A study of β-hydride abstraction from alkanediyl homobimetallic complexes [{Cp(CO)2Fe}2{μ-(CnH2n)}] (n = 4-10, Cp = η5-C5H5)

Article abstract of DOI:10.1016/j.jorganchem.2006.11.017

The alkyl-bridged iron(II) complexes [{Cp(CO)₂Fe}₂{μ-(C_nH_2n)}] (n = 6-10, Cp = η⁵-C₅H₅) undergo both single and double hydride abstraction when reacted with one equivalent of Ph₃CPF₆ to give both the monocationic complexes, [{Cp(CO)₂Fe}₂{μ-(C_nH_2n-1)}]PF₆, and the dicationic complexes, [{Cp(CO)₂Fe}₂{μ-(C_nH_2n-2)}](PF₆)₂. The ratios of monocationic to dicationic complexes decrease with the increase in the value of n. The complexes where n = 4 and 5 undergo only single hydride abstraction under similar conditions. When reacted with two equivalents of Ph₃CPF₆, the complexes where n = 6-10 undergo double hydride abstraction to give dicationic complexes only. In contrast, the complex where n = 5 gives equal amounts of the monocationic and the dicationic complexes, while the complex where n = 4 only gives the monocationic complex. ¹H and ¹³C NMR data show that in the monocationic complexes one metal is σ-bonded to the carbenium ion moiety while the other is bonded in a η²-fashion forming a chiral metallacylopropane type structure. In the dicationic complexes both metals are bonded in the η²-fashion. The monocationic complexes where n = 4-6, react with methanol to give η¹-alkenyl complexes[Cp(CO)₂Fe(CH₂)_nCH{double bond, long}CH₂] (n = 2-4) as the major products and σ-bonded ether products [{Cp(CO)₂Fe}₂{μ-(CH₂)_nCH(OCH₃)CH₂}] as the minor products. The complex where n = 8 reacted with iso-propanol to give the η¹-alkenyl complex [Cp(CO)₂Fe(CH₂)₆CH{double bond, long}CH₂]. The dicationic complexes where n = 5, 8 and 9 were reacted with NaI to give the respective α, ω-dienes and [Cp(CO)₂FeI].

Full text of DOI:10.1016/j.jorganchem.2006.11.017

Journal of Organometallic Chemistry 692 (2007) 1138–1149
www.elsevier.com/locate/jorganchem
A study of b-hydride abstraction from alkanediyl
homobimetallic complexes [{Cp(CO)2Fe}2{l-(CnH2n)}]
(n = 4–10, Cp = g5-C5H5)
*
Evans O. Changamu, Holger B. Friedrich
School of Chemistry, University of KwaZulu-Natal, Durban 4041, South Africa
Received 6 September 2006; received in revised form 10 November 2006; accepted 10 November 2006
Available online 18 November 2006
Abstract
The alkyl-bridged iron(II) complexes [{Cp(CO)2Fe}2{l-(CnH2n)}] (n = 6–10, Cp = g5-C5H5) undergo both single and double hydride
abstraction when reacted with one equivalent of Ph3CPF6 to give both the monocationic complexes, [{Cp(CO)2Fe}2{l-(CnH2nꢀ1)}]PF6,
and the dicationic complexes, [{Cp(CO)2Fe}2{l-(CnH2nꢀ2)}](PF6)2. The ratios of monocationic to dicationic complexes decrease with the
increase in the value of n. The complexes where n = 4 and 5 undergo only single hydride abstraction under similar conditions. When
reacted with two equivalents of Ph3CPF6, the complexes where n = 6–10 undergo double hydride abstraction to give dicationic com-
plexes only. In contrast, the complex where n = 5 gives equal amounts of the monocationic and the dicationic complexes, while the com-
1
plex where n = 4 only gives the monocationic complex. H and 13C NMR data show that in the monocationic complexes one metal is
r-bonded to the carbenium ion moiety while the other is bonded in a g2-fashion forming a chiral metallacylopropane type structure. In
the dicationic complexes both metals are bonded in the g2-fashion. The monocationic complexes where n = 4–6, react with methanol to
give g1-alkenyl complexes[Cp(CO)2Fe(CH2)nCH@CH2] (n = 2–4) as the major products and r-bonded ether products [{Cp(CO)2-
Fe}2{l-(CH2)nCH(OCH3)CH2}] as the minor products. The complex where n = 8 reacted with iso-propanol to give the g1-alkenyl
complex [Cp(CO)2Fe(CH2)6CH@CH2]. The dicationic complexes where n = 5, 8 and 9 were reacted with NaI to give the respective
a,x-dienes and [Cp(CO)2FeI].
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Alkyl-bridged complexes; Dicationic; Monocationic; Hydride abstraction; Metallacyclopropane; Carbenium ion
1. Introduction
been reported [7,8]. These long chain alkanediyl complexes
are of interest because they may have two effectively inde-
pendent b-CH2 groups, each of which is capable of under-
going hydride abstraction (Fig. 1). No reports on double
hydride abstraction from the same alkanediyl complex
have appeared in the literature. Archer et al. [9] concluded
from IR and NMR data that in heterobimetallic alkanediyl
complexes, where the metals are separated by more than
three CH2 groups, the metals do not influence each other.
This implied that, if the metals were separated by a suffi-
ciently long alkyl bridge, it may be possible to activate both
b-CH2 groups in these dinuclear complexes.
Since King and Bisnette reported the first hydride
abstraction from the alkyl-bridged complex [{Cp(CO)2-
Fe}2{l-(CH2)3}] in 1967 [1], there have been few reports
involving other homodinuclear [2,3] and heterodinuclear
[4–6] complexes. However, there have been no reports of
hydride abstraction reactions involving alkanediyl com-
plexes where the metal centres are separated by more than
six methylene groups, even though these complexes have
*
Friedrich and Moss [6] showed that the reactions of
[{Cp(CO)2Fe(CH2)nRu(CO)2Cp] (n = 4 or 6) with Ph3CPF6
Corresponding author. Tel.: +27 31 2603107; fax: +27 31 2603109.
E-mail address: friedric@ukzn.ac.za (H.B. Friedrich).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.11.017

E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
1139
Cp
H
Cp
H
Fp
H
γ
α
β
β
α
β
β
Fp
C
Fe CH2
CO
CH2
CH2
CH2
CH2
CH2 Fe
OC
C
+
2Ph3CPF6
n = 5 - 10
+
n
OC
CO
CH2
C
α
C
α
n-4
Fp CH2
H
H
Fp
Fig. 1. Structural formula of an alkanediyl complex showing labeling of
CH2 positions.
H
n
n = 6 - 10
Ph3CPF6
H
Fp
gave a mixture of equal amounts of the compounds
[Cp(CO)2Fe{CH2CH(CH2)n}Ru(CO)2Cp]PF6 and [Cp-
(CO)2Fe{(CH2)nCHCH2}Ru(CO)2Cp]PF6 (n = 2 or 4).
There was no evidence of hydride abstraction from both b
carbon atoms. More importantly, Lennon et al. [10,11]
reported the synthesis of stable long chain dicationic iro-
n(II) complexes by a ligand exchange reaction involving
[Cp(CO)2Fe(isobutylene)]+ and a,x-dienes or by treatment
of the corresponding diepoxide CH2(O)CH(CH2)nCH-
(O)CH2 (n = 3–5) with two equivalents of Na[Cp(CO)2Fe],
followed by dehydration with HBF4.
β
n = 4 - 10
C
+
Fp
CH2
C
α
n-2
Fp = Cp(CO)2Fe
H
H
Scheme 1. Reaction of alkanediyl complexes with one and two equivalents
of Ph3CPF6.
dicationic complexes [{Cp(CO)2Fe}2{l-(CnH2nꢀ2)}](PF6)2
(see Scheme 1). The dicationic complexes are formed as yel-
low precipitates after about 2 h of reaction and are easily
separated by filtration under nitrogen. The monocationic
complexes remain in solution and are precipitated as yellow
microcrystalline solids by addition of diethyl ether to the
filtrates obtained after the separation of the dicationic
products. It can be seen from Table 1 that the ratio of mon-
ocationic to dicationic products decreases with increase in
chain length of the bridging alkyl group. Thus it is easier
to remove hydrides from both b-positions in the same
molecule when these are further apart.
The complexes where n = 4 and 5 react with one equiv-
alent of the hydride abstractor to give only the known
monocationic products [{Cp(CO)2Fe}2{l-(CnH2nꢀ1)}]PF6
[3]. There was no evidence of dicationic complexes in the
reaction mixtures even after standing under nitrogen over-
night. This shows that once one hydride is abstracted it
becomes difficult to abstract a second hydride from a
CH2 group near a charged CHd+ moiety, because this
would be strongly held to the carbon atom due to the
inductive effect caused by the CHd+ group. The influence
of the positive charge is seen in the resonances of the pro-
tons and carbon atoms in the 1H and 13C NMR spectra, in
Although valuable information on the nature of metal-
ligand bonding may be obtained from a systematic study
of 13C chemical shifts of a series of compounds [12], most
of the reported mono and dicationic complexes of the types
[{Cp(CO)2Fe}2{l-(CnH2nꢀ1)}]X, and [{Cp(CO)2Fe}2{l-
(CnH2nꢀ2)}]X2 ðX ¼ PFꢀ6 ; BF4ꢀ or BPh4ꢀÞ have not been
studied by 13C NMR spectroscopy. We were, therefore,
interested in the possibility of abstracting two hydrides
from long chain alkyl-bridged complexes to give dicationic
1
complexes and to systematically study their H and 13C
NMR spectra and now report our findings.
2. Results and discussion
2.1. Reactions of [{Cp(CO)2Fe}2{l-(CH2)n}] (n = 4–10)
with one equivalent of Ph3CPF6
The alkanediyl complexes [{Cp(CO)2Fe}2{l-(CH2)n}]
(n = 6–10) react with one equivalent of the hydride
abstractor Ph3CPF6 at room temperature to give
both monocationic [{Cp(CO)2Fe}2{l-(CnH2nꢀ1)}]PF6 and
Table 1
Data for monocationic and dicationic iron (II) complexes
Compound
M.p. (°C)
%Yielda
Elemental analysis
%C Found (Calc)
IR m(CO)/KBr
%H Found (Calc)
[{Cp(CO)2Fe}2(C5H9)]PF6
[{Cp(CO)2Fe}2(C5H8)](PF6)2
[{Cp(CO)2Fe}2(C6H11)]PF6
[{Cp(CO)2Fe}2(C6H10)](PF6)2
[{Cp(CO)2Fe}2(C7H13)]PF6
[{Cp(CO)2Fe}2(C7H12)](PF6)2
[{Cp(CO)2Fe}2(C8H15)]PF6
[{Cp(CO)2Fe}2(C8H14)](PF6)2
[{Cp(CO)2Fe}2(C9H17)]PF6
[{Cp(CO)2Fe}2(C9H16)](PF6)2
[{Cp(CO)2Fe}2(C10H19)]PF6
[{Cp(CO)2Fe}2(C10H18)](PF6)2
a
Dec > 120
Dec > 125
Dec > 119
Dec > 130
Dec > 110
Dec > 130
Dec > 85
Dec > 135
Dec > 90
Dec > 95
Dec > 98
Dec > 135
(40)
(48)
40.2 (41.3)
32.0 (32.1)
40.9 (41.2)
32.8 (33.1)
43.4 (42.3)
33.7 (34.1)
43.6 (43.3)
35.2 (35.1)
44.2 (44.3)
35.8 (36.0)
46.6 (45.2)
36.7 (36.8)
3.4 (3.4)
2.4 (2.6)
3.7 (3.6)
2.6 (2.8)
4.1 (3.8)
3.0 (3.0)
4.0 (4.1)
3.2 (3.2)
4.0 (4.4)
3.2 (3.4)
4.5 (3.6)
3.7 (3.6)
2075, 2032, 1998, 1934
2079, 2039
2076, 2038, 2003, 1941
2073, 2036
2075, 2043, 1989, 1942
2079, 2037
2075, 2035, 1994, 1932
2069, 2015
2076, 2044, 1987, 1929
2076, 2032
2076, 2034, 1998, 1937
2080, 2035
55
4
65
6
18
57
15
32
5
(73)
(73)
(90)
(87)
(88)
27
Values in brackets are yields obtained by reacting starting materials with 2 equiv. of Ph3CPF6.

1140
E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
which the signals are significantly shifted downfield with
respect to the corresponding peaks in the starting materials
(Sections 2.4–2.7).
length of the polymethylene chain. The data are summa-
rized in Table 1. These complexes show a single medium
intensity band in the olefinic C–H stretching region at
3125–3129 cmꢀ1 and a weak band in the C@C stretching
region at 1515–1527 cmꢀ1. The C@C bands are shifted to
smaller wavenumbers by >115 cmꢀ1 relative to free alkenes
as expected for coordinated alkenes [14].
2.2. Reactions of [{Cp(CO)2Fe}2{l-(CH2)n}] (n = 4–10)
with two equivalents of Ph3CPF6
The reactions of the alkanediyl complexes [{Cp(CO)2-
Fe}2{l-(CH2)n}] (n = 6–10) with two equivalents of
Ph3CPF6 result in immediate formation of the dicationic
complexes [{Cp(CO)2Fe}2{l-(CnH2nꢀ2)}](PF6)2 in >70%
yields. These precipitate as soon as the solutions of the
reactants are mixed and are easily separated by filtration
under nitrogen. A minute amount of the monocationic
complex was detected (IR m(CO)) in the filtrate of the reac-
tion of the complex where n = 6 only, but there was too lit-
tle to isolate. The dications are air stable yellow powders,
which thermally decompose without melting in the range
120–135 °C. They are insoluble in most common organic
solvents (e.g. CHCl3, CH2Cl2, and hexane) and were char-
1
2.4. H NMR spectroscopy of the monocationic complexes
[{Cp(CO)2Fe}2{l-(CnH2nꢀ1)}]PF6 (n = 7–10)
1
The H NMR data for the monocationic complexes are
summarized in Table 2. The complexes show two charac-
teristic singlet peaks at 4.9 ppm and 5.9 ppm for the five
equivalent Cp protons of the neutral and cationic Fp
groups, respectively. This is in good agreement with the
data reported for similar complexes [3]. These positions
are not altered with change in alkenyl chain length. The
spectra also show two characteristic doublets (each inte-
grating for 1H) at 4.06 ppm (average JHH = 8.3 Hz) and
3.64 ppm (average JHH = 14.6 Hz) assigned to the diaste-
reotopic protons of the CH2 a to the cationic Fp+ group.
These two protons are cis and trans to the b-CH proton,
respectively, as determined from the coupling constants,
and they show no geminal coupling. The protons of the
CH2 group alpha to the CHd+ (i.e. c to the cationic Fp+,
see Scheme 1) show separate resonances, a distinct multi-
plet at around 2.50 ppm and a multiplet at about
1.60 ppm. Similarly, the protons of the d-CH2 show sepa-
rate resonances, distinct multiplets at 1.69 ppm and at
about 1.40 ppm, respectively. The spectra of the complexes
where n = 7–10 also show unresolved proton resonances
between 1.10 and 1.68 ppm.
1
acterised by H and 13C NMR spectroscopy, IR and ele-
mental analysis.
The complex where n = 4 gave only the monocationic
complex, even after standing for 16 h. Sanders and Giering
reported the synthesis of the dicationic complex [{Cp(CO)2
Fe}2{l-(C4H6)}](HCl2)2 by the reaction of the butadiene
complex [{Cp(CO)2Fe}2{l-(C4H6)}] with anhydrous HCl
gas [13]. However, they did not isolate the compound but
inferred its structure by IR and by its thermal decomposi-
tion to Cp(CO)2FeCl. These authors did not report detec-
tion of butadiene or any other C4 alkene.
The complex where n = 5 gave almost equal amounts of
the monocationic and dicationic complexes after overnight
reaction with two equivalents of Ph3CPF6. Attempts to
force the reaction to go to completion by reaction with
4 mol of Ph3CPF6 only increased the amount of the dicat-
ionic product relative to the monocationic product, but the
reaction did not go to completion. The dicationic complex
[{Cp(CO)2Fe}2{l-(C5H8)}](PF6)2 was found to be unstable
in solution due to the lability of the Cp(CO)2Fe groups.
For example, it was noted that when alkanediyl complex
was reacted with 4 mol of Ph3CPF6 and the mixture
allowed to stand overnight without stirring, the products
obtained were the dicationic complex [{Cp(CO)2Fe}2{l-
(C5H8)}](PF6)2 and the monometallic cationic product
[Cp(CO)2FeCH2@CHC3H7}]PF6.
The presence of the two well resolved doublets assign-
able to the a-CH2 protons, and the observation that both
the c-CH2 (the peaks are ꢁ0.9 ppm apart) and d-CH2
(the peaks are ꢁ0.2 ppm apart) protons are diastereotopic
1
in the H NMR spectra of these complexes is convincing
evidence that the complexes are chiral. The b-CH carbon
is the chiral centre and it is therefore expected that the
methylene protons in its neighbourhood should be non-
equivalent [15]. The influence of an asymmetric centre is
often observed in protons that are more than two bonds
away from the asymmetric centre. The pattern of signals
in the spectra, especially the signals assignable to the
a-CH2 protons, resemble those observed in the reported
complexes [{Cp(CO)2Fe(CH2@CHOEt)]PF6 [16] and
[{Cp(CO)2Fe(CH2@CHOMe)]PF6 [17] in which the metals
have been shown to be g2-bonded to the carbenium ion
moieties. Evidently, therefore, the same bonding prevails
in these bimetallic complexes.
2.3. IR spectroscopy
The monocationic complexes, [{Cp(CO)2Fe}2{l-
(CnH2nꢀ1)}]PF6 (n = 4–10), show four carbonyl absorption
peaks that characterise the separate cationic and neutral Fp
centres (Fp@Cp(CO)2Fe; cationic Fp: mCO above 2030 and
2070 cmꢀ1; neutral Fp: mCO around 1940 and 2012 cmꢀ1).
The dications on the other hand show only the two peaks
characteristic of the cationic Fp centres. There is no signif-
icant shift in the mCO peak positions upon changing the
2.5. 13C NMR spectroscopy of the monocationic complexes
[{Cp(CO)2Fe}2{l-(CnH2nꢀ1)}]PF6
The 13C NMR data for the monocationic complexes are
summarized in Table 3. These complexes show two peaks

Table 2
1H NMR data for the monocationic complexes [{Cp(CO)2Fe}2{l-(CnH2nꢀ1)}]PF6 in acetone-d6
n
r-CpFe
p-CpFe
cis-FeCH2, 3J(HH)b trans-FeCH2, 3J(HH)b b-CH
c-CH2
d-CH2
Others (not resolved) BPh4
4a
5a
7
8
9
5.0 (5H, s)
4.9 (5H, s)
4.9 (5H, s)
4.9 (5H, s)
4.9 (5H, s)
4.9 (5H, s)
5.8 (5H, s)
5.8 (5H, s)
5.9 (5H, s)
5.9 (5H, s)
5.9 (5H, s)
5.9 (5H, s)
3.9 (1H, d, 6.7)
4.0 (1H, d, 7.9)
4.1 (1H, d, 8.2)
4.1 (1H, d, 8.4)
4.1 (1H, d, 8.2)
4.1 (1H, d, 8.2)
3.5 (1H, d, 14.7)
3.6 (1H, d, 13.7)
3.6 (1H, d, 14.7)
3.7 (1H, d, 14.5)
3.7 (1H, d, 14.6)
3.7 (1H, d, 14.3)
5.3 (1H, m)
5.3 (1H, m)
5.3 (1H, m)
5.3 (1H, m)
5.3 (1H, m)
5.3 (1H, m)
2.5 (1H, m); 1.3 (1H, m) 1.6 (2H, m)
2.6 (1H, m); 1.5 (1H, m) 1.8 (1H, m); 1.6 (1H, m) 1.8 (2H, m)
2.5 (1H, m); 1.4 (1H, m) 1.7 (1H, m);1.5 (1H, m) 1.4–1.6m
2.5 (1H, m)
2.5 (1H, m); 1.3 (1H, m)
2.5 (1H, m);
7.4s, 7.0t, 6.8t
7.4s, 7.0t, 6.8t
1.3–1.7m
1.3–1.6m
1.1–1.7m, 15H
10
a
Counter ion is BPhꢀ4 .
Coupling constants are given in Hz.
b
Table 3
13C NMR data for the complexes [Cp(CO)2Fe(CnH2nꢀ1)Fe(CO)2]PF6
a
n
r-CpFeCO
p-CpFeCO
r-CpFe
p-CpFe
p-FeCH2
CH
CHCH2
CHCH2CH2
CHCH2CH2CH2
a-CH2
b-CH2
c-CH2
d-CH2
BPh4
4b
5b
7
8
9
217.3, 217.2
217.8
218.0
218.1
218.1
210.7, 208.5
210.6, 208.4
210.4, 208.2
210.5, 208.2
210.4, 208.2
210.5, 208.2
85.7
85.6
85.5
85.5
85.5
85.3
88.8
89.0
89.1
89.1
89.1
89.3
51.5
53.6
53.8
53.9
53.9
53.7
89.2
87.9
88.8
88.3
88.3
88.0
44.3
41.3
33.8
34.2
34.4
34.4
5.2
1.4
2.3
2.6
2.7
2.4
135.9, 124.9d, 121.1
135.9, 124.8d, 121.1
41.1
32.1
32.5
32.4
34.3
37.5
37.7
37.8
37.6
36.2
28.4
27.8
28.6
36.1
28.0
32.2
36.1
36.3
10
a
218.3
CH2 a to the r-bonded Fe etc.
b
counter ion is BPhꢀ4 .

1142
E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
at about 86 ppm and 89 ppm assignable to the Cp carbons
of the neutral and cationic Fp groups, respectively. These
positions are in good agreement with the data reported
for mononuclear cationic complexes [18] and dinuclear
neutral complexes [19]. The neutral Fp carbonyls show
one peak at around 217 ppm, while the cationic Fp carbo-
nyls show separate peaks at 210 ppm and 208 ppm, respec-
tively, indicating that the carbonyls are non-equivalent, as
expected for these structures in which the b carbon is chi-
ral. Furthermore, molecular structures of the complexes
[Cp*(CO)2Fe{l-(C3H5)}Fe(CO)2Cp]PF6 [4], [Cp*(CO)2-
+
β
Cp(CO)Fe
Fe(CO)2Cp
Fe(CO)2Cp
Cp(CO)Fe
β
+
α
α
(a)
(b)
Fig. 2. (a) Metallacyclopropane structure, (b) p-bonded structure.
chain carbenium ion complexes. It therefore seems more
accurate to represent the bonding between the carbenium
ion and the transition metal as a metallacyclopropane type
structure as shown in Fig. 2a rather than the traditional
side-on bonding structure [14,20] in Fig. 2b.
Fe{l-(C3H5)}Ru(CO)2Cp]PF6
(Cp* = g5-C5Me5)
[5],
It has been reported that p-complexation with an Fp+
group shifts an unsubstituted alkene carbon upfield by
60 ppm in the 13C NMR spectra [12]. Given that the chem-
ical shifts of the a and b olefinic carbons of terminal olefins
normally appear at about 114 and 140 ppm, respectively
[15], p-complexation with an Fp+group would shift the a
carbon resonances upfield to about 54 ppm and the b car-
bon to about 80 ppm. This is in close agreement with the
data given in column 6 of Table 3, but the b @CH reso-
nances are shifted much further upfield than expected for
this bonding mode (see column 7 in Table 3). Furthermore,
considering the increased chemical shift differences between
the olefinic carbon atoms of the carbenium ion complexes
(Table 4), it is clear that there is a much greater contribu-
tion from back-donation to the overall bonding between
the metals and the ‘‘carbenium ions’’ [12]. Increased
back-donation from the metal to the carbenium ion can
also be deduced from the deshielding of the carbon atoms
of the cyclopentadienyl ring of the Fp+ group (d 89.1 ppm)
relative to those of the neutral Fp group (d 85.5 ppm)
(Table 3).
[{Cp(CO)2Fe(CH2@CHOEt)]PF6 [16] and [{Cp(CO)2-
Fe(CH2@CHOMe)]PF6 [17] show that one of the carbonyls
is cis to the a-CH2, while the second is cis to b CHd+, which
form the metallacyclopropane structure with the Fe atom.
Therefore, they are effectively in different magnetic envi-
ronments and hence they show different signals in the 13C
NMR. They are shielded by more than 7 ppm relative to
the starting materials. This may be due to reduced back
donation from the metal to the CO because the electrons
are directed to the b-CHd+ group. The reduced back dona-
tion causes the oxygen atom to donate more electrons to
the C atom thus causing shielding. This is corroborated
by the IR spectra in which the cationic Fp carbonyls occur
at higher wavenumbers, indicating strengthened C–O
bonds as compared to the neutral Fp carbonyls.
All the complexes show a weak resonance at about
88 ppm assignable to the carbon of the b CHd+ group in
the carbenium ion moiety. This is significantly less
deshielded than the b CH moiety of [{Cp(CO)2Fe}2{l-
(C3H5)}]PF6, which resonates at 128 ppm, but sufficiently
significantly deshielded to imply a considerable degree of
carbenium ion character. The carbon of the CH2 a to the
Fp+ group shows a resonance at about 54 ppm which is
more deshielded than the a carbon atom of the com-
plex [{Cp(CO)2Fe}2{l-(C3H5)}]PF6 which resonates at
24 ppm. In all the complexes the carbon atom of the CH2
group a to the b CHd+ group (c to the Fp+ group) is sig-
nificantly less deshielded than would be expected for a
CH2 group next to a positively charged CH group. For
example, in the neutral complex [{Cp(CO)2Fe}2{l-
(CH2)4}], the b-CH2 carbon atoms resonate at 43.6 ppm
in the 13C NMR (acetone-d6) spectrum. On the other hand,
in the corresponding carbenium ion complex [{Cp(CO)2-
Fe}2{l-(C4H7)}]PF6, the c-CH2 (a to CHd+ group and b
to the neutral Fp group) resonates at 44.3 ppm in the 13C
NMR spectrum. Thus the c-CH2 is shifted downfield by
only 0.7 ppm relative to the neutral complex. Similar obser-
vations have been made in the 13C NMR spectra of the
shorter chain complexes [Cp*(CO)2Fe{l-(C3H5)}Fe-
(CO)2Cp]PF6 and [Cp*(CO)2Fe{l-(C3H5)}Ru(CO)2Cp]-
PF6 (Cp* = g5-C5Me5). X-ray crystallographic data of
these complexes show that the metal attached to the Cp*
ligand is coordinated to the carbenium ion in a g2-fashion
leading to a metallacyclopropane type structure [4,5]. This
suggests that similar coordination is present in these long
1
2.6. H NMR spectroscopy of the dicationic complexes
[{Cp(CO)2Fe}2{l-(CnH2nꢀ2)}](PF6)2 (n = 5–10)
The 1H NMR data for these complexes are summarized
in Table 5. The spectra show that hydrides were abstracted
from both of the b-CH2 groups. For example, they show
only one singlet peak at about 5.90 ppm assignable to the
10 equiv. Cp protons of the cationic Fp groups. This posi-
tion does not significantly change with increase in the car-
bocation chain length and is deshielded relative to that of
the Cp group in the starting material (4.7 ppm). These
complexes have two chiral centres (one at each b-CH
Table 4
Chemical shifts of olefinic carbon atoms of some compounds and the
differences between them
Compound
@CH2(C1)
@CH(C2)
d(C2 ꢀ C1)
[{Cp(CO)2Fe}2(C4H7]BPh4)
[{Cp(CO)2Fe}2(C5H9)]BPh4
[{Cp(CO)2Fe}2(C7H12)](PF6)2
[{Cp(CO)2Fe}2(C8H14)](PF6)2
[{Cp(CO)2Fe}2(C9H16)](PF6)2
[{Cp(CO)2Fe}2(C10H19)]PF6
51.5
53.6
53.8
53.9
53.9
53.7
89.2
87.9
88.8
88.3
88.3
88.0
36.7
34.3
35.0
34.4
34.4
34.3

E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
1143
group) and thus there are two diastereomeric possibilities:
RR(SS) and RS(SR) which may be present in equal
amounts in solution. However, the spectra of the com-
plexes where n = 7–10 do not show any evidence to support
the existence of more than one diastereomer in solution.
This is not surprising given the fact that in these complexes
the chiral centres are separated by more than three CH2
groups, in which case they are too far apart to induce a
diastereomeric effect. Thus, the spectra observed for the
diastereomers are indistinguishable by NMR spectroscopy.
This is confirmed by the 13C NMR spectra (Section 2.7).
The spectrum of the complex where n = 6 suggests that
the chiral centres are sufficiently close and there appear to
be two pairs of diastereomers in equal amounts in solu-
tion. For example, the expected doublets assignable to
the a-CH2 protons overlap partially to resemble triplets,
but the signals of the other methylene protons overlap
completely so that they are indistinguishable. The spec-
trum of the complex where n = 5 clearly shows the pres-
ence of two pairs of diastereomers in solution. Four
signals are observed as expected for each pair of diaste-
reomers as follows: a multiplet for the b-CH protons,
two doublets for the diastereotopic a-CH2 protons and
a multiplet assignable to the two c-CH2 protons, which
may be equivalent because their environments are mirror
images. The chemical shifts of the signals are significantly
different so that all eight signals are seen separately in the
spectrum.
2.7. 13C NMR spectroscopy of the dicationic complexes
[{Cp(CO)2Fe}2{l-(CnH2nꢀ2)}](PF6)2
The 13C NMR data are summarized in Table 6. The
number of peaks assignable to the carbon atoms of the car-
benium ion moiety in the spectra of the complexes where
n = 6–10 support the conclusion that the two pairs of dia-
stereomers are not distinguishable by NMR. For example,
in the complexes where n is even the number of peaks
observed is 1/2n, while 1/2n + 1 peaks were observed in
spectra of the complexes where n is odd. Thus, the chiral
centres are sufficiently far apart that they do not interact
and the possible diastereomers are not distinguishable by
13C NMR spectroscopy. All the spectra show one peak
around 89 ppm assigned to the Cp carbons of the cationic
Fp group. This is in good agreement with the data reported
for mononuclear monocationic complexes [18]. The spectra
show two resonances at about 210.6 ppm and 208.2 ppm
assignable to the cationic Fp carbonyls. The number of
peaks observed in the spectrum of the complex where
n = 5 supports the suggestion that there are two pairs of
diastereomers in solution. For example, it shows four reso-
nances at 210.7, 210.5, 208.7 and 208.6 ppm assignable to
the cationic Fp carbonyl carbon atoms. Moreover, the
spectrum also shows that the signals of the carbon atoms
closest to the chiral centres (i.e. a-CH2 and c-CH2) are
split. This is convincing evidence that diastereomers are
present in solution [21]. There are no 13C NMR data for

1144
E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
Table 6
13C NMR data for [{Cp(CO)2Fe}2{l-(CnH2nꢀ2)}](PF6)2 in acetone-d6
n
CO
Cp
FeCH2
b-CH
c-CH2
d-CH2
x-CH2
BPh4
5a
6b
7
210.7, 210.5,208.7, 208.6
211.3, 209.1
210.2, 208.0
210.3, 208.1
211.5, 209.5
210.4, 208.2
210.3, 208.3
211.5, 209.3
90.6
90.2
89.2
89.2
90.4
89.2
89.0
90.3
56.3, 55.3
56.0
54.3
54.1
55.5
54.1
53.9
55.1
87.9
85.6
86.5
87.4
88.3
87.8
87.4
89.1
42.8, 42.7
39.5
35.4
35.7
37.2
35.9
36.0
37.2
136.9, 125.8, 122.2
29.3
31.7
33.1
32.0
32.2
33.4
8
8a
9
137.1, 126.1d, 122.4
135.9, 124.9, 121.2
28.5
28.3
29.4
9a
10
a
Counter ion is BPhꢀ4 .
Recorded in CD3CN.
b
long chain dicationic complexes of this type in the litera-
ture to compare.
talline, but only when n = 4 and 5 was a change observed
from microcrystals in the PF6 salts to bright yellow plates
in the BPh4 salts. The other complexes still formed powders
(see Table 7).
2.8. Reaction with sodium tetraphenylborate
When reacted with sodium tetraphenylborate in ace-
tone, the complexes [{Cp(CO)2Fe}2(C4H7)]PF6, [{Cp-
(CO)2Fe}2(C5H9)]PF6, [{Cp(CO)2Fe}2(C5H8)](PF6)2 and
[{Cp(CO)2Fe}2(C9H16)](PF6)2 readily underwent counter
ion exchange. The displacement of the PFꢀ6 by BPh4ꢀ was
confirmed by 1H- and 13C NMR spectroscopy and elemen-
tal analysis. The counter ion BPhꢀ4 confers more stability to
the dicationic complexes and makes them more soluble in
deuterated acetone. Thus, whereas the PFꢀ6 complexes give
broad signals in the 1H NMR spectra, the BPhꢀ4 complexes
give spectra with sharp and well resolved resonances in
solution. However, even when this counter ion was present,
the dicationic complex where n = 5 still decomposed in ace-
tone-d6 with the loss of Fp+ groups to give the FpBPh4 salt
and 1,4-pentadiene. It had been anticipated that the change
of the counter ion would make the compounds more crys-
2.9. Reactions with NaI, CF3COOH, CH3OH and
(CH3)2CH2OH
When the dicationic complexes where n = 5, 8 and 9
reacted with NaI in deuterated acetone in NMR tubes they
liberated the respective a,x-dienes which were detected by
proton NMR spectroscopy (see Scheme 2). This is further
evidence that the long chain alkanediyl complexes under-
went double hydride abstraction. The monometallic com-
plex [Cp(CO)2Fe(C5H10)]BPh4 gave pentene on reaction
with NaI. The fact that the complexes react with a nucleo-
phile (Iꢀ) to give alkenes indicates that there is more posi-
tive charge on the metal centre than on the olefinic carbon
atoms, making the alkene group less reactive towards
nucleophiles. This behaviour is similar to umpolung,a phe-
nomenon observed in transition metal olefin complexes
Table 7
Data for [Cp(CO)2Fe(CnH2nꢀ1)Fe(CO)2] BPh4
n
%Yield
M.p. (°C)
IR m(CO) (cmꢀ1) in CH2Cl2
Elemental analysis
C Found (Calc)
H Found (Calc)
4
5
5a
8a
9a
57
72
70
74
79
Dec > 120
Dec > 128
Dec > 115
Dec > 110
Dec > 125
2071, 2034, 2008, 1950
2073, 2036, 2004, 1945
2079b, 2041
69.4 (69.2)
68.7 (69.6)
74.5 (75.9)
76.4 (76.3)
76.7 (76.4)
5.1 (5.1)
5.3 (5.5)
5.8 (5.6)
5.8 (5.9)
5.9 (6.0)
2072b, 2034
2071b, 2033
a
Dicationic complex.
KBr pellet.
b
H
C
H
Fp
H
Fp
C
CH CH2
+
CH2
NaI
Acetone -d6
CH
2FpI
+
+
CH2
CH2
n-4
C
C
n-4
H
H
H
n = 5, 8, 9
Scheme 2. Reactions with sodium iodide.

E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
1145
[22]. This reaction also supports the conclusion that the
bonding between the metal and the carbenium ion moiety
tends more towards the metallacyclopropane model than
the p-bonded model.
The most significant difference (chemically) between
metallacyclopropanes and those olefins coordinated
according to the Dewar–Duncason–Chatt model is that
the latter tend to have a residual positive charge on the
vinylic carbon while the former have it on the metal. The
latter are subject to nucleophilic attack on the vinylic car-
bon [22] leading to nucleophilic addition products rather
than olefin liberation.
CH(OCH3)(CH2)6Fe(CO)2Cp] as the minor product. Sub-
limation at 80 °C under reduced pressure gave the g1-alke-
nyl complex as the sublimate but the ether complex
decomposed in the process. Thus, the low yields of the
r-bonded ether complexes [Cp(CO)2FeCH2CH{OCH-
(CH3)2}R] (R@CH3, n-C4H9 and n-C13H27) reported by
Clayton et al. [23] in the reactions of the monometallic
olefin complexes [Cp(CO)2Fe(g2-CH2@CHR)]+ with iso-
propanol may be due to the fact that the free olefin, which
they may not have detected, is the major product.
These reactions indicate that the metal centre is more
electrophilic than both olefinic carbons. The formation of
the r-bonded ether complexes does, however, indicate that
there is some degree of the positive charge on the b-CHd+
group.
The complex [{Cp(CO)2Fe}2(C4H7)]PF6 reacted with
CF3COOH in THF to give the previously reported cationic
monometallic complex [Cp(CO)2FeCH2@CHCH2CH3]PF6
[23] and the acetate complex [Cp(CO)2FeOOCCF3] as
detected by NMR and IR spectroscopy. The NMR spectra
indicate that the metal in the complex [Cp(CO)2-
FeCH2@CHCH2CH3]PF6 forms a metallacyclopropane
type structure with the carbenium ion moiety. For exam-
ple, the protons of both the a- and c-CH2 groups are dia-
stereotopic, and the 13C NMR spectrum shows two
carbonyl peaks.
The monocationic complexes [{Cp(CO)2Fe}2{l-
(CnH2nꢀ1)}]PF6, (n = 4–6) react with methanol to form
the previously reported [24] g1-alkenyl complexes,
[Cp(CO)2Fe(CH2)nꢀ2CH@CH2], as the main products
and the new r-bonded ether complexes, [Cp(CO)2FeCH2-
CH(OCH3)(CH2)nꢀ2Fe(CO)2Cp] as the minor products
(see Scheme 3). The r-bonded ether complexes were very
unstable and were only detected by 1H NMR spectroscopy.
The monometallic olefin complex [Cp(CO)2FeCH2@
CHCH2CH3]PF6 reacted with methanol in an NMR tube
giving 1-butene as the major product and the r-bonded
ether complex, [Cp(CO)2FeCH2CH(OCD3)CH2CH3], as
the minor product. Monometallic ether complexes have
been reported in high yields (>70%) [25] when Fp ethene
and propene complexes were reacted with methanol, while
a lower yield of 18% was achieved with a styrene complex.
The complex [{Cp(CO)2Fe}2{l-(C8H15)}]PF6 reacted
with iso-propanol to give the g1-alkenyl complex
[Cp(CO)2Fe(CH2)6CH@CH2] as the major product (95%
yield) and the r-bonded ether complex [Cp(CO)2FeCH2-
2.10. Conclusions
The reactions of the complexes [{Cp(CO)2Fe}2{l-
(CnH2n)}], where n = 4–10, with one and two equivalents
of Ph3CPF6 have shown that the CH2 groups b to the metal
centres can be activated independently in complexes where
n P 5. The NMR data have shown that in the monocat-
ionic complexes, one metal centre is r-bonded to one end
of the carbenium ion moiety, while the other is bonded
to the olefinic end in a fashion leading to chiral metallacy-
clopropane type structures. In the dicationic complexes,
both metals form chiral metallacyclopropane type struc-
tures with the carbenium ion moieties. The complex where
n = 4 did not give the dicationic complex under any of the
conditions used and thus n = 5 appears to be the lower
limit for double hydride abstraction.
3. Experimental
3.1. General procedures
All manipulations of the organometallic compounds
were carried out under nitrogen using standard Schlenk
line techniques. The complexes [Cp(CO)2Fe]2 [26],
[{Cp(CO)2Fe}2{l-(CH2)n}] (n = 4–10) [27] were synthes-
ised by published methods. Triphenylcarbenium hexaflu-
orophosphate (Aldrich) was used as purchased without
H
CH3O
C
Fp
CH2
Fp
CH2
n
H
C
Fp
H
minor product
H
C
CH3OH
Na2CO3
+
CH2
Fp
n
H
C
CH2
H
C
H
CH2
CH2
Fp
+ [Cp(CO)2Fe]2
H2C
n
major product
Scheme 3. Reaction of the carbenium ion complexes with methanol.

1146
E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
further purification. Tetrahydrofuran and hexane were dis-
tilled from sodium/benzophenone ketyl under nitrogen.
Diethyl ether was dried and distilled from sodium wire.
Dichloromethane was dried and distilled from phospho-
rous pentoxide under nitrogen. Acetone was dried by
refluxing over anhydrous calcium chloride and distilling
under nitrogen. Hexane, THF and diethyl ether were kept
over sodium wire; the other solvents were kept over molec-
ular sieves and nitrogen saturated before use.
3.5. Reaction of [{Cp(CO)2Fe}2{l-(CH2)4}] with two
equivalents of Ph3CPF6
A filtered solution of Ph3CPF6 (0.33 g, 0.84 mmol) in
CH2Cl2 (10 ml) was added to a solution of [{Cp(CO)2-
Fe}2{l-(CH2)4}] (0.17 g, 0.42 mmol) in CH2Cl2 (2 ml) in
a Schlenk tube and the mixture allowed to stand for 10 h
at room temperature under nitrogen. No precipitate was
observed. The IR m(CO) spectrum showed that only the
monocationic complex had formed. Work-up was done
as in Section 3.2. The elemental analysis data and IR spec-
trum matched that of the reported compound [{Cp(CO)2-
Fe}2{l-(C4H7)}]PF6 [3].
3.2. Reaction of [{Cp(CO)2Fe}2{l-(C4H8)}] with one
equivalent of Ph3CPF6
A filtered solution of Ph3CPF6 (0.30 g, 0.50 mmol) in
CH2Cl2 (10 ml) was added to a solution of the complex
[{Cp(CO)2Fe}2{l-(CH2)4}] (0.19 g, 0.50 mmol) in CH2Cl2
(2 ml) in a Schlenk tube and the mixture allowed to stand
for 16 h under nitrogen at room temperature. The orange
red solution was then filtered through a cannula into a
clean pre-weighed Schlenk tube. Dry nitrogen-saturated
diethyl ether was added to the mother liquor until the yel-
low solid precipitated out. This was allowed to settle and
the mother liquor syringed off. The solid was dried under
reduced pressure and found to be the reported monocat-
ionic complex [{Cp(CO)2Fe}2{l-(C4H7)}]PF6 [3].
3.6. Reaction of [{Cp(CO)2Fe}2{l-(CH2)5}] with two
equivalents of Ph3CPF6
A filtered solution of Ph3CPF6 (0.68 g, 1.76 mmol) in
CH2Cl2 (10 ml) was added to a solution of [{Cp(CO)2-
Fe}2{l-(CH2)5}] (0.37 g, 0.88 mmol) in CH2Cl2 (2 ml) in
a Schlenk tube and the mixture was allowed to stand over-
night under nitrogen at room temperature. At the end of
the reaction period a yellow precipitate had settled at the
bottom of the Schlenk tube. The mother liquor was filtered
through a cannula into a pre-weighed Schlenk tube, the
precipitate washed twice with 2 ml portions of CH2Cl2
and dried under reduced pressure. This was found to be
the new dicationic compound [{Cp(CO)2Fe}2{l-(C5H8)}]-
(PF6)2. Diethyl ether was added to the mother liquor and
a yellow solid precipitated out. The mother liquor was
syringed off and the solid dried under reduced pressure.
The elemental analysis data and IR spectrum matched that
of the reported compound [{Cp(CO)2Fe}2{l-(C5H9)}]PF6
[3].
3.3. Reaction of [{Cp(CO)2Fe}2{l-(C5H10)}] with one
equivalent of Ph3CPF6
The same procedure as described in Section 3.2 was used
and only the reported [3] monocationic [{Cp(CO)2Fe}2{l-
(C5H9)}]PF6 complex was obtained.
3.4. Reactions of [{Cp(CO)2Fe}2{l-(CnH2n)}] (n = 6–10)
with one equivalent of Ph3CPF6
3.7. Reaction of [{Cp(CO)2Fe}2{l-(CH2)5}] with four
equivalents of Ph3CPF6
The procedure for the complex where n = 6 will be
described to illustrate the general procedure followed. A
filtered solution of Ph3CPF6 (0.42 g, 1.07 mmol) in
CH2Cl2 (10 ml) was added to a solution of the complex
[{Cp(CO)2Fe}2{l-(CH2)6}] (0.47 g, 1.07 mmol) in CH2Cl2
(2 ml) in a Schlenk tube and the mixture allowed to stand
under nitrogen at room temperature. After 2 h a yellow
precipitate had settled at the bottom of the Schlenk tube.
The mother liquor was then filtered through a cannula
into a pre-weighed Schlenk tube and treated as explained
below. The precipitate was washed twice with 2 ml por-
tions of CH2Cl2 and dried under reduced pressure and
found to be the dicationic compound [{Cp(CO)2Fe}2{l-
(C6H10)}](PF6)2. Diethyl ether was added to the mother
liquor until the yellow solid precipitated out. This was
allowed to settle and the mother liquor syringed off.
The solid was dried under reduced pressure and found
to be the monocationic complex [{Cp(CO)2Fe}2{l-
(C6H11)}]PF6 [3]. The complexes where n = 7–10 were
treated similarly and gave the new monocationic and
dicationic complexes.
A solution of Ph3CPF6 (1.83 g, 4.72 mmol) in 10 ml
CH2Cl2 was added to a solution of [{Cp(CO)2Fe}2{l-
(CH2)5}] (0.5 g, 1.2 mmol) in 2 ml CH2Cl2 and the mixture
allowed to stand under nitrogen for 4 h. The solution
turned yellow green and a yellow precipitate was observed
at the bottom of the reaction vessel. Work-up proceeded as
reported in Section 3.2 above to give the dicationic com-
plex [{Cp(CO)2Fe}2{l-(C5H8)}](PF6)2 and the monocat-
ionic complex [{Cp(CO)2Fe}2{l-(C5H9)}]PF6.
In another experiment, the reaction above was allowed
to continue overnight instead of 4 h. Again the dicationic
product was obtained but in place of the bimetallic mocat-
ionic complex, the previously reported [23] monometallic
cationic product complex [Cp(CO)2FeCH2@CHC3 H7]PF6
was isolated after work-up. M.p. = 110–114 °C (partial
1
decomposition). IR m(CO) (cmꢀ1) 2075, 2038; H NMR
(acetone-d6) in ppm, 5.95 (Cp, singlet, 5H), 5.28m
(CH2@CH, 1H); 4.08d (cis-CH2@CH, 1H, JHH = 5.0 Hz),
3.67d (trans-CH2@H, 1H, JHH = 14.2 Hz), 2.52m, 1.71m

E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
1147
(CHCH2, 2H), 1.53m (CHCH2CH2, 2H), 0.97t (CH3 3H,
JHH = 6.3 Hz); 13C NMR in ppm, 90.4 (Cp), 89.0
(CH2@CH), 55.3 (CH2@CH), 39.1 (CHCH2), 26.5
(CHCH2CH2), 13.7 (CH3); elemental analysis, Found
(Calc) %, C, 36.9 (36.7); H, 3.7 (4.1).
nula into a pre-weighed Schlenk tube. Diethyl ether was
added to the solution to precipitate the product. A yellow
powder precipitated. The mother liquor was syringed off
and the solid [Cp(CO)2Fe]2{l-(C5H8)}](BPh4)2 dried under
reduced pressure.
In a separate experiment, the reaction above was
allowed to continue overnight. After work up, the mono-
metallic complex [Cp(CO)2FeCH2@CHC3H7]BPh4 was
isolated and not the expected dicationic complex. The com-
pound decomposed above 115 °C; IR m(CO) (CH2Cl2)
3.8. Reactions of the [{Cp(CO)2Fe}2{l-(CH2)n}]
(n = 6–10) with two equivalents of Ph3CPF6
The procedure for the complex where n = 6 is described
as an example of the general procedure used in these reac-
tions. A filtered solution of Ph3CPF6 (0.61 g, 1. 76 mmol)
in CH2Cl2 (10 ml) was added to a solution of [{Cp(CO)2-
Fe}2{l-(CH2)6}] (0.35 g, 0.79 mmol) in CH2Cl2 (2 ml) in a
Schlenk tube. A yellow precipitate appeared upon mixing
of the solutions. However, the mixture was allowed to stand
for 2 h under nitrogen at room temperature to ensure com-
plete reaction. The mother liquor was filtered through a
cannula into a pre-weighed Schlenk tube, the precipitate
washed twice with 2 ml portions of CH2Cl2 and dried under
reduced pressure. This was found to be the dicationic com-
pound [{Cp(CO)2Fe}2{l-(C6H10)}](PF6)2. A very small
amount of the monocationic product was detected by IR
in the mother liquor, but there was too little to isolate.
The complexes where n = 7–10 were treated in the same
way as the complex where n = 6 and only dicationic com-
plexes were obtained. No monocationic complexes were
detected in the respective mother liquors.
1
(cmꢀ1) 2071, 2035; H NMR (acetone-d6) in ppm, 7.36s,
6.95t, 6.80t (BPh4) 5.85 (Cp, singlet, 5H), 5.28m
(CH2@CH, 1H); 4.04d (cis-CH2@CH, 1H, JHH = 10.5 Hz),
3.65d (trans-CH2@CH, 1H, JHH = 14.8 Hz), 2.51m, 1.70m
(CHCH2, 2H), 1.53m (CHCH2CH2, 2H), 0.99t (CH3, 3H,
JHH = 7.1 Hz); 13C NMR in ppm, 135.9, 124.9d (B-C,
JBC = 5.9 Hz), 121.1 (BPh4), 89.1 (Cp), 87.8 (CH2@CH),
54.0 (CH2@CH), 38.0 (CHCH2), 25.4 (CHCH2CH2), 12.6
(CH3); elemental analysis, Found (Calc)%, C, 74.5 (76.5);
H, 5.9 (6.1).
3.12. Reaction of [{Cp(CO)2Fe}2{l-(C9H16)}](PF6)2
with NaBPh4
The complex [{Cp(CO)2Fe}2{l-(C9H16)}](PF6)2 (0.20 g,
0.26 mmol) and NaBPh4 (0.21 g, 0.63 mmol) were weighed
into a Schlenk tube and 10 ml acetone added. The mixture
was stirred for 3 h (the dicationic complex is sparingly sol-
uble in acetone). The mixture was filtered through a can-
nula into a pre-weighed Schlenk tube. Diethyl ether was
added to the solution to precipitate the product as a yellow
powder. The mother liquor was syringed off and the solid
dried under reduced pressure.
3.9. Reaction of [{Cp(CO)2Fe}2{l-(C4H7)}]PF6 with
NaBPh4
The compound [{Cp(CO)2Fe}2{l-(C4H7)}]PF6 (0.12 g,
0.22 mmol) and NaBPh4 (0.17 g, 0.48 mmol) were weighed
into a Schlenk tube and 10 ml acetone added. The mixture
was stirred for 1 h. The solvent was then removed under
reduced pressure. The residue was extracted thrice with
20 ml CH2Cl2 and filtered through a cannula into a pre-
weighed Schlenk tube. Diethyl ether was added to the solu-
tion to precipitate the product. A bright yellow-orange
solid precipitated as thin plates. The mother liquor was syr-
inged off and the solid dried under reduced pressure.
3.13. Reactions of some of the cationic complexes with
sodium iodide
Approximately 10 mg of a given complex was dissolved
in N2-saturated deuterated acetone in an NMR tube and its
1H NMR spectrum recorded. About 10 mg of NaI was
added to the solution in the NMR tube and the reaction
followed by recording spectra at 5 min intervals until there
was no more change observed in the spectra. The com-
plexes [{Cp(CO)2Fe}2{l-(CnH2nꢀ2)}](BPh4)2 (n = 5, 8, 9)
gave the corresponding a,x-dienes, while the monometallic
cationic complex [Cp(CO)2FeCH2@CHC3H7]BPh4 gave 1-
pentene as detailed below.
3.10. Reaction of [{Cp(CO)2Fe}2{l-(C5H9)}]PF6 with
NaBPh4
This was carried out in the same manner as reported in
Section 3.9 above, except that the reaction time was only
10 min.
(a) [Cp(CO)2FeCH2@CHC3H7]BPh4 showed the follow-
ing peaks: 5.72m (@CH), 4.94m (@CH2), 1.92m
(@CHCH2), 1.36m (CH2CH3), 0.84t (CH3).
(b) [{Cp(CO)2Fe}2{l-(C5H8)}](BPh4)2 showed the fol-
lowing peaks: 6.10 (@CH), 5.04m (@CH2), 3.14m
(@CHCH2), 5.35s (C5H5(CO)2FeI).
(c) [{Cp(CO)2Fe}2{l-(C8H14)}](BPh4)2 showed the fol-
lowing peaks: 5.84m (@CH), 4.94m (@CH2), 2.04m
(@CHCH2), 1.43m (@CHCH2CH2).
3.11. Reaction of [{Cp(CO)2Fe}2{l-(C5H8)}](PF6)2 with
NaBPh4
The complex [Cp(CO)2Fe]2{l-(C5H8)}](PF6)2 (0.40 g,
0.53 mmol) and NaBPh4 (0.40 g, 1.1 mmol) were weighed
into a Schlenk tube and 10 ml acetone added. The mixture
was stirred for 4 h. The mixture was filtered through a can-

1148
E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
(d) [{Cp(CO)2Fe}2{l-(C9H16)}](BPh4)2 showed the fol-
dimer [Cp(CO)2Fe]2. The complexes [{Cp(CO)2Fe}2{l-
(CnH2nꢀ1)}]PF6 (where n = 4, 5) were treated in the same
way and gave the same results. However, the amounts of
the r-ether complexes observed were very small for
these two complexes. [{Cp(CO)2Fe}2{l-CH2CH(OCH3)-
(CH2)4}] 1H NMR (CD3Cl), 4.73s, 4.70s (Cp), 1.50m
{CH2CH(OCH3)CH2}, 3.27s (OCH3), 2.98m (CH2CH),
2.03m {CH(OCH3)CH2}, 1.42m (CH2)3; 13C NMR, 85.3,
85.6 (Cp), 6.0 (FpCH2CH), 67.9 (FpCH2CH), 55.9
(OCH3), 38.6 {CH(OCH3)CH2}, 36.0 {CH(OCH3)-
CH2CH2}, 30.8 (CH2CH2Fe), 3.7 (CH2Fe).
lowing peaks: 5.84m (@CH), 4.91 (@CH2), 2.05m
(@CHCH2), 1.43m (@CHCH2CH2).
3.14. Reaction of [{Cp(CO)2Fe}2{l-(C4H7)}]PF6 with
CF3COOH
One milliliter of CF3COOH was added to a solution of
[{Cp(CO)2Fe}2{l-(C4H7)}]PF6 (0.2 g, 0.36 mmol) in THF
(10 ml). The mixture was stirred at room temperature over-
night. A yellow solid was seen in the reaction mixture. It
was allowed to settle and the mother liquor removed
through a cannula into a pre-weighed Schlenk tube. The
solid was washed with 3 ml diethyl ether, dried under
reduced pressure and found to be the reported butenyl
complex [Cp(CO)2Fe(C4H8)}]PF6 [23]. Dry diethyl ether
was added to the mother liquor to precipitate a yellow
micro-crystalline solid. The mother liquor was removed
through a cannula into a pre-weighed Schlenk tube, the
solid dried under reduced pressure and found to also be
butenyl complex [Cp(CO)2Fe(C4H8)]PF6. The mother
liquor was evaporated to dryness under reduced pressure
to give a maroon gum which was found to consist mainly
of the acetyl complex [Cp(CO)2FeOOCCF3] with small
quantities of the iron dimer [Cp(CO)2Fe]2. [Cp(CO)2FeO-
OCCF3] IR (CH2Cl2) cmꢀ1 2062, 2016 (Fp CO), 1689 (ace-
tyl CO); 1H NMR (acetone-d6) ppm, 5.43s (Cp);
The above reaction was carried out with the complexes
[{Cp(CO)2Fe}2{l-(C6H11)}]PF6 and [Cp(CO)2Fe(C4H8)}]-
PF6 in NMR tubes in CD3OD and the reactions followed
1
by recording H NMR spectra at intervals of 5 min until
there was no further change observed in the spectra. After
20 min all the [{Cp(CO)2Fe}2{l-(C6H11)}]PF6 had reacted
and the spectrum showed the presence of two products in
solution as follows:
[Cp(CO)2Fe2{l-CH}2CH(OCD3)(CH2)4] in CD3OD/
ppm, 5.32s (CpFeCH2CH) 4.94s (CpFeCH2CH2), 2.93m
{CH(OCD3)}, 2.16m {CH(OCH3)CH2}, 1.53m (CH2)2
and CH2Fe;
[Cp(CO)2Fe(CH2)4CH@CH2] in CD3OD/ppm, 5.84m
(CH2@CH), 5.14m (CH2@CH), 4.93s (Cp), 2.12m
(CHCH2), 1.54m (@CH2)2 and CH2Fe. The g1-olefin
complex, [{Cp(CO)2Fe(CH2)4CH@CH2], was the major
product.
The reaction of [Cp(CO)2Fe(C4H8)}]PF6 with CD3OD
did not go to completion even after 40 min. The spectrum
showed the presence of four compounds which were iden-
tified as the unreacted starting complex [Cp(CO)2-
Fe(C4H8)}]PF6, free 1-butene, the iron dimer and the
r-ether complex [Cp(CO)2FeCH2CH(OCD3)CH2CH3]. 1-
Butene was the major product as judged from the intensity
of the peaks. The peaks appeared as follows: 1-butene
(CD3OD)/ppm, 5.93m (@CH), 5.04m (@CH2), 1.63m
(@CHCH2), 0.91t (CH3); [Cp(CO)2FeCH2CH(OCD3)-
CH2CH3], 5.53s (Cp), 3.14m (CH2CH), 1.45m (FeCH2),
1.16t (CH3); [Cp(CO)2Fe(C4H8)}]PF6, 5.77s (Cp), 5.15m
(CH), 3.93d (J = 8.2 Hz, cis-CH2), 3.53d (J = 14.7 Hz,
trans-CH2), 2.42m, 1.63m (@CHCH2), 1.28t (CH3).
[Cp(CO)2Fe]2 mCO (CH2Cl2) 2057, 1956, 1772 cmꢀ1
.
3.15. Reactions of the complexes [{Cp(CO)2Fe}2{l-
(CnH2nꢀ1)}]PF6 with methanol
The procedure for the reaction of the complex
[{Cp(CO)2Fe}2{l-(C6H11)}]PF6 is described as an illustra-
tion of the general procedure followed in these reactions.
The compound [{Cp(CO)2Fe}2{l-(C6H11)}]PF6 (0.26 g,
0.44 mmol) and Na2CO3 (0.06 g, 0.55 mmol) were weighed
into a Schlenk tube and 25 ml methanol added. The yellow
complex dissolved completely after 10 min and the solution
became maroon in colour. The mixture was stirred for 1 h
during which time all the carbonate dissolved. The solvent
was removed under reduced pressure to give a maroon res-
idue. The residue was extracted twice with 20 ml hexane
and filtered through a cannula. The solvent was evaporated
under reduced pressure, leaving a maroon oily material. 1H
and 13C NMR spectra showed this oily solid to contain
[Cp(CO)2Fe(CH2)4CH@CH2] as the major product,
[Cp(CO)2Fe]2 and [{Cp(CO)2Fe}2{l-CH2CH(OCH3)-
(CH2)4}] as the minor product. The oily material was
dissolved in minimum of hexane and transferred to an alu-
mina column prepared in hexane and eluted with hexane. A
yellow band was collected and the solvent removed under
reduced pressure leaving amber oil. IR and NMR data
showed this to be the previously reported complex
[Cp(CO)2FeCH2(CH2)3CH@CH2] [24]. The maroon layer
was eluted with CH2Cl2 and found to contain only the iron
3.16. Reaction of [{Cp(CO)2Fe}2{l-(C8H15)}]PF6 with
iso-propanol
The complex [{Cp(CO)2Fe}2{l-(C8H15)}]PF6 (0.03 g,
0.05 mmol) was weighed into a Schlenk tube and 10 ml ace-
tone was added, followed by 6 ml iso-propanol and
Na2CO3 (0.005 g, 0.05 mmol). The mixture was stirred
for 3 h at room temperature. The solids dissolved after
1 h but the mixture was stirred for two more hours. The
solvent was removed under reduced pressure leaving an
amber oily residue. Sublimation under reduced pressure
at 80 °C gave amber oil on the cold finger. IR and NMR
spectroscopy showed that this was the reported complex
[Cp(CO)2Fe(CH2)6CH@CH2] [24]. The maroon residue left

E.O. Changamu, H.B. Friedrich / Journal of Organometallic Chemistry 692 (2007) 1138–1149
1149
[9] S.J. Archer, K.P. Finch, H.B. Friedrich, J.R. Moss, A.M. Crouch,
Inorg. Chim. Acta 182 (1991) 145.
[10] P. Lennon, M. Rosenblum, J. Am. Chem. Soc. 105 (1983) 1233.
[11] J.P. Lennon, A. Rosan, M. Rosenblum, J. Tancrede, P. Waterman,
J. Am. Chem. Soc. 102 (1980) 7033.
behind consisted mainly of the iron dimer and some of the
unsublimed complex [Cp(CO)2Fe(CH2)6CH@CH2].
Acknowledgements
[12] K.R. Aris, V. Aris, J.M. Brown, J. Organomet. Chem. 42 (1972) C67.
[13] A. Sanders, W.P. Gierring, J. Organomet. Chem. 104 (1976) 67.
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[15] (a) R.M. Silverstein, F.X. Webster, D.J. Kiemle, Spectrometric
Identification of Organic Compounds, 7th ed., John Wiley & Sons
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(b) H. Gunther, NMR Spectroscopy, Basic Principles, Concepts and
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Chem. 27 (2003) 1769.
We thank the University of KwaZulu-Natal (URF), the
National Research Foundation (NRF) and the Depart-
ment of Trade and Industries (THRIP) for funding.
E.O.C. thanks Kenyatta University for study leave. The
assistance of Ms. Z. Mabuza in the laboratory is also
acknowledged. We further thank a referee and Drs. H.G.
Kruger, G.E.M. Maguire and N.A. Koorbanally (all
UKZN) for valuable comments on chirality.
[17] T.C.T. Chang, B.M. Foxman, M. Rosenblum, C. Stockman, J. Am.
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