Rare-earth metal complexes having an unusual indolyl-1,2-dianion through C-H activation with a novel η1:(μ2- η1:η1) bonding with metals

Article abstract of DOI:10.1039/c2cc36045d

Studies on the reactions of 3-(tert-butyliminomethine)indole or 3-(tert-butylaminomethylene)indole with rare-earth metal amides [(Me ₃Si)₂N]₃RE^III(μ-Cl)Li(THF) ₃ (RE = Y, Yb) led to the discovery of different reactivity patterns with isolation of novel rare-earth metal complexes having a unique indolyl-1,2-dianion in a novel η¹:(μ₂- η¹:η¹) bonding mode through C-H activation. The Royal Society of Chemistry.

Full text of DOI:10.1039/c2cc36045d

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Rare-earth metal complexes having an unusual indolyl-1,2-dianion
through C–H activation with a novel g1:(l2–g1:g1) bonding with metalsw
Xiancui Zhu,a Shuangliu Zhou,a Shaowu Wang,*ab Yun Wei,a Lijun Zhang,a Fenhua Wang,a
Shaoyin Wangac and Zhijun Fenga
Received 21st August 2012, Accepted 1st September 2012
DOI: 10.1039/c2cc36045d
Studies on the reactions of 3-(tert-butyliminomethine)indole or
3-(tert-butylaminomethylene)indole with rare-earth metal amides
[(Me3Si)2N]3REIII(l-Cl)Li(THF)3 (RE = Y, Yb) led to the discovery
of different reactivity patterns with isolation of novel rare-earth metal
complexes having a unique indolyl-1,2-dianion in a novel g1:(l2–g1:g1)
Fig. 1 The reported bonding mode of an indolyl ligand with transi-
bonding mode through C–H activation.
tion metals.
may be potentially applicable in decomposition of nitrogen-
Functionalization of heterocyclic compounds through C–H
containing impurities from fuels.4 (4) C–H bond activation
bond cleavage is a concerted research effort not only for the
initiated by well-defined rare-earth metal amido complexes that
reasons that the heterocyclic frameworks have been widely
is relatively less documented.5 (5) Very recently, rare-earth metal
accepted as a pivotal structure in numerous natural products
imido complexes that initiated C–H activation were reported to
and pharmaceutical agents, but also for the reasons that the
display a new kind of reactivity of rare-earth metal complexes.6
C–H and C–N bond activation may be important processes in
To the best of our knowledge, the only reported mono-anion
the removal of heterocyclic compounds-containing impurities
from fuels.1 The C–H bond activation initiated by rare-earth
indolyl ligands have been found to bind with transition metal in an
Z1-mode through the nitrogen atom,7a an Z3-fashion via the
metal complexes can be classified as the following. (1) Rare-earth
nitrogen atom and the fused carbons of the indolyl ring,7a an
metal aluminum mixed metal complexes initiated C–H activation
Z5-manner through the five-membered heterocyclic ring,7b an
leading to isolation of the novel methylene or methine bridged
Z6-mode through the benzo ring,7c and a m2–Z1:Z1 bonding mode
lanthanide–aluminum metal clusters or aluminum-free rare-earth
with iron7d (see Fig. 1). Rare-earth metal complexes supported
by functionalized indolyl ligands displayed activities in olefin
polymerization in the presence of aluminum alkyl cocatalyst.8
All of the reported indolyl complexes to date incorporated indolyl
mono-anions, the indolyl-1,2-dianion and its bonding mode with
transition metals remain to be reported (Fig. 3).
metal clusters.2 (2) Reactions of rare-earth metal alkyls (for
example [RE(CH2SiMe3)3(thf)x] or hydrides with suitable ligands
afforded new kinds of the C–H bond activation rare-earth metal
complexes.3 (3) Reactions of structurally well-defined cyclopenta-
dienyl or cyclopentadienyl-free ligands supported rare-earth metal
alkyl complexes with aromatic compounds produced the sp2 or sp3
C–H bond activation complexes, of these, reactions of chelating
ferrocene–diamido rare-earth metal complexes with N-heterocyclic
compounds are noticeable, that led to not only C–H bond
activation, but also to the C–C coupling and ring-opening which
Herein, we will report the first example of novel tetranuclear
rare-earth metal complexes incorporating a unique indolyl-
1,2-dianion ligand having an unusual Z1:(m2–Z1:Z1) bonding
mode with metals through imino-directed C–H bond activation
initiated by rare-earth metal amido complexes (Fig. 2 and 3).
Reactions of [(Me3Si)2N]3REIII(m-Cl)Li(THF)3 (RE = Y,
Yb) with 1.5 equivalents of 3-(tert-butyliminomethine)indole
(3-(t-Bu–NQCH)C8H5NH) in toluene at 110 1C produced
the tetranuclear complexes {[Z1:(m2–Z1:Z1):Z1-3-(t-BuNQCH)-
C8H4N]REIII2(m2-Cl)2(THF)[N(SiMe3)2](Z1:Z1-[m–Z5:Z2-3-(t-Bu-
NQCH)C8H5N]2Li)}2 (RE = Y(1), Yb (2)) (Scheme 1, route 1,
Fig. 2 and 3) having a rare indolyl-1,2-dianion ligand in an
unusual Z1:(m2–Z1:Z1) bonding mode with rare-earth metals in
good yields. The complexes were characterized by elemental
a Anhui Laboratory of Molecule-Based Materials, Institute of Organic
Chemistry, School of Chemistry and Materials Science,
Anhui Normal University, Wuhu, Anhui 241000, P. R. China.
E-mail: swwang@mail.ahnu.edu.cn; Fax: +86-553-3883517;
Tel: +86-553-5910015
b State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, Shanghai 200032,
P. R. China. E-mail: swwang@mail.ahnu.edu.cn
c Department of Chemistry, Wannan Medical College, Wuhu,
Anhui 241003, P. R. China
w Electronic supplementary information (ESI) available: Experimental
details, characterization data for new compounds, scheme for prepara-
tion of 4 and 5, figures for structures of complexes 1–7. CCDC
842358–842362 (1–5), 896822 (6), and 896821 (7). For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
c2cc36045d
1
analyses, IR, H and 13C NMR spectroscopy as well as X-ray
analyses. They are air and moisture sensitive, but stable in an
inert atmosphere for months. They are soluble in polar solvents
and toluene.
c
12020 Chem. Commun., 2012, 48, 12020–12022
This journal is The Royal Society of Chemistry 2012

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½Ap02YCH2SiMe3ðthfÞꢀ ðAp02 ¼ 2; 6 ꢁ ðdiisopropylphenylÞ[6-(2,6-
dimethylphenyl)pyridin-2-yl]amido (2.342(5) A),11 [[t-BuC6H3-
(CHQN)C6H3-i-Pr2]2YCH2SiMe2Ph] (2.384(2) A),11 [O{(CH2)2-
C9H6}2YCH2SiMe3] (2.376(8), 2.35 (1) A),11 [Ln(CH2SiMe3)3-
(NHC)] (2.363(2), 2.355(2), 2.345(2) A, NHC = 1,3-bis(2,6-diiso-
propylphenyl)imidazol-2-ylidene),11 and those found in s-boryl
ligand supported rare-earth metal alkyls,12 the RE–C(1) distances
found in 1 and 2 can still be comparable to those of Ln–C(1)
(carbene carbon) distances,13 and the Y–C distances (av. 2.61 A)
in bridging methyl ligands in eight-coordinate [(1,3-Me2C5H3)2Y-
(m-Me)]2.14 Comparing bond distances of Li(1)–N(4) (2.010(2) A),
Li(1)–C(22) (2.530(2) A), Li(1)–C(15) (2.550(2) A), Li(1)–C(16)
2.560(2) A), Li(1)–C(21) (2.600(2) A), and Li(1)–N(6) (1.990(2)
A), Li(1)–C(35) (2.610(2) A), Li(1)–C(28) (2.760(2) A), Li(1)–C(29)
(2.740(2) A), Li(1)–C(34) (2.670(2) A) with those of Li to C5
ring distances found in CpLi(solvent)x and IndLi(solvent)x
(here ind = indenyl),15 the bonding between lithium and
indolyl ligands can be best described as Z5:Z2 mode.
Fig. 2 Representative molecular structure of complexes 1 and 2.
When the 3-(tert-butyliminomethine)indole 3-(t-BuNQCH)-
C8H5NH was reacted with excess lithium amide LiN(SiMe3)2
(2 equivalents), the dimeric lithium product {Z4:Z2:Z1-3-
(t-BuNQCH)C8H5NLi2[N(SiMe3)2]}2 (3) (Scheme 1, route 2,
Fig. S3 (ESIw)) was isolated and characterized, no C–H bond
activation product was observed. This result suggested that the
formation of the unique indolyl 1,2-dianion is not due to the
decomposition of the [(Me3Si)2N]3REIII(m-Cl)Li(THF)3 to
LiN(SiMe3)2, which is then responsible for the C–H bond
cleavage, but the rare-earth metal amides [(Me3Si)2N]3REIII-
(m-Cl)Li(THF)3 would be responsible for the C–H bond activa-
tion. The bonding of the ligand 3-(t-Bu–NQCH)C8H5N with
metal found in 3 also represents the first example of (Z4:Z2:Z1)
bonding mode of indolyl ligands to be reported by comparing the
lithium to indolyl ring distances with those of Li to C5 ring
distances found in CpLi(solvent)x and IndLi(solvent)x.15
Fig. 3 The bonding of the unique indolyl 1,2-dianion with metals in
complexes 1 and 2.
On the basis of these results, the formation of the unique indolyl-
1,2-dianion may first go through silylamine elimination to give the
indole deprotonated intermediate, which then coordinated to
[(Me3Si)2N]3REIII(m-Cl)Li(THF)3 with subsequent C–H activation/
cyclometallation affording the intermediate with the unique indolyl-
1,2-dianion having unusual Z1:(m2–Z1:Z1) bonding with metals,
further reactions with rare-earth metal amides followed by
reassembly produced the final products (see Scheme S1, ESIw).
Further experiments reveal that reactions of rare-earth
metal amides [(Me3Si)2N]3REIII(m-Cl)Li(THF)3 with 3-(tert-
butylaminomethylene)indole 3-(t-BuNHCH2)C8H5NH pro-
duced, after workup, the only indole deprotonated complexes
[m-{[Z1:Z1:Z1:Z1-3-(t-BuNHCH2)Ind]2Li}RE[N(SiMe3)2]2] (RE =
Y(4), Yb(5)), even the protons on the amino groups have
not been removed. No C–H bond activation was observed
(see Scheme S2 and Fig. S4 and S5 for the structures of
complexes 4 and 5 in ESIw), and the indolyl ligand bonded
with the rare-earth metal through nitrogen in an Z1 mode.
These results are completely different to those results indicated
in Scheme 1 (route 1), the results suggested that substituents
on the indolyl ring have a great influence on the reactivity of
the indoles with the rare-earth metal amides and the bonding
of the indolyl ligands with the rare-earth metals.
Scheme 1 Reactions of 3-(tert-butyliminomethine)indole with rare-
earth metal amides and lithium amide.
Solid state structural analyses revealed that complexes 1
and 2 are centrosymmetric dimeric clusters consisted of
four rare-earth metal ions and two lithium ions supported
by four imino-substituted indolyl monoanions coordinated to
rare-earth metals in an Z1 mode through an indolyl nitrogen
atom, two amido ligands N(SiMe3)2, and two unique imino-
substituted indolyl-1,2-dianions having a novel Z1:(m2-Z1:Z1)
bonding with metals as indicated in Fig. 3. The formation of
the unique indolyl 1,2-dianion clearly indicates that an sp2
C–H activation occurred.
The Y–C(1) bond lengths of 2.551(8) A and 2.665(8) A in
complex 1 are comparable to the Yb–C(1) bond lengths of
2.506(12) A and 2.654(10) A found in complex 2 taking into
account the ionic radii difference between the yttrium and
ytterbium ions.9 Although Ln–C(1) distances in complexes 1
and 2 are significantly longer than the values reported for
related compounds [Y(CH2SiMe3)3(THF)2] (2.427(19) A),10
Experiments for study on the reactivity of the complexes 1
and 2 with amidine (2,6-iPr2C6H3)NQCH–NH(2,6-iPr2C6H3)
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 12020–12022 12021

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G. K. Fukin, A. V. Cherkasov, A. S. Shavyrin, A. A. Trifonov,
L. Luconi, C. Bianchini, A. Meli and G. Giambastiani, Organo-
metallics, 2009, 28, 1227–1232; (c) B. Liu, D. M. Cui, J. Ma,
X. S. Chen and X. B. Jing, Chem.–Eur. J., 2007, 13, 834–845;
(d) Liu, Y. Yang, D. M. Cui, T. Tang, X. S. Chen and X. B. Jing,
Dalton Trans., 2007, 4252–4254; (e) D. Wang, D. M. Cui,
W. Miao, S. H. Li and B. T. Huang, Dalton Trans., 2007,
4576–4581; (f) J. Okuda, Dalton Trans., 2003, 2367–2378;
(g) W. Fegler, T. P. Spaniol and J. Okuda, Dalton Trans., 2010,
39, 6774–6779; (h) S. Arndt, T. P. Spaniol and J. Okuda, Eur. J.
Inorg. Chem., 2001, 73–75.
Scheme 2 Reactivity of complexes having indolyl-1,2-dianion.
4 (a) S. Arndt, B. R. Elvidge, P. M. Zeimentz, T. P. Spaniol and
J. Okuda, Organometallics, 2006, 25, 793–795; (b) K. C. Jantunen,
B. L. Scott, J. C. Gordon and J. L. Kiplinger, Organometallics, 2007,
26, 2777–2781; (c) K. L. Miller, C. T. Carver, B. N. Williams and
P. L. Diaconescu, Organometallics, 2010, 29, 2272–2281;
(d) P. L. Diaconescu, Acc. Chem. Res., 2010, 43, 1352–1363;
(e) S. Arndt, B. R. Elvidge, P. M. Zeimentz, T. P. Spaniol and
J. Okuda, Organometallics, 2006, 25, 793–795; (f) C. T. Carver and
P. L. Diaconescu, J. Am. Chem. Soc., 2008, 130, 7558–7559;
(g) C. T. Carver, D. Benitez, K. L. Miller, B. N. Williams,
E. Tkatchouk, W. A. Goddard, III and P. L. Diaconescu, J. Am.
Chem. Soc., 2009, 131, 10269–10278; (h) B. N. Williams, D. Benitez,
K. L. Miller, E. Tkatchouk, W. A. Goddard, III and P. L. Diaconescu,
J. Am. Chem. Soc., 2011, 133, 4680–4683; (i) K. L. Miller,
B. N. Williams, D. Benitez, C. T. Carver, K. R. Ogilby,
E. Tkatchouk, W. A. Goddard, III and P. L. Diaconescu, J. Am.
Chem. Soc., 2010, 132, 342–355; (j) W. Huang, S. I. Khan and
P. L. Diaconescu, J. Am. Chem. Soc., 2011, 133, 10410–10413.
5 (a) P. Cui, Y. F. Chen, G. Y. Li and W. Xia, Angew. Chem., Int.
afforded the complexes having an N-coordinated indolyl ligand
and the corresponding amidinate ligand [(2,6-iPr2C6H3N)2CH]ꢁ
(Scheme 2, Fig. S6 and S7 (ESIw)). The results indicated that a
carbon anion in the indolyl-1,2-dianion abstracted the proton
from the pro-ligand amidine, as a result, the indolyl-1,2-dianion
was transferred to a normal indolyl anion and the amidine was
transferred to an amidinate ligand to form the final complexes 6
and 7, indicating that the carbon anion is more reactive than the
indolyl nitrogen anion.
In summary, reactivity studies between 3-(tert-butylimino-
methine)indole or 3-(tert-butylaminomethylene)indole and rare-
earth metal amides have led to the discovery of different reaction
patterns with isolation of novel rare-earth metal complexes
{[Z1:(m2–Z1:Z1):Z1-3-(t-BuNQCH)C8H4N]REIII2(m2-Cl)2(THF)-
[N(SiMe3)2](Z1:Z1-[m–Z5:Z2-3-(t-BuNQCH)C8H5N]2Li}2 incor-
porating an unusual indolyl 1,2-dianion in a novel Z1:(m2-Z1:Z1)
bonding mode through C–H activation. The results suggested
that substituents on the indole ring have a great influence on
the reactivity patterns of indoles with rare-earth metal amides.
Further study on the reactivity of substituted indole with rare-
earth metal amides is now in progress.
Ed., 2008, 47, 9944–9947; (b) A. Otero, A. Lara-Sa
J. Fernandez-Baeza, C. Alonso-Moreno, I. Marquez-Segovia,
L. F. Sanchez-Barba, J. A. Castro-Osma and A. M. Rodrıguez,
´
nchez,
´
´
´
´
Dalton Trans., 2011, 40, 4687–4696; (c) F. Han, J. Zhang, W. Yi,
Z. Zhang, J. Yu, L. Weng and X. Zhou, Inorg. Chem., 2010, 49,
2793–2798.
6 E. L. Lu, J. X. Chu, Y. F. Chen, M. V. Borzovb and G. Y. Li,
Chem. Commun., 2011, 47, 743–745.
7 (a) W. J. Evans, J. C. Brady and J. W. Ziller, Inorg. Chem., 2002,
The authors thank the financial support for this work from
the National Natural Science Foundation of China (20832001,
20802001, 21072004, 21202002), the National Basic Research
Program of China (2012CB821604), and grants from the
Ministry of Education (20103424110001) and Anhui province
(TD200707, 11040606M36).
41, 3340–3346; (b) K. Muller-Buschbaum, Z. Anorg. Allg. Chem.,
¨
2004, 630, 895–899; (c) G. Zhu, J. M. Tanski, D. G. Churchill,
K. E. Janak and G. Parkin, J. Am. Chem. Soc., 2002, 124,
13658–13659; (d) W. Imhof, J. Organomet. Chem., 1997, 553,
31–43.
8 Y. Yang, Q. Y. Wang and D. M. Cui, J. Polym. Sci., Part A:
Polym. Chem., 2008, 5251–5261.
9 R. D. Schannon, Acta Crystallogr., Sect. A, 1976, 32, 751–767.
10 W. J. Evans, J. C. Brady and J. W. Ziller, J. Am. Chem. Soc., 2001,
123, 711–712.
Notes and references
11 (a) G. G. Skvortsov, G. K. Fukin, A. A. Trifonov, A. Noor,
C. Doring and R. Kempe, Organometallics, 2007, 26, 5770–5773;
´
1 (a) X. L. Hou, Z. Yang and H. N. C. Wong, in Progress in
Heterocyclic Chemistry, ed. G. W. Gribble and T. L. Gilchrist,
Pergamon, Oxford, U.K., 2003, vol. 15; (b) B. A. Keay and
P. W. Dibble, in Comprehensive Heterocyclic Chemistry II, ed.
C. W.Katrizky and E. F. V. Scriven, Elsevier, Oxford, U.K., 1997,
vol. 2; (c) R. J. Sundberg, Indoles, Academic, San Diego, 1996;
(d) E. Furimsky and F. E. Massoth, Catal. Rev. Sci. Eng., 2005, 47,
297–489, and references therein.
2 (a) J. Q. Hong, L. X. Zhang, X. Y. Yu, M. Li, Z. X. Zhang,
P. Z. Zheng, M. Nishiura, Z. M. Hou and X. G. Zhou, Chem.–Eur. J.,
2011, 17, 2130–2137; (b) A. Venugopal, I. Kamps, D. Bojer,
R. J. F. Berger, A. Mix, A. Willner, B. Neumann, H.-G. Stammler
and N. W. Mitzel, Dalton Trans., 2009, 5755–5765; (c) H. M. Dietrich,
(b) B. Liu, D. Cui, J. Ma, X. Chen and X. Jing, Chem.–Eur. J., 2006,
13, 834–845; (c) C. Qian, G. Zou and J. Sun, J. Chem. Soc., Dalton
Trans., 1999, 519–520; (d) G. A. Molander, E. D. Dowdy and
B. C. Noll, Organometallics, 1998, 17, 3754–3758; (e) W. Fegler,
T. P. Spaniol and J. Okuda, Dalton Trans., 2010, 39, 6774–6779.
12 L. M. A. Saleh, K. H. Birjkumar, A. V. Protchenko, A. D. Schwarz,
S. Aldridge, C. Jones, N. Kaltsoyannis and P. Mountford, J. Am.
Chem. Soc., 2011, 133, 3836–3839.
13 (a) P. L. Arnold, Z. R. Turner, R. Bellabarba and R. P. Tooze,
J. Am. Chem. Soc., 2011, 133, 11744–11756; (b) B. Wang,
D. Wang, D. Cui, W. Gao, T. Tang, X. Chen and X. Jing,
Organometallics, 2007, 26, 3167; (c) Z. R. Turner, R. Bellabarba,
R. P. Tooze and P. L. Arnold, J. Am. Chem. Soc., 2010, 132,
4050–4051, and references therein.
K. W. Tornroos and R. Anwander, J. Am. Chem. Soc., 2006, 128,
¨
¨
9298–9299; (d) H. M. Dietrich, H. Grove, K. W. Tornroos and
R. Anwander, J. Am. Chem. Soc., 2006, 128, 1458–1459; (e) W.-X.
Zhang, Z. Wang, M. Nishiura, Z. Xi and Z. Hou, J. Am. Chem. Soc.,
2011, 133, 5712–5715, and references therein.
14 W. J. Evans, D. K. Drummond, T. P. Hanusa and R. J. Doedens,
Organometallics, 1987, 6, 2279.
15 R. Michel, R. Herbst-Irmer and D. Stalke, Organometallics, 2011,
30, 4379–4386.
3 (a) W. Fegler, T. Saito, K. Mashima, T. P. Spaniol and J. Okuda,
J. Organomet. Chem., 2010, 695, 2794–2797; (b) D. M. Lyubov,
c
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