Cyclopentadienyl Yttrium Ene-Diamido Complexes: Coupling of the

Feb 4, 2015 - The yttrium ene-diamido complexes supported by Cp (C5H5) and Cp* (C5Me5) ligands have been synthesized and characterized...
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Cyclopentadienyl Yttrium Ene-Diamido Complexes: Coupling of the Ene-Diamido Ligand with Isocyanate Jianfeng Li, Hanmin Huang, Fengxin Wang, and Chunming Cui* State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Nankai University, Tianjin 300071, People’s Republic of China

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ABSTRACT: The yttrium ene-diamido complexes supported by Cp (C5H5) and Cp* (C5Me5) ligands have been synthesized and characterized. The reactions of the Cp* derivative with the isocyanate ArNCO (Ar = 2,6-iPr2C6H3) led to the C−C coupling of the ene-diamido ligand with ArNCO, while reaction of the Cp derivative resulted in not only the same C−C coupling but also the C−N coupling of the C−C coupling product with another molecule of ArNCO, demonstrating the unique reactivity of enediamido ligands in rare-earth chemistry. The products have been characterized by X-ray single-crystal analysis.

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Scheme 1. Synthesis of 2 and 3

ne-diamido ligands have attracted intense interest in the past several decades as some of the most frequently employed noninnocent ligands in organometallic chemistry, due to their unique electronic structures.1,2 Despite the importance of rare-earth complexes in stoichiometric and catalytic applications,3 there have been only very limited studies on rare-earth ene-diamido complexes, and the reactivity studies on these types of rare-earth complexes are even more scarce. It has been shown by Fedushkin and co-workers that the reaction of divalent rare-earth acenaphthene-1,2-diamido complexes with 1,2-dibromostilbene or iodine resulted in a two-electrontransfer process.4 Additionally, Scholz and co-workers have demonstrated that samarium ene-diamido ate complexes reacted with ketone to give formal cycloaddition products.5 These studies indicate that the ene-diamido frameworks are active ligands in rare-earth chemistry and may participate in diverse reactions. Herein, we report on the synthesis of enediamido yttrium complexes stabilized by cyclopentadienyl and pentamethylcyclopentadienyl ligands and their reactivity toward an isocyanate, leading to the novel C−C coupling of the enediamido moiety with the isocyanate. The cyclopentadienyl yttrium ene-diamido complexes CpY(DAB)(THF)2 (2; DAB = [ArNC(H)C(H)NAr]2−, Ar = 2,6iPr2C6H3, Cp = C5H5) and Cp*Y(DAB)(THF) (3; Cp* = C5Me5) were obtained as colorless and pale yellow crystals in 77 and 71% yields, respectively, by the salt elimination reaction of [(DAB)YCl(THF)2]2 (1) with 2 equiv of NaC5R5 (R = H, Me) (Scheme 1). Compounds 2 and 3 have been characterized by elemental analysis, 1H NMR, 13C NMR, and IR spectroscopy. The 1H NMR spectra of 2 and 3 exhibited singlets at δ 5.45 and 5.39 ppm, respectively, attributed to the olefinic protons of the DAB framework. In the 13C NMR spectra of 2 © 2015 American Chemical Society

and 3, the resonances of olefin carbons on the N−C−C−N framework were observed at δ 112.6 and 113.1 ppm, respectively. These data indicated the similar coordination modes of the ene-diamido ligand in the two compounds. The solid-state structure of 2 was determined by X-ray single-crystal analysis, which is depicted in Figure 1 with the relevant bond parameters.6 The yttrium atom in 2 is surrounded by one DAB ligand, one η5-coordinated Cp ligand, and two THF molecules. The DAB ligand is chelated to the yttrium atom with an N−Y−N bite angle of 81.22(7)°. The Y− CCp (average 2.708 Å), Y−N (average 2.234 Å), and Y−O (average 2.412 Å) bond distances in complex 2 are slightly longer than those (2.658, 2.171, and 2.372 Å) in the previously reported yttrium complex CpY(ArN(CH2)3NAr)(THF).7 The C1−C2 bond length of 1.359(3) Å in the N1−C1−C2−N2 framework of 2 is slightly lengthened, while the average C−N distance of 1.408(3) Å is shortened, in comparison to those observed in the corresponding free ene-diamine (C−C = Received: December 8, 2014 Published: February 4, 2015 683

DOI: 10.1021/om501257r Organometallics 2015, 34, 683−685

Communication

Organometallics

of 4 were obtained from THF at −35 °C. The structure of 4 is shown in Figure 2 with selected bond parameters.13 The

Figure 1. ORTEP representation of the X-ray structure of 2. Hydrogen atoms have been omitted for clarity. Thermal ellipsoids are drawn at the 30% probability level. Selected bond lengths (Å) and angles (deg): Y1−N1 2.235 (2), Y1−N2 2.234(2), Y1−O1 2.389 (2), Y1−O2 2.434 (2), Y1−C1 2.632(2), Y1−C2 2.627(2), C1−N1 1.410(3), C2−N2 1.406(3), C1−C2 1.359(3); N1−Y1−N2 81.22(7).

Figure 2. ORTEP representation of the X-ray structure of 4. Hydrogen atoms and iPr groups have been omitted for clarity. Thermal ellipsoids are drawn at the 30% probability level. Selected bond lengths (Å) and angles (deg): Y1−O1 2.159(2), Y1−O2 2.158(2), Y1−O3 2.356(2), Y1−O4 2.363(2), C1−O2 1.317(3), C3− O1 1.309(3), C1−N1 1.298(3), C1−N2 1.406(3), C2−N2 1.486(3), C2−C28 1.502(3), C28−N3 1.280(3), C2−C3 1.553(3), C3−N4 1.282(3); O1−Y1−O2 82.69(7).

1.339(2), C−N = 1.431(2) Å),8 indicating the noticeable electron delocalization of the N1−C1−C2−N2 framework. The short distances (2.632(2) and 2.627(2) Å) between the yttrium atom and the carbon atoms of the N−C−C−N framework and the folded N−C−C−N−Y five-membered ring (dihedral angle of the N−Y−N and N−C−C−N planes 123.4°) indicate the σ2,π coordination mode of the DAB ligand in 2.9−12 The reactions of 2 and 3 with aryl isocyanate (ArNCO, Ar = 2,6-iPr2C6H3) were studied. It was found that 2 consumed 2 equiv of ArNCO to yield 4, while 3 only reacted with 1 equiv of ArNCO to give 5 under the same conditions (Scheme 2).

yttrium atom in 4 is bonded to an oxygen atom with an O−Y− O bite angle of 82.69(7)°. Apparently, the DAB ligand coupled with two ArNCO molecules to form the new Y1O1C3C2N2C1O2 seven-membered ring, in which all of the bond lengths indicated that they are single bonds. The yttrium−oxygen bond distances (Y1−O1 2.159(2) Å and Y1−O2 2.158(2) Å) are longer than those (2.096(4) and 2.059(3) Å) observed in the cyclopentadienyl yttrium complex with two alkoxyl ligands Cp*Y(OC6H3tBu2)2.14 The short C1−N1, C3−N4, and C28− N3 bond lengths are indicative of the three imine functionalities. The solid-state structure of 4 is well correlated with the spectroscopic data. Although we were unable to perform an X-ray single-crystal analysis of 5, its structure can be deduced from the structure of 4 and by the comparison of the spectroscopic data of 4 with those of 5. The 13C NMR spectrum of 5 clearly showed that there exist two imine functional groups in the molecule, corresponding to the C−C coupling of the imine with 1 equiv of ArNCO. The alternative 1,2-insertion product in the reaction of 3 with 1 equiv of ArNCO can be ruled out on the basis of the NMR spectroscopic data. Although detailed reaction pathways to 4 and 5 are not clear at present, it is quite possible that the initial coordination of ArNCO to the metal center followed by the nucleophilic attack of the central carbon atom by one of the olefinic carbon atoms took place, leading to the C−C coupling and formation of the yttrium−oxygen bond accompanied by the leaving of the new imine nitrogen from the yttrium atom (Scheme 3).15 The formation of 4 is very likely to go through the intermediate 4′,

Scheme 2. Reactions of 2 and 3 with ArNCO

Complexes 4 and 5 were obtained as colorless crystals from toluene and have been fully characterized by 1H NMR, 13C NMR, and IR spectroscopy and elemental analysis. In the 1H spectrum of 4, the resonances for the olefin fragment in the DAB ligand disappeared and two new doublets at δ 8.06 and 5.76 ppm were observed. In accordance with the changes observed in the 1H NMR spectrum, the original olefinic carbon resonance at δ 112.6 in 2 also vanished. The four new carbon resonances at δ 75.0, 160.8, 163.0, and 166.2 ppm appearing in the 13C NMR spectrum of 4 indicated the coupling of the enediamido ligand with two ArNCO molecules. Similarly, the 1H NMR spectrum of 5 displayed two new doublets at δ 8.16 and 5.54 ppm and the resonances of the olefinic protons also disappeared. In contrast, only three new resonances at δ 73.7, 164.2, and 165.7 ppm were observed in the 13C NMR spectrum of 5. In the IR spectra of 4 and 5, the strong absorptions observed at 1631−1654 and 1647−1654 cm−1 indicated the existences of imine functionalities in the two compounds, in line with the low-field-shifted resonances (160.8−166.2 ppm) observed in the 13C NMR spectra of 4 and 5. To elucidate the molecular structures of 4 and 5, X-ray single-crystal analysis of 4 has been conducted. Single crystals

Scheme 3. Proposed Mechanism

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(5) Scholz, J.; Görls, H.; Schumann, H.; Weimann, R. Organometallics 2001, 20, 4394. (6) Crystallographic data for 2: C39H56N2O2Y, Mw = 673.77, monoclinic, space group Cc, a = 21.938(7) Å, b = 10.170(3) Å, c = 17.773(5) Å, α = 90°, β = 110.049(4)°, γ = 90°, V = 5019(2) Å3, Z = 4, dcalcd = 1.201 Mg/m3, T = 113(2) K, final R = 0.0412 (GOF = 1.007) for 7434 observed reflections with I > 2σ(I), Rw = 0.0722 for 8542 relections, all unique data. CCDC 1030400. (7) Roesky, P. W. Organometallics 2002, 21, 4756. (8) Gans-Eichler, T.; Gudat, D.; Nättinen, K.; Nieger, M. Chem. Eur. J. 2006, 12, 1162. (9) Vasudevan, K.; Cowley, A. H. Chem. Commun. 2007, 3464. (10) Panda, T. K.; Kaneko, H.; Pal, K.; Tsurugi, H.; Mashima, K. Organometallics 2010, 29, 2610. (11) Mahrova, T. V.; Fukin, G. K.; Cherkasov, A. V.; Trifonov, A. A.; Ajellal, N.; Carpentier, J.-F. Inorg. Chem. 2009, 48, 4258. (12) Trifonov, A. A.; Borovkov, I. A.; Fedorova, E. A.; Fukin, G. K.; Larionova, J.; Druzhkov, N. O.; Cherkasov, V. K. Chem. Eur. J. 2007, 13, 4981. (13) Crystallographic data for 4: C73H107N4O6Y, Mw = 1225.54, triclinic, space group P1̅, a = 11.859(5) Å, b = 15.809(7) Å, c = 19.598(8) Å, α = 108.427(7)°, β = 98.172(4)°, γ = 90.564(7)°, V = 3445(2) Å3, Z = 2, dcalcd = 1.182 Mg/m3, T = 113(2) K, final R = 0.0605 (GOF = 0.966) for 10206 observed reflections with I > 2σ(I), Rw = 0.1317 for 16248 relections, all unique data. CCDC 1030401. (14) Schaverien, C. J.; Frijns, J. H. G.; Heeres, H. J.; van den Hende, J. R.; Teuben, J. H.; Spek, A. L. J. Chem. Soc., Chem. Commun. 1991, 642. (15) (a) Fedushkin, I. L.; Moskalev, M. V.; Lukoyanov, A. N.; Tishkina, A. N.; Baranov, E. V.; Abakumov, G. A. Chem. Eur. J. 2012, 18, 11264. (b) Fedushkin, I. L.; Nikipelov, A. S.; Morozov, A. G.; Skatova, A. A.; Cherkasov, A. V.; Abakumov, G. A. Chem. Eur. J. 2012, 18, 255. (c) Fedushkin, I. L.; Moskalev, M. V.; Baranov, E. V.; Abakumov, G. A. J. Organomet. Chem. 2013, 747, 235. (d) Fedushkin, I. L.; Nikipelov, A. S.; Lyssenko, K. A. J. Am. Chem. Soc. 2010, 132, 7874. (16) (a) Zhang, J.; Ruan, R.; Shao, Z.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2002, 21, 1420. (b) Zhang, J.; Cai, R.; Weng, L.; Zhou, X. J. Organomet. Chem. 2003, 672, 94. (c) Zhang, J.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2003, 22, 5385. (d) Zhou, X.; Zhang, L.; Zhu, M.; Cai, R.; Weng, L.; Huang, Z.; Wu, Q. Organometallics 2001, 20, 5700. (e) Zhang, J.; Zhou, X.; Cai, R.; Weng, L. Inorg. Chem. 2005, 44, 716. (f) Zhu, X.; Fan, J.; Wu, Y.; Wang, S.; Zhang, L.; Yang, G.; Wei, Y.; Yin, C.; Zhu, H.; Wu, S.; Zhang, H. Organometallics 2009, 28, 3882. (g) Li, T.; Nishiura, M.; Cheng, J.; Li, Y.; Hou, Z. Chem. Eur. J. 2012, 18, 15079. (h) Tardif, O.; Hashizume, D.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 8080. (i) Shen, Q.; Li, H.; Yao, C.; Yao, Y.; Zhang, L.; Yu, K. Organometallics 2001, 20, 3070. (j) Li, S.; Wang, M.; Liu, B.; Li, L.; Cheng, J.; Wu, C.; Liu, D.; Liu, J.; Cui, D. Chem. Eur. J. 2014, 20, 15493. (17) (a) Sun, Y.; Zhang, Z.; Wang, X.; Li, X.; Weng, L.; Zhou, X. Organometallics 2009, 28, 6320. (b) Sun, Y.; Zhang, Z.; Wang, X.; Li, X.; Weng, L.; Zhou, X. Dalton Trans. 2010, 39, 221. (c) Zhang, C.; Liu, R.; Zhang, J.; Chen, Z.; Zhou, X. Inorg. Chem. 2006, 45, 5867. (d) Gao, D.; Hu, H.; Cui, C. Acta Chim. Sinica 2013, 71, 1125. (e) Xu, X.; Qi, R.; Xu, B.; Yao, Y.; Nie, K.; Zhang, Y.; Shen, Q. Polyhedron 2009, 28, 574.

which is structurally very similar to 5. However, in this case, ArNCO insertion into the Y−N bond in 4′ took place, leading to the formation of new C−N and Y−O bonds. It is evident that the bulky Cp* group in 5 blocks the second ArNCO insertion and renders compound 5 relatively stable. Many attempts to isolate the intermediate 4′ have been unsuccessful to date, indicating the pronounced steric effects of the reaction. The reactions of isocyanate with rare-earth complexes have been extensively investigated in the past decade due to their fundamental interest and potential application in organic transformation.16,17 It has been established that an isocyanate could insert into a Ln−E bond (E = H, C, N, O, S). However, the C−C coupling of ene-diamido ligands with an isocyanate has not been reported for any metal ene-diamido complex. In summary, we have demonstrated that the ene-diamido ligands in rare-earth ene-diamido complexes are active to an isocyanate, leading to the novel C−C coupling reaction. This reactivity may be related to the highly ionic bonding nature of the ene-diamido ligand with the rare-earth cation, rendering the coordinated ene-diamido ligand highly nucleophilic. Further investigation of the ene-diamido ligand with other substrates may result in the discovery of valuable transformations of rareearth ene-diamido complexes.

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ASSOCIATED CONTENT

S Supporting Information *

Text giving experimental details and characterization data for 2−5 and CIF files giving crystallographic data for compounds 2 and 4. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for C.C.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the National Natural Science Foundation of China and 973 program (2012CB821600, 21202085, 21390401), the Natural Science Foundation of Tianjin (12JCYBJC31100), and Programs Foundation of Ministry of Education of China (20120031120001) for financial support.

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DOI: 10.1021/om501257r Organometallics 2015, 34, 683−685