Dibenzo[f,h]quinoline Cr(CO)3 Complexes: Synthesis by Chromium

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Organometallics 2010, 29, 3308–3317 DOI: 10.1021/om100258c

Dibenzo[ f,h]quinoline Cr(CO)3 Complexes: Synthesis by Chromium-Templated Benzannulation, Cyclomanganation, and Haptotropic Chromium Migration Julien Dubarle Offner,† Gregor Schnakenburg,‡ Franc-oise Rose-Munch,§ Eric Rose,*,§ and Karl Heinz D€ otz*,† †

Kekul e-Institut f€ ur Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms Universit€ at Bonn, Gerhard-Domagk-Strasse 1, D-51121 Bonn, Germany, ‡Institut f€ ur Anorganische Chemie, Rheinische Friedrich-Wilhelms Universit€ at Bonn, Gerhard-Domagk-Strasse 1, D-52121 Bonn, Germany, and § UPMC Univ Paris 06, Institut Parisien de Chimie Mol eculaire (UMR CNRS 7201), Case 181, Equipe de Chimie Organique et Organom etallique, 4 Place Jussieu, 75005 Paris, France Received April 1, 2010

Methoxy(benzo[h]quinolinyl)carbene chromium 2, accessible from benzo[h]quinoline in a two-step protocol, undergoes a chromium-templated benzannulation by 3-hexyne to give (dibenzo[ f,h]quinoline)tricarbonylchromium complex 3, in which the hydroquinoid ring is selectively labeled by a Cr(CO)3 fragment. Cyclomanganation of (benzo[h]quinolinyl)carbene complex 2 gives bimetallic chromium carbene 6, the π-skeleton of which, upon reaction with 3-hexyne, is extended to the hydroquinoid dibenzo[ f,h]quinoline σ-manganese-π-chromium complex 7. Comparative timeresolved NMR studies reveal first-order kinetics for the thermo-induced chromium migration along the N-heterocyclic platform from the hydroquinoid to the terminal benzene ring. The cyclomanganation decreases the free activation enthalpy, ΔG‡, and thus accelerates the haptotropic metal shift. The molecular structures of both the chromium carbenes 2 and 6 and the pairs of mono- and heterobimetallic (Cr,Mn) haptotropomers 3/4 and 7/8 are characterized by X-ray analysis.

Introduction Haptotropic metal migration is observed for transition metal π-complexes in which the π-bound ligand offers different coordination possibilities. So far, most examples refer to arene chromium complexes in which the metal fragment is shifted between terminal benzene rings of a fused arene ligand and, thus, can be considered as a moveable *To whom correspondence should be addressed. E-mail: doetz@ uni-bonn.de; [email protected]. (1) For key publications and reviews, see: (a) Deubzer, B.; Fritz, € H. P.; Kreiter, C.; Ofele, K. J. Organomet. Chem. 1967, 7, 289. (b) D€otz, K. H.; Dietz, R. Chem. Ber. 1977, 110, 1555. (c) K€undig, E. P.; Desobry, V.; Grivet, C.; Rudolph, B.; Spichiger, S. Organometallics 1987, 6, 1173. (d) Ustynyuk, N. A. Organomet. Chem. USSR 1989, 2, 20; Metalloorg. Khim. 1989, 2, 43; Chem. Abstr. 1989, 111, 115236. (e) Morris, M. J. In Comprehensive Organometallic Chemistry II; Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Labinger, J. A.; Winter, M. J., Vol. Eds.; Pergamon: Oxford, UK, 1995; Vol. 5, pp 501-504. (f) D€ otz, K. H.; Stinner, C. Tetrahedron: Asymmetry 1997, 8, 1751. (g) Oprunenko, Y. F. Russ. Chem. Rev. 2000, 69, 683–704; Usp. Khim. 2000, 69, 744-746; Chem. Abstr. 2000, 134, 178576. (h) Gloriozov, I. P.; Vasilkov, A. Y.; Oprunenko, Y. F.; Ustynyuk, Y. A. Russ. J. Phys. Chem. 2004, 78, 244. (i) D€otz, K. H.; Szesni, N.; Nieger, M.; N€attinen, K. J. Organomet. Chem. 2003, 671, 58. (j) D€ otz, K. H.; Jahr, H. C. Chem. Rec. 2004, 4, 61. (k) D€otz, K. H.; Wenzel, B.; Jahr, H. C. Top. Curr. Chem. 2004, 248, 63. (l) Jahr, H. C.; Nieger, M.; D€ otz, K. H. Chem.;Eur. J. 2005, 11, 5333. (m) D€otz, K. H.; Stendel, J., Jr. Chem. Rev. 2009, 109, 3227. (2) (a) D€ otz, K. H.; Stendel, J., Jr.; M€ uller, S.; Nieger, M.; Ketrat, S.; Dolg, M. Organometallics 2005, 24, 3219. (b) Ketrat, S.; M€uller, S.; Dolg, M. J. Phys. Chem. 2007, 111, 6094. (c) D€otz, K. H.; Stendel, J., Jr.; Nieger, M. Z. Allg. Anorg. Chem. 2009, 635, 221. pubs.acs.org/Organometallics

Published on Web 07/02/2010

functional group. These η6-η6 metal shifts have been widely studied for naphthalene1 and some phenanthrene complexes.2 Metal migration also occurs across five-membered heteroarene spacers as demonstrated for Cr(CO)3 benzonaphthofuran complexes.3 The chromium-templated [3þ2þ1]benzannulation4 is the method of choice for the regioselective synthesis of arene Cr(CO)3 complexes required for the study of the haptotropic metal shift. Under kinetic control it affords exclusively the regioisomer bearing the Cr(CO)3 fragment coordinated to the hydroquinoid ring. Upon warming, a thermo-induced metal migration provides the thermodynamically stable haptotropomer. With the aim of exploiting metal-metal interactions, heterobimetallic complexes have become a prominent field of organometallic research.5,6 We became interested in whether the chromium migration can be controlled by another metal moiety coordinated to an extended π-platform. Recently, we reported on a chromium shift in binuclear (Cr, Mn) dibenzo[c,e]indene complexes.7 In this paper, we focus on dibenzoquinoline (3) Jahr, H. C.; Nieger, M.; D€ otz, K. H. J. Organomet. Chem. 2002, 641, 185. (4) First report: (a) D€ otz, K. H. Angew. Chem. 1975, 87, 672; Angew. Chem., Int. Ed. Engl. 1975, 14, 644. For recent reviews, see: (b) D€ otz, K. H.; Tomuschat, P. Chem. Soc. Rev. 1999, 28, 187. (c) D€otz, K. H.; Stendel, J., Jr. In Modern Arene Chemistry; Astruc, D., Ed.; Wiley-VCH: Weinheim, 2002; pp 250-296. (d) Minatti, A.; D€otz, K. H. Topics in Organometallic Chemistry; D€otz, K. H., Ed.; Springer: Berlin, 2004; Vol. 13, p 23. (e) Waters, M. L.; Wulff, W. D. Org. React. 2008, 70, 121. (f) Ref 1m. r 2010 American Chemical Society

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Organometallics, Vol. 29, No. 15, 2010

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Scheme 1. Chromium Carbene Functionalization of Benzo[h]quinoline

manganese chromium complexes bearing a terminal pyridine ring, which is well-suited for σ-coordination of lowvalent transition metals.

Results and Discussion Synthesis of Tricarbonyl Dibenzo[ f,h]quinoline Chromium Complex 3. For the synthesis of chromium manganese complexes we developed a strategy that combined the chromiumtemplated benzannulation of Fischer aryl carbenes8 with the cyclomanganation of an N-heterocyclic arene via intramolecular C-H activation.6 The starting material 5-bromobenzo[h]quinoline (1) was prepared according to the protocol reported for the synthesis of 5-bromoisoquinoline.9 Bromination of benzo[h]quinoline with N-bromosuccinimide in concentrated sulfuric acid afforded 5-bromobenzo[h]quinoline (1) as a single regioisomer in 77% yield after crystallization from petroleum ether. Lithiation in THF at -78 °C with n-BuLi and subsequent addition of Cr(CO)6 generated the aryl chromate which, after O-alkylation by MeSO3CF3 at -50 °C in dichloromethane, afforded pentacarbonyl[5-benzo[h]quinolyl(methoxy)carbene]chromium (2) in 53% isolated yield (Scheme 1). The application of 1 equiv of all the reactants is crucial in order to avoid (5) (a) Bitterwolf, T. E.; Raghuveer, K. S. Inorg. Chim. Acta 1990, 172, 59. (b) Li, J.; Hunter, A. D.; McDonald, R.; Santarsiero, B. D.; Bott, S. G.; Atwood, J. L. Organometalllics 1992, 11, 3050. (c) Sun, S.; Dullaghan, C. A.; Carpenter, G. B.; Rieger, A. L.; Rieger, P. H.; Sweigart, D. A. Angew. Chem., Int. Ed. Engl. 1995, 34, 2540. (d) Clark, G. R.; Metzler, M. R.; Whitaker, G.; Woodgate, P. D. J. Organomet. Chem. 1996, 513, 109. (e) Lee, S. S.; Lee, T.-Y.; Lee, J. E.; Chung, Y. K.; Lah, M. S. Organometallics 1996, 15, 3664. (f) Quian, C.; Guo, J.; Sun, J.; Chen, J.; Zheng, P. Inorg. Chem. 1997, 36, 1286. (g) Heck, J.; Dabeck, S.; MeyerFriedrichsen, T.; Wong, H. Coord. Chem. Rev. 1999, 190-192, 1217. (h) Tamm, M.; Bannenberg, T.; Baum, K.; Fr€ohlich, R.; Steiner, T.; MeyerFriedrichsen, T.; Heck, J. Eur. J. Inorg. Chem. 2000, 1161. (i) Schouteeten, S.; Tranchier, J.-P.; Rose-Munch, F.; Rose, E.; Auffrant, A.; Stephenson, G. R. Organometallics 2004, 23, 4308. (j) Prim, D.; Andrioletti, B.; RoseMunch, F.; Rose, E.; Couty, F. Tetrahedron 2004, 60, 3325. (k) Jacques, B.; Tranchier, J.-P.; Rose-Munch, F.; Rose, E.; Stephenson, G. R.; GuyardDuhayon, C. Organometallics 2004, 23, 184. (l) Bitta, J.; Fassbender, S.; Reiss, G.; Frank, W.; Ganter, C. Organometallics 2005, 24, 5176. (m) Bennewitz, J.; Nieger, M.; Lewall, B.; D€otz, K. H. J. Organomet. Chem. 2005, 690, 5892. (n) Djukic, J.-P.; Michon, C.; Berger, A.; Pfeffer, M.; de Cian, A.; Kyritsakas-Gruber, N. J. Organomet. Chem. 2006, 691, 846. (o) Packheiser, R.; Walfort, B.; Lang, H. Organometallics 2006, 25, 4579. (p) Li, M.; Riache, N.; Tranchier, J.-P.; Rose-Munch, F.; Rose, E.; Herson, P.; Bossi, A.; Rigamonti, C.; Licandro, E. Synthesis 2007, 2, 277. (q) Djukic, J.-P.; Hijazi, A.; Flack, H. D.; Bernardinelli, G. Chem. Soc. Rev. 2008, 37, 406. (6) (a) Clark, G. R.; Metzler, M. R.; Whitaker, G.; Woodgate, P. D. J. Organomet. Chem. 1996, 513, 109. (b) Djukic, J.-P.; Maisse, A.; Pfeffer, M.; de Cian, A.; Fischer, J. Organometallics 1997, 16, 657. (c) Djukic, J.-P.; Maisse, A.; Pfeffer, M. J. Organomet. Chem. 1998, 567, 65. (d) Djukic, J.-P.; Maisse, A.; Pfeffer, M.; D€otz, K. H.; Nieger, M. Eur. J. Inorg. Chem. 1998, 1781. (e) Djukic, J.-P.; Maisse, A.; Pfeffer, M.; D€otz, K. H.; Nieger, M. Organometallics 1999, 18, 2786. (7) Dubarle Offner, J.; Fr€ ohlich, R.; Kataeva, O.; Rose-Munch, F.; Rose, E.; D€ otz, K. H. Organometallics 2009, 28, 3004. (8) (a) Fischer, E. O.; Maasb€ ol, A. Angew. Chem. 1964, 76, 644. (b) Fischer, E. O. Auf dem Weg zu Carben- und Carbin-Komplexen (Nobel Lecture). Angew. Chem. 1974, 86, 651–663. (9) Brown, W. D.; Gouliaev, A. H. Org. Synth. 2005, 81, 98.

Figure 1. Molecular structure of complex 2 with thermal ellipsoids at the 50% probability level. The numbering of atoms differs from that used in the text and in the NMR characterization. Peripheral dihedral angle: j (C9-C9a-C9b-N) = 1.57(6)°. Selected bond lengths (A˚): Cr-C10 2.00(1), Cr-CO 1.90(3).

side-reactions such as N-alkylation and formation of an N-pentacarbonylchromium complex (by a simple ligand exchange) as previously observed for similar N-heteroarene complexes.10 The molecular structure of chromium benzoquinolylcarbene 2 was established by X-ray analysis. Dark red crystals of 2 were obtained from dichloromethane at 4 °C. The benzo[h]quinoline skeleton reveals an almost perfect coplanarity, as indicated by a small dihedral angle j (C9-C9a-C9b-N)= 1.6°. The chromium carbene plane is perpendicular to the N-heteroarene plane, as shown by the two torsion angles j1 (Cr-C10-C4-C3a) = 91.56(5)° and j2 (Cr-C10C4-C5) = -86.60(5)° (Figure 1 and Table 1). The chromium-templated benzannulation of carbene complex 2 afforded the hydroquinoid tetracyclic N-heteroarene tricarbonylchromium complex 3. Complex 2 was warmed in tert-butyl methyl ether with 3-hexyne for two hours; in situ protection of the hydroxy-N-heteroarene complex by addition of tert-butyldimethylsilyl triflate in the presence of triethylamine at room temperature resulted in the formation of tricarbonyl{η6-{4b,5,6,7,8,8a}-(6,7-diethyl5-methoxy-8-[(tert-butyl)dimethylsilyloxy]dibenzo[ f,h]quinoline)}chromium (3) in 40% isolated yield (Scheme 2). Dark red crystals of 3 were grown from dichloromethane at 4 °C. The X-ray analysis indicates a moderate deviation of the extended π-N-heteroarene skeleton from coplanarity, as demonstrated by the dihedral angle j (C11-C11aC11b-N) of 9.5° and a long Cr-C7 bond (2.30(1) A˚) due to the bulky electron-donating group TBS,11 implying a helical twist of the dibenzo[ f,h]quinoline platform (Figure 2 and Table 1). The Cr(CO)3 tripod adopts an almost eclipsed (10) K€ uhn, E. Diploma Thesis, University of Bonn, September 2006. (11) Rose-Munch, F.; Rose, E.; Djukic, J.-P.; Vaissermann, J. Eur. J. Inorg. Chem. 2000, 1295.

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Table 1. Crystal Data and Structure Refinement Parameters for Complexes 2, 3, and 4 2 empirical formula

C20H11CrNO6

fw temperature [K] wavelength [A˚] cryst syst space group unit cell dimens a [A˚] b [A˚] c [A˚] R [deg] β [deg] γ [deg] V [A˚3] Z Dcalcd [mg/m3] μ [mm-1] F(000) cryst size [mm] diffractometer θ range [deg] limiting indices reflns collected/unique refinement method data/restraints/params goodness-of-fit on F2 final R indices [I > 2σ(I)] R indices (all data) largest diff in peak/hole [e 3 A˚-3] CCDC deposition number

3

4

413.30 123(2) 0.71073 monoclinic P21/n (No. 14)

C31H35CrNO5SiCH2Cl2 666.62 123(2) 0.71073 triclinic P1 (No. 2)

C31H35CrNO5SiCH2Cl2 666.62 150(2) 0.71073 monoclinic P21/c (No. 14)

6.6296(4) 11.1970(9) 23.8845(18) 90 90.670(4) 90 1772.9(2) 4 1.548 0.684 840 0.48 0.08 0.04 Nonius KappaCCD 2.01 to 27.50 -8 e h e 7 -13 e k e 14 -31 e l e 21 9732/4039 [R(int) = 0.0781] full-matrix least-squares on F 2 4039/0/253 0.942 R1 = 0.0545 wR2 = 0.1103 R1 = 0.1181 wR2 = 0.1297 0.360/-0.608 705504

9.5995(4) 10.4632(4) 18.2902(8) 78.377(2) 80.366(2) 63.336(2) 1601.84(11) 2 1.382 0.602 696 0.80 0.40 0.16 Nonius KappaCCD 2.62 to 30.00 -13 e h e 13 -14 e k e 14 -25 e l e 25 20 658/9304 [R(int) = 0.0539] full-matrix least-squares on F 2 9304/4/415 1.029 R1 = 0.0490 wR2 = 0.1333 R1 = 0.0766 wR2 = 0.1442 0.793/-0.982 705502

8.9672(2) 37.3182(5) 10.4100(2) 90 110.588(2) 90 3261.11(11) 4 1.358 0.591 1392 0.40 0.10 0.10 STOE IPDS-2T 2.16 to 28.00 -11 e h e 11 -49 e k e 49 -13 e l e 12 85 943/7876 [R(int) = 0.0746] full-matrix least-squares on F 2 7876/0/387 1.180 R1 = 0.0627 wR2 = 0.1386 R1 = 0.0737 wR2 = 0.1427 0.793/-0.596 705507

Scheme 2. Synthesis of Dibenzo[f,h]quinoline Complex 3 via Chromium-Templated Benzannulation

conformation, as quantified by the torsion angles R, R1, and R2 of 6-8°. Haptotropic Metal Migration. A solution of the kinetic tricarbonylchromium complex 3 in a polar high-boiling solvent such as di-n-butyl ether was warmed to 105 °C, and the reaction was monitored by IR spectroscopy with aliquots taken every 15 minutes. The kinetic complex 3 revealed a strong A1 band at 1961 cm-1, which progressively shifted during the reaction to 1971 cm-1, indicating the formation of the thermodynamically stable complex 4. After two hours the metal migration was completed, and tricarbonyl{η6{8b,9,10,11,12,12a}-(6,7-diethyl-5-methoxy-8-[(tert-butyl)dimethylsilyloxy]dibenzo[ f,h]quinoline)}chromium (4) was isolated in 90% yield after flash chromatography with silica gel (Scheme 3). The structure of the rearranged haptotropomer was studied by 1H and 13C NMR of the dibenzo[ f,h]quinoline system, which demonstrated that the Cr(CO)3 fragment has migrated to the less electron-rich benzene ring and not to the

Figure 2. Molecular structure of complex 3 with thermal ellipsoids at the 50% probability level. The numbering of atoms differs from that used in the text and in the NMR characterization. Peripheral dihedral angle: j (C11-C11a-C11b-N) = 9.46(5)°. Torsion angles: R (C5-Crproj.-Cr-C23) = -5.74°, R1 (C3B-Crproj.-Cr-C24) = -5.86°, and R2 (C7-Crproj.Cr-C25) = -7.68° (Crproj. is the projection of the chromium atom onto the plane of the arene ring). Selected bond lengths (A˚): Cr-C3B 2.18(1), Cr-C4 2.23(1), Cr-C5 2.22(1), Cr-C6 2.28(1), Cr-C7 2.30(1), Cr-C7A 2.21(1).

N-heterocyclic ring. A comparison of the 1H NMR spectra of 3 and 4 reveals an upfield shift of 1.2-1.7 ppm for the hydrogen atoms H9-H12 in the rearranged product 4.

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Scheme 3. Haptotropic migration of the Cr(CO)3 Fragment Across the Dibenzo[f,h]quinoline Platform in Complex 3

Table 2. Selected 1H NMR of Complexes 3 (CD3COCD3), 4, 7, and 8 (CD2Cl2)a entry 1 2 3 4 5

6 a

complex and Δδ kinetic complex 3 thermodynamic complex 4 Δδ (δHicomplex 4 δHicomplex 3) cyclomanganated kinetic complex 7 cyclomanganated thermodynamic complex 8 Δδ (δHicomplex 8 δHicomplex 7)

H2

H3

H4

H9

H10

H11

H12

8.64 7.37

9.15

8.79

7.33

7.30

8.67

8.76 7.52

9.51

7.44

5.64

5.59

7.44

0.12 0.15

0.36 -1.35 -1.69 -1.71 -1.24

9.50 7.50

9.03

8.12

7.55

8.68

9.63 7.50

8.84

7.44

5.46

6.23

Figure 3. Kinetic plot for the haptotropic metal migration of the tricarbonyl(dibenzo[f,h]quinoline)chromium complex 3 at 353 K.

0.13 0.00 -0.19 -1.89 -2.09 -1.24

General formula with atom numbers used for 1H NMR analyses:

A slight displacement of the signals H2-H4 to higher frequencies indicates that the heteroarene is slightly deprived of electrons (Table 2, entries 1, 2, and 3). In addition, the coordinated carbon atoms C9-C12 in the 13C NMR spectra are significantly shifted upfield by 30-40 ppm, which is a very clear indication of the haptotropic chromium migration. On the other hand, 1H NMR data show a large difference of chemical shift between the two ortho protons H11 and H12, which is unusual for tricarbonyl(arene)chromium complexes.12 The intramolecular nature of the metal shift as required for a haptotropic migration is supported by a kinetic NMR study. A perfluorinated arene has been used as a solvent to avoid any competing coordination of the Cr(CO)3 fragment to solvent molecules. The reaction was performed at T = 353 K (80 °C) for three hours in hexafluorobenzene using a DMSO-d6 inlet as an external reference. The study resulted in first-order kinetics with a rate constant k = (3.4 ( 0.5) 10-3 s-1 and a free activation enthalpy ΔG‡ = 103.6 ( 0.3 kJ 3 mol-1 (Figure 3). (12) (a) van Meurs, F.; van der Toorn, J. M.; van Bekkum, H. J. Organomet. Chem. 1976, 113, 341. (b) Boutonnet, J. C.; Levisalles, J.; Rose, E.; Precigoux, G.; Courseille, C.; Platzer, N. J. Organomet. Chem. 1983, 255, 317. (c) Boutonnet, J. C.; Rose-Munch, F.; Rose, E.; Jeannin, Y.; Robert, F. J. Organomet. Chem. 1985, 297, 185. (d) Rose-Munch, F.; Rose, E.; Semra, A.; Philoche-Levisalles, M. J. Organomet. Chem. 1989, 363, 297. (e) Ohlsson, B.; Ullenius, C.; Jaguer, S.; Grivet, C.; Wenger, E.; K€undig, E. P. J. Organomet. Chem. 1989, 365, 243. (f) Rose-Munch, F.; Aniss, K.; Rose, E.; Vaissermann, J. J. Organomet. Chem. 1991, 415, 223. (g) Djukic, J.-P.; Rose-Munch, F.; Rose, E.; Dromzee, Y. J. Am. Chem. Soc. 1993, 115, 6434.

Figure 4. Molecular structure of complex 4 with thermal ellipsoids at the 50% probability level. The numbering of atoms differs from that used in the text and in the NMR characterization. Peripheral dihedral angle: j (C11-C11a-C11b-N) = 14.63°(2). Torsion angles: R (C9-Crproj.-Cr-C23) = -28.88°, R1 (C7B-Crproj.-Cr-C24) = -32.49°, and R2 (C11-Crproj.Cr-C25) = -26.47° (Crproj. is the projection of the chromium atom onto the plane of the arene ring). Selected bond lengths (A˚): Cr-C7B 2.26(3), Cr-C8 2.20(3), Cr-C9 2.21(3), Cr-C10 2.22(3), Cr-C11 2.21(3), Cr-C11A 2.22(3).

Dark red crystals of 4 suited for X-ray analysis were grown from dichloromethane at 4 °C, which allowed for a comparison of the molecular structures of haptotropomers 3 and 4. The thermodynamic haptotropomer 4 reveals a significantly increased dihedral angle j (C11-C11a-C11b-N) of 14.6°, resulting in an enhanced helical twist of the π-platform. The Cr(CO)3 fragment tends to turn toward the outside of the ligand, as previously observed for a series of 1,2-disubstituted arene Cr(CO)3 complexes.12a,b The average distance between the chromium atom and the six carbon atoms C7B, C8, C9, C10, C11, and C11A of the coordinated ring, 2.21 ( 0.01 A˚, is only slightly shorter than in the kinetic complex 3 (Figure 4 and Table 1) and comparable to other tricarbonyl(arene)chromium complexes.12 Synthesis of Cyclomanganated Tricarbonyl Dibenzo[ f,h]quinolyl Chromium Complex 7. In order to incorporate a second metal unit into the dibenzo[ f,h]quinoline system, we

3312



focused on the ortho-manganation of 5-bromobenzo[h]quinoline (1), which was synthesized via an elegant procedure reported by Djukic et al.6b-e using pentacarbonyl(benzyl-κC1)manganese(I) in refluxing heptane. The tetracarbonyl{5-bromobenzo[h]quinolyl-κC10-κN}manganese(I) complex 5 was obtained in almost quantitative yield (98%) as a yellow airstable powder (Scheme 4). Crystallization of 5 from dichloromethane at 4 °C gave yellow crystals suited for X-ray crystallography. The orthomanganated ligand represents a plane with a marginal dihedral angle j (C9-C9a-C9b-N) = 0.32(8)°. The hexacoordinated manganese atom is in an octahedral configuration with Mn-C9 and Mn-N bond lengths of 2.06(2) and 2.07(2) A˚, which are significantly longer than the four Mn-CO bonds (average 1.84 A˚) (Figure 5 and Table 3). Attempts to modify the tetracarbonyl{5-bromobenzo[h]quinolyl-κC10-κN}manganese(I) complex (5) into a chromium carbene via the standard Fischer route failed. We speculate that under these conditions n-butyllithium tends to add to the carbonylmanganese moiety rather than to effect the bromine-lithium exchange and to induce the decomposition Scheme 4. Ortho-Manganation of 5-Bromobenzo[h]quinoline

of the manganese complex despite the mild low-tempertaure conditions applied. Thus, we followed a reverse strategy for the synthesis of the desired heterobimetallic chromium carbene complex 6 and concentrated on the ortho-manganation of the pentacarbonyl[5-benzo[h]quinolyl(methoxy)carbene]chromium(0) complex, 2. A similar protocol;using the pentacarbonyl(benzyl-κC1)manganese(I) complex in refluxing heptane;as applied in the synthesis of the tetracarbonyl{5-bromobenzo[h]quinolylκC10-κN}manganese(I) complex (5) resulted in a straightforward access to tetracarbonyl{pentacarbonyl[benzo[h]quinolyl-κC10κN-5-(methoxy)carbene]chromium(0)}manganese(I) (6), which

Figure 5. Molecular structure of complex 5 with thermal ellipsoids at the 50% probability level. The numbering of atoms differs from that used in the text and in the NMR characterization. Peripheral dihedral angle: j (C9-C9a-C9b-N) = 0.32(8)°. Selected bond lengths (A˚): Mn-N 2.07(2), Mn-C9 2.06(2), Mn-CO 1.84(5).

Table 3. Crystal Data and Structure Refinement Parameters for Complexes 5 to 8 5

6

empirical formula

C17H7BrMnNO4

C24H10CrMnNO10

fw temperature [K] wavelength [A˚] cryst syst space group unit cell dimens a [A˚] b [A˚] c [A˚] R [deg] β [deg] γ [deg] V [A˚3] Z Dcalcd [mg/m3] μ [mm-1] F(000) cryst size [mm] diffractometer θ range [deg] limiting indices

424.09 123(2) 0.71073 triclinic P1 (No. 2) 6.4995(4) 10.8762(9) 11.2558(11) 92.791(4) 104.229(5) 100.301(5) 755.24(11) 2 1.865 3.540 416 0.48 0.16 0.08 Nonius KappaCCD 2.81 to 28.99 -8 e h e 8 -14 e k e 14 -13 e l e 15 8727/3881 [R(int) = 0.0434] full-matrix least-squares on F2 3881/0/217 1.026 R1 = 0.0370 wR2 = 0.0945 R1 = 0.0548 wR2 = 0.1005 1.646/-0.465 705503

reflns collected/unique refinement method data/restraints/params goodness-of-fit on F2 final R indices [I > 2σ(I)] R indices (all data) largest diff in peak/hole [e 3 A˚-3] CCDC deposition number

7

8 C35H34CrMnNO9Si

579.27 123(2) 0.71073 monoclinic P21/c (No. 14)

C35H34CrMnNO9SiCH2Cl2 832.59 123(2) 0.71073 orthorhombic Pbca (No. 61)

6.66030(10) 12.9097(2) 26.8855(5) 90 96.4883(9) 90 2296.87(7) 4 1.675 1.084 1160 0.56 0.16 0.12 Nonius KappaCCD 2.78 to 30.00 -9 e h e 6 -18 e k e 17 -37 e l e 36 26 444/6649 [R(int) = 0.1067] full-matrix least-squares on F2 6649/0/335 1.031 R1 = 0.0544 wR2 = 0.1320 R1 = 0.0737 wR2 = 0.1403 1.551/-1.112 705505

13.0742(2) 21.2949(4) 27.0004(5) 90 90 90 7517.3(2) 8 1.471 0.853 3424 0.24 0.23 0.10 Nonius KappaCCD 1.91 to 27.49 -16 e h e 16 -27 e k e 27 -35 e l e 32 46 089/8569 [R(int) = 0.0525] full-matrix least-squares on F2 8569/0/479 1.008 R1 = 0.0365 wR2 = 0.0955 R1 = 0.0615 wR2 = 0.1041 0.594/-0.515 705508

10.5612(3) 11.7284(4) 15.3659(6) 70.3134(16) 83.4606(18) 77.2105(18) 1746.00(10) 2 1.422 0.761 772 0.80 0.60 0.60 Nonius KappaCCD 2.69 to 29.00 -14 e h e 14 -15 e k e 15 -17 e l e 20 21 735/9256 [R(int) = 0.0426] full-matrix least-squares on F2 9256/0/441 1.032 R1 = 0.0482 wR2 = 0.1475 R1 = 0.0626 wR2 = 0.1551 1.137/-1.419 705506

747.67 123(2) 0.71073 triclinic P1 (No. 2)

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Figure 6. Molecular structure of complex 6 with thermal ellipsoids at the 50% probability level. The numbering of atoms differs from that used in the text and in the NMR characterization. Peripheral torsion angle: j (C9-C9a-C9b-N) = 0.91(1)°. Selected bond lengths (A˚): Mn-N 2.07(2), Mn-C9 2.06(1), Mn-CO 1.84(6), Cr-C10 2.02(1), Cr-CO 1.92(4). Scheme 5. Ortho-Manganation of the Fischer-Carbene Complex 2

could be isolated in 94% yield (Scheme 5). It is important to note that, even under these high-temperature conditions (100 °C), the chromium carbene is stable toward decomposition. Crystallization of 6 from dichloromethane at 4 °C gave red crystals suited for X-ray analysis, which allowed establishing the molecular structure of the bimetallic chromium carbene. The small torsion angle j (C9-C9a-C9b-N) = 0.91(1)° indicates that the introduction of the chromium carbene moiety does not hamper the coplanarity of the heteroarene skeleton linking both metal functionalities. As observed for the non-manganated analogue 2, the chromium carbene plane in the bimetallic complex 6 is distinctly turned out of the benzoquinoline plane, as quantified by the torsion angles j1 (Cr-C10-C4-C3a) = 107.28(1)° and j2 (Cr-C10C4-C5) = -78.06(1)° (Figure 6 and Table 3). The heterobimetallic carbene complex 6 undergoes a chromium-templated benzannulation, as demonstrated by reaction with 3-hexyne. The resulting hydroxy-N-heteroarene was O-protected by addition of tert-butyl dimethylsilyl triflate in the presence of triethylamine at room temperature to afford tetracarbonyl{tricarbonyl(η6-{4b,5,6,7,8,8a}-(6,7diethyl-5-methoxy-8-[(tert-butyl)dimethylsilyloxy]dibenzo[ f,h]quinolyl-κC12-κN)chromium(0)}manganese(I) (7) (Scheme 6). The yield of 65% significantly exceeds that obtained in the synthesis of the non-cyclomanganated analogue 3, which may be explained by the fact that the ability of the benzoquinoline to act as an N-ligand is blocked by cyclomanganation, while the free N-functionality in 2 may compete with the alkyne for coordination at chromium during the synthesis of 3. The IR spectrum of complex 7 in the ν(CO) range resembles the virtual superposition of the IR spectra of the tricarbonylchromium and the tetracarbonylmanganese complexes 3 and 5, suggesting that there is no evident interaction between the two metal carbonyl groups. Crystallization of 7 from dichloromethane at 4 °C afforded dark red crystals. The Cr(CO)3 tripod is almost


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Figure 7. Molecular structure of complex 7 with thermal ellipsoids at the 50% probability level. The numbering of atoms differs from that used in the text and in the NMR characterization. Peripheral torsion angle j (C11-C11a-C11b-N) = 6.26(2)°. Torsion angles: R (C3B-Crproj.-Cr-C27) = 8.12°, R1 (C7Crproj.-Cr-C28) = 10.39°, and R2 (C5-Crproj.-Cr-C29) = 10.50° (Crproj. is the projection of the chromium atom onto the plane of the arene ring). Selected bond lengths (A˚): Mn-N 2.07(2), Mn-C11 2.05(3), Cr-C3B 2.31(2), Cr-C4 2.23(2), Cr-C5 2.21(2), Cr-C6 2.29(2), Cr-C7 2.30(2), Cr-C7A 2.21(2). Scheme 6. Benzannulation of the Cyclomanganated (Benzo[h]quinolyl)chromium Carbene Complex 6

eclipsed with the carbon atoms C3B, C5, and C7. In contrast to mono- and bimetallic chromium quinolylcarbenes 2 and 6, the benzo[h]quinoline skeleton in the benzannulation product 7 distinctly deviates from coplanarity. Generally, the benzannulation of chromium phenanthrenylcarbene results in a helical twist of the triphenylene platform, as also observed for dibenzoquinoline complex 3, where j (C11C11a-C11b-N) = 9.46(5)°. However, this deformation is reduced by cyclomanganation, which tends to maintain the coplanarity of the benzo[h]quinoline skeleton, as indicated by a torsion angle j (C11-C11a-C11b-N) of 6.26(2)° (Figure 7 and Table 3). Haptotropic Metal Migration. To study the influence of cyclomanganation on the haptotropic migration of the Cr(CO)3 fragment, complex 7 was warmed in di-n-butyl ether to 105 °C while the reaction was monitored by IR spectroscopy. Complex 7 reveals a very strong A1 band at 1963 cm-1, which is shifted during the reaction to 1975 cm-1, indicating the formation of the thermodynamically stable tetracarbonyl{tricarbonyl(η6-{8b,9,10,11,12,12a}-(6,7-diethyl5-methoxy-8-[(tert-butyl)dimethylsilyloxy]dibenzo[ f,h]quinoline-κC12-κN)chromium(0)}manganese(I) complex (8). After three hours the reaction was complete and after chromatography on silica gel a 52% yield of 8 was obtained (Scheme 7). As expected, the tricarbonylchromium moiety has migrated to the terminal benzene ring and not to the N-heterocyclic ring; the presence of the manganese moiety is compatible with the

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Scheme 7. Haptotropic Migration of the Cr(CO)3 Fragment in the Heterobimetallic (Cr, Mn) Dibenzo[f,h]quinoline Complex 7

metal rearrangement, although in lower yield. The haptotropic migration of the chromium moiety results in a significant increase of 12 cm-1 for the Cr(CO)3-A1 band when complex 7 (1963 cm-1) is rearranged to its haptotropomer 8 (1975 cm-1). The ν(CO) absorptions of the tricarbonylchromium moieties in complexes 4 and 8 do not indicate a significant interaction between the Cr(CO)3 and the Mn(CO)4 moieties. A comparison of the 1H NMR spectra of 7 and 8 reveals an upfield shift of 1.2-2.1 ppm for the hydrogen atoms H9-H11 for the thermodynamically stable haptotropomer (Table 2, entries 4, 5, and 6). Similarly, the aromatic carbon atoms C9-C11 in the 13C NMR spectra are shifted upfield in complex 8 by 30-38 ppm. These shifts are typical for the haptotropic chromium rearrangement. The chemical shifts observed for H9, H10, and H11 resonating at 6.23, 5.46, and 7.44 ppm, respectively, are unusual. As encountered with complex 4, to our knowledge Δδ = δH11 - δH10 = 2.02 ppm represents the largest difference of chemical shifts between two adjacent hydrogen atoms in (arene)tricarbonylchromium complexes, probably due to the constrained conformation of the chromium moiety and intensified by the carbonyl ligand formed by C29 and O9 of the Mn(CO)4 entity.12 Crystallization of 8 from dichloromethane at 4 °C resulted in dark red crystals with a triclinic structure from the space group P1. The haptotropic migration slightly increases the helical distortion of the benzoquinoline platform, as shown by the dihedral angle j (C11-C11a-C11b-N) = -8.93(4)°, which is less pronounced than in the non-cyclomanganated congener 4 (-14°). The Cr(CO)3 tripod is almost staggered, indicating a steric interference with the Mn(CO)4 moiety and the respective carbonyl ligands. Furthermore, the Cr-C11 bond is the longest Cr-C bond, suggesting that the Mn(CO)4 acts like an electron-donating substituent, which moves the carbon atom C11 away from the chromium fragment (Figure 8 and Table 3). To establish the intramolecular nature of the metal migration and to quantify the influence of the cyclomanganation on this process, a kinetic NMR study in C6F6 was carried out. The study performed at T = 353 K (80 °C) established a first-order reaction and resulted in a rate constant k = (10.7 ( 0.5) 10-3 s-1 and a free activation enthalpy for the transition state ΔG‡ = 100.3 ( 0.3 kJ 3 mol-1, both consistent with an intramolecular migration of the Cr(CO)3 fragment (Figure 9). The rate constants obtained from the comparative kinetic studies of complexes 3 and 7 demonstrate that cyclomanganation speeds up the chromium migration: The metal shift in the cyclomanganated complex 7 occurs about 3 times faster than in the Mn-free analogue 3. This reflects the decrease of the free activation enthalpy by ca. 3 kJ 3 mol-1 upon cyclometalation. In summary, cyclomanganation favors the haptotropic migration of the Cr(CO)3 fragment but results in lower yield, which might be caused by a partial decomplexation of the heterobimetallic complex during the metal shift.

Figure 8. Molecular structure of complex 8 with thermal ellipsoids at the 50% probability level. The numbering of atoms differs from that used in the text and in the NMR characterization. Peripheral dihedral angle: j (C11-C11a-C11b-N) = -8.93(4)°. The torsion angles are R (C8-Crproj.-Cr-C23) = 24.59°, R1 (C11A-Crproj.-Cr-C24) = 18.88°, and R2 (C10Crproj.-Cr-C25) = 22.28° (Crproj. is the projection of the chromium atom onto the plane of the arene ring). Selected bond lengths (A˚): Mn-N 2.07(2), Mn-C11 2.05(2), Cr-C7B 2.34(2), Cr-C8 2.21(2), Cr-C9 2.22(2), Cr-C10 2.29(2), Cr-C11 2.35(2), Cr-C11A 2.20(2).

Figure 9. Kinetic plot of the haptotropic metal migration of the cyclomanganated tricarbonyl(dibenzo[f,h]quinoline)chromium complex 7 at 353 K.

Conclusion A Cr(CO)3-coordinated hydroquinoid dibenzo[ f,h]quinoline skeleton is accessible from benzo[h]quinoline in a threestep sequence via benzannulation of a chromium benzo[h]quinolinylcarbene by an alkyne as the key step. Under kinetic control the hydroquinoid ring is exclusively labeled by the chromium fragment. Upon warming, the Cr(CO)3 fragment undergoes a regioselective haptotropic metal migration to the other terminal benzene ring in excellent yield. Comparative kinetic studies reveal that cyclomanganation of the benzo[h]quinoline entity decreases the barrier of activation for the metal shift by 3 kJ 3 mol-1 and accelerates the metal

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migration by a factor of 3. This example demonstrates that functionalization of the π-platform by both a heterocycle and another metal fragment is suited to control the haptotropic metal migration by a proper adjustment of the electronic and steric properties of the aromatic skeleton.

Experimental Section General Procedures. All experiments involving organometallic compounds were carried out under an argon atmosphere by using standard Schlenk techniques. Solvents were distilled, dried using standard methods, saturated, and stored under argon. Degassed Macherey Nagel silica gel MN 60 (0.015-0.025 mm) was used for column chromatography. 1H and 13C NMR spectra were recorded on a Bruker DRX 500 at room temperature. The solvent used for the NMR monitoring of the haptotropic migration was carefully degassed using the pumpfreeze-thaw method (three cycles), saturated, and stored under argon. IR spectra were recorded in petroleum ether with a Nicolet Magna 550 FT spectrometer. Mass spectra (FABþ and EI) were obtained from Kratos MS 50. Melting points were determined with a Reichert Austria apparatus. X-ray crystallographic analyses were performed using a Nonius KappaCCD diffractometer equipped with a low-temperature device (Oxford Cryosystems, 600er series, samples of 2-6, 8) and on a STOE IPDS-2T diffractometer equipped with a low-temperature device (Oxford Cryosystems, 700er series, sample of 7) using graphite-monochromated Mo KR radiaton (λ = 0.71073 A˚). The structures were solved using direct methods and were refined by full-matrix least-squares techniques on F2 using the ShelX program system.13 All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were included in calculated positions using a riding model. Crystallographic data as well as CCDC deposition numbers can be found in Tables 1 and 3. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam. ac.uk/data_request/cif. The numbering of the atoms in the X-ray structures differs from that used for the nomenclature and the NMR spectra. 5-Bromobenzo[h]quinoline (1). In a coolable Schlenk tube concentrated H2SO4 (50 mL) was cooled to 0 °C under argon; then benzo[h]quinoline (5.0 g, 27.9 mmol) was slowly added to the acid. The reaction is very exothermic and should not reach more than 30 °C. The solution was cooled to -26 °C, and N-bromosuccinimide was slowly added while the temperature was kept between -26 and -22 °C. The suspension was stirred at -22 °C for 1 h and then at -18 °C for another 1.5 h. The mixture was poured on 250 g of crushed ice, and 25% ammonia solution was added until pH = 9 was reached while the temperature was kept under 25 °C. The mixture was extracted with Et2O. The organic phase was washed first with 15% aqueous NaOH and then twice with distilled water and dried over MgSO4. The compound was purified by crystallization: It was dissolved in 100 mL of petroleum ether and 10 mL of dichloromethane and then placed in a refrigerator to give 5.5 g (77%) of small yellow needles. 1H NMR (500 MHz, CDCl3): δ (ppm) 7.60 (1H, dd, 3J = 4.3 Hz, 3J = 8.2 Hz, H3), 7.68 (1H, ddd, 3J = 7.0 Hz, 3J = 8.0 Hz, 4J = 1.4 Hz, H8), 7.75 (1H, ddd, 3 J = 7.9 Hz, 3J = 7.0 Hz, 4J = 1.3 Hz, H9), 7.80 (1H, ddd, 3J = 7.9 Hz, 4J = 1.4 Hz, 5J = 0.7 Hz, H10), 8.12 (1H, s, H6), 8.58 (1H, dd, 3J = 8.2 Hz, 4J = 1.7 Hz, H4), 8.99 (1H, dd, 3J = 4.3 Hz, 4J = 1.7 Hz, H2), 9.25 (1H, ddd, 3J = 8.0 Hz, 4J = 1.3 Hz, 5 J = 0.7 Hz, H7). 13C NMR (125 MHz, CDCl3): δ (ppm) 120.3 (C5), 123.2 (C3), 125.4 (C10), 126.3 (ArC), 127.7 (C7), 128.2, 129.6 (C8, C9), 131.6 (C6), 131.7, 134.3 (2 ArC), 136.3 (C4), 147.8 (C10b), 150.0 (C2). (13) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.

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Pentacarbonyl[5-benzo[h]quinolyl(methoxy)carbene]chromium(0) (2). 5-Bromobenzo[h]quinoline (1) (1.29 g, 5.0 mmol) was dissolved in 30 mL of freshly distilled absolute tetrahydrofuran to produce a yellow solution. n-BuLi (a 2.5 M solution in hexane (2.0 mL, 5.0 mmol)) was added dropwise at -78 °C. The solution became brown immediately; after 5 min Cr(CO)6 (1.10 g, 5.0 mmol) was added. The solution was allowed to reach 20 °C within 1 h, and then the solvent was evaporated via a vacuum pump. The resulting brown oil was dissolved in 30 mL of dichloromethane, and the solution was cooled to -50 °C. Methyltriflate (0.82 g, 5.0 mmol) was added slowly, and the resulting solution was warmed to room temperature within 30 min and stirred for one extra hour. The solution became deeply dark red. Chromatography on silica gel at 5 °C with petroleum ether/dichloromethane (1:1) afforded 1.10 g (53%) of complex 2 as an air-sensitive dark red product. Crystallization from dichloromethane at 4 °C gave dark red crystals suitable for X-ray analysis. IR (petroleum ether): ν(CO) 2065 (A1, m), 1957 (E, vs) cm-1. 1H NMR (500 MHz, acetone-d6): δ (ppm) 4.48 (3H, s, OCH3), 7.62 (1H, s, H6), 7.71 (1H, dd, 3 J = 8.3 Hz, 3J = 4.3 Hz, H3), 7.80 (2H, m, H8 and H9), 8.03 (1H, dd, 3J = 8.3 Hz, 4J = 1.5 Hz, H4), 8.09 (1H, dd, 3J = 5.1 Hz, 4 J = 1.8 Hz, H10), 9.07 (1H, dd, 3J = 4.3 Hz, 4J = 1.5 Hz, H2), 9.32 (1H, m, H7). 13C NMR (125 MHz, acetone-d6): δ (ppm) 67.1 (OCH3), 119.7 (C5), 122.3, 124.2, 127.7, 128.5, 128.8 (5 ArCH), 130.8, 131.9, 132.4 (3 ArC), 145.6 (C10b) 149.5 (C2), 215.7 (4 trans-Cr(CO)), 224.5 (1 cis-Cr(CO)), 356.8 (C10). MS (EI): m/z 413 [Mþ, 3], 385 [Mþ - 1CO, 14], 357 [Mþ - 2CO, 7],329 [Mþ - 3CO, 6],301 [Mþ - 4CO, 24], 273 [Mþ - 5CO, 99]. Tricarbonyl{η6-4b,5,6,7,8,8a-(6,7-diethyl-5-methoxy-8-[(tertbutyl)dimethylsilyloxy]dibenzo[ f,h]-quinoline)}chromium(0) (3). A solution of pentacarbonyl[5-benzo[h]quinolyl(methoxy)carbene]chromium(0) (2) (0.40 g, 0.97 mmol) and 3-hexyne (0.318 g, 3.88 mmol) in 15 mL of tert-butyl methyl ether was warmed to 65 °C (oil bath temperature) for 2 h. Then the phenolic group was protected at room temperature by addition of triethylamine (0.36 mL, 4.0 mmol) and tert-butyldimethylsilyl triflate (1.05 g, 4.0 mmol). After stirring for 2 h, chromatography on silica gel at 5 °C with petroleum ether/dichloromethane (1:1) afforded 0.23 g of complex 3 (40%) as an air-sensitive red powder. Crystallization from dichloromethane at 4 °C afforded dark red crystals suitable for X-ray analysis. Mp: up to 230 °C. IR (petroleum ether): ν(CO) 1961(A1, vs), 1903 (E, s), 1886 (E, s) cm-1. 1H NMR (500 MHz, acetone-d6): δ (ppm) -0.65 (3H, s, SiCH3), -0.23 (3H, s, SiCH3), 0.82 (9H, s, SiC(CH3)3), 1.06-1.12 (6H, m, CH2CH3, CH2CH3), 2.16-2.23 (1H, m, CH2CH3), 2.41-2.51 (2H, m, CH2CH3), 2.68-2.75 (1H, m, CH2CH3), 3.45 (3H, s, OCH3), 7.30 (1H, dt, 3 J = 8.0 Hz, 4J = 1.2 Hz, H11), 7.33 (1H, dt, 3J = 7.1 Hz, 4J = 1.5 Hz, H10), 7.37 (1H, dd, 3J = 8.5 Hz, 3J = 4.3 Hz, H3), 8.64 (1H, dd, 3J = 4.3 Hz, 4J = 1.6 Hz, H2), 8.67 (1H, dd, 3J = 8.0 Hz, 4 J = 1.2 Hz, H12), 8.79 (1H, dd, 3J = 7.8 Hz, 4J = 1.5 Hz, H9), 9.15 (1H, dd, 3J = 8.5 Hz, 4J = 1.6 Hz, H4). 13C NMR (125 MHz, acetone-d6): δ (ppm) -4.9, -3.9 (Si(CH3)2), 14.2 (CH3), 18.0 (SiC), 18.3 (CH3), 19.2 (CH2), 21.3 (CH2), 25.1 (SiC(CH3)3), 65.3 (OCH3), 84.1, 102.0, 105.6, 114.1, 122.2 (5 ArC), 122.6 (C3), 124.9, 127.3, 128.1, 128.2 (C9, C10, C11, C12), 129.3, 129.9, 131.7 (3 ArC), 136.8 (C4), 140.5 (ArC), 148.6 (C12b), 150.2 (C2), 233.5 (Cr(CO)3). MS (EI): m/z 581.2 [Mþ, 3], 497.2 [Mþ - 3CO, 5], 445.2 [Mþ - Cr - 3CO, 99]. HRMS (ESI): m/z [M þ H]þ calcd 582.1768, found 582.1763. Tricarbonyl{η6-8b,9,10,11,12,12a-(6,7-diethyl-5-methoxy-8[(tert-butyl)dimethylsilyloxy]dibenzo[ f,h]quinoline)}chromium(0) (4). A solution of the tricarbonyl(η6-4b,5,6,7,8,8a-(6,7-diethyl-5-methoxy-8-[(tert-butyl)dimethylsilyloxy]dibenz[ f,h]quinoline)chromium(0) complex (3) (0.50 g, 0.86 mmol) in 60 mL of di-n-butyl ether was warmed to 105 °C and stirred for 2 h under an argon atmosphere. Chromatography on silica gel at 5 °C in dichloromethane afforded 0.45 g of complex 4 (90%) as an air-sensitive redorange powder. Crystallization from dichloromethane at 4 °C afforded red crystals suitable for X-ray analysis. Mp: 207 °C. IR (petroleum ether): ν(CO) 1971 (A1, vs), 1907 (E, s) cm-1. 1H NMR

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(500 MHz, CD2Cl2): δ (ppm) -0.32 (3H, s, SiCH3), -0.13 (3H, s, SiCH3), 1.12 (9H, s, SiC(CH3)3), 1.25-1.29 (6H, m, CH2CH3, CH2CH3), 2.60-2.67 (1H, m, CH2CH3), 2.70-2.77 (1H, m, CH2CH3), 2.87-3.00 (2H, m, CH2CH3), 3.63 (3H, s, OCH3), 5.59 (1H, dt, 3J = 6.7 Hz, 4J = 1.0 Hz, H11), 5.64 (1H, dt, 3J = 6.0 Hz, 4J = 1.3 Hz, H10), 7.42-7.45 (2H, m, H9 and H12), 7.52 (1H, dd, 3J = 8.5 Hz, 3J = 4.3 Hz, H3), 8.76 (1H, dd, 3J= 4.3 Hz, 4 J = 1.5 Hz, H2), 9.51 (1H, dd, 3J = 8.5 Hz, 4J = 1.5 Hz, H4). 13C NMR (125 MHz, CD2Cl2): δ (ppm) -5.2, -3.0 (Si(CH3)2), 15.0 (CH3), 15.7 (CH3), 18.5 (SiC), 20.5 (CH2), 21.1 (CH2), 26.0 (SiC(CH3)3), 61.3 (OCH3), 89.5, 91.6, 92.4, 93.2 (C9-C12), 99.2, 107.6, 120.5, 121.9 (4 ArC), 124.0 (C3 or C4), 125.0 (ArC), 135.5 (C3 or C4), 137.6, 138.8, 146.1, 147.2 (4 ArC), 148.1 (C2), 152.6 (C12b), 233.1 (Cr(CO)3). MS (EI): m/z 581.1 [Mþ, 8], 497.1 [Mþ - 3CO, 69], 445.2 [Mþ - Cr - 3CO, 66]. MS (ESI): m/z [M þ H]þ calcd 582.1768, found 582.1763. Tetracarbonyl{5-bromobenzo[h]quinoline-KC10-KN}manganese(I) (5). 5-Bromobenzo[h]quinoline (1) (1.29 g, 5.0 mmol) and pentacarbonyl(benzyl-κC1)manganese(I) (1.43 g, 5.0 mmol) were dissolved in n-heptane (200 mL). The mixture was stirred and warmed to the solvent’s boiling point (98 °C) during 2 h. Chromatography on silica gel at 10 °C with petroleum ether/ dichloromethane (3:1) afforded 2.08 g (98%) of tetracarbonyl{5-bromobenzo[h]quinoline-κC10-κN}manganese(I) (5) as a yellow powder. Crystallization from dichloromethane at 4 °C gave yellow crystals suitable for X-ray analysis. Mp: 147 °C. IR (petroleum ether): ν(CO) 2079 (m), 1998 (vs), 1984 (s), 1944 (s) cm-1. 1H NMR (500 MHz, acetone-d6): δ (ppm) 7.75 (1H, dd, 3 J = 6.8 Hz, 3J = 7.9 Hz, H8), 7.79 (1H, dd, 3J = 7.9 Hz, 4J = 1.1 Hz, H9), 7.90 (1H, dd, 3J = 8.2 Hz, 3J = 5.2 Hz, H3), 8.26 (1H, dd, 3J = 6.8 Hz, 4J = 1.1 Hz, H7), 8.38 (1H, s, H6), 8.80 (1H, dd, 3J = 8.2 Hz, 4J = 1.3 Hz, H4), 9.32 (1H, dd, 3J = 5.2 Hz, 4J = 1.3 Hz, H2). 13C NMR (125 MHz, acetone-d6): δ (ppm) 116.6 (C5), 121.7 (C9), 123.2 (C3), 126.1 (ArC), 130.0 (C8), 132.3 (C6), 133.4 (ArC), 136.8 (C4), 139.4 (C7), 141.5 (ArC), 154.6 (C2), 155.6 (ArC), 171.9 (C10), 213.9, 220.4 (Mn(CO)4). MS (EI): m/z 422.9 [Mþ, 7], 338.9 [Mþ - 3CO, 11], 310.9 [Mþ - 4CO, 99], 256.9 [Mþ - Mn - 4CO, 54], 177 [Mþ - Mn - 4CO Br, 20]. Tetracarbonyl{pentacarbonyl[benzo[h]quinolyl-KC10-KN-5(methoxy)carbene]chromium(0)}manganese(I) (6). A solution of pentacarbonyl[5-benzo[h]quinolyl(methoxy)carbene]chromium(0) (2) (3.00 g, 7.25 mmol) and pentacarbonyl(benzyl-κC1)manganese(I) (2.50 g, 8.74 mmol, 1.2 equiv) in n-heptane (180 mL) was warmed to 98 °C under stirring for 2 h. Chromatography on silica gel at 5 °C with petroleum ether/dichloromethane (1:1) afforded 3.95 g (94%) of tetracarbonyl{pentacarbonyl-5-[benzo[h]quinolyl-κC10-κN-(methoxy)carbene]chromium(0)}manganese(I) (6) as an air-sensitive red powder. Crystallization from dichloromethane at 4 °C gave dark red crystals suitable for X-ray analysis. Determination of the melting point resulted in decomposition. IR (petroleum ether): ν(CO) 2079 (m), 2067 (A1, m), 1996 (vs), 1984 (vs), 1957 (E, s), 1943 (s) cm-1. 1H NMR (500 MHz, acetone-d6): δ (ppm) 4.62 (3H, s, OCH3), 7.70 (1H, s, H6), 7.74 (1H, dd, 3J = 7.2 Hz, 3J = 7.7 Hz, H8), 7.81 (1H, dd, 3 J = 8.2 Hz, 3J = 5.0 Hz, H3), 7.86 (1H, d, 3J = 7.7 Hz, H9), 8.24-8.27 (2H, m, 3J = 7.2 Hz, 3J = 8.2 Hz, H4 and H7), 9.30 (1H, d, 3J = 5.0 Hz, H2). 13C NMR (125 MHz, acetone-d6): δ (ppm) 122.1 (C5), 122.8, 122.9, 123.2, 125.6, 128.2, 130.2 (6 ArCH), 132.2, 134.3 (2 ArC), 139.7 (ArCH), 141.3, 152.1 (2 ArC), 154.4 (C2), 171.9 (C10), 213.8, 213.9 (Mn(CO)4), 215.6 (4 transCr(CO)), 220.4 (Mn(CO)4), 224.4 (1 cis-Cr(CO)), 355.5 (C11). MS (EI): m/z 578.9 [Mþ, 8], 550.9 [Mþ - 1CO, 22], 522.9 [Mþ 2CO, 2], 466.9 [Mþ - 4CO, 38], 438.9 [Mþ - 5CO, 60], 410.9 [Mþ - 6CO, 32], 354.9 [Mþ - 8CO, 25], 326.9 [Mþ - 9CO, 48]. Tetracarbonyl{tricarbonyl(η6-4b,5,6,7,8,8a-(6,7-diethyl-5methoxy-8-[(tert-butyl)dimethylsilyloxy]dibenzo[ f,h]quinolineKC 12 -KN)chromium(0)}manganese(I) (7). A solution of tetracarbonyl{pentacarbonyl[5-benzo[h]quinolyl-κC10-κN-(methoxy)carbene]chromium(0)}manganese(I) (6) (1.80 g, 3.10 mmol)

Dubarle Offner et al. and 3-hexyne (1.02 g, 12.40 mmol) in 35 mL of tert-butyl methyl ether was warmed to 65 °C (oil bath temperature) during 2 h. Then the phenolic group was protected at room temperature by addition of triethylamine (0.56 mL, 6.2 mmol) and tert-butyldimethylsilyl triflate (1.43 mL, 6.2 mmol). After stirring for 1.5 h, chromatography on silica gel at 5 °C with petroleum ether/ dichloromethane (1:1) afforded 1.50 g (65%) of complex 5 as an air-sensitive red powder. Crystallization from dichloromethane at 4 °C gave dark red crystals suitable for X-ray analysis. Mp: 86 °C. IR (petroleum ether): ν(CO) 2079 (m), 2000 (vs), 1983 (vs), 1963 (A1, s), 1942 (s), 1907 (E, m), 1890 (E, m) cm-1. 1H NMR (500 MHz, CD2Cl2): δ (ppm) -0.22 (3H, s, SiCH3), 0.08 (3H, s, SiCH3), 1.18 (9H, s, SiC(CH3)3), 1.40-1.43 (3H, t, 3J = 7.45 Hz, CH2CH3), 1.45-1.48 (3H, dt, 3J = 7.45 Hz, CH2CH3), 2.47 (1H, m, 3J = 7.35 Hz, CH2CH3), 2.72-2.81 (2H, m, CH2CH3), 3.02 (1H, m, 3J = 7.55 Hz, CH2CH3), 3.76 (3H, s, OCH3), 7.50 (1H, dd, 3J = 8.4 Hz, 3J = 5.3 Hz, H3), 7.55 (1H, dd, 3J = 8.2 Hz, 3J = 7.0 Hz, H10), 8.12 (1H, dd, 3J = 7.0 Hz, 4 J = 0.9 Hz, H9), 8.68 (1H, dd, 3J = 8.2 Hz, 4J = 0.9 Hz, H11), 9.03 (1H, dd, 3J = 5.3 Hz, 4J = 1.4 Hz, H4), 9.50 (1H, dd, 3J = 8.4 Hz, 4J = 1.4 Hz, H2). 13C NMR (125 MHz, CD2Cl2): δ (ppm) -3.6, -2.9 (Si(CH3)2), 15.3 (CH3), 18.9 (SiC), 19.1 (CH3), 20.1 (CH2), 21.9 (CH2), 26.1 (SiC(CH3)3), 66.2 (OCH3), 86.3, 99.6, 106.5, 113.7 (4 ArC), 122.7 (C3), 123.9 (C9 or C11), 125.1 (ArC), 129.6 (C10), 131.1, 132.8 (2 ArC), 138.7 (C4), 139.3 (ArC), 140.4 (C9 or C11), 140.5 (ArC), 154.6 (C2), 159.8, 173.3 (2 ArC), 213.9, 214.6, 220.7 (Mn(CO)4), 233.9 (Cr(CO)3). MS (EI): m/z 747.2 [Mþ, 25], 691.2 [Mþ - 2CO, 18], 663.1 [Mþ - 3CO, 6], 635.2 [Mþ - 4CO, 11], 607.1 [Mþ - 5CO, 9], 581.2 [Mþ - 6CO, 8], 551.2 [Mþ - 7CO, 27], 497.2 [Mþ - 7CO - Cr, 99], 445.2 [Mþ 7CO - Cr - Mn, 42]. MS (ESI): m/z [M þ H]þ calcd 770.0764, found 770.0681. Tetracarbonyl{tricarbonyl(η6-8b,9,10,11,12,12a-(6,7-diethyl5-methoxy-8-[(tert-butyl)dimethylsilyloxy]dibenzo[ f,h]quinolineKC 12 -KN)chromium(0)}manganese(I) (8). A solution of tetracarbonyl{tricarbonyl(η6-4b,5,6,7,8,8a-(6,7-diethyl-5-methoxy8-[(tert-butyl)dimethylsilyloxy]-dibenzo[ f,h]quinoline-κC12-κN)chromium(0)manganese(I) (7) (0.91 g, 1.21 mmol) in 60 mL of di-n-butyl ether was warmed to 105 °C and stirred for 3 h under an argon atmosphere. Chromatography on silica gel at 5 °C in dichloromethane afforded 0.47 g (52%) of complex 8 as an airsensitive red-orange powder. Crystallization from dichloromethane at 4 °C gave red crystals suitable for X-ray analysis. Mp: 60 °C. IR (petroleum ether): ν(CO) 2085 (m), 2006 (vs), 1988 (s), 1975 (A1, s), 1950 (s), and 1898 (E, m) cm-1. 1H NMR (500 MHz, CD2Cl2): δ (ppm) -0.28 (3H, s, SiCH3), -0.12 (3H, s, SiCH3), 1.12 (9H, s, SiC(CH3)3), 1.26 (3H, t, 3J = 7.45 Hz, CH2CH3), 1.27 (3H, t, 3J = 7.35 Hz, CH2CH3), 2.62 (1H, m, CH2CH3), 2.72 (1H, m, CH2CH3), 2.87-2.99 (2H, m, CH2CH3), 3.66 (3H, s, OCH3), 5.46 (1H, dd, 3J = 6.9 Hz, 3J = 5.9 Hz, H10), 6.23 (1H, dd, 3J = 5.9 Hz, 4J = 1.2 Hz, H11), 7.44 (1H, dd, 3J = 6.9 Hz, 4J = 1.2 Hz, H9), 7.50 (1H, dd, 3J = 8.5 Hz, 3J = 5.2 Hz, H3), 8.84 (1H, dd, 3 J = 5.2 Hz, 4J = 1.3 Hz, H4), 9.63 (1H, dd, 3J = 8.5 Hz, 4J = 1.3 Hz, H2). 13C NMR (125 MHz, CD2Cl2): δ (ppm) -5.1, -3.0 (Si(CH3)2), 14.9 (CH3), 15.7 (CH3), 18.5 (SiC), 20.5 (CH2), 21.2 (CH2), 26.0 (SiC(CH3)3), 61.3 (OCH3), 91.9 (C10), 93.5 (C9 or C11), 104.6 (ArC), 108.0 (C9 or C11), 109.7, 120.2, 121.8 (3 ArC), 124.6 (C3), 127.9, 134.4 (2 ArC), 137.4 (C2), 138.4, 139.0, 147.5 (3 ArC), 152.5 (C4), 153.0, 158.1 (2 ArC), 211.2 211.7, 212.7, 219.6 (Mn(CO)4), 235.4 (Cr(CO)3). MS (EI): m/z 747.1 [Mþ, 1], 663.1 [Mþ - 3CO, 29], 635.1 [Mþ - 4CO, 36], 607.1 [Mþ - 5CO, 26], 551.1 [Mþ - 7CO, 2] 497.2 [Mþ - 7CO - Cr, 99], 445.3 [Mþ - 7CO - Cr - Mn, 14]. MS (ESI): m/z [M þ H]þ calcd 770.0764, found 770.0681. Kinetic NMR Studies of the Haptotropomerization. Concentrated solutions of dibenzo[ f,h]quinoline-Cr(CO)3 and cyclomanganated dibenzo[ f,h]quinoline-Cr(CO)3 complexes in 0.5 mL of hexafluorobenzene (saturated with argon by three freezepump-thaw cycles prior to use) were filtered through a pad of Celite into NMR tubes under argon. The NMR measurements were

Article performed in the presence of an external standard (dimethyl sulfoxide-d6) at 80 °C with a Bruker DRX-500 NMR spectrometer. NMR spectra were recorded in intervals of 10 min, and the ratio of the two regioisomers was determined by integration of the signal of one proton of the terminal aromatic ring.

Acknowledgment. The authors are grateful to the Deutsche Forschungsgemeinschaft for financial support


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granted within the Sonderforschungsbereich SFB 624 (Template-Vom Design Chemischer Schablonen zur Reaktionssteuerung). Supporting Information Available: 1H and 13C NMR spectra of compounds 1-8 and CIF files with listings of the crystallographic and structural data for complexes 2-8. This material is available free of charge via the Internet at http://pubs.acs.org.

Dibenzo[f,h]quinoline Cr(CO)3 Complexes: Synthesis by Chromium

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