Synthesis, immobilization, MAS and HR-MAS NMR of a new chelate phosphine linker system, and catalysis by rhodium adducts thereof

Article abstract of DOI:10.1002/adsc.201000585

A new class of tridentate phosphine ligands with the general formula [MeP{(CH₂)_xPPh₂}₃]⁺I ^- (x=4, 7, 11) and [MeP(CH₂PPh₂) ₃]⁺OTf^-, has been synthesized and fully characterized. The linkers have been immobilized on silica with their phosphonium moieties via electrostatic interactions, and their mobility and leaching has been studied by solid-state HR-MAS (high-resolution magic angle spinning) NMR in various solvents. Immobilized Wilkinson-type rhodium complexes have been obtained by ligand exchange with the surface-bound linkers. The activities and lifetimes of the catalysts have been tested with respect to the hydrogenation of 1-dodecene. The rhodium catalyst precursor bound by the immobilized linker [MeP{(CH₂)₇PPh₂} ₃]⁺I^- led to material with the highest activity and lifetime, and it could be recycled for 30atimes in a batchwise manner. The other catalysts show shorter lifetimes. For all catalysts the formation of rhodium nanoparticles with a narrow size distribution around 4anm has been proven.

Full text of DOI:10.1002/adsc.201000585

FULL PAPERS
DOI: 10.1002/adsc.201000585
Synthesis, Immobilization, MAS and HR-MAS NMR of a New
Chelate Phosphine Linker System, and Catalysis by Rhodium
Adducts Thereof
J. Guenther,a J. Reibenspies,a and J. Blꢀmela,*
a
Texas A&M University, Department of Chemistry, P.O. Box 30012, College Station, TX 77842-3012, USA
Fax : (+1)-979-845-5629; phone: (+1)-979-845-7749; e-mail: bluemel@tamu.edu
Received: July 24, 2010; Revised: December 21, 2010; Published online: February 16, 2011
Abstract: A new class of tridentate phosphine li- hydrogenation of 1-dodecene. The rhodium catalyst
gands
{(CH2)xPPh2}3]+IÀ (x=4, 7, 11) and [MeP-
ACHTUNGTRENNUNG
(CH2PPh2)3]+OTfÀ, has been synthesized and fully tivity and lifetime, and it could be recycled for
with
the
general
formula
[MeP- precursor bound by the immobilized linker [MeP-
A
ACHTUNGTRENNUNG
characterized. The linkers have been immobilized on 30 times in a batchwise manner. The other catalysts
silica with their phosphonium moieties via electro- show shorter lifetimes. For all catalysts the formation
static interactions, and their mobility and leaching of rhodium nanoparticles with a narrow size distribu-
has been studied by solid-state HR-MAS (high-reso- tion around 4 nm has been proven.
lution magic angle spinning) NMR in various sol-
vents. Immobilized Wilkinson-type rhodium com-
plexes have been obtained by ligand exchange with Keywords: chelate phosphines; immobilization; im-
the surface-bound linkers. The activities and lifetimes mobilized catalysts; phosphonium salts; rhodium
of the catalysts have been tested with respect to the complexes; rhodium nanoparticles
Introduction
ously studied nickel[3] and rhodium[4] catalysts, which
have been obtained by ligand exchange with
Catalysts immobilized on solid supports are of grow- ClRhACHTNUTRGEN(UNG PPh3)3 (1), we could prove that dimerization or
ing academic and industrial interest, because they agglomeration of the surface-bound catalysts leads to
combine the advantages of homogeneous catalysts their deactivation[4] or loss of selectivity.[3] The dimeri-
with those of heterogeneous catalysts. Immobilized zation can be prevented by diluting the catalysts on
catalysts are highly active and selective, while they the surface.[4] However, this is less desirable in an in-
can be easily separated from the reaction mixtures dustrial setting, because it increases the amount of
and recycled many times.[1] The most favorable sup- bulk material per metal center, leading to bigger,
port material is silica,[2] and bifunctional phosphines more expensive reactors with correspondingly larger
such as Ph2P
ACHTUNGTRENNUNG(CH2)3SiACHTUNREGTN(GNUN OEt)3 or Ph2PACTHNGUTREN(NUGN CH2)3PPh- amounts of solvents and ensuing safety issues.
A
E
Linkers play a crucial role for all immobilized cata-
to very successful immobilized nickel[3] and rhodium[4] lysts.[1d] Therefore, problems (i) and (ii) can be solved
catalysts for cyclotrimerizations of acetylenes and by new generations of linkers. One successful ap-
olefin hydrogenations. To further improve this type of proach we explored recently makes use of rigid tetra-
immobilized catalysts, two remaining problems have phenyl-element scaffolds based on the tetrahedral
to be solved. (i) The catalysts, especially in their acti- [R2PACHTNUTRGNE(GNU p-C6H4)]4E (E=C, Si, Sn; R=alkyl, aryl) struc-
vated form, can decompose if they come into contact tural units.[5] However, chelate versions of these rigid
with the reactive oxide surface. This is, for example, linkers for better coordination and retention of the
obvious in the gradually darkening grey color of the metal centers have not yet been synthesized. An alter-
originally white, bright yellow, or red catalysts with native for solving both problems (i) and (ii) would be
every recycling step. At the moment, this problem to use long alkyl chains, draped around the metal
might only be ameliorated by the additional step of center in a chelating arrangement, to protect the cata-
“end-capping” of the oxide surface with SiMe3 groups lytically active metal centers. Even one alkyl chain
after the immobilization of the catalyst,[2] a procedure has some protecting effect. For example, recently we
that many catalysts cannot tolerate. (ii) For the previ- found that a Pt complex containing a long alkyl chain
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Scheme 1. Syntheses of the monodentate phosphines 2–5, their phosphonium salts 6–9, and the chelate ligands 10–12, their
immobilized versions 10i–12i, and the surface-bound Rh complexes 13i–15i.
does not decompose on silica,[6] although analogous and the former only monodentate. This might be due
Pt complexes with triaryl ligands do. Three chelating to the fact that longer alkyl chains allow increased
alkyl chains should protect a metal center optimally.
mobility of the immobilized catalyst and thus help to
Regarding their design, these alkyl linkers should mimic homogeneous catalysis. One more positive
be robust, and not decompose on the surface, as bi- effect of longer chains is that not only conventional
sphosphinoamines[7a] or dppm-type linkers,[7b] for ex- solid-state CP/MAS (cross-polarization with magic
ample, do. The ethoxysilane linker EtOSiACTHNUTRGNEUNG
(CH2PPh2)3 angle spinning) or MAS NMR[10] can be measured,
with the shortest possible alkyl chains is not sensitive but the HR-MAS (high-resolution magic angle spin-
in solution, but it obviously has too short a distance ning) signals of species with alkyl chains that are suffi-
between the phosphine and the reactive ethoxysilane ciently mobilized in the presence of a solvent are ex-
groups and decomposes on a silica surface, while tremely narrow.[7a,8,9,11]
EtOSi
G
Here, we present a new class of chelating tridentate
11 methylene groups between the phosphine and phosphine ligands with long alkyl chains that are im-
ethoxysilane groups, however, led to mono- and bi- mobilized via electrostatic interactions of phosphonium
dentate linkers with reduced oxygen sensitivity, that moieties with a silica surface. They are characterized
can cleanly be immobilized on oxide supports.[9]
by solid-state NMR, and their leaching has been stud-
Furthermore, results with Wilkinson-type catalysts ied. The long alkyl chains increase the mobility of the
tethered to the support by linkers with long alkyl bound Wilkinson-type catalysts and in this way opti-
chains show that they display higher activity and mally mimic a homogeneous scenario for the respec-
better recycling characteristics than catalysts bound tive catalysts. The three alkyl chains per metal center
by shorter linkers,[4] even when the latter are chelating are also expected to prevent dimerization of the bound
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Synthesis, Immobilization, MAS and HR-MAS NMR of a New Chelate Phosphine Linker System
complexes, because, when arranged in a balloon-type tion via radicals[13] takes place, and therefore we have
manner, they cannot interpenetrate the alkyl chains of not pursued the linker with C3 chains any further.
a neighboring molecule. Furthermore, since the “bal-
Methyl iodide as the quaternizing reagent for 16
loon” cannot roll over, any deactivation by contact led to a mixture of different phosphonium salts.
with the reactive support surface should be impossible. Therefore, methyl triflate has been applied as a more
The catalytic activities, selectivities, and lifetimes are selective quaternizing agent that alkylated only the
studied with respect to olefin hydrogenation.
most basic, the trialkylphosphine moiety of 16
(Scheme 2). The purification process was also facili-
tated by this reagent, and therefore clean 17 has been
obtained in a good overall yield of 72%. Crystals suit-
able for X-ray structure determination[17] (Figure 1)
could be grown from an acetonitrile solution. As with
Results and Discussion
Synthesis of the Phosphine Linkers
the X-ray structure of the analogous compound
[8]
The phosphine ligand 3 has been synthesized starting EtOSiACHTUNRTGNE(UNG CH2PPh2)3 the orientation of the phosphine
from the corresponding commercially available groups is not preorganized for coordination, but do-
bromo compound BrACTHNUTRGEN(UNG CH2)2CH=CH2 according to the minated by the crystal packing. As expected, the tri-
procedure by Clark and Hartwell[12a] (Scheme 1). The flate counteranion occupies the sterically least crowd-
1H,[12a,b] 31P, [12a] and 13C[12c] NMR data are in accord- ed space close to the methyl group of the phosphoni-
ance with the literature values. It should be noted um moiety. This constellation indicates that the linker
that we were not able to isolate the phosphine 17 would indeed “stand upright” on the surface, when
P(CH2CH=CH2)3 (2) in high yields in an analogous the phosphonium group is bound to the silica via elec-
manner, most probably because the allyl substituents trostatic interactions (see below).
are vulnerable to polymerization or formation of five-
The triphosphines 10–12 (Scheme 1) have been ob-
membered rings via radicals.[13] The phosphines 4 and tained from 7–9 by applying an excess of HPPh2 and,
5 have been synthesized from the corresponding bro- with respect to the whole molecule, a stoichiometric
moalkenes as described by the Gladysz group.[14] amount of AIBN as the radical source, slightly modi-
Ligand 16 (Scheme 2) with the shortest possible alkyl fying the procedure described by Stelzer.[18] Photo-
chain could be obtained in a very good yield of 87% chemical hydrophosphination without a radical form-
by reacting Ph2PCH2Li·TMEDA[15] with PCl3. The ing reagent, as successfully applied previously,[9,19] is
data of 16 are in accordance with the data obtained possible here, but the reaction is more sluggish in the
for 16 synthesized from PACHTNUTGRNEUNG
(CH2SiMe3)3 and ClPPh2.[16] final stage. Overall, the general synthesis route for
The phosphonium salts 7–9 (Scheme 1) have been this ligand class, as outlined for specific cases in
synthesized in quantitative yields by stirring the corre- Scheme 1, is very versatile, as the chain lengths, the
sponding phosphines 3–5 with an excess of CH3I in substituents at phosphorus, and the counteranions can
toluene overnight. The methyl phosphonium salt be varied easily.
[CH3P(CH2CH=CH2)3]+IÀ (6) has been obtained by
The presence of the phosphonium functionality
the one-pot reaction described in the Experimental does not disturb the coordination of the phosphine
Section, but during the subsequent hydrophosphina- groups to metal centers. This has been demonstrated
tion with AIBN again polymerization or a ring forma-
Scheme 2. Syntheses of ligand 16, its phosphonium salt 17,
and the Rh complex 18.
Figure 1. Single crystal X-ray structure of chelate ligand
17.[17]
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Figure 2. Single crystal X-ray structure of the Rh norbornadiene complex 18.[20] In the left presentation the counteranions
À
OTfÀ and PF6 , and the phenyl rings have been removed for clarity.
by the synthesis of 18 by reacting 17 with the norbor- ethoxysilane linkers can leach from the surface,[24a]
nadiene complex [RhACHTNUGRTNEUNG(nbd)2]PF6. The Rh complex has and furthermore the ethoxysilanes can lead to the in
been fully characterized, and a single crystal X-ray situ quaternization of the phosphine groups.[25] We
structure[20] has been obtained (Figure 2). The cation have applied this reaction recently to bind rigid tetra-
incorporating the Rh center is well defined, and over- phenyl-element phosphine linkers without intramolec-
all the structure of 18 resembles the analogous Si-tri- ular ethoxysilane groups to silica supports.[5] In the
phos[21a] and triphos[21b] Rh structures. The coordina- course of these studies we found that phosphonium
tion of all three phosphine groups of 16 is obvious, as salts are also bound strongly via electrostatic interac-
it is the case in an analogous methoxy-norbornadienyl tions to the oxide support,[5,25] and that preformed
Rh complex,[22] as well as, for example, in various phosphonium salts can be immobilized directly on
other tripod Rh[23a] and Cu[23b] complexes, and Sn,[23c] oxide supports, without addition of alkoxysilanes.[25]
Ir,[23d] and Rh[23e] complexes with borate tripod li- Therefore, besides their applications as flame retard-
gands. In contrast to these systems, 18 needs two ants and polymerization starters, their interesting
counteranions to satisfy the positive charges of the NMR characteristics,[5,25,26] and previous applications
Rh(I) center and the phosphonium ligand. Although for ionic liquids[27] and liquid-liquid biphase cataly-
the counteranions are less well defined, Àit is obvious sis,[28] as fluoride ion sensors[29a] and chelators,[29b] and
from the structure that OTfÀ and PF6 each have as dihydrogen cleavage reagents,[30] we can use phos-
their specific place in the lattice and are not inter- phonium salts also as linkers now, which tether a cata-
changeable. Interestingly, the closest counteranions in lyst to an oxide support.
the lattice are both located at the same side of the
The linkers 10–12 have been immobilized on silica
complex, a fact that should facilitate the later well-de- to give 10i–12i according to the straightforward stan-
fined binding of 18 to the silica surface. Furthermore, dard procedure of stirring the mixture in toluene
the phenyl rings are fanning out of the ligand, and overnight at 508C. The counteranion does not play a
thus might form a protecting “umbrella” that prevents crucial role for the immobilization of phosphonium
the interaction of the Rh center with the reactive sur- salts on silica, and therefore 17i with the triflate in-
face.
stead of the iodide counteranion could be generated
by the same procedure. The resulting surface coverag-
es are given in Table 1, together with the data for the
corresponding immobilized Rh complexes, which
have been obtained by ligand exchange at room tem-
perature (13i–15i, Scheme 1), and reaction of 18 with
Immobilization of the Phosphine Linkers and Rh
Complexes
One conventional way of binding metal complexes to silica to give 18i. Although this work focuses on silica
oxide surfaces is, for example, using ethoxysilane con- as the support, it should be mentioned that other
taining
(CH2)3PPh2,[24a] which form covalent Si O Si bonds phonium immobilization, too. The experimental maxi-
with silica. Under certain conditions, however, the mal surface coverages for a monolayer of linker or
linkers,[2–4,7–9,11,24]
such
as (EtO)3Si- oxide supports like alumina are favorable for phos-
À À
ACHTUNGTRENNUNG
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Synthesis, Immobilization, MAS and HR-MAS NMR of a New Chelate Phosphine Linker System
Table 1. Surface coverages[a] of the modified silica 10i–15i
and 17i–21i with the corresponding molecular species X
(10–15, 17–21).
The most powerful method for characterizing all
surface-bound species is solid-state NMR spectrosco-
py.[10] For the chemistry presented here, 31P is the ana-
lytically most valuable nucleus. Whenever the materi-
als or molecules are rigid by nature, the classical way
of measurement, which involves filling the dry materi-
al into a rotor and spinning with the magic angle
(MAS) while cross-polarizing (CP) the proton mag-
netization, is the only option.[5a] Possible drawbacks of
CP/MAS are that the signals can no longer be inte-
grated, and that at higher rotational frequencies the
Hartmann–Hahn matching pattern splits into separate
bands and signal intensity might be lost.[10d]
However, in cases where the species possess some
degree of motional freedom in the presence of a sol-
vent, spinning a slurry of the material reduces the line
widths substantially in an HR-MAS (high-resolution
MAS)[11] spectrum. Problems associated with CP are
avoided, because HR-MAS spectra are best recorded
with high-power decoupling only.[11a] Our surface-
bound linkers 17i and 10i–12i with their long flexible
alkyl chains are sufficiently mobile in the presence of
a solvent such as benzene to be amenable to HR-
Material Molecules per
100 nm2 SiO2
mg of X per mmol of X per
g SiO2
g SiO2
10i
11i
12i
17i
13i
14i
15i
18i
19i
20i
21i
3.25
2.14
1.57
2.88
3.25
2.14
1.57
2.88
34.3
47.7
39.3
36
28
24
28
42
31
27
36
0.041
0.027
0.020
0.036
0.041
0.027
0.020
0.036
0.427
0.593
0.489
147
304
238
[a]
All surface coverages correspond to 25% of the maximal
coverage of the surface with a monolayer of the molecu-
lar species X, with the exception of 19i–21i, where the
surface coverage is 100%.
Rh complex on the silica surface have always been MAS. Figure 3 shows for 11i as an example that due
below the theoretically possible surface coverage. A to the mobilizing effect of the solvent, combined with
rough estimate of the calculated maximal surface cov- MAS, very narrow lines can be obtained with HR-
erage can be obtained by using the linker chain MAS. The half-widths of the HR-MAS signals
length, including the phenyl groups, as the radius of a (middle) for both the phosphonium and phosphine
circle that would describe the footprint of the mole- moiety of 11i are, with 92 and 73 Hz, nearly as small
cule if it was planar. For example, the chain lengths as those in the solution spectrum (bottom). In contrast
for 10 and 11 can be estimated to be 11.3 and 14.9 ꢂ, to this, the corresponding signals of the classical MAS
respectively, and their (flat) foot print would be about spectra of the dry material 11i are much broader with
401 and 698 ꢂ2. Taking into account that only 78.5% 421 and 635 Hz. All chemical shifts and half-widths of
of a flat surface can be filled with circles, this would the 31P MAS signals of the dry materials 10i–12i and
translate into surface coverages of about 20 molecules 17i, and for their HR-MAS resonances are given in
per 100 nm2 surface for 10i and about 11 per 100 nm2 Table 2. As expected, the longer the alkyl chains, the
for 11i. The experimentally determined maximal sur- higher is the mobility in the presence of the solvent,
face coverages of about 14 and 8 molecules of 10i and in accordance with the results of a study with mono-
11i on 100 nm2 of silica surface are lower, most proba- dentate, covalently bound linkers with long alkyl
bly due to the fact that favorable binding sites are not chains.[9] But even for the linker 17i with the shortest
homogeneously distributed on the surface. Addition- possible alkyl chain, the HR-MAS signals show sub-
ally, the narrow ends of the irregular pores, which
count for the silica surface area when determined by
BET measurements, might not be accessible for the
rather large linker systems 10i–12i. The surface cover-
ages with the model phosphonium salts 19–21 are
much higher (Table 1 gives the maximal experimental
coverages), because the chains are shorter without the
extending diphenylphosphine groups, and this leads to
smaller foot prints. Most importantly, while statistical-
ly many linkers are still in contact with each other on
the surface, when they are immobilized with maximal
coverage, at 25% of the maximal loading the linkers
Figure 3. 31P NMR of 11 (solution in C6D6, bottom), 31P HR-
MAS of a slurry of 11i with C6D6 (middle, spinning frequen-
cy 2 kHz), and 31P MAS NMR of dry 11i (top, rotational fre-
quency 4 kHz).
are well separated from each other. This means that
the Rh complexes immobilized with 25% of the maxi-
mal coverage should not be able to dimerize and
therewith lose their catalytic activity prematurely.
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Table 2. 31P MAS and HR-MAS NMR chemical shifts d and
signal half-widths n1/2 for the phosphonium and phosphine
signals (P+/P) of the linker-modified silica 10i–12i and 17i
with maximal surface coverages (values for 25% coverage
see Table 1). Rotational frequencies were 4 kHz for MAS
measurements of dry materials, and 2 kHz for HR-MAS of
slurries with C6D6.
be able to simulate the performance of a homogene-
ous catalyst. As it is already known from earlier stud-
ies without sample rotation,[24a] the 31P NMR line-
widths obtained from slurries of immobilized linkers
are dependent on the solvent. In general, the less vis-
cous and more polar the solvent is, the narrower are
the signals. This is in accordance with the 31P HR-
MAS signals of the linkers presented here, so even
with spinning at 2 kHz the solvent plays a major role
for the spectrum quality. As an example, 12i has also
been measured in the presence of a variety of organic
solvents other than benzene, and the resulting phos-
phine signals are displayed in Figure 4. The chemical
shifts change over a range of maximally 0.4 ppm in
the different solvents, which does not exceed the
chemical shift changes one would find in solution.
The line-widths are smallest with 20–24 Hz for the
Material
(P+/P)
d
N
dA
n1/2
n1/2 (HR-
(MAS)
[ppm]
17i
10i
11i
12i
35.0/À29.2 33.7/À31.2
31.8/À15.9 30.0/À17.8
31.5/À15.9 30.4/À17.0
31.6/À16.0 30.4/À16.9
835/1780 300/505
666/1448 604/239
421/635 92/73
352/416 100/39
stantially narrower lines, in accordance with the case least viscous and most polar solvents, such as di-
of a covalently bound tripod-type ethoxysilane con- chloromethane, acetonitrile and methanol, while the
taining linker.[8] When the surface coverage with unpolar hexane leads to a comparatively broad line
linker is lowered to 25% of the maximal coverage, with a half-width of 134 Hz. However, while the link-
typically the signal half-widths increase. For example, ers 10i–12i and 17i are rather robust, taking the coor-
the half-width for the phosphonium (phosphine) dinated metal complexes into account, non-protic and
moiety of 11i increases from 92 (73) to 278 (189) Hz. non-coordinating solvents are preferred for catalysis.
This again corroborates former results that have been Fortunately, the line-widths of 12i in toluene (26 Hz)
obtained without spinning.[24a] The lower surface cov- and benzene (43 Hz) imply that the linkers are still
erage leads to reduced mobility of the phosphine very mobile under the conditions of catalysis
group, because now there are enough surface sites left (Figure 4, Table 2). Therefore, toluene as the solvent
for the phosphine to adsorb. This in turn also reduces for the Rh catalysts 13i–15i and 18i should provide
the rotational and overall mobility of the phosphoni- conditions as close as possible to homogeneous
um group.
catalysis with respect to catalyst mobility.
Interestingly, although the effect is not as pro-
The linkers 10i–12i and 17i are bound to the sup-
nounced as with the phosphine groups, even for the port via electrostatic interactions of the phosphonium
phosphonium 31P HR-MAS signals of all surface- groups with the silica surface. While covalently bound
bound linkers the line-widths become smaller linkers such as ethoxysilanes show some detachment
(Table 2). This indicates that in spite of the strong from the surface under harsh conditions,[24a] for sur-
electrostatic interactions with the surface some mobi- face-bound phosphonium salts the database is rather
lity of the phosphonium moiety must be possible. Pre- slim. Our preliminary experiments show that the
liminary studies using the deuterated phosphonium
salt [Ph3PCD3]I bound to the silica surface via electro-
static interactions prove that there is no translational
motion of the salt on the surface in the absence of a
solvent. Whether the mobility of the linkers presented
here is of a wagging or rotational type, will be the
subject of a future, more detailed study. Most impor-
tant with respect to catalysis is that the phosphine
groups, and therewith the linker chains, are sufficient-
ly mobile in a solvent to allow the later bending to-
wards and coordination of the Rh complex. Further-
more, since translational mobility of the linkers can
be excluded, the catalysts 13i–15i should not be vul-
nerable to deactivation by dimerization.[4]
One key question in our quest for the optimal im-
mobilized catalyst is whether the catalytic activity and
selectivity depend on the chain length and therewith
the mobility of the linker and the catalyst. The more
Figure 4. 31P HR-MAS lineshapes with indicated half-widths
(left), and signal positions for 12i in the corresponding sol-
mobile the immobilized catalyst, the better it should vents. Rotational frequency 2 kHz.
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Synthesis, Immobilization, MAS and HR-MAS NMR of a New Chelate Phosphine Linker System
tons of the surface silanol groups,[31] or the formation
of new boron-containing species on the surface.[32]
Rather, the solubility of the phosphonium salts in the
corresponding solvents and the ability of the solvent
to replace the salts from the surface seem to play
major roles. This is reflected in the fact that THF and
methanol lead to the largest amounts of detached
phosphonium salts from the surface. Toluene is the
most favorable solvent for later catalysis, as it hardly
leads to any leaching (Figure 5). As compared to the
surface-bound model phosphonium salts 19i–21i, the
linkers 10i–12i and 17i should be somewhat more
robust towards leaching, or else one would have de-
tected the signals of free phosphines in solution in the
HR-MAS spectra of Figure 4. Probably, the diphenyl-
phosphine groups reduce the solubility and addition-
ally function as a shield against detachment by the
solvents. The single-crystal X-ray structure of 18 with
its “umbrella” of phenyl groups (Figure 2) supports
this assumption.
Figure 5. Graphic display of the leaching studies for the
model phosphonium salts 19–21. Leaching test: 400 mg of
functionalized SiO2 were suspended in the respective solvent
and stirred for 24 h at room temperature. The amount of
leached phosphonium salt in the supernatant was deter-
mined gravimetrically.
Immobilized Rhodium Catalysts
The immobilized Rh complexes 13i–15i have been ob-
binding of tetraarylphosphonium salts to a silica sur- tained from 10i–12i by ligand exchange with Wilkin-
face is rather strong, and arylphosphonium salts sonꢃs catalyst ClRh(PPh3)3 (1) at room temperature
AHCTUNGTRENNUNG
proved impossible to remove from the support in sub- (Scheme 1). With 25% surface coverage of the linkers
stantial amounts by ion exchange or other reagents only one Rh center should be bound per immobilized
without dissolving the oxide support.[5a] However, the linker molecule. The immobilized complex 18i has
solubility of the molecular phosphonium salts in the been obtained by directly attaching 18 (Scheme 2) on
given solvents might play a role, and it should be the silica surface. The catalyst obtained after immobi-
higher for alkylphosphonium salts. Naturally, leaching lizing 17 to give 17i, and then treating it with 1 dis-
due to linker detachment is a major issue for immobi- played catalysis characteristics identical with those of
lized catalysts, and therefore we probed the leaching 18i. The 31P MAS spectra prove that, after washing
of alkylphosphonium salts quantitatively and in detail. the materials thoroughly, there is no adsorbed PPh3
In order to be able to work with large quantities and left. Furthermore, no uncoordinated linker phos-
determine the leaching gravimetrically, while avoiding phines are present, and most importantly, no phos-
the expensive bromoalkene starting materials, we syn- phine oxide signals with their characteristic chemical
thesized the phosphonium salts 19–21 (Figure 5) as shift anisotropy (CSA) pattern.[10a,25] This is, for exam-
model compounds and immobilized them with maxi- ple, shown in the spectrum of 15i in Figure 6
mal surface coverage as 19i–21i (Table 1). The leach- (bottom). The phosphonium signal and the signal of
ing test revealed that practically no leaching occurs in the phosphines in trans positions to each other over-
non-polar solvents. Most importantly, the solvent used
for the catalysis, toluene, does not detach measurable
amounts of the phosphonium salts from the surface
(Figure 5). However, polar and protic solvents, such
as THF and methanol should be avoided as reaction
medium for catalysis, since they lead to major detach-
ment of the linker system from the SiO2 surface.
Hereby, the phosphonium salt with the shortest alkyl
chains, 19i, is most vulnerable to leaching. Interesting-
ly, the binding is practically independent of the nature
of the counteranion. This indicates that, for the tested
salts, the electrostatic interactions are not substantial-
Figure 6. 31P MAS spectra of catalyst 15i before (bottom)
ly augmented by additional F···H hydrogen bonds be-
À
tween the F atoms of the BF4 counteranion and pro- and after (top) catalysis.
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lap at about 30 ppm, while the resonance of the phos- in comparison with Wilkinsonꢃs catalyst in solution.
phorus nucleus trans to Cl appears at about 41 ppm. Encouraged by the catalytic activity of other Rh nor-
Overall the 31P MAS spectrum resembles the ones of bornadienyl complexes with chelate ligands,[35] we in-
various immobilized Wilkinson-type Rh complexes cluded 18i with the shortest possible alkyl chains in
that we studied earlier.[4] We could prove that in tolu- this study. The graphic representation of the results in
ene, as anticipated from the linker leaching studies Figure 7 shows that according to expectation, the ho-
described above, all catalysts are firmly tethered to mogeneous catalyst ClRhACHTNUTRGNE(UNG PPh3)3 is the fastest, be-
the support and that no noticeable leaching of the cause the substrate does not have to diffuse into the
ligand or the metal center into solution occurs, even pores of a support material and contains triaryl- in-
after stirring the material for a prolonged period of stead of diarylalkylphosphine ligands. Regarding the
time in toluene.
chain lengths of the linkers, the catalyst with the lon-
Olefin hydrogenation is one of the best developed gest alkyl chain, 15i, is the most active in the hydroge-
and most important catalytic reactions in academia nation of 1-dodecene (Figure 7), probably due to its
and industry,[33] therefore we use the catalytic hydro- maximal mobility. It is followed by the C7 species 14i,
genation of 1-dodecene as a model test reaction and finally 13i. In contrast to our anticipation, howev-
(Scheme 3). This also allows the comparison with ear- er, the catalyst 18i that is bound to the surface via a
lier results of our group[4] and others,[34] especially tripod-type linker is only in the beginning the least
since we retain the standard reaction conditions active. After an induction period of about two hours,
(Scheme 3). The only difference here is that the cata- it catalyzes the hydrogenation even faster than 15i,
lysts bound by the new alkylphosphine ligands need a and reaches 100% substrate conversion at about the
slightly higher temperature of 608C to perform within same overall reaction time (Figure 7). The 31P MAS
reasonable time frames. As expected from our earlier spectrum of 15i after catalysis (Figure 6, top) shows
work on hydrogenation catalysis,[4a,b] reducing the sur- basically the same signals as the spectrum recorded of
face coverage with catalyst to 25% of the maximal the material prior to catalysis. Only the relative signal
coverage prevents the dimerization of the Rh cata- intensities are changed, a phenomenon observed pre-
lysts, and leads to increased catalytic activity. These viously.[3c,4b] Most importantly, no signals of dimeric
early results also corroborated the assumption that species of the type [(R3P)2RhCl]2 are visible.
the linkers and thus metal centers are initially evenly
Next, the recycling characteristics of all immobi-
distributed on the surface, and do not form patches or lized catalysts have been tested. In earlier findings for
clusters. The results presented here are in accord with immobilized Wilkinson-type catalysts at room temper-
this assumption. For example, when 15i with maximal ature,[4] the first run had always shown the fastest con-
surface coverage (100%, 6.28 molecules per 100 nm2 version, and the activity slowly decreased with every
SiO2 surface, 108 mg of 15 per g of SiO2, 0.08 mmol of subsequent batchwise recycling step. The catalysts
15 per g of SiO2) is used for catalysis, only about 50% 13i–15i and 18i, however, display a different scenario,
H2 conversion is obtained after 20 h of reaction time. as the first run is often comparatively slow (Figure 8).
With 25% surface coverage (data in Table 1), quanti- Then, the activity increases with every recycling step
tative hydrogenation of 1-dodecene is achieved within and reaches a maximum at the third or fourth run,
10 h. Therefore, if not mentioned otherwise, in the before the activity finally consolidates at about 100%
following all catalysts studied have been immobilized
with 25% surface coverage.
Systems designed earlier using an ethoxysilane
linker could be recycled up to 13 times.[4] As the
record so far, a Wilkinson-type Rh catalyst immobi-
lized recently via a phosphonium-bound rigid tetra-
phenyltin scaffold can be recycled 30 times until the
H2 consumption drops below 100% within 100 h.[5b]
Following the usual test protocol for new linker sys-
tems, we probed the first run of the catalysts 13i–15i
Scheme 3. Catalytic hydrogenation of 1-dodecene; pressure
1.1 atm, substrate:catalyst ratio 100:1, reaction temperature:
608C, surface coverage of catalyst: ca. 2 metal centers per
100 nm2.
Figure 7. Activities of the indicated homogeneous and im-
mobilized catalysts for the hydrogenation of 1-dodecene in
the first run.
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Synthesis, Immobilization, MAS and HR-MAS NMR of a New Chelate Phosphine Linker System
Figure 9. Hydrogen consumption during 30 batchwise cata-
lytic runs using 14i. Only every fifth run is shown for clarity.
Figure 8. Hydrogen consumption during 14 batchwise cata-
lytic runs using 18i.
conversion within 30 to 40 h. For 18i there is even an below), or the catalyst decomposes partly by the inter-
induction period of about two hours. These phenom- action with the silica surface.
ena can be explained based on the catalysis results
discussed below.
The most impressive recycling performance has
been found for 14i, which can be recycled for 30
Interestingly, 18i shows a better recycling character- times in a batchwise manner, before the conversion of
istic than 13i, although the alkyl chains of the linker 1-dodecene to dodecane drops below 100% within
are shorter. Catalyst 18i can be recycled for a respect- 50 h (Figure 9). Interestingly, between the batchwise
able 14 times, before the conversion no longer reaches recycling runs, the washed and dried immobilized cat-
100% within 35 h (Figure 8). The catalyst 13i can only alyst can be stored under an inert gas atmosphere for
be recycled 3 times, before the conversion drops months without losing activity, when the recycling ex-
below 85% within 120 h. End-capping of residual sur- periments are resumed. Wilkinson-type Rh catalysts
face silanol groups after the linker tethering and prior immobilized with other linker types are less robust in
to the catalyst immobilization with trimethylsilyl this respect.[4b]
(TMS) groups improved the recycling characteristics
Encouraged by the positive effect of end-capping
of 13i substantially. Now, 13i can be recycled 7 times on 13i, in order to further increase the activity and
with 100% conversion of 1-dodecene within 35 h. prolong the lifetime of 14i, we attached TMS and tri-
Therefore, we conclude that with short linkers and in phenylsilyl groups on the silica surface after the im-
the absence of “shielding” counteranions (see X-ray mobilization of 11i, and prior to the generation of 14i.
structure in Figure 2), the decomposition of the cata- However, practically no change in the catalytic activi-
lytically active species by contact with the reactive ty or lifetime of silyl-capped 14i versus unmodified
silica surface is a major problem that can be amelio- 14i has been observed. Obviously, for 14i a robust cat-
rated with TMS-capping. However, the increase in alytic species is formed, whose performance is no
catalytic activity from the first run with only 70% longer dependent on the nature of the silica surface.
conversion within 30 h to the third, fourth and consec-
From the above results we conclude that there is at
utive runs with 100% indicates the formation of a least one additional species, other than 13i–15i, and
second catalytically active species even after end-cap- 18i, formed during catalysis, when we apply the new
ping (see below).
linkers. The most basic question in order to narrow in
In contrast to our expectation, based on the activity the nature of the new species is, whether the catalytic
in the first run (Figure 7) and the fact that the catalyst activity remains with the support, or whether it is
15i incorporates the longest linker alkyl chains that found in solution now. In order to check this issue, a
are supposed to keep the catalyst at a distance from split test has been performed on 14i (Figure 10).
the surface, the recycling characteristics of 15i are dis- After about 8 h of the third catalytic run with 14i and
appointing. In the second and third recycling run, 15i 40% conversion, an aliquot of the supernatant was re-
needs about 100 h to reach 80% conversion. We inter- moved from the reaction mixture. Then, the support-
pret this scenario as an optimally mimicked homoge- ed catalyst with the remaining supernatant, and also
neous catalysis in the first run, while subsequently an- the aliquot of the supernatant, were subjected again
other, catalytically less active species is formed (see to the hydrogenation conditions. While the solid re-
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Figure 11. Three-phase test using immobilized allyltriethoxy-
silane (details see text and Experimental Section).
Figure 10. Split test to prove that no Rh species in solution,
but only the surface-bound catalyst 14i hydrogenates the
substrate 1-dodecene (details see Experimental Section).
hydrogenation activity due to the spill-over effect of
the metal particles.
mains catalytically active and consumes all residual 1-
In order to check, whether indeed metal particles
dodecene, the supernatant does not show any sub- form with our new linker system during catalysis, we
strate conversion (Figure 10). Therefore, we conclude performed a test developed by the Crabtree group.[38]
that all catalytically active species involved stay firmly Homogeneous, molecular Rh catalysts can be pois-
attached to the support.
oned
by
adding
DBCOT
(dibenzo-
Another test that confirms that the catalytically
ACHTUNGTREN[NGNU a,e]cyclooctatetraene) to the reaction mixture.
active species stays on the support involves covalently DBCOT is a strong ligand, but is not hydrogenated.
binding an olefin to a different batch of support mate- Therefore, once DBCOT binds to the Rh center, it
rial and checking whether it is hydrogenated by the prevents further hydrogenation of other substrates.
immobilized catalyst.[36] For this three-phase test, al- However, DBCOT does not strongly bind to metal
lyltriethoxysilane was covalently bound to a different surfaces due to steric constraints. Therefore, it cannot
À À
batch of silica via Si O Si linkages according to the inhibit the catalytic activity of metal particles.
well-explored procedure.[24b,c] Then, the batch with al-
Figure 12 shows the DBCOT poisoning results and
lyltriethoxysilane-modified silica was combined with a the validity of the test. When two equivalents of
batch of 14i and the hydrogenation procedure was
started. The immobilized catalyst 14i did not hydro-
genate any of the tethered olefin, as checked by mon-
itoring the hydrogen consumption (Figure 11) and 13C
HR-MAS[11a] of the tethered olefin. When, as a con-
trol experiment, the homogeneous catalyst ClRh-
ACHTUNGTRENNUNG(PPh3)3 (1) was added, however, all surface-bound
allyl groups were hydrogenated. Therefore, we con-
clude that no catalytically active species leaches from
14i into solution.
In order to better describe the new surface-bound
catalyst that forms during the reaction, we took the
following observation into account: In contrast to ear-
lier hydrogenation scenarios,[5b] here we also noticed
that, with the new linker system, the silica-bound cat-
alyst turned from orange to black already within 5 h
during the first run. This indicates the formation of
metal particles in addition to the molecular catalyst,
and based on the pioneering work of Angelici
et al.,[37] this would explain the initial increase of the
Figure 12. Hydrogen consumption of the shown catalysts
with and without the poisoning agent DBCOT (dibenzo-
AHCTUNGTRENN[GUN a,e]cyclooctatetraene) (see text).
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Synthesis, Immobilization, MAS and HR-MAS NMR of a New Chelate Phosphine Linker System
DBCOT are added to the homogeneous Wilkinsonꢃs be solely based on the formation of metal particles,
catalyst in solution, the conversion of dodecene de- which coincides with the color change occurring with
creases from originally 100% within 4 h to about 43% the onset of the hydrogen consumption.
in 25 h. For the test with the immobilized catalyst 14i,
Further evidence for this assumption is based on
one batch of TMS-capped 14i at the 8th run has been the selectivity of the hydrogenation reaction. It is
studied. In comparison, 14i at the 9th run has been known that heterogeneous catalysts that consist of
tested in the presence of two equivalents of DBCOT. metal particles can shift double bonds in linear 1-alke-
Both substrate consumption curves are nearly identi- nes,[39a] as well as cyclic olefins.[39b] This double bond
cal. Therefore we conclude that at the 8th catalytic shift only takes place in the presence of H2. For exam-
run at the latest the catalyst consists mainly of metal ple, material containing Rh(0) on silica, obtained by
particles that are not affected by the DBCOT, and depositing [(COD)RhCl]2 on silica according to the
not of molecular single-site species.
literature procedure[40] (see Experimental Section),
Next we studied whether the metal particle forma- did not isomerize 1-dodecene under the standard cat-
tion coincides with the catalyst turning black in the alysis conditions, but in the absence of H2, as proven
1
first run. For this purpose, fresh TMS-capped 14i has by H NMR. The same result was obtained for 18i
been split into two batches, and one has been allowed after the 14th run, when it was stirred with 1-dodecene
to hydrogenate 1-dodecene under the standard condi- under the standard conditions, but without H2. Since
tions, while the other has been additionally poisoned this isomerization will not be obvious for 1-dodecene
with 2 equivalents of DBCOT. In the first 5 h both after quantitative hydrogenation, we investigated the
batches showed an orange color, and while the pois- reaction mixture of the third catalytic run by GC and
oned batch only reached about 30%, the pristine 1H NMR at about 40% conversion with catalyst 14i.
1
batch gave about 44% conversion (Figure 13). After Indeed, not only resonances for the terminal olefin H
5 h, the poisoned catalyst turned black and its catalyt- signals of residual 1-docedene with a relative intensity
ic activity soon matched the one of the pristine batch. of about 2%, but also ca. 98% of signal intensity for
Therefore, we conclude that the formation of metal protons at different internal double bonds have been
particles correlates with the color change of the cata- found. The reason why 1-dodecene is present in only
lyst, and that this takes place within the first 5 to 10 h 2% is most probably because it is more easily trans-
of hydrogenation. So, in the beginning of the first cat- formed into dodecane than the dodecene isomers
alytic run, both surface-bound molecular complexes, with internal double bonds, and is therefore continu-
as well as metal particles take part in the catalytic hy- ally removed from the equilibrium. As a comparison,
drogenation.
we checked the reaction mixture after 52% substrate
For 18i the extended induction period is most prob- conversion by Wilkinsonꢃs catalyst, and found less
1
ably not due to the norbornadiene dissociation, be- than 20% of H signal intensity stemming from dode-
cause the molecular complex 18 in solution is not cat- cene isomers with internal double bonds.
alytically active. The catalytic activity of 18i seems to
Finally, the nitrobenzene test[38] has been applied to
prove the presence of metal particles on the silica sur-
face of catalyst 13i. According to this test, only heter-
ogeneous metal particles catalyze the reduction of ni-
trobenzene to aniline. Indeed, Wilkinsonꢃs catalyst in
solution does not consume hydrogen in the presence
of nitrobenzene within the first 10 h of reaction. Hy-
drogen consumption only starts when the solution
turns black and cloudy, indicating decomposition of
the homogeneous catalyst under formation of metal
particles. Catalyst 13i, after an induction period of
about 10 h, starts to transform nitrobenzene into ani-
line, and achieves about 85% conversion after 200 h
reaction time.
Next we sought to generate catalytically active
metal particles to prove our hypothesis. The immobi-
lized catalyst 14i can be stirred at 708C under a nitro-
gen atmosphere overnight without a visible change of
the orange color taking place. However, with admis-
sion of hydrogen, the color darkens slightly even at
room temperature. At 708C, exposure of 14i to a hy-
drogen atmosphere leads to the blackening of the ma-
terial within one hour. Therefore, we conclude that
Figure 13. Hydrogen consumption of the TMS-capped cata-
lyst 14i in the first run with and without the poisoning agent
DBCOT (dibenzoACHTUNGTRENNUNG[a,e]cyclooctatetraene) (see text).
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Figure 14. TEM images (left) of Rh nanoparticles that formed during catalysis with 13i (top), 14i (middle), and 15i (bottom),
and their corresponding size distributions (right).
hydrogen is the reducing agent, while the temperature are reasonable, as the activity does not change sub-
is only a minor issue, and the olefin does not play a stantially between the second and the third runs. In-
significant role in this process. Based on this insight, terestingly, comparing the obtained hydrogen con-
[(COD)RhCl]2 was deposited on silica according to sumption curves with those of 15i, they are nearly
the literature procedure[40] (see Experimental Sec- identical. Therefore, we conclude that due to the long
tion), and the dry material was reduced in a stream of linker alkyl chains that allow maximal mobility, inter-
hydrogen, while increasing the temperature from 60 actions with the surface, and hydrogen access, 15i is
to 1208C for 4 h. During this time, the color of the reduced rapidly and forms metal particles.
powder changed from yellow to black. The resulting
In order to confirm these assumptions and probe
material contains 0.04 weight% of Rh. The heteroge- the sizes of the formed metal particles, we recorded
neous catalyst obtained in this way is rather slow with TEM measurements of 13i–15i. The pictures in
respect to hydrogenation. For about 85% conversion Figure 14 show clearly that Rh nanoparticles[41] form
it needs 80 h. However, the recycling characteristics within the silica. Their size distribution is similar and
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Synthesis, Immobilization, MAS and HR-MAS NMR of a New Chelate Phosphine Linker System
1
ments H high-power decoupling was applied. The recycle
rather narrow, with an average diameter of 3 to 4 nm.
The diameter is most probably dominated by the
average pore size of the support material (4 nm), that
prevents the particles from growing any larger. There-
fore, the size distribution proves that the nanoparti-
cles reside within the pores of the support material.
The inclusion of the nanoparticles within the pores
explains the optimal recyclability of the catalysts, and
the absence of leaching. The formation of 100%
nanoparticles from the starting immobilized catalysts
is unlikely, since the 31P solid-state NMR spectra of
the materials before and after catalysis (Figure 6) are
very similar. It is also noteworthy that no resonance
for uncoordinated, surface-bound phosphines occurs.
Unfortunately, the TEM measurements do not allow
precise quantification of the Rh centers. However,
clearly only a fraction of the metal centers is exposed
on the surface and accessible for the substrate. But on
the other hand, the longevity of the nanoparticle cata-
lysts is yet another proof that the pores of the silica
are not clogged by the substrate or products, or any
decomposed catalyst.
delays were 5 s for HR-MAS and 10 s for MAS spectra. For
more measurement details, see ref.[11a] GC analyses were car-
ried out on a Shimadzu GC 2010 gas chromatograph
equipped with a SHRXI-5MS column (15 mꢄ0.25 mmꢄ
0.25 mm) and a flame ionization detector (GC:FID). TEM
images were obtained on an FEI Tecnai G2 F20 microscope
and ImageJ software was used to determine the particle size
distribution. All reactions were carried out using standard
Schlenk techniques and a purified N2 atmosphere, if not
stated otherwise. Reagents purchased from Sigma Aldrich
or VWR were used without further purification. Solvents
were dried by boiling them over Na, distilled, and stored
under N2. CH2Cl2 was obtained from a solvent purification
system. The silica (Merck, 40 ꢂ average pore diameter,
0.063 to 0.2 mm average particle size, specific surface area
750 m2 gÀ1) was rigorously dried under vacuum at 4008C for
4 days to remove adsorbed water and condense surface sila-
nol groups. Ligand 3 has been synthesized according to the
procedure given by Clark and Hartwell,[12a] the phosphines 4
and 5 as described by Gladysz.[14]
General Procedure for the Immobilization of
Phosphine Linkers 10–12 and 17, and Rh Complex 18
via the Phosphonium Group
Phosphine linker 11 (67 mg, 0.065 mmol) was dissolved in
toluene (15 mL) and added to a suspension of 2.434 g of
SiO2 in toluene (40 mL). The mixture was stirred overnight
at 508C. The silica was allowed to settle down and the su-
pernatant was removed. The functionalized silica 11i was
then washed with toluene (2ꢄ10 mL) and with Et2O (2ꢄ
10 mL). Subsequently the silica was dried under vacuum for
several hours. The supernatant and the solvents from the
washing process were combined and all volatile matter was
removed under vacuum. The residue showed no 31P NMR
resonance, so all the linker 11 was immobilized on the sup-
port, resulting in 11i with about 2 molecules per 100 nm2 of
silica surface (data for all immobilized species are given in
Table 1).
Conclusions
Using a new trisphosphine chelate linker system we
could obtain immobilized Rh catalysts that can be re-
cycled more than 30 times without major loss of activ-
ity. It has been demonstrated that in contrast to previ-
ous Rh-catalyst systems that were immobilized via
rigid tetraphenyl-element linker scaffolds that prevent
interactions with the silica surface,[5b] here due to the
reducing effect of hydrogen, a second catalytically
active species forms at the higher temperatures of
608C needed for these catalysts with alkyldiphenyl-
phosphine ligands to be active. It could be proven by
catalytic test reactions, catalyst poisoning experi-
ments, and TEM measurements that the new active
species consist of Rh nanoparticles.[41] All linkers
lead, on a different time scale, basically to the same
nanoparticles, explaining their very similar catalytic
characteristics. Future work will be devoted to defin-
ing the process of nanoparticle formation quantita-
tively.
General Procedure for the Catalyst Preparation
ClRhACHTNUTGRNEGNU(PPh3)3 (23 mg, 0.025 mmol), dissolved in 10 mL of tol-
uene, was added to a slurry of the functionalized silica 11i
(1.006 g, 0.026 mmol ligand) in 10 mL of toluene. The mix-
ture was stirred overnight at room temperature, then the
silica was allowed to settle down and the supernatant was
removed. The catalyst-containing silica 14i was washed with
toluene (3ꢄ10 mL) and dried under vacuum for 4 h. The su-
pernatant and the washing portions were combined and the
solvent was removed under vacuum. The residue was ana-
lyzed by NMR and showed only the 31P resonance of PPh3.
Experimental Section
General Remarks
General Procedure for TMS-Capped Catalysts
1
The H, 13C, 19F, and 31P NMR spectra of liquids were re-
To prepare catalyst 14i-TMS with end-capped SiOH groups,
ligand 11 was protected as the BH3 adduct by adding
BH3 SMe2 (0.5 mL, 400 mg, 5.265 mmol) to a solution of 11
(240 mg, 0.235 mmol) in toluene (20 mL). The reaction mix-
ture was stirred for 5 h at room temperature and the quanti-
tative conversion to 11.BH3 was checked by 31P NMR
(broad signal, d=15.5 ppm). Then the solvent was removed
corded at 499.70, 125.66, 202.28, and 470.17 MHz on a
.
500 MHz Varian spectrometer. The 13C, 19F, and 31P spectra
1
were recorded with H decoupling if not stated otherwise.
The solid-state NMR spectra were measured with a Bruker
Avance 400 widebore NMR spectrometer with 4 or 7 mm
MAS probeheads. For the 31P HR-MAS and MAS measure-
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under vacuum and the precipitate washed with pentane (2ꢄ
5 mL). 11.BH3 was then immobilized according to the gener-
al procedure described above. 4 mL of Me3SiOEt were
added to 11i.BH3 (2.999 g, 0.080 mmol ligand) and the mix-
ture was stirred at 608C for 40 h. Then the supernatant was
removed and the functionalized silica was washed with tolu-
ene (3ꢄ10 mL) and dried under vacuum. Then 11i.BH3-
TMS was added to 139 mg (1.239 mmol) of DABCO (1,4-
and filtered through a frit. Both the remaining reaction mix-
ture with the silica support and the filtered supernatant
were reconnected to separate hydrogenation apparatuses,
and the hydrogen consumption was monitored for both sam-
ples. After the hydrogen uptake had stopped, for both cases
1
the reaction mixtures were analyzed by GC and H NMR.
General Procedure for the Rh(0) Catalyst
Preparation[40]
diazabicycloACHTUNGTRENNUNG[2.2.2]octane), dissolved in 30 mL of toluene,
and stirred overnight. Finally, the supernatant was removed,
and 11i-TMS was washed two times with 10 mL aliquots of
toluene. Then 14i-TMS was prepared from 11i-TMS accord-
ing to the general procedure for the catalyst preparation de-
scribed above.
Silica (1.029 g) was suspended in 15 mL of toluene.
[(COD)RhCl]2 (10 mg, 0.020 mmol) was dissolved in 10 mL
of toluene, added to the silica slurry, and the mixture was
stirred for 3 h at room temperature. Then the solvent was
removed under vacuum to give a yellow powder. This mate-
rial was then heated from 608C to 1208C over 4 h in an H2
gas stream. The material darkened gradually until it became
black.
General Procedure for the Catalytic Hydrogenation
The immobilized catalyst 14i (386 mg, 0.010 mmol Rh) was
added to 4 mL of toluene in a Schlenk flask. Then the
Schlenk flask was attached to the standardized hydrogena-
tion apparatus[4c] and warmed up to 608C. The apparatus
was allowed to stand under H2 prior to catalysis in order to
make sure that H2 is not lost due to a leakage. Additionally,
any loss of H2 after 100% conversion of the substrate was
monitored and excluded. To start the catalysis, 1 mmol of 1-
dodecene, dissolved in 1 mL of toluene, was added to the
suspension through the stopcock via syringe. Then the sus-
pension was stirred vigorously with a magnetic stir bar and
the hydrogen uptake was monitored. After complete con-
sumption of the hydrogen the silica was allowed to settle
down, the supernatant was removed and the silica was
washed with toluene (2ꢄ4 mL). The supernatant was ana-
Catalyst Poisoning Experiment with DBCOT
The immobilized catalyst 14i-TMS (375 mg, 0.010 mmol Rh)
was stirred in 4 mL of toluene in a Schlenk flask. Then
dibenzoACHTNUTRGNE[UNG a,e]cyclooctatetraene DBCOT (4 mg, 0.020 mmol)
was added and the mixture was stirred for 2 h at room tem-
perature. The Schlenk flask was attached to the standar-
dized hydrogenation apparatus[4c] and warmed to 608C.
Then 1 mmol of 1-dodecene, dissolved in 1 mL of toluene,
was added to the slurry through the stopcock via syringe.
While the mixture was stirred, the hydrogen uptake was
monitored. After complete conversion the silica was allowed
to settle down. Then the supernatant was removed and the
silica was washed with toluene (2ꢄ4 mL). The supernatant
1
lyzed by GC and H NMR to confirm quantitative conver-
1
was analyzed by GC and H NMR to confirm 100% conver-
sion of the olefin to dodecane. The H2 consumption always
matched the substrate formation within the error margins of
the analytical methods. For example, after the consumption
of 54% H2 in the 15th catalytic run with 14i, the GC and
1H NMR analyses indicated 57 and 55% dodecane forma-
tion.
sion.
Methyltris(prop-2-enyl)phosphonium Iodide (6)
Procedure for the Three-Phase Test
Immobilized catalyst 14i-TMS (375 mg, 0.01 mmol Rh) and
allyltriethoxysilyl-functionalized silica[24] (890 mg, 0.5 mmol
allyl groups) were added to a Schlenk flask with 5 mL of tol-
uene and warmed to 608C. Then the Schlenk flask was
purged with H2, connected to the standardized hydrogena-
tion apparatus,[4c] and the H2 consumption was monitored.
As a control experiment the same procedure was carried
out with Wilkinsonꢃs catalyst (8 mg, 0.01 mmol) instead of
immobilized catalyst 14i-TMS.
PCl3 (254 mg, 1.849 mmol) was dissolved in Et2O (10 mL)
and added dropwise to a 1M ether solution of allylmagnesi-
um bromide (5.5 mL, 5.500 mmol), diluted with 40 mL in
Et2O, over 1 h at 08C. Then the reaction mixture was al-
lowed to warm up to room temperature and stirred over-
night. After the reaction mixture was cooled to 08C and
quenched with 20 mL of H2O, the mixture was stirred at
room temperature for 2 h. The organic layer was filtered
through Na2SO4 and the aqueous layer was washed twice
with 30 mL portions of Et2O. The organic layers were com-
bined, 947 mg (6.672 mmol) of methyl iodide was added,
and the reaction mixture was stirred overnight at room tem-
perature. Then the solvent was removed under vacuum. The
crude product was washed with pentane (6ꢄ15 mL) to give
Procedure for the Split Test
Immobilized catalyst 14i (386 mg, 0.010 mmol Rh) was
added to 4 mL of toluene in a Schlenk flask. Then the
Schlenk flask was attached to the standardized hydrogena-
tion apparatus[4c] and warmed to 608C. To start the catalysis
1-dodecene (1 mmol, dissolved in 1 mL of toluene) was
added. The hydrogen consumption was monitored and after
ca. 40% conversion the hydrogen reservoir was disconnected
and the silica support was allowed to settle down. Then
2 mL of the hot supernatant were removed with a syringe
triallylACTHNUTRGENUG(N methyl)phosphonium iodide as a colorless waxy
solid; yield: 263 mg (0.977 mmol, 53%). 1H NMR (CDCl3,
3
499.70 MHz): d=5.70–5.87 (m, 3H, H-2), 5.58 [ddq, Jtrans
-
(1H-1H)=16.9 Hz, 3J(1H-1H)=5.3 Hz, 2J(1H-1H)=1.0 Hz,
AHCTUNGTREUNNGN ACHTUNGTRENNUNG ACTHNUGTRENNGUN
456
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 443 – 460

Synthesis, Immobilization, MAS and HR-MAS NMR of a New Chelate Phosphine Linker System
3H, H-3Z], 5.49 [ddd, 3J
cisA
4.8 Hz, 2J (1H-1H)=0.8 Hz, 3H, H-3E], 3.52 [dd, 2J-
(31P-1H)=15.8 Hz, J
CHTUNGTRENNUNG CAHTUNGTRENNUNG
(1H-1H)=9.9 Hz, 3J(1H-1H)=
Methyltris(undec-10-enyl)phosphonium Iodide (9)
CHTUNGTRENNUNG
3
2
G
A
3H,
H4];
13C NMR
(31P-13C)=12.2 Hz, C-2],
(CDCl3,
125.66 MHz): d=125.32 [d, 3J
G
2
1
123.17 [d, J
47.7 Hz, C-1], 4.14 [d, J
(31P-13C)=10.3 Hz, C-3], 25.72 [d, J
G
1
N
Phosphine 6 (431 mg, 0.878 mmol) was dissolved in 20 mL
of toluene and 463 mg of CH3I (0.203 mL, 3.272 mmol) was
added. The reaction mixture was stirred at room tempera-
ture for 24 h. Then the solvent was removed under vacuum
and the remaining residue was washed with pentane to give
(CDCl3, 202.28 MHz): d=27.47.
Methyltris(but-3-enyl)phosphonium Iodide (7)
9 as a colorless oil; yield: 490 mg (0.774 mmol, 88%).
3
1H NMR (C6D6, 499.70 MHz): d=5.82 [ddt, J
(1H-1H)=
transACHTNUGTRENNUNG
15.0 Hz, 3J
(1H-1H)=10.2 Hz, 3J(1H-1H)=6.7 Hz, 3H, H-
cisACHTUGTNRENNUG AHCTUNGTRENNGUN
10], 4.96–5.14 (m, 6H, overlapping H-11cis and H-11trans),
1
2.45–2.60 (m broad, 6H, H-1), 2.33 [d, JACTHNUTRGNEUNG
(31P-1H)=13.8 Hz,
Phosphine 4 (311 mg, 1.584 mmol) was dissolved in 20 mL
of toluene and 0.43 mL of CH3I (800 mg, 5.654 mmol) was
added. The reaction mixture was stirred at room tempera-
ture for 48 h. Then the solvent was removed under vacuum
and the remaining residue was washed with pentane to give
3H, H-12], 2.07 (q, J=7.3 Hz, 6H, H-2*), 1.94–2.05 (m, 6H,
H-9*), 1.20–1.51 (b, 36H, H-3, H-4, H-5, H-6, H-7, H-8);
13C NMR (C6D6, 125.66 MHz): d=139.26 (s, C-10), 114.58
3
(s, C-11), 34.29 (s, C-9), 31.11 [d, J
(31P-13C)=15.1 Hz, C-3],
29.99# (s), 29.93# (s), 29.64# (s), 29.56# (s), 29.43# (s), 22.17 [d,
2J(31P-13C)=4.6 Hz, C-2], 20.96 [d, 1J(31P-13C)=48.5 Hz, C-
1], 6.09 [d, 1J(31P-13C)=51.4 Hz, C-12]; 31P NMR (C6D6#,
7 as a colorless solid; yield: 401 mg (1.185 mmol, 75%).
3
1H NMR (CDCl3, 499.70 MHz): d=5.88 [ddt, J
(1H-1H)=
transACHTNUGTRENNUNG
A
ACHTUNGTRENNUNG
3
3
16.6 Hz, J
5.23 [ddt, 3J
(1H-1H)=1.5 Hz, 3H, H-4cis], 5.16 [ddt, 3J
CHTUNGTRENNUNG
cisA
(1H-1H)=6.4 Hz, 3H, H-3],
(1H-1H)=2.1 Hz, 4J-
cisA
(1H-1H)=
R
202.28 MHz): d=31.11 (s) (* assignments interchangeable,
T
no assignments of C-4 to C8 possible).
A
2
4
10.2 Hz, JACHTUNGTRENNUNG ACHTGNUTRENNUNG
(1H-1H)=2.3 Hz, J
2
2.67 (m, 6H, H-1), 2.46 (m, 6H, H-2), 2.02 [d, J
A
Methyltris(4-diphenylphosphinobutyl)phosphonium
Iodide (10)
13.5 Hz, 3H, H-5); 13C NMR (CDCl3, 125.66 MHz): d=
3
134.75 [d, J
ACHTUNGTRENNUNG
2
1
[d, J
(31P-13C)=4.1 Hz, C-2], 20.53 [d, J
C-1], 6.43 [d, J
(31P-13C)=47.8 Hz,
(31P-13C)=50.9 Hz, C-5]; 31P NMR (CDCl3,
1
202.28 MHz): d=33.28 (s).; melting range 170–1738C.
Methyltris(hept-6-enyl)phosphonium Iodide (8)
Phosphonium salt 7 (246 mg, 0.727 mmol), AIBN (119 mg,
0.724 mmol), and 0.9 mL of Ph2PH (963 mg, 5.172 mmol)
were combined in a Schlenk flask, heated under an N2 at-
mosphere to 708C and stirred for 3.5 days. The conversion
was monitored by 31P NMR of the reaction mixture. After
completion of the reaction, 2 mL of toluene were added to
remove excess Ph2PH, and the product precipitated after
adding 3 mL of pentane. The supernatant was discarded and
the solid was again treated with 2 mL of toluene and pre-
cipitated with 3 mL of pentane. The precipitate was dried
under vacuum at 708C to give 10 as a colorless powder;
Phosphine 5 (362 mg, 1.123 mmol) was dissolved in 30 mL
of toluene and 0.3 mL of CH3I (684 mg, 4.819 mmol) was
added. The reaction mixture was stirred at room tempera-
ture for 36 h. Then the solvent was removed under vacuum
and the remaining residue was washed with pentane to give
1
yield: 640 mg (0.725 mmol, quantitative). H NMR (CDCl3,
499.70 MHz): d=7.42–7.37 (m, 12H, Ho), 7.34–7.28 (m,
8 as a colorless oil; yield: 356 mg (0.766 mmol, 68%).
3
1H NMR (C6D6, 499.70 MHz): d=5.89 [tdd, J
(1H-1H)=
transACHTNUGTRENNUNG
3
3
16.9, 3 Hz, J
H-6], 5.17 [ddt, 3J
4J(1H-1H)=1.5 Hz, 3H, H-7cis], 5.07 [tdd, 3J
10.2 Hz, 2J(1H-1H)=2.3 Hz, 4J(1H-1H)=1.2, 3 Hz, 3H, H-
trans], 2.39–2.56 (m, 6H, H-1), 2.19 [d, JACTHNUTRGNEUNG
(31P-1H)=13.8 Hz,
G
ACHTUNGTRENNUNG
18H, Hp, Hm), 2.31 (m, 6H, H-1), 2.09 (m, 6H, H-3), 1.95 [d,
(1H-1H)=17.1 Hz, 2J
ACHTUNGTRENNUNG
ACTHNUTRGNEUNG
2J(31P-1H)=13.3, 3H, H-5], 1.65–1.55 (m, 12H, overlapping
1
H-2, H-4); 13C NMR (CDCl3, 125.66 MHz): d=137.99 [d, J-
G
CHTUNGTRENNUNG
2
(31P-13C)=12.4 Hz, Ci], 132.72 [d, J
E
G
2
3
128.81 (s, Cp), 128.58 [d, J
G
(31P-13C)=6.79 Hz, Cm], 27.06 [d,
(31P-13C)=12.6 Hz, C-4], 26.85 [dd, 2J(31P-13C)=16.8 Hz,
(31P-13C)=15.6 Hz, C-3], 22.59 [dd, 3J(31P-13C)=13.0 Hz,
(31P-13C)=4.3 Hz, C-2], 20.45 [d, 1J(31P-13C)=48.3 Hz, C-
(31P-13C)=51.9 Hz, C-5]; 31P NMR (C6D6,
7
1J
3J
2J
3H, H-8], 2.04–2.16 (m, 6H, H-5), 1.41 (b, 18H, H-2, H-3,
H-4); 13C NMR (C6D6, 125.66 MHz): d=139.05 (s, C-6),
N
E
3
114.98 (s, C-7), 33.94 (s, C-5), 30.89 [d, J
N
C-3], 28.61 (s, C-4), 21.90 [d, 2J
20.83, [d, 1J(31P-13C)=48.2 Hz, C-1], 5.87 [d, 1J
51.5 Hz, C-8]; 31P NMR (C6D6, 202.28 MHz): d=29.69 (s).
ACHTUNGTRENNUNG
1], 5.49 [d, 1J
U
A
ACHTUNGTRENNUNG
202.28 MHz): d=31.56 (s, R3MeP+), À16.49 (s, RPh2P). The
material is softening over the temperature range of 50–
708C. HR-MS (MALDI+): m/z=769.4390, calcd. for
C49H57P4 [M+]: 769.3411; 785.4048, calcd. for C49H57P4O
[MO+]: 785.3360; 801.4435, calcd. for C49H57P4O2 [MO2 ]:
801.3309; 817.4487, calcd. for C49H57P4O3 [MO3 ]: 817.3258.
Adv. Synth. Catal. 2011, 353, 443 – 460
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
457

J. Guenther et al.
FULL PAPERS
H-7, H-8, H-9); 13C NMR (C6D6, 125.66 MHz): d=140.03 [d,
Methyltris(7-diphenylphosphinoheptyl)phosphonium
Iodide (11)
2
1J
A
G
3
128.71 [d, JACTHNUTRGNEUNG
(31P-13C)=6.4 Hz, Cm], 128.63 (s, Cp), 31.69 [d,
3J(31P-13C)=12.7 Hz, C-9*], 31.14 [d, 3J(31P-13C)=15.0 Hz,
ACTHNUTRGENNUG CAHTUNGTRENNUGN
C-3], 30.11 (s, C-4#), 30.07 (s, C-5#), 29.98 (s, C-6#), 29.79 (s,
C-7#), 29.61 (s, C-8#), 28.67 [d, J
A
2
1
2
26.56 [d, J
G
G
1
Phosphonium salt 8 (442 mg, 0.952 mmol), AIBN (155 mg,
0.944 mmol), and 1.0 mL of Ph2PH (1007 mg, 5.323 mmol)
were combined in a Schlenk flask, heated under an N2 at-
mosphere to 708C and stirred for 3.5 days. The conversion
was monitored by 31P NMR of the reaction mixture. After
completion of the reaction 2 mL of toluene were added to
remove excess Ph2PH, and the product precipitated after
adding 3 mL of pentane. The supernatant was discarded and
the solid was again treated with 2 mL of toluene and pre-
cipitated with 3 mL of pentane. The precipitate was dried
under vacuum at 708C to give 11 as a colorless oil; yield:
971 mg (0.950 mmol, quantitative). 1H NMR (C6D6,
4.7 Hz, C-2], 20.93 [d, JACTHUNGETRNNUG
(31P-13C)=48.2 Hz, C-1], C-12 signal
not localized; 31P NMR (C6D6, 202.28 MHz): d=31.37 (s,
R3MeP+), À16.32 (s, RPh2P) (*, assignments interchange-
#
AHCTUNGTRENNUNG
able); HR-MS (MALDI+): m/z=1063.6920, calcd. for
C70H99P4 [M+]: 1063.6697; 1079.6873, calcd. for C70H99P4O
[MO+]: 1079.6646; 1095.7205, calcd. for C70H99P4O2 [MO2 ]:
+
1095.6596.
Methyltris(diphenylphosphinomethyl)phosphonium
Triflate (17)
Phosphine 16 (868 mg, 1.382 mmol) was dissolved in 50 mL
of toluene and MeOTf (227 mg, 1.383 mmol), dissolved in
10 mL of toluene, was added dropwise over a period of 3 h.
Then the reaction mixture was stirred overnight at room
temperature. The product precipitated after adding 30 mL
of pentane to the reaction mixture. The supernatant was re-
moved and the precipitate was washed with pentane (2ꢄ
10 mL), and subsequently with 50 mL of degassed H2O. The
residue was dried under vacuum to give 17 as a colorless
powder; yield: 709 mg (0.894 mmol, 65%). Single crystals
suitable for X-ray structure determination were grown from
a solution in MeCN by slow evaporation of the solvent.
499.70 MHz): d=7.52 [dd, 3J
G
E
3
7.6 Hz, 12H, Ho], 7.14 [t, J
G
3
[t, J
2J(31P-1H)=13.9 Hz, 3H, H-8], 2.09 (m, 6H, H-6), 1.53 (m,
6H, H-7), 1.48–1.20 (m, 24H, H-2, H-3, H-4, H-5);
13C NMR (C6D6, 125.66 MHz): d=139.98 [d, 1J(31P-13C)=
(31P-13C)=18.5 Hz, Co], 128.79 [d,
(31P-13C)=6.5 Hz, Cm], 128.65 (s, Cp), 31.26 [d, J(31P-13C)=
12.7 Hz, C-3*], 30.89 [d, J
(31P-13C)=15.1 Hz, C-5*), 29.05 (s,
C-4), 28.59 [d, J
(31P-13C)=12.5 Hz, C-6*], 26.47 [d, J-
(31P-13C)=16.3 Hz, C-7*], 22.10 [d, J
ACHTUNGTRENNUNG
(1H-1H)=7.4 Hz, 6H, Hp], 2.47 (m, 6H, H-1), 2.32 [d,
ACHTUNGTRENNUNG
2
14.5 Hz, Ci], 133.24 [d, J
3J
ACHTUNGTRENNUNG
G
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
A
1H NMR (C6D6, 499.70 MHz): d=7.45–7.40 (m, 12H, Hortho),
20.86 [d, 1J(31P-13C)=47.9 Hz, C-1], 6.01 [d, 1J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
2
(31P-1H)=14.4 Hz,
51.56 Hz, C-8]; 31P NMR (C6D6, 202.28 MHz): d=31.34 (s,
R3MeP+), À16.34 (s, RPh2P) (* assignments interchange-
7.38–7.35 (m, 18H, Hmeta, Hpara), 2.99 [d, J
6H, CH2], 1.33 [d, 2J
(31P-1H)=14.4 Hz, 3H, CH3]; 13C-
ACHTUNGTRENNUNG
{31P} NMR (C6D6, 125.66 MHz): d=134.85 (Ci), 133.00 (Co),
ACHTUNGTRENNUNG
able); HR-MS (MALDI+): m/z=895.5497, calcd. for
130.37 (Cp), 129.32 (Cm), 21.73 (CH2), 8.48 (CH3); 31P NMR
C58H75P4 [M+]: 895.4819; 911.5306, calcd. for C58H75P4O
(C6D6, 202.28 MHz): d=35.16 [q, 2J
A
[MO+]: 911.4768; 927.5779, calcd.for C58H75P4O2 [MO2 ]:
R3MeP+], À29.41 [d, J
(31P-31P)=54.5 Hz, RPh2P]; 19F NMR
ACHTUNGTRENNUNG
2
927.4718.
(CDCl3, 470.17 MHz): d=À78.13 (CF3); melting range 161–
1658C.
Methyltris(11-diphenylphosphinoundecyl)phos-
Rhodium Complex 18
Ligand 17 (36 mg, 0.045 mmol) was dissolved in 4 mL of
CH2Cl2 under an N2 atmosphere. Then [RhACHTNUTGRNEUNG(nbd)2]PF6
(20 mg, 0.046 mmol), dissolved in 2 mL of CH2Cl2, was
added. The reaction mixture was stirred for 30 min at room
temperature, before the solvent was removed under vacuum
and an orange powder was obtained. The residue was
washed with pentane (2ꢄ5 mL) and dried under vacuum to
give 18 as an orange powder; yield: 52 mg (0.54 mmol,
quantitative). Single crystals suitable for X-ray structure de-
termination were obtained by applying a pentane layer over
a saturated solution of 18 in CH2Cl2. 1H NMR (C6D6,
phonium Iodide (12)
Phosphonium salt 9 (507 mg, 0.801 mmol), AIBN (130 mg,
0.792 mmol), and Ph2PH (0.9 mL, 963 mg, 5.172 mmol) were
combined in a Schlenk flask, heated under an N2 atmos-
phere to 708C and stirred for 4 d. The conversion was moni-
tored by 31P NMR of the reaction mixture. After completion
of the reaction 2 mL of toluene were added to remove
excess Ph2PH, and the product precipitated after adding
3 mL of pentane. The supernatant was discarded and the
solid was again treated with 2 mL of toluene and precipitat-
ed with 3 mL of pentane. The precipitate was dried under
vacuum at 708C to give 12 as a colorless oil; yield: 940 mg
(0.789 mmol, quantitative). 1H NMR (C6D6, 499.70 MHz):
499.70 MHz): d=7.37 [t, 3J
A
3
3
[t, J
G
(31P-1H)=
3
8.3 Hz, J
(s, 4H, =CH), 3.48 [d, JAHCTUNTGRENNUNG
(1H-1H)=7.7 Hz, 12H, Ho], 3.84 (s, 2H, CH), 3.64
ACHTUNGTERNNUNG
2
2
[d, J
AHCTUNGTRENNUNG
d=7.48 [dd, 3J
Ho], 7.16–7.05 (m, 18H, Hm, Hp), 2.53 (m, 6H, H-1), 2.33 [d,
2J(31P-1H)=13.8 Hz, 3H, H-12], 2.02 (m, 6H, H-10), 1.54
(m, 6H, H-11), 1.49–1.21 (m, 48H, H-2, H-3, H-4, H-5, H-6,
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
(31P-1H)=7.7 Hz, 3J(1H-1H)=7.6 Hz, 12H,
(Ci), 132.03 (Co), 131.61 (Cp), 129.82 (Cm), 75.60 (CH2),
63.00 [d, 1J(103Rh-13C)=3.3 Hz, =CH*], 50.45 [d,
2J(103Rh-13C)=5.8 Hz, PCH2*], 46.6 (CH), 19.36 (CH3);
ACHTUNGTRENNUNG
ACTHNUTRGNEUNG
31P NMR (C6D6, 202.28 MHz): d=38.88 [dq, 2J(31P-31P)=
458
asc.wiley-vch.de
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 443 – 460

Synthesis, Immobilization, MAS and HR-MAS NMR of a New Chelate Phosphine Linker System
21.3 Hz,
3J(103Rh-31P)=7.8 Hz,
R3MeP+],
7.19
RPh2P],
[d,
[9] R. Fetouaki, A. Seifert, M. Bogza, T. Oeser, J. Blꢀmel,
Inorg. Chim. Acta 2006, 359, 4865–4873.
1J(103Rh-31P)=118.3 Hz,
2J(31P-31P)=21.2 Hz,
ACHTUNGRTENNUGN
1
À145.00 [sept, J
ACHTUNGTRENNUNG
(31P-19F)=712.5 Hz, PF6]; 19F NMR (CDCl3,
[10] a) T. M. Duncan, A Compilation of Chemical Shift Ani-
sotropies, Farragut Press, Chicago, IL, 1990; b) C. A.
Fyfe, Solid-State NMR for Chemists, C. F. C. Press,
Guelph, Canada, 1983; c) M. J. Duer, Introduction to
Solid-State NMR Spectroscopy, Blackwell Publishing,
Oxford, 2004; d) S. Reinhard, J. Blꢀmel, Magn. Reson.
Chem. 2003, 41, 406–416.
[11] a) S. Brenna, T. Posset, J. Furrer, J. Blꢀmel, Chem. Eur.
J. 2006, 12, 2880–2888; b) T. Posset, J. Blꢀmel, J. Am.
Chem. Soc. 2006, 128, 8394–8395.
[12] a) P. W. Clark, J. L. S. Curtis, P. E. Garrou, G. E. Hart-
well, Can. J. Chem. 1974, 52, 1714–1720; b) P. W.
Clark, G. E. Hartwell, Inorg. Chem. 1970, 9, 1948–
1951; c) P. W. Clark, A. J. Jones, J. Organomet. Chem.
1976, 122, C41-C48.
[13] T. Hirai, L.-B. Han, Org. Lett. 2007, 9, 53–55.
[14] a) T. Shima, F. Hampel, J. A. Gladysz, Angew. Chem.
2004, 116, 5653–5656; Angew. Chem. Int. Ed. 2004, 43,
5537–5540; b) A. J. Nawara-Hultzsch, K. Skopek, T.
Shima, M. Barbasiewicz, G. D. Hess, D. Skaper, J. A.
Gladysz, Z. Naturforsch. 2010, 65b, 414–424.
470.17 MHz): d=À71.38 [d, 1J
(31P-19F)=712.5 Hz, PF6],
ACHTUNGTRENNUNG
À78.71 (CF3) (* assignments interchangeable).
Acknowledgements
We thank The Welch Foundation (A-1706) and NSF (CHE-
0911207) for financial support. The FE-SEM acquisition was
supported in part by the National Science Foundation under
Grant No. DBI-0116835, and we thank Dr. Z. Luo of the Mi-
croscopy and Imaging Center (MIC) of Texas A&M Univer-
sity for the measurements. We thank Prof. Dr. G. Helmchen
for a sample of DBCOT.
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[15] G. Fraenkel, W. R. Winchester, P. G. Williard, Organo-
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[17] X-ray data for ligand 17: C41H39F3O3P4S, M=792.66,
colorless needle, 0.20ꢄ0.10ꢄ0.10 mm3, monoclinic,
space group P21/c (No. 14), a=15.693(4), b=12.853(3),
c=18.548(4) ꢂ, b=94.480(3)8, V=3730.0(15) ꢂ3, Z=4,
1cald =1.412 gcmÀ3, F000 =1648, Bruker APEX-II CCD,
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MoKa radiation, l=0.71073 ꢂ, T=113(2) K, 2qmax
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=
=
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R indices based on 4560 reflections with I>2sigma(I)
(refinement on F2), 469 parameters, 0 restraints. Lp and
absorption corrections applied, m=0.313 mmÀ1. Further
crystallographic data for this structure have been de-
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Center as supplementary publication no. CCDC
782510. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
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FULL PAPERS
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distances and the thermal ellipsoids meaningful. Resid-
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