Highly Unsaturated Phosphorus Compounds ... - ACS Publications

Mar 26, 2009 - Alex S. Ionkin,* William J. Marshall, Brian M. Fish, Matthew F. ... DeVelopment, Experimental Station, Wilmington, Delaware 19880-0500...
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Highly Unsaturated Phosphorus Compounds: Generation and Reactions on Both Multiple Bonds of Vinyl Phosphaalkyne† Alex S. Ionkin,* William J. Marshall, Brian M. Fish, Matthew F. Schiffhauer, Fredric Davidson, and Charles N. McEwen DuPont Central Research & DeVelopment, Experimental Station, Wilmington, Delaware 19880-0500 ReceiVed December 29, 2008

4,7-Di-tert-butyl-2,2,9,9-tetramethyl-5,6-bis-trimethylsilanyloxy-deca-3,5,7-triene (14), 3,5-bis(1-tertbutyl-3,3-dimethyl-but-1-enyl)-1,2,4-oxadiphosphole (11), 2,3-di-tert-butyl-5-(1-tert-butyl-3,3-dimethylbut1-enyl)-4-trimethylsilanyloxy-2H-phosphole (10), 2,4,6-tris(1-tert-butyl-3,3-dimethylbut-1-enyl)-1,3,5triphosphinine (9), 4,5-di-tert-butyl-2-(1-tert-butyl-3,3-dimethylbut-1-enyl)-8-(1-tert-butyl-3,3-dimethylbutylidene)-1,3,7-triphosphabicyclo[4.2.0]octa-2,5-diene (8), cesium 3,5-bis(1-tert-butyl-3,3-dimethylbut1-enyl)-4H-1,2,4-triphospholide (12), and cesium 5-(1-tert-butyl-3,3-dimethylbut-1-enyl)-1H-1,2,3,4tetraphospholide (13) were isolated in in situ generation of R,β-di-tert-butylvinylphosphaalkyne (4) by CsF-catalyzed methodology between tris(trimethylsilyl)phosphine (6) and Z-2-tert-butyl-4,4-dimethylpent2-enoyl chloride (7). The preference of cycloaddition reactions on the CP triple bond over the CC double bond was observed. The introduction of a vinyl moiety led to the suppression of cage polyphosphorus structures, which are typically formed in the reactions of nonconjugated tert-butyl-substituted derivatives. Introduction Conjugated carbon and nitrogen compounds with triple and double bonds, e.g., vinyl acetylene (1) and acrylonitrile (2), have had an enormous impact on biomedical research,1 theoretical chemistry2 and polymer science.3 The electron rich “naked” phosphorus analog (3) has been detected by microwave spectroscopy during FVP of allyldichlorophosphine4 and during pyrolysis of triallylphosphine.5 Generation of sterically protected R,β-di-tert-butylvinylphosphaalkyne (4) by the traditional hexamethyldisiloxane route resulted in intramolecular [2+2]cycloaddition.6 Consequently we decided to apply a recently developed CsF-catalyzed methodology for the generation of 4.7a Sodium hydroxide,7b-d tetra-n-butylammonium fluoride,7e aluminum trichloride,7f and anhydrous zinc chloride7g have been used for the catalytic elimination of hexamethyldisiloxane to generate PdC and PtC bonds. †

DuPont publication #8877. * Corresponding author. E-mail: [email protected]. (1) Shi Shun, A. L. K.; Tykwinski, R. R. Angew. Chem., Int. Ed. 2006, 45, 1034–1057. (2) Nemirowski, A.; Reisenauer, H. P.; Schreiner, P. R. Chem.-Eur. J. 2006, 12, 7411–7420. (3) Polymerizing organic liquids. (E. I. Du Pont de Nemours & Co.) GB Patent 518657, 1940. (4) (a) Burckett-St. Laurent, J. C. T. R.; Cooper, T. A.; Kroto, H. W.; Nixon, J. F.; Ohashi, O.; Ohno, K. J. Mol. Struct. 1982, 79, 215–20. (b) Ohno, K.; Kroto, H. W.; Nixon, J. F. J. Mol. Struct. 1981, 90, 507–511. (5) Mathey, F.; Le Floch, P. J. Org. Chem. 2004, 69, 5100–5103. (6) Ionkin, A. S.; Marshall, W. J.; Fish, B. M.; Schiffhauer, M. F.; Davidson, F.; McEwen, C. N. Chem. Commun. 2008, 5432–5434. (7) (a) Ionkin, A. S.; Marshall, W. J.; Fish, B. M.; Marchione, A. A.; Howe, L. A.; Davidson, F.; McEwen, C. N. Eur. J. Inorg. Chem. 2008, 15, 2386–2390. (b) Dillon, K. D.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy; Wiley: Chichester, 1998. (c) Quin, L. D. A Guide to Organophosphorus Chemistry; A John Wiley & Sons, Inc.: New York, 2000. (d) Regitz, M.; Scherer, O. J. Multiple Bonds and Low Coordination in Phosphorus Chemistry; Georg Thieme Verlag: Stuttgart, 1990. (e) Allspach, T.; Regitz, M.; Becker, G.; Becker, W. Synthesis 1986, 31. (f) Mack, A.; Pierron, E.; Allspach, T.; Bergstra¨sser, U.; Regitz, M. Synthesis 1998, 1305. (g) Becker, G.; Brombach, H.; Horner, S. T.; Niecke, E.; Schwarz, W.; Streubel, R.; Wuerthwein, E.-U. Inorg. Chem. 2005, 44, 3080–3086.

Chart 1

Results and Discussion The interaction of cesium fluoride (5), tris(trimethylsilyl)phosphine (6), and Z-2-tert-butyl-4,4-dimethylpent-2-enoyl chloride8 (7) afforded seven major products (8-14, Scheme 1). The yields of the above compounds depend on the reaction times and ratios between starting reagents. If the reaction mixture was heated for up to 2 days at 90 °C in dioxane, the first four products in Scheme 1 formed prevailingly. Heating of the reaction mixture up to 10 days resulted in predominant formation of cesium 3,5-bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-4H-1,2,4triphospholide (12) and cesium 5-(1-tert-butyl-3,3-dimethylbut1-enyl)-1H-1,2,3,4-tetraphospholide (13). Different ratios between 6 and 7 were tested. Theoretically a ratio of 1:1 between 6 and 7 would be the best for the generation of 4, and this ratio led to the predominant formation of compounds 8-11. It has been found experimentally that two molar excess of 7 relative to 6 resulted in better overall yields of all compounds. The ratio between cesium fluoride (5) and tris(trimethylsilyl)phosphine (6) was kept at 2.3. An excess of cesium fluoride, due to moderate solubility of it in dioxane, was found to be beneficial to yields of the products. 31P NMR spectroscopy was used to monitor the progress of the reaction. It was not a selective reaction; chemical shifts of all products were observed in the reaction mixture before isolation. Compound 4 was not isolated, and we are reluctant to make an assignment of its chemical shift at this point. A mass spectrum of the reaction mixture shows the presence of an M+ ion at 182.12, corresponding to C11H9P, which can be attributed to vinyl phosphaalkyne 4. (8) Ionkin, A. S.; Marshall, W. J.; Fish, B. M. Org. Lett. 2008, 10, 2303– 2306.

10.1021/om801224d CCC: $40.75  2009 American Chemical Society Publication on Web 03/26/2009

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Scheme 1. Three-Component Reaction between Tris(trimethylsilyl)phosphine (6), Cesium Fluoride (5), and Z-2-tert-Butyl4,4-dimethylpent-2-enoyl Chloride (7)

Figure 2. ORTEP drawing of 2,4,6-tris(1-tert-butyl-3,3-dimethylbut-1-enyl)-1,3,5-triphosphinine (9). Thermal ellipsoids are drawn to the 20% probability level. The structure is displayed showing disorder that is typical in compounds containing the R,β-di-tertbutylvinyl group. Compounds 8, 9, 11, 12, and 14 all contain similar disorder. Scheme 2

Scheme 3

A new type of polyphosphorus heterocycle 8 is the product of two hydrogen abstractions of the intermediate 15, resulting from [2+2+4]-cyclotrimerization of vinyl phosphaalkyne 4 with involvement of the vinyl functionality (Scheme 2 and Figure 1). 2,4,6-Tris(1-tert-butyl-3,3-dimethylbut-1-enyl)-1,3,5-triphosphinine (9) is the product of [2+2+2]-cyclotrimerization of the CP triple bonds of vinyl phosphaalkyne 4. In contrast to its tert-butyl derivative,9 9 has two chemical shifts in the 31P NMR spectrum at 242.90 and 242.11 ppm in a 3:2 ratio. The presence of two conformational isomers can be explained by the different

symmetrical orientations of the R,β-di-tert-butylvinyl groups around the six-membered 1,3,5-triphosphinine ring (Figure 2). The formation of 2,3-di-tert-butyl-5-(1-tert-butyl-3,3-dimethylbut-1-enyl)-4-trimethylsilanyl-oxy-2H-phosphole (10) can be explained by the [2+3]-cycloaddition of vinyl phosphaalkyne 4 and a vinyl siloxycarbene intermediate 16 (Scheme 3 and Figure 3). It should be noted that this vinyl siloxycarbene reacts regioselectively as a 1,3-dipole with the CP triple bond, not by the [2+1]-cycloaddition route known to form phosphirenes from the tert-butyl analogue and perchlorovinyl carbene.10 The dimer of vinyl siloxycarbene (14) was isolated as well (Figure 4). 4,7-

Figure 1. ORTEP drawing of 4,5-di-tert-butyl-2-(1-tert-butyl-3,3dimethylbut-1-enyl)-8-(1-tert-butyl-3,3-dimethylbutylidene)-1,3,7triphosphabicyclo[4.2.0]octa-2,5-diene (8). Thermal ellipsoids are drawn at the 50% probability level. Disordered positions are not included for clarity.

(9) (a) Tabellion, F.; Nachbauer, A.; Leininger, S.; Peters, C.; Preuss, F.; Regitz, M. Angew. Chem., Int. Ed. 1998, 37, 1233–1235. (b) Gleiter, R.; Lange, H.; Binger, P.; Stannek, J.; Krueger, C.; Bruckmann, J.; Zenneck, U.; Kummer, S. Eur. J. Inorg. Chem. 1998, 11, 1619–1621. (10) (a) Memmesheimer, H.; Al-Dulayymi, J. R.; Baird, M. S.; Wettling, T.; Regitz, M. Synlett 1991, 6, 433–435. (b) Denifl, P.; Hradsky, A.; Bildstein, B.; Wu¨rst, K. J. Organomet. Chem. 1996, 523, 79–91. (11) (a) Brook, A. G.; Vandersar, J. D.; Limburg, W. Can. J. Chem. 1958, 56, 1758. (b) Degl’Innocenti, A.; Pike, S.; Walton, D. R. M. Chem. Commun. 1980, 1201.

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Figure 3. ORTEP drawing of 2,3-di-tert-butyl-5-(1-tert-butyl-3,3dimethylbut-1-enyl)-4-trimethylsilanyloxy-2H-phosphole (10). Thermal ellipsoids are drawn at the 50% probability level.

Figure 4. ORTEP drawing of 4,7-di-tert-butyl-2,2,9,9-tetramethyl5,6-bis-trimethylsilanyloxy-deca-3,5,7-triene (14). Thermal ellipsoids are drawn at the 50% probability level. Disordered positions are not included for clarity.

Di-tert-butyl-2,2,9,9-tetramethyl-5,6-bis-trimethylsilanyloxydeca-3,5,7-triene (14) formation can be explained by the ability of fluoride anions to catalyze the generation of siloxy carbene (16) from intermediate phosphaalkene (17). The generation of siloxy carbenes from the acylsilanes, which are analogues to vinyl acylphosphines /phosphaalkene 17, is known (Scheme 3).11 3,5-Bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-1,2,4-oxadiphosphole (11) is the product of oxidative dimerization of vinyl phosphaalkyne 4. This mechanism was evoked in the formation of the tert-butyl and mesityl analogues.11 11 is the first structurally characterized 1,2,4-oxadiphosphole (Figure 5). Cesium 3,5-bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-4H-1,2,4triphospholide (12) exists as two conformational isomers in solution, showing two sets of signals in the 31P NMR spectrumsthe major isomer at 259.38 ppm (d, 2JPP ) 38.3 Hz, 2P), 277.84 ppm (t, 2JPP ) 38.3 Hz, 1P) and minor isomer at 259.94 ppm (d, 2JPP ) 38.1 Hz, 2P), 276.15 ppm (t, 2JPP ) 38.31 Hz, 1P)swith a 10:9 ratio of isomers. The most deshielded resonances were observed for cesium 5-(1-tert-butyl-3,3-dimethylbut-1-enyl)-1H-1,2,3,4-tetraphospholide (13). They represent an AA′MM′ spin system at 351.30

Ionkin et al.

Figure 5. ORTEP drawing of 3,5-bis(1-tert-butyl-3,3-dimethylbut1-enyl)-1,2,4-oxadiphosphole (11). Thermal ellipsoids are drawn at the 20% probability level. Disordered positions are not included for clarity.

Figure 6. ORTEP drawing of the cesium salt of 3,5-bis(1-tertbutyl-3,3-dimethylbut-1-enyl)-4H-1,2,4-triphosphole (12) showing connectivity around cesium. Thermal ellipsoids are drawn at the 50% probability level. Disordered positions and hydrogen atoms are not included for clarity.

ppm for PA and PA′ atoms and at 378.90 ppm for PM and PM′ atoms. The simulated coupling constants are 1JAA′ ) -485.60 Hz, 3JMM′ ) 52.20 Hz, 1JAM ) -486.80 Hz, and 2JAM′ ) 2.00 Hz (Figure 7). The simulated coupling constants of 13 are basically identical to those of the supermesityl (2,4,6-tri-tertbutylphenyl) derivative, which was also characterized by X-ray analysis.7a The 13C NMR spectrum of 13 has a triplet of triplets for the carbon atom of the five-membered ring at 206.60 ppm with 1JPC ) 84.9 Hz and 2JPC ) 9.9 Hz (Figure 7). Reports of isolated tetraphospholide anions are extremely rare. In addition to the cesium supermesityl derivative mentioned above, sodium tetraphospholide was observed in the reaction mixture, but was not isolated.13 (12) (a) Weidner, S.; Renner, J.; Bergstraesser, U.; Regitz, M.; Heydt, H. Synthesis 2004, 2, 241–248. (b) Mack, A.; Bergstraesser, U.; Reiss, G. J.; Regitz, M. Eur. J. Org. Chem. 1999, 3, 587–595. (13) (a) Baudler, M.; Du¨ster, D.; Ouzounis, D. Z. Anorg. Allg. Chem. 1987, 544, 87. (b) Baudler, M.; Hahn, J. Z. Naturforsch. 1990, 45, 1139.

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Figure 7. Lower spectrum is the 31P NMR spectrum of 13, and the upper spectrum shows the triplet of triplets of the teraphospholide carbon atom in the 13C NMR spectrum of 13.

According to Scheme 3, formation of 4,7-di-tert-butyl-2,2,9,9tetramethyl-5,6-bis-trimethylsilanyloxy-deca-3,5,7-triene (14) requires also the generation of trimethylsilylphospinidene (20), which is known to be highly reactive and unstable at ambient conditions. Early research on the fate of trimethylsilylphospinidene (20) concluded that P-7 phospholide is one of the most abundant and stable products of its decomposition.14 The formation of even higher polyphosphides (e.g., Na3P19, Na3P21) with low solubility was detected in numerous studies on the metalation of silylphosphines with alkali derivatives. Prolonged heating of cesium fluoride with tris(trimethylsilyl)phosphine and with the products of the decomposition of trimethylsilylphospinidene should result in the analogous higher cesium polyphosphides, e.g., 21. The reaction between chlorotrimethylsilane and our insoluble fraction of the three-component reaction between tris(trimethylsilyl)phosphine, cesium fluoride, and Z-2tert-butyl-4,4-dimethylpent-2-enoyl chloride was undertaken in order to extract and make heavier polyphosphides soluble in common solvents. According to 31P NMR spectroscopy, only the signals of tris(trimethylsilyl)heptaphosphine (22) were observed (see Experimental Section). Trimethylsilylphospinidene (20) may also be responsible for the formation of cesium 3,5-bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-4H-1,2,4-triphospholide (12). [2+1]-Cycloaddition of two molecules of phosphaalkyne (4) and trimethylsilylphospinidene (20) can lead to the trimethylsilyl derivative of triphospholide (23), which should react with CsF to afford cesium 3,5-bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-4H-1,2,4-triphospholide (12) and fluorotrimethylsilane (Scheme 4). An alternative mechanism for the formation of cesium 3,5bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-4H-1,2,4-triphospholide (12) is the [2+1]-cycloaddition of two molecules of the phosphaalkyne (4) and cesium bis(trimethylsilyl)phosphide (24). Cesium bis(trimethylsilyl)phosphide (24) is the first product of the reaction between tris(trimethylsilyl)phosphine (6) and cesium (14) (a) Fritz, G.; Ha¨rer, J. Z. Anorg. Allg. Chem. 1983, 504, 23–37. (b) Fritz, G.; Ha¨rer, J.; Scheider, K. H. Z. Anorg. Allg. Chem. 1982, 487, 44– 58.

fluoride (5), due to high F-Si bond energy of fluorotrimethylsilane.15 The aromatization of intermediate 25 by loss of two trimethylsilyl groups will afford 12 (second equation in Scheme 4). The last mechanism has been widely used to explain the formation of lithium and sodium analogues of 1,2,4-triphospholes.16 Plausible mechanisms for the formation of cesium 5-(1-tertbutyl-3,3-dimethylbut-1-enyl)-1H-1,2,3,4-tetraphospholide (13) are shown in Scheme 5. The first equation represents the [2+3]cycloaddition of phosphaalkyne (4) and the phosphorus analogue of cesium azide (26) to give 13. This is a direct analogy of the mechanism of formation of cesium salts of tetrazoles.17 It is known that 20 can be a source of the triphosphirene moiety, which is a cyclic form of phosphorus analogues of azide (26).18 A replacement reaction between the phosphaalkyne (4) and cesium pentaphosphacyclopentadienide (27) can also afford 13. The pentaphosphacyclopentadienides are also among the most abundant heavier polyphosphides, and some replacement reactions have been described.19 Disproportionation of cesium 3,5bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-4H-1,2,4-triphospholide (12) to cesium 5-(1-tert-butyl-3,3-dimethylbut-1-enyl)-1H1,2,3,4-tetraphospholide (13) and tris-vinyl-substituted diphosphole is also possible. Disproportionations of phospholes are known.16 However, we did not find any experimental evidence of the formation of such diphosphole, which would be very sterically strained with three R,β-di-tert-butylvinyl groups. All mecha(15) (a) Larson, J. W.; McMahon, T. B. J. Am. Chem. Soc. 1985, 107, 766. (b) Leroy, G.; Temsamani, D.; Riffi; Wilante, C. THEOCHEM 1994, 112, 21. (16) Mueller, C.; Bartsch, R.; Fischer, A.; Jones, P. G.; Schmutzler, R. J. Organomet. Chem. 1996, 512, 141. (17) Arp, H. P. H.; Decken, A.; Passmore, J.; Wood, D. J. Inorg. Chem. 2000, 39, 1840. (18) Peruzzini, M.; Stoppioni, P. J. Organomet. Chem. 1985, 288, C44. (19) (a) Miluykov, V.; Kataev, A.; Sinyashin, O.; Loennecke, P.; HeyHawkins, E. Organometallics 2005, 24, 2233. (b) Baudler, M.; Etzbach, T. Angew. Chem., Int. Ed. Engl. 1991, 30, 580. (c) Baudler, M.; Akpapoglou, S.; Ouzounis, D.; Wasgestian, F.; Meinigke, B.; Budzikiewicz, H.; Muenster, H. Angew. Chem. 1988, 100, 288.

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Ionkin et al. Scheme 4

Scheme 5

nisms are highly speculative and can be used only as a guide to the chemistry of these new systems. The solid state structure is also consistent with different orientations of the R,β-di-tert-butylvinyl groups above and below the five-membered ring of 12 (Figure 6). The fivemembered ring in 12 is planar, and the bond lengths within the five-membered ring are averaged, indicating aromaticity of this triphospholide anion.20 The cesium atom is pentacoordinated in 12: two η1 coordination bonds to dioxane, one η1 coordination bond to diethyl ether, one η1 coordination bond to phosphorus, and one η2 coordination bond to PdP. Despite the planarity of the five-membered ring in 12 and sufficient electrons available, no η5 coordination mode was detected in 12. This is the case when the commonly expected η5 coordination mode is not preferable and a set of η2 coordination to PdP and η1 (20) (a) Dransfeld, A.; Nyula´szi, L.; Schleyer, P. v. R. Inorg. Chem. 1998, 37, 4413. (b) Nyula´szi, L.; Nixon, J. F. J. Organomet. Chem. 1999, 588, 28. (c) Egan, W.; Tang, R.; Zon, G.; Mislow, K. J. Am. Chem. Soc. 1970, 92, 1443. (d) Andose, J. D.; Rauk, A.; Mislow, K. J. Am. Chem. Soc. 1974, 96, 6904. (e) Nyula´szi, L. Chem. ReV. 2001, 101, 1229. (f) Nyula´szi, L. Tetrahedron 2000, 56, 79. (g) Caliman, V.; Hitchcock, P. B.; Nixon, J. F. Chem. Commun. 1995, 1661. (h) Nyula´szi, L.; Bergstra¨sser, U.; Regitz, M.; Schleyer, P. v. R. New J. Chem. 1998, 651. (i) Niecke, E.; Fuchs, A.; Baumeister, F.; Nieger, M.; Schoeller, W. W. Angew. Chem., Int. Ed. 1995, 34, 555.

coordination to oxygen prevail over a possible η5 coordination mode. This phenomenon is often observed in cyclopentadienyl derivatives of alkali and alkali earth metals. For example, the η5 coordination mode is only 1.4 times more energetically favorable than η2 coordination according to theoretical calculations for lithium cyclopentadienyl derivatives.21 Favorable coordination of cesium with the oxygen atoms of the dioxane also contributes to the overall preference for η2 and η1 coordination over possible η5 coordination in 12. The cesium cation in 12 forms a hexameric cyclic structure in the solid state (see graphical image). The “nano-wheel”, supported by six intercoordinated cesium 3,5-bis(1-tert-butyl-3,3-dimethylbut-1enyl)-4H-1,2,4-triphospholides, has a diameter of 2.7 nm. Each “nano-wheel” is composed of six cesiums alternating with phosphorus groups around the cycle. A diethyl ether molecule is bonded to each cesium and extends outward in the plane of the wheel. Dioxane molecules are bonded above and below the plane of the wheel and connect to adjacent “nano-wheels”. There is one molecule of hexamethyldisiloxane inside each “nanowheel”. The hexamethyldisiloxane sits in the cavity at the center of the wheel on a crystallographic 3-fold center of symmetry. Use of large alkali cations (e.g., cesium) leads to increased coordination numbers and the ability to form three-dimensional coordination polymers in the solid state.7a In conclusion, we present here in situ generation of highly unsaturated vinyl phosphaalkyne 4, which led to novel cycloaddition patterns with the participation of both vinyl and CP centers, e.g., [2+2+4]-self-trimerization in 8. The potential of cycloaddition reactions will be further explored in reactions with different dienophiles. It should be noted that the introduction of a vinyl moiety led to the suppression of cage polyphosphorus structures, which are typically formed in the reactions of nonconjugated tert-butyl-substituted derivatives. We conclude from the available data that reaction of CP triple bonds over (21) (a) Harder, S. Coord. Chem. ReV. 1998, 176, 17. (b) Harder, S. Chem.-Eur. J. 1999, 5, 1852. (c) Dinnebier, R. E.; Smaalen, S.; Olbrich, F.; Carlson, S. Inorg. Chem. 2005, 44, 964. (d) Kopp, M. R.; Neumueller, B. Organometallics 1997, 16, 5623.

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CC double bonds predominates. Novel electron-rich heterocyclic ligands will be tested in homogeneous catalysis, and CsFcatalyzed methodology will be applied to the generation of other conjugated and functionalized phosphaalkyne systems.

Experimental Section All air-sensitive compounds were prepared and handled under a N2/Ar atmosphere using standard Schlenk and inert-atmosphere box techniques. Anhydrous solvents were used in the reactions. Solvents were distilled from drying agents or passed through columns under an argon or nitrogen atmosphere. Dioxane, cesium fluoride, tris(trimethylsilyl)phosphine, pentane, and diethyl ether were purchased from Aldrich. trans-2-tert-Butyl-4,4-dimethylpent-2enoyl chloride was prepared according to literature procedures.8 Melting points are uncorrected. The mass spectra were collected on an Orbitrap mass spectrometer (ThermoFisher Scientific Bremen, Germany). All NMR experiments were run on a Bruker 500 AMX spectrometer. Tris(trimethylsilyl)phosphine (5.00 g, 0.020 mol), 4.05 g (0.020 mol) of trans-2-tert-butyl-4,4-dimethylpent-2-enoyl chloride, and 7.0 g (0.046 mol) of cesium fluoride were heated in 80 mL of 1,4dioxane at 90 °C for 2 days. The reaction mixture was filtered. The solvent was removed from the organic phase in 1 mmHg vacuum, and the residue was purified by chromatography on silica gel with petroleum ether/ethyl ether, 10:2, as eluent. The first fraction consists of 4,7-di-tert-butyl-2,2,9,9-tetramethyl-5,6-bis-trimethylsilanyloxy-deca-3,5,7-triene (14). The yield of 14 was 0.3 g (6.3%) as white crystals that sublime at 128 °C. 1 H NMR (500 MHz, CD2Cl2, TMS): δ 0.00 (s, 9H, Me-Si), 3.92 (s, 9H, Me-Si), 1.04 (s, 9H, Me), 1.05 (s, 9H, Me), 1.07 (s, 9H, Me), 1.08 (s, 9H, Me), 5.41 (s, 1H, CdC-H), 5.43 (s, 1H, CdC-H). 13C NMR (500 MHz, CD2Cl2): δ 3.40 (s, Si-Me), 3.44 (s, Si-Me), 31.00 (s, Me), 31.20 (s, Me), 32.50 (s, Me), 32.70 (s, Me), 33.30 (s, C-Me), 33.50 (s, C-Me), 38.70 (s, C-Me), 38.90 (s, C-Me), 134.00 (s, CdC), 134.20 (s, CdC), 139.70 (s, HCdC), 140.10 (s, CdC), 140.30 (s, CdC), 140.90 (s, HCdC). The structure was confirmed by X-ray analysis. Anal. Calcd for C28H56O2Si2 (MW: 480.91): C, 69.93; H, 11.74. Found: C, 71.15; H, 12.01. The second fraction consists of 3,5-bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-1,2,4-oxadiphosphole (11). The yield of 11 was 0.6 g (14.5%) as white crystals with mp 143 °C. 1H NMR (500 MHz, CD2Cl2, TMS): δ 0.91 (s, 9H, Me), 0.99 (s, 9H, Me), 1.07 (s, 9H, Me), 1.09 (s, 9H, Me), 5.67 (s, 1H, CdC-H), 5.75 (s, 1H, CdC-H). 13C NMR (500 MHz, CD2Cl2): δ 29.20 (d, 5JCP ) 2.2 Hz, Me), 30.40 (t, 5JCP + 5JCP ) 1.9 Hz, Me), 30.70 (d, 4JCP ) 2.4 Hz, Me), 32.60 (t, 4JCP + 4JCP ) 2.8 Hz, Me), 33.30 (s, C-Me), 33.90 (s, C-Me), 35.60 (d, 4JCP ) 5.6 Hz, C-Me), 37.00 (dd, 3JCP ) 3.4 Hz, 3JCP ) 1.0 Hz, C-Me), 135.50 (dd, 3JCP ) 5.7 Hz, 3JCP ) 5.9 Hz, HCdC), 137.10 (t, 2JCP + 2JCP ) 12.6 Hz, CdC), 140.60 (d, 3JCP ) 6.7 Hz, CdC), 141.70 (d, 2JCP ) 14.5 Hz, CdC), 189.40 (dd, 1JCP ) 62.6 Hz, 1JCP ) 62.2 Hz, P-CdP), 205.50 (dd, 1JCP ) 58.1 Hz, 2JCP ) 5.2 Hz, CdP-O). 31P NMR (500 MHz, CD2Cl2): δ 296.92 (d, 2JPP ) 19.7 Hz, 1P), 153.18 (d, 2JPP ) 19.7 Hz, 1P). 1,2,4-Oxadiphosphole 11 was identified by mass spectrometry (ASAP method), which gave a MH+ ion at 381.25 corresponding to C22H39OP2. The structure was confirmed by X-ray analysis. Anal. Calcd for C22H38OP2 (MW: 380.48): C, 69.45; H, 10.07; P, 16.28. Found: C, 69.50; H, 10.21; P, 16.34. The third fraction consists of 2,3-di-tert-butyl-5-(1-tert-butyl-3,3dimethylbut-1-enyl)-4-trimethylsilanyloxy-2H-phosphole (10). The yield of 10 was 0.55 g (13.0%) as colorless crystals, which start to sublimate at 70 °C and then melt at 76-78 °C. 1H NMR (500 MHz, CD2Cl2, TMS): major isomer: δ 0.16 (s, 9H, Me-Si), 0.92 (s, 9H, Me), 1.04 (s, 9H, Me), 1.12 (s, 9H, Me), 1.15 (s, 9H, Me), 2.97 (d, 2 JCP ) 7.0 Hz, 1H, HC-P), 5.42 (d, 4JCP ) 1.4 Hz, 1H, HCdC);

minor isomer: δ 0.15 (s, 9H, Me-Si), 0.86 (s, 9H, Me), 1.06 (s, 9H, Me), 1.10 (s, 9H, Me), 1.18 (s, 9H, Me), 3.03 (d, 2JCP ) 7.7 Hz, 1H, HC-P), 5.24 (s, 1H, HCdC). 13C NMR (500 MHz, CD2Cl2): major isomer: δ 2.60 (s, Me-Si), 30.71 (s, Me), 31.11 (s, Me), 32.54 (s, Me), 33.29 (s, Me), 33.84 (s, C-Me), 36.50 (d, 2JCP ) 4.6 Hz, C-Me), 37.00 (d, 2JCP ) 8.0 Hz, C-Me), 39.50 (d, 2JCP ) 3.4 Hz, C-Me), 63.80 (d, 1JCP ) 38.3 Hz, C-P), 138.40 (d, 3JCP ) 9.5 Hz, CdC-H), 143.20 (d, 2JCP ) 8.5 Hz, CdC), 146.30 (d, 2JCP ) 9.7 Hz, CdC), 157.40 (d, 2JCP ) 13.5 Hz, CdC-O), 195.20 (d, 1JCP ) 31.0 Hz, CdP); minor isomer: δ 2.90 (s, Me-Si), 30.58 (s, Me), 31.06 (s, Me), 32.52 (s, Me), 33.37 (s, Me), 33.73 (s, C-Me), 36.40 (d, 2JCP ) 4.4 Hz, C-Me), 37.90 (d, 2JCP ) 5.3 Hz, C-Me), 39.10 (d, 2JCP ) 4.3 Hz, C-Me), 62.90 (d, 1JCP ) 38.00 Hz, C-P), 135.00 (d, 3JCP ) 10.9 Hz, CdC-H), 141. 00 (d, 2JCP ) 7.3 Hz, CdC), 145.20 (d, 2JCP ) 9.9 Hz, CdC), 158.00 (d, 2JCP ) 14.6 Hz, CdCO), 196.00 (d, 1JCP ) 30.9 Hz, CdP). 31P NMR (500 MHz, CD2Cl2): δ 273.25 (s, 1P, minor isomer), 260.70 (s, 1P, major isomer), the ratio between isomers is 2:3. The structure was confirmed by X-ray analysis. Anal. Calcd for C25H47OPSi (MW: 422.70): C, 71.04; H, 11.21; P, 7.33. Found: C, 71.26; H, 11.28; P, 7.56. The next band from the chromatography was 2,4,6-tris(1-tertbutyl-3,3-dimethylbut-1-enyl)-1,3,5-triphosphinine (9). The yield of 9 was 1.1 g (30.1%) as yellow crystals with mp at 224-226 °C. 1 H NMR (500 MHz, C6D6, TMS): major isomer: δ 0.90 (s, 27H, Me), 1.30 (s, 27H, Me), 5.90 (s, 3H, H-CdC); minor isomer: 0.85 (s, 27H, Me), 1.25 (s, 27H, Me), 5.85 (s, 3H, H-CdC). 13C NMR (500 MHz, C6D6, selected signals for major isomer): δ 191.20 (td, 1 JPC ) 78.3 Hz, 3JPC ) 15.7 Hz, CdP). 31P NMR (500 MHz, C6D6): δ 242.90 (s, 1P, minor isomer), 242.11 (s, 1P, major isomer), the ratio between isomers is 3:2. 1,3,5-Triphosphinine 9 was identified by the mass spectrometry (ASAP method), which gave a M+ ion at 546.37 corresponding to C33H57P3. The structure was confirmed by X-ray analysis. Anal. Calcd for C33H57P3 (MW: 546.73): C, 72.50; H, 10.51; P, 17.00. Found: C, 72.64; H, 10.58; P, 17.28. The next band from the chromatography was 4,5-di-tert-butyl2-(1-tert-butyl-3,3-dimethylbut-1-enyl)-8-(1-tert-butyl-3,3-dimethylbutylidene)-1,3,7-triphosphabicyclo[4.2.0]octa-2,5-diene (8). The yield of 8 was 1.0 g (27.3%) as slightly yellow crystals with mp at 150-155 °C. 1H NMR (500 MHz, CD2Cl2, TMS): δ major isomer 0.91 (s, 9H, Me), 1.01 (s, 9H, Me), 1.03 (s, 9H, Me), 1.09 (s, 9H, Me), 1.10 (s, 9H, Me), 1.12 (s, 9H, Me), 2.10 (d, 2JHH ) 13.9 Hz, 1H, HC-CdC-P), 2.60 (d, 2JHH ) 13.9 Hz, 1H, HC-CdCP), 3.70 (dd, 2JCP ) 7.3 Hz, 4JCP ) 1.7 Hz, 1H, HC-P), 5.20 (s, 1H, H-CdC), 6.50 (d, 1JPH ) 184.7 Hz, 1H, P-H); minor isomer 0.83 (s, 9H, Me), 0.97 (s, 9H, Me), 1.02 (s, 9H, Me), 1.04 (s, 9H, Me), 1.08 (s, 9H, Me), 1.14 (s, 9H, Me), 2.15 (d, 2JHH ) 13.0 Hz, 1H, HC-CdP), 2.55 (d, 2JHH ) 13.0 Hz, 1H, HC-CdP), 3.65 (dd, 2 JCP ) 6.1 Hz, 4JCP ) 3.0 Hz, 1H, HC-P), 5.25 (s, 1H, H-CdC), 6.45 (d, 1JPH ) 186.9 Hz, 1H, P-H). 13C NMR (500 MHz, CD2Cl2, selected signals): δ major isomer: 199.50 (dd, 1JCP ) 60.1 Hz, 1JCP ) 35.6 Hz, 1C, CdP); minor isomer 198.10 (dd, 1JCP ) 62.1 Hz, 1 JCP ) 28.2 Hz, 1C, CdP). 31P NMR (500 MHz, CD2Cl2): major isomer: δ 222.60 (dd, 2JPP ) 22.2 Hz, 4JPP ) 3.3 Hz, 1P), 101.30 (dd, 2JPP ) 22.2 Hz, 2JPP ) 6.4 Hz, 1P), -10.05 (ddd, 1JPH ) 184.7 Hz, 4JPP ) 3.3 Hz, 2JPP ) 6.4 Hz, 1P); minor isomer: 222.60 (dd, 2 JPP ) 14.9 Hz, 4JPP ) 2.0 Hz, 1P), 95.50 (dd, 2JPP ) 14.9 Hz, 2JPP ) 5.3 Hz, 1P), -5.80 (ddd, 1JPH ) 186.9 Hz, 4JPP ) 2.0 Hz, 2JPP ) 5.3 Hz, 1P); the ratio between isomers is 10:9. The structure was confirmed by X-ray analysis. Anal. Calcd for C33H59P3 (MW: 548.74): C, 72.23; H, 10.84; P, 16.93. Found: C, 72.28; H, 11.03; P, 17.11. Cesium 3,5-Bis(1-tert-butyl-3,3-dimethylbut-1-enyl)-4H-1,2,4triphospholide (12). Tris(trimethylsilyl)phosphine (5.00 g, 0.020 mol), 4.05 g (0.020 mol) of trans-2-tert-butyl-4,4-dimethylpent-2enoyl chloride, and 7.0 g (0.046 mol) of cesium fluoride were heated in 80 mL of 1,4-dioxane at 90 °C for 5 days. The reaction mixture was filtered. The solvent was removed from the organic phase in

2416 Organometallics, Vol. 28, No. 8, 2009 1 mmHg vacuum. The residue was treated with 20 mL of pentane. The resultant yellow solid was recrystallized from diethyl ether at -30 °C. Yield of the cesium salt of 3,5-bis(1-tert-butyl-3,3dimethylbut-1-enyl)-4H-1,2,4-triphosphole as a complex with two molecules of dioxane and one molecule of ether and 1/6 of hexamethyldisiloxane was 1.12 g (23.4%). 1H NMR (500 MHz, THF-d8, TMS): δ major isomer: 0.20 (s, 1/6 of 18H of (Me3Si)2O), 0.90 (s, 18H, Me), 0.95 (t, 3JHH ) 6.8 Hz, 6H, Et2O), 1.30 (s, 18H, Me), 3.44 (q, 3JHH ) 6.8 Hz, 4H, Et2O), 3.58 (s, 8H, dioxane), 5.30 (s, 1H, H-CdC); minor isomer: 0.20 (s, 1/6 of 18H of (Me3Si)2O), 0.92 (s, 18H, Me), 0.97 (t, 3JHH ) 6.8 Hz, 6H, Et2O), 1.28 (s, 18H, Me), 3.46 (q, 3JHH ) 6.8 Hz, 4H, Et2O), 3.56 (s, 8H, dioxane), 5.32 (s, 1H, H-CdC). 13C NMR (500 MHz, THF-d8, selected signals): 183.00 (br, CdP). 31P NMR (500 MHz, THFd8): major isomer: δ 259.38 (d, 2JPP ) 38.3 Hz, 2P), 277.84 (t, 2JPP ) 38.3 Hz, 1P); minor isomer: δ 259.94 (d, 2JPP ) 38.1 Hz, 2P), 276.15 (t, 2JPP ) 38.31 Hz, 1P); the ratio between isomers is 10:9. The structure was confirmed by X-ray analysis. Anal. Calcd for C31H59CsO3.17P3Si0.33 (MW: 717.61): C, 51.88; H, 8.29; P, 12.95. Found: C, 52.07; H, 8.44; P, 13.19. Cesium 5-(1-tert-Butyl-3,3-dimethylbut-1-enyl)-1H-1,2,3,4-tetraphospholide (13). Tris(trimethylsilyl)phosphine (5.00 g, 0.020 mol), 4.05 g (0.020 mol) of trans-2-tert-butyl-4,4-dimethylpent-2enoyl chloride, and 7.0 g (0.046 mol) of cesium fluoride were heated in 80 mL of 1,4-dioxane at 90 °C for 10 days. The reaction mixture was filtered. The solvent was removed from the organic phase in 1 mmHg vacuum. The residue was treated with 20 mL of pentane. The resultant yellow solid was additionally recrystallized from pentane at -30 °C. Yield of cesium salt of 5-(1-tert-butyl-3,3dimethylbut-1-enyl)-1H-1,2,3,4-tetraphosphole as a complex with three molecules of dioxane was 1.48 g (44.0%). 1H NMR (500 MHz, THF-d8, TMS): δ: 0.95 (br, 9H, Me), 1.30 (br, 9H, Me), 3.60 (s, 24H, 3 dioxanes), 5.46 (br, 1H, H-CdC). 13C NMR (500 MHz, THF-d8): 32.20 (t, 5JPC ) 2.7 Hz, Me), 32.80 (t, 4JPC ) 3.8 Hz, Me), 34.30 (br, C-Me), 36.90 (t, 3JPC ) 2.7 Hz, C-Me), 68.19 (s, CH2-O), 132.11 (7, 3JPC ) 7.9 Hz, CdC), 149.25 (t, 2JPC )

Ionkin et al. 17.9 Hz, CdC), 206.60 (tt, 1JPC ) 84.9 Hz, 2JPC ) 9.9 Hz, C-P4). 31 P NMR (500 MHz, THF-d8, AA′MM′ spin system): δ 351.30 ppm for PA and PA′ atoms and at 378.90 ppm for PM and PM′ atoms, 1 JAA′ ) -485.60 Hz, 3JMM′ ) 52.20 Hz, 1JAM ) -486.80 Hz, 2JAM′ ) 2.00 Hz (simulated values). 13 was identified by mass spectrometry (electrospray negative), which gave a M- anion at 275.08 corresponding to C11H19P4 (calcd: 275.04). Anal. Calcd for C23H43CsO6P4 (MW: 672.38): C, 41.08; H, 6.45; P, 18.43. Found: C, 41.19; H, 6.58; P, 18.54. Tris(trimethylsilyl)heptaphosphine (22). A 2.0 g sample of the first precipitate from the above reaction and 5 mL of chlorotrimethylsilane in 20 mL of dioxane were stirred at 50 °C for 2 h. The reaction mixture was filtered. The filtrate was analyzed by 31P NMR spectrometry. Only signals of tris(trimethylsilyl)heptaphosphine (22) were detected. 31P NMR (500 MHz, C6D6): δ 13.29 (m, 3P), -86.43 (m, 1P), -143.94 (m, 3P), which are close to values recorded in a mixture of monoglyme and toluene.14 X-ray Diffraction Studies. Data for all structures were collected using a Bruker CCD system at -100 °C. Structure solution and refinement were performed using the Shelxtl22 set of programs. The structures are plagued with disorder due mostly to the presence of the di-tert-butylvinyl group. In the checkcif report there are a number of A-level errors that all result from the disorder or nonmerohedral twinning in the case of compound 9.

Acknowledgment. The authors thank Karin Karel for correcting the English in the manuscript and for valuable suggestions. Supporting Information Available: Crystallographic data of 8-12 and 14. This material is available free of charge via the Internet at http://pubs.acs.org. OM801224D (22) Sheldrick, G. Shelxtl Software Suite, Version 5.1; Bruker AXS Corp: Madison, WI, 1996.