Published on Web 07/07/2006
Rhodium-Mediated Stereoselective Polymerization of
“Carbenes”
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†
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Dennis G. H. Hetterscheid, Coen Hendriksen, Wojciech I. Dzik, Jan M. M. Smits,
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Ernst R. H. van Eck, Alan E. Rowan, Vincenzo Busico, Michele Vacatello,
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Valeria Van Axel Castelli, Annalaura Segre, Erica Jellema,
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Tom G. Bloemberg, and Bas de Bruin*
Contribution from the Institute for Molecules and Materials (IMM), Radboud UniVersity
Nijmegen, ToernooiVeld 1, 6525 ED Nijmegen, The Netherlands, Dipartimento di Chimica,
UniVersit a` di Napoli “Federico II”, Via Cintia, 80126 Naples, Italy, Istituto di Metodologie
Chimiche, CNR, 00016 Montelibretti, Italy, and Department of Homogeneous Catalysis,
Van ‘t Hoff Institute for Molecular Sciences (HIMS), UniVersity of Amsterdam,
Nieuwe Achtergracht 166, 1018 WV, Amsterdam, The Netherlands
Abstract: Unprecedented rhodium-catalyzed stereoselective polymerization of “carbenes” from ethyl
diazoacetate (EDA) to give high molecular mass poly(ethyl 2-ylidene-acetate) is described. The mononuclear,
I
neutral [(N,O-ligand)M (cod)] (M ) Rh, Ir) catalytic precursors for this reaction are characterized by (among
others) single-crystal X-ray diffraction. These species mediate formation of a new type of polymers from
EDA: carbon-chain polymers functionalized with a polar substituent at each carbon of the polymer backbone.
The polymers are obtained as white powders with surprisingly sharp NMR resonances. Solution and solid
state NMR data for these new polymers reveal a highly stereoregular polymer, with a high degree of
crystallinity. The polymer is likely syndiotactic. Material properties are very different from those of atactic
poly(diethyl fumarate) polymer obtained by radical polymerization of diethyl fumarate. Other diazoacetates
are also polymerized. Further studies are underway to reveal possible applications of these new materials.
Introduction
synthesis. The most frequently observed reactions include
carbene dimerization to form olefins, carbene transfer to olefins
The thermal decomposition of diazomethane (reported around
in cyclopropanation reactions, and carbene insertion into O-H,
N-H, and C-H bonds. The reactions are often mediated by
transition metals such as platinum, copper, rhodium acetates,
and ruthenium catalysts, which have been reported to give
efficient and, in many cases, stereoselective conversion of the
carbenoid to more or less sophisticated products.7 In this
framework, though, only three reports describe the polymeri-
zation (oligomerization) of R-carbonyl stabilized “carbenes”
from diazocarbonyl compounds. This concerns Cu- and Pd-
mediated formation of low molecular mass polymers (oligomers)
from alkyl diazoacetates and related diazocarbonyls (number
1
1900) is the first known route to polymethylene. Neither this
2
explosive process, however, nor the milder catalytic versions
ever found large scale practical applications, and it was more
than half a century later that transition metal mediated ethene
polymerization gave easy access to linear polyethylene.
Unlike the inherently unstable diazoalkanes, diazocarbonyl
compounds such as diazoacetates (N2CHCO2R) are reasonably
stable, safe (even in large scale/industrial synthesis), easy to
3
4
,5
6
prepare, and extensively used as carbene precursors in organic
†
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Radboud University Nijmegen.
Universit a` di Napoli “Federico II”.
Istituto di Metodologie Chimiche.
University of Amsterdam.
8,9
average degree of polymerization up to ca. 100). These
materials are notable because they carry a polar functionality
(
1) (a) von Pechmann, H. Ber. Dtsch. Chem. Ges. 1898, 31, 2643. (b)
Bamberger, E.; Tchirner Ber. Dtsch. Chem. Ges. 1900, 33, 956.
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7
1
1
7, 206-210. (b) Bahwn, C. E. H.; Ledwith, A.; Matthies, P. J. Pol. Sci.
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(
3) For recent studies on polymethylene synthesis, see the following. (a) Via
decomposition of diazomethane on TM surfaces: Bai, D.; Jennings, G. K.
J. Am. Chem. Soc. 2005, 127, 3048. (b) Via boron-catalyzed polymerization
of sulfoxonium ylides: Busch, B. B.; Paz, M..M.; Shea, K. J.; Staiger, C.
L.; Stoddard, J. M.; Walker, J. R.; Zhou, X.-Z.; Zhu, H. J. Am. Chem. Soc.
2
002, 124, 3636-3646 and references therein.
(
4) Ziegler-Natta catalyst: (a) Ziegler, K.; Breil, H.; Martin, H.; Holzkamp,
R. German Patent 973726, 1953. (b) Natta, G.; Pino, P.; Mazzanti, G. U.S.
Patent 3715344, 1954. (c), Natta, G. J. Polym. Sci. 1955, 16, 143-154.
5) Phillips catalyst: Hogan, J. P.; Banks, R. L. U.S. Pattent 2,825,721, 1985.
(
(b) McDaniel, M. P. AdV. Catal. 1995, 33, 47-98.
9746
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J. AM. CHEM. SOC. 2006, 128, 9746-9752
10.1021/ja058722j CCC: $33.50 © 2006 American Chemical Society