New chiral palladacycles from an unprecedented cyclopalladation of cyclobutadiene-bound phenyl groups of cobalt sandwich compounds

Article abstract of DOI:10.1021/om500004n

Reaction of in situ generated {η⁵-[MeOC(O)]C ₅H₄}Co(PPh₃)₂ with methyl 3-phenyl-2-propynoate followed by diphenylacetylene in refluxing toluene resulted in the formation of the cobalt sandwich compound {η⁵- [MeOC(O)]C₅H₄}Co{η⁴-C₄Ph ₃[C(O)OMe]} (1), having methyl ester units on both the cyclopentadienyl (Cp) and cyclobutadiene (Cb) rings. Hydrolysis of the ester groups using aqueous KOH resulted in the dicarboxylic acid {η⁵- C₅H₄[C(O)OH]}Co{η⁴-C₄Ph ₃[C(O)OH]} (2). The dicarboxylic acid 2 was converted to the novel bis(oxazolinyl) derivative [η⁵-(4-iPr-2-Ox)C₅H ₄]Co[η⁴-C₄Ph₃(4-iPr-2-Ox)] (3; Ox = oxazolinyl) by its reaction with oxalyl chloride, (S)-2-amino-3-methyl-1- butanol, triethylamine, and mesyl chloride. Reaction of the chiral bis(oxazoline) ligand 3 with Pd(OAc)₂ in acetic acid at 60 C resulted in the formation of the novel chiral palladacycle 4, resulting from an unprecedented cyclopalladation involving one of the cyclobutadiene-bound phenyl groups. Palladacycle 4 has two trans-oriented oxazolinyl units and one of the phenyl groups of the cyclobutadiene ring bound to the palladium center along with an acetyl group. The reaction of KX (X = Br, I) with 4 in acetone-water medium yielded the bromo- and iodo-derived chiral palladacycles 5a,b. Compounds analogous to 3 having a chiral oxazolinyl unit on the Cb ring and a methyl or acetyl unit on the Cp ring, (η⁵-RC₅H ₄)Co(η⁴-C₄Ph₃R′) (R′ = oxazolinyl; R = acetyl (8a), methyl (8b)) were also prepared and characterized. Analogous reactions of 8a,b with 1.5 equiv of Pd(OAc)₂ in acetic acid at 60 C gave the chiral palladacycles 9a,b. Analysis of these compounds indicated that, in contrast to the monomeric chiral palladacycle obtained from the reaction of 3, compounds 9a,b are molecules with a unique linear tetraacetate-bridged tripalladium core having the two cyclopalladated cobalt sandwich units at the periphery. Structural analysis of 9a indicated that the molecule possesses the same type of seven-membered palladacycle observed in the cases of 4 and 5a,b.

Full text of DOI:10.1021/om500004n

Article
pubs.acs.org/Organometallics
New Chiral Palladacycles from an Unprecedented Cyclopalladation
of Cyclobutadiene-Bound Phenyl Groups of Cobalt Sandwich
Compounds
Jatinder Singh, Dheeraj Kumar, Nem Singh, and Anil J. Elias*
Department of Chemistry, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, India
S
* Supporting Information
ABSTRACT: Reaction of in situ generated {η5-[MeOC(O)]C5H4}Co(PPh3)2 with methyl 3-phenyl-2-propynoate followed by
diphenylacetylene in refluxing toluene resulted in the formation of the cobalt sandwich compound {η5-[MeOC(O)]C5H4}Co{η4-
C4Ph3[C(O)OMe]} (1), having methyl ester units on both the cyclopentadienyl (Cp) and cyclobutadiene (Cb) rings.
Hydrolysis of the ester groups using aqueous KOH resulted in the dicarboxylic acid {η5-C5H4[C(O)OH]}Co{η4-
C4Ph3[C(O)OH]} (2). The dicarboxylic acid 2 was converted to the novel bis(oxazolinyl) derivative [η5-(4-iPr-2-
Ox)C5H4]Co[η4-C4Ph3(4-iPr-2-Ox)] (3; Ox = oxazolinyl) by its reaction with oxalyl chloride, (S)-2-amino-3-methyl-1-butanol,
triethylamine, and mesyl chloride. Reaction of the chiral bis(oxazoline) ligand 3 with Pd(OAc)2 in acetic acid at 60 °C resulted in
the formation of the novel chiral palladacycle 4, resulting from an unprecedented cyclopalladation involving one of the
cyclobutadiene-bound phenyl groups. Palladacycle 4 has two trans-oriented oxazolinyl units and one of the phenyl groups of the
cyclobutadiene ring bound to the palladium center along with an acetyl group. The reaction of KX (X = Br, I) with 4 in acetone−
water medium yielded the bromo- and iodo-derived chiral palladacycles 5a,b. Compounds analogous to 3 having a chiral
oxazolinyl unit on the Cb ring and a methyl or acetyl unit on the Cp ring, (η5-RC5H4)Co(η4-C4Ph3R′) (R′ = oxazolinyl; R =
acetyl (8a), methyl (8b)) were also prepared and characterized. Analogous reactions of 8a,b with 1.5 equiv of Pd(OAc)2 in acetic
acid at 60 °C gave the chiral palladacycles 9a,b. Analysis of these compounds indicated that, in contrast to the monomeric chiral
palladacycle obtained from the reaction of 3, compounds 9a,b are molecules with a unique linear tetraacetate-bridged
tripalladium core having the two cyclopalladated cobalt sandwich units at the periphery. Structural analysis of 9a indicated that
the molecule possesses the same type of seven-membered palladacycle observed in the cases of 4 and 5a,b.
cyclopentadienyl group with one or more functional sub-
stituents.1a,2a,4 The phenyl groups on the cyclobutadiene ring
have remained passive to all such reactions carried out on the
cyclopentadienyl ring, except for an acylation performed on
{η5-[MeOC(O)]C5H4}Co(η4-C4Ph4) by Richards and co-
workers.5 The steric bulkiness of these cyclobutadiene-bound
phenyl groups has also been extended by Gandon and co-
workers: however, starting with a tetrakis(4-bromophenyl)
derivative of (η5-Cp)Co(η4-C4Ph4).6
INTRODUCTION
■
Among metal sandwich compounds, one of the best
competitors for ferrocene with regard to stability, ease of
synthesis, and reaction chemistry is the 18-electron cobalt
sandwich compound [(η5-Cp)Co(η4-C4Ph4)].1 While the
molecule as such is much less reactive than ferrocene, its
cyclopentadienyl derivatives, especially the carboxylate ester,
have shown excellent potential for developing novel chiral
organometallic compounds for asymmetric catalysis ably
assisted by the bulky tetraphenylcyclobutadiene moiety.2 The
electron donor capability of this sandwich compound has also
been utilized for realizing new luminescent materials and
photovoltaic devices.3 To date, the chemistry centered on this
molecule has been mostly focused on derivatizing the
Monomeric and dimeric palladacycles based on (η5-Cp)Co-
(η4-C4Ph4) and [(η5-Cp)Co(η4-C4Ph3)]2 are well documented,
Received: January 5, 2014
© XXXX American Chemical Society
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Scheme 1. Synthesis of the Diester Derivative 1 of the Cobalt Sandwich Compound
Scheme 2. Synthesis of Dicarboxylic Acid 2 and the Bis(oxazoline)-Derived Cobalt Sandwich Compound 3
Scheme 3. Synthesis of the Chiral Bis(oxazolinyl) Palladacycles 4 and 5a,b
with established utility in homogeneous asymmetric catalysis.7,8
However, all of these cobalt sandwich based palladacycles had
the chiral binding moiety positioned on the cyclopentadienyl
ring and the palladacycles were formed from a C−H activation
followed by cyclopalladation of cyclopentadienyl-bound pro-
tons. We introduce herein a new type of [(η5-RCp)Co(η4-
C4Ph3R′)] type bis(oxazoline) compound having chiral
oxazolinyl units on both the cyclobutadiene and cyclo-
pentadienyl rings of the cobalt sandwich compound. We report
the formation of a palladacycle resulting from the cyclo-
palladation of one of the cyclobutadiene-bound phenyl groups
of the cobalt sandwich compound. This kind of ortho
palladation, involving cyclobutadiene-bound phenyl groups, is
unprecedented in the chemistry of CpCoCb (Cb = cyclo-
butadiene) type sandwich compounds.9 We also report the
synthesis of mono(oxazoline)-derived CpCoCb type com-
pounds having the chiral oxazoline unit bound only to the
cyclobutadiene ring and show their differences in palladacycle
formation in comparison to the bis(oxazoline)-derived
sandwich compounds, resulting in unique linear tripalladium
complexes bridged by acetate groups and flanked by the
palladacycles at the periphery.
oxalyl chloride followed by (S)-2-amino-3-methyl-1-butanol,
triethylamine, and mesyl chloride, was converted to [η5-(4-iPr-
2-Ox)C5H4]Co[η4-C4Ph3(4-iPr-2-Ox)] (3; Ox = oxazolinyl)
(Scheme 2). Reaction of the bis(oxazoline) complex 3 with
palladium acetate in acetic acid at 60 °C resulted in the novel
palladacycle 4, where one of the phenyl groups bound to the
cyclobutadiene ring was found to get ortho-palladated, forming
a novel seven-membered palladacycle (Scheme 3).
The identity of the palladacycle 4 was conclusively proved by
single-crystal X-ray diffraction analysis (Figure 2) and NMR
1
spectral analysis. H and 13C NMR analysis of 4 in the crude
and in the crystalline form also revealed that 4 is a single
compound. Palladacycle 4 was found to be optically active with
35
a specific rotation, [α]D = +160°. The acetate group of the
palladacycle 4 was replaced by bromo and iodo groups by
reacting with KBr and KI in acetone−water medium to give
35
35
chiral palladacycles 5a ([α]D = +175°) and 5b ([α]D
=
+197°) (Scheme 3). The palladacycles 4 and 5a,b were found
to be soluble in solvents such as chloroform, dichloromethane,
ethyl acetate, and tetrahydrofuran and were also found to be
highly stable to air and moisture.
Since both the cyclopentadienyl- and cyclobutadiene-bound
oxazolinyl groups along with a terminal acetate ligand were
involved in the palladacycle formation of 4, we were keen to see
if an analogous aryl C−H activation and subsequent cyclo-
palladation of the phenyl group could be brought about in the
absence of the Cp-bound oxazolinyl group. A cyclopentadienyl-
unsubstituted analogue of 3 was prepared. However, its
reaction with Pd(OAc)2 resulted in a yellow solid which was
highly insoluble in common organic solvents. With a view to
increase solubility, we prepared the chiral oxazolines 8a,b,
RESULTS AND DISCUSSION
■
{η5-[MeOC(O)]C5H4}Co{η4-C4Ph3[C(O)OMe]} (1), the
diester derivative of the cobalt sandwich compound, was
prepared by the stepwise addition of methyl 3-phenyl-2-
propynoate and diphenylacetylene to in situ prepared {η5-
[MeOC(O)]C5H4}Co(PPh3)2 (Scheme 1). Compound 1 was
hydrolyzed to its dicarboxylic acid 2 by refluxing with aqueous
KOH in ethanol. The dicarboxylic acid, by its reaction with
B
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Scheme 4. Synthesis of Mono(oxazoline) Derivatives 8a,b Having the Chiral Oxazoline Unit Bound Only to the Cyclobutadiene
Ring
Scheme 5. Synthesis of Tetraacetate-Bridged Tripalladium Complexes 9a,b Having the Cyclopalladated Cobalt Sandwich Units
at the Periphery
having acetyl and methyl groups bound to the Cp ring,
respectively (Scheme 4).
workers on the importance of basal bulkiness of the sandwich
compounds for realizing enantioselectivity in catalysis involving
cobalt oxazolinyl palladacycles.11
In total contrast to the reaction of 3, reaction of 6a with
palladium acetate in acetic acid resulted in complex 9a, having
an unusual linear tetraacetate-bridged tripalladium core with
two cyclopalladated cobalt sandwich units flanking both ends
(Scheme 5). Irrespective of the stoichiometry of compound 8a
and palladium acetate used in the reaction, the same compound
was found to form, but the best yield (66%) resulted from a 2:3
molar ratio reaction. Due to the poor quality of the crystals, the
structure of 9a could not be solved. However, an exactly
identical reaction was shown by 8b, having a methyl-substituted
Cp ring, resulting in the tripalladium complex 9b in 69% yield,
whose crystal structure was determined (Figure 5). Interest-
ingly, similar to compound 4, the seven-membered palladacycle
formation resulting from phenyl cyclopalladation was found to
happen on both the cobalt sandwich units of this compound as
well. The tripalladium complexes 9a,b were both found to be
NMR Spectral Studies. Quite interestingly, both the
monomeric bis(oxazoline)-derived palladacycles (4 and 5a,b)
and the mono(oxazoline)-based palladacycles having a
1
tripalladium core (9a,b) showed very similar H NMR peak
splitting patterns for the aryl protons (see the Supporting
Information), confirming the similarity of the palladacycle ring
formation. In addition, a decrease of one unit was observed in
the integration of the phenyl groups of these palladacycles in
comparison to their parent oxazoline-derived sandwich
compounds. While all the phenyl protons of the bis(oxazoline)
3 appear in the range 7.05−7.71 ppm, spectra of the
palladacycles derived from 3 showed further splitting and a
noticeable upfield shift to 6.65−6.98 ppm for three of the aryl
protons. Quite similar splitting of the phenyl protons was
1
observed in the H NMR spectra of compounds 9a,b, which
35
optically active with specific rotations: [α]D = −30.6 and
indicated that the same cyclopalladation has happened in these
compounds as well. The palladium-bound carbon atoms in the
13C NMR spectra of 4, 5a,b, and 9a,b showed a downfield shift
to 138.20−147.03 ppm, in comparison to other phenyl carbon
atoms, which appeared in the range 122.97−130.06 ppm. Such
downfield shifts of palladium-bound carbon atoms of phenyl
groups have been reported for five-membered phenyl-bound
palladacycles.12 The 13C NMR for the carbonyl carbon of the
terminal acetate group bound to the palladium of palladacycle 4
appeared at 177.25 ppm, similar to the case for {[η5-(4-iPr-2-
Ox)Cp]Co(η4-C4Ph3)}2PdOAc, where it was observed at
176.62 ppm.8a The two carbonyl carbon peaks of the four
bridging acetate units were observed at 182.54−184.13 ppm in
compounds 9a,b. These values for bridging acetate groups are
akin to those reported for the ferrocene-derived tripalladium
complexes, where they were observed at 181.70−184.40 ppm.10
−26.5°, respectively. The structure of 9b shows similarity to a
tripalladium complex reported by Moyano and co-workers from
a reaction of oxazolinyl ferrocene and palladium acetate carried
out in benzene medium.10 In contrast to the seven-membered
palladacycle observed in this study, their tripalladium complex
showed a six-membered palladacycle having both palladium and
iron as part of the ring.
Recent reports from our group on the palladium complex of
1,3-cyclopentadienyl bis(oxazoline)-derived [(η5-Cp)Co(η4-
C4Ph4)] and chiral palladacycles derived from cyclobutadiene-
bridged dimeric cobalt sandwich compounds have shown
excellent enantioselectivity for the Overman−Claisen rear-
rangement of trichloroacetimidates.7b,8 However, analogous
catalysis attempted with the chiral palladacycles 4 and 5a,b did
not show any enantioselectivity, This observation supports the
theoretical and kinetic studies carried out by Overman and co-
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Figure 1. Molecular structure of the compound 2 showing the intermolecular hydrogen bonding.
X-ray Crystal Structures of Compounds 2, 4, 5b, 7a,
and 9b. Molecular structures of the compounds 4, 5b, and 9b
and crystal-packing diagrams of the compounds 2 and 7a are
given in Figures 1−5 (molecular structures of compounds 2
and 7a are given in the Supporting Information). Structural
analysis of the dicarboxylic acid 2 shows an interesting
selectivity in the intermolecular hydrogen bonding shown by
the two carboxylic acid groups. The carboxylic acid group of the
Cp ring is connected specifically to the carboxylic acid group of
the Cp ring belonging to another molecule. A similar selectivity
in binding is observed for the carboxylic acid group bound to
the Cb rings, resulting in a zigzag-chain-like arrangement of the
molecules with the tetraphenylcyclobutadiene units placed at
the periphery of this chain (Figure 1). Unlike the hydrogen
bonding observed in 2 which resulted in this polymeric
assembly, the hydrogen bonding observed in the reported
crystal structures of both ferrocene-1,1′-dicarboxylic acid and
ruthenocene-1,1′-dicarboxylic acid resulted only in dimeric
units.13 The crystal structure of the palladacycle 4 (Figure 2)
shows a square-planar palladium center to which the two
isopropyl-substituted trans-oriented oxazolinyl units are at-
tached at an angle of 162.9(2)°. The acetate group is found to
be located anti (177.6(2)°) to the cyclopalladated carbon of the
phenyl ring. In contrast, the reported crystal structure of a very
similar 1,1′-bis(oxazolinyl)ferrocene-based palladium dichloride
complex shows a cis orientation of the two oxazolinyl groups.14
More interestingly, no C−H activation and palladacycle
formation was observed for this ferrocene-derived complex. A
comparison of the crystal structures of the two bis(oxazoline)
palladacycles 4 and 5b (Figure 3) showed some minor
variations. The angle formed by the cyclopalladated carbon
with palladium and acetate (C(22)−Pd(1)−O(3)) was found
to be more linear (177.6(2)°) in comparison to the
corresponding angle (C(25)−Pd(1)−I(1)) of the iodo
complex (169.8(8)°).
Figure 2. Molecular structure of chiral palladacycle 4. Thermal
ellipsoids are drawn at the 30% probability level. Some hydrogen
atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Pd(1)−C(25), 1.987(5); Pd(1)−N(1), 2.043(5);
Pd(1)−N(2), 2.030(5); Pd(1)−O(3), 2.138(4); C(25)−Pd(1)−
N(2), 92.1(2); C(25)−Pd(1)−N(1), 85.5(2); N(2)−Pd(1)−N(1),
162.9(2); C(25)−Pd(1)−O(3), 177.6(2); N(2)−Pd(1)−O(3),
90.1(2); N(1)−Pd(1)−O(3), 92.7(2).
group of the cyclobutadiene ring is involved in hydrogen
bonding with the acetyl group of the cyclopentadiene ring and
vice versa. The crystal structure of the palladacycle 9b (Figure
5) shows a tripalladium core bridged by four acetate groups
having the phenyl cyclopalladated cobalt sandwich units at the
periphery. There are interesting structural features of the
tripalladium compound 9b that are noticeable. The three
palladium atoms show an almost linear arrangement with a
departure from linearity of 9.1°. The departure from linearity
observed in the only other reported example of a tetraacetate-
bridged tripalladium complex is 1.1°, which is a ferrocene-based
complex.10 The Pd−Pd bond distance of 2.980(1) Å observed
The hydrogen bonding observed in the case of 7a (Figure 4)
interestingly shows dimer formation, but instead of two
carboxylic acid groups forming a hydrogen bond, which is the
normal feature of carboxylic acid hydrogen bonds, the acid
D
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derivative of the cobalt sandwich compounds 8a,b with
Pd(OAc)2 led to linear tetraacetate-bridged tripalladium
compounds with cyclopalladated cobalt sandwich units at the
periphery. Formation of palladacycles 4, 5a,b, and 9a,b indicate
the first observation of C−H activation followed by ortho
palladation involving phenyl groups bound to the cyclo-
butadiene ring of CpCoCb type cobalt sandwich compounds.
To the best of our knowledge, compounds 4 and 5 are also the
first examples of transition-metal complexes based on the η5-
CpCo(η4-C4R4) scaffold where functional groups present on
both the Cp and Cb rings of the sandwich compound are
involved in coordination as a chelating bidentate ligand, thus
opening up a new class of cobalt sandwich based bidentate
ligands similar to 1,1′-bis(oxazolinyl)ferrocene and dppf.
EXPERIMENTAL SECTION
■
General Methods. All manipulations of the complexes were
carried out using standard Schlenk techniques under a nitrogen
atmosphere. All solvents were freshly distilled and used. The sodium
salt of carbomethoxycyclopentadiene15 and tris(triphenylphosphine)
cobalt chloride16 were prepared according to literature procedures.
Dimethyl carbonate, triphenylphosphine (Spectrochem), L-valinol,
mesyl chloride, and methyl phenylpropiolate (Alfa Aesar) were used as
received.
Figure 3. Molecular structure of chiral palladacycle 5b. Thermal
ellipsoids are drawn at the 30% probability level. Some hydrogen
atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Pd(1)−C(23), 2.003(3); Pd(1)−N(2), 2.016(2);
Pd(1)−N(1), 2.034(2); Pd(1)−I(1), 2.769(4); C(23)−Pd(1)−N(2),
88.7(1); C(23)−Pd(1)−N(1), 85.7(1); N(2)−Pd(1)−N(1),
164.0(9); C(23)−Pd(1)−I(1), 169.8(8); N(2)−Pd(1)−I(1),
90.1(7); N(1)−Pd−I(1), 98.1(7).
1
Instrumentation. H and 13C{1H} spectra were recorded on a
Bruker Spectrospin DPX-300 NMR spectrometer at 300 and 75.47
MHz, respectively. IR spectra in the range 4000−250 cm−1 were
́
recorded on a Nicolet Protege 460 FT-IR spectrometer as KBr pellets.
Elemental analyses were carried out on a Carlo Erba CHNSO 1108
elemental analyzer. Mass spectra were recorded on a Bruker Micro-
TOF QII quadrupole time-of-flight (Q-TOF) mass spectrometer.
Optical rotations of the chiral compounds were measured on an
Autopol V (Rudolph Research, Flanders, NJ) instrument. All of the
rotations were measured at 589 nm (sodium “D” line) using
dichloromethane as solvent, and readings were cross-checked by
taking measurements at two different concentrations.
X-ray Crystallography. Suitable crystals of compounds 2, 4, 5b,
7a, and 9b were obtained by slow evaporation of their saturated
solutions in ethyl acetate/hexane, dichloromethane/hexane, and
toluene/hexane mixtures. Single-crystal diffraction studies were carried
out on a Bruker SMART APEX CCD diffractometer with a Mo Kα (λ
= 0.71073 Å) sealed tube. All crystal structures were solved by direct
methods. The program SAINT (version 6.22) was used for integration
of the intensity of reflections and scaling. The program SADABS was
used for absorption correction. The crystal structures were solved and
refined using the SHELXTL (version 6.12) package.17 All hydrogen
in 9b is appreciably shorter than that observed in the reported
ferrocene-based tripalladium complex (3.046(5) Å). The two
sandwich units in 9b are not trans to each other, as the angle
between Cp rings of the two sandwich units is 67.3(4)°.
CONCLUSIONS
■
In conclusion, we report the first synthesis of cobalt sandwich
compounds of the type (η5-RCp)Co(η4-C4Ph3R′) having chiral
oxazolinyl groups on the cyclobutadiene ring alone as well on
both the cyclopentadienyl and cyclobutadiene rings. Reaction
of the bis(oxazoline)-derived sandwich compound with Pd-
(OAc)2 led to the formation of the novel monomeric chiral
palladacycle 4, resulting from an unprecedented cyclopallada-
tion of one of the phenyl groups bound to the cyclobutadiene
ring. In contrast, the reaction between the mono(oxazoline)
Figure 4. Molecular structure of compound 7a, showing the intermolecular hydrogen bonding.
E
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Figure 5. Molecular structure of 9b with thermal ellipsoids at the 30% probability level. Some hydrogen atoms have been omitted for clarity. Selected
bond lengths (Å) and angles (deg): Pd(1)−C(22), 1.967(1); Pd(1)−N(1), 2.012(8); Pd(1)−O(2), 2.179(8); Pd(1)−O(4), 2.054(8); Pd(1)−
Pd(2), 2.980(1); Pd(1)−Pd(2)−Pd(1), 170.9(6); C(22)−Pd(1)−N(1), 91.7(4); C(22)−Pd(1)−O(4), 87.6(4); N(1)−Pd(1)−O(4), 173.2(3);
C(22)−Pd(1)−O(2), 175.0(4); N(1)−Pd(1)−O(2), 91.1(3); O(4)−Pd(1)−O(2), 89.2(3); C(22)−Pd(1)−Pd(2), 111.4(3).
Table 1. X-ray Crystal Structure Parameters of Compounds 2, 4, 5b, 7a, and 9b
param
2
4
5b
7a
9b
formula
mol wt
C29H21CoO4
492.39
C42H43Cl2CoN2O2Pd
876.01
C46H46CoIN2O2Pd
951.08
C30H23CoO3
490.41
C76H74Co2N2O10Pd3
1612.43
orthorhombic
P21212
cryst syst
triclinic
monoclinic
P21
orthorhombic
P212121
13.194(2)
13.586(2)
12.268(3)
90
monoclinic
P21/n
space group
a (Å)
P1
̅
9.802(2)
10.506(2)
12.417(2)
81.318(3)
68.052(2)
78.993(3)
1159.9(3)
2
9.729(2)
14.665(3)
13.281(2)
90
8.033(2)
29.032(8)
21.731(6)
90
15.803(4)
28.301(7)
9.025(2)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
102.566(3)
90
90
92.532(6)
90
90
90
90
1849.5(6)
2
3991.5(8)
4
5063(2)
8
4036.4(2)
2
T/K
298(2)
150(2)
150(2)
298(2)
0.71073
1.287
150(2)
λ (Å)
0.71073
1.410
0.71073
1.573
0.71073
1.583
0.71073
1.327
ρcalcd (g/cm3)
μ (mm−1
)
0.774
1.125
1.680
0.706
1.109
goodness of fit
θ range (deg)
1.075
1.025
1.051
1.026
1.115
1.77−25.00
6119
1.57−24.99
17826
1.76−25.00
38299
1.17−25.0
48571
1.44−25.00
38964
total no. of rflns
no. of unique rflns
no. of obsd data (I > σ(I))
Rint
4059
6500
7031
8927
7117
3753
5814
6911
5673
5789
0.0272
0.0610
0.0312
0.1139
0.1042
a
R1, wR2 (I > 2σ(I))
0.0375, 0.1112
0.0399, 0.1132
0.0465, 0.0977
0.0535, 0.1004
0.00(2)
0.0201, 0.0483
0.0207, 0.0486
0.01(1)
0.0682, 0.1549
0.1145, 0.1712
0.0659, 0.1936
0.0804, 0.2021
0.04(5)
a
R1, wR2 (all data)
Flack param
a
R1 = ∑||Fo| − |Fc||/∑|Fo|; wR2 = ∑(|Fo|2 − |Fc|2)2]}1/2
.
atoms were included in idealized positions, and a riding model was
used. Non-hydrogen atoms were refined with anisotropic displacement
parameters. Table 1 gives the data collection and structure solution
parameters for compounds 2, 4, 5b, 7a, and 9b. The highly distorted
solvent molecules in the crystals of 7a and 9b were omitted using the
SQUEEZE algorithm. The resulting new data sets were generated, and
the structures were refined to convergence.18 Selected bond distances
and angles for all the compounds are given in the Supporting
Information.
{η5-[MeOC(O)]C5H4}Co{η4-[MeOC(O)]C4Ph3} (1). Co(PPh3)3Cl
(8.80 g, 10.00 mmol) was added to a solution of Na{[MeOC(O)]-
C5H4} (1.75 g, 12.00 mmol) in 10 mL of THF, and the mixture was
stirred for 5 min. To this was added methyl 3-phenyl-2-propynoate
(1.60 g, 10.00 mmol) in 100 mL of toluene, and the mixture was
stirred for 40 min. To the resultant solution was added
diphenylacetylene (1.78 g, 10.00 mmol), and the mixture was refluxed
for 5 h. The reaction mixture was cooled, the solvent was evaporated
off, and the residue was chromatographed on a neutral alumina
F
dx.doi.org/10.1021/om500004n | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
column. Triphenylphosphine was removed by eluting the column with
hexane. When the polarity was gradually increased (10% ethyl
acetate−90% hexane) {η5-[MeOC(O)]C5H4}Co(C4Ph4) was eluted
followed by a third fraction, which on evaporation of the solvent gave a
yellow crystalline powder characterized as {η5-[MeOC(O)]C5H4}Co-
{η4-[MeOC(O)]C4Ph3} (1). Yield: 3.64 g, 7.00 mmol, 70%. Mp: 98−
100 °C. Anal. Found: C, 71.50; H, 4.90. Calcd for C31H25O4Co: C,
71.54; H, 4.84. IR (ν, cm−1): 1708 vs (CO). 1H NMR (δ, 300 MHz,
CDCl3): 3.37 [3H, s, C(O)OCH3], 3.83 [3H, s, C(O)OCH3], 4.84
(2H, s, CpH), 5.27 (2H, s, CpH), 7.22−7.66 (15H, m, PhH); 13C
NMR (δ, 75 MHz, CDCl3): 51.35−51.53 [C(O)OCH3], 56.89, 79.66,
80.71 (C4Cb), 84.25, 86.17, 86.84 (CpC), 127.18−133.47 (PhC),
165.90, 171.85 C(O). HRMS: calcd for C31H25O4CoNa 543.0977,
found 543.0969.
Acetic acid was removed under vacuum, and the resulting red mixture
was dissolved first in 2 mL of dichloromethane followed by 5 mL of
hexane, upon which a brown precipitate was found to form. The clear
red solution was decanted to a conical flask, which upon standing for 2
h gave red crystals which were characterized as 4. Yield: 0.16 g, 0.20
mmol, 76%. Mp: 174−176 °C dec. [α]D35 = +160° (c 0.20 in CH2Cl2).
Anal. Found: C, 62.12; H, 5.19; N, 3.65. Calcd for C41H41O4N2Co: C,
1
62.25; H, 5.22; N, 3.54. IR (ν, cm−1): 1713, 1632. H NMR (δ, 300
3
MHz, CDCl3): 0.51−0.54 (3H, d, J = 6.6 Hz, CHCH3), 0.73−0.75
(3H, d, 3J = 6.6 Hz, CHCH3), 0.86−0.89 (3H, d, 3J = 6.6 Hz,
3
CHCH3), 0.97−1.00 (3H, d, J = 6.9 Hz, CHCH3), 1.97 [1H, bs,
CH(CH3)2], 2.02 [3H, bs, OC(O)CH3], 2.46 [1H, bs, CH(CH3)2],
4.07−4.12 (2H, m, CHCH2), 4.17−4.19 (4H, m, CHCH2), 4.61 (2H,
s, CpH), 5.04(2H, s, CpH), 6.65−7.47 (14H, m, PhH). 13C NMR (75
MHz, CDCl3): 15.21, 16.13, 17.77, 18.56 CHCH3, 25.13 (OC(O)
CH3), 29.93, 30.84 [CH(CH3)2], 58.47(C4Cb), 68.97, 69.36
(CHCH2), 69.36, 71.13 (CHCH2), 74.75, 79.66, 81. 50 (C4Cb),
82.64, 85.70, 86.70, 87.83, 89.30 (CpC), 123.07, 124.76, 126.11,
127.31, 127.61, 128.31, 128.46, 129.46, 134.15, 134.83, 135.64, 136.27,
143.59 (PhC), 165.04, 168.65 (CN), 177.25 (OCOCH3). HRMS:
calcd for C39H38CoN2O2Pd 731.1300, found 731.1319.
[η5-(COOH)C5H4]Co[η4-(COOH)C4Ph3] (2). Potassium hydroxide
(1.12 g, 20.00 mmol) dissolved in 8 mL of water was mixed with 1
(1.00 g, 1.92 mmol) in 100 mL of ethyl alcohol, and the mixture was
refluxed for 30 h. The reaction was quenched with 2 M HCl (50 mL).
After extraction with CH2Cl2 (100 mL), the organic phase was washed
with 100 mL of 2 M aqueous HCl, dried over anhydrous sodium
sulfate, filtered, and concentrated under reduced pressure to give a
yellow solid which was identified as 2. Yield: 0.90 g, 1.83 mmol, 96%.
Mp: 226−228 °C. Anal. Found: C, 70.60; H, 4.40. Calcd for
Pd(Br)[η5-(4-iPr-2-Ox)C5H4]Co[η4-(4-iPr-2-Ox)C4Ph2(C6H4)]
(5a). The palladacycle 4 (0.10 g, 0.13 mmol) was dissolved in 1 mL of
acetone, and to this solution was added aqueous potassium bromide;
the resulting mixture was stirred at room temperature overnight. The
resulting precipitate was dissolved in dichloromethane (20 mL), and
the solution was transferred to a separating funnel and washed with
water (2 × 20 mL). The organic layer was dried over Na2SO4, filtered,
and concentrated using a rotary evaporator. The orange powder
obtained was characterized as 5a. Yield: 0.09 g, 0.11 mmol, 86%. Mp:
1
C29H21O4Co: C, 70.74; H, 4.30. IR (ν, cm−1): 1669 vs (CO). H
NMR (δ, 300 MHz, d6-DMSO): 4.84 (2H, s, CpH), 5.16 (2H, s,
CpH), 7.20−7.59 (15H, m, PhH); 13C NMR (δ, 75 MHz, d6-DMSO):
58.47, 80.31, 81.24 (C4Cb), 85.00, 87.39, 88.72 (CpC), 128.20−
134.67 (PhC), 167.75, 173.17 C(O). HRMS: calcd for C29H21O4CoNa
515.0670, found 515.0645.
[η5-(4-iPr-2-Ox)C5H4]Co[η4-(4-iPr-2-Ox)C4Ph3] (3). Crude acid 2
(0.50 g, 1.02 mmol) was dissolved in CH2Cl2 (20 mL). Oxalyl chloride
(0.28 g, 2.24 mmol) and DMF (1 drop) were added sequentially.
Upon addition of the latter, gas evolution was observed. The resulting
solution was stirred at room temperature. After 60 min, the solution
was concentrated using a rotary evaporator. Excess oxalyl chloride and
byproducts were removed by repeated extraction of the residue with
CH2Cl2 (3 × 20 mL) to yield the acid chloride as a red-brown solid,
which was used directly in the next step.
35
1
178−179 °C dec. [α]D = +175° (c 0.20 in CH2Cl2). H NMR (δ,
3
300 MHz, CDCl3): 0.54−0.57 (3H, d, J = 6.9 Hz, CHCH3), 0.64−
3
3
0.67 (3H, d, J = 6.9 Hz, CHCH3), 0.87−0.89 (3H, d, J = 6.6 Hz,
CHCH3), 1.05−1.08 (3H, d, 3J = 6.9 Hz, CHCH3), 1.71−1.79 [1H, m,
CH(CH3)2], 2.28−2.57 [1H, m, CH(CH3)2], 3.87−4.00 (2H, m,
CHCH2), 4.07−4.55 (4H, m, CHCH2), 4.63 (2H, s, CpH), 5.96 (2H,
s, CpH), 6.66−8.01 (14H, m, PhH). 13C NMR (δ, 75 MHz, CDCl3):
15.99, 16.60, 17.46, 19.56 CHCH3, 29.51, 30.92 [CH(CH3)2], 69.31,
69.51 (CHCH2), 71.12, 71.47 (CHCH2), 58.31, 74.70, 79.61, 79.93
(C4Cb), 82.77, 85.82, 86.22, 87.26, 87.88 (CpC), 123.70−146.94
(PhC), 164.02, 167.97 (CN).
(S)-2-Amino-3-methyl-1-butanol (L-valinol; 0.21 g, 2.03 mmol) was
taken up in a mixture of triethylamine (4 mL) and CH2Cl2 (15 mL). A
solution of the crude acid chloride in 20 mL of CH2Cl2 was also
transferred to this flask. The resulting solution was stirred at room
temperature and, after 2 h, was cooled to 0 °C using an ice bath. Mesyl
chloride (0.46 g, 4.00 mmol) was added, and the resulting solution was
warmed to room temperature. After it was stirred for 16 h, the solution
was washed with 30 mL of saturated aqueous sodium bicarbonate and
30 mL of brine using a separating funnel. The organic layer was dried
over Na2SO4, filtered, and concentrated using a rotary evaporator. The
residue was purified using a silica gel column with a 20% ethyl
acetate−80% hexane mixture as eluent. Evaporation of the solvent gave
Pd(I)[η5-(4-iPr-2-Ox)C5H4]Co[η4-(4-iPr-2-Ox)C4Ph2(C6H4)] (5b).
The palladacycle 4 (0.11g, 0.14 mmol) was dissolved in 1 mL of
acetone, and to this solution was added aqueous potassium iodide; the
resulting mixture was stirred at room temperature overnight. The
resulting precipitate was dissolved in dichloromethane (20 mL),
transferred to a separating funnel, and washed with water (2 × 20 mL).
The organic layer was dried over Na2SO4, filtered, and concentrated
using a rotary evaporator. The concentrate was dissolved in a
minimum amount of toluene, and this solution upon standing at room
temperature gave red crystals characterized as 5b. Yield: 0.11 g, 0.13
mmol, 92% Mp: 183−185 °C dec. [α]D35 = +197° (c 0.20 in CH2Cl2).
35
3 as a yellow viscous semisolid. Yield: 0.43 g, 0.69 mmol, 67%. [α]D
= −51.1° (c 0.20 in CH2Cl2). Anal. Found: C, 74.60; H, 6.10; N, 4.64.
Calcd for C39H39O2N2Co: C, 74.75; H, 6.27; N, 4.47. IR (ν, cm−1):
1648 vs (CN). 1H NMR (δ, 300 MHz, CDCl3): 0.63−0.66 (3H, d,
3J = 6.6 Hz, CHCH3), 0.83−0.85(3H, d, 3J = 6.0 Hz, CHCH3), 0.89−
3
1H NMR (δ, 300 MHz, CDCl3): 0.61−0.63 (3H, d, J = 6.6 Hz,
CHCH3), 0.71−0.73 (3H, d, 3J = 6.6 Hz, CHCH3), 0.93−0.96 (3H, d,
3J = 6.6 Hz, CHCH3), 1.12−1.15 (3H, d, 3J = 6.9 Hz, CHCH3), 1.82−
1.84 [1H, m, CH(CH3)2], 2.60−2.65 [1H, m, CH(CH3)2], 3.98−4.04
(2H, m, CHCH2), 4.15−4.63 (4H, m, CHCH2), 4.87 (2H, s, CpH),
5.03 (2H, s, CpH), 6.73−8.07 (14H, m, PhH). 13C NMR (δ, 75 MHz,
CDCl3): 16.05, 16.67, 17.55, 19.65 CHCH3, 29.57, 30.99 [CH-
(CH3)2], 69.38, 69.56 (CHCH2), 71.18, 71.54 (CHCH2), 58.39, 74.74,
79.66, 80.00 (C4Cb), 82.87, 85.89, 86.33, 87.33, 87.96 (CpC), 123.79−
147.03 (PhC), 164.08, 168.02 (CN).
3
3
0.91(3H, d, J = 6.0 Hz, CHCH3), 0.96−0.98(3H, d, J = 6.0 Hz,
CHCH3), 1.46−1.52 [1H, m, CH(CH3)2], 1.84−1.86 [1H, m,
CH(CH3)2], 3.34−3.39 (1H, m, CHCH2), 3.45−3.66 (2H, m,
CHCH2), 3.81−3.89 (1H, m, CHCH2), 3.96−4.23 (2H, m,
CHCH2), 4.63 (1H, s, CpH), 4.72 (1H, s, CpH), 5.03 (1H, s,
CpH), 5.22 (1H, s, CpH), 7.05−7.71 (15H, m, PhH). 13C NMR (δ, 75
MHz, CDCl3): 18.13, 18.54, 18.76, 19.42, [CH(CH3)2], 32.64, 32.71
[CH(CH3)2], 58.27 (C4Cb), 69.28, 69.58 (CHCH2), 72.62, 73.00
(CHCH2), 78.03, 79.72 (C4Cb), 82.21, 83.72, 84.26, 85.42, 85.54
(CpC), 126.42−134.61 (PhC), 160.08, 164.02 (CN), HRMS: calcd
for C39H39O2N2CoH 627.2722, found 627.2408.
{η5-[MeC(O)]C5H4}Co{η4-[MeOC(O)]C4Ph3} (6a). Using the same
procedure utilized for the synthesis of 1, compound 6a was prepared
by starting with Na{[MeC(O)]C5H4} (1.56 g, 12.00 mmol). The
orange crystalline powder obtained was characterized as 6a. Yield: 3.24
g, 6.43 mmol, 64%. Mp: 88−91 °C. Anal. Found: C, 73.60; H, 4.65.
Calcd for C31H25O3Co: C, 73.81; H, 5.00. IR (ν, cm−1): 1703, 1670.
1H NMR (δ, 300 MHz, CDCl3): 1.79 [3H, s, C(O)CH3], 3.86 [3H, s,
C(O)OCH3] 4.89 (2H, s, CpH), 5.24 (2H, s, CpH), 7.03−7.66 (15H,
Pd(OAc)[η5-(4-iPr-2-Ox)C5H4]Co[η4-(4-iPr-2-Ox)C4Ph2(C6H4)]
(4). Palladium acetate (0.06 g, 0.27 mmol) was added to a solution of
3 (0.17 g, 0.27 mmol) in acetic acid (1.5 mL), and the mixture was
stirred at room temperature for 5 min and then at 60 °C for 20 min.
G
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Organometallics
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m, PhH). 13C NMR (δ, 75 MHz, CDCl3): 27.05 [C(O)CH3], 51.61
[C(O)OCH3], 57.31, 79.96, 81.00 (C4Cb), 83.45, 87.27, 93.92 (CpC),
127.33−133.41 (PhC), 171.85 (COOCH3), 196.74 (COCH3).
HRMS: calcd for C31H25O3CoNa 527.1033, found 527.1001.
(PhC), 164.98 (CN). HRMS: calcd for C34H32ONCoH 530.1894,
found 530.1875.
Synthesis of Palladacycle 9a. Palladium acetate (0.07 g, 0.31
mmol) was added to a solution of 8a (0.12 g, 0.21 mmol) in acetic acid
(1 mL). The red solution was stirred at room temperature and then
heated to 60 °C. An orange precipitate was found to form as the
reaction proceeded. The solution was cooled to room temperature,
and the precipitate was filtered and washed with glacial acetic acid. The
orange compound obtained was characterized as 9a. Yield: 0.12 g, 0.07
[η5-(Me)C5H4]Co{η4-[MeOC(O)]C4Ph3} (6b). Using the same
procedure utilized for the synthesis of 1, compound 6b was prepared
by starting with Na[(Me)C5H4] (1.30 g, 12.74 mmol). The orange
crystalline powder obtained was characterized as 6b. Yield: 2.63 g, 5.52
mmol, 55%. Mp: 115−117 °C. Anal. Found: C, 75.60; H, 5.40. Calcd
35
1
for C30H25O2Co: C, 75.63; H, 5.29. IR (ν, cm−1): 1710. H NMR (δ,
mmol, 66%. Mp: 180−183 °C dec. [α]D = −30.6° (c 0.20 in
CH2Cl2). Anal. Found: C, 56.05; H, 4.39; N, 1.69. Calcd for
300 MHz, CDCl3): 1.70 (3H, s, CH3), 4.49 (2H, s, CpH), 4.60 (2H, s,
CpH), 7.05−7.68 (15H, m, PhH). 13C NMR (δ, 75 MHz, CDCl3):
10.83 (CH3), 75.27, 78.53, 82.24 (C4Cb), 82.27, 82.85, 93.78 (CpC),
125.83−132.62 (PhC), 171.76 (COOCH3). HRMS: calcd for
C30H25O2CoNa 499.1084, found 499.1078.
C78H74Co2N2O12Pd3: C, 56.15; H, 4.47; N, 1.68. IR (ν, cm−1): 1630 vs
1
3
(CN), 1573. H NMR (300 MHz, CDCl3): δ 0.25−0.27 (3H, d, J
3
= 6.6 Hz, CHCH3), 0.75−0.77 (3H, d, J = 6.9 Hz, CHCH3), 1.87
[6H, s, C(O)CH3], 1.91 (12H, s, OC(O)CH3), 3.22 [2H, bs,
CH(CH3)2], 4.42−4.46 (2H, m, CHCH2), 4.61−4.65 (4H, m,
CHCH2), 5.54 (2H, s, CpH), 5.78 (2H, s, CpH), 6.19 (2H, s,
CpH), 6.28 (2H, s, CpH), 6.62−7.78 (28H, m, PhH). 13C NMR (δ, 75
MHz, CDCl3): 13.05, 17.46, 22.61, 22.67 [CH(CH3)2], 26.37
[Cp(COCH3)], 28.49 [CH(CH3)], 53.27 (C4Cb), 69.12 (CHCH2),
69.77 (CHCH2), 74.69, 78.92, 81.11 (C4Cb), 84.30, 84.89, 89.09,
90.40, 94.45 (CpC), 120.83, 122.15, 124.86, 125.15, 126.28, 126.74,
127.00, 127.46, 127.62, 128.04, 128.89 (PhC), 169.06 (CN), 182.66,
184.04 (COCH3), 197.48 [Cp(COCH3)].
{η5-[MeC(O)]C5H4}Co[η4-(COOH)C4Ph3] (7a). Compound 6a
(1.00 g, 1.98 mmol) was converted to the corresponding acid 7a by
adopting the procedure used in the synthesis of 2, which resulted in an
orange powder. Yield: 0.95 g, 1.94 mmol, 98%. Mp: 158−160 °C.
Anal. Found: C, 73.40; H, 4.70. Calcd for C30H23O3Co: C, 73.47; H,
4.73. IR (ν, cm−1): 1659. 1H NMR (δ, 300 MHz, CDCl3): 1.83 (3H, s,
COCH3), 4.98 (2H, s, CpH), 5.33 (2H, s, CpH), 7.28−7.71 (15H, m,
PhH). 13C NMR (δ, 75 MHz, CDCl3): 27.32 (COCH3) 80.85, 81.91
(C4Cb), 83.72, 87.62, 94.24 (CpC), 127.66−133.32 (PhC), 177.11
(COOH), 197.10 (COCH3). HRMS: calcd for C30H23O3CoNa
513.0877, found 513.0851.
Synthesis of Palladacycle 9b. Palladium acetate (0.14 g, 0.62
mmol) was added to a solution of 8b (0.22 g, 0.41 mmol) in acetic
acid (1 mL). The red solution was stirred at room temperature and
then heated to 60 °C. An orange precipitate was found to form as the
reaction proceeded. The solution was cooled to room temperature,
and the precipitate was filtered and washed with glacial acetic acid. The
orange compound obtained was characterized as 9b: Yield: 0.23 g, 0.14
[η5-(Me)C5H4]Co[η4-(COOH)C4Ph3] (7b). Compound 6b (1.00g,
2.10 mmol) was converted to the corresponding acid 7b by adopting
the procedure used in the synthesis of 2, which resulted in an orange
powder. Yield: 0.91 g, 1.96 mmol, 94%. Mp: 197−199 °C. Anal.
Found: C, 75.20; H, 4.93. Calcd for C29H23O2Co: C, 75.32; H, 5.01.
35
mmol, 69%. Mp: 185−188 °C dec. [α]D = −26.5° (c 0.20 in
1
IR (ν, cm−1): 1662. H NMR (δ, 300 MHz, CDCl3): 1.73 (3H, s,
CH2Cl2). Anal. Found: C, 56.45; H, 4.65; N, 1.89. Calcd for
CH3), 4.57 (2H, s, CpH), 4.69 (2H, s, CpH), 6.93−7.64 (15H, m,
PhH). 13C NMR (δ, 75 MHz, CDCl3): 11.22 (CH3) 77.36, 79.18,
83.51 (C4Cb), 82.90, 83.94, 95.67 (CpC), 126−134 (PhC), 173.29
(COOH). HRMS: calcd for C29H23O2CoNa 485.0928, found
485.0930.
C76H74Co2N2O10Pd3: C, 56.61; H, 4.63; N, 1.74. IR (ν, cm−1): 1625 vs
1
(CN), 1574. H NMR (δ, 300 MHz, CDCl3): 0.25−0.27 (3H, 3J =
6.6 Hz, CHCH3), 0.75−0.77 (3H, d, 3J = 6.9 Hz, CHCH3), 1.65 [6H,
s, Cp(CH3)], 1.89 (12H, s, OC(O)CH3), 3.30 [2H, bs, CH(CH3)2],
4.44 (2H, s, CHCH2), 4.59−4.65 (4H, m, CHCH2), 4.79 (2H, s,
CpH), 5.36 (2H, s, CpH), 5.55 (2H, s, CpH), 5.94 (2H, s, CpH),
6.62−7.86 (28H, m, PhH). 13C NMR (75 MHz, CDCl3): 11.58
Cp(CH3), 13.98, 18.51 [CH(CH3)2], 23.53, 23.76 COCH3, 29.50
[CH(CH3)], 53.18 (C4Cb), 68.95 (CHCH2), 69.77 (CHCH2), 71.80,
79.99 (C4Cb), 84.71, 85.26, 85.39, (CpC), 122.84, 125.17, 125.76,
126.19, 126.93, 127.76, 128.24, 128.30, 130.06, 135.74, 136.45, 138.21,
138.25 (PhC), 169.80 (CN), 182.54, 184.13 (COCH3).
{η5-[MeC(O)]C5H4}Co[η4-(4-iPr-2-Ox)C4Ph3] (8a). Using the
procedure adopted for the synthesis of the bis(oxazoline) 3,
compound 8a was prepared by starting with 7a (0.50 g, 1.02
mmol). Compound 8a was obtained as an orange viscous semisolid.
35
Yield: 0.42 g, 0.75 mmol, 74%. [α]D = −20.5° (c 0.20 in CH2Cl2).
Anal. Found: C, 75.20; H, 5.85; N, 2.60. Calcd for C35H321O2N1Co: C,
75.39; H, 5.78; N, 2.51. IR (ν, cm−1): 1626 vs (CN). H NMR (δ,
3
300 MHz, CDCl3): 0.92−0.95 (3H, d, J = 6.9 Hz, CHCH3), 1.03−
1.05(3H, d, 3J = 6.9 Hz, CHCH3), 1.65 [3H, s, C(O)CH3], 1.76−1.82
[1H, m, CH(CH3)2], 3.85−3.93 (1H, m, CHCH2), 4.01−4.06 (1H, m,
CHCH2), 4.29−4.35 (1H, m, CHCH2), 4.77 (2H, s, CpH), 5.11 (1H,
s, CpH), 5.16(1H, s, CpH), 7.08−7.66 (15H, m, PhH). 13C NMR (δ,
75 MHz, CDCl3): 18.93, 19.26 [CH(CH3)2], 27.15 (COCH3), 33.03
[CH(CH3)2], 58.95 (C4Cb), 70.22 (CHCH2), 73.48 (CHCH2), 78.05,
78.43, 80.46 (C4Cb), 83.22, 83.43, 87.15, 87.17, 93.90 (CpC), 127.11−
134.50 (PhC), 163.72 (CN), 197.16 (COCH3). HRMS: calcd for
C35H32O2NCoH 558.1843, found 558.1818.
ASSOCIATED CONTENT
■
S
* Supporting Information
Tables, figures, and CIF files giving selected bond lengths and
angles and crystallographic data for compounds 2, 4, 5b, 7a,
and 9b, X-ray crystal structures of compounds 2 and 7a, and 1H
and 13C NMR spectra of compounds 4 and 9a,b. This material
is available free of charge via the Internet at http://pubs.acs.org.
[η5-(Me)C5H4]Co[η4-(4-iPr-2-Ox)C4Ph3] (8b). Using the proce-
dure adopted for the synthesis of the bis(oxazoline) 3, compound 8b
was prepared by starting with 7b (0.50 g, 1.02 mmol). Compound 8b
was obtained as an orange viscous semisolid. Yield: 0.12 g, 0.23 mmol,
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for A.J.E.: eliasanil@gmail.com.
35
75%. [α]D = −18.6° (c 0.20 in CH2Cl2). Anal. Found: C, 77.10; H,
Notes
6.20; N, 2.70. Calcd for C34H32O1N1Co: C, 77.11; H, 6.09; N, 2.64. IR
1
(ν, cm−1): 1627 vs (CN). H NMR (δ, 300 MHz, CDCl3): 1.03−
The authors declare no competing financial interest.
3
3
1.05 (3H, d, J = 6.6 Hz, CHCH3), 1.12−1.14 (3H, d, J = 6.6 Hz,
CHCH3), 1.63 [3H, s, Cp(CH3)], 1.81−1.91 [1H, m, CH(CH3)2],
3.96−4.03 (1H, m, CHCH2), 4.09−4.14 (1H, m, CHCH2), 4.34−4.40
(1H, m, CHCH2), 4.53 (2H, s, CpH), 4.63 (2H, s, CpH), 7.21−7.79
(15H, m, PhH). 13C NMR (δ, 75 MHz, CDCl3): 11.55 [3H, s,
Cp(CH3)], 18.83, 19.16 [CH(CH3)2], 33.19 [CH(CH3)2], 57.13
(C4Cb), 69.93 (CHCH2), 73.09 (CHCH2), 75.87, 78.88, 83.05
(C4Cb), 82.41, 82.53, 83.42, 83.58, 95.36 (CpC), 126.23−135.86
ACKNOWLEDGMENTS
■
The authors thank the Department of Science and Technology
(DST) of India and CSIR India for financial assistance in the
form of research grants to A.J.E. (DST SR/SI/IC-43/2010 and
CSIR 01(2693)/12/EMR-II). J.S. thanks the UGC and D.K.
thanks the CSIR for research fellowships. We thank the DST-
H
dx.doi.org/10.1021/om500004n | Organometallics XXXX, XXX, XXX−XXX

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dx.doi.org/10.1021/om500004n | Organometallics XXXX, XXX, XXX−XXX