Formation of phosphanoxy-substituted phosphaalkenes via sterically promoted cleavage of the P=P diphosphene bond

Article abstract of DOI:10.1039/c4cc03274h

The reaction of a kinetically stabilized diphosphene (Mes* PPMes*: Mes* = 2,4,6-tri-tert-butylphenyl) with an organolithium reagent and an acyl halide afforded the corresponding phosphanoxy-substituted phosphaethene [((phosphinidene)methoxy)phosphine] via sterically-promoted bond-cleavage of the P-P bond. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4cc03274h

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Formation of phosphanoxy-substituted
phosphaalkenes via sterically promoted cleavage
Cite this: Chem. Commun., 2014,
50, 9204
Q
of the P P diphosphene bond†
Received 2nd May 2014,
Accepted 26th June 2014
Shigekazu Ito,* Shunsuke Okabe, Yasuhiro Ueta and Koichi Mikami
DOI: 10.1039/c4cc03274h
www.rsc.org/chemcomm
Q
The reaction of a kinetically stabilized diphosphene (Mes*P PMes*: unique bonding properties. In addition, a bulky diphosphane
Mes* = 2,4,6-tri-tert-butylphenyl) with an organolithium reagent and bearing four bis(trimethylsilyl)methyl groups may exhibit facile
an acyl halide afforded the corresponding phosphanoxy-substituted homolytic cleavage providing the phosphinyl radicals.5
phosphaethene [((phosphinidene)methoxy)phosphine] via sterically-
In the course of our research on low-coordinated phosphines,
we have explored the sterically promoted P–P bond cleavage of 1 for
synthesizing structurally attractive phosphorus compounds. The
promoted bond-cleavage of the P–P bond.
In 1981, Yoshifuji and co-workers succeeded in isolating and conversion of 1 into several phosphacumulenes via additions of
characterizing a ‘‘phosphobenzene’’ derivative by using bulky dihalocarbene species has been reported, indicating that this
2,4,6-tri-tert-butylphenyl (Mes*) groups.1 This isolable diphosphene approach may be suitable for constructing P2 molecular skeletons
(1) has stimulated synthetic studies of various low-coordinated in low-coordination states.6,7
heavier main group elements through use of the kinetic stabilization
technique.2,3 In contrast, the sterically congested double bond has an acyl halide induced formal P–P cleavage leading to phosphanoxy-
shown several unique reactive properties.
substituted phosphaalkenes.8 The structure and physicochemical
Here we report that treating 1 with an organolithium reagent and
For example, diphosphene 1 undergoes a bond-cleavage reaction properties of the novel phosphaalkene derivative were investigated.
providing a primary phosphine (Mes*PH2) and a phosphonic acid Additionally, we discuss the formal P–P cleavage based on DFT
monoester [Mes*P(O)(OH)(OCOAr)] (Scheme 1).4 In this reaction, the calculations.
intermediate oxophosphanylidenephosphorane (Int-I) is attacked by
Diphosphene 1 was prepared according to a reported procedure,1
the resultant m-chlorobenzoic acid, and the facile P–P bond cleavage and was reacted with 1 equiv. of n-butyllithium to generate the
of Int-II occurs in the presence of water. Therefore, the steric corresponding anionic diphosphane (2)9 at À40 1C. Subsequently a
encumbrance around the diphosphane structure can induce these solution of anion 2 was quenched with benzoyl chloride (Scheme 2).
Structural analyses confirmed that the yellow product purified by
Scheme 1 Reaction of diphosphene 1 with mCPBA resulting in the P–P
bond cleavage.
Department of Applied Chemistry, Graduate School of Science and Engineering,
Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8552, Japan.
E-mail: ito.s.ao@m.titech.ac.jp; Fax: +81 3 5734 2143
† Electronic supplementary information (ESI) available. CCDC 1000474. For ESI
Scheme 2 P–P bond cleavage of diphosphene 1 affording phosphaalkene
(methylenephosphine) 3.
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c4cc03274h
9204 | Chem. Commun., 2014, 50, 9204--9206
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Fig. 1 An ORTEP drawing for 3 (50% probability levels). Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and angles (1): P1–
C1 1.702(1), P1–C2 1.847(1), C1–C3 1.487(2), C1–O 1.395(2), P2–O 1.682,
P2–C4 1.860(1), P2–C5 1.841(1), P1 Á Á Á P2 3.062(1), C1–P1–C2 103.7(1),
P1–C1–C3 134.2(1), P1–C1–O 117.3(1), C3–C1–O 108.5(1), C1–O–P2
120.9(1), O–P2–C4 97.1(1), O–P2–C5 110.3(1), C4–P2–C5 96.7(1).
recrystallization (AcOEt–MeCN, 80 1C) was a single diastereomer of
novel phosphanoxy-substituted phosphaalkene 3 (68% yield). The
predicted benzoyl-substituted diphosphane (4) was not isolated at
all. Crystalline 3 was air-stable and slightly unstable on silica gel.
In the 31P NMR spectrum, the sp2-phosphorus of 3 was observed
Fig. 2 Decisive molecular orbitals of 3 for the UV-vis spectroscopic
property [B3LYP/6-31G(d)].
at a higher field (167 ppm) than most of the hydrocarbon- the reaction procedures with an alkyllithium and an acyl halide. This
substituted phosphaalkenes2 because of the –OP(nBu)Mes* moiety is comparable to the Becker method of synthesizing phosphaalkenes
at the b-position, and the sp3-phosphorus was observed at around via silyl migration.17 The steric encumbrance around the phos-
135 ppm. The canonical structure of the phosphanoxy-substituted phorus atoms would induce P–P cleavage in the putative
phosphaalkene [Mes*PÀ–C(Ph)QO+–P(nBu)Mes*] affected the reaction intermediate or the transition state. To understand
31P NMR shift.10 Compared with the JPP coupling constant of most the steric effects promoting the P–P cleavage of 1 leading to
acyclic 1,3-diphosphapropenes,11 the JPP of 135 Hz of this com- the phosphanoxy-substituted phosphaalkene, we performed DFT
pound was smaller because of the increase in the PÁÁÁP distance. In calculations16 for the model compounds (Fig. 3). For methyl-
the 13C NMR, the PQC carbon had a relatively low-field chemical substituted 3A and 4A, the acetyl-substituted diphosphane
shift (195 ppm). Fig. 1 shows the X-ray structure of 3. The structure 4A was energetically preferable. However, 4B bearing
E-isomeric PQC–O–Po skeleton exhibited an s-cis type conforma- the 2,6-di-tert-butylphenyl groups was less stable than the
tion. The PÁÁÁP distance of 3.062 Å indicated no covalent bonding phosphaalkene 3B, which was consistent with the experimental
character between the phosphorus atoms. The P1–C2 distance results. Thus, the steric encumbrance should induce the P–P cleavage
confirmed the double bond structure and was comparable to that of putative intermediate 4B.18,19 Alternatively, taking into account the
of 2-siloxy-substituted phosphaalkenes.12 The skeletal parameters possible unusual P–P bonding character in the sterically congested
of 3 were similar to those of most Mes*-substituted phospha- environment, a mechanism through which a phosphanyl radical pair
alkenes.2,13 The steric bulkiness induced remarkable distortion formed by homolytic cleavage is also possible.5,20 Variable tempera-
of the Mes* aromatic rings into the boat-like structures.14 The ture NMR monitoring of the reaction mixture of 1, butyllithium, and
2-phenyl group and the PQC plane formed a twisted conformation benzoyl chloride revealed that the initial product putatively bearing
with a torsion angle of 301. The P1–C1–O–P2 torsion angle of a P–P bond [dP 2.4, À2.8; JPP = 360.3 Hz, at À40 1C] completely
14.1(1)1 indicated an interaction between the PQC p-bond and the disappeared at 25 1C, and formation of 3 was observed at 0 1C
lone pair, which was consistent with the 31P NMR data. The UV-vis together with unidentified products. We are currently characterizing
spectrum of 3 showed absorptions from 300 to 400 nm. TD-DFT the observed intermediates.
calculations [wB97XD/6-31G(d,p)]15,16 for 3 suggested that the small
The procedure shown in Scheme 2 prompted us to synthesize
and large absorptions mainly arose from the HOMO to LUMO several phosphanoxy-substituted phosphaalkenes with organo-
(340 nm) and HOMO À 1 to LUMO (300 nm) transitions, respec- lithium reagents and acyl halides. We prepared air-tolerant crystalline
tively (Fig. 2, see also ESI†). The large contribution of the lone pair 5–8 together with 3 (Table 1). Acyl chlorides bearing electron-deficient
to the sp2-phosphorus in the HOMO and p-orbital of the PQC and electron-rich aryl substituents were used for the P–P cleavage of 2
bond to HOMO À 1 is consistent with the experimentally observed and the corresponding phosphaalkenes 5and 6were isolated. Pivaloyl
UV-vis properties. Additionally, the phenyl ring in the 2-position chloride was used to prepare 7. The diphoshanyl anion generated
contributed strongly to the frontier orbitals.
from 1 and phenyllithium at room temperature was reacted with
The formation of 3 indicated formal cleavage of the phosphorus– benzoyl chloride to give 8 in moderate yield. All the phosphanoxyl-
phosphorus bond of 1 and concomitant creation of the P–O bond in substituted phosphaalkenes were air-tolerant crystalline compounds
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Notes and references
1 M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu and T. Higuchi, J. Am.
Chem. Soc., 1981, 103, 4587; M. Yoshifuji, I. Shima, N. Inamoto,
K. Hirotsu and T. Higuchi, J. Am. Chem. Soc., 1982, 104, 6167.
2 (a) K. B. Dillon, F. Mathey and J. F. Nixon, Phosphorus: The Carbon
Copy, Wiley, Chichester, 1998; (b) Multiple Bonds and Low Coordina-
tion in Phosphorus Chemistry, ed. M. Regitz, Thieme, Stuttgart, 1990.
3 (a) R. C. Fischer and P. P. Power, Chem. Rev., 2010, 110, 3877;
(b) P. P. Power, Nature, 2010, 463, 171.
4 M. Yoshifuji, K. Ando, K. Toyota, I. Shima and N. Inamoto, J. Chem.
Soc., Chem. Commun., 1983, 419.
5 (a) S. L. Hinchley, C. A. Morrison, D. W. H. Rankin, C. L. B. Macdonald,
R. J. Wiacek, A. H. Cowley, M. F. Lappert, G. Gundersen, J. A. C. Clyburne
and P. P. Power, Chem. Commun., 2000, 2045; (b) S. L. Hinchley,
C. A. Morrison, D. W. H. Rankin, C. L. B. Macdonald, R. J. Wiacek,
A. Voigt, A. H. Cowley, M. F. Lappert, G. Gundersen, J. A. C. Clyburne
and P. P. Power, J. Am. Chem. Soc., 2001, 123, 9045.
6 (a) M. Yoshifuji, S. Sasaki, T. Niitsu and N. Inamoto, Tetrahedron Lett.,
1989, 30, 187; (b) M. Gouygou, C. Tachon, R. El Quatib, G. Etemad-
Moghadam and M. Koenig, Tetrahedron Lett., 1989, 30, 177.
7 M. Yoshifuji, J. Chem. Soc., Dalton Trans., 1998, 3343.
Fig. 3 DFT-calculated relative energies of the model compounds 3 and 4
[B3LYP/6-31G(d)].
8 Examples of phosphanoxy-substituted phosphaalkenes: (a) Y. A. Veits,
E. G. Neganova, A. A. Borisenko and V. L. Foss, Zh. Obshch. Khim., 1990,
60, 2028; (b) E. G. Neganova, Y. A. Veits, V. K. Byistro, N. M. Semenenko,
A. A. Borisenko and V. L. Foss, Zh. Obshch. Khim., 1990, 60, 2036;
(c) L. Weber, G. Noveski, S. Uthmann, H.-G. Stamler and B. Neumann,
Eur. J. Inorg. Chem., 2007, 4011.
Table 1 Preparation of phosphanoxy-substituted phosphaalkenes via the
PQP cleavage
9 M. Yoshifuji, K. Shibayama and N. Inamoto, Chem. Lett., 1984, 115.
10 (a) V. A. Wright, B. O. Patrick, C. Schneider and D. P. Gates, J. Am.
Chem. Soc., 2006, 128, 8836; (b) V. A. Wright and D. P. Gates, Angew.
Chem., Int. Ed., 2002, 41, 2389; (c) K. Issleib, H. Schmidt and
E. Leissring, J. Organomet. Chem., 1990, 382, 53.
11 (a) S. Ito, T. Nakagawa and K. Mikami, Chem. Commun., 2013,
49, 9221; (b) H. Liang, S. Ito and M. Yoshifuji, Org. Lett., 2004,
6, 425; (c) S. Ito and M. Yoshifuji, Chem. Commun., 2001, 1208.
12 (a) A. Orthaber, F. Belaj and R. Pietschnig, Inorg. Chim. Acta, 2011,
374, 211; (b) R. Appel, J. Hu¨nerbein, F. Knoch and M. Nieger,
J. Organomet. Chem., 1988, 346, 379; (c) M. Yoshifuji, K. Toyota,
N. Inamoto, K. Hirotsu, T. Higuchi and S. Nagase, Phosphorus, Sulfur
Silicon Relat. Elem., 1985, 25, 237.
Compound
R1
R2
Yield (%)
3
5
6
7
8
nBu
nBu
nBu
nBu
Pha
Ph
68
42
74
41
55
4-CF3C6H4
4-MeOC6H4
tBu
Ph
a
Reaction of 1 with phenyllithium was performed at RT.
and able to be purified by recrystallization. Thus, these products
would be suitable to coordination chemistry and catalysis.
13 M. Yoshifuji and S. Ito, Top. Curr. Chem., 2003, 227, 67.
14 S. Ito, H. Miyake and M. Yoshifuji, Phosphorus, Sulfur Silicon Relat.
Elem., 2009, 184, 917.
In conclusion, we have established a synthetic procedure for
air-tolerant crystalline phosphanoxy-substituted phosphaalk-
enes via the sterically promoted P–P bond cleavage of the
diphosphene 1. The structural and physicochemical properties of
3 were analyzed, and the metathesis-like reaction was analyzed
further based on DFT calculations. These novel phosphanoxy-
substituted phosphaethenes could be used for developing unique
applications in fields such as coordination chemistry and catalysis.
Additionally, we are currently attempting to elucidate the reaction
mechanism, with particular focus on the P–P bond cleavage.
This work was supported in part by Grants-in-Aid for Scien-
tific Research (KAKENHI; No. 22350058, 23655173, 25288033
and 25109518) from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan, the Collaborative Research
Program of Institute for Chemical Research, Kyoto University
15 J.-D. Chai and M. Head-Gordon, Phys. Chem. Chem. Phys., 2008, 10, 6615.
16 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,
T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M. Bearpark,
J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith,
R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, 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, R. L. Martin, K. Morokuma,
V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,
S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz,
J. Cioslowski and D. J. Fox, Gaussian 09, Revision B.01, Gaussian,
Inc., Wallingford CT, 2010.
17 G. Becker, Z. Anorg. Allg. Chem., 1976, 423, 242.
(grant # 2013-10), Sumitomo Chemical Co., Ltd, and Nissan 18 Transition state from 4A to 3A was optimized and indicated an
activation energy of 41.2 kcal molÀ1. See ESI†.
19 Attempts to optimize a possible transition state from 4B to 3B failed.
20 Compound 4B exhibited almost closed shell character in a CASSCF
Chemical Industries, Ltd. The authors thank Prof. Hiroharu
Suzuki and Dr Masataka Oishi of Tokyo Institute of Technology
for support of X-ray crystallographic analyses.
calculation. See ESI†.
9206 | Chem. Commun., 2014, 50, 9204--9206
This journal is ©The Royal Society of Chemistry 2014