P. Pregosin, L. F. Veiros, A. Albinati et al.
CCDC 713671 (6 f) and 713672 (6c) contain the supplementary crystallo-
graphic data for these structures. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
NMR measurements: Samples of 9, 10 and 12 where prepared in an
Argon dry box. All the PGSE diffusion measurements were performed
at a concentration of 2 mm by using the standard stimulated echo pulse
sequence by using 400 MHz Bruker Avance spectrometer equipped with
a microprocessor-controlled gradient unit and an inverse multinuclear
probe with an actively shielded Z-gradient coil. The shape of the gradient
pulse was rectangular, its duration d was 1.75 ms and its strength varied
automatically in the course of the experiments. The calibration of the
gradients was carried out via a diffusion measurement of HDO in D2O.
slowly concentrated under vacuum. The resulting crude was triturated
with Et2O and dried under vacuum affording a white powder.
[Brucinium][BArF] (6e): CH2Cl2 (2 mL) was added to a Schlenk con-
taining BruciniumBF4 (6a) (51 mg, 0.092 mmol). After addition of
NaBArF (79.7 mg, 0.092 mmol) a crystalline precipitate formed and the
mixture was stirred for 3 h at RT and subsequently filtrated through
Celite. The filtrate was slowly concentrated under vacuum and Et2O was
added. The solution was stored at 48C for 2 days and the formed crystals
separated from the solution. The solution was concentrated under
vacuum and the resulting crude was washed with hexane (59 mg, 58%).
Elemental analysis calcd (%) for C55H39N2O4BF24 (1258.7): C 52.48, H
3.12, N 2.23; found: C 52.30, H 3.01, N 2.27.
1
In the H-PGSE experiments, D[13] was set to 117.75 ms and 167.75 ms, re-
spectively. The number of scans varied between 8 and 32 per increment
with a recovery delay of 10 to 24 s. Typical experimental times were 2–
8 h. For 19F, D was set to 117.75 and 167.75 ms, respectively. 16 scans
were taken with a recovery delay of 12 to 24 s, and a total experimental
time of ꢁ2.5–6 h.
All the spectra were acquired using 32 K points and a spectral width of
2796.4–4006.4 Hz (1H) and 1882.5 Hz (19F) and processed with a line
broadening of 1 Hz (1H) and 2 Hz (19F). The slopes of the lines, m, were
obtained by plotting their decrease in signal intensity vs G2 using a stan-
dard linear regression algorithm. Normally, 12–20 points have been used
for regression analysis and all of the data leading to the reported D
values afforded lines whose correlation coefficients were >0.999. The
gradient strength was incremented in 2–4% steps from 2–4% to 40–
[Brucinium][PtCl3(C2H4)] (6 f): Acetone (35 mL) was added to a Schlenk
containing bruciniumchloride (103.6 mg, 0.24 mmol). Addition of MeOH
(2 mL) provided a clear solution. K[PtCl3(C2H4)] (88.6 mg, 0.264 mmol)
was added upon which a white precipitate formed. The suspension was
stirred for 14 h at RT and filtrated. The filtrate was evaporated to dryness
and extracted with CH2Cl2 (2ꢅ2 mL). The solution was concentrated
under vacuum affording a yellow solid (109 mg, 63%). Elemental analy-
sis calcd (%) for C25H31N2O4PtCl3 (725.0): C 41.42, H 4.31, N 3.86;
found: C 41.63, H 4.32, N 3.80; MS (MALDI): m/z: 395.2 (M+).
1
80%. A measurement of H and 19F T1 was carried out before each diffu-
sion experiment and the recovery delay set to (at least) 5 times T1. We
estimate the experimental error in D values at ꢃ2%. The hydrodynamic
radii, rH, were estimated using the Stokes–Einstein equation (c=6) or by
introducing a semi-empirical estimation of the c factor.[49,50]
The 1H, 19F HOESY measurements were acquired using the standard
[N-(4-tBu-benzyl)brucinium][PF6] (7): To
a
solution of brucine
four-pulse sequence[51] on
a 400 MHz Bruker Avance spectrometer
(134.1 mg, 0.34 mmol) in CH2Cl2 (6 mL) a solution of 4-tBu-benzylbro-
mide in CH2Cl2 (5 mL) was added dropwise. The reaction solution was
stirred for 3 h at RT. Addition of Et2O resulted in a white precipitate
which was filtered, washed with Et2O and Et2O/CH2Cl2 (1:1) and dried
under vacuum. The resulting N-(4-tBu-benzyl)bruciniumbromide
(172.4 mg, 82%), was reacted with Ag[PF6] as described for 6a–d, yield-
ing (7) (26.1 mg, 78%).
equipped with a doubly tuned (1H, 19F) TXI probe. A mixing time of
800 ms was used. The number of scans was 8–16 and the number of incre-
ments in the F1 dimension 512. The delay between the increments was
set to 0.8 s. The concentration of the sample was 10 mm unless otherwise
stated.
The 1H and 195Pt spin-lattice relaxation times T1 were measured for
K[PtCl3(C2H4)] in [D6]acetone (2 mm and 15 mm) and for 6 f in
[D6]acetone (2 mm and 10 mm) and CD2Cl2 (2 mm and 10 mm), respec-
tively. The sample temperature was calibrated to 303 K.
Carbonium ions 9–12: 4,4’-Bis(dimethoxy)benzhydrilium tetrafluorobo-
rate (9a),[28a] and 4,4’,4’’-Trimethoxytrityl tetrafluoroborate (10a)[28b] were
synthesized following literature procedures.
1
The H spin-lattice relaxation times T1 were determined by the inversion-
4,4’-Bis(dimethylamino)benzhydrilium tetrafluoroborate (9b): 9b was
prepared by a modified version of Daubenꢀs[28c] procedure. 4,4’-Bis(dime-
thylamino)benzhydrol (105.3 mg, 0.39 mmol) was dissolved in CH2Cl2
(3 mL). Addition of HBF4·OEt2 (57 mL, 0.39 mmol) resulted in a deep
blue solution. The solution was stirred at RT for 15 min and then in an
ice bath for 30 min. Addition of Et2O resulted in a dark blue precipitate
which was filtered, washed with Et2O and dried under vacuum (106 mg,
80%).
recovery experiment. A recovery delay of 6 s was used and 13 different
delay times t where applied. The number of sampling points was 72k,
and the observed frequency range was 6.4 kHz, resulting in a digital reso-
lution of 0.087 Hz.
The 195Pt spin-lattice relaxation times T1 were determined using the inver-
sion-recovery experiment followed by a polarization transfer to 1H.[52]
The 195Pt p (hard) pulse was calibrated prior to the measurement. T1
values were determined at a magnetic field corresponding to a proton
frequency of 400, 500 and 700 MHz, respectively. A recovery delay of 1 s
was used and 10 different delay times t where applied. The number of
sampling points was 16k, and the frequency range was 1.6 kHz, resulting
in a digital resolution of 0.098 Hz.
4,4’-Dimethoxytrityl tetrafluoroborate (10b) and 4,4’,4’’-Tris(dimethyl-
AHCTUNGTERGaNNUN mino)trityl tetrafluoroborate (11) were prepared from the chloride salts
as described for 6–9.
4-Methoxytrityl tetrafluoroborate (10c): 4-Methoxytrityl alcohol was re-
crystallized from hot hexane/Et2O (10:1) prior to use. 4-Methoxytrityl al-
cohol (228.5 mg, 0.79 mmol) was dissolved in Ac2O (1.5 mL). Addition of
HBF4·OEt2 (196 mL, 1.58 mmol) resulted in an orange solution, which
was stirred at RT for 60 min. Addition of Et2O lead to an orange precipi-
tate which was filtered and washed with Et2O until the washing solution
was colorless. The orange powder was dried under vacuum (262 mg,
92%).
General procedure for the synthesis of brucinium salts 6a–f and 7:
[Brucinium][Cl]: In a two-neck flask brucine (600 mg) was dissolved in
CH2Cl2 (40 mL). HCl (g), evolving from the slow addition of H2SO4 to
NaCl using a dropping funnel, was flushed for 1.5 h trough the reaction
solution at RT. The solution was then slowly concentrated under vacuum
and the resulting precipitate filtrated off.
[Brucinium][X] (X=BF4, PF6, OMs, OTf) (6a–d): In a typical procedure
bruciniumchloride (0.2 mmol) was dissolved in CH2Cl2 (2 mL) and added
to a solution of AgX (1 equiv) in CH3CN (0.3 mL). An immediate pre-
cipitate was formed and the reaction solution stirred for 4 h at RT in the
dark. After filtration of the suspension through Celite the filtrate was
Carbonium ions 9, 10 and 12 were stored in an Ar dry box at 243 K.
Model compounds: CPh4 was recrystallized from hot benzene prior to
use. [PPh4][PF6] was prepared as described elsewhere.[24]
6860
ꢄ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 6848 – 6862
Moreno, Aitor
