Reactivity of paramagnetic FeII-bis(amidinate) complexes

Article abstract of DOI:10.1002/ejic.201000717

Synthesis and characterisation of ether adducts of bis(amidinate) Fe ^II complexes are described [amidinate = 2,6-iPr₂C ₆H₃-NC(Ph)N-Ph]. The isolation of these five-coordinate complexes contrasts with the homolep

Full text of DOI:10.1002/ejic.201000717

FULL PAPER
DOI: 10.1002/ejic.201000717
Reactivity of Paramagnetic FeII–Bis(amidinate) Complexes
Erica Jellema,[a] Timo J. J. Sciarone,*[a][‡] Noa M. Navarrete,[a] Marten J. Hettinga,[a]
Auke Meetsma,[a] and Bart Hessen[a]
Keywords: Iron / N ligands / Carbonylation / Lewis bases / Magnetic properties
Synthesis and characterisation of ether adducts of bis(amid-
inate) FeII complexes are described [amidinate
2,6-
= 2,6-iPr2C6H3, 2,6-Me2C6H3) The more accessible ether ad-
ducts show enhanced reactivity towards Lewis bases and
=
iPr2C6H3–NC(Ph)N–Ph]. The isolation of these five-coordi- towards the π-acid carbon monoxide. Reaction with excess
nate complexes contrasts with the homoleptic bis(amidinate)
Fe complexes obtained previously with the sterically more
demanding amidinate ligands 2,6-iPr2C6H3–NC(Ph)N–Ar (Ar
amounts of CO results in carbonyl insertion into the Fe–N
bonds, thereby giving rise to a diamagnetic bis(CO) adduct
supported by two carbamoyl ligands.
transition metals and FeII in particular. Thus, using benz-
amidinate ligands [Dipp2L]– and [DippXylL]–, homoleptic bis-
(amidinate) complexes were isolated with an unusual planar
geometry (Scheme 2),[4] whereas other structurally charac-
terised homoleptic FeII–bis(amidinates) invariantly exhibit
tetrahedral geometries.[5–9]
Introduction
Amidinates, [(RN)CRЈ(NRЈЈ)]–, have been used exten-
sively as ligands for transition metals and lanthanides. With
transition metals in particular, they show versatile binding
modes (monodentate, bridging, chelating). The coordina-
tion mode is determined to a large extent by the nature of
the C- and N-substituents. For chelating amidinate ligands,
the size of the N-substituents can also influence the coordi-
nation geometry in complexes. This becomes especially ap-
parent in homoleptic bis(amidinate)–metal complexes. In
cases in which the electronic preference of the metal is not
too strong, the steric demands of the ligands can actually
outweigh the preference of the metal. The groups of
Gambarotta and Winter have demonstrated this for CrII by
using amidinates with simple alkyl or silyl substituents on
the C and N atoms. For the bulkier N-substituents (CMe3
or SiMe3), the geometry of these d4 complexes deviates
from the planar situation found with smaller substituents
(R = Cy, iPr).[1,2]
Scheme 1.
Although most studies on bis(amidinate) complexes have
focussed on the relation between ligand steric bulk and co-
ordination chemistry, interesting consequences may also be
expected for the reactivity of such complexes. Particularly
in mononuclear cases in which 2,6-disubstituted aryl groups
are present on all four nitrogen atoms, the accessibility of
the metal centre could be effectively limited. Thus, the cat-
ion [L2ZrMe]+ has been reported not to interact with eth-
ene for L = Dipp2L, whereas the analogous cation with L =
DippXylL induced slow olefin polymerisation.[10] For first-
row transition metals, such shielding effects are expected to
be even more pronounced due to their smaller ionic radius.
In this contribution we investigate the reactivity of FeII–
bis(amidinate) complexes toward σ-base as well as π-acid
ligands as a function of gradual decrease in the steric de-
mands of the amidinate ligand. To this end, the benzamid-
inate [PhC(N-2,6-iPr2C6H3)(NPh)]– ([DippPhL]–, Scheme 1)
is introduced. The reduced steric bulk of the latter is found
to open up reactivity pathways unavailable to the more
crowded analogues [Dipp2L]– and [DippXylL]–.
By using o-disubstituted aryls on the N-donor atoms,
Boeré characterised a highly unusual planar Mg–bis(amid-
inate).[3] This approach introduces steric protection above
and below the NMN coordination plane. Our group has
employed related amidinate ligands (Scheme 1) in the prep-
aration of mono- and bis(amidinate) complexes of first-row
[a] Stratingh Institute for Chemistry and Chemical Engineering,
University of Groningen, Nijenborgh 4,
9747 AG Groningen, The Netherlands
[‡] Present address: Polymer Chemistry Group, Eindhoven
University of Technology
P. O. Box 513, 5600 MB Eindhoven, The Netherlands
Fax: +31-40-246-3966
E-mail: t.j.j.sciarone@tue.nl
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000717.
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Scheme 2.
centres in the adducts 1c are located somewhat above the
N4 basal planes [0.107(1) Å for 1c·THF, 0.064(2) Å for
1c·Et2O] and the amidinate NCN planes are slightly bent
away from the ether ligands. The amidinates in the basal
plane assume a mutual trans relation, thus avoiding steric
interactions between 2,6-iPr2C6H3 groups from the two li-
gands. The Fe–O distance in 1c·Et2O is about 0.02 Å longer
than that in 1c·THF, as expected for the weaker Lewis base.
The Fe–N distances do not appear to be a direct function
of the steric bulk on the nitrogen atoms, since for 1c·THF
the NPh–Fe distance is larger than NDipp–Fe, whereas the
situation is reversed for 1c·Et2O.
Results and Discussion
Synthesis and Characterisation of Bis(amidinates) with
[
DippPhL]–
Amidine DippPhLH was synthesised by standard method-
ology[3] in 70% yield from N-(2,6-diisopropylphenyl)benzi-
midoyl chloride and aniline. The amidine crystallises as the
Z-anti isomer as found by X-ray diffraction (see the Sup-
porting Information). Also, in CDCl3, only one isomer is
observed.
In situ deprotonation (nBuLi) and subsequent salt me-
tathesis with FeCl2 in THF affords the new bis(amidinate)
complex 1c·THF (Scheme 2) after removal of the reaction
solvent in vacuo followed by extraction with hexanes. The
isolation of a five-coordinate adduct contrasts with the pre-
viously reported base-free complexes 1a and 1b and seems
a direct consequence of the reduction of ligand steric bulk.
To test whether a homoleptic complex (DippPhL)2Fe could
be isolated, the complexation was also performed in the
weaker donor solvent diethyl ether. Again, a five-coordinate
adduct, [(DippPhL)2Fe(Et2O)] (1c·Et2O) was isolated. In this
case, the poor solubility of the product in alkane solvents
necessitated extraction with diethyl ether. Nevertheless, the
ether ligand was not lost by drying in vacuo. Attempts to
remove the ether molecule from 1c·Et2O by vacuum subli-
mation at 150 °C/200 mTorr led to decomposition of the
complex and afforded the parent amidine and unidentified
green/brown products. Preparation of base-free 1c by salt
metathesis of Li[DippPhL] with FeCl2 in toluene was unsuc-
cessful. Although initially a green colour reminiscent of that
of (Dipp2L)2Fe was observed, no Fe complex was isolated.
The solid-state structures of 1c·THF[11] and 1c·Et2O
(Figure 1 and Figure 2) display approximate (noncrystallo-
graphic) C2 symmetry with the C2 axis passing through the
Fe–O vector. The complexes are best described as square
Figure 1. Molecular structure of 1c·THF (50% thermal ellipsoids).
Selected bond lengths [Å] and angles [°]: Fe11–O11 2.0714(14),
Fe11–N11 2.1090(16), Fe11–N12 2.1304(15), Fe11–N13 2.1182(15),
Fe11–N14 2.1329(15), N11–C113 1.326(2), N12–C113 1.334(2),
N13–C138 1.332(2), N14–C138 1.335(2); O11–Fe11–N11
104.63(6), O11–Fe11–N12 98.24(6), O11–Fe11–N13 111.57(6),
O11–Fe11–N14 105.75(6), N11–Fe11–N12 62.84(6), N11–Fe11–
N13 143.80(6), N11–Fe11–N14 108.11(6), N12–Fe11–N13
110.18(6), N12–Fe11–N14 155.94(6), N13–Fe11–N14 62.74(6).
Magnetic susceptibility measurements show Curie–Weiss
pyramidal with the four nitrogen atoms forming the basal behaviour for 1c·THF and 1c·Et2O in the temperature
plane and the ether ligands as apexes (τ parameter[12] = 0.20 range 50–300 K with θ = 2.1 K for 1c·THF and θ = 4.8 K
and 0.10 for 1c·THF and 1c·Et2O, respectively). In contrast, for 1c·Et2O (Figure 3). The room-temperature magnetic
a trigonal bipyramidal geometry was reported for the moments of 5.3 and 5.0 μB, respectively, are consistent with
tmeda adduct [{PhC(NSiMe3)(N-2,6-Me2C6H3)}2Fe(κ1- high-spin (S = 2) FeII with four unpaired electrons. The
tmeda)] (tmeda
=
Me2NCH2CH2NMe2).[13] The iron effective magnetic moments are virtually temperature inde-
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Reactivity of Paramagnetic FeII–Bis(amidinate) Complexes
Figure 2. Molecular structure of 1c·Et2O (50% thermal ellipsoids).
Selected bond lengths [Å] and angles [°]: Fe–O 2.0932(18), Fe–N1
2.164(2), Fe–N2 2.089(2), Fe–N3 2.157(2), Fe–N4 2.095(2), N1–
C13 1.328(3), N2–C13 1.347(3), N3–C38 1.326(3), N4–C38
1.341(3); O–Fe–N1 108.26(7), O–Fe–N2 107.08(8), O–Fe–N3
102.76(7), O–Fe–N4 97.78(8), N1–Fe–N2 62.75(8), N1–Fe–N3
148.97(8), N1–Fe–N4 111.72(8), N2–Fe–N3 108.44(8), N2–Fe–N4
155.04(8), N3–Fe–N4 62.67(8).
Figure 4. 1H NMR spectra (300 MHz, C6D6, 298 K) of (A) 1c·THF
and (B) 1c·Et2O. Asterisks denote C6D5H and residual pentane.
equivalent protons give rise to resonances with identical in-
tegrals and similar linewidths. The C2h-symmetric spectra
with only two iPr–Me and three m-H resonances suggest
fast site exchange of ether ligands on the 1H NMR spectro-
scopic timescale (Scheme 3).
pendent down to approximately 50 K. Below this tempera-
ture, the value of μeff drops due to zero-field splitting of
5
the D ground state. Zero-field splitting parameters |D| =
6.0 cm–1 for 1c·THF and |D| = 8.3 cm–1 for 1c·Et2O were
obtained by least-squares fitting procedures using g = 2.18
for 1c·THF and g = 2.05 for 1c·Et2O. These |D| values are
in the range usually observed for tetra- and pentacoordinate
FeII complexes.[14]
Scheme 3.
Assignment of the resonances for coordinated THF (δ =
14.9 and 3.9 ppm) was confirmed by reaction with [D8]THF
(vide infra). Both adducts 1c are thermally stable for at least
24 h at 80 °C in C6D6.
Reactivity towards σ Bases
The reactivity of homoleptic 1a, 1b and ether adducts 1c
towards σ donors was studied by 1H NMR spectroscopy in
C6D6. Addition of 1 equiv. [D8]THF to 1a or 1b, however,
does not affect their spectra. For the alkaline earth metals,
the THF adducts [{HC(NAr)2}2M(THF)n] (M = Ca, n = 1;
M = Sr, Ba, n = 2; Ar = 2,6-iPr2C6H3) have been structur-
ally characterised.[15] Although the shielding properties of
the formamidinate resemble those of [Dipp2L]–, the larger
ionic radii of the divalent group II ions may enable accom-
modation of THF ligands.
Figure 3. μeff and χ–1 (inset) versus T for 1c·THF (Δ) and 1c·Et2O
(᭺).
The paramagnetism of ether adducts 1c·THF and
Whereas 1a and 1b do not coordinate THF, reaction with
1c·Et2O is reflected in their 1H NMR spectra in C6D6, the stronger Lewis base pyridine differentiates between the
which show broad, shifted resonances from around δ = +30 accessibility of the metal centres in 1a and 1b. The most
to –15 ppm (Figure 4). In spite of the paramagnetism of the hindered complex 1a requires more than 1 equiv. of pyr-
iron complexes, their NMR spectra were found to be quite idine to observe a colour change from green to yellow. Only
1
informative.
minor changes are visible in the H NMR spectrum, even
Assignment of the resonances was aided by comparison when an excess amount of pyridine is used, thereby suggest-
to the spectra of 1a and 1b. Complete assignment, however, ing that coordination of pyridine is weak. For the slightly
is precluded by the fact that some sets of magnetically in- more open complex 1b, this colour change is observed with
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1
only 1 equiv. of pyridine. The H NMR spectrum of the cess amount of [D5]pyridine are shown in parts B and C of
product, tentatively formulated as 1b·py, shows significant Figure 5. Significant broadening of the iPr–Me resonances
shifts and broadening of several resonances with respect to is observed upon addition of 2 equiv. of pyridine, whereas
those of 1b (see the Supporting Information). Addition of one of the Ar–Hm signals is sharpened. The fast exchange
more pyridine leads to coalescence of some lines and sharp- regime is reached with an excess amount of pyridine as evi-
ening of others, thereby suggesting that 1b·py undergoes site denced by the C2h-symmetric spectrum with only two dia-
exchange like the ether adducts 1c, but complete assignment stereotopic iPr–Me resonances (Figure 5, C). Removal of
of the spectra proved impossible.
all volatiles in vacuo and subsequent redissolution in C6D6
The more accessible iron centres in the adducts 1c react restores the spectrum of 1c·py, thereby indicating that only
even more readily with Lewis bases under replacement of one pyridine is retained in the solid state. Preparative scale
the ether ligand. Thus, addition of [D8]THF to 1c·Et2O experiments in toluene afforded 1c·py as an orange powder.
leads to clean formation of 1c·[D8]THF with liberation of Although analytically pure material could not be obtained,
diethyl ether. This experiment also permitted unambiguous
assignment of the THF resonances in 1c·THF. Reaction of
either 1c·THF or 1c·Et2O with 1 equiv. pyridine leads to a
sole product 1c·py and is accompanied by a colour change
from yellow to orange. The 1H NMR spectrum (Figure 5A)
shows four separate resonances for the iPr–Me protons,
which indicates magnetic inequivalence of the dia-
stereotopic methyl groups above and below the N4 plane.
In addition, one of the m-aryl signals is significantly broad-
ened. The C2v-symmetric spectrum shows that site exchange
for pyridine is slower than for THF on the NMR spectro-
scopic timescale. The fact that the pyridine ligand does ex-
change becomes apparent when more pyridine is added.
Spectra that result from the addition of 2 equiv. and an ex- Figure 6. Molecular structure of 1c·bpy.
1
Figure 5. H NMR spectra (300 MHz, C6D6, 298 K) of 1c·THF + pyridine: (A) 1 equiv., (B) 2 equiv.; (C) excess amount of [D5]pyridine.
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Reactivity of Paramagnetic FeII–Bis(amidinate) Complexes
1
Figure 7. H NMR spectrum (300 MHz, C6D6, 298 K) of 1c·bpy. Asterisks denote C6D5H and residual toluene.
1
the H NMR spectrum of the powder is identical to that
The influence of steric bulk in 1a and 1b becomes appar-
obtained from the reaction on the scale of an NMR spec- ent when the ether adducts of 1c are treated with CO under
troscopy tube with 1 equiv. of pyridine.
the same conditions. The more accessible Fe centres in
With the chelating Lewis base 2,2Ј-bipyridine (bpy), 1c·THF and 1c·Et2O react rapidly, as indicated by a colour
1c·Et2O reacts in toluene to give the corresponding adduct. change from greenish yellow to red. After three days the
Dark green crystals of 1c·bpy could be isolated in 64% colour changes to yellow again and the diamagnetic com-
yield. The molecular structure (Figure 6) shows a pseudo- pound 2 is formed quantitatively (Scheme 4).
octahedral coordination environment with the nitrogen
atoms bearing the N-2,6-iPr2C6H3 substituents in a trans
arrangement. Unfortunately, no crystals of sufficient qual-
ity were obtained, but the X-ray structure serves to confirm
the connectivities of the non-hydrogen atoms. The asym-
metric unit consists of one molecule of 1c·bpy and highly
disordered toluene molecules.
Six-coordinate 1c·bpy is paramagnetic and magnetic
measurements (superconducting quantum interference de-
vice, SQuID) indicate a room-temperature magnetic mo-
ment of 4.9 μB, consistent with 4 unpaired electrons (high-
spin FeII). The paramagnetic 1H NMR spectrum shows res-
onances from δ = +60 to –20 ppm and tentative assign-
ments were made (Figure 7). Most amidinate protons are
Scheme 4.
observed around the shifts for the related adducts 1c·L (L
= THF, Et2O, py). Two characteristic resonances attributed
to the bpy ligand are found further downfield at δ = 56.4
and 43.6 ppm.
On a preparative scale, the final product 2 can be isolated
in 33% yield as a yellow powder. It was characterised by
standard spectroscopic methods and combustion analysis.
An X-ray structure confirmed the formulation of 2 as a bis-
(carbamoyl) complex that results from the uptake of
Reactivity towards π Acids
4 equiv. of CO. In addition to the two terminal carbonyl
ligands, two more CO molecules are inserted into the amid-
To probe the reactivity of the bis(amidinate) complexes inate Fe–N bonds. Carbonyl insertion is relatively common
1 towards π-acid ligands, their reactivity towards carbon for Fe and Co amidinates with bulky substituents.[16,18,19]
monoxide was studied. Exhaustive carbonylation often con- The regiochemistry seems to be determined by steric factors
verts paramagnetic bis(amidinate)–FeII complexes into the as insertion usually occurs next to the nitrogen that carries
corresponding 18-electron bis-CO adducts.[8,9,16,17] On ac- the most sterically demanding substituent.[17] Attempts to
count of their diamagnetism, these are amenable to NMR characterise the red intermediate {presumably the bis-CO
spectroscopic structure analysis. The sterically encumbered adduct [(DippPhL)2Fe(CO)2]} were unsuccessful. Treatment
complexes 1a or 1b, however, fail to react with an excess of 1c·Et2O with 2 equiv. CO in C6D6 generated a red solu-
1
amount of carbon monoxide (1 atm.) in C6D6, possibly due tion, but H NMR spectroscopic analysis showed no other
to the inaccessibility of the iron centres. Incomplete carbon- species than unreacted 1c·Et2O and 2.
ylation due to inaccessibility of the Fe centre has been re-
The solid-state structure of 2 (Figure 8) shows a pseudo-
ported previously for Kawaguchi’s bis(amidinate)–diiron octahedrally coordinated iron centre ligated by two κ2-N,C-
complex.[9] In this dimer, only one of the two iron centres carbamoyl ligands and two terminal CO ligands in a cis
was found to react with CO as a result of a more sterically configuration. The structure has approximate (noncrys-
hindered conformation induced by carbonylation of the tallographic) C2 symmetry with the C2 axis bisecting the
first Fe centre.
angle between the two terminal carbonyls. In contrast to
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the parent ether adducts, in which identical C–N distances five- and six-coordinate Lewis base adducts can be obtained
were observed in the amidinate ligands (ca. 1.33 Å), these as well as a bis(carbamoyl) complex that results from carb-
distances differ significantly in the carbamoyl moieties in 2 onyl insertion. The accommodation of a fifth ligand, how-
(ca. 1.36 and 1.30 Å). However, the (near) planarity of all ever, is also a function of the strength of the added Lewis
carbon and nitrogen atoms in the carbamoyl rings (sum of base.
angles around C = 360°, sum of angles around N = 357.6–
359.6°) indicates significant conjugation. The bite angle of
the carbamoyl chelate is approximately 82°, comparable to
the FeII–carbamoyl chloride complex [κ3-{Me2N(CH2)
Experimental Section
2NC(Ph)N(Ar)C(O)}FeCl(CO)2] (ca. 85°).[17]
General: All manipulations, except for amidine synthesis, were car-
ried out under a dry nitrogen atmosphere using standard glovebox,
Schlenk and vacuum-line techniques. Pentane, hexanes and toluene
were passed over columns of Al2O3 (Fluka), BASF-R3-11-sup-
ported Cu oxygen scavenger and molecular sieves (Aldrich, 4 Å).
THF and Et2O (Aldrich, anhydrous, 99.8%) were dried by percola-
tion with Al2O3 (Fluka). [D8]THF and C6D6 were distilled from
Na/K. [D5]Pyridine (Acros) was used as received.
Starting Materials: Pyridine (Merck) was distilled from calcium hy-
droxide. 2,2Ј-Bipyridine (Merck, 99.5%), aniline, triethylamine,
nBuLi (2.5 m in hexanes) (Acros) and CO (Praxair, 99.997%) were
used as received. FeCl2,[20] Dipp2L]2Fe (1a)[4] and [DippXylL]2Fe (1b)
[
[4]
were prepared according to literature procedures.
Instrumentation: 1H and 13C{1H} NMR spectra were recorded at
ambient temperature with a Varian VXR 300 spectrometer op-
erating at 299.968 MHz (1H) and a Mercury Plus 400 operating
at 100.573 (13C{1H}) and 399.931 MHz (1H). NMR spectra were
referenced internally using the residual solvent resonances (CHCl3,
δ = 7.26 ppm; C6D5H, δ = 7.15 ppm) relative to Si(CH3)4 (δ =
0 ppm). Proton NMR spectroscopic data for paramagnetic com-
Figure 8. Molecular structure of 2 (30% thermal ellipsoids). Se-
lected bond lengths [Å] and angles [°]: Fe–N2 1.961(3), Fe–N4
1.960(3), Fe–C51 1.953(3), Fe–C52 1.958(3), Fe–C53 1.810(4), Fe–
C54 1.809(4), N1–C13 1.367(4), N2–C13 1.304(5), N3–C38
1.362(4), N4–C38 1.298(4), O1–C51 1.209(4), O2–C52 1.211(4),
O3–C53 1.142(5), O4–C54 1.144(5); N2–Fe–N4 169.03(10), N2–
Fe–C51 81.53(13), N2–Fe–C52 90.38(13), N2–Fe–C53 92.83(14),
N2–Fe–C54 93.33(13), N4–Fe–C51 90.24(13), N4–Fe–C52
81.58(13), N4–Fe–C53 94.74(14), N4–Fe–C54 94.29(13), C51–Fe–
C52 84.58(12), C51–Fe–C53 92.22(15), C51–Fe–C54 173.31(15),
C52–Fe–C53 175.09(15), C52–Fe–C54 91.20(15), C53–Fe–C54
92.31(17).
pounds are listed as δ [ppm] (Δν [Hz], integral, tentative assign-
½
ment). IR spectra were recorded with a 4020 Mattson Instruments
FTIR spectrophotometer using nujol mulls between KBr discs. Ele-
mental analyses were performed at the Microanalytical Depart-
ment of the University of Groningen or by H. Kolbe, Mikroanalyti-
sches Laboratorium, Mülheim an der Ruhr. Reported values are
the average of two independent determinations. MS spectra were
NMR and IR spectroscopy for diamagnetic 2 are consis- obtained with a Jeol JMS-600 spectrometer in electron ionisation
tent with the C2 symmetry observed in the solid state. 13C
(EI) mode.
NMR spectroscopic resonances for the terminal carbonyls
N-Phenyl-NЈ-(2,6-diisopropylphenyl)benzamidine
(
DippPhLH):
A
and the carbamoyl carbonyls are found at δ = 219.9 and
solution of aniline (2.46 mL, 27 mmol), triethylamine (3.0 mL) and
N-(2,6-diisopropylphenyl)benzimidoyl chloride (8.54 g, 27 mmol)
in toluene (100 mL) was heated at reflux for 24 h. The mixture was
washed with water (3ϫ) and with a saturated solution of NaCl.
Toluene was removed in vacuo. The solid was dissolved in ethanol
and dried in vacuo to remove residual toluene. After recrystalli-
sation from ethanol/water, white crystals were obtained (6.70 g,
19 mmol, 70%). 1H NMR (200 MHz, CDCl3, 298 K): δ = 7.63–
6.27 (m, 13 H, Ar-CH), 3.16–3.23 (sept., J = 6.6 Hz, 2 H, iPr-CH),
1.24 (d, J = 6.6 Hz, 12 H, iPr-CH3) ppm. 13C{1H} NMR (75 MHz,
CDCl3, 298 K): δ = 153.75, 140.11, 139.06, 135.03, 129.73, 128.86,
128.71, 128.26, 123.57, 122.48, 28.16 (iPr-CH), 23.92, 23.53
1
209.4 ppm, respectively. The H NMR spectrum indicates
hindered rotation of the 2,6-iPr2C6H3 group around the N–
Cipso bond. The IR spectrum shows strong absorptions at
2020 and 1961 cm–1 for the terminal carbonyls, whereas the
CO stretching band of the carbamoyl is found at 1659 cm–1.
Similar values were found for other FeII–carbamoyl com-
plexes.[16,17]
(2ϫiPr-CH ) ppm. IR (KBr): ν = 3359 (s, N–H), 3062 (m), 3055
˜
3
Conclusion
(m), 3044 (m), 2921 (s), 2910 (s), 1669 (w), 1637 (s), 1597 (s), 1587
(s), 1579 (m), 1496 (s), 1448 (s), 1436 (m), 1414 (m), 1359 (m), 1343
(s), 1329 (s), 1303 (m), 1289 (m), 1261 (w), 1253 (m), 1244 (m),
1234 (m), 1194 (m), 1178 (w), 1109 (w), 1093 (m), 1075 (m), 1059
(w), 1043 (w), 1028 (w), 959 (w), 936 (w), 902 (m), 834 (w), 809
(w), 803 (w), 788 (w), 768 (s), 758 (s), 737 (s), 702 (s), 692 (s),
558 (w), 509 (w), 490 (m) cm–1. HRMS (EI): calcd. for C25H28N2:
The use of o-disubstituted aryls 2,6-R2C6H3 as nitrogen
substituents in bis(benzamidinate)–FeII complexes can
render the metal centre virtually inaccessible to Lewis bases.
Stepwise reduction of the size of R, however, gradually ex-
poses the FeII nucleus and restores much of the reactivity
common to more open FeII–amidinate complexes. Thus, 356.2252; found 356.2240.
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Eur. J. Inorg. Chem. 2011, 91–100

Reactivity of Paramagnetic FeII–Bis(amidinate) Complexes
Preparation of Li[DippPhL]: N-Phenyl-NЈ-(2,6-diisopropylphenyl)-
benzamidine (1.00 g, 2.74 mmol) was treated with n-butyllithium
(1.1 mL, 2.5 m in hexanes, 2.8 mmol) in diethyl ether. After stirring
for 0.5 h at room temperature, the solvent was removed in vacuo.
The product was suspended in pentane and subsequently dried in
vacuo to remove residual volatiles; yield 0.96 g (2.64 mmol, 96%).
1H NMR (300 MHz, [D8]THF/C6D6, 298 K): δ = 7.23–6.55 (m, 13
H, iPr-CH3 + Ar-Hp), –4.7 (176, 12 H, iPr-CH3), –5.6 (48, 2 H,
Ar-Hp), –7.0 (241, 2 H, iPr-CH), –11.2 (55, 2 H, Ar-Hp) ppm. The
1H NMR spectrum of 1c·Et2O is concentration dependent. The
resonances at δ = 25.4, 13.7 and –0.9 ppm shift to lower field at
higher concentrations. IR (KBr): ν = 3055 (m), 3015 (m), 1594 (m),
˜
1579 (s), 1492 (s), 1465 (s), 1426 (s), 1380 (s), 1360 (s), 1319 (s),
1288 (m), 1270 (m), 1254 (m), 1237 (m), 1189 (m), 1172 (m), 1151
H, Ar-CH), 3.55 (septet, J = 7.0 Hz, 2 H, iPr-CH), 1.17 (d, J = (w), 1121 (w), 1101 (m), 1088 (w), 1075 (w), 1042 (m), 1027 (m),
7.0 Hz, 6 H, iPr-CH3), 1.03 (d, J = 7.0 Hz, 6 H, iPr-CH3) ppm. 996 (w), 950 (m), 936 (w), 917 (w), 896 (w), 831 (w), 803 (w), 790
13C{1H} NMR (75 MHz, [D8]THF/C6D6, 298 K): δ = 178.10 (m), 766 (s), 732 (m), 698 (s), 576 (w), 562 (w), 510 (w), 497 (w)
(NCN), 160.85, 155.13, 140.97, 137.27, 131.02, 128.36, 127.46,
cm–1. μeff (SQuID, 298 K) = 5.0 μB. C54H64FeN4O (840.97): calcd.
127.31, 123.67, 122.81, 121.58, 116.94, 28.39 (iPr-CH), 25.30, 23.03 C 77.12, H 7.67, N 6.66; found C 76.97, H 7.62, N 6.56.
(2ϫiPr-CH3) ppm.
Reaction of [Dipp2L]2Fe (1a) with Pyridine: A green solution of
[
Preparation of [DippPhL]2Fe(THF) (1c·THF): nBuLi (2.1 mL, 2.5 m
in hexane, 5.2 mmol) was added dropwise over 30 min at room tem-
perature to a solution of N-phenyl-NЈ-(2,6-diisopropylphenyl)-
benzamidine (1.86 g, 5.2 mmol) in 30% THF/pentane. The solvents
were removed in vacuo and the product was dissolved in pentane
(20 mL). The pentane was removed in vacuo. The lithium N-
phenyl-NЈ-(2,6-diisopropylphenyl)benzamidinate in THF (15 mL)
was added to a stirred suspension of FeCl2 (0.33 g, 2.6 mmol) in
THF (15 mL) at room temperature. The colour of the mixture
changed from transparent through yellow/green to brown. The re-
action mixture was stirred for 2 h. The solvents were removed and
the remainder was suspended in pentane. The pentane was removed
under reduced pressure and the solid was extracted with hexane
(40 mL). The obtained brown solution was decanted from the yel-
low solid. The solid was washed with pentane and dried in vacuo;
yield 0.76 g (35%). 1H NMR (300 MHz, C6D6, 298 K): δ = 28.2
(23, 4 H, Ar-Hm), 23.9 (216, 4 H, Ar-Ho), 18.4 (32, 4 H, Ar-Hm),
14.9 (979, 2 H, THF), 11.2 (20, 4 H, Ar-Hm), 3.9 (53, 4 H, THF),
0.6 (78, 4 H, Ar-Ho), –0.3 (19, 2 H, Ar-Hp), –1.3 (23, 2H Ar-Hp),
–2.4 (43, 12 H, iPr-CH3), –4.2 (488, 12 H, iPr-CH3), –14.1 (22, 2
Dipp2L]2Fe (11 mg, 0.01 mmol) in C6D6 (ca. 0.4 mL) was reacted
with pyridine (1 equiv., 1 mg, 0.01 mmol). No colour change was
observed. The colour of the solution changed to yellow upon ad-
dition of a second equivalent. The colour remained yellow after
subsequent addition of a few drops (excess amount) of pyridine.
1H NMR (300 MHz, C6D6, 1 equiv. pyridine, 298 K): δ = 56.4
(887), 31.7 (41, 4 H), 22.2 (41, 4 H), 16.8 (22, 4 H), 14.6 (141, 12
H), 8.3, 7.6, 6.9 (pyridine), 6.4 (100, 4 H), 3.8 (97, 12 H), –2.0 (23,
1
2 H), –5.1 (58, 12 H), –6.2 (29, 4 H), –29.0 (249, 12 H) ppm. H
NMR (300 MHz, C6D6, 2 equiv. pyridine, 298 K): δ = 55.8 (857),
31.6 (45, 4 H), 22.1 (44, 4 H), 16.8 (25, 4 H), 14.5 (150, 12 H), 12.3
(383, 4 H), 7.7, 7.3, 6.9 (pyridine), 6.5 (107, 4 H), 3.8 (107, 12 H),
–1.9 (26, 2 H), –5.0 (64, 12 H), –6.3 (31, 4 H), –28.9 (261, 12 H)
ppm. 1H NMR (300 MHz, C6D6, excess amount of pyridine,
298 K): δ = 36.1 (679), 27.8 (62, 4 H), 22.2 (50, 4 H), 17.5 (22, 4
H), 11.2 (130), 9.6–6.6 (br., pyridine and C6D5 H), 3.6 (116, 12 H),
–1.7 (75, 12 H), –7.2 (27, 4 H), –14.7 (928), –24.6 (225, 12 H) ppm.
Reaction of [DippXylL]2Fe·C6H6 (1b·C6H6) with Pyridine: A solution
of [DippXylL]2Fe·C6H6 (12 mg, 0.01 mmol) in C6D6 (ca. 0.4 mL) was
treated successively with 1 equiv. (1 mg, 0.01 mmol), 2 equiv. and
an excess amount of pyridine. The colour of the solution changed
to yellow immediately after the first equivalent of pyridine was
added. 1H NMR (300 MHz, C6D6, 1 equiv. pyridine, 298 K): δ
H, Ar-H ), –18.2 (1488, 2 H, iPr-CH) ppm. IR (KBr): ν = 3053
˜
p
(m), 3049 (m), 3035 (m), 3012 (m), 2965 (s), 2961 (s), 2957 (s), 2951
(s), 2948 (s), 2944 (s), 2941 (s), 2938 (s), 2935 (s), 2931 (s), 2927 (s),
2920 (s), 2913 (s), 2910 (s), 2905 (s), 2902 (s), 2898 (s), 2891 (s),
2881 (s), 2871 (s), 2863 (s), 2858 (s), 1638 (w), 1592 (m), 1579 (m),
1491 (s), 1467 (s), 1454 (s), 1438 (s), 1435 (s), 1360 (s), 1340 (m),
1319 (m), 1288 (m), 1269 (m), 1253 (m), 1237 (m), 1190 (w), 1179
(w), 1173 (w), 1157 (w), 1152 (w), 1121 (m), 1100 (m), 1075 (w),
1054 (w), 1040 (w), 1026 (s), 997 (w), 954 (m), 949 (w), 914 (w),
871 (m), 787 (m), 765 (s), 731 (m), 702 (s), 696 (s), 560 (w), 507
(w) cm–1. μeff (SQuID, 298 K) = 5.3 μB. C54H62FeN4O (838.96):
calcd. C 77.31, H 7.45, N 6.68; found C 77.41, H 7.38, N 6.64.
(Δν , Hz) = 63.0 (br), 29.3 (1827), 26.2 (972), 19.8 (27), 17.6 (168),
½
12.5 (395), 4.2 (40), 1.1 (60), –9.5 (30), –14.0 (90), –16.8 (179) ppm.
1H NMR (300 MHz, C6D6, 2 equiv. pyridine, 298 K): δ (Δν , Hz)
½
= 25.9 (1128), 20.6 (23), 19.8 (73), 10.5 (256), 5.3 (21), 1.3 (70),
1
–9.5 (30), –15.1 (36), –18.6 (66) ppm. H NMR (300 MHz, C6D6,
excess amount of pyridine, 298 K): δ (Δν , Hz) = 25.9 (998), 20.4
½
(28), 20.2 (169), 12.1–4.4 (br., overlapping with pyridine and
C6D5H), 5.4 (44), 1.3 (95), –9.6 (37), –15.3 (39), –18.9 (76) ppm.
Reactions of [DippPhL]2Fe(THF) (1c·THF) with Pyridine: A solution
of [DippPhL]2Fe(THF) (10 mg, 0.01 mmol) in C6D6 (ca. 0.4 mL) was
treated with pyridine (1 mg, 0.01 mmol). The colour of the solution
changed to yellow. 1H NMR (300 MHz, C6D6, 1 equiv. pyridine,
Preparation of
[
DippPhL]2Fe(Et2O) (1c·Et2O): n-Butyllithium
(1.8 mL, 2.5 m in hexanes, 4.4 mmol) was added dropwise over
30 min at room temperature to a solution of N-phenyl-NЈ-(2,6-di-
isopropylphenyl)benzamidine (1.56 g, 4.4 mmol) in diethyl ether
(30 mL). The solvent was removed in vacuo and the remainder was
suspended in pentane and dried (2ϫ) to remove residual volatiles.
The lithium N-phenyl-NЈ-(2,6-diisopropylphenyl)benzamidinate
was dissolved in diethyl ether (15 mL) and added to a stirred sus-
pension of FeCl2 (0.28 g, 2.2 mmol) in diethyl ether (20 mL) at
room temperature. The colour of the mixture changed from trans-
parent through yellow and green to brown. The reaction mixture
was stirred for 16 h and subsequently the solid was extracted with
diethyl ether. The greenish yellow solution in diethyl ether was con-
centrated and stored at –20 °C to afford yellow crystals (1.34 g,
298 K): δ (Δν , Hz) = 120.3 (448), 44.1 (190), 24.0 (22, 4 H, Ar-
½
Hm), 16.9 (306, 4 H, Ar-Hm), 14.0 (30, 4 H, Ar-Hm), 8.6 (165, 4 H,
Ar-Ho), 6.4 (92, 4 H, Ar-Ho), 3.6 (s, THF), 3.1 (351, 6 H, iPr-CH3),
1.4 (s, THF), 1.3 (24, 2 H, Ar-Hp), –1.9 (241, 6 H, iPr-CH3), –5.8
(21, 2 H, Ar-Hp), –7.2 (300, 6 H, iPr-CH3), –13.0 (280, 6 H, iPr-
CH3), –15.7 (20, 2 H, Ar-Hp), –18.6 (308, iPr-CH) ppm.
A solution of [DippPhL]2Fe(THF) (18 mg, 0.02 mmol) in C6D6 (ca.
0.4 mL) was treated with pyridine (4 mg, 0.04 mmol). The colour
of the solution changed to yellow immediately. 1H NMR
(200 MHz, C6D6, 2 equiv. pyridine, 298 K): δ = 24.2 (18, 4 H, Ar-
Hm), 17.1 (23, 4 H, Ar-Hm), 14.0 (21, 4 H, Ar-Hm), 8.9 (128, 4 H,
1
1.6 mmol, 73%). H NMR [300 MHz, C6D6 (36 mm), 298 K]: δ =
26.8 (55, 4 H, Ar-Hm), 25.4 (117, 4 H, Ar-Ho), 21.0 (37, 4 H, Ar- Ar-Ho), 6.3 (56, 4 H, Ar-Ho), 3.6 (s, THF), 1.4 (s, THF), 1.2 (23,
Hm), 13.7 (31, 4 H, Ar-Hm overlapping with broad signal for Et2O- 2 H, Ar-Hp), 0.6 (390, 12 H, iPr-CH3), –5.8 (18, 2 H, Ar-Hp), –10.1
CH2), 2.2 (111, 4 H, Ar-Ho), 0.6 (78, 6 H, Et2O-Me), –0.9 (38, 14 (392, 12 H, iPr-CH3), –15.9 (17, 2 H, Ar-Hp) ppm.
Eur. J. Inorg. Chem. 2011, 91–100
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
97

T. J. J. Sciarone et al.
FULL PAPER
A few drops of [D5]pyridine were added to a solution of [DippPhL]2-
Fe(THF) (14 mg, 0.01) in C6D6 (ca. 0.4 mL). The colour of the
solution immediately changed to yellow. 1H NMR (300 MHz,
C6D6/C5D5N, 298 K): δ = 23.9 (20, 4 H, Ar-Hm), 16.9 (22, 4 H,
the product could be isolated as an orange powder (0.21 g, 60%).
The H NMR spectrum in C6D6 is identical to that obtained from
the reaction of 1c·THF with 1 equiv. pyridine as described above.
C55H59FeN5 (845.95): calcd. C 78.09, H 7.03, N 8.28; found C
1
Ar-Hm), 14.0 (26, 4 H, Ar-Hm), 8.4 (171, 4 H, Ar-Ho), 6.4 (83, 4 76.60, H 6.60, N 7.86. IR (KBr): ν = 3057, 1636, 1592, 1579, 1434,
˜
H, Ar-Ho), 3.6 (s, THF), 1.4 (s, THF), 1.3 (32, 2 H, Ar-Hp), 0.6
(390, 12 H, iPr-CH3), –5.8 (21, 2 H, Ar-Hp), –10.2 (329, 12 H, iPr-
CH3), –15.7 (21, 2 H, Ar-Hp) ppm.
1322, 1288, 1268, 1254, 1237, 1213, 1192, 1171, 1155, 1120, 1100,
1071, 1055, 1040, 1026, 997, 952, 936, 916, 896, 841, 804, 788, 766,
732, 699, 559, 536, 508 cm–1.
Preparation of [DippPhL]2Fe(bpy) (1c·bpy): One equivalent of 2,2Ј-
bipyridine (0.19 g, 1.192 mmol) was added to a yellow/brown solu-
tion of 1c·Et2O (1.00 g, 1.19 mmol) in toluene (about 10 mL) and
an immediate change of colour to dark green was observed. The
reaction mixture was reduced to about two thirds of its original
volume and stored at –80 °C for one day. The product was isolated
Pyridine (8 μL, 0.12 mmol) was added to a solution of [DippPhL]2-
Fe(THF) (24.6 mg, 0.029 mmol) in C6D6 (ca. 0.4 mL). The colour
of the solution changed from brown to orange/light brown. 1H
NMR (300 MHz, C6D6, 298 K): δ = 23.9 (34, 4 H, Ar-Hm), 17.0
(37, 4 H, Ar-Hm), 14.0 (40, 4 H, Ar-Hm), 11–6.7 (br., C6D5H and
pyridine obscuring paramagnetic signals), 6.3, 3.6 (THF), 1.4
(THF), –5.8 (32, 2 H, Ar-Hp), –10.2 (384, 12 H, iPr-CH3), –15.7
(30, 2 H, Ar-Hp) ppm. Removal of the volatiles and redissolution
in C6D6 resulted in a 1H NMR spectrum identical to that obtained
from reaction of 1c·THF with 1 equiv. of pyridine.
1
as dark green crystals; yield 0.703 g (0.765 mmol, 64%). H NMR
(300 MHz, C6D6, 298 K): δ (Δν , Hz): 112.6 (351, 1 H), 56.4 (66,
½
2 H, bpy), 43.6 (62, 2 H, bpy), 17.5 (277, 4 H, Ar-Hm), 15.2 (61, 8
H, 2ϫAr-Ho), 14.6 (53, 4 H, Ar-Hm), 13.1 (110, 2 H, bpy), 5.4 (36,
2 H, Ar-Hp), 4.4 (348, 12 H, iPr-CH3), 1.2 (46, 2 H, bpy), –3.1 (82,
12 H, iPr-CH3), –11.3 (36, 2 H, Ar-Hp), –16.1 (38, 2 H, Ar-Hp),
Reaction of [DippPhL]2Fe(Et2O) (1c·Et2O) with [D8]THF: A yellow
solution of [DippPhL]2Fe(Et2O) (15 mg, 0.02 mmol) in C6D6 (ca.
0.4 mL) in an NMR spectroscopy tube was reacted with a drop of
[D8]THF. The colour of the solution became slightly darker. 1H
–22.0 (256, 4 H, iPr-CH) ppm. IR (KBr): ν = 2137, 2070, 1779,
˜
1632, 1595, 1580, 1315, 1260, 1237, 1190, 1151, 1111, 1098, 1077,
1058, 1024, 874, 804, 790, 767, 710, 698, 619, 597, 559, 530, 465
cm–1. C60H62FeN6 (C7H8)0.5 (969.11): calcd. C 78.70, H 6.86, N
9.10; found C 78.65, H 6.90, N 8.67.
1
NMR (300 MHz, C6D6, 298 K): similar to the H NMR spectrum
of 1c·THF but without resonances at δ = 14.9 and 3.91 ppm (coor-
dinated THF molecule). Free diethyl ether is observed at δ = 3.30
and 1.12 ppm.
Preparation of [{C(O)N(Ph)C(Ph)NAr}2Fe(CO)2] (2): A solution of
1c·Et2O (313 mg, 37 mmol) in diethyl ether was degassed by three
freeze–pump–thaw cycles. Afterwards an excess amount of CO
(1 atm.) was admitted. The colour of the solution changed immedi-
ately from yellow to red. The reaction mixture was stirred for 3 d.
Subsequently a yellow powder precipitated from the clear brown
Preparation of [DippPhL]2Fe(pyridine) (1c·py): Pyridine (0.1 mL,
1.23 mmol) was added to a brown solution of 1c·Et2O (0.36 g,
0.43 mmol) in toluene (15 mL). The colour changed to orange/light
brown. The reaction mixture was stored at –80 °C for one day and
Table 1. Crystal collection and refinement data.
1c·THF
1c·Et2O
1c·bpy
2
Formula
Mr
C54H62N4OFe
838.96
C54H64N4OFe
840.97
C60H62FeN6
923.04
C54H54N4O4Fe
878.89
Dimensions [mm]
Colour, habit
Crystal system
Space group, no.[24]
a [Å]
b [Å]
c [Å]
0.43ϫ0.41ϫ0.35
yellow, block
monoclinic
P21, 4
13.0056(5)
18.6888(7)
20.2539(8)
106.866(1)
4
4711.1(3)
1.183
2.18–28.28
0.71073
100(1)
0.17ϫ0.16ϫ0.15
yellow, parallelepiped
monoclinic
P21/c, 14
11.5817(7)
23.119(1)
17.937(1)
98.933(1)
4
4744.5(4)
1.177
2.30–25.02
0.71073
0.28ϫ0.22ϫ0.14
dark green, block
monoclinic
P21/c, 14
12.305(2)
32.647(4)
15.802(2)
101.913(2)
4
6211.3(15)
0.987
2.29 – 23.53
0.71073
100(1)
0.15ϫ0.12ϫ0.09
yellow, block
monoclinic
P21/c, 14
13.9144(8)
18.004(1)
19.112(1)
98.649(1)
4
4733.4(5)
1.233
2.26–25.03
0.71073
β [°]
Z
V [Å3]
ρcalcd. [gcm3]
θ range [°]
λ [Å] (Mo-Kα)
T [K]
100(1)
200(1)
Collection time [h]
Measured reflections
Unique reflections
M [cm–1]
8.0
43373
22725
3.62
1577
0.0496, 0.0
0.0375
0.0869
–0.23, 0.45(5)
1.006
18.3
34022
8372
3.55
18
38504
9223
2.79
613
0.1, 0.0
0.1184
0.2879
18.3
33835
8347
3.68
Parameters
Weighting scheme a, b[a]
R(F) for Fo Ն4σ(Fo)[b]
wR(F2)[c]
551
576
0.0420, 0.8754
0.0476
0.1098
–0.31, 0.45(5)
1.011
0.0435, 2.0026
0.0583
0.1399
–0.25, 0.38(6)
1.010
Residual el. density [eÅ–3]
GoF[d]
–0.6, 0.6(1)
1.155
½
[a] w = 1/[σ2(F2o) + (aP)2 + bP], P = [max(F2o,0) + 2F2c]/3. [b] R(F) = Σ(||Fo| – |Fc||)/Σ|Fo|. [c] wR(F2) = {Σ[w(F2o – Fc2)2]/Σ[w(F2o)2]} . [d] GoF
½
= {Σ[w(F2o – F2c)2]/(n – p)} ; n = number of reflections, p = number of parameters refined.
98
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 91–100

Reactivity of Paramagnetic FeII–Bis(amidinate) Complexes
solution. The brown solution was decanted and the remaining yel-
low powder was dried in vacuo; yield 107 mg (0.12 mmol, 33%).
The yield was not optimised. H NMR (300 MHz, C6D6, 298 K):
Effective magnetic moments were calculated as Equation (2).
1
δ = 7.97 (d, J = 7.7 Hz, 2 H, Ar-CH), 7.07–6.45 (m, 24 H, Ar-CH),
3.64 (septet, J = 6.7 Hz, 2 H, iPr-CH), 3.40 (septet, J = 6.7 Hz, 2
H, iPr-CH), 1.63 (d, J = 6.6 Hz, 6 H, iPr-CH3), 1.45 (d, J = 7.0 Hz,
6 H, iPr-CH3), 1.27 (d, J = 7.0 Hz, 6 H, iPr-CH3), 1.11 (d, J =
6.6 Hz, 6 H, iPr-CH3) ppm. 13C{1H} NMR (75 MHz, C6D6,
298 K): δ = 219.9 (CϵO), 209.5 (C=O), 167.0 (NCN), 152.8, 148.7,
146.9, 135.0, 130.8 (5ϫCipso), 129.3, 129.1, 129.0, 128.4, 127.3,
126.0, 125.6, 124.4, 124.2, 123.4 (10ϫCAr, 3 resonances obscured
by C6D6), 29.8, 28.9 (2ϫiPr-CH), 27.2, 26.8, 23.4, 22.8 (4ϫiPr-
(2)
Zero-field splitting parameters were obtained by least-squares fit-
ting of the observed susceptibility to the following Equation (3).[26]
CH ) ppm. IR (KBr): ν = 3061 (w), 3023 (w), 2020 (s, CϵO), 1961
˜
3
(s, CϵO), 1937 (w), 1659 (s, C=O), 1592 (m), 1584 (m), 1494 (w),
1321 (w), 1277 (w), 1186 (w), 1173 (w), 1102 (w), 1073 (w), 1040
(w), 1027 (w), 1003 (w), 989 (m), 930 (w), 898 (w), 796 (m), 761
(w), 743 (w), 706 (m), 693 (m), 652 (w), 598 (w), 579 (w), 544 (w),
470 (w), 449 (w) cm–1. C54H54N4O4Fe (878.89): calcd. C 73.80, H
6.19, N 6.37; found C 73.71, H 6.13, N 6.44.
(3)
Supporting Information (see also the footnote on the first page of
this article): X-ray structure of amidine DippPhLH, 1H NMR spectra
for reactions of 1b with pyridine and magnetic susceptibility data
for 1c·bpy.
X-ray Diffraction: Crystals suitable for X-ray analysis were ob-
tained at room temperature by layering a concentrated THF solu-
tion with hexanes (1c·THF), by layering a concentrated Et2O solu-
tion with pentane (1c·Et2O), by layering a toluene solution with
pentane (1c·bpy) or by recrystallisation from toluene (2). Crystals
were picked from the mother liquor and covered with inert oil to
avoid deterioration due to loss of solvent from the crystal lattice.
For 2, the scattering power of the crystals was very weak: around
half of the unique (till Θ = 23.53°) merged reflections obey the
Fo Ն4.0 σ(Fo) criterion of observability. This implies that the mean
standard uncertainty (estimated standard deviation) is large com-
pared to the mean magnitude of the (even more than double of the
squared) structure factor. The weak scattering power might be the
result of disorder. Refinement was also complicated by a disorder
problem: from the solution it was clear that the solvate molecules
were highly disordered and partly occupied. No satisfactory dis-
crete model could be fitted in this density. The solvent contribution
was taken into account using the SQUEEZE procedure in the
PLATON program[21] (1521.5 Å3 per unit cell). The program PLA-
TON[21] was used for geometrical analysis. Illustrations were gener-
ated using the programs ORTEP[22] and POV-Ray[23] (rendering).
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2003, 125, 7774–7775.
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Dalton Trans. 1998, 4147–4154; b) R. T. Boeré, M. L. Cole,
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(1)
Eur. J. Inorg. Chem. 2011, 91–100
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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FULL PAPER
[23] Rendering was made with POV-Ray 3.6, Persistence of Vision
Pty. Ltd. (2004), Persistence of Vision Raytracer (version 3.6),
retrieved from http://www.povray.org/download/.
[24] International Tables for Crystallography, Kluwer Academic
Publishers, Dordrecht, The Netherlands, 1992.
[25] O. Kahn, Molecular Magnetism, VCH Publishers, New York,
1993, p. 3.
[26]
C. J. O’Connor, Magnetochemistry – Advances in Theory and
Experimentation, in: Progress in Inorganic Chemistry, Wiley,
New York, 1982, pp. 203–283.
Received: June 30, 2010
Published Online: December 3, 2010
100
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 91–100