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One-Component Catalysts for Thermal and Photoinduced Ring Opening Metathesis Polymerization.

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a single diastereorner by chromatography. The sense of asymmetric induction in this cycloaddition is consistent with a Lewis
acid catalyzed Diels-Alder reaction on the s-cis ZnBr, complex 8a.
In analogy to previous experiments, Diels-Alder adduct 9
was transformed to the corresponding P-ketothioester in 90%
yield and smoothly decarboxylated (70 "C, 24 h) to afford ketone 10 in 86% yield without epimerization at the ring fusion.
The synthesis was completed by treatment of 10 with Tebbe
reagent"81 to afford synthetic a-himachalene (11) (92% yield),
whose spectroscopic and analytical data are identical in all respects to literature values ('HNMR, IR, TLC, [a]D).[151
The removable auxiliary X = COX, described here should
prove useful in enantioselective ketone-based bond constructions. Although the methodology has been highlighted with aldo1 and Diels-Alder reactions, absolute stereochemical control
of other transformations such as the Michael reaction should
also be possible. Studies extending the scope of these concepts
are currently underway.
Experimental Section
General one-flask procedure for the decarboxylation of b-ketoimides: A stirred
suspension of KH (1.2 mmol) in THF (10 mL) under argon was charged with EtSH
(1 3 mmol) and gas evolved. The white suspension was stirred for 1 h before a
solution of /I-oxoimide (1 mmol) in THF (10 mL) was added by cannula. The
reaction mixture was stirred until the starting material had been consumed. To the
reaction mixture was added water (4 mL) and 2,6-lutidine (10 mmol), followed by
AgNO, (2.5 mmol). The reaction mixture was protected from light and stirred for
two days. The pale yellow suspension was filtered through Celite with ether, and the
organic solution was extracted between ether (50 mL) and aqueous CuSO, solution
(50 mL). The ether layer was separated, dried over MgSO,, and concentrated in
vacuo. Chromatography on silica gel using an appropriate solvent mixture provided
pure ketone.
Received: April 7, 1997 [Z103131E]
German version: Angew. Chem. 1997, 109, 2208-2210
Keywords: aldol reactions chiral auxiliaries decarboxylations
Diels-Alder reactions himachalene
[I] S. Shambayati, S. L. Schreiber in Comprehensive Orgunic Spthesis, Vol. f
(Eds.: B. M Trost. 1. Fleming), Pergamon, New York, 1991, pp. 283-324.
[2] a ) D. Enders. B. B. Lohray, Angew Chem. 1988,100,594-596; Angew. Chem.
In[. Ed. Engl. 1988,27,581-582; b) B. B. Lohray, D Enders, Helr. Chim. Acta
1989. 72.980- 984; c) B. 8. Lohray, R. Zimbiniski, Tetrahedron Lerr. 1990.31,
7273 -7276.
[ 3 ] Another important approach to the construction of ketone-derived chiral auxiliaries has been through the use of chiral metalloenamines: a) S. F. Martin in
Comprehensiw Organic Synrhesis, Vol. 2(Eds.: B. M. Trost, 1. Fleming), Pergamon. New York, 1991, pp. 475-502.
[4] a) C. H. Heathcocb., M. C. Pirrung, C. T. Buse, J. P. Hagen, S. D. Young, J E.
Sohn. J Ani. Cheni. Sor. 1979, 101, 7017-7079; b) S. Masamune. W. Choy,
F. A. Kerdecky, B. Imperiali. J. Am. Chem. SOC.1981. 103, 1566-1568; c) S.
Masamune, L. A. Reed 111, J. T. Davis, W. Choy, J Org. Chem. 1983, 48.
[5] D A. Evans. M El. Ennis, T. Le. N Mandel, G. Mandel. J Am. Chsm. Soc.
1984. 106. 1 I54 I I56
[6] The experimental details for the synthesis o l 1 have been reported: D. A
Evans, H. P. Ng. J S. Clark, D. L. Rieger, Tetrahedron 1992, 48, 2127-2142.
[7] D. A. Evans. J. S. Clark, R. Metternich, V. J. Novack, G. S . Sheppard, J. Am.
Chrm. Sol. 1990, if2, 866-868.
I81 D.A Evans. E Uipi. T C. Somers. J. S. Clark, M. T Bilodeau, J. Am. Chem.
Sol. 1990. 112, 82'.5-8216.
[91 a ) D. A. Evans, H. P. Ng. D. L. Rieger, J. Am. Chem. Soc. 1993, fl5, 1144611459 (see the transformation 7 -18 in Scheme VIII); b) D. A. Evans, A. M.
Ratz. B E.Huff. C . S. Sheppard, J Am. Chem. SOC.1995,117,3448-3467 (see
the transformation 4 +.- 17 in Scheme VII).
[lo] Initial studies utilizing the Krapcho decarboxylation conditions (DMSO, H,O,
140 C ) on P-oxoiinide aldol adducts afforded only moderate yields of the
desired ketone products accompanied by significant amounts ofb-elimination:
a ) A P. Krapcho, Smrhesis 1982, 805-822. b) 893-914.
[I 11 R. E. Damon. G. lvl. Coppola, Terruhedron Lerr. 1990, 31, 2849-2852.
[12] a) E.J. Corey, bI. C Bock, Terrahedron Lrrr. 1975, 3269-3270, b) R.
Schwyzer. C . Hurlimann, Heir*. Chim. Acta 1954, f8, 155-166.
[131 Thiophenolate and 2-methyl-2-propanethiolate both failed to react, whde ben4 t h g o l a t r provides results comparable to those ofethanethiolate.
Angew Chem. In1 Ed. EngI 1997, 36, No. 19
[14] a ) J. L. Duffy, T. P. Yoon, D.A. Evans, Tetrahedron Lei1 1995.36,9245-9248:
b) D. A. Evans, M. G. Yang, M. J. Dart, J. L. Duffy, ihid. 1996,37, 1957- 1960;
c) D. A. Evans, M. G. Yang, M. J. Dart, J. L. Duffy, A. S. Kim. J. Am. Chem
Soc. 1995, 117,9598-9599; d) D. A. Evans, D. L. Rieger. M . T. Bilodeau, I:
Urpi,J Am. Chern.Soc. 1991,113,1047-1049;e)D. A Evans,M. J.Dart, J. L.
Duffy, D. L. Rieger, ibid. 1995,117,9073-9074.
[IS] a) T. C. Joseph, S. Dev, Tetrahedron Lerr. 1961,216-222, b) Terruhedron 1968,
24. 3841 -3852,3853-3859; c) W. Oppolzer, R. L. Snowden. Helv. Chim. Acru
1981, 64, 2592-2597; d) E. Wenkert, K. Naemura, Svnrh Comm. 1973, 3.
[16] D. A. Evans, J. Bartroli, T. L Shih, J. Am. Chem. Sor. 1981. 103, 2127-2129.
1171 J. R. Parikh, W. von E. Doering, J Am. Chem. Soc. 1967.89. 5505-5507.
[18] S. H. Pine, R. Zahler, D. A. Evans, R. H. Grubbs, J Am. Chim. Soc 1980,102,
3270- 3272.
One-Component Catalysts for Thermal and
Photoinduced Ring Opening Metathesis
Andreas Hafner,* Andreas Miihlebach, and
Paul A. van der Schaaf
New generations of stereospecific olefin polymerization catalysts have catapulted the polymer industry into a new area. A
large variety of thermoplastic materials, based on r-olefins, of
well-defined tacticity and block length are expected to be commercialized in the near future."] A similar development can be
foreseen for thermoset materials. In this respect ring opening
metathesis polymerization (ROMP)['] offers new types of polymers with attractive mechanical and electrical properties. Currently applied industrial catalysts for ROMP are multicomponent systems based on early transition metal complexes and
water-sensitive alkylaluminum cocatalysts. In the mid 1980s the
first well-defined, one-component catalysts for ROMP were developed by Osborn (e. g., [WC1,(=CHCMe,)(OR),])'3' and
Schrock (e. g., [Mo( =CHCMe,)( =NAr)(OR),]) .[41 However,
these catalysts are air- and moisture-sensitive as well, and
sparsely tolerate monomers bearing protic substituents, fillers,
or other additives.
In contrast to early transition metal catalysts, ruthenium- and
osmium-based complexes are water-stable and possess remarkable tolerance towards most functional groups.[5'Therefore, the
use of these catalysts goes far beyond the classical scope of
olefin-metathesis reactions.
When we started our work in the field of ROMP by studying
the reactivity of [Ru(H,0),l2+, we were able to prepare polymers and copolymers from cyclic olefins containing a large variety of functional groups.[61Using the concept of photoinduced
arene displacement, we developed the first photocatalysts for
ROMP (PROMP) by generating [Ru(H20)J2+ from [Ru(q6arene)2]2+.r7,A disadvantage of these catalysts is their cationic character, which restricts their applicability to polar environments, and their moderate reactivities. Therefore, we focused
our attention on more soluble and more active arene complexes
of ruthenium and osmium.
In 1992 Grubbs et al. reported the synthesis of the first welldefined, metathesis-active ruthenium -carbene complex by ring
opening of a substituted cyclopropene with [RuCl,(PPh,),] ,Ig1
Dr A. Hafner, Dr. A. Muhlebach, Dr. P. A. van der Schaaf
Ciba Specialty Chemicals Inc.
Additives Research
CH-1723 Marly 1 (Switzerland)
Fax: Int. code +(26)435-6219
e-maif : andreas.hafner@chma
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In 1995 Noels et al. reported the in situ formation of carbene
complexes from arene ruthenium phosphane complexes and
These studies showed that the
cone angle 8 of the coordinating phosphane determines the activity of the catalyst. We also investigated the photoactivity of a
series of arene ruthenium phosphane and arene osmium phosphane complexes." l ]
Osmium complexes of the type [Os(p-cymene)Cl,(PR,)]
(R=cyclohexyl (Cy; l), iPr (2), nBu (3), Ph (4), Me (9,
C,H4CH,-3 (m-Tol; 6)) do not initiate the thermal polymerization of norbornene (NBE). However, when they were activated
by UV irradiation (200-W Hg lamp, 5 min), active ROMP catalysts were obtained. The results of the photoinduced poIymerization of NBE in toluene initiated by 1-6 are depicted in Figure la. Figure 1b shows the comparison of ROMP and PROMP
activity for 1.
Active photocatalysts were obtained with the sterically demanding phosphane ligands PCy, and PzFr, (8 = 170 and 160",
respectively), whereas very slow or no polymerization was observed for complexes with less bulky phosphanes (PPh,, PnBu,,
or Pme,; 8 =145, 130, and 120", respectively). Surprisingly, 6
(8 = 165") was inactive as well.
The corresponding ruthenium complexes [Ru(p-cymene)Cl,(PR,)] (R = Cy (7), nBu (8), rn-Tol(9)) showed much higher
reactivity for NBE polymerization;
none of these complexes
was thermally latent towards NBE. Complex 7 was already
known to initiate NBE polymerization without activation of
diazomethane derivatives as cocatalyst (80 % poly(NBE) after
15 min at 50 "C) .I1
31 Both 8 and 9 yield traces of poly(NBE) after
1 h at 80°C. However, under similar conditions 8 yields 80%
poly(NBE) when irradiated for 5 min at room temperature.
The low reactivity of 6 and 9 can be explained by the work of
von Philipsborn et al.["'] The 1870sNMR chemical shift for
arene osmium phosphane complexes, including 1-6, correlates
extremely well with Toleman's steric parameter^."^^ The reported 0 for Prn-Tol, is 165", assuming C,, symmetry, whereas a
value of 150" was measured with the chemical-shift method.
This can be explained by a nonsymmetrical orientation of the
phenyl rings of the phosphane ligand in 9.[151To have direct
proof for the proposed importance of the steric parameters (for
example the asymmetry of the Pm-Tol, ligand), X-ray structure
determinations of 7 and 9 were carried out (Figure 2).[16]
c 31
c 31
tlrninFigure 1. a) Real-time viscosimetric measurements of the photopolymerization of
norborneneintoluene(10wt%)withl-6(2mol%each;o:R = Cy(1);o: R = iPr
(2); A: R = nBu (3);0 : R = Ph (4); 0 : R = Me (5). 0 :R = m-Tol(6)). b) Thermal
latency versus the photoactvity of 1 in the polymerization of norbornene ( A : 30 "C,
UV irradiation; o: SOT, without irradiation). V = viscosity (arbitrary units).
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
Flgure 2. Molecular structures of 7 (top) and 9 (bottom); hydl-ogen atoms are
ommited for clarity. In both cases only one of two molecules from the asymmetric
unit cell is depicted.
0570-OS33/97/3619-2122 $ 17.50+ S0/0
Angeu,. Chem. Int.
Ed. Engf. 1997,36, No. 19
The assumed asymmetry of the Pm-Tol, ligand was confirmed
with the molecular structure of 9: C33 points into the ligand
sphere of the phosphane, whereas C34 and C35 point outwards.
The larger tilting of the p-cymene ring relative to the Cl-C1-P
plane in 7 (6") than in 9 (1.5") can be explained by the steric
interaction with the more bulky PCy, ligand. This is also reflected by the fact that p-cymene is liberated at lower temperatures
from 7 (150°C) than from 8 and 9 (180 and 200 "C, respectively), as measured by differentia1 scanning calorimetry (DSC).
By allowing 7 1 0react with less reactive monomers we coincidentally found that it is a very efficient catalyst for the thermal,
solvent-free polymerization of dicyclopentadiene (DCPD) at
temperatures above 80 "C. This was completely unexpected,
since, to our knowledge, no ruthenium catalysts were known for
the polymerization of DCPD. In fact, it was reported that
DCPD is a poison for ruthenium-initiated ROMP." 'I Surprisingly, "solutions'" of 7 in DCPD are stable for weeks at room
temperature with no increase in viscosity. We think that the
active species is an arene-free ruthenium phosphane complex, as
described by Noels et al., formed by thermal arene displacement. Furthermore, the arene-free complexes [Ru(PCy,),(MeOH),Tos,] (10) and [RuCl,(PCy,),] (11) are also active with
Figure 3 shows a dynamic and isothermic DSC scan of the
DCPD polymeriza.tion initiated with 7 (0.3 wto/o). The exothermic curing reaction starts around 100 "C, and the curing heat
reaches a maximum of AH = 364 Jg-'. This AH value corresponds well to the theoretical value, calculated from the ring
strains of NBE and cyclopentene, for about 95% conversion
and a cross-link density of 10-20 O h for the polymer. This crosslink density is supported by swelling experiments of poly(DCPD) in toluene (weight increase of about 100%). Another
fascinating aspect of the DSC experiment is the flatness of the
curve up to 100 "C, which demonstrates the excellent latency of
the system at room temperature. Gel times of more than three
weeks at 20 "C, 270 min at 60 "C, 102 rnin at 70 "C, and 38 min
at 80 "C were determined with vicosimetric measurements under
the conditions described above. The isothermal DSC scan at
100°C shows a fast polymerization reaction with a peak maximum after 6min. At this temperature the polymerization is
completed after about 40 min.
Due to the amazing tolerance of 7 towards impurities and
water, we were able to incorporate almost any type of filler (for
example SO,, AI(OH),, A1 powder, or CaCO,) in amounts of
up to 70 wt YO; the good electrical and mechanical properties of
poly(DCPD) were thus preserved. These properties makes this
system extremely interesting for new types of thermosets. For
example, the dielectric constant for poly(DCPD) with quartz
powder (60 wtY0) is still as low as 3.3 with an E modulus of
6200 MPa. Poly(DCPD) loaded with A1 powder (60 wtoh) is a
perfect insulator with a surface resistivity of greater than lo1' R
up to 1000 V.[l91 Catalyst 7 even allows aqueous dispersion
polymerization of NBE and DCPD.[*''
The good mechanical properties of this material are partially
due to additional cross-linking of the cyclopentene ring. A second ring opening metathesis reaction is the accepted mechanism
for the cross-linking in poIy(DCPD) polymerized with early
transition metal catalysts.["] However, Wagener et al. recently
reported a model study from which they concluded that crosslinking occurs by a vinyl-addition reaction.[''] To elucidate the
structure of cross-linked poly(DCPD) obtained by solvent-free
polymerization of DCPD with 7 (0.3 wt%), I3C CP-MAS
NMR spectra of the material were measured (Figure 4). Inte-
Figure 4. "CP-MAS NMR spectrum of poly(DCPD); the asterisk indicates spinning side bands.
t l rnin
Figure 3. Dynamic (top) and isothermal DSC scan (bottom) of the polymerization
of DCPD initiated bq 7 (0.3 wt%). W = heat flow.
Angeu Chem Ini Ed E n d 1997.36, N o 19
gration of the olefinic and aliphatic "C signals provided a ratio
of exactly 2:3. This strongly suggests that in this case ring opening of the cyclopentene ring is the predominant cross-linking
mechanismpoly(DCPD) .
Polymers with two double bonds per repeat unit are supposed
to be oxidatively very unstable. However, almost no weight
loss ( < l o / , ) was measured for 4-mm plates of unstabilized
poly(DCPD) heated in air at 180°C for 100 days. We suppose
that the oxidized surface forms a dense layer which hinders 0,
penetration and therefore protects the deeper material from further oxidation. The thickness of this hard and dense oxide layer
was estimated to be about 4 gm from surface-roughness and
micro-hardness measurements.
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
0570-083319713619-2123S 17 SO+ SOjO
Due to the tolerance of catalyst 7 in combination with the
interesting properties of poly(DCPD), new filled or unfilled
thermosets could be prepared, which should find novel applications in the field of electro casting, insulation, and tooling
(among others) in the near future. Work to improve catalysts
and polymer systems are ongoing.
Experimental Section
The ruthenium and osmium complexes were prepared according to literature procedures [ll] . NBE was purchased from Fluka, and DCPD (technical quality, 94%)
from Shell and used as received. Viscosimetric measurements were performed on a
home-built, real-time viscosimeter. Gel times were recorded on a Brookfield viscosimeter, DSCs on a Mettler DSC30 with a Mettler T Cll controller, TGAs on a
Mettler TG50 with a Mettler TCfOA controller, and surface roughness on a Form
Talysurf S3C-50. Micro hardness was determined on a Fischerscope H100. I3C
CP-MAS NMR spectra of a piece of poly(DCPD) that was tightly fitted into the
spinner were recorded on a Bruker 400-MHz instrument with a MAS rate of 11 kHz
and a pulse delay of 5 s (a pulse delay of 60 s gave an identical result).
Received: March 17, 1997 [Z10252IE]
German version: Angeu. Chem. 1997, 109. 2213-2216
Keywords: metathesis
polymerization * ruthenium
. ring-opening
(I] a) J. Boor, Ziegler-Nuttu Catalysts and Polymerization, Academic Press, New
York, 1979; b) H. H. Brintzinger, D. Fischer, R. Miihlhaupt, B. Rieger, R.
Waymouth, Angew. Chem. 1995,107,1255; Angen. Chem. tnr. Ed. Engl. 1995,
34, 1143, and references therein.
[2] K J. Ivin, J. C. Mol, Olefin Metathesis andMetathesis Polmerizution, Academic
Press, London, 1996.
[3] a) J. Kress, J. A. Osborn, V. Amir-Ebrahimi, K J. Ivin, J. J. Rooney, J Chem.
Soc. Chem. Commun. 1988, 1164; b) J. Kress, J. A. Osborn, K. J. Ivin, ibid.
1989, 1234; c) K. J. Ivin. J. Kress, I. A. Osborn, J. Mol. C a d . 1988,46, 351;
d) R. M. E. Greene, K. J. Ivin, J. J. Rooney, J. Kress, J. A. Osborn, Makromol.
Chem. 1988, 189, 2797; e) R. M. E. Greene, K. J. Ivin, J. Kress, J. A. Osborn,
J. J. Rooney, British Polymer J. 1989, 21, 237.
[4] a) R. R. Schrock, Acc. Chem. Res. 1990, 23, 158; b) C. J. Schaverien, J. C.
Dewan, R. R. Schrock, J. Am. Chem. SOC.1986,108, 2771; c) R. R. Schrock,
R. T. DePue, J. Feldman, C. J. Schaverien, J. C. Dewan, A. H. Liu, ihid. 1988,
110, 1423; d) R. R. Schrock, J. Feldman, L. F. Cannizzo, R. H. Grubbs,
Macromolecules 1987, 20, 1172; e) R. R. Schrock, S. A. Krouse, K. Knoll,
J. Feldman, J. S. Murdzek, D. C. Yang, J Mol. Catul. 1988, 46, 243.
IS] a) B. M. Novak, R. H Grubbs, J. Am. Chem. SOC.1988, 110, 960; b) B. M.
Novak, R. H. Grubbs, ibid. 1988, 110. 7542; b) W. J. Feast, D. B. Harrison,
J Mol. Catul. 1991, 65,63.
[6] a) A. Miihlebach, P. Bernhard, N. Biihler, T. Karlen. A Ludi, J. Mol. C u r d
1994, 90, 143; b) A. Mhhlebach, U. Schadeli, Zrradiation of Polymers (Eds.:
R. L. Clough, S. W Shalaby), ACS Synip. Ser. 1996, 620, 364.
[7] a) A. Miihlebach, P. Bernhard, A. Hafner, T. Karlen, A. Ludi, (CibaGeigy AG), WO P a f . 95 07,310 1995 [Chem. Abstr. 1993, 123, 3148731;
b) T. Karlen, A. Ludi, A. Miihlebach, P. Bernhard. C. Pharisa. J: Polyrn. Sci.
Polym. Chem. Ed. 1995,33, 1665.
[S] Our second-generation PROMP catalysts are based on high-valent alkyl tungsten complexes. P. A. van der Schaaf, A. Hafner, A. Muhlebach, Angeu.
Chem. 1996, 108,1974; Angew. Chem., h i . Ed. Engl. 1996,35, 1845.
[9] a) S. T. Nguyen, L. K. Johnson, R. H. Grubbs, J. W. Ziller, J. Am. Chem. SOC.
1992, 114, 3974; b) S. T. Nguyen, R. H. Grubbs, J. W. Ziller, ibid. 1993, 115,
[lo] A. W. Stumpf, E. Saive, A. Demonceau, A. F. Noels, J. Chen?. SOC.Chem.
Commun. 1995, 1127.
I1 11 a) A. J. Lindsay, G. Wilkinson, M. Motevalli, M. B. Hursthouse. J. Chem. SOC.
Dalton Trans. 1985,2321 ; b) A. J Lindsay, G. Wilkinson, M. Motevalli, M. B.
Hursthouse, ibid. 1987, 2723; c) F. A. Cotton, V. M. Miskowski, B. Zhong,
J. Am. Chem. SOC.1989, l f f , 6177; d ) R. A. Zelonka, M. C. Baird, Can. J
Chern. 1972, 50, 3063, e) J. A. Cabeza, P. M. Maitlis, J. Chem. Soc. Dalton
Trans. 1985, 573; f) H. Werner, K. Zenkert, J Organomet. Chem. 1988,345,
151; g) W. A. Kiel, R. G. Ball, W. A. Graham, ibid. 1990, 383, 481; h) T.
Arthur, T. A. Stephenson, ibid. 1981, 208, 396; i) A. Bell, W. Kozminski,
A. Linden, W. von Philipsborn, Orgunometnl/ics 1996, 15, 3124.
I121 Reaction of NBE (0.5 g) and catalyst (0.6 wt%) in CHCI, (3 mL).
[13] A. Demonceau, A. F. Noels, E. Saive,A. J. Hubert, J. Mol. Catal. 1992,76,123.
[14] C. A. Toolman, Chem. Rev. 1977, 77, 313.
(151 On the basis of a nonsymmetrical arrangement of the phenyl rings, 0 = 148"
was calculated: D. White, N. J. Coville, J. Organomer. Chem 1992, 440. 15.
[16] Crystals of7.CH30H were grown by cooling a saturated solution in methanol
to -30"C;crystalsize0.90x0.36x0.12 mm; triclinic,spacegroupPT;Z = 4;
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
a = 20.148, b = 15.333, c = 10.337
c( = 89.41, B =102.34, y = 107.26";
V = 3046.2A3, poa,cd=l.336gcm-3; 6 5 2 8 5 4 4 " (Mo,,, i.=0.70926A,
graphite monochromator, 20-8 scan, T = 298 K); of 8003 reflections measured, 5879 were observed with F>3o>(F) Crystals of 9 were grown by
cooling a saturated solution in methanol to -30°C; crystal size
0.8 xO.3 xO.1 mm; monoclinic, space group P2,ln; Z = 8; n =17.632,
b = 18.450, c = 17.872
96.60"; V = 5775.4 A', psalsd= 1.402 gcm- ';
6 5 2 0 5 4 6 ' (Mo,,, i, = 0.70926
graphite monochromator, 20-0 scan,
T = 298K); of 8677 reflections measured, 6158 were observed with
F> 30>(F'. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-100452. Copies
of the data can be obtained free of charge on application to The Director,
CCDC, 12 Union Road, CambridgeCB21EZ, UK(fax: int.code +(1223)336033; e-mail:
[17] C. Tanielian, A. Kiennemann, T. Osparpucu, Can. J. Chem. 1979, 57, 2022.
[18] NBE (0.5 g) with 10 (5 ppm!) gave poly(NBE) quantitatively after 48 hr at
50 "C.
[19] Physical properties of poly(DCPD) filled with 60% quarz powder and unfilled
poly(DCPD) (values for the latter are given in parentheses): density: 1.64
(1.04) g ~ m - glass-transition
temperature, 120 (120) "C; e-modulus: 6200
(2020) MPa; elongation at break: 2.6 (14.5)%; double-torsion test: K,c: 3.0
(3.7) MPam-'!', GIc: 1300 (5800) Jm-*; coefficient of linear thermal expansion: 56-59 (109- 1 IS) ppm K; water absorption (10d at 23 "C): 0.06 (0.13)%;
dielectric constant (c, 50 Hz. RT): 3.3 (2.4).
[20] A. Miihlebach, P. A. van der Schaaf, A. Hafner, unpublished results.
[21] a) A. Bell, The Role of'Catalysts in Polymer Synthesis(Eds.: E. J. Vandenberg,
J. C Salamone), ACS Symp. Ser. 1992, 469, 21; b) R. A. Fischer, R. H.
Grubbs, Makromol. Chem. Mucromol. Symp. 1992, 63, 271.
[22] T. A. Davidson, K. B. Wagener. D. B Priddy, Macromolecules 1996, 29, 786.
The Amidinium- Carboxylate Salt Bridge as a
Proton-Coupled Interface to Electron Transfer
Yongqi Deng, James A. Roberts, Shie-Ming Peng,
C. K. Chang, and Daniel G. Nocera*
Proton motion coupled to electron transfer is a basic energy
conversion mechanism. Many proteins and enzymes function by
utilizing the energy gathered along a charge-separating network
to drive a proton pump, which in turn is manifested in a
transmembrane chemical potential that provides the energy for
the synthesis of complex biomolecules.[" Yet some thirty years
after Mitchell's initial proposal of proton translocation driven
by electron transfer,[*] the mechanistic details of how the eiectron couples to the proton remain undefined."". 31 To unravel
the relationship between the proton and the electron, we have
developed the following approach: electron transfer is photoinduced within photoexcitable electron donor-acceptor supramolecule complexes formed from the association of a proton
transfer interfa~e.'~]
We have concentrated on asymmetric inter[*] Prof. D G. Nocera
Department of Chemistry
Massachusetts Institute of Technology
77 Massachusetts Avenue, Cambridge, MA 02139-4307 (USA)
Fax: Int. code +(617)253-7670
e-mail: nocera(
Y Deng, J. A. Roberts, Prof. C . K. Chang
Department of Chemistry
Michigan State University
East Lansing. MI 48824 (USA)
Prof. S. M. Peng
Department of Chemistry
National Taiwan University
Taipei (Taiwan)
This work was supported financially by the National Institutes of Health (GM
47274). J. A. R. acknowledges support from the Carl H. Brubaker Jr Fellowship in Chemical Sciences
0570-083319713619-2124 $17.50+ .SO/O
Angew. Chem. tnt. Ed. Engl. 1997, 36, No. 19
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thermal, metathesis, one, photoinduced, opening, components, ring, catalyst, polymerization
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