Organometallics
Article
[Rh(bdmpza)Cl3]−N(Et)4+ (Et4N-1). [Rh(bdmpza)Cl3]−Li+ (174.1 mg,
0.3 mmol) was dissolved in 10 mL of ethanol in a round-bottom
flask. Tetraethylammonium chloride (79.1 mg, 0.4 mmol) was first
dissolved in 2 mL of ethanol and added dropwise. After 15 min of
stirring, anion exchange occurred with precipitation, and a new solid
exchange of ΔG⧧ = 25.6 kcal/mol indicates that this might be
possible, in contrast to what is observed experimentally,
although the barrier is not as low as when trifluoroacetate is
present. Davies and Macgregor have examined the effects of
different basic ligands (O2CMe, O2CCF3, SO3CF3, O2COH,
O2CPh, O2CCCl3) on the barrier to C−H activation using
DFT and found that trifluoroacetate had the lowest barrier
(∼O2CCCl3), with the barrier for acetate about 4 kcal mol−1
higher.51 Experimentally, however, acetate catalyzed exchange
much faster than triflate, leading them to conclude that C−H
activation was not rate determining. The same may be true in
the present case, where 5 (or 5′) must form by displacement of
a bound solvent molecule. If acetic acid were to bind more
strongly, this could account for the observed lack of reactivity in
CD3CO2D.
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was isolated by filtration. Yield: 0.075 g (34%). H NMR (CDCl3,
400 MHz): δ 1.35 (Et4N+), 2.44 (s, 6H, CH3), 2.84 (s, 6H, CH3), 3.44
(Et4N+), 6.01 (s, 2H, CH), 6.37 (s, 1H, HCCO2). Anal. Calcd for
C20H35N5O2Cl3Rh: C, 40.94; H, 6.01; N, 11.94. Found: C, 41.11; H,
5.96; N, 11.50.
[Rh(bdmpza)Cl3]−Na+ (Na-1). A round-bottom flask was charged
with Li-bdmpza (343.0 mg, 1.3 mmol), RhCl3·H2O (357.4 mg,
1.3 mmol), sodium chloride (89.0 mg, 1.5 mmol), and 30 mL of
methanol. The mixture was heated at 50 °C in an oil bath for 20 h.
The flask was then placed on ice to allow the product to precipitate.
The product was collected by filtration, and a crude yield of 331.6 mg
(51%) was obtained. 1H NMR (D2O, 400 MHz): δ 2.53 (s, 6H, CH3),
2.59 (s, 6H, CH3), 6.21 (s, 2H, CH), 6.75 (s, 1H, HCCO2). 13C{1H}
NMR (D2O, 100 MHz): δ 11.04 (CH3), 14.59 (CH3), 68.89 (CH),
110.67, 145.17, 158.34, 168.91.
[Ir(bdmpza)Cl3]−Na+ (Na-2). A round-bottom flask was charged
with bdmpza (281.7 mg, 1.1 mmol), IrCl3·H2O (349.5 mg, 1.1 mmol),
sodium chloride (66 mg, 1.1 mmol), and 30 mL of methanol. The
mixture was refluxed for 4 h. Solvent was removed from the reaction
under vacuum, and a crude yield of 214.4 mg (34%) was obtained.
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Complex Na-2 was purified by Soxhlet extraction using methanol. H
In all of these calculations a polarized continuum model
(PCM) solvation correction is applied to these species using
acetic acid as the solvent, as Gaussian does not offer TFA as a
solvent, which may also introduce some inaccuracy.
NMR (D2O, 400 MHz): δ 2.61 (s, 6H, CH3), 2.68 (s, 6H, CH3), 6.25
(s, 2H, CH), 6.69 (s, 1H, HCCO2). 13C{1H} NMR (D2O, 100 MHz):
δ 10.89 (CH3), 13.97 (CH3), 68.52 (CH), 110.11, 144.80, 158.21,
169.61. Anal. Calcd for C12H15N4O2Cl3NaIr: C, 25.34; H, 2.66; N,
9.85. Found: C, 25.42; H, 2.91; N, 9.33.
CONCLUSION
[Rh(bdmpza)Cl2(py)] (3a). A round-bottom flask was charged
with bdmpza (49.5 mg, 0.18 mmol), RhCl3·H2O (47.4 mg, 0.18 mmol),
and 5 mL of ethanol. The mixture was heated at 50 °C for 30 min.
Pyridine (15 μL, 0.18 mmol) was added to the flask and heating
was continued for 1 h. Removal of ethanol gave 3a. Yield: 50.1 mg
(51%). 1H NMR (CD2Cl, 500 MHz): δ 1.83 (s, 6H, CH3), 2.54
(s, 6H, CH3), 6.10 (s, 2H, CH), 6.59 (s, 1H, HCCO2), 7.19 (t, J =
6.3 Hz, 1H, py), 7.60 (t, J = 7 Hz, 1H, py), 7.63 (d, J = 7 Hz, 1H, py),
7.94 (t, J = 7.4 Hz, 1H, py), 9.53 (d, J = 6.0 Hz, 1H, py). The
observation of five pyridine resonances implies hindered rotation
around the Rh−N bond.
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Three new rhodium and iridium complexes were synthesized
and characterized with the fac-chelating ligand bdmpza.
Catalytic benzene H/D exchange was observed when trifluoro-
acetic acid-d was used as the deuterium source. This reaction
was optimized, with the best conditions being the addition of
3 equiv of silver triflate to form the active catalyst in situ. These
conditions were then employed to investigate H/D exchange of
substituted arenes. Aromatic exchange was the most facile.
Notably, branched alkyl substituents on arenes showed H/D
exchange exclusively into the sp3 β-C−H bonds but not into
the α-C−H bonds. DFT calculations suggested η1-C−H arene
coordination followed by base-assisted C−H activation of the
β-C−H bond leading to H/D exchange.
[Rh(bdmpza)Cl2(py)] (3b). A round-bottom flask was charged
with bdmpza (297.7 mg, 1.1 mmol), RhCl3·H2O (305.2 mg, 1.1 mmol),
pyridine (93 μL, 1.1 mmol), and 50 mL of ethanol. The mixture was
heated to reflux for 24 h. The mixture was then filtered and the
product washed with cold ethanol. Finally, the product was extracted
using methylene chloride. Removal of CH2Cl2 gave 3b. Yield:
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EXPERIMENTAL SECTION
289.6 mg (50%). H NMR (CD2Cl2, 400 MHz): δ 1.76 (s, 3H,
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CH3), 2.53 (s, 3H, CH3), 2.54 (s, 3H, CH3), 2.80 (s, 3H, CH3),
6.05 (s, H, CH), 6.16 (s, H, CH), 6.56 (s, 1H, HCCO2), 7.46 (t, J =
7.0 Hz, 2H, py), 7.94 (t, J = 7.6 Hz, 1H, py), 8.78 (d, J = 5.6 Hz, 2H, py).
13C{1H} NMR (CD2Cl2, 125 MHz): δ11.65 (CH3), 11.74 (CH3), 13.38
(CH3), 15.23 (CH3), 70.31 (CH), 110.37, 110.50, 125.50 (py), 139.38
(py), 142.78, 143.41, 154.46 (py), 156.05, 158.59, 165.78. Anal. Calcd
for C17H20N4O2Cl2Rh: C, 40.82; H, 4.03; N, 14.00. Found: C, 41.45; H,
4.32; N, 13.6.
[Rh(bdmpz)Cl3(py)] (4). In air, rhodium trichloride hydrate
(152.4 mg, 0.57 mmol), bis(3,5-dimethylpyrazole)methane (118.0 mg,
0.57 mmol), and pyridine (47 μL, 0.58 mmol) were added to a round-
bottom flask with 10 mL of ethanol. The reaction mixture was heated
to reflux overnight. The solid was collected and extracted with
methylene chloride to isolate 4. Yield: 33.5 mg (12%). 1H NMR
(DMSO-d6, 400 MHz): δ 2.11 (s, 6H, CH3), 2.57 (s, 6H, CH3), 6.34
(s,2 H, CH), 6.57 (d, J = 15.3 Hz, H, HCCO2), 7.46 (t, J = 6.9 Hz, 2H,
py), 7.77 (d, J = 15.1 Hz, 2H, H2CCO2), 7.93 (t, J = 7.5 Hz, 1H, py),
9.28 (d, J = 5.6 Hz, 2H, py). Anal. Calcd for C16H21Cl3N5Rh: C, 39.01;
H, 4.30; N, 14.22. Found: C, 38.76; H, 4.25; N, 13.95.
All procedures were carried out in air unless otherwise noted. Li-
bdmpza was prepared according to literature methods.32,33 Rhodium
trichloride hydrate and iridium trichloride hydrate were purchased
from Pressure Chemical Co. Deuterated solvents were purchased from
Cambridge Isotopes. A Bruker-AXS SMART platform diffractometer
equipped with an APEX II CCD detector was use for X-ray crystal
structure determination. Elemental analyses were obtained from
Columbia Analytical Services and the CENTC Elemental Analysis
Facility at the University of Rochester. All H, H, and 13C spectra
were recorded on Bruker Avance 400 and 500 MHz spectrometers. All
GCMS data were collected on a Shimadzu QP2010 single quadrapole
GCMS.
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[Rh(bdmpza)Cl3]−Li+ (Li-1). A round-bottom flask was charged
with Li-bdmpza (487.1 mg, 1.9 mmol), RhCl3·H2O (503.0 mg,
1.9 mmol), and 30 mL of ethanol. After gentle heating for 8 h the
solvent was removed under vacuum. The solid was washed with
methylene chloride (3 × 5 mL) by filtration. The solid was then
dissolved in THF, and insoluble impurities were removed. THF
solvent was evaporated under vacuum, yielding 0.428 g (48%) of
product. 1H NMR (THF-d8): δ 2.61 (s, 6H, CH3), 2.70 (s, 6H, CH3),
6.05 (s, 2H, CH), 7.13 (s, 1H, HCCO2), 10.86 (br, ∼1H, H2O).
General Procedure for Catalytic H/D Exchange Experiments
with Benzene. In a typical reaction, a 4 mL ampule was charged with
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dx.doi.org/10.1021/om2012419 | Organometallics 2012, 31, 1943−1952