4,6-Bis(supermesitylphosphanylidenemethyl)dibenzofuran. Synthesis, X-ray structure and reactivity towards group 11 metals

Article abstract of DOI:10.1039/b508678g

New kinetically stabilized mono- and bis-phosphaalkene ligands (2 and 3, respectively) were synthesized via the phospha-Wittig approach. Ligand 3 was characterized by X-ray diffraction. The coordinating behaviour of the bidentate ligand was investigated t

Full text of DOI:10.1039/b508678g

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4,6-Bis(supermesitylphosphanylidenemethyl)dibenzofuran. Synthesis, X-ray
structure and reactivity towards group 11 metals†
Eliane Deschamps, Bernard Deschamps, Jeanne Laure Dormieux, Louis Ricard,
Nicolas Me´zailles and Pascal Le Floch*
Received 22nd June 2005, Accepted 9th September 2005
First published as an Advance Article on the web 28th October 2005
DOI: 10.1039/b508678g
New kinetically stabilized mono- and bis-phosphaalkene ligands (2 and 3, respectively) were
synthesized via the phospha-Wittig approach. Ligand 3 was characterized by X-ray diffraction. The
coordinating behaviour of the bidentate ligand was investigated towards group 11 metal centers in
order to test its capacity to bind two coordination sites located in a trans-fashion. The [Au(3)][BF4],
[Ag(3)(H2O)][BF4] and [Cu(3)(CH3CN)][BF4] complexes 4, 5 and 6, respectively, were characterized by
X-ray diffraction. The peculiar geometries of 4 and 6 were rationalized by means of DFT calculations.
Introduction
=
Low-coordinate phosphorus molecules incorporating P C dou-
ble bonds are slowly emerging as a very important class of
ligands with unique electronic properties that markedly differ
from that of classical tertiary phosphines and sp2-hybridized
nitrogen ligands.1 Over the last decade, a great deal of effort
Scheme 1
As part of a program aimed at developing the use of such
polydentate ligands featuring sp2-hybridized phosphorus atoms
in coordination chemistry and catalysis,8 we recently investigated
the synthesis of bidentate structures featuring the dibenzofuran
skeleton. Indeed, 4,6-bis(carbaldehyde)dibenzofuran proved to be
a convenient precursor for the elaboration of bidentate ligands
featuring imines9 or oxazolines (DBFOX ligands) as pendant
ligands which can bind a metal centre in a trans-fashion. Some
DBFOX-based complexes proved to be particularly efficient in
some catalytic transformations.10 Herein, we wish to report on
these syntheses as well as on the coordinating behaviour of this
new type of ligands towards group 11 metals.
has been devoted to the understanding both of their electronic
properties and their use in coordination chemistry of low valent
and reduced transition metals. Thus, it was shown that ligands
such as phosphinines and their functional derivatives can act as
efficient ligands for the stabilization of various electron rich or
electron excessive metal fragments.2 Much more recently, due to
their strong p-accepting capacity, these ligands were also employed
in the stabilization of gold nanoparticles presenting unique optical
properties.3 On the other hand, some low-coordinate phospho-
rus ligands have found promising applications in homogeneous
catalysis. Thus, phosphaferrocenes4 and kinetically stabilized
phosphaalkenes5 were successfully employed as ligands in some
catalytic processes of synthetic relevance such as C–X bond
forming reactions, ethylene polymerization, nucleophilic allylic
substitutions and hydrogenations. Concerning phosphalkenes,
much effort have focused on the use of phosphorus equivalents
of 1,4-diazabutadienes, namely 1,4-diphosphabutadienes such as
1,2-diaryl-3,4-diphosphinidene cyclobutene (DCPB) developed by
the group of Yoshifuji.5 Though some studies were devoted to the
synthesis of tridentate pincer ligands featuring two phosphaalkene
moieties as pendant ligands (Mes* = 2,4,6-tris(tert-butyl)phenyl)
and a carbon6 or nitrogen atom as central binding site (Scheme 1),7
little information is available on the coordination chemistry of
these ligands and the catalytic activity of their corresponding
complexes.
Results and discussion
Syntheses of ligands 2 and 3
=
Various methods are available for the synthesis of P C double
bonded systems. One of the most attractive approaches, which
was initially developed in our laboratories for the synthesis of
phosphaalkene complexes of metal carbonyls (M = Cr, Mo, W,
Fe), is the well known phospha-Wittig reaction, a transformation
that mimics the ubiquitous Wittig process.11 This reaction which
relies on the reactivity of phosphoranylidenephosphine complexes
towards aldehydes was further extended to the synthesis of uncom-
plexed phosphaalkenes by Protasiewicz et al.12 In practice, free
phosphoranylidenephosphine reagents (phospha-Wittig) reagents
are available through the reaction of PMe3 with dichlorophos-
phines in the presence of zinc as reducing agent.12 Among all
methods available this approach offers several decisive advantages:
its simplicity (a one-step process), the use of mild conditions and
cheap reagents (Scheme 2).
Laboratoire ꢀꢀ He´te´roe´le´ments et Coordinationꢁꢁ , Department of Chemistry,
UMR CNRS 7653, DCPH, Ecole Polytechnique, 91128, Palaiseau Cedex,
France. E-mail: lefloch@poly.polytechnique.fr; Fax: +33 1 69333990
† Electronic supplementary information (ESI) available: View, cartesian
coordinates and frequencies of the theoretical structures I and II. See
http://dx.doi.org/10.1039/b508678g
594 | Dalton Trans., 2006, 594–602
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ꢀ
ꢀ
doublet (AAꢂXXꢂ spin system) at 8.4 ppm ( J(H–P) = 42 Hz,
means sum). In the 13C NMR spectrum, the corresponding signal
appears as the expected second-order signal at 167.1 ppm (AXXꢂ
ꢀ
spin system, J(C–P) = 51.7 Hz).
Scheme 2 The phospha-Wittig approach.
Single crystals of compound 3 were obtained by crystallization
in MeOH at room temperature. An X-ray crystal structure analysis
was carried out and a view of one molecule of 3 is presented
in Fig. 1 as well as the most relevant bond distances and bond
angles. Crystal data and structural refinement details are presented
in Table 1. The compound has crystallographically imposed
twofold symmetry. As can be seen the E-stereochemistry of both
phosphaalkene moieties is confirmed. Interestingly, one can note
As a prerequisite to these syntheses, 4,6-bis(carbaldehyde)-
dibenzofuran was synthesized according to a well-known re-
ported procedure that involves the dimetallation of dibenzofu-
ran with n-butyllithium followed by a trapping reaction with
dimethylformamide.13 The phospha-Wittig reagent 1 was conven-
tionally prepared by reacting Mes*PCl2 with PMe3 (2.6 equiv.) in
the presence of Zn as reductant in THF at 0 ◦C. Reaction of 1.1
equivalent of 1 with 4,6-bis(carbaldehyde)dibenzofuran readily
occurred at room temperature to cleanly yield phosphaalkene
2. After 3 h of reaction, analysis of the crude mixture by 31P
NMR spectroscopy revealed the presence of a very characteristic
downfield shifted signal at 273.9 ppm. After extraction with
dichloromethane, washings with water and crystallization from
MeOH, compound 2 was isolated in a 60% yield as a very air stable
pale yellow powder. The E-stereochemistry of 2 was confirmed by
=
that two P C bonds are coplanar with the dibenzofuran skeleton
probably indicating that a weak delocalization occurs between the
=
aromatic part of the molecules and the two P C units. Besides,
this is confirmed by the short C–C connection between the C9
carbon atoms and the C13 carbon atoms of the phosphaalkenes
˚
(d(C(9)–C(13)) = 1.454(2) A). Apart from this, the structure of 3
deserves no special comments.
1
the analysis of the H NMR spectrum which exhibits a doublet
at 8.58 ppm (2J(H–P) = 25.3 Hz). No trace of the Z-isomer
was observed in the crude mixture (Scheme 3). The formulation
proposed for 2 was confirmed by NMR and mass spectrometry as
well as by elemental analyses.
Scheme 3 Reagents and conditions: (i) THF, RT, 3 h.
Fig. 1 ORTEP view of one molecule of 3 (50% ellipsoids). The numbering
is arbitrary and different from that used in NMR data. Atoms marked
with a prime (ꢂ) are at equivalent position (−1 − x, y, −1 − z). Selected
The bis-phosphaalkene derivative 3 was prepared following
a similar strategy by using the phospha-Wittig reagent 1 in
excess (2.2 equivalents). A prolonged reaction time (15 h) was
needed to obtain a complete conversion. Importantly, 31P NMR
spectroscopy revealed that only one stereoisomer is formed.
Compound 3 was isolated following a similar workup in a 50%
yield as a very stable pale yellow solid. The structure of 3 was easily
established on the basis of 1H, 13C NMR data, mass spectrometry
◦
˚
bond lengths (A) and bond angles ( ): C(13)–P(1) 1.674(3), C(3)–P(1)
1.852(1), C(13)–C(9) 1.454(2), C(9)–C(5) 1.405(2), C(5)–O(2) 1.379(1);
C(3)–P(1)–C(13) 98.72(1), P(1)–C(13)–C(9) 128.5(1).
Table 1 Crystal and refinement parameters for 3 and 4
=
and elemental analyses. As in 2, the presence of a P C double
bond was evidenced by the presence of a downfield signal in 31P
3
4
NMR (d(THF) = 273 ppm) (Scheme 4). The presence of two
Formula
Mr
C50H66OP2
744.97
Monoclinic
C2
15.966(1)
10.407(1)
14.099(1)
105.260(1)
2
C50H66AuBF4OP2·C4H10O
1
phosphaalkene moieties is proven first by H NMR. The signal
1102.86
Orthorhombic
P212121
11.647(1)
16.895(1)
27.329(1)
90.00
of the phosphaalkene appears as a deceptively simple doublet of
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
b/◦
Z
4
l/cm−1
0.130
2.846
Reflections measured
Reflections used
7551
5376
27925
13250
wR2
R1
0.0924
0.0349
0.0701
0.0340
Scheme 4 Reagents and conditions: (i) THF, RT, 15 h.
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Reactivity of 3 towards group 11 metals
distances and bond angles. Crystal data and structural refinement
details are presented in Table 1.
In order to test the capacity of 3 to bind metals through a trans
fashion, we focused our study on the coordination of group 11
cationic metal fragments which are known to form linear 14 VE
ML2 complexes. The gold complex 4 was readily prepared in one
pot via a two-step sequence (Scheme 5).
The only apparent feature of this complex is the significant
deviation from linearity observed for the P–Au–P angle (167.56◦).
Moreover, this deviation brings the gold center away from the
oxygen atom of the furan moiety. As will be seen further, this can
be easily rationalized by considering a simple molecular orbital
diagram.
We next investigated the coordination to silver, which was
readily achieved by the stoichiometric reaction of ligand 3 with
AgBF4 (Scheme 6). After a few minutes, the 31P NMR of the crude
mixture proves the formation of a single complex at 204 ppm.
Unlike many Ag+ complexes, coupling of the two phosphorus
atoms with both isotopes of Ag, namely Ag107 and Ag109 which
both possess a spin of 1/2, was observed resulting in two sets
1
of doublets (1J(Ag109–P) = 686 Hz and J(Ag107–P) = 596 Hz).
Scheme 5 Reagents and conditions: THF, RT, 3 h.
After isolation, complex 5 was obtained as an air-stable solid.
It was fully characterized by usual NMR techniques. In fact, a
first surprising piece of information was given by a broad peak at
2.5 ppm in the 1H NMR spectrum. This peak integrated for two
protons which suggested the coordination of a water molecule.
We verified that the same complex is formed when the reaction
is carried out in air. Therefore, it seems likely that the water-free
complex adopts a distorted linear geometry like the gold analogue
described above. The silver centre then picks up water from the
solvent to complete the coordination sphere yielding the observed
complex which possesses a trigonal planar geometry. The presence
of a water molecule was confirmed by elemental analyses. In the
The stoichiometric reaction of [AuCl·SMe2] and ligand 3 in
THF led to a pale yellow solution. A 31P NMR of this mixture
showed a very broad peak which revealed a weak interaction.
Addition of solid AgBF4 resulted in the very fast formation of
characteristic silver salt indicating the end of chloride abstraction.
31P NMR spectroscopy showed the formation of a single complex
characterized by a singlet at 201 ppm (d(3) = 273 ppm, Dd =
−72 ppm). The mixture was filtered through a pad of Celite and
concentrated to give the desired complex 4 in near quantitative
yield. The complex was fully characterized by usual NMR
techniques as well as elemental analyses. Compared to the spectra
of the starting ligand 3, complex 4 varies only marginally. In
particular, the phosphaalkene proton is upfield shifted to 8.2 ppm
and appears as a virtual triplet (simplified AAꢂXXꢂ spin system),
because the magnitude of the J(P–P) increases upon coordination.
In the 13C spectrum the two carbon atoms which are bound to
the phosphorus atom are upfield shifted by ca. 10 ppm upon
coordination. Single crystals of 4 were grown by a slow diffusion
of diethyl ether in a THF solution of the complex. A view of one
molecule of 4 is presented in Fig. 2 as well as the most relevant bond
1H NMR spectrum also, the phosphaalkene proton appears as the
ꢀ
expected signal for an AAꢂXXꢂ spin system (d = 8.23 ppm, J =
40 Hz). In fact, the silver analogue gives very similar spectra than
the gold complex.
Scheme 6 Reagents and conditions: CH2Cl2, air (traces of water), RT,
5 min.
Single crystals were obtained by a slow diffusion of hexanes
into a CH2Cl2 solution of the complex, in air. We were both quite
surprised and pleased to see in the structure (Fig. 3) that the
coordination sphere of the metal had been completed by water
during crystallisation. Indeed, this definitely proves that, unlike
classical phosphaalkenes, the bulky derivatives are very robust
toward hydrolysis, even once coordinated to a metal centre.
Fig. 2 ORTEP view of one molecule of 4 (50% ellipsoids). The
numbering is arbitrary and different from that used in NMR data.
BF4 counter ion and methyl groups of the tert-butyl substituents
˚
The P–Ag bond lengths Ag(1)–P(1) 2.388(1) A, Ag(1)–P(2)
˚
2.403(1) A) are significantly longer than the P–Au bond lengths
˚
have been omitted for clarity. Selected bond lengths (A) and bond
˚
˚
(Au(1)–P(1) 2.267(1) A, Au(1)–P(2) 2.267(1) A) as expected. The
angles (◦): Au(1)–P(1) 2.267(1), Au(1)–P(2) 2.267(1), Au(1) · · · O(1) 2.699,
C(1)–P(1) 1.669(3), C(14)–P(2) 1.663(3), C(15)–P(1) 1.804(3), C(33)–P(2)
1.807(3), C(1)–C(2) 1.449(4), C(13)–C(14) 1.443(4), C(8)–O(1) 1.396(4),
C(7)–O(1) 1.383(4); P(1)–Au(1)–P(2) 167.56(3), C(1)–P(1)–Au(1) 121.8(1),
C(14)–P(2)–Au(1) 120.3(1), C(1)–P(1)–C(15) 112.3(2), C(15)–P(1)–Au(1)
125.9(1), C(13)–C(14)–P(2) 134.3(3), C(2)–C(1)–P(1) 133.0(3).
ꢀ
geometry at silver is trigonal planar ( angles = 358.24◦) with a
wide P(1)–Ag(1)–P(2) angle at 145.14(4)◦. This increase in the
angle (compared to the gold complex) is accompanied by an
increase in the C P–M angle from ca. 120 to ca. 130 (C(13)–
P(1)–Ag(1) 131.1(2)). The fact that phosphaalkene ligands can
◦
=
596 | Dalton Trans., 2006, 594–602
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singlet at 207 ppm in the 31P NMR spectrum. This complex was
fully characterized by usual NMR techniques as well as elemental
analysis.
Single crystals of complex 6 were obtained by slow diffusion of
hexanes in a CDCl3 solution of complex 6. A view of one molecule
of 6 is presented in Fig. 4 that also lists the most significant bond
lengths and angles. Crystal data and structural refinement details
are presented in Table 2.
Fig. 3 ORTEP view of one molecule of 5 (50% ellipsoids). The
numbering is arbitrary and different from that used in NMR data.
BF4 counter ion and methyl groups of the tert-butyl substituents
˚
have been omitted for clarity. Selected bond lengths (A) and bond
angles (◦): Ag(1)–P(1) 2.388(1), Ag(1)–P(2) 2.403(1), Ag(1)–O(2) 2.316(3),
Ag(1) · · · O(1) 3.095, C(14)–P(2) 1.681(4), C(13)–P(1) 1.672(5), C(2)–C(13)
1.456(6), C(14)–C(11) 1.441(7), C(1)–O(1) 1.383(6), C(12)–O(1) 1.387(6),
C(33)–P(2) 1.840(5), C(15)–P(1) 1.825(5); P(1)–Ag(1)–P(2) 145.14(4),
P(1)–Ag(1)–O(2) 109.8(1), P(2)–Ag(1)–O(2) 103.3(1), C(14)–P(2)–Ag(1)
131.1(2), C(13)–P(1)–Ag(1) 130.6(2), C(11)–C(14)–P(2) 132.6(4),
C(2)–C(13)–P(1) 132.1(4), C(13)–P(1)–C(15) 102.5(2).
Fig. 4 ORTEP view of one molecule of 6 (50% ellipsoids). The
numbering is arbitrary and different from that used in NMR data.
BF4 counter ion and methyl groups of the tert-butyl substituents
accommodate readily such changes in coordination angles reflects
the diffuse nature of the lone pair of sp2 hybridized phosphorus.
To complete this investigation we examined the coordinating
behaviour of 3 toward the catalytically relevant Cu(I) centre. Ace-
tonitrile ligand was readily displaced from the [Cu(CH3CN)4][BF4]
precursor to form a single complex 6 (Scheme 7). It appears as a
˚
have been omitted for clarity. Selected bond lengths (A) and bond
angles (◦): Cu(1)–P(1) 2.221(1), Cu(1)–P(2) 2.230(1), Cu(1)–N(1)
1.958(4), Cu(1) · · · O(1) 2.456, C(1)–P(1) 1.654(5), C(14)–P(2) 1.671(4),
C(1)–C(2) 1.456(6), C(13)–C(14) 1.453(6), C(1)–O(1) 1.393(4), C(8)–O(1)
1.389(4), C(17)–P(1) 1.834(4), C(35)–P(2) 1.827(4); P(1)–Cu(1)–P(2)
132.60(4), P(1)–Cu(1)–N(1) 113.5(1), P(2)–Cu(1)–N(1) 113.7(1),
C(1)–P(1)–Cu(1) 116.5(2), C(14)–P(2)–Cu(1) 120.6(2), C(2)–C(1)–P(1)
130.7(3), C(13)–C(14)–P(2) 127.3(3), Cu(1)–P(1)–C(17) 101.6(2).
As can be seen, the geometry at the copper center is trigonal
ꢀ
planar ( angles = 359.8◦) with a wide P(1)–Cu(1)–P(2) angle at
132.60(4)◦. The P–Cu bond distances are normal at 2.221(1) and
˚
2.230(1) A. The other bond distances and angles are quite similar
than the above mentioned ones, and therefore will not be further
commented on. This complex possesses however a very significant
feature, namely the metal centre is located well above the plane of
the ligand, as clearly shown on the ORTEP plot (dihedral angle
Scheme 7 Reagents and conditions: CH2Cl2, RT, 5 min.
Table 2 Crystal and refinement parameters for 5 and 6
5
6
Formula
Mr
C50H66AgBF4O2P2·1/2CH2Cl2
C52H69BCuF4NOP2·2CHCl3
1175.11
Triclinic
¯
P1
11.931(1)
14.527(1)
19.169(1)
107.920(1)
92.030(1)
109.710(1)
2
1040.57
Monoclinic
C2/c
Crystal system
Space group
˚
a/A
35.058(3)
11.084(1)
30.013(3)
90.00
116.700(2)
90.00
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
Z
8
l/cm−1
0.602
0.748
Reflections measured
Reflections used
17591
7576
16842
13870
wR2
R1
0.2282
0.0724
0.1806
0.0628
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C2–C1–P1–Cu1 = 9◦). This geometry results in a bond distance
˚
of 2.456 A, more consistent with a weak interaction than a true
˚
bond. Indeed, typical Cu–O bond distances of 2.208 A are found
with neutral ligands such as carbaldehyde–pyridine coordination
to the [Cu(PPh3)2]+ fragment.14 For several carboxylate complexes
of the type [Cu(PPh3)2(O2CR)], Hart et al. have shown that the Cu–
=
O C linkage can vary from a true bond for R = CH3 (2.257(7)
˚
˚
A) to a weak interaction for R = CHF2 (2.465(6) A) or R =
15
˚
CF3 (2.545(5) A). In fact, for these two last cases, addition of
ethanol resulted in the breaking of this carboxylate interaction
and ethanol coordination. How can the geometry at the copper
centre of our complex be rationalized? Being in sharp contrast to
the other geometries of the Au and Ag complexes, this fact can not
be fortuitous. Like in the case of 4 and 5, this particular feature can
be easily rationalized first through a qualitative molecular orbital
diagram, and more quantitative DFT calculations.
Fig. 5 Optimized geometry of the model complex I. Mes* groups
at phosphorus have been replaced by xylyl groups. Selected bond
◦
˚
lengths (A) and bond angles ( ): Au(44)–P(25) 2.311, P(25)–C(22) 1.682,
C(22)–C(3) 1.445, C(3)–C(4) 1.409,C(4)–O(19) 1.371; P(24)–Au(44)–P(25)
165.826, Au(44)–P(25)–C(22) 121.050, P(25)–C(22)–C(3) 134.597,
C(22)–C(3)–C(4) 128.947, C(3)–C(4)–O(19) 126.254.
Theoretical calculations
As previously noted, both Au and Ag complexes adopt a non linear
coordination mode. Looking into the simple molecular orbital
diagram of linear ML2 complexes provided a lead toward the
understanding of this peculiar geometry. Indeed, as in d10 ML2
complexes all five d orbitals are filled, four-electron destabilizing
2
2
interactions can occur between the dx
and dxy orbitals at
−y
the metal and the 2px (lone pair) and 2py (p-system) orbitals
at the oxygen atom respectively for obvious symmetry reasons
Fig. 6 H-11, H-12 and H-13 MO of complex I.
2
(Scheme 8). Note that the dz also possesses the appropriate
symmetry to interact with the 2py AO at oxygen. Thus in order to
diminish these repulsive interactions, a bending of the P–Au–P is
observed.
Theoretical calculations were carried out on a model complex I
in which the Mes* groups were replaced by xylyl groups. A view
of the optimized structure is presented in Fig. 5. Though the sub-
stitution scheme of the phosphorus atom is different, a reasonable
agreement was found between theoretical and experimental data
Having rationalized the geometry of the gold and silver com-
plexes, we then turned our attention to the copper complex. The
particular structural arrangement in complex 6 can be explained
as follows. In d10 ML3 16 VE complexes, the five d orbitals are
also filled and but a vacant 3py orbital which is perpendicular to
the plane defined by the three ligands is found as the LUMO. In
complex 6, this orbital points towards the lone pair at the oxygen
2
2
atom. Note that the dy
orbital which is involved in the bonding
−z
˚
˚
(Fig. 5). Thus, the P–Au bonds falls at 2.311 A for 2.267(1) A in
4 and the P–Au–P bending is relatively well reproduced (165.83◦
for 167.56(3)◦ in 4). Examination of MOs allowed to check our
hypothesis and as can be seen in the following figure several
MOs account for this four-electron destabilizing interaction (see
Fig. 6). The H-11 MO and H-13 correspond to the antibonding
with the two phosphorus atoms has the right symmetry to interact
with the oxygen lone pair (Scheme 9). Therefore the bonding
between Cu and O can be described as a classical four-electron
interaction involving three orbitals.
The theoretical structure of complex 6 was calculated. A first
calculation carried out on the model complex featuring xylyl
groups at phosphorus yielded a structure in which the O–Cu bond
2
2
2
interaction between the dx
and the dz with the 2py AO at
−y
˚
oxygen, respectively, whereas the H-12 is antibonding between the
dxy at Au and the 2px at O.
distance was found to be by far too long (2.638 A in II vs. 2.456(3)
˚
A in 6). Therefore, supposing that in this case, the presence of
Scheme 8 Qualitative interaction diagram showing the four-electron destabilizing interactions occurring between the filled d-orbitals at the metal and
2px and 2py orbitals at the oxygen atom.
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Scheme 9 Interaction diagram showing the two-electron stabilizing
interaction occurring between the vacant 3py-orbital at the metal and
2py orbital at the oxygen atom.
Fig. 8 A view of one of the MO describing the Cu–O bond in the model
complex II. The methyl groups of the t-Bu substituents at supermesityl
groups have been omitted for clarity.
the two very bulky tert-butyl groups at the ortho positions would
probably tend to pucker the copper metal towards the oxygen atom
of the furan ligand, calculations were carried out on a complex
featuring these two t-Bu groups. The optimization was carried
out using the ONIOM method (B3PW91/UFF). A view of the
optimized structure is presented in Fig. 7. As can be seen upon
examining the theoretical data, there is a very good agreement
with experimental metric parameters. Importantly, the Cu–O bond
Conclusion
In conclusion, we have synthesized a new trans spanning bidentate
bis phosphaalkene ligand 3 in a one pot procedure from the
readily available 4,6-bis(carbaldehyde)dibenzofuran. Using this
same starting material, the mono-phosphaalkene mono-aldehyde
2 could also be synthesized, which opens the way to mixed ligands
bearing one phosphaalkene moiety. This area is being pursued
in our laboratories. Using the bidentate ligand 3, the series of
complexes of group 11 metals has been synthesized. In the gold
and silver complexes 4 and 5, respectively, a distortion form the
linearity of the initial ML2 fragment was observed, which in the
case of complex 5 resulted in the coordination of a water molecule.
This complex proves the robustness of the phosphaalkene ligands
towards hydrolysis. The observed distortion, which has been
rationalized by DFT calculations, results from a destabilizing
˚
distance at 2.486 A is rather well reproduced as well as the P–Cu–P
angle (132.00 in II vs. 132.60◦ in 6).
2
2
2
interaction between the appropriate filled dx
and dz with the
−y
2py AO at oxygen, and dxy at Au with the 2px at oxygen. The
catalytically relevant Cu(I) complex 6 was also synthesized. The
geometry given by an X-ray structure analysis was rationalized by
ONIOM calculations. In this case, a bonding interaction between,
2
2
on one hand, empty 3py-orbital and filled 3dy
at the copper
−z
and, on the other hand, filled 2py orbital at the oxygen atom,
is responsible for the peculiar geometry. Catalytic tests with this
complex are currently underway and will be reported in due course.
Experimental
Fig. 7 Optimized geometry ◦of the model complex II. Selected bond
General
˚
lengths (A) and bond angles ( ): Cu(26)–P(25) 2.288, P(25)–C(22) 1.683,
All reactions were routinely performed under an inert atmosphere
of argon or nitrogen by using Schlenk and glove-box techniques
and dry deoxygenated solvents. Dry THF and hexanes were
obtained by distillation from Na/benzophenone and dry ether
from CaCl2 and then NaH and dry CH2Cl2 from P2O5. CDCl3
C(22)–C(3) 1.448, C(3)–C(4) 1.406, C(4)–O(19) 1.380, Cu(26)–N(27)
2.054; P(24)–Cu(26)–P(25) 132.004, Cu(26)–P(25)–C(22) 118.546,
P(25)–C(22)–C(3) 129.602, C(22)–C(3)–C(4) 127.453, C(3)–C(4)–O(19)
125.805, P(24)–Cu(26)–N(27) 115.341, P(25)–Cu(26)–N(27) 112.340,
P(24)–Cu(26)–P(25) 132.003.
˚
was dried from P2O5 and stored on 4 A Linde molecular sieves.
As expected, molecular orbital analysis revealed that a bonding
interaction develops between the oxygen and the copper atom.
As can bee seen in Fig. 8 the most important contribution to the
bonding is provided by the interaction between the vacant 3py and
CD2Cl2 was used as purchased and stored in the glove-box.
Nuclear magnetic resonance spectra were recorded on a Bruker
300 AVANCE spectrometer operating at 300.0 MHz for 1H,
75.5 MHz for 13C and 121.5 MHz for 31P. Solvent peaks are
used as internal reference relative to Me4Si for 1H and 13C
2
2
3dy
AOs at Cu and the 2py AO of the oxygen atom (HOMO-19).
−z
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Dalton Trans., 2006, 594–602 | 599
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chemical shifts (ppm); 31P chemical shifts are relative to a 85%
H3PO4 external reference. Coupling constants are given in hertz.
The following abbreviations are used: s, singlet; d, doublet; t,
triplet; q, quadruplet; m, multiplet; v, virtual; b, broad. Mass
spectra were obtained at 70 eV with a HP 5989B spectrometer
couple to a HP 5980 chromatograph by the direct inlet method.
[Cu(CH3CN)4BF4]16 and [AuCl(SMe2)]17 were prepared according
to reported procedures.
Synthesis of 4,6-bis(supermesitylphosphanylidenemethyl)dibenzo-
furan 3. Reagent 1 was cooled to 0 ◦C and cannulated on a sus-
pension of 4,6-bis(carbaldehyde)dibenzofuran (0.27 g, 1.2 mmol,
◦
0.4 equivalent) at 0 C in THF (10 mL). The crude mixture was
stirred during 18 h and cooled to 0 ◦C. CH2Cl2, water and ice were
then added. The organic phase was separated, dried over MgSO4
and filtered. The solvent was then evaporated, MeOH was added
which resulted in the formation of a precipitate which was filtered
off and dried under vacuum. The title compound was obtained as
a white solid. Yield: 55%, 0.50 g.
Phospha-Wittig reagent 1
To a mixture of Mes*PCl2 (1.0 g, 2.9 mmol), Zn (1.0 g, 15.0 mmol)
in THF (10 mL) at 0 ◦C, was syringed PMe3 (1 M, 7.5 mmol,
7.5 mL). The crude mixture was allowed to warm to room
temperature and was stirred for 3 h. The 31P NMR spectrum
showed the formation of the desired reagent which was used
without further purification.
31P NMR (121.5 MHz, THF, 298 K): d 6.6 ppm (1J(P–P) =
577.9, Mes*P), −132.5 ppm (1J(P–P) = 577.9, PMe3).
1NMR (300 MHz, CD2Cl2, 298 K): d 1.40 (s, 18H, para
Synthesis of 4ꢀ-(supermesitylphosphanylidenemethyl)-6-(carba-
ldehyde)dibenzofuran 2. Reagent 1 was cooled to 0 ◦C and
cannulated on a suspension of 4,6-bis(carbaldehyde)dibenzofuran
3
C(CH3)3), 1.56 (s, 36H, ortho C(CH3)3), 7.37 (t, 2H, J(H–H) =
3
7.6, H2, H8), 7.50 (s, 4H, H13), 7.77 (d, 2H, J(H–H) = 5.3, H3,
3
H7), 7.90 (d, 2H, J(H–H) = 7.4, H1, H9), 8.48 (m, AAꢂXXꢂ, m,
◦
ꢀ
(0.75 g, 3.3 mmol, 1.1 equivalent) at 0 C in THF (10 mL). The
J = 41.9, H10, H10 ). 31P NMR (121.5 MHz, CD2Cl2, 298 K):
ꢂ
crude mixture was stirred during 3 h and cooled to 0 ◦C. CH2Cl2,
water and ice were then added. The organic phase was separated,
dried over MgSO4 and filtered. The solvent was then evaporated,
MeOH was added which resulted in the formation of a precip-
itate which was filtered off and dried under vacuum. The title
compound was obtained as a white solid. Yield: 50%, 0.80 g
d 271.5 ppm. 13C NMR (75.5 MHz, CD2Cl2, 298 K) d 30.4 (s,
para C(CH3)3), 33.0 (d, J(C–P) = 3.0, ortho C(CH3)3), 34.1 (s,
4
para C(CH3)3), 37.4 (s, ortho C(CH3)3), 118.94 (s, C1, C9), 121.01
(s, C13), 122.36 (s, C2, C8), 123.70 (m, C4, C6, C3, C7), 124.57 (vt,
ꢀ
ꢀ
AXXꢂ, J(C–P) = 14.4, C9a, C9b), 140.71 (m, AXXꢂ, J(C–P) =
ꢀ
ꢂ
ꢂ
62.7, C11, C11 ), 148.90 (s, C12), 151.55 (vt, AXX , J(C–P) = 12.0,
ꢀ
C4a, C5a), 153.17 (s, C14), 167.09 (m, AXXꢂ, J(C–P) = 51.7, C10,
ꢂ
C10 ). MS: 746 (M + H, 100%).
Synthesis of gold complex 4. [AuCl(SMe2)] (30 mg, 0.10 mmol)
and ligand 3 (75 mg, 0.10 mmol) were dissolved in THF (3 mL).
The solution was stirred for 20 min. AgBF4 was added (19.8 mg,
0.10 mmol) and the solution was stirred for 12 h. The 31P NMR
spectrum of the crude mixture shows the formation of a unique
product. The mixture was filtered on Celite and the solution was
taken to dryness. The product was washed with hexanes and dried
to yield a yellow powder. Yield: 92%, 87 mg. X-Ray quality crystals
were obtained after diffusion of ether into a THF solution of the
complex.
1H NMR (300 MHz, CD2Cl2, 298 K): d 1.48 (s, 18H, para
3
C(CH3)3), 1.67 (s, 36H, ortho C(CH3)3), 7.43 (t, 1H, J(H–H) =
3
7.5, H8), 7.51 (t, 1H, J(H–H) = 7.3, H2), 7.60 (s, 2H, H12), 7.85
1H NMR (300 MHz, CDCl3, 298 K): d 1.40 (s, 18H, para
(dd, 1H, 3J(H–H) = 7.5, 4J(H–H) = 3.5, H3), 7.92 (dd, 1H, 3J(H–
3
C(CH3)3), 1.68 (s, 36H, ortho C(CH3)3), 7.58 (t, 2H, J(H–H) =
4
3
H) = 7.7, J(H–H) = 1.4, H7), 7.99 (dd, 1H, J(H–H) = 7.7,
7.6, H2, H8), 7.67 (s, 4H, H13), 8.17 (t, 3J(H–H) = 8.8, 2H, H3, H7),
4J(H–H) = 1.2, H9), 8.22 (dd, 1H, J(H–H) = 7.6, J(H–H) =
3
4
ꢀ
8.37 (m, AAꢂXXꢂ, m, J = 7.0, H10, H10 ). 31P NMR (121.5 MHz,
ꢂ
2
1.2, H1), 8.58 (d, 1H, J(H–P) = 25.3, H10) 10.75 (s, 1H, CHO).
CDCl3, 298 K): d 200.2. 13C NMR (75.5 MHz, CDCl3, 298 K):
d 32.9 (s, para C(CH3)3), 36.5 (s, ortho C(CH3)3), 37.2 (s, para
C(CH3)3), 40.6 (s, ortho C(CH3)3), 118.2 (s, C9a,9b), 121.1 (m, C1,2,8,9),
31P NMR (121.5 MHz, CD2Cl2, 298 K): d 273.9 ppm. 13C NMR
(75.5 MHz, CD2Cl2, 298 K): d 30.34 (s, para C(CH3)3), 32.96 (d,
3J(C–P) = 7.2, ortho C(CH3)3), 34.12 (s, para C(CH3)3), 37.42 (s,
122.3 (s, C13), 122.4 (s, C4,6), 131.1 (m, C3,7,11), 148.2 (AAꢂXXꢂ, m,
J = 8.0, C4a,5a), 151.7 (s, C12), 152.9 (s, C14), 157.9 (AAꢂXXꢂ, m,
3
ꢀ
ortho C(CH3)3), 119.01 (d, J(C–P) = 7.1, C7), 120.31 (s, C4 or
C9b), 121.20 (s, C13, C15), 122.23 (s, C2), 122.38 (d, 4J(C–P) = 2.8,
ꢀ
ꢂ
J = 69, C10,10 ).
4
3
C9a), 122.98 (d, J(C–P) = 3.9, C8), 124.49 (d, J(C–P) = 23.0,
2
C3), 124.66 (d, J(C–P) = 14.5, C6), 124.89 (s, C9), 124.96 (s, C9b
Synthesis of silver complex 5. Ligand 3 (57 mg, 0.07 mmol)
was dissolved in CH2Cl2 (1 mL) and in the glove-box, solid AgBF4
(15 mg, 0.07 mmol) was added. The initially colorless solution
rapidly turned bright yellow. The 31P NMR spectrum of the crude
mixture shows the formation of a unique product. The solution
1
or C4), 125.80 (s, C1), 138.96 (d, J(C–P) = 54.4, C11), 149.18 (s,
3
C12, C16), 151.87 (d, J(C–P) = 11.3, C5a), 153.28 (s, C14), 155.67
(s, C4a), 166.60 (d, 1J(C–P) = 39.0, C10).
MS: 485 (M + H, 100%).
600 | Dalton Trans., 2006, 594–602
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was taken to dryness. The product was washed with hexanes and
dried to yield a yellow powder. Yield: 95%, 57 mg. X-Ray quality
crystals were obtained after diffusion of hexanes into a CH2Cl2
solution of the complex.
then POV-Ray.24 contain the supplementary crystallographic data
for this paper.
CCDC reference numbers 275394–275397.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b508678g
1H NMR (300 MHz, CD2Cl2, 298 K): d 1.39 (s, 18H, para
C(CH3)3), 1.63 (s, 36H, ortho C(CH3)3), 2.52 (s, H2O), 7.41 (d,
2H, 3J(H–H) = 7.7, H1,9), 7.53 (t, 3J(H–H) = 7.7, 2H, H2,8), 7.63
Acknowledgements
3
4
(s, 4H, H13), 8.18 (dd, 2H, J(H–H) = 7.7, J(H–P) = 1.3, H3,7),
ꢀ
8.23 (AAꢂXXꢂ, m, 2H, J = 41.9, H10,10 ). 31P NMR (121.5 MHz,
ꢂ
The CNRS and the Ecole Polytechnique are thanked for support-
ing this work. The use of computational facilities from the IDRIS
institute (University Paris XI, Orsay, France) is also gratefully
acknowledged.
CD2Cl2, 298 K): d 204.9 (d + d, 1J(P–Ag) = 686, 1J(P–Ag) = 596).
13C NMR (75.5 MHz, CD2Cl2, 298 K): d 31.7 (s, para C(CH3)3),
4
35.4 (d, J(C–P) = 3.0, ortho C(CH3)3), 36.1 (s, para C(CH3)3),
39.7 (s, ortho C(CH3)3), 122.2 (s, C9a,9b), 123.8 (m, C1,2,8,9), 125.1 (s,
C13), 125.7 (s, C4,6), 129.2 (d, 1J(P–C) = 15.5, C11), 133.8 (C), 153.4
ꢀ
References
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ꢀ
169.6 (AXXꢂ, m, J(C–P) = 40.3, C10).
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Synthesis of copper complex 6. [Cu(CH3CN)4][BF4] (34.5 mg,
0.13 mmol) and ligand 3 (100 mg, 0.13 mmol) were dissolved in
CH2Cl2 (7 mL). The 31P NMR spectrum of the crude mixture
shows the formation of a unique product. The volume of the
solution was reduced, hexanes were added which resulted in the
precipitation of a yellow solid. It was filtered, washed with hexanes
then dried. Yield: 95%, 116 mg. X-Ray quality crystals were
obtained after diffusion of hexanes into a CDCl3 solution of the
complex.
1H NMR (300 MHz, CD2Cl2, 298 K): d 1.38 (s, 18H, para
C(CH3)3), 1.61 (s, 36H, ortho C(CH3)3), 7.34 (m, H2,8), 7.50 (m,
2H, H1,9), 7.61 (s, 4H, H13), 8.10 (m, 4H, H3,7,10,10 ). 31P NMR
ꢂ
(121.5 MHz, CD2Cl2, 298 K): d 207.6. 13C NMR (75.5 MHz,
CD2Cl2, 298 K): d 31.3 (s, para C(CH3)3), 34.9 (s, ortho C(CH3)3),
35.6 (s, para C(CH3)3), 39.0 (s, ortho C(CH3)3), 123.1 (s, C9a,9b),
123.3 (s, C1,2,8,9), 123.6 (s, C13), 125.4 (s, C4,6), 129.4 (d, 1J(P–C) =
ꢀ
ꢀ
20, C11), 131.4 (m, J = 26, C3,7), 152.4 (AXXꢂ, m, J(C–P) =
ꢀ
14, C4a,5a), 153.7 (s,C12), 156.2 (s, C14), 163.8 (AXXꢂ, m, J(C–P) =
46, C10).
Computational details
All computations were performed using the Gaussian 03 suite of
programs and gradient corrected density functional theory using
the B3PW91 functional.18,19 All optimizations were carried out
using the 6-31 G(d) basis set for H, C, N, O, P. The basis set
employed for the Cu and Au atoms incorporate the Hay and
Wadt small-core relativistic effective core potential and double-
f valence basis set.20 For complex II, the ONIOM method was
employed with the UFF force field (for methyl groups of the xylyl
substituents).21 Full optimizations were followed by analytical
computation of the Hessian matrix to confirm the nature of the
located minima on the potential energy surface. Minima were
characterized by no imaginary frequency.
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Crystallography
Data were collected at 150.0(1) K on a Nonius Kappa CCD
˚
diffractometer using a Mo-Ka (k = 0.71073 A) X-ray source and
a graphite monochromator. All data were measured using phi and
omega scans. Experimental details are given in Tables 1 and 2. The
crystal structure was solved using SIR 9722 and SHELXL-97.23
Molecular drawings were made using ORTEP III for Windows
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602 | Dalton Trans., 2006, 594–602
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The Royal Society of Chemistry 2006
©