Redox Chemistry between Europium(III) Amide and Pyrrolyl

Feb 14, 2011 - Zhijun Feng , Xiancui Zhu , Shaoyin Wang , Shaowu Wang , Shuangliu Zhou , Yun Wei , Guangchao Zhang , Baojia Deng , and Xiaolong Mu...
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Organometallics 2011, 30, 992–1001 DOI: 10.1021/om101043t

Redox Chemistry between Europium(III) Amide and PyrrolylFunctionalized Secondary Amines. Synthesis and Structural Characterization of Lithium and Novel Lanthanide Complexes Incorporating Functionalized Pyrrolyl Ligands Qinghai Li,† Jiewei Rong,† Shaowu Wang,*,†,‡ Shuangliu Zhou,† Lijun Zhang,† Xiancui Zhu,† Fenhua Wang,† Song Yang,† and Yun Wei† †

Laboratory of Functionalized Molecular Solids, Ministry of Education, Anhui Laboratory of MoleculeBased Materials, Institute of Organic Chemistry, School of Chemistry and Materials Science, Anhui Normal University, Wuhu, Anhui 24100, People’s Republic of China, and ‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s Republic of China Received November 5, 2010

The redox reaction between the europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 and pyrrolyl-functionalized secondary amines was found for the first time. The interactions of 2(2,6-R2C6H3NHCH2)C4H3NH (R = CH3 (1), R = iPr (2)) with 2 equiv of europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 led to oxidation of the secondary amine with isolation of iminofunctionalized pyrrolyl lithium complexes {[η2:η1-2-(2,6-R2C6H3NdCH)C4H3N]Li(THF)}2 (R = CH3 (4), R = iPr (5)). When the deuterated compounds 2-(2,6-R2C6H3NHCHD)C4H3NH (R = CH3 (1a), R = iPr (2a)) were respectively treated with 2 equiv of europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3, the corresponding mixture of deuterated imino-functionalized pyrrolyl lithium complexes {[η2:η1-2-(2,6-Me2C6H3NdCD)C4H3N]Li(THF)}2 (4a) and 4 and {[η2:η1-2-(2,6-iPr2C6H3NdCD)C4H3N]Li(THF)}2 (5a) and 5 were produced upon analyses of the NMR spectra of the complexes. Treatment of 2-(2,6-iPr2C6H3NHCHD)C4H3NH (2a) with excess (Me3Si)2NLi gave the only pyrrole deprotonated product, {[η5:η2:η1-2-(2,6-iPr2C6H3NHCHD)C4H3N]Li2N(SiMe3)2}2 (6). When 2-(2,6-iPr2C6H3NHCH2)C4H3NH (2) was treated with ytterbium(III) amide [(Me3Si)2N]3YbIII(μ-Cl)Li(THF)3, a dinuclear ytterbium(III) amide with formula {[(μ-η5:η1):η1-2-[(2,6-iPr2C6H3)NCH2]C4H3N]YbN(SiMe3)2}2 (7) was isolated and no oxidation of the secondary amine was observed. Reduction of ytterbium or imino-functionalized pyrrolyl compound was not observed by refluxing the toluene solution of complex 7 for 2 days. Treatment of equal equivalents of grease (Me2SiO)3, 2-(2,6-iPr2C6H3NHCH2)C4H3NH (2), and europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3, after workup, afforded the europium(II) complex {[μη5:η1:η1-2-(ArN(Me2SiO)CH2)C4H3N]EuII[η5-2-(ArNdCH)C4H3N]Li2[N(SiMe3)2]}2 (Ar = 2,6i Pr2C6H3) (8) with reduction of europium(III) to europium(II) and oxidation of the secondary amine to an imino group. Reaction of a pyrrolyl-functionalized linked secondary diamine [5-tBu-C4H2NH2-CH2NHCH2]2 (3) with [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 produced a novel centrosymmetric macrocyclic complex with six europium(II) ions and six lithium ions, {[(5-tBu-C4H2N-2CHdNCH2)2]4[(5-tBu-2-CH3NdCH(C4H2N)]Eu3Li3}2 (9) with observation of redox chemistry between europium(III) and the linked secondary amine. When the linked secondary diamine [5-tBu-C4H2NH-2-CH2NHCH2]2 (3) was treated with [(Me3Si)2N]3DyIII(μ-Cl)Li(THF)3 to produce a novel four-sandwiched-lithium-supported tetranuclear dysprosium(III) complex, {η2:η2-[η1:η1-(μη5:η5-[5-tBu-C4H2N-2-CH2NCH2CH2N-2-CH2-5-tBu-C4H2N]Li)2]Dy2(μ3-Cl)Li}2 (10), no redox chemistry was observed. All compounds were characterized by spectroscopic methods and elemental analyses; complexes 4-10 were also characterized by X-ray structure analyses.

Imines are important intermediates in organic synthesis, which can act as electrophiles in many different reactions such as reductions, additions, condensations, and cycloadditions. Many of these transformations can be achieved with a high *To whom correspondence should be addressed. E-mail: swwang@ mail.ahnu.edu.cn. pubs.acs.org/Organometallics

Published on Web 02/14/2011

enantioselectivity. So, there has been a continuous interest in development of new pathways to obtain imines apart from the general standard method by condensation of a carbonyl compound (aldehydes or ketones) with an amine. Catalytic conversions of secondary amines to imines in the presence of aerobic oxygen1 or tert-butyl hydroperoxide (TBHP)2 or other oxidants3 are notable methods. These methods usually involve r 2011 American Chemical Society

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Scheme 1

using expensive late transition metals such as ruthenium,1a,c,d gold,1b or palladium1e compounds as catalysts, and several catalytic processes were proposed to involve the β-hydrogen elimination reaction of amido intermediates. The β-hydrogen elimination reaction of amido complexes is also a possible way to obtain imines. Although it has been concluded that βhydrogen elimination reaction of late transition metal amido complexes is much slower than elimination of the corresponding alkyl complexes4 and is less studied in comparison with βhydrogen elimination reaction of alkyl complexes,5 reports on (1) (a) Yamaguchi, K.; Mizuno, N. Angew. Chem., Int. Ed. 2003, 42, 1480–1483. (b) Zhu, B.; Angelici, R. J. Chem. Commun. 2007, 2157–  A. H.; B€ackwall, J. E. Chem. Eur. J. 2005, 2159. (c) Samec, J. S. M.; Ell, 11, 2327–2334. (d) Yamaguchi, K.; Mizuno, N. Chem. Eur. J. 2003, 9, 4353–4361. (e) Wang, J.-R.; Fu, Y.; Zhang, B.-B.; Cui, X.; Liu, L.; Guo, Q.-X. Tetrahedron Lett. 2006, 47, 8293–8297. (2) Choi, H.; Doyle, M. P. Chem. Commun. 2007, 745–747. (3) (a) Mukaiyama, T.; Kawana, A.; Fukuda, Y.; Matsuo, J.-i. Chem. Lett. 2001, 390–391. (b) Kamal, A.; Devaiah, V.; Reddy, L. K.; Shankaraiah, N. Adv. Synth. Catal. 2006, 348, 249–254. (4) Hartwig, J. F. J. Am. Chem. Soc. 1996, 118, 7010–7011. (5) (a) Cross, R. J. In The Chemistry of the Metal Carbon Bond; Hartley, F. R.; Patai, S., Eds.; Wiley: New York, 1985; Vol. 2, pp 559-624. (b) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry, 2nd ed.; University Science Books: Mill Valley, CA, 1987; pp 383-388.  (6) Matas, I.; C ampora, J.; Palma, P.; Alvarez, E. Organometallics 2009, 28, 6515–6523. (7) Dimitrov, A.; Seidel, S.; Seppelt, K. Eur. J. Inorg. Chem. 1999, 95–99. (8) Tsai, Y.-C.; Johnson, M. J. A.; Mindiola, D. J.; Cummins, C. C. J. Am. Chem. Soc. 1999, 121, 10426–10427. (9) (a) Scoles, L.; Ruppa, K. B. P.; Gambarotta, S. J. Am. Chem. Soc. 1996, 118, 2529–2530. (b) Castro, I.; Galakhov, M. V.; G omez, M.; omez-Sal, P.; Royo, P. Organometallics 1996, 15, 1362–1368. (c) Cai, G H.; Chen, T.; Wang, X.; Schultz, A. J.; Koetzle, T. F.; Xue, Z. Chem. Commun. 2002, 230–231.

the β-hydrogen elimination reaction of transition metal amido complexes such as iridium,4 nickel,6 tungsten,7 molybdenum,8 tantalum,9 and niobium10 amido complexes to give η2-imine complexes or imines have been documented. However, the βhydrogen elimination reaction of lanthanide amido complexes to give imine complexes11 or redox chemistry between lanthanide amide and secondary amines has not been observed. In this paper, we will for the first time report the redox reaction between europium(III) amide [(Me3Si)2N]3EuIII(μCl)Li(THF)3 and pyrrolyl-functionalized secondary amines to produce imino-functionalized pyrrolyl lithium and europium complexes. The synthesis and characterization of some lithium and novel lanthanide complexes incorporating functionalized pyrrolyl ligands12 will also be reported.

Results and Discussion Treatment of 2-(2,6-R2C6H3NHCH2)C4H3NH (R = CH3 (1), R = iPr (2)) with 2 equiv of europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 led to oxidation of the (10) (a) Berno, P.; Gambarotta, S. Organometallics 1995, 14, 2159– 2161. (b) Figueroa, J. S.; Piro, N. A.; Mindiola, D. J.; Fickes, M. G.; Cummins, C. C. Organometallics 2010, DOI: 10.1021/om100522p. (11) Scherer, W.; Wolstenholme, D. J.; Herz, V.; Eickerling, G.; Br€ uck, A.; Benndorf, P.; Roesky, P. W. Angew. Chem., Int. Ed. 2010, 49, 2242–2246. (12) Some recent works on organolanthanide complexes with pyrrolyl ligands: (a) Hao, J.; Song, H.; Cui, C. Organometallics 2009, 28, 3970–3972. (b) Nishiura, M.; Mashiko, T.; Hou, Z. Chem. Commun. 2008, 2019–2021. (c) Yang, Y.; Liu, B.; Lv, K.; Gao, W.; Cui, D.; Chen, X.; Jing, X. Organometallics 2007, 26, 4575–4584. (d) Yang, Y.; Cui, D.; Chen, X. Dalton Trans. 2010, 39, 3959–3967. (e) Liu, C.; Zhou, S.; Wang, S.; Zhang, L.; Yang, G. Dalton Trans. 2010, 39, 8994–8999.

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Figure 1. Molecular structure of compound 4. Hydrogen atoms are omitted for clarity. N(2)-C(5), 1.283(2) A˚. More bond distances and angles can be found in the Supporting Information.

secondary amine with the isolation of imino-functionalized pyrrolyl lithium complexes {[η2:η1-2-(2,6-R2C6H3NdCH)C4H3N]Li(THF)}2 (65% isolated yield for R = CH3 (4), 53% isolated yield for R = iPr (5)) (Scheme 1) based on X-ray and NMR analyses. 1H NMR spectra of complexes 4 and 5 showed that the protons of methylene CH2 resonances of 1 or 2 disappeared; instead, the clear resonances of protons of the imine (NdCH) at about 7.90 ppm were observed. The 13C NMR also displayed the resonances of carbons of the imines (NdCH) at about 160 ppm (see Supporting Information). These results proved the formation of imino groups. Treatment of deuterated compounds 2-(2,6-R2C6H3NHCHD)C4H3NH (R = CH3 (1a), R = iPr (2a)) respectively with 2 equiv of europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 produced the corresponding mixture of deuterated imino-functionalized pyrrolyl lithium complexes {[η2:η1-2-(2,6-Me2C6H3NdCD)C4H3N]Li(THF)}2 (4a) and 4 and {[η2:η1-2-(2,6-iPr2C6H3NdCD)C4H3N]Li(THF)}2 (5a) and 5 (Scheme 1) upon analyses of the NMR spectra of the reaction products. From the spectra (see Supporting Information), we can see that the protons in compounds 4 and 4a, or in compounds 5 and 5a, gave the same resonances, the resonances of deuterated methylene protons CHD in 1a or 2a disappeared, and the imine proton (NdCH) resonances appeared at about 7.90 ppm and the imino-carbon (NdCH) resonances at about 160 ppm. The integrations of the imino protons in the two mixtures are all slightly less than 0.5 (the expected ratio for 4 and 4a or 5 and 5a should be 1:1, respectively), probably due to isotopic effect, suggesting that the process of deprotonation of the methylene CH2 may not be the rate-determining step. These results further demonstrated that the secondary amines were oxidized to imino groups. X-ray analyses further confirmed that complexes 4 and 5 (Figures 1 and 2) are dimeric iminofunctionalized pyrrolyl lithium compounds with the nitrogen atoms of the pyrrolyl ring as bridges coordinated to the lithium metal in η2 modes to form a tetrahedral geometry of the lithium. The C-N (NdCH) bond distance (1.283(2) A˚) is the same in the two complexes, which can be comparable to those found in transition metal complexes,6-10 further proving that the secondary amines were oxidized to imino groups.

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Figure 2. Molecular structure of compound 5. Hydrogen atoms are omitted for clarity. N(2)-C(5), 1.283(2) A˚. More bond distances and angles can be found in the Supporting Information.

Scheme 2

The reaction of secondary amine 2-(2,6-iPr2C6H3NHCHD)C4H3NH (2a) with lithium amide LiN(SiMe3)2 was carried out under the same conditions for the preparation of the above complexes to see if the lithium amide LiN(SiMe3)2 could deprotonate the methylene group of the secondary amine. It is found that reaction of 2-(2,6i Pr2C6H3NHCHD)C4H3NH (2a) with excess (3 equiv) lithium amide (Scheme 2) LiN(SiMe3)2 afforded the only pyrrole ring deprotonated product, {[η5:η2:η1-2-(2,6-iPr2C6H3NHCHD)C4H3N]Li2N(SiMe3)2}2 (6), in 62% isolated yield; no imine product was observed. An NMR spectral study indicated that the proton of the deuterated methylene CHD of 6 resonates at 4.03 ppm, and no imino carbon resonance at about 160 ppm was obseved. These results demonstrated that the amido group N(SiMe3)2 cannot abstract the proton of methylene CH2. The pyrrolyl ring is η5 bonded with the lithium ion in 6 (see Figure 3 and Supporting Information), which is different from those found in 4 and 5. The lithium to π-bonded pyrrolyl ring distances range from 2.325(3) to 2.490(3) A˚, with an average of 2.417(3) A˚. This result suggested that the formation of the imino products 4 and 4a or 5 and 5a is not due to the dissociation of [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 to LiN(SiMe3)2, which then reacted with the secondary amines to generate the secondary amine dehydrogenated products of imines. When 2-(2,6-iPr2C6H3NHCH2)C4H3NH (2) was treated with ytterbium(III) amide [(Me3Si)2N]3YbIII(μ-Cl)Li(THF)3, a dinuclear ytterbium(III) amide with formula {[(μ-η5:η1):η1-2[(2,6-iPr2C6H3)NCH2]C4H3N]YbN(SiMe3)2}2 (7) (Scheme 1) was isolated in 57% yield and characterized. X-ray analyses

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Figure 3. Molecular structure of compound 6. Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚): N(1)-C(13) 1.5054(18), C(14)-C(13)-N(1) 109.83(11). More bond distances and angles can be found in the Supporting Information.

Figure 4. Molecular structure of one of two independent units of 7. Hydrogen atoms are omitted for clarity. Yb(1)-Pyrav 2.707(7) A˚, N(2)-C(5) 1.467(8) A˚, Yb(10 )-Pyr0 2.703(9) A˚, C(50 )-N(20 ) 1.452(10) A˚. Other bond distances and angles can be found in the Supporting Information.

revealed that the N(2)-C(5) bond distance of 1.467(8) A˚ is normally observed for a C-N single bond. Hydrolysis of the ytterbium(III) complex 7 gave pure compound 2, indicating that no redox chemistry between the ytterbium(III) amide and the secondary amine happened. Thus, we can get informations from the reaction for the formation of 7: (1) redox potentials of Ln3þ/Ln2þ have a great influence on the reactivity of lanthanide amides with pyrrolyl-functionalized secondary amines; no oxidation of amine to imine in the ytterbium(III) case may be due to the relatively high redox potential of Yb3þ/Yb2þ;13 (2) the dianion {2-[(2,6-R2C6H3)NCH2]C4H3N}2- (R = CH3, i Pr) may be formed at first in the processes for the formation of 4 and 5, and the dinuclear complexes {[(μ-η5:η1):η1-2-[(2,6R2C6H3)NCH2]C4H3N]EuIIIN(SiMe3)2}2 (R = CH3, iPr) may serve as the intermediates for the formation of 4 and 5. Reduction of ytterbium or imino-functionalized pyrrolyl compounds was not observed by refluxing a toluene solution of complex 7 for 2 days by carefully examining the hydrolysis product of the complex. This result suggested that the formation of the imino group in complexes 4 and 5 may not be due to the abstraction of a proton by the amido group N(SiMe3)2. Complex 7 (Figure 4) is a centrosymmetric dimeric ytterbium(III) amide with the dianion {2-[(2,6- i Pr 2 C 6 H 3 )NCH 2]C4H3N}2- bridging two central metal ions through the pyrrolyl five-membered rings bonded with one metal in an η5 mode and with the nitrogen atom of the pyrrolyl ring and the tethered nitrogen anion bonded with another metal in an η1 fashion. This bonding mode is different from that of so-called constrained geometry ligand [Me2Si(NR)(C5Me4)]2- (R = tBu or Ar), which generally is bonded with only one metal in a η5:η1 mode.14 The bond distances between the ytterbium ion and the five-membered ring ranges from 2.630(7) to 2.787(7) A˚, with an average of 2.707(7) A˚, in the normal ranges observed for the six-coordinate octahedral geometry ytterbium(III) complexes. Oxidation of secondary amines to imino groups in 4 and 5

means that other reactants were reduced. Attempts have been made to isolate the reduced components from the above reaction systems. Treatment of equal equivalents of grease (Me2SiO)3, 2-(2,6-iPr2C6H3NHCH2)C4H3NH (2), and europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3, after workup, afforded the europium(II) complex {[μ-η5:η1:η1-2-(ArN(Me2SiO)CH2)C4H3N]EuII[η5-2-(ArNdCH)C4H3N]Li2[N(SiMe3)2]}2 (Ar = 2,6-iPr2C6H3) (8) in 39% yield (Scheme 1). X-ray analyses revealed that the [2-(2,6-iPr2C6H3Nd CH)C4H3N] ligand is the imino-functionalized pyrrolyl ligand with a C-N bond distance of 1.262(9) A˚, having a double-bond character, indicating that the secondary amine is oxidized to an imino group. It is also found that the central europium metals are in the oxidation state of þ2. This result suggests that a redox reaction between the europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 and pyrrolyl-functionalized secondary amine happened, the secondary amine was oxidized to imine, and the europium(III) ion itself was reduced to europium(II) in the reaction process. The reduction of europium(III) to europium(II) process may be through homolysis of the Eu-N(SiMe3)2 bond15 of the intermediate {[(μ-η5:η1):η1-2-[(2,6-iPr 2C6H3)NCH2]C4H3N]EuIIIN(SiMe3)2}2 on the basis of the result for the formation of complex 7. The formation of the dianion [2,6-iPr2C6H3N(Me2SiO)CH2)C4H3N]2- ligand in the complex may be through the insertion of (Me2SiO)3 to the Eu-N(C6H3iPr22,6) bond of the intermediate.16 The result indicated that the deprotonation of the methylene CH2 for the formation of the imino-functionalized pyrrolyl ligand [2-(2,6-iPr2C6H3Nd CH)C4H3N] in 8 may be after the insertion of (Me2SiO)3 to the Eu-N(C6H3iPr2-2,6) bond. The structure of 8 (Figure 5) reveals a novel centrosymmetric dinuclear europium(II) complex consisting of a bridged ligand [2,6-iPr2C6H3N(Me2SiO)CH2)C4H3N]2- with pyrrolyl ring η5 bonded to

(13) Evans, W. J. Coord. Chem. Rev. 2000, 206-207, 263. (14) (a) Shapiro, P. J.; Bunel, E.; Schaefer, W. P.; Bercaw, J. E. Organometallics 1990, 9, 867–869. (b) Shapiro, P. J.; Schaefer, W. P.; Labinger, J. A.; Bercaw, J. E.; Cotter, W. D. J. Am. Chem. Soc. 1994, 116, 4623–4640. (c) Hultzsch, K. C.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 1999, 38, 227–230. (d) Zhang, W.-X.; Nishiura, M.; Hou, Z. Chem. Eur. J. 2007, 13, 4037-4051, and references therein.

(15) (a) Wang, S.; Zhou, S.; Sheng, E.; Xie, M.; Zhang, K.; Cheng, L.; Feng, Y.; Mao, L.; Huang, Z. Organometallics 2003, 22, 3546–3552. (b) Zhang, K.; Zhang, W.; Wang, S.; Sheng, E.; Yang, G.; Xie, M.; Zhou, S.; Feng, Y.; Mao, L.; Huang, Z. Dalton Trans. 2004, 1029–1037. (16) 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– 3888.

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Figure 5. Molecular structure of compound 8. Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚): Eu(1)-Pyr 2.888(8), N(1)-C(13) 1.262(9), N(3)-C(30) 1.467(8). More bond distances and angles can be found in the Supporting Information.

one metal with bond distances ranging from 2.822(6) to 2.917(8) A˚ and with the nitrogen atom of the pyrrolyl ring and the tethered oxygen atom bonded to another metal in η1 fashion. The pyrrolyl ring of the imino-functionalized pyrrolyl ligand [2-(2,6-iPr2C6H3NdCH)C4H3N]- is η5 bonded to the europium(II) ion with bond distances of 2.838(7) to 2.989(8) A˚, the nitrogen atom of the pyrrolyl ring is coordinated to two lithium ions, and the imino nitrogen is coordinated to one lithium ion. The average bond distance of 2.888(8) A˚ of the η5-bonded pyrrolyl ring to the europium ion is in the normal range observed in the indenyl europium(II) complexes.15 A novel centrosymmetric macrocyclic complex with six europium(II) ions and six lithium ions, {[(5-tBu-C4H2N-2CHdNCH2)2]4[(5-tBu-2-CH3NdCH(C4H2N)]Eu3Li3}2 (9) (Scheme 3), was isolated in 53% yield and characterized by treatment of linked diamine [5-tBu-C4H2NH-2-CH2NHCH2]2 (3) with europium(III) amide [(Me3Si)2N]3EuIII(μCl)Li(THF)3. The result further proved that the redox reaction of europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 with secondary amine could happen. As indicated by structural analyses (Figure 6), the complex consists of eight bis-imino-linked dipyrrolyl dianions [(5-t Bu-C4 H2 N-2CHdNCH2)2]2-, which take the bridged forms to bond with different metals, and two [5-tBu-C4H2N-2-CHdNCH3]-. All the secondary amino groups were oxidized to imino groups, europium(III) ions were reduced to europium(II), and one of linked diamines was even cleaved to form an imino ligand, [5-tBu-C4H2N-2-CHdNCH3]-. The Eu(1) and Eu(3) are sandwiched by two pyrrolyl rings in η5 modes with an average Eu(1) to pyrrolyl ring distance (Eu(1)-Pyr) of 2.904(19) A˚ and an average Eu(3) to pyrrolyl ring distance (Eu(3)-Pyr) of 2.898(17) A˚. The Eu(1) or Eu(3) is coordinated by another pyrrolyl nitrogen and an imino nitrogen atoms, whereas the Eu(2) is half-sandwiched by one pyrrolyl ring in an η5 mode and is coordinated by another four nitrogen atoms of one [(5-tBu-C4H2N-2-CHdNCH2)2]2- ligand. The average

Eu(2) to pyrrolyl ring distance (Eu(2)-Pyr) of 2.976(16) A˚ is longer than those of Eu(1)-Pyr and Eu(3)-Pyr in 9 and Eu(1)-Pyr in 8, as the Eu(2) in 9 has coordination numbers of only seven, while Eu(1) and Eu(3) in 9 and Eu(1) in 8 have eight coordinates. The average Eu(1)-Pyr and Eu(3)-Pyr distances in 9 are comparable to that of Eu(1)-Pyr in 8. There is clear evidence for the existence of the dysprosium(II) complexes;17 thus the pyrrolyl-functionalized linked secondary diamine [5-tBu-C4H2NH-2-CH2NHCH2]2 (3) was treated with dysprosium(III) amide [(Me3Si)2N]3DyIII(μ-Cl)Li(THF)3 to see if the redox reaction could happen between these materials. As a result, a novel four-sandwichedlithium-supported tetranuclear dysprosium(III) complex, {η2:η2-[η1:η1-(μ-η5:η5-[5-tBu-C4H2N-2-CH2NCH2CH2N-2-CH25-tBu-C4H2N]Li)2]Dy2(μ3-Cl)Li}2 (10) (Scheme 3, Figure 7), was isolated in 46% yield and characterized. The reactivity and bonding modes of the ligand with dysprosium are completely different from those of europium chemistry. But, from the reaction for the preparation of the dysprosium complex, we may get information that the tetraanion [5-tBu-C4H2N-2CH2NCH2CH2N-2-CH2-5-tBu-C4H2N]4- may be formed at first in the formation of 9, and the redox potentials of Ln3þ/ Ln2þ have a great influence on the results of reactions of the pyrrolyl-functionalized secondary amines with lanthanide amides [(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3. The staggered sandwiched Li(2) to pyrrolyl ring distances range from 2.201(8) to 2.426(8) A˚, with an average of 2.304(8) A˚ (Li(2)-Pyr). The eclipsed sandwiched Li(3) to pyrrolyl ring distances range from 2.293(9) to 2.534(8) A˚, with an average of 2.417(9) A˚ (Li(3)-Pyr), which is longer than that of Li(2)-Pyr. In comparison of the lithium to pyrrolyl ring distances, the distances of (17) (a) Evans, W. J.; Allen, N. T. J. Am. Chem. Soc. 2000, 122, 11749–11750. (b) Bochkarev, M. N.; Fagin, A. A. Chem. Eur. J. 1999, 5, 2990–2992. (c) Evans, W. J.; Allen, N. T.; Ziller, J. W. Angew. Chem., Int. Ed. 2002, 41, 359–361.

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{[(μ-η 5 :η 1 ):η 1 -2-[(2,6- i Pr 2 C 6 H 3 )NCH 2 ]C 4 H 3 N]Eu III N(SiMe3)2}2 as intermediates A, and homolysis of the Eu-N bond16,19 led to reduction of Eu3þ to Eu2þ to give europium(II) intermediates B {[(μ-η5:η1):η1-2-[(2,6-R2C6H3)NCH2]C4H3N]EuII}2. β-Hydrogen elimination of the intermediate B afforded the europium(II) hydride C, having an imino-functionalized ligand, and acid-base exchange of C with HN(SiMe3)2 produced a new amido intermediate, D, which underwent ligand redistribution or dissociation to produce the final products. The intermediate B partially reacted with grease followed by βhydrogen elimination, acid-base exchange, and reassemble processes to give 8 as the final product (Scheme 4). However, another possibility cannot be ruled out.

Conclusion In summary, the redox reaction of europium(III) amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 with pyrrolyl-functionalized secondary amines leading to oxidation of pyrrolylfunctionalized secodary amines to imino groups and reduction of europium(III) to europium(II) was for the first time observed. The chemistry may inovlve important processes such as silylamine elimination reaction, coordination-promoted homolysis of the Eu-N bond resulting in reduction of Eu3þ to Eu2þ, and β-hydrogen elimination of amido intermediates. The results indicated that the redox potentials of Ln3þ/Ln2þ have a great influence on the reactions of the pyrrolyl-functionalized secondary amines with lanthanide amides [(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3. This finding provided a new pathway for the synthesis and characterization of imino-functionalized pyrrolyl organometallics. Further study on the dehydrogenation reaction of secondary amines of the early transition metal complexes including rare-earth metal complexes is underway in our laboratory.

Experimental Section

Li(3)-N(8) (2.534(8) A˚), Li(3)-C(33) (2.432(9) A˚), Li(3)C(36) (2.468(9) A˚), Li(3)-N(1A) (2.529(8) A˚), Li(3)-C(5A) (2.424(9) A˚), and Li(3)-C(8A) (2.478(8) A˚) are significantly longer than those of Li(3)-C(34) (2.293(9) A˚), Li(3)-C(35) (2.324(9) A˚), Li(3)-C(6A) (2.327(9) A˚), and Li(3)-C(7A) (2.359(9) A˚), suggesting that the pyrrolyl rings tend to bond with lithium (Li(3)) in η2:η2 modes. Our previous results indicated heating of [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 in refluxing toluene or sublimation of it under reduced pressure did not lead to reduction of europium(III) to europium(II).18 On the basis of these results, we can propose that the above redox reaction occurs between europium(III) amide and the pyrrolyl-functionalized secondary amines as follows: silylamine elimination of pyrrolyl-functionalized secondary amines with [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 produced the amido complexes (18) Zhou, S.; Wang, S.; Yang, G.; Liu, X.; Sheng, E.; Zhang, K.; Cheng, L.; Huang, Z. Polyhedron 2003, 22, 1019-1024.

General Procedures. All syntheses and manipulations of airand moisture-sensitive materials were performed under dry argon and an oxygen-free atmosphere using standard Schlenk techniques. All solvents were refluxed and distilled over sodium benzophenone ketyl under argon prior to use unless otherwise noted. [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 (Ln = Eu, Dy, Yb) were prepared according to literature methods.18,19c Elemental analyses data were obtained on a Perkin-Elmer 2400 Series II elemental analyzer. 1H NMR and 13C NMR spectra for analyses of compounds were recorded on a Bruker AV-300 NMR spectrometer (300 MHz for 1H; 75.0 MHz for 13C). Chemical shifts (δ) are reported in ppm. J values are reported in Hz. IR spectra were recorded on a Shimadzu FTIR-8400s spectrometer (KBr pellet). Mass spectra were performed on a Micromass GCT-MS spectrometer. Melting points were determined in sealed capillaries and are uncorrected. Preparation of 2-(2,6-Me2C6H3NHCH2)C4H3NH (1). The compound 2-(2,6-Me2C6H3NdCH)C4H3NH20 (6.0 g, 30.26 mmol) in CH3OH (30 mL) solution was reduced with NaBH4 (1.76 g, 46.52 mmol) at 50 °C for 5 h; then it was hydrolyzed. The organic layer was separated, and the aqueous layer was (19) (a) Wang, S.; Tang, X.; Vega, A.; Saillard, J.-Y.; Zhou, S.; Yang, G.; Yao, W.; Wei, Y. Organometallics 2007, 26, 1512–1522. (b) Wang, S.; Tang, X.; Vega, A.; Saillard, J.-Y.; Sheng, E.; Yang, G.; Zhou, S.; Huang, Z. Organometallics 2006, 25, 2399–2401. (c) Sheng, E.; Wang, S.; Yang, G.; Zhou, S.; Zhang, K.; Cheng, L.; Huang, Z. Organometallics 2003, 22, 684–692. (d) Bojer, D.; Venugopal, A.; Neumann, B.; Stammler, H.-G.; Mitzel, N. W. Angew. Chem., Int. Ed. 2010, 49, 2611–2614. (20) Yang, Y.; Liu, B.; Lu, K.; Gao, W.; Cui, D. M.; Chen, X. S.; Jing, X. B. Organometallics 2007, 26, 4575–4584.

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Figure 6. Molecular structure of compound 9. Hydrogen atoms and tert-butyl groups are omitted for clarity. Selected bond lengths (A˚): C(9)-N(2) 1.28(2), C(18)-N(4) 1.39(2), C(21)-N(5) 1.29(2), C(38)-N(8) 1.273(19), C(41)-N(9) 1.40(2), C(58)-N(12) 1.33(2), C(61)-N(13) 1.28(2), C(78)-N(16) 1.28(2), C(89)-N(18) 1.28(2), Eu(1)-Pyr 2.904(17), Eu(2)-Pyr 2.976(16), Eu(3)-Pyr 2.898(17). More bond distances and angles can be found in the Supporting Information.

Figure 7. Molecular structure of compound 10. Hydrogen atoms and tert-butyl groups are omitted for clarity. Li(2)-Pyrav. 2.304(8) A˚, Li(3)-Pyrav 2.417(9) A˚, N(2)-C(9) 1.461(4) A˚, N(3)-C(12) 1.482(4) A˚, N(6)-C(29) 1.481(4) A˚, N(7)-C(32) 1.455(4) A˚. More bond distances and angles can be found in the Supporting Information. extracted with diethyl ether (3  20 mL). The organic fractions were combined and dried with anhydrous MgSO4, filtered, and evaporated to dryness. Recrystallization of the crude product from hexane gave the product 2-(2,6-Me2C6H3NHCH2)C4H3NH (1) (5.45 g, 90% yield). Mp: 69-71 °C. 1H NMR (300 MHz, CDCl3): δ 8.32 (br, 1H, NH), 7.06-6.88 (m, 3H, C6H3), 6.75 (s, 1H, C4H3N), 6.18 (s, 1H, C4H3N), 6.10 (s, 1H, C4H3N), 4.11 (s, 2H,CH2), 3.22 (br, 1H, NH), 2.28 (s, 6H, CH3). 13 C NMR (75.0 MHz, CDCl3): δ 145.5 (C6H3), 130.6 (C4H3N), 130.2 (C6H3), 128.9 (C6H3), 122.7 (C6H3), 117.4 (C4H3N), 108.3 (C4H3N), 106.2 (C4H3N), 45.4 (NHCH2), 18.3 (CH3). IR (KBr pellet, cm-1): ν 3210 (m), 3082 (w), 2967 (m), 2859 (m), 1574 (m), 1474 (vs), 1427 (s), 1373 (m), 1339 (m), 1196 (vs), 1130 (s), 1092

(vs), 1061 (s), 1026 (s), 976 (m), 949 (m), 791 (m), 772 (m), 725 (vs), 633 (m), 606 (s), 544 (m). HRMS (EI) m/z: calcd for C13H16N2 200.1313; found 200.1311. Anal. Calcd for C13H16N2: C, 77.96; H, 8.05; N, 13.99. Found: C, 77.63; H, 8.37; N, 13.69. Preparation of 2-(2,6-Me2C6H3NHCHD)C4H3NH (1a). This compound was prepared by using procedures similar to those used for the preparation of 1 with NaBD4 as reductant. Mp: 70-71 °C. 1H NMR (300 MHz, CDCl3): δ 8.27 (br, 1H, NH), 7.03-6.85 (m, 3H, C6H3), 6.72 (m, 1H, C4H3N), 6.16 (m, 1H, C4H3N), 6.07 (s, 1H, C4H3N), 4.08 (s, 1H,CHD), 2.65 (br, 1H, NH), 2.26 (s, 6H, CH3). 13C NMR (75.0 MHz, CDCl3): δ 145.7 (C6H3), 130.9 (C4H3N), 130.4 (C6H3), 129.1 (C6H3), 122.9 (C6H3), 117.6 (C4H3N), 108.6 (C4H3N), 106.3 (C4H3N), 45.7, 45.4, 45.1 (CHD), 18.5 (CH3). IR (KBr pellet, cm-1): ν 3209 (m), 3086 (w), 2956 (m), 1574 (m), 1442 (s), 1384 (m), 1330 (m), 1186 (s), 1128 (s), 1092 (s), 1043 (s), 1024 (s), 927 (m), 761 (m), 711 (s), 667 (m), 607 (m), 544 (m). HRMS (EI) m/z: calcd for C13H16DN2 (M þ H)þ 202.1455; found 202.1442. Anal. Calcd for C13H15DN2: C, 77.57; H, 8.51; N, 13.92. Found: C, 77.85; H, 8.35; N, 13.78. Preparation of 2-(2,6-iPr2C6H3NHCH2)C4H3NH (2). This compound was isolated as colorless crystals in 77% yield by using procedures similar to those used for the preparation of 1. Mp: 74-75 °C. 1H NMR (300 MHz, CDCl3): δ 8.50 (br, 1H, NH), 7.16 (m, 3H, C6H3), 6.80 (s, 1H, C4H3N), 6.23 (m, 1H, C4H3N), 6.13 (s, 1H, C4H3N), 4.07 (s, 2H, CH2), 3.23-3.36 (hepta, J = 6.8 Hz, 2H, CHMe2), 1.27 (d, J = 6.8 Hz, 12H, CH(CH3)2). 13C NMR (75.0 MHz, CDCl3): δ 143.0 (C6H3), 142.8 (C6H3), 130.7 (C4H3N), 124.8 (C6H3), 124.1 (C6H3), 117.7 (C4H3N), 108.7 (C4H3N), 106.3 (C4H3N), 49.2 (CH2), 28.1 (CHMe2), 24.7 (CH3). IR (KBr pellet, cm-1): ν 2959 (m), 2864 (m), 1591 (w), 1576 (w), 1481 (m), 1458 (m), 1439 (m) 1422 (m), 1385 (m), 1364 (m), 1321 (m), 1254 (m), 1240 (m), 1198 (m), 1184 (m), 1099 (m), 1026 (m), 968 (m), 934 (m), 883 (m), 825 (m), 804 (m), 787 (m), 766 (m), 721 (m), 610 (m). HRMS (EI) m/z: calcd for C17H25N2 (M þ H)þ 257.2018; found 257.2006. Anal. Calcd for C17H24N2: C, 79.64; H, 9.44; N, 10.93. Found: C, 79.65; H, 9.06; N, 10.79. Preparation of 2-(2,6-iPr2C6H3NHCHD)C4H3NH (2a). This compound was prepared by using procedures similar to those used for the preparation of 2 with NaBD4 as reductant. Mp: 75-77 °C. 1H NMR (300 MHz, CDCl3): δ 8.43 (br, 1H, NH), 7.12 (m, 3H, C6H3), 6.76 (m, 1H, C4H3N), 6.18 (m, 1H, C4H3N),

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Scheme 4. Proposed Pathway for the Formation of Redox Products

6.10 (s, 1H, C4H3N), 4.02 (s, 1H, CHD), 3.33-3.19 (hepta, J = 6.9 Hz, 2H, CHMe2), 1.23 (d, J = 6.9 Hz, 12H, CH(CH3)2). 13 C NMR (75.0 MHz, CDCl3): δ 142.80 (C6H3), 142.46 (C6H3), 130.57 (C4H3N), 124.35 (C6H3), 123.68 (C6H3), 117.29 (C4H3N), 108.39 (C4H3N), 105.88 (C4H3N), 48.76, 48.48, 48.20 (CHD), 27.78 (CHMe2), 24.29 (CH3). IR (KBr pellet, cm-1): ν 3287 (m), 3099 (m), 2980 (m), 2940 (m), 2855 (m), 1593 (w), 1566 (w), 1473 (m), 1458 (m), 1439 (m), 1377 (m), 1377 (m), 1255 (m), 1207 (m), 1126 (m), 1097 (m), 1024 (m), 920 (m), 877 (m), 773 (m), 731 (m), 642 (m). HRMS (EI) m/z: calcd for C17H24DN2 (M þ H)þ 258.2081; found 258.2065. Anal. Calcd for C17H23DN2: C, 79.33; H, 9.79; N, 10.88. Found: C, 79.01; H, 9.49; N, 10.53. Preparation of [5-tBu-C4H2NH-2-CH2NHCH2]2 (3). 5-tertButyl-2-formylpyrrole (15.12 g, 0.1 mol) was mixed with ethylenediamine (3.00 g, 0.05 mol). To the mixture was added a 50 mL of methanol. The mixture was then stirred overnight at room temperature after the addition, and a large amount of white precipitate appeared. The white solid was isolated upon filtration and was dissolved in methanol (100 mL). To the solution was stepwise added NaBH4 (7.56 g, 0.2 mol), and the mixture was then stirred for another 12 h. To the solution was slowly added a saturated aqueous solution of NH4Cl (50 mL). The mixture was extracted with 50 mL of diethyl ether, the aqueous fraction was extracted with diethyl ether (3  20 mL), and the extraction was combined, washed with water (3  50 mL), and dried over NaSO4. The crude product can be obtained by evaporation of solvents. A white solid can be obtained by recrystallization of the crude product from a toluene solution

(13.16 g, 80%). Mp: 152-154 °C. 1H NMR (300 MHz, CDCl3): δ 8.63 (br, 2H, NH), 5.89 (s, 2H, C4H3N), 5.79 (s, 2H, C4H3N), 3.74 (s, 4H, NCH2C4H3N), 2.75 (s, 4H, NCH2CH2N), 1.96 (br, 2H, NH), 1.29 (s, 18H, (CH3)3). 13C NMR (75.0 MHz, CDCl3): δ 142.27 (C4H3N), 128.29 (C4H3N), 106.34 (C4H3N), 101.82 (C4H3N), 48.54 (NCH2), 46.81 (NCH2CH2N), 31.56 (C(CH3)3), 30.73 (CH3). IR (KBr pellet, cm-1): ν 2963 (m), 2864 (m), 1591 (w), 1557 (w), 1537 (w), 1514 (m), 1470 (m), 1427 (m), 1362 (m), 1329 (m), 1287 (m), 1233 (m), 1206 (m), 1189 (w), 1101 (w), 1061 (m), 1042 (m), 966 (m), 930 (m), 764 (m), 698 (m), 638 (m). HRMS (EI) m/z: calcd for C20H35N4 (M þ H)þ 331.2862; found 331.2846. Anal. Calcd for C20H34N4: C, 72.68; H, 10.37; N, 16.95. Found: C, 72.97; H, 10.43; N, 16.59. Preparation of {[η2:η1-2-(2,6-Me2C6H3NdCH)C4H3N]Li(THF)}2 (4). To a toluene solution (40 mL) of [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 (2.030 g, 2.28 mmol) was slowly added a toluene solution (10.0 mL) of 2-(2,6-Me2C6H3NHCH2)C4H3NH (1) (0.228 g, 1.14 mmol). The reaction mixture was stirred at room temperature for 6 h. It was then stirred at 100 °C for 24 h, and the color of the mixture gradually changed from dark to red. The solvent was evaporated, and the solid was extracted with hexane (2  15 mL). The extraction was combined and concentrated to 10 mL. Colorless crystals were obtained upon standing the solution at 0 °C for several days. The crystals were identified as 4 (0.204 g, 65% based on amine). Mp: 210-212 °C. 1H NMR (300 MHz, C6D6): δ 7.88 (s, 2H, CHdN), 7.41 (s, 2H, C4H3N), 7.26-7.12 (m, 6H, C6H3), 6.99 (d, 2H, C4H3N), 6.58 (m, 2H, C4H3N), 3.18 (m, 8H, THF), 2.32 (s, 12H, CH3), 1.25 (m, 8H, THF). 13C NMR (75.0 MHz, C6D6): δ 160.6 (NdCH), 152.3

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(C6H3), 139.4 (C4H3N), 136.1 (C4H3N), 129.5 (C6H3), 128.7 (C6H3), 123.9 (C4H3N), 120.4 (C6H3), 112.5 (C4H3N), 67.7 (THF), 25.3 (THF), 18.7 (CH3). IR (KBr pellet, cm-1): ν 3202 (s), 2967 (m), 2859 (w), 1632 (s), 1589 (m), 1558 (w), 1509 (w), 1474 (m), 1339 (m), 1312 (m), 1261 (m), 1188 (m), 1134 (s), 1088 (s), 1034 (s), 918 (m), 860 (m), 833 (m), 767 (m), 741 (m), 606 (m). Anal. Calcd for C34H42O2N4Li2þ2THF: C, 72.39; H, 8.39; N, 8.04. Found: C, 73.04; H, 8.60; N, 8.16. Reaction of 1a with [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3: Characterization of the Mixture of {[η2:η1-2-(2,6-Me2C6H3NdCD)C4H3N]Li(THF)}2 (4a) and 4. Compound 1a was treated with 2 equiv of [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 following procedures similar to those used for the preparation of 4 to give a mixture of 4a and 4. 1H NMR (300 MHz, C6D6): δ 7.84 (s, 0.47H, CHdN), 7.38 (s, 1H, C4H3N), 7.22-7.09 (m, 3H, C6H3), 6.96 (s, 1H, C4H3N), 6.57 (s, 1H, C4H3N), 3.13 (m, 4H, THF), 2.29 (s, 6H, CH3), 1.21 (m, 4H, THF). 13C NMR (75.0 MHz, C6D6): δ 160.3 (NdCH), 151.9 (C6H3), 139.1 (C4H3N), 135.8 (C4H3N), 129.2 (C6H3), 128.4 (C6H3), 123.6 (C4H3N), 120.1 (C6H3), 112.2 (C4H3N), 67.4 (THF), 25.0 (THF), 18.4 (CH3). Preparation of {[η2:η1-2-(2,6-iPr2C6H3NdCH)C4H3N]Li(THF)]}2 (5). This compound was isolated as colorless crystals in 53% yield (based on amine) by treatment of [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 (1.925 g, 2.16 mmol) with 2-(2,6-iPr2C6H3NHCH2)C4H3NH (2) (0.277 g, 1.08 mmol) following procedures similar to those used for the preparation of 4. Mp: 201-203 °C. 1H NMR (300 MHz, CDCl3): δ 7.96 (s, 2H, CHdN), 7.26-7.17 (m, 6H, C6H3), 7.08 (s, 2H, C4H3N), 6.76 (d, J = 3.3 Hz, 2H, C4H3N), 6.27 (dd, J = 3.3 Hz, 2H, C4H3N), 3.41 (m, 8H, THF), 3.23 (hepta, J = 6.8 Hz, 4H, CHMe2), 1.75 (m, 8H, THF), 1.19 (d, J = 6.8 Hz, 24H, CH(CH3)2). 13C NMR (75.0 MHz, CDCl3): δ 160.3 (NdCH), 149.2 (C6H3), 140.3 (C6H3), 139.1 (C4H3N), 136.2 (C4H3N), 124.1 (C4H3N), 123.2 (C6H3), 119.3 (C6H3), 111.2 (C4H3N), 67.6 (THF), 27.5 (CH3), 25.4 (THF), 24.4 (CHMe2). IR (KBr pellets, cm-1): ν 3059 (w), 2926 (m), 2900 (m), 2868 (m), 1747 (w), 1722 (w), 1626 (s), 1585 (m), 1552 (m), 1458 (m), 1418 (m), 1339 (s), 1310 (m), 1254 (w), 1180 (m), 1132 (m), 1090 (m), 1032 (m), 932 (w), 885 (m), 860 (m), 781 (m), 745 (m), 608 (w). Anal. Calcd for C42H58O2N4Li2: C, 75.88; H, 8.79; N, 8.43. Found: C, 75.85; H, 8.63; N, 9.04. Reaction 2a with [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3: Characterization of the Mixture of {[η2:η1-2-(2,6-i Pr 2C6 H3 NdCD)C 4H3N]Li(THF)]}2 (5a) and 5. Compound 2a was treated with 2 equiv of [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 following procedures similar to those used for the preparation of 5 to give a mixture of 5a and 5. 1H NMR (300 MHz, CDCl3): δ 7.92 (s, 0.43H, CHdN), 7.21-7.16 (m, 3H, C6H3), 7.04 (s, 1H, C4H3N), 6.73 (d, 1H, C4H3N), 6.24 (s, 1H, C4H3N), 3.28 (m, 4H, THF), 3.17 (hepta, J = 6.9 Hz, 2H, CHMe2), 1.69 (s, 4H, THF), 1.14 (d, J = 6.9 Hz, 12H, CHMe2). 13 C NMR (75.0 MHz, CDCl3): δ 160.1 (NdCH), 149.1 (C6H3), 140.3 (C6H3), 138.6 (C4H3N), 135.5 (C4H3N), 124.2 (C4H3N), 123.2 (C6H3), 119.3 (C6H3), 111.3 (C4H3N), 67.6 (THF), 27.6 (CHMe2), 25.4 (THF), 24.3 (CH3). Preparation of {[η5:η2:η1-2-(2,6-iPr2C6H3NHCHD)C4H3N]Li2N(SiMe3)2}2 (6). To a toluene solution (10 mL) of 2-(2,6-iPr2C6H3NHCHD)C4H3NH (2a) (0.969 g, 3.8 mmol) was added a toluene (20 mL) solution of (Me3Si)2NLi (1.908 g, 11.4 mmol) at room temperature. After the reaction mixture was stirred at 100 °C for 48 h, the solvent was evaporated under reduced pressure. The residue was extracted with n-hexane (10 mL). The colorless crystals were obtained upon standing the solution at room temperature for 12 h (1.01 g, 62%). Mp: 93-94 °C. 1H NMR (300 MHz, C6D6): δ 7.06 (s, 2H, C4H3N), 6.96-6.86 (m, 6H, C6H3), 6.32 (s, 2H, C4H3N), 5.96 (s, 2H, C4H3N), 4.03 (br, 2H, CHD), 3.93 (br, 2H, CHMe2), 3.10 (br, 2H, CH(CH3)2), 2.13 (br, 2H, NH), 0.95 (s, 24H, CH(CH3)2), 0.15 (s, 36H, Si(CH3)3). 13C NMR (75.0 MHz, C6D6): δ 140.3 (C6H3), 139.3 (C4H3N), 137.3 (C6H3), 128.1 (C6H3), 123.9 (C6H3), 121.8 (C4H3N), 106.4 (C4H3N), 102.6 (C4H3N), 50.6, 50.3, 50.0 (CHD), 25.6 (CHMe2), 21.7 (CH3), 3.5 (SiMe3). IR

Li et al. (KBr pellets, cm-1): ν 3086 (s), 2868 (s), 1591 (w), 1576 (m), 1462 (s), 1442 (s), 1364 (m), 1256 (m), 1186 (m), 1101 (w), 1043 (m), 1024 (m), 934 (m), 883 (m), 837 (m), 802 (m), 762 (s), 721 (s), 609 (m). Anal. Calcd for C46H80D2Li4N6Si4: C, 64.15; H, 9.83; N, 9.76. Found: C, 63.87; H, 9.72; N, 9.55. Preparation of {(μ-η5:η1:η1-2-[(2,6-iPr2C6H2)NCH2]C4H3N)YbN(SiMe3)2}2 (7). This complex was isolated as dark red crystals in 57% yield by treatment of 2 (0.477 g, 1.86 mmol) with [(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 (1.698 g, 1.86 mmol) using procedures similar to those described above for the preparation of 4. Mp: 270-272 °C. IR (KBr pellets, cm-1): ν 2958 (s), 2864 (m), 1624 (w), 1575 (w), 1441 (s), 1385 (m), 1331 (m), 1312 (m), 1256 (m), 1198 (m), 1184 (m), 1099 (m), 1043 (m), 1026 (m), 968 (w), 934 (w), 883 (m), 804 (s), 766 (m), 723 (m), 610 (m). 1H NMR spectrum of the complex gave several resonances that cannot be assigned. Anal. Calcd for C46H80N6Si4Yb2: C, 47.00; H, 6.86; N, 7.15. Found: C,47.05; H, 6.98; N, 7.03. Hydrolysis of complex 7 gave pure compound 2, which was identified by 1H NMR and 13C NMR spectra analyses. Refluxing the toluene solution of 7 did not lead to reduction and formation of imino-functionalized product by careful analysis of the 1H NMR spectra of hydrolysis product. Preparation of {[μ-η 5 :η 1 :η 1 -2-(2,6- i Pr 2 C 6 H 3 N(Me 2 SiO)CH2)C4H3N]Eu[μ-η5:η1:η2-2-(2,6-iPr2C6H3NdCH)C4H3N]Li2[N(SiMe3)2]}2 3 C6H14 (8). This complex was isolated as red crystals in 39% yield (based on amine) by treatment of [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 (1.823 g, 2.04 mmol) with 2-(2,6-iPr2C6H3NHCH2)C4H3NH (2) (0.524 g, 2.04 mmol) and (Me2SiO)3 (0.152 g, 0.68 mmol) by employing procedures similar to those used for the preparation of 4. Mp: 236-237 °C. IR (KBr pellets, cm-1): ν 2960 (s), 2866 (m), 1624 (s), 1587 (m), 1560 (m), 1496 (m), 1460 (m), 1436 (m), 1383 (m), 1361 (m), 1340 (m), 1319 (m), 1274 (s), 1232 (m), 1203 (w), 1182 (m), 1140 (w), 1098 (m), 1043 (s), 1001 (w), 932 (w), 868 (m), 777 (m), 745 (m), 704 (m), 657 (m), 633 (w), 550 (w). Attempts to get NMR spectra of the complex failed due to lack of locking signals for the paramagnetic property of the complex. Anal. Calcd for C93H155Eu2Li4N10O2Si6þ2C6H14: C, 59.55; H, 8.71; N, 6.61. Found: C, 59.59; H, 8.13; N, 6.80. Preparation of {[(5-t Bu-C4 H2 N-2-CHdNCH 2)2]4(5-t Bu-2CH3NdCHC4H2N)Eu3Li3}2 (9). To a toluene (30.0 mL) solution of [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 (2.327 g, 2.61 mmol) was added a toluene (10.0 mL) solution of [5-tBu-C4H2NH-2CH2NHCH2]2 (3) (0.216 g, 0.65 mmol) at room temperature. After the reaction mixture was stirred for 24 h at 100 °C. The solvent was evaporated under reduced pressure. The residue was extracted with hexane (2  15.0 mL). The extraction was combined and dried under vacuum to afford complex 9 in 53% yield (0.149 g, based on amine). Red crystals for X-ray analysis were obtained from hexane at 0 °C within a week. Mp: 247-248 °C. IR (KBr pellets, cm-1): ν 3263 (m), 2965 (s), 2338 (m), 1635 (s), 1568 (s), 1492 (m), 1461 (s), 1415 (m), 1367 (m), 1280 (m), 1251 (m), 1203 (m), 1145 (m), 1041 (s), 962 (m), 929 (w), 880 (m), 843 (m), 785 (m). Attempts to get NMR spectra of the complex failed due to lack of locking signals for the paramagnetic property of the complex. Anal. Calcd for C180H254Eu6Li6N36þC6H14: C, 56.39; H, 6.82; N, 12.73. Found: C, 56.15; H, 7.14; N, 12.27. Preparation of {η2:η2-[η1:η1-(μ-η5:η5-[5-tBu-C4H2N-2-CH2NCH 2 CH 2N-2-CH 2-5-t Bu-C 4H 2N]Li)2]Dy 2(μ3-Cl)Li}2 (10). This complex was isolated as colorless crystals in 46% yield by treatment of 3 (0.396 g, 1.20 mmol) with [(Me3Si)2N]3Dy(μ-Cl)Li(THF)3 (2.165 g, 2.40 mmol) using procedures similar to those described above for the preparation of 9. Mp: 265-266 °C. IR (KBr pellets, cm-1): ν 3085 (m), 2988 (s), 2850 (w), 1564 (m), 1480 (m), 1450 (m), 1389 (m), 1368 (w), 1342 (m), 1300 (m), 1240 (m), 1198 (w), 1185 (m), 1148 (m), 1102 (m), 1068 (s), 1019 (m), 967 (w), 915 (m), 883 (m), 876 (m), 858 (m), 782 (m), 728 (m), 656 (m), 605 (m). Attempts to get NMR spectra of the complex failed due to lack of locking signals for the strong paramagnetic property of the complex. Anal. Calcd for

Article C80H120Cl2Dy4Li6N16þ3C6H14: C, 50.58; H, 7.02; N, 9.63. Found: C, 50.47; H, 6.99; N, 9.25. Crystal Structure Determinations. A suitable crystal of complexes 4-10 was each mounted in a sealed capillary. Diffraction was performed on a Bruker SMART CCD area detector diffractometer using graphite-monochromated Mo KR radiation (λ = 0.71073 A˚). An empirical absorption correction was applied using the SADABS program.21 All structures were solved by direct methods, completed by subsequent difference Fourier syntheses, and refined anisotropically for all non-hydrogen atoms by full-matrix least-squares calculations on F2 using the SHELXTL program package.22 All hydrogen atoms (21) Sheldrick, G. M. SADABS: Program for Empirical Absorption Correction of Area Detector Data; University of G€ ottingen: Germany, 1996. (22) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure Determination Software Programs; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 1997.

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were refined using a riding model (crystal data and refinements can be found in the Supporting Information, Tables 1 and 2).

Acknowledgment. This work is supported by the National Natural Science Foundation of China (20832001, 20802001, 21072004) and grants from the Ministry of Education (20103424110001) and Anhui Province (TD 200707, 2007Z016). The help for this work of Prof. Dr. Hai-bin Song from Nankai University is acknowledged. Supporting Information Available: Full experimental details, characterization data for new compounds, and crystallographic data and refinements for complexes 4-10. Figures for 4-10 with bond distances and angles. X-ray crystallographic files, in CIF format, for structure determination of complexes 4-10. This material is available free of charge via the Internet at http:// pubs.acs.org.