Chapter 4: A Homologous Series of Cobalt, Rhodium, and Iridium Metalloradicals
4.4 Experimental Section
4.4.6 Synthesis
Synthesis of {[SiPiPr3]Co(PMe3)}BArF4 (4.1). [SiPiPr3]Co(N2) (30 mg, 0.043 mmol) was dissolved in 8 mL THF. FcBArF4 (45.4 mg, 0.043 mmol) was dissolved in 2 mL THF.
Both were cooled to −78 oC. PMe3 (13 μL, 0.043 mmol) was syringed into the [SiPiPr3]Co(N2) solution. The FcBArF4 solution was subsequently added to the reaction mixture. The orange solution was stirred at −78 oC for 10 min, and concentrated. The residues were washed with pentane to removed the ferrocene, and the product was extracted into ether, and filtered through celite. Recrystallization by layering pentane over a concentrated ether solution yielded analytically pure product (40 mg, 58%).
Recrystallization by slow evaporation of a concentrated ether/methylcyclohexane solution into methylcyclohexane yielded crystals suitable for X-ray diffraction. 1H NMR (C6D6, δ): 18.0, 14.8, 8.7, 7.9, 7.5, 5.6, 4.4, −4.9, −6.6. ]). μeff (Evans’ method, C6D6:d8- THF = 10:1, 23 oC) = 1.8 μB. Anal. Calcd for C71H75SiP4BF24Co: C, 53.10; H, 4.71; N.
0.00. Found: C, 52.88; H, 4.42; N, 0.00. UV-VIS (in THF): (nm, ε [mol-1 cm-1]), 368 (3100), 403 (2030, sh), 567 (220).
Synthesis of [SiPiPr3]Rh(H)(Cl) (4.7). [SiPiPr3]H (220 mg, 0.36 mmol) and [RhCl(COD)]
(88 mg, 0.18 mmol) were dissolved in 15 mL of THF and stirred for 3 h. The solution was concentrated, and the products were extracted into benzene and filtered through celite. The resulting solution was concentrated, washed with pentane (4 x 1 mL), and dried to yield the pale yellow product (232 mg, 87%). 1H NMR (C6D6, δ): 7.99 (d, J = 7.2 Hz, 2H), 7.82 (d, J = 7.2 Hz, 1H), 7.38-6.99 (m, 9H), 2.72 (s, 2H), 2.58 (m, J = 6.6 Hz, 2H), 2.46 (m, J = 7.2 Hz, 2H), 1.82 (q, J = 7.2 Hz, 6H), 1.42 (q, J = 6.9 Hz, 6H), 1.30 (m,
6H), 1.09-0.95 (m, 12H), 0.54 (q, J = 6.9 Hz, 6H), −10.4 (dm, J = 143 Hz, 1H). 13C{1H}
NMR (C6D6, δ): 155.4 (d, J = 46 Hz), 152.7 (t, J = 22 Hz), 146.4 (t, J = 22 Hz), 143.8 (d, J = 32 Hz), 133.2 (d, J = 19 Hz), 133.1 (t, J = 9.6 Hz), 128.8, 128.6, 128.2, 128.0, 126.6 (d, J = 5.0 Hz), 29.7 (m), 28.9 (m), 21.4, 19.8, 19.2, 18.8, 18.5. 31P{1H} NMR (C6D6, δ):
57.2 (d, J = 109 Hz, 2P ) 47.9 (br, 1P). IR (KBr, cm-1): 2037 (ν[Rh−H]).
Synthesis of [SiPiPr3]Rh(N2) (4.5). [SiPiPr3]Rh(H)(Cl) (150 mg, 0.20 mmol) was dissolved in 12 mL of THF. MeMgCl (75 L, 0.22 mmol, 3M sln) was diluted with 3 mL of THF. Both were cooled to −78 oC. The MeMgCl solution was added dropwise to the pale yellow solution of the complex, resulting in a color change to red/orange. The resulting mixture was stirred for 15 min at −78 oC, and then stirred at RT for 1.5 h, yielding a dark green solution. The solution was concentrated, and the product was extracted into a 2:1 solution of benzene:pentane, and filtered through celite.
Concentration of the solution yielded the product (141 mg, 97%). 1H NMR (C6D6, δ):
7.98 (d, J = 7.2 Hz, 3H), 7.30 (d, J = 7.5 Hz, 3H), 7.19-7.04 (m, 6H), 2.44 (m, 6H), 1.06 (m, 18H), 0.72 (m, 18H). 13C NMR (C6D6, δ): 155.6 (m), 145.3 (m), 132.5 (m), 128.0, 128.0, 126.2, 28.9, 18.8, 18.7. 31P NMR (C6D6, δ): 59.5 (d, J = 160 Hz).
Synthesis of [SiPiPr3]Rh(PMe3) (4.8). [SiPiPr3]Rh(N2) (90 mg, 0.13 mmol) was dissolved in 10 mL THF. The solution was cooled to −78 oC and PMe3 (26 L, 0.25 mmol) was syringed in. The solution was stirred at room temperature for 5 min, and concentrated.
Trituration with hexamethyldisiloxane yielded a yellow powder (95 mg, 95%). 1H NMR (C6D6, δ): 8.17 (d, J = 6.9 Hz, 3H), 7.45 (d, J = 7.8 Hz, 3H), 7.23 (t, J = 7.2 Hz, 3H), 7.11 (t, J = 7.2 Hz, 3H), 2.30 (br, 6H), 1.65 (d, J = 4.8 Hz, 3H), 0.97 (br, 18H), 0.80 (br, 18H).
13C NMR (C6D6, δ): 156.6 (m), 148.3 (m), 132.3, 128.4 (br), 128.0, 126.1, 29.9, 28.9,
20.2, 18.6. 31P NMR (C6D6, δ): 54.3 (dd, J = 153, 39 Hz, 3P), −29.5 (dq, J = 106 Hz, 39 Hz, 1P).
Synthesis of {[SiPiPr3]Rh(PMe3)}BArF4 (4.2). [SiPiPr3]Rh(PMe3) (50 mg, 0.064 mmol) was dissolved in 8 mL THF. FcBArF4 (67 mg, 0.064 mmol) was dissolved in 3 mL THF.
Both were cooled to −78 oC. The FcBArF4 solution was added dropwise to the [SiPiPr3]Rh(PMe3) solution, causing a color change to green. The reaction mixture was stirred for 10 min, after which the reaction mixture was stirred for 30 min The mixture was concentrated, and the residues were washed with pentane. The product was extracted into ether, and filtered through celite. Recrystallization from layering pentane over a concentrated ether solution yielded crystals suitable for x-ray diffraction (69 mg, 66%).
1H NMR (C6D6:d8-THF = 10:1, δ): 12.0, 9.8, 8.4, 7.7, 5.3, −0.1. ]). μeff (Evans’ method, C6D6: d8-THF = 10:1, 23 oC) = 1.6 μB. Anal. Calcd for C71H75SiP4BF24Rh: C, 51.68; H, 4.58; N. 0.00. Found: C, 51.33; H, 4.48; N, 0.00. UV-VIS (in THF): (nm, ε [mol-1 cm-1]), 307 (5900, sh), 639 (320).
Synthesis of [SiPiPr3]Ir(PMe3) (4.9). [SiPiPr3]Ir(N2) (90 mg, 0.11 mmol) was dissolved in 6 mL THF. The solution was cooled to −78 oC and PMe3 (34 L, 0.033 mmol) was syringed into the reaction mixture. The reaction mixture was stirred for 5 min at −78 oC and concentrated. The residues were extracted into ether, filtered through celite, and concentrated. Trituration with hexamethyldisiloxane resulted in a yellow powder (95 mg, 99%). 1H NMR (C6D6, δ): 8.25 (d, J = 7.5 Hz, 3H), 7.42 (d, J= 8 Hz, 3H), 7.20 (t, J = 7 Hz, 3H), 7.07 (t, J = 7.5 Hz, 3H), 2.38 (s, 6H), 1.88 (d, J = 6.0 Hz, 3H), 0.94 (s, 18H), 0.75 (s, 18H). 13C NMR (C6D6, δ): 155.5 (m), 149.8 (m), 131.9 (q, J = 6.3 Hz), 127.7,
126.0, 31.6 (d, J = 22.1 Hz), 31.4 (br), 20.0, 18.6. 31P NMR (C6D6, δ): 27.8 (br, 3P),
−74.0 (q, J = 27.2 Hz, 1P).
Synthesis of {[SiPiPr3]Ir(PMe3)}BArF4 (4.3). [SiPiPr3]Ir(PMe3) (30 mg, 0.038 mmol) was dissolved in 5 mL Et2O. FcBArF4 (40 mg, 0.038 mmol) was dissolved in 2 mL Et2O. Both were cooled to −78 oC. The FcBArF4 solution was added dropwise to the [SiPiPr3]Ir(PMe3) solution. An immediate color change from yellow to purple resulted. The reaction mixture was stirred for 2 min at −78 oC, and was stirred at 5 min, at RT. The reaction mixture was concentrated and the residues were washed with pentane. The solids were extracted into ether, filtered through celite, and concentrated to yield the purple product.
Layering pentane over a concentrated ether solution resulted in purple crystals (58 mg, 87%). Crystals of the product with OTf- as the anion, [SiPiPr3]Ir(PMe3)}OTf (4.3’), which was synthesized by the addition of AgOTf to [SiPiPr3]Ir(PMe3) in THF, were obtained from recrystallization by layering pentane over a concentrated dichloromethane solution.
These crystals were amenable to X-ray diffraction. 1H NMR (C6D6:d8-THF = 10:1, δ):
15.9, 10.9, 9.1, 8.3, 7.7, 5.9, −0.5. ]). μeff (Evans’ method, C6D6: d8-THF = 10:1, 23 oC) = 1.7 μB. Anal. Calcd for C71H75SiP4BF24Ir: C, 49.03; H, 4.35; N. 0.00. Found: C, 49.47; H, 4.56; N, 0.00. UV-VIS (in THF): (nm, ε [mol-1 cm-1]), 366 (138, sh), 482 (360, sh), 566 (470).
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