The ethylsulfinate ligand: A highly efficient initiating group for the zinc β-diiminate catalyzed copolymerization reaction of CO2 and epoxides

Article abstract of DOI:10.1021/om020734f

The quantitative synthesis of a series of new zinc(II) sulfinate complexes (4a-e) by insertion of SO₂ into zinc-ethyl bonds of β-diiminate complexes ((ArN=C(CH₃)CH=(CH₃)CNAr)Zn(O(S=O)Et); Ar = 2,6-diisopropylphenyl (4a), 2

Full text of DOI:10.1021/om020734f

Organometallics 2003, 22, 211-214
211
Th e Eth ylsu lfin a te Liga n d : A High ly Efficien t In itia tin g
Gr ou p for th e Zin c â-Diim in a te Ca ta lyzed
Cop olym er iza tion Rea ction of CO2 a n d Ep oxid es
Robert Eberhardt,1a Markus Allmendinger,1a Gerrit A. Luinstra,1b and
Bernhard Rieger*,1a
Department of Materials and Catalysis, University of Ulm, D-89069 Ulm, Germany, and
BASF Aktiengesellschaft, D-67056 Ludwigshafen, Germany
Received September 6, 2002
Summary: The quantitative synthesis of a series of new
zinc(II) sulfinate complexes (4a -e) by insertion of SO2
into zinc-ethyl bonds of â-diiminate complexes ((ArNd
C(CH3)CHd(CH3)CNAr)Zn(O(SdO)Et); Ar ) 2,6-diiso-
propylphenyl (4a ), 2,6-diethylphenyl (4b), 2-ethyl-6-
isopropylphenyl (4c), 2,6-diphenylphenyl (4d ), 2,6-bis(4-
tert-butylphenyl)phenyl (4e)) is described. X-ray structure
analysis reveals a dinuclear, µ-ethylsulfinate-bridged
structure for 4a in the solid state, which in solution exists
in an equilibrium with the mononuclear species. The
easily accessible complexes 4a -c are highly active
catalysts for the alternating copolymerization of CO2 and
cyclohexene oxide, leading to products with narrow
molecular weight distributions.
X as the initiating group and are already active under
mild conditions. Chiral, 2-methyloxazoline-substituted
catalysts even afforded stereoregular polycarbonates.5
Diethylzinc reacts easily with ligands bearing an
acidic proton (e.g. BDI-H) to form 1 equiv of ethane.
Unfortunately, the resulting (BDI)ZnEt complexes are
not able to initiate the copolymerization reaction. A
known route for activation is their conversion to alco-
holates (Scheme 1b).4 This, however, results only in
moderate catalyst yield through protonolysis of the BDI
complexes with alcohols.
We report here on a new and simple strategy to yield
active single-component catalysts (4a -e) in quantitative
yield (Scheme 1b).6 The essential feature of the struc-
tures 4a -e is the ethylsulfinate ligand [(BDI)ZnOS(O)-
Et] that results from a quantitative insertion of dry SO2
into the Zn-carbon bond of 3a -e.7 In addition to the
behavior of this initiating group, also the influence of
BDI-H ligands of variable steric demand on the copo-
lymerization reaction is discussed.
In tr od u ction
Aliphatic polycarbonates are materials with interest-
ing properties, which are accessible by a metal-catalyzed
copolymerization reaction of CO2 and epoxides. The
combination of exergonic epoxide ring opening with
endergonic carbonate formation is presumably one of
the most important examples for CO2 activation, since
valuable materials are obtained. Furthermore, CO2 and
epoxides are cheap building blocks and especially CO2
is readily available. Early attempts to catalyze this
copolymerization reaction were hardly efficient. Usually
undefined zinc alkyl/alcohol mixtures or simple metal
salts have been applied.2
One of the first well-defined catalysts (zinc(II) bis-
(phenoxide)) was developed by Darensbourg in the
1990s.3 Coates et al. reported in 1998 on â-diimine Zn-
(II) complexes ((BDI)ZnX) as excellent catalysts for the
copolymerization reaction of CO2 and cyclohexene oxide
(CHO).4 These complexes of the general type (BDI)ZnX
(X ) alcoholate, acetate, bis(trimethylsilyl)amide) bear
Resu lts a n d Discu ssion
Syn th esis a n d Str u ctu r e of Zin c Su lfin a te Com -
p lexes. The â-diimine ligands 2a -d were prepared by
refluxing 2 equiv of the desired aniline with 1 equiv of
2,4-pentanedione in acidified ethanol, yielding the cor-
responding hydrochlorides or hydrobromides (Scheme
1a).8 Neutralization with aqueous carbonate solution
gives 2a -d in yields up to 80% after recrystallization.
Preparation of 2e works best in a two-step process.
Excess 2,4-pentanedione is condensed with aniline in
benzene. The isolated monoimine is heated under reflux
after addition of 1.1 equiv of aniline hydrobromide in
ethanol, resulting in a mixture of the â-diimine 2e and
* To whom correspondence should be addressed. E-mail:
bernhard.rieger@chemie.uni-ulm.de.
(1) (a) University of Ulm. (b) BASF Aktiengesellschaft.
(4) (a) Cheng, M.; Lobkovsky, E. B.; Coates, G. W. J . Am. Chem.
Soc. 1998, 120, 11018-11019. (b) Cheng, M.; Moore, D. R.; Reczek, J .
J .; Chamberlain, B. M.; Lobkovsky, E. B.; Coates, G. W. J . Am. Chem.
Soc. 2001, 123, 8738-8749. (c) Moore, D. R.; Lobkovsky, E. B.; Coates,
G. W. Angew. Chem. 2002, 114, 2711-2714. (d) Coates, G. W.; Cheng,
M. PCT Int. Appl. WO 2000008088, 2000; Chem. Abstr. 2000, 132,
152332. (e) Chisholm, M. H.; Gallucci, J .; Phomphrai, K. Inorg. Chem.
2002, 41, 2785-2794.
(2) (a) Inoue, S.; Koinuma, H.; Tsuruta, T. J . Polym. Sci., Part B:
Polym. Lett. 1969, 7, 287-292. (b) Soga, K.; Uenishi, K., Hosoda, S.;
Ikeda, S. Makromol. Chem. 1977, 178, 893-897. (c) Gorecki, P.; Kuran,
W. J . Polym. Sci., Part B: Polym. Lett. 1985, 23, 299-304. (d) Ree,
M.; Bae, J . Y.; J ung, J . H.; Shin, T. J . J . Polym. Sci., Part A: Polym.
Chem. 1999, 37, 1863-1876.
(3) (a) Darensbourg, D. J .; Holtcamp, M. W. Macromolecules 1995,
28, 7577-7579. (b) Darensbourg, D. J .; Niezgoda, S. A.; Draper, J . D.;
Reibenspies, J . H. J . Am. Chem. Soc. 1998, 120, 4690-4698. (c)
Darensbourg, D. J .; Holtcamp, M. W.; Struck, G. E.; Zimmer, M. S.;
Niezgoda, S. A.; Rainey, P.; Robertson, J . B.; Draper, J . D.; Reibenspies,
J . H. J . Am. Chem. Soc. 1999, 121, 107-116. (d) Darensbourg, D. J .;
Wildeson, J . R.; Yarbrough, J . C.; Reibenspies, J . H. J . Am. Chem.
Soc. 2000, 122, 12487-12496. (e) Dinger, M. B.; Scott, M. J . Inorg.
Chem. 2001, 40, 1029-1036.
(5) Cheng, M.; Darling, N. A.; Lobkovsky, E. B.; Coates, G. W. Chem.
Commun. 2000, 2007-2008.
(6) Another one-step route to BDI-zinc complexes starts from
commercially available Zn[N(SiMe3)2]2, which yields (BDI)ZnN(SiMe3)2
catalysts after several days in quantitative yield.4b
(7) (a) Hobson, J . T. J ustus Liebigs Ann. Chem. 1857, 102, 73-85.
(b) Wischin, G. J ustus Liebigs Ann. Chem. 1866, 139, 364-372. (c)
Carey, N. A. D.; Clark, H. C. Can. J . Chem. 1968, 46, 649-651.
(8) Feldman, J .; McLain, S. J .; Parthasarathy, A.; Marshall, W. J .;
Calabrese, J . C.; Arthur, S. D. Organometallics 1997, 16, 1514-1516.
10.1021/om020734f CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/02/2002

212 Organometallics, Vol. 22, No. 1, 2003
Notes
Sch em e 1
F igu r e 1. ORTEP plot of 4a with thermal ellipsoids drawn
at the 50% probability level. Hydrogen atoms are omitted
for clarity. Atoms labeled with a slanted prime (′) were
generated by symmetry operations.
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for 4a
empirical formula
fw
C64H96Cl4N4O4S2Zn2
1322.11
220(2)
0.710 73
monoclinic
C2/c
temp (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
20.752(4)
b (Å)
c (Å)
12.4136(16)
27.113(5)
â (deg)
101.19(2)
6852(2)
V (Å3)
Z
4
Dc (Mg/m3)
abs coeff, µ (mm-1
F(000)
1.282
0.963
2800
)
the aniline 1e. Separation can be accomplished by
conversion of the product mixture into hydroperchlor-
ates and subsequent crystallization.
cryst size (mm3)
0.62 × 0.42 × 0.38
1.92-24.12
-23 e h e 23
-14 e k e 14
-31 e l e 31
21 700
5417 (R(int) ) 0.0449)
4087
1.007
R1 ) 0.0384, wR2 ) 0.0914
R1 ) 0.0562, wR2 ) 0.0979
0.00050(11)
0.723 and -0.612
θ range for data collecn (deg)
index ranges
The conversion of dialkylzinc reagents with SO2 to
produce O-bound zinc(II) bis(alkyl) sulfinates, which
after acidic workup yield sulfinic acids, is a known
reaction.7 We investigated the synthesis of (BDI)ZnO-
(SO)Et complexes (4a -e), due to the structural similar-
ity of these alkyl sulfinates to carboxylates and carbon-
ates, that allow a CO2/epoxide copolymerization reaction
to occur. Reaction of (BDI)H with ZnEt2 gives (BDI)-
ZnEt in quantitative yield.4 Treatment with excess SO2
in toluene at -10 °C leads to an orange solution. After
the temperature is raised and SO2 is removed, the
(BDI)ZnO(SO)Et complexes were isolated quantitatively
as white (4a -c) or pale yellow (4d ,e) solids. The
complex 4a exists as a µ-sulfinate-bridged dimer in the
solid state (X-ray structure analysis; see Figure 1).9 The
eight-membered jagged metallacycle shows a torsion
angle of about 96° at each zinc sulfinate moiety (O(2,2′)-
S(S′)-O(1,1′)-Zn(Zn′)). The Zn-Zn′ separation is 4.98
Å, and the six-membered chelate ring is slightly puck-
ered (torsion angle C(2,2′)-C(1,1′)-N(1,1′)-Zn,Zn′ )
7.2°). However, the dimeric 4a exists in solution in an
equilibrium with its mononuclear analogue. Variable-
temperature 1H NMR investigations in toluene revealed
two sets of resonances whose intensities vary with
temperature. The set that becomes more intense with
no. of rflns collected
no. of indep rflns
no. of obsd rflns (I > 2σ(I))
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
extinction coeff
largest diff peak and hole (e Å-3
)
higher temperatures is assigned to the monomeric
complex. The calculated equilibrium constants Keq([Zn2]
h 2[Zn]) for the monomer and dimer of 4a (toluene-d8;
at 60 °C, Keq ) 2.2 × 10-4 M, and at 80 °C, Keq ) 2.6 ×
10-3 M) show that the equilibrium favors the dimeric
species more than in the case of the analogous acetate
1
complexes (C6D6, 20 °C, 2.9 × 10-2 M).4a The H NMR
spectra of 4b-e show only one set of signals. These are
attributed to the sulfinate-bridged species for the less
crowded complexes 4b,c and to the monomeric forms
of 4d ,e, which carry bulky terphenylaniline and (sub-
stituted terphenyl)aniline moieties.
Cop olym er iza tion of Cycloh exen e Oxid e a n d
Ca r bon Dioxid e. Polymerization experiments with the
single-component catalysts 4a -e were performed in
neat CHO at 10 bar of CO2 pressure (Table 2). All
polycarbonates produced are atactic, with chains com-
(9) A similar structure was also found for sulfinate complexes of
Pd: Gates, D. P.; White, P. S.; Brookhart, M. Chem. Commun. 2000,
47-48.

Notes
Organometallics, Vol. 22, No. 1, 2003 213
Ta ble 2. CHO/CO2 Cop olym er iza tion Resu lts
tion (Mw/Mn ) 4.3). Further increase of Tp affords higher
activities, and the molecular weights reach a maximum
at Tp ) 60 °C (Mn ) 40 000).13 The molecular weight
distributions at elevated temperatures (Tp ) 50-60 °C)
are narrow andsmost interestinglysshow a shoulder
at higher molecular weights. This prompted us to
investigate a possible correlation of these bimodal
distributions with the observed temperature-dependent
monomer/dimer equilibrium of the organometallic spe-
cies. Therefore, we performed one experiment using a
temperature gradient (25 f 60 °C) which was shown
by means of variable-temperature NMR to be the
decisive temperature range for the equilibrium (Table
2, entry 6). Indeed, the resulting polymer material gave
a clearly bimodal distribution with two maximums at
Mn ) 4800 and Mn ) 56 000. This observation led us to
the assumption that monomer and dimer of 4a are
active catalysts, affording lower and higher molecular
weight products, respectively.14 The dimeric 4a decays
slowly into the monomeric species, which might give an
explanation for the observed broader molecular weight
distribution at 40 °C. In addition, the difference in
polymerization performance between 40 and 50 °C
suggests also a slow initiation of the polymerization
reaction at lower temperature.15
Obta in ed w ith Ca ta lysts 4a -ea
carbonate
temp time
(°C)
(h) 10-3Mn Mn
Mwb/ linkagesc
TOF
e
b
entry cat.
(%)
TONd (h-1
)
1
2
3
4
5
6
7
8
4a
4a
4a
4a
4a
4a
40
2
2
2
2
2
25.9
38.7
39.8
34.0
32.0
7.6
31.8
49.6
20.8
29.3
4.29
1.11
1.11
1.50
1.40
5.57
1.13
1.30
1.30
3.20
90
98
97
94
93
87
97
96
95
38
16
128
284
312
336
330
64
50
60
70
80
142
156
168
165
25-60f 0.5
4b 60
2
3
2
4
3
328
651
270
16
164
217
135
4
4bg 60
9
10
11
4c
4d h 90
4e 60
60
9
3
a
All reactions were performed in 50 mL steel autoclaves at 10
bar of CO2 pressure in neat cyclohexene oxide with [Zn]:[epoxide]
b
) 1:1000. Determined by gel-permeation chromatography in
THF, calibrated with narrow polystyrene standards. c Calculated
d
by 1H NMR in CDCl3. In units of (mol of CHO converted to
poly(cyclohexene carbonate))/(mol of zinc). e In units of (mol of CHO
converted to poly(cyclohexene carbonate))/((mol of zinc) h). f The
g
temperature was raised from 25 to 60 °C within 30 min. The
reaction was carried out in a 250 mL Bu¨chi reactor equipped with
h
an online ATR-IR system. Because of poor catalyst solubility, the
reaction was carried out in 2000 equiv of CHO at 90 °C.
Sch em e 2
Polymers produced with 4b,c show similar activity
and molecular weights and also give a shoulder at
higher Mn, indicating a behavior comparable to that of
4a . The sterically more crowded complexes 4d ,e produce
only traces of polymers with a surprisingly high ether
content.16
prising only trans-cyclohexane linkages.10 The carbonate
content of the obtained polymers was higher than 87%,
except of those produced with 4d ,e, which show pre-
dominantly polyether sequences. Experiments in an
autoclave equipped with online ATR-IR monitoring
(Table 2, entry 8) indicated an immediate initiation after
addition of CO2 and a nearly linear increase of polycar-
bonate concentration.11
Quenching of the polymerization experiments after
20 min resulted in the formation of low-molecular-
weight poly(cyclohexene carbonate) that enabled us to
analyze endgroups. The 1H NMR spectrum (CDCl3)
shows two sextets at δ 2.35 and 2.46 (J ) 7.5 Hz), which
are attributed to diastereotopic protons of the methylene
groups in ethylsulfinic acid esters which result from
epoxide insertion into a zinc-ethylsulfinate bond (Scheme
2).12
4a shows nearly constant polymerization activity at
reaction temperatures between 60 and 80 °C and
produces polymers with predominantly carbonate link-
ages.13 The activities are similar to those reached with
corresponding (BDI)ZnX complexes bearing other ini-
tiating groups. Polymerization experiments at Tp ) 40
°C (Table 2, entry 1) lead to medium-molecular-weight
products, however, of broad molecular weight distribu-
Exp er im en ta l Section
Gen er a l Com m en ts. Unless otherwise specified, all syn-
theses and manipulations were carried out under a dry argon
atmosphere using conventional Schlenk techniques. Toluene
and THF were dried by distillation from LiAlH4. Dichlo-
romethane and cyclohexene oxide were distilled from CaH2.
Diethylzinc (solution in toluene 15%), epoxides, and sulfur
dioxide were purchased from Fluka and Aldrich. Dry carbon
dioxide was purchased from BASF Aktiengesellschaft, Lud-
wigshafen, Germany. â-Diiminate ligands 2a -c and 2,6-
diarylanilines 1d ,e were prepared according to literature
procedures.8,17 Diffraction data were recorded on an IPDS
instrument from STOE. Crystal data and structure refinement
details are presented in Table 1. Absorption corrections were
not applied. The structure was solved by direct methods
(SHELXS-86). Refinement was performed with the SHELXL-
97 program.
2d . To a mixture of 2,4-pentanedione (1.85 mL, 18 mmol)
and 2,6-diphenylaniline (1d ; 9.8 g, 40 mmol) in 120 mL of
ethanol was added concentrated HCl (1.5 mL, 18 mmol). After
the mixture was stirred for 72 h under reflux, ethanol was
removed in vacuo. The residue was suspended in 50 mL of
dichloromethane and vigorously mixed with a sodium carbon-
ate solution (2 M). The organic layer was separated and
washed with 20 mL of water and dried over sodium sulfate.
Solvent was removed under vacuum, and the remaining yellow
(10) Determined by 13C NMR spectroscopy.
(11) The linear increase of the carbonate band was observed only
over the first 1 h, which might be due to the high viscosity of the
reaction media.
(14) For the low-molecular-weight fraction, molecular weights are
comparable to results found by Coates et al. with acetate and alcoholate
complexes.4a,b
(15) In contrast to similar complexes from Coates et al., 4a shows
no activity at 20 °C, which is presumably due to a hindered initiation
at low temperature.
(12) Norton, R. V.; Douglass, I. B. Org. Magn. Reson. 1974, 6, 89-
91.
(13) Visible amounts of cyclic carbonate are formed at reaction
temperatures above 60 °C, presumably due to a depolymerization
reaction of previously formed polycarbonate. This additional process
helps to explain the nearly constant polymerization activity (cyclic
carbonate is not considered) over a broad temperature range and the
lower molecular weights occurring at higher temperatures.
(16) Similar behavior (no activity) was also found for complexes
bearing 2,6-di-n-propyl substitution.4b
(17) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskela¨, M.; Rieger, B.
Organometallics 2001, 20, 2321-2330.

214 Organometallics, Vol. 22, No. 1, 2003
Notes
oil was mixed with ethanol and refluxed for a few minutes,
yielding a slightly yellow powder, which was isolated. To a
solution of the powder in a minimum amount of dichlo-
romethane was added methanol. Overnight at 4 °C a yellow
powder precipitated, which was isolated and dried under
vacuum, to give 5.4 g of clean product 2d (54%). Anal. Calcd
for C41H34N2: C, 88.77; H, 6.18; N, 5.05. Found: C, 88.64; H,
6.24; N, 5.04. 1H NMR (400 MHz, C2D2Cl4): δ 1.17 (s, 6H),
4.07 (s, 1H), 7.06 (d, 8H), 7.15 (d, 8H), 7.25 (t, 2H), 7.32 (d,
4H), 12.02 (s, 1H). 13C NMR (100 MHz, C2D2Cl4): δ 20.78,
96.28, 123.88, 126.30, 127.79, 129.08, 129.54, 131.95, 136.58,
140.57, 159.48.
2-Hyd r oxy-4-(2,6-bis(4-ter t-bu tylp h en yl)p h en yl)im in o-
2-p en ten e. 2,6-Bis(4-tert-butylphenyl)phenylamine (1e; 1.6 g,
4.5 mmol), 2,4-pentanedione (0.91 mL, 6.3 mmol), and toluene-
4-sulfonic acid (10 mg) was dissolved in 60 mL of benzene and
refluxed for 18 h using a Dean-Stark condenser. Benzene was
removed completely, and the remaining sticky solid was
dissolved in 3 mL of dichloromethane. After addition of 15 mL
of methanol, dichloromethane was partially removed under
vacuum, yielding a white precipitate, which was isolated (1.78
g, 90%). Anal. Calcd for C31H37NO: C, 84.69; H, 8.48; N, 3.19.
Found: C, 84.88; H, 8.42; N, 3.10. 1H NMR (400 MHz,
CDCl3): δ 1.28 (s, 3H), 1.33 (s, 18H), 1.92 (s, 3H), 4.76 (s, 1H),
7.32-7.40 (m, 11H), 12.13 (s, 1H). 13C NMR (100 MHz,
CDCl3): δ 19.50, 28.91, 31.44, 34.52, 96.42, 125.22, 125.48,
127.71, 128.96, 129.91, 133.72, 136.08, 140.40, 150.10, 162.22,
195.22.
11.33, 24.09, 31.47, 34.55, 97.42, 125.28, 125.33, 130.11,
131.03, 137.09, 138.57, 145.30,149.37, 167.09.
Gen er a l Syn th esis of Eth ylsu lfin a te Com p lexes 4a -
e. A solution of 3a -e (2 mmol) in 40 mL of toluene was cooled
to -10°C. An excess of dry SO2 was added with rapid stirring.
The solution turned immediately to red-orange and was stirred
for 15 min at -10 °C. The mixture was warmed to room
temperature and stirred another 15 min at 50 °C. Solvent and
excess SO2 were removed in vacuo while the solution discol-
ored. The solid product could be isolated in quantitative yield.
In some cases small amounts of hydrolyzed products were
found. Purification was achieved by dissolving the complex in
toluene, dichloromethane, or THF, filtering the insoluble
residues, and crystallizing in a minimum amount of the
desired solvent.
4a . This compound is a white solid and can be crystallized
from toluene or dichloromethane at -30 °C. X-ray analysis of
the crystals revealed that the complex exists as µ,η2-sulfinato
dimer in the solid state. Anal. Calcd for C62H92N4O4S2Zn2: C,
1
64.63; H, 8.05, N, 4.86. Found: C, 64.42, H, 7.97, N, 4.84. H
NMR (500 MHz, 80 °C, toluene-d8, “M” denotes monomer, “D”
denotes dimer): δ 0.53 (t, 6H, O(SO)CH2CH3, M), 0.91 (t, 6H,
O(SO)CH2CH3, D), 1.05 (d, 12H, CHMeMe, M), 1.17 (d, 48H,
CHMeMe, D), 1.40 (d, 12H, CHMeMe, M), 1.59 (s, 12H, R-Me,
D), 1.73 (s, 6H, R-Me, M), 2.13 (m, 6H, O(SO)CH2CH3, M +
D), 3.28 (m, 12H, CHMe2, M + D), 4.63 (s, 2H, â-CH, D), 4.89
(s, 1H, â-CH, M), 7.11 (m, 18H, Ar H, M + D).
4b. This compound is a white solid and can be crystallized
from toluene at -30 °C. Anal. Calcd for C54H76N4O4S2Zn2: C,
2e. 2-Hydroxy-4-((2,6-bis(4-tert-butylphenyl)phenyl)imino)-
2-pentene (1.23 g, 2.8 mmol) and (2,6-bis(4-tert-butylphenyl)-
phenyl)ammonium bromide (1.36 g, 3.1 mmol) were dissolved
in 15 mL of ethanol and refluxed for 65 h. All volatiles were
removed under vacuum, and the remaining solid was sus-
pended in dichloromethane and treated with aqueous sodium
carbonate solution until all solid was dissolved. The organic
layer was separated and the volume reduced to about 5 mL.
The ligand was precipitated with 25 mL of methanol, filtered,
washed with methanol, and dried under vacuum to yield 1.2
g of 2e (54%). Anal. Calcd for C57H66N2: C, 87.87; H, 8.54; N,
1
62.36; H, 7.37, N, 5.39. Found: C, 61.95, H, 7.43, N, 5.29. H
NMR (500 MHz, 60 °C, benzene-d6): δ 0.79 (t, 6H, O(SO)-
CH2CH3), 1.10 (t, 24H, CH2Me), 1.51 (s, 12H, R-Me), 1.82 (q,
4H, O(SO)CH2CH3), 2.59 (m, 16H, CH2Me), 4.63 (s, 2H, â-CH),
7.04 (m, 12H, Ar H).
4c. This compound is a white solid and can be crystallized
from toluene at -30 °C. Anal. Calcd for C54H76N4O4S2Zn2: C,
1
62.36; H, 7.37, N, 5.39. Found: C, 62.18, H, 7.45, N, 5.33. H
NMR spectroscopic analysis shows multiple signal sets sug-
gesting a mixture of isomers (combination of cis and trans
1
1
configuration in dimers). H NMR (500 MHz, 70 °C, toluene-
3.60. Found: C, 87.48; H, 8.48; N, 3.49. H NMR (400 MHz,
d8): δ 0.92 (m, 6H, O(SO)CH2CH3), 1.11 (m, 24H, CHMeMe),
1.58 (m, 12H, R-Me), 2.06 (m, 12H, o-Me), 2.21 (m, 4H, O(SO)-
CH2CH3), 3.36 (m, 2H, CHMe2), 4.67 (m, 2H, â-CH), 6.92 (m,
4H, Ar H), 7.04 (m, 8H, Ar H).
CDCl3): δ 1.13 (s, 6H), 1.18 (s, 36H), 4.05 (s, 1H), 7.13-7.27
(m, 22H), 12.27 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 20.81,
31.22, 34.28, 96.97, 123.80, 124.76, 128.89, 129.62, 137.69,
140.90, 148.76, 159.70.
4d . This compound is a slightly yellow solid and can be
crystallized from THF at -30 °C. Anal. Calcd for C43H38N2O2-
SZn: C, 72.52; H, 5.38, N, 3.93. Found: C, 71.89, H, 5.44, N,
3.78. 1H NMR (500 MHz, 70 °C, C2D2Cl4): δ 0.26 (t, 3H, O(SO)-
CH2CH3), 1.28 (q, 2H, O(SO)CH2CH3), 1.38 (s, 6H, R-Me), 4.05
(s, 1H, â-CH), 7.23 (m, 20H, Ar H), 7.36 (m, 6H, Ar H).
4e. This compound is a slightly yellow solid and can be
crystallized from THF at -30 °C. Anal. Calcd for C59H70N2O2-
SZn: C, 75.66; H, 7.53, N, 2.99. Found: C, 74.95, H, 7.53, N,
2.92. 1H NMR (500 MHz, 70 °C, toluene-d8): δ 0.55 (t, 3H,
O(SO)CH2CH3), 1.16 (q, 2H, O(SO)CH2CH3), 1.31 (s, 6H, R-Me),
1.33 (s, 18H, CMe3), 1.47 (s, 18H, CMe3), 3.98 (s, 1H, â-CH),
7.38 (m, 22H, Ar H).
Gen er a l Syn th esis of 3a -e (Mod ified fr om Ref 4a ). To
a solution of 2a -e (4 mmol) in 40 mL of toluene at 0 °C was
added a solution of ZnEt2 (16 mmol) in 14.5 mL of toluene.
The mixture was stirred for 18 h at 80 °C, and the clear
solution was dried under vacuum, giving a quantitative yield
of the desired compound as a light yellow oil or solid.
1
3a . H NMR (500 MHz, toluene-d8): δ 0.36 (q, 2H), 1.02 (t,
3H), 1.38 (d, 12H), 1.45 (d, 12H), 1.90 (s, 6H), 3.36 (m, 4H),
5.17 (s, 1H), 7.29 (m, 6H). 13C NMR (125 MHz, toluene-d8): δ
-1.30, 12.04, 23.23, 23.47, 24.20, 28.51, 95.41, 123.73, 125.95,
141.48, 145.02, 167.32.
3b. 1H NMR (500 MHz, benzene-d6): δ 0.22 (q, 2H), 0.92 (t,
3H), 1.16 (t, 12H), 1.63 (s, 6H), 2.45 (m, 4H), 2.61 (m, 4H),
4.93 (s, 1H), 7.04 (m, 6H). 13C NMR (500 MHz, benzene-d6): δ
-2.01, 12.09, 14.56, 22.99, 25.18, 95.42, 125.37, 126.74, 136.92,
146.83, 167.00.
Ack n ow led gm en t. We thank Prof. Ulf Thewalt,
Section for X-ray and Electron Diffraction, University
of Ulm, for the X-ray analysis of 4a . We are grateful to
the Bundesministerium fu¨r Bildung und Forschung
(BMBF, Grant FZ 03C0310) as well as to BASF Ak-
tiengesellschaft for generous financial support.
1
3c. H NMR spectroscopic analysis revealed a 1:1 mixture
1
of the cis and trans isomers. H NMR (500 MHz, benzene-d6):
δ 0.25 (q, 4H), 0.92 (t, 3H), 0.95 (t, 3H), 1.15 (d, 12H), 1.21 (d,
12H), 1.63 (s, 12H), 2.14 (s, 12H), 3.16 (m, 4H), 4.95 (s, 1H),
4.96 (s, 1H), 7.01 (m, 4H), 7.11 (m, 2H).
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data, bond distances, bond angles, anisotropic dis-
placement parameters, all atom coordinates, and thermal
parameters. This material is available free of charge via the
Internet at http://pubs.acs.org.
3d . 1H NMR (500 MHz, benzene-d6): δ 0.13 (q, 2H), 0.97 (t,
3H), 1.39 (s, 6H), 4.20 (s, 1H), 6.99 (t, 2H), 7.11 (m, 4H), 7.18
(d, 4H), 7.21 (m, 16 H).
3e. 1H NMR (500 MHz, benzene-d6): δ 0.04 (q, 2H), 0.78 (t,
3H), 1.27 (s, 36H), 1.48 (s, 6H), 4.34 (s, 1H), 7.035 (t, 2H), 7.31
(d, 4H), 7.38 (d, 8H), 7.53 (d, 8H). 13C NMR (benzene-d6): δ
OM020734F