 243 least-squares parameters. line solid. Yield: 77 mg, 58%. IR, dcm-' (KBr): M-CO 2055, 2012, C=O 1798,1769,1736. 'H-NMR iCDC13): b 5.83 (t,JH-H = 2.5 Hz, 2H, -C5H4), 5.29 (t, JH-H = 2.5 Hz, 2H, -CsH4), Acknowledgment. We would like to thank CNRS 2.90 (s,4H, -CHz-CHz-, -NS). 13CNMR ((CD&CO): d 210, (France) for supporting this work. 53 iM-CO), 168.46, 160.38 (C-Oi, 90.17,85.78, 75.22 (-C5H4), 25.70 (-CHz-CHz-, -NS). Supporting Information Available: Anisotropic disSynthesis of [(~5-CfiCONH(CH2)2COOEt)Mo(CO)~elplacement parameters (Tables S1 and S4) and bond distances (11). A solution ofp-alanine ethyl ester (46 mg, 0.3 mmol) in and angles (Tables S2 and S5) for 5 and 7, respectively ( 5 8 mL of THF was added dropwise to a solution of 5 (120 mg, pages). Ordering information is given on any current mast0.3 mmol) in 12 mL of THF, and the reaction mixture was head page. stirred for 12 h. The solution was concentrated under vacuum, OM950170Y and the residue was chromatographed on silica gel plates with toluene/acetone ( 1 O : l ) as eluent. A yellow band was separated, I141 Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 159. which afforded a yellow microcrystalline solid. Yield: 36 mg, 115)Watkin, D. J.; Carruthers, J. R.; Betteridge, P. W. Crystals User 30%)). IR, idem-' (KBr): M-CO 2023,1936, C-0 1726, CON Guide; Chemical Crystallography Laboratory: University of Oxford: Oxford, England, 1986. 1664, 1522. 'H-NMR (CDC13): b 6.64 (m, l H , -NH), 5.67 ( t , 116)International Tables for X-ray Crystallography: Kynoch Press: JH-H = 2.5 Hz, 2H, -CsH4), 5.29 (t,JH-H = 2.5 Hz, 2H, -C5H4), Birmingham, England, 1974: Vol. IV. 4.19 (q, 2H, -N-CHz), 2.59 (t, 2H, -O-CHd, 1.26 (q, 3H, ( 17)Sheldrick, G. M. SHELXS86, Program for Crystal Structure -OCHz-CHs), 0.44 (s,3H, Mo-CHsj. Solution. University of Gottingen, 1986.