Selective synthesis of the 2-hydroxyferrocene-aldimine enantiomers - Extended planar chiral analogues of the "flat" salicylaldimine ligand family

DOI: 10.1039/b822735g

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Dalton Transactions p. 3716 - 3730 (2009)

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Niemeyer, Jochen

Kehr, Gerald

Froehlich, Roland

Erker, Gerhard

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Article abstract of DOI:10.1039/b822735g

Efficient selective synthetic pathways to the O-(tert-butyl)diphenylsilyl- protected 2-hydroxyferrocene carbaldehyde enantiomers [(p-S)-12 and (p-R)-12, each >99.5% ee] are described. The general synthesis starts from Kagan's ferrocene carbaldehyde acetal

Full text of DOI:10.1039/b822735g

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Dalton

Transactions

An international journal of inorganic chemistry

www.rsc.org/dalton

Number 19 | 21 May 2009 | Pages 3617–3868

ISSN 1477-9226

HOT ARTICLE

Erker et al.

Selective synthesis of the 2-hydroxyfer- Bis(“ferrocene-saliminato”) group 4

HOT ARTICLE

rocene-aldimine enantiomers—

extended planar chiral analogues of

the“ﬂat”salicylaldimine ligand family

metal complexes:synthesis,structural

features and use in homogenous

Ziegler–Natta polymerization catalysis probing the chemistry of the U–I bond

Hayton et al.

Reactivity of UI₄(OEt₂)₂with phenols:

View Article Online

PAPER

www.rsc.org/dalton | Dalton Transactions

Selective synthesis of the 2-hydroxyferrocene-aldimine

enantiomers—extended planar chiral analogues of the “ﬂat”

salicylaldimine ligand family†

Jochen Niemeyer, Gerald Kehr, Roland Fro¨hlich‡ and Gerhard Erker*

Received 19th December 2008, Accepted 6th March 2009

First published as an Advance Article on the web 8th April 2009

DOI: 10.1039/b822735g

Efﬁcient selective synthetic pathways to the O-(tert-butyl)diphenylsilyl-protected 2-hydroxyferrocene

carbaldehyde enantiomers [(p-S)-12 and (p-R)-12, each >99.5% ee] are described. The general synthesis

starts from Kagan’s ferrocene carbaldehyde acetal [(S,S)-6], bearing the (2S,4S)-[4-(methoxymethyl)-1,

3-dioxan-2-yl] chiral auxiliary. The synthetic route to (p-S)-12 involves a sequence of directed

ortho-lithiation/iodination, followed by acetoxylation (Cu₂O/acetic acid), saponiﬁcation and

protection by the TBDPS silyl-protective group. Acid-catalyzed hydrolysis of the chiral acetal then gave

the O-TBDPS-protected (p-S)-conﬁgurated hydroxyferrocene carbaldehyde enantiomer in an overall

yield of 76% over 4 steps. The (p-R)-12 enantiomer was prepared by a similar route starting from

(S,S)-6 using the –SiMe₃group as a reversible blocking group to direct the required functionalization to

the (p-R)-series. A total of six steps furnished (p-R)-12 in a combined yield of 27%. The aldehyde

enantiomers of 12 were used for the synthesis of the corresponding N-2,6-diisopropylphenyl-imines.

Subsequent deprotection gave the new “ferrocene-salimine” ligands 2-hydroxy-[N-(2,6-diisopropyl-

phenyl)iminomethyl]-ferrocene (p-S)-2a and (p-R)-2a, respectively. We also synthesized the

(p-S)-enantiomers of the corresponding N-mesityl and N-pentaﬂuorophenyl aldimine derivatives

[(p-S)-2b, (p-S)-2c].

The framework of the salicylaldiminato ligands (1^-) is ﬂat

Introduction

and, therefore, they are as such achiral. Often bulky aryl

groups attached at the imino nitrogen atom favour a geometry

perpendicular to the core plane. This creates an element of

axial prochirality along the N–C(arene) vector, but truly chiral

salicylaldiminato systems must rely on the presence (and action)

of chiral substituents attached at their periphery.^5–7,15

A true element of chirality would be introduced to the core of

these ligand systems by extending them vertically to the central

arene plane. This would introduce a unit of planar chirality.¹⁶

Principally, this could be achieved by forming p–arene metal com-

plexes of, for example, the system 1.¹⁷We here want to present and

discuss an alternative approach, namely the development of viable

syntheses to the corresponding 2-hydroxyferrocene aldimines and

their anions (2^-), the “ferrocene-saliminato” ligands.

The salicylaldiminato ligand family (1^-; Scheme 1) has become of

great importance in coordination chemistry and catalysis.¹Various

substituted derivatives have been employed as chelate ligands

for making respective metal complexes throughout the periodic

table.^2–4The salicylaldiminato functionality has been employed

as a building block in the important class of the salen-type

ligands.⁵This has led to a variety of signiﬁcant developments in

homogeneous catalysis,^6,7ranging for example from acid-catalyzed

processes⁸over redox reactions^9,10all the way to employing suitably

substituted salicylaldiminato complexes of the group 4 metals in

homogeneous Ziegler–Natta oleﬁn polymerization.^11–14

For practical reasons the use of these ligands in coordination

chemistry and catalysis will be greatly facilitated by (or even

requires) the easy availability of these planar chiral ligand systems

in enantiomerically pure (or at least highly enriched) form.¹⁸

Preferably, both enantiomers of a given system of this kind should

be readily available. Such a development will be presented here.

Ito et al. described the preparation of optically active

2-hydroxyferrocene carbaldehyde (3; Scheme 2).¹⁹Their synthesis

was based on a resolution process at the stage of the corresponding

carboxylic acid derivatives. Bildstein et al. described the related

hydroxymethylferrocene carbaldehydes (4) optically resolved.²⁰

Kagan et al. introduced a synthetic route to selectively functional-

ize ferrocene carbaldehyde (5) via its chiral cyclic acetal (6) making

use of the very pronounced directing effect of this speciﬁc chiral

Scheme 1

Organisch-Chemisches Institut, Universita¨t Mu¨nster, Corrensstraße 40, D-

41849, Mu¨nster, Germany. E-mail: erker@uni-muenster.de; Fax: +49-251-

8336503

† Electronic supplementary information (ESI) available: Details of

NMR spectroscopic characterizations. CCDC reference numbers 714358–

714372. For ESI and crystallographic data in CIF or other electronic

format see DOI: 10.1039/b822735g

‡ X-Ray crystal structure analyses.

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Scheme 2

auxiliary.²¹Treatment of 6 with an alkyl lithium reagent produced

7 in a directed ortho-metallation. Various interesting bidentate

chelate ligands were derived by treatment of 7 with a series of

electrophiles. Among them the 2-hydroxyferrocene carbaldehyde

was mentioned but to the best of our knowledge not used to any

signiﬁcant extent, probably due to its high sensitivity.²¹

For our study we have made use of the general Kagan approach

to optically enriched 2-hydroxyferrocene carbaldehyde derivatives,

but tried to avoid the isolation of the sensitive aldehyde (3)

itself.²²Both the enantiomers of the “ferrocene-salimine” DIPP

derivative (2a; Scheme 3) were selectively prepared and a few other

derivatives made at least in one enantiomeric series. The syntheses

and characterization of these interesting planar chiral chelate

ligand systems will be reported in this paper. An accompanying

manuscript will describe some of their use in coordination

chemistry and catalysis.²³

Scheme 4 i: ^secBuLi, THF, then I₂in THF; ii: Cu₂O/CH₃CO₂H, CH₃CN

(64%); iii: NaOCH₃, DMF, then ClSi(^tBu)Ph₂(Cl-TBDPS) (85%); iv:

p-TsOH, CH₂Cl₂–H₂O (78%).

and acetic acid in acetonitrile.²⁶The new product (rac)-10 was

obtained in 64% yield after column chromatography. It features

a H NMR h -C₅H₅singlet at d 4.29 (¹³C: d 70.6) and an ABC

pattern of H NMR resonances of the three remaining “Cp”-

hydrogen atoms at the “upper” disubstituted h -C₅H₃ring [d

4.45/3.71/4.34 (¹³C NMR signals at d 114.1, 78.7, 62.8, 62.4,

61.9 (C1–C5)]. The ¹³C NMR carbonyl resonance of the acetyl

group is at d 168.4, the protected aldehyde ¹H NMR signal (6-H)

at d 5.47.

Trans-esteriﬁcation of the acetyl group with sodium methox-

ide in dimethylformamide generated the corresponding oxy-

ferrocene anion intermediate in situ that was immediately

trapped as the –TBDPS derivative²⁷by treatment with tert-

butyldiphenylchlorosilane to yield (rac)-11 (isolated in 85% yield

after column chromatography). The acetal was then opened by

acid-catalyzed hydrolysis (p-toluene sulfonic acid in a biphasic

CH₂Cl₂–water system) to give the O-protected hydroxyferrocene

carbaldehyde product (rac)-12 in ca. 80% yield. Compound (rac)-

12 features ¹³C Cp NMR signals at d 70.6 (Cp), d 125.0, 69.7, 61.5,

65.5 and 63.4 (C1–C5) and the typical spectroscopic features of

Scheme 3

the ferrocene bound –CH O functionality [ C NMR: d 190.9, H

NMR: d 10.8, IR: 1674 cm^-1(n C O)].

All four products (rac)-9 to (rac)-12 were characterized by X-ray

crystal structure analyses. The structures of the new compounds

(rac)-10 and (rac)-12 are depicted in Fig. 1 and 2, respectively.

Details of the structures of the previously described system (rac)-9

and of (rac)-11 are provided in the ESI.†

Results and discussion

Syntheses in the racemic series

For the purpose of comparison and as a reference for the

enantiomeric analysis we needed the target systems as racemates.

Therefore, we will ﬁrst describe the synthesis and characterization

of the O-silyl-protected 2-hydroxyferrocene carbaldehyde deriva-

tive (rac)-12 (Scheme 4).

The acetal 8 was prepared from ferrocene carbaldehyde ac-

cording to a procedure described by Bunz et al.²⁴It was then

converted to the previously described ortho-iodo derivative (rac)-

9 in a directed metallation by means of treatment with sec-

butyllithium followed by “quenching” with elemental iodine.²⁵The

product (rac)-9 was obtained only in ca. 75% purity admixed with

some unknown byproducts. We have then used the crude mixture

for conversion into the doubly protected 2-hydroxyferrocene

carbaldehyde derivative (rac)-10 by reacting it with copper(I) oxide

Fig. 1 A projection of the molecular geometry of (rac)-10.

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Fig. 2 Molecular structure of the protected hydroxyferrocene carbalde-

hyde system (rac)-12.

Scheme 5 i: BuLi, ether, then I₂in THF (95%); ii: Cu₂O/CH₃CO₂H,

CH₃CN (94%); iii: NaOCH₃, DMF, then ClSi(^tBu)Ph₂(95%); iv: p-TsOH,

CH₂Cl₂–H₂O (89%).

The ferrocene derivative (rac)-10 features a typical linear met-

allocene structure in the crystal [Cp(centroid)–Fe–Cp(centroid)

179.0^◦]. The Fe–C(Cp) bond lengths to the unsubstituted C₅H₅

shown in Scheme 5 were characterized spectroscopically. In

addition the ﬁnal product [(p-S)-12] was also characterized by

an X-ray crystal structure analysis (see below). Its optical purity

was analyzed by chiral HPLC (relative to (rac)-12, for details see

the Experimental Section and the ESI†) and found to be >99.5%

ee after two-fold recrystallization from pentane.

ring are in a uniform range between 2.029(3) A and 2.051(3)

A. At the doubly substituted C₅H₃ring the Fe–C(Cp) distances

amount to 2.050(3) A (Fe–C3), 2.044(3) A (Fe–C4), and 2.039(3)

A (Fe–C5), whereas the Fe–C_ipso(Cp) distances are slightly shorter

at 2.035(3) A (Fe–C1) and 2.025(3) A (Fe–C2). The 1,3-dioxane

ring (C1–C6 1.494(4) A, C6–O1 1.414(3) A, C6–O2 1.395(3) A)

adopts a chair conformation. The acetyl protective group at O3

Synthesis and characterization of the

(p-R)-hydroxyferrocenecarbaldehyde derivatives

(C2–O3 1.397(3) A) is turned away from the complex core (C10–

◦

O4 1.187(4) A, O3–C10 1.370(3) A, angle C2–O3–C10 115.3(2) ,

dihedral angle C2–O3–C10–O4 14.2(4)^◦).

The synthesis of the enantiomer (p-R)-12 was carried out starting

from the same precursor that was used for the synthesis of

(p-S)-12 described above, namely the chiral, enantiomerically-pure

ferrocene carbaldehyde acetal (S,S)-6.²¹This strategy required a

selective blocking of the “p-S” ortho position. We decided on the

introduction of the –SiMe₃group, a pathway that was indepen-

dently developed and subsequently published by Jaouen et al.²⁹

The starting material (S,S)-6 was subjected to a highly stere-

oselective directed ortho-metallation as usual by treatment with

tert-butyllithium in ether at low temperature. “Quenching” with

trimethylchlorosilane then gave the silyl derivative (S,S,p-S)-16

in >90% yield after chromatographic puriﬁcation. Subsequent

treatment again with tert-butyllithium opened a way to rather

selectively functionalize the remaining ortho-position to the acetal-

protected aldehyde functionality at the “upper” ferrocene Cp-

ring. Followed by iodination, this furnished the respective iodo-

derivative (S,S,p-R)-17. However, the two-step reaction sequence

of lithiation/halogenation in this case was less selective than in

the cases studied before (see above). We note that a substantial

quantity (ca. 30%) of a byproduct was formed, which was

identiﬁed as the di-iodination product 18 (see Scheme 6). This

required a chromatographic separation at this stage of the syn-

thetic sequence. The target product (S,S,p-R)-17 was consequently

isolated pure in ca. 50% yield. The undesired byproduct 18 could be

reconverted to the TMS-derivative (S,S,p-S)-16 bydehalogenation

(iodine/lithium exchange followed by addition of water) in almost

quantitative yield.

The structure of the aldehyde derivative (rac)-12 features

Fe–C(Cp) distances in an overall range between 2.026(3) A and

2.051(3) A. The aldehyde functionality has its C O bond (C6–

◦

O2 1.209(3) A, C2–C6 1.452(3) A, angle C2–C6–O2 125.5(3) )

oriented in plane with the adjacent C1 to C5 Cp ring system. The

aldehyde oxygen is found rotated away from the adjacent bulky

–OTBDPS substituent (C1–O1 1.361(3) A, O1–Si1 1.657(2) A,

angle C1–O1–Si1 134.1(1)^◦).

Synthesis of the (p-S)-ortho-hydroxyferrocenecarbaldehyde

derivatives

The synthesis initially followed the pathway outlined by Kagan

et al.²¹We therefore employed the (S)-1,2,4-butantriol-derived

protective group of ferrocene carbaldehyde as the directing chiral

auxiliary, which is readily available by LiAlH₄reduction of the

dimethylester of malic acid.²⁸

The chiral acetal (S,S)-6 was subjected to the directed lithiation.

Treatment with tert-butyllithium in ether (-78 ^◦C) gave the

respective lithioferrocene derivative in situ which was then directly

halogenated by “quenching” it with elemental iodine in THF. The

planar chiral iodo derivative (S,S,p-S)-13 was obtained in 95%

yield with >90% de. It was converted to the acetate (S,S,p-S)-14 by

reaction with copper(I)oxide/acetic acid. The acetate was cleaved

(sodium methoxide in dimethylformamide) and the resulting

ferrocenolate O-silylated. In the ﬁnal step of the synthetic sequence

acid-catalyzed hydrolysis of the acetal function regenerated the

free aldehyde group. The target molecule (p-S)-12 was thus

obtained starting from (S,S)-6 in a four step synthetic sequence

with an overall combined yield of ca. 76%. The intermediates

The remaining steps of the synthesis were straightforward and

were carried out each in excellent yields. De-silylation of (S,S,p-

R)-17 with tetra-n-butyl ammonium ﬂuoride gave (S,S,p-R)-13

in 94% yield. Oxidation [Cu₂O/CH₃CO₂H] furnished the acetate

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Scheme 6 i: ^tBuLi, ether, then ClSiMe₃(91%); ii: ^tBuLi, ether, then I₂in THF, chromatographic separation (51%); iii: ⁿBuLi, THF, then H₂O (97%); iv:

ⁿBu₄N⁺F^-, THF (94%); v: Cu₂O/CH₃CO₂H, CH₃CN (93%); vi: NaOCH₃, DMF, then ClSi(^tBu)Ph₂(92%); vii: p-TsOH, CH₂Cl₂–H₂O (71%).

(S,S,p-R)-14 which was converted to the corresponding O-TBDPS

silylated derivative (S,S,p-R)-15 (92%). Eventually, we liberated

the O-protected hydroxyferrocene carbaldehyde enantiomer (p-

R)-12 by acid-catalyzed hydrolysis of the cyclic acetal. Its enan-

tiomeric purity was again determined by HPLC. Thus, we pre-

pared the (p-R)-12 enantiomer starting from the same precursor

[(S,S)-6] that was used for the (p-S)-12 synthesis in a combined

yield of 27% over 6 steps. The hydroxyferrocene carbaldehyde

derivative (p-R)-12 was obtained with >99.5% ee.

We characterized both the aldehydes (p-S)-12 and (p-R)-12

by X-ray diffraction. Also the synthetic intermediates (S,S,p-

S)-16, (S,S,p-R)-17, (S,S,p-R)-13 and (S,S,p-R)-14 were char-

acterized by X-ray crystal structure analyses. In Fig. 3 we

have depicted views of the molecular structures of the inde-

pendently prepared (p-S)-12 and (p-R)-12 enantiomers. Their

characteristic structural parameters are similar to those of

(rac)-12 (see above and Fig. 2). Details are provided in the

ESI.†

The trimethylsilyl “blocked” system (S,S,p-S)-16 shows a

typical ¹H NMR –SiMe₃singlet at d 0.40 (9H). It features a single

¹H NMR Cp-resonance at d 4.11 (5 H, s; ¹³C: d 69.3) and the

usual set of three C₅H₃¹H NMR signals at d 4.00, 4.12 and 4.83.

Upon iodination this was reduced to a set of two C₅H₂¹H NMR

In the ortho-silylated derivative (S,S,p-S)-16 we ﬁnd the

4-methoxymethyl-substituted chiral 1,3-dioxane auxiliary sub-

stituent in a typical chair conformation. It is rotated such that

the oxygen atom tip (O20) of the chair is oriented away from the

bulky –SiMe₃group. The remaining ring oxygen atom (O16) and

the equatorial –CH₂OCH₃substituent are oriented towards the

–SiMe₃substituent (see Fig. 4).

The conformational arrangement of the 4-methoxymethyl-1,3-

dioxane moiety in the tri-substituted (S,S,p-R)-17 derivative is

distinctly different. Here the O16 oxygen center and its adjacent

equatorial –CH₂OCH₃substituent are oriented toward the bulky

trimethylsilyl group, whereas the iodine substituent at the same

ferrocene Cp-rang faces the “back-side” of the chiral auxiliary

(see Fig. 4). For the structures of the derivatives (S,S,p-R)-13 and

(S,S,p-R)-14 see the ESI.†

resonances at d 4.39/3.99 (AB, J = 2.4 Hz) in (S,S,p-R)-17.

The ¹H NMR spectrum of the de-silylated compound (S,S,p-R)-

13 again features an ABC system of H NMR resonances of the

“upper” C₅H₃ring (d 4.57/4.25/3.86) as does the acetate (S,S,p-

R)-14 (for details see the Experimental section). In the series

of acetal derivatives the chiral cyclic acetal moiety shows very

characteristic NMR features [e.g. (S,S,p-R)-15, ¹³C NMR: d 99.6

(C-6), 76.8 (C-8), 76.0 (C-12), 66.8 (C-10), 59.2 (OCH₃), 28.3 (C-

9); the 9-H and 10-H atoms of the acetal core give well separated

¹H NMR signals aside from the OCH₃resonance at d 3.22 (s, 3H)].

Fig. 3 A view of the molecular structures of the (p-S)-12 (left) and (p-R)-12 (right) enantiomeric pair.

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Fig. 4 A comparison of the molecular geometries of the compounds

(S,S,p-S)-16 (left) and (S,S,p-R)-17 (right).

Synthesis and characterization of the free

N-aryl-“ferrocene-salimine” ligand systems

Scheme 7 i: 2,6-diisopropylaniline, p-TsOH, toluene; ii: ⁿBu₄N⁺F^-, THF.

We wanted to avoid the involvement of the sensitive parent

2-hydroxyferrocene carbaldehyde system.²²Therefore, the imine

synthesis was carried out by acid-catalyzed condensation of

the O-TBDPS protected aldehydes with the respective aniline

derivatives. We here describe the formation of the respective 2,6-

diisopropylphenyl imines derived from both the (p-S)-12 and (p-

R)-12 enantiomers. In addition, we have prepared the respective

N-mesityl and N-C₆F₅-substituted imine systems in the (p-S)-

enantiomeric series.

Both of the pairs (p-S)-19a/(p-R)-19a and (p-S)-2a/(p-R)-

2a enantiomers were characterized by X-ray diffraction. The

structure of (p-S)-19a (see Fig. 5) features the very bulky –

Si(^tBu)Ph₂protecting group at the ferrocenolate oxygen atom

(O1–C6_◦1.372(3) A, O1–Si1 1.670(2) A, angle C6–O1–Si1

125.2(2) ). At the same Cp-ring the –CH N–DIPP group is

attached, resulting in an element of planar chirality of absolute

The aldehydes (p-S)-12 and (p-R)-12 were each condensed with

2,6-diisopropylaniline under acid catalysis to form the corre-

sponding aldimine products (p-S)-19a and (p-R)-19a, respectively.

These compounds were isolated in 80 to 90% yields. Subsequent

deprotection was then achieved by ﬂuoride-induced desilylation

using tetra-n-butyl ammonium ﬂuoride³⁰to yield our target

compounds (p-S)-2a and (p-R)-2a, respectively (see Scheme 7).

The “ferrocene-salimine” system 2a features a ¹H NMR Cp singlet

at d 4.24 (s, 5H) and an ABC system of the ferrocene C₅H₃protons

at d 4.54/4.14/4.03. The –OH functional group gives rise to a

p-S conﬁguration. The –CH N–group is E-co_◦nﬁgurated (C11–

N12 1.272(3) A, angles C7–C11–N12 123.8(2) , C11–N12–C13

117.6(2)^◦, dihedral angle C7–C11–N12-C13 176.3(2)^◦) and the

imine substituent lies in the Cp-plane (dihedral angle C6–C7–

C11–N12 -166.5(2)^◦). The bulky DIPP substituent at the imine

nitrogen atom is oriented close to normal to the adjacen_◦t central

Cp–CH N– ligand plane (C11–N12–C13–C14 -103.3(3) ).

The “ferrocene-salimine” products (p-S)-2a and (p-R)-2a adopt

a different conformational arrangement of the pair of ortho func-

tional groups at the C₅H₃ring (see Fig. 6). Both the E-conﬁgurated

imino group and the –OH function are arranged coplanar

with the adjacent Cp-ring, so that they can form a hydrogen

bridge between them. The characteristic structural parameters of

(p-S)-2a amount to C6–N1 1.275(3) A, C2–O1 1.348(2) A, angles

O1–C2–C1 124.7(2)^◦, C2–C1–C6 123.4(2)^◦, C1–C6–N1 119.6(2)^◦,

C6–N1–C7 119.9(2)^◦, dihedral angles O1–C2–C1–C6 1.0(3)^◦,

C2–C1–C6–N1 -2.1(3)^◦, C1–C6–N1–C7 -178.0(2)^◦). The plane of

broad H NMR resonance at d 9.02 (in CDCl₃). The aldimine

–CH N– NMR signals appear at d 8.30 ( H) and d 168.1 ( C),

respectively. The 2,6-diisopropylphenyl substituent at the imine

nitrogen shows a 2H intensity ¹H NMR septet of the 2,6-isopropyl

methine protons and a typical pair of diastereotopic –CH(CH₃)₂

methyl resonances [¹H: d 1.22 and 1.18 (each d, each 6H), ¹³C: d

23.7 and 23.4 (CH₃)].

Fig. 5 A view of the molecular geometries of the enantiomers (p-S)-19a (left) and (p-R)-19a (right).

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Fig. 6 Projection of the molecular geometries of the (p-S)-2a (left) and

(p-R)-2a (right) enantiomeric pair.

the bulky DIPP ligand at the imine nitrogen center is again rotated

close to normal to the central adjacent ligand plane (dihedral angle

C6–N1–C7–C12 -76.9(3)^◦).

The imine synthesis by acid-catalyzed condensation of the

protected hydroxyferrocene aldehyde (p-S)-12 with mesitylamine

proceeds analogously. We isolated the silylated imine (p-S)-19b

in 85% yield. Desilylation was again achieved by treatment with

ﬂuoride ion to give (p-S)-2b in a moderate yield (Scheme 8). The

product (p-S)-2b features the expected typical spectroscopic data

[ H NMR: d 8.76 (OH), d 8.35 (–CH N–), ¹³C NMR: d 169.0

Scheme 9

(CH N)].

Fig. 7 Molecular geometry of compound (p-S)-20.

Scheme 8

angles C1–C2–C6–N1 -30.9(5)^◦, C2–C6–N1–C7 -3.4(5)^◦, C6–

N1–C7–C12 35.6(5)^◦, N1–C7–C12–O1 -0.4(5)^◦, C7–C12–O1–C1

-55.5(4)^◦, C12–O1–C1–C2 53.0(4)^◦] (values taken from molecule

A). The central seven-membered ring contains a tetraﬂuoro-o-

phenylene unit annelated with its C7 and C12 carbon atoms and

Eventually we have reacted (p-S)-12 with pentaﬂuoroaniline

to give the corresponding imine (p-S)-19c. Its treatment with

tetra-n-butyl ammonium ﬂuoride resulted in a successful de-

silylation reaction, as expected. However, we could not isolate

the C₆F₅-substituted “ferrocene-salimine” system (p-S)-2c from

this reaction, but obtained the cyclized product (p-S)-20 instead

(isolated in ca. 50% yield) (see Scheme 9). Apparently, the initially

formed aldimino-ferrocenolate anion intermediate [(p-S)-2c^-] was

not protonated with sufﬁcient efﬁciency under these special

the h -C₅H₃ligand of the ferrocene unit annelated through its

carbon atoms C1 and C2.

We consequently carried out the de-silylation reaction of (p-S)-

19c under protic conditions to suppress the undesired formation of

the S_NArproduct (p-S)-20. Treatment of (p-S)-19c with the triethyl-

amine trihydroﬂuoride reagent³²was successful and converted (p-

S)-19c to (p-S)-2c (isolated in ca. 70% yield). The product (p-S)-2c

features a typical set of three ¹⁹F NMR resonances of the –C₆F₅

substituent at d -154.4 (o-F), -161.7 (p-F) and -163.8 (m-F) in a

reaction conditions, so that it could stabilize itself by an S_NAr

reaction initiated by intramolecular ferrocenolate anion attack at

the adjacent activated arene system.³¹

Compound (p-S)-20 shows four characteristic ¹⁹F NMR reso-

nances (d -147.0, -159.6, -160.4, -164.8) in an equal intensity

ratio and the signals of the imine functionality (¹H: d 8.39,

¹³C: d 164.5). In addition, compound (p-S)-20 was characterized

by X-ray diffraction (see Fig. 7). The structure of (p-S)-20

features a ferrocene unit that contains the heterocyclic ring

2 : 1 : 2 intensity ratio. The ¹H NMR spectrum shows a broad OH

resonance at d 8.36 and the –CH N signal at d 8.09 ( C: d 174.5).

The X-ray crystal structure analysis of compound (p-S)-2c

(Fig. 8) features a six-membered ring system formed by in-

tramolecular hydrogen bonding between the O–H at C1 of the

system annelated with the h -C₅H₃ring. It shows a central seven-

Cp ring (C1–O1 1.365(4) A) and the imino nitrogen atom N1

◦

membered ring that is distorted from planarity into the direction

(C11–N1 1.292(4) A, angles C2–C11–N1 119.0(3) , C11–N1–C12

122.2(3)^◦, dihedral angle C2–C11–N1–C12 -178.5(8)^◦). We notice

that the plane of the C₆F₅substituent at N1 is only slightly rotated

of a boat-like conformation [C6–N1 1.283(4) A, angles C2–C6–N1

127.9(3)^◦, C6–N1–C7 122.1(2)^◦, C1–O1–C12 114.7(2)^◦, dihedral

This journal is

The Royal Society of Chemistry 2009

Dalton Trans., 2009, 3716–3730 | 3721

View Article Online

the respective solvent signal]; polarimetric measurements: Perkin-

Elmer Polarimeter 341.

X-Ray crystal structure determinations. Data sets were col-

lected with a Nonius KappaCCD diffractometer, equipped with

a rotating anode generator. Programs used: data collection

COLLECT,³³data reduction Denzo-SMN,³⁴absorption cor-

rection SORTAV³⁵and Denzo,³⁶structure solution SHELXS-

97,³⁷structure reﬁnement SHELXL-97,³⁸graphics SCHAKAL.³⁹

X-Ray crystal structure data are given in Table 1.

Fig. 8 A view of the molecular structure of compound (p-S)-2c.

out of the adjacent ligand plane (dihedral angle C11–N1–C12–

Synthesis of the racemic series

C17 -160.6(3)^◦).

(rac)-2-(1,3-Dioxan-2-yl)-1-iodoferrocene

((rac)-9). sec-

Butyllithium (24.9 ml, 32.3 mmol, 1.3 M solution in pentane)

was added to a solution of the dioxane 8 (8.00 g, 29.4 mmol)

in tetrahydrofuran (150 ml) at -78 ^◦C and the mixture was

subsequently stirred for one hour at -10 ^◦C, yielding a bright

orange precipitate. The mixture was cooled to -78 ^◦C and iodine

(8.20 g, 32.3 mmol), dissolved in tetrahydrofuran (100 ml), was

slowly added. After warming to room temperature and stirring

for another hour, the reaction was terminated by addition of a

saturated sodium thiosulfate solution (50 ml). The organic layer

was separated, dried over magnesium sulfate, ﬁltered and the

solvent was removed. The crude residue was puriﬁed by ﬁltration

on silica (cyclohexane : triethylamine = 9 : 1), yielding 8.19 g of a

yellow oil. This crude product was a mixture of starting material,

product and another unknown byproduct, containing about 75%

of the desired product. The mixture was inseparable by means

of column chromatography, but could be used directly for the

next reaction. Analytically pure material could be obtained by

threefold recrystallisation from pentane at -30 ^◦C, yielding yellow

crystals of (rac)-9 suitable for X-ray analysis (reaction scale:

3.67 mmol, yield: 433 mg, 29.7%). Mp 89 ^◦C (DSC); (found:

C, 42.18; H, 3.70. C₁₄H₁₅FeIO₂requires C, 42.25; H, 3.80%);

Conclusions

Our synthetic scheme has made the protected 2-hydroxyferrocene

carbaldehyde enantiomer (p-S)-12 available by a short preparative

route in excellent yield (76% over four consecutive steps) with

>99.5% ee. The enantiomer (p-R)-12 was prepared starting from

the same starting material using the same chiral auxiliary. Its

synthesis required two more steps due to the necessary blocking

of the 2-position and consequently the de-blocking step. The

enantiomer (p-R)-12 was obtained in a lower overall yield (27%

over six steps) but in the same enantiomeric purity (>99.5% ee). We

have shown that the systems 12 serve as reliable starting materials

for the synthesis of the corresponding imines by condensation

with three examples of differently substituted anilines, and we

have found in each case suitable simple deprotection routes

for the liberation of the –OH group at the imino-ferrocene

nucleus. This has made a variety of highly enantiomerically-

enriched “ferrocene-salimine” ligand systems easily available.

These three-dimensionally extended analogues of the ubiquitous

salicylaldimine ligand family will subsequently be used as building

blocks in coordination chemistry and catalysis.²³

_max(KBr)/cm^-12967, 1378, 1276, 1237, 1146, 1105, 1004, 989,

936 and 820; d_H(500 MHz; C₆D₆; Me₄Si) 5.39 (1 H, t, J =

Experimental

0.5 Hz, J = 0.5 Hz, 6-H), 4.58 (1 H, ddd, J = 2.7 Hz, J =

1.4 Hz, ⁴J = 0.5 Hz, 3-H), 4.24 (1 H, dd, ³J = 2.4 Hz, ⁴J = 1.4 Hz,

5-H), 4.10 (5H, s, Cp), 3.91 (1 H, dddd, ²J = 11.3 Hz, ³J = 5.0 Hz,

⁴J = 1.8 Hz, ³J = 1.3 Hz, 8-H_eq), 3.84 (1 H, ddd, ³J = 2.7 Hz, ³J =

General comments

Materials. 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. Solvents

were dried and distilled prior to use. Unless otherwise noted,

all starting materials were commercially available and were used

without further puriﬁcation. Ferrocenes 8,²⁴(S,S)-6,²¹(S,S,p-S)-

13,²¹(S,S,p-S)-16²¹were prepared according to literature proce-

dures. The syntheses of the ferrocenes (rac)-9,²⁵(S,S,p-S)-17²⁹and

(S,S,p-R)-13²⁹were independently developed and subsequently

published, differing only slightly from the syntheses presented

here. The X-ray crystal structure analyses of compounds (rac)-

9, (S,S,p-S)-16, (S,S,p-S)-17 and (S,S,p-R)-13 are to the best of

our knowledge reported for the ﬁrst time within this publication.

2.4 Hz, J = 0.5 Hz, 4-H), 3.83 (1 H, dddd, J = 11.3 Hz, J =

5.0 Hz, J = 1.8 Hz, J = 1.3 Hz, 10-H_eq), 3.55 (1 H, ddd, J =

12.5 Hz, ²J = 11.3 Hz, ³J = 2.6 Hz, 10-H_ax), 3.50 (1 H, ddd, ³J =

12.5 Hz, J = 11.3 Hz, J = 2.6 Hz, 8-H_ax), 1.83 (1 H, dtt, J =

13.3 Hz, J = 12.5 Hz, J = 5.0 Hz, 9-H_ax) and 0.64 (1 H, dtt,

²J = 13.3 Hz, J = 2.6 Hz, J = 1.3 Hz, 9-H_eq); d_C(126 MHz;

C₆D₆; Me₄Si) 101.3 (C-6), 87.5 (C-2), 75.1 (C-5), 72.2 (Cp), 68.9

(C-4), 67.3, 67.2 (C-8, C-10), 66.9 (C-3), 42.0 (C-1) and 25.9 (C-9)

[relative assignment for positions 8 and 10]; m/z (EI) 398 (M⁺,

100%), 275 (9), 212 (16), 121 (15) and 57 (61).

(rac)-1-Acetoxy-2-(1,3-dioxan-2-yl)ferrocene ((rac)-10). The

crude iodide (rac)-9 (8.20 g, 20.6 mmol) and copper(I) oxide

(2.95 g, 20.6 mmol) were suspended in acetonitrile (300 ml). After

addition of acetic acid (2.94 ml, 51.5 mmol), the mixture was

heated to reﬂux for three hours. Removal of the solvent gave

the crude product which was puriﬁed by column chromatography

(cyclohexane : triethylamine = 8 : 1). The product was obtained as

a yellow solid (4.39 g, 64.6%). X-Ray quality crystals were obtained

Techniques. The following instruments were used for phys-

ical characterization of the compounds: melting points: TA-

instruments DSC Q-20; elemental analyses: Foss–Heraeus

CHNO-Rapid; HPLC: Chiralcel OD-H column; IR: Varian 1300

FT-IR; NMR: Varian UNITY plus NMR spectrometer; Varian

INOVA 500 [NMR chemical shifts rel. Me₄Si were referenced to

3722 | Dalton Trans., 2009, 3716–3730

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Table 1 X-Ray crystal structure data

Comp.

(rac)-10

(rac)-12

(rac)-9

(rac)-11

(p-S)-12

(p-R)-12

(S,S,p-S)-16

(S,S,p-R)-17

Formula

C₁₆H₁₈FeO₄C₂₇H₂₈FeO₂Si C₁₄H₁₅FeIO₂

330.15 468.43 398.01

C₃₀H₃₄FeO₃Si C₂₇H₂₈FeO₂Si

526.51 468.43

C₂₇H₂₈FeO₂Si

468.43

C₁₉H₂₈FeO₃Si C₁₉H₂₇FeIO₃Si

388.35

514.25

Monoclinic

P2₁(4)

8.6461(2)

10.4222(2)

12.2221(3)

96.712(1)

1093.80(4)

1.561

Crystal syst.

Space group

Monoclinic Triclinic

Orthorhombic Triclinic

Orthorhombic Orthorhombic Triclinic

P2₁/c (14)

16.662(1)

7.647(1)

11.332(1)

90.75(1)

1443.7(2)

1.519

P1 (2)

P2₁2₁2₁(19)

7.938(1)

9.716(1)

17.680(1)

1363.6(2)

1.939

3.360

P1 (2)

P2₁2₁2₁(19)

10.155(1)

13.060(1)

17.630(1)

2338.2(3)

1.331

0.717

P2₁2₁2₁(19)

10.1788(3)

13.0739(4)

17.6425(8)

2347.8(2)

1.325

0.714

P1 (1)

9.4036(2)

10.1503(2)

11.0179(3)

102.777(1)

104.675(1)

91.046(1)

989.07(4)

1.304

a/A

9.377(1)

10.308(1)

12.984(1)

91.75(1)

103.04(1)

106.67(1)

1165.14(2)

1.335

7.465(1)

12.947(1)

14.191(1)

102.67(1)

92.54(1)

95.95(1)

1327.8(2)

1.317

b/A

c/A

a/^◦

b/^◦

g /^◦

V/A

D_c/g cm^-3

m/mm^-1

1.057

0.720

0.642

0.836

2.169

l/A

0.71073

293(2)

9482

0.71073

198(2)

10991

0.62

0.71073

198(2)

9338

0.71073

198(2)

12783

0.62

0.71073

198(2)

11052

0.66

0.71073

223(2)

19459

0.62

4759

0.093

0.71073

223(2)

9259

0.71073

223(2)

7850

T/K

Reﬂ. collected

-1

[(sin q)/l]/A

0.67

6913

0.66

4845

Reﬂ. indep.

R_int

3519

0.061

2514

4713

0.039

3438

3270

0.022

3182

5383

4550

0.046

3905

0.044

3805

0.036

6087

0.031

4188

Reﬂ. observed

3305

Reﬁned param. 191

283

0.045

0.117

163

319

0.044

0.099

283

0.053

0.106

-0.01(2)

441

0.039

0.098

-0.00(1)

230

0.034

0.077

0.02(2)

R [I > 2s(I)]

0.050

0.104

0.021

0.049

-0.03(2)

0.036

0.070

-0.03(1)

wR²

Flack param.

Comp.

(S,S,p-R)-13

(S,S,p-R)-14

(p-S)-19a

(p-R)-19a

(p-S)-2a

(p-R)-2a

(p-S)-20

(p-S)-2c

Formula

C₁₆H₁₉FeIO₃

442.06

C₁₈H₂₂FeO₅

374.21

Orthorhombic Monoclinic

P2₁2₁2₁(19)

8.5104(1)

8.8078(2)

23.3727(5)

C₃₉H₄₅FeNOSi C₃₉H₄₅FeNOSi C₂₃H₂₇FeNO

C₂₃H₂₇FeNO

389.31

C₁₇H₉F₄FeNO C₁₇H₁₀F₅FeNO

627.70

Monoclinic

P2₁(4)

9.1488(2)

11.8559(2)

16.8475(4)

389.31

375.10

395.11

Monoclinic

P2₁(4)

6.1035(1)

9.8860(2)

12.2284(3)

Crystal syst.

Space group

Monoclinic

P2₁(4)

9.8132(1)

20.1279(3)

16.9731(2)

93.464(1)

3346.39(7)

1.755

Orthorhombic Orthorhombic Monoclinic

P2₁(4)

9.144(1)

11.841(1)

16.838(1)

P2₁2₁2₁(19)

6.046(1)

16.281(1)

20.324(1)

P2₁2₁2₁(19)

6.0629(1)

16.3389(3)

20.3700(6)

P2₁(4)

13.0568(3)

7.2896(2)

15.2684(5)

a/A

b/A

c/A

a/^◦

b/^◦

g /^◦

103.20(1)

103.095(1)

104.131(1)

95.327(1)

V/A

1751.97(6)

1.419

0.884

1775.0(3)

1.174

0.488

1779.88(6)

1.171

0.486

2000.6(4)

1.293

0.764

2017.88(8)

1.281

0.0758

0.71073

223(2)

13523

0.66

4672

0.065

3317

240

1409.25(7)

1.768

1.121

734.67(3)

1.786

1.089

D_c/g cm^-3

m/mm^-1

2.752

0.71073

223(2)

l/A

0.71073

223(2)

13367

0.66

4124

0.057

0.71073

198(2)

9817

0.71073

223(2)

12584

0.67

0.71073

198(2)

13921

0.66

0.71073

223(2)

11237

0.67

0.71073

223(2)

4869

0.66

2991

T/K

Reﬂ. collected 22945

-1

[(sin q)/l]/A

Reﬂ. indep.

R_int

Reﬂ. observed 10864

Reﬁned param. 761

0.66

13402

0.024

0.66

6966

0.027

5788

7634

0.032

5448

4547

0.031

4110

6691

0.036

5682

0.031

2725

3344

219

395

240

433

227

R [I > 2s(I)]

0.040

0.085

0.037

0.078

-0.01(2)

0.038

0.078

-0.02(1)

0.045

0.097

-0.04(1)

0.032

0.076

0.00(2)

0.048

0.096

0.01(2)

0.037

0.084

-0.01(1)

0.033

0.082

-0.00(2)

wR²

Flack param. -0.02(2)

from a solution of (rac)-10 in pentane at -30 ^◦C. Mp 74 ^◦C (DSC);

³J = 2.6 Hz, 8-H_ax), 3.47 (1 H, ddd, ³J = 12.4 Hz, ²J = 11.2 Hz,

³J = 2.6 Hz, 10-H_ax), 1.83 (1 H, dtt, ²J = 13.3 Hz, ³J = 12.4 Hz,

³J = 5.0 Hz, 9-H_ax), 1.78 (3 H, s, COMe) and 0.66 (1 H, dtt, ²J =

(found: C, 58.11; H, 5.45. C₁₆H₁₈FeO₄requires C, 58.21; H, 5.50%);

_max(KBr)/cm^-12830, 1755, 1450, 1378, 1362, 1205, 1141, 1090,

1008 and 888; d_H(500 MHz; C₆D₆; Me₄Si) 5.47 (1 H, s, 6-H), 4.45

(1 H, dd, ³J = 2.7 Hz, ⁴J = 1.6 Hz, 5-H), 4.34 (1 H, dd, ³J = 2.7 Hz,

⁴J = 1.6 Hz, 3-H), 4.29 (5 H, s, Cp), 3.87 (1 H, dddd, ²J = 11.3 Hz,

³J = 5.0 Hz, ⁴J = 1.8 Hz, ³J = 1.3 Hz, 8-H_eq), 3.82 (1 H, dddd, ²J =

11.2 Hz, ³J = 5.0 Hz, ⁴J = 1.8 Hz, ³J = 1.3 Hz, 10-H_eq), 3.71 (1 H,

t, ³J = 2.7 Hz, 4-H), 3.49 (1 H, ddd, ³J = 12.4 Hz, ²J = 11.3 Hz,

13.3 Hz, J = 2.6 Hz, J = 1.3 Hz, 9-H_eq); d_C(126 MHz; C₆D₆;

Me₄Si) 168.4 (COMe), 114.1 (C-1), 99.3 (C-6), 78.7 (C-2), 70.6

(Cp), 67.03, 66.99 (C-8, C-10), 62.8 (C-3), 62.4 (C-4), 61.9 (C-5),

26.1 (C-9) and 20.7 (COMe) [relative assignment for positions 8

and 10]; m/z (EI) 330 (M⁺, 100%), 288 (89), 230 (52), 164 (37) and

101 (11).

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Dalton Trans., 2009, 3716–3730 | 3723

View Article Online

(rac)-1-(tert-Butyldiphenylsiloxy)-2-(1,3-dioxan-2-yl)ferrocene

((rac)-11). Sodium methoxide (600 mg, 11.1 mmol) was added

to a solution of the acetate (rac)-10 (3.35 g, 10.1 mmol) in N,N-

dimethylformamide (30 ml), yielding a deep red reaction mixture.

After 90 min, tert-butyldiphenyl-silylchloride (2.63 ml, 10.1 mmol)

was added and the bright yellow mixture was stirred overnight.

Removal of the solvent and puriﬁcation of the crude material

by column chromatography (cyclohexane : triethylamine = 9 : 1)

yielded 4.52 g (85.3%) of the product as a yellow solid. X-Ray

quality crystals_◦were obtained from a solution of (rac)-11 in

C₃₀H₃₄FeO₃Si requires C, 68.43; H, 6.51%); n_max(KBr)/cm^-12961,

2854, 1463, 1427, 1096, 998, 900, 814, 742 and 701; d_H(500 MHz;

CDCl₃; Me₄Si) 7.94 (2 H, ps d, o-Ph), 7.66 (2 H, ps d, o-Ph¢),

7.54–7.46 (3 H, m, m-Ph, p-Ph), 7.39 (1 H, m, p-Ph¢), 7.33 (2 H,

m, m-Ph¢), 5.77 (1 H, s, 6-H), 4.34 (1 H, dddd, ²J = 11.4 Hz, ³J =

Synthesis of the (p-S) series

(S,S,p-S)-(-)-1-Acetoxy-2-(4-methoxymethyl-1,3-dioxan-2-yl)

ferrocene ((S,S,p-S)-14). The iodoferrocene (S,S,p-S)-13 (17.2 g,

38.9 mmol) and copper(I)oxide (5.57 g, 38.9 mmol) were suspended

in acetonitrile (500 ml). After addition of acetic acid (11.2 ml, 195

mmol), the mixture was heated to 80 ^◦C for three hours under an

argon atmosphere. The solvent was removed and the crude prod-

uct was puriﬁed by column chromatography (cyclohexane : ethyl

acetate = 2 : 1) to yield the product (S,S,p-S)-14 as an orange oil

(13.7 g, 94.1%). [a]²_D⁰-111 (c 1.02 in CH₂Cl₂); (found: C, 57.51; H,

5.96. C₁₈H₂₂FeO₅requires C, 57.77; H, 5.93%); n_max(ATR)/cm^-1

2924, 2851, 1757, 1438, 1367, 1198, 1145, 1095, 1002, 954 and

817; d_H(500 MHz; C₆D₆; Me₄Si) 5.55 (1 H, s, 6-H), 4.47 (1 H,

◦

pentane at -30 C. Mp 98 C (DSC); (found: C, 68.05; H, 6.40.

dd, J = 2.7 Hz, J = 1.6 Hz, 5-H), 4.35 (1 H, dd, J = 2.7 Hz,

⁴J = 1.6 Hz, 3-H), 4.27 (5 H, s, Cp), 3.92 (1 H, ddd, ²J = 11.4 Hz,

³J = 5.1 Hz, ³J = 1.4 Hz, 10-H_eq), 3.75 (1 H, dddd, ³J = 11.4 Hz,

5.0 Hz, J = 1.8 Hz, J = 1.2 Hz, 8-H_eq), 4.18 (1 H, dddd, J =

³J = 5.7 Hz, J = 4.7 Hz, J = 2.5 Hz, 8-H), 3.70 (1 H, t, J =

11.4 Hz, ³J = 5.0 Hz, ⁴J = 1.8 Hz, ³J = 1.2 Hz, 10-H_eq), 4.12 (5

2.7 Hz, 4-H), 3.51 (1 H, ddd, J = 12.5 Hz, J = 11.4 Hz, J =

2.6 Hz, 10-H_ax), 3.29 (1 H, dd, ²J = 10.2 Hz, ³J = 5.7 Hz, 12-H),

H, s, Cp), 4.07 (1 H, dd, J = 2.7 Hz, J = 1.5 Hz, 3-H), 4.06

(1 H, m, 8-H_ax), 3.94 (1 H, m, 10-H_ax), 3.55 (1 H, t, ³J = 2.7 Hz,

4-H), 3.49 (1 H, dd, ³J = 2.7 Hz, ⁴J = 1.5 Hz, 5-H), 2.22 (1 H, dtt,

3.14 (1 H, dd, J = 10.2 Hz, J = 4.7 Hz, 12-H¢), 3.11 (3 H, s,

OMe), 1.82 (3 H, s, COMe), 1.62 (1 H, dddd, ²J = 13.2 Hz, ³J =

12.5 Hz, ³J = 11.4 Hz, ³J = 5.1 Hz, 9-H_ax) and 1.01 (1 H, dtd, ²J =

²J = 13.4 Hz, J = 12.5 Hz, J = 5.0 Hz, 9-H_ax), 1.41 (1 H, dtt,

²J = 13.4 Hz, ³J = 2.4 Hz, ³J = 1.2 Hz, 9-H_eq) and 1.11 (9 H, s,

C(CH₃)₃); d_C(126 MHz; CDCl₃; Me₄Si) 135.60, 135.58 (o-Ph, o-

Ph¢), 133.8 (i-Ph), 132.1 (i-Ph¢), 130.0 (p-Ph), 129.7 (p-Ph¢), 127.7

(m-Ph), 127.5 (m-Ph¢), 120.2 (C-1), 99.6 (C-6), 75.0 (C-2), 69.7

(Cp), 67.6 (C-8), 67.2 (C-10), 60.3 (C-4), 59.7 (C-3), 59.6 (C-5),

26.5 (C(CH₃)₃), 25.8 (C-9) and 19.4 (C(CH₃)₃) [relative assignment

for position 8 and 10]; m/z (EI) 526 (M⁺, 100%), 431 (8), 375 (10),

275 (3) and 135 (15).

13.2 Hz, J = 2.5 Hz, J = 1.4 Hz, 9-H_eq); d_C(126 MHz; C₆D₆;

Me₄Si) 168.4 (COMe), 114.3 (C-1), 99.0 (C-6), 78.3 (C-2), 76.3

(C-8), 75.8 (C-12), 70.6 (Cp), 66.6 (C-10), 62.8 (C-3), 62.4 (C-4),

62.0 (C-5), 59.1 (OMe), 28.7 (C-9) and 20.7 (COMe); m/z (EI)

374 (M⁺, 80%), 332 (55), 238 (6), 230 (100), 164 (27), 103 (57) and

75 (12).

(rac)-1-(tert-Butyldiphenylsiloxy)-2-formylferrocene ((rac)-12).

The acetal (rac)-11 (4.52 g, 8.58 mmol) and p-toluene sulfonic

acid (3.26 g, 17.2 mmol) were dissolved in a two-phase mixture

of dichloromethane (150 ml) and water (50 ml). The mixture

was heated to reﬂux for three hours 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

(cyclohexane : ethyl acetate = 4 : 1). The resulting deep red oil was

(S,S,p-S )-(-)-1-(tert-Butyldiphenylsiloxy)-2-(4-methoxy-

methyl-1,3-dioxan-2-yl)ferrocene ((S,S,p-S)-15). The acetate

(S,S,p-S)-14 (7.50 g, 20.0 mmol) was dissolved in N,N-

dimethylformamide (60 ml) and sodium methoxide (1.19 g, 22.0

mmol) was added in one portion, yielding a dark red solution.

After 90 min, tert-butylchlorodiphenylsilane (5.73 ml, 22.0 mmol)

was added and the bright yellow mixture was stirred overnight.

The solvent was removed and the residue was puriﬁed by column

chromatography (cyclohexane : ethyl acetate = 6 : 1) to yield

(S,S,p-S)-15 (10.8 g, 94.6%) as a yellow oil. [a]²_D⁰-140 (c 1.01

in CH₂Cl₂); (found: C, 67.18; H, 6.84. C₃₂H₃₈FeO₄Si requires C,

67.36; H, 6.71%); n_max(ATR)/cm^-12930, 2856, 1460, 1428, 1289,

1201, 1144, 1103, 1031, 1000, 957, 888, 847, 819, 742, 699 and

616; d_H(600 MHz; CDCl₃; Me₄Si) 7.91 (2 H, ps d, o-Ph), 7.66

(2 H, ps d, o-Ph¢), 7.50–7.44 (3 H, m, m-Ph, p-Ph), 7.37 (1 H, m,

p-Ph¢), 7.31 (2 H, m, m-Ph¢), 5.78 (1 H, s, 6-H), 4.34 (1 H, dd, ²J =

◦

dissolved in pentane (30 ml) and the solution was stored at 4 C

overnight. Removal of the supernatant liquid gave a red solid,

which was dried in vacuo (3.12 g, 77.6%). X-Ray quality crystals

were obtained from a solution of (rac)-12 in pentane at -30 ^◦C. Mp

90 ^◦C (DSC); (found: C, 69.15; H, 5.97. C₂₇H₂₈FeO₂Si requires C,

69.23; H, 6.02%); n_max(ATR)/cm^-12860, 2811, 1674, 1461, 1447,

1429, 1285, 1207, 1104, 1015, 894, 820, 762, 700 and 606; d_H

(600 MHz; C₆D₆; Me₄Si) 10.8 (1 H, s, CHO), 7.85 (2 H, ps d,

o-Ph), 7.62 (2 H, ps d, o-Ph¢), 7.24–7.19 (3 H, m, m-Ph, p-Ph), 7.13

(1 H, p-Ph¢), 7.09 (2 H, m, m-Ph¢), 4.48 (1 H, dd, ³J = 2.8 Hz, ⁴J =

1.5 Hz, 3-H), 3.93 (5 H, s, Cp), 3.74 (1 H, dd, ³J = 2.8 Hz, ⁴J =

1.5 Hz, 5-H), 3.55 (1 H, t, ³J = 2.8 Hz, 4-H), 1.08 (9 H, s, C(CH₃)₃);

d_C(151 MHz; C₆D₆; Me₄Si) 190.9 (CHO), 136.0 (o-Ph), 135.8 (o-

Ph¢), 133.4 (i-Ph), 132.1 (i-Ph¢), 130.6 (p-Ph), 130.4 (p-Ph¢), 128.2

(m-Ph, m-Ph¢), 125.0 (C-1), 70.6 (Cp), 69.7 (C-2), 65.5 (C-4), 63.4

(C-5), 61.5 (C-3), 26.7 (C(CH₃)₃), 19.6 (C(CH₃)₃); m/z (EI) 468

(M⁺, 55%), 411 (100), 345 (11), 197 (10) and 135 (11); HPLC

(Chiralcel OD-H, hexanes : isopropanol = 95 : 5, 1 ml min^-1) t_r

(min) 4.858 (50.00%), 6.516 (50.00%).

11.4 Hz, J = 4.8 Hz, 10-H_eq), 4.09 (5 H, s, Cp), 4.06–3.96 (3 H,

m, 3-H, 8-H, 10-H_ax), 3.51 (1 H, t, ³J = 2.5 Hz, 4-H), 3.45 (1 H,

m, 5-H), 3.44 (1 H, dd, ²J = 10.0 Hz, ³J = 5.0 Hz, 12-H), 3.36 (1

H, dd, ²J = 10.0 Hz, ³J = 5.6 Hz, 12-H¢), 3.30 (3 H, s, OMe), 1.86

(1 H, dtd, ²J = 13.2 Hz, ³J = 12.5 Hz, ³J = 5.0 Hz, 9-H_ax), 1.56

(1 H, broad d, J = 13.2 Hz, 9-H_eq) and 1.07 (9 H, s, C(CH₃)₃);

d_C(151 MHz; CDCl₃; Me₄Si) 135.7, 135.6 (o-Ph, o-Ph¢), 133.8 (i-

Ph), 132.1 (i-Ph¢), 130.0 (p-Ph), 129.7 (p-Ph¢), 127.7 (m-Ph), 127.5

(m-Ph¢), 120.3 (C-1), 99.5 (C-6), 76.0 (C-8), 75.3 (C-12), 74.7 (C-

2), 69.7 (Cp), 67.2 (C-10), 60.3 (C-4), 60.0 (C-3), 59.8 (C-5), 59.3

(OMe), 28.5 (C-9), 26.5 (C(CH₃)₃) and 19.4 (C(CH₃)₃); m/z (EI)

570 (M⁺, 100%), 411 (9), 403 (6), 135 (8).

3724 | Dalton Trans., 2009, 3716–3730

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The Royal Society of Chemistry 2009

View Article Online

(p-S)-(+)-1-(tert-Butyldiphenylsiloxy)-2-formylferrocene ((p-S)-

12). The acetal (S,S,p-S)-15 (16.7 g, 29.3 mmol) and p-toluene

sulfonic acid (11.1 g, 58.5 mmol) were dissolved in a two-phase

mixture of dichloromethane (300 ml) and water (100 ml). The

mixture was heated to reﬂux for three hours 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

(cyclohexane : ethyl acetate = 4 : 1). The resulting deep red oil

was dissolved in pentane (150 ml) and the solution was stored

added to a solution of the trimethylsilyl-derivative (S,S,p-S)-16

(20.8 g, 53.6 mmol) in diethyl ether (250 ml) at -78 ^◦C. The mixture

was slowly warmed up and stirred for 90 min at room temperature.

After cooling to -78 ^◦C, a solution of iodine (20.4 g, 80.4 mmol)

in tetrahydrofuran (150 ml) was added. The mixture was allowed

to warm to room temperature and stirred overnight. A saturated

solution of sodium thiosulfate (100 ml) was slowly added, the

aqueous phase was extracted with diethyl ether (100 ml) and the

organic phases were dried over magnesium sulfate. Filtration and

removal of the solvent gave the crude product, which was puriﬁed

by careful column chromatography (pentane : diethyl ether =

20 : 1). The ﬁrst fraction yielded 14.2 g (51.5%) of the desired

trisubstituted product (S,S,p-R)-17 as a yellow solid, further

elution gave a second fraction of the 1,1¢-bis(iodination) product

18 (yellow solid, 10.7 g, 31.2%). X-Ray quality crystals of (S,S,p-

S)-_◦17 were obtained from a solution in pentane at -30 ^◦C. Mp

69 C (DSC); [a]²_D⁰+31.6 (c 1.00 in CH₂Cl₂); (found: C, 44.40; H,

5.29. C₁₉H₂₇FeIO₃Si requires C, 44.38; H, 5.29%); n_max(ATR)/cm^-1

2888, 2847, 1243, 1202, 1154, 1122, 1103, 1036, 1009, 985, 948, 835,

817, 755, 691 and 637; d_H(600 MHz; C₆D₆; Me₄Si) 5.42 (1 H, s,

6-H), 4.39 (1 H, d, ³J = 2.4 Hz, 5-H), 4.20 (5 H, s, Cp), 3.99 (1 H,

d, ³J = 2.4 Hz, 4-H), 3.83 (1 H, ddd, ²J = 11.4 Hz, ³J = 5.2 Hz,

³J = 1.3 Hz, 10-H_eq), 3.78 (1 H, dddd, ³J = 11.6 Hz, ³J = 6.5 Hz,

³J = 4.4 Hz, ³J = 2.5 Hz, 8-H), 3.50 (1 H, ddd, ³J = 12.4 Hz, ²J =

◦

at 4 C overnight. Removal of the supernatant liquid gave a red

solid, which was recrystallized twice from pentane at -30 ^◦C. This

gave 12.2 g of the product (88.7%, ee > 99.5%). X-Ray quality

crystals were obtained from a solution of (p-S)-12 in pentane

◦

at 4 ^◦C. Mp 117 C (DSC); [a]_D²⁰+495 (c 0.53 in CH₂Cl₂);

(found: C, 69.24; H, 6.01. C₂₇H₂₈FeO₂Si requires C, 69.23; H,

6.02%); n_max(ATR)/cm^-1/d_H/d_C/m/z: all IR/NMR/MS data are

like (rac)-12; HPLC (Chiralcel OD-H, hexanes : isopropanol =

95 : 5, 1 ml min^-1) t_r(min) 4.857 (99.77%), 6.546 (0.23%).

Synthesis of the (p-R) series

(S,S,p-S)-(-)-2-(4-Methoxymethyl-1,3-dioxan-2-yl)-1-trime-

thylsilylferrocene ((S,S,p-S)-16). A solution of tert-butyllithium

(42.9 ml, 68.7 mmol, 1.6 M in pentane) was slowly added to

a solution of the acetal (S,S)-6 (18.1 g, 57.3 mmol) in diethyl

ether (250 ml) at -78 ^◦C. The mixture was slowly warmed up

and stirred for one hour at room temperature. After cooling to

-78 ^◦C, chlorotrimethylsilane (8.68 ml, 68.7 mmol) was added.

The mixture was allowed to warm to room temperature and stirred

overnight. Brine (10 ml) and water (30 ml) were slowly added, the

aqueous phase was extracted with diethyl ether (30 ml) and the

organic phases were dried over magnesium sulfate. Filtration and

removal of the solvent gave the crude product, which was puriﬁed

by column chromatography (pentane : diethyl ether = 6 : 1) to give

20.3 g (91.2%) of the trimethylsilyl-derivative (S,S,p-S)-16 as a

yellow solid. X-Ray quality crystals were obtained from a solution

11.4 Hz, J = 2.5 Hz, 10-H_ax), 3.35 (1 H, dd, J = 9.9 Hz, J =

6.5 Hz, 12-H), 3.12 (1 H, dd, J = 9.9 Hz, J = 4.4 Hz, 12-H¢),

3.11 (3 H, s, OMe), 1.59 (1 H, dddd, ²J = 13.2 Hz, ³J = 12.4 Hz,

³J = 11.6 Hz, ³J = 5.2 Hz, 9-H_ax), 0.90 (1 H, dtd, ²J = 13.2 Hz,

³J = 2.5 Hz, ³J = 1.3 Hz, 9-H_eq) and 0.41 (9 H, s, ²J_SiH= 6.8 Hz,

SiMe₃); d_C(151 MHz; C₆D₆; Me₄Si) 102.2 (C-6), 90.8 (C-2), 76.9

(C-5), 76.3 (C-8), 75.8 (C-4), 75.6 (C-12), 72.4 (Cp), 71.0 (C-3),

66.8 (C-10), 58.7 (OMe), 47.0 (C-1), 27.8 (C-9) and 1.3 (¹J_SiC

53.6 Hz, SiMe₃); m/z (EI) 514 (M⁺, 100%), 397 (6), 213 (6), 121

(8), 73 (9).

Byproduct: (S,S,p-R)-1,1¢-diiodo-2-(4-methoxymethyl-1,3-di-

oxan-2-yl)-3-trimethylsilylferrocene (18). The byproduct was

identiﬁed as the tetrasubstituted ferrocene 18 by NMR-

spectroscopy. d_H(600 MHz; C₆D₆; Me₄Si) 5.36 (1 H, s, 6-H), 4.34

(1 H, m, CpI), 4.33 (1 H, d, ³J = 2.5 Hz, 5-H), 4.29 (1 H, m, CpI),

4.21 (1 H, m, CpI), 4.07 (1 H, m, CpI), 3.94 (1 H, d, ³J = 2.5 Hz,

◦

of (S,S,p-S)-16 in pentane at -30 ^◦C. Mp 54 C (DSC); [a]²_D⁰

-25.6 (c 1.01 in CH₂Cl₂); (found: C, 58.61; H, 7.19. C₁₉H₂₈FeO₃Si

requires C, 58.76; H, 7.27%); n_max(ATR)/cm^-12957, 2876, 1239,

1143, 1102, 1003, 957, 895, 754 and 692; d_H(600 MHz; C₆D₆;

Me₄Si) 5.45 (1 H, s, 6-H), 4.83 (1 H, dd, ³J = 2.4 Hz, ⁴J = 1.4 Hz,

3-H), 4.12 (1 H, t, ³J = 2.4 Hz, 4-H), 4.11 (5 H, s, Cp), 4.00 (1 H,

dd, ³J = 2.4 Hz, ⁴J = 1.4 Hz, 5-H), 3.94 (1 H, ddd, ²J = 11.4 Hz,

³J = 5.1 Hz, ³J = 1.4 Hz, 10-H_eq), 3.77 (1 H, dddd, ³J = 11.4 Hz,

4-H), 3.80 (1 H, ddd, J = 11.4 Hz, J = 5.1 Hz, J = 1.1 Hz,

10-H_eq), 3.77 (1 H, m, 8-H), 3.49 (1 H, ddd, J = 12.5 Hz, J =

11.4 Hz, J = 2.6 Hz, 10-H_ax), 3.31 (1 H, dd, J = 9.9 Hz, J =

6.4 Hz, 12-H), 3.09 (3 H, s, OMe), 3.08 (1 H, dd, J = 9.9 Hz,

³J = 4.4 Hz, 12-H¢), 1.57 (1 H, dddd, ²J = 13.2 Hz, ³J = 12.5 Hz,

³J = 11.6 Hz, ³J = 5.1 Hz, 9-H_ax), 0.88 (1 H, dtd, ²J = 13.2 Hz,

³J = 2.5 Hz, ³J = 1.1 Hz, 9-H_eq) and 0.40 (9 H, s, ²J_SiH= 6.8 Hz,

SiMe₃); d_C(151 MHz; C₆D₆; Me₄Si) 101.5 (C-6), 91.2 (C-2), 81.1

(C-5), 80.4 (C-4), 79.8 (CpI), 76.9 (CpI), 76.2 (C-8), 75.5 (C-12),

75.3 (CpI), 72.5 (C-3), 72.3 (CpI), 66.8 (C-10), 58.6 (OMe),

48.3 (C-1), 42.4 (C-13), 27.7 (C-9) and 1.4 (¹J_SiC= 53.7 Hz,

SiMe₃).

³J = 6.0 Hz, J = 4.9 Hz, J = 2.5 Hz, 8-H), 3.47 (1 H, ddd,

³J = 12.5 Hz, ²J = 11.4 Hz, ³J = 2.5 Hz, 10-H_ax), 3.33 (1 H, dd,

²J = 9.9 Hz, ³J = 6.0 Hz, 12-H), 3.10 (1 H, dd, ²J = 9.9 Hz, ³J =

4.9 Hz, 12-H¢), 3.08 (3 H, s, OMe), 1.58 (1 H, dddd, ²J = 13.1 Hz,

³J = 12.5 Hz, ³J = 11.4 Hz, ³J = 5.1 Hz, 9-H_ax), 1.03 (1 H, dtd,

²J = 13.1 Hz, ³J = 2.5 Hz, ³J = 1.4 Hz, 9-H_eq) and 0.40 (9 H, s,

²J_SiH= 6.8 Hz, SiMe₃); d_C(151 MHz; C₆D₆; Me₄Si) 100.9 (C-6),

91.3 (C-2), 75.9 (C-8), 75.8 (C-12), 74.8 (C-5), 70.5 (C-3), 70.4

(C-1), 69.8 (C-4), 69.3 (Cp), 66.6 (C-10), 58.9 (OMe), 28.4 (C-9)

and 0.6 (¹J_SiC= 52.9 Hz, SiMe₃); m/z (EI) 388 (M⁺, 100%), 343

(6), 271 (21), 213 (9), 121 (15), 85 (6).

Dehalogenation of the byproduct 18. A solution of n-butyl-

lithium (844 ml, 1.35 mmol, 1.6 M in pentane) was slowly added to

a solution of 18 (288 mg, 0.450 mmol) in tetrahydrofuran (3 ml)

at -78 ^◦C. The mixture was slowly warmed up and stirred for

thirty minutes at room temperature. Water (10 ml) and diethyl

ether (10 ml) were added, the aqueous phase was extracted with

(S,S,p-R)-(+)-1-Iodo-2-(4-methoxymethyl-1,3-dioxan-2-yl)-3-

trimethylsilylferrocene ((S,S,p-R)-17).

A solution of tert-

butyllithium (42.8 ml, 64.3 mmol, 1.5 M in pentane) was slowly

This journal is

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Dalton Trans., 2009, 3716–3730 | 3725

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diethyl ether (10 ml) and the organic phases were dried over

magnesium sulfate. Filtration and removal of the solvent gave

the trimethylsilyl-derivative (S,S,p-S)-16 (170 mg, 97.3%), which

was pure according to ¹H-NMR.

³J = 2.5 Hz, J = 1.3 Hz, 9-H_eq); d_C(151 MHz; C₆D₆; Me₄Si)

168.6 (COMe), 114.0 (C-1), 98.7 (C-6), 79.0 (C-2), 76.04 (C-12),

76.01 (C-8), 70.7 (Cp), 66.5 (C-10), 63.1 (C-3), 62.4 (C-4), 61.7

(C-5), 59.0 (OMe), 28.2 (C-9) and 20.7 (COMe); m/z (EI) 374

(M⁺, 57%), 332 (40), 230 (100), 164 (29), 121 (36), 103 (32), 75 (9),

56 (6).

(S,S,p-R)-(-)-1-Iodo-2-(4-methoxymethyl-1,3-dioxan-2-yl)fer-

rocene ((S,S,p-R)-13). The trisubstituted ferrocene (S,S,p-R)-17

(10.1 g, 19.6 mmol) and tetra-n-butyl ammonium ﬂuoride (12.4 g,

39.3 mmol) were dissolved in tetrahydrofuran (150 ml). The

mixture was heated to reﬂux for 16 h under an argon atmosphere

and the solvent was removed to give the crude product, which was

puriﬁed by column chromatography (cyclohexane : ethyl acetate =

8 : 1) to give a yellow oil. The oil was dissolved in pentane (200 ml)

and the solution was stored at -30 ^◦C, giving a yellow precipitate.

The supernatant liquid was removed and the yellow solid of

(S,S,p-R)-13 was dried (8.15 g, 94.1%). X-Ray quality crystals

were obtained from a solution of (S,S,p-R)-13 in pentane at

-30 ^◦C. Mp 57 ^◦C (DSC); [a]_D²⁰-49.4 (c 1.01 in CH₂Cl₂); (found:

C, 42.88; H, 4.31. C₁₆H₁₉FeIO₃requires C, 43.47; H, 4.33%);

(S,S,p-R)-(+)-1-(tert-Butyldiphenylsiloxy)-2-(4-methoxy-

methyl-1,3-dioxan-2-yl)ferrocene ((S,S,p-R)-15). The acetate

(S,S,p-R)-14 (2.80 g, 7.48 mmol) was dissolved in N,N-

dimethylformamide (20 ml) and sodium methoxide (444 mg,

8.23 mmol) was added in one portion, yielding a dark red

solution. After 90 min, tert-butyl-chlorodiphenylsilane (2.14 ml,

8.23 mmol) was added and the bright yellow mixture was stirred

overnight. The solvent was removed and the residue was puriﬁed

by column chromatography (cyclohexane : ethyl acetate = 6 : 1) to

yield (S,S,p-R)-15 (3.94 g, 92.3%) as a yellow oil. [a]²_D⁰+102 (c 1.03

in CH₂Cl₂); (found: C, 67.82; H, 7.08. C₃₂H₃₈FeO₄Si requires C,

67.36; H, 6.71%); n_max(ATR)/cm^-12930, 2856, 1460, 1428, 1104,

1032, 1006, 891, 846, 820, 742, 699 and 615; d_H(500 MHz; C₆D₆;

Me₄Si) 8.05 (2 H, m, o-Ph), 7.81 (2 H, m, o-Ph¢), 7.32–7.25 (3 H,

m, m-Ph, p-Ph), 7.17–7.10 (3 H, m, m-Ph¢, p-Ph¢), 5.86 (1 H, s,

6-H), 4.27 (1 H, dd, ³J = 2.6 Hz, ⁴J = 1.5 Hz, 3-H), 4.25 (5 H, s,

_max(ATR)/cm^-12974, 2920, 1241, 1149, 1100, 1037, 981, 929 and

821; d_H(600 MHz; C₆D₆; Me₄Si) 5.41 (1 H, s, 6-H), 4.57 (1 H, dd,

³J = 2.6 Hz, ⁴J = 1.4 Hz, 3-H), 4.25 (1 H, dd, ³J = 2.5 Hz, ⁴J =

1.4 Hz, 5-H), 4.15 (5 H, s, Cp), 3.88 (1 H, ddd, ²J = 11.4 Hz, ³J =

5.1 Hz, ³J = 1.3 Hz, 10-H_eq), 3.86 (1 H, t, ³J = 2.5 Hz, 4-H), 3.76

(1 H, dddd, ³J = 11.6 Hz, ³J = 6.2 Hz, ³J = 4.4 Hz, ³J = 2.5 Hz,

Cp), 3.96 (1 H, ddd, J = 11.5 Hz, J = 5.0 Hz, J = 1.3 Hz,

8-H), 3.56 (1 H, ddd, J = 12.4 Hz, J = 11.4 Hz, J = 2.5 Hz,

10-H_eq), 3.89 (1 H, dddd, ³J = 11.5 Hz, ³J = 6.2 Hz, ³J = 4.6 Hz,

10-H_ax), 3.38 (1 H, dd, J = 10.3 Hz, J = 6.2 Hz, 12-H), 3.17

(3 H, s, OMe), 3.16 (1 H, dd, ²J = 10.3 Hz, ³J = 4.4 Hz, 12-H¢),

1.58 (1 H, dddd, ²J = 13.1 Hz, ³J = 12.4 Hz, ³J = 11.6 Hz, ³J =

³J = 2.5 Hz, 8-H), 3.66 (1 H, ddd, J = 12.4 Hz, J = 11.5 Hz,

³J = 2.5 Hz, 10-H_ax), 3.57 (1 H, dd, ³J = 2.6 Hz, ³J = 1.5 Hz, 5-H),

3.46 (1 H, dd, ²J = 10.2 Hz, ³J = 6.2 Hz, 12-H), 3.36 (1 H, t, ³J =

2.6 Hz, 4-H), 3.24 (1 H, dd, ²J = 10.2 Hz, ³J = 4.6 Hz, 12-H¢), 3.22

(3 H, s, OMe), 1.67 (1 H, dddd, ²J = 13.0 Hz, ³J = 12.4 Hz, ³J =

11.5 Hz, ³J = 5.0 Hz, 9-H_ax), 1.22 (9 H, s, C(CH₃)₃) and 1.04 (1 H,

dtd, ²J = 13.0 Hz, ³J = 2.5 Hz, ³J = 1.3 Hz, 9-H_eq); d_C(126 MHz;

C₆D₆; Me₄Si) 136.1 (o-Ph¢), 136.0 (o-Ph), 134.3 (i-Ph), 132.6 (i-

Ph¢), 130.3 (p-Ph), 130.1 (p-Ph¢), 128.1 (m-Ph), 127.97 (m-Ph¢),

120.9 (C-1), 99.6 (C-6), 76.8 (C-8), 76.0 (C-12), 75.8 (C-2), 70.3

(Cp), 66.8 (C-10), 61.2 (C-3), 60.6 (C-4), 60.1 (C-5), 59.2 (OMe),

28.3 (C-9), 26.8 (C(CH₃)₃) and 19.7 (C(CH₃)₃); m/z (EI) 570 (M⁺,

100%), 411 (13), 403 (7), 197 (8), 135 (14), 121 (14).

5.1 Hz, 9-H_ax) and 0.92 (1 H, dtd, J = 13.1 Hz, J = 2.5 Hz,

³J = 1.3 Hz, 9-H_eq); d_C(151 MHz; C₆D₆; Me₄Si) 100.9 (C-6), 87.3

(C-2), 76.4 (C-8), 75.8 (C-12), 75.0 (C-5), 72.3 (Cp), 68.9 (C-4),

67.0 (C-3), 66.8 (C-10), 59.1 (OMe), 42.3 (C-1) and 28.0 (C-9);

m/z (EI) 442 (M⁺, 100%), 212 (16), 141 (9), 128 (9), 121 (13),

56 (7).

(S,S,p-R)-(+)-1-Acetoxy-2-(4-methoxymethyl-1,3-dioxan-2-yl)

ferrocene ((S,S,p-R)-14). The iodoferrocene (S,S,p-R)-13

(3.56 g, 8.05 mmol) and copper(I)oxide (1.15 g, 8.05 mmol)

were suspended in acetonitrile (150 ml). After addition of

acetic acid (2.30 ml, 40.3 mmol), the mixture was heated to

80 ^◦C for three hours under an argon atmosphere. The solvent

was removed and the crude product was puriﬁed by column

chromatography (cyclohexane : ethyl acetate = 4 : 1) to yield the

product (S,S,p-R)-14 as a yellow solid (2.80 g, 92.9%). X-Ray

quality crystals were obtained_◦from a solution of (S,S,p-R)-14

in pentane at -30 ^◦C. Mp 85 C (DSC); [a]²_D⁰+62.1 (c 1.03 in

CH₂Cl₂); (found: C, 57.71; H, 5.88. C₁₈H₂₂FeO₅requires C, 57.77;

H, 5.93%); n_max(ATR)/cm^-12878, 1749, 1440, 1368, 1217, 1151,

1096, 1066, 1010, 992, 951, 909, 820, and 603; d_H(600 MHz;

C₆D₆; Me₄Si) 5.47 (1 H, s, 6-H), 4.41 (1 H, dd, ³J = 2.6 Hz, ⁴J =

1.6 Hz, 5-H), 4.34 (1 H, dd, ³J = 2.6 Hz, ⁴J = 1.6 Hz, 3-H), 4.33

(p-R)-(-)-(tert-Butyldiphenylsiloxy)-2-formylferrocene ((p-R)-

12). The acetal (S,S,p-R)-15 (4.73 g, 8.29 mmol) and p-toluene

sulfonic acid (3.16 g, 16.6 mmol) were dissolved in a two-phase

mixture of dichloromethane (200 ml) and water (100 ml). The

mixture was heated to reﬂux for three hours 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 (cyclohexane : ethyl acetate = 4 : 1). The resulting deep red

oil was dissolved in pentane (50 ml) and the solution was stored

at -30 ^◦C overnight. Removal of the supernatant liquid gave a red

solid, which was recrystallized twice from pentane at -30 ^◦C. This

gave 2.75 g of the product (70.8%, ee > 99.5%). X-Ray quality

(5 H, s, Cp), 3.86 (1 H, ddd, J = 11.3 Hz, J = 5.0 Hz, J =

1.3 Hz, 10-H_eq), 3.73 (1 H, dddd, ³J = 11.6 Hz, ³J = 6.5 Hz, ³J =

4.0 Hz, J = 2.5 Hz, 8-H), 3.72 (1 H, t, J = 2.6 Hz, 4-H), 3.46

crystals were obtained from a solution of (p-R)-12 in pentane at

◦

(1 H, ddd, J = 12.4 Hz, J = 11.3 Hz, J = 2.5 Hz, 10-H_ax),

^◦C. Mp 117 C (DSC); [a]_D²⁰-469 (c 0.52 in CH₂Cl₂); (found:

3.32 (1 H, dd, J = 10.3 Hz, J = 6.5 Hz, 12-H), 3.14 (3 H, s,

C, 69.16; H, 6.02. C₂₇H₂₈FeO₂Si requires C, 69.23; H, 6.02%);

_max(ATR)/cm^-1/d_H/d_C/m/z: all IR/NMR/MS data are like

OMe), 3.10 (1 H, dd, J = 10.3 Hz, J = 4.0 Hz, 12-H¢), 1.86 (3

H, s, COMe), 1.54 (1 H, dddd, ²J = 13.1 Hz, ³J = 12.4 Hz, ³J =

(rac)-12; HPLC (Chiralcel OD-H, hexanes : isopropanol = 95 : 5,

11.6 Hz, J = 5.0 Hz, 9-H_ax) and 0.89 (1 H, dtd, J = 13.1 Hz,

3726 | Dalton Trans., 2009, 3716–3730

1 ml min^-1) t_r(min) 6.523 (100.00%).

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The Royal Society of Chemistry 2009

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Synthesis of the ligand systems

and p-toluene sulfonic acid (112 mg, 0.587 mmol) were dissolved

in toluene (50 ml) and heated to 80 ^◦C overnight. Removal of

the solvent gave the crude product, which was puriﬁed by column

chromatography (cyclohexane : triethylamine = 9 : 1) to give the

imine (p-R)-19a as an orange solid (3.02 g, 82.0%). X-Ray quality

crystals were obt_◦ained from a solution of (p-R)-19a in pentane at

-30 ^◦C. Mp 119 C (DSC); [a]_D²⁰-498 (c 1.00 in CH₂Cl₂); (found:

74.12; H, 7.21; N, 2.13. C₃₉H₄₅FeNOSi requires C, 74.62; H, 7.23;

N, 2.23%); n_max(ATR)/cm^-1/d_H/d_C/m/z: all IR/NMR/MS data

are like (p-S)-19a.

(p-S)-(+)-N-2,6-Diisopropylphenyl-1-tert-butyldiphenylsiloxy-

2-iminomethylferrocene ((p-S)-19a). The aldehyde (p-S)-12

(5.00 g, 10.7 mmol), 2,6-diisopropylaniline (10.1 ml, 53.4 mmol)

and p-toluene sulfonic acid (203 mg, 1.07 mmol) were dissolved

in toluene (40 ml) and heated to 80 ^◦C overnight. Removal of

the solvent gave the crude product, which was puriﬁed by column

chromatography (cyclohexane : triethylamine = 9 : 1) to give the

imine (p-S)-19a as an orange solid (6.27 g, 93.3%). X-Ray quality

crystals were obtained from a solution of (p-S)-19a in pentane at

-30 ^◦C. Mp 116 ^◦C (DSC); [a]_D²⁰+505 (c 1.03 in CH₂Cl₂); (found:

C, 75.09; H, 7.34; N, 2.29. C₃₉H₄₅FeNOSi requires C, 74.62; H,

7.23, N, 2.23%); n_max(KBr)/cm^-12959, 2930, 2861, 1629, 1460,

1428, 1106, 905, 854, 820, 743 and 700; d_H(500 MHz; CDCl₃;

Me₄Si) 8.51 (1 H, t, ⁴J = 0.6 Hz, ⁵J = 0.6 Hz, CHN), 7.85 (2 H,

m, o-Ph), 7.60 (2 H, m, o-Ph¢), 7.50 (1 H, m, p-Ph), 7.46 (2 H,

m, m-Ph), 7.42 (1 H, m, p-Ph¢), 7.34 (2 H, m, m-Ph¢), 7.16 (2 H,

(p-R)-(+)-N-2,6-Diisopropylphenyl-2-iminomethylferrocen-1-ol

((p-R)-2a). The imine (p-R)-19a (1.62 g, 2.58 mmol) and tetra-

n-butyl ammonium ﬂuoride (1.63 g, 5.16 mmol) were dissolved in

tetrahydrofuran (30 ml) and the solution was stirred for two hours.

The solvent was removed and the crude product was puriﬁed

by column chromatography under argon (cyclohexane : ethyl

acetate : triethylamine = 8 : 1 : 1, solvents were degassed before

use). The solvent was removed to give an oily residue, which was

redissolved in pentane (100 ml). The solution was kept at -30 ^◦C

overnight and the resulting precipitate was isolated by removal of

the mother liquor to give a ﬁrst fraction of 510 mg of the product.

m, m-aryl), 7.10 (1 H, m, p-aryl), 4.66 (1 H, ddd, J = 2.7 Hz,

⁴J = 1.5 Hz, J = 0.6 Hz, 3-H), 4.15 (5 H, s, Cp), 3.92 (1 H, td,

³J = 2.7 Hz, ⁵J = 0.6 Hz, 4-H), 3.72 (1 H, dd, ³J = 2.7 Hz, ⁴J =

1.5 Hz, 5-H), 3.16 (2 H, sept, ³J = 7.0 Hz, CH), 1.27 (6 H, d, ³J =

◦

7.0 Hz, CH₃), 1.20 (6 H, d, J = 7.0 Hz, CH₃¢) and 1.02 (9 H, s,

Further storage of the mother liquor at -30 C yielded another

C(CH₃)₃); d_C(126 MHz; CDCl₃; Me₄Si) 160.8 (CHN), 149.8 (i-

aryl), 138.0 (o-aryl), 135.7 (o-Ph), 135.5 (o-Ph¢), 133.3 (i-Ph), 132.0

(i-Ph¢), 130.3 (p-Ph), 130.1 (p-Ph¢), 127.9 (m-Ph), 127.8 (m-Ph¢),

123.7 (p-aryl), 123.4 (C-1), 122.9 (m-aryl), 70.4 (C-2), 69.9 (Cp),

63.6 (C-4), 61.5 (C-5), 60.0 (C-3), 27.7 (CH), 26.7 (C(CH₃)₃), 23.8

(CH₃¢), 23.6 (CH₃) and 19.4 (C(CH₃)₃); m/z (EI) 627 (M⁺, 100%),

546 (11), 135 (9).

310 mg of the product (p-R)-2a as deep red crystals (total yield

820 mg, _◦81.6%). The crystals were suitable for X-ray analysis.

Mp 165 C (DSC); [a]²_D⁰+1698 (c 0.212 in CH₂Cl₂); (found: C,

70.98; H, 7.11; N, 3.90. C₂₃H₂₇FeNO requires C, 70.96; H, 6.99;

N, 3.60%); n_max(ATR)/cm^-1/d_H/d_C/m/z: all IR/NMR/MS data

are like (p-S)-2a.

(p-S)-(+)-N-2,4,6-Trimethylphenyl-1-tert-butyldiphenylsiloxy-

2-iminomethylferrocene ((p-S)-19b). The aldehyde (p-S)-12

(4.40 g, 9.39 mmol), 2,4,6-trimethylaniline (6.59 ml, 47.0 mmol)

and p-toluene sulfonic acid (179 mg, 0.939 mmol) were dissolved

in toluene (100 ml) and heated to 80 ^◦C for three hours. Removal of

the solvent gave the crude product, which was puriﬁed by column

chromatography (cyclohexane : triethylamine = 9 : 1) to give the

imine (p-S)-19b as a yellow oil (4.68 g, 85.1%). [a]²_D⁰+602 (c 1.00

in CH₂Cl₂); (found: C, 74.51; H, 7.01; N, 2.46. C₃₆H₃₉FeNOSi

requires C, 73.83; H, 6.71; N, 2.39%); n_max(ATR)/cm^-12957, 2928,

2856, 1628, 1459, 1428, 1316,1287, 1205, 1105, 1108, 904, 855,

819, 741, 700 and 502; d_H(600 MHz; CD₂Cl₂; Me₄Si) 8.54 (1 H, s,

CHN), 7.89 (2 H, m, o-Ph), 7.65 (2 H, m, o-Ph¢), 7.54 (1 H, m,

p-Ph), 7.50 (2 H, m, m-Ph), 7.45 (1 H, m, p-Ph¢), 7.38 (2 H, m,

m-Ph¢), 6.91 (2 H, m, m-Mes), 4.65 (1 H, ddd, ³J = 2.8 Hz, ⁴J =

(p-S)-(-)-N-2,6-Diisopropylphenyl-2-iminomethylferrocen-1-ol

((p-S)-2a). The imine (p-S)-19a (5.19 g, 8.27 mmol) and tetra-

n-butyl ammonium ﬂuoride (5.22 g, 16.5 mmol) were dissolved

in tetrahydrofuran (200 ml) and the solution was stirred for

two hours. The solvent was removed and the crude product was pu-

riﬁed by column chromatography under argon (cyclohexane : ethyl

acetate : triethylamine = 8 : 1 : 1, solvents were degassed before

use). Two fractions were collected and the solvent was removed.

The oily residues were dissolved in pentane (100 ml each) and the

solutions were kept at -30 ^◦C for two days. The deep red crystals

of (p-S)-2a were isolated by removal of the mother liquors, to give

a combined yield of 3.0_◦3 g (94.1%). The crystals were suitable for

X-ray analysis. Mp 161 C (DSC); [a]²_D⁰-1657 (c 0.208 in CH₂Cl₂);

(found: C, 70.82; H, 6.95; N, 3.64. C₂₃H₂₇FeNO requires C, 70.96;

H, 6.99; N, 3.60%); n_max(KBr)/cm^-12954, 2865, 1615, 1590, 1470,

1104, 934, 903 and 802; d_H(500 MHz; CDCl₃; Me₄Si) 9.02 (1 H,

1.5 Hz, J = 0.6 Hz, 3-H), 4.19 (5 H, s, Cp), 3.94 (1 H, td, ³J =

2.8 Hz, J = 0.6 Hz, 4-H), 3.79 (1 H, dd, J = 2.8 Hz, J =

1.5 Hz, 5-H), 2.30 (3 H, s, p-CH₃), 2.19 (6 H, s, o-CH₃) and 1.07 (9

H, s, C(CH₃)₃); d_C(151 MHz; CD₂Cl₂; Me₄Si) 161.5 (CHN), 150.2

(i-Mes), 136.0 (o-Ph), 135.9 (o-Ph¢), 133.6 (i-Ph), 132.6 (p-Mes),

132.5 (i-Ph¢), 130.6 (p-Ph), 130.5 (p-Ph¢), 129.0 (m-Mes), 128.21

(m-Ph), 128.15 (m-Ph¢), 127.2 (o- Mes), 123.8 (C-1), 71.0 (C-2),

70.4 (Cp), 63.8 (C-4), 62.1 (C-5), 60.3 (C-3), 26.8 (C(CH₃)₃), 20.9

(p-CH₃), 19.7 (C(CH₃)₃) and 18.5 (o-CH₃); m/z (ESI) 586.2210

(M + H⁺. C₃₆H₄₀FeNOSi requires 586.2224).

br, OH), 8.30 (1 H, d, J = 0.6 Hz, CHN), 7.17–7.10 (3 H, m,

m-aryl, p-aryl), 4.54 (1 H, ddd, J = 2.7 Hz, J = 1.4 Hz, J =

0.6 Hz, 3-H), 4.24 (5 H, s, Cp), 4.14 (1 H, dd, ³J = 2.7 Hz, ⁴J =

1.4 Hz, 5-H), 4.03 (1 H, t, ³J = 2.7 Hz, 4-H), 3.07 (2 H, sept, ³J =

7.0 Hz, CH), 1.22 (6 H, d, ³J = 7.0 Hz, CH₃) and 1.18 (6 H, d, ³J =

7.0 Hz, CH₃¢); d_C(126 MHz; CDCl₃; Me₄Si) 168.1 (CHN), 147.4

(i-aryl), 138.5 (o-aryl), 126.4 (C-1), 124.8 (p-aryl), 123.0 (m-aryl),

69.6 (Cp), 63.8 (C-2), 63.1 (C-4), 62.6 (C-5), 58.2 (C-3), 27.9 (CH),

23.7 (CH₃¢) and 23.4 (CH₃).

(p-S)-(-)-N-2,4,6-Trimethylphenyl-2-iminomethylferrocen-1-ol

((p-S)-2b). The imine (p-S)-19b (4.40 g, 7.51 mmol) and tetra-

n-butyl ammonium ﬂuoride (4.74 g, 15.0 mmol) were dissolved

in tetrahydrofuran (200 ml) and the solution was stirred for

(p-R)-(-)-N-2,6-Diisopropylphenyl-1-tert-butyldiphenylsiloxy-

2-iminomethylferrocene ((p-R)-19a). The aldehyde (p-R)-12a

(2.75 g, 5.87 mmol), 2,6-diisopropylaniline (5.54 ml, 29.4 mmol)

This journal is

The Royal Society of Chemistry 2009

Dalton Trans., 2009, 3716–3730 | 3727

View Article Online

two hours. The solvent was removed and the crude product was pu-

riﬁed by column chromatography under argon (cyclohexane : ethyl

acetate : triethylamine = 8 : 1 : 1, solvents were degassed before

use). The solvent was removed to give an oily residue, which was

dissolved in pentane (100 ml). The solution was kept at -30 ^◦C

overnight, yielding a red precipitate. Removal of the mother liquor

and drying of the solid gave 1.13 g (43.3%) of (p-S)-2b. Mp 104 ^◦C

(DSC); [a]²_D⁰-1666 (c 0.198 in CH₂Cl₂); (found: C, 68.98; H,

6.38; N, 3.97. C₂₀H₂₁FeNO requires C, 69.18; H, 6.10; N, 4.03%);

-30 ^◦C overnight, yielding a third fraction of the product (280 mg,

total yield 2.15 g, 69.3%). X-Ray quality crystals were obtained

from a solution of (p-S)-2c in toluene at -30 ^◦C. Mp 164 ^◦C

(DSC); [a]²_D⁰-296 (c 0.198 in CH₂Cl₂); (found: C, 52.30; H, 2.92;

N, 3.23. C₁₇H₁₀F₅FeNO requires C, 51.68; H, 2.55; N, 3.55%);

_max(KBr)/cm^-13094, 2931, 1647, 1586, 1512, 1501, 1470, 1345,

1201, 1107, 1021, 999, 974, 820, 663, 618 and 618; d_H(600 MHz;

C₆D₆; Me₄Si) 8.36 (1 H, br, OH), 8.09 (1 H, br, CHN), 4.51 (1 H,

ddd, ³J = 2.7 Hz, ⁴J = 1.4 Hz, ⁴J = 0.6 Hz, 3-H), 4.04 (5 H, s, Cp),

_max(KBr)/cm^-12908, 2855, 1616, 1601, 1470, 1410, 1326, 1210,

3.75 (1 H, t, J = 2.7 Hz, 4-H) and 3.73 (1 H, dd, J = 2.7 Hz,

⁴J = 1.4 Hz, 5-H); d_F(564 MHz; C₆D₆; CCl₃F) -154.4 (2 F, m,

o-C₆F₅), -161.7 (1 F, t, ³J_FF= 21.8 Hz, p-C₆F₅) and -163.8 (2 F,

m, m-C₆F₅); d_C(151 MHz; C₆D₆; Me₄Si) 174.5 (CHN), 140.2 (dm,

¹J_FC= 247 Hz, C₆F₅), 138.0 (dm, ¹J_FC= 254 Hz, 2 ¥ C₆F₅), 127.3

(C-1), 125.7 (i-C₆F₅) 70.7 (Cp), 65.5 (C-4), 63.8 (C-5), 63.3 (C-2)

and 60.3 (C-3).

1188, 1139, 1106, 1001, 856, 837, 818, 799, 711, 678, 651, 569 and

524; d_H(600 MHz; CD₂Cl₂; Me₄Si) 8.76 (1 H, br, OH), 8.35 (1 H,

d, ⁴J = 0.6 Hz, CHN), 6.90 (2 H, m, m-Ph), 4.51 (1 H, ddd, ³J =

2.7 Hz, ⁴J = 1.4 Hz, ⁴J = 0.6 Hz, 3-H), 4.23 (5 H, s, Cp), 4.17 (1

H, dd, ³J = 2.7 Hz, ⁴J = 1.4 Hz, 5-H), 4.02 (1 H, t, ³J = 2.7 Hz,

4-H), 2.27 (3 H, s, p-CH₃) and 2.19 (6 H, s, o-CH₃); d_C(151 MHz;

CD₂Cl₂; Me₄Si) 169.0 (CHN), 147.6 (i-Mes), 133.9 (p-Mes), 129.2

(m-Mes), 127.8 (o-Mes), 126.9 (C-1), 70.1 (Cp), 64.3 (C-2), 63.5

(C-4), 63.1 (C-5), 58.4 (C-3), 20.8 (p-CH₃) and 18.7 (o-CH₃).

Nucleophilic aromatic substitution product from imine (p-S)-

19c: ring closure product 20. The imine (p-S)-19c (350 mg,

0.552 mmol) and tetra-n-butyl ammonium ﬂuoride (349 mg,

1.10 mmol) were dissolved in tetrahydrofuran (10 ml) and the

solution was stirred for two hours. The solvent was removed and

the crude product was puriﬁed by column chromatography (cy-

clohexane : triethylamine = 9 : 1) to give the ring-closure product

20 as a red solid (110 mg, 53.1%). X-Ray quality crystals were

obtained by slow evaporation of a solution of 20 in pentane. Mp

164 ^◦C (DSC); [a]_D²⁰-2174 (c 0.200 in CH₂Cl₂); (found: C, 54.00;

H, 3.08; N, 3.25. C₁₇H₉F₄FeNO requires C, 54.43; H, 2.42; N,

3.73%); n_max(KBr)/cm^-12959, 2931, 2857, 1510, 1485, 1428, 1109,

1000, 952, 820, 740, 709 and 608; d_H(500 MHz; CD₂Cl₂; Me₄Si)

(p-S)-(+)-N -Pentaﬂuorophenyl-1-tert-butyldiphenylsiloxy-2

-iminomethylferrocene ((p-S)-19c). The aldehyde (p-S)-12

(3.93 g, 8.39 mmol), pentaﬂuoroaniline (7.67 g, 41.9 mmol) and

p-toluene sulfonic acid (160 mg, 0.839 mmol) were dissolved in

toluene (40 ml) and heated to 80 ^◦C for three hours. Removal of

the solvent gave the crude product, which was puriﬁed by column

chromatography (cyclohexane : triethylamine = 9 : 1) to give a red

oil. Addition of pentane (100 ml) and subsequent removal of the

solvent_◦to gave the imine (p-S)-19c as a red solid (3.56 g, 67.0%).

Mp 36 C (DSC); [a]²_D⁰+568 (c 0.202 in CH₂Cl₂); (found: C, 63.22;

H, 4.61; N, 2.04. C₃₃H₂₈F₅FeNOSi requires C, 62.57; H, 4.45; N,

2.21%); n_max(KBr)/cm^-12930, 1608, 1516, 1503, 1461, 1428, 1107,

1006, 969, 829, 820, 743, 698, 615 and 571; d_H(600 MHz; C₆D₆;

Me₄Si) 9.06 (1 H, t, ⁴J = 0.5 Hz, ⁵J = 0.5 Hz, CHN), 7.87 (2 H,

m, o-Ph), 7.64 (2 H, m, o-Ph¢), 7.24–7.21 (3 H, m, m-Ph, p-Ph),

8.39 (1 H, br, CHN), 4.62 (1 H, ddd, J = 2.8 Hz, J = 1.5 Hz,

⁴J = 0.6 Hz, 3-H), 4.29 (5 H, s, Cp), 4.29 (1 H, t, ³J = 2.8 Hz, 4-H)

and 4.24 (1 H, dd, ³J = 2.8 Hz, ⁴J = 1.5 Hz, 5-H); d_F(470 MHz;

CD₂Cl₂; CCl₃F) -147.0 (1 F, dd, ³J_FF= 22.0 Hz, ⁵J_FF= 6.6 Hz),

-160.4 (1 F, dd, ³J_FF= 22.0 Hz, ⁵J_FF= 6.6 Hz) (F-6, F-9), -159.6 (1

F, t, ³J_FF= 22.0 Hz), -164.8 (1 F, t, ³J_FF= 22.0 Hz) (F-7, F-8); d_C

(126 MHz; CD₂Cl₂; Me₄Si) 164.5 (CHN), 129.0 (C-1), 71.3 (Cp),

68.1 (C-2), 66.6 (C-4), 64.9 (C-5) and 63.5 (C-3), signals for C₆F₄

were not located; m/z (EI) 375 (M⁺, 100%), 326 (7), 310 (9), 281

(6), 252.1 (6), 216 (37), 187 (12), 121 (28). 56 (14).

7.14–7.09 (3 H, m, m-Ph¢, p-Ph¢), 4.77 (1 H, ddd, J = 2.8 Hz,

⁴J = 1.4 Hz, ⁴J = 0.5 Hz, 3-H), 4.08 (5 H, s, Cp), 3.83 (1 H, dd,

³J = 2.8 Hz, ⁴J = 1.4 Hz, 5-H), 3.67 (1 H, td, ³J = 2.8 Hz, ⁵J =

0.5 Hz, 4-H) and 1.12 (9 H, s, C(CH₃)₃); d_F(564 MHz; C₆D₆;

CCl₃F) -155.6 (2 F, m, o-C₆F₅), -163.2 (1 F, t, J_FF= 21.8 Hz,

p-C₆F₅) and -164.1 (2 F, m, m-C₆F₅); d_C(151 MHz; C₆D₆; Me₄Si)

168.3 (CHN), 140.2 (dm, J_C,Fª 245 Hz, C₆F₅), 138.2 (dm, J_C,F

Acknowledgements

ª 248 Hz, C₆F₅), 137.5 (dm, J_C,Fª 246 Hz, C₆F₅), n.o (i-C₆F₅),

136.0 (o-Ph), 135.8 (o-Ph¢), 133.3 (i-Ph), 132.0 (i-Ph¢), 130.7

(p-Ph), 130.5 (p-Ph¢), 128.24, 128.22 (m-Ph, m-Ph¢), 124.6 (C-1),

71.0 (Cp), 69.4 (C-2), 65.5 (C-4), 63.0 (C-5), 61.3 (C-3), 26.8

(C(CH₃)₃) and 19.6 (C(CH₃)₃); m/z (EI) 633 (M⁺, 100%), 576

(11), 197 (21), 135 (33).

Financial support from the Deutsche Forschungsgemeinschaft

and the Fonds der Chemischen Industrie is gratefully acknowl-

edged. We thank the BASF for a gift of solvents.

Notes and references

(p-S )-(-)-N -Pentaﬂurophenyl-2-iminomethylferrocen-1-ol

((p-S)-2c). The imine (p-S)-19c (4.97 g, 7.85 mmol) and triethy-

lamine trihydroﬂuoride (427 ml, 2.62 mmol) were dissolved in

tetrahydrofuran (30 ml) and the solution was stirred for one hour.

The solvent was removed and the residue was redissolved in

toluene (50 ml) and pentane (200 ml). The solution was stored

at -30 ^◦C overnight, yielding a purple precipitate (1.27 g). The

mother liquor was evaporated to a volume of 30 ml and stored

at -30 ^◦C for another night, yielding a second fraction of the

product (600 mg). The remaining mother liquor was evaporated,

fresh toluene (30 ml) were added and the solution was stored at

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