Mendeleev Communications Electronic Version, Issue 3, 2001 (pp. 85–124) The first phosphagermacyclopropane prepared via cycloaddition of dimethylgermylene to the C=P double bond of phosphaalkene Boris G. Kimel, Vasilii V. Tumanov, Mikhail P. Egorov* and Oleg M. Nefedov N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation. Fax: +7 095 135 5328; e-mail: mpe@cacr.ioc.ac.ru 10.1070/MC2001v011n03ABEH001445 The cycloaddition reaction of phosphaalkene 2 with dimethylgermylene generated thermally in situ leads to the first representative of phosphagermacyclopropanes 3. The [1+2] cycloaddition of heavy carbene analogues, silylenes and germylenes, to the C=C double bond has been successfully used for the synthesis of sila- and germacyclopropanes.1–3 The interactions of carbene analogues with isolated carbon–heteroatom multiple bonds are studied much lesser.In particular, only two examples of the cycloaddition of silylene4 and germylene5 to the carbon–phosphorus triple bond resulted in the formation of phosphasila- and phosphagermacyclopropenes, respectively, are known. Reactions of carbene analogues with C=P bonds of phosphaalkenes have not been described up to now.Here we report on the generation of the first phosphagermacyclopropane (phosphagermirane) by cycloaddition of shortlived dimethylgermylene to phosphaalkene (Me3Si)2C=PPh 2. The choice of 2 among the variety of known phosphaalkenes was prompted by the stability of 2 in an inert atmosphere at room temperature and, on the other hand, by the steric availability of the P=C double bond in 2, since our preliminary studies have shown that phosphaalkenes with bulkier substituents were inert towards dimethylgermylene.According to the 31P NMR spectroscopy data, the reaction of Me2Ge (thermally generated at 60 °C from 7,7-dimethyl-7- germanorbornadiene derivative 16) with phosphaalkene 27 (molar ratio 1:2 = 1.5:1) led to the formation of a single phosphoruscontaining reaction product.The reaction occurs with 100% conversion of the phosphaalkene; the overall integral intensity of the 31P NMR signals remained unchanged. An excess of the Me2Ge precursor should be used because of the polymerization of dimethylgermylene in the course of the reaction. The 31P NMR spectrum of the reaction product exhibits one singlet at –137.1 ppm.The position of this signal is characteristic of phosphiranes (–120 to –150 ppm).8 The 1H NMR spectrum of the product exhibits two signals of protons of two nonequivalent Me3Si groups of the (Me3Si)2C fragment (a singlet at –0.05 ppm and a doublet at 0.28 ppm, 4JPH 2.2 Hz) and two signals of protons of methyl groups of the Me2Ge fragment (a singlet at 0.70 ppm and a doublet at 0.62 ppm, 3JPH 3.3 Hz) with the integral intensity ratio 3:3:1:1. The characteristic constant 3JPH observed for one of the signals due to the Me2Ge group indicates the presence of a Ge–P bond in the product.The signals of phenyl protons are overlapped with those of 1,2,3,4-tetraphenylnaphthalene, which is formed upon the thermolysis of 7-germanorbornadiene 1.In the 13C NMR spectrum of the reaction product, the signal of the quaternary carbon atom of the (Me3Si)2C fragment is observed at 23.0 ppm (which is typical of phosphirane carbon atom signals9) as a doublet with the coupling constant 1JPC 69 Hz. We were unable to assign the signals of the carbon atoms of the Me3Si and Me2Ge groups since they overlap with numerous signals of the (Me2Ge)n polymers in the region from –5 to +5 ppm.In the 29Si NMR spectrum of the reaction product, two doublets (at 0.29 and 0.93 ppm) of the non-equivalent Me3Si groups are present. The coupling constants 2JPSi equal to 21.4 and 4.8 Hz, respectively, correspond to the suggested structure of 3. Thus, the spectroscopic data indicate that the product of the reaction of dimethylgermylene with phosphaalkene 2 has the structure of phosphagermirane 3.† Phosphagermirane 3 is a highly labile compound, which rapidly decomposes on air or upon heating.Our attempts to isolate 3 from solution were unsuccessful. We attempted to prepare other phosphagermiranes by reactions of phosphaalkene 2 with stable germylenes and their complexes.We found that GeI2 and [(Me3Si)2N]2Ge do not react with 2 at room temperature, while the interaction of 2 with GeCl2·dioxane resulted in a mixture of oxidation products of phosphaalkene 2. To obtain the silicon analogue of 3, we studied the reaction of phosphaalkene 2 with dimethylsilylene generated photochemically from the silicon analogue of 1, 7,7-dimethyl-7-silanorbornadiene 410 (C6D6, 20 °C, 2:4 = 1:1).The 31P NMR spectrum of reaction products exhibits a singlet at –132.4 ppm, which can be assigned to corresponding 1,1-dimethyl-2-phenyl-3,3-bis(trimethylsilyl)- 2-phosphasilirane 5 by analogy with phosphagermirane 3. Unfortunately, phosphaalkene 2 is a photolabile compound and partially photodecomposes during the reaction to give a number of products. These products exhibit signals in the 1H, 13C and 31P NMR spectra; thus, we failed to assign unequivocally the signals belonging to phosphasilirane 5 in the 1H and 13C NMR spectra.This work was supported by the Russian Foundation for Basic Research (grant nos. 98-03-32935 and 00-15-97387), the State Subprogramme ‘Fundamental Problems of Modern Chemistry’ (grant no. 9.3.03) and INTAS (grant no. 97-30344). References 1 W. P. Neumann, Chem. Rev., 1991, 91, 311. 2 O. M. Nefedov, M. P. Egorov and S. P. Kolesnikov, Sov. Sci. Rev. B. Chem., 1988, 12, 53. 3 W. Ando, H. Ohgaki and Y. Kabe, Angew. Chem., Int. Ed. Engl., 1994, 33, 659. 4 A. Shaefer, M. Weidenbruch, W. Saak and S. Pohl, Angew. Chem., 1987, 99, 806. Ge Ph Ph Ph Ph Me Me P Ge Me3Si Me3Si Me Me 1 3 C6H6 60 °C Me2Ge P Me3Si Me3Si 2 † 2,2-Dimethyl-1-phenyl-3,3-bis(trimethylsilyl)-1,2-phosphagermirane 3.An NMR sample tube was charged with 85 mg (0.32 mmol) of phosphaalkene 2 and 258 mg (0.48 mmol) of 7,7-dimethyl-1,4,5,6-tetraphenyl- 2,3-benzo-7-germanorbornadiene 1 in 1.0 ml of C6D6. The reaction mixture was heated at 60 °C in the spectrometer probehead. During the reaction the intensity of the 31P NMR signal of starting phosphaalkene 2 at +376 ppm decreased down to zero and another signal at –137.1 ppm appeared simultaneously.The reaction was complete in 3 h. 1H NMR (C6D6) d: –0.05 (s, 9H, Me3Si), 0.28 (d, 9H, Me3Si, 4JPH 2.2 Hz), 0.62 (d, 3H, Me, 3JPH 3.3 Hz), 0.70 (s, 3H, Me). 13C NMR (C6D6) d: 23.0 [d, C(SiMe3)2, 1JPC 68.9 Hz]. 29Si NMR (C6D6) d: 0.29 (d, Me3Si, 2JPSi 21.4 Hz), 0.93 (d, Me3Si, 2JPSi 4.8 Hz). 31P NMR (C6D6) d: –137.1 (s).Mendeleev Communications Electronic Version, Issue 3, 2001 (pp. 85–124) 5 A. H. Cowley, S. W. Hall, C. M. Nunn and J. M. Power, J. Chem. Soc., Chem. Commun., 1988, 753. 6 W. P. Neumann and M. Schriewer, Tetrahedron Lett., 1980, 21, 3273. 7 R. Appel, J. Peters and A. Westerhaus, Tetrahedron Lett., 1981, 22, 4957. 8 A. Marinetti and F. Mathey, Organometallics, 1984, 3, 456. 9 M. J. M. Vlaar, A.W. Ehlers, F. de Kanter and K. Lammertsma, Angew. Chem., Int. Ed. Engl., 2000, 39, 2943. 10 J. A. Hawari and D. Griller, Organometallics, 1984, 3, 11. Received: 23rd February 2001; Com. 01/1771