Formation of CC and CO bonds via solvothermal in situ metal-ligand reaction: Synthesis and crystal structures of two novel nickel(II) complexes supported by in situ generated polydentate Schiff base ligands

Article abstract of DOI:10.1016/j.inoche.2013.01.026

Under solvothermal conditions, complexes Ni(HL2) (1) and Ni(L3)·MeOH (2·MeOH) (H₃L2 = N-(2-(2-hydroxybenzylideneamino)-1-(2- hydroxyphenyl)-2-(pyridin-2-yl)ethyl)picolinamide; H₂L3 = 1-(pyridin-2-yl)prop-1-ene-1,2-diyl)bis(azan-1-yl-

Full text of DOI:10.1016/j.inoche.2013.01.026

Inorganic Chemistry Communications 30 (2013) 92–96
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Formation of C\C and C\O bonds via solvothermal in situ metal–ligand reaction:
Synthesis and crystal structures of two novel nickel(II) complexes supported by
in situ generated polydentate Schiff base ligands
Tao Lei a,b, Qian Gao a, Wen-Qian Chen a, Yan-Mei Chen a, Wei Liu a, Shu-Min Yang a, Wei-Wei Chen a,
Wu Li b, Yahong Li a,c,
⁎
a
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
CAS Key Laboratory of Salt Lake Resources and Chemistry, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Under solvothermal conditions, complexes Ni(HL2) (1) and Ni(L3)·MeOH (2·MeOH) (H3L2=N-(2-
(2-hydroxybenzylideneamino)-1-(2-hydroxyphenyl)-2-(pyridin-2-yl)ethyl)picolinamide; H2L3=1-(pyridin-2-
yl)prop-1-ene-1,2-diyl)bis(azan-1-yl-1-ylidene)bis((methan-1-yl-1-ylidene)diphenol) have been synthesized
from the reaction of Ni(CH3COO)2·4H2O with 2-((pyridin-2-ylmethyleneamino)methyl)phenol (HL1) at 70 and
90 °C, respectively. The complexes were characterized by X-ray single crystal diffraction, IR spectroscopy, and
elemental analysis. The plausible mechanisms for the formation of H3L2 and H2L3 via solvothermal in situ
metal–ligand reactions were proposed.
Received 8 October 2012
Accepted 29 January 2013
Available online 4 February 2013
Keywords:
Crystal structures
Nickel(II) complexes
In situ metal–ligand reaction
Carbon–carbon bond making
Carbon–oxygen bond formation
© 2013 Elsevier B.V. All rights reserved.
Since the first example of solvothermal in situ metal–ligand reaction
on the rearrangement of 2,2′-dipyridylamine into dipyrido-[1,2-a:2′,3′-
d]imidazole, which was discovered by Li and coworkers, appeared in
the literature [1], solvothermal in situ metal–ligand reaction has
attracted continuous interest from many groups around the world
[2–4]. Many novel coordination complexes as well as unusual ligands
which could not be accessible from conventional synthetic methods
have been achieved via solvothermal in situ metal–ligand reaction. Up
to date, more than 10 types of solvothermal in situ metal–ligand reactions
have been reported, which include carbon–carbon bond formation [5,6],
carbon–oxygen bond making [7–9], and tetrazole and triazole formations
[4,10,11], as well as cleavage and formation of S\S bond [12–14]. It has
been found that many metals, including CuI/II [9,15], FeII/III [16,17], CdII
[5], ZnII [18], CoII [16,19], AgI [20] and AuI [21], could initiate the
solvothermal in situ metal–ligand reaction. However, the examples of
NiII-mediated solvothermal in situ metal–ligand are rare [22]. Recently,
we reported FeII/III, CoII and CuII-mediated carbon–carbon bond-making
reactions under solvothermal conditions [16]. As an extension of our pre-
vious work, we conducted the reaction of Ni(CH3COO)2·4H2O with
2-((pyridin-2-ylmethyleneamino)methyl)phenol (HL1) [23] at different
temperatures under solvothermal conditions. Two novel coordination
complexes Ni(HL2) (1) and Ni(L3)·MeOH (2·MeOH) (H3L2=N-(2-(2-
hydroxybenzylideneamino)-1-(2-hydroxyphenyl)-2-(pyridin-2-yl)
ethyl)picolinamide; H2L3=1-(pyridin-2-yl)prop-1-ene-1,2-diyl)
bis(azan-1-yl-1-ylidene)bis((methan-1-yl-1-ylidene)diphenol) have
been synthesized. Herein we report the synthesis, crystal structures of
the complexes, as well as the detailed analysis of mechanisms for the
formation of the H3L2 and H2L3 ligands.
The initial experiment was conducted by heating the mixture of HL1
and Ni(CH3COO)2·4H2O in MeOH/MeCN at 70 °C under solvothermal
conditions. Red crystals of complex 1 were obtained. The most remark-
able feature of this reaction is the in situ formation of the H3L2 ligand,
which was assumed to be generated via carbon–carbon coupling reac-
tion and oxidation of methylene to form a carbonyl (Scheme 1).
The ligand H3L2 was isolated and the structure of which was de-
termined by NMR spectroscopy (Figs. S3 and S4).
As the temperature of the mixture was increased to 90 °C, namely,
treatment of Ni(CH3COO)2·4H2O with 2 equiv of HL1, complex 2·MeOH
was produced (Scheme 1). A prominent feature regarding the synthesis
of 2·MeOH is the simultaneous formation of C_C and C_N bonds in a
one-pot reaction.
The single crystal X-ray diffraction determination reveals that com-
plex 1 [24] crystallizes in the triclinic crystal system of P-1 space group.
Complex 1 is mononuclear and consists of one NiII ion and one HL22−
ligand (Fig. 1a). The central NiII ion is four-coordinate and adopts square
planar geometry. The NiII ion is located in the inner N3O cavity of the
new Schiff base ligand HL22−. The Ni\O(1), Ni(1)\N(1), Ni(1)\N(2)
⁎
Corresponding author at: Key Laboratory of Organic Synthesis of Jiangsu Province,
College of Chemistry, Chemical Engineering and Materials Science, Soochow University,
Suzhou 215123, China. Fax: +86 512 65880089.
E-mail address: liyahong@suda.edu.cn (Y. Li).
1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2013.01.026

T. Lei et al. / Inorganic Chemistry Communications 30 (2013) 92–96
93
Scheme 1. Synthesis of complexes 1 and 2·MeOH. MeOH molecule was omitted for clarity.
and Ni(1)\N(3) bond lengths are 1.815(1), 1.891(2), 1.825(2) and
1.823(2) Å, respectively. The O(1)\Ni(1)\N(1), O(1)\Ni(1)\N(2),
N(1)\Ni(1)\N(3), and N(2)\Ni(1)\N(3) angles differ only slightly
from 90°, whereas the O(1)\Ni(1)\N(3) and N(1)\Ni(1)\N(2) an-
gles are close to 180°. The bond distances and bond angles around the
NiII ion indicate that the geometry around the metal is perfectly
square-planar.
Complex 1 features intermolecular C_O…H hydrogen contacts
between OH group of phenol ring as hydrogen atom donor and oxy-
gen atom from carbonyl as acceptor, and C\H…O bondings between
CH group of pyridine as hydrogen atom donor and oxygen atom from
OH group of phenol ring as acceptor. In addition, noticeable intramo-
lecular C\H…O contacts from CH group of (H)C_N (donor) to the
OH group of phenol ring (acceptor) are determined. These hydrogen
contacts connect the molecules to generate an infinite 2D network
(Fig. 1b).
Single crystal X-ray analysis reveals compound 2·MeOH [25] crys-
tallizes in the monoclinic crystal system of the P 21/c space group. Com-
plex 2·MeOH is also mononuclear and exhibits pseudo square-planar
geometry (Fig. 2a). The NiII ion sits in the macro-cyclic cavity and is
coordinated by two nitrogen atoms (N(1) and N(2)) from two imine
groups and two oxygen atoms (O(1) and O(2)) from two phenol groups
of the in situ formed L32− ligand. The Ni\O(1), Ni(1)\O(2), Ni(1)\N(1)
and Ni(1)\N(2) bond lengths are 1.842(3), 1.836(3), 1.855(3) and
1.851(3) Å, respectively. The N(O)\Ni\O(N) bond angles vary from
83.64° to 177.76°, indicating that the square-planar geometry of NiII ion
is slightly distorted.
There are five types of intermolecular hydrogen bondings in 2·MeOH,
namely, two O\H…O hydrogen contacts between OH group of methanol
(donor) and OH groups (acceptor) of two phenol rings of one H2L3 li-
gand, two C\H…O contacts between OH group of methanol (acceptor)
and one pyridine molecule and one (H)C_N group (donors) of another
equiv of the H2L3 ligand, and C\H…O bonding between OH group of
phenol (acceptor) and CH group of pyridine (donor). The intramolecular
C\H…N contacts from CH group of methyl group to the N atom of pyri-
dine are determined. These hydrogen contacts connect the molecules to
generate a 1D chain structure (Fig. 1b).
and 2·MeOH are in good agreement with each other, indicating that
the synthesized complexes are sufficiently pure.
Naturally, we were interested in the mechanisms for the formations
of the H3L2 and H2L3 ligands, i.e., the plausible pathways for the one-pot
formation of C\C and C_O bonds in H3L2, and C_C and C_N bonds in
H2L3.
Probable mechanisms for the formation of H3L2 are shown in
Scheme 2a. In the presence of Lewis base CH3COO−, C_N bond shift oc-
curs to generate an intermediate IN1 (step 1). Oxidation of the active
methylene group in IN1 proceeds in the presence of O2 and H2O to pro-
duce the metastable imide intermediate IN2 (step 2). In the C\C
bond-forming step 3, carbon–carbon coupling occurs between IN2
and IN1, yielding H3L2 as the final product.
The pathway for the formation of H2L3 (Scheme 2b) is assumed to
be slightly different from that of H3L2. First, two independent reactions
may occur. (1) The double bond shift of HL1 gives alcoholic intermediate
IN1, which is subsequently oxidized by O2 (in the presence of H2O) to
yield a new intermediate IN3. (2) The condensation between CH3COOH,
which is possibly derived from Ni(CH3COO)2·4H2O or CH3CN, and
2-(aminomethyl)phenol (which is probably to be generated from hydro-
lysis of HL1) gives intermediate IN4. The intermediate IN4 subsequently
undergoes double bond shift to afford IN5. Next, double condensations
between IN3 and IN5 produce H2L3.
In summary, two novel coordination complexes Ni(HL2) (1) and
Ni(L3)·MeOH (2·MeOH) have been synthesized by in situ generated
H3L2 and H2L3 ligands. Formations of H3L2 and H2L3 involve oxida-
tion of methylene followed by carbon–carbon coupling reaction of
HL1 under solvothermal conditions. The complexes were characterized
by X-ray single crystal diffraction, IR spectroscopy, and elemental anal-
ysis. The reactions for creating different ligands at different tempera-
tures are rare in coordination chemistry as well as in synthetic organic
chemistry, demonstrating the synthetic novelty of this work.
Acknowledgments
The authors appreciate the financial supports of Natural Science
Foundation of China (20872105, 21272167), Open Project of Key Lab-
oratory for Magnetism and Magnetic Materials of the Ministry of Ed-
ucation of Lanzhou University (LZUMMM2010003) and Graduation
Education Innovation Project in Jiangsu Province (CXZZ12_0808).
In order to confirm the phase purity of complexes 1 and 2·MeOH,
X-ray powder diffraction (XRD) experiments were conducted (Figs.
S5 and S6). The experimental and computer-simulated patterns of 1

94
T. Lei et al. / Inorganic Chemistry Communications 30 (2013) 92–96
a
b
Fig. 1. (a) ORTEP representation of the structure of 1 from X-ray diffraction (30% probability). (b) Packing diagram of 1.
Appendix A. Supplementary material
[4] H. Zhao, Z.R. Qu, H.Y. Ye, R.G. Xiong, In situ hydrothermal synthesis of tetrazole
coordination polymers with interesting physical properties, Chem. Soc. Rev. 37
(2008) 84–100.
CCDC 880375 and 880376 contain the supplementary crystallo-
graphic data for complexes 1 and 2·MeOH. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data as-
sociated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.inoche.2013.01.026.
4+
[5] N. Zheng, X. Bu, P. Feng, Self-assembly of novel dye molecules and [Cd8(SPh)12
]
cubic clusters into three-dimensional photoluminescent superlattice, J. Am. Chem.
Soc. 124 (2002) 9688–9689.
[6] S. Hu, J.C. Chen, M.L. Tong, B. Wang, Y.X. Yan, S.R. Batten, Cu2+-mediated
dehydrogenative coupling and hydroxylation of an N-heterocyclic ligand: from gen-
eration of a new tetratopic ligand to the designed assembly of three-dimensional
copper(I) coordination polymers, Angew. Chem. Int. Ed. 44 (2005) 5471–5475.
[7] Y.Z. Zheng, M.L. Tong, X.M. Chen, Controlled hydrothermal synthesis of copper(II or I, II)
coordination polymers via pH-dependent in situ metal/ligand redox reactions, New J.
Chem. 28 (2004) 1412–1415.
References
[8] X.M. Zhang, M.L. Tong, X.M. Chen, Hydroxylation of N-heterocycle ligands observed
in two unusual mixed-valence CuI/CuII complexes, Angew. Chem. Int. Ed. 41 (2002)
1029–1031.
[9] J. Tao, Y. Zhang, M.L. Tong, X.M. Chen, T. Yuen, C.L. Lin, X.Y. Huang, J. Li, A
mixed-valence copper coordination polymer generated by hydrothermal metal/ligand
redox reactions, Chem. Commun. (2002) 1342–1343.
[10] J.P. Zhang, S.L. Zheng, X.C. Huang, X.M. Chen, Two unprecedented 3-connected
three-dimensional networks of copper(I) triazolates: in situ formation of
ligands by cycloaddition of nitriles and ammonia, Angew. Chem. Int. Ed. 43
(2004) 206–209.
[1] J.Y. Lu, B.R. Cabrera, R.-J. Wang, J. Li, Chemical rearrangement under hydrothermal
conditions: formation of polymeric chains (CuX)2(dpiz) and (CuX)3(dpiz) (X=Cl, Br;
dpiz=dipyrido-[1,2-a:2′,3′-d]imidazole) and crystal structures of ∞1[(CuCl)2(C10H7N3)]
and ∞1 [(CuBr)3(C10H7N3)], Inorg. Chem. 37 (1998) 4480–4481.
[2] X.M. Chen, M.L. Tong, Solvothermal in situ metal–ligand reactions: a new bridge
between coordination chemistry and organic synthetic chemistry, Acc. Chem. Res.
40 (2007) 162–170.
[3] X.M. Zhang, Hydro(solvo)thermal in situ ligand syntheses, Coord. Chem. Rev. 249
(2005) 1201–1219.

T. Lei et al. / Inorganic Chemistry Communications 30 (2013) 92–96
95
a
b
Fig. 2. (a) ORTEP representation of the structure of 2·MeOH from X-ray diffraction (30% probability). Solvated molecule was omitted for clarity. (b) Packing diagram of 2·MeOH.
[11] J.P. Zhang, Y.Y. Lin, X.C. Huang, X.M. Chen, Copper(I) 1,2,4-triazolates and related
complexes: studies of the solvothermal ligand reactions, network topologies, and
photoluminescence properties, J. Am. Chem. Soc. 127 (2005) 5495–5506.
[12] D. Li, T. Wu, Transformation of inorganic sulfur into organic sulfur: a novel
photoluminescent 3D polymeric complex involving ligands in situ formation,
Inorg. Chem. 44 (2005) 1175–1177.
solvothermal syntheses, structures and magnetic property, Inorg. Chem.
Commun. 19 (2012) 4–9.
[18] O.R. Evans, W.B. Lin, Synthesis of zinc oxalate coordination polymers via unprec-
edented oxidative coupling of methanol to oxalic acid, Cryst. Growth Des. 1
(2001) 9–11.
[19] C.M. Liu, S. Gao, H.-Z. Kou, Dehydrogenative coupling of phenanthroline under
[13] D. Li, T. Wu, X.-P. Zhou, R. Zhou, X.-C. Huang, Twelve connected net with face-
centered cubic topology: a coordination polymer based on [Cu12(4-SCH3)6]6+
clusters and CN-linkers, Angew. Chem. Int. Ed. 44 (2005) 4175–4178.
[14] X.-P. Zhou, D. Li, T. Wu, X. Zhang, Syntheses of supramolecular CuCN complexes
by decomposing CuSCN: a general route to CuCN coordination polymers, Dalton
Trans. (2006) 2435–2443.
[15] X.M. Zhang, M.L. Tong, M.L. Gong, H.K. Lee, L. Luo, K.F. Li, Y.X. Tong, X.M. Chen,
Syntheses, crystal structure, and physical properities of dinuclear copper(I) and
tetranuclear mixed-valence copper(I, II) complexes with hydroxylated bipyridyl-like li-
gands, Chem. Eur. J. 8 (2002) 3187–3194.
hydrothermal conditions: crystal structure of a novel layered vanadate
complex constructed of 4,8,10-net sheets: [(2,2′-biphen)Co]V3O8.5, Chem.
Commun. (2001) 1670.
[20] A.J. Blake, N.R. Champness, S.S.M. Chung, W.S. Li, M. Schröder, In situ ligand
synthesis and construction of an unprecedented three-dimensional array
with silver(I): a new approach to inorganic crystal engineering, Chem. Commun.
17 (1997) 1675–1676.
[21] Q.-H. Wei, L.-Y. Zhang, G.-Q. Yin, L.-X. Shi, Z.-N. Chen, Luminescent
heteronuclear AuI5AgI8 complexes of {1,2,3-C6(C6H4R-4)3}3− (R=H, CH3, But) by
cyclotrimerization of arylacetylides, J. Am. Chem. Soc. 126 (2004) 9940.
[22] D.R. Xiao, Y. Hou, E.B. Wang, J. Lü, Y.G. Li, L. Xu, C.W. Hu, Dehydrogenative cou-
pling of 2,2′-bipyridine: hydrothermal synthesis and crystal structure of a novel
polyoxovanadate decorated with the 2,2′;6′,2″;6″,2‴-quaterpyidine ligand, Inorg.
Chem. Commun. 7 (2004) 437–439.
[16] Y.M. Chen, L. Li, Z. Chen, Y.L. Liu, H.L. Hu, W.Q. Chen, W. Liu, Y.H. Li, T. Lei, Y.Y. Cao,
Z.H. Kang, M.S. Lin, W. Li, Metal-mediated controllable creation of secondary, tertia-
ry, and quaternary carbon centers: a powerful strategy for the synthesis of iron, co-
balt, and copper complexes with in situ generated substituted 1 pyridineimidazo
[1,5 a]pyridine ligands, Inorg. Chem. 51 (2012) 9705–9713.
[23] Z. Chen, J. Wu, Y.M. Chen, L. Li, Y.Z. Xia, Y.H. Li, W. Liu, T. Lei, L.J. Yang, D.D. Gao, W.
Li, Rapid access to substituted piperazines via Ti(NMe2)4-mediated C\C bond-
making reactions, Organometallics 31 (2012) 6005–6013.
[17] W.Q. Chen, Y.M. Chen, T. Lei, W. Liu, Y.H. Li, V-shaped Fe3III and linear FeII/FeIII/FeII
complexes supported by phenyl-pyridine-2-yl-methanone oxime ligand:

96
T. Lei et al. / Inorganic Chemistry Communications 30 (2013) 92–96
a
C=N double bond shift
Step 1
OH
N
N
Ν
N
N
Η
Ν
OH
OH
Step 3
IN1
HL1
O
Ν
Step 2 O2
Ν
ΗΟ
H3L2
N
O
N
OH
IN2
b
C=N double
bond shift
O2
N
N
N
N
N
N
HO
OH
OH
OH
OH
HL1
IN1
IN3
N
N
+
OH
OH
C=N double
bond shift
H3C
N
OH
NH2
OH
+
N
N
O
HO
HO
IN4
HO
IN5
H2L3
Scheme 2. Possible mechanisms for the formation of the H3L2 (a) and H2L3 (b) ligands.
[24] Crystallographic analysis of 1 (C26H20N4NiO3): M=495.17, Triclinic, P-1, crystal
size 0.15×0.10×0.08 mm, V=1103.71(19) Å3, a=9.1759(8) Å, b=9.4944(8) Å,
c=14.3254(12) Å, α=104.438 (6) °, β=101.047 (6)°, γ=107.488 (6)°,
T=298(2) K, Z=2, ρcal =1.490 Mg/m3, Mo K(α1)=0.71073 Å. 24666 reflec-
tions measured, of which 5502 were unique. R1=0.0505, wR2=0.0856,
GooF=0.957. The structure was solved by direct methods (SHELXS-97) and
refined with SHELXS-97.
[25] Crystallographic analysis of 2 (C23H18N4NiO2): M=441.12, Monoclinic, P21/c, crys-
tal size 0.30×0.08×0.08 mm, V=2041.3(3) Å3, a=9.7807(9) Å, b=15.5684(14) Å,
c=14.7984(12) Å, β=115.067(5)°, T=299(2) K, Z=4, ρcal=1.435 Mg/m3, Mo
K(α1)=0.71073 Å. 16127 reflections measured, of which 4405 were unique.
R1=0.0557, wR2=0.1387, GooF=0.977. The structure was solved by direct
methods (SHELXS-97) and refined with SHELXS-97.