Synthesis and structure of the lithium, zirconium and hafnium N-silyl-N′-benzyl-benzamidinates

Article abstract of DOI:10.1016/j.ica.2008.03.112

The interaction of LiN(SiMe₃)CH₂Ph with one equivalent of benzenitrile gave the N-silyl-N′-benzyl-benzamidinato-lithium compound [{Me₃SiNC(Ph)N(CH₂Ph)}Li(Et₂O)]₂ (1). The derivative zirconi

Full text of DOI:10.1016/j.ica.2008.03.112

Inorganica Chimica Acta 362 (2009) 583–586
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Note
Synthesis and structure of the lithium, zirconium and hafnium
N-silyl-N0-benzyl-benzamidinates
*
Yong Zhang, Jian-Ren Xie, Jian-Ping Guo, Xue-Hong Wei, Shu-Ping Huang, Dian-Sheng Liu
Institute of Applied Chemistry, Shanxi University, Taiyuan 030006, PR China
a r t i c l e i n f o
a b s t r a c t
The interaction of LiN(SiMe3)CH2Ph with one equivalent of benzenitrile gave the N-silyl-N0-benzyl-benz-
amidinato-lithium compound [{Me3SiNC(Ph)N(CH2Ph)}Li(Et2O)]2 (1). The derivative zirconium and haf-
nium compounds were produced by the treatment of 1 with ZrCl4 or HfCl4 in tetrahydrofuran or diethyl
ether at ambient temperature, respectively, with the general formula [Me3SiNC(Ph)N(CH2Ph)]3MCl
(M = Zr (2), Hf (3)). Compounds 1, 2 and 3 were also characterized by X-ray single crystal diffraction and
NMR analysis.
Article history:
Received 21 June 2007
Received in revised form 15 March 2008
Accepted 29 March 2008
Available online 3 April 2008
Keywords:
N-silyl-N0-benzyl-benzamidinates
Lithium
Ó 2008 Elsevier B.V. All rights reserved.
Zirconium
Hafnium
Crystal structure
1. Introduction
2. Experimental
Amidinates [RC(NR0)2]ꢀ exhibit versatile, and flexible coordina-
tion properties and have received increasing attention as ancillary
ligands for both main-group and transition-metal complexes
[1–15]. The alkali-metal chemistry of bis(aryl)formamidinate li-
gands has also been active for the past 5 years [16]. These anions
make attractive ligands because of their steric and electronic tena-
bility through the programmed variation of the N and C substituents
[17–20]. The transition metal amidinates have been used as ancil-
lary ligands in olefin polymerization catalysts [21]. The applicability
of these ligands could be enhanced considerably with the ability to
introduce additional functionalities as pendant groups on the amidi-
nate ligand framework. Recently, we reported a convenient route for
the synthesis of silyl-linked bis(amidinate)ligands, group (I) metal
derivatives [22] and the chelating diamido zirconium and hafnium
compounds [23]. In this contribution we describe the synthesis of
such a functionalized amidinate, [Me3SiNC(Ph)N(CH2Ph)]ꢀ, which
has a pendant benzyl group attached to one of the amidinate nitro-
gens. The zirconium and hafnium compounds with this ligand were
prepared and structurally characterized by X-ray single crystal
diffraction.
2.1. Materials and apparatus
All the reactions were carried out under nitrogen atmosphere in
a flamed Schlenk-type glassware on a dual manifold Schlenk line.
Solvents were pre-dried. All the chemicals used were of reagent
grade, obtained from ACROS. 1H and 13C NMR spectra were re-
corded on a Bruker DRX-300 spectrometer. Elemental analyses
were performed on a Vario EL-III instrument.
2.2. Synthesis
2.2.1. Li2[Me3SiNC(Ph)NCH2Ph]2(OEt2)2 (1)
A solution of LiBun in hexane (6.94 mmol) was added dropwise
to a stirred solution of Me3SiNHCH2Ph (1.244 g, 6.94 mmol) in
diethyl ether (30 ml) at 0 °C. The mixture was then warmed to
room temperature and stirred for 12 h. PhCN (0.687 ml,
6.94 mmol) was added to the above reactant mixture dropwise at
0 °C. The reactant mixture was concentrated in vacuo to ca.
10 ml and stored at ꢀ15 °C, yielding colourless crystals of 1
(2.11 g, 84%). 1H NMR (300 MHz, C6D6): d 0.15 (s, SiMe3), 1.11
(t, J = 6.9 Hz, CH3 of Et2O), 3.26 (q, J = 6.9 Hz, OCH2 of Et2O), 4.431
(s, CH2), 7.170–7.379 (m, phenyls). 13C{1H} NMR (75.5 MHz,
C6D6): d 2.28 (q, J = 117.8 Hz, SiMe3), 15.3 (q, J = 125.8 Hz, CH3 of
Et2O), 53.9 (t, J = 131.8 Hz, CH2), 65.7 (t, J = 139.8 Hz, OCH2 of
Et2O), 125.3, 125.8, 126.4, 127.2, 129.3, 129.7, 141.5, 144.4
* Corresponding author.
E-mail address: dsliu@sxu.edu.cn (D.-S. Liu).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.03.112

584
Y. Zhang et al. / Inorganica Chimica Acta 362 (2009) 583–586
Scheme 1. Synthesis of compound 1, 2 and 3.
(phenyls), 179.6 (N–C–N). Anal. Calc. for C42H62Li2N4O2Si2: C,
69.57; H, 8.55; N, 7.72; O, 4.41. Found: C, 69.50; H, 8.62; N, 7.70;
O, 4.36%.
yield, as shown in Scheme 1. Treatment of 1 with ZiCl4 or HfCl4
in diethyl ether gave a pendant benzyl group amidinate zirconium
2 or hafnium 3 in good yield, 88% and 82%, respectively. The three
products are colorless crystals and air sensitive. Compounds 1–3
2.2.2. ZrCl[Me3SiNC(Ph)NCH2Ph]3 (2)
ZrCl4 (0.343 g, 1.47 mmol) was added in small portions to a stir-
red solution of 1 (1.273 g, 4.42 mmol) in Et2O (30 ml) at ꢀ78 °C.
The solution was warmed to room temperature and stirred for
24 h. The solvent was removed in vacuo. The remaining solid
was dissolved in dichloromethane (ca. 10 ml) and filtered. The fil-
trate was concentrated under vacuum and stored at ꢀ15 °C, yield-
ing colorless crystals of compound 2 (2.51 g, 88%). 1H NMR
(300 MHz, CDCl3): d 0.05 (s, SiMe3, 27H), 4.24 (d, J = 16.2 Hz,
CH2, 3H), 4.64 (d, J = 16.2 Hz, CH2, 3H), 6.70–7.51 (m, phenyls,
30H). 13C{1H} NMR (75.5 MHz, CDCl3): d 2.33 (q, J = 118.9 Hz,
SiMe3), 53.3 (t, J = 134.7 Hz, CH2), 124.8, 126.2, 127.1, 128.4,
129.2, 130.4, 136.0, 142.4 (phenyls), 180.1 (N–C–N). Anal. Calc.
for C51H63ClN6Si3Zr: C, 63.08; H, 6.49; N, 8.65. Found: C, 62.93;
H, 6.52; N, 8.53%.
C17
C15
C16
Si1
C18
C21
C19
C9
O1
N2
C8
C20
’
C1
C11
C12
C10
Li1
’
N1
C14
C13
’
C8
N1
C1
’
Li1
’
C2
’
C3
O1
N2
’
C4
C7
C6
C5
Si1
2.2.3. HfCl[Me3SiNC(Ph)NCH2Ph]3 (3)
This compound was synthesized using the similar procedure of
compound 2, yield 82%. 1H NMR (300 MHz, CDCl3): d 0.01 (s, SiMe3,
27h), 4.27 (d, J = 16.2 Hz, CH2, 3H), 4.62 (d, J = 16.2 Hz, CH2, 3H),
6.67–7.42 (m, phenyls, 30H). 13C{1H} NMR (75.5 MHz, CDCl3):
d2.29 (q, J = 118.8 Hz, SiMe3), 52.5 (t, J = 134.8 Hz, CH2), 124.7,
126.0, 126.9, 128.1, 129.0, 130.2, 136.4, 142.1 (phenyls), 179.6
(N–C–N). Anal. Calc. for C51H63ClHfN6Si3: C, 57.83; H, 5.95; N,
7.93. Found: C, 57.92; H, 5.85; N, 7.89%.
Fig. 1. Molecular structure of compound 1.
C12
C13
C14
C11
C10
2.3. X-ray crystal structure determination for 1–3
C17
Si1
C15
C9
The intensity data were collected with a Bruker SMART APEX CCD
area-detector diffractometer with graphite-monochromated Mo Ka
radiation (k = 0.71073 Å) at 293 K. The collected frames were pro-
cessed with the proprietary software SAINT [24] and an absorption
correction was applied (SADABS [25]) to the collected reflections.
The structures of these molecules were solved by direct methods
and expanded by standard difference Fourier syntheses using the
software SHELXTL [26]. Structure refinements were made on F2 using
the full-matrix least-squares technique. All the non-hydrogen atoms
were refined with anisotropic displacement parameters. Hydrogen
atoms were placed in their idealized positions and allowed to ride
on the respective parent atoms. Pertinent crystallographic data
and other experimental details are summarized in Table 2.
N2
C8
C16
C1’
N1’
Si1’’
Cl1
Zr1
N2’’
C1’’
N1’’
C8’’
C8’
N1
N2’
Si1’
C3
C1
C2
C4
C5
3. Results and discussion
C7
3.1. Synthesis of complexes
C6
The reaction of Me3SiNHCH2Ph with n-butyllithium and then
with PhCN gave [{Me3SiNC(Ph)NCH2Ph}Li(Et2O)]2 (1) in 84.0%
Fig. 2. Molecular structure of compound 2.

Y. Zhang et al. / Inorganica Chimica Acta 362 (2009) 583–586
585
were characterized by NMR (1H NMR and13C NMR), elemental
analysis and X-ray diffraction determination.
nium. The four-membered ring is almost planar, with a mean devi-
ation of 0.0673 Å from the plane. Within the amidinato ligand, the
similarity between the N1–C8A [1.328(3) Å] and C8–N2
[1.335(3) Å] distances shows complete delocalization within the
N–C–N framework. The N–Zr–N bond angle of amidinato with zir-
conium is 59.08(7)°. The attached phenyl ring forms a 60.1° dihe-
dral angle with the four-membered ring (Fig. 2).
In 3 (see Fig. 3), similar to 2, the bidentate amidinato ligand
forms a nearly planar four-membered metallacycle with the metal
ion. The Hf–N distances are 2.272(3) (Hf1–N1) and 2.208(3) (Hf1–
N2) Å, respectively. The similar C–N distances, N1–C8 [1.318(6) Å]
and C8–N2 [1.330(6) Å], indicate complete delocalization within
the N–C–N framework. The four-membered ring forms a 60.2°
dihedral angle with the attached phenyl. Selected bond lengths
and angles of compounds 1–3 are listed in Table 1.
3.2. X-ray structure of 1–3
3.2.1. X-ray structure of 1
Fig. 1 shows the molecular structure of lithium compound 1.
The molecule is a centro-symmetric dimer with the center of par-
allelogram Li1–N1–Li10–N10. Each lithium of the dimer is coordi-
nated by three nitrogen atoms, two of these belong to one
amidinate anion and the third belongs to another, and one oxygen
atom of diethyl ether. The four coordination atoms adopt the
tetragonal geometry with Li–N distances of 2.145(6) (Li1–N1),
2.049(6) (Li1–N10) and 2.018(6) Å (Li1–N2).
3.2.2. X-ray structure of 2 and 3
Structural analyses of 2 and 3 reveal that their molecular struc-
tures are very similar. Both 2 and 3 adopt a C3 rotational symmetry
along the zirconium(IV)–Cl or hafnium(IV)–Cl. The metal(IV)–Cl
axis is located at the center defined by the six nitrogen atoms of
the three amidinato ligands. In 2, with Zr–N distances of
2.2905(18) (Zr1–N1) and 2.2265(19) (Zr1–N2) Å. Each bidentate
amidinato ligand forms a four-membered metallacycle with zirco-
Table 2
Crystallographic data for compound 1–3
Compound
1
2
3
Empirical formula
Crystal system, space triclinic, P1
group
C21H31LiN2SiO
C51H63Cl1ZrN6Si3
cubic, I43d
C51H63ClHfN6Si3
cubic, I43d
ꢀ
ꢀ
ꢀ
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a (°)
10.202(4)
10.833(5)
12.278(5)
108.612(5)
114.169(6)
100.183(5)
1096.6(8)
2
27.460(3)
27.460(3)
27.460(3)
90
90
90
20707(4)
16
1.246
0.373
27.377(2)
27.377(2)
27.377(2)
90
90
90
20519(3)
16
1.370
2.195
b (°)
c (°)
Si1’
V (Å3)
Z
Dcalc (mg mmꢀ3
)
1.098
N2’
C16
Absorption coefficient 0.118
(mmꢀ1
F (000)
C8’
)
Cl1
392
8160
8672
N1’
C1’’
N1’’
C1’
Crystal size (mm3)
h Range for data
collection (°)
0.30 ꢁ 0.20 ꢁ 0.20 0.50 ꢁ 0.40 ꢁ 0.30 0.40 ꢁ 0.35 ꢁ 0.35
Hf1
1.87–25.01
1.82–25.98
1.82–25.00
C17
Si1
C8’’
C15
Limiting indices
ꢀ11 6 h 6 12
ꢀ12 6 k 6 12
ꢀ14 6 l 6 11
4551
3792 (0.0946)
ꢀ33 6 h 6 30
ꢀ33 6 k 6 29
ꢀ25 6 l 6 33
52123
3401 (0.0363)
ꢀ32 6 h 6 29
ꢀ32 6 k 6 14
ꢀ32 6 l 6 32
39315
3018 (0.0864)
N2
N2’’
C8
Reflections collected
Independent
reflections (R)
Completeness to
h = 25° (%)
N1
Si1’’
C7
C9
C1
C2
97.9
100
100
C10
C3
GOF
1.034
1.106
1.049
C6
C14
C13
C11
C12
Final R indices
[I > 2r(I)]
R1 = 0.0827,
wR2 = 0.2037
R1 = 0.0280,
wR2 = 0.0687
R1 = 0.0268,
wR2 = 0.0612
C5
C4
R indices (all data)
R1 = 0.1020,
R1 = 0.0316,
R1 = 0.0295,
wR2 = 0.2189
wR2 = 0.0723
wR2 = 0.0623
Fig. 3. Molecular structure of compound 3.
Table 1
Selected bond lengths (Å) and angles (°) of compound 1–3
Compound 1
Compound 2
Compound 3
Li1–N1
Li1–N2
Li1–N1A
Li1–O1
Li1–Li1A
N1–C1
N1–C8
N2–C8
N2–Si1
N1–C8–N2
N1–Li1–N2
N1–Li1–N1A
Li1–N1–Li1A
2.145(6)
2.018(6)
2.049(6)
1.932(6)
2.500(11)
1.468(4)
1.323(4)
1.321(4)
1.707(3)
Zr1–N1
Zr1–N2
Zr1–Cl1
N1–C1
N1–C8A
N2–C8
N2–Si1
N1B–C8–N2
N1–Zr1–N2A
N1–Zr1–N1A
N2–Zr1–N2A
Cl1–Zr1–N1
Cl1–Zr1–N2
2.2905(18)
2.2265(19)
2.4779(10)
1.452(3)
1.328(3)
1.335(3)
1.7493(19)
113.52(19)
59.08(7)
Hf1–N1
Hf1–N2
Hf1–Cl1
N1–C1
N1–C8
N2–C8
N2–Si1
N1–C8–N2
N1–Hf1–N2
N1–Hf1–N1A
N2–Hf1–N2A
Cl1–Hf1–N1
Cl1–Hf1–N2
2.272(3)
2.208(3)
2.4570(19)
1.442(5)
1.318(6)
1.330(6)
1.751(3)
113.9(4)
59.39(12)
87.95(12)
119.16(3)
126.70(8)
84.71(9)
118.0(3)
87.14(7)
65.9(2)
106.9(2)
73.1(2)
119.320(14)
127.26(5)
85.25(5)

586
Y. Zhang et al. / Inorganica Chimica Acta 362 (2009) 583–586
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This work was supported by grants from the Natural Science
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