Bimetallic calcium and zinc complexes with bridged β-diketiminate ligands: Investigations on epoxide/CO2 copolymerization

Article abstract of DOI:10.1021/om800597f

A series of dinucleating bis(β-diketiminate) ligands with rigid bridges has been prepared. In all cases the β-diketiminate unit is 2,6-iPr₂C₆H₃NC(Me)C(H)C(Me)N-(bridge), and the bridges are either paraphenylene, meta-phenylene or 2, 6-pyridylene (the dinucleating ligands are abbreviated as PARA-H₂, META-H₂ and PYR-H₂, respectively). These ligands have been converted to heteroleptic bimetallic calcium and zinc complexes. For calcium, only the PARA-phenylene bridged ligand led to a heteroleptic bimetallic calcium amide complex PARA-[CaN(SiMe₃)₂ · THF]₂. For the other ligands, homoleptic complexes have been isolated: META-Ca and PYR-Ca. For zinc, the whole range of heteroleptic amides could be isolated: PARA-[ZnN(SiMe₃)₂]₂, META-[ZnN(SiMe ₃)₂]₂, and PYR-[ZnN(SiMe₃) ₂]₂. Analogue ethylzinc complexes have been prepared in quantitative yields: PARA-(ZnEt)₂, META-(ZnEt)₂, and PYR-(ZnEt)₂. Reactions of the ethylzinc complexes with SO₂ gave access to the ethylsulfinate complexes META-(ZnO2SEt)2 and PYR-(ZnO ₂SEt)₂; for the para-phenylene bridged ligand no products could be isolated. Crystal structures of the following complexes are presented: (META-Ca)₂, PARA-[CaN(SiMe₃)₂ ... THF]₂, PARA[ZnN(SiMe₃)₂]₂, META-[ZnN(SiMe₃)₂]₂, PYR-(ZnEt)₂, and PYR-(ZnO₂SEt)₂. All heteroleptic complexes have been tested for activity in me copolymerization of cyclohexene oxide (CHO) and CO₂. The bimetallic complex PARA-[CaN(SiMe₃)₂ · THF]₂ is not active. For zinc, the PARA and META complexes were found to be active under highly concentrated conditions (Zn/CHO ratio of 1/1000; no solvent), but no significant polymer yields could be achieved with PYR complexes. This is either due to conformational changes of the complex or to coordination of the pyridylene N atom to the catalytic centers. The order of activity found in the bimetallic zinc complexes is META > PARA. This is likely due to a more advantageous Zn · Zn distance in the meto-phenylene bridged bimetallic catalysts. There are several indications for bimetallic action. First of all, the ethylzinc systems PARA-(ZnEt)₂ and META-(ZnEt)2 initiate CHO/CO₂ copolymerization, whereas monometallic ethylzinc catalysts are not reactive. Second, the bimetallic zinc catalysts are also highly active under diluted conditions: a low metal/CHO ratio of 1/3000 gave high-MW polymers (M_n > 100.000, PDI = 1.33) with essentially only carbonate linkages. In contrast, monometallic systems show a drastic loss of activity upon dilution. Finally, the bimetallic catalyst META-[ZnN(SiMe ₃)₂]₂ shows a significantly higher activity than a comparable monometallic model system.

Full text of DOI:10.1021/om800597f

6178
Organometallics 2008, 27, 6178–6187
Bimetallic Calcium and Zinc Complexes with Bridged
ꢀ-Diketiminate Ligands: Investigations on Epoxide/CO2
Copolymerization
Dirk F.-J. Piesik, Sven Range, and Sjoerd Harder*
Anorganische Chemie, UniVersita¨t Duisburg-Essen, UniVersita¨tsstraꢀe 5-7, 45117 Essen, Germany
ReceiVed June 27, 2008
A series of dinucleating bis(ꢀ-diketiminate) ligands with rigid bridges has been prepared. In all cases
the ꢀ-diketiminate unit is 2,6-iPr2C6H3NC(Me)C(H)C(Me)N-(bridge), and the bridges are either para-
phenylene, meta-phenylene or 2, 6-pyridylene (the dinucleating ligands are abbreviated as PARA-H2,
META-H2 and PYR-H2, respectively). These ligands have been converted to heteroleptic bimetallic calcium
and zinc complexes. For calcium, only the PARA-phenylene bridged ligand led to a heteroleptic bimetallic
calcium amide complex PARA-[CaN(SiMe3)2 · THF]2. For the other ligands, homoleptic complexes have
been isolated: META-Ca and PYR-Ca. For zinc, the whole range of heteroleptic amides could be isolated:
PARA-[ZnN(SiMe3)2]2, META-[ZnN(SiMe3)2]2, and PYR-[ZnN(SiMe3)2]2. Analogue ethylzinc complexes
have been prepared in quantitative yields: PARA-(ZnEt)2, META-(ZnEt)2, and PYR-(ZnEt)2. Reactions
of the ethylzinc complexes with SO2 gave access to the ethylsulfinate complexes META-(ZnO2SEt)2 and
PYR-(ZnO2SEt)2; for the para-phenylene bridged ligand no products could be isolated. Crystal structures
of the following complexes are presented: (META-Ca)2, PARA-[CaN(SiMe3)2 · THF]2, PARA-
[ZnN(SiMe3)2]2, META-[ZnN(SiMe3)2]2, PYR-(ZnEt)2, and PYR-(ZnO2SEt)2. All heteroleptic complexes
have been tested for activity in the copolymerization of cyclohexene oxide (CHO) and CO2. The bimetallic
complex PARA-[CaN(SiMe3)2 · THF]2 is not active. For zinc, the PARA and META complexes were
found to be active under highly concentrated conditions (Zn/CHO ratio of 1/1000; no solvent), but no
significant polymer yields could be achieved with PYR complexes. This is either due to conformational
changes of the complex or to coordination of the pyridylene N atom to the catalytic centers. The order
of activity found in the bimetallic zinc complexes is META > PARA. This is likely due to a more
advantageous Zn · · · Zn distance in the meta-phenylene bridged bimetallic catalysts. There are several
indications for bimetallic action. First of all, the ethylzinc systems PARA-(ZnEt)2 and META-(ZnEt)2
initiate CHO/CO2 copolymerization, whereas monometallic ethylzinc catalysts are not reactive. Second,
the bimetallic zinc catalysts are also highly active under diluted conditions: a low metal/CHO ratio of
1/3000 gave high-MW polymers (Mn > 100.000, PDI ) 1.33) with essentially only carbonate linkages.
In contrast, monometallic systems show a drastic loss of activity upon dilution. Finally, the bimetallic
catalyst META-[ZnN(SiMe3)2]2 shows a significantly higher activity than a comparable monometallic
model system.
catalysts4 for high molecular weight polycarbonates has led to
Introduction
a boost in research activities.
As the need for biodegradable polymers from biorenewable
feedstocks is becoming urgent,1 research on the alternating
epoxide/CO2 copolymerization is rapidly increasing.2,3 Notably,
Coates’ landmark discovery of highly active homogeneous Zn
These catalysts in question are composed of a bulky
ꢀ-diketiminate ligand, chelating the Zn center, and an initiating
group that can be (Me3Si)2N-, an alkoxide, or acetate. Alkyl
groups such as Et are not active, however, can be conveniently
converted to ethylsulfinates (EtSO2-), which are highly active
initiators.5 There is ample evidence for a bimetallic mechanism
with a carboxylate end group as the resting state (epoxide
insertion is the rate-determining step; Scheme 1).4 It has been
shown that the intermediate carboxylate species are in a
monomer-dimer equilibrium that is highly sensitive toward the
nature of the aryl subtituents in the ꢀ-diketiminate ligand. As
* To whom correspondence should be sent. E-mail: sjoerd.harder@
uni-due.de.
(1) (a) Chisholm, M. H.; Zhou, Z. J. Mater. Chem. 2004, 14, 3081–
3092. (b) Domb, A. J. Polymer Prepr. 2007, 48, 640. (c) van Beilen, J. B.;
Poirier, Y. Plant J. 2008, 54, 684–701.
(2) Recent reviews: (a) Darensbourg, D. J.; Holtcamp, M. W. Coord.
Chem. ReV. 1996, 153, 155–174. (b) Darensbourg, D. J.; Mackiewicz, R. M.;
Phelps, A. L.; Billodeaux, D. R. Acc. Chem. Res. 2004, 37, 836–844. (c)
Sugimoto, H.; Inoue, S. J. Polym. Sci., Part A: Polym. Chem. 2004, 42,
5561–5573. (d) Coates, G. W.; Moore, D. R. Angew. Chem. 2004, 116,
6784-6806; (e) Coates, G. W.; Moore, D. R. Angew. Chem. Int. Ed. 2004,
43, 6618-6639.
(3) (a) Darensbourg, D. J.; Holtcamp, M. W. Macromolecules 1995,
28, 7577–7579. (b) Super, M.; Berluche, E.; Costello, C.; Beckman, E.
Macromolecules 1997, 30, 368–372. (c) Darensbourg, D. J.; Holtcamp,
M. W.; Struck, G. E.; Zimmer, M. S.; Niezgoda, S. A.; Rainey, P.;
Robertson, J. B.; Draper, J. D.; Reibenspies, J. H. J. Am. Chem. Soc. 1999,
121, 107–116.
(4) (a) Cheng, M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc.
1998, 120, 11018–11019. (b) Cheng, M.; Moore, D. R.; Reczek, J. J.;
Chamberlain, B. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc.
2001, 123, 8738–8749. (c) Moore, D. R.; Cheng, M.; Lobkovsky, E. B.;
Coates, G. W. J. Am. Chem. Soc. 2003, 125, 11911–11924.
(5) Eberhardt, R.; Allmendinger, M.; Luinstra, G. A.; Rieger, B.
Organometallics 2003, 22, 211–214.
10.1021/om800597f CCC: $40.75
2008 American Chemical Society
Publication on Web 11/05/2008

Bimetallic Calcium and Zinc Complexes
Organometallics, Vol. 27, No. 23, 2008 6179
Scheme 1
Scheme 2. Reagents and conditions: (i) [Et3O]+[BF4]-,
CH2Cl2, 20 °C; (ii) Et3N and diamine, 20 °C
mers such as lactides and cyclic carbonates,14 hitherto no
calcium catalysts have been reported for CHO/CO2 copolym-
erization. It is highly likely that, similar to the Zn catalysts, a
bimetallic mechanism could be operative. Therefore, we directed
our research to the syntheses of dinuclear complexes of calcium
and zinc. Dinucleating bis(salicylaldimide) ligands were found
to be unsuitable in the stabilization of bimetallic calcium or
zinc amides.15 We now introduce a set of dinucleating ligands
based on the bulkier ꢀ-diketiminate unit with a variety of rigid
bridges and evaluate the possibility of obtaining heteroleptic
bimetallic calcium and zinc complexes. The use of these
complexes in CHO/CO2 copolymerization and the influences
of the bridging units will be discussed.
the dimer is the prominent active species,6 the activities of the
polymerization catalysts can be controlled by small variations
in the ꢀ-diketiminate ligands. Also, catalyst concentration is a
decisive factor for activity: at very low concentration the
monomer-dimer equilibrium is shifted to the monomeric side
and hardly any catalytic activity can be observed.7,9,16 This is
a serious drawback since monomer-to-polymer conversion is
generally limited on account of viscosity problems.7-9 Dilution
of the system by either addition of monomer or an inert solvent
would shift the monomer-dimer equilibrium to the monomeric
side, thus reducing catalyst activity.
Results and Discussion
Recent research focuses on the introduction of dinucleating
ligands (1-3) that circumvent the equilibrium between the active
dimer and inactive (or less active) monomer. The dinuclear Zn
catalyst 1 has been shown to be highly active for the copolym-
erization of CHO and CO2.7 Even under very diluted conditions,
high molecular weight polymers (Mn up to 284 000) could be
obtained. Dinuclear Zn complexes based on parallel ꢀ-diketimi-
nate ligands (2) were only moderately active, probably on
account of overcrowding in the reaction pocket.10 A bimetallic
Zn complex with the Trost ligand (3-Zn) has been shown to be
active in CHO/CO2 copolymerization in diluted solutions and
under the remarkably low CO2 pressure of 1 bar.11 Interestingly,
the analogue dinuclear Mg complex 3-Mg was also found to
be active in CHO/CO2 copolymerization.12
Dinucleating Ligands. Three bridged ꢀ-diketiminate ligands
have been prepared in reasonable yields by a two-step standard
condensation route given in Scheme 2. The diprotic ligands are
abbreviated according to the nature of the bridging unit: 1,4-
phenylene (PARA-H2), 1,3-phenylene (META-H2), or 2,6-
pyridylene (PYR-H2). The dinucleating ligands PYR and META
allow for a wide range of metal · · · metal distances (2.5-8 Å),
whereas the metal · · · metal distances in a bimetallic complex
with the PARA ligand lies in the range of approximately
5.5-8.5 Å.16 The PYR ligand is a potential pentadentate ligand
and has been incorporated to study the effect of additional metal
coordination.
Bimetallic Calcium Complexes. Two-fold deprotonation of
PARA-H2 with two equivalents of [(Me3Si)2N]2Ca · (THF)2 gave
exclusively the heteroleptic complex PARA-[CaN-
(SiMe3)2 · THF]2 in a reasonable yield (Scheme 3). This bimetal-
lic complex is also, in benzene solution, stable toward ligand
exchange, and the Schlenk equilibrium is fully at the heteroleptic
side. Deprotonation of META-H2 with two equivalents of
[(Me3Si)2N]2Ca · (THF)2 in either benzene or THF gave a
mixture of heteroleptic META-[CaN(SiMe3)2 · (THF)x]2 and
Because the use of calcium reagents in catalysis is one of
our main research areas,13 we are interested in exploring their
potential in the alternating CHO/CO2 copolymerization. Al-
though well-defined calcium catalysts have recently been
introduced for the ring opening polymerization of polar mono-
(6) There are indications that also the monomeric species is active in
epoxide/CO2 copolymerization, albeit with much slower conversion rates.4c,5
(7) Lee, B. Y.; Kwon, H. Y.; Lee, S. Y.; Na, S. J.; Han, S.; Yun, H.;
Lee, H.; Park, Y.-W. J. Am. Chem. Soc. 2005, 127, 3031–3037.
(8) Cohen, C. T.; Thomas, C. M.; Peretti, K. L.; Lobkovsky, E. B.;
Coates, G. W. Dalton Trans. 2006, 237–249.
(9) van Meerendonk, W. J.; Duchateau, R.; Koning, C. E.; Gruter, G.-
J. M. Macromol. Rapid Commun. 2004, 25, 382–386.
(10) Pilz, M. F.; Limberg, C.; Lazarov, B. B.; Hultzsch, K. C.; Ziemer,
B. Organometallics 2007, 26, 3668–3676.
(14) (a) Chisholm, M. H.; Gallucci, J.; Phomphrai, K. Chem. Commun.
2003, 48–49. (b) Zhong, Z.; Schneiderbauer, S.; Dijkstra, P. J.; Wester-
hausen, M.; Feijen, J. J. Polym. Bull. 2003, 51, 175–182. (c) Chisholm,
M. H.; Gallucci, J.; Phomphrai, K. Inorg. Chem. 2004, 43, 6717–6725. (d)
Darensbourg, D. J.; Choi, W.; Ganguly, P.; Richers, C. P. Macromolecules
2006, 39, 4374–4379.
(11) Xiao, Y.; Wang, Z.; Ding, K. Chem.sEur. J. 2005, 11, 3668–3678.
(12) Xiao, Y.; Wang, Z.; Ding, K. Macromolecules 2006, 39, 128–137.
(13) (a) Harder, S.; Feil, F.; Knoll, K. Angew. Chem., Int. Ed. 2001, 40,
4261–4264. (b) Buch, F.; Brettar, J.; Harder, S. Angew. Chem., Int. Ed.
2006, 45, 2741–2745.
(15) Range, S.; Piesik, D. F.-J.; Harder, S. Eur. J. Inorg. Chem. 2008,
22, 3442–3451..
(16) This range of metal · · · metal distances is based on simple geo-
metrical calculations using a general M-O and M-N distance of 2.5 Å
and allowing for rotation around the N-C(bridge) bonds.

6180 Organometallics, Vol. 27, No. 23, 2008
Piesik et al.
Scheme 3. Syntheses of Bimetallic Ca and Zn Complexes
homoleptic (META-Ca)2. The homoleptic dimer (META-Ca)2
could be obtained in crystalline purity. For the pyridylene-
bridged ligand, the Schlenk equilibrium was found to be
completely to the homoleptic side and only (PYR-Ca)x could
be observed and isolated. The crystal structures of the complexes
PARA-[CaN(SiMe3)2 · THF]2 and (META-Ca)2 are described
below.
Bimetallic Zinc Complexes. Reactions of the dinucleating
ligands with [(Me3Si)2N]2Zn gave in all cases good yields of
the heteroleptic complexes PARA-[ZnN(SiMe3)2]2, META-
[ZnN(SiMe3)2]2, and PYR-[ZnN(SiMe3)2]2. Deprotonation with
Et2Zn gave quantitative conversion to PARA-(ZnEt)2, META-
(ZnEt)2, and PYR-(ZnEt)2. In all cases the complexes are
completely stable against ligand exchange reactions and the
Schlenk equilibrium is not an issue. The heteroleptic ethylzinc
compounds PYR-(ZnEt)2 and META-(ZnEt)2 cleanly reacted
with SO2 to form ethylsulfinate complexes. Reaction of PARA-
(ZnEt)2 with SO2 gave a mixture of unidentified products.
Crystal structures for PARA-[ZnN(SiMe3)2]2, META-[ZnN-
(SiMe3)2]2, PYR-(ZnEt)2, and PYR-(ZnO2SEt)2 are described
below.
neither the Ca-N bond distances nor the geometry of the
NCCCN backbone.
PARA-[CaN(SiMe3)2 · THF]2 crystallizes as a crystallographi-
cally C2-symmetric complex (Figure 2) in which each Ca2+ ion
is bound to a ꢀ-diketiminate unit, a (Me3Si)2N- ligand and a
THF ligand. The distorted tetrahedral coordination sphere is
further filled with an agostic interaction between Ca and C25
(3.315(4) Å). The latter weak interaction is also evident from
the asymmetric coordination of the (Me3Si)2N- ligand; the
Crystal Structures. META-Ca crystallizes as a crystallo-
graphically C2-symmetric dimer (Figure 1). The Ca2+ ions are
4-fold coordinated by two N,N-chelating ꢀ-diketiminate units.
These ꢀ-diketiminate units coordinate in significantly different
fashions. One of the ligands binds face-on to Ca (N1, N2). This
allows for a slightly bonding contact to the central carbon atom
C3 (2.841(5) Å), which on account of charge delocalization is
significantly negatively charged. The other ligand (N3, N4)
coordinates edge-on, and the Ca2+ ion is situated in the NCCCN
plane. These fundamentally different coordination modes affect
Figure 1. Crystal structure of [META-Ca]2 (viewed perpendicular
on the vertically oriented C2-axis). For clarity, hydrogen atoms and
iPr-substituents have been omitted. Selected bond distances in Å:
Ca-N1 2.326(3), Ca-N2 2.302(3), Ca-N3′ 2.300(3), Ca-N4′
2.366(3), Ca-C3 2.841(5), and Ca · · · Ca′ 7.017(2).

Bimetallic Calcium and Zinc Complexes
Organometallics, Vol. 27, No. 23, 2008 6181
Ca-N3-Si2 angle of 110.8(1)° is significantly smaller than the
angle Ca-N3-Si1 of 119.8(1)°. The bond distances to Ca
correspond well to those observed in the comparable unbridged
complex 4.14c
PARA-[ZnN(SiMe3)2]2 crystallizes as a complex of ap-
proximate (noncrystallographic) C2-symmetry (Figure 3). The
tricoordinate Zn atoms are situated at opposite sides of the bridge
plane. The metal coordination geometry and the bond distances
to the zinc atoms are very similar to those in the mononuclear
species 5.4b
META-[ZnN(SiMe3)2]2 crystallizes, similar to PARA-
[ZnN(SiMe3)2]2, as an approximately C2-symmetric complex
(Figure 4). The tricoordinate Zn atoms are situated at opposite
sides of the bridge plane. The metal coordination geometry and
the bond distances to the zinc atoms do not differ significantly
from those observed in PARA-[ZnN(SiMe3)2]2. The only notable
difference is the Zn · · · Zn distance (6.098(2) Å), which is shorter
than that in PARA-[ZnN(SiMe3)2]2 (8.173(2) Å).
PYR-(ZnEt)2 crystallizes as a nonsymmetric complex in
which the dinucleating ligand possesses approximate (noncrys-
tallographic) Cs-symmetry (Figure 5). The tricoordinate Zn
atoms are situated at the same side of the bridge plane and there
are no evident pyridyl-Zn interactions. Bond distances to the
Zn atoms are similar to those in the mononuclear complex 6.17
not give polymeric products, at least not under standard
conditions. Hitherto it is not clear whether bimetallic calcium
complexes are a priori not active or if the initiation of the
polymerization reaction by the amide (Me3Si)2N- ion is
troublesome. Analogue (ꢀ-diketiminate)ZnN(SiMe3)2 catalysts
initiate the polymerization reaction by insertion of CO2 to form
the carbamate (ꢀ-diketiminate)ZnO2CN(SiMe3)2, which rear-
ranges via a 1,3-shift of the Me3Si group to the true initiator
(ꢀ-diketiminate)ZnOSiMe3 and OdCdN-SiMe3.4c Because the
(ꢀ-diketiminate)ZnN(iPr)2 catalyst is not active in CHO/CO2
copolymerization and only reacts to (ꢀ-diketiminate)ZnO2-
CN(iPr)2,18 this rearrangement is essential for activity. Since it
is not clear if such rearrangements are also operative in calcium
chemistry, we also ran polymerizations in which the PARA-
[CaN(SiMe3)2 · THF]2 catalyst was pretreated with two equiva-
lents of iPrOH (at -80 °C). This should give in situ formation
of the bimetallic calcium alkoxide initiator PARA-
[CaOiPr · (THF)x]2. However, under no circumstance could we
isolate significant amounts of polymer. We are currently
investigating why calcium catalysts fail to produce polymer.
Although monomeric ꢀ-diketiminate ethylzinc complexes do
not initiate the CHO/CO2 copolymerization, fair-to-good activity
has been observed for the bimetallic catalysts PARA-(ZnEt)2
and META-(ZnEt)2 (Table 1, entries 1-2); polymers with a
high content of carbonate linkages could be isolated. The striking
inactivity of monometallic ethylzinc complexes can be explained
by the incapability of the ethyl groups to bridge between two
Zn atoms, thus inhibiting formation of catalytically active
bimetallic zinc complexes. Also, CO2 does not insert in the Et-
Zn bond to give a dimeric complex with bridging carboxylate
anions.19 Only activation of the Et-Zn bond by SO2 insertion
has been shown to give an active dimeric system with bridging
EtSO2-moieties.5 PARA-(ZnEt)2 and META-(ZnEt)2 are active
without SO2 activation on account of their bimetallic nature. A
similar observation has been made for the bimetallic catalyst
2; in this case the ethylzinc species is even a better initiator
than the ethylsulfinate complex.10
PYR-(ZnO2SEt)2 crystallizes as a monomeric complex of
approximate (noncrystallographic) C2-symmetry (Figure 6). The
-
Zn atoms are bridged by the two EtSO2 ligands and show
The activity of META-(ZnEt)2 is substantially higher than
that of the corresponding PARA-(ZnEt)2 complex. This shows
the effect of the metal · · · metal distance on the transition states
and the importance of its modulation by ligand design. The
polymer obtained with PARA-(ZnEt)2 has a bimodal molecular
weight (MW) distribution with a rather high PDI of 3.28.
Polymerization with the META-(ZnEt)2 catalyst is much more
controlled, and polymer with a narrow MW distribution is
obtained (PDI ) 1.32). Whereas the META-(ZnEt)2 catalyst
showed high activity, no activity was found for catalyst PYR-
(ZnEt)2 (not even after prolonged reaction times, entry 3 in Table
1). As both catalysts are meta-bridged ꢀ-diketiminate ethylzinc
species, this striking difference should be explained by the
presence of the N heteroatom. Partial intramolecular coordina-
tion of the central nitrogen atom to both Zn atoms might reduce
their Lewis-acidity, thus inhibiting CHO coordination (the
resting state of the catalyst PYR-(ZnO2CR)2 should be structur-
ally similar to PYR-(ZnO2SEt)2, shown in Figure 6). Another
explanation might involve the conformation of the bimetallic
catalyst. N-Aryl-substituted ꢀ-diketiminate ligands typically
show structures in which the aryl plane and the N-C-C-C-N
plane are never coplanar on account of repulsion with the Me
substituent in the backbone. A pyridyl substituent, however,
allows this planar conformation, which might be even favored
on account of intramolecular C-H · · · N interactions (7).
distorted tetrahedral coordination. There is, however, indication
for an additional weak interaction between the pyridyl bridge
and the metal centers. In general, the NCCCN-plane of the
ꢀ-diketiminate unit is typically oriented perpendicular to the
plane of the bridging ring. In the current structure, however,
interplanar angles of 31.5(1)° and 40.1(1)° are observed. This
is likely due to attracting forces between the metal centers and
the pyridylene nitrogen atom. The ligand geometry also results
in repulsion between the Me substituent and the bridge and gives
rise to rather acute N-C-N angles (N2-C-N3 ) 112.4(1)°
and N3-C-N4 ) 111.2(1)°), further enforcing the interaction
between the Zn atoms and N3. The Zn · · · Zn separation of
3.7916(5) Å is considerably smaller than that in an EtSO2-
bridged dimeric Zn complex (4.98 Å).5 Likewise, this might
be explained by attracting forces between the pyridylene bridge
and both Zn atoms.
Polymerization Experiments. The alternating copolymeriza-
tions of CHO and CO2 have been performed under standard
conditions that are comparable to earlier work (polymerization
in neat CHO of 60 °C, metal/monomer ratio ) 1/1000, 10 bar
CO2 pressure).4b,10 A summary of the results for several catalysts
can be found in Table 1.
Use of the heteroleptic complex PARA-[CaN(SiMe3)2 · THF]2
as a potential catalyst in the CHO/CO2 copolymerization did
(17) Prust, J.; Stasch, A.; Zheng, W.; Roesky, H. W.; Alexopoulos, E.;
Uso´n, I.; Bo¨hler, D.; Schuchardt, T. Organometallics 2001, 20, 3825–3828.
(18) Chisholm, M. H.; Gallucci, J.; Phomphrai, K. Inorg. Chem. 2002,
41, 2785–2794.

6182 Organometallics, Vol. 27, No. 23, 2008
Piesik et al.
indeed gave a much higher polymer yield (entry 12) than the
maximum yields obtained in neat CHO. Under these diluted
conditions, the EtSO2-group is a better initiatior than the
(Me3Si)2N-group and conversion up to 87% could be achieved
(entry 13). Runs in which dilution of the reaction mixture was
achieved by a reduction of the Zn/CHO ratio (instead of by
addition of toluene) likewise gave improved absolute polymer
yields (entry 14; because relative yields are based on CHO, these
are lower). Extending the polymerization time under these
diluted conditions allowed access to high-MW polycarbonates
(>100 000) with a narrow MW distribution and essentially only
carbonate linkages (entry 15).
The results discussed above are a clear indication of bimetallic
action. To supply additional evidence for the observed synergetic
effects of two adjacent Zn centers, we ran polymerizations with
comparable monozinc complexes. Results obtained for polym-
erization with one of the best monometallic catalysts (5; entry
16) are comparable to those reported earlier.4b The yield of
polymer for catalyst 5 is slightly higher than that obtained with
the similar but bimetallic catalyst: META-[ZnN(SiMe3)2]2 (entry
5). It seems that under exactly comparable conditions (temper-
ature, pressure, reaction times, reactor, and stirring) a yield
slightly higher than the earlier observed 2.04 g limit can be
obtained. This might be due to a somewhat lower viscosity for
reaction mixtures with monometallic catalysts; bimetallic propa-
gating species have a higher average MW than monometallic
propagating species, even when the latter are in monomer-dimer
equilibrium. As is typical for the monometallic catalysts,
moderate dilution of the reaction mixture with toluene gave a
significant cut-back in the polymer yield (entry 17).
In fact, a similar conformation was found to be very stable
for a Zn complex with the earlier mentioned 2,6-pyridylene
bridged bis(salicylaldimide) ligand.15 A planar arrangement like
in 7 could inhibit the catalyst activity by separation of the metal
centers or by alteration of the electronic properties of the
ꢀ-diketiminate unit by the electron-withdrawing pyridyl bridge.
Because electron-withdrawing substituents generally increase
the activity,4 the latter seems less likely.
Although the ethylzinc functionality turned out to be an
efficient initiator in a bimetallic environment, increased polymer
yields could be obtained with (Me3Si)2N- as an initiating group
(entries 4-5 in Table 1). Under these circumstances the
polymerization with the PARA-bridged catalyst is also more
controlled (PDI ) 1.48). The same trends in activity are
observed: META-[ZnN(SiMe3)2]2 > PARA-[ZnN(SiMe3)2]2,
-
and PYR-[ZnN(SiMe3)2]2 is not active. Catalysts with EtSO2
as initiating group did not improve these results, and again PYR-
[ZnO2SEt]2 is not active (entries 6-7 in Table 1).
The effect of temperature was studied for the most active
catalyst META-[ZnN(SiMe3)2]2 (entries 8-10 in Table 1).
Lowering the temperature from 60 °C (standard conditions) to
40 °C and, finally, to 20 °C shows, not unexpectedly, gradual
lowering of isolated yields (and therefore reduced TON/TOF
values), shortening of polymer chains, and narrowing of the
MW distribution. The percentage of polycarbonate linkages
remains the same under all conditions. Increasing the polym-
erization temperature from 60 to 80 °C, however, does not result
in further increase of the yield. It should be mentioned that in
the later stage of these polymerization experiments, reaction
mixtures are highly viscous (nearly glassy), making magnetic
stirring impossible. Therefore, polymer yields might be con-
trolled by mass-transfer problems rather than by other factors.
The yield of 2.04 g, which has been obtained in three
independent polymerization runs (entries 5-6 and 10), might
be the maximum yield on account of high viscosity. Increasing
the polymerization time from 2 to 42 h (entry 11) indeed gave
a hardly improved yield (2.37 g). Interestingly, polymer obtained
after prolonged reaction times shows a much lower content of
carbonate linkages (indicative for CO2 transport problems) and
a broad MW-distribution with a shoulder in the low MW-range
(indicative of an inhomogeneous system). Viscosity as a limiting
factor for polymer yield has been discussed before.7-9It should
be noticed that such viscosity problems especially play a role
for bimetallic systems: the connection of catalytic centers also
connects two polymer chains essentially doubling the molecular
weight of the propagating species with respect to a mononuclear
catalyst.
Because the bridge in the bimetallic catalyst does not contain
bulky iPr substituents (which are known to improve catalyst
activity), the asymmetric catalyst 8 would be a better mono-
metallic model for META-[ZnN(SiMe3)2]2. This catalyst clearly
shows a much lower polymer yield (entry 18) in comparison to
the meta-bridged bimetallic system (entry 5). Therefore, con-
nection of two (ꢀ-diketiminate)ZnN(SiMe3)2 through a meta-
phenylene bridge improves the activity of the catalyst signifi-
cantly (even despite its more severe viscosity problems).
Conclusions
A series of dinucleating bis(ꢀ-diketiminate) ligands with rigid
bridges is easily accessible. Binuclear calcium amide reagents
could only be obtained with the para-phenylene bridge: PARA-
[CaN(SiMe3)2 · THF]2. Attempted isolation of similar calcium
amide reagents with meta-phenylene or 2,6-pyridylene bridges
gave exlusively the bimetallic homoleptic complexes (META-
Ca)2 and (PYR-Ca)x. However, for Zn the whole series of
bimetallic ethyl or amide complexes could be obtained and
ligand exchange processes are not an issue.
PARA-[CaN(SiMe3)2 · THF]2 is not active in the CHO/CO2
copolymerization; however, various zinc complexes were found
to be efficient catalysts. The activity is highly dependent on
the nature of the bridging unit. The meta-phenylene bridged
catalysts are superior to the para-phenylene bridged systems.
This noticeable difference is likely due to the differences in
Zn · · · Zn distances. Another explanation for the much better
activity of the meta-bridged catalyst might be the formation of
an advantageous reaction pocket (the structure shown in Figure
6 could be a model for the resting state). The 2,6-pyridylene
bridged catalyst showed essentially no activity. This might be
Viscosity problems can be avoided by dilution of the reaction
mixture. For monometallic zinc catalysts, dilution of the reaction
mixture with CHO monomer, that is, reduction of the catalyst
concentration, results in reduced polymer yields (likely on
account of steering the monomer-dimer equilibrium to the less
active monomeric species).9 Bimetallic systems do not suffer
from this problem and also show good conversion under diluted
conditions.7,11 Dilution of the reaction mixture with toluene
(19) Tang, Y.; Kassel, W. S.; Zakharov, L. N.; Rheingold, A. L.; Kemp,
R. A. Inorg. Chem. 2005, 44, 359–364.

Bimetallic Calcium and Zinc Complexes
Organometallics, Vol. 27, No. 23, 2008 6183
Figure 2. Crystal structure of PARA-[CaN(SiMe3)2 · THF]2 (viewed perpendicular on the vertically oriented C2-axis). For clarity, hydrogen
atoms have been omitted. Selected bond distances in Å: Ca-N1 2.368(2), Ca-N2 2.356(2), Ca-N3 2.300(2), Ca-O1 2.362(2), Ca · · · C25
3.315(4), and Ca · · · Ca′ 7.8409(8).
Figure 3. Crystal structure of PARA-[ZnN(SiMe3)2]2. For clarity, hydrogen atoms have been omitted. Selected bond distances in Å: Zn1-N1
1.947(2), Zn1-N2 1.952(2), Zn1-N5 1.882(2), Zn2-N3 1.945(2), Zn2-N4 1.949(2), Zn2-N6 1.887(2), and Zn1 · · · Zn2 8.173(2).
pylphenyl)amino-2-pentene-4-(phenyl)imine23 were prepared ac-
due to either additional coordination of the pyridyl base to the
cording to the literature. SO2 was dried by passing it through a
column of P4O10 and was condensed at -30 °C in a Schlenk tube.
Et3N was dried over CaH2. Cyclohexene oxide was vacuum-distilled
metal centers or a higher degree of conformational freedom on
account of changing a CH fragment for N. Differences in
electronic effects are also not ruled out.
1
over KH and stored in a glovebox prior to use. H and 13C NMR
Bimetallic action is an important aspect of these dinuclear
Zn catalysts. First of all, the ethylzinc systems PARA-(ZnEt)2
and META-(ZnEt)2 initiate CHO/CO2 copolymerization, whereas
monometallic ethylzinc catalysts are not reactive. Second, the
bimetallic zinc catalysts are also highly active under diluted
conditions, whereas monometallic systems show a drastic loss
of activity upon dilution. Finally, the bimetallic catalyst META-
[ZnN(SiMe3)2]2 shows a significantly higher activity than a
comparable monometallic model system (8).
spectra were recorded on a Bruker DPX300 spectrometer operating
at 300 and 75.5 MHz, respectively. Molecular weight distributions
of the polycarbonates were determined by GPC versus polystyrene
standards using chloroform as eluent at 25 °C. Crystals were
measured on a Siemens Smart diffractometer with APEXII area
detector system.
Synthesis of 2-Hydroxy-4-(2,6-diisopropylphenyl)imino-2-
Pentene. 2,6-Diisopropylaniline (40.0 g, 201 mmol), 2,4-pentanedi-
one (40.0 g, 400 mmol), and montmorillonite K10 (15 g) were
stirred at room temperature for 90 h. The suspension was diluted
with 100 mL of CH2Cl2, separated from the solid material, and
dried over MgSO4. After removing the excess of 2,4-pentanedione
under vacuum at 80 °C for several hours, a white solid was obtained
in quantitative yield.
Experimental Section
General Procedures. All experiments were carried out under
argon atmosphere using freshly dried solvents and standard Schlenk
line and glovebox techniques. The ligands PARA-H2, META-H2,
and PYR-H2 have been prepared via a procedure similar to that
for an earlier reported ethylene-bridged bis(ꢀ-diketiminate) ligand.20
[(Me3Si)2N]2Ca · (THF)2,21 [(Me3Si)2N]2Zn,22 and 2-(2,6-diisopro-
Anal. Calcd for C17H25NO (259.39): C, 78.72; H, 9.71. Found:
C, 78.58; H, 9.88. Mp: 49 °C. 1H NMR (300 MHz, CDCl3): δ
(22) Darensbourg, D. J.; Holtcamp, M. W.; Struck, G. E.; Zimmer, M. S.;
Niezgoda, S. A.; Rainey, P.; Robertson, J. B.; Draper, J. D.; Reibenspies,
J. H. J. Am. Chem. Soc. 1999, 121, 107.
(23) Yao, Y.; Xue, M.; Luo, Y.; Zhang, Z.; Jiao, R.; Zhang, Y.; Shen,
Q.; Wong, W.; Yu, K.; Sun, J. J. Organomet. Chem. 2003, 678, 108.
(20) Vitanova, D. V.; Hampel, F.; Hultzsch, K. C. Dalton Trans. 2005,
9, 1565.
(21) Westerhausen, M. Inorg. Chem. 1991, 30, 96.

6184 Organometallics, Vol. 27, No. 23, 2008
Piesik et al.
Figure 4. Crystal structure of META-[ZnN(SiMe3)2]2. For clarity, hydrogen atoms have been omitted. Selected bond distances in Å: Zn1-N1
1.950(5), Zn1-N2 1.964(5), Zn1-N5 1.898(4), Zn2-N3 1.949(5), Zn2-N4 1.946(5), Zn2-N6 1.878(4), and Zn1 · · · Zn2 6.098(2).
Figure 5. Crystal structure of PYR-(ZnEt)2. For clarity, hydrogen atoms have been omitted. Selected bond distances in Å: Zn1-N1 1.968(2),
Zn1-N2 1.974(2), Zn1-C40 1.955(3), Zn2-N3 1.962(2), Zn2-N4 1.969(2), Zn2-C42 1.961(3), and Zn1 · · · Zn2 6.4754(4).
(CH(CH3)2), 29.1 (CH3COH), 95.6 (CH3C(OH)CH), 123.5 (CHN-
aryl), 128.2 (CHN-aryl), 133.5 (Cq), 146.3 (Cq), 163.3 (Cq), 195.9
(CH3COH).
Synthesis of PARA-H2. Triethyloxonium tetrafluoroborate (18.2
g, 85.2 mmol) dissolved in 20 mL of dichloromethane was added
over a period of 25 min to a stirred solution of 2-hydroxy-4-(2,6-
diisopropylphenyl)imino-2-pentene (20.0 g, 77.1 mmol) in 100 mL
of dichloromethane under an argon atmosphere. The mixture was
stirred overnight. An equimolar portion of dry triethylamine (8.62
g, 85.2 mmol) was slowly added to the red-brown solution. After
being stirred for another 20 min, a suspension of p-phenylenedi-
amine (4.17 g, 38.6 mmol) in 16 mL of triethylamine was added
to the mixture. The mixture was stirred for 60 h at ambient
temperature. All volatiles were removed in vacuum, and the crude
product was washed with acetone to yield PARA-H2 as a yellow
powder: 12.4 g, 54%.
Figure 6. Crystal structure of PYR-(ZnO2SEt)2. For clarity,
hydrogen atoms have been omitted. Selected bond distances in Å:
Zn1-N1 1.998(2), Zn1-N2 1.966(3), Zn1-O1 1.936(2), Zn1-O4
1.986(2), Zn1 · · · N3 2.841(3), Zn2-N4 1.960(3), Zn2-N5 2.008(3),
Zn2-O2 1.971(2), Zn2-O3 1.945(2), Zn2 · · · N3 2.693(3), and
Zn1 · · · Zn2 3.7916(5).
Anal. Calcd for C40H54N4 (590.90): C, 81.31; H, 9.21. Found:
C, 81.30; H, 9.48. Mp: 237 °C. 1H NMR (300 MHz, C6D6): δ 1.14
3
3
(d, JH-H ) 6.8 Hz, 12H, CH(CH3)2), 1.18 (d, JH-H ) 6.9 Hz,
12H, CH(CH3)2), 1.73 (s, 6H, CH3CN), 1.83 (s, 6H, CH3CN), 3.18
(m, 4H, CH(CH3)2), 4.85 (s, 2H, CH3CNCH), 6.86 (s, 4H, CHN-
aryl), 7.15 (s, 6H, CHN-aryl), 13.2 (s, 2H, NH). 13C NMR (75 MHz,
C6D6): δ 21.0 (CH3CN), 21.5 (CH3CN), 23.2 (CH(CH3)2), 24.7
(CH(CH3)2), 29.1 (CH(CH3)2), 96.8 (CH3CNCH), 123.8 (CHN-aryl),
124.1 (CHN-aryl), 125.4 (CHN-aryl), 140.5 (Cq), 141.3 (Cq), 143.7 (Cq),
157.5 (Cq), 163.9 (Cq).
1.25 (d, 3JH-H ) 6.7 Hz, 6H, CH(CH3)2), 1.32 (d, 3JH-H ) 6.8 Hz,
6H, CH(CH3)2), 1.75 (s, 3H, CH3C(N)), 2.21 (s, 3H, CH3C(OH)),
3.14 (m, 2H, CH(CH3)2), 5.36 (s, 1H, CH3C(OH)CH), 7.26-7.42
(m, 3H, CHN-aryl), 12.2 (s, 1H, OH). 13C NMR (75 MHz, CDCl3):
δ 19.2 (CH3CN), 22.7 (CH(CH3)2), 24.6 (CH(CH3)2), 28.5
Synthesis of META-H2. This compound was synthesized
according to the same procedure as described for PARA-H2. It was

Bimetallic Calcium and Zinc Complexes
Organometallics, Vol. 27, No. 23, 2008 6185
Table 1. Summary of Results for the Cyclohexene Oxide/CO2 Copolymerizationa
entry
catalyst
t (h)
T (°C)
P (bar)
TONb
TOFc
isolated yield
Mn(× 10-3)/PDI
carbonate linkages (%)d
1
2
3
4
5
6
7
8
PARA-(ZnEt)2
META-(ZnEt)2
PYR-(ZnEt)2
2
2
17
2
2
2
2
2
2
2
42
5
5
2
6
2
2
2
60
60
60
60
60
60
60
20
40
80
60
60
60
60
60
60
60
60
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
72
257
36
129
0.41 g, 7.2%
1.50 g, 27%
14.2/3.28 bimodal
98.7/1.32
>99
98
PARA-[ZnN(SiMe3)2]2
META-[ZnN(SiMe3)2]2
META-(ZnO2SEt)2
PYR-(ZnO2SEt)2
META-[ZnN(SiMe3)2]2
META-[ZnN(SiMe3)2]2
META-[ZnN(SiMe3)2]2
META-[ZnN(SiMe3)2]2
META-[ZnN(SiMe3)2]
META-(ZnO2SEt)2
META-(ZnO2SEt)2
META-(ZnO2SEt)2
5
127
346
363
63
173
181
0.75 g, 13%
2.04 g, 36%
2.04 g, 36%
37.7/1.48
74.1/1.33
39.4/1.28
97
97
96
113
204
359
428
748
866
525
1196
416
202
239
57
102
179
10
150
173
262
199
208
101
120
0.65 g, 12%
1.16 g, 20%
2.04 g, 36%
2.37 g, 43%
4.25 g, 75%
4.95 g, 87%
3.00 g, 18%
6.94 g, 41%
2.34 g, 41%
1.14 g, 20%
1.35 g, 24%
28.2/1.19
56.3/1.25
75.0/1.42
88.6/4.23
97.7/1.39
89.6/1.56
45.7/1.28
110/1.33
86.7/1.23
54.8/1.24
74.5/1.37
98
99
98
9
10
11
12e
13e
14f
15f
16
17g
18
91
>99
>99
>99
>99
96
2
5
8
95
97
a Standard conditions: neat CHO (3.93 g, 40.0 mmol) with 20.0 µmol of a bimetallic catalyst or 40.0 µmol of a monometallic catalyst (metal/CHO )
1/1000). b The turnover number (TON) is defined as the average number of combined CHO/CO2 insertions per metal center. c The turnover frequency
(TOF) is defined here as TON/hour. d The percentage of carbonate linkages has been determined by NMR. e Reaction mixture diluted with toluene:
metal/CHO/toluene ) 1/1000/2000. f Metal/CHO ) 1/3000. g Reaction mixture diluted with toluene: metal/CHO/toluene ) 1/1000/1000.
purified by crystallization of the crude product, a white solid, from
ethanol at -28 °C: 10.1 g, 44%.
(CH(CH3)2), 28.8 (CH(CH3)2), 69.3 (THF), 96.8 (CH3CNCH), 124.6
(CHN-aryl), 125.0 (CHN-aryl), 125.3 (CHN-aryl), 141.8 (Cq), 147.0 (Cq),
163.8 (Cq), 166.6 (Cq).
Anal. Calcd for C40H54N4 (590.90): C, 81.31; H, 9.21. Found:
C, 81.26; H, 9.28. Mp: 139 °C. 1H NMR (300 MHz, C6D6): δ 1.11
Synthesis of (META-Ca)2. A solution of META-H2 (1.14 g,
1.93 mmol) and [(Me3Si)2N]2Ca · (THF)2 (974 mg, 1.93 mmol)
dissolved in 10 mL of benzene was heated overnight at 70 °C. A
slight precipitate formed that was removed by centrifugation. The
solvent was removed under vacuum, and the remaining yellow-
brown solid was crystallized from a hot hexane solution. Cooling
to 5 °C gave yellow crystals suitable for X-ray analysis: 1.62 g,
65%. Anal. Calcd for C80H104Ca2N8 (1257.93): C, 76.39; H, 8.33.
Found: C, 75.93; H, 8.18. Mp: 152 °C (dec). 1H NMR analysis of
the product dissolved in benzene showed over a large temperature
range extremely broad lines. Therefore, the composition of the
product was checked by hydrolysis of the complex in CD3OD,
which gave essentially the starting material (META-D2).
Synthesis of (PYR-Ca)x. PYR-H2 (867 mg, 1.47 mmol) and
[(Me3Si)2N]2Ca · (THF)2 (760 mg, 1.50 mmol) were dissolved in
10 mL of benzene. After 2 h at room temperature the reaction is
completed, and the solvent was removed in vacuum. Cooling a
concentrated hexane solution to -80 °C gave white crystals: 1.24 g,
67%. Anal. Calcd for C78H102Ca2N10 (1259.91): C, 74.36; H, 8.16.
Found: C, 74.13; H, 7.89. Mp: 116 °C (dec). Similar to that
described for (META-Ca)2, 1H NMR analysis of the product
dissolved in benzene showed over a large temperature range
extremely broad lines. Therefore, the composition of the product
was checked by hydrolysis of the complex in CD3OD, which gave
essentially the starting material (PYR-D2).
3
3
(d, JH-H ) 6.8 Hz, 12H, CH(CH3)2), 1.19 (d, JH-H ) 7.0 Hz,
12H, CH(CH3)2), 1.64 (s, 6H, CH3CN), 1.87 (s, 6H, CH3CN), 3.17
3
(m, 4H, CH(CH3)2), 4.84 (s, 2H, CH3CNCH), 6.68 (d, JH-H
)
2.0 Hz, 1H, CHN-aryl), 6.71 (d, 3JH-H ) 2.0 Hz, 1H, CHN-aryl), 6.78
3
(dd, 1H, CHN-aryl), 7.02 (t, JH-H ) 7.9 Hz, 1H, CHN-aryl), 7.15 (s,
6H, CHN-aryl), 13.1 (s, 2H, NH). 13C NMR (75 MHz, C6D6): δ 21.2
(CH3CN), 21.3 (CH3CN), 23.1 (CH(CH3)2), 24.7 (CH(CH3)2), 29.1
(CH(CH3)2), 97.1 (CH3CNCH), 116.8 (CHN-aryl), 117.8 (CHN-aryl),
123.8 (CHN-aryl), 125.7 (CHN-aryl), 130.0 (CHN-aryl), 141.7 (Cq), 143.0
(Cq), 146.4 (Cq), 157.9 (Cq), 163.2 (Cq).
Synthesis of PYR-H2. This compound was synthesized accord-
ing to the same procedure as described for PARA-H2. Crystallization
by cooling a hot, saturated ethanol solution to room temperature
gave the product as a yellow solid: 9.6 g, 42%.
Anal. Calcd for C39H53N5 (591.89): C, 79.14; H, 9.03. Found:
C, 79.48; H, 9.13. Mp: 163 °C. 1H NMR (300 MHz, C6D6): δ 1.25
3
3
(d, JH-H ) 6.8 Hz, 12H, CH(CH3)2), 1.26 (d, JH-H ) 6.9 Hz,
12H, CH(CH3)2), 1.68 (s, 6H, CH3CN), 2.40 (s, 6H, CH3CN), 3.12
(m, 4H, CH(CH3)2), 4.89 (s, 2H, CH3CNCH), 6.21 (d, JH-H
3
)
3
7.9 Hz, 2H, CHN-aryl), 6.92 (t, JH-H ) 7.9 Hz, 1H, CHN-aryl),
7.21-7.28 (m, 6H, CHN-aryl), 13.8 (s, 2H, NH). 13C NMR (75 MHz,
C6D6): δ 22.3 (CH3CN), 23.4 (CH(CH3)2), 24.8 (CH(CH3)2), 29.4
(CH(CH3)2), 100.5 (CH3CNCH), 107.0 (CHN-aryl), 124.0 (CHN-aryl),
124.9 (CHN-aryl), 139.0 (CHN-aryl), 139.9 (Cq), 146.4 (Cq), 152.3 (Cq),
154.9 (Cq), 167.4 (Cq).
Synthesis of PARA-(ZnEt)2. A suspension of PARA-H2 (1.57
g, 2.64 mmol) and diethyl zinc (1 M in hexane, 4.04 g, 5.56 mmol)
in 12 mL of benzene was stirred at ambient temperature for 22 h.
After removing the solvent under vacuum, pure PARA-(ZnEt)2 was
obtained in quantitative yield. Light colored yellow crystals suitable
for X-ray analysis could be obtained by slowly cooling a hot hexane
solution to -28 °C.
Synthesis of PARA-[CaN(SiMe3)2 · THF]2. A solution of PARA-
H2 (1.30 g, 2.20 mmol) and [(Me3Si)2N]2Ca · (THF)2 (4.21 g, 8.33
mmol) dissolved in 12 mL of benzene was heated for 7 h at 70 °C.
After evaporation of the solvent, the yellow-brown solid was washed
three times with hexane and dried in vacuum to give an essentially
pure crude product: 1.62 g, 65%. Colorless crystals suitable for
X-ray analysis could be obtained by cooling a concentrated benzene
solution to 7 °C.
Anal. Calcd for C44H62N4Zn2 (777.77): C, 67.94; H, 8.04. Found:
C, 68.11; H, 7.82. Mp: 180 °C. 1H NMR (300 MHz, C6D6): δ 0.38
Anal. Calcd for C60H104Ca2N6O2Si4 (1134.04): C, 63.55; H, 9.24.
Found: C, 63.03; H, 9.12. Mp: 108 °C (dec). 1H NMR (300 MHz,
C6D6): δ 0.23 (s, 36H, Si(CH3)3), 1.16 (m, 8H, THF), 1.20 (d, 3JH-H
3
3
(q, JH-H ) 8.3 Hz, 4H, CH2CH3), 1.07 (t, JH-H ) 8.1 Hz, 6H,
CH2CH3), 1.14 (d, 3JH-H ) 6.9 Hz, 12H, CH(CH3)2), 1.17 (d, 3JH-H
) 6.8 Hz, 12H, CH(CH3)2), 1.68 (s, 6H, CH3CN), 1.84 (s, 6H,
CH3CN), 3.14 (m, 4H, CH(CH3)2), 4.95 (s, 2H, CH3CNCH), 6.78
(s, 4H, CHN-aryl), 7.11 (s, 6H, CHN-aryl). 13C NMR (75 MHz, C6D6):
δ -1.87 (CH2CH3), 12.3 (CH2CH3), 23.3 (CH3CN), 23.4 (CH3CN),
23.5 (CH(CH3)2), 24.4 (CH(CH3)2), 28.4 (CH(CH3)2), 96.4
3
) 6.8 Hz, 12H, CH(CH3)2), 1.30 (d, JH-H ) 6.8 Hz, 12H,
CH(CH3)2), 1.77 (s, 6H, CH3CN), 1.96 (s, 6H, CH3CN), 3.20-3.28
(m, 12H, CH(CH3)2 + THF), 4.92 (s, 2H, CH3CNCH), 7.09-7.15
(m, 10H, CHN-aryl). 13C NMR (75 MHz, C6D6): δ 6.23 (Si(CH3)3),
24.1 (CH3CN), 24.6 (CH(CH3)2), 24.9 (CH3CN), 25.2 (THF), 25.4

6186 Organometallics, Vol. 27, No. 23, 2008
Piesik et al.
(CH3CNCH), 123.8 (CHN-aryl), 125.3 (CHN-aryl), 126.0 (CHN-aryl),
141.6 (Cq), 144.9 (Cq), 146.9 (Cq), 166.7 (Cq), 167.5 (Cq).
Synthesis of META-(ZnEt)2. This compound was prepared
according to the procedure described for PARA-(ZnEt)2 and could
be obtained in quantitative yield as a white powder.
124.3 (CHN-aryl), 126.5 (CHN-aryl), 128.9 (CHN-aryl), 142.3 (Cq), 144.3
(Cq), 149.6 (Cq), 167.8 (Cq), 169.6 (Cq).
Synthesis of PYR-[ZnN(SiMe3)2]2. A solution of PYR-H2 (835
mg, 1.41 mmol) and [(Me3Si)2N]2Zn (1.10 g, 2.85 mmol) in 10
mL of benzene was heated for 18 h at 70 °C. The solution was
concentrated to 3 mL and stored at 5 °C. After a few days PYR-
[ZnN(SiMe3)2]2 could be obtained as colorless needles: 710 mg,
49%.
Anal. Calcd for C44H62N4Zn2 (777.77): C, 67.94; H, 8.04. Found:
C, 67.61; H, 7.83. Mp: 183 °C. 1H NMR (300 MHz, C6D6): δ 0.37
3
3
(q, JH-H ) 8.1 Hz, 4H, CH2CH3), 1.04 (t, JH-H ) 8.1 Hz, 6H,
CH2CH3), 1.17 (d, 3JH-H ) 6.9 Hz, 12H, CH(CH3)2), 1.18 (d, 3JH-H
) 6.8 Hz, 12H, CH(CH3)2), 1.67 (s, 6H, CH3CN), 1.86 (s, 6H,
CH3CN), 3.15 (m, 4H, CH(CH3)2), 4.95 (s, 2H, CH3CNCH), 6.47
Anal. Calcd for C51H87N7Si4Zn2 (1041.41): C, 58.82; H, 8.42.
Found: C, 58.64; H, 8.37. Mp: 188 °C. 1H NMR (300 MHz, C6D6):
3
δ 0.01 (s, 36H, Si(CH3)3), 1.11 (d, JH-H ) 6.5 Hz, 12H,
3
3
(s, 1H, CHN-aryl), 6.65 (d, JH-H ) 7.8 Hz, 2H, CHN-aryl), 7.00 (t,
CH(CH3)2), 1.36 (d, JH-H ) 6.5 Hz, 12H, CH(CH3)2), 1.61 (s,
3JH-H ) 7.9 Hz, 1H, CHN-aryl), 7.10 (s, 6H, CHN-aryl). 13C NMR
(75 MHz, C6D6): δ -1.95 (CH2CH3), 12.4 (CH2CH3), 23.4
(CH3CN), 23.4 (CH3CN), 23.5 (CH(CH3)2), 24.4 (CH(CH3)2), 28.5
(CH(CH3)2), 96.4 (CH3CNCH), 121.0 (CHN-aryl), 121.5 (CHN-aryl),
123.9 (CHN-aryl), 126.1 (CHN-aryl), 129.5 (CHN-aryl), 141.7 (Cq), 145.0
(Cq), 151.4 (Cq), 166.4 (Cq), 167.6 (Cq).
6H, CH3CN), 2.18 (s, 6H, CH3CN), 3.20 (m, 4H, CH(CH3)2), 4.86
3
(s, 2H, CH3CNCH), 6.77 (d, JH-H ) 7.6 Hz, 2H, CHN-aryl), 7.13
(s, 6H, CHN-aryl), 7.23 (t, 3JH-H ) 7.6 Hz, 1H, CHN-aryl). 13C NMR
(75 MHz, C6D6): δ 5.26 (Si(CH3)3), 24.4 (CH(CH3)2), 24.7
(CH3CN), 25.0 (CH(CH3)2), 28.4 (CH(CH3)2), 97.4 (CH3CNCH),
116.3 (CHN-aryl), 124.3 (CHN-aryl), 126.6 (CHN-aryl), 138.6 (Cq), 142.1
(CHN-aryl), 144.1 (Cq), 159.9 (Cq), 166.7 (Cq), 170.7 (Cq).
Synthesis of META-(ZnO2SEt)2. An excess of SO2 was
condensed to a precooled (-25 °C) yellow solution of META-
(ZnEt)2 (938 mg, 1.21 mmol) in 15 mL of toluene. The yellow
solution immediately turned deep-red and was stirred for ap-
proximately 30 min at this temperature. The cooling bath was
removed, and the solution was slowly warmed to room temperature.
After removal of SO2 the solution turned yellow again. Solvents
were removed under high vacuum. The raw product was washed
three times with 10 mL portions of hexane to yield a white
precipitate: 823 mg, 75%.
Synthesis of PYR-(ZnEt)2. This compound was prepared
according to the procedure described for PARA-(ZnEt)2. The
reaction times could be reduced to 1 h, and the product was obtained
in quantitative yield. Colorless crystals suitable for X-ray analysis
could be obtained by slowly cooling a hot hexane solution to room
temperature.
Anal. Calcd for C43H61N5Zn2 (778.75): C, 66.32; H, 7.90. Found:
C, 66.68; H, 8.24. Mp: 175 °C. 1H NMR (300 MHz, C6D6): δ 0.44
3
(q, JH-H ) 8.1 Hz, 4H, CH2CH3), 1.04-1.14 (m, 30H, CH2CH3
+ CH(CH3)2), 1.64 (s, 6H, CH3CN), 2.05 (s, 6H, CH3CN), 3.05
3
(m, 4H, CH(CH3)2), 4.96 (s, 2H, CH3CNCH), 6.52 (d, JH-H
)
7.7 Hz, 2H, CHN-aryl), 7.08-7.15 (m, 7H, CHN-aryl). 13C NMR (75
MHz, C6D6): δ -1.46 (CH2CH3), 12.4 (CH2CH3), 23.4 (CH3CN),
23.5 (CH(CH3)2), 23.9 (CH3CN), 24.2 (CH(CH3)2), 28.4
(CH(CH3)2), 97.5 (CH3CNCH), 114.5 (CHN-aryl), 123.9 (CHN-aryl),
126.1 (CHN-aryl), 139.0 (Cq), 141.5 (CHN-aryl), 144.8 (Cq), 161.6 (Cq),
165.7 (Cq), 168.6 (Cq).
Anal. Calcd for C44H62N4O4S2Zn2 (905.89): C, 58.34; H, 6.90.
Found: C, 57.98; H, 6.98. Mp: 258 °C (dec). 1H NMR (300 MHz,
3
THF-d8): δ 0.40-0.85 (m, 6H, CH2CH3), 1.10 (d, JH-H ) 6.9
3
Hz, 12H, CH(CH3)2), 1.24 (d, JH-H ) 6.7 Hz, 12H, CH(CH3)2),
1.63 (s, 6H, CH3CN), 2.00-2.15 (m, 4H, CH2CH3), 2.26 (s, 6H,
CH3CN), 3.13 (m, 4H, CH(CH3)2), 4.82 (s, 2H, CH3CNCH), 6.65
3
Synthesis of PARA-[ZnN(SiMe3)2]2. A solution of PARA-H2
(1.08 g, 1.83 mmol) and [(Me3Si)2N]2Zn (1.46 g, 3.78 mmol) in
10 mL of benzene was heated for 8 h at 70 °C. The solution was
concentrated to 3.5 mL, warmed to 70 °C, and slowly cooled to
room temperature. The product crystallized in the form of light
yellow large crystals: 1.08 g, 57%.
(d, JH-H ) 7.7 Hz, 2H, CHN-aryl), 7.05-7.14 (m, 7H, CHN-aryl),
7.63 (s, 1H, CHN-aryl). 13C NMR (75 MHz, THF-d8): δ 5.48
(CH2CH3), 23.7 (CH3CN), 24.7 (CH3CN), 25.1 (CH(CH3)2), 25.4
(CH(CH3)2), 28.8 (CH(CH3)2), 54.0 (CH2CH3), 97.1 (CH3CNCH),
119.5 (CHN-aryl), 121.8 (CHN-aryl), 124.7 (CHN-aryl), 126.6 (CHN-aryl),
130.0 (CHN-aryl), 143.8 (Cq), 145.4 (Cq), 149.9 (Cq), 166.2 (Cq),
170.1 (Cq).
Anal. Calcd for C52H88N6Si4Zn2 (1040.42): C, 60.03; H, 8.52.
Found: C, 59.88; H, 8.54. Mp: 253 °C. 1H NMR (300 MHz, C6D6):
Synthesis of PYR-(ZnO2SEt)2. This compound was synthesized
according to the procedure described for the preparation of META-
(ZnO2SEt)2. After evaporation of all volatiles, the product was
extracted twice with 6 mL of benzene: 538 mg, 49%. Yellow
crystals suitable for X-ray analysis could be obtained by slowly
cooling a hot hexane/THF (8:1) solution to -28 °C.
3
δ 0.01 (s, 36H, Si(CH3)3), 1.12 (d, JH-H ) 6.8 Hz, 12H,
3
CH(CH3)2), 1.37 (d, JH-H ) 6.8 Hz, 12H, CH(CH3)2), 1.66 (s,
6H, CH3CN), 1.93 (s, 6H, CH3CN), 3.26 (m, 4H, CH(CH3)2), 4.87
(s, 2H, CH3CNCH), 6.95 (s, 4H, CHN-aryl), 7.14 (s, 6H, CHN-aryl).
13C NMR (75 MHz, C6D6): δ 5.13 (Si(CH3)3), 24.0 (CH3CN), 24.0
(CH3CN), 24.2 (CH(CH3)2), 24.7 (CH(CH3)2), 28.2 (CH(CH3)2),
96.2 (CH3CNCH), 124.1 (CHN-aryl), 126.0 (CHN-aryl), 126.1 (CHN-
aryl), 142.0 (Cq), 144.0 (Cq), 145.7 (Cq), 168.3 (Cq), 169.4 (Cq).
Synthesis of META-[ZnN(SiMe3)2]2. A solution of META-H2
(918 mg, 1.55 mmol) and [(Me3Si)2N]2Zn (1.26 g, 3.26 mmol) in
10 mL of benzene was heated overnight at 70 °C. The solution
was concentrated to 3.5 mL, warmed to 70 °C, and slowly cooled
to room temperature. After a few minutes META-[ZnN(SiMe3)2]2
crystallized as colorless crystals: 823 mg, 51%.
Anal. Calcd for C43H61N5O4S2Zn2 (906.88): C, 56.95; H, 6.78.
Found: C, 56.81; H, 6.53. Mp: 235 °C (dec). 1H NMR (300 MHz,
3
C6D6): δ 0.59 (m, 6H, CH2CH3), 1.14 (d, JH-H ) 6.8 Hz, 12H,
3
CH(CH3)2), 1.32 (d, JH-H ) 6.5 Hz, 12H, CH(CH3)2), 1.68 (s,
6H, CH3CN), 2.00 (s, 6H, CH3CN), 2.24 (m, 4H, CH2CH3), 3.44
3
(m, 4H, CH(CH3)2), 4.74 (s, 2H, CH3CNCH), 6.18 (d, JH-H
)
7.8 Hz, 2H, CHN-aryl), 6.93 (t, 3JH-H ) 7.6 Hz, 1H, CHN-aryl), 7.08
(s, 6H, CHN-aryl). 13C NMR (75 MHz, C6D6): δ 6.45 (CH2CH3),
24.4 (CH3CN), 24.5 (CH(CH3)2), 25.3 (CH(CH3)2), 25.5 (CH3CN),
28.6 (CH(CH3)2), 53.6 (CH2CH3), 99.0 (CH3CNCH), 111.1 (CHN-
aryl), 124.4 (CHN-aryl), 126.3 (CHN-aryl), 138.3 (Cq), 142.8 (CHN-aryl),
144.9 (Cq), 160.1 (Cq), 163.5 (Cq), 171.0 (Cq).
Anal. Calcd for C52H88N6Si4Zn2 (1040.42): C, 60.03; H, 8.52.
Found: C, 60.24; H, 8.75. Mp: 229 °C. 1H NMR (300 MHz, C6D6):
3
δ 0.00 (s, 36H, Si(CH3)3), 1.14 (d, JH-H ) 6.8 Hz, 12H,
3
Synthesis of 8. A solution of 2-(2,6-diisopropylphenyl)amino-
2-pentene-4-(phenyl)imine (512 mg, 1.53 mmol) and
[(Me3Si)2N]2Zn (592 mg, 1.53 mmol) in 7 mL of benzene was
heated for 18 h at 70 °C. The solvent was evaporated in vacuum,
and the crude product was washed with two 5 mL portions of
hexane to obtain 8 as a white solid: 663 mg, 82%.
CH(CH3)2), 1.38 (d, JH-H ) 6.8 Hz, 12H, CH(CH3)2), 1.61 (s,
6H, CH3CN), 2.04 (s, 6H, CH3CN), 3.24 (m, 4H, CH(CH3)2), 4.84
(s, 2H, CH3CNCH), 6.78-6.85 (m, 3H, CHN-aryl), 7.10-7.14 (m,
6H, CHN-aryl). 13C NMR (75 MHz, C6D6): δ 5.30 (Si(CH3)3), 24.2
(CH3CN), 24.3 (CH3CN), 24.4 (CH(CH3)2), 25.0 (CH(CH3)2), 28.5
(CH(CH3)2), 96.6 (CH3CNCH), 122.3 (CHN-aryl), 123.8 (CHN-aryl),

Bimetallic Calcium and Zinc Complexes
Organometallics, Vol. 27, No. 23, 2008 6187
Anal. Calcd for C29H47N3Si2Zn (559.27): C, 62.28; H, 8.47.
hydrogen atoms of the Me3Si groups and the THF ligand have been
placed on calculated positions and were refined in a riding mode.
Crystal Data for PARA-[ZnN(SiMe3)2]2. Measurement at -70
°C, MoKR, θmax ) 27.6°, 88 638 reflections measured, 15 599
independent reflections (Rint ) 0.079), 10 876 reflections observed
with I > 2σ(I), monoclinic, space group P21/n, a ) 18.469(4), b
) 21.213(4), c ) 19.522(4), ꢀ ) 117.927(10), V ) 6758(2) Å3,
formula C52H88N6Si4Zn2 · (C6H6)2, Z ) 4, R ) 0.0397, wR2 )
0.1038, GOF ) 0.99, Fmax ) 0.43 e Å-3, Fmin ) -0.33 e Å-3. All
hydrogen atoms have been placed on calculated positions and were
refined in a riding mode. One of the cocrystallized benzene
molecules is perfectly ordered, the other was disordered and was
treated with the SQUEEZE procedure incorporated in the program
PLATON.25
Crystal Data for META-[ZnN(SiMe3)2]2. Measurement at -80
°C, MoKR, θmax ) 28.4°, 136 020 reflections measured, 17 484
independent reflections (Rint ) 0.114), 9114 reflections observed
with I > 2σ(I), monoclinic, space group P21/n, a ) 10.9191(8), b
) 35.169(3), c ) 18.4217(14), ꢀ ) 95.451(5), V ) 7042.2(10)
Å3, formula C52H88N6Si4Zn2 · (C6H6)2, Z ) 4, R ) 0.0708, wR2 )
0.2374, GOF ) 1.08, Fmax ) 0.72 e Å-3, Fmin ) -0.82 e Å-3. All
hydrogen atoms have been placed on calculated positions and were
refined in a riding mode. Both cocrystallized benzene molecules
were fully disordered and were treated with the SQUEEZE
procedure incorporated in the program PLATON.25
Found: C, 62.65; H, 8.76. Mp: 142 °C. 1H NMR (300 MHz, C6D6):
3
δ -0.01 (s, 18H, Si(CH3)3), 1.12 (d, JH-H ) 6.7 Hz, 6H,
CH(CH3)2), 1.35 (d, 3JH-H ) 6.8 Hz, 6H, CH(CH3)2), 1.64 (s, 3H,
CH3CN), 1.71 (s, 3H, CH3CN), 3.24 (m, 2H, CH(CH3)2), 4.83 (s,
2H, CH3CNCH), 6.94-6.99 (m, 3H, CHN-aryl), 7.12-7.14 (m, 5H,
CHN-aryl). 13C NMR (75 MHz, C6D6): δ 5.78 (Si(CH3)3), 23.4
(CH3CN), 24.9 (CH3CN), 25.0 (CH(CH3)2), 25.5 (CH(CH3)2), 29.0
(CH(CH3)2), 96.9 (CH3CNCH), 125.1 (CHN-aryl), 125.7 (CHN-aryl),
126.6 (CHN-aryl), 127.1 (CHN-aryl), 129.8 (CHN-aryl), 142.8 (Cq), 144.8
(Cq), 149.4 (Cq), 168.6 (Cq), 170.2 (Cq).
Crystal Structure Determination. Structures have been solved
and refined using the programs SHELXS-97 and SHELXL-97,
respectively.24 All geometry calculations and graphics have been
performed with PLATON.25 Crystallographic data (excluding
structure factors) have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication No. CCDC
692794-692799. Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK
(fax: (+44)1223-336-033; E-mail: deposit@ccdc.cam.ac.uk).
General Procedure for the Cyclohexene Oxide/CO2
Copolymerization. A 20.0 µmol portion of a bimetallic catalyst
(or 40.0 µmol of a monometallic catalyst) was dissolved in 3.93 g
(40.0 mmol) of cyclohexene oxide in a glovebox. This solution
was injected into a preheated reactor (60 °C) that was immediately
pressurized with CO2 (10 bar). After the mixture was stirred at the
desired temperature, pressure, and time, the mixture was cooled to
ambient temperature and the CO2 pressure was slowly released.
The normally very viscous mixture was diluted with 100 mL of
CH2Cl2. After the solution was concentrated, the polymer was
precipitated by adding 100 mL of methanol, filtered off, and dried
under vacuum for 5 h at 100 °C. The obtained polymer was
Crystal Data for PYR-(ZnEt)2. Measurement at -70 °C, MoKR
,
θmax ) 27.1°, 80 788 reflections measured, 9230 independent
reflections (Rint ) 0.047), 7312 reflections observed with I > 2σ(I),
triclinic, space group P-1, a ) 11.6831(4), b ) 14.2544(5), c )
14.5619(5), R ) 67.162(2), ꢀ ) 79.572(2), γ ) 70.257(2), V )
2100.10(13) Å3, formula C43H61N5Zn2, Z ) 2, R ) 0.0333, wR2
) 0.0878, GOF ) 1.07, Fmax ) 0.59 e Å-3, Fmin ) -0.64 e Å-3
.
1
analyzed via H NMR.
All hydrogen atoms have been placed on calculated positions and
were refined in a riding mode.
Crystal Data for (META-Ca)2. Measurement at -70 °C, MoKR
,
θmax ) 24.4°, 41 637 reflections measured, 6380 independent
reflections (Rint ) 0.157), 3787 reflections observed with I > 2σ(I),
monoclinic, space group C2/c, a ) 30.800(4), b ) 16.172(2), c )
16.660(2), ꢀ ) 107.606(8), V ) 7909.6(17) Å3, formula
C80H104Ca2N8 · C6H6, Z ) 4, R ) 0.0872, wR2 ) 0.2436, GOF )
1.04, Fmax ) 0.74 e Å-3, Fmin ) -0.60 e Å-3. All hydrogen atoms
have been placed on calculated positions and were refined in a riding
mode. The somewhat poor crystal quality is due to the small size
of the crystal (0.3 × 0.1 × 0.05 mm3) and twinning problems (a
penetrating second crystal lattice has been separated from the main
crystal lattice).
Crystal Data for PYR-(ZnO2SEt)2. Measurement at -70 °C,
MoKR, θmax ) 25.7°, 89 534 reflections measured, 8731 independent
reflections (Rint ) 0.096), 6174 reflections observed with I > 2σ(I),
monoclinic, space group P21/n, a ) 11.2229(3), b ) 28.1674(8), c
) 15.3663(2), ꢀ ) 108.547(2), V ) 4605.3(2) Å3, formula
C43H61N5O4S2Zn2, Z ) 4, R ) 0.0439, wR2 ) 0.1091, GOF )
1.05, Fmax ) 0.63 e Å-3, Fmin ) -0.68 e Å-3. All hydrogen atoms
have been placed on calculated positions and were refined in a riding
mode. One of the EtSO2-ligands is disordered over two positions
in a 90/10 ratio. Figure 6 shows the position with highest
occupation.
Crystal Data for PARA-[CaN(SiMe3)2 · THF]2. Measurement
at -70 °C, MoKR, θmax ) 25.4°, 49 558 reflections measured, 6281
independent reflections (Rint ) 0.075), 4038 reflections observed
with I > 2σ(I), orthorhombic, space group Pccn, a ) 34.0276(9),
b ) 10.3059(3), c ) 19.5596(5), V ) 6859.3(3) Å3, formula
C60H104Ca2N6O2Si4, Z ) 4, R ) 0.0495, wR2 ) 0.1470, GOF )
1.03, Fmax ) 0.25 e Å-3, Fmin ) -0.34 e Å-3. Most hydrogen
atoms have been observed and were refined isotropically. The
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft for financial support of this work
(AM2-net). Professor Dr. R. Boese and D. Bla¨ser (Universita¨t
Duisburg-Essen) are thanked for collection of the X-ray
diffraction data, and D. Jacobi (Universita¨t Duisburg-Essen)
is thanked for the GPC analyses.
Supporting Information Available: The cif files and ORTEP
plots for all crystal structures are available as Supporting Informa-
tion. This material is available free of charge via the Internet at
http://pubs.acs.org.
(24) (a) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure
Solution; Universita¨t Go¨ttingen: Germany, 1997; (b) Sheldrick, G. M.
SHELXL-97, Program for Crystal Structure Refinement; Universita¨t Go¨t-
tingen: Germany, 1997;.
(25) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 2000.
OM800597F