A R T I C L E S
Curtis et al.
and manipulations of air-sensitive compounds were carried out using
Schlenk and drybox techniques.
Electrochemical Studies. All electrochemical experiments were
was collected by filtration and dried under vacuum (0.28 g, 62% yield).
Anal. Cald for C22
8.21. H NMR (CD
H
53
P
5
F
6
Ni: C, 40.95; H, 8.28. Found: C, 40.55; H,
CN): δ 1.03 (m, PCH CH ), 1.62 (seven line
CH ), 1.65-2.0 (m, PCH CH CH P), -15.69
(quintet, JP-H ) 3.0 Hz, Ni-H). P NMR (CD CN): δ 3.28 (s).
[Ni(depp) ](BF . To a suspension of depp (0.88 g, 0.004 mol) in
acetonitrile (30 mL) at room temperature was added solid [Ni(CH
CN)6.5](BF (1.0 g, 0.002 mol) and the resulting dark red solution
1
3
2
3
carried out under an atmosphere of N
2
in 0.3 M Bu
4
NBF
4
in benzonitrile
pattern, J ) 7.5 Hz, PCH
2
3
2
2
2
2
31
or 0.3 M Et NBF in acetonitrile. Cyclic voltammetry experiments were
4
4
3
carried out on a Cypress Systems computer-aided electrolysis system.
The working electrode was a glassy carbon disk (2 mm diameter), and
the counter electrode was a glassy carbon rod. A platinum wire
immersed in a permethylferrocene/permethylferrocenium solution was
used as a pseudoreference electrode to fix the potential. Ferrocene was
used as an internal standard, and all potentials are referenced to the
ferrocene/ferrocenium couple.
Materials. Bis(1,5-cyclooctadiene)nickel(0), dichloro(1,5-cyclo-
octadiene)platinum(II), and diethylphosphine were purchased from
Strem Chemical Co. and used without further purification. Anhydrous
benzonitrile, anhydrous acetonitrile, 1,3-dibromopropane, benzonitrile-
2
4 2
)
3
-
4 2
)
was stirred overnight. The solvent was then removed under vacuum
and the dark red powder that remained was used without further
purification (1.23 g, 91%). Anal. Calcd for C22
H
52
P
4
B
2
F
8
Ni: C, 39.27;
1
H, 7.79. Found: C, 39.67; H, 7.81. H NMR (CD
PCH CH ), 1.94 (m, PCH CH ), 2.0-2.2 (m, PCH
NMR (CD CN): δ 3.22 (s).
[Pt(depp) ](PF . To a suspension of depp (1.10 g, 0.005 mol) in
acetonitrile (50 mL) was added solid Pt(COD)Cl (0.93 g. 0.0025 mol).
The solution was stirred overnight and the solvent was removed under
vacuum to give a yellow solid. This was dissolved in H O (50 mL)
and solid NH PF (1.50 g, 0.009 mol) was added, precipitating the
3
CN): δ 1.28 (m,
3
1
2
3
2
3
2
CH
2
CH
2
P).
P
3
2
6 2
)
2
d
5
, TMG, ammonium hexafluorophosphate, p-bromoaniline, pyridine,
and triethylamine were purchased from Aldrich Chemical Co. and used
as received. CD CN and toluene-d purchased from Aldrich Chemical
Co. were vacuum transferred from CaH and stored in the glovebox.
2
3
8
4
6
product as a white powder. This was collected by filtration, washed
with water (20 mL) and diethyl ether (20 mL), and then dried under
2
Anisidine was purchased from Aldrich Chemical Co. and sublimed.
Tetrahydrofuran and diethyl ether were purchased from Aldrich
Chemical Co. and distilled over Na/benzophenone prior to use. HPLC
grade N,N-dimethylformamide was purchased from Burdick & Jackson,
52 6 12
vacuum to give 2.40 g (96%) of product. Anal. Calcd for C22H P F -
1
Pt: C, 28.55; H, 5.66. Found: C, 27.97; H, 5.38. H NMR (CD
δ 1.19 (m, PCH CH ), 2.1 (m, PCH CH ), 2.1-2.4 (m, PCH CH CH
CN): δ 5.72 (s, JPt-P ) 2087 Hz).
of [HNi(depp) ]PF in Benzonitrile. [HNi(depp)
g, 0.037 mmol) was placed in a 5 mm NMR tube, benzonitrile-d
3
CN):
2
3
2
3
2
2
2
P).
31
1
purged with nitrogen, and stored in the glovebox. LiPEt
by deprotonation of HPEt with butyllithium in hexane. [Ni(CH
was prepared by the published procedure.58 [Ni(diphosphine)
and [Pt(diphosphine) ](PF complexes used for hydrogen
2
was prepared
P NMR (CD
pK
3
3
CN)6.5]-
a
2
6
2 6
]PF
(0.024
(0.7
2
(
(
BF
BF
4
)
)
2
2
]-
5
)
2
mL) was added, and the tube was capped with a rubber septum. TMG
4
2
2
6
1
activation and electrochemical studies were prepared as described
(2.0 µL) was then added via syringe. The H NMR spectrum of the
3
6,59
previously.
ethanol, recrystallized from CH
Et P(CH PEt , depp. A solution of Et
KOPh was prepared from KOH and phenol in absolute
CN, and stored in the glovebox.
PLi (2.40 g, 0.025 mol) in
sample was monitored for 3 days, during which time resonances for
Ni(depp) grew and those of the starting hydride diminished. After 3 d
2
3
)
2 3
2
2
the reaction had stopped and the concentrations of Ni(depp)
2
and [HNi-
2
+
THF (100 mL) was cooled to -80 °C and 1,3-dibromopropane (2.52
g, 0.0125 mol) was added with a syringe. The color changed rapidly
from yellow to colorless. The solution was then allowed to warm to
room temperature and stirred for 60 min. Then the solvent was removed
under vacuum and the residue extracted with diethyl ether (100 mL).
The ether phase was washed with water (2 × 50 mL) and dried over
2
(depp) ] were estimated using the peak heights of the respective methyl
resonances at 1.62 and 1.03 ppm in the 500 MHz spectrum. Once these
+
concentrations were known, [TMGH ] was assumed to be equal to
+
[Ni(depp)
2
], [TMG] was found by subtracting [TMGH ] from the
amount initially added, and the equilibrium constant for reaction 7 was
evaluated. Equation 18 and the known pK
of TMGH+ (23.3) were
a
MgSO
4
. This was filtered and the solvent was removed from the filtrate
then used to calculate the pK
a
of the nickel hydride.
1
under vacuum to yield 2.15 g (78%) of colorless liquid product. H
3
3
+
NMR (toluene-d
PCH CH
); 1.23 (q, 3JH-H ) 7.0 Hz, PCH
.36 (m, -CH CH
P). 31P NMR (toluene-d
Ni(depp) . A solution of depp (0.88 g, 0.004 mol) in THF (30 mL)
was cooled to - 80 °C, solid Ni(COD) (0.55 g, 0.002 mol) was added,
and the mixture was allowed to warm to room temperature. After stirring
0 min at room temperature, the solvent was removed from the yellow
solution to give an oily white solid. This was washed with acetonitrile
30 mL) and filtered and the white solid collected was dried under
vacuum (0.85 g, 85% yield). Crystalline material for analysis was
obtained by deprotonating a sample of [HNi(depp) ](PF ) in acetonitrile
8
): δ 1.00 (d of t, JH-H ) 7.0 Hz, JP-H ) 15.0 Hz,
CH ); 1.57 (m, -CH CH P);
): δ -23.3 (s).
pK (MH) ) pK (BH ) + pK
(18)
a
a
eq
2
3
2
3
2
2
1
2
2
8
pK
a
of [HPt(depe)
2
]PF
6
in Acetonitrile. [HPt(depe)
2 6
](PF ) (21-
2
2
9 mg, 0.028-0.038 mmol) was weighed into five NMR tubes. The
2
tubes were then treated with aliquots of 0.051 M KOPh solution in
CH
CH
3
CN (0.30, 0.40, 0.50, 0.60, 0.70 mL, 0.0153-0.0357 mmol) and
CN was added to bring the volume in each tube to 0.7 mL. As a
3
3
check of the KOPh solution, another tube was prepared using 25 mg
0.033 mmol) of [HPt(depe) ](PF ) and 0.30 mL of 0.100 M KOPh
(
(
2
6
solution (0.030 mmol). Equilibrium was established within 30 min,
2
6
31
and the P spectra were recorded. The concentrations of the hydride
with a 5-fold excess of 1,1,3,3-tetramethylguanidine. This is a slow
reaction and crystals form over 2 days. The crystals were collected,
and Pt(0) complexes were then determined by integration of the
appropriate resonances. The phenol and phenoxide concentrations were
then calculated from the amount of phenoxide added and the reaction
stoichiometry, and corrected for the association of phenol with
washed with acetonitrile, and dried under vacuum. Anal. Calcd for
1
C
22
H
52
P
4
Ni: C, 52.93; H, 10.50. Found: C, 51.70; H, 10.29. H NMR
(
toluene-d
PCH CH CH
HNi(depp)
.0007 mol) in acetonitrile (30 mL) was added solid NH
8
): δ 1.01 (m, PCH
2
2
CH
P). P NMR (toluene-d
](PF ). To a stirred suspension of Ni(depp) (0.35 g,
6
PF (0.12 g,
3
); 1.34 (m, PCH
2
CH
3
); 1.5-1.9 (m,
6
phenoxide using the method described by Norton. The equilibrium
3
1
2
2
8
): δ 3.82 (s)
constant for the deprotonation reaction was then calculated and eq 18
[
2
6
2
was used to determine the pK
Hydrogen Activation with [Ni(dmpp)
carried out five times with different ratios of 4-bromoaniline/4-bromo-
anilinium in each run. [Ni(dmpp) ](BF (22-24 mg, 0.039-0.043
mmol), 4-BrC NH (34-87 mg, 0.20-0.51 mmol), and [4-BrC
NH ](BF ) (6-48 mg, 0.02-0.18 mmol) were weighed into five NMR
tubes and 0.7 mL of CD CN was added to each. The tubes were capped
with septa and H was bubbled slowly through a needle into each
solution for 10 min to produce a saturated solution at 1 atm (620
a
value for the hydride complex.
0
0
4
2
](BF . The reaction was
4 2
)
.00075 mol). This was stirred for 1 h, during which time a clear, yellow
solution formed. The solvent was removed under vacuum and the
residue was dissolved in warm ethanol (25 mL) and filtered. When
this solution was cooled to -20 °C, yellow crystals formed. The product
2
4 2
)
H
6 4
2
6 4
H -
3
4
3
(
58) Hathaway, B. J.; Holah, D. G.; Underhill, A. E. J. Chem. Soc. 1962, 2444.
59) Miedaner, A.; Haltiwanger, R. C.; DuBois, D. L. Inorg. Chem. 1991, 30,
2
(
4
17-427.
1924 J. AM. CHEM. SOC.
9
VOL. 124, NO. 9, 2002