Modular phosphole-methano-bridged-phosphine(borane) ligands. Application to rhodium-catalyzed reactions

Article abstract of DOI:10.1021/om2008265

The synthesis of the phospholyl(phosphinoborane)methane air- and moisture-stable hybrid ligands 4a-f, starting from 1-phenylphospholes 1a-d, was performed via P-C bond coupling on the methano bridge. Two strategies were investigated, according to the phospholyl moiety used as a nucleophilic or an electrophilic reagent. In the first pathway, the phospholyl anions react with the easily available (chloromethyl)diphenylphosphine-borane 3 to afford ligands 4a-d in 29-67% isolated yields. In the second pathway, the phospholyl(dicyclohexylphosphinoborane)methane ligands 4e,f were synthesized in 18-23% yields, through a nucleophilic substitution on the cyanophosphole. Removal of the BH₃ moiety on 4a-c assisted by DABCO leads to the hybrid phospholyl(diphenylphosphino)methanes 5a-c. Compounds 4 and 5 were fully characterized by multinuclear NMR spectroscopy (¹H, ³¹P, ¹³C, ¹¹B), mass spectrometry, and elemental analysis, and the X-ray crystal structures of 4a,c and 5a,b have been established. Ligands 5a,b were used to prepare the cationic rhodium complexes [Rh(η⁴- COD)(5a)]⁺ (8a′), [Rh(η⁴-COD)(5b)]⁺ (8b), [Rh(5a)₂]⁺ (9a′), and [Rh(5b) ₂]⁺ (9b), containing four-membered chelate rings with BF₄^- or CF₃SO₃^- as counterions. Ligands 4a-f were also used to synthesize the [Rh(η ⁴-COD)(4)]⁺ chelate complexes 10a-f, resulting from coordination of the phospholyl part and the BH₃ group via a η² mode with two bridging B-H-Rh 3c-2e bonds, as shown by the X-ray crystal structures of the complexes 10b,c. Rhodium complexes 8 and 10 isolated or formed in situ with ligands 4 and 5 were studied for catalytic hydrogenation of methyl 2-(acetamidomethyl)acrylate (11) and hydroboration of styrene (13) with catecholborane. In both reactions, the catalytic systems prepared either from the phospholyl(phosphinoborane)methane ligands 4 or the corresponding free ligands 5, gave good to excellent conversions. In addition, the regioselectivity of the catalyzed hydroboration is slightly influenced using these ligands. Finally, the use of hybrid phospholyl(phosphinoborane)methanes as ligands offers a new, efficient way to improve catalytic processes, for designing both the structure and the electronic properties of the catalyst, or still to implement it without removing the borane protecting group.

Full text of DOI:10.1021/om2008265

Article
pubs.acs.org/Organometallics
Modular Phosphole-Methano-Bridged-Phosphine(Borane) Ligands.
Application to Rhodium-Catalyzed Reactions
Duc Hanh Nguyen,†,‡ Jerome Bayardon,§ Christine Salomon-Bertrand,§ Sylvain Juge,*,§ Philippe Kalck,†,‡
́
̂
́
Jean-Claude Daran,†,‡ Martine Urrutigoity,†,‡ and Maryse Gouygou*,†,‡
†CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, F-31077 Toulouse, France
‡Universite
de Toulouse, UPS, INPT, LCC, F-31077 Toulouse, France
§Institut de Chimie Molec
ulaire de l’Universite de Bourgogne, UMR CNRS 5260, 9, Avenue Alain Savary BP 47870, 21078 Dijon
́
́
́
Cedex, France
S
* Supporting Information
ABSTRACT: The synthesis of the phospholyl(phosphinoborane)methane air- and moisture-stable hybrid ligands 4a−f, starting
from 1-phenylphospholes 1a−d, was performed via P−C bond coupling on the methano bridge. Two strategies were
investigated, according to the phospholyl moiety used as a nucleophilic or an electrophilic reagent. In the first pathway, the
phospholyl anions react with the easily available (chloromethyl)diphenylphosphine−borane 3 to afford ligands 4a−d in 29−67%
isolated yields. In the second pathway, the phospholyl(dicyclohexylphosphinoborane)methane ligands 4e,f were synthesized in
18−23% yields, through a nucleophilic substitution on the cyanophosphole. Removal of the BH3 moiety on 4a−c assisted by
DABCO leads to the hybrid phospholyl(diphenylphosphino)methanes 5a−c. Compounds 4 and 5 were fully characterized by
multinuclear NMR spectroscopy (1H, 31P, 13C, 11B), mass spectrometry, and elemental analysis, and the X-ray crystal structures
of 4a,c and 5a,b have been established. Ligands 5a,b were used to prepare the cationic rhodium complexes [Rh(η4-COD)(5a)]+
(8a′), [Rh(η4-COD)(5b)]+ (8b), [Rh(5a)2]+ (9a′), and [Rh(5b)2]+ (9b), containing four-membered chelate rings with BF4− or
CF3SO3− as counterions. Ligands 4a−f were also used to synthesize the [Rh(η4-COD)(4)]+ chelate complexes 10a−f, resulting
from coordination of the phospholyl part and the BH3 group via a η2 mode with two bridging B−H−Rh 3c−2e bonds, as shown
by the X-ray crystal structures of the complexes 10b,c. Rhodium complexes 8 and 10 isolated or formed in situ with ligands 4 and
5 were studied for catalytic hydrogenation of methyl 2-(acetamidomethyl)acrylate (11) and hydroboration of styrene (13) with
catecholborane. In both reactions, the catalytic systems prepared either from the phospholyl(phosphinoborane)methane ligands
4 or the corresponding free ligands 5, gave good to excellent conversions. In addition, the regioselectivity of the catalyzed
hydroboration is slightly influenced using these ligands. Finally, the use of hybrid phospholyl(phosphinoborane)methanes as
ligands offers a new, efficient way to improve catalytic processes, for designing both the structure and the electronic properties of
the catalyst, or still to implement it without removing the borane protecting group.
membered metallacycles) or bridging geometries (including A-
frame complexes).1a
Such unusual coordination behavior of these small-bite-angle
diphosphines has been recently exploited in a range of catalytic
processes. Indeed, diphosphinomethane complexes have been
shown to be excellent precursors for the polymerization and
INTRODUCTION
■
Bidentate phosphorus-containing ligands display a widespread
use in coordination catalysis.1 One subclass is small-bite-angle
diphosphines in which the two phosphorus centers are
separated only by a single-atom linker unit, the archetypical
example being 1,1-bis(diphenylphosphino)methane (dppm).2
This diphosphinomethane ligand family is well-established for
giving flexible coordination modes, being monodentate or
bidentate in either chelating (resulting in highly strained four-
Received: September 2, 2011
Published: January 20, 2012
© 2012 American Chemical Society
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Scheme 1. Reaction Pathways for Synthesis of Ligands 4a−f and 5a−d
oligomerization of ethylene,3 hydrogenation of a broad range of
were investigated in catalyzed hydrogenation or hydroboration
reactions with cationic rhodium complexes.
substrates,4 hydrosilylation of simple ketones,5 and C−C bond
coupling reactions.6
RESULTS AND DISCUSSION
The reactivity and catalytic properties of diphosphino-
methane complexes depend largely on the substituents on the
phosphino groups.7 Especially bulky substituents, in particular
alkyl, are better σ-donors toward the metal center than
diphosphine ligands bearing smaller substituents and con-
sequently stabilize four-membered chelate structures.8 It is
worth noting that the stereoselective synthesis of P-chirogenic
diphosphinomethane (RR′PCH2PRR′) ligands has been
recently described, as well as their use for enantioselective
metal-catalyzed reactions,9 chiral-cluster chemistry,10 and
coordination polymers.11
However, unsymmetrical diphosphinomethane
(R2PCH2PR′2) compounds possessing chemically and elec-
tronically different phosphorus atoms have attracted less
attention, and to the best of our knowledge, their catalytic
activity has been only investigated in hydrogenation.12 A priori,
a hemilabile behavior could be envisaged with such ligands.12c
In order to extend the chemistry of the unsymmetrical dppm-
type ligands, we considered their synthesis with one phospholyl
moiety on the methano bridge. Phosphole ligands are sterically
and electronically different from phosphines and are also
efficient in promoting homogeneous transition-metal cataly-
sis.13 Such a synthesis is challenging, since both phosphorus
moieties with their different donation/back-donation abilities
can introduce steric and electronic dissymmetry in the
coordination sphere of the metal center. Therefore, the design
of such ligands is a powerful tool for stereochemically
controlling the substrates and reagents in the coordination
sphere of the metal during the catalytic cycle.
As part of our ongoing program on organophosphorus
synthesis using phosphine−borane chemistry,14 we investigated
the synthesis of phospholylphosphinomethane ligands by P−C
bond formation on the methano bridge, using electrophilic or
nucleophilic phosphine−borane building blocks. In a prelimi-
nary work, we reported the first synthesis of
dibenzophospholyl(diphenylphosphinoborane)methane ligand
through a Pd-catalyzed reaction of (chloromethyl)-
diphenylphosphine−borane with the dibenzophospholyl
anion.15 Using this methodology and a second new one, we
describe in this full paper the synthesis of several substituted
phospholyl(phosphinoborane)methanes and the corresponding
free modified dppm. The applications of both kinds of ligands
■
1. Synthesis of Phospholyl(phosphino)methane Li-
gands. The synthesis of phospholyl(diphenylphosphino)-
methane ligands was performed following two strategies
starting from 1-phenylphospholes 1a−d, depending on whether
the phospholyl reagent is a nucleophilic or an electrophilic
species, as shown in Scheme 1.
In the first pathway, the reductive cleavage of the exocyclic
phosphorus−phenyl bond of 1a−d with an excess of metallic
lithium, followed by neutralization of PhLi using AlCl3 (1/3
equiv), led quantitatively to the lithium phospholide reagents
2a−d. Their reaction with the easily available (chloromethyl)-
diphenylphosphine−borane 3 affords the corresponding hybrid
phospholyl(phosphinoborane)methane 4a−d by chloride sub-
stitution.
The nucleophilic substitution of chloroalkyl derivatives with
the lithium phospholide is relatively rare,16 because this anion is
a poor nucleophilic reagent due to the delocalization of the
negative charge within the heterocycle. Moreover, the chloro
substituent is also a poor leaving group. Indeed, the direct
reaction of the anions 2a−d (1 equiv) with the (chloromethyl)-
phosphine−borane 3 in THF at room temperature over 48 h
resulted in low yields (<10%) in each case. Better results (32−
52%) were obtained using catalytic conditions with the
palladium complex [Pd(OAc)2(dppf)].17 However, in spite of
these conditions, the complete conversion of 3 was not
achieved and small amounts of methyldiphenylphosphine−
borane,18 dppf−diborane adducts,19 and free phospholyl-
(phosphino)methane 5 were observed.20 Complete conversion
was achieved by reaction of 2 equiv of 2a−d with 3 even in the
absence of Pd(II), in THF at room temperature during 48 h,
affording compounds 4a−d in high isolated yields (29−67%).
I n t h e s e c o n d p a t h w a y , t h e p h o s p h o l y l -
(dicyclohexylphosphinoborane)methane 4e,f were obtained in
18 and 23% yields, respectively, by reaction of the α-carbanion
resulting from the deprotonation of the dicyclohexylmethyl-
phosphine−borane 7 with the corresponding cyanophosphole
6 (Scheme 1).
Compounds 4 were generally isolated as air- and moisture-
stable solids and were fully characterized by conventional NMR
1
techniques (31P, H, 13C, 11B), mass spectrometry, elemental
analysis, and single-crystal X-ray analyses. 31P{1H} NMR
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Figure 1. 31P{1H} NMR spectra of 4a and 5a.
Figure 2. 31P NMR spectra of 4b and 5b.21
spectra showed two groups of signals: a doublet for the
phosphorus atom of the phospholyl part P(1) and a broad
lower field signal for that of the phosphino group P(2), which is
consistent with bonding to the quadrupolar boron atom
(Figure 1). In the 31P NMR spectrum of 4b, the phosphole
phosphorus atom P(1) resonated as an enlarged pseudotriplet
due to the coupling with two equivalent protons of the
heterocycle and the phosphine phosphorus atom (Figure 2).
Interestingly, the 31P chemical shifts of 4a−d lie systemati-
cally at high field relative to both 1a−d and 3 (δ +23.7 ppm),
around 20 and 8 ppm away for phospholyl-P(1) and
phosphino-P(2), respectively (see the Supporting Information).
The more basic P(cHex)2 moiety induces a displacement of
chemical shifts of P(1) toward lower field (2 ppm for 4e with
respect to 4a and 6 ppm for 4f vs 4b). The presence of the BH3
moiety to the P(2) atom results in larger H−P(2) coupling
constants (ca. 10 Hz) than for H−P(1) (∼2 Hz) (see the
Supporting Information).
Suitable crystals for X-ray analysis were obtained by
recrystallization from CH2Cl2/n-pentane at −20 °C. The
molecular view of the BH3-protected ligand 4a has already
been reported.15 The crystal structure of 4c is shown in Figure
3. A selection of relevant bond lengths and angles of 4a,c is
given in the Supporting Information. The two X-ray crystal
structures of 4a15 and 4c clearly reveal the presence of the BH3
group coordinated to PPh2 with P(2)−B(1) bond lengths of
1.9085(17) and 1.9152(19) Å, respectively.
Figure 3. Molecular view of 4c with the atom-labeling scheme.
Ellipsoids are drawn at the 30% probability level. H atoms are
represented as small spheres of arbitrary radii.
the corresponding value reported for the bis-
(diphenylphosphino)methane−borane ligand (dppm·BH3).22
These angles around the bridging carbon atom are consistent
with a tetrahedral geometry at the methylene carbon atom. In
both ligands, the phosphole ring is slightly bent with respect to
the P(1)−C(5)−P(2) plane, making dihedral angles of
83.06(4)° for 4a and 82.44(7)° for 4c. The distances and
angles in the phosphole ring are similar to those previously
reported for common phosphole compounds.23 In each case,
the phosphorus P(1) of the phosphole ring is slightly out of the
C(1)C(2)C(3)C(4) plane by 0.140(1) and 0.262(3) Å,
respectively, as already observed in phosphole ligands.24
In the last step, the BH3 decomplexation reaction was
performed using DABCO, as previously described25 (Scheme
1). Phospholyl(diphenylphosphino)methane ligands 5a−c were
The phosphorus atom of the phosphino group adopts a
tetrahedral geometry, as confirmed by the angles about the
P(2) atom in the range of 104−114°. The P(1)−C(5)−P(2)
angles of 110.20(7)° for 4a and 109.48(8)° for 4c are close to
1
quantitatively isolated and fully characterized by H, 31P, and
13C NMR spectroscopy, mass spectrometry (DCI), elemental
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analyses, and single-crystal X-ray analyses. The 31P{1H} NMR
spectra display AX systems for the two nonequivalent
phosphorus atoms, except for ligand 5a, which exhibits an AB
system (Figure 1), consistent with two phosphorus atoms in
close electronic environments. It is worth mentioning that the
loss of BH3 results not only in resonances of P(2) at higher
field but also in a significant displacement of the P(1) chemical
shifts to lower field (around 10 ppm), revealing a lower
electron density and thus an electron transfer toward the PPh2
moiety. In addition, the 31P spectrum of 5b shows the
resonance of the P(1) atom at δ −8.17 ppm, displayed as a
atoms is pyramidal in both ligands 5a,b with the sum of the
three C−P−C angles lying between 290 and 304°.
As for the two BH3 protected ligands 4a,c, the bridging
carbon atom is tetrahedral and the P(1)−C(5)−P(2) plane is
slightly bent with respect to the phosphole ring (dihedral angles
of 77.67(8)° [74.65(8)°] for 5a and 86.5(6)° for 5b). The
P(1)−C(5)−P(2) angles (109° for 5a and 117.7(6)° for 5b)
are higher than the corresponding value (106°) reported for the
dppm ligand,26 presumably related to the steric bulk of the
phospholyl moiety. The BH3 deprotection does not influence
the bond lengths within the phospholyl(diphenylphosphino)-
methane framework in 5a,b, and even the bond angles are not
significantly affected. Indeed, all bond lengths and bond angles
of the phosphole rings compare favorably to those of other
common phosphole compounds, and the P(1) atom is slightly
out of the C(1)C(2)C(3)C(4) planes by 0.082(1) and 0.19(2)
Å, respectively.
doublet of sharp triplets as previously observed for 4b (JHP(1)
=
10.2 Hz, JP(1)P(2) = 46.0 Hz; Figure 2). The molecular structures
of 5a,b have been established by single-crystal X-ray diffraction
studies.
The molecular view of 5a is shown in Figure 4 (for 5b see
the Supporting Information). The lone pairs of the two
2. Synthesis of Rhodium Complexes. The reaction of
[Rh2(μ−Cl)2(η4-COD)2] with 2 equiv of 5a,b in dichloro-
methane at −90 °C, using AgBF4 as a halide abstracting agent
and warming slowly to room temperature, yielded the cationic
rhodium complexes [Rh(η4-COD)(5)][BF4] (8a,b, respec-
tively) (Scheme 2). An alternative synthesis was also developed
using the cationic precursor [Rh(η4-COD)2][CF3SO3] with a
stoichiometric amount of 5a,b under similar conditions.
Complexes 8a′,b gave yellow moderately air-stable powders
after evaporating the solvent. As all attempts at purification
1
failed, they were identified in solution by H and 31P NMR
spectroscopy and mass spectrometry. FAB-MS spectra in
positive mode displayed a strong ion peak of m/z 593 for 8a′
and 645 for 8b, corresponding to the [Rh(η4-COD)-
(phospholyl(diphenylphosphino)methane)]+ fragment. The
31P{1H} NMR spectra of 8a′,b consisted of two groups of
sharp doublet of doublets due to the P−P and P−Rh couplings
(see the Supporting Information), represented by the cross
peaks on the COSY 2D 31P{1H}−31P{1H} spectrum and
interpreted as an AMX spin system (see the Supporting
Information). The higher field doublet of doublets pattern can
be assigned to the P(2) atom of the diphenylphosphino group
and the lower field doublet of doublets to the P(1) atom of the
phospholyl group, via 1H−31P{1H} HMQC experiments.
Moreover, the high-field chemical shift signals observed for
Figure 4. Molecular view of 5a (only one molecule represented) with
the atom-labeling scheme. Ellipsoids are drawn at the 30% probability
level. H atoms are represented as small spheres of arbitrary radii.
phosphorus atoms point away from each other, as indicated by
the lone pair−P(1)−C(5)−P(2) torsion angles of 132° for 5a
and 160° for 5b (the lone pair has been figured as a virtual H
position). The phosphorus geometry of the two P(1) and P(2)
Scheme 2
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both P(1) and P(2) atoms with respect to the free ligands 5a,b
are typical of a four-membered chelate ring.27
respect to those of the ligands 5a,b is typical of a four-
membered chelating ring.27 All chemical shifts and coupling
constants are displayed in the Supporting Information. The
31P{1H} NMR spectra are consistent with the formation of the
pure trans-[Rh(phospholyl(diphenylphosphino)methane)2] di-
astereoisomeric complex in both cases.
In all cases, traces of [Rh(5)2]X complexes 9a′,b were also
observed by 31P{1H} NMR. Complexes 9a′,b were independ-
ently prepared from the [Rh2(μ-Cl)2(η4-COD)2] or [Rh(η4-
COD)2][CF3SO3] precursors. After evaporation of the solvent,
complexes 9a′,b were isolated as yellow air-sensitive powders
and all attempts to isolate them failed. They were identified in
The phospholyl(phosphinoborane)methane 4a−c,e,f act as
chelating P-(η2-BH3) ligands toward the rhodium center,
affording air- and moisture-stable complexes as already
described.15 Thus, the reaction of [Rh2(μ-Cl)2(η4-COD)2]
with 2 equiv of ligand 4 in dichloromethane, using AgBF4,
afforded the rhodium complexes [Rh(η4-COD){(η2-BH3-
phosphine)(κ1-phosphole)}][BF4] (10a−c,e,f) in excellent
yields (61−91%) (Scheme 3). It is worth noting that an excess
of 4a added to 10a at room temperature does not displace the
COD ligand. Alternatively, using the cationic precursor [Rh(η4-
COD)2][CF3SO3] with a stoichiometric amount of 4a−c in
dichloromethane provided the complexes [Rh(η4-COD){(η2-
BH3-phosphine)(κ1-phosphole)}][CF3SO3] (10a′−c′) in very
good yields. Complexes 10a−f were fully characterized by
NMR spectroscopy, mass spectrometry, elemental analysis, and
single-crystal X-ray determinations. The BF4− metathesis of 10a
with the bulky BPh4− anion gave 10a′′, whose crystals were
suitable for an X-ray structure determination, as previously
reported.15 However for 10b,c, monocrystals were grown by
slow diffusion of diethyl ether into dichloromethane solutions
at −20 °C.
1
solution by H and 31P NMR and mass spectrometry. The
positive ion FAB-MS spectra display a strong ion peak of m/z
867 for 9a′ and 971 for 9b, which correspond to the
[Rh{phospholyl(diphenylphosphino)methane}2]+ fragment.
The 31P{1H} NMR spectrum of 9a′ consisted of two groups
of signals, each one containing eight sharp lines derived from an
AA′MXX′ spin system (M = Rh, Figure 5). This is consistent
The molecular structure of the rhodium complex 10b is
displayed in Figure 6 (for 10c see the Supporting Information).
Figure 5. 31P{1H} NMR spectrum of 9a′.
with a centrosymmetric structure in which one phosphorus
atom A is coupled to the other one A′ trans to the rhodium
center and to the two other phosphorus atoms in a trans
configuration as well (X and X′). Of the two eight-line patterns,
that at lower field is assigned to the P-dibenzophospholyl group
and that at higher field to the PPh2 group.
The 31P{1H} NMR spectrum of 9b is more complex than
that of 9a′ and is interpreted as an A2B2X spin system (X = Rh),
due to the proximity of the two chemical shifts rather than an
AA′BB′X system, as shown by the two experimental and
simulated 31P{1H} NMR spectra (see the Supporting
Information). As previously mentioned for 8, the upfield 31P
resonance for the phosphorus atoms P(1) and P(2) with
Figure 6. Molecular view of complex 10b with the atom-labeling
scheme. Ellipsoids are drawn at the 30% probability level. For the sake
of clarity, only H atoms attached to boron were represented as small
spheres of arbitrary radii. H bonds are shown as dashed lines.
Scheme 3
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In all complexes, the phospholyl(phosphinoborane)methane
ligands 4 bind to the metal center through the phosphorus
atom of the phosphole moiety (P(1)) and the BH3 group in a
η2 mode. The latter involves two B−H−Rh three-center−two-
electron bonds, as observed in [Rh(η4-COD){(η2-BH3-
phosphine)(κ1-dibenzophosphole)methane}][BPh4] (10a′′).15
The Rh center has a square-planar geometry defined by the
two centroids of the two CC bonds of the COD ligand, the
P(1), and the Rh−B(1) direction. However, the geometry of 10
could also be viewed as a trigonal bipyramid with one centroid
and the H(1) and H(2) atoms in the equatorial plane.
A similar pentacoordination has been observed previously in
[(η4-COD)Rh{(η2-H3B)Ph2PCH2PPh2}][BPh4].28 The biden-
tate coordination mode of BH3, with a 3c−2e bond, has also
been observed in [8,8-η2-{η2-(BH3)·dppm}-nido-8,7-
RhSB9H10] and [9,9-η2-{η2-(BH3)·dppm}-nido-9,7,8-
RhC2B8H11].29 The Rh−H and B−H distances are in good
agreement, within experimental error, the shortest B−H
distance corresponding to the noncoordinated H atom. The
selected relevant bond lengths and angles are given in Table 1.
maintained in solution. T1 measurements, obtained by the
conventional inversion−recovery method, have been carried
out also for 10b. At any temperature, an average T1 for the
three protons of BH3 was observed showing a fast exchange on
the T1 relaxation time scale, even at 183 K, where the exchange
is slow on the NMR time scale (see the Supporting
Information).15 The remaining observed 31P, 11B, and 13C
resonances are entirely consistent with the solid-state structure.
The boron chemical shift downfield of that of ligand 4 is similar
to that of Weller’s Rh complex.28 In the 31P{1H} NMR spectra,
the doublet of doublets for P(1) and the broad signal for P(2)
are shifted to lower fields. All representative NMR data of
10a′′,b,c,e,f are collected in the Supporting Information.
3. Investigation of the Catalytic Properties of the
Rhodium Complexes. As cationic rhodium complexes are
good precursors for the hydrogenation of CC double
bonds,32 we explored in a first approach the catalytic activity
of the rhodium complexes containing ligands 4 and 5 in the
hydrogenation of methyl 2-(acetamidomethyl)acrylate (11).
This preliminary investigation is devoted to the performance of
the catalytic system under mild conditions. We extended this
study to the hydroboration of styrene 13 operating with
catecholborane 14, this catalysis using BH3-protected ligands
having been hardly explored.33,34
Table 1. Selected Bond Distances (Å) and Angles (deg) for
a
10a″,b,c
10b
10c
10a″15
3a. Hydrogenation Catalysis. The catalytic performances of
the new ligands 4 and 5 were explored in the hydrogenation
reaction of (11) (Scheme 4). In the first set of experiments, the
Rh−P(1)
Rh−B(1)
Rh−B(1)−P(2)
Rh−P(1)−C(5)
Rh−H(1)
2.280(1)
2.364(5)
110.7(2)
112.66(13)
1.83(5)
2.2598(8)
2.302(4)
113.61(17)
111.55(10)
1.80(3)
2.24532(16)
2.331(2)
113.48(9)
111.561(5)
1.85(3)
Scheme 4. Hydrogenation of Methyl 2-
(Acetamidomethyl)acrylate 11
Rh−H(2)
2.06(5)
1.89(3)
1.96(3)
B(1)−H(1)
B(1)−H(2)
B(1)−H(3)
1.18(5)
1.17(3)
1.24(3)
1.09(5)
1.14(3)
1.13(3)
1.05(5)
0.97(3)
1.00(3)
a
P(1) = P-phosphole, P(2) = PPh2.
rhodium complexes generated in situ by addition of ligands 5 to
the [Rh(η4-COD)2][CF3SO3] precursor have been investigated
(Table 2).
The coordination brings back the phosphorus into the plane
of the phosphole ring, as already observed in phosphole-ligated
rhodium complexes; the deviations of the P(1) atom from the
C(1)−C(2)−C(3)−C(4) mean plane are 0.0081 and 0.1076
for 10b,c, respectively (vs 0.262(3) Å for 4c; see the
Supporting Information).
Table 2. Rh-Catalyzed Hydrogenation of Methyl 2-
(Acetamidomethyl)acrylate 11
As observed previously for 10a, NMR monitoring at 188 K of
entry
ligand
substrate/Rh
PH
yield (%)
2
10b confirms that the molecular structure described above is
a
1
maintained in solution. In the H{11B,31P} NMR spectrum, a
1
5a
50
100
50
20
20
20
20
20
20
20
20
10
40
40
40
100
3
a
singlet30 at δ −1.23 corresponding to 2H of BH3 was observed,
the third proton of BH3 probably being included in the massif
(2.0−2.6 ppm) of the CH2 protons of the COD ligand. By 1D
1H EXSY experiment with broad-band decoupling of 11B and
31P, two singlets29 for the three protons of BH3 at 2.08 ppm
(1H) and −1.23 ppm (2H) were observed and assigned to the
terminal B−H and to the two bridging Rh−H−B bonds,
respectively. The variable-temperature 1H{11B,31P} NMR
spectra, from 183 to 298 K, show that these two singlets
2
5a
a
3
5b
100
80
a
4
5b
100
100
100
200
400
100
100
50
b
5
5a
100
100
100
91
b
6
5b
b
7
5b
b
8
5b
b
9
5b
100
17
b
10
11
12
4a
b
4b
100
collapsed (Tc = 233 K, ΔG⧧ = 42.3
1 kJ/mol). At room
b
4b
100
85
temperature, a pseudodoublet at −0.06 ppm (JHRh ≈ 11 Hz)
was observed, consistent with three equivalent BH3 protons.
This suggests that the BH3 group is fluxional in solution, as
observed in other rhodium complexes,22,28,29,31 due to the rapid
exchange of the three B−H bonds, their bonding to the Rh
center occurring through rotation around the P−B bond
according to the mechanism proposed by Barton.29 Therefore,
the η2-BH3 binding motif determined in the solid state is not
a
Experimental conditions: [Rh(η4-COD)2][CF3SO3], solvent MeOH,
b
t = 20 h, T = 25 °C, [P]/[Rh] = 2. Experimental conditions:
formation of the precatalyst during 3 h in the absence of H2.
The addition of 1 equiv of ligands 5a,b to [Rh(η4-COD)2]+
presumably provides the complexes [Rh(η4-COD)(5)]+
(8a′,b′) and then the solvated derivatives [Rh(5)(MeOH)2]+,
862
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by hydrogenation of the COD in methanol.35 When the 11/
[Rh] ratio is 50/1, the substrate is quantitatively hydrogenated
at 20 bar in 20 h (entries 1 and 3), whereas for a 100/1 ratio,
the product 12 is obtained in 3% yield for 5a and 80% yield for
5b, indicating that rhodium complex 8b′ with a 2,5-
diphenylphospholyl moiety is catalytically more active than
8a′ with a dibenzophospholyl moiety (entries 2 and 4). This
difference in reactivity is presumably due to the pronounced
electronic dissymmetry shown by the ligand 5b.
Scheme 5. Hydroboration of Styrene 13 with Catechol
Borane 14
corresponding alcohols. After workup, the conversion and the
1
regioselectivities were determined by H NMR spectroscopy.
Preforming the rhodium catalyst by mixing [Rh(η4-COD)2]+
with 1 equiv of 5a,b (P/Rh = 2) and a large excess of substrate
11 at room temperature for 3 h, in the absence of H2, gives
more satisfactory results. A 100% hydrogenation yield is
reached for either a 11/[Rh] ratio of 100 with 5a, and with a
ratio of 100 or 200 with 5b (entries 5−7). As already observed,
the rhodium catalyst bearing the 2,5-diphenylphospholyl
substituent (5b) is more active. Thus, increasing the 11/[Rh]
ratio to 400 with 5b still provides the product 12 in 91% yield
(entry 8). Higher reactivity with the preformed Rh species
could be consistent with the formation of the rhodium−
substrate complex [Rh(5)(11)]+ under such conditions. This
preformed species should then react directly with dihydrogen
to produce [Rh(H)2(5b)(11)]+ going along the catalytic cycle.
Thus, reducing the H2 pressure to 10 bar for a 11/[Rh] ratio of
100 still allows complete conversion (entry 9). Similar activities
were reported for rhodium cationic complexes containing chiral
d i p h o s p h i n e l i g a n d s , 3 6 i n c l u d i n g 1 , 2 - b i s -
(alkylmethylphosphino)methane4a for the hydrogenation re-
action of methyl 2-(acetamidomethyl)acrylate (11).
The results are reported in Table 3.
a
Table 3. Rhodium-Catalyzed Hydroboration of Styrene
b)
b)
15/16
entry
cat.
Rh/L
conversn (%)
1
no cat.
[Rh]/dppm
[Rh]/17
10g
16
95
80
83
92
90
84
87
60
57
69
50
63
100/0
23/77
69/31
64/36
46/54
46/54
51/49
43/57
48/52
35/65
43/57
55/45
53/47
2
1/1
1/1
3
4
5
[Rh]/5a
[Rh)/5b
10a
1/1
1/1
6
7
8
10b
9
10e
10
11
12
13
10f
[Rh]/17
[Rh]/4a
[Rh]/4b
1/2
1/2
1/2
a
Experimental conditions: [Rh] = [Rh(η4-COD)2][BF4] (1 mol %), T
= 25 °C, t = 22 h; solvent THF (2 mL), styrene (1 mmol),
b)
1
catecholborane (1 mmol). Determined by H NMR.
Interestingly, phospholyl(phosphinoborane)methane ligands
4a,b give Rh catalytic systems that are active in the
hydrogenation of 11. With 4b, complete conversion is achieved
for a 11/[Rh] ratio of 50 and 85% conversion for a ratio of 100,
under a higher pressure of H2 (40 bar, entries 11 and 12). For
4a, the results are less spectacular, although a moderate yield of
17% is still observed (entry 10). Catalytic activities of the
phospholyl(phosphinoborane)methane−rhodium systems are
lower than those observed with the deprotected ligands 5a,b.
Presumably, this reactivity difference means that the
dihydrogen oxidative addition is the rate-determining step in
this catalytic hydrogenation, directly connected to the electron
density on the metal center. It is worth noting that these results
demonstrate the possibility to use the phosphine−borane
ligand in Rh-catalyzed hydrogenation without removing the
borane-protecting group. Moreover, the phospholyl-
(phosphinoborane)methane seems to really act as a bidentate
ligand.37
First, hydroboration with no rhodium catalyst gives a low
conversion and leads regiospecifically to the linear alcohol 15
(entry 1). When the reaction is catalyzed by a rhodium
complex, the conversions are good to excellent (50−95%) and
a mixture of linear/branched alcohols 15/16 in ratios ranging
from 23/77 to 64/36 are obtained, depending on the ligands
used (entries 2−13). The catalyst generated by mixing [Rh(η4-
COD)2][BF4] and 1 equiv of dppm in THF for 30 min leads to
the alcohols with a linear/branched 15/16 ratio of 23/77 (entry
2). On the other side, using the dppm·BH3 ligand 17 produces
higher quantities of the linear isomer with a 15/16 ratio of 69/
31 (entry 3). It is worth noting that when the rhodium complex
[Rh(η4-COD)(17)][BF4] (10g) is directly introduced, the
catalyzed hydroboration induces roughly the same regioselec-
tivity: i.e., 64/36 vs 69/31 (entries 3 and 4).
3b. Catalysis of Hydroboration. The catalyzed hydro-
boration reaction is a powerful method for the chemo-, regio-,
and stereoselective synthesis of organoborane compounds,
from which numerous functional derivatives can be pre-
pared.38,39 The use of rhodium phosphine complexes in the
reaction of catecholborane with olefins favors Markovnikov
addition and, therefore, the formation of branched products. In
some cases, the regioselectivity of the addition is sensitive to
the oxidation of the catalytic system.38 We investigated herein
the use of ligands 4 and 5 in the hydroboration catalysis of
styrene 13 with catecholborane 14 (Scheme 5). The catalytic
reactions were performed using either the previously isolated
complexes 10 or species prepared in situ (1 mol %) in THF by
mixing the precursor [Rh(η4-COD)2][BF4] and 4 or 5. The
reactions were carried out at room temperature for 22 h, and
then the crude organoborane mixtures were oxidized into the
The rhodium complexes prepared in situ from 5a,b afford the
alcohol mixture with excellent conversions (90−92%) and with
similar 15/16 ratios of 46/54 (entries 5 and 6). No significant
differences in terms of regioselectivity are observed with
isolated complexes 10a (15/16 = 51/49, entry 7) or 10b (15/
16 = 43/57, entry 8) in comparison to Rh catalysts formed in
situ from the corresponding free ligands 5a,b. In addition,
unlike the case for the rhodium-bound dppm complex giving
higher branched regioslectivity than with 5a,b (entries 2, 5, 6),
complex 10g containing the chelating dppm·BH3 ligand
generates less branched isomer 16 than 10a,b (entry 4). It is
863
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μm). All NMR spectral data were recorded on Bruker DRX 300 or
Avance 300−500 spectrometers with TMS as internal reference for 1H
and 13C, 85% phosphoric acid as external reference for 31P, and
BF3·Et2O for 11B. Spectral assignments were made by means of routine
one- and two-dimensional NMR experiments where appropiate. T1
relaxation times were mesured by the conventional inversion−recovery
method. Simulated spectra were obtained using the gNMR v 4.1
program (Cherwell Scientific Ltd). Mass spectral analyses were
performed on a Bruker ESI microTOF-Q (HR) apparatus and on a
TSQ 7000 Thermoquest instrument (DCI). The major m/z peak was
reported with the intensity as a percentage of the base peak in
brackets. Elemental analyses were measured with a precision superior
to 0.3% at the Microanalysis Laboratory of the LCC at Toulouse. X-
ray structures were determined on an Oxford Diffraction Xcalibur
CCd diffractometer. Commercially available diphenylphosphine,
palladium(II) acetate, 1,1-bis(diphenylphosphino)methane, 1,1′-bis-
(diphenylphosphino)ferrocene, [Rh(η4-COD)2][CF3SO3], [RhCl(η4-
COD)]2, silver tetrafluoroborate, and tetraphenylborate were used as
received. The ligands 1-phenyldibenzophosphole (1a),40 1,2,5-
triphenylphosphole (1b),41 1-phenyl-2,3,4,5-tetramethylphosphole
(1c),42 1-phenyl-3,4-dimethylphosphole (1d),43 1-cyanodibenzo-
phosphole (6a), 1-cyano-2,5-diphenylphosphole (6b),44
(chloromethyl)diphenylphosphine−borane (3),45 dicyclohexylmethyl-
worth noting that in spite of the lower conversions observed
with both 10e,f containing the more basic P(cHex)2 moiety
(57−60%), in comparison with 10a,b,g (83−87%), the best
branched regioselectivity is obtained with the Rh complex 10f
(15/16 = 35/65, entry 10).
The influence of the [Rh]/ligand ratio on the catalytic
reactivity has been studied as well. In fact, adding 2 equiv of
dppm·BH3 (17) results in both a lower conversion and the
reverse linear/branched 15/16 ratio with respect to 1 equiv
added in the reaction: i.e. 43/57 vs 69/31 (entries 3 and 11).
Similarly, introducing 2 equiv of ligands 4a,b to the rhodium
precursor also induces a lower conversion (50−63%) (entries
12 and 13). However, the 15/16 ratios seem to be not strongly
affected, with values of 51/49 vs 55/45 for 4a (entries 7 and
12) and 43/57 vs 53/47 for 4b (entries 8 and 12), slightly in
favor of the formation of the linear isomer 15.
Therefore, in the absence of a catalyst, the hydroboration of
styrene provides after oxidation and workup the linear alcohol.
Introduction of a rhodium cationic catalyst containing one of
the hybrid phosphine−phosphole ligands of this study allows us
to increase the yields and to produce the branched alcohol with
selectivities ranging from 31 to 65%. The selectivity is
somewhat better when a BH3-protected ligand is used to
generate the catalyst.
47
phosphine−borane (7),46 and dppm·BH3 were prepared according
to the literature.
General Procedure for the Synthesis of the Hybrid
Phospholyl(diphenylphosphinoborane)methane Ligands 4a−
d. To a solution of 1-phenylphosphole 1 (4.8 mmol) in THF (40 mL)
was added at 0 °C metallic lithium in excess (0.20 g). The reaction
mixture was vigorously stirred for 1 h at 0 °C and then for 3 h at room
temperature to afford the phospholyl anion 2 and PhLi. After removal
of the unreacted lithium, the dark red solution was cooled to −20 °C
and anhydrous AlCl3 (0.8 mmol) was added. The reaction mixture was
warmed to room temperature and stirred again for 30 min. To the
resulting solution of 2 was added at −78 °C a solution of
(chloromethyl)diphenylphosphine−borane (3; 2.4 mmol) in THF
(10 mL). The obtained solution was warmed to room temperature and
stirred for 48 h. The solution mixture was concentrated to 5 mL and
quenched with degassed H2O (20 mL), and the aqueous phase was
extracted with dichloromethane (3 × 30 mL). The combined extracts
were dried over MgSO4 and evaporated under reduced pressure to
afford a yellow residue. Successive purifications of the yellow crude
products by chromatography on a silica gel column (eluent CH2Cl2/n-
hexane, 50/50 or 40/60) and recrystallization in a CH2Cl2/n-pentane
mixture at −20 °C gave the pure compounds 4. For 4d, which was
partially oxidized during chromatography (see the Supporting
Information), pure compound was obtained by repeated crystallization
with a CH2Cl2/Et2O mixture at −20 °C.
CONCLUSION
■
We have prepared hybrid phospholyl(phosphino)methane
ligands, and their monoborane protected forms, with a
methylene bridge between the phospholyl and phosphino
moieties. Two synthetic pathways have been used to graft the
phosphorus blocks onto the CH2 motif by P−C bond
formation. The first pathway involves the nucleophilic attack
of a phospholyl anion on the (chloromethyl)-
diphenylphosphine−borane as the key step. In the second
case, the synthesis is based on the nucleophilic substitution of
an electrophilic phospholyl species by a dicyclohexyl-
(phosphino)methylenic anion. Both synthetic strategies allow
us to obtain phospholylphosphinomethane derivatives with
various aryl or alkyl substituents.
The two types of phospholylphosphinomethane ligands,
complexed to a borane or not, have been used for the
preparation of rhodium(I) cationic complexes. Both kinds of
rhodium complexes are active in the catalyzed hydrogenation
and hydroboration reactions. Particularly interesting results
have been gained with the hybrid phospholyl-
(phosphinoborane)methane ligands, which act as chelating P-
(η2-BH3) entities toward the rhodium center and present good
reactivity in hydrogenation and, more especially, promising
activity and regioselectivity in hydroboration.
This study shows that the use of hybrid phospholyl-
(phosphinoborane)methanes as ligands offers a new way to
improve a catalytic process, for designing both its structure and
its electronic properties, or still to implement the catalyst
without removing the borane protecting group before use.
Dibenzophospholyl(diphenylphosphinoborane)methane (4a).
White solid. Yield: 67%. 1H NMR (298 K, CDCl3, 300.13 MHz,
4
3
ppm): δ 7.88 (dd, 2H, CH−, JHH = 0.6 Hz, JHH = 7.5 Hz,
phosphole), 7.75 (m, 4H, CH−, 4JHH = 1.2 Hz, 3JHH = 8.4 Hz, JHP
=
1.5 Hz, Ph), 7.40−7.58 (m, 4H of phosphole and 6H of Ph, =CH−),
7.25 (t, 1H, CH−, 3JHH = 7.2 Hz, 3JHP = 1.0 Hz, phosphole), 7.24 (t,
1H, CH−, 3JHH = 7.2 Hz, 3JHP = 1.0 Hz, phosphole), 2.63 (dd, 2H,
2
2
>CH2, JHP(1)= 2.1 Hz, JHP(2) = 10.8 Hz, P(1)CH2P(2)), 1.34 (br q,
3H, JHB = 88.5 Hz, BH3). H{11B} NMR (298 K, CDCl3, 300.13
MHz, ppm): δ selected 1.34 (d, 3H, 1JHP(2) = 15.9 Hz, BH3). 31P{1H}
NMR (298 K, CDCl3, 121.495 MHz, ppm): δ +15.58 (br, P(2),
1
1
2
Ph2P·BH3), −29.70 (d, P(1), JPP = 68.0 Hz, phosphole). 11B{1H}
NMR (298 K, CDCl3, 96.294 MHz, ppm): δ −38.44 (d, 1B, JBP = 40.7
Hz, BH3). 13C{1H} NMR (298 K, CDCl3, 75.468 MHz, ppm): δ
143.53 (d, >C, JCP = 1.8 Hz, phosphole), 142.85 (t, >C, JCP = 7.3
Hz, phosphole), 132.45 (d, JCP = 8.7 Hz, Ph), 131.95 (d, JCP = 2.4 Hz,
EXPERIMENTAL SECTION
■
General Procedures. All reactions were carried out under an
argon atmosphere in dried glassware. Solvents were dried and freshly
distilled under an argon atmosphere over sodium/benzophenone for
THF and diethyl ether, P2O5 for CH2Cl2, CaH2 for n-pentane, and
sodium for toluene. Thin-layer chromatography was performed on
silica gel (60 F254) and visualized by UV, iodine, or permanganate
treatment. Flash chromatography was performed on silica gel (35−70
Ph), 130.58 (d, >C, JCP = 22.4 Hz, phosphole), 129.81 (d, JCP
=
55.3 Hz, Ph), 129.78 (d, JCP = 55.2 Hz, Ph), 129.0 (s, >C,
phosphole), 128.93 (d, JCP = 10.1 Hz, Ph), 127.59 (d, CH−, JCP
=
=
7.3 Hz, phosphole), 121.33 (s, CH−, phosphole), 27.82 (dd, JCP
33.0, 40.4 Hz, P(1)CH2P(2)). MS (DCI, NH3): m/z (%) 397.2 (100)
[M + H]+. Anal. Calcd for C25H23BP2: C, 75.79; H, 5.85. Found: C,
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Article
75.61; H, 5.99. Crystals suitable for an X-ray diffraction study were
obtained by recrystallization from CH2Cl2/n-pentane solution at −20
°C.
solution of cyanophosphole 6 (0.49 mmol) in THF (5 mL) was added
at 0 °C and the solution was stirred at room temperature overnight.
The reaction mixture was hydrolyzed with water (5 mL), and the
aqueous phase was extracted with methylene chloride (3 × 5 mL). The
combined organic phases were dried over MgSO4 and filtered and the
solvent removed in vacuo to give a residue, which was purified by
chromatography on a silica gel column using toluene as eluent.
Dibenzophospholyl(dicyclohexylphosphinoborane)methane
2,5-Diphenylphospholyl(diphenylphosphinoborane)methane
(4b). Yellow solid. Yield: 51%. 1H NMR (298 K, CDCl3, 300.13 MHz,
ppm): δ 7.49 (m, 4H, CH−, JHH = 1.5, 7.6 Hz, JHP = 9.0 Hz), 7.36
(tt, 6H, CH−, JHH = 1.5, 6.3 Hz, −Ph, phosphole), 7.18−7.28 (m,
10H, =CH−), 7.11 (dd, CH−, JHP = 1.5, 9.9 Hz, phosphole), 2.68
(dd, >CH2, JHP(1) = 3.0 Hz, JHP(2) = 11.1 Hz, P(1)CH2P(2)), 1.17 (br,
1
(4e). White solid. Yield: 18%. H NMR (298 K, CDCl3, 300.13 MHz,
1
3H, BH3). H{11B} (298 K, CDCl3, 300.13 MHz, ppm): δ selected
ppm): δ 7.98−7.96 (m, 2H, CH−, phosphole), 7.93 (d, 2H, 
CH−, J = 7.6 Hz, phosphole), 7.50 (td, 2H, CH−, J = 1.1 Hz, J =
7.7 Hz, phosphole), 7.40 (tdd, 2H, CH−, J = 1.0 Hz, 3.0 Hz, J = 7.4
Hz, phosphole), 2.00 (dd, 2H, >CH2, JHP(1) = 2.0 Hz, JHP(2) = 9.7 Hz,
P(1)CH2P(2)), 2.01−1.86 (m, 10H, cHex), 1.50−1.45 (m, 4H, cHex),
1.33−1.27 (m, 8H, cHex), 0.71 (m, 3H, BH3). 31P{1H} NMR (298 K,
CDCl3, 121.495 MHz, ppm): δ +25.48 (br, P(2), (cHex)2P·BH3),
1.17 (d, 3H, JHP = 16.0 Hz, BH3). 31P{1H} NMR (298 K, CDCl3,
121.495 MHz, ppm): δ +16.79 (br, P(2), Ph2P·BH3), −19.33 (d, P(1),
JP1P(2) = 60.8 Hz, phosphole). 11B{1H} NMR (298 K, CDCl3, 96.294
MHz, ppm): δ −38.33 (br, BH3). 13C{1H} NMR (298 K, CDCl3,
75.468 MHz, ppm): δ 152.17 (d, >C, JCP = 6.2 Hz), 152.10 (d,
>C, JCP = 6.0 Hz), 136.01 (d, >C, JCP = 17.4 Hz), 132.73 (d, 2C,
CH−, JCP = 8.7 Hz, phosphole), 132.14 (d, CH−, JCP = 9.4 Hz),
131.20 (CH−, phosphole), 131.17 (CH−, phosphole), 129.65
(d, >C, JCP = 54.8 Hz), 129.62 (d, >C, JCP = 54.9 Hz), 128.78
(CH−, phosphole), 128.55 (d CH−, JCP = 10.0 Hz), 127.20 (
CH−, phosphole), 126.96 (d, CH−, JCP = 9.6 Hz), 21.07 (dd,
>CH2, JCP =31.6, 33.9 Hz, P(1)CH2P(2)). MS (DCI, NH3): m/z (%)
449.2 (100) [M + H]+. Anal. Calcd for C29H27BP2: C, 77.70; H, 6.07.
Found: C, 77.46; H, 6.23.
2
−27.70 (d, P(1), JPP = 47.5 Hz, phosphole). 13C{1H} NMR (298 K,
CDCl3, 75.468 MHz, ppm): δ 143.52 (dd, JCP = 5.6 Hz, JCP = 7.7 Hz,
phosphole), 143.40 (d, JCP = 2.1 Hz, phosphole), 130.74 (d, JCP = 22.0
Hz, phosphole), 128.94 (s, phosphole), 127.62 (d, JCP = 6.9 Hz,
phosphole), 121.36 (s, phosphole), 32.80 (dd, >CHP, JCP = 3.2, 31.1
Hz, cHex), 27.15 (s, >CH2, cHex), 27.00 (t, >CH2, JCP = 2.0 Hz,
cHex), 26.92 (s, >CH2, cHex), 26.85 (s, >CH2, cHex), 25.97 (s, >CH2,
cHex), 20.91 (dd, >CH2, JCP = 26.8, 39.9 Hz, P(1)CH2P(2)). MS
(ESI): m/z (%) 431.2 (100) [M + Na]+.
2,3,4,5-Tetramethylphospholyl(diphenylphosphinoborane)-
1
methane (4c). White solid. Yield: 60%. H NMR (298 K, CDCl3,
2,5-Diphenylphospholyl(dicyclohexylphosphinoborane)methane
1
300.13 MHz, ppm): δ 7.75 (m, 4H-o, CH−; JHH = 1.5, 6.3 Hz), 7.49
(4f). Yellow solid. Yield: 23%. H NMR (298 K, C6D6, 300.13 MHz,
(m, 4H-m and 2H-p, CH−), 2.53 (dd, 2H, >CH2, JHP(1) = 2.4 Hz,
ppm): δ 7.77−7.74 (m, 4H, CH−, Ph), 7.33−7.29 (m, 4H, CH−,
Ph), 7.18−7.13 (m, 2H, CH−, Ph), 6.97 (dd, 2H, CH−, J = 1.0
Hz, J = 9.3 Hz, phosphole), 2.08 (dd, 2H, >CH2, JHP(1) = 3.4 Hz, JHP(2)
= 9.8 Hz, P(1)CH2P(2)), 1.71−1.68 (m, 4H, >CHP and >CH2,
cHex), 1.57−1.49 (m, 8H, >CH2, cHex), 1.35−1.26 (m, 4H, >CH2,
cHex), 0.84−1.00 (m, 6H, >CH2, cHex), 1.35 (m, 3H, BH3). 31P{1H}
NMR (298 K, C6D6, 121.495 MHz, ppm): δ +32.99 (br, P(2),
(cHex)2P·BH3), −13.10 (d, P(1), 2JPP = 39.4 Hz, phosphole). 13C{1H}
NMR (298 K, C6D6, 75.468 MHz, ppm): δ 153.68 (d, JCP = 5.4 Hz,
phosphole), 153.61 (d, JCP = 5.5 Hz, phosphole), 137.28 (d, CH−,
JCP = 17.4 Hz, Ph, phosphole), 123.16 (d, CH−, JCP = 8.4 Hz,
phosphole), 129.28 (s, Ph, phosphole), 127.84 (s, Ph, phosphole),
127.76 (s, Ph, phosphole), 33.14 (dd, >CHP, JCP = 2.0, 30.1 Hz,
cHex), 27.17 (s, >CH2, cHex), 27.11 (s, >CH2, cHex), 26.80 (d,
>CH2, JCP = 3.6 Hz, cHex), 26.65 (d, >CH2, JCP = 3.3 Hz, cHex),
25.98 (d, >CH2 JCP = 0.9 Hz, cHex), 15.89 (dd, >CH2, JCP = 24.9, 33.4
Hz, P(1)CH2P(2)). MS (ESI): m/z (%) 483.2 (100) [M + Na]+.
General Procedure for Decomplexation. The decomplexation
reaction was performed as previously described. The reaction mixture
of 1 equiv of phospholyl(diphenylphosphinoborane)methane 4 and 5
equiv of DABCO in toluene (5 mL) was heated at 50 °C under an
argon atmosphere for 14 h. The resulting solution was filtered through
a neutral alumina column with the use of degassed AcOEt/toluene (1/
9) as eluent. After removal of the solvents, the free phosphole−
phosphino methane compounds 5 were obtained in 80−90% yield.
Suitable crystals for X-ray structure determinations were obtained by
recrytallization in diethyl ether at −20 °C.
4
JHP(2) = 10.2 Hz, P(1)CH2P(2)), 1.85 (d, 6H, −CH3, JHP = 2.1 Hz,
phosphole), 1.79 (d, 6H, −CH3, JHP = 10.2 Hz, phosphole), 1.13 (3H,
BH3, JHP(2) = 16.0 Hz, BH3). 31P{1H} NMR (298 K, CDCl3, 161.976
MHz, ppm): δ +16.10 (br, P(2), Ph2P·BH3), −8.25 (d, P(1), JP1P(2)
=
55.2 Hz, phosphole). 31P NMR (298 K, CD2Cl2, 161.976 MHz, ppm):
δ +15.77 (br, P(2), H3B·PPh2), −23.43 (q, P(1), JP1H = 40.8 Hz, JP1P(2)
= 43.4 Hz, phosphole). 11B{1H} NMR (298 K, CDCl3, 96.294 MHz,
ppm): δ −38.03 (d, JBP = 56.9 Hz, BH3). 13C{1H} NMR (298 K,
CDCl3, 75.468 MHz, ppm): δ 143.19 (d, >C, JCP = 11.3 Hz),
134.28 (d, >C, JCP = 6.8 Hz), 134.25 (d, >C, JCP = 6.8 Hz),
132.48 (d, 4C, CH−, JCP = 9.8 Hz), 131.22 (d, 2C, CH−, JCP
3.0 Hz), 128.68 (d, 4C, CH−, JCP = 9.8 Hz), 19.69 (dd, >CH2, JCP
=
=
38.2, 32.6 Hz, P(1)CH2P(2)), 13.90 (d, 2C, −CH3, JCP = 2.6 Hz,
phosphole), 12.69 (d, 2C, −CH3, JCP = 22.3 Hz, phosphole). MS
(DCI, NH3): m/z (%) 353.2 (100) [M + H]+. Anal. Calcd for
C21H27BP2: C, 71.62; H, 7.73. Found: C, 71.70; H, 7.71. Crystals
suitable for an X-ray diffraction study were obtained by recrystalliza-
tion in diethyl ether at −20 °C.
3,4-Dimethylphospholyl(diphenylphosphinoborane)methane
(4d). White solid. Yield: 29%. 1H NMR (298 K, CDCl3, 400.13 MHz,
ppm): δ 7.73 (m, 4H-o, CH−, JHH = 6.8 Hz, −Ph), 7.51 (m, 2H-p,
CH−, JHH = 7.2 Hz, JHP = 1.6 Hz, −Ph), 7.46 (td, 4H-m, CH−,
JHH = 7.6 Hz, JHP = 2.0 Hz, −Ph), 6.16 (d, 2H, CH−, JHP = 39.2 Hz,
phosphole), 2.53 (d, 2H, >CH2, JHP(2) = 10.4 Hz, P(1)CH2P(2)), 2.00
(d, 6H, −CH3, JHP = 2.8 Hz, phosphole), 1.12 (br, 3H, BH3). 1H{11B}
NMR (298 K, CDCl3, 300.13 MHz, ppm): δ selected 1.12 (d, 3H, JHP
= 15.6 Hz, BH3). 31P{1H} NMR (298 K, CDCl3, 161.976 MHz, ppm):
δ +15.82 (br, P(2), Ph2P·BH3), −23.51 (d, P(1), JP(2)P(1) = 44.4 Hz,
phosphole). 11B{1H} NMR (298 K, CDCl3, 96.294 MHz, ppm): δ
−38.38 (d, JBP = 46.2 Hz, BH3). 13C{1H} NMR (298 K, CDCl3,
100.613 MHz, ppm): δ 149.42 (d, >C, JCP = 7.65 Hz), 132.37 (d,
CH−o, JCP = 9.3 Hz, −Ph), 131.31 (d, CH−p, JCP = 2.3 Hz,
−Ph), 130.00 (t, JCP = 6.2 Hz, CH−, phosphole), 129.89 (d, >C,
JCP = 55.4 Hz, −Ph), 129.87 (d, >C, JCP = 55.2 Hz, −Ph), 128.70
(d, CH−m, JCP = 10.1 Hz, −Ph), 21.14 (dd, >CH2, JCP(1) = 31.8,
35.4 Hz, P(1)CH2P(2)), 17.67 (d, −CH3, JCP = 3.6 Hz, phosphole).
General Procedure for the Synthesis of Phospholyl-
(dicyclohexylphosphinoborane)methanes 4e,f. To a solution
of dicyclohexylmethylphosphine−borane (7; 0.44 mmol), previously
prepared according to the literature procedure,46 in THF (2 mL) was
added dropwise t-BuLi (0.49 mmol) at 0 °C. After the mixture was
stirred for 30 min at 0 °C and then for 90 min at room temperature, a
Dibenzophospholyl(diphenylphosphino)methane (5a). White
1
solid. Yield: 84%. H NMR (298 K, CDCl3, 400.13 MHz, ppm): δ
7.92 (d, 2H, CH−, JHH = 8.0 Hz, phosphole), 7.66 (dd, 2H, 
CH−, JHH = 7.4 Hz, JHP = 3.6 Hz, phosphole), 7.40−7.50 (m, 6H, 
CH−, Ph), 7.25−7.38 (m, 8H, =CH−), 2.54 (t, 2H, >CH2, JHP = 1.2
Hz, P(1)CH2P(2)). 31P{1H} NMR (298 K, CDCl3, 121.495 MHz,
ppm): δ −21.2 (d, P(1), JP(1)P(2) = 99.5 Hz, phosphole), −22.45 (d,
P(2), JP(2)P(1) = 99.5 Hz, PPh2). 13C{1H} NMR (298 K, CDCl3, 75.468
MHz, ppm): δ 143.58 (s, >C), 143.31 (t, >C, JCP = 4.3 Hz),
138.80 (d, >C, JCP = 10.3 Hz), 138.77 (d, >C, JCP = 10.3 Hz),
132.96 (d, CH−, JCP = 4.3 Hz), 132.75 (d, CH−, JCP = 4.4 Hz),
132.17 (d, CH−, JCP = 18.3 Hz), 128.77(s, CH−, phosphole),
128.61 (s, CH−, phosphole), 128.44 (d, CH−, JCP = 5.4 Hz),
127.18 (d, CH−, JCP = 1.4 Hz), 127.09 (d, CH−, JCP = 1.4 Hz),
121.30 (s, =CH−), 29.17 (dd, >CH2, JCP = 28.0, 55.5 Hz, P(1)
865
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Article
CH2P(2)). MS (DCI, NH3): m/z (%) 383.1 (100) [M + H]+. Anal.
Calcd for C25H20P2: C, 78.53; H, 5.27. Found: C, 78.27; H, 5.29.
2,5-Diphenylphospholyl(diphenylphosphino)methane (5b). Yel-
General procedure for Trans Rhodium Complex 9. Method
A. Starting from [Rh(μ-Cl)(η4-COD)]2, complex 9 has been
synthesized as described for 8, except that 4 equiv of ligands 5 was
added.
1
low solid. Yield: 87%. H NMR (298 K, CD2Cl2, 300.13 MHz, ppm):
Method B. The reaction was carried out using [Rh(η4-COD)2]-
[CF3SO3] and 2 equiv of ligands 5 under the same conditions as
described above for complexes 8.
δ 7.46 (m, 4H, CH−, JHH = 5.7 Hz), 7.34 (t, 4H, CH−, JHH = 5.4
Hz), 7.28−7.22 (m, 4H, =CH−), 7.17 (m, 10H, =CH−), 2.62 (bd,
2H, >CH2, JHP = 1.5 Hz, P(1)CH2P(2)). 31P NMR (298 K, CD2Cl2,
161.976 MHz, ppm): δ −8.17 (dt, P(1), JHP(1) = 10.2 Hz, JP1P(2) = 46.0
Hz, phosphole), −22.03 (d, P(2), JP(2)P(1) = 50.0 Hz, PPh2). 31P{1H}
NMR (298 K, CD2Cl2, 161.976 MHz, ppm): δ −8.16 (d, P(1), JP(1)P(2)
= 46.3 Hz, phosphole), −22.03 (d, P(2), JP(2)P(1) = 46.3 Hz, PPh2).
13C{1H} NMR (298 K, CD2Cl2, 100.613 MHz, ppm): δ 151.31 (d,
>C, JCP = 1.9 Hz), 151.24 (d, >C, JCP = 1.9 Hz), 136.67 (d, >C
, JCP = 16.9 Hz), 139.08 (d, >C, JCP = 3.8 Hz), 138.91 (d, >C, JCP
= 3.7 Hz), 132.50 (d, CH−, JCP = 19.9 Hz), 131.98 (d, CH−, JCP
= 8.95 Hz), 128.66 (s, =CH−), 128.51 (s, =CH−), 128.08 (d, 
CH−, JCP = 6.7 Hz), 127.01 (s, =CH−), 126.42 (d, CH−, JCP = 9.9
Hz), 21.37 (dd, >CH2, JCP = 21.7, 32.60 Hz, P(1)CH2P(2)). MS
(DCI, NH3): m/z (%) 435.1 (100) [M + H]+. Anal. Calcd For
C29H24P2: C, 80.17; H, 5.57. Found: C, 80.32; H, 5.67.
2,3,4,5-Tetramethylphospholyl(diphenylphosphino)methane
(5c). Colorless oil liquid. Yield: 92%. 1H NMR (298 K, CDCl3, 300.13
MHz, ppm): δ 7.32−7.41 (m, 10H, CH−, Ph), 2.52 (dd, 2H, >CH2,
JHP(1) = 2.1 Hz, JHP(2) = 0.90 Hz, P(1)CH2P(2)), 1.89 (d, 6H, −CH3,
JHP = 7.8 Hz, phosphole), 1.87 (s, 6H, −CH3, phosphole). 31P NMR
(298 K, CDCl3, 121.495 MHz, ppm): δ + 1.97 (d, P(1), JP(1)P(2) = 36.1
Hz, phosphole), −22.32 (d, P(2), JP(2)P(1) = 36.21 Hz, PPh2). 13C
trans-[Rh(dibenzophospholyl(diphenylphosphino)methane)2]-
1
[CF3SO3] (9a′). H NMR (298 K, CD2Cl2, 300.13 MHz, ppm): δ
selected 3.28 (dd, >CH2, JHP(1) = 14.1 Hz, JHP(2) = 12.3 Hz,
P(1)CH2P(2)). 31P{1H} NMR (298 K, CD2Cl2, 121.495 MHz, ppm):
spin system AA′XX′M, δ −20.14 (ddd, A, JAX = 37.7 Hz, JAX′ = 40.1
Hz, JAM = 113.0 Hz), −33.03 (ddd, B, JXA = 37.7 Hz, JXA′ = 40.1 Hz,
JXM = 80.2 Hz). MS (FAB, MNBA): m/z (%) 867 (100) [M]+.
trans-[Rh(2,5-diphenylphospholyl(diphenylphosphino)-
methane)2][BF4] (9b). 1H NMR (298 K, CD2Cl2, 300.13 MHz, ppm):
δ 8.18 (d, 6H, −CH, JHH = 7.5 Hz), 7.48 (m, 4H, −CH, JHP = 8.7
Hz), 7.37 (m, 8H, −CH, JHH = 7.5 Hz), 7.20−7.32 (m, 10H,
−CH), 7.14 (t, 10H, −CH, JHH = 7.7 Hz), 7.02 (t, 6H, −CH,
JHH = 7.7 Hz), 4.32 (m, 4H, >CH2, P(1)CH2P(2)).31P{1H} NMR
(298 K, CD2Cl2, 121.495 MHz, ppm): spin system AABBX, δ −31.73
(JAB = 25.0 Hz, JAX = JBX = 108.0 Hz), −31.93 (JAB = 25.0 Hz, JAX = JBX
= 110 Hz); MS (FAB, MNBA): m/z (%) 971 (100) [M]+.
General Procedure for Synthesis of the Rhodium Complexes
10. To a solution of ligands 4 (0.149 mmol) in CH2Cl2 (10 mL) was
added a solution of [Rh2(μ-Cl)2(η4-COD)2] (0.037 g, 0.075 mmol) in
CH2Cl2 (10 mL) at 0 °C. The reaction mixture was stirred at this
temperature for 15 min, then AgBF4 (0.032 g, 0.164 mmol) was
introduced, and the resulting mixture was warmed to room
temperature and stirred for 14 h. The solution was filtered through
a Celite column and concentrated, and n-pentane was added to afford
10 as a yellow-green solid. Workup with diethyl ether (3 × 10 mL)
gave the clean product (yields 61−94%).
NMR (298 K, CDCl3, 75.468 MHz, ppm): δ 143.04 (d, =C<, JCP
11.0 Hz), 134.03 (d, =C<, JCP = 6.6 Hz), 132.95 (d, CH−, JCP
=
=
14.4 Hz, Ph), 128.47 (d, CH−, JCP = 6.9 Hz, Ph), 128.19 (d, 
CH−, JCP = 6.6 Hz, Ph), 20.48 (dd, >CH2, JCP(1) = 31.4 Hz, JCP(2)
26.3 Hz, P(1)CH2P(2)), 13.78 (d, −CH3, JCP = 2.9 Hz, phosphole),
13.11 (d, −CH3, JCP = 21.4 Hz, phosphole), 13.07 (d, −CH3, JCP
=
[Rh(η4-COD)(η2-BH3-phosphino)(κ1-dibenzophospholyl)-
methane][BPh4] (10a′′). Complex 10a″ was synthesized by metathesis
of a dichloromethane solution of 10a with NaBPh4 in excess. 1H NMR
=
21.5 Hz, phosphole). MS (DCI, NH3): m/z (%) 339.1 (100%) [M +
H]+. Anal. Calcd for C21H24P2: C, 74.54; H, 7.15. Found: C, 74.87; H,
7.90.
(298 K, CD2Cl2, 300.13 MHz, ppm): δ 7.97 (dd, 2H, CH−, JHH
=
General Procedure for Rhodium Complex 8. Method A. To
a solution of [Rh(μ-Cl)(η4-COD)]2 (0.081 mmol, 0.04 g) in CH2Cl2
(15 mL) was slowly added a solution of 2 equiv of phospholyl-
(diphenylphosphino)methane ligand 5 (0.162 mmol) in CH2Cl2 (10
mL) with stirring at −90 °C. The reaction mixture was kept at the
same temperature for 15 min, and then AgBF4 (0.032 g, 0.164 mmol)
was introduced. The resulting mixture was warmed slowly to room
temperature and stirred for 2 h. The final solution was filtered and
evaporated to dryness. Since the purification of this yellow residue was
not successful, the crude product was directly characterized by NMR
spectroscopy.
7.7 Hz, JHP = 0.9 Hz, phosphole), 7.67 (m, 8H, =CH−), 7.56 (m, 4H,
CH−, JHH = 7.8 Hz, JHP = 3.6 Hz), 7.41 (bm, 8H-o, CH−, JHH
=
7.8 Hz, BPh4), 7.25−7.33 (m, 4H, =CH−), 7.09 (t, 8H-m, CH−,
JHH = 7.3 Hz, BPh4), 6.95 (t, 4H-p, CH−, JHH = 7.2 Hz, BPh4), 5.93
(br s, 2H, CH−, COD), 3.32 (br s, 2H, CH−, COD), 2.64 (t,
2H, >CH2, JHP(1) = JHP(2) = 11.71 Hz, P(1)CH2P(2)), 2.12−2.54 (m,
8H, >CH2, COD), −0.04 (b, 3H, JHP = 11.4 Hz, BH3). 31P{1H} NMR
(298 K, CD2Cl2, 121.495 MHz, ppm): δ +47.42 (dd, P(1), JP(1)Rh
=
139.5 Hz, JP(1)P(2) = 68.2 Hz, phosphole), 20.13 (br, P(2), PPh2·BH3).
11B{1H} NMR (298 K, CDCl3, 96.294 MHz, ppm): δ −6.51 (s, BPh4),
−26.00 (d, JBP(2) = 77.0 Hz, BH3). 13C{1H} NMR (298 K, CD2Cl2,
75.468 MHz, ppm): δ 164.78 (d, >C, JCP = 49.3 Hz), 163.47 (d,
>C, JCP = 49.3 Hz), 142.57 (d, >C, JCP = 9.9 Hz), 136.02 (bs, 
CH−o, BPh4), 133.50 (d, CH−, JCP = 2.5 Hz), 132.97 (d, CH−,
JCP = 1.2 Hz), 132.32 (d, CH−, JCP = 10.6 Hz), 131.00 (d, CH−,
JCP = 14.8 Hz), 130.00 (d, CH−, JCP = 11.5 Hz), 130.24 (d, >C,
JCB = 4.5 Hz, BPh4), 129.20 (d, CH−, JCP = 11.1 Hz), 125.67 (br,
CH−m, BPh4), 124.65 (d, >C, JCP = 64.68 Hz, PPh2), 124.59 (d,
>C, JCP = 64.8 Hz, PPh2), 122.40 (d, CH−, JCP = 6.2 Hz,
Method B. To a solution of [Rh(η4-COD)2][CF3SO3] (0.028
mmol, 0.013 g) in CH2Cl2 (10 mL) was added a solution of
phospholyl(diphenylphosphino)methane ligand 5 (0.028 mmol) in
CH2Cl2 (5 mL) at −90 °C. The reaction mixture was stirred for 15
min at this temperature and then warmed to room temperature, at
which the yellow solution was stirred for a further 2 h. The resulting
solution was finally evaporated to dryness.
[Rh(η4-COD)(dibenzophospholyl(diphenylphosphino)methane)]-
1
[CF3SO3] (8a′). H NMR (298 K, CD2Cl2, 400.13 MHz, ppm): δ
phosphole), 121.74 (s, CH−p, BPh4), 106.86 (dd, CH, JCRh
=
selected 4.26 (td, 2H, >CH2, JHP(1) = JHP(2) = 10.2 Hz, JHRh = 2.0 Hz,
P(1)CH2P(2)). 31P{1H} NMR (298 K, CD2Cl2, 161.976 MHz, ppm):
AMX, δ −31.42 (dd, JP(2)P(1) = 85.0 Hz, JP(2)Rh = 128.5 Hz,
phosphole), −37.36 (dd, JP(1)P(2) = 85.0 Hz, JP(1)Rh = 130.7 Hz,
−PPh2). MS (FAB, MNBA): m/z (%) 593 (100) [M]+.
10.2 Hz, JCPtrans = 6.1 Hz, COD), 74.90 (dd, JCRh = 13.1 Hz, JCP = 0.9
Hz), 33.51 (s, >CH2, COD), 33.47 (s, >CH2, COD), 28.60 (dd, JCP(1)
= 42.5 Hz, JCP(2) = 11.3 Hz, P(1)CH2P(2)), 28.25 (s, >CH2, COD).
MS (FAB, MNBA): m/z (%) 607 (100) [M]+. Anal. Calcd for
C57B2H55P2Rh: C, 73.89; H, 5.98. Found: C, 73.83; H, 5.83. Crystals
suitable for an X-ray diffraction study were obtained by slow
evaporation of the concentrated dichloromethane solution at room
temperature.
[Rh(η4-COD)(2,5-diphenylphospholyl(diphenylphosphino)-
1
methane)][BF4] (8b). H NMR (298 K, CD2Cl2, 300.13 MHz, ppm):
δ selected 5.72 (br s, 2H, CH−, COD), 5.26 (br s, 2H, CH−,
COD), 4.13 (td, 2H, >CH2, JHP(1) = JHP(2) = 10.7 Hz, JHRh = 1.2 Hz,
P(1)CH2P(2)), 2.16−2.60 (m, >CH2, COD). 31P{1H} NMR (298 K,
CD2Cl2, 161.976 MHz, ppm): AMX, δ −36.64 (dd, JP(1)P(2) = 77.8 Hz,
JP(1)Rh = 116.4 Hz, phosphole), −40.74 (dd, JP(2)P(1) = 77.8 Hz, JP(2)Rh
= 124.4 Hz, −PPh2). MS (FAB, MNBA): m/z (%) 645 (100) [M]+.
[Rh(η4-COD)(η2-BH3-phosphino)(κ1-2,5-diphenylphospholyl)-
1
methane][BF4] (10b). Yellow solid. Yield: 94%. H NMR (298 K,
CD2Cl2, 300.13 MHz, ppm): δ 7.95 (m, 4H, CH−, JHH = 2.1, 7.8
Hz, Ph), 7.50 (m, 6H, CH−, JHH = 7.5 Hz, Ph), 7.34−7.42 (m, 10H,
CH−, Ph), 7.31 (dd, 2H,, CH−, JHP = 1.2, 27.0 Hz, phosphole),
866
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6.02 (d, 2H, CH−, JHP = 1.8 Hz, COD), 3.70 (s, CH−, 2H,
COD), 2.71 (t, 2H, >CH2, JHP = 11.4 Hz, P(1)CH2P(2)), 2.47−2.65
(m, 2H, >CH2, COD), 2.24−2.44 (m, 6H, >CH2, COD), −0.06 (br,
3H, BH3). 1H{11B} NMR (298 K, CDCl3, 300.13 MHz, ppm): δ
selected −0.06 (t, 3H, JHP = 10.5 Hz, BH3). 11B{1H} NMR (298 K,
CD2Cl2, 96.294 MHz, ppm): δ −27.66 (d, JBP or JBRh = 82.8 Hz, BH3).
31P{1H} NMR (298 K, CD2Cl2, 121.495 MHz, ppm): δ +52.97 (dd,
P(1), JPRh = 130.36 Hz, JP(1)P(2) = 81.6 Hz, phosphole), 28.63 (br,
P(2), H3B·PPh2). 13C{1H} NMR (298 K, CD2Cl2, 75.468 MHz, ppm):
[Rh(η4 -COD)(η2 -BH3 -dicyclohexylphosphino)(κ1 -2,5-
1
diphenylphospholyl)][BF4] (10f). Yellow solid. Yield: 64%. H NMR
(298 K, CD2Cl2, 300.13 MHz, ppm): δ 8.08−8.07 (m, 4H, CH−,
Ph, phosphole), 7.59−7.53 (m, 6H, CH−, Ph, phosphole), 7.25 (d,
2H, CH−, J = 12.9 Hz, phosphole), 5.93 (sl, 2H, CH−, COD),
3.66 (sl, 2H, CH−, COD), 2.56−2.44 (m, 4H, >CH2, COD), 2.33−
2
2
2.28 (m, 4H, >CH2, COD), 1.86 (t, 2H, >CH2, JHP(1) = JHP(2) = 5.4
Hz, P(1)CH2P(2)), 1.72−1.62 (m, 12H, >CHP and >CH2, cHex),
1.12−0.98 (m, 12H, >CH2, cHex), −0.83 (m, 3H, BH3). 31P{1H}
NMR (298 K, CD2Cl2, 121.495 MHz, ppm): δ +57.91 (dd, P(1), 1JPRh
= 131.3 Hz, JPP = 55.8 Hz, phosphole), 45.96 (br, P(2),
(cHex)2P·BH3). MS (ESI): m/z (%) 671.3 (100) [M]+.
δ 143.08 (d, >C, JCP = 43.0 Hz, phosphole), 143.02 (d, >C, JCP
=
43.1 Hz, phosphole), 136.38 (d, CH−, JCP = 14.3 Hz, phosphole),
132.97 (d, CH−, JCP = 2.6 Hz, Ph), 132.22 (d, >C, JCP = 14.4 Hz,
−Ph, phosphole), 131.79 (d, CH−, JCP = 10.7 Hz, Ph), 129.59 (d,
CH−, JCP = 11.5 Hz, −Ph), 129.25 (s, CH−, −Ph, phosphole),
129.05 (s, CH−, −Ph, phosphole), 127.08 (d, CH−, JCP = 7.0
Hz, −Ph), 124.76 (d, >C, JCP = 65.0 Hz, −Ph), 124.68 (d, >C,
[ R h ( η4 - C O D ) ( η2 - B H3 - d i p h e n y lp h os p h i n o b o ra n e ) -
{(diphenylphosphino)methane}][BF4] (10g). Yellow solid. Yield: 68%.
1H NMR (298 K, CD2Cl2, 300.13 MHz, ppm): δ 7.63−7.60 (m, 4H,
CH−, Ph), 7.56−7.50 (m, 6H, CH−, Ph), 7.49−7.47 (m, 2H, 
CH−, Ph), 7.43−7.40 (m, 8H, CH−, Ph), 5.84 (sl, 2H, CH−,
COD), 3.34 (sl, 2H, CH−, COD), 3.28 (t, 2H, J = 11.7 Hz, >CH2,
Ph2PCH2PPh2·BH3), 2.52−2.49 (m, 4H, >CH2, COD), 2.32−2.27 (m,
4H, >CH2, COD), −0.25 (m, 3H, BH3). 31P{1H} NMR (298 K,
JCP = 65.1 Hz, −Ph), 106.04 (dd, CH−, JCPphosphole = 6.7 Hz, JCRh
=
9.0 Hz, COD), 77.46 (d, CH−, JCRh = 13.0 Hz, COD), 33.56 (s,
>CH2, COD), 33.52 (s, >CH2, COD), 28.58 (s, >CH2, COD), 28.56
(s, >CH2, COD), 22.18 (dd, >CH2, JCP(1) = 15.6, 43.88 Hz, P(1)
CH2P(2)). MS (FAB, MNBA): m/z (%) 659 (100) [M]+. Anal. Calcd
for C37H39B2F4P2Rh: C, 59.56; H, 5.27. Found: C, 60.59; H, 5.30.
Yellow crystals suitable for X-ray diffraction were obtained by slow
diffusion of diethyl ether into a concentrated solution of 10b in
CH2Cl2 at −20 °C.
CD2Cl2, 121.495 MHz, ppm): δ +46.65 (dd, JPRh = 140.9 Hz, JPP
=
70.3 Hz, Ph2PCH2PPh2·BH3), 19.57 (br, Ph2PCH2PPh2·BH3). MS
(ESI): m/z: (%) 696.1 (100%) [M]+.
General Experimental Procedure for Hydrogenation. Me-
thod A. Into glassware was added a mixture of [Rh(η4-COD)2]-
[CF3SO3] (3.0 mg, 0.0064 mmol), ligands 4 and 5 (0.0064 mmol),
substrate (50−400 equiv), and MeOH (10 mL). The glassware was
placed in a stainless steel autoclave. Hydrogenation was performed at
the desired temperature (25−40 °C) under hydrogen pressure (10−40
bar) for 20 h. After the autoclave was cooled, the hydrogen pressure
was slowly released. Solvent was removed under vacuum, and
[ R h ( η 4 - C O D ) ( η 2 - B H 3 - p h o s p h i n o ) ( κ 1 - , 2 , 3 , 4 , 5 -
tetramethylphospholyl)methane][BF4] (10c). Yellow solid. Yield:
90%. 1H NMR (298 K, CD2Cl2, 300.13 MHz, ppm): δ 7.80 (m, 4H-o,
CH−, JHH = 0.9, 8.4 Hz, JHP = 12.3 Hz, Ph), 7.59−7.72 (m, 4H-m
and 2H-p, CH−, JHP = 2.1 Hz, Ph), 5.75 (s, 2H, CH−, COD),
3.43 (br, 2H, JHP = 3.0 Hz, CH−, COD), 2.58 (t, JHP(1) = JHP(2)
=
1
conversion was determined by H NMR.
11.7 Hz, P(1)CH2P(2)), 2.37−2.46 (m, 4H, >CH2, COD), 2.20−2.32
Method B. Precatalysts were prepared by mixing [Rh(η4-COD)2]-
[CF3SO3] (3.0 mg, 0.0064 mmol), ligands 4 and 5 (0.0064 mmol),
and substrate (50−400 mol equiv) under an argon atmosphere in a
Schlenk tube. MeOH (10 mL) was added, and the solution was stirred
for 3 h at room temperature. The reaction solution was transferred
into glassware. The hydrogenation procedure was performed as
described in method A.
(m, 4H, >CH2, COD), 1.93 (d, 6H, −CH3, JHP = 0.6 Hz, phosphole),
1.69 (d, 6H, −CH3, JHP = 12.6 Hz, phosphole), −0.43 (brq, 3H, JHB
=
108.9 Hz, BH3). 1H{11B} NMR (298 K, CD2Cl2, 300.13 MHz, ppm):
selected δ −0.43 (t, JHP = JHRh = 11.4 Hz, BH3). 31P{1H} NMR (298
K, CD2Cl2, 121.495 MHz, ppm): δ +66.23 (dd, P(1), JP(1)P(2) = 63.5
Hz, JP(1)Rh = 128.9 Hz, phosphole), 24.32 (br, P(2), Ph2P·BH3). 11B
NMR (298 K, CD2Cl2, 96.294 MHz, ppm): δ −26.02 (t, JBH = JBP (or
JBRh) = 91.5 Hz, BH3), −1.12 (s, BF4). 13C{1H} NMR (298 K, CD2Cl2,
75.468 MHz, ppm): δ 149.15 (d, 2C, >C, JCP = 16.6 Hz, −Ph),
133.23 (d, 2C, CH−p, JCP = 3.0 Hz, −Ph), 132.24 (d, 4C, CH−o,
JCP = 10.6 Hz, −Ph), 129.87 (d, 4C, CH−m, JCP = 11.3 Hz, −Ph),
126.74 (d, 1C, >C, JCP = 46.8 Hz, phosphole), 126.69 (d, 1C, >C,
JCP = 46.0 Hz, phosphole), 125.55 (d, 1C, >C, JCP = 64.1 Hz,
phosphole), 125.49 (d, 1C, >C, JCP = 64.1 Hz, phosphole), 105.16
(ddd, 1C, CH−, JCP(1) = 6.0 Hz, JCRh = 9.8 Hz, JCB or JCP(2) = 1.5
Hz, COD), 74.65 (d, 1C, CH−, JCP(1) or JCRh = 13.6 Hz, COD),
General Procedure for Catalyzed Hydroboration Reaction-
s. Method A (Using Isolated Rhodium Complexes). Rhodium
complexes 10 (10 μmol) in dry THF (2 mL) were placed under argon
in a Schlenk tube. Catecholborane (1 M in THF, 1 mL, 1 mmol) was
added, and the light brown solution was stirred for 5 min at room
temperature. Styrene (0.11 mL, 1 mmol) was then injected and the
reaction mixture was stirred for 22 h at room temperature. The
reaction mixture was then cooled to 0 °C, and ethanol (2 mL) was
added followed by NaOH (1 M, 6 mL) and H2O2 (6 mL). The ice
bath was removed, and the solution was stirred for 1 h at room
temperature. The reaction mixture was transferred to a separatory
funnel, and diethyl ether (10 mL) was added. The organic layer was
washed with NaOH (1 M, 10 mL) and brine (10 mL) and dried over
MgSO4. The solution was filtered, and the solvent was removed in
vacuo to give the hydroborated product. Conversion and regiose-
33.84 (d, 2C, >CH2, JCP = 2.9 Hz, COD), 28.21 (d, 4C, >CH2, JCP
=
1.2 Hz, COD), 23.04 (dd, 1C, >CH2, JCP(1) = 11.8, 44.6 Hz, P(1)
CH2P(2)), 13.85 (d, 2C, −CH3, JCP = 10.5 Hz, phosphole), 11.62 (d,
2C, −CH3, JCP = 16.8 Hz, phosphole). MS (FAB, MNBA): m/z (%)
563 (100) [M]+. Anal. Calcd for C29H39B2F4P2Rh: C, 53.58; H, 6.05:
Found: C, 53.75; H, 6.40. Crystals suitable for an X-ray diffraction
study were obtained by slow diffusion of diethyl ether into
concentrated solution of 10c in CH2Cl2 at −20 °C.
1
lectivity were determined by H NMR.
Method B (Using in Situ Prepared Rhodium Complexes). [Rh(η4-
COD)2][BF4] (10 μmol) and the ligand (11 or 22 μmol) in dry THF
(2 mL) were placed under argon in a Schlenk tube and stirred for 30
min at room temperature. Catecholborane (1 M in THF, 1 mL, 1
mmol) was added, and the light brown solution was stirred for 5 min
at room temperature. Styrene (0.11 mL, 1 mmol) was then injected
and the reaction mixture was stirred for 22 h at room temperature.
Treatment of the reaction mixture was carried out as described above
for method A.
[ R h ( η 4 - C O D ) ( η 2 - B H 3 - d i c y c l o h e x y l p h o s p h i n o ) ( κ 1 -
dibenzophospholyl)methane][BF4] (10e). Yellow-brown solid. Yield:
61%. 1H NMR (298 K, CD2Cl2, 300.13 MHz, ppm): δ 8.00 (d, 2H, 
CH−, J = 7.7 Hz, phosphole), 7.85 (t, 2H, CH−, J = 8.2 Hz,
phosphole), 7.73 (t, 2H, CH−, J = 7.7 Hz, phosphole), 7.63−7.60
(m, 2H, CH−, phosphole), 5.79 (sl, 2H, CH−, COD), 3.16 (sl,
2H, CH−, COD), 2.39−2.37 (m, 2H, >CHP, cHex), 2.28−2.16 (m,
4H, >CH2, COD), 2.14−2.04 (m, 4H, >CH2, COD), 2.04 (t, 2H,
>CH2, 2JHP(1) = 2JHP(2) = 10.9 Hz, P(1)CH2P(2)), 1.94−1.83 (m, 10H,
>CH2, cHex), 1.40−1.31 (m, 10H, >CH2, cHex), −0.85 (m, 3H,
BH3). 31P{1H} NMR (298 K, CD2Cl2, 121.495 MHz, ppm): δ +52.28
1
1-Phenylethanol. H NMR (298 K, CDCl3, 300.13 MHz, ppm): δ
7.42−7.28 (m, 5H, CH−, Ph), 4.93 (q, 1H, J = 6.4 Hz, >CH−),
1.52 (d, 3H, J = 6.4 Hz, −CH3).
1
2-Phenylethanol. H NMR (298 K, CDCl3, 300.13 MHz, ppm): δ
1
(dd, P(1), JPRh = 140.4 Hz, JPP = 58.7 Hz, phosphole), 40.88 (br,
7.27−7.14 (m, 5H, CH−, Ph), 3.78 (t, 2H, J = 6.6 Hz, CH2O), 2.79
P(2), (cHex)2P·BH3). MS (ESI): m/z (%) 619.3 (100) [M]+.
(t, 2H, J = 6.6 Hz, CH2Ph).
867
dx.doi.org/10.1021/om2008265 | Organometallics 2012, 31, 857−869

Organometallics
Article
X-ray Structure Determination. A single crystal of each
compound was mounted under inert perfluoropolyether at the tip of
a glass fiber and cooled in the cryostream of either an Oxford-
Diffraction XCALIBUR CCD diffractometer for 4a, 5a,b, and 10b,c or
a Bruker APEX2 diffractometer for 4c. Data were collected using
monochromatic Mo Kα radiation (λ = 0.710 73 Å). The structures
were solved by direct methods (SIR97)48 and refined by least-squares
procedures on F2 using SHELXL-97.49All H atoms attached to carbon
were introduced in calculations in idealized positions and treated as
riding models. The coordinates of H atoms attached to the boron for
compounds 4a,c were refined using similar distance restraints (SADI
within SHELXL-9749) and overall isotropic thermal parameters,
whereas for 10b,c, the H coordinates were freely refined. In compound
10b, the COD ligand was partially disordered over two positions. This
disorder was modelized using the tools available in SHELXL-97.49 The
data for compound 5b were of very bad quality, and thus the
refinement gave very poor results, even if there is no doubt about the
structure itself. The drawing of the molecules was realized with the
help of ORTEP-32.50
Hoge, G. Org. Lett. 2004, 6, 3645−3647. (f) Lorenzini, F.; Hindle, K.
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́
́
Crystallographic data (excluding structure factors) have been
deposited at the Cambridge Crystallographic Data Centre as
Supplementary Publication Nos. CCDC 804802−804807. Copies of
the data can be obtained free of charge on application to the Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, (+44) 1223-
336-033; e-mail, deposit@ccdc.cam.ac.uk).
́
S.; Harvey, P. D. Eur. J.
Inorg. Chem. 2011, 16, 2597−2609.
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1776. (b) Wolf, J.; Manger, M.; Schmidt, U.; Fries, G.; Barth, D.;
Weberndorfer, B.; Vicic, D. A.; Jones, W. D.; Werner, H. J. Chem. Soc.,
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ASSOCIATED CONTENT
* Supporting Information
Figures, tables, and CIF files giving molecular views of 4a, 5b,
and 10b and NMR spectra and crystal data and refinement
parameters for compounds 4a,c, 5a,b, and 10b,c. This material
is available free of charge via the Internet at http://pubs.acs.org.
■
S
(13) Some recent examples of phosphole in catalysis: (a) Fagan, P. J.;
Li, G.; Guan, Z.; Wang, L. (Du Pont De Nemours and Company)
Patent WO0021970A1, 2000. (b) Doherty, S.; Robins, E. G.; Knight, J.
G.; Newman, C. R.; Rhodes, B.; Champkin, P. A.; Clegg, W. J.
Organomet. Chem. 2001, 640, 182−196. (c) Sauthier, M.; Leca, F.;
AUTHOR INFORMATION
Corresponding Author
*E-mail: Sylvain.Juge@u-bourgogne.fr (S.J.); Maryse.
Gouygou@lcc-toulouse.fr (M.G.).
■
Toupet, L.; Rea
J.; Gouygou, M.; Dallemer, F.; Daran, J. C.; Balavoine, G. G. A.
Tetrahedron: Asymmetry 2002, 1097−1102. (e) Keglevich, G.; Kegl, T.;
́
u, R. Organometallics 2002, 21, 1591−1602. (d) Hydrio,
́
Chuluunbaatar, T.; Dajka, B.; Matyus, P.; Balogh, B.; Kollar, L. J. Mol.
Catal. A: Chem. 2003, 200, 131−136. (f) Mourgues, S.; Serra, D.;
Lamy, F.; Vincendeau, S.; Daran, J. C.; Manoury, E.; Gouygou, M. Eur.
J. Inorg. Chem. 2003, 2820−2826. (g) de Souza, R. F.; Bernado-
ACKNOWLEDGMENTS
We are grateful to the CNRS, the “Minister
Nationale et de la Recherche”, the ANR program 07-BLAN-
0292-01 (MetChirPhos) for financial support, postdoc grants
(to D.H.N. and C.S.-B.), and Dr. D. Neibecker for a gift of
1,2,5-triphenylphosphole. We also thank M.-J. Ondel-Eymin
■
̀
e de l’Education
Gusmao, K.; Cunha, G. A.; Loup, C.; Leca, F.; Rea
́
u, R. J. Catal. 2004,
226, 235−239. (h) Thoumazet, C.; Ricard, L.; Grutzmacher, H.; Le
̈
Floch, P. Chem. Commun. 2005, 1592−1594. (i) Mora, G.; von
Zutphen, S.; Thoumazet, C.; Le Goff, X. F.; Ricard, L.; Grutzmacher,
H.; Le Floch, P. Organometallics 2006, 25, 5528−5532. (j) Matano, Y.;
Miyajima, T.; Nakabuchi, T.; Imahori, H.; Ochi, N.; Sakaki, S. J. Am.
Chem. Soc. 2006, 128, 11760−11761. (k) Lopez-Cortes, J. G.; Ramon,
O.; Vincendeau, S.; Serra, D.; Lamy, F.; Daran, J. C.; Manoury, E.;
Gouygou, M. Eur. J. Inorg. Chem. 2006, 5148−5147. (l) Odinets, I.;
(Universite
́
de Bourgogne) for providing technical support.
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phosphine−borane moiety in the rhodium coordination sphere.
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doublet of doublets at 52.6 ppm (JPP = 69.0 and JRhP = 125.9 Hz) and
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