Synthesis and reactivity of mono(amidinate) organoiron(II) complexes

Article abstract of DOI:10.1039/b608108h

The mono(amidinate) iron(ii) ferrate complex [{PhC(NAr)₂}FeCl(- Cl)Li(THF)₃] (1, Ar = 2,6-iPr₂C₆H₃) was prepared and was found to undergo ligand redistribution in non-coordinating solvents to give the homoleptic [{PhC(NAr)₂}₂Fe] (2) as the only isolable product. Reaction of 1 with alkylating agents also induces this redistribution, but the presence of pyridine allows isolation of the four-coordinate 14 VE monoalkyl complex [{PhC(NAr)₂}FeCH ₂SiMe₃(py)] (4). Generation of the 12 VE alkyl via pyridine abstraction from 4 by B(C₆F₅)₃ again induced ligand redistribution. Attempts to trap a 12 VE alkyl species with CO led to the isolation of a dimeric Fe(0)-Li-ferrate complex (3) with a carbamoyl ligand, derived from CO insertion into the iron-amidinate bond. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b608108h

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis and reactivity of mono(amidinate) organoiron(II) complexes
Timo J. J. Sciarone, Christian A. Nijhuis, Auke Meetsma and Bart Hessen*
Received 7th June 2006, Accepted 11th August 2006
First published as an Advance Article on the web 23rd August 2006
DOI: 10.1039/b608108h
The mono(amidinate) iron(II) ferrate complex [{PhC(NAr)
,6-iPr ) was prepared and was found to undergo ligand redistribution in non-coordinating
solvents to give the homoleptic [{PhC(NAr) Fe] (2) as the only isolable product. Reaction of 1 with
alkylating agents also induces this redistribution, but the presence of pyridine allows isolation of the
four-coordinate 14 VE monoalkyl complex [{PhC(NAr) }FeCH SiMe (py)] (4). Generation of the
2 VE alkyl via pyridine abstraction from 4 by B(C again induced ligand redistribution. Attempts
2
}FeCl(l-Cl)Li(THF)
3
] (1, Ar =
2
2
C
6
H
3
2 2
}
2
2
3
1
6
F
)
5 3
to trap a 12 VE alkyl species with CO led to the isolation of a dimeric Fe(0)–Li–ferrate complex (3) with
a carbamoyl ligand, derived from CO insertion into the iron–amidinate bond.
Introduction
Reduction of the chelate ring size by two carbons is found to
result in organoiron(II) chemistry very distinct from that of the
Electron-poor (≤14 valence electrons (VE)) alkyl complexes of
iron are of interest because of their likely involvement in the
coordination polymerisation of olefins. Recently, 14 VE cationic
Fe(II) monoalkyls supported by a terdentate pyridine-2,6-diimine
related b-diketiminate ligands.
Results and discussion
(
PDI) ligand were isolated and were shown to be competent in
Reaction of equimolar amounts of Li[PhC(NAr)
THF forms the pale yellow ferrate complex [{PhC(NAr)
Cl)Li(THF) ] (1) (Scheme 1).
2
] and FeCl
2
in
1,2
the catalytic polymerisation of ethene. Nevertheless, definite
proof for the nature of the active species in this system remains
to be obtained. Thus far, high activity in Fe-catalysed olefin
polymerisation has been achieved only using neutral ligands
2
}FeCl(l-
3
3
incorporating the PDI skeleton.
Neutral bidentate ligands have been employed to stabilise
4,5
Fe(II) dialkyls, but none of these has been reported as a
polymerisation catalyst. Also, no highly active catalysts supported
by monoanionic ligands have been reported, although various
6–9
interesting Fe(II) monoalkyls with 14 VE are known. More
electron-deficient, three-coordinate Fe(II) monoalkyls (12 VE)
have been obtained with b-diketiminate ligands with sterically
10,11
Scheme 1
demanding 2,6-iPr
2
C
6
3
H substituents on the nitrogen atoms.
These do not display alkene insertion into the Fe–alkyl bond,
however, although alkene insertion into the Fe–H bond of the
corresponding hydride has been observed.
Isolation was performed by extraction with pentane and
crystallisation from THF–hexanes. The isolated yields (20–70%)
were found to depend critically on the workup conditions. The
extraction must be conducted rapidly and at low temperatures as
the monoamidinate complex is unstable in hydrocarbon solvents
10c,d
A possible way to enhance the reactivity of these neutral
2 VE systems is to open up the available space around the metal
1
centre by the (conceptual) removal of two carbon atoms from
the b-diketiminate NCCCN backbone: this leads to the amidinate
ligand framework. Previous studies on the coordination chemistry
of bis(amidinate) Fe(II) complexes with sterically demanding
(
vide infra).
The molecular structure of 1 (Fig. 1) was established by
X-ray diffraction. Selected interatomic distances and bond angles
are given in Table 1. The asymmetric unit contains one ferrate
complex and an uncoordinated THF molecule, which is readily
lost from the lattice in vacuo or upon drying in a nitrogen stream.
The iron centre is pseudotetrahedrally coordinated by a chelating
amidinate ligand and two chlorides. One of the chlorides bridges
to a lithium ion, which is solvated by three THF molecules. Two
of these are heavily disordered (see Experimental for details).
In contrast to the related b-diketiminate ferrate
ꢀ
−
ꢀ
benzamidinates [PhC(NAr)(NAr )] , (Ar = 2,6-iPr
2
C
6
H
3
, Ar =
Ar, 2,6-Me
2
C
6
H
3
) have shown that the amount of steric congestion
imposed by these ligands can have important consequences for the
12
coordination geometry of the resulting Fe(II) complexes.
Here we describe the preparation and reactivity of
mono(amidinate) organoiron(II) complexes of the sterically de-
−
manding benzamidinate [PhC(NAr)
2
]
(Ar = 2,6-iPr
2
C
6
3
H ).
1
3
[
{H(C(Me)NAr)
2
}Fe(l-Cl)
2
Li(THF) ], in which both chlorides
2
Dutch Polymer Institute/Center for Catalytic Olefin Polymerization,
Stratingh Institute for Chemistry and Chemical Engineering, University
of Groningen, Nijenborgh 4, 9747, AG Groningen, The Netherlands
E-mail: b.hessen@rug.nl; Fax: +31 50 363 4315; Tel: +31 50 363 4322
bridge the Fe and Li centres, the amidinate complex 1 displays one
bridging and one terminal chloride. Consistently, the Cl–Fe–Cl
◦
angle in 1 is ca. 22 wider than in the b-diketiminate complex,
4
896 | Dalton Trans., 2006, 4896–4904
This journal is © The Royal Society of Chemistry 2006

View Article Online
Table 1 Selected bond angles and distances for 1
some tentative assignments could be made for the larger signals.
For instance, the diastereotopic methyls of the isopropyl groups
Bond lengths/A˚
appear at d − 17.9 (Dm1/2 = 356 Hz, 12H) and d 8.9 ppm (Dm1/2
=
1
69 Hz, 12H). The presence of only two iPr Me resonances
Fe–Cl1
Fe–Cl2
Fe–N1
2.2778(12)
2.2443(13)
2.088(4)
Fe–N2
N1–C13
N2–C13
2.093(3)
1.327(6)
1.337(5)
suggests the presence of an exchange process leading to apparent
C2v symmetry. Upon dissolution of 1 in THF-d , a significantly
8
different spectrum is obtained (in addition to the appearance of
resonances for free THF, due to exchange of THF coordinated
◦
Bond angles/
to the Li ion in 1 by THF-d
solvent. The spectrum displays nine lines with smaller widths
compared to solutions in C , thus facilitating assignment of the
spectrum. Again, the presence of only two signals for the iPr–Me
protons and only one m-HAr resonance, suggests a C2v symmetric
molecule in solution. It appears that the Lewis basic solvent
is able to (reversibly) displace the LiCl moiety to generate the
8
), suggesting involvement of the
Cl1–Fe–Cl2
Cl1–Fe–N1
Cl1–Fe–N2
Cl2–Fe–N1
Cl2–Fe–N2
N1–Fe–N2
118.46(5)
114.46(10)
111.60(8)
114.94(10)
121.86(9)
63.76(14)
Fe–N1–C1
141.3(3)
92.4(3)
124.6(4)
91.9(2)
139.3(2)
125.3(3)
Fe–N1–C13
C1–N1–C13
Fe–N2–C13
Fe–N2–C20
C13–N2–C20
6
D
6
adduct [{PhC(NAr)
2
}FeCl(THF-d
8
)]. This is also suggested by the
to C solutions
observation that addition of excess pyridine-d
5
6
D
6
of 1 induces a colour change to deep yellow and formation of a
precipitate. Assuming a tetrahedral coordination geometry around
Fe, the apparent C2v symmetry can be accounted for by fast site
exchange of THF-d
8
in the adduct [{PhC(NAr)
2
}FeCl(THF-d
8
)].
The symmetrisation in THF-d
8
is fast on the NMR timescale
◦
down to −50 C.
Thermal stability
As noted above, the isolated yield in the preparation of 1 depends
strongly on the workup conditions. Solutions of pale yellow
1
in aromatic hydrocarbons or alkane solvents are not stable
at room temperature, slowly turning green over the course of
several hours with concomitant precipitation of a white solid.
1
The green product was identified by H NMR spectroscopy as the
previously described bis(amidinate) complex [{PhC(NAr)
2
}
2
Fe]
12
(
2) (Scheme 1), which could be isolated in 48% yield (based
Fig. 1 Molecular structure of 1. Hydrogen atoms and uncoordinated
THF molecule have been omitted for clarity. Thermal ellipsoids at 50%.
on Fe). The precipitate was not characterised, but mass balance
suggests that it consists of LiCl and FeCl2.
There are several literature examples in which the synthesis
of mono(amidinate) transition metal complexes is complicated
or thwarted by ligand redistribution leading to bis(amidinate)
in response to the smaller bite angle of the amidinate ligand
compared to the b-diketiminate. The aryl rings make angles of
◦
17,18
6
9.4(2) and 80.3(2) with the N–Fe–N coordination plane. In
complexes, regardless of the stoichiometry employed.
comparison with the b-diketiminate ferrate complex mentioned
above, the aryl groups in 1 are less efficiently shielding the
iron centre, as evidenced by the comparatively large Cipso–N–Fe
Amidinate ligand redistribution can sometimes be cir-
cumvented by employing additional chelating donor lig-
ands. Thus, Lee et al. isolated the mono(amidinate) complex
◦
◦
13
ꢀ
2
ꢀ
angles (140.3 (av.) for 1 vs. 117.1 (av.) for the b-diketiminate).
[{PhC(NAr )(NSiMe
3
)}FeCl(j –TMEDA)] (Ar = 2,6-Me
2
C
6
H )
3
The Fe–N distances are identical within experimental error,
indicating symmetric coordination of the ligand. The N1–Fe–N2
from reaction of FeCl
2
with the TMEDA adduct of the lithium
19
amidinate at low temperature.
◦
bite angle (63.78(11) ) is within the range usually observed for
A stabilising effect of donor solvents, preventing ligand redis-
14,15
amidinates.
Delocalisation within the amidinate NCN frame
tribution, was also observed by Cotton et al. in the synthesis of
20
is evidenced by the equal CN bond lengths, although the nitrogen
chromium(II) amidinate complexes. Accordingly, solutions of 1
◦
atoms show some slight deviation from planarity (RN1 = 358.3 ,
in THF-d
8
do not show significant formation of the bis(amidinate)
◦
◦
R
N2 = 356.5 ).
complex 2 even after heating at 100 C for 24 h.
Compound 1 possesses a room temperature magnetic moment
l
eff. = 5.4 l
B
in benzene, consistent with 4 unpaired electrons in
Alkylation
16
combination with a small orbital contribution. The paramag-
netism of 1 is also evident from its H NMR spectrum in C
1
6
D
6
.
Alkylation of 1 was initially attempted using LiCH(SiMe
3
2
) .
Seven broad resonances are observed between +30 and −30 ppm in
a 300 ppm frequency window. The broadness and consequent low
intensity of some of the resonances renders integration inaccurate,
complicating full interpretation of the spectrum. Nevertheless,
However, reaction of 1 with the lithium alkyl in THF, fol-
lowed by pentane extraction, yielded the bis(amidinate) iron
complex 2 as the only isolable product. Amidinate scrambling
upon alkylation has precedent in the methylation of the Ti(IV)
This journal is © The Royal Society of Chemistry 2006
Dalton Trans., 2006, 4896–4904 | 4897

View Article Online
complex [{PhC(NSiMe
3
)
2
}(l-Cl)TiCl
2
]
2
. Instead of the desired
TiMe ] was isolated,
Table 2 Selected bond angles and distances for 3
[
{PhC(NSiMe
3
)
2
}TiMe
3
], [{PhC(NSiMe
3
)
2
}
2
2
Bond lengths/A˚
possibly as a result of redistribution of the ligands in the
monoamidinate titanium trimethyl complex to give the observed
bis(amidinate) species and unstable TiMe
Fe11–N11
Fe11–C132
Fe11–C133
Fe11–C134
Fe11–C135
N11–C113
N12–C113
N12–C132
1.996(3)
1.927(3)
1.769(4)
1.798(4)
1.725(4)
1.297(4)
1.384(4)
1.443(4)
Fe41–N41
Fe41–C432
Fe41–C433
Fe41–C434
Fe41–C435
N41–C413
N42–C413
N42–C432
1.9961(6)
1.935(4)
1.766(4)
1.798(4)
1.720(4)
1.301(3)
1.380(3)
1.443(4)
21
4
. Similar observations
were made by Nelkenbaum et al. upon attempted alkylation of
22
Ni(II) monoamidinate complexes.
The in situ generation of iron alkyl species from 1 was probed by
1
H NMR spectroscopy in THF-d
8
. Reactions of 1 with equimolar
amounts of KCH Ph or LiCH EMe
2
2
3
(E = C, Si) were accompanied
by colour changes from pale yellow via red to dark yellow.
◦
Bond angles/
1
The H NMR spectra showed formation of new paramagnetic
1
species, presumably the alkyls [{PhC(NAr)
2
}FeR(THF)]. The H
N11–Fe11–C132
N11–Fe11–C133
N11–Fe11–C134
N11–Fe11–C135
C132–Fe11–C133
C132–Fe11–C134
C132–Fe11–C135
C133–Fe11–C134
C133–Fe11–C135
C134–Fe11–C135
Fe11–N11–C11
Fe11–N11–C113
C11–N11–C113
C113–N12–C120
C113–N12–C132
C120–N12–C132
Fe11–C132–O11
Fe11–C132–N12
O11–C132–N12
N11–C113–N12
N11–C113–C114
N12–C113–C114
81.01(12)
114.80(16)
95.13(14)
132.59(17)
89.19(17)
173.36(16)
87.90(16)
97.36(19)
110.93(19)
90.81(18)
123.4(2)
116.2(2)
120.2(3)
121.8(3)
115.1(3)
118.5(2)
132.9(3)
112.6(2)
114.4(3)
115.1(3)
126.4(3)
118.3(3)
N41–Fe41–C432
N41–Fe41–C433
N41–Fe41–C434
N41–Fe41–C435
C432–Fe41–C433
C432–Fe41–C434
C432–Fe41–C435
C433–Fe41–C434
C433–Fe41–C435
C434–Fe41–C435
Fe41–N41–C41
Fe41–N41–C413
C41–N41–C413
C413–N42–C420
C413–N42–C432
C420–N42–C432
Fe41–C432–O41
Fe41–C432–N42
O41–C432–N42
N41–C413–N42
N41–C413–C414
N42–C413–C414
81.05(11)
115.63(13)
94.72(12)
131.53(17)
89.21(18)
173.01(18)
88.49(18)
97.66(19)
111.4(2)
90.21(18)
123.25(3)
115.99(14)
120.31(14)
121.03(18)
115.2(2)
119.65(19)
132.9(3)
112.4(2)
114.6(3)
115.3(2)
125.9(3)
118.6(3)
NMR spectra of these paramagnetic species could not be fully
assigned, but some characteristic resonances could be identified by
integration (iPr–CH
all cases, the ligand iPr-methyl protons show only two resonances
integrating for 12 H each), which suggests fast site exchange
of coordinated THF. Pumping off THF-d and redissolution of
3
, tBu and SiMe groups, see Experimental). In
3
(
8
the residue in cyclohexane-d12 again induced amidinate redis-
1
tribution: the H NMR spectra in this solvent showed mainly
the resonances of bis(amidinate) 2. In an experiment employing
LiCH
Me SiCH
12 solution.
2
SiMe
3
as the alkylating agent, the alkyl coupling product
SiMe was detected (GC-MS) in the cyclohexane-
3
2
CH
2
3
d
Apparently, the putative iron alkyls, like the chloride precursor
, decompose in the absence of a donor solvent. The formation
1
of alkyl coupling products suggests that decomposition involves
radical pathways, or reductive elimination from FeR
latter stemming from the ligand redistribution.
2
species, the
The nature of 3 was established by single crystal X-ray diffrac-
tion (Fig. 2). Pertinent bond lengths and bond angles are listed in
Table 2.
Alkylation in the presence of CO
An attempt was made to trap the putative amidinate iron alkyl
species with CO. Earlier it was reported that three-coordinate (b-
diketiminate)Fe(alkyl) compounds react with CO to form stable
23
five-coordinate acyl dicarbonyl complexes. Reaction of 1 with
LiCH(SiMe in the presence of excess CO led to the isolation of
)
3 2
the dark red dimeric lithium carbamoyl ferrate 3 (Scheme 2).
Fig. 2 Molecular structure of 3. Hydrogen atoms and the uncoordinated
THF molecule have been omitted for clarity. Thermal ellipsoids at 50%.
Scheme 2
Each ferrate anion in 3 contains a formal Fe(0) centre, indicating
that a reductive process has taken place. Formation of 3 also
involves insertion of carbon monoxide into one of the Fe–
N(amidinate) bonds. Hagadorn et al. observed insertion of CO
The unit cell contains one diiron compound with a non-
crystallographic inversion centre and two non-coordinated
THF molecules. The dimer consists of 18 VE [{C(O)N(Ar)-
−
into the amidinate complex [Cp{FcC(NCy)
carbamoyl complex [Cp{N(Cy)C(Fc)N(Cy)C(O)}Fe(CO)] (Cy =
c-C )Fe(C )).
11, Fc = (C
2
}Fe(CO)] to give the
C(Ph)N(Ar)}Fe(CO)
3
]
ferrate anions bridged by two solvated
+
Li ions. Each iron is bound to a chelating carbamoyl ligand and
three carbonyls, one of which is bridging in a linear fashion to the
24
6
H
5
H
4
5
H
5
4
898 | Dalton Trans., 2006, 4896–4904
This journal is © The Royal Society of Chemistry 2006

View Article Online
+
Li ion. The latter is also bound to the carbamoyl oxygen of the
possible, but that a Lewis base is required to suppress ligand
redistribution leading to 2.
other ferrate fragment, and two THF molecules.
The ligands establish a distorted trigonal bipyramidal coor-
dination geometry around iron with the carbamoyl carbon and
one terminal carbonyl occupying the apical positions (C132–
Apparently, THF is an insufficiently strong base to remain
bound to iron during the workup procedure. Therefore, alkylation
of 1 was studied in the presence of a stronger donor ligand than
THF. In a one-pot reaction, ferrate 1 was generated in THF and
◦
Fe–C134 = 173.36(16) ). The equatorial plane is defined by
the carbamoyl nitrogen (N11) and the two other carbonyls, the
reacted in situ with pyridine followed by addition of LiCH
Extraction with pentane and crystallisation from the same solvent
SiMe (py)] (4) in
2
SiMe
3
.
◦
sum of their angles with the iron centre being 358 . Within the
˚
carbamoyl moiety, C113–N11 (1.297(4) A) is significantly shorter
afforded orange crystals of [{PhC(NAr)
2
}FeCH
2
3
˚
than C113–N12 (1.383(4) A), giving the former slightly more
38% isolated yield (Scheme 4). The modest isolated yield appears
double bond character. The chelate ring, however, is essentially
planar, indicating at least some delocalisation. The linear bridging
mode is unusual for the CO ligand, though not unprecedented.
In cases where CO acts as a linearly bridging ligand, the most
electropositive metal centre is usually bound to the oxygen
to be mainly due to the high solubility of 4 in pentane.
25–27
atom.
Characterisation of 3 by H NMR spectroscopy was frustrated
by the persistent presence of metallic iron in the red THF-d
1
8
solutions of this compound, possibly as a result of photolysis of the
product. The spectra show broad, overlapping resonances between
+
10 and 0 ppm. The chemical shift range confirms the diamagnetic
Scheme 4
nature of 3 as suggested by its 18-valence electron count. The IR
spectrum is more informative and consistent with the solid state
structure. Absorptions for the terminal carbonyls (vCO(term.)) are
Fig. 3 shows the solid state structure of 4 as determined by
X-ray diffraction. The asymmetric unit contains two independent
molecules of the iron complex. In view of their structural similarity,
only one of these is discussed here. Pertinent bond lengths and
bond angles for 4 are listed in Table 3.
The iron centre in 4 is ligated in a distorted tetrahedral
fashion with angles between the coordinating atoms in the
range of 64–135 . The bite angle (N11–Fe–N12 = 63.62(7) )
is close to that in 1. The amidinate ligand is bound to Fe in
the chelating mode, although slightly less symmetrically than
−
1
found at 1883 and 1961 cm , while the linearly bridging COs
−
1
absorb at a lower frequency (vl-CO = 1814 cm ). The carbamoyl
−
1
CO stretching absorption vC(O)N for 3 is observed at 1556 cm .
Due to its light-sensitivity and loss of cocrystallised THF from
the lattice, no satisfactory elemental analysis could be obtained
for the compound.
◦
◦
Although mechanistic details for the formation of 3 are unclear,
reduction of Fe(II) is likely to be induced by the alkyllithium
reagent, as ferrate 1 itself does not react with CO under similar
conditions. GC-MS analysis of the reaction mixture revealed the
presence of bis(trimethylsilyl)methane, probably formed through
hydrogen abstraction from the solvent by bis(trimethylsilyl)methyl
in 1, as evidenced by small, but significant differences in the
˚
Fe–N and amidinate C–N distances (DFe–N ≈ 0.04 A, DC–N
≈
˚
0
.03 A). This small tendency towards amido–imino character is
◦
also evident from the full planarity of N12 (RLN12 = 359.65 ), while
radicals. The coupling product of CH(SiMe
3
2
) radicals, 1,1,2,2-
◦
N11 is more distorted (RLN11 = 354.80 ). The pyridine ligand is
tetrakis(trimethylsilyl)ethane, however, was not observed, sug-
gesting that reductive elimination from a dialkyliron(II) species
does not take place here. The chromatogram also showed the
presence of a compound with m/z = 186, which corresponds
◦
roughly orthogonal (84.58(11) ) to the Fe–N–C–N coordination
plane, while the aryl groups and the phenyl ring are inclined
at 66.15(10), 74.83(10) (Ar) and 43.42(10) (Ph) with respect to
this plane. The Fe–C distance in 4 (2.049(2) A) is similar to
◦
˚
28
to bis(trimethylsilyl)ketene (Me
3
Si)
2
C=C=O. The ketene might
be the b-H-elimination product of an iron acyl complex [Fe]–
C(O)CH(SiMe , which in turn could be formed by CO insertion
into the Fe–C bond of an iron alkyl species (Scheme 3).
Table 3 Selected bond angles and distances for 4
)
3 2
Bond lengths/A
˚
Fe1–N11
Fe1–N12
Fe1–N13
2.0864(18)
2.1226(18)
2.1314(18)
Fe1–C137
N11–C113
N12–C113
2.049(2)
1.351(3)
1.323(3)
◦
Bond angles/
N11–Fe1–N12
N11–Fe1–N13
N12–Fe1–N13
C137–Fe1–N11
C137–Fe1–N12
C137–Fe1–N13
Fe1–N11–C11
Fe1–N11–C113
C11–N11–C113
63.62(7)
107.47(7)
101.65(7)
135.02(8)
122.06(9)
113.63(9)
140.06(13)
92.43(13)
122.31(18)
Fe1–N12–C113
Fe1–N12–C120
C113–N12–C120
Fe1–N13–C132
Fe1–N13–C136
C132–N13–C136
N11–C113–N12
N11–C113–C114
N12–C113–C114
Fe1–C137–Si1
91.67(13)
141.52(14)
126.46(18)
118.43(15)
124.14(15)
117.02(19)
112.14(18)
122.25(19)
125.52(19)
118.76(14)
Scheme 3 Possible mechanism for the formation of bis(trimethyl-
silyl)ketene.
Alkylation in the presence of pyridine
The NMR tube scale alkylation experiments described above
suggest that substitution of chloride in 1 for an alkyl ligand is
This journal is © The Royal Society of Chemistry 2006
Dalton Trans., 2006, 4896–4904 | 4899

View Article Online
was obtained. The observed lack of activity for 4/MAO contrasts
with the patent literature, in which the benzamidinate iron alkyl
complex [{PhC(N-2,4,6-Me
as a catalyst precursor for olefin polymerisation upon activation
with aluminoxanes or B(C (although characterisation data or
activity figures are not provided for this specific iron complex).
The reaction of 4 with the Lewis acid B(C could proceed
either by alkyl abstraction, or by abstraction of the pyridine base.
The latter reaction is seen to occur upon treatment 4 with B(C
3
C
6
H
2
)
2
}FeCH
2
SiMe
3
(py)] is claimed
6
F
)
5 3
31
6
F
)
5 3
6
F
5 3
)
1
19
in C
spectroscopy, are the pyridine adduct of the borane (identified
by independent generation from B(C and pyridine in C
Fe] (2). A black
6
D
6
. The major products, as detected by H and F NMR
6
F
5
)
3
6
D )
6
and the bis(amidinate) complex [{PhC(NAr)
2 2
}
film was deposited on the walls of the NMR tube suggesting co-
formation of Fe(0). Consistently, 1,2-bis(trimethylsilyl)ethane was
detected by GC-MS analysis.
These products can be accounted for by the stoichiometry
shown in Scheme 5. Formation of 2 upon pyridine abstraction
from 4 is consistent with the instability of three-coordinate Fe(II)
−
complexes of [PhC(NAr)
2
] described above.
Fig. 3 X-Ray structure of 4. Hydrogen atoms have been omitted for
clarity. Thermal ellipsoids at 50%.
those observed in the four-coordinate bis(trimethylsilylmethyl)
ˆ
ˆ
compounds [(NN)Fe(CH
2
SiMe
3
)
2
] (NN = chelating diamine or
29
˚
diimine, Fe–C = 2.042(3)–2.0963(13) A) reported by Bart et al.
◦
The Fe–C–Si angle (118.76(14) ) is relatively large, probably in
response to steric interactions between the trimethylsilyl group and
the iPr substituents of the ligand. Steric crowding is also evident
from the unsymmetric C–Fe–N(amidinate) angles of 135.02(8)
◦
and 122.06(9) .
Monoalkyl complex 4 has an effective magnetic moment leff.
=
5
.5 l in benzene at ambient temperature. The high-spin nature
B
Scheme 5
1
of the compound is also manifested in the H NMR spectrum
which consists of broad and shifted lines. The spectrum indicates
an averaged C2v symmetry in solution as judged from the presence
of only two iPr–Me resonances (d 5.0 and −25.0 ppm, 12 H each)
and one m-HAr resonance (d 11.6 ppm, 4H). The apparent C2v sym-
metry of the molecule can be accounted for by fast site exchange
of the pyridine molecule on the NMR timescale. The related four-
Conclusions
Mono(amidinate) iron(II) complexes with the sterically demand-
ing amidinate [PhC(NAr)
pared, but are subject to ligand redistribution processes in
the absence of additional Lewis bases. In contrast to the cor-
responding b-diketiminate ligand, the orientation of the 2,6-
−
2
]
(Ar = 2,6-iPr
2
C
6
3
H ) can be pre-
coordinate pyridine adduct [{HC(C(Me)NAr)
2
}FeCH
2
Ph(py)] of
the b-diketiminate monobenzyl complex was found to exhibit
30
similar site exchange of the pyridine ligand. Taking the fluxional
process into account, the number of observed resonances (9)
is smaller than expected (13), leaving 4 resonances unobserved.
This could be due to extreme line broadening for protons close
iPr
sufficient steric protection to stabilise three-coordinated alkyl
complexes of the type [{PhC(NAr) }FeR]. Nevertheless, four-
coordinated (mono)amidinate Fe(II) alkyls can be generated as
2
C
6
H
3
substituents in the amidinate apparently offers in-
2
to the paramagnetic centre (e.g. o-Hpy, Fe–CH
2
, o-HPh, iPr–CH).
their Lewis-base adducts [{PhC(NAr) }FeR(L)], although THF is
2
The SiMe proton resonances of the alkyl ligand (9H) are found
3
too weakly coordinating to allow the isolation of these compounds.
This is possible when the stronger base pyridine is used.
at d 35.6 ppm. The assignments of the 5 remaining peaks are
ambiguous due to their similar integrals (1H or 2H).
Experimental
Reactivity with Lewis acids and ethene
General considerations
Using methyl alumoxane (MAO) as cocatalyst (Al/Fe = 500), the
chloride complex 1 and alkyl derivative 4 were tested for activity
All complexes are air-sensitive and were handled under a
dry dinitrogen atmosphere using standard Schlenk and drybox
techniques. THF (99.9% Aldrich) was percolated over a column
◦
in ethene polymerisation (PC2H4 = 10 bar, T = 50 C). In neither
case was significant ethene consumption seen, and no polymer
4
900 | Dalton Trans., 2006, 4896–4904
This journal is © The Royal Society of Chemistry 2006

View Article Online
of Al
2
O
3
and stored under nitrogen. Hexane and pentane (99.9%
C230 and C231 has been described by two site occupancy factors
with separately refined displacement parameters. The s.o.f. of the
major fraction of the component of the disorder model refined to
a value of 0.612(10).
Aldrich) were percolated over a column packed with molecular
sieves 4 A (90 wt%) and Al
Toluene (99.9% Aldrich) used for polymerisation experiments
˚
2
O (10 wt%) and stored under nitrogen.
3
˚
was percolated over a column packed with molecular sieves 4 A
90 wt%) and Al (10 wt%) and freed of oxygen by passing it
over BASF-R3-11 supported Cu-catalyst. Pyridine was dried over
CaH . Deuterated solvents (Aldrich) were dried over Na/K alloy
, THF-d , cyclohexane-d12) or used as received and stored
CCDC reference numbers 610249–610251. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b608108h
(
2
O
3
2
(
C
6
D
6
8
Starting materials and reagents
under nitrogen.
3
4
35
36
Anhydrous FeCl
2
,
FeCl
2
(THF)1.5
,
LiCH
and B(C
2
SiMe
3
,
LiCH -
2
37
38
39
40
CMe
3
,
LiCH(SiMe
3
)
2
,
KCH
2
Ph
6
F
5
)
3
were
Instrumentation
ꢀ
prepared according to literature procedures. [N,N -bis(2,6-
diisopropylphenyl)benzamidine was deprotonated by standard
methodology using nBuLi (2.5 M in hexanes) in THF at RT.
41
NMR spectra were recorded on Varian Inova 500, VXR 300 and
Varian Gemini 200 MHz instruments. H NMR chemical shifts are
1
12
reported in ppm relative to residual protiated solvent in C
6
D
6
(7.15
All other chemicals are commercially available and were used
without further purification.
ppm) or THF-d (3.57 ppm). Shifts for paramagnetic compounds
8
are followed by their linewidth at half height (in Hz), integrals,
and assignment where possible. IR spectra were recorded on a
Mattson 4020 Galaxy FT-IR spectrometer. GC-MS analyses were
conducted using a HP 5973 mass-selective detector attached to a
HP 6890 GC instrument. Elemental analyses were performed by
the Microanalytical Department at the University of Groningen
or by Mikroanalytisches Laboratorium H. Kolbe, M u¨ lheim an
der Ruhr, Germany. Reported values are the averages of two
independent determinations. Solution effective magnetic moments
Preparation of [{PhC(NAr) }FeCl Li(THF) ]·THF (1)
2
2
3
A solution of Li[PhC(NAr) ] (1.02 g, 2.27 mmol) in THF (15 mL)
2
was added to a suspension of FeCl
2
(0.287 g, 2.27 mmol) in THF
◦
(
10 mL) at 0 C and the reaction mixture was stirred for 1 h
◦
at 0 C. The solvent was removed in vacuo and residual THF
was removed by stirring the mixture with pentane (10 mL) which
was subsequently removed in vacuo. The product was extracted at
were determined at 298 K in C
according to Evans’ method. Magnetic data were corrected
for diamagnetism using Pascal’s constants. Effective magnetic
moments were calculated as leff = 2.828
6
2
H
6
/C
6
D
6
(0.375 mL/0.125 mL)
◦
3
0 C with pentane (40 mL) until the pentane was colourless. The
33
combined extracts were evaporated to dryness, leaving a yellow
solid. The solid was washed with cold pentane (15 mL, 2 times).
√
m
v T.
◦
The crude product was recrystallised from THF–hexane at −30 C,
yielding yellow crystals. Yield: 1.22 g (1.59 mmol, 70%).
X-Ray structure determinations
l
eff. (C
6
H
6
, 298 K) = 5.4 l
B
.
1
Collection, refinement and crystallographic data are given in
Table 4.
H NMR (300 MHz, C D , RT): d (Dm ) = 23.1 (73 Hz, 2H),
6
6
1/2
18.7 (800 Hz), 13.2 (415 Hz), 8.9 (169 Hz, 12H, iPr–CH ), 6.3
3
(
(
90 Hz, 12H, coord. THF), 2.7 (65 Hz, 12H, coord. THF), −17.9
356 Hz, 12H, iPr–CH ) ppm (Hz).
H NMR (500 MHz, THF-d
, RT): d (Dm1/2) = 19.0 (23 Hz,
H, m-HPh), 15.6 (32 Hz, 4H, m-HAr), 14.6 (849 Hz, 4H, iPr–CH),
1.8 (134 Hz, 2H, o-HPh), 5.5 (45 Hz, 12H, iPr–CH ), 3.6 (16 Hz,
2H, THF), 2.3 (20 Hz, 1H, p-HPh), 1.7 (13 Hz, 12H, THF), −12.9
1
.
Suitable crystals were obtained by slow cooling of a hexane–
◦
3
THF solution to −30 C. The crystal was picked from the mother
liquor and was covered with inert oil to avoid deterioration due to
loss of solvent from the crystal lattice. Some atoms (C24, C32, C64)
belonging to the coordinated THF molecules showed unrealistic
displacement parameters when allowed to vary anisotropically,
suggesting dynamic disorder. The most heavily disordered THF
ligands (ring 2 : O2–C36.C39 and ring 3 : O3–C40.C43) have
been described by two site occupancy factors each. The s.o.f.s of
the major fractions refined to values of 0.533(6) and 0.518(6),
respectively.
1
8
2
1
1
3
(
171 Hz, 12H, iPr–CH
3
), −22.5 (24 Hz, 2H, p-HAr) ppm.
−1
IR (nujol mull, KBr): vmax/cm 1623w, 1580m, 1326s, 1272s,
253s, 1238s, 1183w, 1097w, 1045s, 959m, 935w, 919w, 893 m,
03w, 784m, 766s, 696s.
1
8
Anal. Found: C, 64.89; H, 8.04; N, 3.57; Fe, 6.98; Li, 0.84. Calc.
for C43
0.88%.
H
63Cl
2
FeLiN
2
3
O : C, 65.40; H, 8.04; N, 3.55; Fe, 7.07; Li,
3
. Suitable crystals were obtained by recrystallisation from
THF. The electron density of C33 was disordered over two posi-
tions, indicating conformational disorder. The s.o.f. of the major
fraction of the component of the twin model refined to a value of
Thermally induced ligand rearrangement of 1
0
.70(1). Some other atoms (O31, C31, C32, C64) belonging to the
A suspension of 1 (0.30 g, 0.38 mmol) in pentane (40 mL) was
stirred at room temperature for 48 h. During this period, the colour
changed from yellow to dark green and precipitation of a white
salt was observed. The solution was filtered and concentration of
the filtrate to ca. 5 mL afforded 2 as a dark green crystals. Yield
coordinated THF molecules also showed unrealistic displacement
parameters suggesting some degree of disorder, which is in line
with the weak scattering power of the crystals investigated.
4. Suitable crystals were obtained by recrystallisation from
1
pentane. Some atoms (C230 and C231) showed unrealistic
displacement parameters when allowed to vary anisotropically,
suggesting dynamic disorder. The smeared electron density for
0.17 g (0.18 mmol, 48% based on Fe). The spectroscopic (IR, H
NMR) properties of the product correspond to those reported
12
previously for 2.
This journal is © The Royal Society of Chemistry 2006
Dalton Trans., 2006, 4896–4904 | 4901

View Article Online
Table 4 Collection and crystallographic data for 1, 3 and 4
1
3
4
Formula
FW
C
861.78
43
H
63
N
2
O
3
FeCl
2
Li·THF
C
86
H
110
N
4
O
12Fe
2
·2THF
C
661.82
40 55 3
H N FeSi
1661.63
Cryst. dim./mm
Colour, habit
Crystal system
0.22 × 0.21 × 0.20
Yellow, block
Triclinic
0.35 × 0.27 × 0.15
Red, irregular
Monoclinic
0.50 × 0.34 × 0.24
Orange, prism
Monoclinic
42
¯
Space group, no.
P1, 2
P2
1
/c, 14
P2 /c, 14
1
a/A˚
13.1932(7)
13.4944(7)
14.321(1)
79.239(1)
84.262(1)
72.039(1)
2
2380.3(2)
1.202
2.23–20.34
0.71073 (Mo Ka)
100(1)
21.5290(1)
10.7289(5)
39.956(2)
90
91.712(1)
90
22.329(1)
17.831(1)
20.489(1)
90
109.342(1)
90
b/A˚
c/A˚
◦
a/
b/
◦
◦
c /
Z
4
4
V/A˚
3
8994.1(8)
1.227
2.17–24.43
0.71073 (Mo Ka)
110(1)
13.0
63345
15868
7697.2(7)
1.142
2.25–26.72
0.71073 (Mo Ka)
100(1)
8.0
60961
15636
−
3
q
calc/g cm
◦
h range/
k/A˚
T/K
Data collect. time/h
No. of meas. refl.
No. of unique refl.
7.9
22682
11506
R
int.
0.0841
4.71
0.0530
3.86
0.0609
4.52
−
1
l/cm
No. of parameters
Weighting scheme: a, b
634
0.0514, 0.0
0.0728
1041
0.0795, 15.4628
0.0683
1250
0.0509, 0.0148
0.0440
a
b
R(F) for F
0
≥ 4r(F
0
)
2
c
wR(F )
0.1628
0.1841
0.1057
Res. el. dens./e A˚
−
3
−0.44, 0.58(8)
−0.75, 0.86(7)
−0.25, 0.46(6)
d
GoF
0.984
1.027
1.018
a
2
2
2
2
2
b
c
2
2
2
2
2
2
1/2
d
w = 1/[r (F
o
) + (aP) + bP], P = [max(F
o
,0) + 2F
c
]/3. R(F) = R(ꢁF
o
| − |F
c
ꢁ)/R |F
o
|, wR(F ) = [R[w(F
o
− F
c
) ]/R[w(F
o
) ]]
,
GoF =
2
2
2
1/2
[R[w(F
o
− F ) ]/(n − p)] , n = # refl., p = # param. refined.
c
Reaction of 1 with LiCH
2
SiMe
3
via red to dark yellow was observed. Precipitation of KCl was
noted. H NMR data for the new species:
1
LiCH
2
SiMe
3
(3.6 mg, 38 lmol) was added to a solution of 1 (30 mg,
(0.5 mL). A colour change from pale yellow
1
H NMR (500 MHz, THF-d
8
, RT): d (Dm1/2) = 55.9 (1599 Hz),
38 lmol) in THF-d
8
3
(
5.5 (143 Hz), 31.8 (193 Hz), 29.9 (213 Hz), 21.9 (233 Hz), 20.5
122 Hz), 19.4 (257 Hz), 16.9 (206 Hz), 15.7 (197 Hz), 14.7 (363
Hz), 13.9 (166 Hz), 12.4 (337 Hz), 5.4 (421 Hz), 3.6 (55 Hz, THF),
1
via red to dark yellow was observed. H NMR data for the new
species:
1
H NMR (500 MHz, THF-d
), 13.4 (109 Hz, 4H), 10.5 (166 Hz, 1H),
.8 (40 Hz, 5H), 6.6 (48 Hz, 2H), 5.5 (480 Hz, 12H, iPr–CH ), 3.6
8
, RT): d (Dm1/2) = 19.3 (44 Hz, 1H),
1
.7 (53 Hz, THF), −1.7 (441 Hz), −5.4 (212 Hz), −6.3 (798 Hz),
1
6
6.9 (254 Hz, 9H, SiMe
3
−
−
−
11.0 (470 Hz), −13.2 (1317 Hz), −14.3 (264 Hz), −18.7 (994 Hz),
19.7 (269 Hz), −21.1 (114 Hz), −29.3 (667 Hz), −44.5 (539 Hz),
55.9 (126 Hz) ppm.
3
(
29 Hz, 16H, THF), 1.72 (24 Hz, 16H, THF), −12.4 (302 Hz,12H,
iPr–CH
3
), −21.5 (45 Hz, 1H) ppm.
Preparation of [{C(O)(2,6-iPr
2
C
6
H
3
)NC(Ph)N(2,6-iPr
2
C
6
H
3
)}-
Reaction of 1 with LiCH
2
CMe
3
Fe(CO) -l-((CO)Li(THF) )]
2
2
2
·2THF (3)
◦
LiCH
2
CMe
3
(3.0 mg, 38 lmol) was added to a solution of 1 (30 mg,
(0.5 mL). A colour change from pale yellow
All manipulations were performed at 0 C. A solution of
Li[PhC(NAr) ] (1.02 g, 2.27 mmol) in THF (10 mL) was added
to a suspension of FeCl (0.144 g, 1.13 mmol) in THF (5 mL)
and the reaction mixture was stirred for 1 hour. A solution of
LiCH(SiMe (0.188 g, 1.13 mmol) in THF (10 mL) was added
38 lmol) in THF-d
8
2
1
via red to dark yellow was observed. H NMR data for the new
2
species:
1
H NMR (500 MHz, THF-d
8
, RT): d (Dm1/2) = 43.0 (490 Hz,
)
3 2
9
5
1
−
H, tBu), 20.7 (27 Hz, 2H), 14.4 (247 Hz, 2H), 13.0 (232 Hz, 4H),
.5 (66 Hz, 12H, iPr–CH ), 3.6 (13 Hz, 12H, THF), 1.7 (13 Hz,
2H, THF), −12.7 (194 Hz, 2H), −14.9 (348 Hz, 12H, iPr–CH ),
21.3 (25 Hz, 2H) ppm.
dropwise to the reaction mixture in 30 min. After 30 min the
reaction mixture was degassed and CO was admitted. After 3 h,
the solution was allowed to warm to RT and THF was removed
in vacuo. The residue was extracted with pentane (30 mL, 3×) and
hot hexane (30 mL, 1×). The alkane solvent was removed in vacuo
and the crude product was dissolved in THF. The solution was
concentrated and pentane was slowly diffused into the solution
yielding dark red, block-shaped crystals (0.20 g, 0.12 mmol, 21%
3
3
Reaction of 1 with KCH Ph
2
KCH
2
Ph (5.0 mg, 38 lmol) was added to a solution of 1 (30 mg,
3
8 lmol) in THF-d (0.5 mL). A colour change from pale yellow
8
based on FeCl
2
).
4
902 | Dalton Trans., 2006, 4896–4904
This journal is © The Royal Society of Chemistry 2006

View Article Online
−
1
IR (nujol mull, KBr): vmax/cm 3058w, 1961s (C≡O), 1883s
C≡O), 1814s (C≡OLi), 1582w, 1556s (C=O), 1526w, 1493w,
Ethene polymerisation tests with 1 and 4
(
1
A stainless steel 1L autoclave (Medimex), fully temperature
and pressure controlled and equipped with solvent and catalyst
320w, 1262w, 1175w, 1103w, 1054m, 1009m, 913w, 834w, 805w,
84w, 747w, 711m, 696w, 679w, 631w, 587w, 551w, 538w, 477w.
H NMR analysis of the complex was frustrated by the
formation of Fe(0) in the NMR tube, possibly due to photolysis.
Broad, overlapping signals were observed in the diamagnetic
region (+10–0 ppm).
Satisfactory elemental analysis for 3 could not be obtained
due to the light-sensitivity of the crystals and the fact that
cocrystallised THF is easily lost from the lattice.
7
◦
1
injection systems, was preheated in vacuo for 45 min at 100 C prior
◦
to use. The reactor was cooled to 50 C, charged with 250 mL of
toluene and pressurised with ethene (10 bar). Cocatalyst (PMAO
solution in toluene, 4.9 wt% Al (Al/Fe = 500)) was injected,
followed by injection of the Fe complex in toluene (20 lmol in
5
mL). Temperature and pressure were monitored. After 30 min the
runs were aborted by venting the reactor and addition of ethanol.
Excess MAO was further destroyed by treatment of the toluene
solution with ethanol/dilute hydrochloric acid. No significant
amount of polymer was obtained.
Preparation of [{PhC(NAr)
2
}Fe(CH
2
SiMe )(py)] (4)
3
ꢀ
N,N -2,6-(Diisopropylphenyl)benzamidine (780 mg, 1.77 mmol)
was dissolved in THF (20 mL). n-BuLi (2.5 M in hexanes,
References
0
.7 mL, 1.77 mmol) was added. The darkened solution was
1 M. W. Bouwkamp, S. C. Bart, E. J. Hawrelak, R. J. Trovitsch, E.
Lobkovsky and P. J. Chirik, Chem. Commun., 2005, 3406.
stirred for 30 min and transferred to a dropping funnel. The Li–
amidinate solution was added dropwise to a stirred suspension of
FeCl (THF)1.5 (416 mg, 1.77 mmol) in THF (10 mL). After 1 h,
pyridine (0.3 ml, 3.7 mmol) was added to the dark yellow solution.
The colour of the solution became more intensely yellow in the
course of 15 min. LiCH
2
3
M. W. Bouwkamp, E. Lobkovsky and P. J. Chirik, J. Am. Chem. Soc.,
2
005, 27, 9660.
2
(a) G. J. P. Britovsek, V. C. Gibson, B. S. Kimberley, P. J. Maddox,
S. J. McTavish, G. A. Solan, A. J. P. White and D. J. Williams, Chem.
Commun., 1998, 849; (b) B. L. Small, M. Brookhart and A. M. A.
Bennett, J. Am. Chem. Soc., 1998, 120, 4049.
2
SiMe (167 mg, 1.77 mmol) was added,
3
4
S. C. Bart, E. J. Hawrelak, A. K. Schmisseur, E. Lobkovsky and P. J.
Chirik, Organometallics, 2004, 23, 237.
resulting in a dark yellow solution. After stirring for 15 min, all
volatiles were pumped off. Residual THF/excess pyridine were
removed by suspending the residue in hexanes and subsequent
removal of all volatiles in vacuo (10 ml, 4×). The residue was
then extracted with hexanes (30 ml, 3×), leaving an off-white
5
6
A. R. Hermes and G. S. Girolami, Organometallics, 1987, 6, 763.
J. L. Kisko, T. Hascall and G. Parkin, J. Am. Chem. Soc., 1998, 120,
1
0561.
7
(a) M. Akita, N. Shirasawa, S. Hikichi and Y. Mora-oka, Chem.
Commun., 1998, 973; (b) N. Shirasawa, M. Akita, S. Hikichi and K.
Morokuma, Chem. Commun., 1999, 417; (c) N. Shirasawa, T. T. Nguyet,
S. Hikichi, Y. Moro-oka and M. Akita, Organometallics, 2001, 20, 3582.
V. C. Gibson, S. K. Spitzmesser, A. J. P. White and D. J. Williams,
J. Chem,. Soc., Dalton Trans., 2003, 2718.
◦
salt. Cooling to −25 C afforded orange crystals. Yield 440 mg
(
0.66 mmol, 38%).
8
l
1
eff (C
6
H
6
, 298 K) = 5.5 l
H NMR (500 MHz, C
5.6 (200 Hz, 9H, SiCH
B
.
6
D
6
, RT) d (Dm1/2) = 83.3 (1980 Hz, 2H),
9 M. D. Fryzuk, D. B. Leznoff, E. S. F. Ma, S. J. Rettig and V. G. Young,
Jr., Organometallics, 1998, 17, 2313.
0 (a) J. M. Smith, R. J. Lachicotte and P. L. Holland, Organometallics,
3
2
3
), 31.8 (233 Hz, 2H), 27.5 (195 Hz, 2H),
1
6.0 (25 Hz, 2H), 11.6 (176 Hz, 4H, m-HAr), 5.0 (752 Hz, 12H, iPr–
), −19.9 (22 Hz, 2H, p-HAr), −25.0 (435 Hz, 12H, iPr–CH
ppm.
2
002, 21, 4808; (b) H. Andres, E. L. Bominaar, J. M. Smith, N. A.
CH
3
3
)
Eckert, P. L. Holland and E. M u¨ nck, J. Am. Chem. Soc., 2002, 124,
3
012; (c) J. Vela, J. M. Smith, R. J. Lachicotte and P. L. Holland, Chem.
−
1
Commun., 2002, 2886; (d) J. Vela, S. Vaddadi, T. R. Cundari, J. M.
Smith, E. A. Gregory, R. J. Lachicotte, C. J. Flaschenriem and P. L.
Holland, Organometallics, 2004, 23, 5226.
IR (nujol mull, KBr) vmax/cm = 3053m, 2962s, 2905s, 2893s,
601w, 1579w, 1507s, 1482s, 1454s, 1434s, 1401s, 1360s, 1316,
270m, 1251m, 1239s, 1214m, 1177w, 1153w, 1121w, 1098m,
068w, 1053w, 1042w, 1027w, 1011w, 951w, 935w, 917w, 874, 851m,
24m, 808m, 785m, 770m, 761m, 751m, 738m, 724m, 697s, 551w,
1
1
1
8
5
11 T. J. J. Sciarone, A. Meetsma, B. Hessen and J. H. Teuben, Chem.
Commun., 2002, 1580.
1
2 C. A. Nijhuis, E. Jellema, T. J. J. Sciarone, A. Meetsma, P. H. M.
Budzelaar and B. Hessen, Eur. J. Inorg. Chem., 2005, 2089.
−
1
39m, 510m, 492w, 477w cm .
13 J. M. Smith, R. J. Lachicotte and P. L. Holland, Chem. Commun., 2001,
1
542.
Anal. Found: C, 72.83; H, 8.45; N, 6.44. Calc. for C40
H
55
3
N FeSi:
1
1
1
4 F. T. Edelmann, Coord. Chem. Rev., 1994, 137, 403.
5 J. Barker and M. Kilner, Coord. Chem. Rev., 1994, 133, 219.
6 A. Earnshaw, Introduction to Magnetochemistry, Academic Press Inc.
Ltd., London, 1968.
C, 72.59; H, 8.38; N, 6.35%.
Reaction of 4 with B(C
6
F
5
)
3
17 P. J. Stewart, A. J. Blake and P. Mountford, Inorg. Chem., 1997, 36,
982.
8 J. A. R. Schmidt and J. Arnold, J. Chem. Soc., Dalton Trans., 2002,
454.
9 H. K. Lee, T. S. Lam, C.-K. Lam, H.-W. Li and S. M. Fung,
New J. Chem., 2003, 27, 1310.
1
1
1
B(C
9 lmol) in C
to yellow was observed. By H and F NMR spectroscopy,
the formation of 2 and C NB(C was observed. 1,2-
Bis(trimethylsilyl)ethane was detected by GC-MS analysis.
NMR data for C NB(C
6
F
5
)
3
(25 mg, 49 lmol) was added to a solution of 4 (30 mg,
3
4
6
D
6
(0.5 mL). A colour change from bright orange
1
19
20 F. A. Cotton, L. M. Daniels, C. A. Murillo and P. Schooler, J. Chem.
Soc., Dalton Trans., 2000, 2001.
5
H
5
6
F
5
)
3
2
1 J. C. Flores, J. C. W. Chien and M. D. Rausch, Organometallics, 1995,
4, 1827.
5
H
5
6
F ) :
5
3
1
1
H NMR (300 MHz, C
6
D
6
, RT): d = 8.01 (2H, o-H), 6.80 (1H,
, RT): d = − 131.4 (d, JFF = 19.2 Hz,
22 E. Nelkenbaum, M. Kapon and M. S. Eisen, Organometallics, 2005,
24, 2645.
23 J. M. Smith, R. J. Lachicotte and P. L. Holland, Organometallics, 2002,
p-H), 6.40 (2H, m-H) ppm.
1
9
F NMR (188 MHz, C D
6
6
2
1, 4808.
2
F, o-F), −155.2 (t, JFF = 21.1 Hz, 1F, p-F), −162.3 (m, 2F,
2
4 J. R. Hagadorn and J. Arnold, J., J. Organomet. Chem., 2001, 637–639,
m-F) ppm.
521.
This journal is © The Royal Society of Chemistry 2006
Dalton Trans., 2006, 4896–4904 | 4903

View Article Online
2
2
5 H. Deng and S. G. Shore, Inorg. Chem., 1992, 31, 2289.
6 J. A. Marsella, J. C. Huffman, K. G. Caulton, B. Longato and J. R.
Norton, J. Am. Chem. Soc., 1982, 104, 6360.
33 O. Kahn, Molecular Magnetism, VCH, New York, 1993.
34 P. Kovacic and N. O. Brace, Inorg. Synth., 1960, 6, 172.
35 R. J. Kern, J. Inorg. Nucl. Chem., 1962, 24, 1105.
36 H. L. Lewis and T. L. Brown, J. Am. Chem. Soc., 1970, 92, 4664.
37 R. R. Schrock and J. D. Fellman, J. Am. Chem. Soc., 1978, 100,
3359.
2
2
2
3
7 D. M. Hamilton, Jr., W. S. Willis and G. D. Stucky, J. Am. Chem. Soc.,
1
981, 103, 4255.
8 B. L. Groh, G. R. Magrum and T. J. Barton, J. Am. Chem. Soc., 1987,
09, 7568.
1
38 N. Wiberg and G. Wagner, Chem. Ber., 1986, 119, 1455.
39 L. Lochmann and J. Trekoval, J. Organomet. Chem., 1987, 326, 1.
40 J. L. W. Pohlmann and F. E. Brinckmann, Z. Naturforsch., 1965, 20b,
5.
9 S. C. Bart, E. J. Hawrelak, A. K. Schmisseur, E. Lobkovsky and P. J.
Chirik, Organometallics, 2004, 23, 237.
0 T. J. J. Sciarone, A. Meetsma and B. Hessen, Inorg. Chim. Acta, 2006,
3
59, 1815.
41 S. Bambirra, D. van Leusen, A. Meetsma and J. H. Teuben, Chem.
3
3
1 WO Pat., 99/05154, 1999.
Commun., 2003, 522.
2 (a) D. F. Evans, J. Chem. Soc., 1959, 2003; (b) E. M. Schubert, J. Chem.
Educ., 1992, 69, 62.
42 International Tables for Crystallography, Kluwer Academic Publishers,
Dordrecht, The Netherlands, 1992.
4
904 | Dalton Trans., 2006, 4896–4904
This journal is © The Royal Society of Chemistry 2006