Cyclopentadienyl-bis(oxazoline) Magnesium and Zirconium Complexes in Aminoalkene Hydroaminations

Article abstract of DOI:10.1021/acs.organomet.5b00771

A new class of cyclopentadiene-bis(oxazoline) compounds and their piano-stool-type organometallic complexes have been prepared as catalysts for hydroamination of aminoalkenes. The two compounds MeC(Ox^Me2)₂C₅H₅ (

Full text of DOI:10.1021/acs.organomet.5b00771

Article
pubs.acs.org/Organometallics
Cyclopentadienyl-bis(oxazoline) Magnesium and Zirconium
Complexes in Aminoalkene Hydroaminations
Naresh Eedugurala, Megan Hovey, Hung-An Ho, Barun Jana, Nicole L. Lampland, Arkady Ellern,
and Aaron D. Sadow*
U.S. DOE Ames Laboratory and Department of Chemistry, Iowa State University, 1605 Gilman Hall, Ames, Iowa 50011-3111, United
States
*
S Supporting Information
ABSTRACT: A new class of cyclopentadiene-bis(oxazoline)
compounds and their piano-stool-type organometallic com-
plexes have been prepared as catalysts for hydroamination of
Me2
aminoalkenes. The two compounds MeC(Ox ) C H
2
5
5
M
Me2
(
(
(
Bo CpH; Ox
= 4,4-dimethyl-2-oxazoline) and MeC-
Ox ) C Me H (Bo Cp H) are synthesized from C R HI
R = H, Me) and MeC(Ox )2Li. These cyclopentadiene-
Me2
M
tet
2
5
4
5 4
Me2
bis(oxazolines) are converted into ligands that support a
variety of metal centers in piano-stool-type geometries, and
here we report the preparation of Mg, Tl, Ti, and Zr
M
M
tet
compounds. Bo CpH and Bo Cp H react with
MgMe (O C H ) to give the magnesium methyl complexes
2
2
4
8 2
M
M
tet
M
{
Bo Cp}MgMe and {Bo Cp }MgMe. Bo CpH and
Bo Cp H are converted to Bo CpTl and Bo Cp Tl by reaction with TlOEt. The thallium derivatives react with
TiCl (THF) to provide [{Bo Cp}TiCl(μ-Cl)] and [{Bo Cp }TiCl(μ-Cl)] , the former of which is crystallographically
characterized as a dimeric species. Bo CpH and Zr(NMe ) react to eliminate dimethylamine and afford {Bo Cp}Zr(NMe ) ,
which is crystallographically characterized as a monomeric four-legged piano-stool compound. {Bo Cp}Zr(NMe ) ,
Bo Cp}MgMe, and {Bo Cp }MgMe are efficient catalysts for the hydroamination/cyclization of aminoalkenes under mild
M
tet
M
M
tet
M
M
tet
3
3
2
2
M
M
2
4
2 3
M
2
3
M
M
tet
{
conditions.
INTRODUCTION
Chart 1. Linked Cyclopentadienyl−Donor Ligand
Complexes Providing Piano-Stool Geometry Compounds
■
5
Early metal piano-stool compounds of the type (η -C R )MX
n
are important for stabilizing reactive moieties such as
alkylidenes and dinitrogen compounds, and this class of
5
5
1
compounds also provide catalytic sites for olefin polymer-
2
ization. The constrained-geometry class of catalysts {Me Si-
2
(
C R )NR′}MX exemplify the applications of piano-stool
5
4
compounds in catalysis (Chart 1). These compounds suggest
that strained systems can have further enhanced catalytic
properties. Recently we showed that oxazolinylborate-sub-
3
stituted cyclopentadienyl ligands provide highly active and
enantioselective piano-stool zirconium and hafnium hydro-
4
amination/cyclization catalysts. This reactivity contrasts with
that reported for constrained-geometry group 4 catalysts in
5
hydroamination, which require more forcing conditions.
Trivalent rare earth catalysts supported by constrained-
geometry-type ligands are highly reactive for hydroamination/
cyclization reactions, in contrast to the group 4 examples.
6
supported by monoanionic cyclopentadienyl ligands have not
been explored in catalytic hydroamination.
The closest examples are dianionic ligands noted above,
namely, the constrained-geometry class and our examples
Monoanionic constrained-geometry-like cyclopentadienyl phos-
phazene or 2,2-bis(pyrazol-1-yl)ethyl lutetium dialkyl com-
pounds (bpzcp)Lu(CH SiMe ) (bpzcp = 2-[2,2-bis(3,5-
2
3 2
dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene)
also catalyze the cyclization of aminoalkenes to 2-alkylpyrro-
lidines. However, group 4 piano-stool-type compounds
Received: September 9, 2015
7
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00771
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Organometallics
Article
5
,8
involving cyclopentadienyl-bis(oxazolinyl)borates. High oxi-
0
dation state d group 4 compounds are distinguished from rare
earth catalysts by the valence of the metal center, with the latter
class of compounds having one fewer valence, assuming the
ancillary ligands’ valence are equivalent. Thus, another
approach to controlling the available reactive valence is through
modification of the ancillary ligands’ valence requirements.
Given the high activity of group 4 compounds supported by
R
2−
4a,c,d
these dianionic [PhB(Ox ) C H ] ligands,
we targeted
4
2
5
4
R
−
corresponding monoanionic [RC(Ox ′) C R″ ] ligands,
2
5
which might impart high reactivity upon group 4 metal sites
in hydroamination and allow further comparisons in the series
R
R
of compounds {PhB(Ox ) C H }LnX, {PhB(Ox ) C H }MX ,
2
5
4
2
5
4
2
1
R
R
C H group. The H NMR spectrum acquired in benzene-d
6
{
RC(Ox ′) C R″ }LnX , and {RC(Ox ′) C R″ }MX (Ln =
5
5
2
5
4
2
2
5
4
3
Me2
contained two MeC(Ox ) C H resonances at 2.10 and 2.04
trivalent group 3 or lanthanide element, M = tetravalent group
2
5
5
ppm (normalized to 6 H total) that appeared in a 1.15:1
4
metal center, X = monovalent ligand).
Typically, cyclopentadienyl ligand derivatives are synthesized
integrated ratio. In addition, two singlets at 3.46 and 2.73 ppm
3
(
4 H total) were assigned to sp -hybridized portions of the
by reaction of a nucleophilic C R H anion and an electrophile
such as a halosilane. The monoanionic cyclopentadienylphos-
phazene ligands are also synthesized through the reaction of
C R H and R PCl. Alternatively, reactions of fulvene
derivatives with nucleophiles provide a CR linker between
5
4
2
C H , whereas the signals assigned to sp -hybridized cyclo-
5
5
pentadienyl group integrated to a total of 6 H. From these data,
−
9
two isomers are present that contain C−C connectivities with
5
4
2
2
the bis(oxazoline) group bonded to an sp -hybrid carbon on
2
M
the C H unit. The IR spectrum of Bo CpH contained a band
the cyclopentadiene and donor groups, such as in bis-
5
5
1
0
−1
at 1656 cm assigned to the oxazoline νCN, and this is the only
(
pyrazolyl)ethylcyclopentadienyl ligands (bpzcp).
The above routes imply that preparation of one-carbon-
band in this region. Interestingly, the IR spectrum of the borato
Me2
R
2−
compound H[PhB(Ox ) C H ], which is isolated as a
linked analogues of [PhB(Ox ) C H ]
coupling of two typically nucleophilic cyclopentadienide and
would involve
2
5
5
2
5
4
mixture of three isomers and contains a H that is likely
R
−
bonded to one or both oxazolines, also contained only one ν
[
RC(Ox ′) ] species. Instead, we investigated a strategy for
CN
2
−1
band, but that band was red-shifted by ca. 60 cm in
coupling the stabilized anions of bis(oxazolines) with electro-
4a
11
M
comparison to Bo CpH. We attribute this significant change
philic cyclopentadienyl groups. The reaction of deprotonated
bis(oxazoline) and organic electrophiles has been very useful to
obtain tris(oxazolinyl)ethane (tris-ox) ligands or side-arm-
containing bis(oxazolines) that show improved enantioselec-
tivity in a host of catalytic conversions. Recently, we reported
the synthesis of the tetramethylcyclopentadienyl ligand MeC-
in energy of the νCN to the substitution of a four-coordinate
12
Me2
anionic boron in PhB(Ox )2Cp for a neutral carbon linker in
M
Bo Cp, and this may hint at inequivalent coordination
13
properties of the oxazoline donors in the two ligands.
The generality of this synthetic approach is supported by the
synthesis of the bulkier tetramethylcyclopentadienyl derivative.
Me2
Me2
(
Ox ) C Me H (Ox
= 4,4-dimethyl-2-oxazoline) and a
2
5
4
1
5
Me2
14
C Me HI is allowed to react with MeC(Ox )2Li to provide
series of lutetium compounds coordinated by this ligand.
5
4
Me2
M
tet
MeC(Ox ) C Me H (Bo Cp H) as a white solid in 68%
Here we describe the full synthesis of achiral monoanionic
cyclopentadienyl bis(oxazoline) compounds, magnesium and
thallium main group compounds, and titanium and zirconium
compounds. We also report an initial study of the magnesium
and zirconium compounds’ reactivity in hydroamination of
aminoalkenes. Comparisons between the parent CpZr(NMe ) ,
2
5
4
yield (eq 2). As noted above, we recently reported the
2
3
the new bis(oxazoline)-substituted cyclopentadienyl zirconium
derivative, and previously reported bis(oxazolinyl)borate-
substituted zirconium catalysts suggest trends in hydro-
amination activity corresponding to cyclopentadienyl substu-
tion and the metal center’s reactive valence number.
M
tet
application of Bo Cp H in the synthesis of piano-stool
RESULTS AND DISCUSSION
14
■
lutetium compounds, while the synthesis and characterization
Synthesis and Characterization of Bis(4,4-dimethyl-2-
of the organic compound are reported here.
M
M
M
tet
oxazoline)cyclopentadiene (Bo CpH) and Bis(4,4-di-
In contrast to Bo CpH, Bo Cp H was isolated as only one
isomer from this reaction, although a second isomer crystallized
from a hydrolyzed organometallic compound (see below and
the Supporting Information (SI)). This formulation was
methyl-2-oxazoline)tetramethylcyclopentadiene
M
tet
(
Bo Cp H). The desired mixed cyclopentadiene-bis(2-oxazo-
line) proligands are synthesized by reaction of nucleophilic
lithium bis(2-oxazolinyl)methylcarbide and iodocyclopenta-
diene reagents. In the first example, reaction of C H I and
Me2
suggested by the diagnostic signal from MeC(Ox ) C Me H
that appeared at 1.61 and 16.41 ppm in the H and C{ H}
NMR spectra. Two singlet and two coupled doublet H NMR
2
5
4
1
13
1
5
5
Me2
Me2
M
1
MeC(Ox )2Li provides MeC(Ox ) C H (Bo CpH, eq 1).
2
5
5
For this reaction, iodocyclopentadiene is generated from
signals were assigned to diasterotopic methyl and methylene
oxazoline moieties, indicating that the oxazoline groups are
thallium cyclopentadienide and iodine in benzene at 12 °C
1
1
M
tet
and used in situ.
equivalent. These data indicate that Bo Cp H is C symmetric,
s
M
3
At least three isomers of Bo CpH are possible, the structures
of which are related by the position of the unique H on the
placing the proton on the sp -hybridized C12 (identified in
Figure 1). The infrared spectrum of Bo Cp H contained two
M
tet
B
DOI: 10.1021/acs.organomet.5b00771
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Organometallics
Article
1
M
symmetric isomer. The H NMR spectra of Bo CpTl and
M
tet
Bo Cp Tl did not show evidence of coupling to the thallium
Tl and Tl are I = 1/2). The cyclopentadienyl resonances
in the C{ H} NMR spectrum of Bo CpTl also did not
contain evidence for JTlC; however, the spectrum of Bo Cp Tl
contained two broad signals at 114.8 ppm (38 Hz at half-
height) and 114.1 ppm (and 30 Hz at half-height) and one
sharper signal at 115.94 ppm (8 Hz at half-height). In addition,
the C Me methyl groups appeared as doublets at 12.6 ppm
203
205
(
13
1
M
M
tet
Figure 1. Rendered thermal ellipsoid diagram of MeC-
Me2
M
tet
(
Ox ) C Me H (Bo Cp H) with ellipsoids plotted at 35%
2 5 4
5
4
probability. H atoms were placed in calculated positions, refined
isotopically using the riding model, and excluded from the illustration
for clarity, with the exception of the H atom on C12. Selected
interatomic distances (Å): C1−C12, 1.567(2); C1−C6, 1.521(1);
C1−C11, 1.521(1); C1−C24, 1.532(2); C12−C13, 1.521(2); C12−
C19, 1.521(2); C13−C15, 1.346(2); C15−C17, 1.477(2); C17−C19,
(
JTlC = 57.4 Hz) and 11.1 ppm (JTlC = 44.8 Hz). For
comparison, the methyl groups in C Me Tl provided a doublet
5
5
(
JTlC = 79.4 Hz), as did the cyclopentadienyl carbons (114.6
16
15
ppm, JTlC = 102.2 Hz). The N NMR chemical shifts,
1
15
15
determined by H− N HMBC experiments (at N natural
abundance) are −130 and −128 ppm, respectively, and these
are in the region of noncoordinated oxazoline (e.g., 2H-4,4-
dimethyl-2-oxazoline: −128 ppm). The IR spectra (acquired
in a KBr matrix) of Bo CpTl and Bo Cp Tl contained one
1.350(2); C6−N1, 1.247(2); C11−N2, 1.260(2). Selected interatomic
angles (deg): C1−C12−C13, 112.7(1); C1−C12−C19, 114.8(1);
C13−C12−C19, 103.0(1).
17
M
M
tet
−
1
−1
(
1647 cm ) and two (1654 and 1637 cm ) bands,
−1
bands at 1661 and 1640 cm , which were assigned to
M
respectively, assigned to the ν . Thus, both Bo CpH and
CN
symmetric and asymmetric νCN. These two bands for a single
M
Bo CpTl each produced one similar ν IR band, while the
spectra for both Bo Cp H and Bo Cp Tl contained two ν
bands. The IR bands for the Tl derivatives were slightly red-
shifted in comparison to the protonated ligands.
Magnesium cyclopentadienyl compounds are also reagents
for transmetalation, and oxazoline-coordinated magnesium
compounds have applications as catalysts. The reactions of
MgMe (O C H ) and Bo CpH or Bo Cp H give the
magnesium methyl complexes {Bo Cp}MgMe and
{
CN
isomer contrast the single ν signal observed for the multiple
M
tet
M
tet
CN
M
Me2
CN
isomers of Bo CpH and H[PhB(Ox ) C H ] noted above.
2
5
5
M
tet
X-ray-quality crystals of Bo Cp H were obtained from a
pentane solution at −30 °C (Figure 1).
The single-crystal diffraction study confirms the connectivity
and the electronic configuration of the cyclopentadiene group
18
M
tet
in Bo Cp H. Thus, the C1 connects two oxazoline, a methyl,
and a tetramethylcyclopentadienyl group. Moreover, the3
cyclopentadienyl C12 linked to the bis(oxazoline) unit is sp
hybridized, determined on the basis of single bonds to
neighboring carbons (∼1.5 Å), the sum of C−C12−C angles
of 335°, and the C−C distances in the diene portion of the
C Me HR ring. Interestingly, the molecule adopts a con-
M
M
tet
2
2
4
8 2
M
M
tet
Bo Cp }MgMe (eq 4). These compounds are isolated as
5
4
formation that gives a noncrystallographical pseudomirror
plane, which contains the C1, C12, H12, and C24, bisects
the C Me moiety, and relates the two oxazolines. A second X-
5
4
M
tet
ray-quality crystal of Bo Cp H was obtained from the
hydrolysis of a magnesium complex (see below) that proved
to be an isomer in which the H atom bonded to the
cyclopentadiene is located on the C13 rather than C12 (see the
Supporting Information). This second isomer was not detected
in the NMR spectra of characterized material.
M
M
tet
Main Group Compounds {Bo Cp}M and {Bo Cp }M
M
M
tet
(
M = Mg, Tl). Metalation of Bo CpH and Bo Cp H is
achieved through protonolysis of Brønsted basic X-type ligands
in MX compounds. This route provides access to thallium
n
reagents that are useful for transmetalation. Reactions of
off-white solids and are best stored at −30 °C to avoid thermal
M
M
tet
Bo CpH or Bo Cp H and thallium ethoxide provide
decomposition. In addition, we note that the carbon
M
M
tet
M
M
Bo CpTl or Bo Cp Tl (eq 3). The formation of Bo CpTl
occurs over 2 h in diethyl ether at room temperature and is
combustion analyses of both {Bo Cp}MgMe and
M
tet
{Bo Cp }MgMe are consistently low, while hydrogen and
nitrogen values are close to the expected values. In general,
isolation of the magnesium compounds was challenging, and
typically their reactivity was surveyed by in situ generated
species and later repeated and verified with isolated materials.
M
tet
significantly faster than the synthesis of Bo Cp Tl, which
requires 10 days in THF.
1
13
1
M
The H and C{ H} NMR spectra of Bo CpTl and
M
tet
Bo Cp Tl indicate that each compound is a single C -
s
C
DOI: 10.1021/acs.organomet.5b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
8a
These magnesium compounds are pseudo-C symmetric at
IR spectrum. A similar effect may account for the single ν
CN
s
1
13
1
M
M
tet
room temperature, as determined by H and C{ H} NMR
spectra acquired of benzene-d6 solutions. However, the
structures are more complicated than pentahapto cyclo-
pentadienyl and bidentatate oxazoline coordination as
suggested by several pieces of data including an X-ray crystal
in {Bo Cp}MgMe and {Bo Cp }MgMe.
Support for a dimeric structure is obtained in the solid state
from an X-ray diffraction study on {Bo Cp }MgMe. The
results indicate that only one oxazoline ring coordinates per
magnesium, and the methyl groups bridge between the two
magnesium centers (Figure 2). The cyclopentadienyl group
M
tet
M
tet
structure of {Bo Cp }MgMe (see below). For example, the
1
M
H NMR signals of {Bo Cp}MgMe were sharp for in situ
generated samples that contained dioxane, but broad signals
were obtained from samples dried by evaporation of all volatiles
and redissolution in benzene-d . The spectra of isolated,
6
M
tet
exhaustively dried {Bo Cp }MgMe were broad as well.
Addition of THF to the samples that gave broad NMR signals
1
resulted in reproducibly sharp H NMR signals, equivalent to
spectra obtained from in situ samples. We conclude that drying
removes coordinated ethers and affects the appearance of NMR
spectra, but drying does not result in demetalation or
protonation of the cyclopentadienyl ligands. Moreover, the
1
13
H and C NMR chemical shifts of dioxane, THF, or Et O in
2
M
tet
Figure 2. Rendered thermal ellipsoid plot of [{Bo Cp }MgMe] at
3
the presence of the cyclopentadienylmagnesium compounds
were identical or nearly identical to the ethers’ resonances in
only benzene-d6.
2
5% probability. H atoms are not included in the representation.
Atoms marked with # are crystallographic symmetry-generated
positions. Selected interatomic distances (Å): Mg1−C22, 2.267(2);
Mg1−C22#, 2.271(2); Mg1−N2, 2.214(1); Mg1−C13, 2.284(2);
Mg1−C14, 2.400(2); Mg1−C16, 2.681(2); Mg1−C18, 2.821(2);
Mg1−C20, 2.658(2); C13−C14, 1.437(2); C14−C16, 1.412(2);
C16−C18, 1.404(2); C18−C20, 1.410(2), C13−C20, 1.421(2).
The NMR data discussed here describe dioxane-containing
samples (<1 equiv). Two C H signals at 6.44 and 6.33 ppm
5
4
and two C Me methyls at 2.33 and 2.24 ppm were observed in
5
4
1
M
M
tet
the H NMR spectra of {Bo Cp}MgMe and {Bo Cp }-
MgMe, respectively, as were the typical two oxazoline methyl
signals and two coupled diastereotopic CH2 resonances
associated with Cs structures. The magnesium methyl
resonances appeared as broad singlets at −0.05 and −0.9 in
the H NMR spectra of {Bo Cp}MgMe and {Bo Cp }-
MgMe, respectively. At the same time, the cyclopentadienyl-
bis(oxazoline) signals were sharp, further indicating complex
2
coordinates to the magnesium center through a η -C Me R
5
4
interaction in which the magnesium−carbon distances are
inequivalent. The short Mg−C distances involve the bis-
(oxazoline)-substituted carbon (Mg1−C13, 2.384(2) Å) and
the adjacent carbon (Mg1−C14, 2.400(2) Å). The next shorter
distances of Mg1−C16 and Mg1−C20, 2.681(2) and 2.658(2)
Å, respectively, are significantly longer. The magnesium−
carbon distances of the bridging methyl groups are similar but
unequal (Mg1−C22, 2.267(2) and Mg1−C22#, 2.271(2) Å)
and similar to the shortest distance in the magnesium-
cyclopentadienyl interaction. The bridging Mg−C distances
are similar to those in [(C Me Et)Mg(μ-Me)THF] . This
structure is distinguished from the monomeric structures
obtained with κ -η -{HC(Pz ) (Ph CC H )}MgR (Pz
,5-dimethylpyrazolyl; R = CH SiMe , Bu), although a
number of cyclopentadienyl magnesium piano-stool com-
pounds have been crystallographically characterized to contain
monohapto to pentahapto coordination modes, including (η -
)(η -C
Notably, the solid-state IR spectrum of amorphous material
suggests equivalent oxazolines. Therefore, crystallized
1
M
M
tet
1
M
tet
structures. Moreover, the H NMR spectrum of {Bo Cp }-
MgMe acquired at −63 °C contained four methyl resonances
and four coupled diastereotopic CH resonances assigned to
2
inequivalent oxazoline groups, and four signals were observed
for cyclopentadienyl methyl groups. Thus, the low-temperature
19
structure is C symmetric. The magnesium methyl and 2-C of
5
4
2
1
1
3
1
the oxazoline were difficult to observe in the C{ H} NMR
spectra of these compounds, either generated in situ or of
isolated materials. However, with small amounts of dioxane, the
2
5
Me2
Me2
=
2
2
5
4
t
20
3
2 3
15
MgMe resonance was observed at −11 ppm. Interestingly,
N
NMR signals were observed as weak cross-peaks at −146 ppm
1
M
tet
M
for {Bo Cp }MgMe and −147 ppm for {Bo Cp}MgMe using
5
21
1
15
C
H
5
5
H )MgTHF .
5 5 2
H− N HMBC experiments (room temperature), and these
chemical shifts are ca. 20 ppm upfield of 4,4-dimethyl-2-
oxazoline (−128 ppm) referenced in the above discussion.
In addition, the infrared spectra (in KBr) of powdered
M
tet
{
Bo Cp }MgMe was subjected to IR analysis, which revealed
−1
two νCN peaks at 1657 and 1628 cm . The two bands in this
spectrum are consistent with expectations based on the X-ray
diffraction study, with the lower energy band assigned to the
coordinated oxazoline.
The solution-phase structure might involve formation of a
dimeric species, so the diffusion rate was measured by H
M
M
tet
samples of {Bo Cp}MgMe and {Bo Cp }MgMe, obtained by
evaporation of frozen benzene solutions, each contained a
single band in the region associated with the CN stretch of
−1
the oxazoline group at 1658 cm . The observation of one IR
M
tet
M
tet
band contrasts the spectra of Bo Cp H and Bo Cp Tl,
which contained two νCN bands. One IR band is commonly
observed in tridentate tris(oxazolinyl)borate compounds, and
we attribute this to weak intensity of the asymmetric mode. For
1
DOSY experiments and compared to known monomeric
M
tet
magnesium species. The diffusion constant for {Bo Cp }-
MgMe (392.25 amu as a monomer) is 7.9 × 10− m /s (at
10
2
M
M
example, To MgMe (To = tris(4,4-dimethyl-2-oxazolinyl)-
23.5 mM), whereas the diffusion constants of monomeric
M
M
phenylborate) is C3v symmetric, all three oxazolines are
To MgSi(SiHMe ) (611.29 amu) and To MgMe (421.24
2 3
22
1
5
−10
−10
2
coordinated to magnesium(II), its N NMR chemical shift is
amu) are 6.95 × 10 and 8.5 × 10 m /s, respectively.
M tet
1
−
157 ppm, and the νCN absorption appears at 1592 cm− in the
The value of {Bo Cp }MgMe is between these two
D
DOI: 10.1021/acs.organomet.5b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
compounds, suggesting an averaged molecular weight of rapidly
exchanging monomer and dimers.
(Figure 3). The compound crystallizes as a dimer with each Ti
coordinated in a four-legged piano-stool geometry, with two
M
M
tet
Group 4 {Bo Cp}M and {Bo Cp }M (M = Ti, Zr)
M
Compounds. The reactions of TiCl (THF) with Bo CpTl or
3
3
M
tet
M
Bo Cp Tl provide paramagnetic [{Bo Cp}TiCl(μ-Cl)] or
2
M
tet
[
{Bo Cp }TiCl(μ-Cl)] (eq 5).
2
M
Figure 3. Rendered thermal ellipsoid plot of [{Bo Cp}TiCl(μ-Cl)] .
2
Ellipsoids are plotted at 35% probability, and H atoms are not
illustrated for clarity. Selected interatomic distances (Å): Ti1−Cl1,
M
2
.435(1); Ti1−Cl1#, 2.570(1); Ti1−Cl2, 2.366(1); Ti1−N2,
The infrared spectrum of [{Bo Cp}TiCl(μ-Cl)] acquired in
2
−1
2.238(2); Ti1−C14, 2.328(3); Ti1−C15, 2.312(4); Ti1−C16,
a KBr matrix contained two signals at 1662 and 1635 cm ,
which were assigned to CN stretching modes of non-
coordinated and coordinated oxazoline groups. Similarly, the
2.339(4); Ti1−C17, 2.396(4); Ti1−C18, 2.404(4); Ti1−Ti1#,
3.844(2); C14−C15, 1.429(5); C15−C16, 1.415(4); C16−C17,
1.424(6); C17−C18, 1.393(6); C18−C14, 1.418(4).
M
tet
infrared spectrum of [{Bo Cp }TiCl(μ-Cl)] contained ν
2
CN
−1
bands at 1661 and 1641 cm . The structures of these two
compounds were assigned based on the correspondence of the
IR data to the dimeric structure of [{Bo Cp}TiCl(μ-Cl)]2
indicated by a single-crystal X-ray diffraction study (see below)
bridging chloride ligands, a terminal chloride, the cyclo-
M
pentadienyl group, and one oxazoline ligand. The two
M
{
Bo Cp}Ti groups in the dimer are related by a crystallo-
graphically imposed inversion center. The Ti−Ti distance is
3.844(2) Å, which is slightly smaller than the distances of
and EPR data.
1
Although the H NMR signals appeared in the typical region
at 0−7 ppm, the spectra of [{Bo Cp}TiCl(μ-Cl)] or
{Bo Cp }TiCl(μ-Cl)] were not initially useful for assigning
structure or monitoring reaction progress because of the d
Ti(III) centers. The H NMR spectrum of [{Bo Cp}TiCl(μ-
Cl)] contained three broad aliphatic resonances at 0.5, 0.8, and
ppm likely from methyl groups present in the Bo Cp ligand,
and these were the most intense signals in the spectrum.
Cyclopentadienyl signals were barely detected. In the H NMR
spectrum of [{Bo Cp }TiCl(μ-Cl)] , ca. 20 signals at 0.5−2.0
ppm were observed. Despite the complex spectrum, multiple
preparations provided reproducible H NMR spectra with these
signals assigned to methyl groups in C Me and Ox
moieties. All these signals were weak with respect to the
residual benzene-d signal, but unlike monomeric Cp* TiCl,
M
3.943(2) and 3.926(3) Å in [Cp
2
Ti(μ-Cl)]
2
and
2
25
M
tet
[(C H Me) Ti(μ-Cl)] .
5 4 2 2
Only one oxazoline ring coordinates
[
2
1
per titanium center, and a similar pentahapto-monodentate
1
M
coordination is observed for the zirconium compound
M
{
Bo Cp}Zr(NMe ) described below.
2
3
2
M
The terminal Ti1−Cl2 is the shortest distance (2.366(1) Å)
1
of the three Ti−Cl bonds, and the two bridging Ti1−Cl1−Ti1#
interactions have inequivalent Ti−Cl distances (Ti1−Cl1,
2.435(1); Ti1−Cl1#, 2.570(1) Å). The unequal bridging Ti−
1
M
tet
2
Cl distances also contrast the molecular structures of [Cp Ti(μ-
2
1
Cl)] and [(C H Me) Ti(μ-Cl)] , which contain similar
2 5 4 2 2
Me2
internal distances (e.g., in the latter, Ti−Cl = 2.566(2),
5
4
2
.526(2), 2.535(2), and 2.562(2) Å).
M
The reaction of Bo CpH and Zr(NMe ) in benzene at
2
4
6
2
M
2
3
room temperature yields {Bo Cp}Zr(NMe ) with the loss of
2 3
these methyl signals are not paramagnetically shifted. In
addition, we note that carbon combustion analyses were
consistently lower than expected, although hydrogen and
nitrogen match calculated values.
M
tet
dimethylamine (eq 6). However, Bo Cp H does not react
with Zr(NMe2)4 in benzene or THF, even at elevated
temperatures up to 120 °C over 2 days.
The room-temperature magnetic susceptibility values (meas-
−
ured by Evan’s method) were 1.60 μ (0.886 e ) and 1.25 μ
(
(
B
B
−
0.69 e ) per Ti center. Electron paramagnetic resonance
EPR) experiments on point samples measured at room
temperature provided g-values of 1.984 and 1.989 for
M
M
tet
[
{Bo Cp}TiCl(μ-Cl)] and {Bo Cp }TiCl(μ-Cl)] , respec-
2
2
tively. Moreover, EPR spectra of glassed 9 mM toluene
M
M
tet
solutions of [{Bo Cp}TiCl(μ-Cl)] and [{Bo Cp }TiCl(μ-
2
Cl)] measured at 10 K contained a signal at half-field that
2
1
indicated the presence of a triplet diradical in the samples. The
A H NMR spectrum of a micromolar-scale reaction showed
24
M
triplet signal is also observed for (Cp TiCl) , and that
that {Bo Cp}Zr(NMe
temperature. A singlet resonance at 3.08 ppm (18 H) in the
H NMR spectrum was assigned to the apparently equivalent
2
)
3
forms within 10 min at room
2
2
compound also exhibits weak antiferromagnetic coupling of the
1
25
1
two d Ti(III) centers. Thus, the EPR spectrum provides
additional evidence for dimeric structures of the two titanium-
NMe groups. In addition, one set of oxazoline signals, with
2
(
III) compounds. In contrast, the triplet EPR signal was not
two signals corresponding to inequivalent methyl and two
doublets assigned to diastereotopic methylenes, was observed
in the spectrum acquired at room temperature. At −70 °C, the
oxazolines were inequivalent and revealed four methyl
observed in glassed 2-methyl THF at 10 K.
M
X-ray-quality crystals of [{Bo Cp}TiCl(μ-Cl)]2 were
obtained from a toluene/pentane solution cooled at −30 °C
E
DOI: 10.1021/acs.organomet.5b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
coordinated and noncoordinated oxazolines exchange rapidly.
The exchange process is slowed at low temperature, while a
1
second process that affects the NMe on the order of the H
2
NMR time scale occurs at −78 °C.
As in the magnesium compounds described above, the νCN
features in the infrared spectra varied between solution phase,
amorphous material obtained from fast evaporation of solvent,
and crystalline material. In benzene solution, two bands at 1659
and 1641 cm− were observed, while amorphous material (in a
1
KBr matrix) provided a spectrum with only one ν at 1646
CN
−1
M
cm . {Bo Cp}Zr(NMe ) that was crystallized from a mixture
2
3
of pentane and toluene provided an IR spectrum that contained
two bands at 1657 and 1636 cm . In spectra from the crystal
M
Figure 4. Rendered thermal ellipsoid plot of Bo CpZr(NMe ) . H
−1
2
3
atoms are not depicted for clarity. Selected interatomic distances (Å):
or solution-phase samples, the low-energy band was assigned to
coordinated oxazoline, and the high-energy stretch was assigned
to a noncoordinated group. Presumably, both oxazolines are
coordinated in the amorphous material.
Zr1−C1, 2.573(2); Zr1−C2, 2.580(2); Zr1−C3, 2.617(2); Zr1−C4,
2
.641(2); Zr1−C5, 2.599(2); Zr1−N1, 2.536(1); Zr1−N3, 2.071(2);
Zr1−N4, 2.092(1); Zr1−N5, 2.101(2). Selected angles (deg): N1−
Zr1−N5, 163.36(6), N3−Zr1−N4, 120.40(6).
M
A single-crystal X-ray diffraction study of {Bo Cp}Zr-
(
NMe ) showed one coordinated and one noncoordinated
resonances. Four cyclopentadienyl signals also appeared. The
NMe2 signal broadened from its sharp nature at room
temperature to a broad signal that overlapped with oxazoline
methylene signals at −78 °C. Thus, at room temperature, the
2 3
oxazoline. The zirconium center adopts a four-legged piano-
stool geometry, an open site trans to the cyclopentadienyl
group. The Zr1−N1 distance of 2.536(1) Å is significantly
Table 1. Catalytic Hydroamination of Aminoalkenes
a
b
c
d
See ref 18a. See ref 4a. Isolated yield. NMR yield.
F
DOI: 10.1021/acs.organomet.5b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
longer than the distances to the amides (Zr1−N3, 2.071(2);
Zr1−N4, 2.092(1); Zr1−N5, 2.101(2) Å).
CONCLUSIONS
■
These new monoanionic cyclopentadienyl-bis(oxazoline) li-
gands provide chelating piano-stool compounds of Tl, Mg, Ti,
and Zr. The syntheses of the ligands described here employ the
combination of electrophilic cyclopentadienyl derivatives with
nucleophilic, stabilized bis(oxazoline) carbanions. This cyclo-
pentadienyl ligand construction is opposite the synthesis of
ansa-type dimethylsilyl-bis(cyclopentadiene) or constrained-
geometry-type dimethylsilyl-cyclopentadiene-amido ligands
that employ nucleophilic cyclopentadienide derivatives com-
The mutually trans dimethylamide ligands of N3 and N4 are
planar (∑ angles around N3 and N4 is 360°), while the
dimethylamide of N5 (pseudo trans to the oxazoline) is slightly
pyramidalized (∑ angles around N5 is 356°). In addition, the
N5 dimethylamide is oriented with both methyls equidistant
from the Cp centroid, whereas N3 and N4 dimethylamide
planes are roughly orthogonal to the cyclopentadienyl plane.
Catalytic Hydroamination/Cyclization of Aminoal-
kenes. Catalytic cyclization reactions of aminoalkenes provide
an initial test of the reactivity of the magnesium and group 4
compounds supported by these cyclopentadienyl-bis-
3
b
bined with electrophilic silicon centers. Likewise, the
synthesis of the optically active dianionic cyclopentadienyl-
bis(oxazolinyl)borate ligands [PhB(Ox ) C H ] involves the
R
2−
2
5
4
(
oxazoline) ligands. These reactions also provide means for
reaction of cyclopentadienide nucleophile NaC H and electro-
5 5
M
18a
R
4a−c
comparing reactivity with previously reported To MgMe,
To Zr(NMe ) , and {PhB(Ox ) Cp}Zr(NMe ) , as well
as the unsubstituted piano-stool compound CpZr(NMe ) . It is
worth noting that the amide groups in To Zr(NMe ) are not
readily substituted and that the compound is not a good
catalyst for cyclization of aminoalkenes. CpZr(NMe ) is
isoelectronic with To Zr(NMe ) , but to our knowledge, the
former compounds’ reactivity in catalytic hydroamination/
philic borane PhB(Ox )
.
2
Here, we have shown that
M
26
Me2
4a
reversing the electrophilic and nucleophilic components in this
alternative synthetic approach has some generality in terms of
varying steric properties on the cyclopentadienyl group. The
synthetic approach, then, lends itself to a range of combinations
through the variation of groups on the cyclopentadienyl ring as
well as the substituents on the oxazoline ring. Because
oxazolines are readily prepared in enantiopure chiral form
with a number of substituents in the 4 and 5 positions, optically
active piano-stool compounds may readily be prepared for
application in asymmetric catalysis, including hydroamination.
We are currently synthesizing a range of derivatives of this
ligand class. Moreover, this approach may be generally useful
for the synthesis of cyclopentadienyl ligands with new
substitution patterns and substituents derived from nucleo-
philes rather than electrophiles.
2
3
2
2 2
2
3
M
2
3
26
2
3
M
2
3
cyclization has not previously been described.
M
M
tet
M
{
Bo Cp}MgMe, {Bo Cp }MgMe, and {Bo Cp}Zr-
(
NMe ) are precatalysts for the cyclization of aminoalkenes
2
3
to heterocyclic amines as reported in Table 1. Upon addition of
primary amines to the magnesium methyl or zirconium
dimethylamide compounds, methane or dimethylamine is
observed, indicating that a metal amide is formed. Comparison
of Mg and Zr catalysts with the same ancillary ligand shows that
magnesium catalysts are generally more reactive than
zirconium, i.e., To MgMe > To Zr(NMe ) and {Bo Cp}-
MgMe > {Bo Cp}Zr(NMe ) . In the magnesium series,
relative reaction rates show {Bo Cp}MgMe ∼ {Bo Cp }
MgMe > To MgMe as catalysts for aminoalkene cyclization.
In this context, it is interesting to note that the combination
of the bis(oxazoline) and cyclopentadienyl ligands on
zirconium gives more reactive catalytic species than the
oxazoline-free CpZr(NMe ) catalyst precursor. We are not
M
M
M
2
3
M
2
3
2
3
M
M
tet -
aware of prior studies of the parent piano-stool compound
CpZr(NMe ) as a catalyst for cyclization of aminoalkenes, and
M
2
3
M
M
tet
Notably, both {Bo Cp}MgMe and {Bo Cp }MgMe readily
afford pyrrolidine at room temperature. The diastereoselectivity
for cyclization of amino dialkene by {Bo Cp}MgMe or
{
this compound is surprisingly reactive under catalytic
M
26
conditions. In contrast, the compound To Zr(NMe ) ,
2 3
M
which is isoelectronic with CpZr(NMe ) , is inert toward
2 3
M
tet
Bo Cp }MgMe is 1:1.
substitution of dimethylamide groups by amines and is not an
active catalyst for hydroamination/cyclization. That is, the
introduction of oxazoline donors does not inherently enhance
the reactivity of dimethylamido zirconium sites in hydro-
amination. However, the combination of cyclopentadienyl and
oxazoline ligands on zirconium leads to more reactive catalytic
sites than parent cyclopentadienyl or tris(oxazolinyl)borate
ligands. Moreover, the comparison of zwitterionic borate
In the zirconium series, the relative reactivity follows the
trend {PhB(OxMe2) Cp}Zr(NMe ) > {Bo Cp}Zr(NMe ) >
CpZr(NMe ) ≫ To Zr(NMe ) . At room temperature under
equivalent conditions, the turnover rate for cyclization to 2-
methyl-4,4-diphenylpyrrolidine by {Bo Cp}Zr(NMe ) is
approximately 5× faster than CpZr(NMe ) but 3× slower
than {PhB(Ox ) Cp}Zr(NMe ) . Although CpZr(NMe ) is
the least reactive of the cyclopentadienyl-coordinated precata-
lysts, catalytic conversion is observed at room temperature.
This activity is perhaps surprising given the few examples of
zirconium complexes that catalyze hydroamination/cyclization
at room temperature. For example, the N for constrained-
geometry {Me Si(C R )NR′}ZrMe is 0.07 h at 100 °C in a
conversion that gives 4,4-dimethyl-2-methylpyrrolidine, where-
M
2
2 2
2 3
M
2
3
2 3
M
2
3
2
3
Me2
2
2 2
2 3
Me2
M
complex {PhB(Ox ) Cp}Zr(NMe ) with {Bo Cp}Zr-
2
2 2
(
NMe ) reveals that the divalent ancillary ligand gives more
2 3
reactive zirconium sites. We are continuing to study and
compare these ligand classes in catalytic chemistry to further
discover systematic trends of reactivity and selectivity.
t
−1
2
5
4
2
EXPERIMENTAL SECTION
■
M
−1
as the N for {Bo Cp}Zr(NMe ) is 0.4 h at 60 °C.
Interestingly, a slightly faster conversion is catalyzed by
{
1
General Procedures. All reactions were performed under a dry
argon atmosphere using standard Schlenk techniques or under a
nitrogen atmosphere in a glovebox, unless otherwise indicated. Dry,
oxygen-free solvents were used throughout. Benzene, toluene, pentane,
methylene chloride, diethyl ether, and tetrahydrofuran were degassed
by sparging with nitrogen, filtered through activated alumina columns,
and stored under nitrogen. Benzene-d , toluene-d , and tetrahydrofur-
t
2 3
−
1
Me Si(C R )NR′}ZrCl(NMe ) with an N of 0.14 h at
2
5
4
2
t
5
M
00 °C. As noted above, To Zr(NMe ) , which is
2 3
isoelectronic with CpZr(NMe ) , is not a catalyst for cyclization
2
3
of aminoalkenes, and this inactivity may relate to its six-
coordinate zirconium center and substitutionally inert coordi-
nation sphere.
6
8
an-d were heated to reflux over Na/K alloy and vacuum-transferred.
8
Anhydrous TiCl (THF) and TlOEt were purchased from Aldrich and
3
3
G
DOI: 10.1021/acs.organomet.5b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Me2 27
28
used as received. MeHC(Ox ) , MgMe (O C H ) , Zr-
was then extracted with benzene, filtered, and dried under reduced
pressure to give the product as a brown solid (0.537 g, 1.09 mmol,
2
2
2
4
8 2
29
30
31
M
tet 14
(
NMe ) , Tl[C H ], C Me H , Bo Cp H, 2,2-diphenyl-4-
2
4
5
5
5
4
2
3
2
33
1
penten-1-amine,
2,2-dimethyl-4-penten-1-amine,
(1-
and C-(1-allyl-cyclopentyl)-
methylamine were prepared according to the literature. 1H and
83%). Mp: 168−171 °C (dec). H NMR (benzene-d , 600 MHz): δ
6
3
4
2
allylcyclohexyl)methylamine,
6.56 (s, 2 H, C H ), 6.29 (s, 2 H, C H ), 3.65 (d, 2 H, J = 8 Hz,
5
4
5
4
HH
34
2
CNCMe CH O), 3.59 (d, 2 H, J = 8 Hz, CNCMe CH O), 2.14 (s,
2
2
HH
2
2
1
3
1
Me2
C{ H} NMR spectra were collected on either a Bruker DRX-400
3 H, MeC(Ox ) ), 1.03 (s, 6 H, CNCMe CH O), 1.01 (s, 6 H,
2
2
2
CNCMe
(CNCMe
80.14 (CNCMe
CH
O). 13C{ H} NMR (benzene-d
O), 124.22 (C ), 107.90 (C
CH O), 67.31 (CNCMe CH
), 28.46 (CNCMe CH O), 28.39 (CNCMe
). N NMR (benzene-d , 61 MHz): δ −130
O). IR (KBr, cm ): 3075 m, 2966 s, 2930 m, 2887
1
, 151 MHz): δ 170.92
), 107.52 (C ),
O), 44.21 (Me-
CH O), 25.17
spectrometer, a Bruker Avance III 600 spectrometer, or an Agilent MR
2
2
6
1
15
4
00 spectrometer. 15N chemical shifts were determined by H− N
2
CH
2
5
H
4
5
H
4
H
5 4
15
HMBC experiments on a Bruker Avance III 600 spectrometer.
N
2
2
2
2
Me2
chemical shifts were originally referenced to liquid NH3 and
recalculated to the CH NO chemical shift scale by adding −381.9
C(Ox
(MeC(Ox
(CNCMe
)
2
2
2
2
2
Me2
15
)
2
3
2
2
6
−
1
ppm.
2
CH
MeC(OxMe2)2Li. MeHC(OxMe2)2 (2.000 g, 8.92 mmol) was
dissolved in pentane (50 mL), the solution was cooled to −78 °C,
s, 1647 s (CN), 1463 m, 1383 w, 1365 m, 1349 w, 1276 m, 1248 m,
1200 m, 1080 s, 1042 vw, 1028 w, 975 m. Anal. Calcd for
n
and BuLi in hexane (9.0 mmol, 3.6 mL) was added. The mixture was
C
17
H
23
N
2
O
2
Tl: C, 41.52; H, 4.71; N, 5.70. Found: C, 41.14; H,
stirred at this temperature for 2 h, and then the solution was warmed
to room temperature and stirred for 12 h. The solvent was removed by
filtration, and the solid product was washed with pentane (50 mL).
Evaporation of residual solvent under reduced pressure provided white
solid MeC(Ox ) Li in good yield (1.912 g, 8.3 mmol, 93%). Mp:
4.61; N, 5.67.
M
tet
Bo Cp Tl. TlOEt (84.9 μL, 1.20 mmol) was added to a THF
M
tet
solution of Bo Cp H (0.377 g, 1.09 mmol), and the reaction mixture
was stirred at room temperature for 10 days. The volatile materials
were evaporated, and the solid was washed with pentane (3×). The
residue was extracted with benzene and dried under reduced pressure
to give the product as a green solid (0.512 g, 0.933 mmol, 85.5%). Mp:
Me2
2
1
2
92−294 °C (dec). H NMR (THF-d , 600 MHz): δ 3.59 (s, 4 H,
8
Me2
CNCMe CH O), 1.69 (s, 3 H, MeC(Ox ) ), 1.13 (s, 12 H,
2
2
2
13
1
1
2
CNCMe CH O). C{ H} NMR (THF-d , 151 MHz): δ 170.51
162−164 °C (dec). H NMR (benzene-d
6
, 600 MHz): δ 3.65 (d, JHH
2
2
8
2
(
5
(
(
CNCMe CH O), 77.84 (CNCMe CH O), 65.39 (CNCMe CH O),
= 8.1 Hz, 2 H, CNCMe
2
CH
2
O), 3.63 (d,
Me
), 1.11 (s, 6 H, CNCMe
J
HH = 8.1 Hz, 2 H,
Me ), 2.20 (s,
O), 1.10 (s, 6 H,
, 151 MHz): δ 170.23
), 114.8 (C Me ), 114.1 (br,
O), 67.62 (CNCMe CH O), 46.53
), 28.76 (CNCMe CH O), 28.26 (CNCMe CH O),
), 12.63 (d, JTlC = 57.4 Hz, C Me ), 11.14 (d, JTlC
, 61 MHz): δ −128.1
O). IR (KBr, cm ): 2971 s, 2961 m, 2923 m, 2889 m,
2
2
2
2
2
2
Me2
7.01 (MeC(Ox ) ), 30.04 (CNCMe CH O), 12.41 (MeC-
CNCMe
3 H, MeC(Ox
CNCMe CH O). C{ H} NMR (benzene-d
(CNCMe CH O), 115.94 (C Me
Me ), 79.83 (CNCMe CH
(MeC(Ox
26.65 (MeC(Ox
= 44.8 Hz, C Me
(CNCMe CH
2
CH
2
O), 2.36 (s, 6 H, C
5
4
), 2.24 (s, 6 H, C
5
4
2
2
2
Me2
15
1
Me2
Ox )2). N{ H} NMR (THF-d , 61 MHz): δ −211.3
)
2
2
CH
2
8
−1
13
1
CNCMe CH O). IR (KBr, cm ): 2964 s, 2928 m, 2867 m, 1671
2
2
6
2
2
w, 1615 s, 1590 s, 1543 m, 1509 s, 1460 m, 1397 m, 1361 m, 1293 m,
245 w, 1189 m, 1070 m, 1019 s, 980 m, 922 w, 828 w, 767 w, 732 w.
Anal. Calcd for C H LiN O : C, 62.6; H, 8.32; N, 12.17. Found: C,
2
2
5
4
5
4
1
C
5
4
2
2
2
2
Me2
)
12
19
2
2
2
2
2
2
2
Me2
6
2.29; H, 8.55; N, 12.06.
)
2
5
4
M
15
Bo CpH. Tl[C H ] (1.44 g, 5.35 mmol) was slurried in benzene
10 mL) in a 100 mL Schlenk flask. The flask was fitted with an
5
4
). N NMR (benzene-d
6
5
5
−
1
(
2
2
addition funnel, and the solution was cooled to 12 °C using a dioxane/
dry ice bath. A solution of iodine (1.24 g, 4.86 mmol) in benzene (50
mL) was added to the slurry in a dropwise fashion over 1.5 h while
maintaining the temperature at 12 °C to form a cloudy yellow solution
2855 m, 1654 m (CN), 1637 s (CN), 1457 w, 1381 m, 1362 w,
1343 w, 1267 m, 1246 m, 1194 m, 1091 m, 1075 m, 1042 w, 993 m,
973 m, 936 w, 897 w. Anal. Calcd for C21
H N O Tl: C, 46.04; H,
31 2 2
5.70; N, 5.11. Found: C, 46.21; H, 5.79; N, 5.06.
Me2
M
of C H I. MeC(Ox )2Li (1.12 g, 4.86 mmol) dissolved in THF (20
{Bo Cp}MgMe. MgMe (O C H ) (0.049 g, 0.230 mmol) was
2 2 4 8 2
5
5
M
mL) was added to the iodocyclopentadiene mixture via cannula. The
solution was then warmed to room temperature and stirred overnight.
The solution was filtered in air, and the solvent was evaporated on a
Rotovapor at 100 mTorr. The crude oily product was purified by silica
gel chromatography in ethyl acetate to give a brown oil, which was
dissolved in benzene and stirred over phosphorus pentoxide for 6 h to
remove any water. The solution was filtered and the solvent was
added to a benzene solution of Bo CpH (0.066 g, 0.230 mmol), and
the reaction mixture was stirred at room temperature for 1.5 h. Gas
formation was observed over the course of the reaction. The solution
was filtered, and the filtrate was evaporated under reduced pressure to
give a pink oil. The oil was washed with pentane (3×) and dried under
reduced pressure to give a white solid, which was stored at −30 °C
(0.051 g, 0.157 mmol, 68.3%). Exhaustive evaporation to remove
residual dioxane and diethyl ether gives broad spectra. Data given here
contain residual ethers, the 2C and magnesium methyl signals were
M
removed under reduced pressure to provide brown, oily Bo CpH as a
mixture of two isomers (0.789 g, 2.753 mmol, 57%). 1H NMR
1
3
1
not detected in the C{ H} NMR spectrum or through 2D
correlation spectroscopy, and C analyses were systematically lower
(
benzene-d , 600 MHz): δ 7.04 (m, 1 H, H C H ), 6.58 (s, 1 H,
6
2
5
3
H C H ), 6.41 (m, 1 H, H C H ), 6.35 (m, 2 H, H C H ), 6.31 (m, 1
2
5
3
2
5
3
2
5
3
1
than calculated values. Mp: 145−147 °C (dec). H NMR (benzene-d ,
H, H C H ), 3.66−3.58 (m, 8 H, CNCMe CH O), 3.46 (s, 2 H,
6
2
5
3
2
2
Me2
6
00 MHz): δ 6.44 (s, 2 H, C H ), 6.33 (s, 2 H, C H ), 3.66 (d, 2 H,
H C H ), 2.73 (s, 2 H, H C H ), 2.10 (s, 3 H, MeC(Ox ) ), 2.04 (s,
H, MeC(Ox ) ), 1.11 (v t, 24 H, CNCMe CH O). C{ H} NMR
5
4
5
4
J
2
5
3
2
5
3
2
Me2
13
1
2
2
3
J
HH = 8.1 Hz, CNCMe
CNCMe CH
CNCMe CH
C{ H} NMR (benzene-d
(C H ), 102.46 (C H ), 81.16 (CNCMe CH O), 66.94
2
CH
2
O), 3.55 (d, 2 H,
HH = 8.1 Hz,
), 1.16 (6 H,
O), −0.05 (br s, MgMe).
, 151 MHz): δ 118.46 (C ), 108.54
2
2
2
Me2
(
(
(
1
benzene-d , 151 MHz): δ 166.56 (CNCMe CH O), 166.23
2
2
O), 2.06 (s, 3 H, MeC(Ox
O), 1.13 (6 H, CNCMe CH
)
2
6
2
2
CNCMe CH O), 148.24 (H C H ), 147.17 (H C H ), 135.26
2
2
2
2
2
2
2
5
3
2
5
3
13
1
H C H ), 133.46 (H C H ), 132.55 (H C H ), 132.18 (H C H ),
6
H
5 4
2
5
3
2
5
3
2
5
3
2
5
3
29.60 (H C H ), 128.92 (H C H ), 79.55 (CNCMe CH O), 79.53
2
5
3
2
5
3
2
2
5
4
5
4
2
2
Me2
(
CNCMe CH O), 67.72 (CNCMe CH O), 67.66 (CNCMe CH O),
(CNCMe CH O), 44.89 (MeC(Ox ) ), 28.29 (CNCMe CH O),
2
2
2
2
2
2
2 2 2 2 2
Me2
Me2
15
4
5.31 (H C H ), 44.68 (H C H ), 43.21 (MeC(Ox )2), 41.42
28.22 (CNCMe CH O), 22.20 (MeC(Ox )2). N NMR (benzene-
2 2
2
5
3
2
5
3
Me2
−1
(
2
(
MeC(Ox ) ), 28.60 (CNCMe CH O), 28.55 (CNCMe CH O),
d , 61 MHz): δ −147.4 (CNCMe CH O). IR (KBr, cm ): 2968 s,
2
2
2
2
2
6
2
2
Me2
8.51 (CNCMe CH O), 24.48 (MeC(Ox )2), 23.83 (MeC-
2931 m, 2897 m, 1658 s (CN), 1547 w, 1463 m, 1366 m, 1309 w,
1292 w, 1255 w, 1202 w, 1192 m, 1084 s sh, 1041 s, 974 w, 960 w, 934
w, 874 m, 809 w, 750 m. Anal. Calcd for C H MgN O : C, 66.17; H,
2
2
Me2
15
Ox )2).
N NMR (benzene-d , 61 MHz): δ −132.5
6
−1
(
CNCMe CH O). IR (KBr, cm ): 2968 s, 2930 m, 2890 m, 1656 s
2 2
18 26
2
2
(
9
CN), 1462 m, 1364 m, 1286 m, 1249 w, 1193 m, 1084 m, 974 m,
33 w, 900 w, 732 w. Anal. Calcd for C H N O : C, 70.80; H, 8.39;
8.02; N, 8.57. Found: C, 63.34; H, 7.61; N, 8.67.
{Bo Cp }MgMe. A benzene solution of Bo Cp H (0.129 g,
M
tet
M
tet
17
24
2
2
N, 9.71. Found: C, 70.30; H, 8.78; N, 9.69.
0.373 mmol) was allowed to react with MgMe (O C H ) (0.080 g,
2
2
4
8 2
M
M
Bo CpTl. Bo CpH (0.375 g, 1.31 mmol) was dissolved in diethyl
ether. Thallium ethoxide (102 μL, 1.44 mmol) was added, and a
brown precipitate immediately formed. The solution was stirred at
room temperature for 2 h. The mixture was centrifuged, and the
solvent was decanted. The solid was washed with pentane (3×) and
0.373 mmol) at room temperature for 4 h. Gas formation was
observed over the course of the reaction. The reaction mixture was
filtered and evaporated to dryness under reduced pressure to give a
yellow oil. The oil was washed with pentane (3×) and dried under
reduced pressure to give a white solid, which was stored at −30 °C
H
DOI: 10.1021/acs.organomet.5b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
Me2
(
(
3
0.110 g, 0.286 mmol, 76.9%). Mp: 145−146 °C (dec). H NMR
67.81 (CNCMe CH O), 47.36 (NMe ), 43.92 (MeC(Ox ) ), 27.33
2 2 2 2
2
Me2
benzene-d , 600 MHz): δ 3.70 (d, 2 H, J = 8.3 Hz, CNCMe CH O),
.58 (d, 2 H, J = 8.3 Hz, CNCMe CH O), 2.33 (s, 6 H, C Me ), 2.24
s, 6 H, C Me ), 2.11 (s, 3 H, MeC(Ox )2), 1.08 (s, 6 H,
CNCMe CH O), 1.05 (s, 6 H, CNCMe CH O), −0.91 (s, 3 H,
MgMe). C{ H} NMR (benzene-d , 151 MHz): δ 173.8
CNCMe CH O), 113.66 (C Me ), 108.19 (C Me ), 107.47
C Me ), 80.81 (CNCMe CH O), 66.51 (CNCMe CH O), 46.69
(CNCMe CH O), 27.03 (CNCMe CH O), 22.42 (MeC(Ox )2).
N NMR (benzene-d , 61 MHz): δ −138 (CNCMe CH O);
Zr(NMe2)3 was not detected. IR (KBr, cm , amorphous solid):
2965 s, 2930 m 2890 m, 2865 m, 2819 m, 2759 m, 2736 m, 1645 s
(CN), 1460 m, 1364 m, 1314 m, 1288 m, 1235 m, 1203 m, 1139 s,
1122 m, 1102 m, 1083 m, 1046 s, 975 s, 957 m, 938 m, 875 m, 786 s,
715 m, 712 s. Anal. Calcd for C H N O Zr: C, 54.08; H, 8.09; N,
6
2
2
2 2 2 2
2
15
2
2
5
4
6
2
2
Me2
−1
(
5
4
2
2
2
2
1
3
1
6
(
(
(
2
(
2 2 5 4 5 4
5
4
2
2
2
2
23 41
5
2
Me2
MeC(Ox ) ), 28.61 (CNCMe CH O), 27.73 (CNCMe CH O),
13.71. Found: C, 53.63; H, 7.57; N, 13.30.
2
2
2
2
2
Me2
4.11 (MeC(Ox ) ), 14.01 (C Me ), 11.97 (C Me ), −10.84
General Procedure for Catalytic Hydroamination. Micro-
molar-Scale Catalysis. In a typical small-scale hydroamination
experiment, a J. Young style NMR tube was charged with 100 μmol
of aminoalkene substrate, 10 μmol of catalyst, and 0.5 mL of solvent
(benzene-d ). The J. Young tube was sealed with a Teflon valve, and
the reaction progress was monitored by H NMR spectroscopy at
regular intervals to determine the conversion.
2
5
4
5
4
1
5
MgMe).
N NMR (benzene-d , 61 MHz): δ −145.7
6
−1
(
CNCMe CH O). IR (KBr, cm , amorphous solid): 2996 s, 2928
2
2
s, 2866 s, 2726 w sh, 1658 s (CN), 1496 m, 1467 m, 1304 m, 1306
m, 1283 m, 1252 m, 1192 m, 1087 m, 1024 w, 991 w, 974 m, 962 m,
6
−
1
1
9
2
34 m, 893 w, 829 w. IR (crystallized sample, KBr, cm ): 2966 s,
928 s, 2897 s, 2867 s, 1657 s, 1627 s, 1462 m, 1365 m, 1307 m, 1253
w, 1190 m, 1088 s, 1024 w, 961 m, 935 m, 831 w. Anal. Calcd for
C H MgN O : C, 69.02; H, 8.95; N, 7.32. Found: C, 67.48; H, 9.35;
Scaled-Up Hydroamination Catalysis. A Schlenk flask was charged
M
M
tet
with the catalyst {Bo Cp}MX or {Bo Cp }MX (0.200 mmol), the
appropriate aminoalkene (2.00 mmol), and benzene (10 mL). The
solution was stirred for 4 to 48 h at room temperature. The products
were isolated by evaporation of the solvent and purified using flash
22
34
2
2
N, 6.95.
M
[
{Bo Cp}TiCl(μ-Cl)] . TiCl (THF) (0.194 g, 0.523 mmol) was
dissolved in benzene (10 mL) and added to a benzene solution of
Bo CpTl (0.257 g, 0.523 mmol) to produce a cloudy green solution.
2 3 3
M
column chromatography (silica gel, CH Cl /MeOH = 9.5:0.5).
2 2
The reaction mixture was stirred for 8 h. The solution was filtered, and
the filtrate was evaporated to dryness under reduced pressure to give a
brown solid. The solid was recrystallized at −30 °C in a mixture of
toluene and pentane to give green, paramagnetic X-ray quality crystals
ASSOCIATED CONTENT
■
*
S
Supporting Information
(
0.113 g, 0.278 mmol, 53.1%). Mp: 140−142 °C (dec). IR (KBr,
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00771.
−1
cm ): 3117 w, 2970 m, 1662 s (CN), 1635 s (CN), 1461 m,
1
368 s, 1323 s, 1290 m, 1258 m, 1190 m, 1109 s, 1090 s, 1050 w, 1036
w, 982 s, 960 s, 935 m, 874 w, 822 s 808 s, 773 w. Anal. Calcd for
1H, 13C{ H}, and 15N NMR spectra of new compounds
1
C H Cl N O Ti: C, 50.27; H, 5.71; N, 6.90. Found: C, 49.92; H,
17
23
2
2
2
5
.64; N, 6.84.
Magnetic susceptibility was measured using Evan’s method at room
(PDF)
M
tet
Crystallographic information files for Bo Cp H,
temperature using a Bruker 400 mHz NMR spectrometer. A sample of
M
tet
M
M
M
{Bo Cp }MgMe, {Bo Cp}TiCl ) , and {Bo Cp}Zr-
Bo CpTiCl (5.7 mg, 0.014 mmol) was dissolved in benzene-d (0.90
2 2
2
6
mL) to give a 15.6 mM solution. The solution (0.60 mL) was placed in
(NMe ) (CIF)
2
3
an NMR tube. A capillary was charged with benzene-d and placed in
6
1
the NMR tube. The H NMR spectrum showed a paramagnetic shift
in the benzene-d peak. Using Evan’s method, the following values
AUTHOR INFORMATION
6
■
*
−3
3
were obtained: Δδ = 0.070 ppm, χ = 1.07 × 10 cm /mol, μ = 1.60
μ , n = 0.885 electron. The data are consistent with a d Ti(III)
mol
Corresponding Author
E-mail: sadow@iastate.edu.
1
B
complex.
M
tet
[
{Bo Cp }TiCl(μ-Cl)] . TiCl (THF) (0.071 g, 0.192 mmol) was
2 3 3
Present Addresses
dissolved in benzene (5 mL) and added to a benzene solution of
Megan Hovey, Oxbow Carbon LLC, 11826 N 30th Street,
Kremlin, Oklahoma 73753, United States.
Hung-An Ho, Catal Material Co. Ltd., 33 Guangfu Road, Jiatai
Industrial Park, Chiayi, Taiwan 61252.
Barun Jana, Department of Inorganic Chemistry, Indian
Association for the Cultivation of Science, Kolkata, 700032
India.
Nicole L. Lampland, Pharmaceutical Speciality, Inc. 1620
Industrial Drive NW, Rochester, Minnesota 55901, United
States.
M
tet
Bo Cp Tl (0.257 g, 0.523 mmol), resulting in a cloudy green
solution. The reaction mixture was stirred for 18 h. The solution was
filtered, and the filtrate was evaporated to dryness under reduced
pressure. The solid was then extracted with benzene and dried under
reduced pressure to give a green solid (0.070 g, 0.151 mmol, 79%).
−1
Mp: 141−143 °C (dec). IR (KBr, cm ): 2964 s, 2927 m, 2871 w,
661 m sh (CN), 1641 s (CN), 1570 w, 1463 m, 1366 m, 1322
m, 1285 w, 1253 w, 1190 m, 1170 m, 1096 m, 1029 w, 973 m, 956 m,
35 w, 832 w. n = 0.69 by Evan’s method. Anal. Calcd for
C H Cl N O Ti: C, 54.56; H, 6.76; N, 6.06. Found: C, 53.82; H,
1
9
21
31
2
2
2
6
.75; N, 5.84.
M
M
{
Bo Cp}Zr(NMe ) . Benzene solutions of Bo CpH (0.100 g, 0.347
Notes
2
3
mmol) and Zr(NMe ) (0.093 g, 0.347 mmol) were mixed, allowed to
The authors declare no competing financial interest.
2
4
stir for 1 h at room temperature, and then filtered. Evaporation of the
filtrate to dryness under reduced pressure provided a yellow gel, which
was washed with pentane (3 × 5 mL). Further drying under vacuum
ACKNOWLEDGMENTS
■
M
yielded {Bo Cp}Zr(NMe ) as a yellow, analytically pure solid (0.168
Drs. Sarah Cady and Toshia Zessin are thanked for valuable
assistance with EPR spectra measurements and analysis. This
research was supported by the U.S. Department of Energy,
Office of Basic Energy Sciences, Division of Chemical Sciences,
Geosciences, and Biosciences, through the Ames Laboratory
Catalysis Program (Contract No. DE-AC02-07CH11358).
M.H. was supported by Office of Workforce Development for
Teachers and Scientists through the Summer Undergraduate
Laboratory Internship Program through the Ames Laboratory.
2
3
g, 0.329 mmol, 94.9%). X-ray quality single crystals were obtained
from a toluene and pentane solution of the product at −30 °C. Mp:
1
3
1
2
8
29−132 °C. H NMR (benzene-d , 600 MHz): δ 6.24 (t, 2 H, J
=
=
6
HH
3
2
.2 Hz, C H ), 6.20 (t, 2 H, J = 2.2 Hz, C H ), 3.63 (d, 2 H, J
.1 Hz, CNCMe CH O), 3.52 (d, 2 H, JHH = 8.1 Hz,
5
4
HH
5
4
HH
2
2
2
Me2
CNCMe CH O), 3.09 (s, 18 H, NMe ), 1.92 (s, 3 H, MeC(Ox )2),
2
2
2
13
1
1
.02 (s, 6 H, CNCMe CH O), 0.97 (s, 6 H, CNCMe CH O). C{ H}
2 2 2 2
NMR (151 MHz, benzene-d ): δ 170.42 (CNCMe CH O), 126.30
6
2
2
(
ipso-C H ), 109.36 (C H ), 108.98 (C H ), 80.73 (CNCMe CH O),
5 4 5 4 5 4 2 2
I
DOI: 10.1021/acs.organomet.5b00771
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
21) Jaenschke, A.; Paap, J.; Behrens, U. Organometallics 2003, 22,
REFERENCES
■
1
(
167−1169.
22) Mukherjee, D.; Lampland, N. L.; Yan, K.; Dunne, J. F.; Ellern,
A.; Sadow, A. D. Chem. Commun. 2013, 49, 4334−4336.
23) Pattiasina, J. W.; Heeres, H. J.; Van Bolhuis, F.; Meetsma, A.;
Teuben, J. H.; Spek, A. L. Organometallics 1987, 6, 1004−1010.
24) Samuel, E.; Harrod, J. F.; Gourier, D.; Dromzee, Y.; Robert, F.;
Jeannin, Y. Inorg. Chem. 1992, 31, 3252−3259.
25) Jungst, R.; Sekutowski, D.; Davis, J.; Luly, M.; Stucky, G. Inorg.
Chem. 1977, 16, 1645−1655.
26) Dunne, J. F.; Su, J.; Ellern, A.; Sadow, A. D. Organometallics
008, 27, 2399−2401.
27) Dagorne, S.; Bellemin-Laponnaz, S.; Welter, R. Organometallics
004, 23, 3053−3061.
28) Tobia, D.; Baranski, J.; Rickborn, B. J. Org. Chem. 1989, 54,
253−4256.
(29) Diamond, G. M.; Jordan, R. F.; Petersen, J. L. J. Am. Chem. Soc.
(
1) (a) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J.; MacGillivray,
L. R. J. Am. Chem. Soc. 1993, 115, 5336−7. (b) Hirotsu, M.; Fontaine,
P. P.; Epshteyn, A.; Sita, L. R. J. Am. Chem. Soc. 2007, 129, 9284−
(
9
285. (c) Hirotsu, M.; Fontaine, P. P.; Zavalij, P. Y.; Sita, L. R. J. Am.
Chem. Soc. 2007, 129, 12690−12692. (d) Shima, T.; Hu, S.; Luo, G.;
(
Kang, X.; Luo, Y.; Hou, Z. Science 2013, 340, 1549−1552.
(
2) (a) Arndt, S.; Okuda, J. Chem. Rev. 2002, 102, 1953−1976.
(
(
b) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2002, 103, 283−316.
3) (a) Okuda, J. Chem. Ber. 1990, 123, 1649−1651. (b) Shapiro, P.
J.; Bunel, E.; Schaefer, W. P.; Bercaw, J. E. Organometallics 1990, 9,
67−869. (c) Stevens, J. C. InsiteTM Catalysts Structure/Activity
(
(
2
(
2
(
4
8
Relationships for Olefin Polymerization. In Catalyst Design for Tailor-
Made Polyolefins: Proceedings of the International Symposium on Catalyst
Design for Tailor-Made Polylefins; Kanazawa, March 10−12, 1994, Soga,
K.; Terano, M., Eds.; Elsevier: Tokyo, 1994; Vol. 89, pp 277−284.
(
(
3
d) Chen, Y.-X.; Marks, T. J. Organometallics 1997, 16, 3649−3657.
4) (a) Manna, K.; Ellern, A.; Sadow, A. D. Chem. Commun. 2010, 46,
39−341. (b) Manna, K.; Kruse, M. L.; Sadow, A. D. ACS Catal. 2011,
1996, 118, 8024−8033.
(30) Corey, E. J.; Koelliker, U.; Neuffer, J. J. Am. Chem. Soc. 1971, 93,
1489−1490.
1
, 1637−1642. (c) Manna, K.; Xu, S.; Sadow, A. D. Angew. Chem., Int.
(31) Fendrick, C. M.; Schertz, L. D.; Day, V. W.; Marks, T. J.
Organometallics 1988, 7, 1828−1838.
Ed. 2011, 50, 1865−1868. (d) Manna, K.; Everett, W. C.; Schoendorff,
G.; Ellern, A.; Windus, T. L.; Sadow, A. D. J. Am. Chem. Soc. 2013,
(32) Hong, S.; Tian, S.; Metz, M. V.; Marks, T. J. J. Am. Chem. Soc.
2003, 125, 14768−83.
1
(
6
(
35, 7235−7250.
5) Stubbert, B. D.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 6149−
167.
6) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J.
Organometallics 1999, 18, 2568−2570.
7) (a) Hangaly, N. K.; Petrov, A. R.; Rufanov, K. A.; Harms, K.;
Elfferding, M.; Sundermeyer, J. Organometallics 2011, 30, 4544−4554.
b) Otero, A.; Lara-Sanchez, A.; Najera, C.; Fernandez-Baeza, J.;
Marquez-Segovia, I.; Castro-Osma, J. A.; Martínez, J.; Sanchez-Barba,
L. F.; Rodríguez, A. M. Organometallics 2012, 31, 2244−2255.
8) Bertolasi, V.; Boaretto, R.; Chierotti, M. R.; Gobetto, R.; Sostero,
S. Dalton Trans. 2007, 5179−5189.
9) Rufanov, K. A.; Petrov, A. R.; Kotov, V. V.; Laquai, F.;
Sundermeyer, J. Eur. J. Inorg. Chem. 2005, 3805−3807.
10) (a) Otero, A.; Fernandez-Baeza, J.; Antinolo, A.; Tejeda, J.;
(33) Bender, C. F.; Widenhoefer, R. A. J. Am. Chem. Soc. 2005, 127,
1070−1071.
(34) Riegert, D.; Collin, J.; Meddour, A.; Schulz, E.; Trifonov, A. J.
Org. Chem. 2006, 71, 2514−2517.
(
(
́
́
́
́
́
(
(
(
Lara-Sanchez, A.; Sanchez-Barba, L.; Rodriguez, A. M.; Maestro, M. A.
J. Am. Chem. Soc. 2004, 126, 1330−1331. (b) Otero, A.; Fernandez-
Baeza, J.; Antinolo, A.; Tejeda, J.; Lara-Sanchez, A.; Sanchez-Barba, L.
F.; Sanchez-Molina, M.; Rodriguez, A. M.; Bo, C.; Urbano-Cuadrado,
M. Organometallics 2007, 26, 4310−4320.
(
11) Breslow, R.; Canary, J. W. J. Am. Chem. Soc. 1991, 113, 3950−
952.
12) (a) Gade, L. H.; Bellemin-Laponnaz, S. Chem. - Eur. J. 2008, 14,
142−4152. (b) Bellemin-Laponnaz, S.; Gade, L. H. Chem. Commun.
002, 1286−1287.
13) Liao, S.; Sun, X.-L.; Tang, Y. Acc. Chem. Res. 2014, 47, 2260−
272.
14) Lampland, N. L.; Zhu, J.; Hovey, M.; Jana, B.; Ellern, A.; Sadow,
A. D. Inorg. Chem. 2015, 54, 6938−6946.
15) Bauer, A.; Hilbig, H.; Hiller, W.; Hinterschwepfinger, E.; Ko
F. H.; Neumayer, M. Synthesis 2001, 778−782.
16) Werner, H.; Otto, H.; Kraus, H. J. J. Organomet. Chem. 1986,
15, C57−C60.
17) Pawlikowski, A. V.; Gray, T. S.; Schoendorff, G.; Baird, B.;
Ellern, A.; Windus, T. L.; Sadow, A. D. Inorg. Chim. Acta 2009, 362,
517−4525.
18) (a) Dunne, J. F.; Fulton, D. B.; Ellern, A.; Sadow, A. D. J. Am.
3
(
4
2
(
2
(
(
̈
hler,
(
3
(
4
(
Chem. Soc. 2010, 132, 17680−17683. (b) Mukherjee, D.; Ellern, A.;
Sadow, A. D. Chem. Sci. 2014, 5, 959−964. (c) Sibi, M. P.; Shay, J. J.;
Liu, M.; Jasperse, C. P. J. Am. Chem. Soc. 1998, 120, 6615−6616.
(
19) Westerhausen, M.; Makropoulos, N.; Wieneke, B.; Karaghiosoff,
K.; Noth, H.; Schwenk-Kircher, H.; Knizek, J.; Seifert, T. Eur. J. Inorg.
Chem. 1998, 965−971.
20) Garces, A.; Sanchez-Barba, L. F.; Alonso-Moreno, C.; Fajardo,
M.; Fernandez-Baeza, J.; Otero, A.; Lara-Sanchez, A.; Lopez-Solera, I.;
Rodríguez, A. M. Inorg. Chem. 2010, 49, 2859−2871.
̈
(
́
́
́
́
́
J
DOI: 10.1021/acs.organomet.5b00771
Organometallics XXXX, XXX, XXX−XXX