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Organometallics 2010, 29, 4154–4158 DOI: 10.1021/om100691g
Fragmentation of an N-Substituted One-Coordinate Phosphorus (Phosphaalkyne): Plausible Generation of Monovalent Phosphorus Species† Alex S. Ionkin,* William J. Marshall, Brian M. Fish, and Laurie A. Howe DuPont Central Research & Development, Experimental Station, Wilmington, Delaware 19880-500 Received July 14, 2010
A new one-step synthesis of a stable nitrogen-substituted phosphaalkyne (5) was developed, by the condensation of CsF (2), tris(trimethylsilyl)phosphine (3), and supermesityl isocyanate (4). Compound 5 has the longest terminal CP bond (1.617 A˚) of any phosphaalkyne. Due to electron delocalization on the terminal phosphorus atom in 5, fragmentation to a monovalent phosphorus species (CsP (9)) and supermesityl isonitrile (8) is plausible. Isonitrile (8) was isolated in pure form. CsP (9) was trapped as a tricesium pentaphosphorus compound (10) and also as cesium [1,2,4]triphospholide (13).
Monovalent compounds of phosphorus have proven difficult to isolate and even to generate.1 Analogous to carbenes and nitrenes, such phosphorus species should contain six electrons. They can be considered as electron-deficient with diradical character (the triplet state) or as having two electron pairs (the singlet state). Most monovalent phosphorus species are predicted to be in the triple state, with extremely large singlet-triplet separation, making it difficult to investigate such species.2 Generation and ESR detection of carbon-substituted monovalent mesitylphosphinidene in a liquid helium cryostat (4 K) by Gaspar confirmed the existence of such species.3 It should be noted that the simplest monovalent phosphorus compound, H-P (1), has been detected in interstellar space4a and has been isolated as a carbene-stabilized entity by Robinson.4b Care should be taken in postulating the existence of monovalent species, since alternative mechanisms not involving phosphinidenes are often equally plausible. One-coordinate trivalent phosphorus species with a triple bond to carbon;phosphaalkynes;were once considered to † This is a DuPont publication #2010-117. *Corresponding author. E-mail:
[email protected]. (1) (a) Dillon, K. D.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy; Wiley: Chichester, 1998. (b) Quin, L. D. A Guide to Organophosphorus Chemistry; A John Wiley & Sons, Inc.: New York, 2000. (c) Regitz, M.; Scherer, O. J. Multiple Bonds and Low Coordination in Phosphorus Chemistry; Georg Thieme Verlag: Stuttgart, 1990. (2) (a) Nguyen, M. T.; McGinn, M. A.; Hegarty, A. F. Inorg. Chem. 1986, 25, 2185. (b) Kim, S.-J.; Hamilton, T. P.; Schaefer, H. F., III. J. Phys. Chem. 1993, 97, 1872. (3) (a) Li, X.; Weissman, S. I.; Lin, T.-S.; Gaspar, P. P.; Cowley, A. H.; Smirnov, A. I. J. Am. Chem. Soc. 1994, 116, 7899. (b) Li, X.; Lei, D.; Chiang, M. Y.; Gaspar, P. P. J. Am. Chem. Soc. 1992, 114, 8526. (c) Aktas, H.; Slootweg, J. C.; Lammertsma, K. Angew. Chem., Int. Ed. 2010, 49, 2102. (4) (a) Thorne, L. R.; Anicich, V. G.; Huntress, W. T. Chem. Phys. Lett. 1983, 98, 162. (b) Wang, Y.; Xie, Y.; Abraham, M. Y.; Gilliard, Jr. R. J.; Wei, P.; Schaefer, H. F., III; Schleyer, P. v. R.; Robinson, G. H. Organometallics, article ASAP, DOI: 10.1021/om100335j. (5) (a) Bergstraesser, U. Sci. Synth. 2004, 19, 427. (b) Nixon, J. F. Chem. Rev. 1988, 88, 1327. (c) Nixon, J. F. Coord. Chem. Rev. 1995, 145, 201. (d) Cummins, C. C. Angew. Chem., Int. Ed. 2006, 45, 862.
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be “nonexistent” due to the so-called “double-bond rule”. This area of chemistry has been the subject of several review articles.5 Application of the kinetic stabilization rule and use of sterically hindered groups (e.g., tert-butyl,6a adamantyl,6b supermesityl,6c and terphenyl6d) led to the isolation of carbon-substituted phosphaalkynes. Use of the thermodynamic stabilization rule resulted in isolation of nitrogensubstituted phosphaalkynes with remarkably different reactivity and structural properties.7 It has been recently shown that CsF (2) can be used for the generation of supermesityland alkenyl-substituted phosphaalkynes.8 We have now applied this technique to the synthesis of nitrogen-substituted phosphaalkynes. Thus, an equimolar reaction between CsF (2), tris(trimethylsilyl)phosphine (3), and supermesityl isocyanate (4) in dioxane at 90 °C for 2 weeks afforded nitrogensubstituted phosphaalkyne (5) (Scheme 1). There are only a few X-ray structures of phosphaalkynes. Selected results are summarized in Table 1. Carbon-substituted derivatives tend to have a shortened CP bond (1.516 to 1.541 A˚). The C-CP angles are close to linear. The introduction of a heteroatom (e.g., oxygen,9a sulfur,9b or nitrogen) tends to (6) (a) Becker, G.; Gresser, G.; Uhl, W. Z. Naturforsch. 1981, 36B, 16. (b) Barron, A. R.; Cowley, A. H.; Hall, S. W. J. Chem. Soc., Chem. Commun. 1987, 980. (c) Arif, A. M.; Barron, A. R.; Cowley, A. H.; Hall, S. W. J. Chem. Soc., Chem. Commun. 1988, 171. (d) Jones, C.; Waugh, M. J. Organomet. Chem. 2007, 692, 5086. (e) Chernega, A. N.; Antipin, M. Y.; Struchkov, Y. T.; Meidine, M. F.; Nixon, J. F. Heteroat. Chem. 1991, 2, 665. (7) (a) Becker, G.; Brombach, H.; Horner, S. T.; Niecke, E.; Schwarz, W.; Streubel, R.; Wurthwein, E.-U. Inorg. Chem. 2005, 44, 3080. (b) Becker, G.; Bohringer, M.; Gleiter, R.; Pfeifer, K.-H.; Grobe, J.; Le Van, D.; Hegemann, M. Chem. Ber. 1994, 127, 1041. (c) Chernega, A. N.; Koidan, G. N.; Marchenko, A. P.; Korkin, A. A. Heteroat. Chem. 1993, 4, 365. (d) Grobe, J.; Le Van, D.; Pohlmeyer, T.; Immel, F.; Pucknat, H.; Krebs, B.; Kuchinke, J.; L€age, M. Terahedron 2000, 56, 27. (8) (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) Ionkin, A. S.; Marshall, W. J.; Fish, B. M.; Schiffhauer, M. F.; Davidson, F.; McEwen, C. N. Organometallics 2009, 28, 2410. (c) Ionkin, A. S.; Marshall, W. J.; Fish, B. M. Dalton Trans. 2009, 10574. (9) (a) Becker, G.; Schwarz, W.; Seider, N.; Westerhausen, M. Z. Anorg. Allg. Chem. 1992, 612, 72. (b) Becker, G.; Hubler, K. Z. Anorg. Allg. Chem. 1994, 620, 405. r 2010 American Chemical Society
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Table 1. Selected Bond Lengths (A˚) and Angles (deg) of Phosphaalkynes and Related Phosphacumulene
Mes*(Cs)N-CP (5) i Pr(K-Crwn)N-CP i Pr(Tms)N-CP Dme3Li-S-CP Dme2Li-O-CP t Bu-CP Mes*-CP Mes*-NdCdP-Ph
P-C (A˚)
C-N, C-C, C-S, or C-O (A˚)
N-C (A˚)
P-C-N (deg)
1.617(4) 1.603(3) 1.558(1) 1.555(11) 1.555(3) 1.541(2) 1.516(3) 1.651(3)
1.215(4) 1.248(5) 1.315(2) 1.620(11) 1.198(4) 1.470(3) 1.427 1.209(4)
1.388(4) 1.409(6) 1.499(2) N/A N/A 1.539(2) N/A N/A
172.9(3) 174.8(3) 178.7(10) 178.9(7) 178.5(3) 179.3(2) 177.006 N/A
Scheme 1
increase the bond length between the heteroatom and the carbon of the CP group to 1.555 to 1.558 A˚. This bond length increase (up to 1.603 A˚) is even greater in the case of the potassium anion of N-substituted phosphaalkyne.7a The angle of the N-CP fragment in the potassium anion of N-substituted phosphaalkyne also decreased to 174.8° to accommodate the η3coordination mode. Such dramatic structural changes can be explained by invoking a substantial contribution from the mesomeric phosphaallene form and transformation of the coordination mode between potassium and phosphaalkyne from the η1 to the η3 mode. Side-on coordination (the η2-coordination mode) of phosphaalkynes to metals increases the CP length (e.g., 1.646 A˚10a for a Ni complex and 1.694 A˚ for a Ta10b complex), even if the phosphaalkyne has no N-substitution. Direct P-coordination (η1-coordination mode) does not significantly change the CP bond length (e.g., 1.511 A˚ for the Fe complex10c and 1.521 A˚ for the Mo complex10d). X-ray analysis of 5 reveals that it has a long terminal CP bond (1.617 A˚), although this is still shorter than the double CP bond in 1-aza-3λ3-phosphaallene (1.651 A˚).7a Compound 5 is the most bent of the phosphaalkynes, with a N-C-P angle of 172.9°. It also has the shortest N-CP bond (1.215 A˚). Compound 5 also has a short bond (1.388 A˚) between the aromatic supermesityl carbon and the nitrogen atom. The supermesityl group and CP group are in a syn-conformation in 5 (Figure 1). Anionic phenylcyanamides with sterically hindered ortho-substituents exhibit a similar syn-conformation, which was rationalized as an optimum π-interaction between the phenyl group and the cyanamide group.11 The steric repulsion between supermesityl group and cesium cation should shift the cesium atom into coordination through the phosphorus atom. These observations support the contribution of mesomeric forms 5b and 5c for the 1-aza-3λ3-phosphaallenide and phosphinidene anions, respectively (Scheme 2). (10) (a) Schaub, T.; Radius, U. Z. Anorg. Allg. Chem. 2006, 632, 981. (b) Burrows, A. D.; Dransfeld, A.; Green, M.; Jeffery, J. C.; Jones, C.; Lynam, J. M.; Nguyen, M. T. Angew. Chem., Int. Ed. 2001, 40, 3221. (c) Meidine, M. F.; Lemos, M. A. N. D. A.; Pombeiro, A. J. L.; Nixon, J. F.; Hitchcock, P. B. J. Chem. Soc., Dalton Trans. 1998, 3319. (d) Hitchcock, P. B.; Maah, M. J.; Nixon, J. F.; Zora, J. A.; Leigh, G. J.; Bakar, M. A. Angew. Chem., Int. Ed. Engl. 1987, 26, 474. (e) Burckett-St. Laurent, J. C. T. R.; Hitchcock, P. B.; Kroto, H. W.; Nixon, J. F. J. Chem. Soc., Chem. Commun. 1981, 1141. (11) Crutchley, R. J. Coord. Chem. Rev. 2001, 219-221, 125.
Figure 1. ORTEP drawing of cesium phosphanylidynemethyl(2,4,6-tri-tert-butylphenyl)amide (1). Thermal ellipsoids are drawn at the 50% probability level; hydrogens are omitted for clarity. It shows a pseudo η3-coordination mode. Cesium and phosphorus atoms form an infinite latttice structure with phosphaalkyne and pyridine groups extending outward from the core lattice. There are four phosphaalkyne groups in the asymmetric unit of the structure. The cesium-phosphorus bonds range from 3.54 to 3.77 A˚. The cesium-nitrogen bonds range from 3.26 to 3.56 A˚. The cesium-carbon bonds range from 3.30 to 3.45 A˚. The carbon-phosphorus bonds range from 1.615 to 1.624 A˚. The carbon-nitrogen bonds range from 1.215 to 1.229 A˚. Scheme 2. Mesomeric Forms of Compound 5 as Amide 5a, Phosphanide 5b, and Phosphinidene 5c
This is the first time that X-ray studies support the existence of mesomeric form 5c and phosphinidene character for phosphaalkynes. Taking into account the stability of the isonitrile functionality in 5c, the fragmentation of 5 into supermesityl isonitrile (8) and cesium phosphinidene (9) is not unexpected. Electron-donating substituents (e.g., amino groups) have been shown to stabilize phosphinidenes.1 Cesium can stabilize unusual anions because the surface charge density of the cation is decreased by more than a factor of
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Figure 3. ORTEP drawing of the cesium salt of N,N0 -bis(2,4,6-tritert-butylphenyl)-4H-[1,2,4]triphosphole-3,5-diamine (13). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms and dioxane solvent molecules are omitted for clarity. Figure 2. ORTEP drawing of the tricesium salt of 1-[2,4-bis(2,4,6-tri-tert-butylphenylimino)[1,3]diphosphetan-1-ylphosphanyl]-2,4-bis-(2,4,6-tri-tert-butylphenylimino)[1,3]diphosphetane (10). Thermal ellipsoids are drawn at the 30% probability level. Hydrogens, disordered cesium positions, and dioxane solvent molecules are omitted for clarity. Scheme 3. Generation of Isonitrile (8) and Formal Generation of Six-Electron Cesium Phosphinidene (9)
4 on going from lithium to cesium in the first group of elements in the periodic table.12 After heating a dioxane solution of 5 for 4 weeks, supermesityl isonitrile (8) was isolated, along with tricesium pentaphosphorus compound (10), which contained a “trapped” cesium phosphinidene (9) (Scheme 4). Tricesium phosphide (11) should be assumed in this reaction to balance the equation. Sublimation of 5 also led to isolation of supermesityl isonitrile (8). The second polyphosphoric product containing a trapped cesium phosphinidene is the cesium salt of N,N0 -bis(2,4,6-tri-tertbutylphenyl)-4H-[1,2,4]triphosphole-3,5-diamine (13), which is the expected product of the reaction between intermediate metal phosphinidenes and phosphaalkynes (Scheme 5). This is also the first known 2,4-dinitrogen-substituted triphosphole. The 31P NMR spectrum of 5 has an upfield singlet at -244.7 ppm, which is in agreement with the chemical shifts of electronrich, nitrogen-substituted phosphaalkynes, such as the potassium anion coordinated with 18-crown-6 iPrNCP (-226.1 ppm).7a The 31P NMR spectrum of 10 consists of one singlet (165.1 ppm), a doublet (109.5 ppm, 1JPP = 385.1 Hz, 2P), and an upfield triplet (-82.2 ppm, 1JPP = 385.1 Hz, 2P). The upfield signal at -82.2 ppm corresponds to the central bridged phosphorus atom. The two downfield signals correspond to the (12) Kellogg, R. M. Sci. Synth. 2006, 8b, 1484. (13) (a) Weber, L.; Buchwald, S.; Lentz, D.; Stamm, O.; Preugschat, D.; Marschall, R. Organometallics 1994, 13, 4406. (b) David, M.-A.; Alexander, J. B.; Glueck, D. S.; Yap, G. P. A.; Liable-Sands, L. M.; Rheingold, A. L. Organometallics 1997, 16, 378.
four-membered-ring phosphorus atoms. Similar patterns in the P NMR spectra of analogous 2,4-diimino-1,3-diphosphetanes have been described.13 The low-temperature (-80 °C) 31P NMR spectrum of 13 allows one to observe two distinctive modes of coordination between the Cs cation and the triphosphole ring: η1-coordination to the P-1 phosphorus and η1-coordination to the P-3 phosphorus, in a 1 to 5 ratio. Solid-state analysis revealed only η2coordination to the P-3 and P-4 phosphorus atoms, perhaps due to steric hindrance and crystal cell packing. The symmetrical η1isomer has a triplet (160.5 ppm, 2JPP = 40.0 Hz, 1P) and a doublet (124.7 ppm, 2JPP = 40.0 Hz, 2P). The predominant isomer with η1-coordination to the P-3 phosphorus has an ABX spin system at 111.4 and 118.3 ppm for A and B phosphorus atoms (1JPP = 414.1 Hz and 2JPP = 44.0 Hz) and a triplet at 156.4 ppm for the X atom, (2JPP = 44.0 Hz). The roomtemperature 31P NMR spectrum of 13 has extremely broad 30 ppm lines, as shown in Figure 4. The 13C NMR spectrum of 5 has a typical downfield doublet at 161.1 ppm with 1JPC = 49.1 Hz, corresponding to a triple bond between carbon and phosphorus. The above-mentioned potassium anion exhibits a similar doublet at 178.8 ppm, with 1 JPC = 45.8 Hz. In conclusion, a new synthesis of anionic stabilized nitrogensubstituted phosphaalkynes was developed on the basis of the condensation of CsF, tris(trimethylsilyl)phosphine, and sterically hindered isocyanates. Due to electron delocalization on the terminal phosphorus atom in 5, fragmentation to a monovalent phosphorus species (phosphinidene (9)) and a supermesityl isonitrile (8) is plausible. Two compounds containing formally trapped cesium phosphinide (9) were isolated. Phosphinidene generation is analogous to other fragmentation of heteroallenes (e.g., desulfurization of thioisocyanate or transfer of naked sulfur from thioisocyanate14a,b) and reduction of isocyanates to isonitriles.14c This fragmentation can be a convenient source of metal phosphinidenes. 31
Experimental Section Cesium Phosphanylidynemethyl(2,4,6-tri-tert-butylphenyl)amide with One Molecule of 1,4-Dioxane (5). Tris(trimethylsilyl)phosphine (3) (5.0 g, 20 mmol), 5.74 g (20 mmol) of 1,3,5-tri-tert-butyl-2isocyanatobenzene isocyanate (4), and 3.53 g (23 mmol) of CsF (2) (14) (a) Liu, Y.; Bei, M.; Zhou, Z.; Takaki, K.; Fujiwara, Y. Chem. Lett. 1992, 7, 1143. (b) Wang, M.; Lu, S.; Meizhi, B.; Hefu, G.; Z., J. J. Organomet. Chem. 1993, 447, 227. (c) Baldwin, J. E.; Bottaro, J. C.; Riordan, P. D.; Derome, A. E. J. Chem. Soc., Chem. Commun. 1982, 16, 942.
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Figure 4. (Top) 31P NMR spectrum of 13 at -80 °C. (Bottom) 31P NMR spectrum of 13 at ambient temperature (30 °C). Scheme 4
Scheme 5
were heated in 60 mL of 1,4-dioxane at 90 °C for 2 weeks. The resultant precipitate was filtered and recrystallized from 100 mL of 1,4-dioxane. Yield of cesium phosphanylidynemethyl(2,4,6-tri-tertbutylphenyl)amide as an adduct with one molecule of 1,4-dioxane (5) was 8.46 g (81%) as a golden solid, with a mp starting at 267 °C and complete decomposition at 390 °C. 1H NMR (500 MHz, THFd8, TMS): δ 1.25 (s, 18H, Me), 1.52 (s, 9H, Me), 3.55 (s, 8H, dioxane), 7.13 (s, 2H, Ar-H). 13C NMR (126 MHz, THF-d8): δ 32.0 (s, Me), 33.9 (s, tertiary-C), 36.8 (s, Me), 37.4 (s, tertiary-C), 121.3 (s, Ar-C), 139.9 (s, Ar-C), 140.8 (s, Ar-C), 143.2 (s, Ar-C), 161.1 (d, 1 JCP = 49.1 Hz, CP). 31P NMR (202 MHz, THF-d8): δ -244.7 (s, 1P). Anal. Calcd for C23H37CsNO2P (MW: 523.42): C, 52.78; H, 7.12; N, 2.68; P, 5.92. Found: C, 53.02; H, 7.26; N, 2.81; P, 6.14. The structure was confirmed by X-ray analysis. A crystal was grown from pyridine, which replaced dioxane in the coordination sphere of cesium. Fragmentation of Cesium Phosphanylidynemethyl(2,4,6-tritert-butylphenyl)amide with One Molecule of 1,4-Dioxane (5): Tricesium salt of 1-[2,4-bis-(2,4,6-tri-tert-butylphenylimino)[1,3]diphosphetan-1-ylphosphanyl]-2,4-bis(2,4,6-tri-tert-butylphenylimino)[1,3]diphosphetane (10) and cesium salt of N,N0 -bis(2,4,6tri-tert-butylphenyl)-4H-[1,2,4]triphosphole-3,5-diamine (13), supermesitylisonitrile (8).
Cesium phosphanylidynemethyl(2,4,6-tri-tert-butylphenyl)amide (5) (2.00 g, 3.82 mmol) was heated in 20 mL of dioxane for 4 weeks. Bright yellow crystals of the tricesium salt of 1-[2,4bis(2,4,6-tri-tert-butylphenylimino)[1,3]diphosphetan-1-ylphosphanyl]-2,4-bis(2,4,6-tri-tert-butylphenylimino)[1,3]diphosphetane (10) were formed upon cooling the reaction mixture to room temperature. The crystals were filtered and recrystallized from 20 mL of THF. Yield of 10 was 0.52 g (32%) as a yellow solid with a mp of 218 °C (dec). 1H NMR (500 MHz, THF-d8, TMS): δ 1.25 (s, 36H, Me), 1.29 (s, 18H, Me), 1.46 (s, 18H, Me), 1.50 (s, 36H, Me), 1.80 (b, 20H, THF), 3.40 (b, 20H, THF), 3.60 (s, 8H, dioxane), 7.12 (s, 4H, Ar-H), 7.25 (s, 4H, Ar-H). 31P NMR (202 MHz, THF-d8): δ 165.1 (s, 2P), 109.5 (d, 1JPP = 385.1 Hz, 2P), -82.2 (t, 1JPP = 385.1 Hz, 2P). 13C NMR (126 MHz, selected signals, THF-d8): δ 204.5 (dd, 1 JCP = 55.8 Hz, 1JCP = 6.2 Hz, P2CdN), 186.8 dd, 1JCP = 32.4 Hz, 1JCP = 10.5 Hz, P2CdN). Anal. Calcd for C103H172Cs3N4O7P5 (complex with 5 molecules of THF and 1 molecule of dioxane) (MW: 2132.07): C, 58.02; H, 8.13; N, 2.63; P, 7.26. Found: C, 58.23; H, 8.17; N, 2.71; P, 7.34. The structure was confirmed by X-ray analysis. The mother liquor from the above recystallization was concentrated in 1 mm vacuum to about 5 mL and dissolved in 10 mL of
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dioxane. Golden crystals of the cesium salt of N,N0 -bis(2,4,6-tri-tertbutylphenyl)-4H-[1,2,4]triphosphole-3,5-diamine (13) were formed, which were filtered, washed with 10 mL of pentane, and dried in 1 mm vacuum. The yield of 13 was 0.32 g (18%) as golden crystals with a mp of 241 °C (dec). 1H NMR (500 MHz, THF-d8, TMS): δ 1.20 (s, 18H, Me), 1.25 (s, 9H, Me), 1.51 (s, 9H, Me), 1.54 (s, 18H, Me), 3.58 (s, 104H, dioxane), 7.10 (s, 2H, Ar-H), 7.31 (s, 2H, Ar-H). 31 P NMR (202 MHz, -80 °C, THF-d8): δ 156.4 (t, 2JPP = 44.0 Hz, 1P), 111.4 ppm (dd, 1JPP = 414.1 Hz, 2JPP = 44.0 Hz, 1P), 118.3 ppm (dd, 1JPP = 414.1 Hz, 2JPP = 44.0 Hz, 1P) (major isomer). 13C NMR (126 MHz, selected signals, THF-d8): δ 209.8 (b, 2P, CdP). Anal. Calcd for C128H220Cs2N4O26P6 (MW: 2682.78 as a dimer with 13 molecules of dioxane): C, 57.31; H, 8.27; N, 2.09; P, 6.93. Found: C, 57.46; H, 8.22; N, 2.15; P, 7.15. The structure was confirmed by X-ray analysis. The residue from the above-mentioned experiments was purified by chromatography on silica gel with petroleum ether/ethyl ether, 10:2, as eluent. Yield of supermesitylisonitrile (8) was 0.29 g (28%) as a white solid, with a mp of 113 °C
Ionkin et al. (lit. 112-114 °C).15 1H NMR (500 MHz, CH2Cl2-d2, TMS): δ 1.25 (s, 9H, Me), 1.57 (s, 18H, Me), 7.36 (s, 2H, Ar-H). 13C NMR (126 MHz, CH2Cl2-d2): δ 32.4 (s, Me), 34.0 (s, Me), 38.2 (s, tertiary-C), 38.3 (s, tertiary-C), 122.1 (s, Ar-C), 146.2 (s, Ar-C), 150.6 (s, Ar-C), 174.5 (s, CdN). Anal. Calcd for C19H29N (MW: 271.44): C, 84.07; H, 10.77; N, 5.16. Found: C, 84.09; H, 10.81; N, 5.22. The structure was confirmed by X-ray analysis.
Acknowledgment. The authors thank Karin Karel for correcting the English in the manuscript and for valuable suggestions. Supporting Information Available: Crystallographic information files (CIF) for compounds 5, 8, 10, and 13. This material is available free of charge via the Internet at http://pubs.acs.org. (15) Habib, N. S.; Rieker, A. Z. Naturforsch., B: Anorg. Chem. Org. Chem. 1984, 39B, 1593.
