Influence of N-substitution on the oxidation of 2-pyridylmethylamines with Bis(trimethylsilyl)amides of Iron(III) - Synthesis of heteroleptic Iron(II) 2-pyridylmethylamides

Article abstract of DOI:10.1002/ejic.201001166

The reaction of (thf)Fe[N(SiMe₃)₂]₂Cl with (2-pyridylmethyl)(diphenylphosphanyl)amine (1) in hot tetrahydrofuran (THF) yields dinuclear [(ClFe)₂{μ-N(SiMe₃) ₂}{Ph₂P(NCH₂

Full text of DOI:10.1002/ejic.201001166

FULL PAPER
DOI: 10.1002/ejic.201001166
Influence of N-Substitution on the Oxidation of 2-Pyridylmethylamines with
Bis(trimethylsilyl)amides of Iron(III) – Synthesis of Heteroleptic Iron(II)
2-Pyridylmethylamides
Astrid Malassa,[a] Benjamin Schulze,[a] Brigitte Stein-Schaller,[a] Helmar Görls,[a]
Birgit Weber,[b] and Matthias Westerhausen*[a]
Keywords: Iron / Oxidation / Pyridylmethylamide ligands / Magnetic properties
The reaction of (thf)Fe[N(SiMe3)2]2Cl with (2-pyridylmethyl)-
(diphenylphosphanyl)amine (1) in hot tetrahydrofuran (THF)
yields dinuclear [(ClFe)2{μ-N(SiMe3)2}{Ph2P(NCH2Py)2}] (2)
and [ClFe{Ph2P(O)-NCH2Py}]2 (3) with the oxygen atom
stemming from THF degradation. The formation of 2 requires
a P–N bond cleavage and reformation leading to the tetra-
dendate diphenyl-bis(2-pyridylmethylamido)phosphonium
ion. If this reaction of (thf)Fe[N(SiMe3)2]2Cl with 1 is per-
formed at room temperature, no P–N bond cleavage is ob-
served. Instead of that, ether degradation occurs yielding
[Fe4(μ4-O)(μ2-Cl)2(Ph2P-NCH2Py)4] (4) with a central oxygen-
centered iron tetrahedron as well as complex 3. Recrystalli-
zation of 3 from dichloromethane leads to addition of HCl
and to the formation of [FeCl2·{Ph2P(O)-N(H)-CH2Py}] (5).
The phosphonium ion of 2 is isoelectronic to the correspond-
ing diphenyl-bis(2-pyridylmethylamino)silane (6). Lithiation
of 6 followed by a metathetical reaction with (thf)2FeCl2
yields the trinuclear complex [Fe3Cl2{Ph2Si(NCH2Py)2}2] (7)
with antiferromagnetic interactions.
bases such as Grignard reagents[9] or methyllithium in hex-
ane.[10] These dianions (L)2– can be oxidized with e.g. white
phosphorus[11] leading to the formation of (Lox1)–. If the
deprotonation reaction is performed with organometallics
containing less electropositive metals, this oxidation process
leads to precipitation of metal and immediately yields
(Lox1)–. This anion dimerizes and forms the tetradentate di-
anion (Lox12)2–. In the case of R being an alkyl group this
Introduction
Picolylamines (2-pyridylmethylamines) and their depro-
tonated derivatives (picolylamides, 2-pyridylmethylamides)
gained a tremendous importance in bioinorganic chemistry
as models mostly for histidine in metal enzymes.[1] However,
these ligands do not only behave as spectator ligands but
are also involved in redox processes in the environment of
transition metals. A general reactivity diagram is shown in
Scheme 1 with protonation/deprotonation reactivity shown
in the upper line and with oxidation/reduction equilibria
presented in the column. The redox activity was often ob-
served as an unexpected side reaction which is catalyzed by
transition metal complexes such as, for example, cobalt(II)
in the presence of air.[2] Iron complexes are well-known to
oxidize hydrocarbons whereby the most reactive com-
pounds often contain picolylamine fragments in the coordi-
nation spheres of the metal cations.[3–8]
equilibrium could be observed in solution whereas in the
2–
crystalline state only the dimer (Lox1
)
was observed.[12]
2
For R = SiRЈ3 only the dimeric ligand (Lox1
)
was found
2–
2
in solution and the solid state.[9,13] A second oxidation step
leads to the formation of 2-pyridylmethylidene amines
(Lox2)0 which usually remain in the coordination sphere of
the metals. This general reactivity depends not only on the
oxidizing ability of the organometallics (redox potential of
the metals) but also on the electronic nature and bulkiness
of the N-bound substituent R.
Deprotonation of picolylamine (H2L) yields the amides
The use of picolylamine (2-pyridylmethylamine, Py–
CH2–NH2, R = H) offers not only the pathway shown in
Scheme 1 but a second deprotonation step can also be per-
formed at the amide functionality leading to imide Py–
CH2–N2–. In addition with the lack of steric protection a
variety of subsequent reactions are possible leading to nu-
merous products. Thus, the reaction of methylzinc picolyl-
amide with dimethylzinc leads to C–C coupling reactions
but these intermediate products (MeZn)2(Lox12) (R = H)
show a similar reactivity than the starting materials and
undergo subsequent degradation reactions.[14] Substitution
(HL)– which can be deprotonated again to (L)2– with strong
[a] Institut für Anorganische und Analytische Chemie, Friedrich-
Schiller-Universität Jena,
August-Bebel-Str. 2, 07743 Jena, Germany
Fax: +49-3641-948102
E-mail: m.we@uni-jena.de
[b] Anorganische Chemie II, Universität Bayreuth,
Universitätsstraße 30, NW I, 95440 Bayreuth, Germany
Fax: +49-921 552157
E-mail: weber@uni-bayreuth.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201001166.
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Reactions of Iron-Based Metalation Reagents
Scheme 1. Reactivity diagram of picolylamine. The upper row shows the deprotonation/protonation equilibria, the column outlines the
redox equilibria.
of this hydrogen atom by a N-bound trialkylsilyl group hin- mixture thus preventing subsequent degradation reac-
2–
ders these degradation reactions and (Lox1
)
is accessible tions.[23,24] However, soluble heteroleptic RM-N(CH2-Py)2
2
with good yields.[9,13] Bulky aryl substituents such as 2,6- (M = Mn, Fe, Co, Zn) as well as the metallation of dipicol-
diisopropylphenyl groups at the amido unit stabilize the ylamine with M[N(SiMe3)2]2 lead to the formation of
radical anion (Lox1)– and allow the crystallization of homo- metal(II) bis[1,3-bis(2-pyridyl)-2-azapropenide] (Lox2–H –
)
leptic compounds [M(Lox1)2] (M = Cr, Mn, Fe, Co, Ni, (see Scheme 1).[23,25] These complexes are stable and also
Zn).[15]
accessible via metalation of N-picolyl-(2-pyridylmethyli-
A second oxidation of the radical anion (Lox1)– leads to dene)amine or metathetical via the reaction of lithium [1,3-
the formation of neutral 2-pyridylmethylidene amines bis(2-pyridyl)-2-azapropenide] with metal halides.[24] A sim-
(Lox2)0. Even though iron(II) and iron(III) complexes of ilar reaction sequence for dipicolylamine can be assumed
picolylamine (H2L) are stable,[16,17] complexes containing because intermediate structures of the type (HL)– (dipicol-
amides (HL)– are strongly destabilized due to the fact that ylamide) and (Lox2 0
)
[N-picolyl(2-pyridylmethylidene)-
these anions represent strong σ- and strong π-donors which amine] were found in the vicinity of rhodium(I)[26] and iridi-
disfavour complexes with electron-rich late transition met- um(I) starting from metalated dipicolylamine.[27]
als.[18] Therefore, the doubly deprotonated species (L)2– are
In order to further elucidate the influence of the N-
unstable in the presence of strong oxidizing reagents such bound substituent, we investigated the reaction of iron-
as, for example, cobalt(III)[19] and iron(III)[20] leading im- based metalation reagents with N-diphenylphosphanyl-pic-
mediately to the imines (Lox2)0. These imines are bound at olylamine[28] which offers an additional Lewis base.
the metal(II) cations or readily form adducts with iron(II)
complexes.[21]
More complicated situations can be expected for dipicol-
ylamines [bis(2-pyridylmethyl)amines] because two methyl-
Results and Discussion
ene moieties are now available for a second metalation reac-
In order to estimate the electronic stabilization of 2-pyr-
tion. Again, iron(II) complexes of dipicolylamine are stable idylmethylamines by N-bound substituents, (2-pyridyl-
with this ligand acting as a tridentate chelate ligand coordi- methyl)(diphenylphosphanyl)amine (1)[27] was included in
nating in a facial manner.[17,22,23] In contrast to cobalt(II) our investigations. Depending on the reaction conditions
chloride, the iron(II) chloride complexes react differently two different products were isolated from the reaction of
with air: Oxygen inserts between the iron atoms raising the (thf)Fe[N(SiMe3)2]2Cl with 1 in THF solutions. In hot
oxidation state from iron(II) to iron(III) without oxidation THF, the pale yellow dinuclear complex 2 was isolated after
of the coordinated bis(2-pyridylmethyl)amine molecules.[22] eight hours according to equation (1). Whereas 2 precipi-
As expected from the findings described above, depro- tated as single crystalline material, complex 3 precipitated
tonation of dipicolylamine leads to very reactive iron(II) as a microcrystalline powder. In complex 2, a new tetraden-
bis(dipicolylamide) which precipitates from the reaction tate ligand was formed which can be regarded as a phos-
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M. Westerhausen et al.
FULL PAPER
phonium cation with two phenyl and two 2-pyridylmeth-
ylamido groups. During this reaction, a reduction of
iron(III) to iron(II) was observed. One of the bis(trimethyl-
silyl)amido ligands was maintained as a bridging ligand in
the coordination spheres of the metal atoms which is not
unusual; e.g. in dimeric [Fe{N(SiMe3)2}2]2 also bridging
N(SiMe3)2 groups exist (Fe–Nterm 192.5 pm, Fe–Nbr
208.5 pm).[29] As observed earlier, the iron-bound chlorine
atoms showed no reactivity towards this secondary amine
and were preserved at iron; see Equation (1).
(2)
(1)
picolylamino-diphenylphosphane oxide at iron(II) chloride
(5) according to Equation (3). An X-ray diffraction experi-
ment verified that ligand 3 binds via the oxygen atom to
the iron(II) cation.
(3)
At room temperature a very slow reaction was observed
and within two weeks bright red crystals of tetranuclear 4
precipitated besides already known complex 3; see Equa-
tion (2). In 4, the iron atoms form an oxygen-centered Fe4
tetrahedron. Two opposite Fe···Fe edges are bridged by
chlorine atoms. In addition each iron(II) atom is bound to
None of the above mentioned reactions allowed the oxi-
2–
the nitrogen atoms of the bidentate (2-pyridylmethyl)(di- dative C–C bond formation to yield (Lox1
)
or the isola-
2
phenylphosphanyl)amido substituent whereas the diphenyl- tion of an iron complex of the imine (Lox2)0 (see Scheme 1).
phosphanyl moiety coordinates to another iron center. Instead of the synthesis of these oxidized ligands P–N bond
Thus, all iron atoms exhibit a coordination number of five cleavage and THF degradation was observed because the
(two N, O, Cl, P). Such a tetrahedral (Fe4O)6+ unit was oxygen atoms in compounds 3 and 4 stem from ether cleav-
observed earlier by, for example, Cotton et al.,[30,31] The age reactions; hydrolysis (reaction with water) and oxi-
oxygen source was most probably the THF solvent which dation with oxygen (air) can safely be excluded. On the one
was oxidized and cleaved by iron(III). Similar to the N- hand, iron(III) chloride hexa(hydrate) proofed to be an un-
trialkylsilyl-substituted 2-pyridylmethylamides, no com- suitable starting material for the reaction with (2-pyridyl-
plexes of iron(III) with (2-pyridylmethyl)(diphenylphos- methyl)(diphenylphosphanyl)amine (1). Also the presence
phanyl)amides were observed.
of oxygen did not enhance the yield of [{(Ph2PN-CH2-2-
We were unable to obtain single crystals of 3 but the Py)Fe}4(μ-Cl)2(μ4-O)] (4). On the other hand, ether cleavage
composition of this compound was deduced from analytical reactions are well-known side reactions in the chemistry of
data. In order to prove the constitution of this iron(II) com- electropositive metals,[32,33] but also in iron-based chemis-
plex (2-pyridylmethyl)(diphenylphosphanyl)amine (1) was try.[34–37] Li and co-workers[34] described in detail the degra-
lithiated and then reacted with FeCl3 in THF solution. dation of THF in the vicinity of iron(III); addition of
During this redox reaction the phosphorus atom was oxid- TEMPO suppressed this THF degradation. This finding
ized and the resulting complex 3 showed the same analytical was interpreted in the sense of a radical mechanism.
data as the microcrystalline material shown in Equation (1)
The substitution of the P+ atom of the tetradentate li-
and (2). Recrystallization of 3 from dichloromethane led gand of 2 by a silicon atom yields an isoelectronic tetraden-
to the addition of HCl and finally yielded an adduct of tate ligand. In order to investigate the coordination behav-
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Reactions of Iron-Based Metalation Reagents
iour of this ligand, we reacted [PyCH2N(H)]2SiPh2 (6) with
two equivalents of nBuLi and thereafter with an appropri-
ate amount of (thf)2FeCl2 according to Equation (4). The
trinuclear complex 7 combines two well-known structural
units, namely the heteroleptic dimeric 2-pyridylmeth-
ylamido iron(II) chloride moiety and the iron(II) bis(2-pyr-
idylmethylamide) unit which are interconnected via di-
phenylsilyl fragments.
Figure 1. Molecular structure and numbering scheme of [(ClFe)2-
{Ph2P(N-CH2-2-Py)2}{μ-N(SiMe3)2}] (2). The ellipsoids represent
a probability of 40%, H atoms are neglected for clarity reasons.
Selected bond lengths [pm]: Fe1–N1 213.8(3), Fe1–N2 202.5(3),
Fe1–N5 209.1(3), Fe1–Cl1 227.9(1), Fe2–N3 202.2(3), Fe2–N4
214.4(3), Fe2–N5 209.9(3), Fe2–Cl2 226.4(1), P1–N2 160.8(3), P1–
N3 160.3(3), P1–C13 181.7(4), P1–C25 186.9(4), N2–C6 146.8(4),
N3–C7 146.0(4), N5–Si1 177.0(2), N5-Si2 176.2(3); angles [°]: Cl1–
Fe1–N1 95.14(8), Cl1–Fe1–N2 122.42(8), Cl1–Fe1–N5 117.87(8),
N1–Fe1–N2 78.9(1), N1–Fe1–N5 125.9(1), N2–Fe1–N5 110.9(1),
Cl2–Fe2–N3 121.68(8), Cl2–Fe2–N4 95.39(8), Cl2–Fe2–N5
117.12(7), N3–Fe2–N4 79.0(1), N3–Fe2–N5 112.1(1), N4–Fe2–N5
125.9(1), Si1–N5–Si2 119.3(2).
(4)
The bridging bis(trimethylsilyl)amido ligand displays
rather large Si–N5 bond lengths of 176.6 pm due to the
coordination number of four and sp3 hybridization for N5.
The Si1–N5–Si2 angle of 119.3(2)° is the largest angle at
N5 due to the repulsion of the bulky trimethylsilyl groups.
The rather large Fe–N bond lengths allow a small angle of
99.5(1)° whereas the Fe–N5–Si angles adopt values between
106.4(1) and 111.7(1)°. Due to the steric strain induced by
the bulky SiMe3 groups the Fe–N5 distances with an
average value of 209.5 pm are larger than the Fe1–N2 and
Molecular Structures
Molecular structure and numbering scheme of 2 are rep- F2–N3 bond lengths.
resented in Figure 1. The iron atoms are in distorted tetra-
The molecular structure of [Fe4{N(PPh2)CH2Py}4Cl2O]
hedral environments. Due to the electrostatic attraction the (4) is displayed in Figure 2. Symmetry-related atoms are
Fe1–N2 and Fe2–N3 bond lengths of the amide are with marked with the letters “A“ (–y + 5/4, x – 3/4, –z + 5/4),
an average value of 202.4 pm significantly shorter than the “B“ (y + 3/4, –x + 5/4, –z + 5/4), and “C“ (–x + 2, –y + 1/2,
Fe–N distances to the pyridyl units with an average value z). The central structural fragment consists of an oxygen-
of 214.1 pm.
centered iron(II) tetrahedron. Two opposite Fe···Fe edges
The phosphonium ligand shows average P–C and P–N are bridged by chlorine ligands, all other edges are bridged
bond lengths of 181.8 and 160.6 pm, respectively. Compar- by the N–P bonds of the (2-pyridylmethyl)(diphenylphos-
able bis(benzylamido)diphenylphosphonium anions show phanyl)amido substituents. All iron(II) atoms are embedded
similar P–N bond lengths between 160 and 163 pm and act in a trigonal bipyramidal environment with the oxygen
as bidentate ligands at titanium and zirconium.[38] The devi- atom and the pyridyl group in apical positions [O–Fe–N1
ation of the angles at P1 in 3 from tetrahedral geometry is 175.03(8)°]. The equatorial positions are occupied by Cl, P,
smaller than Ϯ4°. The N–P–N values between 95 and 98° and N2 atoms. Distortions from the trigonal bipyramidal
for the group 4 complexes with bis(benzylamido)diphenyl- coordination sphere result from the bite of the 2-pyridyl-
phosphonium ligands are much smaller. The coordination methylamido unit leading to a N1–Fe–N2 angle of only
behaviour of the tetradentate bis(2-pyridylmethylamido)di- 76.3(1)°.
phenylphosphonium anions in 3 deviates significantly be-
In 5 a Fe–O distance of 202.87(5) pm is observed (Fig-
cause the iron atoms are bound to the 2-pyridylmeth- ure 3). This value is in agreement to the Fe–O distances
ylamido moieties forming five-membered rings whereas the of the discrete [Fe4(μ-O)]6+ unit with an average value of
bis(benzylamido)diphenylphosphonium unit is only able to 198.3 pm (varying between 193.4(5) and 201.0(5) pm) re-
behave as a bidentate ligand via the amido nitrogen bases.
ported by Cotton and co-workers[30] for [Fe4(NPy2)6O]; the
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M. Westerhausen et al.
FULL PAPER
(NPy2)6O] of Cotton et al.[30] the negative charge is delocal-
ized within the whole ligand, leading to a reduced electro-
static attraction and larger Fe–N distances. The Fe–Cl bond
lengths of 250.1(1) pm are significantly larger (approx.
10%) than observed for the terminal Cl substituents in 2
(Table 1). This fact can be addressed to the bridging posi-
tions of the chloride anions and to the larger coordination
number of the iron atoms.
Figure 2. Molecular structure and numbering scheme of [{(Ph2PN-
CH2-2-Py)Fe}4(μ-Cl)2(μ4-O)] (4). Ellipsoids represent a probability
of 40%, H atoms are omitted for clarity reasons. Symmetry-related
atoms are labelled with the letters “A“ (–y + 5/4, x – 3/4, –z + 5/
4), “B“ (y + 3/4, –x + 5/4, –z + 5/4), and “C“ (–x + 2, –y + 1, z).
Hydrogen atoms are not shown. Selected bond lengths [pm]: Fe1–
O1 202.87(5), Fe1–Cl1 250.1(1), Fe1–P1 246.8(1), Fe1–N1 223.1(3),
Fe1–N2 201.0(3), P1–N2 164.9(3), P1–C7 183.3(4), P1–C13
184.0(4), N2–C6 146.1(5); angles [°]: Fe1–O1–Fe1A 112.92(2), Fe1–
O1–Fe1B 112.93(2), Fe1–O1–Fe1C 102.77(3), O1–Fe1–Cl1
89.28(3), O1–Fe1–N1 175.03(8), O1–Fe1–N2 103.75(9), O1–Fe1–
P1A 95.30(3).
Figure 3. Molecular structure and numbering scheme of [{2-Py-
CH2-N(H)-P(O)Ph2}FeCl2] (5). Selected bond lengths [pm]: Fe1–
O1 198.3(2), Fe1–N1 213.8(3), Fe1–Cl1 228.52(9), Fe1–Cl2
226.20(9), P1–O1 150.6(2), P1–N2 161.9(3), P1–C7 178.9(3), P1–
C13 179.3(3), N2–C6 146.8(4), C5–C6 150.8(4); angles [°]: O1–Fe1–
N1 102.74(9), O1–Fe1–Cl1 116.54(7), O1–Fe1–Cl2 108.96(6), N1–
Fe1–Cl1 97.66(7), N1–Fe1–Cl2 112.93(7), Cl1–Fe1–Cl2 116.67(4),
slightly smaller value stems from the smaller coordination
number of four for one of the iron(II) atoms. Due to a
strong electrostatic attraction between the positive metal
center and the negatively charged amido function a short
Fe–N2 bond of 201.0(3) was found whereas in [Fe4- O1–P1–N2 115.7(1), P1–N2–C6 123.1(2), N2–C6–C5 111.9(2).
Table 1. Crystal data and refinement details for the X-ray structure determinations of the compounds 2, 4, 5, 6 and 7.
Compound
Formula
2
4
5
6
7
C30H40Cl2Fe2N5PSi2·
C4H8O
812.52
–90(2)
triclinic
C72H64Cl2F4 N8OP4· C18H17Cl2FeNOP
4(C4H8O)
C24H24N4Si
C48H44Cl2Fe3N8Si2·
1.25C4H8O
1117.67
–90(2)
monoclinic
C2/c
29.0168(6)
14.3573(2)
29.3947(7)
90
110.805(1)
90
11447.4(4)
8
1.297
9.29
30551
Fw [gmol–1]
T [°C]
Crystal system
Space group
A [Å]
B [Å]
c [Å]
A [°]
1763.91
–90(2)
tetragonal
I41/a
17.2104(4)
17.2104(4)
34.3545(8)
90
435.06
–90(2)
396.56
–90(2)
monoclinic
P21/c
10.9830(3)
8.7586(4)
22.0613(8)
90
100.611(3)
90
2085.91(13)
4
1.263
1.3
13892
monoclinic
P21/n
12.9227(7)
11.6608(6)
13.7635(7)
90
113.760(3)
90
1898.22(18)
4
¯
P1
11.4040(5)
13.0271(6)
14.3238(5)
100.878(3)
105.210(2)
100.136(2)
1958.60(14)
2
1.378
10.13
13406
5344
Β [°]
90
90
γ [°]
V [Å3]
10175.7(4)
4
1.151
7.21
34376
Z
ρ [gcm–3]
µ [mm–1]
Measured data
Data with IϾ2σ(I)
1.522
11.69
12552
2737
4177
3147
8336
Unique data (Rint
)
8860/0.0392
0.1277
0.0511
1.006
0.424/–0.420
none
5822/0.0533
0.2307
0.0665
1.031
4326/0.0746
0.1047
0.0443
0.998
0.175/–0.187
4759/0.0538
0.1218
0.0468
1.006
12827/0.0564
0.2223
0.0734
1.021
0.296/–0.349
wR2 (all data, on F2)[a]
R1 [IϾ2σ(I)][a]
S[b]
Residual electron density [eÅ–3]
Absorption method
0.839/–0.458
0.257/–0.344
2 2
2
[a] Definition of the R indices: R1 = (Σ||Fo| – |Fc||)/Σ|Fo|. wR2 = {Σ[w(Fo2 – Fc ) ]/Σ[w(Fo2)2]}1/2 with w–1 = σ2(Fo2) + (aP)2 + bP; P = [2Fc
+ max(Fo2)/3]. [b] s = {Σ[w(Fo – Fc ) ]/(No – Np)}1/2
.
2
2 2
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Reactions of Iron-Based Metalation Reagents
Due to reduced electrostatic attraction in comparison to
complex 4, the P–C (average 183.7 pm) and P–N2 bonds
[164.9(3) pm] are elongated. In 4 the tetradentate bis(2-pyr-
idylmethylamido)diphenylphosphonium ligand contains a
positively charged P atom which has a smaller radius than
a neutral P atom in 5 with a phosphanyl group. The N2
atom displays a nearly planar coordination sphere (angle
sum at N2 359.4°).
The molecular structure of 6 is represented in Figure 4.
The Si–N bonds with an average value of 170.5 pm are
rather short. The planar coordination spheres of N1 and
N3 suggest an sp2(N) hybridization with the possibility of
the pz(N) lone pair to interact with σ*(Si–C) bonds. The
Si–C bond lengths display an average value of 186.7 pm.
The coordination sphere of the silicon atom shows only
slight deviations from the tetrahedron.
Figure 5. Molecular structure and numbering scheme of
[Cl2Fe3{Ph2Si(N-CH2-2-Py)2}2] (7). Ellipsoids represent a prob-
ability of 40%, H atoms are omitted for clarity reasons. The ligands
are distinguished by the letters “A“ and “B“. Selected bond lengths
[pm]: Fe1–N1A 208.5(4), Fe1–N2A 199.8(4), Fe1–N1B 209.3(5),
Fe1–N2B 199.6(4), Fe2–Cl1 236.6(1), Fe2–N2A 224.1(4), Fe2–N3A
221.6(4), Fe2–N4A 217.9(4), Fe2–N3B 205.3(4), Fe3–Cl2 237.8(1),
Fe3–N2B 219.7(4), Fe3–N3B 223.0(4), Fe3–N4B 216.9(4), Fe3–
N3A 206.0(4), Si1A–N2A 172.7(4), Si1A–N3A 172.0(4), Si1B–N2B
173.0(4), Si1B–N3B 171.1(4), N2A–C6A 147.1(6), N3A–C19.A
146.3(6), N2B–C6B 146.4(6), N3B–C19B 147.6(6).
The iron atom Fe2 binds to the three nitrogen atoms
N2A, N3A, and N4A of the ligand A, Fe3 to N2B, N3B,
and N4B of ligand B. This fact leads to small N2–Si1–N3
bond angles of 98.2(2)° (ligand A) and 99.2(2)° (ligand B)
whereas free Ph2Si[N(H)CH2Py]2 (6) shows an N–Si–N an-
gle of 113.59(9)°. The tetracoordinate amido N atoms N2
and N3 show a distorted tetrahedral coordination sphere
which reduces the possibility of hyperconjugation [back-
donation of charge from pz(N) into σ*(Si–C)] thus leading
to an elongation of the Si–N bonds (average Si–N
172.2 pm).
Figure 4. Molecular structure and numbering scheme of
[Ph2Si(NH-CH2-2-Py)2] (6). The ellipsoids represent a probability
of 40%. Selected bond lengths [pm]: Si–N1 170.8(2), Si–N3
170.2(2), Si–C13 186.8(2), Si–C19 186.5(2), N1–C1 145.5(2), N3–
C7 145.3(2); angles [°]: N1–Si–N3 113.59(9), N1–Si–C13 110.03(8),
N1–Si–C19 104.59(9), N3–Si–C13 106.37(9), N3–Si–C19 111.54(8),
C13–Si–C19 110.80(8), Si–N1–C1 124.2(2), Si–N3–C7 122.5(2),
N1–C1–C2 115.0(2), N3–C7–C8 115.1(2).
Magnetic Properties
Whereas the magnetic properties of 2 and 4 were dis-
Figure 5 shows the molecular structure of 7. The bis(2- cussed earlier[39] the iron atoms in complex 7 show an ar-
pyridylmethylamido)diphenylsilane ligands are distin- rangement as an isosceles triangle. Magnetic susceptibility
guished by the letters “A“ and “B“. The iron atom Fe1 is measurements were performed in the temperature range
in a distorted tetrahedral environment whereas the pentaco- from 300 K to 2 K for the trinuclear complex 7 using a
ordinate Fe2 and Fe3 atoms display distorted trigonal bipy- Quantum design MPMSR-5S-SQUID magnetometer. Fig-
ramidal coordination spheres. The Cl1–Fe2–N3A and Cl2– ure 6 displays the thermal dependence of the χMT product
Fe3–N3B angles show values of 151.7(1)° and 152.6(1)°, (with χM being the molar susceptibility and T the tempera-
respectively. Due to the coordination number of five for Fe2 ture) at 0.2 T. The room temperature value is with
and Fe3, an elongation of the Fe–Cl bonds (average 5.32 cm3 Kmol–1 significantly lower than the expected one
237.2 pm) is observed in comparison to 2. For the same for three non-interacting S = 2 centers (9.00 cm3 Kmol–1
reason, the Fe1–N distances are significantly smaller than for g = 2). Upon cooling the χMT product decreases further
the Fe2–N and Fe3–N values of the pentacoordinate to reach a plateau at 60 K with an average value of χMT =
iron(II) atoms. The environment of Fe1 is comparable to 3.58 cm3 Kmol–1. This value is in the region expected for
Fe[N(SiMe2tBu)CH2Py]2,[21] however, in 3 the N–Fe–N an- one iron(II) center with considerable orbital momentum.
gle of the amido functions was widened [155.5(1)°] due to Below 25 K the χMT product decreases further, most likely
the bulky tert-butyldimethylsilyl groups. In 7 the N2A–Fe1– this can be attributed to zero-field splitting. The observed
N2B bond angle displays a value of 125.7(2)° due to a re- behaviour is typical for trinuclear systems with antiferro-
duced steric hindrance at the silyl fragments.
magnetic interactions.
Eur. J. Inorg. Chem. 2011, 1584–1592
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. Westerhausen et al.
FULL PAPER
Conclusions
Amides are strong σ- and π-donors and hence, reactive
metal-nitrogen bonds are formed with electron-rich late 3d
metals. 2-Pyridylmethylamides offer a variety of possible re-
action pathways such as deprotonation of the methylene
unit together with redox behaviour (see Scheme 1) finally
leading to 2-pyridylmethylidene amines (2-pyridylmethyl-
imines). N-Bound trialkylsilyl groups support this reaction
Scheme and mainly the redox potential of the metal atom
determines whether a dianion (L)2– (lithium, magnesium),
Figure 6. Plot of the χMT product (open circles) vs. T for com-
pound 7 at 0.2 T. The solid line represents the calculated tempera-
ture dependence with the model described in the text.
2–
a radical (Lox1)– or its dimer (Lox1
)
(zinc), or even an
2
electroneutral imine (Lox2)0 [iron(III)] is formed. Substitu-
tion of the silyl group by a diphenylphosphanyl moiety (1)
expands the reactivity pattern in the presence of iron(III).
In THF solution cleavage of P–N bonds and formation of
bis(2-pyridylmethylamido) diphenylphosphonium anions
(bound at FeII as in 2) are observed. This reaction is ac-
companied by oxidative THF degradation reactions leading
to oxygen-centered iron cages (with Fe4O fragments as in
4) and to (2-pyridylmethylamido) diphenylphosphane oxide
anions (bound at FeII as in 3). Addition of HCl to 3 yields
neutral (2-pyridylmethylamino)diphenylphosphane oxide in
The results from the X-ray structure analysis indicate
that the system is best described as isosceles triangle ABA
with J and JЈ as interaction parameters. Fe2 and Fe3 (A
and AЈ) are linked over two bridging nitrogen atoms (N3A
and N3B) with a Fe2···Fe3 distance of 281.79(9) pm and a
Fe–N–Fe angle of 82.4°. The Fe1–Fe2 (and Fe1–Fe3 with
Fe1 = B) interaction is mediated over the bridging nitrogen
atom N2A (N2B) with Fe1···Fe2 and Fe1···Fe3 distances of
321.6(2) and 306.7(2) pm, respectively, and a Fe–N–Fe
bond angle of 98.5°. For such trinuclear systems with anti-
ferromagnetic interactions it is not possible to align all local
spins antiparallel to each other as illustrated in Figure 7.
Therefore, the ratio ρ = JЈ/J (with J being the A–B interac-
tion parameter and JЈ corresponding to the A–A interac-
tion parameter) is of interest in order to distinguish be-
tween the possible interaction schemes given in Figure 7.
the vicinity of iron(II) (as a FeCl2 adduct as in 5). We were
2–
unable to isolate C–C coupled amides of the type (Lox1
)
2
or imines such as (Lox2)0. The silicon-based ligand isoelec-
tronic to the bis(2-pyridylmethylamido) diphenylphospho-
nium anion, namely bis(2-pyridylmethylamido) diphenylsi-
lane (6), expresses a straight-forward coordination behav-
iour and trinuclear 7 was obtained. Each iron center in this
trinuclear complex has four unpaired electrons. The antifer-
romagnetic coupling between two of these iron(II) atoms
(high spin 3d6 iron cations) leads to a spin-frustrated sys-
tem.
Experimental Section
General: All manipulations were carried out in an argon atmo-
sphere under anaerobic conditions. Prior to use, all solvents were
thoroughly dried and distilled in an argon atmosphere. The re-
ported iron complexes are moisture and air sensitive. DEI-mass
spectra were obtained on a Finnigan MAT SSQ 710 system (2,4-
dimethoxybenzyl alcohol as matrix), IR measurements were carried
out on a Perkin–Elmer System 2000 FT-IR. Starting [(thf)-
Fe{N(SiMe3)2}2Cl],[36,41] Py-CH2-N(H)-PPh2 (1),[28] and Py-C(Ph)-
Figure 7. Schematic representation of the possible interaction
schemes in an isosceles triangle in dependence of the ratio ρ = JЈ/
J.
For the determination of J and JЈ the data were analysed
assuming three interacting S = 2 spin centres with the Ham-
iltonian given as[40]
[42]
H-N(H)-PPh2 were prepared according to literature procedures.
(ClFe)2{Ph2P(N-CH2-2-Py)2}{μ-N(SiMe3)2} (2):
A solution of
H = –J(SA1SB + SA2SB) – JЈSA1SA2
0.33 g of Py-CH2-N(H)-PPh2 (1) (1.12 mmol) in 10 mL of THF
was added at room temp. to a solution of 0.59 g of [(thf)-
Fe{N(SiMe3)2}2Cl] (1.22 mmol). This reaction mixture was heated
under reflux for 6 h. After cooling to room temp. the volume of
the solution was reduced until crystal formation was observed. At
room temp. 0.11 g of pale yellow crystals of 2 (0.15 mmol, 25%)
precipitated which were washed with a few mL of THF and dried
in vacuo. Prolonged crystallization for several days at room temp.
also afforded crystals of [{2-Py-CH2-N-P(O)Ph2}FeCl] (3).
where the local spins are denoted SA1, SA2 and SB. The
resulting expression for the magnetic susceptibility is given
in the Supporting Information. A good agreement between
calculated and experimental data was obtained with the pa-
rameters J = –55.6Ϯ1.9 cm–1, JЈ = 6.0Ϯ0.4 cm–1, gA
=
3.12Ϯ0.03, and gB = 3.20Ϯ0.06. The strong A–B antifer-
romagnetic interaction polarizes SA1 and SA2 ferromag-
netically (case 1 in Figure 7). As each iron center has four
unpaired electrons the determination of the exact interac-
tion path between the iron centers is difficult.
Physical Data of 2: M.p. 175 °C. IR (Nujol, KBr windows): ν =
˜
1606 (m), 1569 (w), 1483 (m), 1437 (m), 1287 (m), 1246 (m), 1145
(s), 1112 (m), 1065 (w), 1050 (w), 1019 (w), 943 (m), 871 (s), 846
1590
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Eur. J. Inorg. Chem. 2011, 1584–1592

Reactions of Iron-Based Metalation Reagents
(m br), 757 (m), 720 (m), 699 (m), 674 (w), 650 (w), 599 (w), 567 LiCl) was removed by filtration. All volatile materials were re-
(m), 537 (m), 512 (m), 488 (w). MS (DE): m/z (%) = 488 (10) [{(Py-
CH2N)2PPh2}FeCl]+, 452 (5) [{(Py-CH2N)2PPh2}Fe]+, 161 (50) remaining brown oil solidified slowly within several days; yield
[HN(SiMe3)2]+, 146 (97) [HNSi2Me5]+, 130 (100) [HNSi2Me4]+. 86%; m.p. 87 °C. IR (Nujol, KBr windows): ν = 3390 (s), 3046 (m),
moved from the filtrate by distillation under reduced pressure. The
˜
C34H48Cl2Fe2N5OPSi2 (812.52): calcd. C 50.26, H 5.95, N 8.62;
found C 49.88, H . 5.78, N 8.96.
2926 (vs), 2676 (vw), 1968 (vw), 1908 (vw), 1591 (s), 1567 (m), 1467
(vs), 1427 (vs), 1397 (vs), 1343 (m), 1219 (m), 1185 (vw), 1119 (vs),
1079 (s), 1046 (m), 993 (m), 961 (w), 889 (w), 850 (vs), 786 (s), 758
(vs), 745 (vs), 726 (s), 701 (vs), 680 (w), 620 (vw), 594 (m), 535 (s),
[{(Ph2PN-CH2-2-Py)Fe}4(μ-Cl)2(μ4-O)] (4): A solution of 0.38 g of
Py-CH2-N(H)-PPh2 (1) (1.30 mmol) in 10 mL of THF was dropped
at room temp. into a solution of 0.62 g of [(thf)Fe{N(SiMe3)2}2Cl]
(1.30 mmol). Thereafter, stirring was continued for 43 h. Then the
volume of the solution was reduced to 5 mL in vacuo. This solution
was stored at room temp. and after a few days, dark red, octahe-
dron-shaped crystals of 4 precipitated. After collection of these
crystals the mother liquor was stored at room temp. and colorless
needles of [{2-Py-CH2-N-P(O)Ph2}FeCl] (3) formed. Yield of sin-
gle-crystalline 4: 0.08 g (0.06 mmol, 18%); m.p. 180 °C. IR (Nujol,
1
500 (s), 464 (m). H NMR (200 MHz, [D6]benzene): δ = 4.20 (d, 4
H, CH2), 6.53 (m, 2 H, Pyr2), 6.77 (d, 2 H, Pyr4), 6.93 (dt, 2 H,
Pyr3), 7.03–7.15 (m, Ph), 7.67–7.76 (m, Ph), 8.37–8.41 (m, Pyr1)
ppm. 13C{1H} NMR (50 MHz, [D6]benzene): δ = 47.2 (CH2), 120.9
(Pyr2), 121.1 (Pyr4), 128.0 (Ph), 129.5 (Ph), 135.0 (Pyr3), 135.6
(Ph), 136.9 (Ph), 149.1 (Pyr1), 162.3 (Pyr5) ppm. MS (EI): m/z (%)
= 397 (5) [M+], 319 (100) [M – C6H6]+; 289 (100) [M –
C6H7N2]+; 260 (23); 211 (289 – C6H6, 100); 182 (50) [M – 2 Pyrid-
yl]+; 167 (20); 135 (80); 107 (100); 93 (80); 80 ([C5H6N]+, 90).
C24H24N4Si (396.56): calcd. C 72.68, H 6.10, N 14.13; found C
71.53, H . 6.29, N 13.50.
KBr windows): ν = 3086 (w), 1568 (w), 1435 (m), 1282 (w), 1125
˜
1097, 1048 (m), 907 (s), 820 (w), 744 (s), 696 (s), 641 (m), 563 (m),
508 (w). MS (DE): m/z (%) = 797 (Ͻ1) [{Py-CH2NPOPh2}-
Fe2Cl2]+, 760 (Ͻ1) [{Py-CH2NPOPh2}Fe2Cl]+, 670 (1) [{Py-
CH2NPOPh2}Fe]+, 578 (Ͻ1) [{Py-CH2NPOPh2}Fe{NPOPh2}]+,
292 (56) [{Py-CH2N(H)PPh2}Fe2Cl2]+, 200 (100) [HNPPh2]+, 107
([Py-CH2NH]+, 100). C80H80Cl2Fe4N8O3P4 (1619.72): calcd. C
59.32, H 4.98, N 6.92; found C 56.70, H . 5.36, N 6.89.
[Cl2Fe3{Ph2Si(N-CH2-2-Py)2}2] (7): A 1.6 m solution of nBuLi in
hexane (1.6 mL, 2.56 mmol) was dropped at –78 °C into a solution
of 0.50 g of 6 (1.23 mmol) in 10 mL of THF. This violet solution
was added to
a suspension of 0.24 g of anhydrous FeCl2
(1.88 mmol) in 10 mL of THF. This solution was warmed to room
temp., filtered and the volume of the solution reduced to half of
the original volume. Storage at room temp. leads to the formation
of 0.39 g of dark brown rod-shaped crystals of 7 (0.38 mmol, 60%);
Physical Data of [{2-Py-CH2-N-P(O)Ph2}FeCl]2 (3): IR (Nujol,
KBr windows): ν = 1605 (s), 1568 (m), 1482 (m), 1438 (s), 1359
˜
(m), 1285 (m), 1258 (w), 1216 (w), 1153 (m), 1127 (vs), 1059 (s),
1021 (m), 998 (m), 944 (s), 834 (m), 767 (m), 726 (vs), 701 (s), 650
(m), 626 (m), 576 (s), 536 (s). MS (DE): m/z (%) = 796 (Ͻ1) [{Py-
CH2NPOPh2}Fe2Cl2]+, 760 (34) [{Py-CH2NPOPh2}Fe2Cl]+, 670
(22) [{Py-CH2NPOPh2}Fe]+, 363 (3) [{Py-CH2NPOPh2}Fe]+, 306
(3) [Py-CHNPOPh2]+, 201 (100) [OPPh2]+, 107 (24) [Py-CH2NH]
+, 44 (100). C36H32Cl2Fe2N4O2P2 (797.21): calcd. C 54.10, H 4.29,
N 7.01; found C 54.46, H . 4.30, N 6.84.
m.p. 215 °C. IR (Nujol, KBr windows): ν = 3042 (m), 1602 (w),
˜
1565 (w), 1427 (s), 1280 (w), 1150 (w), 1113 (s), 1083 (vs), 1048
(m), 802 (s), 762 (m), 738 (m), 701 (s), 608 (w), 540 (m), 504 (m).
MS (DE): m/z (%) = 486 (4) [Ph2Si{NCH2Py}2FeCl]+, 448 (10)
[Ph2Si{NCH2Py}2FeCl]+, 319 (25) [PhSi{NCH2Py}2]+, 289 (100)
[Ph2Si{NCH2Py}]+, 198 (35) [ClFeNHCH2Py]+, 181 (15) [SiPh2]+,
137 (15) [Py-CH2 – NHSiH2]+, 108 (100) [Py-CH2–NH2]+, 79
([Py]+, 85). C48H44Cl2Fe3N8Si2 (1027.52): calcd. C 56.10, H 4.32,
N 10.91; found C 55.42, H . 4.58, N 10.43.
[{2-Py-CH2-N(H)-P(O)Ph2}FeCl2] (5): A 1.6 m solution of nBuLi
in hexane (1.7 mL, 1.12 mmol) was dropped into a cooled solution
(–78 °C) of 0.34 g of 1 (1.15 mmol) in 10 mL of THF. At –78 °C
this red solution was added to a suspension of 0.19 g of FeCl3 in
10 mL of THF. Thereafter the reaction mixture was warmed to
room temp. and stirred for 24 h. Then all volatile materials were
removed in vacuo. The dried residue was dissolved in 20 mL of
CH2Cl2 and solid materials removed by filtration. At room temp.
0.05 g of colorless needles of 5 (0.11 mmol, 9%) formed; m.p.
X-ray Structure Determinations: The intensity data for the com-
pounds were collected on a Nonius KappaCCD diffractometer
using graphite-monochromated Mo-Kα radiation. Data was cor-
rected for Lorentz and polarization effects but not for absorption
effects.[43,44] The structures were solved by direct methods
(SHELXS[45]) and refined by full-matrix least-squares techniques
2
against Fo (SHELXL-97[45]). The hydrogen atoms for the amine
groups compound 5 and 6 were located by difference Fourier syn-
thesis and refined isotropically.[45] All other hydrogen atoms were
included at calculated positions with fixed thermal parameters. All
non-hydrogen atoms were refined anisotropically.[45] Crystallo-
graphic data as well as structure solution and refinement details
are summarized in Table 1. XP (SIEMENS Analytical X-ray In-
struments, Inc.) was used for structure representations.
219 °C. IR (Nujol, KBr windows): ν = 3220 (s), 1604 (m), 1589
˜
(w), 1571 (w), 1480 (m), 1439 (s), 1309 (m), 1203 (w), 1143 (s), 1129
(m), 1099 (m), 1083 (m), 1069 (m), 1023 (w br), 996 (w), 976 (w),
968 (w), 889 (w), 860 (m), 762 (m), 729 (s), 698 (m), 608 (m), 564
(m), 519 (s). MS (DE): m/z (%)
=
398 (4) [{Py-
CH2NHPOPh2}FeCl]+, 362 (2) [{Py-CH2NHPOPh2}Fe]+, 308 (4)
[Py-CH2NHPOPh2]+, 201 (48) [OPPh2]+, 107 ([Py-CH2NH]+, 100).
C18H17Cl2FeN2OP (435.07): calcd. C 49.62, H 3.94, N 6.44; found
C 47.33, H . 4.15, N 6.68.
CCDC-798041 (for 2), -798042 (for 4), -798043 (for 5), -798044 (for
6), and -798045 (for 7). Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [E-mail: deposit@ccdc.cam.ac.uk]. Supplementary mate-
rial regarding the magnetic properties is also available.
Ph2Si(NH-CH2-2-Py)2 (6): A solution of 1.5 mL of 2-pyridylmeth-
ylamine (14.4 mmol, 1.56 g) in 10 mL of toluene was cooled to
–78 °C. Thereafter 9 mL of a 1.6 m nBuLi solution in hexane
(14.4 mmol) were added dropwise. The solution turned violet. This
solution was added very slowly at –78 °C to a pre-cooled solution
of 1.5 mL dichloro-diphenylsilane (7.2 mmol, 1.82 g) in 5 mL of
toluene. (Attention: Addition of the dichlorodiphenylsilane solu-
tion to the violet lithium 2-pyridylmethylamide solution lowered
the yield significantly). After complete addition, the reaction mix-
ture was slowly warmed to room temp. The precipitate (mainly
Supporting Information (see footnote on the first page of this arti-
cle): Derivation of the equation for the magnetic susceptibility.
Acknowledgments
We thank the Deutsche Forschungsgemeinschaft (DFG) for gener-
ous financial support. A. M. is thankful to the Carl-Zeiss-Stiftung
Eur. J. Inorg. Chem. 2011, 1584–1592
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. Westerhausen et al.
FULL PAPER
[21] V. G. Gibson, R. K. O’Reilly, D. F. Wass, A. J. P. White, D. J.
Williams, Dalton Trans. 2003, 2824–2830.
[22] C. J. Davies, G. A. Solan, J. Fawcett, Polyhedron 2004, 23,
3105–3114.
(Stuttgart, Germany) for a Ph. D. stipend. The authors also
acknowledge the help of Mrs. C. Felbel and Prof. Dr. W. Plass.
[23] A. Malassa, C. Agthe, H. Görls, M. Friedrich, M. Westerhau-
sen, J. Organomet.-Chem. 2010, 695, 1641–1650.
[24] B. A. Frazier, P. T. Wolczanski, E. B. Lobkovsky, T. R. Cund-
ari, J. Am. Chem. Soc. 2009, 131, 3428–3429.
[25] M. Westerhausen, A. N. Kneifel, Inorg. Chem. Commun. 2004,
7, 763–766.
[26] C. Tejel, M. A. Ciriano, M. P. del Río, F. J. van den Bruele,
D. G. H. Hetterscheid, N. T. i Spithas, B. de Bruin, J. Am.
Chem. Soc. 2008, 130, 5844–5845.
[27] a) S. Thewissen, M. D. M. Reijnders, J. M. M. Smits, B.
de Bruin, Organometallics 2005, 24, 5964–5972; b) C. Tejel,
M. A. Ciriano, M. P. del Río, D. G. H. Hetterscheid, N. T.
i Spithas, J. M. M. Smits, B. de Bruin, Chem. Eur. J. 2008, 14,
10932–10936; c) C. Tejel, M. P. del Río, M. A. Ciriano, E. J.
Reijerse, F. Hartl, S. Zálisˇ, D. G. H. Hetterscheid, N. T.
i Spithas, B. de Bruin, Chem. Eur. J. 2009, 15, 11878–11889.
[28] D. Olbert, A. Kalisch, H. Görls, I. M. Ondik, M. Reiher, M.
Westerhausen, Z. Anorg. Allg. Chem. 2009, 635, 462–470.
[29] M. M. Olmstead, P. P. Power, S. C. Shoner, Inorg. Chem. 1991,
30, 2547–2551.
[30] F. A. Cotton, L. M. Daniels, L. R. Falvello, J. H. Matonic,
C. A. Murillo, X. Wang, H. Zhou, Inorg. Chim. Acta 1997, 266,
91–102.
[31] F. A. Cotton, L. M. Daniels, G. T. Jordan, C. A. Murillo, I.
Pascual, Inorg. Chim. Acta 2000, 297, 6–10.
[1]
a) D. M. Roundhill, Chem. Rev. 1992, 92, 1–27; b) W. Kaim,
B. Schwederski: Bioinorganic Chemistry: Inorganic Elements in
the Chemistry of Life, Wiley: Chichester, 1994; c) R. H. Holm,
P. Kennepohl, E. I. Solomon, Chem. Rev. 1996, 96, 2239–2314;
d) J. J. R. Fraústo da Silva, R. J. P. Williams: The Biological
Chemistry of the Elements, 2nd ed., Oxford University Press,
Oxford, 2001; e) T. A. Jackson, L. Que, in: Concepts and Mod-
els in Bioinorganic Chemistry (Eds.: H.-B. Kraatz, N. Metzler-
Nolte), Wiley-VCH, Weinheim, 2006, p. 259–286.
a) Y. Okamoto, K. Ogura, T. Kinoshita, Polyhedron 1984, 3,
635–638; b) K. Ogura, Y. Kurasawa, Y. Yamaguchi, Y. Okam-
oto, Heterocycles 2003, 59, 283–291.
K. Chen, M. Costas, L. Que, J. Chem. Soc., Dalton Trans. 2002,
672–679.
[2]
[3]
[4]
[5]
A. L. Gavrilova, B. Bosnich, Chem. Rev. 2004, 104, 349–383.
M. Costas, M. P. Mehn, M. P. Jensen, L. Que, Chem. Rev. 2004,
104, 939–986.
[6]
[7]
X. Shan, L. Que, J. Inorg. Biochem. 2006, 100, 421–433.
M. Ostermeier, C. Limberg, B. Ziemer, V. Karunakaran, An-
gew. Chem. 2007, 119, 5423–5426; Angew. Chem. Int. Ed. 2007,
46, 5329–5331.
K. Visvaganesan, R. Mayilmurugan, E. Suresh, M. Palanian-
davar, Inorg. Chem. 2007, 46, 10294–10306.
M. Westerhausen, T. Bollwein, N. Makropoulos, S. Schnei-
derbauer, M. Suter, H. Nöth, P. Mayer, H. Piotrowski, K. Pol-
born, A. Pfitzner, Eur. J. Inorg. Chem. 2002, 389–404.
M. Westerhausen, A. N. Kneifel, N. Makropoulos, Inorg.
Chem. Commun. 2004, 7, 990–993.
[8]
[9]
[32] A. Maercker, Angew. Chem. 1987, 99, 1002–1019; Angew.
Chem. Int. Ed. Engl. 1987, 26, 972–989.
[33] a) R. E. Mulvey, V. L. Blair, W. Clegg, A. R. Kennedy, J. Klett,
L. Russo, Nat. Chem. 2010, 2, 588–591; b) S. Krieck, H. Görls,
M. Westerhausen, J. Organomet. Chem. 2009, 694, 2204–2209;
c) J. Langer, S. Krieck, R. Fischer, H. Görls, D. Walther, M.
Westerhausen, Organometallics 2009, 28, 5814–5820; d) A. R.
Kennedy, J. Klett, R. E. Mulvey, D. S. Wright, Science 2009,
326, 706–708; e) M. Gärtner, H. Görls, M. Westerhausen, J.
Organomet. Chem. 2008, 693, 221–227; f) M. Gärtner, H.
Görls, M. Westerhausen, Synthesis 2007, 725–730.
[34] X. Guo, S. Pan, J. Liu, Z. Li, J. Org. Chem. 2009, 74, 8848–
8851.
[35] E. Bartmann, J. Organomet. Chem. 1985, 284, 149–158.
[36] J. Zeller, S. König, U. Radius, Inorg. Chim. Acta 2004, 357,
1813–1821.
[37] M. T. Hay, B. J. Hainaut, S. J. Geib, Inorg. Chem. Commun.
2003, 6, 431–434.
[10]
[11] M. Westerhausen, A. N. Kneifel, P. Mayer, Z. Anorg. Allg.
Chem. 2006, 632, 634–638.
[12] a) J. T. B. H. Jastrzebski, J. M. Klerks, G. van Koten, K. Vrieze,
J. Organomet. Chem. 1981, 210, C49–C53; b) G. van Koten,
J. T. B. H. Jastrzebski, K. Vrieze, J. Organomet. Chem. 1983,
250, 49–61; c) E. Wissing, S. van der Linden, E. Rijnberg, J.
Boersma, W. J. J. Smeets, A. L. Spek, G. van Koten, Organome-
tallics 1994, 13, 2602–2608.
[13] M. Westerhausen, T. Bollwein, N. Makropoulos, T. M. Rotter,
T. Habereder, M. Suter, H. Nöth, Eur. J. Inorg. Chem. 2001,
851–857.
[14] M. Westerhausen, T. Bollwein, P. Mayer, H. Piotrowski, A.
Pfitzner, Z. Anorg. Allg. Chem. 2002, 628, 1425–1432.
[15] C. C. Lu, E. Bill, T. Weyhermüller, E. Bothe, K. Wieghardt, J.
Am. Chem. Soc. 2008, 130, 3181–3197.
[38] R. Vollmerhaus, R. Tomaszewski, P. Shao, N. J. Taylor, K. J.
Wiacek, S. P. Lewis, A. Al-Humydi, S. Collins, Organometallics
2005, 24, 494–507.
[16] a) G. Chen, Y.-X. Sun, M. Sun, W. Qi, Acta Crystallogr., Sect.
E 2004, 60, m1547–m1549; b) K. W. Törnroos, D. Chernyshov,
M. Hostettler, H.-B. Bürgi, Acta Crystallogr., Sect. C 2005, 61,
m450–m452.
[39] M. Podewitz, C. Herrmann, A. Malassa, M. Westerhausen, M.
Reiher, Chem. Phys. Lett. 2008, 451, 301–308.
[40] O. Kahn, Molecular Magnetism, VCH, Weinheim, Germany,
1993.
[17] A. Malassa, H. Görls, A. Buchholz, W. Plass, M. Westerhau-
sen, Z. Anorg. Allg. Chem. 2006, 632, 2355–2362.
[18] a) D. C. Bradley, M. H. Chisholm, Acc. Chem. Res. 1976, 9,
273–280; b) M. F. Lappert, P. P. Power, A. R. Sanger, R. C. Sri-
vastava, Metal and Metalloid Amides: Syntheses, Structures,
and Physical and Chemical Properties, Ellis Horwood, Chiches-
ter, 1980, chapter 8, p. 465–544; c) M. Lappert, A. Protchenko,
P. Power, A. Seeber, Metal Amide Chemistry, Wiley, Chichester,
2009, chapter 6, p. 149–204.
[19] N. Y. M. Iha, M. A. de Almeida Azzelini, S. Utsuno, Polyhe-
dron 1998, 17, 3379–3390.
[20] A. Malassa, N. Herzer, H. Görls, M. Westerhausen, Dalton
Trans. 2010, 39, 5356–5366.
[41] J. S. Duncan, T. M. Nazif, A. K. Verma, S. C. Lee, Inorg.
Chem. 2003, 42, 1211–1224.
[42] D. Olbert, H. Görls, D. Conrad, M. Westerhausen, Eur. J. In-
org. Chem. 2010, 1791–1797.
[43] COLLECT, Data Collection Software, Nonius B. V., The Ne-
therlands, 1998.
[44] Processing of X-ray Diffraction Data Collected in Oscillation
Mode: Z. Otwinowski, W. Minor, in: Methods in Enzymology
(Eds.: C. W. Carter, R. M. Sweet ), vol. 276, Macromolecular
Crystallography, part A, p. 307–326, Academic Press, 1997.
[45] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
Received: November 3, 2010
Published Online: February 15, 2011
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