2 Quinquecovalent Phosphorus Compounds

BY S. TRIPPETT

1 Introduction Further developments in the chemistry of hydroxyphosphoranes have occurred since the synthesis by Ramirez,I reported last year, of (2) by the action of dry hydrogen chloride on the silyl-oxyphosphorane (1). The same hydroxyphosphorane (2) has now been obtained2 by hydrolysis of the chlorophosphorane (3) and trapped as (1) by the action of Me3SiC1 plus Et,N (Scheme 1). The crystalline material obtained by Ramirez from solutions containing an equilibrium mixture of (2) and (4) proved, on X-ray analysis, to be the phosphate (4).9

OSiMe, OH

(3) OH

(4 1

Reagents: i, HC1; ii, MesSiC1, Et3N; iii, 1 molar equivalent of HzO.

Scheme 1

Details have appeared2 of the interconversion of the isomeric phosphinates and phosphinothioates (5 ) and (6) via hydroxy- and hydrothio-phosphoranes respectively. The latter were not trapped on treatment with diazomethane.

The hydroxy-spirophosphorane (7), obtained4 as shown in Scheme 2, is in equilibrium in solution with the corresponding phosphinate. In methanol the

F. Ramirez, M. Nowakowski, and J. F. Marecek, J . Am. Chem. SOC., 1977,99,4515. 2 G. Kemp and S. Trippett, J. Chern. Sac., Perkin Trans. 1, 1979, 879. 3 R. Sarma, F. Ramirez, B. McKeever, M. Nowakowski, and J. F. Marecek, J. Am. Chem.

4 I. Granoth and J. C. Martin, J . Am. Chem. SOC., 1978,100, 5229. Suc., 1978, 100, 5391.

33

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34 Organophosphorus Chemistry

( 5 ) X = 0 or S

Reagents: i, MeMgBr; ii, Mg, THF; iii, POC13; iv, H2O; v, NaOMe, MeOH or NaH, THF;

Scheme 2

vi, BusLi, THF; vii, POC13; viii, NH4C1, HzO; ix, KOH.

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Quinquecovalent Phosphorus Compounds 35

mixture titrated as a weak acid to give the phosphoranoxide anion (8; R= Me); the analogous anion (8; R=CF,) was prepared as showas With trifluoro- methanesulphonic acid, (7) gave the salt (9), which was reduced with LiAlH, to the phosphoranide anion (lo), as shown in Scheme 3.6 When it reacted with trifluoroacetic acid (TFAA), the phosphinic acid (1 1) gave the hydroxy- spirophosphorane (12) as a crystalline 1 : 1 complex with TFAA.'

Reagents: i, CF3S03H; ii, LiAlH4; iii, H+.

Scheme 3

The PH-hydroxyphosphorane (14) has been detected * as an intermediate in the hydrolysis of the bicyclic phosphoramidite (1 3). Clearly, hydroxyphosphoranes are destined to play an increasing role in our understanding of organophosphorus chemistry.

E. F. Perozzi and J. C. Martin, J. Am. Chem. SOC., 1979,101, 1591. 6 I. Granoth and J. C. Martin, J. Am. Chem. SOC., 1978,100,7434. 7 Y. Segall and I. Granoth, J. Am. Chem. SOC., 1978,100,5130. See also K. A. Petrov, V. A.

Chauzov, N. Yu. Mal'kevich, and S . M. Kostrova, J, Gen. Chem. USSR, (Engl. Transl.) 1978, 48, 91.

* D. Houalla, M. Sanchez, R. Wolf, and F. H. Osman, Tetrahedron Lett., 1978, 4675.

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36 Organophosphorus Chemistry

2 Structure and Bonding The stereochemistry of five- and six-co-ordinate phosphorus derivatives has been revie~ed.~ X-Ray analysis has revealed geometry varying between trigonal- bipyramidal and square-pyramidal in the phosphoranes (15),7 (16),1° (17),11 (18),11 (19),12 (20),13 (21),14 (22),15 (23),lS (24),17 and (25).18 In (24) the selenium atom is equatorial in a slightly distorted tbp; in (25) the benzoyl group is in the equatorial plane. X-Ray analysis has shownlQ that the compound originally obtained by

8 10

11 i a i a

14 15 16

1 7

1s

19

(17; X = 0 or S) (20) Ad = l-adamantyl

0 yy;cJfF3-m

C,F,PCL, + rn-CF,C,H,N(SiMeJCONMe(SiMe,) --+ MeN-1, I p\c6F5

W. S . Sheldrick, Top. Curr. Chem., 1978, 73, 1. W. Schwarz, E. Fluck, and M. Vargas, Phosphorus Surur, 1978,5, 217. A. C. Sau and R. R. Holmes, J. Organomet. Chem., 1978,156, 253. W. Althoff, R. 0. Day, R. K. Brown, and R. R. Holmes, Inorg. Chem., 1978, 17, 3265. J.-V. Weiss, R. Schmutzler, D. Schomburg, and W. S . Sheldrick, Chem. Ber., 1979, 112, 1464. H. W. Roesky, K. Ambrosius, and W. S . Sheldrick, Chem. Ber., 1979,112, 1365. R. K. Brown, R. 0. Day, S. Husebye, and R. R. HoImes, Inorg. Chem., 1978, 17, 3276. P. F. Meunier, R. 0. Day, J. R. Devillers, and R. R. Holmes, Inorg. Chem., 1978,17, 3270. K. Burger, R. Ottlinger, A. Frank, and U. Schubert, Angew. Chem., Int. Ed. Engi., 1978, 17,774. S . Neumann, D. Schomburg, G. Richtarsky, and R. Schmutzler, J. Chem. SOC., Chem. Commun., 1978, 946. A. Schmidpeter, T. von Criegern, W. S. Sheldrick, and D. Schomburg, Tetrahedron Lett., 1978,2857.

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Quinquecovalent Phosphorus Compounds 37

(22) R = Ph or But

F

Ph,POEt + PhCOF - phc-p 11 I'Ph O F

I / P h

(25)

Anschiitz 2o from PCI, and catechol (2: 5) in boiling benzene, and now obtained from P4SIu and catechol in refluxing a n i s ~ l e , ~ ~ does indeed have the bisphosphorane structure (26), as formulated by Anschiitz, despite several recent claims to the contrary.

' 0 L. Anschiitz, H. Broeker, and F. Wenger, Justus Liebigs Ann. Chem., 1927,454, 71.

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38 Organophosphorus Chemistry

CND0/2 calculations21 on the structures (27) and (28) when Y = 0, X = N or CH and X = N, Y = H+ or OH+ predict the formation of a P-N bond on protona- tion of the phosphoryl oxygen of (27; Y = 0, X = N) and lead to a lowest-energy geometry corresponding to (28) when Y = H+, X= N, as found. Because of ring strain, the phosporanyl radical (29) retains its trigonal-bipyramidal geometry rather than revert to the tetrahedral form favoured by aryl phosphoranyl radicals not having highly electron-withdrawing substituents attached to phosphorus. 2 2

3 Acyclic Systems The and C a ~ e l l ~ ~ have extended their studies of the conformations of (trifluoro- methy1)phosphoranes to a variable-temperature lSC n.m.r. investigation of the phosphoranes (CF3),MePX, where X is F, C1, OMe, SMe, NMe,, and Me. The trifluorophosphoranes (30; R = CH,CCl,) and (30; R = CH,CF,) rearrange at room temperature to give the crystalline salts (31).24 Solutions of (30; R= CH2CC13) in CD,Cl, at 25 "C contain the equilibria shown in Scheme 4.

< ooc R.T. PF, + 2Me3SiOR PF,(OR), __+ ;(OR), PF;

(30) (31)

+ P(OR), PF6- * 2PF3(OR), k = 12 t 1.3 mol I-' 2PFAOR)Z PF,(OR), + PF,(OR) k = 0.9 * 0.04

Scheme 4

The difluoro(viny1)phosphoranes (32), prepared by direct fluorination of the corresponding phosphines, undergo base-catalysed addition of PH-phosphines to give, for example, (33).25 A range of phosphoranes containing from one to four OCH(CF3), groups has been described.2s The crystalline, highly hindered, phosphorane (34) is not attacked by nucleophiles.27 The use of pentamethoxy- phosphorane as a methylating agent has been described. 28

F2 Ph,,P(CH--CH$,-n Ph,PFz(CH=CH,), - n

n = 1 or 2 (32)

(32; n = 2) + Ph,PH P~PF,CH,CH,PYh,

Ph,PBr, + 2Ph(CF,),CONa

D. van Aken, A. M. C. F. Casteliiius. J. G

(33) - Ph,P[OC(CF,),Ph] 0°C

CH,Cl, (34)

Verkade, and H. M. Buck, Recl. Trau. Chim' - - Pays-Bas, 1979, 98, 12. J. H. H. Hamerlinck, P. Schipper, and H. M. Buck, J. Chem. SOC., Chem. Commun., 1979, 350. R. A. Cavell, J. A. Gibson, and K. I. The, Inorg. Chem., 1978, 17, 2880.

s4 F. Jeanneaux and J. G Riess, Tetrahedron L e t t , 1978, 4845. s5 I. Ruppert, Z. Naturforsch., Teil B, 1979, 34, 662. ld D. Dakterniers, G. V. Roschenthaler, and R. Schmutzler, J . Fluorine Chern., 1978, 12,413. ST T. Kubota, T. Kitazume, and N. Ishikawa, Chem. Lett., 1978, 889. Id D. B. Denney, R. Melis, and A, D. Pense, J. Org. Chem., 1978, 43, 4762.

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Quinquecovalent Phosphorus Compounds 39 4 Three-membered Rings

The phosphorane ( 3 9 , 31P at - 87 p.p.m., has been detected at low temperature in the reaction of 1 -phenylphosphiran with trimethyl-1 ,Zdioxetan. At room temperature, (35) dekomposes with the formation of ethylene.

5 Four-membered Rings Among an extensive range of bicyclic phosphoranes (37) prepared as shown from the imine (36) were the bisphosphorane (38) and phosphorane (39), existing in solution as a mixture of isomers.so

Ph

(38) (39)

The cyclic i16-phosphazenes (40) add to isothiocyanates,al diphenylketer~,~~ and the phosphazenes (41)s3 to give the crystalline bicyclic phosphoranes shown. Among other phosphoranes containing four-membered rings were (42)34 and (43).35

OQ B. C. Campbell, D. B. Denney, D. Z. Denney, and Li Shang Shih, J. Chem. Suc., Chem.

so A. Schmidpeter and J. H. Weinmaier, Chem. Ber., 1978, 111, 2086. 8 1 A. Schmidpeter and T. von Criegern, Angew. Chem., Int. Ed. Engl., 1978, 17, 443. ** A. Schmidpeter and T. von Criegern, Chem. Ber., 1978, 111, 3747. 88 A. Schmidpeter and T. von Criegern, 2. Naturforsch., Teil B, 1978, 33, 1330. J4 G. V. Roschenthaler, K. Sauerbrey, and R. Schmutzler, Chem. Ber., 1978,111, 3105. 16 R. Ketari and A. Foucaud, Tetrahedron Lett.. 1978. 4515.

Commun., 1978, 854.

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40 Organophosphorus Chemistry

I I (40) + Ph,C=C=o R',P-N

Me0 ,C UP h, CO@e

X Me3SiN- PN(SiMe,),

I I (40) + (Me,Si),NP=NSiMe, --+ R',P-N

(4 X 1) M e O , C U P h , C0,Me X = lone pair or NSiMe,

(Me,Si),N P-N SiM e, I I + c F , c o c o c F 3

Me,SiN-PN (SiMe,), (Me,Si),N-P-NSiMe,

I t

(42)

Me,SiN-PN(SiMe,),

(43) n = 0 or 1

6 Five-membered Rings Phospho1es.-Variable-temperature n.m.r. spectroscopy has given AG* = 18.2 kcal mol-1 for equivalence of the methyl groups of (44) uia a high-energy tbp with a diequatorial ring.36 Racemization of the optically active phosphorane (45) via a similar intermediate has AG* = 27.6 kcal m01-l.~'

a* D. Hellwinkel, W. Lindner, and W. Schmidt, Chern. Ber., 1979,112, 218. *' D. Hellwinkel and W. Krapp, Chem. Ber., 1979,112,292.

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Quinquecovalent Phosphorus Compounds 41

1,2-Oxaphospholans.-The initial products formed from the phosphonamidite (46) and acrylic acids when allowed to react at low temperature are the PH- phosphoranes (47). These, on heating, give the spirophosphoranes (48). 38 The ylides (49) react exothermically with oxiran to give the phosphoranes (50).3B With oxetan, the same ylides, and also Me,P=CH,, require heating to 120-140 "C before they form analogous phosphoranes such as (51). The variable-temperature lH and 13C n.m.r. spectra of (50) and (51) were recorded; pseudorotations are slow on the n.m.r. time-scale at low temperatures.

S. A. Terent'eva, M. A. Pudovik, and A. N. Pudovik, Izv. Akad. Nauk SSSR, Ser. Khim., 1978, 2185 (Chem. Abs., 1979,90,23 186).

a* H. Schmidbaur and P. Holl, Chern. Ber., 1979,112, 501.

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42 Organophosphorus Chemistry

1,2-0xaphospholens.-The rate constants for the addition of the arylphosphon- ites (52) to crotonaldehyde correlate with the 31P chemical shifts of (52) and are consistent with a two-stage mechanism involving initial nucleophilic attack of phosphorus. 40 The variable-temperature lH n.m.r. spectra of the phosphoranes (53) have been Dehydration of the dicarboxylic acid (54) to give the bicyclic phosphorane (55) occurs on refluxing in acetic anhydride.'

(5 3) R2 = Ph, OEt, or NEt, R3 = Me or Ph

0 (55)

1,3,2Dioxaphospholans.-Phosphine oxides, on treatment with trifluoro- methanesulphonic anhydride and 1 ,2-diols (including perfluoropinacol and catechols) in the presence of di-isopropylamine, give the phosphoranes (56).4a The spirophosphoranes (58) are obtained on treating the phosphine-imine (57) with di01s.*~ The 31P n.m.r. spectrum of (58; n = 5) consists of two signals, due to two conformers, which coalesce at N 120 "C.

40 V. V. Vasil'ev and N. A. Razumova, J. Gen. Chem. USSR (Engl. Transl.), 1978,48,1361. 41 V. V. Ragulin, N. A. Razumova, V. I. Zakharov, and A. A. Petrov, J. Gen. Chem. USSR

(Engl. Transl.), 1978, 48, 650. S. Antczak and S. Trippett, J. Chem. Soc., Perkin Trans. I , 1978, 1326.

4s J. I. G. Cadogan, N. J. Stewart, and N. J. Tweddle, J. Chem. SOC., Chem. Commun., 1979, . A .

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Quinquecovalent Phosphorus Compounds Ph

43

(59) R = CF,

R = F, Me, But, Ph, or Me (61)

Details have appeared of the preparation of a range of PH-phosphoranes from a-hydroxy-acids or alkyl tartrates and tervalent phosphorus corn pound^.^^ Among new phosphoranes formally derived from perfiuoropinacol are (59),45 (a), and (61)," prepared as shown.

Detailed studies have appeared of the hydrolyses of a range of spiro- pho~phoranes.~~ Those, i.e. (62), derived from ethylene glycol react exothermically with one mole of water to give the phosphonates (63), whereas phosphoranes containing pinacol residues, e.g. (64), give mixtures of cyclic (65) and acyclic (66) esters, probably formed via phosphonates analogous to (63). The positions of the equilibria (65) + (66) depend on solvent, temperature, the nature of R, and the amount of water present.

(62)

R

44 M. Koenig, A. Munoz, B. Gamgues, and R. Wolf, Phosphorus Sulfur, 1979,6,435. 45 G. V. Roschenthaler, K. Sauerbrey, and R. Schmutzler, 2. Naturforsch., Teil B, 1979, 34,

46 H. B. Eikmeier, K. C. Hodges, 0. Stelzer, and R. Schmutzler, Chem. Ber., 1978,111,2077. 47 G. V. Roschenthaler, K. Sauerbrey, and R. Schmutzler, Isr. J. Chem., 1978, 17, 143. 48 H. Goncalves and J. P. Majoral, Phosphorus Suqur, 1978,4343,357,

107.

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44 Organophosphorus Chemistry

1,3,2-Dioxaphospholens.-The phosphine-imine (67), with catechol or o-phenyl- enediamine, gave the phosphoranes (68). 49 The chloroisothiocyanatophosphorane (70) was detected by 31P n.m.r. spectroscopy as an intermediate in the conversion of the dichlorophosphorane (69) into the bisisothiocyanatophosphorane (71) by the action of lead thiocyanate or of potassium thiocyanate in the presence of 18-crown-6 ether.

(67) Ar = C,H,Cl-p X = 0 or NH (6 8)

Sulphoxides are rapidly deoxygenated by the PH-phosphorane (72) in the presence of a catalytic amount of iodine, probably as shown in (73).61

The stereochemistry of nucleophilic substitution of chlorine in the phosphorane (74) has been studied.s2 At - 78 "C in THF, dimethylamine gives predominantly inversion of configuration at phosphorus, whereas sodium phenoxide leads to almost equal amounts of inversion and retention.

0 0 0 ,*\ I G-

(73) (74)

40 V. P. Kukhar, E. V. Grishkun, and V. P. Radavskii, J. Gen. Chem. USSR (Engl. Trawl.),

he J. Burski, J. Kieszkowski, J. Michalski, M. Pakulski, and A. Skowronska, J. Chem. SOC.,

'1 P. Savignac, A. Brkque, B. Bartet, and R. Wolf, C.R. Hebd. Seances Acad. Sci., Ser. C,

I* S. Trippett and R. E. L. Waddling, Tetrahedron Lett., 1979, 193.

1978,48,1308.

Chem. Commun., 1978,940.

1978, 287, 13.

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Quinquecovalent Phosphorus Compounds 45

Radicals such as (75), which are stable in the absence of oxygen, have been obtained as shown in Scheme 5.63 Variabletemperature e.s.r. spectroscopy demonstrated the rapid intramolecular exchange of free valence and a bond in these radicals.

K+ P4

But

Reagents: i, hv; ii, PbO2 or (ButO)2, hv. Scheme 5

Nitrogen-containing Rings.-A general synthesis of phosphoranes of structure (77) has appeared involving the reaction of tervalent phosphorus compounds with a wide range of 2-substituted azides (76).64 Several bicyclic PH-phosphoranes (78) containing chiral carbon centres as well as chiral phosphorus have been des- cribed.66 The fluotophosphoranes (79) are sufficiently stable to be recrystallized

b* A. I. Prokof'ev, A. A. Khodak, N. A. Malysheva, P. V. Petrovskii, N. N . Bubnov, S. P. Solodovnikov, and M. I. Kabachnik, Dokl. Chem. (Engl. Transl.), 1978, 240, 188; A. I. Prokof'ev, A. A. Khodak, N. A. MaIysheva, N. N. Bubnov, S. P. Solodovnikov, I. S. Belostotskaya, V. V. Ershov, and M. I. Kabachnik, ibid., p. 222; I. S. Belostotskaya, N. L. Komissarova, T. 1. Prokof'eva, A. I. Prokof'ev, V. V. Ershov, and M. I. Kabachnik, Bull. Acad. Sci. USSR, Div. Chem. Sci., 1978, 27, 1064.

64 J. I. G. Cadogan, I. Gosney, E. Henry, T. Naisby, B. Nay, N. J. Stewart, and N. J. Tweddle, J. Chem. SOC., Chem. Commun., 1979, 189.

66 C. Bonninque, J. F. Brazier, D. Houalla, and F. H. Osman, Phosphorus Surfur, 1978,5,159.

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46 Organophosphorus Chemistry

from benzenemethanol. 66 They display a nearly linear correlation between JPF and SF.

Using slP n.m.r. spectroscopy, kinetic parameters have been obtained for the ring-opening of the PH-phosphorane (81) to give (80) and for the ring-closure of (82) to give the PH-phosphorane (83).&' The variable-temperature lH n.m.r. spectra of the phosphoranes (84) have been recorded.s8

The PH-phosphoranes (85), which have not been observed spectroscopically in their PI1*-N1I1 tautomeric forms, complex as these with rhodium(1) to give the monomeric complexes (86).6a Whereas the product from TDAP and the macro-

3

- slow

(84) (85) R = H or Me

p

(86) Y = CO or C,H,

I* H. B. Stegmann, H. V. Dumm, and K. Schemer, Phosphorus Suljlur, 1978,5, 159. ' 7 B. Garrigues, C. Bui Cong, A. Munoz, and A. Klakbk, J . Chem. Res. (S) , 1979, 172. 68 B. Garrigues, D. Houalla, J. F. Brazier, and R. Wolf, Bull. SOC. Chim. Fr.,Purf 2,1978,65. so D. Boudoux, I. Tratchenko, D. Houalla, R. Wolf, C. Pradat, J. Riesa, and B. F. Mentzen,

J- Chem. SOC.. Chem. Commun., 1978, 1022.

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Quinquecovalent Phosphorus Compounds 47

cyclic tetra-amine (87) exists entirely in the phosphorane form (88),60 the corresponding phosphorus triamides are favoured as the ring size of the tetra- amine is increased.61

NH HN + P(NMe,),

Details have appeared of the formation of amino(thiy1) phosphoranes in the de-oxygenation of aryl2-nitroaryl sulphides with tervalent phosphorus species.6* Another study has been made of the formation of phosphoranes based on aroyl hydroxamic acids.68 Among other nitrogen-containing phosphoranes described are (89)84 and (90),6s prepared as shown.

,NO2 + /o - (Ma)$ + Me,CHCH=C - (MeO)$' g*r

Me2CH 'Br

R'

(CFa,C=NCPh=NR' + R2R3R4P _.f phrN\PR2R3R4

N7( F3C CFs

(90)

MisceUaneous.-The synthesis of phosphoranes from P*II compounds and 1,2- diols in the presence of N-chlorodi-isopropylamine has been extended to include the use of a wide range of 1,2-difunctional species (91).66 A range of phosphor- anes derived from the dithiete (92) has been de~cribed,6~ among them (93), in

+ R1R2R3P + Pri2NC1 - +>PR1R2R3 + Pri2&Hz C1'

(91) X,Y = 0, S, or NR ' 0 J. E. Richman and T. J. Atkins, Tetrahedron Lett., 1978,4333. 61 T. J. Atkins and J. E. Richman, Tetrahedron Lett., 1978, 5149. 62 J. I. G. Cadogan and N. J. Tweddle, J. Chem. SOC., Perkin Trans. I , 1979, 1278. 6* E. V. Hinrichs and I. Ugi, J . Chem. Res. (S ) , 1978, 338. 64 R. D. Gareev, G. M. Loginova, and A. N. Pudovik, Bull. Acad. Sci. USSR, Div. Chem.

65 K. Burger and S. Penninger, Synthesis, 1978, 526. '6 S. Singh, M. Swindles, S. Trippett, and R. E. L. Waddling, J. Chem. Soc., Perkin Trans. I ,

6' B. C. Burros, N. J. De'ath, D. B. Denney, D. 2. Denney, and I. J. Kipnis,J. Am. Chem. Soc.,

Sci., 1978, 27, 400.

1978,1438.

1978,100,7300.

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48 Organophosphorus Chemistry

which the barrier to equivalence of the trifluoromethyl groups is about 13 kcal mol-l.

7 Six-co-ordinate Species X-Ray analyses have been reported on the six-co-ordinate molecules (94),08 (95):@ and (96).'O That on (94) confirmed the cis relationship of the phenoxy- groups that had originally been suggested on the basis of the l@F n.m.r. spectrum. The Lewis-acid character of the phosphorus of five-co-ordinate phosphoranes is increased by the presence of carbonyl groups, as in (97) or (9Q4' or by increased

H

H

; R0,C

+ Et,NH

HO CO,R / \

R02C C0,R

68 R. Sarma, F. Ramirez, B. McKeever, J. F. Marecek, and V. A. V. Prasad, Phosphorus

'0 W. S . Sheldrick, J. Gibson, and G. V. Roschenthaler, Z. Naturforsch., Teil B, 1978, 33,

TO W: S. Sheldrick. A. Schmidpeter, and T. von Criegern, 2. Naturforsch., Teil B. 1978. 33.

Sulfur, 1979, 5, 323.

1102.

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Quinquecovalent Phosphorus Compounds 49

ring strain in the phosphorane, as in (99),30 one of whose reactions as a Lewis acid is shown in Scheme 6.

Reagents: i, MX, Kryptofix 222 (X = F, AcO, MeO, ArO, CIH~N, or CN).

Scheme 6

The 1-pyrazolylphosphoranes (100) are in equilibrium in acetonitrile solution with the six-co-ordinate dimers (101), and with pyrazoles they give the strongly hydrogen-bonded adducts (102).71

A detailed kinetic study of the racemizations of the optically active salts (103)--(105) has shown that these are acid-catalysed irregular processes involving P-0 bond fission.7a

MeCN -

7 1 T. von Criegern and A. Schmidpeter, 2. Nafurforsch., Teil B, 1979, 34, 762. 7s J. Cavezzan, G. Etemad-Mogadam. M. Koenig, and A. Klakbk. Tetrahedron Left. 1979,

795.

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50 Organophosphorus Chemistry

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