Organometallics
Article
model complex c,t-RuH2(2-NH2CH2Py)(PMe3)2 (21) to give
2-propanol and the amido complex 32 (via TS30‑31 and
intermediates 30 and 31) is endergonic by 30.2 kcal/mol. On
the other hand, the hydrogenation of acetone by the model
complex t,c-RuH2(2-NH2CH2Py)(PMe3)2 (21-trans) to give 2-
propanol and the five-coordinate amido complex 35 is
exergonic by 5.7 kcal/mol. The barrier for the forward reaction
is 9.6 kcal/mol from 21-trans or 16.8 kcal/mol from 21. The
barrier for the reverse reaction is 15.3 kcal/mol from 35. The
results are in good agreement with those reported by Morris et
al. for the reaction of acetone with the model complex c,t-
RuH2(2-NH2CH2Py)(PH3)2.25c
It is noted that the energy of the rate-determining transition
state (TS33‑34) for the hydrogenation/dehydrogenation reaction
(24.3 kcal/mol; Figure 4) is comparable to that of TS23‑24 for
the H/D exchange reaction (24.1 kcal/mol; Figure 2). The
results suggest that hydrogenation of carbonyl compounds and
dehydrogenation of alcohol mediated by the hydride complex
21 could proceed at a rate similar to that of the H/D exchange
reaction of the hydride complex 21 with D2O, consistent with
our experimental observations that that the α protons of
alcohols can also undergo H/D exchange with D2O in reactions
catalyzed by RuCl2(2-NH2CH2Py)(PPh3)2.
EXPERIMENTAL SECTION
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All manipulations were carried out under a nitrogen atmosphere using
standard Schlenk techniques unless otherwise stated. Solvents were
distilled under nitrogen from sodium/benzophenone (n-hexane,
diethyl ether, THF), or calcium hydride (dichloromethane). Other
solvents were purged with nitrogen for 10 min before use. The
complexes CpRuCl(PPh3)2,26 Cp*RuCl(PPh3)2,27 (η5-indenyl)RuCl-
(PPh3)2,28 RuCl2(DMSO)4,29 RuHCl(CO)(PPh3)3,30 RuCl2(PPh3)3,31
RuCl2(2-PyCH2NH2)(dppf),32 RuCl2(NH2CH2CH2NH2)(PPh3)2,33
RuHCl{(R,R)-dach}(PPh3)2,34 RuCl2(2-H2NCH2Py)(PPh3)2,25a
RuHCl(2-H2NCH2Py)(PPh3)2,25a RuH2(2-H2NCH2Py)(PPh3)2,25a
(p-cymene)RuCl2 (PPh3 ),35 and (η6 -cymene)Ru{(S,S)-
NHCHPhCHPhNTs}23a were synthesized according to reported
procedures. Deuterium oxide, 99.9 atom % D, was purchased from
Aldrich Chemical Co. and used as received. All other reagents were
used as purchased from Aldrich Chemical Co., Acros Organics,
International Laboratory, or Kodak. H and 13C{1H} NMR spectra
1
were collected on a Bruker ARX 300 MHz spectrometer or a Bruker
2
AV 400 MHz spectrometer. D NMR spectra were collected on a
Bruker AV 400 MHz spectrometer.
General Procedure for the H/D Exchange Reactions
between PhCH2CH2OH and D2O in the Screening Experiments
(for Entries in Table 1). A mixture of a ruthenium complex (0.04
mmol), KOH in D2O (1.84 M solution, 110 μL, 0.20 mmol), 2-
phenylethanol (240 μL, 2.0 mmol), and D2O (720 μL, totally 830 μL,
45.87 mmol) was heated at 80 °C for 3.5 h. The resulting solution was
analyzed by 1H NMR. The percentage of deuterium incorporated was
1
CONCLUSION
estimated on the bsis of H NMR integrations.
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General Procedure for H/D Exchange Reactions between
Alcohols and D2O Catalyzed by RuCl2(PPh3)2(2-NH2CH2Py) (for
Entries in Table 2). In a Schlenk tube charged with RuCl2(2-
NH2CH2Py)(PPh3)2 (32 mg, 0.04 mmol) and alcohol (2 mmol) were
placed KOH in D2O (110 μL, 1.84 M, 0.2 mmol) and D2O. The molar
ratio of substrate and D2O was chosen such that the expected
percentage of deuterium incorporation at the α- and β-carbon
positions is about 90%. The mixture was heated at 80 °C for a period
We have studied the catalytic properties of a series of
ruthenium complexes for H/D exchange between D2O and
alcohols. The catalytic activity of the ruthenium complexes and
the regioselectivity of the H/D exchange reactions between
D2O and alcohols are dependent on the auxiliary ligands.
Ruthenium p-cymene complexes supported by an amine ligand
such as [(p-cymene)RuCl(NH2CH2CH2NTs)]Cl and (η6-
cymene)Ru{(S,S)-NHCHPhCHPhNTs} were found to be
able to catalyze regioselective deuteration of alcohols with
deuterium oxide at the β-carbon positions only. In contrast,
octahedral ruthenium complexes supported by an amine ligand
such as RuCl2(2-NH2CH2Py)(PPh3)2 (2-NH2CH2Py = 2-
aminomethylpyridine) and RuCl2(NH2CH2CH2NH2)(PPh3)2
catalyzed regioselective H/D exchange reactions between D2O
and alcohols at both the α- and β-carbon positions of alcohols.
The H/D exchange reactions proceed through reversible
dehydrogenation of alcohols and hydrogenation of carbonyl
compounds involving hydride species and H/D exchange
among D2O and carbonyl and hydride species.
1
of time. The progress of the reaction was monitored by H NMR.
After the reaction was completed, the product was extracted with
diethyl ether, washed with water, and purified by column
chromatography. The product was analyzed by 1H and 2D NMR.
The percentage of deuterium incorporated was estimated on the basis
1
of H NMR integrations.
General Procedure for H/D Exchange Reactions between
Alcohols and D2O Catalyzed by (η6-cymene)Ru{(S,S)-NHCH-
(Ph)CH(Ph)NTs}. In a Schlenk tube charged with (η6-cymene)Ru-
{(S,S)-NHCH(Ph)CH(Ph)NTs} (8 mg, 0.013 mmol) and an alcohol
(0.66 mmol) were placed KOH in D2O (36 mL, 1.84 M, 0.066 mmol)
and D2O. The molar ratio of the substrate and D2O was chosen such
that the expected percentage of deuterium incorporated at the α- and
β-carbon positions is about 90%. The mixture was heated at 80 °C for
3.5 h. The resulting solution was analyzed by 1H NMR, and the
percentage of deuterium incorporated was estimated on the basis of
1H NMR integrations.
Experimental and computational studies suggest that the
different regioselectivities of the H/D exchange reactions can
be related to the relative ease of exchange reactions of
ruthenium hydride intermediates with D2O. In the case of
octahedral ruthenium complexes supported by an amine ligand,
ruthenium hydride intermediates can undergo H/D exchange
with D2O via Ru(η2-HD) intermediates with a barrier similar to
that of hydrogenation. Thus, H/D exchange can take place at
both α- and β-carbon positions. In the case of ruthenium p-
cymene complexes supported by an amine ligand, Ru(η2-HD)
intermediates are not easily accessible and the barrier for H/D
exchange between ruthenium hydride intermediates with D2O
is substantially higher than that of hydrogenation. Thus, H/D
exchange can only take place at β-carbon positions. It is noted
H/D Exchange between (p-cymene)RuH{(S,S)-
H2NCHPhCHPhNTs} and D2O. About 0.02 mL of 2-propanol
(0.262 mmol) was placed in an NMR tube containing (p-cymene)-
Ru{(S,S)-HNCHPhCHPhNTs} (8 mg, 0.013 mmol) and 0.4 mL of
C6D6. The purple solution turned red in 20 min, indicating the
formation of (p-cymene)RuH{(S,S)-H2NCHPhCHPhNTs}.23a Then
0.1 mL of MeOD-d4 (2.462 mmol) was added. 1H NMR spectra of the
solution were collected after the solution stood at room temperature
for 30 min and 3 h and heated for 30 min, 3 h, and overnight. The 1H
NMR spectra displayed no NH2 peak at 2.79 and 5.29 ppm, suggesting
that the NH2 protons undergo rapid exchange with MeOD-d4. The
relative intensities of the RuH signal (at −5.25 ppm) in comparison to
that of CH on p-cymene at 4.62 ppm did not change appreciably.
H/D Exchange between RuH2(2-NH2CH2Py)(PPh3)2 and D2O.
About 0.05 mL of D2O (2.763 mmol) was placed in an NMR tube
containing RuH2(2-NH2CH2Py)(PPh3)2 (10 mg, 0.0136 mmol) and
́ ́
that Jalon, Lledos, and their co-workers recently reported that
Ru(η2-HD) species also play an key role in alcohol deuteration
by transfer hydrogenation of ketones using HCOOH/
HCOONa in D2O.2t
1
0.4 mL of C6D6. H NMR spectra of the solution were collected after
J
Organometallics XXXX, XXX, XXX−XXX
Bai, Wei
