The following compounds were synthesized according to literature procedures: Ethan‐1,2‐diyl‐
bis‐(trifluormethanesulfonate),[484] methylenediformamide,[485] 4,5‐dimethylimidazole,[486]
bisimidazol‐1‐yl‐methane,[487] bis‐(4,5‐dimethylimidazol‐1‐yl)‐methane,[185] 1,1′‐
methylenebis‐(4,5‐dimethylimidazole),[185] H4L1(OTf)4 XII,[184] H4L3(PF6)4 XXII,[182]
[Ag4(L1)2](OTf)4 25[192] and dimethyloxyrane[206].
5.4.1.1 3,9,14,20-tetraaza-1,6,12,17-tetraazonia-penta-cyclohexacosane-1(23),4,6(26), 10,12(25),15,17(24),21-octaene tetrachloride H4L1(Cl)4 (XXIV)
A solution of tetra‐n‐butyl‐ammonium chloride (278 mg, 1.00 mmol, 10 eq) in MeCN (1 mL) was added to a solution of H4L1(OTf)4 (105 mg, 0.10 mmol, 1.0 eq) in MeCN (4 mL) and DMSO (1.5 mL) and stirred at ambient temperature for 18 h. The voluminous precipitate formed was filtered off and suspended in CH2Cl2 (3 mL). Filtration and drying in vacuo yielded H4L1(Cl)4
XXIV (50 mg, 0.10 mmol, quant.) as white solid.
Formula (molecular weight) C18H26N8(Cl)4 (492.2 g/mol)
1H NMR (300 MHz, DMSO‐d6) δ (ppm) = 9.95 (s, 4H, CH2), 8.17 (s, 8H, Im 4,5‐H), 6.85 (s, 8H, CH2CH2).
The imidazole H‐2 protons were not detected due to fast exchange with D2O.
5.4.1.2 4,5,10,11,15,16,21,22-Octamethyl-3,9,14,20-tetraaza-1,6,12,17-tetraazonia-penta-cyclohexacosane-1(23),4,6(26),10,12(25),15,17(24),21-octaene tetratriflate H4L2(OTf)4
(XXI)
A solution of ethan‐1,2‐diyl‐bis‐(trifluormethanesulfonate) XVI (17.8 g, 54.7 mmol, 1.0 eq) in MeCN (100 mL) was slowly added over a period of 6 h to a solution of 1,1′‐methylenebis‐(4,5‐
dimethylimidazole) XX (11.2 g, 54.7 mmol, 1.0 eq) in MeCN (100 mL) at ambient temperature.
The reaction mixture was heated at reflux for 2 d. The volatiles were removed under reduced pressure and the light brown crude product recrystallized from MeCN (35 mL). The white precipitate was isolated by filtration and washed with MeCN (15 mL). The filtrate was dried under reduced pressures and the residue was recrystallized a second time from MeCN (10 mL).
Drying of the combined solids in vacuo led to the ligand XXI (9.66 g, 9.11 mmol, 33%) as a white solid.
143 5.4 Macrocylic Tetracarbene Ligands and Complexes Formula (molecular weight) C26H40N8(CF3SO3)4 (1060.1 g/mol)
1H NMR (300 MHz, acetonitrile‐d3) δ (ppm) = 8.41 (s, 4H, Im 2‐H), 6.28 (s, 4H, CH2), 4.57 (s, 8H, CH2CH2), 2.35 (s, 12H, CH3), 2.28 (s, 12H, CH3).
13C NMR (75 MHz, acetonitrile‐d3) δ (ppm) = 134.7 (Im C‐2), 131.0 (Im C‐4/5), 129.9 (Im C‐
4/5), 58.2 (CH2), 47.4 (CH2CH2), 9.0 (CH3), 8.6 (CH3).
MS (ESI, MeCN) m/z (%) = 911.2 (15, [H4L2(OTf)3]+), 381.2 (100, [H4L2(OTf)2]2+).
5.4.1.3 4,5,9,10,14,15,19,20-Octamethyl-3,8,13,18-tetraaza-1,6,11,16-tetraazoniuapenta-cylcotetracosan-1,4,6,9,11,14,16-octene-tetrakis-(hexafluorophosphate) H4L4(PF6)4
(XXIII)
A solution of bis‐(4,5‐dimethyl‐1H‐imidazole‐1‐yl)‐methane XX (1.38 g, 6.76 mmol, 1.0 eq) and tetra‐n‐butyl‐ammonium chloride (4.00 g, 14.4 mmol, 2.1 eq) in dibromomethane (20 mL, 287 mmol, 42 eq) was stirred at ambient temperature for 24 h and then heated at reflux for 12 h. The reaction mixture was cooled to ambient temperature, filtered and the formed yellow solid washed with MeCN (25 mL). The solid was solved in water (4 mL) and treated with a sat.
aq. solution of potassium hexafluorophosphate. The resulting precipitate was washed with water (15 mL). Recrystallisation from methanol yielded H4L4(PF6)4 XXIII (1.08 g, 1.06 mmol, 31 %) as white solid.
Formula (molecular weight) C24H36N8(PF6)4 (1016.2 g/mol)
1H NMR (300 MHz, acetonitrile‐d3) δ (ppm) = 9.30 (s, 4H, Im 2‐H), 6.48 (s, 8H, CH2), 2.33 (s, 24H, CH3).
13C NMR (75 MHz, acetonitrile‐d3) δ (ppm) = 136.6 (Im C‐2), 129.1 (Im C‐4, C‐5), 56.2 (CH2), 7.6 (CH3).
EA (%) Calcd. for C24H36N8F24P4: C 28.3, H 3.50, N 11.0. Found: C 28.5, H 3.82, N 11.0.
5.4.2 Complex Synthesis 5.4.2.1 [Ag4(L2)2](OTf)4 (26)
To a suspension of H4L2(OTf)4 (800 mg, 0.75 mmol, 1.0 eq) in MeCN (100 mL) in the dark silver oxide (376 mg, 1.58 mmol, 2.1 eq) was added. The suspension was heated to an oil bath temperature of 70 °C for 24 h and then stirred at ambient temperature for 6 h. The reaction mixture was filtered through Celite® and the filtrate was layered with Et2O (400 mL). The
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Experimental Section
brown crude product was filtered off. Drying in vacuo yielded [Ag4(L2)2](OTf)4 26 (599 mg, 0.31 mmol, 41 %) as light brown solid.
Formula (molecular weight) C52H72N16Ag4(OTf)4 (1949.0 g/mol)
1H NMR (300 MHz, acetonitrile‐d3) δ (ppm) = 6.23 (dt, J = 17.2, 14.4, 14.4 Hz, 8H, CH2), 4.51 (d, J = 14.8 Hz, 4H, CH2CH2), 4.20 (td, J = 14.3, 13.5, 2.5 Hz, 4H, CH2CH2), 4.02 (td, J = 13.6, 12.5, 1.7 Hz, 4H, CH2CH2), 3.50 (d, J = 14.3 Hz, 4H, CH2CH2), 2.42 (d, J = 0.6 Hz, 12H, CH3), 2.17 (d, J = 0.6 Hz, 12H, CH3), 1.90 (d, J = 0.6 Hz, 12H, CH3), 1.51 (d, J = 0.7 Hz, 12H, CH3).
13C NMR (75 MHz, acetonitrile‐d3) δ (ppm) = 180.4 (Im C‐2), 131.1 (Im C‐4/5), 131.0 (Im C‐4/5), 129.0 (Im C‐4/5), 128.9 (Im C‐4/5), 128. 5 (Im C‐4/5), 128.4 (Im C‐4/5), 126.7 (Im C‐4/5), 126.6 (Im C‐4/5), 61.0 (CH2), 50.1 (CH2CH2), 47.9 (CH2CH2), 9.6 (CH3), 9.0 (5CH3), 8.65 (5CH3), 8.5 (CH3).
MS (ESI, MeCN) m/z (%) = 825.0 (82, [Ag2L2(OTf)]+), 381.2 (100, [Ag2L2(H2O)]2+), 338.1 (65, [Ag2L2]2+), 284.6 (24, [AgL2]2+).
5.4.2.2 [Ag4(L3)2](PF6)4 (27)
To a suspension of H4L3(PF6)4 (904 mg, 1.00 mmol, 1.0 eq) in MeCN (70 mL) in the dark silver oxide (464 mg, 2.00 mmol, 2.0 eq) was added. The suspension was heated to an oil bath temperature of 70 °C for 5 h and then stirred at ambient temperature overnight. The reaction mixture was filtered through Celite® and the filtrate was layered with Et2O (100 mL). The brown crude product was filtered off, dried in vacuo yielding 645 mg of 27 and used without further purification for transmetallation attempts.
Formula (molecular weight) C32H32N16Ag4(PF6)4 (1652.0 g/mol)
1H NMR (300 MHz, acetonitrile‐d3) δ (ppm) = 7.57 (s, 8H, Im H‐4/H‐5), 7.42 (s, 8H, Im H‐4/H‐5), 6.27 (d, J = 14.0 Hz, 8H, CH2), 6.12 (d, J = 14.1 Hz, 8H, CH2).
5.4.2.3 [Ag4(L4)2](PF6)4 (28)
To a suspension of H4L4(PF6)4 (102 mg, 0.10 mmol, 1.0 eq) in MeCN (20 mL) in the dark silver oxide (46.3 mg, 0.20 mmol, 2.0 eq) was added. The suspension was heated to an oil bath temperature of 70 °C for 5 h and then stirred at ambient temperature overnight. The reaction mixture was filtered through Celite® and the filtrate was layered with Et2O (50 mL). The brown
145 5.4 Macrocylic Tetracarbene Ligands and Complexes crude product was filtered off, dried in vacuo yielding 20 mg of 28 and used without further purification for complexation attempts.
Formula (molecular weight) C48H64N16Ag4(PF6)4 (1876.5 g/mol)
1H NMR (300 MHz, acetonitrile‐d3) δ (ppm) = 6.06 (s, 16H, CH2), 2.26 (2, 48H, CH2).
5.4.2.4 [NiL1](OTf)2 (29)
[Ag4(L1)2](OTf)4 (50.0 mg, 29.0 µmol, 1.0 eq) and NiBr2(dme) (18.8 mg, 60.9 µmol, 2.1 eq) were suspended in dry MeCN (10 mL) for 1 d. The reaction mixture was filtered through Celite® twice. Drying the filtrate in vacuo yielded [NiL1](OTf)2 (13 mg, 18.5 µmol, 32 %) as yellow solid.
Crystals suitable for X ray diffraction analysis were obtained by layering a concentrated MeCN solution with Et2O.
Formula (molecular weight) C18H20N8Ni(OTf)2 (705.2 g/mol)
1H NMR (500 MHz, acetonitrile‐d3) δ (ppm) = 7.39 (d, J = 2.0 Hz, 2H, Im 4/5‐H), 7.18 (d, J = 2.0 Hz, 2H, Im 4/5‐H)), 6.14 (d, J = 12.9 Hz, 2H, CH2), 6.06 (d, J = 12.9 Hz, 2H, CH2), 4.98 – 4.89 (m, 4H, CH2CH2), 4.52 – 4.42 (m, 4H, CH2CH2).
13C NMR (75 MHz, acetonitrile‐d3) δ (ppm) = 170.1 (s, Im C‐2), 123.7 (s, Im C‐4/5), 123.1 (s, Im C‐4/5), 63.2 (s, CH2), 49.1 (s, CH2CH2).
19F NMR (282 MHz, acetonitrile‐d3) δ (ppm) = ‐79.32 (OTf‐).
MS (ESI, MeCN) m/z (%) = 555.0 (15, [NiL1](OTf)+), 203.0 [100, [NiL1]2+).
UV/vis (MeCN): λmax (nm) (ϵ [M −1 cm−1]) = 233 (14909), 300 (6858), 330 (8070).
EChem (MeCN, 0.1 M nBu4NPF6): E1/2 [V vs Fc/Fc+] = +1.67 V (irreversible, NiII/NiIII) +1.89 V (irreversible, NiIII/NiIV)
‐1.48 V (irreversible, NiI/NiII) EA Calcd. for C20H20F6N8NiS2O6: C 34.06, H 2.86, N 15.89. Found: C 31.23, H 2.98, N 14.54.
5.4.2.5 [NiL1](Cl)2 (30)
A suspension of H4L1(Cl)4 (145 mg, 295 µmol, 1.0 eq), Ni(OAc)2·4H2O(73.1 mg, 295 µmol, 1.0 eq) and sodium acetate (96.8 mg, 1,18 mmol, 4.0 eq) was refluxed in DMSO (8 mL) for 20 h.
The volatiles were removed in vacuo. The crude product was dissolved in water (2 mL) and
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Experimental Section
layered with acetone. The resulting oil was taken up in MeOH (2 mL) and layered with Et2O.
Isolating the yellow needles and drying the these in vacuo yielded [NiL1](Cl)2 (66 mg, 138 µmol, 47 %) as yellow solid. Crystals suitable for X ray diffraction analysis were obtained by layering a concentrated aqueous solution with acetone.
Formula (molecular weight) C18H20N8Ni(Cl)2 (478.0 g/mol)
1H NMR (500 MHz, acetonitrile‐d3) δ (ppm) = 7.58 (d, J = 2.0 Hz, 2H, Im 4/5‐H), 7.37 (d, J = 2.0 Hz, 2H, Im 4/5‐H), 6.36 (dd, J = 32.8, 12.7 Hz, 2H, CH2), 5.17 – 4.99 (m, 2H, CH2CH2), 4.66 – 4.48 (m, 2H, CH2CH2).
13C NMR (75 MHz, acetonitrile‐d3) δ (ppm) = 170.3 (s, Im C‐2), 124.0 (s, Im C‐4/5), 123.1 (s, Im C‐4/5), 118.2 (s, OTf‐), 63.3 (s, CH2), 49.6 (s, CH2CH2).
MS (ESI, MeCN) m/z (%) = 441.1 (38, [NiL1](Cl)+), 203.0 [100, [NiL1]2+).
EChem (MeCN, 0.1 M nBu4NPF6): E1/2 [V vs Fc/Fc+] = +0.426 V (irreversible, NiII/NiIII) +0.833 V (irreversible, NiIII/NiIV)
‐1.34 V (irreversible, NiI/NiII)
‐1.69 V (irreversible, Ni0/NiI)
5.4.2.6 [NiL2](OTf)2 (31)
a) [Ag4(L2)2](OTf)4 (1.53 g, 0.79 mmol, 1.0 eq) and NiBr2(dme) (487 mg, 1.58 mmol, 2.0 eq) were suspended in dry MeCN (30 mL) for 3 d and heated to 60 °C for 18 h. The formed silver salts were separated by filtration through glas fibre filters. The volatiles were removed in vacuo, yielding the crude product (1.03 g) as yellow solid. According to 1H NMR spectroscopy, there were 5 % free ligand in the mixture. To obtain pure 31, a part of the crude product (300 mg) was dissolved in methanol (2 mL) and filtered through a plug of reversed phase silica. The volatiles of the filtrate were removed in vacuo and the product extracted with CH2Cl2 (2 x 3 mL).
Drying in vacuo yielded [NiL2](OTf)2 (63 mg, 77.1 µmol, approx. 20 %) as yellow solid. Crystals suitable for X ray diffraction analysis were obtained by layering a concentrated EtCN solution with Et2O.
b) A suspension of H4L2(OTf)4 (318 mg, 0.30 mmol, 1.0 eq), NiCl2 (39.0 mg, 0.30 mmol, 1.0 eq) and Cs2CO3 (390 mg, 1.20 mmol, 4.0 eq) in dry MeCN (20 mL) was stirred at ambient temperature for 20 h. The volatiles were removed under reduced pressure and the crude product was extracted with CH2Cl2 (10 mL) and purified by size exclusion chromatography
147 5.4 Macrocylic Tetracarbene Ligands and Complexes (Sephadex®, eluent CH2Cl2). Drying in vacuo yielded [NiL2](OTf)2 31(124 mg, 0.15 mmol, 50 %) as yellow‐orange solid.
Formula (molecular weight) C26H36N8Ni(OTf)2 (817.5 g/mol)
1H NMR (500 MHz, acetonitrile‐d3) δ (ppm) = 5.88 (d, J = 13.4 Hz, 2H, CH2), 5.80 (d, J = 13.3 Hz, 2H, CH2), 4.81 – 4.73 (m, 4H, CH2CH2), 4.36 – 4.29 (m, 4H, CH2CH2), 2.24 – 2.23 (m, 12H, CH3), 2.16 – 2.14 (m, 12H, CH3).
13C NMR (126 MHz, acetonitrile‐d3) δ (ppm) = 169.1 (s, Im C‐2), 127.4 (s, Im C‐4/5), 126. 7 (s, Im C‐4/5), 120.8 (s, OTf‐), 57.8 (s, CH2), 46.0 (s, CH2CH2), 8.8 (s, CH3), 8.8 (s, CH3).
19F NMR (471 MHz, acetonitrile‐d3) δ (ppm) = ‐79.30 (OTf‐).
MS (ESI, MeCN) m/z (%) = 667.1 (10, [NiL2](OTf)+), 259.1 [100, [NiL2]2+).
UV/vis (MeCN): λmax (nm) (ϵ [M−1 cm−1]) = 253 (10 163), 343 (12 044).
ATR-IR (solid sample): ν [cm‐1] = 403 (w), 414 (w), 516 (s), 533 (w), 541 (w), 557 (w), 572 (m), 636 (s), 755 (w), 842 (w), 853 (w), 888 (m), 977 (w), 1026 (s), 1089 (w), 1140 (s), 1196 (w), 1222 (s), 1249 (s), 1376 (m), 1392 (m), 1412 (w), 1436 (w), 1445 (w), 1468 (w), 1478 (w), 1641 (w), 1660 (w), 2869 (w), 2925 (w), 2957 (w).
EChem (MeCN, 0.1 M nBu4NPF6): E1/2 [V vs Fc/Fc+] = +0.748 V (irreversible, NiII/NiIII) +1.20 V (irreversible, NiIII/NiIV)
‐1.25 V (irreversible, NiI/NiII)
‐2.41 V (irreversible)
‐2.51 V (irreversible)
EA Calcd. for C28H36F6N8NiO6S2: C 41.14, H 4.44, N 13.71 S 7.85. Found: C 44.28, H 5.63, N 14.73 S 6.43.
5.4.2.7 [NiL1](OTf)3-xFx
A solution of [NiL1](OTf)2 29 (7.0 mg, 10 µmol, 1.0 eq) in MeCN (0.6 mL) and XeF2 (1.7 mg, 10 µmol, 1.0 eq) in MeCN (0.4 mL) were combined at –35°C. An instant color change from yellow to orange was observed. A sample for an EPR measurement was directly frozen in liquid nitrogen.
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Experimental Section
5.5 Two-in-one Pincer Ligands and Complexes