Ruthenium arene derivatives of chiral ferrocene-based P,N or P,O ligands. Transformation of chloro-alcohol into hydrido-carbonyl complexes

Article abstract of DOI:10.1021/om1008132

Several ferrocene-based chiral nonracemic aminophosphine and racemic hydroxyphosphine ligands have been used in the synthesis of Ru ^II(arene) derivatives (arene = p-cymene, benzene). The reaction of suitable ruthenium complexes with the aminoph

Full text of DOI:10.1021/om1008132

ARTICLE
pubs.acs.org/Organometallics
Ruthenium Arene Derivatives of Chiral Ferrocene-Based
P,N or P,O Ligands. Transformation of ChloroꢀAlcohol into
HydridoꢀCarbonyl Complexes
Javier Torres,† Francisco Sepꢀulveda,† M. Carmen Carriꢀon,†,‡ Fꢀelix A. Jalꢀon,† Blanca R. Manzano,*,†
§
||
||
^
ꢀ
Ana M. Rodriguez, Afrooz Zirakzadeh, Walter Weissensteiner, Antonio E. Mucientes, and
M. Angeles de la Pe~na^
†
ꢀ
ꢀ
ꢀ
Departamento de Quimica Inorgꢀanica, Orgꢀanica y Bioquimica, Facultad de Quimicas, IRICA, Universidad de
Castilla-La Mancha, Avda. C. J. Cela, 10, 13071 Ciudad Real, Spain
‡Fundaciꢀon PCYTA, Paseo de la Innovaciꢀon, 1, Edificio Emprendedores, 02006 Albacete, Spain
§
ꢀ
ꢀ
Departamento de Quimica Inorgꢀanica, Orgꢀanica y Bioquimica, Escuela Tꢀecnica Superior de Ingenieros Industriales,
Avda. C. J. Cela, 3, 13071 Ciudad Real, Spain
Faculty of Chemistry, University of Vienna, W€ahringer Strasse 38, 1090, Wien, Austria
^
ꢀ
ꢀ
ꢀ
Departamento de Quimica Fisica, Facultad de Quimicas, Universidad de Castilla-La Mancha, Avda. C. J. Cela, 10,
13071 Ciudad Real, Spain
S Supporting Information
b
ABSTRACT: Several ferrocene-based chiral nonracemic ami-
nophosphine and racemic hydroxyphosphine ligands have been
used in the synthesis of RuII(arene) derivatives (arene =
p-cymene, benzene). The reaction of suitable ruthenium com-
plexes with the aminophosphine (P,N) ligands and NaBPh4 led
to chelate complexes [RuCl(arene)(P,N)]BPh4 in which the ferrocenyl ligand is coordinated in a bidentate fashion. When these
reactions were carried out with the hydroxyphosphine (P,O) ligands the alcohol functionality was oxidized, and hydridoꢀketone (or
hydridoꢀaldehyde) derivatives of the type [RuH(arene)(PCdO)]BPh4 were obtained. The structures of two derivatives
containing either an aminophosphine or a ketophosphine ligand were determined by X-ray diffraction. The reaction of the
hydroxyphosphine ligands with the ruthenium precursors was studied in detail. Derivatives with coordinated hydroxyphosphine
ligands were isolated and, in the case of a p-cymene hydroxyphosphine derivative, the rate constants and also the thermal and
thermodynamic activation parameters were calculated for the hydride formation. The effects of certain parameters on the hydride
generation, such as the type of solvent, the counterion, pH, and solvent deuteration, were also analyzed. In addition, a new
ruthenium ether derivative was obtained. This compound was formed by reaction of the alcohol group with methanol-d4 in the
presence of the acid that is released in the hydride generation step. A mechanism for the transformation of the hydroxyphosphine
complex into the hydride or ether derivatives is proposed. Furthermore, a number of ruthenium complexes with P,N ligands were
tested in the catalytic transfer hydrogenation of acetophenone.
’ INTRODUCTION
isolation of metal alkoxides is usually associated with the problem
of sensitivity to β-hydride elimination.5 This difficulty can be
avoided by using tertiary alcohol fragments.6 However, the use of
ligands with primary or secondary alcohol functionalities also
appears to be interesting, especially when the coordinated
alcohols are prone to oxidation to carbonyl compounds and
the newly formed carbonyl groups are retained in the metal
coordination sphere. In such cases, it might be possible that the
carbonyl unit reacts with hydrogen in a reversible way and
consequently acts as a reservoir for hydrogen in hydrogenation
processes. Therefore, we questioned whether experimental
In recent years, there has been considerable interest not only
in chelating diphosphine but also in monophosphine ligands
containing additional nitrogen- and/or oxygen-based functional
groups.1 Ligands that combine donor atoms with different “hard”
or “soft” character are frequently considered to behave as
hemilabile ligands. Complexes containing aminophosphine or
other P,N chelating ligands are common2 and have often been
used as ligands in a wide variety of catalytic asymmetric hydro-
genation processes.2 However, examples of phosphino alcohols
with the alcohol function coordinated to a metal center are
scarce.3 On the basis of Pearson’s HSAB concept, coordination of
an alcohol to a late transition metal would imply rather unfavor-
able “hardꢀsoft” interactions. Additionally, the OꢀH bond
could, in principle, be transformed into an alkoxide.4 The
Received: August 19, 2010
Published: June 15, 2011
r
2011 American Chemical Society
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|

Organometallics
ARTICLE
Chart 1
Scheme 1
conditions could be identified that would allow some control
over the reactivity of alcohols at a metal center.
Herein, we report on the isolation and characterization of
chelate complexes formed on coordination of the amino-
phosphine or the hydroxyphosphine ligands to a “Ru(arene)Cl”
fragment. Furthermore, the evolution of the hydroxyphosphine
complexes [RuCl(arene)(P,O)] to hydridoꢀcarbonyl com-
plexes [RuH(arene)(P,CdO)] is described. This process was
analyzed in detail, and the effect of different parameters on the
hydride formation was evaluated. For a p-cymene derivative the
thermal and thermodynamic parameters for the hydride forma-
tion were calculated and a mechanism for the formation of the
product was proposed. In addition, preliminary results on
transfer hydrogenations of acetophenone are reported.
In this study, we focused specifically on the coordination
behavior of [RuII(arene)] fragments to the chiral ferrocenyl
ligands depicted in Chart 1. All ligands used are asymmetric
and contain two different donor atoms: either P,N or P,O. One
might consider that because of the chelate effect both the P,N and
the P,O ligands are able to coordinate to ruthenium in a bidentate
fashion. On bidentate coordination of an asymmetric ferrocenyl
ligand, the Ru atom becomes a stereogenic center and two
diastereomers may be formed with either R or S configuration
at ruthenium. Consequently, information concerning the relative
kinetic and thermodynamic stability of these species may be
obtained by NMR spectroscopy.
’ RESULTS AND DISCUSSION
Considering the work of Noyori and other authors in the field
of catalytic hydrogenation and transfer hydrogenation of ketones
and aldehydes, which was carried out with “RuII(arene)” com-
plexes of chiral amino alcohols or diamines,7,8 we decided to
explore briefly the catalytic behavior of some of the aminophosphine
complexes in the transfer hydrogenation of acetophenone.
The synthesis of all aminophosphine ligands has been re-
ported previously (I,9 II,8 and III10), but their use as ligands in
catalysis is very scarce.11 However, some of their imine deriva-
tives have been extensively used as ligands in different rhodium-,12
iridium-,13 ruthenium-,14,15 or palladium-catalyzed12,16,17 pro-
cesses. Other derivatives of ligands IꢀIII, such as amides,
amidines, and phosphino amides, have been applied in a number
of different catalytic processes.8b,9b,18
Synthesis of Ruthenium Complexes. In this study, the
ferrocenyl aminophosphines IꢀIII (Chart 1) were used in their
enantiopure forms but racemates of the hydroxyphosphines IV
and V were employed.
The cationic arene rutꢀhenium derivatives of all P,N ligands
(IꢀIII) containing BPh4 as the counteranion were obtained
usingproceduresanalogoustothosedescribedpreviouslyforother
typesofligands21 byreaction of thecorrespondingmetal precursor
and the ligand followed by addition of the NaBPh4 salt (see
Scheme 1). As expected, all P,N ligands form chelate complexes
with both donor atoms coordinated to ruthenium ([RuCl-
(p-cymene)(P,N)]BPh4, 1ꢀ3; [RuCl(benzene)(P,N)]BPh4, 4ꢀ6).
In all cases except for 4, which was obtained as a single
diastereomer, two isomers were detected that differed in the
configuration at ruthenium (diastereoisomers RRu and SRu).22
The diastereomeric ratios were calculated from the 31P{1H}
Ferrocenyl alcohols IV18 and V19 (Chart 1) are also known
compounds but were used only recently as ligands in palladium-
catalyzed SuzukiꢀMiyaura cross-coupling reactions.20
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ARTICLE
NMR data (see Table 1) after determining the absolute config-
uration of the major diastereomer by NOE studies (see below).
A different type of product was obtained when the reaction was
performed under the same conditions with the hydroxyphosphine
ligands (see Scheme 2). Interestingly, with the precursor
[RuCl2(p-cymene)]2 and ligands IV and V, as well as with
[RuCl2(benzene)(MeCN)] and ligand IV, the single products
7BPh4ꢀ9BPh4 were obtained, while with [RuCl2(benzene)-
(MeCN)] and ligand V a mixture of four products was formed
possibility of an interconversion of two isomers on the NMR
time scale, the 1H NMR spectrum of 7BPh4 was registered at low
temperature (acetone-d6, ꢀ80 ꢀC). Splitting or broadening of signals
was not observed and—assuming the absence of accidental iso-
chrony—this indicates either the unique existence of one diaster-
eoisomer or—rather unlikely—a very fast isomer interconversion.
Examples of metalꢀhydride complexes with coordinated
ketone or aldehyde ligands have been reported.23ꢀ25
In order to obtain more information about the formation of
the hydride complexes, additional experiments were carried out.
In the absence of NaBPh4 the reactions between the arene
1
(for a discussion see below). Each of the H NMR spectra of
7BPh4ꢀ9BPh4 evidence the presence of a hydride ligand (about
ꢀ7 ppm, doublet, due to JHP coupling) and in the IR spectra a
band at 1580ꢀ1590 cmꢀ1, which is probably due to a coordinated
CdO group, is observed. This evidence reflects activation of the
alcohol group and the formation of hydridoꢀketone or hydridoꢀ
aldehyde complexes, a result later confirmed by an X-ray
diffraction study of 7BPh4 (see below). In the cases of
7BPh4ꢀ9BPh4 only one diastereomer—with the R configura-
tion at ruthenium (deduced from NOE studies)—is formed for
the R,Sp-configured enantiomer. In order to eliminate the
1
precursors and ligands IV and V were monitored by H NMR
spectroscopy in methanol-d4 solutions in NMR tubes. The
instantaneous formation of chloroꢀalcohol derivatives
11Clꢀ14Cl was observed together with a small amount of
hydride species (about 4%) that contained chloride as the
counteranion (7Clꢀ10Cl). The evolution with time of deriva-
tives 11Clꢀ14Cl depended on both the arene and the ligand
present. In fact, an increase in the amount of hydride derivative
7Cl was observed only when the p-cymene precursor and ligand
IV were used (see below for more information concerning this
evolution). In the case of the p-cymene precursor and ligand V, it
was verified that the amount of hydride was only about 4% even
after 3 days in solution. Considering this information, we
performed the same reactions on a larger scale in Schlenk tubes.
After a short reaction time of 0.5ꢀ1 h, derivatives 11Clꢀ14Cl
were obtained, and these were once again accompanied by small
amounts of the hydride complexes.
Table 1. Isomer Ratio for Complexes 1ꢀ6, 11Cl, and 13Cl
1a
2a
3a
4a
5a
6a
11Clb
13Clb
R,Sp,RRu
R,Sp,SRu
90
10
75
25
90
10
>99
<1
67
33
75
25
95
5
89
11
a Acetone-d6. b Methanol-d4.
Scheme 2
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Interestingly, the course of the reaction changed completely on
addition of NaBPh4. To analyze the effect of the NaBPh4 salt at
short reaction times, the metal precursor [RuCl2(p-cymene)]2 was
reacted in methanol with ligandIV. After 0.5 h the NaBPh4 salt was
added and the reaction was stopped after a total of 2 h. In this case
the hydride derivative 7BPh4 was obtained as the only product.
The pronounced effect of the addition of NaBPh4 may be due to
the insolubility of the hydride derivatives in methanol
(precipitation of these derivatives was observed). As mentioned
above, during the preparation of 11Clꢀ14Cl in methanol the
hydrides 7Clꢀ10Cl were also formed in all cases. Therefore, we
carried out the reaction between the Ru precursor and the ligand in
acetone. In this case, the hydrides were not formed and derivatives
11Clꢀ14Cl could be isolated. This findingreflects a clear influence
of the solvent on the process and shows that the presence of
methanol enables the hydride formation. This is not unexpected,
because it is well-known that alcohol favors hydride formation.
Complex 11BF4 was synthesized in order to carry out further
mechanistic studies (see below). This compound was obtained
by reaction of [RuCl2(p-cymene)]2 with ligand IV in the
presence of NaBF4 (Scheme 2). In the synthesis of
[RuCl(arene)(P,O)] complexes 11Cl and 13Cl (Table 1) two
stereoisomers were obtained, while for 11BF4, 12Cl, and 14Cl
the amount of the minor isomer was below 1%.
As stated above, when [RuCl2(benzene)(MeCN)] was re-
acted in methanol with ligand V and NaBPh4, four products were
obtained, as deduced by 31P{1H} NMR spectroscopy. Of these,
the three major components could be identified and these were
the hydride 10BPh4 and the two isomers of the chloroꢀalcohol
14BPh4. Considering that the evolution of the chloride toward
the hydride complexes could involve the initial loss of HCl, we
performed this reaction in methanol in the presence of NEt3 (1.15
equiv). As expected, the formation of the hydride complex 10BPh4
and the corresponding ammonium salt was observed (see eq 1).
Chart 2
The mass spectra (FABþ and ESI-TOF) were recorded for the
alcohol derivatives 11Clꢀ14Cl and 11BF4. In all cases, the peaks
corresponding to the cations [RuCl(arene)(L)]þ (L = IV, V)
were detected along with the peaks corresponding to the species
formed after loss of HCl. Interestingly, the ratio of the latter peak
with respect to the cation [RuCl(arene)(L)]þ peak decreased in
the order 11Cl > 12Cl > 13Cl > 14Cl. This trend reflects a higher
tendency for HCl loss in the case of p-cymene than in the
benzene derivatives and in the case of ligand IV with respect to
ligand V. This finding is consistent with our experimental
observations of reactivity differences and indicates that groups
that donate more strongly to the ruthenium center or to the
ligand (Me against H) favor HCl loss.
For the chloride derivatives, the phosphorus resonances appear
in the range 19ꢀ33 ppm, whereas the corresponding resonances
for the hydride complexes appear at lower field (between 48and57
ppm). The change in chemical shift is as one would expect,
considering that it has been reported that substitution of Clꢀ by
Hꢀ induces a clear deshielding in the P resonances.26 In the
corresponding 1H and 13C{1H} NMR spectra, all the resonances
of the major isomers (except some quaternary carbons) and some
of the minor isomers have been assigned. As expected, in all p-
cymene complexes of the asymmetric ligands IꢀVII (see Chart 2
for ligands VI and VII), the isopropyl methyl groups are
diastereotopic.
NEt3
14BPh4
s
ꢀNHEt3Cl
10BPh4
ð1Þ
f
In all ruthenium derivatives the respective phosphine phenyl
groups (labeled up and down; for a graphical representation see
the Experimental Section) appear to be diastereotopic. It is
noticeable that, in contrast to the case for the free ligands, for
all derivatives the difference in chemical shift for the ortho
protons of these two rings is in the range 0.7ꢀ1.2 ppm, a fact
that is probably due to chelate coordination.
The amino proton resonances were not always visible. How-
ever, in derivative 4, the NH2 resonances appear as two separate
signals, which clearly reflects coordination. In the spectra of the
hydroxyphosphine derivatives 11Clꢀ14Cl, in methanol-d4 solu-
tions, the methyne hydrogen of the CH(Me)OH group of ligand
IV and the methylene hydrogens of the CH2OH group of ligand
V show a significant downfield shift of about 0.7 ppm with
respect the signals for the free ligand. The resonances of 11Cl
and 11BF4 were found to be very similar. All of these data are
consistent with coordination of the hydroxyl group to the metal.
The 1H NMR spectra of derivatives 11Clꢀ14Cl and 11BF4 in
acetone-d6 warrant particular attention. In the case of the
benzene derivatives (13Cl and 14Cl) and 11BF4 one species is
observed in solution (apart from the small amount of diaster-
eomer SRu in the case of 13Cl). However, for the p-cymene
complexes 11Cl and 12Cl, in addition to the SRu isomer of 11Cl,
in each case one additional species is evident in solution and this
In summary, aminophosphine ligands IꢀIII react in methanol
in the presence of NaBPh4 and precursors [RuCl2(benzene)-
(MeCN)] and [RuCl2(p-cymene)]2 to give chelate complexes
of the type [RuCl(arene)(P,N)]BPh4. Under the same conditions,
the reaction of phosphino alcohols IV and V gave hydri-
doꢀcarbonyl chelate complexes of the type [RuH(arene)-
(P,CdO)]BPh4 with the carbonyl group coordinated to ruthe-
nium. This reaction was accompanied by loss of HCl. In the
absence of NaBPh4, ligands IV and V reacted instantaneously to
give the hydroxyphosphino complexes [RuCl(arene)(P,O)]Cl.
In these cases only very small amounts of hydride complexes
[RuH(arene)(PCdO)]Cl are seen at first (up to 4%). Over time,
however, the electron-rich hydroxyphosphino complexes react
further to give the hydrido ꢀcarbonyl complexes. However, on
addition of NaBPh4 the hydridoꢀcarbonyl complexes are formed
very quickly. When acetone was used as the solvent, with alcohols
IV and V only the hydroxyphosphino complexes [RuH(arene)
(P,O)]Cl were observed and these did not react further to the
hydridoꢀcarbonyl complexes.
Structural Characterization of the New Derivatives. The
structural characterization of the products was carried out by
elemental analysis, IR spectroscopy, mass spectrometry (some
derivatives), and 31P{1H}, 1H, and 13C{1H} NMR spectroscopy.
X-ray diffraction studies were carried out on 5 and 7BPh4.
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Scheme 3
is present at a level of approximately 40%. Compound 11Cl was
selected for further mechanistic studies, and its spectrum was
therefore analyzed in more detail. According to a COSY experi-
ment, all proton signals fall into two groups assigned to complex
11Cl and the novel derivative 11Cl0. In the case of 11Cl (about
60%) all the signals of the CHMeOH group are shifted downfield
with respect to those in the free ligand (see, for example, the OH
resonance: 2.94 ppm for IV and 10.23 ppm for 11Cl). In addition,
a difference of about 0.8 ppm is observed for the ortho phenyl
resonances of both phenyl rings. However, for 11Cl0 the behavior
is different: the ortho phenyl protons appear to be very similar,
while the CH(Me) resonances are shifted to higher field (the OH
resonance was not observed). In addition, in the solvent used
(acetone-d6) the resonances of 11Cl and 11BF4 are very similar.
Onthe basisof these results, wepropose that 11Cland 11Cl0 differ
in the way in which the ligand and the chlorides are coordinated to
ruthenium, with 11Cl being a cationic chelate complex and 11Cl0
being a neutral ruthenium dichloride complex with the ferrocene
ligand coordinated in a monodentate fashion (Scheme 3). When
this sample (measured in acetone-d6) was evaporated to dryness
and then redissolved in methanol-d4, a single product was
observed. This observation shows the reversibility of this process,
the hemilability of the ligand, and also the influence of the solvent
in this type of ligand coordination. The spectral differences are
clearly caused by the fact that methanol is more prone to dissociate
chloride from the metal center than acetone.
Figure 1. ORTEP representation of the cation of complex 5. Ellipsoids
are given at the 40% probability level.
NOE or NOESY spectra allowed the determination of the
structures of the respective major diastereomers as well as the R
configuration at ruthenium for all complexes of the amino-
phosphine ligands. When the minor isomer was present in a
reasonable amount along with the major isomer, a magnetization
transfer between the resonances of the two isomers was ob-
served. This finding is consistent with a diastereomer intercon-
version process taking place in solution (for further details see the
Supporting Information).
Molecular Structures of 5 and 7BPh4. The molecular struc-
tures of complexes 5 and 7BPh4 were determined by X-ray
diffraction (the X-ray crystallographic data and bond distances
and bond angles are given in the Supporting Information). Both
derivatives have a three-legged piano-stool structure. The corre-
sponding ORTEP diagrams are displayed in Figures 1 and 2.
As mentioned previously, two diastereomers were observed in
solution for complex 5. However, in the solid state only one
diastereomer was formed and the molecular structure of this
corresponds to the major isomer in solution (RRu). In addition to
benzene, a chloride and the N,P-bidentate ferrocenyl ligand are
coordinated to ruthenium. Together with the metal, the ferroce-
nyl ligand forms a chelate ring that adopts a distorted twist
conformation.
Figure 2. ORTEP representation of the cation of complex 7BPh4.
Ellipsoids are given at the 40% probability level.
As in complex 5, the ferrocenyl unit acts as a bidentate ligand and
coordinates through its phosphino phosphorus P1 and the ketone
oxygen O1 to the metal. Interestingly, the hydride hydrogen H1
could be located in the electron density map and, with respect to
the chelate ring, it is located in a pseudoaxial position with the
bond Ru1ꢀH1 pointing toward uncoordinated CP ring. The six-
membered chelate ring adopts a half-chair conformation, with the
atoms P1, C8, C4, C2, and O1 lying almost in the mean Cp plane
defined by atoms C4ꢀC8. Only Ru1 is positioned significantly
below that plane (0.47 Å). The CꢀO distance was found to be
1.246 Å, a value in accordance with the presence of a carbonꢀ
oxygen double bond.
It is worth mentioning that inꢀcomplex 7BPh4 the p-cymene
and one phenyl ring of the BPh4 anion show a πꢀπ stacking
interaction27 (centroidꢀcentroid distance, 4.09 Å; centroidꢀ
least-squares plane distance, 3.28 and 3.50 Å; angle R between the
planes, 9.4ꢀ). In the case of complex 5, a similar—but less
pronounced—interaction between the ruthenium-coordinated ben-
zene and one phenyl ring of the anion was also observed.
In the racemic complex 7BPh4, the p-cymene unit, the
ferrocenyl ligand, and one hydride are coordinated to ruthenium.
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Mechanistic Studies. In an effort to gain an insight into the
transformation of chloroꢀalcohol into hydridoꢀcarbonyl com-
plexes, the evolution of 11Cl into 7Cl (and in some cases of
11BF4 into 7BF4) was investigated in more detail by 1H NMR
spectroscopy. Product distributions were analyzed, and rate
constants were calculated. On the basis of the resulting data, a
mechanism is proposed that describes the formation of the
hydridoꢀcarbonyl complexes and an additional product, 15Cl
(see below).
Initially the dependence of the concentration of the hydro-
xyphosphine complex 11Cl on the hydride formation (7Cl) was
studied. The evolution of 1.85 ꢁ 10ꢀ3, 1.29 ꢁ 10ꢀ2, and 1.72 ꢁ
10ꢀ2 M solutions of 11Cl in methanol-d4 (referred to as low,
1
intermediate, and high concentration) was monitored by H
Table 2. Ratios of 11X, 15Cl, and 7X Obtained at 1.25 and
15 h in Different Experiments Monitoring the Evolution of
11Cl or 11BF4 in CD3OD (Runs 1ꢀ11) or CH3OH (Runs 12
and 13) at 22.6 ꢀC by 1H or 31P{1H} NMRa
NMR. The product distributions (%) recorded after 1.25 and 15
h for the different experiments are gathered in Table 2.
At low concentration (run 1) only the hydride 7Cl is formed
and after 15 h this coexists with the starting material 11Cl in a
66:34 ratio. For a graphical representation see Figure 3a. How-
ever, at high concentration (run 3) the hydride 7Cl is present
only in a very minor amount (7%) while a new product 15Cl
(32%) is formed. This derivative was identified as a phosphinoꢀ
ether ruthenium complex (Scheme 5; for a discussion see below).
At an intermediate concentration (run 2) both species 7Cl and
15Cl are formed in 11% and 23% amounts, respectively
(Figure 3b). At this concentration the evolution with time of
7Cl and 15Cl is clearly different (compare the data for reaction
times 1.5 and 15 h and see Figure 3b and the expansion in
Figure 3c). Initially 7Cl is formed at a higher rate, but after a
certain time the rate of formation of 15Cl exceeds that of 7Cl.
Next, a kinetic analysis of the evolution of 11Cl into 7Cl was
carried out (see the Supporting Information). In order to avoid
problems caused by the formation of 15Cl, the data recorded for
the solution of low concentration were analyzed. The experi-
mental and simulated profiles of 11Cl and 7Cl are plotted in
Figure 4 along with the simulated profiles of I1 (see Scheme 5 for
the structure proposed for I1) and DCl. The program Facsimil v
4.0 was used to simulate the changes in concentration of 11Cl
and 7Cl with time, and the results were fitted to the experimental
data, leaving the rate constants as adjustable parameters. An
excellent fit was obtained for a two-step process in which both
steps were reversible. The following rate constants were
product distribn (%)
after 1.25 h
after 15 h
starting
run material concn (M) additive 11X 15Cl 7X 11X 15Cl 7X
1
2
3
4
5
6
7
8
9
11Cl
11Cl
11Cl
1.85 ꢁ 10ꢀ3
1.29 ꢁ 10ꢀ2
1.72 ꢁ 10ꢀ2
69
90
93
74
89
0
3
31 34
0
66
7
2
66
61
23 11
5
32
0
7
85
31
0
11BF4 1.85 ꢁ 10ꢀ3
0
26 15
11 69
11BF4 1.72 ꢁ 10ꢀ2
0
0
11Cl
11Cl
11Cl
1.85 ꢁ 10ꢀ3 5 HClb 21
1.85 ꢁ 10ꢀ3 1 HClb 82
1.72 ꢁ 10ꢀ2 1 HClb 33
79
13
60
0
0
5
7
3
3
22
89
21
78
30
78
11
77
17
70
0
2
11BF4 1.85 ꢁ 10ꢀ3 1 HClb 97
5
10 11BF4 1.72 ꢁ 10ꢀ2 1 HClb 39
58
0
0
11 11BF4 1.72 ꢁ 10ꢀ2 1 LiClc 89
11 68
83 17
17 54
13 19
12d 11Cl
13d 11Cl
1.85 ꢁ 10ꢀ3
1.72 ꢁ 10ꢀ2
17
83
0
0
83
0
0
46
a X = Cl, BF4, depending on the starting material. b Some decomposition
is observed at 15 h. c Addition of 1 equiv of LiCl after 3 h. d In CH3OH,
monitored by 31P{1H} NMR.
Figure 3. Evolution with time at 22.6 ꢀC of an (a) 1.85 ꢁ 10ꢀ3 M and a (b) 1.29 ꢁ 10ꢀ2 M solution of 11Cl in methanol-d4 and (c) expansion of (b) for
the initial evolution of 7Cl and 15Cl.
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Scheme 4
The 1H NMR spectrum of 15Cl shows an asymmetric
p-cymene group and, as for 11Cl (see above), the methyne
hydrogen of the CHMeOCD3 group is shifted from 5 ppm in the
free ligand to 3.74 ppm in 15Cl (methanol-d4). Furthermore, a
sample of 15BF4 was synthesized and it was verified that the 1H
NMR resonances, in both methanol-d4 and in acetone-d6, were
essentially identical with those of 15Cl. Both of these findings
again point to a chelate complex in which ligand VIII acts as a
bidentate ligand.
On the basis of our experimental data and kinetic analysis, a
mechanism for the transformation of 11Cl into 7Cl and 15Cl is
proposed (Scheme 5). When 11Cl is dissolved in methanol-d4,
an H/D exchange of the hydroxyl proton is likely to take place,
thus giving 11Cl in its deuterated form (Scheme 5).
The two products 7Cl and 15Cl evolve directly from 11Cl. The
hydride 7Cl is formed in a two-step process. Initially 11Cl releases
DCl (step i), and this yields the alkoxide intermediate I1, which
could not be detected by NMR spectroscopy. However, experi-
mental evidence was provided by mass spectroscopy and the effect
of NEt3 was observed in the formation of 10BPh4. As described
above (see eq 1 in Synthesis of Ruthenium Complexes), not only is
the transformation of the chloroꢀhydroxyl complex 14BPh4
promoted by triethylamine but also the formation of the corre-
sponding ammonium salt is observed, thus proving the formation
of DCl. Furthermore, in the mass spectra of complexes 11Clꢀ14Cl
the [Mþ ꢀ DCl] peaks are observed in addition to the [Mþ] peaks
(see Structural Characterization of the New Derivatives).
In comparison to acetone, methanol is a polar solvent and this
seems to favor the release of DCl by better promoting the
dissociation of chloride from ruthenium and by better solvating
DCl. This accounts for the fact that in acetone-d6 11Cl does not
react further to the hydride complex 7Cl. In the second step, after
decoordination of the solvent molecule from the alkoxide com-
plex I1, a β-hydride elimination (step ii) can occur that generates
the hydride derivative 7Cl.
It is important to note that a number of mechanistic features
related to our proposal for the transformation of the alcohol
derivative 11Cl into the ketone 7Cl have been described
previously. In this respect, the loss of HCl, the formation of
alkoxide intermediates, and the β-hydride elimination step are
particularly significant.
For example, HCl elimination to form alkoxide derivatives has
been reported by Noyori in transfer hydrogenations that involve
areneꢀchloride ruthenium derivatives containing ethanolamine
ligands. In this particular case a base such as KOH28 is required.
Other examples of alcohol activation by external3a,d or internal
bases have been described.3c,29
Furthermore, the conversion of alcohols to aldehydes or
ketones with use of platinum metal species has been employed
extensively. In the presence of base, alkoxides are formed and
subsequent β-hydride elimination results in metal hydrides30 and
weakly coordinated aldehydes or ketones. These carbonyl deri-
vatives usually dissociate readily from the metal.
Figure 4. Experimental and simulated profiles for the evolution at
22.6 ꢀC of 11Cl into 7Cl (see Scheme 5). T = 295.6 K, [11Cl]0 = 1.85 ꢁ
10ꢀ3 M (exp = experimental, sim = simulated).
obtained: k1 = 3.48 ꢁ 10ꢀ5 sꢀ1, k2 = 5.85 Mꢀ1 sꢀ1, k3 = 2.22 ꢁ
10ꢀ3 sꢀ1, and k4 = 9.00 ꢁ 10ꢀ6 sꢀ1 (see Scheme 4). It is worth
mentioning that, according to the simulations, the concentration
of intermediate I1 should be very low throughout the whole
period of evolution and this agrees with the fact that intermediate
I1 could not be detected by NMR spectroscopy.
Overall the kinetic data for the evolution of 11Cl into 7Cl are
in accordance with a two-step process in which the step 11Cl f
I1 is significantly slower than the step I1 f 7Cl (Scheme 4).
According to the calculations, the step 11Cl f I1 is likely to be
the rate-determining step in the formation of 7Cl.
The thermal and thermodynamic activation parameters cor-
responding to step 11Cl f I1 were calculated from the values of
k1 obtained by simulation at different temperatures (from 17.1 to
37.3 ꢀC) and the values obtained were Ea = 67.1 ( 0.8 kJ/mol,
ΔHq = 64.5 ( 0.8 kJ/mol, and ΔSq = ꢀ114.9 ( 3.7 J/(mol K). In
addition, by applying the initial-rates method a first-order reac-
tion with respect to [11Cl] was deduced and it was verified that
the experimental rate constants, k0, obtained by dividing the
initial rate of reaction, v0, between [11Cl]0 were very close to
those calculated by simulation.
In addition to the evolution of 11Cl into 7Cl, the evolution of
1
11BF4 at low and high concentration was also studied by H
NMR spectroscopy (Table 2, entries 4 and 5). In both cases the
hydride 7BF4 was observed, although in neither case was a
product of type 15BF4 formed. It is worth mentioning that DCl
must be released during the transformation of 11Cl into 7Cl
while the transformation of 11BF4 into 7BF4 releases DBF4.
Identification of 15Cl. An ESI mass spectrum was recorded
for a sample containing 15Cl along with 11Cl and 7Cl (ratio
37:49:14, respectively). In addition to the peaks corresponding
to [RuH(p-cymene)(VI)]þ (see Chart 2 for ligand VI) and
[RuCl(p-cymene)(VI)]þ, which are related to hydride 7Cl and/
or 11Cl, a peak at 702 Da was assigned to 15Cl (see the
Supporting Information). In agreement with the isotope dis-
tribution, this peak corresponds to the species [RuCl-
(p-cymene)(VIII)]þ (see Chart 2 for ligand VIII). We were
surprised to find that the structure of the phosphinoꢀalcohol
complex had changed to a phosphinoꢀether derivative, and this
must be the result of a reaction between ligand IV and CD3OD
(see Scheme 5). In order to confirm this assignment, ligand VIII
was synthesized separately from the corresponding acetate and
methanol-d4. The reaction of ligand VIII with [RuCl2(p-cym-
ene)]2 gave derivative 15Cl as a pure species, and this was found
to be identical with the second product observed along with 7Cl
in the evolution of 11Cl at intermediate and high concentrations.
A reaction sequence that is closely related to that shown in
Scheme 5 has been described for catalytic dehydrogenations
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Scheme 5
(oxidant-free oxidations) of primary and secondary alcohols. In
addition, the formation of an alkoxide from an alcohol and
further evolution to a hydride has been proposed as a part of
the catalytic cycles of aerobic catalytic oxidation of alcohols, in
both homogeneous and heterogeneous systems.31
Furthermore, in an elegant mechanistic study of the catalytic
racemization of secondary alcohols with ruthenium derivatives,
B€ackvall demonstrated that the alkoxide formed from the corre-
sponding alcohol suffers a β-hydride elimination to give a hydrideꢀ
ketone intermediate. Although this species was not detected, it
was concluded that the ketone remains coordinated to the
ruthenium center.32
The chloroꢀether complex 15Cl is formed reversibly from
11Cl. Reversibility is evidenced by the fact that a magnetization
transfer was observed between the two complexes by 1H NMR
spectroscopy. In addition, it was found that the formation of
15Cl requires the presence of acid as well as chloride.
All of these data are in agreement with the view that HCl or DCl
participates in one step of the formation of 15Cl.
As pointed out above, solutions of 11BF4 in methanol-d4 do
form the hydride complex 7BF4 but, unlike 11Cl, this does not
evolve to products such as 15BF4. However, when 1 equiv of LiCl
was added to a concentrated solution of 11BF4 (after 3 h of
evolution), the formation of the chloroꢀether derivative was
detected instantaneously. Furthermore, to solutions of 11BF4 at
both high and low concentrations was added 1 equiv of HCl (runs
9 and10). Inboth cases the rutheniumꢀether complex was formed
and the amount of hydride was reduced. From these data we
conclude that the formation of 15Cl requires not only the presence
of acid but also the presence of a significant amount of chloride.
Although it was not detected duringthe evolution processby NMR
spectroscopy, the formation of a ruthenium dichloride complex of
the type 11Cl0 seems to be likely. For some experimental evidence
see Scheme 3 and Synthesis of Ruthenium Complexes. It should
also be mentioned that, under comparable conditions, 11BF4
always evolves more quickly to the hydride complex than does
11Cl (runs 1 and 4 vs runs 3 and 5, reaction time 15 h).
For the formation of 15Cl from 11Cl a reversible four-step
sequence is proposed. In the presence of chloride 11Cl is
transformed into the neutral ruthenium dichloride complex
11Cl0 (Scheme 5, step iii). On addition of chloride the hydroxyl
oxygen is decoordinated from ruthenium and is subsequently
prone to deuteration by DCl (step iv), which itself is released
during the formation of intermediate I1 (step i). In the next step,
a nucleophilic substitution of D2O by CD3OD takes place. After
release of DCl (step v) 15Cl0 is formed and in the last step this
evolves further to 15Cl (step vi). Overall, this reaction sequence
is catalytic in Dþ.
The influence of the concentration of Hþ or Dþ on the
formation of 15Cl was analyzed by 1H NMR spectroscopy. To
solutions of 11Cl in methanol-d4 was added HCl and the
evolution of the product with time was recorded (see Table 2;
only the data recorded after 1.25 h were used for the analysis,
since longer reaction times led to decomposition products). At a
low concentration of 11Cl, the addition of 1 equiv of HCl
(compare runs 1 and 7) leads to the formation of 15Cl (13% at
1.25 h) and at the same time the amount of hydride 7Cl is
reduced. The effect is much more pronounced when 5 equiv of
HCl is added (runs 1 and 6). In this case 79% of 15Cl is observed
but 7Cl is absent. Similarly, the addition of 1 equiv of HCl to a
concentrated solution of 11Cl (runs 3 and 8) leads to signifi-
cantly more 15Cl than do reactions in the absence of added HCl.
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Table 3. Data for the Catalytic Tests for the Acetophenone
Hydrogenation at 85 ꢀC in 10 mL of 2-Propanol with 2 mmol
of Substrate and 0.002 mmol of Precatalyst
Chart 3
ee of R
time
(h)
KOH:
precat.
yield
(%)
alcohol
(%)
TOFa
TON (hꢀ1
run precat.
)
1
2
3
4
5
6
7
1
2
3
1
1
1
1
2
2
200
200
200
1000
100
10
89
59
84
90
55
50
9
38
27
17
34
18
5
890
590
840
900
550
500
90
445
295
420
450
79
2
2
When the precatalyst to base ratio was reduced to 1:100 or 1:10,
both the ee values and the product yield dropped significantly
(runs 5 and 6) and longer reaction times were required. In the
absence of base and with a reaction time of 24 h, only 9% of the
product was obtained and this was almost racemic.
7
24
24
21
0
1
4
a TOF calculated at the end of the specified time.
Several studies were performed to gain an insight into the
mechanism of the catalytic process. In order to differentiate
between a mono- and a dihydride mechanism, the reaction of
acetophenone using complex 1 was carried out with (CH3)2-
CHOD. A monohydride mechanism should lead to a selective
transfer of deuterium to the oxygen atom of the product
[PhCH(OD)CH3], while in a dihydride mechanism the deuterium
would be scrambled between the benzylic carbon and oxygen.35
Deuterium (eq 2) was selectively transferred to the product oxygen
atom, and so a monohydride mechanism is proposed. Considering
this fact and the presence of NH groups in all three precatalyst
ligands, a metalꢀligand bifunctional catalysis or an outer-sphere
mechanism—as proposed by Noyori—might be assumed. In an
effort to obtain more information, we replaced the NH2 group of
ligand I by an NMe2 group (2-PPh2-1-MeCH(NMe2)-Fc, PPFA)
(Chart 3). The complex [RuCl(p-cymene)(PPFA)]BPh4 was
prepared and tested in the transfer hydrogenation of acetophenone.
A similar complex, [RuCl(p-cymene)(PPFA)]CF3SO3, had been
tested previously in asymmetric transfer hydrogenations of various
ketones.36 In these cases, only moderate activity and no product
enantioselectivity was found. A catalytic test reaction was carried
out using [RuCl(p-cymene)(PPFA)]BPh4 as the precatalyst and
acetophenone as the substrate (standard conditions, reaction time
2 h, substrate to precatalyst to base ratio of 1000:1:200). In this case
the product yield did not exceed 20%. This yield is clearly lower
than those obtained with complexes 1ꢀ3. Furthermore, in this case
only racemic product was obtained. Although this precatalyst
shows some activity, the strong reduction in yield reflects the
importance of the NH group and points to a Noyori mechanism, at
least as the main route in the cases of derivatives 1ꢀ3.
In order to evaluate a possible isotope effect, the evolution of
11Cl in CH3OH instead of CD3OD was monitored by 31P{1H}
NMR spectroscopy at 22.6 ꢀC. At low concentration 11Cl in
CH3OH evolved to hydride 7Cl significantly more quickly than
in methanol-d4 (Table 2, runs 1 and 12). This effect was even
stronger for a solution of high concentration (runs 3 and 13),
because in this case only the hydride 7Cl (not 15Cl) was
obtained. In comparison to CD3OD, the rate of formation of
7Cl in CH3OH is increased while that of 15Cl is decreased. The
increase in the rate of formation of 7Cl is probably the result of an
increased rate of formation of intermediate I1, with HCl being
released more rapidly than DCl.
Catalytic Transfer Hydrogenation of Acetophenone. Pre-
liminary transfer hydrogenations of acetophenone were per-
formed using 2-propanol as the hydrogen source and
complexes 1ꢀ3 as the precatalysts. The asymmetric transfer
hydrogenation of prochiral ketones is considered to be an
attractive and mild method for the preparation of enantiomeri-
cally enriched secondary alcohols, which constitute an important
class of intermediates for fine chemicals and pharmaceuticals.7,33
The precatalysts 1ꢀ3 (of the type [RuCl(p-cymene)-
(P,N)]BPh4) contain P,N ligands that differ only in the substitu-
tion pattern of the amino group (NH2, NHMe, NHEt). Initial
tests were carried out in the presence of KOH as the base with a
substrate to precatalyst to base ratio of 1000:1:200. In each case,
the only product obtained was 1-phenyl-1-ethanol. The results
obtained for different catalysts and reaction conditions are given
in Table 3. Complexes 1 and 3 were found to be quite active, and
after a reaction time of 2 h good yields of product were obtained.
In general, only moderate ee values could be achieved and
derivative 1 gave the best results (38%). Interestingly, the
enantioselectivity was found to depend on the substitution
pattern of the amino group. An increase in the size of the amino
substituent led to a drop in the ee value (compare runs 1ꢀ3).
The evolution of yield and ee were followed with time (see the
Supporting Information). As frequently encountered, the pro-
duct yield increased with time, while a reduction in ee with time
was observed. This drop in enantioselectivity is likely to be
caused by the presence of excess base in conjunction with a
higher reaction temperature.
’ CONCLUSIONS
Novel arene ruthenium chelate complexes of three chiral
nonracemic ferrocenyl aminophosphine and two racemic hydro-
xyphosphine ligands were synthesized. In all cases the ferrocene
ligands were found to be coordinated to ruthenium in a bidentate
fashion. On complexation of the ferrocenyl ligands, the ruthe-
nium atom is transformed into a stereogenic center. In some
cases, both possible diastereomers are formed. For all ligands that
have an R,Sp configuration, a clear preference for the R
In addition, precatalyst 1 was used to study the influence of the
amount of base (Table 3, compare runs 1 and 4ꢀ7). When the
precatalyst to base ratio was changed from 1:200 to 1:1000
(run 4), the product yield was almost unaffected but, as expected
from literature data,34 a reduction in the ee value was observed.
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configuration at Ru is seen. Interconversion between the corre-
sponding diastereomers was observed in solution.
Chart 4
In the case of the hydroxyphosphine ligands, when the
reaction was performed in the presence of NaBPh4, the forma-
tion of hydridoꢀketone or hydridoꢀaldehyde complexes oc-
curred and in all cases the carbonyl group was coordinated to the
metal center. This process is favored by the addition of a base
such as NEt3 and by electron-donating arene ligands.
The transformation of the ruthenium hydroxyphosphine
complex [RuCl(p-cymene)(IV)]Cl (11Cl) into the correspond-
ing hydride derivative [RuH(p-cymene)(VI)]Cl (7Cl) was
studied in detail. This process proceeded easily when metha-
nol-d4 was used as the solvent but did not take place in acetone-d6.
When the evolution of a dilute solution of 11Cl was monitored
by 1H NMR spectroscopy in methanol-d4, only the formation of
the hydridoꢀketone complex 7Cl was observed. At higher
concentration a second product, 15Cl, was also formed. Com-
plex 15Cl contained a coordinated phosphinoꢀether ligand,
which was found to be the result of a reaction between the
hydroxyphosphino ligand of complex 11Cl and the solvent
CD3OD. This reaction requires an acidic medium as well as
the presence of chloride. In this particular case, DCl is released
when 11Cl transforms into 7Cl. Generally, the addition of HCl
favors the formation of 15Cl and disfavors formation of the
hydride complex. A pronounced kinetic isotope effect was found
when CD3OD was replaced by CH3OH as the solvent. CH3OH
strongly favored the formation of the hydride complex and even
reversed the course of the reaction. A mechanism is proposed for
the evolution of 11Cl into 7Cl and/or 15Cl. A kinetic study of
the transformation 11Cl f 7Cl in dilute solutions allowed the
calculation of rate constants for both of the steps involved.
Thermal and thermodynamic activation parameters for the first
step were also determined.
All of the data outlined above led to the conclusion that the
course of the evolution of 11Cl can be controlled by the reaction
conditions used, in the sense that the formation of the hydride is
favored by the presence of CH3OH, dilute solutions, counter-
anions such as BF4ꢀ and BPh4ꢀ, and a basic medium. Our results
also stress that for these types of transformations methanol is a
noninnocent solvent.
NMR data support the view that in ruthenium arene com-
plexes hydroxyꢀphosphine and etherꢀphosphine derivatives
behave as hemilabile ligands.
Shimadzu IRPrestige-21 IR spectrometer equipped with a Pike Tech-
nologies ATR. The FABþ mass spectrometry measurements were made
with a Thermo MAT95XP mass spectrophotometer with magnetic
sector. The ESI mass spectra were recorded with a Bruker MICRO-
TOF-Q instrument. The optical rotations were measured with a JASCO
P-2000 polarimeter in acetone and a Perkin-Elmer 241 polarimeter. 1H
and 13C{1H} NMR spectra were recorded on Varian Innova 500 and
Varian Unity 400 and 300 MHz spectrometers. Chemical shifts (ppm)
are relative to TMS (1H, 13C NMR) or H3PO4/85% (31P). The
1
numbering scheme is reflected in Chart 4. 1Hꢀ H COSY spectra:
standard pulse sequence with an acquisition time of 0.214 s, pulse width
1
13
10 ms, relaxation delay 1 s, 16 scans, 512 increments. For Hꢀ C
g-HMBC and g-HMQC spectra the standard Varian pulse sequences
were used (VNMR 6.1 C software). The spectra were acquired using
7996 Hz (1H) and 25 133.5 Hz (13C) widths; 16 transients of 2048 data
points were collected for each of the 256 increments. NOESY spectra
were acquired using 8000 Hz width, and 16 transients of 2048 data
points were collected for each of the 256 increments, with a pulse time of
1 s and mixing time of 1 s. For variable-temperature spectra, the probe
temperature ((0.1 K) was controlled by a standard unit calibrated with a
methanol reference. In the NMR analysis s, d, t, q, sept, m, and bs denote
singlet, doublet, triplet, quartet, septuplet, multiplet, and broad signal,
respectively. o, m, and p stand for ortho, meta, and para. Phu is the phenyl
group up, and Phd is the phenyl group down (see Chart 4). Unless
otherwise stated, the 13C{1H} NMR signals are singlets. Signals assigned
to the BPh4ꢀ counteranion are not included in the NMR description and
are as follows for all the complexes. 1H NMR (acetone-d6): 6.79 (t, 4H, p-
Ph, J = 7.1 Hz), 6.93 (t, 8H, m-Ph, J = 7.3 Hz), 7.35 (bs, 8H, o-Ph) ppm.
13C{1H} NMR (acetone-d6): 121.59 (p-Ph), 125.32 (m-Ph), 136.41 (o-
Ph), 164.32 (m, Cipso Ph, JCꢀB = 49.4 Hz) ppm. The ligands I,9 II,8 III,10
IV,18 and V19 were prepared according to the methods described in the
literature. The starting materials [RuCl2(p-cymene)]2,37 [RuCl2-
(C6H6)]2,37 and [RuCl2(C6H6)(CH3CN)]38 were prepared according
to literature procedures. NaBPh4 was used as purchased from Aldrich.
The synthesis and characterization data of some derivatives are
included in this section. Those of complexes 2ꢀ6, 8BPh4ꢀ10BPh4,
and 12Clꢀ14Cl are gathered in the Supporting Information.
In addition, the formation of 15Cl indicates that great care
must be taken when working with ligands that contain an alcohol
functionality and when an acidic medium is generated during the
course of a reaction.
Preliminary catalytic transfer hydrogenations of acetophenone
have been carried out with p-cymene complexes that contain the
aminophosphine ligands. These precatalysts gave high conver-
sions but only moderate product ee values. The best results were
obtained with the primary aminophosphine ligand. The catalysts
applied follow a monohydride mechanism, which is most likely to
be of the outer-sphere type.
Preparation of [RuCl(p-cymene)((R,Sp)-I)][BPh4] (1). [RuCl2-
(p-cymene)]2 (40.0 mg, 0.06 mmol) and the corresponding enantiopure
ligand (R,SP)-I (53.7 mg, 0.13 mmol) were mixed in 5 mL of methanol.
After the mixture was stirred for 8 h, a solution of 5 mL of NaBPh4
(60.0 mg, 0.20 mmol) in methanol was added to the initial reddish
orange solution. After 16 h of stirring at room temperature, three-fourths
of the volume of solvent was evaporated. The yellow solid obtained was
then filtered off and dried under vacuum. It was recrystallized from
dichloromethane/diethyl ether. Yield: 118.7 mg, 91%. Anal. Calcd for
C58H58BClFeNPRu CH2Cl2: C, 65.12; H, 5.56; N, 1.29. Found: C,
3
65.07; H, 5.52; N, 1.30. Diastereomer RRu: 1H NMR (acetone-d6, 500
MHz, 298 K) 1.14 (d, 3H, MeiPr(p-cym), J = 6.8 Hz), 1.24 (d, 3H,
’ EXPERIMENTAL SECTION
0
General Considerations. All manipulations were carried out
under an atmosphere of dry oxygen-free nitrogen using standard Schlenk
techniques. Solvents were distilled from the appropriate drying agents
and degassed before use. Elemental analyses were performed with a
Thermo Quest FlashEA 1112 microanalyzer and IR spectra on a
MeiPr (p-cym), J = 6.9 Hz), 1.52 (d, 3H, MeC*, J = 6.5 Hz), 1.58 (s, 3H,
MeTol(p-cym)), 2.69 (sept, 1H, CHiPr(p-cym)), 3.85 (s, 5H, Cp0), 4.47
(bs, 2H, H4þ5(Cp)), 4.73 (s, 1H, H3(Cp)), 4.80 (t, 1H, NH, JHꢀH
JHꢀP = 6.4 Hz), 4.90 (q, 1H, HC*), 5.20 (d, 1H, H3 (p-cym),
J = 5.5 Hz), 5.42 (d, 1H, H2(p-cym), J = 5.7 Hz), 5.56 (bd, 1H, NH,
≈
0
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0
J = 6.4 Hz), 5.84 (d, 1H, H2 (p-cym), J = 5.9 Hz), 5.89 (d, 1H, H3(p-cym),
J = 5.9 Hz), 7.25 (t, 2H, o-PPhu, JHꢀH ≈ JHꢀP = 7.9 Hz), 7.42 (m, 3H,
mþp-PPhu), 7.68 (m, 3H, mþp-PPhd), 8.36 (dd, 2H, o-PPhd, J = 10.9/7.9
Hz) ppm; 13C{1H} NMR (acetone-d6, 125 MHz, 298 K): 16.12 (MeTol(p-
ligand IV (53.8 mg, 0.13 mmol) were mixed in 5 mL of methanol. The
mixture was stirred for 30 min to completely dissolve the starting
material. The solvent was evaporated to dryness to yield a dark reddish
oil, which was triturated with diethyl ether (5 mL) under ultrasound for
10 min. The solvent was evaporated to half-volume, and the resulting
solid was filtered off. Complex 11Cl was obtained as a dark orange solid
by crystallization from acetone/diethyl ether. Yield: 39.3 mg, 42%. Anal.
Calcd for C34H37Cl2FeOPRu: C, 56.68; H, 5.18. Found: C, 56.60; H,
5.10. Diastereomer RRu: 1H NMR (methanol-d4, 500 MHz, 298 K) 1.15
0
cym)), 20.54 (MeiPr(p-cym)), 21.89 (MeC*), 22.62 (MeiPr (p-cym)), 30.34
(CHiPr(p-cym)), 44.67 (C*), 70.02 (d, C3(Cp), JCꢀP = 8.3 Hz), 70.31 (d,
C4(Cp), JCꢀP = 6.2 Hz), 70.43 (C5(Cp)), 71.12 (Cp0), 84.04 (Cꢀ(p-
2
0
cym)), 88.83 (C3(p-cym)), 89.33 (C2(p-cym)), 93.43 (C3 (p-cym)), 95.42
(d, C1(Cp), JCꢀP = 16.9 Hz), 98.52 (C2(Cp)), 128.17 (d, m-PPhd, JCꢀP
11.0 Hz), 128.55 (d, m-PPhu, JCꢀP = 10.0 Hz), 130.32 (d, p-PPhu, JCꢀP
=
=
0
(d, 3H, MeiPr (p-cym), J = 6.9 Hz), 1.27 (d, 3H, MeiPr(p-cym), J = 6.9
2.4 Hz), 131.68 (d, p-PPhd, JCꢀP = 2.6 Hz), 132.17 (d, o-PPhu, JCꢀP = 9.5
Hz), 1.57 (d, 3H, MeC*, J = 6.7 Hz), 1.77 (s, 3H, MeTol(p-cym)), 2.49
(sept, 1H, CHiPr(p-cym), J = 7.0 Hz), 3.76 (s, 5H, Cp0), 4.40 (m, 1H,
H5(Cp)), 4.42 (t, 1H, H4(Cp), J = 2.6 Hz), 4.65 (s, 1H, H3(Cp)), 5.06
Hz), 132.78 (d, Cipso-PPhu/d, JCꢀP = 54.7 Hz), 136.08 (d, o-PPhd, JCꢀP
=
11.0 Hz), 141.33 (d, Cipso-PPhu/d, JCꢀP = 52.2 Hz) ppm; 31P{1H} NMR
(acetone-d6, 121.4 MHz, 298 K) 25.94 ppm. Diastereomer SRu: 1H NMR
(acetone-d6, 500 MHz, 298 K) 0.92 (d, 3H, MeiPr(p-cym), J = 5.8 Hz), 1.02
0
(d, 1H, H3(p-cym), J = 5.7 Hz), 5.12 (d, 1H, H2 (p-cym), J = 6.0 Hz),
5.58 (d, 1H, H2(p-cym), J = 6.2 Hz), 5.73 (q, 1H, HC*), 5.88 (d, 1H,
0
0
(d, 3H, MeiPr (p-cym), J = 7.3 Hz), 1.79 (d, 3H, MeC*, J = 6.4 Hz), 1.94 (s,
H3 (p-cym), J = 5.3 Hz), 7.24 (m, 2H, o-PPhu), 7.47 (m, 3H, mþp-
3H, MeTol(p-cym)), 2.25 (sept, 1H, CHiPr(p-cym)), 4.05 (s, 5H, Cp0),
4.37/4.58 (3H, H3þ4þ5(Cp)), 5.52, 5.71, 5.93, and 6.07 (d, 4H, H(p-
cym)), 7.35 (bs, 8H, o-PPh(BPh4)), 7.58 and 7.75 (m, m/p-6H, PPhu/d),
8.02 and 8.08 (t, 4H, o-Phu/d, JHꢀH ≈ JHꢀP = 3.9 Hz) ppm; 13C-
{1H}NMR (acetone-d6, 125 MHz, 298 K) 17.03 (MeTol(p-cym)), 21.30
PPhu), 7.68 (m, 2H, m-PPhd), 7.72 (m, 1H, p-PPhd), 8.28 (m, 2H, o-
PPhd) ppm; 13C{1H} NMR (methanol-d4, 125 MHz, 298 K) 16.45
(MeTol(p-cym)), 19.05 (MeC*), 20.86 (MeiPr (p-cym)), 20.98 (MeiPr(p-
cym)), 30.60 (CHiPr(p-cym)), 65.00 (C*), 69.78 (C3(Cp)), 70.96
(C5(Cp)), 70.97 (Cp ), 74.59 (C4(Cp)), 86.10 (d, C3 (p-cym), JCꢀP
= 3.9 Hz), 86.80 (d, C3(p-cym), JCꢀP = 5.9 Hz), 90.80 (Cꢀ(p-cym)),
0
0
0
0
(MeiPr(p-cym)), 21.44 (MeC*), 21.60 (MeiPr (p-cym)), 30.34 (CHiPr(p-
2
cym)), 52.99 (C*), 121.59 (p-Ph(BPh4)), 125.32 (m-Ph(BPh4)), 136.41
(o-Ph(BPh4)), 164.32 (m, Cipso-Ph(BPh4), JCꢀB= 49.4 Hz) ppm;
31P{1H} NMR (acetone-d6, 121.4 MHz, 298 K) 33.17 ppm. IR: 3277
(ν(NꢀH)), 3055 (ν(CaromꢀH)), 2981 (ν(CalkꢀH)), 1573
(δ(NꢀH)), 1479 (δ(CaromꢀH)), 1427 (δ(CaromꢀH)), 1151
90.00 (d, C2(p-cym), JCꢀP = 3.5 Hz), 127.50 (d, m-PPhu, JCꢀP = 10.5
Hz), 128.00 (d, m-PPhd, JCꢀP = 11.0 Hz), 128.10 (d, p-PPhd, JCꢀP = 10.1
Hz), 130.20 (p-PPhu), 132.00 (d, o-PPhu, JCꢀP = 9.5 Hz), 136.25 (d, o-
PPhd, JCꢀP = 11.1 Hz) ppm; 31P{1H} NMR (methanol-d4, 161.8 MHz,
1
298 K) 22.24 ppm. Diastereomer SRu: H NMR (methanol-d4, 500
25
(δ(CCpꢀH)), 1030 (ν(CꢀP)), 835 (δ(CaromꢀH)) cmꢀ1. [R]D
MHz, 298 K) 1.02 (d, 3H, MeiPr (p-cym), J = 7.0 Hz), 1.06 (d, 3H,
0
(0.5 g/100 mL; acetone) = ꢀ130.0ꢀ.
MeiPr(p-cym), J = 7.0 Hz), 1.61 (d, 3H, MeC*, J = 6.3 Hz) ppm. 11Cl: 1H
0
Preparation of [RuH(p-cymene)(VI)][BPh4] (7BPh4). [RuCl2-
(p-cymene)]2 (40.0 mg, 0.06 mmol) and the corresponding racemic
ligand (R,Sp and S,Rp) IV (53.8 mg, 0.13 mmol) were mixed in 5 mL of
methanol. After 8 h of stirring, a solution of NaBPh4 (60.0 mg, 0.20
mmol) in 5 mL of methanol was added to the initial intensely red
solution. A red solid started to precipitate instantly, and the mixture was
stirred for 24 h for the complete precipitation. After this time, the solvent
was evaporated to half-volume under vacuum, and the resulting solid was
NMR (acetone-d6, 400 MHz, 298 K) 1.08 (d, 3H, MeiPr (p-cym), J = 6.8
Hz), 1.17 (d, 3H, MeiPr(p-cym), J = 7.0 Hz), 1.44 (d, 3H, MeC*, J = 6.7
Hz), 1.62 (s, 3H, MeTol(p-cym)), 2.56 (sept, 1H, CHiPr(p-cym), J = 6.0
Hz), 3.70 (s, 5H, Cp0), 5.36 (d, 1H, H3(p-cym), J = 5.7 Hz), 5.43 (d, 1H,
0
H2 (p-cym), J = 6.0 Hz), 5.58 (d, 1H, H2(p-cym), J = 6.2 Hz), 5.62 (q,
0
1H, HC*, J = 3.3 Hz), 5.95 (d, 1H, H3 (p-cym), J = 5.3 Hz), 7.22 (m, 2H,
o-PPhu), 7.37 (m, 3H, mþp-PPhu), 7.58 (m, 2H, m-PPhd), 7.62 (m, 1H,
p-PPhd1), 8.22 (m, 2H, o-PPhd), 10.22 (d, 1H, OH, J = 8.6 Hz) ppm.
11Cl0: H NMR (acetone-d6, 400 MHz, 298 K) 0.91 (d, 3H, MeiPr (p-
0
filtered off. Yield: 52.6 mg, 45%. Anal. Calcd for C58H56BFeOPRu
3
MeOH: C, 70.88; H, 6.05. Found: C, 70.63; H, 5.96. 1H NMR (acetone-
cym), J = 6.5 Hz), 1.07 (d, 3H, MeiPr(p-cym), J = 6.1 Hz), 1.23 (d, 3H,
MeC*, J = 6.7 Hz), 1.64 (s, 3H, MeTol(p-cym)), 4.25 (s, 5H, Cp0), 3.55
(q, 1H, HC*, J = 3.5 Hz), 8.50 (m, 2H, o-PPhu), 8.38 (m, 2H, o-PPhd),
7.45ꢀ7.65 (m, 6H, mþp-PPhu/d) ppm; 31P{1H} NMR (methanol-d4,
161.8 MHz, 298 K) 28.88 ppm. IR: 3406 (ν(OꢀH)), 3053 (ν(CaromꢀH)),
2965 (ν(CalkꢀH)), 1481 (δ(CaromꢀH)), 1433 (δ(CaromꢀH)), 1157
(δ(CCpꢀH)), 1024 (ν(CꢀP)), 822 (δ(CaromꢀH)) cmꢀ1. MS (FAB)þ:
m/z (%) 649 (100) [M ꢀ Cl2H]þ.
d6, 500 MHz, 298 K): ꢀ7.01 (d, 1H, RuꢀH, JHꢀP = 45.4 Hz), 1.23 (d,
0
3H, MeiPr(p-cym), J = 6.9 Hz), 1.24 (d, 3H, MeiPr (p-cym), J = 6.9 Hz),
1.91 (s, 3H, MeTol(p-cym)), 2.54 (sept, 1H, CHiPr(p-cym), J = 6.9 Hz),
2.57 (s, 3H, MeCO), 4.12 (s, 5H, Cp0), 4.95 (s, 1H, H5(Cp)), 5.13 (s, 1H,
0
H4(Cp)), 5.20 (d, 1H, H3(p-cym), J = 5.9 Hz), 5.42 (d, 1H, H2 (p-cym),
J = 6.1 Hz), 5.45 (d, 1H, H3(Cp), J = 6.0 Hz), 5.64 (d, 1H, H2(p-cym), J =
0
6.0 Hz), 5.79 (d, 1H, H3 (p-cym), J = 6.0 Hz), 7.20 (m, 2H, o-PPhu,
Preparation of [RuCl(p-cymene)(IV)]BF4 (11BF4). [RuCl2(p-
cymene)]2 (40.0 mg, 0.06 mmol) and the corresponding racemic ligand
IV (53.8 mg, 0.13 mmol) were mixed in 5 mL of acetone. The mixture
was stirred for 30 min to completely dissolve the starting material, and
14.5 mg of NaBF4 in 5 mL of acetone was added. The solution was
stirred for 18 h, and the solvent was evaporated to dryness, yielding a
dark reddish oil. The product was extracted into 5 mL of CH2Cl2, and
the resulting solution was evaporated to dryness to give a dark orange oil,
which was triturated with pentane (10 mL) under ultrasound for 10 min.
The solvent was evaporated to half-volume, and the resulting solid was
filtered off. Complex 11BF4 was obtained as an orange solid. Yield: 56
mg, 56%. Anal. Calcd forC34H37BClF4OPFeRu: C, 52.91; H, 4.83.
Found: C, 52.91; H, 4.80. 1H, 13C{1H}, and 31P{1H} NMR (methanol-d4)
signals are similar to those described for 11Cl. IR: 3405 (ν(OꢀH)),
3051 (ν(CaromꢀH)), 2967 (ν(CalkꢀH)), 1480 (δ(CaromꢀH)), 1425
(δ(CaromꢀH)), 1156 (δ(CCpꢀH)), 1058 (ν(BꢀF)), 1021 (ν(CꢀP)),
819 (δ(CaromꢀH)) cmꢀ1. MS (ESI)þ: m/z (%) 685 (22) [M ꢀ BF4]þ,
649 (100) [M ꢀ ClHBF4]þ.
J = 8.1 Hz), 7.47 (m, 3H, mþp-PPhu), 7.73 (m, 3H, mþp-PPhd), 8.14
(dd, 2H, o-PPhd J = 11.6/7.2 Hz) ppm. 13C{1H} NMR (acetone-d6,
125 MHz, 298 K): 18.31 (MeTol(p-cym)), 22.12 (MeiPr(p-cym)),
0
23.18 (MeiPr (p-cym)), 27.60 (MeCO), 31.44 (CHiPr(p-cym)), 70.58
(C5(Cp)), 72.43 (Cp0), 76.55 (bs, C3(Cp)), 77.88 (bs, C4(Cp)),
79.44 (d, C1(Cp), JCꢀP = 14.0 Hz), 84.84 (Cꢀ(p-cym)), 87.81 (C3(p-
2
0
cym)), 89.95 (C3 (p-cym)), 92.78 (C2(p-cym)), 102.19 (C2(Cp)),
128.46 (m-PPhd), 128.55 (d, m-PPhu, JCꢀP = 3.2 Hz), 129.74
(p-PPhu), 130.64 (d, o-PPhu, JCꢀP = 10.2 Hz), 131.95 (d, p-PPhd,
J
CꢀP = 1.7 Hz), 132.00 (d, Cipso-PPhu/d, JCꢀP = 64.2 Hz), 135.12 (d,
o-PPhd, JCꢀP = 12.9 Hz), 140.98 (d, Cipso-PPhu/d, JCꢀP = 45.2 Hz),
211.97 (CdO) ppm. 31P{1H} NMR(acetone-d6, 121.4 MHz,
298 K): 50.74 ppm. IR: 3055 (ν(CaromꢀH)), 2966 (ν(CalkꢀH)),
1959 (ν(RuꢀH)), 1581 (ν(CdO)), 1469 (δ(CaromꢀH)), 1433
(δ(CaromꢀH)), 1168 (δ(CCpꢀH)), 1031 (ν(CꢀP)), 839
(δ(CaromꢀH)) cmꢀ1
.
Preparation of [RuCl(p-cymene)(IV)]Cl (11Cl). [RuCl2-
(p-cymene)]2 (40.0 mg, 0.06 mmol) and the corresponding racemic
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dx.doi.org/10.1021/om1008132 |Organometallics 2011, 30, 3490–3503

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ARTICLE
Preparation of 1-(Diphenylphosphino)-2-(1-trideuterio-
methoxyethyl)ferrocene (VIII). This compound was prepared
analogously to the nondeuterated derivative.13,39 A solution of (R,Sp)-
2-(diphenylphosphino)-1-(1-acetoxyethyl)ferrocene (665 mg, 1.51
mmol) in CD3OD (5 mL) was refluxed for 2 h. After removal of the
solvent, the crude product was chromatographed on silica gel with 10/1
hexane/ethyl acetate as the eluent. The title compound was obtained as a
yellow powder. Yield: 519 mg, 80%. Mp: 122 ꢀC. 1H NMR (CDCl3, 400
MHz, 298 K): 1.58 (d, 3H, MeC*, J = 6.5 Hz), 3.81ꢀ3.84 (m, 1H, H3),
3.98 (s, 5H, Cp0), 4.31 (t, 1H, H4, J = 26.5 Hz), 4.49ꢀ4.52 (m, 1H, H5),
Found: C, 53.62; H, 5.15. 1H, 13C{1H}, and 31P{1H} NMR (methanol-
d4) signals are nearly identical with those described for 15Cl. IR:
3047 (ν(CaromꢀH)), 2958 (ν(CalkꢀH)), 1475 (δ(CaromꢀH)), 1435
(δ(CaromꢀH)), 1157 (δ(CCpꢀH)), 1049 (ν(BꢀF)), 1029 (ν(CꢀP)),
819 (δ(CaromꢀH)) cmꢀ1. MS (ESI)þ: m/z 702 [M ꢀ BF4] þ. [R]25
D
(10 mg/100 mL; acetone): ꢀ154ꢀ.
Mechanistic Studies in NMR Tubes. Run 1: A 1 mg portion
(0.001 39 mmol) of 11Cl was dissolved in 0.75 mL of methanol-d4 under
a N2 atmosphere. The solution was transferred to an NMR tube, and the
evolution of the reaction was monitored by 1H NMR spectroscopy over
a range of times.
4.57ꢀ4.65 (m, 1H, HC*), 7.17ꢀ7.25 (m, 5H, o-PPhA þ m-PPhA
þ
p-PPhA), 7.35ꢀ7.41 (m, 3H, m-PhB þ p-PhB), 7.54ꢀ7.62 (m, 2H, o-
PhB). 13C{1H} NMR (CDCl3, 100.6 MHz, 298 K): 18.1 (MeC*), 68.6
(d, C5, J = 4.5 Hz), 69.2 (bs, C4), 69.6 (Cp0), 71.7 (d, C3, J = 4.8 Hz),
73.5 (d, C*, J = 9.6 Hz), 127.5 (p-PPhA), 127.7 (d, 2C, m-PPhA, J = 6.4
Hz), 128.1 (d, 2C, m-PhB, J = 7.9 Hz), 129.1 (p-PhB), 132.5 (d, 2C, o-
PhA, J = 18.1 Hz), 135.3 (d, 2C, o-PhB, J = 21.4 Hz); CD3, C1, C2, ipso-
PhA, and ipso-PhB not observed. 31P{1H} NMR (100.6 MHz, CDCl3):
ꢀ21.8 (PPh2). HRMS (EI, 30 ꢀC): m/z [M þ Na]þ calcd for
C25H22D3FeOPNa 454.1079, found 454.1094. [R]20λ: ꢀ324.8ꢀ
(589 nm), ꢀ348.8ꢀ (578 nm), ꢀ454ꢀ (546 nm) (c 0.40, CHCl3).
Preparation of [RuCl(p-cymene)(VIII)]Cl (15Cl). [RuCl2-
(p-cymene)]2 (40.0 mg, 0.06 mmol) and the corresponding enantiopure
ligand VIII (56 mg, 0.13 mmol) were mixed in 5 mL of acetone. After the
mixture was stirred for 45 min to completely dissolve the starting
material, the solvent was evaporated to dryness, yielding a dark reddish
oil that was triturated with pentane (10 mL) under ultrasound for 10
min. The solvent was evaporated to half-volume, and the resulting solid
was filtered off. Complex 15Cl was obtained as an orange solid. Yield: 46
mg, 51%. Anal. Calcd for C35H36D3Cl2FeOPRu: C, 57.00; H, 5.74.
Found: C, 56.94; H, 5.60. 1H NMR (methanol-d4, 400 MHz, 298 K):
Run 2: The sample was prepared in the same way as for run 1, using 7
mg (0.009 68 mmol) of 11Cl.
Run 3: The sample was prepared in the same way as for run 1, using
9.3 mg (0.0129 mmol) of 11Cl.
Run 4: The sample was prepared in the same way as for run 1, using
1.1 mg (0.001 39 mmol) of 11BF4.
Run 5: The sample was prepared in the same way as for run 1, using 10
mg (0.0129 mmol) of 11BF4.
Run 6: A 1 mg portion (0.001 39 mmol) of 11Cl was dissolved in
0.75 mL of methanol-d4 under a N2 atmosphere. The solution was
transferred to an NMR tube. A solution of HCl (0.1 M) was prepared by
adding 8.2 μL of HCl (37%) to methanol-d4, to give a final volume of
1 mL. A 69.3 μL portion (5 equiv) of this solution was added to the
1
NMR tube. After mixing, the H NMR spectra were recorded over a
range of times.
Run 7: The sample was prepared in the same way as for run 6, but
adding 14 μL (1 equiv) of the HCl solution.
Run 8: The sample was prepared in the same way as for run 6, but
adding 9.3 mg (0.0129 mmol) of 11Cl and 129 μL (1 equiv) of the HCl
solution.
0
1.02 (d, 3H, MeiPr (p-cym), J = 7.1 Hz), 1.18 (d, 3H, MeiPr(p-cym), J =
Run 9: The sample was prepared in the same way as for run 6, but
adding 1.1 mg (0.001 39 mmol) of 11BF4 and 14 μL (1 equiv) of the
HCl solution.
Run 10: The sample was prepared in the same way as for run 6, but
adding 10 mg (0.0129 mmol) of 11BF4 and 129 μL (1 equiv) of the HCl
solution.
7.1 Hz), 1.25 (s, 3H, MeTol(p-cym)), 1.32 (d, 3H, MeC*, J = 6.5 Hz), 2.53
(sept, 1H, CHiPr(p-cym), J = 6.0 Hz), 3.75 (q, 1H, HC*, J = 6.0 Hz), 4.04
(s, 5H, Cp0), 4.65 (bs, 2H, H5þH4(Cp)), 5.06 (bs, 1H, H3(Cp)), 5.16
0
(d, 1H, H3(p-cym), J = 6.2 Hz), 5.19 (d, 1H, H2 (p-cym), J = 6.0 Hz),
0
5.36 (d, 1H, H2(p-cym), J = 6.2 Hz), 5.41 (d, 1H, H3 (p-cym), J = 5.3
Hz), 7.35ꢀ7.55 (m, 6H, mþp-PPhu/d), 7.84 (m, 2H, o-PPhu), 8.06 (m,
Run 11: A 10 mg portion (0.0129 mmol) of 11BF4 was dissolved in
0.75 mL of methanol-d4 under a N2 atmosphere. After that, 0.55 mg of
LiCl was added, the solution was transferred to an NMR tube, and the
1H NMR spectra were recorded over a range of times.
Run 12: A 1 mg portion (0.00139 mmol) of 11Cl was dissolved in
0.75 mL of CH3OH under a N2 atmosphere. The solution was
transferred to a Teflon-capped NMR tube, and a closed capillary filled
with D2O was placed inside the tube. 31P{1H} NMR spectra were
recorded.
Run 13: The sample was prepared in the same way as for run 12, using
9.3 mg (0.0129 mmol) of 11Cl.
Kinetic Studies. The program Facsimil v 4.0 was used to obtain the
rate constants (corresponding to Scheme 4) at different temperatures.
The initial-rate method was also used to determine the k1 rate
constants.
2H, o-PPhd), 13C{1H} NMR (methanol-d4, 100 MHz, 298 K): 19.96
0
(MeC*), 22.23 (MeiPr (p-cym)), 22.98 (MeiPr(p-cym)), 29.59 (MeTol(p-
cym)), 31.62 (CHiPr(p-cym)), 70.94 (C3(Cp)), 71.14 (C5(Cp)), 72.40
(Cp0), 73.72 (C*), 79.91 (d, C4(Cp), JCꢀP = 18 Hz), 87.35 (d, C3 (p-
0
cym), JCꢀP = 6.3 Hz), 87.67 (d, Cꢀ(p-cym), JCꢀP = 5.7 Hz), 90.21 (d,
2
C2(p-cym), JCꢀP = 3.6 Hz), 92.18 (d, C3(p-cym), JCꢀP = 5.6 Hz), 127.66
(d, m-PPhu/d, JCꢀP = 10.2 Hz), 128.80 (d, m-PPhu/d, JCꢀP = 10.2 Hz),
130.89 (d, p-PPhu/d, JCꢀP = 2.5 Hz), 131.59 (d, p-PPhu/d, JCꢀP = 2.7 Hz),
135.80 (d, o-PPhu, JCꢀP = 9.9 Hz), 136.91 (d, o-PPhd, JCꢀP = 9.9 Hz)
ppm. 31P{1H} NMR (acetone-d6, 161.8 MHz, 298 K): 18.33 (s) ppm.
IR: 3047 (ν(CaromꢀH)), 2958 (ν(CalkꢀH)), 1475 (δ(CaromꢀH)),
1435 (δ(CaromꢀH)), 1157 (δ(CCpꢀH)), 1029 (ν(CꢀP)), 819
(δ(CaromꢀH)) cmꢀ1. MS (ESI)þ: m/z = 702 [M ꢀ Cl]þ. [R]25
D
(10 mg/100 mL; acetone): ꢀ128ꢀ.
Preparation of [RuCl(p-cymene)(VIII)]BF4 (15BF4). [RuCl2-
(p-cymene)]2 (40.0 mg, 0.06 mmol) and the corresponding enantiopure
ligand VIII (56 mg, 0.13 mmol) were mixed in 5 mL of acetone and
stirred for 45 min to completely dissolve the starting material. After this
time, 14.5 mg of NaBF4 in 5 mL of acetone was added and the solution
was stirred for 18 h. The solvent was evaporated to dryness, yielding a
dark reddish oil. The productwasextracted with 5 mL of CH2Cl2, and the
solution obtained was evaporated to dryness, yielding a dark orange oil
that was triturated with pentane (10 mL) under ultrasound for 10 min.
The solvent was evaporated to half-volume, and the resulting solid was
filtered off. Complex 15BF4 was obtained as an orange solid. Yield: 48
mg, 50%. Anal. Calcd for C35H36D3BClF4FeOPRu: C, 53.29; H, 5.37.
Hydrogen-Transfer Catalysis. A typical procedure for the cata-
lytic hydrogen-transfer reaction under basic conditions is as follows. A
mixture of acetophenone (0.23 mL, 2 mmol), KOH (10 mL, 0.008 M in
2-propanol), and the catalyst (0.004 mmol) was heated at reflux under
nitrogen. At the desired reaction times, aliquots were extracted from the
1
reaction vessel and the yields were determined by H NMR spectros-
copy. The ee values were determined by gas chromatography using a
Varian GC 3900 gas chromatograph equipped with an automatic
injector (Varian CP 8410) and an FID detector. For the separation of
the R and S isomers of 1-phenyl-1-ethanol, a Supelco β-DEX 110
column, of 30 m length and 0.25 mm diameter, was used. Helium was
used as the carrier gas and nitrogen as the auxiliary gas, with a column
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dx.doi.org/10.1021/om1008132 |Organometallics 2011, 30, 3490–3503

Organometallics
ARTICLE
flow of 0.7 mL/min and a total flow of 18 mL/min. The injector
temperature was 210 ꢀC, and the detector temperature was 215 ꢀC. For
optimal separation of the enantiomers, an oven ramp was used, starting
at 60 ꢀC for 30 min, increasing to 125 ꢀC at a rate of 1.3 ꢀC/min, and
finally to 200 ꢀC at 30 ꢀC/min. Retention times for the products are
45.11 min for the R isomer and 46.32 min for the S isomer. All of the
catalytic reactions were run at least three times to ensure the reprodu-
cibility of the results.
X-ray Structure Determination for 5 and 7BPh4. Data were
collected on a Bruker X8 APEX 2 CCD-based diffractometer, equipped
with a graphite-monochromated Mo KR radiation source (λ = 0.710 73
Å). The crystal data, data collection, structural solution, and refinement
parameters are summarized in the Supporting Information. Data were
integrated using SAINT,40 and an absorption correction was performed
with the program SADABS.41 A successful solution by direct methods
provided most non-hydrogen atoms from the E map. The remaining
non-hydrogen atoms were located in the alternating series of least-
squares cycles and difference Fourier maps.42 All non-hydrogen atoms
were refined with anisotropic displacement coefficients unless specified
otherwise. All hydrogen atoms were included in the structure factor
calculations at idealized positions and were allowed to ride on the
neighboring atoms with relative isotropic displacement coefficients.
For compound 5, some phenyl rings in the structure are disordered
over two positions in an approximately 50:50 relation. It was not possible
to refine all atoms anisotropically, and some restraints were used. For
7BPh4 the Flack parameter has a value of 0.49(2), which corresponds to
the presence of both enantiomers.
(2) (a) Xie, J.-B.;Xie, J.-H.;Liu, X.-Y.;Kong, W.-L.;Li, S.; Zhou, Q.-L.
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’ ASSOCIATED CONTENT
S
Supporting Information. Text, tables, figures, and CIF
b
files giving details of the synthesis and characterization data for
some derivatives, NMR information and mass spectra, X-ray
crystallographic information, catalytic results, and data from the
kinetic studies. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: blanca.manzano@uclm.es.
’ ACKNOWLEDGMENT
This work was supported by the MICINN of Spain
(CTQ2008-03783/BQU) and the Junta de Comunidades de
Castilla-La Mancha-FEDER Funds (project PEII11-0214 and
contract to M.C.C. in the INCRECYT program). Professor
Mariano Laguna form the University of Zaragoza is acknowl-
edged for the recording of the mass spectra.
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(12) Hu, X.; Chen, H.; Dai, H.; Zheng, Z. Tetrahedron: Asymmetry
2003, 14, 3415–3421.
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