Synthesis and X-ray crystal structures of heteroleptic zinc amidinate complexes

Article abstract of DOI:10.1515/mgmc-2012-0004

The synthesis of heteroleptic zinc amidinate complexes is reported. Reactions of LZnI [L=t-BuC(NDipp)₂; Dipp=2,6-i-Pr₂-C ₆H₃] with diisopropylcarbodiimide (i-PrN)₂C yielded the Lewis acid-base adduct

Full text of DOI:10.1515/mgmc-2012-0004

Main Group Met. Chem., 2012;35(1-2):35–40 © 2012 by Walter de Gruyter • Berlin • Boston. DOI 10.1515/mgmc-2012-0004
Synthesis and X-ray crystal structures of heteroleptic zinc
amidinate complexes
(X=Cl, Br, I; H, CCH, CCPh). Moreover, hetero- and homo-
leptic zinc complexes of the type LZnX and L2Zn were syn-
thesized by salt and alkane elimination reactions (Eisenmann
et al., 2008; Schulz et al., 2008; Schmidt et al., 2009a,b,
2010; Jones et al., 2010).
Herein we report on reactions of LZnI [L=t-BuC(NDipp)2;
Dipp=2,6-i-Pr2-C6H3] with (i-PrN)2C, yielding the expected
Lewis acid-base adduct LZn(I)-N(i-Pr)CN(i-Pr) 1. In addi-
tion, the synthesis of the heteroleptic zinc amidinate com-
plex LZnN(SiMe3)2 2 and its reaction with (i-PrN)2C, which
occurred with formation of the heteroleptic bis(amidinate)
complex LZnL′ 3 [L′=(Me3Si)2NC(Ni-Pr)2], is described.
Sarah Schmidt, Stephan Schulz*, Dieter Bläser
and Christoph Wölper
Institute of Inorganic Chemistry, University of
Duisburg-Essen, D-45117 Essen, Germany
*Corresponding author
e-mail: stephan.schulz@uni-due.de
Abstract
The synthesis of heteroleptic zinc amidinate complexes is
reported. Reactions of LZnI [L=t-BuC(NDipp)2; Dipp=2,6-i-
Pr2-C6H3] with diisopropylcarbodiimide (i-PrN)2C yielded the
Lewis acid-base adduct LZn(I)-N(i-Pr)CN(i-Pr) 1. In addi-
tion, the synthesis of LZnN(SiMe3)2 2 and its reaction with
(i-PrN)2C, which occurred with formation of the heteroleptic
amidinate-guanidinate complex LZnL′ 3 [L′=(Me3Si)2NC(Ni-
Pr)2], is reported. Compounds 1–3 were characterized by
nuclear magnetic resonance (1H, 13C) and infrared spectro-
scopy, elemental analysis, and single crystal X-ray diffraction
(1 and 2), respectively.
Results and discussion
Equimolar amounts of LZnI [L=t-BuC(NDipp)2; Dipp=2,6-
i-Pr2-C6H3] and diisopropylcarbodiimide (i-PrN)2C reacted
at ambient temperature with formation of the expected
Lewis acid-base adduct LZn(I)-N(i-Pr)CNi-Pr 1, which was
obtained as a colorless crystalline solid after storage at 4°C
1
in almost quantitative yield (Scheme 2). The H spectrum
of 1 showed resonances due to the amidinate ligand (L) and
the carbodiimide in the expected 1:1 ratio. The 13C nuclear
magnetic resonance (NMR) spectrum shows a characteristic
resonance at 147.7 ppm due to the presence of a carbodiimide
moiety, which is supported by the IR spectrum of 1, showing
a characteristic absorption band due to the N=C=N unit of the
carbodiimide at 2139 cm-1.
Keywords: amidinate; crystal structure; zinc.
Introduction
Monoanionic amidinates (L-) [L-=RC(NR′)2 ] are well-
-
established chelating organic ligands in main group metal and
transition metal chemistry. Their steric and electronic proper-
ties can easily be modified by variation of the organic substit-
uents (R, R′) (see review articles by Barker and Kilner, 1994;
Coles, 2006; Edelmann, 2008, 2009) and they were found to
Carbodiimide adducts of metal complexes are of particu-
lar interest as experimental findings and theoretical calcula-
tions on reactions of carbodiimides with organoboron and
-aluminum compounds proved the insertion reaction most
likely to proceed via initial formation of a Lewis acid-base
adduct (Hill et al., 2005; Rowley et al., 2005; Pierce et al.,
2007). Moreover, Lechler et al. (1989) demonstrated that the
Lewis acidity of the metal complex plays an important role on
the reaction pathway, demonstrating that AlMe3 reacts with
(Me3SiN)2C with insertion in the Al-Me bond and subsequent
formation of [MeC(NSiMe3)2]AlMe2, whereas GaMe3 and
InMe3 yielded the 1:1 adducts Me3M-N(SiMe3)=C=NSiMe3,
respectively. In contrast, AlMe3 was found to react with N,N′-
dialkylcarbodiimides (RN)2C (R=i-Pr, Cy) with formation
of the Lewis acid-base adducts (Kottmair-Maieron, 1987).
Unfortunately, these adducts are often reaction intermediates.
As a consequence, only six adducts were structurally charac-
terized to date (Anderson and Einstein, 1978; Hausen et al.,
1986; Hill et al., 2005; Schulz et al., 2008; Neumüller and
Dehnicke, 2010; Pi et al., 2010). Therefore, we became inter-
ested in the solid-state structure of 1.
1
bind either as monodentate two-electron donor (η ), chelat-
2
1
1
ing (η ), or bridging monodentate (μ-η -η ) four-electron
donor (Scheme 1). Further binding modes have been sum-
marized by Junk and Cole (2007). According to their flex-
ible properties, amidinate complexes are of potential interest
for technical applications in catalysis (Coles et al., 1997;
Radzewich et al., 1998; Dagorne et al., 2000; Foley et al.,
2000) and material sciences (Barker et al., 1996; Baunemann
et al., 2008). Surprisingly, zinc amidinate complexes were
almost unknown until we and others started to investigate
them in more detail. Reactions of ZnMe2 with carbodiimides
C(NR)2 (R=Et, i-Pr, Cy, Ph) unexpectedly yielded multinu-
clear complexes such as {C[C(NR)2ZnMe]}4 (Münch et al.,
2008; Schmidt et al., 2009b, 2011), which were shown by
Gutschank et al. (2010a,b) to be suitable starting reagents
for the synthesis of the corresponding halide-, hydride-,
and acetylide-substituted derivatives {C[C(Ni-Pr)2ZnX]}4
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36 S. Schmidt et al.
are almost identical, proving a delocalized π-electron sys-
tem within the NCN unit of the amidinate ligand. The Zn-N
bond length of the coordinated carbodiimide [2.0858(15)
Å] is slightly elongated compared to those of the amidinate
group [2.0368(14), 2.0589(13) Å] as was expected. The car-
bodiimide is almost linear [N4-C30-N3 172.74(19)°], and
the three-fold coordinated N3 donor atom adopts a trigo-
nal-planar coordination sphere (sum of bond angles 360°).
Comparable values were previously reported by Schulz et al.
(2008) for [Me(Cl)Zn-N(i-Pr)CNi-Pr] [N-C-N 358.4°; sum
of bond angles 175.4(3)°] and other carbodiimide adducts.
In contrast, the carbodiimide units in [Be(i-PrNCNi-Pr)4](I3)2
largely deviated from linearity (155°), most likely due to the
strong polarizing effect of the beryllium ion (Neumüller and
Dehnicke, 2010).
Scheme 1 Typical binding modes in metal amidinate complexes.
Homoleptic bis(amidinate) complexes of the type L2Zn
[L=RC(NR′) ] have been prepared in the past by reaction
of ZnR2 (R=2alkyl, amide) with carbodiimides as well as by
alkane and salt elimination reactions. Unfortunately, the syn-
thesis of heteroleptic amidinate complexes of the type LZnR
is often complicated due to the formation of the correspond-
ing bis(amidinate) complexes. Very recently, Schmidt et al.
(2010) reported on the reaction of ZnMe2 with an equimolar
amount of amidine LH with elimination, which gave access to
the heteroleptic zinc amidinate complex LZnMe. We became
further interested to expand this reaction to other starting
reagents and report herein on the reaction of Zn[N(SiMe3)2]2
with LH. Zn[N(SiMe3)2]2 was previously reported by Coles
and Hitchcock (2004) to react with carbodiimides with inser-
tion into the Zn-N bonds and formation of the corresponding
bis(guanidinate) complexes.
Scheme 2 Synthesis of 1.
Single crystals of 1 were obtained from a solution in tol-
uene upon storage at 4°C (Figure 1). Compound 1, which
represents only the second example of a carbodiimide-zinc
adduct, crystallizes in the orthorhombic space group P212121.
Compound 1 is monomeric in the solid state, whereas the
starting reagent LZnI adopts an iodine-bridged dimeric form
…
(Schmidt et al., 2010). However, a CH π interaction leads
to the formation of chains along the 21-axis parallel to b
(Figure 2). The Zn-I bond length in 1 [2.5198(2) Å] is sig-
nificantly shorter than that in LZnI [2.615(2) Å], whereas the
C-C and C-N bond lengths as well as the N-C-N, C-N-C, and
C-C-N bond angles within the amidinate group in 1 and LZnI
Zn[N(SiMe3)2]2 reacts with an equimolar amount of LH with
elimination of HN(SiMe3)2 and formation of LZnN(SiMe3)2 2
in almost quantitative yield. Compound 2 further reacts with
(i-PrN)2C with insertion of the carbodiimide into the Zn-amide
bond and formation of the heteroleptic amidinate-guanidinate
complex LZnL′ 3 [L′=(Me3Si)2NC(Ni-Pr)2] (Scheme 3).
1
The H spectra of 2 and 3 showed resonances due to the
amidinate (L) and the amide/guanidinate substituent in the
expected 1:1 ratio. Even though single crystals of 3 suitable
for an X-ray diffraction study were not obtained, the forma-
tion of the homoleptic complexes L2Zn and L2′Zn can be
excluded based on the different NMR chemical shifts of 3
compared to those of the homoleptic complexes (Coles and
Hitchcock, 2004; Jones et al., 2010).
Single crystals of 2 were obtained from a solution in tolu-
ene upon storage at -30°C. Compound 2 crystallizes in the
_
triclinic space group P1 with two molecules in the asymmet-
ric unit (Figure 3). The two molecules show pseudo-trans-
lational symmetry along [110]. However, reducing the cell
resulted in a severe disorder of the molecule. Consequently,
the initial cell was kept. Figure 4 shows an overlay of the
independent molecules to demonstrate the differences
in their conformation. The Zn-N [2.040(1), 1.992(1) Å]
and C-N bond lengths [1.332(2), 1.339(2) Å] and N-C-N
[108.83(10)°] and N-Zn-N bond angles [65.22(4)°] within the
amidinate group in 2 are almost identical to those observed
for LZnMe and LZnI and 1, respectively. The values clearly
Figure 1 Solid-state structure of 1 (thermal ellipsoids are shown at
50% probability levels; H atoms are omitted for clarity).
Selected bond lengths (Å) and angles (°): Zn(1)-I(1) 2.5198(2), Zn(1)-
N(1) 2.0589(13), Zn(1)-N(2) 2.0368(14), Zn(1)-N(3) 2.0858(15),
N(1)-C(1) 1.336(2), N(2)-C(1) 1.346(2), N(3)-C(30) 1.245(2),
N(4)-C(30) 1.195(2), N(2)-Zn(1)-N(1) 65.24(5), N(2)-Zn(1)-N(3)
111.54(6), N(1)-Zn(1)-N(3) 109.33(6), N(2)-Zn(1)-I(1) 125.33(4),
N(1)-Zn(1)-I(1) 133.57(4), N(3)-Zn(1)-I(1) 106.45(4), C(30)-N(3)-
C(31) 118.10(15), C(30)-N(3)-Zn(1) 121.08(12), C(31)-N(3)-Zn(1)
120.82(11), N(4)-C(30)-N(3) 172.74(19).
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Zinc amidinate complexes 37
Figure 2 Chains parallel to b in the packing of 2 (residual groups are partially omitted for clarity, #1: 2-x, 0.5+y, 1.5-z).
C35-H35B···(C2, C3, C4, C5, C6, C7)#1 d(H···centroid) 2.99 Å, <(CH···centroid) 155.4°, <(H···centroid···plane of the ring) 72.8°; C36-
H36B···(C2, C3, C4, C5, C6, C7)#1 d(H···centroid) 3.16 Å, <(CH···centroid) 146.8°, <(H···centroid···plane of the ring) 56.6°.
commercially available and used as received. 1H, 13C{1H} NMR
show the formation of a delocalized π-electron system within
spectra were recorded on a Bruker DMX 300 spectrometer (Bruker
the NCN unit of the amidinate ligand. The Zn-Namide bond
BioSpin MRI GmbH, Ettlingen, Germany) and are referenced to in-
length is significantly shorter compared to the Zn-Namidinate
bonds, but agrees well with the values observed by Margraf
et al. (2004) for Zn[N(SiMe3)2]2 [1.833(11) Å] and other
zinc bis(trimethylsilyl)amides as revealed by a Cambridge
ternal C6D5H (1H: δ=7.154; 13C: δ=128.0). IR spectra were recorded
on a Bruker ALPHA-T Fourier transform IR spectrometer (Bruker
Optik GmbH, Ettlingen, Germany) equipped with a single reflection
attenuated total reflectance sampling module. Melting points were
structural database (CSD) search. The CSD search gave 75
measured in sealed capillaries and were not corrected. Elemental
complexes containing a Zn-N(SiMe3)2 bond. Zn-N bond
lengths range from 1.812 to 2.028 Å (av. value 1.914 Å)
(CSD, Version 5.33 with update November 2011) (Allen,
2002).
analyses were performed at the Elementaranalyse Labor of the
University of Essen (Essen, Germany).
Synthesis of 1–3
[t-BuC(NDipp)2]Zn(I)-N(i-Pr)CNi-Pr
1 ( i-PrN)2C (1.26 g, 10
Experimental section
General procedures
mmol) was added via syringe to a solution of {[t-BuC(NDipp)2]-
ZnI}2 (6.12 g, 5 mmol) in 20 ml of toluene at -30°C. The solution
was warmed to ambient temperature and stirred for 2 h, concentrated
in vacuum to 10 ml, and stored at 4°C. Colorless crystals of 1 were
formed within 12 h.
AllmanipulationswereperformedinaGlovebox(MBraun, München,
Germany) under Ar atmosphere or using standard Schlenk line tech-
niques. Dry solvents were obtained from a solvent purification sys-
tem (MBraun, München, Germany) and degassed prior to use. LH
and LZnI (Schmidt et al., 2010) as well as Zn[N(SiMe3)2]2 (Bürger
et al., 1965) were prepared according to literature method, whereas
(i-PrN)2C (Sigma-Aldrich Chemie GmbH, München, Germany) was
Yield 7.23 g (98%). Melting point: >220°C. Anal. found (calcd.)
for C36H57IN4Zn (738.13 g/mol): H, 7.8 (7.8); C, 58.6 (58.5);
N, 7.6 (7.5). 1H NMR (300 MHz, C6D6, 25°C): δ=0.93 [s, 9H,
3
3
C(CH3)3], 0.97 [d, JHH=6.7 Hz, 12H, CH(CH3)2], 1.31 [d, JHH=6.8
3
Hz, 12H, CH(CH3)2], 1.34 [d, JHH=6.8 Hz, 12H, CH(CH3)2], 3.49
3
3
[sept, JHH=6.8 Hz, 2H, CH(CH3)2], 3.75 [sept, JHH=6.8 Hz, 2H,
CH(CH3)2], 7.07 (m, 6H, ArH). 13C NMR (75 MHz, C6D6, 25°C):
δ=21.4 [CH(CH3)2], 22.7 [CH(CH3)2], 23.1 [CH(CH3)2], 24.2
[CH(CH3)2], 25.6 [CH(CH3)2], 27.3 [CH(CH3)2], 27.8 [CH(CH3)2],
28.7 [CH(CH3)2], 29.9 [CH(CH3)2], 43.9 [C(CH3)3], 49.6 [C(CH3)3],
123.0 (Ar-C), 127.4 (Ar-C), 147.7 (NCN), 158.6 (NCN). IR: ν=2967,
2866, 2139, 1487, 1445, 1432, 1399, 1366, 1300, 1254, 1240, 1212,
1176, 1165, 1131, 1105, 1058, 1044, 962, 934, 916, 896, 803, 763,
729, 715, 639, 579, 463, 433, 408 cm-1.
[t-BuC(NDipp)2]ZnN(SiMe3)2
2 A solution of Zn[N(SiMe3)2]2
(1.79 g, 5 mmol) in 10 ml of toluene was added dropwise to
t-BuC(NHDipp)(NDipp) (2.10 g, 5 mmol) dissolved in 10 ml of tolu-
ene at ambient temperature. The resulting solution was stirred for
72 h, concentrated in vacuum to 10 ml, and stored at -30°C. Colorless
crystals of 2 were formed within 24 h.
Yield 3.06 g (95%). Melting point: 118°C. Anal. found (calcd.) for
C35H61N3Si2Zn (645.42 g/mol): H, 9.4 (9.5); C, 64.9 (65.1); N, 6.4
Scheme 3 Synthesis of 2 and 3.
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38 S. Schmidt et al.
Figure 3 Solid-state structure of 2 (thermal ellipsoids are shown at 50% probability levels; H atoms are omitted for clarity; relative orienta-
tion of the molecule does not resemble the arrangement within the asymmetric unit).
Selected bond lengths (Å) and angles (°): Zn(1)-N(3) 1.8512(10), Zn(1)-N(2) 1.9926(10), Zn(1)-N(1) 2.0401(11), Si(1)-N(3) 1.7256(11), Si(2)-
N(3) 1.7328(11), N(1)-C(1) 1.3329(15), C(1)-N(2) 1.3399(16), N(3)-Zn(1)-N(2) 149.72(5), N(3)-Zn(1)-N(1) 145.05(4), N(2)-Zn(1)-N(1)
65.22(4), C(1)-N(1)-C(2) 133.54(11), C(1)-N(1)-Zn(1) 92.02(8), C(2)-N(1)-Zn(1) 134.43(8), C(1)-N(2)-C(14) 132.97(10), C(1)-N(2)-Zn(1)
93.92(7), C(14)-N(2)-Zn(1) 132.93(8), N(1)-C(1)-N(2) 108.83(10), Si(1)-N(3)-Si(2) 121.79(6), Si(1)-N(3)-Zn(1) 118.58(6), Si(2)-N(3)-Zn(1)
119.63(6), Zn(2)-N(53) 1.8540(11), Zn(2)-N(52) 2.0027(10), Zn(2)-N(51) 2.0289(11), Si(3)-N(53) 1.7263(11), Si(4)-N(53) 1.7296(12),
N(51)-C(51) 1.3396(16), C(51)-N(52) 1.3389(16), N(53)-Zn(2)-N(52) 148.03(5), N(53)-Zn(2)-N(51) 146.36(5), N(52)-Zn(2)-N(51) 65.44(4),
C(51)-N(51)-Zn(2) 92.19(8), C(52)-N(51)-Zn(2) 133.40(9), C(51)-N(51)-C(52) 130.02(11), C(51)-N(52)-C(64) 132.82(11), C(51)-N(52)-
Zn(2) 93.37(8), C(64)-N(52)-Zn(2) 133.80(8), N(52)-C(51)-N(51) 108.92(11), Si(3)-N(53)-Si(4) 121.71(6), Si(3)-N(53)-Zn(2) 118.46(6),
Si(4)-N(53)-Zn(2) 119.67(6).
(6.5). 1H NMR (300 MHz, C6D6, 25°C): δ=0.11 [s, 18H, Si(CH3)3],
(Ar-C), 142.8 (Ar-C), 142.9 (Ar-C), 180.7 (NCN). IR: ν=2959, 2871,
2170, 1436, 1403, 1364, 1313, 1246, 1211, 1178, 1095, 1056, 1029,
980, 943, 875, 815, 801, 760, 708, 671, 615, 472 cm-1.
3
0.95 [s, 9H, C(CH3)3], 1.32 [d, JHH=6.9 Hz, 12H, CH(CH3)2],
3
3
1.33 [d, JHH=7.1 Hz, 12H, CH(CH3)2], 3.59 [sept, JHH=6.9 Hz,
4H, CH(CH3)2], 7.06 (m, 6H, ArH). 13C NMR (75 MHz, C6D6,
25°C): δ=5.6 [Si(CH3)3], 22.7 [CH(CH3)2], 25.3 [CH(CH3)2], 28.9
[CH(CH3)2], 30.0 [CH(CH3)2], 41.7 [C(CH3)3], 123.7 (Ar-C), 125.4
[t-BuC(NDipp)2]Zn{(i-PrN)2C[N(SiMe3)2]} 3 ( i-PrN)2C (0.63 g,
5 mmol) was added via syringe to a solution of [t-BuC(NDipp)2]-
Figure 4 Overlay of the independent molecules of 2 (molecule containing Zn(2) in dashed lines).
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Zinc amidinate complexes 39
equivalent reflections on the basis of multiscans (Bruker AXS
APEX2) was applied. All non-hydrogen atoms were refined aniso-
tropically, and hydrogen atoms by a riding model. Despite resolving
the pseudo-translational symmetry of 2, the ADP of C(9, 10, 58, 59)
still indicate a severe disorder which could not be resolved. Bond
length and angles of these atoms should not be considered reliable.
(SHELXL-97; Sheldrick, 1997; see also Sheldrick, 2008; Hübschle
et al., 2011).
The crystallographic data of the structures (excluding structure
factors) have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-869941 (1) and
CCDC-869940 (2). Copies of the data can be obtained free of charge on
application to The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [Fax: int.code_(1223)336-033; e-mail for inquiry: fileserv@
ccdc.cam.ac.uk; e-mail for deposition: deposit@ccdc.cam.ac.uk].
Table 1 Crystallographic details of 1 and 2.
1
2
Empirical formula
Molecular mass
Crystal system
Space group
a (Å)
C36H57IN4Zn
738.13
C35H61N3Si2Zn
645.42
Triclinic
Orthorhombic
P212121
11.9250(4)
15.3035(5)
19.8272(7)
90
90
90
3618.3(2)
4
_
P1
11.4985(2)
11.4985(2)
19.9837(4)
80.4660(10)
86.8710(10)
88.7140(10)
3732.69(12)
4
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
T (K)
100(1)
1.561
1.355
61
100(1)
0.748
1.148
58
μ (mm-1)
Acknowledgements
Dcalcd. (g cm-3)
2θmax (°)
S. Schulz thanks the University of Duisburg-Essen and the German
Science Foundation (DFG) for financial support.
Crystal size (mm)
Number of reflections
Number of unique
reflections
Rint
0.28×0.17×0.05
49,879
10,671
0.35×0.33×0.28
56,306
19,824
References
0.0274
379/0
0.0185
739/0
Number of parameters
refined/restraints
Flack-Parameter x
R1a
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lion crystal structures and rising. Acta Crystallogr., Sect. B:
Struct. Crystallogr. Cryst. Chem. 2002, 58, 380–388.
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butylcarbodiimide)palladium(II). Acta Crystallogr., Sect. B:
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0.001(7)
0.0229
0.0563
1.053
–
0.0312
0.0868
1.026
0.75/0.67
b
wR2
Goodness of fitc
Maximum/Minimum
transmission
0.75/0.64
Barker, J.; Kilner, M. The coordination chemistry of the amidine
ligand. Coord. Chem. Rev. 1994, 133, 219–300.
Barker, J.; Blacker, N. C.; Phillips, N. C.; Alcock, N. W.; Errington,
W.; Wallbridge, M. G. H. Synthesis and properties of some
gallium amidine complexes [GaXyL3-y][X=Me, Et or Cl;
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aR1=Σ(||Fo|-|Fc||)/Σ|Fo| [for I>2σ(I)].
bwR2={Σ[w( Fο2-Fc2)2]/Σ[w( Fο2)2]}1/2
.
cGoodness of fit={Σ[w(|Fο2|-|Fc2|)2]/(Nobservns-Nparams)}1/2
.
w-1=σ2( Fο2)+(aP)2+bP, where P=( Fο2+2Fc2)/3; a and b are constants
chosen by the program.
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M.; Gemel, C.; Fischer, R. A. Mixed amido/imido/guanidinato
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schwinkungsspektren von silylamiden der elemente zink, cad-
mium und quecksilber (Syntheses and vibrational spectra of
silylamides of the elements zinc, cadmium and mercury). J.
Organomet. Chem. 1965, 3, 113–120.
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dination chemistry. Dalton Trans. 2006, 985–1001.
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application in ring-opening polymerisation catalysis. Eur. J.
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ZnN(SiMe3)2 2 (3.22 g, 5 mmol) in 20 ml of toluene at ambient
temperature. The resulting solution was stirred for 12 h at 50°C, con-
centrated in vacuum to 10 ml, and stored at -30°C. Colorless crystals
of 3 were formed within 24 h.
Yield 3.47 g (90%). Melting point: 136°C. Anal. found (calcd.)
for C42H75N5Si2Zn (771.63 g/mol): H, 9.2 (9.1); C, 65.6 (65.4); N, 9.1
1
(9.1). H NMR (300 MHz, C6D6, 25°C): δ=0.32 [s, 18H, Si(CH3)3],
1.01 [s, 9H, C(CH3)3], 1.12 [d, 3JHH=6.7 Hz, 12H, CH(CH3)2], 1.39 [d,
3JHH=6.5 Hz, 12H, CH(CH3)2], 1.43 [d, 3JHH=6.5 Hz, 12H, CH(CH3)2],
3.65 [sept, 3JHH=6.4 Hz, 2H, CH(CH3)2], 3.82 [sept, 3JHH=6.7 Hz, 4H,
CH(CH3)2], 7.04–7.14 (m, 6H,ArH). 13C NMR (75 MHz, C6D6, 25°C):
δ=2.4 [Si(CH3)3], 26.7 [CH(CH3)2], 28.9 [CH(CH3)2], 44.3 [C(CH3)3],
44.7 [C(CH3)3], 123.3 (Ar-C), 165.2 (NCN). IR: ν=2965, 2866, 1622,
1585, 1460, 1429, 1375, 1360, 1321, 1230, 1202, 1167, 1141, 1093,
1071, 1019, 944, 895, 797, 756, 728, 686, 660, 619, 528 cm-1.
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X-ray crystallography
Crystallographic data for 1 and 2 were collected on a Bruker AXS
D8 Kappa diffractometer with APEX2 detector [Mo-Kα radia-
tion, λ=0.71073 Å; T=100(1) K]. Crystallographic data for 1 and
2 are summarized in Table 1. The structures were solved by Direct
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Received March 7, 2012; accepted March 21, 2012
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