Versatile reactions of a para-bromophenylacetylide iron (II) derivative and X-ray structure of the fluoro analogue. Synthesis of new redox-active organoiron (II) synthons

Journal of Organometallic Chemistry 670 (2003) 108ꢁ122

/

www.elsevier.com/locate/jorganchem

Versatile reactions of a para-bromophenylacetylide iron(II) derivative

and X-ray structure of the ﬂuoro analogue.

Synthesis of new redox-active organoiron(II) synthons

James Courmarcel ^a, Gildas Le Gland ^a, Loic Toupet ^b, Fre´de´ric Paul ^a,*,

Claude Lapinte ^a,*

^aUMR CNRS 6509, Organome´talliques et Catalyse: Chimie et Electrochimie Mole´culaires, Institut de Chimie, Universite´ de Rennes 1, Campus de

Beaulieu, 35042 Rennes Cedex, France

^bUMR CNRS 6626, Groupe Matie`re Condense´e et Mate´riaux, Universite´ de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France

Received 23 October 2002; received in revised form 15 November 2002; accepted 15 November 2002

Abstract

The synthesis of the new (h²-dppe)(h⁵-C₅Me₅)FeÃ

1,4-(C₆H₄I) (2c) complexes, as well as the solid-state structure of the known (h²-dppe)(h⁵-C₅Me₅)FeÃ

complex are described. The catalytic coupling reactions of the bromo complexes with various alkynes were next investigated.

Starting from the known (h²-dppe)(h⁵-C₅Me₅)FeÃ 1,4-(C₆H₄Br) complex (2b), the synthesis of the (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ

CÅCÃ1,4-(C₆H₄)ÃCÅCÃ CÅCÃ1,4-

H complex (6d) and of the corresponding silyl-protected precursors (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)CÅCÃ Pr/Me) are reported. By use of lithiumÃbromine exchange reactions on 2b, the silyl- (7a; EꢀSi; Rꢀ

SiR₃(6b/6c; Rꢀⁱ

Me) and tin- (7bꢁ7d; EꢀSn; Rꢀ CÅCÃ1,4-(C₆H₄)ER₃are also

Me, Bu, Ph) substituted analogues (h²-dppe)(h⁵-C₅Me₅)FeÃ

isolated. The spectroscopic and electrochemical characterisations of all these new Fe(II)/Fe(III) redox-active building blocks are

C’’ group are determined by means of ¹⁹F-

/

CÅ

/

CÃ

/

1,3-(C₆H₄X) (m-2a/2b; Xꢀ

/

F/Br) and (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ

/

CÅCÃ1,4-(C₆H₄F) (2a)

/

presented and the electronic substituent parameters for the ‘‘(h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

NMR.

Keywords: Aryl halides; Organoiron; Acetylides; Redox-active; Synthesis; Hammett

1. Introduction

iron(III) substituents. Such homopolymetallic com-

plexes are simply obtained following classic

activationꢁdeprotonation synthetic sequence (or ‘‘vinyl-

idene route’’) from the symmetric bridge precursor and

corresponding equivalents of the terminal complex

a

We have been engaged for several years in the study of

redox-active polynuclear organoiron compounds featur-

ing several electroactive (h²-dppe)(h⁵-C₅Me₅)Fe units

connected to a central aromatic unit via alkynyl linkers

/

precursors [2,9ꢁ

distinct endgroups, like (B), have also attracted con-

siderable attention [17ꢁ19]. Actually, the inherent

/

16]. More recently, molecules with

[1ꢁ8]. Depending on their structure and on the oxida-

/

tion state of the iron centres, these symmetric molecules

exhibit electronic properties potentially useful for the

realisation of various molecular-scaled devices [1,2]. As

shown in Scheme 1 for dinuclear representatives,

compounds like (A) can therefore be envisioned as an

aromatic core featuring two identical organoiron(II) or -

/

polarisation of the organic bridge does enlarge the

perspectives opened by such organometallic assemblies

regarding more specific applications, like second har-

monic generation for instance [20ꢁ22]. Until now, these

/

heterobimetallic structures were accessed from a non-

symmetrical mononuclear synthon like (C). This pivotal

building block (C) can often be isolated by reacting an

excess of the organic symmetric dialkyne bridge pre-

cursor with the complex precursor, as reported for

* Corresponding authors.

E-mail addresses: frederic.paul@uni v -rennes1.fr (F. Paul),

claude.lapinte@uni v -rennes1.fr (C. Lapinte).

PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 2 1 3 7 - X

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

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109

Scheme 1.

several Fe(0) [23], Ru(II) [24ꢁ

/

27] or Os(II) [18] com-

species and allowing for the isolation of new organoiron

synthons like (C) bearing the electron-rich ‘‘(h²-

dppe)(h⁵-C₅Me₅)Fe’’ electroactive centre (see Scheme

2).

plexes. Unfortunately, with the electron-rich (h²-

dppe)(h⁵-C₅Me₅)FeX complexes ([Fe]X in Scheme 1),

isolation of the desired mono-metallated complexes (C)

proves difficult by this route. Indeed, the selective and

stepwise activation of only one of the terminal alkyne

functionalities is not observed and formation of a

mixture takes place readily, from which (C) cannot be

cleanly recovered. In this connection, new and versatile

synthetic protocols allowing to isolate compounds like

(B) or (C) with the electron-rich (h²-dppe)(h⁵-C₅Me₅)Fe

endgroup are now highly desirable [2].

2. Results

2.1. Synthesis of halogenated precursors

As reported previously [34], the use of the palladiumÃ

/

copper catalysed coupling reaction in di-iso-propyla-

mine starting from 1 and various 1,4-aryl bromides lead

to isolation of the corresponding iron alkynyls 2a and 2b

in very good yields (Scheme 3). These complexes can be

isolated pure at the gram scale in one step, the excess of

unreacted dihalogeno aryl being removed by washings

or sublimation. From a synthetic standpoint, this route

compares favourably with the more classic vinylidene

route (Scheme 4), starting from (h²-dppe)(h⁵-

C₅Me₅)FeCl (4) and pre-formed para-bromophenylalk-

yne [38].

We have previously developed a ‘‘metalla-Sonoga-

shira’’ coupling reaction, allowing us to specifically

append an iron alkynyl fragment onto various substi-

tuted bromo-aromatics using this simple and efficient

catalytic coupling reaction [28ꢁ31]. Bruce et al. [32,33]

/

also had successfully used such an approach to functio-

nalise various terminal diynyl Mo(II) or W(II) com-

plexes. Thus, starting from the organometallic terminal

alkynyl complex (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

[5,34], the corresponding halogeno-substituted organoir-

on(II) complexes (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,4-

(C₆H₄X) (XꢀF/Br; 2a/2b) or

(h²-dppe)(h⁵-

C₅Me₅)FeÃCÅCÃm,n-(C₅H₄N)Br (m,nꢀ2, 5/3, 4; 3a/

/

CÃ

/

H (1)

/

The catalytic coupling reaction can be extended to

other commercial dihalogenoaromatic substrates, lead-

ing to isolation of the corresponding new meta-sub-

/

stituted isomers (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄X) (XꢀF: m-2a; Xꢀ

similar conditions, we were however not able to isolate

the para-iodo analogue (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ

/

CÅ

/

CÃ/1,3-

3b) were isolated from the commercial dihalogenoaro-

matic precursors in a straightforward way [35]. Given

the huge synthetic potential of aromatic bromides [36],

the Fe(II) alkynyl complexes 2b, 3a and 3b were quite

promising as starting organoiron synthons to access

structures like (B) or (C). Accordingly, such compounds

have been isolated from 3a and 3b, via a second

Sonogashira coupling at the bromine site. Complex 2b

was apparently less reactive under similar conditions

[37]. We know report on simple reactions involving this

/

Br: m-2b; Scheme 3). Under

/

1,4-(C₆H₄I) 2c completely free from unreacted 1,4-

diiodobenzene. Alternatively, when the previous reac-

tion is run with a stoichiometric amount of 1,4-

diiodobenzene,

C₅Me₅)FeÃCÅC]₂Ã

5% by LSI-MS) and remains admixed with 2c. The new

some

dinuclear

[(h²-dppe)(h⁵-

/

/1,4-(C₆H₄) (5) [39] is formed (ca.

110

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

/122

Scheme 2.

complexes m-2a and m-2b, and 2c were characterised by

the usual methods and exhibit the spectroscopic features

expected for such compounds (Table 1).

distance between the para-fluorine atom and the iron

˚

centre is 8.68 A.

2.3. Derivation of Hammett electronic substituent

parameters (ESPs) of the ‘‘(h²-dppe)(h⁵-C₅Me₅)FeÃ

2.2. X-ray structure of (h²-dppe)(h⁵-C₅Me₅)FeÃ

1,4-(C₆H₄F) (2a)

/

CÅ

/

CÃ

/

CÅ

/

CÃ

/

’’ fragment

Deep-orange crystals of the complex 2a were grown

and its solid-state structure has been solved (Fig. 1). The

complex crystallises in the triclinic P1 group, with two

molecules in the asymmetric unit (Section 5). Selected

bond distances and angles are given in Table 2. The

structure shows the classical pseudo-octahedral coordi-

nation geometry around the iron(II) centre, with bond

distances and angles in the usual range [35]. The para-

fluorophenyl mean plane is nearly perpendicular to the

Fe-Cp* centroid vector, as shown by its dihedral angle

When two equivalents of 1 are used, the formation of

the known dinuclear complexes 5 or m-5 [8,39] is not

possible following a one-pot procedure (Scheme 5). Only

traces of 5 or m-5 (around 1%) can be detected in the

reaction media by NMR or LSI-MS after 15 h. This

explains a posteriori why the isolation of 2b and m-2b is

so clean, according to the reaction given in Scheme 3.

No really improved formation of 5 takes place when 1,4-

diiodobenzene is used in place of 1,4-dibromobenzene.

Thus, everything looks as if the reaction would stop

after the first coupling and essentially 2b, m-2b or 2c are

present in the reaction media, among unreacted 1 and

unidentified minor side products. These observations

are very similar to those previously made with 3a and 3b

with the C39ꢁ

/

C40 axis (78.38). The C42-F1 bond also

˚

presents a very classic length (1.364 A) for such type of

˚

bond (ca. 1.363 A) [40], suggesting no particular

interaction with the phenyl ring in this complex. The

Scheme 3.

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

/122

111

Scheme 4.

[37]. The quasi-absence of di-coupling finds possibly its

origin in the electron-releasing effect of the organoir-

on(II) substituent, which deactivates the halogen atom

of the intermediates 2b and 2c or m-2b toward further

oxidative addition (Scheme 6). In order to verify this

hypothesis, we have derived experimentally the Ham-

be exerted by an hydroxy group and explain the low

conversion to the dinuclear complexes 5 or m-5 when

the coupling is attempted with the organoiron bromoar-

yls 2b or m-2b, under the present conditions [29]. In this

respect, the disappointing results obtained with the iodo

analogue 2c, expected to be more reactive, are more

surprising and suggest that other factors than the purely

electronic influence of the organoiron substituent could

come in play in this case [44].

mett ESPs of the ‘‘(h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ/’’

fragment when affixed in meta- or para-positions on

the phenyl ring. These data can easily be obtained from

the fluorinated analogues 2a and m-2a, by means of ¹⁹F-

NMR, using the simple procedure described by Taft et

al. [41,42] in 1963 (Section 5.15). Accordingly, the

2.4. Sonogashira coupling reactions of 2b with organic

alkynes

measurement gives values of ꢂ

/

0.37 and ꢂ0.28 for s_m

/

and s_p, respectively, which indeed confirm a relatively

strong electron-releasing power for the ‘‘(h²-dppe)(h⁵-

As had been done for 3a and 3b [37], we have used a

large excess (10 eq.) of alkyne reactant, in order to

overcome the sluggishness of the second Sonogashira

coupling on 2b or m-2b. We started our investigations

C₅Me₅)FeÃ

/

CÅ

/

CÃ

/

’’ fragment [36,43]. Such electron-

releasing capabilities are stronger than those that would

Table 1

Selected spectroscopic data and yields for (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ/Ar complexes

a

b

Compound

Ar

IR

n_CÅC(cm^ꢂ1

¹H-NMR

d_Cp*(ppm)

³¹P-NMR

d_dppe(ppm)

¹³C-NMR

Yield

(%)

)

d_CÅC(ppm)

c

2a

m-2a

1,4-(C₆H₄)F

1,3-(C₆H₄)F

1,4-(C₆H₄)Br

1,3-(C₆H₄)Br

1,4-(C₆H₄)I

2057

2044

2054

1.53

1.50

1.58

1.50

1.52

1.49

1.50

1.55

1.54

101.7

101.1

101.4

101.1

101.4

136.9 (39 ^d)/118.8

74

72

80

55

e

143.5 (40 ^d)/119.4

c

e

2b

m-2b

2c

142.2 (39 ^d)/119.5

f

2060/2033

2052

144.6 (39 ^d)/119.6

143.5 (40 ^d)/119.4

g

h

m-6a

6b

6c

1,3-(C₆H₄)CÅ

1,4-(C₆H₄)CÅ

1,4-(C₆H₄)SiMe₃

/

CÃ

/

Ph

2134, 2046

Si(ⁱPr)₃2145, 2042

101.4

/

67

/

101.3

101.7

101.6

146.1 (39 ^d)/122.0, 110.5/91.8

146.5 (39 ^d)/122.1, 108.4/94.2

85

70

81

78

/

SiMe₃

H

2146, 2038

f

i

6d

7a

/

2105, 2049/2030

2053

2055

146.0 (39 ^d)/121.8, 85.9/78.1(250 )

Not obs./121.5

7b

7c

1,4-(C₆H₄)SnMe₃

1,4-(C₆H₄)SnBu₃

1,4-(C₆H₄)SnPh₃

139.4 (38 ^d)/121.4

/

141.6 (39 ^d)/120.6

j

2061

2058

j

7d

/

a

In CH₂Cl₂/KBr windows unless precised.

In C₆D₆unless precised.

Data from [35].

b

c

d

e

f

³J_PCcoupling in Hz.

In CDCl₃.

Fermi coupling, see [52].

In CD₂Cl₂.

Spectroscopic yield.

¹J_CHcoupling in Hz.

In Nujol suspension/KBr windows.

g

h

i

j

112

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ122

/

2135 cm^ꢂ1. This evidences that the quasi-quantitative

replacement of the second bromine atom by an alkynyl

substituent in m-2b is envisionable using a Sonogashira

coupling procedure, but remains difficult, since largely

disfavoured by kinetics. Purification of m-6a was not

attempted and we focused on Sonogashira couplings

between 2b, the para-substituted analogue of m-2b, and

silylated alkynes (Scheme 8). Indeed, para-substitution

is much more attractive when a strong interaction is

sought with the organoiron(II) substituent, while sily-

lated alkynes are potential precursors of terminal

alkynes [45,46].

After optimisation of these reactions, the desired new

complexes

(C₆H₄)CÅCÃ

tatively isolated from 2b after 40ꢁ

(h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

Pr/Me; 6b/6c) could be quanti-

64 h, using a fivefold

/

CÃ

/

1,4-

/

SiR₃(Rꢀⁱ

/

excess of organic alkyne (Scheme 8). The compounds

were obtained pure after the usual work up, based on

³¹P- and ¹H-NMR data, and were characterised by LSI-

MS. As for m-6a, the presence of the new alkynyl

substituent in 6b and 6c does also give rise to a weak

additional mode in the infrared region corresponding to

the organic alkynyl stretch, and to characteristic signals

in ¹³C-NMR (Table 1). Importantly, given the volatility

of trimethylsilylacetylene, the corresponding coupling

reaction was performed in a sealed vessel and care must

be taken to prevent explosion hazards by use of a

screening shield.

Complex 6c could also be isolated with 78% yield by

performing a metalla-Sonogashira coupling between 1

and the pre-synthesised 1-(para-bromophenyl)-2-tri-

methylsilylacetylene (Scheme 9). However, on synthetic

grounds, given that the organic alkyne reactant is used

in excess in both cases, our former approach (Scheme 8)

is more interesting since 6c is much more readily purified

from volatile trimethylsilylacetylene than from 1-(para-

bromophenyl)-2-trimethylsilylacetylene.

Fig. 1. Solid-state structure of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄F) (2a).

/

CÅ

/

CÃ1,4-

/

Table 2

˚

Selected bond lengths (A) and angles (8) for (h²-dppe)(h⁵-

1,4-(C₆H₄)F (2a)

C₅Me₅)FeCÅ

/

CÃ

/

Selected bond lengths

[4]

FeÃ

C37Ã

C38Ã

C39Ã

/

Cent. ^a(Cp*)

P1

P2

1.740

2.1877(8) C41Ã

2.1955(11) C42Ã

C40Ã

/

C41

C42

C43

C44

C39

F1

1.386(4)

1.352(5)

1.377(5)

1.394(4)

1.393(4)

1.364(4)

/

/C37

1.902(2)

1.217(3)

1.444(3)

1.406(4)

C43Ã

C44Ã

C42Ã

/

C38

C39

C40

/

Selected bond angles

[4]

P1Ã

P2Ã

FeÃ

C37Ã

/

FeÃ

/

P2

86.51(3)

82.76(7)

86.46(7)

179.4(2)

175.3(2)

C40Ã

C41Ã

C43Ã

FeÃ

C40

/

C39Ã

C42Ã

/

C44

C43

F1

116.8(2)

122.3(3)

119.3(3)

118.4(3)

/

/C37

/

The silylated alkynyl substituent in either 6b or 6c can

be removed using classic deprotection sequences to give

/

/C37

/

C37Ã

/C38

/

F1

the terminal alkynyl complex (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

b

/

C38Ã

/

C39

/

Cent. ^a(Cp*)/C39Ã

/

73.3

CÅ

/

CÃ

/

1,4-(C₆H₄)CÅ

/

CÃ

/

H (6d; Scheme 10) [47ꢁ49]. The

/

tris(iso-propyl)silyl substituent in 6b is quite robust and

deprotection has to be performed with equimolar

amounts of tetrabutylammonium fluoride (TBAF) at

50 8C. The purification of 6d from the TBAF residual

salts proves, however, rather difficult.

In this respect, the trimethylsilyl-substituted complex

6c is a better precursor to access 6d. Deprotection takes

place readily with potassium carbonate under milder

conditions and purification of the product is also much

easier. After toluene extraction and pentane washings,

pure samples of 6d can be obtained, as indicated by ³¹P-

and ¹H-NMR. This compound was characterised by

LSI-MS and the usual spectroscopic techniques (Table

1). The presence of a terminal hydrogen atom is

evidenced by specific signatures in infrared (n_CHat

a

Centroid vector.

Dihedral angle.

b

with the least deactivated meta-bromo complex m-2b

(Scheme 7). Commercial phenylacetylene was preferred

for the testing procedure, since 1 complicates the

purification and analysis procedures. Following the

usual work up, ca. 67% of coupled product m-6a is

formed after 15 h under reflux admixed with unreacted

m-2b (27%) and traces of an unidentified complex (6%).

The new complex (h²-dppe)(h⁵-C₅Me₅)FeÃ

Ph (m-6a) could be characterised by spec-

troscopic methods (Table 1) and LSI-MS. Its new

/

CÅ

/

CÃ/1,3-

(C₆H₄)CÅ

/

CÃ

/

alkyne stretch shows up very weakly in infrared at

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

/122

113

Scheme 5.

1

3307 cm^ꢂ1), in H-NMR (d_Hat 2.84 ppm) and ¹³C-

Lin and co-workers [51] with closely related Ru(II)

acetylides, but apparently failed in some instances. This

is not surprising, since the anionic intermediate (2^ꢂ) is

expected to be very reactive, especially given the

electron-releasing capability exerted by the organoiro-

n(II) substituent. We have, therefore, not attempted to

isolate the lithium salt of 2^ꢂand have preferred to trap

NMR (¹J_CHof 250 Hz for Å

/

CÃH), and by the

/

disappearance of the trialkylsilyl-substituent signals.

The 50 cm^ꢂ1infrared shift of the additional alkyne

stretch between 6b or 6c and 6d is also diagnostic of the

removal of the trimethylsilyl group.

it, in situ, with chlorotrimethylsilane at ꢂ

(Scheme 11).

Under such conditions, the formation of 2^ꢂtakes

place since the new complex (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,4-(C₆H₄)-SiMe₃(7a) is isolated with good yields

/

80 8C

2.5. HalogenÃ

/

lithium exchange reactions of 2b and

reaction with electrophiles

/

In the previous couplings, 2b behaves as an electro-

philic synthon, the bromine substituent being replaced

by an alkynyl nucleophile. From a synthetic standpoint,

it was also interesting to be able to use 2b as a

nucleophilic synthon. In principle, this is possible if a

/

and was fully characterised by spectroscopic methods

and LSI-MS (Table 1). We next decided to extend this

protocol to various tin electrophiles (7b and 7d), since

tin compounds should preserve an anion-like reactivity

at the para-carbon site [36]. The corresponding com-

bromineÃ

/

lithium exchange reaction can be realised with

2b [36]. Such a reaction has seldom been performed on

organometallic substrates [50]. It was notably used by

plexes (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ

/

1,4-(C₆H₄)Ã

/

SnR₃

Scheme 6.

114

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ122

/

Scheme 7.

(Rꢀ

/

Me: 7b; Rꢀ

/

Bu: 7c; Rꢀ

/

Ph: 7d) were isolated in a

probe, when they are in close proximity [55ꢁ57]. Indeed,

/

similar fashion (Scheme 11). The reaction works appar-

ently similarly in all cases, as revealed by infrared, LSI-

MS and NMR spectroscopy (Table 1), but leads to a

tractable product only in the case of 7b. Indeed, 7b can

be isolated pure as a brown powder, while 7c and 7d

have a gummy consistency limiting their handling and

evaluation of the corresponding yields. The presence of

the tin substituent in 7b is also evidenced by the

a transition metal nucleus could exert an unwanted

influence on the paramagnetic term in the shift of the

fluorine atom [56,58ꢁ60]. However, with 2a, the crystal

/

structure data indicate that the iron and fluorine atoms

˚

are more than 8 A apart, and also suggest that this

˚

distance will be more than 7 A for the meta isomer m-

2a. These distances seem sufficient for neglecting any of

the unwanted effects on the fluorine shift previously

envisioned.

characteristic signal at ꢂ

30.1 ppm in ¹¹⁹Sn{¹H}-NMR.

/

Accordingly, the values presently found for ‘‘(h²-

dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ/C’’ are in the range reported by

Stewart and Treichel [61] for various organometallic

complexes. They also appear consistent with the value of

s_preported for the ‘‘(PPh₃)₂(h⁵-C₅Me₅)Ru’’ fragment

3. Discussion

Recent investigations on mononuclear model com-

plexes have shown that the alkynyl bridge mediates very

efficiently the electronic interaction between the metal-

based d-orbitals and the p- and s-manifolds based on

the aromatic group, regardless of the oxidation state of

(ꢂ0.81) by Sato and et al. [62], and obtained from

/

electrochemical measurements. Notably, the electron-

releasing power for these s-alkynyl complexes is much

more pronounced than for the para- or meta-ferrocenyl

substituents (ꢂ

/

0.18 and ꢂ0.15, respectively), where the

/

the metal [52ꢁ54]. Accordingly, the derivation of the

/

metal centre is connected to the organic substrate in a p-

fashion [63].

Aryl bromides presenting transition metal complexes

as substituents are increasingly used as reactants in

related coupling reactions to access larger metal-con-

Hammett ESPs effected here for the metal fragment by

¹⁹F-NMR from 2a and m-2a gave rather large and

negative values on the Hammett scale. The organoiron

substituent on the halide complexes 2a and 2c or m-2a

and 2b behaves apparently as an electron-releasing

group via both the p- and s-molecular orbitalar

manifolds, as suggested by the values of the inductive

taining architectures [50,64ꢁ

point of view, the electronic effect exerted by the ‘‘(h²-

dppe)(h⁵-C₅Me₅)FeÃ

CÅC’’ substituent is very interest-

/73]. Thus, from a synthetic

/

(s_Iꢀ

/

ꢂ

/

0.20) and resonant (s_Rꢀ

/

ꢂ0.17) contributions.

/

Some doubts have been raised regarding the appro-

priateness of NMR spectroscopy for obtaining the ESPs

of metallic substituents bonded directly to the phenyl

ring, given the possibility to have a specific interaction

between the metal centre and the nucleus used as a

ing, since mononuclear organoiron(II) aryl bromides

like 2b or m-2b can easily be accessed in one step and

isolated pure from the corresponding commercial di-

bromo precursors. Actually, reports on acetylide com-

plexes possessing a halogenated aryl group are scarce

Scheme 8.

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

/122

115

Scheme 9.

[44,74], and preparations of some of these compounds

appear less attractive from a strictly synthetic point of

view [74]. We also show here that the remaining bromine

atom in these organometallic synthons remains reactive

and that 2b can be used in classic coupling reactions

undergone by organic aryl bromides, similarly to what

has been previously stated with 3a and 3b [37]. Thus, the

reaction reported in Scheme 3 constitutes an efficient

mean to discriminate the two halogen functions and

allows for further functionalisation of the iron-substi-

tuted phenyl moiety, as illustrated by the synthesis of 6b

and 6c. In this connection, 2b and m-2b can be

considered as new organometallic synthons that can be

opposed to various nucleophiles in Sonogashira cou-

plings. However, as established during this work, the

electron-releasing power of iron(II) alkynyl substituent

limits somewhat the synthetic scope of such a reaction,

since rather harsh conditions, high catalyst loadings and

excess alkyne substrate are needed for a quantitative

coupling to take place. Notably, closely related Sonoga-

shira couplings were recently reported with a para-iodo

phenylacetylide complex of Ru(II) by Humphrey and

co-workers [44]. Interestingly, these reactions take place

under much milder conditions, suggesting an increased

reactivity of the corresponding para-iodo Cl(h²-

should not suffer from the electronic effect of the

organoiron(II) group. The synthetic scope that species

like 6d ((C) in Scheme 1) possess to access unsymme-

trical di- or polynuclear complexes have recently been

underlined by several groups for related ruthenium(II)

or osmium(II) acetylides [17ꢁ

species like 7b should also present a very rich chemistry

as nucleophile in catalytic Stille couplings [75ꢁ77].

/

19,44]. Alternatively, a

/

Finally, it is worth recalling that all Fe(II) acetylides

synthesised during this work are redox-active and

present a chemically reversible oxidation potential well

above that of the standard calomel electrode (SCE) used

as reference (Table 3). The potential shifts induced by

replacement of the aryl para-bromo substituent are

rather slight (ca. 65 mV), but are in line with the

electron-releasing capabilities of the new substituents

(SnMe₃SnBu₃ꢀ

SiMe₃ꢀCÅCÃH), while the seemingly counter-intuitive

order found for the halogen substituents (FꢀBrꢀI)

has already been observed and discussed for the related

series of (h²-dppe)(h⁵-C₅Me₅)FeX complexes (Xꢀ

F,

/

SnPh₃SiMe₃ꢀ

/

CÅ

/

CÃ

/

Si(ⁱPr)₃ꢀ

/

CÅ

/

CÃ

/

Cl, Br, I) [78]. Without surprise [43], the terminal para-

alkyne renders the oxidation more difficult relative to

2b, while all other substituents facilitate it, the effect

being more prominent for tin derivatives 7b and 7c. This

is in line with the slight carbanionic character expected

the para-carbon of the aryl ring. The comparison

between 6c and 7a also shows that inserting an

dppe)₂RuÃ

/

CÅ

/

CÃ

/

1,4-(C₆H₄I) complex relative to 2c.

In contrast, 6d or 7b can be envisioned as nucleophilic

organoiron(II) synthons and their coupling reactions

Scheme 10.

116

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

/122

Scheme 11.

acetylenic unit between the aryl ring and trimethylsilyl

substituent ‘‘decreases’’ its electronic influence of ca. 30

mV.

the realisation of larger symmetric or non-symmetric

organometallic architectures containing at least one

redox-active ‘‘(h²-dppe)(h⁵-C₅Me₅)FeÃ

organoiron(II) fragment [2,44].

/

CÅ

/

CÃ

/

(C₆H₄)’’

4. Conclusions

5. Experimental

In this contribution, we have reported efficient

synthetic ways to access new organoiron(II) phenylace-

Reagent grade tetrahydrofuran (THF), diethylether

and n-pentane were dried and distilled from sodium

benzophenone ketyl prior to use. Acetonitrile was dried

on P₂O₅and distilled over Na₂CO₃and di-iso-propyla-

mine was distilled over NaOH before use. Pentamethyl-

cyclopentadiene was prepared according to the

published procedure and other chemicals were used as

tylides presenting Br, I, CÅ

/

CÃ/H or SnR₃substituents on

the aryl ring and have fully characterised these species.

Considering the well-known reactivity of the pre-cited

functional groups, these new Fe(II) synthons constitute

promising non-symmetric building blocks to access

heterobinuclear analogues of 5 and m-5, but also for

Table 3

Electrochemical data for (h²-dppe)(h⁵-C₅Me₅)FeÃ

a

/

CÅ

/

CÃAr complexes

/

b

Compound

Ar

DE_p(V)

E₀(V)

i_c/i_a

References

2a

m-2a

2b

1,4-(C₆H₄)F

1,3-(C₆H₄)F

1,4-(C₆H₄)Br

1,3-(C₆H₄)Br

1,4-(C₆H₄)I

0.08

0.09

0.08

0.09

0.08

0.12

0.08

0.10

ꢂ

/

0.15

0.11

0.13

0.10

0.12

0.13

0.14

0.12

0.11

0.16

0.18

0.17

0.16

1

[35]

This work

ꢂ

/

c

ꢂ

/

[35]

m-2b

2c

ꢂ

/

This work

ꢂ

/

m-6a

6b

6c

1,3-(C₆H₄)CÅ

1,4-(C₆H₄)CÅ

1,4-(C₆H₄)SiMe₃

/

CÃ

/

Ph

ꢂ

/

Si(ⁱPr)₃

SiMe₃

H

ꢂ

/

ꢂ

/

6d

7a

/

ꢂ

/

ꢂ

/

7b

7c

1,4-(C₆H₄)SnMe₃

1,4-(C₆H₄)SnBu₃

1,4-(C₆H₄)SnPh₃

ꢂ

/

ꢂ

/

7d

ꢂ/

a

All E values in V vs. SCE. Conditions: CH₂Cl₂solvent, 0.1 M [n-Bu₄N^ꢃ][PF₆^ꢂ] supporting electrolyte, 20 8C, Pt electrode, sweep rate 0.100

V s^ꢂ1. The ferrocene/ferrocenium (Fc/Fc^ꢃ) was used as an internal calibrant for potential measurements [90].

b

E₀values corrected for Fc/Fc^ꢃat 0.460 V vs. SCE in CH₂Cl₂.

The value of 0.12 V previously reported was re-determined (0.128 V).

c

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

/122

117

received. All manipulations were carried out under

argon atmosphere using Schlenk techniques or in a

Jacomex 532 dry box under nitrogen. Transmittance

FTIR spectra were recorded using a Bruker IFS28

spectrometer, using a Nernst Globar source and a KBr

ppm) 8.10ꢁ

/

6.95 (m, 22H, H_Ar/dppe

ꢃ

/

H_ArBr); 6.20 (d, 2H,

¹J_PF

CH(ArBr)); 3.30 (m, 2H, CH_2dppe); 2.70 (m, 2H,

ꢀ

/

7.2 Hz, H_ArBr); 5.02 (broad singlet, 1H, Ä

/

CH_2dppe); 1.59 (s, 15H, C₅(CH₃)₅). ¹³C{¹H}-NMR (d,

2

CDCl₃, 50 MHz, ppm) 360.4 (t, J_CP

ꢀ

/

34 Hz, FeÄ

C_ArBr); 101.1

(s, C₅(CH₃)₅); 29.6 (m, CH_2dppe); 10.8 (s, ¹J_CH

128 Hz,

/

C Ä

/

separator with a DTGS detector (400ꢁ

/

7500 cm^ꢂ1). The

C); 136.0ꢁ

/

119.8 (m, FeÄ

/

CÄ/CH, C_Ar/dppe

ꢃ

/

Raman spectra of m-2b were obtained by diffuse

scattering on a solid sample in a sealed glass tube and

ꢀ

/

C₅(CH₃)₅). The vinylidene salt (1.246 g, 1.362 mmol) is

then stirred 1 h in THF (25 ml), in the presence of excess

potassium tert-butoxide (0.250 g, 2.212 mmol). After

evacuation of the solvent and extraction with toluene,

recorded in the 100ꢁ

3300 cm^ꢂ1range (Stokes emission)

/

using a Bruker RFS 100 spectrometer with a laser

excitation source at 1064 nm. Under the same condi-

tions, m-2a presented a strong fluorescence, which

precluded the observation of meaningful Raman lines.

High-field NMR spectra experiments were performed

on a multinuclear Bruker 300 MHz or 200 MHz

instrument (AM300WB and 200DPX). Chemical shifts

are given in parts per million relative to tetramethylsi-

the desired brownish-orange (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,4-(C₆H₄)Br (2b) complex is isolated and ad-

/

mixed with a degradation product. Concentration of the

extract to 15 ml and subsequent precipitation with n-

pentane (15 ml) gives 2b in low yield.

1

lane (TMS) for H- and ¹³C-NMR spectra, CFCl₃for

5.2. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄I) (2c)

/

CÅ

/

CÃ/1,4-

¹⁹F-NMR spectra, H₃PO₄for ³¹P-NMR spectra and

SnMe₄for ¹¹⁹Sn-NMR spectra. Cyclic voltammograms

were recorded using a PAR 263 instrument. LSI-MS

analyses were done at the ‘‘Centre Regional de Mesures

Physiques de l’Ouest’’ (CRMPO) on a high-resolution

MS/MS ZabSpec TOF Micromass spectrometer (8 kV).

Elemental analyses were performed at the Centre for

Microanalyses of the CNRS at Lyon-Solaise, France.

In

a

Schlenk tube, 0.400

g

of (h²-dppe)(h⁵-

of

C₅Me₅)FeÃ

/

CÅCH (1; 0.650 mmol), 0.046

/

g

(PPh₃)₂PdCl₂(0.065 mmol, 10%), 0.025 g of CuI (0.13

mmol, 20%), 0.380 g of 1,4-diiodobenzene (1.15 mmol)

and 20 ml of di-iso-propylamine are introduced under

argon. The reaction mixture is refluxed for 14 h and the

amine is removed in vacuum. The dark residue is then

extracted with toluene (10 ml) and filtered on a celite

pad. Precipitation from the toluene with n-pentane (7

ml), followed by filtration and repeated washings with

The syntheses of complexes (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ (1), CÅCÃ1,4-

(h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄X) (2a and 2b; Xꢀ

F, Br) and (h²-dppe)(h⁵-

C₅Me₅)Fe(Cl) (4) have been previously reported

[35,79,80], while Me₃SiÃCÅCÃ1,3-(C₆H₄)Br and HÃ

CÅCÃ1,4-(C₆H₄)Br were obtained following literature

procedures [73,81].

/

/H

/

cold acetonitrile (ꢂ

(2ꢄ

5 ml), yield the desired (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,4-(C₆H₄I) complex (2c) as an orange powder

/

30 8C, 2ꢄ3 ml), then n-pentane

/

(0.508 g total), admixed with starting 1,4-diiodobenzene

(ca. 2 eq.). MS (positive LSI, 3-NBA, m/z) 816 ([(h²-

5.1. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄Br) (2b) by the vinylidene route

/

CÅ

/

CÃ

/

1,4-

dppe)(h⁵-C₅Me₅)FeCÅ

/

C(C₆H₄I)]^ꢃ,

15%);

5%);

690

589

([(dppe)(C₅Me₅)FeCÅ

/

C(C₆H₄)ꢃ

1]^ꢃ,

/

([(dppe)(C₅Me₅)Fe]^ꢃ, 65%). FTIR (KBr/Nujol, n,

(h²-dppe)(h⁵-C₅Me₅)Fe(Cl) (4; 1.006 g, 1.610 mmol),

NH₄PF₆(0.270 g, 1.656 mmol) and 4-bromophenylace-

tylene (0.350 g, 1.930 mmol) were suspended in 40 ml

methanol and the solution was stirred 12 h at ambient

temperature. The initially green solution turns brown.

After removal of the solvent, the orange residue was

extracted with dichloromethane and the extract concen-

trated in vacuo and precipitated with excess n-pentane.

Several washings with ether yielded the slightly air-

cm^ꢂ1) 2150 (s, FeÃ

/

CÅ

/

C). H-NMR (200 MHz, C₆D₆,

1

d, ppm) 7.92 (m, 4H, H_{ortho/Ar/dppe}); 7.43ꢁ6.76 (m, 20H,

/

H_ar); 2.57 (m, 2H, CH_2dppe); 1.80 (m, 2H, CH_2dppe); 1.50

(s, 15H, C₅(CH₃)₅). ¹³C{¹H}-NMR (50 MHz, C₆D₆, d,

2

ppm) 143.5 (t, J_CP

ꢀ

/

40 Hz, FeÃ

CÅC); 88.6 (s, C₅(CH₃)₅); 87.3

I); 31.4 (m, CH_2dppe); 11.0 (s, J_CH

C₅(CH₃)₅).

/

C Å

/

C); 140.5ꢁ128.0

/

(phenyls); 120.3 (s, FeÃ

/

1

(s, C Ã

/

ꢀ126 Hz,

/

sensitive brownish-orange [(h²-dppe)(h⁵-C₅Me₅)FeÄ

/

CÄ

/

5.3. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄F) (m-2a)

/

CÅ

/

CÃ/1,3-

CH{1,4-(C₆H₄)Br}^ꢃ][PF₆^ꢂ] complex (1.246 g, 1.362

mmol, 85%). MS (positive LSI, 3-NBA, m/z) 816

([(dppe)(C₅Me₅)FeCÄ

/

CHÃ

C(C₆H₄)ꢃ

/

(C₆H₄Br)]^ꢃ,

1]^ꢃ,

7%);

³₄1%);

690

The reaction was effected as described above from

CH (1; 0.325

mmol) and 2.5 eq. of 3-bromofluorobenzene (0.090 ml,

0.200 g of (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

([(dppe)(C₅Me₅)FeCÅ

/

589

([(dppe)(C₅Me₅)Fe]^ꢃ, 100%). FTIR (KBr/Nujol, n,

cm^ꢂ1) 1617 (s, FeÄ C). ³¹P-NMR (d, CDCl₃, 81

CÄ

MHz, ppm) 87.5 (s, 2P, dppe); ꢂ142.9 (septuplet, 1P,

712 Hz, PF₆). H-NMR (d, CDCl₃, 200 MHz,

/

0.812 mmol). The desired complex (h²-dppe)(h⁵-

/

C₅Me₅)FeÃ

/

CÅ

/

CÃ

/

1,3-(C₆H₄)F (m-2a) was isolated as

an orange solid (0.171 g, 0.240 mmol, 74%). Anal. Calc.

1

¹J_PF

ꢀ

/

118

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ122

/

for C₄₄H₄₃F₁P₂Fe₁: C, 74.58; H, 6.12; F, 2.68. Found:

C, 74.05; H, 5.99; F, 2.28%. MS (positive LSI, 3-NBA)

brown solid, admixed with starting complex (m-2a;

27%) and traces of an unidentified side product (ca.

m/z 708 ([(dppe)(C₅Me₅)FeCÅ

([(dppe)(C₅Me₅)FeCÅC(C₆H₄)ꢃ

([(dppe)(C₅Me₅)Fe]^ꢃ, 30%). FTIR (KBr/Nujol, n,

cm^ꢂ1) 2032 (s, CÅC). ¹⁹F{¹H}-NMR (d, C₆D₆, 188

MHz, ppm) ꢂ

115.2 (s, C₆H₄F). ¹H-NMR (d, C₆D₆, 200

MHz) 7.95 (m, 4H, H_{ortho//Ph/dppe}); 7.29ꢁ6.94 (m, 20H,

H_Ar/dppeH_ArF); 2.57 (m, 2H, CH_2dppe); 1.80 (m, 2H,

CH_2dppe); 1.50 (s, 15H, C₅(CH₃)₅). ¹³C{¹H}-NMR (d,

CDCl₃, 50 MHz, ppm) 163.5 (d, ¹J_CF

242 Hz, FÃC_Ar);

143.5 (t, ²J_CPC); 133.2 (d, ³J_CF

40 Hz, FeÃC Å ca. 20

Hz, CÅCÃC_ArF); 139.8ꢁ128.0 (m, 8C_Ar/dppe1 C Ã

H_ArF); 125.1 (d, J_CFH_ortho/ArF);

ca. 148 Hz, C Ã

119.4 (s, FeÃCÅC); 116.9 (d, J_CF

162 Hz, C ÃH_ArF); 110.1 (d, J_CF

165 Hz, C ÃH_ArF); 88.4 (s, C₅(CH₃)₅); 31.3 (m,

CH_2dppe); 10.8 (s, J_CH

/

C(C₆H₄F)]^ꢃ, 100%); 691

5%).

([(dppe)(C₅Me₅)FeÃ

655 ([(dppe)FeÃCÅ

([(dppe)(C₅Me₅)Fe]^ꢃ, 55%). FTIR (KBr/Nujol, n,

cm^ꢂ1) 2135 (vw, CÅ C). ¹H-NMR

C); 2045 (vs, CÅ

(200 MHz, C₆D₆, d, ppm); 8.03ꢁ6.90 (m, 29H, m-

C₆H₄ꢃC₆H₅ꢃ4C₆H_5dppe); 2.61 (m, 2H, CH_2dppe); 1.80

(m, 2H, CH_2dppe); 1.52 (s, 15H, C₅(CH₃)₅).

MS

(positive-LSI,

CÅC(C₆H₄)CÅ

C(C₆H₄)CÅCÃ

3-NBA,

m/z)

790

100%);

/

2]^ꢃ,

5%);

589

/

CÃ

/

Ph]^ꢃ,

/

Ph]^ꢃ, 10%); 589

/

ꢃ

/

ꢀ

/

ꢀ

/

ꢀ

/

5.6. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)ÃCÅCÃ

Si(ⁱPr)₃(6b)

/

CÅ

/

CÃ/1,4-

/

ꢃ

/

2

ꢀ

/

4

1

/

ꢀ

/

ca. 20 Hz, J_CH

ꢀ

/

Starting from 0.500 g of (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÃ1,4-(C₆H₄Br) (2b; 0.650 mmol), 0.046

/

CÅ

/

3

1

/

ꢀ

/

ca. 21 Hz, J_CH

ꢀ

/

g

of

/

(PPh₃)₂PdCl₂(0.065 mmol, 10%), 0.025 g of CuI (0.13

mmol, 20%), in 35 ml of di-iso-propylamine are

introduced and 0.73 ml of tris(iso-propyl)silylacetylene

is syringed (3.25 mmol) under argon. The reaction

mixture is refluxed for 40 h and the amine is removed

in vacuum. The dark residue is then extracted with

toluene and filtered on a celite pad. Evaporation of

toluene followed by repeated washings with cooled

1

ꢀ126 Hz, C₅(CH₃)₅).

/

5.4. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄Br) (m-2b)

/

CÅ

/

CÃ

/

1,3-

The reaction was effected as described above for

compound 2c with 2.0 eq. of 3-dibromobenzene (0.150

ml, 1.30 mmol). The desired (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

acetonitrile (ꢂ

ml) yield the desired (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)ÃCÅCÃ

Si(ⁱPr)₃complex (6b) as dark orange

powder (0.479 g, 0.55 mmol, 85%). MS (positive LSI,

3-NBA, m/z) 871 ([(dppe)(C₅Me₅)FeÃCÅCÃ1,4-

(C₆H₄)ÃCÅCÃ 1], 20%); 589 ((dppe)(C₅-

Si(ⁱPr)₃ꢃ

Me₅)Fe, 100%). FTIR (KBr/Nujol, n, cm^ꢂ1) 2145 (m,

CÅCÃSi), 2044 (s, FeÃCÅ

C). ¹H-NMR (200 MHz,

C₆D₆, d, ppm) 7.91 (m, 4H, H_{ortho/Ar/dppe}); 7.45ꢁ6.98

(m, 20H, H_Ar); 2.54 (m, 2H, CH_2dppe); 1.78 (m, 2H,

/

30 8C, 2ꢄ

/

3 ml) and n-pentane (2ꢄ

/

3

CÅ

orange powder (0.400 g, 0.52 mmol, 80%). MS (positive

LSI, 3-NBA) m/z 769 ([(dppe)(C₅Me₅)FeCÅCÃ

(C₆H₄Br)ꢃ

1]^ꢃ, 70%); 690 ([(dppe)(C₅Me₅)FeCÅ

C(C₆H₄)ꢃ

1]^ꢃ, 10%); 589 ([(dppe)(C₅Me₅)Fe]^ꢃ,

100%). FTIR (KBr/Nujol, n, cm^ꢂ1) 2048, 2022 (m,

CÅ

C). Raman (Neat sample, n, cm^ꢂ1) 2024, 2047 (s, CÅ

/

CÃ

/

1,3-(C₆H₄Br) complex (m-2b) is isolated as an

/

CÅCÃ1,4-

/

1

C). H-NMR (200 MHz, C₆D₆, d, ppm) 7.81 (m, 4H,

/

H_{ortho/Ar/dppe}); 7.40ꢁ6.90 (m, 19H, H_Ar/dppeH_ArBr);

/

ꢃ

/

7.78 (m, 1H, H_ArBr); 2.52 (m, 2H, CH_2dppe); 1.77 (m,

2H, CH_2dppe); 1.58 (s, 15H, C₅(CH₃)₅). ¹³C{¹H}-NMR

CH_2dppe); 1.48 (s, 15H, C₅(CH₃)₅); 1.21ꢁ1.02 (m, 21H,

/

Si[CH(CH₃)₂]₃). ¹³C{¹H}-NMR (50 MHz, C₆D₆, d,

2

C, J_PC

2

(50 MHz, C₆D₆, d, ppm) 144.6 (t, FeÃ

/

C Å

/

ꢀ

/

39

ppm) 146.1 (t, FeÃ

(phenyls); 122.0 (s, FeÃ

C ÃCÅC); 110.5 (s, SiÃCÅ

C₅(CH₃)₅); 31.5 (m, CH_2dppe); 19.5 (s, J_CH

Si[CH(CH₃)₂]₃); 12.3 (s, 124

¹J_CH

Si[CH(CH₃)₂]₃); 11.0 (s, J_CH

/

C Å

/

C, J_PC

ꢀ

/

39 Hz); 140.5ꢁ

/

128.0

2

Hz); 140.1ꢁ123.0 (phenyls); 123.0 (s, BrÃC); 119.6 (s,

ca. 4 Hz); 88.3 (s, C₅(CH₃)₅); 31.1 (m,

/

CÅ

/C); 118.0 (s, J_CH

ꢀ/10 Hz,

3

C, J_PC

FeÃ

/

CÅ

/

ꢀ

/

C); 91.8 (s, SiÃ

/

C Å

/

C); 88.6 (s,

1

CH_2dppe); 10.7 (s, J_CH

1

ꢀ/126 Hz, C₅(CH₃)₅).

ꢀ

/

126 Hz,

Hz,

ꢀ

/

5.5. Coupling of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)Br with phenylacetylene (m-6a)

/

CÅ

/

CÃ/1,3-

ꢀ

/126 Hz, C₅(CH₃)₅).

1

5.7. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)ÃCÅCÃSiMe₃(6c)

/

CÅ

/

CÃ/1,4-

The coupling was attempted as usual (see above),

from 0.210 g of complex m-2b (0.33 mmol), 0.020 g of

/

bis(triphenylphosphine)dichloropalladium

complex

In

a

Schlenk tube, 0.500

g

of (h²-dppe)(h⁵-

(0.03 mmol), 0.010 g of copper iodide (0.06 mmol) and

0.3 ml of phenylacetylene (3.30 mmol) in 10 ml of di-iso-

propylamine. The reaction mixture is refluxed for 15 h,

the solvent is then removed in vacuum and the brown

C₅Me₅)FeÃ

/

CÅCÃ1,4-(C₆H₄Br) (2b; 0.650 mmol), 0.046

/

g of (PPh₃)₂PdCl₂(0.065 mmol, 10%), 0.025 g of CuI

(0.13 mmol, 20%) in 35 ml of di-iso-propylamine are

introduced and 0.46 ml of trimethylsilyl acetylene is

syringed (3.25 mmol) under argon. The reaction mixture

is refluxed for 64 h in a sealed vessel and the amine is

removed in vacuum. The dark residue is then extracted

with toluene and filtered on a celite pad. Evaporation of

toluene followed by repeated washings with cooled

residue is extracted with toluene (8ꢄ

on a celite pad. Evaporation of the toluene and washings

with small portions of n-pentane and methanol (2ꢁ5 ml)

at ꢂ

40 8C yield the desired (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,3-(C₆H₄)ÃCÅCÃPh complex (m-6a; 67%), as a

/10 ml) and filtered

/

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

/122

119

acetonitrile (ꢂ

ml) yield the desired (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)ÃCÅCÃSiMe₃complex (6c) as a pale brown

/

30 8C, 2ꢄ

/

3 ml) and n-pentane (2ꢄ

/

3

2049 (s), 2030 (m, FeÃ

/

CÅ

/

C). ¹H-NMR (200 MHz,

/

CÅCÃ1,4-

/

C₆D₆, d, ppm) 7.93 (m, 4H, H_{ortho/Ar/dppe}); 7.45ꢁ

(m, 18H, H_Ar); 2.84 (s, 1H, CÅCÃH); 2.58 (m, 2H,

CH₂); 1.80 (m, 2H, CH₂); 1.50 (s, 15H, C₅(CH₃)₅).

¹³C{¹H}-NMR (50 MHz, C₆D₆, d, ppm) 146.0 (t, FeÃ

/6.89

/

powder after drying in vacuo (0.435 g, 0.55 mmol,

85%). MS (positive LSI, 3-NBA, m/z) 786

CSiMe₃]^ꢃ,

/

2

([(dppe)(C₅Me₅)FeCÅ

/

C(C₆H₄)Ã

/

CÅ

/

15%);

589 ([(dppe)(C₅Me₅)Fe]^ꢃ, 100%). FT-IR (KBr/Nujol,

C Å

FeÃ

C₅(CH₃)₅); 85.9 (s, C Å

HÃC ÅC); 31.4 (m, CH_2dppe); 11.0 (s, J_CH

C₅(CH₃)₅).

/

C, J_PC

CÅC); 117.0 (s, J_CH

CÃ

ꢀ

/

39 Hz); 140.5ꢁ

/

126.3 (phenyls); 121.8 (s,

2

/

ꢀ

/

9 Hz, C Ã

/

CÅ

/

C); 88.7 (s,

n, cm^ꢂ1) 2147 (s, CÅ

NMR (200 MHz, C₆D₆, d, ppm) 7.91 (m, 4H,

/

CÃ

/

Si), 2037 (vs, FeÃ

/

CÅ

/

H); 78.1 (s, J_CH

ꢀ/250 Hz,

1

C). H-

2

1

/

ꢀ/126 Hz,

H_{ortho/Ar/dppe}); 7.52ꢁ6.89 (m, 20H, H_Ar); 2.55 (m, 2H,

/

CH_2dppe); 1.79 (m, 2H, CH_2dppe); 1.49 (s, 15H,

C₅(CH₃)₅); 0.25 (s, 9H, Si(CH₃)₃). ¹³C{¹H}-NMR (50

5.10. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ/1,4-

MHz, C₆D₆, d, ppm) 146.5 (t, FeÃ

140.5ꢁ127.9 (phenyls); 122.1 (s, FeÃ

²J_CH

9 Hz, C ÃCÅC); 108.4 (s, SiÃCÅ

C ÅC); 88.7 (s, C₅(CH₃)₅); 31.5 (m, CH_2dppe); 11.0 (s,

¹J_CH

126 Hz, C₅(CH₃)₅); 0.46 (s, Si(CH₃)₃).

/

C Å

/

C, ²J_PC

CÅC); 117.9 (s,

C); 94.2 (s, SiÃ

ꢀ

/

39 Hz);

(C₆H₄)Ã

/

SiMe₃(7a)

/

ꢀ

/

In

a

Schlenk tube, 0.300

g

of (h²-dppe)(h⁵-

1,4-(C₆H₄Br) (2b; 0.390 mmol) in 15

/

C₅Me₅)FeÃ

/

CÅ

/

CÃ

/

ꢀ

/

ml THF is cooled to ꢂ

/

80 8C and 0.48 ml of butyl

lithium (1.6 M commercial solution in hexanes, 0.780

mmol) is added. The reaction mixture is stirred for 2 h at

this temperature, after that 0.13 ml of Me₃SiCl is

syringed (0.975 mmol). The temperature is further

5.8. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)ÃCÅCÃSiMe₃(6c) via a metalla-Sonogashira

coupling

/

CÅ

/

CÃ

/

1,4-

/

maintained at ꢂ80 8C for 30 min and the reaction is

/

In

a

Schlenk tube, 0.485

g

of (h²-dppe)(h⁵-

of

then left stirring at ambient temperature for 1 h. The

solvents are removed and the residue is extracted with

toluene. After evaporation of toluene, followed by

C₅Me₅)FeÃ

/

CÅCH (1; 0.790 mmol), 0.042

/

g

(PPh₃)₂PdCl₂(0.059 mmol, 7.5%), 0.023 g of CuI

(0.118 mmol, 15%), 0.300 g of 1-(trimethylsilylacety-

lene)-4-bromobenzene (1.18 mmol) and 25 ml of di-iso-

propylamine are introduced under argon. The reaction

mixture is heated at 85 8C for 12 h and the amine is

removed in vacuum. The dark residue is then extracted

with toluene (10 ml) and filtered on a celite pad.

Precipitation from the toluene with n-pentane (7 ml),

followed by filtration and repeated washings with cold

repeated washings with cooled n-pentane (ꢂ

2ꢄ

ml) and vacuum drying, the desired (h²-

dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,4-(C₆H₄)SiMe₃complex

/

30 8C,

/3

/

(7a) is isolated as an orange powder (0.241 g, 0.316

mmol, 81%). MS (positive LSI, 3-NBA, m/z) 762

([(dppe)(C₅Me₅)FeCÅ

([(dppe)(C₅Me₅)Fe]^ꢃ, 100%). FT-IR (KBr/Nujol, n,

cm^ꢂ1) 2058 (vs, FeÃ C). ¹H-NMR (200 MHz,

CÅ

C₆D₆, d, ppm) 8.04 (m, 4H, H_{ortho/Ar/dppe}); 7.53ꢁ6.99

/

C(C₆H₄)SiMe₃]^ꢃ, 80%); 589

/

acetonitrile (ꢂ

ml), yield the desired (h²-dppe)(h⁵-C₅Me₅)FeÃ

1,4-(C₆H₄)ÃCÅCÃSiMe₃complex (6c) admixed with

1,4-Br(C₆H₄)ÃCÅCÃSiMe₃(ca. 0.7 eq.), as an orange

powder (0.645 g total).

/

30 8C, 2ꢄ

/

3 ml), then n-pentane (2ꢄ

/

5

/

CÅCÃ

/

(m, 20H, H_Ar); 2.69 (m, 2H, CH_2dppe); 1.85 (m, 2H,

CH_2dppe); 1.55 (s, 15H, C₅(CH₃)₅); 0.25 (s, 9H,

Si(CH₃)₃). ¹³C{¹H}-NMR (50 MHz, C₆D₆, d, ppm)

/

140.5ꢁ

/

125.5 (FeÃ

/

C Å

/

C and phenyls); 121.5 (s, FeÃ

/

CÅ

/

C); 88.5 (s, C₅(CH₃)₅); 31.5 (m, CH_2dppe); 11.0 (s,

¹J_CH

Si(CH₃)₃).

1

0.2 (s, J_CH

5.9. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)ÃCÅCH (6d)

/

CÅ

/

CÃ

/

1,4-

ꢀ

/

126 Hz, C₅(CH₃)₅); ꢂ

/

ꢀ118 Hz,

/

In

a

Schlenk tube, 0.350

g

of (h²-dppe)(h⁵-

SiMe₃(7c; 0.440

5.11. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ/1,4-

C₅Me₅)FeCÅ

/

CÃ1,4-(C₆H₄)ÃCÅCÃ

/

(C₆H₄)Ã

/

SnMe₃(7b)

mmol) and 0.123 g of K₂CO₃(0.89 mmol) are intro-

duced in a MeOH/THF (1:1) mixture under argon. The

reaction mixture is stirred for 12 h at ambient tempera-

ture and the solvents are removed. The residue is then

In

a

Schlenk tube, 0.350 g

of (h²-dppe)(h⁵-

C₅Me₅)FeÃ

ml THF is cooled to ꢂ

/

CÅ

/

CÃ

/

1,4-(C₆H₄Br) (2b; 0.455 mmol) in 15

80 8C and 0.57 ml of butyl

/

extracted with toluene (4ꢄ

pentane (2ꢄ3 ml) and dried in vacuo. The desired

(h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,4-(C₆H₄)ÃCÅCH

/

30 ml), washed with n-

lithium (1.6 M commercial solution in hexanes, 0.910

mmol) is added. The reaction mixture is stirred for 2 h at

this temperature, after that 0.227 g of Me₃SnCl is added

(1.137 mmol). The temperature is further maintained for

/

complex (6d) is isolated as an orange-brown solid (0.220

g, 0.31 mmol, yield: 70%). MS (positive LSI, 3-NBA, m/

30 min at ꢂ80 8C and the reaction is then left stirring at

/

z) 714 ([(dppe)(C₅Me₅)FeCÅ

15%); 589 ([(dppe)(C₅Me₅)Fe]^ꢃ, 100%). FT-IR (KBr/

Nujol, n, cm^ꢂ1) 3307 (m, Å

CÃH), 2097 (vw, CÅCÃH),

/

C(C₆H₄)CÅ

/

CHꢃ

/

1]^ꢃ,

ambient temperature for 1 h. The solvents are removed

and the residue is extracted with toluene. After evapora-

tion of toluene followed by one washing with cooled n-

/

120

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ122

/

pentane (ꢂ

desired

/

30 8C, ꢀ

/

3 ml) and drying in vacuo, the

CÅCÃ1,4-(C₆H₄)-

SnMe₃complex (7b) is isolated as a brown powder

4H, H_{ortho/Ar/dppe}); 7.72ꢁ7.05 (m, 35H, H_Ar); 2.67 (m,

2H, CH_2dppe); 1.84 (m, 2H, CH_2dppe); 1.54 (s, 15H,

C₅(CH₃)₅). ¹³C{¹H}-NMR (50 MHz, C₆D₆, d, ppm)

/

(h²-dppe)(h⁵-C₅Me₅)FeÃ

/

2

C, J_PC

(0.303 g, 0.355 mmol, 78%). MS (positive LSI, 3-NBA,

C(C₆H₄)SnMe₃]^ꢃ,

141.6 (t, FeÃ

/

C Å

/

ꢀ

/

39 Hz); 141.2ꢁ

/

127.7 (phe-

CÅC); 88.1

126 Hz,

m/z) 854 ([(dppe)(C₅Me₅)FeÃ

/

CÅ

/

nyls); 125.8 (s, C Ã

/

Sn(CH₃)₃); 120.6 (s, FeÃ

/

8%); 589 ([(dppe)(C₅Me₅)Fe]^ꢃ, 100%). FT-IR (KBr/

(s, C₅(CH₃)₅); 29.3 (m, CH_2dppe); 10.7 (s, ¹J_CH

C₅(CH₃)₅).

ꢀ

/

Nujol, n, cm^ꢂ1) 2057 (s, FeÃ

MHz, C₆D₆, d, ppm) ꢂ

(200 MHz, C₆D₆, d, ppm) 8.04 (m, 4H, H_{ortho/Ar/dppe});

/

CÅ

/

C). ¹¹⁹Sn-NMR (112

1

/

30.14 (s, Sn(CH₃)₃). H-NMR

5.14. Crystal structure determination for (h²-dppe)(h⁵-

C₅Me₅)FeÃCÅCÃ1,4-(C₆H₄F) (2a)

7.76ꢁ6.99 (m, 20H, H_Ar); 2.67 (m, 2H, CH_2dppe); 1.84

/

(m, 2H, CH_2dppe); 1.55 (s, 15H, C₅(CH₃)₅); 0.30 (s, 9H,

Sn(CH₃)₃). ¹³C{¹H}-NMR (50 MHz, C₆D₆, d, ppm)

Complex 2a was crystallised by slow diffusion of n-

pentane in a toluene solution of the compound. The

2

139.4 (t, FeÃ

/

C Å

/

C, J_PC

ꢀ

/

36 Hz); 140.8ꢁ

C); 88.5 (s, C₅(CH₃)₅); 30.9 (m,

CH_2dppe); 11.2 (s, J_CH126 Hz, C₅(CH₃)₅); ꢂ8.1 (s,

¹J_CH

129 Hz, Sn(CH₃)₃).

/128.2 (phe-

nyls); 121.4 (s, FeÃ

/

CÅ

/

sample (0.32ꢄ

NONIUS CAD4 with graphite monochromatised

MoK_aradiation [82]. Formula: C₄₄H₄₃F₁P₂Fe₁, Mrꢀ

/

0.25ꢄ

0.25 mm³) was studied on a

/

1

ꢀ

/

ꢀ

/

˚

708.57, triclinic, P1, aꢀ

/

12.127(4) A, bꢀ

/

12.277(3) A,

71.50(2)8, gꢀ

2, Dxꢀ1.256 mg

5.12. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)ÃSnBu₃(7c)

/

CÅ

/

CÃ/1,4-

cꢀ

/

15.469(2) A, aꢀ

/

73.14(2)8, bꢀ

/

˚

1873.5(8) A^ꢂ3, zꢀ

/

˚

/

60.37(3)8, Vꢀ

/

m^ꢂ3, l(MoK_a)ꢀ

744, Tꢀ

fitting a set of 25 high-theta reflections. The data

collection [83] (2u_max548, scan v/2uꢀ1, t_max60 s

and h k l range*h: 0,15; k: ꢂ15,15; l: ꢂ19, 19) gives

8930 reflections, from which 6191 were retained (I ꢀ

/

0.71073 A, mꢀ

/

5.22 cm^ꢂ1, F(000)ꢀ

/

˚

Following a rigorously similar procedure to that

employed in the synthesis of 7b, from 0.350 g of (h²-

/

293 K. The cell parameters are obtained by

dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ/1,4-(C₆H₄Br) (2b; 0.455

ꢀ

/

ꢀ

/

mmol) and 0.31 ml of Bu₃SnCl (1.137 mmol), the

desired CÅCÃ1,4-(C₆H₄)-

(h²-dppe)(h⁵-C₅Me₅)FeÃ

/

SnBu₃complex (7c) is precipitated by the addition of

an equivalent volume of n-pentane, separated by

decantation and washed further by n-pentane, before

being dried in vacuo. The product is isolated as a viscous

gum. MS (positive LSI, 3-NBA, m/z) 980

2.0s(I)). After Lorentz and polarisation corrections

[84], the structure was solved with SIR-97 which reveals

the non-hydrogen atoms of structure [85]. Anisotropic

refinement allows for finding the remaining atoms by a

Fourier difference map. The whole structure was refined

with ^SHELXL97[86] by the full-matrix least-square

techniques (use of F-square magnitude; x, y, z, b_ijfor

Fe, P, C and O atoms, x, y, z in riding mode for H

atoms with 434 variables and 6191 observations; calc.:

([(dppe)(C₅Me₅)FeÃ

([(dppe)(C₅Me₅)Fe]^ꢃ, 100%). FT-IR (KBr/Nujol, n,

cm^ꢂ1) 2061 (vs, FeÃ C). ¹H-NMR (200 MHz,

CÅ

C₆D₆, d, ppm) 8.03 (m, 4H, H_{ortho/Ar/dppe}); 7.52ꢁ6.05

/

CÅ

/

C(C₆H₄)SnBu₃]^ꢃ, 35%); 589

/

(m, 20H, H_Ar); 2.67 (m, 2H, CH_2dppe); 1.82 (m, 2H,

CH_2dppe); 1.54 (s, 15H, C₅(CH₃)₅); 0.57, 1.34, 1.10 (m,

wꢀ

with the resulting Rꢀ

1.088 (residual Drꢀ

0.39 eA^ꢂ3). Atomic scattering

/

1/[s²(Fo²)ꢃ

/

(0.077P)²] where Pꢀ

/

(Fo²ꢃ2Fc²)/3

/

0.040, R_wꢀ0.119 and S_wꢀ

/

˚

3ꢄ

/

6H, Sn(CH₂CH₂CH₂CH₃)₃), 0.95 (t, 9H,

/

Sn(CH₂CH₂CH₂CH₃)₃).

factors were taken from the literature [87]. ^ORTEPviews

of 2a were realised with ^PLATON98and ORTEP-3 [88,89].

All the calculations were performed on a Pentium NT

Server computer.

5.13. Synthesis of (h²-dppe)(h⁵-C₅Me₅)FeÃ

(C₆H₄)ÃSnPh₃(7d)

/

CÅ

/

CÃ/1,4-

/

Following a rigorously similar procedure to that

employed in the synthesis of 7b, from 0.350 g of (h²-

5.15. ¹⁹F-NMR derivation of Hammett parameters for

‘‘(h²-dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ

/

’’

dppe)(h⁵-C₅Me₅)FeÃ

/

CÅ

/

CÃ/1,4-(C₆H₄Br) (2b; 0.455

mmol) and 0.438 g of Ph₃SnCl (1.137 mmol), the desired

(h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,4-(C₆H₄)SnPh₃com-

plex (7d) is precipitated by the addition of one equiva-

lent volume of n-pentane, separated by decantation and

washed further n-pentane, before being dried in vacuo.

Likewise to 7c, it is also isolated as a viscous gum. MS

Pure samples of the compounds 2a and m-2a (0.05

mmol) were solubilised each in 1 ml freshly distilled and

degassed CCl₄. These solutions were then transferred in

NMR tubes under argon and 5 ml (0.076 mmol) of

fluorobenzene was syringed in the tube, as internal

reference. After homogenisation of the solution, the

{¹H}¹⁹F-NMR spectra were recorded at 25 8C. The

values of s_Iand s_Rwere derived from the values of the

various ¹⁹F-NMR shift differences, using the correlation

established by Taft et al. [41,42] for meta- and para-

fluorobenzene derivatives. From these values, s_pand s_m

/

(positive LSI, 3-NBA, m/z) 1040 ([(dppe)(C₅Me₅)FeÃ

CÅ

C(C₆H₄)SnPh₃]^ꢃ, 15%); 589 ([(dppe)(C₅Me₅)Fe]^ꢃ,

100%). FT-IR (KBr/Nujol, n, cm^ꢂ1) 2058 (vs, FeÃ

CÅ

C). ¹¹⁹Sn-NMR (112 MHz, C₆D₆, d, ppm) ꢂ

81.6 (s,

SnPh₃). H-NMR (200 MHz, C₆D₆, d, ppm) 8.02 (m,

/

1

J. Courmarcel et al. / Journal of Organometallic Chemistry 670 (2003) 108ꢁ

/122

121

[15] H. Werner, P. Bachmann, M. Laubender, O. Gevert, Eur. J.

Inorg. Chem. (1998) 1217.

were next computed considering the following equa-

tions:

[16] M. Uno, P.H. Dixneuf, Angew. Chem. Int. Ed. Engl. 37 (1998)

1714.

s_pꢀs_Iꢃs_R;

s_mꢀs_Iꢃ¹₂s_R:

(1)

(2)

[17] M.I. Bruce, B.C. Hall, P.J. Low, B.W. Skelton, A.H. White, J.

Organomet. Chem. 592 (1999) 74.

[18] M. Younus, N.J. Long, P.R. Raithby, J. Lewis, J. Organomet.

Chem. 570 (1998) 55.

[19] O. Lavastre, J. Plass, P. Bachmann, S. Guesmi, C. Moinet, P.H.

Dixneuf, Organometallics 16 (1997) 184.

[20] S. di Bella, Chem. Soc. Rev. 30 (2001) 355.

[21] B.J. Coe, Chem. Eur. J. 5 (1999) 2464.

6. Supplementary material

[22] I.R. Whittall, A.M. MacDonagh, M.G. Humphrey, M. Samoc,

Adv. Organomet. Chem. 42 (1998) 291.

Crystallographic data for (h²-dppe)(h⁵-C₅Me₅)FeÃ

CÅCÃ1,4-(C₆H₄)ÃF has been deposited to the Cam-

bridge Crystallographic Data centre, as CCDC-197242.

Copies of this information may be obtained free of

charge from The Director, CCDC, 12 Union Road,

/

[23] C. Gauss, D. Veghini, H. Berke, Chem. Ber. 130 (1997) 183.

[24] H. Werner, P. Bachmann, M. Martin, Can. J. Chem. 79 (2001)

519.

/

[25] R.B. Bedford, C.S.J. Cazin, J. Organomet. Chem. 598 (2000) 20.

[26] G. Albertin, S. Antoniutti, E. Bordignon, M. Granzotto, J.

Organomet. Chem. 585 (1999) 83.

Cambridge CB2 1EZ, UK (fax: ꢃ44-1223-336033; e-

/

[27] M.I. Bruce, B.C. Hall, B.D. Kelly, P.J. Low, B.W. Skelton, A.H.

White, J. Chem. Soc. Dalton Trans. (1999) 3719.

[28] P. Siemsen, R.C. Livingstone, F. Diederich, Angew. Chem. Int.

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Article Doi

Versatile reactions of a para-bromophenylacetylide iron (II) derivative and X-ray structure of the fluoro analogue. Synthesis of new redox-active organoiron (II) synthons

DOI: 10.1016/S0022-328X(02)02137-X

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