On the influence of arm-on, arm-off processes on alkene hydrogenation catalysed by a rhodium triphos complex

Article abstract of DOI:10.1002/ejic.200700496

The influence of phosphane arm-on, arm-off association/ dissociation in rhodium catalysed alkene hydrogenation using [Rh(COD)(κ³-triphos)]PF₆ {1, COD = cyclooctadiene, triphos = 1,1,1-tris(diphenylphosphanylmethyl)ethane} has been investigated by comparison of the activity of 1 to mixtures of the related diphosphane complex, [Rh(COD)(κ²-dppp)]PF₆ {2, dppp = 1,3-bis(diphenylphosphanyl)propane} and triphenylphosphane (THF, 50°C, 1 bar H₂). These investigations are supplemented by a demonstration of the κ²-κ³ fluxionally of the triphos coordination in 1 by reversible reaction with [RuCl₂(p-cymene)]₂ at room temperature in CH₂Cl₂. The product of this reaction, the bimetallic complex [(p-cymene)Cl₂Ru{(PPh₂CH ₂)CMe(CH₂PPh₂)₂}Rh(COD)]PF ₆, was isolated and fully characterized, including determination of the solid-state structure by X-ray diffraction analysis. Despite this evidence for facile arm-off dissociation of the triphos ligand in 1, complex 2, with or without triphenylphosphane, was found to be more efficient for the hydrogenation of styrene and cyclohexene. Notably, use of triphenylphosphane together with 2 was found to have beneficial effects - increasing the rate of styrene hydrogenation (in some cases) and helping to stabilise the metal center during cyclohexene hydrogenation. These observations are supported by mercury poisoning experiments and reactivity experiments with 2 in medium pressure sapphire NMR tubes. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700496

FULL PAPER
DOI: 10.1002/ejic.200700496
On the Influence of “Arm-on, Arm-off” Processes on Alkene Hydrogenation
Catalysed by a Rhodium Triphos Complex
Adrian B. Chaplin[a] and Paul J. Dyson*[a]
Keywords: Rhodium / Homogeneous catalysis / Hydrogenation / Tripodal ligands / Phosphane ligands
The influence of phosphane “arm-on, arm-off” association/
dissociation in rhodium catalysed alkene hydrogenation
using [Rh(COD)(κ3-triphos)]PF6 {1, COD = cyclooctadiene,
triphos = 1,1,1-tris(diphenylphosphanylmethyl)ethane} has
of the solid-state structure by X-ray diffraction analysis. De-
spite this evidence for facile arm-off dissociation of the
triphos ligand in 1, complex 2, with or without triphenylphos-
phane, was found to be more efficient for the hydrogenation
been investigated by comparison of the activity of 1 to mix- of styrene and cyclohexene. Notably, use of triphenylphos-
tures of the related diphosphane complex, [Rh(COD)(κ2-
dppp)]PF6 {2, dppp = 1,3-bis(diphenylphosphanyl)propane}
and triphenylphosphane (THF, 50 °C, 1 bar H2). These in-
vestigations are supplemented by a demonstration of the κ2–
κ3 fluxionally of the triphos coordination in 1 by reversible
reaction with [RuCl2(p-cymene)]2 at room temperature in
CH2Cl2. The product of this reaction, the bimetallic complex
[(p-cymene)Cl2Ru{(PPh2CH2)CMe(CH2PPh2)2}Rh(COD)]PF6,
was isolated and fully characterized, including determination
phane together with 2 was found to have beneficial effects –
increasing the rate of styrene hydrogenation (in some cases)
and helping to stabilise the metal center during cyclohexene
hydrogenation. These observations are supported by mer-
cury poisoning experiments and reactivity experiments with
2 in medium pressure sapphire NMR tubes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Although commonly found in a tridentate (κ3) coordina-
tion mode,[1] κ2-coorindination of triphos is also observed
in a number of transition metal complexes.[10] The intercon-
version between these κ2 and κ3 coordination modes by
“arm-on, arm-off” association/dissociation of one of the
phosphane arms has been implicated in the reactivity and
catalytic activity of triphos complexes, particularly those of
rhodium.[10c,11] Notably, Kiss and Hováth demonstrated a
reversible arm-off dissociation in [Rh(CO)H(κ3-triphos)],
an active hydroformylation catalyst,[3a] and addition of CO
under hydroformylation conditions at room temperature by
high pressure IR and 31P NMR spectroscopy (Scheme 1).[12]
Caulton and co-workers have further affirmed the impor-
tance of this arm-off mechanism in hydroformylation catal-
ysis by reactions of related hydride, alkyl and acetyl rho-
dium triphos complexes.[13] During their investigation of
rhodium triphos, and related tripodal phosphane com-
plexes, Huttner and co-workers suggested that the κ3-coor-
dination of the phosphane hinders hydrogenation,[14] and
Introduction
Tripodal triphosphane ligands have found widespread
application in inorganic and organometallic chemistry.[1]
Among these ligands, the C3 symmetric 1,1,1-tris(diphenyl-
phosphanylmethyl)ethane (triphos) and it’s derivatives are
among the most extensively investigated, forming a large
variety of transition metal complexes, many of which have
found applications in catalysis.[1,2] Bianchini and co-
workers, in particular, have pioneered the use of this ligand
in transition metal catalysis, using platinum group metals
for a number of processes, including hydrogenation and hy-
droformylation of alkenes,[3] oxidation of catechols,[4] coup-
ling reactions of alkynes,[5] and the hydrogenation, hydro-
genolyis and hydrodesulfurisation of thiophenes.[6] Func-
tionalisation of the triphos ligand by derivation of the
bridgehead atom with appropriate moieties has allowed the
formation of metallo-dendrimers[7] or immobilisation of
metal complexes on silica[8] or into biphases;[9] facilitating
catalyst reuse or modifying reactivity. Such immobilization
is complemented by the tridentate nature of the ligand, sta-
bilising the metal center during catalysis and reducing
leaching.
[a] Institut des Sciences et Ingénierie Chimiques, Ecole Polytech-
nique Fédérale de Lausanne (EPFL),
1015 Lausanne, Switzerland
E-mail: paul.dyson@epfl.ch
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Scheme 1.
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4973

A. B. Chaplin, P. J. Dyson
FULL PAPER
they demonstrated that related diphosphane complexes are minutes, analysis of the reaction solution by 31P NMR spec-
significantly more active for the hydrogenation of (Z)-α-N- troscopy revealed the formation of the bimetallic complex,
acetamidocinnamic acid.[15] Burk and co-workers have also [(p-cymene)Cl2Ru{(PPh2CH2)CMe(CH2PPh2)2}-Rh(COD)]-
reported similar behaviour for other rhodium tripodal PF6 3, identified by the presence of characteristic singlet
phosphane systems.[16]
and doublet (1JRhP = 141 Hz) resonances at δ = 16.6 and
To further investigate the importance of phosphane arm- 13.1 ppm, respectively, in a 1:2 ratio together with a small
on, arm-off processes in the hydrogenation activity of rho- quantity of 1 (Scheme 3). Subsequently, 3 was isolated, al-
dium triphos complexes, we report here a comparison of beit in moderate yield (54%), following recrystallisation and
the activity of [Rh(COD)(κ3-triphos)]PF6 (1) with mixtures the structure was further verified by 1H and 13C NMR spec-
of the related diphosphane complex, [Rh(COD)(κ2-dppp)]-
PF6 (2), and triphenylphosphane (Scheme 2).[14a,15] To com-
plement these investigations, relevant in situ reactivity stud-
ies are also presented together with the demonstration of
the κ2–κ3 interconversion in complex 1 using a ruthenium
complex.
Scheme 2.
Results and Discussion
1. Reaction of 1 with [RuCl2(p-cymene)]2
To probe the presence of an arm-on, arm-off process, 1
was reacted at room temperature with the dinuclear ruthe-
nium complex [RuCl2(p-cymene)]2, well known to react
rapidly with phosphane ligands,[17] in an attempt to trap
Scheme 3. Formation and equilibrium of complex 3 (with NMR
the κ2-coordination mode of the triphos ligand. After 30 numbering scheme).
Figure 1.ORTEP representation of 3; thermal ellipsoids drawn at 50%. Solvent molecules and counter anion omitted for clarity. Key
bond lengths [Å] and angles [°]: Ru1–Cl1 2.420(3), Ru1–Cl2 2.421(2), Ru1–P3 2.356(3); Cl1–Ru1–Cl2 88.23(8), Cl1–Ru1–P3 88.37(9),
Cl2–Ru1–P1 83.78(8); Ru1–C1 2.200(9), Ru1–C4 2.227(9), Ru1–Cavg 2.21(2), Rh1–P1 2.287(3), Rh1–P2 2.286(3); P2–Rh1–P3 88.06(10);
Rh1–C11 2.274(8), Rh1–C18 2.263(9), Rh1–C14 2.217(10), Rh1–C15 2.226(10).
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Rhodium-Triphos-Catalysed Alkene Hydrogenation
troscopy and electrospray ionization mass spectrometry close to complete conversion (Ͼ 90%), resulting in longer
(ESI-MS). Furthermore, the solid-state structure of 3 has reactions times than in the absence of triphenylphosphane
been established by X-ray diffraction analysis – depicted in (see insert in Figure 2). Addition of mercury, a selective poi-
Figure 1. The bonding parameters about the Ru center are son for heterogeneous catalysis, did not inhibit catalytic ac-
similar to related [RuCl2(κ1-phosphane)(p-cymene)] (Ru–P tivity for 2 + nPPh3 (n = 0 or 1) significantly.[22]
≈ 2.4 Å)[18] complexes, while those about the Rh center are
similar to [Rh(COD)(κ2-dppp)]BF4 {1·BF4, Rh–P 2.311(2),
2.319(2) Å; P–Rh–P 90.81(4)°},[19] although the Rh–P bond
length and P–Rh–P angle are slightly contracted in 3 in
comparison to 1·BF4 {Rh1–P1, 2.287(3) Å; Rh1–P2,
2.286(3) Å; P1–Rh–P2, 88.06(10)°}. In CD2Cl2 solution at
room temperature, 3 undergoes a slow equilibration reac-
tion (t1/2 = 22Ϯ3 h) in which dissociation of the phosphane
from the ruthenium-arene moiety results in an mixture of
1, 3, and [RuCl2(p-cymene)]2 with a equilibrium constant,
K, of approximately 2, demonstrating the reversible nature
of the triphos coordination.
Table 1. Hydrogenation of styrene using 1 and 2 + nPPh3.[a]
n
50% Conversion
Time/h
Ͼ 99% Conversion
Time/h
TOF[b] /h–1
1
2.83
1.72
1.81
1.63
1.50
1.49
1.65
1.65
32
68
62
74
80
80
72
70
10
2
0
0
0.5
1
1
2
5
3.5
4.5
3.5
3.0
3.5
4.0
4.5
2[c]
2
2
2[c]
2
2
[a] Conditions: 2.6ϫ10–5 mol pre-catalyst, S/C = 200:1, 20 mL of
THF, 0.1 mL of octane (internal standard), 1 bar H2. Conversion
determined by GC analysis of reaction aliquots. [b] Calculated at
50% conversion from hydrogenation progress. [c] 0.1 mL of Hg
added.
2. Catalytic Activity
The catalytic activity of 1 and solutions of 2 containing
various quantities of triphenylphosphane were first investi-
In comparison to styrene, the initial rate of cyclohexene
gated for the hydrogenation of styrene. The hydrogenation hydrogenation using 2 is significantly reduced by the ad-
experiments were carried out in THF, a weakly coordinat- dition of 1 equiv. of triphenylphosphane (Figure 3). How-
ing solvent,[20] at 50 °C under 1 bar of H2 with a substrate ever, mercury poisoning experiments suggest a significant
to catalyst (S/C) ratio of 200:1; 2 was investigated with 0, degree of heterogeneous character to the active species for
0.5, 1, 2, and 5 equiv. of triphenylphosphane. Conversion 2 alone, whereas, with 1 equiv. of triphenylphosphane there
was monitored by GC during the reaction and results are is no significant change in activity in the presence of mer-
listed in Table 1 with selected data depicted in Figure 2. cury (Figure 3 and Table 2). This difference is also apparent
Both complexes were found to exhibit incubation periods, to some degree by significant darkening of the reaction
consistent with previously reported kinetic studies on di- solution after ca. 90 min in the absence of triphenylphos-
phosphane rhodium complexes containing the COD ligand phane, whereas with 1 equiv. of triphenylphosphane the
(attributed to hydrogenation of the diene).[21] From the hy- solution remains yellow throughout the reaction. For 1, the
drogenation curves (Figure 2) it is apparent that 1 is signifi- initial rate of hydrogenation is comparable to 2 with 1 equiv.
cantly less active than 2 under these conditions. Catalytic of triphenylphosphane, although activity is gradually re-
runs carried out with 2 in the presence of added tri- duced and is accompanied by the reaction solution becom-
phenylphosphane showed enhanced rates of hydrogenation ing green/brown – consistent with decomposition into inac-
at 50% conversion in comparison to 2 alone – most pro- tive molecular species.
nounced with 1 equiv. of the phosphane. However, in the
Together, these results are consistent with the ability of
presence of excess triphenylphosphane significant re- the triphos ligand to undergo reversible phosphane arm-off
ductions in the rate of hydrogenation with 2 are observed coordination during catalysis. While the catalytic activity of
Figure 2. Hydrogenation of styrene using 1 (–᭿–) and 2 + nPPh3 (n = 0, –᭡–; 1, –o–; 2, –᭢– insert only; 5, –᭹– insert only). Mercury
poisoning experiments for 2 + nPPh3 (n = 0, --∆--; 1, -- --) are shown with dashed lines.
Eur. J. Inorg. Chem. 2007, 4973–4979
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A. B. Chaplin, P. J. Dyson
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Figure 3. Hydrogenation of styrene using 1 (–᭿–) and 2 + nPPh3 (n = 0, –᭡–; 1, –o–). Mercury poisoning experiments for 2 + nPPh3 (n
= 0, --∆--; 1, -- --) are shown with dashed lines.
Table 2. Hydrogenation of cyclohexene using 1 and 2 + nPPh3.[a]
composition with only a minor decrease in activity. For sty-
rene, addition of, for example, one equivalent of tri-
phenylphosphane noticeably increased the rate of hydrogen-
ation. As Osborn-type rhodium and iridium complexes are
known to react with arenes under hydrogenation conditions
to form inactive species of the type, [M(η6-arene)L2]+,[20]
reversible coordination of triphenylphosphane may help
prevent the formation of species of this nature and thus
enhance the rate of hydrogenation. This possibility was thus
investigated further (see below).
n
50% Conversion
Time/h
TOF[b] /h–1
[c]
[c]
1
–
–
2
0
0
1
1
2.81
8.78
4.36
4.59
24
6
22
26
2[d]
2
2[d]
[a] Conditions: 2.6ϫ10–5 mol pre-catalyst, S/C = 200:1, 20 mL of
THF, 0.1 mL of octane (internal standard), 1 bar H2. Conversion
determined by GC analysis of reaction aliquots. [b] Calculated at
50% conversion from hydrogenation progress. [c] Conversion
Ͻ 50%. [d] 0.1 mL of Hg added.
3. Effect of Triphenylphosphane on the Formation of
[Rh(η6-toluene)(κ2-dppp)]+
1 is attributed to the ability of the triphos ligand to undergo
an arm-off dissociation process, leading to active species
To further investigate the enhancement of catalytic ac-
containing the κ2-coordinated ligand and a vacant coordi- tivity of 2 with triphenylphosphane for styrene hydrogena-
nation site (i.e. becoming directly analogous to 2), the adop- tion, reactions of 2 with hydrogen (ca. 12 bar) in the pres-
tion of the κ3-mode during catalysts is suggested to com- ence of toluene (ca. 80 equiv.) and triphenylphosphane were
plete with substrate significantly during catalysis resulting carried out in medium pressure sapphire NMR tubes.[24,25]
in significantly lower activity than 2. This suggestion is sup- In the absence of triphenylphosphane, following COD hy-
ported by similar reductions in activity observed for the hy- drogenation, [Rh(η6-toluene)(κ2-dppp)]+ 4 is formed quan-
drogenation of styrene with 2 and excess triphenylphos- titatively.[26] However, in the presence of 5 equiv. of tri-
phane, but only near reaction completion, when substrate phenylphosphane 4 cannot be detected and instead a spe-
concentration is low. The reduced effect of triphenylphos- cies assigned to cis-[RhH2(PPh3)2(κ2-dppp)]+ 5 is observed
phane coordination in comparison to the arm-on, arm-off in ca. 94% yield.[27] The identity and geometry of this spe-
process in 1 is presumably due to the absence of the chelate cies is deduced primarily from the 31P{1H} NMR spectrum,
effect and the bulky nature of triphenylphosphane. (Note: which exhibits four distinct phosphorus resonances with
no reaction with 2 and triphenylphosphane can be detected characteristic multiplicity and coupling constants (Fig-
in THF cf. κ3-coordination of the triphos ligand in 1.) The ure 4). Notably, those centred at δ = 31.3 and 18.3 ppm
2
failure of 1 to hydrogenate cyclohexene to completion may exhibit large JPP coupling constants of 318 Hz, suggesting
also be rationalised by the tendency of the triphos ligand a trans arrangement of two of the phosphane moieties,[28]
1
in 1 to adopt a κ3-coordination mode. This feature together and JRhP coupling constants of ca. 100 Hz. The other
with the more hindered nature of cyclohexene could be re- phosphorus resonances, centred at 21.6 and –3.6 ppm, have
1
sponsible for the decomposition observed with this sub- smaller JRhP coupling constants (82 and 85 Hz) consistent
strate in comparison with styrene.
with phosphane moieties trans to hydride ligands.[29] The
2
While the arm-on coordination appears to be detrimental remaining JPP coupling constants, ca. 20 Hz, are typical
the catalytic activity of 1, the addition of triphenylphos- for cis-coordinated phosphane ligands.[28] Furthermore, the
phane, in an attempt to mimic this behaviour,[23] during ca- 1H NMR spectrum exhibits two broad doublets at –10.55
2
talysis with 2 had a number of beneficial outcomes. For and –11.33 ppm with JPH coupling constants of 132 and
example, in the hydrogenation of cyclohexene with 2, ad- 136 Hz, respectively. A similar species, containing instead a
dition of triphenylphosphane appeared to stabilise the tetradentate phosphane, has been reported by Bianchini
metal center, i.e. by reversible coordination, preventing de- and co-workers.[30]
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Rhodium-Triphos-Catalysed Alkene Hydrogenation
Figure 4. 31P{1H} NMR spectrum of 5. * PPh3 (δ ≈ 5 ppm) and OPPh3 (δ ≈ 24 ppm), † denotes complex 6.
In the presence of 1 equiv. of triphenylphosphane 4 is κ3-coordination motif in the triphos complex, added tri-
formed, although only in modest yield (ca. 24%), together phenylphosphane results in the enhancement of the rate of
with a new species, exhibiting two broad doublets of dou- catalytic activity during the hydrogenation of styrene with
blets at 45.0 (2JPP = 340 Hz, 1JRhP = 112 Hz) and 24.0 ppm 2, although with excess triphenylphosphane, reduction in
1
(2JPP = 340 Hz, JRhP = 112 Hz) and a broad resonance at the hydrogenation rate close to completion is observed –
5.8 ppm (ca. 54%), and a small amount of 5 (ca. 12%). This upholding the proposed reduction of activity by κ3-coordi-
new species is tentatively assigned as cis-[RhH2(THF)- nation of the triphos ligand in 1. The enhanced rate of sty-
(PPh3)(κ2-dppp)]+ (6, Scheme 4) on the basis of these rene hydrogenation is attributed to the ability of tri-
data and their good agreement with that of the known phenylphosphane to prevent the coordination of the sub-
complex cis-[RhH2Cl(PPh3)(κ2-{PPh2CH2}2CHOH)]
7
strate or product (by weak and reversible coordination)
(Scheme 4).[27,31] A small quantity of this complex is also during catalysis, and this hypothesis is supported by me-
observed during the reaction with 5 equiv. (ca. 4%).
dium pressure in situ reactions of 2 with H2, toluene and
different quantities of triphenylphosphane. The use of tri-
phenylphosphane with 2 also has the beneficial effect of
stabilizing the metal center towards decomposition during
catalysis as demonstrated in the hydrogenation of cyclohex-
ene.
Experimental Section
Scheme 4. Proposed structure of 6 and the known compound 7
{annotated with 31P NMR spectroscopic data ([D8]toluene /
ppm)}.[31]
General: All organometallic manipulations were carried out under
a nitrogen atmosphere using standard Schlenk techniques. Solvents
(CH2Cl2, THF, toluene) were dried catalytically under dinitrogen
using a solvent purification system, manufactured by Innovative
Technology Inc. All other solvents were p.a. quality and saturated
with nitrogen prior to use. Styrene and cyclohexene were saturated
with nitrogen and stored over activated molecular sieves.
Combined these data are consistent with the ability of
triphenylphosphane to hinder the coordination of arene
substrates or products under catalytic conditions, support-
ing the observation of enhanced activity on addition of tri-
phenylphosphane during hydrogenation of styrene with
complex 2.
[Rh(COD)(κ3-triphos)]PF6 (1),[15] [Rh(COD)(κ2-dppp)]PF6 (2),[14a]
[32]
and [RuCl2(p-cymene)]2
were prepared as described elsewhere.
All other chemicals are commercial products and were used as re-
ceived. NMR spectra were recorded with a Bruker Avance 400
spectrometer at room temperature, unless otherwise stated. Chemi-
cal shifts are given in ppm and coupling constants (J) in Hz. The
NMR labelling for complex 3 is given in Scheme 3. ESI-MS were
recorded on a Thermo Finnigan LCQ DecaXP Plus quadrupole
ion trap instrument according to a literature protocol;[33] CH2Cl2
was used as the solvent for all experiments with a capillary tem-
perature of 80 °C and spray voltage of 5.0 kV.
Concluding Remarks
The influence of the phosphane arm-on, arm-off process
in rhodium triphos complexes for hydrogenation catalysis
has been further established by comparison to related dppp
systems with added triphenylphosphane. Despite further
evidence for facile dissociation of one of the triphos arms
in these systems, by the reaction of 1 with [RuCl2(p-cy-
mene)]2, the tendency of this ligand to adopt a κ3-coordina-
tion appears to significantly encumber catalytic activity by
competing with the substrate for vacant coordination sites
Preparation of [(p-Cymene)Cl2Ru{(PPh2CH2)CMe(CH2PPh2)2}-
Rh(COD)]PF6 (3):
(0.070 g, 0.071 mmol)
A
solution of [Rh(COD)(κ3-triphos)]PF6
and
[RuCl2(p-cymene)]2
(0.022 g,
0.036 mmol) in CH2Cl2 (10 mL) was stirred at room temp. for
30 min. The solution was then concentrated to ca. 5 mL and hex-
on the metal. In comparison, in an attempt to mimic the ane (ca. 10 mL) added precipitating out a small amount of a un-
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4977

A. B. Chaplin, P. J. Dyson
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identified brown impurity, which was removed by filtration. The
product was obtained as a microcrystalline orange solid from the
filtrate upon standing at –20 °C. Yield 0.049 g (54%). Crystals suit-
reduction was performed using CrysAlis RED.[34] The structure
was solved using SIR97,[35] and refined (full-matrix least-squares
on F2) using SHELXTL.[36] An absorption correction was applied
to the data set (empirical, DELABS).[37] All non-hydrogen atoms
able for X-ray diffraction were obtained from a CH2Cl2/hexane
1
solution of the complex at –20 °C. H NMR (CD2Cl2): δ = 7.26– were refined anisotropically, with hydrogen atoms placed in calcu-
3
3
7.92 (m, 30 H), 5.12 (d, JHH = 6.1, 2 H, H3), 5.07 (d, JHH = 5.7, lated positions using the riding model. The occupancy of one of
2 H, H2), 4.74–4.84 (m, 2 H, H8), 4.01–4.11 (m, 2 H H9), 3.00–3.10 the CH2Cl2 molcules was refined to 66% and it was necessary to
(m, 2 H, H13), 2.70–2.78 (m, 2 H, H14), 2.59 (sept, JHH = 6.9, 1
H, H6), 2.41–2.50 (m, 2 H, H10), 2.30–2.41 (m, 2 H, H10Ј), 2.06–
2.21 (m, 4 H, H11), 1.83–1.96 (m, 2 H, H13Ј), 1.78 (s, 3 H, H5), 1.05
retrain the displacement parameters of some atoms. The graphical
3
representation of 3 was made with ORTEP3.[38]
(d, JHH = 7.0, 6 H, H7), –0.09 (s, 3 H, H15) ppm. 13C{1H} NMR
Table 3. Crystal data and details of the structure determinations of
3.
3
(CD2Cl2): δ = 127–135 (m), 109.6 (s, C4), 104.4–104.9 (m, C9),
98.8–99.3 (m, C8), 95.3 (s, C1), 89.9 (d, JPC = 3, C2), 86.3 (d, JPC
2
2
Formula
C59H65Cl2F6P4RhRu·4.66CH2Cl2
= 6, C3), 45.0–45.7 (m, C14), 39.7 (d, JPC = 6, C12), 36.2–36.9 (m,
2
M
1682.81
triclinic
P1
C13), 31.4 (s, C15), 30.3 (s, C6), 30.0 (s, C10), 29.9 (s, C11), 21.4 (s,
Crystal system
Space group
C7), 17.1 (s, C5) ppm. 31P{1H} NMR (CD2Cl2): δ = 16.6 (s, 1 P,
¯
1
1
a /Å
b /Å
c /Å
α /°
11.8544(10)
16.506(2)
19.485(2)
105.563(10)
90.054(8)
100.954(9)
3600.5(7)
2
RuPPh2), 13.1 (d, JRhP = 141, 2 P, RhPPh2), –144.4 (sept, JPF
=
711, 1 P, PF6) ppm. ESI-MS (CH2Cl2, 80 °C, 5 kV) positive ion:
m/z, 834 (30%) [M –RuCymeneCl2]+, 1141 [M]+. ESI-MS2 (+1141):
m/z, 834 [M – RuCymeneCl2]+. C59H65Cl2F6P4RhRu (1286.94
gmol–1): calcd. C 55.07, H 5.09; found C 55.14, H 5.11.
β /°
δ /°
V /Å3
Z
Medium Pressure NMR Experiments: Reactions of 2 (9 mg) with
H2 (12 bar) and toluene (0.1 mL, ca. 80 equiv.) were carried out in
10 mm sapphire NMR tubes in THF (2.5 mL) with the appropriate
quantity of triphenylphosphane. All samples were prepared under
nitrogen. Reaction progress was followed by 31P NMR spec-
troscopy until complete consumption of 2 was observed, typically
Ͻ 5 h (no further change in product distributions were observed).
Selected 1H and 31P{1H} NMR spectroscopic data for 5 and 6 fol-
low; referenced externally to TMS and 85% H3PO4, respectively.
Density /gcm–3
1.552
1.002
µ /mm–1
θ range /°
Measured reflections
Unique reflections
3.09 Ͻ θ Ͻ 25.25
21093
11146 [Rint = 0.0832]
Number of data/restraints/parameters 11146/126/798
R1, wR2 [IϾ2σ(I)][a]
Largest diff. peak and hole /eÅ–3
GoF[b]
R1 = 0.0622, wR2 = 0.1122
1.377 and –0.975 [rms = 0.112]
0.819
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|, wR2 = {Σ[w(Fo2 – Fc2)2]/Σ[w(Fo2)2]}1/2. [b]
2
1H NMR (5, THF, hydride region): δ = –10.55 (br. d, JPH = 132,
2 2
GoF = {Σ[w(Fo2 – Fc ) ]/(n – p)}1/2 where n is the number of data and
2
1 H), –11.33 (br. d, JPH = 136, 1 H) ppm. 31P{1H} NMR (5,
p is the number of parameters refined.
1
2
THF): δ = 31.3 (ddt, 2JPP = 318, JRhP = 102, JPP = 21, 1 P), 21.6
1
2
2
1
(dq, JRhP = 85, JPP = 20, 1 P), 18.3 (dddd, JPP = 318, JRhP
=
CCDC-645738 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
2
2
1
2
104, JPP = 26, JPP = 16, 1 P), 3.6 (dq, JRhP = 82, JPP = 23, 1
P) ppm. 31P{1H} NMR (6, THF): δ = 45.0 (br. d, 2JPP = 340, 1JRhP
2
1
= 112, 1 P), 24.0 (br. d, JPP = 340, JRhP = 112, 1 P) 5.8 (br., 1 P)
ppm. The hydride region of the 1H NMR spectrum of 6 was broad
and uninformative.
Supporting Information (see also the footnote on the first page of
this article): Full hydrogenation profiles for catalysis with 1 and 2.
Catalytic Evaluations: Catalytic experiments were conducted in a
50 mL three-necked round-bottomed flask equipped with a 2.0 L
latex balloon (Dräger/2165694) connected via a 6 cm reflux con-
denser and gas tap, a septum cap and gas adaptor. Following press-
urisation of the balloon with hydrogen (1 bar), via successive vac-
uum hydrogen cycles, the flask was charged with pre-catalyst
(2.6ϫ10–5 mol) and magnetic stirring bar and placed under an
inert atmosphere. THF (20 mL), octane (0.1 mL), substrate
(5.2ϫ10–3 mol) and, for the poisoning experiments, mercury
(0.1 mL) were then added via syringe through the septum cap. The
system was then placed under H2 by three vacuum/H2 cycles and
then heated at 50 °C. The hydrogenation was followed by sampling
the reaction solution at t = 10, 20, 30, 60, 90, 120, 180, 210, 240,
270, 300 min and every successive hour up to t = 12 h by GC (Var-
ian chrompack CP-3380 gas chromatograph) or until reaction com-
pletion. Full hydrogenation data is given in the supplementary ma-
terial.
Acknowledgments
This work was supported by the Ecole Polytechnique Fédérale de
Lausanne (EPFL) and the Swiss National Science Foundation. We
are grateful to Dr. R. Scopelliti and Dr. E. Solari for assistance
with crystallography. We also thank the New Zealand Foundation
for Research, Science and Technology for a Top Achiever Doctoral
Fellowship (to A. B. C.).
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Received: May 8, 2007
Published Online: September 11, 2007
Eur. J. Inorg. Chem. 2007, 4973–4979
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4979