Catalytic C-N bond formation in guanylation reaction by N-heterocyclic carbene supported magnesium(II) and zinc(II) amide complexes

Article abstract of DOI:10.1016/j.jorganchem.2014.07.021

The catalytic activity of N-heterocyclic carbene (NHC) supported magnesium(II) and a zinc(II) amide complex towards the addition of N-H bond of amine to carbodiimide was studied. Treatment of a free carbene i.e., 1,3-di-tert-butylimidazol-2-ylidene (I^tBu) with magnesium and zinc bis(amide) i.e., M[N(SiMe₃)₂]₂, M = Mg or Zn in toluene led to the formation of I^tBu:M[N(SiMe₃) ₂]₂, M = Mg(1) and Zn(2) compounds, respectively. Both 1 and 2 were characterized by multinuclear (¹H, ¹³C and ²⁹Si) NMR spectroscopy and single X-ray crystal structure analysis. Solid state structures revealed that both complexes are monomeric in nature and their magnesium and zinc atoms are three coordinated and distorted trigonal planar in geometries. Furthermore, compounds 1 and 2 were tested as catalysts for the guanylation reaction of addition of amine to carbodiimide and turned to be excellent catalysts.

Full text of DOI:10.1016/j.jorganchem.2014.07.021

Journal of Organometallic Chemistry 769 (2014) 112e118
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Catalytic CeN bond formation in guanylation reaction by
N-heterocyclic carbene supported magnesium(II) and zinc(II) amide
complexes
Ashim Baishya, Milan Kr. Barman, Thota Peddarao, Sharanappa Nembenna*
School of Chemical Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar 751005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The catalytic activity of N-heterocyclic carbene (NHC) supported magnesium(II) and a zinc(II) amide
complex towards the addition of NeH bond of amine to carbodiimide was studied. Treatment of a free
carbene i.e., 1,3-di-tert-butylimidazol-2-ylidene (ItBu) with magnesium and zinc bis(amide) i.e., M
[N(SiMe3)2]2, M ¼ Mg or Zn in toluene led to the formation of ItBu:M[N(SiMe3)2]2, M ¼ Mg(1) and Zn(2)
compounds, respectively. Both 1 and 2 were characterized by multinuclear (1H, 13C and 29Si) NMR
spectroscopy and single X-ray crystal structure analysis. Solid state structures revealed that both com-
plexes are monomeric in nature and their magnesium and zinc atoms are three coordinated and dis-
torted trigonal planar in geometries. Furthermore, compounds 1 and 2 were tested as catalysts for the
guanylation reaction of addition of amine to carbodiimide and turned to be excellent catalysts.
© 2014 Elsevier B.V. All rights reserved.
Received 6 June 2014
Received in revised form
19 July 2014
Accepted 25 July 2014
Available online 4 August 2014
Keywords:
Catalysis
Guanidine
Magnesium
Neutral ligand
Zinc
Introduction
(addition of amine NeH bond to carbodiimide) was achieved by the
transition [10] and lanthanide [11] metal complexes. Additionally,
Metal catalyzed CeN bond formation reactions by the addition
of amine to carbodiimide are important in guanidine synthesis [1].
Guanidines are used as bases as well as catalysts in organic syn-
thesis [2]. And also, they are used as ancillary ligands [3] in a variety
of main group [4], transition [5] and lanthanide [6] metal com-
plexes. Moreover, guanidines are the important structural motifs
found in many biologically and pharmaceutically active molecules
[7]. Thus, synthesis of guanidines has attracted much attention in
organic synthesis and coordination/organometallic chemistry. The
synthesis of guanidines has been thoroughly examined by a variety
of methods [8]. Among all methods, the convenient method is the
direct addition of primary aliphatic amine to carbodiimide, but it
requires very harsh reaction conditions [9]. In contrast to primary
aliphatic amines, primary aromatic and secondary amines do not
react with carbodiimide, even at harsh reaction conditions.
Therefore, the catalytic hydroamination of carbodiimides is the
most attractive method. This is an atom economical and most
convenient approach for the synthesis of guanidines. In recent
years, the construction of a new CeN bond in guanylation reaction
there are few reports on the main group metal catalyzed hydro-
amination of carbodiimides. In 2006, Richeson's group reported the
first example of the commercially available lithium amide catalyzed
CeN bond formation in guanylation reaction [12]. Hill and co-
workers have shown the heavier group 2 element catalyzed
hydroamination of carbodiimides [13]. Alonso-Moreno et al.,
demonstrated the lithium alkyl and magnesium dialkyls catalyzed
reaction of amines with carbodiimides [14]. Moreover, very
recently, Bergman's group described the guanidinato stabilized
aluminum(III) alkyl complex catalyzed hydroamination of carbo-
diimide. [15] And also, Zhang and coworkers have used commer-
cially available AlMe3 as catalyst for the guanylation reaction [16].
To the best of our knowledge there are no reports on N-heterocyclic
carbene (NHC) stabilized magnesium and zinc bis(amides) as cat-
alysts for guanylation reaction of both primary aromatic and cyclic
secondary amines with carbodiimides.
In 1991, Arduengo and coworkers reported the synthesis and
characterization of the first room temperature stable crystalline N-
heterocyclic carbene (NHC) [17]. Since then NHC's have got enor-
mous importance in both organometallic synthesis and catalysis
[18]. Their strong s donating properties led to the isolation of stable
metal complexes that are usually resistant to decomposition.
Despite the widely developed coordination chemistry of NHC's
* Corresponding author. Tel.: þ91 674 2304126; fax: þ91 674 2302436.
E-mail address: snembenna@niser.ac.in (S. Nembenna).
http://dx.doi.org/10.1016/j.jorganchem.2014.07.021
0022-328X/© 2014 Elsevier B.V. All rights reserved.

A. Baishya et al. / Journal of Organometallic Chemistry 769 (2014) 112e118
113
with p-block elements, especially NHC supported unusual main
Solid state crystal structures of compound 1 and 2
group molecules [19], the chemistry of NHC as ligand to s-block
elements is remain less widely considered. There are some reports
on the NHC stabilized group 1 and group 2 metal complexes [20].
Monodentate and nonfunctionalized NHC stabilized zinc(II) alkyls,
alkoxides, halides etc., are known in the literature [21]. Surpris-
ingly, NHC stabilized zinc(II) bis(amide) complex is not known. In
connection to our work, it is worthy of note that Hill and coworkers
reported soluble magnesium hydride, which is prepared by the
The molecular structure of compounds 1 and 2 were further
confirmed by single crystal X-ray diffraction analysis. Crystals of 1
and 2 suitable for X-ray structure determination were grown from a
toluene solution by slow cooling to ꢀ25 ꢁC. Molecular structures of
1 and 2 and selected bond lengths and bond angles are summarized
in Figs. 1 and 2, respectively.
Compounds 1 and 2 were crystallized in the monoclinic P2(1)/n
and monoclinic P2(1) space groups, respectively. Both compounds
exist as monomers and their metal atoms are bonded to one car-
benic carbon atom and two nitrogen atoms of the amido ligands.
Thus, both magnesium and zinc atoms are three coordinated with a
distorted structure from the trigonal planar by widening the angles
between two silylamide groups (N4eMg1eN5 ¼ 128.42(7)) and
N(4)eZn(1)eN(3) 131.43(18) [ꢁ], in complexes 1 and 2 respectively.
This is due the larger steric demands of the substitution.
treatment IPr (IPr
¼
1,3-bis(2,6-diisopropylphenyl)imidazol-2-
ylidene)magnesiumbis(amide) adduct with phenylsilane [20b].
Very recently, Okuda and coworkers isolated dimeric zinc dihy-
dride compounds, those are supported by IPr and IMes (IMes ¼ 1,3-
bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) ligands and soluble
in organic solvents [22].
Herein, we report the synthesis and characterization of N-het-
erocyclic carbene supported magnesium(II) and zinc(II) amide
complexes and their catalytic application towards the guanylation
reaction of primary aromatic and cyclic secondary amines with
N,N0-dialkyl carbodiimides.
The MgeCNHC bond length in complex 1 is 2.241(2) Å, which is
longer than that of ZneCNHC bond distance in complex
2
(2.082(5) Å), this is due to the 0.19 Å longer covalent radii of
magnesium element (1.41 Å) than that of zinc element (1.22 Å) [23].
The bond distance of MgeCNHC of 1 (2.241(2) Å) is in good agree-
ment with other NHC Mg (II) adducts (2.194e2.279 Å)
[20a,20b,20e,20f]. And also, ZneCNHC bond distance (2.082(5) Å) in
2 is matches well with recently reported Okuda's NHC stabilized
zinc dihydride complexes ((IMes:ZnH2)2 2.052(3) Å and (IPr:ZnH2)2
2.054(3) Å) [22].
Results and discussion
Syntheses of N-heterocyclic carbene adducts of metal bis(amide)
The synthesis of NHC adducts of magnesium and zinc bis(amide)
i.e. ItBu:M[N(SiMe3)2]2, (ItBu ¼ 1,3-di-tert-butylimidazol-2-ylidene)
M ¼ Mg(1), Zn(2), has been achieved by the treatment of ItBu with
corresponding metal bis(amides) M[N(SiMe3)2]2, in toluene at
room temperature for 12 h (Scheme 1).
Catalytic activity
Guanylation of both primary aromatic and cyclic secondary amines
with carbodiimides
The catalytic activity of NHC supported magnesium(II) and
zinc(II) amide complexes 1 and 2 were investigated by performing
the reaction of aniline with isopropyl carbodiimide (Table 1).
The crude compounds were recrystallized from toluene
at ꢀ25 ꢁC to give colorless crystals with moderate yields 68 and 62%
for complexes 1 and 2 respectively. The isolated crystals of 1 and 2
are melting without any decomposition at temperatures 128 and
120 ꢁC, respectively. The compounds 1 and 2 are freely soluble in
organic solvents such as tetrahydrofuran, toluene, and benzene and
sparingly soluble in hexane. Both compounds are sensitive toward
air and moisture and require inert atmosphere for their stability.
The compounds 1 and 2 were characterized by multinuclear (1H,
13C and 29Si) NMR spectroscopic methods. Furthermore, the mo-
lecular structures of compounds 1 and 2 were confirmed by single
crystal X-ray structural analysis.
1H NMR spectrum of complex 1 in C6D6 exhibits three reso-
nances as singlets, two singlet resonances for the NHC ligand at
6.35 and 1.42 ppm and one singlet for amide ligand i.e. N (SiMe3)2 at
0.38 ppm. Similarly, 1H NMR spectrum for complex 2 shows two
singlets for the NHC ligand at 6.41 and 1.44 ppm and a broad signal
at 0.36 ppm for the amide ligand. 13C {1H} NMR signals appear at
178 and 176 ppm corresponding to carbene carbon of compounds 1
and 2, respectively (in free ItBu, carbene carbon resonates at
213 ppm). In 29Si {1H} NMR complex
1 exhibits a peak
at ꢀ17.12 ppm for the silyl group, where as a peak at ꢀ5.00 ppm for
compound 2 was observed.
N(SiMe3)2
N
N
N
N
M[N(SiMe3)2]2
toluene, r.t.
M
N(SiMe3)2
Fig. 1. Molecular structure of 1. All hydrogen atoms are removed for the clarity. (Due to
N4eSi4 rotation, positional disorder of three methyl groups attached to Si4 have been
observed and that is solved by splitting of each methyl group by two) Selected bond
lengths [Å] and angles [ꢁ]: Mg1eC1 2.241(2), Mg1eN4 2.0142(18), N1eC4 1.4895(28),
C1eN1 1.3670(25); C1eMg1eN4 116.97(7), C1eMg1eN5 114.59(7), N4eMg1eN5
128.42(7).
M = Mg(1), Zn(2)
Scheme 1. Synthesis of 1 and 2.

114
A. Baishya et al. / Journal of Organometallic Chemistry 769 (2014) 112e118
reaction temperature 60 ꢁC without any solvent (Table 1, Entry
5 and 7). From the above reactions, it is indicated that com-
pound 1 slightly better catalyst than that of Mg[N(SiMe3)2]2. In
addition to this compound 1 catalyzed (1 mol %) guanylation
reaction was performed in toluene and thf solvents at room
temperature led to the formation of product in quantitative
yield (Table 1, Entry 8 and 9).
The scope of compound ItBu:Mg[N(SiMe3)2]2 (1) catalyzed
addition of amines to carbodiimides was examined by taking ex-
amples of a wide variety of primary aromatic and cyclic secondary
amines. The results are given in Tables 2 and 3. Herewith, worthy to
mention that considering the same catalytic activities of both
compounds 1 and 2 in the reaction of aniline with 1,3-diisopropyl
carbodiimide (Table 1, Entries 9,10 and 7 & 11) for further re-
actions, selection of only compound 1 is justified.
It is notable from Table 2 that the catalyst 1 is compatible with
various substituents on the phenyl ring such as eOCH3, CH3, Cl, etc.,
and formation of corresponding N,N0,N00-trisubstituted guanidine
products (1ae17a) in high yields, except 9a. When the substituents
on the phenyl ring are electron donating such as eCH3, eOCH3,
excellent yields were obtained at room temperature (Table 2, En-
tries 3, 4 and 5, 6). In case of electron withdrawing substituent as Cl,
on the phenyl ring, good yield (Table 2, Entry 8) was obtained at
room temperature. No product could be isolated from the reaction
of 4-NO2 aniline with isopropyl carbodiimide at 60 ꢁC for 24 h
(Table 2, Entry 9) in presence of catalyst 1. This indicates that the
electronic factor has a great influence on the catalytic activity of the
reaction. The steric effect also shows influence on the catalytic re-
action. The reaction of 2-methyl aniline with isopropyl carbodii-
mides produced almost quantitative yield (96%) (Table 2, Entry 10),
while the reaction with 2,6 dimethyl aniline gave a good yield 81%
over room temperature stirring for 2 h (Table 2, Entry 12). Inter-
estingly, if the methyl substituent at both ortho positions of the
phenyl ring and more bulky alkyl group such as tert-butyl group at
the para position of the phenyl ring led to the formation of expected
product in quantitative yields (Table 2, Entries 13e16). In fact the
reaction of more bulky aniline, 2,6-diisopropylphenylamine with
isopropyl carbodiimide requires higher temperature (Table 2, Entry
17).
Fig. 2. Molecular structure of 2. All hydrogen atoms are removed for the clarity.
Selected bond lengths [Å] and angles [ꢁ]: Zn(1)eC(1) 2.082(5), Zn(1)eN(3) 1.958(5),
C1eN1 1.3612(66), N1eC23 1.4943(67), Zn(1)eN(4) 1.956(5); C(1)eZn(1)eN(3)
110.90(19), C(1)eZn(1)eN(4) 117.66(19), N(3)eZn(1)eN(4) 131.43(18).
The addition of aniline to isopropyl carbodiimide in the
presence of 1 mol % either compound 1 or 2 at room tem-
perature without solvent, immediate formation of the N,N0,N00-
trisubstituted guanidine product was occurred (Table 1, Entry 1
and 2). To know the effect of ItBu, which is coordinated to the
metal bis(amide), alternatively another reaction performed by
using Mg[N(SiMe3)2]2 as catalyst (at same reaction conditions)
led to no change in the product yield (Table 1, Entry 3).
Furthermore, compounds Mg[N(SiMe3)2]2 and
1 were tested
with less catalyst load of 0.1% at reaction temperature 50 ꢁC in
thf (Table 1, Entry 4 and 6) and also 0.5% catalyst load at
Table 1
Metal catalyzed reaction of aniline with N,N0-diisopropylcarbodiimide.
NH2
NH
cat.
N
C
N
N
NH
1,3-diisopropylphenylguanidine
1,3-diisopropylcarbodiimide
aniline
Entry
Catalyst
Catalyst load [mol%]
Temp. [ꢁC]
Solvent
Time [min]
Yield [%]a
1
2
3
4
5
6
7
8
1
2
1
1
1
0.1
0.5
0.1
0.5
1
25
25
25
50
60
50
60
25
25
25
60
e
1
1
1
Quant.
Quant.
Quant.
73a
e
Mg[N(SiMe3)3]2
Mg[N(SiMe3)3]2
Mg[N(SiMe3)3]2
1
1
1
1
2
2
e
thf(d8)
e
720
120
120
5
120
120
120
5
80
thf(d8)
e
88b
94
thf
Quant.
Quant.
Quant.
92
9
10
11
1
1
0.5
Toluene
Toluene
e
The reaction was performed by treating 1 equiv of aniline with 1 equiv of N,N0-diispropyl carbodiimide.
a
Isolated yield.
b
NMR yield measured by integration of consumption of starting material relative to the formation of product.

A. Baishya et al. / Journal of Organometallic Chemistry 769 (2014) 112e118
115
Table 3
Results of reaction of various cyclic secondary amines with N,N0-dialkyl carbodii-
mides catalyzed by ItBu:Mg[N(SiMe3)2]2 (1).
Table 2
Results of reaction of various anilines with N,N0-dialkyl carbodiimides catalyzed by
ItBu:Mg[N(SiMe3)2]2 (1).
R
R1
N
cat. 1 (3 mol%)
R
R1R2NH
+
N
R N C N R
toluene, 110 0C
24 h
Ar
NH
R
NH
1
cat. (1 mol%)
R2
+
R N C N R
ArNH2
N
neat
NH
R
Entry
R
R1R2NH
Producta
Yield [%]b
Entry
R
ArNH2
Temp Time
Producta Yield
[%]b
[ꢁC]
[min]
1
2
3
4
5
6
7
i-Pr
Cy
1b
2b
3b
4b
5b
6b
7b
96
96
92
95
93
96
86
1
2
3
4
5
6
7
8
9
i-Pr
Cy
25
25
25
25
25
25
25
60
60
1
40
1a
2a
3a
4a
5a
6a
7a
8a
9a
94
99
97
98
97
96
97
66
i-Pr
Cy
i-Pr
Cy
1
i-Pr
Cy
60
i-Pr
Cy
1
i-Pr
10
i-Pr
Cy
240
720
1440
8
i-Pr
i-Pr
8b
9b
97
93
i-Pr
No reaction
9
10
11
12
i-Pr
Cy
25
25
25
60
20
10a
11a
12a
96
96
81
a
Reaction was performed by treating 1 equiv of cyclic secondary amine with
1 equiv of N,N0-dialkyl cabodiimide.
b
Isolated yield.
Furthermore, we examine catalytic activity of compound 1 to-
wards the addition of a various cyclic secondary amines with car-
bodiimides (Table 3). N,N0,N00-trisubstituted guanidine products
(1be9b) were obtained in good to excellent yields. However, the
reaction generally requires a higher temperature 110 ꢁC and longer
reaction time 24 h for the completion. From the above results
(Tables 2 and 3), it indicates that catalyst 1 is compatible towards
hydroamination of various amines.
i-Pr
120
13
14
15
16
i-Pr
Cy
25
25
25
25
1
10
10
5
13a
14a
15a
16a
94
95
96
96
i-Pr
Cy
Proposed mechanism for guanylation reaction
Based on the above results, a possible catalytic cycle for the
addition of primary aromatic or cyclic secondary amines to carbo-
diimides is proposed in Scheme 2.
The reaction of primary/secondary amine with NHC metal
bis(amide) adduct gave the new bis(amido) intermediate A through
an elimination of HN(SiMe3)2. The postulated intermediate A
further reacts with carbodiimide to produce metal guanidinate
intermediate B through an insertion reaction. Interaction of metal
guanidinate species B with amines releases the guanidine product
along with the regeneration of the catalytically active species. For
primary aromatic amines, a 1,3-H shift occurs to give the final stable
guanylation product. Efforts were made to isolate and characterize
the intermediates A and B and turned to be unsuccessful.
17
i-Pr
100
720
17a
86c
a
The reaction was performed by treating 1 equiv of aromatic amine with 1 equiv
of N,N0-dialkyl carbodiimide.
b
Isolated yield.
c
The reaction was done in toluene at 100 ꢁC for 12 h.

116
A. Baishya et al. / Journal of Organometallic Chemistry 769 (2014) 112e118
(400 MHz, C6D6, 25 ꢁC):
0.38 (s, 36H, N{Si(CH3)3}2) ppm. 13C {1H} NMR (100 MHz, C6D6,
25 ꢁC):
¼ 177.7 (carbene C), 119.1 (CH), 57.5 (C(CH3)3), 31.0 (CH3),
6.9 (SiCH3) ppm. 29Si {1H} NMR (80 MHz, C6D6, 25 ꢁC):
¼ ꢀ17.12 N(SiMe3)2 ppm.
d
¼ 6.35 (s, 2H, CH), 1.42 (s, 18H, C(CH3)3),
R
ItBu: Mg[N(SiMe3)2]2
R1R2NH
Ar
HN
N
d
HN
R
HN(SiMe3)2
ItBu: Mg[N(SiMe3)2(NR1R2)]
d
R1 = Ar
R2 = H
1,3-H shift
Synthesis of ItBu:Zn[N(SiMe3)2]2 (2)
A
R
N
This compound was synthesized following the same procedure
as described above with starting materials 1,3-di-tert-butylimida-
zol-2-ylidene (0.190 g and 1.1 mmol) and Zn[N(SiMe3)2]2 (0.427 g
and 1.1 mmol). Colorless crystalline solid compound 2 was obtained
from toluene. Yield: 0.367 g (62%). M. p. 120 ꢁC. 1H NMR (400 MHz,
R1
N
C N
R
R
N
HN
R
R2
C6D6, 25 ꢁC):
d
¼ 6.41 (s, 2H, CH), 1.44 (s, 18H, CH3), 0.36 (br, 36H,
R1R2NH
N(SiCH3)3) ppm. 13C {1H} NMR (100 MHz, C6D6, 25 ꢁC):
d
¼ 175.7
R
(carbene C), 119.2 (CH), 58.6 (C(CH3)3), 31.4 (CH3), 6.9 (SiCH3) ppm.
R1
N
29Si {1H} NMR (80 MHz, C6D6, 25 ꢁC):
d
¼ ꢀ5.00 N(SiMe3)2 ppm.
N
R2
(Me3Si)2N Mg
ItBu:
N
X-ray crystallography
R
B
Suitable crystals of complexes 1 and 2 were mounted on a glass
fiber. The crystallographic data for these compounds are summa-
rized in Table 4.
Scheme 2. Proposed mechanism for the guanylation reaction catalyzed by the ItBu:Mg
[N(SiMe3)2]2 (1).
Geometry and intensity data were collected with a Bruker
SMART D8 goniometer equipped with an APEX CCD detector and
with an INCOATEC micro source (Mo-K
a
radiation,
l
¼ 0.71073 Å,
Conclusion
multilayer optics). Temperature was controlled using an Oxford
Cryostream 700 instrument. Intensities were integrated with
SAINTþ [26] and corrected for absorption with SADABS [27]. The
structures were solved by direct methods and refined on F2 with
SHELXL-97 [28]. Hydrogen atoms were fixed at calculated positions
and their positions were refined by a riding model. All non-
hydrogen atoms were refined with anisotropic displacement
parameters.
In summary, we have synthesized nonfunctionalized mono-
dentate NHC supported magnesium(II) and zinc(II) amide com-
plexes by simple addition of 1,3-di-tert-butylimidazol-2-ylidene
(ItBu) to the metal bis(amide). These NHC metal bis(amide)
adduct exhibited catalytic activity toward addition of primary ar-
omatic and cyclic secondary amines with carbodiimide. Moreover,
compound 1 is compatible to a wide range of substrates and sol-
vents. Further studies are underway aimed at the catalytic addition
of terminal alkynes and phosphines to carbodiimides, and also
complex 1 catalyzed ring opening of cyclic esters.
General procedure for the direct synthesis of guanidines from the
reaction of primary aromatic amines with carbodiimides catalyzed
by 1
A 30 mL Schlenk tube under inert atmosphere (N2-glovebox)
was charged with the catalyst ItBu:Mg[N(SiMe3)2]2 (0.01 equiv),
aromatic amine (1 equiv). To the above mixture carbodiimide
Experimental section
General
All manipulations were carried out using standard Schlenk line
and glovebox techniques under an inert atmosphere of dinitrogen.
NMR reactions were conducted in Young valve NMR tubes and
sealed in a glovebox. NMR spectra were recorded on Bruker AV
400 MHz spectrometer for 1H NMR (13C{1H} NMR 100 MHz and 29Si
{1H} NMR 80 MHz). Solvents (toluene, benzene, and hexane) were
collected from MBraun Solvent Purification System. Solvent thf was
dried over sodium and stored in Na wire. C6D6 was purchased from
SigmaeAldrich and dried over sodium before distillation under
nitrogen and storage over molecular sieves. ItBu [24] and Mg
[N(SiMe3)2]2 [25] were prepared according to reported literature
procedures. All amines were predried or distilled before use. Zn
[N(SiMe3)2]2, N,N0-diisopropylcarbodiimide and N,N0-dicyclohexyl-
carbodiimide were purchased from SigmaeAldrich and used
without further purification.
Table 4
Crystal data and structure refinement for 1 and 2.
1
2
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C23H56MgN4Si4
525.39
Monoclinic
P2(1)/n
11.949(5)
23.325(9)
12.104(5)
95.190(5)
3360(2)
100
1.039
4
1160
C23H56ZnN4Si4
566.45
Monoclinic
P2(1)
11.334(5)
12.060(5)
11.995(5)
96.655(5)
1628.5(12)
100
b (Å)
c (Å)
b
(ꢁ)
V (Å3)
T (K)
Density (calc.) mg/m3
1.155
2
616
18,736
Z
F(000)
No. of reflections collected
No. of independent reflections
58,716
10,229
6046
Synthesis and characterization of complexes 1 and 2
Synthesis of ItBu:Mg[N(SiMe3)2]2 (1)
[R(int) ¼ 0.0423]
[R(int) ¼ 0.1017]
0.71069
0.918
1.71e25.50
0.859
l
(Å)
0.71073
Absorption coefficient (mmꢀ1
Theta range (deg)
)
0.212
2.51e30.66
1.041
1,3-Di-tert-butylimidazol-2-ylidene (ItBu) (1.27
g
and
Goodness-of-fit on F2
7.07 mmol) and Mg[N(SiMe3)2]2 (2.44 g and 7.07 mmol) were dis-
solved in toluene and stirred at room temperature for 12 h. Upon
concentration and cooling to ꢀ25ꢁ the formation of compound 1 as
colorless crystals yielded. Yield: 2.516 g (68%). M. p. 128 ꢁC. 1H NMR
R [I > 2
d
(I)]
R1 ¼ 0.0442,
wR2 ¼ 0.0940
0.503, ꢀ0.290
R1 ¼ 0.0538,
wR2 ¼ 0.1268
1.268, ꢀ0.716
Largest diff. peak and
hole (e Åꢀ3
)

A. Baishya et al. / Journal of Organometallic Chemistry 769 (2014) 112e118
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Acknowledgments
S.N. acknowledges Science and Engineering Research Board
(SERB), Department of Science and Technology (DST) for the
research grant No. SR/S1/IC-52/2012. A.B. and T.P. acknowledge
University Grant Commission (UGC) for their fellowships.
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Appendix A. Supplementary material
CCDC 985052 and 985053 contains the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
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