Insertion of phosphinidene complexes into the P-H bond of secondary phosphine oxides: A new version of the phospha-Wittig synthesis of P=C double bonds

Article abstract of DOI:10.1039/c5dt04245c

Terminal phosphinidene complexes [RP-W(CO)₅], as generated at 60 °C in the presence of copper chloride from the appropriate 7-phosphanorbornadiene complexes, react with secondary phosphine oxides Ar₂P(O)H to give the insertion products into the P-H bonds. After metalation with NaH, these products react with aldehydes to give the corresponding phosphaalkenes which are trapped by dimethylbutadiene.

Full text of DOI:10.1039/c5dt04245c

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Insertion of phosphinidene complexes into the
P–H bond of secondary phosphine oxides:
a new version of the phospha-Wittig synthesis
of PvC double bonds†
Cite this: DOI: 10.1039/c5dt04245c
Received 29th October 2015,
Accepted 3rd December 2015
DOI: 10.1039/c5dt04245c
www.rsc.org/dalton
Yanwei Hao,a Di Wu,a Rongqiang Tian,*a Zheng Duan*a and François Mathey*a,b
Terminal phosphinidene complexes [RP-W(CO)5], as generated at
60 °C in the presence of copper chloride from the appropriate
7-phosphanorbornadiene complexes, react with secondary phos-
phine oxides Ar2P(O)H to give the insertion products into the P–H
bonds. After metalation with NaH, these products react with alde-
hydes to give the corresponding phosphaalkenes which are
trapped by dimethylbutadiene.
For a long time, the development of the carbene-like chemistry
of electrophilic terminal phosphinidene complexes [RP-M] (M
= Cr, Mo, W(CO)5, Fe(CO)4 and cationic complexes) was cen-
tered on cycloaddition reactions.1 The systematic development
of insertion reactions into A–H σ bonds is more recent.2 Note-
worthy are the insertions into Si–H3 and B–H4 bonds. In both
cases, the reaction is favored by the interaction of the electro-
philic phosphinidene phosphorus with the hydridic hydrogen.
The case of the P–H bond is more delicate. A secondary phos-
phine tends to displace the phosphinidene from its complex,
thus leading to the failure of the insertion reaction. When
replacing the secondary phosphine by its P-W(CO)5 complex,
no reaction is observed. Reactions using secondary phosphine
oxides were more productive. These experiments are the
subject of this report.
Scheme 1 Insertion of [RP-W(CO)5] into the P–H bond of secondary
phosphine oxides.
The insertion products 2 were characterized by NMR and
HRMS. The 31P NMR data are collected in Table 1.
These data are very similar to those of the phosphonate
analogues, the so-called phospha-Wittig reagents.6 Compound
2a was further characterized by X-ray crystal structure analysis
(Fig. 1).
It is known that an easy tautomerism takes place between
secondary phosphine oxides and phosphinous acids. The
process is bimolecular and involves 6-membered transition
states with activation barriers in the range 5–15 kcal mol−1 7
.
The key question concerning the mechanism of the insertion
of phosphinidene complexes into the P–H bonds of secondary
phosphine oxides is whether [RP-W(CO)5] reacts with Ar2P(O)H
or Ar2P-OH. We have studied the interaction of [MeP-W(CO)5]
with Ph2P(O)H and Ph2P-OH by DFT at the B3LYP/6-31G(d)-
The copper chloride-catalyzed decomposition of 7-phospha-
norbornadiene P-W(CO)5 complexes 1 was used as a source of
phosphinidene complexes.5 The reaction was carried out at
60 °C in toluene or THF. Successful insertions of the phosphi-
nidenes into the P–H bond were observed with secondary
diphenyl and di-2-thienylphosphine oxides (Scheme 1).
Table 1 31P NMR for compounds 2
aCollege of Chemistry and Molecular Engineering, International Phosphorus
Laboratory, International Joint Research Laboratory for Functional
Organophosphorus Materials of Henan Province, Zhengzhou University, Zhengzhou
450001, P. R. China
Product
δ
31P
1JPP (Hz)
1JPW (Hz)
1JPH (Hz)
2a
2b
2c
2d
2e
2f
34.0, −33.2
34.2, −68.3
34.7, −53.7
34.1, −61.5
34.4, −53.7
21.0, −19.9
20.7, −54.2
72.0
62.7
65.8
64.3
66.1
46.9
38.2
226.4
223.6
223.9
226.7
231.6
228.3
226.0
327.8
320.4
330.1
323.2
336.3
330.6
322.9
bDivision of Chemistry & Biological Chemistry, School of Physical & Mathematical
Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
†Electronic supplementary information (ESI) available: Synthesis and characteri-
zation of compounds 2–9. X-ray data for 2a. CCDC 1045537. For ESI and crystal-
lographic data in CIF or other electronic format see DOI: 10.1039/c5dt04245c
2g
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Fig. 2 Computed structure of the adduct [MeP-W(CO)5]-HOPPh2. Main
bond lengths (Å) and angles (°): P5–O40 2.042, P17–O40 1.770, P5–C1
1.870, O40–H41 0.977; P5–O40–P17 136.06, P5–O40–H41 111.06,
P17–O40–H41 109.89, C1–P5–O40–H41 66.96.
Fig. 1 X-ray crystal structure analysis of compound 2a. Main bond
lengths (Å) and angles (°): P1–P2 2.2081(18), P1–C6 1.824(5), P1–W1
2.5058(13), P2–O6 1.489(4), P2–C12 1.797(5), P2–C18 1.814(5); P2–P1–
W1 113.54(6), C6–P1–W1 121.45(18), C6–P1–P2 100.97(16), C12–P2–
C18 107.3(2), O6–P2–P1 109.97(17), O6–P2–C12 113.1(2), O6–P2–C18
113.8(3), C12–P2–P1 107.98(16), C18–P2–P1 104.14(18).
Lanl2dz (W) level.8 We have not detected any interaction with
the secondary phosphine oxide but a well defined P⋯O adduct
is formed with the phosphinous acid (Fig. 2).
This adduct which corresponds to a local minimum (no nega-
tive frequency) is formed by the interaction of the phosphinidene
LUMO with the in-plane lone pair of the hydroxyl oxygen. On
this basis, we propose the mechanism depicted in Scheme 2 for
the insertion of phosphinidenes into the P–H bonds.
The first two steps are very similar to those proposed for
the insertion of phosphinidene complexes into water.2 When
the diaryl is replaced by a dialkylphosphine oxide, the phos-
phinous acid tautomer becomes such a strong ligand that it
becomes able to displace tungsten from the phosphinidene
complex or from its precursor and the insertion fails. For
example, with secondary di-n-butylphosphine oxide, the main
product is (nBu2POH)W(CO)5 (3) isolated in 41% yield.
It is possible to alkylate the PH bonds of the insertion pro-
ducts 2 as shown in Scheme 3.
Scheme 2 Insertion mechanism of [RP-W(CO)5] into the P–H bond of
Ar2P(O)H.
Scheme 3 Alkylation of insertion products 2.
But the most interesting aspect of the chemistry of these
insertion products is their use as phospha-Wittig reagents9 for
the conversion of carbonyl derivatives into PvC double bonds
(Scheme 4).
The phosphaalkene intermediates were trapped as [2 + 4]
cycloadducts with dimethylbutadiene. Adducts 6 and 9 were
obtained as single diastereomers but their stereochemistry was
not determined.
Finally, a few words on the thermal stability of compounds
2 are appropriate. The experiments were performed with 2a. Scheme 4 Compound 2 as phospha-Wittig reagents.
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2 F. Mathey and Z. Duan, Dalton Trans., DOI: 10.1039/
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3 K. Vaheesar, T. M. Bolton, A. L. L. East and
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M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross,
C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, J. J. Dannenberg, V. G. Zakrzewski,
S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas,
D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford,
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P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith,
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Scheme 5 Thermal decomposition of 2a.
Compound 2a decomposes in boiling toluene to give a
plethora of products (Scheme 5).
The initial step of the decomposition seems to be the de-
insertion of the phosphinidene from the P–H bond giving back
the secondary phosphine oxide 10 in high yield. The suspected
phosphinidene complex gives a variety of products 11, 12 and
14. 11 and 14 apparently come from the reaction of the phos-
phinidene with hydrogen10 whose source is unknown. 12 and
13 probably arise from a H to OH exchange between the tauto-
mers of 10 and 11. Alternatively, the decomposition of 2a could
also occur via a bimolecular mechanism.
Acknowledgements
This work was supported by the National Natural Science
Foundation (21302174, 21272218), Specialized Research Fund
for
the
Doctoral
Program
of
Higher
Education
9 Selected references: A. Marinetti and F. Mathey, Angew.
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J. D. Protasiewicz, Chem. Commun., 1998, 1585; S. Shah and
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(20134101110004), Henan Science and Technology Depart-
ment (no. 144300510011) and Zhengzhou Science and Tech-
nology Department (131PYSGZ204) of China.
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