Zinc carbodiimide cluster complexes: synthesis, x-ray crystal structures, and reaction mechanism

Article abstract of DOI:10.1021/om900373p

Reactions of Me₂Zn with carbodiimides C(NR)₂ in different molar ratios at elevated temperature were investigated, a possible reaction mechanism was identified, and the single-crystal X-ray structures of polynuclear amidinate zinc com

Full text of DOI:10.1021/om900373p

Organometallics 2009, 28, 4371–4376 4371
DOI: 10.1021/om900373p
Zinc Carbodiimide Cluster Complexes: Synthesis, X-ray Crystal
Structures, and Reaction Mechanism
€
Sarah Schmidt, Sebastian Gondzik, Stephan Schulz,* Dieter Blaser, and Roland Boese
Institute of Inorganic Chemistry, University of Duisburg-Essen, 45117 Essen, Germany
Received May 11, 2009
Reactions of Me2Zn with carbodiimides C(NR)2 in different molar ratios at elevated temperature
were investigated, a possible reaction mechanism was identified, and the single-crystal X-ray
structures of polynuclear amidinate zinc complexes {C[C(NCy)2ZnMe]4}, 1, {C[C(NCy)2ZnMe]3-
(ZnMe)}, 3, and {C[C(NCy)2ZnMe]3(ZnMe)(MeZnOMe)}, 5, are reported.
Scheme 1. Salt Elimination Reaction and Carbodiimide Inser-
tion Reaction
Introduction
Guanidinate1 and amidinate anions2 have a long tradi-
tion in coordination chemistry of s-, p-, d-, and f-block
metals.3 They can bind to the metal center as monodentate
(η1, a), chelating (η2, b), or bridging monodentate (μ-η1-
η1, c) four-electron donor ligands,4 and their steric and
electronic properties can easily be tuned by variation of the
organic substituents R and R0, rendering them very sui-
table for the synthesis of tailor-made complexes. These
complexes, which show promising applications in cataly-
sis,5 material sciences (i.e., precursors for CVD),6 and the
synthesis of organic-inorganic hybrid materials, are
typically prepared by salt elimination reaction or carbo-
diimide insertion reaction into metal-C and metal-N
bonds.7
Considering the general interest in metal amidinate com-
plexes, it came to us as a surprise that zinc amidinate
complexes were almost unknown,8 whereas the correspond-
ing guanidinate complexes, which are of potential interest in
ROP catalysis, have been studied in more detail.9 Therefore,
we became interested in this specific class of compounds and
reported very recently on the synthesis of several mono- and
bisamidinate complexes of the type LZnX and L2Zn (L =
amidinate) by salt elimination reaction.10 Moreover, reac-
tions of carbodiimides C(NR)2 with ZnR2 were shown to
proceed either with insertion of the carbodiimide into the
Zn-C bond and subsequent formation of the expected
amidinate complex such as [EtC(Ni-Pr)2ZnEt]2 or with un-
expected formation of cluster-type complexes such as {C-
[C(Ni-Pr)2ZnMe]4}.11
To the best of our knowledge, the latter reaction, which
proceeds with C-C bond formation, is without precedent in
carbodiimide chemistry. Therefore, we studied reactions of
ZnMe2 with different carbodiimides in more detail in order
to clarify if this is a general reaction pathway for organozinc
reagents and to identify a possible reaction mechanism.
Herein, we report on the synthesis and characterization
of four amidinate zinc complexes: {C[C(NCy)2ZnMe]4}, 1,
{C[C(NCy)2ZnMe]2[C2(NCy)3]}, 2, {C[C(NCy)2ZnMe]3-
(ZnMe)}, 3, and {C[C(NCy)2ZnMe]3(NCy2ZnMe)}, 4. In
addition, the partially oxidized complex {C[C(NCy)2Zn-
Me]3(ZnMe)(MeZnOMe)}, 5, was characterized by single-
crystal X-ray diffraction.
*To whom correspondence should be addressed. Phone: þ49 0201-
1834635. Fax: þ49 0201-1834635. E-mail: stephan.schulz@uni-due.de.
(1) Bailey, P. J.; Pace, S. Coord. Chem. Rev. 2001, 214, 91.
(2) (a) Barker, J.; Kilner, M. Coord. Chem. Rev. 1994, 133, 219. (b)
Edelmann, F. Adv. Organomet. Chem. 2008, 57, 183.
(3) The coordination chemistry of neutral amidines and guanidines
was recently described: Coles, M. P. J. Chem. Soc., Dalton Trans. 2006,
985.
(4) Further bindings modes see: Junk, P. C.; Cole, M. L. J. Chem.
Soc., Chem. Commun. 2007, 1579.
(5) (a) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Jr.
Organometallics 1997, 16, 5183. (b) Radzewich, C. E.; Coles, M. P.; Jordan,
R. F. J. Am. Chem. Soc. 1998, 120, 9384. (c) Dagorne, S.; Guzei, I. A.;
Coles, M. P.; Jordan, R. F. J. Am. Chem. Soc. 2000, 122, 274.
(6) See the following and references cited therein: Baunemann, A.;
Bekermann, D.; Thiede, T. B.; Parala, H.; Winter, M.; Gemel, C.;
Fischer, R. A. J. Chem. Soc., Dalton Trans. 2008, 3715.
(7) See the following and references cited therein: (a) Sita, L. R.;
Babcock, J. R. Organometallics 1998, 17, 5228. (b) Tunge, J. A.;
Czerwinski, C. J.; Gately, D. A.; Norton, J. R. Organometallics 2001, 20,
254. (c) Xia, A.; El-Kaderi, H. M.; Heeg, M. J.; Winter, C. H. J. Organomet.
Chem. 2003, 682, 224. (d) Baker, R. J.; Jones, C. J. Organomet. Chem.
2006, 691, 65.
(8) Only a handful of benzamidinate, formamidinate, and boraami-
dinate complexes have been structurally characterized: (a) Buijink,
J.-K.; Noltemeyer, M.; Edelmann, F. T. Z. Naturforsch. B 1991, 46,
1328. (b) Cotton, F. A.; Daniels, L. M.; Falvello, L. R.; Matonic, J. H.;
Murillo, C. A.; Wang, X.; Zhou, H. Inorg. Chim. Acta 1997, 266, 91.
(c) Cole, M. L.; Evans, D. J.; Junk, P. C.; Louis, L. M. New J. Chem. 2002,
26, 1015. (d) Chivers, T.; Eisler, D. J.; Fedorchuk, C.; Schatte, G.; Tuononen,
H. M. Inorg. Chem. 2006, 45, 2119. (e) Fedorchuk, C.; Copsey, M.; Chivers,
T. Coord. Chem. Rev. 2007, 251, 897.
(9) (a) Coles, M. P.; Hitchcock, P. B. Eur. J. Inorg. Chem. 2004, 2662.
(b) Birch, S. J.; Boss, S. R.; Cole, S. C.; Coles, M. P.; Haigh, R.; Hitchcock, P.
B.; Wheatley, A. E. H. J. Chem. Soc., Dalton Trans. 2004, 356.
€
(10) Eisenmann, T.; Khanderi, J.; Schulz, S.; Florke, U. Z. Anorg.
Allg. Chem. 2008, 634, 507.
€
€
(11) (a) Schulz, S.; Munch, M.; Florke, U. Z. Anorg. Allg. Chem.
€
2008, 634, 2221. (b) M€unch, M.; Florke, U.; Bolte, M.; Schulz, S.; Gudat, D.
Angew. Chem. 2008, 120, 1535.; Angew. Chem., Int. Ed. 2008, 47, 1512.
r
2009 American Chemical Society
Published on Web 06/18/2009
pubs.acs.org/Organometallics

4372 Organometallics, Vol. 28, No. 15, 2009
Schmidt et al.
Figure 1. Solid-state structure of 1 (stick-and-ball model). H
atoms are omitted for clarity; Me and Cy groups are presented in
˚
a diminished fashion. Selected bond lengths [A] and angles [deg]:
Figure 2. Solid-state structure of complex 2 illustrating the
connectivity within this complex. H atoms are omitted for
clarity; Me and Cy groups are presented in a diminished fashion.
Zn1-N1 2.151(3), Zn1-N2 2.145(3), Zn1-N4 2.172(3), N1-
C28 1.311(5), N2-C28a 1.350(5), N3-C27a 1.318(5), N4-C27
1.346(5), C27-C29 1.564(5), C28-C29 1.564(5); N1-Zn1-N2
93.73(12), N2-Zn1-N4 83.27(12), N1-Zn1-N4 97.24(12),
N3a-C27-N4 137.3(3), N1-C28-N2a 137.4(4), C27-C29-
C28 101.06(18), C27a-C29-C28 130.78(19), C28a-C29-C28
98.7(4).
Scheme 2. Complexes Resulting from Insertion Reactions of
C(Ni-Pr)2 with ZnMe2 and ZnEt2
Figure 3. Solid-state structure of 3 (stick-and-ball model). H
atoms are omitted for clarity; Me and Cy groups are presented in
˚
a diminished fashion. Selected bond lengths [A] and angles [deg]:
Results and Discussion
Zn1-N1 2.051(3), Zn1-N2 1.990(3), Zn2-N1 2.059(3), Zn2-
N3 1.968(3), N1-C7 1.429(5), N2-C7 1.331(5), N3-C9 1.342(4),
C7-C8 1.425(4), C8-C9 1.499(7); N1-Zn1-N2 66.58(12),
N1-Zn2-N3 92.36(12), N1-C7-N2 106.9(3), N3-C7-C8
122.3(3), C7-C8-C7a 123.7(5), C7-C8-C9 118.1(2).
Solutions of equimolar amounts of ZnMe2 and C(NR)2 (R=
t-Bu, SiMe3, Cy, Dipp) in toluene were stirred at 110 °C for
60 h. No reaction was observed for the sterically hindered
carbodiimides (R=t-Bu, SiMe3, Dipp),12 whereas reac-
tions with cyclohexyl carbodiimide C(NCy)2 produced
more or less complex reaction mixtures of complexes 1-4.
A rather strong influence of several specific reaction
parameters such as molar ratio, reaction temperature (90,
110 °C), and reaction time (3-5 days) on the formation of the
preferred reaction product(s) 1-4 was observed. Moreover,
the use of carefully purified cyclohexyl carbodiimide turned
out to be essential; otherwise the partially oxidized complex
{C[C(NCy)2ZnMe]3(ZnMe)(MeZnOMe)}, 5, was formed to
some extent.13
1H NMR spectra of the bulk reaction products typically
showed multiple resonances due to the presence of nonequiva-
lent Zn-Me and Cy groups.14 Complexes {C[C(NCy)2Zn-
Me]4}, 1, {C[C(NCy)2]2Zn2Me2[C2(NCy)3]}, 2, {C[C(NCy)2-
ZnMe]3(ZnMe)}, 3, and {C[C(NCy)2ZnMe]3(NCy2ZnMe)}, 4,
(12) More drastic reaction conditions (no solvent, T=140 °C) results
in decomposition of ZnMe2 with subsequent formation of elemental
zinc.
(13) The reaction of ZnMe2 with unpurified C(NCy)2 was repeated
several times, in all cases yielding mixtures of 1-5 with up to 5% 5.
Single crystals of 5 (mixture together with 2) were isolated from different
reaction batches after fractional crystallization from solutions in n-
pentane at -30 °C and identified by single-crystal X-ray diffraction.
(14) The methine H atom (C1H) is the only resonance of the Cy group
that clearly indicates the formation of multiple species since the resonances
of other H atoms of this group (C2H-C6H) are rather broad and overlap.

Article
Organometallics, Vol. 28, No. 15, 2009 4373
Scheme 3. Synthesis of Complexes 1-5
Figure 5. Central cluster cores of 5 and 6 demonstrating the
structural relationship between both clusters. Substituents
bound to the N atoms have been omitted for clarity.
Figure 4. Solid-state structure of 5 (stick-and-ball model). H
atoms are omitted for clarity; Me and Cy groups are presented in
˚
a diminished fashion. Selected bond lengths [A] and angles [deg]:
Table 1. Influence of Specific Reaction Parameters on the For-
mation of Complexes 1-4a
Zn1-O1 2.015(2), Zn1-N3 2.269(2), Zn1-N5 2.249(2), Zn2-
N1 2.121(2), Zn2-N3 2.148(2), Zn3-N2 2.098(2), Zn3-N5
2.187(2), Zn4-N4 2.027(2), Zn4-N6 2.031(2), Zn5-N1 2.027(2),
Zn5-N2 2.043(2), N1-C1 1.416(3), N2-C1 1.422(3), N3-C2
1.369(3), N4-C2 1.310(3), N5-C3 1.366(3), N6-C3 1.317(3),
C1-C4 1.358(4), C2-C4 1.507(3), C3-C4 1.509(3); N1-Zn2-
N3 92.77(8), N2-Zn3-N5 92.32(8), N4-Zn4-N6 95.78(9),
N1-Zn5-N2 69.02(9), N1-C1-N2 108.7(2), N3-C2-N4
135.4(2), N5-C3-N6 135.1(2), C1-C4-C2 121.8(2), C1-
C4-C3 122.0(2), C2-C4-C3 113.8(2).
molar ratio (ZnMe2/C(NCy)2); reaction temperature [°C]
1:2
1:1
2:1
reaction time
[d]
90 °C 110 °C 90 °C 110 °C 90 °C 110 °C
3
4
5
3
2
4
3 þ 4
2
1
a {C[C(NCy)2ZnMe]4}, 1, {C[C(NCy)2]2Zn2Me2[C2(NCy)3]}, 2, {C[-
C(NCy)2ZnMe]3(ZnMe)}, 3, {C[C(NCy)2ZnMe]3(NCy2ZnMe)}, 4.
were isolated from these reaction mixtures by fractional crystal-
lization from solutions in cyclohexane (1, 3, 4) at þ4 °C or
(X=Cl, Br), whereas spectra recorded at 500 MHz show
well-resolved resonances of the axial H atoms (Hax) with large
coupling constants to the axial (dihedral angle around 180°)
and small coupling constants to the equatorial H atoms
(dihedral angle around 60°) of adjacent CH2 groups. For
instance, the H1ax protons (triplet of triplet) and the H4ax
protons (triplet of quartet) of 1-4 show significantly larger
1
pentane/toluene (2) at -30 °C. H and 13C NMR spectra of
pure 1-4 show the expected resonances of the organic substit-
uents. Only a single resonance for the Zn-Me group is observed
for 1-3, indicating these complexes adopt symmetric structures
in solution. In contrast, complex 4 shows four Zn-Me reso-
nances, as was observed for the corresponding i-Pr-substituted
complex.11 The Cy groups of 1-4show more complex patterns,
including two (1) andthree (2) resonances of the C1Hax protons
with expected 1:1 (1) and 4:2:1 (2) molar ratios. 3 shows only a
single C1Hax resonance, whereas four well-separated C1Hax
resonances with equal intensity and one broad resonance with a
4-fold intensity due to an overlap of four Cy groups are
observed for 4. 1H NMR spectra of 1-4 recorded at
300 MHz show rather broad signals, as was previously ob-
served for monoamidinate zinc halides [t-BuC(NCy)2]ZnX
coupling constants to the axial H atoms (3JH H =10-13 Hz)
ax ax
than to the equatorial ones (3JH H =3-4 Hz). In contrast, the
equatorial H atoms show only broad doublets due to large
ax eq
2
geminal JHH couplings, with the broadening resulting from
small 3JHH couplings to the magnetically nonequivalent axial
and equatorial H atoms of the adjacent CH2 groups (spectrum
of higher order). Comparable findings were previously ob-
served for the bisamidinate complex [t-BuC(NCy)2]2Zn, in
1
which the H resonances were assigned by HH-COSY and

4374 Organometallics, Vol. 28, No. 15, 2009
Schmidt et al.
Scheme 4. Possible Mechanism of a Stepwise Deprotonation/
Carbodiimide Insertion Reaction
bridging bidentate ligands, resulting in the formation of a
12-membered Zn3(μ-NCN)3 ring. In addition, one of the
three amidinate moieties (N1-C1-N2) in 5 binds to a fourth
Zn atom (Zn5) in a N,N0-chelating mode. Even more re-
markable are the different bonding situations within the
˚
central CC3 moieties. 3 shows two short (C8-C7 1.425(4) A)
˚
and one long C-C bond (C8-C9 1.499(7) A), whereas in 5,
˚
two long (C2-C4 1.507(3), C3-C4 1.509(3) A) and one
˚
short C-C bond (C1-C4 1.358(4) A) rather point to the
formation of two C-C single and one CdC double bond.
The π-electron systems of two amidinate groups in 3 (N1-
C1-N2) and 5 (N3-C2-N4, N5-C3-N6) are signifi-
cantly disturbed and show different C-N bond lengths
˚
˚
(1.331(5), 1.429(5) A 3; 1.310(3)-1.369(3) A 5), most likely
caused by the different coordination numbers of the N atoms
(three vs four). In contrast, the N-C bond lengths within
the N3-C9-N3a unit in 3 indicate a delocalized π-electron
˚
system (1.342(4) A), whereas those of the N1-C1-N2
moiety in 5 rather point to N-C single-bond character
(1.416(3), 1.422(3) A).
DPFGSE-NOE spectroscopy studies.10 5 was formed as a
byproduct in low yields only when the carbodiimide was used
as received.15 The most prominent resonances for 5 are sharp
singlets at 3.58 and -0.37 ppm due to the presence of the
MeZnOMe moiety. Single crystals of 5 were isolated manually
from a mixture of 2 and 5 after recrystallization from a solution
in n-pentane at -30 °C.
˚
The formation of the new cluster-type complexes 1-5 can
be rationalized by a stepwise metalation reaction of the zinc
amidinate complex [MeC(NCy)2]ZnMe, A, which is most
likely initially formed in the reaction, followed by insertion
of the carbodiimide into the as-formed Zn-C bond with
subsequent formation of complexes B and C.16
Single crystals of 1, 2, 3, and 5 were obtained from
solutions in cyclohexane (1, 3), n-pentane/toluene (2), and
n-pentane (5), respectively. Unfortunately, the quality of the
crystals of 2 was too low to allow a reasonable refinement of
the data, but the connectivity of the atoms within 2 was
proven without any doubts. Moreover, the structures of 1
and 2 are comparable to those observed for the i-Pr-sub-
stituted complexes,11b clearly demonstrating that the forma-
tion of such polynuclear clusters is a general reaction path-
way in ZnMe2/carbodiimide chemistry. Both complexes contain
a central C atom (C29 1, C50 2), which is tetrahedrally co-
ordinated by four C atoms of adjacent amidinate groups.
Complexes A, B, and C may also adopt heterocyclic
structures with bridging amidinate groups rather than with
N,N0-chelating groups, as was observed for {[t-BuC(Ni-Pr)2]-
ZnMe}2.17 Moreover, C can undergo a keto-enol transfor-
mation with subsequent formation of C0. As a consequence,
deprotonation reaction with ZnMe2 can occur at either the
carbon or the nitrogen atom, yielding two different reaction
products, D and D0.
D reacts with C(NCy)2 with insertion into the Zn-C bond
and subsequent formation of E, which after rearrangement
of the amidinate groups from a chelating to a bridging
binding mode yields 1, whereas the reaction of D0, which
represents exactly the cluster core as observed in 5 (5 contains
only an additionally coordinated MeZnOMe molecule), with
C(NCy)2 occurs with insertion into the Zn-N bond (Zn5-
N1) and formation of E0, containing a guanidinate group, as
was previously observed in {(MeZn)4C[(i-PrNCNi-Pr)4]},
6.11b In 6 the carbodiimide insertion occurred into the
Zn4-N8 bond, yielding the guanidinate moiety N6-C26
(N7)-N8. Chang et al. and Barry et al. previously reported
that sterically less hindered carbodiimides prefer inser-
tion reaction into an Al-N bond, whereas sterically more
hindered carbodiimides insert into the Al-Me bond of
Me2AlNMe2.18
˚
The equal C-C bond lengths in 1 (1.564(2) A) clearly prove
the formation of C-C single bonds. The almost equal
˚
Zn-N bond lengths in 1 (2.141(3)-2.180(3) A) are slightly elon-
gated compared to the i-Pr-substituted derivative (2.108(2)-
˚
2.134(2) A), whereas the Zn-C bond lengths of 1 (1.979(4),
˚
1.983(4) A) are slightly shorter. The N-C bond lengths within
the amidinate groups in 1 indicate a delocalized π-electron
system, even though the N-C bond lengths of the 3-fold-
˚
coordinated N atoms (N1-C28 1.311(5), N3-C27A 1.318(5) A)
are slightly shorter compared to those of the 4-fold-coordinated
˚
N atoms (N2-C28A 1.350(5), N4-C27 1.346(5) A), as was
expected.
The structures of 3 and 5 are more complex compared to 1
and 2. Both complexes exhibit a central cluster core built by
three amidinate and four ZnMe groups, and the C atoms of
the amidinate groups (C7, C9, C7a 3; C1, C2, C3 5) bind to a
central, trigonal-planar coordinated carbon atom (C8 3; C4
5). However, the bonding situation in 3 and 5 clearly differs.
In 3, one amidinate group serves as bridging and two as
chelating ligand, whereas in 5, the amidinate groups serve as
As a consequence of this insertion reaction, an NCNCN
unit is formed as is observed in {C[C(NCy)2]2Zn2Me2-
[C2(NCy)3]}, 2, as well as in the i-Pr-substituted complex
(16) Since ZnMe2 is a rather poor base, it is not quite clear why the
deprotonation reaction occurs in these reactions. Moreover, we have not
found any indication for a deprotonation mechanism in reactions of
carbodiimides with AlMe3 and GaMe3, respectively, even at elevated
temperatures. Currently we are investigating reactions of monoamidi-
nate zinc complexes of the type [MeC(NR)2]ZnMe with strong bases
such as organolithium compounds.
(17) Schmidt, S.; Schulz, S.; Bolte, M.; Z. Anorg. Allg. Chem. 2009,
in press.
(18) (a) Chang, C.-C.; Hsiung, C.-S.; Su, H.-L.; Srinivas, B.; Chiang,
M. Y.; Lee, G.-H.; Wang, Y. Organometallics 1998, 17, 1595. (b) Rowley,
C. N.; DiLabio, G. A.; Barry, S. T. Inorg. Chem. 2005, 44, 1983.
(15) Even though 1-4 as well as ZnMe2 are sensitive to oxygen, the
formation of 5 due to the presence of adventitious oxygen in the system
can be excluded. According to 1H NMR spectroscopic studies, 5 was
only formed in three different reactions when the carbodiimide was used
as received. In contrast, no indication for the formation of 5 was found in
reactions with purified carbodiimide.

Article
Organometallics, Vol. 28, No. 15, 2009 4375
Scheme 5. Keto-Enol Tautomerism Yields Two Possible Reaction Intermediates (D and D0), Which React with C(NCy)2 with Subsequent
Formation of Cluster-Type Complexes E and E0
Scheme 6. Possible Reaction Mechanism for the Formation of 3 and 5
{C[C(Ni-Pr)2]2Zn2Me2[C2(Ni-Pr)3]}, 7. Formally, 2 and 7
are formed by elimination of one molecule of RN(ZnMe)2.
The formation of complexes 3 and 5 starting from D0 can
also be explained by rearrangement of the amidinate units
from a chelating into a bridging binding mode. 3 is formed by
rearrangement of two amidinate units, whereas 5 results
from a rearrangement of three amidinate units, as shown in
Scheme 6.
to internal C6D5H (1H: δ=7.154; 13C: δ=128.0). IR spectra
were recorded on an ALPHA-T FT-IR spectrometer either in
Nujol between KBr plates or with a single-reflection ATR
sampling module. Melting points were measured in sealed
capillaries and were not corrected. Elemental analyses were
performed at the Elementaranalyse Labor of the University
of Essen.
{C[C(NCy)2ZnMe]4}, 1. ZnMe2 (4.2 mL, 1.2 M in toluene,
5 mmol) and 1.03 g (5 mmol) of purified (CyN)2C were
stirred for 5 days at 110 °C. All volatiles were removed
at reduced pressure, and the resulting solid was dissolved
in 30 mL of cyclohexane and stored at þ4 °C. Colorless
crystals of 1 were formed within 24 h and isolated by
filtration.
Conclusions
Cluster-type zinc amidinate complexes 1-5 were
synthesized by reaction of ZnMe2 and cyclohexyl carbo-
diimide and structurally characterized. A possible reaction
mechanism, which explains the formation of the com-
plexes 1-5 as well as those reported previously, has been
identified. Further studies on the reaction of ZnMe2 with
carbodiimides and other heterocumulenes are currently
under investigation.
Yield (isolated crystals): 0.84 g (58%). Melting point: >210 °C.
Anal. Found (calcd) for C57H100N8Zn4 (1158.95 g/mol): H, 8.72
(8.70); C, 59.19 (59.07); N, 9.62 (9.67). H NMR (500 MHz,
1
C6D6, 25 °C): δ 0.14 (s, 3H, ZnMe), 1.19-1.24 (m, 6H, CH2),
1.51-1.54 (m, 2H, CH2), 1.69 (m (br), 2H, CH2), 1.85 (m (br),
8H, CH2), 2.36-2.40 (m, 2H, CH2), 3.68 (tt, 3JH
=10.6 Hz,
axHax
1H, H(1)ax), 4.01 (m, 1H, H(1)ax). 13C NMR (125 MHz, C6D6,
25 °C): δ 1.0 (s, ZnMe), 26.1 (s, C3/C5), 27.2 (s, C4), 34.7 (C2/
C6), 34.8 (C2/C6), 56.4 (s, N-C1), 58.6 (s, N-C1), 170.6 (s,
NCN). IR: ν 2924, 2849, 2657, 1688, 1550, 1510, 1449, 1379,
1342, 1279, 1259, 1086, 1014, 957, 930, 891, 863, 795, 702, 678,
Experimental Details
All manipulations were performed under an Ar atmo-
sphere. Solvents were carefully dried over Na/K and degassed
prior to use. Cyclohexyl carbodiimide was heated to 40 °C and
evacuated for 6 h at 10-3 mbar. A 1.2 M solution of ZnMe2 in
659, 515 cm-1
.
{C[C(NCy)2ZnMe]2[C2(NCy)3]}, 2. ZnMe2 (4.2 mL, 1.2 M
in toluene, 5 mmol) and 2.06 g (10 mmol) of purified
(CyN)2C were stirred for 5 days at 110 °C. All volatiles were
removed at reduced pressure, and the resulting solid was
dissolved in 30 mL of cyclohexane and stored at þ4 °C.
1
toluene was purchased from Acros and used as received. H
and 13C{1H} NMR spectra were recorded on Bruker DMX
300 or Bruker Avance 500 spectrometers and are referenced

4376 Organometallics, Vol. 28, No. 15, 2009
Schmidt et al.
Colorless crystals of 2 were formed within 24 h and isolated
by filtration.
(s, NCN), 165.2 (s, NCN), 170.1 (s, NCN). IR (Nujol): ν 2924,
2853, 1573, 1534, 1462, 1377, 1341, 1302, 1276, 1260, 1166, 1153,
1128, 1086, 1057, 1043, 1023, 974, 955, 890, 840, 799, 722, 705,
Yield (isolated crystals): 0.61 g (27%). Melting point: 118 °C.
Anal. Found (calcd) for C49H83N7Zn2 (900.98 g/mol): H, 9.18
(9.28); C, 65.24 (65.32); N, 10.85 (10.88). 1H NMR (500 MHz,
C6D6, 25 °C): δ 0.13 (s, 6H, ZnMe), 0.79 (m, 3H, CH2), 1.05-
1.21 (m, 7H, CH2), 1.34 (m (br), 16H, CH2), 1.48-1.74 (m, 12H,
CH2), 1.80-2.05 (m (br), 28H, CH2), 2.18-2.21 (m, 4H, CH2),
676, 661, 646, 561, 545, 529 cm-1
.
{C[C(NCy)2ZnMe]3(ZnMe)(MeZnOMe)}, 5, was obtained
as a byproduct only when the carbodiimide was used as
received. Unfortunately, we were not able to isolate a larger
amount of 5, but its formation is indicated by sharp singlets at
3.43 (tt, 3JH
=11.3 Hz, 1H, H(1)ax), 3.54 (tt, 3JH
=10.8
axHax
3.58 and -0.37 ppm due to the MeZnOMe moiety in the H
1
axHax
Hz, 3JH
=3.8 Hz, 2H, H(1)ax), 3.96 (tt, 3JH
=10.3 Hz, 4H,
axHax
NMR spectra of the raw products of several reaction batches.
According to these NMR spectra, 5 is formed in less than 5%
yield.
axHeq
H(1)ax). 13C NMR (125 MHz, C6D6, 25 °C): δ -3.9 (s, ZnMe),
25.5 (s, Cy), 26.1 (s, Cy), 26.4 (s, Cy), 26.5 (s, Cy), 26.6 (s, Cy),
27.2 (s, Cy), 29.6 (s, Cy), 31.5 (s, CC4), 34.2 (s, C2/C6), 36.0 (s,
C2/C6), 36.5 (s, C2/C6), 57.0 (N-C1), 58.8 (N-C1), 155.5 (s,
NCN), 160.0 (s, NCN). IR (Nujol): ν 2924, 2854, 1686, 1556,
1462, 1377, 1344, 1312, 1286, 1260, 1090, 1021, 889, 799, 722,
Single-Crystal X-ray Analyses. Data were collected on a
Bruker AXS SMART APEX CCD diffractometer (Mo KR
˚
radiation, λ=v 0.71073 A; T=173(2) K). The structures were
solved by direct methods (SHELXS-97)19 and refined by
full-matrix least-squares on F2. Semiempirical absorp-
tion corrections were applied. All non-hydrogen atoms
were refined anisotropically, and hydrogen atoms by a riding
model (SHELXL-97, Program for Crystal Structure Re-
finement).20
652, 512 cm-1
.
{C[C(NCy)2ZnMe]3(ZnMe)}, 3. ZnMe2 (8.4 mL, 1.2 M in
toluene, 10 mmol) and 1.03 g (5 mmol) of purified (CyN)2C were
stirred for 5 days at 110 °C. All volatiles were removed at
reduced pressure, and the resulting solid was dissolved in
30 mL of cyclohexane and stored at þ4 °C. Colorless crystals
of 2 were formed within 24 h and isolated by filtration.
1: C57H100N8Zn4 2.5C6H12 1.5C6H6, M=1486.48, colorless
crystal (0.26 ꢀ 0.18 ꢀ 0.13 mm); monoclinic, space group C2/c;
3
3
˚
˚
˚
Yield (isolated crystals): 0.58 g (49%). Melting point: 140 °C.
Anal. Found (calcd) for C44H78N6Zn4 (952.62 g/mol): H, 8.19
(8.25); C, 55.33 (55.48); N, 8.74 (8.82). H NMR (500 MHz,
a = 27.9483(7) A, b = 15.6718(4) A, c = 26.9271(10) A; β =
3
-1
˚
115.2140(10)°, V=v 10670.4(6) A ; Z=4; μ v=0.923 mm
ber. =0.925 g cm-3; 63 763 reflections (2θmax=56.6°), 13 204
unique (Rint=0.0581); 529 parameters; largest max./min. in the
;
1
F
C6D6, 25 °C): δ 0.03 8s, 3H, ZnMe), 1.02-1.11 (tt, 1H, 3JH
=
axHax
13.1 Hz, 3JH
=3.7 Hz, H(4)ax), 1.19-1.28 (m, 4H, H(3/5)ax),
final difference Fourier synthesis 0.769 e A /-0.584 e A ;
-3
-3
˚
˚
axHeq
1.38-1.45 (m, 4H, H(2/6)ax), 1.51 (d (br), 2H, H(4)eq), 1.69 (d
=
axHax
max./min. transmission 0.75/0.64; R1=0.0738 (I>2σ(I)), wR2
(all data)=0.2344. The cyclohexane and benzene molecules
refined with reduced SOF 0.5 together with the riding hydrogen
atoms. In spite of the reduced SOFs of the solvent molecules, the
ADPs still indicate severe disorder, which could not be re-
(br), 4H, H(3/5)eq), 2.10 (d (br), 4H, H(2/6)eq), 3.56 (tt, 3JH
3
10.7 Hz, JH
=3.5 Hz, 2H, H(1)ax). 13C NMR (125 MHz,
axHeq
C6D6, 25 °C): δ 1.4 (s, ZnMe), 24.9 (s, Cy), 25.6 (s, Cy), 25.8
(s, Cy), 25.9 (s, Cy), 26.1 (s, Cy), 26.5 (s, Cy), 26.8 (s, Cy), 27.2 (s,
Cy), 35.4 (s, Cy), 36.5 (s, Cy), 37.3 (s, Cy), 37.5 (s, Cy), 37.8 (s,
Cy), 38.9 (s, Cy), 39.0 (s, Cy), 39.4 (s, Cy), 53.6 (s, Cy), 57.3
(s, Cy), 57.5 (s, Cy), 61.0 (s, Cy), 174.4 (s, NCN). IR (Nujol):
ν 2924, 2853, 1644, 1529, 1506, 1461, 1406, 1377, 1341, 1309,
1262, 1242, 1194, 1177, 1088, 1072, 1026, 976, 890, 841, 803, 723,
solved. 3: C44H78N6Zn4 2C5H12, M=1120.92, colorless crystal
(0.26 ꢀ 0.18 ꢀ 0.15 mm); monoclinic, space group P2/c; a =
3
˚
˚
˚
10.4638(7) A, b=14.5915(9) A, c=19.999(12) A; β=95.887(4)°,
V=3037.5(3) A ; Z=2; μ=1.598 mm-1; Fber.=1.226 g cm-3
;
3
˚
44 047 reflections (2θmax=49.6°), 5212 unique (Rint=0.0769);
862, 652, 603, 564, 548 cm-1
.
293 parameters; largest max./min. in the final difference Fourier
-3
synthesis 0.524 e A /-0.329 e A-3; max./min. transmission
0.75/0.53; R1 = 0.0425 (I>2σ(I)), wR2 (all data)=0.1122. The
elemental cell contains two cyclohexane C(31)-C(36) and
C(41)-C(46), which are disordered over two sites with SOF
0.5 together with the riding hydrogen atoms and refined with
˚
˚
{C[C(NCy)2ZnMe]3(NCy2ZnMe)}, 4. ZnMe2 (4.2 mL, 1.2 M
in toluene, 5 mmol) and 1.03 g (5 mmol) of purified (CyN)2C
were stirred for 4 days at 90 °C. All volatiles were removed at
reduced pressure, and the resulting solid was dissolved in 30 mL
of cyclohexane and stored at þ4 °C. Colorless crystals of 4 were
formed within 24 h and isolated by filtration.
isotropic displacement parameters. 5: C46H84N6OZn5 1.25
C5H12, M=1161.26, colorless crystal (0.32 ꢀ 0.26 ꢀ 0.22 mm);
3
Yield (isolated crystals): 1.45 g (78%). Melting point: 150 °C.
Anal. Found (calcd) for C57H100N8Zn4 (1158.95 g/mol): H, 9.33
(8.70); C, 61.18 (59.07); N, 8.94 (9.67). H NMR (500 MHz,
˚
triclinic, space group P1; a=12.8446(9) A, b=13.7719(10)A, c=
˚
1
˚
19.7904(13) A; R = 94.978(4)°, β=108.659(3)°, γ=103.379(4)°,
3
V=3177.3(4) A ; Z=2; μ=1.968 mm-1; Fber.=1.214 g cm-3
;
˚
C6D6, 25 °C): δ -0.08 (s, 3H, ZnMe), -0.06 (s, 3H, ZnMe), -
0.02 (s, 3H, ZnMe), 0.08 (s, 3H, ZnMe), 1.01-1.15 (m, 6H,
CH2), 1.16-1.37 (m, 20H, CH2), 1.42-1.45 (m, 2H, CH2),
1.46-1.55 (m, 14H, CH2), 1.56-1.67 (m, 8H, CH2), 1.67-1.78
(m, 12H, CH2), 1.79-1.95 (m, 6H, CH2), 2.03-2.20 (m, 6H,
CH2), 2.22-2.28 (m, 2H, CH2), 2.29-2.38 (m, 4H, CH2), 2.39-
65 125 reflections (2θmax v=56.6°), 15 491 unique (Rint=0.0484);
577 parameters; largest max./min. in the final difference
Fourier synthesis 0.859 e A /-0.547 e A-3; max./min. trans-
mission 0.79/0.65; R1 = 0.0408 (I > 2σ(I)), wR2 (all data) =
0.1204. The elemental cell also contains three n-pentane
molecules (carbon atoms C(71) to C(95)), which are dis-
ordered over two sites with SOF 0.5 together with the riding
hydrogen atom.
-3
˚
˚
2.51 (m, 2H, CH2), 3.16 (tt, 3JH
=10.7 Hz, 3JH
=3.4 Hz,
axHeq
axHax
1H, H(1)ax), 3.70 (tt, 1H, H(1)ax), 3.71 (tt, 1H, H(1)ax), 3.77 (1H,
=3.8 Hz, 1H,
H(1)ax), 3.83 (tt, 3JH =10.9 Hz, 3JH
axHax
H(1)ax), 4.00 (1H, H(1)ax), 4.22 (tt, 3JH
axHeq
=10.7 Hz, 3JH
=
axHeq
axHax
3.6 Hz, 1H, H(1)ax), 4.40 (tt, 3JH
=10.6 Hz, 3JH
=3.9 Hz,
axHeq
Acknowledgment. S. Schulz thanks the German
Science Foundation (DFG) for financial support.
axHax
1H, H(1)ax). 13C NMR (125 MHz, C6D6, 25 °C): δ -10.8 (s,
ZnMe), -10.2 (s, ZnMe), -7.9 (s, ZnMe), -7.2 (s, ZnMe), 25.4
(Cy), 25.6 (Cy), 25.8 (Cy), 25.9 (Cy), 26.0 (Cy), 26.0 (Cy), 26.0
(Cy), 26.0 (Cy), 26.1 (Cy), 26.2 (Cy), 26.2 (Cy), 26.3 (Cy), 26.3
(Cy), 26.4 (Cy), 26.7 (Cy), 27.2 (Cy), 30.2 (s, Cy), 31.4 (s, Cy),
32.3 (s, Cy), 33.2 (s, Cy), 35.7 (s, Cy), 36.0 (s, Cy), 36.3 (s, Cy),
36.3 (s, Cy), 36.4 (s, Cy), 36.8 (s, Cy), 36.9 (s, Cy), 37.4
(s, Cy), 37.6 (s, Cy), 37.8 (s, Cy), 37.8 (s, Cy), 38.2 (s, Cy), 38.5
(s, Cy), 56.1 (s, Cy), 56.2 (s, Cy), 56.3 (s, Cy), 56.7 (s, Cy), 56.9 (s,
Cy), 57.3 (s, Cy), 58.3 (s, Cy), 64.4 (s, Cy), 152.5 (s, NCN), 159.5
Supporting Information Available: Tables, text, thermal
ellipsoid plots, and a CIF file giving X-ray crystallo-
graphic data of 1, 3, and 5. This material is available
free of charge via the Internet at http://pubs.acs.org.
(19) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(20) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
€
€
Refinement; Universitat Gottingen, 1997.