Copper (I) 1,3-R2-3,4,5,6-tetrahydropyrimidin-2-ylidenes (R=mesityl, 2-propyl): Synthesis, X-ray structures, immobilization and catalytic activity

Article abstract of DOI:10.1016/j.tet.2005.07.116

The synthesis of novel copper (I) N-heterocyclic carbene complexes is described. Thus, reaction of CuX with 1,3-di(2-propyl)-3,4,5,6- tetrahydropyrimidin-2-ylidene yields CuX(1,3-di(2-propyl)-3,4,5,6- tetrahydropyrimidin-2-ylidene) (X=Cl, (1a), Br (1b));

Full text of DOI:10.1016/j.tet.2005.07.116

Tetrahedron 61 (2005) 12145–12152
Copper (I) 1,3-R -3,4,5,6-tetrahydropyrimidin-2-ylidenes
2
(
RZmesityl, 2-propyl): synthesis, X-ray structures,
immobilization and catalytic activity
a,b
a,b
c
Bhasker Bantu, Dongren Wang, Klaus Wurst and Michael R. Buchmeiser
a,b,
*
a
Leibniz Institut f u¨ r Oberfl a¨ chenmodifizierung (IOM) e. V., Permoserstr. 15, D-04318 Leipzig, Germany
b
Institut f u¨ r Technische Chemie, Universit a¨ t Leipzig, Linn e´ str. 3, D-04103 Leipzig, Germany
Institut f u¨ r Allgemeine, Anorganische und Theoretische Chemie, Leopold-Franzens-Universit a¨ t Innsbruck, Innrain 52a,
A-6020 Innsbruck, Austria
c
Received 1 July 2005; revised 31 July 2005; accepted 31 July 2005
Available online 28 October 2005
Abstract—The synthesis of novel copper (I) N-heterocyclic carbene complexes is described. Thus, reaction of CuX with 1,3-di(2-propyl)-
3
,4,5,6-tetrahydropyrimidin-2-ylidene yields CuX(1,3-di(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) (XZCl, (1a), Br (1b)); however,
reaction of CuCl with 1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene yields the bis-N-heterocylcic carbene complex Cu(1,3-dimesityl-
C
K
3
propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) (3) was prepared from 1 and PS-DVB–CH –OCO–CF –CF –CF –COOAg. A copper
,4,5,6-tetrahydropyrimidin-2-ylidene)
2 2 2 2 2 2
CuBr (2). A supported version of 1, i.e. PS-DVB–CH –OCO–CF –CF –CF –COOCu(1,3-di(2-
2
2
2
2
loading of 4.15 mmol/g was realized. The new compounds were used as catalysts in carbonyl hydrosilylation and cyanosilylation reactions.
Excellent reactivity was observed, giving raise to turn-over numbers (TONs) of up to 100,000. Compounds 1a, 1b, and 2 have also been used
as catalysts for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). A linear conversion of monomer with time
was observed, however, no control over molecular weight of PMMA was observed.
q 2005 Elsevier Ltd. All rights reserved.
1
. Introduction
pyrimidin-2-ylidene(]CHR)). Encouraged by the high
reactivity of these complexes, we were interested in the
synthesis and catalytic behaviour of the corresponding
Cu (I) NHC compounds. So far, only few reports exist on
1
–6
N-heterocyclic carbenes (NHCs)
are currently among
the most intensively investigated compounds since the
corresponding transition metal complexes were found to
possess good stabilities and high activities in various
2
3–25
Cu (I) complexes of N-heterocyclic carbenes.
In the
following, their synthesis, characterization, X-ray structures
and catalytic activities are reported.
7
–14
catalytic processes.
novel NHC complexes of Ag (I), Pd (II), Rh (I), Ir (I), and
Recently, our group reported on
Ru (II) based on 1,3-R -3,4,5,6-tetrahydropyrimidin-2-
2
1
5–22
ylidenes (RZmesityl, 2-propyl).
NHC-complexes of the general formula MX(1,3-R -3,4,5,6-
In this context, novel
2. Results and discussion
2
tetrahydropyrimidin-2-ylidene)(COD) (MZRh, Ir; XZCl,
2.1. Synthesis and X-ray structure of compounds 1a
and 1b
4
Br; RZ2-Pr, mesityl; CODZh K1,5-cyclooctadiene) have
been used for carbonyl arylation and hydrosilylation
1
9–21
reactions and were found to possess excellent activity.
The same applies to the palladium complex PdCl (1,3-(2-
Compound 1a was prepared in 77% isolated yield from CuCl
and 1,3-di(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene
in THF (Scheme 1). The latter was generated from 1,3-di(2-
propyl)-3,4,5,6-tetrahydropyrimidinium tetrafluoroborate
2
Pr) -3,4,5,6-tetrahydropyrimidin-2-ylidene) and ruthenium
2
complexes
RuCl (1,3-dimesityl-3,4,5,6-tetrahydro-
2
1
7
and sodium tert-butoxide as described in the lit.
Compound 1a (Fig. 1) was characterized by X-ray
crystallography. A summary of the data is given in Tables 1
and 2.
Keywords: N-heterocyclic carbenes; Tetrahydropyrimidin-2-ylidenes;
Copper; Atom-transfer radical polymerization; Hydrosilylation; Cyanosi-
lylation; Homogeneous catalysis; Heterogeneous catalysis.
*
Corresponding author. Tel.: C49 341 235 2229; fax: C49 341 235 2584;
e-mail: michael.buchmeiser@iom-leipzig.de
Compound 1a crystallizes in the orthorhombic space group
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.07.116

12146
B. Bantu et al. / Tetrahedron 61 (2005) 12145–12152
Table 1. Crystal data and structure refinement for 1a and 2
1
a
2
Molecular formula
Fw
Cryst syst
Space group
a (pm)
b (pm)
c (pm)
a (deg)
b (deg)
C
10
H
20ClCuN
2
C
44 4
H56Br1.74Cl0.26Cu2N
267.27
Orthorhombic
916.27
Monoclinic
C2/c (No. 15)
1540.04(3)
1450.36(2)
1916.18(5)
90
95.088(2)
90
4.26452(15)
4
233(2)
1.427
2.678
Colorless prism
3156
1.047
Pnnm (No. 58)
1220.30(6)
986.16(3)
1045.55(5)
90
90
90
g (deg)
Vol (nm )
3
1.25823(9)
4
233(2)
1.411
1.915
Colorless prism
1276
1.057
Z
Temperature (K)
3
Density (calcd) (Mg/m )
K1
Abs coeff (mm
Color, habit
)
No. of rflns with IO2s(I)
Goodness-of-fit on F
2
R indices IO2s(I)
R
1
Z0.0208
R Z0.0347
uR Z0.0846
1
2
2
uR Z0.0543
Table 2. Bond lengths (pm) and angles (8) for 1a
Cu(1)–C(1)
Cu(1)–Cl(1)
191.50(19)
211.06(6)
2
3
2
-ylidene) (195.3 pm). This finding underlines the fact
that N-heterocyclic carbenes based on tetrahydropyrimidin-
-ylidenes are among the most basic ones. In due
2
consequence, a pronounced trans-effect on the halogen
ligand had to be expected and was in fact found. Thus, the
distance Cu(1)–Cl(1) in 1a (211.06(6) pm) is longer than the
one observed in CuCl 1,3-(2,6-(2-Pr) -C H ) (imidazol-2-
2
6 3
ylidene) (208.90 pm).
Scheme 1. Synthesis of Cu–NHC complexes 1a, 1b and 2.
In a similar way, 1b was prepared in 75% yield from CuBr
and 1,3-di(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene
in THF (Scheme 1). Due to structural similarity, no further
discussion appears necessary.
2
.2. Synthesis and X-ray structure of compound 2
Compound 2 was prepared in 88% isolated yield from CuCl
and 1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene in
THF (Scheme 1). The latter was generated from 1,3-
dimesityl-3,4,5,6-tetrahydropyrimidinium bromide and
1
7
sodium tert-butoxide as described in the literature. The
complex that forms is remarkable. Thus, a cationic Cu (I)
bis-(NHC) compound with a CuBr anion forms instead of
2
the expected neutral CuBr(NHC) complex. So far, we have
no conclusive explanation for this finding, the more, as the
sterically demanding ligand should favor a Cu-mono-NHC-
complex. Compound 2 (Fig. 2) was characterized by X-ray
crystallography. A summary of the data is given in Tables 1
and 3.
Figure. 1. X-ray structure of compound 1a.
Table 3. Bond lengths (pm) and angles (8) for 2
Cu(1)–C(1)
Cu(1)–C(1)#1
193.4(2)
193.4(2)
Pnnm with aZ1220.30(6) pm, bZ986.16(3) pm and cZ
C(1)–Cu(1)–C(1)#1
Cl(1)#2–Cu(2)–Br(1)
Br(1)#2–Cu(2)–Br(1)
178.73(13)
179.29(4)
179.29(4)
1
045.55(5) pm, aZbZgZ908, ZZ4. The distance Cu(1)–
C(1) is 191.50(19) pm, which is significantly shorter than
the one reported for CuCl 1,3-(2,6-(2-Pr) -C H )(imidazol-
2
6 3

B. Bantu et al. / Tetrahedron 61 (2005) 12145–12152
12147
accomplished. With this set of catalysts in hand, a series of
catalytic reactions as outlined below were investigated.
2.4. Catalytic activity of compounds 1a, 1b and 2 in
C]O cyanosilylation reactions
Compounds 1a, 1b and 2 were used in the cyanosilylation of
various carbonyl compounds including aromatic aldehydes
and ketones (Scheme 3). A summary of the results is given
in Table 4, entries 1–8.
Figure. 2. X-ray structure of compound 2.
Compound 2 crystallizes in the monoclinic space group C2/
c with aZ1540.04(3) pm, bZ1450.36(2) pm and cZ
1
916.18(5) pm, aZgZ908, bZ95.088(2), ZZ4. As
expected, the distances Cu(1)–C(1) and Cu(1)–C(1)# are
identical (193.42(2) pm). This distance is only slightly
longer than in the one found in 1a indicating only minor, if
any, steric repulsion of the two NHC ligands. The angle
C(1)–Cu(1)–C(1)# is 178.73(13)8, illustrating an almost
perfect alignment of the two NHC ligands. As expected, the
Scheme 3. C]O hydrosilylation, C]O cyanosilylation reactions and
attempted ATRP of MMA.
As can be seen, catalyst 1b showed excellent reactivity in
this type of reaction. Yields were in the 22–100% range,
TONs up to 50,000 were obtained. The more stable complex
CuBr anion is almost perfectly linear with an angle Brl(1)–
2
2
resulted in even improved yields (80–100%), TONs
Cu(1)–Br(1)# of 179.29(4)8. It should be emphasized that
the anion is in fact best described by the formula
CuBr1.74Cl0.26. This irregularity may also account for the
slight (calculated) deviation in the linearity of this anion.
reached 100,000. The supported version 3 gave signifi-
cantly, however, still acceptable yields approaching 100%
in selected cases. As a consequence of both the low copper
loadings (12–71 mmol%) and the immobilization, products
obtained with 3 were basically free of any copper residues
(
!1 ppm).
2
.3. Synthesis of an immobilized version of 1a/1b
2
6
In view of the high demand on supported catalysts, we
synthesized a supported version of 1a respectively 1b by
reaction with a perfluoroglutaric acid-derivatized PS-DVB-
based support according to an established procedure
2.5. Catalytic activity of compounds 1a, 1b and 2 in
C]O hydrosilylation reactions
Copper (I) catalyzed C]O hydrosilylation reactions
(Scheme 3) were first described by Nolan and coworkers
2
7,28
(
Scheme 2).
A catalyst loading of 4.15 mmol/g was
Scheme 2. Immobilization of 1a on a PS-DVB-based support.

12148
B. Bantu et al. / Tetrahedron 61 (2005) 12145–12152
Table 4. Cyanosilylation of carbonyl compounds using trimethylsilylcyanide
a
1b /yield
(%)
c
2 /Yield
(%)
#
Educt/product
Time
(
TON
Time
(h)
TON
mmol
(%) 3
Yield
b
(%)
TON
b
b
h)
1
2
3
4
5
6
7
8
4-Chlorobenzaldehyde/2-(4-Cl-phenyl)-2-
trimethylsilyloxyacetonitrile
4-Fluorobenzaldehyde/2-(3-F-phenyl)-2-
trimethylsilyloxyacetonitrile
3-Hydroxybenzaldehyde/2-(3-trimethylsilyl-
oxyphenyl)-2-trimethylsilyloxyacetonitrile
Benzoin/1,2-diphenyl-1,2-bis(trimethylsilyl-
oxy)propionitrile
Benzoylacetone/1-trimethylsilyloxy-1-methyl-3-
benzoylpropionitrile
4-Bromoacetophenone/2-(4-Br-phenyl)-2-tri-
methylsilyloxypropionitrile
Benzaldehyde/1-phenyl-trimethylsilyloxy-
acetonitrile
Diphenyldiketone/2,3-diphenyl-2,3-bis(trimethyl-
silyloxy)butanedinitrile
1
100
100
80
22
80
0
50,000
50,000
40,000
11,000
40,000
0
0.75 100
100,000
50,000
98,000
80,000
80,000
80,000
99,000
100,000
12
2.2
20
71
54
66
18
70
100
93
100
4
8600
1
1
6
1
1
1
100
98
42,300
4900
60
6
80
1
80
81
0
1500
0
24
1.5
1.5
48
1
80
90
99
45,000
49,500
99
80
93
4500
1300
1
100
a
b
c
0
.002 mol% of 1b.
Determined by GC–MS. Reactions were run in dichloroethane at 75 8C.
.001 mol% of 2.
0
2
3,24
for Cu-imidazol-2-ylidenes.
With their systems, excel-
2.6. Differences in catalyst structure accounting for
differences in reactivity
lent yields approaching 100% were achieved using 3 mol%
of the corresponding catalyst, translating into maximum
turn-over numbers (TONmax) of 33.
From the set of data presented above, three important
conclusions may be drawn. Firstly, ALL catalysts presented
here are by far the most reactive Cu (I)–N-heterocyclic
carbene complexes that have been prepared for the above-
mentioned reactions. Secondly, no change in selectivity is
observed upon immobilization of 1a, respectively 1b on a
Merrifield type support. However, presumably due to
diffusion issues, reactivity is reduced, however, still exceeds
any system reported so far. Thirdly, complex 2 is by far the
more reactive one. This is believed to be a direct
As can be deduced from Table 5, entries 1–9, catalyst 1b, if
used on a 0.002 mol% scale, allowed for TONs up to
0,000. Yields were in the 80–100% range. Even better,
catalyst 2, used on a 0.001 mol% scale, allowed for TONs
up to 100,000, yields for all substrates investigated were in
the 70–100% range. The supported version 3 showed again
reduced, however, still acceptable activity, allowing for
TONs up to 42,500 and yields up to 100%.
5
Table 5. Hydrosilylation of carbonyl compounds using triethylsilane
a
1b /Yield
(%)
c
2 /Yield
(%)
#
Educt/product
Time
h)
TON
Time
(h)
TON
mmol%
of 3
Yield
b
(%)
TON
b
b
(
1
2
3
4
5
4-Chlorobenzaldehyde/4-Cl-phenyl-
1-triethoxysilylmethane
4-Fluorobenzaldehyde/4-F-phenyl-
triethoxysilylmethane
4-Bromoacetophenone/2-(4-Br-phenyl)-
1 h
100
100
0
50,000
50,000
0
45 min
100
100
100
98
100,000
100,000
100,000
98,000
29
1.1
33
30
12
100
23
0
38,800
21,000
0
45 min
24 h
1.5 h
2 h
0.5
1
1-triethoxysilylethane
Benzophenone/diphenyltriethoxy-
methane
4-N,N-Dimethylaminobenzaldehyde/4-
N,N-dimethylaminophenyl-triethoxy-
silylmethane
4-Chloroacetophenone/2-(4-Cl-phenyl)-
1-triethoxysilylethane
Benzaldehyde/4-Cl-phenyl-triethoxy-
silylmethane
90
90
45,000
45,000
1.5
1
20
40
660
98
98,000
3200
c
6
7
8
24 h
1 h
0
0
5
98
98,000
100,000
80,000
26
0
0
98
80
49,000
40,000
1
1
100
80
24
100
54
42,500
5300
Norborn-5-ene-2-carbaldehyde/
norborn-5-ene-2-yltriethoxysilyl-
methane
1 h
102
9
Benzoin/1,2-diphenyl-2-triethoxysilyl-
ethanol
1.5 h
0
0
1.5
70
70,000
35
0
0
Room temperature.
a
0
.002 mol%.
b
c
Determined by GC–MS. Reactions were run in THF at 65 8C using 0.15 mmol% of NaO-tert-Bu.
.001 mol%.
0

B. Bantu et al. / Tetrahedron 61 (2005) 12145–12152
12149
Scheme 4. Proposed mechanism for the cyanosilylation (left) and C]O hydrosilylation (right). Bromide may (in part) be replaced by tert-butoxide.
consequence of the structure of 2. As a matter of fact, it
consists of a cationic Cu (I) species, well protected by the
two N-heterocyclic carbenes, and a ‘naked’ dibromocup-
rate. However, according to the mechanism proposed by
Nolan et al. (Scheme 4), the formation of CuBr(1,3-
dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene) and
Cu(tert-butoxy)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-
the molecular weight. Instead, PMMA with similar
molecular weights in the range of 70,000–90,000 g/mol
was produced. The reason for this behavior apparently lies
in the insolubility of 2 in the polymerization medium. Thus,
once polymerization commences, the back reaction,
forming the ‘dormant species’ is hindered, resulting in the
rapid production of polymer. Once the deactivation step is
successfully accomplished, reactivation of the polymer
chain does not occur. Instead, the initiator forms new
growing polymer chains facing the same fate.
2
-ylidene), respectively, in course of the reaction is
proposed. Here the copper center is well-protected by the
large N-heterocyclic carbene ligand and the mesityl
moieties, respectively, leaving still enough space for the
substrates to coordinate. Unfortunately, we were not able to
retrieve unambiguous experimental evidence for this
assumption so far.
Therefore, 1b was used. This complex is more soluble and
in fact allowed for a more controlled polymerization of
MMA. Graphs of monomer conversion versus time as well
as a graph showing M versus the number of monomer
n
2
.7. Attempted ATRP of MMA using compounds 1b and 2
equivalents added (N) are shown in Figs. 3 and 4,
respectively. Polymerization results are summarized in
Table 6.
Atom transfer radical polymerization (ATRP) is a well-
developed polymerization technique for the synthesis of
2
9
narrow disperse polymers. The polymerization mechan-
ism involves a metal complex, where the metal changes
reversibly its oxidation state. In addition, some additional
free metal has been identified to play a positive role. In due
consequence, the new copper (I) complexes and in
particular complex 2 were expected to be suitable. However,
As can be seen, monomer consumption proceeded linearly
over time. Similarly, molecular weights developed linearly
up to a monomer:catalyst ratio of 300 and then remained
unchanged. However, molecular weights, as determined by
light scattering, were about twice as high as calculated. This
clearly indicates an initiation efficiency of roughly 0.5. In
view of this finding and the comparably high polydispersity
2
failed to provide an ATRP system capable of controlling
Figure. 3. Graph showing monomer conversion versus time for the
polymerization of MMA by 1b.
Figure. 4. Graph of number of monomer equivalents added (N) versus M
.
n
.
The line shows the theoretical values for M
n

12150
B. Bantu et al. / Tetrahedron 61 (2005) 12145–12152
Table 6. Summary of polymerization results for MMA using 1b
dichloromethane/pentane to yield 0.56 g (77%) of the
desired compound. FTIR (ATR): 2965 (m), 2929 (m),
2
Entry
N
M
n
(calcd)
M
n
(found)
PDI
1
868 (m), 1677 (m), 1518 (s), 1311 (s), 1169 (m). H NMR
1
2
3
4
100
200
300
400
10,000
20,000
30,000
40,000
4700
7400
8600
8708
1.39
1.53
1.55
1.82
(CDCl ) d 1.19 (d, 12H, CH ), 1.86 (q, 2H, CH ), 3.0 (t, 4H,
NCH ), 4.59 (m, 2H, NCH). C NMR (CDCl )d 194.7 (C:–
3 3 2
13
2
3
N), 60.3 (N–H), 37.1 (N–H ), 20.5 (CH ), 20.4 (CH ).
2
2
3
N, number of monomer equivalents added. Polymerizations were carried
out at 90 8C in diphenyl ether.
3
.1.2. Synthesis of CuBr(1,3-di(2-Pr)-3,4,5,6-tetrahydro-
pyrimidin-2-ylidene) (1b). In a 100 mL Schlenk flask were
added copper (I) chloride (120 mg, 1.21 mmol), 1,3-bis(2-
propyl)-3,4,5,6-tetrahydropyrimidinium bromide (300 mg,
indices (1.4–1.8, Table 6), the polymerization certainly does
not fulfil the stringent criteria of a true, controlled ATRP.
However, it should be emphasized, that this is the first report
on the use of an N-heterocyclic carbene–Cu system for these
purposes.
1
.20 mmol) and sodium tert-butoxide (118 mg, 1.23 mmol).
Dry THF was added (25 mL) under argon and the mixture
was stirred for 24 h at room temperature. The reaction
mixture was filtered through celite and the solvent was
removed in vacuo, leaving a brown coloured precipitate
behind. Recrystallization from dichloromethane/pentane
3. Experimental
yielded 285 mg (75%) of 1b. FTIR (ATR): 2968 (m),
2
1
932 (m), 2869 (m), 1517 (s), 1311 (s), 1169 (s). H NMR
3
.1. General
(CDCl ) d 1.19 (d, 12H, CH ),1.84 (q, 2H, CH ), 3.0 (t, 4H,
NCH ), 4.6 (m, 2H, NCH); C NMR (CDCl ) d 195.1
3 3 2
3
1
2
3
All manipulations were performed under a nitrogen
atmosphere in a glove box (MBraun LabMaster 130) or
by standard Schlenk techniques. Purchased starting
materials were used without any further purification.
Pentane, diethyl ether, toluene, methylene chloride and
tetrahydrofurane (THF) were dried using a solvent dry
(C:–N), 60.7 (N–H), 38.4 (N–H ), 20.5 (CH ), 20.7 (CH );
elemental analysis calcd for C H BrCuN: C, 38.41; H,
2 3 2
1
0 20
6
.77; N, 8.96; found, C, 38.81; H, 6.12; N, 9.04.
3
ylidene) CuBr ] (2). In a 100 mL Schlenk flask were
.1.3. [Cu(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-
C
2
K
2
system (SDS, MBraun). Chloroform-d was distilled from
1
added copper (I) chloride (0.370 g, 3.74 mmol), 1,3-
dimesityl-3,4,5,6-tetrahydropyrimidinium bromide (1.50 g,
3.74 mmol) and sodium tert-butoxide (0.36 g, 3.75 mmol).
Dry THF was added (40 mL) under an inert atmosphere and
the mixture was magnetically stirred for 24 h at room
temperature. The reaction mixture was filtered through a
plug of celite and the solvent was evaporated in vacuo,
leaving a light pink colored precipitate behind. Recrystalliz-
ation from dichloromethane/pentane yielded 2.3 g (88%) of
the desired compound. FTIR (ATR mode): 3275 (br), 2944
calcium hydride. Styrene and methyl methacrylate (MMA)
were dried over CaH overnight, distilled under vacuum and
2
stored under argon at K15 8C. The initiator ethyl-2-bromo
isobutyrate (EBIB) was distilled under reduced pressure
prior to use. Diphenyl ether was dried over molecular sieves
˚
(
3 A) and distilled prior to use.
NMR data were obtained at 300.13 MHz for proton and
5.74 MHz for carbon in the indicated solvent at 25 8C on a
7
Bruker Spectrospin 300 and are listed in parts per million
downfield from tetramethylsilane for proton and carbon.
Coupling constants are listed in Hz. IR spectra were
recorded on a Bruker Vector 2000 using ATR technology.
Elemental analyses were carried out at the Mikroanaly-
tisches Labor, Anorganisch-Chemisches Institut, TU
M u¨ nchen, Germany. Molecular weights and polydispersity
indices (PDIs) of the polymers were determined by GPC at
(
br), 2912 (br), 1608 (br), 1509 (s), 1481 (br), 1443 (br),
1
302 (s), 1205 (s), 1034 (br), 993 (br), 856 (s), 722 (br), 649
br), 611 (br) cm . H NMR (CDCl ) d 1.74 (24H, O–H
K1
1
(
of mesityl), 2.10 (m, 4H of CH ), 2.27 (s, p–CH of mesityl),
3 3
2
3
13
3
.10 (t, 8H, N–H ), 6.89 (s, 8H, aromatic); C NMR
2
(CDCl ): d 18.2 (o–CH of mesityl), 21.2 (p-CH3 of
mesityl), 20.0 (CH ), 44.3 (N–H ), 130.1, 135.1, 138,7,
1
for C H Br Cu N : C, 56.96; H, 6.08; N, 6.04. Found: C,
3 3
2
2
41.9 (aromatic C), 198.9 (C:–N); elemental analysis calcd
3
0 8C on Polymer Laboratories columns (PLgel 10 mm
4
4
56
2
2 4
MIXED-B, 7.5!300 mm) in THF at 25 8C using a Waters
Autosampler, a Waters 484 UV detector (254 nm), a light
scattering detector (Wyatt) and an Optilab Rex refractive
index detector (685 nm, Wyatt). The flow rate was 0.7 mL/
5
7.63; H, 6.14; N, 6.05.
3.1.4. PS-DVB–CH –OCO–CF NCF NCF –COOCu(1,3-
di(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) (3).
PS-DVB-CH -OH (1.00 g, 1.1 mmol OH/g) was suspended
2
in dry THF (20 mL). Perfluoroglutaric anhydride (1.00 mol
equiv, 246 mg, 1.10 mmol) was added. Stirring was continued
for 2 h, then the product was filtered off and washed three
times with THF. Itwas dried in vacuo resulting in a white solid
(1.35 g). FT-IR (ATR-mode): 3024 (br), 2 920(br), 1773 (s),
1600 (br), 1492 (s), 1451(s), 1306 (br), 1240 (br), 1174 (br),
1141 (br), 1046 (br), 1028 (br), 942 (br,) 871 (br), 823 (w), 747
2
2
2
2
min. A dn/dc of 0.086 was used for the determination of Mw
by light scattering.
3
.1.1. Synthesis of CuCl(1,3-di(2-Pr)-3,4,5,6-tetrahydro-
pyrimidin-2-ylidene) (1a). In a 100 mL Schlenk flask were
added copper (I) chloride (0.28 g, 2.82 mmol), 1,3-bis(2-
propyl)-3,4,5,6-tetrahydropyrimidinium tetrafluoroborate
(
2
0.70 g, 2.73 mmol) and sodium tert-butoxide (0.27 g,
.82 mmol). Dry THF was added (25 mL) under argon
K1
(s), 696 (s) cm . The solid was re-suspended in THF (10 mL)
and the mixture was stirred for 24 h at room temperature.
The reaction mixture was filtered through celite and the
solvent was evaporated in vacuo. A light green colored solid
was obtained, which was recrystallized from
and 1.0 equiv of NaOH (46 mg) dissolved in 25 mL of water
was added. The mixture was stirred for 2 h, then the solid was
filtered off, washed three times with water and re-suspended in
20 mL of water. AgNO3 (1.30 mol equiv, 230 mg,

B. Bantu et al. / Tetrahedron 61 (2005) 12145–12152
12151
1
.43 mmol), dissolved in 10 mL of water, was added and
3.5. X-ray measurement and structure determination of
1a and 2
stirring was continued for a further 4 h. The product was
filtered and washed three times each with water, diethyl ether
and pentane. Drying in vacuo gave a white solid (1.52 g). FT-
IR (ATR-mode): 3058 (br), 3024 (br), 2918 (br), 2848 (br),
1
1
8
Data collection was performed on a Nonius Kappa CCD
equipped with graphite-monochromatized Mo-K -radiation
a
˚
772 (br), 1654 (br), 1600 (br), 1510(s), 1492 (s), 1450 (s),
372 (w), 1177 (w), 1153 (w), 1027 (w), 906 (br), 841 (w),
20, (w), 749 (m), 696 (s). The solid was re-suspended in THF
(lZ0.71073 A) and a nominal crystal to area detector
distance of 36 mm. Intensities were integrated using
3
0
DENZO and scaled with SCALEPACK. Several scans
in f and u direction were made to increase the number of
redundant reflections, which were averaged in the refine-
ment cycles. This procedure replaces in a good approxi-
mation an empirical absorption correction. The structures
were solved with direct methods SHELXS86 and refined
(
25 mL) and 2 (65 mg, 0.20 mmol) was added. Stirring was
continued for a further 4 h. The product was filtered off,
washed with THF, dichloromethane and pentane and dried in
vacuo to yield a brown colored powder (1 g). FT-IR (ATR-
mode): 3057 (br), 3023 (br), 2918 (br), 2848 (br), 1657 (br),
1
1
2
31
600 (br), 1491 (s), 1450 (br), 1370 (br), 1285 (br), 1155 (w),
K1
055 (w), 1027 (w), 947 (br), 835 (br), 749 (m), 696 (s) cm
against F SHELX97. The function minimized was
Z
2
o
2 2
K1
.
S[w(F KF ) ] with the weight defined as w
c
2
2
2
2
2
Cu content as determined by ICP-OES after dissolving a
2
[s (F )C(xP) CyP] and PZ(F C2F )/3. All non-hydro-
o o c
0.0 mg sample in aqua regia: 4.15 mmol/g.
gen atoms were refined with anisotropic displacement
parameters. Positions of hydrogen atoms were calculated
and refined isotropically.
3
.2. Typical procedure for hydrosilylation reactions
3.6. Supporting information available
In a 50 mL Schlenk tube the catalyst (1.0 mmol%) was
dissolved in 1 mL of THF, sodium tert-butoxide (5.5 mg,
The crystallographic data for 1 and 2 have been deposited
with the CCDC-No. xxx and xxy, and at the Cambridge
Crystallographic Data Centre. The coordinates can be
obtained, on request, from the Director, Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge,
CB2 1EZ, UK. (fax: C44 1223 336033; e-mail: deposit@
ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).
1
1
5
5 mmol%) and 4 mol equiv of triethylsilane (166 mg,
.42 mmol) were added and the solution was stirred for
min. Then, the carbonyl compound (0.20–0.40 mmol),
dissolved in 2 mL of THF, was added to the reaction
mixture. The solution was heated to 65 8C. Product
conversion was monitored by GC–MS at defined time
intervals. Compounds were identified by GC–MS. Quanti-
fication was accomplished using an internal standard (tert-
butylbenzene).
4. Summary
3
.3. Typical procedure for cyanosilylation reactions
In summary we have developed new copper (I)-1,3-R2-
,4,5,6-tetrahydropyrimidin-2-ylidene-based catalysts.
3
In a 50 mL Schlenk tube the catalyst (1.0 mmol%) was
dissolved in 1 mL of dichloroethane, then 2 mol equiv of
trimethylsilylcyanide (71 mg, 0.71 mmol), dissolved in
Immobilization was accomplished at a Merrifield type
support. All catalysts showed unprecedented high activity in
the cyanosilylation and C]O hydrosilylation reactions
resulting in TONs up to 100,000. Unfortunately, all catalysts
failed to provide suitable ATRP systems capable of
polymerizing methyl methacrylate (MMA) in a perfectly
controlled way.
2
(
7
mL of dichloroethane, as well as the carbonyl compound
0.20–0.40 mmol) were added. The solution was heated to
5 8C. Product conversion was monitored by GC–MS at
defined time intervals. Compounds were identified by
GC–MS. Quantification was accomplished using an internal
standard (tert-butylbenzene).
Acknowledgements
3
.4. Typical procedure for the ATRP of MMA
Our work was supported in part by a grant of the Austrian
Science Fund (START Y-158).
A 50 mL Schlenk flask was charged with 5 mL of diphenyl
ether and the corresponding catalyst (0.5 mmol%), MMA
(
3.0 mL 28.3 mmol), EBIB (1.0 mmol%) and 0.500 mol
equiv of tert-butylbenzene (internal standard for monitoring
of monomer conversion) were added. 0.200 mL of the
reaction solution was withdrawn, mixed with acetone, and
used as reference solution. Then the reaction mixture was
heated to 90 8C. At appropriate timed intervals, 0.500 mL
aliquots of the solution were withdrawn and 3.0 ml thereof
were dissolved in acetone. Acetone solutions were analysed
by GC–MS, percent conversions were calculated relative to
the reference solution. The rest of the 0.500 mL samples
were mixed with methanol, the polymer that precipitated
was filtered off, washed with methanol and re-dissolved in
THF, passed through 0.2 mm Teflon filters and analysed by
GPC.
Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.tet.2005.07.116
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