Graziani et al.
1
(CD3COCD3): δ 6.81 (d, 3 H, H-5, 3JH-H ) 2.2 Hz), 5.96 (d, 3 H,
H-4, JH-H ) 2.2 Hz), 3.08 (sept, 3 H, CH(CH3)2, JH-H ) 7.0
Hz), 1.25 (d, 18 H, CH(CH3)2, 3JH-H ) 7.0 Hz), 0.79 (s, 9 H, t-Bu).
11B NMR (CD3COCD3, 96.28 MHz): δ 3.79 (br s).
Found: C, 46.66; H, 6.60; N, 12.87. H NMR (CD3COCD3): δ
7.66 (d, 3 H, H-5, 3JH-H ) 2.4 Hz), 6.20 (d, 3 H, H-4, 3JH-H ) 2.2
Hz), 1.32 (s, 27 H, t-Bu-pz), 1.10 (s, 9 H, t-Bu-B). 13C{1H} NMR
(CD3COCD3): δ 162.7 (C-3), 136.0 (C-5), 101.7 (C-4), 32.2
[(CH3)3C-pz], 31.4 [(CH3)3C-pz], 30.7 [(CH3)3C-B].
3
3
(d) R ) t-Bu: Li[t-BuTpt-Bu] (1d). t-BuBH3Li‚0.5Et2O, 2.53
g (22.0 mmol); 3(5)-tert-butylpyrazole, 9.0 g (73.0 mmol); 1 h at
120 °C and 5 h at 220 °C. Purification was performed as described
above for Li[t-BuTpi-Pr] with vacuum distillation of the excess tert-
butylpyrazole at 190 °C (8 mm Hg). Yield: 8.0 g (18.0 mmol,
(e) R ) Ph: Tl[t-BuTpPh] (2e). Li[t-BuTpPh] (1e), 1.00 g (1.98
mmol) in 15 mL of methanol; TlNO3, 0.58 g (2.2 mmol) in 15 mL
of water. Yield: 1.00 g (1.4 mmol, 72%). mp: 178-180 °C. Anal.
Calcd for C31H30BN6Tl: C, 53.06; H, 4.31; N, 11.97. Found: C,
1
3
1
82%). H NMR (CD3COCD3): δ 6.80 (d, 3 H, H-5, JH-H ) 2.2
53.12; H, 4.48; N, 11.95. H NMR (CD3COCD3): δ 7.87-7.82
3
(m, 6 H, Ph), 7.45-7.30 (m, 9 H, Ph), 7.41 (d, 3 H, H-5, 3JH-H
)
Hz), 5.98 (d, 3 H, H-4, JH-H ) 2.2 Hz), 1.33 (s, 27 H, t-Bu-pz),
3
0.88 (s, 9 H, t-Bu-B).
2.2 Hz), 6.68 (d, 3 H, H-4, JH-H ) 2.4 Hz), 1.15 (s, 9 H, t-Bu).
13C{1H} NMR (CD3COCD3): δ 152.2 (C-3), 137.5 (C-5), 134.9
(Cipso Ph), 129.1 (o-C Ph), 127.6 (p-C Ph), 126.4 (m-C Ph), 102.7
(C-4), 29.6 (C(CH3)3).
(e) R ) Ph: Li[t-BuTpPh] (1e). t-BuBH3Li‚0.5Et2O, 3.53 g (30.1
mmol); 3(5)-phenylpyrazole, 14.61 g (101.0 mmol); 1 h at 120 °C
1
and 12 h at 220 °C. Yield: 9.95 g (19.2 mmol, 64%). H NMR
(CD3COCD3): δ 7.91-7.86 (m, 6 H, Ph), 7.42-7.23 (m, 9 H, Ph),
7.08 (d, 3 H, H-5, 3JH-H ) 2.4 Hz), 6.54 (d, 3 H, H-4, 3JH-H ) 2.4
Hz), 1.09 (s, 9 H, t-Bu).
Thallium tert-Butyl[bis(3,5-dimethylpyrazolyl)]borate, Tl[t-
BuBH(pzMe2)2] (3). A three-necked 500 mL round-bottom flask
fitted with a water-cooled condenser was charged with a magnetic
stir bar, t-BuBH3Li‚0.5Et2O (2.40 g, 21.0 mmol), and 3,5-
dimethylpyrazole (8.0 g, 84.0 mmol). The mixture was stirred and
heated first at 120 °C until the evolution of hydrogen ceased (1 h).
The melt was then heated to 220 °C for 16 h. The mixture was
cooled to room temperature, affording a solid block. Extraction as
described above for Li[t-BuTpR] salts provided a white powder
which was washed with 50 mL of pentane, filtered, and dried in
vacuo. This crude off-white solid was then dissolved in 50 mL of
methanol, and an aqueous solution of TlNO3 (6.0 g, 21.0 mmol)
was added. A white precipitate formed immediately. It was collected
on a glass frit, thoroughly washed with 2 × 30 mL of methanol,
and dried in vacuo. Yield: 2.0 g (7.0 mmol, 33%). mp: 164-166
°C. Anal. Calcd for C14H24BN4Tl: C, 36.28; H, 5.22; N, 12.09.
Found: C, 36.32; H, 5.31; N, 12.12. IR (Nujol, cm-1): νBH 2458.
1H NMR (CD3COCD3): δ 5.77 (s, 2 H, H-4), 2.35, 2.34 (two s,
each 6 H, Me), 0.76 (s, 9 H, t-Bu). 13C{1H} NMR (CD3COCD3):
δ 146.4 (C-3 or C-5), 145.5 (C-5 or C-3), 105.2 (C-4), 29.8
[C(CH3)3], 13.6, 12.5 (Me).
Thallium tert-Butyl[tris(3-R-pyrazolyl)]borate, Tl[t-BuTpR]
(2a-e). General Procedure. The solid lithium salts Li[t-BuTpR]
(1a-e), prepared as described above, were dissolved in methanol.
The addition of an aqueous thallium nitrate (1.1 equiv) solution
caused the immediate precipitation of a white powder. The solid
was filtered, thoroughly washed twice with methanol (50 mL), and
dried in vacuo. For the five compounds 2a-e, the tertiary C atom
[B-C(CH3)3] bonded to the boron atom was never observed in the
13C NMR spectra.
(a) R ) H: Tl[t-BuTp] (2a). Li[t-BuTp] (1a), 1.00 g (3.62
mmol) in 30 mL of methanol; TlNO3, 1.10 g (4.0 mmol) in 15 mL
of water. Yield: 1.31 g (2.31 mmol, 65%). mp: 238-240 °C. Anal.
Calcd for C13H18BN6Tl: C, 32.98; H, 3.83; N, 17.75. Found: C,
33.10; H, 3.83; N, 17.32. 1H NMR (CD3COCD3): δ 7.60 (d, 3 H,
3
3
H-5, JH-H ) 1.8 Hz), 7.17 (d, 3 H, H-3, JH-H ) 2.0 Hz), 6.24
3
3
(dd, 3 H, H-4, JH-H ) 2.0 Hz, JH-H ) 1.8 Hz), 0.92 (s, 9 H,
t-Bu). 13C{1H} NMR (CD3COCD3): δ 139.2 (C-3), 136.5 (C-5),
104.5 (C-4), 29.5 [BC(CH3)3].
(b) R ) Me: Tl[t-BuTpMe] (2b). Li[t-BuTpMe] (1b), 0.5 g (1.57
mmol) in 10 mL of methanol; TlNO3, 0.43 g (1.60 mmol) in 50
mL of water. Because 2b is slightly soluble in methanol, the white
precipitate was washed with water (2 × 30 mL), dissolved in
30 mL of CH2Cl2, and dried over MgSO4. After filtration, the
solvent was evaporated and the white residue washed with 5
mL of cold pentane (-20 °C) and dried in vacuo. Yield: 0.73 g
(1.42 mmol, 90%); no mp detected up to 265 °C. Anal. Calcd for
C16H24BN6Tl: C, 37.27; H, 4.70; N, 16.30. Found: C, 37.67; H,
4.31; N, 16.37. 1H NMR (CD3COCD3): δ 7.55 (d, 3 H, H-5, 3JH-H
) 2.2 Hz), 6.12 (d, 3 H, H-4, 3JH-H ) 2.2 Hz), 2.33 (s, 9 H, Me),
0.87 (s, 9 H, t-Bu). 13C{1H} NMR (CD3COCD3): δ 143.2 (C-3),
134.5 (C-5), 104.5 (C-4), 27.0 [C(CH3)3], 11.3 (Me).
{Li[t-BuB(pzt-Bu
)2(µ-OH)]}2 (4). This reaction was performed
without any precautions to exclude air, moisture, and light. In a
well-ventilated fume hood, Li[t-BuTpt-Bu
] (1d; 0.500 g, 1.125
mmol) was dissolved in 5 mL of benzene in an open beaker and
heated to 50 °C until it was completely dissolved. The solution
was filtered through a filter funnel filled with glass wool into an
Erlenmeyer flask and allowed to slowly cool in the fume hood.
After 5 days, well-shaped colorless crystals deposited. They were
collected by filtration on a glass frit and dried under a nitrogen
stream. Yield: 0.364 g (0.40 mmol, 70%). Some crystals were
subjected to elemental analysis, whereas an especially well-shaped
one was selected for X-ray diffraction study. Anal. Calcd for
C50H88B2Li2N12O2: C, 64.94; H, 9.59; N, 18.17. Found: C, 64.71;
(c) R ) i-Pr: Tl[t-BuTpi-Pr] (2c). Li[t-BuTpi-Pr] (1c), 1.43 g
(3.55 mmol) in 10 mL of methanol; TlNO3, 1.05 g (3.9 mmol) in
50 mL of water. Yield: 1.46 g (2.4 mmol, 69%). mp: 120-122
°C. Anal. Calcd for C22H36BN6Tl: C, 44.06; H, 6.05; N, 14.01.
H, 9.60; N, 18.18. The rest of the crystals were ground in a mortar
and dried at 170 °C (8 mm Hg) for 16 h in order to remove the
1
free tert-butylpyrazole. H NMR (CDCl3): δ 7.53 (d, 4 H, H-5,
3
3JH-H ) 2.0 Hz), 6.18 (d, 4 H, H-4, JH-H ) 2.0 Hz), 1.40 (s, 18
1
H, t-Bu-B), 1.32 (s, 36 H, t-Bu-pz).
Found: C, 43.87; H, 5.97; N, 14.04. H NMR (CD3COCD3): δ
7.35 (d, 3 H, H-5, 3JH-H ) 2.0 Hz), 6.12 (d, 3 H, H-4, 3JH-H ) 2.2
Bis{tert-butyl[tris(pyrazolyl)]borato}iron(III) Hexafluoro-
phosphate, [Fe(t-BuTp)2]PF6 (5). To a pale green solution of
FeCl2(THF)1.5 (0.166 g, 0.71 mmol) in dichloromethane (30 mL)
was added solid Li[t-BuTp] (1a; 0.429 g, 1.55 mmol). A pink slurry
formed immediately upon stirring that was maintained for 6 h. Then,
ferrocenium hexafluorophosphate (0.222 g, 0.67 mmol) and 30 mL
of dichloromethane were added to the reaction mixture, and the
stirring was continued for 16 h. The dark blue suspension
progressively turned red. After filtration to leave LiCl behind and
3
Hz), 3.13 (sept, 3 H, CH(CH3)2, JH-H ) 6.8 Hz), 1.27 (d, 18 H,
3
CH(CH3)2, JH-H ) 6.8 Hz), 1.02 (s, 9 H, t-Bu). 13C{1H} NMR
(CD3COCD3): δ 159.5 (C-3), 136.3 (C-5), 100.9 (C-4), 30.0
[C(CH3)3], 27.9 [CH(CH3)2], 23.6 [CH(CH3)2].
(d) R ) t-Bu: Tl[t-BuTpt-Bu] (2d). Li[t-BuTpt-Bu] (1d), 1.03
g (2.32 mmol) in 5 mL of methanol; TlNO3, 0.68 g (2.55 mmol)
in 25 mL of water. Yield: 0.79 g (1.6 mmol, 70%). mp: 212-214
°C. Anal. Calcd for C25H42BN6Tl: C, 46.78; H, 6.60; N, 13.09.
5664 Inorganic Chemistry, Vol. 45, No. 14, 2006