J.C.S. Perkin I Organometallic Complexes in Synthesis. Part 9.l Tricarbonyliron Deriva- tives of Dihydroanisic Esters By Arthur J. Birch and Anthony J. Pearson, Research School of Chemistry, Australian National University, P.O. Box 4, Canberra, A.C.T. 2600, Australia Tricarbonyliron complexes of a number of dihydroanisic esters have been prepared and characterised, and their re- actions with triphenylmethyl tetrafluoroborate studied. Only three of the complexes undergo hydride abstraction. The resulting dienyl complexes were found to react cleanly with dimethyl sodiomalonate in the expected manner. PREVIOUSwork from this laboratory described the preparation and some of the chemistry of several tri- carbonyliron complexes of cyclohexadienecarboxylic esters, including a number of methyl-substituted deriva- tives2 We were subsequently interested in the prepar- ation and characterisation of some tricarbonyliron derivatives of dihydroanisic esters, since these are of interest from the point of view of (a)the greater function- ality present in the molecules, and (b) the structures of dienyl complexes derived by reaction with triphenyl- methyl tetrafluoroborate.The latter subject is im-portant since it is these types of dienyl complexes which are most likely to find application in organic synthesis. In the monosubstituted series, hydride abstraction from tricarbonyl- (2-met hoxycarbonylcyclohexa-l,3-diene)iron (1) results in tricarbonyl-(3-methoxycarbonyl-cyclohexadieny1)iron tetrafluoroborate (3) as the major product, the 2-substituted isomer (5) being the minor Part 8, A.J. Birch, P. W. Westerman, and A. J. Pearson, Austral. J. Chern., 1976, 29, 1671. A. J. Birch and D. H. Williamson, J.C.S., Perkin I, 1973, 1892. product.lY2 On the other hand, the methoxy-substituted analogue (2) gives rise to tricarbonyl-(2-methoxy-cyclohexadieny1)iron tetrafluoroborate (6) as major, and R R R (1) R = C0,Me (3) R = C0,Me (5) R = C0,Rle (2) R = OMe (4) R = OMe (6) R = OMe tricarbonyl-(3-methoxycyclohexadienyl)irontetrafluoro-borate (4) as minor products.3~~A major factor in determining which dienyl complex is formed may be a thermodynamic one, and in consequence it is of interest to determine how these substituents interact in the dihydroanisic ester complexes and whether the hydride abstraction results are predictable on the basis of those for the mono-substituted compounds. R.E. Ireland, G. G. Brown, jun., R. H. Stanford, jun., and T. C. McKenzie, J. Org. Chem., 1974, 39, 51. A. J. Birch, P. E. Cross, J. Lewis, D. A. White, and S. B. Wild, J. Chem. SOC.(A),1968, 332. 1978 639 RESULTS AND DISCUSSION proton resonance of (9, exo-C0,Me) is at higher field than Preparation of Co~~Zexes.-2-Methoxycyclohexa-2,5-dienecarboxylic acid (7), prepared according to the literature pr~cedure,~ was treated with dimethyl sulphate to give the corresponding ester (8). Reaction of this COZR R60""' R3 (7) K = H (I))K1= OMe, R2 = R3 = R4 = R5= H, R6 = C0,Me (8) 13 = Me (10)R1 = R2 = R3 = K4= R5 = H, R6 = C0,-Me (11) R1 = OMe, R2 = CO,Me, R3 = R4 = R5 = R6 = H (12) R1 = R4 = R5 == R6 = H, R2 = OMe, R3 = C0,Me (13) R1 = CO,Me, 332 = OMe, R3 = R4 = R5 = R6 = H (14) R1 = OMe, R2 == R4 = R5 = R6 = H, R3 = C0,Me(15) R1 = CO,Me, K2= R4 = R5 = Re = H, R3 = OMe (16) R1 = R3 = R4 = R6= H, R2= OMe, R5 = CN (17) R* = Ohre, R2 = R3 = R5 = Re = H, R4 = C0,Me (18) R1 = OMe, RZ = R3 = R5 = Re = H, R4= Me compound with iron pentacarbonyl in the usual way produced a diene-Fe(CO), complex which gave a single band on chromatography and was isolated as a yellow oil but which nevertheless contained two isomeric com-pounds as shown by the lH n.m.r. spectrum.Repeated recrystallisation from light petroleum at -78 "C and finally at -20 "C produced a pure sample of the major component which had spectral properties consistent with the structure (9). Thus, the OMe resonance at 6 3.42 showed this group to be on the terminal diene carbon atom (2-methoxy substituents resonate at 6 ca. 3.6 and l-methoxy substituents at 6 ca. 3.4 394*6) and the signals at 6 2.90, 5.14, and 5.45 due to the diene protons 4-, 3-, and 2-H unambiguously define this structure. Removal of solvent from the mother liquors gave a product the major component of which was the isomer of (9), which could not be obtained pure. From the lH n.m.r. spectrum of (9) and its isomer it was apparent that the isomer had the same substitution pattern as (9) and differed only in the stereochemistry at C-6.The n.m.r. spectral details are shown in Table 1, and we have assigned to the pure component isolated the structure (9) with an exo-C0,Me group occupying the opposite face of the diene to that occupied by Fe(CO),, the minor component being the endo-C0,Me isomer. This con-clusion is based on the observation that the C0,Me I. Alfaro, W. Ashton, L. D. McManus, R. C. Newstead, K. L. Rabone, N. A. J. Rogers, and (in part) W. Kernick, Tetrahedron, 1970, 26, 201. A. J. Birch, K. B. Chamberlain, M. A. Haas,and D. J,Thomp-son, J.C.S. Perkin I, 1973, 1882. ' A. J. Pearson, Austral. J. Chem., 1976, 29, 1101. -4.L. Burrows, B. F. G. Johnson, J.Lewis, and D. G. Parker,J. Organometallic Chem., 1977, 127, C22. that of (9, endo-CO,Me), as is observed for exo and endo protons in other tricarbonyliron complexes.7~8 This behaviour is in contrast to that observed for the com- plexation of methyl cyclohexa-2,5-dienecarboxylate which has been reported to give the endo derivative (10, R6= endo-C0,Me) indicating that the ester unit directs the Fe(CO), group to the same face.s Birch and Williamson reported the formation of two com-plexes, tricarbonyl-(2-methoxycarbonylcyclohexa-1,3-diene)iron and tricarbonyl-(5-methoxycarbonylcyclo-hexa-l,3-diene)iron, the latter being the major isomer and of undefined stereochemistry.2 We have repeated this work using the reaction conditions employed for the dihydroanisic esters, and the distilled complexes obtained did indeed correspond to the reported mixture, except the presence of a third minor compound was shown by the lH n.m.r.spectrum. This complex gave a singlet in the C0,Me region which was 0.07 p.p.m. upfield from that corresponding to the major component. Since the olefinic region of the spectrum indicated the presence only of the aforementioned two isomers, we conclude that the third component is the diastereoisomer of (10) and is therefore the exo-C0,Me complex. These observ- ations support the conclusion that the lower-field signal corresponds to the endo-C02Me isomer and thereby show that the major product obtained from (8) is indeed the exo-C0,Me complex. The reason for this difference in behaviour is not known at present.The observation that the methoxycarbonyl group remains bonded to an sf3 hybridised carbon atom during reaction is consistent with a conjugation mechanism involving transfer of hydride anion to iron giving allyl- complex intermediates such as (19), which has a formal positive charge on the allyl ligand.1deg; This is clearly destabilised by the methoxycarbonyl group in the isomeric intermediate (20),which would be necessary COzMe C02Me H bOMe 60Me'i' R26;'( COhFeI (CO),Fe (19) (20) (21) R' =OMe, R2 =H (22) R1 =H, R2=OMe for the formation of complexes such as (11)-(13). Consequently, this pathway and these complexes are not observed in the preparation. When the reduction of o-methoxybenzoic acid was carried out without acidification and isolation of (7), but followed by direct methylation in the presence of the lithium ethoxide produced during reduction, the ester isolated contained a major proportion of the T.H. Whitesides, R. W. Slaven, and J. C. Calabrese, Inorg.Chem., 1974, 13, 1895. lo H. Alper, P. C. Le Port, and S. Wolfe, J. Amev. Chem. SOC., 1969, 91, 7553; F. G. Cowherd and J. L. von Rosenberg, ibid., p. 2157; W. T. Hendrix, F. G. Cowherd, and J. L. von Rosenburg,Chem. Comm., 1968, 97; R. Pettit and G. F. Emerson, Adv. Organometallic Chem., 1964, 1, 1. conjugated diene (21). Treatment of this compound with pentacarbonyl iron produced a yellow oil which gave the major product (11)on crystallisation from light petroleum at -78 "C.Again, the OMe resonance at 6 3.46 is consistent with this group being on the diene terminus (C-1), and the methoxycarbonyl singlet at 6 3.78 shows it to be on C-2, by comparison with the simple monosubstituted analogues., The occurrence of a doublet at 6 5.57 (3-H), in the region associated with 2- and 3-H of a 1,3-diene c~mplex,~~~~ rules out the structure (12). The mixture of endo- and exo-isomers (9) obtained above was refluxed in 10 methanolic sulphuric acid and gave the isomer (13),as expected from the results of isomerisation of the analogous monosubstituted com-plex., This compound still contained a minor amount of (9, exo-CO,Me), which could not be removed by chromatography, and we were unable to crystallise (13).Prolonged refluxing with methanolic sulphuric acid led to higher losses without increasing the proportion of the desired compound (13). The lH n.m.r. spectrum of this compound showed the methoxy singlet at 6 3.70 and the methoxycarbonyl resonance at 6 3.76, as expected (these assignments may be reversed, but this does not affect the structural implications). The ester carbonyl i.r. stretching frequencies for compounds (11) and (13) compare well with the unsubstituted ester analogues. Thus, it has been shown that the i.r. band for a l-CO,Me substituent occurs at 1698 cm-l, that for a 2-C02Me substituent being at 1 717 cm-l. Complexes (11) and (13) give bands at 1 720 and 1700 crn-l, respectively, again consistent with the assigned substitution patterns (Table 2).Reaction of the ester (22) l2 with nonacarbonyliron in refluxing diethyl ether gave the expected complex (14) which could be purified by crystallisation from light petroleum, as above. Treatment of this compound with refluxing methanolic sulphuric acid produced the isomeric complex (15) in 78 yield, which was homo- geneous on t.l.c., and appeared 95 pure from its 1H n.m.r. spectrum, but which could not be induced to crystallise. The structures of (14) and (15) were again readily deduced from their n.m.r. and i.r. spectral data (Tables 1 and 2). The corresponding para-disubstituted diene complex (23) cannot be produced via Birch reduction of 9-anisic acid since this compound is known to be demethoxylated under metal-ammonia reducing ~0nditions.l~ Conse- quently, we treated tricarbonyl-(2-methoxycyclohexa-dieny1)iron hexafluorophosphate (6, PF,-salt) with aqueous sodium cyanide to produce exclusively the nitrile (16).4 Since this compound was quite unstable it was not purified, and the crude complex was subjected to acid methanolysis in the usual way2 to give, after crystallisation from light petroleum, the ester complex (17), again easily identified from its n.m.r.and i.r. spectra. l1 M. L.H.Green, L. Pratt, and G. Wilkinson, J. Chem. Soc., 1959, 3753. J.C.S. Perkin I Reaction of Complexes with Triphenylmethyl Tetra-Jluoroborate.-Only three of the complexes were found to undergo hydride abstraction on treatment with trityl fluoroborate : (13)-( 15).No dienyl complexes could be obtained from (9, exo-CO,Me), (ll),and (17) and un- changed starting material was recovered in each case. Compounds (13), (14), and (15) all lost hydride from the position remote from the terminal substituent, giving the dienyl complexes (23), (24), and (25), respectively. RL H (23) R1= C02Me, R2 = OMe, R3= R4 = H (24) R1= OMe, R2 = R4= H,R3= C0,Me (25) R1= CO,Me, R2 = R4= H, R3 = OMe (26) R1= K4= H, R2= OMe, R3 = C0,Me (27) R1= CO,Me, R2= R3 = H,R4= Ohle (28)R1= Me, R2= R3 = H,R4= OMe These were identified from their lH n.m.r. spectra, by comparison with the appropriate monosubstituted com-pounds. Thus, (23) shows singlets at 6 3.73 and 4.10, typical of 2-OMe and 1-C0,Me dienyl substituents, respectively, whilst 3-H appears as a doublet at the characteristically low field of 6 7.0, 4-H as a triplet at 8 5.86, and 5-H as a triplet, owing to coupling with 4- and endo-6-H, at 6 4.53.The remaining spectral details for this compound, (24) and (25) are given in Table 3. The changes in chemical shift difference between exo-and endo-6-H probably reflect the influence of 1- or 3-C02Me substituents on the conformation of the molecule. The lack of reactivity of complex (9, exo-C0,Me) is readily rationalised in terms of steric hindrance by the methoxycarbonyl group, as is the case with analogous alkyl substituted complexe~.~ However, we should have expected (11) and (17) to give rise to the cations (26) and (27), respectively, in which the substituents occupy positions which are stable in the mono-substituted com- pounds, e.g.(2) and (5). Prolonged treatment with trityl fluoroborate led only to extensive decomposition, but no salt formation. That this lack of reactivity is not due to steric hindrance by the methoxy-substituent CH(COzMe)2 CH (COzMe12 OMe (29) (30) is adequately demonstrated by the ready hydride abstraction from (18), an analogue of (17), to give the salt (28). It would appear then that the stabilising 12 M. E. C. Biffin, A. G. Moritz, and D. B. Paul, Austral. J. Chem., 1972, 25, 1329. 13 A. J. Birch, A. R. Murray, and H. Smith, J. Chena. SOC., 1951, 1945. 1978 641 TABLE1 IH N.m .r.spectral data for tricarbonyl(dihydroanisic ester)iron complexes; 6 values for solutions in CDCl, ; Me,Si internal reference; J values in Hz Compound 2-H 3-H 4-H 5- H 6H OMe C0,Me (9, exo-C0,Me) 5.45,d 5.14,t 2.90,m 1.68-2.28,m 3.3,m 3.42 3.60 J2.3 Jz.3 = J3.4 = 6(9, endo-C0,Me) 5.36,d 4.94,dd 2.85,t 3.42 3.63 J2.3 J3.4 6 J3.4 = J4.5 = 6 Ja.3 5(11) 5.57,d 3.0,m 1.64-2.36 1.64-2.36 3.46 3.78 J3.4 7 (13) 5.05,d 2.9,m 1.2-2.3 1.2-2.3 3.70" 3.76" J3.4 7 (14) 5.96,s(br) 3.49 1.6-2.5 1.6-2.5 3.49 3.79 (15) 5.70,d 3.55,m 1.2-2.2 1.2-2.2 3.65" 3.68" J2.4 (23) 5.28,d 5.68,d 1.P-2.5 1.4-2.5 3 44 3.60 J2.3 12.3 Assignments may be reversed. b Long-range coupling of ca, 0.7 Hz resolvable. Coincident with methoxy resonance (integral 4 H).This coupling is characteristic of complexes having 2-Me0 substituents.6 factors of the methoxy and methoxycarbonyl sub-TricarbonyZ-( 1-methoxy-6-methoxycarbonyZcycloh.exa-1,3-stituents are not additive, and their mode of interaction diene)iron (9).-The acid (7) was methylated in the usual way with dimethyl sulphate in refluxing acetone, in the with each other and the complexed dienyl ligand are at presence of excess of potassium carbonate, to give the present unknown. ester (8) in 70 yield, 6 6.1 (2 H, m, vinyl H), 4.90 (1 H,TABLE2 t, vinyl H), 3.92 (3 H, s, CO,Me), 3.74 (3 H, s, OMe), 3.9 1.r. spectral data for tricarbonyl(dihydroanisicester)iron (1 H, m, 1-H), and 3.0 (2 H, m, methylene). The crude complexes (CC1, solution) compound (4.0 g) was treated with pentacarbonyliron Compound vF,(coamp;rn-1 vc-o/cm-l (10 g) in refluxing dibutyl ether (50 ml) in the usual way 396 (9, exo-CO,Me) 2 040,1960 1725 and excess of solvent and pentacarbonyliron were removed (11) (2-C0,Me) 2 050, 1975 1720 at aspirator pressure.Excess of ester (8) was removed at(13) (1-C02Me) 2 055, 1975 1700 (14) (2-C0,Me) 2 045, 1970 1720 ca. 80 "C and 0.05 mmHg and the residual complexes were (15) (1-C0,Me) 2 060, 1 980 1702 chromatographed on silica. Minor products were eluted (23) (1-C0,Me) 2 065, 1980 1708 with benzene, and a major band was eluted with benzene- ethyl acetate (10 : 1) to give the complexes (9) (4.0g, 55)Predictably, the dienyl complexes obtained above as a mixture of endo-and exo-C0,Me isomers. This reacted with nucleophiles at the unsubstituted terminus.mixture was dissolved in light petroleum (150 ml) at room Thus, the salts (23) and (25) reacted with dimethyl temperature and the solution was cooled to -78 "C. The TABLE3 lH N.m.r. spectral data for dienyl-Fe(CO), complexes; 6 values ; Me,Si internal reference; J values in Hz Compound Solvent 2-H 3-H 4-H 5-H endo-6-H exo-6-H C0,Me OMe (24) CD,CN 7.0 5.86 4.53 3.14 2.16 4.10 3.73 d, J3.4 7 t, J3.4 = Jb.5 = 7 t,J4.s = J5,~cmio = 7 dd, Jgcm IlrJ.5,~ 7 Jgcm 11 (25) CF,C02H 4.90 7.76 4.3 " 3.4 2.86 4.18 4.02 s,br dp J4.5 7 m, dd, Jgcm 15, J5.6 4 d, Jgcm 15 (26) CF,C02H 7.62 7.06 4.64 3.42 1.98 4.30 3.98 s,br d, J4.5 7 t, J4.5 = J5.6crtddo = 7 dd, Jgcm 16, J5.6 7 d, Jgem 16 a Partly obscured by C0,Me.sodiomalonate in tetrahydrofuran to give (29) and (30), pale yellow solid was filtered off, using previously cooled respectively, again readily identified from their lH apparatus, to give a compound which melted at room tem- perature. This was redissolved in light petroleum (70 ml),n.m.r. and i.r. spectra (Experimental section). again cooled to -78 "C, and the solid thus obtained was EXPERIMENTAL finally recrystallised from light petroleum (b.p. 30-40 "C) 1f.p.s points were determined on a Reichert hot stage by cooling to -20 "C, to give yellow crystals, m.p. 44-apparatus and are uncorrected. 1.r. spectra were measured 45 "C (1.0 8). Concentration of the combined washings did for solutions in carbon tetrachloride, unless otherwise not allow any further isolation of crystalline material.stated, using a Perkin-Elmer 257 instrument, mass spectra The compound thus obtained was shown to be (9, exo-with an A.E.J. MS9, and 100 MHz lH n.m.r. spectra with C0,Me) by i.r. and n.m.r. spectroscopy and had M 308 Varian HA 100 or JEOL Minimar spectrometers, The (Found: C, 46.5; H, 4.1. Cl,Hl,Fe06 requires C, 46.8; anisic acids, dimethyl malonate, pentacarbonyliron, and H, 3.9). The compound obtained from the mother nonacarbonyliron were obtained from commercial sources. liquors was set aside for the preparation of complex (I 3). All chromatographic operations were conducted under a TricarbonyZ-( 1-methoxy-2-methoxycarbonylcyclohexa-1,3-nitrogen atmosphere.Light petroleum refers to the diene)iron ( 11).-Removal of ammonia from the Birch fraction of b.p. 40-60 "C unless otherwise stated. reduction product of o-anisic acid, followed by refluxing the alkaline material for 5 h in methanol with dimethyl sulphate and potassium carbonate afforded a crude ester in 50 yield, in which the major component was (21), formed by the metal alkoxide-catalysed conjugation of the cyclohexa- 1,Cdiene derivatives. Treatment of the crude ester (7.0 g) with pentacarbonyliron in the above manner gave a single major complex (5.0 g, 39) on chromatography, shown to be almost pure (1 1) from its n.m.r. spectrum. An analytical sample was obtained by crystallisation from light petroleum as for complex (9) and gave M 308 (Found: C, 46.6; H, 4.1y0), m.p. 64-66 "C.Spectral details are given in Tables 1 and 2. Tricarbonyl- (2-methoxy- l-methoxycarbonylcyclohexa-1,3-diene)iron (13) .-The mixture of exo- and endo-isomers of (9) (1.9 g) from the aforementioned crystallisation procedure was refluxed in 10 methanolic sulphuric acid (250 mi) under nitrogen for 24 h. The solution was poured into water (500 ml) and extracted with ether in the usual way to give the crude product (0.9 g, 47). This was homo-geneous on t.1.c. and attempts to crystallise the compound from light petroleum ether gave only a gum. lH N.m.r. spectroscopy showed the product to be (13) together with a small amount of unchanged (9). Spectral details are given in Tables 1 and 2.Prolonged refluxing gave rise to extensive decomposition without change in the proportion of residual (9). Tricarbonyl-( l-methoxy-3-metJzoxycarbonylcycloJzexa-1,3-diene)iron (14).-The ester (22) was prepared by reaction of the corresponding acid l2 with dimethyl sulphate in the usual way and gave n.ni.r. resonances at 6 6.76 (1 H, in, vinyl H), 5.42 (1 H, s, vinyl H), 3.72 (3 H, s, CO,Me), 3.62 (3 H, s, OMe), and 2.5-2.1 (4 H, m, CH,). A stirred mixture of the crude ester (3.5 g) and nonacarbonyliron (8 g) in diethyl ether (100 ml) was refluxed for 4 h under nitrogen, the product filtered through Celite, and the solvent removed. Excess of ester (1.0 g, 29) was removed at 70-80 "C and 0.05 mmHg, and the residual complexes were chromatographed on silica to give a single major compound, eluted with benzene.Two recrystallisations from light petroleum, at -78 and at -10 "C, gave 2.4 g (38)of pure (18), m.p. 57.5-59 "C, M 308 (Found: C, 47.2; H, 4.0). Further spectral details are in Tables 1 and 2. Tricarbonyl- (3-methoxy- l-methoxycarbonylcyclohexa-1,3-diene)iron (15).-Complex (14) (900 mg) was treated with 10 methanolic sulphuric acid as above to give (15) (700 mg, 78y0), which was homogeneous on t.1.c. and which could not be induced to crystallise from light petroleum. The lH n.m.r. spectrum showed no evidence of impurities and the compound gave M 308 (Found: C, 46.9; H, 3.8). Tricarbonyl-(1-methoxy-4-metJtoxycarbonylcyclohexa-1,3-diene)iron (17).-The nitrile complex (16) (980 mg) was treated with refluxing 10 methanolic sulphuric acid as above to give crude (17) (400 mg) which was recrystallised from light petroleum at -20 "C to give the pure complex (200 mg, 18), m.p.76-77 "C, M 308 (Found: C, 46.7; H, 4.2). Reaction of Complexes with Triphenylmethyl Tetrajztoro- borate.-Triphenylmethyl tetrafluoroborate (530 mg) was dissolved in the minimum volume of dichloroniethane and added to the dihydroanisic ester complex (500 mg) in a similar volume of dichloromethane. The solution was kept at room temperature for 30-40 min and sufficient ' wet ' ether was added to cause complete precipitation of dienyl complexes (use of 'wet' ether removes any excess tri-phenylmethyl tetrafluoroborate by hydrolysis).The pro- J.C.S. Perkin I duct was filtered off under reduced pressure and washed with ether. Paramagnetic impurities resulting from decom-position were removed by dissolving the complex in aceto- nitrile, centrifuging, adding the clear supernatant liquid dropwise to stirred dry ether, and filtering as above. Anyunchanged starting material was recovered by removing the ether from the washings, dissolving the product in light petroleum and filtering to remove triphenylmethanol (from ' wet ' ether hydrolysis) which sometimes cochromato-graphed with the complexes, and finally purifying by preparative layer chromatography. The recovered diene complexes were identified by 'H n.m.r. spectroscopy.The n.m.r. spectra of the salts obtained are given in Table 3. Complexes (9, exo-CO,Me), (II), and (17) gave only un-changed starting materials (60, 40, and 720/b, respectively). Complex ( 13) gave tricarbonyl-( 2-methoxy- l-methoxy- carbonylcyclolzexadienyl) iron tetrafluorobornte (23) (73yo), vmax.(KBr) 2 120, 2 055, 1970, and 1710 cm-l (Found: C, 37.0; H, 3.0. C12HllBF4Fe0, requires C, 36.6; H, 2.8). Complex ( 14) gave tricarbonyl-( I-methoxy-3-methoxy-carbonylcyclohexadieny1)iron tetrafluoroborate (24) (39) which was hydrolysed very rapidly by atmospheric moisture, vmax.(Nujol) 2 115, 2 080, 2 050, and 1 720 cm-l. Un-changed (14) accounted for a further 40 of the starting material. Complex ( 15) gave tricarbonyl- (3-methoxy- 1-methoxy-carbonylcyclohexadieny1)irontetrafluoroborate (25) (32 yo)and unchangecl (15) (50).Prolonged treatment led to extensive decomposition of complexes, ~,~;~~.(Nujol) 2 1 15, 2 065, 2 050, and 1 707 cm-l (Found: C, 36.4; H, 3.2). Reaction of Dienyl Complexes udh Dimethyl Sodio-ma1onate.-To a stirred suspension of the dienyl-Fe(CO), salt (170 mg) in dry tetrahydrofuran (5 nil) at room tem- perature and under nitrogen was added a 10 molar excess of dimethyl sodiomalonate in tetrahydrofuran (previously prepared from sodiuni hydride and dimethylmalonate), using typical syringe techniques. When all the iron complex had dissolved the mixture was poured into water and the product extracted with light petroleum. Complex (23) gave tricarbonyl(dirnethy1 4-methoxy-5- methoxycarbonylcyclohexa-2,4-dienylmalonate)iron (29), ob- tained as pale yellow crystals from light petroleum (100 mg, 53y0), m.p.86-88 "C; V~,,..~~(CCI,)2 065, 1 990, 1 750, 1 738, and 1 707 (1-C0,Me) cn-l; G(CDC1,) 1.46 (1 H, dd, J,,,, 14 Hz, J5,62.5 Hz, exo-6-H), 2.46 (1 H, dd, JDerrL14 Hz, J5,,11 Hz, endo-6-H), 2.75 l H, m, 4-H (confirmed by spin decoupling: irradiation of 3-H leads to appropriate change), 2.9 (1 H, m, 5-H), 3.07 (1 H, d, J 8 Hz, malonyl CH), 3.68 (6 H, s), 3.73 (3 H, s), and 3.77 (3 H, s) (3 x C0,Me and OMe), and 4.97 (1 H, d, J3,4 6.5 Hz, 3-H); M 438 (Found: C, 46.8; H, 4.1. C,,Hl,FeOlo requires C, 46.6; H, 4.1). Complex (25) gave tricarbonyl-(dimethyl 3-methoxy-5- metlioxycarbonylcycloliexa-2,4-dienylmalonate)iron (30) which could not be crystallisecl from light petroleum and so was purified by preparative layer chromatography to give a yellow viscous oil (100 mg, 53); vmax.(CC14) 2 065, 1 990, 1 750, 1 735, and 1 705 (1-C0,Me) cm-l; G(CDC1,) 1.22 (1 H, dd, Js,,, 14 Hz, J5,64 Hz,,exo-6-H), 2.40 (1 H, dd, J,,, 14 Hz, J5., 11 Hz, endo-6-H), 2.92 (1 H, m, 5-H), 3.14 (1 H, d, J 8 Hz, malonyl CH), 3.40 (1H, m, 4-H), 3.62 (9 H, s), and 3.68 (3 H, s, 3 x C0,Me and OMe), and 5.68 (1 H, d, J2.4 2 Hz, 2-H); M 438. 7/1407 Received, 2nd August, 19771
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