Metal-free dihydrogen activation chemistry: Structural and dynamic features of intramolecular P/B pairs

Article abstract of DOI:10.1039/b815832k

Hydroboration of allyl(dimesityl)phosphane with HB(C₆F ₅)₂ gives the intramolecular five-membered P-B Lewis pair 7, that was characterized by X-ray diffraction. Similarly, HB(C ₆F₅)₂ addition to the substrates (mesityl) ₂P-CRCH₂ (R = CH₃, Ph) yield the corresponding (mesityl)₂P(μ-CHRCH₂)B(C₆F₅) ₂ products 9a (R = CH₃) and 9b (R = Ph) that show a weak intramolecular P...B interaction. The activation energy of the (reversible) P...B cleavage of these substrates was determined by dynamic ¹⁹F NMR spectroscopy (9a: ΔG^≠_inv (280 K) = 11.7 ± 0.4 kcal mol^-1). Compounds 9b and 9c show similar values. Compound 9c was prepared by HB(C₆F₅)₂ addition to (mesityl)₂P-CHCHSiMe₃. Compound 9a reacts rapidly with dihydrogen (2.5 bar) at room temperature in pentane to give the zwitterionic H₂-activation product (mesityl)₂PH ⁺(μ-CHMeCH₂)BH^-(C₆F ₅)₂ (11). The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b815832k

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PAPER
www.rsc.org/dalton | Dalton Transactions
Metal-free dihydrogen activation chemistry: structural and dynamic features
of intramolecular P/B pairs†‡
Patrick Spies, Gerald Kehr, Klaus Bergander, Birgit Wibbeling, Roland Fro¨hlich and Gerhard Erker*
Received 10th September 2008, Accepted 7th November 2008
First published as an Advance Article on the web 20th January 2009
DOI: 10.1039/b815832k
Hydroboration of allyl(dimesityl)phosphane with HB(C6F5)2 gives the intramolecular five-membered
P–B Lewis pair 7, that was characterized by X-ray diffraction. Similarly, HB(C6F5)2 addition to the
=
substrates (mesityl)2P–CR CH2 (R = CH3, Ph) yield the corresponding (mesityl)2P(m-
CHRCH2)B(C6F5)2 products 9a (R = CH3) and 9b (R = Ph) that show a weak intramolecular P ◊ ◊ ◊ B
interaction. The activation energy of the (reversible) P ◊ ◊ ◊ B cleavage of these substrates was determined
by dynamic 19F NMR spectroscopy (9a: DGπ (280 K) = 11.7 0.4 kcal mol-1). Compounds 9b and 9c
inv
=
show similar values. Compound 9c was prepared by HB(C6F5)2 addition to (mesityl)2P–CH CHSiMe3.
Compound 9a reacts rapidly with dihydrogen (2.5 bar) at room temperature in pentane to give the
zwitterionic H2-activation product (mesityl)2PH+(m-CHMeCH2)BH-(C6F5)2 (11).
revealed some interesting structural features of 16 such as a
Introduction
p–p stacking interaction between a mesityl group at phosphorus
and a parallel pentafluorophenyl substituent at boron,10 which
actually contributes a substantial fraction of the total phosphane–
borane interaction energy of this intramolecular Lewis pair.
S. Grimme’s DFT calculation6 has also revealed that this Lewis
pair is easily cleaved: two conformationally different open local
isomeric minima (3) were found to be both just ca. 7 kcal mol-1 in
energy above the global minimum (1).
In this study, we have prepared a close structural model of 1 with
regard to thep–p stacking interaction of the aryl substituents along
the P ◊ ◊ ◊ B vector.10 In addition, we have gained some experimental
evidence for the rapid endothermic 1 ꢀ 3 equilibration by
preparing suitably substituted derivatives of 1 and investigating
their dynamic features.
Following the pioneering work by Stephan et al.1 an increasing
number of metal-free heterolytic hydrogen splitting systems based
on “frustrated”2 (or “antagonistic”)3 Lewis pairs are beginning
to appear in the literature.4,5 We have contributed a remarkable
early example.6 The system 1 contains a weakly intramolecularly
interacting phosphane Lewis base/borane Lewis acid pair that
splits dihydrogen rapidly at room temperature and low H2
pressure to yield the ethylene-linked phosphonium–hydridoborate
zwitterion 2. The betaine 2 transfers (Scheme 1) the activated
H+/H- pair under very mild conditions to a variety of unsaturated
compounds. The 1–2 pair serves as an efficient hydrogenation
catalyst7 for a variety of substrates, such as enamines, bulky imines
and (less efficiently) silyl enol ethers.8,9
Results and discussion
Hydroboration of allyl(dimesityl)phosphane
The reaction of chlorodimesitylphosphane (4)11 with allylmag-
nesium bromide in THF gave allyldimesitylphosphane (5) in
60% yield. This was then treated with an equimolar amount of
HB(C6F5)2 (6).12 A clean regioselective hydroboration reaction
took place at ambient conditions in pentane. We isolated the
trimethylene-bridged phosphane/borane product (7) in ca. 70%
yield as a white solid (Scheme 2).
Scheme 1
So far the intramolecular Lewis pair 1 has not been structurally
characterized by X-ray diffraction due to the lack of suitable
single crystals. However, a state of the art DFT calculation has
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40,
48149 Mu¨nster, Germany. E-mail: erker@uni-muenster.de; Fax: +49 251
83 36503
† Electronic supplementary information (ESI) available: Lineshape anal-
ysis of 9a and error calculations of kinetic parameters. CCDC reference
number 701817 for compound 7. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/b815832k
‡ Dedicated to Professor Hans-Joachim Galla on the occasion of his 60th
birthday.
Scheme 2
Compound 7 features three 1H NMR CH2 multiplets at d 2.73,
1.77 and 1.72 ppm with corresponding 13C NMR signals at d 27.0
(1JPC = 39.8 Hz), 24.6 (broad) and 21.9 ppm (2JPC = 12.7 Hz). The
31P NMR signal is at d 20.8 ppm and the 11B NMR resonance was
located at d -2.7 ppm (in [D6]benzene). Compound 7 features a
1534 | Dalton Trans., 2009, 1534–1541
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set of 19F NMR signals at d -127.4 (o), -158.4 (p) and -164.4 ppm
(m-F of C6F5). The Dd (m-F)–(p-F) separation is consistent with a
tetracoordinate boron situation, but we note that it is slightly larger
at Dd = 6 ppm than typically observed of classical RB(C6F5)3
borate examples.13
The angles inside the five-membered heterocycle are small
(e.g. C1–P1–B1 93.8(3)◦, C3–B1–P1 91.5(4)◦). The P1–B1 bond
˚
length is 2.092(7) A. This is slightly longer as compared to the
˚
related reference compounds [Ph2P(CH2)3B(C6F5)2] (2.060(2) A)
˚
or [Ph2P(CH2)4B(C6F5)2] (2.021(3) A) that we had previously
Compound 7 was characterized by an X-ray crystal structure
analysis (single crystals from ether). In the crystal, the system 7
exhibits a cyclic framework that consists of three carbon atoms,
the phosphorus and the boron center. These make up a core of
the molecule that features a slightly distorted cyclopentane-like
envelope conformation (see Fig. 2).14 The carbon atoms C1, C2,
C3 and the phosphorus atom P1 are arranged almost co-planar
(dihedral angle -11.3(6)◦). The boron atom marks the “tip” of
the envelope structure (dihedral angles C2–C1–P1–B1 -18.2(5)◦,
C1–P1–B1–C3 39.5(4)◦). In this characteristic conformation the
C31–C36 C6F5 group at boron and the C11–C16 mesityl sub-
stituent at phosphorus come into an arrangement (see Fig. 1) that
indicates some potential◦p–p stacking interaction (dihedral angle
described.14,15
Hydroboration of alkenyl(dimesityl)phosphanes
Three differently substituted alkenyl(dimesityl)phosphanes were
prepared by the reactions of Mes2PCl (4) with the respective
alkenyl Grignard or alkenyl lithium reagents. Compound 8a was
thus obtained in 49% yield from the reaction of the substrate 4 with
2-propenylmagnesiumbromide. a-Lithiostyrene was generated by
treatment of a-bromostyrene with n-butyl lithium. Its subsequent
reaction with 4 then gave the alkenylphosphane 8b (21% isolated).
Eventually, we treated 4 with E-(2-TMS-vinyl)MgBr and isolated
the corresponding trimethylsilyl-substituted alkenyl phosphane
product 8c in 26% yield after chromatographic purification.
Each of the three alkenylphosphanes (8) was then subjected
to the hydroboration reaction with HB(C6F5)2 (6) in pentane at
ambient reaction conditions. The corresponding alkylene-bridged
phosphane/borane products 9a–9c were isolated as off-white
solids in 64–96% yield (Scheme 3).
˚
C11–P1–B1–C31 44.5(5) , C16 ◊ ◊ ◊ C36 separation 3.213(9) A).
Fig. 1 A view of the molecular geometry of compound 7 (hydro◦gen atoms
˚
omitted for clarity): selected bond lengths (A) and angles ( ): P1–B1
Scheme 3
2.092(7), P1–C1 1.827(6), P1–C11 1.848(7), P1–C21 1.856(6), C1–C2
1.563(8), C2–C3 1.541(9), C3–B1 1.615(9), B1–C31 1.641(10), B1–C41
1.651(9); B1–P1–C1 93.8(3), B1–P1–C11 106.0(3), B1–P1–C21 131.8(3),
C1–P1–C11 113.6(3), C1–P1–C21 103.4(3), C11–P1–C21 107.5(3),
P1–C1–C2 107.5(4), C1–C2–C3 110.1(5), C2–C3–B1 108.9(5), C3–B1–P1
91.5(4), C3–B1–C31 117.7(5), C3–B1–C41 105.8(5), C31–B1–C41
112.8(5).
The products 9 were characterized by C, H elemental analysis
and by NMR spectroscopy. In [D6]benzene at 298K, compound
9a features a very typical set of NMR signals of the central
P–CH(CH3)CH2 unit. It shows a 1H NMR dd of the methyl
substituent at carbon atom C1 at d 0.87 ppm (3JPH = 15.5 Hz,
3JHH = 6.8 Hz, 3H). The bridge CH2 unit features diastereotopic
hydrogens (d 2.96 and 1.69 ppm), one of which shows a very large
3JPH = 106.9 Hz coupling constant.16 The 31P NMR resonance of
9a appears at d 33.2 ppm and the 11B NMR signal is observed
at d 3.2 ppm. The mesityl substituents at P are diastereotopic.
1
We monitor two mesityl m-CH H NMR signals at d 6.56 and
6.35 ppm, each of 2H intensity.
The 19F NMR spectrum of compound 9a is strongly temperature
dependent. In [D8]toluene at 323K, we observe a set of only three
signals at d -128.8 (br. 4F, o), -157.2 (2F, p) and -163.5 ppm
(4F, m-C6F5). Upon lowering the temperature we monitor a series
of decoalescing signals indicating the presence of a combination
of three dynamic processes that become subsequently frozen out
Fig. 2 A projection of the envelope-shaped core of compound 7.
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on the NMR time scale (19F, 564 MHz). Upon cooling, the single
(averaged) p-C6F5 resonance rapidly broadens and decoalesces to
a 1 : 1 intensity pair (Tcoal = 280 K) with a separation of Dn =
1015 Hz at 233 K. This feature is probably due to the reversible
opening process of the P–B linkage in 9a, resulting in a symmetry
equivalence of the pair of C6F5 substituents at the trigonally planar
coordinated boron center at the stage of the alleged equilibrating
acyclic isomeric intermediate.
Table 1 Gibbs activation energies of the P–B cleavage of the complexes 9
a
(DGπinv) and energy barriers of the B–C6F5 rotational processes (DGπ
)
rot
Compound
9a (1-CH3)
9b (1-Ph)
9c (2-SiMe3)
DGπ (T/K)
11.7 (280)
11.2 (295)
9.1 (238)
12.6 (303)
11.9 (313)
9.7 (253)
11.8 (298)
9.6 (248)
9.5 (248)
inv
DGπ (T/K)
rot1
DGπ (T/K)
rot2
a DGπ values 0.4 kcal mol-1, Tcoal. in K, for details see the ESI†.
The analogous process can be followed by the line shape analysis
of the o- and m-C6F5 19F NMR resonances. The decoalescence
behaviour of the o-C6F5 signal at d -128.8 ppm is complicated
by the overlapping of the freezing of two different dynamic
processes within the same temperature range. Consequently, the
d -128.8 ppm signal splits into three signals upon lowering
the temperature to 253 K, namely a 1 : 1 intensity pair at d
-123.7 and -137.0 ppm (Dn = 7557 Hz) and a broad singlet at
d -127.7 ppm of 2F relative intensity (see Fig. 3). This latter
o-C6F5 19F NMR resonance splits into another 1 : 1 pair of
resonances (d -123.2 and -132.0 ppm Dn = 5076 Hz) upon
further lowering the monitoring temperature. The pair of m-C6F5
resonances analogously decoalesces upon further lowering the
temperature eventually to a tight group of four resonances, each
of 1F relative intensity.
For the B(C6F5)2 pair we have found two rather different Gibbs
activation energy barriers of DGπ
(295 K) = 11.2 0.4 kcal
rot 1
mol-1 and DGπ (238 K) = 9.1 0.4 kcal mol-1.
rot 2
Scheme 4
Compound 9b features similar NMR data [31P: d 40.3 ppm; 11B:
d 2.5 ppm; 1H: d (CH2) = 3.19 ppm (3JPH = 110.1 Hz), 2.30 ppm].
The 19F NMR spectrum is again dynamic. From the decoalescence
of the respective o- and p-C6F5 resonances we have calculated the
set of three Gibbs activation energies of 9b, which were in a similar
range as found for 9a (see Table 1 and Fig. 4).
Fig. 4 Dynamic 19F NMR spectra (564 MHz) of compound 9b (in
[D8]toluene).
Fig. 3 Temperature-dependent dynamic 19F NMR spectra of compound
9a (in [D8]toluene, 564 MHz).
Compound 9c features the SiMe3 substituent at the b-carbon
atom of the bridge, adjacent to the boron center. This gives rise
1
We assume that the decoalescence process of the p-C6F5
signal corresponds to the ring opening process of the four-
membered heterocyclic framework structure of 9a by cleavage of
the phosphorus boron linkage (9 ꢀ 10) (see Scheme 4). From the
lineshape analysis17 (for details see the ESI†) we have calculated a
Gibbs activation energy of DGπinv (280 K) = 11.7 0.4 kcal mol-1.
For the temperature range between 333–233 K this led to values
of DHπ = 15.9 kcal mol-1 and DSπ = 15.0 cal Grd.-1 mol-1. The
additional decoalescence processes that we have observed are likely
to correspond to freezing the rotation of the B–C6F5 linkages.18
to a H NMR trimethylsilyl singlet at d -0.14 ppm. Again, the
almost temperature invariant 13C NMR spectrum features signals
of a pair of diastereotopic mesityl substituents at phosphorus [d
22.7/22.6 (o-CH3) and d 20.7/20.3 ppm (p-CH3)]. Compound
9c also shows temperature dependent dynamic 19F NMR spectra
(see Fig. 5). From the decoalescence of the p-F resonance of the
B(C6F5)2 unit we have obtained the barrier of the P–B dissociation
of compound 9c and the analysis of the complex decoalescence of
the corresponding o-F resonance gave us the barrier of rotation
about the B–C6F5 vectors in 9c (see Table 1 and Fig. 5).
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Fig. 6 1H NMR spectrum of the zwitterion 11 (in [D8]THF).
Conclusions
We recently described the metal-free hydrogen activation system
1, which probably is one of the most active system of its kind
at present.6,7 The 1–2 system is a very active catalyst for the
hydrogenation of enamines and of bulky imines under very mild
conditions and it transfers the H+/H- pair catalytically to other
acceptors. The state of the art DFT analysis6,21 of 1 has revealed
its characteristic bonding features—it is described as an almost
planar four-membered heterocycle containing a rather weak
P ◊ ◊ ◊ B linkage. One pair of mesityl and C6F5 substituents at P/B,
arranged close to parallel to each other at the framework, is in an
orientation to support the weak P ◊ ◊ ◊ B contact by an energetically
favourable p–p-stacking interaction between an electron-rich and
an electron-poor arene system.
The calculation has also revealed a potential equilibration of the
cyclic system 1 with an open isomer (3). Two almost isoenergetic
local minima of open isomers were found in the calculation,
both being ca. 7 kcal mol-1 higher in energy than the global
minimum structure 1. The calculated isomers of 3 only differed in
their conformational arrangement of the bulky substituents at the
m-C2-bridge (idealized: gauche and anti-periplanar). The present
experimental study was aimed at confirming the facile ring opening
of the P ◊ ◊ ◊ B linkage in the system 1 or suitable derivatives of
1, respectively. The attachment of a single substituent at the
C2-bridge has introduced an element of central chirality into
systems 9. In the cyclic, closed form the presence of a single
element of chirality makes the hydrogen atoms at the adjacent CH2
group diastereotopic as well as the pairs of mesityls at phosphorus
and the C6F5 groups at boron. Cleavage of the P ◊ ◊ ◊ B linkage (to
generate the not directly observable isomers 10) would, of course,
leave the CH2 hydrogens diastereotopic. This process would also
leave the mesityl groups at P diastereotopic since the resulting
tricoordinate phosphane in the alleged structure of 10 remains a
stereogenic center, i.e. it features a persistent non-planar coordina-
tion geometry at the heavy group 15 element. Consequently, the 1H
NMR mesityl features of the systems 9 remain almost temperature
invariant in the high temperature regime indicating the presence
of a pair of persistently diastereotopic mesityl substituents in the
respective temperature range.
Fig. 5 Dynamic 19F NMR spectra (564 MHz) of compound 9c (in
[D8]toluene).
Reaction with dihydrogen
We did not observe a reaction of the compounds 7, 9b and
9c with dihydrogen under our typical reaction conditions (i.e.
ambient temperature in pentane or toluene at 2.5 bar or 60
bar H2 pressure). In contrast, the a-methyl-substituted derivative
9a splits the dihydrogen molecule heterolytically19 under mild
reaction conditions. Stirring of a solution of 9a, in situ gener-
ated in pentane, at room temperature under an atmosphere of
dihydrogen (2.5 bar) produced a white precipitate of the zwit-
terionic phosphonium/hydridoborate product 11 (49% isolated)
(Scheme 5).
Scheme 5
Product 11 contains a prochiral phosphorus and prochiral
boron center in addition to the chiral a-carbon center in the
bridge. Consequently, we observed the NMR signals of a pair
of diastereotopic mesityl groups at phosphorus (e.g. featuring a
1
1 : 1 pair of H NMR m-resonances at d 7.12 and 7.10 ppm)
and of a pair of diastereotopic C6F5 substituents at boron [e.g.
showing marginally separated 19F NMR resonances of the o-F (d
-132.8 ppm, 4F), p-F (d -165.6/-165.9 ppm, 1F each) and m-F
1
(d -167.8/-168.1 ppm, 2F each) pairs. The H NMR spectrum
of compound 11 features a PH resonance at d 7.66 ppm (dd,
1H). It shows a very typical large PH coupling constant of 1JPH
=
475.8 Hz16 and a smaller JHH of 10.9 Hz. We observed the H
NMR BH resonance at d 3.01 ppm (1 : 1 : 1 : 1 q, broadened
by beginning relaxation).20 The corresponding 31P NMR signal
of 11 is found at d 2.3 ppm and the 11B NMR resonance at d
-21.7 ppm. The protons of the CH(CH3)–CH2 bridge give rise to
a broad ABX-type 1H NMR pattern with a sharp dd resonance of
the methyl group at d 1.42 ppm (3JPH = 23.7 Hz, 3JHH = 7.1 Hz)
(for further details see Fig. 6 and the Experimental).
3
1
The situation at boron is distinctively different. Cleaving
the P–B linkage changes the coordination geometry at boron
from pseudotetrahedral to planar-tricoordinate. The loss of the
prochiral character of the R–B(C6F5)2 moiety makes the pair of
C6F5 groups symmetry equivalent. This consequently results in
a coalescence of the corresponding pairs of 19F NMR signals in
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the high temperature regime. In all three examples investigated
(i.e. 9a–9c) we have observed the respective pairs of p-F 19F
NMR resonances to coalesce to a single averaged signal at high
temperature. From this coalescence behaviour of the p-F NMR
signals we have calculated the activation energies of the P ◊ ◊ ◊ B
150.8 MHz; 31P = 242.8 MHz; 19F = 564.2 MHz). X-Ray crystal
structure determination, data set was collected with Nonius Kap-
paCCD diffractometer, equipped with a rotating anode generator.
Programs used: data collection COLLECT (Nonius B.V., 1998),
data reduction Denzo-SMN (Z. Otwinowski and W. Minor,
Methods in Enzymol., 1997, 276, 307–326), absorption correction
SORTAV (R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51,
33–37; R. H. Blessing, J. Appl. Crystallogr. 1997, 30, 421–426) and
Denzo (Z. Otwinowski, D. Borek, W. Majewski and W. Minor,
Acta Crystallogr., Sect. A, 2003, 59, 228–234), structure solution
SHELXS-97 (G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990,
46, 467–473), structure refinement SHELXL-97 (G. M. Sheldrick,
Universita¨t Go¨ttingen, 1997), graphics SCHAKAL (E. Keller,
Universita¨t Freiburg, 1997).
dissociation process (see Table 1) [e.g. 9a: DGπ (280 K) =
inv
11.7 0.4 kcal mol-1]. The obtained positive activation entropy
[DSπinv = 15.0 cal Grd.-1 mol] of this example is consistent with the
observation of a bond breaking reaction by this NMR experiment.
The behaviour of the o- and m-F NMR signals is more
complicated. Coincidence of the P ◊ ◊ ◊ B bond breaking process
(leading to C6F5 inversion at boron) with freezing the B–C6F5
rotation results in more complicated spectra. Thus, for compound
9a, the energy barrier of P ◊ ◊ ◊ B dissociation (DGπinv) is almost the
same as the rotational energy barrier of one of the B–C6F5 units
(DGπrot 1). The barrier of rotation of the remaining B–C6F5 moiety
(DGπrot 2) is lower. So consequently, if we increase the temperature
in the monitoring of the o-19F NMR signals from 233 K we first
observed the coalescence of the d -123.0/-132.0 ppm pair of
General procedure for the preparation of compounds 5, 8a and 8c.
Chlorodimesitylphosphane (4) (1 equiv.) was dissolved in THF
(50 mL) and the respective Grignard reagent was added carefully
at room temperature. After stirring the solution for one hour at
ambient temperature, the solvent was removed in vacuo and the
obtained residue was extracted with pentane. The crude product
was purified by chromatography after removing pentane.
o-F NMR resonances [DGπ
(238 K) ª 9.1 kcal mol-1). Above
rot 2
ca. 263 K we begin to observe the coalescence of the second o-F
pair (d -123.4/-136.8 ppm), but this process [DGπ
(295 K) ª
rot 1
11.2 kcal mol-1] overlaps with the (C6F5)2B “inversion” process,
originating from the reversible P ◊ ◊ ◊ B bond cleavage, which has
a very similar activation energy barrier (see above). Complex 9b
(R = a-phenyl) shows an analogous behaviour and consequently
features very similar temperature dependent 19F NMR spectra.
Complex 9c (R = b-SiMe3) features two almost identical B–C6F5
rotational barriers and a markedly higher activation energy of
P ◊ ◊ ◊ B dissociation.
The observed kinetic features of all three compounds 9 fit
very well with the (calculated) thermodynamic properties of 1
with regard to their thermally induced ring opening process and
equilibration with the respective (not directly observed) acyclic
isomers (3, 10). It is remarkable that all three examples studied
here, namely 9a, 9b and 9c, show similar activation barriers of
ring opening. Nevertheless, only the compound 9a was found to
be an active system for heterolytic H2-splitting under our typical
reaction conditions. This indicates that P ◊ ◊ ◊ B bond cleavage seems
not to be a limiting factor, at least not in the systems 1 and 9, for H2-
activation, however, steric interactions may play a significant role,
as the results from our investigation of this series of compounds
suggest.
Compound 5. The reaction of chlorodimesitylphosphane (4)
(5.00 g, 16.4 mmol) and allylmagnesium bromide (1.7 M solu-
tion in THF) yielded after chromatography (silicagel; CH2Cl2–
cyclohexane 3 : 10, Rf = 0.26) the product as a colourless oil
(3.03 g, 60%). mp 59◦C. ESI+MS (m/z for C21H28P+): calcd:
311.1923, found: 311.1926. 1H-NMR (400 MHz, 300 K, benzene-
4
d6) d/ppm: 6.67 (4H, m, JPH = 2.3 Hz, m-Mes), 5.67 (1H, m,
2
P
=
=
CH ), 4.86 (2H, m, CH2), 3.24 (2H, m, JPH = 7.5 Hz, CH2),
2.30 (12H, s, o-CH3Mes), 2.07 (6H, s, p-CH3Mes). 13C{ H}-NMR
1
(101 MHz, 300 K, benzene-d6) d/ppm: 142.0 (d, 2JPC = 13.5 Hz,
o-Mes), 137.5 (p-Mes), 134.5 (d, 2JPC = 11.4 Hz, CH ), 133.6 (d,
=
1JPC = 24.7 Hz, i-Mes), 130.3 (d, JPC = 2.6 Hz, m-Mes), 117.1
3
3
1
=
(d, JPC = 11.5 Hz, CH2), 33.6 (d, JPC = 17.8 Hz, CH2), 23.4
(d, JPC = 13.2 Hz, o-CH3Mes), 20.9 (p-CH3Mes). 31P{ H}-NMR
3
1
(162 MHz, 298 K, benzene-d6) d/ppm: -23.4 (n1/2 = 3 Hz).
Compound 8a. The reaction of chlorodimesitylphosphane (4)
(5.60 g, 18.4 mmol) and (2-propenyl)magnesium bromide (0.5 M
solution in THF) (37.0 mL, 16.0 mmol) after chromatography
(silicagel; CH2Cl2–cyclohexane 2 : 10) yielded the product as a
colourless oil (2.81 g, 9.01 mmol, 49%). mp 66◦C. Anal. calcd
for C21H27P (310.41 g mol-1), C 81.25, H 8.77, found: C 80.99,
1
H 8.78. H-NMR (400 MHz, 300 K, benzene-d6) d/ppm: 6.73
4
3
(4H, dm, JPH = 2.4 Hz, m-Mes), 5.29 (1H, dm, JPH,trans
=
Experimental
3
=
=
18.4 Hz, CH2(trans)), 5.12 (1H, JPH,cis = 7.6 Hz, CH2(cis)), 2.42
3
(12H, s, o-CH3Mes), 2.08 (6H, s, p-CH3Mes), 2.04 (3H, dm, JPH
=
General
12.4 Hz, CH3). 13C{ H}-NMR (101 MHz, 300 K, benzene-d6)
1
All reactions involving air or moisture-sensitive compounds were
carried out under an inert gas using Schlenk-type glassware or in
a glovebox. Solvents were dried and distilled prior to use. Unless
otherwise noted, starting materials were prepared according to
literature procedures. Commercially available starting compounds
were used without further purification. The following instruments
were used for physical characterisation of the compounds: melting
points, DSC 2010 TA-instruments; elemental analyses, Foss–
Heraeus CHNO-Rapid; NMR, Bruker ARX 300 (1H = 300 MHz;
13C = 75 MHz, 31P = 121.5 MHz; 19F = 282.4 MHz), Varian
UNITY plus NMR spectrometer (1H = 599.9 MHz; 13C =
2
1
d/ppm: 143.4 (d, JPC = 15.6, o-Mes), 143.4 (d, JPC = 18.0 Hz,
1
P
=
i-Mes), 138.2 (p-Mes), 130.3 (d, JPC = 18.3 Hz, C ), 130.3 (d,
JPC = 3.9 Hz, m-Mes), 120.8 (d, 2JPC = 10.6 Hz, CH2), 23.9 (d,
3
=
2JPC = 34.8 Hz, CH3), 22.5 (d, 3JPC = 15.7 Hz, o-CH3Mes), 20.9 (p-
CH3Mes). 31P{ H}-NMR (162 MHz, 298 K, benzene-d6) d/ppm:
1
-17.4 (n1/2 = 5 Hz).
Compound 8c. Trans-[2-(trimethylsilyl)vinyl]magnesium bro-
mide solution in THF (0.5 M) was freshly prepared by addition
of trans-[2-(trimethylsilyl)vinyl]bromide (5.80 g, 32.4 mmol)–THF
(20 mL) solution to a suspension of magnesium turnings (780 mg,
1538 | Dalton Trans., 2009, 1534–1541
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©

View Article Online
32.1 mmol) in THF (50 mL). Subsequently, the reaction of
chlorodimesitylphosphane (4) (5.10 g, 16.7 mmol) with trans-[2-
(trimethylsilyl)vinyl]-magnesium bromide solution (0.5 M in THF,
34.0 mL, 16.7 mmol) after chromatography (silicagel; CH2Cl2–
cyclohexane 3 : 10, Rf = 0.55) gave the product as a white solid
(1.61 g, 4.34 mmol, 26%). mp 75 ◦C. Anal. calcd for C23H33PSi
(368.57 g mol-1) C 74.95, H 9.02, found: C 74.79, H 9.01.
1H-NMR (400 MHz, 300 K, benzene-d6) d/ppm: 7.42 (1H, dd,
(o-Mes), 141.0 (p-Mes), 139.4 (dm, 1JFC = 248 Hz, p-C6F5), 137.3
1
(dm, JFC = 244 Hz, C6F5), 131.2 (m-Mes), 120.8 (br., i-C6F5),
1
B
n.o. (i-Mes), 27.0 (d, JPC = 39.8 Hz, PCH2), 24.6 (br., CH2 ),
2
23.3 (o-CH3Mes), 21.9 (d, JPC = 12.7 Hz, CH2), 20.4 (p-CH3Mes).
31P{1H}-NMR (122 MHz, 300 K, benzene-d6) d/ppm: 20.8 (n1/2
=
40 Hz). 19F-NMR (282 MHz, 300 K, benzene-d6) d/ppm: -127.4
(br., 4F, o-C6F5), -158.4 (2F, p-C6F5), -164.4 (br., 4F, m-C6F5).
1
11B{ H}-NMR (96 MHz, 300 K, benzene-d6) d/ppm: -2.7 (n1/2
=
2
P
4
JPH = 34.3 Hz, 3JHH = 19.8 Hz, CH ), 6.71 (4H, d, JPH = 2.7 Hz,
400 Hz).
=
m-Mes), 6.14 (1H, dd, 3JHH = 19.8 Hz, 3JPH = 15.8 Hz, CHTMS),
Crystal data for C33H28BF10P: M = 656.33 g mol-1, monoclinic,
space group P21/c (no. 14), a = 12.0881(5), b = 10.3454(5),
=
2.40 (12H, s, o-CH3Mes), 2.06 (6H, s, p-CH3Mes), 0.00 (9H, s, 2JSiH
=
◦
1
3
6.8 Hz, (CH3)3Si). 13C{ H}-NMR (101 MHz, 300 K, benzene-d6)
c = 24.1019(12) A, b = 101.884(3) , V = 2949.5(2) A , Dc =
˚
˚
P
2
-3
-1
d/ppm: 145.5 (d, 1JPC = 24.2 Hz, CH ), 142.8 (d, JPC = 14.4 Hz,
1.478 g cm , m = 1.612 mm , Z = 4, l = 1.54178 A, T = 223(2)
˚
=
2
-1
o-Mes), 138.1 (p-Mes), 137.1 (d, JPC = 4.5 Hz, CHTMS), 131.2
K, 20 597 reflections collected ( h, k, l), [(sinq)/l] = 0.60 A ,
˚
=
(d, 1JPC = 17.3 Hz, i-Mes), 130.3 (d, 3JPC = 3.4 Hz, m-Mes), 23.3
5064 independent (Rint = 0.062) and 2801 observed reflections [I ≥
2s(I)], 412 refined parameters, R = 0.084, wR2 = 0.228.
3
4
(d, JPC = 14.0 Hz, o-CH3Mes), 20.9 (p-CH3Mes), -1.53 (d, JPC
=
1.5 Hz, JSiC = 52.2 Hz, (CH3)3Si). 31P{ H}-NMR (162 MHz,
1
1
298 K, benzene-d6) d/ppm: -16.1 (n1/2 = 2 Hz).
Compound 9a. The reaction of dimesityl(2-propenyl)-
phosphane (8a) (70.0 mg, 0.23 mmol) and HB(C6F5)2 (6) (78.0 mg,
0.23 mmol) yielded 9a (96.0 mg, 0.15 mmol, 64%) as a yellow solid.
mp 160 ◦C (decomp.). Anal. calcd for C33H28BF10P (656.34 g mol-1)
Preparation of compound 8b. n-Butyllithium (1.6 M in hexane)
◦
was added to a pre-cooled solution (-78 C) of a-bromostyrene
(3.90 g, 2.90 mL, 21.2 mmol) in THF (80 mL). After stirring
the reaction mixture for 30 min at -78 ◦C, a solution of
chlorodimesitylphosphane (4) (6.49 g, 21.2 mmol) in THF (20 mL)
was added. Stirring was continued overnight. Then the solvent
was removed, the obtained residue was extracted with pentane
(200 mL) and after removing pentane in vacuo the crude product
was purified by chromatography (silicagel; CH2Cl2–cyclohexane
3 : 10, Rf = 0.66). Compound 8b was obtained as a colourless
1
C 60.39, H 4.30, found: C 59.37, H 4.43. H-NMR (600 MHz,
298 K, benzene-d6) d/ppm: 6.56 (2H, br. s, m-Mes), 6.35 (2H, br. s,
2
m-Mes¢), 3.82 (1H, oct, 3JHH(anti) = 13.5 Hz, 3JHH(syn) ª JPH = 8.2 Hz,
3
2
3JHH(Me) = 6.8 Hz, CH), 2.96 (1H, ddd, JPH = 106.9 Hz, JHH
=
13.5 Hz, 3JHH(syn) = 8.3 Hz, BCHanti), 1.96, 1.91 (br., s, CH3Mes), 1.69
2
3
2
B
(1H, td, JHH ª JHH(anti) = 13.5 Hz, JPH = 9.7 Hz, CHsyn), 0.87
(3H, dd, 3JPH = 15.5 Hz, 3JHH = 6.8 Hz, CH3) [coupling constants
from 1H{ H} and 1H{ P} decoupling NMR experiments and
1
31
◦
oil (1.65 g, 4.43 mmol, 21%). mp 98 C. Anal. calcd for C26H29P
simulation of the spin system]. 13C{ H}-NMR (151 MHz, 298 K,
1
1
(372.48 g mol-1) C 83.84, H 7.85, found: C 83.65, H 8.00. H-
1
benzene-d6) d/ppm: 148.0 (br., dm, JFC = 243 Hz, C6F5), 142.9
NMR (300 MHz, 300 K, benzene-d6) d/ppm: 7.90 (2H, m, Ph),
3
4
(d, JPC = 7.4 Hz, o-Mes), 141.1 (br., o-Mes¢), 141.1 (d, JPC
=
7.06 (3H, m, Ph), 6.68 (4H, d, 4JPH = 2.8 Hz, m-Mes), 5.75 (1H,
4
2.5 Hz, p-Mes), 140.8 (d, JPC = 2.5 Hz, p-Mes¢), 140.2 (br. dm,
1JFC = 254 Hz, p-C6F5), 137.6 (dm, 1JFC = 260 Hz, C6F5), 131.2 (d,
3JPC = 7.1 Hz, m-Mes), 130.7 (d, 3JPC = 8.9 Hz, m-Mes¢), 125.9 (d,
1JPC = 19.5 Hz, i-Mes¢), 124.0 (d, 1JPC = 24.2 Hz, i-Mes), 119.5 (br.,
3
2
=
dd, JPH,trans = 11.6 Hz, JHH = 1.4 Hz, CH2(trans)), 5.23 (1H, dd,
3JPH,cis = 4.7 Hz, 2JHH = 1.4 Hz,=CH2(cis)), 2.39 (12H, s, o-CH3Mes),
2.04 (6H, s, p-CH3Mes). 13C{ H}-NMR (76 MHz, 300 K, benzene-
1
2
2
d6) d/ppm: 146.8 (d, JPC = 18.8 Hz, i-Ph), 143.6 (d, JPC
=
i-C6F5), 38.1 (d, 1JPC = 31.2 Hz, CH), 29.5 (br., BCH2), 23.6 (JPC
=
15.9 Hz, o-Mes), 142.5 (d, 1JPC = 26.7 Hz, i-Mes), 138.4 (p-Mes),
2
6.5 Hz), 23.1 (br.), 20.6, 20.5 (CH3Mes), 18.3 (d, JPC = 4.8 Hz,
3
1
P
=
130.4 (d, JPC = 4 Hz, m-Mes), 130.1 (d, JPC = 15.8 Hz, C ),
CH3). 31P{ H}-NMR (122 MHz, 300 K, benzene-d6) d/ppm: 33.2
1
4
5
128.8 (d, JPC = 1.7 Hz, m-Ph), 128.1 (d, JPC = 2.0 Hz, p-Ph)
(n1/2 = 19 Hz). 31P-NMR (122 MHz, 300 K, benzene-d6) d/ppm:
33.2 (d, 3JPH = 106.9 Hz). 19F-NMR (282 MHz, 300 K, benzene-d6)
d/ppm: -128.8 (br., 4F, o-C6F5), -157.4 (2F, p-C6F5), -163.5 (4F,
3
[observed in DEPT-135], 127.4 (d, JPC = 15.9 Hz, o-Ph), 120.1
(d, 2JPC = 6.1 Hz, CH2), 22.7 (d, JPC = 15.4 Hz, o-CH3Mes), 20.9
3
=
(p-CH3Mes). 31P{ H}-NMR (122 MHz, 300 K, benzene-d6) d/ppm:
1
m-C6F5). 11B{ H}-NMR (96 MHz, 300 K, benzene-d6) d/ppm:
1
-24.2 (n1/2 = 1 Hz).
3.2 (n1/2 = 500 Hz).
General procedure for the preparation of compounds 7, 9a and 9b.
The respective phosphane (1 equiv.) and HB(C6F5)2 (1 equiv.) were
dissolved in pentane (10 mL) and stirred for 10 min at ambient
temperature. The resulting yellow solution was evaporated to
dryness in vacuo.
Compound 9b. The reaction of dimesityl(1-phenylvinyl)-
phosphane (8b) (90.0 mg, 0.24 mmol) and HB(C6F5)2 (6) (84.0 mg,
0.24 mmol) yielded 9b (116 mg, 0.16 mmol, 67%) as a yellow solid.
mp 219 ◦C (decomp.). Anal. calcd for C38H30BF10P (718.41 g
mol-1) C 63.53, H 4.21, found: C 63.19, H 4.72. 1H-NMR
(300 MHz, 300 K, benzene-d6) d/ppm: 6.91 (m), 6.83 (m), 6.69
(m), 6.37 (br.) (R9H, Ph, m-Mes), 5.08 (1H, dt, 3JHH(anti) = 14.7 Hz,
Compound 7. The reaction of allyldimesitylphosphane (5)
(83.0 mg, 0.27 mmol) and HB(C6F5)2 (6) (93.0 mg, 0.27 mmol)
yielded 7 (124 mg, 0.19 mmol, 70%) as a white solid. mp
2
3
3JHH(syn) ª JPH = 8.1 Hz, CHP), 3.19 (1H, dm, JPH = 110.1 Hz,
◦
184 C. Anal. calcd for C33H28BF10P (656.34 g mol-1) C 60.39,
BCH2anti), 2.30 (m, BCH2syn), 2.07, 1.91, 1.90 (br., s, CH3Mes).
1
1
H 4.30, found: C 59.54, H 4.73. H-NMR (600 MHz, 298 K,
31P{ H}-NMR (122 MHz, 300 K, benzene-d6) d/ppm: 40.3 (n1/2
=
benzene-d6) d/ppm: 6.42 (4H, br., m-Mes), 2.73 (2H, br., PCH2),
2.05 (12H, br., o-CH3Mes), 1.91 (6H, s, p-CH3Mes), 1.77 (2H, br.,
17 Hz). 31P-NMR (122 MHz, 300 K, benzene-d6) d/ppm: 40.3
3
(d, JPH = 110.1 Hz). 19F-NMR (282 MHz, 300 K, benzene-d6)
CH2 ), 1.72 (2H, br., CH2). 13C{ H}-NMR (151 MHz, 298 K,
d/ppm: -124.0, -127.1, -135.6 (br., R4F, o-C6F5), -157.0 (br., 2F,
B
1
1
1
benzene-d6) d/ppm: 149.0 (dm, JFC = 240 Hz, C6F5), 142.5
p-C6F5), -163.1 (br., 4F, m-C6F5). 11B{ H}-NMR (96 MHz, 300 K,
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1534–1541 | 1539
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benzene-d6) d/ppm: 2.5 (n1/2 = 600 Hz). UV-vis (pentane): lmax
=
(122 MHz, 300 K, THF-d8) d/ppm: = 2.3 (n1/2 = 40 Hz).
1
434 nm, c = 1.7 ¥ 10-3mmol cm-3, d = 1 cm, e = 118 cm2 mmol-1.
31P-NMR (122 MHz, 300 K, THF-d8) d/ppm: 2.3 (dm, JPH
=
476 Hz). 19F-NMR (282 MHz, 300 K, THF-d8) d/ppm: -132.8
(4F, o-C6F5), -165.6, -165.9 (each 1F, p-C6F5), -167.8, -168.1
Preparation of compound 9c. Dimesityl(trans-2-(trimethyl-
silyl)vinyl)phosphane (8c) (150 mg, 0.41 mmol) and HB(C6F5)2
(6) (141 mg, 0.41 mmol) were dissolved in toluene (10 mL) and
stirred at 80 ◦C for 25 min. Then the solvent was removed in
vacuo and the obtained residue was dissolved in pentane (5 mL).
The resulting yellow solution was evaporated to dryness in vacuo
to yield 9c as a yellow solid (280 mg, 0.39 mmol, 96%). mp
1
(each 2F, m-C6F5). 11B{ H}-NMR (96 MHz, 300 K, THF-d8)
d/ppm: -21.7 (n1/2 = 65 Hz). 11B-NMR (96 MHz, 300 K, THF-d8)
d/ppm: -21.7 (d, 1JBH ª 95 Hz).
Acknowledgements
◦
56 C. Anal. calcd for C33H34BF10PSi (714.50 g mol-1) C 58.83,
1
Financial support from the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie is gratefully acknowl-
edged. We thank BASF for a gift of solvents.
H 4.80, found: C 58.33, H 4.85. H-NMR (400 MHz, 300 K,
4
benzene-d6) d/ppm: 6.55 (2H, d, JPH = 2.7 Hz, m-Mes), 6.39
4
P
(2H, d, JPH = 2.9 Hz, m-Mes¢), 2.90 (2H, br. m, CH2, CHTMS),
2.62 (1H, m, PCH2¢), 2.29 (6H, s, o-CH3Mes), 2.15 (6H, s, o-CH3Mes¢),
1.97 (3H, s, p-CH3Mes), 1.92 (6H, s, p-CH3Mes¢), -0.14 (9H, s, TMS).
Notes and references
13C{ H}-NMR (101 MHz, 300 K, benzene-d6) d/ppm: 147.9 (dm,
1
1JFC = 232 Hz, C6F5), 142.5 (d, JPC = 8.5 Hz, o-Mes), 142.4 (d,
2
1 G. C. Welch, R. R. San Juan, J. D. Masuda and D. W. Stephan, Science,
2006, 314, 1124.
2 J. S. J. McCahill, G. C. Welch and D. W. Stephan, Angew. Chem., 2007,
119, 5056, (Angew. Chem., Int. Ed., 2007, 46, 4968).
3 (a) G. Wittig and E. Bunz, Chem. Ber., 1959, 92, 1999; (b) W.
Tochtermann, Angew. Chem., 1966, 78, 355, (Angew. Chem., Int. Ed.,
1966, 5, 351), and references cited therein.
2JPC = 9.0 Hz, o-Mes¢), 140.7 (dm, 1JFC = 242 Hz, p-C6F5), 140.4
(d, 4JPC = 1.4 Hz, p-Mes), 140.2 (d, 4JPC = 1.9 Hz, p-Mes¢), 137.8
(dm, 1JFC = 246 Hz, C6F5), 131.3 (d, 4JPC = 6.8 Hz, m-Mes¢), 130.2
4
(d, JPC = 5.6 Hz, m-Mes), n.o. (i-Mes), 120.1 (br., i-C6F5), 27.1
(d, 1JPC = 21.5 Hz, PCH2), 22.7, 22.6 (each d, each 3JPC = 7.9 Hz,
4 (a) See also: G. C. Welch and D. W. Stephan, J. Am. Chem. Soc., 2007,
129, 1880; (b) G. C. Welch, L. Carbrea, P. A. Chase, E. Hollink, J. D.
Masuda, P. Wei and D. W. Stephan, Dalton Trans., 2007, 3407; (c) G. C.
Welch, T. Holtrichter-Roessmann and D. W. Stephan, Inorg. Chem.,
2008, 47, 1904; (d) Review: D. W. Stephan, Org. Biomol. Chem., 2008,
6, 1535; (e) P. A. Chase, T. Jurca and D. W. Stephan, Chem. Commun.,
2008, 1701; (f) D. Chen and J. Klankermayer, Chem. Commun., 2008,
2130; (g) P. A. Chase and D. W. Stephan, Angew. Chem., 2008, 120,
7543, (Angew. Chem., Int. Ed., 2008, 47, 7433); (h) D. Holschumacher,
T. Bannenberg, C. G. Hrib, P. G. Jones and M. Tamm, Angew. Chem.,
2008, 120, 7538, (Angew. Chem., Int. Ed., 2008, 47, 7428); (i) V. Sumerin,
o-CH3Mes), 22.2 (br., CHTMS), 20.7, 20.3 (p-CH3Mes), -1.6 (TMS).
31P{ H}-NMR (122 MHz, 300 K, benzene-d6) d/ppm: 15.9 (n1/2
=
1
27 Hz). 19F-NMR (282 MHz, 300 K, benzene-d6) d/ppm: -126.8
(br., 4F, o-C6F5), -155.6 (br., 2F, p-C6F5), -163.5 (br., 4F, m-C6F5).
19F-NMR (564 MHz, 198 K, toluene-d8) d/ppm: -120.6, -125.6,
-127.1, -134.4 (each 1F, o-C6F5), -155.8, -157.5 (each 1F, p-C6F5),
-161.4, -163.9, -164.1, -165.1 (each 1F, m-C6F5). 11B{ H}-NMR
1
(96 MHz, 300 K, toluene-d8) d/ppm: 23.2 (n1/2 = 700 Hz). UV-vis
(pentane): lmax = 368 nm, c = 1.8 ¥ 10-3mmol cm-3, d = 1 cm, e =
514 cm2 mmol-1.
F. Schulz, M. Nieger, M. Leskela¨, T. Repo and B. Rieger, Angew. Chem.,
2008, 120, 6090, (Angew. Chem., Int. Ed., 2008, 47, 6001).
5 (a) Theoretical analysis: T. A. Rokob, A. Hamza, A. Stirling, T. Soo´s
and I. Pa´pai, Angew. Chem., 2008, 120, 2469, (Angew. Chem. Int. Ed.,
2008, 47, 2319); (b) A. Stirling, A. Hamza, T. A. Rocob and I. Pa´pai,
Chem. Commun., 2008, 3148; (c) Y. Guo and S. Li, Inorg. Chem., 2008,
47, 6212.
Preparation of Compound 11. Dimesityl(2-propenyl)-
phosphane (8a) (660 mg, 2.13 mmol) and HB(C6F5)2 (6) (736 mg,
2.13 mmol) were suspended in pentane (10 mL) and stirred for
5 min at ambient temperature. The resulting yellow solution was
stirred under a hydrogen atmosphere (2.5 bar) for 15 min. During
this time a white precipitate was formed. It was collected by
filtration, washed with pentane (10 mL) and dried in vacuo. The
product 11 (645 mg, 1.03 mmol, 49%) was obtained as a white
6 P. Spies, G. Erker, G. Kehr, K. Bergander, R. Fro¨hlich, S. Grimme and
D. W. Stephan, Chem. Commun., 2007, 5072.
7 P. Spies, S. Schwendemann, S. Lange, G. Kehr, R. Fro¨hlich and G.
Erker, Angew. Chem., 2008, 120, 7654, (Angew. Chem., Int. Ed., 2008,
47, 7543).
8 H. Wang, R. Fro¨hlich, G. Kehr and G. Erker, Chem. Commun., 2008,
5966.
◦
solid. mp 94 C. Anal. calcd for C33H30BF10P (627.39 g mol-1)
9 (a) For other examples of metal-free hydrogenation reactions see: C.
Walling and L. Bollyky, J. Am. Chem. Soc., 1961, 83, 2968; (b) E. J.
DeWitt, F. L. Ramp and L. E. Trapasso, J. Am. Chem. Soc., 1961, 83,
4672; (c) F. L. Ramp, E. J. DeWitt and L. E. Trapasso, Org. Chem.,
1962, 27, 4368; (d) C. Walling and L. Bollyky, J. Am. Chem. Soc., 1964,
86, 3750; (e) M. Siskin, J. Am. Chem. Soc., 1974, 96, 3641; (f) J. Wristers,
J. Am. Chem. Soc., 1975, 97, 4312; (g) E. Osthaus, M. W. Haenel, Coal
Science and Technology, (Proceedings 1987 International Conference of
Coal Science), ed. J. A. Moulijin, K. A. Nater and H. A. G. Chermin,
Elsevier, Amsterdam, 1987, vol. 11, p. 765; (h) M. Yalpani, T. Lunow
and R. Ko¨ster, Chem. Ber., 1989, 122, 687;(i) M. Yalpani and R. Ko¨ster,
Chem. Ber., 1990, 123, 719; (j) M. Yalpani, R. Ko¨ster and M. W. Haenel,
Erdoel Kohle Erdgas Petrochem., 1990, 43, 344; (k) M. W. Hanenel, J.
Narangerel, U.-B. Richter and A. Rufinska, Angew. Chem., 2006, 118,
1077, (Angew. Chem., Int. Ed., 2006, 45, 1061); (l) M. W. Hanenel, J.
Narangerel, U.-B. Richter and A. Rufinska, Prep. Pap. Am. Chem. Soc.
Div. Fuel Chem., 2006, 51, 741; (m) M. Rueping, A. P. Antonchick
and T. Theissmann, Angew. Chem., 2006, 118, 3765, (Angew. Chem.,
Int. Ed., 2006, 45, 3683); (n) M. Rueping, A. P. Antonchick and T.
Theissmann, Angew. Chem., 2006, 118, 6903, (Angew. Chem., Int. Ed.,
2006, 45, 6751); (o) M. Rueping and A. Antonchick, Angew. Chem.,
2007, 119, 4646, (Angew. Chem., Int. Ed., 2007, 46, 4562); (p) D. Frey,
1
C 60.20, H 4.59, found: C 59.47, H 4.46. H-NMR (600 MHz,
1
3
298 K, THF-d8) d/ppm: 7.66 (1H, dd, JPH = 475.8 Hz, JHH
=
4
10.9 Hz, PH), 7.12 (2H, d, JPH = 3.9 Hz, m-Mes), 7.10 (2H,
4
P
d, JPH = 4.1 Hz, m-Mes¢), 3.21 (1H, m, CHMe), 3.01 (1H, br.
1
1
1 : 1 : 1 : 1 q [partially relaxed JBH], JBH ª 95 Hz, BH), 2.46
(6H, s, o-CH3Mes), 2.42 (6H, s, o-CH3Mes¢), 2.32 (s, 3H, p-CH3Mes),
2.31 (s, 3H, p-CH3Mes¢), 1.53 (1H, br. m, BCH2), 1.42 (3H, dd,
3JPH = 23.7 Hz, JHH = 7.1 Hz, CH3), 1.25 (1H, br. m, CH2¢).
3
B
13C{ H}-NMR (151 MHz, 298 K, THF-d8) d/ppm: 149.1 (dm,
1
1JFC = 261 Hz, C6F5), 146.0 (d, JPC = 2.7 Hz, p-Mes), 145.8 (d,
4
4JPC = 2.7 Hz, p-Mes¢), 144.7 (d, 2JPC = 8.5 Hz, o-Mes¢), 144.5 (d,
2JPC = 9.0 Hz, o-Mes), 137.3 (dm, 1JFC = 249 Hz, C6F5), 132.4 (d,
3JPC = 6.9 Hz, m-Mes), 132.3 (d, 3JPC = 6.9 Hz, m-Mes¢), n. o. (p-,
i-C6F5), 115.0 (d, 1JPC = 67.4 Hz, i-Mes), 114.0 (d, 1JPC = 76.7 Hz,
i-Mes¢), 33.5 (d, JPC = 30.0 Hz, CHMe), 26.3 (br., CH2), 22.31
1
P
B
(d, 3JPC = 6.2 Hz, o-CH3Mes), 22.27 (d, 3JPC = 6.0 Hz, o-CH3Mes¢),
21.12 (p-CH3Mes), 21.09 (p-CH3Mes¢), 17.5 (CH3). 31P{ H}-NMR
1
1540 | Dalton Trans., 2009, 1534–1541
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