Synthesis of (η6-arene)(η5-cyclopentadienyl) iron (II) complexes with heteroatom and carbonyl substituents. Part I: Oxygen and carbonyl substituents

Article abstract of DOI:10.1016/j.jorganchem.2005.12.070

A series of reactions have been used to introduce oxygen substituents into (η-arene)(η-cyclopentadienyl) iron (II) complexes. Photochemical ligand exchange led to the formation of the first recorded trioxygenated complex as well as mono- and di-oxygenated species. Using microwave techniques, reaction times for S_NAr displacement reactions of halobenzene complexes by phenols were reduced from several hours to a few minutes. Phenols protected by either t-butylation or trimethylsilylation were found to give modest yields of the corresponding phenol complexes, using conventional thermal ligand exchange reactions. Without such protection, yields were extremely low. The above method led to the synthesis of the first example of a dihydroxybenzene complex. Some miscellaneous syntheses are also reported. The Nef reaction has been adapted to convert (η⁶-α-nitroalkylarene)(η⁵-Cp) iron (II) salts to corresponding aldehyde and ketone complexes. The α-nitroalkyl arene complexes were synthesised in good yields from (η⁶-halobenzene)(η⁵-Cp) iron (II) complexes using NaOtBu in DMSO. H/D exchange reactions with ²[H]₆-DMSO in the presence of K₂CO₃ showed partial D incorporation in the methyl group for the unreacted α-nitroethylbenzene complex and complete exchange for the carbanion generated by deprotonation. Conversion of the α-nitroalkylarene complexes to the corresponding aldehyde and ketone complexes was accomplished in moderate yields using three methods:. (A)H₂O₂ and NaOtBu in DMSO followed by reaction with CF₃CO₂H.(B)SnCl₂/aq. HCl.(C)K₂CO₃ in DMF using microwave-mediated reactions. In addition, two one-pot syntheses are reported using methods B and C.

Full text of DOI:10.1016/j.jorganchem.2005.12.070

Journal of Organometallic Chemistry 691 (2006) 2641–2647
www.elsevier.com/locate/jorganchem
Synthesis of (g6-arene)(g5-cyclopentadienyl) iron (II) complexes
with heteroatom and carbonyl substituents. Part I:
Oxygen and carbonyl substituents
R.M.G. Roberts
Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK
Received 11 March 2005; received in revised form 20 December 2005; accepted 20 December 2005
Available online 24 April 2006
Abstract
A series of reactions have been used to introduce oxygen substituents into (g-arene)(g-cyclopentadienyl) iron (II) complexes. Photo-
chemical ligand exchange led to the formation of the first recorded trioxygenated complex as well as mono- and di-oxygenated species.
Using microwave techniques, reaction times for SNAr displacement reactions of halobenzene complexes by phenols were reduced from
several hours to a few minutes. Phenols protected by either t-butylation or trimethylsilylation were found to give modest yields of the
corresponding phenol complexes, using conventional thermal ligand exchange reactions. Without such protection, yields were extremely
low. The above method led to the synthesis of the first example of a dihydroxybenzene complex. Some miscellaneous syntheses are also
reported.
The Nef reaction has been adapted to convert (g6-a-nitroalkylarene)(g5-Cp) iron (II) salts to corresponding aldehyde and ketone
complexes. The a-nitroalkyl arene complexes were synthesised in good yields from (g6-halobenzene)(g5-Cp) iron (II) complexes using
NaOtBu in DMSO. H/D exchange reactions with 2[H]6-DMSO in the presence of K2CO3 showed partial D incorporation in the methyl
group for the unreacted a-nitroethylbenzene complex and complete exchange for the carbanion generated by deprotonation. Conversion
of the a-nitroalkylarene complexes to the corresponding aldehyde and ketone complexes was accomplished in moderate yields using three
methods:
(A) H2O2 and NaOtBu in DMSO followed by reaction with CF3CO2H.
(B) SnCl32/aq. HCl.
(C) K2CO3 in DMF using microwave-mediated reactions.
In addition, two one-pot syntheses are reported using methods B and C.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Microwave; Photochemical; Synthesis; Iron; Nef reaction
1. Introduction
and efficient preparation [3] and this, together with facile
decomplexation techniques [3,4], allows convenient routes
to aromatic compounds which may otherwise be difficult
to obtain. The following papers deal with the synthesis of
ArFeCp complexes containing oxygen, nitrogen and car-
bonyl substituents.
(g6-Arene)(g5cyclopentedienyl) iron (II) complexes,
ArFeCp, have found many uses in organic synthesis [1].
New microwave methods [2] have resulted in their rapid
The first part (A) of the work described here
deals with the preparation of hydroxyl-, alkoxy- and
E-mail address: rogermgroberts@yahoo.com.
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.12.070

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R.M.G. Roberts / Journal of Organometallic Chemistry 691 (2006) 2641–2647
aryloxy-substituted complexes using a range of synthetic
routes including microwave-mediated techniques. Part (B)
reports on the use of the Nef reaction in the synthesis of
ArFeCp complexes containing carbonyl substituents.
No attempt has been made to optimise yields, since the
purpose of the work was to investigate the range and appli-
cability of these diverse routes.
has been known for many years [1] and has been improved
with the advent of microwave-mediated methods [3].
ðiÞ AlCl3; Al
FcH þ ArX ꢀꢀꢀꢀꢀꢀꢀꢀꢀ!½ðArXÞFeðCpÞꢁ½PF6ꢁ
ð2Þ
ðiiÞ HPF6
The success of the latter depends on the absorption of
microwave energy by dipolar species in the reaction med-
ium. In this connection, a series of semi-quantitative exper-
iments have been performed to determine the key
microwave absorbers in the system. The following results
were obtained using 1,2,4-trichlorobenzene (TCB) as sol-
vent, and recording the temperature of components of
the mixture immediately after an irradiation time of
4 min on a medium microwave oven setting.
(Components followed by temperatures in parentheses)
TCB (50); TCB/FcH(60); TCB/Al (80); TCB/AlCl3 (96);
TCB/FcH/Al (78); TCB/FcH/ALCl3 (170); TCB/Al/AlCl3
(90); TCB/FcH/Al/AlCl3 (180).
2. Results and discussion
2.1. Part A – oxygen-substituted complexes
2.1.1. Photochemical ligand exchange
This synthetic method was devised by Gill and Mann
[5–7]. Using this technique, the 1,3,5-trimethoxybenzene
complex has been prepared in 46% yield from the 1,2-
dichlorobenzene complex using a 300 W tungsten lamp as
the radiation source.
It is clear from these results that the combination of fer-
rocene and AlCl3 has by far the greatest absorption of
microwave radiation. This is strong evidence of a highly
dipolar complex intermediate, probably of the type
(1)*
This complex cannot be obtained by the usual SNAr dis-
placements [8] since the precursor 1,3,5-trichlorobenzene
complex cannot be prepared by conventional thermal
ligand exchange owing to the strong electron withdrawal
by three chlorine substituents. The advent of a simple
method of heterolytic C–O bond cleavage in arylether com-
plexes to give p phenate complexes [9] should prove useful
in the case of the 1,3,5-trimethoxybenzene complex and
would result in the formation of an important template
for the synthesis of polymeric ArFeCp compounds [10].
The corresponding methoxy- and 1,2-dimethoxybenzene
complexes were obtained in 35% and 32% yields, respec-
tively. Both the phenol and 1,3-dihydroxybenzene com-
plexes were likewise obtained in 20% yields. Use of the
naphthalene complex in these photolytic ligand exchange
reactions generally led to lower yields. Inter alia, it is worth
noting that the phenylsilatrane complex can be synthesized
in 46% yield using this method, whereas no product is
formed in thermal ligand exchange reactions due to deacti-
vation of AlCl3 by strong complexation with the oxygen
atoms in the silatrane moiety. The 13C NMR spectrum of
the phenylsilatrane complex shows strong deshielding at
the C2, C6 positions in the aromatic ring indicating power-
ful electron withdrawal by the silatrane substituent even
when the phenyl ring has the strongly electron withdrawing
[FeCp]+ group attached.
2.1.2.1. Synthesis of (ArOH)FeCp complexes. Applica-
tion of the microwave-assisted ligand exchange reactions
to the synthesis of phenolic complexes gave very low yields,
e.g., <1% for phenol itself. This is probably due to strong
complexation or reaction with AlCl3, thus destroying the
latter’s Lewis acid strength. Improved yields were obtained
when the phenolic OH group was protected. Thus, phenyl
t-butylether gave a mixture of the phenyl t-butylether com-
plex (5%) and the phenol complex (45%) after a 4 min reac-
tion time. Electron withdrawing substituents led to a
marked inhibition of reaction, exemplified by a 5% yield
for the 4-chlorophenol complex from 4-chlorophenyl-t-
butylether.
The readily available O-trimethylsilyphenols [11] also
show promise in these reactions. The reaction of O-trim-
ethylsilyphenol gave a 44% yield of the phenol complex
in 4 min. As before, electron withdrawing substituents
cause a lowering of yield. Thus, O-trimethylsilyl 4-fluor-
2.1.2. Microwave-mediated synthesis
Synthesis of the starter complexes [ArXFeCp][PF6] by
thermal ligand exchange reactions using ferrocene (FcH)

R.M.G. Roberts / Journal of Organometallic Chemistry 691 (2006) 2641–2647
2643
ophenol gave a 16% yield of the corresponding phenol
complex. Both OH groups in catechol can be trimethylsily-
lated in 72% yield, and the resultant bis-silyl ether gave 9%
of the corresponding catechol complex. This is the first
report of an ArFeCp complex containing two OH groups.
However, no product was obtained from resorcinol using
this procedure. Silylated 2-phenylphenol gave a 30% yield
of the 2-phenylphenol complex with the FeCp group bound
to the monosubstituted phenyl ring. AlCl3 complexes with
the oxygen atom in the phenol moiety thus deactivating
this ring to complexation by the FeCp group. 4-Aminophe-
nol can be silylated at both oxygen [12] and nitrogen atoms
(69%), and the resultant silylated material gave a 7% yield
of the 4-aminophenol complex.
Clearly, both tBu and Me3Si groups afford some protec-
tion in these ligand exchange reactions, presumably by ste-
ric inhibition of complexation by AlCl3. There is, however,
a balance between this protection and the ease of removal
of the protecting group. The Me3Si group is much more
labile than the t-butyl group in this reaction, but silylation
is much easier to achieve than t-butylation particularly for
adjacent OH groups. There are, of course, more sophisti-
cated OH protecting groups which could well improve on
the yields obtained here. The above reactions, however,
do allow extra scope in synthetic strategy for oxygen con-
taining ArFeCp complexes.
The microwave-mediated reaction of 4-phenylazophenol
with ferrocene, AlCl3, and Al in 1,2,4-trichlorobenzene
resulted in a 53% yield of the aniline complex (after
4 min reaction time) instead of the hoped-for-4-aminophe-
nol complex.
2.2. Part B – complexes with carbonyl substituent
The Nef reaction [13,14] converts primary or second-
ary nitroalkanes into the corresponding carbonyl com-
pounds and is thus an important tool for the synthetic
organic chemist. ArFeCp complexes containing carbonyl
substituents have been reported. Those complexes bear-
ing methylene substituents can be converted into oximes
which can then be hydrolysed by aqueous HF [15]. How-
ever, only keto-complexes are formed by this method.
The Nef reaction has been used for ArFeCp complexes,
though again only for the synthesis of keto complexes.
The precursor nitroalkane derivatives can be prepared
in good yields by reaction of nitromethane or nitroe-
thane with halo-arene complexes in the presence of
K2CO3 [16,17].
Other methods for ArFeCp complexes include direct
thermal ligand exchange using fluorene and related species
with ferrocene and AlCl3 followed by permanganate oxida-
tion to form the keto complexes [18]. The purpose of this
paper is to further investigate the Nef reaction with a view
to the synthesis of aldehyde-containing ArFeCp complexes.
2.1.2.2. Synthesis of (ArOR)FeCp complexes. Hitherto,
these complexes have been prepared by SNAr displace-
ments of halogen substituents in the sandwich complexes
by the appropriate alcohol in the presence of base.
2.2.1. a-Nitroarene complexes (see Table 1 for 13C NMR
data)
The precursor a-nitroarene complexes for the Nef reac-
tion can be readily synthesised in good yields from SNAr
displacements in the corresponding haloarene complexes
by nitroalkanes in strongly basic media.
ð3Þ
These reactions generally require long reaction times [8]
(12–15 h). Using microwave irradiation, the diphenylether
complex can be obtained in 25% yields in 5 min from the
reaction of the chlorobenzene complex with phenol in the
presence of Et3N in solvent DMF. During the period of
microwave irradiation, the temperature of the reaction
mixture rose to near the boiling point of solvent DMF.
To verify the effectiveness of microwave assistance, a con-
trol experiment was performed in refluxing DMF (5 min).
This resulted in only a yield of 8% of the diphenylether
complex, thus demonstrating the effectiveness of the micro-
wave method. Interestingly, when flaked graphite (an excel-
lent microwave absorber) is used, the phenol complex is
formed in 20% yield. This is probably due to dephenylation
of the diphenylether complex at the surface of the graphite
where high local temperatures are generated.
ð4Þ
NaOtBu was chosen as the base rather than the K salt
since the latter causes significant decomplexation even at
room temp. The fluoroarene complexes were more reactive
than the chloro analogues. Thus, the a-nitroethylbenzene
complex (III) was obtained in 52% yield from the fluoro-
benzene complex whereas little reaction was observed for
the chlorobenzene complex.
A doubling of signals was observed for C2,6 and C3,5 in
the 13C NMR spectrum for III. This is due to the chiral
nature of the substituent which renders these ring carbons
diastereotopic. The reaction of the 3,4-dichlorobenzene
complex with nitromethane shows some regiospecificity,
there being a preponderance of one regio-isomer over the
other (60:40) though it is not possible to identify each from
NMR data.
2.1.3. Miscellaneous reactions
Deprotonation of dimethylphosphite with NaH, fol-
lowed by reaction with the fluorobenzene complex gave a
30% yield of the anisole complex. The mechanism of this
reaction is uncertain.

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R.M.G. Roberts / Journal of Organometallic Chemistry 691 (2006) 2641–2647
dehyde (IVA), 35%, m-tolualdehyde (VA), 22%, p-
tolualdehyde (IA), 26%. The above method was developed
into a one-pot procedure. Thus, reaction of (g6-fluoroben-
zene)(g5-Cp) iron (II) PF6 with nitromethane and NaOtBu
in dry DMSO, followed by SnCl2/HCl treatment gave a
33% yield of the benzaldehyde complex.
A microwave-mediated one-pot reaction has also been
developed (Method C). Reaction of the fluorobenzene
complex with nitroethane and K2CO3 in dry DMF gave
the a-nitroethylbenzene complex after 1 min irradiation,
and the acetophenone complex (55% yield) after a further
1 min irradiation in the presence of 2 N HCl.
ð5Þ
In addition, there are two pairs of Cp signals, each pair
separated by approximately 0.1 ppm in the 13C NMR spec-
trum. This suggests restricted rotation about the C–
CH2NO2 bond which would generate two different
configurations.
In an NMR study, the formation of the carbanion by
deprotonation of the a-nitroethylbenzene complex (III)
using K2CO3 in [2H]6-DMSO showed a 77% conversion
after 5 min. The 1H NMR spectrum of the carbanion
showed no signal for the methyl group, indicating complex
H/D exchange. There was no evidence of any exchange of
arene or cyclopentadienyl hydrogens but integration of the
methyl group of the unreacted parent complex showed 27%
H/D exchange. The 13C NMR spectrum of the carbanion
showed no methyl resonance due to C–D coupling making
the resulting low intensity septet undetectable. The Cp sig-
nal appeared some 4 ppm upfield from the parent a-nitro-
ethylbenzene complex reflecting the electron-rich nature of
the carbanion.
ð8Þ
Finally, it is worth noting that the SnCl2/HCl Nef reaction
did not occur when argon was passed through the reaction
medium. This indicates a radical-dependent mechanism for
the ArFeCp complexes.
3. Experimental
2.2.2. (g6-ArCOR)(g5-Cp) iron (II) complexes (see Table
2 for 13C NMR and CH analyses)
Microwave-mediated syntheses were conducted using a
conventional unmodified domestic microwave oven [Sharp
Easy Chef, Model R5A53, 850 W], using solid CO2 as cool-
ant in an apparatus described in Ref. [3].
Attempts to prepare these complexes by the usual ther-
mal ligand exchange reactions always resulted in the for-
mation of the corresponding ArCH(OH)RFeCp
complexes due to reduction during the exchange process.
Oxidation of the alcohol complexes to the carbonyl com-
plexes has proved very difficult.
Hydrogen peroxide has been used to convert nitroalk-
anes into aldehydes and ketones in weakly basic media
[19]. This method (Method A) was modified for the
ArFeCp complexes by using a much more strongly basic
medium and led to a moderate yield of the benzaldehyde
complex (IIA).
1H and 13C NMR were recorded on a Jeol EX 270 spec-
trophotometer, using [2H6]-acetone as the solvent unless
otherwise stated. Chemical shifts (d) are in ppm relative
to TMS [s, singlet; d, doublet; tr, triplet; m, mulitplet].
For the BPh4 salts, the signals for the BPh4 group are
not reported in the interest of brevity. Mass spectra were
obtained in-house, using a Kratos MS 50 double focusing
instrument with a FAB source and employing a matrix of
3-nitrobenzyl alcohol. The masses of the cations of the
complexes, M+, reported were accurate to within 0.5
mass numbers.
ð6Þ
CHN analyses were performed at the Analytical Labo-
ratory of the University of Manchester.
This is the first example of an ArFeCp complex containing
an aldehydic substituent. A second route to aldehyde deriv-
atives was devised (Method B) based on the Nef reaction.
The usual acid-catalysed Nef reactions [20] for (g6-a-nitro-
alkylarene)(g5-Cp) iron (II) complexes is accompanied by
further oxidation to the carboxylic acid complex for pri-
mary a-nitroalkyl complexes. To circumvent this, reactions
were carried out in the presence of SnCl2 to give moderate
yields of the corresponding aldehyde complexes.
4. Syntheses
4.1. Part A – oxygen-substituted complexes
4.1.1. Photochemical ligand exchange
4.1.1.1. Synthesis of (g6-1,3,5-trimethoxybenzene)(g5-cyclo-
pentadienyl) iron (II) hexafluorophosphate. (g6-1,
2-Dichlorobenzene)(g5)-cyclopentadienyl iron (II) hexaflu-
orophosphate (0.82 g, 2.0 mmol) was dissolved in CH2Cl2
(25 ml) in a 100 ml RB flask equipped with a condenser,
and 1,3,5-trimethoxybenzene (1.00 g, 5.9 mmol) added.
The mixture was irradiated with stirring for 312 h using a
300 W tungsten lamp held close to the reaction vessel.
The cooled mixture was filtered into Et2O (100 ml) and
ð7Þ
The following aldehyde and ketone complexes were pre-
pared by this method: acetophenone (IIIA) 43%, o-tolual-

R.M.G. Roberts / Journal of Organometallic Chemistry 691 (2006) 2641–2647
2645
the resultant dark green precipitate. Filtered off, washed
with Et2O, then air dried to give 0.50 g crude product. This
was purified by recrystallisation from CH2Cl2/Et2O to give
0.40 g pure product in 46% yield. 1H NMR: dH, 4.08
(OMe), 5.10 (Cp), 6.28 (H2,4,6). 13C NMR: dC, 57.90
(C2,4,6), 59.98 (OMe), 76.58 (Cp), 133.72 (C1,3,5).
Anal. Found: C, 38.76; H,3.94%. Calc. for
C14H17F6FeO3P: C, 38.71; H, 3.92. Similarly, the methoxy-
benzene and 1,2-dimethoxybenzene complexes were pre-
pared in 35% and 32% yields, respectively.
resultant flocculent yellow precipitate was stirred well for
a few minutes then filtered off and washed with a little cold
distilled H2O to give a yellow solid (1.7 g) which comprised
the phenol and the phenyl-t butylether complex in a ratio
of 9:1 as shown by NMR in [2H6]-DMSO. 13C NMR for
the phenol complex, dC 74.85 (C2,6), 75.57 (Cp), 82.36
(C4), 86.22 (C3,5), 134.62 (C1); for the o-t-butyl complex,
30.24 (Me), 73.50 (C2,6), 74.98 (Cp), 81.67 (C4), 86.22
(C3,5), 133.64 (C1). (Quaternary carbon for t-butyl group
not observed.)
Phenol gave a 21% yield of the corresponding complex
and a similar yield was obtained for the 1,3-dihydroxyben-
zene complex. 13C NMR: dC, 66.30 (C2), 71.05 (C4,6),
76.61 Cp, 84.27 (C5), 130.04 (C1,3).
Using the above method, the 4-chlorophenol complex
was formed in 5% yield. 13C NMR: dC, 74.28 (3,5) 78.16
(Cp) 87.82 (2,4), 101.59 (C1), 133.27 (C4).
Anal. Found: C, 35.32;
C11H11F6FeO2P: C, 35.14; H, 2.95.
H
3.00%. Calc. for
4.1.3.2. Protection by trimethylsilylation. Catechol (5.5 g,
0.05 mol) in trimethylchlorosilane (20 ml) was refluxed
overnight excluding moisture. The reaction mixture was
treated with a little decolourising charcoal and 40:60
pet.ether added. Filtration and evaporation gave 9.1 g
(72%) of the bis-silylated product.
The phenylsilatrane complex can also be obtained in
46% yield. 1H NMR: dH, 3.21 t, J = 5.9 Hz, (N–CH2);
3.99t, J = 5.9 Hz (O–CH2); 5.01s, (Cp); 6.2–6.3m (Ph).
13C NMR: dC, 51.60 (N–CH2) 58.21 (O–CH2), 76.94
(Cp), 87.20 (C4), 88.14 (C3,C5), 93.59 (C2,C6).
13C NMR: dC, 0.41 (Me), 121.99 (C2,6), 122.75
(C4,5), 147.43 (C1,2). The product (2.5 g 0.01 mol), ferro-
cene (5.6 g, 0.03 mol), Al powder (3.0 g, 0.11 mol) and
AlCl3 powder (4.0 g, 0.03 mol) were mixed with TCB
(11 g) and microwaved for 4 min on a medium setting.
After decomposition with ice, followed by filtration, a
deep green solution was obtained which gave no precip-
itate with NH4PF6. This solution was evaporated to dry-
ness and the residue taken up into hot acetone (100 ml),
filtered, and evaporated. After washing well with Et2O, a
dark oil was obtained. This was redissolved in acetone
and added dropwise to aq. 0.15 M NaBPh4 (10 ml).
The resultant pale green solid was filtered off, washed
with a little ice-water, then air dried to give 0.5 g (9%)
product.
4.1.2. Microwave syntheses
4.1.2.1. Synthesis of (g6-diphenylether)(g5-cyclopentadie-
nyl) iron (II) hexaflurophosphate. (g6-Chloroben-
zene)(g5-cyclopentadienyl) iron (II) hexafluorophosphate
(1.1 g, 2.9 mmol), phenol (0.6 g 6.4 mmol) and Et3N
(1.0 g, 10 mmol) were dissolved in dry DMF (10 ml) and
the solution irradiated in microwave oven for 5 min at a
medium setting in the apparatus described in Ref. [3].
The mixture was filtered into Et2O (200 ml) to give a brown
oil. The supernatant Et2O was decanted off, and the residue
dissolved in acetone (15 ml) and filtered slowly into 0.08 M
NH4PF6 (50 ml).
The mixture was allowed to stand at 0 ꢁC for 3 days
whereupon a yellow crystalline solid was obtained. Yield:
1H NMR: dH, 4.73 (Cp), 5.54 (H3,6), 5.97 (H4,5). 13C
NMR: dC, 74.73 (C3,6), 75.64 (Cp), 80.20 (C4,5), 121.48
(C1,2). M+: Found: 230.9; calcd. 231.
Similarly prepared were the phenol complex (44%), the
4-fluorophenol complex (16%). M+: Found: 232.8; calcd.
233, the 4-aminophenol complex (7%) [NB: no complex
was formed with the unsilylated phenol] 13C NMR: dC,
67.06 (C3,5), 72.33 (2,6), 75.79 (Cp), 121.71 (C4), 127.38
(C1) and the 4-chloro-2-methylphenol complex (12%) 13C
NMR: dC, 15.39 (Me), 76.05 (C6), 78.41 (Cp), 84.71 (C5),
88.16 (C3), 89.90 (C2), 100.87 (C4), 131.31 (C1).
No reaction was observed for resorcinol. Reaction using
2-phenyphenol gave mainly complexation at the mono-
substituted ring (30%). Reaction 2,20-biphenol gave a 5%
yield of the mono-complexed product. M+: Found: 307.1,
calcd. 307.
1
0.31 g, 25%. H and 13C NMR agreed with the literature
values [21]. The experiment was repeated in the presence
of flaked graphite (2 g) and led to the formation of the phe-
nol complex in 25% yield.
4.1.3. Syntheses using –OH group protection
4.1.3.1. Protection by t-butylation. Phenol was t-butylated
by reaction with tBuBr in dry pyridine for 2 h at 30 ꢁC [22]
to give a 65% yield of pure product. Phenyl-t butylether
(1.5 g, 0.01 mol), ferrocene (5.6 g, 0.03 mol) Al powder
(3 g, 0.111 mol) and AlCl3 powder (8.1 g, 0.06 mol) were
mixed with 1,2,4-trichlorobenzene (TCB) (10.8 g) and
microwaved for 4 min on a medium setting. The excess
AlCl3 was carefully decomposed by the addition of small
portions of ice (50 g). The aqueous mixture was filtered,
and the filtrate treated with 1 M, NH4PF6 (10 ml), then
extracted with CH2Cl2 (2 · 150 ml). After drying the com-
bined CH2Cl2 extracts with anhydrous MgSO4, the CH2Cl2
was removed by rotary evaporation to give an oily solid.
This was dissolved in acetone (10 ml) and added dropwise
to a cold aqeous solution of 0.5 M NaBPh4 (10 ml). The
4.1.4. Miscellaneous reactions
Deprotonation of dimethylphosphite with 60% NaH,
followed by reaction with (g6-fluorobenzene)(g5-cyclopen-
tadienyl) iron (II) hexafluorophosphate in dry THF (RT,
24 h) yielded the methoxybenzene complex (30%). The

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R.M.G. Roberts / Journal of Organometallic Chemistry 691 (2006) 2641–2647
microwave-mediated reaction of 4-phenylazophenol with
ferrocene, Al, AlCl3 in TCB (4 min MED) yielded the ani-
line complex in 53% yield instead of the hoped-for-4-ami-
nophenol complex.
4.2.1.2. H/D exchange reactions. A slurry of dry K2CO3
(0.15 g, 1.1 mmol) in [2H]6-DMSO (1.0 ml) was treated
with III (0.15 g, 0.35 mmol). The mixture shaken for
5 min then filtered directly into an NMR tube and 1H
1
and 13C NMR obtained on the deep red solution. The H
4.2. Part B – complexes with carbonyl substituents
spectrum showed a 77% conversion to the corresponding
carbanion whose d values were: 4.86s (Cp), 6.00 br.s
(H4), 6.14 br.s.(H2,6), 6.85 br.s (H3,5). No signal was
observed for the Me group. From integration, the Me
group of the unreacted parent complex a 27% H/D
exchange had occurred. 13C NMR of the carbanion gave
75.16 (Cp), 77.85 (carbanionic C) 82.60 br (C2,4,6) 86.05
(C3,5). No signal was observed for the Me group.
4.2.1. a-Nitroarene complexes
4.2.1.1. Synthesis of (g6-a-nitro-p-xylene)(g5-cyclopentadi-
enyl) iron (II) PF6(I). To a solution of nitromethane
(1.2 g, 16 mmol) in dry DMSO (10 ml) was added sodium
t-butoxide (0.8 g, 8 mmol) and the whole stirred at RT
for 0.5 h to form a slurry of the nitronate. (g6-4-fluorotol-
uene) (g5-Cp) iron (II) PF6 (1.0 g, 2.6 mmol) was added
and the mixture stirred for 5 min to give a deep red colour.
CF3CO2H (1.4 g, 12 mmol) was added and the mixture
shaken to give a clear brown solution which was added
dropwise to 0.05 M NH4PF6 (75 ml). The resultant yellow
precipitate. was filtered off, washed with distilled H2O and
dried at 100 ꢁC for 2 h.
4.2.2. Syntheses of arylaldehyde and arylketone complexes
4.2.2.1. Method A
4.2.2.1.1. Hydrogen peroxide. (g6-a-Nitrotoluene)(g5-
Cp) iron (II) PF6 (1.0 g, 2.4 mmol) was dissolved in dry
DMSO (20 ml) and NaOtBu (0.3 g, 3.1 mmol) added.
The mixture was stirred for 10 min then 30% H2O2 (5 ml)
added and was accompanied by an exotherm and consider-
able frothing. On cooling, CF3CO2H (1.5 g, 13 mmol) was
added dropwise to give a clear brown-red solution. This
was added slowly to cold aqueous 0.02 M NaBPh4
(75 ml) to give a pale yellow precipitate. which was filtered
off, washed with distilled H2O then air dried to give 0.71 g
A (g6-benzaldehyde)(g5-Cp) iron (II) BPh4, IIA, (43%).
Yield: 0.79 g, 70%. 1H NMR: [2H]6-acetone, d, 2.62s
(Me); 5.26s (Cp); 6.04s (CH2); 6.59d · 2, J = 6.6 Hz,
(H2,3,5,6).
The following a-nitroalkyl complexes were prepared by
the above method (yields in parentheses): a-nitrotoluene,
II, (71%): 1H NMR, d, 5.28, 5.31s (Cp); 6.06s (CH2);
6.64s, 6.68s (H3,4,5,6).
1
a-Nitroethyl benzene, III, (52%): H NMR, d, 2.03d,
J = 6.9 Hz (Me); 5.19s (Cp); 6.17q, J = 6.9 Hz (CH);
6.50m (H2,3,5,6); 6.59m (H4).
4.2.2.2. Method B
4.2.2.2.1. Acidic tin (II) dichloride. (g6-a-Nitrotolu-
ene)(g5-Cp) iron (II) PF6 (1.0 g 2.6 mmol) was added to
SnCl2 (2.2 g, 12 mmol) in conc. HCl (100 ml) and the whole
refluxed for 1.5 h with stirring. The mixture was cooled to
0 ꢁC then filtered and the filtrate treated dropwise with aq
0.3 M NaBPh4 (10 ml) to give a flocculent yellow precipi-
tate. This was filtered and air dried, then extracted with
acetone (80 ml) and chromatographed on neutral alumina
(10 g) eluting with acetone to give 0.32 g IIA, (24%) prod-
uct. The following complexes were obtained by this method:
a-Nitro-o-xylene, IV, (70%), a-nitro-m-xylene, V, 90%:
1H NMR, d, 2.61s (Me); 5.26s (Cp); 6.04s, 6.01s (H2,
CH2); 6.60m (H4,5,6). a-nitro-2-chlorotoluene, VI, (54%).
a-Nitro-2-chloro-p-xylene, VII (70%), a-nitro-4-methy-
lacetanilide, VIII (91%).
The a-nitro-o-toluidine complex, IX, was prepared in
50% yield by treatment of VI with (Me3Si)2NH as
described the following paper [23]. 13C NMR data appear
in Table 1.
Table 1
13C chemical shifts for (g6-a-nitroalkylarene)(g5-Cp) iron (II) complexes
Complex
C1
C2
C3
C4
C5
C6
Cp
Others
I
92.48
93.97
98.63
90.41
90.95
87.60
88.55
104.16
91.43
89.79
105.69
89.60
83.55
89.79
89.40
88.05
88.28
86.79
89.22
88.59
88.01
88.25
90.41
90.95
87.60
88.55
89.88
88.84
89.04
89.31
89.52
78.94
78.62
77.45
20.59, Me; 77.50, CH2
77.72, CH2
17.55, Me; 85.85, CH
II
III
89.40
88.05
88.28
89.31
105.33
90.80
88.84
88.95
IVa
91.25
93.56
88.34
90.05
90.28
87.92
90.03
90.17
77.45
78.96
79.48
78.74
78.82
79.82
79.93
75.18
17.50, Me; 75.40, CH2
20.55, Me; 77.84, CH2
75.18, CH2
19.29, 19.49, Me
74.95, 75.27, CH2
V
VIa,b
VIIa,b
108.62
107.24
103.38
IX
79.39
126.10
69.30
85.56
79.32
87.85
77.25, CH2
a
Solvent [2H]6-DMSO.
BPh4 salt.
b

R.M.G. Roberts / Journal of Organometallic Chemistry 691 (2006) 2641–2647
2647
Table 2
13C NMRa and analytical datab for aldehyde and ketone ArFeCp complexesc
Complex
C1
C2
C3
C4
C5
C6
Cp
CH2
CO
CH analysis
C
H
IA
89.27
90.82
92.31
90.32
90.37
86.99
87.60
87.17
104.36
87.38
89.27
88.95
88.61
89.07
104.59
105.88
90.01
89.58
89.52
90.44
89.27
88.95
88.61
87.60
88.32
86.99
87.60
87.17
86.27
86.10
77.90
77.64
77.70
77.86
77.97
20.24
–
27.00
17.56
19.96
193.22
193.29
198.13
193.18
193.41
79.43 (79.31)
79.0 (79.15)
–
–
–
5.78 (5.94)
5.89 (5.72)
–
–
–
IIA
IIIA
IVA
VA
a
Solvent [2H]6-DMSO.
Calculated values in parentheses.
BPh4 salts.
b
c
acetophenone, IIIA, (43%), o-tolualdehyde, IVA, (35%), m-
tolualdehyde, VA, (22%), p-tolualdehyde, IA, (26%).
The a-nitro-4-methylacetanilide complex gave an insep-
arable mixture of starting material and product. Reaction
of the a-nitrotoluene complex in the absence of SnCl2 gave
a mixture of the corresponding aldehyde and carboxylic
acid complexes.
Acknowledgements
The work was self supported. The author wishes to
thank the University of Essex for laboratory facilities,
Mr. R.J. Ranson for running the NMR spectra, and Mr.
N. Barnard for the mass spectra.
The same reaction with SnCl2 was performed whilst
bubbling argon through the reaction mixture. No product
was formed under these conditions. 13C NMR data and
CH analyses appear in Table 2.
References
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1991.
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4.2.2.2.2. One-pot reaction. The intermediate a-nitro-
toluene complex was prepared as above, using (g6-fluoro-
benzene)(g5-Cp) iron (II) PF6 (0.5 g, 1.38 mmol),
nitromethane (1.2 g 16 mmol), and NaOtBu (0.8 g
8.2 mmol) in dry DMSO (10 ml) with a total reaction time
of 45 min. A solution of SnCl2 (1.1 g, 5.8 mmol) in 6 N
HCl (50 ml) was added to the reaction mixture to give a yel-
low-orange precipitate. The mixture was refluxed for 4 h
and the resultant clear light brown solution cooled in ice
then filtered. The filtrate was extracted with CH2Cl2
(6 · 75 ml). This extract was dried (anhydrous MgSO4)
and evaporated to give a yellow-orange oil which was added
dropwise to 0.06 M aq. NaBPh4 (20 ml). The resultant pre-
cipitate was filtered off, washed with distilled H2O and dried
at 80 ꢁC overnight to give 0.27 g product (33%).
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4.2.2.3. Method C. (g6-Fluorobenzene)(g5-Cp) iron (II)
PF6 (1.0 g, 2.8 mmol) was dissolved in a mixture of dry
DMF (10 ml) and nitroethane (5 ml) and dry, finely ground
K2CO3 (1.2 g, 8.7 mmol) added. The whole was micro-
waved for 60 s on a high setting in the apparatus described
in Ref. [3]. The resulting deep red reaction mixture was
treated with 2 N HCl (25 ml), and the whole microwaved
on a medium setting for a further 60 s. The clear brown
solution was cooled to 0 ꢁC then extracted with CH2Cl2
(3 · 50 ml). After drying and evaporation, a brown solu-
tion was obtained which was washed well with Et2O to
remove residual DMF. The resultant oil was taken up in
acetone (10 ml) and added dropwise to a cold aq. 0.17 M
solution of NaBPh4 (10 ml). The resultant precipitate was
filtered off, washed well with distilled H2O then dried at
70 ꢁC to give a pale yellow solid (0.86 g, 55%) shown by
13C NMR to be the acetophenone complex.