CERTIFICATE
Scheme 4.14: Upgradation of ethanol catalyzed by phosphine based pincer-ruthenium catalysts immobilized on solid supports
3.5 Experimental section
3.5.1 General methods and materials
All optimizations were carried out under purified Ar using a standard double manifold or a glove box. The solvents such as tetrahydrofuran (THF), hexane and toluene were dried via double distillation over Na/Benzophenone prior to the experiment.77-78 Ethanol was dried and distilled under argon condition according to the literature procedure.77-78 All other compounds including pryidine-2,6-dicarboxylic acid, 4-hydroxypryidine-2,6-dicarboxylic acid, o- penylenediamnine, [RuCl2(p-cymene)]2, Al2O3, SiO2, MgSiO3, DMSO-d6 and CDCl3 were purchased either from MERCK or Sigma-Aldrich and were used as such. The complexes (4.19a-d and 4.20a-d) were prepared according to the procedure reported in Chapter II and III.69, 71
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Kanu Das, Ph.D Thesis, IIT Guwahati 170
1H, 13C, 31P NMR spectra were recorded either on Bruker ASCEND 600 operating at 600 MHz for 1H, 150 MHz for 13C & 243 MHz for 31P or on Bruker AVANCE 400 operating at 400 MHz for 1H, 100 MHz for 13C & 162 MHz for 31P. The mass analysis was done using an Agilent Accurate-Mass Q-Toff ESI-MS 6520. Fourier Transform Infrared (FT-IR) were recorded on Perkin Elmer Spectrum Two FT-IR spectrometer at room temperature with the region 400- 4000 cm-1. All microwave reactions were performed using a CEM Discover microwave system unit (operating at 110 V, microwave irradiation of 2.45 GHz, maximum microwave output of 300 W) in a 10 mL microwave tube. GC analyses (FID detection) were performed on a Agilent 8860-GC instrument fitted with Agilent Front SSL inlet N2 HP-5 column (30 m length ´ 0.32 mm ID) using the following method: Agilent 8860-GC Detector, Oven temperature 60-300
C, Time at starting temp: 0 min, Final time = 10 min, Flow rate (carrier): 1 mL/min (N2), Split ration: 250, Inlet temperature: 250 C, Detector temperature: 300 C. H2 gas analysis (TCD detection) was performed on a Agilent 7820-GC instrument fitted with Agilent Front SSZ Inlet N2 HP-PLOT Q column (30 m length ´ 0.53 mm ID) using the following method: Agilent 7820-GC Detector, Oven temperature 40 C, Time at starting temp: 0 min, Hold time = 10 min, Flow rate (carrier): 1 mL/min (N2), Split ration: 50, Inlet temperature: 40 C, Detector temperature: 250 C. XPS analysis was carried out in ULVAC-PHI measurement in PHI 5000 Versa Prob III scanning XPS microprobe.
4.5.2 Synthesis of complexes of the type [(p-zR2NNN)RuCl(PPh3)2]Cl (4.21a; R = Bim, z
= H, 4.21b; R = Bim, z = OH, 4.21c and R = MeBim, z = H) and (p-zR2NNN)RuCl2(CO) (4.22a; R = Bim, z = H, 4.22b; R = Bim, z = OH, 4.22c and R = MeBim, z = H).
Synthesis of 2,6-bis(1H-benzimidazol-2-yl)pyridine (4.25a): To a two-necked round bottom flask (100 mL) containing pyridine-2,6- dicarboxylic acid (4.23a) (0.050 g, 0.6 mmol) and o- phenylenediamine (4.24) (0.260 g, 1.2 mmol), orthophosphoric acid (10 mL) was added. The reaction mixture was heated overnight at 150 C. A bluish green precipitate was obtained to which sodium bicarbonate solution (10 mL) was added. The residue was filtered and washed with water. The product was crystallized in methanol to obtain 0.135 g of an off-white solid in 74% yield. 1H NMR (400 MHz, DMSO-d6) δ = 12.99 (s, 2H, NH), 8.34 (d, J = 7.8 Hz, 2H, Ar), 8.17 (t, J = 9.0 Hz, 1H, Ar), 7.78 (d, J = 8.0 Hz, 2H, Ar), 7.73 (d, J = 7.9 Hz, 2H, Ar), 7.35 (t, J = 7.5 Hz, 2H, Ar), 7.28 (t, J = 7.6 Hz, 2H, Ar). 13C NMR (101 MHz, DMSO-d6) δ = 149.98, 147.23, 143.67, 138.70, 133.87, 123.24, 121.71, 120.88, 119.23, 111.27 (Ar). HRMS (ESI): m/z calculated for [C19H13N5+H]+; = 312.1243, Found = 312.1413.
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Kanu Das, Ph.D Thesis, IIT Guwahati 171 Synthesis of 2,6-bis(1H-benzo[d]imidazol-2-yl)pyridin-4-ol (4.25b): To a two-necked round bottom flask (100 mL) containing 4-Hydroxypyridine-2,6-dicarboxylic acid (4.23b) (0.2 g, 1.09 mmol) and o-phenylenediamine (4.24) (0.236 g, 2.18 mmol), orthophosphoric acid (20 mL) was added. The reaction mixture was heated overnight at 150
C. A bluish green precipitate was obtained to which sodium bicarbonate solution (10 mL) was added. The residue was filtered and washed with water (10 mL). The product was crystallized in methanol to obtain 0.195 g of an off-white solid in 55% yield. 1H NMR (600 MHz, DMSO- d6) δ = 13.10 (s, 2H, NH), 7.70-7.64 (m, Hz, 4H, Ar), 7.43 (d, J = 19.7 Hz, 2H, Ar), 7.22 (d, J
= 14.1 Hz, 4H, Ar). 13C NMR (151 MHz, DMSO-d6) δ = 169.74, 166.40, 166.05, 165.21, 150.64, 149.91, 149.23, 148.80, 122.94, 112.49, 111.16, 108.76 (Ar). HRMS (ESI): m/z calculated for [C19H13N5O+H]+; = 328.1198, Found = 328.1187
Synthesis of 2,6-bis(1-methyl-1H-benzo[d]imidazol-2- yl)pyridine (4.26): To a round bottom flask (50 mL) containing 4.25a (0.100 g, 0.32 mmol) and KOH (0.090, 1.60 mmol), acetone (10 mL) was added and stirred for 15 minutes. Subsequently, methyl iodide (0.2 mL, 3.2 mmol) was added in dropwise fashion. The reaction was stirred at room temperature for additional 3 hours. The reaction mixture was poured into water (50 mL) and the resulting white precipitate was filtered. The residue was dried and recrystallized in methanol (off white solid, 0.098 g, 90% yield). 1H NMR (400 MHz, DMSO-d6) δ = 8.40 (d, J
= 7.7 Hz, 2H, Ar), 8.22 (t, J = 7.6 Hz, 1H, Ar), 7.77 (d, J = 8.0 Hz, 2H, Ar), 7.70 (d, J = 8.0 Hz, 2H, Ar), 7.34 (dt, J = 24.4, 7.3 Hz, 4H, Ar), 4.27 (s, 6H, NCH3) 13C NMR (101 MHz, DMSO-d6) δ = 149.73, 149.30, 142.10, 138.54, 137.10, 125.05, 123.32, 122.51, 119.52, 110.92 (Ar), 32.56 (NCH3). HRMS (ESI): m/z calculated for [C21H17N5+H]+; = 340.1556, Found = 340.1585.
Synthesis of [(Bim2NNN)RuCl(PPh3)2]Cl (4.21a): To a two neck round bottom flask (25 mL) 2,6-bis(1H-benzimidazol-2- yl)pyridine (4.25a) (0.07 g, 0.224 mmol) and RuCl2(PPh3)3
(0.215 g, 0.224 mmol) were taken in dry THF (5 mL) under argon atmosphere. Then the reaction mixture was reflux for 12 h under argon. The color of the reaction mixture changed from brown to orange turbid. After that the solvent was evaporated under vacuum and the residue was washed with dry ether (3 x 5 mL) followed by hexane (3 x 5 mL). A yellowish reddish orange color solid (0.181 g) was obtained
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Kanu Das, Ph.D Thesis, IIT Guwahati 172 in 81% yield. 1H NMR (400 MHz, CDCl3) δ = 14.30 (s, 2H, NH), 8.49 (d, J = 8.1 Hz, 2H, Ar), 8.05 (br, 2H, Ar), 7.68 (dd, J = 12.0, 7.0 Hz, 1H, Ar), 7.55 (dd, J = 26.3, 5.3 Hz, 4H, Ar), 7.26 – 6.80 (m, 32H, Ar). 31P NMR (162 MHz, CDCl3) δ = 29.99 (minor, cis), 22.67(major, trans).
HRMS(SEI): Calculated for [C55H43ClN5P2Ru]+;= 972.1758, found 972.2608.
Synthesis of [(p-OHBim2NNN)RuCl](PPh3)2]Cl (4.21c): To a two-necked round bottom flask (25 mL) containing 2,6-bis(1H- benzo[d]imidazol-2-yl)pyridin-4-ol (4.25b) (0.093 g, 0.28 mmol) and RuCl2(PPh3)3 (0.270 g, 0.28 mmol), dry THF (5mL) was added under argon atmosphere. The reaction mixture was then refluxed for 12 h under argon. During the reaction, the color of the reaction mixture changed from brown to light pink. Subsequently, the solvent was evaporated under reduced pressure to obtain a dark green colored gel. The residue was washed with dry diethyl ether (3 x 5 mL) followed by hexane (3 x 5 mL). A green color solid (0.23 g) was obtained in 79% yield. 1H NMR (600 MHz, CDCl3) δ = 7.68 (dd, J = 12.0, 7.4 Hz, 4H, Ar), 7.55 (t, J = 7.4 Hz, 2H, Ar), 7.47 (dt, J = 8.0, 4.0 Hz, 4H, Ar), 7.38 – 6.17 (m, 24H, Ar). 31P NMR (243 MHz, CDCl3) δ = 29.81. HRMS (ESI): m/z calculated for [C57H45N6P2ORu]+; = 993.2205, Found = 993.2131.
Synthesis of [(MeBim2NNN)RuCl(PPh3)2]Cl (4.21b): To a two- necked round bottom flask (25 mL) containing 2,6-bis(1-methyl- 1H-benzo[d]imidazol-2-yl)pyridine (4.26) (0.07 g, 0.206 mmol) and RuCl2(PPh3)3 (0.215 g, 0.207 mmol), dry THF (5mL) was added under argon atmosphere. The reaction mixture was then refluxed for 12 h under argon. During the reaction, the color of the reaction mixture changed from brown to light pink. Subsequently, the solvent was evaporated under reduced pressure to obtain a dark pink colored gel. The residue was washed with dry diethyl ether (3 x 5 mL) followed by hexane (3 x 5 mL). A purple color solid (0.135 g) was obtained in 63% yield. 1H NMR (600 MHz, CDCl3) δ = 8.76 (bs, 2H, Ar), 8.40 (bs, 1H, Ar), 8.27 (bs, 1H, Ar), 8.00 (bs, 1H, Ar), 7.84 (bs, 1H, Ar), 7.67 (dd, J = 11.7, 7.8 Hz, 5H, Ar), 7.57 – 7.52 (m, 4H, Ar), 7.47 (t, J = 6.3 Hz, 5H, Ar), 7.39 (bs, 3H, Ar), 7.08 (d, J = 44.4 Hz, 15H, Ar), 6.84 (bs, 9H, Ar), 3.72 (bs, 6H, NCH3). 13C NMR (151 MHz, CDCl3) δ = 158.80, 151.70, 150.38, 141.93, 136.02, 133.27, 133.24, 133.21, 132.86, 132.19, 132.12, 132.05, 132.03, 131.03, 130.90, 130.78, 129.65, 128.63, 128.55, 128.24, 128.22, 125.75, 125.41, 124.50, 123.75, 122.58, 122.37, 122.16, 122.05, 119.70, 119.12, 110.42 (Ar), 29.75 (NCH3).31P NMR (243 MHz, CDCl3) δ =
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Kanu Das, Ph.D Thesis, IIT Guwahati 173 29.29(1P), 23.27 (1P). HRMS (ESI): m/z calculated for [C57H47ClN5P2Ru]+; = 1000.2039, Found = 1000.2236.
Synthesis of (Bim2NNN)RuCl2(CO) (4.22a): To a two-necked round bottom flask (25 mL) containing ligand 4.25a (0.025 g 0.08 mmol) and [RuCl2(p-Cymene)]2 (0.025 g, 0.04 mmol), dry THF (5 mL) was added under argon atmosphere. The reaction mixture was heated at 60 C for 2 h under argon atmosphere. Subsequently an atmosphere of CO was introduced and the reaction mixture was further heated for another 10 h. During the course of the reaction, the color of the reaction mixture changed from brown to straw color. Solvent evaporation yielded a dark brown solid which upon washing with dry diethyl ether (3 x 5 mL) followed by hexane (2 x 5 mL) and the solid was dried under vacuum. An orange yellowish solid 0.031 g of 4.22a in 74% yield. Low solubility posed challenges in NMR characterization.
IR (cm-1): = 3448 (br), 3053 (br), 2062, 1965 (s),1605, 1591, 1494, 1487, 1458, 1379, 1346, 1320, 1278, 1233, 1174, 1118, 1022, 996, 912, 849, 809, 761, 746, 674, 634, 596, 583, 572, 492, 434, 415. HRMS (ESI): m/z calculated for [4.22a−Cl]+ [C20H13ClN5ORu]+ = 475.9884, Found = 476.0372.
Synthesis of (MeBim2NNN)RuCl2(CO) (4.22b): To a two-necked round bottom flask (25 mL) containing ligand 4.25a (0.03 g 0.08 mmol) and [RuCl2(p-Cymene)]2 (0.025 g, 0.04 mmol), dry THF (5 mL) was added under argon atmosphere. The reaction mixture was heated at 60 C for 2 h under argon atmosphere. Subsequently an atmosphere of CO was introduced and the reaction mixture was further heated for another 10 h. During the course of the reaction, the color of the reaction mixture changed from brown to straw color. Solvent evaporation yielded a dark brown solid which upon washing with dry diethyl ether (3 x 5 mL) followed by hexane (2 x 5 mL) and the solid was dried under vacuum. A brown yellowish solid 0.035 g of 4.22b in 71% yield. Low solubility posed challenges in NMR characterization. IR (cm-1): = 1939, 1598, 1508, 1473, 1420, 1337, 1255, 1162, 1009, 866, 813, 801, 772, 758, 739, 602, 492, 435. HRMS (ESI): m/z calculated for [C22H17ClN5ORu]+; = 504.0197, Found = 504.0289; m/z calculated for [C24H20ClN6ORu]+; = 545.0463, Found = 545.0539.
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Kanu Das, Ph.D Thesis, IIT Guwahati 174 Synthesis of (p-OHBim2NNN)RuCl2(CO) (4.22c): To a two- necked round bottom flask (25 mL) containing 2,6-bis(1H- benzo[d]imidazol-2-yl)pyridin-4-ol (4.25b) (0.07g, 0.206 mmol) and RuCl2(PPh3)3 (0.200g, 0.207 mmol), dry THF (5mL) was added under argon atmosphere. The reaction mixture was then refluxed for 12 h under argon. During the reaction, the color of the reaction mixture changed from pink to brown color. Then the solvent was evaporated under reduced pressure to obtain a dark brown colored gel. The residue was washed with dry diethyl ether (3 x 5 mL) followed by hexane (3 x 5 mL). A yellowish-brown color solid (0.07g) was obtained in 86% yield. IR (cm-1): = 3049. 2068, 1958, 1611, 1450, 1409, 1372, 1257, 1228, 1096, 1022, 866, 800, 734, 619, 543, 449, 422. HRMS (ESI): m/z calculated for [C20H13N5ClO2Ru]+; = 491.9833, Found = 491.9790 4.5.3 General procedure for Guerbet reaction under thermal condition. A 5 mL Schlenk flask was charged with 4.22a (1.8 mg, 4.28 μmol), ethanol (0.5 mL, 8.56 mmol) and NaOEt (58 mg, 0.86 mmol). The volume was made up to 0.7 mL by using toluene which is used as an internal standard. The vessel was sealed and the reaction mixture was heated at 140 °C for 72 h. At regular intervals, an aliquot was taken out and the products were analyzed by GC.
4.5.4 General procedure for the Guerbet reaction under microwave. A 10 mL microwave vial was charged with NaOEt (10 mol %) (0.116 g, 1.71 mmol) and 4.22a (0.0013 g, 2.5 mol) inside the glove box. This was followed by addition of dry ethanol (1 mL, 17.12 mmol) and dry toluene (50 L) as an internal standard. The reaction mixture was heated at 110 C under microwave conditions at an operating power of 75 W. At regular intervals about 20 L of the sample was collected and analyzed by GC. The product was analyzed by GC analysis.
4.5.5 General synthesis procedure for heterogenization. A 10 mL Schlenk flask was charged with solid support (Al2O3, SiO2 and MgSiO3) (300 mg) and the catalyst (15 mg, 5%
wt./wt.) inside the glovebox. Then KOH (4 mg) was introduced followed by addition of dry toluene (5 mL). The reaction mixture was then stirred for two days under argon. The immobilization of the complex onto the solid was confirmed by its coloration and the concomitant decoloration of the solution. The excess solvent was decanted and the solid was washed by toluene (5mL). The solid was then dried under vacuum prior to its use in catalysis.
4.5.6 Computational details
The geometries of all the considered complexes were fully optimized using the DFT (PBEPBE)79 method on the Gaussian-16 program package.80 The LANL2DZ81-83 and 6- TH-3049_166122006
Kanu Das, Ph.D Thesis, IIT Guwahati 175 311G(d,p) basis set were used respectively for the metal (Ru) and non-metal atoms. Genecp (gen keyword with the effective core potential) was included to define the basis set. Method and basis set was selected on the basis of previous reports on pincer complexes.68-69, 73 Frequency calculations characterize the obtained stationary points as minima structures or transition states based on the number of imaginary frequencies. Single point calculations were performed to calculate the relative free energy values at 110 C.
Table 4.15. Crystallographic data of complex [(Bim2NNN)RuCl(PPh3)2]PF6 (4.21a)
Name [(Bim2NNN)RuCl(PPh3)2]PF6 (4.21a)
CCDC 2009680
Empirical formula C55H43ClF6N5P3Ru
Formula weight 1117.37
Crystal size (mm3) 0.32 x 0.28 x 0.24
Crystal system monoclinic
Space group P21/n
a (Å) 9.9974(5)
b (Å) 38.806(4)
c (Å) 13.9459(7)
(deg) 90.00
(deg) 92.722(5)
(deg) 90.00
V (Å3) 5404.4(7)
Z 4
calc (g cm-3) 1.373
(M0 K) (mm-1) 0.494
F (000) 2272.0
T(K) 296
Range of indices (h; k; l) -11, 11; -39, 46; -16, 16 Number of reflection collected 20714
Unique reflection 8995
Completeness to 2 99.9
Rint 0.0848
Data / restraints / parameters 9501/448/704
goodness-of-fit 1.148
R1[I 2 (I)] 0.1203
wR2[I 2 (I)] 0.2244
R1 (all data) 0.1516
wR2 (all data) 0.2418
r (max, min) e Å-3 0.93/-2.14
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Kanu Das, Ph.D Thesis, IIT Guwahati 176 Table 4.16. Selected Bond lengths (Å) and angles () around metal center in [(Bim2NNN)RuCl(PPh3)2](PF6) (4.21a)
[(Bim2NNN)RuCl(PPh3)2]PF6 (4.21a)
Ru1−N1 2.089 (7) Ru1−P1 2.418 (3)
Ru1−N3 2.010 (8) Ru1−P2 2.417 (3)
Ru1−N5 2.092 (8) Ru1−Cl1 2.459 (2)
N1−Ru1−N3 79.2 (3) N3−Ru1−Cl1 174.1 (2)
N1−Ru1−N5 157.7 (3) N5−Ru1−P1 87.6 (2)
N1−Ru1−P1 89.1 (2) N5−Ru1−P2 90.2 (2)
N1−Ru1−P2 93.1 (2) N5−Ru1−Cl1 105.2 (2)
N1−Ru1−Cl1 97.1 (2) Cl1−Ru1−P1 94.44 (9)
N3−Ru1−N5 78.8 (3) Cl1−Ru1−P2 85.84 (9)
N3−Ru1−P1 90.0 (2) P1−Ru1−P2 177.79 (9)
N3−Ru1−P2 89.8 (2)
Supporting information (containing NMR spectra of various compound, IR, HRMS, EDX, Kinetics data and Cartesian coordinates of the computed complexes) for chapter IV is available as appendix III and can be found at
https://drive.google.com/file/d/1X7JRlSmfIlof5NVGMfEf2g-zNxTkNJsc/view?usp=sharing