Cationic rhodium-BINAP complexes: Full characterization of solvate- and arene-bridged dimeric species

Article abstract of DOI:10.1021/om200486t

In the asymmetric hydrogenation promoted by rhodium-diphosphine complexes in coordinating solvents such as methanol, the solvate complex is regarded as the catalytically active species. Here, we present for the first time the X-ray structures of rhodium-diphosphine solvate complexes [Rh((S)-BINAP)(MeOH) ₂]BF₄, [Rh((R)-BINAP)(acetone)₂]BF₄, and [Rh((S)-BINAP)(THF)₂]BF₄. In noncoordinating solvents such as dichloromethane or dichlorethane hydrogenation of the diolefin in cationic precatalysts of the type [Rh(BINAP)(diolefin)]X (X = noncoordinating anion) results in the formation of the dimeric arene-bridged species [Rh(BINAP)]₂(BF₄)₂. The X-ray structure of the dinuclear species reveals that each BINAP acts as both a chelating and bridging ligand that coordinates a second unsaturated rhodium center through one of the phosphorus phenyl substituents.

Full text of DOI:10.1021/om200486t

ARTICLE
pubs.acs.org/Organometallics
Cationic Rhodium-BINAP Complexes: Full Characterization
of Solvate- and Arene-Bridged Dimeric Species
Angelika Preetz, Christian Fischer, Christina Kohrt, Hans-Joachim Drexler, Wolfgang Baumann, and
Detlef Heller*
Leibniz Institute f€ur Katalyse an der Universit€at Rostock, Albert-Einstein-Strasse 29A, D-18059 Rostock, Germany
S Supporting Information
b
ABSTRACT: In the asymmetric hydrogenation promoted by
rhodium-diphosphine complexes in coordinating solvents such
as methanol, the solvate complex is regarded as the catalytically
active species. Here, we present for the first time the X-ray
structures of rhodium-diphosphine solvate complexes [Rh((S)-
BINAP)(MeOH)2]BF4, [Rh((R)-BINAP)(acetone)2]BF4, and
[Rh((S)-BINAP)(THF)2]BF4. In noncoordinating solvents such
as dichloromethane or dichlorethane hydrogenation of the diolefin in cationic precatalysts of the type [Rh(BINAP)(diolefin)]X (X =
noncoordinating anion) results in the formation of the dimeric arene-bridged species [Rh(BINAP)]2(BF4)2. The X-ray structure of the
dinuclear species reveals that each BINAP acts as both a chelating and bridging ligand that coordinates a second unsaturated rhodium
center through one of the phosphorus phenyl substituents.
’ INTRODUCTION
Although the best results were obtained in combination with
ruthenium,13 BINAP-rhodium complexes have been successfully
applied in a variety processes, e.g., CÀC bond formation under
hydrogenative conditions4 or the [2+2+2] cycloaddition of
alkynes.5 A summary of published results obtained in asymmetric
hydrogenation catalyzed by BINAP-rhodium complexes can be
found in ref 14.
This work focuses on the characterization of several BINAP-
rhodium solvate complexes as produced in coordinating solvents,
including the first ever reported X-ray structures of this type of
complexes, and of the arene-bridged dimers arising in noncoor-
dinating solvents.
Commonly applied complexes in homogeneous catalysis are
rhodium-diphosphine systems. Cationic complexes of the type
[Rh(PP)(diolefin)]X (PP = chelating diphosphine, X = non-
coordinating anion, e.g., BF4À, ClO4À, PF6À, diolefin = (Z,Z)-
1,5-cyclooctadiene (cod), norbornadiene (nbd)) are used as
catalyst precursors to promote, among others, asymmetric
hydrogenation,1 hydroformylation,2 ring-opening of oxabicyclic
alkenes,3 CÀC bond formation under hydrogenative con-
ditions,4 [2+2+2] cycloaddition of alkynes,5 and the 1,4-addition
of organoboronic acids.6 Such complexes can be used as pre-
formed catalyst precursors, many of which are commercially
available, or prepared in situ through reaction of a diolefin
complex such as [Rh(cod)2]X (“procatalyst“) with a dipho-
sphine ligand (“cocatalyst“).7 In the latter case main advantages
are the easy handling and operational simplicity of routine
applications and the possibility to vary the ligand to metal ratio.8
However, the application of the in situ procedure in the
asymmetric hydrogenation of prochiral olefins can result in
induction periods, due to which the hydrogenation rate increases
in the beginning of the reaction.9,10 On the other hand, if the
solvate complex is used, which is formed by hydrogenation of the
diolefin in the precatalyst prior to hydrogenation of the prochiral
olefin, the reaction proceeds at the maximum rate from the very
beginning. Investigations dealing with the determination of rate
constants of diolefin hydrogenations, i.e., the transformation of
the precatalyst into the active species, have been carried out in
our group for a wide range of rhodium-diphosphine complexes.9
Nonetheless, detailed investigations into the nature of the
resulting solvate complexes are still scarce.
’ RESULTS AND DISCUSSION
Thehydrogenationof[Rh(BINAP)(cod)]BF4 or [Rh(BINAP)-
(nbd)]BF4 in methanol9a,14 results in the solvate complex
[Rh(BINAP)(MeOH)2]BF4 (1). From a concentrated solution
of [Rh(BINAP)(MeOH)2]BF4 dark red prisms suitable for
X-ray analysis were crystallized. Analysis of these highly air
sensitive crystals isolated under a film of perfluorinated oil gave
the structure of the methanol complex shown in Figure 1.
Although to the best of our knowledge only one similar solvate
complex has been isolated before,15 the X-ray structure of 1
represents the first ever reported one of a rhodium-diphosphine
complex: this species is regarded as the active catalyst in
asymmetric hydrogenation.16 Two solvent molecules are coor-
dinated to each rhodium center, in the same fashion as in
[Rh(DIPAMP)(MeOH)2]+, as shown earlier by EXFAS.17
BINAP and its derivatives are recognized as “privileged ligands”11
that have found widespread application in homogeneous catalysis.12
Received: June 7, 2011
Published: September 08, 2011
r
2011 American Chemical Society
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Encouraged by this result, we tried to isolate single crystals of
other solvate complexes and were indeed successful. Figure 2
shows the X-ray structures of solvate complexes [Rh((S)-
BINAP)(THF)2]BF4 (2) and [Rh((R)-BINAP)(acetone)2]-
BF4 (3).
Crystallographic data of crystal structures 1À3 as well as of
known diolefin complexes14 are summarized in Table 1. The
RhÀP distances are slightly shortened (by ca. 0.1 Å) in compar-
ison with those found in the parent diolefin complexÀes
[Rh(BINAP)(diolefin)]X (with diolefin = nbd, cod, X = BF4
,
OTfÀ, ClO4À), while the bite angles of the BINAP ligand lie
between those observed in the nbd and cod complexes. RhÀO
distances fall within the range of the corresponding RhÀCM
distances (CM = centroid of the double bond), given in ref 14.
Solvate complexes 1À3 surprisingly show a deviation from
the ideal square-planar coordination around the rhodium center
as defined by the angle of the two planes PÀRhÀP and OÀ
RhÀO: an average tetrahedral distortion of ca. 10° is found. Such
deviation had been observed before for a number of diolefin and
catalyst substrate complexes.1a,b,18 In[Rh((R)-BINAP)(acetone)2]-
BF4 (3) the acetone molecules coordinate end-on through the
O atoms as expected.
Figure 1. X-ray structure of [Rh((S)-BINAP)(MeOH)2]BF4 (1). The
anion BF4À and the hydrogen atoms of the ligand are omitted for clarity
(ORTEP, 30% probability ellipsoids).
In other coordinating solvents the hydrogenation of [Rh-
(BINAP)(nbd)]BF4 leads to the corresponding solvate com-
plexes, too. Table S1 (Supporting Information) summarizes their
NMR data and also lists the 103Rh NMR chemical shifts of
complexes 1À3.
The formation of such solvate complex structures, however,
cannot be translated into noncoordinating solvents. The NMR
spectra of solutions obtained by dissolving isolated crystals of
[Rh(BINAP)(MeOH)2]BF4 in CD2Cl2 or by direct hydrogena-
tion of [Rh(BINAP)(nbd)]BF4 in the same solvent are identical,
yet very different from those recorded in MeOH-d4. The experi-
mental findings (i.e., high-field protons at 5.15 and 5.25 ppm in
MeOH-d4 and additionally diagnostic protons at 4.95 and 5.40 ppm
in trifluoroethanol (TFE)) suggest the formation of a dimeric arene-
bridged species, similar to others reported before,19 although
Figure 2. X-ray structures of [Rh((S)-BINAP)(THF)2]BF4 (2) (left)
and [Rh((R)-BINAP)(acetone)2]BF4 (3) (right). The anions BF4À and
hydrogen atoms are omitted for clarity (ORTEP, 30% probability
ellipsoids).
2+ 20
2+ 21
only for [Rh(DPPE)]2
structures been unambiguously assigned by X-ray analysis.
and [Rh(DIPAMP)]2
have the
Table 1. Selected Distances [Å] and Angles [deg] for Solvate Complexes 1À3
tetrahedral
distortion
complex
RhÀP
PÀRhÀP
RhÀO
OÀRhÀO
1
2.179(1)
2.191(1)
2.177(1)
2.179(1)
2.181(2)
2.196(2)
90.9(1)
2.151(2)
2.169(2)
2.165(2)
2.187(2)
2.140(4)
2.161(4)
76.2(1)
10.7(2)
11.7(1)
9.6(2)
2
3
90.3(1)
91.4(1)
80.9(1)
78.7(2)
a
RhÀCM
CMÀRhÀCM
14
14
[Rh((R)-BINAP)-(cod)]BF4
2.318
89.6(1)
91.7(1)
88.7(1)
91.6(1)
91.8(1)
2.123À
2.145(4)
2.073À
2.084(6)
2.128À
2.130(5)
2.084À
2.107(4)
2.096À
2.113(5)
83.3(1)
7.5(1)
13.2(1)
16.8(1)
0.3(1)
14.9
2.335(2)
2.308
[Rh((R)-BINAP)-(nbd)]BF4
[Rh((R)-BINAP)-(cod)]OTf14
[Rh((R)-BINAP)-(nbd)]OTf14
68.1(1)
84.2(1)
66.5(1)
68.9(1)
2.311(2)
2.304
2.329(3)
2.319
2.325(2)
2.305
12a,b
[Rh((R)-BINAP)-(nbd)]ClO4
2.321(1)
a CM = centroid of the double bond.
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ARTICLE
2+
1
Although the complex [Rh(BINAP)]2 has been described in
the literature before, its molecular structure was not proven,12a,b
and difficulties in its synthesis were described.19e,f
By recording the 1HÀ H COSY NMR spectrum in
CF3CD2OD, the structure of the less concentrated species could
be likewise described as a phenylÀphenyl bridged dimer, Figure
S9 (Supporting Information). The correlation of the proton
signals is very similar to that found for the more abundant dimer;
therefore the two species are most probably diastereomers.
Accordingly, the chemical shifts of the two supposedly dia-
stereomeric species do not differ much on the 103Rh NMR scale
(À382 and À345 ppm), Figure S10.
Dark brown crystals were isolated from a solution of [Rh((R)-
BINAP)]2(BF4)2 (4) in dichloromethane that was layered with
diethyl ether. Single crystals suitable for X-ray analysis were
obtained by recrystallization from TFE; Figure 3 shows the X-ray
structure of 4.
In 4 each BINAP acts as a bridging ligand between two
rhodium atoms, the second unsaturated rhodium center being
coordinated through one of the phenyl rings of the ligand
The stability of dimers [Rh(DIPAMP)]2(BF4)2 and [Rh-
(BINAP)]2(BF4)2 relative to the corresponding solvate complexes
in MeOH can be easily assessed by NMR: while [Rh(DIPAMP)]2-
(BF4)2 coexists in equilibrium with the solvate complex [Rh-
(DIPAMP)(MeOH)2]BF4,21 the equilibrium between solvate
complex and dimer in the case of BINAP is entirely on the side
of the solvate complex [Rh(BINAP)(MeOH)2]BF4.23
2+
backbone, in the same fashion as in [Rh(DPPE)]2 and
[Rh(DIPAMP)]22+. In Table 2 characteristic crystallographic
data are summarized together with data of analogous arene-
bridged dinuclear rhodium diphosphine complexes.22
Average RhÀC(coordinated phenyl ring) distances are similar
among the four complexes. In 4 the RhÀRh distance is 4.498 Å
and thus ca. 0.22 and 0.35 Å longer than in the corresponding
bridged dimers of DPPE (4.277 Å) and DIPAMP (4.144 Å).21
The bite angle of BINAP in 4 (88.5À89.5) does not differ
notably from those of the parent cod complexes (Table 1).14
In 4, upon coordination to the second rhodium center through
one of their phenyl substituents, both phosphorus atoms P1 and
P3 of axially chiral BINAP become chiral. The X-ray structure
shows that both the BINAP molecules are of R-configuration.
For the interpretation of NMR patterns first the spectra in
CD2Cl2 were analyzed, showing two species in a ratio of 9:1. In
the 31P NMR spectrum the higher concentrated species exhibits
two signal sets. The low-field signal set (46.6 ppm) is split into
two multiplets, whereas the high-field signals (42.5 ppm) repre-
sent two doublets, Figure 4.
’ CONCLUSION
Solvate complexes as the catalytically active species in asym-
metric hydrogenation have been characterized for the first time
byX-rayanalysisusing[Rh(BINAP)(solvent)]+ as an example, with
MeOH, THF, and acetone as coordinating solvents. In nonpolar
solvents, such as dichloromethane and dichloroethane, but also in
trifluoroethanol, the hydrogenation of the cationic precursor
[Rh(BINAP)(nbd)]BF4 results in the formation of phenylÀphenyl
bridged dimers [Rh(BINAP)]2(BF4)2, which were characterized
both in the solid (X-ray analysis) and in solution (NMR).
’ EXPERIMENTAL SECTION
1
In the H NMR spectrum diagnostic high-field-shifted pro-
All manipulations were carried out using standard Schlenk techniques
under argon.
tons are visible (5.2 and 5.1 ppm), which belong to the phenyl
rings coordinated to a rhodium atom. The 1HÀ H COSY NMR
1
measurement confirms the phenylÀphenyl bridged structure
found in the solid state, Figure 5.
Figure 3. X-ray structure of [Rh((R)-BINAP)]2(BF4)2 (4). The anions
À
BF4 and hydrogen atoms are omitted for clarity (ORTEP, 30%
probability ellipsoids). Selected distances [Å] and angles [deg]: RhÀRh
4.498(3), RhÀP 2.231À2.246(3), PÀRhÀP 88.5À89.5(1), RhÀC
2.269À2.379(9).
Figure 4. 31P{1H} NMR spectrum of 4 in CD2Cl2. Low-field signals of
the lower concentrated species are overlapped by signals of the higher
concentrated species.
Table 2. Crystallographic Data of Arene Bridged Dimeric Diphosphine Complexes
complex
RhÀRh [Å]
RhÀP [Å]
PÀRhÀP [deg]
RhÀC [Å]
[Rh((R)-BINAP)]2(BF4)2 (4)
4.498(2)
4.275(1)
4.277(1)
4.144(1)
2.231À2.246(3)
2.230, 2.240(2)a
2.218, 2.222(2)a
2.221, 2.228(2)a
88.5, 89.5(1)
2.269À2.379(9)
2.285À2.368
2.266À2.358(5)
2.258À2.346(8)
[Rh(DPPE)]2(BF4)2 CF3CH2OH20
21
b
3
[Rh(DPPE)]2(BF4)2
84.2(1)a
84.2(1)a
21
[Rh((S,S)-DIPAMP)]2(BF4)2
a Half of the molecule had been generated from a symmetric operation. b Value was not reported.
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1
1
Figure 5. Details of the HÀ H COSY NMR spectrum of 4 in CD2Cl2. The protons of the arene bridge of the more abundant diastereomer are
encircled.
[Rh((R)-BINAP)(nbd)]BF4 and [Rh((S)-BINAP)(nbd)]BF4 were
synthesized according to ref 14. BINAP was supplied by Suzhou LAC
Co. Ltd. (www.suzhoulac.com) and used as received.
Diethyl ether and THF were distilled from sodium benzophenone
ketyl immediately prior to use. MeOH was distilled from Mg turnings
prior to use; CD3OD from LiAlH4. CH2Cl2 and CD2Cl2 were distilled
from P4O10; dichloroethane and ClCD2CD2Cl from CaH2. CF3CD2OD
and THF-d8 were stored and distilled from activated molecular sieves
and subsequently frozen and evaporated (3Â) to remove remaining
traces of oxygen.
Crystallographic Data Centre as supplementary publication nos.
CCDC-842944 for [Rh((S)-BINAP)(MeOH)2]BF4 5MeOH, CCDC-
3
842946 for [Rh((S)-BINAP)(THF)2]BF4 thf, CCDC-842947 for
3
[Rh((R)-BINAP)(acetone)2]BF4 1/2 acetone 1/2 diethyl ether, and
3
3
CCDC-842945 for [Rh((R)-BINAP)]2(BF4)2.
Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge, CB21EZ, UK (fax: int. code +
(1223) 336-033; e-mail: deposit@ccdc.cam.ac.uk.
Hydrogenation of [Rh(BINAP)(nbd)]BF4 in polar solvents leads to
the corresponding solvate complexes [Rh(BINAP)(solvent)2]BF4; see
Table S1 for 31P NMR data and Supporting Information for spectra.
Single crystals of [Rh(BINAP)(MeOH)2]BF4 (1) and [Rh(BINAP)-
(acetone)2]BF4 (3), suitable for X-ray analysis, were obtained by
hydrogenation (ca. 3 min) of 0.04 mmol of [Rh(BINAP)(nbd)]BF4
in 1 mL of the corresponding solvent and subsequent removal of
hydrogen gas from the solution by application of three freezeÀthaw
cycles. [Rh(BINAP)(THF)2]BF4 (2) was generated by hydrogenation
(ca. 3 min) of 0.005 mmol of [Rh(BINAP)(nbd)]BF4 in 1 mL of THF.
After removal of hydrogen gas, the resulting solution was layered with
diethyl ether. In all cases the solutions were allowed to stand overnight,
during which time single crystals precipitated.
NMR spectra were recorded on a Bruker ARX-400 spectrometer
(400 MHz for 1H) at 297À298 K. Chemical shifts are reported in parts
1
per million (ppm) referenced to the deuterated solvent for H NMR.
For chemical shifts in 31P NMR spectra (in ppm), 85% H3PO4 was used
as an external standard. 103Rh NMR chemical shifts (in ppm) were deter-
mined in 31PÀ103Rh HMQC measurements (under proton decoupling).
The reference frequency was determined individually for each sample
with Ξ(103Rh) = 3.16 MHz.
Crystal data and details of the structure solution are summarized in
Table S2 (Supporting Information). Diffraction data were collected on a
STOE-IPDS II diffractometer using graphite -monochromated Mo Kα
radiation. The structures were solved by direct methods (SHELXS-
97)24 and refined by full matrix least-squares techniques against F2
(SHELXL-97).24 XP (Siemens Analytical X-ray Instruments, Inc.) was
used for structure representations.
The non-hydrogen atoms, except the partially occupied atoms of the
solvents and anions, were refined anisotropically. The hydrogen atoms
were placed into theoretical positions (except the hydrogen atoms of the
OH group from the coordinated methanol in [Rh((S)-BINAP)(MeOH)2]-
1
[Rh(BINAP)(MeOH)2]BF4 (1). H NMR (CD3OD): 8.06À7.99
(4H, m); 7.79 (4H, br s); 7.59À7.53 (10H, m); 7.40À7.28 (4H, m);
7.02À6.97 (2H, m); 6.82À6.70 (6H, m); 6.51À6.48 (2H, m);
4.87 (CH3OH, s); 3.32 (CH3OH) (spectrum contains signals of
norbornane). 31P NMR (CD3OD): 55.1 (JPÀRh = 205.8 Hz). 103Rh
NMR (CD3OD): 327 (Ξ = 3.161033 MHz).
[Rh(BINAP)(THF)2]BF4 (2). The complex is poorly soluble in
THF-d8, and a minor species is also detected in solution (δ 47.7 ppm,
JPÀRh = 200 Hz). Therefore, 1H NMR data are not available. 31P NMR
(THF-d8): 54.2 (d, JPÀRh = 207.5 Hz). 103Rh NMR (THF-d8): 350 (Ξ =
3.161106 MHz).
BF4 5MeOH) and were refined by using the riding model. The weighting
3
schemes used in the last cycles of refinement are w = 1/[σ2(Fo ) +
2
(0.00.0471P)2 + 0.0000P] for [Rh((S)-BINAP)(MeOH)2]BF4 5MeOH,
3
w = 1/[σ2(Fo ) + (0.0348P)2 + 0.1294P] for [Rh((S)-BINAP)(THF)2]-
2
1
[Rh(BINAP)(acetone)2]BF4 (3). H NMR (acetone-d6): 7.89À
2
BF4 thf, w = 1/[σ2(Fo ) + (0.0884P)2 + 0.0000P] for [Rh((R)-BINAP)-
7.84 (8H, m); 7.74À7.71 (2H, m); 7.66À7.60 (4H, m); 7.54À7.51
(6H, m); 7.36À7.32 (2H, m); 7.02À6.98 (2H, m); 6.81À6.74 (6H, m);
6.44À6.41 (2H, m); 2.04 ((CH3)2CO, s) (spectrum contains signals of
norbornane). 31P NMR (acetone-d6): 53.4 (d, JPÀRh = 200.9 Hz). 103Rh
NMR (acetone-d6): 365 (Ξ = 3.161153 MHz).
3
2
(acetone)2]BF4 1/2 acetone 1/2 diethyl ether, and w = 1/[σ2(Fo ) +
3
3
(0.0120P)2 + 0.0000P] for [Rh((R)-BINAP)]2(BF4)2.
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited at the Cambridge
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ARTICLE
[Rh(BINAP)(BF4)]2 (4). [Rh(BINAP)(nbd)]BF4 (0.04 mmol) was
hydrogenated in 3 mL of MeOH. The resulting solution of [Rh-
(BINAP)(MeOH)2]BF4 was concentrated in vacuo, and the precipitate
was redissolved in 1 mL of dichloromethane and layered with 5 mL of
diethyl ether. Dark brown crystals precipitated within an hour. The
mother liquor was removed via syringe; the crystals were washed with
diethyl ether twice and dried in vacuo. Single crystals suitable for X-ray
analysis were gained from recrystallization with trifluoroethanol.
1H NMR (CD2Cl2): 8.60À8.55 (2H, m); 8.19À8.14 (2H, m); 7.65À
7.26 (34H, m); 7.14À7.01 (8H, m); 6.91À6.86 (4H, m); 6.81À6.77
(2H, m); 6.61À6.55 (2H, m); 6.47À6.45 (2H, m); 6.42À6.36 (2H, m);
6.21À6.18 (2H, m); 5.25À5.20 (2H, m); 5.13À5.09 (2H, m). 31P NMR
(CD2Cl2): 42.5 (JPÀRh = 194 Hz; JPÀP = 45 Hz); 46.6 (JPÀRh = 212 Hz;
JPÀP = 45 Hz); approximate values as the spectrum is of higher order.
103Rh NMR (CD2Cl2): À394 (Ξ = 3.158755 MHz).
investigations in asymmetric catalysis with model substrate (Z)-α-
acetamido cinnamate are carried out using catalysts prepared in situ.
(8) Reetz, M. T. Angew. Chem., Int. Ed. 2008, 47, 2556.
(9) (a) Preetz, A.; Drexler, H.-J.; Fischer, C.; Dai, Z.; B€orner, A.;
Baumann, W.; Spannenberg, A.; Thede, R.; Heller, D. Chem.—Eur. J.
2008, 1445. (b) Heller, D.; de Vries, A. H. M.; de Vries, J. G. In
Handbook of Homogeneous Hydrogenation; deVries, J. G.; Elsevier, C.,
Eds.; Wiley-VCH: Weinheim, 2007; Chapter 44, p 1483.
(10) The more or less pronounced induction periods are dependent
not only on the diolefin but also on the substrate and its concentration
(Michaelis constant), on the chiral ligand and on the solvent.
(11) Yoon, T. P.; Jacobsen, E. N. Science 2003, 299, 1691.
(12) (a) Miyashita, A.; Yasuda, A.; Takaya, H.; Toriumi, K.; Ito, T.;
Souchi, T.; Noyori, R. J. Am. Chem. Soc. 1980, 102, 7932. (b) Miyashita, A.;
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(14) Preetz, A.; Drexler, H.-J.; Schulz, S.; Heller, D. Tetrahedron:
Asymmetry 2010, 21, 1226, and references therein.
’ ASSOCIATED CONTENT
(15) The structure of the related complex [Rh(DPEPHOS)-
(acetone)2]CB11H6Cl6 as catalyst for hydroacylation reactions is re-
ported (Moxham, G. L.; Randell-Sly, H. E.; Brayshaw, S. K.; Woodward,
R. L.; Weller, A. S.; Willis, M. C. Angew. Chem., Int. Ed. 2006, 45, 7618);
however, as an eight-membered chelate complex, it does not represent a
typical hydrogenation catalyst and also has never been tested as such.
(16) Rh(I) complexes in which ether oxygen atoms of redox-switch-
able hemilabile ligands are coordinated to rhodium instead of a solvent
are also known. (a) Allgeier, A. M.; Slone, C. S.; Mirkin, C. A.; Liable-
Sands, L. M.; Yap, G. P. A.; Rheingold, A. L. J. Am. Chem. Soc. 1997,
119, 550. (b) Allgeier, A. M.; Singewald, E. T.; Mirkin, C. A.; Stern, C. L.
Organometallics 1994, 13, 2928.
S
Supporting Information. NMR spectra and X-ray dif-
b
fraction data for complexes 1À4 including tables of positional
and isotropic thermal parameters and anisotropic thermal para-
meters. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: detlef.heller@catalysis.de.
(17) Stults, B. R.; Friedman, R. M.; Koenig, K.; Knowles, W. S.;
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’ ACKNOWLEDGMENT
We thank Suzhou LAC Co. Ltd (www.suzhoulac.com) for the
generous supply of BINAP.
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(23) The crystalline dimer [Rh(BINAP)(BF4)]2 characterized by
X-ray analysis is well soluble in MeOH, a result that is not consistent with
results previously reported in the literature.12a,b Noyori et al. describe
that upon hydrogenation of [Rh(BINAP)(nbd)]ClO4 in MeOH, two
species result in a ratio of 9:1: the solvate complex [Rh(BINAP)-
(MeO(H)2]ClO4 and the postulated and, according to the authors,
poorly soluble dimer [Rh(BINAP)(ClO4)]2. If the species were as-
signed correctly in ref 12a and 12b, the discrepancy might be explained
by a pronounced anion effect (BF4À vs ClO4À).
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dx.doi.org/10.1021/om200486t |Organometallics 2011, 30, 5155–5159