Novel ruthenium(II) N-heterocyclic carbene complexes as catalyst precursors for the Ring-Opening Metathesis Polymerization (ROMP) of enantiomerically pure monomers: X-ray structures, reactivity, and quantum chemical considerations

Article abstract of DOI:10.1002/ejic.200700041

Four chiral, enantiomerically pure monomers, exo,exo-N,N-(norborn-5-ene-2, 3-dicarbimido)-L-valine ethyl ester (exo-1), endo,endo-N,N-(norborn-5-ene-2,3- dicarbimido)-L-valine ethyl ester (endo-1), exo,exo-N,N-(norborn-5-ene-2,3- dicarbimido)-L-valine-ferr-butylamide (exo-2), and endo,endo-N,N-(norborn-5-ene- 2,3-dicarbimido)-L-valine-tert-butylamide (endo-2), were subjected to ring-opening metathesis polymerization (ROMP) with Ru(CF₃CO ₂)₂(IMesH₂)(p-cymene) (3), Ru(CF ₃CO₂)₂(IMes)(p-cymene) (4), RuCl ₂(IMes)-(p-cymene) (5), Ru(PCy₃)(CF₃CO ₂)₂(p-cymene) (6), Ru(CF₃CO₂) ₂(p-cymene)·CF₃COOAgPCy₃(6a),Ru(CF ₃CO₂)₂-(PPh₃)(p-cymene) (7), Ru(CF₃CO₂)₂(IMes)(PhNC)₃ (8), and Ru(CF₃CO₂)₂(IMesH₂)(PhNC) ₃ (9) (IMes = 1,3-dimesitylimidazol-2-ylidene, IMesH₂ = 1,4-dimesityl-4,5-diyhdroimidazolin-2-ylidene, PCy₃ = tricyclohexylphosphane). X-ray structures of precatalysts 3 and 6-9 are presented. Compounds 3 and 4 displayed significant ROMP activity, allowing for the controlled, yet nonliving synthesis of the corresponding polymers with polydispersity indices (PDIs) in the range of 1.17-2.14. In all cases the exo isomers of compounds 1 and 2 were polymerized by preference. While poly(endo-1) was formed in an all-trans form, poly(exo-1) and poly(exo-2) were produced in their cis/trans forms with a cis content of around 40%. Calculations carried out at the B3LYP/LACVP* level suggest two possible mechanisms for the increased reactivity of the 2,3-R₂-exo,exo isomers of norborn-5-ene-2,3-dicarbimido derivatives resulting in the formation of the ROMP-active Ru^IV alkylidene. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700041

FULL PAPER
DOI: 10.1002/ejic.200700041
Novel Ruthenium(II) N-Heterocyclic Carbene Complexes as Catalyst
Precursors for the Ring-Opening Metathesis Polymerization (ROMP) of
Enantiomerically Pure Monomers: X-ray Structures, Reactivity, and Quantum
Chemical Considerations
Michael R. Buchmeiser,*[a,b] Dongren Wang,[a] Yan Zhang,[a] Sergej Naumov,[a] and
Klaus Wurst[c]
Keywords: Carbene ligands / Ruthenium / ROMP / Quantum chemistry
Four chiral, enantiomerically pure monomers, exo,exo-N,N-
(norborn-5-ene-2,3-dicarbimido)- -valine ethyl ester (exo-1),
endo,endo-N,N-(norborn-5-ene-2,3-dicarbimido)- -valine
ethyl ester (endo-1), exo,exo-N,N-(norborn-5-ene-2,3-dicarb-
imido)- -valine-tert-butylamide (exo-2), and endo,endo-
N,N-(norborn-5-ene-2,3-dicarbimido)- -valine-tert-butyl-
amide (endo-2), were subjected to ring-opening metathesis
polymerization (ROMP) with Ru(CF3CO2)2(IMesH2)(p-cy-
mene) (3), Ru(CF3CO2)2(IMes)(p-cymene) (4), RuCl2(IMes)-
(p-cymene) (5), Ru(PCy3 )(CF3CO2 )2 (p-cymene) (6),
Ru(CF3CO2)2(p-cymene)·CF3COOAgPCy3(6a),Ru(CF3CO2)2-
(PPh3)(p-cymene) (7), Ru(CF3CO2)2(IMes)(PhNC)3 (8), and
Ru(CF3CO2)2(IMesH2)(PhNC)3 (9) (IMes = 1,3-dimesitylimid-
azol-2-ylidene, IMesH2 = 1,4-dimesityl-4,5-diyhdroimidazol-
in-2-ylidene, PCy3 = tricyclohexylphosphane). X-ray struc-
tures of precatalysts 3 and 6–9 are presented. Compounds 3
and 4 displayed significant ROMP activity, allowing for the
controlled, yet nonliving synthesis of the corresponding poly-
mers with polydispersity indices (PDIs) in the range of 1.17–
2.14. In all cases the exo isomers of compounds 1 and 2 were
polymerized by preference. While poly(endo-1) was formed
in an all-trans form, poly(exo-1) and poly(exo-2) were pro-
duced in their cis/trans forms with a cis content of around
40%. Calculations carried out at the B3LYP/LACVP* level
suggest two possible mechanisms for the increased reactivity
of the 2,3-R2-exo,exo isomers of norborn-5-ene-2,3-dicarb-
imido derivatives resulting in the formation of the ROMP-
active RuIV alkylidene.
L
L
L
L
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
(arene)H[P–O] complexes.[4] Noels et al. showed that com-
plexes of the general formula RuCl2(PCy3)(arene) can be
activated by treatment with diazo compounds to form
ROMP-active Grubbs-type catalysts.[5] RuCl2(IMes)(p-cy-
mene) (5) (IMes = 1,3-dimesitylimidazol-2-ylidene) was
first reported by Nolan et al., who showed that this com-
plex was capable of performing ring-closing metathesis
(RCM) reactions.[6] Later, Dixneuf et al. reported on the in
situ formation of 5 and RuCl2(IMesH2)(p-cymene) (IMesH2
= 1,4-dimesityl-4,5-diyhdroimidazolin-2-ylidene) and their
use in RCM, enyne metathesis reactions,[7–10] and later in
ROMP.[11] Noels et al. suggested the use of 5, RuCl2-
(IMesH2)(p-cymene), and derivatives thereof as photoinitia-
tors that can be activated by visible light.[12,13] However, in
view of their inherent activity even in the absence of light,[14]
they appear less suitable for these applications. As a matter
of fact, calculations at the B3LYP/LACVP* level indicate a
dissociation energy Ediss of only 8.7 kcal/mol for the dissoci-
ation of the p-cymene ligand in RuCl2(IMesH2)(p-cymene).
In an ongoing project we are interested in the synthesis
of novel latent metathesis catalysts[15,16] that may be con-
verted into the active species in the presence of a monomer
either thermally or by the action of (UV) light.[14] Key
properties of such compounds are high thermal stability of
Introduction
The first reports on the activity of ruthenium(II) com-
plexes in ring-opening metathesis polymerization (ROMP)
were published some 15 years ago[1] and may certainly be
regarded as the basis for the development of well-defined
ruthenium(IV)–alkylidene complexes.[1,2] In 1997, Hafner et
al. reported on the photo- and thermal activation of RuII
and OsII arene complexes of the general formula
MCl2(PR3)(p-cymene) (M = Ru, Os) in the polymerization
of norborn-2-ene.[3] Thermal initiation of the ROMP of
norborn-2-ene was also observed by Lindner et al. for Ru-
[a] Leibniz-Institut für Oberflächenmodifizierung e.V. (IOM),
Permoserstr. 15, 04318 Leipzig, Germany
Fax: +49-341-235-2584
E-mail: michael.buchmeiser@iom-leipzig.de
dongren.wang@iom-leipzig.de
chem_yzhang@yahoo.com
sergej.naumov@iom-leipzig.de
[b] Institut für Technische Chemie, Universität Leipzig,
Linnéstr. 3, 04103 Leipzig, Germany
[c] Institut für Allgemeine, Anorganische und Theoretische
Chemie, Leopold-Franzens-Universität Innsbruck,
Innrain 52 a, 6020 Innsbruck, Austria
E-mail: klaus.wurst@uibk.ac.at
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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Catalyst Precursors for the ROMP of Enantiomerically Pure Monomers
FULL PAPER
the precatalyst at least up to 45 °C and prolonged stor- level and propose a model that explains the superior reac-
ability of ready-to-use monomer–precatalyst mixtures up to tivity of exo isomers compared to their endo analogues in
this temperature. Vice versa, either by the action of UV ROMP.
light or by thermal treatment, the precatalyst should, to-
gether with the monomer, form the active species to initiate
ROMP. Despite selected reports on such systems,[3,17–20]
these suffer from drawbacks such as thermal or visible light
activation and significant metathesis activity at room tem-
perature and below. In view of the pronounced changes in
Results and Discussion
Synthesis of Monomers and Catalyst Precursors
The synthesis of the endo monomers endo-1 and endo-
reactivity observed for bis(trifluoroacetate)-derived Grubbs 2,[28] the CF3COO-derived precatalysts 3, 4, 8, and 9,[14] as
and Grubbs–Hoveyda systems,[21–27] we were interested to well as of precatalyst 5,[6] is described elsewhere. Monomer
what extent the replacement of the chlorine groups by tri- exo-1 was prepared by esterification of exo,exo-(norborn-5-
fluoroacetate groups would have influence on the ROMP ene-2,3-dicarbimido)--valine with ethanol. Monomer exo-
activity of the resulting precatalysts. Instead of using nor- 2 was synthesized by reaction of -valine-exo,exo-N,N-(nor-
born-2-ene, which is polymerized to some extent by vir- born-2-ene-5,6-dicarbimide) with dicyclohexyldicarbodi-
tually any metathesis catalyst, we focused on more complex imide (DCC) followed by the reaction of tert-butylamine.
molecules. On the basis of previous reports on the superior- All structures are shown in Figure 1. In addition to the data
ity of exo isomers in ROMP,[1] we prepared enantiomer- already reported, the X-ray structures of compounds 3, 6a,
ically pure exo and endo isomers of two monomers, exo,exo- 7, 8, and 9 are presented here. Thus, compound 3 crys-
¯
N,N-(norborn-5-ene-2,3-dicarbimido)--valine ethyl ester tallizes in the triclinic space group P1 with
a =
(exo-1), endo,endo-N,N-(norborn-5-ene-2,3-dicarbimido)-- 11.3770(4) Å, b = 12.1632(5) Å, c = 14.5978(6) Å, α =
valine ethyl ester (endo-1), exo,exo-N,N-(norborn-5-ene-2,3- 104.636(2)°, β = 96.217(2)°, γ = 113.276(2)°, Z = 2. The
dicarbimido)--valine-tert-butylamide (exo-2), endo,endo- distance Ru(1)–C(11) is 2.109(2) Å; the complex exists in a
N,N-(norborn-5-ene-2,3-dicarbimido)--valine-tert-butyl- distorted octahedral form (Figure 2).
amide (endo-2) and investigated their polymerization using
Precatalyst 6 was prepared from [RuCl2(p-cymene)]2 by
Ru(CF3CO2)2(IMesH2)(p-cymene) (3), Ru(CF3CO2)2- reaction with 2 equiv. of PCy3 followed by reaction with
(IMes)(p-cymene) (4), RuCl2(IMes)(p-cymene) (5), Ru- 2 equiv. of CF3COOAg. The compound crystallizes as the
¯
(PCy3)(CF3CO2)2(p-cymene) (6), Ru(CF3CO2)2(p-cymene)· CF3COOAg·PCy3 adduct 6a in the triclinic space group P1
CF3COOAgPCy3 (6a), Ru(CF3CO2)2(PPh3)(p-cymene) (7), with a = 10.2007(4) Å, b = 13.8886(4) Å, c = 14.9130(6) Å,
Ru(CF3CO2)2(IMes)(PhNC)3 (8), and Ru(CF3CO2)2- α = 107.497(2)°, β = 94.569(2)°, γ = 95.552(2)°, Z = 2. The
(IMesH2)(PhNC)3 (9) (IMes = 1,3-dimesitylimidazol-2- complex again exists with a distorted octahedral coordina-
ylidene, IMesH2 = 1,3-dimesityl-4,5-diyhdroimidazolin-2- tion for the Ru and a distorted tetrahedral coordination for
ylidene, PCy3 = tricyclohexylphosphane). In addition, the the Ag center (Figure 3).
structure of the final polymers was investigated. Finally, we
In a similar manner, precatalyst 7 was prepared from
performed theoretical calculations at the B3LYP/LACVP* [RuCl2(p-cymene)]2 by reaction with 2 equiv. of PPh3 fol-
Figure 1. Monomers exo-1, endo-1, exo-2, endo-2, and precatalysts 3–10 used.
Eur. J. Inorg. Chem. 2007, 3988–4000
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FULL PAPER
Figure 4. X-ray structure of 7. Selected bond lengths [Å] and angles
[°]: Ru(1)–O(3) 2.093(2), Ru(1)–O(1) 2.107(2), Ru(1)–C(6) 2.169(2),
Ru(1)–C(5) 2.179(2), Ru(1)–C(3) 2.189(2), Ru(1)–C(2) 2.230(3),
Ru(1)–C(4) 2.240(2), Ru(1)–C(1) 2.265(3), Ru(1)–P(1) 2.3654(7);
O(3)–Ru(1)–O(1) 78.89(7), O(3)–Ru(1)–P(1) 89.59(5), O(1)–Ru(1)–
P(1) 79.71(5).
Figure 2. X-ray structure of 3. Selected bond lengths [Å] and angles
[°]: Ru(1)–C(11) 2.109(2), Ru(1)–O(1) 2.113(2), Ru(1)–O(3)
2.113(2), Ru(1)–C(5) 2.174(3), Ru(1)–C(6) 2.175(3), Ru(1)–C(4)
2.208(3), Ru(1)–C(1) 2.216(3), Ru(1)–C(2) 2.262(3), Ru(1)–C(3)
2.266(2); C(11)–Ru(1)–O(1) 87.37(9), C(11)–Ru(1)–O(3) 82.52(9),
O(1)–Ru(1)–O(3) 76.20(8).
Again, the complex exists with a distorted octahedral co-
ordination of the Ru core. Compound 8 was prepared by
reaction of 4 with excess phenylisonitrile.[14] It crystallizes
in the orthorhombic space group P212121 with a =
10.8932(2) Å, b = 16.4398(4) Å, c = 26.9136(7) Å, α = β =
γ = 90°, Z = 4 (Figure 5). The Ru center again shows a
slightly distorted octahedral coordination sphere with all
angles close to 90 and 180°, respectively. One of the three
phenylisonitrile ligands is arranged in a position trans to
Figure 3. X-ray structure of 6a. Selected bond lengths [Å] and
angles [°]: Ru(1)–O(1) 2.1082(18), Ru(1)–O(3) 2.121(2), Ru(1)–O(5)
2.131(2), Ru(1)–C(3) 2.155(3), Ru(1)–C(2) 2.156(3), Ru(1)–C(5)
2.166(2), Ru(1)–C(1) 2.168(3), Ru(1)–C(6) 2.169(2), Ru(1)–C(4)
2.185(2), Ag(1)–O(2) 2.348(2), Ag(1)–P(1) 2.362(1), Ag(1)–O(3)
2.478(2), Ag(1)–O(5) 2.507(2); O(1)–Ru(1)–O(3) 86.44(7), O(1)–
Ru(1)–O(5) 84.57(7), O(3)–Ru(1)–O(5) 80.29(6), O(2)–Ag(1)–P(1)
143.72(5), O(2)–Ag(1)–O(3) 74.93(6), P(1)–Ag(1)–O(3) 132.63(4),
O(2)–Ag(1)–O(5) 75.94(6), P(1)–Ag(1)–O(5) 132.12(4), O(3)–
Ag(1)–O(5) 66.70(5).
Figure 5. X-ray structure of 8. Selected bond lengths [Å] and angles
[°]: Ru(1)–C(27) 1.968(6), Ru(1)–C(20) 1.980(7), Ru(1)–C(34)
1.986(7), Ru(1)–O(3) 2.091(4), Ru(1)–O(1) 2.096(4), Ru(1)–C(1)
2.112(5); C(20)–Ru(1)–C(34) 164.9(2), O(3)–Ru(1)–O(1) 172.1(2),
C(27)–Ru(1)–C(1) 178.5(2), Ru(1)–C(20)–N(3) 166.1(5), Ru(1)–
C(27)–N(4) 177.2(6), Ru(1)–C(34)–N(5) 162.3(5).
lowed by reaction with 2 equiv. of CF3COOAg. Compound
7 crystallized in the monoclinic space group C2/c with a =
27.0985(3) Å, b = 14.4321(4) Å, c = 20.3053.(5) Å, α = γ =
90°, β = 109.654(2)°, Z = 8 (Figure 4).
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Catalyst Precursors for the ROMP of Enantiomerically Pure Monomers
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the N-heterocyclic carbene ligand. The two trifluoroacetate endo-2. In all cases, only precatalysts 3 and 4 were found to
ligands are trans to each other. possess significant polymerization activity. Poly(endo-1) was
Because of its structural similarity to 8, compound 9 prepared by the action of both precatalysts 3 and 4 (Table 1,
again crystallizes in the orthorhombic space group P212121 entries 1–13) in the molecular weight range of 25000–
with a = 10.8403(2) Å, b = 16.5038(3) Å, c = 27.1075(4) Å, 160000 g/mol and polydispersity indices (PDIs) in the range
α = β = γ = 90°, Z = 4 (Figure 6). The arrangement of the of 1.17–1.54. A graph of the number of equivalents of the
two phenylisonitrile and trifluoroacetate ligands is identical monomer with respect to the precatalyst (N) versus Mn il-
to that in 8.
lustrates these results (Figure 7).
Figure 7. Plot of Mn vs. number of monomer equivalents (N). 1:
precatalyst 3 with endo-1; 2: precatalyst 4 with exo-2; 3: precatalyst
3 with exo-2; 4: calculated values for monomer 2; 5: calculated
values for monomer 1.
Figure 6. X-ray structure of 9. Selected bond lengths [Å] and angles
[°]: Ru(1)–C(27) 1.967(5), Ru(1)–C(20) 1.986(5), Ru(1)–C(34)
1.986(5), Ru(1)–O(3) 2.096(3), Ru(1)–O(1) 2.102(3), Ru(1)–C(1)
2.123(4), C(20)–Ru(1)–C(34) 164.4(2); O(3)–Ru(1)–O(1) 172.6(1),
C(27)–Ru(1)–C(1) 178.5(2), Ru(1)–C(20)–N(3) 166.1(4), Ru(1)–
C(27)–N(4) 178.4(5), Ru(1)–C(34)–N(5) 161.8(4).
As can be deduced therefrom, polymerization proceeds
in a controlled manner, that is, the values of Mn increase
linearly with increasing N. The stepwise synthesis of poly-
(endo-1)100 (Table 1, entry 13) yields a polymer similar to
the one prepared in a one-step procedure (Table 1, entry 9),
however with higher PDI. This suggests that the polymeri-
Reactivity in ROMP
All precatalysts, 3–9, were investigated for their activity zation does not proceed in a truly living[29] manner. The
in ROMP using the monomers exo-1, endo-1, exo-2, and fact that the values for Mn as determined by light scattering
Table 1. Polymerization results for endo-1 and exo-1 catalyzed by the action of precatalysts 3 and 4. Solvent: ClCH2CH2Cl, 70 °C, 8 h.
Entry
Monomer
Catalyst
N
Mn (theor.)[a]
Mn (LS)
PDI
Yield [%]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
endo-1
endo-1
endo-1
endo-1
endo-1
endo-1
endo-1
endo-1
endo-1
endo-1
endo-1
endo-1
endo-1
exo-1
4
4
4
4
4
3
3
3
3
3
3
3
3
4
4
4
4
4
3
3
10
30
50
70
100
10
30
50
70
100
50[b]
50
50–100
10
30
50
70
100
50
2913
8740
14567
20393
29134
2913
–
–
–
–
oligomer
oligomer
40000
85000
91000
25300
57500
82000
109000
158300
50800
88000
166000
–
1.37
1.25
1.38
1.17
1.24
1.34
1.35
1.38
1.40
1.39
1.54
–
10
23
43
52
72
80
80
85
8740
14567
20393
29134
14567
14567
29134
2913
48
[c]
80
oligomer
oligomer
42
60
78
100
100
exo-1
8740
–
–
exo-1
14567
20393
29134
14567
29134
64500
55700
152000
58600
116000
2.00
1.94
1.71
2.09
2.14
exo-1
exo-1
exo-1
exo-1
100
[a] Without end groups. [b] 1 equiv. of pyridine. [c] Taken from experiment entry 13 prior to addition of second 50 equiv. of monomer.
Eur. J. Inorg. Chem. 2007, 3988–4000
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M. R. Buchmeiser, D. Wang, Y. Zhang, S. Naumov, K. Wurst
FULL PAPER
are much higher than the calculated ones also suggests a
It is worth noting that 3 is far more reactive than 4, as
nonquantitative initiation of the precatalysts. Not unexpec- illustrated by the comparably low yields (Յ43%) obtained
tedly, addition of pyridine (Table 1, entry 11) reduces the with the latter. The lower activity of 4 in comparison to 3
molecular weight of the polymer.
may be rationalized by the fact that precatalyst 3 is believed
Table 2. Polymerization results for endo-2 and exo-2 catalyzed by the action of precatalysts 3 and 4. Solvent: ClCH2CH2Cl, 70 °C, 8 h.
Entry
Monomer
Catalyst
N
Mn (theor.)[a]
Mn (LS)
PDI
Yield [%]
1
2
3
4
5
6
7
endo-2
endo-2
endo-2
endo-2
endo-2
endo-2
endo-2
4
4
4
4
4
3
3
10
30
50
70
100
50
3182
9546
15910
22274
31820
15910
31820
insoluble
insoluble
insoluble
insoluble
insoluble
–
–
–
–
–
–
–
–
8
10
10
15
18
oligomer
oligomer
100
–
8
9
exo-2
exo-2
exo-2
exo-2
exo-2
exo-2
exo-2
exo-2
exo-2
exo-2
4
4
4
4
4
3
3
3
3
3
10
30
50
70
100
10
30
50
70
100
3182
9546
15910
22274
31820
3182
25000
33000
73000
93200
130000
36000
44000
59000
74000
106000
1.83
2.05
1.91
1.88
1.68
1.25
1.50
1.56
1.55
1.49
52
53
61
75
77
35
68
61
74
73
10
11
12
13
14
15
16
17
9546
15910
22274
31820
[a] Without end groups.
Figure 8. Structures of the studied complexes for the reaction of the exo and endo isomers with RuCl2(IMesH2)(p-cymene).
3992 Eur. J. Inorg. Chem. 2007, 3988–4000
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Catalyst Precursors for the ROMP of Enantiomerically Pure Monomers
FULL PAPER
to form a 1,3-dimesityl-3,4-dihydroimidazolin-2-ylidene- forms of N,N-(norborn-5-ene-2,3-dicarbimide)--valine
based propagating species. These types of initiators have ethyl ester (NB-R1) and N,N-(norborn-5-ene-2,3-dicarb-
been reported to be far more active than the corresponding imide)--valine-tert-butylamide (NB-R2). For these calcula-
1,3-dimesitylimidazol-2-ylidene-derived ones.[30] An impor- tions, the catalyst RuCl2(IMesH2)(p-cymene) was chosen as
tant finding is the fact that the parent complex 5 is virtually a model compound. Calculations revealed that the exo
inactive in the ROMP of exo-1, endo-1, exo-2, and endo-2. forms of both monomers studied are only insignificantly
Thus, the exchange of both chlorine ligands by trifluoroace- more stable (Ͻ2 kcal/mol) than the corresponding endo
tates appears to be a necessary prerequisite for the forma- forms. Additionally, there is no essential effect of the sub-
tion of an active precatalyst. Similar behavior has been ob- stituent R {H, CH3, 2-propyl, CH[CH(CH3)2]COOEt,
served in the Ru–alkylidene-initiated cyclopolymerization CH[CH(CH3)2]CONH-tBu} and conformation (exo vs.
of 1,6-heptadiynes, where substitution of both chlorines of endo) on the Mulliken atomic charges and electron density
the Grubbs-[24] and Grubbs–Hoveyda-type initiators[21–23,31] at the C=C double bond of monomers. Thus, the calculated
by trifluoroacetate groups was necessary to generate poly- Mulliken atomic charges at the C atoms forming the double
merization-active systems. Precatalysts 6 and 6a, as well as bond are –0.106/–0.104 and –0.119/–0.118 for the exo and
7, apparently decompose upon heating the polymerization endo forms, respectively (R = CH3/R = H). Additionally,
mixture prior to any initiation. Finally, both precatalysts 8 the calculated relative energies of the different Ru–alkylid-
and 9 are composed upon heating in the presence of any ene complexes for NB-R1 {R = CH[CH(CH3)2]COOEt}
monomer. We tentatively assign this finding to an imine- differ only slightly (Ͻ1 kcal/mol) from those calculated for
type metathesis-type reaction[32,33] of dissociated phenyl- R = H and CH3. Therefore, a simplified form of the mono-
isonitrile with any in situ formed Ru–alkylidene complex mers with R = H, which is not too time-consuming in fre-
resulting in cleavage of the Ru moiety from the polymer quency analysis, was used for further calculations.
chain.
After dissociation of the p-cymene ligand (∆Utot =
Polymerization results similar to those obtained for endo- 6.2 kcal/mol), the formation of the corresponding Ru–alk-
1 were observed for exo-1. Again, precatalyst 3 turned out ylidene complexes was calculated. In the case of the exo-
to be more reactive than 4. The values for Mn of poly(exo- form, four possible stable structures for the catalyst–mono-
1) as determined by LS (Table 1, entries 19 and 20) were mer complexes (exo-IIIa, exo-IIIb, exo-IIIc, and exo-IIId)
significantly lower than those for poly(endo-1) (Table 1, en- (Figure 8) were optimized, with exo-IIIa with C7 in proxim-
tries 8 and 10), indicative of a higher initiation efficiency of ity to the Ru center being the most stable one.
the precatalyst for the exo monomer. Such higher reactivity
Complexes exo-IIIa and exo-IIIb are characterized by
of exo isomers versus Grubbs-type initiators was also re- monomer C=C double bonds orthogonal to the Ru–NHC
ported by other groups.[34] In contrast to endo-1, polymeri- bond. In contrast, the C=C double bond in exo-IIIc and
zation of endo-2 with either 3 or 4 resulted only in oligo- exo-IIId (Figure 8) is almost parallel to the Ru–NHC bond.
meric or insoluble products that were isolated in low yields, The calculated relative stabilities of different structures are
typically Ͻ20% (Table 2, entries 1–7).
given in Table 3.
However, exo-2 may be polymerized by both precatalysts
All four exo-monomer–Ru complexes are stable (∆Utot is
3 and 4 in a controlled way (Table 2, entries 8–17). PDIs negative) and their possible transformations were further
were in the range of 1.69–2.05 for precatalyst 4 and 1.25– analyzed (Scheme 1).
1.56 for precatalyst 3. An illustration is given in Figure 8.
Similar to the exo form, two stable catalyst–endo-mono-
mer complexes with the C=C double bond of the monomer
orthogonal to the Ru–NHC bond (endo-IIIa and endo-IIIb,
Figure 8) were identified, endo-IIIa with C7 in proximity
to the Ru center being the most stable one (Scheme 2). In
addition, two structures, that is, endo-IIIc and endo-IIId
with the C=C double bond of the monomer almost parallel
to the Ru–NHC bond, are stable. Because of a strong steric
interaction with the norborn-2-ene moiety, the Cl atom is
trans to the N-heterocyclic carbene in endo-IIId. The calcu-
lated relative stabilities of the Ru–endo-monomer complexes
(Table 3) indicate that formation of the structures endo-IIIa,
endo-IIIb, endo-IIIc, and endo-IIId is exothermic (∆Utot is
negative) and their possible transformations were therefore
further analyzed (Scheme 2). In addition, it could be argued
that the existence of an additional interaction between Ru
and the N atom of the monomer in the case of the endo
Polymer Structure
The structure of poly(endo-1) prepared by the action of
either 3 or 4 was identical to the one published pre-
viously.[35] An atactic, all-trans structure was assigned to
this polymer. In contrast to poly(endo-1), poly(exo-1) and
poly(exo-2), whether prepared by the action of 3 or 4,
showed a cis content of roughly 40%, as evidenced by sig-
1
nals in the H NMR at δ = 5.44 ppm and in the 13C NMR
spectrum around δ = 132 ppm and 52 ppm, respectively. For
NMR assignment of signals, see refs.[36–38]
Theoretical Considerations
Quantum chemical calculations were carried out to shed form (structure endo-IIIb, Figure 8, Ru–N = 0.2407 nm)
some light on the possible mechanism of the formation of may prevent further transformation. Here the question
ROMP-active Ru–alkylidene complexes and to provide an arose whether an additional interaction between the Ru and
explanation for the different reactivity of the exo and endo the N atoms of the monomer calculated for the cut-down
Eur. J. Inorg. Chem. 2007, 3988–4000
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FULL PAPER
Table 3. Relative energies [kcal/mol] of the different Ru complexes and activation energies Uact(E0 + EZP) [kcal/mol] for intramolecular
C1–C2 H-shift. Uact was estimated for a simplified structure of the NHC (Supporting Information).
Structure exo
Relative energy
Structure endo
Relative energy
∆E0
I
–8.73
–6.24
9.71
I
–8.73
–6.24
9.71
∆Utot (E0 + EZP
∆Gtot (Utot – TS)
)
∆E0
II
0
0
0
II
0
0
0
∆Utot (E0 + EZP
∆Gtot (Utot – TS)
)
∆E0
exo-IIIa
exo-IIIb
exo-IIIc
exo-IIId
exo-IV
exo-V
–28.4
–26.00
–11.85
endo-IIIa
endo-IIIb
endo-IIIc
endo-IIId
endo-IV
–28.44
–26.05
–11.31
∆Utot (E0 + EZP
∆Gtot (Utot – TS)
)
∆E0
–20.05
–18.24
–3.55
–13.82
–11.53
+5.19
∆Utot (E0 + EZP
∆Gtot (Utot – TS)
)
∆E0
–15.64
–13.11
+2.42
–13.76
–11.46
+3.40
∆Utot (E0 + EZP
∆Gtot (Utot – TS)
)
∆E0
–5.45
–3.27
+12.02
–9.1
–7.0
+11.2
∆Utot (E0 + EZP
∆Gtot (Utot – TS)
∆E0
–28.38
–26.40
–12.78
–27.25
–25.33
–9.02
∆Utot (E0 + EZP
∆Gtot (Utot – TS)
)
∆E0
–17.96
–17.36
–4.33
∆Utot (E0 + EZP
∆Gtot (Utot – TS)
)
Uact (E0 + EZP
Uact (E0 + EZP
Uact (E0 + EZP
Uact (E0 + EZP
Uact (E0 + EZP
Uact (E0 + EZP
)
)
)
)
)
)
TS(I) exo-3a Ǟ 4
TS(II) exo-3a Ǟ 4
TS(I) exo-3b Ǟ 4
TS(II) exo-3b Ǟ 4
TS(II) exo-3c Ǟ 4
TS(II) exo-3d Ǟ 4
73
41
67
33
28
18
TS(I) endo-3a Ǟ 4
TS(II) endo-3a Ǟ 4
TS(I) endo-3b Ǟ 4
TS(II) endo-3b Ǟ 4
TS(II) endo-3c Ǟ 4
TS(II) endo-3d Ǟ 4
74
46
–
38
34
36
Scheme 1. Energy diagram and two possible reaction pathways calculated at the B3LYP/LACVP* level for the reaction of an exo isomer
with RuCl2(IMesH2)(p-cymene). Transition-state energies TS(I) and TS(II) are estimated for a simplified structure of the NHC (Support-
ing Information).
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Catalyst Precursors for the ROMP of Enantiomerically Pure Monomers
FULL PAPER
Scheme 2. Energy diagram and possible reaction pathways calculated at the B3LYP/LACVP* level for the reaction of an endo isomer with
RuCl2(IMesH2)(p-cymene). Transition-state energies TS(I) and TS(II) are estimated for a simplified structure of the NHC (Supporting
Information).
model N-R-norborn-5-ene-2,3-dicarboximide (R = H, CH3)
Though structures exo-IV and endo-IV are energetically
existed also for the actual monomers {R = CH[CH(CH3)2]- possible, the intramolecular C1 Ǟ C2 H-shift proceeds with
COOEt, CH[CH(CH3)2]CONH-tBu} or whether other ste- a high activation barrier and should therefore be analyzed.
ric effects would dominate. To shed light on this point, cal- However, in contrast to stable structures, the optimization
culations were carried out on the unrestricted monomers of transition states for such large molecules is comparably
NB-R1 and NB-R2. As a matter of fact, these not only complicated. So, we were forced to use simplified molecular
confirmed that this extra interaction exists, but revealed structures for the estimation of the barrier for possible
that the oxygen atom from the 2,3-dicarbimide group inter- models of intramolecular H-shifts. Thus, in the search of
acts very strongly with the Ru atom, thus forming an ad- the transition state for the H-shift from C1 to C2 of the
ditional O–Ru bond. In due consequence, these two ad- double bond we started from the corresponding exo and
ditional N–Ru and O–Ru interactions should aggravate any endo monomers (i.e., exo- and endo-N-R-norborn-5-ene-
further transformation of endo-IIIb and thus further ex- 2,3-dicarboximide, respectively; R = H, CH3) not bonded
plain the reduced reactivity of the endo-monomer. The cal- to the Ru moiety. We found no effect of the substituents R
culated endo-IIIb structures for NB-R1 and NB-R2 are on the nitrogen of the monomer on the structure and acti-
given in Figure S2 in the Supporting Information.
vation energy for the H-shift from C1 to C2. The calculated
To form the ROMP-active Ru–alkylidene complexes, the activation energy was very high (73 kcal/mol, 70 kcal/mol
following mechanism may be proposed: one H atom from with Zero Point Energy correction). Transition structures
the C1=C2 double bond shifts from C1 to C2 followed by of the monomer obtained that way were used as initial tran-
formation of the Ru–alkylidene complex, leading to struc- sition structures for the modeling of the different Ru–
tures exo-IV or endo-IV (Schemes 2 and 3).
monomer complexes. A simplified catalyst structure with
N–H instead of N-mesityl substituents was used.
Starting from the stable structures exo-3a and exo-3b
(Scheme S1, Supporting Information), the transition struc-
tures [TS(I)] for the H-shift from C1 to C2 could be local-
ized. The activation energy (given in Table 3) was again, as
in the case of the nonbonded monomer, comparably high
(up to 73 kcal/mol). However, when the H-shift from C1 to
C2 was in conjunction with a concomitant formation of a
Ru–alkylidene complex [TS(II)], the activation energy was
essentially reduced, to 41 kcal/mol and 33 kcal/mol for exo-
3a and exo-3b, respectively. Starting from the stable struc-
tures exo-3c and exo-3d (Scheme S1, Supporting Infor-
mation), the transition structures [TS(I)] could not be local-
ized and transformed directly into the corresponding sec-
Scheme 3. Proposed reaction cascade for the formation of a
ROMP-active RuIV alkylidene (structure exo-5).
Eur. J. Inorg. Chem. 2007, 3988–4000
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M. R. Buchmeiser, D. Wang, Y. Zhang, S. Naumov, K. Wurst
FULL PAPER
ond transition structures [TS(II)]. This is a consequence of All these findings may be indicative of a lower activity of
the geometries of TS(II), which have the alkylidene parallel the endo forms of the monomers investigated in comparison
to the Ru–NHC bond and do not need any additional rota- to the corresponding exo forms.
tion of the ruthenacyclopropane ring as is the case in exo-
An additional, alternative activation mechanism for the
3a and exo-3b. Vice versa, the ruthenacyclopropane rings in formation of Ru–alkylidene complexes necessary for ROMP
exo-3c and exo-3d also already occupy a parallel orientation may explain the different reactivity of the exo and endo
with respect to the Ru–NHC bond. The analysis of the forms of 1 and 2. While there is no essential difference be-
TS(II) structures showed that in the case of the exo form tween the exo and endo forms of monomers in the electronic
only two structures of the TS(II) with very small differences parameters, such as charge and electron density at the
in energy (Ͻ1 kcal/mol) exist. Here, the exo-3a structure is double bond, there is a deciding contrast in geometry. As
identical to exo-3c and exo-3b is identical to exo-3d (Sup- can be seen in Figure 9, there is a significant difference in
porting Information).
the distances between the C1 atom of the double bond and
Starting from the stable structure endo-3a (Scheme S2, the H5 atom at the exo or endo position (0.269 nm and
Supporting Information), the transition structure [TS(I)] for 0.367 nm, for exo or endo respectively).
the H-shift from C1 to C2 could be localized with a very
high activation energy (74 kcal/mol). In case the H-shift oc-
curs concomitantly to a rotation of the ruthenacyclobutane,
formation of a Ru–alkylidene complex occurs, and the acti-
vation energy is again essentially reduced to 46 kcal/mol
[TS(II)] (Scheme S2, Supporting Information). TS(I) could
not be localized for endo-3b, endo-3c, and endo-3d and
transformed directly into the second transition structure
[TS(II)]. Again, the TS(II) of endo-3a is identical to that of
endo-3c. Formation of the TS(II) of endo-3b, being identical
to that of endo-3d, was calculated to be slightly more favor-
able (about 2 kcal/mol) than the TS(II) of endo-3a and
endo-3c.
Figure 9. Distances between C1/C2 atoms of the double bond (the
pz orbitals) and the H atoms at C4/C5 in the exo and endo forms.
Consequently, the positively charged H atom in the exo
Activation energies for the intramolecular C1 Ǟ C2 H- position interacts strongly with the pz orbital on the nega-
shift were calculated for the simplified structure of the tively polarized C1, thus facilitating the intramolecular C5
NHC ligand with N–H instead of N-mesityl groups. These Ǟ C1 (or C4 Ǟ C2) H-shift to the double bond. As geome-
were further used for the analysis of the possible transfor- try optimization reveals, the weakening of the C3–C4 bond
mations of the Ru–alkylidene complexes (Table 3). How- could be followed by ring opening, concomitant intramolec-
ever, it should be noted that the calculated activation ener- ular H-shift from C2 to C1, and formation of a Ru=C
gies for the 1,2-H-shift for the simplified form of the mono- double bond. All these intramolecular transformations can
mer (R = H) should be used on a qualitative rather than apparently occur concomitantly (Scheme 3) with low acti-
on a quantitative base. From the analysis of the data sum- vation energies leading to the structure exo-V. However,
marized in Table 3 it can be seen that the formation of such transformation is impossible in the case of the endo
TS(II) is particularly favorable (18 kcal/mol) in case the re- form. For this reaction pathway, the starting complexes exo-
action proceeds via the exo-IIId structure.
IIIb and especially exo-IIId appear to be more favorable
From the analysis of the formation of the ROMP-active than complexes exo-IIIa and exo-IIIc for two reasons. First,
structures exo-IV and endo-IV through C1 Ǟ C2 H-shift as a consequence of the interaction between the double
(Schemes 1 and 2) follows: (i) the ROMP-active structure bond and the Ru center, the geometry on C1 and C2 is no
exo-IV can be built starting from all four stable structures longer planar (there is some admixture of sp3 hybridiza-
exo-IIIa, exo-IIIb, exo-IIIc, and exo-IIId; its formation is tion), thus leading to the deformation of pz electron density
energetically favorable (∆Utot = –26.0 kcal/mol, –18.2 kcal/ from the C atoms in the direction of the H atom at C4 and
mol, –13.1 kcal/mol, and –3.3 kcal/mol, respectively); (ii) C5, respectively. This facilitates the interaction with the H
the transformation starting from the less stable complex atom and consequently the H-shift. This also explains the
exo-IIId occurs with lower activation energy (only 18 kcal/ stability of the monomer in the absence of any catalyst. Sec-
mol) than from the most stable structure exo-IIIa, indicat- ond, as revealed by calculations, complexes exo-IIIb and
ing a low-energy pathway; (iii) the formation of endo-IV by exo-IIId are also energetically favorable for transformation
the low-energy pathway starting from the less stable struc- into the activated catalyst exo-V (∆Gtot = –0.8 kcal/mol and
ture endo-IIIc occurs with activation energy 31 kcal/mol, ∆Gtot = –16.35 kcal/mol respectively).
which is 13 kcal/mol higher than that for the pathway start-
It should be emphasized that so far the discussed mecha-
ing from exo-IIId. Moreover, the structure endo-IIIb seems nism through the possible H-shift from C4 to C2 is only
to be inactive because of additional Ru–N bonding. Finally, qualitative because of computational restrictions in the se-
the structure endo-IV must be further expected to be vir- arch for transition structures that operate through a con-
tually ROMP-inactive because of the formation of an ad- certed transformation (H-shifts and ring opening). How-
ditional Ru–O bond (Scheme 2, bond length = 0.240 nm). ever, such transformations are expected to occur easily be-
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Catalyst Precursors for the ROMP of Enantiomerically Pure Monomers
FULL PAPER
Scheme 4. Most stable structures of Ru–alkylidene complexes (B3LYP/LACVP*).
cause of a favorable geometry for the H-shift in the exo- endo forms. Thus, though the ring-opening reaction is ener-
IIIb and exo-IIId complexes and the better interaction of getically favorable in all three cases, the formation of the
the proton with the pz electrons of the double bond.
MCB structure is very different for exo and endo forms. In
The mechanism discussed so far for the formation of Ru– the cases of exo-IV and exo-V, stable structures of the MCB
alkylidene complexes (structures exo-IV, exo-V, and endo- were calculated with reaction enthalpies around –1.0 kcal/
IV) necessary for ROMP clearly shows the difference be- mol and –2.5 kcal/mol for exo-VII (MCB) and exo-X
tween the exo and endo forms. However, it might be of (MCB) respectively. On the contrary, endo-VII (MCB) is
interest to identify the rate-determining step of the overall only a transition structure requiring an activation energy
polymerization reaction. To understand differences in reac- for MCB formation of about 17 kcal/mol. Such different
tivities of the exo and endo forms, further insertion reac- behavior of the endo form is apparently caused by a strong
tions of a second norborn-2-ene monomer into exo-IV, exo- steric interaction of the Cl ligand with the substituents at
V, and endo-IV were calculated. The calculated structures the N-imido group. In due consequence, the large activation
are shown in Scheme 4.
energy for the MCB formation in the case of the endo form
It was found that both active complexes exo-IV and may be the rate-determining step of the overall polymeriza-
endo-IV form stable π complexes (structures exo-VI and tion reaction. A comprehensive study on the different reac-
endo-VI) with stabilization energies of 2.6 kcal/mol and tivity of various exo- and endo-norborn-5-ene-2,3-dicarb-
0.6 kcal/mol respectively. The active complex exo-V can imides is now in progress.
form a stable π complex (exo-IX) with norborn-2-ene (stabi-
lization energy 3.1 kcal/mol) too. However, the next steps,
that is, the conversion of the π complex into the corre-
sponding metallacyclobutane (MCB) structures exo-VII
Conclusions
(MCB), exo-X (MCB), and endo-VII (MCB) (Scheme 4)
A series of novel RuII-derived precatalysts have been in-
followed by ring opening (structures exo-VIII, exo-XI, and vestigated for their polymerization behavior in the ROMP
endo-VIII), proceed energetically differently for the exo and of exo- and endo-norborn-5-ene-2,3-dicarbimides. Our in-
Eur. J. Inorg. Chem. 2007, 3988–4000
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M. R. Buchmeiser, D. Wang, Y. Zhang, S. Naumov, K. Wurst
FULL PAPER
and the reaction mixture was stirred for 12 h. Finally, the ammo-
nium salt was filtered off. Acetonitrile was evaporated under re-
duced pressure until an oily residue remained, which was dissolved
in diethyl ether. The ether solution was subsequently washed with
0.1  hydrochloric acid and saturated aqueous sodium hydrogen
carbonate and finally dried with sodium sulfate. The solution was
concentrated, and about the same amount of pentane was added.
Crystallization was performed at –18 °C. Yield: 2.6 g (43%). IR
vestigations revealed that precatalysts containing an N-het-
erocyclic carbene ligand, two trifluoroacetate groups, and
one labile ligand are best suited for the thermal initiation
of ROMP. The exo isomer was preferentially polymerized
in both cases. Quantum chemical calculations propose pos-
sible mechanisms for the formation of ROMP-active struc-
tures, which could also explain the experimental findings of
the better reactivity of the exo form. Additionally, the dif-
ferent activation energies for MCB formation of the exo
(ATR-mode): ν = 3353 (m), 2965 (w), 2929 (m), 2864 (m), 1690 (s),
˜
1523 (m), 1454 (m), 1376 (s), 1352 (s), 1212 (w), 1182 (s), 1044 (m),
and endo forms may be the rate-determining step of the 927 (m), 891 (m), 858 (m), 823 (m), 777 (m), 720 (w) cm–1. 1H
NMR (CDCl3): δ = 6.63 (br. s, 1 H, NH), 6.11 (m, 2 H), 3.94 (d,
overall polymerization reaction. Further work will focus on
the construction of suitable labile ligands that allow for a
quantitative initiation of the precatalysts.
2J = 11.54 Hz, 1 H, CH), 3.42 (br., 2 H), 3.29 (m, 2 H), 2.60 (m, 1
1
1
H), 1.74 (d, J = 8.8 Hz, 1 H), 1.54 (d, J = 8.9 Hz, 1 H), 1.30 (s,
2
2
9 H, tBu), 0.98 (d, J = 6.67 Hz, 3 H, CH3), 0.75 (d, J = 6.52 Hz,
3 H, CH3) ppm. 13C NMR (CDCl3): δ = 178.31, 177.83, 167.50,
134.89, 134.6, 65.03, 52.35, 51.03, 45.58, 45.41, 45.12, 28.53, 26.50,
19.54 ppm. MS: calcd. for C18H26N2O3 [M·]+ 318.19; found 276
[M· – H3C–CH=CH2]+.
Experimental Section
All manipulations were performed under nitrogen in a glovebox
(MBraun LabMaster 130) or by standard Schlenk techniques. Pur-
chased starting materials were used without any further purifica-
tion. Dichloroethane was distilled from calcium hydride under ni-
trogen. Tetrahydrofuran (THF), pentane, diethyl ether, toluene, and
dichloromethane were dried by an MBraun solvent purification
system (SPS). NMR spectroscopic data were obtained at
250.13 MHz for proton and 62.90 MHz for carbon in the indicated
solvent at 25 °C on a Bruker Spectrospin 250 and are listed in parts
per million downfield from tetramethylsilane for proton and car-
bon. IR spectra were recorded with a Bruker Vector 22 using ATR
technology. Molecular weights and polydispersity indices (PDIs)
of the polymers were determined by GPC at 30 °C on Polymer
laboratories columns (PLgel 10 µm MIXED-B, 7.5ϫ300 mm) in
THF at 25 °C using a Waters Autosampler, a Waters 484 UV spec-
trometer detector (254 nm), an Optilab Rex refractive index detec-
tor (Wyatt), and a MiniDawn light-scattering detector (Wyatt).
Synthesis and structural data of compounds endo-1 and endo-2,[28]
3, 4, 9, 10,[14] and 5[6] have been reported elsewhere. Values for
dn/dc for endo-1, exo-1, and exo-2 were 0.119, 0.126, and 0.116,
respectively.
[39]
[Ru(CF3CO2)(p-cymene)PCy3] (6): [RuCl2(p-cymene)]2
was
treated with 2 equiv. of PCy3 and [RuCl2(p-cymene)PCy3] was ob-
tained in 90% yield according to ref.[5]. 1H NMR (CDCl3): δ = 5.58
(br. s, 4 H, ArH), 2.83 [pent, 2J = 6.9 Hz, 1 H, CH(CH3)2], 2.42
(q, J = 22.3, 11.4 Hz, 3 H, cyclohexyl), 2.14 (s, 3 H, CH3), 2.09
(br., 6 H, cyclohexyl), 1.88–1.66 (m, 9 H, cyclohexyl), 1.30 [d, 2J =
7.0 Hz, 6 H, CH(CH3)2], 1.56–1.10 (m, 15 H, cyclohexyl) ppm. 13
NMR (CDCl3): δ = 106.7, 94.2, 88.2 (J = 3.8 Hz), 83.7
C
31P–13
C
31P–13
(J
C
31P–13
C
= 4.9 Hz), 35.7 (J
= 17.9 Hz, cyclohexyl), 30.4 (s,
31P–13
C
31P–13
cyclohexyl), 29.5 (J
= 2.1 Hz, cyclohexyl), 27.4 (J
=
C
9.8 Hz, cyclohexyl), 26.3 [CH(CH3)2], 22.3 [CH(CH3)2], 17.7 (CH3)
ppm.
[RuCl2(p-cymene)PCy3] (114 mg, 0.20 mmol) was dissolved in THF
and added to a solution of silver trifluoroacetate (97.2 mg,
0.44 mmol) in THF, both cooled to –36 °C. After mixing, the solu-
tion was stirred for another 4 h, allowing it to reach room tempera-
ture. During that time a white precipitate of AgCl formed. The
mixture was filtered through celite and the THF was removed in
vacuo. Methylene chloride was added to dissolve the residue and
the solution was again concentrated in vacuo. Diethyl ether and n-
pentane were successfully layered over the red, saturated solution.
exo,exo-N,N-(Norborn-5-ene-2,3-dicarbimido)-L-valine Ethyl Ester
(exo-1): exo,exo-N,N-(Norborn-5-ene-2,3-dicarbimido)--valine
Yield: 82%. FTIR (ATR mode): ν = 2934, 2853, 2052, 1701, 1448,
˜
(575 mg, 2.18 mmol) and p-toluenesulfonic acid (17 mg,
0.08 mmol) were dissolved in dry ethanol and refluxed for 8 h. The
ethanol was evaporated and the residue was dissolved in diethyl
ether. The ether solution was subject to flash chromatography over
silica gel 60 (diethyl ether/pentane, 5:1). Recrystallization gave exo-
1396, 1187, 1126, 1006, 837, 784, 725, 672 cm–1. 1H NMR (CDCl3):
δ = 6.14 (d, 2J = 5.9 Hz, 2 H, ArH), 6.14 (d, 2J = 6.1 Hz, 2 H,
ArH), 2.60 [pent, 2J = 6.9 Hz, 1 H, CH(CH3)2], 2.25 (q, J =
11.9 Hz, 3 H, cyclohexyl), 2.07 (s, 3 H, CH3), 1.98–1.69 (m, 15 H,
2
cyclohexyl), 1.56–1.22 (m, 15 H, cyclohexyl), 1.18 [d, J = 6.9 Hz,
1 as white needles in 35% yield (220 mg). IR (ATR): ν = 2975 (w),
˜
2
6 H, CH(CH3)2] ppm. 13C NMR (CDCl3): δ = 163.0 [dq, J
19F–13
C
1739 (m), 1693 (s), 1526 (m), 1380 (s), 1352 (m), 1281 (w), 1186 (s),
1097 (m), 1050 (m), 1018 (m), 969 (m), 892 (m), 825 (m), 771 (m),
= 36.3, 2.5 Hz, CO], 114.6 (q, 1J
= 291.1 Hz, CF3), 107.2,
= 3.9 Hz), 35.6 (J
C
31P–13 31P–13
19F–13
C
1
724 (w), 673 (m) cm–1. H NMR (CDCl3): δ = 6.30 (s, 2 H), 4.34
31P–13
94.8, 84.2 (J
C
C
= 3.0 Hz), 81.8 (J
1
31P–13
C
= 17.0 Hz, cyclohexyl), 31.5 (cyclohexyl), 29.3 (J
= 2.2 Hz,
(d, J = 8.1 Hz, 1 H), 4.25–4.08 (m, 2 H), 3.31 (br. s, 2 H), 2.78–
2.57 (m, 3 H), 1.53 (m, 2 H), 1.20 (t, 2J = 7.17 Hz, 3 H, CH3), 1.10
(d, 2J = 6.67 Hz, 3 H, CH3), 0.84 (d, 2J = 6.84 Hz, 3 H, CH3) ppm.
13C NMR (CDCl3): δ = 177.4, 177.26, 168.3, 137.9, 61.37, 57.7,
47.8, 47.3, 45.6, 45.37, 42.8, 27.9, 22.3, 21.03, 19.34, 14.01 ppm.
MS: calcd. for C16H21NO4 [M·]+ 291.15; found 291.
31P–13
C
cyclohexyl), 27.7 (J
= 9.9 Hz, cyclohexyl), 26.4 [CH(CH3)2],
22.5 [CH(CH3)2], 18.8 (CH3) ppm. C32H47F6O4PRu (742.22): calcd.
C 51.82, H 6.39; found C 51.87, H 6.50. Crystals of compound 6
were obtained in the form of its CF3COOAg adduct (6a).
[Ru(CF3CO2)2(p-cymene)PPh3] (7): [RuCl2(p-cymene)]2 was treated
with PPh3 (2 equiv.) according to the literature to give [RuCl2(p-
cymene)PPh3] in 98% yield.[33] 1H NMR (CDCl3): δ = 7.87–7.79
(m, 6 H, Ph), 7.40–7.32 (m, 9 H, Ph), 5.24 (d, 2J = 6.2 Hz, 2 H,
ArH), 4.98 (dd, 2J = 6.2, 1.2 Hz, 2 H, ArH), 2.85 [pent, 2J = 6.2 Hz,
exo,exo-N,N-(Norborn-5-ene-2,3-dicarbimido)-L-valine-tert-butyl-
amide (exo-2): Dicyclohexyldicarbodiimide (DCC, 1.96 g,
0.95 mmol) was added to -valine-exo,exo-N,N-(norborn-2-ene-5,6-
dicarbimide) (5.0 g, 1.9 mmol) dissolved in acetonitrile. Soon after
addition of DCC, dicyclohexylurea (DCU) precipitated, and the 1 H, CH(CH3)2], 1.86 (s, 3 H, CH3), 1.09 [d, 2J = 6.2 Hz, 6 H,
reaction mixture was stirred for a further 6 h. DCU was filtered
off, tert-butylamine (2.0 mL, 1.9 mmol) was added to the filtrate,
CH(CH3)2] ppm. 13C NMR (CDCl3): δ = 134.3 (2J
31P–13
C
= 9.4 Hz,
= 2.2 Hz, Ph),
Ph), 133.7 (1J
= 45.7 Hz, Ph), 130.2 (4J
31P–13
C
31P–13
C
3998
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 3988–4000

Catalyst Precursors for the ROMP of Enantiomerically Pure Monomers
127.9 (3J = 9.9 Hz, Ph), 111.2 (2J
= 3.3 Hz, p-Cym), spectra of poly(exo-2) prepared by the action of 4 (Mn = 130000 g/
FULL PAPER
31P–13
C
31P–13
C
95.9 (p-Cym), 89.0 (2J
= 3.3 Hz, p-Cym), 87.1 (2J
=
mol; Mw = 218500 g/mol; PDI = 1.68) were identical.
31P–13
C
31P–13
C
3.3 Hz, p-Cym), 30.2, 21.8, 17.7 (mesityl) ppm.
Computational Methods: Density Functional Theory (DFT) calcu-
lations were carried out using Becke’s three-parameter functional
(B3)[40,41] in combination with the Lee, Yang, and Parr (LYP) corre-
lation functional[42] with the LACVP* basis set (Jaguar, version 6.5
program[43]). The LACVP* basis set uses the standard 6-31G* basis
set for light elements and the LAC pseudopotential[44] for the Ru
atom. The molecular geometries and energies of all calculated
structures were obtained at the same B3LYP/LACVP* level of
theory. The B3LYP/LACVP* method has already been successfully
used in many studies.[45–48] To prove the ability of this method, the
calculated molecular structure of precatalyst 3 was compared with
its X-ray structure.
[RuCl2(p-cymene)PPh3] (56.8 mg, 0.10 mmol) was dissolved in
THF and added to a solution of silver trifluoroacetate (44.2 mg,
0.20 mmol) in THF, both cooled to –36 °C. After mixing, the solu-
tion was stirred for another 4 h, allowing it to reach room tempera-
ture. During that time a white precipitate of AgCl formed. The
mixture was filtered through celite and the THF was removed in
vacuo. Methylene chloride was added to dissolve the residue and
the solution was again concentrated in vacuo. Diethyl ether and n-
pentane were successfully layered over the red, saturated solution.
Red crystals formed at –36 °C. Yield: 62.2 mg, 86%. FTIR: ν =
˜
3057, 1679, 1436, 1405, 1183, 1139, 1095, 845, 788, 750, 694,
620 cm–1. 1H NMR (CDCl3): δ = 7.51–7.43 (m, 9 H, Ph), 7.40–
The calculated parameters of structure 3 were in good agreement
with those of the X-ray structure (given in Supporting Information
Figure S1 and Table S1). Frequency analysis was used throughout
for identification of the stationary points, which is especially im-
portant for the search of the transition states, and to obtain ther-
mochemistry parameters such as zero point energy (EZP), entropy
(S), total internal energy (Utot), total enthalpy (Htot), and total
Gibbs free energy (Gtot) at 298 K. The relative stability of the dif-
ferent structures was calculated as a balance of both Utot and Gtot
relative to those of the intermediary RuCl2(IMesH2) complex
(structure II in Scheme 1).
2
2
7.34 (m, 6 H, Ph), 6.26 (d, J = 5.1 Hz, 2 H, ArH), 4.98 (d, J =
2
5.1 Hz, 2 H, ArH), 2.58 [pent, J = 6.9 Hz, 1 H, CH(CH3)2], 1.68
(s, 3 H, CH3), 1.26 (d, 2J = 6.9 Hz, 6 H, CH3) ppm. 13C NMR
(CDCl3): δ = 163.6 (dq, 2J
= 36.6, 1.8 Hz, CO), 134.4
= 2.3 Hz, Ph), 129.5
19F–13
C
(2J
(1J
1J
= 10.4 Hz, Ph), 130.9 (4J
= 47.2 Hz, Ph), 128.4 (3J
31P–13
31P–13
C
C
31P–13
C
31P–13
C
= 10.4 Hz, Ph), 114.8 (q,
= 291.1 Hz, CF3), 115.2 (2J
= 8.4 Hz, p-Cym), 95.7
19F–13
C
31P–13
C
(p-Cym), 86.6, 86.5 (2J
= 3.4 Hz, p-Cym), 82.8 (p-Cym), 31.4
31P–13
C
[CH(CH3)2], 21.8, 18.1 (CH3) ppm.
Typical Procedure for ROMP: Polymerizations were performed un-
der argon. A solution of the corresponding initiator (5 mg) in
ClCH2CH2Cl (1 mL) was added to a solution of the monomer in
ClCH2CH2Cl (3 mL). The mixture was stirred at 70 °C for 8 h, then
concentrated to about 1 mL, then the polymer was precipitated by
dropwise addition of the solution to 30 mL of acidic methanol. The
product was then filtered and dried in vacuo to give an off-white
to light yellow powder.
X-ray Measurement and Structure Determination of 3, 6a, and 7–9:
Data collection was performed with a Nonius Kappa CCD
equipped with graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å) and a nominal crystal-to-area detector distance of
36 mm. Intensities were integrated using DENZO and scaled with
SCALEPACK.[49] Several scans in φ and ω directions were made
to increase the number of redundant reflections, which were
averaged in the refinement cycles. This procedure replaces in a good
approximation an empirical absorption correction. The structures
were solved with direct methods SHELXS86 and refined against
Poly(exo-1) Prepared by the Action of 3: Mn = 88000 g/mol; Mw
=
209000 g/mol; PDI = 2.36. IR (ATR): ν = 2964, 1740, 1702, 1456,
˜
1375, 1269, 1182, 1129, 1025, 968, 812, 650 cm–1. 1H NMR
(CDCl3): δ = 5.76 (br. s), 5.44 (br. s), 4.28–4.16 (m, 3 H), 3.04 (m,
3 H), 2.62 (m, 2 H), 2.15 (m, 1 H), 1.62 (m, 1 H), 1.23 (t, 2J =
F2 SHELXL97.[50] The function minimized was Σ[w(Fo – Fc ) ]
2
2 2
with the weight defined as w–1 = [σ2(Fo2) + (xP)2 + yP] and P =
(Fo + 2Fc )/3. All non-hydrogen atoms were refined with aniso-
tropic displacement parameters. Positions of hydrogen atoms were
calculated using a riding model. Compound 3: Triclinic space
2
2
2
2
7.1 Hz, 3 H), 1.10 (d, J = 6.5 Hz, 3 H), 0.83 (d, J = 6.7 Hz, 3 H)
ppm. 13C NMR (CDCl3): δ = 177.6, 168.3, 132 (unresolved m),
131.6, 61.3, 57.5, 52.0 (unresolved), 50.6, 45.9, 41.8, 27.7, 21.2,
19.3, 14.1 ppm. NMR spectra of poly(exo-1) prepared by the action
of 4 (Mn = 130200 g/mol; Mw = 225800 g/mol; PDI = 1.73) were
identical.
¯
group P1 (no. 2), a = 11.3770(4) Å, b = 12.1632(5) Å, c =
14.5978(6) Å, α = 104.636(2)°, β = 96.217(2)°, γ = 113.276(2)°, V
= 1745.50(12) Å3, Z = 2, ρcalcd = 1.461 g/cm3, T = 233 K, µ =
0.521 mm–1, orange prism, 6121 reflections Ͼ 2σ(I), R1 = 0.0350,
Poly(endo-1) Prepared by the Action of 3: Mn = 158300 g/mol; Mw
¯
and ωR2 = 0.0804. Compound 6a: Triclinic space group P1, a =
= 218900 g/mol; PDI = 1.38. IR (ATR): ν = 2967, 1739, 1700 (s),
˜
10.2007(4) Å, b = 13.8886(4) Å, c = 14.9130(6) Å, α = 107.497(2)°
1461, 1380, 1274, 1188, 1133, 1028, 969, 922, 821, 715, 661 cm–1.
1H NMR (CDCl3): δ = 5.65 (br. m, 2 H), 4.33 (m, 1 H), 4.14 (m,
2 H), 3.24 (br. s, 3 H), 2.93 (br. s, 1 H), 2.58 (br. s, 1 H), 1.86 (br.
s, 1 H), 1.35–1.22 (m, 4 H), 1.08 (br. s, 3 H), 0.79 (br. s, 3 H) ppm.
13C NMR (CDCl3): δ = 176.1, 175.3, 168.3, 129.3, 61.4, 57.7, 48.4,
45.5, 40.3, 37.3 (br), 27.5, 21.2, 19.4, 14.1 ppm. NMR spectra of
poly(endo-1) prepared by the action of 4 (Mn = 90900 g/mol; Mw
= 125600 g/mol; PDI = 1.39) were identical.
β = 94.569(2)° γ = 95.552(2)°, V = 1992.37(13) Å3, Z = 2, ρcalcd
=
1.605 g/cm3, T = 233 K, µ = 0.993 mm–1, orange prism, 6844 reflec-
tions Ͼ 2σ(I), R1 = 0.0282, and ωR2 = 0.0648. Compound 7:
Monoclinic space group C2/c (no. 15), a = 27.0985(3) Å, b =
14.4321(4) Å, c = 20.3053(5) Å, β = 109.654(2)°, V = 7478.5(3) Å3,
Z = 8, ρcalcd = 1.413 g/cm3, T = 233 K, µ = 0.528 mm–1, orange
prism, 5820 reflections Ͼ 2σ(I), R1 = 0.0348, and ωR2 = 0.0784.
Compound 8: Orthorhombic space group P212121 (no. 19), a =
10.8932(2) Å, b = 16.4398(4) Å, c = 26.9136(7) Å, α = β = γ = 90°,
V = 4819.74(19) Å3, Z = 4, ρcalcd = 1.414 g/cm3, T = 233 K, µ =
0.506 mm–1, colorless prism, 6183 reflections Ͼ 2σ(I), R1 = 0.0548,
and ωR2 = 0.1203. Compound 9: Orthorhombic space group
P212121, a = 10.8403(2) Å, b = 16.5038(3) Å, c = 27.1075(4) Å, α
= β = γ = 90°, V = 4849.70(14) Å3, Z = 4, ρcalcd = 1.408 g/cm3, T
Poly(exo-2) Prepared by the Action of 3: Mn = 106000 g/mol; Mw
= 158000 g/mol; PDI = 1.49. IR (ATR): ν = 2963, 1772, 1697,
˜
1
1536, 1455, 1360, 1183, 1131, 967, 650 cm–1. H NMR (CDCl3): δ
= 6.75 (br. s), 5.75–5.48 (m), 4.05 (m, 1 H), 3.02 (br. s, 3 H), 2.68
(br. s, 2 H), 2.15 (br. s, 1 H), 1.62 (m, 1 H), 1.31 (s, 9 H), 1.03 (d,
2J = 6.24 Hz, 3 H), 0.79 (d, 2J = 6.18 Hz, 3 H) ppm. 13C NMR
(CDCl3): δ = 178.4, 167.4, 132 (unresolved m), 131.6, 64.8, 51.2 = 233 K, µ = 0.503 mm–1, colorless prism, 7510 reflections Ͼ 2σ(I),
(unresolved), 50.4, 46.2, 41.8, 28.5, 26.7, 19.6, 19.3 ppm. NMR
R1 = 0.0461, and ωR2 = 0.1181.
Eur. J. Inorg. Chem. 2007, 3988–4000
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3999

M. R. Buchmeiser, D. Wang, Y. Zhang, S. Naumov, K. Wurst
FULL PAPER
[19] G. Bhukta, R. Manivannan, G. Sundarajan, J. Organomet.
Chem. 2000, 601, 16–21.
Supporting Information (see footnote on the first page of this arti-
cle): Comparison of the calculated most stable structure of 3 with
its X-ray structure; the most stable structure of endo-IIIb-type Ru–
alkylidene complexes; energy diagram and structures of the transi-
tion states for the H-shift from C1 to C2 for both exo-3a and endo-
3a.
[20] B. Gita, G. Sundararajan, J. Mol. Catal. A 1997, 115, 79–84.
[21] J. O. Krause, M. T. Zarka, U. Anders, R. Weberskirch, O.
Nuyken, M. R. Buchmeiser, Angew. Chem. 2003, 115, 6147–
6151; Angew. Chem. Int. Ed. 2003, 42, 5965–5969.
[22] J. O. Krause, O. Nuyken, M. R. Buchmeiser, Chem. Eur. J.
2004, 10, 2029–2035.
CCDC-631369 to -631371, -631373, and -631374 (for compounds
3, 6a and 7–9) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[23] J. O. Krause, D. Wang, U. Anders, R. Weberskirch, M. T.
Zarka, O. Nuyken, C. Jäger, D. Haarer, M. R. Buchmeiser,
Macromol. Symp. 2004, 217, 179–190.
[24] T. S. Halbach, S. Mix, D. Fischer, S. Maechling, J. O. Krause,
C. Sievers, S. Blechert, O. Nuyken, M. R. Buchmeiser, J. Org.
Chem. 2005, 70, 4687–4694.
[25] T. S. Halbach, J. O. Krause, O. Nuyken, M. R. Buchmeiser,
Macromol. Rapid Commun. 2005, 26, 784–790.
[26] T. S. Halbach, J. O. Krause, O. Nuyken, M. R. Buchmeiser, Po-
lym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 2005, 46,
615–616.
[27] L. Yang, M. Mayr, K. Wurst, M. R. Buchmeiser, Chem. Eur.
J. 2004, 10, 5761–5770.
Acknowledgments
Our work was supported by grants from the Deutsche Forschungs-
gemeinschaft (DFG, BU2174/2-1) and the Freistaat Sachsen.
[28] M. R. Buchmeiser, F. Sinner, M. Mupa, K. Wurst, Macromole-
cules 2000, 33, 32–39.
[1] R. H. Grubbs, Handbook of Metathesis, 1st ed., Wiley-VCH,
Weinheim, 2003, vols. 1–3.
[2] T. M. Trnka, R. H. Grubbs, Acc. Chem. Res. 2001, 34, 18–29.
[3] A. Hafner, A. Mühlebach, P. A. van der Schaaf, Angew. Chem.
1997, 109, 2213–2216; Angew. Chem. Int. Ed. Engl. 1997, 36,
2121–2123.
[29] K. Matyjaszewski, Macromolecules 1993, 26, 1787–1788.
[30] C. W. Bielawski, R. H. Grubbs, Angew. Chem. 2000, 112, 3025–
3028; Angew. Chem. Int. Ed. 2000, 39, 2903–2906.
[31] J. O. Krause, K. Wurst, O. Nuyken, M. R. Buchmeiser, Chem.
Eur. J. 2004, 10, 777–784.
[32] G. K. Cantrell, S. J. Geib, T. Y. Meyer, Organometallics 2000,
[4] E. Lindner, S. Pautz, R. Fawzi, M. Steimann, Organometallics
1998, 17, 3006–3014.
19, 3562–3568.
[33] J. Zhang, T. B. Gunnoe, Organometallics 2003, 22, 2291–2297.
[5] A. Demonceau, A. W. Stumpf, E. Saive, A. F. Noels, Macro- [34] J. D. Rule, J. S. Moore, Macromolecules 2002, 35, 7878–7882.
molecules 1997, 30, 3127–3136.
[35] D. Wang, L. Yang, U. Decker, M. Findeisen, M. R. Buch-
meiser, Macromol. Rapid Commun. 2005, 26, 1757–1762.
[36] K. J. Ivin, J. Kress, J. A. Osborn, J. Mol. Catal. 1988, 46, 351–
358.
[37] E. Khosravi, A. A. Al-Hajaji, Polymer 1998, 39, 5619–5625.
[38] E. Khosravi, A. A. Al-Hajaji, Eur. Polym. J. 1998, 34, 153–157.
[39] R. A. Zelonka, M. C. Baird, Can. J. Chem. 1972, 50, 3063–
3072.
[40] A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652.
[41] A. D. Becke, J. Chem. Phys. 1996, 104, 1040–1046.
[42] C. T. Lee, W. T. Yang, R. G. Parr, Phys. Rev. B: Condens. Mat-
ter 1988, 37, 785–789.
[43] Jaguar, Schrodinger LLC, New York, 2005.
[44] W. R. Wadt, P. J. Hay, J. Chem. Phys. 1985, 82, 284–298.
[45] S. Fomine, S. M. Vargas, M. A. Tlenkopatchev, Organometal-
lics 2003, 22, 93–99.
[46] S. Fomine, J. V. Ortega, M. A. Tlenkopatchev, J. Mol. Catal. A
2005, 236, 156–161.
[47] S. Fomine, J. V. Ortega, M. A. Tlenkopatchev, Organometallics
2005, 24, 5696–5701.
[48] B. F. Straub, Angew. Chem. 2005, 117, 6129–6132; Angew.
Chem. Int. Ed. 2005, 44, 5974–5978.
[49] Z. Otwinowski, W. Minor, Methods in Enzymology, Academic
Press, New York, 1997, vol. 276.
[6] L. Jafarpour, J. Huang, E. D. Stevens, S. P. Nolan, Organome-
tallics 1999, 18, 3760–3763.
[7] L. Ackermann, C. Bruneau, P. H. Dixneuf, Synlett 2001, 3,
397–399.
[8] D. Sémeril, C. Bruneau, P. H. Dixneuf, Helv. Chim. Acta 2001,
84, 3335–3341.
[9] D. Sémeril, M. Cléran, C. Bruneau, P. H. Dixneuf, Adv. Synth.
Catal. 2001, 343, 184–187.
[10] D. Sémeril, C. Bruneau, P. H. Dixneuf, Adv. Synth. Catal. 2002,
344, 585–595.
[11] R. Castarlenas, I. Alaoui-Abdallaoui, D. Sémeril, B. Mernari,
S. Guesmi, P. H. Dixneuf, New J. Chem. 2003, 27, 6–8.
[12] L. Delaude, A. Demonceau, A. F. Noels, Chem. Commun.
2001, 986–987.
[13] L. Delaude, M. Szypa, A. Demonceau, A. F. Noels, Adv. Synth.
Catal. 2002, 344, 749–756.
[14] Y. Zhang, D. Wang, P. Lönnecke, T. Scherzer, M. R. Buch-
meiser, Macromol. Symp. 2006, 236, 30–37.
[15] T. Ung, A. Hejl, R. H. Grubbs, Y. Schrodi, Organometallics
2004, 23, 5399–5401.
[16] A. Hejl, M. W. Day, R. H. Grubbs, Organometallics 2006, 25,
6149–6154.
[17] P. A. van der Schaaf, R. Kolly, H. J. Kirner, F. Rime, A. Mühle-
bach, A. Hafner, J. Organomet. Chem. 2000, 606, 65–74.
[18] A. Hafner, P. van der Schaaf, A. Mühlebach, P. Bernhard, U.
Schaedeli, T. Karlen, A. Ludi, Prog. Org. Coat. 1997, 32, 89–
96.
[50] G. M. Sheldrick, Program package SHELXTL V.5.1, Bruker
Analytical X-ray Instruments Inc, Madison, USA, 1997.
Received: January 12, 2007
Published Online: July 6, 2007
4000
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 3988–4000