The Reaction of Terminal Phosphinidene Complexes [RP-W(CO)5] with Vinylboronic Acids: Cycloaddition vs. P-C Bond Formation

Article abstract of DOI:10.1002/ejic.201500594

The reaction of terminal phosphinidene complexes [RP-W(CO)₅] with vinylboronic acids is very sensitive to the presence or absence of solid K₃PO₄ in suspension in the reaction medium. The products are phosphirane complexes without the salt and secondary vinylphosphine complexes in the presence of the salt. This shift of the reaction pathway is explained by the formation of vinyborates in the presence of potassium phosphate.

Full text of DOI:10.1002/ejic.201500594

DOI: 10.1002/ejic.201500594
Communication
CLUSTER
ISSUE
Terminal Phosphinidenes
The Reaction of Terminal Phosphinidene Complexes
RP–W(CO) ] with Vinylboronic Acids: Cycloaddition vs. P–C
[
5
Bond Formation
[a]
[a]
Yong Xiang Ng and François Mathey*
Abstract: The reaction of terminal phosphinidene complexes the salt and secondary vinylphosphine complexes in the pres-
RP–W(CO) ] with vinylboronic acids is very sensitive to the ence of the salt. This shift of the reaction pathway is explained
[
5
presence or absence of solid K PO in suspension in the reac- by the formation of vinyborates in the presence of potassium
3
4
tion medium. The products are phosphirane complexes without phosphate.
Introduction
Results and Discussion
Since P–C bond formation requires the presence of K PO as a
catalyst, we first decided to check whether this solid salt could
block the cycloaddition of terminal phosphinidene complexes
3
4
New methods for the formation of phosphorus–carbon bonds
are always of current interest, since they lie at the core of
[
1]
organophosphorus chemistry. We have recently described
one such method involving the reaction of terminal phosphin-
(
as generated from the appropriate 7-phosphanorbornadiene
[5]
complexes ) with alkenes. This is not the case, as shown in
Equation (1).
[
2]
idene complexes [RP–W(CO) ] with arylboronic acids. The pro-
5
ducts are secondary arylphosphine complexes. The reaction
fails with alkylboronic acids. The proposed mechanism involves
the insertion of phosphorus into the B–OH bond, followed by
the migration of the aryl group from the borate to the phos-
[
3]
phorus center. One question immediately arises: Is it possible
to transpose this reaction with vinylboronic acids? In this case,
of course, the formation of a phosphirane by cycloaddition of
the phosphinidene with the C=C double bond[ can compete
with P–C bond formation. In this report, we show that it is
(
1)
4]
Then, we investigated the reaction of vinylboronic acids with
possible to shift from one to the other reaction pathway by terminal phosphinidene complexes in boiling toluene without
changing the experimental conditions. K PO [Equation (2)].
3
4
(
2)
[
a] Nanyang Technological University,
The products are the phosphirane complexes 3 obtained as
mixtures of two isomers that have lost their boronic substitu-
ents during the course of the reaction as checked by NMR spec-
troscopy on the crude mixtures before chromatographic purifi-
cation. The traces of water in the reaction medium are responsi-
Division of Chemistry & Biological Chemistry,
2
1 Nanyang Link, Singapore 637371
E-mail: fmathey@ntu.edu.sg
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejic.201500594.
Eur. J. Inorg. Chem. 2016, 616–619
616
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
ble for this hydrolysis. When an extensive drying of vinylboronic
In order to understand this complete change of reaction
acid 2a is performed by Dean–Stark azeotropic distillation be- pathway, we decided to compare the electronic structures of
fore running the reaction, it is possible to get the primary phos- the parent vinylboronic acid and its vinylborate adduct with the
31
phiranylboronic acid 4 and to characterize it by P NMR spec- phosphate anion. The computations were performed by using
[
6]
troscopy and HRMS (calcd. mass for C H BO PW 580.0080, DFT at the B3LYP/ 6-311+G(d,p) level. The occupied frontier
19
14
7
found 580.0081) [Equation (3)]. But this product proved to be orbitals of the two vinylboron species are shown in Figure 1.
rather unstable on standing.
The HOMO of vinylboronic acid is essentially the π C=C bond
with a small contribution from the π lone pairs at oxygen. The
boron atom is positively charged (+0.47 e; Mulliken). The select-
ive reaction of the electrophilic phosphinidene with the vinyl
group is, thus, quite logical. The situation is entirely different
for the vinylborate. Here the HOMO is exclusively localized on
(3)
When the reaction of [RP–W(CO) ] with vinylboronic acids
5
was run in the presence of K PO , a drastic change of the reac-
3
4
tion pathway was observed. The main products of the reaction
are now the secondary vinylphosphine complexes 5 [Equa-
tion (4)].
We have checked that there is no interconversion between
phosphirane and vinylphosphine complexes in the presence of
K PO in boiling toluene. Thus, the vinylphosphine complexes
3
4
are the primary products of the reaction. When the phosphin-
idene substituent is ClCH CH , some cyclization is observed to
2
2
give the C-unsubstituted phosphirane complexes 6 [Equa-
tion (5)].
Figure 1. HOMO (Kohn–Sham) of vinylboronic acid, HOMO and HOMO–1 of
vinylborate [CH =CH–B(OH) (PO )] .
2 2 4
3
–
Both 5h and 6a are obtained in the reaction of 1d with 2a.
(
4)
(
5)
Eur. J. Inorg. Chem. 2016, 616–619
www.eurjic.org
617
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
ously proposed mechanism involving the insertion of the phos-
phinidene into the B–O bond can also intervene in this case.
Anyhow, this vinylation reaction is original in itself, but the com-
plete change of reaction pathway induced by the addition of a
solid salt insoluble in the reaction medium is certainly the strik-
ing point of this report. From a synthetic standpoint, the sec-
ondary vinylphosphine complexes thus obtained are easily
transformed into other products via their anions as shown in
Equation (7).
Experimental Section
All reactions were performed under nitrogen with solvents dried by
standard methods. NMR spectra were obtained by using a Bruker
Figure 2. Computed structure of adduct 7 (R = Me). Main distances [Å] and
angles [°]: P15–W 2.898, P15–O13 1.649, O13–P11 1.737, P11–O9 1.605, O9–
B10 1.550, B10–C4 1.642, C4···P15 5.110; W–P15–C28 103.38, W–P15–O13
1
11.80, O13–P15–C28 103.81 (C dark gray, H gray, B pink, O red, P orange, W
1
AV400 spectrometer operating at 400 MHz for H, 100.64 MHz for
blue).
13
31
C, and 162.02 MHz for P. Spectra were recorded at 298 K in
CD Cl . All coupling constants (J values) are reported in Hertz (Hz).
2
2
HRMS spectra were obtained with a Water Q–Tof Premier mass
spectrometer. Silica gel (230–400 mesh) was used for the chromato-
graphic separations. Phosphanorbornadiene complexes were pre-
the terminal oxygen atoms of the phosphate. A significant con-
tribution of the borate oxygen lone pairs only appears in the
HOMO–1. Both for steric and electronic reasons, the phosphin-
[5]
pared by procedures based on those reported in the literature.
idene will tend to react with the terminal oxygen atoms of the Commercially available alkenylboronic acids were dried with the
phosphate. A theoretical investigation of this point led to ad- Dean–Stark technique prior to use. 31P{ H} NMR spectra for com-
1
plexes 3 and 5 correspond mostly to crude reaction mixtures to
illustrate the selectivity of the reactions. H and C{ H} NMR spectra
for complexes 3 and 5 correspond to purified samples.
duct 7 (R = Me), whose computed structure is shown in Fig-
ure 2. It is important to note that, even if it formally bears a
negative charge, the phosphinidene phosphorus is still electro-
1
13
1
philic in 7 (Mulliken charge: +0.64). The negative charge is delo- General Synthesis of Phosphirane Complex 3: A toluene mixture
(
2 mL) of phosphanorbornadiene complex 1 (0.3 mmol) and
alkenylboronic acid 2 (0.9 mmol) in a sealed tube was heated at
10 °C for 18 h under an inert atmosphere. The solvent was evapo-
calized onto the tungsten pentacarbonyl complexing group.
Since the vinylic carbon bonded to B bears a negative charge
1
(
–0.12), the transfer of the vinyl group from B to P in 7 appears
rated, and the residue was strained onto silica. Purification was per-
formed by cold column chromatography at 0 °C with hexane.
to be favored. The proposed mechanism is depicted in Equa-
tion (6).
General Synthesis of Vinylphosphine Complex 5: A toluene mix-
ture (3 mL) of phosphanorbornadiene complex 1 (0.3 mmol), alk-
enylboronic acid 2 (0.9 mmol), and anhydrous K PO (1.2 mmol) in
3
4
a sealed tube was heated at 110 °C for 18 h under an inert atmos-
phere. The solvent was evaporated, and the residue was strained
onto silica. Purification was performed by cold column chromatog-
raphy at 0 °C with 15:1 hexane/dichloromethane.
Supporting Information (see footnote on the first page of this
article): Experimental data and NMR spectra for compounds 3, 5, 6,
8, and 9.
(6)
Acknowledgments
This mechanism can also operate in the arylation of The authors thank the Nanyang Technological University in
phosphinidenes by arylboronic acids in the presence of Singapore for the financial support of this work and the Minis-
potassium phosphate, although this arylation also works with try of Education for a Tier 1 grant (no M4011247. The authors
lower yields in the absence of K PO . This means that the previ- declare no competing financial interests.
3
4
(
7)
Eur. J. Inorg. Chem. 2016, 616–619
www.eurjic.org
618
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
[
[
5] A. Marinetti, F. Mathey, J. Fischer, A. Mitschler, J. Chem. Soc., Chem. Com-
mun. 1982, 667; B. Deschamps, F. Mathey, Tetrahedron Lett. 1985, 26,
Keywords: Phosphorus · Boron · Cycloaddition · Phosphines
4
595; J.-M. Alcaraz, J. Svara, F. Mathey, New J. Chem. 1986, 10, 321.
6] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, J. A. Montgomery Jr., T. Vreven, K. N. Kudin, J. C. Burant,
J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G.
Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken,
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. Ragha-
vachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J.
Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi,
R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonza-
lez, J. A. Pople, Gaussian 03, Revision B.05, Gaussian, Inc., Pittsburgh PA,
2003.
[
1] Some recent reviews: M. C. Mitchell, T. P. Kee, Coord. Chem. Rev. 1997,
58, 359; B. A. Trofimov, S. N. Arbuzova, N. K. Gusarova, Russ. Chem. Rev.
999, 68, 215; F. Alonso, I. P. Beletskaya, M. Yus, Chem. Rev. 2004, 104,
079; A. L. Schwan, Chem. Soc. Rev. 2004, 33, 218; L. Coudray, J.-L. Mon-
1
1
3
tchamp, Eur. J. Org. Chem. 2008, 3601; S. Van der Jeught, C. V. Stevens,
Chem. Rev. 2009, 109, 2672; F. M. J. Tappe, V. T. Trepohl, M. Oestreich,
Synthesis 2010, 3037; D. Zhao, R. Wang, Chem. Soc. Rev. 2012, 41, 2095;
O. Berger, C. Petit, E. L. Deal, J.-L. Montchamp, Adv. Synth. Catal. 2013,
3
55, 1361.
2] Y. X. Ng, F. Mathey, Angew. Chem. Int. Ed. 2013, 52, 14140; Angew. Chem.
013, 125, 14390.
[
2
[
3] Y. X. Ng, F. Mathey, Organometallics 2014, 33, 1322.
[
4] Recent reviews: J. C. Slootweg, K. Lammertsma, Science Synthesis 2009,
4
2
2, 15; R. Waterman, Dalton Trans. 2009, 18; F. Mathey, Dalton Trans.
007, 1861; K. Lammertsma, Top. Curr. Chem. 2003, 229, 95; K. Lam-
mertsma, M. J. M. Vlaar, Eur. J. Org. Chem. 2002, 1127; F. Mathey, N. H.
Tran Huy, A. Marinetti, Helv. Chim. Acta 2001, 84, 2938.
Received: June 3, 2015
Published Online: July 14, 2015
Eur. J. Inorg. Chem. 2016, 616–619
www.eurjic.org
619
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim