CO2 and SnII adducts of N-heterocyclic carbenes as delayed-action catalysts for polyurethane synthesis

Article abstract of DOI:10.1002/chem.200802670

A series of CO₂-protected pyrimidin-2-ylidenes as well as 1,3-dimesitylimidazol-2-ylidene and dimesitylimidazolin-2-ylidene complexes of Sn^II have been prepared. Selected single-crystal X-ray structures are reported. The new compound

Full text of DOI:10.1002/chem.200802670

FULL PAPER
DOI: 10.1002/chem.200802670
CO2 and SnII Adducts of N-Heterocyclic Carbenes as Delayed-Action
Catalysts for Polyurethane Synthesis
Bhasker Bantu,[a] Gajanan Manohar Pawar,[a] Ulrich Decker,[a] Klaus Wurst,[c]
Axel M. Schmidt,[b] and Michael R. Buchmeiser*[a, d]
Abstract: A series of CO2-protected
pyrimidin-2-ylidenes as well as 1,3-di-
mesitylimidazol-2-ylidene and dimesi-
tylimidazolin-2-ylidene complexes of
SnII have been prepared. Selected
single-crystal X-ray structures are re-
ported. The new compounds were in-
vestigated for their catalytic behavior
in polyurethane (PUR) synthesis. All
compounds investigated showed excel-
lent catalytic activity, rivaling the in-
dustrially most relevant catalyst di-
nounced latent behavior, in selected
cases rivaling and exceeding the indus-
trially relevant latent catalyst phenyl-
mercury neodecanoate both in terms of
latency and catalytic activity. This
allows for creating one-component
PUR systems with improved pot life-
times. Pseudo-second-order kinetics
were found for both CO2-protected tet-
rahyropyrimidin-2-ylidenes and for
[SnCl2(1,3-dimesityldihydroimidazol-2-
ylidene)], indicating a fast pre-catalyst
decomposition prior to polyurethane
formation. 1,3-DiACTHNUTRGNE(NUG 2-propyl)tetrahydro-
pyrimidin-2-ylidene was additionally
found to be active in the cyclotrimeri-
zation of various isocyanates, offering
access to a broad variability in polymer
structure, that is, creating both ure-
thane and isocyanurate moieties within
the same polymer.
Keywords: catalysts · N-heterocy-
clic carbenes · polyaddition · poly-
urethanes · tin
ACHTUNGTRENNUNGbutyltin dilaurate. Even more impor-
tant, all compounds displayed pro-
Introduction
and created a multi-billion Euro business.[3,4] Polyurethanes
are produced through a polyaddition reaction of an at least
difunctional alcohol (polyol) to an at least difunctional iso-
cyanate in the presence of a catalyst. Catalysts commonly
used in PUR synthesis are tertiary amines, for example,
Since Otto Bayerꢀs discovery of polyurethanes (PURs),[1,2]
this class of polymers experienced a fantastic success story
diazabicycloACTHUNTGRNEUNGoctane (DABCO) and N-alkylmorpholines, as
[a] B. Bantu, G. M. Pawar, Dr. U. Decker, Prof. Dr. M. R. Buchmeiser
Leibniz-Institut fꢁr Oberflꢂchenmodifizierung e.V. (IOM)
Permoserstr. 15, 04318 Leipzig (Germany)
Fax : (+49)341-235-2584
well as organometallic compounds, such as dibutyltin dilau-
rate (DBTDL, A). The former activate the alcohol, thus in-
creasing its nucleophilicity, while the latter are Lewis acids
and thus activate the isocyanates and make them more elec-
trophilic. DBTDL is among the most active catalysts, out-
rivaling most organic bases including DABCO. Many appli-
cations require a long pot lifetime combined with fast
curing. Therefore, in reaction injection molding (RIM) ap-
plications, phenylmercury neodecanoate (PMND, B) is still
used as a latent curing catalyst. In combination with suitable
polyols and isocyanates, such latent, delayed-action catalysts
allow for the premixing of the components and their storage
at room temperature and slightly above for a given time
(pot life). Polyaddition is then usually triggered thermally.
Unfortunately, in special applications PMND is the only cat-
alyst so far that combines sufficient latency and high reactiv-
ity at elevated temperatures. In many markets the ban on
heavy metal containing materials is increasingly implement-
Homepage: http://www.iom-leipzig.de
E-mail: michael.buchmeiser@iom-leipzig.de
[b] Dr. A. M. Schmidt
BAYER MaterialScience AG
51368 Leverkusen (Germany)
[c] Dr. K. Wurst
Institut fꢁr Allgemeine
Anorganische und Theoretische Chemie
Universitꢂt Innsbruck
Innrain 52a, 6020 Innsbruck (Austria)
[d] Prof. Dr. M. R. Buchmeiser
Institut fꢁr Technische Chemie
Universitꢂt Leipzig
Linnꢃstr. 3, 04103 Leipzig (Germany)
Supporting information for this article contains X-ray and structural
data on compounds 1, 3 and 4, selected FT-IR and NMR data, and is
available on the WWW under http://dx.doi.org/10.1002/
chem.200802670.
Chem. Eur. J. 2009, 15, 3103 – 3109
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3103

ed. As a consequence, a growing demand for the replace-
ment of heavy metals, such as mercury, evolves.
dropyrimidin-2-ylidenes,[11,12] of which catalysts 1 and 2
(Figure 2) in fact turned out to satisfy our demands. The
high latency of these pre-catalysts can be rationalized by the
fact that tetrahydropyrimidin-2-ylidenes are characterized
by a small angle defined by the two substituents at N-1 and
N-3, which provides sufficient steric protection of the C-2
carbon as well as by the efficient charge delocalization (vide
infra). Both are expected to lead to a lower proneness of
the C-2 carbon to nucleophilic attacks, e.g., by alcoholates.
The X-ray structure of catalyst 1 is shown in Figure 3.
Compound 1 crystallizes in the monoclinic space group
In view of this unsatisfying situation, we aimed on the de-
velopment of novel delayed-action catalysts for PUR syn-
thesis that would satisfy the requirements of i) being stable
at room temperature, ii) displaying high activity upon ther-
mal initiation, iii) displaying low, or even better, no toxicity.
With the reports on the use of (protected) N-heterocyclic
carbenes (NHCs) for the polymerization of lactide published
by Waymouth et al. in mind,[5–7] we started to design protect-
ed NHCs for the use as latent catalysts in PUR synthesis.
Results and Discussion
We commenced our investigations with the haloform and
alkoxide protected NHCs based on imidazol-2-ylidenes and
imidazolin-2-ylidenes, which have been reported by Way-
mouth et al. to present latent catalysts for the ring-opening
polymerization of cyclic esters (Figure 1).[8,9]
Figure 3. X-ray structure of 1.
P21/n with a=738.75(2) pm, b=2140.81(7) pm, c=
1472.40(3) pm, b=95.612(2)8, Z=4. As expected, both the
Figure 1. Structure of haloform- and alkoxide-protected NHCs.
À
À
two C O [123.4(2) and 123.0(2) pm] and the two C N
bonds [132.6(2) versus 132.3(2) pm] are almost identical, in-
Disappointingly, we found them unsuitable for our pur-
poses. Though many of these compounds were stable up to
1008C in the absence of a polyol based on a hydroxy-func-
dicating uniform charge distribution. In addition, we pre-
II
À
pared a series of Sn NHC complexes of which catalysts 3
and 4 also displayed latent behavior, as well as high activity.
The X-ray structures of both 3 and 4 were also solved.
Compound 3 (Figure 4) crystallizes in the orthorhombic
space group Pna21 with a=2220.94(4) pm, b=787.15(1) pm,
c=1281.83(2) pm, a=b=g=908, Z=4. The angles C-Sn-
Cl(1), C-Sn-Cl(2) and Cl(1)-Sn-Cl(2) are 95.89(7)8, 92.63(6)8
tionalized polyACHTUNGTRENNUNG(acrylate) and a commercial triisocyanate,
that is, cyclotrimeric hexamethylene diisocyanate (HDI-cy-
clotrimer, Figure 2), and some of these compounds were in
fact active catalysts for PUR synthesis, no latent behavior
was observed at all when these compounds were mixed with
both the polyol and the HDI-cyclotrimer. We therefore pre-
pared a series of CO2-protected NHCs[10] based on tetrahy-
À
and 94.22(5)8 respectively. The Sn(1) C(1) bond length is
233.9(2) pm.
Compound 4 (Figure 5) crystal-
lizes in the triclinic space group
¯
P1 with a=873.38(2) pm, b=
1500.20(3) pm, c=1849.40(4) pm,
a=111.564(1), b=100.736(1), g=
90.266(1)8, Z=4. The angles C-
Sn-Cl(1), C-Sn-Cl(2) and Cl(1)-
Sn-Cl(2) are 95.89(7)8, 92.63(6)8
and 94.22(5)8, respectively. The
À
Sn(1) C(1) bond length is
231.1(3) pm.
The values for the bond
lengths and angles found for both
3 and 4, as well as the chemical
shift in the 119Sn NMR (d=À61.5
and À63.9 ppm, respectively) are
comparable to the corresponding
Figure 2. Structure of catalysts 1–4, A, B and of the monomers used.
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Catalysts for Polyurethane Synthesis
FULL PAPER
Figure 4. X-ray structure of 3.
Figure 6. Reactivity and latent behavior of catalysts 1–4 in comparison to
A and B in the polyaddition reaction of the polyol with HDI-cyclotrimer:
&
without catalyst ( ), 1 (?), 2 ( ), 3 ( ), 4 ( ), A at room temperature
for 120 min (ꢅ), B ( ).
„
45 minutes, while DBTDL (A) did not at all. Following
heating to 658C the polyaddition reaction commenced in-
stantly, triggered by either 1–4 or B.
Using identical amounts of catalyst, that is, 3.5 mmol%
(0.63–1.8 wt.%) based on the HDI-cyclotrimer, catalysts 1–4
clearly outrivaled B in terms of activity as evidenced by the
slopes in the graph of isocyanate concentration vs. time. In
fact catalysts 3 and 4 displayed the highest activity of all
compounds measured.
For externally catalyzed polyaddition reactions, e.g., those
catalyzed by a base, the number average degree of polymer-
ization=1/(1À((A0ÀA)/A0))=1+kA0t, (A0, A=initial and
G
time-dependant isocyanate concentration, respectively, and
k=rate constant of polymerization), provided the fact that
the reaction is pseudo-second-order kinetics, that is, the ini-
tial concentration of the base is constant and not a function
Figure 5. X-ray structure of 4.
of time. In that case, the graph 1/(1À((A0ÀA)/A0)) versus
G
time should be linear. This was in fact found to be true for
the polyaddition reactions catalyzed by 1, 2, 4 and B, sug-
gesting that for these pre-catalysts decomposition and for-
mation of the active catalyst is fast and quantitative com-
pared to the polyaddition reaction (Figure 7). Since A0 was
identical in all experiments, the slopes of the graphs in
Figure 7 are proportional to k and clarify the order of reac-
tivity, which is 3>4>1>2>B.
We next turned to possible modifications in the polymer
structure. NHCs have already been reported to catalyze the
cyclotrimerization of isocyanates.[14] While 1, 3 and 4 were
inactive in the cyclotrimerization of many aliphatic and aro-
matic isocyanates up to catalyst loadings of 0.1 mol%
(yields !5%), 2 allowed for the cyclotrimerization of a
series of aromatic isocyanates in virtually quantitative yields
down to catalyst loadings of 1 mmol% (Table 1). Interest-
ingly, cyclohexylisocyanate could not be cyclotrimerized by
the action of 2, while cyclotrimeric HDI, which is also an
aliphatic isocyanate, can be subject to cyclotrimerization re-
sulting in a crosslinked polymer (vide infra). Similarly, the
values found for [SnCl2(1,3-diisopropyl-4,5-dimethylimida-
zol-2-ylidene)],[13] for which a pyramidal coordination geom-
etry for Sn and a strong s-character of the non-binding elec-
tron pair has been suggested.
Both the activity of the initiators and their latency were
monitored by real-time FT-IR. For these purposes, the poly-
addition reaction between a commercial polyol based on a
hydroxy-functionalized poly
ACHTUNGTRNE(NUNG acrylate) and a commercial tri-
ACHTUNGTRENNUNG
(HDI-cyclotrimer, Figure 2) was monitored. The decrease in
intensity of the isocyanate band at n˜ =2265 cmÀ1 was chosen
as a measure for conversion (Figure S1 in the Supporting In-
formation). The results are summarized in Figure 6.
Note that any initial increase in the isocyanate concentra-
tion is the sole result of the evaporation of the solvent (bu-
tylacetate) that was used for the premixing of the educts. As
can be deduced there from, catalysts 1–4 and PMND (B)
displayed excellent latency at room temperature for at least
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M. R. Buchmeiser et al.
HDI-cyclotrimer by the action of 2 was characterized by
two bands at n˜ =1461 and 1429 cmÀ1, while PUR prepared
from the same educts by the action of 1 only showed only
one band at n˜ =1460 cmÀ1 (Figure S5 in the Supporting In-
formation). These data illustrate the potential of these new
delayed-action catalysts in terms of tailoring the final poly-
mer structure (Scheme 1): PURs with or without additional
cyanurate moieties can be realized.
Figure 7. Graph of 1/(1À
concentration, A=time-dependant isocyanate concentration) for the
polyaddition reaction of polyol with HDI-cyclotrimer catalyzed by 1–4
((A0ÀA)/A0)) versus time (A0 =initial isocyanate
ACHTUNGTRENNUNG
&
and B. 1 (?), 2 ( ), 3 ( ), 4 ( ), B ( ).
„
Table 1. Results for the cyclotrimerization of isocyanates by the action of
2.
Substrate
t [h][a]
2, Yield [%][b]
phenyl isocyanate
0.5
1
1
1
1
0.5
1
1
99
99
99
95
99
100
99
0
4-(benzyloxy)phenyl isocyanate
4-methoxyphenyl isocyanate
3-methylphenyl isocyanate
4-methylphenyl isocyanate
4-fluorophenyl isocyanate
4-chlorphenyl isocyanate
cyclohexyl isocyanate
Scheme 1. Different polymer structures that may form through the PUR
reaction (right) and isocyanate cyclotrimerization, that is, isocyanurate
formation (left).
We next focused on some mechanistic investigations on
the mode of action of these new catalysts. The mechanism
of initiation is a quite simple one for CO2-protected NHCs.
As might be anticipated, an increase in temperature results
in the release of CO2 and concomitant formation of the free
carbene, which immediately reacts with the alcohol to pro-
duce the alcoholate and the corresponding tetrahydropyri-
midinium salts (Scheme 2). In fact, quantitative formation of
the latter was observed in the reaction of 1 with ethylene
glycol in C2D4Cl2 at 708C (Figure S6 in the Supporting Infor-
mation). It was clearly identified by the typical 1H NMR
chemical shift of the pyrimidinium proton at d=7.87 ppm
and by the corresponding signal for the pyrimidinium
carbon at d=155.1 ppm, respectively. Concomitantly, in the
13C NMR we observed resonances for the 2-hydroxy-1-eth-
[a] 10À3 mol% of 2 were used. [b] Isolated yields.
cyclotrimerization reaction of 2,4-toluene diisocyanate
(TDI) triggered by 2 occurred (isocyanurate band at n˜ =
1701 cmÀ1) while no reaction was observed with 1. The capa-
bility of 2 to cyclotrimerize isocyanates is attributed to the
more basic character that may be anticipated for the free
NHC that forms from 2 compared to the NHC formed from
1 (+I versus ÀI and M effect of the 2-Pr and mesityl group,
respectively).
Consequently, compound 2 was used for the reaction of
ethylene glycol with TDI to form PUR containing additional
isocyanurate moieties. Isocyanurate formation was con-
firmed by IR spectroscopy (Figures S2 and S3 in the Sup-
porting Information). Thus, in addition to the typical broad
PUR bands at n˜ =1700 and 1221 cmÀ1, the band around n˜ =
1530 cmÀ1 (dNH) split into two signals at n˜ =1531 and
1514 cmÀ1.[15] Treating HDI-cyclotrimer with 2 also resulted
in cyclotrimerization and the reaction mixture solidified. In
the FT-IR, the peak around n˜ =1426 cmÀ1 became stronger
(Figure S4 in the Supporting Information). Again, the use of
1 resulted in no conversion at all. Consequently, a mixture
of the polyol and the HDI-cyclotrimer prepared by the
action of 2 contained additional isocyanurate moieties while
PUR prepared by the action of 1 did not. Accordingly, the
IR spectrum of PUR prepared from the polyol and the
AHCTUNGTREGaNNNU nolate at d=67.34 and 62.51 ppm, respectively. Similar re-
sults were found for the reaction of 1 with the polyol or
with the polyol and the HDI-cyclotrimer. Thus, heating a
mixture of these three compounds in CD2Cl2 to 708C results
in the quantitative formation of the pyrimidinium salt (Fig-
ure S6 in the Supporting Information) and the polyaddition
reaction occurs.
The role of compounds 3 and 4 in PUR synthesis, howev-
er, was less obvious. In principle, one might regard both
compounds as SnCl2-protected NHCs, which, upon heating
decompose into the corresponding free NHC and SnCl2
(Scheme 2). To shed some light on that issue, we carried out
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Catalysts for Polyurethane Synthesis
FULL PAPER
isocyanate reaction through co-
ordination to the isocyanate
oxygen. This way, upon activa-
tion both building blocks of 3
and 4, that is, the SnCl2 and
the NHC, act as catalysts. This
explains for the high catalytic
activity of these compounds
compared to other systems as
well as for their latency.
Conclusion
In summary, we have estab-
lished two classes of latent
(“delayed action”) catalysts
based on CO2-protected NHCs
À
and NHC Sn complexes for
polyurethane synthesis that
may be triggered thermally
Scheme 2. Proposed pre-catalyst activation and PUR reaction (x+y=2).
and exceed existing systems
some 1H- and 119Sn-NMR experiments. The reaction of 3
with ethylene glycol and TDI in C2D4Cl2 at 708C resulted in
the quantitative formation of a 1,3-dimesityl-4,5-dihydroimi-
dazolium salt as evidenced by 1H NMR (dH-2 =8.15 ppm)
and 13C NMR (dC-2 =159.0 ppm, Figure S7, Supporting Infor-
mation). No signal for a Sn-species (any) was observed in
the 119Sn NMR, strongly suggesting a polymer-bound Sn-spe-
cies that precipitates with the polymer. Again, the same ac-
counts for the reaction of the polyol and the HDI-cyclotri-
both in activity and latency. Particularly the CO2-protected
pre-catalysts circumvent the use of toxic heavy metals such
as HgII or SnIV. Current work focuses on the investigation of
other metal- and CO2-protected NHCs as (latent) pre-cata-
lysts for PUR synthesis.
Experimental Section
ACHTUNGTRENNUNGmer triggered by 3. Rapid formation of a 1,3-dimesityl-4,5-
General: Except where noted, all manipulations were performed under a
dinitrogen atmosphere in a glove box (MBraun LabMaster 130) or by
standard Schlenk techniques. Pentane, toluene, diethyl ether, methylene
chloride and tetrahydrofuran (THF) were dried using a solvent purifica-
tion system (SPS, MBraun). Benzene and n-hexane were distilled from
sodium/benzophenone ketyl under argon. All commercially available
starting materials were purchased from Aldrich or Fluka and were used
without any further purification. The polyol, the HDI-cyclotrimer, di-
dihydroimidazolium salt was observed, again no Sn-signal
was observable. Evidence for a polymer-bound Sn-species
was provided by FT-IR. Thus, reaction of ethylene glycol
with TDI in the presence of 1 equiv of 3 resulted in the for-
mation of PUR. Its IR-spectrum displayed the correspond-
ing signals, in addition signals at n˜ =1098 and 1045 cmÀ1
could be assigned to those for a Sn-O-CH2-R species.[16] To
provide further proof for the reaction of compounds 3 or 4
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
from Thor Especialidades, S.A., Spain. NMR spectra were recorded by
using a Bruker Avence 250 (250.13 MHz for proton and 62.90 MHz for
with the alcohol, we reacted both 3 and 4 with LiACHTNUGTRNEG(UN OC2H5) to
form the corresponding NHC-Sn-alcoholate species. Our at-
tempts to isolate [Sn(1,3-dimesitylimidazolin-2-ylidene)-
ACHTUNGTRENNUNG
carbon) or
a Bruker Avence 600 (600.25 MHz for proton and
150.93 MHz for carbon) spectrometer at room temperature unless speci-
fied otherwise. Proton and carbon spectra were referenced to an internal
solvent resonance and are reported in ppm relative to tetramethylsilane.
AHCTUNGTRENNUNG
119Sn NMR spectra were recorded at room temperature by using
a
1
Bruker AVANCE II+ 600 spectrometer at 224 MHz for 119Sn. Each
sample was dissolved in [D8]tetrahydrofuran or CDCl3 up to concentra-
tions of 10 wt.% in NMR-tubes (5 mm o.d.). 119Sn NMR spectra were ref-
d=À146.3 ppm, H NMR d=3.79 (m, 2H; CH2,), 1.19 ppm
(t, 3H; CH3) and the free carbene IMesH2. Together, these
findings now allow for identifying the actual role of both 3
and 4 in the thermally triggered polyaddition reaction. Thus,
both 3 and 4 are inactive pre-catalysts, Upon heating, both 3
and 4 decompose (pathway A, Scheme 2) or reaction with
erenced to [SnACHTNUGTRNEN(UG CH3)4]/10 vol.% C6D6 according to the recommended
UPAC X-scale. Mass spectra were recorded on a VG ZAB HS, Bruker
Esquire 300 plus and Finnigan-MAT 8200, respectively. Infrared spectra
were recorded from n˜ =4000–400 cmÀ1 by means of a Bruker Vector 22
using ATR technology. The absorption bands are reported in wave num-
bers (cmÀ1). Elemental analyses were carried out at the Mikroanalytisch-
es Labor, Institut fꢁr Physikalische Chemie, Universitꢂt Wien, Austria.
the alcohol occurs and the resulting SnACTHNUTRGNE(NUG NCH)-alcoholates
decompose (pathway B, Scheme 2). As found for both 1 and
2, the free carbenes formed from either 3 or 4 then deproto-
nate the polyol, thus simply serving as bases and catalyzing
the base reaction. The SnII-alcoholates (any) that form, how-
ever, act as Lewis acids, which are known to catalyze the
1,3-Dimesityl-3,4,5,6-tetrahydropyrimidin-1-ium-2-carboxylate (1): In
a
250 mL Schlenk flask equipped with a stirring bar, 1,3-dimesityl-3,4,5,6-
tetrahydropyrimidin-1-ium bromide[11] (5.0 g, 12.46 mmol) was suspended
in 100 mL of THF. Potassium tert-butoxide (1.68 g, 14.95 mmol) was sepa-
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3107

M. R. Buchmeiser et al.
rately suspended in THF (10 mL) and added to the suspension of 1,3-di-
mesityl-3,4,5,6-tetrahydropyrimidin-1-ium bromide. Then carbon dioxide
was bubbled through the reaction mixture at 08C for 1 hour. During this
procedure a sticky white precipitate formed. The solvent was removed in
vacuo, and the residue was recrystallized from dichloromethane and di-
ethyl ether (4.07 g, 90.0%). Single crystals suitable for X-ray analysis
were obtained from acetonitrile/diethyl ether. 1H NMR (250.13 MHz,
CDCl3): d=2.24, 2.28 (s, 6H), 2.34, 2.44 (s, 12H), 2.64 (m, 2H), 3.60 (t,
2H), 4.15 (t, 2H), 6.87, 6.95 ppm (s, 4H); 13C NMR (62.89 MHz, CDCl3):
d=17.7, 18.0, 19.5, 20.3, 21.0, 46.5, 46.7, 129.7, 130.1, 134.3, 135.5, 136.4,
137.2, 139.1, 140.5, 163.0 ppm; FTIR (ATR mode): n˜ =2968 (w), 1672 (s,
CO), 1573 (s), 1305 (s), 1475(m), 851 cmÀ1 (s); elemental analysis (%)
calcd for C23H28N2O2: C 75.79, H 7.74, N 7.69; found: C 75.47, H 7.42, N
7.59.
the isocyanates was monitored by the decrease of absorbance of the
NCO band at 2265 cmÀ1
.
Typical procedure for the recording of the reaction kinetics (latency):
The catalyst (3.5 mmol%) with respect to isocyanate was dissolved in a
minimum amount of dichloro
ACHTUNGTRENNUNG
of the polyol (30 wt.-% in but
N
1
(10 wt.% in butylacetate) (molar ratio of OH/NCO=1:1) was added to
the catalyst solution. The mixture was mixed for 3.0 min, kept at room
temperature for 45 min; then the temperature was raised to 658C. The
entire process of PUR formation (3D-crosslinked) was monitored by
real-time FT-IR using a BIO-RAD FTS 6000 spectrometer.
Typical procedure for the cyclotrimerization of isocyanates: A solution of
4-methylphenyl isocyanate (1:1 v/v in THF) was added to 1,3-diisoprop-
yl-3,4,5,6-tetrahydropyrimidin-1-ium-2-carboxylate (3.0 mg, 1.0 mmol%).
The reaction mixture was stirred at 758C for 1 h. The resulting precipi-
tate was filtered off, washed with pentane, and dried in vacuo to afford
the isocyanurate as a white solid in 99% yield.
1,3,5 Triphenyl-1,3,5-triazanine-2,4,6-trione: 1H NMR (250.13 MHz,
CDCl3): d=7.38–7.5 ppm (m, 15H; of phenyl); 13C NMR (62.89 MHz,
CDCl3): d=148.8, 133.6, 129.5, 128.5 ppm; FTIR (ATR mode): n˜ =3044
(br), 1688 (s, CO), 1488 (m), 1395 (m), 758 (s), 686 cmÀ1 (s); ESI-MS m/z
calcd for C21H15N3O3: 357.11; found: 380.10 [M+Na+].
1,3-Diisopropyl-3,4,5,6-tetrahydropyrimidin-1-ium-2-carboxylate (2): 1,3-
Diisopropyl-3,4,5,6-tetrahydropyrimidin-1-ium tetrafluoroborate[11] (1.0 g,
3.90 mmol) was suspended in 20 mL of THF. Potassium tert-butoxide
(0.52 g, 4.68 mmol) was suspended in THF (5.0 mL) and added to this
suspension. The reaction mixture was stirred for 16 h. It was then filtered
through celite to remove residual salts. The filtrate was transferred to a
100 mL Schlenk flask and removed from the glove box. Carbon dioxide
was bubbled through the solution at 08C for 30 min, during this time a
white precipitate formed. The solvent was removed in vacuo, and the res-
idue was washed with diethyl ether (0.70 g, 85.0%). 1H NMR
(250.13 MHz, CD3OD): d=1.27 (d, 12H; of CH3), 2.00 (m, 2H; of CH2),
3.36 (t, 4H; N-CH2), 4.13 ppm (m, 2H; CH); 13C NMR (62.89 MHz,
CD3OD): d=19.6, 20.2, 38.5, 55.8, 160.3, 162.7 ppm; FTIR (ATR mode):
n˜ =2971 (w), 1651 (s, CO), 1591 (s), 1312 (m), 1166 (s), 863 (s), 760 cmÀ1
(s); ESI-MS: m/z calcd for C11H20N2O2: 212.15, found: 213.2 [M+H]+.
1,3,5-Tris(4-methoxyphenyl)-1,3,5-triazinane-2,4,6-trione:
1H NMR
(250.13 MHz, CDCl3): d=7.29 (d, 2H), 6.98 (d, 2H), 3.8 ppm (s, 3H);
13C NMR (62.89 MHz, CDCl3): d=160.0, 149.2, 129.5, 126.38, 114.7,
55.6 ppm; FTIR (ATR mode): n˜ =2938 (br), 1688 (s, CO), 1508 (s), 1409
(m),1248 (m), 1168 (s), 1026 (s), 818 (s), 756 cmÀ1 (s); ESI-MS m/z calcd
for C24H21N3O6: 447.14, found: 470.13 [M+Na+].
1,3,5-Tris(3-methlyphenyl)-1,3,5-triazinane-2,4,6-trione:
1H NMR
ACHTUNGTRENNUNG[SnCl2(1,3-dimesitylimidazolin-2-ylidene)] (3): In a 50.0 mL Schlenk flask
(250.13 MHz, CDCl3): d=7.25 (m, 9H), 7.41 (m, 3H), 2.43 ppm (s, 9H);
13C NMR (62.89 MHz, CDCl3): d=148.9, 139.6, 133.6, 130.3, 129.3, 129.0,
125.5, 21.3 ppm; FTIR (ATR mode): n˜ =2917 (m), 1698 (s, CO), 1488 (s),
1404 (br), 875 (m), 785 (s), 690 cmÀ1 (s); ESI-MS m/z calcd for
C24H21N3O3: 399.16; found: 422.15 [M+Na+].
equipped with a stirring bar, 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-
ylidene (100 mg, 0.32 mmol) was dissolved in 20.0 mL of dry THF. Then
SnCl2 (62.0 mg, 0.33 mmol) was added. The mixture was stirred for 3 h;
then all volatiles were evaporated. The resulting white solid was dis-
solved in dichloromethane and filtered through glass fiber filter paper.
The solvent was evaporated and the white solid was recrystallized from
dichloromethane and diethyl ether (145.0 mg, 90.0% yield). Single crys-
tals suitable for X-ray analysis were obtained from dichloromethane: di-
1,3,5-Tris(4-methlyphenyl)-1,3,5-triazinane-2,4,6-trione:
1H NMR(250.13 MHz, CDCl3): d=7.28 (s, 12H), 2.39 ppm (s, 9H);
13C NMR (62.89 MHz, CDCl3): d=148.9, 139.3, 131.1, 130.0, 128.1,
1
21.32 ppm; FTIR (ATR mode): n˜ =2916 (br), 1696ACTHUNRTGNEUNG(m, CO), 1509 (s),
ethyl ether. H NMR (600.25 MHz, CDCl3): d=2.31 (s, 6H; p-CH3), 2.40
1402 (br), 807 (s), 749 cmÀ1 (s); ESI-MS m/z calcd for C24H21N3O3:
(s, 12H; o-CH3), 4.01 (s, 4H; N-CH2), 6.97 ppm (s, 4H; Mes); 13C NMR
(150.92 MHz, CDCl3): d=18.3, 20.2, 51.94, 129.9, 132.9, 136.1, 139.7,
204.7 ppm; 119Sn NMR (192.5 MHz, THF): d=À61.5 ppm; FTIR (ATR
mode): n˜ =2915 (br), 1623 (m), 1481 (br), 1262 (m), 1030 (br), 850 cmÀ1
(m); elemental analysis (%) calcd for C21H26Cl2N2Sn: C, 50.85, H, 5.28,
N, 5.65; found: C, 50.49, H, 5.30, N, 5.58.
399.16; found: 422.15 [M+Na+].
1,3,5-TrisACTHNUTRGNEUNG
(4-fluoro)-1,3,5-triazinane-2,4,6-trione: 1H NMR (250.13 MHz,
CDCl3): d=7.5 (m), 7.36 (m), 7.18 (m), 7.10 (m), 7.05 (m), 7.01 ppm (m);
13C NMR (62.89 MHz, CDCl3): d=163.7, 162.0, 161.2, 60.7, 159.6, 159.1,
151.0, 148.6, 130.4 (d), 129.3 (d), 126.2 (d), 118.7 (d), 116.7 ppm (m);
FTIR (ATR mode): n˜ =3294 (br), 2291 (br), 1697ACTHNUTRGNE(NUG m, CO), 1505 (s), 1403
ACHTUNGTRENNUNG[SnCl2(1,3-dimesitylimidazol-2-ylidene)] (4): In a 100.0 mL Schlenk flask
(m), 828 cmÀ1 (s); ESI-MS m/z calcd for C21H12F3N3O3: 411.08; found:
equipped with a stirring bar, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-yli-
dene[17,18] (0.5 g, 1.64 mmol) was dissolved in 50.0 mL of dry THF. Then
SnCl2 (0.31 g, 1.64 mmol) was added to the reaction. The mixture was
stirred for 3 h; then all volatiles were evaporated. The resulting white
solid was dissolved in dichloromethane and filtered through glass fiber
filter paper. The solvent was evaporated and the remaining white solid
was recrystallized from dichloromethane and diethyl ether (730.0 mg,
90.0% yield). Single crystals suitable for X-ray analysis were obtained
434.0. [M+Na+].
1,3,5-TrisACTHNUTRGNEUNG
(4-chloro)-1,3,5-triazinane-2,4,6-trione: 1H NMR(250.13 MHz,
CDCl3): d=7.32 (d, 6H), 7.46 ppm (d, 6H); 13C NMR (62.89 MHz,
CDCl3): d=129.8, 131.8, 135.6, 148.2 ppm; FTIR (ATR mode): n˜ =2976
(br), 2852 (br), 1701 (m, CO), 1489 (m), 1419 (br), 1086 cmÀ1 (m); ESI-
MS m/z calcd for C21H12Cl3N3O3: 460.70, found: 460.0.
1,3,5-Tris(4-benzyloxyphenyl)-1,3,5-triazinane-2,4,6-trione:
1H NMR
1
from dichloromethane: diethyl ether. H NMR (600.25 MHz, CDCl3): d=
(250.13 MHz, CDCl3): d=7.42 (m), 7.29 (m), 7.14 (d), 7.06 (d), 6.93 (d)
(aromatic 27H), 5.12 (s), 5.08 (s), 5.04 ppm (s, 6H CH2); 13C NMR
(62.89 MHz, CDCl3): d=159.2, 158.8, 149.2, 137.0, 131.0, 129.5, 128.7,
128.1, 127.6, 127.5, 122.6, 116.6, 115.6, 115.3, 70.4 ppm; FTIR (ATR
mode): n˜ =3292 (br), 3034 (br), 1711 (br), 1640 (s), 1507 (s), 1235 cmÀ1
(br); ESI-MS m/z calcd for C42H33N3O6: 675.24, found: 698.2 [M+Na+].
2.18 (s, 12H; o-CH3), 2.36 (s, 6H; p-CH3), 7.03 (s, 4H; Mes), 7.17 ppm (s,
2H; N-CH2); 13C NMR (150.92 MHz, CDCl3): d=17.8, 21.3, 123.3, 129.2,
133.2, 135.0, 140.6, 181.6 ppm; 119Sn NMR (192.5 MHz, THF) d=
À63.9 ppm; FTIR (ATR mode): n˜ =2915 (br), 1600 (m), 1540 (m), 1476
(br), 1226 (m), 1030 (br), 852 cmÀ1 (s); HR-MS: m/z calcd for
C21H24Cl2N2Sn: 494.03; found: 494.03.
X-ray measurement and structure determination of 1, 3 and 4: Data col-
lection was performed by using a Nonius Kappa CCD equipped with
graphite-monochromatized MoKa radiation (l=0.71073 ꢆ) and a nomi-
nal crystal to area detector distance of 36 mm. Intensities were integrated
using DENZO and scaled with SCALEPACK.[19] Several scans in f and
w direction 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
Real-time FTIR-ATR spectroscopy: Investigations on the kinetics of the
polyaddition reactions were carried out by means of real-time FTIR-
ATR spectroscopy by using a Digilab FTS 6000 spectrometer and a heat-
able Golden Gate diamond ATR accessory (Specac). The monomer was
applied as a small droplet to the ATR crystal, which was preheated to
the appropriate temperature. Infrared spectra with a spectral resolution
of 4 cmÀ1 were taken every 10 s over a period a 120 min. Conversion of
3108
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Catalysts for Polyurethane Synthesis
FULL PAPER
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placement parameters. CCDC 715973 (1), 715974 (3) and 715975 (4) con-
tain 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
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Received: December 18, 2008
Published online: February 11, 2009
Chem. Eur. J. 2009, 15, 3103 – 3109
ꢄ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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