Synthesis, Insertion Reactivity, and Transmetalation Reactions of the Lithium Complex [{2-(6-R-Pyr)(Me3Si)}CHLiOEt2]2 (R = H or Me)

Article abstract of DOI:10.1002/ejic.200900239

Treatment of 6-R-2-(Me₃SiCH₂)C₅H ₃N (R = H or Me) with nBuLi in diethyl ether affords the dimeric lithium complexes [{2-(6-R-Pyr)(Me₃Si}CHLi-OEt₂] ₂= pyridine, C₅H

Full text of DOI:10.1002/ejic.200900239

FULL PAPER
DOI: 10.1002/ejic.200900239
Synthesis, Insertion Reactivity, and Transmetalation Reactions of the Lithium
Complex [{2-(6-R-Pyr)(Me3Si)}CHLi·OEt2]2 (R = H or Me)
Xia Chen,*[a] Lingling Guan,[a] Moris S. Eisen,[b] Haifen Li,[a] Hongbo Tong,[a]
Liping Zhang,[a] and Diansheng Liu*[a]
Keywords: N ligands / Insertion / Nitriles / Coordination chemistry / Structure elucidation
Treatment of 6-R-2-(Me3SiCH2)C5H3N (R = H or Me) with
nBuLi in diethyl ether affords the dimeric lithium complexes
[{2-(6-R-Pyr)(Me3Si)}CHLi·OEt2]2 (Pyr = pyridine, C5H3N) in
high yields. In these complexes, the two anionic ligands have
different bonding modes. These complexes easily undergo
insertion reactions with nitriles to form six-membered cyclic
dimeric complexes in good yields. Further transmetalations
of the six-membered cyclic complexes with CuCl, SnCl4, or
CoCl2 allow the formation of new metal complexes that
maintain the frameworks of the six-membered metallacycles.
All complexes represented above were fully characterized by
methods including single-crystal X-ray crystallography.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
Introduction
Trimethylsilyl-substituted methylpyridines are interesting
ligands with regard to their coordination chemistry and as
ancillary ligands in main-group and transition-metal orga-
nometallic compounds.[1] These bulky ligands with multi-
functional σ and π metal–ligand bonding modes stabilize
their metal complexes by the three electronic displacement
forms that the picolyl anions can adopt: carbanion, η3-
azaallyl, and enamide (Figure 1).[2] The silylated ligands are
normally encountered in the azaallyl form commonly found
in compounds like [(2-Pyr)(SiMe3)CHLi·(Et2O)]2,[3a] while
Figure 1. Tautomeric forms of the picolyl anion.
reagent bis(trimethylsilyl)methyllithium, Li[CHR2] (R =
SiMe3), or the complex 1-azaallyllithium, [LiN(R)C(tBu)-
CHR]2, with α-hydrogen-free nitriles, RЈCN (RЈ = Me2N,
1-piperidyl or o-, m-, p-pyridyl), lead to a dimeric or a poly-
meric complex of β-diketiminatolithium.[6] However, little
attention has been devoted to pyridyl-substituted azaallyl
complexes that possess a nitrogen heterocycle aromatic ring
as part of the ligand backbone relative to β-diketiminato
ligands with the same substituent groups on the two ter-
minal nitrogen atoms.[4] Recently, Leung et al. have reported
the synthesis and the structures of the 2,6-pyridyl-linked
bis(1-azaallyl) and 2,3-pyrazyl-linked bis(1-azaallyl)alkali-
metal compounds.[7,8] Furthermore, a series of derived pyr-
idyl-1-azaallyl low-valent group 14 compounds were de-
scribed.[9,10] The synthesis of [MCl2{N(SiMe3)-C(Ph)C-
(H)(C9H6N-2)}] (M = Hf and Zr) from the reaction of
MCl4 with the quinolyl-1-azaallyllithium complex [Li{N-
the ligands with the enamide disposition are observed in
[3a]
complexes like [(2-Pyr)(SiMe3)CHLi·(tmeda)]2
or [(2-
Pyr)(SiMe3)CHLi·(sparteine)].[3b] We have noted that all of
the dimeric complexes of the type [(2-Pyr)(SiMe3)CHLi·
(L)]2 have the common feature of a central symmetric struc-
ture; however, to date there have been no examples of com-
pounds with dimeric complexes with an asymmetric
pattern.
The insertion of α-hydrogen-free nitriles into a Li–C
bond of these complexes has introduced a synthetic utility
in preparing pyridyl-substituted azaallyls.[4] Metal 1-azaal-
lyls and β-diketiminates have been studied and reported.[5]
Recently, we have reported that insertion reactions of the
(SiMe3)C(Ph)C(H)(C9H6N-2)}]2
was
reported
pre-
viously,[11] as well as the synthesis of Pd complexes contain-
ing the 1-azaallyl ligand of [{[N(R)C(tBu)CH]2C5H3N-
2,6}{Li2(tmen)}] and [{[N(R)C(Ph)CH]2C5H3N-2,6}{Li-
(tmen)2}].[12]
[a] School of Chemistry and Chemical Engineering, Shanxi Uni-
versity,
Taiyuan 030006, People’s Republic of China
Fax: +86-351-7011688
E-mail: chenxia@sxu.edu.cn
In this paper, we report the synthesis of dimeric [{2-(6-
R-Pyr)(Me3Si)}CHLi·OEt2]2 [R = H (1a) or Me (1b)], in
which two lithium atoms have different bonding modes in
an asymmetric pattern, and their insertion products to form
the corresponding pyridyl-1-azaallyllithium complexes [{2-
dsliu@sxu.edu.cn
[b] Schulich Faculty of Chemistry and Institute of Catalysis Sci-
ence and Technology, Technion-Israel Institute of Technology,
Haifa 32000, Israel
Fax: +972-4-8295705
E-mail: chmoris@tx.technion.ac.il
3488
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 3488–3495

Synthesis and Reactions of [{2-(6-R-Pyr)(Me3Si)}CHLi·OEt2]2 (R = H or Me)
(6-Me-Pyr)C(H)C(RЈ)N(SiMe3)}Li]2 [RЈ = tBu (2) or Ph carbon and nitrogen centers, but there are additional lith-
(3)] or [{(2-Pyr)C(H)C(Ph)N(SiMe3)}Li]2 (4). These pyr- ium–anion contacts, viz. Li2–C11, in addition to the nitro-
idyl-1-azaallyl-lithium salts were also used as ligand trans- gen bridges among the two lithium atoms.[20]
fer reagents when reacted with a variety of metal halides,
CuCl, CoCl2, and SnCl4, to produce the corresponding
complexes
[{2-(6-Me-Pyr)C(H)C(Ph)N(SiMe3)}Cu]2(µ-
CuCl) (5), [{(2-Pyr)C(H)C(Ph)N(SiMe3)}SnCl3] (6), and
[{(2-Pyr)C(H)C(Ph)N(SiMe3)}2Co] (7). Complex 5 was ob-
tained as an unusual trinuclear dimer in which two mono-
mers of pyridyl-1-azaallyl-copper(I) are bridged by a neu-
tral CuCl moiety. Complex 6 adopts an enamido bonding
mode in which the pyridyl-1-azaallyl motif bonds to the
metal center, whereas in complex 7 a mononuclear pyridyl-
1-azaallyl–metal complex was obtained in a terminal N,NЈ-
chelating fashion, in which the metal has a distorted tetra-
hedral environment. The bonding within the NCCCN li-
gand backbone framework for complexes 5 and 6 is highly
localized, in contrast to complex 7, in which a partial delo-
calization is observed.
Figure 2. Molecular structure and atom numbering scheme for 1b.
Results and Discussion
Table 1. Selected bond lengths [Å] and angles [°] for 1b and 2.
The starting material for the synthetic procedure was the
trimethylsilymethyl-substituted pyridine 6-R-2-(Me3Si-
CH2)C5H3N (R = H or Me)[3a,13–14] The general synthesis
route for the different complexes presented in this paper are
illustrated in Scheme 1.
1b
Li1–C1
Li2–N1
Li2–C11
Li2–O2
C1–C2
C12–N2
O1–Li–N2
O1–Li1–C1
O2–Li2–N2
O2–Li2–C11 121.7(5)
N2–Li2–C11 61.4(3)
2.207(11)
2.023(11)
2.544(12)
1.962(10)
1.406(7)
1.396(7)
118.8(5)
129.6(5)
107.3(5)
Li1–N2
Li1–O1
Li2–N2
C11–C12
C2–N1
2.018(10)
1.901(10)
2.076(11)
1.381(7)
1.381(6)
O2–Li2–N1
N1–Li2–N2
N1–Li2–C11
N1–C2–C1
N2–C12–C11
127.8(6)
122.6(5)
96.5(4)
119.2(4)
119.0(5)
N2–Li1–C1
111.2(5)
2
Li–N1
N1–C6
C6–C7
N1–C6–C7
C7–C8–N2
Li–N1–C6
N2–Li–N2
2.036(4)
1.346(3)
1.460(3)
120.05(19)
125.03(19)
111.38(17)
104.21(16)
Li–N2
N2–C8
C7–C8
C6–C7–C8
Li–N2–C8
N1–Li–N2
Li–N2–LiЈ
2.027(4)
1.390(3)
1.357(3)
129.9(2)
120.07(17)
99.28(17)
75.79(16)
Scheme 1. Synthetic pathway to complexes 1–7.
Metalation of 6-R-2-(Me3SiCH2)C5H3N (R = H or Me)
Complex 1b consists of two different lithium environ-
by 1 equiv. nBuLi in hexane and in the presence of diethyl ments caused by steric crowding. The bonding features of
ether yields η3-azaallyllithium 1a or 1b. It is important to Li1 and Li2 are η1-alkyl and η3-azaallyl, respectively, in
mention that complex 1a has been previously reported by which the bond lengths of Li–C or Li–N are 2.01–2.54 Å.
Papasergio.[3a]
One lithium atom has three coordination sites, whereas the
The molecular structure of 1b is illustrated in Figure 2, second lithium atom is four-coordinate. Each one of the
and selected bond lengths and angles are presented in two lithium atoms is also bound by diethyl ether, above and
Table 1. Orange crystals of complex 1b are obtained from below the η3-azaallyl planes. Two of the ipso carbon atoms
Et2O as dimers, in which part of the dimer acts as an η3- are coplanar with the pyridine rings. Their mean deviations
azaallyl ligand to one lithium atom and the same nitrogen from planarity are 0.0149 and 0.0267 Å, with a dihedral
atom also coordinates to the second lithium atom. This co- angle between the two pyridyl moieties of 53.3°. The dihe-
ordination mode is quite unique and is different from those dral angle between the Li2N2C11 plane and the pyridine
reported for similar [{Li(Et2O)[2-CH(SiMe3)C5H4N]}2][3a] N2C12C13C14C15C16 is 52.6°. It is worth noting that the
and [{Li(Et2O)[C6H5N(C(CH2)tBu)]}2][19] complexes. Com- distances of Li1 and Li2 to the pyridine rings
plex 1b has an eight-membered ring with respect to the ipso N2C12C13C14C15C16 are 1.224 and 1.562 Å, respectively.
Eur. J. Inorg. Chem. 2009, 3488–3495
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X. Chen, L. Guan, M. S. Eisen, H. Li, H. Tong, L. Zhang, D. Liu
FULL PAPER
The bond lengths C1–C2 and N1–C2 are 1.406(7) and cluding the pyridyl-substituted 1-azaallyls I and II,[6] and
1.381(6) Å, respectively, which are similar to C11–C12 the β-diketiminates III (Figure 4).[21]
[1.381(7) Å] and C12–N2 [1.396(7) Å], indicating the pres-
A comparison of some of the relevant bond lengths for
ence of a delocalized NCC fragment. The lithium–ligand complex 2 with those of I,[6] II,[6] and III[21] is presented in
interactions are related to the steric and electronic nature Table 2. The bonding within the NCCCN ligand backbone
of the group at the ipso carbon atoms.[3a]
in 2, I,[6] and II[6] is highly localized: RC=C double bonds
The pyridyl-substituted 1-azaallyl complexes 2–4 were (R = Ph or tBu) leave the aromaticity of the pyridine ring
prepared under mild conditions from 1 and PhCN or largely unaffected. This is, however, in contrast to [LiN-
tBuCN, in a 1:1 molar ratio in diethyl ether.[4] Compounds (SiMe3)C(Ph)C(H)C(Ph)N(SiMe3)]2, which displays, at
2–4 were obtained in good yields (more than 70%), as yel- least to some extent, delocalization in the ligand back-
low complexes that were soluble in Et2O but had a fairly bone.[7] The Li–N distances of the bridging NSiMe3 groups
low solubility in hexane. Complex 2 was obtained as a dark- (Li1–N2) are almost identical, and the Li–pyridyl bonds
yellow crystalline material suitable for X-ray diffraction [2.036(4) (2), 1.968(6) (I) and 1.981(7) Å (II)] are considered
studies. Compounds 3 and 4 were also isolated as yellow to be unexceptionally dative and can be compared with the
solid powders and were reacted directly to continue the re- Li–pyridine distance in the three-coordinate lithium com-
action pathway (Scheme 1) with the corresponding metal plex 1b [2.018(10) Å] and in [Li{2-C(SiMe3)2C5H4N}-
chlorides.
{CH(SiMe3)2-C5H4N-2}] [2.010(10) Å],[4] all of them falling
The molecular structure of 2 is illustrated in Figure 3, in the normal range 1.895–2.087 Å for Li–N (amido)
and selected bond lengths and angles are presented in bonds.[3a,22–24] The metallacycle LiNCCCN is highly puck-
Table 1. The molecular structure of complex 2 is that of a ered and exhibits a dihedral angle between the N1Li1N2
centrosymmetric dimer with a central LiNLiN rhombohe- and N2C7C8 planes of 65.0°.
dral geometry having NSiMe3 as bridging groups. The
angles at the nitrogen atom [75.79(16)°] are narrower than
those at the Li atom [104.21(16)°]. Each lithium atom is
coordinated with three nitrogen atoms from two corre-
sponding ligands. These features are similar to those of sev-
Table 2. Comparison of selected bond lengths [Å] (as marked in
complexes I–III) for 2 and I–III.
Complex
Bond a
Bond b
Bond c
Ref.
2
2.036(4)
1.968(6)
1.981(7)
1.952(10)
2.027(4)
2.012(9)
1.998(6)
1.965(9)
2.040(4)
2.032(6)
2.026(6)
2.095(9)
this work
eral other known N,NЈ-chelating monoanionic ligands, in-
[6]
I
[6]
II
III
[22]
Treatment of complex 3 with anhydrous CuCl in a 2:3
molar ratio in Et2O or THF at low temperature afforded
complex 5. CuI complex 5 was isolated by crystallization
from diethyl ether as a brown-yellow crystalline solid in
good yields (ca. 60%). To the best of our knowledge, several
diketiminate CuI compounds such as [Cu{[N(Ar)C(Me)]2-
CH}(L)] {L = C2H4,[15] Ge(NR2)2[16]}, [Cu{[N(R)C(Ar)]2-
SiR}]2(thf) (R = SiMe3, Ar = C6H3Me2-2,6),[17] and
[Cu{N(Ar)C(Me)C(H)C(Me)N[C6H3(iPr-2)-(CH2SMe-
[18]
6)]}]4 have been described. However, among all of them,
complex 5 is the first structurally characterized dimeric tri-
nuclear pyridyl-1-azaallyl–CuI complex, in which the di-
meric NCCCN backbone is bridged by a neutral CuCl mo-
lecular moiety.
Figure 3. Molecular structure and atom numbering scheme for 2.
Figure 4. 1-azaallyl complexes I–III.
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Eur. J. Inorg. Chem. 2009, 3488–3495

Synthesis and Reactions of [{2-(6-R-Pyr)(Me3Si)}CHLi·OEt2]2 (R = H or Me)
The molecular structure of 5 is illustrated in Figure 5, respectively. Thus, the bonding within the NCCCN ligand
and selected bond lengths and angles are presented in backbone is localized, and the pyridyl-1-azaallyl ligand
Table 3. The core of 5 exhibits a six-membered NCuN- bonds to the metal center can be related to an enamido
CuClCu puckered ring, with an unusual CuCl bridging bonding model.
mode. It may be regarded as being an adduct of CuCl and
two [{2-(6-Me-Pyr)C(H)C(Ph)N(SiMe3)}Cu] moieties, in
Table 3. Selected bond lengths [Å] and angles [°] for 5.
which Cu1 and Cu2 atoms are bridged by a Cl atom, while
the Cu3 atom bridges atoms N2 and N4. The two three-
coordinate Cu1 and Cu2 atoms are in a distorted trigonal-
planar environment, and the dihedral angle between the
Cu1N1N2Cl1 and Cu2N3N4Cl1 planes is 85.6°, while the
Cu3 atom chelated to nitrogen atoms shows an approxi-
mately linear coordination mode, in which the angle of N2–
Cu3–N4 is 171.0(3)°. The linear N–Cu–N coordination im-
Cu1–N1
Cu1–Cl1
Cu2–N3
Cu2–Cl1
Cu3–N2
Cu3–Cu1
C6–C7
N2–C8
1.991(6)
2.251(2)
2.061(6)
2.216(2)
1.916(6)
2.4602(14)
1.438(11)
1.407(9)
1.366(11)
1.365(11)
104.6(3)
57.55(4)
143.11(18)
171.0(3)
117.0(5)
112.6(5)
117.6(5)
80.8(2)
Cu1–N2
Cu1–Cu2
Cu2–N4
Cu2–Cu3
Cu3–N4
N1–C6
C7–C8
C23–C24
C25–N4
2.067(6)
2.8507(15)
2.093(6)
2.5793(14)
1.875(6)
1.360(10)
1.355(11)
1.456(11)
1.419(10)
C24–C25
N3–C23
poses
a relatively short distance between Cu3–Cu1
[2.460(14) Å] and Cu3–Cu2 [2.579(14) Å], as compared to
the chlorine atom bridging distance between Cu1–Cu2
[2.850(15) Å]. In searching for different molecular struc-
tures of β-diketiminatocuprate complexes, we encounter
some dimeric structures with short Cu···CuЈ contacts that
have been reported, such as in [Cu{[N(R)C(Ar)]2SiR}]2,[17]
N1–Cu1–N2
Cu3–Cu1–Cu2
N4–Cu2–Cl1
N4–Cu3–N2
C6–N1–Cu1
C8–N2 –Cu1
C23–N3–Cu2
Cu3–N4–Cu2
C8–C7–C6
N3–C23–C24
C24–C25–N4
N2–Cu1–Cl1
N3–Cu2–N4
Cu3–Cu2–Cu1
Cu1–Cu3–Cu2
C8–N2–Cu3
Cu3–N2–Cu1
C25–N4–Cu2
N1–C6–C5
126.03(19)
45.87(17)
53.59(3)
68.86(4)
107.3(4)
76.1(2)
104.3(4)
119.2(7)
126.0(7)
130.2(7)
[Cu{N(iPr)C(Me)N(iPr)}]2,[25]
Bu)}]2,[26]
[Cu{N(C6H3Me2-2,6)C(Ph)N(C6H3Me2-
[Cu{N(sBu)C(Me)N(s-
136.4(7)
120.1(7)
122.9(7)
C7–C8–N2
C25–C24–C23
2,6)}]2,[27] [Cu{N(R)C(Ph)N(R)}]2,[28] and 1-azaallyl
[Cu{N(R)C(tBu)C(H)R}]2;[29] however, in all these com-
plexes the Cu···CuЈ distances are between 2.40–2.49 Å. The
bond lengths Cu1–N1, Cu1–N2, Cu2–N3, and Cu2–N4 are
1.989(6)–2.093(6) Å, which are longer than the bridging
bond lengths Cu3–N2 [1.916(6) Å] and Cu3–N4
[1.875(6) Å]. The geometries of the two β-diketiminate
backbones are different; the N1C6C7C8N2 backbone is
planar (mean deviation 0.0079 Å) and is coplanar with the
pyridine ring (mean deviation 0.0176 Å), while the
N3C23C24C25N4 backbone is twisted away from the plane
of the pyridine and possesses a half-chair conformation.
The short C7–C8 and C24–C25 and long N2–C8 and N4–
C25 bond lengths correspond to double and single bonds,
The reaction of complex 4 with an equimolar amount of
SnCl4 in Et2O and the subsequent recrystallization of the
reaction mixture from CH2Cl2 gave the metal enamide com-
plex 6 as yellow crystals in 78% isolated yield.
The molecular structure of 6 is illustrated in Figure 6,
and selected bond lengths and angles are presented in
Table 4. Crystalline complex 6 has a tin atom in a distorted
trigonal-bipyramidal environment with the Cl2 and N1
atoms in the axial position [N1–Sn–Cl2 176.52(14)°]. The
diketiminato ligand acts in an η2 bonding mode with Sn–
N bond lengths of 2.025(5) and 2.236(5) Å. The NCCCN
backbone is essentially planar, with a mean deviation of
0.0679 Å, and the dihedral angle between the NCCCN and
the pyridine ring is 19.9°, whereas the Sn atom is 0.9966 Å
out of the NCCCN plane. In the NCCCN moiety, the bond
lengths N1–C5, C5–C6, C6–C7, and C7–N2 are 1.348(8),
1.442(9), 1.346(8), and 1.414(7) Å, respectively, indicating
an obvious short-long-short-long pattern of bond lengths.
This pattern indicates that the β-diketiminato ligand is a
characteristic example for a conjugated system. In compar-
ing the compounds [Sn{[N(H)C(Ph)]2CH}Cl(Me)2],
[Sn{[N(SiMe3)C(Ph)]2CH}Cl(Me)2],[30] and complex 6, the
main difference is the {SnNaC–C–CNb(Sn-Nb)} skeleton
plane, which is almost planar for [Sn{[N(H)C(Ph)]2CH}-
Cl(Me)2], whereas the Sn atoms in [Sn{[N(SiMe3)C(Ph)]2-
CH}Cl(Me)2] and in complex 6 are approximately 1.37 and
1.00 Å out of the NCCN plane, respectively.
A similar reaction of complex 4 with CoCl2 in a 2:1 mo-
lar ratio in Et2O afforded red crystals of complex 7 in 64%
isolated yield. The molecular structure of 7 is illustrated in
Figure 7, and selected bond lengths and angles are pre-
Figure 5. Molecular structure and atom numbering scheme for 5.
Eur. J. Inorg. Chem. 2009, 3488–3495
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X. Chen, L. Guan, M. S. Eisen, H. Li, H. Tong, L. Zhang, D. Liu
FULL PAPER
Figure 7. Molecular structure and atom numbering scheme for 7.
Table 5. Selected bond lengths [Å] and angles [°] for 7.
Figure 6. Molecular structure and atom numbering scheme for 6.
Table 4. Selected bond lengths [Å] and angles [°] for 6.
Co1–N2
Co1–N1
N1–C5
N3–C21
1.958(4)
1.985(4)
1.354(6)
1.353(6)
1.428(7)
1.426(7)
99.01(16)
122.6(3)
120.3(4)
127.4(4)
Co1–N4
Co1–N3
N2–C7
N4–C23
1.964(4)
1.995(4)
1.345(6)
1.339(6)
1.374(7)
1.381(7)
99.59(17)
118.5(3)
131.3(4)
C5–C6
C6–C7
C21–C22
N2–Co1–N1
C5–N1–Co1
N1–C5–C6
N2–C7–C6
C22–C23
N4–Co1–N3
C7–N2–Co1
C7–C6–C5
Sn1–N2
Sn1–Cl3
Sn1–Cl2
C5–C6
2.025(5)
2.3277(19)
2.3954(18)
1.442(9)
1.414(7)
88.46(18)
87.14(14)
86.14(13)
95.03(14)
90.92(8)
117.4(4)
121.7(6)
124.8(6)
Sn1–N1
Sn1–Cl1
N1–C5
C6–C7
2.236(5)
2.3277(17)
1.348(8)
1.346(8)
1.493(9)
125.42(15)
115.93(14)
117.97(8)
176.52(14)
92.22(7)
114.3(4)
129.9(6)
N2–C7
C7–C8
N2–Sn1–N1
N1–Sn1–Cl3
N1–Sn1–Cl1
N2–Sn1–Cl2
Cl3–Sn1–Cl2
C5–N1–Sn1
N1–C5–C6
C6–C7–N2
N2–Sn1–Cl3
N2–Sn1–Cl1
Cl3–Sn1–Cl1
N1–Sn1–Cl2
Cl1–Sn1–Cl2
C7–N2–Sn1
C7–C6–C5
Conclusions
We have here disclosed a simple and effective synthesis
for a family of pyridyl-substituted 1-azaally ligands and
their corresponding metal complexes starting from lithiated
2-methylpyridine or 2,6-dimethylpyridine followed by a 1,2-
insertion of a suitable nitrile and with a concomitant 1,3-
trimethylsilyl shift. Both of the nitrogen atoms of these
monoanionic ligand complexes are expected to be good σ-
and π-donors, and like cyclopentadienyl ligands, they can
formally be considered as six-electron donors. In addition,
the substituents on the ligand backbone can be easily var-
ied, which is important for the fine tuning of the steric and
electronic properties of the ligands. Compound such as
complex 5 may serve as a precursor for Metal Organic
Chemical Vapor Deposition (MOCVD) or as a magnetic
material in microeletronics.[31] Complex 7 is a potential cat-
alyst in olefin polymerization, and further studies are un-
derway.[32] In addition, complementary research on the co-
ordination chemistry of this interesting class of pyridyl-1-
azaallyl ligands and other applications of their metal com-
plexes are presently in progress.
sented in Table 5. The central cobalt atom is located in a
tetrahedral environment defined by the four nitrogen atoms
from the two bidentate 2-pyridyl-1-azaallyl ligands with a
fully perpendicular dihedral angle (90.0°) between N1CoN2
and N3CoN4. The Co–N bond lengths are in the range
1.964(4)–1.995(4) Å, which are shorter than corresponding
values found in complex [Co{[N(SiMe3)C(Ph)]2CH}2][5c]
[Co–N 1.994(7)–2.007(6) Å]. The bond angles N1–Co–N2
and N3–Co–N4 are 99.01(16) and 99.59(17)°, respectively,
which are smaller than those in [Co{[N(SiMe3)C(Ph)]2-
CH}2] [103.0(2) and 119.4(3)°]. Each bidentate 2-pyridyl-1-
azaallyl ligand forms
a
six-membered metallacycle
MNCCCN, where the MNCCCN ring is highly coplanar
with the pyridine ring with a mean deviation of 0.0122 Å.
The congestion at the NCCCN skeleton is revealed by the
large out-of-plane rotation of the phenyl group relative to
the NCCCN plane, and the dihedral angle between the
phenyl and N2C3 moiety is 93.1°, which prevents a steric
hindrance with the hydrogen atoms attached to the C6=C7
double bond. This steric congestion has also been observed
in the molecular structure of complexes 5 and 6.
Experimental Section
All manipulations and reactions were performed under an inert
atmosphere of nitrogen by means of standard Schlenk techniques.
Solvents were predried with sodium, distilled from sodium/potas-
sium alloy (hexane), sodium/benzophenone (diethyl ether, tetra-
hydrofuran), and stored over molecular sieves (4 Å). Deuterated
3492
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 3488–3495

Synthesis and Reactions of [{2-(6-R-Pyr)(Me3Si)}CHLi·OEt2]2 (R = H or Me)
solvents were dried with sodium/potassium alloy (C6D6) and mo-
lecular sieves (4 Å) (CDCl3). All solvents were degassed prior to
use. Chemicals were purified by distillation before use. CuCl,
CoCl2, SnCl4, trimethylacetonitrile, and n-butyllithium in hexane
(2.8 moldm–3) were purchased from Alfa Aesar and used without
[{2-(6-Me-Pyr)C(H)C(Ph)N(SiMe3)}Li]2 (3): PhCN (1.08mL,
10.57 mmol) was added with a syringe to a stirred solution of 1b
(5.48 g, 10.57 mmol) in Et2O (20 mL) at 0 °C. The resulting brown
solution was warmed to room temperature and stirred for a further
10 h. The solvents were removed in vacuo to give a yellow solid
(4.34 g, 70% yield). C34H42Li2N4Si2 (558.80): calcd. C 70.80, H
1
further purification. H and 13C NMR spectra were recorded with
1
a Bruker DRX-300 spectrometer. Elemental analyses were per-
formed with a Vario EL-III instrument.
7.34, N 9.71; found C 69.88, H 7.62, N 9.82. H NMR (C6D6): δ
= 0.085 [s, Si(CH3)3, 9 H], 2.200 (s, 3 H,CH3), 6.286 (m, 1 H, -CH-
of pyridyl), 6.651 (m, 1 H, -CH- of pyridyl), 6.983 (m, 1 H, -CH-
of pyridyl), 7.155 (m, 3 H, -CH- of benzene), 7.890 (m, 2 H, -CH-
of benzene) ppm. 13C NMR (C6D6): δ = 2.087 [s, Si(CH3)3], 24.086
(s, -CH3 of pyridyl), 105.650, 116.654, 118.722, 120.251, 136.868,
147.555, 154.807, 159.684 (-CH- of pyridyl and -CH- of ph), 99.820
(-CH-C=N), 163.600 (-CN of PhCN) ppm.
[(2-Pyr)(Me3Si)CHLi·OEt2]2 (1a): nBuLi (9.5 mL, 27.59 mmol in
hexane) was added with a syringe to a stirred solution of 2-methyl-
pridine (2.569 g, 27.59 mmol) in Et2O (30 mL) at 0 °C. The re-
sulting red solution was warmed to room temperature and stirred
for a further 3–4 h. At 0 °C, ClSiMe3 (3.49 mL, 27.59 mmol) was
added to the above solution, and the mixture was stirred at room
temperature for 4 h and then filtered. The pale yellow filtrate was
added to nBuLi (8.8 mL, 25.66 mmol in hexane) at 0 °C. The re-
sulting solution was stirred for 4 h at room temperature to give a
heavy red solution. Then PhCN (2.49 mL, 24.37 mmol) was added
at 0 °C. The resulting brown mixture was warmed to room tem-
perature and stirred for a further 3–4 h, and then filtered. The fil-
trate was concentrated and allowed to stand for 3 d at –30 °C to
afford yellow crystals of 1a (6.1 g, 91%). C26H48Li2N2O2Si2
(490.72): calcd. C 63.64, H 9.86, N 5.71; found C 63.88, H 9.98, N
5.66. 1H NMR (25 °C, 300 MHz, C6D6): δ = 0.51 [s, 9 H,
-Si(CH3)3], 2.90 (s, 1 H, -CH-SiMe3), 5.9 (m, 1 H, -CH- of pyridyl),
[{(2-Pyr)C(H)C(Ph)N(SiMe3)}Li]2 (4): nBuLi (9.5 mL, 27.59 mmol
in hexane) was added with a syringe to a stirred solution of 2-
methylpridine (2.569 g, 27.59 mmol) in Et2O (30 mL) at 0 °C. The
resulting red solution was warmed to room temperature and stirred
for a further 3–4 h. At 0 °C, ClSiMe3 (3.49 mL, 27.59 mmol) was
added to the above solution, and the mixture was stirred at room
temperature for 4 h and then filtered. The pale yellow filtrate was
added to nBuLi (8.8 mL, 25.66 mmol in hexane) at 0 °C. The re-
sulting solution was stirred for 4 h at room temperature to give a
heavy red solution. Then PhCN (2.49 mL, 24.37 mmol) was added
at 0 °C. The resulting brown mixture was warmed to room tem-
6.7 (m, 2 H, -CH- of pyridyl), 7.8 (m, 1 H, -CH- of pyridyl) ppm. perature and was stirred for a further 3–4 h, and then filtered. The
13C NMR (75 MHz, C6D6): δ = 166.95, 148.20, 134.32, 117.53,
103.24 (-CH- of pyridyl), 65.70 (SiCH-), 1.43 [-Si(CH3)3] ppm.
filtrate was concentrated and allowed to stand for 3 d at –30 °C to
give yellow crystals (6.08 g, 91% yield). C32H38Li2N4Si2 (548.72):
calcd. C 70.04, H 6.98, N 10.21; found C 69.88, H 7.62, N 9.82.
1H NMR (C6D6): δ = 0.077 [s, Si(CH3)3, 9 H], 6.48 (m, 1 H, -CH-
of pyridyl), 6.81 (m, 1 H, -CH- of pyridyl), 7.066 (m, 2 H, -CH- of
pyridyl), 7.598 (m, 3 H, -CH- of benzene), 7.968 (m, 2 H, -CH- of
benzene) ppm. 13C NMR (C6D6): δ = 1.974 [s, Si(CH3)3], 116.794,
123.362, 136.561, 146.542, 147.990, 159.83 (-CH- of pyridyl and
-CH- of ph), 106.089 (-CH-C=N), 164.996 (-CN of PhCN) ppm.
[2-(6-Me-Pyr)(Me3Si)CHLi·OEt2]2 (1b): nBuLi (7.58 mL, 2.57  in
hexane) was added with a syringe to a stirred solution of 2,6-di-
methylpridine (2.162 g, 20.18 mmol) in Et2O (30 mL) at 0 °C. The
resulting orange solution was warmed to room temperature and
stirred for a further 4 h. At 0 °C, ClSiMe3 (2.55 mL, 20.18 mmol)
was added to the above solution, and the mixture was stirred at
room temperature for 5 h and then filtered. The pale yellow filtrate
was added to nBuLi (7.58 mL, 2.57  in hexane) at 0 °C. The re-
sulting solution was stirred for 4 h at room temperature to give a
red solution. This clear solution was concentrated to give orange
crystals of 1b (7.3 g, 70%). The X-ray diffraction R values of 1b
are not very good, because of coordination by solvent, causing dis-
order of ether. C28H52Li2N2O2Si2 (518.78): calcd. C 64.83, H 10.10,
N 5.40; found C 62.82, H 9.59, N 5.38. 1H NMR (25 °C, 300 MHz,
[{2-(6-Me-Pyr)C(H)C(Ph)N(SiMe3)}Cu]2(µ-CuCl)
(5):
CuCl
(0.56 g, 5.66 mmol) was added to a solution of 3 (4.476 mmol) in
Et2O at –78 °C. The mixture was warmed to room temperature
slowly, stirred for 24 h, and filtered. The brown filtrate was concen-
trated and allowed to stand for one week at –30 °C to give yellow
crystals of 5 (1.82 g, 60%). C34H42ClCu3N4Si2 (788.97): calcd. C
51.76, H 5.37, N 7.01; found C 52.45, H 5.63, N 6.95. 1H NMR
C6D6): δ = 0.02 [s, 9 H, -Si(CH3)3], 2.40 (s, 1 H, -CH-SiMe3), 2.51 (25 °C, 300 MHz, CDCl3): δ = 0.05 (s, 9 H, SiMe3), 2.51 (s, 3 H,
(s, 3 H, pyridyl -CH3), 6.63, 6.65, 7.14 (m, 3 H, -CH- of pyridyl)
-CH3 of pyridyl), 5.25 (s, 1 H, -CH-C=N-), 6.76–6.79 (m, 2 H,
-CH- of pyridyl), 7.30–7.45 (m, 6 H, -CH- of pyridyl and benzene)
ppm. 13C NMR (75 MHz, C6D6): δ = 163.95, 160.54 (ipso-C of
pyridyl), 138.58, 121.74, 120.94 (-CH- of pyridyl), 63.74 (-CH-Si), ppm. 13C NMR (75 MHz, CDCl3): δ = 159.0, 157.4 (C of pyridyl),
32.81 (-CH3 of pyridyl), 27.28 (-CH- of pyridyl), 1.98 [-Si(CH3)3]
ppm.
136.1, 128.8, 128.2, 127.9, 119.0, 116.85 (-CH- of pyridyl and
-CH- of ph), 46.6 (-CH-C=N), 45.0 (-CN, of PhCN), 24.3 (-CH3
of pyridyl), 1.3 (-CH3 of SiMe3) ppm.
[{2-(6-Me-Pyr)C(H)C(tBu)N(SiMe3)}Li]2 (2): tBuCN (0.40 mL,
3.57 mmol) was added with a syringe to a stirred solution of 1b
(1.85 g, 3.57 mmol) in Et2O (20 mL) at 0 °C. The resulting orange
solution was warmed to room temperature and stirred for a further
10 h. The clear orange solution was concentrated and left to stand
for one week at –30 °C, affording dark yellow crystals of 2 (0.66 g,
69%). C30H50Li2N4Si2 (536.80): calcd. C 67.12, H 9.39, N 10.44;
[{(2-Pyr)C(H)C(Ph)N(SiMe3)}SnCl3]
(6):
SnCl4
(0.53 mL,
4.5 mmol) was added with a syringe to a solution of 4 (1.234 g,
4.5 mmol) in Et2O (10 mL) at –78 °C. The resulting yellow mixture
was warmed to room temperature slowly and stirred for 12 h. Then,
the solvents were removed in vacuo, and CH2Cl2 was added. LiCl
precipitated, and the filtrate was concentrated and allowed to stand
found C 66.78, H 9.37, N 10.28. 1H NMR (25 °C, 300 MHz, C6D6): for 3 d at room temperature to give yellow crystals of 6 (1.7 g,
δ = 0.38 (s, 9 H, -SiMe3), 1.36 [s, 9 H, (CH3)3C=N-], 2.50 (s, 3 H, 78%). C16H19Cl3N2SiSn (492.46): calcd. C 39.02, H 3.89, N 5.69;
-CH3 of pyridyl), 6.09 (s, 1 H, CH of -CH-C=N-), 6.38, 6.57, 7.05 found C 39.23, H 3.91, N 5.59. 1H NMR (300 Hz, CDCl3): δ =
(d, d, t, J = 7.2, 7.4, 7.9 Hz, 3 H, -CH- of pyridyl) ppm. 13C NMR
0.14 (s, 9 H, SiMe3), 5.97 (s, 1 H, CH), 7.20–7.86 (m, 8 H, -CH-
(75 MHz, C6D6): δ = 178.03 (CN, of tBu-C=N-), 163.46, 157.64 of pyridyl and -CH- of benzene), 8.96 (d, J = 6.0 Hz, 1 H, Pyr)
(ipso-C of pyridyl), 120.55, 123.43, 140.10 (-CH- of pyridyl), 108.29
ppm. 13C NMR (75 MHz, CDCl3): δ = 120.48–161.29 (-CH- of
(-CH-C=N), 42.70 [(CH3)3C=N-], 32.85 [(CH3)3C=N-], 27.46 pyridyl, -CH- of ph, and C=N), 106.63 (-CH-C=N), 3.14 (-CH3 of
(-CH3 of pyridyl), 6.65 (-CH3 of -SiMe3) ppm. SiMe3) ppm.
Eur. J. Inorg. Chem. 2009, 3488–3495
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3493

X. Chen, L. Guan, M. S. Eisen, H. Li, H. Tong, L. Zhang, D. Liu
FULL PAPER
Table 6. Crystallographic data for 1b, 2, 5, 6, and 7.
1b
2
5
6
7
Formula
Fw
C28H52Li2N2O2Si2
518.78
C15H25LiN2Si
268.40
C34H42ClCu3N4Si2
788.97
C16H19Cl3N2SiSn
492.46
C32H38CoN4Si2
593.77
Crystal system
Space group
monoclinic
P21/n
monoclinic
C2/c
triclinic
P1
monoclinic
Pc
orthorhombic
Pbca
¯
a [Å]
b [Å]
c [Å]
α [°]
9.452(2)
19.319(5)
18.524(4)
90.00
95.611(4)
90.00
3366.4(13)
4
1.024
9.726(3)
18.299(5)
18.385(5)
90.00
94.539(4)
90.00
3261.7(16)
8
1.093
9.528(2)
11.540(3)
17.630(4)
78.899(4)
87.297(4)
66.846(3)
1748.1(7)
2
7.1641(13)
8.9159(16)
15.297(3)
90.00
92.574(2)
90.00
976.1(3)
2
1.676
13.299(2)
15.057(2)
32.152(5)
90.00
90.00
90.00
6438.1(16)
8
1.225
β [°]
γ [°]
V [Å3]
Z
Dc [gcm–3]
1.499
1.983
µ [mm–1]
0.129
0.132
1.780
0.634
F(000)
1136
5901
4384, 0.0536
0.1354, 0.2744
0.1700, 0.2919
1.274
1168
6657
2870, 0.0307
0.0525, 0.1295
0.0632, 0.1363
1.066
812
7194
6001, 0.0233
0.0750, 0.1489
0.0846, 0.1524
1.182
488
3305
1978, 0.0196
0.0282, 0.0656
0.0287, 0.0659
1.037
2504
5654
4897, 0.0660
0.0904, 0.1706
0.1052, 0.1771
1.299
Reflections collected
Independent reflections, Rint
R1, wR2 [IϾ2σ(I)]
R1, wR2 (all data)
Goodness of fit, F2
Largest diff. peak and hole [eÅ–3] 0.491 to –0.391
0.289 to –0.166
0.616 to –0.643
0.762 to –0.321
0.528 to –0.531
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[{(2-Pyr)C(H)C(Ph)N(SiMe3)}2Co] (7): CoCl2 (0.387 g, 2.98 mmol)
was added to a solution of 4 (0.012 g, 2.98 mmol) in Et2O (10 mL)
at –78 °C. The resulting heavy blue mixture was warmed to room
temperature slowly and stirred for 24 h, and then filtered. The fil-
trate was concentrated and allowed to stand for 3 d at room tem-
perature to give pink crystals (0.57 g, 64%). C32H38CoN4Si2
(593.78): calcd. C 64.73, H 6.45, N 9.44; found C 64.63, H 6.41, N
9.49. Complex 7 is NMR-silent because of the paramagnetic nature
of the compound.
[2]
[3]
X-ray Crystallography: Data collection for 1b, 2, and 5–7 was per-
formed with Mo-Kα radiation (λ = 0.71073 Å) by using a Bruker
Smart Apex CCD diffractometer at 298(2) or 213(2) K. Crystals
were coated in oil and then directly mounted on the diffractometer
under a stream of cold nitrogen gas. A total of N reflections were
collected in the ω scan mode. Corrections were applied for Lorentz
and polarization effects as well as absorption by using multiscans
(SADABS).[33] The structure was solved by direct methods
(SHELXS-97).[34] Then, the remaining non-hydrogen atoms were
obtained from the successive difference Fourier maps. All non-hy-
drogen atoms were refined with anisotropic displacement param-
eters, whereas hydrogen atoms were constrained to parent sites, by
using a riding mode (SHELXTL).[35] Crystal data and details of
data collection and refinements for 1b, 2, and 5–7 are summarized
in Table 6. Selected bond lengths and bond angles are listed in
Tables 1, 3, 4, and 5. CCDC-723219, -723220, -723221, -723222,
-723223 (1b, 2, 5, 6, 7, respectively) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/datarequest/cif.
[4]
[5]
[6]
[7]
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[9]
Acknowledgments
We thank the Natural Science Foundation of China (20772074) and
Natural Science Foundation of Shanxi (20051011).
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3494
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 3488–3495

Synthesis and Reactions of [{2-(6-R-Pyr)(Me3Si)}CHLi·OEt2]2 (R = H or Me)
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