The reaction between Co(II)ambch 154 and r-butyl-phenol (molar ratio 1 : 3.6) in CDCI3
was followed by ^H-NMR. Experiments were run after 30 min, 45 min, 1 h and 2.5 h. Broad signals appeared in the sample after 30 min, but after 1 h the compound seemed to be diamagnetic. After 2.5 h the product (red-brown) precipitated at the bottom o f the tube and the solution presented NMR signals only for unreacted 4- tert-butyl-phenol.
The aromatic protons overlap forming multiplets between 8 . 8 and 6.2 ppm, while two
singlets at 5.91 and 5.39 ppm could be distinguished. These two singlets might indicate the presence o f quinones in the system, but the complexity aromatic region prevented full interpretation. However, they are present in low amount (less than 10 %) as resulted from integration o f the corresponding tert-butyl-proton signals.
N M R exp erim en t 2
NMR experiments were run after 30 min, 45 min and 3 h on a red-brown solution obtained by mixing Co(ambch) 154 and r-butyl-phenol (molar ratio 1 : 1) in CDCI3.
Broad signals appear in the sample even after Ih and the sample proved hard to shim. Compared with the previous ^H-NMR experiments, a new peak at 3.54 ppm appeared in the spectra which indicated a side reaction that occurred in CDCI3. This reaction seemed
rather fast in the conditions employed. Signals in the aromatic region are broad and they overlap, making the NMR spectra not very informative. However, in the region corresponding to the tert-butyl protons only one singlet (at ô 1.1) could be distinguished
apart from that o f the f-butyl-phenol (ô 1.35) which suggested that the reaction led mainly to one product. After 3 h the solvent was evaporated and the IR o f the sample was obtained. The sample was a mixture o f Co(ambch), r-butyl-phenol and Co(ambch)(0 -C6H4-4-Bu^) complex.
IR (KBr, cm"^): 3443 br, s, 3042 w, 2936 w, 2858 w, 1603 vs, 1582 m, 1539 s, 1443 s, 1381 m, 1346 m, 1306 w, 1238 w, 1190 m, 1155 m, 1126 w, 1022 w, 912 w, 746 s, 694 w, 571 w, 457 w.
5.9.5.1 Oxidation of Co(ambch) in benzene N = = N :ca 154 ,N=' '=N, Bu' 158
To a solution o f tert-butyl-phenol (0.095 g, 0.6 mmol) in benzene (22 mL) was added Co(ambch) (0.08 g, 0.2 mmol) under stirring. The solid dissolves quickly and the solution changes its colour from bright red to dark-brown red in about 5 min. The mixture was stirred at room temperature for 1 h, then it was filtered to give a dark filtrate. This was concentrated and addition o f diethyl ether to it induced precipitation o f a dark-black precipitate o f Co(ambch)(0-C6H4-4-Bu^)(158, 83 % yield).
The precipitate was washed several times with diethyl ether and analyzed by IR and EA, while the brown ethereal washings were analyzed by IR and NMR. The brown solution contained mainly unreacted r-butyl-phenol according to ^H-NMR and IR, additionally the IR spectrum presented bands which might be assigned to a substituted benzoquinone.
IR (brown sample, KBr, cm”*): 3435 br, vs, 2963 s, 2905 w, 2868 w, 1650 m(*), 1614 s, 1599 m(*), 1514 vs, 1447 w, 1385 m, 1362 w, 1244 s, 1182 m, 1113 w, 829 s, 816 w, 550 m, 478 w (main component - tert-butyl-phenol; * band assigned to a quinone).
IR (dark-black precipitate, KBr, cm”*): 3441 br, vs, 2947 m, 2858 w, 1609 vs, 1535 w, 1514 w, 1493 s, 1445 s, 1385 s, 1362 w, 1344 w, 1277 m, 1261 m, 1240 w, 1175 w, 1153 m, 1124 m, 1020 w, 912 w, 833 w, 746 s, 567 w, 552 w.
Elemental analysis calculated for: C3oH3 5N4 0Co(CioHnO): C, 70.98; H, 7.29; N, 8.28.
5.9.5.2 Reaction of Co(ambch) with 2,4-di-t-butyI-phenoi
This reaction was performed in a similar manner as described for 4-^-butyl-phenol. The solution changed more slowly the colour from red to brown. After 1 b it was filtered to give a red precipitate containing mainly unreacted Co(ambcb) and a brown solution. Bands characteristic o f quinones indicated their presence in small amounts in the precipitate, while in solution these bands were more intense.
IR (precipitate, KBr, cm"^): 3038 w, 2936 m, 2861 w, 1654 w(*), 1603 vs, 1580 s, 1560 w, 1541 vs, 1509 w, 1476 w, 1450 s, 1440 vs, 1400 m, 1381 m, 1348 s (*), 1340 m, 1306 m, 1238 m, 1217 w, 1190 m, 1155 m, 1124 w, 1022 w, 910 w, 825 w (*), 748 s, 737 s, 694 m (main component - Co(II)(ambch), * band assigned to a quinone)
IR (solution, KBr, cm"*): 2954 vs, 2906 s, 2866 s, 1654 m(*), 1604 s, 1590 (sh) s(*), 1577 s, 1571 m, 1561 s, 1540 m, 1534 m, 1528 m, 1524 m, 1520 m, 1509 s, 1475 s, 1458 s, 1447 s, 1439 s, 1408 s, 1389 s, 1361 s, 1306 m, 1278 s, 1255 s, 1232 s, 1201 s, 1176 m, 1155 m, 1122 w, 1088 w, 1023 w, 824 w(*), 749 m, 738 m ( contains 2,4-di-^- butyl-pbenol; * band assigned to a quinone)
5.9.5.3 Oxidation of Co(ambch) in chloroform
N=' '=N , :co: ,N = = N 'Co' 01 CHCI3 162
Upon stirring Co(ambcb) at room temperature in CHCI3, the system changed colour
from red to brown and a fine homogeneous suspension was formed within 5 min. This was stirred overnight and the following day, evaporation o f the solvent under vacuum led to a black-grey residue that was washed several times with petroleum spirit and analyzed by IR. The attempt to run an NMR experiment was not successful, due to the paramagnetism o f the compound.
IR (KBr, cm"*): 1602.7 vs, 1570 m, 1543 m, 1440.7 s, 1384.8 vs, 1355.9 m, 1325 w, 1193.9 m, 1153.4 s, 1124.4 s, 1024 m, 916.1 w, 758 s, 619 w
Elemental analysis calculated for: C20H22N4CIC0 • CH2CI2: C, 50.66; H, 4.82; N, 11.25.
Found: C, 52.99; H, 5.11; N, 11.20.
S.9.5.4 Oxidation of Co(ambch) in 2-butanoI
Co(ambch) (0.022 g, 0.06 mmol) was stirred at room temperature in 2-butanol (7.5 mL). After 30 min DCM and H2O were added to the system, but even so the solution
maintained its initial red colour. Therefore, the mixture was left under stirring at 50 °C overnight. The following day, unreacted Co(ambch) complex was separated by filtration from the dark black solution which was concentrated and layered with petroleum spirit. More red precipitate deposited overnight and after its separation, the filtrate was evaporated to give a brown powder which was washed with petroleum spirit and dried under vacuum. 0 \ CH-CH2~CH3 CH3 159 brown powder m. (KBr, cm '): 2980 w (*), 2933 m, 2860 w, 1720 m (*), 1660 s, 1634 s, 1607 vs, 1576 s, 1559 s, 1539 s, 1526 s, 1509 m, 1448 m, 1384 s, 1321 m, 1260 m, 1208 w, 1120 w, 1031 w, 763 w (main component Co(ambch)(OBu); * band which might indicate the presence o f 2-butanone)
5.9.S.5 Oxidation of Co(ambch) in ethanol
N = C H3C O O EtOH N=' ‘Co' OAc 163
A solution o f Co(II) ambch (0.5 mmol in 10 mL ethanol), generated as described in section 5.9.4.1 was opened to air and stirred at room temperature for 2 h. After this period, the solvent was evaporated and the obtained dark residue (0.163 g, 80 % yield) was washed several times with petroleum spirit. The product was analysed by elemental analysis and IR.
IR (KBr, cm~^); 3423 s, 2936 w, 2860 w, 1649 s, 1597 vs, 1570 vs, 1447 m, 1400 m, 1335 m, 1256 w, 1231 w, 1157 w, 1123 w, 1024 w, 764 w, 671 w, 617 w, 573 w, 461 w.
Elemental analysis calculated for: C22H25N402Co*(CH3COOH)(H20): C, 56.03; H, 6.07; N 10.89 . Found: C, 53.74; H, 5.84; N, 10.57.
5.10 Synthesis of VO (ambch) complexes
5.10.1 Complexation o f ambch with VO(acac) 2
2 CH3—C—CH2“C—CH3
II ^ II
o
o
This reaction was performed under nitrogen. Ethanol was degassed by bubbling nitrogen through it for minimum 30 min before the beginning o f the reaction. Under stirring, to a warm (50 °C) ethanolic solution o f ligand (0.216 g, 0.67 mmol, 15 mL) was added dropwise a solution o f V0(acac)2 (0.179 g, 0.67 mmol) in ethanol (30 mL). At the end o f the addition, temperature was raised to 90 °C and kept constant for 3 h. After this period, the reaction mixture was filtered hot to give a green-grey precipitate and a green- yellow solution. The latter was concentrated to half o f the initial volume and cooled. Light-blue crystals were formed overnight which were decanted from the yellow-brown solution with a cannula. Evaporation o f this solution gave a brown-orange oil. The oil was washed with dry petroleum spirit to give a yellow solution and a brown-orange