Synthesis of heteroleptic iron(II) 2-pyridylmethylamides and 2-pyridylmethylideneamines via the reaction of [(thf)Fe{N(SiMe3) 2}2Cl] with (2-pyridylmethyl)(trialkylsilyl)amines

Article abstract of DOI:10.1039/b926723a

The deprotonation of (2-pyridylmethyl)(triorganylsilyl)amines of the type Py-CH₂-N(H)-SiR₃ with SiR₃ = SiMe ₂tBu (1a), SiMe₂(CMe₂iPr) (1b), SiiPr ₃ (1c) and SiPh₃ (1d) with (thf)Fe[N(SiMe ₃)₂]₂Cl in THF is accompanied by redox reactions and leads to the formation of iron(ii) compounds. The products with lower solubility precipitated first and are the pale yellow and paramagnetic complexes chloro-(2-pyridylmethyl)(triorganylsilyl)amido iron(ii) [SiR ₃ = SiMe₂tBu (2a), SiMe₂(CMe₂iPr) (2b), SiiPr₃ (2c), and SiPh₃ (2d)]. These complexes crystallized dimeric with Fe₂N₂ rings with different Fe-N bond lengths (average values of 211.1 and 203.2 pm). The Fe-Cl distances vary around an average value of 225.6 pm. Another isolated product consists of orange to blue crystals of dichloro-(2-pyridylmethylidene)(triorganylsilyl)amino iron(ii) [SiR₃ = SiMe₂tBu (3a), SiMe₂(CMe ₂iPr) (3b), SiiPr₃ (3c), and SiPh₃ (3d)] which are obtained from very concentrated reaction solutions. These (2-pyridylmethylidene)(triorganylsilyl)amino ligands (imines) act as bidentate bases at FeCl₂ with average Fe-N and Fe-Cl bond lengths of 211.8 and 223.5 pm, respectively. The metallation of the (2-pyridylmethyl) (triorganylsilyl)amines with dimeric Fe[N(SiMe₃)₂] ₂ yields homoleptic iron(ii) bis[(2-pyridylmethyl)(triorganylsilyl) amides] (4) with distorted tetrahedrally coordinated iron centers. Metathesis reactions of FeCl₃ with lithium (2-pyridylmethyl)(triorganylsilyl) amide as well as employing a mixture of Fe[N(SiMe₃)₂] ₂ and FeCl₃ with (2-pyridylmethyl)(triorganylsilyl)amine give similar results and the formation of chloro-(2-pyridylmethyl) (triorganylsilyl)amido iron(ii) (2) and dichloro-(2-pyridylmethylidene) (triorganylsilyl)amino iron(ii) (3) are observed.

Full text of DOI:10.1039/b926723a

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www.rsc.org/dalton | Dalton Transactions
Synthesis of heteroleptic iron(II) 2-pyridylmethylamides and
2-pyridylmethylideneamines via the reaction of [(thf)Fe{N(SiMe3)2}2Cl] with
(2-pyridylmethyl)(trialkylsilyl)amines†
Astrid Malassa, Nicole Herzer, Helmar Go¨rls and Matthias Westerhausen*
Received 18th December 2009, Accepted 13th April 2010
First published as an Advance Article on the web 6th May 2010
DOI: 10.1039/b926723a
The deprotonation of (2-pyridylmethyl)(triorganylsilyl)amines of the type Py-CH2-N(H)-SiR3 with
SiR3 = SiMe2tBu (1a), SiMe2(CMe2iPr) (1b), SiiPr3 (1c) and SiPh3 (1d) with (thf)Fe[N(SiMe3)2]2Cl in
THF is accompanied by redox reactions and leads to the formation of iron(II) compounds. The
products with lower solubility precipitated first and are the pale yellow and paramagnetic complexes
chloro-(2-pyridylmethyl)(triorganylsilyl)amido iron(II) [SiR3 = SiMe2tBu (2a), SiMe2(CMe2iPr) (2b),
SiiPr3 (2c), and SiPh3 (2d)]. These complexes crystallized dimeric with Fe2N2 rings with different Fe–N
bond lengths (average values of 211.1 and 203.2 pm). The Fe–Cl distances vary around an average value
of 225.6 pm. Another isolated product consists of orange to blue crystals of
dichloro-(2-pyridylmethylidene)(triorganylsilyl)amino iron(II) [SiR3 = SiMe2tBu (3a), SiMe2(CMe2iPr)
(3b), SiiPr3 (3c), and SiPh3 (3d)] which are obtained from very concentrated reaction solutions. These
(2-pyridylmethylidene)(triorganylsilyl)amino ligands (imines) act as bidentate bases at FeCl2 with
average Fe–N and Fe–Cl bond lengths of 211.8 and 223.5 pm, respectively. The metallation of the
(2-pyridylmethyl)(triorganylsilyl)amines with dimeric Fe[N(SiMe3)2]2 yields homoleptic iron(II)
bis[(2-pyridylmethyl)(triorganylsilyl)amides] (4) with distorted tetrahedrally coordinated iron centers.
Metathesis reactions of FeCl3 with lithium (2-pyridylmethyl)(triorganylsilyl)amide as well as employing
a mixture of Fe[N(SiMe3)2]2 and FeCl3 with (2-pyridylmethyl)(triorganylsilyl)amine give similar results
and the formation of chloro-(2-pyridylmethyl)(triorganylsilyl)amido iron(II) (2) and
dichloro-(2-pyridylmethylidene)(triorganylsilyl)amino iron(II) (3) are observed.
Introduction
The amides of the late transition metals have attracted consid-
erable interest due to their application in chemical processes1
and as models in biomimetic studies.2 Oxidation reactions of
biological processes often are catalyzed by iron enzymes such
as lipoxygenases and methane monooxygenases.3 These non-
heme iron enzymes are able to oxidize unsaturated fatty acids
or methane with oxygen after activation of the appropriate
C–H bonds. The catalytic activity led to a large interest in
compounds with iron–nitrogen bonds and in many biomimetic
model complexes, substituted pyridine ligands are employed to
mimic the reactivity of these iron enzymes.4 Iron complexes
are known to oxidize hydrocarbons whereby the most reactive
compounds contain pyridylmethylamine fragments in the coordi-
nation sphere.5-8 Recently, Ostermeier et al.9 oxidized 1,4-bis(2-
pyridylmethyl)piperazine in the coordination sphere of FeCl3
(eqn (1)).
(1)
Wieghardt and coworkers10 reacted the imine (Lox2)0 with the
transition metal salts MIICl2 of Cr, Mn, Fe, Co, Ni, and Zn and
reduced these complexes with sodium in 1,2-dimethoxyethane,
(Lox2) being the imine [2-Py-CH N–C6H3iPr2]. This reduction
0
=
gave the complexes [MII(Lox1)2] (see Scheme 1). Cyclovoltammetric
investigations showed that this redox reaction is reversible. The
oxidation of these complexes with [Cp2FeIII]+ in THF yielded
[(thf)MII(Lox1)(Lox2)]+ (M = Cr, Mn, Fe, Co), [ZnII(Lox1)(Lox2)]+,
and [Ni(Lox2)2]+, respectively. In [FeII(Lox1)2] average Fe–N bond
lengths of 198.5 and 204.5 pm were observed to the amide and
the pyridyl bases. In [(thf)FeII(Lox1)(Lox2)]+ the Fe–N distances of
Institut fu¨r Anorganische und Analytische Chemie, Friedrich-Schiller-
Universita¨t Jena, August-Bebel-Str. 2, D-07743, Jena, Germany. E-mail:
m.we@uni-jena.de; Fax: +49 3641 948102
† CCDC reference numbers 676619–676626 and 736365–736366. For
crystallographic data in CIF or other electronic format see DOI:
10.1039/b926723a
198.9 and 200.4 pm are very much alike (Fe–O 206.0 pm).10
The radical anion (Lox1
-
)
has already been observed earlier
by van Koten and coworkers11 as alkylzinc adduct [RZn(Lox1)].
In the solid state this zinc complex crystallizes as a dimer,
5356 | Dalton Trans., 2010, 39, 5356–5366
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the coordinated bis(2-pyridylmethyl)amine molecules.18 Further-
more, various 2-pyridylmethylamine complexes of iron(II)19-21 and
iron(III)21 were prepared and structurally investigated. From these
amine complexes of iron halides, amide formation and liberation
of HX was not observed.
(3)
In contrast to these amine adducts of iron, dialkylamides of
the late transition metals Fe, Co, Ni, and Cu are not stable
because amides act as a two-electron s-donor and as a two-
electron p-donor which is only advantageous for electron-poor
early transition metals.22-24 A trialkylsilyl substituent at nitrogen
reduces the charge at the amide unit via backdonation from
the pz(N) lone pair into a s*(Si–C) bond and therefore, the
trialkylsilyl-substituted amides of iron are well-known.25,26
Scheme
2-pyridylmethylamides.
1
Deprotonation/protonation and redox equilibria of
namely bis(alkylzinc) 1,2-bis(2-pyridyl)-1,2-bis(alkylamido)-
ethane [(RZn)2(Lox12)]. Bis(amide) complexes (containing the
ligand (L)2-) are only stable with very electropositive metals such
as lithium12 (as [Li2(L)]8) and magnesium13 (as [(thf)Mg(L)]2);
the oxidation of [Li2(L)]8 with white phosphorous leads to the
formation of [Li2(Lox12)·Li(HL)] and Li3P7.14 In Scheme 1 the
reaction diagram shows the interconversion of the bisamide (L)2-
into (Lox2)0 which can also be prepared from an aldehyde and a
primary amine.
Metal-mediated oxidation of nitrogen-bound 2-pyridylmethyl
groups is restricted to less electropositive metals. Thus, zinc
complexes are able to initiate an oxidative C–C coupling reaction
at elevated temperatures according to eqn (2).13,15 In course of
this oxidation process of (2-pyridylmethyl)(trialkylsilyl)amides of
zinc (A) in the presence of dialkylzinc, zinc metal precipitates and
di(methylzinc) 1,2-di(2-pyridyl)-1,2-bis(trialkylsilylamido)ethane
(B) forms. Nobler metals such as tin(II) afford less drastic reaction
conditions in order to enable this oxidative C–C coupling reaction.
In the presence of air, 2-pyridylmethylamine can be oxidized by
cobalt(II) yielding 2,3,5,6-tetra(2-pyridyl)pyrazine.16,17
On the one hand, these investigations showed that the
bis(trimethylsilyl)amido group reacts as a metallating func-
tionality in contrast to the chloride anion. On the other
hand, the presence of chloro ligands allowed the synthesis of
heteroleptic amido iron(II) chlorides which can be modified
thereafter. In order to investigate oxidative C–C coupling
reactions similar to Scheme 1, iron(III) compounds were re-
acted with (2-pyridylmethyl)(trialkylsilyl)amines. However, in
27
Fe[N(SiMe3)2]3 the metal center is shielded quite effectively by
three bulky bis(trimethylsilyl)amido ligands. Therefore, (thf)Fe-
[N(SiMe3)2]2Cl,28,29 a mixture of FeCl3 and [Fe{N(SiMe3)2}2]2, and
the use of FeCl3 after lithiation of the amine were employed for
these investigations regarding the influence of the bulkiness of
the N-bound trialkylsilyl groups of 2-pyridylmethylamine on the
reactivity.
Results and discussion
(2-Pyridylmethyl)(trialkylsilyl)amines of the type Py-CH2-N(H)-
SiR3 (SiR3 = SiMe2tBu (1a),15 SiMe2(CMe2iPr) (1b), SiiPr3 (1c),13
and SiPh3 (1d)) were deprotonated with (thf)Fe[N(SiMe3)2]2Cl
and metallated [leading to the amide ligands (HL)- of 2]
0
or oxidized [yielding imine ligands (Lox2
)
of 3] as shown in
eqn (4). The pale yellow complexes chloro-(2-pyridylmethyl)-
(trialkylsilyl)amidoiron(II) [SiR3 SiMe2tBu (2a), SiMe2-
(CMe2iPr) (2b), SiiPr3 (2c), and SiPh3 (2d)] precipitated with yields
between 16% (2c) and 42% (2a). These compounds are paramag-
netic with high-spin iron atoms which show an antiferromagnetic
coupling.
=
(2)
Iron(II) chloride complexes react with air as shown in eqn (3)
via insertion of oxygen between the iron atoms of C raising the
oxidation state from iron(II) to iron(III) in D without oxidation of
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The intermediate of the reaction of homoleptic iron(II) bis[(2-
pyridylmethyl)(trialkylsilyl)amides] 4 with FeCl3 could be a mixed
valent, dinuclear coordination compound G which contains
iron(II) as well as iron(III) (eqn (6)). An additional chloro ligand
ensures electro-neutrality. This intermediate could also resemble
the intermediate in the other reaction sequences described in
eqn (6).
(4)
During this metallation reaction, the iron(III) atoms were
reduced to iron(II), elemental iron was not observed. The expected
coupling product 1,2-dipyridyl-1,2-bis(trialkylsilylamino)ethane
was neither detected in the mass spectrometric investigations nor
after common work-up procedures. In addition, the formation
of tetrakis(trimethylsilyl)hydrazine could be excluded as well.
However, the use of the silyl groups SiMe2tBu, SiMe2(CMe2iPr),
SiiPr3, and SiPh3 led to the crystallization of red by-products which
were identified as the (2-pyridylmethylidene)(triorganylsilyl)amine
adducts of FeCl2 (3a, 3b, 3c and 3d).
(2-Pyridylmethyl)(tert-butyldimethylsilyl)amido groups stabi-
lize iron(II). In contrast to the stability of Fe[N(SiMe3)2]3 no deriva-
tives of iron(III) were obtained for these 2-pyridylmethylamido
ligands. Furthermore, the zinc(II) complexes were able to induce
an oxidative C–C coupling of these ligands with formation of
zinc metal as shown in eqn (2). Oxidative C–C coupling reactions
of the (2-pyridylmethyl)(trialkylsilyl)amido moieties were neither
observed from the redox reactions of the iron(III) complexes nor
from the metathesis reactions of the iron(II) species. However,
iron(III) was reduced to iron(II). In order to test the influence
of the bis(trimethylsilyl)amido groups, the metathesis reaction of
FeCl3 with LiN(SiR3)CH2Py was investigated. This reaction also
led to a reduction of Fe3+ and iron(II) complexes 2a and 2d as well
as 3b and 3c were isolated.
From a mixture of [Fe{N(SiMe3)2}2]2 and (2-pyridylmethyl)-
(trialkylsilyl)amine the homoleptic complexes 4a to 4d were
prepared (eqn (5)).26 Addition of FeCl3 (1 : 1 ratio of Fe2+ : Fe3+) to
this solution led to the formation of the imino complexes 3a to 3d
and to the amido complexes 2a to 2d of iron(II) (eqn (5)). Besides
compounds 2 and 3, the well-known (thf)6Fe4Cl830 was also found.
However, no iron(III) compounds were observed in this reaction;
iron(III) was reduced to iron(II) and the amine was oxidized to the
imino ligand yielding complexes 3a to 3d.
(6)
Deprotonation of the methylene moiety can be achieved
by strong bases. Lithiation and magnesiation of 2-
pyridylmethylamides lead to dianions of the type (L)2-12,13
which can be characterized by X-ray crystallography because
these metal cations are non-redox active. A similar metallation
reaction of [Fe{N(SiMe3)2}2]2 and (thf)Fe[N(SiMe3)2]2Cl or
of iron(II) bis[(2-pyridylmethyl)(trialkylsilyl)amides] 4 in the
presence of iron(III) would initiate an immediate redox reaction
yielding the imine complexes 3a to 3d.
Molecular structures
The molecular structure of (2-pyridylmethyl)(triphenylsilyl)amine
(1d) is displayed in Fig. 1. The hydrogen atom H1 at N1 was
refined isotropically and a N1–H1 bond length of 84(2) pm was
observed. This N1 atom lies in a nearly planar environment with
an angle sum of 351◦. The N1–Si bond length of 171.4(2) pm is
rather short. This shortening is a consequence of a larger s-orbital
participation in the amine 1d due to a sp2 hybridized N1 atom. The
N1–C1 distance of 145.9(3) pm resembles a characteristic single
bond.
The molecular structures of 2a to 2d are very sim-
ilar (Table 1) and therefore, only the structures of (2-
pyridylmethyl)(tert-butyldimethylsilyl)amido iron(II) chloride (2a)
and (2-pyridylmethyl)(triphenylsilyl)amido iron(II) chloride (2d)
are shown in Fig. 2 and 3, respectively, as representative examples.
The central four-membered Fe2N2 rings of 2a, 2b, and 2d contain
crystallographic inversion centers and consequently, these rings
are strictly planar and the symmetry-equivalent groups are on dif-
ferent sides of the Fe2N2 plane (trans-annular trans arrangement).
The iron and amide nitrogen atoms show distorted tetrahedral
environments. However, due to ring strain the endocyclic bond
angles at iron display very small values (N1–Fe–N2 81.8(1)◦,
N2–Fe–N2A 95.9(1)◦). The Fe–N2 and Fe–N2A bond lengths
differ significantly. The Fe–N2 bond lengths are larger than
the Fe–N2A values because the Fe–N2 values resemble bonds
with ring strain due to annelated four- and five-membered rings
whereas Fe–N2A bonds are only a bond of a four-membered cycle.
(5)
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Fig.
1 Molecular structure and numbering scheme of (2-pyridyl-
methyl)(triphenylsilyl)amine (1d). The ellipsoids represent a probability of
40%. Hydrogen atoms with the exception of the NH moiety are neglected
for clarity reasons. Selected bond lengths (pm): Si–N1 171.4(2), Si–C7
188.3(2), Si–C13 186.8(2), Si–C19 187.0(2), N1–C1 145.9(3), N1–H1 84(2),
C1–C2 150.9(3), N2–C2 133.8(3), N2–C6 134.2(3); selected angles (◦):
Si–N1–C1 125.0(1), C1–N1–H1 111(2), Si–N1–H1 115(2), N1–C1–C2
112.3(2).
Fig.
2
Molecular structure and numbering scheme of chloro-
(2-pyridylmethyl)(tert-butyldimethylsilyl)amidoiron(II) (2a). The ellip-
soids represent a probability of 40%. H atoms are not shown due to clarity
reasons. Symmetry-related atoms (-x + 2, -y + 1, -z) are marked with
“A”. Selected structural data are given in Table 1.
Table 1 Selected structural data of heteroleptic [ClFe-N(SiR2R¢)-
(CH2Py)]2 (2a–d)
2a
2b
2c
2d
R
R¢
Fe–Cl
Fe–N2
Fe–N2A
Fe–N1
Si–N2
N2–C6
Me
tBu
Me
iPr
Ph
Ph
CMe2iPr
226.25(6)
211.1(2)
202.0(2)
208.2(2)
176.0(2)
148.7(2)
150.6(3)
275.20(6)
101.84(5)
134.06(5)
113.32(5)
81.91(7)
130.09(7)
96.49(7)
113.8(2)
iPr
225.27(8)
211.1(2)
201.8(2)
208.4(2)
175.4(2)
149.0(3)
150.9(4)
272.98(8)
102.09(7)
128.61(6)
117.03(6)
82.01(8)
127.91(9)
97.24(7)
113.5(2)
225.3(1)
210.9(2)
205.0(2)
207.8(2)
176.6(2)
148.9(4)
151.5(4)
275.43(7)
101.05(7)
131.55(7)
115.53(7)
82.44(9)
128.90(9)
96.92(9)
114.8(2)
225.7(1)
211.4(3)
203.9(3)
208.7(3)
174.1(3)
149.8(4)
150.3(5)
278.1(1)
101.2(1)
135.40(9)
113.34(9)
81.8(1)
130.5(1)
95.9(1)
113.7(3)
C5–C6
Fe ◊ ◊ ◊ FeA
Cl–Fe–N1
Cl–Fe–N2
Cl–Fe–N2A
N1–Fe–N2
N1–Fe–N2A
N2–Fe–N2a
N2–C6–C5
Increasing bulkiness of the trialkylsilyl groups leads to enhanced
non-bonding transannular Fe ◊ ◊ ◊ FeA contacts.
Furthermore, the N2–C6 distances of the dimeric (2-
pyridylmethyl)(trialkylsilyl)amido iron(II) chlorides with an aver-
age value of 149.1 pm are significantly larger than the correspond-
ing value of 1d (145.9(3) pm). The Si–N2 bond lengths of 175.5
pm (av. value) are also larger due to the coordination number of
four which suggests a sp3 hybridization of N2 and consequently a
reduced s-orbital participation in the bonds.
Fig.
3
Molecular structure and numbering scheme of chloro-
(2-pyridylmethyl)(triphenylsilyl)amidoiron(II) (2d). The ellipsoids repre-
sent a probability of 40%. H atoms are omitted for clarity reasons.
Symmetry-related atoms (-x + 3/2, -y + 1/2, -z) are marked with “A”.
Selected structural data are summarized in Table 1.
Selected structural parameters of the monomeric (2-
pyridylmethylidene)(trialkylsilyl)amine complexes of FeCl2 (3a to
3c) as well as of dimeric 3d are summarized in Table 2. As a
representative example of a monomeric derivative 3a is shown in
Fig. 4. The iron atoms are in a distorted tetrahedral environment
with average Fe–Cl distances of 223.45 pm which is a slightly
smaller value than observed for 2. The Fe–N2 bond lengths are
slightly larger than in 2 due to the reduced electrostatic attraction
in 3.
The imino ligand contains a planar coordinated N2 atom with a
=
N2 C6 double bond (av. value 127.6 pm). However, there is nearly
no interaction with the p-system of the pyridyl unit; the slight
shortening of this bond compared to 2 results from an enhanced
s-orbital contribution. Surprisingly, the N2–Si bond lengths are
rather large and show an average value of 179.9 pm (compare with
2: av. N2–Si 175.5 pm). This fact can be explained by reduced
electrostatic attraction due to the lack of anionic charge on the
ligand which also reduces the negative hyperconjugation from the
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Table 2 Selected structural data for the imine complexes 3 of the type
=
(2-Py-CH N-SiR2R¢)FeCl2. Complex 3d precipitates as a dimer whereas
3a–3c crystallize monomeric
3
3b
3c
3d
R
R¢
Fe–Cl1
Fe–Cl2
Fe–Cl1A
Fe–N2
Fe–N1
Si–N2
Me
tBu
223.12(9)
223.63(9)
—
Me
iPr
Ph
Ph
CMe2iPr
223.63(9)
223.37(9)
—
iPr
224.19(7)
222.78(7)
—
213.0(2)
210.9(2)
180.9(2)
127.5(3)
147.8(3)
79.227
105.54(5)
122.09(3)
113.98(5)
120.2(2)
111.4(1)
128.41(9)
121.6(2)
237.27(8)
226.40(8)
253.53(7)
221.7(2)
213.0(2)
178.9(2)
127.6(4)
147.2(4)
77.68(8)
106.91(7)
136.15(3)
91.77(6)
118.9(2)
110.5(2)
130.0(1)
121.9(2)
212.0(2)
210.9(2)
178.8(3)
127.6(4)
146.7(4)
78.82(9)
111.62(7)
121.67(4)
113.85(7)
123.4(2)
112.3(2)
124.1(1)
120.8(3)
213.9(2)
210.0(2)
180.0(2)
127.8(4)
147.7(4)
78.91(9)
114.56(7)
119.13(4)
124.4(2)
121.4(2)
111.8(2)
126.4(1)
120.7(3)
N2–C6
C5–C6
Fig.
5
Molecular structure and numbering scheme of dichloro-
(2-pyridylmethylidene)(triphenylsilyl)aminoiron(II) (3d). Symmetry-
related atoms (-x + 2, -y + 1, -z + 1) are marked with an apostrophe.
The ellipsoids represent a probability of 40%. H atoms are neglected
for clarity reasons. Selected structural data are summarized in Table 2.
Coordination sphere of Fe1 (◦): N1–Fe1–N2 77.68(8), N1–Fe1–Cl1
106.91(7), N1–Fe1–Cl2 116.57(7), N1–Fe1–Cl1A 94.20(6), N2–Fe1–Cl1
92.06(6), N2–Fe1–Cl2 91.77(6), N2–Fe1–Cl1A 170.98(6), Cl1–Fe1–Cl2
136.15(3), Cl1–Fe1–Cl1A 86.53(2), Cl2–Fe1–Cl1A 95.42(3).
N2–Fe–N1
N1–Fe–Cl1
Cl1–Fe–Cl2
Cl2–Fe–N2
Si–N2–C6
C6–N2–Fe
Fe–N2–Si
N2–C6–C5
Table 3 Comparison of selected structural data of iron(II) bis[2-
pyridylmethyl)(tert-butyldimethylsilyl)amide] 4a25 and iron(II) bis[2-
pyridylmethyl)(triphenylsilyl)amide] 4d
4a (R = SiMe2tBu)
4d (R = SiPh3)
Fe1–N1
Fe1–N2
Si1–N2
N2–C6
C6–C5
C5–N1
Si–C7
N2–Fe1–N1
N2A–Fe1–N1
N2–Fe1–N2A
N1–Fe–N1A
212.3(2)
196.1(2)
170.3(2)
145.3(2)
150.4(3)
133.8(2)
188.7(2)
82.21(6)
111.79(6)
155.5(1)
112.54(8)
211.2(2)
196.7(2)
168.8(2)
145.6(3)
150.7(4)
134.7(3)
189.0(3)
81.86(9)
122.30(9)
143.4(1)
102.7(1)
It is remarkable that the imino complexes 3a–c are monomeric
whereas 3d crystallizes as a dimer. This fact shows that the triph-
enylsilyl group induces smaller steric strain than the trialkylsilyl
groups which allows a larger coordination number at the iron
center. Similar structural parameters of the imino ligands in 3a–d
exclude strong electronic effects.
Molecular structure and numbering scheme of 4d is shown in
Fig. 6. The iron atom is in a distorted tetrahedral environment.
Selected structural parameters of this complex are compared with
those of 4a in order to detect the influence of steric hindrance
(Table 3).25 The bond lengths show nearly no dependency whether
SiMe2tBu or SiPh3 groups are attached to N2. The endocyclic
N1–Fe–N2 also show very similar values. However, all endocyclic
bond angles differ strongly because the triphenylsilyl substituents
are less bulky than the tert-butyldimethylsilyl groups. This fact
leads to a smaller N2–Fe–N2A angle whereas the N2A–Fe–N1
angle is widened by approximately 10◦. These distortions allow a
coplanar alignment of the pyridyl group and one of the silicon-
bound phenyl substituents.
Fig.
4 Molecular structure and numbering scheme of dichloro-
(2-pyridylmethylidene)(tert-butyldimethylsilyl)aminoiron(II) (3a). The
ellipsoids represent a probability of 40%. H atoms are neglected for clarity
reasons. Selected structural data are summarized in Table 2.
nitrogen lone pair into the s*(Si–C) bond. The larger N2–C6–C5
angles in 3 also lead to larger N1–Fe–N2 angles.
The molecular structure and numbering scheme of dimeric
dichloro-(2-pyridylmethylidene)(triphenylsilyl)aminoiron(II) (3d)
is shown in Fig. 5. The dimeric nature of this complex nearly does
not affect the imino ligand. However, the coordination sphere at
the penta-coordinate iron atom differs strongly from those of the
monomeric derivatives. In the trigonal bipyramidal environment
of iron the atoms N2 and Cl1A are arranged in axial positions (N2–
Fe–Cl1A 170.98(6)◦) whereas N1, Cl1 and Cl2 form the trigonal
plane. Due to the trans arrangement of the atoms N2 and Cl1A
and due to the high spin state of the iron center the Fe–N2 as
well as Fe–Cl1A bonds are elongated. A detailed discussion of
a bonding situation in comparable iron complexes regarding the
trigonal bipyramidal as well as the square pyramidal coordination
sphere at iron can be found elsewhere.32
The aggregation degree strongly depends on the bulkiness of the
N-bound substituent. Gibson et al.31 already found monomeric
5360 | Dalton Trans., 2010, 39, 5356–5366
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(trialkylsilyl)amide also allow the preparation of 2. In addition,
the redox reaction of lithium (2-pyridylmethyl)(trialkylsilyl)amide
with FeCl3 yields the heteroleptic complexes 2a to 2d as well as 3a
to 3d.
A comparison of the structures with terminally iron-bound
=
2-pyridylmethylideneamines 2-Py-CH NR or their reduced
forms is shown in Table 4. The CN bond varies from a double
bond (average C N 127.5 pm) for the Lox2 type ligand, the reduced
=
(Lox1)- type with C–N values of 133.9 pm to a single bond for
the 2-pyridylmethylamides (HL- type) with C–N distances of
145.5 pm. Increasing negative charge on the nitrogen atoms leads
to a shortening of the Fe–N bonds. In addition, a lengthening of
the Fe–N bonds (which can either affect the bond to the imino or
the pyridyl groups) is also observed for dimeric complexes with
penta-coordinate metal atoms.
Fig.
6
Molecular structure and numbering scheme of iron(II)
Experimental
bis[(2-pyridylmethyl)(triphenylsilyl)amide] 4d. Symmetry-related atoms
(-x + 1/2, -y + 1/2, z) are marked with an “A”. The ellipsoids
represent a probability of 40%. Hydrogen atoms are not drawn for clarity
reasons. Selected bond lengths (pm): Fe1–N1 211.2(2), Fe1–N2 196.7(2),
Si1–N2 168.8(2), N1–C1 134.9(4), N1–C5 134.7(3), C1–C2 136.8(4),
C2–C3 138.4(5), C3–C4 137.7(4), C4–C5 138.4(4), C5–C6 150.7(4).
Angles (◦): N1–Fe1–N2 81.86(9), N1–Fe1–N1A 102.7(1), N1–Fe1–N2A
122.30(9), N2–Fe1–N2A 143.4(1), Fe1–N2–Si1 122.9(1), Fe1–N2–C6
113.4(2), Si1–N2–C6 123.7(2).
General procedure
All manipulations were carried out in an argon atmosphere
under anaerobic conditions. The compounds are moisture and
air sensitive. Prior to use, all solvents were thoroughly dried
and distilled in an argon atmosphere. (thf)Fe{N(SiMe3)2}Cl28,29
and the (2-pyridylmethyl)(trialkylsilyl)amines of the type Py-CH2-
N(H)-SiR3 with SiR3 = SiMe2tBu (1a)15 and SiiPr3 (1c)13 were
prepared according to literature procedures.
=
complexes of the type [Cl2Fe(2-Py¢-CH NR)] (Py¢ = 6-methyl-
(2-Pyridylmethyl)(1,1,2-trimethylpropyl-dimethylsilyl)amine (1b)
2-pyridyl) for ligands with nitrogen-bound cyclo-dodecyl groups.
Less bulky n-propyl and ortho-diisopropylphenyl substituents give
A 2.5 M n-BuLi solution in hexane (8.0 ml, 20 mmol) was dropped
into a solution of 2.2 g of 2-aminomethylpyridine (20 mmol) in
10 ml of THF. Chloro-1,1,2-trimethylpropyl-dimethylsilane (3.6 g,
20 mmol) dissolved in 10 ml of THF was added dropwise to this
mixture at -78 ◦C. Thereafter the solution was warmed to r.t.
and stirred for an additional 20 h. Then all volatile materials were
removed under reduced pressure and the residue was dissolved
in 10 ml of pentane. After removal of insoluble lithium salts, the
solvent was removed again. Distillation gave 4.45 g of a colorless
oil of 1b (17.8 mmol, 89%) with a boiling point of 100 ◦C at
=
dimeric molecules [(2-Py¢-CH NR)Fe(Cl)(m-Cl)]2 with penta-
coordinate iron atoms in distorted trigonal bipyramidal and
square pyramidal environments, respectively. An enhanced coor-
dination number of iron also leads to elongated Fe–N bonds.
Iron(III) has to be considered as a rather strong oxidation
reagent. Therefore, the oxidation of ligands of the type (L)2- always
led to the formation of imines (Lox2)0 (see eqn (2)). Milder oxidation
reagents such as zinc(II) and tin(II) allowed the observation and
isolation of (Lox1)- and its dimer (Lox12)2-.
1
10-3 mbar. H NMR (C6D6, d (ppm)): 0.05 (s, 6H, SiCH3), 0.83
Conclusion
(s, 6H, SiC(CH3)2), 0.86 (d, 6H, CH(CH3)2), 1.22 (br, 1H, NH),
1.58 (hept, 1H, CH(CH3)2), 4.09 (2H, CH2), 6.63 (dd, 1H, Pyr2),
7.01 (d, 1H, Pyr4), 7.12 (dd, 1H, Pyr3), 8.42 (d, 1H, Pyr1),
3J(CH3-CH) = 6.8 Hz), 3J(CH-CH3) = 6.8 Hz, 3Jo(H2-H1/3) =
The iron(III) complex (thf)Fe[N(SiMe3)2]2Cl is a valuable start-
ing material for the synthesis of pale yellow heteroleptic
[ClFeN(SiR3)CH2Py]2 (2) because the chloride anion acts as a
spectator ligand and shows no tendency to interfere with the
metallation reaction. The bis(trimethylsilyl)amide group, however,
is an effective metallating functionality. During the metallation
of (2-pyridylmethyl)(trialkylsilyl)amine (1), iron(III) is reduced
to iron(II). In course of this redox reaction, red crystals of the
(2-pyridylmethylidene)(trialkylsilyl)amine adducts of FeCl2 (3)
precipitate. These imino ligands form via an oxidation of the
iron-bound (2-pyridylmethyl)(trialkylsilyl)amide substituents. A
proposed reaction sequence which explains the formation of 2
and 3 is summarized in Scheme 2.
3
3
6 Hz and 5.9 Hz), Jo(H3-H4) = 7.6 Hz), Jo(H3-H2/4) = 7.3
1
Hz), 3Jo(H1-H2) = 4.4 Hz). 13C{ H} NMR (C6D6, d (ppm)): 2.4
(Si(CH3)2), 18.9 (SiC(CH3)2), 21.1 (SiC(CH3)2), 24.7 (CH(CH3)2),
34.7 (CH(CH3)2), 48.7 (CH2), 120.8 (Pyr4), 121.3 (Pyr2), 135.9
(Pyr3), 149.2 (Pyr1), 163.7 (Pyr5). MS (DEI, m/z): 249 (M+ - H);
164 (Pyr-CH2-N-Si(CH3)2). IR (pure, KBr, n/cm-1: 3374 vs, 3067
w, 2957 vs, 2865 vs, 1591 vs, 1570 s, 1468 vs, 1433 vs, 1404 vs,
1377 s, 1343 w, 1318 w, 1249 vs, 1197 w, 1124 vs, 1085 s, 1047 m,
994 m, 971 w, 873 s, 825 vs, 775 vs, 678 w, 659 m, 628 w, 603 w,
494 w.
The compounds described here are not only accessible via
the metallation reaction of (2-pyridylmethyl)(trialkylsilyl)amines
with (thf)Fe[N(SiMe3)2]2Cl, but metathesis reactions of FeCl2
with an equimolar amount of lithium (2-pyridylmethyl)-
(2-Pyridylmethyl)(triphenylsilyl)amine (1d)
2-Aminomethylpyridin (1.1 g, 10.2 mmol) was deprotonated in
◦
10 ml of THF at -78 C with 6.3 ml of a 1.6 M n-BuLi solution
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Scheme 2 Proposed mechanism for the synthesis of 2 and 3 via the oxidation of 2-pyridylmethylamides with iron(III).
Table 4 Comparison of selected bond lengths of iron complexes with terminally bound 2-Py-CH NR ligands (Lox2) and their reduced forms (see text
=
and eqn (2))
Compounda
R
Type
Fe–Namide (pm)
Fe–NPy (pm)
NC/pm
Ref.
=
[Cl2Fe(Py¢-CH NR)]
cC12H23
SiMe2tBu
SiMe2(CMe2iPr)
SiiPr3
Lox2
211.1
212.0
213.9
213.0
221.7
222.7
211.9
199.0
198.5
196.1
196.7
214.5
210.9
210.0
210.9
213.0
215.0
221.9
200.4
204.5
212.3
211.2
127.7
127.6
127.8
127.5
127.6
127.2
127.4
131.5
133.9
145.3
145.6
31
Lox2
This work
This work
This work
This work
31
31
10
=
[Cl2Fe(Py-CH NR)] (3a)
=
[Cl2Fe(Py-CH NR)] (3b)
Lox2
=
[Cl2Fe(Py-CH NR)] (3c)
Lox2
b
=
[Cl2Fe(Py-CH NR)] (3d)
SiPh3
Lox2
b
=
[Cl2Fe(Py-CH NR)]
C6H3iPr2
nPr
C6H3iPr2
C6H3iPr2
SiMe2tBu
SiPh3
Lox2
b
=
[Cl2Fe(Py¢-CH NR)]
Lox2
+
=
[(thf)Fe(Py-CH NR)2]
Lox1/Lox2
Lox1
10
25
=
[Fe(Py-CH NR)2]
[Fe(Py-CH2-NR)2] (4a)
[Fe(Py-CH2-NR)2] (4d)
HL
HL
This work
a Py = 2-pyridyl, Py¢ = 6-methyl-2-pyridyl. b Compound is dimeric with bridging chloride anions.
in hexane (10.1 mmol). Then a solution of 3.0 g of chloro-
triphenylsilane (10 mmol) was dropped at -78 ◦C into this mixture.
After warming to r.t. and stirring for an additional 12 h, all
volatile materials were removed under vacuum. The violet residue
was dissolved in 15 ml of toluene and solids were removed by
filtration. Removal of the solvent afforded 3.48 g of crystalline
1d (9.48◦mmol, 95%) which can be recrystallized from toluene.
M.p. 93 C. 1H NMR ([D6]benzene, d (ppm)): 8.39 (d, 3J(H1H2) =
4.4 Hz), 7.69–7.67 (m, 6H, o-Ph), 7.15–7.10 (m, 9H, m-Ph, p-Ph),
3
4
6.94 (td, J(H3H2/4) = 8 Hz, J(H3H1) = 4.0 Hz, 1H, Py3), 6.70
3
3
(d, J(H4H3) = 7.6 Hz, 1H, Py4) 6.54 (dd, J(H2H1/3) = 6.8 Hz
3
and 7.2 Hz, 1H, Py2), 4.22 (d, J(CHNH) = 7.2 Hz, 2H, CH2),
2.53 (s, br., 1H, NH). 13C{ H}NMR ([D6]benzene, d (ppm)): 161.8
1
(Py5), 149.2 (Py1), 136.2 (Py3), 136.0 (o-Ph), 129.8 (p-Ph), 128.0
(m-Ph), 121.1 (Py2), 119.2 (Py4), 48.2 (CH2). IR (Nujol, KBr,
n/cm-1: 3370 s, 3063 s, 2666 w, 1957 w, br., 1892 w, br., 1827 w,
5362 | Dalton Trans., 2010, 39, 5356–5366
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br., 1585 s, 1568 m, 1471 s, 1426 vs, 1402 s, 1308 w, 1276 w, 1203
w, 1180 w, 1143 m, 1113 vs, 1085 s, 1064 w, 1046 w, 1029 w, 994
m, 894 w, 843 s, 819 s, 763 s, 747 s, 738 s, 706 vs, 674 w, 620
w, 596 m, 523 s, 504 vs, 492 s, 455 m. MS (DEI, m/z): 365 (M+,
2%), 290 ([Py-CH2-NH-SiH2Ph + H]+, 98%), 259 ([SiPh3]+, 100%),
211([Py-CH2-NH-SiH2Ph + H]+, 34%), 181 ([Py-CH-NPh - H]+,
30%), 108 ([Py-CH2-NH2]+, 7%). Elemental analysis (C24H21N2Si,
366.53): calc.: C 78.64, H 6.05, N 7.64; found: C 77.82, H 5.95, N
7.60.
of THF was dropped at r.t. into a solution of 0.52 g of
(thf)Fe{N(SiMe3)2}Cl (1.10 mmol) in 10 ml of THF. After stirring
for one day, the volume of the solution was reduced to a third
of the original volume. At r.t. yellow platelets and brown needles
crystallized. These crystals (0.07 g, 0.10 mmol, 17%) were isolated
and X-ray diffraction studies showed that these crystals consisted
of 2b in the same space group. These crystals were washed with
a few millilitres of THF and dried in vacuo. The mother liquor
was concentrated to a few millilitres and then 0.04 g of orange-red
needles of 3b (0.11 mmol, 10%) precipitated within a few days.
Chloro-(2-pyridylmethyl)(tert-butyldimethylsilyl)amidoiron(II)
(2a) and dichloro-(2-pyridylmethylidene)(tert-butyldimethylsilyl)-
aminoiron(II) (3a)
Method B. (2-Pyridylmethyl)(1,1,2-trimethylpropyl-dimethyl-
silyl)amine 1b (0.37 g, 1.5 mmol), dissolved in 5 ml of THF,
was deprotonated with 1 ml of a 1.6 M solution of nBuLi in
hexane (1.6 mmol) at -78 ◦C. This solution was dropped to a
suspension of 0.24 g of FeCl3 (1.5 mmol) in 5 ml of THF at
-78 ◦C. Then the reaction mixture was warmed to -20 ◦C and
stirred for two hours. Thereafter all solids were removed and the
volume of the filtrate reduced to a few millilitres. Storage at -20 ◦C
afforded the crystallization of 0.03 g of orange-red needles of 3b
(0.08 mmol, 6%). If the reaction mixture was warmed to r.t. during
this procedure, the yield was even lower.
Method A. A solution of 0.20 g of (2-pyridylmethyl)(tert-
butyldimethylsilyl)amine 1a (0.97 mmol) in 5 ml of THF was
dropped at r.t. to a solution of 0.47 g of (thf)Fe{N(SiMe3)2}2Cl
(0.97 mmol) in 15 ml of THF. After stirring for one day the
volume of the green-brown solution was reduced to half of the
original volume. After filtration 0.13 g of pale yellow cuboids of
2a (0.21 mmol, 43%) precipitated at r.t. the crystals were washed
with a small amount of THF. After slight reduction of the volume
of the mother liquor another crop of crystals were collected. Now
the volume of the residue was strongly reduced and 0.01 g of red
platelets of 3a (0.03 mmol, 3%) were collected.
Data of 2b. M.p. 166 ◦C (dec.). IR (Nujol, KBr, n/cm-1: 1606
m, 1570 w, 1438 s, 1278 w, 1250 m, 1161 w, 1027 s, 993 w, 813 s,
775 vs, 744 w, 705 w, 659 w, 637 w, 528 w. MS (DEI, m/z): 680
(M+, 0,3%), 595 ([M - tHex]+, 0.9%), 554 ([M - FeCl2]+, 4.6%), 469
([M - FeCl2 - tHex]+, 9.7%), 165 ([ampSiMe2]+, 100%). Elemental
analysis (C28H50N4Cl2Fe2Si2, 681.49): calc.: C 49.35, H 7.40, N
8.22; found: C 47.54, H 7.32, N 7.85.
Method B. (2-Pyridylmethyl)(tert-butyldimethylsilyl)amine
(0.4 g, 1.8 mmol) in 5 ml of THF was lithiated at -78 ◦C with
1.1 ml of n-butyl lithium solution in hexane (1.6 M, 1.8 mmol).
This solution was added dropwise at -78 ◦C to a solution of
0.15 g of FeCl3 (0.9 mmol) in 5 ml of THF. After warming to r.t.
and stirring for an additional 20 h, the solution was filtered. The
volume of the filtrate was reduced to half of the original volume.
At r.t. 0.05 g thin pale yellow needles of 2a (0.08 mmol, 17%)
precipitated within several days.
Data of 3b. M.p. 270 ◦C. IR (Nujol, KBr plates, n/cm-1: 1617
w, 1590 m, 1297 m, 1259 s, 1222 w, 1155 w, 1099 m, br., 1021
m, br., 891 m, 822 s, br., 789 m, 771 m, 723 w, 672 w. MS (DEI,
m/z): 374 (M+, 1.1%), 339 ([M - Cl]+, 2%), 289 ([M - tHex]+,
+
=
1.8%), 254 ([M - tHex - Cl] , 1.5%), 233 ([Py-CH N-SiMe2tHex -
Data of 2a. M.p. 179 ◦C (dec.). IR (Nujol, KBr, n/cm-1: 1608
m, 1568 w, 1437 m, 1487 m, 1286 w, 1255 m, 1155 m, 1104 w, 1026
m, 991 m, 965 w, 899 w, 823 s br., 780 vs, 754 w, 709 w, 660 m,
638 w, 525 m, 467 w. MS (DEI, m/z): 625 (M+, 1%), 567 ([M -
tBu]+, 1%), 498 ([M - FeCl2]+, 4%), 441 ([M - FeCl2 - tBu]+, 9%),
165 ([ampSiMe2]+, 100%). Elemental analysis (C24H42Cl2Fe2Si2N4;
625.71): calc.: C 46.07, H 6.77, N 8.95; found: C 45.43, H 6.59, N
8.81. Magnetism: meff = 5.25 mB, 300 K.
+
+
=
Me] , 5,5%), 165 ([Py-CH2-N SiMe2] , 100%). Elemental analysis
(C14H24N2Cl2FeSi, 375.24): calc.: C 44.81, H 6.46, N 7.47; found:
C 43.73, H 6.35, N 7.11. Magnetism: meff = 5.2 mB, 300 K.
Chloro-(2-pyridylmethyl)(triisopropylsilyl)amidoiron(II) (2c) and
dichloro-(2-pyridylmethylidene)(triisopropylsilyl)aminoiron(II) (3c)
Method A. A solution of 0.34 g of (2-pyridylmethyl)-
(triisopropylsilyl)amine 1c (1.29 mmol) in 20 ml of THF was added
to a solution of 0.63 g of (thf)Fe{N(SiMe3)2}Cl (1.29 mmol) in
10 ml of THF. After reduction of the volume of the reaction
mixture to half of the original volume and during storage at
-20 ◦C, 0.07 g of pale yellow cuboids of 2c (0.10 mmol, 16%)
precipitated. Another crop of crystals were obtained after a
repetition of this procedure. The crystals were washed with THF
and dried under vacuum. The volume of the filtrate was strongly
reduced and now, 0.09 g of violet platelets of 3c (0.23 mmol, 18%)
crystallized.
Data of 3a. IR (Nujol, KBr, n/cm-1: 1622 m, 1593 s, 1568
w, 1298 m, 1255 m, 1222 m, 1156 w, 1102 w, 1020 m, 889
m, 840 s, 777 s, 681 w, 646 w. MS (DEI, m/z): 346 ([M]+,
+
+
=
5%), 311 ([M - Cl] , 11%), 221 ([Py-CH NSiMe2tBu] , 32%),
+
+
=
=
205 ([Py-CH NSiMetBu] , 72%), 164 ([Py-CH NSiMe2] , 98%),
149 ([Py-CH NSiMe2] , 72%), 136 ([Py-CH NSiMeH2] , 85%),
106 ([Py-CH NH] , 82%), 79 ([Py] , 100%). Elemental analysis
(C12H20Cl2FeSiN2, 347.14): calc.: C 41.52, H 5.81, N 8.07; found:
C 40.69, H 5.40, N 7.63. Magnetism: meff = 5.1 mB, 300 K.
+
+
=
=
+
+
=
Method B. The reaction of 0.8 ml of 1.6 M n-butyl
lithium solution in hexane with 0.34 g of (2-pyridylmethyl)-
(triisopropylsilyl)amine (1.29 mmol) in 5 ml of THF at -78 ◦C
gave the corresponding lithium amide which was added at -78 ◦C
to a suspension of 0.21 g of FeCl3 (1.3 mmol) in 5 ml of THF.
Thereafter the reaction mixture was warmed to -20 ◦C and stirred
Chloro-(2-pyridylmethyl)(1,1,2-trimethylpropyl-dimethylsilyl)-
amidoiron(II) (2b) and dichloro-(2-pyridylmethylidene)(1,1,2-
trimethylpropyl-dimethylsilyl)aminoiron(II) (3b)
Method A. A solution of 0.27 g of (2-pyridylmethyl)(1,1,2-
trimethylpropyl-dimethylsilyl)amine 1b (1.10 mmol) in 10 ml
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Table 5 Crystal data and refinement details for the X-ray structure determinations
Compound
Formula
1d
2a
2b
2c
2d
3a
3b
3c
3d
4d
C24H22N2Si C24H42Cl2 C28H50Cl2- C30H54Cl2- C48H42Cl2- C12H20Cl2- C14H24Cl2- C15H26Cl2- C48H40Cl4- C48H42-
Fe2N4Si2· Fe2N4Si2
Fe2N4Si2
Fe2N4Si2·
0.5 C4H8O
949.69
FeN2Si
FeN2Si
FeN2Si
Fe2N4Si2,
2(C4H8O)
1126.73
-90(2)
FeN4Si2
C6H14
Fw/g mol-1
T/◦C
Crystal
system
366.53
-90(2)
Triclinic
711.57
-90(2)
Triclinic
681.50
-90(2)
Monoclinic Triclinic
709.55
-90(2)
347.14
-90(2)
375.19
-90(2)
389.22
-90(2)
786.89
-90(2)
-90(2)
Monoclinic Monoclinic Triclinic
Monoclinic Monoclinic Orthorhombic
¯
¯
¯
P1
¯
P1
Space group P1
P1
8.4163(7) 10.3393(5) 9.6409(4)
10.3387(6) 10.9918(13) 11.7681(3) 11.7277(7) 14.6411(7) 13.2269(5) 8.0232(5)
15.1982(8) 11.0332(12) 14.5255(7) 17.5459(9) 16.8566(6) 7.8214(5) 17.7411(13) 15.8045(13) 15.8978(4) 9.6921(5)
P21/c
C2/c
P21/c
P21/c
17.7619(15) 9.0029(4)
7.6925(5)
P21/n
Fdd2
22.4134(8)
˚
a/A
6.4898(3)
20.0652(8) 16.8690(9) 7.2991(5)
˚
b/A
18.7006(7) 37.3593(16)
˚
c/A
a/◦
b/◦
g /◦
93.801(2)
100.954(3) 99.969(6) 99.333(2)
112.081(5) 90
73.23(3)
88.47(3)
70.86(3)
90
104.800(3) 100.908(3) 80.001(4)
90 90 64.211(4)
1713.62(16) 918.29(11) 1992.9(3)
90
81.560(5)
90
112.645(3) 91.290(2)
90 90
90
90.00
90.00
90.00
99.192(3)
983.38(9)
2
1.238
1.3
94.411(6) 90
920.20(17) 1743.98(13) 1789.36(16) 4787.8(3)
1
1.284
10.23
6066
3
˚
V/A
2675.87(17) 8115.7(6)
2
1.398
8.32
17 985
Z
2
2
4
4
2
4
8
r/g cm-3
1.298
10.77
12 182
1.317
10.52
12 389
1.318
8.07
16 771
1.346
12.48
11 398
1.357
11.7
5715
1.297
10.81
12 798
1.288
4.7
14 135
m/cm-1
Measured
data
6965
Data with
I > 2s(I)
Unique
data/Rint
2950
2902
3025
5781
3358
2832
3280
3588
4170
3281
4448/
0.0371
wR2 (all data, 0.1272
4028/
0.0319
0.1018
3986/
0.0463
0.0977
8068/
0.0311
0.1125
5453/
0.0730
0.1800
3899/
0.0497
0.1171
3947/
0.0268
0.1182
4424/
0.0358
0.1048
6082/
0.0601
0.1155
4559/
0.0796
0.0851
on F2)a
R1 (I >
2s(I))a
sb
0.0513
0.0431
0.0373
0.0448
0.0567
0.0473
0.0444
0.0372
0.0454
0.0428
1.013
1.007
1.013
0.996
1.019
1.013
1.002
1.074
1.008
0.977
Res. dens./
0.277/
-0.303
676619
0.334/
-0.422
676620
0.296/
-0.375
676621
0.814/
-0.437
676622
0.894/
-0.450
676623
0.593/
-0.374
676624
0.918/
-0.776
676625
0.364/
-0.384
676626
0.555/
-0.431
736365
0.271/
-0.232
736366
-3
˚
e A
CCDC No.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
1/2
2
2
a Definition of the R indices: R1 = ( ꢀFo| - |Fcꢀ)/ |Fo| wR2 = { [w(Fo - Fc2)2]/ [w(Fo2)2]} with w-1 = s (Fo2) + (aP)2. b s = { [w(Fo
-
1/2
Fc2)2]/(No - Np)}
.
◦
for an additional 2.5 h. Then the solution was filtered at -20 C
and the volume was reduced under reduced pressure also at this
temperature. Storage at -20 ◦C leads to the precipitation of 0.06 g
of violet needles of 3c (0.15 mmol, 12%). Warming of the reaction
mixture to r.t. led to yields of less than 5%.
Chloro-(2-pyridylmethyl)(triphenylsilyl)amidoiron(II) (2d) and
dimeric dichloro-(2-pyridylmethylidene)(triphenylsilyl)amino-
iron(II) (3d)
Method A.
A
solution of 0.27
g
of (2-pyridyl-
methyl)(triphenylsilyl)amine (0.73 mmol) in 10 ml of THF
was added to a solution of 0.37 g of (thf)Fe{N(SiMe3)2}Cl
(0.75 mmol) in 10 ml of THF. After stirring for one day, the
volume of the reaction mixture was reduced to half of the original
volume. After filtration the filtrate was stored at r.t. Within
two days 0.12 g of pale yellow platelets of 2d (1.3 mmol, 36%)
precipitated and were dried in vacuo. After reduction of the
volume of the mother liquor blue needles of 3d were obtained,
however, this compound always contained varying amounts of
2d. Therefore, only an X-ray structure determination of 3d was
performed in order to proof the constitution of this complex.
◦
Data of 2c. M.p. 179 C (dec.), IR (Nujol, KBr, n/cm-1:
1605 m, 1570 m, 1480 m, 1437 s, 1281 m, 1249 w, 1153 w, 1105
w, 1051 w, 1026 m, 1001 m, 976 m, 917 w, 882 m, 822 w, 771 vs,
751 s, 707 m, 666 m, 650 m, 510 m, 471 m. MS (DEI, m/z):
709 (M+, 0.04%), 666 ([M - iPr]+, 0.1%), 582 ([M - FeCl2]+,
0.8%), 539 ([M - FeCl2 - iPr]+, 1%), 264 ([ampSiiPr3]+, 6%), 220
([ampSiiPr2 - H]+, 100%), 135 ([ampSi - H]+, 90%). Elemental
analysis (C30H54N4Cl2Fe2Si2; 709.54): calc.: C 50.78, H 7.67, N
7.90; found: C 49.36, H 7.67, N 7.64.
◦
Data of 3c. M.p. 226 C. IR (Nujol, KBr, n/cm-1: 1615 m,
1591 s, 1566 w, 1300 m, 1221 w, 1102 w, 1020 m, 883 s, 789 m, 776 m,
692 m, 655 w, 623 w, 508 w, 489 w. MS (DEI, m/z): 388 (M+, 40%),
353 ([M - Cl]+, 98%), 345 ([M - iPr]+, 28%), 310 ([M - iPr - Cl]+,
Method B. A solution of 0.66 g of {Fe[N(SiMe3)2]2}2
(0.88 mmol) in 5 ml of THF was added to a solution of 0.60 g (2-
pyridylmethyl)(triphenylsilyl)amine (1.63 mmol) in 5 ml of THF.
After stirring at r.t. for 30 min all solids were removed by filtration.
The filtrate was layered with 5 ml of THF and then with a solution
of 0.26 g of iron(III)chloride (1.63 mmol) in 5 ml of THF. Diffusion
at r.t. led to crystallization of 2d and 3d in the shape of dark blue
needles and also of Fe4Cl8(thf)6 in the shape of colorless cuboids.
i
+
i
+
=
=
45%), 261 ([Py-CH NSi( Pr)3] , 13%), 218 ([Py-CH NSi( Pr)2] ,
i
+
+
=
=
100%), 176 ([Py-CH NSi Pr] , 16%), 133 ([Py-CH NSi] , 88%)
+
=
106 ([Py-CH NH] , 71%). Elemental analysis (C15H26N2Cl2FeSi;
389,22): calc.: C 46.29, H 6.73, N 7.20; found: C 44.57, H 6.43, N
7.40. Magnetism: meff = 4.9 mB, 300 K.
5364 | Dalton Trans., 2010, 39, 5356–5366
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Separation and purification of 3d failed, the impurities consisted
of 2d and Fe4Cl8(thf)6.
(Frankfurt/Main, Germany). A. Malassa thanks the Carl-Zeiss-
Stiftung (Germany) for a generous Ph.D. grant.
◦
Physical data of 2d. M.p. 120 C. IR (Nujol, KBr windows,
References
n/cm-1: 3065 m, 3042 m, 2683 br. w, 1976 br. w, 1906 br. w, 1831
br. w., 1605 s, 1587 m, 1570 m, 1483 s, 1440 s, 1426 s, 1281 m,
1259 m, 1259 m, 1188 w, 1161 m, 1110 br. s, 1068 m, 1026 s, 988 m,
911 w, 889 w, 820 w, 781 vs, 748 s, 710 vs, 670 w, 650 m, 636 s, 550
vs, 516 vs, 495 s, 485 m, 459 w. MS (DEI, m/z): 356 ([amp-SiPh3]+,
4%), 289 ([amp-SiPh2]+, 100%), 259 ([SiPh3]+, 97%), 181 ([SiPh2]+,
59%), 105 ([SiPh]+, 40%), 78 ([Ph + H]+, 20%). Elemental analysis
(C48H42N4Si2Fe2Cl2, 913.64): calc.: C 63.10, H 4.63, N 6.13; found:
C 62.90, H 5.26, N 5.79.
1 D. M. Roundhill, Chem. Rev., 1992, 92, 1–27.
2 R. H. Holm, P. Kennepohl and E. I. Solomon, Chem. Rev., 1996, 96,
2239–2314.
3 (a) W. Kaim and B. Schwederski, Bioinorganic Chemistry: Inorganic
Elements in the Chemistry of Life, Wiley, Chichester, 1994; (b) J. J. R.
Frausto da Silva and R. J. P. Williams, The Biological Chemistry of the
Elements, 2nd edn, Oxford University Press, Oxford, 2001.
4 T. A. Jackson, L. Que, H.-B. Kraatz and N. Metzler-Nolte, Concepts
and Models in Bioinorganic Chemistry, Wiley-VCH, Weinheim, 2006,
pp. 259–286.
´
5 K. Chen, M. Costas and L. Que, J. Chem. Soc., Dalton Trans., 2002,
Data of 3d. MS (DIE, m/z): 492 (M+, > 1%), 456 ([M - Cl]+,
> 1%), 364 ([Py-CH NSiPh3] , 2%).
672–679.
+
6 A. L. Gavrilova and B. Bosnich, Chem. Rev., 2004, 104, 349–
383.
=
7 M. Costas, M. P. Mehn, M. P. Jensen and L. Que, Chem. Rev., 2004,
104, 939–986.
Iron(II) bis[(2-pyridylmethyl)(triphenylsilyl)amide] (4d)
8 X. Shan and L. Que, J. Inorg. Biochem., 2006, 100, 421–433.
9 M. Ostermeier, C. Limberg, B. Ziemer and V. Karunakaran, Angew.
Chem., 2007, 119, 5423–5426; M. Ostermeier, C. Limberg, B. Ziemer
and V. Karunakaran, Angew. Chem., Int. Ed., 2007, 46, 5329–5331.
10 C. C. Lu, E. Bill, T. Weyhermu¨ller, E. Bothe and K. Wieghardt, J. Am.
Chem. Soc., 2008, 130, 3181–3197.
11 (a) J. T. B. H. Jastrzebski, J. M. Klerks, G. van Koten and K. Vrieze,
J. Organomet. Chem., 1981, 210, C49–C53; (b) G. van Koten, J. T. B. H.
Jastrzebski and K. Vrieze, J. Organomet. Chem., 1983, 250, 49–61; (c) E.
Wissing, S. von der Linden, E. Rijnberg, J. Boersma, W. J. J. Smeets,
A. L. Spek and G. van Koten, Organometallics, 1994, 13, 2602–2608.
12 M. Westerhausen, A. N. Kneifel and N. Makropoulos, Inorg. Chem.
Commun., 2004, 7, 990–993.
13 M. Westerhausen, T. Bollwein, N. Makropoulos, S. Schneiderbauer, M.
Suter, H. No¨th, P. Mayer, H. Piotrowski, K. Polborn and A. Pfitzner,
Eur. J. Inorg. Chem., 2002, 389–404.
14 M. Westerhausen, A. N. Kneifel and P. Mayer, Z. Anorg. Allg. Chem.,
2006, 632, 634–638.
15 M. Westerhausen, T. Bollwein, N. Makropoulos, T. M. Rotter, T.
Habereder, M. Suter and H. No¨th, Eur. J. Inorg. Chem., 2001, 851–
857.
A solution of 0.47 g of {Fe[N(SiMe3)2]2}2 (0.63 mmol) in
5 ml of toluene was added to a solution of 0.46 g of (2-
pyridylmethyl)(triphenylsilyl)amine (1.25 mmol) in 5 ml of
toluene. After stirring for 30 min all solid materials were removed
by filtration. Thereafter the solvent was removed in vacuum
and the green residue was dried under reduced pressure. After
dissolving in diethyl ether orange crystals precipitated at r.t. which
were washed with small portions of ether and dried in vacuo. Yield:
0.35 g (0.44 mmol, 70%). M.p. 195 ◦C. IR (Nujol, KBr windows,
n/cm-1: 3043 m (sh), 2013 w, 1952 w, 1880 w, 1826 w, 1765 w,
1713 w, 1598 m, 1562 m, 1341 m, 1302 m, 1276 m, 1186 w, 1150 m,
1113 m (br)., 1045 m, 977 m, 952 m, 887 m (br)., 806 m, 737 s (br).,
700 s (br)., 609 m, 563 m, 500 m (br). MS (DIE, m/z): 786 (M+, 5%),
709 ([M - Ph]+, 1%), 631 ([M - 2Ph]+, 1%], 420 ([M - Py - CH2 -
NHSiPh3]+, 5%], 289 ([Py - CH2 - NHSiPh2]+, 100%]. Elemental
analysis (C48H42N4FeSi2, 786.89): calc.: C: 73.26, H 5.28, N 7.12,
found: C 72.76, H 5.44, N 6.89. Magnetism: meff = 6.3 mB, 300 K.
16 Y. Okamoto, K. Ogura and T. Kinoshita, Polyhedron, 1984, 3, 635–
638.
17 K. Ogura, Y. Kurasawa, Y. Yamaguchi and Y. Okamoto, Heterocycles,
2003, 59, 283–291.
X-Ray structure determinations
18 C. J. Davies, G. A. Solan and J. Fawcett, Polyhedron, 2004, 23, 3105–
3114.
The intensity data for the compounds were collected on a Nonius
KappaCCD diffractometer using graphite-monochromated Mo-
Ka radiation. Data were corrected for Lorentz and polarization ef-
fects but not for absorption effects.33,34 Crystal data and refinement
details for the X-ray structure determinations are summarized in
Table 5.
19 G. Chen, Y.-X. Sun, M. Sun and W. Qi, Acta Crystallogr., Sect. E:
Struct. Rep. Online, 2004, 60, m1547–m1549.
20 K. W. To¨rnroos, D. Chernyshov, M. Hostettler and H.-B. Bu¨rgi, Acta
Crystallogr., Sect. C: Cryst. Struct. Commun., 2005, 61, m450–m452.
21 A. Malassa, H. Go¨rls, A. Buchholz, W. Plass and M. Westerhausen,
Z. Anorg. Allg. Chem., 2006, 632, 2355–2362.
22 D. C. Bradley and M. H. Chisholm, Acc. Chem. Res., 1976, 9, 273–280.
23 M. F. Lappert, P. P. Power, A. R. Sanger and R. C. Srivastava, Metal
and Metalloid Amides: Syntheses, Structures, and Physical and Chemical
Properties, Ellis Horwood, Chichester, 1980, ch. 8, pp. 465–544.
24 M. Lappert, A. Protchenko, P. Power and A. Seeber, Metal Amide
Chemistry, Wiley, Chichester 2009, ch. 6, pp. 149–204.
25 R. A. Andersen, K. Faegri, J. C. Green, A. Haaland, M. F. Lappert,
W.-P. Leung and K. Rypdal, Inorg. Chem., 1988, 27, 1782–1786.
26 C. Koch, A. Malassa, C. Agthe, H. Go¨rls, R. Biedermann, H.
Krautscheid and M. Westerhausen, Z. Anorg. Allg. Chem., 2007, 633,
375–382.
The structures were solved by direct methods (SHELXS)35
2
and refined by full-matrix least squares techniques against Fo
(SHELXL-97).36 For the amine-group at N1 of 1d and for the
methylene-group at C6 at 2a the hydrogen atoms were located by
difference Fourier synthesis and refined isotropically. The other
hydrogen atoms were included at calculated positions with fixed
thermal parameters. All non-disordered, non-hydrogen atoms
were refined anisotropically.36 XP (SIEMENS Analytical X-ray
Instruments, Inc.) was used for structure representations.
27 D. C. Bradley, R. G. Copperthwaite, M. W. Extine, W. W. Reichert and
M. H. Chisholm, Inorg. Synth., 1978, 18, 112–120.
28 J. S. Duncan, T. M. Nazif, A. K. Verma and S. C. Lee, Inorg. Chem.,
2003, 42, 1211–1224.
29 J. Zeller, S. Ko¨nig and U. Radium, Inorg. Chim. Acta, 2004, 357, 1813–
1821.
30 H. Zhao, R. Cle´rac, J.-S. Sun, X. Ouyang, J. M. Clemente-Juan, C. J.
Go´mez-Garc´ıa, E. Coronado and K. R. Dunbar, J. Solid State Chem.,
2001, 159, 281–292.
Acknowledgements
This work was supported by the Deutsche Forschungsgemein-
schaft (DFG, Bonn-Bad Godesberg, Germany). We also ac-
knowledge the support by the Fonds der Chemischen Industrie
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The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 5356–5366 | 5365
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31 V. C. Gibson, R. K. O’Reilly, D. F. Wass, A. J. P. White and D. J.
Williams, Dalton Trans., 2003, 2824–2830.
32 See e.g. (a) J. E. Huheey, Anorganische Chemie: Prinzipien von Struktur
und Reaktivita¨t, 3rd edn, Harper & Row: New York, 1983, pp. 517–530;
(b) M. Mohan, S. G. Mittal, H. C. Khera and A. K. Sirivastava, Gazz.
Chim. Ital., 1977, 107, 393–397.
34 Processing of X-Ray Diffraction Data Collected in Oscillation Mode,
Z. Otwinowski, W. Minor, in C. W. Carter, R. M. Sweet, ed.: Methods
in Enzymology, Vol. 276, Macromolecular Crystallography, Part A,
pp. 307–326, Academic Press, 1997.
35 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 1990,
46, 467–473.
33 COLLECT, Data Collection Software Nonius B.V., Netherlands,
1998.
36 G. M. Sheldrick, SHELXL-97 (Release 97-2), University of Go¨ttingen,
Germany, 1997.
5366 | Dalton Trans., 2010, 39, 5356–5366
This journal is
The Royal Society of Chemistry 2010
©