Diamagnetic 8-amidoquinoline and 8-(trialkylsilylamido)quinoline complexes of divalent nickel and zinc

Article abstract of DOI:10.1016/j.ica.2007.09.007

Transamination of Zn[N(SiMe₃)₂]₂ with 8-(triisopropylsilylamino) (1a) and 8-(tert-butyldimethylsilylamino)quinoline (1b) yields monomeric heteroleptic bis(trimethylsilyl)amido zinc 8-(trialkylsilylamido)quinoline (2a, 2b). The reaction of Zn[N(SiMe₃)₂]₂ with 8-aminoquinoline leads to the formation of heteroleptic dimeric 8-amidoquinoline zinc bis(trimethylsilyl)amide (3). This compound shows fluxionality on the NMR time scale due to a transannular trans-cis isomerization process and also a strong temperature dependency of the ratio of these two isomers. Variation of the stoichiometry allows the synthesis and isolation of homoleptic zinc bis(8-amidoquinoline) (4) with the zinc atoms in a distorted tetrahedral environment. The metallation of 8-aminoquinoline with (tmeda)NiMe₂ yields diamagnetic nickel bis(8-amidoquinoline) (5) with a nickel center showing a distorted square planar coordination sphere. Dinuclear zinc complexes are accessible employing tetra-dentate di(8-aminoquinolyl)diphenylsilane (6). The metallation of 6 with dimethylzinc yields dimeric zinc di(8-amidoquinolyl)diphenylsilane (7) with tetrahedrally coordinated zinc atoms. A comparison of the molecular structures of 1a, 2b, 3, 4, 5, 6, and 7 shows nearly no dependency of the structural data of the quinolyl unit on the substitution pattern of the amino function. The metal-nitrogen bond lengths depend on the coordination numbers of the metal and the nitrogen atoms (terminal or bridging position) as well as the electrostatic attraction between the metal cations and the amino bases.

Full text of DOI:10.1016/j.ica.2007.09.007

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 1405–1414
www.elsevier.com/locate/ica
Diamagnetic 8-amidoquinoline and 8-(trialkylsilylamido)
quinoline complexes of divalent nickel and zinc
Astrid Malassa, Christian Koch, Brigitte Stein-Schaller, Helmar Go¨rls,
*
Manfred Friedrich, Matthias Westerhausen
Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-Universita¨t Jena, August-Bebel-Str. 2, D-07743 Jena, Germany
Received 28 June 2007; received in revised form 15 August 2007; accepted 4 September 2007
Available online 12 September 2007
Abstract
Transamination of Zn[N(SiMe3)2]2 with 8-(triisopropylsilylamino) (1a) and 8-(tert-butyldimethylsilylamino)quinoline (1b) yields
monomeric heteroleptic bis(trimethylsilyl)amido zinc 8-(trialkylsilylamido)quinoline (2a, 2b). The reaction of Zn[N(SiMe3)2]2 with 8-ami-
noquinoline leads to the formation of heteroleptic dimeric 8-amidoquinoline zinc bis(trimethylsilyl)amide (3). This compound shows
fluxionality on the NMR time scale due to a transannular trans–cis isomerization process and also a strong temperature dependency
of the ratio of these two isomers. Variation of the stoichiometry allows the synthesis and isolation of homoleptic zinc bis(8-amidoquin-
oline) (4) with the zinc atoms in a distorted tetrahedral environment. The metallation of 8-aminoquinoline with (tmeda)NiMe2 yields
diamagnetic nickel bis(8-amidoquinoline) (5) with a nickel center showing a distorted square planar coordination sphere. Dinuclear zinc
complexes are accessible employing tetra-dentate di(8-aminoquinolyl)diphenylsilane (6). The metallation of 6 with dimethylzinc yields
dimeric zinc di(8-amidoquinolyl)diphenylsilane (7) with tetrahedrally coordinated zinc atoms. A comparison of the molecular structures
of 1a, 2b, 3, 4, 5, 6, and 7 shows nearly no dependency of the structural data of the quinolyl unit on the substitution pattern of the amino
function. The metal–nitrogen bond lengths depend on the coordination numbers of the metal and the nitrogen atoms (terminal or bridg-
ing position) as well as the electrostatic attraction between the metal cations and the amino bases.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Amides; Aminoquinoline; Metallation reactions; Transamination reactions; Nickel; Zinc
1. Introduction
in carbonic anhydrases, peptidases, proteases, deaminases
and others. In agreement with the importance of zinc in
biological systems many review articles summarize the
results on this topic [4–8]. Due to a similar size of divalent
3d transition metals, zinc can often be replaced by other
metals [9]. Nickel(II) can be an exception because it shows
tetrahedral and square planar coordination spheres with
different spin states dependent on steric strain and donor
strength of the ligands. Due to these reasons we were inter-
ested in the coordination behaviour of 8-amidoquinoline
and 8-(trialkylsilylamido)quinoline at Zn(II) and Ni(II)
and the influence of steric strain, induced by trialkylsilyl
groups and bis(trimethylsilyl)amido ligands.
The amides of the late transition metals nickel [1] and
zinc [2] have attracted considerable interest as models in
biomimetic studies. Nickel in a biological environment
shows a variety of oxidation and spin states and is often
found in hydrogenases [3]. In contrast to nickel, different
factors are responsible for the importance of zinc such as
redox stability, coordination geometry (no ligand field sta-
bilization due to d10 configuration) and a hardness of the
metal which accepts a broad variety of N-, O- and S-bases.
Dependent on the coordination sphere, zinc plays key roles
Two reaction pathways allow the synthesis of 8-amido-
quinoline complexes of transition metals according to Eq.
(1). The metathesis reaction of lithium N-trialkylsilyl-8-
*
Corresponding author. Fax: +49 (0) 3641 948110.
E-mail address: m.we@uni-jena.de (M. Westerhausen).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.09.007

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A. Malassa et al. / Inorganica Chimica Acta 361 (2008) 1405–1414
amidoquinoline with anhydrous nickel(II) chloride or nick-
elocene yielded homoleptic paramagnetic reddish brown
nickel bis(N-trialkylsilyl-8-amidoquinoline) [10]. The met-
allation of N-trimethylsilyl-8-aminoquinoline with dialkyl-
magnesium or -zinc gave the corresponding deep-red metal
bis(N-trialkylsilyl-8-amidoquinoline)s [11]. The corre-
sponding cadmium derivative eliminated CdMe2 and
ligands at zinc and nickel, these side reactions can be
avoided.
N
N
N
R'R2Si
Me
N
Zn Me
N SiR'R2
+ ZnMe2
- 2 MeH
- Zn
yielded
1,1,3,3-tetramethyl-2,4-diquinolyl-2,4-diaza-1,3-
ð2Þ
Zn
R'R2Si
N
N
SiR'R2
disiletane according to the following equation [11].
N
Zn
Zn
Me
Me
G
F
N
N
2
2
N
N
Li
SiMe3
H
SiMe3
2. Results and discussion
+ MR2
- 2 RH
+ MX2
- 2 LiX
2.1. Syntheses
N-trialkylsilyl substituted 8-aminoquinolines were acces-
sible via the metathesis reaction of lithium 8-amidoquino-
line with chloro-trialkylsilane [19,20]. The transamination
of zinc bis[bis(trimethylsilyl)amide] with 8-(trialkylsilylami-
no)quinoline (1) yielded heteroleptic N-trialkylsilyl-8-
amidoquinoline zinc bis(trimethylsilyl)amide (2) with a
three-coordinate metal atom (Eq. (3)). Use of a more reac-
tive zincation reagent such as diethylzinc yields homoleptic
zinc(II) bis(N-trialkylsilyl-8-amidoquinoline) [11] with a
tetra-coordinate metal atom in a strongly distorted tetrahe-
dral environment. The low coordination number of zinc in
2 is a consequence of effective shielding by the bulky
(Me3Si)2N group and a reduced nucleophilicity of this pla-
nar anion due to negative hyperconjugation. Compound 2a
was obtained as a waxy solid which contained traces of
impurities, and recrystallization from common organic sol-
vents failed.
N
M
N
ð1Þ
SiMe3
2
M = Mg (A), Ni (B), Zn (C), Cd (D)
M = Cd
N
Me2Si
N
CdMe2
+
N
SiMe2
N
E
In contrast to the very limited number of complexes
with anionic 8-amidoquinoline substituents, the neutral 8-
aminoquinoline molecule was widely used as a ligand in
coordination compounds. Representative examples are
[M(H2O)2L2]X2 (M = Fe, Co, Ni, Cu; L = 8-aminoquino-
line; X = Cl, Br) with the water molecules in a trans posi-
N
+ MR2
- RH
N
(Me3Si)2N-Zn
N
ð3Þ
N
H
SiR'R"2
2þ
SiR'R"2
tion [12]. The cation of comparable ½Znð H2OÞL2ꢀ
R = N(SiMe3)2
R', R" = iPr (1a)
R' = tBu, R" = Me (1b)
2ꢁ
R', R" = iPr (2a)
R' = tBu, R" = Me (2b)
ZnX4 contains a penta-coordinate zinc atom [13]. For
bis(8-aminoquinoline)nickel(II) chloride a pale grey-olive
mono-hydrate as well as a grey-green dihydrate are well-
known [14]. Recently these nickel complexes were applied
in ethylene polymerization processes in the presence of
co-catalysts such as methylalumoxane (MAO) and zircon-
ocene dichloride (Cp2ZrCl2) [15].
2-Pyridylmethylamides are bidentate Lewis bases with
very similar coordination behaviour. However, C–C cou-
pling reactions were observed as prominent side reactions
according to Eq. (2) [16–18]. The first reaction step is the
metallation at the methylene unit, followed by an oxidative
C–C coupling reaction under the precipitation of zinc
metal. As of yet we were unable to isolate appropriate
nickel complexes with 2-pyridylmethylamido anions. With
Unsubstituted 8-aminoquinoline reacted stepwise with
zinc bis[bis(trimethylsilyl)amide]. Therefore heteroleptic
bis(trimethylsilyl)amido zinc(II) 8-amidoquinoline (3) was
accessible according to Eq. (4) and crystallized dimeric with
the 8-amidoquinoline groups in bridging positions. The
basicity of the trialkylsilyl substituted amides is strongly
reduced due to an effective negative hyperconjugation
and charge backdonation from the pz(N) orbital into
r*(Si–C) antibonds of the trialkylsilyl groups. Due to this
fact, trialkylsilyl substituted amido groups avoid bridging
positions which explains the observation that sterically
shielded and thus doubly transaminated products are
favoured for trialkylsilyl substituted 8-amidoquinolines in
comparison to heteroleptic compounds with three-coordi-
8-amidoquinoline
and
8-(trialkylsilylamido)quinoline

A. Malassa et al. / Inorganica Chimica Acta 361 (2008) 1405–1414
1407
nate metal atoms. It also explains the monomeric nature of
heteroleptic bis(trimethylsilyl)amidozinc 8-(trialkylsilylam-
ido)quinoline (2).
in Fig. 1. At high temperatures only one resonance was
observed for the trimethylsilyl groups whereas at low tem-
peratures two signals were found. The intensity ratio also
varies with the temperature. Two processes are overlap-
ping, namely the transannular trans–cis isomerization
occurs within the NMR time scale and the trans–cis ratio
strongly depends on the temperature. In addition, with
increasing temperature the chemical shift of the NH proton
shows a strong high field shift.
Zincation of 8-aminoquinoline yielded zinc(II) bis(8-
amidoquinoline) (4) according to Eq. (5). The structure is
comparable to the already well-known N-trialkylsilyl
substituted molecule zinc(II) bis[8-(trimethylsilylami-
do)quinoline] with tetra-coordinate zinc atoms [11].
(Me3Si)2N
N
Zn
+ 2 ZnR2
- 2 RH
2
NH HN
N
ð4Þ
NH2
N
Zn
H
N(SiMe3)2
R = N(SiMe3)2
3
The heteroleptic dimeric compound 3 can adopt two iso-
meric structures, namely the transannular cis- and trans-
arrangement as shown in Scheme 1. In the crystalline state
only centrosymmetric A was found. However, for dimeric
methylzinc (N-trialkylsilyl)(pyridylmethyl)amide both of
these isomers are well-known in the solid state [16–18].
The diamagnetic zinc complex 3 offers the possibility to
study isomerization processes in solution. Dynamic NMR
investigations showed a strong temperature dependency
of the 1H NMR spectrum in [D8]THF solution as displayed
+ Zn[N(SiMe3)2]2
HN(SiMe )
N
2
Zn
N
ð5Þ
- 2
3
2
N
H
NH2
H
2
4
Nickel(II) bis[bis(trimethylsilyl)amide] decomposes very
fast [21] and therefore, another protocol has to be applied.
Well-known [22] (tmeda)NiMe2 offers an alternative as
metallation reagent towards 8-aminoquinoline. Regardless
of the stoichiometric ratio of the reagents, homoleptic nick-
el(II) bis(8-amidoquinoline) (5) was obtained according to
Eq. (6). This compound of a d8 transition metal is diamag-
netic and, hence, a square planar molecular structure has to
be expected, different than observed for 4 or found for the
paramagnetic 8-(trialkylsilylamido)quinolines of nickel(II)
[10].
N(SiMe3)2
N
N
N
N
H
Zn
N
H
N
N
H
Zn
N(SiMe3)2
Zn
(Me3Si)2N
Zn
(Me3Si)2N
N
H
B
A
Scheme 1. Drawing of the transannular cis- and trans-arrangement of
dimeric heteroleptic bis(trimethylsilyl)amido-metal(II) 8-amidoquinoline
derivatives.
Fig. 1. The dynamic 1H NMR experiments of 6 show the temperature dependency of ratio of trans- and cis-isomers as well as the isomerization process
within the NMR time scale. For the values of the chemical shifts and coupling constants see Table 1 and Section 4 (to the left: quinolyl resonances, middle:
NH-fragment, to the right: trimethylsilyl resonances).

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A. Malassa et al. / Inorganica Chimica Acta 361 (2008) 1405–1414
vated temperatures C–C coupling reactions according to
Eq. (2) occurred; however, homoleptic zinc bis[(2-pyr-
idylmethyl)(trialkylsilyl)amides] were not obtained from
this procedure. The enhanced reactivity towards 8-amino-
quinoline moieties allowed the synthesis of dinuclear bis[-
zinc-di(8-quinolylamido)diphenylsilane] (7) from the
metallation of di(8-quinolylamino)diphenylsilane (6) with
dimethylzinc according to Eq. (7). The central structural
moiety consists of an eight-membered Si2Zn2N4 ring.
+ (tmeda)NiMe2
N
2
Ni
N
ð6Þ
- 2 MeH
- TMEDA
N
H
NH2
H
2
5
In Table 1 a comparison of the NMR data of 8-amino-
quinoline, zinc(II) (4) and nickel(II) bis(8-amidoquinoline)
(5) is shown. The numbering scheme of the atoms for the
interpretation of the NMR spectra is given in Scheme 2.
The differences between tetrahedral 4 and planar 5 are
rather small with the exception of the NH function.
Whereas in 8-aminoquinoline and the zinc complexes d val-
ues between 4.1 and 5.6 are observed, the amido proton of
nickel complex 5 is strongly shifted towards higher field.
This fact can be addressed to intramolecular steric
repulsion.
N
N
N
N
N
Zn
Zn
N
N
NH
NH
+ 2 ZnMe2
- 4 MeH
Ph2Si
2 Ph2Si
SiPh2
ð7Þ
N
N
N
The straight forward synthesis of homoleptic 4 was sur-
prising because in many other examples dialkylzinc is only
able to react once with amines yielding heteroleptic alkyl-
zinc amides [23,24]. A strongly reduced metallation force
of the remaining methyl group was also observed for alkyl-
zinc (2-pyridylmethyl)(trialkylsilyl)amides [16–18]. At ele-
6
7
2.2. Molecular structures
For comparison reasons, the molecular structure of the
starting amine 1a was determined and is represented in
Fig. 2. In Table 2 selected bond lengths and angles are sum-
marized together with the values of the metal complexes 2a,
3, 4 and 5. Uncoordinated 8-aminoquinoline was reported
earlier which cocrystallized with cis–cis-1,3,5-trimethylcy-
clohexane-1,3,5-tricarboxylic acid [25]. A comparison of
these data shows that the influence of the deprotonation
Table 1
Comparison of the NMR data of 8-aminoquinoline (H), bis(trimethyl-
silyl)amido zinc(II) 8-amidoquinoline (3), zinc(II) di(8-amidoquinoline)
(4), and nickel(II) di(8-amidoquinoline) (5) (conditions: 25 °C, [D8]THF)
Assignm.a
H
3b
4
5
1H NMR
d(H1)
d(H2)
d(H3)
d(H5)
d(H6)
d(H7)
d(NH)
8.67 dd
7.32 dd
8.04 dd
7.01 dd
7.25 dd
6.83 dd
5.59 s
7.94 d
6.96 m
7.68 s, br
7.22 m
7.36 t
8.16 dd
7.29 dd
8.14 dd
6.62 dd
7.19 t
8.05 d
7.21 dd
8.01 d
6.33 d
7.02 t
6.34 d
2.08 s
6.96 m
4.10 s
6.69 dd
4.50 s
13C{1H} NMR
d(C1)
d(C2)
d(C3)
d(C4)
d(C5)
d(C6)
d(C7)
d(C8)
d(C9)
a
147.4
121.7
136.2
129.8
114.8
128.1
109.3
146.3
139.2
139.2
121.2
146.4
130.3
117.9 br
129.4
115.6 br
152.5
144.4
121.6
139.1
131.1
106.9
130.7
109.9
156.4
139.4
138.2
121.3
146.5
131.3
105.5
130.8
108.6
159.7
146.0
141.0
Assignment, see Scheme 2.
Measurement at 330 K, N(SiMe3)2: d(1H) = 0.00; d(13C{1H}) = 5.7.
b
3
5
2
1
4
9
6
7
N
8
Fig. 2. Molecular structure of 8-(triisopropylsilylamino)quinoline (1a).
The ellipsoids represent a probability of 40%, C-bound H atoms are
neglected for clarity reasons. Selected structural parameters are given in
Table 2.
NH2
Scheme 2. Numbering scheme for the assignment of the NMR data.

A. Malassa et al. / Inorganica Chimica Acta 361 (2008) 1405–1414
1409
Table 2
Comparison of selected bond lengths (pm) and angles (°) of 8-(triisopropylsilylamino)quinoline 1a and complexes 2b, 3, 4 and 5. The radii r(M2+) (pm)
refer to tetrahedrally coordinated metal cations, the metal radii r(Mmetal) refer to the metal structures with 12-coordinate metal atoms
M
H (1a)
Zn (2b)
Zn (3)
Zn (4)
Ni (5)
r(M2+
)
74
74
74
69
r(Mmetal
SiR0R2
M–N1
M–N2
N2–Si
N1–C1
N1–C9
N2–C8
C1–C2
C2–C3
C3–C4
C4–C5
C4–C9
C5–C6
C6–C7
C7–C8
C8–C9
)
133.5
133.5
H
210.8(2)
206.3(2)
a
133.5
H
208.1(1)
191.9(2)
81(2)a
124.6
H
192.4(2)
186.6(2)
84(3)a
SiiPr3
SiMe2tBu
206.8(2)
190.7(2)
173.8(2)
133.0(3)
135.9(3)
138.2(3)
140.1(4)
134.9(5)
141.9(4)
140.5(4)
142.5(4)
136.6(4)
140.3(4)
138.5(4)
144.9(3)
85.71(9)
a
a
172.8(3)
131.4(6)
136.7(5)
137.4(5)
139.1(8)
135.8(7)
141.4(6)
140.3(6)
142.4(6)
137.1(6)
140.2(6)
138.2(5)
144.3(5)
132.4(3)
137.7(3)
139.7(3)
140.5(3)
136.3(3)
141.1(3)
141.3(3)
141.2(3)
136.1(3)
140.9(3)
137.5(3)
143.5(3)
80.70(7)
132.3(2)
136.6(2)
135.0(2)
140.0(2)
136.7(3)
141.3(3)
141.4(3)
141.5(2)
136.7(3)
140.0(3)
139.7(2)
144.3(2)
83.34(6)
132.8(3)
137.4(3)
134.6(2)
140.7(3)
136.2(3)
142.4(3)
141.8(3)
141.1(3)
137.5(3)
140.4(3)
139.9(3)
143.2(3)
83.61(7)
N1–M–N2
a
N–H bond length.
at N2 on the molecular structure of the quinoline moiety is
very small.
Larger variations are observed for the N2–C8 bond
lengths. The molecular structures of the zinc complexes
2b, 3 and 4 are represented in Figs. 3–5, respectively. Due
to steric reasons a three-coordinate zinc atom is observed
in 2b. Electrostatic attraction leads to short zinc-amide
bonds whereas the distance to the pyridyl fragment is much
larger. The bis(trimethylsilyl)amido group exhibits a planar
N3 atom with a large Si2–N3–Si3 angle of 127.2(1)° due to
repulsive forces between the bulky trimethylsilyl groups
Fig. 4. Molecular structure of dimeric 8-amidoquinoline zinc bis(trimeth-
ylsilyl)amide (3a). Symmetry-related atoms (ꢁx, ꢁy, ꢁz) are marked with
an ‘‘A’’. The ellipsoids represent a probability of 40%, C-bound H atoms
are neglected for clarity reasons.
Fig. 5. Molecular structure of tetrahedral zinc 8-amidoquinoline (4).
Symmetry-related atoms (ꢁx + 1, ꢁy + 1, z) are marked with an ‘‘A’’. The
ellipsoids represent a probability of 40%, C-bound H atoms are omitted
for clarity reasons.
Fig. 3. Molecular structure of monomeric 8-(tert-butyldimethylsilylami-
do)quinoline zinc bis(trimethylsilyl)amide (2b). The ellipsoids represent a
probability of 40%, H atoms are omitted for clarity reasons.

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A. Malassa et al. / Inorganica Chimica Acta 361 (2008) 1405–1414
[26]. The Zn–N3 bond length of 187.2(2) pm is elongated
compared to Zn[N(SiMe3)2]2 with a two-coordinate metal
atom (solid state Zn–N 183(1) pm [27], gas phase
182(1) pm [28]). In other homoleptic crystalline zinc com-
pounds small bond lengths were found due to the coordina-
tion number of two [29–32]. Dimerization leads to larger
coordination numbers of three at Zn and, hence, to longer
Zn–N bonds also for the terminally bound ligands [32,33].
The bond lengths in dimeric Zn(NPh2)2 adopt the values of
185.9(2) and 204.0(2) pm to the terminally and bridging
bound diphenylamide substituents [33]. This fact is not lim-
ited to homoleptic compounds, e.g. the dimer [(Me3Si)2N–
Zn(l-OCEt3)]2 shows Zn–N bond lengths to the terminal
amide of 186.8(3) pm [34].
In 3 the dimerization yields tetra-coordinate zinc atoms
and, therefore, larger Zn–N3 distances of 192.1(2) pm are
observed. These values are very similar to zinc amides with
terminally bound amide groups at tetra-coordinate metal
atoms such as (thf)2Zn(NPh2)2 (Zn–N 191.9(4) and
192.2(5) pm [33]). The bridging 8-amidoquinoline groups
with tetra-coordinate N2 atoms show very large Zn–N2
distances of 206.3(2) and 208.9(2) pm due to electronic
repulsion between the anionic amide groups and the bulk-
iness of the bis(trimethylsilyl)amide moiety. Again, the pyr-
idyl group shows the longest Zn–N1 bond of 210.8(2) pm
due to missing electrostatic attraction.
In distorted tetrahedral zinc complex 4 the Zn–N bond
lengths differ due to the electrostatic attraction. Thus the
Zn–N2 bond with a value of 191.9(2) pm is much shorter
than the Zn–N1 bond to the pyridyl unit (208.1(1) pm).
This complex is rather similar to the tetrahedral nickel
complex of the trialkylsilyl-substituted 8-amidoquinoline
anion [10]. Neglection of this trialkylsilyl protection of
the amide function leads to the formation of centrosym-
metric planar 5 with a trans-arrangement of the amide
groups. The molecular structure of nickel di(8-amidoquin-
oline) (5) is represented in Fig. 6. The Ni–N1 and Ni–N2
bond lengths show values of 192.4(2) and 186.6(2) pm
which are much smaller than observed for the tetrahedral
paramagnetic complexes. However, the quality of the X-
ray crystal structure determinations is rather poor and
large standard deviations as well as differences between
similar bond types are the consequence {nickel bis[8-(tri-
methylsilylamino)quinoline]: Ni–Namide 192(1) to 194(1) pm,
Ni–Npyridyl 192(1) to 206(1) pm; nickel bis[8-(tert.buty-
ldimethylsilylamino)quinoline]:
Ni–Namide
185(1),
203(1) pm, Ni–Npyridyl 200(1), 203(1) pm} [10]. In these tri-
alkylsilyl substituted complexes large N–Ni–N angles of
158.1(4)° (SiMe2tBu) as well as 138.2(2)° and 138.9(2)°
(SiMe3) are observed. Even though the square planar
arrangement enhances the intramolecular strain, shorter
Ni–N bond lengths are observed due to the possibility of
charge transfer from the p-orbitals of the planar nitrogen
atoms to the metal atom.
The molecular structure of di(8-quinolylamino)diphe-
nylsilane (6) is displayed in Fig. 7. The structural parame-
ters are within characteristic regions. Due to the bulkiness
of the 8-aminoquinolyl groups the N1–Si1–N3 angle is
slightly widened. Furthermore, the C–N–Si1 angles with
values of 131.2(1)° and 132.0(1)° are very large. The dinu-
clear zinc complex 7 is shown in Fig. 8. The central struc-
tural feature is an eight-membered Zn2Si2N4 ring with
four-coordinate zinc atoms. A comparison of the structural
data of 6 and 7 as well as the comparison with the mono-
nuclear complexes shows that the intramolecular steric
strain is rather poor. The Zn–N bond lengths lie within
characteristic ranges as discussed earlier. The quinolyl N-
atoms are in a planar environment whereas the amido N-
Fig. 7. Molecular structure of di(8-quinolylamino)diphenylsilane (6). The
ellipsoids represent a probability of 40%, C-bound H atoms are omitted
for clarity reasons. Selected bond lengths (pm): Si–N1 172.4(1), Si–N3
171.5(1), Si–C19 186.1(2), Si–C25 186.0(2), N1–C1 138.7(2), N3–C10
139.1(2); angles (°): N1–Si–N3 111.64(7), N1–Si–C19 103.68(7), N1–Si–
C25 113.34(7), N3–Si–C19 112.79(7), N3–Si–C25 104.05(7), C19–Si–C25
111.61(7), Si–N1–C1 132.0(1), Si–N3–C10 131.2(1).
Fig. 6. Molecular structure of square planar nickel 8-amidoquinoline (5).
Symmetry-related atoms (ꢁx, ꢁy, ꢁz + 2) are marked with ‘‘A’’. The
ellipsoids represent a probability of 40%, C-bound H atoms are omitted
for clarity reasons.

A. Malassa et al. / Inorganica Chimica Acta 361 (2008) 1405–1414
1411
NiMe2 [22] and N-tert-butyldimethylsilyl-8-aminoquino-
line [20] were prepared according to the literature proce-
dures. For a listing of NMR data of 3–5, see Table 1.
Synthesis of 8-(triisopropylsilylamino)quinoline (1a): 8-
Aminoquinoline (3.0 g, 20.8 mmol) was dissolved in 50 ml
of THF and cooled to ꢁ78 °C. A 1.6 M solution of n-buty-
llithium in hexane (13 ml, 20.8 mmol) was added. Thereaf-
ter, 4 g of chloro-triisopropylsilane (20.8 mmol) was
dropped into this reaction mixture. After complete addi-
tion the solution was warmed to r.t. All volatile materials
were removed under vacuum. The residue was dissolved
in pentane and filtered through a frit. The filtrate was con-
centrated. Slightly brown crystals of N-triisopropylsilyl-8-
aminoquinoline formed within a few days. Yield: 6.0 g
(20.0 mmol, 96%). M.p. 83 °C. 1H NMR ([D6]benzene):
d = 8.57 (H1), 7.55/7.58 (H3/5); 7.27 (H6); 7.15 (H2);
7.04 (H5); 6.92 (H7); 6.80 (NH); 1.15–1.30 (CH; CH3).
13C{1H} NMR ([D6]benzene): d 147 (C1); 146 (C8); 140
(C9); 136 (C3); 129 (C4); 127 (C7); 121 (C6); 115 (C2);
110 (C5); 18.8 (CH); 12.8 (CH3). IR (Nujol, cmꢁ1): 3318
vw, 3038 vw, 2925 vs, 2865 vs, 1612 w, 1572 w, 1507 w,
1473 w, 1416 w, 1378 w, 1324 w, 1231 w, 1096 w, 1062
w, 1029 vw, 1015 w, 994 vw, 912 m, 882 m, 919 m, 807 s,
789 s, 741 m, 727 m, 674 m, 667 m, 648 m, 573 m, 502
m, 484 m, 461 m. MS (DEI; m/z): 300 (M+, 52%), 257
([MꢁiPr]+, 100%), 215 ([Mꢁ(iPr)2]+, 4%), 171
([Mꢁ(iPr)3]+, 60%), 43 (iPr+, 48%). Elemental Anal. Calc.
for C18H28N2Si (300.52): C, 71.94; H, 9.39; N, 9.32. Found:
C, 70.94; H, 9.55; N, 9.40%.
Fig. 8. Molecular structure of dimeric zinc di(8-quinolylamido)diphe-
nylsilane (7). The molecular halves are distinguished by the letters ‘‘A’’
and ‘‘B’’. The ellipsoids represent a probability of 40%, H atoms are
omitted for clarity reasons. Selected bond lengths (pm): ZnA–N1A
207.6(4), ZnA–N2A 197.2(4), ZnA–N3A 208.7(4), ZnA–N4A 195.6(3),
ZnB–N1B 208.2(4), ZnB–N2B 197.7(4), ZnB–N3B 208.9(4), ZnB–N4B
196.6(4), SiA–N2A 171.9(4), SiA–N4B 172.5(4), SiA–C19A 187.6(5), SiA–
C25A 188.5(5), SiB–N2B 171.4(4), SiB–N4A 171.9(4), SiB–C19B 188.5(5),
SiB–C25B 187.2(5); angles (°): N2A–ZnA–N4A 145.7(1), N1A–ZnA–N2A
84.0(1), N3A–ZnA–N4A 84.0(1), N2B–ZnB–N4B 146.0(1), N1B–ZnB–
N2B 84.0(2), N3B–ZnB–N4B 83.9(1), SiA–N2A–ZnA 117.7(2), SiB–N2B–
ZnB 116.1(2), SiA–N4B–ZnB 120.2(2), SiB–N4A–ZnA 120.4(2),
N2A–SiA–N4B 103.4(2), N2B–SiB–N4A 102.2(2), SiA–N2A–C8A
127.3(3), SiB–N4A–C17A 125.3(3), SiB–N2B–C8B 128.3(3), SiA–N4B–
C17B 125.9(3).
Synthesis of bis(trimethylsilyl)amido-zinc 8-(tert-butyl-
dimethylsilylamido)quinoline (2b): A solution of 0.15 ml
Zn[N(SiMe3)2]2 (3.9 mmol) in THF was dropped to a solu-
tion of 0.10 g of N-(tert-butyldimethylsilyl)-8-aminoquino-
line (3.9 mmol) in 30 ml of THF which was cooled to
ꢁ78°C. After complete addition the reaction mixture was
warmed to r.t. Then all volatile materials were removed
under reduced pressure and the residue dissolved in pen-
tane. Within a few days, 1.41 g of orange crystals of 3
(mmol, 75%) precipitated from concentrated solutions.
M.p. 125 °C. 1H NMR ([D6]benzene): d 8.28 (dd, 1H,
Chin1), 7.49 (dd, 1H, Chin7), 7.20-7.31 (m, 2H Chin3/5),
6.69 (dd, 1H, Chin6), 6.57–6.64 (q, 1H, Chin2), 1.13 (s,
9H, CMe3), 0.34 (s, 6H, CH3), 0.38 (s, 18H, SiMe3).
13C{1H} NMR ([D6]benzene): d 147.1 (Chin9), 146.2
(Chin1), 140.3 (Chin8), 136.0 (Chin6), 129.4 (Chin4),
121.4 (Chin2), 115.2 (Chin7), 110.1 (Chin3/5), 26.5
(CMe3), 18.3 (CMe3), 3.6 (SiMe3), ꢁ4.5 (SiMe2). IR
(Nujol, cmꢁ1): 2924 vs, 2854 vs, 1567 w, 1497 w, 1456 s,
1386 m, 1323 m, 1283 vw, 1249 w, 1118 m, 999 w, 941 w,
844 m, 788 m, 737 vw, 667 vw. MS (DEI; m/z [%]): 481
(M+ [10]); 243 ([MꢁZnN(SiMe3)]+ [9]); 160 ([N(SiMe3)2]+
atoms show slight deviations from planarity (angle sums of
N2A/B and N4A/B between 354.5° and 357.6°).
3. Conclusion
The transamination reaction of Zn[N(SiMe3)2]2 is a
valuable access route to various hetero- and homoleptic
zinc amides whereas the use of dialkylzinc often leads to
heteroleptic alkylzinc amides [23,24]. However, dimethyl-
zinc can be employed for the metallation of di(8-quin-
olylamino)diphenylsilane (6) yielding dinuclear zinc di(8-
quinolylamido)diphenylsilane (7). For the synthesis of
the corresponding nickel complex, (tmeda)NiMe2 [22]
proved to be more appropriate due to a higher stability
than Ni[N(SiMe3)2]2 [21]. In contrast to the paramagnetic
nickel bis[8-(trialkylsilylamido)quinolines] [10] with tetra-
hedrally coordinated nickel centers, diamagnetic nickel
di(8-amidoquinoline) shows a square planar molecular
structure.
[16]); 146 (½SiMe3ꢀ [100]); 131 ([HNSiMe2tBu]+ [40]); 73
þ
2
4. Experimental
([SiMe3]+ [17]); 57 (tBu+ [11]).
Synthesis of bis[bis(trimethylsilyl)amido-zinc 8-amido-
quinoline] (3): A solution of 0.47 g of Zn{N(SiMe3)2}2
(1.21 mmol) in 2 ml of diethylether was layered at r.t. with
a solution of 0.18 g of 8-aminoquinoline (1.20 mmol) in
General procedure: All manipulations were carried out in
an anhydrous argon atmosphere and the solvents were
thoroughly dried. Starting Zn[N(SiMe3)2]2 [35], (tmeda)-

1412
A. Malassa et al. / Inorganica Chimica Acta 361 (2008) 1405–1414
10 ml of Et2O. Within one day 0.36 g of colorless needles of
6 (0.48 mmol, 81%) precipitated and were isolated and
dried under vacuum. This solid is extremely sensitive and
its color turned orange within a few days. Dec. above
62.66; H, 4.10; N, 16.24. Found: C, 62.27; H, 4.22; N,
16.29%.
Synthesis of di(8-quinolylamino)diphenylsilane (6): A
1.6 M solution of n-butyllithium in hexane was added at
0 °C to a solution of 2.0 g of 8-aminoquinoline (13.7 mmol)
in 35 ml of toluene. Thereafter, the orange reaction mixture
was cooled to ꢁ78 °C and dropped to a precooled (ꢁ78 °C)
solution of 1.4 ml of dichloro-diphenylsilane (6.9 mmol) in
10 ml of toluene. Thereafter, the reaction mixture was stir-
red for 15 h at r.t. All solids were removed and the volume
of the solution was reduced to a volume of 10 ml. The oily
orange-brown residue solidified and was washed with 8 ml
of cold toluene. A second crop of crystalline 6 was collected
from the toluene fractions. All volatiles were removed in
vacuo and the residue suspended in cold pentane and then
collected. Yield: 1.38 g of colorless crystals of 6 (3.0 mmol,
1
50 °C. H NMR ([D8]THF, 193 K): d 8.99 (d, J = 4.4 Hz,
1H, Chin-H), 8.6 (d, J = 8.6 Hz, 1H, Chin-H), 8.04 (d,
J = 7.6 Hz, 3.5 H, Chin-H), 7.80 (d, J = 4.6 Hz, 0.7 H,
Chin-H), 7.76 (d, J = 4.6 Hz, 0.7 H, Chin-H), 7.56–7.32
(m, 13.9 H, Chin-H), 7.10 (d, J = 7 Hz, 3.9 H, Chin-H),
6.96 (d, J = 4.6 Hz, 2H, Chin-H), 6.91 (d, J = 4.6 Hz, 2
H, Chin-H), 4.73 (s, 3.2 H, NH), 4.60 (s,1.1 H, NH), 0.01
(s, 70.8 H, Si(CH3)3), ꢁ0.38 (s, 15.7 H, Si(CH3)3). IR
(Nujol, cmꢁ1): 3405 w, 3336 m, 1596 w, 1581 m, 1571 m,
1501 s, 1430 m, 1349 m, 1327 m, 1269 m, 1244 m, 1226
m, 1171 m, 1098 m, 1065 w, 1035 m, 993 vs, 931 w, 879
m, 820 s, 788 s, 753 m, 732 m, 701 m, 669 m, 642 w, 612
w, 595 w, 530 w, 505 m. MS (DEI, m/z [%]): 369 ([M+/
2]+ [32]), 352 ([M+/2ꢁMe]+ [20]), 161 ([HN(SiMe3)2]+
[12]), 146 ([HN(SiMe3)2ꢁMe]+ [96]), 130 ([HN(Si-
Me3)2ꢁ2Me]+ [52]).
1
44%). M.p.: 170 °C. H NMR ([D6]benzene): d 8.58 (dd,
1H, H1), 8.06–8.04 (m, 2H, o-Ph), 7.75 (s, 1H, NH), 7.52
(d, 1H, H7), 7.47 (dd, 1H, H3), 7.12–7.07 (m, 3H, p-Ph,
m-Ph), 6.87 (t, 1H, H6), 6.81–6.79 (m, 1H, H5), 6.76 (dd,
1H, H2), 3J(H1, H2) = 4.0 Hz, 3J(H2, H3) = 8.3 Hz,
3J(H6, H7) = 8.0 Hz, 4J(H1, H3) = 1.6 Hz. 13C{1H}
NMR ([D6]benzene): d 147.3 (C1), 144.2 (C8), 140.0 (C9),
136.1 (C3), 134.9 (o-Ph), 130.4 (p-Ph), 129.1 (C4), 128.7
(m-Ph), 121.1 (C2), 116.6 (C5), 112.2 (C7); C6 and i-Ph-car-
bon were not detected. 1H NMR ([D8]THF): d 8.72 (m, 1H,
H1), 8.10 (dd, 1H, H3) 7.88-7.86 (m, 2H, o-Ph), 7.42–7.33
(m, 4H, H2, p-Ph, m-Ph), 7.26 (s, 1H, NH), 7.20–7.18 (m,
1H, H7), 7.10–7.05 (m, 2H, H6,H5), 3J(H2,
H3) = 8.4 Hz, 4J(H1, H3) = 1.6 Hz. 13C{1H} NMR
([D8]THF): d 148.0 (C1), 144.7 (C8), 140.4 (C9), 136.8
(C3), 136.0 (i-Ph), 135.3 (o-Ph), 130.8 (p-Ph), 129.8 (C4),
129.0 (m-Ph), 128.2 (C6), 122.2 (C2), 116.9 (C5), 112.4
(C7). IR (Nujol, cmꢁ1): 3334 m, 3316 m, 3065 w, 1614 w,
1591 w, 1575 m, 1507 vs, 1427 m, 1416 s,1321 vs, 1270 w,
1234 m, 1183 w, 1114 m, 1095 s, 1061 w, 1029 w, 998 w,
924 m, 911 w, 823 s, 806 m, 7,93 m, 748 s, 726 m, 702 m,
645 m, 586 m, 537 m, 515 m, 506 m, 495 m, 472 m. MS
(DEI, m/z): 468 ([M]+, 1%), 291([MꢁPh]+, 2%), 325
([Mꢁach]+, 100%), 171 ([achSi]+, 18%), 144 ([ach]+,
24%), 117 ([achꢁC2H3]+, 8%). Elemental Anal. Calc. for
C30H24N4Si (468.62): C, 76.89; H, 5.16; N, 11.96. Found:
C, 73.95; H, 5.70; N, 12.12%.
Synthesis of zinc bis(8-amidoquinoline) (4): A solution of
0.57 g of Zn{N(SiMe3)2}2 (1.47 mmol) in 2 ml of THF was
layered with 2 ml of THF at r.t. On top of this two-phase sys-
tem a solution of 0.42 g 8-aminoquinoline (2.94 mmol) in
6 ml of THF was layered very carefully. Diffusion led to
the precipitation of 0.32 g of red crystals of 7 (0.92 mmol,
63%). M.p. 275 °C. 1H NMR: coupling constants
3J(H1H2) = 4.6 Hz, 3J(H2H3) = 8.4 Hz, 3J(H5H6) = 8.0 Hz,
3J(H6H7) = 8.0 Hz, 4J(H1H3) = 1.5 Hz, 4J(H5H7) = 0.7 Hz.
IR (Nujol, cmꢁ1): 3404 m, 1595 m, 1570 s, 1498 s, 1464 vs,
1428 m, 1396 w, 1370 vs, 1348 s, 1289 w, 1244 m, 1229 w,
1194 m, 1167 w, 1135 w, 1102 s, 1063 m, 1035 m, 980 w,
842 w, 817 s, 802 m, 788 s, 750 s, 730 s, 645 w, 636 w, 618
w, 584 w, 544 s, 530 s, 497 w, 466 w. MS (DEI, m/z [%]):
354 ([M]+ [28]), 209([Mꢁach]+ [5]), 144 ([ach]+ [97]), 117
([achꢁC2H3]+ [100]). Elemental Anal. Calc. for C18H14N4Zn
(353.77): C, 61.46; H, 4.01; N, 15.93. Found: C, 60.61; H,
4.43; N, 16.46%.
Synthesis of nickel bis(8-amidoquinoline) (5): A solution
of 0.31 g of (tmeda)NiMe2 (1.5 mmol) in 6 mL of THF was
carefully covered with 9 mL of THF. Thereafter, a solution
of 0.43 g of 8-aminoquinoline (3.0 mmol) was layered on this
mixture. At the border between the two layers a green ring
appears immediately. After several minutes the color chan-
ged to blue. Within two days blue-black cuboids precipi-
tated. These crystals were only moderately air-sensitive
whereas the solutions of 5 proved to be much more reactive
towards air. Stirring of the solution immediately led to the
precipitation of a black powder. Yield: 0.42 g (1.23 mmol,
82%). M.p.: 318 °C. 1H NMR: coupling constants
3J(H1H2) = 5.1 Hz, 3J(H2H3) = 8.1 Hz, 3J(H5H6) = 7.9 Hz,
3J(H6H7) = 7.9 Hz. IR (Nujol, cmꢁ1): 3386 s, 1589 s, 1566 vs,
1504 vs, 1353 s, 1224 m, 1203 m, 1165 m, 1114 m, 975 w. br,
918 w, 823 w, 809 m, 776 s, 747 m, 733m, 724 m, 667 w, 637 m,
535 m, 514 w, 485 m. MS (DEI, m/z [%]): 344 ([M]+ [100]),
201([Mꢁach]+ [56]), 144 ([ach]+ [96]), 117 ([achꢁC2H3]+
[46]). Elemental Anal. Calc. for C18H14N4Ni (345.02): C,
Synthesis of dimeric zinc di(8-quinolylamido)diphenylsi-
lane (7): A 2.0 M solution of dimethylzinc in toluene
(0.95 ml, 1.9 mmol) was dropped to a solution of 0.44 g
of di(8-quinolylamino)diphenylsilane (6) in 3 ml of toluene.
The liberation of methane was observed immediately and
the reaction mixture turned slightly orange. All solids were
removed and the volume of the solution was reduced to a
third of the original volume. Storage at ꢁ20 °C afforded
0.81 g of colorless crystalline 7 (0.76 mmol, 81%). M.p.:
1
92 °C (dec.). The H NMR spectrum in [D6]benzene solu-
tion gave unresolved multiplets between d = 6.23 and
8.21. 13C{1H} NMR ([D6]benzene): d 109.6 and 110.6
(C7), 116.8 and 117.1 (C5), 120.3 and 120.6 (C2), 120.8
and 121.1 (C6), 125.6 (C4), 128.3 (Ph), 129.5 (Ph), 130.8

A. Malassa et al. / Inorganica Chimica Acta 361 (2008) 1405–1414
1413
Table 3
Crystal data and refinement details for the X-ray structure determinations
Compound
1a
2b
3
4
5
6
7
Formula
Fw (g molꢁ1
T (°C)
C18H28N2Si
300.51
ꢁ90(2)
monoclinic
C2/c
22.2294(9)
8.6948(5)
20.9076(8)
90.00
118.624(3)
90.00
C21H39N3Si3Zn
483.19
C30H50N6Si4Zn2
737.86
C18H14N4Zn
351.70
ꢁ90(2)
tetragonal
I41/a
15.2955(4)
15.2955(4)
13.2066(3)
90.00
90.00
90.00
3089.71(13)
8
1.512
C18H14N4Ni
345.04
ꢁ90(2)
monoclinic
P21/n
6.7065(3)
9.7614(5)
10.4571(4)
90.00
90.812(3)
90.00
C30H24N4Si
468.62
ꢁ90(2)
monoclinic
P21/c
16.9122(5)
10.0621(3)
15.7696(5)
90.00
114.204(2)
90.00
C81H68N8Si2Zn2
1340.35
ꢁ90(2)
)
ꢁ90(2)
ꢁ90(2)
Crystal system
triclinic
triclinic
monoclinic
P21/c
ꢀ
ꢀ
Space group
P1
P1
˚
a (A)
8.6354(3)
11.6898(5)
13.7655(5)
77.008(2)
89.647(2)
77.375(2)
1319.91(9)
2
8.7735(3)
9.6227(4)
11.6784(5)
74.740(2)
85.135(2)
72.461(2)
906.95(6)
1
12.9349(4)
26.3182(9)
20.0149(4)
90.00
103.516(2)
90.00
6624.8(3)
4
1.344
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
3547.1(3)
8
1.125
684.50(5)
2
1.674
2447.64(13)
4
1.272
Z
q (g cmꢁ3
)
1.216
10.78
1.351
14.83
l (cmꢁ1
)
1.29
15.93
14.21
1.22
8.13
Measured data
Data with I > 2r(I)
Unique data
11760
3119
4036
0.2420
0.0980
1.248
9587
4586
5975
0.1079
0.0422
1.012
6250
3420
3876
0.0764
0.0304
1.020
10322
1542
1774
0.0729
0.0261
1.022
4441
1269
1551
0.0866
0.0307
1.041
16988
4138
5594
0.1167
0.0435
1.020
36086
7992
14635
0.1707
0.0703
1.014
wR2 (all data, on F2)a
R1 (I > 2r(I))a
sb
ꢁ3
˚
Residual density (e A
Absorption method
)
1.182/ꢁ0.324
0.440/ꢁ0.447
0.288/ꢁ0.411
0.379/ꢁ0.274
0.318/ꢁ0.458
0.221/ꢁ0.299
1.053/ꢁ0.524
multi-scan
multi-scan
multi-scan
multi-scan
multi-scan
none
multi-scan
Absorption correction T
Minimum/maximum
CCDC No.
0.8200/0.8941
0.8000/0.8741
0.7581/0.7895
651242
0.7312/0.7760
651243
0.7890/0.8301
651244
0.8549/0.9042
651246
651240
651241
651245
P
P
P
P
2
2
1=2
2
a
Definition of the R indices: R1 = ( jjFoj ꢁ jFcjj)/ jFoj. wR2 ¼ f ½wðF 2o ꢁ F c2Þ ꢀ= ½wðF o2Þ ꢀg with wꢁ1 ¼ r2ðF o2Þ þ ðaPÞ .
P
2
1=2
b
s ¼ f ½wðF 2o ꢁ F c2Þ ꢀ=ðNo ꢁ NpÞg
.
(Ph), 135.2 (Ph), 135.3 and 135.7 (C3), 137.0 and 138.5
(C9), 144.2 and 144.4 (C8), 153.5 and 154.2 (C1). IR
(Nujol, cmꢁ1): 2924 vs, 2854 vs, 1594 vw, 1568 w, 1502,
1456 s, 1377 m, 1319 m, 1281 w, 1261 w, 1117 m, 1036
w, 944 vw, 819 w, 789 w, 739 w, 701 vw, 533 vw, 483 vw.
Structure determinations: The intensity data were col-
lected on a Nonius Kappa CCD diffractometer using
graphite-monochromated Mo Ka radiation (k =
the Deutsche Forschungsgemeinschaft (DFG, Bonn-Bad
Godesberg, Germany) for generous funding. We also
acknowledge the support by the Fonds der Chemischen
Industrie (Frankfurt/Main, Germany). A. Malassa thanks
the Carl-Zeiss-Stiftung (Germany) for a generous Ph.D.
Grant.
˚
References
0.71073 A). Data were corrected for Lorentz polarization
and except for compound 6 for absorption effects [36–38].
The crystal data and refinement details are summarized
in Table 3. The structures were solved by direct methods
(SHELXS [39]) and refined by full-matrix least squares tech-
niques against F 2o (SHELXL-97 [40]). The carbon atom C16
of 1a (Fig. 2) shows an elongated ellipsoid, however, a
refinement with a split model was not possible.
[1] T.C. Harrop, P.K. Mascharak, in: H.-B. Kraatz, N. Metzler-Nolte
(Eds.), Concepts and Models in Bioinorganic Chemistry, Wiley-VCH,
Weinheim, 2006, p. 309 (Chapter 14).
[2] N. Burzlaff, in: H.-B. Kraatz, N. Metzler-Nolte (Eds.), Concepts and
Models in Bioinorganic Chemistry, Wiley-VCH, Weinheim, 2006, p.
397 (Chapter 17).
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Acknowledgements
This work was supported in the collaborative research
initiative of the DFG (SFB 436) and we are grateful to

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