Regioselective Single and Double Hydrophosphination and Hydrophosphinylation of Unactivated Alkynes

Article abstract of DOI:10.1021/acscatal.9b01538

A lanthanum-based N,N-dimethylbenzylamine complex was used as a precatalyst for both hydrophosphination and hydrophosphinylation of alkynes under mild conditions. In the case of hydrophosphination, the catalyst induced monoaddition with high regiospecific

Full text of DOI:10.1021/acscatal.9b01538

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Article
Regioselective Single and Double Hydrophosphination
and Hydrophosphinylation of Unactivated Alkynes
Miriam M.I. Basiouny, Deborah A Dollard, and Joseph A. R. Schmidt
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 24 Jun 2019
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Regioselective Single and Double Hydrophosphination and
Hydrophosphinylation of Unactivated Alkynes
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Miriam M.I. Basiouny, Deborah A. Dollard and Joseph A.R. Schmidt*
Department of Chemistry & Biochemistry, School of Green Chemistry and Engineering, College
of Natural Sciences and Mathematics, The University of Toledo, 2801 W. Bancroft St. MS 602,
Toledo, Ohio 43606-3390, USA.
*Corresponding Author
E-mail: Joseph.Schmidt@utoledo.edu. Phone: 419-530-1512. Fax: 419-530-4033.
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Abstract
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A lanthanum-based N,N-dimethylbenzylamine complex was used as a precatalyst for
both hydrophosphination and hydrophosphinylation of alkynes under mild conditions. In the case
of hydrophosphination, the catalyst induced mono-addition with high regiospecificity, yielding
only the anti-Markovnikov product, and stereoselectivity that could be controlled based on the
reaction conditions. Undertaking the catalysis with excess phosphine yielded the E isomer as the
major product; however, using excess alkyne, the Z isomer was instead isolated as the major
product. A brief investigation into the catalytic cycle suggested that a dimeric form of the
lanthanum phosphide active catalyst provided the Z isomers as kinetic products that then
underwent isomerization to yield the final E isomers. In the case of hydrophosphinylation, the
chemoselectivity depended on the nature of the alkyne used. Terminal alkynes gave only double
addition products while both single and double addition products were successfully isolated in
the case of internal alkynes. The hydrophosphinylation also showed high chemo- and
regioselectivity as only the anti-Markovnikov products were isolated. Mono-
hydrophosphinylation of internal alkynes gave almost exclusively the E isomer and double
hydrophosphinylation of all alkynes led to 1,2-addition products.
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Keywords: Hydrophosphination, Hydrophosphinylation, Lanthanum, Vinylphosphine, E-alkene,
Z-alkene
TOC Graphic:
HP(O)Ph2
Ph2(O)P
R
P(O)Ph2
R'
PPh2
R'
R
HPPh2
R'
La
P(O)Ph2
R'
RCCH
R
PPh2
RCCR'
R
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Introduction
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Phosphines and phosphine oxides are among the most common ligands utilized in the field of
organometallic chemistry.1 Nearly every type of catalytic reaction takes advantage of phosphine
ligands in one fashion or another. Phosphines are attractive ligands because of their broad steric
and electronic tunability.2 Traditional phosphine synthesis has employed radical, super basic, or
acidic conditions; however, these reactions commonly lack chemo-, regio- and stereoselectivity.3
In an effort to improve selectivity, the catalytic addition of H-P and H-P(O) across unsaturated
systems, referred to as hydrophosphination and hydrophosphinylation, respectively, has been
investigated in recent years.4 Traditionally, palladium, platinum, and some early transition metals
have been used in catalytic hydrophosphination and hydrophosphinylation, and although these
reactions show high chemoselectivity, they often still lack regio- and stereoselectivity (Table
1).3b, 5 Additionally, with the use of various designer ligands, some earth abundant metals such as
iron, copper, calcium, and the lanthanides have been successful in the hydrophosphination and
hydrophosphinylation of unsaturated systems.6, 7
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Table 1. Selected Examples of Previously Published Simple Metal Catalysts and Their
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Corresponding Selectivity
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Ph2P
Ph
Ph
Ph
9
[M]
+
+
+
Ph
HPPh2
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PPh2 Ph2P
B
C
A
A:B:C
Yield (%) ( )
Catalyst [M]
Pd(PPh3)4
Pd(OAc)2
Conditions
CH3CN, 130 oC, 18h
CH3CN, 130 oC, 7h
CH3CN, 180 oC, 12h
C6H6, 80 oC, 10h
C6H6, 80 oC, 10h
C6H6, 80 oC, 10h
Toluene, 80 oC, 2h
95 (0:14:86)
89 (87:7:6)
>92 (92:4:4)
>93 (10:45:45)
85 (86:14:0)
90 (95:5:0)
Pd(PPh3)4 + AcOH
Ni[P(OEt)3]4
NiBr2
Ni(acac)2 + HP(O)(OEt)2
Co(PMe3)4
73 (0:0:100)
Cp*FeMe(CO)py
Toluene, 110 oC, 48h
C6H6, 25 oC, 1h
90 (0:10:90)
(IMe4)2Yb(N(SiMe3)2)2
>95 (0:15:85)
Many catalyst systems utilize bidentate phosphine ligands, where two phosphorus atoms
coordinate to the same metal center, represented most famously by dppe ligands and their
derivatives.1 One method to produce a bidentate phosphine ligand is through the double
hydrophosphination/hydrophosphinylation of alkynes. Hydrophosphination has been achieved
with solvent-free radical conditions, but has required high temperatures and long reaction times.8
Catalytic double addition reactions have also been successful using both early and late transition
metal catalysts.9 Recently, Nakazawa et al. described iron catalysts for the double
hydrophosphination of terminal aryl alkynes. Unfortunately, the reaction required three days of
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heating at 110 °C.6a Webster et al. also used an iron (II) catalyst for the intramolecular
hydrophosphination of alkenes and alkynes, once again requiring elevated temperatures and
lengthy reaction times.6e Recently, Waterman et al. used a dimeric iron complex to induce the
double hydrophosphination of alkynes, requiring light or heat.10 Copper catalysts have been used
in the double hydrophosphination of both aryl and aliphatic alkynes. Though the copper systems
required low catalytic loading, they too required high temperatures.11 In related chemistry,
europium has been successful in the single hydrophosphination of alkynes, although the reaction
was not stereospecific and again required high temperatures.12
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Similar to the double hydrophosphination reactions outlined above, double
hydrophosphinylation of alkynes has also been investigated broadly. Han et al. successfully
double hydrophosphinylated terminal alkynes using a strong base (LiOtBu) and high
temperatures.3e Rhodium catalysts were also used to hydrophosphinylate alkynes under
microwave irradiation and yielded mono- or double addition products depending on the loading
of the phosphine oxide.13 Manganese and rhenium catalysts have also been used to effect the
single or double hydrophosphinylation of terminal aryl acetylenes although both required high
temperatures.14
Overall, the hydrophosphination and hydrophosphinylation of acetylenes are both known
reactions that have been achieved using a variety of catalysts. In the reported systems, these
addition reactions have thus far only been studied independently and have not been examined
simultaneously utilizing the same catalytic system. Both reactions generally required high
temperatures and elongated reaction times with limited selectivity. Herein, we describe the first
lanthanum-based catalyst, to our knowledge, capable of both hydrophosphination and
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hydrophosphinylation of acetylenes under very mild conditions (25-60 °C) with tunable chemo-
and stereoselectivity.
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Results and Discussion
Recently, we reported the catalytic effectiveness of an α-metalated dimethylbenzylamine
lanthanum complex (La(Dmba)3) in the double hydrophosphinylation of unactivated nitriles
under mild conditions; the reaction showed regioselectivity based on the nature of the nitrile.15 In
an attempt to further expand the utility of these lanthanum catalysts in hydrophosphination and
hydrophosphinylation reactions, unactivated alkynes were investigated as alternative substrates.
La(Dmba)3 proved to be an effective precatalyst for the hydrophosphination of alkynes
with diphenylphosphine. The reactions reached completion in 12-48 h with 5 mol% catalytic
loading in pyridine at room temperature while using a 1:1.6 alkyne to diphenylphosphine ratio.
Pyridine was selected as the solvent because we previously showed that it solvated both
hydrophosphination and hydrophosphinylation active catalysts.15 The reactions proceeded to
100% conversion when using aryl alkynes, giving exclusively the anti-Markovnikov product in
all cases (Table 2). The catalysts showed tolerance to both electron donating and even slightly
acidic alkynes (Table 2, 2d), and the reaction was successful when using both internal and
terminal aryl alkynes. In contrast, aliphatic alkynes, both terminal (1-hexyne) and internal (4-
octyne), yielded no hydrophosphination even at high temperatures and elongated reaction times.
Only a highly activated internal aliphatic alkyne was successfully hydrophosphinated (Table 2,
2g). Double addition products were not observed when reacting with excess diphenylphosphine,
even with heating and longer reaction times, while the E alkene monoaddition isomer was the
major product in all cases. In an effort to explore the catalytic cycle, the hydrophosphination of
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phenylacetylene (Table 2, 2a) was monitored hourly via 31P{1H} NMR spectroscopy in d5-
pyridine. To our surprise, initially only the Z isomer (31P{1H} = -23.5 ppm) was observed, which
then proceeded to slowly isomerize to the E isomer (31P{1H} = -10.0 ppm). This observation
seems counterintuitive to the expected [2+2] addition mechanism, which would be predicted to
form the E product directly (Scheme 1). Because of the unexpected stereochemistry found in the
kinetic product, we began to wonder if the process was more complicated than merely a simple
insertion reaction at a single metal center. In order to make sure that catalyst decomposition was
not playing a role in the process, a hydrophosphination reaction between phenylacetylene and
diphenylphosphine was set up with the usual conditions and allowed to react for 12 hours. An
aliquot removed from the solution showed no evidence of leftover diphenylphosphine and a 95:5
ratio of E:Z alkenes. Addition of another portion of reactants (phenylacetylene and
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diphenylphosphine) led to continued catalytic reaction with complete conversion to product after
another 12 hours and retention of the expected 95:5 isomer ratio.
[La]
[La] PPh2
H
[La] PPh2
H
PPh2
Ph
Ph
Ph
H
Scheme 1. Typical [2+2] addition mechanism, portrayed with anti-Markovnikov addition of a
lanthanum phosphide to phenylacetylene. Note that subsequent protonation of the La-C bond
would give the E isomer (trans alkene).
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Table 2. Hydrophosphination of Internal and Terminal Alkynes
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N
5 mol% La(Dmba)3
PPh2
N
+ HPPh2
R
R'
R
La
N
Pyridine
r.t.
R'
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12-48h
La(Dmba)3
Entry
2a
Alkyne
(R on left; R’ on right)
Reaction Time (h) Yield (%)a
E:Zb
95:5
12
12
12
12
12
48
48
87
82
85
73
90
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2b
2c
2d
2e
2f
95:5
95:5
90:10
80:20
80:20
95:5
H2N
O
O
O
O
2g
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Catalytic reactions were carried out with La(Dmba)3 (13.5 mg; 5 mol%), acetylene (0.5 mmol)
and diphenylphosphine (0.8 mmol) in pyridine (2 ml) for 12-48 h at room temperature. [a]
Isolated yields. [b] Ratio determined by 31P{1H} NMR spectroscopy.
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Furthermore, when the reaction was carried out under the same conditions, but with
reversed ratios of 1:1.6 diphenylphosphine to alkyne, the Z isomer became the major isomer
produced with only small amounts of the E isomer formed after 12 hours. This proved to be the
case with all three different alkynes tested in this way (Scheme 2). Further control experiments
showed that the isomerization did not occur with heating, elongated reaction time, light, Lewis
acid catalyst, or diphenylphosphine catalyst, nor without lanthanum tris-phosphide active
catalyst. This further supports the idea that the Z isomer is the kinetic product of the
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hydrophosphination, which then undergoes isomerization catalyzed by lanthanum phosphide to
produce the thermodynamic E isomer. Thus, not only was the hydrophosphination regiospecific,
but its stereoselectivity could be controlled depending on the reactant ratios used for the reaction.
PPh2
PPh2
0.6 eq. HPPh2
La(Dmba)3
12 h
1.6 eq. HPPh2
La(Dmba)3
12 h
R
R
R
major isomer
major isomer
R= H
4-Et
88%
85%
(>95% Z)
(>95% Z)
(>80% Z)
R= H
4-Et
87%
82%
(>95% E)
(2a')
(2b')
(2d')
(2a)
(2b)
(2d)
(>95% E)
(>90% E)
3-NH2 80%
3-NH2 73%
Scheme 2. Stereoselectivity depends on diphenylphosphine loading
Based on the stereochemical observations made above, it became clear that the reaction
mechanism does not follow the traditional monometallic insertion ([2+2] addition) followed by
protonolysis mechanism (Scheme 1). To understand the catalytic cycle further, some additional
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experiments were carried out. Using an internal standard, the stoichiometric reaction of
La(Dmba)3 with diphenylphosphine was shown to yield three equivalents of neutral
dimethylbenzylamine (HDmba), while concurrently forming only the lanthanum tris-phosphide
complex as the active catalyst. To investigate catalyst order, the hydrophosphination of
phenylacetylene was monitored via 1H NMR spectroscopy in d5-pyridine every two minutes
using three different catalyst loadings (2.5, 3.5, and 5.0 mol%; see Supporting Information).
Since the isomerization requires the active lanthanum tris-phosphide complex, a slight excess of
alkyne was used to suppress the isomerization, forming almost only the Z alkene. This data
suggests that the catalysis is second order in lanthanum.
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In the hydrophosphination of alkynes, mechanisms involving catalysts using first-row
transition metals are among those investigated in the greatest detail, although previous reports
have led to more questions than answers unfortunately.6e, 11, 16 For example, experimental results
in the case of iron catalysis have shown that the initial hydrophosphination occurred with
primarily the Z configuration that gradually transformed to the E isomer, much like we have
observed herein.6a A subsequently reported extensive DFT study on this iron-based system failed
to effectively elucidate the reasons behind the observed selectivity.16 In fact, the final
mechanistic scheme presented in that report shows a standard [2+2] addition mechanism (giving
the E isomer kinetically, despite the contrast between this and the experimentally observed
results).16 The Z isomer’s presence is explained by an undefined isomerization reaction between
E and Z isomers while bound to the metal center.16 Another study involving NHC coordinated
copper catalysts determined a slight energetic preference for the E product (only 0.7 kcal/mol),
but made no mention of the transition state structures leading to either the E or Z isomers in the
insertion reaction.11
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With little hard evidence in the literature available to rationalize the hydrophosphination
mechanism present with the lanthanum-based catalysis reported herein, we propose a plausible
catalytic cycle in line with the results above (Scheme 3). Two key details that required inclusion
were the second order dependency on lanthanum and the Z stereoselectivity displayed by the
kinetic product. To the first point, we propose that the lanthanum phosphido complex exists as a
dimer, with diphenylphosphide ligands bridging the two lanthanum metal centers. The potential
equilibrium between a lanthanum monomer and the catalytic lanthanum dimer present in the
rate-determining step is consistent with the second order dependency on lanthanum. With our
current evidence, we cannot speculate at what point a monomer is present within the entire
reaction process. Mechanistically, the alkyne coordinates to one of the lanthanum centers,
possibly disrupting one of the phosphido bridges. The coordination of alkenes and alkynes to
lanthanides is well established in the rare-earth-metal polymerization literature.17 Once
coordinated to the lanthanum, the alkyne can undergo nucleophilic attack by a phosphide from
the second lanthanum center, which effectively rationalizes the production of the Z-alkene as the
kinetic product (Scheme 3, top right). Finally, protonolysis by diphenylphosphine yields the free
Z isomer and regenerates the dimeric active species. The Z alkene is then subsequently
isomerized to the thermodynamic E final product by the lanthanum phosphide active species.
This isomerization could involve insertion of the product alkene into the La-P bond of the active
catalyst, single bond rotation, and then subsequent -phosphido elimination to produce the trans
isomer (Scheme 4). This insertion-elimination sequence would allow equilibration between the
E- and Z-isomers, ultimately leading to the more stable E-alkene products observed
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experimentally. Assuming insertion of the alkyne is more facile than insertion of the
vinylphosphine due to sterics, hydrophosphination would be kinetically favored over
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isomerization until the alkyne was almost completely consumed. The isolation of the kinetic Z-
isomer under phosphine limiting conditions supports this process since the La-P bonds necessary
for isomerization would not be present when the reaction runs out of phosphine substrate.
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R
R
Ph2
P
PPh2
[La]
[La]
[La]
[La]
P
P
Ph2
Ph2
Alkyne
coordination
Bimetallic
Insertion
R
[La] = La(PPh2)2(py)n
PPh2
Ph2
P
R
[La]
[La]
P
Ph2
Protonolysis
3 HDmba
[La]
[La]
P
Ph2
HPPh2
R
R
PPh2
La(Dmba)3
+
3 HPPh2
Isomerization
Precatalyst
Activation
PPh2
Scheme 3. Proposed catalytic cycle for lanthanum catalyzed hydrophosphination of alkynes
-phosphide
elimination
[La] PPh2
[La]
H
PPh2
[La]
H
PPh2
PPh2
[La] PPh2
[2+2] addition
bond
+
+
-phosphide
elimination
rotation
[2+2] addition
H
R
H
H
R
PPh2
H
PPh2
H
R
R
PPh2
H
Scheme 4. Isomerization from the Z to E alkene could proceed via an insertion/deinsertion
pathway.
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Using the same conditions as hydrophosphination, La(Dmba)3 was investigated as a
precatalyst for the addition of diphenylphosphine oxide to internal and terminal alkynes. These
hydrophosphinylation reactions proceeded with notable chemoselectivity. Intially, all the
reactions were undertaken using the same conditions: 10 mol% catalytic loading and 1:1.3
alkyne to diphenylphosphine oxide in pyridine for 14 h. Interestingly, the reaction products were
different depending on the nature of the alkyne tested. Terminal alkynes gave only double
hydrophosphinylation products while internal alkynes resulted in single addition products.
Therefore, the reactions of the terminal alkynes were repeated with a 1:2.3 alkyne to
diphenylphosphine oxide ratio in order to optimize yield of the double addition products (Table
3), each of which was produced with 1,2-addition giving dppe-like compounds. Reduction of
these doubly oxidized species to the dppe analogues could be undertaken using a variety of
methods,18 though this remains beyond the scope of the current report.
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Table 3. Double Hydrophosphinylation of Terminal Alkynes
5
P(O)Ph2
6
7
8
9
10 mol% La(Dmba)3
Ar
+ 2 HP(O)Ph2
P(O)Ph2
Pyridine
14 h
Ar
r.t.
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Yield(%)a
95
Entry
Alkyne
4a
90
90
4b
4c
4d
82
H2N
Catalytic reactions were carried out with La(Dmba)3 (27 mg; 10 mol%), alkyne (0.5 mmol), and
diphenylphosphine oxide (1.15 mmol) in pyridine (2 ml) for 14 h at room temperature. [a]
Isolated yields.
At room temperature with 1.3 eq. of phosphine oxide, internal alkynes yielded single
hydrophosphinylation products with only traces of the double hydrophosphinylation products
detected. The reaction was completely regiospecific and highly stereoselective, yielding almost
completely the E isomer in all cases. To induce complete conversion to the double addition
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products using internal alkynes, the reactions required higher temperature (60 °C) and elongated
reaction times (Table 4).
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Table 4. Single and Double Hydrophosphinylation of Internal Alkynes
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Ph2(O)P
R
P(O)Ph2
R'
P(O)Ph2
R'
1.3 eq. HP(O)Ph2
2.3 eq. HP(O)Ph2
R
R'
10 mol% La(Dmba)3
10 mol% La(Dmba)3
R
48 h
r.t.
48 h
60 oC
Yield(%)a
Alkyne
Yield(%)a
E:Zb
4e
) 80
(
5a
95:5
95:5
95:5
(
) 82
) 70
) 65
4f
( ) 60
5b
(
O
O
O
O
4g
) 60
(
5c
(
Catalytic reactions were carried out with La(Dmba)3 (27 mg; 10 mol%), alkyne (0.5 mmol) and
diphenylphosphine oxide (0.65 or 1.15 mmol) in pyridine (2 ml) for 48 h at room temperature or
60 °C. [a] Isolated yield. [b] Ratio determined by 31P{1H} NMR.
Unlike diphenylphosphine, which formed only monoaddition hydrophosphination
products (Table 2), the production of double addition products in this case may be related to the
ability of diphenylphosphine oxide to tautomerize (Scheme 5).19 Since no double addition was
observed in the case of hydrophosphination (Table 2), this tautomerization may play a crucial
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role in the second addition, perhaps by reducing the steric strain at the metal center. On the other
hand, we cannot discount the possibility that the difference in reactivity is simply a matter of
activation by the electron withdrawing oxygen atom in this substrate. We know that during
precatalyst activation, three equivalents of dimethylbenzylamine (HDmba) are liberated by
reaction with diphenylphosphine oxide, creating the active catalyst in situ. Unlike the lanthanum
trisphosphide used in the hydrophosphination reactions (La(PPh2)3), the diphenylphosphine
oxide ligand can coordinate to lanthanum through either the phosphorus or the oxygen depending
on the tautomer utilized. In order to look at this tautomerization effect experimentally, we
undertook a series of stoichiometric reactions on an NMR scale in a J-Young tube (Figure 1).
The precatalyst La(Dmba)3 was first treated with three equivalents of diphenylphosphine in
deuterated pyridine to produce La(PPh2)3, the hydrophosphination catalyst discussed above. The
solution turned from clear to dark red with no precipitate observed and its 31P{1H} NMR
spectrum was collected. Because both lanthanum isotopes are quadrupolar: 138La (0.09%
abundance, I = 5/2) and 139La (99.91% abundance, I = 7/2), no phosphorus signal was detected
for the resulting lanthanum phosphide complex.20 To elaborate further, the nuclear spin of the
lanthanum isotopes present resulted in broadening of the phosphorus signal to the point where it
was lost in the baseline noise. Subsequently, an excess of diphenylphosphine oxide (six
equivalents) was added to the solution, causing the reaction color to change from red to a
colorless homogeneous solution. In this case, the corresponding 31P{1H} NMR spectrum showed
three signals. A free diphenylphosphine resonance appeared at -40.0 ppm, a peak at 17.0 ppm
corresponded to leftover excess diphenylphosphine oxide, and a new signal appeared at 87.2
ppm that we attribute to the activated La(O-PPh2)3 catalyst (Figure 1). Because the peak at 87.2
ppm was visible and not appreciably broadened, we believe this indicates coordination of the
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phosphine oxide ligands via the oxygen donor atom, leaving the phosphorus atom further from
the quadrupolar lanthanum center and thus visible in the 31P NMR spectrum. A calcium complex
of the O-bound Ph2PO- moiety was previously reported to have a 31P NMR resonance at 89.6
ppm, well in line with that observed in our system.21 We cannot discount the possibility that the
observed peak at 87.2 ppm is an uncoordinated Ph2PO- anion, though this seems unlikely in the
presence of the highly oxophilic La3+ ions. Moreover, a control experiment in which HP(O)Ph2
was dissolved in pyridine showed no evidence for deprotonation by pyridine (see Supporting
Information). This was unsurprising as the pKa of HP(O)Ph2 has been reported as 20.6 (in
DMSO)22 and the pKb of pyridine is 8.77.23 Utilizing these values, the approximate equilibrium
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constant for their acid-base reaction is around 1 x 10-15
.
H
O
O
P
P
H
Scheme 5. Tautomerization of diphenylphosphine oxide
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La(PPh2)3 + 6 HP(O)Ph2
La(O-PPh2)3 + 3 HP(O)Ph2 + 3 HPPh2
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La(Dmba)3 + 3 HPPh2
La(PPh2)3 + 3 HDmba
(no signal
observed)
Free HPPh2
190
170
150
130
110
90
80
70
60
50
f1 (ppm)
40
30
20
10
0
-10 -20 -30 -40 -50 -60 -70 -80 -90
Figure 1. 31P{1H} NMR spectra in d5-pyridine of reaction sequence displaying evidence for the
tautomerization of phosphine oxide when coordinated to lanthanum
Mechanistically, stoichiometric reaction of the precatalyst with phosphine oxide leads to creation
of the active catalyst in situ. Based on the NMR scale experiments above, this species is likely
the pyridine solvated, O-bound lanthanum complex: La(O-PPh2)3(py)n. The next step likely
involves coordination of an alkyne to the La, but due to tautomerization of the phosphine oxide
ligand, direct insertion would not lead to formation of a carbon-phosphorus bond. Rather,
production of the putative insertion products likely occurs via a [3+2]-cycloaddition process
(Scheme 6). A [3+2]-addition process such of this is also facilitated by the tautomerization as
shown by the electron pushing arrows in Scheme 6. Catalysis then continues in a similar fashion
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to the hydrophosphination catalytic cycle with protonolysis via another equivalent of
diphenylphosphine oxide as shown in the full catalytic cycle (Scheme 7). As mentioned above,
the mono-addition product can only be isolated in the case of internal alkynes, showing high
regio- and stereoselectivity producing almost exclusively the E isomer. Given the oxophilicity of
lanthanum and the ability of phosphine oxide to tautomerize, the intermediates likely have O-
bound phosphine oxides, significantly reducing the steric bulk at the metal center. Since mono-
addition products cannot be isolated with terminal alkynes, it is believed that the intermediate
mono-addition alkene remains coordinated to the metal center. The greatly reduced steric
congestion around the metal center then allows for rapid addition of another phosphine oxide
moiety to the alkene unit, with final protonolysis by diphenylphosphine oxide yielding the
double addition products (Scheme 7).
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[La]
O
O
O
[La]
Ph
PPh2
H
[La]
PPh2
PPh2
Ph
H
Ph
H
Scheme 6. Tautomerization of the phosphine oxide ligands leads to a [3+2] cycloaddition
mechanism.
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HP(O)Ph2
4
5
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7
Ph2
P
Ph2
P
R'
Protonolysis
O
O
R'
(Ph2(O)P)2La
(Ph2(O)P)3La
R
R
8
9
Alkene
phosphinylation
Alkyne [3+2]-
cycloaddition
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R
R'
R'
Ph2(O)P
R
La(P(O)Ph2)3
(Ph2(O)P)2La
PPh2
O
Protonolysis
3 HDmba
R'
HP(O)Ph2
La(Dmba)3
+
3 HP(O)Ph2
R
Ph2(O)P
P(O)Ph2
Precatalyst
Activation
Scheme 7. Proposed catalytic cycle for lanthanum catalyzed mono- and double
hydrophosphinylation of alkynes (pyridine solvation omitted for clarity).
Conclusions
We demonstrated the ability of La(Dmba)3 to induce both hydrophosphination and
hydrophosphinylation of alkynes. Interesting chemoselectivity was observed: the catalyst
induced only mono-addition in hydrophosphination reactions but mono- and double addition in
hydrophosphinylation reactions. Both mono-addition reactions showed high regioselectivity,
where only anti-Markovnikov products were observed. In hydrophosphination, the
stereoselectivity could be controlled depending on the reaction conditions employed. A brief
investigation of the catalytic cycle suggested the formation of a dimeric lanthanum phosphide
active catalyst and the formation of the Z isomer as the kinetic product, which then underwent
isomerization to yield the thermodynamic E isomer. Control reactions showed that the presence
of the active catalyst was imperative for the isomerization to occur.
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Hydrophosphinylation reactions led directly to double addition products when using terminal
alkynes; however, both mono- and double addition products could be isolated when using
internal alkynes. Overall, we demonstrated a new pathway to mono- and bidentate phosphine and
phosphine oxide ligands using relatively mild conditions with high chemo-, regio-, and
stereoselectivity.
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Experimental
Lanthanum tris(N,N-dimethylbenzylamine) (La(Dmba)3) was synthesized as previously
reported.24 All acetylenes were purchased from Alfa Aesar or AK Scientific, dried over calcium
hydride, filtered, freeze-pump-thawed three times, and stored in a nitrogen filled glovebox. All
solvents were dried before use; diethyl ether, dichloromethane, and pentane were passed through
columns of 4Å molecular sieves and degassed with nitrogen. Pyridine was purchased from Alfa
Aesar, and dried over sodium metal, distilled under nitrogen, freeze-pump-thawed three times,
and stored in a nitrogen filled glovebox. Diphenylphosphine oxide was purchased from Glass
City Chemicals, stored in a glovebox, and used without further manipulations.
Diphenylphosphine was synthesized by the reduction of chlorodiphenylphosphine with lithium
aluminum hydride and stored in a glovebox.25 All reactions were carried out in the glovebox
under nitrogen atmosphere. CDCl3 was purchased from Cambridge Isotope Laboratories, and for
air sensitive purposes, it was dried over calcium hydride, vacuum transferred, freeze-pump-
thawed three times, and stored over molecular sieves in a nitrogen filled glovebox. All 1H and
13C NMR spectra were collected on a 600 MHz Bruker Avance III spectrometer at 599.9 and
150.8 MHz, respectively, and referenced to the residual solvent peaks of chloroform at 7.26 and
77.3 ppm. All 31P NMR spectra were collected on a 400 MHz Varian VXRS NMR spectrometer
at 161.9 MHz and externally referenced to 0.00 ppm with 5% H3PO4 in D2O. Infrared spectra
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were collected on a PerkinElmer Frontier spectrometer with Pike miracle ATR. High resolution
mass spectra were determined at the Department of Chemistry and Biochemistry, University of
Toledo, OH, USA, using a Waters Synapt high-definition mass spectrometer (HDMS) equipped
with a nano-ESI source.
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Hydrophosphination of Alkynes (E-isomer).
In the glovebox, an oven dried Schlenk tube was charged with La(Dmba)3 (13.5 mg; 5 mol%)
and pyridine (1 ml), resulting in an orange solution. Diphenylphosphine (0.8 mmol, 139.2 µl)
was measured with a micropipette and added to the La(Dmba)3, resulting in a deep red solution
after 5 minutes. Acetylene (0.5 mmol) was then dissolved in pyridine (1 ml) and added to the
lanthanum phosphide solution resulting in a color change to a pale yellow or colorless solution.
The Schlenk tube was removed from the glovebox and the reaction was stirred for 12-48 h at
room temperature. The solvent was then removed under vacuum and the products were washed
with cold pentane (2x5 ml) under air sensitive conditions.26 Clean products were afforded by
recrystallization from diethyl ether. Hydrophosphination products 2a,27 2e,27 and 2f28 were
identified by comparison to previously reported NMR spectral data. Note that the 1H NMR of 2f
as previously reported seems incorrect so we have included our data herein for comparison.
PPh2
(2b) Off white solid, 130.0 mg (82%), M.P: 110-113°C. 1H NMR
(CDCl3): δ 7.76-7.73 (m, 3H), 7.55-7.52 (m, 2H), 7.48-7.44 (m, 6H), 7.36-7.29 (m, 2H), 7.21 (d,
3JH-H= 8.0Hz, 2H), 6.77 (dd, 3JH-H= 20.0Hz, 2JH-P= 17.0Hz, 1H), 2.66 (q, JH-H= 7.6Hz, 2H), 1.23
3
(t, 3JH-H= 7.6Hz, 3H). 13C{1H} NMR (CDCl3): δ 147.5 (d, JC-P = 4.0Hz), 146.7, 133.4, 132.7 (d,
JC-P = 20.0Hz), 131.8 (d, JC-P = 2.2Hz), 131.6 (d, JC-P = 9.8Hz), 128.9 (d, JC-P = 12.0Hz), 128.7,
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128.1, 117.8 (d, JC-P = 18.0Hz), 29.0, 15.7. 31P{1H} NMR (CDCl3): δ -10.6. IR (cm-1): 2963.1
(m), 1606.5 (m), 1523.3 (w), 1511.1 (w), 1470.0 (w), 1436.2 (m), 1349.8 (w), 1310.3 (m),
1179.0 (s), 1137.6 (m), 1118.3 (s), 1110.1 (s), 1060.3 (w), 1047.0 (w), 1012.0 (m), 810.5 (s),
769.1 (m), 742.0 (s), 720.2 (m), 707.4 (m), 691.4 (s), 594.0 (m), 523.8 (s), 497.4 (m), 462.0 (m).
HRMScalc for C22H22OP [M+H+O]+:29 333.1408, HRMSmeas: 333.1422.
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PPh2
1
(2c) White solid, 146.5 mg (85%). H NMR (CDCl3): δ 7.76-7.73
(m, 4H), 7.55-7.52 (m, 2H), 7.48-7.45 (m, 6H), 7.41-7.39 (m, 2H), 7.29-7.27 (m, 1H), 6.77 (dd,
3JH-H = 22.3Hz, 2JH-P = 17.0Hz, 1H), 1.32 (s, 9H). 13C{1H} NMR (CDCl3): δ 153.9, 147.7 (d, JC-P
= 3.0Hz), 133.7, 133.0, 132.7 (d, JC-P = 18.1Hz), 132.1 (d, JC-P = 3.0Hz), 131.7 (d, JC-P = 10.0Hz),
128.9 (d, JC-P = 12.1Hz), 128.3 (d, JC-P = 12.1Hz), 127.9, 126.1, 118.7, 35.1, 31.4. 31P{1H} NMR
(CDCl3): δ -10.7. HRMScalc for C24H26OP [M+H+O]+:29 361.1721, HRMSmeas: 361.1724.
PPh2
NH2
(2d) Off white solid, 111.0 mg (73%), M.P: 116-122°C. 1H NMR
(CDCl3): δ 7.47-7.44 (m, 4H), 7.34-7.31 (m, 6H), 7.12-7.10 (m, 2H), 6.91-6.85 (m, 2H), 6.61-
6.60 (m, 1H), 6.42 (dd, 3JH-H = 13.0Hz, 2JH-P = 3.0Hz, 1H), 3.61 (br s, 2H). 13C{1H} NMR
(CDCl3): δ 146.4, 144.6 (d, JC-P = 19.0Hz), 139.8 (d, JC-P = 10.0Hz), 138.2 (d, JC-P = 2.3Hz),
133.3 (d, JC-P = 19.0Hz), 129.8, 129.5 (d, JC-P = 16.0Hz), 129.3, 129.0, 128.9 (d, JC-P = 6.0Hz),
128.8 (d, JC-P = 6.0Hz), 128.7, 120.5 (d, JC-P = 8.0Hz), 116.3 (d, JC-P = 8.0Hz), 115.3. 31P{1H}
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NMR (CDCl3): δ -10.7. IR (cm-1): 2962.0 (m), 2156.3 (w), 1580.5 (w), 1516.6 (m), 1434.2 (w),
1345.8 (w), 1257.7 (s), 1224.2 (w), 1070.1 (s), 1056.3 (m), 1009.5 (s), 931.0 (w), 863.1 (m),
847.7 (m), 786.1 (s), 692.6 (s), 594.0 (w), 471.1 (s). HRMScalc for C20H18NOP [M +O]+:29
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319.1126, HRMSmeas: 319.1122.
PPh2
(2f)28 White solid, 118.5 mg (65%). 1H NMR (CDCl3): δ 7.68-7.65 (m,
4H), 7.60 (d, 3JH-P = 21.0Hz, 1H), 7.52-7.49 (m, 2H), 7.40 (td, 3JH-H = 7.8Hz, 4JH-P = 2.8Hz, 4H),
7.22-7.16 (m, 4H), 7.13 (t, 3JH-H = 7.8Hz, 2H), 7.04 (d, 3JH-H = 7.5Hz, 2H), 6.91 (d, 3JH-H = 6.5Hz,
2H). 13C{1H} NMR (CDCl3): δ 150.1, 143.3 (d, JC-P = 9.0Hz), 135.9, 135.8 (d, JC-P = 9.0Hz),
135.3, 135.1 (d, JC-P = 17.0Hz), 132.6 (d, JC-P = 9.0Hz), 132.1 (d, JC-P = 2.0Hz), 131.6, 130.9,
130.5, 130.2 (d, JC-P = 4.0Hz), 129.1, 129.0, 128.5, 128.4 (d, JC-P = 2.0Hz), 127.8, 124.0. 31P{1H}
NMR (CDCl3): δ 9.5.
O
O
O
O
(2g) Yellow solid, 107.0 mg (60%). M.P: 140-146°C. 1H NMR
Ph2P
(CDCl3): δ 7.72-7.69 (m, 2H), 7.35-7.34 (m, 3H), 7.30-7.26 (m, 3H), 7.20 (t, 3JH-H = 7.8Hz, 2H),
4.16 (d, 3JH-P = 7.0Hz, 1H), 3.98-3.97 (m, 1H), 3.88-3.86 (m, 1H), 3.54-3.52 (m, 1H), 3.44-3.41
(m, 1H), 0.83 (t, 3JH-H = 7.4Hz, 3H), 0.71 (t, 3JH-H = 7.4Hz, 3H). 13C{1H} NMR (CDCl3): δ 169.9,
150.2, 135.1 (d, JC-P = 11.0Hz), 134.6 (d, JC-P = 13.0Hz), 134.2 (d, JC-P = 17.2Hz), 133.9 (d, JC-P
=
10.0Hz), 129.7 (d, JC-P = 11.0Hz), 128.8 (d, JC-P = 11.0Hz), 60.7 (d, JC-P = 2.0Hz), 46.6 (d, JC-P
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2.0Hz), 13.8, 13.6. 31P{1H} NMR (CDCl3): δ 3.6. IR (cm-1): 3053.5 (m), 2981.7 (m), 2283.1
(w), 1720.1 (s), 1584.7 (m), 1537.4 (w), 1478.5 (m), 1434.3 (s), 1240.5 (m), 1220.4 (w), 1189.9
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(m), 1150.1 (m), 1090.1 (m), 1069.2 (w), 1025.7 (s), 999.1 (w), 910.6 (w), 888.6 (m), 853.0 (w),
795.6 (s), 740.8 (m), 692.6 (s), 647.2 (m), 617.8 (w), 561.8 (w), 483.8 (w), 471.9 (w), 455.0 (w).
HRMScalc for C20H22O5P [M+H+O+]:29 373.1205, HRMSmeas:373.1207.
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Hydrophosphination of Alkynes (Z-isomer).
In the glovebox, an oven dried Schlenk tube was charged with La(Dmba)3 (13.5 mg; 5 mol%)
and pyridine (1 ml), resulting in an orange solution. Diphenylphosphine (0.5 mmol, 93 μl) was
measured with a micropipette and added to the La(Dmba)3 resulting in a deep red solution after 5
minutes. Acetylene (0.8 mmol) was then dissolved in pyridine (1 ml) and added to the lanthanum
phosphide solution resulting in a color change to a pale yellow or colorless solution. The Schlenk
tube was removed from the glovebox and the reaction was stirred for 12 h at room temperature.
The solvent was then removed under vacuum and the products were extracted with diethyl ether
(2x5 ml) under air sensitive conditions. Diethyl ether was then removed under reduced pressure
to afford clean product. Hydrophosphination product 2a’8, 12, 30 was identified by comparison to
previously reported NMR spectral data.
PPh2
(2b’) Off-white solid, 134.5 mg (85%), M.P: 100-110°C. 1H NMR
(CDCl3): δ 7.47-7.43 (m, 5H), 7.38 (d, 3JH-H = 12.6Hz, 1H), 7.35-7.31 (m, 8H), 7.16 (d, 3JH-H
8.0Hz, 1H), 6.40 (dd, 3JH-H = 12.6Hz, 2JH-P = 3.0Hz, 1H), 2.63 (q, 3JH-H = 7.6Hz, 2H), 1.22 (t, 3JH-
H = 7.6Hz, 3H). 13C{1H} NMR (CDCl3): δ 144.6, 144.3 (d, JC-P = 19.0Hz), 139.6 (d, JC-P
=
=
9.0Hz), 134.5 (d, JC-P = 2.0Hz), 132.8 (d, JC-P = 18.6Hz), 129.7 (d, JC-P = 8.0Hz), 128.6 (d, JC-P
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6.0Hz), 128.6, 128.3 (d, JC-P = 15.0Hz), 127.8, 28.9, 15.7. 31P{1H} NMR (CDCl3): δ -23.7.
IR(cm-1): 3052.5 (w), 2930.0 (w), 1587.1 (w), 1508.0 (m), 1455.1 (w), 1432.2 (m), 1333.2 (w),
1303.5 (w), 1184.9 (w), 1154.5 (w), 1092.0 (m), 1067.2 (m), 1050.9 (w), 1025.8 (m), 971.9 (m),
912.2 (m), 845.6 (s), 826.9 (s), 737.2 (s), 695.7 (s), 655.9 (m). HRMScalc for C22H22P [M+H+]:
317.1459, HRMSmeas: 317.1464.
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PPh2
NH2
(2d’) Pale yellow solid, 121.3 mg (80%), M.P: 95-100°C. 1H NMR
(CDCl3): δ 7.45-7.43 (m, 6H), 7.35-7.31 (m, 8H), 6.63 (dd, 3JH-H = 12.6Hz, 3JH-P = 1.4Hz, 1H),
6.41 (dd, 3JH-H = 12.6Hz, 2JH-P = 3.0Hz, 1H), 3.68 (br s, 2H). 13C{1H} NMR (CDCl3): δ 146.1,
144.3 (d, JC-P = 19.0Hz), 139.5 (d, JC-P = 9.4Hz), 132.8 (d, JC-P = 19.0Hz), 129.5, 129.1, 128.6 (d,
JC-P = 9.0Hz), 118.5, 116.5 (d, JC-P = 8.4Hz), 116.0. 31P{1H} NMR (CDCl3): δ -25.2. IR (cm-1):
3142.5 (w), 2990.9 (m), 1590.1 (w), 1500.0 (m), 1443.3 (w), 1400.2 (m), 1299.9 (m), 1154.8
(w), 1144.4 (w), 1091.9 (w), 1077.1 (m), 1050.9 (w), 1049.3 (m), 980.1 (w), 900.1 (m), 845.6
(s), 823.2 (s), 776.2 (s). HRMScalc for C20H19NP [M+H+]: 304.1255, HRMSmeas: 304.1272.
Double Hydrophosphinylation of Alkynes.
In the glovebox, an oven dried vial was charged with La(Dmba)3 (27 mg; 10 mol%) and pyridine
(2 ml) resulting in an orange solution. Diphenylphosphine oxide (232.5 mg; 1.15 mmol) was
added to the La(Dmba)3 solution, resulting immediately in a clear and colorless solution.
Acetylene (0.5 mmol) was then added to the lanthanum phosphinyl oxide solution. The vial was
then removed from the glovebox and the reaction was stirred for 12-48 h at room temperature or
60°C. The solvent was removed under vacuum and the products were washed with diethyl ether
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(2x5 ml) under ambient conditions, filtered, and recrystallized from dichloromethane (5 ml) to
afford clean product. Hydrophosphination products 4a31 and 4f32 were identified by comparison
to previously reported NMR spectral data.
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P(O)Ph2
P(O)Ph2
(4b) White solid, 240.5 mg (90%), M.P: 206°C dec. 1H NMR
(CDCl3): δ 8.05-8.02 (m, 2H), 7.59-7.50 (m, 5H), 7.44-7.40 (m, 2H), 7.36-7.25 (m, 6H), 7.19-
7.14 (m, 3H), 7.04 (td, 3JH-H = 5.4Hz, 4JH-P = 1.0Hz, 2H), 6.97 (d, 3JH-H = 7.6Hz, 2H), 6.63 (d, 3JH-
H = 7.6Hz, 2H), 4.28-4.23 (m, 1H), 3.15-3.10 (m, 1H), 2.84-2.77 (m, 1H), 2.37 (q, 3JH-H = 7.6Hz,
2H), 1.05 (t, 3JH-H = 7.6Hz, 3H). 13C{1H} NMR (CDCl3): δ 135.0, 134.4, 133.2 (d, JC-P = 2.5Hz),
132.7 (d, JC-P = 10.0Hz), 132.5 (d, JC-P = 16.0Hz), 132.2 (d, JC-P = 3.0Hz), 132.1 (d, JC-P = 8.6Hz),
131.9, 131.8 (d, JC-P = 6.0Hz), 131.7, 131.4 (d, JC-P = 8.6Hz), 131.3 (d, JC-P = 8.6Hz), 130.8 (d, JC-
P = 10.0Hz), 130.6 (d, JC-P = 6.0Hz), 129.6 (d, JC-P = 11.0Hz), 129.5 (d, JC-P = 13.0Hz), 129.2 (d,
JC-P = 11.0Hz), 128.8 (d, JC-P = 13.0Hz), 128.6 (d, JC-P = 12.0Hz), 128.5 (d, JC-P = 12.0Hz), 128.4,
127.9, 39.3 (dd, JC-P = 66.0Hz, JC-P = 3.5Hz), 30.7 (d, JC-P = 69.0Hz), 28.9, 16.2. 31P{1H} NMR
(CDCl3): δ 38.0 (d, 3JP-P = 47.0Hz), 32.6 (d, 3JP-P = 47.0Hz). IR (cm-1): 3054.4 (w), 2966.0 (w),
2901.9 (w), 1671.2 (w), 1590.8 (w), 1513.1 (w), 1483.6 (w), 1436.1 (m), 1310.6 (w), 1181.5 (m),
1128.8 (s), 1069.8 (m), 1045.5 (s), 1021.0 (s), 996.6 (m), 948.2 (m), 887.8 (m), 839.7 (m), 796.4
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(w), 742.8 (m), 724.4 (s), 690.0 (m), 556.1 (s), 517.8 (s), 509.1 (s). HRMScalc for C34H33O2P2
[M+H+]: 535.1956, HRMSmeas: 535.1965.
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P(O)Ph2
P(O)Ph2
(4c) White solid, 253.0 mg (90%), M.P: >250°C. 1H NMR
(CDCl3): δ 8.06-8.04 (m, 2H), 7.73-7.68 (m, 1H), 7.57-7.53 (m, 5H), 7.43 (td, 3JH-H = 7.3Hz, 4JH-
H = 1.3Hz , 1H), 7.36-7.34 (m, 2H), 7.30-7.29 (m, 2H), 7.25-7.24 (m, 1H), 7.17-7.11 (m, 4H),
7.05-7.02 (m, 2H), 6.95 (d, 3JH-H = 7.6Hz, 2H), 6.81 (d, 3JH-H = 8.2Hz, 2H), 4.27-4.22 (m, 1H),
3.17-3.12 (m, 1H), 2.84-2.77 (m, 1H), 1.14 (s, 9H). 13C{1H} NMR (CDCl3): δ 134.5, 132.1,
131.8, 131.7 (d, JC-P = 8.4Hz), 131.4, 131.1, 130.9 (d, JC-P = 9.1Hz), 130.8 (d, JC-P = 3.1Hz), 130.7
(d, JC-P = 9.5Hz), 130.6 (d, JC-P = 13.0Hz), 130.5 (d, JC-P = 13.0Hz), 130.2 (d, JC-P = 9.5Hz), 129.7
(d, JC-P = 5.5Hz), 129.1 (d, JC-P = 11.0Hz), 128.9 (d, JC-P = 13.0Hz), 128.6 (d, JC-P = 12.0Hz),
127.8 (d, JC-P = 12.0Hz), 124.7, 38.7 (dd, JC-P = 66.0Hz, JC-P = 3.3Hz), 34.0, 31.2, 30.0 (d, JC-P
=
69.0Hz). 31P{1H} NMR (CDCl3): δ 36.5 (d, 3JP-P = 47.0Hz), 31.0 (d, 3JP-P = 47.0Hz). IR (cm-1):
3054.2 (w), 2965.1 (w), 2937.1 (w), 1591.8 (w), 1511.4 (w), 1484.0 (w), 1437.8 (m), 1365.5 (w),
1339.8 (w), 1264.8 (w), 1182.1 (s), 1119.7 (s), 1102.8 (m), 1071.8 (w), 1045.3 (m), 1021.8 (m),
997.1 (w), 887.2 (w), 839.0 (m), 790.1 (w), 773.0 (w), 762.8 (w), 746.0 (m), 729.3 (m), 720.2
(s), 692.9 (s), 661.2 (w), 574.5 (w), 558.9 (w), 535.8 (w). HRMScalc for C36H37O2P2 [M+H+]:
563.2269, HRMSmeas: 563.2259.
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NH2
(4d) White solid, 216.4 mg (83%), M.P: >250°C. 1H NMR (CDCl3): δ
8.03-7.99 (m, 2H), 7.71-7.67 (m, 1H), 7.54-7.48 (m, 5H), 7.43-7.39 (m, 1H), 7.37-7.32 (m, 6H),
7.25-7.20 (m, 1H), 7.17-7.10 (m, 4H), 6.58 (t, 3JH-H = 7.8Hz, 1H), 6.48-6.45 (m, 2H), 6.17 (d, 3JH-
H = 7.8Hz, 1H), 4.18-4.13 (m, 1H), 3.30 (bs, 2H), 3.12-3.06 (m, 1H), 2.81-2.74 (m, 1H).
13C{1H} NMR (CDCl3): δ 135.4 (d, JC-P = 6.0Hz), 134.6, 134.0, 132.8 (d, JC-P = 2.3Hz), 132.6 (d,
JC-P = 8.5Hz), 132.2 (d, JC-P = 2.3Hz), 132.0, 131.8 (d, JC-P = 2.3Hz), 131.7 (d, JC-P = 8.5Hz),
131.5 (d, JC-P = 2.3Hz), 131.4, 131.3, 131.1 (d, JC-P = 9.0Hz), 130.9 (d, JC-P = 10.0Hz), 130.4 (d,
JC-P = 9.0Hz), 129.4, 129.2 (d, JC-P = 11.5Hz), 129.1 (d, JC-P = 13.0Hz), 128.8 (d, JC-P = 11.5Hz),
128.5 (d, JC-P = 10.0Hz), 128.1 (d, JC-P = 11.5Hz), 127.9 (d, JC-P = 13.0Hz), 120.9 (d, JC-P
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6.0Hz), 116.8 (d, JC-P = 6.0Hz), 114.3 (d, JC-P = 2.0Hz), 39.2 (dd, JC-P = 66.0Hz, JC-P = 3.0Hz),
30.2 (d, JC-P = 69.0Hz). 31P{1H} NMR (CDCl3): δ 36.3 (d, 3JP-P = 47.0Hz), 31.1 (d, 3JP-P
=
47.0Hz). IR(cm-1): 3053.9 (w), 2933.9 (w), 1604.3 (w), 1484.7 (m), 1464.8 (w), 1437.0 (m),
1310.3 (w), 1257.5 (w), 1181.7 (s), 1166.0 (m), 1118.5 (m), 1102.7 (m), 1072.9 (w), 1047.4 (w),
1029.0 (w), 997.0 (w), 879.4 (w), 843.8 (w), 795.1 (w), 729.5 (s), 690.4 (s), 618.2 (w), 607.9
(w), 539.8 (w), 498.2 (w), 481.1 (w), 460.4 (w). HRMScalc for C32H30NO2P2 [M+H+]: 522.1752,
HRMSmeas: 522.1765.
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