On the way to biodegradable poly(hydroxy butyrate) from propylene oxide and carbon monoxide via β-butyrolactone: Multisite catalysis with newly designed chiral indole-imino chromium(III) complexes

Journal of Organometallic Chemistry 694 (2009) 2493–2512

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Journal of Organometallic Chemistry

journal homepage: w ww.elsevier.com/locate/jorganchem

On the way to biodegradable poly(hydroxy butyrate) from propylene oxide

and carbon monoxide via b-butyrolactone: Multisite catalysis with newly

designed chiral indole-imino chromium(III) complexes

Heimo Wölﬂe ^a, Holger Kopacka ^a, Klaus Wurst ^a, Peter Preishuber-Pﬂügl ^b, Benno Bildstein ^a,

*

^aInstitute of General, Inorganic and Theoretical Chemistry, Faculty of Chemistry and Pharmacy, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria

^bBASF SE, R&D Engineering Plastics, 67056 Ludwigshafen, Germany

a r t i c l e i n f o

a b s t r a c t

Article history:

Enantioenriched poly(hydroxy butyrate) (PHB) is a biodegradable polyester of signiﬁcant commercial

interest as an environmentally benign substitute of commodity polyoleﬁnes. We report on the design

and development of new chiral indole-based ligand families and on their chromium(III) complexes as

enantioselective catalysts for the conversion of propylene oxide and carbon monoxide to enantioenriched

b-butyrolactone, the key monomer for the production of PHB by ring-opening polymerization. The enan-

tioselective carbonylation catalysts are based on new chiral tri- and tetradentate [N₂O] and [N₄] chro-

mium(III) complexes containing chiral indolaldimine ligand scaffolds. The conceptual design of these

ligands is inspired by Jacobsen’s salicylaldimine lead structure; the key difference is an exchange of

the salicyl-O-donor against an indole-N-donor, allowing additional structural diversity and stereoelec-

tronic tuning by the indole substitution pattern. Synthetically, chiral indolealdimines are easily accessible

from 7-formylindoles by standard Schiff base condensation with chiral amine building blocks; the 7-

formylindoles in turn are synthesized from the corresponding 7-bromoindoles by the Rapoport synthesis,

and the starting 7-bromoindoles are accessible from 2-bromoaniline by the classical Fischer indole syn-

thesis. Three generations of chiral [N₂O] and [N₄] chromium(III) catalysts have been developed and eval-

uated in the enantioselective carbonylation of racemic propylene oxide with carbon monoxide using

tetracarbonylcobaltate as the nucleophilic reagent for the insertion of carbon monoxide into the activated

propylene oxide/chiral Lewis acid complex. The best catalyst out of 10 candidates showed at a temper-

ature of 80 °C an activity of 37% conversion, 100% chemoselectivity, and 19% stereoselectivity.

Received 29 January 2009

Received in revised form 8 April 2009

Accepted 14 April 2009

Available online 22 April 2009

Keywords:

Asymmetric catalysis

Carbon monoxide

Propylene oxide

Indoles

b-Butyrolactone

Poly(hydroxybutyric acid)

1. Introduction

a M_nof 150 000, shows a glass transition at 4 °C and melts at

180 °C. In its mechanical properties, it is similar to poly(ethylene

In the past decades, an enormous market for biologically com-

patible products evolved. In this context, biologically degradable

polymers are still rather underdeveloped. Although well known

in principle, application of these materials has been limited to only

specialized usage in medicine. However, there is without doubt

great commercial potential of biodegradable plastics as substitute

for polyoleﬁn commodities like polypropylene (PP) and polyethyl-

ene (PE), but currently the high costs and the limited availability of

these materials stand in the way of a broad introduction to a ready

market [1].

One of these promising materials is poly[(R)-3-hydroxybutyric

acid] (PHB). PHB is naturally produced by various bacteria as a re-

serve polymer and has found a small and very specialized applica-

tion as medical sewing and tissue-supporting material. Pure,

naturally produced PHB is strictly isotactic has a M_wof 500 000,

terephthalate) (PET). Since its melting point is problematically

close to its decomposition point, it is imperative to lower it in order

to obtain a processible material. Biotechnological strategies involve

the change of fermentation conditions to obtain a blended material

(e.g. with some percentage of valerianic units in the polymer

chain) or to produce copolymers with terephtalic esters. However,

all these strategies are too expensive for a marketable, reasonable

cheap commodity [2].

Hence a petrochemical approach starting from readily available

cheap feedstock is an interesting alternative. Conceptually, the

lowering of PHB’s melting point can be realized by a controlled de-

crease of its tacticity. This results in the softening of the polymer as

well and so a sheet-material similar to PP can be obtained. Mech-

anistically, PHB can be conveniently synthesized by ring-opening

polymerization (ROP) of b-butyrolactone (BL) (Scheme 1) [3].

This reaction and its catalysis are well known and are exten-

sively treated in the literature [4]. The control of the tacticity of

the resulting polymer is achieved by the use of appropriate mix-

* Corresponding author. Tel.: +43 512 507 5141; fax: +43 512 507 2934.

E-mail address: benno.bildstein@uibk.ac.at (B. Bildstein).

doi:10.1016/j.jorganchem.2009.04.013

2494

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

tive: this can be achieved by use of a stereo-inducing Lewis acid

which effects a kinetic resolving activation [8].

2. Results and discussion

Scheme 1. Ring-opening polymerization of b-butyrolactone to yield PHB.

2.1. Proof of principle with Jacobsen catalysts

tures of enantiomers of b-butyrolactone. Doi and co-workers corre-

lated mechanical properties, melting point and tacticity of PHB and

found an optimal range to be between 70% and 80% isotacticity for

a PP-like material with a melting point between 95 and 130 °C [5].

These ﬁndings make enantioenriched b-butyrolactone (BL) the key

monomer for an industrial production of environmentally benign

PHB. To get access to enantioenriched BL on an industrial scale,

the most promising method consists in the enantioselective car-

bonylation of racemic propylene oxide (PO). The goal of the present

work was to develop a catalytic process for this purpose.

In general, the carbonylation of epoxides is a deeply investi-

gated topic and extensive investigations have shown that the most

promising catalyst system for such a multisite catalysis is a combi-

nation of a suitable Lewis acid for the electrophilic activation of the

epoxide and a nucleophilic carbonylating reagent for the insertion

of carbon monoxide into the activated epoxide [6]. As shown by

Coates, tetracarbonylcobaltate with various counterions [Lewis

acid]⁺[Co(CO)₄]^ꢀ, under application of high carbon monoxide pres-

sures is the best available carbonylating system in that context [7].

By the use of a chiral Lewis acid, it should be possible to achieve

the deﬁned goal (Scheme 2).

A multisite catalyst system to produce enantioenriched BL has

to fulﬁl three main tasks: First, the system has to be active: Propyl-

ene oxide has to be activated and carbon monoxide has to be con-

sumed by insertion. Second, the system has to be chemoselective:

as a side reaction – when the carbonylation is too slow-activated

propylene oxide can undergo an undesired rearrangement to form

acetone. Therefore a critical balance between the nucleophilicity of

the carbonylating reagent and the electrophilic activation by the

Lewis acid is mandatory. Third, the system has to be stereoselec-

Seminal work by Jacobsen has shown that chiral salicylimidato

transition metal complexes are well capable to activate epoxides in

a stereoselective manner [9]. As a starting point for the enantiose-

lective formation of BL from PO and CO according to Scheme 1, we

investigated Jacobson’s classical tri- and tetradentate chro-

mium(III)-salicylimidato complexes 1–3 (Fig. 1, Table 1).

The results clearly showed that chromium(III) complexes con-

taining a chiral ligand backbone are in principle capable of catalyz-

ing the chemoselective and (in the case of bulky tridentate

complexes 2 and 3) even stereoselective carbonylation of propyl-

ene oxide. In addition to their stereoselectivity, the tridentate

[NO₂]–chromium(III) salicylimidates are also faster than a classical

tetradentate [N₂O₂]-system like 1. Based on these promising ﬁrst

results we set out to design and develop novel chiral ligand struc-

tures aiming at an improvement of the catalytic performance of

their chromium(III) complexes.

2.2. Indole-based building blocks for new tridentate [N₂O] and

tetradentate [N₄] ligand families

Since salicylaldimines are such extremely versatile ligands for

purposes as ROP and activation of epoxides, aziridines, lactones

and other cyclic polar substrates, it is of great interest to develop

novel ligand families based on this ‘‘privileged” structural motif

[10]. On the search for such salicyl-analoguos systems we have re-

ported earlier on planar–chiral ferrocene ligands [11]; here we

summarize our results on new indole-based [N₂O] and [N₄] ligand

families who were designed to be as close-as-possible to Jacobsen’s

successful [NO₂] and [N₂O₂] motive. Conceptually, these new li-

gands should be accessible in a straightforward and modular man-

Scheme 2. Illustration of the targeted catalytic reaction.

Fig. 1. Jacobsen’s salicylaldiminato chromium(III) complexes.

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2495

Table 1

Enantioselective carbonylation with Jacobsen’s chromium(III) complexes.

p^a[bar]

TO_BL[%]

TO_AC[%]

BL_rel[%]

ee^e[%]

b

c

d

Catalyst

T [°C]

t [h]

D

1

80

40

80

40

80

40

6

22

6

22

6

22

18

17

27

6

28

8

19

11

27

6

27

7

4

2

1

3

1

83

85

93

86

90

88

–

7, R

13, R

25, R

2

3

a

Decrease of carbon monoxide pressure.

Yield of b-butyrolactone (turnover).

Yield of acetone (turnover).

Percentage b-butyrolactone in product mixture (chemoselectivity).

Enantiomeric excess of BL-isomer (stereoselectivity).

b

c

d

e

ner and they should incorporate the important structural features

of the Jacobsen systems. These considerations led to 7-formylin-

doles as the key building blocks for such new [N₂O] and [N₄] ligand

families (Fig. 2).

quence, therefore it seemed especially suitable for the synthesis

of a library of new 2-substituted 7-formylindole building blocks.

The necessary starting materials, 2-substituted 7-bromoindoles,

should in principle be accessible by applying the classical Fischer

indole synthesis [16] on the corresponding bromo derivatives. This

was indeed the case: First, 2-bromophenylhydrazine 4 was pre-

pared in excellent yield by reduction of the diazonium chloride

of 2-bromoaniline with tin(II)chloride [17]. Second, 4 was con-

densed with various methyl ketones to hydrazones 5–11 by aceo-

tropic removal of water (Scheme 4).

Third, hydrazones 5–11 were transformed to 7-bromoindoles

13–16 by reﬂuxing in mesitylene in the presence of an excess of

zinc(II)chloride as Lewis acid following the standard conditions

of Fischer’s indole synthesis [16]. From hydrazones 5–8 containing

a methyl and a ‘‘normal” aromatic substituent at the imino-carbon,

the desired 7-bromoindoles 13–16 were obtained without difﬁcul-

ties (Fig. 3), but aliphatic t-butyl hydrazone 10 failed to react in the

anticipated manner, suggesting limitation of this method to

methyl/aryl hydrazone substrates. Furthermore, pentaﬂuorohyd-

razone 11 rearranged to tetraﬂuorobenzodiazole 12 in a reaction

that has precedence in the literature as was found afterwards

(Scheme 5) [18], and isopropyl/phenyl hydrazone 9 reacted to iso-

indole 17 [19].

In medicinal and pharmaceutical chemistry, indoles are very

important constituents of physiologically active compounds, there-

fore many substituted indoles are known, but-unfortunately-not

many 7-formylindoles [12]. The parent compound, 7-formylindole,

is the main target and ﬁrst example of Bartoli’s indole synthesis.

Even though it is commercially available, it is rather expensive.

However, by Dobson’s variation of the Bartoli synthesis it is easily

accessible from cheap starting materials [13]. In contrast, for the

synthesis of substituted 7-formylindoles, there are only very few

methodologies known. In our context, 2-substituted-7-formylin-

doles are especially important building blocks, because the steric

bulk of the substituent in the vicinity of the indole–N-donor will

be beneﬁcial for the catalytic performance of their [N₂O] or [N₄]

chromium(III) complexes, in analogy to Jacobsen’s systems. In a

carefully performed literature search, we came across the work

of Black [14] who has already used 7-formylindoles as building

blocks for chelating ligands of late transition metal complexes.

Their synthesis involves a Vilsmeyer strategy on methoxy-pro-

tected indoles, however, for our purposes this reaction sequence

is too cumbersome and too limited in scope. In a more useful orga-

nometallic approach, Rapoport reported the synthesis of 2-methyl-

7-formylindole from the corresponding 7-bromoindole in good

yield [15]. This strategy involves the protection of the amine func-

tion by its potassium salt, followed by metal–halogen exchange of

the bromine by t-BuLi in ether at low temperature, and ﬁnally con-

version of the doubly metalated indole to its 7-formyl derivative by

reaction with dimethylformamide (DMF) (Scheme 3).

With these four new 7-bromoindoles in hand, the corresponding

7-formylindoles 20–23 as well as the known representatives 18, 19

were synthesized in good yield by Rapoport’s method (Scheme 3)

[15] resulting in a library of the desired 7-formylindole key syn-

thons (Fig. 4). The new indole aldehydes 20–23 were fully charac-

terized by ¹H NMR, ¹³C NMR and by IR-spectroscopy as well as by

mass spectrometry. Characteristic features of the aldehyde group

included low-ﬁeld NMR signals (¹H NMR: d = 10.1–10.2 ppm; ¹³C

This method has the great advantage of introducing the rather

labile aldehyde functionality in the last step of the reaction se-

NMR: d = 193.7–193.9 ppm) and strong IR absorptions (m_C@O=

1668–1675 cm^ꢀ1), the N–H proton of the indole heterocyclic core

was clearly evidenced by observation of low-ﬁeld, broad ¹H NMR

signals (d = 10.0–10.7 ppm) and strong IR absorptions (m_N–H

=

3340–3384 cm^ꢀ1).

Furthermore, isoindole 17 could be transformed to 7-formylind-

oline 24 by a similar organometallic route: reaction with three

equivalents of phenyl lithium effected ﬁrst nucleophilic addition

to the isoindole imine bond followed by bromine–lithium exchange

and, after addition of dimethylformamide and aqueous workup, for-

mation of novel 7-formylindoline 24 (Fig. 4). Although in retrospect

this reaction looks rather simple, experimentally it was quite difﬁ-

cult to ﬁnd the proper work-up conditions. In principle, many other

organyl lithium compounds than phenyl lithium would also effect

this 7-formylindoline formation, allowing thereby further structural

diversity, but with the drawback of producing racemic mixtures due

to the new chiral center at the 2-indoline position. In comparison to

indole aldehydes 18–23, indoline aldehyde 24 showed similar spec-

tral features characteristic of its aldehyde group [d(¹H) = 9.9 ppm,

Fig. 2. 7-Formylindole building blocks based on the salicyl aldehyde lead structure.

Scheme 3. Rapoport’s 7-formylindole synthesis.

d(¹³C) = 193.2 ppm,

m

_C@O= 1661 cm^ꢀ1

]

and slightly different

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H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

Scheme 4. Modular route to hydrazones 5–11.

Scheme 5. Rearrangement of hydrazone 11 to benzodiazole 12.

Fig. 3. Library of 2-substituted-7-bromoindoles 13–16 and 7-bromoisoindole 17.

Fig. 4. Library of 2-substituted-7-formyl-indoles 18–23 and indoline 24.

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2497

features for its non-aromatic heterocyclic N–H proton

[d(¹H) = 7.3 ppm, _N–H= 3380 cm^ꢀ1].

These indole (18–23) and indoline (24) aldehydes constituted

now the key precursors for novel achiral/chiral salicylaldiminato-

analogous [N₂O] and [N₄] ligand libraries and their chromium(III)

complexes.

The general method for the synthesis of salophen chromium(III)

complexes consists in a simple ligand exchange with chromium(II)

halide precursors in basic medium, followed by oxidation in air to

the desired chromium(III) complexes [9]. The obvious advantage of

this procedure is the use of substitution-labile Cr(II) instead of

kinetically inert Cr(III), however, the products are usually difﬁcult

to purify. Impure metal complexes hamper the accuracy and inter-

pretation of their catalysis data, therefore a more deﬁned complex/

catalyst synthesis was desirable. Hence we avoided the oxidation

step and used a standard organometallic transmetalation method,

consisting in deprotonation of the ligands in dry THF with butyl

lithium, followed by slow transmetalation with anhydrous CrCl₃

and removal of lithium chloride by ﬁltration. In practice, this meth-

od afforded the desired [N₄]Cl(THF)Cr complexes 29 and 30 on a

millimolar scale in reaction periods of 24 h as red solids in quanti-

tative yield (Fig. 5). Due to their paramagnetism, no useful NMR

data could be obtained and-unfortunately-all attempts to grow

suitable single crystals for X-ray structure analysis met so far with

failure.

Chromium(III) complexes 29 and 30 are potential catalysts for

ring-opening polymerization (ROP) of racemic b-butyrolactone

(Scheme 1). To test their applicability in this regard, preliminary

tests were performed which showed that these metal Lewis acids

are rather poor ROP catalysts, only oligomers instead of polymers

were obtained (Table 2).

In summary, tetradentate salophen-analogous ‘‘indolophen”

[N₄]H₂ligands are accessible by forced microwave-assisted con-

densation of 7-formylindole with o-phenylenediamines. Their

chromium(III) complexes may be prepared without the need of

an oxidation step in excellent yield by standard organometallic

procedures. Their use as catalysts for ring-opening polymerization

of lactones has been tested, however, their catalytic performance is

rather poor in comparison to established other metal complex Le-

wis acids.

m

2.3. Achiral indolyl [N₄] Cr(III) catalysts

In general, salicylaldimine ligands are easily synthesized by

simple condensation of salicylaldehyde with various amines. In

analogy, starting from indol(in)e aldehydes 18–24 the correspond-

ing Schiff bases should be easily accessible. In a ﬁrst attempt,

unsubstituted 7-formylindole 18 was chosen to investigate its

applicability as a salicylaldehyde analogue in the condensation

with o-phenylenediamines. Much to our surprise and against all

chemical intuition, this seemingly simple reaction proved quite

difﬁcult. First, applying all standard condensation methods failed

completely, no reaction was observed. Second, nickel-templated

condensation according to Black’s procedure [20] did afford the ex-

pected indolylimidato-nickel complex 25 as a purple and rather

insoluble solid, but all attempts to remove the coordinated Ni²⁺

by hydrochloric acid, sulﬁde, or cyanide [21] failed to give the free

[N₄]H₂ligand. Interestingly, with cyanide as de-metalating agent

an undesired but already reported oxidation to bis(indolyl)quinox-

aline 26 with concomitant formation of elemental nickel was ob-

served (Scheme 6) [22].

Third, applying brute force gave ﬁnally access to the desired

salophen-analogous ‘‘indolophen” [N₄]H₂ligands: heating a stoi-

chiometric mixture of the starting materials at 600 W for 45 min

in a microwave reactor [23], followed by extraction of the cooled

melt, allowed the isolation of tetradentate ligands 27 and 28 in

47% and 39% yield, respectively (Fig. 5). The spectral properties of

these two [N₄]H₂ligands were in line with their structures, charac-

teristic features included ¹³C NMR signals of the imine carbons [27:

d(¹³C) = 161.2 ppm, 28: d(¹³C) = 160.4 ppm] shifted towards high

ﬁeld in comparison to their aldehyde precursor 18, and strong IR

absorptions of the hydrogen-bridged indole N–H protons [27: m_N–

2.4. Chiral indolyl [N₂O] and [N₄] Cr(III) catalysts

As has been shown above (Fig. 1, Table 1), Jacobsen’s chiral sal-

icylaldiminato [N₂O] and [N₂O₂] chromium(III) complexes 1, 2 and

3 are capable of catalyzing the stereoselective carbonylation of pro-

pylene oxide to enantioenriched b-butyrolactone, the key precursor

of biodegradable poly(hydroxy butyrate) (PHB). The enantiomeric

excess was rather low and tridentate [NO₂]L₂ClCr complexes 2

and 3 performed better than tetradentate [N₂O₂]LClCr complex 1.

_H= 3390, 3359 cm^ꢀ1, 28:

m

_N–H= 3388, 3317 cm^ꢀ1] as well as strong

_C@N= 1621 cm^ꢀ1].

imine bands [27:

m

_C@N= 1619 cm^ꢀ1, 28:

m

Table 2

ROP of racemic b-butyrolactone with [N₄]Cl(THF)Cr complexes 29 and 30.

Catalyst

Turnover [%]^a

Polymerization degree n^b

29

30

95

94

13

15

a

Calculated from ¹H NMR data.

1-Crotonyl-endgroup per n repetition units.

b

Scheme 6. Cyanide-induced oxidation of 25.

Fig. 5. Indolophen ligands 27, 28 and their chromium(III) complexes 29, 30 [L = THF].

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H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

Therefore we anticipated that analogous chiral indole-based cata-

lyst systems would be active as well and hoped that their perfor-

mance would surpass that of Jacobsen’s complexes.

Synthesis of a ﬁrst generation of such chiral indole-based li-

gands was easily accomplished by standard Schiff base condensa-

tion of 7-formylindole 18 with both diastereomers of cis-1-

aminoindane-2-ol and R,R-cyclohexane-1,2-diamine in dry, boiling

methanol to give 31, 32 and 33 in 78%, 69% and 85% yield, respec-

tively (Fig. 6). Gratifyingly, the ease of these condensations with

aliphatic aminoalcohols allowed access to the targeted ligands

without any problems, whereas severe activation proved necessary

for indolophen ligands 27 and 28 (vide supra). The quantitative

conversion of 31, 32 and 33 to their corresponding chromium(III)

catalysts 34, 35, 36 was achieved by a similar transmetalation

route as described above starting from the lithiated ligands and

anhydrous chromium(III) chloride.

Fig. 7. Molecular structure of 32.

Spectroscopically, ligands 31–33 were fully characterized by ¹H,

¹³C NMR, IR-spectroscopy as well as mass spectrometry and

showed the expected features of their aldimine functionalities

plexes 34 and 35 exhibited better performance as compared to tet-

radentate [N,N,N,N]-complex 36.

[31: d(¹H) = 8.77 ppm, d(¹³C) = 164.9 ppm,

m

_C@N= 1628 cm^ꢀ1; 32:

_C@N= 1627 cm^ꢀ1

33:

_C@N= 1631 cm^ꢀ1], indole

m

_N–H= 3416 cm^ꢀ1, 32: d(¹H) =

Based on these ﬁrst promising results a second generation of

catalysts had to be developed. The main guiding principle was to

introduce additional steric shielding in the vicinity of the indole-

N-donor and to modulate the electronic properties of this substitu-

ent as well. To this end, ligands 37–39 (Fig. 8), containing either a

methyl or a phenyl substituent in the indole-2-position, and their

Cr(III) complexes 40–42 (Fig. 8) were synthesized starting from

the corresponding 2-substituted 7-formylindoles 19 or 20 (Fig. 4).

Spectroscopically, ligands 37–39 were fully characterized by

¹H, ¹³C NMR, IR-spectroscopy as well as mass spectrometry and

showed the expected features of their aldimine functionalities

d(¹H) = 8.82 ppm, d(¹³C) = 165.8 ppm,

d(¹H) = 8.48 ppm, d(¹³C) = 161.6 ppm,

m

;

m

moieties [31: d(¹H) = 10.86 ppm,

10.35 ppm,

3328 cm^ꢀ1], and hydroxyl groups [31: d(¹H) = 3.99 ppm, m_O–H

3489 cm^ꢀ1, 32: d(¹H) = 2.65 ppm,

m

_N–H= 3419 cm^ꢀ1

,

33: d(¹H) = 10.77 ppm, m_N–H

=

m

_O–H= 3492 cm^ꢀ1]. In addition,

for ligand 32 a single crystal structure is available (Fig. 7), giving

full structural proof and illustrating the orthogonal steric shielding

of the chiral indanyl moiety vs. the principal [O,N,N]H₂coordina-

tion plane. In contrast, no informative NMR signals could be mea-

sured for the paramagnetic Cr(III) complexes 34–36, and up to now

no suitable single crystals for X-ray structure analysis could be

obtained.

Of prime interest was the catalytic performance of this ﬁrst gen-

eration of new catalysts in the carbonylation of propylene oxide

(Table 3). In general, the results were encouraging: Whereas activ-

ity (TO_BL) was slightly lower than with Jacobsen’s catalysts 1–3

(compare Table 1), chemoselectivity (BL_rel) was signiﬁcantly im-

proved with comparable stereoselectivity (ee). The conformations

of the catalysts and their products were consistent, S,R-catalyst

31 yielded R-BL while R,S-catalyst 32 gave S-BL. Analogously as

in the case of Jacobsen’s catalysts 1–3, tridentate [N,N,O]-com-

[31: d(¹H) = 8.56 ppm, d(¹³C) = 161.7 ppm,

m

_C@N= 1630 cm^ꢀ1; 38:

_C@N= 1625 cm^ꢀ1

39:

_C@N= 1626 cm^ꢀ1], indole

m

_N–H= 3351 cm^ꢀ1, 38: d(¹H) =

d(¹H) = 8.78 ppm, d(¹³C) = 166.0 ppm,

d(¹H) = 8.82 ppm, d(¹³C) = 165.1 ppm,

m

;

m

moieties [37: d(¹H) = 10.56 ppm,

10.01 ppm,

3381 cm^ꢀ1], and hydroxyl groups [38: d(¹H) = 2.69 ppm, m_O–H

3536 cm^ꢀ1, 39: d(¹H) = 2.35 ppm,

m

_N–H= 3427 cm^ꢀ1

,

39: d(¹H) = 10.85 ppm, m_N–H

=

m

_O–H= 3567 cm^ꢀ1]. In addition,

for ligands 38 and 39 single crystal structures are available (Figs. 9

and 10), giving full structural proof and once again illustrating the

orthogonal steric shielding of the indanyl groups vs. the principal

[O,N,N]H₂coordination planes. In comparison to the structure of

unsubstituted ligand 32 (vide supra), the additional steric pressure

Fig. 6. First generation of chiral indolyl ligands 31–33 and their Cr(III) complexes 34–36 (L = THF).

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2499

Table 3

Enantioselective carbonylation with 1st generation indole-catalysts 34–36.

p^a[bar]

TO_BL[%]

TO_AC[%]

BL_rel[%]

ee^e[%]

b

c

d

Catalyst

T [°C]

t [h]

D

34

80

40

80

40

80

40

6

22

6

22

6

10

2

18

5

10

4

8

4

15

5

7

3

1

0

1

0

3

89

100

83

100

50

16, R

19, R

8, S

11, S

5, S

–

35

36

22

a

Decrease of carbon monoxide pressure.

Yield of b-butyrolactone (turnover).

Yield of acetone (turnover).

Percentage b-butyrolactone in product mixture (chemoselectivity).

Enantiomeric excess of BL-isomer (stereoselectivity).

b

c

d

e

Fig. 8. Second generation of chiral indolyl ligands 37–39 and their Cr(III) complexes 40–42 (L = THF).

Fig. 9. Molecular structure of ligand 38.

Fig. 10. Molecular structure of ligand 39.

by the methyl (Fig. 9) or phenyl (Fig. 10) group around the coordina-

tion site is clearly evident. In contrast, no informative NMR signals

could be measured for the paramagnetic Cr(III) complexes 40–42,

and up to now no suitable single crystals for X-ray structure analysis

could be obtained.

The catalytic performance of these second generation catalysts

(Table 4) was gratifyingly a signiﬁcant improvement, at least in

the case of tridentate [N,N,O] complexes 41 and 42. Tetradentate

[N,N,N,N]-complex 40 gave quite similar results as its non-methyl-

ated relative 36 (vide supra, Table 3), indicating that a further mod-

iﬁcation of this backbone will not serve our purpose. In stark

contrast, tridentate R,S-aminoindanol-derived catalysts 41 and 42

showed clearly that their additional substituent at the 2-indole-po-

sition was very beneﬁcial in comparison to unsubstituted relative

35 (vide supra, Table 3), thereby giving access to catalysts with

doubled activity as well as stereoselectivity. In terms of activity,

the electron-withdrawing phenyl group (catalyst 42) is clearly

2500

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

Table 4

Enantioselective carbonylation with 2nd generation indole-catalysts 40–42.

p^a[bar]

TO_BL[%]

TO_AC[%]

BL_rel[%]

ee^e[%]

b

c

d

Catalyst

T [°C]

t [h]

D

40

80

40

80

40

80

40

6

22

6

22

6

11

2

20

12

33

16

8

0

23

13

37

20

1

0

1

0

89

–

96

100

6, S

–

16, S

19, R

16, R

41

42

22

a

Decrease of carbon monoxide pressure.

Yield of b-butyrolactone (turnover).

Yield of acetone (turnover).

Percentage b-butyrolactone in product mixture (chemoselectivity).

Enantiomeric excess of BL-isomer (stereoselectivity).

b

c

d

e

much better than an electron-donating methyl substituent (cata-

lyst 41). Therefore we anticipated that aryl groups containing elec-

tron-accepting moieties will increase the activity of the next

generation of catalysts.

Based on these ﬁndings and considerations, the third and last

generation of catalysts focused on tridentate [N,N,O]H ligands

based on chiral aminoindanol and 7-formylindol(in)e building

blocks 21–24 (vide supra, Fig. 4) containing various aryl substitu-

ents in the 2-indol(in)e-position (Fig. 11).

3384 cm^ꢀ1], and hydroxyl groups [43: d(¹H) = 2.64 ppm, m_O–H

3547 cm^ꢀ1, 44: d(¹H) = 2.79 ppm, _O–H= 3538 cm^ꢀ1; 45: d(¹H) =

2.72 ppm, _O–H= 3541

=

m

_O–H= 3564 cm^ꢀ1; 46: d(¹H) = 2.73 ppm,

m

cm^ꢀ1]. In contrast, no informative NMR signals could be measured

for the paramagnetic Cr(III) complexes 47–50, and-unfortunately-

up to now no suitable single crystals for X-ray structure analysis

could be obtained.

In this last family of catalysts, indoline compound 48 was ex-

pected to show the highest stereoselectivity on cost of activity

due to the high steric demand by the two geminal phenyl groups.

p-Fluorophenyl-indole complex 49 was expected to show similar

stereoselectivity as 42 but increased activity due to its electroni-

cally withdrawing ﬂuoro substituent. The same consideration

should hold true for the 2-naphthyl-indole derivative 47. Finally,

o-chlorophenyl-indole complex 50 should represent the ‘‘best” cat-

alyst due to its balanced stereoelectronic properties by the elec-

tronically withdrawing and at the same time slightly sterically

active o-chloro substituent. These considerations, although some-

what logical, were dramatically proven wrong by the actual cata-

lytic experiments (Table 5).

Synthetically, ligands 43–46 were easily accessible by standard

Schiff base condensation in good to excellent yields of 58–99%.

Complexation of the ligands with Cr(III) to the target catalysts

47–50 was achieved as described above in quantitative yield by

transmetalation from the lithiated ligands.

Spectroscopically, ligands 43–46 were fully characterized by ¹H,

¹³C NMR, IR-spectroscopy as well as mass spectrometry and

showed the expected features of their aldimine functionali-

ties [43: d(¹H) = 8.85 ppm, d(¹³C) = 165.4 ppm,

m

_C@N= 1628 cm^ꢀ1

_C@N= 1625 cm^ꢀ1; 45:

_C@N= 1630 cm^ꢀ1

46:

_C@N= 1628 cm^ꢀ1], indole

_N–H= 3374 cm^ꢀ1, 45: d(¹H) =

46: d(¹H) = 11.21 ppm, m_N–H

=

;

44: d(¹H) = 8.65 ppm, d(¹³C) = 165.7 ppm,

m

d(¹H) = 8.80 ppm, d(¹³C) = 165.3 ppm,

d(¹H) = 8.82 ppm, d(¹³C) = 165.0 ppm,

m

;

m

As can be seen from inspection of Table 5, the performance of

the catalysts of the third generation was inferior in comparison

to second generation complex 42 containing an unsubstituted phe-

moieties [43: d(¹H) = 10.73 ppm,

m

10.72 ppm,

m

_N–H= 3342 cm^ꢀ1

,

Fig. 11. Third generation of chiral indol(in)yl ligands 43–46 and their Cr(III) complexes 47–50 (L = THF).

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2501

Table 5

Enantioselective carbonylation with 3rd generation indol(in)e-catalysts 47–50.

p^a[bar]

TO_BL[%]

TO_AC[%]

BL_rel[%]

ee^e[%]

b

c

d

Catalyst

T [°C]

t [h]

D

47

80

40

80

40

80

40

80

40

6

24

6

24

6

24

6

24

30

11

7

36

11

6

1

0

1

0

1

0

97

100

96

100

95

100

8, R

16, R

6, S

48

49

50

6

5

6, S

21

11

24

11

22

13

18

11

14, S

16, S

14, S

16, S

a

Decrease of carbon monoxide pressure.

Yield of b-butyrolactone (turnover).

Yield of acetone (turnover).

Percentage b-butyrolactone in product mixture (chemoselectivity).

Enantiomeric excess of BL-isomer (stereoselectivity).

b

c

d

e

nyl moiety (vide supra, Table 4), indicating that increasing elec-

tron-withdrawal at this substituent is counterproductive. The

anticipated lower activity of indoline-catalyst 48 as the bulkiest

system was indeed observed, however, without a concomitant in-

crease in stereoselectivity. The activity and stereoselectivity of

naphthyl-catalyst 47 was more or less the same as for phenyl-cat-

alyst 42, suggesting that possible intermolecular p-stacking of the

2-aryl-indole substituent plays no role in this multisite catalytic

system.

a clean manner from the lithiated ligands and anhydrous CrCl₃

by a standard transmetalation procedure.

The catalytic performance of three successive generations of

catalysts was evaluated (Fig. 12); in the end complex 42 turned

out to be the best catalyst for the enantioselective carbonylation

of propylene oxide. Its performance [42 (80 °C): TO_BL= 37%,

TO_AC= 0%, BL_rel= 100%, ee = 19 R] compares favourably with the

best of Jacobsen’s catalysts [3 (80 °C): TO_BL= 27%, TO_AC= 3%,

BL_rel= 90%, ee = 13 R], but our goal of optimizing these catalysts

to an enantioselectivity > 70% according to Doi’s proposal [5] could

unfortunately not be achieved. Hence it will be necessary to design

completely new catalyst structures for this purpose in the future.

On the other hand, our newly developed [N,N,N,N]H₂and

[O,N,O]H₂ligand systems based on the ‘‘privileged” indole scaffold

might ﬁnd use in other chiral Lewis acids for applications in enan-

tioselective homogeneous catalysis.

2.5. Summary and conclusions

The goal of this work was to develop a catalyst system capable

of enantioselective conversion of racemic propylene oxide to enan-

tioenriched b-butyrolactone as the key monomer for ring-opening

polymerization to give access to poly(hydroxybutyric acid), a bio-

degradable polymer of signiﬁcant commercial interest.

Mechanistically, this multisite catalytic system is composed of a

chiral Lewis acid for the enantioselective activation of propylene

oxide and tetracarbonylcobaltate as the nucleophilic carbonylation

reagent responsible for the chemoselective insertion of carbon

monoxide.

3. Experimental

3.1. Catalysis: conversion of propylene oxide and carbon monoxide to

enantioenriched b-butyrolactone

The catalyst design of the chiral Cr(III) Lewis acid focused on no-

vel indole-based ligand structures inspired by the successful sali-

cylaldimine lead structure of Jacobsen. The key building blocks

are new 7-formylindoles which were accessible in a modular and

straightforward manner from the corresponding 7-bromo-indoles.

By condensing these indole aldehydes with various achiral and chi-

ral amino compounds new [N,N,N,N]H₂and [O,N,O]H₂ligand li-

braries were realized. Their Cr(III) complexes were synthesized in

Carbonylation experiments were performed in a steel autoclave

equipped with gas inlet, thermo- and pressure-sensor. The catalyst

system was produced in situ by mixing 3 mmol of Lewis acid [1, 2,

3 (Jacobsen complexes); 34, 35, 36 (1st generation catalysts); 40,

41, 42 (2nd generation catalysts); 47, 48, 49, 50 (3rd generation

catalysts] with 3 mmol of sodium tetracarbonylcobaltate followed

by addition of 1 ml racemic PO in 1 ml diglyme, corresponding to

2% catalyst loading. The autoclave was closed, heated to the appro-

Fig. 12. Catalytic performance at 80 °C of catalysts 1, 2, 3 (Jacobsen complexes); 34, 35, 36 (1st generation catalysts); 40, 41, 42 (2nd generation catalysts); and 47, 48, 49, 50

(3rd generation catalysts).

2502

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

priate temperature and 60 bar of CO–pressure were applied. This

presents the optimized system to have all analytical concentra-

tions reasonable on the one hand, but also to have a sufﬁcient dilu-

tion to allow conclusions about the catalytic performance on the

other hand. Since reactions are faster at higher temperatures and

heating is cheaper than cooling, it is preferable to run the carbon-

ylation at temperatures as high as possible. However, since kinetic

resolution is better at lower temperatures, a temperature optimum

with balanced turn-over-frequency (TOF) and enantiomeric excess

(ee) must exist. The reaction conditions were designed to get

reproducible and comparable data. Therefore the reaction of pro-

pylene oxide (PO) to b-butyrolactone (BL) was run at two temper-

atures and for deﬁned periods in order to be able to compare the

time-dependent conversion. Reactions performed at 40 °C were

stirred for 22 h and those performed at 80 °C were stirred for 6 h.

During the reaction the pressure decrease of carbon monoxide

was monitored as a functional dimension for the catalyst activity.

The yields of b-butyrolactone (BL) and acetone (AC) were deter-

mined by ¹H NMR spectroscopy and the stereoselectivity of the

catalysts was ascertained by chiral gas chromatography.

3.3. General procedure for the preparation of hydrazones 5–11

A Dean–Stark apparatus was charged with 1.0 equivalent of 4,

1.2 equivalent of ketone, 0.1 equivalent of p-toluenesulfonic acid

monohydrate and 100 ml of toluene. The mixture was reﬂuxed

over night, cooled to room temperature, diluted with 50 ml tolu-

ene, washed twice with saturated K₂CO₃solution, dried over

Na₂SO₄, ﬁltered and evaporated. The oily residue was dissolved

in approximately 5 ml of ether and eluted with a mixture of hex-

ane/ether (v/v = 1/1) through a short column of basic alumina,

affording the pure hydrazone as the ﬁrst fraction. The hydrazone

should be used immediately for further reactions.

3.3.1. N-(2-Bromphenyl)-N⁰-[1-phenyl-ethylidene]-hydrazine 5

Starting materials:

4 (760 mg, 3.74 mmol), acetophenone

(450 mg, 3.74 mmol), p-toluenesulfonic acid monohydrate (40 mg,

0.2 mmol). 79% Yield (882 mg, 2.90 mmol, brown oil). ¹³C NMR

(75.432 MHz, CD₂Cl₂) d [ppm]: 143.9 (7), 142.3 (9), 139.1 (2),

132.5 (6), 128.9 (12), 128.6 (13, 11), 128.6 (5), 126.0 (14, 10),

120.9 (4), 114.8 (3), 108.0 (1), 12.3 (8). ¹H NMR (300 MHz, CD₂Cl₂)

d [ppm]: 7.88 (3H, d, t, 12, 10, 14); 7.74 (1H, dd, 6); 7.55-7.34 (5H,

m, NH, 11, 13, 3, 4); 6.81 (1H, dt, 5); 2.29 (3H, s, 8). IR (ATR)

m

3.2. General

[cm^ꢀ1]: 3355w (NH), 3055w, 2923w, 1587s (C@N), 1570m,

1509m, 1490s, 1443s, 1368w, 1333m, 1307w, 1282m, 1239s,

1183w, 1139s, 1105w, 1067m, 1040w, 1020s, 970w, 929w, 911w,

824w, 758s, 741s, 689s, 677m, 634m, 587w, 559w, 533w, 474w,

453w, 433m, 419w, 408w (Fig. 14).

Commercially available starting materials were used as ob-

tained. Solvents were dried, deoxygenated, and saturated with ar-

gon according to standard procedures in organometallic chemistry.

Reactions of air-sensitive materials were performed in Schlenk

glassware under an atmosphere of argon using techniques com-

mon in organometallic chemistry.

3.3.2. N-(2-Bromphenyl)-N⁰-[1-(4-ﬂuorophenyl)-ethylidene]-

hydrazine 6

Starting materials: 4 (2.055 g, 11 mmol), p-ﬂuoroacetophenone

(1.824 g, 13.2 mmol), p-toluenesulfonic acid monohydrate

(210 mg, 1.1 mmol). 93% Yield (3.146 g, 10.24 mmol, pale yellow

oil). ¹³C NMR (75.432 MHz, CDCl₃) d [ppm]: 163.2 (d, 12), 142.5

(7), 142.1 (2), 135.2, 135.2 (9), 132.5 (6), 129.0 (5), 127.8, 127.7

(14, 10), 121.0 (4), 115.7, 114.9 (11, 13), 115.4 (3), 108.1 (1),

12.2, 12.15 (8). ¹H NMR (300 MHz, CDCl₃) d [ppm]: 7.79-7.73

(4H, m, 10, 14, 6, NH); 7.54 (1H, d, 3); 7.39 (1H, t, 4); 7.15 (2H, t,

3.2.1. 2-Bromophenylhydrazine 4

A 100 ml three-necked ﬂask was charged with 2-bromoaniline

(8.6 g, 50 mmol) and aqueous HCl (21 ml, 6 N, 2.5 eq.). After the stir-

red suspension was cooled to ꢀ15 °C a solution of NaNO₂(3.45 g,

50 mmol) in 20 ml of water was added dropwise keeping the inter-

nal temperature below 5 °C. The resulting cold diazonium chloride

solution was then added dropwise and under mechanical stirring to

a chilled (ꢀ30 °C) solution of SnCl₂(33.85 g, 150 mmol) in 35 ml

aqueous HCl keeping the internal temperature during addition be-

low ꢀ10 °C. The resulting off-white solid was stored overnight at

4 °C, collected by ﬁltration, triturated with aqueous NaOH until ba-

sic, and immediately extracted with four portions of diethyl ether.

The combined organic layers were washed with water, saturated

bicarbonate solution and brine, dried over sodium sulfate, ﬁltered

and evaporated. The crude reddish hydrazine was repeatedly ex-

tracted with hot petrol ether; on cooling the product crystallized

as a colorless cotton–wool-like solid (8.2 g, 44 mmol, 88% yield).

¹³C NMR (75.432 MHz, CDCl₃) d [ppm]: 145.9 (3), 130.7 (5), 126.8

(7), 118.0 (6), 110.5 (8), 106.2 (4). ¹H NMR (300 MHz, CDCl₃) d

[ppm]: 7.47 (1H, dd, 5); 7.32 (1H, dt, 7); 7.12 (1H, dd, 8); 6.74

11, 13); 6.83 (1H, t, 5); 2.17 (3H, s, 8). IR (ATR)

m

[cm^ꢀ1]: 3357w

(NH), 3064w, 1590s (C@N), 1497s, 1452m, 1404w, 1368w,

1330m, 1283m, 1224s, 1158w, 1140s, 1100w, 1068w, 1040w,

1019s, 972w, 930w, 831s, 738s, 704w, 664w, 635w, 610w, 579w,

555w, 531w, 496m, 434m (Fig. 15).

3.3.3. N-(2-Bromphenyl)-N⁰-[1-(2-chlorophenyl)-ethylidene]-

hydrazine 7

Starting materials: 4 (2.167 g, 11.6 mmol), o-chloroacetophe-

none (2.685 g, 17.4 mmol), p-toluenesulfonic acid monohydrate

(1H, dt, 6); 3.94 (3H, bs, 1, 2). IR (ATR)

m

[cm^ꢀ1]: 3538s (NH, NH₂),

3265w, 3090w, 2978w, 1670w, 1591s, 1485 m, 1425w, 1391w,

1365w, 1299w, 1235w, 1151w, 1118w, 1079w, 1026s, 938w,

860m, 750s, 656w, 572w, 514w, 472w, 430w (Fig. 13).

Fig. 14. Numbering of 5 for NMR assignment.

Fig. 13. Numbering of 4 for NMR assignment.

Fig. 15. Numbering of 6 for NMR assignment.

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2503

(579 mg, 0.57 mmol). 89% Yield (3.351 g, 10.3 mmol, colorless so-

lid). ¹³C NMR (75.432 MHz, CDCl₃) d [ppm]: (mixture of two iso-

mers in a 4:6 ratio) 144.8, 144.3 (7), 142.0, 141.9 (9), 139.6,

134.6 (2), 132.7, 131.9 (14), 132.5, 132.4 (10), 130.9, 130.88 (12),

130.7, 130.3 (11), 129.7, 128.8 (6), 129.0, 128.9 (13), 128.3, 127.2

(5), 121.2, 120.4 (4), 115.0, 114.3 (3), 108.0, 107.3 (1), 24.1, 16.8

(8). ¹H NMR (300 MHz, CDCl₃) d [ppm]: (mixture of two isomers

in a 4:6 ratio) 7.96 (0.6 H, s, NH); 7.65 (1H, d, 6); 7.61–7.27 (6.4

H, m, 4, 3, NH, 10–13); 6.81 (0.6 H, t, 5); 6.73 (0.4 H, t, 5); 2.41,

2.39 (3H, 2s, 8) (Fig. 16).

Fig. 17. Numbering of 8 for NMR assignment.

3.3.4. N-(2-Bromphenyl)-N⁰-[1-(1-naphth-1-yl)-ethylidene]-

hydrazine 8

Starting materials: 4 (2.000 g, 10.7 mmol), 2-naphthylmethylk-

etone (2.184 g, 12.8 mmol), p-toluenesulfonic acid monohydrate

(203 mg, 1.08 mmol). 91% Yield (3.290 g, 9.7 mmol, yellow oil).

¹³C NMR (75.432 MHz, CDCl₃) d [ppm]: (mixture of two isomers;

major isomer) 146.4 (7), 142.4 (9), 134.3 (2), 133.9 (14), 132.6

(6), 129.9 (17), 129.4 (12), 129.2 (13), 129.0 (16), 127.9 (15),

127.2 (11), 126.5 (5), 125.6 (18), 125.3 (10), 120.4 (4), 114.4 (3),

107.4 (1), 25.77 (8); (mixture of two isomers; minor isomer)

145.6, 138.5, 134.6, 132.7, 131.4, 129.3, 129.2, 127.0, 126.7,

125.8, 121.2, 115.2, 108.2, 25.7. ¹H NMR (300 MHz, CDCl₃) d

[ppm]: (mixture of two isomers in a 85:15 ratio) 8.08–8.07 (2H,

m, 10, 12); 8.01–7.94 (2H, m, 17, 14); 7.87 (1H, s, NH); 7.74–7.64

(3H, m, 11, 15, 16); 7.55 (1H, dd, 6); 7.50–7.45 (2H, m, 3, 4); 6.92

(0.15 H, dt, 5); 6.81 (0.85 H, dt, 5); 2.70 (2.55 H, s, 8); 2.56 (0.45

Fig. 18. Numbering of 9 for NMR assignment.

reaction mixture was cooled to ambient temperature, triturated

with diluted hydrochloric acid, and extracted with three portions

of ether. The combined organic layers were washed with water,

saturated Na₂CO₃solution, water, brine, dried over Na₂SO₄, and ﬁl-

tered. Volatile materials were stripped off in vacuum, ﬁrst on a ro-

tary evaporator, then in high vacuum to remove most of the high-

boiling mesitylene. The resulting oily solid was puriﬁed by chro-

matography (silica, CH₂Cl₂/toluene = 1/2).

H, s, 8). IR (ATR)

m

[cm^ꢀ1]: 3328w (NH), 3057w, 2905w, 1588s

(C@N), 1497s, 1452m, 1425w, 1396w, 1369w, 1319w, 1284m,

1241 m, 1194w, 1128s, 1097m, 1063w, 1041w, 1020s, 987w,

951w, 930w, 862w, 846w, 800s, 775s, 742s, 675w, 660w, 634w,

623w, 599w, 563w, 534w, 491w, 469w, 434m (Fig. 17).

3.4.1. 7-Bromo-2-phenyl-1H-indole 13

Starting materials:

5 (1.400 g, 4.84 mmol), ZnCl₂(7.000 g,

5 meq.). 67% Yield (882 mg, 3.24 mmol, pale yellow solid, m.p.:

111–113 °C). ¹³C NMR (75.432 MHz, CD₂Cl₂) d [ppm]: 138.9 (9),

135.7 (10), 131.9 (2), 130.6 (4), 129.3 (14, 12), 128.5 (7), 125.5

(11, 15), 124.8 (13), 121.6 (6), 120.0 (5), 104.5 (8), 101.1 (3). ¹H

NMR (300 MHz, CD₂Cl₂) d [ppm]: 8.57 (1H, bs, 1); 7.72 (2H, d, 11,

15); 7.57 (1H, d, 5); 7.48 (2H, t, 12, 14); 7.40–7.33 (2d, 2H, 7,

3.3.5. N-(2-Bromphenyl)-N⁰-[1-(2-methyl-1-phenyl-propylidene]-

hydrazine 9

Starting materials: 4 (2.115 g, 11.3 mmol), a-methylpropiophe-

none (1.840 g, 12.4 mmol), p-toluenesulfonic acid monohydrate

(105 mg, 0.55 mmol). 76% Yield (2.713 g, 8.6 mmol, yellow oil).

¹³C NMR (75.432 MHz, CDCl₃) d [ppm]: 154.8 (7), 142.6 (1), 134.6

(8), 132.4 (3), 129.7 (12, 10), 129.2 (5), 128.7 (4), 127.9 (9, 13),

120.0 (11), 114.3 (6), 107.3 (2), 36.4 (14), 20.8 (15, 16). ¹H NMR

(300 MHz, CDCl₃) d [ppm]: 7.80 (1H, s, NH); 7.64 (1H, d, 3);

7.59–7.54 (2H, m, 13, 9); 7.48 (1H, d, 6); 7.38–7.29, (4H, m, 5,

10–12); 6.68 (1H, dt, 4); 2.94 (1H, hep, 14); 1.26 (6H, d, 15, 16).

13); 7.01 (1H, bt, 6); 6.91 (1H, d, 3). IR (ATR)

m

[cm^ꢀ1]: 3434s

(NH), 2922m, 2852m, 1726w, 1600w, 1566m, 1518w, 1482m,

1451m, 1430w, 1389w, 1350m, 1324m, 1297m, 1274w, 1241w,

1192m, 1160w, 1135s, 1097w, 1074w, 1049w, 1028w, 991w,

965w, 939w, 913w, 872w, 842w, 806s, 766s, 731s, 688s, 583m,

566w, 519s, 485s, 426s. MS (EI pos) m/z: 270.99 (Mꢀ1), 271.99

(M), 272.99 (M+1), 274.0 (M+2). Anal. Calc. for C₁₄H₁₀BrN

(272.15): C, 61.79; H, 3.70; N, 5.15. Found: C, 61.57; H, 3.58; N,

5.11% (Fig. 19)

IR (ATR)

m

[cm^ꢀ1]: 3332m (NH), 3058w, 2963m, 2926w, 2868w,

1588s (C@N), 1495s, 1452s, 1429w, 1381w, 1362w, 1305m,

1289m, 1241m, 1170w, 1134m, 1066s, 1045w, 1019s, 928w,

883w, 846w, 776s, 741s, 701s, 665w, 617w, 604w, 569w, 551w,

534w, 480w, 436m, 418w (Fig. 18).

3.4.2. 7-Bromo-2-(4-ﬂuorophenyl)-1H-indole 14

Starting materials: 6 (3.150 g, 10.24 mmol), ZnCl₂(16.000 g,

5 meq.). 34% Yield (1.000 g, 3.45 mmol, pale yellow solid, m.p.:

64–66 °C). ¹³C NMR (75.432 MHz, CDCl₃) d [ppm]: 164.5, 161.2

(13), 137.9 (9), 135.7 (2), 130.5 (4), 128.3, 128.29 (10), 127.4,

127.3 (11, 15), 124.9 (7), 121.8 (6), 120.0 (5), 116.6, 116.3 (12,

14), 104.6 (8), 101.1 (3). ¹H NMR (300 MHz, CDCl₃) d [ppm]: 8.37

(1H, bs, 1); 7.67–7.62 (2H, m, 11, 15); 7.56 (1H, d, 5); 7.35 (1H,

3.4. General procedure for the preparation of the 2-aryl-7-

bromoindoles 13–16

A Schlenk tube was charged with 1 equivalent of hydrazone 5–

8, mesitylene (30 ml) and 5 equivalents of anhydrous ZnCl₂. The

suspension was heated to reﬂux under efﬁcient stirring for at least

48 h. After complete conversion was indicated by TLC analysis, the

Fig. 16. Numbering of 7 for NMR assignment.

Fig. 19. Numbering of 13 for NMR assignment.

2504

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

dd, 7); 7.16 (2H, tt, 12, 14); 7.02 (1H, t, 6); 6.81 (1H, d, 3). IR (ATR)

m

[cm^ꢀ1]: 3422s (NH), 1601w, 1567w, 1543w, 1498m, 1484m,

1429m, 1422m, 1378w, 1341w, 1322w, 1296m, 1233s, 1190m,

1159m, 1131w, 1099m, 1045w, 1011w, 955w, 937w, 904m,

847w, 836s, 797s, 771m, 734s, 715m, 666w, 654w, 631w, 606w,

550m, 533m, 517m, 497m, 447s. MS (EI pos) m/z: 289.03 (Mꢀ1),

290.04 (M), 291.03 (M+1), 292.04 (M+2). Anal. Calc. for C₁₄H₉BrFN

(290.14): C, 57.96; H, 3.13; N, 4.83. Found: C, 57.89; H, 3.04; N,

4.77% (Fig. 20).

Fig. 21. Numbering of 15 for NMR assignment.

3.4.3. 7-Bromo-2-(2-chloro-phenyl)-1H-indole 15

Starting materials: 7 (2.707 g, 8.36 mmol), ZnCl₂(27.000 g,

10 meq.). 50% Yield (1.294 g, 4.2 mmol, yellow oil). ¹³C NMR

(75.432 MHz, CDCl₃) d [ppm]: 135.9 (10), 135.4 (9), 131.8 (2),

131.2 (7), 130.9 (12), 130.8 (11), 129.5 (13), 129.4 (4), 127.6 (14),

125.1 (15), 121.6 (6), 120.3 (5), 104.8 (3), 104.8 (8). ¹H NMR

(300 MHz, CDCl₃) d [ppm]: 8.91 (1H, s, 1); 7.67 (1H, dd, 5); 7.63

(1H, dd, 12); 7.52 (1H, dd, 7); 7.41 (1H, dd, 15); 7.37–7.31, (2H,

Fig. 22. Numbering of 16 for NMR assignment.

dt 13, 14); 7.05 (1H, t, 6); 6.96 (1H, d, 3). IR (ATR)

m

[cm^ꢀ1]:

3450s (NH), 3060w, 2922w, 2845w, 1594w, 1596m, 1492w,

1471w, 1458m, 1428s, 1385w, 1349w, 1341w, 1318w, 1303s,

1254w, 1230m, 1191s, 1161w, 1134m, 1076m, 1034s, 943w,

914s, 863w, 846w, 799s, 752s, 729s, 662m, 589m, 551w, 521w,

494w, 459s. MS (EI pos) m/z: 307.02 (M), 308.03 (M+1), 309.03

(M+2). Anal. Calc. for C₁₄H₉BrClN (306.59): C, 54.85; H, 2.96; N,

4.57. Found: C, 54.78; H, 2.92; N, 4.52% (Fig. 21).

¹³C NMR (75.432 MHz, CDCl₃) d [ppm]: 184.4 (8), 151.7 (6), 149.6

(5), 133.1 (9), 131.4 (12), 131.3 (2), 128.9 (10, 11), 127.5 (4),

120.3 (3), 115.3 (1), 55.6 (7), 25.0, 24.97 (13, 14). ¹H NMR

(300 MHz, CDCl₃) d [ppm]: 8.23–8.20 (2H, d, 10); 7.52 (1H, d, 2);

7.49–7.47 (3H, m, 11, 12); 7.25 (1H, d, 4); 7.11 (1H, t, 3); 1.56

(6H, s, 13, 14). MS (EI pos) m/z: 299.01 (Mꢀ1), 300.01 (M),

301.01 (M+1). Anal. Calc. for C₁₆H₁₄BrN (300.02): C, 64.02; H,

4.70; N, 4.67. Found: C, 63.96; H, 4.65; N, 4.60% (Fig. 23).

3.4.4. 7-Bromo-2-(2-naphth-1-yl)-1H-indole 16

Starting materials:

8 (3.577 g, 10 mmol), ZnCl₂(36.000 g,

3.5. General procedure for the preparation of the 2-alkyl/aryl-7-

formylindoles 19–23

10 meq.). 23% Yield (740 mg, 2.3 mmol, pale orange oil). ¹³C NMR

(75.432 MHz, CDCl₃) d [ppm]: 137.6 (9), 135.4 (2), 134.1 (10),

131.7 (4), 130.7 (14), 130.1 (19), 129.3 (7), 128.8 (12), 127.7 (15),

127.2 (18), 126.5 (13), 125.7 (16), 125.6 (17), 124.7 (6), 121.6 (5),

120.0 (11), 104.9 (3), 104.6 (8). ¹H NMR (300 MHz, CDCl₃) d

[ppm]: 8.51 (1H, s, 1); 8.33–8.30 (1H, m, 13); 7.97–7.93 (2H, m,

15, 18); 7.70–7.65 (2H, 2t, 12, 17); 7.60–7.55 (3H, m, 5, 11, 16);

A dry Schlenk tube was charged under an argon atmosphere

with

1 equivalent of 7-bromoindole (13–16) and dry ether

(50 ml). The solution was cooled to ꢀ30 °C, 1.2 equivalents of KH

was added and the resulting suspension was stirred at room tem-

perature for approximately 1 h until all gas evolution has subsided.

After cooling the mixture to ꢀ90 °C, 2 equivalents of a t-BuLi-solu-

tion were added in one portion, stirring at ꢀ90 °C was continued

for 30 min, the cooling bath was removed, and the stirred mixture

was allowed to warm to room temperature during 2 h. After the

addition of 3 equivalents of dry dimethylformamide, the mixture

was stirred overnight. Workup: the mixture was poured on satu-

rated ammonium chloride solution and extracted with four por-

tions of ether. The combined organic layers were washed with

water and brine, dried over sodium sulfate, ﬁltered and evapo-

rated. The crude formylindoles were puriﬁed by chromatography

(silica; CH₂Cl₂/toluene = 1/1).

7.41 (1H, dd, 7); 7.09 (1H, t, 6); 6.89 (1H, d, 3). IR (ATR)

m

[cm^ꢀ1]: 3417s (NH), 3047m, 2922m, 1591w, 1564m, 1534w,

1505w, 1488w, 1459w, 1429s, 1385s, 1332s, 1296s, 1260w,

1235w, 1190s, 1159w, 1133m, 1111m, 1046w, 1022w, 10007w,

969w, 952w, 928w, 907m, 864w, 795s, 789s, 729s, 686s, 666s,

637w, 616w, 589m, 572m, 537m, 520w, 476s, 415s. MS (EI pos)

m/z: 321.10 (Mꢀ1), 322.11 (M), 323.10 (M+1), 324.11 (M+2). Anal.

Calc. for C₁₈H₁₂BrN (322.21): C, 67.10; H, 3.75; N, 4.35. Found: C,

67.02; H, 3.68; N, 4.28% (Fig. 22).

3.4.5. 7-Bromo-3,3-dimethyl-2-phenyl-3H-indole 17

A dry Schlenk tube was charged with hydrazone 9 (3.3 g,

10.4 mmol), anhydrous ZnCl₂(10.5 g, 77 mmol, 7.4 eq.) and dry

ethanol (25 ml). The solution was reﬂuxed for three days under

an argon atmosphere. After cooling to room temperature, the mix-

ture was poured on 4 N hydrochloric acid and extracted with three

portions of ether. The combined organic layers were washed twice

with a saturated NaHCO₃solution, once with water and brine,

dried over sodium sulfate, ﬁltered and evaporated. The residual or-

ange oil was puriﬁed by chromatography (silica; hexanes/ethyl

acetate = 95/5) to yield 1.29 g (4.3 mmol, 41%) 17 as a yellow oil.

3.5.1. 2-Methyl-1H-indole-7-carbaldehyde 19

Starting

materials:

2-methyl-7-bromoindole

(575 mg,

2.74 mmol), KH (110 mg, 2.74 mmol), t-BuLi (1.7 molar solution

in pentane, 3.3 ml, 5.48 mmol), dimethylformamide (406 mg,

0.43 ml, 5.5 mmol). 53% Yield (232 mg, 1.46 mmol, pale yellow so-

lid, m.p.: 62–64 °C). ¹³C NMR (75.432 MHz, CD₂Cl₂) d [ppm]: 193.8

(9), 137.8 (10), 134.1 (2), 130.5 (4), 127.7 (7), 126.9 (5), 120.0 (8),

Fig. 20. Numbering of 14 for NMR assignment.

Fig. 23. Numbering of 17 for NMR assignment.

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2505

119.4 (6), 100.4 (3), 13.7 (11). ¹H NMR (300 MHz, CD₂Cl₂) d [ppm]:

10.09 (1H, s, 9); 10.02 (1H, bs, 1); 7.80 (1H, d, 5); 7.56 (1H, dd, 7);

7.21 (1H, t, 6); 6.31 (1H, d, 3); 2.49 (3H, s, 11). IR (ATR)

[cm^ꢀ1]:

m

3384s (NH), 3360s (NH); 2797 m, 2721w, 1668s (C@O), 1605m,

1589m, 1556s, 1487m, 1451m, 1375m, 1346m, 1331m, 1282m,

1233m, 1196m, 1172m, 1146m, 1061w, 1044m, 993w, 975w,

951w, 896w, 874w, 794s, 761m, 738s, 693s, 661s, 610w, 590w,

574w, 550w, 465w, 421m. Anal. Calc. for C₁₀H₉NO (159.19): C,

75.45; H, 5.70; N, 8.80. Found: C, 75.42; H, 5.67; N, 8.74% (Fig. 24).

Fig. 25. Numbering of 20 for NMR assignment.

3.5.2. 2-Phenyl-1H-indole-7-carbaldehyde 20

Starting materials: 13 (1.437 g, 5.3 mmol), KH (253 mg,

6.34 mmol), t-BuLi (1.7 molar solution in pentane, 6.2 ml,

10.6 mmol), dimethylformamide (0.9 ml, 10.6 mmol). 89% Yield

(1.035 g, 4.7 mmol, orange solid, m.p.: 127–129 °C). ¹³C NMR

(75.432 MHz, CD₂Cl₂) d [ppm]: 193.7 (9); 140.0 (10); 134.9 (2);

131.8 (11); 130.6 (4); 129.3 (13, 15); 128.9 (14); 128.5 (7); 127.8

(5); 125.6 (12, 16); 120.6 (8); 120.1 (6); 99.6 (3). ¹H NMR

(300 MHz, CD₂Cl₂) d [ppm]: 10.39 (1H, bs,1); 10.13 (1H, s, 9);

7.92 (1H, d, 5); 7.76 (2H, dd,12, 16); 7.65 (1H, dd, 7); 7.48 (2H,

t,13, 15); 7.37 (1H, tt, 14); 7.27 (1H, t, 6); 6.91 (1H, d,3). IR (ATR)

Fig. 26. Numbering of 21 for NMR assignment.

132.1 (4), 131.2 (7), 130.8 (5), 130.76 (11), 129.6 (12), 129.5 (13),

129.4 (15), 128.3 (14), 127.5 (16), 120.6 (8), 120.0 (6), 103.6 (3).

¹H NMR (300 MHz, CDCl₃) d [ppm]: 10.67 (1H, bs, 1); 10.14 (1H,

s, 9); 7.95 (1H, d, 5); 7.67 (2H, 2 dd, 13, 16); 7.51 (1H, dd, 7);

m

[cm^ꢀ1]: 3349s (NH), 3050w, 2921w, 2835w, 2809w, 2728w,

1675s (C@O), 1605w, 1591m, 1580w, 1545m, 1484m, 1451m,

1384w, 1358m, 13340w, 1303m, 1280w, 1222s, 1194w, 1170w,

1099w, 1047s, 1029s, 955w, 930w, 911m, 897w, 877w, 849w,

805s, 774s, 756s, 738s, 689m, 669m, 607s, 574m, 518m, 474w,

442w. MS (FAB pos, NOBA) m/z: 221.11 (M), 222.12 (M+1). Anal.

Calc. for C₁₅H₁₁NO (221.26): C, 81.43; H, 5.01; N, 6.33. Found: C,

81.37; H, 4.94; N, 6.28% (Fig. 25).

7.38–7.26 (3H, m, 6, 14, 15); 6.97 (1H, d, 3). IR (ATR)

m

[cm^ꢀ1]:

3340s (NH), 3060w, 2808w, 2729w, 1670s (C@O), 1592m,

1566w, 1551w, 1471m, 1452w, 1435w, 1396w, 1378w, 1351m,

1302w, 1264w, 1242w, 1221m, 1161w, 1127w, 1080w, 1065w,

1047m, 1036m, 943w, 932w, 893w, 860w, 799s, 767w, 745s,

736s, 723s, 699w, 684m, 657w, 618m, 586w, 571w, 551w, 479w,

454w, 445w, 427w. MS (EI pos) m/z: 255.10 (M), 256.10 (M+1),

257.10 (M+2). Anal. Calc. for C₁₅H₁₀ClNO (255.71): C, 70.46; H,

3.94; N, 5.48. Found: C, 70.44l; H, 3.98; N, 5.45% (Fig. 27).

3.5.3. 2-(4-Fluoro-phenyl)-1H-indole-7-carbaldehyde 21

Starting materials: 14 (900 mg, 3.1 mmol), KH (150 mg, 3.72

mmol), t-BuLi (1.7 molar solution in pentane, 3.65 ml, 6.2 mmol),

dimethylformamide (453 mg, 0.48 ml, 6.2 mmol). 56% Yield

(412 mg, 1.7 mmol, pale yellow solid, m.p.: 141–144 °C). ¹³C

NMR (75.432 MHz, CDCl₃) d [ppm]: 193.9 (9), 164.5, 161.3 (14),

139.1 (10), 134.9 (2), 130.5 (4), 128.9 (7), 128.2, 128.1 (11), 128.0

(5), 127.5, 127.4 (12, 16), 120.5 (8), 120.2 (6), 116.5, 116.2 (13,

15), 99.57 (3). ¹H NMR (300 MHz, CDCl₃) d [ppm]: 10.19 (1H, bs,

1); 10.11 (1H, s, 9); 7.89 (1H, d, 5); 7.68 (2H, m, 12, 16); 7.62

(1H, dd, 7); 7.26 (1H, t, 6); 7.15 (2H, m, 13, 15); 6.79 (1H, d, 3).

3.5.5. 2-Naphth-1-yl-1H-indole-7-carbaldehyde 23

Starting materials: 16 (1.301 g, 4 mmol), KH (200 mg,

4.8 mmol), t-BuLi (1.7 molar solution in pentane, 4.7 ml, 8 mmol),

dimethylformamide (585 mg, 0.62 ml, 8 mmol). 73% Yield

(792 mg, 2.9 mmol, yellow solid, m.p.: 115–117 °C). ¹³C NMR

(75.432 MHz, CDCl₃) d [ppm]: 193.8 (9), 138.9 (10), 134.4 (2),

134.2 (11), 131.6 (20), 130.5 (4), 130.3 (8), 129.3 (7), 129.0 (13),

128.8 (16), 128.1 (19), 127.7 (14), 127.2 (17), 126.5 (18), 125.7

(6), 125.6 (12), 120.6 (15), 120.1 (5), 103.7 (3). ¹H NMR

(300 MHz, CDCl₃) d [ppm]: 10.41 (1H, bs, 1); 10.15 (1H, s, 9);

8.35 (1H, d, 14); 8.02 (1H, d, 19); 7.97–7.92 (2H, m, 5, 13); 7.61–

IR (ATR)

m

[cm^ꢀ1]: 3344s (NH), 3055w, 2819w, 2742w, 1672s

(C@O), 1609w, 1591s, 1549s, 1504s, 1486s, 1427m, 1385w,

1342m, 1304m, 1217s, 1164w, 1102w, 1062m, 1050s, 1014w,

957w, 932w, 902w, 880w, 836s, 799s, 766w, 742s, 728s, 711w,

675w, 655m, 634w, 605m, 575w, 563w, 522m, 491w, 443w,

415m. MS (EI pos) m/z: 238.09 (Mꢀ1), 239.10 (M), 240.10 (M+1).

Anal. Calc. for C₁₅H₁₀FNO (239.25): C, 75.30; H, 4.21; N, 5.85.

Found: C, 75.32; H, 4.24; N, 5.78% (Fig. 26).

7.53 (3H, m, 7, 12, 16); 7.35 (1H, t, 6); 6.91 (1H, d, 3). IR (ATR)

m

[cm^ꢀ1]: 3349s (NH), 2981m, 2793w, 2712w, 1673s (C@O),

1604w, 1591m, 1560w, 1539m, 1508w, 1486w, 1449w, 1395w,

1377w, 1345m, 1300m, 1259w, 1245w, 1227w, 1191w, 1169w,

1110m, 1064m, 1050s, 1033m, 1001m, 1001w, 958w, 909w,

887w, 879w, 861w, 818w, 806m, 786s, 769s, 737m, 718m, 698m,

663w, 635w, 621m, 567w, 535w, 499w, 472w, 453w, 440w,

424w, 414w, 401w. MS (EI pos) m/z: 270.17 (Mꢀ1), 271.16 (M),

272.16 (M+1). Anal. Calc. for C₁₉H₁₃NO (271.32): C, 84.11; H,

4.83; N, 5.16. Found: C, 84.06; H, 4.80; N, 5.12% (Fig. 28).

3.5.4. 2-(2-Chloro-phenyl)-1H-indole-7-carbaldehyde 22

Starting materials: 15 (1.225 g, 4 mmol), KH (200 mg,

4.8 mmol), t-BuLi (1.7 molar solution in pentane, 4.7 ml, 8 mmol),

dimethylformamide (585 mg, 0.62 ml, 8 mmol). 62% Yield

(632 mg, 2.5 mmol, yellow solid, m.p.: 104–106 °C). ¹³C NMR

(75.432 MHz, CDCl₃) d [ppm]: 193.7 (9), 137.1 (10), 134.2 (2),

Fig. 24. Numbering of 19 for NMR assignment.

Fig. 27. Numbering of 22 for NMR assignment.

2506

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

3.6.1. N,N⁰-Bis-[1-(1H-indol-7-yl)-methylidene]-benzyl-

1,2-diamine 27

Starting materials: 7-formylindole (871 mg, 6 mmol), o-phenyl-

enediamine (324 mg, 3 mmol). 47% Yield (514 mg, 1.4 mmol, yel-

low solid). ¹³C NMR (75.432 MHz, CDCl3) d [ppm]: 161.2 (9),

145.3 (11), 134.3 (10), 129.0 (8), 127.3 (13), 126.8 (5), 125.7 (2),

125.1 (6), 120.2 (4), 119.8 (7), 119.1 (12), 102.7 (3). ¹H NMR

(300 MHz, CDCl3) d [ppm]: 11.02 (1H, bs, 1); 8.83 (1H, s, 9); 7.83

(1H, d, 5); 7.45 (1H, dd, 7); 7.36 (2H, s, 12, 13); 7.22 (1H, t, 6);

Fig. 28. Numbering of 23 for NMR assignment.

6.81 (1H, t, 2); 6.57 (1H, t, 3). IR (ATR)

m

[cm^ꢀ1]: 3390s (NH),

3359s (NH), 3063w, 2923w, 2887w, 1619s (C@N), 1595s, 1569s,

1506w, 1478m, 1441m, 1405w, 1365s, 1333s, 1277w, 1249w,

1208m, 1172m, 1093s, 1065m, 1034s, 974w, 947w, 932w, 898m,

879w, 853w, 821m, 792s, 760m, 749w, 724s, 692m, 630m, 595s,

575w, 554s, 530m, 502w, 465w. MS (FAB pos, NOBA) m/z:

362.14 (M), 363.14 (M+1), 364 15 (M+2). Anal. Calc. for C₂₄H₁₈N₄

(362.44): C, 79.54; H, 5.01; N, 15.46. Found: C, 79.48; H, 4.97; N,

15.40% (Fig. 30).

3.5.6. 3,3-Dimethyl-2,2-diphenyl-2,3-dihydro-1H-indole-

7-aldehyde 24

A Schlenk vessel was charged with 17 (1.29 g, 4.3 mmol) and

dry ether (50 ml). After the solution was cooled to ꢀ100 °C in an

ethanol/liquid nitrogen cooling bath, phenyllithium (4 eq., 1.8 M

in cyclohexane/ether; 9.6 ml, 17.2 mmol) was added in one por-

tion, the mixture was stirred for one hour at to ꢀ100 °C and then

allowed to warm to ambient temperature. Dry dimethylformamide

(585 mg, 0.62 ml, 8 mmol) was added and the solution was stirred

over night. Workup: the mixture was poured on cold, saturated

ammonium chloride solution, extracted with three portions of

ether, the combined organic layers were washed with water and

brine, dried over sodium sulfate, ﬁltered and evaporated. Decaline

(30 ml, mixture of cis/trans-isomers) was added to the residue and

volatile materials were evaporated under high vacuum at 70 °C.

The residue was puriﬁed by chromatography (silica; hexane/

ether = 3/1) to yield 895 mg 24 as a pale yellow solid (2.7 mmol;

63%), mp.: 138–141 °C. ¹³C NMR (75.432 MHz, CDCl₃) d [ppm]:

193.2 (9), 150.2 (10), 142.8 (11), 141.5 (4),131.3 (7), 128.1 (13),

127.7 (12), 127.6 (14), 126.8 (5), 117.8 (6), 117.0 (8), 80.6 (2),

48.9 (3), 27.2 (15). ¹H NMR (300 MHz, CDCl₃) d [ppm]: 9.93 (1H,

s, 9); 7.43 (1H, d, 5); 7.38 (4H, dd, 12); 7.29–7.26 (7H, m, 1, 13,

3.6.2. N,N⁰-Bis-[1-(1H-indol-7-yl)-methylidene]-4,5-dimethyl-benzyl-

1,2-diamine 28

Starting materials: 7-formylindole (871 mg, 6 mmol), 4,5-di-

methyl-1,2-phenylendiamine (409 mg, 3 mmol). 39% Yield

(461 mg, 1.18 mmol, yellow solid, m.p.: 116–118 °C). ¹³C NMR

(75.432 MHz, CDCl₃) d [ppm]: 160.4 (9), 143.0 (11), 135.8 (13),

134.3 (10), 129.0 (8), 126.6 (5), 125.6 (2), 124.8 (6), 120.4 (4),

120.2 (7), 119.7 (12), 102.7 (3), 20.0 (14). ¹H NMR (300 MHz,

CDCl₃) d [ppm]: 11.07 (1H, bs, 1); 8.83 (1H, s, 9); 7.82 (1H, d, 5);

7.45 (1H, d, 7); 7.22 (1H, t, 6); 7.17 (1H, s, 12); 6.82 (1H, t, 2);

6.58 (1H, t, 3); 2.40 (3H, s, 14). IR (ATR)

m

[cm^ꢀ1]: 3388s (NH),

3317s (NH), 3053w, 2881w, 1621s (C@N), 1584s, 1490m, 1439m,

1394w, 1361m, 1335s, 1278w, 1232m, 1205w, 1191w, 1169m,

1096s, 1063m, 1034s, 1001m, 965w, 884m, 867s, 792s, 725s,

641m, 613w, 603w, 593w, 574w, 560m, 535w, 510w, 491w,

472w, 440w, 425w, 415w. MS (EI pos) m/z: 390.22 (M), 391.22

(M+1). Anal. Calc. for C₂₆H₂₂N₄(390.49): C, 79.97; H, 5.68; N,

14.35. Found: C, 79.88; H, 5.59; N, 14.28% (Fig. 31).

14); 7.20 (1H, d, 7); 6.83 (1H, t, 6); 1.21 (6H, s, 15). IR (ATR)

m

[cm^ꢀ1]: 3380m (NH), 3056w, 2963w, 2926w, 2813w, 2727w,

1702w, 1661s (CHO), 1611m, 1589s, 1517w, 1493w, 1461s,

1443s, 1378m, 1337m, 1263m, 1196s, 1155w, 1127m, 1083w,

1056w, 1033w, 1014w, 1000w, 989m, 931w, 903w, 882w, 786w,

765m, 749m, 723m, 698s, 641w, 631w, 591w, 562w, 516m,

489m. MS (EI pos) m/z: 327.17 (M), 328.17 (M+1). Anal. Calc. for:

C, 84.37; H, 6.46; N, 4.28. Found: C, 84.32; H, 6.42; N, 4.23%

(Fig. 29).

3.7. (N,N⁰-Bis-[1-(1H-indolato-7-yl)-meth-(E)-ylidene]-benzyl-1,2-

diamino)-chloro-tetrahydrofurano-chromium(III) 29

A Schlenk tube was charged with 27 (120 mg, 0.33 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 0.41 ml, 0.66 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room tempera-

ture. Anhydrous CrCl₃(104 mg, 0.66 mmol) was added and stirring

was continued for 24 h. Workup: solvents and volatile materials

were stripped off in vacuum, the residue was triturated with dry

dichloromethane (20 ml), the resulting suspension was ﬁltered

through Celite^Ò, the ﬁltrate was evaporated and the product was

dried in vacuum, affording 29 (175 mg, 0.33 mmol, 99%) as a red,

3.6. General procedure for the preparation of achiral

indolophenligands 27 and 28

A mixture of 7-formylindole (2 equivalents) and one equivalent

of the respective o-phenylenediamine was heated for 15 min at

600 W power in an ‘‘Anton Paar Synthos 3000” microwave reactor.

The resulting cake was dissolved in dichloromethane, dried over

sodium sulfate, ﬁltered and evaporated. The crude ligands were

puriﬁed by chromatography (silica; hexane/ether = 1/1).

Fig. 29. Numbering of 24 for NMR assignment.

Fig. 30. Numbering of 27 for NMR assignment.

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2507

Fig. 31. Numbering of 28 for NMR assignment.

Fig. 32. Numbering of 31 for NMR assignment.

paramagnetic solid. Anal. Calc. for C₂₈H₂₄ClCrN₄O (519.97): C,

64.68; H, 4.65; N, 10.78. Found: C, 64.56; H, 4.53; N, 10.64%.

dry methanol (10 ml). The mixture was reﬂuxed over night. On

cooling to room temperature, the product precipitated as a colorless

solid. Workup: the solid was collected, washed three times with

small portions of cold methanol, and recrystallized from methanol.

Yield: 69% (190 mg, 0.69 mmol, colorless solid). ¹³C NMR

(75.432 MHz, CD₂Cl₂) d [ppm]: 165.8 (9), 142.0 (19), 141.7 (14),

133.9 (10), 128.8 (8), 128.4 (17), 127.0 (16), 126.6 (15), 125.6 (2),

124.9 (93), 124.6 (5), 119.6 (6), 119.2 (23), 102.6 (3), 77.9 (12),

75.7 (11), 40.2 (13). ¹H NMR (300 MHz, CD₂Cl₂) d [ppm]: 10.35

(1H, bs, 1); 8.82 (1H, s, 9); 7.79 (1H, d, 5); 7.44 (1H, dd, 7); 7.34

(1H, d, 18); 7.28 (1H, d, 15); 7.24–7.15 (4H, m, 17, 16, 6, 2); 6.58

(1H, t, 3); 4.84 (1H, d, 11); 4.47 (1H, q, 12); 3.20 (2H, dq, 13); 2.65

3.8. (N,N⁰-Bis-[1-(1H-indolato-7-yl)-meth-(E)-ylidene]-4,5-dimethyl-

benzyl-1,2-diamino)-chloro-tetrahydrofurano-chromium(III) 30

A Schlenk tube was charged with 28 (398 mg, 1 mmol) and dry

THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M solu-

tion in hexane, 1 ml, 2 mmol) was added in one portion, and the

stirred mixture was allowed to warm to room temperature. Anhy-

drous CrCl₃(316 mg, 2 mmol) was added and stirring was contin-

ued for 24 h. Workup: solvents and volatile materials were

stripped off in vacuum, the residue was triturated with dry dichlo-

romethane (20 ml), the resulting suspension was ﬁltered through

Celite^Ò, the ﬁltrate was evaporated and the product was dried in

vacuum, affording 30 (583 mg, 1 mmol, 99%) as a red, paramag-

netic solid. Anal. Calc. for C₃₀H₂₈ClCrN₄O (548.02): C, 65.75; H,

5.15; N, 10.22. Found: C, 65.58; H, 5.01; N, 10.11%.

(1H, bs, 20). IR (ATR)

m

[cm^ꢀ1]: 3492m (OH), 3419s (NH), 3022w,

2919w, 2837w, 1627s (C@N), 1599s, 1517w, 1485m, 1467m,

1475w, 1442w, 1428w, 1400w, 1388w, 1360w, 1335m, 1288m,

1259m, 1240m, 1208w, 1187s, 1171s, 1158w, 1120w, 1089s,

1060m, 1039s, 989s, 978m, 956w, 945w, 922w, 890w, 873w,

861w, 842w, 830w, 749s, 754s, 746m, 731s, 721w, 694w, 670s,

602w, 578s, 565m, 529w, 504w, 478w, 452m, 421w, 414w. MS

(FAB pos, NOBA) m/z: 276.2 (M), 277.17 (M+1), 278.17 (M+2). Anal.

Calc. for C₁₈H₁₆N₂O (276.34): C, 78.24; H, 5.84; N, 10.14. Found: C,

78.20; H, 5.79; N, 10.07% (Fig. 33).

3.9. (1S,2R)-(ꢀ)-cis-1-{[1-(1H-Indol-7-yl)-methylidene]-amino}-

indan-2-ol 31

A Schlenk tube was charged with 7-formylindole (207 mg,

1.4 mmol), (1S,2R)-(ꢀ)-cis-1-aminoindan-2-ol (209 mg, 1.4 mmol)

and dry methanol (5 ml). The mixture was reﬂuxed over night.

On cooling to room temperature, the product precipitated as a col-

orless solid. Workup: the solid was collected, washed three times

with small portions of cold methanol, and recrystallized from

dichloromethane. Yield: 78% (300 mg, 1.08 mmol, colorless solid,

m.p.: 153–157 °C). ¹³C NMR (75.432 MHz, THF-d8) d [ppm]:

164.9 (9), 143.9 (19), 142.4 (14), 134.2 (10), 129.6 (8), 128.2 (17),

126.9 (16), 126.3 (15), 126.1 (7), 125.7 (2), 125.2 (18), 124.2 (5),

120.4 (4), 119.3 (6), 102.2 (3), 78.8 (12), 76.2 (11), 40.9 (13). ¹H

NMR (300 MHz, THF-d8) d [ppm]: 10.86 (1H, bs,1); 8.77 (1H, s,

9); 7.67 (1H, d, 5); 7.36 (1H, d, 7); 7.28–7.08 (6H, m, 2, 6, 15–

18); 6.47 (1H, t, 3); 4.77 (1H, d, 11); 4.56 (1H, t, 12); 3.99 (1H, d,

3.11. (1R,2R)-N,N⁰-Bis-[1-(1H-indol-7-yl)-methylidene]-cyclohexane-

1,2-diamine 33

A Schlenk tube was charged with 7-formylindole (290.3 mg,

2 mmol), (1R,2R)-cyclohexane-1,2-diamine (114.2 mg, 1 mmol)

and dry methanol (20 ml). The mixture was reﬂuxed over night.

On cooling to room temperature, the product precipitated as a col-

orless powder. Workup: the solid was collected and washed three

times with small portions of cold methanol. Yield: 85% (312 mg,

0.85 mmol, colorless powder). ¹³C NMR (75.432 MHz, CD₂Cl₂) d

[ppm]: 161.6 (9), 134.2 (10), 128.5 (8), 125.2 (5), 125.1 (2), 123.4

(7), 119.7 (4), 119.3 (6), 102.2 (3), 74.6 (11), 33.7 (12), 25.0 (13).

¹H NMR (300 MHz, CD₂Cl₂) d [ppm]: 10.77 (1H, bs, 1); 8.48 (1H,

20); 3.12 (2H, m,13). IR (ATR)

m

[cm^ꢀ1]: 3489 m (OH), 3416s

(NH), 3059w, 3023w, 2920w, 2838w, 1628s (C@N), 1599s,

1558w, 1541w, 1508w, 1476m, 1457w, 1443w, 1428w, 1400w,

1387w, 1360m, 1335s, 1288m, 1257m, 1241m, 1208w, 1184m,

1171m, 1157m, 1059s, 1061m, 1039s, 989m, 977m, 956w, 946w,

890m, 874w, 862w, 842w, 829m, 794s, 753s, 747s, 730s, 721m,

669s, 602w, 577m, 564m, 529w, 504w, 473w, 452w, 403m. MS

(FAB pos, NOBA) m/z: 276.1 (M), 277.2 (M+1). Anal. Calc. for

C₁₈H₁₆N₂O (276.34): C, 78.24; H, 5.84; N, 10.14. Found: C, 78.15;

H, 5.76; N, 10.08% (Fig. 32).

3.10. (1R,2S)-(+)-cis-1-{[1-(1H-Indol-7-yl)-methylidene]-amino}-

indan-2-ol 32

A Schlenk tube was charged with 7-formylindole (145 mg,

1 mmol), (1R,2S)-(+)-cis-1-aminoindan-2-ol (150 mg, 1 mmol) and

Fig. 33. Numbering of 32 for NMR assignment.

2508

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

s, 9); 7.66 (1H, d, 5); 7.26 (1H, t, 2); 7.15 (1H, dd, 7); 7.06 (1H, t, 6);

6.55 (1H, t, 3); 3.53 (1H, ddd, 11 diast.); 1.99 (3H, m,13, 12 E); 1.61

(1H, dd, 12 Z). IR (ATR)

solution in hexane, 0.73 ml, 1.46 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room tempera-

ture. Anhydrous CrCl₃(221 mg, 1.4 mmol) was added and stirring

was continued for 24 h. Workup: solvents and volatile materials

were stripped off in vacuum, the residue was triturated with dry

dichloromethane (20 ml), the resulting suspension was ﬁltered

through Celite^Ò, the ﬁltrate was evaporated and the product was

dried in vacuum, affording 36 (394 mg, 0.75 mmol, 99%) as a

brown, paramagnetic solid. Anal. Calc. for C₂₈H₃₀ClCrN₄O

(526.01): C, 63.93; H, 5.75; N, 10.65. Found: C, 63.80; H, 5.62; N,

10.52%.

m

[cm^ꢀ1]: 3328s (NH), 3055w, 3010w,

2942w, 2905w, 2852w, 1631s (C@N), 1597s, 1520w, 1481m,

1458w, 1444m, 1400w, 1372m, 1338s, 1306m, 1238m, 1202s,

1169s, 1142w, 1097s, 1064s, 1028s, 968w, 938w, 899w, 858s,

846s, 817w, 791s, 754w, 731s, 722s, 667m, 632w, 602m, 572s,

549w, 539s, 495w, 457w, 432w. MS (FAB pos, NOBA) m/z: 368.21

(M), 369.22 (M+1), 370.22 (M+2). Anal. Calc. for C₂₄H₂₄N₄

(368.49): C, 78.23; H, 6.57; N, 15.21. Found: C, 78.14; H, 6.50; N,

15.10% (Fig. 34).

3.12. Bis(tetrahydrofurano)-chloro-(1S,2R)-(ꢀ)-cis-

1-{[1-(1H-indolato-7-yl)-meth-(E)-ylidene]-amino}-indan-2-olato-

chromium(III) 34

3.15. (1R,2R)-N,N⁰-Bis-[1-(2-methyl-1H-indol-7-yl)-methylidene]-

cyclohexane-1,2-diamine 37

A Schlenk tube was charged with 19 (120 mg, 0.75 mmol),

(1R,2R)-cyclohexane-1,2-diamine (43 mg, 0.38 mmol) and dry

methanol (20 ml). The mixture was reﬂuxed over night. On cooling

to room temperature, the product precipitated as a pale yellow

powder. Workup: the solid was collected and washed three times

with small portions of cold methanol. Yield: 97% (148 mg,

0.37 mmol, pale yellow powder). ¹³C NMR (75.432 MHz, CD₂Cl₂)

d [ppm]: 161.7 (9), 136.4 (10), 134.5 (2), 129.8 (8), 124.3 (5),

122.4 (7), 119.1 (6), 118.9 (4), 100.2 (3), 74.4 (11), 33.7 (12), 25.1

(13), 13.8 (14). ¹H NMR (300 MHz, CD₂Cl₂) d [ppm]: 10.56 (1H,

bs,1); 8.56 (1H, s, 9); 7.62 (1H, d, 5); 7.18 (1H, d, 7); 7.12 (1H, t,

6); 6.31 (1H, t, 3); 3.62 (1H, ddd, 11 diast.); 2.48 (3H, s, 14); 2.08

A Schlenk tube was charged with 31 (97 mg, 0.35 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 0.35 ml, 0.7 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room tempera-

ture. Anhydrous CrCl₃(112 mg, 0.7 mmol) was added and stirring

was continued for 24 h. Workup: solvents and volatile materials

were stripped off in vacuum, the residue was triturated with dry

dichloromethane (20 ml), the resulting suspension was ﬁltered

through Celite^Ò, the ﬁltrate was evaporated and the product was

dried in vacuum, affording 34 (188 mg, 0.37 mmol, 99%) as a

brown, paramagnetic solid. Anal. Calc. for C₂₆H₃₂ClCrN₂O₃

(507.99): C, 61.47; H, 6.35; N, 5.51. Found: C, 61.31; H, 6.23; N,

5.42%.

(3H, m, 13, 12 E); 1.68 (1H, dd, 12 Z). IR (ATR)

m

[cm^ꢀ1]: 3351s

(NH), 2927s, 2851s, 1630s (C@N), 1604s, 1556m, 1489m, 1443m,

1397w, 1377m, 1345m, 1298m, 1239w, 1190w, 1173m, 1143m,

1090m, 1056s, 1025w, 968w, 934w, 895w, 856w, 846w, 794s,

758m, 743s, 659s, 596w, 572m, 548w, 524w, 494w, 475w, 432w,

416w. MS (FAB pos, NOBA) m/z: 396.25 (M), 397.26 (M+1),

398.26 (M+2). Anal. Calc. for C₂₆H₂₈N₄(396.54): C, 78.75; H,

7.12; N, 14.13. Found: C, 78.78; H, 7.14; N, 14.07% (Fig. 35).

3.13. Bis(tetrahydrofurano)-chloro-(1R,2S)-(+)-cis-1-{[1-(1H-

indolato-7-yl)-meth-(E)-ylidene]-amino}-indan-2-olato-

chromium(III) 35

A Schlenk tube was charged with 32 (118 mg, 0.43 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 0.43 ml, 0.86 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room temperature.

Anhydrous CrCl₃(138 mg, 0.86 mmol) was added and stirring was

continued for 24 h. Workup: solvents and volatile materials were

stripped off in vacuum, the residue was triturated with dry dichlo-

romethane (20 ml), the resulting suspension was ﬁltered through

Celite^Ò, the ﬁltrate was evaporated and the product was dried in

vacuum, affording 35 (218 mg, 0.43 mmol, 99%) as a brown, para-

magnetic solid. Anal. Calc. for C₂₆H₃₂ClCrN₂O₃(507.99): C, 61.47;

H, 6.35; N, 5.51. Found: C, 61.36; H, 6.27; N, 5.45%.

3.16. (1R,2S)-(+)-cis-1-{[1-(2-Methyl-1H-indol-7-yl)-methylidene]-

amino}-indan-2-ol 38

A Schlenk tube was charged with 19 (159 mg, 1 mmol), (1R,2S)-

(+)-cis-1-aminoindan-2-ol (150 mg, 1 mmol) and dry methanol

(5 ml). The mixture was reﬂuxed over night. Workup: volatile

materials were removed in vacuo, the residual oil was triturated

with ether, and the solidiﬁed product was collected. Yield: 78%

(226 mg, 0.78 mmol, colorless solid, m.p.: 122–125 °C). ¹³C NMR

(75.432 MHz, CD₂Cl₂) d [ppm]: 166.0 (9), 142.8 (19), 141.6 (14),

136.8 (2), 134.2 (10), 129.9 (8), 128.3 (17), 127.0 (16), 125.6 (7,

15), 124.9 (18), 123.4 (5), 119.3 (6), 118.4 (4), 100.5 (3), 78.0

(12), 75.6 (11), 40.1 (13), 13.9 (21). ¹H NMR (300 MHz, CD₂Cl₂) d

[ppm]: 10.01 (1H, bs, 1); 8.78 (1H, s, 9); 7.65 (1H, d, 5); 7.37–

7.13 (6H, m, 6, 7, 15–18); 6.27 (1H, t, 3); 4.83 (1H, d, 11); 4.67

(1H, dd, 12); 3.20 (2H, dq, 13); 2.69 (1H, bs, 20); 2.41 (3H, s, 21).

3.14. (1R,2R)-N,N⁰-Bis-[1-(1H-indolato-7-yl)-methylidene]-

cyclohexan-1,2-diamino-chloro-tetrahydrofurano-

chromium(III) 36

A Schlenk tube was charged with 33 (270 mg, 0.73 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

Fig. 34. Numbering of 33 for NMR assignment.

Fig. 35. Numbering of 37 for NMR assignment.

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2509

IR (ATR)

m

[cm^ꢀ1]: 3536m (OH), 3427s (NH), 3022w, 2964w,

2920w, 2826w, 1625s (C@N), 1602s, 1561m, 1540w, 1507w,

1488w, 1474m, 1455m, 1445m, 1384m, 1345m, 1317w, 1286m,

1253w, 1239m, 1179m, 1146m, 1099m, 1074m, 1053s, 1024w,

978m, 948w, 920w, 880w, 849w, 831m, 799s, 769s, 746s, 737s,

668m, 646s, 598w, 575s, 550s, 528w, 507w, 468m, 438w. MS

(FAB pos, glycerine) m/z: 289.10 (Mꢀ1), 290.11 (M), 291.11

(M+1), 292.12 (M+2). Anal. Calc. for C₁₉H₁₈N₂O (290.36): C,

78.59; H, 6.25; N, 9.65. Found: C, 78.51; H, 6.17; N, 9.55% (Fig. 36).

3.17. (1S,2R)-(ꢀ)-cis-1-{[1-(2-Phenyl-1H-indol-7-yl)-methylidene]-

amino}-indan-2-ol 39

A Schlenk tube was charged with 20 (200 mg, 0.9 mmol),

(1S,2R)-(ꢀ)-cis-1-aminoindan-2-ol (134 mg, 0.9 mmol) and dry

methanol (5 ml). The mixture was reﬂuxed over night. Workup:

volatile materials were removed in vacuo, the oily residue was

recrystallized from ethanol. Yield: 84% (226 mg, 0.75 mmol, pale

yellow crystals, m.p.: 106–110 °C). ¹³C NMR (75.432 MHz, CD₂Cl₂)

d [ppm]: 165.1 (9), 142.5 (19), 141.3 (14), 138.9 (2), 135.2 (10),

132.2 (21), 129.9 (8), 129.3 (23, 26), 128.4 (17), 128.0 (24), 127.1

(16), 126.4 (15), 125.6 (7), 125.2 (22, 25), 124.9 (18), 124.2 (5),

112.0 (6), 119.2 (4), 99.4 (3), 77.2 (12), 75.7 (11), 40.2 (13). ¹H

NMR (300 MHz, CD₂Cl₂) d [ppm]: 10.85 (1H, bs, 1); 8.82 (1H, s, 9);

7.76 (1H, dd, 5); 7.60 (2H, d,7,18); 7.43–7.20, (9H, m, 6, 15–17,

22–26); 6.89 (1H, t, 3); 4.89 (1H, d, 11); 4.74 (1H, dd,12); 4.24

Fig. 37. Numbering of 39 for NMR assignment.

3.19. Bis(tetrahydrofurano)-chloro-(1R,2S)-(+)-cis-1-

{[1-(2-methyl-1H-indolato-7-yl)-meth-(E)-ylidene]-amino}-indan-

2-olato-chromium(III) 41

A Schlenk tube was charged with 38 (235 mg, 0.85 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 0.85 ml, 0.8 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room tempera-

ture. Anhydrous CrCl₃(267 mg, 1.7 mmol) was added and stirring

was continued for 24 h. Workup: solvents and volatile materials

were stripped off in vacuum, the residue was triturated with tolu-

ene (20 ml), the resulting suspension was ﬁltered through Celite^Ò,

the ﬁltrate was evaporated and the product was dried in vacuum,

affording 41 (415 mg, 0.8 mmol, 94%) as a brown, paramagnetic so-

lid. Anal. Calc. for C₂₇H₃₆ClCrN₂O₃(524.04): C, 61.88; H, 6.92; N,

5.35. Found: C, 61.73; H, 6.80; N, 5.22%.

(2H, dq,13); 2.35 (1H, bs, 20). IR (ATR)

m

[cm^ꢀ1]: 3567m (OH),

3381s (NH), 3058w, 3016w, 2919w, 2853w, 1626s (C@N), 1597s,

1545w, 1478s, 1453m, 1425w, 1374m, 1358s, 1336w, 1304m,

1288w, 1239w, 1223w, 1185w, 1167w, 1156w, 1097s, 1081m,

1049s, 1036s, 976m, 899w, 880w, 865w, 843w, 827w, 797s,

774m, 758s, 733s, 683m, 700w, 646w, 595w, 572w, 521w, 504w,

471w, 409w. MS (FAB pos, NOBA) m/z: 352.14 (M), 353.15 (M+1),

354.15 (M+2). Anal. Calc. for C₂₄H₂₀N₂O (352.45): C, 81.79; H,

5.72; N, 7.95. Found: C, 81.63; H, 5.66; N, 7.87% (Fig. 37).

3.20. Bis(tetrahydrofurano)-chloro-(1S,2R)-(ꢀ)-cis-1-{[1-(2-phenyl-

1H-indolato-7-yl)-meth-(E)-ylidene]-amino}-indan-2-olato-

chromium(III) 42

3.18. (1R,2R)-N,N⁰-Bis-[1-(2-methyl-1H-indolato-7-yl)-methylidene]-

cyclohexane-1,2-diamino-chloro-tetrahydrofurano-chromium(III) 40

A Schlenk tube was charged with 39 (275 mg, 0.78 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 0.78 ml, 1.56 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room tempera-

ture. Anhydrous CrCl₃(190 mg, 1.2 mmol) was added and stirring

was continued for 24 h. Workup: solvents and volatile materials

were removed in vacuum, the residue was triturated with dichlo-

romethane (20 ml), the resulting suspension was ﬁltered through

Celite^Ò, the ﬁltrate was evaporated and the product was dried in

vacuum, affording 42 (437 mg, 0.75 mmol, 96%) as a brown, para-

magnetic solid. Anal. Calc. for C₃₂H₃₄ClCrN₂O₃(582.08): C, 66.03;

H, 5.89; N, 4.81. Found: C, 65.91; H, 5.76; N, 4.72%.

A Schlenk tube was charged with 37 (100 mg, 0.25 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 0.25 ml, 0.5 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room temperature.

Anhydrous CrCl₃(80 mg, 0.5 mmol) was added and stirring was

continued for 24 h. Workup: solvents and volatile materials were

stripped off in vacuum, the residue was triturated with dry dichlo-

romethane (20 ml), the resulting suspension was ﬁltered through

Celite^Ò, the ﬁltrate was evaporated and the product was dried in

vacuum, affording 40 (146 mg, 0.25 mmol, 99%) as a brown, para-

magnetic solid. Anal. Calc. for C₃₀H₃₆ClCrN₄O (556.09): C, 64.80;

H, 6.53; N, 10.08. Found: C, 64.67; H, 6.41; N, 9.94%.

3.21. (1S,2R)-(ꢀ)-cis-1-{[1-(2-Naphthalin-1-yl-1H-indol-7-yl)-

methylidene]-amino}-indan-2-ol 43

A Schlenk tube was charged with 22 (508 mg, 1.87 mmol),

(1S,2R)-(ꢀ)-cis-1-aminoindan-2-ol (284 mg, 1.9 mmol) and dry

methanol (5 ml). The mixture was reﬂuxed over night. Workup:

volatile materials were removed in vacuo, the oily residue was dis-

solved in hexane, the solution was ﬁltered through Celite^Ò, hexane

was evaporated, affording the solid product. Yield: 88% (660 mg,

1.64 mmol, pale yellow solid, m.p.: 58–60 °C). ¹³C NMR

(75.432 MHz, CDCl₃) d [ppm]: 165.4 (9), 142.0 (19), 141.2 (14),

138.3 (2), 134.7 (10), 134.3 (27), 131.5 (22), 130.9 (21), 129.8 (8),

129.0 (29), 128.9 (28), 128.6 (17), 127.5 (25), 127.2 (24), 127.1

(16), 126.6 (30), 126.4 (15), 125.8 (23, 26), 125.5 (7), 124.9 (18),

124.6 (5), 120.0 (6), 119.1 (4), 103.6 (3), 77.5 (12), 75.6 (11), 40.2

Fig. 36. Numbering of 38 for NMR assignment.

2510

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

(13). ¹H NMR (300 MHz, CDCl₃) d [ppm]: 10.73 (1H, bs, 1); 8.85

(1H, s, 9); 8.39 (1H, d, 28); 7.93 (3H, m,5, 23, 30); 7.66 (1H, d, 7);

7.57–7.21 (9H, m, 6, 15–18, 24–26, 29); 6.93 (1H, s, 3); 4.87 (1H,

d, 11); 4.72 (1H, q, 12); 3.17 (2H, dd, 13); 2.64 (1H, bs, 20). IR

(ATR)

m

[cm^ꢀ1]: 3547w (OH), 3374s (NH), 3047m, 2910m, 1628m

(C@N), 1598s, 1541w, 1508w, 1490w, 1476w, 1458w, 1437m,

1393m, 1376m, 1348m, 1299m, 1262m, 1228w, 1168w, 1109w,

1051m, 1020w, 978w, 947w, 912w, 861w, 798s, 776s, 734s,

693m, 664w, 637w, 595w, 569w, 518w, 484w, 466w, 453w,

423m. MS (EI pos) m/z: 402.20 (M), 403.20 (M+1). Anal. Calc. for

C₂₈H₂₂N₂O (402.49): C, 83.56; H, 5.51; N, 6.96. Found: C, 83.59;

H, 5.55; N, 6.89% (Fig. 38).

3.22. (1R,2S)-(+)-cis-1-{[1-(3,3-Dimethyl-2,2-diphenyl-2,3-dihydro-

1H-indole-7-yl)-methylidene]-amino}-indan-2-ol 44

Fig. 39. Numbering of 44 for NMR assignment.

A Schlenk tube was charged with 24 (665 mg, 2 mmol), (1R,2S)-

(+)-cis-1-aminoindan-2-ol (313 mg, 2 mmol) and dry methanol

(5 ml). The mixture was reﬂuxed over night. Workup: volatile

materials were removed in vacuo, the residue was dissolved in

dichloromethane, the resulting suspension was ﬁltered through

Celite^Ò, the ﬁltrate was evaporated and the product was dried in

vacuum. Yield: 98% (900 mg, 1.96 mmol, yellow–green solid). ¹³C

NMR (75.432 MHz, CDCl₃) d [ppm]: 165.7 (9); 149.1 (10); 143.9,

143.3 (21); 142.4 (19); 141.1 (14); 140.6 (4); 130.3, 128.3 (24);

128.1, 128.0 (23, 25); 127.6, 127.5 (22, 26); 127.2, 127.1, 127.0

(15, 16, 17); 125.7 (5); 124.7 (18); 123.9 (7); 118.0 (6); 115.4

(8); 80.4 (2); 77.2 (12); 75.3 (11); 49.0 (3); 40.0 (13); 27.8, 26.3

(27). ¹H NMR (300 MHz, CDCl₃) d [ppm]: 8.65 (1H, s, 9); 7.42–

7.17 (16 H, m, arom., 1); 6.95 (1H, d, 5); 6.85 (1H, t, 6); 4.76 (1H,

d,11); 4.64 (1H, t, 12); 3.12 (2H, dd, 13); 2.79 (1H, bs, 20); 1.30,

solved in dichloromethane, the resulting suspension was ﬁltered

through Celite^Ò, the ﬁltrate was evaporated and the product was

dried in vacuum. Yield: 58% (313 mg, 0.84 mmol, yellow–green so-

lid, m.p.: 136–138 °C). ¹³C NMR (75.432 MHz, CDCl₃) d [ppm]:

165.3 (9), 164.3, 161.1 (24), 142.1 (19), 141.0 (14), 138.2 (2),

135.2 (10), 130.0 (8), 128.9, 128.5 (21), 128.6 (17), 127.3 (16),

127.1, 127.0 (22, 26), 126.5 (15), 125.8 (7), 124.9 (18), 124.4 (5),

120.1 (6), 119.0 (4), 116.5, 116.2 (23, 25), 99.5 (3), 77.2 (12), 75.6

(11), 40.2 (13). ¹H NMR (300 MHz, CDCl₃) d [ppm]: 10.72 (1H,

bs,1); 8.80 (1H, s, 9); 7.78 (1H, d, 5); 7.75 (2H, 2d, 7, 18); 7.41–

7.06 (8H, m, 6, 15–17, 22–25); 6.80 (1H, d, 3); 4.89 (1H, d, 11);

4.76 (1H, dd, 12); 3.26 (2H, dq, 13); 2.72 (1H, bs, 20). IR (ATR)

m

[cm^ꢀ1]: 3564w (OH), 3342m (NH), 3068w, 2918m, 2839m, 1630s

(C@N), 1602s, 1592s, 1547m, 1502s, 1484s, 1458m, 1441w,

1425m, 1373m, 1353s, 1305w, 1232s (C–F), 1179w, 1159s,

1098m, 1078w, 1049s, 1033w, 1012w, 974m, 948w, 935w, 913w,

900w, 884w, 836s, 803s, 757s, 742s, 711m, 661m, 634w, 596w,

572m, 515m, 470m, 426w, 404w. MS (EI pos) m/z: 370.20 (M),

371.20 (M+1), 372.21 (M+2). Anal. Calc. for C₂₄H₁₉FN₂O (370.42):

C, 77.82; H, 5.17; N, 7.56. Found: C, 77.76; H, 5.11; N, 7.48%

(Fig. 40).

1.19 (2x3H, 2s, 27). IR (ATR)

m

[cm^ꢀ1]: 3538w (OH), 3307w (NH),

3054m, 2962m, 2923m, 1625s (C@N), 1588s, 1491m, 1460s,

1443s, 1386m, 1364w, 1330m, 1263m, 1217w, 1201m, 1155w,

1127w, 1097w, 1081w, 1051m, 1033m, 982w, 947w, 912w,

885w, 860w, 825w, 788w, 748s, 699s, 642w, 593w, 530w, 497w,

467w, 454w, 415w. MS (EI pos) m/z: 458.30 (M), 459.30 (M+1),

460.30 (M+2). Anal. Calc. for C₃₂H₃₀N₂O (458.59): C, 83.81; H,

6.59; N, 6.11. Found: C, 83.78; H, 6.56; N, 6.05% (Fig. 39).

3.24. (1R,2S)-(+)-cis-1-{[1-[2-(2-Chloro-phenyl)-1H-indol-7-yl]-

3.23. (1R,2S)-(+)-cis-1-{[1-[2-(4-Fluoro-phenyl)-1H-indol-7-yl]-

methylidene]-amino}-indan-2-ol 46

methylidene]-amino}-indan-2-ol 45

A Schlenk tube was charged with 23 (493 mg, 1.93 mmol),

(1R,2S)-(+)-cis-1-aminoindan-2-ol (291 mg, 1.93 mmol) and dry

methanol (10 ml). The mixture was reﬂuxed over night. Workup:

volatile materials were removed in vacuo, the residue was dis-

solved in dichloromethane, the resulting suspension was ﬁltered

through Celite^Ò, the ﬁltrate was evaporated and the product was

dried in vacuum. Yield: 99% (738 mg, 1.91 mmol, colorless solid).

A Schlenk tube was charged with 21 (350 mg, 1.46 mmol),

(1R,2S)-(+)-cis-1-aminoindan-2-ol (220 mg, 1.48 mmol) and dry

methanol (10 ml). The mixture was reﬂuxed over night. Workup:

volatile materials were removed in vacuo, the residue was dis-

Fig. 38. Numbering of 43 for NMR assignment.

Fig. 40. Numbering of 45 for NMR assignment.

H. Wölﬂe et al. / Journal of Organometallic Chemistry 694 (2009) 2493–2512

2511

3.27. Bis(tetrahydrofurano)-chloro-(1R,2S)-(+)-cis-1-{[1-[2-(4-ﬂuoro-

phenyl)-1H-indolato-7-yl]-meth-(E)-ylidene]-amino}-indan-2-olato-

chromium(III) 49

A Schlenk tube was charged with 45 (265 mg, 0.715 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 0.715 ml, 1.43 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room tempera-

ture. Anhydrous CrCl₃(226 mg, 1.43 mmol) was added and stirring

was continued for 24 h. Workup: solvents and volatile materials

were removed in vacuum, the residue was triturated with dichlo-

romethane (20 ml), the resulting suspension was ﬁltered through

Celite^Ò, the ﬁltrate was evaporated and the product was dried in

vacuum, affording 49 (449 mg, 0.75 mmol, 99%) as a brown, para-

magnetic solid. Anal. Calc. for C₃₂H₃₃ClCrFN₂O₃(600.06): C, 64.05;

H, 5.54; N, 4.67. Found: C, 63.91; H, 5.41; N, 4.50%.

Fig. 41. Numbering of 46 for NMR assignment.

¹³C NMR (75.432 MHz, CDCl₃) d [ppm]: 165.0 (9), 142.2 (19), 141.3

(14), 136.5 (2), 134.6 (10), 131.3 (22), 131.2 (23), 130.9 (21), 130.8

(26), 129.1 (24), 128.9 (8), 128.6 (17), 127.5 (25), 127.2 (16), 127.0

(15), 125.7 (7), 125.0 (18), 124.7 (5), 120.0 (6), 119.2 (4), 102.1 (3),

77.5 (12), 75.7 (11), 40.2 (13). ¹H NMR (300 MHz, CDCl₃) d [ppm]:

11.21 (1H, bs, 1); 8.82 (1H, s, 9); 7.83 (1H, d, 5); 7.68 (1H, d, 7);

7.47–7.18 (9H, m, 6, 15–18, 23–26); 6.93 (1H, t, 3); 4.86 (1H, d,

11); 4.76 (1H, d, 12); 3.29 (2H, m, 13); 2.73 (1H, bs, 20). IR (ATR)

3.28. Bis(tetrahydrofurano)-chloro-(1R,2S)-(+)-cis-1-{[1-[2-(2-

chlorphenyl)-1H-indolato-7-yl]-meth-(E)-ylidene]-amino}-indan-2-

olato-chromium(III) 50

A Schlenk tube was charged with 46 (436 mg, 1.15 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 1.15 ml, 3.3 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room tempera-

ture. Anhydrous CrCl₃(365 mg, 2.3 mmol) was added and stirring

was continued for 24 h. Workup: solvents and volatile materials

were removed in vacuum, the residue was triturated with dichlo-

romethane (20 ml), the resulting suspension was ﬁltered through

Celite^Ò, the ﬁltrate was evaporated and the product was dried in

vacuum, affording 50 (710 mg, 1.15 mmol, 99%) as a brown, para-

magnetic solid. Anal. Calc. for C₃₂H₃₃Cl₂CrN₂O₃(616.52): C, 62.34;

H, 5.40; N, 4.54. Found: C, 62.18; H, 5.27; N, 4.44%.

m

[cm^ꢀ1]: 3541w (OH), 3384s (NH), 3060w, 2910m, 1628s (C@N),

1597s, 1565w, 1533w, 1470m, 1456s, 1439s, 1376m, 1358m,

1304m, 1260w, 1238w, 1215m, 1168w, 1123w, 1098m, 1080s,

1052s, 1032s, 979w, 946w, 858w, 805s, 742s, 698m, 677m,

634w, 590m, 505w, 474w, 448m, 426w, 415w. MS (EI pos) m/z:

386.14 (M), 388.14 (M+2). Anal. Calc. for C₂₄H₁₉ClN₂O (386.87):

C, 74.51; H, 4.95; N, 7.24. Found: C, 74.50; H, 4.91; N, 7.20%

(Fig. 41).

3.25. Bis(tetrahydrofurano)-chloro-(1S,2R)-(ꢀ)-cis-1-{[1-(2-napht-1-

yl-1H-indolato-7-yl)-meth-(E)-ylidene]-amino}-indan-2-olato-

chromium(III) 47

Acknowledgements

We thank Karl-Hans Ongania from the Institute of Organic

Chemistry of the University of Innsbruck for mass spectrometric

measurements. H.W. thanks BASF SE, R&D Engineering Plastics,

67056 Ludwigshafen, Germany for ﬁnancial support.

A Schlenk tube was charged with 43 (530 mg, 1.3 mmol) and

dry THF (20 ml). The solution was cooled to ꢀ80 °C, n-BuLi (2 M

solution in hexane, 1.3 ml, 2.6 mmol) was added in one portion,

and the stirred mixture was allowed to warm to room tempera-

ture. Anhydrous CrCl₃(417 mg, 2.6 mmol) was added and stirring

was continued for 24 h. Workup: solvents and volatile materials

were removed in vacuum, the residue was triturated with dichlo-

romethane (20 ml), the resulting suspension was ﬁltered through

Celite^Ò, the ﬁltrate was evaporated and the product was dried in

vacuum, affording 47 (820 mg, 1.3 mmol, 99%) as a brown, para-

magnetic solid. Anal. Calc. for C₃₆H₃₆ClCrN₂O₃(632.13): C, 68.40;

H, 5.74; N, 4.43. Found: C, 68.32; H, 5.66; N, 4.38%.

Appendix A. Supplementary material

CCDC 705051, 705052 and 705053 contain the supplementary

crystallographic data for the structures of 32, 38 and 39. These data

can be obtained free of charge from The Cambridge Crystallo-

graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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ylidene]-amino}-indan-2-olato-chromium(III) 48

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Article Doi

On the way to biodegradable poly(hydroxy butyrate) from propylene oxide and carbon monoxide via β-butyrolactone: Multisite catalysis with newly designed chiral indole-imino chromium(III) complexes

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