("Ferrocene-salaldiminato") Zirconium complexes for ethylene polymerization catalysis: The role of the bulky substituents

Article abstract of DOI:10.1021/om3004509

We prepared the 2-hydroxy-5-trimethylsilylferrocenecarbaldimine systems 13 enantioselectively by a short synthetic route starting from the chiral ferrocene carbaldehyde acetal 5. The imines 13a-c were used to synthesize the zwitterionic ("ferrocene-salald

Full text of DOI:10.1021/om3004509

Article
pubs.acs.org/Organometallics
(“Ferrocene-salaldiminato”)zirconium Complexes for Ethylene
Polymerization Catalysis: The Role of the Bulky Substituents
Xiaowu Wang,† Roland Frohlich,†,§ Constantin G. Daniliuc,†,§ Bernhard Rieger,‡ Aleksandra Jonovic,‡
̈
Gerald Kehr,† and Gerhard Erker*,†
†Organisch-Chemisches Institut der Universitat Munster, Corrensstrasse 40, 48149 Munster, Germany
̈
̈
̈
‡WACKER-Lehrstuhl fur Makromolekulare Chemie, Technische Universitat Munchen, Lichtenbergstraße 4, 85747, Garching bei
̈
̈
̈
Munchen, Germany
̈
S
* Supporting Information
ABSTRACT: We prepared the 2-hydroxy-5-trimethylsilylferrocenecar-
baldimine systems 13 enantioselectively by a short synthetic route
starting from the chiral ferrocene carbaldehyde acetal 5. The imines 13a−
c were used to synthesize the zwitterionic (“ferrocene-salaldimina-
to”)2ZrCl4 complexes 14a−c. Activation with MAO gave homogeneous
Ziegler−Natta catalysts, which showed only a moderate ethylene
polymerization activity, similar to the unsubstituted parent “ferrocene-
salaldiminato” zirconium systems. Consequently, a synthetic route was
devised and carried out to make the corresponding 2-hydroxy-3,5-bis(trimethylsilyl)ferrocenecarbaldimines (21) available. The
enantiomerically highly enriched ligands (pS)-21a and -d derived from the aldehyde and aniline or cyclohexylamine, respectively,
were used to synthesize the corresponding (“ferrocene-salaldiminato”)2ZrCl4 complexes 22a,d. Both gave highly active
homogeneous Ziegler−Natta catalysts upon activation with MAO for the formation of linear low molecular weight polyethylene.
Complex 22d and many ligand precusors from both sequences were characterized by X-ray diffraction.
Scheme 1
INTRODUCTION
■
Homogeneous Ziegler−Natta olefin polymerization catalysis
based on group 4 metal complexes has undergone much
development during the last decades. An enormous number of
publications have described the various metallocene catalysts,1
different types of mono-Cp metal systems including the Cp/
amido (“constrained geometry”) systems,2 and a variety of non-
Cp (“postmetallocene”)3 catalyst developments. Among the
latter the salicyl-aldiminato-derived group 4 complexes4
constitute an interesting and important subclass in homoge-
neous olefin polymerization catalysis.
We had introduced the salicylaldimine-related 2-hydroxy-
ferrocenecarbaldimine ligands 2 (in this account for simplicity
termed as "ferrocene-salaldiminato" or "Fe-salaldiminato").5−8
In contrast to the systems 1, their nonplanar structure
introduces an element of planar chirality into this chemistry.
We had developed viable syntheses of the homochiral bis-
κO,N[“Fe-salaldiminato”]-chelate zirconium dichloride com-
plexes 3 as well as the related zwitterionic octahedral bis
κO[“Fe-salaldiminato”]ZrCl4 complexes 4. We were able to
synthesize both the (pS, pS) and (pR, pR) enantiomers
selectively (Scheme 1).5−8
Activation of both systems 3 and 4 with excess MAO gave
ethylene polymerization catalysts of almost equal activity. They
formed linear polyethylene at temperatures up to 125 °C but
with rather low catalytic activities. It was previously shown that
the catalyst activities of the bis(salicylaldiminato)ZrCl2-derived
systems [(1)2ZrCl2] dependend critically on the substituents at
the arene moieties of the chelate ligand.
The parent compound (R = H) showed low polymerization
activities,9 whereas systems bearing bulky substituents (R =
tBu) gave highly active ethylene polymerization catalysts upon
activation.10 Therefore, we have now carried out a benchmark
study on our ferrocene-derived “three-dimensional” analogues
of the (salicylaldiminato)zirconium systems and attached bulky
substituents at the functionalized Cp-ring of the “Fe-
Received: May 23, 2012
© XXXX American Chemical Society
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a
salaldiminato” systems (2) in order to investigate the crucial
role of steric bulk in different positions of these systems. For
reasons of easy synthetic feasibility, we chose −SiMe3
substituents for this study.
Scheme 3.
RESULTS AND DISCUSSION
■
Attachment of a Bulky Trimethylsilyl Substituent at a
Site Adjacent to the Aldimine Group. We had previously
used variants of the Kagan route8 for the selective synthesis of
the hydroxyferrocenecarbaldimine enantiomers (pS)-2-H and
(pR)-2-H, respectively. Both started from the ferrocene
aldehyde acetal 5. The (pS)-OH group was introduced by
means of a directed metalation, halogenation, and oxidation
sequence. For the synthesis of the (pR)-OH isomer, we also
started from 5, used a similar metalation/halogenation/
metalation sequence to block the “o-(pS) position” by the
−SiMe3 substituent, and then introduced the −OH substituent
at the remaining o-position by a similar sequence5 (see Scheme
2), which involved fluoride-induced removal of the −SiMe3
placeholder at some intermediate stage.
a
Conditions: (i) Cu2O/AcOH, 80 °C, 74%, (ii) NaOMe, dmf, then
t
t
Ph2 BuSiCl ([Si] = Ph2 BuSi, 84%), (iii) p-TsOH/H2O, 87%, (iv)
ArNH2, p-TsOH, 80 °C (a, Ar = Ph, quant, b, Ar = Mes, 89%, c, Ar =
C6F5, 60%), (v) Et3N·3HF/THF (a, Ar = Ph, 77%, b, Ar = Mes, 65%,
c, Ar = C6F5, 74%).
Scheme 2
three substituents at the “upper” Cp ring of the ferrocene
framework of compound (pS)-13a: the −OH group (C2−O1:
1.349(2) Å) is in 1,2-position to the carbaldimine function
(C3−C11: 1.443(2) Å) and in 1,3-position to the −SiMe3
group (C4−Si1: 1.876(2) Å). The carbaldimine moiety (C11−
N1: 1.286(2) Å) is oriented in-plane with the Cp-ring and
oriented toward the adjacent −OH group (θ O1−C3−C2−C9
= 1.50°, C2−C3−C11−N1 = 4.05°, C3−C11−N1−C21 =
177.57°). There is evidence for internal hydrogen bonding
between the −OH group and the imino-nitrogen (see Figure
1).
In solution compound (pS)-13a features the 1H NMR −OH
1
resonance at δ 9.88 (benzene-d6). It shows the H/13C NMR
signals of the aldimine −CH[N] unit at δ 8.78/166.3, and it
Starting material of this synthesis was the ferrocene derivative
(S,S,pR)-8. This iodoferrocene was heated with Cu2O/acetic
acid in acetonitrile11 at elevated temperature to yield the
acetoxyferrocene acetal (S,S,pS)-9 (see Scheme 3). Compound
9 was isolated in >70% yield (see the Experiment Section and
the Supporting Information for its characterization). Subse-
quent treatment with sodium methoxide followed by tert-
butyl(chloro)diphenylsilane then gave the O-silyl-protected α-
hydroxylferrocene carbaldehyde acetal (S,S,pS)-10 in 84% yield.
The acetal was converted to the free aldehyde 11 by treatment
t
with p-toluene sulfonic acid. The Ph2 BuSi-protected aldehyde
(pS)-11 was then converted to three aldimine derivatives [12a
(Ar = Ph), 12b (Ar = mesityl), 12c (Ar = C6F5)] by acid-
catalyzed condensation with the respective primary aromatic
amines. The ligand synthesis was then successfully finished by
Et3N·3HF-induced deprotection to give the respective free 2-
hydroxy-5-trimethylsilylferrocene carbaldimines (pS)-13a (Ar =
Ph), (pS)-13b (Ar = mesityl), and (pS)-13c (Ar = C6F5) (see
Scheme 3).
The compounds 13 were characterized by spectroscopy and
C,H,N-elemental analysis. Compound (pS)-13a (Ar = Ph) was
also characterized by X-ray diffraction. The X-ray crystal
structure analysis confirmed the specific arrangement of the
Figure 1. Molecular structure of (pS)-13a.
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features the NMR signals of the −SiMe3 substituent at δ 0.18
(1H, s, 9 H) and −0.4 (29Si).
Table 1. Ethene Polymerization with the (pS,pS)-14/MAO
Catalyst Systems
a
The ligand system (pS)-13a reacted at room temperature in
dichloromethane (2 h) with zirconium tetrachloride in a molar
ratio of 2:1 to yield the blue zwitterionic pseudooctahedral
complex 14a (91%). A closely related example of this general
complex type will be described below. Complex (pS,pS)-14a
b
c
complex
T (°C)
yield (g PE)
activity
Tm (°C)
14a
14a
14b
14b
14c
14c
25
80
25
80
25
80
0.28
0.25
0.68
0.48
1.26
1.13
14
12
34
24
63
56
137
138
139
137
136
n.o.
1
shows the typical H/13C NMR features of the symmetry
equivalent pair of −CHNPhH+ iminium funtional groups at
δ 8.87/161.3 (CH, d, 3JHH = 14.8 Hz) and 12.2 (broad, NH),
respectively. The ligands (pS)-13b and (pS)-13c reacted
analogously with ZrCl4 to give the corresponding zwitterionic
complexes (pS,pS)-14b (Ar = mesity, 76%), and (pS,pS)-14c
(Ar = C6F5, 79%) as deep blue solids. Since we employed
highly enantiomerically enriched, chiral O,N-chelated com-
plexes, we obtained in each case a single diastereomer of the
(κO-ligand)2ZrCl4 systems as single enantiomers (see Scheme
4). Consequently, complex (pS,pS)-14c features a single set of
19F NMR resonances at δ −147.8 (o), −154.0 (p), and −160.3
(m F of C6F5).
a
Polymerization conditions: P(ethene) = 2 bar, toluene = 200 mL, 2 h.
Polymerizations were carried out in 1 L autoclave reactors with 5 μmol
of Zr (14a 4.5 mg, 14b 5.4 mg, 14c 5.8 mg) preactivated with 400
equiv of MAO in 5 mL of toluene. The remaining 1600 equiv of MAO
b
c
was then added. In g/(mmol × bar × h). DSC, second run.
metalation for the introduction of the −SiMe3 substituent at
the alternative site adjacent to the −OH group in the “Fe-
salaldiminato” ligand system.
Again, the Kagan methodology was employed to introduce a
bromo substituent stereoselectively at the ferrocene carbalde-
t
hyde nucleus. The chiral acetal (S,S)-5 was treated with BuLi,
followed by α,α′-dibromoxylene15 to yield (S,S,pS)-15 (see
Scheme 5). Its stereochemistry was confirmed by an X-ray
crystal structure analysis (for details see the Supporting
Information).
Scheme 4
a
Scheme 5
The complexes (pS,pS)-14a−c were activated by treatment
with an excess of methylaluminoxane (MAO) to give
homogeneous Ziegler−Natta catalysts for the polymerization
of ethene. The polymerization reactions were carried out in
toluene solution at 2 bar ethene pressure at two different
temperatures. In all cases, linear polyethylene (PE) was
obtained (see Table 1) that was close to insoluble in
chlorobenzene at 80 °C. We assume that the (pS,pS)-14/
MAO catalysts produced ultrahigh linear PE12 under these
conditions. However, the catalyst activities at all three catalysts
were quite low (see Table 1), similar to that observed using the
unsubstituted parent 3/4 plus MAO systems.6
These results indicated that the attachment of the bulky
trimethylsilyl substituents at the carbaldimine side of the “Fe-
salaldiminato” ligands had almost no influence on the behavior
of the polymerization catalysts derived from the hydroxyferro-
cene carbaldimine ligands. We, therefore, consequently
introduced the bulky −SiMe3 substituent at the α position
adjacent to the −OH group.
Attachment of a Bulky Substituent (−SiMe3) at a Site
Adjacent to the −OH Group. We used the established ability
of the bromo substituent at arenes13 and ferrocenes14 to direct
a
Conditions: (i) tBuLi, ether, then C6H4(CH2Br)2, 83%, (ii) LiTMP 1
equiv, then Me3SiCl, (iii) LiTMP 2.5 equiv, then Me3SiCl, 68%, (iv)
Cu2O, AcOH, CH3CN reflux, 58%, (v) p-TsOH/H2O, 98%, (vi) 10%
KOH, C2H5OH, rt, 85%, (vii) R-NH2, p-TsOH, R = Ph (a) 84%, R =
Mes (b) quant, R = C6F5 (c) 83%, R = cyclohexyl (d) 89%.
We then treated (S,S,pS)-15 with the Li-TMP base (TMPH
= 2,2,6,6-tetramethylpiperidine), followed by treatment with
trimethylsilyl chloride. The reaction in an equimolar ratio gave
a mixture of the mono- and disilylated product (16 or
potentially an isomer and 17). They were hard to separate.
Therefore, we treated (S,S,pS)-15 with a 2.5 molar excess of the
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Li-TMP base and obtained the disilylated product (S,S,pR)-17
selectively and in good yield (68%). From then on, we tried a
few protocols (for details see the Supporting Information) and
eventually arrived at the synthetic sequence depicted in Scheme
5.
Scheme 6
The bromo substituent in 17 was exchanged for acetoxy by
the established Cu2O/AcOH reaction. Then the acetal auxiliary
was removed by treatment with acid/water to give the aldehyde
19. Saponification of the acetate eventually gave the free α-
hydroxyferrocene-carbaldehyde product (pS)-20 bearing a
bulky trimethylsilyl group adjacent to the −OH functionality
at the “upper” ferrocene Cp-ring.
Compound (pS)-20 was characterized spectroscopically
[1H/13C NMR: δ 10.20/199.0 (−CHO), 8.00 (−OH), 0.36
and 0.11 (1H of −SiMe3; IR (KBr): ν
̃
3420 (bs, OH), 1635
cm−1 (CO)], by C,H elemental analysis, and by X-ray
diffraction. The X-ray crystal structure analysis of (pS)-20 (see
Figure 2) shows a pair of Me3Si− substituents at the “upper”
Figure 2. View of the molecular structure of compound (pS)-20.
ferrocene Cp-ring, one directly adjacent to the −CHO unit
(C1−Si1: 1.865(3) Å) and one in ortho position to the −OH
group (C4−Si2: 1.860(3) Å). The aldehyde carbonyl group lies
in the Cp-plane (θ C3−C2−C11−O2: −3.22°; C11−O2 =
1.216(5) Å), and it is oriented toward the −OH group (C3−
O1 = 1.361(4) Å), probably because of the formation of an
intramolecular hydrogen bond.
We then prepared a series of corresponding “Fe-salaldi-
mines” (21) by condensation of the doubly Me3Si-substituted
hydroxy-ferrocene carbaldehyde (pS)-20 with the primary
amines aniline (a), mesityl amine (b), pentafluoroaniline (c),
and cyclohexylamine (d), respectively. The corresponding
imines 21a−d were obtained in good yield (see Scheme 6).
Both compounds (pS)-21a (R = Ph) and (pS)-21d (R = Cy)
were characterized by X-ray crystal structure analysis (see
Figure 3). In (pS)-21a, the hydrogen bridge between −OH and
the imine nitrogen leads to a syn orientation of the −CHN
unit toward the hydroxyl group in-plane with the substituted
ferrocene Cp-ring. The phenyl substituent at nitrogen is rotated
slightly outside the imine plane [C11−N1: 1.272(3) Å, θ C11−
N1−C21−C26 = 33.63°]. The structure of the cyclohexylimine
derivative (pS)-21d features a similar overall structural
composition [C11−N1 = 1.266(7) Å, C11−N1−C21−C26 =
−119.29°].
Figure 3. Molecular structure of the “Fe-salaldimines” (pS)-21a (R=
Ph; top) and (pS)-21d (R = cyclohexyl; bottom).
deep blue solid in 76% yield. In solution, the C2-symmetric
1
complex features a single set of H/13C NMR ligand signals
[e.g., δ 8.35 (d 3JHH = 16.8 Hz)/167.1 (−CH[N])]. It shows
1
a broad NH-Cy H NMR resonance at δ 11.19.
Single crystals of (pS,pS)-22d suitable for the X-ray crystal
structure analysis were obtained from an ether solution by slow
evaporation of the solvent. Complex (pS,pS)-22d possesses C2-
symmetry in the crystal. It features a pseudo-octahedral
coordination geometry at the central zirconium atom with
both “Fe-salaldiminato” ligands trans-κ,O-coordinated (Zr1−
O1: 1.992(6) Å) and the four chloride ligands in the meridial
positions. The “Fe-salaldiminato” ligands are found as their
The C6F5-substituted imine (pS)-21c was also characterized
by X-ray diffraction. For details including a scheme of the
structure see the Supporting Information.
Treatment of the N-cyclohexyl-substituted bulky hydrox-
yferrocene carbaldimine (pS)-21d with zirconium tetrachloride
in a 2:1 molar ratio gave bis κO-ligand-substituted Zr complex
(pS,pS)-22d. The zwitterionic complex 22d was isolated as a
D
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CNHCy+ tautomeric iminium forms (C11−N1: 1.239(10)
Å). Both the ferrocene units are arranged at the linear −O−
Zr−O−core such that their substituted Cp-rings are syn-
oriented in the overall C2-symmetric arrangement (see Figure
4).
They produced linear low molecular weight polyethylene with
16
1
vinyl end groups (determined by H NMR). We noticed the
influence of the Al/Zr ratio on the catalyst performance (see
Table 2), with an optimized situation being achieved at Al/Zr
ratios between 1000 and 500.
At low reaction times (30 min to 1 h), the corresponding
(pS,pS)-22a/MAO ethene polymerization catalyst (R = Ph)
shows a similar performance in the 0 to 50 °C temperature
range. Again, we notice a tendency toward even higher catalyst
activities at low Al/Zr ratios (see Table 3). The (pS,pS)-22a/
MAO catalyst exibits high catalytic activity. It forms rather low
molecular weight linear polyethylene with a vinyl end group.
A comparison of the polymerization results obtained with the
(pS,pS)-22a, 22d/MAO catalysts, having a bulky −SiMe3 group
adjacent to the −O[Zr] moiety of the (“Fe-salaldiminato”)2Zr
complexes, with those of the less substituted 14/MAO systems
clearly confirms the crucial role of the presence of steric bulk
near the oxygen site of these catalyst systems.
The doubly silyl-substituted “Fe-salaldiminato”-derived cata-
lyst (pS,pS)-22a (R = Ph)/MAO system shows another
peculiarity; at longer reaction times (≥2 h, see Table 3), it
increasingly forms polyethylene with a pronounced bimodal
distribution. Along with the low molecular weight PE, we
observed the formation of a high molecular weight linear PE
fraction as a minor byproduct (ca. 10% to 30%). Preactivation
with MAO over a long period of time (6 h, entry 8 in Table 3)
leads to a situation where the usual major low molecular weight
PE formation has become completely suppressed in favor of the
sole formation of the high molecular weight PE product, albeit
at the cost of a substantial reduction of the catalyst activity. A
comparison with the low activity/high molecular weight
producing less substituted 14/MAO catalyst system (see
above) lets us assume that the 22a/MAO system is not stable
for prolonged times under our typical polymerization reaction
conditions potentially due to loss of the “proximate” −SiMe3
substituent.
Figure 4. Projection of the molecular structure of complex (pS,pS)-
22d.
Complex (pS,pS)-22a (R = Ph) was formed analogously by
reaction of the neutral ligand (pS,pS)-21a with ZrCl4 in a 2:1
molar ratio. The deep blue product was isolated in ca. 70%
yield.
The C2-symmetric complex (pS,pS)-22a shows a broad NH
1H NMR resonance at δ 12.30 in solution and the typical
1H/13C NMR signals of the pair of −CHNHPh units at the
3
ferrocene framework [δ 8.80 (d, JHH = 15.4 Hz)/161.7]. The
pair of unsubstituted ferrocene Cp-ligands gives rise to a sharp
1
1H NMR signal at δ 4.58, and we monitored H NMR signals
of the pairs of −SiMe3 substituents at δ 0.58 and 0.38.
Complexes (pS,pS)-22a and -d were used for the generation
of homogeneous ethene polymerization catalysts. We first
activated the system (pS,pS)-22d (R = cyclohexyl) by treatment
with excess MAO and performed polymerization reactions at
three different temperatures (0, 25, 50 °C, toluene solution, 2
bar ethylene pressure); under the three conditions, the “Fe-
salaldiminato” Zr/MAO systems were very active catalysts.
CONCLUSIONS
■
Our study shows that the three-dimensional analogues of the
salicylaldiminato metal complexes, the “Fe-salaldiminato”
complexes, can readily be synthesized. In contrast to their
“flat” aromatic analogues, these di- and multisubstituted
ferrocene derivatives are planarly chiral. A combination of
Table 2. Ethene Polymerization with the (pS,pS)-22d/MAO Catalyst System
a
b
c
d
d
entry
[Al]/[Zr]
Tp (°C)
time (h)
yield (g PE)
A
Tm
Mn
Mw
PDI
1
2000
2000
2000
2000
2000
2000
1000
1000
1000
500
0
0
0.5
1
3.2
7.2
3.4
5.9
4.8
7.4
6.0
11.0
3.6
5.2
3.4
0.8
650
720
128
125
129
130
125
127
124
132
130
130
130
130
1480
1400
1870
1240
1200
1160
1680
1400
5150
2370
2200
3960
4920
5130
3.3
3.7
2.4
4.0
3.1
3.0
3.8
3.7
2.8
4.7
4.0
2.8
2
3
25
25
50
50
25
25
50
25
25
25
0.5
1
670
4490
4
590
4930
5
0.5
1
960
3730
6
740
3460
7
0.5
1
1200
1100
720
6420
8
5130
9
0.5
0.5
0.25
0.5
14 020
11 270
8990
10
11
12
1050
1340
160
500
250
11 120
a
Polymerization conditions: P(ethene) = 2 bar, toluene = 200 mL. Polymerizations were carried out in 1 L autoclave reactors with 5 μmol of Zr
complex (5.7 mg) preactivated with 400 equiv of MAO in 5 mL of toluene; the remaining 1600 equiv of MAO was added with an addition funnel
b
c
d
while the autoclave was charged with Ar. Values of selected representative experiments are listed. g/(mmol·bar·h). °C, DSC, second run. g/mol.
E
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Table 3. Ethene Polymerization with the (pS,pS)-22a/MAO Catalyst System
a
b
c
d
d
entry
[Al]/[Zr]
T (°C)
time (h)
yield (g PE)
A
Tm
Mn
Mw
PDI
1
2
3
4
2000
2000
2000
2000
0
25
25
25
0.5
0.5
1
4.6
4.9
580
980
900
810
117
118
122
127
750
860
1600
1960
2.1
2.3
2.8
2.9
2.1
3.5
2.8
2.8
3.1
4.5
3.1
3.0
3.3
2.7
2.6
9.0
1100
1440
3100
2
16.2
4260
120 000 (84:16)
1010
250 000
3490
5
6
2000
2000
50
50
0.5
1
5.3
1060
1130
122
125
11.3
1130
3120
93 000 (84:16)
1180
260 000
3620
7
2000
50
2
15.9
800
127
140 000 (72:28)
397 000
640 000
1 230 000
4190
e
8
2000
1000
1000
50
25
25
0.5
0.5
1
0.14
4.6
30
920
840
137
123
126
9
1380
10
8.4
1690
5530
190 000 (91:9)
2080
520 000
5470
11
500
25
0.5
2.8
550
127
a
Polymerization conditions: P(ethene) = 2 bar, toluene = 200 mL. Polymerizations were carried out in 1 L autoclave reactors with 5 μmol of Zr
complex (5.7 mg) preactivated with 400 equiv of MAO in 5 mL of toluene; the remaining 1600 equiv of MAO was added with an addition funnel
b
c
d
while the autoclave was charged with Ar. Values of selected representative experiments are listed. g/(mmol·bar·h). °C, DSC, second run. g/mol.
e
5 μmol of Zr complex in 5 mL of toluene activated with 400 equiv of MAO; the solution was stirred at rt for 6 h and then injected into the
autoclave. The remaining 1600 equiv of MAO was subsequently injected.
Chemicals: Unless otherwise noted all chemicals were used as
purchased. 2,6-Diisopropylaniline and 2,4,6-trimethylaniline were
stirred over calcium hydride and distilled prior to use. Trimethyl
chlorosilane, dimethylformamide, and acetonitrile were purified
according to the standard purification method.20 The following
instruments were used for physical characterization of the compounds:
melting points: TA-Instruments DSC Q-20; elemental analyses: Foss−
Heraeus CHNO-Rapid; IR: Varian 1300 FT-IR; NMR: Bruker AC-
200 P-FT (1H, 200 MHz), Bruker AV 300 (1H, 300 MHz; 29Si, 60
MHz, dept based on nJSiH = 7 Hz, δ29Si(SiMe4) = 0), Bruker AMX-400
(1H, 400 MHz), Varian 500 MHz INOVA (1H, 500 MHz; 13C, 126
MHz), Varian UNITY plus NMR spectrometer (1H, 600 MHz; 13C,
151 MHz). [NMR chemical shifts were referenced to the respective
solvent signal; numbering of the compounds see the Supporting
Information.] X-ray diffraction: Data sets were collected with a Nonius
KappaCCD diffractometer. Programs used: data collection, COL-
LECT (Nonius B.V., 1998); data reduction, Denzo-SMN;21
absorption correction, Denzo;22 structure solution, SHELXS-97;23
structure refinement, SHELXL-97;24 and graphics, XP (BrukerAXS,
2000). Thermal ellipsoids are shown with 50% probability, R-values
are given for observed reflections, and wR2 values are given for all
reflections. The optical rotations were determined using a Perkin-
Elmer 341 polarimeter. The measurements were performed at room
temperature using a Na lamp. The solvent and the respective
wavelength used for the measurement are indicated within the
experimental details. The unit for all values of optical rotation is [deg
× cm2 × g−1]; the respective concentration is given in units of [g ×
mL−1].25
Polymer samples were dissolved at 140 °C before GPC on a
Polymer Laboratories PL-GPC 220 high-temperature chromatograph,
equipped with 2 Olexis 300·7.5 mm columns and triple detection by a
differential refractive index detector, a PL-BV 400 HT viscometer, and
a Precision Detectors model 2040 light scattering detector (15°, 90°).
The solvent was 1,2,4-trichlorbenzene (BHT stabilized) at 160 °C,
with a PE standard.
Materials. Compound 5 was synthesized according to the
literature.8b Ferrocenecarboxaldehyde and (S)-1,2,4-butanetriol were
purchased from Sigma-Aldrich and Alfa Aesar, respectively, and used
without further purification. Ferrocenes (S,S,pS)-7, (S,S,pR)-8 and 15
were prepared according to literature procedures.1 The syntheses of
the ferrocenes (S,S,pS)-9, 10, 16, (S,S,pR)-17, 18, and (pS)-11, 12a,
12b, 12c, 13a, 13b, 13c, 20, 21a, 21b, 21c, and 21d were
independently developed analogously to published procedures, and
optimized modifications are presented here. In particular, dilithiation
two imine ligands at a group 4 metal center as commonly takes
place in the respective homogeneous Ziegler−Natta catalyst
precursors would result in the formation of a mixture of
diastereomers if starting from the racemic ligand systems.
Therefore, we have from the beginning used highly
enantiomerically enriched “Fe-salaldiminato” ligands. The
enantioselective synthesis of these ligands proved no problem,
and they have become available by straightforward variations of
literature routes from stereoselective synthetic ferrocene
chemistry.8,17 The polymerization results from this and
previous studies showed broad parallels between established
salicylaldiminato group 4 catalyst chemistry10,18 and the
catalytic behavior of the new “Fe-salaldiminato” zirconium
systems. In both series, the unsubstituted parent compounds
gave at best catalysts of mediocre activities. However, this is
changed drastically upon attachment of bulky substituents at
the right position or the arene (or ferrocene) ring systems,
namely, directly adjacent to the −OH (or −O[M])
functionality. In our case, we used the −SiMe3 group for
reasons of synthetic simplification, but this was sufficient for
proof of principle, although our new catalyst systems may have
been somewhat hampered due to the potential instability of this
substituent under actual catalytic reaction upon prolonged
exposure. It might be that the respective tert-butyl-substituted
“Fe-salaldiminato” catalyst systems will be more stable. It will
be interesting to see whether such ferrocene-derived ligands
might become useful additions to the broad catalyst repertoire
in homogeneous “postmetallocene” Ziegler−Natta chemistry.
EXPERIMENTAL SECTION
■
General Information. All reactions involving air- or moisture-
sensitive compounds were carried out under an inert gas atmosphere
(argon) by using Schlenk-type glassware or in a glovebox. All solvents
were dried and degassed before use, if necessary, for the respective
reaction. Attention should be paid to the purification of the ferrocene
hydroxyl derivatives due to their facile oxidation. Dichloromethane,
diethyl ether, pentane, tetrahydrofuran, and toluene were dried using a
solvent drying system as described by Grubbs.19 Dimethylformamide
was stirred over calcium hydride and distilled prior to use. Deuterated
solvents used for NMR spectroscopy were dried if necessary.
F
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conditions of compound 15 with TMP-Li were well developed, and we
present the optimized conditions. Caution: triethylamine trihydro-
fluoride is very toxic and causes severe burns; alkyllithium reagents are
extremely pyrophoric. All such reagents must be handled with due
care.
Ph′), 7.22 (m, 1H, p-Ph), 7.20 (m, 2H, m-Ph), 7.13 (m, 1H, p-Ph′),
7.07 (m, 2H, m-Ph′), 3.97 (s, 5H, C5H5), 3.96 (d, 3JHH = 2.6 Hz, 1H,
3
5
4-H), 3.76 (dd, JHH = 2.6 Hz, JHH = 0.7 Hz, 1H, 5-H), 1.07 (s, 9H,
2
tBu), 0.40 (s, JSiH = 6.8 Hz, 9H, SiMe3). 13C{1H} NMR (151 MHz,
[D6]-benzene, 298 K): δ 192.2 (CHO), 136.1 (o-Ph), 135.9 (o-Ph′),
133.3 (i-Ph), 131.9 (i-Ph′), 130.7 (p-Ph), 130.5 (p-Ph′), 128.2 (m-Ph),
128.2 (m-Ph′), 128.5 (C2), 73.7 (C3), 71.9 (C5), 70.6 (C5H5), 65.9
(C1), 65.1 (C4), 26.8 (tBu), 19.6 (tBu), 0.2 (SiMe3). [α]2D0 = −30.7 (c
0.00215, dichloromethane).
Preparation of Compound (S,S,pS)-9. The iodoferrocene
(S,S,pR)-8 (15.63 g, 30.4 mmol, 1 equiv) and copper(I) oxide (1.01
g, 7.08 mmol, 1.5 equiv) were suspended in acetonitrile (300 mL).
After addition of acetic acid (9.13 g, 152 mmol, 5 equiv), the mixture
was heated to 80 °C for 3 h under an argon atmosphere. The solvent
was removed, and the crude product was purified by column
chromatography (silica gel, cyclohexane/ethyl acetate, 4:1) to yield
10.09 g (22.6 mmol, 74%) of the desired product as a yellow oil. Anal.
Calcd for C21H30FeO5Si: C, 56.50; H, 6.77. Found: C, 56.74; H, 6.77.
1H NMR (600 MHz, [D6]-benzene, 298 K): δ 5.45 (s, 1H, 6-H), 4.72
Preparation of Compound (pS)-12a. The aldehyde (pS)-11
(483 mg, 0.89 mmol, 1 equiv), aniline (0.40 mL, 4.5 mmol, 5 equiv),
and p-toluenesulfonic acid (16.9 mg, 0.089 mmol, 0.1 equiv) were
dissolved in dry toluene (10 mL) in a Schlenk vessel and heated at 80
°C for 18 h. Removal of the solvent gave the crude product, which was
purified by column chromatography (cyclohexane/triethylamine/ethyl
acetate, 66:1:1, Rf = 0.74) to give a red oil quantitatively. Anal. Calcd
for C36H41FeNOSi2: C, 70.22; H, 6.71; N, 2.27. Found: C, 70.09; H,
3
3
(d, JHH = 2.6 Hz, 1H, 4H)t, 4.33 (s, 5H, C5H5), 3.84 (d, JHH = 2.6
Hz, 1H, 5H)t, 3.82 (ddd, 2JHH = 11.4 Hz, 3JHH = 5.0 Hz, 3JHH = 1.3 Hz,
1H, 10-Heq), 3.77 (m, 1H, 8-H), 3.44 (ddd, JHH = 12.4 Hz, JHH
11.4 Hz, JHH = 2.6 Hz, 1H, 10-Hax), 3.35 (dd, JHH = 9.9 Hz, JHH
3
2
1
=
=
6.80; N, 2.04. H NMR (600 MHz, [D6]-benzene, 298 K): δ 9.09 (d,
3
2
3
5JHH = 0.5 Hz, 1H, CHN), 7.88 (m, 2 H, o-Ph), 7.62 (m, 2H, o-Ph′),
7.34 (m, 2 H, o-PhN), 7.222 (m, 2H, m-PhN)1, 7.215 (m, 1H, p-Ph)1,
7.22 (m, 2H, m-Ph)1, 7.12 (m, 1H, p-Ph′), 7.07 (m, 2H, m-Ph′), 7.04
(m, 1H, p-PhN), 4.05 (s, 5H, C5H5), 4.02 (d, 3JHH = 2.6 Hz, 1H, 4-H),
3.80 (dd, 3JHH = 2.6 Hz, 5JHH = 0.6 Hz, 1H, 5-H), 1.1 (s, 9H, tBu), 0.50
(s, 2JSiH = 6.7 Hz, 9H, SiMe3), [1 from the ghsqc NMR experiment].26
13C{1H} NMR (151 MHz, [D6]-benzene, 298 K): δ 159.1 (CHN),
153.7 (i-PhN), 136.2 (o-Ph), 136.0 (o-Ph′), 133.6 (i-Ph), 132.3 (i-Ph′),
130.6 (p-Ph), 130.4 (p-Ph′), 129.6 (m-PhN), 128.2 (m-Ph), 128.1 (m-
Ph′), 126.9 (C2), 125.4 (p-PhN), 120.9 (o-PhN), 75.6 (C3), 70.6 (C5),
70.5 (C5H5), 64.9 (C1), 64.0 (C4), 26.9 (tBu), 19.6 (tBu), 1.0
(SiMe3). [α]2D0 = −4.3 (c 0.01, dichloromethane).
6.4 Hz, 1H, 12-H), 3.10 (dd, 2JHH = 9.9 Hz, 3JHH = 4.4 Hz, 1H, 12-H′),
3.10 (s, 3H, OCH3), 1.81 (s, 3H, AcCH3), 1.56 (dddd, 2JHH = 13.1 Hz,
3JHH = 12.4 Hz, 3JHH = 11.5 Hz, 3JHH = 5.0 Hz, 1H, 9-Hax), 0.93 (dtd,
2JHH = 13.1 Hz, 3JHH = 2.6 Hz, 3JHH = 1.3 Hz, 1H, 9-Heq), 0.40 (s, 2JSiH
= 6.7 Hz, 9H, SiMe3), [t tentative assignment]. 13C{1H} NMR (151
MHz, [D6]-benzene, 298 K): δ 168.3 (CO), 117.0 (C3)t, 99.6 (C6),
82.3 (C2)t, 76.2 (C8), 75.9 (C12), 70.7 (C5H5), 69.3 (C5), 66.6
(C10), 66.2 (C1), 63.8 (C4), 58.8 (OMe), 28.1 (C9), 20.7 (AcCH3),
1.2 (SiMe3) [t tentative assignment]. [α]2D0 = +8.1 (c 0.01055,
dichloromethane).
Preparation of Compound (S,S,pS)-10. The acetate (S,S,pS)-9
(10.09 g, 22.6 mmol, 1 equiv) was dissolved in N,N-dimethylforma-
mide (100 mL), and sodium methoxide (1.34 g, 24.9 mmol, 1.1 equiv)
was added in one portion, yielding a dark red solution. After 90 min,
tert-butylchlorodiphenylsilane (6.83 g, 24.9 mmol, 1.1 equiv) was
added, and the bright yellow mixture was stirred overnight. The
solvent was removed, and the residue was purified by column
chromatography to yield 12.26 g (19.1 mmol, 84%) of a yellow oil
(silica gel, cyclohexane/ethyl acetate, 15:1). Anal. Calcd for
C35H46FeO4Si2: C, 65.40; H, 7.21. Found: C, 65.61; H, 7.16. 1H
NMR (600 MHz, [D6]-benzene, 298 K): δ 7.99 (m, 2 H, o-Ph), 7.75
(m, 2 H, o-Ph′), 7.28 (m, 2 H, m-Ph), 7.26 (m, 1H, p-Ph), 7.11(m, 1H,
p-Ph′), 7.10 (m, 2H, m-Ph′), 5.84 (s, 1H, 6-H), 4.23 (s, 5H, C5H5),
3.95 (m, 1H, 10-H′), 3.92 (m, 1H, 8-H), 3.76 (d, 3JHH =2.6, 1H, 4-H),
3.63 (m, 1H, 10-H), 3.52 (d, 3J HH =2.6, 1H, 5-H), 3.46 (dd, 2JHH = 9.7
Hz, 3JHH = 6.4 Hz, 1H, 12-H), 3.22 (dd, 2JHH = 9.7 Hz, 3JHH = 4.7 Hz,
1H, 12-H′), 3.16 (s, 1H, OMe), 1.67 (m, 1H, 9-H), 1.21 (s, 9H, tBu),
Preparation of Compound (pS)-13a. The imine (pS)-12a (0.519
g, 0.84 mmol, 1 equiv) and triethylamine trihydrofluoride (0.09 mL,
0.56 mmol, 2/3 equiv) were dissolved in tetrahydrofuran (20 mL), and
the solution was stirred for 2 h. The solvent was removed, and the
crude product was purified by column chromatography under argon
(silica gel, cyclohexane/ethyl acetate/triethylamine, 20:1:1, solvents
were degassed before use). Removal of the solvent under vacuum gave
quantitative (pS)-13a. X-ray quality crystals were obtained from a
solution in pentane at −30 °C. Anal. Calcd for C20H23FeNOSi: C,
63.66; H, 6.14; N, 3.71. Found: C, 64.00; H, 6.34; N, 3.54. Mp: 102
1
°C (DSC). H NMR (600 MHz, [D6]-benzene, 298 K): δ 9.88 (bs,
5
1H, OH), 8.78 (d, JHH = 0.5 Hz, 1H, CHN), 7.12 (m, 2H, m-PhN),
3
7.07 (m, 2H, o-PhN), 7.01 (m, 1H, p-PhN), 4.69 (dm, 1H, JHH = 2.6
3
Hz, 4-H), 4.03 (s, 5H, C5H5), 3.74 (d, 1H, JHH = 2.6 Hz, 5-H), 0.18
2
(s, JSiH = 6.6 Hz, 9H, SiMe3). 13C{1H} NMR (151 MHz, [D6]-
benzene, 298 K): δ 166.3 (CHN), 151.0 (i-PhN), 130.9 (C2)t, 129.7
(m-PhN), 126.1 (p-PhN), 120.8 (o-PhN), 70.4 (C5), 70.3 (C5H5), 68.3
(C3)t, 66.0 (C1), 61.6 (C4), 0.8 (1JSiC = 52.6 Hz, SiMe3) [1 tentative
assignment]. [α]2D0 = +0.7 (c 0.001, dichloromethane).
2
2
1.05 (dm, JHH = 13.2 Hz, 1H, 9-H′), 0.44 (s, JSiH = 6.8 Hz, 9H,
SiMe3). 13C{1H} NMR (151 MHz, [D6]-benzene, 298 K): δ 136.1 (o-
Ph, o-Ph′), 134.2 (1JSiC = 75.1 Hz, i-Ph), 132.6 (1JSiC = 74.4 Hz, i-Ph′),
130.4 (p-Ph), 130.1 (p-Ph′), 128.1 (m-Ph), 128.0 (m-Ph′), 123.7
(C3)t, 100.4 (C6), 79.9 (C2)t, 76.7 (C8), 75.9 (C12), 70.3 (C5H5),
67.3 (C5), 67.0 (C10), 64.0 (1JSiC = 71.8 Hz, C1), 61.6 (C4), 58.8
X-ray crystal structure analysis of 13a: formula C20H23FeNOSi,
M = 377.33, red crystal, 0.45 × 0.20 × 0.10 mm, a = 7.8042(2), b =
10.3403(3), c = 22.6773(6) Å, V = 1830.01(9) Å3, ρcalc = 1.370 g cm−3,
μ = 0.895 mm−1, empirical absorption correction (0.688 ≤ T ≤ 0.915),
Z = 4, orthorhombic, space group P212121 (No. 19), λ = 0.71073 Å, T
= 223(2) K, ω and φ scans, 31 085 reflections collected ( h, k, l),
[(sin θ)/λ] = 0.60 Å−1, 4532 independent (Rint = 0.030) and 4317
observed reflections [I > 2σ(I)], 223 refined parameters, R = 0.022,
wR2 = 0.062, max. (min.) residual electron density 0.27 (−0.17) e Å−3,
hydrogen atoms calculated and refined as riding atoms, Flack
parameter −0.008(10).
(OMe), 28.3 (C9), 26.9 (tBu), 19.7 (1JSiC = 69.1 Hz, tBu), 1.4 (1JSiC
=
53.2 Hz, SiMe3) [t tentative assignment]. [α]2D0 = +10.8 (c 0.01,
dichloromethane).
Preparation of Compound (pS)-11. The acetal (S,S,pS)-10
(11.64 g, 18.1 mmol, 1 equiv) and p-toluenesulfonic acid (6.90 g, 36.3
mmol, 2 equiv) were dissolved in a two-phase mixture of
dichloromethane (80 mL) and water (20 mL). The mixture was
heated to reflux for 3 h under vigorous stirring. The phases were
separated, and the organic phase was dried over magnesium sulfate.
Filtration and removal of the solvent gave the crude product, which
was purified by filtration on silica gel (cyclohexane/ethyl acetate, 4:1).
Attempts to crystallize the product in pentane did not yield the
compound, so further purification was achieved by column
chromatography on silica gel (cyclohexane/ethyl acetate/triethyl-
amine, 66:1:1), yielding 7.72 g (76%) of a red oil after removal of the
solvent. Anal. Calcd for C30H36FeO2Si2: C, 66.65; H, 6.71. Found: C,
Preparation of Compound (pS)-12b. The aldehyde (pS)-11
(1.70 g, 3.15 mmol), 2,4,6-trimethylaniline (2.2 mL, 15.7 mmol, 5
equiv), and p-toluenesulfonic acid (60 mg, 0.315 mmol, 0.1 equiv)
were dissolved in dry toluene (40 mL) in a Schlenk vessel and heated
at 125 °C for 7 h. Removal of the solvent gave the crude product,
which was purified by column chromatography (cyclohexane/triethyl-
amine/ethyl acetate, 66:1:1, Rf = 0.74) to give 1.85 g (89%) of the
imine as an orange foam solid. Anal. Calcd for C39H47FeNSi2O: C,
1
1
67.02; H, 6.90. H NMR (600 MHz, [D6]-benzene, 298 K): δ 10.80
71.21; H, 7.20; N, 2.13. Found: C, 71.84; H, 7.61; N, 2.20. H NMR
5
(d, JHH = 0.7 Hz, 1H, CHO), 7.83 (m, 2H, o-Ph), 7.58 (m, 2 H, o-
(500 MHz, [D6]-benzene, 298 K): δ 8.84 (m, 1H, CHN), 7.86 (m,
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2H, o-Ph), 7.64 (m, 2H, o-Ph′), 6.84 (s, 2H, m-Mes), 7.20 (m, 2H,
m,p-Ph), 7.12 (m, 1H, p-Ph′)1, 7.09 (m, 2H, m-Ph′)1, 4.17 (s, 5H,
assignment]. 19F NMR (564 MHz, [D2]-dichloromethane, 298 K): δ
3
−154.6 (m, 2F, o-C6F5), −161.7 (t, JFF = 21.3 Hz, 1F, p-C6F5),
3
3
C5H5), 3.98 (d, JHH = 2.6 Hz, 1H, 4H), 3.77 (d, JHH = 2.6 Hz, 1H,
5H), 2.35 (s, 6H, o-CH3Mes), 2.19 (s, 3H, p-CH3Mes), 1.02 (s, 9H, tBu),
−164.0 (m, 2F, m-C6F5). [α]2D0 = +38.9 (c 0.00115, dichloromethane).
Preparation of Compound (pS,pS)-14a. The alcohol (pS)-13a
(125.4 mg, 0.33 mmol, 2 equiv) and zirconium tetrachloride (38.7 mg,
0.17 mmol, 1 equiv) were dissolved in dichloromethane (5 mL),
instantly giving a deep blue solution. The mixture was stirred for 2 h,
and the solvent was removed. The dark blue solid can be washed with
pentane or ether (1 mL). This gave 187 mg (0.15 mmol, 91%) of
complex (pS,pS)-14a as a deep blue solid. Anal. Calcd for
C40H46Cl4Fe2N2O2Si2Zr: C, 48.64; H, 4.69; N, 2.84. Found: C,
2
0.46 (s, JSiH = 6.7 Hz, 9H, SiMe3) [1 from the ghsqc NMR
experiment].26 13C{1H} NMR (126 MHz, [D6]-benzene, 298 K): δ
162.4 (CHN), 151.1 (i-Mes), 136.0 (o-Ph), 135.9 (o-Ph′), 133.8 (i-
Ph), 132.5 (i-Ph′), 132.2 (p-Mes), 130.5 (p-Ph), 130.3 (p-Ph′), 129.4
(m-Mes), 128.2 (m-Ph), 128.1 (m-Ph′), 127.0 (C2)t, 126.8 (o-Mes),
74.8 (C3)t, 70.5 (C5), 70.3 (C5H5), 64.9 (C1), 63.8 (C4), 26.8 (tBu),
20.8 (p-CH3Mes), 19.6 (tBu), 19.0 (o-CH3Mes), 1.0 (SiMe3), [t tentative
assignment]. [α]2D0 = −20.7 (c 0.0115, dichloromethane).
1
46.82 ; H, 4.84; N, 2.52. Mp: 215 °C. H NMR (600 MHz, [D2]-
3
Preparation of Compound (pS)-13b. The imine (pS)-12b (1.23
g, 1.87 mmol, 1 equiv) and triethylamine trihydrofluoride (201 μL,
1.24 mmol, 2/3 equiv) were dissolved in tetrahydrofuran (30 mL), and
the solution was stirred for 2 h. The solvent was removed, and the
crude dark red oil product was purified by column chromatography
under argon (silical gel, cyclohexane/ethyl acetate/triethylamine,
20:1:1, solvents were degassed before use). Deep red solid of (Sp)-
13b was isolated by removal of solvents, yield: 0.52 g (1.23 mmol,
66%). Anal. Calcd for C23H29FeNSiO: C 65.86; H 6.97; N 3.34.
Found: C, 65.23; H, 7.18; N, 3.23. Mp: 131 °C (DSC). 1H NMR (600
MHz, [D6]-benzene, 298 K): δ 9.91 (bs, 1H, OH), 8.50 (m, 1H,
dichloromethane, 298 K): δ 12.17 (d, JHH = 14.8 Hz, 1H, NH), 8.87
(d, 3JHH = 14.8 Hz, 1H, CHN), 7.75 (m, 2H, o-PhN), 7.53 (m, 2H, m-
PhN), 7.46 (m, 1H, p-PhN), 6.04 (br, 1H, 4-H), 4.92 (br, 1H, 5-H),
4.66 (s, 5H, C5H5), 0.35 (s, 9H, SiMe3). 13C{1H} NMR (151 MHz,
[D2]-dichloromethane, 298 K): δ 161.3 (CHN), 138.4 (i-PhN), 130.7
(m-PhN), 128.6 (p-PhN), 119.6 (o-PhN), 135.3 (C3)t, 81.3 (br, C5),
73.2 (C5H5), 72.3 (br, C4), 70.0 (C1), 64.9 (C2)t, 0.6 (1JSiC = 53.8 Hz,
SiMe3) [t tentative assignment]. [α]2D0 = +1.9 (c 0.00085, dichloro-
methane).
Preparation of Compound (pS,pS)-14b. The alcohol (pS)-13b
(46.0 mg, 0.11 mmol, 2 equiv) and zirconium tetrachloride (13.1 mg,
0.056 mmol, 1 equiv) were dissolved in dichloromethane (3 mL),
instantly giving a deep blue solution. The mixture was stirred overnight
and the solvent was removed to afford 46.0 mg (0.086 mmol, 76%) of
complex (pS,pS)-14b as a deep blue solid. Anal. Calcd for
C46H58Cl4Fe2N2O2Si2Zr: C, 51.55; H, 5.45; N, 2.61. Found: C,
3
CHN), 6.78 (m, 2H, m-Mes), 4.66 (d, JHH = 2.6 Hz, 1H, 4-H), 4.10
3
(s, 5H, C5H5), 3.74 (d, JHH = 2.6 Hz, 1H, 5-H), 2.15 (s, 3H, p-
CH3Mes), 2.14 (s, 6H, o-CH3Mes), 0.14 (s, 9H, SiMe3). 13C{1H} NMR
(151 MHz, [D6]-benzene, 298 K): δ 169.5 (CHN), 147.9 (i-Mes),
133.8 (p-Mes), 131.0 (C2)t, 129.5 (m-Mes), 127.7 (o-Mes), 70.2
(C5H5), 69.9 (C5), 68.1 (C3)t, 65.8 (C1), 61.2 (C4), 20.8 (p-CH3Mes),
18.7 (o-CH3Mes), 0.7 (SiMe3), [t tentative assignment]. [α]2D0 = +158.2
(c 0.00045, dichloromethane).
1
51.68; H, 5.57; N, 2.52. Mp: 129 °C. H NMR (600 MHz, [D2]-
3
dichloromethane, 298 K): δ 11.99 (d, JHH = 15.4 Hz, 1H, NH), 8.30
(d, 3J = 15.4 Hz, 1H, CHN), 7.02 (s, 2H, m-Mes), 5.98 (br, 1H, 4-H),
4.80 (d, 3JHH = 2.3 Hz, 1H, 5-H), 4.60 (s, 5H, C5H5), 2.42 (bs, 6H, o-
CH3Mes), 2.34 (s, 3H, p-CH3Mes), 0.28 (SiMe3). 13C{1H} NMR (151
MHz, [D2]-dichloromethane, 298 K): δ 173.5 (CHN), 139.8 (p-Mes),
135.0 (i-Mes), 134.9 (C-3)t, 133.2 (o-Mes), 129.9 (m-Mes), 79.7
(C5), 72.1 (C5H5), 70.7 (br, C4), 70.2 (C1), 63.2 (C2)t, 21.0 (p-
CH3Mes), 18.8 (o-CH3Mes), 0.5 (1JSiC = 53.2 Hz, SiMe3) [t tentative
assignment]. [α]2D0 = +14.4 (c 0.00125, dichloromethane).
Preparation of Compound (pS)-12c. The aldehyde (pS)-11
(1.70 g, 3.15 mmol, 1 equiv), 2,3,4,5,6-pentafluoroaniline (2.95 g, 16.1
mmol, 5 equiv), and p-toluenesulfonic acid (61.3 mg, 0.32 mmol, 0.1
equiv) were dissolved in dry toluene (40 mL) in a Schlenk vessel and
heated at 125 °C for 7 h. Removal of the solvent gave the crude
product, which was purified by column chromatography (silica gel,
cyclohexane/triethylamine/ethyl acetate, 66:1:1, Rf = 0.74) to give the
imine 12c as an purple-red foam solid; yield 1.37 g, 1.90 mmol, 60.3%.
Anal. Calcd for C36H36F5NFeOSi2: C, 61.27; H, 5.14; N, 1.98. Found:
Preparation of Compound (pS,pS)-14c. The alcohol (pS)-13c
(52.8 mg, 0.11 mmol, 2 equiv) and zirconium tetrachloride (13.2 mg,
0.056 mmol, 1 equiv) were dissolved in dichloromethane (3 mL),
instantly giving a deep blue solution. The mixture was stirred
overnight, and the solvent was removed, giving 52 mg (0.045 mmol,
79%) of complex (pS,pS)-14c as a deep purple solid. Anal. Calcd for
C40H36Cl4F10Fe2N2O2Si2Zr: C, 41.15; H, 3.11; N, 2.40. Found: C,
1
C, 61.58; H, 5.26; N, 1.93. H NMR (600 MHz, [D6]-benzene, 298
K): δ 9.12 (bs, 1H, CHN), 7.85 (m, 2H, o-Ph), 7.60 (m, 2H, o-Ph′),
7.22 (m, 3H, m,p-Ph), 7.12 (m, 1H, p-Ph′), 7.07 (m, 2H, m-Ph′), 4.08
(s, 5H, C5H5), 4.06 (d, 3JHH = 2.7 Hz, 1H, 4-H), 3.88 (dd, 3JHH = 2.6
5
t
Hz, JHH = 0.5 Hz, 5-H), 1.11 (s, 9H, Bu), 0.45 (s, 9H, SiMe3).
13C{1H} NMR (151 MHz, [D6]-benzene, 298 K): δ 169.0 (br, CHN),
136.1 (o-Ph), 135.9 (o-Ph′), 133.2 (i-Ph), 131.9 (i-Ph′), 130.8 (p-Ph),
130.5 (p-Ph′), 128.3 (m-Ph), 128.2 (m-Ph′), 127.8 (C2)t, 73.5 (C3)t,
72.2 (C5), 70.9 (C5H5), 65.4 (C1), 64.7 (C4), 26.8 (tBu), 19.6 (tBu),
0.5 (SiMe3), n.o. (C6F5) [t tentative assignment]. 19F NMR (564
MHz, [D6]-benzene, 298 K): δ −155.3 (m, 2F, o-C6F5), −163.2 (t,
3JFF = 21.9 Hz, 1F, p-C6F5), −164.0 (m, 2F, m-C6F5). [α]2D0 = −14.0 (c
0.00205, dichloromethane).
1
40.40; H, 3.15; N, 2.41. Mp: 147 °C. H NMR (600 MHz, [D2]-
3
dichloromethane, 298 K): δ 11.32 (d, JHH = 14.4 Hz, 1H, NH), 8.58
(d, 3JHH = 14.4 Hz, 1H, CHN), 6.28 (br, 1H, 4-H), 5.16 (d, 3JHH = 2.7
Hz, 5-H), 4.72 (s, 5H, C5H5), 0.26 (s, 9H, SiMe3). 13C{1H} NMR
(151 MHz, [D2]-dichloromethane, 298 K): δ 163.3 (CHN), 136.1 (C-
3)t, 84.6 (C5), 74.8 (C5H5), 74.0 (br, C4), 70.3 (C1), 63.3 (C2)t, 0.3
(SiMe3) [t tentative assignment; C6F5 not listed]. 19F NMR (564
MHz, [D2]-dichloromethane, 298 K): δ −147.8 (br, 2F, o-C6F5),
3
−154.0 (t, JFF = 20.7 Hz, 1F, p-C6F5), −160.3 (br, 2F, m-C6F5).
Preparation of Compound (pS)-13c. The imine (pS)-12c (0.54
g, 0.76 mmol, 1 equiv) and triethylamine trihydrofluoride (41 μL, 0.25
mmol, 1/3 equiv) were dissolved in tetrahydrofuran (15 mL), and the
solution was stirred for 2 h. The solvent was removed, and the purple
oily residues were dissolved in pentane (10 mL) and filtered.
Evaporation of pentane gave a crude purple product, which was
further purified by column chromatography under Ar (silical gel,
cyclohexane/ethyl acetate/triethylamine, 20:1:1, solvents were de-
gassed before use). Purple solids of (pS)-13c were isolated by removal
of solvents; yield 264.5 mg, 0.566 mmol, 74%. Anal. Calcd for
C20H18F5FeNOSi: C, 51.41; H, 3.88; N, 3.00. Found: C, 51.90; H,
3.68; N, 2.80. Mp: 85 °C. 1H NMR (600 MHz, [D2]-dichloromethane,
Preparation of Compound (S,S,pS)-16. To a degassed solution
of bromo-substituted ferrocene acetal (S,S,pS)-15 (2.68 g, 6.8 mmol, 1
equiv) in THF (40 mL) was added dropwise at −78 °C Li-TMP in
THF/hexane (prepared in situ, 7.5 mmol, 1.1 equiv). The reaction
mixture was subsequently stirred for 30 min at −78 °C followed by 3 h
at −30 °C. The temperature was again lowed to −78 °C, and ClSiMe3
was injected. The temperature was raised to 0 °C, and stirring was
continued for 16 h. The reaction was quenched with saturated aqueous
Na2CO3 (30 mL) before diethyl ether was added, and the phases were
separated. The aqueous phase was extracted three times with diethyl
ether (each time 10 mL). The combined organic phases were dried
over MgSO4, and the solvents were removed under reduced pressure.
The orange residue was chromatographed on silica gel (cyclohexane/
ethyl acetate, 20:1) to afford a bright yellow oil (0.85 g, 27%). Anal.
Calcd for C19H27FeBrO3Si: C, 48.84; H, 5.82. Found: C, 44.60; H,
5.84. 1H NMR (600 MHz, [D6]-benzene, 298 K): δ 5.51 (s, 1H, 6-H),
3
298 K): δ 8.96 (s, 1H, CHN), 8.60 (s, 1H, OH), 4.86 (d, JHH = 2.7
3
Hz, 1H, 4-H), 4.22 (s, 5H, C5H5), 4.15 (d, JHH = 2.7 Hz, 5-H), 0.31
(s, 9H, SiMe3). 13C{1H} NMR (151 MHz, [D2]-dichloromethane, 298
K): δ 175.7 (CHN), 130.3 (C2)t, 72.1 (C5), 71.0 (C5H5), 68.0 (C1),
67.2 (C3)t, 62.7 (C4), 0.6 (SiMe3), n.o. (C6F5) [t tentative
H
dx.doi.org/10.1021/om3004509 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
4.38 (d, 3JHH = 2.4 Hz, 1H, 5-H), 4.17 (s, 5H, C5H5), 3.89 (m, 1H, 10-
1H, H-12), 3.11 (dd, 2JHH = 10.0 Hz, 3JHH = 4.7 Hz, 1H, H-12′), 3.07
3
3
Heq), 3.87 (d, JHH = 2.4 Hz, 1H, 4-H), 3.75 (m, 1H, 8-H), 3.51 (m,
(s, 3H, OCH3), 1.92 (s, 3H, COCH3), 1.58 (dddd, JHH = 12.5 Hz,
2
3
2JHH = 13.1 Hz, 3JHH = 11.6 Hz, 3JHH = 5.1 Hz, 1H, 9-Hax), 0.96 (dtd,
2JHH = 13.1 Hz, 3JHH = 2.6 Hz, 3JHH = 1.3 Hz, 1H, 9-Heq), 0.37 (s, 2JSiH
= 6.7 Hz, 9H, 4-SiMe3), 0.33 (s, 2JSiH = 6.7 Hz, 9H, 1-SiMe3). 13C{1H}
NMR (151 MHz, [D6]-benzene, 298 K): δ 169.1 (CO), 120.9
(C2)t, 100.0 (C6), 85.4 (C3)t, 76.3 (C8), 75.6 (C12), 74.1 (C5), 70.9
(C5H5), 69.7 (C4), 67.8 (C1), 66.3 (C10), 58.9 (OCH3), 28.2 (C9),
20.5 (AcCH3), 1.1 (4-SiMe3), −0.1 (1-SiMe3) [t tentative assignment].
29Si dept (60 MHz, [D6]-benzene, 298 K): δ −2.4, −4.0. [α]2D0 = −3.4
(c 0.00555, dichloromethane).
1H, 10-Hax), 3.30 (dd, JHH = 9.9 Hz, JHH = 5.4 Hz, 1H, 12-H), 3.16
2
3
(m, JHH = 9.9 Hz, JHH = 5.2 Hz, 1H, 12-H′), 3.06 (s, 3H, OCH3),
1.68 (ddd, 2JHH = 13.3 Hz, 3JHH = 12.1 Hz, 3JHH = 5.3 Hz, 1H, 9-Hax),
1.05 (dm, JHH = 13.3 Hz, 1H, 9-Heq), 0.41 (s, 9H, SiMe3). 13C{1H}
2
NMR (151 MHz, [D6]-benzene, 298 K): δ 100.5 (C6), 89.0 (C2)t,
81.8 (C1)t, 76.5 (C8), 75.5 (C12), 73.1 (C4), 72.4 (C5), 71.8 (C5H5),
70.1 (C3), 66.7 (C10), 58.8 (OCH3), 28.2 (C9), 1.2 (SiMe3) [t
tentative assignment]. [α]2D0 = −3.5 (c 0.00225, dichloromethane).
Preparation of Compound (S,S,pR)-17. To a degassed solution
of the bromo-substituted ferrocene acetal (S,S,pS)-15 (1.32 g, 3.35
mmol, 1 equiv) in THF (15 mL) was added dropwise at −78 °C Li-
TMP in THF/hexane (prepared in situ, 8.37 mmol, 2.5 equiv). The
reaction mixture was subsequently stirred for 30 min at −78 °C
followed by 6 h at −30 °C. The temperature was again cooled to −78
°C, and ClSiMe3 was injected. The temperature was raised to 0 °C,
and stirring was continued for 16 h. The reaction was quenched with
saturated aqueous Na2CO3 (30 mL) before diethyl ether was added,
and the phases were separated. The aqueous phase was extracted three
times with diethyl ether (each time 10 mL). The combined organic
phases were dried over MgSO4, and the solvents were removed under
reduced pressure. The orange residue was chromatographed on silica
gel to yield 1.23 g (68%) of a yellow oil (cyclohexane/ethyl acetate,
20:1). Anal. Calcd for C22H35BrFeO3Si2: C, 48.98; H, 6.54. Found: C,
Preparation of Compound (pS)-19. The acetoxyl acetal
(2S,4S,pS)-18 (10.50 g, 20.3 mmol) was dissolved under Ar in
dichloromethane (100 mL), and water (40 mL) was added, followed
by addition of p-toluenesulfonic acid monohydrate (7.70 g, 40.5 mmol,
2 equiv). The mixture was heated to reflux for 3 h under vigorous
stirring, the phases were separated, and the organic phase was dried
over magnesium sulfate. Filtration and removal of the solvent gave the
crude product, which was purified by column chromatography on silica
gel (cyclohexane/ethyl acetate/triethylamine, 15:1:1). The desired
product was isolated as orange crystalline needles in a 98% yield (8.27
g, 19.9 mmol). X-ray quality crystals were obtained from a solution in
diethyl ether at −30 °C. Anal. Calcd for C19H28FeO3Si2: C, 54.80; H,
1
6.78. Found: C, 55.10; H, 7.00. Mp: 86.6 °C. H NMR (500 MHz,
[D6]-benzene, 298 K): δ 10.18 (m, 1H, CHO), 4.19 (m, 1H, 5-H),
49.00; H, 6.41. 1H NMR (600 MHz, [D6]-benzene, 298 K): δ 5.57 (s,
4.10 (s, 5H, C5H5), 1.75 (s, 3H, AcCH3), 0.32 (s, 2JSiH = 6.7 Hz, 9H, 4-
2
1H, 6-H), 4.25 (s, 5H, C5H5), 4.09 (s, 1H, 5-H), 3.88 (ddd, JHH
=
2
SiMe3), 0.21 (s, JSiH = 6.7 Hz, 9H, 1-SiMe3). 13C{1H} NMR (126
3
3
11.5 Hz, JHH = 5.3 Hz, JHH = 1.3 Hz, 1H, 10-Heq), 3.76 (m, 1H, 8-
H), 3.52 (ddd, 3JHH = 12.6 Hz, 2JHH = 11.5 Hz, 3JHH = 2.6 Hz, 1H, 10-
Hax), 3.29 (dd, 2JHH = 9.8 Hz, 3JHH = 5.3 Hz, 1H, 12-H), 3.15 (m, 2JHH
= 9.8 Hz, 3JHH = 5.3 Hz, 1H, 12-H′), 3.04 (s, 3H, OCH3), 1.69 (dddd,
2JHH = 13.2 Hz, 3JHH = 12.6 Hz, 3JHH = 11.5 Hz, 3JHH = 5.3 Hz, 1H, 9-
Hax), 1.05 (dm, 2JHH2 = 13.2 Hz, 1H, 9-Heq), 0.44 (s, 2JSiH = 6.7 Hz, 9H,
4-SiMe3), 0.35 (s, JSiH = 6.7 Hz, 9H, 1-SiMe3). 13C{1H} NMR (151
MHz, [D6]-benzene, 298 K): δ 100.7 (C6), 92.0 (C3)t, 87.9 (C2)t,
78.7 (C5), 76.5 (C8), 75.5 (C12), 74.2 (C1), 72.5 (C4), 71.9 (C5H5),
66.7 (C10), 58.8 (OCH3), 28.2 (C9), 1.3 (1JSiC = 53.6 Hz, 4-SiMe3),
0.1 (1JSiC = 53.3 Hz, 1-SiMe3) [t tentative assignment]. [α]2D0 = +0.7 (c
0.00095, dichloromethane).
Preparation of Compound (S,S,pS)-18. A mixture of compound
(S,S,pR)-17 (1.02 g, 1.89 mmol, 1 equiv), acetic acid (0.54 mL, 9.45
mmol, 5 equiv, previously dried over 4 Å molecular sieves), and Cu2O
(0.30 g, 2.08 mmol, 1.1 equiv) was heated to reflux in CH3CN (25
mL) for 15 h under nitrogen. After cooling to room temperature,
CH2Cl2 (30 mL) was added, and the reaction mixture was filtered over
Celite. The residue was then washed with additional CH2Cl2 (20 mL).
The filtrate and washings were combined, washed with water (20 mL),
and dried over MgSO4. The solvent was removed in vacuo, and the
resultant crude yellow crystalline solid was purified by column
chromatography (silica gel, hexane/EtOAc, 10:1) to yield the product
as a yellow oil in 58.9% yield (0.58 g, 1.1 mmol).
MHz, [D6]-benzene, 298 K): δ 191.5 (CHO), 169.5 (CO), 124.6
(C2)t, 78.3 (C3)t, 78.0 (C5), 72.9 (C1), 72.7 (C4), 71.1 (C5H5), 20.2
(AcCH3), 0.3 (1JSiC = 53.5 Hz, 4-SiMe3), −0.5 (1JSiC = 53.8 Hz, 1-
SiMe3) [t tentative assignment]. 29Si dept (60 MHz, [D6]-benzene,
298 K): δ −2.4, −3.9. [α]2D0 = +14.1 (c 0.0021, dichloromethane).
X-ray crystal structure analysis of (pS)-19: formula
C19H28FeO3Si2, M = 416.44, orange crystal, 0.35 × 0.07 × 0.05 mm,
a = 23.4373(5) Å, b = 23.4373(5) Å, c = 7.6500(1) Å, γ = 120.00°, V =
3639.21(12) Å3, ρcalc = 1.140 g cm−3, μ = 0.733 mm−1, empirical
absorption correction (0.783 ≤ T ≤ 0.964), Z = 6, trigonal, space
group P65 (No. 170), λ = 0.71073 Å, T = 223(2) K, ω and φ scans, 23
609 reflections collected ( h, k, l), (sin θ)/λ = 0.66 Å−1, 5364
independent (Rint = 0.041) and 4728 observed reflections [I > 2σ(I)],
233 refined parameters, R = 0.058, wR2 = 0.158, max. (min.) residual
electron density 0.87 (−0.32) e Å−3, hydrogen atoms calculated and
refined as riding atoms, Flack parameter 0.07(3).
Preparation of Compound (pS)-20. A Schlenk vessel was
charged with the acetoxy aldehyde (pS)-19 (8.27 g, 19.9 mmol, 1
equiv) under Ar, and 10% KOH (100 mL) and ethanol (120 mL) were
added subsequently. The reaction mixture immediately became a dark
purple-red suspension. The reaction mixture was allowed to stir at rt
for 1 h before the evaporation of ethanol. The residue was extracted
with pentane (100 mL × 3). The combined organic phases were
extracted with water (100 mL) and quickly dried over MgSO4.
Evaporation of the solvent gave a dark red crystalline solid. The crude
hydroxyl aldehyde was purified by FC on silica gel (cyclohexane/
ethylacetate/triethylamine, 15:1:1). The fraction should be collected
under argon. The pure oxygen-sensitive compound was isolated as a
bright red solid in 85% yield (6.35 g, 17.0 mmol). Anal. Calcd for
C17H26FeO2Si2: C, 54.54; H, 7.00. Found: C, 54.64; H, 6.94. Mp: 88
Improved Method. A mixture of the bromo acetal (S,S,pR)-17
(21.20 g, 39.3 mmol, 1 equiv), acetic acid, and acetic anhydride (acetic
acid 5.63 mL, 98.3 mmol, 2.5 equiv, acetic anhydride 9.23 mL, 98.3
mmol, 2.5 equiv, previously mixed and heated at 80 °C for 1 h) and
Cu2O (6.19 g, 43.2 mmol, 1.1 equiv) was heated to reflux in CH3CN
(130 mL) for 15 h under nitrogen. After cooling to rt, CH2Cl2 (30
mL) was added and the reaction mixture was filtered over Celite. The
residue was then washed with additional CH2Cl2 (100 mL). The
filtrate and washings were combined and extracted with water (50
mL), and the green-yellow organic phase was dried over MgSO4. The
solvent was removed in vacuo, and the resultant crude yellow
crystalline solid was purified by column chromatography (silica gel,
hexane/etheyl acetate, 10:1) to yield the product as a yellow oil in
78.6% yield (16.026 g, 30.9 mmol). Anal. Calcd for C24H38FeO5Si2: C,
1
°C. H NMR (600 MHz, [D6]-benzene, 298 K): δ 10.20 (m, 1H,
CHO), 8.00 (br, 1H, OH), 4.00 (s, 5H, C5H5), 3.91 (s, 1H, 5-H), 0.36
(s, 2JSiH = 6.7 Hz, 9H, 1-SiMe3), 0.11 (s, 2JSiH = 6.6 Hz, 9H, 4-SiMe3).
13C{1H} NMR (151 MHz, [D6]-benzene, 298 K): δ 199.9 (CHO),
135.8 (C2)t, 77.1 (C5), 70.5 (C5H5), 70.2 (C3)t, 69.3 (C4), 67.0
(C1), 0.7 (1JSiC = 53.2 Hz, 4-SiMe3), −0.4 (1JSiC = 53.3 Hz, 1-SiMe3) [t
tentative assignment]. 29Si dept (60 MHz, [D6]-benzene, 298 K): δ
−3.0, −3.8. [α]2D0 = −124.7 (c 0.00105, dichloromethane).
X-ray crystal structure analysis of (pS)-20: formula
C17H26FeO2Si2, M = 374.41, red crystal, 0.30 × 0.17 × 0.10 mm, a
= 12.2088(2) Å, b = 19.7299(4) Å, c = 8.1404(1) Å, V = 1960.85(6)
Å3, ρcalc = 1.268 g cm−3, μ = 0.895 mm−1, empirical absorption
1
55.59; H, 7.39. Found: C, 55.49; H, 7.44. H NMR (600 MHz, [D6]-
benzene, 298 K): δ 5.42 (s, 1H, 6-H), 4.33 (s, 5H, C5H5), 3.93 (s, 1H,
5-H), 3.81 (ddd, 2JHH =11.3 Hz, 3JHH = 5.1 Hz, 3JHH = 1.3 Hz, 1H, 10-
3
2
Heq), 3.64 (m, 1H, 8-H), 3.42 (ddd, JHH = 12.5 Hz, JHH = 11.3 Hz,
3JHH = 2.6 Hz, 1H, 10-Hax), 3.25 (dd, JHH = 10.0 Hz, JHH = 5.7 Hz,
2
3
I
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correction (0.775 ≤ T ≤ 0.915), Z = 4, orthorhombic, space group
P21212 (No. 18), λ = 0.71073 Å, T = 223(2) K, ω and φ scans, 12 101
reflections collected ( h, k, l), (sin θ)/λ = 0.60 Å−1, 4594
independent (Rint = 0.046) and 4163 observed reflections [I > 2σ(I)],
206 refined parameters, R = 0.042, wR2 = 0.094, max. (min.) residual
electron density 0.29 (−0.28) e Å−3, hydrogen atoms calculated and
refined as riding atoms, Flack parameter −0.07(2).
1H, 5-H), 0.45 (s, 2JSiH = 6.6 Hz, 9H, 1-SiMe3), 0.22 (s, 2JSiH = 6.6 Hz,
9H, 4-SiMe3). 13C{1H} NMR (151 MHz, [D6]-benzene, 298 K): δ
175.2 (CHN), 135.6 (C2)t, 76.7 (C5), 70.8 (C5H5), 69.5 (C4), 69.1
(C3)t, 66.8 (C1), 0.7 (1JSiC = 53.0 Hz, 4-SiMe3), −0.3 (1JSiC = 53.2 Hz,
1-SiMe3) [t tentative assignment; C6F5 not listed]. 19F NMR (470
MHz, [D6]-benzene, 298 K): δ −154.8 (m, 2F, o-C6F5), −161.5 (t, 3JFF
= 21.3 Hz, 1F, p-C6F5), −163.5 (m, 2F, m-C6F5). 29Si dept (60 MHz,
[D6]-benzene, 298 K): δ −3.1, −3.6. [α]2D0 = −1.0 (c 0.0011,
dichloromethane).
Preparation of Compound (pS)-21a. The aldehyde (pS)-20
(1.57 g, 4.2 mmol, 1 equiv), aniline (1.92 mL, 21 mmol, 5 equiv), and
p-toluenesulfonic acid (80 mg, 0.42 mmol, 0.1 equiv) were dissolved in
dry toluene (50 mL) in a Schlenk vessel and heated at 125 °C for 2.5
h. Removal of the solvent gave the crude dark red product, which was
purified by column chromatography under argon (silica gel, cyclo-
hexane/triethylamine/ethyl acetate, 10:1:1) to give the bright red
product in a 84.0% yield (1.59 g, 3.5 mmol). X-ray quality crystals
were obtained from a solution in pentane at −30 °C. Anal. Calcd for
C23H31FeNOSi2: C 61.45; H 6.95; N 3.12. Found: C, 62.04; H, 7.03;
N, 2.67. Mp: 120 °C. 1H NMR (500 MHz, [D2]-dichloromethane, 298
K): δ 9.59 (br, 1H, OH), 8.83 (s, 1H, CHN), 7.41 (m, 2H, m-Ph),
7.26 (m, 1H, p-Ph), 7.22 (m, 2H, o-Ph), 4.15 (s, 5H, C5H5), 3.89 (s,
1H, 5-H), 0.37 (s, 2JSiH = 6.8 Hz, 9H, 1-SiMe3), 0.35 (s, 2JSiH = 6.6 Hz,
9H, 4-SiMe3). 13C{1H} NMR (126 MHz, [D2]-dichloromethane, 298
K): δ 166.6 (CHN), 150.8 (i-Ph), 135.0 (C2)t, 129.7 (m-Ph), 126.2
(p-Ph), 120.9 (o-Ph), 75.3 (C5), 70.3 (C5H5), 69.9 (C3)t, 68.8 (C4),
64.9 (C1), 0.8 (1JSiC = 52.9 Hz, 4-SiMe3), −0.3 (1JSiC = 53.3 Hz,1-
SiMe3) [t tentative assignment]. 29Si dept (60 MHz, [D2]-dichloro-
methane, 298 K): δ −2.8, −3.7. [α]D20 = −106.4 (c 0.0007,
dichloromethane).
X-ray crystal structure analysis of (pS)-21c: formula
C23H26F5FeNOSi2, M = 539.48, red crystal, 0.40 × 0.30 × 0.10 mm,
a = 10.9331(2) Å, b = 11.0599(2) Å, c = 21.0231(3) Å, V =
2542.09(7) Å3, ρcalc = 1.410 g cm−3, μ = 0.740 mm−1, empirical
absorption correction (0.756 ≤ T ≤ 0.929), Z = 4, orthorhombic,
space group P212121 (No. 19), λ = 0.71073 Å, T = 223(2) K, ω and φ
scans, 15 873 reflections collected ( h, k, l), (sin θ)/λ = 0.66 Å−1,
5958 independent (Rint = 0.037) and 5650 observed reflections [I >
2σ(I)], 305 refined parameters, R = 0.037, wR2 = 0.086, max. (min.)
residual electron density 0.37 (−0.22) e Å−3, hydrogen atoms
calculated and refined as riding atoms, Flack parameter 0.103(15).
Preparation of Compound (pS)-21d. The aldehyde (pS)-20
(1.59 g, 4.3 mmol, 1 equiv), cyclohexylamine (2.4 mL, 21.3 mmol, 5
equiv), and p-toluenesulfonic acid (81 mg, 0.43 mmol, 0.1 equiv) were
dissolved in dry toluene (30 mL) in a Schlenk vessel and heated at 125
°C for 3 h. Removal of the solvent gave the crude purple-red product,
which was purified by column chromatography under argon (silical gel,
cyclohexane/triethylamine/ethyl acetate, 10:1:1) to give a purple solid
in 89% yield (1.73 g, 3.8 mmol). X-ray quality crystals were obtained
from a solution in pentane at −30 °C. Anal. Calcd for
C23H37FeNOSi2: C, 60.64; H, 8.19; N, 3.07. Found: C, 61.30; H,
X-ray crystal structure analysis of (pS)-21a: formula
C23H31FeNOSi2, M = 449.52, red crystal, 0.35 × 0.20 × 0.04 mm, a
= 8.3549(2) Å, b = 10.0008(2) Å, c = 28.5722(7) Å, V = 2387.37(9)
Å3, ρcalc = 1.251 g cm−3, μ = 0.745 mm−1, empirical absorption
correction (0.780 ≤ T ≤ 0.971), Z = 4, orthorhombic, space group
P212121 (No. 19), λ = 0.71073 Å, T = 223(2) K, ω and φ scans, 15 610
1
7.92; N, 2.95. Mp: 140 °C. H NMR (500 MHz, [D6]-benzene, 298
K): δ 10.39 (s, 1H, OH), 8.53 (s, 1H, CHN), 4.11 (s, 5H, C5H5), 3.83
(s, 1H, 5-H), 2.86 (m, 1H, 8-H), 1.63/1.18 (10-H)t,1, 1.62/1.38 (13-
H)t,1, 1.60/1.13 (12-H)t,1, 1.57/1.32 (9-H)t,1, 1.44/1.09 (11-H)t,1, 0.48
(s, 9H, 1-SiMe3), 0.25 (s, 9H, 4-SiMe3) [t tentative assignment; 1 from
ghsqc NMR experiment].26 13C{1H} NMR (126 MHz, [D6]-benzene,
298 K): δ 164.0 (CHN), 135.7 (C2)t, 73.7 (C5), 70.3 (C5H5), 70.0
(C3)t, 68.5 (C8), 67.1 (C4), 63.9 (C1), 35.2 (C9)t,1, 34.3 (C13)t,1,
25.8 (C11)t,1, 24.5 (C10)t,1, 24.7 (C12)t,1, 0.9 (1JSiC = 52.7 Hz, 4-
SiMe3), −0.1 (1JSiC = 52.8 Hz, 1-SiMe3) [t tentative assignment; 1 from
ghsqc NMR experiment].26 29Si dept (60 MHz, [D6]-benzene, 298 K):
δ −3.2, −3.8. [α]2D0 = −106.3 (c 0.0006, dichloromethane)
reflections collected ( h,
k,
l), (sinθ)/λ = 0.60 Å−1, 5312
independent (Rint = 0.048) and 5035 observed reflections [I > 2σ(I)],
260 refined parameters, R = 0.039, wR2 = 0.088, max. (min.) residual
electron density 0.31 (−0.33) e Å−3, hydrogen atoms calculated and
refined as riding atoms, Flack parameter 0.002(16).
Preparation of Compound (pS)-21b. The aldehyde (pS)-20
(0.51 g, 1.35 mmol), 2,4,6-trimethylaniline (0.95 mL, 6.76 mmol, 5
equiv), and p-toluenesulfonic acid (25.7 mg, 0.14 mmol, 0.1 equiv)
were dissolved in dry toluene (20 mL) in a Schlenk vessel and heated
at 125 °C for 4.5 h. Removal of the solvent gave the crude dark red
product, which was purified by column chromatography under argon
(silica gel, cyclohexane/triethylamine/ethyl acetate, 10:1:1) to give the
bright red product in a quantitative yield (0.66 g, 1.35 mmol). Anal.
Calcd for C26H37FeNOSi2: C 63.52; H 7.59; N 2.85. Found: C, 63.49;
H, 7.72; N, 2.76. Mp: 111 °C. 1H NMR (600 MHz, [D6]-benzene, 298
K): δ 9.92 (br, 1H, OH), 8.53 (s, 1H, CHN), 6.76 (m, 2H, m-Mes),
4.16 (s, 5H, C5H5), 3.92 (s, 1H, 5-H), 2.15 (s, 3H, p-CH3Mes), 2.13 (s,
6H, o-CH3Mes), 0.48 (s, 9H, 1-SiMe3), 0.17 (s, 9H, 4-SiMe3). 13C{1H}
NMR (151 MHz, [D6]-benzene, 298 K): δ 169.5 (CHN), 147.8 (i-
Mes), 135.7 (C2)t, 133.7 (p-Mes), 129.5 (m-Mes); 127.7 (o-Mes), 74.5
(C5), 70.3 (C5H5), 69.9 (C3)t, 68.3 (C4), 64.6 (C1), 20.8 (p-CH3Mes),
18.8 (o-CH3Mes), 0.7 (1JSiC = 52.9 Hz, 4-SiMe3), −0.1 (1JSiC = 53.1 Hz,
1-SiMe3) [t tentative assignment]. 29Si dept (60 MHz, [D6]-benzene,
298 K): δ −3.3, −3.7. [α]2D0 = −164.1 (c 0.00085, dichloromethane).
Preparation of Compound (pS)-21c. The aldehyde (pS)-20 (1.2
g, 3.2 mmol, 1 equiv), 2,3,4,5,6-pentafluoroaniline (3.0 g, 16 mmol, 5
equiv), and p-toluenesulfonic acid (61 mg, 0.32 mmol, 0.1 equiv) were
dissolved in dry toluene (40 mL) in a Schlenk vessel and heated at 125
°C for 2.5 h. Removal of the solvent gave the crude purple-red
product, which was purified by column chromatography under argon
(silica gel, cyclohexane/triethylamine/ethyl acetate, 10:1:1) to give a
purple solid in 84% yield (1.44 g, 2.7 mmol). X-ray quality crystals
were obtained from a solution in pentane at −30 °C. Anal. Calcd for
C23H26F5FeNOSi2: C, 51.21; H, 4.86; N, 2.60. Found: C, 51.55; H,
5.09; N, 2.37. Mp: 97 °C. 1H NMR (600 MHz, [D6]-benzene, 298 K):
δ 9.01 (s, 1H, OH), 8.90 (br, 1H, CHN), 4.13 (s, 5H, C5H5), 4.02 (s,
X-ray crystal structure analysis of (pS)-21d: formula
C23H37FeNOSi2, M = 449.52, red crystal, 0.55 × 0.30 × 0.25 mm, a
= 7.4546(3) Å, b = 15.3671(6) Å, c = 10.8018(4) Å, β = 92.031(2)°, V
= 1236.63(8) Å3, ρcalc = 1.223 g cm−3, μ = 0.720 mm−1, empirical
absorption correction (0.693 ≤ T ≤ 0.840), Z = 2, monoclinic, space
group P21 (No. 4), λ = 0.71073 Å, T = 223(2) K, ω and φ scans, 5865
reflections collected ( h,
k,
l), (sin θ)/λ = 0.60 Å−1, 4766
independent (Rint = 0.039) and 4625 observed reflections [I > 2σ(I)],
260 refined parameters, R = 0.064, wR2 = 0.168, max. (min.) residual
electron density 1.21 (−0.70) e Å−3, hydrogen atoms calculated and
refined as riding atoms, Flack parameter 0.02(3).
Preparation of Compound (pS,pS)-22a. A solution of the
alcohol (pS)-21a (170.3 mg, 0.38 mmol, 2 equiv) in dichloromethane
(8 mL) was slowly added to a suspension of zirconium tetrachloride
(44.1 mg, 0.19 mmol, 1 equiv) in dichloromethane (5 mL), instantly
giving a deep blue solution. The mixture was stirred overnight, and the
solvent was evaporated, giving a deep blue solid. The deep blue solid
was washed with pentane (5 mL), and removal of the pentane solution
gave 150.6 mg (0.13 mmol, 70%) of complex (pS,pS)-22a as a deep
blue solid. Anal. Calcd for C46H62Cl4Fe2N2O2Si4Zr: C, 48.80; H, 5.52;
1
N, 2.47. Found: C, 48.81; H, 5.49; N, 2.30. Mp: 159 °C. H NMR
(500 MHz, [d2]-dichloromethane, 298 K): δ 12.30 (br, 1H, NH), 8.80
3
(d, JHH = 15.4 Hz, 1H, CHN), 7.73 (m, 2H, o-Ph), 7.49 (m, 2H, m-
Ph), 7.45 (m, 1H, p-Ph), 4.71 (s, 1H, 5-H), 4.58 (s, 5H, C5H5), 0.58
(s, 9H, 1-SiMe3), 0.38 (s, 9H, 4-SiMe3). 13C{1H} NMR (126 MHz,
[d2]-dichloromethane, 298 K): δ 161.7 (CHN), 138.8 (i-Ph), 138.2
(br, C2)t, 130.4 (m-Ph), 128.6 (p-PhC), 120.1 (o-Ph), 87.4 (C5). 76.8
(C1), 74.4 (br, C4), 72.8 (C5H5), 67.2 (C3)t, 1.0 (1-SiMe3), 0.8 (4-
J
dx.doi.org/10.1021/om3004509 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
SiMe3) [t tentative assignment]. 29Si dept (60 MHz, [d2]-dichloro-
methane, 298 K): δ −2.54, −2.55. [α]D20 = +1.6 (c 0.0007,
dichloromethane).
Dragutan, I.; Dragutan, V.; Verpoort, F. Adv. Synth. Catal. 2005, 347,
1721−1743.
(5) (a) Niemeyer, J.; Kehr, G.; Frohlich, R.; Erker, G. Dalton Trans.
̈
Preparation of Compound (pS,pS)-22d. A solution of the
alcohol (pS)-21d (230.3 mg, 0.51 mmol, 2 equiv) in dichloromethane
(15 mL) was slowly added to a suspension of zirconium tetrachloride
(58.9 mg, 0.25 mmol, 1 equiv) in dichloromethane (5 mL), instantly
giving a deep blue solution. The mixture was stirred overnight, and the
solvent was evaporated, giving a purple solid. The purple solid was
washed with pentane (5 mL), and removal of the pentane solution
gave 220.6 mg (0.193 mmol, 76.3%) of complex (pS,pS)-22d as a deep
purple solid. X-ray quality crystals were obtained from a solution in
ether/toluene at room temperature. Anal. Calcd for
C46H74Cl4Fe2N2O2Si4Zr: C, 48.29; H, 6.52; N, 2.45. Found: C,
2009, 3716−3730. (b) Niemeyer, J.; Kehr, G.; Frohlich, R.; Erker, G.
̈
Dalton Trans. 2009, 3731−3741.
(6) Niemeyer, J.; Kehr, G.; Frohlich, R.; Erker, G. Chem.Eur. J.
̈
2008, 14, 9499−9502.
(7) See also: (a) Niemeyer, J.; Kehr, G.; Frohlich, R.; Erker, G. Eur. J.
Inorg. Chem. 2010, 680−684. (b) Niemeyer, J.; Cloppenburg, J.;
Frolich, R.; Kehr, G.; Erker, G. J. Organomet. Chem. 2010, 695, 1801−
̈
̈
1812.
(8) (a) Riant, O.; Samuel, O.; Kagan, H. B. J. Am. Chem. Soc. 1993,
115, 5835−5836. (b) Riant, O.; Samuel, O.; Flessner, T.; Taudien, S.;
Kagan, H. B. J. Org. Chem. 1997, 62, 6733−6745. (c) Masson-
Szymczak, A.; Riant, O.; Gref., A.; Kagan, H. B. J. Organomet. Chem.
1996, 511, 193−197.
1
49.13; H, 6.75; N, 2.23. Mp: >350 °C. H NMR (500 MHz, [d2]-
3
dichloromethane, 298 K): δ 11.19 (br, 1H, NH), 8.35 (d, JHH = 16.8
Hz, 1H, CHN), 4.44 (s, 5H, C5H5), 4.40 (s, 1H, 5-H), 3.62 (m, 1H, 8-
H), 2.23/1.67 (9-H)t,1, 2.22/1.71 (13-H)t,1, 1.92, 1.90/1.42, 1.40
(10,12-H)t,1, 1.73/1.25 (11-H)t,1, 0.53 (s, 9H, 1-SiMe3), 0.34 (s, 9H, 4-
(9) Strauch, J.; Warren, T. H.; Erker, G.; Frohlich, R.; Saarenketo, P.
̈
Inorg. Chim. Acta 2000, 300−302, 810−821.
(10) (a) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.; Tanaka,
H.; Fujita, T. Chem. Lett. 1999, 28, 1263−1264. (b) Matsui, S.; Tohi,
Y.; Mitani, M.; Saito, J.; Makio, H.; Tanaka, H.; Nitabaru, M.; Nakano,
T.; Fujita, T. Chem. Lett. 1999, 28, 1065−1066. (c) Mitani, M.; Mohri,
J.-I.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui, S.; Furuyama, R.;
Nakano, T.; Tanaka, H.; Kojoh, S.-I.; Matsugi, T.; Kashiwa, N.; Fujita,
T. J. Am. Chem. Soc. 2002, 124, 3327−3336. (d) Mitani, M.;
Furuyama, R.; Mohri, J.; Saito, J.; Ishii, S.; Terao, H.; Nakano, T.;
Tanaka, H.; Fujita, T. J. Am. Chem. Soc. 2003, 125, 4293−4305.
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(f) Makio, H.; Terao, H.; Iwashita, A.; M., T.; Fujita, T. Chem. Rev.
2011, 111, 2363−2449.
SiMe3) [t tentative assignment; from ghsqc NMR experiment].26
1
13C{1H} NMR (126 MHz, [d2]-dichloromethane, 298 K): δ 167.1
(CHN), 137.6 (C2)t, 84.4 (C5), 74.3 (C1), 73.0 (C4), 72.1 (C5H5),
65.2 (C3)t, 61.9 (C8), 32.1 (C9)t,1, 33.2 (C13)t,1, 25.25, 25.28 (C10,
12)t,1, 25.31 (C11)t,1, 1.1 (1-SiMe3), 0.8 (4-SiMe3). 29Si dept (60
MHz, [d2]-dichloromethane, 298 K): δ −2.8, −2.9.
X-ray crystal structure analysis of (pS,pS)-22d: formula
C50H84Cl4FeN2O3Si4Zr, M = 1218.27, red crystal, 0.25 × 0.20 ×
0.10 mm, a = 12.2271(3) Å, b = 17.1048(4) Å, c = 29.5106(7) Å, V =
6171.9(3) Å3, ρcalc = 1.311 g cm−3, μ = 0.918 mm−1, empirical
absorption correction (0.803 ≤ T ≤ 0.914), Z = 4, orthorhombic,
space group C2221 (No. 20), λ = 0.71073 Å, T = 223(2) K, ω and φ
scans, 18 787 reflections collected ( h, k, l), (sin θ)/λ = 0.66 Å−1,
7131 independent (Rint = 0.056) and 6553 observed reflections [I >
2σ(I)], 306 refined parameters, R = 0.103, wR2 = 0.246, max. (min.)
residual electron density 0.63 (−0.83) e Å−3, hydrogen atoms
calculated and refined as riding atoms, Flack parameter 0.33(6).
(11) (a) Sato, M.; Motoyama, I.; Hata, K. Bull. Chem. Soc. Jpn. 1970,
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Macromolecules 1998, 31, 8448−8454. (e) Wang, W.; Yan, D.; Zhu, S.;
ASSOCIATED CONTENT
* Supporting Information
This material is available free of charge via the Internet at
http://pubs.acs.org.
■
Hamielec, A. E. Macromolecules 1998, 31, 8677−8683. (f) Kooko, E.;
S
Lehmus, P.; Leino, R.; Luttikhedde, H. J. G.; Ekholm, P. J.; Nasman,
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H.; Seppala, J. V. Macromolecules 2000, 33, 9200−9204. (g) Sun, M.
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T.; Xu, T. Q.; Cao, W.; Liu, Y.; Wu, Q. L.; Mu, Y.; Ye, L. Dalton Trans.
2011, 40, 10184−10194.
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1965, 30, 1600−1604. (b) Slocum, D. W.; Jennings, C. A.; Engelmann,
T. R.; Rockett, B. W.; Hauser, C. R. J. Org. Chem. 1971, 36, 377−381.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: erker@uni-muenster.de.
■
Author Contributions
§X-ray crystal structure analyses.
(14) (a) Butler, I. R.; Drew, M. G. B. Inorg. Chem. Commun. 1999, 2,
234−237. (b) Butler, I. R.; Drew, M. G. B.; Plath, M. Inorg. Chem.
Commun. 1999, 2, 424−427. (c) Butler, I. R.; Drew, M. G. B. C.;
Notes
The authors declare no competing financial interest.
Greenwell, H.; Lewis, E.; Plath, M.; Mussig, S.; Szewczyk, J. Inorg.
̈
ACKNOWLEDGMENTS
Financial support from the Deutsche Forschungsgemeinschaft
is gratefully acknowledged. X.W. thanks Prof. Rene
helpful discussions.
Chem. Commun. 1999, 2, 576−580. (d) Steurer, M.; Wang, Y. P.;
Mereiter, K.; Weissensteiner, W. Organometallics 2007, 26, 3850−
3859.
■
́
Rojas for
(15) (a) Holger, S.; Fritz, V. Synthesis 1999, 295−305. (b) Nasser, I.
Eur. J. Org. Chem. 2006, 483−488. (c) Marjan, J. Helv. Chim. Acta
2009, 92, 555−566. (d) Ramin, G. V. Tetrahedron Lett. 2009, 50,
1861−1865.
(16) Galland, G. B.; Quijada, R.; Rojas, R.; Bazan, G.; Komon, Z. J. A.
Macromolecules 2002, 35, 339−345.
(17) (a) Ferrocenes: Homogeneous Catalysis, Organic Synthesis,
Materials Science; Togni, A.; Hayashi, T., Eds.; VCH: Weinheim,
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