Full text of DOI:10.1002/1521-3773(20010601)40:11<2153::AID-ANIE2153>3.0.CO;2-W

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and Zimmerman and Corbin[11] have developed heterocycles
that dimerize strongly through an array of four hydrogen
bonds arranged in a self-complementary donor-donor-accept-
or-acceptor (DDAA) manner. For example, 2-ureido-4[1H]-
pyrimidinones[12] structurally similar to the one pictured in
Figure 1 exhibit the dimerization constant Kdimer of 6Â
Polymerization of Ureidopyrimidinone-
Functionalized Olefins by Using Late-
Transition Metal Ziegler± Natta Catalysts:
Synthesis of Thermoplastic Elastomeric
Polyolefins**
1
1
Lee R. Rieth, Robert F. Eaton, and
Geoffrey W. Coates*
107 m
(in chloroform) and 6 Â 108 m
(in toluene) at
298 K.[9] Meijer, Sijbesma, and co-workers have demonstrat-
ed that telechelic oligomers with these 2-ureido-4[1H]-pyr-
imidinone endgroups self-assemble into supramolecular
structures that behave like high molecular weight poly-
mers;[8, 13±15] further stabilization by phase separation is not
observed.[16]
Many natural and synthetic polymers derive their unique
functions and precise structures from hydrogen bonding. The
double-helix conformation of DNA and the secondary
structures of many proteins, both vital to the central
mechanisms of living organisms, depend strongly upon the
formation of specific hydrogen bonds. The amazing tensile
strength and elasticity observed in spider silk results from
strong intra- and intermolecular hydrogen bonds that stabilize
the formation of helices and b-sheets.[1] Hydrogen bonding
between polymer chains also dictates the mechanical proper-
ties of many synthetic polymers: the high tensile strength of
aromatic polyamides[2] and the elastomeric properties of
polyurethane block copolymers[3] arise from intermolecular
hydrogen bonding.
nPr
H
O
N
nPr
N
nBu
N
H
N
H
N
O
-1
M
Kdimer > 107
CDCl3
H
O
N
2
H
N
H
N
nBu
O
N
N
N
H
O
nBu
H
N
O
UPcap
H
nPr
Figure 1. Quadruple hydrogen bonding of 2-ureido-4[1H]-pyrimidinones.
The introduction of hydrogen bonding arrays into poly-
olefins is particularly attractive.[4] The nonpolar environment
of the polyolefin matrix helps overcome the relative weakness
of hydrogen bonds (compared to covalent bonds) and the
entropic barrier to formation of hydrogen bond aggregates.
Stadler et al. have shown that the hydrogen-bonding inter-
actions of (4-carboxyphenyl)urazole moieties grafted onto
polybutadiene significantly affect the properties of the bulk
polymer due to the formation of a thermoreversible net-
work.[5] This system relies on highly ordered urazole junction
zones which phase separate from the amorphous polymer; the
hydrogen-bonding interactions between urazole groups are,
We are investigating the utility of 2-ureido-4[1H]-pyrimi-
dinone derivatives as reversible crosslinks in polyolefin
elastomers. Herein we report a simple method for randomly
incorporating small percentages of olefinic 2-ureido-4[1H]-
pyrimidinone (UP) derivatives within the main chain of
amorphous polyolefins. The resulting pendant UP groups
dimerize within the purified polymer matrix to form a
reversible network,[8, 16] with properties strikingly different
from those of comparable polyolefin homopolymers.
To synthesize these novel materials, we employ a coordi-
nation polymerization route utilizing catalyst precursor 1
(Figure 2), recently developed by Brookhart et al. for poly-
merization of a-olefins.[17±19] These catalysts undergo b-
1
individually, fairly weak (Kdimer < 102 m in chloroform for
typical donor± acceptor dimers).[6]
Recent interest in the development of supramolecular
polymers[7] has led to synthesis of complementary hydrogen
bonding arrays with extremely high dimerization constants in
nonpolar environments. Meijer, Sijbesma, and co-workers[8±10]
y
1) UPcap, Et2AlCl
2)
x
y
+
x
7
7
[*] Prof. G. W. Coates, L. R. Rieth, R. F. Eaton
Department of Chemistry and Chemical Biology, Baker Laboratory
Cornell University
H
H
iPr
iPr
iPr
iPr
O
N
O
N
N
N
nBu
nBu
N
H
N
H
N
O
Ni
N
N
H
N
O
Ithaca, NY 14853-1301
H
Br
Br
Fax : (‡1)607-255-4137
UPmon
1
coP
E-mail: gc39@cornell.edu
[**] This work was supported by the Eastman Chemical Company and the
Cornell Nanobiotechnology Center (which is supported in part by the
STC Program of the National Science Foundation (NSF); ECS-
9876771). This work made use of the Cornell Center for Materials
Research Shared Experimental Facilities, supported through the NSF
Materials Research Science and Engineering Centers program
(DMR-0079992). G.W.C. gratefully acknowledges a David and Lucile
Packard Foundation Fellowship in Science and Engineering, an Alfred
P. Sloan Research Fellowship, an NSF CAREER Award (CHE-
9875261), an Arnold and Mabel Beckman Foundation Young Inves-
tigator Award, a Camille Dreyfus Teacher-Scholar Award, a 3M
Untenured Faculty Grant, and a Union Carbide Innovation Recog-
nition Award. We thank Prof. E. W. Meijer and Dr. S. R. Turner and
Dr. P. B. Mackenzie for helpful discussions.
H
O
N
nBu
N
H
N
H
N
O
Figure 2. Synthesis and schematic drawing of 2-ureido-4[1H]-pyrimidi-
none-functionalized poly(1-hexene) (coP). The structure of the copolymer
is more complicated than depicted due to chain-walking by the catalyst
during polymerization, resulting in random branching in the main chain.
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hydride elimination followed by reinsertion (chain-walking)
on a time scale faster than propagation, giving rise to unique,
branched polyolefin architectures. Due to the low oxophilicity
of nickel, they are also tolerant of functional Lewis basic
groups, and are used here to copolymerize olefins with small
amounts of UPmon (typically 2%). Initial efforts have focused
on 1-hexene as the primary comonomer. The relative rates of
polymerization of 1-hexene and UPmon are similar, ensuring
that random copolymers are formed. Diethylaluminum chlor-
ide (Et2AlCl) serves two purposes in this reaction. First, it
activates the nickel catalyst precursor and serves as a weakly
coordinating counteranion for the resultant cationic alkyl-
nickel catalyst. Second, the aluminum reacts with UP
derivatives, removing acidic hydrogens and protecting Lewis
basic sites from reaction with the Ni center.[20] Initial efforts to
copolymerize 1-hexene and UPmon led to precipitation of the
growing polymer during the reaction. We attribute this
phenomenon to the ability of aluminum to coordinate more
than one UP molecule, leading to formation of Al/UP clusters
and an insoluble network. The presence of three equivalents
of non-olefinic UP (UPcap) during the polymerization pre-
vents formation of an insoluble network and leads to a
homogeneous solution throughout the reaction. Subsequent
precipitation of the copolymer with acidic methanol displaces
aluminum and returns the UP derivatives to their original
state. UPcap and aluminum remain in solution and are
eliminated from the polymer.
viscosity of toluene solutions of homopolymer hP2 (Table 1)
increases linearly with concentration (Figure 3). Solutions of
coP2, however, show exponential increase in viscosity with
increasing concentration. This phenomenon reveals the
Table 1. Homopolymers and UP-copolymers of 1-hexene prepared by
using the Et2AlCl-activated (a-diimino)NiBr2 complex 1.
[b]
[b]
Sample
%UP in polymer[a]
Mn
Mw/Mn
hP1
hP2
coP1
coP2
coP3
0
0
2.1
1.9
2.0
39000
104000
33000
74000
104000
1.6
1.2
1.4
1.3
1.2
[a] % mol of UP versus 1-hexene; determined by UV absorption.
[b] Determined by using GPC versus monodisperse polystyrene standards.
To investigate the nature of the reaction between UP and
the aluminum cocatalyst, UPcap was stirred with Et2AlCl
overnight; the reaction was then quenched with HCl/H2O.
The resulting organic-soluble product, recovered in 85%
yield, proved to be UPcap (by 1H NMR spectroscopy), thereby
verifying that comonomer UPmon returns to its original state
after the acidic quench. In a similar experiment, the reaction is
instead quenched with DCl/D2O; 1H NMR spectroscopy
reveals a considerable decrease in the intensities of shifts of
protons attached to the urea and pyrimidine nitrogen atoms.
These sites, which pose the biggest threat to the activity of the
Ni catalyst,[19] are apparently protected by aluminum during
the polymerization.
Figure 3. Relative viscosity (hrel, versus pure toluene) of toluene solutions
&
of homopolymer hP2 (Â), copolymer coP2 ( ), and coP2 with three molar
*
equivalents of UPcap
(
) at various concentrations.
NMR spectroscopy and gel permeation chromatography
(GPC) studies provide evidence that UP is incorporated into
the polymer and forms reversible crosslinks in solution. The
proton NMR spectrum of the copolymer shows the same
peaks above d ˆ 2.0 found in the spectrum of UPmon (in its
H-bonded dimer form), except the olefin peaks have disap-
peared. This suggests that UPmon has been incorporated into
the polymer, and the incorporated UP groups are dimerizing
(i.e. forming crosslinks). Furthermore, the GPCꢁs UV detec-
tor (254 nm) generates a signal at the same elution volume as
the RI-detected polymer, demonstrating that the chromo-
phoric UP moiety must be covalently attached to the polymer
backbone. Poly(1-hexene) homopolymer, made by homopo-
lymerization of 1-hexene under the same conditions, shows no
significant UV absorption. NMR and GPC studies also verify
the complete elimination of UPcap from the copolymer after
precipitation.
reversible nature of the UP crosslinks: at low copolymer
concentrations, the equilibrium concentration of dimerized
units is low, and the polymer behaves like the homopolymer.
At higher copolymer concentration, the equilibrium concen-
tration of dimerized units is high, and the effective molecular
weight dramatically increases, leading to a large increase in
viscosity. In fact, dissolving even higher concentrations of
1
coP2 in toluene (>20 gL ) leads to gelation.
Addition of three equivalents of UPcap to solutions of the
copolymer coP2 completely eliminates the crosslinking effect
of the attached UP groups. This solution displays a viscosity
profile very similar to the homopolymer hP2 (Figure 3). The
1
viscosity of an 8.0 gL solution of coP2 in toluene rapidly
decreases as UPcap is added, approaching near constant
viscosity at UPcap/UPpol ˆ 1. These experiments suggest that
individual sets of hydrogen-bonded dimers are the predom-
inant source of network formationÐstacks or clusters of UP
moieties would not be completely broken down by the
presence of UPcap, and must therefore not be a significant
Viscosity experiments support our assertion that pendant
UP groups dimerize strongly in solution. As expected, the
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source of crosslinking.[8, 14, 15] The clear, colorless appearance
of the bulk copolymer further supports this assessment.
While the solution properties of the copolymer are intrigu-
ing, the primary motivation for this research was to demon-
strate that the bulk copolymer forms an amorphous network
with elastomeric properties. Consequently, tensile tests were
performed on films of homopolymer and copolymer. Low
molecular weight homopolymer hP1, a waxlike material,
displayed tensile properties typical of a viscous liquid (Fig-
ure 4). After initial deformation associated with uncoiling the
Experimental Section
Synthesis: Catalyst 1,[17] monomer UPmon [15] and UPcap[10] were synthesized
,
by using modifications of literature preparations. Diethylaluminum chlor-
ide (1.8m in toluene) was purchased from Aldrich. Toluene and 1-hexene
were distilled from sodium benzophenone ketyl and 4 Š molecular sieves,
respectively, and degassed by three freeze/pump/thaw cycles prior to use.
All polymerizations were conducted under nitrogen using glovebox and
Schlenk techniques. Reaction conditions: UPmon (0.30 g, 0.80 mmol) and
UPcap (0.60 g, 2.4 mmol) were dissolved in toluene (75 mL). 1.8m Et2AlCl
(10.0 mL) was added, and the resulting solution was stirred for 15 min.
1-Hexene (5.0 mL, 40.0 mmol) was added, followed by Ni catalyst (20 mg)
dissolved in toluene (25 mL). The reaction mixture was stirred at 08C (high
molecular weight) or room temperature (lower molecular weight) for 20 h.
The reaction was then quenched by slowly adding acidic methanol
(100 mL; 1% HCl v/v), which caused the polymer to precipitate. The
polymer was isolated (by decanting), washed with methanol, and dried in
vacuo at 808C overnight. Residual aluminum was removed by redissolving
the polymer in toluene (200 mL) and refluxing overnight with acidic
methanol (20 mL; 5% HCl); then the polymer was reisolated by concen-
trating in vacuo and precipitating with excess methanol. Yields ranged
between 75% and 80%.
Characterization of coP1 ± 3: 1H NMR (300 MHz, [D8]toluene): d ˆ 13.4 (s,
ˆ
1H; NH), 12.3 (s, 1H; NH), 10.9 (s, 1H; NH), 5.7 (s, 1H; CH), 3.4 (t, 2H;
ˆ
CH2NHC( O)), 0.8 ± 1.8 (m; aliphatic CH, CH2, CH3). Molecular weights
and molecular weight distributions were determined by gel permeation
chromatography using THF solution versus polystyrene standards. Incor-
poration of UP monomer was determined by UV absorption at 245 nm in
chloroform. Elemental analysis for residual aluminum (<0.02%) was
performed by Desert Analytics. Viscosity measurements were performed
by using a Canon 0B C202 Ubbelohde viscometer at 30.08C. Toluene
solutions of the compounds were filtered through glass wool prior to
testing. Relative viscosities are based on pure toluene. Tensile measure-
ments were performed at an extension rate of 100 mmmin 1. Films were
prepared by solvent evaporation from chloroform solutions, and samples
were subsequently cut into strips (typical cross sections ˆ 5.0 mm Â
0.20 mm; clamp distance ˆ 25.0 mm).
Figure 4. Stress ± strain data for hP1, coP1, hP2, and coP3 (X ˆ nominal
stress; E ˆ percent elongation).
Received: February 12, 2001 [Z16601]
amorphous polymer chains, the stress required to continue
elongation increased minimally. The lack of strong intermo-
lecular forces allows the chains to freely reptate under low
stresses. In contrast, coP1 displayed an elastomeric tensile
profile: initial elongation again occurs at low stresses because
the amorphous polymer chains can easily uncoil. However,
crosslinks inhibit the chains from moving past each other. As a
result, stresses required to continue deformation increase
dramatically once chains have uncoiled; bond stretching and
bond angle deformation become the principle routes to
further elongation.[21] Thus, much higher stresses are observed
at rupture. Higher molecular weight polymers hP2 and coP3
showed similar behavior under tension, except stresses and
elongations were considerably higher at rupture, which we
attribute to the increased intermolecular interactions of
longer chains.
[1] Y. Termonia, Macromolecules 1994, 27, 7378; A. H. Simmons, C. A.
Michal, L. W. Jelinski, Science 1996, 271, 84.
[2] E. Baer, A. Moet, High Performance Polymers: Structure, Properties,
Composites, Fibers, Oxford University Press, New York, 1991.
[3] G. Oertel, Polyurethane Handbook: Chemistry, Raw Materials,
Processing, Application, Properties, Macmillan, New York, 1985.
[4] R. F. M. Lange, E. W. Meijer, Macromolecules 1995, 28, 782; M.
Â
Müller, A. Dardin, U. Seidel, V. Balsamo, B. Ivan, H. W. Spiess, R.
Stadler, Macromolecules 1996, 29, 2577.
[5] C. Hilger, R. Stadler, Macromolecules 1992, 25, 6670; C. Hilger, L. L.
de Lucca Freitas, R. Stadler, Polymer 1990, 31, 818; C. Hilger, R.
Stadler, Polymer 1991, 32, 3244; C. Hilger, R. Stadler, Makromol.
Chem. 1990, 191, 1347; C. Hilger, M. Draeger, R. Stadler, Macro-
molecules 1992, 25, 2498; C. Hilger, R. Stadler, Macromolecules 1990,
23, 2095.
[6] S. Zimmerman, T. Murray, Philos. Trans. R. Soc. London A 1993, 345,
49.
In conclusion, we report a convenient, one-pot synthesis of
a new polyolefin elastomer. The polymer utilizes strongly
dimerizing hydrogen-bonding arrays to form noncovalent
crosslinks within the polymer matrix. The bulk polymer
displays elastomeric properties at room temperature, verify-
ing the formation of a network. Viscosity tests show, however,
that the crosslinks are reversible: the copolymers are soluble
in chloroform and toluene, and addition of small amounts of
endcapper leads to dramatic decreases in viscosity. Studies of
the thermomechanical properties of the polymer are under-
way.
[7] For an overview of supramolecular polymers, see: D. C. Sherrington,
K. A. Taskinen, Chem. Soc. Rev. 2001, 30, 83; V. Percec, W. D. Cho, G.
Ungar, D. J. P. Yeardley, Angew. Chem. 2000, 112, 1661; Angew. Chem.
Int. Ed. 2000, 39, 1597; L. Brunsveld, B. J. B. Folmer, E. W. Meijer,
MRS Bull. 2000, 25, 49; J. M. Lehn, Supramolecular ChemistryÐ
Concepts and Perspectives, VCH, Weinheim, 1995; N. Zimmerman,
J. S. Moore, S. C. Zimmerman, Chem. Ind. 1998, 15, 604; Supra-
molecular Polymers (Ed.: A. Ciferri), Marcel Dekker, New York,
2000; E. A. Archer, H. Gong, M. J. Krische, Tetrahedron 2001, 57,
1139.
[8] R. P. Sijbesma, F. H. Beijer, L. Brunsveld, B. J. B. Folmer, J. H. K. K.
Hirschberg, R. F. M. Lange, J. K. L. Lowe, E. W. Meijer, Science 1997,
278, 1601.
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8H2O] at 10008C[5] or by calcining zirconium hydroxide in
O2 at 5008C.[1g, 3a] Base-assisted hydrolysis of organozirconium
chlorides results in the formation of organozirconium oxide
complexes containing chloride or hydroxide ligands, such as
[(Cp2ZrCl)2(m-O)],[6] [{(Cp*ZrCl)(m-OH)}3(m3-OH)(m3-O)] ´
2THF,[7] [{(Cp*ZrCl)(m-OH)}3(m3-O)(m-Cl)].[8] To the best of
our knowledge so far no larger aggregate of an organo-
zirconium oxide has been isolated or detected.
[9] S. H. M. Söntjens, R. P. Sijbesma, M. H. P. van Genderen, E. W.
Meijer, J. Am. Chem. Soc. 2000, 122, 7487.
[10] F. H. Beijer, R. P. Sijbesma, H. Kooijman, A. L. Spek, E. W. Meijer, J.
Am. Chem. Soc. 1998, 120, 6761.
[11] P. S. Corbin, S. C. Zimmerman, J. Am. Chem. Soc. 1998, 120, 9710.
[12] For other recent work utilizing UP groups in organic chemistry, see:
Â
Â
J. J. Gonzalez, S. Gonzalez, E. M. Priego, C. Luo, D. M. Guldi, J.
Â
de Mendoza, N. Martín, Chem. Commun. 2001, 163; J. J. Gonzalez, P.
Prados, J. de Mendoza, Angew. Chem. 1999, 111, 546; Angew. Chem.
Â
Int. Ed. 1999, 38, 525; M. T. Rispens, L. Sanchez, J. Knol, J. C.
We are interested in studying the products formed by the
reaction of early transition metal compounds in the liquid
ammonia/toluene two-phase system. Recently we reported
on the reaction of [L2TiCl2] (L ˆ p-MeC6H4C(NSiMe3)2)
with NaNH2 in liquid ammonia and toluene[9] to yield
[(LTi)6(m3-N)2(m3-NH)6] ´ 6(C7H8), and on the formation of
[{(MeC5H4)Zr}5(m5-N)(m3-NH)4(m-NH2)4] from the reaction of
[(MeC5H4)2ZrCl2] with K in liquid ammonia and toluene.[10]
The imido-bridged dinuclear zirconium complex [{(h3-L')Zr(m-
NH)}2] (L' ˆ (tBuNP)2(tBuN)2) was obtained by treating
[L'ZrCl2] with KH in liquid ammonia and toluene.[11] These
results prompted us to attempt the complete hydrolysis of
metal chlorides, which is difficult to achieve under base-
assisted conditions at low temperatures.
Hummelen, Chem. Commun. 2001, 161.
[13] B. J. B. Folmer, E. Cavini, R. P. Sijbesma, E. W. Meijer, Chem.
Commun. 1998, 1847; A. El-ghayoury, E. Peeters, A. P. H. J. Schen-
ning, E. W. Meijer, Chem. Commun. 2000, 1969.
[14] B. J. B. Folmer, R. P. Sijbesma, R. M. Versteegen, J. A. J. van der Rijt,
E. W. Meijer, Adv. Mater. 2000, 12, 874.
[15] J. H. K. K. Hirschberg, F. H. Beijer, H. A. van Aert, P. C. M. M.
Magusin, R. P. Sijbesma, E. W. Meijer, Macromolecules 1999, 32, 2696.
[16] R. F. M. Lange, M. Van Gurp, E. W. Meijer, J. Polym. Sci. A 1999, 37,
3657.
[17] L. K. Johnson, C. M. Killian, M. Brookhart, J. Am. Chem. Soc. 1995,
117, 6414.
[18] C. M. Killian, D. J. Tempel, L. K. Johnson, M. Brookhart, J. Am.
Chem. Soc. 1996, 118, 11664; S. A. Svejda, L. K. Johnson, M.
Brookhart, J. Am. Chem. Soc. 1999, 121, 10634; D. P. Gates, S. A.
Ä
Svejda, E. Onate, C. M. Killian, L. K. Johnson, P. S. White, M.
Brookhart, Macromolecules 2000, 33, 2320.
[19] S. D. Ittel, L. K. Johnson, M. Brookhart, Chem. Rev. 2000, 100, 1169.
[20] S. G. Correia, M. M. Marques, J. R. Ascenso, A. F. G. Ribeiro, P. T.
Gomes, A. R. Dias, M. Blais, M. D. Rausch, J. C. W. Chien, J. Polym.
Sci. A 1999, 37, 2471; for a review of efforts to utilize alkylaluminum
compounds as protecting groups for amines and amides in olefin
copolymerization using other catalyst systems, see: B. M. Novak, L. S.
Boffa, Chem. Rev. 2000, 100, 1479.
Herein we report on the reaction of [(EtMe4C5)ZrCl3] (1)
with H2O (1:1.5 molar ratio) in toluene at room temperature
with successive treatment by KH (1:3 molar ratio) in liquid
ammonia and toluene at 788C. The strong basic reagent KH
affords the complete removal of chloride and the formation of
the organozirconium oxide 2 [Eq. (1)]. The influence of the
solvent on the solid-state structure of 2 was demonstrated by
recrystallization of 2 from mesitylene which gave cluster 3
[Eq. (2)].
[21] N. M. Bikales, Mechanical Properties of Polymers, Wiley-Interscience,
New York, 1971.
1: toluene; RT; 2 h
2: 18 KH; liq: NH3
;
toluene; 78 oC:
Base-Assisted Formation of Organozirconium
Oxides with the [Zr6(m6-O)(m3-O)8] Core
Structure**
6[(EtMe4C5)ZrCl3] ‡ 9H2O
(1)
(2)
!
[{(EtMe4C5)Zr}6(m6-O)(m3-O)8] ´ C7H8
1
‡ 18KCl ‡ 18H2
2
mesitylene
[{(EtMe4C5)Zr}6(m6-O)(m3-O)8] ´ C7H8
!
Guangcai Bai, Herbert W. Roesky,* Peter Lobinger,
Mathias Noltemeyer, and Hans-Georg Schmidt
toluene
2
[{(EtMe4C5)Zr}6(m6-O)(m3-O)8]´C9H12
3
Dedicated to Professor Dieter Sellmann
on the occasion of his 60th birthday
A proposed mechanism for the formation of 2 is given in
Equations (3) ± (8) (Cp' ˆ EtMe4C5; X ˆ Cl, NH2, or OH).
The first step of the reaction involves the formation of the
water adduct 4 [Eq. (3)]. The acidic nature of the hydrogen
atoms of the coordinated H2O results in hydrogen chloride
elimination under formation of ammonium chloride in the
presence of NH3 [Eq. (4)]. We were unable to isolate 2 from
the reaction of 1 with H2O in liquid ammonia and toluene.
Excess of ammonia does not result in a complete hydrolysis of
1. Partial hydrolysis and ammonolysis have been also ob-
served in the base-assisted hydrolysis of [Cp*ZrCl3][7, 8] and
the ammonolysis of ZrX4 (X ˆ Cl, Br) in liquid NH3.[12] In the
presence of KH, NH4Cl is converted to KCl and hydrogen
[Eq. (5)]. On the other hand KH reacts with ammonia under
formation of KNH2 and hydrogen [Eq. (6)].[13] Moreover, we
have shown that KNH2 reacts with a compound containing a
Zr Cl bond to yield the amide [Eq. (7)].[10] Due to the Lewis
acidity of the ZrIV center, the OH group functions as an acid
Zirconium oxides have long-been used as catalysts for the
hydrogenation of carbon monoxide[1] and ethylene,[2] the
highly selective isomerization of 1-butene and the formation
of 1-butene from 2-butanol or 2-butanamine,[3] and the
selective oxidation of hydroxy-containing organic compounds.[4]
In general, complete hydrolysis of zirconium chlorides leading
to zirconium oxides without an appreciable amount of chloride
and hydroxide is difficult to achieve and only possible at very
high temperatures. ZrO2 is prepared by treating [ZrOCl2 ´
[*] Prof. H. W. Roesky, G. Bai, P. Lobinger, M. Noltemeyer,
H.-G. Schmidt
Institut für Anorganische Chemie der Universität
Tammannstrasse 4, 37077 Göttingen (Germany)
Fax : (‡49)551-39-3373
E-mail: hroesky@gwdg.de
[**] This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
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