Revisiting the phospha-Wittig-Horner reaction

Article abstract of DOI:10.1021/om201158k

P,P-Dichlorophosphines 2a-c (RPCl₂, R = Ph (a), t-Bu (b), 2,4,6-Me₃Ph (c)) and P,P-dibromophosphines 4d,e (RPBr₂, R = (i-Pr)₃SiC≡C (d) and H₂C=CH (e)) react with triethylphosphite under Michaelis-Arbuzov conditions to give phosphinodiphosphonates 3a-e in quantitative yields. After complexation to W(CO)₅ and treatment with CH₃ONa, phospha-Wittig-Horner reagents 9a,b are obtained on a multigram scale in good overall yield. Phospha-Wittig-Horner reagents with unsaturated substituents at ^IIIP (10d,e) can be prepared in analogous procedures; however, they prevail in an unusual ylide form that allows conjugation between the lone pair and the acetylene and vinyl π-systems, respectively. Phosphinophosphonate 9a has been characterized by X-ray crystallography and is shown to react smoothly with acetone within minutes. The resulting W(CO)₅-coordinated phosphaalkene is shown to dimerize to a 1,2-diphosphitane or to undergo a 1,3-proton shift depending on the reaction conditions. In addition, a one-pot synthetic sequence starting from W(CO)₅-coordinated phosphinodiphosphonates 5d,e has been developed to engage compounds with vinyl and acetylene substituents in phospha-Wittig-Horner reactions.

Full text of DOI:10.1021/om201158k

Article
pubs.acs.org/Organometallics
Revisiting the Phospha-Wittig−Horner Reaction
Anna I. Arkhypchuk, Marie-Pierre Santoni, and Sascha Ott*
Department of Chemistry, Ångstrom Laboratories, Uppsala University, Box 523, 75120 Uppsala, Sweden
̈
S
* Supporting Information
ABSTRACT: P,P-Dichlorophosphines 2a−c (RPCl2, R = Ph
(a), t-Bu (b), 2,4,6-Me3Ph (c)) and P,P-dibromophosphines
4d,e (RPBr2, R = (i-Pr)3SiCC (d) and H2CCH (e)) react
with triethylphosphite under Michaelis−Arbuzov conditions to
give phosphinodiphosphonates 3a−e in quantitative yields.
After complexation to W(CO)5 and treatment with CH3ONa,
phospha-Wittig−Horner reagents 9a,b are obtained on a
multigram scale in good overall yield. Phospha-Wittig−Horner
reagents with unsaturated substituents at IIIP (10d,e) can be
prepared in analogous procedures; however, they prevail in an
unusual ylide form that allows conjugation between the lone
pair and the acetylene and vinyl π-systems, respectively. Phosphinophosphonate 9a has been characterized by X-ray
crystallography and is shown to react smoothly with acetone within minutes. The resulting W(CO)5-coordinated phosphaalkene
is shown to dimerize to a 1,2-diphosphitane or to undergo a 1,3-proton shift depending on the reaction conditions. In addition, a
one-pot synthetic sequence starting from W(CO)5-coordinated phosphinodiphosphonates 5d,e has been developed to engage
compounds with vinyl and acetylene substituents in phospha-Wittig−Horner reactions.
PC bond. In a further development of the above protocols,
INTRODUCTION
■
Protasiewicz and co-workers developed a metal-free “one-pot”
protocol for the preparation of phosphanylidenephosphoranes
(type A), reported its crystal structure,8 and demonstrated their
reactivity toward aldehydes.9 However it should be noted that
this protocol is applicable mainly for P,P-dichlorophosphines
bearing bulky substituents (Mes* or Dmp), while smaller
substituents give unsatisfactory results.6 For reagents of type B,
a metal-free version has remained elusive.
The direct conversion of aldehydes and ketones into olefins
using phosphonium ylide reagents is an important reaction in
organic chemistry and was awarded the Nobel Prize in
chemistry to Georg Wittig in 1979.1 Inspired by the similarities
between low-valent phosphorus and carbon chemistry,2,3
Mathey and co-workers developed the so-called phospha-
Wittig reactions, i.e., an analogous procedure that allows the
access of phosphaalkenes from carbonyl compounds (Scheme
1).4,5 In analogy to the carbon case, two different reagents have
been reported that can be used for these transformations. Both
consist of a tervalent phosphorus center (PIII) that is bound to a
high-valent PV unit. Reagents that contain a −PR3 group as the
PV unit (R = Me, Bu, Ph, etc.) have been termed phospha-
Wittig reagents (type A, Scheme 1), while those that contain
(RO)2PO units are usually referred to as phospha-Wittig−
Horner reagents (type B, Scheme 1).
Preparation of both type of reagents is greatly facilitated by
the coordination of a metal−carbonyl fragment, frequently a
W(CO)5 unit, to stabilize the highly reactive low-valent
phosphorus center. Depending on the structure of the PV
center, two different reactivity patterns can be observed:
reagents of type A can be easily prepared in only two steps
starting from dichlorophosphines, but are reactive only toward
aldehydes.6,7 On the other hand, W(CO)5-coordinated
phosphinophosphonates (type B) have been shown to react
with aldehydes and ketones under basic conditions to afford
W(CO)5-coordinated phosphaalkenes.4,5 The latter reaction
produces phosphaalkenes that are more stable than those that
are accessible from aldehydes due to the presence of two
substituents at the PC carbon that kinetically stabilize the
We have recently commenced a program to combine low-
valent phosphorus with acetylene chemistry, thus introducing
intrinsic metal binding sites into oligoacetylene scaffolds.10−12
At the same time, P-inclusion in the resulting acetylenic
phosphaalkenes leads to decreased HOMO−LUMO gaps
compared to those in all-carbon-based compounds with
comparable π-systems.13−16 In this context, we became
interested in the phospha-Wittig−Horner reaction, as it appears
as an elegant entry into hitherto unavailable P,C-diacetylenic
phosphaalkenes. Since the latter compounds presumably suffer
from stability issues, W(CO)5 coordination is desirable to
stabilize the PC bond.17
During first exploratory studies, severe difficulties in the
preparation of reported phospha-Wittig−Horner reagents were
encountered that prompted us to develop an alternative
approach that allows the preparation of the reagents on a
multigram scale. With certain adjustments, the reaction
sequence is feasible also for substrates with nontraditional
unsaturated P-substituents. Depending on the substituent at
Received: November 20, 2011
Published: January 24, 2012
© 2012 American Chemical Society
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Scheme 1. Difference in Reactivity of Phospha-Wittig (Type A) and Phospha-Wittig−Horner (Type B) Reagents
a
Scheme 2. Summary of Literature Procedures toward Phospha−Wittig Reagents
a
Conditions: (a) R = Ph, t-Bu,5 (b) R = Mes, Ment,18,19 (c) R = Me, Ph, t-Bu, PhCHCH, BuOCHCH, 2-thienyl.18.
PIII, different isomeric forms of the phospha-Wittig−Horner
reagents are observed.
with unprecedented terminal vinyl and TIPS-acetylene (TIPS =
triisopropylsilyl) substituents were prepared in addition to
those that carry more conventional Ph, t-Bu, and Mes (Mes =
2,4,6-Me3Ph) groups.
RESULTS AND DISCUSSION
■
Preparation of P,P-Dichlorophosphine. While PhPCl2
(2a) and t-BuPCl2 (2b) are commercially available, MesPCl2
(2c) and TIPSCCPCl2 (2d) can be prepared by literature
methods,21 the latter in analogy with a procedure for the
synthesis of PhCCPCl2.22 The literature procedure for the
preparation of H2CCHPCl2 (2e) however requires the use of
highly toxic divinyl mercury,23 and it is therefore imperative to
develop a new synthetic protocol for 2e (Scheme 3).
Scheme 2 summarizes three synthetic protocols that are
described in the literature for the preparation of phospha-
Wittig−Horner reagents.4,5,18,19
The crucial step of routes (a) and (b) in Scheme 2 involves
2-fold lithiation of the primary phosphine tungsten complex III,
which in our hands proved to be difficult. According to 31P
NMR analysis of the reaction mixture, III undergoes only
partial lithiation with BuLi or t-BuLi and only at temperatures
higher than −20°, irrespective of whether commercial or freshly
prepared BuLi was used. Warming the mixture to higher
temperatures leads to decomposition. Lithiation was alter-
natively attempted with LDA, an approach that initially
converts primary phosphine III to its monolithium salt;
however, it ultimately suffers from the addition of [(i-Pr)2N]−
to the phosphorus precursor and the formation of N,N-
diisopropylamino-O,O-diethylphosphonate, which is difficult to
separate from the desired product by chromatography. Protocol
(c) is the synthetically most reliable; however, it requires the
preparation of the NaOP(OEt)2 reagent. The latter is
somewhat tedious, as the amount of added sodium has to be
controlled precisely, as an excess will reduce the dichloro-
phosphine I. In our hands, all three routes (a)−(c)
unfortunately produce numerous side products that are
difficult, if not impossible, to remove by recrystallization and
column chromatography.
Scheme 3. Preparation of RPCl2 2d,e
Vinyl magnesium bromide was thus reacted with bis-
(diethylamino)chlorophosphine to afford bis(diethylamino)-
vinylphosphine 1e in good yield. Conversion to the
corresponding dichlorophosphine 2e using an ethereal solution
of anhydrous hydrochloric acid results in reaction mixtures that
are difficult to purify due to considerable heat, oxygen, and
moisture sensitivity of 2e. To avoid complicated purification
steps, we developed an alternative procedure that is based on a
chloride/amine exchange between bis(diethylamino)-
vinylphosphine 1e and phosphorus trichloride. Treatment of
bis(diethylamino)vinylphosphine 1e with two equivalents of
PCl3 under solvent-free conditions at room temperature results
Considering the above problems, we sought an alternative
access to phospha-Wittig−Horner reagents that would circum-
vent some of the problems encountered in the published
procedures. In particular the Michaelis−Arbuzov reaction
seemed to be a viable alternative to convert P,P-dichlorophos-
phines to the phosphinodiphosphonates VIII.20 With our
interest in phosphaalkenes that are in π-conjugation with other
unsaturated organic groups, phospha-Wittig−Horner reagents
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Scheme 4. Michaelis−Arbuzov Reaction of RPCl2 2a−e to Phosphinodiphosphonates 3a−e
Scheme 5. Coordination of W(CO)5 to 3a−e and Treatment of the Latter with Potassium tert-Butoxide
Scheme 6. Hydrolysis of Phosphinodiphosphonates Metal Complexes
in quantitative formation of desired P,P-dichlorovinylphosphine
2e and dichloro(diethylamino)phosphine within 5 minutes. 2e
is isolated as a colorless liquid in 75% yield by vacuum
distillation at −20 °C.
phospha-Wittig−Horner reagents and their phosphaalkenes.
Thus, freshly prepared W(CO)5CH3CN5 was mixed with
solutions of compounds 3a−e in THF to afford complexes
5a,b,d,e in moderate to good yields (65−84%). Only in the
case of mesityl-substituted 3c could no coordination to the
metal fragment be observed due to steric crowding, even after
prolonged heating at increased temperatures.
Michaelis−Arbuzov Phosphorylation of P,P-Dichloro-
phosphines. With 2a−e in hand, their reactivity with
triethylphosphite in Michaelis−Arbuzov reactions to afford
phosphinodiphosphonates 3a−e was investigated (Scheme 4).
While in the case of 2a−c, the desired phosphinodiphosph-
onates 3a−c could be obtained in good yields, the reaction of
2d,e proceeded very dissatisfactory, and only minor amounts of
3d,e could be isolated. 31P NMR spectra of the reaction
mixtures suggest that the majority of 2d,e undergoes
scrambling reactions with triethylphosphite to afford mixtures
of ethylchlorophosphites with varying numbers of chloro and
ethoxy groups (Scheme 4). Since bromides are known to be
more reactive than chlorides and react under milder conditions
in Michaelis−Arbuzov reactions,24 we converted 2d,e into the
corresponding P,P-dibromophosphines 4d,e. This transforma-
tion is achieved using trimethylsilyl bromide as bromide source
under solvent-free conditions.25 Conversion is complete after
15 min at room temperature, and the dibromides 4d,e are
obtained in good yields (88−92%). With the dibromides in
hand, their reaction with P(OEt)3 proceeds smoothly and
affords phosphinodiphosphonates 3d,e as colorless, oxygen-
and water-sensitive liquids in good yield.
Complexes 5 are moderately moisture sensitive, oily
compounds that can be stored for several weeks at −20 °C
under an argon atmosphere without visible decomposition.
While phospha-Wittig reagents of type A that lack a stabilizing
metal center are known,9 the corresponding phospha-Wittig−
Horner reagents of type B have previously been reported only
as metal complexes. With 3a−c in hand, we examined the
possibility to prepare such species by hydrolysis. The difficulties
to do so became immediately evident when 2a was treated with
potassium tert-butoxide, resulting in the replacement of one
phosphonate group by a tert-butoxide and the formation of 6a
and KOP(OEt)2. In the case of 3b, a new product (7b) was
observed in addition to the formation of the analogous 6b. A
corresponding new species (7c) featured as the exclusive
product in the reaction of the mesityl-substituted 3c and was
identified as the enolate form of the phospha-Wittig−Horner
reagent of type B (Scheme 5). The assignment can be made on
the basis of the characteristic high-field 31P NMR chemical shift
of the PIII center (δ(PIII) = −165.6 ppm, δ(PV) = 79.8 ppm)
and the unusually large JPP = 569 Hz coupling constant.26
1
Coordination to W(CO)5 Core. At the stage of
phosphinodiphosphonates 3a−e, W(CO)5 metal fragments
were introduced to increase the stability of the subsequent
7b,c can be generated only in situ, and attempts to quench and
isolate the salts resulted in decomposition. Nevertheless, our
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experiments suggest that a certain amount of steric bulkiness
will prevent reaction at the tervalent phosphorus center and can
drive the reaction toward 7.
H···A = 168.7°) between the phosphine proton of the first and
a phosphonate oxygen of the second molecule. The tendency to
form hydrogen bonds is consistent with the necessity to use
hydrophobic silica gel for purification of the compound. The
Also for the metal-coordinated 5a,b,d,e, treatment with
NaOMe or KOt-Bu results in the first instance in the formation
of the enolate form of the phospha-Wittig−Horner reagents
8a,b,d,e (Scheme 6) with characteristic 31P NMR spectra that
feature two doublets typically around 65 ppm (PV) and
between −113.4 (8e) and −75.4 (8b) ppm (PIII) with large
1JP−P coupling constants between 340 (8e) and 429.7 (8b) Hz.
Aqueous workup of 8a,b that possess somewhat classical
substituents at the PIII center proceeds without difficulties, and
9a,b can be obtained in good yield. In fact, 9a could be
obtained from 2a on a 15 g scale with a total yield of 62% over
three steps. In our hands, the new procedure that relies on a
Michaelis−Arbuzov reaction is a vast improvement compared
to existing literature methods (Scheme 2). Compound 9a
needs to be stored at low temperature under inert atmosphere
to avoid decomposition, which otherwise occurs within several
hours at room temperature. Recrystallization from pentane at
−30 °C gives 9a as white crystals suitable for X-ray analysis.
Figure 1 shows the first crystal structure of a phospha-Wittig−
́
P−W distance is 2.49 Å and, thus, in the expected region for
compounds of the general formula (CO)5W-PR3.27 Complex
9a adopts a staggered conformation across the P−P bond in the
solid state. The bulky W(CO)5 fragment avoids steric
congestion with the ethoxy groups by having a −sc relationship
with the PO according to the Klyne−Prelog classification.
The W−P−PO dihedral angles in the two molecules of the
crystallographic cell are 57.0(2)° for W1−P1−P2−O6 and
49.4(2)° for W2−P3−P4−O21.
While 9a,b can be obtained in high yields, a more
complicated picture emerges during the quenching of 8d,e
containing appended π-systems (Scheme 6). In the case of
TIPS-ethynyl-substituted 8d, treatment with aqueous NH4Cl
results in the formation of 10d, which can in principle be
described by two structures: as the enol form of the desired
phospha-Wittig−Horner reagent with a formal PP double
bond or as an ylide as depicted in Scheme 6. The structural
assignment of the product was made on the basis of the rather
1
small coupling constant of JP−P = 89 Hz, which points toward
an ylide-type structure. The stability of this compound as
compared to the elusive phospha-Wittig−Horner reagent 9d is
presumably due to π-conjugation of the lone pair at the low-
valent phosphorus center to the appended acetylene unit. The
conjugation is also evident from the UV/vis spectrum of 10d
(in CH3OH), which features a longest wavelength absorption
maximum as a shoulder around 360 nm that trails well into the
visible. The corresponding absorption of phenyl-substituted 9a
can be observed at higher energy around 345 nm. The
quenching products of 8e resemble those of 8d, even though an
additional complication obscures the picture somewhat. When
8e is quenched with aqueous NH4Cl, 10e is observed only in
minor amounts, and a new major product (11e) is detected
instead. 11e is the dimerization product of a reaction where a
IIIP nucleophile has attacked the vinyl group of a second
compound, followed by an intramolecular ring-closure
following the same mechanism. It is noteworthy that only the
cis-isomer is formed, the structure of which can easily be
assigned by 31P and 13C NMR.28 Similar reactivity was observed
by Mathey et al. with the divinylphosphine(pentacarbonyl)
tungsten complex, which upon treatment with BuLi forms 1,4-
diphosphorinane.29 The dimerization can however be avoided
by quenching 8e under strongly acidic conditions, thereby
preventing the formation of presumably anionic PIII nucleo-
philes. Addition of an aqueous solution of p-toluene sulfonic
acid results in the initial formation of 9e, which however
isomerizes to the thermodynamically more stable 10e over
hours. Phosphinylidenephosphites 10d,e are stable compounds
and can be purified by column chromatography.
Figure 1. Crystal structure of phospha-Wittig−Horner complex 9a.
ORTEP drawing (50% probability) All hydrogens except for H1 are
omitted for clarity. Selected bond lengths (Å): W1−P1 2.4966(16),
P1−H1 1.000, P1−P2 2.187(2), P2O6 1.471(5), P2−O7 1.575(5),
P2−O8 1.565(5).
Horner reagent. The crystallographic cell of complex 9a
consists of two molecules that interact with each other via a
́
hydrogen bond (D−H···A = 2.676 Å and dihedral angle D−
Scheme 7. Phospha-Wittig−Horner Reaction of 9a with Acetone to Form Phosphaalkene 12 and Subsequent Head-to-Head
a
Dimerization and 1,3-Proton Shift
a
Conditions: (i) LDA, THF, −78 °C, 30 min, or DABCO, rt; (ii) dry acetone, rt, 6−12 h.
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Figure 2. 31P NMR spectroscopic study of the transformation of 12 to 13 in THF solution, using C6D6 as internal standard. 31P NMR after 5 min, 1
h, 3 h, 5 h, 7 h, 9 h, and 11 h. Reaction was run at 22 °C, using 20 mg (0.035 mmol) of 9a in 0.5 mL of THF and 4 mg (0.035 mmol) of DABCO.
Scheme 8. In Situ Generation of 8e-Li and Its Reaction with Acetone
Test Reaction with Acetone. In order to verify the
reactivity of the phospha-Wittig−Horner reagents and to
investigate the effect of the different substituents and isomeric
forms on the formation of phosphaalkenes, test reactions of
9a,e with acetone were performed. Addition of DABCO to 9a
initiates the experiment (Scheme 7), the course of which was
monitored by 31P{H} NMR. As visible from Figure 2, the
reaction is rather fast and phosphaalkene 12 can be identified
by its 31P chemical shift at δTHF = 170 ppm (δCDCl3 = 176
ppm)4 as the only product after 5 minutes (Scheme 5). Upon
prolonging the reaction times, phosphaalkene 12 is consumed
and the new species 13 emerges, which is characterized by a 31P
chemical shift of δ = 105 ppm. The conversion is complete after
ca. 10 hours. HRMS studies show a molecular weight of m/z =
1092.89844 (13 + 2H2O + Ag) for the new species, i.e., twice
that of phosphaalkene 12. Compound 13 shows a characteristic
ABX coupling pattern of diasteriotopic methyl groups to two
shifts the product distribution of 13 vs 14 to 1:1. It is necessary
to underline that under such reaction conditions the 31P NMR
signal of 13 is very broad and relatively easy to overlook.
The reaction between 9a and acetone can also be promoted
by the addition of one equivalent of LDA. The transient lithium
salt that is formed quantitatively after 30 minutes at −30 °C is
best described as the lithium analogue of 8a with PP double-
bond character and 31P NMR chemical shifts of 62.7 and
−107.5 ppm (1JPP = 383.3 Hz).5 Addition of acetone and
stirring of the reaction mixture at room temperature results in
mixtures of 12 and 13, the ratio of which depends on reaction
times.
The presence of unsaturated substituents at the PIII disallows
the DABCO-promoted preparation of phosphaalkenes from
9d,e. However, a one-pot synthetic strategy that generates the
Li analogue of 8e (31P NMR: 63.4 (PV) and −113.2 (PIII) with
1JPP = 350 Hz) in situ starting from bis(phosphonato)-
phosphine 5e upon treatment with methanolic lithium
methoxide can be used for the reaction with ketones such as
acetone. After 8 hours, 8e-Li is completely converted to
phosphaalkene 15, which can be trapped by the addition of
methanol (Scheme 8). Phosphaalkene 15 is thermally unstable
and decomposes in the absence of trapping reagent, presumably
to polymeric materials.
1
phosphorus atoms in the H NMR. Together, the analytical
data allow the assignment of a 1,2-diphosphitane structure to
complex 13. Head-to-head type dimerization of 12 can be
explained by steric factors as the longer P−P bond compared to
the C−P bond presumably allows the bulky W(CO)5 groups to
avoid severe steric repulsion.
The head-to-head dimerization that we observe for 12
contrasts a report by Marinetti et al., who describe a different
subsequent chemistry for 12.5 According to this report, a 1,3-
proton shift occurs on 12 and a secondary vinylphosphane, 14,
is obtained instead. In our hands, the 1,3-proton shift is
observed only as a side reactions in less than 3% yield, as judged
by 31P NMR. The discrepancy between the two experimental
findings lies in the amount of DABCO that is used to promote
the reaction. Increasing the amount of base to two equivalents
CONCLUSIONS
■
We have developed a reliable synthetic protocol that allows the
preparation of phospha-Wittig−Horner reagents on a multi-
gram scale in three steps and good overall yields. Compound 9a
is the first phospha-Wittig−Horner reagent that has structurally
been characterized and has been shown to react quantitatively
with acetone to give phosphaalkene 12 in less than 5 minutes.
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suspension was allowed to warm to room temperature and stirred for
12 h. The solid was removed by filtration under argon, and the filtrate
concentrated under vacuum to afford a pale yellow oil. Fractional
distillation gives P,P-dichloro(TIPS-acetylene)phosphine (2d) as a
colorless, water- and oxygen-sensitive oil (bp 170 °C/1 Torr). Yield:
Prolonged reaction times result in subsequent transformations
to 1,2-diphosphitane 13 and vinylphosphine 14. Nontraditional
phospha-Wittig−Horner reagents with unsaturated, π-conju-
gated substituents at PIII can be prepared in analogous
procedures; however, they prevail in an unusual ylide form. A
one-pot synthetic sequence starting from phosphinodiphosph-
onates 5 has been developed to engage also the compounds
with such unsaturated substituents in phospha-Wittig−Horner
reactions. The knowledge obtained in this work encourages the
use of phospha-Wittig−Horner reagents as starting materials
for the construction of highly unsaturated P,C systems. Efforts
in these directions are currently in progress in our laboratories.
1
3.01 g, 63%. 31P (CDCl3), {H}): 117. H (CDCl3): 1.11 (s, 21H,
2
Si(CH(CH3)2)3). 13C (CDCl3, {H}): 122.1 (d, JC−P = 1.0, −CC−
1
P), 105.7 (d, JC−P = 81, −CC−P), 18.4 (s, Si(CH(CH3)2)3), 11.0
5
(d, JC−P = 2.0, Si(CH(CH3)2)3).
P,P-Dichlorovinylphosphine (2e). A 1.8 g (8.9 mmol) of 1e was
placed in a flame-dried flask connected to a Schlenck tube, and 2.44 g
(17.8 mmol) of phosphorus trichloride was added in one portion. The
reaction mixture was stirred for 15 min at rt. After this, the Schlenck
tube was cooled to −78 °C and exposed to vacuum (12 Torr). 2e was
collected in a Schlenck flask as a very moisture- and oxygen-sensitive
and highly odorous, colorless liquid. Yield: 0.7 g, 61%. 31P (CDCl3,
EXPERIMENTAL SECTION
■
2
3
{H}): 159.7. 1H (CDCl3): 6.9 (ddd, 3JH−H = 18.7, JH−P = 12.6, JH−H
General Procedures. All reactions were performed under argon
using Schlenck techniques. Diethyl ether and THF were freshly
3
3
= 11.9, PCHCH2), 6.10 (dd, JH−H = 18.7, JH−P = 18.7, PCHCH2),
3
3
distilled from sodium/benzophenone prior to use. H, 13C, and 31P
6.06 (dd, JH−P = 45.18, JH−H = 11.9, PCHCH2). 13C (CDCl3, {H}):
1
1
2
spectra were recorded on a 400 MHz spectrometer. Chemical shifts
(ppm) were reported and referenced to the internal signal of residual
protic solvent. High-resolution mass spectral analyses (HRMS) were
performed on a high-resolution and FTMS+pNSI mass spectrometer
(OrbitrapXL) or on a MicroTOF spectrometer with ESI source.
X-ray Data. Crystal structure data for compound 9a were
deposited at the Cambridge Crystallographic Data Centre under the
number CCDC 816416.
142.2 (d, JC−P = 51.3, PCHCH2), 130.6 (d, JC−P = 46.2, PCHCH2).
M i c h a e l i s − A r b u z o v R e a c t i o n o f 1 a − c w i t h
Triethylphosphite. Bis(O,O-diethyl)phosphonato)-
phenylphosphine (3a). A 14.69 g (0.088 mol) of O,O,O-
triethylphosphite was added dropwise to a solution of 7.91 g (0.044
mol) of P,P-dichlorophenylphosphine 2a in 25 mL of dry toluene at
room temperature. The reaction mixture was slowly heated to 110 °C
(gas evolution starts at ca. 60 °C) and heated to reflux for 6 h. After
complete conversion of the starting materials (as judged by 31P NMR
analysis), the reaction mixture was cooled to room temperature.
Removal of all volatiles under vacuum gave 3a as a colorless oil. The
Bis((N,N-dimethyl)amino)TIPS-acetylenephosphine (1d). A
solution of 7.53 g (0.041 mol) of TIPS-acetylene in 250 mL of
THF was cooled to −78 °C, and 16.4 mL (2.5 M solution in THF) of
BuLi was added dropwise over 20 min. The reaction mixture was
stirred for 30 min at −78 °C and 10 min at room temperature. The
reaction mixture was then cooled to −40 °C, and a solution of 6.38 g
(0.041 mol) of ((N,N-dimethyl)diamino)chlorophosphine in 10 mL of
THF was added over 10 min. The reaction mixture was allowed to
warm to room temperature and stirred for an additional 4 h. The
solution was concentrated under vacuum to a volume of 50 mL. The
residue was diluted with dry pentane (100 mL), the formed precipitate
removed by filtration, and the solvent removed by vacuum. The
remaining oily residue was fractionally distilled under vacuum (bp 176
°C/1 Torr), affording product as a colorless oil. Yield: 10 g, 81%. 31P
1
compound was pure by H NMR analysis and was used in the next
step without further purification. NMR data are consistent with those
described in the literature.20 Yield: 95%. 31P (CDCl3, {H}): 28.5 (d,
1
PV), −62.0 (t, JP−P= 131.8, PIII).
Bis(O,O-diethyl)phosphonato)tert-butylphosphine (3b). A 3.21 g
(0.02 mol) of 2b was placed in a flame-dried flask, and 6.71 g (0.04
mol) of O,O,O-triethylphosphite was added dropwise at room
temperature. The reaction mixture was slowly heated to 140 °C (gas
evolution starts at ca. 110 °C) and heated for 6 h. After complete
conversion of the starting materials (as judged by 31P NMR analysis),
the reaction mixture was cooled to room temperature. Removal of all
volatiles under vacuum gave a colorless oil of 3b as a pure compound
by 1H NMR analysis, which was used in the next step without further
purification. NMR data are consistent with those described in the
literature.18 Yield: 99%. 31P (CDCl3, {H}): 31.3 (d, 1JP−P = 210.4, PV),
−33.3 (t, PIII). 1H (CDCl3): 4.19−4.11 (m, 8H, OCH2CH3), 1.37 (d,
3
(CDCl3), {H}): 69.8. 1H (CDCl3): 2.74 (d, JH−P = 12.0, 12H,
NCH3), 1.09 (s, 21H, Si(CH(CH3)2)3). 13C (CDCl3, {H}): 108.7 (d,
2
1JC−P = 2.0, −CC−P), 106.8 (d, JC−P = 5.0, −CC−P), 41.1 (d,
2JC−P = 15.1, NCH3), 18.6 (s, Si(CH(CH3)2)3), 11.2 (s, Si(CH-
(CH3)2)3). HRMS (methanol): found 317.2171, calcd 317.2178,
C15H34N2PSi, [mol + H]+.
3
3JH−P = 12.0, 9H, t-Bu), 1.28 (t, JH−H = 8, 6H, OCH2CH3), 1.27 (t,
3JH−H = 8, 6H, OCH2CH3).
Bis((N,N-diethyl)amino)vinylphosphine (1e). A solution of
21.07 g (0.1 mol) of bis((N,N-diethyl)amino)chlorophosphine in
250 mL of THF was cooled to −78 °C, and 100 mL of a solution of
vinylmagnesium bromide (1 M solution in THF) was added over 30
min. The resulting suspension was allowed to warm to room
temperature and stirred for 12 h. The solvent was removed under
vacuum until ca. 100 mL of a suspension was left. Then 150 mL of dry
pentane was added to the suspension, the solid removed by filtration,
and the filtrate concentrated under vacuum. The resulting yellowish oil
was fractionally distilled to afford 1e as a colorless oil. Yield: 15.4 g,
Bis(O,O-diethyl)phosphonato)mesitylphosphine (3c). 3c was
prepared applying the same protocol as for 3b using 2.27 g (10.3
mmol) of 2c and 3.4 g (21 mmol) of O,O,O-triethylphosphite.
Reaction mixture was heated for 2 h at 140 °C. Resulting crude 3c was
dissolved in diethyl ether and chromatographed on silica gel using
diethyl ether to elute side products and methanol to elute 3c as a
colorless oil. Yield: 4 g, 90%. 31P (CDCl3, {H}): 29.4 (d, 1JP‑P = 187.7,
PV), −73.2 (t, PIII). 1H (CDCl3): 6.91 (s, 2H, Ph), 4.24−4.09 (bs, 8H,
OCH2CH3), 2.75−2.60 (bs, 6H, o-CH3Ph), 3.33 (s, 3H, p-CH3Ph),
1.27 (bs, 12H, OCH2CH3). 13C (CDCl3, {H}): 146.5 (s, o-Ph), 141.1
1
2
76%. 31P (CDCl3, {H}): 90.0. H (CDCl3): 6.16 (ddd, JC−P = 24.2,
3JH−H = 18.5, JH−H = 12.2, 1H, PCHCH2), 5.66 (ddd, JH−P = 20.6,
3
3
1
(s, p-Ph), 129.8 (s, m-Ph), 118.3 (d, JC−P = 15.1, ipso-Ph), 63.3 (s,
3JH−H = 12.2, JH−H = 2.6, 1H, PCHCH2), 5.46 (ddd, JH−H = 18.5,
2
3
OCH2CH3), 24.5 (d, 3JC−P = 16.1, o-CH3Ph), 21.0 (s, p-CH3Ph), 16.3
3JH−P = 8.1, JH−H = 2.6, PCHCH2), 3.10−2.94 (m, 8H, NCH2CH3),
2
3
(d, JC−P = 5.0, OCH2CH3). HRMS (methanol): found 447.12219,
1.03 (t, JH−H = 7.1, 12H, NCH2CH3). 13C (CDCl3, {H}): 139.8 (d,
3
calcd 447.12312, C17H31O6P3Na, [mol + Na]+.
1JC−P = 1.5, PCHCH2), 124.1 (d, JC−P = 15.8, PCHCH2), 42.7 (d,
2
Conversion of P,P-Dichlorophosphites into P,P-Dibromo-
phosphites; General Procedure. To 1 equiv (0.79 g, 2.8 mmol of
2d or 0.6 g, 4.6 mmol of 2e) of P,P-dichlorophosphine was added
dropwise 4 equiv (1.71 g, 11 mmol for 4d or 2.81 g, 18.4 mmol for 4e)
of TMSBr at room temperature. The reaction mixture was stirred for
10 min before all volatilities were removed under vacuum (12 Torr) at
room temperature, giving P,P-dibromophosphines 4d,e as pale orange
2JC−P = 15.4, NCH2CH3), 14.8 (d, JC−P = 3.5, NCH2CH3).
3
P,P-Dichloro(TIPS-acetylene)phosphine (2d). A solution of 5 g
(0.017 mol) of bis((N,N-dimethyl)amino)TIPS-acetylenephosphine
(1d) in 250 mL of diethyl ether was cooled to −30 °C, and 33.3 mL (2
M solution in diethyl ether) of hydrochloric acid solution was added
dropwise over 15 min. A white precipitate formed immediately. The
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1
oils. Compounds 4 were pure by H, 13C, and 31P NMR analysis and
2
3
1JC−W = 125.3, CO), 134.8 (dt, JC−P = 12.1, JC−P = 5.0, o-Ph), 131.3
4
5
3
used in the next step without further purification.
(dt, JC−P = 2.0, JC−P = 2.0, p-Ph), 128.8 (d, JC−P = 11.1, m-Ph),
124.7 (dt, 1JC−P = 39.2, 2JC−P = 2.0 ipso-Ph), 64.8 (d, 2JC−P = 3.0, CH2),
64.7 (dd, 2JC−P = 4.0, 3JC−P = 1, CH2), 64.5 (d, 2JC−P = 4.0, CH2), 64.5
P,P-Dibromo(TIPS-acetylene)phosphine (4d). Yield: 0.93 g,
89%. 31P (CDCl3, {H}): 92.6. 1H (CDCl3): 1.11 (s, 21H,
Si(CH(CH3)2)3). 13C (CDCl3, {H}): 126.1 (d, JC−P = 3.01, −C
2
2
(d, JC−P = 4.0, CH2), 16.3 (m, CH3).
1
C−P), 102.8 (d, JC−P = 91.5, −CC−P), 18.5 (s, Si(CH(CH3)2)3),
Bis(O,O-diethyl)phosphonato)tertbutylphosphine Tungsten
Pentacarbonyl (5b). Preparation according to the general procedure:
4.51 g (12.5 mmol) of 3b, 1.39 g (12.5 mmol) of Me3NO·2H2O, and
4.40 g (12.5 mmol) of W(CO)6. The 31P NMR of compound 5a has
been described in the literature18 and is consistent with that found by
5
11.1 (d, JC−P = 2.0, Si(CH(CH3)2)3).
P,P-Dibromovinylphosphine (4e). Yield: 0.92 g, 93%. 31P
1
3
2
(CDCl3, {H}): 147.1. H (CDCl3): 7.17 (ddd, JH−H = 18.5, JH−P
=
3
3
3
15.0, JH−H = 11.7, PCHCH2), 6.02 (dd, JH−H = 18.5, JH−P = 18.5,
us. Yield: 5.93 g, 69%. 31P (CDCl3, {H}): 23.6 (d, PV), 13.9 (t, 1JP−P
=
PCHCH2), 5.89 (dd, JH1−P = 43.2, JH−H = 11.7, PCHCH2). 13C
3
3
27.7, 1JP−W= 213, PIII). 1H (CDCl3): 4.39−4.29 (m, 8H, POCH2CH3),
2
(CDCl3, {H}): 139.8 (d, JC−P = 56.6, PCHCH2), 129.6 (d, JC−P
=
2
3
1.50 (d, JP−H = 16.7, 9H, t-Bu), 1.38 (t, JH−H = 6.9, 6H,
44.0, PCHCH2).
POCH2CH3), 1.37 (t, JH−H = 6.9, 6H, POCH2CH3). 13C (CDCl3,
3
Michaelis−Arbuzov Reaction of 4e,d with Triethylphos-
phite; General Procedure. One equivalent of P,P-dibromophos-
phine 4d,e was dissolved in 5 mL of dry, oxygen-free toluene, and the
resulting solution heated to 110 °C. Then 2 equiv of triethylphosphite
was added in one portion to the refluxing solution of 4d,e. Vigorous
reaction with gas evolution started immediately. As soon as the color
of the solution disappeared (ca. 5 min), heating was ceased. Removing
of solvents under vacuum (1 Torr, heating bath from rt to 100 °C, 2 h)
gave bis(O,O-diethyl)phosphonatophosphine as colorless oils. Com-
pounds 3d,e were pure by 1H, 13C, and 31P NMR analysis and used in
the next step without further purification.
{H}): 197.5 (d, 2JC−P = 25.4, CO), 196.2 (dt, 2JC−P = 6.1, 3JC−P = 2.3,
2
3
2
CO), 64.2 (dd, JC−P = JC−P = 3.9, POCH2CH3), 63.8 (dd, JC−P
=
3JC−P = 3.9, POCH2CH3), 37.9 (dt, 1JC−P = 4.8, 2JC−P = 1.3, C(CH3)3),
2
3
29.2 (dt, JC−P = 6.1, JC−P = 4.6, C(CH3)3), 16.5−16.4 (m,
POCH2CH3).
Bis(O,O-diethyl)phosphonato)(TIPS-acetylene)phosphine
Tungsten Pentacarbonyl (5d). Preparation according to the general
procedure: 1.09 g (2.2 mmol) of 3d, 0.28 (2.5 mmol) of
Me3NO·2H2O, and 0.88 g (2.5 mmol) of tungstenhexacarbonyl.
Complex 5d appears to be extremely moisture sensitive and could be
isolated only in a mixture with 20% hydrolysis product, which we
Bis((O,O-diethyl)phosphonato)(TIPS-acetylene)phosphine
(3d). 3d was prepared according to the general procedure using 0.93 g
(2.5 mmol) of 4e and 0.83 g (5 mmol) of triethylphosphite. Yield:
believe to be 9d (31P (CDCl3, {H}): 16.3 (d, JP−P = 126.2, PV),
1
−103.0 (d, PIII). 31P (CDCl3): 16.3 (d, JP−P = 126.2, PV), −103.0 (d,
1
1.09 g, 88%. 31P (CDCl3, {H}): 24.6 (d, JP−P = 155.4, PV), −96.5 (t,
1
1JP−H = 357.7 PIII).
PIII). H (CDCl3): 4.36−4.27 (m, 8H, POCH2CH3), 1.38−1.34 (m,
1
5d. 31P (CDCl3, {H}): 15.3 (d, 1JP−P = 97.1, PV), −61.7 (t, 1JP−W
=
12H, POCH2CH3), 1.08 (bs, 21H, Si(CH(CH3)2)3). 13C (CDCl3,
221.7, PIII). 1H (CDCl3): 4.46−4.25 (m, 8H, POCH2CH3), 1.40−1.34
(m, 12H, POCH2CH3), 1.10 (s, 21H, Si(CH(CH3)2)3).
2
5
{H}): 61.9 (d, JC−P = 6.0, POCH2CH3), 18.4 (d, JC−P = 2.0,
Si(CH(CH3)2)3), 16.3 (d, JC−P = 7.0, POCH2CH3), 10.9 (d, JC−P
3
4
=
Bis((O,O-diethyl)phosphonato)vinylphosphine Tungsten
Pentacarbonyl (5e). Preparation according to the general procedure:
1.28 g (4.1 mmol) of 3e, 0.46 (4.1 mmol) of Me3NO·2H2O, and 1.44
g (4.1 mmol) of tungstenhexacarbonyl. Yield: 1.6 g, 62%. 31P (C6D6,
6.0, Si(CH(CH3)2)3). HRMS (methanol): found 509.1766, calcd
509.1783, C19H41O6P3Si [M + Na]+.
Bis((O,O-diethyl)phosphonato)vinylphosphine (3e). 3e was
prepared according to the general procedure using 0.92 g (4.3 mmol)
of 4e and 1.42 g (8.6 mmol) of triethylphosphite. Yield: 1.28 g, 95%.
{H}): 19.5 (d, JP−P = 79.3, PV), −28.3 (t, JP−3W = 223.3, PIII). H
1
1
1
3
2
3
(C6D6): 6.58 (dddt, JH−H = 18.1, JH−P = 13.9, JH−H = 11.6, JH−P
=
6.0, 1H, PCHCH2), 6.17 (ddt, 3JH−P = 21.1, 3JH−H = 18.1, 4JP−H = 2.8,
31P (CDCl3, {H}): 29.0 (d, JP−P = 165.7, PV), −68.7 (t, PIII). H
(CDCl3): 6.60−6.64 (m, 1H, PCHCH2), 6.14−6.01 (m, 2H,
PCHCH2), 4.25−4.16 (m, 8H, OCH2CH3), 1.35−130 (m, 12H,
1
1
3
3
1H, PCHCH2), 5.71 (dd, JH−P = 44.9, JH−H = 11.6, 1H, PCHCH2),
4.28−4.07 (m, 8H, OCH2CH3), 1.08 (t, 3JH−H = 7.1, OCH2CH3), 1.04
(t, JH−H = 7.1, OCH2CH3). 13C (C6D6, {H}): 198.0 (d, 2JC−P = 25.8,
3
OCH2CH3). 13C (CDCl3, {H}): 136.4 (dt, JC−P = 32.2, JC−P = 15.1,
1
2
2
3
2
2
3
CO), 195.8 (dt, JC−P = 6.0, JC−P = 2.0, CO), 137.3 (dt, JC−P = 9.0,
PCHCH2), 123.2 (dt, JC−P = 16.1, JC−P = 5.0, PCHCH2), 63.5 (bs,
OCH2CH3), 16.4 (s, OCH2CH3). HRMS (CH3CN): found
333.07802, calcd 333.07857, C10H24O6P3 [M + H]+.
3JC−P = 9.0, PCHCH2), 125.3 (d, JC−P = 25.2, PCHCH2), 64.6 (d,
1
2JC−P = 7.3, OCH2CH3), 64.6 (d, JC−P = 6.9, OCH2CH3), 16.3 (dd,
2
3JC−P = 3.0, 4JC−P = 3.0, OCH2CH3), 16.2 (dd, 3JC−P = 3.2, 4JC−P = 3.2,
Coordination to the Tungsten Core; General Procedure.
(CH3CN)W(CO)5 was prepared in a modified literature proce-
dure:5,18 1 equiv of Me3NO·2H2O was added in small portions over 20
min to a suspension of 1 equiv of tungstenhexacarbonyl in acetonitrile.
During addition, the reaction temperature was kept below 10 °C. After
gas evolution ceased and all precipitate was dissolved (ca. 30 min), the
solvent was removed under vacuum, keeping the temperature of the
bright yellow solution below 10 °C. The resulting solid (CH3CN)-
W(CO)5 was dried at high vacuum for 5 h. (CH3CN)W(CO)5 was
then dissolved in THF and a solution of 1 equiv of diphosphonato-
phosphine 3a,b,d,e in toluene was slowly added. The reaction mixture
immediately turned dark green and was stirred at 40 °C for 10 h.
Solvent was removed under vacuum, and the residue extracted with
pentane (3 × 50 mL). The afforded bright yellow solution was
concentrated under vacuum to give 5a,b,d,e as yellow oils. The
material was used for the next step without further purification.
Bis(O,O-diethyl)phosphonato)phenylphosphine Tungsten
Pentacarbonyl (5a). Preparation according to the general procedure:
31.1 g (0.044 mol) of 3a, 4.89 g (0.044 mol) of Me3NO·2H2O, and
15.48 g (0.044 mol) of tungstenhexacarbonyl. The 31P NMR of
compound 5a has been described in the literature18 and is consistent
with that found by us. Yield: 26.13 g, 84%. 31P (CDCl3, {H}): 20.0 (d,
OCH2CH3). HRMS (methanol): found 678.9847, calcd 678.9860,
C15H23O11P3WNa [M + Na]+. IR (solution in pentane, cm−1): 2078,
1983, 1960, 1379, 1267, 1251, 1163, 1032, 1018.
Synthesis of 9a,b; General Procedure. A solution of compound
5a,b (26.13 g, 0.037 mol of 5a and 5.93 g, 8.6 mmol of 5b) in THF
(250 mL) was cooled to −30 °C, and 1 equiv (74 mL for 5a and 17.3
mL for 5b) of a 0.5 M solution of sodium methanolate in methanol
was added dropwise over 20 min. The reaction mixture was stirred at
−30 °C for 30 min and quenched by the addition of a 10% solution of
ammonium chloride (100 mL). Once the mixture reached room
temperature, the phases were separated and the water phase extracted
three times with 100 mL of diethyl ether. Combined organic extracts
were washed with brine and dried over magnesium sulfate. The solvent
was removed under vacuum, and the residue chromatographed on
silica gel (Merck, grade 7734, mesh 70−230) using a diethyl ether/
pentane, 1:1, mixture as eluent to give phosphinophosphonates 9a,b as
a white solid.
Alternatively, 5a can be dissolved in pentane and chromatographed
on Al2O3 using diethyl ether/pentane, 1:1, as eluent, affording 9a,
however in lower overall yield of 40% over three steps. Analytical data
are consistent with those described in the literature.5
(O,O-Diethyl)phosphonato)phenylphosphine Tungsten
Pentacarbonyl (9a). Yield: 15.6 g, 75%. 31P (CDCl3, {H}): 21.9
(d, PV), −49.0 (d, 1JP−P = 79.8, 1JP−W = 225.4, PIII). 1H (CDCl3): 1.24
(t, 3JH−H = 7.3, 3H, CH3), 1.25 (t, 3JH−H = 7.0, 3H, CH3), 4.05 (m, 4H,
1
1
PV), −19.5 (t, JP−P= 65.9, JP−W = 225.4, PIII). 1H (CDCl3): 1.24 (m,
6H, CH3), 1.34 (m, 6H, CH3), 4.24 (m, 8H, CH2), 7.17 (m, 1H, Ph),
7.24 ((m, 1H, Ph), 7.49 (m, 2H, Ph), 8.14 (m, 1H, Ph). 13C (CDCl3,
{H}): 197.8 (d, 2JC−P = 26.1, CO), 195.7 (dt, 2JC−P = 6.0, 3JC−P = 2.0,
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CH2), 5.99 (d, JH−P= 338.0, 1H, H−P), 7.47 (m, 3H, Ph), 7.68 (m,
1.5, 1H, PCHCH2), 5.50 (ddd, 3JH−P = 36.2, 3JH−H = 11.4, 2JH−H = 1.5,
2H, Ph). 13C (CDCl3, {H}): 197.7 (d, JC−P = 23.1, CO), 195.0 (dd,
2
3
3
1H, PCHCH2), 4.13 (pentet, JH−H = JH−P = 7.1, 4H, OCH2CH3),
2JC−P = 7.0, JC−P = 3.0, JC−W = 126.7, CO), 133.7 (dd, JC−P = 11.1,
3JC−P = 4.0, o-Ph), 131.3 (dd, 4JC−P = 2.0, 5JC−P = 2.0, p-Ph), 129.2 (dd,
3JC−P = 10.1, 4JC−P = 2.0, m-Ph), 125.3 (d, 1JC−P = 39.2, ipso-Ph), 64.1
(d, 2JC−P = 8.0, CH2), 63.8 (d, 2JC−P = 8.0, CH2), 16.3 (d, 3JC−P = 2.0,
3
1
2
3
1.30 (t, JH−H = 7.1, 6H, OCH2CH3). HRMS (CH3CN): found
558.9519, calcd 558.9520, C11H14O9P2WNa, [M − H + NaOH]+. IR
(solution in methanol, cm−1): 2069, 2054, 1940, 1916, 1892.
1,4-(O,O-Diethyl)diphosphonate-1,4-diphosphinane Tung-
sten Pentacarbonyl (11e). Yellow solid. Yield: 0.33 g, 25%. 31P
3
CH3), 16.2 (d, JC−P = 2.0, CH3). IR (solution in pentane, cm−1):
1
1
(CDCl3), {H}): 24.4 (d, JP−P = 76.1, PV), −27.5 (dd, JP−P = 76.1,
2078, 1990, 1952, 1921, 1257(PO), 1041, 1017, 967(P−H).
(O,O-Diethyl)phosphonato)tertbutylphosphine Tungsten
Pentacarbonyl (9b). Yield: 2.58 g, 57%. 31P (CDCl3, {H}): 24.0
(d, 1JP−P = 43.7, PV), −18.2 (d, 1JP−W = 216.9, PIII). 1H (CDCl3): 4.92
(d, 1JH−P = 315.8, 1H, HP), 4.29−4.17 (m, 4H, OCH2CH3), 1.43 (dd,
3JP−P = 6.5, IIIP), −27.4 (dd, JP−P = 76.1, JP−P = 6.5, IIIP). 1H
1
3
2
3
(CDCl3): 4.31 (dq, JH−P = 8.7, JH−H = 7.1, 8H, OCH2CH3), 3.17−
2.94 (m, 4H, PCH2), 2.41−2.20 (m, 4H, PCH2), 1.40 (t, 3JH−H = 7.1,
OCH2CH3). 13C (CDCl3, {H}): 197.2 (d, 2JC−P = 23.1, CO), 195.5 (d,
4
3
1
2
1
3JH−P = 16.79, JH−P = 0.8, 9H, t-Bu), 1.38 (t, JH−H = 6.79, 3H,
2JC−P = 2, JC−W = 125.7, CO), 195.4 (d, JC−P = 2, JC−W = 124.7,
OCH2CH3), 1.37 (t, JH−H = 6.79, 3H, OCH2CH3). 13C (CDCl3,
CO), 63.8 (d, 2JC−P = 8.0, OCH2CH3), 22.0 (dd, 1JC−P = 15.9, 2JC−P
=
3
{H}): 197.7 (d, 2JC−P = 24.1, CO), 195.9 (dd, 2JC−P = 7.0, 3JC−P = 3.0,
3.8, PCH2), 21.9 (dd, JC−P = 16.3, JC−P = 3.4, PCH2), 16.6 (d, 3JC−P
= 5.0, OCH2CH3). HRMS (CH3OH): found 1062.9248, calcd
1062.9244, C22H28O16P4W2Na, [M + Na]+.
1
2
3
3
4
CO), 63.4 (d, JC−P = 7.0, OCH2CH3), 62.8 (dd, JC−H = 8.0, JC−P
=
1
2
1, OCH2CH3), 33.5 (dd, JC−P = 18.1, JC−P = 2.0, PC(CH3)3), 29.7
(dd, 2JC−P= 3JC−P = 5.0, PC(CH3)3), 16.4 (d, 3JC−P = 1.3, OCH2CH3),
16.3 (d, 3JC−P = 1.6, OCH2CH3). IR (solution in pentane, cm−1): 2076,
1984, 1950, 1930, 1910, 1379, 1251, 1043, 1018.
Reaction of 9a with Acetone. A 0.84 g (1.5 mmol) sample of 9a
was dissolved in 15 mL of THF and cooled to −10 °C. Then 0.75 mL
of a 2 M solution of LDA was added dropwise. The reaction mixture
changed color to bright yellow. Formation of the lithium salt 8a-Li was
Hydrolysis of 5d. A 2.1 g (2.2 mmol) portion of the reaction
mixture from the previous step was dissolved in 25 mL of THF and
stirred open to air for 30 min. Solvents were removed under vacuum,
and the resulting oily residue was dissolved in diethyl ether, which was
directly transferred to a silica gel column. Side products were washed
with diethyl ether. Target complex 10d was recovered with 10%
methanol in diethyl ether and obtained as a pale yellow solid.
10d. Yield: 0.3 g, 20%. 31P (CD3OD, {H}): 37.2 (d, 1JP−P = 89, PV),
confirmed by 31P NMR (63.8 (d, J1P−P = 381 Hz), −106.4 (d, J1
=
P−W
98 Hz)).5 The reaction mixture was then cooled to −78 °C, and 5
equiv of dry acetone was added. The reaction mixture was warmed to
room temperature and stirred for 6 h. Solvent removal under vacuum
resulted in a yellow residue, which was purified by column
chromatography on silica gel using diethyl ether/pentane, 1:9, as
eluent. The simultaneous formation of 12 and 13 was observed. If the
reaction mixture was stirred for longer times (15−24 h), only 13 was
obtained. The analytical data for 12 are in accordance with the
literature data.4
−138.7 (d, JP−W = 195.8, PIII). H (CD3OD): 4.23 (dq, JP−H = 8.0,
1
1
2
3JH−H = 8.0, 4H, OCH2CH3), 1.31 (t, JH−H = 8.0, 6H, OCH2CH3),
3
1.10 (s, 21H, TIPS). 13C (CD3OD, {H}): 203.4 (d, 2JC−P = 15.1, CO),
200.7 (dd, 2JC−P = 4.0, 3JC−P = 4.0, 1JC−W = 127.7, CO), 109.2 (d, 1JC−P
Diphosphitane 13. Colorless oil that solidifies in the freezer.
2
3
1
Yield: 0.38 g, 53%. 31P (CDCl3, {H}): 121.4 (1JP−W = 267.0). H
= 11.1, −CC-P), 106.6 (dd, JC−P = 10.1, JC−P = 8.0, −CC−P),
2
4
(CDCl3): 7.57−7.40 (m, 5H, Ph), 1.20 (dd, 3JP−H = 16.0, JP−H = 8.0,
63.6 (d, JC−P = 8.0, OCH2CH3), 19.2 (s, Si(CH(CH3)2)3), 16.8 (d,
3JC−P = 6.0, OCH2CH3), 12.8 (s, Si(CH(CH3)2)3). HRMS (ACN
solution): found 713.07005, calcd 713.06978, C20H32O9P2SiWNa, [M
− H + NaOH]+. IR (solution in methanol, cm−1): 2068, 2057, 1944,
1917, 1891.
6H, CH3), 1.03 (dd, 3JP−H = 16.0, 4JP−H = 4.0, 6H, CH3). 13C (CDCl3,
2
2
1
{H}): 198.8 (d, JC−P = 22.1, CO), 196.6 (d, JC−P = 7.0, JC−W
=
1
4
125.3), 139.6 (d, JC−P = 39.2, ipso-Ph), 130.3 (d, JC−P = 3.0, p-Ph),
2
3
128.6 (d, JC−P = 13.1, o-Ph), 128.4 (d, JC−P = 10.1, m-Ph), 36.9 (d,
1JC−P = 28.2), 16.7 (d, JC−P = 4.0, CH3), 16.2 (s, CH3). HRMS
3
Hydrolysis of 5e. A 1.6 g (2.5 mmol) amount of 5e was dissolved
in 25 mL of THF and cooled to −25 °C. After this, 6.3 mL (3.1 mmol,
0.5 M solution in methanol) of a sodium methoxide solution was
added dropwise. The reaction mixture was stirred for 30 min and
quenched with water. The resulting solution was allowed to warm to
rt, and organic solvents were removed under vacuum. The residue was
extracted with diethyl ether (3 × 25 mL). The organic washings were
combined, washed with brine, and dried over magnesium sulfate.
Solvent was removed to leave 5 mL of solution, which was directly
applied to a silica gel column. Small amounts of byproducts were
washed with diethyl ether. 10e was washed with a solution of 20%
methanol in diethyl ether. 11e was washed from the column with pure
methanol. Removal of the solvent resulted in a yellow oil, which upon
treatment with pentane afforded a pale yellow precipitate of 11e.
When the reaction mixture after sodium methoxide treatment was
quenched with an aqueous solution of p-toluenesulfonic acid (2
equiv), 9e was the only product formed (as detected by NMR). The
separated organic layer was dried over magnesium sulfate, and the
solvent removed under vacuum to afford crude 9e. 9e is unstable
under chromatography conditions and slowly polymerizes.
(solution in methanol with addition of AgOOCF3): 1092.89844, calcd
1092.90034, C28H22O10P2W2(H2O)2Ag. IR (solution in pentane,
cm−1): 2073, 1981, 1957, 1946, 1930, 1108, 1034, 1010.
In Situ Generation of 8e-Li and Its Reaction with Acetone. A
0.203 g (0.3 mmol) amount of 5e was dissolved in 5 mL of THF, and
0.16 mL (0.3 mmol, 2 M solution in methanol) of lithium methoxide
solution was added at rt. The reaction mixture was stirred for 10 min,
and an aliquot taken for NMR showed complete formation of 8e-Li.
8e-Li: 31P (THF/methanol, C6D6 as internal locking standard, {H}):
1
1
63.44 (d, JP−P = 350.3, PV), −113.1 (d, JP−W = 97.1, PIII). After this
0.1 mL of dry acetone was added to the reaction mixture, and the
resulting solution stirred for 8 h at room temperature. Solvents were
removed under vacuum, and the yellow, oily residue was chromato-
graphed on silica gel using pentane as eluent (Rf = 0.4). 16 was
obtained as a colorless oil.
16. Yield: 0.041 g, 28%. 31P (CDCl3, {H}): 137.8 (1JP−W = 270.3).
3
3
1H (CDCl3): 6.24 (ddd, 2JH−P = 23.2, JH−H = 18.0, JH−H = 12.2, 1H,
3
3
PCHCH2), 6.04 (dd, JH−P = 34.9, JH−H = 12.2, 1H, PCHCH2), 5.87
(dd, 3JH−H = 18.0, 3JH−P = 18.0, 1H, PCHCH2), 3.51 (d, 2JH−P = 12.5,
3H, OCH3), 2.29−2.17 (m, 1H, PCH(CH3)2), 1.17 (dd, 3JH−P = 17.6,
3JH−H = 7.3, 3H, PCH(CH3)2), 1.10 (dd, 3JH−P = 17.8, 3JH−H = 7.3, 3H,
(O,O-Diethyl)phosphonatovinylphosphine Tungsten Penta-
carbonyl (9e). 31P (CDCl3, {H}): 21.7 (d, JP−P = 95.5, PV), −60.8
1
(d, JP−W = 225, PIII). 31P (CDCl3): 21.7 (d, JP−P = 95.5, PV), −60.8
1
1
PCH(CH3)2). 13C (CDCl3, {H}): 198.6 (d, JC−P = 24.2, CO), 196.5
2
(dm, JH−P = 336, PIII). H (CDCl3): 6.50−6.33 (m, 1H, PCHCH2),
1
1
(d, 2JC−P = 7.7, 1JC−W = 125.7, CO), 135.9 (d, 1JC−P = 29.2, PCHCH2),
131.6 (d, 2JC−P = 4.7, PCHCH2), 54.5 (d, 2JC−P = 4.3, OCH3), 34.2 (d,
1
3
6.25−6.06 (m, 2H, PCHCH2), 5.59 (dd, JH−P = 336.2, JH−H = 5.9,
3
PH), 4.31−4.18 (m, 4H, OCH2CH3), 1.38 (t, JH−H = 6.8, 3H,
2
1JC−P = 32.4, PCH(CH3)2), 16.5 (d, JC−P = 3.8, PCH(CH3)2), 15.9
3
OCH2CH3), 1.36 (t, JH−H = 6.8, 3H, OCH2CH3).
10e. Yellow solid. Yield: 0.14 g, 10%. 31P (CD3OD, {H}): 43.9 (d,
(d, 2JC−P = 4.7, PCH(CH3)2). HRMS (solution in mixture of methanol
and chloroform): found 918.00045, calcd 917.99999,
C22H25O12P2W2Li, Coulomb dimer [M2 − H + Li]+ . IR (solution
in pentane, cm−1): 2073, 1979, 1955, 1944, 1914, 1379, 1033.
1JP−P = 111.7, PV), −96.6 (d, JP−W = 161.8, PIII). H (CD3OD): 6.68
1
1
3
2
3
3
(dddd, JH−H = 18.0, JH−P = 14.4, JH−H = 11.4, JH−P = 10.5, 1H,
PCHCH2), 5.62 (dddd, 3JH−H = 18.0, 3JH−P = 17.9, 4JH−P = 3.1, 2JH−H
=
1125
dx.doi.org/10.1021/om201158k | Organometallics 2012, 31, 1118−1126

Organometallics
Article
(29) Mercier, F.; Mathey, F. Tetrahedron Lett. 1985, 26, 1717−1720.
ASSOCIATED CONTENT
* Supporting Information
Summary of the X-ray data of 9a and copies of the NMR
spectra.This material is available free of charge via the Internet
at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: sascha.ott@fotomol.uu.se.
■
ACKNOWLEDGMENTS
This work was supported by the Swedish Research Council, the
■
Goran Gustafsson Foundation, Uppsala University through the
̈
U3MEC molecular electronics priority initiative, and COST
0802 PhoSciNet. We wish to thank Dr. Heinrich Luftmann
(University of Muenster, Germany) for HRMS.
REFERENCES
■
(1) http://nobelprize.org/nobel_prizes/chemistry/laureates/1979/
wittig-lecture.pdf.
(2) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon
Copy; John Wiley & Sons: Chichester, 1998.
(3) Gates, D. P. Top. Curr. Chem. 2005, 250, 107−126.
(4) Marinetti, A.; Mathey, F. Angew. Chem., Int. Ed. Engl. 1988, 27,
1382−1384.
(5) Marinetti, A.; Bauer, S.; Ricard, L.; Mathey, F. Organometallics
1990, 9, 793−798.
(6) Shah, S.; Protasiewicz, J. D. Coord. Chem. Rev. 2000, 210, 181−
201.
(7) Wang, H.; Zhao, W.; Zhou, Y.; Duan, Z.; Mathey, F. Eur. J. Inorg.
Chem. 2011, 4585−4589.
(8) Shah, S.; Yap, G. P. A.; Protasiewicz, J. D. J. Organomet. Chem.
2000, 608, 12−20.
(9) Shah, S.; Protasiewicz, J. D. Chem. Commun. 1998, 1585−1586.
(10) Diederich, F. Chem. Commun. 2001, 219−227.
̈
(11) Schafer, B.; Oberg, E.; Kritikos, M.; Ott, S. Angew. Chem., Int.
̈
Ed. 2008, 47, 8228−8231.
(12) Geng, X.-L.; Ott, S. Chem.Eur. J. 2011, 17, 12153−12162.
̈
(13) Oberg, E.; Schafer, B.; Geng, X.-L.; Pettersson, J.; Hu, Q.;
̈
Kritikos, M.; Rasmussen, T.; Ott, S. J. Org. Chem. 2009, 74, 9265−
9273.
(14) Geng, X.-L.; Ott, S. Chem. Commun. 2009, 45, 7206−7208.
(15) Geng, X.-L.; Hu, Q.; Schafer, B.; Ott, S. Org. Lett. 2010, 12,
̈
692−695.
̈
(16) Oberg, E.; Geng, X.-L.; Santoni, M.-P.; Ott, S. Org. Biomol.
Chem. 2011, 9, 6246−6255.
(17) Mercier, F.; Hugel-leGoff, C.; Mathey, F. Tetrahedron Lett.
1989, 30, 2397−2398.
(18) Bauer, S.; Marinetti, A.; Mathey, F. Heteroat. Chem. 1991, 2,
277−281.
(19) deVaumas, R.; Marinetti, A.; Ricard, L.; Mathey, F. J. Am. Chem.
Soc. 1992, 114, 261−266.
(20) Fluck, E.; Binder, H. Inorg. Nucl. Chem. Lett. 1967, 3, 307−313.
(21) Liddle, S. T.; Izod, K. Organometallics 2004, 23, 5550−5559.
(22) Ito, S.; Nishide, K.; Yoshifuji, M. Tetrahedron Lett. 2002, 43,
5075−5078.
(23) Kaesz, H. D.; Stone, F. G. A. J. Org. Chem. 1959, 24, 635−637.
(24) Arbuzov, B. A. Pure Appl. Chem. 1964, 9, 307−353.
(25) Miroshnichenko, V. V.; Yurchenko, R. I.; Feschenko, N. G.
Zhurnal Obshchei Khimii 1993, 63, 231−232.
(26) Regitz, M.; Scherer, O. J. Multiple Bonds and Low Coordination in
Phosphorus Chemistry; Thieme Medical Publishers, Inc.: New York,
1990; Chapter 10, pp 338−351.
(27) Rooney, C. P.; Wade, J. L.; Hinkle, A. C.; Stolley, R. M.; Miller,
S. M.; Helm, M. L. Main Group Chem. 2008, 7, 155−165.
(28) Brooks, P. J.; Gallagher, M. J.; Sarroff, A.; Bowyer, M.
Phosphorus, Sulfur Silicon 1989, 44, 235−247.
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