Palladacycles Based on 8-Aminoquinoline ... - ACS Publications

Oct 15, 2015 - Jatinder Singh, Mayukh Deb, and Anil J. Elias. Department of Chemistry, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110...
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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 palladacycles reacted with MeI and EtI in acetic acid, resulting in monoand 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.

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catalysis.9 The commercially available chiral cobalt oxazolinyl palladacycles (COP catalysts) prepared from this carboxylic acid and related oxazoline-based palladium catalysts have given 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 photovoltaic devices.12 Herein we report the synthesis of the first 8aminoquinoline 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 ferrocene-based carboxamides.

INTRODUCTION 8-Aminoquinoline, the basic structural unit of antimalarial drugs such as primaquine, tafenoquine, and pamaquin, has recently 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 arylcarboxamides 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(η4C4Ph4) has proved to be an excellent competitor to ferrocene carboxylic acid in the design of chiral ligands for asymmetric © XXXX American Chemical Society

Received: June 11, 2015

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DOI: 10.1021/acs.organomet.5b00504 Organometallics XXXX, XXX, XXX−XXX

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RESULTS AND DISCUSSION The acid chloride derivatives {η5-C5H4[C(O)Cl]}Co(η4C4Ph4) 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 αdialkylation 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

DOI: 10.1021/acs.organomet.5b00504 Organometallics XXXX, XXX, XXX−XXX

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Organometallics 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-aminoquinolinederived palladacycles with an organometallic sandwich compound also provide crucial mechanistic evidence for the C−H activation step of 8-aminoquinoline carboxamides.1,5,7

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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 8aminoquinoline 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 aminoquinoline moiety in their 1H 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 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

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).

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 C

DOI: 10.1021/acs.organomet.5b00504 Organometallics XXXX, XXX, XXX−XXX

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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 redcolored 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. 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, 67.44; H, 4.53; N, 7.86. IR (ν, cm−1): 3360, 1656. 1H 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. 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: C, 52.67; H, 3.42; N, 8.38. 1H 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. 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 C45H35O1N2Co: C, 79.63; H, 5.20; N, 4.13. 1H 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,

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 fivemembered 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 2,5disubstitution on the cyclopentadiene ring of the sandwich compounds. The dihedral angle between the cyclopentadiene and 8-aminoquinoline unit in 5 is 33.2(1)°. 1H and 13C NMR also support the identity of the 2,5-di-α-alkylated cobalt sandwich carboxamide.

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CONCLUSIONS We report the synthesis and single-crystal X-ray structural characterization of the first examples of 8-aminoquiolinederived 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 Cpderived 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.

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EXPERIMENTAL SECTION

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 according to literature procedures. Dimethylcarbonate, triphenylphosphine, oxalyl chloride (Spectrochem), 8-aminoquinoline, and palladium acetate (Alfa Aesar) were used as received. 1H 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 Protége 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 [η5-(N-Quinolin-8-yl)C5H4]Co(η4-C4Ph4), 1. Monocarboxylic 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. D

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Organometallics

Yield: 0.023 g, 20%. 1H 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 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 compounds 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. Nonhydrogen 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.

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. 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 C47H39O1N2Co: C, 79.87; H, 5.56; N, 3.96. 1H 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. Calcd for C45H35O1N2Co: C, 79.63; H, 5.20; N, 4.13. 1H 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). 13 C 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 C22H20O1N2Fe: C, 68.77; H, 5.25; N, 7.29. 1H 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.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00504. Experimental data and tables giving selected bond lengths and angles for compounds 1, 3, 4, and 5 (PDF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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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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REFERENCES

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DOI: 10.1021/acs.organomet.5b00504 Organometallics XXXX, XXX, XXX−XXX