An Efficient, Modular Route to New 2-Acyl-6-aminopentafulvenes

Organometallics 2009, 28, 5575–5586 DOI: 10.1021/om900549c

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An Efficient, Modular Route to New 2-Acyl-6-aminopentafulvenes and Planar-Chiral [N,O]-Functionalized Pentamethylruthenocenes Barbara Enk,† Holger Kopacka,† Klaus Wurst,† Thomas M€ uller,‡ and Benno Bildstein*,† †

Institute of General, Inorganic and Theoretical Chemistry, Faculty of Chemistry and Pharmacy, University of Innsbruck, Innrain 52a, 6020 Innsbruck, Austria, and ‡Institute of Organic Chemistry, Faculty of Chemistry and Pharmacy, University of Innsbruck, Innrain 52a, 6020 Innsbruck, Austria Received June 25, 2009

A modular, one-pot synthetic protocol was developed for new pentafulvenes containing hydrogenbridged amino and carbonyl substituents. Starting from sodium cyclopentadienide, first an acyl functionality is introduced by reaction with various carboxylic esters, followed by regioselective iminoacylation with differently substituted imidoyl chlorides, giving access to a first family of 10 different 2-acyl-6-aminopentafulvenes. After deprotonation, these new ambidentate [N,O]H ligands react with early/hard transition metal synthons to give seven-membered metal-chelate κ2-complexes, or with electron-rich late transition metal synthons, e.g., pentamethylruthenium(II) hexafluorophosphate, to give planar-chiral, functionalized η5-sandwich complexes. A second family of 1-acyl-2imidoylpentamethylruthenocenes is thereby easily accessible as new ruthenocene [N,O]-metalloligands and for further use as planar-chiral synthons. Chemoselective and diastereoselective reduction of the acyl functionality gives imino(pentamethyl)ruthenocene alcohols as a third family of [N,O]H-metalloligands. For one case it is shown that such imino(pentamethyl)ruthenocene alcohols react with oxophilic Zr(IV) under ring closure to a novel pentamethylruthenoceneannelated 2H-pyrrolium salt. All new compounds were fully characterized by spectroscopic methods, and 22 single-crystal X-ray analyses are reported.

Introduction In organometallic chemistry, functionalized pentafulvenes are very useful precursors for η5-Cp early to late transition metal complexes that are inaccessible by common methodology.1 *Corresponding author. E-mail: [email protected]. (1) Recent reviews: (a) Erker, G.; Kehr, G.; Fr€ ohlich, R. Organometallics 2008, 27, 3–14. (b) Erker, G. Coord. Chem. Rev. 2006, 250, 1056– 1070. (2) (a) Linn, W. J.; Sharkey, W. H. J. Am. Chem. Soc. 1957, 79, 4970– 4972. (b) Little, W. F.; Koestler, R. C. J. Org. Chem. 1961, 26, 3245–3247. (c) Hafner, K.; H€afner, K. H.; K€onig, C.; Kreuder, M.; Ploss, G.; Schulz, G.; Sturm, E.; V€ opel, K. H. Angew. Chem. 1963, 75, 35–46. (d) Hafner, K.; Schulz, G.; Wagner, K. Justus Liebigs Ann. Chem. 1964, 678, 39–53. (e) Hartke, K.; Kohl, A.; K€ampchen, T. Chem. Ber. 1983, 116, 2653–2667. (f) Dong, Y.-B.; Geng, Y.; Ma, J.-P.; Huang, R.-Q. Organometallics 2006, 25, 447–462. (g) Li, J.; Ma, J.-P.; Liu, F.; Wu, X.-W.; Dong, Y.-B.; Huang, R.-Q. Organometallics 2008, 27, 5446–5452. (3) (a) Klass, K.; Duda, L.; Kleigrewe, N.; Erker, G.; Fr€ ohlich, R.; Wegelius, E. Eur. J. Inorg. Chem. 1999, 11–19. (b) Klass, K.; Fr€ohlich, R.; Erker, G. J. Chem. Soc., Dalton Trans. 1999, 4457–4461. opel, K. H.; Ploss, G.; K€ onig, C. Justus Liebigs (4) (a) Hafner, K.; V€ Ann. Chem. 1963, 661, 52. (b) Hafner, K.; V€opel, K. H.; Ploss, G.; K€onig, C. Org. Synth. 1967, 47, 52. (c) M€uller-Westerhoff, U. J. Am. Chem. Soc. 1970, 92, 4849–4855. (d) Ammon, H. L.; Mueller-Westerhoff, U. Tetrahedron 1973, 30, 1437–1443. (e) Etkin, N.; Ong, C. M.; Stephan, D. W. Organometallics 1998, 17, 3656–3660. (f) Claramunt, R. M.; Sanz, D.; Alarcon, S. H.; Torralba, M. P.; Elguero, J.; Foces-Foces, C.; Pietrzak, M.; Langer, U.; Limbach, H.-H. Angew. Chem., Int. Ed. 2001, 40, 420–423. (g) Sanz, D.; Perez-Torralba, M.; Alarcon, S. H.; Claramunt, R. M.; Foces-Foces, C.; Elguero, J. J. Org. Chem. 2002, 67, 1462–1471. (h) Perrin, C. L.; Ohta, B. K. J. Mol. Struct. 2003, 644, 1–12. (i) Del Amo, J. M. L.; Langer, U.; Torres, V.; Buntkowsky, G.; Vieth, H.-M.; Perez-Torralba, M.; Sanz, D.; Claramunt, R. M.; Elguero, J.; Limbach, H.-H. J. Am. Chem. Soc. 2008, 130, 8620–8632. r 2009 American Chemical Society

Due to the importance of donor-functionalized sandwich complexes in catalytic, supramolecular, sensoric/electrochemical, and biological applications; there is an ongoing interest in new complexes of this type. Whereas pentafulvenes containing one functional group are quite numerous, there are only very few doubly functionalized representatives known, including 2-acyl6-hydroxyfulvenes2 A, related 2-carbamoyl-6-amino-6-hydroxyfulvenes3 A, and 2-imidoyl-6-aminofulvenes4 B (Scheme 1). From an organometallic chemist’s point of view, these systems are interesting ambidentate ligands that may be considered as either “fulvenologous” β-dicarbonyl compounds or β-diimines, respectively, or as 1,2-disubstituted cyclopentadiene equivalents. In the first case, κ2-[O,O]/[N,N] metal complexes D and E are formed with hard, early transition metal electrophiles,3a,4e,5 whereas in the second case η5-[1,2-difunctionalized] metallocenes G and H are accessible with soft, electron-rich late transition metal electrophiles.5c,6 Ligands A are of course related to the ubiquitous β-diketonato chelating ligands,7 but in contrast they form seven-membered instead of six-membered metal chelates D; (5) (a) Calucci, L.; Englert, U.; Pampaloni, G.; Pinzino, C.; Volpe, M. J. Organomet. Chem. 2005, 690, 4844–4855. (b) Calucci, L.; Cloke, F. G. N.; Englert, U.; Hitchcock, P. B.; Pampaloni, G.; Pinzino, C.; Puccini, F.; Volpe, M. Dalton Trans. 2006, 4228–4234. (c) Bailey, P. J.; Melchionna, M.; Parsons, S. Organometallics 2007, 26, 128–135. (6) (a) Wallace, C. E.; Selegue, J. P.; Carillo, A. Organometallics 1998, 17, 3390–3393. (b) Snyder, C. A.; Selegue, J. P.; Tice, N. C.; Wallace, C. E.; Blankenbuehler, M. T.; Parkin, S.; Allen, K. D. E.; Beck, R. T. J. Am. Chem. Soc. 2005, 127, 15010–15011. (7) Mehrotra, R. C.; Bohra, R.; Gaur, D. P. Metal β-Diketonates and Allied Derivatives; Academic Press: New York, 1978. Published on Web 09/02/2009

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Scheme 1. Doubly Functionalized Pentafulvenes and Their K2/η5-Complexes

therefore they might be considered “γ-diketonato” ligands where the conjugation between the two oxygen donors is mediated by the cross-conjugated pentafulvene. Similarly, ligands B are related to β-diketiminato ligands8 and may be termed “γ-diketiminato” ligands; the additional N-substituents in comparison to A make them very useful spectator ligands with tunable steric demands. On the other hand, compounds A and B are convenient precursors of metallocenes G and H; these are interesting 1,2-difunctionalized metallocenes, which themselves either are new [O,O]/[N,N]ligands or may be used as functionalized, redox-responsive metallocene synthons in organometallic synthesis. In this contribution, we report on the synthesis, structure, and reactivity of novel 2-imidoyl-6-hydroxyfulvenes C. Conceptually, we follow a ligand-oriented catalyst design principle with a modular synthetic approach that allows stereoelectronic tuning of the catalytic performance of their κ2/η5-complexes F and I. These new ligand systems C may be considered “γ-enaminoketonato” ligands, resembling the well-known β-enaminoketonato ligands9 that are successful (salicylaldimine) ligand frameworks of highly active early10 and late11 transition metal olefin polymerization catalysts. In contrast to β-enaminoketonato ligands, they form seven-membered metal chelates F, and due to their ambidenticity they are also able to form 1-acyl-2-imidoyl-metallocenes I. In their steric bulk, [N,O] ligands C are intermediate between symmetric [O,O]/[N,N] ligands A and B, but due to their unequal donor sites, they allow access to planar-chiral (8) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002, 102, 3031–3065. (9) (a) Holm, R. H.; Everett, G. W.; Charavorty, A. Prog. Inorg. Chem. 1966, 7, 83–214. (b) Calligaris, M.; Randiccio, L. Comprehensive Coordination Chemistry; Wilkinson, G.; Gillard, R. D.; McCleverty, J. A., Eds.; Pergamon: Oxford, U.K., 1987; Vol. 2, p 20.1. (10) Reviews: (a) Matsugi, T.; Fujita, T. Chem. Soc. Rev. 2008, 37, 1264–1277. (b) Sakuma, A.; Weiser, M.-S.; Fujita, T. Polym. J. 2007, 39, 193–207. (c) Nakayama, Y.; Saito, J.; Bando, H.; Fujita, T. Chem.;Eur. J. 2006, 12, 7546–7556. (d) Furuyama, R.; Saito, J.; Ishii, S.; Makio, H.; Mitani, M.; Tanaka, H.; Fujita, T. J. Organomet. Chem. 2005, 690, 4398–4413. (e) Makio, H.; Kashiwa, N.; Fujita, T. Adv. Synth. Catal. 2002, 344, 477–493. (11) (a) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Waltman, A. W.; Grubbs, R. H. Chem. Commun. 2003, 2272–2272. (b) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460–462. (c) Wang, C. M.; Friedrich, S. K.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149–3151.

metallocenes I, in contrast to achiral metallocenes G and H. The carbonyl functional group in metallocenes I may be modified by common carbonyl reactions, e.g., condensations; thereby compounds of type I serve as an entry into novel tri- and tetradentate planar-chiral metallocene ligands.

Results and Discussion Synthesis of 2-Acyl-6-aminopentafulvenes. An efficient modular protocol for the synthesis of 2-acyl-6-aminopentafulvenes was developed (Scheme 2): The first step consists in a selective monosubstitution of cyclopentadienide with carboxylic acid esters based on earlier work by Rausch.12 The conversion to the intermediate acylcyclopentadienide salts is complete after 24-48 h; they may be isolated and prepared on a large scale, offering the possibility of a combinatorial ligand library synthesis. If desired, NMR spectroscopy under exclusion of air is useful to check the completeness of the reaction and the purity of the intermediates. Note that only carboxylic esters as poor electrophiles give monosubstituted cyclopentadienides, and stronger electrophiles like acid halides form disubstituted 2-acyl-6-hydroxyfulvenes2 A (Scheme 1). This first step of the synthesis is of wide scope; almost any acyl group 1R-C(O) [(1R = H, CH3, C6H5, CF3)] can be attached to the cyclopentadienide moiety in this manner. Unexpectedly, with methyl pentafluorobenzoate as ester substrate none of the desired pentafluorobenzoylcyclopentadienide is obtained, instead a 1,3-bis-arylated cyclopentadiene containing two methyl para-tetrafluorobenzoate substituents is formed by a nucleophilic aromatic substitution,13 in analogy with the reaction of cyclopentadienide with hexafluorobenzene.14 (12) (a) Hart, W. P.; Macomber, D. W.; Rausch, M. D. J. Am. Chem. Soc. 1980, 102, 1196–1198. (b) Grundke, G.; Hoffmann, H. M. R. J. Org. Chem. 1981, 46, 5428–5431. (c) Rogers, R. D.; Atwood, J. L. J. Organomet. Chem. 1982, 238, 79–85. (d) Hart, W. P.; Shihua, D.; Rausch, M. D. J. Organomet. Chem. 1985, 282, 111–121. (e) Bildstein, B.; Hradsky, A.; Kopacka, H.; Malleier, R.; Ongania, K.-H. J. Organomet. Chem. 1997, 540, 127–145. (f) Bitterwolf, T. E.; Gallagher, S.; Rheingold, A. L.; Yap, G. P. A. J. Organomet. Chem. 1997, 545-546, 27–33. (g) Norinder, J.; Cotton, H. K.; B€ackvall, J.-E. J. Org. Chem. 2002, 67, 9096–9098. (13) Enk, B.; Bildstein, B.; Wurst, K. 2009, submitted. (14) (a) Deck, P. A.; Jackson, W. F. Organometallics 1996, 15, 5287– 5291. (b) Thornberry, M. P.; Slebodnick, C.; Deck, P. A. Organometallics 2000, 19, 5352–5369.

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Scheme 2. Modular One-Pot Synthesis of 2-Acyl-6-aminopentafulvenes

In the second step, the imino functionality is attached by reaction of the intermediate acylcyclopentadienide salts with imidoyl chloride reagents. This electrophilic substitution occurs in a regioselective manner due to the formation of a N-H-O hydrogen bond in the final product, analogous to that in the cases of 2-acyl-6-hydroxyfulvenes,2 2-carbamoyl6-amino-6-hydroxyfulvenes,3 and 2-imidoyl-6-aminofulvenes.4 Imidoyl chlorides with N-aryl substituents are conveniently accessible in a wide range of substitution patterns by either dehydration and chlorination of amides with thionyl chloride15 or a one-pot reaction between trifluoroacetic acid, (substituted) aniline, and carbon tetrachloride in the presence of triethylamine and triphenylphosphine.16 In general, these imidoyl chlorides are very versatile electrophilic reagents for the introduction of sterically bulky (e.g., 2,6-disubstituted N-aryl groups) and acceptor-substituted (e.g., 2,6-dihalogenated N-aryl groups and trifluoroacetimidoyl groups) imino substituents. This makes them valuable tools in ligand-oriented catalyst research, because their tunable steric bulk and electron-withdrawing power allows optimization of the selectivity and activity of metal catalysts with ligands containing N-aryl-imino groups derived from these reagents. It is interesting to note that almost all successful non-metallocene olefin polymerization catalysts contain such bulky N-aryl groups and that the most active catalysts are usually those with electronegative fluoro substituents.17 In terms of modular synthesis, 40 different 2-acyl-6-aminopentafulvenes are in principle accessible by combination of the building blocks shown in Scheme 2. However, only 10 selected representatives were actually realized, clearly proving the versatility of this synthetic protocol. Practically, these 2-acyl-6-aminopentafulvenes are obtained in 7.9-45.4% isolated yield, dependent on the electrophilicity and steric hindrance of the acyl (step 1) and imidoyl (step 2) reagents. For example, the highest yields (9: 45.4%; 6: 31.1%) are obtained with methyl trifluoroacetate as the most electrophilic ester in step 1 and with imidoyl chlorides of ordinary steric bulk in step 2, whereas the lowest yield (8: 7.9%) is (15) (a) Boere, R. T.; Klassen, V.; Wolmersh€auser, G. J. Chem. Soc., Dalton Trans. 1998, 4147–4154. (b) Krajete, A.; Steiner, G.; Kopacka, H.; Ongania, K.-H.; Wurst, K.; Kristen, M. O.; Preishuber-Pfl€ugl, P.; Bildstein, B. Eur. J. Inorg. Chem. 2004, 1740–1752. (16) Tamura, K.; Mizukami, H.; Maeda, K.; Watanabe, H.; Uneyama, K. J. Org. Chem. 1993, 58, 32–35. (17) Review: Gibson, V. C.; Marshall, E. L. Metal Complexes as Catalysts for Polymerization Reactions. In Comprehensive Coordination Chemistry II; Elsevier: Amsterdam, 2004; Vol. 9, pp 1-74.

observed with low-electrophilic and very bulky reagents. Physically, 2-acyl-6-aminopentafulvenes 1-10 are airstable, yellow materials with a high tendency to crystallize, an advantageous feature in their purification and structural proof by single-crystal structure analysis. Structure of 2-Acyl-6-aminopentafulvenes. All 2-acyl-6aminopentafulvenes 1-10 exist exclusively in their N-H-O hydrogen-bridged ketoenamine form without any equilibrium between the two formal tautomers C depicted in Scheme 1, as expected and in analogy to β-enaminoketonato ligands.9 Well-resolved NMR spectra (compare experimental part) allow an unambiguous structural assignment in solution: the enamineketone functionality is most clearly evidenced by observation of characteristic carbonyl signals in the 13C NMR spectra (1-10: δCdO=173.0-194.7 ppm) and by detection of the intramolecular hydrogen bond as a sharp signal at low field in the 1H NMR spectra (1-10: δN-H-OdC = 14.38-15.46 ppm). Besides these diagnostic signals, in favorable cases all scalar couplings of all hydrogens can be inferred from two-dimensional NMR measurements (Figure 1). Due to the ketoenamine functional group, one would expect a prominent carbonyl stretching vibration νCdO in the range 1550-1630 cm-1 in the IR spectra of 1-10. However, the rather strong, overlapping carbon-carbon stretching vibrations νCdC of the cross-conjugated pentafulvene are comparable in intensity and hamper therefore a clear assignment. Furthermore, high-resolution mass spectrometry of 1-10 confirms their identity by an excellent agreement of experimental and calculated values of their molecular ions. As mentioned above, these 2-acyl-6-aminopentafulvenes crystallize very readily, and therefore single-crystal structures are available for all of them (Supporting Information). Figure 2 shows the molecular structure of 1 as a selected example. Overall, the structure of 1 is a planar, fully conjugated 2-acyl-6-aminopentafulvene molecule with an intramolecular N-H-O hydrogen bond between the acyl oxygen atom and the amino group. The carbon-carbon distances in the pentafulvene subunit are all normal, nonaveraged, and alternating, clearly showing that the exocyclic fulvene double bond is at the amino side of the molecule, whereas the acyl group is a true carbonyl functionality attached by a single bond. This is in contrast to the situation in the symmetrical [O,O]/[N,N] ligand systems 2-acyl-6-hydroxyfulvenes18 A, related 2-carbamoyl-6-amino-6-hydroxyfulvenes3 A, and 2-imidoyl-6-aminofulvenes4 B (Scheme 1), where an (18) Enk, B.; Bildstein, B.; Wurst, K. Z. Kristallogr. NCS 2009, in press.

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Figure 1. H/H-COSY of 4.

Figure 2. Molecular structure of 1.

equilibrium between both tautomers gives rise to averaged carbon-carbon distances of formally 1.5 doubly bonded carbon atoms. As can be seen from inspection of Figure 2, the N-aryl substituent of 1 is roughly orthogonal to the plane of the 2-acyl-6-aminopentafulvene, due to steric hindrance by the 2,6-methyl groups of the N-aryl substituent. Similarly, the phenyl substituent at the exocyclic fulvene carbon is tilted as well with respect to the plane of the 2-acyl-6-aminopentafulvene. Comparable structural properties are observed in the molecular structures of the other representatives 2-10 (Supporting Information). Synthesis of 1-Acyl-2-imidoylpentamethylruthenocenes. 2-Acyl-6-aminopentafulvenes 1-10 are ambidentate [N,O]H ligands that form either κ2 or η5 complexes, depending on the hard/soft character of the metal electrophile. In this contribution, we focus on the use of 1-10 as precursors of functionalized

cyclopentadienides and their reaction with electron-rich ruthenium centers, whereas the coordination chemistry of 1-10 with hard zirconium(IV) metal electrophiles will be published elsewhere.19 According to pioneering work by Selegue6 and recent work by Bailey,5c 2-acyl-6-hydroxyfulvenes A (Scheme 1) and 2-imidoyl-6-aminofulvenes B (Scheme 1) can be converted with suitable pentamethylruthenium(II) synthons to symmetrically 1,2-disubstituted ruthenocenes G and H (Scheme 1). As has been noted by Selegue,6a 1,2-diacylcyclopentadienides are acceptor-substituted cyclopentadienide synthons that give stable η5-sandwich complexes only if the second Cp ligand, e.g., Cp*, is able to compensate for the loss of electron density and if the transition metal allows effective Cp-metal bonding, e.g., Ru(II). Inspired by this work, 2-acyl-6-aminopentafulvenes 1-10 were tested as possible candidates for novel, unsymmetrically functionalized metallocenes (Scheme 3). The synthetic sequence involves first deprotonation of [N,O]H ligands 1-10 by potassium hydride, in contrast to Selegue’s6 work, where poisonous thallous ethoxide was applied. Although rarely used, potassium hydride is a convenient, non-nucleophilic, selective base in coordination/organometallic chemistry: complete deprotonation at ambient temperature is easily achieved in the presence of an excess of potassium hydride. After evolution of dihydrogen has ceased, the insoluble excess of KH can simply be removed by filtration. In addition, in comparison to the principally used lithium compounds, potassium salts of ligands usually give superior results in their transmetalation reactions with transition metal halides due to the lower solubility product and better separation of potassium halides.8,20 As detailed in (19) Enk, B.; Kopacka, H.; Severn, J.; Kokko, E.; Bildstein, B. To be submitted. (20) Pennington, D. A.; Harrington, R. W.; Clegg, W.; Bochmann, M.; Lancaster, S. J. J. Organomet. Chem. 2006, 691, 3183–3188.

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Scheme 3. Synthesis of 1-Acyl-2-imidoylpentamethylruthenocenes

Scheme 3, the resulting intermediate [N,O]K compounds may be described as either κ2-complexes or η5-half-sandwich species, respectively. However, it is beyond question that the hard potassium cation will prefer a κ2-bonding mode and that the formal equilibrium and hapticity change κ2/η5 will lie far on the κ2 side. Nevertheless, the two η5-potassium formulas show clearly that a racemic mixture of planar-chiral21 half-sandwich complexes is possible due to the unequal substituents on the cyclopentadienide ring. Accordingly, a transmetalation reaction in the second step with Cp*Ru(CH3CN)3þPF6- as a convenient source of the electron-rich Cp*Ru(II)þ synthon affords racemic mixtures of 1-acyl-2-imidoylpentamethylruthenocenes 11-18, corresponding to attack from “bottom” or from “top” of the two enantiotopic faces of 1-acyl-2-imidoylcyclopentadienide. No attempts to separate the racemic mixtures 11-18 have been undertaken up to now. These novel racemic, planar-chiral 1-acyl-2-imidoylpentamethylruthenocenes 11-18 are obtained as yellow, air-stable compounds in isolated yields of 52.8-91.5%, dependent on the steric bulk of the substituents 1R, 2R, 3R of the starting materials 1-10. For example, the lowest yields are observed with the most bulky representatives (17: 52.8%, 12: 57.4%), whereas the highest yields are obtained for the less bulky specimens (18: 90.5%, 11: 91.5%). Ruthenocene complexes 11-18 have a very high tendency to crystallize, thereby simplifying their purification and isolation, (21) (a) Schl€ ogl, K. Top. Stereochem. 1967, 1, 39–89. (b) Schl€ogl, K. Pure Appl. Chem. 1970, 23, 413–432. (c) Schl€ogl, K. Top. Curr. Chem. 1984, 125, 27–62. (d) Schl€ogl, K. J. Organomet. Chem. 1986, 300, 219– 248. (e) Eliel, E. L.; Wilen, S. H.; Mander, L. N. Stereochemistry of Organic Compounds; John Wiley & Sons, Inc.: New York, 1994; Chapter 14, p 1119.

similarly to that for the starting ligands 1-10. The ruthenocenes derived from ligands 7 and 9 are not included in this work, because up to now only inseparable mixtures of the trifluoroacetyl-hydrated and nonhydrated form were obtained. On the side and in line with Selegue’s observation6a we note that analogous 1-acyl-2-imidoylpentamethylferrocenes are inaccessible by using an in situ generated Cp*Feþ synthon12e instead of Cp*Ru(CH3CN)3þPF6-, suggesting that only the more electron-rich 4d or 5d transition metals are able to form such acceptor-substituted 1-acyl-2-imidoylpentamethylmetallocenes. Structure of 1-Acyl-2-imidoylpentamethylruthenocenes. In solution, the structure of ruthenocenes 11-18 is most clearly evidenced by characteristic low-field NMR signals for the acyl (13C: δCdO =181.1-198.8 ppm) and imidoyl (13C: δCd N = 165.2-168.4 ppm) functionalities and the strong resonances for the five magnetically equivalent methyl substituents of the Cp* moiety (1H: δCH3 = 1.89-1.96 ppm; 13C: δCH3=11.4-12.0 ppm). In addition, the expected signals and couplings of the other substituents are all observed in the well-resolved NMR spectra (vide infra, Experimental Section). In the IR spectra of 11-18, the assignment for the stretching vibrations of the carbonyl (νCdO = 17081736 cm-1) and imidoyl (νCdN = 1644-1676 cm-1) functionalities are in some cases difficult, due to overlapping νCdC vibrations of the aromatic and cyclopentadienide carbon frameworks of these metallocenes, similarly to the case of the fulvene precursors 1-10 (vide supra). For all ruthenocenes 11-18 the (protonated) molecular ions are detected in the positive mode FAB mass spectra. 1-Acyl-2-imidoylpentamethylruthenocenes 11-18 are well behaved in terms of their crystallization propensity;

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Enk et al. Scheme 4. Synthesis of 1-Hydroxyalkyl-2-imidoylpentamethylruthenocenes

Figure 3. Molecular structure of 12 (only one enantiomer shown).

for all representatives (except for 11) high-quality single crystals were obtained (Supporting Information). Figure 3 shows the molecular structure of 12 as a selected example. Overall, a regular pentamethylruthenocene with quite bulky 1,2-substituents is present. The N-aryl group with its 2,6methyl groups is roughly orthogonal to the imino-cyclopentadienyl plane, as expected. Similarly, the phenyl group at the imidoyl carbon and at the acyl carbon are tilted as well, due to steric hindrance. The structural properties of the other representatives 13-18 (Supporting Information) are more or less comparable, but the relative orientation of the acyl and the imidoyl groups is determined by the substitution pattern of the acyl carbon; they point either toward (12, 16) or against each other (13, 14, 15, 17, 18). Synthesis of 1-Hydroxyalkyl-2-imidoylpentamethylruthenocenes. Ruthenocenes 11-18 are functionalized metallocenes that may be considered as conjugated, neutral, chiral [N,O] ligands with a fused, planar-chiral pentamethylruthenocenyl group, in other words, planar-chiral [N,O] metalloligands. The coordination chemistry of 11-18 has not been investigated by us so far, because our interest is more focused on anionic chelate ligands, which are in general more useful in coordination chemistry due to their stronger bonding to cationic transition metal centers. To this end, the conversion of four representatives of 11-18 to new anionic [N,O]H ligand systems was investigated by a chemoselective and possibly stereoselective reductive alkylation. Nucleophilic attack of methyl and n-butyl carbanions at the acyl carbonyl atom afforded the desired [N,O]H metalloligands 19-22 (Scheme 4). The chemoselectivity of this reaction;reduction of the carbonyl group versus reduction of the imine;is caused by the higher electrophilicity of the acyl carbon in comparison to the imidoyl carbon and by the larger steric hindrance of the N-aryl imine functionality. Stereochemically, the prochiral carbonyl group with its two diastereotopic faces will give rise to two isomers, if the attacking carbanion 4R is different from the acyl substituent 1R, and the ratio of the two diasterioisomers will depend on the size and nucleophilicity of the attacking carbanion. Hence starting from racemic mixtures of planar-chiral 11-16 one has to deal with a maximum of four diastereoisomers or two pairs of enantiomers, respectively. In practice, we performed the reductive alkylation of 11-16 with carbanions equal to the

acyl substituents to avoid formation of diastereomeric mixtures (19, 21) and with carbanions unequal to the acyl substituents to evaluate the diastereoselectivity of this reaction (20, 22). Compounds 19-22 are obtained in 35-74% isolated yield as orange, air-stable materials, which have a high tendency to crystallize, similarly to the case of the starting ruthenocenes 11-18. On the side we note that metalloligands 19-22 are inaccessible by an inversed one-pot reaction sequence starting from 1-10: attempted reductive alkylation of a 2-acyl-6aminopentafulvene by 2 equiv of methyl lithium to an intermediate lithium imidoylpentafulvenoxide followed by transmetalation with Cp*Ru(CH3CN)3þPF6- failed; instead cyclization to an unexpected, novel pentamethylruthena-2H-pyrrolium salt was observed (vide infra). Structure of 1-Hydroxyalkyl-2-imidoylpentamethylruthenocenes. In solution, 19-22 exist as regular pentamethylruthenocenes (1H: δCH3 = 1.88-2.00 ppm; 13C: δCH3 = 12.0-12.5 ppm) with an intramolecular N-H-O hydrogen bond between the nitrogen of the imidoyl group and the hydroxyl group (1H: δN-H-O = 7.72-9.12 ppm; IR: νN-H-O = 3145-3227 cm-1; 13C: δCdN = 172.6-173.6 ppm; 13C: δC-OH=66.3-73.8 ppm). Besides these diagnostic signals, all other expected resonances and scalar couplings are observed in the well-resolved NMR spectra (vide infra, Experimental Section). Stereochemically, in the case of 19 and 21 (1R=4R, no central chirality at the hydroxyl carbon) racemic mixtures 19/21 of planar-chiral ruthenocenes are present. In principle, in the case of 20 and 22 (1R 6¼ 4R) four diastereoisomers are possible, but NMR analysis of 20 (1R= phenyl, 4R=n-butyl) shows that only a racemic mixture 20 of planar-chiral ruthenocenes is present, indicating 100% diastereoselectivity. Mechanistically, it is obvious that the

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carbanion will attack the prochiral carbonyl functionality preferentially from the less hindered side; therefore one can assume that in 20 the rather large n-butyl substituent will be on the opposite side of the bulky pentamethylruthenocenyl group. In contrast, for 22 (1R=trifluoromethyl, 4R=methyl) two sets of NMR signals in a ratio of 5:1 of a mixture of two enantiomeric pairs 22/220 are observed, indicating only 83% diasteroselective attack of the smaller methyl carbanion at the prochiral carbonyl group. These findings suggest that completely diastereoselective reductive alkylation of 1-acyl-2-imidoylpentamethylruthenocenes to 1-hydroxyalkyl-2-imidoylpentamethylruthenocenes is possible with the proper choice of starting materials and synthons. Solid-state structures of all four representatives 19-22 were obtained by X-ray diffraction. Figure 4 shows the molecular structure of 20 as a selected example. The overall structure of 20 is a regular pentamethylruthenocene with intramolecularly hydrogen-bridged 1-hydroxyalkyl and 2-imidoyl substituents, as expected and in accordance with

Figure 4. Molecular structure of 20 (only one enantiomer shown).

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NMR results. Due to steric hindrance, the N-aryl and the C-phenyl group of the imidoyl substituent are tilted with respect to the π-plane of the CdN double bond. The structural properties of the three other representatives 19, 21, and 22 are similar (Supporting Information). Whereas for 19-21 only one pair of enantiomers is present, a mixture of two pairs of enantiomers is found for 22: the methyl and trifluoromethyl groups at the hydroxyl carbon are disordered in a ratio of 5:1, consistent with the observation of two sets of signals in the solution NMR spectra. Synthesis and Properties of a Racemic Pentamethylruthenocene-Annelated Pyrrolium Salt. 1-Hydroxyalkyl-2-imidoylpentamethylruthenocenes 19-22 are potential heterotopic, bidentate, (racemic) planar-chiral κ2-[N,O] metalloligands that resemble the well-known β-enaminoketonato ligands.9 In a first test of their coordination ability with early transition metals, we addressed their zirconium(IV) complexes, motivated by Fujita’s successful (salicylaldiminato)2ZrCl2 precatalysts in olefin polymerization catalysis.10 Surprisingly, instead of the expected zirconium complex a pentamethylruthenocene-annelated pyrrolium salt is obtained (Scheme 5). In the first step, 19 is deprotonated by potassium hydride to afford a yellow solution of a racemic mixture of an intermediate κ2-potassium salt. On addition of zirconium tetrachloride, a sudden color change from yellow to deep red is observed, in contrast to the expected gradual color change from yellow to orange in a transmetalation reaction to a κ2/d0-zirconium complex. The intensive color of the product suggests major altering of the electron distribution, e.g., by formation of a new extended π-chromophore. Mechanistically, Zr(IV) seems to interact with the intermediate κ2-potassium salt by forming a shortlived intermediate [N,O]2ZrCl2 complex, which disaggregates under extrusion of dichlorozirconate [ZrO2Cl2]2- and under concomitant ring-contraction to an enantiomeric pair of the planar-chiral, pentamethylruthenocene-annelated pyrrolium cation 23 with hexachlorozirconate as counterion. Hence in this unusual reaction oxophilic Zr(IV) acts as an

Scheme 5. Synthesis of Racemic Pentamethylruthenocene-Annelated Pyrrolium Salt 23

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Figure 5. Molecular structure of 23.

efficient oxygen scavenger and the deep color of 23 is explainable by electron donation of the electron-rich pentamethylruthenocene to the conjugated iminium nitrogen of the pyrrolium heterocycle. The structure of 23 in solution is evident from observation of diagnostic signals of the pentamethylruthenocene moiety (1H: δCH3 = 1.86 ppm; 13C: δCH3 = 11.8 ppm) and the iminium functionality (13C: δCdNþ = 181 ppm) as well as the expected signals and scalar couplings of the aromatic hydrogens and carbons of the phenyl and metallocenyl groups. The cation of 23 is further corroborated by detection of its molecular ion by positive mode FAB mass spectrometry. In the solid-state structure of 23 (Figure 5) two planar-chiral, enantiomeric monocations are present with an octahedral hexachlorozirconate as their counterion. These two cations are symmetry-related to each other by an inversion center located at the zirconium of the hexachlorozirconate dianion. The overall structure of the two enantiomeric cations is a regular pentamethylruthenocene with an annelated, fully substituted, planar 2H-pyrrole heterocycle carrying the positive charge on the imminium nitrogen. The 2,6-dimethylphenyl substituent on the imminium nitrogen is roughly orthogonal to the pyrrolium plane due to steric hindrance, whereas the phenyl group on the carbon of the pyrrolium ring is less tilted. The unexpected result of this attempted formation of a zirconium complex of 19 suggests that early transition metal complexes of deprotonated 1-hydroxyalkyl-2-imidoylpentamethylruthenocenes 19-22 are unstable and inaccessible. However, [N,O] complexes of less oxophilic late transition metals, e.g., Ni(II) and Pd(II) complexes, should be feasible. Future work will show if such complexes can be synthesized and how they perform catalytically in comparison to structurally related β-enaminoketonato olefin polymerization precatalysts.10

Conclusions Ten new pentafulvenes containing hydrogen-bridged 2-acyl and 6-arylamino groups of various substitution patterns are conveniently accessible by a modular, one-pot synthetic protocol starting from sodium cyclopentadienide, carboxylic esters, and imidoyl chlorides. Structurally, these functionalized pentafulvenes exist only in their enamineketone tautomeric form, as shown by NMR and singlecrystal structure analyses. Chemically, these new ambidentate

[N,O]H ligands form either seven-membered κ2-[N,O]-complexes with hard metal centers or η5-sandwich complexes with electron-rich late transition metal centers. Reaction with pentamethylcyclopentadienylruthenium(II) hexafluorophosphate affords new pentamethylruthenocenes containing 1-acyl and 2-imidoyl functionalities. Stereochemically, due to the enantiotopic faces of the 1,2-disubstituted fulvene/ Cp precursor, racemic mixtures of planar-chiral 1,2-[N,O]pentamethylruthenocenes are obtained, as shown by NMR spectroscopy and X-ray diffraction. These compounds may be considered as new neutral [N,O]-metalloligands or may be used as new chiral metallocene synthons. Chemoselective as well as diastereoselective reductive alkylation at the acyl carbon affords new anionic [N,O]H metalloligands with sterically crowded coordination sites, as shown by singlecrystal structure analyses. On attempted formation of a Zr(IV) complex by reaction with ZrCl4, no isolable [N, O]2ZrCl2 complex is formed; instead a novel pentamethylruthenocene-annelated pyrrolium salt is obtained. Mechanistically, this unusual reaction seems to occur by capture of oxygen and concomitant ring contraction effected by the highly oxophilic Zr(IV) center. In future work we will address the κ2/η5-coordination chemistry of these new [N,O]-fulvenes and [N,O]-metalloligands, their use as planar-chiral synthons for the construction of higher denticity ligand systems, e.g., by condensation reactions of the acyl functionality with (chiral) aminoalcohols or diamines, and their catalytic and electrochemical properties. Furthermore, [N,O]-functionalized metallocenes of other electron-rich metals will be targeted.

Experimental Section General Considerations. All reactions and manipulations of air- and/or moisture-sensitive compounds were carried out in an atmosphere of dry argon using Schlenk techniques or in a conventional dinitrogen-filled glovebox (UNIlab mBraun). Solvents such as toluene, THF, diethyl ether, and n-hexane were dried over and distilled from Na under an argon atmosphere prior to use; dichloromethane was dried over Siccapent. All solvents and other reagents were commercially obtained and used as received unless stated otherwise. NMR spectra were recorded on a Bruker Avance DPX 300 (300 MHz) spectrometer, and 1H and 13C shifts are reported in ppm relative to Si(CH3)4 and were referred internally with respect to the protio solvent 13C resonances. IR spectra were recorded on a THERMO Nicolet 5700 ATR-FT-IR spectrometer, and melting points

Article were measured on a Leica Galen Kofler-microscope. Mass spectra were recorded on a Finnigan MAT 95 mass spectrometer, and single-crystal structure analysis was carried out on a Nonius Kappa CCD diffractometer. Representative Procedure for the Synthesis of 2-Acyl-6-aminopentafulvenes: 1-[5-[1-[N-(2,6-dimethylphenyl)amino]-1-phenylmethylene]cyclopenta-1,3-dien-1-yl]ethanone (1). Step 1: A Schlenk vessel was charged with 30 mL of tetrahydrofuran (THF) and 1 equiv of a 2.0 M solution of sodium cyclopentadienide in THF (8.0 mL, 16 mmol). After the mixture was cooled to -60 °C, a solution of 2 equiv of methyl acetate (2.6 mL, 32 mmol) in 20 mL of THF was added dropwise to the stirred mixture during a period of 30 min. The cooling bath was removed and the mixture was refluxed for 48 h, resulting in a brown solution. Volatile materials (THF, methanol, excess ester) were removed on a vacuum line, affording a tan-colored solid residue of sodium acetylcyclopentadienide. NMR spectroscopy under exclusion of air showed complete conversion to the desired intermediate. Step 2: First, a THF stock solution (c=20.50 g in 100 mL of THF) of N-2,6-dimethylphenylbenzimidoyl chloride was prepared from the corresponding benzamide and thionyl chloride following Boere’s procedure.15 Second, a Schlenk vessel was charged with 30 mL of THF, solid sodium acetylcyclopentadienide (16 mmol) from above, and 1 equiv of the imidoyl solution (16.5 mmol). The mixture was stirred at reflux temperature for 48 h, affording a brown-yellow solution. Workup: THF was removed on a vacuum line and the crude product was extracted into diethyl ether. The combined etheral layers were washed with water, saturated aqueous ammonium chloride solution, and saturated aqueous sodium chloride solution, and the organic phase was dried with anhydrous sodium sulfate. Volatile materials were removed on a rotary evaporator to afford the crude yellow product. After dissolution of the crude product in n-hexane the yellow solution was filtered through a short column of silica. Crystallization from n-hexane afforded yellow crystals of the pure product in 34.5% yield (1.740 g). 1H NMR (CDCl3): δ 2.26 (s, 6H, arylCH3), 2.71 (s, 3H, acetyl-CH3), 6.36 (d d, 1H, 3JH3-H4 =4.0 Hz, 3JH4-H5 =3.6 Hz, fulvene H4), 6.62 (d d, 1H, 3JH3-H4 = 4.0 Hz, 4JH3-H5=2.0 Hz, fulvene H3), 6.95-7.05 (m, 3H, aryl), 7.24-7.29 (m, 2H, aryl), 7.33-7.35 (m, 3H, aryl), 7.54 (d d, 1H, 3JH4-H5 =3.6 Hz, 4JH3-H5 =2.0 Hz, fulvene H5), 15.20 (s, 1H, enamine H). 13C NMR (CDCl3): δ 19.2 (aryl-CH3), 27.2 (acetyl-CH3), 118.2, 119.2, 126.6, 127.4, 127.6, 128.4, 129.3, 129.8, 134.4, 134.6, 135.6, 136.1, 136.9; 165.6 (enamine), 193.6 (acetyl). HR-MS (EI pos): m/z obsd 315.160 (M•þ), calcd 315.162 (monoisotopic). IR (ATR): cm-1 531.8 w, 543.1 w, 588.2 m, 614.7 m, 647.9 s, 702.1 s, 721.0 m, 746.0 vs, 770.0 vs, 823.4 w, 880.1 m, 921.9 m, 946.8 m, 1021.3 m, 1067.8 s, 1087.6 m, 1161.9 m, 1179.3 m, 1217.1 m, 1278.2 m, 1328.0 s, 1361.3 m, 1398.7 s, 1443.4 s, 1494.6 m, 1556.4 s, 1579.9 m, 1613.7 m. Mp: 138 °C. Anal. Calcd for C22H21NO (315.41): C 83.78, H 6.71, N 4.44. Found: C 83.91, H 6.78, N 4.73. Single-crystal X-ray structure: Figure 2, Supporting Information. 1-[5-[1-[N-(2,6-Dimethylphenyl)amino]-1-phenylmethylene]cyclopenta-1,3-dien-1-yl]-1-phenylmethanone (2). Starting materials: 8.0 mmol of NaCp, 2 equiv of methyl benzoate, and 1 equiv of N-2,6-dimethylphenylbenzimidoyl chloride.15 Yield: 14.6%. 1 H NMR (CDCl3): δ 2.35 (s, 6H, aryl-CH3), 6.40 (t, 1H, J = 3.9 Hz), 6.76 (d d, 1H, J = 2.1 Hz), 6.98-7.08 (m, 3H, aryl), 7.29-7.57 (m, 9H, aryl), 7.89 (t t, 2H, J=1.8 Hz), 15.36 (s, 1H, enamine H). 13C NMR (CDCl3): δ 19.25 (aryl-CH3), 118.77, 120.27, 125.80, 127.47, 127.60, 128.03, 128.40, 129.37, 129.42, 129.97, 130.38, 134.49, 134.53, 136.66, 136.92, 140.33, 142.21, 165.84 (enamine), 191.45 (benzoyl). HR-MS (EI pos): m/z obsd 377.173 (M•þ), calcd 377.177 (monoisotopic). IR (ATR): cm-1 446.3 w, 471.7 w, 540.2 w, 586.8 s, 599.5 s, 664.4 vs, 700.3 vs, 735.5 s, 762.4 s, 775.2 vs, 818.9 m, 850.4 m, 907.7 w, 935.3 m, 1024.7 m, 1038.7 m, 1085.0 w, 1134.0 m, 1165.0 w, 1276.7 s, 1322.0 s, 1347.9 s, 1396.8 s, 1439.7 s, 1510.4 m, 1578.7 w, 1612.1 m, 2919.2


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w, 3055.6 w. Mp: 165 °C. Anal. Calcd for C23H21NO (377.49): C 85.91, H 6.14, N 3.71. Found: C 86.15, H6.19, N 4.04. Singlecrystal X-ray structure: Supporting Information. 1-[5-[1-[N-(2,6-Diisopropyl)phenyl)amino]-1-phenylmethylene]cyclopenta-1,3-dien-1-yl]ethanone (3). Starting materials: 3.9 mmol of NaCp, 2 equiv of methyl acetate, and 1 equiv of N-2,6-diisopropylphenylbenzimidoyl chloride.15 Yield: 26.9%. 1 H NMR (CDCl3): δ 1.25 (d, 6H, J=6.9 Hz, -CH(CH3)2), 1.30 (d, 6H, J=6.9 Hz, -CH(CH3)2), 2.79 (s, 3H, acetyl-CH3), 3.33 (sept, 2H, J=6.9 Hz, -CH(CH3)2), 6.46 (pseudo-t, 1H, J=4 Hz, fulvene H4), 6.70 (d d, 1H, 3JH3-H4 =4.2 Hz, 4JH3-H5 =2.0 Hz, fulvene H3), 7.16-7.41 (m, 8H, phenyl), 7.63 (d d, 1H, 3 JH4-H5 =3.6 Hz, 4JH3-H5 =2.0 Hz, fulvene H5), 15.29 (s, 1H, enamine H). 13C NMR (CDCl3): δ 21.7 (-CH(CH3)2), 25.7 (-CH(CH3)2), 27.1 (acetyl-CH3), 29.1 (-CH(CH3)2), 118.1, 119.0, 123.3, 126.7, 127.3, 128.6, 129.34, 129.6, 133.7, 134.0, 135.3, 135.9, 145.1, 165.6 (enamine), 193.5 (acetyl). HR-MS (EI pos): m/z obsd 371.224 (M•þ), calcd 371.224 (monoisotopic). IR (ATR): cm-1 572.3 w, 585.0 w, 647.5 s, 703.0 s, 719.3 w, 747.5 s, 776.6 m, 802.0 w, 877.9 w, 934.1 w, 949.1 w, 1024.6 w, 1071.4 s, 1179.2 m, 1254.9 m, 1279.6 m, 1316.6 m, 1361.7 s, 1399.5 s, 1441.1 s, 1458.4 s, 1511.4 s, 1555.9 vs, 1598.9 m, 1617.8 m, 2867.8 w, 2925.6 w, 2960.2 m, 3062.8 w. Mp: 98 °C. Anal. Calcd for C26H29NO (371.52): C 84.06, H 7.87, N 3.77. Found: C 84.27, H 7.93, N 4.03. Single-crystal X-ray structure: Supporting Information. 1-[5-[1-[N-(2,6-Dibromophenyl)amino]-1-phenylmethylen]cyclopenta-1,3-dien-1-yl]ethanone (4). Starting materials: 5.3 mmol of NaCp, 2 equiv of methyl acetate, and 1 equiv of N-2,6-dibromophenylbenzimidoyl chloride.15 Yield: 17.2%. 1H NMR (CDCl3): δ 2.67 (s, 3H, acetyl-CH3), 6.34 (t, 1H, J = 3.9 Hz, fulvene H-4), 6.57-6.59 (d d, 1H, 1J = 1.9, 2J = 1.9 Hz, fulvene), 6.89 (m, 1H, aryl), 7.22-7.27 (m, 2H, aryl), 7.30-7.36 (m, 1H, aryl), 7.44 (m, 2H, aryl), 7.53-7.56 (d d d d, 3H, J=Hz, fulvene), 15.43 (s, 1H, enamine H). 13C NMR (CDCl3): δ 27.0 (acetyl-CH3), 119.6, 120.2, 124.2, 127.3, 127.4, 129.6, 129.8, 130.0, 132.5, 134.3, 136.7, 138.0, 138.3, 165.1 (enamine), 193.7 (acetyl). HR-MS (FAB pos): m/z obsd 443.960 ([M þ H]þ), calcd 443.967 (monoisotopic). IR (ATR): cm-1 581.8 s, 613.0 s, 647.2 vs, 682.8 s, 699.3 vs, 718.1 s, 751.5 vs, 774.6 vs, 821.1 m, 847.5 m, 919.9 s, 948.3 m, 1020.2 m, 1062.1 m, 1074.9 s, 1087.6 m, 1179.9 m, 1280.9 m, 1330.3 s, 1363.7 s, 1402.0 s, 1434.1 s, 1513.2 s, 1552.3 s, 1595.5 m, 1609.0 m, 3053.3 w. Mp: 148 °C. Anal. Calcd for C20H15Br2NO (445.15): C 53.96, H 3.40, N 3.15. Found: C 54.00, H 3.43, N 3.42. Single-crystal X-ray structure: Supporting Information. 1-[5-[1-[N-(2,6-Dichlorophenyl)amino]-1-phenylmethylen]cyclopenta-1,3-dien-1-yl]ethanone (5). Starting materials: 3.1 mmol of NaCp, 2 equiv of methyl acetate, and 1 equiv of N-2,6dichlorophenylbenzimidoyl chloride.15 Yield: 22.6%. 1H NMR (CDCl3): δ 2.70 (s, 3H, acetyl-CH3), 6.40 (t, 1H, J = 3.9 Hz, fulveneH-4), 6.58 (d d, 1H, 1J=1.8 Hz, 2J=2.4 Hz), 7.01-7.07 (m, 1H, aryl), 7.21-7.35 (m, 5H, aryl), 7.49-7.52 (m, 2H, aryl), 7.56-7.58 (d d, 1H, J=1.9 Hz, aryl), 15.42 (s, 1H, enamineH). 13C NMR (CDCl3): 26.9 (acetyl-CH3), 119.5 (2-C), 120.0, 127.4, 128.5, 128.9, 129.3, 129.9, 134.0, 134.4, 135.6, 136.5, 138.0, 165.5 (enamine), 193.7 (acetyl). HR-MS (FAB pos): m/z obsd 356.060 ([M þ H]þ), calcd 356.060 (monoisotopic). IR (ATR): cm-1 573.5 w, 585.5 w, 631.3 w, 646.9 w, 688.1 w, 704.3 m, 713.5 w, 750.1 m, 774.2 s, 819.9 w, 840.4 w, 950.9 w, 1022.3 m, 1073.2 m, 1091.1 w, 1188.9 w, 1258.6 m, 1280.3 m, 1326.0 m, 1369.7 m, 1401.4 m, 1435.9 m, 1451.7 m, 1510.8 m, 1560.2 m, 1595.5 m, 1611.8 m, 2850.7 w, 2920.3 w, 2961.5 w. Mp: 143 °C. Anal. Calcd for C20H15Cl2NO (356.25): C 67.43, H 4.24, N 3.93. Found: C 67.62, H 4.26, N 3.86. Single-crystal X-ray structure: Supporting Information. 1-[5-[1-[N-(2,6-Dimethylphenyl)amino]-1-phenylmethylene]cyclopenta-1,3-dien-1-yl]-2,2,2-trifluoroethanone (6). Starting materials: 4.1 mmol of NaCp, 2 equiv of methyl trifluoroacetate, and 1 equiv of N-2,6-dimethylphenylbenzimidoyl chloride.15 Yield: 31.1%. 1H NMR(CDCl3): δ 2.24 (s, 6H, aryl-CH3),

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6.44 (t, 1H, J = 4.0 Hz, fulvene H-4), 6.78-6.80 (d d, 1H, J=1.9 Hz, fulvene H-3), 6.94-6.97 (m, 2H, aryl), 7.01-7.06 (m, 1H, aryl), 7.24-7.40 (m, 5H, aryl), 7.71 (m, 1 H, fulvene H-5),14.46 (s, 1H, enamine-H). 13C NMR (CDCl3): 19.2 (arylCH3), 119.1, 120.9, 121.8, 113.9, 117.8, 121.6, 125.4 (trifluoromethyl, 1J(13C-19F)=289.4 Hz), 125.5, 127.7, 128.3, 128.6, 129.2, 130.5, 133.7, 134.5, 136.2, 138.1, 138.2, 138.2, 138.3 (3J(13C-19F) = 3.7 Hz), 140.9, 167.2 (enamine), 172.7, 173.1, 173. 5, 174.0 (CdO, 2J(13C-19F) = 27.8 Hz). HR-MS (FAB pos): m/z obsd 370.138 ([M þ H]þ), calcd 370.141 (monoisotopic). IR (ATR): cm-1 503.1 m, 520.4 m, 546.6 m, 582.6 m, 609.7 m, 618.2 m, 669.2 s, 679.5 s, 699.9 s, 730.9 s, 752.3 s, 777.1 m, 819.3 m, 842.6 m, 866.5 m, 904.0 m, 938.4 m, 979.4 m, 1027.7 m, 1042.9 m, 1090.5 m, 1136.5 s, 1184.3 m, 1224.5 m, 1289.5 m, 1320.6 m, 1361.8 m, 1377.3 m, 1411.7 m, 1442.4 m, 1471.3 m, 1558.8 m, 1580.5 m, 1618.6 m, 2853.8 w, 2907.7 w, 2926.6 w, 2958.3 w. Mp: 114 °C. Anal. Calcd for C22H18F3NO (369.39): C 71.54, H 4.91, N 3.79. Found: C 71.53, H 4.95, N 3.84. Single-crystal X-ray structure: Supporting Information. 1-[5-[2,2,2-Trifluoro-1-[N-(2,6-dichlorophenyl)amino]ethylidene]cyclopenta-1,3-dien-1-yl]ethanone (7). Starting materials: 2.4 mmol of NaCp, 2 equiv of methyl acetate, and 1 equiv of N-phenyltrifluoroacetimidoyl chloride.16 Yield: 27.6%. 1H NMR (CDCl3): δ 2.56 (s, 3H, acetyl-CH3), 6.49-6.52 (2 d, 1H, J = 3.4 Hz, fulvene-H4), 7.25-7.27 (m, 2H, phenyl), 7.29-7.45 (m, 4H, phenyl þ fulvene), 7.56-7.57 (d d, 1H, J = 1.7 Hz, fulvene-H3), 15.46 (s, 1H, enamine-H). 13C NMR (CDCl3): δ 27.2 (acetyl-CH3), 115.8, 119.5, 123.3, 127.0 (trifluoromethyl, 1J(13C-19F)=289.4 Hz), 118.4, 118.4, 122.4, 124.4, 124.4, 127.2, 128.7, 129.5, 132.6, 132.6, 132.7, 132.8 (3J(13C-19F) = 3.7 Hz), 139.41, 141.37, 145.8, 146.2, 146.6, 147.0 (enamine, 2J(13C-19F) = 31.4 Hz), 194.5 (acetyl). HRMS (FAB pos): m/z obsd 280.098 ([M þ H]þ), calcd 280.094 (monoisotopic). IR (ATR): cm-1 512.6 s, 574.4 s, 592.5 s, 654.7 vs, 666.7 vs, 691.3 s, 711.4 s, 741.3 s, 776.8 s, 830.1 s, 875.8 s, 922.4 s, 1002.0 s, 1026.9 s, 1036.7 s, 1073.3 vs, 1106.9 vs, 1131.6 vs, 1167.7 vs, 1206.6 s, 1244.0 s, 1324.3 vs, 1375.2 s, 1393.2 vs, 1489.1 vs, 1522.2 s, 1561.8 vs, 1585.4 vs, 1635.4 s, 2926.6 w, 2958.3 w, 3009.0 w, 3066.0 w, 3094.5 w. Mp: 46 °C. Anal. Calcd for C15H12F3NO (279.26): C 64.51, H 4.33, N 5.02. Found: C 64.63, H 4.39, N 5.31. Single-crystal X-ray structure: Supporting Information. 1-[5-[1-[N-(2,6-Diisopropylphenyl)amino]-1-phenylmethylene]cyclopenta-1,3-dien-1-yl]-1-phenylmethanone (8). Starting materials: 16 mmol of NaCp, 2 equiv of methyl benzoate, and 1 equiv of N-2,6-diisopropylphenylbenzimidoyl chloride.15 Yield: 7.9%. 1H NMR (CDCl3): δ 1.18 (d, 6H, J = 6.9 Hz, -CH(CH3)2), 1.24 (d, 6H, J=6.9 Hz, -CH(CH3)2), 3.31 (sept, 2H, J= 6.6 Hz, -CH(CH3)2), 6.38 (t, 1H, J = 3.8 Hz, fulvene-H4), 6.70-6.72 (d d, 1H, J=2.0 Hz, fulvene), 7.07-7.10 (m, 2H, aryl), 7.22-7.38 (m, 7H, aryl þ fulvene), 7.48-7.54 (m, 3H, aryl), 7.83-7.86 (2 d, 2H, 1J=1.6 Hz, 2J=2.3 Hz), 15.35 (s, 1H, enamine-H). 13C NMR(CDCl3): δ 21.8 (-CH(CH3)2), 25.8 (-CH(CH3)2), 29.2 (-CH(CH3)2), 118.8, 120.2, 123.5, 126.0, 127.5, 128.7, 129.2, 129.6, 129.8, 130.2, 133.8, 134.1, 136.5, 140.2, 142.4, 145.2, 166.0 (enamine), 191.6 (benzoyl). HR-MS (FAB pos): m/z obsd 434.245 ([M þ H]þ), calcd 434.248 (monoisotopic). IR (ATR): cm-1 480.6 w, 560.0 w, 583.2 m, 602.0 m, 670.8 s, 701.4 s, 733.2 m, 751.4 s, 776.8 m, 806.2 m, 817.0 m, 843.5 m, 933.7 w, 1025.1 m, 1039.4 m, 1087.1 m, 1134.3 m, 1166.2 w, 1257.6 m, 1277.6 m, 1316.4 m, 1348.0 m, 1397.2 m, 1434.1 m, 1456.3 m, 1510.3 m, 1530.0 m, 1579.3 w, 1599.6 m, 1619.9 m, 2863.3 w, 2920.3 w, 2963.3 w, 3053.3 w. Mp: 147 °C. Anal. Calcd for C31H31NO (433.59): C 85.87, H 7.21, N 3.23. Found: C 86.08, H 7.26, N 3.48. Single-crystal X-ray structure: Supporting Information. 1-[5-[1-[N-(Phenyl)amino]-1-phenylmethylen]cyclopenta-1,3dien-1-yl]-2,2,2-trifluoroethanone (9).Starting materials: 16 mmol of NaCp, 2 equiv of methyl trifluoroacetate, and 1 equiv of N-phenylbenzimidoyl chloride.15 Yield: 45.4%. 1H NMR(CDCl3): δ 6.44 (t, 1H, J=4.0 Hz, fulvene H-4), 6.79 (d d, 1H, J = 1.2 Hz, fulvene H-3), 6.89 (m, 2H, phenyl), 7.09-7.21

Enk et al. (m, 3H, phenyl), 7.35-7.52 (m, 5H, phenyl), 7.69-7.74 (m, 1H, fulvene H-5), 14.85 (s, 1H, enamine-H). 13C NMR (CDCl3): δ 113.9, 117.8, 121.6, 125.4 (trifluoromethyl, 1J(13C-19F)=289.4 Hz), 119.1, 121.6, 122.9, 124.5, 126.9, 128.7, 129.3, 129.8, 130.5, 133.8, 138.1, 139.1, 139.1, 139.2, 139.2 (3J(13C-19F)=3.6 Hz), 141.0, 163.6 (enamine), 172.7, 172.3, 173. 7, 174.1 (CdO, 2 13 J( C-19F) = 32.6 Hz). MS (ESI pos): m/z (M þ Na)þ = 364.02. IR (ATR): cm-1 522.7 s, 573.5 s, 595.4 s, 614.8 s, 628.0 s, 686.7 vs, 703.9 vs, 732.4 vs, 749.9 vs, 779.4 s, 832.5 vs, 846.1 vs, 907.8 s, 946.4 s, 1029.0 s, 1045.5 vs, 1074.4 s, 1094.1 vs, 1138.5 vs, 1169.3 s, 1188.2 vs, 1227.2 vs, 1283.5 m, 1323.8 s, 1366.1 s, 1413.6 m, 1439.4 s, 1453.8 s, 1468.3 s, 1494.5 m, 1566.5 vs, 1583.3 vs, 1630.2 m, 2850.7 w, 2926.6 w, 2955.1 w. Anal. Calcd for C20H14F3NO (341.33): C 70.38, H 4.13, N 4.10. Found: C70.50, H 4.13, N 4.26. Single-crystal X-ray structure: Supporting Information. 1-[5-[1-[N-(2,6-Dimethylphenyl)amino]-1-phenylmethylen]cyclopenta-1,3-dien-1-yl]carbaldehyde (10). Starting materials: 4.0 mmol of NaCp, 2 equiv of methyl formiate, and 1 equiv of N-2,6-dimethylphenylbenzimidoyl chloride.15 Yield: 22.4%. 1H NMR (CDCl3): δ 2.26 (s, 6H, aryl-CH3), 6.45 (t, 1H, J=3.8 Hz, fulvene H-4), 6.73-6.74 (d d, 1H, 1J=1.4 Hz), 6.97-7.08 (m, 3H, aryl), 7.26-7.37 (m, 5H, aryl), 7.45 (d d, 1H, 1J=2.0 Hz, 2 J=3.4 Hz, fulvene H-5), 9.56 (unresolved m, 1H, formyl-H), 14.38 (s, 1H, N-H). 13C NMR (CDCl3): δ 19.1 (aryl-CH3), 118.7, 120.1, 127.6, 127.8, 128.3, 128.5, 129.3, 130.1, 133.7, 134.7, 136.5, 136.8, 140.9, 165.7 (enamine), 184.4 (formyl). MS (FAB pos): m/z (M þ H)þ =302.16. IR (ATR): cm-1 579.6 m, 686.5 s, 700.2 vs, 740.5 vs, 754.8 vs, 774.5 s, 906.1 m, 1025.8 s, 1073.9 s, 1153.7 s, 1168.1 s, 1214.1 m, 1264.1 s, 1288.5 s, 1310.9 vs, 1342.0 s, 1380.0 s, 1465.2 vs, 1571.6 vs, 1615.1 s, 2746.2 w, 2774.7 w, 2815.8 w, 2923.5 w, 2958.3 w, 3056.5 w. Anal. Calcd for C21H19NO (301.39): C 83.69, H 6.35, N 4.65. Found: C 83.61, H 6.30, N 4.83. Single-crystal X-ray structure: Supporting Information. Representative Procedure for 1-Acyl-2-imidoylpentamethylruthenocenes: 1-[2-[1-[N-(2,6-dimethylphenyl)imino]phenylmethyl]-10 ,20 ,30 ,40 ,50 -pentamethylruthenocen-1-yl]ethanone (11). A Schlenk tube was charged under an atmosphere of argon with 1 (528 mg, 1.67 mmol), 20 mL of dry THF, and a stirring bar. The mixture was cooled to 0 °C, and 74 mg of potassium hydride (1.84 mmol) was added. As the reaction vessel warmed to ambient temperature, formation of dihydrogen was observed, and the solution changed gradually in color from yellow to amber. In the glovebox, the solution was filtered to remove an excess of potassium hydride. The solution was reduced in volume, and Cp*Ru(CH3CN)3PF6 (750 mg, 1.49 mmol) was added at once, accompanied by further darkening of the solution. The solution was stirred overnight at ambient temperature; afterward solvents were removed on a vacuum line. Workup: the reaction mixture was hydrolyzed by addition of water, the organic materials were extracted three times with diethyl ether, and the organic layers were combined and dried over extraction with brine and addition of Na2SO4. The volatile materials were removed on a rotary evaporator. The crude product mixture was dissolved in 3 mL of dichloromethane and filtered through a short column of silica. This way, apolar starting material could be separated by filtration, whereas the more polar product remained immobilized on the column. Elution with diethyl ether and subsequent removal of solvents afforded the pure product as yellow crystals in 87% yield (712 mg). 1H NMR (CDCl3): δ 1.80 (s, 3H, aryl-CH3), 1.93 (s, 15H, Cp*-CH3), 2.06 (s, 3H, aryl-CH3), 2.43 (s, 3H, acetyl-CH3), 4.51 (unresolved m, 1H, Cp-H-4), 4.70 (unresolved m, Cp-H-3), 4.86 (unresolved m, 1H, Cp-H-5), 6.78 (m, 2H, aryl), 7.01-7.13 (m, 6H, aryl). 13C NMR (CDCl3): δ 11.6 (Cp*CH3), 18.7 (aryl-CH3), 19.2 (aryl-CH3), 28.2 (acetyl-CH3), 75.0, 75.5, 81.3, 83.2, 87.9, 94.4, 122.4, 123.5, 127.6, 127.8, 128.2, 128.3, 129.0, 139.1, 149.5, 166.0 (imine), 197.7 (acetyl). MS (FAB pos): m/z (M þ H)þ = 551.17. IR (ATR): cm-1 425.0 m, 460.2 m, 499.2 w, 612.8 w, 688.9 m, 702.2 vs, 764.6 vs, 773.3 m, 829.0 m, 887.9 s, 1031.9 m, 1074.1 m, 1156.9 m, 1216.9 m, 1252.8 m,

Article 1350.9 m, 1380.2 m, 1400.5 m, 1434.8 m, 1442.9 m, 1470.6 m, 1589.8 m, 1615.7 s, 1651.8 s, 2901.3 w, 2952.0 w, 2967.8 w. Anal. Calcd for C32H35NORu (550.71): C 69.79, H 6.41, N 2.54. Found: C 69.86, H 6.46, N 2.77. 1-[2-[1-[N-(2,6-Dimethylphenyl)imino]phenylmethyl]-10 ,20 ,30 , 0 0 4 ,5 pentamethylruthenocen-1-yl]-1-phenylmethanone (12). Starting material: 0.59 mmol of 2. Yield: 57.4%. 1H NMR (CDCl3): δ 1.84 (s, 3H, aryl-CH3), 1.95 (s, 15H, Cp*-CH3), 2.22 (s, 3H, arylCH3), 4.52 (unresolved m, 1H, Cp-H), 4.63 (unresolved m, 1H, Cp-H), 5.04 (unresolved m, 1H, Cp-H), 6.73-6.81 (m, 2H, aryl), 6.91-7.12 (m, 6H, aryl), 7.28-7.33 (m, 2H, aryl), 7.39-7.44 (m, 1H, aryl), 7.68 (m, 2H, aryl). 13C NMR (CDCl3): δ 11.7 (Cp*-CH3), 18.9, 19.1 (aryl-CH3), 75.3, 76.8, 79.5, 85.3, 87.8, 93.8, 122.2, 124.9, 127.2, 127.3, 127.6, 127.8, 128.0, 128.2, 128.4, 128.6, 128.8, 131.1, 131.5, 138.7, 139.9, 149.4, 166.3, 168.0 (imine), 194.4 (benzoyl). MS (FAB pos): m/z (M þ H)þ = 614.18. IR (ATR): cm-1 475.7 m, 663.0 m, 672.3 m, 691.6 s, 700.9 s, 769.7 m, 831.7 w, 869.5 m, 943.4 w, 1029.5 m, 1070.7 m, 1121.4 w, 1159.6 m, 1222.1 m, 1251.2 s, 1342.9 m, 1380.1 m, 1446.3 m, 1588.6 m, 1607.1 m, 1670.4 m, 1725.2 m, 2857.0 w, 2896.6 w, 2955.3 w, 3059.6 w. Anal. Calcd for C37H37NORu (612.78): C 72.52, H 6.09, N 2.29. Found: C 72.71, H 6.13, N 2.46. Single-crystal X-ray structure: Figure 3, Supporting Information. 1-[2-[1-[N-(2,6-Diisopropylphenyl)imino]phenylmethyl]-10 ,20 , 30 ,40 ,50 -pentamethylruthenocen-1-yl]ethanone (13). Starting material: 0.59 mmol of 3. Yield: 78.7%. 1H NMR (CDCl3): δ 0.56 (d, 3H, J = 6.8 Hz, CH(CH3)2), 1.06 (d, 3H, J = 6.8 Hz, CH(CH3)2), 1.30 (2 d, 6H, J = 6.9 Hz, CH(CH3)2), 1.96 (s, 15H, Cp*CH3), 2.20 (s, 3H, acetyl-CH3), 2.67 (sept, 1H, J=6.8 Hz, CH(CH3)2), 3.34 (sept, 1H, J = 6.8 Hz, CH(CH3)2), 4.48 (pseudo-t, 1H, J=2.2 Hz, Cp-H-4), 4.70 (unresolved m, 1H, CpH-3), 4.75 (unresolved m, 1H, Cp-H-5), 6.90 (m, 1H, aryl), 6.99 (m, 1H, aryl), 7.08-7.24 (m, 6H, aryl). 13C NMR (CDCl3): δ 11.4 (Cp*CH3), 22.1, 23.0, 24.7, 24.9 (4 CH(CH3)2), 27.7 (acetyl-CH3), 28.6, 29.1 (2 CH(CH3)2), 75.6, 75.8, 81.4, 84.7, 87.6, 93.4, 122.9, 123.3, 123.4, 123.7, 127.5, 129.1, 133.4, 137.5, 138.6, 146.4, 165.5 (imine), 198.8 (acetyl). MS (ESI pos): m/z (M þ H)þ = 608.16, (M þ Na)þ = 630.16. Anal. Calcd for C36H43NORu (606.81): C 71.26, H 7.14, N 2.31. Found: C 71.49, H 7.20, N 2.52. Single-crystal X-ray structure: Supporting Information. 1-[2-[1-[N-(2,6-Dibromophenyl)imino]phenylmethyl]-10 ,20 ,30 , 40 ,50 -pentamethylruthenocen-1-yl]ethanone (14). Starting material: 0.60 mmol of 4. Yield: 66.9%. 1H NMR (CDCl3): δ 1.91 (s, 15H, Cp*-CH3), 2.04 (s, 3H, acetyl-CH3), 4.52 (unresolved m, 1H, Cp-H), 4.76 (d d, 1H, J = 1.3 Hz, Cp-H-4), 5.06 (unresolved m, 1H, Cp-H), 6.63 (t, J = 8.0 Hz, para-aryl), 7.09-7.26 (m, 6H, aryl), 7.48-7.51 (2 d, 1H, J=1.3 Hz, aryl). 13 C NMR (CDCl3): δ 11.6 (Cp*-CH3), 28.8, (acetyl-CH3), 75.5, 75.9, 83.0, 88.1, 111.9, 117.1, 124.4, 127.6, 128.6, 129.7, 132.0, 132.3, 138.7, 149.0, 171.7 (imine), 197.7 (acetyl). MS (FAB pos): m/z Mþ=681.05. IR (ATR): cm-1 667.9 w, 695.1 s, 724.4 s, 745.9 m, 763.9 m, 889.5 m, 903.8 m, 1029.9 m, 1068.7 m, 1118.7 m, 1222.6 m, 1268.0 m, 1309.7 w, 1353.5 m, 1380.0 m, 1415.1 m, 1448.6 m, 1543.3 w, 1575.6 w, 1609.7 m, 1655.5 m, 1707.6 m, 2859.5 w, 2901.1 w, 2929.8 w, 3059.6 w. Anal. Calcd for C30H29Br2NORu (680.44): C 52.96, H 4.30, N 2.06. Found: C 52.99, H 4.32, N 2.13. Single-crystal X-ray structure: Supporting Information. 1-[2-[1-[N-(2,6-Dichlorophenyl)imino]phenylmethyl]-10 20 ,30 ,40 , 0 5 -pentamethylruthenocen-1-yl]ethanone (15). Starting material: 0.53 mmol of 5. Yield: 79.5%. 1H NMR (CDCl3): δ 1.90 (s, 15H, Cp*CH3), 2.05 (s, 3H, acetyl-CH3), 4.51 (unresolved m, 1H, Cp-H), 4.75 (unresolved m, 1H, Cp-H), 4.95 (unresolved m, 1H, Cp-H), 6.74-6.79 (m, 1H, aryl), 7.01-7.04 (m, 1H, aryl), 7.10-7.27 (m, 6H, aryl). 13C NMR (CDCl3): δ 11.5 (Cp*CH3), 28.9 (acetyl-CH3), 75.8, 76.0, 83.0, 83.4, 88.1, 92.4, 122.6, 123.5, 127.3, 127.6, 128.1, 128.2, 128.4, 129.6, 138.8, 146.9, 172.4 (imine), 197.8 (acetyl). MS (FAB pos): m/z (M þ H)þ=592.06. IR (ATR): cm-1 443.3 w, 469.9 w, 501.1 w, 542.2 w, 595.5 w, 667.4 w, 680.7 m, 698.6 s, 767.4 s, 774.5 s, 822.1 w, 889.9 m, 968.1 w, 1026.9 m, 1045.1 m, 1071.8 m, 1121.9 w, 1228.4


5585

m, 1259.0 s, 1355.2 m, 1379.9 m, 1399.3 m, 1427.3 s, 1577.4 w, 1597.9 m, 1617.6 s, 1643.5 s, 1735.5 w, 2852.7 w, 2920.8 w, 2955.8 w. Anal. Calcd for C30H29Cl2NORu (591.54): C 60.91, H 4.94, N 2.37. Found: C 61.08, H 4.99, N 2.50. Single-crystal X-ray structure: Supporting Information. 2,2,2-Trifluoro-1-[2-[1-[N-(2,6-dimethylphenyl)imino]phenylmethyl]-10 ,20 ,30 ,40 ,50 -pentamethylruthenocen-1-yl]ethanone (16). Starting material: 0.53 mmol of 6. Yield: 90.4%. 1H NMR (CDCl3): δ 1.81 (s, 3H, aryl-CH3), 1.91 (s, 15H, Cp*CH3), 2.46 (s, 3H, aryl-CH3), 4.70 (t, 1H, J = 2.5 Hz, Cp-H), 4.84 (unresolved m, 1H, Cp-H), 5.11 (unresolved m, 1H, Cp-H), 6.80-6.81 (m, 2H, aryl), 7.05-7.12 (m, 6H, aryl). 13C NMR (CDCl3): δ 11.6 (Cp*CH3), 18.7 (aryl-CH3), 19.2 (aryl-CH3), 74.7, 74.7, 77.5, 82.2, 89.4, 95.4, 115.0, 118.9, 124.3, 129.5 (trifluoromethyl, 1J(13C-19F)=337.0 Hz), 122.5, 123.7, 127.5, 127.9, 128.1, 129.1, 138.5, 149.3, 165.2 (imine), 180.4, 180.8, 181.3, 181.8 (CdO, 2J(13C-19F)=34.5 Hz). MS (FAB pos): m/z (M þ H)þ=606.22. IR (ATR): cm-1 470.4 w, 498.7 w, 589.9 w, 616.4 w, 647.1 m, 695.6 s, 730.5 s, 758.2 s, 814.0 m, 836.7 m, 868.3 m, 951.5 m, 1000.7 w, 1029.3 m, 1054.0 m, 1087.2 m, 1110.2 m, 1141.2 s, 1189.2 s, 1222.0 m, 1262.6 m, 1292.1 m, 1357.6 w, 1375.4 m, 1448.6 m, 1590.0 w, 1619.6 m, 1675.4 m, 1727.9 w, 2852.1 w, 2913.0 w, 2958.5 w. Anal. Calcd for C32H32F3NORu (604.68): C 63.56, H 5.33, N 2.32. Found: C 63.67, H 5.38, N 2.43. Single-crystal X-ray structure: Supporting Information. 1-[2-[1-[N-(2,6-Diisopropylphenyl)imino]phenylmethyl]-10 ,20 , 30 ,40 ,50 -pentamethylruthenocen-1-yl]-1-phenylmethanone (17). Starting material: 0.50 mmol of 8. Yield: 52.8%. 1H NMR (CDCl3): δ 0.88 (unresolved m, 6H, CH(CH3)2), 0.94 (d, 3H, CH(CH3)2, J=6.7 Hz), 1.14 (d, 3H, CH(CH3)2, J=6.5 Hz), 1.96 (s, 15H, Cp*-CH3), 2.89 (sept, 2H, CH(CH3)2, J=6.6 Hz), 4.45 (unresolved m, 1H, Cp-H), 4.58 (unresolved m, 1H, Cp-H), 4.88 (unresolved m, 1H, Cp-H), 6.89-7.12 (m, 8H, aryl), 7.23-7.28 (m, 2H, aryl), 7.34-7.39 (m, 1H, aryl), 7.65 (unresolved m, 2H, aryl). 13C NMR (CDCl3): δ 11.8 (Cp*-CH3), 22.2, 22.9, 24.8, 25.0, 28.0, 28.2 (CH(CH3)2), 75.2, 77.2, 77.9, 87.8, 88.2, 92.4, 122.8, 122.9, 123.0, 127.2, 128.1, 128.7, 129.0, 129.1, 131.7, 135.9, 136.8, 137.4, 139.9, 146.7, 165.6 (imine), 194.5 (benzoyl). MS (FAB pos): m/z (M þ H)þ = 669.18. IR (ATR): cm-1 439.4 m, 456.3 w, 479.4 w, 669.5 m, 698.8 s, 759.7 m, 773.6 w, 839.4 w, 865.5 m, 945.9 w, 1028.7 m, 1071.6 w, 1157.2 w, 1209.0 w, 1243.6 m, 1282.1 w, 1324.7 w, 1344.3 m, 1379.6 m, 1431.6 m, 1448.0 m, 1541.0 w, 1587.4 m, 1598.8 m, 1635.6 w, 1676.0 w, 2864.7 w, 2901.1 w, 2956.7 m, 3056.5 w. Anal. Calcd for C41H45NORu (668.88): C 73.62, H 6.78, N 2.09. Found: C 73.68, H 6.85, N 2.22. Single-crystal X-ray structure: Supporting Information. 1-[2-[1-[N-(2,6-Dimethylphenyl)imino]phenylmethyl]-10 ,20 ,30 , 40 ,50 -pentamethylruthenocen-1-yl]carbaldehyde (18). Starting material: 0.50 mmol of 10. Yield: 90.5%. 1H NMR (CDCl3): δ 1.89 (s, 15H, Cp*-CH3), 2.03 (s, 3H, aryl-CH3), 2.07 (s, 3H, arylCH3), 4.54 (d t, 1H, J=2.6 Hz, Cp-H), 4.63 (d d, 1H, J=1.3 Hz, Cp-H), 4.92 (d d, 1H, J=1.2 Hz, Cp-H), 6.71-6.76 (m, 1H, aryl), 6.80-6.87 (m, 2H, aryl), 7.16-7.31 (m, 5H, aryl), 10.32 (s, 1H, formyl-CHO). 13C NMR (CDCl3): δ 12.0, (Cp*CH3), 19,2 (aryl-CH3), 19,8 (aryl-CH3), 74.8, 76.5, 80.6, 81.5, 83.6, 88.2, 88.5, 89.1, 114.6, 116.0, 120.3, 122.6, 125.0, 127.1, 127.4, 127.6, 127.8, 127.9, 129.0, 137.2, 138.0, 149.5, 151.9, 159.4, 168.4 (imine), 192.1 (formyl). MS (FAB pos): m/z Mþ=536.17. IR (ATR): cm-1 455.4 w, 504.5 w, 514.0 w, 669.3 m, 686.7 m, 699.0 s, 759.8 m, 771.1 s, 824.3 m, 857.6 m, 902.2 m, 976.3 w, 1029.7 m, 1041.4 m, 1068.1 w, 1090.2 w, 1159.9 w, 1211.8 m, 1231.1 m, 1248.5 w, 1273.9 w, 1335.3 m, 1375.5 m, 1422.4 m, 1448.8 m, 1472.2 m, 1589.4 m, 1604.0 m, 1656.4 vs, 2847.5 w, 2901.3 w, 2948.8 w. Anal. Calcd for C31H33NORu (536.68): C 69.38, H 6.20, N 2.61. Found: C 69.50, H 6.25, N 2.65. Single-crystal X-ray structure: Supporting Information. Representative Procedure for 1-Hydroxyalkyl-2-imidoylpentamethylruthenocenes: 1-[2-[1-[N-(2,6-Dimethylphenyl)imino]phenylmethyl]-10 ,20 ,30 ,40 ,50 -pentamethylruthenocen-1-yl]-1-methylethan-1-ol (19). A Schlenk tube was charged with 11 (559 mg,

5586


1.02 mmol) and 5 mL of dry diethyl ether. The solution was cooled to 0 °C in an ice bath, and 0.70 mL of a 1.6 M solution of methyllithium (1.12 mmol) was added by syringe. The cooling bath was removed and stirring was continued for 2 days at ambient temperature. Workup: the reaction mixture was quenched by addition of ice and water, and the organic materials were extracted three times with diethyl ether at neutral pH. The organic layers were combined and dried over extraction with brine and addition of Na2SO4. The volatile materials were removed on a rotary evaporator. Chromatography on silica with diethyl ether/n-pentane (v/v=1:1) afforded the product in 64% yield (369 mg). 1H NMR (CDCl3): δ 1.57 (2 s, 6H, alkylCH3), 1.93 (s, 15H, Cp*CH3), 1.95 (s, 3H, aryl-CH3), 2.30 (s, 3H, aryl-CH3), 4.06 (d d, 1H, 3JH3-H4=1.3 Hz, 4JH3-H5=2.5 Hz, Cp-H-3), 4.13 (pseudo-t, 1H, 3J=2.6 Hz, Cp-H-4), 4.45 (d d, 1H, 3JH3-H4=1.4 Hz, 4JH3-H5=2.5 Hz, Cp-H-5), 6.73 (m, 2H, aryl), 6.89 (pseudo-t, 1H, 3Javeraged=4.5 Hz, aryl), 7.14-7.25 (m, 5H, aryl), 7.87 (s, 1H, OH). 13C NMR (CDCl3): δ 12.4 (Cp*CH3), 19.5 (aryl-CH3), 20.0 (aryl-CH3), 29.8 (alkyl-CH3), 32.6 (alkyl-CH3), 68.3, 68.8, 74.1, 77.0, 79.0, 84.1, 86.8, 123.3, 126.4, 127.1, 127.7, 128.1, 128.9, 129.0, 131.1, 138.3, 148.0, 173.3 (imine). MS (ESI pos): m/z (M þ Na)þ = 590.13. IR (ATR): cm-1 422.2 s, 466.5 w, 539.8 w, 582.7 m, 659.7 m, 697.6 vs, 767.5 s, 808.7 m, 897.9 m, 955.6 w, 1022.3 m, 1057.4 w, 1130.5 w, 1155.4 w, 1214.0 m, 1243.9 m, 1339.2 m, 1373.2 m, 1441.7 m, 1467.1 w, 1574.6 m, 1585.3 s, 1603.2 m, 2853.8 w, 2910.0 w, 2965.5 w, 3227.4 w. Anal. Calcd for C33H39NORu (566.75): C 69.94, H 6.94, N 2.47. Found: C 70.12, H 6.98, N 2.53. Singlecrystal X-ray structure: Supporting Information. 1-[2-[1-[N-(2,6-Dimethylphenyl)imino]phenylmethyl]-10 ,20 ,30 , 0 0 4 ,5 -pentamethylruthenocen-1-yl]-1-phenylpentan-1-ol (20). Starting materials: 12 (1.02 mmol), 1 equiv of n-butyllithium. Yield: 35%. 1H NMR (CDCl3): δ 0.70 (s, 3H, aryl-CH3), 0.86 (t, 3H, n-butyl-CH3), 1.26 (2H, n-butyl-CH2), 1.57 (2H, n-butyl-CH2), 1.77 (2H, n-butyl-CH2), 1.97 (s, 15H, Cp*CH3), 2.38 (3H, arylCH3), 4.00 (unresolved m, 1H, Cp-H), 4.22 (t, 1H, J=2.4 Hz, Cp-H), 4.84 (unresolved m, 1H, Cp-H), 6.49 (m, 1H, aryl), 6.65 (m, 1H, aryl), 6.84 (m, 1H, aryl), 6.97-7.00 (m, 2H, aryl), 7.04-7.13 (m, 6H, aryl), 7.30-7.33 (m, 2H, aryl), 8.21 (s, 1H, -OH). 13C NMR (CDCl3): δ 12.5 (Cp*CH3), 14.5 (n-butyl), 17.2 (aryl-CH3), 20.7 (aryl-CH3), 23.7 (n-butyl), 27.7 (n-butyl), 30.2 (n-butyl), 43.1 (n-butyl), 66.3, 73.8, 74.7, 79.0, 84.4, 87.1, 104.0, 123.2, 125.7, 126.6, 126.8, 127.0, 127.1, 127.5, 128.1, 128.3, 128.9, 138.6, 147.5, 149.1, 172.6 (imine). MS (FAB pos): m/ z Mþ =671.27, 614.17 (Mþ - C4H9þ). IR (ATR): cm-1 669.3 w, 702.8 s, 740.6 m, 763.1 m, 781.0 w, 1028.3 w, 1070.5 m, 1120.3 m, 1269.8 s, 1335.2 w, 1378.2 w, 1458.3 m, 1585.6 m, 1600.5 w, 1727.4 s, 2856.8 m, 2923.8 s, 2955.7 s. Anal. Calcd for C41H47NORu (670.90): C 73.40, H 7.06, N 2.09. Found: C 73.46, H 7.11, N 2.18. Singlecrystal X-ray structure: Figure 4, Supporting Information. 1-[2-[1-[N-(2,6-Diisopropylphenyl)imino]phenylmethyl]-10 ,20 , 30 ,40 ,50 -pentamethylruthenocen-1-yl]-1-methylethan-1-ol (21). Starting materials: 13 (0.91 mmol), 1 equiv of methyllithium. Yield: 74%. 1H NMR (CDCl3): δ 0.96 (d, 3H, J=6.8 Hz, CH(CH3)2), 1.07 (d, 3H, J = 6.7 Hz, CH(CH3)2), 1.20 (d, 3H, J = 1.8 Hz, CH(CH3)2), 1.23 (d, 3H, J=1.5 Hz, CH(CH3)2), 1.62 (2 s, 6H, J=2.4 Hz, alkyl-CH3), 2.00 (s, 15H, Cp*CH3), 2.89 (sept, 1H, J=6.8 Hz, CH(CH3)2), 3.25 (sept, 1H, J=6.8 Hz, CH(CH3)2), 4.03 (d d, 1H, 1J=1.4 Hz, 2J=1.3 Hz, Cp-H-4), 4.14 (t, 1H, J= 2.6 Hz, Cp-H-3), 4.70 (d d, 1H, 1J=1.4 Hz, 2J=1.4 Hz, Cp-H5), 6.87-7.00 (m, 3H, aryl), 7.17-7.22 (m, 5H, aryl), 7.72 (s, 1H, -OH). 13C NMR (CDCl3): δ 12.3 (Cp*CH3), 22.2, 22.4, 25.7, 26.0 (4 CH(CH3)2), 28.2, 28.6 (alkyl-CH3), 29.7, 32.6 (2 CH(CH3)2), 68.7 (C-OH), 74.1, 76.8, 79.3, 84.3, 86.8, 103.2, 122.6, 123.0, 124.1, 127.0, 128.2, 128.6, 137.2, 137.6, 137.7, 144.9, 173.3 (imine). MS (FAB pos): m/z Mþ = 623.28. IR (ATR): cm-1 434.2 s, 445.0 s, 536.1 m, 583.6 m, 666.8 m, 700.2 vs, 739.1 m, 759.1 s, 773.1 s, 816.1 s, 897.7 m, 913.3 m, 958.8 m, 1029.0 m, 1056.1 s, 1072.0 m, 1097.9 m, 1138.1 m, 1154.6 m, 1235.9 m, 1255.4 s, 1323.1 m, 1341.7 s, 1380.5 m,

Enk et al. 1432.3 s, 1458.0 s, 1586.5 s, 1644.3 w, 1729.8 w, 2863.6 w, 2920.1 s, 2956.9 s, 3056.5 w, 3145.1 w. Anal. Calcd for C37H47NORu (622.86): C 71.35, H 7.61, N 2.25. Found: C 71.54, H 7.65, N 2.30. Single-crystal X-ray structure: Supporting Information. 2,2,2-Trifluoro-2-methyl-1-[2-[1-[N-(2,6-dimethylphenyl)imino]phenylmethyl]-10 ,20 ,30 ,40 ,50 -pentamethylruthenocen-1-yl]ethan1-ol (22). Starting materials: 16 (0.29 mmol), 1 equiv of methyl lithium. Yield: 58%. 1H NMR (CDCl3): δ 1.73 (s, 3H, arylCH3), 1.86, 1.88 (2 s, 15H, Cp*CH3), 1.92 (s, 3H, alkyl-CH3), 2.40 (s, 3H, aryl-CH3), 4.10 (unresolved m, 1H, Cp-H), 4.19 (unresolved m, 1H, Cp-H), 4.70 (unresolved m, 1H, Cp-H), 6.69-6.79 (m, 2H, aryl), 6.91-6.95 (m, 1H, aryl), 7.16-7.25 (m, 5H, aryl), 9.12 (s, 1H, -OH). 13C NMR (CDCl3): δ 12.0, 12.3 (Cp*CH3), 19.5 (aryl-CH3), 20.3 (aryl-CH3), 25.7 (alkyl-CH3), 73.5, 73.8, 74.2, 74.6 (2J(13C-19F)=28.5 Hz), 75.9, 75.9, 76.0, 76.0 (3J(13C-19F)), 75.1, 75.2, 78.7, 79.3, 80.0, 83.0, 87.4, 87.7, 95.3, 123.8, 126.0, 127.2, 127.8, 128.5, 129.3, 137.8, 147.2, 172.3 (imine), 173.6 (imine); note: not all J(13C-19F)-coupling constants cited due to coexistence of diastereromers. MS (ESI pos): m/z Mþ =621.16. IR (ATR): cm-1 431.4 s, 468.9 m, 659.1 m, 676.4 m, 697.8 vs, 715.8 m, 759.2 m, 769.1 s, 779.0 s, 816.0 m, 898.7 m, 940.5 m, 1019.5 s, 1061.5 s, 1075.0 s, 1086.4 m, 1116.8 vs, 1142.3 vs, 1161.0 s, 1184.4 vs, 1237.1 m, 1340.0 m, 1374.9 m, 1435.2 m, 1443.3 m, 1469.6 m, 1575.1 s, 1585.2 s, 2860.2 w, 2914.0 w, 2939.9 w, 2974.1 w. Anal. Calcd for C33H36F3NORu (620.72): C 63.86, H 5.85, N 2.26. Found: C 64.00, H 5.90, N 2.41. Single-crystal X-ray structure: Supporting Information. Bis([2-(2,6-dimethylphenyl)-1,1-dimethyl-3-phenyl-1,2-dihydrocyclopenta[c]pyrrole-10 ,20 ,30 ,40 ,50 -pentamethylruthenocenyl]immonium) hexachlorozirconate (23). A Schlenk vessel was charged with 19 (364 mg, 0.64 mmol) and 30 mL of dry THF. At a temperature of -30 °C, potassium hydride (31 mg, 0.77 mmol) was added. As the reaction vessel warmed to ambient temperature, formation of dihydrogen was observed and the solution darkened slightly. In the glovebox, the solution was filtered to remove an excess of potassium hydride. After drying, the yellowish powder was triturated with portions of n-hexane to wash off traces of unreacted ligand. Via NMR spectroscopy, the successful deprotonation could be proven. In the second step, the solutions of the ligand salt and of ZrCl4 (154 mg, 0.64 mmol) were combined in the glovebox, and a sudden color change to deep red occurred. After stirring overnight, evaporating under vacuum, and dissolving in dry dichloromethane, the precipitated KCl was separated by filtration. Precipitation from a solution of dichloromethane by addition of n-hexane, filtration, and drying under vacuum resulted in 440 mg (49% yield) of a dark red, air-stable powder. Solvent vapor diffusion of diethyl ether into a solution from dichloromethane yielded crystals suitable for X-ray spectroscopy. 1H NMR (CD2Cl2): δ 1.68 (d, 6H, J=6.0 Hz, aryl-CH3), 1.86 (s, 15H, Cp*CH3), 2.14 (d, 6H, J=4.4 Hz, alkyl-CH3), 4.85 (unresolved m, 1H, fulvene H-4), 5.00 (unresolved m, 1H, fulvene H-3), 5.16 (unresolved m, 1H, fulvene H-5), 7.18-7.23 (m, 2H, aryl), 7.33-7.47 (m, 5H, aryl), 7.64-7.69 (m, 1H, aryl). 13C NMR (CD2Cl2): δ 11.8 (Cp*CH3), 20.2, 20.2 (aryl-CH3), 26.1, 27.3 (2 alkyl-CH3), 69.8, 72.8, 79.4, 84.5, 86.7, 89.4, 108.4, 127.3, 129.5, 130.1, 130.2, 130.5, 130.6, 133.3, 135.3, 135.4, 136.7, 181.0 (imminium). MS (FAB pos): m/z Mþ of cation=550.22. Anal. Calcd for C66H76Cl6N2Ru2Zr (1403.42): C 56.49, H 5.46, N 2.00. Found: C 56.37, H 5.41, N 1.82. Single-crystal X-ray structure: Figure 5, Supporting Information.

Acknowledgment. We thank the FFG, Vienna, Austria, and Borealis Polyolefine GmbH, Linz, Austria, for financial support. Supporting Information Available: Crystallographic data for compounds 1-23 (except for 11) as CIF files. This material is available free of charge via the Internet at http://pubs. acs.org.

An Efficient, Modular Route to New 2-Acyl-6-aminopentafulvenes

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