[ClP(μ-PMes?)]2 - A versatile reagent in phosphorus chemistry

Article abstract of DOI:10.1080/10426507.2015.1128915

The synthesis and some key reactions of the cyclotetraphosphane [ClP(μ-PMes?)]₂ (2, Mes? = 2,4,6-tri-tert-butylphenyl) with Lewis acids and reducing agents are discussed. All products were fully characterized, including single crystal X-ray diffraction, spectroscopic methods as well as computational studies.

Full text of DOI:10.1080/10426507.2015.1128915

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
[ClP(µ-PMes*)]2 – A Versatile Reagent in
Phosphorus Chemistry
Jonas Bresien, Axel Schulz & Alexander Villinger
To cite this article: Jonas Bresien, Axel Schulz & Alexander Villinger (2016): [ClP(µ-PMes*)]2 – A
Versatile Reagent in Phosphorus Chemistry, Phosphorus, Sulfur, and Silicon and the Related
Elements, DOI: 10.1080/10426507.2015.1128915
To link to this article: http://dx.doi.org/10.1080/10426507.2015.1128915
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Date: 29 February 2016, At: 04:49

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[ClP(µ-PMes*)]2 – A Versatile Reagent in Phosphorus Chemistry
Jonas Bresien,1 Axel Schulz,1,2* Alexander Villinger1
1 Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany
2 Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Straße 29a, 18059
Rostock, Germany
*axel.schulz@uni-rostock.de
GRAPHICAL ABSTRACT
Abstract The synthesis and some key reactions of the cyclotetraphosphane [ClP(µ-PMes*)]2 (2,
Mes* = 2,4,6-tri-tert-butylphenyl) with Lewis acids and reducing agents are discussed. All
products were fully characterized, including single crystal X-ray diffraction, spectroscopic
methods as well as computational studies.
Keywords: Ring systems; phosphorus chemistry; cyclo-phosphanes; 31P NMR spectroscopy;
DFT calculations
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INTRODUCTION
Ring systems composed of group 15 elements (pnictogens, Pn) are an interesting and
widely investigated field of main group chemistry.1–3 Especially, phosphorus based ring systems
have received increasing attention,4,5 since various types of mono- and polycyclic phosphanes
were prepared by direct activation of white phosphorus (P4).6–13 However, selective
functionalization of such ring systems was not studied in detail, which is why we set out to
prepare a suitable functionalized P4 precursor and investigate its reactivity. In analogy to the well
explored chemistry of dichloro-cyclo-diphosphadiazanes,1–3 the homologous dichloro-cyclo-
tetraphosphanes seemed a worthwhile target for further chemistry. Known examples of such
halogen
substituted
cyclo-tetraphosphanes
comprised
[ClP(µ-PSi(t-Bu)3)]2
and
[ClP(µ-PSi(t-Bu)3)]2; yet we found their preparation unsuitable for synthetic scale.14,15
RESULTS AND DISCUSSION
Preparation of [ClP(µ-PMes*)]2
In analogy to the synthesis of Mes*NPCl (Scheme 1, top; Mes* = 2,4,6-tri-tert-butyl-
phenyl),16 treatment of Mes*PH2 with PCl3 in the presence of NEt3 led to P–P coupling under
elimination of [HNEt3]Cl. In the first step, the tetraphosphene Mes*P=P–P(Mes*)PCl2 (1) was
formed, which underwent rearrangement to [ClP(µ-PMes*)]2 (2) in polar solvents (Scheme 1,
bottom).17 After optimization of the reaction conditions, compound 2 could be prepared in 50–
60 % yield (5 g scale), which facilitated the investigation of its reactivity.18
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Compound 2 was characterized by an A2X2 spin system in the 31P NMR spectrum (δexptl
=
−8.1, +131.1 ppm; δcalcd = −1.6, 119.9 ppm). Its solid state structure was determined by single
crystal X-ray diffraction. The four membered ring system adopts a puckered conformation, all
substituents are arranged in the equatorial position (Figure 1). The experimental structural data
correspond nicely with calculated structural parameters (PBE0/6-31g(d,p) level of theory).17
Reaction with GaCl3
When 2 was treated with GaCl3 at −80 °C, the intermediate formation of a highly reactive
31
tetraphosphenium cation (3+) could be detected by in situ P NMR spectroscopy (Scheme 2).18
Upon warming to −50 °C, a formal 1,2-Cl shift was observed, resulting in the formation of two
isomers of an unprecedented bicyclic triphosphino-phosphonium cation (4+; Figure 2, left).
In the 31P NMR spectrum, both isomers of 4+ were characterized by A2MX patterns (4a+:
δexptl = −214.5, −89.5, +51.2 ppm; δcalcd = −220.3, −103.8, +24.6 ppm; 4b+: δexptl = −226.4,
−123.6, +9.0 ppm; δcalcd = −227.8, −135.7, −12.0 ppm). The molecular structure of 4a[GaCl4]
was elucidated by single crystal X-ray diffraction.18 The bicyclic P4 scaffold adopts a butterfly
conformation with a fold angle of 102°, which is comparable to other bicyclic tetraphos-
phanes.13,19–25 According to NBO analysis,26 the positive charge is mostly localized at the formal
phosphonium centre (+0.76 e), while the whole P4 scaffold bears a positive charge of +1.37 e.
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The intermediate 3+ could be trapped by a formal [4+2] cycloaddition reaction with
dimethylbutadiene (dmb), resulting in a bicyclic tetraphosphaoctenium cation (5+; Figure 2,
right), which is comparable to previously reported cyclic phosphino-phosphonium cations.27–29
Reduction reactions
Reduction of 2 with Mg selectively afforded the exo-exo isomer of the bicyclic
tetraphosphane Mes*P4Mes* (6a; Scheme 3, top) in good yields (73 %).30 Compound 6 had
previously been prepared by reacting a mixture of Mes*Br and Mes*Li with white phosphorus,
though merely in low yields (5 %).21,31 Intriguingly, the carbene promoted degradation of 2 gave
rise to the elusive endo-exo isomer of Mes*P4Mes* (6b; Scheme 3, bottom),30 which had
previously only been characterized spectroscopically.32
31
Both isomers of 6 were fully characterized. In the P NMR spectrum, 6a is characterized
by an A2X2 pattern (δexptl = −273.2, −128.3 ppm; δcalcd = −271.5, −138.0 ppm), while 6b displays
an A2MX spin system (δexptl = −220.4, −94.8, −54.7 ppm; δcalcd = −217.8, −100.2, −68.0 ppm).
The molecular structure was determined by single crystal X-ray diffraction. In both isomers, the
overall structure of the P4 scaffold is rather similar. The fold angle of the bicyclus in the endo-
exo isomer is significantly larger (108°) than in the exo-exo isomer (96°), presumably due to
Pauli repulsion between the endo-Mes* substituent and the ortho-t-Bu groups of the exo-Mes*
group (Figure 3).
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In conclusion, the synthesis of the cyclo-phosphane 2 was newly developed and
subsequently improved to make it readily available for synthetic use. The introduction of reactive
P–Cl bonds directly at the ring system gave rise to fascinating follow-up chemistry by
abstraction or reductive elimination of the Cl atoms, affording new preparative routes to known
as well as unprecedented phosphorus ring systems. This nicely demonstrates the potential of our
synthetic approach. To extend the product spectrum, the reactivity of 2 towards Lewis bases and
transition metals is currently under investigation.
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REFERENCES
1
2
3
4
5
6
7
8
9
Stahl, L. Coord. Chem. Rev. 2000, 210, 203–250.
Balakrishna, M. S.; Eisler, D. J.; Chivers, T. Chem. Soc. Rev. 2007, 36, 650–664.
He, G.; Shynkaruk, O.; Lui, M. W.; Rivard, E. Chem. Rev. 2014, 114, 7815–7880.
Scherer, O. J. Comm. Inorg. Chem. 1987, 6, 1–22.
Baudler, M.; Glinka, K. Chem. Rev. 1993, 93, 1623–667.
Scheer, M.; Balázs, G.; Seitz, A. Chem. Rev. 2010, 110, 4236–4256.
Giffin, N. A.; Masuda, J. D. Coord. Chem. Rev. 2011, 255, 1342–1359.
Cossairt, B. M.; Piro, N. A.; Cummins, C. C. Chem. Rev. 2010, 110, 4164–4177.
Masuda, J. D.; Schoeller, W. W.; Donnadieu, B.; Bertrand, G. Angew. Chem. Int. Ed. 2007,
46, 7052–7055.
10 Masuda, J. D.; Schoeller, W. W.; Donnadieu, B.; Bertrand, G. J. Am. Chem. Soc. 2007, 129,
14180–14181.
11 Heinl, S.; Reisinger, S.; Schwarzmaier, C.; Bodensteiner, M.; Scheer, M. Angew. Chem. Int.
Ed. 2014, 53, 7639–7642.
12 Heinl, S.; Scheer, M. Chem. Sci. 2014, 5, 3221–3225.
13 Borger, J. E.; Ehlers, A. W.; Lutz, M.; Slootweg, J. C.; Lammertsma, K. Angew. Chem. Int.
Ed. 2014, 53, 12836–12839.
14 Wiberg, N.; Wörner, A.; Lerner, H.-W.; Karaghiosoff, K. Z. Naturforsch. B 2002, 57, 1027–
1035.
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15 Lorbach, A.; Nadj, A.; Tüllmann, S.; Dornhaus, F.; Schödel, F.; Sänger, I.; Margraf, G.;
Bats, J. W.; Bolte, M.; Holthausen, M. C.; Wagner, M.; Lerner, H. Inorg. Chem. 2009, 48,
1005–1017.
16 Niecke, E.; Nieger, M.; Reichert, F. Angew. Chem. Int. Ed. Engl. 1988, 27, 1715–1716.
17 Bresien, J.; Hering, C.; Schulz, A.; Villinger, A. Chem. Eur. J. 2014, 20, 12607–12615.
18 Bresien, J.; Faust, K.; Schulz, A.; Villinger, A. Angew. Chem. Int. Ed. 2015, 54, 6926–6930.
19 Holthausen, M. H.; Surmiak, S. K.; Jerabek, P.; Frenking, G.; Weigand, J. J. Angew. Chem.
Int. Ed. 2013, 52, 11078–11082.
20 Niecke, E.; Rüger, R.; Krebs, B. Angew. Chem. Int. Ed. Engl. 1982, 21, 544–545.
21 Riedel, R.; Hausen, H.-D.; Fluck, E. Angew. Chem. Int. Ed. Engl. 1985, 24, 1056–1057.
22 Power, M. B.; Barron, A. R. Angew. Chem. Int. Ed. Engl. 1991, 30, 1353–1354.
23 Bezombes, J.-P.; Hitchcock, P. B.; Lappert, M. F.; Nycz, J. E. Dalton Trans. 2004, 499–501.
24 Fox, A. R.; Wright, R. J.; Rivard, E.; Power, P. P. Angew. Chem. Int. Ed. 2005, 44, 7729–
7733.
25 Donath, M.; Conrad, E.; Jerabek, P.; Frenking, G.; Fröhlich, R.; Burford, N.; Weigand, J. J.
Angew. Chem. Int. Ed. 2012, 51, 2964–2967.
26 Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.; Bohmann, J. A.;
Morales, C. M.; Weinhold, F. NBO 5.9, Theoretical Chemistry Institute, University of
Wisconsin, Madison, 2011.
27 Burford, N.; Dyker, C. A.; Lumsden, M.; Decken, A. Angew. Chem. Int. Ed. 2005, 44,
6196–6199.
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28 Dyker, C. A.; Burford, N.; Menard, G.; Lumsden, M. D.; Decken, A. Inorg. Chem. 2007, 46,
4277–4285.
29 Weigand, J. J.; Burford, N.; Davidson, R. J.; Cameron, T. S.; Seelheim, P. J. Am. Chem. Soc.
2009, 131, 17943–17953.
30 Bresien, J.; Faust, K.; Hering-Junghans, C.; Rothe, J.; Schulz, A.; Villinger, A. Dalton
Trans. 2016, DOI: 10.1039/C5DT02757H.
31 Fluck, E.; Riedel, R.; Hausen, H.-D.; Heckmann, G. Z. Anorg. Allg. Chem. 1987, 551, 85–
94.
32 Jutzi, P.; Meyer, U. J. Organomet. Chem. 1987, 333, C18–C20.
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NEt3
Mes* NH2 + PCl3
Mes* N P Cl
Cl
PCl2
NEt3
P
P
P
Mes* PH2 + PCl3
½
½ Mes* P P Mes*
Mes*
P
1
Mes*
P
2
Cl
Scheme 1 Top: Synthesis of Mes*NPCl. Bottom: Synthesis of [ClP(µ-PMes*)]2 (2)
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Cl
P
P
P
P
Mes*
Mes*
C
°
0
5
Cl
Cl
–
4a+
GaCl4
GaCl3
P
P
Mes*
P
P Mes*
Mes*
3+
P
P Mes*
P
P
– 80 °C
Mes*
–
5
0
2
Cl
GaCl4
P
P
°
C
P
P
Mes*
Cl
4b+
GaCl4
Scheme 2 The reaction of 2 with GaCl3 leads to the highly reactive intermediate 3+, which
rearranges to the bicyclic cation 4+. The latter is observed as exo-exo (4a+) and endo-exo isomer
(4b+)
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P
P
P
P
P
Mes*
Mes*
Mes*
6a
g
Cl
M
P
Mes* P P Mes*
P
Mes*
2
Cl
P
P
P
+ byproducts
N
N
6b
Scheme 3 Starting from 2, both isomers of the bicyclic tetraphosphane 6 can be obtained
selectively
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Figure 1 Molecular structure of 2 in the crystal (P21/c). Ellipsoids are set at 50% probability
(173 K). Selected bond lengths [Å] and angles [°]: P1–P2 2.2731(5), P1–P4 2.2596(5), P2–P3
2.1905(5), P2–Cl1 2.0967(5), P3–P4 2.2026(5), P4–Cl2 2.1061(6); P1–P2–P3 80.54(2), P1–P2–
Cl1 106.45(2), P3–P2–Cl1 97.97(2), P2–P3–P4 84.65(2), P3–P4–P1 80.58(2), P3–P4–Cl2
97.32(2), P1–P4–Cl2 104.47(2); P1–P2–P4–P3 119.45(3), Cl1–P2–P4–Cl2 −1.06(5) C1–P1–P3–
C19 −17.9(1)
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Figure 2 Molecular structure of 4[GaCl4] (left) and 5+ (right) in the crystal. Ellipsoids are set at
50% probability (173 K). Selected bond lengths [Å] and angles [°]: 4+ P1a–P2a 2.150(2),
P1a–Cl1a 2.009(2), P2a–P2a' 2.244(2), P2a–P3a 2.244(2); Cl1a–P1a–P2a 117.65(7), C1–
P1a–Cl1a 118.7(2), P2a'–P1a–P2a 62.91(7), P1a–P2a–P2a' 58.55(3), P3a–P2a–P2a'
59.99(3), P1a–P2a–P3a 83.60(6), P2a'–P3a–P2a 60.02(7); P1a–P2a–P2a'–P3a −101.68(3);
5+ P1–P2 2.195(1), P1–C19 1.846(3), C19–C20 1.514(4), C20–C21 1.334(4), C21–C22
1.500(4), P2–C22 1.871(3), P4–Cl1 2.068(1); P2–P1–P4 91.78(4), C19–P1–P2 102.3(1),
C19–P1–P4 116.1(1); P1–P2–P4–P3 159.03(1)
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Figure 3 Molecular structures of 6a (left) and 6b (right) in the crystal. Ellipsoids are set at 50%
probability (173 K). Selected bond lengths [Å] and angles [°]: 6a P1–P3 2.2310(7), P1–P4
2.2171(7), P2–P3 2.2294(7), P2–P4 2.2236(7), P3–P4 2.1634(8); P1–P3–P4–P2 −95.66(3);
6b P1–P2 2.2244(7), P1–P3 2.2326(8), P2–P4 2.2131(8), P3–P4 2.2101(8), P2–P3
2.1773(8); P1–P2–P3–P4 107.78(3)
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Cl
Mes*
P
P
P
P
P
P
P
P
Mes*
Mes*
Mes*
Cl
Cl
Cl
Cl
P
Mes*
P
P
Mes* P
P
Mes* P P Mes* Mes* P P Mes*
P
P
P
Cl
Mes*
P
P
P
P
P
P
P
P
Mes*
Mes*
Mes*
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