Rare-earth metal-mediated addition/cyclization of the 2-cyanobenzoamino anion

Article abstract of DOI:10.1039/c1dt10990a

Reaction of two equiv of [2-NCC₆H₄HNLi(THF)] _n (1) with Cp₂LnCl(THF) yields the heterobimetallic complexes Cp₂Ln[κ³-(4-NH(C₈N ₂H₄)(2-NHC₆H_4<

Full text of DOI:10.1039/c1dt10990a

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Rare-earth metal-mediated addition/cyclization of the 2-cyanobenzoamino
anion†
Jie Zhang,* Yanan Han, Zhenxia Chen and Xigeng Zhou*
Received 26th May 2011, Accepted 22nd July 2011
DOI: 10.1039/c1dt10990a
Reaction of two equiv of [2-NCC6H4HNLi(THF)]n (1)
Treatment of LiN(SiMe3)2 with one equiv of anthranilonitrile
in THF at room temperature gave the expected lithium amide [2-
NCC6H4HNLi(THF)]n (1) in almost quantitative yield, as shown
in Scheme 1. The reactions of 1 with another equiv of LiN(SiMe3)2
or excess of LiN(SiMe3)2 with anthranilonitrile only afforded 1.
No further insertion of LiN(SiMe3)2 into the C N triple bond of
the residual cyano group of 1 was observed during these reactions.
This is significantly different from those found in the reaction of
LiN(SiMe3)2 with benzonitrile, where LiN(SiMe3)2 insertion into
the N C triple bond of the nitrile group accompanies a 1,3 silyl
shift to yield the corresponding amidinate lithium,11 an important
precursor for preparation of organometallic amidinate complexes.
This might be attributed to the different reactivity of benzonitrile
and anthranilonitrile.11c,d It should be noted that the reaction of
n-butyllithium with anthranilonitrile under the similar conditions
was complicated, no pure compound 1 was isolated.
with Cp2LnCl(THF) yields the heterobimetallic complexes
Cp2Ln[j3-(4-NH (C8N2H4)(2-NHC6H4)]Li(THF)3 (Cp
=
C5H5; Ln = Er (2), Y(3)), indicating an organolanthanide-
mediated nucleophilic addition/cyclization of the 2-cyano-
benzoamino anion to construct the 4-iminoquinazolinate
dianionic ligand.
There is fundamental interest in the reactivity of organolanthanide
complexes with unsaturated organic small molecules, because this
is the source for developing new catalytic reactions and catalysts.1–3
Many efforts have focused on a detailed understanding of the
insertion of these organic small molecules into lanthanide–ligand
bonds over the last decade.4–8 However, little is known about
the functional substituent participation reaction, when insertion
occurs on the lanthanide–ligand bonds of organolanthanide com-
plexes containing the functional substituent ligands. Recently, our
interest has been focused on the investigation of the addition of the
N–H bonds of organolanthanide derivatives to some unsaturated
organic small molecules to construct a novel neutral or anionic
ligand or an N-heterocyclic skeleton.9,10 As part of this program,
we investigated the reaction of Cp2LnNiPr2 with anthraniloni-
trile, and found an organolanthanide-mediated intermolecular
nucleophilic addition/cyclization of anthranilonitrile to construct
Scheme 1 Synthesis of complexes 1–3.
3
the 4-aminoquinazolinate anionic ligand [k -(4-NH(C8N2H4)(2-
With 1 in hand, we decided to explore its reactivity to-
ward lanthanocene chlorides. Reaction of Cp2LnCl(THF) with
two equiv of 1 in THF at room temperature afforded the
NH2C6H4)]-.10 In this reaction, we suggested that the intermediate
Cp2LnN(H)C6H4CN-2 (I) is formed by the protonolysis of the
diisopropylamine ligand by one anthranilonitrile molecule. To
obtain this intermediate, we synthesized 2-NCC6H4HNLi by
the reaction of LiN(SiMe3)2 with anthranilonitrile, and inves-
tigated its reactivity with Cp2LnCl(THF) (Ln = Er, Y). A
novel rare-earth metal-mediated nucleophilic addition/cyclization
of 2-cyanobenzoamino anion has been observed for the con-
3
isolated and structural characterized complexes Cp2Ln[k -(4-
NH (C8N2H4)(2-NHC6H4)]Li(THF)3 (Ln = Er (2), Y(3)) in 76%
and 81% isolated yield, respectively, as shown in Scheme 1. Struc-
tural analysis results revealed that a novel 4-iminoquinazolinate
3
dianionic ligand [k -(4-NH (C8N2H4)(2-NHC6H4)]2- is formed.
We also investigated the reaction of Cp2LnCl(THF) with one
equiv of 1 under the same conditions, and could not obtain
the intermediate I or lanthanide benzopyrazolate complexes
Cp2Ln[C7H5N2], an intramolecular addition/cyclization product,
but only isolated 2 and 3 in lower yields. These results indicated
that the cyano group of I favours further nucleophilic addition
with another molecule of 1.
A proposed process for the formation of 2–3 is illustrated in
Scheme 2. The first step is a salt-metathesis of Cp2LnCl with 1 to
generate the intermediate I. Further the adjacent nitrile group of
I inserts into the Li–N bond of another molecule of 1, to give A,
3
struction of the 4-iminoquinazolinate dianionic ligand [k -(4-
NH (C8N2H4)(2-NHC6H4)]2-. This reaction process is different
from the aforementioned reaction.10 Herein we wish to report these
results.
Department of Chemistry, Fudan University, Shanghai, 200433, China.
E-mail: zhangjie@fudan.edu.cn; Fax: +86 21 65641740; Tel: +86 21
65643885
† Electronic supplementary information (ESI) available. CCDC reference
numbers 826343–826344. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt10990a
9098 | Dalton Trans., 2011, 40, 9098–9100
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Scheme 2 Plausible mechanism of the formation of 2 and 3.
and then transforms into B through a 1,3 hydrogen shift. The final
products are formed by nitrile insertion into the Li–N bond, a 1,3
hydrogen shift and a 1,5 lithium cation shift. Two nitrile insertions
into Li–N bonds are vital for the formation of 2 and 3, which
3
is different from those found in Cp2Ln[k -(4-NH(C8N2H4)(2-
NH2C6H4)] (Ln = Er, Y),10 in which the quinazoline skeleton
was constructed through two nitrile insertions into Ln–N bonds.
Consideration of the fact that the dimerization/cyclization of 1
cannot occur in the preparation of 1 leads us to suggest that
the activation of the adjacent nitrile group via the coordination
interaction with the Ln3+ ions in the intermediates I and B plays a
key role to this nucleophilic addition/cyclization.
All of these new complexes are air- and moisture-sensitive,
and soluble in THF and toluene. They were fully characterized
by elemental analysis and spectroscopic properties, which are
in good agreement with the proposed structures. In the IR
spectra, 1 exhibits one absorption at 3274 cm-1 attributable to the
Fig. 1 Molecular structure (30% thermal ellipsoids) and packing diagram
of [2-NCC6H4NHLi(THF)]n, 1. Hydrogen atoms have been remov◦ed
˚
for the sake of clarity. Selected bond lengths (A) and angles ( ):
Li1–N1 2.067(5), Li1–N1A 2.038(5), Li1–N2B 2.035(6), Li1–O1 1.936(6);
O1–Li1–N1 108.2(2), O1–Li1–N2B 110.1(3), O1–Li1–N1A 116.6(3),
N1–Li1–N1A 102.1(2), N1–Li1–N2B 114.1(3), N1A–Li1–N2B 105.8(2).
N–H bond, one absorption at 2206 cm-1 attributable to the C
N
triple bond, and two well-defined bands at 1078 and 910 cm-1 for
the coordinated THF. In the 1H NMR spectrum of 3, in addition
to four multiplets for aromatic protons at 7.06, 7.02, 6.83, 6.13
ppm, one broad singlet for NH protons at about 4.86 ppm, and
one singlet for the Cp ring protons at about 6.33 ppm, and two
multiplets for three coordinated THF molecules at 3.54 and 1.45
ppm were obtained. The solid-state structures of 1–2 were also
determined by X-ray single-crystal diffraction analysis.
bimetallic complex. The erbium atom carries two h -Cp rings and
5
3
one k -4-amino(2-imidobenzoyl)quinazolinate ligand to form a
distorted bipyramid geometry. The coordination number of Er3+
is nine. The lithium ion Li+ is coordinated by one k -4-amino(2-
1
amidobenzoyl)quinazolinate ligand and three THF molecules.
The coordination number of Li+ is four. A planar aromatic
quinazoline skeleton has been constructed from the corresponding
bond lengths and angles data.
Compound 1 crystalizes from the solvent mixture of THF
and n-hexane at -20 ◦C in the monoclinic system, space group
P21/c. Structural determination results (Fig. 1) show that 1 is
two-dimension polymer, in which the 2-cyanobenzoamino anionic
ligand displays a m3-bridge bonding mode with three lithium ions.
Each of lithium atoms is coordinated to one oxygen atom form
THF molecule and three nitrogen atoms from three different 2-
cyanobenzoamino ligands to form distorted tetrahedron geom-
The coordinated amidinate moiety forms essentially a
planar four-membered ring with the lanthanide atom and
the bond angles around C1 (sum = 360◦) are consistent
with sp2 hybridization. The C1–N1 distance of [1.291(7)
˚
A] is slightly longer than the accepted value for the
2
12
C(sp2) N(sp ) double-bond (1.28 A). Consistent with this
˚
˚
observation, the Er1–N1 and Er1–N2 distances, 2.345(4) A
˚
and 2.405(5) A, are in the range of Er–N donor bond, and
˚
etry. The N2–C1 distance of the nitrile group (1.129(4) A) is
significantly longer than that of the corresponding Er–N bond
1
comparable to the observed value for a coordinated h -N C triple
of amidine anionic compound Cp2Er[(tBuN)2C(nBu)] (Er–Nav
bond of organonitriles (1.10–1.20 A).11a,b The Li–N bond distances
2.281(5) A). The C1–N2 [1.369(6) A], C8–N2 [1.346(6) A], and
13
˚
˚
˚
˚
˚
˚
˚
˚
(Li1–N1 2.067(5) A, Li1–N1A 2.038(5) A, Li1–N2B 2.035(6) A)
are almost equivalent, and between in the range of Li–N single
and donor bond distance.11a,b
C8–N3 [1.334(6) A] distances are in intermediate values between
the C–N single- and double-bond distances,14 indicating that the
p-electrons of the C N double bond in the present structure
are delocalized over the N1–C1–N2–C8–N3 unit. The distance
Fig. 2 shows the molecular structure of 2 and selected bond
distances and angles. X-Ray analysis shows that 2 is a hetero-
˚
of Er1–N4 is 2.288(6) A, and in the range of an Er–N single
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Fig.
2
Molecular structures (30% thermal ellipsoids) of
Cp2Er[k3-(4-NH(C8N2H4)(2-NH2C6H4)], 2. Hydrogen atoms have
been removed for the sake of clarity. Selected bond lengths (A) and
˚
angles (◦): Er1–N4 2.288(6), Er1–N2 2.345(4), Er1–N1 2.406(5),
Er1–H4N 2.40(6), Li1–N3 2.121(10), N1–C1 1.291(7), N2–C1 1.369(6),
N2–C8 1.346(6), N3–C8 1.334(6), N3–C3 1.392(6), C1–C2 1.454(7),
C2–C3 1.402(6); N1–C1–N2 100.8(6), N1–C1–C2 131.8(6), N2–C1–C2
117.4(5), C8–N2–C1 120.6(5), C8–N3–C3 115.4(5), C3–C2–C1 117.1(5),
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bond.15 Interestingly, the residual hydrogen atom of the amido
group contacts with the erbium ion through an agnostic hydrogen
16
˚
bond interaction (Er1–H4N 2.40(6) A).
In summary, a rare-earth metal-mediated intermolecular nu-
cleophilic addition/cyclization of 2-cyanobenzoamino anion was
reported to construct a 4-iminoquinazolinate dianionic ligand
3
[k -(4-NH (C8N2H4)(2-NHC6H4)]2- for the first time, which
10 J. Zhang, Y. N. Han, F. Y. Han, Z. X. Chen, L. H. Weng and X. G.
Zhou, Inorg. Chem., 2008, 47, 5552.
provided a potential strategy for introducing a substituent at the
N3 atom of the pyrimidine ring skeleton.
We thank The NNSF, NSF of Shanghai (09ZR1403300),
973 program (2009CB825300), and Shanghai Leading Academic
Discipline Project (B108) for financial support.
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9100 | Dalton Trans., 2011, 40, 9098–9100
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©