Palladacycles Based on 8-Aminoquinoline Carboxamides of Cobalt and Iron Sandwich Compounds and a New Method to α-Alkylate Cp Rings of Metal Sandwich Carboxamides

Article abstract of DOI:10.1021/acs.organomet.5b00504

Reactions of {η⁵-C₅H₄[C(O)Cl]}Co(η⁴-C₄Ph₄) and {η⁵-C₅H₄[C(O)Cl]}Fe(η⁵-Cp) with 8-aminoquinoline resulted in cobalt and iron sandwich derived carboxamides. The reaction of these carboxamides with Pd(OAc)₂ in acetonitrile resulted in αC-H activation of the Cp rings of the sandwich compounds and formation of novel palladacycles 3 and 4, having both N-H and one α-C-H hydrogen atom of the Cp ring displaced and palladium forming a square planar complex with acetonitrile as the fourth ligand. These air-stable palladacycles reacted with MeI and EtI in acetic acid, resulting in mono- and 2,5-di-α-alkylated sandwich carboxamides, thereby providing a new method to realize Cp-multisubstituted sandwich compounds. Selectivity in α-substitution was observed in the presence of NaHCO₃. The cobalt sandwich carboxamide 1, the new palladacycles 3 and 4, and the 2,5-dimethylated cobalt sandwich carboxamide 5 have also been structurally characterized using single-crystal X-ray structural studies.

Full text of DOI:10.1021/acs.organomet.5b00504

Article
pubs.acs.org/Organometallics
Palladacycles Based on 8‑Aminoquinoline Carboxamides of Cobalt
and Iron Sandwich Compounds and a New Method to α‑Alkylate Cp
Rings of Metal Sandwich Carboxamides
Jatinder Singh, Mayukh Deb, and Anil J. Elias*
Department of Chemistry, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, India
S
* Supporting Information
ABSTRACT: Reactions of {η5-C5H4[C(O)Cl]}Co(η4-C4Ph4)
and {η5-C5H4[C(O)Cl]}Fe(η5-Cp) with 8-aminoquinoline
resulted in cobalt and iron sandwich derived carboxamides.
The reaction of these carboxamides with Pd(OAc)2 in
acetonitrile resulted in αC−H activation of the Cp rings of the
sandwich compounds and formation of novel palladacycles 3 and
4, having both N−H and one α-C−H hydrogen atom of the Cp
ring displaced and palladium forming a square planar complex
with acetonitrile as the fourth ligand. These air-stable pallada-
cycles reacted with MeI and EtI in acetic acid, resulting in mono-
and 2,5-di-α-alkylated sandwich carboxamides, thereby providing a new method to realize Cp-multisubstituted sandwich
compounds. Selectivity in α-substitution was observed in the presence of NaHCO3. The cobalt sandwich carboxamide 1, the new
palladacycles 3 and 4, and the 2,5-dimethylated cobalt sandwich carboxamide 5 have also been structurally characterized using
single-crystal X-ray structural studies.
catalysis.9 The commercially available chiral cobalt oxazolinyl
palladacycles (COP catalysts) prepared from this carboxylic
acid and related oxazoline-based palladium catalysts have given
INTRODUCTION
■
8-Aminoquinoline, the basic structural unit of antimalarial drugs
such as primaquine, tafenoquine, and pamaquin, has recently
high yields and enantiomeric excess in the Overman−Claisen
rearrangement of trichloroacetimidates.10,11 The electron donor
capability of (η5-RCp)Co(η4-C4Ph4) derivatives has also been
utilized for realizing new luminescent materials and photo-
voltaic devices.12 Herein we report the synthesis of the first 8-
aminoquinoline derivative of [η5-C5H4(COOH)]Co(η4-C4Ph4)
and its reaction with palladium acetate to realize a novel
palladacycle. An analogous ferrocene-derived palladacycle has
also been synthesized. Such palladacycles have been described
as intermediates in the reaction mechanisms proposed for C−H
activation involving arylcarboxamides.1 We have also carried
out reactions of these palladacycles exploring their utility and
selectivity for α-alkylation of metal sandwich carboxylic amides.
Multisubstitution of the Cp ring of sandwich compounds by
two different substituents is not straightforward, often resulting
in mixtures of 1,2- and 1,3-disubstituted isomers.11b,13
However, such multisubstituted sandwich compounds have
established applications as planar chiral ligands in asymmetric
catalysis8,14 and as mediators for lowering the working
electrode potential of blood glucose level monitors.15 This
study provides a new and easy approach to realize 2-alkyl- and
2,5-dialkylcyclopentadienyl-substituted CpCoC4Ph4 and ferro-
cene-based carboxamides.
shown excellent directing group ability especially for ortho C−
H activation of aryl and substituted aryl carboxylic acids.1 Ortho
substitution of the aryl rings of 8-aminoquinoline arylcarbox-
amides has been made possible by aryl C−H activation in the
presence of transition metal salts or complexes of Cu, Ni, Fe,
Pd, and Ru followed by reactions with alkyl and aryl halides,
diselenides, disulfides, etc.2−6 Palladium-catalyzed C−H
functionalization using this directing group has been found to
be highly useful for aryl−aryl, aryl−alkyl, and aryl−alkenyl
coupling reactions.5,7 Almost all of these reactions have been
carried out with Pd(II) salts in the reaction medium and
resulted in substitution at the ortho position of the aryl
carboxamides.
We were interested in extending these reactions to
organometallic sandwich carboxamides. Unlike simple aryls,
organometallic sandwich compounds provide many advantages
in such reactions. These include the possibility of isolating
stable metal complex intermediates that can be structurally
characterized and the prospect of realizing planar chiral
sandwich compounds when a Cp ring of the sandwich
compound is substituted with two different substituents. In
addition, Cp rings of metal sandwich compounds have been
found to show increased reactivity to electrophilic substitution
than simple aryl rings.8 The Cp-derived carboxylic acid of the
stable cobalt sandwich compound [η5-C5H4(COOH)]Co(η4-
C4Ph4) has proved to be an excellent competitor to ferrocene
carboxylic acid in the design of chiral ligands for asymmetric
Received: June 11, 2015
© XXXX American Chemical Society
A
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RESULTS AND DISCUSSION
■
The acid chloride derivatives {η5-C5H4[C(O)Cl]}Co(η4-
C4Ph4) and {η5-C5H4[C(O)Cl]}Fe(η5-Cp) were reacted with
8-aminoquinoline to realize the carboxamides 1 and 2.
Reactions of 8-aminoquinoline-derived amides of (η5-Cp)Co-
(η4-C4Ph4) and ferrocene with palladium acetate in a mixture of
acetic acid and acetonitrile at 90 °C resulted in the formation of
five-membered palladacycles 3 and 4, where both acetyl groups
on the metal were displaced and palladium formed a square
planar complex with acetonitrile as the fourth ligand (Scheme
1). In the absence of acetonitrile, the palladacycles were not
Scheme 1. Synthesis of Palladacycles 3 and 4
Figure 2. Molecular structure of compound 3. Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Pd(1)−C(3) 1.974(8); Pd(1)−N(1) 2.001(6); Pd(1)−N(2)
2.089(7); Pd(1)−N(3) 1.987(8); O(1)−C(1) 1.231(9); C(3)−
Pd(1)−N(3) 96.9(3); C(3)−Pd(1)−N(1) 81.9(3); N(3)−Pd(1)−
N(1) 178.7(3); C(3)−Pd(1)−N(2) 162.5(3); N(3)−Pd(1)−N(2)
99.9(3); N(1)−Pd(1)−N(2) 81.3(3).
found to be isolable. The palladacycles 3 and 4 were structurally
characterized using single-crystal X-ray diffraction analysis
(Figures 2 and 3). The palladacycles were found to be highly
stable to air and moisture and soluble in solvents such as
chloroform, dichloromethane, and tetrahydrofuran.
We were keen to observe the possibility of α-substitution on
the Cp ring of the sterically hindered sandwich compound 1
and also to see if selectivity in α-substitution is possible in such
Figure 3. Molecular structure of compound 4. Thermal ellipsoids are
drawn at the 30% probability level. Solvent molecules and hydrogen
atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Pd(1)−C(6) 1.970(6); Pd(1)−N(1) 1.983(4); Pd(1)−
N(2) 2.095(5); Pd(1)−N(3) 2.011(5); O(1)−C(1) 1.255(6); N(3)−
C(21) 1.115(7); C(21)−C(22) 1.456(8); C(6)−Pd(1)−N(1)
82.4(2); C(6)−Pd(1)−N(3) 95.6(2); N(1)−Pd(1)−N(3) 177.9(2);
C(6)−Pd(1)−N(2) 162.9(2); N(1)−Pd(1)−N(2) 80.5(2); N(3)−
Pd(1)−N(2) 101.4(2).
reactions. In this study, the palladacycles 3 and 4 were directly
reacted with methyl and ethyl iodides, and the products
obtained from the reactions were characterized using various
spectroscopic techniques.
Reactions of the palladacycles with methyl and ethyl iodides
in 1:4 molar ratio carried out in a mixture of dichloroethane
and acetic acid at 90 °C resulted exclusively in C(sp2)−H α-
dialkylation at the 2 and 5 positions of the Cp rings (Scheme
2). Similar to the observation on aryl carboxamides,7g attempts
to achieve monoselective C(sp2)−H α-alkylation of the Cp ring
was found to be unsuccessful by controlling the stoichiometry
alone, as a 1:1 molar ratio reaction of 3 with EtI was found to
give high yields of the Cp diethylated carboxamide 6 (23%)
Figure 1. Molecular structure of compound 1. Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
O(1)−C(34) 1.224(2); N(2)−C(34) 1.363(3); N(2)−C(35)
1.400(3); C(1)−C(2) 1.439(3); C(1)−C(34) 1.480(3); Co(1)−
C(2) 2.062(2); C(41)−N(1)−C(42) 117.0(2); C(34)−N(2)−C(35)
129.5(2); C(5)−C(1)−C(2) 107.2(2).
B
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Scheme 2. C(sp2)−H α-Dialkylation Reactions of the Cp
Ring
4 under analogous reaction conditions indicated the formation
of 2,5-diallyl carboxamide derivatives in 10% and 12% yields,
respectively. Also, reactions of an equimolar mixture of ethyl
iodide and methyl iodide with palladacycles 3 and 4 gave
predominantly the cyclopentadienyl 2,5-dimethylated products
5 (40%) and 8 (32%) along with traces of other products (see
Supporting Information).
With a view to explore if catalytic C−H activation can be
carried out on substrates 1 and 2, we have attempted direct
reactions of 1 and 2 with 4 mol of ethyl iodide along with 10
and 20 mol % of Pd(OAc)2 as catalyst in one-pot reactions.
With 10 mol % of Pd(OAc)2, only traces of products were
formed, which could not be isolated. We observed that the
reactions do occur with 20 mol % of Pd(OAc)2 albeit in poor
yields when AcOH/DCE mixture was used as the solvent
(Table S6). Maximum yields of 35% and 20% were obtained for
6 and 10, respectively, when NaHCO3 was used in place of
acetic acid in these direct reactions (Scheme 3). The
Scheme 3. Catalytic C−H Dialkylation Reactions of the Cp
Ring
along with the Cp monoethylated carboxamide 7 (11%). The
best yields and selectivity for the Cp dialkylated carboxamides
were obtained from 1:4 molar ratio reactions (Scheme 2), and
the 2,5-dimethylated carboxamide 5 has also been structurally
characterized (Figure 4).
structurally characterized examples of 8-aminoquinoline-
derived palladacycles with an organometallic sandwich
compound also provide crucial mechanistic evidence for the
C−H activation step of 8-aminoquinoline carboxamides.1,5,7
SPECTRAL AND STUCTURAL STUDIES
■
Molecular structures of compounds 1, 3, 4, and 5 are given in
Figures 1−4. Structural analysis of compound 1 showed that
the dihedral angle between the cyclopentadiene and 8-
aminoquinoline units is 24.1(6)° as compared to its ferrocene
analogue, where the corresponding dihedral angle is 4.5(5)°.16
Both compounds 1 and 2 showed a similar peak pattern of
Figure 4. Molecular structure of compound 5. Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
O(1)−C(1) 1.213(5); N(1)−C(1) 1.366(6); C(1)−C(2) 1.495(6);
C(3)−C(7) 1.497(7); C(1)−N(1)−C(37) 129.1(4); C(43)−N(2)−
C(44) 117.5; O(1)−C(1)−N(1) 122.9(4); C(2)−C(3)−C(7)
127.7(4).
1
aminoquinoline moiety in their H and 13C NMR spectra.
Structural analysis of the palladacycles 3 and 4 showed
palladium forming a pincer-type complex with square planar
geometry in which the acetonitrile ligand is trans to the
cyclopalladated nitrogen of the 8-aminoquinoline unit. Both
palladacycles crystallized in the triclinic crystal system and have
Monoselective C(sp2)−H α-alkylation of 3 and 4 was
achieved by controlling the stoichiometry (1:1 molar ratio)
along with the use of 1.5 mol of NaHCO3,5a whereby the
monoethylated compound 7 was obtained in 37% yield
(Scheme 2). Exploring further the scope of alkyl halides,
preliminary reactions of allyl bromide with palladacycles 3 and
the same space group, P1.
̅
The 8-aminoquinoline ring in the ferrocene-based palladaycle
4 is almost planar [0.9(2)°] to the substituted Cp ring, but in
the cobalt sandwich palladacycle 3, the angle between them is
10.3(2)°. The dihedral angle between the substituted phenyl
C
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8-Aminoquinoline (0.275 g, 1.91 mmol) was taken in a mixture of
triethylamine (5 mL) and CH2Cl2 (20 mL). A solution of the crude
acid chloride in 20 mL of CH2Cl2 was added to the reaction mixture.
The resulting solution was stirred at room temperature. After 16 h, the
solution was washed with water (30 mL) and brine (30 mL) using the
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 30% ethyl acetate/70% hexane mixture
as eluent. Evaporation of the solvents gave 1 as a yellow solid. Yield:
0.800g, 64%. Found: C, 79.29; H, 4.84; N, 4.36. Calcd for
C43H31O1N2Co: C, 79.38; H, 4.80; N, 4.31. IR (ν, cm−1): 1666 vs
(CO). 1H NMR (δ, 300 MHz, CDCl3): 4.85 (s, 2H), 5.34 (s, 2H),
6.99−7.44 (m, 23H), 8.06−8.08 (d, J = 6 Hz, 1H), 8.46−8.48 (d, J = 6
Hz, 1H), 8.69−8.70 (s, 1H), 9.74 (s, 1H). 13C NMR (δ, 75 MHz,
CDCl3): 76.47, 83.04, 85.81, 91.65, 116.15, 120.56, 121.30, 126.53,
127.40, 127.81, 127.98, 128.79, 134.67, 135.07, 136.09, 138.33, 147.72,
163.06. HRMS: calcd for C43H31O1N2CoH 651.1847, found 651.1858.
Synthesis of Palladacycle 3. Palladium acetate (0.033 g, 0.15
mmol) was added to a solution of 1 (0.100 g, 0.15 mmol) in acetic
acid (2 mL) and acetonitrile (2 mL), and the mixture was stirred at
room temperature for 5 min and then at 90 °C for 30 min. The
resulting precipitate was filtered, which on crystallization gave the red-
colored palladacycle 3. Yield: 0.100 g, 85%. Anal. Found: C, 67.80; H,
4.15; N, 5.30. Calcd for C45H32O1N3CoPd: C, 67.89; H, 4.05; N, 5.28.
IR (ν, cm−1): 2362, 2333, 1601. 1H NMR (δ, 300 MHz, CDCl3): 2.03
(s, 3H), 4.21 (s, 1H), 4.31 (s, 1H), 4.95 (s, 1H), 6.84−7.50 (m, 23H),
7.88−7.96 (m, 2H), 8.60−8.62 (d, J = 6 Hz, 1H). 13C NMR (δ, 75
MHz, CDCl3): 2.01, 75.13, 81.40, 83.77, 86.12, 95.19, 102.22, 116.97,
118.65, 119.11, 120.77, 125.51, 127.47, 128.66, 129.12, 129.77, 136.83,
144.54, 145.43, 148.45, 175.36. HRMS: calcd for C45H32O1N3CoPdH
796.0990, found 796.0967.
ring and the 8-aminoquinoline unit in the recent structurally
characterized benzamide palladacycles varies in the range of
0.0° to 11.5(2)°.5a
Palladacycle 4 shows intermolecular hydrogen bonding
between the complex and two acetic acid molecules that are
incorporated in the crystal lattice. Due to this hydrogen
bonding, the distance of the O(1)−C(1) bond in 4 is slightly
large [1.255(6) Å] when compared to 3, where the analogous
bond distance is 1.231(9) Å. Both palladacycles 3 and 4 showed
very similar 1H NMR peak splitting patterns for the AQ
(aminoquinoline) protons, confirming the similarity of the five-
membered palladacycles. In addition, in both these compounds
the absence of one C−H and the N−H proton in the 1H NMR
further supports palladium binding of the AQ and Cp moieties.
Molecular structure of compound 5 confirmed the 2,5-
disubstitution on the cyclopentadiene ring of the sandwich
compounds. The dihedral angle between the cyclopentadiene
1
and 8-aminoquinoline unit in 5 is 33.2(1)°. H and 13C NMR
also support the identity of the 2,5-di-α-alkylated cobalt
sandwich carboxamide.
CONCLUSIONS
■
We report the synthesis and single-crystal X-ray structural
characterization of the first examples of 8-aminoquioline-
derived palladacycles of {η5-C5H4[C(O)Cl]}Co(η4-C4Ph4)
and {η5-C5H4[C(O)Cl]}Fe(η5-Cp), which are in general
intermediates in carboxamide-induced aryl C−H activation
and ortho-alkylation using palladium salts. These novel air- and
moisture-stable palladacycles provide excellent scope for
realizing a wide range of Cp multisubstituted sandwich
compounds. Reactions of these palladacycles with methyl and
ethyl iodides resulted in mono- and 2,5-bis-dialkylated Cp-
derived metal sandwich carboxamides, thus providing an easy
approach to realize 2-alkyl and 2,5-dialkyl Cp-derived metal
sandwich carboxamides with good selectivity. Direct reactions
of the parent sandwich-based carboxamide with ethyl iodide
and a catalytic amount of Pd(OAc)2 were also found to yield
the cyclopentadienyl diethylated products albeit in lesser yields.
Synthesis of [η5-(N-Quinolin-8-yl)C5H4]Fe(η5-Cp), 2. A modified
procedure of the literature method (where no spectral data were
reported) was used for the synthesis of 2.16 Using the procedure
utilized for the synthesis of 1, compound 2 was prepared by starting
with ferrocene carboxylic acid (1.000 g, 4.35 mmol), and the amide
was obtained as an orange crystalline powder. Yield: 1.121 g, 72%.
Anal. Found: C, 67.40; H, 4.60; N, 7.93. Calcd for C20H16O1N2Fe: C,
1
67.44; H, 4.53; N, 7.86. IR (ν, cm−1): 3360, 1656. H NMR (δ, 300
MHz, CDCl3): 4.28 (s, 5H), 4.46 (s, 2H), 4.96 (s, 2H), 7.47−7.57 (m,
3H), 8.16−8.19 (m, 1H), 8.79−8.89 (m, 2H), 10.31 (s, 1H). 13C
NMR (δ, 75 MHz, CDCl3): 68.70, 70.11, 71.00, 116.31, 121.11,
121.74, 127.70, 128.21, 134.95, 136.49, 138.72, 148.38, 169.22.
HRMS: calcd for C20H16O1N2Fe 356.0612, found 356.0588.
EXPERIMENTAL SECTION
Synthesis of Palladacycle 4. Palladium acetate (0.062 g, 0.28
mmol) was added to a solution of 2 (0.100 g, 0.28 mmol) in acetic
acid (2 mL) and acetonitrile (2 mL), and the mixture was stirred at 90
°C for 30 min. The resulting precipitate was filtered, which on
crystallization gave the red-colored palladacycle 4. Yield: 0.125 g, 89%.
Anal. Found: C, 52.60; H, 3.50; N, 8.48. Calcd for C22H17O1N3FePd:
■
Synthesis and Reagents. 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 carbomethoxycyclopentadiene,17 ferrocene carboxylic acid,18
and tris(triphenylphosphine)cobalt chloride19 were prepared accord-
ing to literature procedures. Dimethylcarbonate, triphenylphosphine,
oxalyl chloride (Spectrochem), 8-aminoquinoline, and palladium
1
C, 52.67; H, 3.42; N, 8.38. H NMR (δ, 300 MHz, CDCl3): 2.31 (s,
3H), 3.98 (s, 1H), 4.20 (s, 5H), 4.46 (s, 1H), 4.46 (s, 1H), 4.65 (s,
1H), 7.04−7.11 (m, 2H), 7.39−7.52 (t, J = 9 Hz, 1H), 7.89−7.91 (d, J
= 6 Hz, 1H), 8.09 (s, 1H), 8.99−9.01(d, J = 6 Hz, 1H). 13C NMR (δ,
75 MHz, CDCl3): 3.67, 66.38, 66.94, 69.91, 71.29, 85.97, 88.80,
117.14, 119.17, 119.50, 120.94, 129.17, 130.07, 137.36, 144.56, 145.75,
148.74, 181.50. HRMS: calcd for C22H17O1N3FePd 500.9756, found
500.9752.
acetate (Alfa Aesar) were used as received. H and 13C{1H} spectra
1
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 Proteg
́
e 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.
Synthesis of Dimethylated Cobalt Sandwich Carboxamide 5.
Methyl iodide (0.034 g, 0.24 mmol) was added to a solution of 3
(0.050 g, 0.06 mmol) in dichloroethane (2 mL) and acetic acid (0.5
mL) in a glass vial, and the mixture was stirred at 90 °C for 20 h. The
reaction mixture was concentrated in a rotary evaporator and purified
using a silica gel column with 5% ethyl acetate/95% hexane mixture as
eluent. Evaporation of solvent gave 5 as yellow-colored solid. Yield:
0.027 g, 66%. Anal. Found: C, 79.58; H, 5.30; N, 4.02. Calcd for
Synthesis of [η5-(N-Quinolin-8-yl)C5H4]Co(η4-C4Ph4), 1. Mono-
carboxylic acid, [η5-(COOH)C5H4]Co(η4-C4Ph4) (1.000 g, 1.91
mmol), was dissolved in CH2Cl2 (20 mL). Oxalyl chloride (0.254 g,
2.00 mmol) and DMF (1 drop) were added sequentially. Upon
addition of DMF, gas evolution was observed. The resulting solution
was stirred at room temperature. After 3 h, 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.
1
C45H35O1N2Co: C, 79.63; H, 5.20; N, 4.13. H NMR (δ, 300 MHz,
CDCl3): 1.92 (s, 6H), 4.54 (s, 2H), 7.01−7.06 (m, 12H), 7.36−7.49
(m, 11H), 8.08−8.11 (d, J = 9 Hz, 1H), 8.63−8.65 (d, J = 6 Hz, 1H),
9.65 (s, 1H). 13C NMR (δ, 75 MHz, CDCl3): 12.52, 75.33, 75.91,
D
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1
83.19, 85.25, 89.00, 95.31, 116.47, 120.79, 121.26, 126.25, 127.50,
128.03, 128.85, 135.26, 136.11, 147.71, 165.45. HRMS: calcd for
C45H35O1N2CoH 679.2160, found 679.2119.
Yield: 0.023 g, 20%. H NMR (δ, 300 MHz, CDCl3): 1.24−1.34 (m,
6H), 2.62−2.85 (m, 4H), 4.23−4.41 (m, 6H), 4.85 (s, 1H), 7.48−7.60
(m, 3H), 8.20−8.23 (m, 1H), 8.82−8.89 (m, 2H), 10.44 (s, 1H). 13C
NMR (δ, 75 MHz, CDCl3): 15.34, 22.01, 22.16 67.56, 68.23, 68.91,
70.53, 70.83, 71.14, 75.55, 91.22, 92.66, 116.28, 121.04, 121.73,
127.72, 128.27, 135.19, 136.51, 138.85, 148.33, 170.18. HRMS: calcd
for C24H24O1N2FeNa 435.1136, found 435.1128.
Synthesis of Diethylated Cobalt Sandwich Carboxamide 6. Ethyl
iodide (0.037 g, 0.24 mmol) was added to a solution of 3 (0.050 g,
0.06 mmol) in dichloroethane (2 mL) and acetic acid (0.5 mL) in a
glass vial, and the mixture was stirred at 90 °C for 20 h. The reaction
mixture was concentrated in a rotary evaporator and purified using a
silica gel column with a 10% ethyl acetate/90% hexane mixture as
eluent. Evaporation of solvent gave 6 as a yellow-colored solid. Yield:
0.024 g, 57%. Anal. Found: C, 79.85; H, 5.60; N, 4.02. Calcd for
Synthesis of Diethylated Cobalt Sandwich Carboxamide 6 by
Direct C−H Activation of 1. Ethyl iodide (0.094 g, 0.60 mmol),
Pd(OAc)2 (0.007 g, 0.03 mmol), and NaHCO3 (0.100 g, 1.12 mmol)
were added to a solution of 1 (0.10 g, 0.15 mmol) in dichloroethane
(2 mL), and the mixture was stirred at 90 °C for 20 h in a sealed glass
vial. The reaction mixture was concentrated in a rotary evaporator and
purified using a silica gel column with a 10% ethyl acetate/90% hexane
mixture as eluent. Evaporation of solvent gave 6 as an orange-colored
solid. Yield: 0.037 g, 35%.
Crystal Structure Determination. Suitable crystals of com-
pounds 1, 3, 4, and 5 were obtained by slow evaporation of their
saturated solutions in suitable solvent mixtures. Single-crystal
diffraction studies were carried out on a Bruker SMART APEX
CCD diffractometer with a Mo Kα (λ = 0.710 73 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.20 All hydrogen atoms were
included in idealized positions, and a riding model was used. Non-
hydrogen atoms were refined with anisotropic displacement
parameters. Table S1 lists the data collection and structure solving
parameters for compounds 1, 3, 4, and 5 (see Supporting
Information). The highly distorted solvent molecules in the crystals
of 3 were omitted using the SQUEEZE algorithm. The resulting new
data set after this omission was generated, and the structure was
refined to convergence.21 Selected bond distances and angles for all
the compounds are given in the Supporting Information.
1
C47H39O1N2Co: C, 79.87; H, 5.56; N, 3.96. H NMR (δ, 300 MHz,
CDCl3): 0.95−0.98 (m, 6H), 2.02−2.14 (m, 2H), 2.54−2.66 (m, 2H),
4.66 (s, 2H), 7.02−7.09 (m, 12H), 7.37−7.45 (m, 11H), 8.10−8.15
(m 1H), 8.62−8.68 (m, 2H), 9.66 (s, 1H). 13C NMR (δ, 75 MHz,
CDCl3): 15.16, 20.01, 75.25, 77.37, 83.51, 87,71, 101.72, 116.69,
120.77, 121.23, 126.26, 127.55, 128.03, 128.83, 135.52, 136.11, 147.62,
165.41. HRMS: calcd for C47H39O1N2CoNa 729.2292, found
729.2287.
Synthesis of Monoethylated Cobalt Sandwich Carboxamide 7.
Ethyl iodide (0.009 g, 0.06 mmol) and NaHCO3 (0.007 g, 0.09 mmol)
were added to a solution of 3 (0.050 g, 0.06 mmol) in dichloroethane
(2 mL), and the mixture was stirred at 90 °C for 20 h in a glass vial.
The reaction mixture was concentrated in a rotary evaporator and
purified using a silica gel column with a 20% ethyl acetate/80% hexane
mixture as eluent. Evaporation of solvent gave 7 as a yellow-colored
solid. Yield: 0.015 g, 37%. Anal. Found: C, 79.60; H, 5.25; N, 4.15.
1
Calcd for C45H35O1N2Co: C, 79.63; H, 5.20; N, 4.13. H NMR (δ,
300 MHz, CDCl3): 0.94−0.96 (m, 3H), 2.16 (m, 1H), 2.68 (m, 1H),
4.70 (s, 1H), 4.76 (s, 1H), 5.18 (s, 1H), 7.00−7.48 (m, 22H), 8.09−
8.12 (m 1H), 8.45−8.47(m, 2H), 8.70−8.71 (m, 1H), 9.75 (s, 1H).
13C NMR (δ, 75 MHz, CDCl3): 15.31, 19.65, 75.86, 82.86, 83.46,
86.65, 88.12, 103.16, 116.31, 120.56, 121.34, 126.42, 127.52, 128.02,
128.85, 135.23, 136.18, 147.76, 164.24. C45H35O1N2CoNa: calcd
701.1979, found 701.1968.
Synthesis of Dimethylated Ferrocene Carboxamide 8. Methyl
iodide (0.056 g, 0.40 mmol) was added to a solution of 4 (0.050 g,
0.10 mmol) in dichloroethane (2 mL) and acetic acid (0.5 mL) in a
glass vial, and the mixture was stirred at 90 °C for 20 h. The reaction
mixture was concentrated in a rotary evaporator and purified using a
silica gel column with a 5% ethyl acetate/95% hexane mixture as
eluent. Evaporation of solvent gave 8 as an orange-colored solid. Yield:
0.020 g, 52%. Anal. Found: C, 68.75; H, 5.30; N, 7.35. Calcd for
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00504.
■
S
Experimental data and tables giving selected bond
lengths and angles for compounds 1, 3, 4, and 5
(PDF)
1
C22H20O1N2Fe: C, 68.77; H, 5.25; N, 7.29. H NMR (δ, 300 MHz,
CDCl3): 2.30 (s, 6H), 4.17 (s, 2H), 4.24 (s, 5H), 7.48 (m, 3H), 8.18−
8.21 (m, 1H), 8.86−8.88 (m, 2H), 10.72 (s, 1H). 13C NMR (δ, 75
MHz, CDCl3): 14.85, 69.91, 71.19, 79.51, 84.38, 116.30, 121.22,
121.75, 127.75, 128.28, 135.19, 136.51, 138.88, 148.37, 170.00.
Synthesis of Monoethylated Ferrocene Carboxamide 9. Ethyl
iodide (0.015g, 0.10 mmol) and NaHCO3 (0.012g, 0.15 mmol) were
added to a solution of 4 (0.050 g, 0.10 mmol) in dichloroethane (2
mL), and the mixture was stirred at 90 °C for 20 h in a glass vial. The
reaction mixture was concentrated in a rotary evaporator and purified
using a silica gel column with a 10% ethyl acetate/90% hexane mixture
as eluent. Evaporation of solvent gave 9 as an orange-colored solid.
Yield: 0.012 g, 31%. 1H NMR (δ, 300 MHz, CDCl3): 1.23−1.31 (t, J =
9 Hz, 3H), 2.71−2.82 (m, 1H), 2.87−2.99 (m, 1H), 4.25−4.38 (m,
7H), 4.83 (s, 1H), 7.45−7.59 (m, 3H), 8.16−8.20 (m, 1H), 8.76−
8.88(m, 2H), 10.41(s, 1H). 13C NMR (δ, 75 MHz, CDCl3): 15.37,
22.15, 68.22, 68.90, 70.52, 70.82, 71.13, 75.51, 92.64, 116.26, 121.03,
121.72, 127.70, 128.25, 135.17, 136.49, 138.81, 148.33, 170.17.
HRMS: calcd for C22H20O1N2FeNa 407.0823, found 407.0817.
Synthesis of Diethylated Ferrocene Carboxamide 10 by Direct
C−H Activation of 2. Ethyl iodide (0.174 g, 1.12 mmol), Pd(OAc)2
(0.012 g, 0.06 mmol), and NaHCO3 (0.188 g, 2.24 mmol) were added
to a solution of 2 (0.10 g, 0.28 mmol) in dichloroethane (2 mL), and
the mixture was stirred at 90 °C for 20 h in a sealed glass vial. The
reaction mixture was concentrated in a rotary evaporator and purified
using a silica gel column with a 5% ethyl acetate/95% hexane mixture
as eluent. Evaporation of solvent gave 10 as an orange-colored solid.
Crystallographic data (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: eliasanil@gmail.com.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank DST, India, and CSIR India, for financial
assistance in the form of research grants to A.J.E. [CSIR
01(2693)/12/EMR-II, DST EMR/2015/000285]. J.S. and
M.D. thank UGC for fellowships. We thank DST-FIST and
IITD for funding the single-crystal X-ray and HRMS facilities at
IIT Delhi.
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