A family of rhodium and iridium complexes with semirigid benzylsilyl phosphines: From bidentate to tetradentate coordination modes

Article abstract of DOI:10.1039/c7dt00727b

The synthesis of a new trisbenzylsilanephosphine P{(o-C₆H₄CH₂)SiMe₂H}₃ (1) is shown to proceed with high yields from P(o-tolyl)₃. Compound 1 coordinates to the Rh and Ir dimers [MCl(COD)]₂ (M = Rh, Ir) in a tetradentate or tridentate fashion, depending on the strict exclusion of water. The dimeric compounds [ClM(SiMe₂CH₂-o-C₆H₄)₂P(o-C₆H₄-CH₂SiMe₂H)]₂, 2Rh and 2Ir, feature a tetradentate coordination of the starting ligand with P and two Si atoms as well as a non-classical agostic Si-H group. The presence of adventitious water in the solvents leads to the formation of two new complexes [(μ²-Cl)₂M₂(SiMe₂CH₂-o-C₆H₄)₂P(o-C₆H₄-CH₂SiMe₂OSiMe₂CH₂-o-C₆H₄-)P(SiMe₂CH₂-o-C₆H₄)₂], 3Rh and 3Ir, which feature a siloxane bridge through Si-H bond breaking in 2. Reaction of [RhCl(COD)]₂ with the bisbenzylsilanephosphine PhP{(o-C₆H₄CH₂)SiMe₂H}₂ leads to the formation of compound 4Rh which features also a dimeric structure with the SiPSi ligand coordinated through the two silicon atoms, one of which occupies the apical position of a square-pyramidal geometry in the solid state, while the second is disposed equatorially trans to π-donor Cl. Finally, bidentate coordination of a PSi ligand is achieved by reaction of [RhCl(COD)]₂ with Ph₂P{(o-C₆H₄CH₂)SiMe₂H} which leads to the monometallic species [RhCl(SiMe₂CH₂-o-C₆H₄-PPh₂)₂], 5Rh, incorporating two chelating PSi ligands and maintaining a Cl ligand.

Full text of DOI:10.1039/c7dt00727b

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A family of rhodium and iridium complexes with
semirigid benzylsilyl phosphines: from bidentate
to tetradentate coordination modes†
Cite this: DOI: 10.1039/c7dt00727b
María Vicky Corona-González,a Julio Zamora-Moreno,a
Cynthia A. Cuevas-Chávez,a,b,c Ernesto Rufino-Felipe,a
Emmanuelle Mothes-Martin,b,c Yannick Coppel,b,c Miguel A. Muñoz-Hernández,a
Laure Vendier,b,c Marcos Flores-Alamo,d Mary Grellier,b,c
a
Sylviane Sabo-Etienne
*
b,c and Virginia Montiel-Palma
*
The synthesis of a new trisbenzylsilanephosphine P{(o-C6H4CH2)SiMe2H}3 (1) is shown to proceed with
high yields from P(o-tolyl)3. Compound 1 coordinates to the Rh and Ir dimers [MCl(COD)]2 (M = Rh, Ir) in
a tetradentate or tridentate fashion, depending on the strict exclusion of water. The dimeric compounds
[ClM(SiMe2CH2-o-C6H4)2P(o-C6H4-CH2SiMe2H)]2, 2Rh and 2Ir, feature a tetradentate coordination of the
starting ligand with P and two Si atoms as well as a non-classical agostic Si–H group. The presence of
adventitious water in the solvents leads to the formation of two new complexes [(μ2-Cl)2M2(SiMe2CH2-o-
C6H4)2P(o-C6H4-CH2SiMe2OSiMe2CH2-o-C6H4–)P(SiMe2CH2-o-C6H4)2], 3Rh and 3Ir, which feature a
siloxane bridge through Si–H bond breaking in 2. Reaction of [RhCl(COD)]2 with the bisbenzylsilane-
phosphine PhP{(o-C6H4CH2)SiMe2H}2 leads to the formation of compound 4Rh which features also a
dimeric structure with the SiPSi ligand coordinated through the two silicon atoms, one of which occupies
the apical position of a square-pyramidal geometry in the solid state, while the second is disposed equa-
torially trans to π-donor Cl. Finally, bidentate coordination of a PSi ligand is achieved by reaction of
[RhCl(COD)]2 with Ph2P{(o-C6H4CH2)SiMe2H} which leads to the monometallic species [RhCl(SiMe2CH2-
o-C6H4-PPh2)2], 5Rh, incorporating two chelating PSi ligands and maintaining a Cl ligand.
Received 27th February 2017,
Accepted 31st March 2017
DOI: 10.1039/c7dt00727b
rsc.li/dalton
steps12 but also to advances in their employment as catalysts13
and use in materials science. For example, Tobita has
Introduction
Even the most superficial glance at the inorganic chemistry informed of a Ru catalyst for alkene hydrogenation bearing a
literature evidences an outburst in the number of studies nonspectator Si,O,P ligand which exhibits interconversion
related to silicon-substituted pincer,1–5 pincer-like6 and mixed between η2-H–Si and silyl functions.14 Turculet successfully
phosphines7–9 as ligands for transition metals.10,11 This employed Pd and Pt silyl pincer complexes for the efficient
upsurge in silylphosphine chemistry has led not only to a catalytic conversion of CO2 to methane.15
number of important discoveries in fundamental reaction
Specifically in the field of catalysis, the design of new cata-
lysts for important transformations such as
hydrosilylation16–20 and dehydrogenative silylation21–23
compels deep knowledge of the fundamental reaction steps
often invoked including Si–H bond activation24 and M–Si25
and Si–C26 bond formation. On the other hand, Rh and Ir com-
plexes are the preferred catalysts in a number of chemical
transformations owing to their high efficiency, high functional
group tolerance27–29 and broad substrate scope.30–33 In parti-
cular, Rh and Ir complexes bearing pincer ligands undergo
remarkably facile Si–H bond activation often invoked to be
partly due to their ability to support high oxidation
states12,18,34 as well as to the various coordination modes
adopted by the ligands on the metal center.35–39
aCentro de Investigaciones Químicas, Instituto de Investigación en Ciencias Básicas
y Aplicadas, Universidad Autónoma del Estado de Morelos, Avenida Universidad 1001,
Col. Chamilpa, Cuernavaca, Morelos, C. P. 62209, México. E-mail: vmontielp@uaem.mx
bCNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne,
BP 44099, F-31077 Toulouse Cedex 4, France. E-mail: sylviane.sabo@lcc-toulouse.fr
cUniversité de Toulouse, UPS, INPT, F-31077 Toulouse Cedex 4, France
dFacultad de Química, Universidad Nacional Autónoma de México,
Mexico City 04510, México
†Electronic supplementary information (ESI) available: Additional spectroscopic
(NMR and IR) characterisation of all complexes and X-ray data of compounds 1,
3Rh, 3Ir, 4Rh and 5Rh. CCDC 1533806–1533808, 1533794 and 1533878. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c7dt00727b
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Stobart,40–44 Sola45 and other workers including our-
selves46,47 have proved that incorporation of a Si–H function
into a semi-rigid polydentate phosphine template leads to very
pronounced stereoelectronic control over substrate entry,
binding and release on a coordinatively unsaturated tran-
sition-metal centre. In light of the above, we sought to investi-
gate the coordination ability to Rh and Ir towards a family of
semirigid benzylsilyl phosphines bearing a single phosphorus
atom and a varying number of potentially coordinating Si–H
moieties.
Results and discussion
Synthesis of tris-(o-benzyldimethylsilyl)phosphine, 1
Fig. 1 Stack plot of the 1H NMR spectra (C7D8) of compound
recorded between 293 and 193 K.
1
Compound 1 was synthesized following the method previously
reported for the synthesis of bis-(o-benzyldimethylsilyl)phenyl-
phosphine.46 Polylithiation of tris-(o-tolyl)phosphine in the
presence of TMEDA and subsequent quenching with excess
HSiMe2Cl led after work up to pure 1 as a white solid in excel-
lent yield (91%, Scheme 1).
with the adoption of a C3 molecular symmetry, a rigid con-
figuration (C1) being adopted at low temperatures due to hin-
dered rotation around the Si–C bonds (ESI†). This is in accord-
ance with the bulkiness of compound 1 which is expected to
be even bulkier than its parent precursor tris-(o-tolyl)phos-
phine which has a Tolman cone angle of 194°.48
The main features of 1 in the 1H NMR spectrum at 298 K in
toluene-d8 are the Si hydride resonance at δ 4.28 which exhi-
5
bits a doublet of nonets multiplicity (3JH–H 3.5 Hz, JP–H 1.5
A singlet close to δ −27 in the 31P{1H} NMR spectrum of 1
is observed at all temperatures while in the 13C{1H} NMR spec-
trum the benzylic carbons appear as a doublet at δ 23.4
(3JP–C 19.3 Hz) and the methyl carbons as a singlet at δ −4.25.
The 29Si signal at δ −12.1 features a 1JSi–H coupling constant
of 189 Hz. No coupling constant between the phosphorus and
the silicon nuclei was measured, therefore ruling out the possi-
bility of any intramolecular phosphorus–silicon bond inter-
action despite the relatively rigid structure of 1 which could
account for a decrease in the distance between these two
atoms. Despite the poor quality of the measurement, X-ray
diffraction analysis confirms the proposed structure (see the
ESI†).
1
Hz) with 29Si satellites and a JSi–H of 189 Hz (Fig. 1). The fine
structure is due to the presence of six neighbouring hydrogens
of the two methyl groups on silicon and one methylene group
which couple equally affording a nonet pattern. The additional
doublet splitting is due to coupling to the phosphorus
nucleus.
The methyl protons appear as a sharp doublet at δ 0.15
(3JH–H 3.5 Hz), while the benzylic resonance centred at δ 2.42 is
broad, indicating deviation from the ideal C3 symmetry.
Indeed, 1 shows dynamic behaviour as evidenced by variable
temperature NMR studies (Fig. 1 and the ESI†). Determination
of ΔG‡ values indicates that an energy barrier of ca.
54 kJ mol−1 is overcome at high temperatures in accordance
Synthesis of complex 2Rh
Room temperature addition of 1 to the rhodium dimer [RhCl
(COD)]2 in toluene-d8 in a 2 : 1 molar ratio afforded gas evol-
ution and isolation after work up of an off-brown solid in a
very good yield (83%) (Scheme 2). Elemental analysis and spec-
troscopic data are in accordance with the formula [ClRh
(SiMe2CH2-o-C6H4)2P(o-C6H4-CH2SiMe2H)]2, 2Rh. The sym-
metrical dinuclear species is characterized by a 31P{1H}
1
doublet at δ 27.8 with a JRhP 154 Hz in accordance with a
Rh(III).49,50 Variable temperature 2D-multinuclear NMR experi-
ments were in particular diagnostic of the existence of two
types of SiMe2CH2-o-C6H4 fragments in a 2 : 1 ratio; one type
comprising two of these fragments forming a six-membered
ring through silyl coordination to the rhodium centre and a
second type displaying a rather weak agostic Si–H coordination
mode to Rh. The 1H NMR spectrum at room temperature
shows a broad doublet at δ 2.56 exhibiting a small JH–Rh of
6.4 Hz which is assigned to the agostic Si–H with satellites and
Scheme 1 Synthesis of tris-(o-benzyldimethylsilyl)phosphine, 1.
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is to be noted. They are also very similar to the ligand precur-
sor 1 despite complexation which implies that the main contri-
bution to the activation energy is rotation around the Si–C
bonds.
At 223 K, the 13C{1H} NMR spectrum shows six methyl
carbon sharp singlets between 10.1 < δ < –4.8 while three
doublets are observed for the benzylic methylene carbons.
Conducting a 13C{1H}{31P} measurement allows the assign-
ment of the methylene attached to the agostic Si–H at δ 22.8.
At room temperature, despite the use of a variety of
sequences, we were unable to detect any reliable 29Si NMR
signal. However, at 223 K, the 29Si DEPT{1H} spectrum shows
1
2
three signals at δ 57.0 (dd, JSi–Rh 37, JSi–P 11 Hz), δ 52.9
1
2
(dd, JSi–Rh 39, JSi–P 12 Hz) and δ −10.5 (s, w1/2 10 Hz) as con-
firmed with {31P} decoupling.
Additionally, by 29Si DEPT{31P}, the signal at δ −10.5 dis-
1
plays a JSi–H coupling constant of 149 Hz which should be
Scheme 2 Synthesis of complexes 2 and 3. Methyl groups on Si are
omitted for clarity.
compared to the value of 189 Hz obtained for free ligand 1
under the same conditions (Fig. 3). This value is in agreement
with a weakly activated agostic Si–H interaction11,46,47,51 and in
1
line with the chemical shift of δ 2.56 observed in the H NMR
an apparent JSi–H of 51 Hz. The complex is fluxional as illus-
trated by the methyl resonances which are characterized at
room temperature by a singlet at δ 0.32 and a broad signal at
δ 0.56 in a 2 : 1 ratio. In the slow exchange regime at 223 K, the
singlet resolves into four singlets at δ 1.22, 0.90, 0.59 and 0.36
whereas the broad signal resolves into two slightly broad
signals at δ 0.54 and δ −0.38, each integrating for a single
methyl (Fig. 2). The activation parameters for the exchange of
the diastereotopic methyl hydrogens were estimated in the
range ΔG‡ 52–55 kJ mol−1 (at Tc est 263 K).
Additionally, the methylene benzylic hydrogens observed at
room temperature as a very broad signal at δ 2.15 resolve in
the slow exchange regime at 223 K, into five signals, one of
them with an integral value double that of the value of the
other four. The calculated energy for activation is 52 kJ mol−1
with an estimated coalescence temperature of 273 K. The simi-
larity of these values for both methyl and benzylic hydrogens
experiment, shifted to a higher field with respect to ligand 1
but still not in the usual metal hydride negative chemical shift
range. More information was gathered from 29Si–1H HMQC
{31P} experiments (see Fig. 4, Experimental section and the
ESI† for full assignment at 293 K and 223 K). The fact that at
room temperature, when there is no distinguishable 29Si
1
signal, a JSi–H value of ca. 50 Hz was determined by H NMR
while it was ca. 150 Hz at the slow exchange regime, implies
that at RT, the single hydrogen nucleus is in fact in exchange
1
between the three Si atoms: an average value JSi–H/3 is
measured due to exchange between H connected to 29Si iso-
1
topes with H connected to 28Si isotopes where JSi–H is zero.
When the exchange process is blocked, the hydride only coor-
dinates to one silicon providing an agostic function and the
corresponding coupling constant is close to 150 Hz.46
It is remarkable that the silyl signals at δ 57.0 and at δ 52.9
show similar coupling constants to rhodium (ca. 38 Hz) in
agreement with the direct bond between the Si and Rh atoms.
Fig. 3 Stack plot of the 29Si DEPT spectra (223 K) of 2Rh with different
Fig. 2 Stack plot of the 1H NMR spectra of 2Rh recorded between 293
and 203 K.
decoupling schemes. Top: 29Si DEPT 31P} without 1H decoupling,
{
middle: 29Si DEPT {1H} and bottom: 29Si DEPT {1H}{31P}.
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Synthesis of compound 2Ir
Compound 2Ir was synthesized from the reaction of
[IrCl(COD)]2 and ligand 1 in a 1 : 2 molar ratio in pentane at
room temperature. A yellow solid was isolated after work up in
quantitative yield (97%). The gathered spectroscopic data are
in accordance with the proposed formula shown in Scheme 2.
At room temperature, the 1H NMR recorded in C6D6 exhibits
two methyl group resonances as two singlets at δ 0.53 and 0.41
while the benzylic methylene hydrogens appear as a doublet at
2
δ 2.13 (d, JH–H 14 Hz) and a doublet of doublets resonance at
2
4
δ 2.05 (dd, JH–H 14 Hz, JP–H 3 Hz). The Si–H resonance is
shown at δ 0.55 as a broad signal with well-resolved 29Si satel-
lites and an apparent JSi–H coupling of 42 Hz. In comparison
to compound 2Rh, the agostic Si–H moieties are slightly more
activated in 2Ir as indicated by the value of the coupling con-
stant JSi–H and the more shielded chemical shift. In contrast to
2Rh, complex 2Ir shows two sets of equally-integrating methyl
and methylene hydrogens implying that at room temperature
the three silicon atoms must be equally sharing the non-classi-
cal hydrogen resulting in only two magnetically different
environments for both the methyl and methylene hydrogens.
This situation would differ to the one proposed for complex
2Rh in which the hydrogen should be jumping between the
three silicons at room temperature but be bound to only one at
a time.
Fig. 4 HMQC 29Si–1H NMR spectrum for 2Rh at 223 K.
In contrast, the JSi–Rh coupling constant for the third silicon
nucleus can be estimated to be less than 10 Hz as inferred
from the w1/2 value of the corresponding signal.
Observation of a signal in the 103Rh NMR spectrum (Fig. 5)
at a chemical shift of δ −8738 (223 K), shifted to a higher field
in comparison with [RhCl(COD)]2 which appears at δ −7212, is
comparable to the case of [Rh(H)2(SiMe2Ph)(PMe3)3] where the
complex shifts over 1000 ppm to the higher field upon com-
plexation in relation to the rhodium precursor.52
In the 13C{1H} NMR spectrum, two methyl carbon signals
are observed as singlets at δ 2.22 and 2.93 while a unique
methylene carbon is observed at δ 27.6 as a doublet due to a
3JP–C (11 Hz). In the 31P{1H} a singlet signal appears at δ 0.21,
thus quite shifted with respect to 2Rh. The 29Si NMR spectrum
measured at 293 K (toluene-d8) shows only one signal at δ 10.0
correlating with the methylene, methyl and Si–H resonances
thus indicating a fast exchange between the three silicon
atoms. Upon lowering the temperature down to 180 K, we were
unable to block the exchange process, all the signals becoming
broad. This is in contrast to the rhodium case for which decoa-
lescence was observed leading to an arrested agostic Si–H
interaction characterized by a 29Si resonance at δ −10.5 with a
1JSi–H of 149 Hz and showing a reduced JSi–Rh < 10 Hz. In the
solid state, the IR spectrum of 2Ir shows the νIrHSi vibration
mode at 2019 cm−1. Attempts at obtaining crystals suitable for
X-ray diffraction analysis failed in our hands due to slow
decomposition of 2Ir in solution (see the ESI†).
Monitoring the reaction in a Young’s NMR tube allows the
detection of released molecular hydrogen and COD upon
addition of 1 to [RhCl(COD)]2. Gradual consumption of H2
leads to the formation of COE upon a period of 2 hours.
Hence, in conclusion upon reaction, the dinuclear structure
with chloro bridges is maintained while COE is released
thanks to COD hydrogenation. This leads to the formation of
the disilyl complex 2Rh with the third silicon atom of the
initial ligand 1 forming a rather weak Rh(η2-SiH) interaction,
the rhodium centre achieving an 18 electron configuration.
In light of the results obtained from the reactivity of
[RhCl(COD)]2 with the trisbenzylsilanephosphine 1 we turned
to study its coordination towards the Ir analogue.
Synthesis of complex 3Rh
Attempts at obtaining crystals of complex 2Rh were unsuccess-
ful. Instead, after days in solution, complex 2Rh reacts with
adventitious water present in the solvent generating complex
3Rh (Scheme 2),
a
species of the formula [(μ2-Cl)2-
Rh2(SiMe2CH2-o-C6H4)2P(o-C6H4-CH2SiMe2OSiMe2CH2-o-C6H4)
P(SiMe2CH2-o-C6H4)2]. This was confirmed by adding distilled
water to a C6D6 solution of 2Rh. Thus, 3Rh formally results
from addition of an O atom to complex 2Rh, with loss of the
agostic interactions Rh(η2-SiH) and dihydrogen evolution.
Fig. 5 HMQC 103Rh–1H of 2Rh at 223 K.
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unknown species. However, when adventitious water was
present, as in the case of the rhodium analogue, 2Ir was trans-
formed into complex 3Ir featuring a siloxane bridge. As in the
case of the Rh analogue, deliberate addition of degassed de-
ionized water to a C6D6 solution of 2Ir led to the formation of
3Ir and H2. The NMR spectra of 3Ir are analogous to those of
3Rh. The 31P{1H} NMR (C6D6) singlet is at δ −4.54, shifted to a
1
higher field with respect to 3Rh. In the H NMR spectrum, six
singlet signals are assigned to the six inequivalent methyl
groups, while again six signals, three doublets and three doub-
lets of doublets with additional phosphorus coupling are
observed for the inequivalent benzylic hydrogens. 3Ir is charac-
terized by three 29Si NMR signals at δ 24.1, 5.1 and 3.5 in the
HMBC 29Si–1H spectrum in toluene-d8.
Red-orange complex 3Ir crystallizes from benzene/hexane
mixtures giving appropriate crystals for X-ray diffraction ana-
lysis (ESI†). The molecular structure (Fig. 8) confirms a
dimeric structure with two iridium centres each coordinated to
a modified ligand 1 through the phosphorus and two silicon
atoms. The third Si atom is again forming part of a Si–O–Si
moiety spanning over the two Ir centres together with two Cl
bridges.
The structure is very similar to that previously discussed for
3Rh also exhibiting a square pyramidal geometry only slightly
deviated from the ideal one.53 ‡ Once again the strong trans
influence of Si is responsible for one of these atoms resting on
the apical position of the square pyramidal while a second is
disposed trans to π-donor Cl on the equatorial base.57,60,61
There are only a few literature precedents for the formation
of siloxane bridges upon reaction with adventitious water.
A siloxane-bridge on a Pt system bearing a PSiP ligand was
described by Milstein as a result of Si–H oxidation.58 Tilley
reported on the addition of O–H across a Ir–Si bond of a dihy-
dride silylene complex resulting in a trihydride siloxane-bridge
dimer.59 Interestingly, formation of the siloxane bridge upon
retention of the unsaturation at a Pt cationic system was
observed by Ozerov.7 Substituted halo-silyl cyclopentadienyl
complexes also react with water to produce the corresponding
siloxane bridge.60 Finally, it is worth stressing that compound
1 on its own does not react with H2O even in the presence of
its large excess (up to 3000 molar excess).
Fig. 6 X-ray diffraction structure of compound 3Rh with thermal ellip-
soids at 30% probability. Selected bond lengths (Å) and angles (°): Rh1–
Si1 2.2921(8), Rh1–Si2: 2.288(1), Rh2–Si3 2.2948(8), Rh2–Si4 2.2887(9),
Rh1–P1 2.2329(7), Rh2–P2 2.2426(8), Si1–Rh1–Si2 88.37(3), Si3–Rh2–
Si4 92.06(3), Si1–Rh1–Cl2 164.66(3), Si3–Rh2–Cl1 166.52(3).
Yellow crystals appropriated for X-ray diffraction analysis
were grown from toluene/diethylether (Fig. 6). The collection
parameters are collected in Table 1. The molecular structure
shows a symmetrical dirhodium dichloride bridged species
with a third bridging ligand. The phosphorus and two silicon
atoms are coordinated to each Rh centre while the third
silicon atoms forms a new Si–O–Si bridging fragment. Each
rhodium atom is thus pentacoordinated with a slightly dis-
torted square pyramidal geometry.53 ‡ Around each Rh centre,
the apical position trans to a vacant site is occupied by the
strongest trans influence ligand, Si, while the other Si is dis-
posed trans to π-donor Cl.54,55 The four Rh–Si bond distances
are approximately equal at ca. 2.29 Å.56
The NMR spectra of the crystals were acquired in C6D6. At
ambient temperature, in contrast to 2Rh, the 1H NMR spec-
trum of 3Rh shows six singlet signals for the methyl groups
and six diastereotopic methylene hydrogen signals indicative
of hindered rotation around the Si–O–Si bridge. In the 31P{1H}
NMR spectrum, a doublet signal at δ 26.8 reflecting the coup-
ling to rhodium (JRh–P 158 Hz) highlights the equivalence of
the two phosphorus atoms and endorses the high symmetry of
the molecule.
The 29Si–1H HMQC NMR experiment (Fig. 7) displays three
Si signals. They are observed at δ 5.17, 42.0 and 67.0 in 3Rh
which should be compared to δ −10.5, 52.9 and 57.0 in 2Rh.
Thus a change of ca. 10 ppm to a lower field except for the
siloxane silicon (δ 5.17) which shifts slightly more. The chemi-
cal shift of rhodium also shifts to a lower field from δ −8738 to
−8417 ppm.
Synthesis of complex 4Rh
Room temperature addition of PhP{(o-C6H4)CH2SiMe2H}2
instead of 1 to [RhCl(COD)]2 in benzene in a 2 : 1 molar ratio
afforded gas evolution, and after work up, isolation of a yellow
solid in a very good yield (78%) (Scheme 3). The solid was ana-
lysed by elemental analysis and solid state NMR spectroscopy
as it turned out to either react or be insoluble in all the avail-
able deuterated solvents for solution studies. However, crystals
suitable for X-ray diffraction analysis could be grown from
hexane solutions. All the data are in agreement with the for-
mulation [μ-Cl-Rh(SiMe2CH2-o-C6H4)2PPh]2, (4Rh) as shown in
Scheme 3.
Synthesis of compound 3Ir
Keeping solutions of 2Ir in very dry solvents (dried over potas-
sium mirror) led after a few days to decomposition into
‡Applying Konno’s equation to 3Rh gives χ values of 0.15 and 0.16; to 4Rh two
values of 0.35; to 5Rh 0.88 and to 3Ir 0.15 and 0.18. Thus, for 3Rh, 4Rh and 3Ir
the geometry is closer to square pyramidal (ideal value χ = 0) and for 5Rh it is
closer to trigonal bipyramidal geometry (ideal value χ = 1).
The molecular structure obtained by X-ray diffraction ana-
lysis (Table 1, Fig. 9) shows a dimeric structure with two chlor-
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Table 1 Crystal data and details of the structure determination of compounds 3Rh, 4Rh, 5Rh and 3Ir
Compound
3Rh
4Rh
5Rh
3Ir
Formula
C54H72Cl2OP2Rh2Si6 C4H8O C48H58Cl2P2Rh2Si4 2(C6H6) C42H44ClP2RhSi2 3(C4H8O) C54H72Cl2Ir2OP2Si6
Formula weight
Crystal system
Space group
a, b, c [Å]
1318.44
Monoclinic
P21/n
1242.18
Monoclinic
P21/c
1021.56
Monoclinic
C2/c
1422.89
Monoclinic
P21/c
18.7944(11), 13.7302(8),
23.8886(13)
90, 94.744(3), 90
6143.4(6)
11.74490(13), 21.9235(2),
12.01200(13)
90, 108.2606(12), 90
2937.20(6)
20.6490(6), 17.2473(4),
13.9539(4)
90, 91.939(3), 90
4966.7(2)
13.7427(3), 24.3307(5),
20.5811(4)
90, 99.626(2), 90
6784.8(2)
α, β, γ [°]
V [Å3]
Z
4
2
4
4
d (calc.) [g cm−3
]
1.425
0.833
2736
1.405
6.956
1280
1.366
0.553
2144
1.393
4.182
2824
μ [mm−1
F(000)
]
Crystal size [mm]
Temperature (K)
Radiation [Å]
0.16 × 0.09 × 0.02
100(2)
MoKα
0.71073
0.03 × 0.09 × 0.13
100
CuKα
1.54184
0.09 × 0.11 × 0.14
100
Mokα
0.71073
0.2 × 0.34 × 0.42
130(2)
Mokα
0.71073
θ min–max [°]
Dataset
Tot., uniq. data, R(int)
2.57, 26.37
−23 : 23, −17 : 17, −29 : 29
240 484, 12 549, 0.0488
4.0, 72.7
2.8, 29.1
3.405, 29.592
−19 : 18, −33 : 33, −27 : 25
105 030, 17 406, 0.0453
17 406/36/615
1.08
R1 = 0.0344, wR2 = 0.0684
R1 = 0.0538, wR2 = 0.0781
2.30, −1.57
−14 : 12; −27 : 25; −9 : 14
11 269, 5700, 0.022
5700/0/320
1.02
R1 = 0.0271, wR2 = 0.0716
R1 = 0.0301, wR2 = 0.0737
1.01, −0.67
−26 : 27; −21 : 23; −17 : 18
20 468, 5972, 0.026
5972/60/289
1.06
R1 = 0.0341, wR2 = 0.0833
R1 = 0.0399, wR2 = 0.0868
1.05, −0.87
Data/restraints/parameters 12 549/0/663
Goodness of fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
1.12
R1 = 0.0318, wR2 = 0.0763
R1 = 0.0420, wR2 = 0.0849
1.23, −0.80
Largest diff. peak and
hole (e Å−3
)
Fig. 8 X-ray diffraction structure of compound 3Ir with thermal ellip-
soids at 50% probability. Selected bond lengths (Å) and angles (°): Ir1–
Cl1 2.5877(10), Ir2–Cl2 2.5721(11), Ir1–Cl2 2.3904(10), Ir2–Cl1 2.3811(9),
Ir1–Si1 2.3050(12), Ir2–Si5 2.3090(13), Ir1–Si2 2.2937(12), Ir2–Si6 2.2914(13),
Ir1–P1 2.2203(10), Ir2–P2 2.2274(11), Ir1–Cl1–Ir2 97.39(3), Ir2–Cl1–Ir1
97.39(3), Ir1–Cl2–Ir2 97.57(4), P1–Ir1–Si2 90.73(4), P1–Ir1–Si1 91.06(4),
Si1–Ir1–Si2 92.22(5), Si2–Ir1–Cl2 97.16(4), Si1–Ir1–Cl1 167.09(4).
Fig. 7 29Si–1H HMQC NMR spectrum for 3Rh at 223 K.
ide atoms bridging the rhodium centres. Each rhodium atom
has a ligand coordinated through the phosphorus and two
silicon atoms in a facial mode. In this case, the geometry
around the rhodium centre, at least in the solid state, can be
best described by applying Konno’s equation as a slightly dis-
torted square pyramid with the apical position being occupied
by one of the silicon atoms.53 ‡ The apical Rh–Si bond distances
are only slightly shorter (2.2825(6) Å) than the corresponding
equatorial Rh–Si bonds (2.2960(6) Å) as expected from the lack
of a trans ligand in the former case. The Rh–Rh bond distance
is 3.7010 Å excluding the existence of a metal–metal bond.61
Selected bond distances and angles are shown in Fig. 9.
gives more information by exhibiting three methyl carbon res-
onances and two benzylic carbon signals. In the 31P NMR spec-
trum, a unique signal is observed at δ 45.3 while in the 29Si
NMR spectrum two signals at δ 54.9 and 64.9 are assigned to
the two distinct Si nuclei. We believe that the solid state NMR
data are fully consistent with the X-ray structure determined
for complex 4Rh.
1
Synthesis of compound 4Ir
The solid state H MAS NMR spectrum of compound 4Rh
shows three signals which can be assigned to the methyl, Compound 4Ir was synthesized in an analogous fashion to
benzylic and aromatic hydrogens. The 13C CP MAS spectrum 4Rh. The yellow crystalline solid, formulated as [μ-Cl-Ir
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Scheme 3 Synthesis of complexes 4.
Scheme 4 Synthesis of complex 5Rh.
All coupling constants and assignments were confirmed by 2D
and decoupling NMR experiments.
More interestingly, a 29Si DEPT{31P} experiment of complex
5Rh shows only one doublet at δ 54.4 (1JSi–Rh 33 Hz). Broad
band coupling of 31P allows for the observation of a doublet of
triplet resonance with couplings of silicon to rhodium and
1
2
phosphorus (td, JSi–Rh 33 Hz, JSi–P 12 Hz). These experiments
confirm the presence of two equivalent silylphosphine chelat-
ing ligands in the molecule in accordance with a highly sym-
metrical molecule.
A suitable crystal for X-ray diffraction analysis was grown
from a concentrated THF solution. The collection parameters
are collected in Table 1. The molecular structure shown in
Fig. 10 confirms a highly symmetric monomeric structure
resulting from coordination of two P,Si chelating ligands. The
coordination geometry around rhodium is best described as a
distorted trigonal bipyramid after applying Konno’s treatment
to the angles around Rh.53 ‡ The two phosphorus atoms
occupy the axial positions while the silicon atoms are disposed
in the equatorial base.
Fig. 9 X-ray diffraction structure of compound 4Rh with thermal ellip-
soids at the 50% probability level. Selected bond lengths (Å) and
angles (°): Rh1–Si1 2.2825(6), Rh1–Si2 2.2960(6), Rh1–Cl1 2.4160(5),
Rh1–P1 2.2075(5).
(SiMe2CH2-o-C6H4)2PPh]2, was characterized by solid state
NMR with a broad signal at δ 11.8 in the 31P CP MAS spectrum,
and two broad signals at δ 22.7 and 13.8 in the 29Si CP MAS
spectrum assigned to two distinct Si nuclei.
Synthesis of complex 5Rh
When employing the monosilicon-substituted diphenylpho-
sphine compound Ph2P(o-C6H4)CH2SiMe2H, the room temp-
erature addition to [RhCl(COD)]2 in toluene in a 4 : 1 molar
ratio afforded gas evolution and isolation after work up of an
off-brown solid in a very good yield (78%) (Scheme 4). Full
characterization of the compound allows us to formulate it as
the 16-electron mononuclear complex [RhCl(SiMe2CH2-o-C6H4-
PPh2)2], 5Rh. This d6 compound is analogous to the previously
reported [RhCl(SiMe2-(CH2)2-PPh2)2] by Stobart as a result of
the reaction of the same rhodium precursor with the alkyl
bridged silylphosphine Ph2P(CH2)2SiMe2H.44 Complex 5Rh
shows a unique signal at δ 23 in the 31P{1H} NMR spectrum
1
with a doublet multiplicity due to coupling to rhodium JRh–P
117 Hz indicating the high symmetry in the molecule.
The diastereotopic benzylic hydrogens appear as two higher
order signals close to δ 2, diastereotopicity being conferred
Fig. 10 X-ray diffraction structure of compound 5Rh with thermal ellip-
soids at 50% probability. Selected bond lengths (Å) and angles (°):
Rh–Si1 2.3415(6), Rh–P1 2.3478(5), Si1–Rh–Si1a 84.76(2), P1–Rh–P1a
because of restricted rotation as a consequence of chelation. 175.93(2), Cl–Rh–Si1 137.62(2).
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Although most d6 ML5 compounds are known to adopt a rhodium dimer was probed toward the monosubstituted ben-
square-pyramidal structure with the apical site being occupied zylsilylphosphine compound Ph2P(o-C6H4)CH2SiMe2H. Here,
by the largest trans influence ligand, it is known that some the dimer core was broken and the corresponding mono-
others adopt a distorted trigonal bipyramid structure when nuclear complex 5Rh was isolated and fully characterized
bearing a π-donor group, even if very weak ones like chlorine including 29Si NMR data in agreement with two equivalent
and fluoroalkoxy groups.57 In fact, this last class of com- silylphosphine chelating ligands.
pounds exhibit a very acute angle between the two groups
We now intend to use this series of benzylsilyl phosphines
opposite to the π-donor ligand which cannot be explained by to explore transition-metal catalysed transformations with a
steric reasons. This acute angle maximizes the electron- specific focus on the role of the agostic Si–H interactions.
donation of the π-donor ligand contributing to a partial metal–
ligand multiple bond. Indeed, 5Rh displays an acute Si1–Rh–
Si2 angle of 84.75(3)° resulting in larger Cl–Rh–Si angles in
Experimental section
agreement with previous theoretical work.57,62 The rest of the
General considerations
bond angles and distances are within the reported parameters
All experiments were performed under an argon atmosphere
using standard Schlenk methods or in MBraun glove boxes.
THF, Et2O, toluene, hexane and pentane were either dried and
distilled from sodium using benzophenone ketyl as an indi-
cator or purified over a MBraun column system. In either case,
they were degassed prior to use. Benzene-d6 and toluene-d8
were either degassed via three freeze–pump–thaw cycles and
stored over molecular sieves or stored over a freshly prepared
potassium mirror in an ampoule fitted with a J. Young’s valve.
[MCl(COD)]2 (M = Rh, Ir) were synthesized according to
reported procedures.63,64 The other reagents were purchased
from Sigma Aldrich and used as received. Nuclear magnetic
resonance spectra in solution were recorded on Bruker Avance
300, 400, 500, Varian Inova 400 MHz and Varian
NMRS-700 MHz spectrometers. Solid-state NMR experiments
for analogous species.
Conclusions
In this study, we have further extended our method for prepar-
ing polyfunctional phosphinosilane compounds. We have
reported the synthesis in excellent yield of the tris-(o-benzyldi-
methylsilyl)phosphine, 1, featuring three Si–H bonds, being
thus able to act as a tetradentate ligand. By studying its coordi-
nation behaviour towards the rhodium and iridium [MCl
(COD)]2 precursors, we were able to show that the denticity of
this new ligand can be modified. In the resulting complexes 2,
a tetradentate ligation was achieved through the coordination
of phosphorus, two silyl moieties resulting from the activation
of two Si–H bonds, and a third Si atom stabilizing the metal
centre via an agostic Si–H coordination mode. The dimeric
central core is preserved and the metal exhibits an oxidation
state of III. In the rhodium case, the agostic Si–H interaction is
rather weak as evidenced by 29Si NMR studies at low tempera-
were recorded on
a Bruker AvanceIII 400 spectrometer
equipped with a 3.2 or 4 mm probe. Samples were spun
between 6 to 16 kHz at the magic angle using ZrO2 rotors. For
31P MAS single pulse experiments, small flip angles (∼30°)
were used with recycle delays of 10 s. 13C, 29Si and 31P-CPMAS
spectra were recorded with a recycle delay of 2 s and contact
times of 2 ms, 3 ms and 2 ms respectively. All chemical shifts
for 1H, 29Si and 13C are relative to TMS. 31P chemical shifts
were referenced to an external 85% H3PO4 sample. Infra-red
spectra were recorded on Nicolet 6700 and Bruker Alpha FT-IR
spectrophotometers in absorbance (KBr disc, Nujol and solu-
tion) and ATR modes. Microanalyses were performed at the
Laboratoire de Chimie de Coordination on a PerkinElmer 2400
series II analyzer.
1
ture with a reduced JSi–H coupling constant of 149 Hz in com-
parison to those of the free ligand (189 Hz). In the iridium
case, a more shielded H resonance and an estimated value of
1
126 Hz (3 × 42 Hz) are in agreement with a slightly higher
degree of activation. The isolation and characterization of com-
plexes 2 proved to be challenging due to their high reactivity to
traces of water. The agostic Si–H bonds are indeed readily
broken to form a bridging siloxane ligand spanning the two
metal centres and resulting in the formation of complexes 3.
When the reaction is carried out with the disubstituted benzyl-
silylphosphine compound PhP{(o-C6H4)CH2SiMe2H}2, the
Synthesis of P{(o-C6H4CH2)SiMe2H}3, 1
dimeric central core is also preserved, the metal centers The phosphine P{(o-C6H4)CH3}3 was made in house from the
achieving a 16-electron configuration with two distinct silyl reaction of three equivalents of BrMg(o-C6H4CH3) and one
groups. Solid state NMR, and particularly 29Si solid state NMR equivalent of PCl3. A THF (5 mL) solution of Br(o-C6H4CH3)
proved to be a valuable tool to better characterize complexes 4 (41.6 mmol) was added dropwise to activated Mg (1 g,
due to their poor solubility. It is worth noting that here the 41 mmol) and the reaction mixture was left to react at reflux
reaction of the phosphinodi(benzylsilane) PhP{(o-C6H4) temperature until the full consumption of the activated mag-
CH2SiMe2H}2 with the rhodium and iridium precursors leads nesium. Addition of PCl3 (1.2 mL, 13.9 mmol) and stirring for
to Si–H bond breaking whereas a pincer-type ligation is 24 h left a yellow solution and a white precipitate of MgBrCl
obtained upon reaction with the ruthenium polyhydride which was separated by filtration. To the solution, ice (2 g) was
RuH2(H2)2(PCy3)2, thus favouring the coordination through added followed by 100 mL of a 0.5 M aqueous NH4Cl solution.
two agostic Si–H bonds.46 Finally, the reactivity of the starting The product was extracted three times with 100 mL of ethylic
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ether using a separating funnel. The ethereal phase was col- Hz, Rh–η2(Si–H)). HMQC 103Rh–1H{31P} NMR: (19.12 MHz,
lected, dried over MgSO4 and finally evaporated to dryness. C7D8) δ: −8738 (s).
The yellowish powder was further purified by recrystallization
Synthesis of compound [Ir2(µ-Cl)2P{[η2-(H-SiMe2)
CH2C6H4][(o-C6H4)CH2SiMe2]2}], 2Ir
from hot ethanol solutions at 263 K to yield a white solid in
1
89%, and its purity was verified by m.p. and H and 31P NMR.
P{(o-C6H4)CH3}3 (1 g, 3.3 mmol) was dissolved in 30 mL of
In a Schlenk flask, compound 1 (71 mg, 0.15 mmol) and
hexane, and then TMEDA (1.48 mL, 9.9 mmol) and titrated
[IrCl(COD)]2 (50 mg, 0.07 mmol) were degassed and then dis-
hexane solution of nBuLi (3.96 mL, 9.9 mmol) were added.
solved in pentane (1.5 mL). The solution was stirred for two
After stirring for 20 h, the bright orange red reaction mixture
hours at room temperature after which it was concentrated
was cooled to 195 K and excess ClSiMe2H (3 mL, 27 mmol)
and kept overnight at 236 K. The resulting yellow solid was
was added via syringe. The off-white suspension was allowed
washed twice with 0.5 mL of cold pentane to yield a light
to warm up to room temperature and kept under stirring for
yellow solid. Yield 97% (103 mg). IR (KBr): ν(Ir⋯H–Si)
12 h, after which the solvent was removed by distillation under
2019 cm−1, ω(Si–H) 796 cm−1. 1H NMR (400 MHz, C6D6, 293 K)
a reduced pressure. The white solid was dissolved in 15 mL of
4
4
3
δ: 6.99 (tt, JP–H 1.6 Hz, JH–H 1.6 Hz; JH–H 7.6 Hz, 6H,
hexane and recrystallized overnight at 263 K. Yield 91% from
P{(o-C6H4)CH3}3. M.p. 375 K. Anal. Calcd for C27H39PSi3: C,
67.73; H, 8.21. Found: C, 67.70; H, 8.15. 1H NMR (C6D6,
3
3
CHaromatic), 6.93 (dd, JP–H 11.2 Hz; JH–H 7.6 Hz, 6H,
3
CHaromatic), 6.86 (pt, JH–H 5.6 Hz, 6H, CHaromatic), 6.73 (dt,
4JP–H 1.6 Hz, JH–H 7.6 Hz, 6H, CHaromatic), 2.13 (d, JH–H 14.4
3
2
3
4
400 MHz, 293 K): δ 7.04 (tt, JH–H 7.7 Hz, JH–H 1.14 Hz, 3H),
2
4
Hz, 6H, CH2), 2.05 (dd, JH–H 14.4 Hz; JP–H 3.2 Hz, 6H, CH2),
3
3
7.01 (m, 6H), 6.82 (t, JH–H 7 Hz, 3H), 4.26 (nd, JH–H 3.6 Hz,
1
0.55 (br. s, JSi–H 42.0 Hz, 2H, σ(SiH)), 0.41 (s, 18H, CH3), 0.53
5JP–H 1.8 Hz, JSi–H 189 Hz satellites, 3H), 2.38 (br. s, 6H), 0.08
1
(s, 18H, CH3). 13C{1H} NMR (C6D6, 175 MHz, 293 K) δ: 147.3
(d, JH–H 3.6 Hz, 18H). 13C{1H} NMR (175 MHz, C6D6) δ 145.1
3
1
2
(d, JP–C 13.5 Hz, Cipso–P), 132.5 (d, JP–C 5.6 Hz, Cipso–C), 131.6
1
2
(d, JP–C 26.3 Hz), 134.1 (s), 133.7 (d, JP–C 10.5 Hz), 129.0 (d,
3
2
(d, JP–C 1.75 H, CHaromatic), 131.5 (d, JP–C 8.93 Hz, CHaromatic),
128.6 (s, CHaromatic), 125.3 (d, 3JP–C 8.75 Hz, CHaromatic), 27.6 (d,
3JP–C 11.4 Hz, CH2), 2.22 (s, CH3), 2.93 (s, CH3). 31P{1H} NMR
(161.9 MHz, C6D6, 293 K) δ: 0.21 (s).
2JP–C 5.3 Hz), 128.7 (s), 125.1 (s), 23.4 (d, JP–C 19.3 Hz, CH2),
3
−4.25 (s, CH3, JSi–C 50.8 Hz, satellites). 31P{1H} NMR
1
(161.9 MHz, C6D6) δ −27.0. 29Si{1H} NMR (75.54 MHz, C6D6)δ
−12.1 (s). IR (KBr disc) 2119 cm−1 (s, νSi–H), 1247 cm−1
(s, νSi–Me2), 887 cm−1 (s, ωSi–H).
Synthesis of [Rh2(μ-Cl)2{P((o-C6H4)CH2SiMe2)3}2]2O, 3Rh
Reaction of 2Rh with adventitious water present in a toluene/
Et2O mixture led to the formation of yellow crystals which were
filtrated and subsequently dried under vacuum. They were
Synthesis of [Rh2(µ-Cl)2P{[η2-(H-SiMe2)CH2C6H4][(o-C6H4)
CH2SiMe2]2}], 2Rh
In a Schlenk flask, compound 1 (215 mg, 0.45 mmol) and soluble in most laboratory solvents. Anal. Calcd for
[RhCl(COD)]2 (110 mg, 0.22 mmol) were degassed and then C54H72Cl2OP2Rh2Si6: C, 52.14; H, 5.79. Found: C, 51.56; H,
1
3
dissolved in toluene-d8 (1.5 mL). The solution was stirred for 5.39. H NMR (400 MHz, C6D6, 293 K) δ: 7.59 ppm (dd, JH–H
two hours at room temperature after which it was concentrated 7.2 Hz, 3JH–P 4.9 Hz, 1H, CH), 7.14–6.94 (m, 5H, CH), 6.94–6.87
3
and kept overnight at 236 K. The resulting yellow solid was (m, 1H, CH), 6.77 (t, JH–H 7.4 Hz, 1H, CH), 6.72–6.60 (m, 4H,
2
2
washed twice with 0.5 mL of Et2O to yield a light brown solid. CH), 3.63 (d, JH–H 14.2 Hz, 1H, CH2), 3.36 (d, JH–H 13.9 Hz,
Yield 83% (91 mg). Anal. Calcd for C54H74Cl2P2Rh2Si6: C, 1H, CH2), 2.89 (dd, 2JH–H 14.5, 4JH–P 3.0 Hz, 1H, CH2), 2.33 (dd,
52.72; H, 6.06. Found: C, 52.96; H, 6.10. 1H NMR (300 MHz, 2JH–H 14.1, JH–P 7.3 Hz, 1H, CH2), 2.01 (d, JH–H 13.8 Hz, 1H,
4
2
2
4
5
C7D8, 293 K): δ 7.10 (br. s, 1H, CH), 7.01 (br. m, 3H, CH), 6.86 CH2), 1.91 (ddd, JH–H 14.2, JH–P 7.1, JH–Rh 2.0 Hz, 1H, CH2),
(br. m, 6H, CH), 6.74 (br. m, 3H, CH), 2.56 (br. d, JH–Rh 6.4 Hz, 1.28 (s, 3H, CH3), 0.65 (s, 3H, CH3), 0.59 (s, 3H, CH3), 0.49 (s,
JH–Si 53.4 Hz from 29Si satellites, 2H, η2-HSi), 2.15 (br ψt, JH–H 3H, CH3), 0.05 (s, 3H, CH3), −0.22 (s, 3H, CH3). 13C{1H} NMR
2
1
16 Hz, 12H, SiCH2), 0.56 (br. s, 12H, SiCH3), 0.32 (s, 24H, (176.048 MHz, C6D6, 293 K) δ: 150.1 (d, JC–P 14.3 Hz, Cipso–C),
SiCH3). 31P{1H} NMR (161.9 MHz, C7D8): δ 27.8 (d, JP–Rh 154 148.2 (d, JC–P 13.6 Hz, Cipso–C), 144.1 (d, JC–P 12.0 Hz, Cipso–C
1
2
2
Hz). 13C{1H} NMR (100.61 MHz, C7D8, 223 K): δ: 146.8 (t, JC–P η2-SiH), 133.8 (dd, JC–P 16.3 Hz, JC–Rh 4.4 Hz, CHaromatic, 4C),
1
12.5 Hz, 2JC–Rh 12.5 Hz, Cipso–P), 144.9 (d, 1JC–P 18.4 Hz, Cipso–P 132.7 (d, JC–P 6.8 Hz, CHaromatic, 2C), 131.7 (d, J
Rh-η2(Si-H)), 135.0 (s, Cipso–C), 135.0 (s, Cipso–C), 131.1 (s, CHaromatic, 2C), 131.3 (s, Cipso–C, 2C), 131.1 (t, J
8.1 Hz,
7.7 Hz,
C–P
C–P
Cipso–C), 131.0–130.8 (overlapped higher order m, CHaromatic), CHaromatic, 4C), 130.9 (s, Cipso–C, 2C), 130.1 (s, Cipso–C, 2C),
130.7 (d, JC–P 4.9 Hz, CHaromatic), 130.5 (d, JC–P 8.0 Hz, 125.6 (d, JC–P 8 Hz, CHaromatic, 2C), 125.4 (dd, JC–P 8.5, JC–Rh 4.9
3
CHaromatic), 130.4 (d, JC–P 5.1 Hz, CHaromatic), 125.5 (d, JC–P 6.3 Hz, CHaromatic, 4C), 33.3 (d, JC–P 13.0 Hz, CH2), 32.1 (d,
3
3
Hz, CHaromatic), 124.6(m, CHaromatic), 32.1 (d, JC–P 18.8 Hz, 3JC–P 8.0 Hz, CH2), 28.7 (d, JC–P 13.0 Hz, CH2), 9.55 (s, CH3),
3
3
CH2), 30.8 (d, JC–P 16.2 Hz, CH2), 22.8 (d, JC–P 4.3 Hz, CH2), 5.20 (s, CH3), 4.70 (s, CH3), 3.81 (s, CH3), 3.10 (s, CH3), 2.95 (s,
10.1 (s, CH3), 9.6 (s, CH3), 5.0 (s, CH3), 3.9 (s, CH3), −4.6 (s, CH3). 31P{1H} NMR (161.9 MHz, C6D6, 293 K) δ: 26.20 (d, 1JP–Rh
CH3), −4.8 (s, CH3). DEPT 29Si{1H} NMR(79.49 MHz, C7D8, 157.1 Hz). 29Si{31P} DEPT NMR (79.49 MHz, C6D6, 293 K)
223 K) δ: 57.0 (dd, JSi–Rh 36.7 Hz, JSi–P 10.9 Hz, Rh–Si), 52.9 δ: 67.04 (s), 42.32 (s) and 5.37 (s). 103Rh–1H{31P} HMBC NMR
1
2
1
2
(dd, JSi–Rh 38.7 Hz, JSi–P 12.3 Hz, Rh–Si), −10.5 (s, w1/2 10.3 (12.59 MHz, C6D6, 293 K) δ: −8416.73 ppm (s).
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Synthesis of compound [Ir2(μ-Cl)2{P((o-C6H4)
CH2SiMe2)3}2]2O, 3Ir
Found: C, 45.42; H, 4.14. 13C (CP MAS) δ: 2.0, 2.8, 3.6,
8.9 (CH3), 25.4, 28.6 (CH2), from 122.6 to 147.5 (Caromatic).
31P (P MAS) δ: 11.8 (br). 29Si (CP MAS) δ: 22.7 (br), 13.8 (br).
Reaction of compound 2Ir with adventitious water present in
the working solvents, led to the formation of red-orange
complex 3Ir featuring a siloxane bridge as in the case of the
rhodium analogue. 1H NMR (400 MHz, C6D6, 293 K) δ:
Synthesis of [Rh{P((o-C6H4)CH2SiMe)Ph2}2Cl], 5Rh
To a 0.5 mL toluene solution of [RhCl(COD)]2 (36 mg,
0.07 mmol), [Ph2P{(o-C6H4)CH2SiMe2H}] (97 mg, 0.29 mmol)
was added under stirring. The solution was left stirring over-
night and then concentrated and stored at 273 K for 10 days.
The yellow precipitate was washed twice with 0.5 mL of cold
toluene. An off-brown solid was obtained. Yield 78% (44 mg).
Anal. Calcd for C42H44ClP2RhSi2: C, 62.64; H, 5.51. Found: C,
1
7.03–6.60 (m, 24H, CHaromatic), 3.52, (d, JH–H 16 Hz, 2H, CH2),
1
4
1
2.86 (dd, JH–H 16 Hz, JPH 4 Hz, 2H, CH2), 2.38 (dd, JH–H
4
1
12 Hz, JP–H 4 Hz, 2H, CH2), 2.18 (d, JH–H 12 Hz, 2H, CH2),
2.17 (d, JH–H 12 Hz, 2H, CH2), 2.03 (dd, JH–H 16 Hz, JP–H
1
1
4
4
Hz, 2H, CH2), 0.50 (s, 6H, CH3), 0.45 (s, 6H, CH3), 0.43 (s, 6H,
CH3), 0.36 (s, 6H, CH3), 0.10 (s, 6H, CH3) and −0.24 (s, 6H,
CH3). 31P{1H} NMR (161.9 MHz, C6D6) δ −6.3 (s). 13C{1H} NMR
(176.008 MHz, C7D8, 293 K) δ: 32.6 (CH2), 30.7 (CH2), 26.5
(CH2), 0.50 (CH3), 0.49 (CH3), 0.48 (CH3), 1.13 (CH3), 0.15
(CH3), −0.18 (s, CH3), all the aromatic carbons are in the range
120–150. 13C{1H} NMR (176.008 MHz, C6D6, 293 K) δ 149.7 (d,
1
62.03; H, 5.22. H NMR (500 MHz, C6D6, 293 K) δ: 8.43 (s, 2H,
CH), 8.07 (ψq, 2H, CH), 7.29 (m, 1H, CH), 7.13–6.91 (m, 2H,
CH), 7.07–6.89 (m, 5H, CHaromatic), 6.95–6.89 (m, 2H, CH), 2.08
2
2
(d, JH–H 13.7 Hz, 1H, CH2), 1.98 (vdt, JH–H 13.8 Hz, |4JH–P
+
6JH–P| = 4.2 Hz, 1H, CH2), 0.53 (s, 3H, CH3), −0.42 (s, 3H, CH3).
13C{1H} NMR (100.61 MHz, C6H6, 293 K) δ: 148.3 (vt, |2JH–P
4JH–P| = 7.3 Hz, CH), 137.6 (vt, |3JH–P 5JH–P| = 7.3 Hz,
2JH–P| =
1
1JP–C 13 Hz, Cipso–P), 148.1 (d, JP–C 12.4 Hz, Cipso–P), 143.0 (d,
+
3
1JP–C 11 Hz, Cipso–P), 133.2 (d, JP–C 6 Hz, Cipso–C), 133.0 (d,
+
3JP–C 5.7 Hz, Cipso–C), 132.9 (s, CHaromatic), 132.5 (s, CHaromatic),
CHaromatic), 135.3 (br. s, CH), 133.1 (vt, |1JH–P
+
3
3
23.3 Hz, CHaromatic), 132.1 (vt, |2JH–P
+
4JH–P| = 3.0 Hz, CH),
132.1 (d, JP–C 7.7 Hz, CHaromatic), 131.4 (d, JP–C 8.6 Hz,
CHaromatic), 131.2 (d,3JP–C 8.8 Hz, CHaromatic), 130.8 (s,
CHaromatic), 130.7 (s, CHaromatic), 130.5 (s, CHaromatic), 129.8 (s,
5
131.6 (vt, |3JH–P + J H–P| = 3.2 Hz, CH), 130.6 (s, CH), 130.4 (d,
5
4JP–Rh 4 Hz, CH), 128.6 (vt, |3JH–P + JH–P| = 4.9 Hz, CH), 125.1
(vt, |2JH–P
+ +
4JH–P| = 3.7 Hz, CH), 34.5 (vt, |3JH–P 5JH–P| =
CHaromatic), 128.0 (d, overlapped with the solvent signal, Cipso
–
2
2
9.9 Hz, CH2), 9.80 (s, CH3), 6.25 (d, 2JP–Rh 1.9 Hz).
C), 125.1 (d, JP–C 9 Hz, CHaromatic), 124.9 (d, JP–C 9.3 Hz,
2
3
CHaromatic), 124.8 (d, JP–C 9.5 Hz, CHaromatic), 32.6 (d, JP–C
3
3
7.2 Hz, CH2), 30.7 (d, JP–C 9.8 Hz, CH2), 26.4 (d, JP–C 10.9 Hz,
CH2), 5.89 (s, CH3), 3.39 (s, CH3), 2.88 (s, CH3), 2.71 (s, CH3),
2.48 (s, CH3), −0.05 (s, CH3). 29Si–1H HMBC NMR (79.49 MHz,
C7D8, 293 K) δ: 24.1 (br), 5.1 (br) and 3.5 (br).
Crystal structure determination of 1, 3Rh, 4Rh, 5Rh, and 3Ir
See Table 1 and other details in the ESI.† The structures have
been deposited at the Cambridge Crystallographic Data Centre
(CCDC 1533794, 1533878, 1533806–1533808).
Synthesis of [Rh2(µ-Cl)2{P(o-C6H4CH2SiMe2)2Ph}], 4Rh
To
a Schlenk flask containing [RhCl(COD)]2 (40 mg,
Acknowledgements
0.08 mmol) dissolved in 1 mL of benzene, [PhP{(o-C6H4)
CH2SiMe2H}2] (65 mg, 0.16 mmol) was added under stirring
and immediate evolution of gas was observed. Stirring was
stopped after ca. 5 min and the reaction mixture was left to
stand at room temperature. The resulting yellow crystals were
filtered and washed twice with toluene. Yield 54% (47 mg).
Anal. Calcd for C48H58Cl2P2Rh2Si4·C6H6: C, 55.72; H, 5.54.
Found: C, 55.89; H, 5.34. The solubility of 4Rh was not enough
for solution NMR studies and it reacted with CD2Cl2, CDCl3
This work was supported by CONACyT (project 242818, PhD
grants for MVCG, CACC, JZM and postdoctoral fellowship to
ERF), ANR-CONACyT (274001), CNRS and Université Paul
Sabatier. We also acknowledge the French-Mexican
International Laboratory (LIA-LCMMC) for support.
Notes and references
1
and DMSO-d6. H NMR (CP MAS) δ: 0.2 (CH3), 2.2 (CH2) and
7.1 (CHaromatic). 13C (CP MAS) δ: 3.1 (CH3), 6.0 (CH3), 12.3
(CH3), 28.7 (CH2), 31.4 (CH2), and for the aromatic carbons
123.3, 129.3, 131.9, 137.7, 147.1. 31P (CP MAS) δ: 45.3 (s). 29Si
(CP MAS) δ: 54.9 (s), 65.0 (s).
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