- Email: [email protected]
Asymmetric β-functionalization of secondary amine with CH2Cl2 on a chiral NCN pincer Rh complex
Journal of Organometallic Chemistry 794 (2015) 318e322
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Asymmetric b-functionalization of secondary amine with CH2Cl2 on a chiral NCN pincer Rh complex Jun-ichi Ito*, Takeshi Miyakawa, Hisao Nishiyama** Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 April 2015 Received in revised form 17 July 2015 Accepted 20 July 2015 Available online 23 July 2015
Functionalization of a b-CeH bond of a secondary aliphatic amine was accomplished using NCN pincer Rh complex 1 with a chiral bis(oxazolinyl)phenyl ligand. Complex 1 underwent asymmetric alkylation of dicyclopentylamine with CH2Cl2 to form azametallacycle complex 2. Additionally, the reaction of 1 with triethylamine in CH2Cl2 resulted in the formation of ammonium ylide complex 3 via CeN bond formation. © 2015 Elsevier B.V. All rights reserved.
Keywords: Rhodium NCN pincer Oxidative addition CeC bond formation Ylide
1. Introduction CeH bond activation and successive CeC bond formation are recognized as an efficient method in synthesis of complex molecules from ubiquitous organic molecules [1]. Since aliphatic amine is an important substructure in a number of bioactive compounds and fine chemicals, functionalization of aliphatic amines involving C(sp3)-H bond activation has been extensively developed in the field of catalysis [2,3]. Regarding functionalization at the b-positions of amines, reaction for dehydrogenation of amines to enamines were developed using PCP pincer Ir complexes [3a], as well as Cp*Rh and Co complexes [3b]. Such dehydrogenation systems were expanded to include a CeC bond-formation reaction, in which in situ generated enamines underwent conjugate addition to nitroolefines [3c] and aldol condensation [3d]. Recently, selective barylation of cyclic amines catalyzed by Pt was reported [3e]. To introduce a CH2 fragment into organic molecules, CH2Cl2 is considered to be a simple and readily available substrate. Thus far, oxidative addition of CH2Cl2 followed by CeX bond formation with a resulting MCH2-Cl fragment were reported by several research groups (X ¼ P [4] N [5], C [6]). Recently, catalytic three-component
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J.-i. Ito), [email protected] (H. Nishiyama). http://dx.doi.org/10.1016/j.jorganchem.2015.07.031 0022-328X/© 2015 Elsevier B.V. All rights reserved.
coupling reactions of CH2Cl2 and tertiary amines with alkynes or phosphonate were developed as a versatile synthetic method for amine derivatives [7]. We previously reported unique CeC bond formation of NHiPr2 with CH2Cl2, mediated by the NCN pincer Rh(III) complex containing bis(oxazolinyl)phenyl (abbreviated as phebox) ligand (Scheme 1) [8]. In this reaction, dehydrogenation of amine followed alkylation with RheCH2Cl was proposed for CeC bond formation at a b-position of the amine. This result encouraged us to study asymmetric CeC bond formation reaction on a chiral Rh complex. Here, we reported b-alkylation of a secondary amine using CH2Cl2 by a chiral phebox Rh complex. 2. Results and discussion To demonstrate the asymmetric CeC bond formation reaction of a secondary amine, chiral Rh complex 1 [9] with benzyl-substituted phebox ligand was selected after several trials. The reaction of 1 with an excess amount of dicyclopentylamine in CH2Cl2 at 35 C for 48 h cleanly proceeded to yield a new Rh complex 2 (Scheme 2). The 1H NMR spectrum showed selective formation of 2 in 80% yield. After purification by column chromatography and recrystallization of the crude product, the complex 2 was isolated in 49% yield as yellow crystals. The complex 2 was identified by means of 1H and 13C NMR spectra and X-ray analysis. In the 1H NMR spectrum of 2, two protons bonding a-CH2 to the Rh center were observed as two
J.-i. Ito et al. / Journal of Organometallic Chemistry 794 (2015) 318e322
319
Scheme 1. Reaction of the phebox Rh complex with NHiPr2 in CH2Cl2.
diastereotopic signals at d 0.48 and 0.90 ppm. The 13C NMR spectrum show a doublet peak at the a-position at d 18.6 ppm with the coupling of Rh (JRhC ¼ 24.1 Hz). The signal of imine carbon was also observed at d 193.3. Additionally, ipso-carbon of the phenyl fragment on the phebox ligand appeared as a doublet peak at d 192.0 ppm with the coupling of Rh (JRhC ¼ 25.1 Hz). The molecular structure of 2 was determined by X-ray analysis using yellow crystals obtained from a solution of CH2Cl2, ethyl acetate and hexane at room temperature (Fig. 1). The Rh center showed pseudo-octahedral geometry with meridionally coordinated phebox ligand. The Rh1eC1 bond length (1.908(10) Å) is similar to the values found for other phebox-Rh complexes [9]. The Rh center contains the five membered metallacycle consisting of Rh1, N3, C27, C28 and C32 atoms. Imine nitrogen N3 is coordinated at the equatorial position, while the Rh1eC27 covalent bond is attached at the axial position. The Rh1eC27 bond length (2.046(9) Å) was identical to that of the related azametallacycle complex (2.045(6) Å) [8]. The N3eC32 bond length (1.269(12) Å) was shorter than the N3eC33 bond length (1.450(12) Å), suggesting the presence of a N]C bond. The sums of angles at N3 and C32 were estimated to be 360 , indicating a planar configuration. The absolute configuration at the C28 center was determined to be R. To obtain an insight into the reaction, we next investigated the reaction of 1 with NEt3 in place of a secondary amine. Previously, NEt3 was found to serve as a reductant of the phebox-Rh(III) complex to form a Rh(I) species, which underwent oxidative addition of chlorobenzene [10]. We intended to prepare a chloromethyl complex by oxidative addition of CH2Cl2 to Rh(I) generated in situ. However the desired chloromethyl complex was not detected when 1 was treated with NEt3 in CH2Cl2 at 35 C. The 1H NMR spectrum of the crude mixture showed the formation of ammonium ylide Rh complex 3 (Scheme 3) [11,12]. The complex 3 was isolated by silica gel column chromatography in 61% yield. In the case of a bulky tertiary amine, NEt(i-Pr)2, the formation of an ylide complex was not detected. In the 1H NMR spectrum of 3, the diastereotopic a-CH2 signals of the ylide were observed at d 2.37 and 3.08 ppm. This chemical shifts moved to lower fields than those of the a-CH2 signals of 2. The CH3 and CH2 signals of the Et groups appeared as a triplet peak at
Fig. 1. ORTEP diagram of 2 with 50% probability level. Selected bond lengths (Å): Rh1eC1 1.908(10), Rh1eC27 2.046(9), Rh1eN1 2.082(7), Rh1eN2 2.071(9), Rh1eN3 2.267(8), Rh1eCl1 2.503(3), N3eC32 1.269(12), N3eC33 1.450(12). Selected bond angles ( ): N2eRh1eN1 157.2(3), C1eRh1eN3 166.6(3), C27eRh1eCl1 175.6(3), C27eRh1eN3 80.4(4), C32eN3eC33 116.8(8), C32eN3eRh1 108.3(6), C33eN3eRh1 134.9(6), N3eC32eC28 120.4(8), N3eC32eC31 129.4(10), C28eC32eC31 110.1(9), C28eC27eRh1 106.3(6).
Scheme 3. Reaction of 1 with NEt3 in CH2Cl2.
d 1.05 ppm (9H), and as two diastereotopic peaks at d 3.30 (3H) and 3.44 in ppm (3H), respectively. The integral ratio of these signals indicated the presence of one NEt3 unit in the molecule. In the 13C NMR spectrum, the signal of a-C was observed at d 48.9 ppm with a coupling of the Rh atom (JRhC ¼ 34.3 Hz). The Et signals of the NEt3 fragment appeared at d 8.7 and 53.9 ppm. These spectral features supported the formation of ammonium ylide. Finally, the molecular structure of 3 was confirmed by X-ray analysis (Fig. 2). The Rh center showed pseudo-octahedral geometry with the meridional phebox ligand and cis-arranged Cl ligands. The RheC bond of the ylide fragment was placed at the axial position. This structural feature is similar to that of other alkyl and aryl complexes with NCN pincer ligands [8,10,13]. The Rh1eC27 bond length (2.079(9) Å) is comparable to that of 2. The Rh1eCl1 bond length (2.4652(19) Å) is slightly shorter than the Rh1eCl2 bond length (2.5133(18) Å), suggesting that the trans-influence of the CH2NEt3 group is weaker
Scheme 2. Reaction of chiral Rh complex 1 with dicyclopentylamine in CH2Cl2.
320
J.-i. Ito et al. / Journal of Organometallic Chemistry 794 (2015) 318e322
Fig. 2. ORTEP diagram of 3 with 30% probability level. Selected bond lengths (Å): Rh1eC1 1.922(7), Rh1eC27 2.079(9), Rh1eCl1 2.4652(19), Rh1eCl2 2.5133(18), Rh1eN1 2.054(7), Rh1eN2 2.077(6), C27eN3 1.503(11). Selected bond angles ( ): N1eRh1eN(2) 158.2(3), C1eRh1eCl2 175.3(3), C27eRh1eCl1 170.5(2), N3eC27eRh1 125.0(6).
Scheme 5. Proposed mechanism for stereochemical control of the CeC bond forming step.
than that of the phebox aryl group. A proposed mechanism is described in Scheme 4. We previously reported oxidative addition of chlorobenzene to the phebox Rh complex in the presence of NHiPr2 [10]. In this case, the formation of imine Me2C]NiPr was detected in the 1H NMR spectrum of the reaction mixture. According to this observation, the first step could be the reduction of Rh(III) to Rh(I) assisted by an amine. In this step, NHiPr2 and NEt3 serve as reductants, whereby the corresponding imine C and iminium ion, respectively, are formed. Then, oxidative addition of CH2Cl2 to Rh(I) intermediate B affords chloromethyl intermediate D [14]. In the presence of NEt3, nucleophilic substitution of the CleCH2 group takes place to afford ammonium ylide complex 3. We currently assume that the formation of 3 is an indirect evidence of D. In addition, substitution of the CleCH2Rh fragment by an amine might be feasible compared to that of free CH2Cl2 by a tertiary amine [15]. In contrast to the reaction with NEt3, a nucleophilic attack by NHiPr2 or C is considered to be inhibited due to steric repulsion. Consequently, coordination of C gives imine adduct E, which is in equilibrium with enamine
intermediate F generated by tautomerization [16]. Finally, a nucleophilic attack by enamine to the CH2Cl group forms a 5membered metallacycle [17]. At this stage, the R-absolute configuration is constructed at the b-carbon. A proposed mechanism for a stereochemical control of the CeC bond-forming step is shown in Scheme 5. As mentioned earlier, the CH2Cl group is likely coordinated at the axial position. At this point, a re-face attack of the enamine gives R-stereochemistry (Path a), while a si-face attack gives S-stereochemistry (Path b). Path b is considered a minor path due to the repulsion between the oxazoline substituent and the five-membered ring of the enamine. Consequently, Path a is predominantly in construction of the structure of 2. Finally, the reactivity of 2 toward hydrogenation and pyrolysis was checked to gain an organic fragment from the azametallacycle. However, 2 was found to be stable in heating under hydrogen or argon atmosphere. In addition, irradiation by UV lamp was also resulted in no reaction. Complex 3 was also inactive in irradiation by UV lamp. In summary, we demonstrated asymmetric b-alkylation of a
Scheme 4. Proposed mechanism for the formation of 2 and 3.
J.-i. Ito et al. / Journal of Organometallic Chemistry 794 (2015) 318e322
secondary amine with CH2Cl2 by the chiral NCN pincer Rh complex 1. In this reaction, the formation of the azametallacycle structure was likely formed by successive sequence of oxidative addition of CH2Cl2, dehydrogenation of an amine to an imine, tautomerization of the imine to an enamine and alkylation of a CleCH2Rh fragment. In contrast to a secondary amine, the reaction of 1 with NEt3 in CH2Cl2 resulted in the formation of the ammonium ylide complex 3 by alkylation of the nitrogen atom. The formation of 3 is considered to be an evidence for a chloromethyl intermediate via oxidative addition of CH2Cl2 to of the Rh(I) species generated in situ. 3. Experimental section 1 H and 13C NMR spectra were recorded on a Varian Mercury 300 spectrometer. 1H NMR chemical shifts were reported in ppm relative to the singlet at 7.26 ppm for CDCl3. 13C NMR spectra were reported relative to the triplet at d 77.0 ppm for CDCl3. Infrared spectra were recorded on a JASCO FT/IR-230 spectrometer. Mass spectrum was recorded on a JEOL JMS-700. Elemental analysis was recorded on a PerkineElmer 2400II. Complex 1 was prepared according to the literature [9].
3.1. Preparation of 2 To a mixture of 1a (59.0 mg, 0.10 mmol) and MS 4 Å (0.2 g) was added CH2Cl2 (2 mL) and dicyclopentylamine (307 mg, 2.0 mmol). After being stirred for 48 h at 35 C, the solvent was removed under reduced pressure. The resulting crude products was passed through silica gel with CH2Cl2/ethyl acetate (¼ 10:1) to remove the residual amine. The filtrate was concentrated and the residue was purified by column chromatography on silica gel with Hexane:ethyl acetate (¼2:1). Recrystallization from a mixed solvent (CH2Cl2/ethyl acetate/hexane) provided yellow crystals of 2 (34.4 mg, 0.049 mmol). 1 H NMR (300 MHz, CDCl3, rt): d 0.48 (t, JHH ¼ 9.2 Hz, 1H), 0.90 (td, JHH ¼ 9.2 Hz, JRhH ¼ 2.7 Hz, 1H), 1.15e1.35 (m, 1H), 1.60e2.25 (m, 13H), 2.39e2.60 (m, 3H), 2.70e2.95 (m, 4H), 3.39 (dd, JHH ¼ 12.9, 3.9 Hz, 1H), 3.69 (dd, JHH ¼ 14.4, 3.6 Hz, 1H), 4.10e4.22 (m, 1H), 4.32 (t, JHH ¼ 9.0 Hz, 1H), 4.40 (t JHH ¼ 8.1 Hz, 1H), 4.52e4.66 (m, 3H), 4.76e4.89 (m, 1H), 7.06 (t, JHH ¼ 7.8 Hz, 1H), 7.18e7.39 (m, 10H), 7.44 (d, JHH ¼ 7.8 Hz, 1H), 7.48 (d, JHH ¼ 7.8 Hz, 1H). 13C NMR (75 MHz, CDCl3, rt): d 18.6 (d, JRhC ¼ 24.1 Hz), 24.6, 24.8, 26.0, 28.9, 31.9, 32.0, 33.6, 39.8, 40.4, 59.7, 63.9, 64.4, 66.8, 74.5, 74.9, 120.4, 126.3, 126.4, 126.8, 128.5, 128.8, 129.1, 129.9, 130.3, 136.6, 137.3, 172.48 (JRhC ¼ 5.2 Hz), 172.54 (JRhC ¼ 5.1 Hz), 192.0 (JRhC ¼ 25.1 Hz), 193.3. IR (KBr, cm1): 1614 (nC]N). Anal. Calcd for C37H41ClN3O2Rh: C, 63.66; H, 5.92; N, 6.02. Found: C, 63.69; H, 6.08; N, 5.58. 3.2. Preparation of 3 To a mixture of 1a (11.8 mg, 0.020 mmol) and MS 4 Å (0.1 g) was added CH2Cl2 (1 mL) and NEt3 (28 mL). After being stirred for 18 h at 35 C, the mixture was filtrated to remove insoluble materials. The filtrate was concentrated and then purified by column chromatography on silica gel with CH2Cl2/MeOH (¼10:1) to give 3 (8.4 mg, 0.012 mmol, 61%). 1 H NMR (300 MHz, CDCl3): 1.05 (t, JHH ¼ 7.2 Hz, 9H), 2.37 (d, JHH ¼ 10.5 Hz, 1H), 2.47 (t, JHH ¼ 12.0 Hz, 1H), 2.78 (dd, JHH ¼ 14.0, 11.6 Hz, 1H), 3.08 (dd, JHH ¼ 10.5 Hz, JRhH ¼ 3.0 Hz, 1H), 3.30 (dq, JHH ¼ 13.6, 6.9 Hz, 3H), 3.44 (dq, JHH ¼ 13.6, 6.8 Hz, 3H), 4.48e4.89 (m, 8H), 7.13e7.35 (m, 11H), 7.52 (d, JHH ¼ 7.8 Hz, 1H), 7.54 (d, JHH ¼ 7.8 Hz, 1H). 13C NMR (CDCl3, 75 MHz): 8.7, 40.5, 40.8, 48.9 (d, JRhC ¼ 34.3 Hz), 53.9, 65.4, 65.6, 75.3, 76.1, 121.6, 126.0, 126.4, 127.4, 128.3, 128.4, 128.8, 129.3, 130.1, 130.4, 137.4, 138.5, 171.6 (JRhC ¼ 4.6 Hz), 172.8 (JRhC ¼ 4.6 Hz), 193.4 (JRhC ¼ 23.9 Hz). HRMS(FAB): 648.1864 [MeCl]. Found: 648.1867.
321
3.3. X-ray analyses The diffraction data of 2 and 3 were collected on a Bruker SMART APEX CCD diffractometer with graphite-monochromated Mo Ka radiation (l ¼ 0.71073 Å). An empirical absorption correction was applied by using SADABS. The structure was solved by direct methods and refined by full-matrix least-squares on F2 using SHELXTL. All non-hydrogen atoms were refined with anisotropic displacement parameters. CCDC 1061627 (2) and CCDC 1061628 (3) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_ request/cif. Crystallographic data for 2: C37H41ClN3O2Rh(C6H14); Mr ¼ 784.26; temperature 153 K; orthorhombic, P212121; a ¼ 9.272(6), b ¼ 16.534(9), c ¼ 24.169(15) Å; V ¼ 3705(4) Å3; Z ¼ 4; rcalcd ¼ 1.406 Mg/m3; m ¼ 0.574 mm1; reflections collected 26,460, independent reflections 8673 [R(int) ¼ 0.1282]; parameters 413; goodness-of-fit on F2 1.059; final R indices [I > 2s(I)] R1 ¼ 0.0766, wR2 ¼ 0.1550; R indices (all data) R1 ¼ 0.1240, wR2 ¼ 0.1738; largest diff. peak/hole 1.194 and 0.841 Å3. Crystallographic data for 3: C33H40Cl2N3O2Rh(CH2Cl2); Mr ¼ 769.41; temperature 153 K; tetragonal, P41; a ¼ 11.6086(10), c ¼ 25.050(4) Å; V ¼ 3375.8(8) Å3; Z ¼ 4; rcalcd ¼ 1.514 Mg/m3; m ¼ 0.858 mm1; reflections collected 27,292, independent reflections 9220 [R(int) ¼ 0.0420]; parameters 401; goodness-of-fit on F2 1.058; final R indices [I > 2s(I)] R1 ¼ 0.0590, wR2 ¼ 0.1516; R indices (all data) R1 ¼ 0.0707, wR2 ¼ 0.1607; largest diff. peak/ hole 1.195 and 1.314 Å3. Acknowledgment This research was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Nos. 22245014, 26410114). Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jorganchem.2015.07.031. References [1] Reviews for C-H functionalization: (a) C.S. Yeung, V.M. Dong, Chem. Rev. 111 (2011) 1215e1292; (b) P.B. Arockiam, C. Bruneau, P.H. Dixneuf, Chem. Rev. 112 (2012) 5879e5918; (c) L. Ackermann, Chem. Rev. 111 (2011) 1315e1345. [2] Reviews for a-functionalization of amines: (a) C. Zhang, C. Tang, N. Jiao, Chem. Soc. Rev. 41 (2012) 3464e3484; (b) A.E. Wendlandt, A.M. Suess, S.S. Stahl, Angew. Chem. Int. Ed. 50 (2011) 11062e11087; (c) C. Liu, H. Zhang, W. Shi, A. Lei, Chem. Rev. 111 (2011) 1780e1824. [3] (a) X. Zhang, A. Fried, S. Knapp, A.S. Goldman, Chem. Commun. (2003) 2060e2061; (b) A.D. Bolig, M. Brookhart, J. Am. Chem. Soc. 129 (2007) 14544e14545; (c) X.-F. Xia, X.-Z. Shu, K.-G. Ji, Y.-F. Yang, A. Shaukat, X.-Y. Liu, Y.-M. Liang, J. Org. Chem. 75 (2010) 2893e2902; (d) B. Sundararaju, M. Achard, G.V.M. Sharma, C. Bruneau, J. Am. Chem. Soc. 133 (2011) 10340e10343; (e) A. Millet, P. Larini, E. Clot, O. Baudoin, Chem. Sci. 4 (2013) 2241e2247. [4] (a) T.B. Marder, W.C. Fultz, J.C. Calabrese, R.L. Harlow, D. Milstein, J. Chem. Soc. Chem. Commun. (1987) 1543e1545; (b) R. Pattacini, S. Jiez, P. Braunstein, Chem. Commun. (2009) 890e892; (c) A. Ghisolfi, F. Condello, C. Fliedel, V. Rosa, P. Braunstein, Organometallics 34 (2015) 2255e2260. [5] (a) E.G. Burns, S.S.C. Chu, P. de Meester, M. Lattman, Organometallics 5 (1986) 2383e2384; (b) P.J. Fennis, P.H.M. Budzelaar, J.H.G. Frijns, J. Organomet. Chem. 393 (1990) 287e298. [6] K.T.K. Chan, L.P. Spencer, J.D. Masuda, J.S.J. McCahill, P. Wei, D.W. Stephan,
322
J.-i. Ito et al. / Journal of Organometallic Chemistry 794 (2015) 318e322
Organometallics 23 (2004) 381e390. [7] (a) Y. Zhao, X. Chen, T. Chen, Y. Zhou, S.-F. Yin, L.-B. Han, J. Org. Chem. 80 (2015) 62e69; (b) X. Chen, T. Chen, Y. Zhou, C.-T. Au, L.-B. Hana, S.-F. Yin, Org. Biomol. Chem. 12 (2014) 247e250. [8] J. Ito, T. Miyakawa, H. Nishiyama, Organometallics 25 (2006) 5216e5218. [9] (a) Y. Kanazawa, Y. Tsuchiya, K. Kobayashi, T. Shiomi, J. Itoh, M. Kikuchi, Y. Yamamoto, H. Nishiyama, Chem. Eur. J. 12 (2006) 63e71; (b) Y. Motoyama, M. Okano, H. Narusawa, N. Makihara, K. Aoki, H. Nishiyama, Organometallics 20 (2001) 1580e1591. [10] J. Ito, T. Miyakawa, H. Nishiyama, Organometallics 27 (2008) 3312e3315. [11] Review for ylide complexes: (a) R. Navarro, E.P. Urriolabeitia, J. Chem. Soc. Dalton Trans. (1999) 4111e4122; (b) U. Belluco, R.A. Michelin, M. Mozzon, R. Bertani, J. Organomet. Chem. 557 (1998) 37e68. [12] Examples of N-ylide complexes: (a) L. Grande, E. Serrano, L. Cuesta, E.P. Urriolabeitia, Organometallics 31 (2012) 394e404; (b) W.B. Cross, S. Razak, K. Singh, A.J. Warner, Chem. Eur. J. 20 (2014) 13203e13209; s, J.J. Carbo , R. Navarro, E. Serrano, E.P. Urriolabeitia, Inorg. Chem. (c) A. Lledo 43 (2004) 7622e7635. [13] J. Ito, H. Nishiyama, Eur. J. Inorg. Chem. (2007) 1114e1119. [14] (a) H. Nishiyama, M. Horihata, T. Hirai, S. Wakamatsu, K. Itoh, Organometallics 10 (1991) 2706e2708; (b) B.,C. de Pater, E.J. Zijp, H. Fruhauf, J.M. Ernsting, C.J. Elsevier, K. Vrieze,
Organometallics 23 (2004) 269e279; (c) H.F. Haarman, J.M. Ernsting, M. Kranenburg, H. Kooijman, N. Veldman, A.L. Spek, P.W.N.M. van Leeuwen, K. Vrieze, Organometallics 16 (1997) 887e900; (d) T.O. Northcutt, R.J. Lachicotte, W.D. Jones, Organometallics 17 (1998) 5148e5152; (e) A.J. Vetter, R.D. Rieth, W.W. Brennessel, W.D. Jones, J. Am. Chem. Soc. 131 (2009) 10742e10752; (f) Y. Jiao, W.W. Brennessel, W.D. Jones, Organometallics 34 (2015) 1552e1566; (g) K.J. Bradd, B.T. Heaton, C. Jacob, J.T. Sampanthar, A. Steiner, J. Chem. Soc. Dalton Trans. (1999) 1109e1112; (h) J.Y. Zeng, M.-H. Hsieh, H.M. Lee, J. Organomet. Chem. 690 (2005) 5662e5671; (i) H.F. Haarman, J.M. Ernsting, M. Kranenburg, H. Kooijman, N. Veldman, A.L. Spek, P.W.N.M. van Leeuwen, K. Vrieze, Organometallics 16 (1997) 887e900. [15] The reaction of CH2Cl2 with NEt3 in DMF proceeded at 100 C to give [Et3NCH2Cl]Cl in 89% yield. See ref. [7a]. [16] C.C. Lu, J.C. Peters, J. Am. Chem. Soc. 126 (2004) 15818e15832. [17] (a) G. Ferguson, Y. Li, A.J. McAlees, R. McCrindle, K. Xiang, Organometallics 18 (1999) 2428e2439; (b) D.B. Grotjahn, Y. Gong, L. Zakharov, J.A. Golen, A.L. Rheingold, J. Am. Chem. Soc. 128 (2006) 438e453.
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Asymmetric b-functionalization of secondary amine with CH2Cl2 on a chiral NCN pincer Rh complex Jun-ichi Ito*, Takeshi Miyakawa, Hisao Nishiyama** Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Chikusa, Nagoya 464-8603, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 April 2015 Received in revised form 17 July 2015 Accepted 20 July 2015 Available online 23 July 2015
Functionalization of a b-CeH bond of a secondary aliphatic amine was accomplished using NCN pincer Rh complex 1 with a chiral bis(oxazolinyl)phenyl ligand. Complex 1 underwent asymmetric alkylation of dicyclopentylamine with CH2Cl2 to form azametallacycle complex 2. Additionally, the reaction of 1 with triethylamine in CH2Cl2 resulted in the formation of ammonium ylide complex 3 via CeN bond formation. © 2015 Elsevier B.V. All rights reserved.
Keywords: Rhodium NCN pincer Oxidative addition CeC bond formation Ylide
1. Introduction CeH bond activation and successive CeC bond formation are recognized as an efficient method in synthesis of complex molecules from ubiquitous organic molecules [1]. Since aliphatic amine is an important substructure in a number of bioactive compounds and fine chemicals, functionalization of aliphatic amines involving C(sp3)-H bond activation has been extensively developed in the field of catalysis [2,3]. Regarding functionalization at the b-positions of amines, reaction for dehydrogenation of amines to enamines were developed using PCP pincer Ir complexes [3a], as well as Cp*Rh and Co complexes [3b]. Such dehydrogenation systems were expanded to include a CeC bond-formation reaction, in which in situ generated enamines underwent conjugate addition to nitroolefines [3c] and aldol condensation [3d]. Recently, selective barylation of cyclic amines catalyzed by Pt was reported [3e]. To introduce a CH2 fragment into organic molecules, CH2Cl2 is considered to be a simple and readily available substrate. Thus far, oxidative addition of CH2Cl2 followed by CeX bond formation with a resulting MCH2-Cl fragment were reported by several research groups (X ¼ P [4] N [5], C [6]). Recently, catalytic three-component
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J.-i. Ito), [email protected] (H. Nishiyama). http://dx.doi.org/10.1016/j.jorganchem.2015.07.031 0022-328X/© 2015 Elsevier B.V. All rights reserved.
coupling reactions of CH2Cl2 and tertiary amines with alkynes or phosphonate were developed as a versatile synthetic method for amine derivatives [7]. We previously reported unique CeC bond formation of NHiPr2 with CH2Cl2, mediated by the NCN pincer Rh(III) complex containing bis(oxazolinyl)phenyl (abbreviated as phebox) ligand (Scheme 1) [8]. In this reaction, dehydrogenation of amine followed alkylation with RheCH2Cl was proposed for CeC bond formation at a b-position of the amine. This result encouraged us to study asymmetric CeC bond formation reaction on a chiral Rh complex. Here, we reported b-alkylation of a secondary amine using CH2Cl2 by a chiral phebox Rh complex. 2. Results and discussion To demonstrate the asymmetric CeC bond formation reaction of a secondary amine, chiral Rh complex 1 [9] with benzyl-substituted phebox ligand was selected after several trials. The reaction of 1 with an excess amount of dicyclopentylamine in CH2Cl2 at 35 C for 48 h cleanly proceeded to yield a new Rh complex 2 (Scheme 2). The 1H NMR spectrum showed selective formation of 2 in 80% yield. After purification by column chromatography and recrystallization of the crude product, the complex 2 was isolated in 49% yield as yellow crystals. The complex 2 was identified by means of 1H and 13C NMR spectra and X-ray analysis. In the 1H NMR spectrum of 2, two protons bonding a-CH2 to the Rh center were observed as two
J.-i. Ito et al. / Journal of Organometallic Chemistry 794 (2015) 318e322
319
Scheme 1. Reaction of the phebox Rh complex with NHiPr2 in CH2Cl2.
diastereotopic signals at d 0.48 and 0.90 ppm. The 13C NMR spectrum show a doublet peak at the a-position at d 18.6 ppm with the coupling of Rh (JRhC ¼ 24.1 Hz). The signal of imine carbon was also observed at d 193.3. Additionally, ipso-carbon of the phenyl fragment on the phebox ligand appeared as a doublet peak at d 192.0 ppm with the coupling of Rh (JRhC ¼ 25.1 Hz). The molecular structure of 2 was determined by X-ray analysis using yellow crystals obtained from a solution of CH2Cl2, ethyl acetate and hexane at room temperature (Fig. 1). The Rh center showed pseudo-octahedral geometry with meridionally coordinated phebox ligand. The Rh1eC1 bond length (1.908(10) Å) is similar to the values found for other phebox-Rh complexes [9]. The Rh center contains the five membered metallacycle consisting of Rh1, N3, C27, C28 and C32 atoms. Imine nitrogen N3 is coordinated at the equatorial position, while the Rh1eC27 covalent bond is attached at the axial position. The Rh1eC27 bond length (2.046(9) Å) was identical to that of the related azametallacycle complex (2.045(6) Å) [8]. The N3eC32 bond length (1.269(12) Å) was shorter than the N3eC33 bond length (1.450(12) Å), suggesting the presence of a N]C bond. The sums of angles at N3 and C32 were estimated to be 360 , indicating a planar configuration. The absolute configuration at the C28 center was determined to be R. To obtain an insight into the reaction, we next investigated the reaction of 1 with NEt3 in place of a secondary amine. Previously, NEt3 was found to serve as a reductant of the phebox-Rh(III) complex to form a Rh(I) species, which underwent oxidative addition of chlorobenzene [10]. We intended to prepare a chloromethyl complex by oxidative addition of CH2Cl2 to Rh(I) generated in situ. However the desired chloromethyl complex was not detected when 1 was treated with NEt3 in CH2Cl2 at 35 C. The 1H NMR spectrum of the crude mixture showed the formation of ammonium ylide Rh complex 3 (Scheme 3) [11,12]. The complex 3 was isolated by silica gel column chromatography in 61% yield. In the case of a bulky tertiary amine, NEt(i-Pr)2, the formation of an ylide complex was not detected. In the 1H NMR spectrum of 3, the diastereotopic a-CH2 signals of the ylide were observed at d 2.37 and 3.08 ppm. This chemical shifts moved to lower fields than those of the a-CH2 signals of 2. The CH3 and CH2 signals of the Et groups appeared as a triplet peak at
Fig. 1. ORTEP diagram of 2 with 50% probability level. Selected bond lengths (Å): Rh1eC1 1.908(10), Rh1eC27 2.046(9), Rh1eN1 2.082(7), Rh1eN2 2.071(9), Rh1eN3 2.267(8), Rh1eCl1 2.503(3), N3eC32 1.269(12), N3eC33 1.450(12). Selected bond angles ( ): N2eRh1eN1 157.2(3), C1eRh1eN3 166.6(3), C27eRh1eCl1 175.6(3), C27eRh1eN3 80.4(4), C32eN3eC33 116.8(8), C32eN3eRh1 108.3(6), C33eN3eRh1 134.9(6), N3eC32eC28 120.4(8), N3eC32eC31 129.4(10), C28eC32eC31 110.1(9), C28eC27eRh1 106.3(6).
Scheme 3. Reaction of 1 with NEt3 in CH2Cl2.
d 1.05 ppm (9H), and as two diastereotopic peaks at d 3.30 (3H) and 3.44 in ppm (3H), respectively. The integral ratio of these signals indicated the presence of one NEt3 unit in the molecule. In the 13C NMR spectrum, the signal of a-C was observed at d 48.9 ppm with a coupling of the Rh atom (JRhC ¼ 34.3 Hz). The Et signals of the NEt3 fragment appeared at d 8.7 and 53.9 ppm. These spectral features supported the formation of ammonium ylide. Finally, the molecular structure of 3 was confirmed by X-ray analysis (Fig. 2). The Rh center showed pseudo-octahedral geometry with the meridional phebox ligand and cis-arranged Cl ligands. The RheC bond of the ylide fragment was placed at the axial position. This structural feature is similar to that of other alkyl and aryl complexes with NCN pincer ligands [8,10,13]. The Rh1eC27 bond length (2.079(9) Å) is comparable to that of 2. The Rh1eCl1 bond length (2.4652(19) Å) is slightly shorter than the Rh1eCl2 bond length (2.5133(18) Å), suggesting that the trans-influence of the CH2NEt3 group is weaker
Scheme 2. Reaction of chiral Rh complex 1 with dicyclopentylamine in CH2Cl2.
320
J.-i. Ito et al. / Journal of Organometallic Chemistry 794 (2015) 318e322
Fig. 2. ORTEP diagram of 3 with 30% probability level. Selected bond lengths (Å): Rh1eC1 1.922(7), Rh1eC27 2.079(9), Rh1eCl1 2.4652(19), Rh1eCl2 2.5133(18), Rh1eN1 2.054(7), Rh1eN2 2.077(6), C27eN3 1.503(11). Selected bond angles ( ): N1eRh1eN(2) 158.2(3), C1eRh1eCl2 175.3(3), C27eRh1eCl1 170.5(2), N3eC27eRh1 125.0(6).
Scheme 5. Proposed mechanism for stereochemical control of the CeC bond forming step.
than that of the phebox aryl group. A proposed mechanism is described in Scheme 4. We previously reported oxidative addition of chlorobenzene to the phebox Rh complex in the presence of NHiPr2 [10]. In this case, the formation of imine Me2C]NiPr was detected in the 1H NMR spectrum of the reaction mixture. According to this observation, the first step could be the reduction of Rh(III) to Rh(I) assisted by an amine. In this step, NHiPr2 and NEt3 serve as reductants, whereby the corresponding imine C and iminium ion, respectively, are formed. Then, oxidative addition of CH2Cl2 to Rh(I) intermediate B affords chloromethyl intermediate D [14]. In the presence of NEt3, nucleophilic substitution of the CleCH2 group takes place to afford ammonium ylide complex 3. We currently assume that the formation of 3 is an indirect evidence of D. In addition, substitution of the CleCH2Rh fragment by an amine might be feasible compared to that of free CH2Cl2 by a tertiary amine [15]. In contrast to the reaction with NEt3, a nucleophilic attack by NHiPr2 or C is considered to be inhibited due to steric repulsion. Consequently, coordination of C gives imine adduct E, which is in equilibrium with enamine
intermediate F generated by tautomerization [16]. Finally, a nucleophilic attack by enamine to the CH2Cl group forms a 5membered metallacycle [17]. At this stage, the R-absolute configuration is constructed at the b-carbon. A proposed mechanism for a stereochemical control of the CeC bond-forming step is shown in Scheme 5. As mentioned earlier, the CH2Cl group is likely coordinated at the axial position. At this point, a re-face attack of the enamine gives R-stereochemistry (Path a), while a si-face attack gives S-stereochemistry (Path b). Path b is considered a minor path due to the repulsion between the oxazoline substituent and the five-membered ring of the enamine. Consequently, Path a is predominantly in construction of the structure of 2. Finally, the reactivity of 2 toward hydrogenation and pyrolysis was checked to gain an organic fragment from the azametallacycle. However, 2 was found to be stable in heating under hydrogen or argon atmosphere. In addition, irradiation by UV lamp was also resulted in no reaction. Complex 3 was also inactive in irradiation by UV lamp. In summary, we demonstrated asymmetric b-alkylation of a
Scheme 4. Proposed mechanism for the formation of 2 and 3.
J.-i. Ito et al. / Journal of Organometallic Chemistry 794 (2015) 318e322
secondary amine with CH2Cl2 by the chiral NCN pincer Rh complex 1. In this reaction, the formation of the azametallacycle structure was likely formed by successive sequence of oxidative addition of CH2Cl2, dehydrogenation of an amine to an imine, tautomerization of the imine to an enamine and alkylation of a CleCH2Rh fragment. In contrast to a secondary amine, the reaction of 1 with NEt3 in CH2Cl2 resulted in the formation of the ammonium ylide complex 3 by alkylation of the nitrogen atom. The formation of 3 is considered to be an evidence for a chloromethyl intermediate via oxidative addition of CH2Cl2 to of the Rh(I) species generated in situ. 3. Experimental section 1 H and 13C NMR spectra were recorded on a Varian Mercury 300 spectrometer. 1H NMR chemical shifts were reported in ppm relative to the singlet at 7.26 ppm for CDCl3. 13C NMR spectra were reported relative to the triplet at d 77.0 ppm for CDCl3. Infrared spectra were recorded on a JASCO FT/IR-230 spectrometer. Mass spectrum was recorded on a JEOL JMS-700. Elemental analysis was recorded on a PerkineElmer 2400II. Complex 1 was prepared according to the literature [9].
3.1. Preparation of 2 To a mixture of 1a (59.0 mg, 0.10 mmol) and MS 4 Å (0.2 g) was added CH2Cl2 (2 mL) and dicyclopentylamine (307 mg, 2.0 mmol). After being stirred for 48 h at 35 C, the solvent was removed under reduced pressure. The resulting crude products was passed through silica gel with CH2Cl2/ethyl acetate (¼ 10:1) to remove the residual amine. The filtrate was concentrated and the residue was purified by column chromatography on silica gel with Hexane:ethyl acetate (¼2:1). Recrystallization from a mixed solvent (CH2Cl2/ethyl acetate/hexane) provided yellow crystals of 2 (34.4 mg, 0.049 mmol). 1 H NMR (300 MHz, CDCl3, rt): d 0.48 (t, JHH ¼ 9.2 Hz, 1H), 0.90 (td, JHH ¼ 9.2 Hz, JRhH ¼ 2.7 Hz, 1H), 1.15e1.35 (m, 1H), 1.60e2.25 (m, 13H), 2.39e2.60 (m, 3H), 2.70e2.95 (m, 4H), 3.39 (dd, JHH ¼ 12.9, 3.9 Hz, 1H), 3.69 (dd, JHH ¼ 14.4, 3.6 Hz, 1H), 4.10e4.22 (m, 1H), 4.32 (t, JHH ¼ 9.0 Hz, 1H), 4.40 (t JHH ¼ 8.1 Hz, 1H), 4.52e4.66 (m, 3H), 4.76e4.89 (m, 1H), 7.06 (t, JHH ¼ 7.8 Hz, 1H), 7.18e7.39 (m, 10H), 7.44 (d, JHH ¼ 7.8 Hz, 1H), 7.48 (d, JHH ¼ 7.8 Hz, 1H). 13C NMR (75 MHz, CDCl3, rt): d 18.6 (d, JRhC ¼ 24.1 Hz), 24.6, 24.8, 26.0, 28.9, 31.9, 32.0, 33.6, 39.8, 40.4, 59.7, 63.9, 64.4, 66.8, 74.5, 74.9, 120.4, 126.3, 126.4, 126.8, 128.5, 128.8, 129.1, 129.9, 130.3, 136.6, 137.3, 172.48 (JRhC ¼ 5.2 Hz), 172.54 (JRhC ¼ 5.1 Hz), 192.0 (JRhC ¼ 25.1 Hz), 193.3. IR (KBr, cm1): 1614 (nC]N). Anal. Calcd for C37H41ClN3O2Rh: C, 63.66; H, 5.92; N, 6.02. Found: C, 63.69; H, 6.08; N, 5.58. 3.2. Preparation of 3 To a mixture of 1a (11.8 mg, 0.020 mmol) and MS 4 Å (0.1 g) was added CH2Cl2 (1 mL) and NEt3 (28 mL). After being stirred for 18 h at 35 C, the mixture was filtrated to remove insoluble materials. The filtrate was concentrated and then purified by column chromatography on silica gel with CH2Cl2/MeOH (¼10:1) to give 3 (8.4 mg, 0.012 mmol, 61%). 1 H NMR (300 MHz, CDCl3): 1.05 (t, JHH ¼ 7.2 Hz, 9H), 2.37 (d, JHH ¼ 10.5 Hz, 1H), 2.47 (t, JHH ¼ 12.0 Hz, 1H), 2.78 (dd, JHH ¼ 14.0, 11.6 Hz, 1H), 3.08 (dd, JHH ¼ 10.5 Hz, JRhH ¼ 3.0 Hz, 1H), 3.30 (dq, JHH ¼ 13.6, 6.9 Hz, 3H), 3.44 (dq, JHH ¼ 13.6, 6.8 Hz, 3H), 4.48e4.89 (m, 8H), 7.13e7.35 (m, 11H), 7.52 (d, JHH ¼ 7.8 Hz, 1H), 7.54 (d, JHH ¼ 7.8 Hz, 1H). 13C NMR (CDCl3, 75 MHz): 8.7, 40.5, 40.8, 48.9 (d, JRhC ¼ 34.3 Hz), 53.9, 65.4, 65.6, 75.3, 76.1, 121.6, 126.0, 126.4, 127.4, 128.3, 128.4, 128.8, 129.3, 130.1, 130.4, 137.4, 138.5, 171.6 (JRhC ¼ 4.6 Hz), 172.8 (JRhC ¼ 4.6 Hz), 193.4 (JRhC ¼ 23.9 Hz). HRMS(FAB): 648.1864 [MeCl]. Found: 648.1867.
321
3.3. X-ray analyses The diffraction data of 2 and 3 were collected on a Bruker SMART APEX CCD diffractometer with graphite-monochromated Mo Ka radiation (l ¼ 0.71073 Å). An empirical absorption correction was applied by using SADABS. The structure was solved by direct methods and refined by full-matrix least-squares on F2 using SHELXTL. All non-hydrogen atoms were refined with anisotropic displacement parameters. CCDC 1061627 (2) and CCDC 1061628 (3) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_ request/cif. Crystallographic data for 2: C37H41ClN3O2Rh(C6H14); Mr ¼ 784.26; temperature 153 K; orthorhombic, P212121; a ¼ 9.272(6), b ¼ 16.534(9), c ¼ 24.169(15) Å; V ¼ 3705(4) Å3; Z ¼ 4; rcalcd ¼ 1.406 Mg/m3; m ¼ 0.574 mm1; reflections collected 26,460, independent reflections 8673 [R(int) ¼ 0.1282]; parameters 413; goodness-of-fit on F2 1.059; final R indices [I > 2s(I)] R1 ¼ 0.0766, wR2 ¼ 0.1550; R indices (all data) R1 ¼ 0.1240, wR2 ¼ 0.1738; largest diff. peak/hole 1.194 and 0.841 Å3. Crystallographic data for 3: C33H40Cl2N3O2Rh(CH2Cl2); Mr ¼ 769.41; temperature 153 K; tetragonal, P41; a ¼ 11.6086(10), c ¼ 25.050(4) Å; V ¼ 3375.8(8) Å3; Z ¼ 4; rcalcd ¼ 1.514 Mg/m3; m ¼ 0.858 mm1; reflections collected 27,292, independent reflections 9220 [R(int) ¼ 0.0420]; parameters 401; goodness-of-fit on F2 1.058; final R indices [I > 2s(I)] R1 ¼ 0.0590, wR2 ¼ 0.1516; R indices (all data) R1 ¼ 0.0707, wR2 ¼ 0.1607; largest diff. peak/ hole 1.195 and 1.314 Å3. Acknowledgment This research was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Nos. 22245014, 26410114). Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jorganchem.2015.07.031. References [1] Reviews for C-H functionalization: (a) C.S. Yeung, V.M. Dong, Chem. Rev. 111 (2011) 1215e1292; (b) P.B. Arockiam, C. Bruneau, P.H. Dixneuf, Chem. Rev. 112 (2012) 5879e5918; (c) L. Ackermann, Chem. Rev. 111 (2011) 1315e1345. [2] Reviews for a-functionalization of amines: (a) C. Zhang, C. Tang, N. Jiao, Chem. Soc. Rev. 41 (2012) 3464e3484; (b) A.E. Wendlandt, A.M. Suess, S.S. Stahl, Angew. Chem. Int. Ed. 50 (2011) 11062e11087; (c) C. Liu, H. Zhang, W. Shi, A. Lei, Chem. Rev. 111 (2011) 1780e1824. [3] (a) X. Zhang, A. Fried, S. Knapp, A.S. Goldman, Chem. Commun. (2003) 2060e2061; (b) A.D. Bolig, M. Brookhart, J. Am. Chem. Soc. 129 (2007) 14544e14545; (c) X.-F. Xia, X.-Z. Shu, K.-G. Ji, Y.-F. Yang, A. Shaukat, X.-Y. Liu, Y.-M. Liang, J. Org. Chem. 75 (2010) 2893e2902; (d) B. Sundararaju, M. Achard, G.V.M. Sharma, C. Bruneau, J. Am. Chem. Soc. 133 (2011) 10340e10343; (e) A. Millet, P. Larini, E. Clot, O. Baudoin, Chem. Sci. 4 (2013) 2241e2247. [4] (a) T.B. Marder, W.C. Fultz, J.C. Calabrese, R.L. Harlow, D. Milstein, J. Chem. Soc. Chem. Commun. (1987) 1543e1545; (b) R. Pattacini, S. Jiez, P. Braunstein, Chem. Commun. (2009) 890e892; (c) A. Ghisolfi, F. Condello, C. Fliedel, V. Rosa, P. Braunstein, Organometallics 34 (2015) 2255e2260. [5] (a) E.G. Burns, S.S.C. Chu, P. de Meester, M. Lattman, Organometallics 5 (1986) 2383e2384; (b) P.J. Fennis, P.H.M. Budzelaar, J.H.G. Frijns, J. Organomet. Chem. 393 (1990) 287e298. [6] K.T.K. Chan, L.P. Spencer, J.D. Masuda, J.S.J. McCahill, P. Wei, D.W. Stephan,
322
J.-i. Ito et al. / Journal of Organometallic Chemistry 794 (2015) 318e322
Organometallics 23 (2004) 381e390. [7] (a) Y. Zhao, X. Chen, T. Chen, Y. Zhou, S.-F. Yin, L.-B. Han, J. Org. Chem. 80 (2015) 62e69; (b) X. Chen, T. Chen, Y. Zhou, C.-T. Au, L.-B. Hana, S.-F. Yin, Org. Biomol. Chem. 12 (2014) 247e250. [8] J. Ito, T. Miyakawa, H. Nishiyama, Organometallics 25 (2006) 5216e5218. [9] (a) Y. Kanazawa, Y. Tsuchiya, K. Kobayashi, T. Shiomi, J. Itoh, M. Kikuchi, Y. Yamamoto, H. Nishiyama, Chem. Eur. J. 12 (2006) 63e71; (b) Y. Motoyama, M. Okano, H. Narusawa, N. Makihara, K. Aoki, H. Nishiyama, Organometallics 20 (2001) 1580e1591. [10] J. Ito, T. Miyakawa, H. Nishiyama, Organometallics 27 (2008) 3312e3315. [11] Review for ylide complexes: (a) R. Navarro, E.P. Urriolabeitia, J. Chem. Soc. Dalton Trans. (1999) 4111e4122; (b) U. Belluco, R.A. Michelin, M. Mozzon, R. Bertani, J. Organomet. Chem. 557 (1998) 37e68. [12] Examples of N-ylide complexes: (a) L. Grande, E. Serrano, L. Cuesta, E.P. Urriolabeitia, Organometallics 31 (2012) 394e404; (b) W.B. Cross, S. Razak, K. Singh, A.J. Warner, Chem. Eur. J. 20 (2014) 13203e13209; s, J.J. Carbo , R. Navarro, E. Serrano, E.P. Urriolabeitia, Inorg. Chem. (c) A. Lledo 43 (2004) 7622e7635. [13] J. Ito, H. Nishiyama, Eur. J. Inorg. Chem. (2007) 1114e1119. [14] (a) H. Nishiyama, M. Horihata, T. Hirai, S. Wakamatsu, K. Itoh, Organometallics 10 (1991) 2706e2708; (b) B.,C. de Pater, E.J. Zijp, H. Fruhauf, J.M. Ernsting, C.J. Elsevier, K. Vrieze,
Organometallics 23 (2004) 269e279; (c) H.F. Haarman, J.M. Ernsting, M. Kranenburg, H. Kooijman, N. Veldman, A.L. Spek, P.W.N.M. van Leeuwen, K. Vrieze, Organometallics 16 (1997) 887e900; (d) T.O. Northcutt, R.J. Lachicotte, W.D. Jones, Organometallics 17 (1998) 5148e5152; (e) A.J. Vetter, R.D. Rieth, W.W. Brennessel, W.D. Jones, J. Am. Chem. Soc. 131 (2009) 10742e10752; (f) Y. Jiao, W.W. Brennessel, W.D. Jones, Organometallics 34 (2015) 1552e1566; (g) K.J. Bradd, B.T. Heaton, C. Jacob, J.T. Sampanthar, A. Steiner, J. Chem. Soc. Dalton Trans. (1999) 1109e1112; (h) J.Y. Zeng, M.-H. Hsieh, H.M. Lee, J. Organomet. Chem. 690 (2005) 5662e5671; (i) H.F. Haarman, J.M. Ernsting, M. Kranenburg, H. Kooijman, N. Veldman, A.L. Spek, P.W.N.M. van Leeuwen, K. Vrieze, Organometallics 16 (1997) 887e900. [15] The reaction of CH2Cl2 with NEt3 in DMF proceeded at 100 C to give [Et3NCH2Cl]Cl in 89% yield. See ref. [7a]. [16] C.C. Lu, J.C. Peters, J. Am. Chem. Soc. 126 (2004) 15818e15832. [17] (a) G. Ferguson, Y. Li, A.J. McAlees, R. McCrindle, K. Xiang, Organometallics 18 (1999) 2428e2439; (b) D.B. Grotjahn, Y. Gong, L. Zakharov, J.A. Golen, A.L. Rheingold, J. Am. Chem. Soc. 128 (2006) 438e453.