Functionalized Iron Ketene Complexes from Carbonyl Coupling

Tracing an organometallic early—late transition element relationship. H. Berke , H. Jacobsen. Russian Chemical Bulletin 1998 47, 841-850 ...
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Organometallics 1998, 17, 960-971

Functionalized Iron Ketene Complexes from Carbonyl Coupling Reactions Helmut Kandler, Wolfgang Bidell, Monika Ja¨nicke, Markus Knickmeier, Dario Veghini, and Heinz Berke* Anorganisch-chemisches Institut der Universita¨ t Zu¨ rich, Winterthurerstrasse 190, CH-8057 Zu¨ rich, Switzerland Received October 23, 1997

The solution mixture of the dinitrogen complexes Fe(CO)2(PEt3)2(N2) (1a) and [Fe(CO)2(PEt3)2]2(µ-N2) (1b) reacts with methyl or ethyl haloacetates to yield the oxidative addition products Fe(CO)2(PEt3)2(X)CH2COOR (X ) Cl, R ) Me, 2a; X ) Br, R ) Me, 2b; X ) I, R ) Et, 2e). These complexes can be transformed in ether to carbonylhalo-bis(triethylphosphane)[1-((trimethylsilyl)oxy)-2-(alkoxycarbonyl)ethenyl]iron compounds (X ) Cl, R ) Me, 7a; X ) Br, R ) Me, 7b; X ) I, R ) Et, 7c) in the presence of LDA and subsequent trapping of the formed anions with Me3SiCl. When DBU is used as a base and 1 bar CO is applied with otherwise similar reaction conditions as before the transformations of 2a-c take the course of the formation of ester-functionalized ketene compounds E,Z-Fe(CO)2(PEt3)2{η2-(C,O)[OCCH(COOR)]} (R ) Me, 8a; R ) Et, 8b) and of dicarbonyl(1-alkoxy-1,3-dioxopropen-3yl)bis(triethylphosphane)iron derivatives (R ) Me, 9a, R ) Et, 9b). In the solid state only the Z form of complexes 8 is found. In a comparable manor as for the synthesis of compounds 2, it is possible to obtain Fe(CO)2(PEt3)2(X)(CH2R) (R ) OMe, 10a; R ) 1,3-dioxolan-2-yl, 10b; R ) 2,4,10-trioxoadamantan-3-yl, 10c) species. While 10a does not react, the derivatives 10b,c are converted in the presence of DBU and CO to E,Z mixtures of ketene complexes Fe(CO)2(PEt3)2 [η2(C,O)-(COCHR)] (R ) 1,3-dioxolan-2-yl, 13bE,Z; R ) 2,4,10-trioxoadamantan-3-yl, 13cE,Z). (13b,c)Z crystallize from solutions. In further attempts comparable to the reactions to 2 and 10, haloorganyliron complexes Fe(CO)2(PEt3)2(X)(CH2Y) (X ) Y ) Cl, 14a; X ) Y ) I, 14b; X ) I, Y ) CH2CN, 14c) could be obtained. All derivatives 14 cannot be transformed to ketene complexes in the presence of DBU and CO. Finally the known complexes Fe(CO)2(I)(PEt3)2(Me, Et) (15a,b) and the new species Fe(CO)2(I)(CH2SiMe3)(PEt3)2 (15c) were attempted to be converted to ketene complexes. By IR spectroscopy it was possible to detect Fe(CO)2(I)(PEt3)2(OCCHR) compounds (R ) H, 17a; R ) Me, 17b; R ) SiMe3, 17c); however, these molecules could not be isolated from the reaction mixtures of the reaction of 15a-c with DBU and CO. 17c was then prepared by an independent route by reacting 1a,b with Me3SiCHdCdO. Under these conditions 17c was much more stable. In an exemplary way it was shown that the ketene unit of 17c can be cleanly replaced by CO to afford Fe(CO)3(PEt3)2 (18). The structures of 7a, 8aZ, 9b, and 14a have been determined by X-ray diffraction studies. Introduction Transition metal ketene complexes have attracted considerable recent interest,1 in particular in conjunction with the proposed role of CCO units as intermediates in homogeneous or heterogeneous Fischer-Tropsch type catalysis2 and the fact that metal ketene compounds have great potential in organic synthesis. Their significance in organic synthesis is for instance nicely demonstrated by the reaction of alkynes with (alkoxyaryl)chromium carbene complexes involving a short-lived vinylketene complex as key intermediate to give 4-alkoxy1-naphthol derivatives.3-8 (1) Geoffroy, G. L.; Bassner, S. L. Adv. Organomet. Chem. 1988, 28, 1. (2) Henrici-Olive´, G.; Olive´, S. Angew. Chem. 1976, 88, 144. (b) Masters, C. Adv. Organomet. Chem. 1979, 17, 61. (c) Rofer-DePoorter, C. K. Chem. Rev. (Washington, D.C.) 1981, 81, 447. (d) Herrmann, W. A. Angew. Chem. 1982, 94, 118. (e) Herrmann, W. A. Kontakte 1991, 1, 22. (f) Herrmann, W. A. Kontakte 1991, 3, 29.

Synthetic access to transition metal attached ketene moieties can be achieved by direct addition of ketenes to unsaturated organometallic complexes,1,9-17 the car(3) Do¨tz, K. H. Angew. Chem. 1975, 87, 672. (4) Grubbs, R. H.; Straus, D. A. J. Am. Chem. Soc. 1982, 104, 5499. (5) Grubbs, R. H.; Ho, S. C. H.; Straus, D. A.; Armantrout, J.; Schaefer, W. P. J. Am. Chem. Soc. 1984, 106, 2210. (6) Grubbs, R. H.; Waymouth, R. M.; Santarsiero, B. D.; Coots, R. J.; Bronikowski, M. J. J. Am. Chem. Soc. 1986, 108, 1427. (7) Do¨tz, K. H. In Organometallics in Organic Synthesis; de Meijere, A, tom Dieck, H., Eds.; Springer: Berlin, 1988. (8) Wulff, W. D. Transition Metal Carbene Complexes: Alkyne and Vinyl Ketene Chemistry. In Comprehensive Organometallic Chemistry II; Hegedus, L. S., Ed.; Elsevier Science: Oxford, U.K., 1995; Vol. 12, Chapter 5.3, p 469. (9) Berke, H.; Birk, R.; Hund, H.-U.; Dahlenburg, L.; Behrens, U.; Sielisch, T. J. Organomet. Chem. 1989, 372, 397. (10) Hofmann P.; Perez-Moya, L. A.; Steigelmann, O.; Riede, J. Organometallics 1992, 11, 1167. Miyashita, A.; Shitara, H.; Nohira, H. J. C. S. Chem. Commun. 1985, 850. Miyashita, A.; Sugai, R.; Nohira, H. Chem. Lett. 1988, 1403. Miyashita, A.; Sugai, R.; Yamamoto, J. J. Organomet. Chem. 1992, 428, 239.

S0276-7333(97)00928-X CCC: $15.00 © 1998 American Chemical Society Publication on Web 02/05/1998

Functionalized Iron Ketene Complexes

bonylation of carbenes,3-8,18-25 or the deprotonation of acyl species.4,15b,26,27 The latter two methods are of synthetic interest, because both could principally involve C-C coupling processes (note that metal-bound acyl units can be obtained by a CO insertion step) for the buildup of ketene moieties and thus circumvent the quite often tedious preparation of free ketene derivatives. Our investigations in the realm of ketene complexes aimed at the utilization of Fe(CO)2(PEt3)2 fragments, since they were deemed to allow facile access to a versatile chemistry not only via known acyl compounds of the type Fe(CO)2(PEt3)2(Hal)COR28 but also via the “parent” alkyl carbonyl molecules Fe(CO)2(PEt3)2(Hal)(R). A metal-mediated buildup of ketene moieties could thus be envisaged by the following formal C-C coupling process involving a carbene unit and CO. B

CHR1R2(Hal) + CO 9 8 R1R2CdCdO -BH(Hal) This quite desirable route is expected to allow the use of simple starting materials and moreover the access to a broad variety of substituted metal-bound ketene units independent of the restriction that the ketenes have to be stable in the free state.

Organometallics, Vol. 17, No. 5, 1998 961

(CO)2L2]2(µ-N2) (L ) phosphorus donor) can be used as versatile starting materials for many types of reactions.28,29 The N2 ligand easily dissociates in solution generating the very reactive 16e- species [Fe(CO)2L2], which can add various types of ligands9 or can undergo oxidative addition reactions of R-X derivatives.28 The PEt3-substituted dinitrogen compounds 1a,b can be obtained by either photolysis of Fe(CO)3(PEt3)228 or by reduction of Fe(CO)2(PEt3)2X2 species (X ) halogen) in the presence of N2.29 Under N2, species 1a,b are in

equilibium, and both are satisfactory starting components in substitution and oxidative addition processes. When etheral solutions of the 1a,b mixture are reacted with XCH2COOR compounds bearing electronwithdrawing ester functionalities, the oxidative addition products Fe(CO)2(PEt3)2(X)(CH2COOR) (2a-c) (eq 1)

Results and Discussion It has been demonstrated in our group that iron dinitrogen complexes of the type Fe(CO)2L2N2 and [Fe(11) Floriani, C.; Fachinetti, G.; Biran, C.; Chiesi-Villa, A.; Gaustini, C. Inorg. Chem. 1978, 17, 2995. (12) Floriani, C.; Gambarotta, S.; Pasquali, M.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1981, 20, 1173. (13) Casey, C. P.; O’Connor, J. M. J. J. Am. Chem. Soc. 1983, 105, 2919. Casey, C. P.; O’Connor, J. M.; Haller, K. J. J. Am. Chem. Soc. 1985, 107, 3172 (14) (a) Bruno, J. W.; Galante, J. M.; Hazin, P. N. Organometallics 1988, 7, 1066. (b) Bruno, J. W.; Halfon, S. E.; Fermin, M. C. J. Am. Chem. Soc. 1989, 111, 5490. (c) Fermin, M. C.; Hneihen, A. S.; Maas, J. J.; Bruno, J. W. Organometallics 1993, 12, 1845. (d) Fermin, M. C.; Bruno, J. W. J. Am. Chem. Soc. 1993, 115, 7511. (15) (a) Grotjahn, D. B.; Lo, H. C. J. Am. Chem. Soc. 1996, 118, 2097. (b) Grotjahn, D. B.; Lo, H. C. Organometallics 1995, 14, 5463. (16) Flu¨gel, R.; Gevert, O.; Werner, H. Chem. Ber. 1996, 129, 405. (17) Antin˜olo, A.; Otero, A.; Fajardo, M.; Gil-Sanz, R.; Herranz, M. J.; Lopez-Mardomingo, C.; Martin, A.; Gomez-Sal, P. J. Organomet. Chem. 1997, 533, 87. (18) Hegedus, L. S. Transition Metal Carbene Complexes. In Comprehensive Organometallic Chemistry II; Hegedus, L. S., Ed.; Elsevier Science: Oxford, U.K., 1995; Chapter 5.4, p 549. (19) Schubert, U.; Kron, J.; Ho¨rnig, H. J. Organomet. Chem. 1988, 355, 243. Kron, J.; Schubert, U. J. Organomet. Chem. 1989, 373, 203. (20) Herrmann, W. A.; Plank, J. Angew. Chem. 1978, 90, 555. (21) Bodnar, T. W.; Cutler, A. R. J. Am. Chem. Soc. 1983, 105, 5926. (22) Lin, Y. C.; Calabrese, J. C.; Wreford, S. S. J. Am. Chem. Soc. 1983, 105, 1679. Lin, Y. C. J. Chin. Chem. Soc. 1985, 32, 295. Lin, Y. C.; Chen, M. C.; Tsai, Y. J.; Chen, C. T.; Tseng, T. W.; Lee, G. H.; Wang, Y. Organometallics 1991, 10, 378. Yang, Y.-L.; Wang, L. J.-J.; Lin, Y. C.; Huang, S.-L.; Chen, M.-C.; Lee, G. H. L.; Wang, Y. Organometallics 1997, 16, 1573. (23) Orpen, A. G.; Doherty, N. M.; Fildes, M. J.; Forrow, N. J.; Knox, S. A. R.; Macpherson, K. A. J. Chem. Soc., Chem. Commun. 1986, 1355. (24) Grubbs, R. H.; Ozawa, F.; Park, J. W.; Mackenzie, P. B.; Schaefer, W. P.; Henling, L. M. J. Am. Chem. Soc. 1989, 111, 1319. (25) Geoffroy, G. L.; Morrison, E. D.; Steinmetz, G. R.; Fultz, W. C.; Rheingold, A. R. J. Am. Chem. Soc. 1983, 105, 4104. Geoffroy, G. L.; Morrison, E. D. J. Am. Chem. Soc. 1985, 107, 3541. Geoffroy, G. L.; Morrison, E. D.; Rheingold, A. L. J. Am. Chem. Soc. 1985, 107, 254. Geoffroy, G. L.; Bassner, S. L.; Morrison, E. D.; Rheingold, A. L. Organometallics 1987, 6, 2207. (26) Templeton, J. L.; Rusik, C. A.; Tonker, T. L. J. Am. Chem. Soc. 1986, 108, 4652. Rusik, C. A.; Collins, M. A.; Gamble, A. S.; Tonker, T. L.; Templeton, J. L. J. Am. Chem. Soc. 1989, 111, 2550. (27) Kreissl, F. R.; Keller, H.; Schu¨tt, W. J. Organomet. Chem. 1992, 441, 75. (28) (a) Berke, H.; Birk, R.; Huttner, G.; Zsolnai, L. J. Organomet. Chem. 1986, 309, C18. (b) Berke, H.; Birk, R.; Huttner, G.; Zsolnai, L. Chem. Ber. 1988, 121, 1557.

can be obtained after chromatographic workup in good to moderate yields. The spectroscopic data for 2a-c are in accord with the presence of cis, trans Fe(CO)2(PEt3)2 units in these molecules. In the 13C spectra two phosphorus-coupled triplets are assigned to the chemically inequivalent CCO nuclei. The low-field ones are attributed to the ligands trans to the alkyl substituents, while the high-field signals correspond to the CO groups trans to the halogen moiety. This assignment is mainly based on the magnitude of the JPC couplings, which have been related to the trans influence of the trans-disposed ligands in structurally similar complexes.30 In addition to this the chemical shifts of the high-field CO signals vary significantly on going from 2a to 2c stressing their trans to halogen positions. The 1H NMR spectra of 2a-c show characteristic triplets for the metal-bound methylene groups, and the trans arrangement of the phosphorus donors is indicated by the observation of higher order splitting patterns of the CH2 groups. Such virtual couplings are typical for trans phosphorus donor moieties. All complexes 2a-c show correct elemental analyses. In Scheme 1 it is suggested that compounds 2a-c can react with bases. There is however strong indication that deprotonation does not occur from 2a-c directly, rather than from their CO inserted η2-acyl isomers 3ac. It should be noted that spontaneous isomerizations (29) Berke, H.; Kandler, H.; Gauss, C.; Bidell, W.; Rosenberger, S.; Bu¨rgi, T.; Eremenko, I. L.; Veghini, D.; Orama, O.; Burger, P. Chem. Eur. J. 1995, 1, 541. (30) (a) Cardaci, G.; Reichenbach, G.; Wassink, B.; Baird, M. C. Organometallics 1988, 7, 2475. (b) Cardaci, G.; Bellachioma, G.; Macchioni, A.; Reichenbach, G. Inorg. Chem. 1992, 31, 63.

962 Organometallics, Vol. 17, No. 5, 1998

Kandler et al. Scheme 1

of iron alkyl carbonyl species into η2-acyl compounds is a quite common phenomenon in the realm of Fe(CO)2L2 chemistry. Selected examples of such (η2-acyl)iron complexes have been isolated and even been structurally characterized.9,28 In a separate exemplary experiment it has then been tested that 2c can react with CO presumably via 3c leading to a trans iodo malonyl compound 4, however, requiring a 20 bar CO pressure. Under ambient conditions 4 is unstable and can only be traced IR spectroscopically, when samples are taken quickly from an autoclave. The IR spectrum shows a very weak and a strong ν(CO) band interpreted as a typical absorption pattern for a trans CO arrangement. In addition to these bands two ν(CdO) absorptions are observed. The apparent instability of 4 under ambient conditions may indicate that under an atmosphere of 1 bar CO, as applied for the reactions of Scheme 1, the η2-acyl complexes of type 3 are probably present in a higher concentration than their η1-congeners of type 4. Nevertheless, 3a-c and also potential intermediates such as 4 are all derivatives of β-keto esters and should therefore display an acidity much higher than that of the parent complexes 2a-c. MeCOCH2COOEt, CH2(COOEt)2, and [DBUH]+ have similar pKa values of 25, 27, and 24 in acetonitrile,31 so that their mutual deprotonation can be anticipated to a kinetically relevant extent by any of their conjugate bases. The pKa effect of substituting the methyl or the ethoxy group in MeCOCH2COOEt or CH2(COOEt)2 for the iron fragment in 3a-c is not easily evaluated. However, it is reasonable to assume that these complexes have pKa (31) Schwesinger, R. Nachr. Chem. Technol. Lab. 1990, 38, 1214.

values in the vicinity of 24 and, hence, DBU could still effect deprotonation to give the isomeric mixture of 5a-c and 6a-c as indicated in Scheme 1. As described for the DBU deprotonation process of 3a-c, the stronger base LDA is expected to generate the equilibrium mixture of the isomeric anions 5a-c and 6a- c, as well. In the subsequent silation with Me3SiCl only the O-silation products 7a-c are isolated, which are related to 6a-c and C-silyl derivatives of 5a-c were not found. From this a predominance of 6a-c may be concluded. In this context it should be noted that trapping of the 5a-c h 6a-c equilibrium positions requires that these equilibrium reactions are slow with respect to any of the silation processes. Silations of O-functionalized anions are presumably quite fast reactions and could perhaps satisfy this condition. However, assuming that they are also faster than C-silations, the rates of the latter could be comparable to those of the above equilibria and then C-silation products ought not to be found. The structures of complexes 7a-c were derived from an exemplary single-crystal X-ray diffraction study on 7a and from their spectroscopic properties. The IR spectra are characterized by one ν(CO) band at 1932 cm-1 for all three derivatives and weak ν(CdO) absorptions in the range between 1550 and 1570 cm-1. Their positions at relatively low wavenumbers are apparently due to the coordination of the oxygen atom. The 1H NMR spectra of these homologous complexes show singlets for the silyl protons between 0.1 and 0.3 ppm and resonances for the methoxy or ethoxy residues in 7a,b and 7c, respectively. The vinylic protons at the metallacyclic rings appear between 5 and 5.2 ppm with an expectedly small coupling to the phosphorus nuclei

Functionalized Iron Ketene Complexes

of 2 Hz. The most prominent characteristics of the 13C NMR spectra of 7a-c consist of resonances at rather low field (270 ppm), which are attributed to the COSiMe3 atoms. This low field position suggests contribution from a carbene type resonance structure (vide infra). Another possibility for the trapping of the 5a-c and 6a-c species turned out to be the reaction with CO, which causes replacement of the X group by CO. Apparently, this step is fast with respect to the establishment of the 5a-c h 6a-c equilibria, since we were able to isolate two series of isomeric compounds: the ketene complexes (8a,b)Z and the (1-alkoxy-1,3-dioxopropan-3-yl) iron species 9a,b. The ratios of the isolated complexes 8aZ:9a and 8bZ:9b were 1:39 and 1:13, respectively. These ratios could indeed reflect the respective 5:6 concentrations in solution. The assumption of slow interconversion rates for the 5 h 6 equilibria is supported further by the observation that the equilibria of the topologically related species 8aZ h 9a and 8bZ h 9b were found to be very slow, as well. Indeed, the NMR spectrocopic pursuit of the equilibration reactions starting from either (8a,b)Z or 9a,b takes a very long time. Nevertheless, these studies revealed additional resonances, which were assigned to the nonisolable E isomers (8a,b)E. As a quite puzzling phenomenon, it was found in our initial experiments that these processes were not always reproducible concerning the reaction rates. Apparently, if they were not conducted under very rigorous conditions, higher reaction rates were observed, and in these cases the transformations were also accompanied by the formation of decomposition products, like Fe(CO)3(PEt3)2. 1H and 31P NMR spectra measured with rigorous exclusion of oxygen and with severely purified C6D6 demonstrated that after 22 months a 50:5:1 ratio of 8aZ:8aE:9a was reached starting from 8aZ or 9a. No other product was formed. A similar situation is observed for the equilibration of 8bZ and 9b in C6D6 where a ratio of 11:1:2.5 (8bZ:8bE:9b) was obtained after the same period of time starting from both types of complexes. Exemplary X-ray diffraction studies have been carried out on 8aZ and 9b. Their structures are in accord with their spectroscopic data, which are related to those of 8bZ and 9b, respectively. The IR spectra of all these complexes are characterized by two ν(CO) bands around 1990 and 1930 cm-1, which are typical of Fe(CO)2L2 units with cis CO groups. In addition to this, both isomeric species show two bands of low intensity in the region of 1700-1500 cm-1. The 1H NMR spectra of (8a,b)Z and 9a,b display signals for the alkoxy residues and signals at about 6 ppm, which are assigned to the vinylic protons. For (8a,b)Z these show coupling to the P nuclei (4JPH ) 3 Hz) and appear about 0.5 ppm lowfield from those of 9a,b, which allows facile distinction of these species. The assignment of the low-field 13C NMR resonances of the chemically inequivalent CO groups is mainly based on their 2JPC values.30 These couplings can again be correlated with the trans influence, which is smaller for the CO ligand located approximately trans to the O-donor atoms. The resonances of the iron-bound carbon nuclei of 9a,b are found ca. 40 ppm down-field

Organometallics, Vol. 17, No. 5, 1998 963

of those of (8a,b)Z. The chemical shifts of these internal Cketene signals of (8a,b)Z compare however well with those of other η2(C,O)-ketene complexes1 and do not match with the expected chemical shifts for η2(C,C) binding. It should finally be noted that the chemical shifts of the 31P NMR resonances of both types of species 8Z and 9 differ also significantly. Due to their generally low equilibrium concentrations the (8a,b)E molecules could not be isolated and were characterized by NMR spectroscopy only. They show 31P resonances at 53.5 (8aE) and 53.4 ppm (8bE) in a chemical shift region expected for Fe(CO)2(PEt3)2(ketene) complexes (cf. resonances of (8a,b)Z, 13a,b and 17c). In addition to this, the ketene protons of (8a,b)E appear downfield from those of (8a,b)Z with somewhat smaller 4JPH couplings for (8a,b)E (2σ(I) abs corr solution method agreement factors:a R, wR2 (%) R1 (obsd) (%) goodness-of-fit a

C20H43ClFeO4P2Si yellow 0.7 × 0.4 × 0.25 monoclinic Cc 17.003(3) 13.789(2) 12.153(2) 93.50(2) 2844.0(8) 4 528.87 1.235 0.800 1128 237(5) 4.0 e 2θ e 58.0 variable; 2.00-14.65 1.20 3899 3630 N/A direct methods 4.66, 9.77 4.19 1.124

C18H34FeO5P2 yellow 0.18 × 0.08 × 0.21 orthorhombic Pna21 24.392(5) 11.509(4) 8.149(2) 2287.6(11) 4 448.2 1.301 0.822 952 240(5) 4.0 e 2θ e 55.0 variable; 1.50-14.65 1.40 2808 2297 N/A direct methods 9.04, 11.35 6.67 1.229

9b

14a

C19H36FeO5P2 yellow 0.2 × 0.2 × 0.1 monoclinic P21/c 11.933(5) 15.715(4) 13.110(4) 93.01(3)° 2455.1(14) 4 462.27 1.251 0.768 984 245(5) 4.0 e 2θ e 55.0 variable; 2.00-14.65 1.40 5652 3536 N/A direct methods 17.96, 18.84 11.27 1.224

C15H32Cl2FeO2P2 yellow 0.6 × 0.4 × 0.25 monoclinic P21/n 7.772(4) 30.671(12) 9.152(2) 104.68(3) 2110.4(16) 4 433.1 1.363 1.123 912 241(5) 5.0 e 2θ e 58.0 variable; 2.00-14.65 1.40 5591 4502 N/A direct methods 9.18, 21.26 7.18 1.245

R ) ∑(Fo - Fc)/∑Fo; wR2 ) [∑{w(F2o - F2c)2}/∑(wFo2)2]1/2.

Table 2. Selected Bond Distances (Å) and Angles (deg) of Complex 7a Fe(1)-Cl(1) Fe(1)-P(1) Fe(1)-P(2) Fe(1)-C(1) Fe(1)-C(2) Fe(1)-O(2) Si(1)-O(4) Cl(1)-Fe(1)-P(1) Cl(1)-Fe(1)-P(2) P(1)-Fe(1)-P(2) Cl(1)-Fe(1)-C(1) Cl(1)-Fe(1)-C(2) C(1)-Fe(1)-C(2) Cl(1)-Fe(1)-O(2) C(1)-Fe(1)-O(2) C(2)-Fe(1)-O(2)

Figure 2. Structure of 7a. Thermal ellipsoids are drawn at the 50% probability level.

structural model of 7a, which reveals pseudo-octahedral coordination of the iron center. The iron atom is part of a nearly planar fivemembered ring system forming an O2-Fe-C2 angle of 81.2(2)° at iron (see Table 2). A striking property, unexpected to the determined extent, is the short FeC(2) distance of 1.880(5) Å, which confirms an FedC multiple bond character. This finding implies a carbenoid nature of the C(2) atom as given in A anticipated

also from the strong low-field position of this carbon atom in the 13C NMR (267 ppm). The electronic

2.3774(12) 2.2760(12) 2.2719(13) 1.728(4) 1.899(4) 2.040(3) 1.681(3) 89.16(4) 88.35(5) 177.50(5) 95.91(13) 169.73(13) 94.35(18) 88.59(9) 175.50(16) 81.15(15)

C(1)-O(1) C(2)-C(3) C(2)-O(4) C(3)-C(4) C(4)-O(2) C(4)-O(3) Fe(1)-C(1)-O(1) Fe(1)-C(2)-C(3) Fe(1)-C(2)-O(4) C(3)-C(2)-O(4) C(2)-C(3)-C(4) C(3)-C(4)-O(2) C(3)-C(4)-O(3) O(2)-C(4)-O(3) Fe(1)-O(2)-C(4)

1.148(5) 1.380(6) 1.351(4) 1.409(6) 1.253(5) 1.346(5) 178.8(4) 115.9(3) 123.1(3) 121.0(3) 111.1(4) 121.2(4) 118.0(4) 120.9(4) 110.7(3)

alternative for the binding of C(2) to the iron atom would be that of a Cvinyl atom as represented by the resonance structure B. Vinyl substituents, however, have been seen to cause comparably long Fe-C bond separations.33 The other bond lengths of the planar five-membered ring of 7a confirm π conjugation with C-C bond distances between those of an isolated double bond and the bond lengths of aromatic systems. For middle and late transition metal complexes the alternative binding mode of a ketene unit cannot easily be predicted, so that we sought to ensure the spectroscopically plausible η2(C,O) coordination of complexes 8 and 13 by an exemplary X-ray diffraction study on 8aZ. Crystals for the X-ray diffraction study of 8aZ were obtained by slow cooling of an ether solution to -30 °C. The crystal, structure solution, and refinement data are given in Table 1. Figure 3 shows that 8aZ is indeed a trigonal bipyramidal complex bearing a η2(C,O) ketene moiety in equatorial position with a Z configuration. The (33) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. II, 1989, S1.

Functionalized Iron Ketene Complexes

Organometallics, Vol. 17, No. 5, 1998 967

Figure 3. Structure of 8aZ. Thermal ellipsoids are drawn at the 50% probability level.

Figure 4. Structure of 9b. Thermal ellipsoids are drawn at the 50% probability level.

Table 3. Selected Bond Distances (Å) and Angles (deg) of Complex 8aZ

Table 4. Selected Bond Distances (Å) and Angles (deg) of Complex 9b

Fe(1)-C(1) Fe(1)-C(2) Fe(1)-O(3) Fe(1)-C(3) Fe(1)-P(1) Fe(1)-P(2) C(1)-O(1) C(1)-Fe(1)-C(2) C(1)-Fe(1)-O(3) C(2)-Fe(1)-O(3) C(1)-Fe(1)-C(3) C(2)-Fe(1)-C(3) P(1)-Fe(1)-P(2) Fe(1)-C(1)-O(1)

1.802(7) 1.764(8) 2.012(5) 1.920(7) 2.270(2) 2.280(2) 1.145(8) 101.5(4) 108.9(3) 149.6(3) 146.7(3) 111.8(3) 175.12(7) 179.6(6)

C(2)-O(2) O(3)-C(3) C(3)-C(4) C(4)-C(5) C(5)-O(4) C(5)-O(5) O(5)-C(6) Fe(1)-C(2)-O(2) Fe(1)-O(3)-C(3) Fe(1)-C(3)-O(3) Fe(1)-C(3)-C(4) O(3)-C(3)-C(4) C(3)-C(4)-C(5)

1.142(9) 1.277(8) 1.358(9) 1.425(10) 1.225(9) 1.365(8) 1.431(9) 179.1(7) 67.2(4) 75.0(4) 153.8(6) 131.2(7) 124.4(7)

general topology of 8aZ is very similar to that of the Fe(CO)2(PEt3)2(Ph2CCO) species9 mentioned in the earlier context. Expectedly, the C(3)-O(3) separation of 1.283(7) Å is longer than in free ketenes (d(C-O) in MeCHdCdO 1.171(2) Å34 ). In contrast to related η2(C,O) ketene complexes of vanadium11,12 and nickel,10 the M-O distance of 8aZ is longer than the M-C separation indicating a strengthened iron-carbon bond (Table 3). As discussed earlier, the Z configuraton at the (CdC)ketene double bond is unexpected. On the basis of merely steric arguments, this coordination mode should not be preferred. A (cp)2V(Me(Ph)CdCdO) compound does indeed show E configuration,12 as well as a unsymmetrically substituted niobium ketene system.14c Constructing the 8aE molecule by a simple static approach from the structural parameters of 8aZ results in a OMe‚‚‚Oketene distance of about 2.54 Å. Since this value lies significantly below the sum of the van der Waals radii of the oxygens, the E-configurated molecules are indeed exptected to face steric O‚‚‚O repulsions. Suitable crystals for the X-ray diffraction study of 9b were obtained by slow cooling of a hexane solution to -30 °C. The crystal, structure solution, and refinement data are given in Table 1. 9b shows pseudo-octahedral coordination at the iron center (Figure 4), so that it seems plausible to attribute it a +II oxidation state. By doing so, one has to assign the (methoxycarbonyl)ketene moiety a two minus charge. Thus, in comparison (34) Christiansen, J. J.; Bak, B.; Kunstmann, K.; Nygaard, L.; Rastrup-Andersen, J. J. Chem. Phys. 1966, 45, 883.

Fe(1)-C(1) Fe(1)-C(2) Fe(1)-C(3) Fe(1)-O(4) Fe(1)-P(1) Fe(1)-P(2) C(1)-Fe(1)-C(2) C(1)-Fe(1)-C(3) C(2)-Fe(1)-C(3) C(1)-Fe(1)-O(4) C(2)-Fe(1)-O(4) C(3)-Fe(1)-O(4) P(1)-Fe(1)-P(2) Fe(1)-C(1)-O(1)

1.823(8) 1.730(8) 2.038(7) 2.019(5) 2.263(2) 2.263(2) 94.4(4) 172.0(3) 93.6(3) 89.1(3) 176.4(3) 82.9(2) 172.94(9) 177.7(8)

C(1)-O(1) C(2)-O(2) C(3)-O(3) C(3)-C(4) C(4)-C(5) C(5)-O(4) Fe(1)-C(2)-O(2) Fe(1)-C(3)-O(3) Fe(1)-C(3)-C(4) O(3)-C(3)-C(4) C(3)-C(4)-C(5) C(4)-C(5)-O(4) Fe(1)-O(4)-C(5)

1.145(9) 1.154(8) 1.214(8) 1.445(9) 1.343(10) 1.284(8) 178.9(8) 127.3(5) 107.8(5) 124.8(6) 115.3(6) 123.7(7) 110.2(4)

to 8, species 9 contain reduced organic residues. Like in the structure of 7a, the iron atom of 9b is part of a planar five-membered ring system. The η2(C,O) coordination of the (methoxycarbonyl)ketene is accomplished via O(4) and C(3), which belong to the ester and the ketene group, respectively. The Fe-C distance of 9b is however about 0.1 Å longer than in 8aZ and lies in the range of M-Cacyl distances33 (Table 4). The C(3)C(4) and C(4)-C(5) distances compare well with those of the structure of 7a and other similar structural units reported in the literature.35 Halomethyl complexes such as 14a,b have only rarely been structurally characterized due to the generally not too high stability of this class of compound.36 However, 14a appeared to be quite stable and could therefore be subjected to an X-ray diffraction study. The crystal, structure solution, and refinement data of 14a are given in Table 1. Figure 5 shows a pseudo-octahedrally coordinated complex with the PEt3 groups in trans position and the two cis CO, the Cl, and the CH2Cl ligands in an equatorial plane. The structural parameters around the iron center (Table 5) are found within the expected range.33 The Fe(1)-C(3) and the C(3)Cl(2) distances do not show unusual features. However, C(3) displays a significant deviation from tetrahedral geometry, since the Fe(1)-C(3)-Cl(2) angle is widened to almost 120°. (35) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1. (36) Friedrich, H. B.; Moss J. R. Adv. Organomet. Chem. 1991, 33, 235.

968 Organometallics, Vol. 17, No. 5, 1998

Kandler et al.

Figure 5. Structure of 14a. Thermal ellipsoids are drawn at the 50% probability level. Table 5. Selected Bond Distances (Å) and Angles (deg) of Complex 14a Fe(1)-C(1) Fe(1)-C(2) Fe(1)-C(3) Fe(1)-P(1) Fe(1)-P(2) Fe(1)-Cl(1) Cl(2)-C(3)

1.744(6) 1.811(7) 2.048(6) 2.2913(17) 2.2919(17) 2.3447(17) 1.824(6)

C(3)-Fe(1)-P(1) C(1)-Fe(1)-P(2) C(2)-Fe(1)-P(2) C(3)-Fe(1)-P(2) P(1)-Fe(1)-P(2) C(1)-Fe(1)-Cl(1) C(2)-Fe(1)-Cl(1)

90.00(17) 88.6(2) 91.3(2) 88.34(17) 178.10(6) 176.5(2) 88.2(2)

C(1)-O(1) C(2)-O(2) C(1)-Fe(1)-C(2) C(1)-Fe(1)-C(3) C(2)-Fe(1)-C(3) C(1)-Fe(1)-P(1) C(2)-Fe(1)-P(1) C(3)-Fe(1)-Cl(1) P(1)-Fe(1)-Cl(1) P(2)-Fe(1)-Cl(1) O(1)-C(1)-Fe(1) O(2)-C(2)-Fe(1) Cl(2)-C(3)-Fe(1)

1.146(7) 1.113(8) 95.1(3) 91.8(3) 173.1(2) 90.5(2) 90.4(2) 84.93(16) 88.28(7) 92.49(7) 179.3(6) 177.7(6) 119.7(3)

Experimental Section General Data. All preparations were carried out under an atmosphere of nitrogen by conventional Schlenk techniques.37 Diethyl ether was dried with 4 Å molecular sieves.38 All other solvents used in the preparations were dried by standard methods.39 Chromatographic separations were performed on 2 × 20 cm columns of silica gel 60 (40-63 µm) cooled to -20 °C. IR spectra were recorded on a Bio-Rad FTS-45 instrument. Mass spectra (EI) were run on a Finnigan MAT 8400 mass spectrometer. 1H and 13C NMR spectra were taken on a Varian Gemini-200 instrument operating at 200 and 50.3 MHz, respectively [δ (ppm) relative to TMS, J (Hz)], and 31P NMR spectra on a Varian-Gemini 300 at 121.5 MHz. The phosphorus chemical shifts [δ (ppm)] are reported referenced to 85% H3PO4 as an external standard. Materials. A 1.5 mol/L cyclohexane solution of lithium diisopropylamide, methyl chloroacetate, methyl bromoacetate, ethyl iodoacetate, 2-(bromomethyl)-1,3-dioxalane, 3-(bromomethyl)-2,4,10-trioxaadamantane, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were used as received from commercial suppliers. Trimethylchlorosilane was distilled before use. Fe(CO)2(PEt3)2Br2 and I2 were prepared by following a literature (37) Shriver, D. F. The Manipulations of Air-sensitive Compounds; McGraw-Hill: New York, 1969. (38) Nautrup, E. P. Standardmethoden der Praktischen Chemie; Vieweg & Sohn: Braunschweig, Germany, 1963. (39) (a) Becker, H. G. O.; Berger, W.; Organikum, 15th ed.; VEB Deutscher Verlag der Wissenschaften: Berlin, 1984. (b) Tietze, L.-F.; Eicher, T. Reaktionen und Synthesen im organisch-chemischen Praktikum; Georg Thieme Verlag: Stuttgart, New York, 1981.

procedure,40 and HC(SiMe3)dCdO was obtained according to ref 41 . 15a,b were prepared according to ref 28. Preparation of Dicarbonylhalo((alkoxycarbonyl)methyl)bis(triethylphosphane)iron, Fe(CO)2(PEt3)2(X)(CH2COOR) (X ) Cl, R ) Me, 2a; X ) Br, R ) Me, 2b; X ) I, R ) Et, 2c). A mixture of 1.20 g (2.0 mmol) of Fe(CO)2(PEt3)2I2 in 250 mL of ether was stirred with sodium amalgam (e1%, ca. 15 mmol of Na) at -25 °C under 1 atm of N2. After 3 h the supernatant suspension was transferred to a frit via a canula. Cold filtration through Celite and reaction of the thus obtained yellow solution of the dinitrogen iron complexes 1a,b with an excess of the corresponding haloacetic acid ester yielded the thermally stable complexes 2a-c. 2a: 0.43 g (4.0 mmol) of methyl chloroacetate. Column chromatography and elution with hexane/ether from 8:1 to 2:1 (bright yellow fraction). Yield: 0.51 g (55%). Anal. Calcd for C17H35ClFeO4P2: C, 44.71; H, 7.72; Fe, 12.23. Found: C, 44.69; H, 8.00; Fe, 12.64. IR (hexane): ν (cm-1) ) 2004, 1944 (s, CtO), 1703 (w, br, CdO). 1H NMR (C6D6): δ ) 0.95 (dt, 3JHH ) 7.5, 3JPH ) 14.5, P(CH2CH3)3), 1.88-2.03 (m, P(CH2CH3)3), 2.51(t, 3JPH ) 9.6, CH2COOCH3), 3.56 (s, OCH3). 13C NMR (C6D6): δ ) 7.5 (s, P(CH2CH3)3), 16.1 (t, 2JPC ) 15, CH2COOCH3), 16.9 (pseudo-t, Jvirt ) 12 P(CH2CH3)3), 49.5 (s, OCH3), 182.9 (s, COOCH3), 211.2 (t, 2JPC ) 21, CtO), 216.8 (t, 2JPC ) 25, CtO). 31P NMR (C6D6): δ ) 35.0. MS (EI, 70 eV): m/z (%) ) 428 [M+• - CO], 400 [M+• - 2CO], 327 (100) [Fe(PEt3)2Cl]+, 292 [Fe(PEt3)2]+, 209 [Fe(PEt3)Cl]+, 146, 118 [PEt3]+, 103, 90, 62. 2b: 0.61 g (4.0 mmol) of methyl bromoacetate. Column chromatography and elution with hexane/ether from 10:1 to 4:1 (orange brown fraction). Yield: 0.69 g (69%). Anal. Calcd for C17H35BrFeO4P2: C, 40.74; H, 7.04; Fe, 11.14. Found: C, 40.63; H, 7.06; Fe, 11.13. IR (hexane): ν (cm-1) ) 2003, 1944 (s, CtO), 1703 (w, br, CdO). 1H NMR (C6D6): δ ) 0.96 (dt, 3J 3 HH ) 7.6, JPH ) 14.4, P(CH2CH3)3), 1.94-2.09 (m, P(CH2CH3)3), 2.60 (t, 3JPH ) 9.8, CH2COOCH3), 3.58 (s, OCH3). 13C NMR (C6D6): δ ) 8.1 (s, P(CH2CH3)3), 13.6 (t, 2JPC ) 14, CH2COOCH3), 18.0 (pseudo-t, Jvirt ) 12, P(CH2CH3)3), 49.7 (s, OCH3), 182.9 (s, COOCH3), 211.1 (t, 2JPC ) 20, CtO), 217.8 (t, 2JPC ) 25, CtO). 31P NMR (C6D6): δ ) 32.8. MS (EI, 70 eV): m/z (%) ) 474 [M+• - CO], 446 [M+• - 2CO], 373 (100) [Fe(PEt3)2Br]+, 292 [Fe(PEt3)2]+, 255 [Fe(PEt3)Br]+, 175, 146, 118 [PEt3]+, 103, 90, 75, 74, 62. 2c: 0.86 g (4.0 mmol) of ethyl iodoacetate. Column chromatography and elution with hexane/ether from 10:1 to 4:1 (dark red fraction). Yield: 0.86 g (76%). Anal. Calcd for C18H37FeIO4P2: C, 38.46; H, 6.63; Fe, 9.93. Found: C, 38.76; H, 6.54; Fe, 10.27. IR (hexane): ν (cm-1) ) 1999, 1943 (s, CtO), 1689 (m, CdO). 1H NMR (C6D6): δ ) 0.95 (dt, 3JHH ) 7.6, 3JPH ) 14.8, P(CH2CH3)3), 1.08 (t, 3JHH ) 7.1, OCH2CH3), 1.97-2.18 (m, P(CH2CH3)3), 2.61 (t, 3JPH ) 9.9, CH2COOEt), 4.16 (q, 3JHH ) 7.1, OCH2CH3). 13C NMR (C6D6): δ ) 8.2 (s, P(CH2CH3)3), 8.4 (t, 2JPC ) 14, CH2COOEt), 14.4 (s, OCH2CH3), 19.1 (pseudo-t, Jvirt ) 12, P(CH2CH3)3), 58.4 (s, OCH2CH3), 183.5 (s, COOEt), 212.6 (t, 2JPC ) 20, CtO), 219.5 (t, 2JPC ) 25, CtO). 31P NMR (C6D6): δ ) 29.8. MS (EI, 70 eV): m/z (%) ) 562 (