Chiral Aminotroponiminate Zinc Complexes - Organometallics (ACS

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Organometallics 2009, 28, 306–311

Chiral Aminotroponiminate Zinc Complexes Nils Meyer† and Peter W. Roesky*,‡ Institut fu¨r Chemie and Biochemie, Freie UniVersita¨t Berlin, Fabeckstrasse 34-36, 14195 Berlin, Germany, and Institut fu¨r Anorganische Chemie, UniVersita¨t Karlsruhe, Engesserstrasse 15, 76128 Karlsruhe, Germany ReceiVed September 4, 2008

The enantiomerically pure bridged aminotroponiminates (S,S)- and (R,R)-H2{(iPrATI)2diph}, in which two amino-isopropyl-troponimine moieties are linked by 1,2-(S,S)- or 1,2-(R,R)-diamino-1,2diphenylethane, have been used as ligands in zinc chemistry. The bimetallic zincmethyl, -ethyl, and phenyl complexes containing the enantiomerically pure bridged aminotroponiminates (S,S)- or (R,R){(iPrATI)2diph}2- were prepared by the reaction of ZnR2 (R ) Me, Et, Ph) with the neutral ligands. As a result the compounds [(S,S)-{(iPrATI)2diph}(ZnR)2] (R ) Me (1), Et (2)) and [(R,R){(iPrATI)2diph}(ZnPh)2] (3) were obtained. Moreover, the new ligands (S,S)-H2{((R)-PhCHCH3ATI)2diph} and (R,R)-H2{((R)-PhCHCH3ATI)2diph}, which are diasteromers, were prepared by using (R)-1-amino1-phenylethane instead of isopropylamine in the ligand synthesis. Reacting these ligands with ZnMe2 resulted in the enantiomerically pure compounds [(S,S)-{((R)-PhCHCH3ATI)2diph}(ZnMe)2] (4) and [(R,R){((R)-PhCHCH3ATI)2diph}(ZnMe)2] (5). Compounds 1-5 were investigated by single-crystal X-ray diffraction, showing a distorted trigonal-planar coordination of the zinc atoms. Introduction Aminotroponimines (ATIHs) are a well-known class of ligands that were discovered in the 1960s.1 It was shown that aminotroponimines could act as ligands for a wide range of main group, transition, and f-block elements.2 Usually ATI ligands behave as anionic bidentate nitrogen donor ligands and form very stable chelate complexes with a delocalization of the negative charge through the seven-membered ring, obtaining a 10π-electron backbone (Scheme 1). The aminotroponiminate ligand was also introduced into the coordination sphere of zinc.3 The first structurally characterized ATI zinc complexes were reported by our group.4 Recently Blechert et al. and our group have also shown that zinc compounds of the type [{(iPr)2ATI}ZnMe] are highly active precatalysts for the hydroamination5,6 of alkenes and alkynes.7 We have also described the preparation of zinc complexes with sterically and electronically modified ATI ligands and the influence of the modifications on their catalytic activity.8 The new zinc precatalysts show, besides their good catalytic activity and selectivity, high tolerance toward polar and functional groups and high stability toward air and moisture. Moreover zinc is nontoxic and one of the least expensive metals. These advantages makes zinc superior to the previous used catalysts for this reaction mainly based on lithium,9 group 4 metals,10 * Corresponding author. E-mail: [email protected]. † Freie Universita¨t Berlin. ‡ Universita¨t Karlsruhe. (1) (a) Brasen, W. R.; Holmquist, H. E.; Brenson, R. E. J. Am. Chem. Soc. 1960, 82, 995–996. (b) Brasen, W. R.; Holmquist, H. E.; Brenson, R. E. J. Am. Chem. Soc. 1961, 83, 3125–3135. (2) Review: (a) Roesky, P. W. Chem. Soc. ReV. 2000, 29, 333–345. (3) (a) Forbes, C. E.; Holm, R. H. J. Am. Chem. Soc. 1970, 92, 2297– 2303. (b) Franz, K. J.; Singh, N.; Spingler, B.; Lippard, S. J. Inorg. Chem. 2000, 39, 4081–4092. (4) (a) Gamer, M. T.; Roesky, P. W. Eur. J. Inorg. Chem. 2003, 2145– 2148. (b) Herrmann, J. S.; Luinstra, G. A.; Roesky, P. W. J. Organomet. Chem. 2004, 689, 2720–2725. (5) Mu¨ller, T. E. In Encyclopedia of Catalysis; Horva´th, J. T., Ed.; Wiley: New York, 2002.

the lanthanides,11-13 the platinum metals,14 calcium,15 copper,16 silver,17 and gold.18 Motivated by these studies, we were interested in the preparation of zinc compounds with chiral ATI ligands. In the present contribution we describe the synthesis and characterization of new enantiomerically pure chiral-bridged aminotropon(6) Recent reviews: (a) Roundhill, D. M. Chem. ReV. 1992, 92, 1–27. (b) Mu¨ller, T. E.; Beller, M. Chem. ReV. 1998, 98, 675–703. (c) Johannsen, M.; Jørgensen, K. A. Chem. ReV. 1998, 98, 1689–1708. (d) Nobis, M.; Driessen-Ho¨lscher, B. Angew. Chem. 2001, 113, 4105–4108; Angew. Chem., Int. Ed. 2001, 40, 3983-3985. (e) Brunet, J.-J.; Neibecker, D. In Catalytic Heterofunctionalization, Togni, A.; Gru¨tzmacher, H., Eds.; VCH: Weinheim, 2001; pp 91-141. (f) Seayad, J.; Tillack, A.; Hartung, C. G.; Beller, M. AdV. Synth. Catal. 2002, 344, 795–813. (g) Pohlki, F.; Doye, S. Chem. Soc. ReV. 2003, 32, 104–114. (h) Bytschkov, I.; Doye, S. Eur. J. Org. Chem. 2003, 935–946. (i) Roesky, P. W.; Mu¨ller, T. E. Angew. Chem. 2003, 115, 2812–2814; Angew. Chem., Int. Ed. 2003, 42, 2708-2710. (j) Hartwig, J. F. Pure Appl. Chem. 2004, 76, 507–516. (k) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673–686. (l) Hultzsch, K. C. AdV. Synth. Catal. 2005, 347, 367–391. (7) Zulys, A.; Dochnahl, M.; Hollmann, D.; Lo¨hnwitz, K.; Herrmann, J.-S.; Roesky, P. W.; Blechert, S. Angew. Chem. 2005, 117, 7972–7976; Angew. Chem., Int. Ed. 2005, 44, 7794-7798. (8) (a) Meyer, N.; Lo¨hnwitz, K.; Zulys, A.; Roesky, P. W.; Dochnahl, M.; Blechert, S. Organometallics 2006, 25, 3730–3734. (b) Dochnahl, M.; Lo¨hnwitz, K.; Pissarek, J. W.; Biyikal, M.; Schulz, S. R.; Scho¨n, S.; Meyer, N.; Roesky, P. W.; Blechert, S. Chem.-Eur. J. 2007, 13, 6654–6666. (c) Dochnahl, M.; Pissarek, J. W.; Blechert, S.; Lo¨hnwitz, K.; Roesky, P. W. Chem. Commun. 2006, 3405–3407. (d) Dochnahl, M.; Lo¨hnwitz, K.; Pissarek, J. W.; Roesky, P. W.; Blechert, S. Dalton Trans. 2008, 2844– 2848. (9) Horrillo Martinez, P.; Hultzsch, K. C.; Hampel, F. Chem. Commun. 2006, 2221–2223. (10) (a) Wood, M. C.; Leitch, D. C.; Yeung, C. S.; Kozak, J. A.; Schafer, L. L. Angew. Chem. 2007, 119, 358–362; Angew. Chem., Int. Ed. 2007, 46, 354-358. (b) Kaspar, L. T.; Fingerhut, B.; Ackermann, L. Angew. Chem. 2005, 117, 6126–6128; Angew. Chem. Int. Ed. 2005, 44, 5972-5974. (c) Heutling, A.; Pohlki, F.; Bytschkov, I.; Doye, S. Angew. Chem. 2005, 117, 3011–3013; Angew. Chem., Int. Ed. 2005, 44, 2951-2954. (11) Conticello, V. P.; Brard, L.; Giardello, M. A.; Tsuji, Y.; Sabat, M.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1992, 114, 2761–2762. (b) Stern, D.; Sabat, M.; Marks, T. J. J. Am. Chem. Soc. 1992, 114, 9558– 9575. (c) Haar, C. M.; Stern, C. L.; Marks, T. J. Organometallics 1996, 15, 1765–1784. (d) Roesky, P. W.; Deninger, U.; Stern, C. L.; Marks, T. J. Organometallics 1997, 16, 4486–4492.

10.1021/om800858t CCC: $40.75  2009 American Chemical Society Publication on Web 12/16/2008

Chiral Aminotroponiminate Zinc Complexes Scheme 1

Organometallics, Vol. 28, No. 1, 2009 307 Scheme 2

imine ligands (S,S)-H2{((R)-PhCHCH3ATI)2diph} and (R,R)H2{((R)-PhCHCH3ATI)2diph} (Scheme 2). These ligands and the previously described (S,S)- or (R,R)-H2{(iPrATI)2diph}19 were used for the preparation of dimetallic zinc alkyl and aryl complexes.

Experimental Section General Procedures. All manipulations of air-sensitive materials were performed with the rigorous exclusion of oxygen and moisture in flame-dried Schlenk-type glassware either on a dual-manifold Schlenk line, interfaced to a high-vacuum (10-4 Torr) line, or in an argon-filled M. Braun glovebox. Ether solvents (tetrahydrofuran and ethyl ether) were predried over Na wire and distilled under nitrogen from K (THF) or Na wire (ethyl ether) benzophenone ketyl prior to use. Hydrocarbon solvents (toluene and n-pentane) were distilled under nitrogen from LiAlH4. Deuterated solvents were obtained from Chemotrade Chemiehandelsgesellschaft mbH (all g99 atom % D) and were degassed, dried, and stored in Vacuo over Na/K alloy in resealable flasks. CDCl3 was used as purchased. NMR spectra were recorded on a JNM-LA 400 FT-NMR spectrometer. Chemical shifts are referenced to internal solvent resonances and are reported relative to tetramethylsilane. Elemental (12) (a) Gagne, M. R.; Marks, T. J. J. Am. Chem. Soc. 1989, 111, 4108– 4109. (b) Gagne, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1992, 114, 275–294. (c) Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1996, 118, 9295– 9306. (d) Roesky, P. W.; Stern, C. L.; Marks, T. J. Organometallics 1997, 16, 4705–4711. (e) Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 1757– 1771. (f) Arredondo, V. M.; McDonald, F. E.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 4871–4872. (g) Arredondo, V. M.; McDonald, F. E.; Marks, T. J. J. Am. Chem. Soc. 1999, 121, 3633–3639. (h) Hong, S.; Marks, T. J. J. Am. Chem. Soc. 2002, 124, 7886–7887. (i) Ryu, J. S.; Li, G. Y.; Marks, T. J. J. Am. Chem. Soc. 2003, 125, 12584–12605. (j) Hong, S.; Tian, S.; Metz, M. V.; Marks, T. J. J. Am. Chem. Soc. 2003, 125, 14768–14783. (13) (a) Kim, Y. K.; Livinghouse, T.; Bercaw, J. E. Tetrahedron Lett. 2001, 42, 2933–2935. (b) Kim, Y. K.; Livinghouse, T. Angew. Chem. 2002, 114, 3797–3799; Angew. Chem., Int. Ed. 2002, 41, 3645-3647. (c) Kim, Y. K; Livinghouse, T.; Horino, Y. J. Am. Chem. Soc. 2003, 125, 9560– 9561. (d) O’Shaughnessy, P. N.; Knight, P. D.; Morton, C.; Gillespie, K. M.; Scott, P. Chem. Commun. 2003, 1770–1771. (e) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F. Chem.-Eur. J. 2003, 9, 4796–4810. (f) Hultzsch, K. C.; Gribkov, D. V. Chem. Commun. 2004, 730–731. (g) Hultzsch, K. C.; Hampel, F.; Wagner, T. Organometallics 2004, 23, 2601–2612. (h) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F. J. Am. Chem. Soc. 2006, 128, 3748– 3759. (i) Riegert, D.; Collin, J.; Medour, A.; Schulz, E.; Trifonov, A. J. Org. Chem. 2006, 71, 2514–2517. (14) Rh:(a) Utsunomiya, M.; Kuwano, R.; Kawatsura, M.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 5608–5609. (b) Takemiya, A.; Hartwig, J. F. J. Am. Chem. Soc. 2006, 128, 6042–6043. (c) Dorta, R.; Egli, P.; Zu¨rchner, F.; Togni, A. J. Am. Chem. Soc. 1997, 119, 10857–10858. Pd: (d) Utsonmiya, M.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 14286–14287. Pt: (f) Bender, C. F.; Widenhoefer, R. A. J. Am. Chem. Soc. 2005, 127, 1070–1071. (15) Crimmin, M. R.; Caseley, I. J.; Hill, M. S. J. Am. Chem. Soc. 2005, 127, 2042–2043. (16) Taylor, J. G.; Whittall, N.; Hii, K. K. Org. Lett. 2006, 8, 3561– 3564. (17) Sun, J.; Kozmin, S. A. Angew. Chem. 2006, 118, 5113–5115; Angew. Chem., Int. Ed. 2006, 45, 4991-4993. (18) (a) Brouwer, C.; He, C. Angew. Chem. 2006, 118, 1776–1779; Angew. Chem., Int. Ed. 2006, 45, 1744-1747. (b) Han, X.; Widenhoefer, R. A. Angew. Chem. 2006, 118, 1779–1781; Angew. Chem., Int. Ed. 2006, 45, 1747-1749. (c) Zhang, Z.; Liu, C.; Kinder, R. E.; Han, X.; Qian, H.; Widenhoefer, R. A. J. Am. Chem. Soc. 2006, 128, 9066–9073. (d) Kang, J. E.; Kim, H. B.; Lee, J. W.; Shin, S. Org. Lett. 2006, 8, 3537–3540. (19) Meyer, N.; Zulys, A.; Roesky, P. W. Organometallics 2006, 25, 4179–4182.

analyses were carried out with an Elementar Vario EL III. (R,R)H2{(iPrATI)2diph},19 (S,S)-H2{(iPrATI)2diph},19 (R)-{(PhCHCH3)AT}H, and ZnPh220 were prepared according to literature procedures. ZnMe2 and ZnEt2 were purchased from Aldrich Inc. (S,S)-H2{((R)-PhCHCH3ATI)2diph} and (R,R)-H2{((R)-PhCHCH3ATI)2diph}. 2-(N-(R)-(1-phenylethylamino)tropone21 (5.9 mmol, 1.33 g) in 10 mL of methylene chloride was slowly added to a solution of Et3OBF4 (5.9 mmol, 1.12 g) in 10 mL of methylene chloride under an argon atmosphere. After stirring at room temperature for 3 h 5 mL of Et3N was added to the orange solution. The mixture was stirred for another 15 min, and then 1,2-(S,S)- or 1,2-(R,R)-diphenylethylendiamine (1.00 g, 4.7 mmol) in 10 mL of methylene chloride was added to the mixture and the solution turned yellow immediately. After stirring for 18 h the volatiles were removed in Vacuo and the residue was extracted twice with toluene. The solution was concentrated to 2 mL and layered with pentane to obtain the product as a yellow powder. (S,S)-H2{((R)-PhCHCH3ATI)2diph}. Yield: 2.14 g (4.3 mmol, 80%). 1H NMR (CDCl3, 400 MHz, 25 °C): δ 1.62 (d, 6 H, CH3, JH,H ) 6.6 Hz), 4.73 (q, 2 H, CH, JH,H ) 6.6 Hz), 5.07 (s, 2 H, CH), 5.99 (t, 2 H, CHring, JH,H ) 9.4 Hz), 6.07 (d, 2 H, CHring, JH,H ) 10.5 Hz), 6.20 (d, 2 H, CHring, JH,H ) 11.2 Hz), 6.49-6.59 (m, 4 H, CHring), 7.14-7.33 (m, 16 H, Ph), 7.62-7.65 (m, 4 H, Ph), 8.72 (br s, 2 H, NH). 13C{1H} NMR (CDCl3, 100.4 MHz, 25 °C): δ 24.9, 54.3, 67.0, 109.9, 113.9, 118.1, 126.1, 126.6, 126.9, 127.7, 128.0, 128.2, 128.5, 129.9, 141.3, 144.9, 151.5, 153.6. MS (EI, 70 eV, 175 °C): m/z (%) 626 [M+] (2), 105 (100). (R,R)-H2{((R)-PhCHCH3ATI)2diph}. Yield: 1.63 g (3.2 mmol, 68%). 1H NMR (CDCl3, 400 MHz, 25 °C): δ 1.53 (d, 6 H, CH3, JH,H ) 6.6 Hz), 4.63 (q, 2 H, CH, JH,H ) 6.6 Hz), 4.98 (s, 2 H, CH), 5.90 (t, 2 H, CHring, JH,H ) 8.5 Hz), 5.98 (d, 2 H, CHring, JH,H ) 10.3 Hz), 6.12 (d, 2 H, CHring, JH,H ) 12.1 Hz), 6.40 - 6.49 (m, 4 H, CHring), 7.07-7.23 (m, 16 H, Ph), 7.53-7.56 (m, 4 H, Ph), 8.59 (br s, 2 H, NH). 13C{1H} NMR (CDCl3, 100.4 MHz, 25 °C): δ 25.3, 54.3, 67.3, 109.9, 113.9, 118.1, 126.1, 126.6, 126.8, 127.8, 128.0, 128.2, 128.5, 128.6, 129.9, 141.3, 148.4, 151.6. TOF MS: 627 [M + H]+ (100). [(S,S)-{(iPrATI)2diph}(ZnR)2] (R ) Me (1), Et (2)). A solution of ZnR2 was slowly added to (S,S)-H2{(iPrATI)2diph} in 20 mL of toluene at -78 °C. The resulting yellow reaction mixture was (20) Kojima, K.; Kimura, M.; Ueda, S.; Tamara, Y. Tetrahedron 2006, 26, 7512–7520. (21) Roesky, P. W. J. Organomet. Chem. 2001, 621, 277–283.

308 Organometallics, Vol. 28, No. 1, 2009 allowed to warm to ambient temperature and stirred for 16 h. The solution was concentrated until a yellow residue appeared. The residue was dissolved by heating, and the resulting orange solution was allowed to stand at room temperature. The product was obtained as yellow crystals after 8 h. X-ray quality crystals were selected directly from this crop. [(S,S)-{(iPrATI)2diph}(ZnMe)2], 1. (S,S)-H2{(iPrATI)2diph}: 0.75 g; 1.5 mmol; ZnMe2: 2 M (toluene), 1.5 mL, 3.0 mmol. Yield: 0.62 g (0.9 mmol, 60%). 1H NMR (C6D6, 400 MHz, 25 °C): δ -0.12 (s, 3 H, ZnCH3), 1.27 (d, 6 H, CH(CH3)2, JH,H ) 6.2 Hz), 1.42 (d, 6 H, CH(CH3)2, JH,H ) 6.2 Hz), 3.98 (sept, 2 H, CH(CH3)3, JH,H ) 6.2 Hz), 5.45 (s, 2 H, CH), 6.46 (t, 2 H, CHring, JH,H ) 9.0 Hz), 6.82 (d, 2 H, CHring, JH,H ) 11.6 Hz), 6.98-7.17 (m, 12 H, CHring + Ph), 7.30-7.36 (m, 4 H, Ph). 13C{1H} NMR (C6D6, 100.4 MHz, 25 °C): δ -12.0 (ZnCH3), 25.7 (CH(CH3)2), 25.4 (CH(CH3)2), 48.3 (CH(CH3)2), 71.2 (CH), 113.4, 114.8, 119.4, 127.3, 128.4, 128.7, 135.0, 135.1, 142.1, 160.8, 161.2. MS (EI): m/z (%) 643 ([M - CH3]+ 2), 564 ([M - CH3 - ZnCH3]+ 95), 521 ([M - CH3 - ZnCH3 - CH(CH3)2]+ 100). C36H42N4Zn2 (661.53): C, 65.36; H, 6.40; N, 8.47. Found: C, 65.35; H, 6.81; N, 8.33. [(S,S)-{(iPrATI)2diph}(ZnEt)2], 2: (S,S)-H2{(iPrATI)2diph}: 1.00 g, 2 mmol; ZnEt2: 1 M (hexane), 4.2 mL, 4.2 mmol. Yield: 0.60 g (0.9 mmol, 45%). 1H NMR (C6D6, 400 MHz, 25 °C): δ 0.49 (dq, 2 H, CH2CH3, JH,H ) 5.1 Hz, JH,H ) 8.2 Hz), 0.55 (dq, 2 H, CH2CH3, JH,H ) 5.1 Hz, JH,H ) 8.2 Hz), 1.06 (d, 6 H, CH(CH3)2, JH,H ) 6.1 Hz), 1.20 (d, 6 H, CH(CH3)2, JH,H ) 6.1 Hz), 1.44 (t, 6 H, CH2CH3, JH,H ) 8.2 Hz), 3.73 (sept., 2 H, CH(CH3)2, JH,H ) 6.2 Hz), 5.27 (s, 2 H, CH), 6.24 (t, 2 H, CHring, JH,H ) 9.2 Hz), 6.57 (d, 2 H, CHring, JH,H ) 11.4 Hz), 6.75 - 6.98 (m, 12 H, CHring + Ph), 7.13-7.15 (m, 4 H, Ph). 13C{1H} NMR (C6D6, 100.4 MHz, 25 °C): δ 1.2 (CH2CH3), 12.9 (CH2CH3), 23.3 (CH(CH3)2), 25.5 (CH(CH3)2), 48.1 (CH(CH3)2), 71.3 (CH), 113.4, 114.6, 119.3, 127.4, 128.4, 128.6, 135.0, 135.1, 142.0, 160.8, 161.0. MS (EI): m/z (%) 659 ([M - CH2CH3]+ 12), 564 ([M - CH2CH3 - ZnCH2CH3]+ 90), 521 ([M - CH2CH3 - ZnCH2CH3 CH(CH3)2]+ 48), 343 ([1/2 M]+ 24), 315 ([1/2 M - CH2CH3]+ 23), 173 (100). C38H46N4Zn2 (689.58): C, 66.19; H, 6.72; N, 8.12. Found: C, 66.10; H, 6.36; N, 8.06. [(R,R)-{(iPrATI)2diph}(ZnPh)2] (3). Toluene (5 mL) was added to a mixture of ZnPh2 (0.33 g, 1.5 mmol) and (R,R)-H2{(iPrATI)2diph} (0.37 g, 0.8 mmol), and the resulting yellow solution was stirred for 2 h at ambient temperature. The solution was concentrated until a yellow residue appeared. The residue was dissolved by heating, and the resulting orange solution was allowed to stand at room temperature. The product was obtained as yellow crystals after 24 h. X-ray quality crystals were selected directly from this crop. Yield: 0.43 g (0.5 mmol, 67%). 1H NMR (C6D6, 400 MHz, 25 °C): δ 0.79 (d, 6 H, CH(CH3)2, JH,H ) 6.1 Hz), 1.08 (d, 6 H, CH(CH3)2, JH,H ) 6.1 Hz), 3.53 (sept, 2 H, CH(CH3)2, JH,H ) 6.1 Hz), 4.96 (s, 2 H, CH), 5.85 (t, 2 H, CHring, JH,H ) 8.7 Hz), 6.02-6.10 (m, 4 H, CHring), 6.37 (d, 2 H, CHring, JH,H ) 11.0 Hz), 6.53 (t, 2 H, CHring, JH,H ) 9.9 Hz), 6.60-6.62 (m, 6 H, Ph), 6.75-6.78 (m, 4 H, Ph), 6.84-6.85 (m, 6 H, Ph), 7.15-7.16 (m, 4 H, Ph). 13C{1H} NMR (C6D6, 100.4 MHz, 25 °C): δ 23.9 (CH(CH3)2), 26.0 (CH(CH3)2), 48.5 (CH(CH3)2), 70.6 (CH), 113.9, 116.2, 120.2, 126.3, 127.3, 127.7, 127.8, 128.0, 134.9, 135.2, 128.7, 141.8, 150.6, 160.6, 160.9. MS (EI): m/z (%) ) 564 ([M - Ph, -Ph]+ 100), 521 ([M - Ph, -Ph, -CH(CH3)2]+ 48). Raman (solid, ν/cm-1): 3053(m), 3043(w), 3033(w), 3000(w), 2970(w), 2929(w), 2861(w), 1593(s), 1576(m), 1506(m), 1468(s), 1429(s), 1419(s), 1395(m), 1269(w), 1226(w), 1022(m), 999(vs). C46H46N4Zn2 (785.66): C, 70.32; H, 5.90; N, 7.13. Found: C, 69.76; H, 5.97; N, 7.09. [(S,S)-{((R)-PhCHCH3ATI)2diph}(ZnMe)2] (4) and [(R,R){((R)-PhCHCH3ATI)2diph}(ZnMe)2] (5). ZnMe2 in toluene (1.2 M, 1.1 mmol, 0.9 mL) was slowly added to (S,S)-H2{((R)PhCHCH3ATI)2diph} or (R,R)-H2{((R)-PhCHCH3ATI)2diph} (0.31

Meyer and Roesky g, 0.5 mmol) in 20 mL of toluene. The resulting orange solution was stirred for 16 h at ambient temperature, filtered off, concentrated, and layered with pentane. The product was obtained as a yellow, crystalline solid. X-ray quality crystals were selected directly from this crop. [(S,S)-{((R)-PhCHCH3ATI)2diph}(ZnMe)2], 4:. Yield: 0.16 g (0.2 mmol, 40%). 1H NMR (C6D6, 400 MHz, 25 °C): δ -0.20 (s, 6 H, ZnCH3), 1.63 (d, 6 H, PhCHCH3, JH,H ) 6.6 Hz), 4.71 (q, 2 H, PhCHCH3, JH,H ) 6.6 Hz), 5.34 (s, 2 H, CH), 6.11-6.16 (m, 2 H, CHring), 6.64-6.66 (m, 4 H, CHring), 6.76-7.11 (m, 20 H, CHring + Ph), 7.22-7.24 (m, 4 H, Ph). 13C{1H} NMR (C6D6, 100.4 MHz, 25 °C): δ -10.6 (ZnCH3), 27.6 (PhCHCH3), 57.89 (PhCHCH3), 70.9 (CH), 114.2, 115.9, 120.1, 126.2, 126.8, 127.3, 128.4, 128.7, 128.9, 134.9, 135.0, 141.9, 145.0, 161.3, 161.5. C46H46N4Zn2 (785.66): C, 70.32: H, 5.90; N, 7.13. Found: C, 70.17; H, 6.23; N, 7.10. [(R,R)-{((R)-PhCHCH3ATI)2diph}(ZnMe)2], 5. Yield: 0.24 g (0.3 mmol, 60%). 1H NMR (C6D6, 400 MHz, 25 °C): δ -0.17 (s, 6 H, ZnCH3), 1.96 (d, 6 H, PhCHCH3, JH,H ) 6.6 Hz), 5.06 (q, 2 H, PhCHCH3, JH,H ) 6.6 Hz), 5.49 (s, 2 H, CH), 6.31 (t, 2 H, CHring, JH,H ) 9.2 Hz), 6.85-6.95 (m, 6 H, CHring), 7.17-7.25 (m, 10 H, CHring + Ph), 7.33-7.40 (m, 12 H, Ph). 13C{1H} NMR (C6D6, 100.4 MHz, 25 °C): δ -12.4 (ZnCH3), 28.3 (PhCHCH3), 58.0 (PhCHCH3), 71.3 (CH), 115.6, 116.2, 120.3, 126.3, 127.0, 127.4, 128.6, 128.7, 129.1, 135.4, 135.5, 142.0, 145.5, 161.3, 161.7. C46H46N4Zn2 (785.66): C, 70.32; H, 5.90; N, 7.13. Found: C, 70.23; H, 5,76; N, 7.24. X-ray Crystallographic Studies of 1, 2, 3, 4, and 5. Crystals of 1, 2 and 3 were grown from saturated toluene solutions. Crystals of 4 and 5 were grown by slow diffusion of pentane into a toluene solution. Suitable crystals were covered in mineral oil (Aldrich) and mounted onto a glass fiber. The crystals were transferred directly to the -70 °C cold N2 stream of a Stoe IPDS 2T diffractometer. Subsequent computations were carried out on an Intel Pentium IV PC. All structures were solved by the Patterson method (SHELXS9722). The remaining non-hydrogen atoms were located from successive difference Fourier map calculations. The refinements were carried out by using full-matrix least-squares techniques on F, minimizing the function (Fo - Fc)2, where the weight is defined as 4Fo2/2(Fo2) and Fo and Fc are the observed and calculated structure factor amplitudes using the program SHELXL-97.23 In the final cycles of each refinement, all non-hydrogen atoms were assigned anisotropic temperature factors. Carbon-bound hydrogen atom positions were calculated. The hydrogen atom contributions were calculated, but not refined. The final values of refinement parameters are given in Table 1. The locations of the largest peaks in the final difference Fourier map calculation as well as the magnitude of the residual electron densities in each case were of no chemical significance. Positional parameters, hydrogen atom parameters, thermal parameters, and bond distances and angles have been deposited as Supporting Information. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. 705512–705516. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: (+(44)1223-336033; e-mail: [email protected]).

Results and Discussion Ligand Synthesis. The synthesis of the enantiomerically pure chiral-bridged aminotroponimine ligands (S,S)-H2{(iPr(22) Sheldrick, G. M. SHELXS-97, Program of Crystal Structure Solution; University of Go¨ttingen: Germany, 1997. (23) Sheldrick, G. M. SHELXL-97, Program of Crystal Structure Refinement; University of Go¨ttingen: Germany, 1997.

Chiral Aminotroponiminate Zinc Complexes

Organometallics, Vol. 28, No. 1, 2009 309

Table 1. Crystallographic Details of 1, 2, 3, 4, and 5a 1 formula fw space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z density (g/cm3) radiation µ, mm-1 absorp corr reflns collected unique reflns obsd reflns data; params R1b; wR2c a

2

3

C36H42N4Zn2 C38H46N4Zn2 C46H46N4Zn2 661.48 689.53 785.61 P21 (No. 2) C2221 (No. 20) C2221 (No. 20) 10.3934(10) 14.4675(7) 16.5128(7) 9.9696(6) 18.2870(14) 17.8044(13) 15.9184 26.9299(18) 27.1153(14) 90.00 90.00 90.00 94.368(8) 90.00 90.00 90.00 90.00 90.00 1644.6(2) 7128.7(8) 7971.9(8) 2 8 8 1.336 1.285 1.309 Mo KR (λ ) 0.71073 Å) Mo KR (λ ) 0.71073 Å) Mo KR (λ ) 0.71073 Å) 1.488 1.376 1.240 Integration (X-Shape) Integration (X-Shape) Integration (X-Shape) 11 772 15 040 20 005 8788 [Rint ) 0.0444] 9353 [Rint ) 0.0284] 10 714 [Rint ) 0.0443] 6992 7991 7980 8788/385 9353/403 10 714/469 0.0401; 0.1117 0.0411; 0.0987 0.0321; 0.0738

4

5

C46H46N4Zn2 785.61 P1 (No. 1) 10.3246(5) 11.0133(5) 17.4536(9) 84.878(4) 81.151(4) 89.787(4) 1953.06(16) 2 1.336 Mo KR (λ ) 0.71073 Å) 1.265 Integration (X-Shape) 24 913 13 074 [Rint ) 0.0342] 12 242 13 074/937 0.0264; 0.0630

C46H46N4Zn2 785.61 P212121 (No. 19) 9.4194(5) 15.4966(7) 27.0132(11) 90.00 90.00 90.00 3943.1(3) 4 1.323 Mo KR (λ ) 0.71073 Å) 1.253 Integration (X-Shape) 35 290 6960 [Rint ) 0.0983] 5500 6960/469 0.0455; 0.0760

All data collected at 203 K. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2.

ATI)2diph} and (R,R)-H2{(iPrATI)2diph}, in which two isopropylaminotroponimine units are linked by enantiomerically pure 1,2-diamino-1,2-diphenylethane, has been described previously by our group, and the ligand was introduced into lanthanide chemistry (Scheme 2).19 They can be obtained in a straightforward synthesis, by reaction of isopropylamine with 2-(tosyloxo)tropone first to form 2-(N-isopropylamino)tropone in almost quantitative yield. Further treatment of 2-(N-isopropylamino)tropone with Me3O · BF4, triethylamine, and 1,2-(S,S)diamino-1,2-diphenylethane (1,2-(R,R)-diamino-1,2-diphenylethane) led to the desired product as a yellow solids. In an attempt to create a sterical, more demanding ligand, we replaced the isopropyl group with enantiopure (R)-1-amino1-phenylethane (Scheme 2). The new ligands (S,S)-H2{((R)PhCHCH3ATI)2diph} and (R,R)-H2{((R)-PhCHCH3ATI)2diph}, which are diasteromers, were prepared in a similar fashion to (S,S)-H2{(iPrATI)2diph}, using (R)-1-amino-1-phenylethane instead of isopropylamine in the first reaction step. The thus obtained 2-(N-(R)-(1-phenylethylamino)tropone21 was then treated with Me3O · BF4, triethylamine, and 1,2-(S,S)- or 1,2-(R,R)diamino-1,2-diphenylethane to give the new chiral enantiopure ligands in good yields (Scheme 2). Both new compounds were characterized by 1H and 13C{1H} NMR and mass spectroscopy. The signals are consistent with the structures given in Scheme 2. It should be mentioned that the chiral nonbridged ligand N-(S)-1-phenylethyl-2-((S)-1-phenylethylamino)troponimine was prepared by H. Brunner et al. in a different approach.24 Metal Complexes. The dimetallic zinc complexes [(S,S){(iPrATI)2diph}(ZnR)2] (R ) Me (1), Et (2)) were synthesized by reaction of the neutral ligand (S,S)-H2{(iPrATI)2diph} with 2 equiv of the corresponding zinc organyls ZnR2 (R ) Me, Et) in toluene at low temperatures (Scheme 3). [(R,R)-{(iPrATI)2diph}(ZnPh)2] (3) was obtained in a similar fashion by reaction of (R,R)-H2{(iPrATI)2diph} with ZnPh2 (Scheme 4). Compounds 1-3 could be obtained as orange, analytically pure solids by crystallization directly from the reaction mixtures. The new complexes have been characterized by standard analytical/ spectroscopic techniques. Complexes 1 and 2 show the characteristic signals for the methyl and ethyl ligands in the 1H and 13C{1H} NMR spectra (1: Zn(CH3), δ(C6D6): 1H, -0.12 ppm, δ(C6D6) 13C{1H}, -12.0 (24) Brunner, H.; Knott, A. J. Organomet. Chem. 1985, 195, 211–221.

Scheme 3

Scheme 4

ppm); 2: Zn(CH2CH3)2, δ(C6D6) 1H, 0.49, 0.55 ppm; δ(C6D6) 13 C{1H}, 1.2 ppm; starting materials ZnMe2, δ 1H, 0.51 ppm, δ 13 C{1H}, -4.2 ppm25 and ZnEt2, δ 1H, 0.08 ppm; δ 13C{1H}, 6.82 ppm).26 While for the ZnCH3 protons for 1 a singlet is observed, the ZnCH2CH3 protons for 2 are split into two doublets of quartets because of geminal coupling, which is a result of diastereotopic splitting and concomitant coupling with the CH3 protons. The diastereotopic splitting is not observed in chiral zincethyl compounds with less sterically demanding ligands.27 Compound 3 also shows the expected set of signals in the 1H and 13C{1H} NMR spectra. The signals of the phenyl ligand can be observed in the aromatic region, but the overlapping with the signals of the ATI and the aromatic protons from the chiral bridge made it difficult to assign them precisely. The EI mass spectra show the [M - R]+ and [M - 2 R]+ (R ) Me, Et, Ph) fragments for compounds 1, 2, and 3. The peaks of the molecular ion [M]+ fragments could not be observed. Furthermore, the structures of 1, 2, and 3 were confirmed by singlecrystal X-ray diffraction in the solid state (Figures 1 -3). Data collection parameters and selected bond lengths and angles are (25) Gayler, L. A.; Wilkinson, G. Inorg. Synth. 1979, 19, 253–257. (26) Abram, M. H.; Rolfe, P. H. J. Organomet. Chem. 1967, 7, 35–43. (b) Mu¨ller, H.; Ro¨sch, L.; Erb, W.; Zeisberg, R. J. Organomet. Chem. 1977, 140, C17-C20. (27) Chakraborty, D.; Chen, E. Y. X. Organometallics 2003, 22, 769– 774.

310 Organometallics, Vol. 28, No. 1, 2009

Figure 1. Perspective ORTEP view of the molecular structure of 1. Thermal ellipsoids are drawn to encompass 30% probability. Hydrogen atoms are omitted for clarity.

Meyer and Roesky

Figure 4. Perspective ORTEP view of the molecular structure of 4. Thermal ellipsoids are drawn to encompass 30% probability. Hydrogen atoms are omitted for clarity. Only one of the independent molecules is shown. Table 2. Crystallographic Details of [(iPrAT)ZnMe]2 (2a) and [(iPrAT)ZnEt]2 (2b) 1

Figure 2. Perspective ORTEP view of the molecular structure of 2. Thermal ellipsoids are drawn to encompass 30% probability. Hydrogen atoms are omitted for clarity.

2

3

Zn1-N1 Zn1-N2 Zn1-C Zn2-N3 Zn2-N4 Zn2-C Zn1-Zn2

1.965(4) 1.968(3) 1.943(4) 1.983(3) 1.982(2) 1.949(4) 3.669(1)

Bond Lengths (Å) 1.975(3) 1.972(3) 1.974(2) 1.945(2) 1.955(4) 1.934(4) 1.970(2) 1.965(2) 1.971(3) 1.968(2) 1.970(4) 1.940(3) 3.867(1) 3.493(1)

N1-Zn1-N2 N1-Zn1-C N2-Zn1-C N3-Zn2-N4 N3-Zn2-C N4-Zn2-C

81.47(14) 139.0(2) 137.90(2) 81.56(13) 144.63(17) 132.72(2)

Bond Angles (deg) 81.55(10) 81.79(11) 138.99(10) 130.29(13) 138.46(10) 146.22(13) 81.37(10) 81.75(9) 141.26(2) 139.72(11) 134.96(2) 137.78(11)

4

5

1.987(2) 1972(2) 1.951(3) 1.981(2) 1.973(2) 1.950(3) 3.662(6)

1.978(3) 1.985(3) 1.928(5) 1.959(3) 1.980(3) 1.940(5) 3.761(1)

82.06(9) 132.18(11) 145.73(12) 81.78(9) 138.83(13) 139.34(13)

81.38(14) 141.95(2) 136.66(2) 82.16(13) 142.98(2) 133.10(2)

Scheme 5

Figure 3. Perspective ORTEP view of the molecular structure of 3. Thermal ellipsoids are drawn to encompass 30% probability. Hydrogen atoms are omitted for clarity.

given in Tables 1 and 2. Compound 1 crystallizes in the chiral monoclinic space group P21 with two molecules in the unit cell, while 2 and 3 crystallize in the orthorhombic chiral space group C2221, with eight molecules in the unit cell. As observed for other aminotroponiminate zinc compounds, the metal atoms of all three complexes are coordinated in a trigonal-planar fashion.4,7,8 Despite the different organic ligands all compounds show a similar geometry. The Zn-N distances are between 1.965(2) and 1.983(3) Å, comparable to the previously published nonchiral ATI zinc compounds.4,7,8 The Zn-C distances are in the range 1.943(4)-1.949(4) Å for 1 and 1.955(4)-1.970(4) Å for 2. These distances are typical for zinc methyl and ethyl bonds.7,8,28 For 3 the Zn-C distances are 1.934(4) and 1.940(3) Å, which is again in the expected range.29 The torsion angles N2-C-C-N3 along the C-C bond of the chiral bridges are 49.4(4)° (1), 53.8(3)° (2), and 55.03° (3). (28) Dove, A. P.; Gibson, V. C.; Marshall, E. L.; White, A. J. P.; Williams, D. J. Dalton Trans. 2004, 570–578. (29) Prust, J.; Stasch, A.; Zheng, W.; Roesky, H. W.; Alexopoulos, E.; Uson, I.; Bo¨hler, D.; Schuchardt, T. Organometallics 2001, 20, 3825–3828.

It should also be mentioned that attempts to synthesize a monometallic complex of the type [(S,S)-{(iPrATI)2diph}Zn] were not successful. Reaction of 1 equiv of dimethyl- or diethylzinc with the neutral ligand, also at elevated temperatures, always gave the dimetallic species 1 or 2 exclusively. Reaction of the sterical more demanding ligands (S,S)H2{((R)-PhCHCH3ATI)2diph} and (R,R)-H2{((R)-PhCHCH3ATI)2diph}, which have four stereocenters, with 2 equiv of ZnMe2 in toluene gave the enantiopure complexes [(S,S)-{((R)PhCHCH3ATI)2diph}(ZnMe)2] (4) and [(R,R)-{((R)-PhCHCH3ATI)2diph}(ZnMe)2] (5) (Scheme 5). Complexes 4 and 5 were obtained as yellow crystalline, analytically pure solids when the concentrated reaction mixtures were layered with pentane. Complexes 4 and 5 were characterized by 1H and 13C NMR spectroscopy and elemental analysis.

Chiral Aminotroponiminate Zinc Complexes

Organometallics, Vol. 28, No. 1, 2009 311

Compounds 1 and 2 were used as catalysts in the intramolecular hydroamination/cyclization reaction of nonactivated terminal aminoolefins. It turned out that the substrates are converted to the cyclic product at elevated temperature in high yields, but almost no enantioselectivities (less than 10%) were obtained. Details of the reactions are found in the Supporting Information.

Summary

Figure 5. Perspective ORTEP view of the molecular structure of 5. Thermal ellipsoids are drawn to encompass 30% probability. Hydrogen atoms are omitted for clarity. 1 H NMR as well as 13C{1H} NMR spectra are consistent with the solid state structures (see below). The signals of the Zn(CH3) group again are observed at a high field (4: δ(C6D6) 1H, -0.19 ppm, δ(C6D6) 13C{1H}, -10.6 ppm; 5: δ(C6D6) 1H, -0.17 ppm, δ(C6D6) 13C{1H}, -12.4 ppm). The molecular structures of 4 and 5 were also confirmed by single-crystal X-ray diffraction in the solid state (Figures 4 and 5). Data collection parameters and selected bond lengths and angles are given in Tables 1 and 2. Compound 4 crystallizes in the chiral triclinic space group P1 with two molecules in the asymmetric unit and in the unit cell; 5, in the chiral monoclinic space group P212121 with four molecules in the unit cell. The Zn-N distances are between 1.972(2) and 1.987(2) Å, almost the same as in the previously described structures of 1, 2, and 3 and comparable zinc methyl compounds.7,8 The Zn-C distances are also in the expected range (1.950(3), 1.951(3) Å (4); 1.928(5), 1.940(5) Å (5)).7,8,25 The torsion angles N2-C-C-N3 along the C-C bond of the chiral bridges are 49.5(3)° (4) and 47.8(4)° (5).

We have prepared dimetallic zincmethyl, -ethyl, and phenyl complexes having the enantiomerically pure bridged aminotroponiminate ligands (S,S)-{(iPrATI)2diph}2-, (R,R)-{(iPrATI)2diph}2-, (S,S)-{((R)-PhCHCH3ATI)2diph}2-, and (R,R){((R)-PhCHCH3ATI)2diph}2- in the coordination sphere. The zinc complexes were obtained by reaction of ZnR2 (R ) Me, Et, Ph) with the corresponding neutral ligands. As a result, the compounds [(S,S)-{(iPrATI)2diph}(ZnR)2] (R ) Me (1), Et (2), [(R,R)-{(iPrATI)2diph}(ZnPh)2] (3), [(S,S)-{((R)-PhCHCH3ATI)2diph}(ZnMe)2] (4), and [(R,R)-{((R)-PhCHCH3ATI)2diph}(ZnMe)2] (5) were synthesized. The molecular structures of all new complexes were confirmed by single-crystal X-ray diffraction in the solid state.

Acknowledgment. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. Additionally, generous support from J. Jenter and A. Zulys is gratefully acknowledged. Supporting Information Available: Experimental details of the hydroamination experiments and X-ray crystallographic files in CIF format for the structure determinations of 1-5 are available free of charge via the Internet at http://pubs.acs.org. OM800858T