V. Sumerin et al. / Journal of Organometallic Chemistry 694 (2009) 2654–2660
2659
on a Bruker ARX-300 spectrometer (1H, 13C, 19F) or Bruker DPX-400
M solution of t-BuLi in pentane (3.6 mL, 6.1 mmol). The solution was
allowed to warm up to room temperature and stirred over night. The
solvent was removed in vacuo and the solid residue suspended in
hexane (5 mL). Filtration yielded the lithium derivative as a fine pale
yellow powder. Without further purification the crude lithium salt
was dissolved in 17.5 mL of a 40:60 hexane/toluene mixture and
cooled to ꢁ20 °C. A solution of (C6F5)2BCl (1.141 g, 3 mmol) in tolu-
ene (5 mL) was added dropwise over 5 min. Immediately, intense
bright yellow coloration indicated formation of the product. The
reaction mixture was stirred over night at room temperature and
the solvent was removed in vacuo. The solid residue was suspended
inhexane(15 mL), thecontentsfiltered. Thesolventpresentinthefil-
trate was removed to give 0.797 g of 1-{2-[bis(pentafluorophe-
(
11B). 1H and 13C NMR spectra are referenced to Me4Si by
referencing the residual solvent peak. 11B, 19F NMR spectra were
referenced externally to BFꢂ Et2O at 0 ppm and CF3CO2H at
3
ꢁ78.5 ppm relative to CFCl3 at 0 ppm, respectively. trans-2,6-Di-
methyl-2,6-diphenylpiperidine, 2-bromo-3-methylbenzyl bromide
and (C6F5)2BCl were prepared by the literature methods [28–30].
8.2. Synthetic methods
8.2.1. Trans-2,6-Dimethyl-2,6-diphenylpiperidinium
hydrido[tris(pentafluorophenyl)]borate (5)
In a glove box, a 25-mL flame-dried Schlenk tube equipped with a
stir bar, a Teflon stopcock and a cap (GlindemannÒ-sealing rings were
used for conical joints instead of grease) was charged with B(C6F5)3
(0.2 mmol, 102.4 mg), 1 mL dry toluene and trans-2,6-dimethyl-2,6-
diphenylpiperidine (0.2 mmol, 53.1 mg). The reaction was degassed
once with a freeze–pump–thaw cycle and refilled with H2 (1 atm).
The reaction wasstirred at RTfor 3 h. All volatiles wereremoved in va-
cuo to give the product 5 (155.9 mg, 100% yield) as a white solid. Crys-
tals suitable for X-ray diffraction were grown from a C6D6 solution at
20 °C. Anal. Calc. for C37H25BF15N: C, 57.02; H, 3.23; N, 1.80. Found: C,
57.30; H, 3.20; N, 1.85%. 1H NMR (CD2Cl2, 300 MHz): d 7.50–7.42 (m,
nyl)boryl]-3-methylbenzyl}-2,2,6,6-tetramethylpiperidine
(yield
45%) as an orange oil. 1H NMR (C6D6, 300 MHz): d 7.90 (d, 1H,
3JHH = 8.0 Hz, ortho-(C6F5)2B-C6H3), d 7.26 (t, 1H, 3JHH = 7.3 Hz, para-
3
(C6F5)2B-C6H3), d 6.91 (d, 1H, JHH = 7.3 Hz, ortho-TMPCH2-C6H3), d
3.70 (s, 2H, TMPCH2), d 2.05 (s, 3H, C6H3CH3), d 1.37 (br. s, 6H,
CH2CH2CH2), d 0.81 (br. s, 12H, CH3). 11B NMR (C6D5CD3, 128 MHz):
d 44.12 (br. s). 13C NMR (C6D6, 75 MHz): d 150.18 (s, quaternary car-
bon of CH3C6H3), d 148.64 (s, quaternary carbon of TMPCH2C6H3), d
1
1
147.09 (dm, JCF = 250 Hz, ortho-C6F5), d 144.50 (dm, JCF = 260 Hz,
1
para-C6F5), d 138.61 (dm, JCF = 255 Hz, meta-C6F5), d 130.64 (s,
para-(C6F5)2B-C6H3), d 127.40 (s, ortho-CH3-C6H3), d 127.40 (s,
ortho-TMPCH2-C6H3), d 64.90 (s, NC(CH3)2CH2), d 50.66 (s, TMPCH2),
d 44.85 (s, CH2CH2CH2), d 30.54 (br. s, CH3), d 22.95 (s, C6H3CH3), d
22.70 (br. s, CH3), d 18.55 (s, CH2CH2CH2). Quaternary carbons of
C6F5 ring and (C6F5)2BC6H3 were not observed. 19F NMR (C6D6,
1
10H, C6H5), d 5.99 (br. t, 2H, JNH = 49 Hz, NH2), d 3.58 (br. q, 1H,
1JBH = 86 Hz), d 2.69 (m, 2H, CH2), d 2.11 (m, 4H, CH2), d 1.44 (s, 6H,
1
CH3). 11B NMR (CD2Cl2, 128 MHz): d ꢁ24.48 (d, JBH = 86 Hz). 13C
1
NMR (C6D6, 75 MHz): d 148.87 (dm, JCF = 241 Hz, ortho-C6F5), d
138.81 (dm, 1JCF = 247 Hz, para-C6F5), d 138.15 (s, Quaternary carbon
3
282 MHz): d ꢁ129.40 (d, 6F, JFF = 21 Hz, ortho-C6F5), d ꢁ145.25 (t,
1
of C6H5), d 137.35 (dm, JCF = 255 Hz, meta-C6F5), d 130.05 (s, para-
3
3F, JFF = 20 Hz, para-C6F5), d -161.11 (m, 6F, meta-C6F5). HRMS
C6H5), d 129.83 (s, meta-C6H5), d 124.35 (s, ortho-C6H5), d 65.48 (s,
NC(CH3)(Ph)CH2), d 32.62 (s, NC(CH3)(Ph)CH2), d 28.17 (s, CH3), d
ESI+-TOF: C29H26BNFꢂ10Hþ; Calc. 590.2077. Found: 590.2076.
16.18 (s, CH2). Quaternary carbon of C6F5 ring was not observed. 19
F
8.2.4. Hydrido{2-methyl-6-[(2,2,6,6-tetramethylpiperidinium-1-
yl)methyl]phenyl} bis(pentafluorophenyl)borate (9)
NMR (CD2Cl2, 282 MHz): d ꢁ134.83 (d, 6F, 3JFF = 21 Hz, ortho-C6F5), d
ꢁ164.48 (t, 3F, 3JFF = 21 Hz, para-C6F5), d ꢁ167.69 (m, 6F, meta-C6F5).
In a glove box, a 100-mL flame-dried Schlenk tube equipped
with a stir bar, a Teflon stopcock and a glass stopper (Glinde-
mannÒ-sealing rings were used for conical joints instead of grease)
was charged with 1-{2-[bis(pentafluorophenyl)boryl]-3-methyl-
benzyl}-2,2,6,6-tetramethylpiperidine (8, 1.0 mmol, 0.589 g) and
10 mL dry toluene. The reaction was degassed once with a freeze–
pump–thaw cycle and refilled with H2 (1 atm). The reaction was
stirred at 1000 rpm at room temperature for 7 days. All volatiles
were removed in vacuo. The solid residue suspended in hexane
(15 mL), the contents filtered to give 0.591 g of the product as a
white solid (yield 100%). 1H NMR (CD2Cl2, 300 MHz): d 7.07–6.95
8.2.2. 1-(2-Bromo-3-methylbenzyl)-2,2,6,6-tetramethylpiperidine
A dry 25 mL Schlenk tube was charged with 1.413 g (10 mmol)
2,2,6,6-tetramethylpiperidine, 2.640 g (10 mmol) 2-bromo-3-
methylbenzyl bromide, 1.6 g (11.6 mmol) K2CO3 and 0.166 g KI
(1 mmol) in 18 mL of dry acetone. The mixture was heated at
95 °C for 48 h. The Schlenk tube was cooled and the contents fil-
tered. The solvent present in the filtrate was removed under re-
duced pressure. The crude product was dissolved in 50 mL of Et2O
and extracted twice with 100 mL of 0.1 M HCl. The aqueous solu-
tion was basified to pH 12 with KOH and extracted twice with
50 mL of CH2Cl2. The resulting organic layer was dried over
K2CO3, passed through a short column with silica gel and rotovaped
to give 2.85 g of 1-(2-bromo-3-methylbenzyl)-2,2,6,6-tetramethyl-
piperidine (yield 88%) as white crystals. 1H NMR (CDCl3, 300 MHz):
3
(m, 3H, C6H3), d 6.11 (br. s, 1H, NH), d 4.57 (d, 2H, JHH = 5.5 Hz
1
TMPNHCH2), d 3.67 (br. q, 1H, JBH = 76 Hz, BH), d 2.05 (s, 3H,
C6H3CH3), d 1.73 (m, 6H, CH2CH2CH2), d 1.53 (s, 6H, CH3), d 1.29
(s, 6H, CH3). 11B NMR (CD2Cl2, 128 MHz): d ꢁ21.69 (d, 1JBH = 76 Hz).
13C NMR (CDCl3, 75 MHz): d 148.29 (dm, 1JCF = 230 Hz, ortho-C6F5), d
3
3
1
d 7.73 (d, 1H, JHH = 7.7 Hz, ortho-CH3-C6H3), d 7.17 (t, 1H, JHH
=
146.55 (s, quaternary carbon of CH3C6H3), d 138.14 (dm, JCF
=
3
1
7.5 Hz, para-Br-C6H3), d 7.06 (d, 1H, JHH = 7.8 Hz, ortho-TMPCH2-
C6H3), d 3.73 (s, 2H, TMPCH2), d 2.41 (s, 3H, –C6H3CH3), d 1.73 (br.
s, 2H, CH2CH2CH2), d 1.54 (br. s, 4H, CH2CH2CH2), d 1.10 (br. s, 6H,
CH3), d 0.86 (br. s, 6H, CH3). 13C NMR (CDCl3, 75 MHz): d 144.01
(s, quaternary carbon of TMPCH2C6H3), d 137.18 (s, quaternary car-
bon of CH3C6H3), d 128.15 (s, ortho-CH3C6H3), d 127.97 (s ortho-
TMPCH2-C6H3), d 125.97 (m, quaternary carbon of Br-C6H3), d
124.89 (s, para-Br-C6H3), d 54.83 (s, NC(CH3)2CH2), d 49.50 (s,
TMPCH2), d 41.30 (s, CH2CH2CH2), d 33.12 (br. s, CH3), d 23.30 (s,
C6H3CH3), d 21.73 (br. s, CH3), d 17.89 (s, CH2CH2CH2).
245 Hz, para-C6F5), d 136.82 (dm, JCF = 250 Hz, meta-C6F5), d
134.95 (s, quaternary carbon of TMPCH2C6H3), d 131.14 (s, para-
(C6F5)2BH-C6H3), d 125.28 (s, ortho-CH3C6H3), d 125.22 (s, ortho-
TMPCH2-C6H3), d 67.60 (s, NC(CH3)2CH2), d 54.85 (s, TMPNHCH2),
d 41.35 (s, CH2CH2CH2), d 31.62 (br. s, CH3), d 23.34 (s, C6H3CH3), d
21.57 (br. s, CH3), d 15.74 (s, CH2CH2CH2). Quaternary carbons of
C6F5 ring and (C6F5)2BC6H3 were not observed. 19F NMR (CD2Cl2,
3
282 MHz): d ꢁ134.06 (d, 6F, JFF = 21 Hz, ortho-C6F5), d ꢁ164.33 (t,
3
3F, JFF = 20 Hz, para-C6F5), d ꢁ167.45 (m, 6F, meta-C6F5). HRMS
ESI+-TOF: C29H28BNFꢂ10Naþ; Calc. 614.2052. Found: 614.2059.
8.2.3. 1-{2-[Bis(pentafluorophenyl)boryl]-3-methylbenzyl}-2,2,6,6-
tetramethylpiperidine (8)
1-(2-Bromo-3-methylbenzyl)-2,2,6,6-tetramethylpiperidine
(0.973 g, 3 mmol) was lithiated at ꢁ70 °C in Et2O (10 mL) using a 1.7
8.2.5. Dehydrogenation of 5
In a glove box, a 25-mL flame-dried Schlenk tube equipped with
a stir bar, a Teflon stopcock and a glass stopper (GlindemannÒ-
sealing rings were used for conical joints instead of grease) was