Reactivity of 3-Imino-Functionalized Indoles with Rare-Earth-Metal

May 20, 2016 - The reactivities of different 3-imino-functionalized indoles with rare-earth-metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 were studied to...
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Reactivity of 3‑Imino-Functionalized Indoles with Rare-Earth-Metal Amides: Unexpected Substituent Effects on C−H Activation Pathways and Assembly of Rare-Earth-Metal Complexes Xiancui Zhu,*,† Yang Li,† Yun Wei,† Shaowu Wang,*,†,‡ Shuangliu Zhou,† and Lijun Zhang† †

Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials, College of Chemistry and Materials Science, Anhui Normal University, Wuhu, Anhui 241000, People’s Republic of China ‡ State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s Republic of China S Supporting Information *

ABSTRACT: The reactivities of different 3-imino-functionalized indoles with rare-earth-metal amides [(Me3Si)2N]3RE(μCl)Li(THF)3 were studied to reveal unexpected substituent effects on C−H bond activation pathways, leading to the formation of unusual rare-earth-metal complexes. The reactions of 3-(tert-butylimino)indole with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 produced tetranuclear rare-earth-metal complexes {[η1:(μ2-η1:η1):η1-3-(tBuNCH)C8H4N]RE2(μ2-Cl)2(THF)[N(SiMe3)2](η1:η1-[μ-η5:η2-3-(tBuNCH)C8H5N]2Li)}2 (RE = Ho (1a), Er (1b)), incorporating a unique indolyl-1,2-dianion through sp2 C−H activation bonded with the central metal in η1:(μ2-η1:η1) mode. The reactions of 3-(phenylimino)indole with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 afforded novel binuclear complexes formulated as {3-[PhNCH(CH2SiMe2)N(SiMe3)]C8H5NRE(THF)(μ2-Cl)Li(THF)2}2 (RE = Y (2a), Sm (2b), Dy (2c), Yb (2d)) through an unexpected sp3 C−H bond activation with subsequent C−C bond coupling reactions. Treatment of 3-(2-methylphenylimino)indole or 3-(4methylphenylimino)indole with [(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 generated the corresponding dinuclear rare-earth-metal amido complexes {3-[(2-MePh)NCH(CH2SiMe2)N(SiMe3)]C8H5NYb(THF)(μ2-Cl)Li(THF)2}2 (3) and {3-[(4-MePh)NCH(CH2SiMe2)N(SiMe3)]C8H5NYb(THF)(μ2-Cl)Li(THF)2}2 (4), following the same pathway for the formation of complexes 2a−d. Treatment of 3-(4-tert-butylphenylimino)indole with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 afforded new hexanuclear rareearth-metal complexes {3-[(4-tBu-Ph)NHCH(CH2SiMe2)N(SiMe3)]C8H5NREN(SiMe3)2}6 (RE = Dy (5a), Ho (5b), Er (5c)) via sp3 C−H bond activation followed by C−C bond coupling reactions. In contrast, under the same conditions as those for the preparation of 5, the reaction with the corresponding yttrium complex provided the new heterohexayttrium complex {3-[(4-tBuPh)NCH(CH2SiMe2)N(SiMe3)]C8H5NYN(SiMe3)2Li(THF)}6 (6), having a 4-tBu-anilido moiety. All of these complexes were fully characterized by elemental analysis, spectroscopic methods, and X-ray structure analysis. Plausible pathways for the formation of these different rare-earth-metal complexes were proposed.

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leading to the findings of different C−H (including sp3 and sp2 C−H) bond functionalization6 and C−C bond coupling reactions.7 Very recently, Hou8 and Mashima9 have independently found that rare-earth-metal complexes could serve as efficient catalysts for the activation of unactivated sp3 or sp2 C−

INTRODUCTION

Reactivity studies between rare-earth-metal complexes and aromatic compounds have been of continuous interest to chemists in the search for efficient strategies to functionalize the aromatic compounds for either industrial or laboratory applications.1 Stoichiometric reactions of rare-earth-metal complexes with heteroaromatic compounds such as pyridines2 or quinolines,3 thiophenes,4 and imidazoles5 have been studied, © XXXX American Chemical Society

Received: March 19, 2016

A

DOI: 10.1021/acs.organomet.6b00221 Organometallics XXXX, XXX, XXX−XXX

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activation of the 2-indole sp2 C−H bond. These complexes have a unique indolyl-1,2-dianion species coordinating to the rare-earth-metal ions in an unusual η1:(μ2-η1:η1) bonding mode (Scheme 1), which are the same as our previous results.19 This

H bonds to produce functionalized arenes or end-functionalized polymers. Rare-earth-metal amido and imido complexes have also been found to exhibit activity in C−H bond functionalization in the reactions of scandium-terminal imido complex [MeC(NAr)CHC(Me)(NCH2CH2NMe2)(DMAP)ScNAr] (DMAP = 4-N,N-dimethylaminopyridine, Ar = 2,6-iPr2C6H3) with aromatic compounds.10 However, the reactivity studies between rare-earth-metal amides and aromatic compounds have been far less studied in comparison with those between rare-earth-metal alkyls, hydrides, and aromatic complexes.11,1f The chemistry of rare-earth-metal complexes incorporating indenyl ligands has been extensively studied.12 Indoles are more electron-rich than indenes, and some new interesting reactivities have been uncovered with rare-earth-metal complexes with indolyl ligands; however, such chemistry is fairly underdeveloped in comparison with that of indenes. For example, the simple indolyl europium(II) complex was prepared under harsh conditions in liquid NH3,13 and 7imino-functionalized indolyl rare-earth-metal alkyls have been synthesized and the dialkyl complexes were found to be active catalysts for isoprene polymerization in the presence of cocatalysts.14 The chemistry of rare-earth-metal complexes having 2,3-dimethylindolyl ligands has been studied to disclose a flexible coordination fashion between the ligand and the central metals.15 Recently, we found that reactions of different 2-functionalized amino indoles with rare-earth-metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 produced different amidoappended or imino-appended indolyl rare-earth-metal complexes depending on the substituents on the amino group.16 We also found that reactions of 2- or 3-imino-functionalized indoles with rare-earth-metal alkyls RE(CH2SiMe3)3(THF)2 afforded rare-earth-metal alkyl complexes with different hapaticities, from which highly efficient catalysts for selective isoprene 1,4-cis polymerization were identified.17 Moreover, the reactions of 1-alkyl-3-imino-functionalized indoles with RE(CH2SiMe3)3(THF)2 involving sp2 C−H bond activation produced the rare-earth-metal complexes having carbon σbonded indolyl ligands, which could also function as highly efficient isoprene 1,4-cis polymerization catalysts.18 In our previous communication, we found that the reactions of 3-(tertbutylimino)indole with rare-earth-metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 produced novel tetranuclear rare-earth-metal complexes {[η1:(μ2-η1:η1):η1-3-(tBuNCH)C8 H4 N]REIII2 (μ2-Cl) 2 (THF)[N(SiMe 3 ) 2](η 1:η1 -[μ-η5 :η 2-3(tBuNCH)C8H5N]2Li)}2 (RE = Y, Yb) via sp2 C−H activation, in which the unusual 1,2-dianion indolyl ligand was found to be bonded with the central metal in a novel η1: (μ2-η1:η1) fashion.19 These results prompted us to systematically study the reactivity of different 3-imino-functionalized indoles with rare-earth-metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3, with the expectation of finding new C−H bond activation pathways and novel rare-earth-metal complexes. Herein, we wish to report these results.

Scheme 1. Synthesis of Complexes 1a,b

result is different from our recent findings that the reactions of rare-earth-metal alkyls Yb(CH2SiMe3)3(THF)2 with 3-(tertbutylimino)indole 3-(tBuNCH)C8H4NH (L1) produced dinuclear ytterbium complexes having indolyl ligands in μη2:η1:η1 hapacities through alkyl insertion, while no C−H bond activation has been observed in the process.17a We have also found that the reactions of 1-alkyl-3-imino-functionalized indoles with RE(CH2SiMe3)3(THF)2 provided the carbon σbonded indolyl-supported rare-earth-metal alkyl complexes through sp2 C−H activation,18 which is believed to be produced via an imino-coordination-promoted process. It has also been proposed that the activation of the α-C−H bond of pyridine8,9 or imidazole20 by rare-earth-metal complexes including alkyl or amido complexes requires coordination of the nitrogen of pyridine to the central metal. On the basis of these results, a plausible pathway of the formation of complexes 1a,b is proposed (Scheme 2). First, 3-(tert-butylimino)indole reacted with rare-earth-metal amides with the elimination of silylamine to produce intermediate A, which then coordinated to [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 to give intermediate B. The latter would undergo a process involving the activation of Scheme 2. Proposed Pathway for the Formation of 1

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RESULTS AND DISCUSSION Reactivity of 3-Imino-Functionalized Indoles with Rare-Earth-Metal Amides. Treatment of 3-(tert-butylimino)indole 3-(tBuNCH)C8H4NH (L1) with [(Me3Si)2N]3RE(μCl)Li(THF)3 in refluxing toluene produced the tetranuclear rare-earth-metal complexes {[η1:(μ2-η1:η1):η1-3-(tBuNCH)C 8 H 4 N]RE 2 (μ 2 -Cl) 2 (THF)[N(SiMe 3 ) 2 ](η 1 :η 1 -[μ-η 5 :η 2 -3(tBuNCH)C8H5N]2Li)}2 (RE = Ho (1a), Er (1b)) through B

DOI: 10.1021/acs.organomet.6b00221 Organometallics XXXX, XXX, XXX−XXX

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Organometallics the 2-indole sp2 C−H bond to produce intermediate C with the indolyl-1,2-dianion being bonded with the central metal in a η1: (μ2-η1:η1) mode. The intermediate C then reacted with 3(tBuNCH)C8H4NH (L1) followed by reassembling to produce the final tetranuclear rare-earth-metal complexes 1. These interesting findings inspired us to further investigate the substituent effects on C−H bond activation pathways between reactions of 3-imino-linked indole and rare-earth-metal amides. When 3-phenylimino-functionalized indole 3-(PhNCH)C8H4NH (L2) was treated with 1 equiv of [(Me3Si)2N]3RE(μCl)Li(THF)3 in refluxing toluene, different from the above results, binuclear rare-earth-metal amido complexes {3[PhNCH(CH2SiMe2)N(SiMe3)]C8H5NRE(THF)(μ2-Cl)Li(THF)2}2 (RE = Y (2a), Sm (2b), Dy (2c), Yb (2d)) were isolated unexpectedly (Scheme 3).

that the electronic and steric nature of the substitutents (tBu vs phenyl) plays a significant role in determining the C−H activation pathways. Motivated by the above interesting results, we next studied the reactivity of other substituted arylimino-functionalized indoles with rare-earth-metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 to further investigate the substituent effects on the C−H bond activation pathway. After treating 3-(2-MeC6H4NCH)C8H4NH (L3) and 3(4-MeC 6 H 4 NCH)C 8 H 4 NH (L 4 ) with 1 equiv of [(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 under the same conditions as described above for the preparation of 1 and 2, the analogous binuclear ytterbium amides {3-[(2-Me-Ph)NCH(CH2SiMe2)N(SiMe3)]C8H5NYb(THF)(μ2-Cl)Li(THF)2}2 (3) and {3[(4-Me-Ph)NCH(CH2SiMe2)N(SiMe3)]C8H5NYb(THF)(μ2Cl)Li(THF)2}2 (4) were obtained in moderate isolated yields (Scheme 3). The pathway leading to complexes 3 and 4 was similar to that for the formation of rare-earth-metal complexes 2a−d through indolyl ligand deprotonation, tandem activation of the sp3 C−H bond of the bis(trimethylsilyl)amide, and then insertion of the imino CN bond to the RE−C bond to form an amido group connected to the central metal, regardless of the steric hindrance and electronic effect of the methyl group on the benzene ring. Encouraged by the above fascinating findings, another arylimino-functionalized indole with a bulky electron-donating tertiary-butyl group 3-(4-tBu-PhNCH)C8H4NH (L5) was treated with 1 equiv of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 in toluene, affording unprecedented hexanuclear complexes {3[(4-tBu-Ph)NHCH(CH 2 SiMe 2 )N(SiMe 3 )]C 8 H 5 NRE III N(SiMe3)2}6 (RE = Dy (5a), Ho (5b), Er (5c)) (Scheme 5).

Scheme 3. Synthesis of Complexes 2, 3, and 4

The formation of this kind of complexes is obviously through activation of the sp3 C−H bond of the silyl group to form a four-membered ring, which has also been proposed in the reactions of KN(SiMe3)2 with TpMe2LnCl221 and group IV metal complexes,22 and subsequent insertion of the imino C N bond to the RE−C bond9a of the intermediate generated the tridentate amido ligand supported binuclear complexes (Scheme 4).

Scheme 5. Synthesis of Complexes 5a−c

Scheme 4. Proposed Pathway for the Formation of 2

Again, activation of the sp3 C−H bond of the silyl group on the amido ligand N(SiMe3)2 followed by insertion of the imino CN bond to the RE−C bond was observed. Different from the above pathways leading to 2, 3, and 4 involving the formation of an anilido group after insertion of the imino C N bond to the RE−C bond, in the present case, the imino group was transferred to the aniline moiety after insertion, and there is one more amido N(SiMe3)2 connected to the rareearth-metal center, indicating a different reaction pathway from those for 2−4. These results suggested that the amido intermediate may be formed first by insertion of the imino CN bond to the RE−C bond, then the bulky tert-butyl group makes the formed amido group abstract a proton from the released amine HN(SiMe3)2 to produce the amino group coordinated to the central metal. The intermediacy of an amido

This chemistry is completely different from the above findings of 2-indole sp2 C−H bond activation resulting in a unique 1,2-indolyl dianion. It is also different from our previous findings that interactions of 2-(2,6-diisopropylphenylimino)indole [2-(2,6-iPr 2 C 6 H 3 NCH)C 8 H 5 NH] with RE(CH2SiMe3)3(THF)2 produced only the indole deprotonated rare-earth-metal alkyl complexes.17b The above results indicated C

DOI: 10.1021/acs.organomet.6b00221 Organometallics XXXX, XXX, XXX−XXX

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The anilido group of D then abstracted a proton from the released amine HN(SiMe3)2 to give the aniline-coordinated hexanuclear rare-earth-metal complexes 5 and lithium amide LiN(SiMe3)2. The lithium amide can react with the released rare-earth-metal chloride [(Me3Si)2N]2RECl(THF)x to produce [(Me3Si)2N]3RE(μ-Cl)Li(THF)x, which can return to the reaction process. Discussion on Structure Data. All the complexes are sensitive to air and moisture. Except for complexes 2−4, these complexes are well soluable in polar solvents, while less soluable in n-hexane. These complexes were fully characterized by IR, elemental analysis, and single-crystal X-ray diffraction. The complexes 2a, 2b, and 6 were additionally characterized by 1 H NMR and 13C NMR spectroscopic study. X-ray diffraction study revealed that complexes 1a and 1b are composed of six imino-functionalized indolyl ligands, four rareearth-metal cations, two lithium ions, and four chloride anions as a bridge to form neutral complexes (Figure 1). From Table

species in this process was supported by the following isolation of yttrium complex 6. When 3-(4-tBuPhNCH)C8H4NH (L5) was treated with 1 equiv of [(Me3Si)2N]3Y(μ-Cl)Li(THF)3 in refluxing toluene for 3 h, the heterometallic hexayttrium complex {3-[(4-tBuPh)NCH(CH 2 SiMe 2 )N(SiMe 3 )]C 8 H 5 NYN(SiMe 3 ) 2 Li(THF)}6 (6) was isolated, in which an anilido group coordinated to a yttrium ion and a lithium ion (Scheme 6). Scheme 6. Synthesis of Complex 6

Also, the activation of the sp3 C−H bond of the silyl group on the amido ligand N(SiMe3)2 followed by insertion of the imino CN bond to the RE−C bond was observed. After this work, we have studied the reactions of sterically bulkier 3-(2,6iPr2PhNCH)C8H4NH with rare-earth-metal amides, but unfortunately, attempts to isolate the corresponding rareearth-metal complexes failed, which may be due to steric reasons. A possible reaction pathway for the formation of complexes 5 is proposed (Scheme 7). Interaction of the arylimino-

Figure 1. ORTEP diagram of representative molecular structure of complexes 1a and 1b. Thermal ellipsoids are set at 30% probability. Hydrogen atoms are omitted for clarity.

Scheme 7. Proposed Pathway for the Formation of 5 1, it is found that the Ho−C1 bond lengths, 2.551(5) and 2.652(5) Å, and the Er−C1 bond lengths, 2.538 (3) and 2.621(3) Å, are close to those of the Y−C1 bond lengths of 2.551(8) and 2.665(8) Å and the Yb−C1 bond lengths of 2.506(12) and 2.654(10) Å,19 which is consistent with their ionic radii (Ho3+ ≈ Y3+ > Er3+ > Yb3+). However, Er−C1 bond lengths of complex 1b are significantly longer than the bond Table 1. Selected Bond Length (Å) and Bond Angle (deg) of Complexes 1a and 1b

RE1−N1 RE1−N3 RE2−N2 RE2−N5 RE2−N7 RE−Nav RE1−C1 RE2−C1 RE1−O1 C9−N2 C35−N6 C22−N4 RE1−C1−RE2 N5−RE2−N7

functionalized indoles with rare-earth-metal amides produced the intermediate A via silylamine elimination. The ensuing activation of the sp3 C−H bond of the H−CH2Me2SiNSiMe3 unit of A produced a four-membered-ring intermediate B,21−23 which then reacted with the imino CN double bond to form a new anilido-ligated intermediate C. The reaction of C with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 by transferring an amido N(SiMe3)2 followed by reassembly afforded the intermediate D (in the case of yttrium, complex 6 was isolated) with the release of rare-earth-metal chloride [(Me3Si)2N]2RECl(THF)x. D

Ho (1a)

Er (1b)

2.214(4) 2.342(4) 2.395(4) 2.298(5) 2.225(4) 2.294(5) 2.652(5) 2.551(5) 2.373(4) 1.319(6) 1.278(7) 1.299(7) 94.86(15) 120.52(17)

2.201(2) 2.321(3) 2.377(3) 2.277(3) 2.225(2) 2.280(3) 2.621(3) 2.538(3) 2.346(2) 1.303(4) 1.288(4) 1.289(4) 94.49(10) 120.16(10)

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Organometallics lengths of Er1−C(sp2), 2.457(3) and 2.466(4) Å, of carbon σbonded indolyl supported rare-earth-metal alkyl complex L2ErCH2SiMe3 (L = 1-Me-3-(2,6-iPr2C6H3NCH)C8H5N),18 which might be due to the bridging μ2-η1:η1 mode.

group. For example, the Y1−N1 bond length is 2.381(3) Å in 2a, which is longer than the Y1−N2 bond length of 2.222(3) Å and the Y1−N3 bond length of 2.205(3) Å, maybe due to the steric effect of the rigid indolyl backbone and the bridged bonding modes. The average RE−Nav bond lengths of 2.326(3) Å in 2b, 2.275(4) Å in 2c, 2.269(3) Å in 2a, and 2.233(8) Å in 2d are in good agreement with the corresponding sequence of their ionic radii. The Sm−Nav bond length of 2.326(3) Å is comparable with 2.312(4) Å of L2SmN(TMS)2 (L = −OMeC6H4COC{C(NCHCHNiPr)}).24 However, the average Yb− Nav bond lengths, ranging from 2.241(4) to 2.233(8) Å, in 2d, 3, and 4 are slightly shorter than those in the average values of bis(β-diketiminate) ytterbium borohydrides,25 2.282(4) and 2.302(3) Å, due to the different coordination environments. A similar phenomenon is also observed with regard to bis(βdiketiminate) yttrium complexes, of 2.340(4) and 2.337(4) Å.25 The C20−C9 or C23−C9 bond lengths from 1.555(6) to 1.543(11) Å and C9−N2 bond lengths from 1.475(5) to 1.464(4) Å for complexes 2, 3, and 4 are all consistent with single bonds, demonstrating the sp3 C−H bond activation of the N(SiMe3)2 group followed by a C−C bond coupling reaction. The 1H NMR spectrum of complex 2a showed the disappearance of the characteristic sharp imine resonance of NCH at 8.63 ppm,26 and instead the appearance of the doublet proton resonances of NCHCH2 at 4.94 ppm (d, J = 11.7 Hz), which is similar to the proton resonances at 5.0 ppm of an amine group formed by an alkyl insertion to the imine group in our previous works.17a The corresponding 13C NMR spectrum showed a resonance at 51.3 ppm. Thus, the 1H (or 13 C) NMR spectra for complex 2a further confirmed the formation of the new C−C bond. X-ray analyses revealed (Figure 5) that complexes 5 were centrosymmetrical isostuctural rare-earth-metal complexes and each of the rare-earth-metal centers has four coordination numbers coordinated by four different nitrogen atoms, an indolyl unit, an aniline group, a N(TMS)2 species, and a N(CH2Me2Si)(SiMe3) species. As shown in Table 3, the usual lanthanide contraction moving from Dy3+ to Yb3+ is clearly reflected by the average Ln−N bond lengths of 2.288(4) Å in 5a, 2.267(3) Å in 5b, and 2.265(4) Å in 5c. The Dy1−N2 (aniline) bond length of 2.323(4) Å found in complex 5a is longer than that of Dy1−N2 (anilido), 2.223(4) Å, found in complex 2c, which could be attributed to the different types of Dy−N bond, and the same phenomenon is also observed in complexes 6 (Y1−N2 2.319(3) Å) and 2a (2.222(3) Å). The normal C−C bond lengths from 1.509(6) to 1.532(5) Å can be found in complexes 5 and 6, which is consistent with those in complexes 2, 3, and 4. The resonance of the proton of NCHCH2 in the 1H NMR spectrum of complex 6 appears at about 5.04 ppm, which is similar to that found in complex 2a. As listed in Table 1, the bond lengths of C9−N2, 1.319(6) Å, C35−N6, 1.278(7) Å, and C22−N4, 1.299(7) Å, for complex 1b reflect normal CN bonds, while the bond length of C9− N2, 1.503(4) Å, found in complex 5b reveals C−N single-bond character formed by tandem sp3 C−H bond activation and C N bond insertion to the RE−C bond.

Figure 2. ORTEP diagram of representative molecular structure of complexes 2. Thermal ellipsoids are set at 30% probability. Hydrogen atoms are omitted for clarity.

Figure 3. ORTEP diagram of molecular structure of complex 3. Thermal ellipsoids are set at 30% probability. Hydrogen atoms are omitted for clarity.

Figure 4. ORTEP diagram of molecular structure of complex 4. Thermal ellipsoids are set at 30% probability. Hydrogen atoms are omitted for clarity.

X-ray crystallography (Figures 2−4) revealed that complexes 2a−d are isostructural heterometallic rare-earth-metal complexes with a central symmetry. Each of the rare-earth metals adopts a five-coordinated distorted trigonal bipyramidal geometry, which contains a tridentate indolyl ligand, a THF molecule, and a chloride. The lithium and rare-earth-metal ions are bridged by a chloride atom. The rare-earth-metal ion and two “N” atoms of the tridentate ligand form a six-membered ring. From Table 2, it is found that RE−N bond lengths from the rare-earth metal to the indolyl backbone are generally longer than those of the metal to the N(SiMe3)2 and anilido

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CONCLUSIONS In summary, the reactivities of various 3-imino-functionalized indoles with rare-earth-metal amides were studied with findings of unexpected substituent effects on the reaction pathways, which led to formation of different rare-earth-metal complexes. The interaction of the 3-(tert-butylimino)indole with rareE

DOI: 10.1021/acs.organomet.6b00221 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Table 2. Selected Bond Length (Å) and Bond Angle (deg) of Complexes 2, 3, and 4 RE1−N1 RE1−N2 RE1−N3 RE1−Nav C20−C9 or C23−C9 C9−N2 N3−RE1−N2 N1−RE1−Cl1

Y (2a)

Sm (2b)

Dy (2c)

Yb (2d)

Yb (3)

Yb (4)

2.381(3) 2.222(3) 2.205(3) 2.269(3) 1.544(5) 1.465(5) 105.07(12) 81.26(8)

2.456(3) 2.263(2) 2.260(3) 2.326(3) 1.554(4) 1.464(4) 103.83(9) 79.81(6)

2.392(4) 2.223(4) 2.212(4) 2.275(4) 1.555(6) 1.465(5) 104.60(13) 81.20(9)

2.342(7) 2.188(8) 2.171(7) 2.233(8) 1.553(12) 1.473(11) 105.6(3) 81.91(19)

2.347(3) 2.204(3) 2.173(4) 2.241(4) 1.548(5) 1.475(5) 106.55(13) 81.57(8)

2.340(8) 2.188(7) 2.182(8) 2.236(8) 1.543(11) 1.466(10) 105.8(3) 82.17(18)

mode. The interactions of 3-substituted arylimino-functionalized indoles with rare-earth-metal amides showed a completely different chemistry from those of reactions of 3(tert-butylimino)indole with rare-earth-metal amides, in that dinuclear or hexanuclear complexes were produced depending on substituents on the aryl group. The corresponding dinuclear complexes were isolated when the phenyl-, 2-methylphenyl-, or 4-methylphenyl-imino-functionalized indoles were treated with rare-earth-metal amides via indole deprotonation, activation of the sp3 C−H bond of the bis(trimethylsilyl)amide group, and then imino CN bond insertion to the RE−C bond, which resulted in a tripodal anionic moiety with the substituted anilido and amido site being coordinated to one metal center and the anionic indolyl ligand being coordinated to the other metal center. When the 4-(tert-butylphenylimino)indole was reacted with rare-earth-metal amides, heterometallic hexanuclear rare-earth-metal amides with tripodal anionic ligand were first produced via a sequence of indole deprotonation, activation of sp3 C−H bond of the bis(trimethylsilyl)amide group, and subsequent imino CN bond insertion to the RE− C bond to form the anilido moiety. The anilido group then abstracted a proton to form the dianionic ligated hexanuclear complexes. The above results, for the first time, disclosed that the substituents on 3-imino-functionalized indoles have a great influence on their reactivity patterns with rare-earth-metal amides, leading to different coordination modes of the ligands with the rare-earth-metal center.

Figure 5. ORTEP diagram of representative molecular structure of complexes 5. Thermal ellipsoids are set at 30% probability. Hydrogen atoms are omitted for clarity.

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EXPERIMENTAL SECTION

General Procedures. All manipulations of air- and moisturesensitive materials were performed under a dry argon atmosphere by standard Schlenk techniques or in a glovebox. All solvents (THF, nhexane, and toluene) were dried by refluxing over sodium/ benzophenone ketyl under argon and distilled prior to use unless otherwise noted. The imino-functionalized indolyl ligands L1−L5 and [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (RE = Sm, Y, Ho, Er, Dy, and Yb) were prepared according to known methods.27,28 IR spectra were recorded on a Shimadzu FTIR-8400s spectrometer (KBr pellet).

Figure 6. ORTEP diagram of molecular structure of complex 6. Thermal ellipsoids are set at 15% probability.

earth-metal amides afforded tetranuclear rare-earth-metal complexes through indole nitrogen deprotonation and 2-indole sp2 C−H bond activation, producing a unique 1,2-indolyl dianion bonded with rare-earth-metal ions in η1:(μ2-η1:η1)

Table 3. Selected Bond Length (Å) and Bond Angle (deg) of Complexes 5 and 6

RE1−N1 RE1−N2 RE1−N3 RE1−N4 RE1−Nav C25−C9 C9−N2 N3−RE1−N2 N2−RE1−N1

Dy (5a)

Ho (5b)

Er (5c)

Y (6)

2.348(4) 2.323(4) 2.226(4) 2.256(4) 2.288(4) 1.509(6) 1.488(6) 101.38(14) 89.64(13)

2.324(3) 2.308(3) 2.200(3) 2.239(3) 2.267(3) 1.517(5) 1.503(4) 103.08(11) 89.60(11)

2.319(4) 2.303(4) 2.197(4) 2.243(4) 2.265(4) 1.531(6) 1.487(6) 103.49(15) 90.72(14)

2.332(3) 2.319(3) 2.222(3) 2.245(3) 2.279(3) 1.532(5) 1.499(4) 102.97(11) 88.57(11)

F

DOI: 10.1021/acs.organomet.6b00221 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

pellet, cm−1): 1614 (s), 1585 (m), 1483 (w), 1456 (w), 1367 (w), 1247 (s), 1103 (w), 802 (w), 746 (s), 692 m). Synthesis of {3-[PhNCH(CH2SiMe2)N(SiMe3)]C8H5NDy(THF)(μ2-Cl)Li(THF)2}2 (2c). This complex was isolated as white crystals in 35% yield by treatment of [(Me3Si)2N]3Dy(μ-Cl)Li(THF)3 (1.21 g, 1.34 mmol) with ligand (0.30 g, 1.34 mmol) following a procedure similar to that for the preparation of 2a. Anal. Calcd for C66H104Cl2Li2N6O6Si4Dy2·C6H14: C, 51.30; H, 7.05; N, 4.98. Found: C, 51.67; H, 7.26; N, 5.02. IR (KBr pellet, cm−1): 1618 (s), 1587 (m), 1527 (w), 1485 (w), 1425 (w), 1246 (s), 1103 (w), 852 (m), 802 (w), 744 (s), 694 (s). Synthesis of {3-[PhNCH(CH2SiMe2)N(SiMe3)]C8H5NYb(THF)(μ2-Cl)Li(THF)2}2 (2d). This complex was isolated as red crystals in 44% yield by treatment of [(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 (1.23 g, 1.35 mmol) with ligand (0.30 g, 1.35 mmol) following a procedure similar to that for the preparation of 2a. Anal. Calcd for C66H104Cl2Li2N6O6Si4Yb2·2C6H14: C, 52.24; H, 7.42; N, 4.69. Found: C, 52.47; H, 7.82; N, 4.60. IR (KBr pellet, cm−1): 1612 (s), 1570 (m), 1483 (m), 1444 (w), 1365 (w), 1247 (s), 1124 (m), 970 (m), 902 (w), 854 (w), 748 (s), 692 (s), 499 (w). Synthesis of {3-[(2-Me-Ph)NCH(CH 2 SiMe 2 )N(SiMe 3 )]C8H5NYb(THF)(μ2-Cl)Li(THF)2}2 (3). This complex was isolated as red block crystals in 43% yield by treatment of [(Me3Si)2N]3Yb(μCl)Li(THF)3 (1.38 g, 1.51 mmol) with ligand (3-(2-MeC6H4N CH)C8H5NH) (0.35 g, 1.51 mmol) following a procedure similar to that for the preparation of 2a. Anal. Calcd for C68H108Cl2Li2N6O6Si4Yb2: C, 49.53; H, 6.60; N, 5.10. Found: C, 49.77; H, 6.95; N, 5.12. IR (KBr pellet, cm−1): 2953 (w), 2360 (w), 1618 (m), 1517 (s), 1456 (w), 1400 (w), 1251 (s), 1182 (w), 933 (m), 839 (m), 740 (m). Synthesis of {3-[(4-Me-Ph)NCH(CH 2 SiMe 2 )N(SiMe 3 )]C8H5NYb(THF)(μ2-Cl)Li(THF)2}2 (4). This complex was isolated as red crystals in 47% yield by treatment of [(Me3Si)2N]3Yb(μCl)Li(THF)3 (1.07 g, 1.17 mmol) with ligand (3-(4-MeC6H4N CH)C8H5NH) (0.27 g, 1.17 mmol) following a procedure similar to that for the preparation of 2a. Anal. Calcd for C34H54ClLiN3O3Si2Yb: C, 49.53; H, 6.60; N, 5.10. Found: C, 49.93; H, 7.03; N, 5.10. IR (KBr pellet, cm−1): 3394 (w), 2360 (w), 1618 (m), 1589 (m), 1498 (s), 1431 (s), 1247 (s), 1111 (m), 750 (s), 584 (m), 538 (m). Synthesis of {3-[(4-tBu-Ph)NHCH(CH 2 SiMe 2 )N(SiMe 3 )]C8H5NDyN(SiMe3)2}6 (5a). To a toluene (10.0 mL) solution of ligand (3-(4-tBuC6H4NCH)C8H5NH) (0.35 g, 1.28 mmol) was added a toluene (10.0 mL) solution of [(Me3Si)2N]3Dy(μ-Cl)Li(THF)3 (1.16 g, 1.28 mmol) at room temperature. The mixture was then stirred at reflux for 12 h. The solvent was removed under reduced pressure, and n-hexane was added to extract the product. White crystals were obtained after standing the extract at room temperature for several days (0.50 g, 52% yield). Anal. Calcd for C186H330Dy6N24Si24·C6H14: C, 49.72; H, 7.48; N, 7.25. Found: C, 49.74; H, 7.31; N, 7.03. IR (KBr pellet, cm−1): 2956 (m), 1597 (w), 1514 (s), 1456(w), 1363 (w), 1247 (s), 1197 (s), 939 (s), 831 (w), 742 (m), 680 (w). Synthesis of {3-[(4-tBu-Ph)NHCH(CH 2 SiMe 2 )N(SiMe 3 )]C8H5NHoN(SiMe3)2}6 (5b). This complex was isolated as orange crystals in 51% yield by treatment of [(Me3Si)2N]3Ho(μ-Cl)Li(THF)3 (1.13 g, 1.25 mmol) with ligand (0.34 g, 1.25 mmol) following a procedure similar to that for the preparation of 5a. Anal. Calcd for C186H330Ho6N24Si24.C6H14: C, 49.57; H, 7.45; N, 7.23. Found: C, 49.78; H, 7.32; N, 7.01. IR (KBr pellet, cm−1): 2956 (m), 1610 (w), 1514 (s), 1433(w), 1363 (w), 1247 (s), 1197 (s), 1033 (w), 939 (s), 831 (w), 742 (m), 678 (w), 551 (w). Synthesis of {3-[(4-tBu-Ph)NHCH(CH 2 SiMe 2 )N(SiMe 3 )]C8H5NErN(SiMe3)2}6 (5c). This complex was isolated as pink crystals in 48% yield by treatment of [(Me3Si)2N]3Er(μ-Cl)Li(THF)3 (1.07 g, 1.18 mmol) with ligand (0.33 g, 1.18 mmol) following a procedure similar to that for the preparation of 5a. Anal. Calcd for C186H330Er6N24Si24·C6H14: C, 49.42; H, 7.43; N, 7.20. Found: C, 49.74; H, 7.31; N, 7.03. IR (KBr pellet, cm−1): 2956 (m), 1610 (w), 1514 (s), 1444(w), 1247 (s), 1197 (s), 1033 (w), 939 (s), 831 (m), 742 (m), 680 (w), 551 (w).

Elemental analyses data were obtained on a PerkinElmer 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) in THF-d8 for rare-earth-metal complexes and in CDCl3 for organic compounds. Chemical shifts (δ) are reported in ppm. J values are reported in Hz. X-ray Crystallographic Studies. A suitable crystal of each rareearth-metal complex was mounted in a sealed capillary. Diffraction was performed on a Bruker SMART CCD area detector diffractometer using graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å). An empirical absorption correction was applied using the SADABS program.29 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.30 All hydrogen atoms were refined using a riding model. Synthesis of {[η1:(μ2-η1:η1):η1-3-(tBuNCH)C8H5N]Ho2(μ2Cl) 2(THF)[N(SiMe 3)2 ](η 1:η 1-[μ-η 5:η 2-3-(tBuNCH)C8H5N] 2Li)}2 (1a). To a solution of (3-(tBu-NCH)C8H5NH) (0.44 g, 2.20 mmol) in toluene (10.0 mL) was added a solution of [(Me3Si)2N]3Ho(μ-Cl)Li(THF)3 (1.33 g, 1.47 mmol) in toluene (20.0 mL) at room temperature. After the reaction mixture was refluxed for 12 h, the solvent was evaporated under reduced pressure, and n-hexane was added to extract the product. Pale yellow crystals were obtained after standing the extract at 0 °C for several days (0.45 g, 50%). Anal. Calcd for C49H70Cl2LiN7OSi2Ho2·2C6H14: C, 51.98; H, 7.01; N, 6.96. Found: C, 52.41; H, 7.13; N, 6.48. IR (KBr pellet, cm−1): 1633 (s), 1519 (w), 1446 (m), 1392 (s), 1296 (w), 1244 (s), 1126 (m), 1083 (m), 788 (m), 759 (w), 640 (s), 601 (w). Synthesis of {[η1:(μ2-η1:η1):η1-3-(tBuNCH)C8H5N]Er2(μ2Cl) 2(THF)[N(SiMe 3)2 ](η 1:η 1-[μ-η 5:η 2-3-(tBuNCH)C8H5N] 2Li)}2 (1b). This complex was isolated as pink crystals in 54% yield by treatment of [(Me3Si)2N]3Er(μ-Cl)Li(THF)3 (1.28 g, 1.41 mmol) with ligand (3-(tBu-NCH)C8H5NH) (0.42 g, 2.11 mmol) following a procedure similar to that for the preparation of 1a. Anal. Calcd for C49H70Cl2LiN7OSi2Er2·2C6H14: C, 51.81; H, 6.99; N, 6.93. Found: C, 52.09; H, 6.74; N, 6.59. IR (KBr pellet, cm−1): 2966 (m), 1625 (s), 1529 (s), 1456 (s), 1354 (w), 1236 (s), 1138 (m), 1116 (m), 1064 (w), 1010 (m), 933 (w), 829 (w), 742 (m), 574 (w). Synthesis of {3-[PhNCH(CH2SiMe2)N(SiMe3)]C8H5NY(THF)(μ2Cl)Li(THF)2}2 (2a). To a solution of ligand (3-(PhNCH)C8H5NH) (0.36 g, 1.62 mmol) in toluene (10.0 mL) was added a solution of [(Me3Si)2N]3Y(μ-Cl)Li(THF)3 (1.34 g, 1.62 mmol) in toluene (10.0 mL) at room temperature. The mixture was then stirred at reflux for 12 h, and the color of the solution gradually changed from colorless to pale yellow. The solvent was removed under reduced pressure, and the mixtures of n-hexane with THF were added to extract the product. White rectangle crystals were obtained after standing the extract at 0 °C for several days (0.48 g, 41% yield). 1H NMR (300 MHz, THF-d8, ppm): δ 7.54 (d, 1H, J = 7.8 Hz), 7.35 (s, 1H), 7.29 (d, 1H, J = 6.6 Hz), 6.87−6.77 (m, 5H), 6.17−6.12 (m, 2H), 4.94 (d, 1H, J = 11.7 Hz), 3.60−3.55 (m, 12H), 1.75−1.69 (m, 12H), 0.05 (s, 15H), −1.04 (s, 2H). 13C NMR (75 MHz, THF-d8, ppm): δ 156.4, 146.4, 135.4, 131.2, 128.8, 125.0, 119.2, 117.9, 117.7, 116.5, 112.7, 107.1, 67.2, 51.3, 25.1, 5.0, 2.8, 2.7, 1.1. Anal. Calcd for C66H104Cl2Li2N6O6Si4Y2: C, 54.57; H, 7.22; N, 5.79. Found: C, 54.95; H, 7.22; N, 5.90. IR (KBr pellet, cm−1): 1614 (w), 1587 (m), 1485 (s), 1456 (m), 1427 (w), 1336 (w), 1246 (s), 1197 (w), 1103 (w), 744 (s), 694 (m). Synthesis of {3-[PhNCH(CH2SiMe2)N(SiMe3)]C8H5NSm(THF)(μ2-Cl)Li(THF)2}2 (2b). This complex was isolated as yellow rectangle crystals in 36% yield by treatment of [(Me3Si)2N]3Sm(μ-Cl)Li(THF)3 (1.67 g, 1.88 mmol) with ligand (0.41 g, 1.88 mmol) following a procedure similar to that for the preparation of 2a. 1H NMR (300 MHz, THF-d8, ppm): δ 11.23 (s, 1H), 9.89 (d, 1H, J = 7.5 Hz), 8.87 (s, 1H), 8.20 (d, 1H, J = 7.5 Hz), 7.30−7.16 (m, 5H), 7.03−6.90 (m, 2H), 3.67−3.58 (m, 12H), 1.77−1.72 (m, 12H), 0.04 (s, 2H), −1.08 (s, 15H). 13C NMR (75 MHz, THF-d8, ppm): δ 156.3, 155.6, 148.5, 147.0, 129.1, 126.2, 123.5, 121.8, 121.4, 121.2, 119.5, 118.4, 115.2, 67.2, 25.1, 3.5, 2.4. Anal. Calcd for C66H104Cl2Li2N6O6Si4Sm2: C, 50.32; H, 6.65; N, 5.33. Found: C, 50.22; H, 6.96; N, 5.37. IR (KBr G

DOI: 10.1021/acs.organomet.6b00221 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Synthesis of {3-[(4-tBu-Ph)NCH(CH 2 SiMe 2 )N(SiMe 3 )]C8H5NYN(SiMe3)2Li(THF) }6 (6). This complex was isolated as white crystals in 54% yield by treatment of [(Me3Si)2N]3Y(μCl)Li(THF)3 (1.27 g, 1.53 mmol) with ligand (0.42 g, 1.53 mmol) following a procedure similar to that for the preparation of 5a, except for a refluxing time of 3 h in toluene. 1H NMR (300 MHz, THF-d8, ppm): δ 8.50 (s, 1H), 7.88 (s, 1H), 7.23−7.14 (m, 4H), 6.92 (s, 1H), 6.70 (d, 2H, J = 8.1 Hz), 5.04 (s, 1H), 3.58 (s, 4H), 1.46 (s, 4H), 1.24 (s, 9H), 0.88(s, 2H), 0.27 (s, 18H), 0.10 (d, 15H, J = 8.4 Hz). 13C NMR (75 MHz, THF-d8, ppm): δ 146.7, 138.1, 128.8, 126.0, 121.6, 120.7, 120.1, 119.7, 118.9, 114.5, 113.3, 111.7, 67.2, 48.5, 31.8, 25.1, 2.5, 2.4, 1.5. Anal. Calcd for C210H372Li6N24O6Si24Y6: C, 55.09; H, 8.19; N, 7.34. Found: C, 54.94; H, 7.85; N, 7.68. IR (KBr pellet, cm−1): 2954 (m), 1612 (w), 1517 (s), 1435(w), 1363 (w), 1249 (s), 1192 (s), 933 (s), 839 (m), 742 (m), 682 (w).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00221. Molecular structures of complexes 1−6; 1H and 13C NMR spectra of complexes 2a, 2b, and 6 (PDF) Crystallographic data of complexes 1−6 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (X. Zhu). *E-mail: [email protected] (S. Wang). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (21202002, 21372010, and 21432001), the National Basic Research Program of China (2012CB821600), Anhui Province (KJ2012A138), and the Special and Excellent Research Fund of Anhui Normal University.

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REFERENCES

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DOI: 10.1021/acs.organomet.6b00221 Organometallics XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.organomet.6b00221 Organometallics XXXX, XXX, XXX−XXX