Neutral and cationic Fe(II) β-diketiminate complexes

Article abstract of DOI:10.1016/j.ica.2005.06.065

The three-coordinate, 12-valence electron complexes [(^MeBDK)FeR] (^MeBDK = [HC(C(Me)NAr)₂]^-, Ar = 2,6-iPr ₂C₆H₃, R = CH₂Ph, CH ₂SiMe₃) are reported as well as their reactivity towards Lewis bases. With perfluoroaryl borane and -borate type activators, the monoalkyls react to give alkyl-free paramagnetic cationic iron species counterbalanced by perfluorinated arylborate anions. The paramagnetic nature of the cations permits the observation of weak and dynamic interactions with these anions via ¹⁹F NMR spectroscopy.

Full text of DOI:10.1016/j.ica.2005.06.065

Inorganica Chimica Acta 359 (2006) 1815–1825
www.elsevier.com/locate/ica
Neutral and cationic Fe(II) b-diketiminate complexes
*
Timo J.J. Sciarone, Auke Meetsma, Bart Hessen
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
Received 3 June 2005; accepted 29 June 2005
Available online 8 August 2005
Dedicated to Professor Gerard van Koten.
Abstract
The three-coordinate, 12-valence electron complexes [(MeBDK)FeR] (MeBDK = [HC(C(Me)NAr)2]ꢀ, Ar = 2,6-iPr2C6H3,
R = CH2Ph, CH2SiMe3) are reported as well as their reactivity towards Lewis bases. With perfluoroaryl borane and -borate type
activators, the monoalkyls react to give alkyl-free paramagnetic cationic iron species counterbalanced by perfluorinated arylborate
anions. The paramagnetic nature of the cations permits the observation of weak and dynamic interactions with these anions via 19
F
NMR spectroscopy.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: b-Diketiminato iron(II) complexes; Monoalkyl complexes; X-ray structures; 19F NMR spectroscopy; Cation–anion interactions
1. Introduction
b-Diketiminate anions of the type [HC{C(R)NAr}2]ꢀ
(RBDK, R = tBu, Me, Ar = 2,6-iPr2C6H3) have found
wide employment for stabilisation of low-coordinate
complexes of transition metals and main group elements
[6]. When coordinating in a chelating fashion to transi-
tion metals, they donate 4 electrons while providing ste-
ric protection of the metal centre by virtue of the
sterically encumbering aryls, which are oriented orthog-
onal to the planar NCCCN backbone. They seem per-
fectly suitable for the stabilisation of low coordination
number iron(II) alkyl species. Indeed, in recent years,
the Holland group [7,8] has reported 12-valence elec-
tron, 3-coordinate iron(II) monoalkyls, initially using
the 2,5-bis(tert-butyl) b-diketiminate ligand tBuBDK.
Subsequent efforts by us [9] and the Holland group
[10,11] showed that also the smaller ligand [MeBDK]ꢀ
was capable of stabilising 3-coordinated Fe(II) mono-
alkyls. Here, we describe the synthesis of the 12-valence
electron three-coordinate iron(II) alkyl complexes
Iron(II) 2,6-diiminopyridine complexes, in conjunc-
tion with methyl alumoxane (MAO) cocatalyst, are
highy active catalysts for the polymerisation and oligo-
merisation of ethene [1–5]. Despite this success, little is
as yet known about the actual active species in this cat-
alyst system, although an electron-deficient cationic iro-
n(II) monoalkyl species appears to be the most likely
candidate. As alkyl abstraction processes from elec-
tron-deficient transition-metal alkyl species, and the cat-
ion–anion interactions in the resulting ionic products,
are basic processes in the generation and action of olefin
polymerisation catalysts, we sought to approach this for
paramagnetic iron(II) species by studying well-defined
electron-deficient iron(II) monoalkyl complexes as
model compounds.
*
Corresponding author. Tel.: +31 50 363 4322; fax: +31 50 363
[
MeBDK]FeCH2R (R = Ph, SiMe3) and alkyl abstrac-
4315.
tion by Lewis and Brønsted acid activators, together
with aspects of the cation–anion interactions in these
E-mail addresses: hessen@chem.rug.nl, B.Hessen@rug.nl (B. Hes-
sen).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.06.065

1816
T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
ionic species. The paramagnetic nature of the Fe(II) cen-
tre is particularly useful in revealing weak cation–anion
interactions in solution, as it can effectively act as a
chemical shift reagent. A part of this study was commu-
nicated previously [9].
[(MeBDK)FeCl2] [13] with two equivalents of the respec-
tive alkylating agents (Scheme 1). The reaction of
[(MeBDK)FeCl2] with one equivalent of PhCH2MgBr
is accompanied by a colour change from purple to yel-
low. Addition of the second equivalent of the Grignard
reagent induces a colour change to brown-red. The for-
mation of 1 was established by NMR spectroscopy, and
GC/MS analysis of the mixture revealed the formation
of dibenzyl, E-stilbene and toluene. Similar observations
were made using Me3SiCH2Li as alkylating agent, and
in this case the formation of Me3SiCH2CH2SiMe3 and
SiMe4 as co-products was established. The colour
change from purple to yellow upon addition of the first
equivalent of alkylating agent indicates that reduction of
Fe(III) to Fe(II) takes place in this stage of the reaction.
2. Results and discussion
2.1. Synthesis and characterisation of (MeBDK)Fe(II)
monoalkyl complexes
The
three-coordinate
monoalkyl
complexes
[(MeBDK)FeR] (R = CH2Ph, 1; CH2SiMe3, 2) were pre-
pared in a one-pot procedure via the ate-complex
[(MeBDK)Fe(l-Cl)2Li(THF)2] [12] that could be conve-
niently generated in situ by reaction of (MeBDK)H with
n-BuLi in THF, followed by reaction with FeCl2 or
FeCl2(THF)1.5. Subsequent reaction with PhCH2MgBr
or LiCH2SiMe3 in THF, followed by extraction with
and crystallisation from pentane, afforded the alkyl com-
plexes 1 (as red crystals of its pentane solvate) and 2 in
71% and 27% isolated yield, respectively (Scheme 1).
The relatively low isolated yield of 2 from this procedure
is due to the high solubility of this compound in pentane.
The Fe(II) monoalkyl complexes 1 and 2 are also
formed in the reactions of the Fe(III) complex
Å
The involvement of free RCH2 radicals in these reduc-
tions is suggested by the organic coproducts, which arise
from radical dimerisation or hydrogen abstraction
processes.
The molecular structures of the b-diketiminate iron
monoalkyl complexes 1 and 2 (Fig. 1) were determined
by single crystal X-ray diffraction. Pertinent bond
lengths and bond angles are listed in Table 1.
Both structures show iron centres coordinated in a
trigonal planar fashion, the sum of the angles around
iron equalling 360ꢁ and 359ꢁ for 1 and 2, respectively.
The iron centre is located slightly out of the least-squares
1.)n-BuLi
2.) FeCl2
THF, R.T.
N
N
N
N
RCH2M
THF, RT
N
N
2 RCH2M
– 0.5 RR
N
N
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Fe
Li
H
Fe
Fe
Cl
Cl
Cl
Cl
R
M = MgBr,
M = Li,
1: R = Ph
2: R = SiMe3
THF THF
Scheme 1.
2
1
Fig. 1. X-ray structures of 1 and 2 with thermal ellipsoids at 50% probability. Hydrogen atoms have been omitted for clarity.

T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
1817
high-spin d6-configuration (4 unpaired electrons). This is
commonly observed in the family of (b-diketimi-
nate)FeIIX complexes [7,8,10,11,13,14].
Table 1
Selected bond distances and bond angles for 1 and 2
1
2
˚
Distances (A)
The presence of unpaired electrons in 1 and 2 results
in 1H NMR spectra consisting of paramagnetically
shifted, broad resonances in the frequency window from
+150 to ꢀ150 ppm. The b-diketiminate resonances can
be assigned on the basis of integration and comparison
to the literature data of related compounds [10,11]. The
methylene resonances from the alkyl moieties are not
observed, which is consistent with the absence of alkyl
a-CH2 signals in the spectra of the b-diketiminate iron
monoalkyls reported by the Holland group [7,8,10,11].
Solutions and solid samples of 1 and 2 are highly air-
sensitive, turning black immediately upon exposure to
air. Under inert atmosphere, however, the complexes
are thermally very robust. Solutions of 1 or 2 in C6D6
are stable at 80 ꢁC for at least 7 days. In toluene-d8
the monoalkyls are stable as well. No significant decom-
position is detected after heating for 8 days at 110 ꢁC.
The observed thermostability parallels that of other re-
ported b-diketiminate Fe(II) monoalkyls lacking b-
hydrogens [8,10,11,15].
Fe–C30
Fe–N1
2.0414(18)
1.9831(11)
1.9807(11)
1.405(2)
1.401(2)
1.3405(18)
1.3321(17)
2.0222(18)
1.9915(13)
1.9926(12)
1.401(2)
1.399(2)
1.334(2)
Fe1–N2
C13–C15
C15–C16
N2–C16
N1–C13
1.336(2)
Angles (ꢁ)
Fe1–C30–C31
Fe–C30–Si
113.18(11)
123.48(10)
94.01(5)
N1–Fe1–N2
C30–Fe–N1
C30–Fe–N2
C13–C15–C16
Fe–N1–C13
Fe–N1–C6
C6–N1–C13
Fe–N2–C16
Fe–N2–C18
C18–N2–C16
94.35(5)
131.81(6)
133.84(6)
128.97(13)
124.38(9)
115.54(8)
120.05(11)
123.69(10)
117.97(9)
118.32(12)
142.06(6)
123.19(6)
129.14(15)
124.34(10)
116.67(10)
118.85(13)
125.01(10)
114.74(10)
119.90(12)
plane through the diketiminate NCCCN backbone
atoms (0.268(1) A in 1 and 0.012(1) A in 2). The iron–
2.2. Reactivity toward Lewis bases
˚
˚
˚
carbon bond lengths (2.0414(18) A in
1
and
Despite their high-spin configuration, with four un-
paired electrons, the three-coordinate (b-diketimi-
nate)Fe(alkyl) species still possess one free available
valence orbital that should be capable to interact with
Lewis basic substrates. Nevertheless, these compounds
do not coordinate alkenes, nor show alkene insertion
into the Fe–alkyl bond. Thus they are not active as eth-
ene polymerisation catalysts, although single insertion
reactions of alkenes into the (b-diketiminate)Fe-hydride
bond have been observed [10,11]. With stronger Lewis
bases, the alkyl compounds 1 and 2 do show adduct for-
mation. Thus, the benzyl complex 1 forms the adduct
[(MeBDK)Fe(CH2Ph)(py)] (3) upon reaction with pyri-
dine. The product crystallises from toluene as deep red
crystals of its toluene solvate 3 Æ (toluene).
˚
2.0222(18) A in 2) lie well in the range of Fe–C distances
observed for three-coordinate b-diketiminate iron alkyls
[7,8,10,11].
The b-diketiminate ligands coordinate in the normal
j2(N,N) chelating mode and the aryl substituents on
the nitrogen atoms are oriented roughly orthogonal to
the coordination plane. The N–Fe–N bite angles of ca.
94ꢁ are common for Fe(II) b-diketiminate complexes
of [MeBDK]ꢀ [10–14].
Despite the formal electron deficiency of the three-
coordinate iron benzyl complex, no interaction between
the arene part of the benzyl group and the iron atom is
˚
present in 1. The Fe–Cipso distance equals 2.9609(16) A
and Fe–CH2–Cipso angle = 113.18(11)ꢁ, indicating that
the aromatic ring of the benzyl group is bent away from
the metal. An even larger angle is found in 2 where Fe–
CH2–Si = 123.48(10)ꢁ. The Fe–CH2–Cipso/Si angles in 1
and 2 are enlarged to minimise steric interactions with
the [MeBDK]ꢀ ligand. Steric hindrance of the (trimethyl-
silyl)methyl group in the small binding pocket of the b-
diketiminate ligand is also expressed in the unsymmetric
Ca–Fe–N angles, which differ by 19ꢁ (only 2ꢁ difference
in 1). Large differences in the Ca–Fe–N angles are also
observed in other b-diketiminate Fe(II) monoalkyls with
sterically demanding alkyl groups (e.g., [(MeBDK)Fe(i-
Bu)], [(tBuBDK)Fe(CH2tBu)]) [10,11].
A crystal structure determination of 3 Æ (toluene)
(Fig. 2, Table 2) shows a pseudotetrahedral coordination
of the iron centre. As expected, the metal–ligand dis-
tances are slightly longer than in the three-coordinated
parent complex 1. The Fe–Npy Bond length is consider-
ably longer than the Fe–NBDK distances and is
t
˚
comparable to the Fe–N Bupy distance (2.124(2) A) in
the 4-tBu-pyridine adduct of a b-diketiminate Fe(II)-hy-
dride species, [(tBuBDK)Fe(H)(4-tBu-py)] [16]. Apart
from the slight difference between the two Fe–NBDK dis-
tances, the geometric parameters relating to the b-diketi-
minate ligand are unexceptional. The Fe–CH2–Cipso
angle in 3 is ca. 6ꢁ larger than in base-free 1. Again, this
is probably the result of increased steric crowding around
the metal centre in the four-coordinated complex.
Both the three-coordinate 12 valence electron com-
pounds 1 and 2 are paramagnetic. Both have a magnetic
moment in benzene solution of 5.6 lB, consistent with a

1818
T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
Table 2
Selected bond distances and bond angles for 3
N
N
N
N
Ar
Ph
Ar
Ar
Ph
Ar
˚
Distances (A)
Fe
Fe
Fe–C35
Fe–N1
Fe–N2
2.107(2)
2.0253(16)
2.0393(15)
2.1154(16)
1.414(3)
1.421(3)
1.340(2)
py
py
Fe–N3
Scheme 2.
C13–C15
C15–C16
N2–C16
N1–C13
tion to ꢀ50 ꢁC reveals 16 sharper resonances. Based
on the solid state structure, a maximum of 18 resonances
might be expected. The missing resonances may be asso-
ciated with the protons closest to the paramagnetic cen-
tre, the pyridine ortho protons and those of the benzyl
methylene group. Warming the solution above ambient
temperature reveals gradual symmetrisation of the spec-
trum. At 110 ꢁC, 12 of the maximum 14 resonances ex-
pected for a time-averaged C2v-symmetric molecule are
visible in the spectrum. Unfortunately, a full asssign-
ment of all the resonances was not possible. The revers-
ibility of the process was confirmed by recooling the
sample to room temperature, which restores the original
broad spectrum. A related fluxional process was inferred
from VT NMR spectroscopy on a few other four-coor-
dinate adduct species [(MeBDK)MX(L)]: M = Fe,
X = NH-2,6-iPr2C6H3, L = THF, MeCN [14], M = Ni,
X = Me, L = 2,4-lutidine [17], M = Mg, Zn, L = THF,
X = OR [18].
1.344(2)
Angles (ꢁ)
N1–Fe–N2
N2–Fe–N3
N1–Fe–N3
C35–Fe–N1
C35–Fe–N2
C35–Fe–N3
Fe1–C35–C36
C13–C15–C16
Fe–N1–C13
Fe–N1–C1
92.47(6)
101.08(6)
102.78(6)
126.19(7)
121.85(7)
108.54(7)
119.18(13)
129.02(17)
124.97(12)
114.84(11)
120.14(15)
124.12(12)
115.28(11)
120.60(15)
C1–N1-C13
Fe–N2–C16
Fe-N2–C18
C18–N2–C16
Although the synthesis of 1 and 2, performed in THF
and followed by pentane extraction, affords the base-
free 12-electron species, solution NMR spectroscopy
suggests that these species also form (relatively weak)
Lewis base adducts with THF. Addition of a drop of
THF-d8 to a solution of 1 in C6D6 induces a colour
change from red to dark orange. Only 10 signals are ob-
served in the 1H NMR spectrum between +70 and
ꢀ100 ppm (cf. +150 to ꢀ150 ppm for 1 in neat C6D6).
The number of resonances for 1 Æ THF-d8 is consistent
with fast site exchange of the THF ligand in the adduct.
In neat THF-d8, site exchange of coordinated solvent in
1 Æ THF-d8 is fast on the NMR timescale down to
ꢀ50 ꢁC.
Fig. 2. Molecular structure of 3 with thermal ellipsoids at 50%
probability. Hydrogen atoms have been omitted for clarity.
2.3. Generation of cationic iron b-diketiminate complexes
Although the electron-deficient three-coordinate al-
kyl compounds 1 and 2 are unable to effect catalytic ole-
fin polymerisation, they are interesting model
compounds to study the generation of cationic species
by alkyl abstraction from the Fe(II) centre through reac-
tions with Lewis or Brønsted acid activators. Reaction
of the benzyl complex 1 with the strong lewis acid
B(C6F5)3 in pentane solvent leads to precipitation of
the contact ion pair complex [(MeBDK)Fe{g2-
PhCH2B(C6F5)3}] (4). The compound was characterised
by X-ray diffraction (Fig. 3, Table 3).
Pyridine adduct 3 possesses a magnetic moment of
4.4 lB in benzene solution, consistent with a high-spin
(S = 2) Fe(II) centre. The H NMR spectrum in tolu-
ene-d8 at room temperature features extremely broad,
overlapping resonances. The line widths and consequent
peak overlap are much greater than for the parent com-
pound 1 under similar conditions, suggesting that the
molecule shows fluxional behaviour in solution. This
process probably involves site-exchange of the coordi-
nated pyridine molecule (Scheme 2). Cooling the solu-
1

T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
1819
Table 3
Selected bond distances and bond angles for 4
˚
Distances (A)
Fe–N1
Fe–N2
1.970(6)
1.973(6)
2.344(8)
2.340(8)
2.592(7)
2.741(7)
2.716(8)
2.604(7)
1.387(11)
1.401(11)
1.349(8)
1.346(8)
1.383(12)
1.387(13)
1.395(9)
1.400(11)
1.392(12)
1.42(1)
Fe–C30
Fe–C31
Fe–C32
Fe–C33
Fe–C34
Fe–C35
C13–C15
C15–C16
N2–C16
N1–C13
C30–C31
C31–C32
C32–C33
C33–C34
C34–C35
C30–C35
Angles (ꢁ)
N1–Fe–N2
N1–Fe–C30
N1–Fe–C31
N2–Fe–C30
N2–Fe–C31
C30–Fe–C31
Fe–N1–C1
Fe–N1–C13
C1–N1–C13
Fe–N2–C16
Fe–N2–C18
C18–N2–C16
C36–B–C37
C36–B–C43
C36–B–C49
C37–B–C43
C37–B–C49
C43–B–C49
B–C36–C35
95.9(2)
103.8(3)
115.6(3)
160.3(3)
134.1(3)
34.4(3)
119.2(4)
122.3(5)
118.5(6)
123.1(5)
118.9(4)
117.6(6)
103.2(6)
111.8(6)
113.8(6)
113.0(6)
112.1(6)
103.3(6)
114.0(6)
Fig. 3. X-ray structure of 4 with thermal ellipsoids at 50% probability.
Hydrogen atoms have been omitted for clarity.
The X-ray structure reveals a contact ion pair in
which the benzyl moiety of the [PhCH2B(C6F5)3]ꢀ anion
is g2-coordinated to iron via the ortho and meta carbon
atoms. The description of the coordination mode as
(predominantly) dihapto is supported by the distances
of the iron centre to C30 and C31, which are at least
˚
0.25 A shorter than the distances to the other ring car-
bons. The phenyl C–C bond lengths, however, are iden-
tical within experimental error, indicating retention of
aromaticity. For the [PhCH2B(C6F5)3]ꢀ anion, g3- and
g6-interactions of the benzyl fragment with metal cen-
tres have been reported previously [19–22]. The g2-
(m,p) coordination of this anion as observed in 4 is
unprecedented. For the [BPh4]ꢀ anion, g2-(m,p)-coordi-
librium between contact ion pair 4 and a solvent-sepa-
rated ion pair [(MeBDK)Fe(C6D5Br)] [PhCH2B(C6F5)3]
(Scheme 3).
1
nation to [Cp02ZrMe]+ has been proposed based on H
NMR data [23] and g2-(o,m)-coordination of [BPh4]ꢀ
to [(en)Cu(CO)]+ (en = 1,2-diaminoethane) has been
established by X-ray diffraction [24].
C6D5Br
N
N
N
N
The iron atom is at the centre of a severely distorted
tetrahedron comprising the two diketiminate nitrogen
atoms and C30 and C31 of the benzyl fragment of the
anion. While N1, N2 and C30 are coplanar with iron,
Ar
Ar
Ar
Ar
Fe
Br
Fe
B(C6F5)3
PhCH2B(C6F5)3
THF
˚
C31 is located 1.194(8) A below this plane. The 2,6-
4
diisopropylphenyl rings make angles of ca. 88ꢁ with
the coordination plane. The phenyl ring of the coordi-
nated benzyl group and the NCCCNFe-coordination
plane are at an angle of 77.1(3)ꢁ.
In C6D5Br solution, 4 shows extremely broad and
overlapping resonances between ꢀ80 and ꢀ170 ppm in
the 19F NMR spectrum, suggesting a coordination equi-
N
N
Ar
Ar
PhCH2B(C6F5)3
Fe
THF
Scheme 3.

1820
T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
Indeed, variable temperature 19F NMR spectroscopy
[PhCH2B(C6F5)3]ꢀ anion of the solvent-separated ion
pair (71% by integration) shows conventional shifts
and sharp 19F resonances, whereas the bound anion in
4 (29%) is characterised by significant contact shifts
and line broadening due to coordination to the para-
magnetic Fe(II) centre (Fig. 4). Addition of THF-d8 to
the sample affords the corresponding adduct [(MeBDK)-
Fe(THF-d8)][PhCH2B(C6F5)3], yielding the 19F NMR
spectrum of the unperturbed [PhCH2B(C6F5)3]ꢀ anion.
Abstraction of the (trimethylsilyl)methyl group from
[(MeBDK)FeCH2SiMe3] (2) was investigated by NMR
tube scale experiments. An orange solution of 2 in
C6D6 turns dark yellow immediately after addition of
the Lewis acid B(C6F5)3 and changes to bright red in
the course of 1 h. At that stage, the 19F NMR spectrum
exhibits three sharp signals characteristic of the borane
Me3SiCH2B(C6F5)2 [25,26]. In addition, two broad res-
onances are observed at d = +118.1 (Dm1/2 = 64 Hz)
and +31.5 (Dm1/2 = 345 Hz) ppm, with an integral ratio
of 1:2. These shifts suggest that C6F5 transfer to the me-
tal has occurred to give [(MeBDK)Fe(C6F5)] (Scheme 4).
The ortho fluorine resonances of the Fe–C6F5 species are
not detected, possibly due to extreme line broadening by
the paramagnetic centre. The 1H NMR spectrum shows
paramagnetic ligand resonances of a single C2v-symmet-
ric b-diketiminate-supported Fe(II) compound, which is
consistent with the formulation of [(MeBDK)Fe(C6F5)].
Transfer of a pentafluorophenyl group from B(C6F5)3
to Fe(II) was recently reported by Chirik [27] in the reac-
demonstrates that at ꢀ20ꢁ in C6D5Br solution two per-
fluorophenyl-containing species are present. The ꢀfreeꢁ
a
-80
-90
-100
-110 -120
-130 -140
-150 -160
ppm
m
b
p
o
p
m
o
-80
-90
-100
-110
-120
-130
-140
-150
-160
ppm
c
-80
-90
-100
-110
-120
-130
-140
-150
-160
ppm
Fig. 4. 19F NMR spectra of
4 in C6D5Br (188 MHz, ambient
temperature) (a), (470 MHz, ꢀ20 ꢁC) (resonances of contact ion pair
are underscored) (b) and 4 + THF-d8 (188 MHz, RT) (c).
C6D5Br
[PhNHMe2] [B(C6F5)4]
–SiMe4
+ PhNMe2
N
N
N
N
N
N
Ar
Ar
Ar
Ar
Ar
Ar
Fe
F
Fe
Fe
N
F
SiMe3
B(C6F5)4
F
2
Ph
F
B(C6F5)3
C6D6
B(C6F5)3
F
THF-d
8
–PhNMe2
N
N
Ar
Ar
Fe
B(C6F5)4
N
N
Ar
Ar
Me3Si
Fe
O
B(C6F5)3
not observed
d
8
–Me3SiCH2B(C6F5)3
N
N
Ar
Ar
Ar = 2,6-iPr2C6H3
Fe
C6F5
Scheme 4.

T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
1821
tion of [(a-diimine)Fe(CH2SiMe3)2] with B(C6F5)3,
yielding Me3SiCH2B(C6F5)2 and [(a-diimine)Fe(CH2Si-
Me3)(C6F5)]. Although the spectroscopic data reported
for the borane are identical to those observed by us,
the 19F NMR shifts attributed by the authors to the
paramagnetic Fe–C6F5 complex (d = ꢀ162.3, ꢀ154.0,
ꢀ139.1 ppm) appear in a region very different from
those in our case, and essentially lie in the normal dia-
magnetic chemical shift range.
spectrum now shows free N,N-dimethylaniline
(d = 2.69 ppm, 6H, PhNMe2) and formation of a single
C2v-symmetric paramagnetic compound, presumably
the THF-d8-adduct [(MeBDK)Fe(THF-d8)]+. Very re-
cently, Gregory et al. reported the cationic b-diketimi-
nate Fe(II) complex [(tBuBDK)Fe(Et2O)]+, which was
prepared from the monomethyl derivative and
[Ph3C][B{3,5-(CF3)2C6H3}4] in diethyl ether solution
[28].
The reaction of
2
with the Brønsted acid
[PhNHMe2][B(C6F5)4] in C6D5Br solvent was used to
generate the cation [(MeBDK)Fe]+ with the perfluori-
nated borate counterion [B(C6F5)4]ꢀ. The reaction was
accompanied by liberation of SiMe4 and a colour
change from yellow to purple-red. No resonances for
free N,N-dimethylaniline could be observed in the
spectrum, but a very broad resonance at d = 30.8 ppm
(Dm1/2 = 1596 Hz), integrating as 3H, was seen in addi-
tion to resonances attributable to the MeBDK ligand
of the paramagnetic iron species. This suggests coordi-
nation of the aniline to the paramagnetic metal centre
(Scheme 4). The broad resonance observed may be asso-
ciated with the aniline protons farthest removed from
the metal centre (phenyl p-H and m-H). Despite the
apparent coordination of the aniline, the 19F NMR
spectrum also gives indication of some degree of associ-
ation of the [B(C6F5)4]ꢀ anion with the paramagnetic
centre: its resonances are significantly shifted relative
to the normal positions of the free anion (Fig. 5(a)). This
indicates that the aniline and the anion are in dynamic
equilibrium with respect to their interaction with the me-
tal centre. Indeed, upon addition of an aliquot of THF-
d8 a colour change from purple-red to green is seen and
the 19F NMR spectrum now showed resonances normal
for the free anion (Fig. 5(b)). Consistently, the 1H NMR
3. Conclusions
The three-coordinate Fe(II) monoalkyl complexes
[(MeBDK)FeR] (R = CH2Ph, 1; CH2SiMe3, 2) were
readily synthesised in a one-pot procedure. Although
these 12 valence electron S = 2 species do not coordinate
or polymerise alkenes, they do interact with Lewis bases
to form pseudo-tetrahedral adducts. For pyridine this
interaction is strong enough to allow isolation of the ad-
duct, but the weaker base THF readily dissociates from
the metal centre upon work-up.
The two alkyl complexes can be used as model sys-
tems to study the generation of ionic species by alkyl
abstraction reactions and the interactions between the
cation and anion in these species, features that are of
general relevance to the generation and action of cat-
ionic olefin polymerisation catalysts. The paramagnetic
nature of the cationic species allows it to act as a chem-
ical shift reagent, revealing weak and dynamic cation–
anion interactions with fluorinated arylborate anions
by 19F NMR spectroscopy. This was possible even for
the very weakly nucleophilic [B(C6F5)4]ꢀ anion, suggest-
ing that the application of paramagnetic metal centres
may be of more general use in the study of weak cat-
ion–anion interactions in solution.
a
4. Experimental
4.1. General considerations and instrumentation
All iron complexes are highly air-sensitive and were
handled under a dry dinitrogen atmosphere using stan-
dard Schlenk and drybox techniques. Diethyl ether
and THF (99.9% Aldrich) were percolated over a col-
umn of Al2O3 and stored under nitrogen. Toluene, hex-
anes and pentane (99.9% Aldrich) were percolated over
-120
-125 -130
-135 -140
-145 -150 -155
-160 -165
ppm
b
˚
a column packed with molecular sieves 4 A (90 wt%)
and Al2O3 (10 wt%) and stored under nitrogen. Deuter-
ated solvents (C6D6, THF-d8 Aldrich) were dried
over Na/K alloy and stored under nitrogen. C6D5Br
(Aldrich) was distilled from CaH2.
-120
-125 -130
-135 -140
-145 -150 -155
-160 -165
ppm
NMR-spectra were recorded on Varian Inova 500,
VXR 300 and Varian Gemini 200 instruments. 1H
chemical shifts are referenced to residual protons in
Fig. 5. 19F NMR (188 MHz, ambient temperature) spectra of 2 +
[PhNHMe2][B(C6F5)4] before (a) and after (b) addition of an aliquot of
THF-d8.

1822
T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
deuterated solvents and are reported relative to tetra-
methylsilane. H NMR spectra of paramagnetic com-
(77 Hz, 2H, p-HAr), ꢀ112.3 (651 Hz, 12H, iPr-Me),
ꢀ119.4 (1302 Hz, 4H, iPr-CH) ppm.
1
pounds were recorded with pulse widths of ca. 25ꢁ and
acquisition times of ca. 200 ms using a window wide en-
ough to place no peaks near the edge of the spectrum. If
possible, concentrations of ca. 50 mg/0.5 mL were used.
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 per-
formed by the Microanalytical Department at the Uni-
versity of Groningen or by Mikroanalytisches
leff.ðC6H6; 298 KÞ ¼ 5.6 lB.
Anal. Calc. for C36H48N2Fe.0.5 C5H12 (600.71) re-
quires: C, 76.98; H, 9.06; N, 4.66; Fe, 9.30. Found: C,
77.47; H, 9.31; N, 4.74; Fe, 9.00%.
4.4. Reaction of 1 with THF-d8
A few drops of THF-d8 (excess) were added to a solu-
tion of 1 (20 mg, 33 lmol) in C6D6 (0.5 mL). The colour
of the solution changed from red to dark orange.
1H NMR (500 MHz, C6D6, RT): d (Dm1/2 integral,
assignment) = 68.0 (667 Hz, 1H, a-H), 42.3 (95 Hz,
2H, m-HBz), 20.3 (1071 Hz, 2H, o-HBz), 18.0 (323 Hz,
6H, c-Me), ꢀ1.6 (47 Hz, 4H, m-HAr), ꢀ11.2 (89 Hz,
12H, iPr-Me), ꢀ45.5 (51 Hz, 1H, p-HBz), ꢀ64.8
(64 Hz, 2H, p-HAr), ꢀ82.7 (515 Hz, 12H, iPr-Me),
ꢀ93.0 (1547 Hz, 4H, iPr-CH) ppm.
Laboratorium H. Kolbe, Mulheim an der Ruhr, Ger-
¨
many. Reported values are the averages of two indepen-
dent determinations. Effective magnetic moments
pffiffiffiffiffiffiffiffi
(calculated as leff. ¼ 2.828 vmT) were determined
by Evansꢁ method in C6H6 at RT [29,30]. The data are
corrected for diamagnetism using Pascalꢁs constants
[31].
4.2. Starting materials
4.5. Preparation of [(MeBDK)FeCH2SiMe3] (2)
[
MeBDK]H [32], LiCH2SiMe3 [33], FeCl2 [34],
n-BuLi (2.5 M in hexanes, 1.67 mL, 4.18 mmol) was
added to a stirred solution of the b-diketimine (1.75 g,
4.18 mmol) in THF (20 mL). The pale yellow solution
was stirred for 30 min. FeCl2(THF)1.5 (982 mg,
4.28 mmol) was added as a solid. The resulting yellow
solution was stirred for 45 min. LiCH2SiMe3 (394 mg,
4.18 mmol) was added as a solid and a very dark solution
was obtained. After 30 min the solution had become
dark red. After another 15 min stirring, all THF was re-
moved under reduced pressure. Any residual THF was
removed by stirring the residue with pentane (25 mL)
and subsequent evaporation of all volatiles (3·). Next,
the residue was extracted with pentane (30 mL, 2·).
The orange extract was concentrated to ca. 10 mL and
cooled to ꢀ25 ꢁC to afford 2 as yellow crystals. Yield:
624 mg (27%). The yield was not optimised.
FeCl2(THF)1.5 [35], and B(C6F5)3 [36] were prepared
by the literature procedures. [(BDK)FeCl2] was pre-
pared according to a modification of a published proce-
dure [13] using THF as reaction solvent and diethyl
ether for extraction and crystallisation. FeCl3 (Acros),
acetylacetone, 2,6-diisopropylaniline, [Ph3C][B(C6F5)4]
(Strem) and [PhNHMe2][B(C6F5)4] (Asahi Glass Co.)
were commercial products and were used without fur-
ther purification.
4.3. Preparation of [(MeBDK)FeCH2Ph] Æ 0.5C5H12
(1) Æ 0.5C5H12
n-BuLi (2.5 M in hexanes) (3.8 mL, 9.6 mmol) was
added to a stirred solution of [MeBDK]H (4.0 g,
9.6 mmol) in THF (30 mL). The solution was stirred
for 30 min at room temperature. FeCl2 (1.21 g,
9.6 mmol) was added and the resulting yellow suspen-
sion was stirred for 18 h. PhCH2MgBr (1.43 M in
Et2O) (6.7 mL, 9.6 mmol) was added. The solution
turned red immediately and was stirred for 4 h at room
temperature. THF was evaporated under reduced pres-
sure. Residual THF was removed by suspending the
dark residue in pentane (30 mL, 3·) followed by re-
moval of pentane in vacuo. The residue was extracted
with pentane (100 mL, 4·). The extract was filtered, con-
centrated to ca. 75% and stored at ꢀ25 ꢁC for 48 h to
give red crystals. Yield: 4.1 g (71%).
1H NMR (500 MHz, C6D6, RT): d (Dm1/2, integral,
assignment) = 115.5 (720 Hz, 1H, a-CH), 74.7 (350 Hz,
6H, c-CH3), 56.1 (396 Hz, 9H, Si(CH3)3), ꢀ9.0 (50 Hz,
4H, m-H), ꢀ14.5(101 Hz, 12H, iPr-CH3), ꢀ68.5
(65 Hz, 2H, p-H), ꢀ100.4 (530 Hz, 12H, iPr-CH3),
ꢀ126.9 (1766 Hz, 4H, iPr-CH) ppm.
leff.ðC6H6; 298 KÞ ¼ 5.6 lB.
Anal. Calc. for C33H52N2FeSi (560.72) requires: C,
70.69; H, 9.35; N, 5.00. Found: C, 70.82; H, 9.26; N,
5.06%.
4.6. Reaction of 2 with B(C6F5)3
1H NMR (500 MHz, C6D6, RT): d (Dm1/2, integral,
assignment) = 117.2 (787 Hz, 1H, a-H), 56.4 (349 Hz,
6H, c-Me), 45.1 (115 Hz, H, m-HBz), 40.4 (1238 Hz,
2H, o-HBz), ꢀ8.7 (55 Hz, 4H, m-HAr), ꢀ17.6 (102 Hz,
12H, iPr-Me), ꢀ43.6 (60 Hz, 1H, p-HBz), ꢀ75.8
Alkyl complex 2 (25 mg, 45 mmol) was dissolved in
C6D6 (0.5 mL). To this solution was added B(C6F5)3
(23 mg, 45 mmol). The orange solution turned slightly
darker. Complete conversion was reached in the course
of 2 days at RT, giving a bright red solution.

T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
1823
[(MeBDK)Fe(C6F5)]: 1H NMR (500 MHz, C6D6, RT)
d (Dm1/2,) = 96.1 (486 Hz, 1H, a-H), 70.2 (242 Hz, 6H, c-
CH3), 7.3 (11.7 Hz, 4H, m-ArH), ꢀ9.7 (79.9 Hz, 12H,
iPr-CH3), ꢀ71.0 (67.4 Hz, 1H, p-ArH), ꢀ84.7 (298 Hz,
12H, iPr-CH3), ꢀ139.0 (1219 Hz, 4H, iPr-CH) ppm.
19F NMR (188 MHz, C6D6, RT) d = 118.1 (s, br,
Dm1/2 = 63.7 Hz, 1F, p-F), 31.5 (s, br, Dm1/2 = 345.0 Hz,
2F, m-F).
1H NMR (500 MHz, PhMe-d8, ꢀ50 ꢁC): (Dm1/2, inte-
gral, assignment) = 58.2 (107 Hz, 1H, a-H), 50.9
(249 Hz, 2H, m-HPh), 48.1 (329 Hz, 1H, m-Hpy), 33.6
(292 Hz, 1H, m-Hpy), 27.5 (130 Hz, 2H, m-HAr), 21.1
(143 Hz, 2H, m-HAr), 14.6 (312 Hz, 6H, iPr-CH3),
ꢀ2.8 (137 Hz, 6H, iPr-CH3), ꢀ8.9 (427 Hz, 6H, iPr-
CH3), ꢀ18.6 (693 Hz, 6H, iPr-CH3), ꢀ24.7 (1784 Hz,
1H, o-Hpy), ꢀ41.3 (2345 Hz, 1H, o-Hpy), ꢀ60.3
(146 Hz, 2H, p-HAr), ꢀ76.2 (149 Hz, 1H, p-HPh),
ꢀ103.1 (594 Hz, 1H, p-Hpy), ꢀ125.7 (478 Hz, 6H, c-
CH3) ppm.
Me3SiCH2B(C6F5)2: 1H NMR (500 MHz, C6D6, RT)
d = 2.16 (s, 2H, CH2SiMe3), 0.07 (s, 9H,
CH2SiMe3) ppm.
19F NMR (188 MHz, C6D6, RT) d = ꢀ130.9 (d,
JFF = 20 Hz, 2F, o-F), ꢀ148.6 (t, JFF = 20 Hz, 1F, p-
F), ꢀ162.2 (m, 2F, m-F) ppm.
leff.ðC6H6; 298 KÞ ¼ 4.4 lB.
Anal. Calc. for C41H53N3Fe (643.74) requires: C,
76.50; H, 8.30; N, 6.53. Found: C, 76.68; H, 8.35; N,
6.42%. Although 1H NMR spectroscopy in C6D6
showed the presence of toluene in the crystals, elemental
analysis was satisfactory for the solvent-free complex,
suggesting loss of toluene from the crystal lattice.
4.7. Reaction of 2 with [PhNHMe2][B(C6F5)4] and
reaction with THF-d8
[PhNHMe2][B(C6F5)4] (36 mg, 44.6 lmol) was added
to a solution of 2 (25 mg, 44.6 lmol) in C6D5Br
(0.5 mL). A dark purple/red solution was obtained.
19F NMR (188 MHz, C6D5Br, RT): d = ꢀ129.0
(30 Hz, 2F, o-F), ꢀ159.9 (34 Hz, 1F, p-F), ꢀ160.4
(58 Hz, 2F, m-F) ppm.
4.9. Preparation of [(MeBDK)Fe{g2-PhCH2B(C6F5)3}]
(4)
A solution of B(C6F5)3 (426 mg, 0.83 mmol) in pen-
tane (20 mL) was added slowly to a stirred solution of
1 (500 mg, 0.83 mmol) in pentane (30 mL). The red solu-
tion almost instantaneously turned dark and a precipi-
tate was formed. The precipitate was filtered off and
repeatedly washed with pentane (50 mL, 8·). The brown
powder was dried in vacuo. Yield: 598 mg, 67% based
on 1.
1H NMR (400 MHz, C6D5Br, RT) d = 54.2 (187, 6H,
c-Me), 50.7 (357, 1H, a-H), 30.8 (1596, 3H, m,p-HPh of
PhNMe2), 8.8 (35, 4H, m-HAr), ꢀ5.1 (75, 12H, iPr-
CH3), ꢀ76.1 (63, 2H, p-HAr), ꢀ77.3 (253, 12H, iPr-
CH3), ꢀ111 (954, 4H, iPr-CH) ppm. No resonances
were observed for the N-Me and o-HPh protons of the
coordinated N,N-dimethylaniline molecule.
Anal. Calc. for C54H48N2FeBF15 (1076.62) requires:
C, 60.24; H, 4.49; N, 2.60. Found: C, 59.62; H, 4.29;
N, 2.60%.
A drop of THF-d8 was added to the NMR tube. A
colour change from dark purple/red to bright green
was observed.
1H NMR (300 MHz, THF-d8 RT): d (Dm1/2,) = 21.3
(26), 11.7 (10), 7.0 (71), 6.6 (17), 6.5 (33), 6.3 (18), 4.4
(6), 3.5 (31), 3.2 (7), 2.7 (13), 2.4 (30), 1.4 (18), 1.2 (9),
0.8 (25), 0.7 (19), 0.6 (19), 0.4 (23) ꢀ8.7 (134), ꢀ17.7
(117), ꢀ25.2 (149), ꢀ37.2 (26)ꢀ38.5 (49), ꢀ39.7 (30),
ꢀ52.0 (94), ꢀ55.9 (97), ꢀ60.2 (138), ꢀ94.6 (299) ppm.
19F NMR (188 MHz, THF-d8 RT): d = ꢀ131.8 (d,
JFF = 21 Hz, 6F, o-F), ꢀ167.3 (t, JFF = 20 Hz, 3F, p-
F), ꢀ169.5 (m, 6F, m-F).
19F NMR (188 MHz, C6D5Br, RT): d = ꢀ131.1
(38 Hz, 2F, o-F), ꢀ161.6 (44 Hz, 1F, p-F), ꢀ165.0
(47 Hz, 2F, m-F) ppm.
1H NMR (400 MHz, C6D5Br, RT) d = 21.9 (34, 4H,
m-HAr), 7.7 (79, 12H, iPr-CH3), ꢀ8.8 (145, 12H, iPr-
CH3), ꢀ39.3 (38, 2H, p-HAr), ꢀ60.0 (131, 6H, c-Me),
ꢀ95.1 (329, 1H, a-H) ppm. No resonance for the iPr-
CH protons was observed, possibly due to extreme line
broadening. Formation of free N,N-dimethylaniline was
noted (d = 2.69 ppm, 6H, PhNMe2).
19F NMR (188 MHz, C6D5Br, RT): d = ꢀ89.7 (br),
ꢀ167.3 (br), ꢀ169.5 (br, with shoulder ꢀ157.7).
19F NMR (470 MHz, C6D5Br) variable temperature
spectra were recorded from ꢀ20 to +30 ꢁC with 5 ꢁC
intervals using 20 mg of 4 dissolved in 0.5 mL solvent.
1H NMR (500 MHz, C6D5Br, ꢀ20 ꢁC): d (Dm1/2,) =
68.3 (457), 47.2 (698), 23.7 (67), 22.4 (429), 9.1 (278),
8.2 (294), 7.2 (18), 6.9 (13), 6.9 (17), 4.8 (26), 3.4 (45),
2.8 (29), 1.6 (20), 1.1 (30), 1.0 (49), 0.8 (71), 0.7 (26),
ꢀ0.5 (122), ꢀ3.9 (187), ꢀ9.2 (9374), ꢀ11.7 (273),
ꢀ48.8 (120), ꢀ68.2 (166), ꢀ73.4 (288), ꢀ76.2 (362) ppm.
19F NMR (470 MHz, C6D5Br, ꢀ20 ꢁC): d = ꢀ82.6
(o-F), ꢀ128.4 (o-F), ꢀ150.7 (m-F), ꢀ152.8 (p-F),
ꢀ161.5 (p-F), ꢀ163.4 (m-F) ppm.
4.8. Preparation of [(MeBDK)Fe(CH2Ph)(py)] (3)
Benzyl complex 1 (200 mg, 0.35 mmol) was dissolved
in toluene (5 mL). Pyridine (1 mL, 12 mmol) was al-
lowed to diffuse into the solution. Dark red crystals of
composition [(MeBDK)Fe(CH2Ph)(py)] Æ toluene had
formed after 16 h. The crystals (69 mg) were isolated
by filtration and dried in vacuo. A second crop
(75 mg) of spectroscopically identical crystals was ob-
tained by concentration of the filtrate. Combined yield:
144 mg (0.20 mmol, 57%).

1824
T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
4.10. Reaction of 4 with THF-d8
Fo P 4r(Fo) = 0.0392, wR(F2) = 0.0997, max. residual
ꢀ3
˚
electron density ꢀ0.22 and 0.43(6) e A
.
To a solution of 4 (20 mg) in C6D5Br (0.5 mL) was
added a drop of THF-d8 The dark brown solution
turned bright yellow instantaneously.
4.11.3. Crystal refinement details for 3
Suitable crystals were obtained by crystallisation
from toluene. No classic hydrogen bonds, no missed
symmetry (MISSYM) or solvent-accessible voids were
detected by procedures implemented in PLATON [40,41].
C41H53N3Fe Æ C7H8, M = 735.88, red, platelet crystal,
0.45 · 0.38 · 0.065 mm, space group Pꢀ1, #2
19F NMR (188 MHz, C6D5Br, RT): d = ꢀ129.7 (d,
JFF = 20.3 Hz, 6F, o-F), ꢀ163.3 (t, JFF = 19.2 Hz, 3F,
p-F), ꢀ165.8 (m, 6F, m-F) ppm.
4.11. Crystal structure determinations
˚
[42], a = 9.2518(8), b = 12.091(1), c = 19.640(2) A,
3
Crystals were mounted on top of a glass fiber, by
using inert-atmosphere handling techniques, and aligned
on a Bruker SMART APEX CCD diffractometer (k
˚
b = 82.446(1)ꢁ, V = 2152.5(3) A , Z = 2, l = 3.85
cmꢀ1, 17162 reflections collected at 100(1) K, 8581 un-
ique reflections (Rint = 0.0354), 6748 reflections ob-
served with [Fo P 4.0r(Fo)], 713 refined parameters,
R(F) for Fo P 4rFo) = 0.0414, wR(F2) = 0.0985, max.
˚
(Mo Ka) = 0.71073 A) [37]. Intensity data were cor-
rected for Lorentz and polarization effects, scale varia-
tion, for decay and absorption:
ꢀ3
a
multi-scan
˚
residual electron density ꢀ0.27 and 0.34(5) e A
.
absorption correction was applied, based on the intensi-
ties of symmetry-related reflections measured at different
angular settings (SADABS), and reduced to F 2o [38]. The
program suite SHELXTL was used for space group deter-
mination (XPREP) [39].
4.11.4. Crystal refinement details for 4
Suitable crystals were obtained by recrystallisation
from bromobenzene. No classic hydrogen bonds, no
missed symmetry (MISSYM), but potential solvent-
3
˚
accessible area (voids of 71.0 A /unit cell) were detected
4.11.1. Crystal refinement details for 1
by procedures implemented in PLATON [40,41].
Suitable crystals were obtained by recrystallisation
from pentane. From the solution it was clear that both
pentane solvent molecules were located over an inver-
sion centre, implying disorder. A disorder model with
a s.o.f. of 0.5 for both pentanes was used in the refine-
ment. No classic hydrogen bonds, no missed symmetry
(MISSYM) or solvent-accessible voids were detected
by procedures implemented in PLATON [40,41].
C54H48N2FeBF15, M = 1076.62, red, platelet crystal,
0.15 · 0.14 · 0.08 mm, space group C2/c, #15
˚
[42], a = 44.806(3), b = 13.349(1), c = 17.780(1) A,
3
˚
b = 113.282(5)ꢁ, V = 9768.5(12) A , Z = 8, l = 4.060
cmꢀ1, 34522 reflections collected at 110(1) K, 11209 un-
ique reflections (Rint = 0.3431), 3022 reflections ob-
served with [Fo P 4.0r(Fo)], 851 refined parameters,
R(F) for Fo P r(Fo) = 0.0678, wR(F2) = 0.1767, max.
ꢀ3
2C36H48N2Fe Æ C5H12, M = 1201.37, red platelet
crystal, 0.45 · 0.40 · 0.12 mm, space group P21/c, #14
˚
residual electron density ꢀ0.51 and 0.43(8) e A
.
˚
[42], a = 15.3319(9), b = 20.652(1), c = 22.408(1) A,
3
˚
b = 90.781(1)ꢁ,
V = 7094.5(6) A ,
Z = 4,
l =
Acknowledgement
4.52 cmꢀ1, 44924 reflections collected at 125(1) K,
18149 unique reflections (Rint = 0.276), 13810 reflec-
tions observed with [Fo P 4.0(Fo)], 1181 refined param-
This research was financially supported by the Dutch
Polymer Institute (project #106).
eters, R(F) for Fo P 4r(Fo) = 0.0430, wR(F2) = 0.11ꢀ343,
˚
max. residual electron density ꢀ0.24 and 0.52(6) e A
.
Appendix A. Supplementary data
4.11.2. Crystal refinement details for 2
Suitable crystals were obtained by recrystallisation
from pentane. No classic hydrogen bonds, no missed
symmetry (MISSYM), but potential solvent-accessible
area (voids of 29.2 A /unit cell) were detected by proce-
dures implemented in PLATON [40,41].
CIF files have been deposited with the Cambridge
Crystallographic Data Centre, CCDC Nos. 185601 (1),
273724 (2), 273725 (3), and 185603 (4). Copies of these
data may be obtained free of charge on application to
The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK, fax: +44 1223 336 033, email: depos-
it@ccdc.cam.ac.uk or on the web www: http://www.
cam.ac.uk. IR spectral data of the isolated compounds,
additional NMR data and experimental details are
available from the author upon request. Supplementary
data associated with this article can be found, in the on-
line version, at doi:10.1016/j.ica.2005.06.065.
3
˚
C33H52N2FeSi, M = 560.72, orange, block crystal,
0.28 · 0.21 · 0.12 mm, space group P21/n, #14 [42],
˚
a = 10.5957(5), b = 21.292(1), c = 14.7768(7) A, b =
3
ꢀ1
˚
97.218(1)ꢁ, V = 3307.3(3) A , Z = 4, l = 5.14 cm
,
30277 reflections collected at 100(1) K, 8215 unique
reflections (Rint = 0.0414), 6349 reflections observed with
[Fo P 4.0r(Fo)], 539 refined parameters, R(F) for

T.J.J. Sciarone et al. / Inorganica Chimica Acta 359 (2006) 1815–1825
1825
[20] M. Bochmann, S.J. Lancaster, M.B. Hursthouse, K.M.A. Malik,
Organometallics 13 (1994) 2235.
References
[21] C. Pellecchia, A. Grassi, A. Immirzi, J. Am. Chem. Soc. 115
(1993) 1160.
[22] L.W.M. Lee, W.E. Piers, M.R.J. Elsegood, W. Clegg, M. Parvez,
Organometallics 18 (1999) 2947.
[23] A.D. Horton, J.H.G. Frijns, Angew. Chem., Int. Ed. Engl. 30
(1991) 1152.
[24] M. Pasquali, C. Floriani, A. Gaetani-Manfredotti, Inorg. Chem.
19 (1980) 1191.
[25] P. Chirik, Personal communication (16-3-2004).
[26] R.E.v.H. Spence, W.E. Piers, Y. Sun, M. Parvez, L.R.
MacGillivray, M.J. Zaworotko, Organometallics 17 (1998)
2459.
[27] S.C. Bart, E.J. Hawrelak, A.K. Schmisseur, E. Lobkovsky, P.J.
Chirik, Organometallics 23 (2004) 237.
[28] E.A. Gregory, R.J. Lachicotte, P.L. Holland, Organometallics 24
(2005) 1803.
[29] E.M. Schubert, J. Chem. Educ. 69 (1992) 62.
[30] D.F. Evans, J. Chem. Soc. (1959) 2003.
[1] B.L. Small, M. Brookhart, A.M.A. Bennett, J. Am. Chem. Soc.
120 (1998) 4049.
[2] B.L. Small, M. Brookhart, J. Am. Chem. Soc. 120 (1998) 7143.
[3] G.J.P. Britovsek, V.C. Gibson, B.S. Kimberley, P.J. Maddox,
S.J. McTavish, G.A. Solan, A.J.P. White, D.J. Williams, Chem.
Commun. (1998) 849.
[4] G.J.P. Britovsek, M. Bruce, V.C. Gibson, B.S. Kimberley, P.J.
Maddox, S. Mastroianni, S.J. McTavish, C. Redshaw, G.A.
Solan, S. Stromberg, A.J.P. White, D.J. Williams, J. Am. Chem.
Soc. 121 (1999) 8728.
[5] G.J.P. Britovsek, S. Mastroianni, G.A. Solan, S.P.D. Baugh, C.
Redshaw, V.C. Gibson, A.J.P. White, D.J. Williams, M.R.J.
Elsegood, Chem. – Eur. J. 6 (2000) 2221.
[6] L. Bourget-Merle, M.F. Lappert, J.R. Severn, Chem. Rev. 102
(2002) 3031.
[7] H. Andres, E.L. Bominaar, J.M. Smith, N.A. Eckert, P.L.
Holland, E. Mu¨nck, J. Am. Chem. Soc. 124 (2002) 3012.
[8] J.M. Smith, R.J. Lachicotte, P.L. Holland, Organometallics 21
(2002) 4808.
[31] O. Kahn, Molecular Magnetism, VCH, New York, 1993.
[32] P.H.M. Budzelaar, N.N.P. Moonen, R. de Gelder, J.M.M. Smits,
A.W. Gal, Eur. J. Inorg. Chem. (2000) 753.
[9] T.J.J. Sciarone, A. Meetsma, B. Hessen, J.H. Teuben, Chem.
Commun. (2002) 1580.
[33] H.L. Lewis, T.L. Brown, J. Am. Chem. Soc. 92 (1970) 4664.
[34] P. Kovacic, N.O. Brace, Inorg. Synth. 6 (1960) 172.
[35] R.J. Kern, J. Inorg. Nucl. Chem. 24 (1962) 1105.
[36] J.L.W. Pohlmann, F.E. Brinckmann, Z. Naturforsch. 20b (1965)
5.
[10] J. Vela, J.M. Smith, R.J. Lachicotte, P.L. Holland, Chem.
Commun. (2002) 2886.
[11] J. Vela, S. Vaddadi, T.R. Cundari, J.M. Smith, E.A. Gregory,
R.J. Lachicotte, C.J. Flaschenriem, P.L. Holland, Organometal-
lics 23 (2004) 5226.
[37] SMART, SAINT, SADABS, XPREP and SHELXTL/NT, Area Detector
Control and Integration Software, Smart Apex Software Refer-
ence Manuals, Bruker Analytical X-ray Instruments. Inc., Mad-
ison, WI, USA, 2000.
[12] J.M. Smith, R.J. Lachicotte, P.L. Holland, Chem. Commun.
(2001) 1542.
[13] A. Panda, M. Stender, R.J. Wright, M.M. Olmstead, P. Klavins,
P.P. Power, Inorg. Chem. 41 (2002) 3909.
[38] G.M. Sheldrick, SADABS – V2 – Multi-Scan Absorption Correction
Program, University of Go¨ttingen, Go¨ttingen, Germany, 2001.
[39] G.M. Sheldrick, SHELXL-97 – Program for the Refinement of
Crystal Structures, University of Go¨ttingen, Go¨ttingen, Germany,
2003.
[40] A.L. Spek, PLATON – Program for the Automated Analysis
of Molecular Geometry (A Multipurpose Crystallographic
Tool), University of Utrecht, Utrecht, The Netherlands,
2002.
[14] N.A. Eckert, J.M. Smith, R.J. Lachicotte, P.L. Holland, Inorg.
Chem. 43 (2004) 3306.
[15] P.L. Holland, T.R. Cundari, L.L. Perez, N.A. Eckert, R.J.
Lachicotte, J. Am. Chem. Soc. 124 (2002) 14416.
[16] J.M. Smith, R.J. Lachicotte, P.L. Holland, J. Am. Chem. Soc. 125
(2003) 15752.
[17] H.L. Wiencko, E. Kogut, T.H. Warren, Inorg. Chim. Acta 345
(2003) 199.
[18] M.H. Chisholm, J.C. Huffman, K. Phomphrai, J. Chem. Soc.,
Dalton Trans. (2001) 222.
[41] A.L. Spek, Acta Crystallogr., Sect. A 46 (1990) C34.
[42] International Tables for Crystallography, Kluwer Academic
Publishers, Dordrecht, The Netherlands, 1992.
[19] C. Pellecchia, A. Immirzi, A. Grassi, A. Zambelli, Organometal-
lics 12 (1993) 4473.