A Lewis acid-mediated synthesis of P-alkyl-substituted phosphaalkenes

Article abstract of DOI:10.1039/c0nj00188k

Treating an equimolar mixture of R¹P(SiMe₃) ₂ (R¹ = ^tBu, Ad, Mes, Me₃Si; Ad = 1-adamantyl, Mes = 2,4,6-trimethylphenyl) and R²C(O)R³ (R²:R³ =

Full text of DOI:10.1039/c0nj00188k

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/njc | New Journal of Chemistry
A Lewis acid-mediated synthesis of P-alkyl-substituted
phosphaalkeneswzy
Joshua I. Bates, Brian O. Patrick and Derek P. Gates*
Received (in Victoria, Australia) 9th March 2010, Accepted 20th April 2010
DOI: 10.1039/c0nj00188k
t
Treating an equimolar mixture of R1P(SiMe3)2 (R1 = Bu, Ad, Mes, Me3Si; Ad = 1-adamantyl,
t
t
t
t
Mes = 2,4,6-trimethylphenyl) and R2C(O)R3 (R2:R3 = Bu:H, Ph:Ph, Bu:tBu, Bu:Ph, Bu:Me)
with AlCl3 (1 equiv.) affords the corresponding phosphaalkenes R1PQCR2R3 as monitored by
31P NMR spectroscopy. This new method was applied to the multigram synthesis of
R1PQCR2R3 [1a: R1 = Bu, R2 = Bu, R3 = H; 2a: R1 = Ad, R2 = Bu, R3 = H; 3a:
t
t
t
R1 = Mes, R2 = Bu, R3 = H; 3b: R1 = Mes, R2 = R3 = Ph] in good isolated yields (1a: 80%;
t
2a: 57%; 3a: 63%; 3b: 76%). Previously unknown 2a has been fully characterized. The reactivity
of 1a and 2a with group 13 Lewis acids was performed in an effort to probe their reactivity and
provide a means to structurally characterize these P-alkyl phosphaalkenes. The X-ray crystal
t
structures of 1aꢀAlCl3, 1aꢀGaCl3 and 2aꢀGaCl3 reveal that the Bu substituents are configured in a
trans arrangement and the PQC bond lengths are as expected (avg. 1.64 A).
Such studies require access to simple and convenient methods
Introduction
to prepare isolable phosphaalkenes bearing a variety of
different substituents.
Possessing a formal (3p–2p)p bond between phosphorus and
carbon, the chemistry of phosphaalkenes (RPQCR2) often
more closely resembles that of olefins (R2CQCR2) than imines
(RNQCR2).1–3 Although the PQC/CQC analogy is common
in molecular chemistry, there has recently been considerable
interest in extending this analogy to polymer science.4 Examples
include the development of p-conjugated polymers containing
PQC bonds5–8 and the addition polymerization of PQC
bonds to afford poly(methylenephosphine)s, PMPs (Scheme 1).9
We have been interested in exploring substituent-effects in
the polymerization of phosphaalkene monomers as a means of
evaluating the scope of this new reaction. Moreover, the
ability to vary substituents is critical to gaining an under-
standing of structure–property relationships in PMPs and to
tune the donor properties of these macromolecular ligands.
Although many methods for the assembly of PQC bonds
are known, the phospha-Peterson reaction10–19 is attractive
due to its versatility as
a route to Mes–P-substituted
phosphaalkenes.20,21 The reaction involves treating ketones
or aldehydes with either RP(SiMe3)2 and a catalyst (e.g. KOH)
or RP(SiMe3)Li alone. While this method is very effective for
the preparation of P-aryl-substituted phosphaalkenes, it is less
suitable when P-alkyl-substituents are desired due to the
difficulty in generating the alkylsilylphosphide intermediates.20
For example, the preparation of tBuPQCHtBu (1a) from
tBuP(SiMe3)2 and tBuC(O)H using KOH as a catalyst requires
ca. 11 weeks.22
We were intrigued with compound 1a because it is a rather
rare example of an isolable P-alkyl-substituted phosphaalkene
and is a precursor to novel P2C and P2C2 heterocycles.23
Clearly, a less time-consuming route to that described above
is desirable. Alternative phospha-Wittig strategies to 1a or
1aꢀW(CO)5 are known (Scheme 2).24,25 We also noted
that treating tBuP(SiMe3)CH(OSiMe3)tBu, derived from
t
tBuP(SiMe3)2 and BuC(O)H, with AlCl3 afforded high yields
Scheme 1 Examples illustrating the use of PQC bonds in polymer
science: (a) p-conjugated polymers; (b) addition polymerization of
PQC bonds.
Department of Chemistry, University of British Columbia,
2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1.
E-mail: dgates@chem.ubc.ca; Fax: +1 604 822 2847;
Tel: +1 604 822 9117
w In memory of Professor Pascal LeFloch and his contributions to the
field of phosphorus chemistry.
z This article is part of a themed issue on Main Group chemistry.
y CCDC reference numbers 768435–768437. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c0nj00188k
Scheme
phosphaalkene 1a or 1aꢀW(CO)5.
2
Known synthetic routes to the tBu–P-substituted
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010
1660 | New J. Chem., 2010, 34, 1660–1666

View Article Online
of 1a (86%).22 Strikingly, no timeframe is specified for this
reaction nor was the direct reaction of tBuP(SiMe3)2 and
tBuC(O)H in the presence of AlCl3 mentioned. Interestingly,
recent work has shown that Lewis acids can catalyze
the coupling of silylphosphines and aldehydes to give
a-siloxyalkylphosphines.26 If such an acid mediated approach
could be applied to the synthesis of 1a, it may provide a
convenient route to P-alkyl-substituted phosphaalkenes for
further study.
Table 1 Selected 31P NMR data (CH2Cl2) for phosphaalkenes
prepared following AlCl3-mediated procedure
R1
R2
R3
Product
31P NMR (d)
tBu
tBu
Ph
H
1a
1b
1c
1d
1e
2a
3a
3b
4a
273
292
295
277
270
268
224
234
240
tBu
Ph
tBu
Ph
Me
H
H
Ph
H
tBu
tBu
tBu
tBu
tBu
tBu
Ph
Herein, we report a simple one-pot synthesis of phosphaalkenes
from RP(SiMe3)2, a ketone or aldehyde, and AlCl3. In addition,
the preparation and molecular structures of the phosphaalkene–
Lewis acid adducts, (Cl3Al)tBuPQCHtBu, (Cl3Ga)tBuPQCHtBu
and (Cl3Ga)AdPQCHtBu (Ad = 1-adamantyl), are also
reported.
tBu
tBu
Ad
Mes
Mes
SiMe3
tBu
Results and discussion
(Table 1). Although phosphaalkene 1b initially forms cleanly,
the previously reported 1,2-diphosphetane is observed on
standing.27 In the case of the extremely hindered 2,2,4,4-
tetramethylpentan-3-one, its reaction with tBuP(SiMe3)2 to
form 1c required prolonged heating (4100 1C for 12 h).
Although the C–Me phosphaalkene 1e could be detected by
31P NMR spectroscopy, this species was present in low
quantities (ca. 25% of total P). Given that tBuPH2 was present
in the reaction mixture (d = ꢂ80, t), it is likely that the readily
To assess the feasibility of a Lewis acid-mediated synthesis of
t
phosphaalkenes, an equimolar mixture of BuP(SiMe3)2 and
tBuC(O)H in dichloromethane was treated with AlCl3
(1 equiv.). Analysis of an aliquot removed from the reaction
mixture by 31P NMR spectroscopy revealed that the signal
t
assigned to BuP(SiMe3)2 (d = ꢂ108) was replaced by a new
signal assigned to 1a (d = 273).22 The separation of 1a from
the side-products, Me3SiCl and [Cl2AlOSiMe3]2, may be
accomplished through the use of reduced pressures to first
remove the solvent and Me3SiCl (25 1C, 200 mmHg).
Subsequently, the phosphaalkene 1a can be distilled
(bp = 75 1C, 60 mmHg). This separation must be performed
carefully in order to avoid contamination of 1a with volatile
[Cl2AlOSiMe3]2. The liquid product 1a is isolated in 80% yield
and its purity was confirmed by NMR spectroscopy and
elemental analysis.
t
enolizable ketone, BuC(O)Me, provided acidic protons for
reaction with tBuP(SiMe3)2. Interestingly, this methodology is
amenable to the preparation of a P-silyl-phosphaalkene as
illustrated by the quantitative formation of 4a from P(SiMe3)3
and pivaldehyde.
In addition to 1a, three other phosphaalkenes have been
isolated on a preparative scale (2a, 3a and 3b) following this
new methodology. The procedure described above for 1a was
followed in each case and analysis of the reaction mixtures by
31P NMR spectroscopy suggested quantitative conversion of
RP(SiMe3)2 to phosphaalkene. The separation of the heavier
phosphaalkenes from the aluminium-containing byproduct
proved impossible by fractional distillation due to the very
similar volatility of these compounds. Instead, [Cl2AlOSiMe3]2
can be removed by extracting a solution of the crude product
with a degassed mixture of aqueous NaOH (B5 M) and
hexanes. The use of hexanes is critical to keep salts out of
the organic layer. Remarkably, the organic layer contained the
unhydrolyzed phosphaalkene product free from Al-containing
impurities. Final purification was accomplished through
vacuum sublimation (2a), distillation (3a) or recrystallization
from hexanes (3b). To our knowledge, the only other isolable
P–Ad substituted phosphaalkene is the Becker phosphaalkene,
AdPQC(tBu)OSiMe3.28 We have previously observed
AdPQCPh2 by 31P NMR spectroscopy (d = 286), however
Given the difficulty in separating [Cl2AlOSiMe3]2 from 1a,
we sought methods to minimize the production of Al-containing
species. Thus, tBuP(SiMe3)2 and tBuC(O)H in dichloro-
methane were treated with substoichiometric amounts of
AlCl3. Monitoring by 31P NMR spectroscopy revealed that
tBuP(SiMe3)2 could be transformed quantitatively to 1a in the
presence of 0.5 to 1.0 equiv. of AlCl3. The reaction times were
substantially longer when less AlCl3 is used. When 0.8 equiv.
AlCl3 was employed, the isolated yield of 1a was ca. 70–80%.
When 0.33 equiv. of AlCl3 was employed, a 2 : 1 mixture of
product 1a and intermediate, tBuP(SiMe3)CH(OSiMe3)tBu,
were observed. Although it appears possible to use reduced
quantities of AlCl3, in the following studies stoichiometric
quantities were employed since this gives the most rapid
reaction.
only
the
head-to-head
dimeric
1,2-diphosphetane,
[AdP–CPh2]2, could be isolated.20
To assess the generality of the AlCl3-mediated synthesis of
phosphaalkenes, we performed a series of NMR scale reactions
involving the mixing of equimolar quantities of R1P(SiMe3)2
Although, pure 3a can be isolated as a colorless oil, after
several days in a sealed vial under inert atmosphere, colorless
crystals precipitate from the oil. Surprisingly, these crystals
were determined to be the diphosphine 5 after analysis using
NMR spectroscopy and X-ray diffraction. Compound 5 had
previously been isolated and crystallographically characterized
t
(R1 = Bu, Ad, Mes), aldehyde/ketone and AlCl3 in CH2Cl2.
In most instances, the phosphaalkene product is rapidly and
quantitatively formed as suggested by 31P NMR spectroscopy
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 1660–1666 | 1661

View Article Online
from the reaction of LiPHMes and 1,2-dibromoethane,29 and
has been detected in solution in several other instances.30
Whether this transformation is caused by the presence of a
trace impurity or is a consequence of some inherent instability
of 3a has not been ascertained. However, it should be noted
that the analogous crystals of 5 are isolated each time 3a is
prepared.
As a means to probe their reactivity and to structurally
characterize P-alkyl phosphaalkenes, the potential formation
of adducts of 1a and 2a with group 13 Lewis acids was
explored. We have previously reported that treating 3b
with group 13 Lewis acids affords the simple P-adduct
(Cl3Ga)MesPQCPh2 (3bꢀGaCl3).31 In contrast, evidence of
C-addition of GaCl3 was observed with bulkier Mes*PQCH2
Fig. 2 ORTEP view of a molecule of 1aꢀGaCl3. Displacement
ellipsoids are shown at the 50% probability level. Selected bond
distances (A) and angles (1) are as follows. P(1)–C(1) 1.655(3),
P(1)–C(6) 1.862(2), P(1)–Ga(1) 2.4164(7), C(1)–C(2) 1.502(3),
C(6)–P(1)–C(1) 113.30(12), C(1)–P(1)–Ga(1) 127.77(9), C(6)–P(1)–Ga(1)
118.84(8), P(1)–C(1)–C(2) 132.7(2), C(6)–P(1)–C(1)–C(2) 179.2(2).
(Mes*
=
2,4,6-tri-tert-butylphenyl) to afford fleeting
phosphenium zwitterion Mes*P–CH2GaCl3.31 Therefore, an
investigation of the reactions of 1a and 2a with GaCl3 and
AlCl3 was conducted. Prior studies had shown that the reaction
of 1a with sources of H+ or Me+ affords novel diphosphiranium
or diphosphetanium cations, respectively.23
Analysis of a solution of phosphaalkene 1a and AlCl3
(1 equiv.) in CH2Cl2 by 31P NMR spectroscopy revealed that
the signal for 1a (d = 273) was not present and a new singlet
resonance was observed (d = 199.8). The chemical shift is
consistent with that reported previously for 1aꢀAlCl3 (d =
1
200.5 in C7D8).22 Furthermore, the H and 13C NMR spectra
of crystals obtained from the reaction solution were also
consistent with adduct formation. Analysis of the crystals by
X-ray diffraction confirmed the adduct formation and the
trans arrangement of the tBu substituents in Z-1aꢀAlCl3
(Fig. 1). Perhaps this indicates that the bulky alkyl substituent
imposes a larger steric demand than the Lewis acid. Similarly,
Fig. 3 ORTEP view of a molecule of 2aꢀGaCl3. Displacement
ellipsoids are shown at the 50% probability level. Selected bond
distances (A) and angles (1) are as follows. P(1)–C(1) 1.647(4),
P(1)–C(6) 1.842(3), P(1)–Ga(1) 2.4178(10), C(1)–C(2) 1.503(5),
C(6)–P(1)–C(1) 112.56(17), C(1)–P(1)–Ga(1) 129.74(14), C(6)–P(1)–Ga(1)
117.30(11), P(1)–C(1)–C(2) 131.7(3), C(6)–P(1)–C(1)–C(2) 179.8(4).
the new adducts Z-1aꢀGaCl3 and Z-2aꢀGaCl3 were isolated
and crystallographically characterized (Fig. 2 and 3, respectively).
Interestingly, the 31P{1H} NMR spectra (300 MHz, 298 K)
of the Ga and Al adducts show very broad resonances. For
example, the full width at half-height (fwhh) for 1aꢀGaCl3
(233 Hz) is much larger than that for uncomplexed 1a (9 Hz).
We speculate that a fluxional process, such as equilibration
between coordinated and free phosphaalkene, may be taking
place in solution. Evidence for weak binding of Lewis acids to
1a has been alluded to previously since AlCl3 is readily
displaced from 1aꢀAlCl3 in the presence of Et2O.22
Fig. 1 ORTEP view of a molecule of 1aꢀAlCl3. Displacement
ellipsoids are shown at the 50% probability level. Selected bond distances
(A) and angles (1) are as follows. P(1)–C(1) 1.652(3), P(1)–C(6) 1.866(3),
P(1)–Al(1) 2.4516(11), C(1)–C(2) 1.502(4), C(6)–P(1)–C(1) 111.96(14),
C(1)–P(1)–Al(1) 128.52(11), C(6)–P(1)–Al(1) 119.46(10), P(1)–C(1)–C(2)
132.5(2), C(6)–P(1)–C(1)–C(2) 179.2(3).
There are very few other Z1 complexes of phosphaalkenes to
p-block metals. We have previously reported the molecular
structure of 3bꢀGaCl3 and detected (Cl3Ga)Mes*PQCH2 at
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010
1662 | New J. Chem., 2010, 34, 1660–1666

View Article Online
37
low-temperature (ꢂ80 1C). It has also been reported that the
inversely polarized phosphaalkene [Cp*(CO)2Fe]PQ
tBuP(SiMe3)2,37 AdP(SiMe3)2,20,38 MesP(SiMe3)2
and
39
P(SiMe3)3 were prepared following literature procedures.
1H, 31P and 13C{1H} NMR spectra were recorded at room
temperature on Bruker Avance 300 or 400 MHz spectro-
meters. Chemical shifts are reported relative to residual
C(NMe2)2 will form Z1 complexes with MMe3 (M = Al,
Ga, In), however crystallographic analysis revealed significant
pyramidalization of the phosphorus atoms (B3401) and
lengthening of the P–C bonds suggests little double bond
character in these species.32 In 1aꢀAlCl3, 1aꢀGaCl3, and 2aꢀ
GaCl3 the sum of the angles at phosphorus are 3601, consistent
with retention of the PQC bond upon complexation.
1
C6HD5 or CHDCl2 (d = 7.16 or 5.32 for H, respectively),
85% H3PO4 as an external standard (d = 0.0 for 31P), and
C6D6 or CD2Cl2 (d = 128 or 53.8 for 13C, respectively). Mass
spectra were recorded on a Kratos MS 50 instrument in EI
mode (70 eV).
Analysis of the metrical parameters reveals that the PQC
bond lengths in 1aꢀAlCl3 [1.652(3) A], 1aꢀGaCl3 [1.655(3) A]
and 2aꢀGaCl3 [1.647(4) A] are similar in length. These PQC
bond lengths lie at shorter end of the range associated with
PQC bonds (1.61–1.71 A),1 but are comparable to
General procedure for NMR scale reactions
To a small vial charged with AlCl3 (33 mg, 0.25 mmol),
dichloromethane (B2 mL) and a small magnetic stir-bar was
added a solution of RP(SiMe3)2 (0.25 mmol) and aldehyde/
ketone (0.25 mmol) in dichloromethane (B2 mL). The mixture
was stirred for 10 min and then an aliquot removed
and analyzed by 31P NMR spectroscopy. The presence of
phosphaalkene is indicated by a diagnostic signal in the
respective NMR spectra (d 4 200).
|
|
(CO)5W[C H2CH2C (1-cyclohexene)]PQCHtBu (1.649 A)33
and (CO)5W(tBu)PQCHiPr (1.652 A),25 and are consistent
with the retention of multiple-bond character upon adduct
formation. The PQC bond length in 3bꢀGaCl3 [1.687(3) A] is
slightly longer than that for 1aꢀGaCl3 and 2aꢀGaCl3 which
likely results from p-delocalization between the PQC bond
and the aryl moiety in the former.
tBuPQCHtBu (1a)
The P–Calkyl bond lengths in 1aꢀAlCl3 [1.866(3) A],
1aꢀGaCl3 [1.862(2) A] and 2aꢀGaCl3 [1.842(3) A] lie towards
the shorter end of the range typical of P–Calkyl bonds (range:
1.85–1.90).34 Interestingly, the P–CtBu bonds are significantly
longer than the P–CAd bond. Presumably this reflects the lower
steric demand of the cyclic Ad substituent. The P–Ga bond
lengths in 1aꢀGaCl3 [2.4164(7) A] and 2aꢀGaCl3 [2.4178(10) A]
are comparable to that in 3bꢀGaCl3 [2.3938(7) A] and are
typical of P–Ga bonds.
To a suspension of AlCl3 (5.6 g, 42 mmol) in dichloromethane
(100 mL) was added a mixture of tBuP(SiMe3)2 (10.0 g,
43 mmol) and pivaldehyde (3.8 g, 44 mmol) in dichloromethane
(50 mL). The resulting mixture was stirred until quantitative
conversion to 1a was observed from 31P NMR spectroscopy
(B30 min). Volatiles (dichloromethane and ClSiMe3) were
removed at reduced pressure (200 Torr). A reduced pressure
distillation (75 1C/60 Torr) affords 1a as a pale yellow oil
(5.4 g, 80%). 31P, 1H and 13C NMR spectra confirmed the
formation of 1: 31P{1H} NMR (C6D6) d 275.7, lit. (CDCl3) d
278.2.22 Found: C, 68.14; H, 12.03%. C9H11P requires C,
68.32; H, 12.10%.
Conclusions
The AlCl3-mediated reaction of bis(silyl)phosphines and
aldehydes or ketones provides a useful one-pot route to
phosphaalkenes. The acid-mediated method is preferable to
base-mediated routes when the preparation of P–alkyl-
substituted phosphaalkenes is desired. A series of phosphaalkenes
bearing P–tBu and P–Ad substituents have been prepared and
isolated following this new methodology. The adducts
Z–(Cl3Ga)tBuPQCHtBu (1aꢀGaCl3), Z–(Cl3Al)tBuPQCHtBu
(1aꢀAlCl3), and Z–(Cl3Ga)AdPQCHtBu (2aꢀGaCl3) are rare
examples of phosphaalkene complexes of a group 13 Lewis
acid and provide a means to investigate the structural features
of P–alkyl-substituted phosphaalkenes.
AdPQCHtBu (2a)
To a suspension of AlCl3 (4.3 g, 32 mmol) in dichloromethane
(100 mL) was added a mixture of AdP(SiMe3)2 (10.0 g,
32 mmol) and pivaldehyde (2.8 g, 33 mmol) in dichloromethane
(50 mL). The resulting mixture was stirred for 1 h and then the
volatiles (dichloromethane and ClSiMe3) were removed at
reduced pressure (200 Torr). The crude product was dissolved
in diethyl ether (100 mL) and added dropwise to a stirred
mixture of degassed 5 M NaOH(aq.) (200 mL) and hexanes
(100 mL). The organic fraction was separated and the aqueous
fraction washed with hexanes (3 ꢃ 30 mL). The combined
organic fractions were dried with anhydrous MgSO4, filtered,
and evaporated to dryness. The crude solid was vacuum
distilled and sublimed (100 1C/2 mmHg) to afford an analytically
pure colorless solid (4.3 g, 57%). 31P{1H} NMR (CD2Cl2)
Experimental
All manipulations were performed under an atmosphere of
nitrogen. Hexanes, dichloromethane and diethyl ether were
deoxygenated with nitrogen and dried by passing through a
column containing activated alumina. Distilled water was
degassed prior to use. C6D6 was stored over molecular sieves
before use and ampules of CD2Cl2 were used as received from
CIL. Benzophenone (Aldrich) was sublimed before use.
Pivaldehyde, 3,3-dimethylbutan-2-one and AlCl3 were used
as received from Aldrich. NaOH and anhydrous MgSO4 were
purchased from Fisher and used as received. 2,2,4,4-Tetra-
methylpentan-3-one,35 2,2-dimethyl-1-phenylpropan-1-one,36
1
2
d 268.4. H NMR (CD2Cl2) d 8.65 (d, JPH = 24.9 Hz, 1H),
1.98 (m, 3H), 1.80 (m, 6H), 1.75 (m, 6H), 1.13 (d, 4JPH = 1.8 Hz,
9H). 13C{1H} NMR (CD2Cl2) d 194.6 (d, JPC = 46.2 Hz),
1
42.6 (d, 2JPC = 8.4 Hz), 38.4 (d, 2JPC = 11.8 Hz), 37.3, 36.1 (d,
1JPC = 34.0 Hz), 31.2 (d, JPC = 12.9 Hz), 29.7 (d, JPC
=
3
3
6.6 Hz). MS (EI): m/z [%] 135, 136 [100, 15, Ad+], 236, 237
[18, 3, M+]. Found: C, 76.56; H, 10.89%. C15H25P requires C,
76.23; H, 10.66%.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 1660–1666 | 1663

View Article Online
MesPQCHtBu (3a)
vacuum distillation and then recrystallization from hexanes to
afford yellow crystals of 3b (4.1 g, 76%). 31P, 1H and 13C
NMR spectra confirmed the formation of 3b: 31P{1H} NMR
(C6D6) d 234.6, lit. (CDCl3) d 233.42 Found: C, 83.17; H,
6.62%. C22H21P requires C, 83.52; H, 6.69%.
To a suspension of AlCl3 (1.7 g, 13 mmol) in dichloromethane
(40 mL) was added a mixture of MesP(SiMe3)2 (4.0 g,
13 mmol) and pivaldehyde (1.1 g, 13 mmol) in dichloro-
methane (25 mL). The resulting mixture was stirred for 1 h
and then the volatiles (dichloromethane and ClSiMe3) were
removed at reduced pressure (200 Torr). The crude product
was dissolved in diethyl ether (100 mL) and added dropwise to
a stirred mixture of degassed 5 M NaOH(aq.) (200 mL) and
hexanes (100 mL). The organic fraction was separated and the
aqueous fraction washed with hexanes (3 ꢃ 30 mL). The
combined organic fractions were dried with anhydrous
MgSO4, filtered, and evaporated to dryness. The crude
product was purified by vacuum distillation (1.9 g, 63%).
31P and 1H NMR spectra confirmed the formation of 3a:
31P{1H} NMR (CD2Cl2) d 224.6, lit. (C6D6) d 228.4.40,41 After
several days, crystals of 5 precipitate from the liquid 3a. 5:
31P{1H} NMR (CD2Cl2) d ꢂ111.9 (60%), ꢂ119.1 (40%), lit.
(C6D6) d ꢂ109.9 (60%), ꢂ117.1 (40%).29
Z–(Cl3Al)tBuPQCHtBu (1aꢀAlCl3)
To a solution of AlCl3 (0.266 g, 2 mmol) in dichloromethane
(2 mL) was added a solution of 1a (0.316 g, 2 mmol) in
dichloromethane (1 mL). Upon the reaction mixture was
layered 1 mL of hexanes. The mixture was stored at ꢂ40 1C
for 24 h at which point crystals of 1aꢀAlCl3 suitable for X-ray
crystallography were harvested (0.25 g, 43%). 31P and 1H
spectra confirmed the formation of 1aꢀAlCl3: 31P{1H} NMR
(CDCl3) d 198.6, lit. (C7D8) d 200.5.22
Z–(Cl3Ga)tBuPQCHtBu (1aꢀGaCl3)
To a solution of GaCl3 (0.350 g, 2 mmol) in dichloromethane
(2 mL) was added a solution of 1a (0.316 g, 2 mmol) in
dichloromethane (1 mL). Upon the reaction mixture was
layered 1 mL of hexanes. The mixture was stored at ꢂ40 1C
for 24 h at which point crystals of 1ꢀGaCl3 suitable for X-ray
crystallography were collected (0.48 g, 72%). 31P{1H} NMR
(CD2Cl2) d 194.4; 1H NMR (CD2Cl2) d 8.74 (d, 2JPH = 24.3 Hz,
MesPQCPh2 (3b)
To a suspension of AlCl3 (2.2 g, 17 mmol) in dichloromethane
(50 mL) was added a mixture of MesP(SiMe3)2 (5.0 g,
16 mmol) and benzophenone (3.1 g, 17 mmol) in dichloro-
methane (50 mL). The resulting mixture was stirred for 1 h and
then the volatiles (dichloromethane and ClSiMe3) were
removed in vacuo. The crude product was dissolved in diethyl
ether (100 mL) and added dropwise to a stirred mixture of
degassed 5 M NaOH(aq.) (200 mL) and hexanes (100 mL).
The organic fraction was separated and the aqueous fraction
washed with hexanes (3 ꢃ 30 mL). The combined organic
fractions were dried with anhydrous MgSO4, filtered, and
evaporated to dryness. The crude product was purified by
3
4
1H), 1.60 (d, JPH = 16.8, 9H), 1.38 (d, JPH = 1.8 Hz, 9H).
1
13C{1H} NMR (CD2Cl2) d 190.8 (d, JPC = 20.6 Hz), 40.9,
40.7 (d, 1JPC = 4.9 Hz), 31.5 (d, 2JPC = 12.9 Hz), 29.9. Found:
C, 32.40; H, 5.89%. C9H19PGaCl3 requires C, 31.82;
H, 5.73%.
Z–(Cl3Ga)AdPQCHtBu (2aꢀGaCl3)
To a solution of GaCl3 (0.200 g, 1.1 mmol) in dichloromethane
(1 mL) was added a solution of 2a (0.260 g, 1.1 mmol) in
Table 2 Crystallographic data for 1aꢀAlCl3, 1aꢀGaCl3 and 2aꢀGaCl3
1aꢀAlCl3
1aꢀGaCl3
2aꢀGaCl3
Formula
fw
C9H19PAlCl3
291.54
C9H19PGaCl3
334.28
C15H25PGaCl3
412.39
Cryst syst
Space group
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
Color
a/A
b/A
c/A
Colorless
11.0934(8)
8.8646(6)
16.1716(11)
90
Colorless
11.0971(14)
8.8556(12)
16.184(2)
90
Colorless
10.5923(11)
15.9466(17)
11.3326(13)
90
a/1
b/1
108.143(2)
90
1511.23(18)
173(2)
108.247(5)
90
1510.5(3)
173(2)
107.238(5)
90
1828.2(3)
100(2)
g/1
V/A3
T/K
Z
4
7.38
4
24.26
4
20.21
m (MoKa)/cmꢂ1
Cryst size/mm3
Calcd density/Mg mꢂ3
2y (max)/1
No. of reflns
No. of unique data
Rint
0.4 ꢃ 0.2 ꢃ 0.1
0.15 ꢃ 0.15 ꢃ 0.10
1.0 ꢃ 0.5 ꢃ 0.3
1.281
55.8
1.470
56.0
1.498
56.4
18581
3626
0.0366
27.26
0.0484; I 4 2s(I)
0.1324
1.154
32228
6868
0.0505
51.25
0.0377; I 4 2s(I)
0.0887
1.097
39679
7795
0.0880
42.14
0.0572; I 4 2s(I)
0.1350
1.077
Refln/param ratio
R1
a
wR2 (all data)b
GOF
P
P
P
P
a
b
2
R1 = ||Fo| ꢂ |Fc||/ |Fo|. wR2(F2 [all data]) = { [w(Fo ꢂ Fc2)2]/ [w(Fo2)2]}1/2
.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010
1664 | New J. Chem., 2010, 34, 1660–1666

View Article Online
dichloromethane (1 mL). The mixture layered with hexanes
(2 mL) and was stored at ꢂ40 1C for 24 h from which crystals
of 2aꢀGaCl3 suitable for X-ray crystallography were grown
(0.34 g, 75%). 31P{1H} NMR (CD2Cl2) d 189.3; 1H NMR
5682–5685; (c) K. J. T. Noonan and D. P. Gates, Angew. Chem.,
Int. Ed., 2006, 45, 7271–7274; (d) K. J. T. Noonan, B. O. Patrick
and D. P. Gates, Chem. Commun., 2007, 3658–3660;
(e) B. H. Gillon, B. O. Patrick and D. P. Gates, Chem.
Commun., 2008, 2161–2163; (f) K. J. T. Noonan, B. H. Gillon,
V. Cappello and D. P. Gates, J. Am. Chem. Soc., 2008, 130,
12876–12877.
2
(CD2Cl2) d 8.60 (d, JPH = 23.7 Hz, 1H), 2.24 (m, 6H), 2.15
4
(m, 3H), 1.81 (m, 6H), 1.37 (d, JPH = 1.8, 9H). 13C{1H}
10 G. Becker, W. Uhl and H. J. Wessely, Z. Anorg. Allg. Chem., 1981,
479, 41–56.
11 O. Mundt, G. Becker, W. Uhl, W. Massa and M. Birkhahn,
Z. Anorg. Allg. Chem., 1986, 541, 319–335.
12 T. van der Does and F. Bickelhaupt, Phosphorus Sulfur Relat.
Elem., 1987, 30, 515–518.
13 A. Jouaiti, M. Geoffroy and G. Bernardinelli, Tetrahedron Lett.,
1992, 33, 5071–5074.
1
(CD2Cl2) d 189.8 (d, JPC = 24.1 Hz), 45.1, 41.0, 40.5, 36.1,
31.5 (d, JPC = 9.6 Hz), 29.4 (d, JPC = 7.1 Hz). Found: C,
3
3
43.67; H, 5.95%. C15H25PGaCl3 requires C, 43.68; H, 6.11%.
X-Ray crystallography
Crystals suitable for diffraction were immersed in Paratone-N
oil and mounted on a glass fiber. Data for 1aꢀGaCl3 were
collected on a Bruker X8 APEX diffractometer and for both
1aꢀAlCl3 and 2aꢀGaCl3 on a Bruker X8 APEX II diffracto-
meter with graphite-monochromated MoKa radiation. Data
were collected and integrated using the Bruker SAINT43
software package and corrected for absorption effects using
SADABS44 (1aꢀAlCl3) or TWINABS45 (1aꢀGaCl3 and
2aꢀGaCl3). 1aꢀGaCl3 crystallizes as a two-component twin
with the two components (major : minor E 3 : 1) related
by a 1801 rotation about the (0 0 1) reciprocal axis. 2aꢀGaCl3
crystallizes as a two-component twin with the two components
(major : minor E 2 : 1) related by a 1801 rotation about the
(1 0 0) reciprocal axis. All data sets were corrected for Lorentz
and polarization effects. All structures were solved by direct
methods46 and subsequent Fourier difference techniques and
refined anisotropically for all non-hydrogen atoms using
the SHELXTL47 crystallographic software package from
Bruker-AXS. H-atoms were included in calculated positions
(riding model). Compounds 1aꢀAlCl3 and 1aꢀGaCl3 are
isomorphous and were refined using the same origin
(Table 2). CCDC 768435 (1aꢀAlCl3), 768436 (1aꢀGaCl3) and
768437 (2aꢀGaCl3).w
14 A. Jouaiti, M. Geoffroy and G. Bernardinelli, Tetrahedron Lett.,
1993, 34, 3413–3416.
15 A. Jouaiti, M. Geoffroy and G. Bernardinelli, Chem. Commun.,
1996, 437–438.
16 H. Kawanami, K. Toyota and M. Yoshifuji, J. Organomet. Chem.,
1997, 535, 1–5.
17 A. S. Ionkin and W. J. Marshall, Heteroat. Chem., 2002, 13,
662–666.
18 O. Daugulis, M. Brookhart and P. S. White, Organometallics,
2002, 21, 5935–5943.
19 A. Termaten, M. van der Sluis and F. Bickelhaupt, Eur. J. Org.
Chem., 2003, 2049–2055.
20 M. Yam, J. H. Chong, C. W. Tsang, B. O. Patrick, A. E. Lam and
D. P. Gates, Inorg. Chem., 2006, 45, 5225–5234.
21 J. Dugal-Tessier, G. R. Dake and D. P. Gates, Angew. Chem., Int.
Ed., 2008, 47, 8064–8067.
22 E. Niecke and E. Symalla, Chimia, 1985, 39, 320–322.
23 J. I. Bates and D. P. Gates, J. Am. Chem. Soc., 2006, 128,
15998–15999.
24 C. C. Cummins, R. R. Schrock and W. M. Davis, Angew. Chem.,
Int. Ed. Engl., 1993, 32, 756–759.
25 A. Marinetti, S. Bauer, L. Ricard and F. Mathey, Organometallics,
1990, 9, 793–798.
26 M. Hayashi, Y. Matsuura, Y. Nishimura, T. Yamasaki, Y. Imai
and Y. Watanabe, J. Org. Chem., 2007, 72, 7798–7800.
27 H. Grutzmacher and H. Pritzkow, Angew. Chem., Int. Ed. Engl.,
¨
1992, 31, 99–101.
28 J. R. Goerlich and R. Schmutzler, Phosphorus, Sulfur Silicon Relat.
Elem., 1995, 101, 245–251.
29 S. Kurz, H. Oesen, J. Sieler and E. Hey-Hawkins, Phosphorus,
Sulfur Silicon Relat. Elem., 1996, 117, 189–196.
Acknowledgements
30 (a) R. Waterman, Organometallics, 2007, 26, 2492–2494;
(b) L. B. Han and T. D. Tilley, J. Am. Chem. Soc., 2006, 128,
13698–13699; (c) R. Wolf, S. Gomez-Ruiz, J. Reinhold,
W. Bohlmann and E. Hey-Hawkins, Inorg. Chem., 2006, 45,
9107–9113; (d) J. D. Masuda, A. J. Hoskin, T. W. Graham,
C. Beddie, M. C. Fermin, N. Etkin and D. W. Stephan,
Chem.–Eur. J., 2006, 12, 8696–8707; (e) S. Blaurock and E.
Hey-Hawkins, Z. Anorg. Allg. Chem., 2002, 628, 37–40;
(f) Z. M. Hou, T. L. Breen and D. W. Stephan, Organometallics,
1993, 12, 3158–3167; (g) S. Kurz and E. Hey-Hawkins,
J. Organomet. Chem., 1993, 462, 203–207.
We are grateful to the Natural Sciences and Engineering
Research Council (NSERC) of Canada, the Canada Foundation
for Innovation and the British Columbia Knowledge
Development Fund for support of this work. J.I.B. thanks
NSERC for PGS M and D scholarships.
Notes and references
31 C. W. Tsang, C. A. Rohrick, T. S. Saini, B. O. Patrick and
D. P. Gates, Organometallics, 2004, 23, 5913–5923.
32 L. Weber, M. H. Scheffer, H. G. Stammler and A. Stammler, Eur.
J. Inorg. Chem., 1999, 1607–1611.
33 T. W. Mackewitz, D. Ullrich, U. Bergstrasser, S. Leininger and
¨
M. Regitz, Liebigs Ann./Recl., 1997, 1997, 1827–1839.
34 Characteristic bond lengths in free molecules, CRC Handbook of
Chemistry and Physics, ed. D. R. Lide, CRC Press, Boca Raton,
FL, 84th edn, 2003.
1 M. Regitz and O. J. Scherer, Multiple bond and low coordination in
phosphorus chemistry, Thieme, Stuttgart, 1990.
2 K. B. Dillon, F. Mathey and J. F. Nixon, Phosphorus: the carbon
copy, Wiley, 1998.
3 F. Mathey, Angew. Chem., Int. Ed., 2003, 42, 1578–1604.
4 J. I. Bates, J. Dugal-Tessier and D. P. Gates, Dalton Trans., 2010,
39, 3151–3159.
5 V. A. Wright and D. P. Gates, Angew. Chem., Int. Ed., 2002, 41,
2389–2392.
35 D. J. Collins and H. A. Jacobs, Aust. J. Chem., 1987, 40,
1989–2004.
6 V. A. Wright, B. O. Patrick, C. Schneider and D. P. Gates, J. Am.
Chem. Soc., 2006, 128, 8836–8844.
36 C. Alvarez-Ibarra, M. S. Arias-Pe
M. A. Rodrıguez-Barranco, Org. Prep. Proced. Int., 1990, 22,
77–84.
´
rez, E. Moya and
7 R. C. Smith, X. F. Chen and J. D. Protasiewicz, Inorg. Chem.,
2003, 42, 5468–5470.
8 R. C. Smith and J. D. Protasiewicz, J. Am. Chem. Soc., 2004, 126,
2268–2269.
´
37 G. Becker, O. Mundt, M. Rossler and E. Schneider, Z. Anorg. Allg.
¨
Chem., 1978, 443, 42–52.
38 H. Stetter and W.-D. Last, Chem. Ber., 1969, 102, 3364.
39 G. Becker and W. Holderich, Chem. Ber., 1975, 108, 2484–2485.
¨
9 (a) C. W. Tsang, M. Yam and D. P. Gates, J. Am. Chem. Soc.,
2003, 125, 1480–1481; (b) C. W. Tsang, B. Baharloo, D. Riendl,
M. Yam and D. P. Gates, Angew. Chem., Int. Ed., 2004, 43,
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 1660–1666 | 1665

View Article Online
40 M. Brym, C. Jones, M. Waugh, E. Hey-Hawkins and F. Majoumo,
New J. Chem., 2003, 27, 1614–1621.
44 Bruker, SADABS, Bruker AXS Inc., Madison, Wisconsin, USA,
2001.
41 J. D. Masuda, K. C. Jantunen, O. V. Ozerov, K. J. T. Noonan,
D. P. Gates, B. L. Scott and J. L. Kiplinger, J. Am. Chem. Soc.,
2008, 130, 2408–2409.
42 T. C. Klebach, R. Lourens and F. Bickelhaupt, J. Am. Chem. Soc.,
1978, 100, 4886–4888.
45 Bruker, TWINABS, Bruker AXS Inc., Madison, Wisconsin, USA,
2001.
46 A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano,
C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori
and R. Spagna, J. Appl. Crystallogr., 1999, 32, 115–119.
47 SHELXTL V. 5.1 ed., Bruker AXS Inc., Madision, Wisconsin,
USA, 1997.
43 SAINT V. 7.03A ed., Bruker AXS Inc., Madison, Wisconsin,
USA, 1997–2003.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010
1666 | New J. Chem., 2010, 34, 1660–1666