Coordination Modes of 2,5-Di(tert-butyl)pyrrolide - Crystal Structures of HPyr*, Pyr*H·thf, (thf)2LiPyr*, and [(Me3Si)3C-Zn]2(μ-Cl)(μ-Pyr*) (Pyr* = 2,5-tBu2NC4H2)

Article abstract of DOI:10.1002/(SICI)1099-0682(199808)1998:8<1175::AID-EJIC1175>3.0.CO;2-B

The lithiation of 2,5-di(tert-butyl)pyrrole (1) yields bis(tetrahydrofuran)lithium 2,5-di(tert-butyl)pyrrolide (2), which is monomeric in solution as well as in the solid state. Due to the coordination number of three for the lithium atom, short Li-O and

Full text of DOI:10.1002/(SICI)1099-0682(199808)1998:8<1175::AID-EJIC1175>3.0.CO;2-B

FULL PAPER
Coordination Modes of 2,5-Di(tert-butyl)pyrrolide – Crystal Structures of
HPyr*, Pyr*H·thf, (thf) LiPyr*, and [(Me Si) C-Zn] (µ-Cl)(µ-Pyr*)
2
3
3
2
(
Pyr* ؍ 2,5-tBu NC H )
2
4
2
Matthias Westerhausen* , Michael Wieneke , Heinrich Nöth , Thomas Seiferta[°], Arno Pfitznerb,[°]
a
a
a[°]
c[°]
c
c
Wolfgang Schwarz , Oliver Schwarz , and Johann Weidlein*
Institut für Anorganische Chemie der Ludwig-Maximilians-Universität Münchena,
Meiserstraße 1, D-80333 München, Germany
Fax: (internat.) ϩ 49(0)89/5902-578
E-mail: maw@anorg.chemie.uni-muenchen.de
Institut für Anorganische Chemie der Universität Siegenb,
Adolf-Reichwein-Straße, D-57068 Siegen, Germany
Institut für Anorganische Chemie der Universität Stuttgartc,
Pfaffenwaldring 55, D-70569 Stuttgart, Germany
Fax: (internat.) ϩ49(0)711/685-4241
Received March 30, 1998
Keywords: Hydrogen bonds / Indium / Lithium / Nitrogen heterocycles / Zinc
The lithiation of 2,5-di(tert-butyl)pyrrole (1) yields
bis(tetrahydrofuran)lithium 2,5-di(tert-butyl)pyrrolide (2),
pyrrolide substituent, while the other bonds to the opposite
C–C bond. At 215 pm, the Zn–N bond is very long compared
which is monomeric in solution as well as in the solid state. to those in alkylzinc amides, whereas the Zn–C distances lie
Due to the coordination number of three for the lithium atom, in the range of Zn–C bond lengths found between zinc and
short Li–O and Li–N bond lengths of 193 pm are observed. η -bonded cyclopentadienide ligands. The molecular
5
The metathesis reaction of
methylzinc chloride (3) gives colorless bis[tris(trimethyl-
2
with tris(trimethylsilyl)-
structures of 1 and of the low-melting THF adduct 1·thf show
a similar 2,5-di(tert-butyl)pyrrole molecule, but in the latter
silyl)methylzinc] chloride 2,5-di(tert-butyl)pyrrolide (4). The case a weak N–H···O bond is observed (N–H 97 pm, O···H
pyrrolide ligand and the chlorine atom bridge the zinc atoms.
One of the zinc atoms is bonded to the nitrogen atom of the
199 pm).
Ϫ
The pyrrolide substituent [NC H ] is isoelectronic with
Here, we describe three different coordination modes of
4
4
Ϫ
the cyclopentadienide anion, and since it possesses 6π elec- the 2,5-di(tert-butyl)pyrrolide anion Pyr* . This ligand
trons can be regarded as a Hückel aromatic system. In con- forms LiϪN σ bonds, but the reaction of LiPyr* with
trast to this (formal) analogy of these ligands, the substi- InCl[ yields the indium(I) derivative with a η -bonded
tution of a cyclopentadienide ligand of the well-known fer- Pyr* anion. The unusual bridging mode is found to be ad-
rocene by a pyrrolide substituent to yield an azaferrocene opted in bis[tris(trimethylsilyl)methylzinc] chloride 2,5-di-
5]
5
[1]
was first reported in 1963. The significantly lower tend- (tert-butyl)pyrrolide. For the sake of comparison, the mole-
ency of the NC H4 anion to coordinate as a π ligand and cular structures of 2,5-di(tert-butyl)pyrrole and of its tetra-
Ϫ
4
the enhanced tendency to form MϪN σ bonds is a conse- hydrofuran complex are also included.
quence of the high electronegativity of the heteroatom. On
the other hand, the bonding properties depend on the sub-
Results
stitution pattern on the pyrrolide ring. In 2,2Ј,5,5Ј-tetra- Preparation
1
methyl-1,1Ј-diazaplumbocene, η bonding to the 2,5-di-
The
starting
material
2,5-di(tert-butyl)pyrrole[6]
methylpyrrolide is observed,[ whereas the corresponding
,5-di-tert-butyl-substituted pyrrolide crystallizes with an
η -bonded ring. In contrast to these findings, the group-
3 metals (boron group, triels) form derivatives of the type
Me M NC H4ϪxRx with σ(MϪN) bonds (η coordi-
nation), although in the solid state the M metal centers
are also bonded to the π-system of a pyrrolide ligand of a
neighboring molecule, thus forming π associates.[
2]
(
HϪPyr*, 1), which crystallizes from a concentrated tetra-
2
hydrofuran solution as a THF solvate (1·thf), has been well
known for more than 30 years. With n-butyllithium, 1 is
lithiated according to eq. 1 to give quantitatively bis(tetra-
hydrofuran-O)lithium 2,5-di(tert-butyl)pyrrolide (2).
5
[3]
1
III
1
2
4
III
(
1)
4]
Meanwhile, the reaction of lithium tris(trimethylsilyl)-
methanide with anhydrous ZnCl yields [(thf) Li][(Me Si) -
[
°]
X-ray structure analysis.
2
4
3
3
Eur. J. Inorg. Chem. 1998, 1175Ϫ1182

WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1434Ϫ1948/98/0808Ϫ1175 $ 17.50ϩ.50/0
1175

M. Westerhausen, J. Weidlein et al.
FULL PAPER
CZn] (µ-Cl) . In order to obtain a product free from lith- lengths N(n)ϪH(n) fall in the narrow range from 83 to 91
2
3
ium halide and THF, tris(trimethylsilyl)methylzinc chloride pm.
(3) was purified by sublimation. Reactions of 3 with alkyl- The molecular structure of the tetrahydrofuran complex
and phenyllithium compounds yield the heteroleptic com- 1·thf is depicted in Figure 2. This adduct shows a crystallo-
pounds (Me Si) CϪZnϪR, which have in part been charac- graphically imposed C2v symmetry. The bond lengths in the
3
3
terized by X-ray crystallography.[ All these derivatives are pyrrole ring are not affected by coordination of a tetra-
7]
monomeric and contain solely σ(ZnϪC) bonds. The meta- hydrofuran molecule to the N1ϪH1 group. Even the
thesis reaction of 3 with (thf) LiPyr* (2) (eq. 2) yields bis- N1ϪH1 distance of 97 pm differs only by 3 times the esd.
2
[
tris(trimethylsilyl)methylzinc] chloride 2,5-di(tert-butyl)- On the other hand, the O2···H1 contact of 199 pm is quite
pyrrolide (4) as a colorless and moisture-sensitive solid with long (cf. the OϪH distances in ice, which vary between 99
a melting point of 74Ϫ75°C.
and 176 pm). This weak interaction explains the low melt-
ing point of 1·thf (below 0°C).
(
2)
The molecular structure of lithium 2,5-di(tert-butyl)pyr-
rolide (2) is shown in Figure 3. To date, only one related
molecule has been described in the literature, namely an N-
lithiocarbazole dimer. Compound 2 crystallizes as a mono-
mer due to the steric shielding of the lithium atom by the
tert-butyl groups. The lithium atom is in a trigonal-planar
coordination sphere, with a short LiϪN bond length of 193
pm. The low coordination number of the alkali metal is
also the reason for the short LiϪO distances of 193 pm. In
comparison to 1, the endocyclic CϪC bond lengths in the
pyrrolide ligand of 2 are 138 and 140 pm for C1ϪC2 and
C2ϪC2Ј, respectively, and are therefore very similar.
The molecular structure of 4 is depicted in Figure 4. The
molecule contains a crystallographic mirror plane, although
this symmetry element does not indicate the molecular sym-
metry, but rather leads to a two-site disorder of the 2,5-
di(tert-butyl)pyrrolide ligand. However, only one orien-
tation is shown in Figure 4. The atoms generated by the
crystallographic mirror plane are marked with apostrophes.
The two zinc atoms of the isomer shown in Figure 4 are in
different environments; Zn has a coordination number of
four, whereas ZnЈ is threefold coordinated by the atoms
C1Ј, Cl and N2.
The stoichiometry of this metathesis reaction obeys a 2:1
ratio, irrespective of the molar ratio of the reactants. Stir-
ring or refluxing of a 1:1 mixture of the starting materials
does not lead to the formation of a halogen-free derivative,
as is known for the metathesis reactions with lithium alkan-
ides. The cryoscopically determined molecular mass of 4
is consistent with the proposed structure shown in eq. 2.
Dissociation into 3 and mononuclear, heteroleptic tris(tri-
methylsilyl)methylzinc 2,5-di(tert-butyl)pyrrolide does not
occur under these conditions.
[
7]
Indium(I) chloride reacts with lithiated 2,5-dimethyl-,
2
,3,4,5-tetramethyl- as well as 2,5-di-tert-butylpyrrole in
toluene, hexane, or tetrahydrofuran at low temperatures.
However, the expected products of the methyl-substituted
species are not isolable, since decomposition occurs even at
temperatures of Ϫ90°C and Ϫ30°C, respectively, and pre-
cipitation of indium metal is observed. In contrast to this
I
instability, indium(I) 2,5-di(tert-butyl)pyrrolide In [Pyr*]
(5), which forms in tetrahydrofuran at low temperatures ac-
cording to eq. 3, can be isolated and purified by distillation
or sublimation in vacuo. During the melting of 5 at
The chlorine atom bridges the two zinc atoms with
ZnϪCl bond lengths of 241 pm and a ZnϪClϪZnЈ bond
angle of 110.3°. Terminal ZnϪCl bond lengths, as for ex-
7
7Ϫ78°C, the compound turns grey. The volatility of In-
[
Pyr*] (5) is comparable to that of hexameric (pentameth-
[8]
ylcyclopentadienyl)indium [pentamethylindocene(I)]. The
sensitivities of these compounds towards oxygen are also
similar, since In[Pyr*] (5) decomposes immediately with
precipitation of metallic indium.
[10]
[11]
ample in (bpy)ZnCl2
or (tmeda)Zn(Cl)R
are typically
around 225 pm, and similar values are observed for various
[12]
zinc(II) chloride modifications.
The ZnϪCl distances in
as well as in dimeric
[13]
dimeric (Me PhSi) CϪZnϪCl
2
3
[14]
F CϪCCl ϪZn(OEt )Cl
are distinctly shorter (average
3
2
2
(
3)
2
33 pm) than those in 4. Moreover, the endocyclic
ZnϪClϪZn angle is approximately 18° smaller than the
corresponding angle in 4. This distortion of the (RZn) Cl
2
moiety is due to the 2,5-di-tert-butylpyrrolide ligand, which
also bridges the two zinc atoms. The planes Cl/Zn/ZnЈ and
Molecular Structures
For comparison purposes, the molecular structure of N2/C21/C22/C23/C24 are oriented almost perpendicular to
HPyr* (1) is briefly described. Suitable single crystals form one another, with an angle between their normals of 93.5°.
during the sublimation of 1 at 35°C in vacuo. The molecu-
Sterically uncrowded cyclopentadienyl complexes of zinc
lar structure is shown in Figure 1. The asymmetric unit con- tend to form polymers. Whereas methyl(cyclopentadienyl)-
tains three crystallographically independent molecules, zinc is monomeric in the gaseous phase, it polymerizes in
Ϫ
which are distinguished by the first digit n ϭ 1, 2 and 3 the solid state to form a structure with bridging C H5 li-
5
following the element symbol. The delocalization within the gands and the metal atoms on opposite sides of the aro-
five-membered ring is disturbed, as is evident from the matic rings.[
15]
Analogous behavior is observed for bis-
1
bond lengths of 137 pm for C(n1)ϪC(n2) and C(n3)ϪC(n4), (cyclopentadienyl)zinc with a bridging and a terminal η -
and the value of 142 pm for C(n2)ϪC(n3). The bond bonded ligand.[ In the gas phase, monomeric decamethyl-
16]
1176
Eur. J. Inorg. Chem. 1998, 1175Ϫ1182

Coordination Modes of 2,5-Di(tert-butyl)pyrrolide
Figure 1. Molecular structure and numbering scheme of the asymmetric unit of HPyr* (1); the ellipsoids represent a probability of 40%;
FULL PAPER
[
a]
the hydrogen atoms of the tert-butyl groups are omitted for clarity; those of the azacyclopentadiene unit are drawn with arbitrary radii
[
a]
Selected bond lengths [pm]: N1ϪH1 85(2), N1ϪC11 137.2(3), N1ϪC14 138.3(3), C11ϪC12 136.4(3), C12ϪC13 141.8(4), C13ϪC14
37.1(3), N2ϪH2 83(3), N2ϪC21 137.5(3), N2ϪC24 137.8(3), C21ϪC22 136.5(3), C22ϪC23 142.4(3), C23ϪC24 136.3(3), N3ϪH3 91(3),
1
N3ϪC31 139.0(3), N3ϪC34 136.3(3), C31ϪC32 135.7(4), C32ϪC33 141.8(4), C33ϪC34 137.0(3).
Figure 2. Molecular structure and numbering scheme of 1·thf; the ellipsoids represent a probability of 40% and the H atoms are drawn
[
a]
with arbitrary radii; the hydrogen bond is shown by a dotted line; symmetry-related atoms are marked with an apostrophe
[
a]
Selected bond lengths [pm]: N1ϪH1 97(3), N1ϪC1 138.1(3), C1ϪC2 137.1(3), C2ϪC2Ј 141.1(5), O2ϪH1 199(3).
zincocene [bis(pentamethylcyclopentadienyl)zinc] has
a
length of 215 pm is very long compared to the values in
1
5
[17]
[11]
structure of the type (η -C Me )(η -C Me )Zn.
The pyr- [tris(trimethylsilyl)methyl]zinc bis(trimethylsilyl)amide
5
5
5
5
rolide substituent in 3 is planar and shows a different coor- (185 pm), in monomeric zinc bis(amides)[ (characteristic
dination behavior. Both the zinc atoms coordinate at the value 182 pm), or even in bridging µ-bonded bis(trimethyl-
same side of the ligand, but one zinc atom bonds via a silyl)amide substituents, where ZnϪN distances of approxi-
σ(ZnϪN2) bond whereas the other metal center shows an mately 200 pm are found.[ The ZnϪN2 vector shows a
18]
19]
2
η coordination to the C22ϪC23 bond. The ZnϪN2 bond deviation of 40.6° from an imaginary in-plane vector; the
Eur. J. Inorg. Chem. 1998, 1175Ϫ1182
1177

M. Westerhausen, J. Weidlein et al.
FULL PAPER
Figure 3. Molecular structure and numbering scheme of (thf)
2
Li-
Figure 4. Molecular structure and numbering scheme of [(Me3-
3 2
Pyr* (2); the ellipsoids represent a probability of 40%; the hydrogen Si) CZn] (µ-Cl)(µ-Pyr*) (4); the ellipsoids represent a probability
atoms are drawn with arbitrary radii; symmetry-related atoms are of 40%; the disordering of the Pyr* ligand is not shown (see text);
marked with an apostrophe; agostic interactions between Li and
all hydrogen atoms are omitted for clarity; symmetry-related atoms
[a]
[a]
the methyl groups are indicated with dotted lines
are marked with an apostrophe
[
a]
Selected bond lengths [pm] and bond angles [°]: LiϪN 193.2(7),
LiϪO2 192.6(4), NϪC1 137.7(3), C1ϪC2 138.4(4), C2ϪC2Ј
1
1
[a]
40.4(5); NϪLiϪO2 127.4(2), O2ϪLiϪO2Ј 105.3(3), LiϪNϪC1
27.0(1), C1ϪNϪC1Ј 106.0(3).
Selected bond lengths [pm] and bond angles [°]: ZnϪC1 201.3(4),
ZnϪCl 241.0(1), ZnЈϪN2 215.1(6), N2ϪC21 126.1(7), N2ϪC24
1
27.5(8), ZnϪC22 219.0(7), ZnϪC23 219.4(7), C1ϪSi11 188.6(4),
C1ϪSi12 188.8(4), C1ϪSi13 188.9(4); C1ϪZnϪCl 120.2(1),
C1ЈϪZnЈϪN2 155.1(2), ClϪZnЈϪN2 84.7(2), ZnϪClϪZnЈ
N2-bonded zinc atom lies 143 pm above the calculated
plane containing the atoms N2, C21, C22, C23, and C24.
The ZnϪC22 and ZnϪC23 distances of 219.0 and 219.4
pm fall within the broad range of values found for multi-
hapto-bonded cyclopentadienide ligands. The chain-like
1
10.32(6).
Scheme 1. Selected bond lengths [pm] in tris(cyclopentadienyl)di-
zinc µ-bis(trimethylsilyl)amide (A)
[
16]
zincocene
has ZnϪC bond lengths between 204 and 241
pm, whereas in the zig-zag chain of methylzinc cyclopen-
[
15]
tadienide
ZnϪC distances of 222 to 241 pm are ob-
served. In both these molecules, the cyclopentadienide sub-
stituents bridge zinc atoms on opposite sides of the aro-
matic ring. Monomeric zincocenes such as decamethyl-,
[
17]
1
,1Ј-diphenyl- and 1,1Ј-bis(trimethylsilyl)zincocene
dis-
1
5
play one η -bonded (ZnϪC 204Ϫ209 pm) and one η -coor-
dinated cyclopentadienide ligand (217Ϫ230 pm). A similar
bonding situation as in 4 is observed for dizinc tris(cyclo- polymer with a similar bridging pattern of the pyrrolide
pentadienide) bis(trimethylsilyl)amide (A)[
19b]
(Scheme 1), substituent.
[20d]
Kuhn et al.
[20c]
linked two octamethyl-1,1Ј-
1
although the bridging ligand in this case is doubly η -coor- diazaferrocene molecules via silver cations σ-bonded to the
dinated; the third ZnϪC distance of 250 pm is clearly too nitrogen atoms.
long to be considered as a bond.
The ZnϪC1 bond length in 4 exceeds the ZnϪC bond
The bridging mode of the ligand Pyr* is not very com- lengths in [tris(trimethylsilyl)methyl]zinc derivatives (Me -
3
mon, however, there are some other examples.[ To the σ- Si) CϪZnϪR with R as phenyl (196 pm), bis(trimethylsi-
20]
[7]
3
bonded nitrogen heterocycles of tricarbonyl(diphenylaceta- lyl)methyl[ (197 pm), and tris(trimethylsilyl)methyl
7]
[7][21]
to)manganese dipyrrolide a tricarbonylmanganese fragment (198 pm); ZnϪC bond lengths of sterically unstrained mol-
[
20a]
is bonded side-on.
Dicarbonylrhodium 2,5-dimethylpyr- ecules are even shorter. All these findings are indicative of
[20b]
rolide dimerizes via an unsymmetric heterocycle bridge.
the steric strain within the molecule. The shielding of the
The bridging mode of the pyrrolide anion in this molecule ClZn moiety by the bulky substituents, which is illustrated
2
is quite similar to the geometry observed for 4 since the in Figure 5, accounts for the fact that this molecule cannot
rhodium atoms do not lie above the center of the NC cycle. react with a further equivalent of lithium 2,5-di(tert-butyl)-
5
Solvent-free sodium tetramethylpyrrolide crystallizes as a pyrrolide (2).
1178
Eur. J. Inorg. Chem. 1998, 1175Ϫ1182

Coordination Modes of 2,5-Di(tert-butyl)pyrrolide
Figure 5. Space-filling model of 4 viewed from the chlorine atom, Me SnϪPyr*, the resonances of these nuclei are shifted to
FULL PAPER
3
2
showing the steric shielding of the Zn Cl fragment
higher field by approximately 20 ppm.
Considering the molecular structure of the zinc derivative
2
, the magnetic equivalence of the tris(trimethylsilyl)methyl
groups was not expected. However, the long distances be-
tween the zinc atoms and the pyrrolide substituent and the
shape of the coordination gap allow a tilting motion, lead-
ing to a dynamic equilibrium through a ZnϪNϪZn-bonded
intermediate, in which the pyrrolide is rotated through ap-
proximately 90°. This situation is depicted in eq. 4.
The mass spectrum of 4 shows the dissociation products
3
and [tris(trimethylsilyl)methyl]zinc 2,5-di(tert-butyl)pyrro-
lide if the sample is heated above the melting point. At 425
K, the mass peaks of these compounds are the signals of
highest intensity, besides that at m/z 179 for HϪPyr*. At
Figure 6 gives a stereoscopic view of the arrangement 460 K, even fragments containing two zinc atoms and one
of 4, together with the incorporated pentane. There are no chlorine atom are detected. Products of a dismutation reac-
significant intermolecular contacts; the pentane molecules tion such as Zn[C(SiMe ) ] or ClϪZnϪPyr* were not ob-
3
3 2
lead to an additional separation of the molecules of 4.
served.
Figure 6. Stereoscopic representation of the molecular packing of 4 in the unit cell; the atoms are drawn with arbitrary radii and H
atoms are omitted for clarity; the n-pentane molecules were refined with a fixed population factor of 0.67; the disordering of the 2,5-
di(tert-butyl)pyrrolide ligand is not shown
Spectroscopic Characterization
Due to the insensitivity of the NMR parameters to the
hapticity of the Pyr* ligand, the characterization of the InI
The NMR parameters of the 2,5-di-tert-butylpyrrolide li- derivative 5 is limited. In this case, the most significant re-
gands of 1؊5 are compared in Table 1, along with data for sults were obtained from Raman spectroscopy, although the
[
2]
[2]
II
[22]
II
I
Me GaϪPyr*, Me SnϪPyr*, Sn [Pyr*] ,
[
and Pb - In derivative 5 decomposes during laser irradiation. For
2
3
2
[
3]
Pyr*]2. The coordination mode of Pyr* does not affect σ(MϪN)- and σ(HϪN)-bonded derivatives such as
the NMR parameters of the tert-butyl groups. The influ- HϪPyr*, Me GaϪPyr*, and Me SnϪPyr*, a characteristic
2
3
Ϫ1
ence of the hapticity of the pyrrolide ligand on the chemical polarized high-intensity band at approximately 1560 cm
shifts of the carbon atoms in the 2- and 5-positions is small, is observed. For the compounds In [Pyr*] (5) and Sn
although η coordination leads to a low-field shift of the [Pyr*] , this band is shifted to lower energies, appearing in
C resonances. The δ values of the carbon atoms in the 3- the region 1500Ϫ1510 cm . On the other hand, other vi-
and 4-positions show no dependency on the coordination brations of the ring at lower frequencies are shifted to
I
II
5
2
13
Ϫ1
IV
1
5
Ϫ1
mode, except that in the case of the Sn
derivative higher values [for example, 1124 (η ) Ǟ 1165 (η ) cm ],
Eur. J. Inorg. Chem. 1998, 1175Ϫ1182
1179

M. Westerhausen, J. Weidlein et al.
LiPyr* (2), [(Me Si) CZn] (µ-Cl)(µ-Pyr*) (4), and
FULL PAPER
Table 1. NMR parameters of the 2,5-di(tert-butyl)pyrrolide ligand in HPyr* (1), (thf)
2
3
3
2
I
[22]
[3]
[2]
[2]
5
In {Pyr}* (5) compared with data for Sn{Pyr*}
2
2 2 3
, Pb{Pyr*} , Me GaϪPyr* and Me SnϪPyr* (M{Pyr*} symbolizes an η -
bonded, MϪPyr* a σ
N
-bonded azacyclopentadienide moiety)
II
II
1
2
4
5
Me
2
GaϪPyr* Sn {Pyr*}
2
3 2
Me SnϪPyr* Pb {Pyr*}
Solvent
C
6
D
6
[D
8
]THF
C
6
Ϫ
D
6
C
6
Ϫ
D
6
C
6
D
6
C
6
Ϫ
D
6
C
6
D
6
6
C D
1H NMR
13C NMR
CH
(M),
7.53
Ϫ
0.19
0.02
Ϫ
3
1
(
H -N)
CH
3
(tBu)
1.17
5.93
1.22
5.59
Ϫ
Ϫ
Ϫ
32.77
123.9
33.47
3.71
100.13
157.03
5.49
Ϫ
1.40
6.22
1.40
5.96
Ϫ
Ϫ
Ϫ
32.44
125.45
32.73
3.85
103.34
167.0
6.2
Ϫ
153.55
1.24
6.23
Ϫ
1.39
5.47
Ϫ
Ϫ
Ϫ
32.01
Ϫ
33.78
1.26
4.86
Ϫ
1.39
5.51
Ϫ
Ϫ
Ϫ
32.69
Ϫ
33.31
3
,4
H
3
J(H3,4, H1) 2.8
Ϫ
Ϫ
C(MϪMe)
Ϫ
Ϫ
0.95
Ϫ5.86
129.8
30.57
125.6
34.59
3.8
81.40
157.8
Ϫ
1
J(C,H)
Ϫ
124.3
32.9
CH
3
(tBu)
30.67
125.5
31.24
3.75
102.53
166.47
34.63
1
J(C,H)
C(tBu)
Ϫ
124.9
32.5
[a]
2
J(C,H)
3
,4
C
104.60
148.57
105.5
163.8
Ϫ
Ϫ
145.3
100.51
105.19
1
3,4
J(C ,H)
2
3
3,4 4,3
J(C ,H ) 7.0
3,4
1
J(C ,H ) 7.05
Ϫ
173.33
2,5
C
139.46
146.72
162.30
161.71
[
a]
Signal not detected.
Conclusion
The diverse coordination modes adopted by the 2,5-di-
(
tert-butyl)pyrrolide ligand have been illustrated by an η5
coordination to an indium(I) atom as well as bridging be-
tween two zinc atoms. Whereas the properties of 2,5-di(tert-
butyl)azaindocene (5) are approximately as one would ex-
pect by analogy with pentamethylindocene, the zinc deriva-
tive 4 shows a unique structure as well as surprisingly low
reactivity. Not even treatment with excess lithium 2,5-di-
(
tert-butyl)pyrrolide (2) leads to substitution of the chloride
(
4) ligand by a pyrrolide anion. The reason for this lack of
reactivity is the steric shielding of the central ClZn moiety
2
by two tris(trimethylsilyl)methyl and two tert-butyl groups.
These demanding substituents also lead to an extension of
the ZnϪCl, ZnϪN and ZnϪC distances.
This work has been generously supported by the Deutsche For-
schungsgemeinschaft (DFG) and the Fonds der Chemischen Indu-
strie.
Experimental Section
General: All experiments and manipulations were carried out un-
4 10
der argon purified by passage through BTS catalyst and P O .
Reactions were performed in dried, thoroughly deoxygenated sol-
vents using standard Schlenk techniques. The starting materials
[
6]
[5]
2
,5-di(tert-butyl)pyrrole (1), indium(I) chloride, and [tris(tri-
which has to be interpreted in terms of a change of the π-
[
26]
methylsilyl)methyl]lithium
were prepared by literature pro-
I
system of the nitrogen heterocycle. Characteristic for the In
cedures. The extreme sensitivity of 5 has thwarted all attempts to
prove its purity by elemental analysis.
Ϫ1
derivative 5 is the vibration In Pyr* at 170 cm , which is
lower in energy by 60 cm compared to the In C mode
Ϫ1
5
of the simple, unsubstituted indocene.[23]
Bis(tetrahydrofuran-O)lithium 2,5-Di(tert-butyl)pyrrolide (2): At
Ϫ78°C, a solution of n-butyllithium (15% in hexane, 9.4 ml) was
added dropwise to a solution of 2,5-di(tert-butyl)pyrrole (2.70 g,
Finally, it should be mentioned that theoretical investi-
gations on a monomeric (hypothetical) 2,5-dimethylazain-
1
5.1 mmol) in 50 ml of n-hexane. On warming to room temp., a
I
docene In (NC H Me -2,5) predict a very short distance of
4
2
2
colorless solid precipitated, which was collected. Washing with two
portions of n-hexane and subsequent drying in vacuo gave lithium
2
38 pm between the indium atom and the heterocycle.[24]
Such a bond length is only comparable with the values de- 2,5-di(tert-butyl)pyrrolide (2.65 g, 14.3 mmol, 95%, dec. at 197°C;
I
[8][25]
termined for the permethylated indocenes In (C R ).
lithium analysis for C12
H
20NLi: calcd. 3.75; found 3.7). Carrying
5
5
1180
Eur. J. Inorg. Chem. 1998, 1175Ϫ1182

Coordination Modes of 2,5-Di(tert-butyl)pyrrolide
FULL PAPER
out this reaction in a solvent mixture of diethyl ether and tetra-
Bis[tris(trimethylsilyl)methyl]zinc Chloride 2,5-Di(tert-butyl)-
hydrofuran yielded colorless 2 after recrystallization from tetra-
pyrrolide (4): At 0°C, a solution of n-butyllithium (2.5  in hexane)
hydrofuran at Ϫ30°C (4.71 g, 14.3 mmol, 95%). Loss of THF at was added dropwise to a solution of 1 (0.65 g, 3.62 mmol) in 20
1
6
0°C, m.p. of the residue 348°C. Ϫ H NMR ([D
8
]THF): δ ϭ 5.59 ml diethyl ether, so as to give a colorless suspension of 2. Sublimed
[CH(Pyr*)], 1.22 [CMe
3
(Pyr*)]. Ϫ 13C NMR ([D
8
3,4
]THF): δ ϭ
3 (2.4 g, 7.2 mmol), dissolved in 20 ml of diethyl ether, was then
1
1
46.72 [C-2,5(Pyr*)], 100.13 [dd, C-3,4(Pyr*), J(C H) ϭ 157.03 slowly added to this suspension. Once a clear solution had been
2
3,4 4,3
7
Hz, J(C
NMR ([D
H
) ϭ 5.5 Hz], 33.47 (CMe
]THF): δ ϭ 3.60. Ϫ IR (Nujol, CsBr): ν ϭ 1584 cm
3
), 32.77 (CMe
3
). Ϫ Li obtained, all volatile materials were removed in vacuo. The residue
˜
Ϫ1
8
was redissolved in n-pentane and insoluble LiCl was filtered off. At
w, 1560 w, 1487 m, 1459 m, 1450 sh, 1392 w, 1388 m, 1381 w, 1348 Ϫ20°C, colorless 4 co-crystallized with a stoichiometric amount of
s, 1299 m, 1265 w, 1248 s, 1200 s, 1139 w, 1051 sh, 1040 vs, 983 m, n-pentane (1.85 g, 2.1 mmol, 58%); dec. at 75°C. Ϫ 1H NMR
9
6
6 6 3 3
54 sh, 949 w, 910 m, 886 s, 848 w, 822 w, 764 w, 732 vs, 713 vs, (C D ): δ ϭ 6.22 [CH(Pyr*)], 1.40 [CMe (Pyr*)], 0.32 [SiMe ]. Ϫ
1
3
74 w, 622 w, 574 m, 519 s, 515 sh, 429 m, 405 w, 337 w. Ϫ MS
C NMR (C
34.63 [CMe
6
D
6
): δ ϭ 148.57 [C-2,5(Pyr*)], 104.60 [C-3,4(Pyr*)],
˜
ϩ
Ϫ1
(70 eV, sample temp. 293 K); m/z (%): 185 (4) [LiPyr* ], 179 (15)
3
], 7.13 [SiMe
3
]. Ϫ IR (Nujol, CsBr): ν ϭ 1364 cm
ϩ
ϩ
ϩ
[HPyr* ], 164 (83) [HPyr* Ϫ Me], 149 (18) [HPyr* Ϫ 2Me], 115 m, 1349 m, 1283 m, 1259 vs, 1248 vs, 1207 m, 1154 w, 1148 sh,
ϩ
ϩ
(73), 72 (100) [thf ], 57 (21) [tBu ].
1077 w, 1047 m, 1021 m, 982 w, 860 vs, 850 sh, 797 s, 782 s, 749
m, 723 m, 673 s, 660 s, 621 m, 550 w, 529 w, 471 m, 442 w, 362 w.
Ϫ MS (70 eV, sample temp. 425 K, source temp. 460 K); m/z (%):
[
Tris(trimethylsilyl)methyl]zinc Chloride (3): Tris(trimethylsilyl)-
methane (8.47 g, 36.4 mmol) was dissolved in a mixture of tetra-
hydrofuran (45 ml) and diethyl ether (8.5 ml). At 0°C, a solution
of methyllithium in diethyl ether (27.7 ml, 1.6 , 44.3 mmol) was
added. After stirring for 8 h at room temp., the solution was heated
under reflux for an additional 6 h to destroy the remaining meth-
ϩ
6
11 (4.5) {[(Me
3
Si)
3
CZn]
2
Cl Ϫ CH
Si)
CZnCl Ϫ Me], 295 (17.3) [(Me
2 3 3
}, 473 (49.5) [(Me Si) -
ϩ
ϩ
CZnPyr* ], 458 (7.9) [(Me
3
3
CZnPyr* Ϫ Me], 315 (54.9)
ϩ
ϩ
[
[
[
(Me
(Me
3
3
Si)
Si)
3
3
3
ϩ
Si)
3
CZn ], 216 (7.4)
ϩ
C
3 3
Ϫ Me], 201 (30.5) [(Me Si) C
HPyr* ]. Ϫ MS (70 eV, sample temp. 460 K, source temp. 460 K);
Ϫ 2Me], 179 (100)
ϩ
2
yllithium. At room temp., anhydrous ZnCl (4.96 g) was added in
ϩ
m/z (%): 626 (1.3) [M Ϫ 2SiMe
3
Ϫ 2MeH], 611 (15.3)
small portions and the mixture was stirred for 8 h. All volatile
materials were then removed in vacuo and the residue was redis-
solved in diethyl ether. The insoluble part of the residue (LiCl) was
filtered off, and the ethereal solution was dried and concentrated.
The solid material was sublimed at 110°C in vacuo to afford LiCl-
free 3 (3.1 g, 9.3 mmol, 26%), m.p. 211°C. Ϫ H NMR ([D
ϩ
ϩ
{[(Me
3 3 2 2 3
Si) CZn] Cl Ϫ CH }, 593 (100) [M Ϫ Me Ϫ 2SiMe Ϫ
ϩ
CH ], 315 (20.6) [(Me
2
3
Si)
3
CZnCl Me], 295 (98.1)
Si) Me], 201 (23.3)
2
74ClNSi Zn : calcd. C 47.58, H 9.24,
Ϫ
ϩ
ϩ
[
[
(Me
(Me
3
Si)
Si)
3
3
CZn ], 216 (8.7) [(Me
C
3
3
C
Ϫ
ϩ
3
Ϫ 2Me]. Ϫ C32
H
6
1
N 1.73; found C 47.65, H 9.23, N 1.44.
8
]THF):
13
1
δ ϭ 0.19. Ϫ C NMR ([D
8
]THF): δ ϭ 6.38 [SiMe
]THF): δ ϭ Ϫ2.75. Ϫ IR: ν ϭ 1462 cm
3
, J(SiC) ϭ 49.8
Indium(I) 2,5-Di(tert-butyl)pyrrolide (5): As described above, a
suspension of LiPyr* was prepared from HPyr* (2.7 g, 15 mmol)
˜
Hz]. Ϫ 29Si NMR ([D
Ϫ1
8
m, 1377 m, 1262 s, 1250 s, 861 vs, 842 vs, 784 w, 725 w, 673 m, 661
and a stoichiometric amount of nBuLi in 50 ml of THF. At
I
m, 630 w, 614 w. Ϫ MS (70 eV, sample temp. 360 K, source temp. Ϫ110°C, In Cl powder (2.2 g, 14.6 mmol) was added. During
ϩ
ϩ
4
2
70 K); m/z (%): 315 (12.8) [M Ϫ Me], 201 (100) [C(SiMe
3
)
3
Ϫ
warming to room temp., the orange color of InCl disappeared.
ϩ
Me], 73 (27) [SiMe
3
]. Ϫ C10
H
27ClSi
3
Zn: calcd. C 36.13, H 8.19; Thereafter, the reaction mixture was stirred for an additional 10 h.
The solution was then concentrated to a volume of approximately
found C 34.57, H 8.19.
Table 2. Crystallographic data of 1, 1·thf, 2, and 4, as well as details of the structure solution and refinement procedures
Compound
1
1·thf
2
4·0.67pentane
Formula
C
12
179.30
¯
H
21
N
C
16
247.37
H
25NO
C
20
H
36LiNO
2
35.33 6 2
C H81.99ClNSi Zn
formula mass [gиmolϪ1]
T [K]
329.44
193(2)
855.70
193(3)
163(2)
163(2)
P2
[
28]
Space group
a [pm]
b [pm]
c [pm]
α [°]
P1 (No. 2)
944.28(5)
1333.07(8)
1494.61(9)
83.516(1)
77.668(1)
80.239(1)
1.8056(2)
6
1
/m (No. 11)
Pnna (No. 52)
1001.3(1)
1759.8(2)
1177.7(2)
90
Pnma (No. 62)
1793.0(3)
1780.8(3)
1575.6(2)
90
642.55(2)
1603.21(5)
802.46(2)
90
β [°]
98.194(2)
90
90
90
90
90
γ [°]
3
V [nm ]
0.81821(4)
2
2.0752(5)
4
5.031(1)
4
Z
3
d
calcd. [gиcm ]
0.989
1.004
1.054
1.130
Ϫ1
µ [mm
F(000)
]
0.057
0.062
0.065
1.172
600
272
728
1848
Scan range [°]
Measured data
Unique data (Rint
Parameters
1.4 < θ < 25
9291
6.8 < θ < 26.4
4471
2.7 < θ < 24.0
14180
1.7 < θ < 26.0
5118
)
4903 (0.025)
382
1357
97
0.1842
0.0883
1075
1596 (0.055)
128
5118
406
0.1773
0.0843
3867
[a]
wR2 (all data)
0.1437
0.2760
0.1015
1362
[
a]
R1 (all data)
0.0806
Data [I > 2σ(I)]
3551
[
a]
R
1
[I > 2σ(I)]
0.0537
0.0703
1.090
0.38/Ϫ0.21
0.0925
1.125
0.63/Ϫ0.26
0.0599
1.084
1.10/Ϫ0.67
[
b]
2
Goof on F
1.021
˚
Residual density [eиAϪ3]
0.19/Ϫ0.28
[
a]
2
2)2]/Σ[w(F
2 2 1/2
) ]} with wϪ1 ϭ σ (F
2
2
2
[b]
Definition of the R values: R ϭ (ΣԽԽF
1
o
Խ Ϫ ԽF
c o
ԽԽ)/ΣԽF Խ; wR
2
ϭ {Σ[w(F
o
Ϫ F
c
o
o
) ϩ (aP) . Ϫ s ϭ
2
2 2
1/2
{
Σ[w(F
o c o p
Ϫ F ) ]/(N Ϫ N )} .
Eur. J. Inorg. Chem. 1998, 1175Ϫ1182
1181

M. Westerhausen, J. Weidlein et al.
FULL PAPER
[
10] [10a]
M. A. Khan, D. G. Tuck, Acta Crystallogr. 1984, C40, 60.
10b]
20 ml and the precipitated LiCl was filtered off. All volatiles were
Ϫ [
R. Gregorzik, H. Vahrenkamp, Chem. Ber. 1994, 127,
then removed in vacuo. Subsequent sublimation at 80°C and 5 ϫ
1
857.
Ϫ3
10
Torr yielded a fraction of InPyr* still contaminated with
[11]
M. Westerhausen, M. Wieneke, W. Schwarz, J. Organomet.
Chem. 1996, 522, 137.
12]
traces of THF. A second sublimation gave colorless cuboids of In-
Pyr* (4.5 mmol, 31%). These crystals were found to be composed
of very thin plates and proved unsuitable for an X-ray structure
determination. For NMR data, see Table 1; for discussion of rel-
[
Struct. Rep. 1960, 25, 283; ibid. 1961, 26, 319; ibid. 1978, 43a,
1
54.
[13]
S. S. Al-Juaid, C. Eaborn, A. Habtemariam, P. B. Hitchcock, J.
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T. Aoyagi, H. M. M. Shearer, K. Wade, G. Whitehead, J. Or-
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evant IR/Raman data, see text. Ϫ C12
H
20NIn (293.12): calcd. In
39.17; found In 38.3 (complexometric titration), 38.9 (ICP).
[
[
14]
15]
X-ray Crystallographic Studies:[27] Suitable single crystals of 1,
·thf, and 4 were covered with Nujol, mounted on a Siemens P4
1
diffractometer, and examined with graphite-monochromated Mo-
radiation (λ ϭ 71.073 pm). For the collection of data sets for 1
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P. H. M. Budzelaar, J. Boersma, G. J. M. van der Kerk, A. L.
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K
α
and 1·thf, the diffractometer was equipped with a Siemens
SMART-CCD area detector. Due to its low melting point, com-
pound 1·thf was kept at temperatures below Ϫ30°C during hand-
ling and mounting on the diffractometer. For the data collection
of 2, a STOE-IPDS diffractometer was used. Crystallographic pa-
rameters and details of the data collection are summarized in
Table 2.
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R. Blom, J. Boersma, P. H. M. Budzelaar, B. Fischer, A.
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18b]
2
3, 1972. Ϫ
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H. Grützmacher, M. Steiner, H. Pritzkow, L. Zsolnai, G.
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31]
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32]
Organometallics 1984, 3, 1187.
[20] [20a]
atoms of 1 and 1·thf were refined as a riding model with restriction
of ideal geometry at the corresponding carbon atoms, whereas the
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atoms of 2 were refined group by group to a common CϪH bond
length while maintaining ideal geometry at the corresponding C
atoms, whereas the azacyclopentadienide-bonded hydrogen atoms
were refined isotropically. The hydrogen atoms of 4 were refined
isotropically, with the exception of those of the tert-butyl groups
and of the n-pentane molecule, which were calculated in ideal posi-
tions with a CϪH distance of 96 pm. The n-pentane molecules
located between the molecules of 4 (Figure 6) were considered to
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W. A. Herrmann, I. Schweitzer, P. S. Skell, M. L. Ziegler,
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[26b]
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Crystallographic data (excluding structure factors) for the struc-
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on application to CCDC, 12 Union Road, Cambridge, CB2
1EZ, U.K. [Fax: (internat.) ϩ 44(0)1223/336033; E-mail: de-
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4
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[
[
8
6] [6a]
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Eur. J. Inorg. Chem. 1998, 1175Ϫ1182