Phosphino-boryl-naphthalenes: Geometrically enforced, yet Lewis acid responsive P → B interactions

Article abstract of DOI:10.1021/ic4003466

Three naphthyl-bridged phosphine-borane derivatives 2-BCy₂, 2-BMes₂, and 2-BFlu, differing in the steric and electronic properties of the boryl moiety, have been prepared and characterized by spectroscopic and crystallographic means.

Full text of DOI:10.1021/ic4003466

Article
pubs.acs.org/IC
Phosphino-Boryl-Naphthalenes: Geometrically Enforced, Yet Lewis
Acid Responsive P → B Interactions
Sebastien Bontemps,†,# Marc Devillard,† Sonia Mallet-Ladeira,‡ Ghenwa Bouhadir,† Karinne Miqueu,*,§
́
and Didier Bourissou*,†
†Universite
LHFA, UMR 5069, 31062 Toulouse, France
‡Institut de Chimie de Toulouse (FR 2599), 118 route de Narbonne, 31062 Toulouse cedex 9, France
§Institut des Sciences Analytiques et de Physico-Chimie pour l’Environnement et les Mater
iaux UMR-CNRS 5254, Universite
et des Pays de l’Adour, Helioparc, 2 avenue du President Angot, 64053 Pau Cedex 09, France
́ ́ ́ ́
de Toulouse, UPS, LHFA (Laboratoire Heterochimie Fondamentale et Appliquee), 118 route de Narbonne, and CNRS,
́
́
de Pau
́
́
S
* Supporting Information
ABSTRACT: Three naphthyl-bridged phosphine-borane de-
rivatives 2-BCy2, 2-BMes2, and 2-BFlu, differing in the steric
and electronic properties of the boryl moiety, have been
prepared and characterized by spectroscopic and crystallo-
graphic means. The presence and magnitude of the P → B
interactions have been assessed experimentally and theoret-
ically. The naphthyl linker was found to enforce the P → B
interaction despite steric shielding, while retaining enough
flexibility to respond to the Lewis acidity of boron.
INTRODUCTION
■
Donor−acceptor (D → A) interactions play a major role in
chemistry. They are found in a broad variety of chemical
structures, including simple Lewis acid/Lewis base adducts
(such as the prototypical compound H3N → BH3),1 hyper-
valent derivatives (typically met with heavier p-block
elements)2 and coordination complexes (extensively found
with s-block metals, transition metals and f-elements). Such
compounds find applications in many fields ranging over
organic synthesis, catalysis, material science, etc., and thus
represent a very fertile ground of research. Two centuries after
the seminal discovery of H3N → BF3 by Gay-Lussac,3 the
precise description of dative interactions as well as the accurate
estimation of their strength also remain a very active field of
research, in particular for computational investigations.4
Connecting donor and acceptor moieties through an organic
linker has proven most valuable in the study and development
of D → A compounds. Indeed, such an intramolecular
approach provides some control over the D → A interaction
by varying the length and rigidity of the spacer. In that respect,
the naphthalene skeleton exhibits unique features, the elements
introduced in peripositions being maintained in close proximity
(2.5 Å when no deformation occurs).5 The propensity of such
naphthalene derivatives to engage into D → A interactions has
been amply substantiated. In particular, amines and phosphines
have been combined with a broad variety of Lewis acid
moieties.6 Representative examples involving group 13, 14, and
15 elements as acceptor centers are depicted in Figure 1.
In recent years, Lewis pairs have attracted tremendous
interest,7 following the discovery of Stephan and Erker that
Figure 1. Selected examples of naphthyl-bridged D → A interactions
involving group 13−15 elements as Lewis acid moieties.
phosphine-boranes, in which P → B interactions are prevented
sterically and/or geometrically, are capable to readily activate
and transfer dihydrogen.8 Accordingly, the factors controlling
the formation and magnitude of P → B interactions are
attracting renewed interest.9
In this context, and as an extension of our work on o-
phenylene bridged phosphine-boranes (PB),10 we turned our
attention to the naphthyl spacer and report here a detailed
study of P → B interactions in such systems. According to a
SciFinder database search, the only examples of such PB
derivatives described so far are the boryl-dichlorophosphino-
naphthalenes A recently prepared by Sasamori and Tokitoh
Received: February 8, 2013
Published: April 1, 2013
© 2013 American Chemical Society
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(Chart 1), en route to the corresponding 1-phospha-2-
boraacenaphthenes. The presence or lack of P → B interactions
We started our investigations with compound 2-BCy2. The
steric demand and Lewis acidity of the dicyclohexylboryl group
is intermediate between those of the dimesitylboryl and
borafluorenyl moieties.13b,15 Compound 2-BCy2 was obtained
as a white powder in 56% yield. It was characterized in solution
by NMR spectroscopy and in the solid state by X-ray diffraction
analysis (Table 1). The 11B NMR signal of 2-BCy2 (δ = 0.1
ppm) appears at much higher field than those of three-
coordinate boron centers (δ = 80.8 ppm for BCy3)16 and falls
in the typical range of tetracoordinate boron compounds.
Consistently, the 31P NMR resonance signal of 2-BCy2 (δ =
23.4 ppm) is shifted to low field by about 20 ppm compared to
that of its phosphine precursor 1 (δ = 1.6 ppm). These NMR
data indicate the presence of a significant P → B interaction in
solution.
Crystals of 2-BCy2 were obtained from a concentrated
pentane solution at −40 °C (Figure 3). The presence of an
intramolecular P → B interaction is clearly apparent from the
pyramidalization of the boron environment [sum of CBC bond
angles ∑αB = 340.7(20)°] and the short PB distance [2.076(2)
Å, vs 1.91 Å for the sum of covalent radii17]. There are only few
crystallographic data available for P → B interactions supported
by C3 linkers. The only system with perisubstitution is the
diphosphino-boryl-anthracene compound described by Akiba
[i-Pr2P → BCat interaction associated with a PB distance of
2.14(1) Å].18 The PB distance observed in 2-BCy2 is shorter
and falls in the range of those found by Erker for R2P →
B(C6F5)2 interactions supported by flexible aliphatic C3 linkers
(PB distances of 2.06−2.09 Å for R = t-Bu, Ph, Mes).9b,c In
order to accommodate the PB distance, the naphthyl backbone
of 2-BCy2 significantly distorts both in-plane [bond angles PCC
= 109.41(13)° and BCC = 118.02(16)°]19 and out-of-plane
[torsion angle PC1C3B = 13.05(10)°].
Chart 1
in compounds A11 was inferred by 11B NMR spectroscopy.
Accordingly, sterically demanding substituents around boron
were proposed to prevent the intramolecular dative bond.
Here we report the synthesis and thorough characterization
of three naphthyl PB derivatives featuring boryl groups of
different steric and electronic properties.12 The naphthyl
backbone is shown to enforce P → B interaction despite steric
shielding, while retaining enough flexibility to respond to the
Lewis acidity of boron. The magnitude of the involved P → B
interactions has been carefully assessed by considering various
experimental and computational descriptors (spectroscopic,
geometric and electronic).
RESULTS AND DISCUSSION
■
The three PB naphthyl derivatives 2-BCy2, 2-BMes2, and 2-
BFlu were synthesized in two steps following the same strategy
as with the o-phenylene linker (Scheme 1, Table 1).13 Starting
Scheme 1. Synthesis of the PB Compounds 2-BCy2, 2-
BMes2, and 2-BFlu
The study was pursued with compound 2-BMes2. Despite
the steric crowding induced by the bulky substituents at
phosphorus and boron, the preparation proceeded smoothly
and 2-BMes2 was isolated in 58% yield after workup. The 11B
NMR signal is observed at δ = 16.2 ppm for 2-BMes2 [vs δ = 79
ppm for BMes3], indicating that the boron center is here also
tetracoordinated. The deshielding of the 31P NMR resonance
signal (δ = 17.4 ppm for 2-BMes2) supports the existence of an
intramolecular P → B interaction, but the NMR shift is less
pronounced than in 2-BCy2, suggesting a somewhat weaker
interaction in 2-BMes2. The crystallographic data confirm this
view (Figure 3, Table 1), with a pyramidalized environment
around boron [∑αB = 341.9 (9)°] and a PB distance of
2.173(4) Å. Compared with 2-BCy2, the P and B atoms are
slightly pushed apart in 2-BMes2, indicating a somewhat
weakened interaction. Nonetheless, the naphthyl spacer
supports such donor−acceptor interactions, despite severe
steric shielding. It is well-known that the presence of two
mesityl groups at boron imparts considerable steric protection
and prevents interaction with most Lewis bases, especially
bulky ones.20,21 Notably, the structure adopted by 2-BMes2 is in
some respect opposite to that encountered in frustrated Lewis
pairs, in which steric shielding prevent P → B interactions.
To explore further the flexibility of the naphthyl spacer with
respect to the P → B interaction, we then investigated
compound 2-BFlu. In contrast with the BMes2 group, the
borafluorenyl moiety BFlu is sterically unhindered and very
electron deficient (because of its formal antiaromatic
character).22 It was thus considered as an ideal candidate to
assess how far the P → B interaction can be strengthened.
Table 1. Selected Spectroscopic and Crystallographic Data
for Compounds 2
2-BMes2
2-BCy2
2-BFlu
δ31P (ppm)
δ11B (ppm)
d(PB) (Å)
∑αB (°)
PC1C2 (°)
BC3C2 (°)
PC1C3B (°)
17.4
23.4
25.1
16.2
0.1
−8.5
2.173(4)
341.9(9)
111.4(3)
119.4(3)
2.6(2)
2.076(2)
340.7(2)
109.4(2)
118.0(2)
13.1(1)
2.011(2)
338.5(5)
109.0(2)
116.6(2)
11.9(2)
from 1,8-diiodonaphthalene, the diisopropylphosphino group
was introduced first by iodine−lithium−phosphorus exchange.
After purification by flash chromatography, compound 1 was
obtained as a yellow oil in 45% yield.14 The different boryl
groups were then installed by iodine−lithium exchange
followed by electrophilic trapping with the corresponding
halogenoborane ClBCy2, FBMes2 or ClBFlu.
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Figure 3. Molecular structure of 2-BMes2, 2-BCy2, and 2-BFlu with thermal ellipsoids drawn at 50% probability. For clarity, the hydrogen atoms and
solvent molecules are omitted, and the substituents at P and B are simplified.
Compound 2-BFlu was isolated in 52% yield. It is stable at
room temperature under inert atmosphere, whereas the
corresponding o-phenylene bridged derivative13b rapidly
decomposes under the same conditions. The 11B and 31P
NMR signals of 2-BFlu (δ = −8.5 and 25.1 ppm, respectively)
are diagnostic of a strong intramolecular P → B interaction
(Table 1). Consistently, the X-ray diffraction study (Figure 3)
revealed a strong pyramidalization of the boron environment
[∑αB = 338.45(5)°] and a very short PB distance [2.011(2) Å,
at the lower limit of those reported to date for phosphine →
borane adducts].23 The strong P → B interaction induces
significant distortions of the naphthyl backbone [in-plane: PCC
= 108.98(13)° and BCC = 116.60(16)°; out-of-plane: PC1C3B
= 11.90°].
Between the two extreme cases 2-BMes2 and 2-BFlu, the
magnitude of the P → B interaction varies significantly, as
shown by the substantial decrease of the PB distance from
2.173(4) to 2.011(2) Å.24 It is remarkable that on one hand,
the naphthyl spacer can compensate for severe steric shielding
and enforce D → A interaction thanks to its rigidity, and that
on the other hand, it retains enough flexibility for the P → B
interaction to respond significantly to the variation of the boron
Lewis acidity.
interaction (B···P: 3.690 Å, ∑αB = 358.8°), the phosphorus-
centered pyramid pointing opposite to the 2p(B) vacant orbital.
The closed form 3c is lower in energy than the open form 3o by
as much as 27 kcal/mol. This contrasts with the small energy
difference predicted between the two forms of the correspond-
ing o-phenylene bridged phosphine-borane (∼3.0 kcal/mol at
the same level of theory) and provides some quantitative
estimation of the influence of the spacer on the strength of the
P → B interaction.
In compounds 2, the phosphorus substituents cannot point
to boron because of steric reasons, and only the closed forms
were found as minima on the respective potential energy
surfaces. The optimized geometries (Table 2) reproduce well
Table 2. Selected Geometric Data for Compounds 2, as
Calculated at the B3PW91/6-31G** Level of theory
2-BMes2
2-BCy2
2-BFlu
d(PB) (Å)
∑αB (°)
PC1C2 (°)
BC3C2 (°)
PC1C3B (°)
2.270
345.4
112.56
121.67
7.8
2.169
345.1
2.040
337.4
110.65
119.50
15.0
109.74
117.88
−6.6
The phosphine → borane interactions of the naphthyl
derivatives were then examined by DFT calculations at the
B3PW91/6-31G** level of theory.25 The model compound 3
(featuring Me groups at the B and P atoms) as well as the full
molecules 2-BCy2, 2-BMes2, and 2-BFlu were investigated.
In line with previous observations for o-phenylene bridged
diphosphine- and triphosphine-boranes,9a two minima were
found on the potential energy surface of the model compound
3 (Figure 4). In the closed form 3c, the PB distance is short
(2.025 Å) and the boron environment is strongly pyramidalized
(∑αB = 340.40°), while in the open form 3o, there is no P → B
the X-ray data (largest deviation of 0.1 Å in the PB bond
distance and 2° in the bond angles). In agreement with the
experimental observations, the PB distance decreases with
increasing the Lewis acidity of the boron center (from 2.270 in
2-BMes2 to 2.040 Å in 2-BFlu). The pyramidalization around
boron increases in the same series (∑αB varies from 337.4° in
2-BFlu to 345.4° in 2-BMes2). The progressive strengthening of
the P → B interaction from BMes2 to BCy2, and BFlu, is also
apparent from the associated Wiberg bond orders (WBI),
which increase from 0.74 in 2-BMes2 to 0.81 in 2-BCy2 and
0.88 in 2-BFlu.
Natural bond orbital (NBO)26 analyses also provide valuable
information about the P → B interactions (Table 3). The
natural population analysis (NPA) charges clearly indicate
some electron transfer from phosphorus to boron. The charge
of the Pi-Pr2 fragment is positive and increases from 2-BMes2
(0.74) to 2-BCy2 (0.81), and 2-BFlu (0.88), while the charge of
the BR2 fragment is negative and decreases in the same series
(from −0.21 in 2-BMes2 to −0.25 in 2-BCy2, and −0.43 in 2-
BFlu). In the NBO analysis, polarized σPB bonds were found at
the first order (Figure 5a). The contribution of phosphorus
prevails (60−70%), but the participation of boron is noticeable
(30−40%) and increases from 2-BMes2 to 2-BCy2, and 2-BFlu.
This trend can be explained by simple molecular orbital
considerations. Indeed, the higher the Lewis acidity of boron,
the smaller is the energy gap between the boron vacant orbital
Figure 4. Optimized geometries of closed and open forms of the model
compound 3. For clarity, the hydrogen atoms are omitted.
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Table 3. Selected Results of the Computational Analysis of Compounds 2
2-BMes2
2-BCy2
0.81
2-BFlu
0.88
NBO analyses
WBI
0.74
NPA charges
Pi-Pr2
0.82
0.87
0.99
BR2
−0.21
−0.25
−0.43
%P in σPB (%s/%p)
%B in σPB (%s/%p)
70.0 (30.6/69.3)
67.8 (32.4/67.5)
61.2 (31.2/68.7)
30.0 (12.8/87.1)
32.2 (14.3/85.6)
38.8 (18.8/81.1)
AIM analyses
BCP (P−B)
ρ(r) (e.bohr−3
∇2ρ(r) (e.bohr−5
H(r)
)
0.06
−0.04
−0.031
0.328
0.08
−0.08
−0.050
0.353
0.10
−0.11
−0.083
0.400
)
δ(P,B)
Figure 5. (a) Plot of the NBO σPB orbital of 2-BCy2 (cutoff: 0.04). (b) Simplified AIM molecular graph for 2-BCy2; the hydrogen atoms and the
BCP associated to the C−H bonds are omitted for clarity. (c) Contour plot of the Laplacian ∇2ρ(BCP) of 2-BCy2 in the P(naphthyl)B plane, with
charge accumulation (∇2ρ(r)<0) in blue lines and charge depletion (∇2ρ(r)>0) in dashed lines.
2p(B) and the phosphorus lone pair nP, thus the more the two
atomic orbitals mix and the more stabilizing is the donor−
acceptor interaction. Accordingly, the less polarized σPB bond
(61.2% P/38.8% B) is found in compound 2-BFlu featuring the
strongest P → B interaction.
the variation of the boron Lewis acidity, both geometrically and
electronically. Future work will seek to explore further the
chemistry of donor−acceptor naphthyl systems, from both
structural and reactivity standpoints.
Finally, the P → B interactions in compounds 2 were
analyzed by atoms in molecules (AIM) calculations.27 The
electron density maps (Figure 5b) show the presence of bond
paths between the phosphorus and boron atoms with localized
bond critical points (BCP). The electron density ρ(r) at the
BCP increases from 0.06 e.bohr−3 for 2-BMes2, to 0.08 e.bohr−3
for 2-BCy2, and 0.10 e.bohr−3 for 2-BFlu, corroborating the
strengthening of the P → B interaction as the Lewis acidity of
boron increases. In agreement with the donor−acceptor
character of the P → B interactions, the Laplacian ∇2ρ(r)
(Figure 5c) and local electronic energy density H(r) at the BCP
are small and negative.28 The sharing of electrons between P
and B was assessed by considering the delocalization index
δ(B,P), often called bond order, as introduced by Bader.27c,29
δ(B,P) follows the same trend as the electron density and
Wiberg bond index, increasing from 0.328 in 2-BMes2, to 0.353
in 2-BCy2, and 0.400 in 2-BFlu.
EXPERIMENTAL SECTION
■
General Comments. All reactions and manipulations were carried
out under an atmosphere of dry argon using standard Schlenk
techniques. All solvents were purged with argon and dried using an
MBraun Solvent Purification System (SPS). 1H, 11B, 13C and 31P NMR
spectra were recorded on Bruker, AMX 400, Avance 500 and Avance
300 spectrometers. Chemical shifts are expressed with a positive sign,
in parts per million, calibrated to residual H (7.24 ppm) and 13C
1
(77.16 ppm) solvent signals, external BF3·OEt2 and 85% H3PO4.
Otherwise stated, NMR spectra were recorded at 293 K.
Chloroborafluorene was synthesized according to literature proce-
dure.30
Compound 1. 2.00 mL of solution of n-BuLi (1.60 M in hexanes,
3.22 mmol) were added dropwise to 1.165 g (3.070 mmol) of 1,8-
diiodonaphtalene solution in THF (40 mL) at −78 °C and the
reaction mixture was stirred 1 h at this temperature. After the
subsequent addition of 488 μL of chlorodiisopropylphosphine (3.07
mmol), the reaction mixture was stirred at rt overnight. The volatiles
were then removed under a vacuum, and the residue was purified by
flash chromatography on silica gel (eluant: pentane) affording the
expected compound as a yellow oil with a 45% yield. 1H NMR (300.2
CONCLUSION
■
Compounds 2-BMes2, 2-BCy2, and 2-BFlu are rare examples of
naphthyl-bridged phosphine-boranes. The involved P → B
interactions have been thoroughly analyzed by experimental
and computational means, substantiating a dual character of the
naphthyl linker. On the one hand, it can overwhelm important
steric crowding and enforce unfavorable P → B interaction
thanks to its rigidity. On the other hand, it retains enough
flexibility for the P → B interaction to respond significantly to
3
3
MHz, C6D6) δ = 0.94 (dd, 6H, JH−P = 12.7 Hz, JH−H = 7.0 Hz,
3
3
CH3iPr), 1.15 (dd, 6H, JHP = 13.7 Hz, JH−H = 7.0 Hz, CH3iPr), 2.08
2
3
[(pseudo)sept-d, 2H, JH−P = 2.2 Hz, JH−H = 7.0 Hz, CHiPr], 6.59
(pseudo-t, 2H, J = 7.5 Hz, Harom.), 7.39−7.45 (m, 2H, Harom.), 7.60−
3
4
7.65 (m, 1H, Harom.), 8.24 (dd, 1H, JH−H = 7.4 Hz, JHH = 1.3 Hz,
Harom.); 13C{1H} (125.81 MHz, C6D6) δ = 20.3 (d, JC−P = 20.5 Hz,
2
2
1
CH3iPr), 21.0 (d, JC−P = 14.2 Hz, CH3iPr), 27.3 (d, JC−P = 20.7 Hz,
CHiPr), 125.1 (s, CHarom.), 126.5 (s, CHarom.), 128.9 (d, JC−P = 57.7 Hz,
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Cquat.), 130.3 (d, JC−P = 1.7 Hz, CHarom.), 130.7 (s, CHarom.), 134.5 (d,
JC−P = 1.9 Hz, CHarom.), 136.2 (d, JC−P = 3.9 Hz, Cquat.), 137.1 (d, JC−P
= 35.9 Hz, Cquat.), 138.6 (d, JC−P = 20.0 Hz, Cquat.), 143.8 (s, CHarom.);
31P{1H} (121.49 MHz, C6D6) δ = 7.9.
C
quat.), 144.3 (s, Cquat.), 147.8 (s, Cquat.), 156.5 (d, JC−P = 16.0 Hz,
Cquat.); 11B{1H} (128.4 MHz, 298 K, CDCl3) δ = 16.2; 31P{1H} (162.0
MHz, 298 K, CDCl3) δ = 17.4.
Compound 2-BFlu. 375 μL of n-BuLi (1.60 M in hexanes, 0.60
mmol) were added dropwise to 222 mg (0.60 mmol) of 1-iodo-8-
diisopropylphosphinonaphtalene in diethylether (2.3 mL) at −50 °C,
and the reaction mixture was stirred at this temperature for 30 min.
The solution was then filtered off and the resulting yellow solid was
washed with diethylether (2 × 1 mL) at −50 °C. The solid was then
dissolved in toluene (2.3 mL) and a toluene solution (1.6 mL) of
chloroborafluorene (119.2 mg, 0.6 mmol) was added at −78 °C. After
warming to rt and stirring overnight, the volatiles were removed under
a vacuum; the residue was dissolved in pentane (5 mL) and filtered
through a plug of Celite. After concentration of the solution,
compound 2-BFlu was obtained at −40 °C as colorless crystals
suitable for X-ray diffraction analysis in 52% yield. mp 172 °C. HRMS
(CI-CH4): exact mass calculated for C28H28BP,421.2100;
Compound 2-BCy2. 375 μL of n-BuLi (1.60 M in hexanes, 0.60
mmol) were added dropwise to 222 mg (0.60 mmol) of 1-iodo-8-
diisopropylphosphinonaphtalene in solution in diethylether (2.3 mL)
at −50 °C. After stirring 30 min at this temperature, the solution was
filtered off and the resulting yellow solid was washed with diethylether
(2 × 1 mL) at −50 °C. The solid was then dissolved in 2.3 mL of
toluene, and dicyclohexylchloroborane (1.0 M in hexanes, 0.6 mmol,
600 μL) was added dropwise at −78 °C. The reaction mixture was
stirred at rt overnight. The volatiles were then removed under a
vacuum; the residue was dissolved in pentane (5 mL) and filtrated
through a plug of Celite. Compound 2-BCy2 was obtained as colorless
crystals suitable for X-ray diffraction analysis from a concentrated
solution of pentane −40 °C in 56% yield. mp 176 °C. HRMS m/z (CI,
CH4): exact mass calculated C48H42BP,421.3195; found, 421.3210;
elementary analysis: calculated C,79.99; H,10.07 found C,80.21;
1
found,421.2095. H NMR (300.16 MHz, C6D6) δ = 0.59 (dd, 6H,
3JH−P = 15.5 Hz, 3JH−H = 7.1 Hz, CH3iPr), 0.65 (dd, 6H, 3JHP = 14.4 Hz,
3JHH = 7.1 Hz, CH3iPr), 2.07 [(pseudo)sept-d, 2H, JH−P = 10.3 Hz,
3
1
3
H,10.47. H NMR (300.18 MHz, C6D6) δ = 0.81 (dd, 6H, JH−P
=
3JH−H = 7.1 Hz, CHiPr], 7.09−7.18 (m, 2H, Harom.), 7.25−7.40 (m, 8H,
Harom.), 7.52−7.56 (m, 1H, Harom.), 7.80−7.85 (m, 1H, Harom.), 7.91−
7.97 (m, 2H, Harom.); 13C {1H} (125.81 MHz, C6D6) δ = 17.7 (d, 2JC−P
13.2 Hz, 3JH−H = 7.1 Hz, CH3iPr), 0.95 (dd, 6H, 3JH−P = 13.2 Hz, 3JH−H
= 7.1 Hz, CH3iPr), 1.16−1.61 (m, 12H, HCy), 1.70−1.88 (m, 6H, HCy),
3
1.96−2.20 (m, 4H, HCy), 2.27 [(pseudo)sept-d, 2H, JH−H = 7.1 Hz,
1
2JH−P = 8.3 Hz, CHiPr], 7.14−7.26 (m, 2H, Harom.), 7.49−7.59 (m, 2H,
= 1.7 Hz, CH3iPr), 18.0 (s, CH3iPr), 23.1 (d, JC−P = 26.4 Hz, CHiPr),
120.1 (d, JC−P = 1.0 Hz, CHarom.), 124.0 (d, JC−P = 1.4 Hz, CHarom.),
125.2 (d, JC−P = 7.4 Hz, CHarom.), 126.1(d, JC−P = 2.8 Hz, CHarom.),
127.0 (d, JCP = 2.6 Hz, CHarom.), 128.35 (br, CHarom.), 129.2 (d, JC−P
2.2 Hz, CHarom.), 129.5 (d, JC−P = 14.0 Hz, CHarom.), 129.75 (d, JC−P
51.4 Hz, Cquat.), 131.3 (d, JC−P = 2.2 Hz, CHarom.), 132.1 (d, JC−P = 2.4
Hz, CHarom.), 133.1 (d, JC−P = 9.3 Hz, Cquat.), 146.3 (d, JC−P = 28.3 Hz,
Cquat.), 150.4 (d, JC−P = 5.7 Hz, Cquat.), 155.7 (br, Cquat.), one
quaternary, in α position of the boron atom is not observed; 11B{1H}
(96.3 MHz, CDCl3) δ = −8.5; 31P{1H} (121.49 MHz, CDCl3) δ =
25.1.
3
Harom.), 7.72 (d-mult, 1H, JH−H = 6.1 Hz, Harom.), 7.76 (d-mult, 1H,
3JH−H = 7.8 Hz, Harom.); 13C{1H} (125.81 MHz, C6D6) δ = 18.3 (d,
2JC−P = 0.8 Hz, CH3iPr), 19.1 (s, CH3iPr), 22.6 (d, JC−P = 18.0 Hz,
1
=
=
CHiPr), 28.2 (s, CH2Cy), 29.7 (s, CH2Cy), 30.2 (s, CH2Cy), 32.1 (d, JC−P
= 7.5 Hz, CH2Cy), 33.8 (d, JC−P = 6.1 Hz, CH2Cy), 123.3 (d, JC−P = 1.8
Hz, CHarom.), 124.8 (d, JC−P = 6.7 Hz, CHarom.), 126.5 (s, CHarom.),
127.9 (d, JC−P = 2.4 Hz, CHarom.), 128.7 (d, JC−P = 16.4 Hz, CHarom.),
130.2 (d, JC−P = 45.6 Hz, Cquat.), 130.9 (d, JC−P = 2.1 Hz, CHarom.),
132.7 (d, JC−P = 9.2 Hz, Cquat.), 145.5 (d, JC−P = 29.6 Hz, Cquat.), the
three carbon atoms in α position of the boron atom are not observed;
11B{1H} (128.4 MHz, CDCl3) δ = 0.1; 31P{1H} (121.49 MHz, CDCl3)
δ = 23.4.
Crystallographic Analyses. Crystallographic data were collected
at 193(2) K on a Bruker-AXS Kappa APEXII Quazar diffractometer
(for 2-BCy2 and 2-BFlu) and on a Bruker−AXS CCD 1000
diffractometer (for 2-BMes2), with Mo Kα radiation (λ = 0.71073
Å) using an oil-coated shock-cooled crystal. Phi- and omega-scans
were used. Semiempirical absorption correction was employed.31 The
structures were solved by direct methods (SHELXS-97)32 and refined
using the least-squares method on F2.33 All non-H atoms were refined
with anisotropic displacement parameters. The H atoms were refined
isotropically at calculated positions using a riding model with their
isotropic displacement parameters constrained to be equal to 1.5 times
the equivalent isotropic displacement parameters of their pivot atoms
for terminal sp3 carbon and 1.2 times for all other carbon atoms.
Computational Studies. Calculations were carried out with the
Gaussian 09 program34 at the DFT level of theory using the hybrid
functional B3PW91.35 B3PW91 is Becke’s 3 parameters functional,
with the nonlocal correlation provided by the Perdew 91 expression.
All the atoms have been described with a 6-31G(d,p) double-ζ basis
set.36 Geometry optimizations were carried out without any symmetry
restrictions, the nature of the extrema (minima or transition state) was
verified with analytical frequency calculations. All total energies and
Gibbs free energies have been zero-point energy (ZPE) and
temperature corrected using unscaled density functional frequencies.
Electronic structure of the different complexes was studied using
natural bond orbital analysis (NBO-5 program).37 The NBO orbital
(σBP) obtained from first-order NBO analysis was plotted by using the
molecular graphic program NBOView 1.1.38 The electron density of
the optimized structures was subjected to an atoms in molecules
analysis (QTAIM analysis)39 using AIMAll software.40
Compound 2-BMes2. 235 μL of n-BuLi (2.50 M in hexanes,0.60
mmol) and 158 mg (0.60 mmol) of dimesitylfluoroborane in solution
of toluene (2 mL) were successively added at −50 °C and −78 °C to a
1-iodo-8-diisopropylphosphinonaphtalene solution (222 mg, 0.6
mmol) in toluene (2 mL). After warming to rt, the volatiles were
removed under a vacuum, the residue was dissolved in pentane (2 × 5
mL), and the salts were removed by filtration. After concentration of
the solution at rt, compound 2-BMes2 is obtained as colorless crystals
suitable for X-ray diffraction analysis in 58% yield. mp 176 °C. m/z
1
(EI, 70 eV): 492 [M]+. H NMR (400.1 MHz, CDCl3) δ = 0.45 (dd,
3
3
3H, JH−P = 12.0 Hz, JH−H = 7.2 Hz, CH3i‑Pr), 1.12 (s, 3H, CH3Mes),
1.13 (dd, 3H, 3JH−3P = 12.0 Hz, 3JH−H = 7.2 Hz, CH3i‑Pr), 1.34 (dd, 3H,
3JH−P = 12,0 Hz, JH−H = 7.2 Hz, CH3i‑Pr), 1.36 (dd, 3H, JH−P = 12,0
3
3
Hz, JH−H = 7.2 Hz, CH3i‑Pr), 1.86 (s, 3H, CH3Mes), 2.01 (s, 3H,
CH3Mes), 2.24 (s, 3H, CH3Mes), 2.26 (s, 3H, CH3Mes), 2.33 (s, 3H,
2
3
CH3Mes), 2.46 [(pseudo)sept-d, 1H, JH−P = 14.0 Hz, JH−H = 7.2 Hz,
2
3
CHi‑Pr], 2.70 [(pseudo)sept-d, 1H, JH−P = 14,0 Hz, JH−H = 7.2 Hz,
CHi‑Pr], 6.50 (s, 1H, HMes), 6.79 (s, 1H, HMes), 6.82 (s, 2H, HMes), 7.46
(m, 2H, Harom.), 7.58 (dd, 1H, 3JH−H = 6,6 Hz, 3JH−H = 7.6 Hz, Harom.),
7.75 (dd, 1H, 3JH−H = 7.2 Hz, 4JH−H = 1.9 Hz, Harom.), 7.78 (pseudo-t,
3
3
3
1H, JH−H = 6.6 Hz, JH−P = 6.6 Hz, Harom.), 8.04 (d, 1H, JH−H = 7.6
Hz, Harom.); 13C{1H} (101.6 MHz, 298 K, CDCl3) δ = 18.1 (s,
2
CH3i‑Pr), 19.2 (s, CH3i‑Pr), 20.0 (s, CH3i‑Pr), 21.2 (d, JC−P = 3.0 Hz,
CH3i‑Pr), 21.3 (s, 2C, CH3Mes), 25.8 (s, CH3Mes), 26.0 (d, JC−P = 2.0
Hz, CH3Mes), 26.3 (s, CH3Mes), 26.6 (s, CH3Mes), 26.8 (d, 1JC−P = 16.0
Hz, CHi‑Pr), 30.3 (s, CHi‑Pr), 125.0 (d, 4JC−P = 5.0 Hz, CHNapht), 125.3
(s, CHNapht), 127.9 (d, JC−P = 1.0 Hz, CHNapht), 128.4 (s, CHMes),
128.4 (s, CHMes), 128.9 (s, Cquat.), 129.2 (s, CHNapht), 129.7 (d, JC−P
=
=
=
ASSOCIATED CONTENT
* Supporting Information
3
■
4 Hz, CHMes), 129.8 (s, CHMes), 130.3 (s, CHMes), 131.1 (d, JC−P
S
2
1.0 Hz, CHNapht), 132.9 (d, JC−P = 14.0 Hz, Cquat.), 133.0 (d, JC−P
Synthetic procedures and analytical data including NMR
spectra for 1, 2-BCy2, 2-BMes2, and 2-BFlu; X-ray crystallo-
graphic data for CCDC 923615 (2-BCy2), 923616 (2-BMes2),
15.0 Hz, CHNapht), 135.1 (s, Cquat.), 136.2 (d, JC−P = 4.0 Hz, Cquat.),
140.7 (d, JC−P = 4 Hz, Cquat.), 142.2 (d, JC−P = 10.0 Hz, Cquat.), 142.5
(d, JC−P = 9.0 Hz, Cquat.), 143.9 (d, JC−P = 33 Hz, Cquat.), 144.0 (s,
4718
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Article
(e) Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich, R.;
̈
and 923617 (2-BFlu) (CIF); Cartesian coordinates for the
optimized structures. This material is available free of charge via
the Internet at http://pubs.acs.org.
Erker, G. Angew. Chem., Int. Ed. 2008, 47, 7543−7546.
(9) (a) Bontemps, S.; Bouhadir, G.; Dyer, P. W.; Miqueu, K.;
Bourissou, D. Inorg. Chem. 2007, 46, 5149−5151. (b) Spies, P.;
Frch
̧
lich, R.; Kehr, G.; Erker, G.; Grimme, S. Chem.Eur. J. 2008, 14,
AUTHOR INFORMATION
Corresponding Author
■
333−343. (c) Spies, P.; Kehr, G.; Bergander, K.; Wibbeling, B.;
Frohlich, R.; Erker, G. Dalton Trans. 2009, 1534−1541. (d) Axenov, K.
̈
V.; Mcm
̧
ming, C. M.; Kehr, G.; Frohlich, R.; Erker, G. Chem.Eur. J.
̈
*E-mail: karinne.miqueu@univ-pau.fr (K.M.), dbouriss@
chimie.ups-tlse.fr (D.B.).
2010, 16, 14069−14073. (e) Wiegand, T.; Eckert, H.; Ekkert, O.;
Frohlich, R.; Kehr, G.; Erker, G.; Grimme, S. J. Am. Chem. Soc. 2012,
̈
Present Address
134, 4236−4249.
#S. Bontemps: CNRS, LCC (Laboratoire de Chimie de
Coordination) 205 route de Narbonne, 31077 Toulouse,
(10) Bouhadir, G.; Amgoune, A.; Bourissou, D. Adv. Organomet.
Chem. 2010, 58, 1−107.
France, and Universite
Toulouse, France.
́
de Toulouse, UPS, INPT 31077
(11) Tsurusaki, A.; Sasamori, T.; Wakamiya, A.; Yamaguchi, S.;
Nagura, K.; Irle, S.; Tokitoh, N. Angew. Chem., Int. Ed. 2011, 50,
10940−10943.
Notes
(12) For related 1,8 EB-naphthalene derivatives (with E = heavier
group 15 elements or group 16 elements), see (a) Zao, H.; Gabbaï, F.
P. Nat. Chem. 2010, 2, 984−990. (b) Wade, C. R.; Saber, M. R.;
Gabbaï, F. P. Heteroat. Chem. 2011, 22, 500−505.
(13) (a) Bontemps, S.; Gornitzka, H.; Bouhadir, G.; Miqueu, K.;
Bourissou, D. Angew. Chem., Int. Ed. 2006, 45, 1611−1614.
(b) Bontemps, S.; Bouhadir, G.; Miqueu, K.; Bourissou, D. J. Am.
Chem. Soc. 2006, 128, 12056−12057. (c) Sircoglou, M.; Bontemps, S.;
Mercy, M.; Saffon, N.; Takahashi, M.; Bouhadir, G.; Maron, L.;
Bourissou, D. Angew. Chem., Int. Ed. 2007, 46, 8583−8586.
(d) Bontemps, S.; Bouhadir, G.; Gu, W.; Mercy, M.; Chen, C.-H.;
Foxman, B. M.; Maron, L.; Ozerov, O. V.; Bourissou, D. Angew. Chem.,
Int. Ed. 2008, 47, 1481−1484.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The Centre National de la Recherche Scientifique (CNRS), the
Universite
́
Paul Sabatier (UPS) and the Agence Nationale de la
Recherche (ANR-10-BLAN-070901) are acknowledged for
financial support of this work. The theoretical work was
granted access to the HPC resources of IDRIS under allocation
2013 (i2013080045) made by GENCI (“Grand Equipement
National de Calcul Intensif”). We thank Dr. Johannes Guenther
for assistance in the preparation of compound 1.
(14) Diarylphosphines related to 1 have been involved as synthetic
intermediates in the preparation of naphthalene-bridged phosphine-
sulfoximine ligands. See Lu, S.-M.; Bolm, C. Adv. Synth. Catal. 2008,
350, 1101−1105.
(15) Bontemps, S.; Bouhadir, G.; Apperley, D. C.; Dyer, P. W.;
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(17) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.;
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(19) Inspection of the structural data available for perisubstituted PB
compounds reveals that in-plane distortions are systematically larger at
boron than at phosphorus. See refs 11 and 18.
(20) Only fluoride and cyanide are able to bind intermolecularly to
aryl dimesityl boranes, and that makes the BMes2 group an ideal
acceptor moiety in anion sensing and optoelectronics. See:
(a) Entwistle, C. D.; Marder, T. B. Chem. Mater. 2004, 16, 4574−
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moieties and involve intramolecular interactions: (a) Bebbington, M.
W. P.; Bontemps, S.; Bouhadir, G.; Bourissou, D. Angew. Chem., Int.
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