2 Quinquecovalent Phosphorus Compounds

BY S. TRIPPETT

1 Introduction Interest in stable quinquecovalent phosphorus compounds has shown remarkable growth in the year under review, published work having quadrupled. This is undoubtedly due to a general realization that a knowledge of the factors which affect the stability of such compounds and control the processes of ligand reorganization within them is essential to a proper understanding of the mechanism of substitutions at phosphorus. Variable-temperature n.m.r. studies on stable phosphoranes are giving an increasing amount of data on the relative apicophilicities of groups and on the preference of small-membered rings for the apical-equatorial position, and it should soon be possible to discuss this area of organophosphorus chemistry on a firm semi-quantitative basis.

2 Ligand Reorganization and Structure Several accounts have appeared of the turnstile rotation (TR) process for the reorganization of the ligands of a trigonal bipyramid. As an alternative to the Berry pseudorotation process (BPR), TR offers the prospect of multiple-TR routes which avoid the high-energy trigonal bipyramids which of necessity must be traversed in comparable BPR routes. However, the experimental evidence for TR is still limited to the adamantoid oxyphos- phoranes derived from hexafluoroacetone,2 and it may be that the possibility of irregular isomerizations has not been entirely eliminated in these cases.3 Until more compelling evidence is forthcoming most workers are using BPR for discussion of their results.

Non-empirical * and semi-empirical lo, MO calculations have appeared on the electronic structure and bonding in simple phosphoranes and on the

(a) F. Ramirez, S. Pfohl, E. A. Tsolis, J. F. Pilot, C. P. Smith, I. Ugi, D. Marquarding, P. Gillespie, and P. Hoffmann, Phosphorus, 1971, 1, 1; (b) I. Ugi, D. Marquarding, H. Klusacek, P. Gillespie, and F. Ramirez, Accounts Chem. Res., 1971, 4, 288; (c) P. Gillespie, P. Hoffmann, H. Klusacek, D. Marquarding, S. Pfohl, F. Ramirez, E. A. Tsolis, and I. Ugi, Angew. Chem. Internat. Edn., 1971,10,687; (d) I. Ugi and F. Ramirez, Chem. in Britain, 1972, 8, 198. ‘Organophosphorus Chemistry’, ed. S. Trippett (Specialist Periodical Reports), The Chemical Society, London, 1972, vol. 3, pp. 39 and 255. See reference l(c) p. 712 for a discussion of this point. A. Rauk, L. C. Allen, and K. Mislow, J. Amer. Chem. Soc., 1972, 94, 3035. (a) J. B. Florey and L. C. Cusachs, J . Amer. Chem. SOC., 1972,94,3040; (6) R. Hoffman, J. M. Howell, and E. L. Muetterties, J. Amer. Chem. Soc., 1972, 94, 3047.

29

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30 0 rganop hospho r us Chemistry

barriers to BPR. They agree with all previous approaches in confirming that the more electronegative substituents will prefer to occupy the apical positions in a trigonal bipyramid. However, other predictions are novel and promise to be of fundamental significance. They can be summarized as follows : (a) Electronegative substituents will prefer to occupy the basal positions in a square ~ y r a m i d , ~ ~ 5 b as will 7r-acceptors 5b; n-donors, on the other hand, favour apical These preferences will affect the energy barriers to Berry pseudorotations. (b) In a trigonal bipyramid, orbital overlap from 7r-donors is substantially greater lc, 5 b from equatorial than from apical positions. Conversely, orbital overlap is greater for n-acceptors in the apical positions. The overall apicophilicity of a group is therefore a balance between electro- negativity and rr-donor or 7r-acceptor proper tie^.^^ This concept has been used independently to explain experimentally derived relative apico- philicities (see below). (c) An equatorial substituent with a single donor orbital will prefer to have that orbital in the equatorial plane.5b Consequently there will be a barrier to rotation round the equatorial bond. This is probably the origin of the slow rotations observed round these bonds in amino- and alkylthio- fluorophosphoranes;8 if so the energy barriers found, ranging from 5 to 12 kcal mol-l, reflect the importance of this effect. (d)An overall stabilization of a trigonal bipyramid occurs when all the equatorial or both of the apical positions are occupied by the same type of substi tuent, lC

Computer simulationD of the line broadening of the methyl resonances in the n.m.r. spectra of the phosphoranes (1; R = Me or Ph) down to - 184 "C gave a value for the free energy of activation for pseudorotation between the equivalent structures (la) and (lb) of 4.9-5.1 kcal mol-l. A

knowledge of the barrier to pseudorotation between trigonal bipyramids of identical energies is important in interpreting the barriers observed between non-identical trigonal bipyramids.

R. K. Oram and S. Trippett, J. C. S. Chem. Comm., 1972, 554. ' M. J. C. Hewson, S. C. Peake, and R. Schmutzler, Chem. Comm., 1971, 1454. S . C. Peake and R. Schmutzler, J . Chem. SOC. (A) , 1970, 1049. C. H. Bushweller, H. S. Bilofsky, E. W. Turnblom, and T. J. Katz, Tetrahedron Letters, 1972, 2401.

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Quinquecoualent Phosphorus Compounds 31

Orbital symmetry considerations 5 b show that the concerted reactions

are symmetry forbidden for apical-equatorial loss or addition, but allowed for apical-apical or equatorial-equatorial.

Further kinetic investigations lo of the reactions of phosphites with a-diketones are held to support the previously suggested mechanism in which the first and slow step involves nucleophilic attack of phosphorus on carbonyl carbon. The relative rates of reaction of a series of phosphines with diethyl peroxide to give diethoxyphosphoranes are in the reverse order of those for reaction with ethyl i0dide.l' The differences involved are small but are consistent with a concerted biphilic addition to the peroxide.

A group theoretical description of isomerization processes in a trigonal bipyramid has been given.12

3 Acyclic Systems

Aminotetrafluorophosphorane has been prepared l3 by amination of the corresponding chloro-compound in the vapour state. Rotation round the PN bond is slow on the n.m.r. timescale at 30°C and analysis of the lH and 19F n.m.r. spectra of the 16N isomer shows that in the ground state the hydrogens and apical fluorines are coplanar, as in (2), with strong intra- molecular hydrogen-bonding.

Full details have appeared l4 of the preparation of aryloxyfluoro- phosphoranes (3) according to the general equation

Ar = CeHS or C6F5 R = Me or Ph n = 0, 1, or 2

The lQF n.m.r. spectrum of PhOPPhzFz did not change down to - 80 "C,

lo Y. Ogata and M. Yamashita, J. C . S. Perkin ZI, 1972, 493; J. Org. Chem., 1971, 36, 2584; Tetrahedron, 1971, 27, 2725.

l1 D. B. Denney, D. Z. Denney, C. D. Hall, and K. L. Marsi, J. Amer. Chem. SOC., 1972, 94, 245.

la J. Brocas and M. Gielen, Bull. SOC. chim. belges, 1971, 80, 207. l3 A. H. Cowley and J. R. Schweiger, J . C. S. Chem. Comm., 1972, 560. l4 S. C. Peake, M. Fild, M. J. C. Hewson, and R. Schmutzler, Znorg. Chem., 1971,10,2723.

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32 Organophosphorus Chemistry

suggesting that rotation round the PO bond is still rapid at this temperature.

-70" C R,P=CH, + HF - R,MePF

(4)

The fluorophosphoranes (4; R = Me, Bu, or Ph) were obtained15 from the corresponding methylenephosphoranes as shown. Although showing unit molecular weights in non-polar solvents, their i.r. and Raman spectra suggest that they are largely ionic, while the lack of HF and PF coupling in their n.m.r. spectra shows that rapid intermolecular fluorine exchange is occurring.

The methoxyphosphorane (5; R = Me) is in rapid equilibrium with the ylide and methanol in non-polar solvents at room temperature, but with the phenoxyphosphorane (5; R = Ph) this equilibration is slow on the n.m.r. timescale under the same conditions.16 Methylmethoxytriphenyl- phosphorane is covalent in the crystalline state, but its solutions are tinged with the yellow of the ylide.

Me,P=CH, + ROH Me,POR

( 5 )

Acyclic phosphoranes containing at least two alkoxy-groups undergo exchange reactions with 1,2- and 1,3-glycols to give phosphoranes con- taining one or two rings.17 Thus pentaethoxyphosphorane with an equi- molar amount of ethylene glycol gave the monocyclic phosphorane (6), whereas with two molar equivalents of glycol the bicyclic phosphorane (7)

was obtained. Other diols used included dZ-butane-2,3-diol, styrene glycol, cis- and trans-cyclohexane-1 ,2-diol, and propylene glycol. However, in the same reaction butane- 1,4-diol and pentane- 1,5-diol gave tetrahydrofuran and tetrahydropyran, respectively, and this heterocyclic synthesis has been extended l8 to other diols and to aminoalcohols. Thus 2-aminoethanol gave aziridine in 70% yield. The mechanism of the reaction is clearly shown by the formation of the oxide (8) from trans-cyclohexane-l,4-diol.

l5 H. Schmidbauer, K.-H. Mitschke, and J. Weidlein, Angew. Chem. Internat. Edit., 1972, 11, 144. H. Schmidbauer and H. Stuhler, Angew. Chem. Internar. Edn., 1972, 11, 145. B. C. Chang, W. E. Conrad, D. B. Denney, D. Z . Denney, R. Edelmann, R. L. Powell, and D. W. White, J. Amer. Chem. SOC., 1971, 93, 4004.

l8 D. B. Denney, R. L. Powell, A. Taft, and D. Twitchell, Phosphorus, 1971, 1, 151.

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Quinquecovalent Phosphorus Compounds U

33

The equilibrium between phosphonium methoxide and methoxyphos- phorane has been ObservedlO in some cases by 31P n.m.r. Thus the 31P chemical shift of a solution of the salt (9) in methanol changes from + 14.5 to + 91.7 p.p.m. as the methoxide ion content is increased to 3 molar

equivalents. The equilibration is slow at low temperature and at - 80 "C the separate phosphonium and phosphorane resonances can be seen.

Molybdenum hexafluoride has been used 2o for the preparation of difluorophosphoranes from phosphines and of trifluorophosphoranes from chlorophosphines.

4 Four-membered Rings

Data on the relative apicophilicities of groups have been obtained6 from a study of the variable-temperature 1°F n.m.r. spectra of the hexafluoro- acetone adducts of 1 -substituted phosphetans. The pseudorotation that can be followed is that which places the four-membered ring diequatorial, i.e. (10) + (11).21 The results (Table 1) were discussed in terms of apico- philicity being a balance between electronegativity, increase in which

H Me M e H M e

C F, (10)

Me

l9 D. W. Allen, B. G. Hutley, and M. T. J. Mellor, J. C. S. Perkin 11, 1972, 63. 2 o F. Mathey, and J. Bensoam, Compt. rend., 1972, 274, C, 1095. *l A. E. Duff, R. K. Oram, and S. Trippett, Chern. Comm., 1971, 1011.

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34 Organophosphorus Chemistry

favours occupation of the apical position, and ability to back-bond into phosphorus d-orbitals, increase in which favours occupation of the equatorial positions (see also Section 1).

Table 1

AG*/kcalmol-l > 22 19.1 17.8 16.9 16.2 N 9 < 7 < 7 R Ph CH=CMe, Pri Me NMe, OPh OCH(CF,), H

The phosphetan (12) with bis(trifluoromethy1) peroxide or bis(trifluor0- methyl) disulphide at - 78 "C gave 23 the difluorophosphorane (13). The 31P and lH n.m.r. spectra at - 100 "C show clearly that the phosphorane is a 2.3:l equilibrium mixture of (13a) and (13c), equilibration via the high energy phosphorane (13b) being slow at this temperature. The apicophilicity of fluorine is balancing the increased strain involved in placing the four-membered ring diequatorial.

Me Me Me

Me

The same phosphetan (12) with the dithieten (14) gavez3 the stabIe adduct (15) whose lH n.m.r. did not change from - 50 to + 147°C. The formation of 1,3,2-dithiaphospholens from (14) and tervalent phos- phorus compounds is a general reaction; they appear to be less stable than the corresponding 1,3,2-dioxaphospholens.

The energy barrier to the pseudorotation (16) + (17) is a function of of the ring size,24 being 16-17 kcal mol-1 for n = 3 and about 13 kcal mol-1

22 N. J. De'ath, D. 2. Denney, and D. B. Denney, J. C. S. Chem. Comm., 1972, 272. 2s N. J. De'ath and D. B. Denney, J . C. S. Chem. Comm., 1972, 395. !?* D. W. White, N. J. De'ath, D. 2. Denney, and D. B. Denney, Phosphorus, 1971,1, 91.

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Q uinqueco valen t Phosphor us Compounds 35

for It = 4. These values compare with 11 kcal mol-1 for the corresponding diethoxy-compounds.

An X-ray structure determination has been reported25 for the 1 ,Zoxaphosphetan (1 8), obtained from ethyldiphenylphosphine and hexafluoroacetone. Oxaphosphetans are probably formed from hexa- fluoroacetone and phosphines containing an a-hydrogen via the ylides (20), formed by proton transfer in the initial 1 : 1 adducts (19).

The exchange of alkoxy-groups when oxyphosphoranes are treated with alcohols is base catalysed.2s When the oxaphosphetan (21) is treated with CD,OD in the presence of tertiary base, CHsOD is liberated before

Mazhar-ul-Haque, C. N. Caughlan, F. Ramirez, J. F. Pilot, and C. P. Smith, J . Amer. Chem. SOC., 1971, 93, 5229.

26 F. Ramirez, G. V. Loewengart, E. A. Tsolis, and K. Tasaka, J. Amer. Chem. Sac., 1972, 94, 353 1.

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36 Organophosphoriis Chemistry

- mo] 1 ‘3‘ f 1,. .o e

I’OCD, OCH(CF3 ) z

i ’OMe OMe

(22)

CD30-/ I‘ -. F3cb 0 C H ( CF3 )

P’-OMe D3 “A Me

-

ir - (CF,).C H 0 -

F 3 C j 3 .OMe

l’OCD3 OMe

(CFS),CHOD in spite of the greater acidity of the latter. Nucleophilic attack probably takes place in the equatorial plane, as shown, while the more rapid formation of CH30D is due to the equilibrium between (21) and (22) being in favour of the former because of the greater apicophilicity of the (CF,),CHO group.

Me Me /N\ ,NSiMe,

o=c, + R2,PFt5-n) A O=C, ,PF(3--n)R274 NSiMe, N R1 R‘

(23) R1 = Me or Ph

F F . . . I /

R I I ..R

I F F

,P-N

,N - P,

F

P-N

,N-P,

F. .. I /

R‘I I ..F

I R F

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Quinquecovalent Phosphorus Compounds 37

Details have appeared 27 of the preparation and lgF n.rn.~-.~~? 28 of the diazaphosphetidinones (23). The variable-temperature l9F n.m.r. of the diazadiphosphetidines (24) has been discussed 28 in terms of the equilibrat- ing isomers (24a) and (24b).

5 Five-membered Rings 1,3,2-Dioxaphospholans.-The cyclic phosphonites (25 ; R = Me or Et) reacted with butadiene and with isoprene less rapidly than did (25; R = Ph), but more rapidly than did (25; R = C1 or NCS).29 The phosphite (25;

R

(24 )

R = PhO) reacted with dienes to give the phosphinate esters (26), doubt- less via the phosphoranes.sO

For the preparation of 1,3,2-dioxaphospholans by exchange reactions between diethoxyphosphoranes and 1 ,2-diols, see Section 3 above.

The 2:l adducts (28) have been prepared from pyruvate esters and the cyclic esters (27).31

9, R’, ,PR2 +

0 MeCOC0,R3

(28)

CHMe CH, CHMe I

CH, CHMe I R’= I , I , or CH, ; R2 = OEt or NMe,; R3 =Me or Et

CH,

27 R. E. Dunmur and R. Schmutzler, J. Chem. SUC. (A). 1971, 1289. ** R. K. Harris, J. R. Woplin, R. E. Dunmur, M. Murray, and R. Schmutzler, Ber.

Bunsengeseilschaft phys. Chem., 1972, 76, 44. as Zh. L. Evtikhov, N. A. Razumova, and A. A. Petrov, J. Gen. Chem. (U.S.S.R.), 1971,

41, 471. Zh. L. Evtikhov, B. B. Shurukhin, N. A. Razumova, and A. A. Petrov, J. Gen. Chern. (U.S.S.R.), 1971, 41, 472.

s1 A. N. Pudovik, I. V. Gur’yanova, L. A. Burnaeva, and E. Kh. Karimullina, J. Gen. Chem. (U.S.S.R.), 1971, 41, 1995.

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38 Organophosphorus Chemistry

1,3,2-Dioxaphospholan-4-ones [ (29) or (31) ] are obtained 32 from a-hydroxy-acids and phosphorus trichloride or the cyclic ethylene esters (30). The betaines (32) are the initial products from a-hydroxy-acids and the phosphoramidite (30; R1 = H, R2 = NEt2).33 The isomers observed by lH n.m.r. in these dioxaphospholan-4-ones seem to be restricted to those due to cis-trans relations among the ring substituents and the P- hydro gen .

H O\l /O

0 0' \o

R3

7 R 4 x P 3 R 1 R' = CI or OAc

(31)

Base-catalysed additions of the phosphoranes (33; X = 0 or NH) to acrylic esters and acrylonitrile have been reported, as well as radical addition of the phosphorane (33; X = 0) to vinyl

H CH,CH,CO,R

[O)!':) + CH,=CHCO,R ---+ x o

CH,CH,OR

AIBN (33 ; X = 0 ) + CH,=CHOR ~

88 M. Koenig, A. Munoz, and R. Wolf, Bull. SOC. chim. France, 1971, 4185. 33 M. Koenig, A. Munoz, R. Wolf, and D. Houalla, Bull. SOC. chim. France, 1972, 1413. 34 N. P. Grechkin and G. S. Gubanova, Bull. Acad. Sci., U.S.S.R., 1970, 2637.

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Quinquecovalent Phosphorus Compounds 39

1,3,2-Dioxaphospholens.-The phosphoranes (34) and (35) have been fully characterized as quinquec~valent,~~ in contrast to the betaine formed from biacetyl and tris(diethy1amino)phosphine.

The bis(trimethylsily1) ether (36) with fluorophosphoranes gave 36 the monocyclic phosphoranes (37), except with tetrafluorophosphoranes and

NEt,

(34)

p R

PF5 when the major products were the bicyclic compounds (38). However, using the bis-t-butyl-substituted ether (39) the monocyclic phosphoranes (40; n = 0 or 1) were obtained as stable distillable l iq~ids .~ ' At - 88 "C the leF n.m.r. of (40; n = 1, R = Me) showed two distinct fluorines, i.e. the pseudorotation which places the two fluorines equatorial is slow on the n.m.r. timescale at this temperature.

Although there is no evidence for the presence of PrI1 species in the tetraoxyphosphoranes (41) and (42), the 31P n.m.r. of the closely related (43) showed the presence of the two phosphites (44) and (45).38

No quinquecovalent adducts were obtained from the phosphines Et2PMR3 (M = Si and Ge) and b i a ~ e t y l . ~ ~

as I. P. Gozman and 0. A. Raevskii, Bull. Acad. Sci., U.S.S.R., 1971, 1393. se G. 0. Doak and R. Schmutzler, J. Chem. SOC. (A) , 1971, 1295. s7 M. Eisenhut and R. Schmutzler, Chem. Comm., 1971, 1452. 38 R. Burgada and D. Bernard, Compr. rend., 1971,273, C, 164. a@ J. SatgC, C . Couret, and J. EscudiC, J. Organometallic Chem., 1971, 30, C70.

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40

8:

Organophosphorus Chemistry

H

M e . A . H

MeCO Ar

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Quinquecovalent Phosphorus Compounds 41

A full account has appeared40 of the reactions of the benzil-trimethyl phosphite adduct with sulphenyl chlorides. The cyclopropanes (47) are obtained 41 from arylidenemalononitriles and the biacetyl-trimethyl phosphite adduct. The preponderance of the isomer shown is held to be due to the greater stability diastereoisomer.

Ph

of the intermediate (46) than of its

Ph

There are several reports in the literature of stable quinquecovalent phosphoranes having an hydroxy-group attached to phosphorus, e.g. (48).42 However, in no case is the evidence compelling and they all seem to require reinvestigation.

1,2-Oxaphospholans.-Full details have appeared 4 3 ~ 44 of the reactions of the lactone and dione dimers of dimethylketen with a series of tervalent phosphorus esters and amides, and the postulated quinquecovalent inter- mediate (49) from the lactone dimer has been isolated in one case.46 Of potential mechanistic significance is the preferred migration of exocyclic substituents in the steps corresponding to (49) -+ (50).

+

NMe,

Me N Me (50) (49)

* O D. N. Harpp and P. Mathiaparanam, J. Org. Chem., 1972, 37, 1367. 41 E. Corre and A. Foucard, Chem. Comm., 1971, 570. 4a F. V. Bagrov and N. A. Razumova, J . Gen. Chem. (U.S.S.R.), 1970,40,2557. 43 W. G. Bentrude, W. D. Johnson, W. A. Khan, and E. R. Witt, J. Org. Chem., 1972

37, 631. 44 W. G. Bentrude, W. D. Johnson, and W. A. Khan, J. Org. Chem., 1972,37, 642. 46 W. G. Bentrude, W. D. Johnson, and W. A. Khan, J . Amer. Chem. SOC., 1972,94,923.

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42 Organophosphorus Chemistry

The formation of a stable 1,2-oxaphospholan from the sodium salt of benzoin and triphenylvinylphosphonium bromide has been extended 46 to substituted vinylphosphonium salts, diastereoisomers being obtained in some cases.

1,2-Oxaphospholens.-Among new ap-unsaturated ketones used in the formation of 1 : 1 adducts with tervalent phosphorus compounds are dibenzylidenecyclohexanone,47 ethyl benzylidenebenzoyla~etate,~~ and the allenic ketones (5 1).49 Hydrogen chloride and the trimethyl phosphite adduct (52) gave the conjugated (53) and non-conjugated (54) isomers in

R L

HC'I (52; R = P r ' ) - Me,CHCO.CH=CMe.P(O)(OMe),

(53 )

+ Me,CHCO-CH,C(:CH,) .P(O)(OMe),

(54)

a ratio of 1 : 9. Additional examples have appeared of the use of methyl vinyl ketone 6o and of ethyl isopropylidenea~etoacetate.~~ With the former, and with mesityl oxide, acetyl ethylene phosphite (55) gave 50 spirophos- phoranes which were stable under the rather vigorous reaction conditions.

The equilibration and the variable-temperature 31P and lH n.m.r. spectra of the isomeric adducts formed from benzylideneacetylacetone and the ethylene phosphites (56; R = OMe or NMe,) have been In

40 E. E. Schweizer and W. S. Creasey, J . Org. Chem., 1971, 36, 2244. 47 B. A. Arbuzov, V. M. Zoroastrova, G. A. Tudrii, and A. V. Fuzhenkova, Doklady

Chern., 1971,200,807. 48 B. A. Arbuzov, E. N. Dianova, and V. S. Vinogradova, Bull. Acad. Sci., U.S.S.R.,

1970, 2338. 49 G. Buono and G. Peiffer, Tetrahedron Letters, 1972, 149. 5 0 A. K. Voznesenskaya, N. A. Razumova, and A. A. Petrov, J. Gen. Chem. (U.S.S.R.),

1971, 41, 228. B. A. Arbuzov, E. N. Dianova, and V. S. Vinogradova, Doklady Chem., 1970,195,898.

5a D. Bernard and R. Burgada, Compt. rend., 1972, 274, C, 288.

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Quinquecoualent Phosphorus Cornpourids 43

Me Me

+

R = OMe, m.p. 135 "C R = NMe,, map. 155 "C

each case fractional crystallization gave one pure isomer. Although equilibration of the isomers was slow on the n.m.r. timescale at high temperatures, and there was no evidence of dipolar species, in each case the four signals observed at low temperatures for the four methyls of the dioxaphospholan rings coalesced to give two signals at higher temperatures. The cause of these changes is not clear; they cannot be brought about by normal Berry pseudorotations.

The thermally stable compound, m.p. 170-172 "C, formed from the ylide (57) and p-bromobenzaldehyde, has been shown by X-ray analysis 63 to be the dioxyphosphorane (58).

Ph. .. I - phOf) O I \ Ph

Ph,P(OEt)=C(COPh) CH,COPh

(57)

0

H C,H,Br-p

( 5 8 )

+ p-BrC,H,CHO

Yo

1,3,2-Oxazaphospholans.-The salts (60) obtained 33p 64 from the ethylene phosphites (59) and /3-amino-alcohols gave the spirophosphoranes (62) on treatment with base, and were re-formed from (62) with carboxylic acids. However, the spirophosphorane (61) was unaffected by benzoic acid and was formed directly in the absence of additional base.

a-Amino-acids and the phosphorochloridite (63) in the presence of base gave the phosphoranes (64).55 The variable-temperature lH n.m.r. of the 68 D. D. Swank, C. N. Caughlan, F. Ramirez, and J. F. Pilot, J. Amer. Chem. Soc., 1971,

93, 5236. 64 R. Burgada, D. Bernard, and C. Laurenco, Compt. rend., 1972, 274, C, 419. 66 A. Munoz, M. Koenig, B. Garrigues, and R. Wolf, Compt. rend., 1972, 274, C, 1413.

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44 Organophosphorus Chemistry

+:)X + HOCHRCH,NH, - q I ) O C H R C H , & H , X-

(60) X = CI o r OAc

,+I

(59) RCO,H Base II

spirophosphoranes (65; R = Me, But, or OMe) have been explained in terms of pseud~rotat ion.~~

An exchange reaction between triethoxydiphenylphosphorane and diethanolamine gave 57 the bicyclic phosphorane (66).

1,3,5-Oxazaphospholens.-Phosphites add rapidly to the acylimines (67) to give the 1 :1 adducts (68), which are stable in the absence of moisture but decompose on attempted dis t i l la t i~n.~~ The 1,3-dipoles (69) formed on thermolysis 59 or photolysis 6o have been trapped with electrophilic olefins and acetylenes and with isocyanides.61

L. Beslier, M. Sanchez, D. Houalla, and R. Wolf, Bull. SOC. chim. France, 1971, 2563. 57 B. C. Chang, unpublished work quoted in reference 11. 58 K. Burger, J. Fehn, and E. Moll, Chem. Ber., 1971, 104, 1826. G9 K. Burger and J. Fehn, Angew. Chem. Internat. Edn., 1971, 10, 728, 729. 6 o K. Burger and J. Fehn, Tetrahedron Letters, 1972, 1263.

K. Burger and J. Fehn, Angew. Chem. Internat. Edn., 1972, 11, 47.

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Quinquecovalent Phosphorus Compounds 45

.$'

l +

(CF,)&=NCOR' + P(OR2), ----+ (CF3)2(I,/0

(67) (OR2),

(68)

h or h v

+ (R20) ,P0 R"NC ,N=CR' ?yR1 +--- (CF3)2C

(69)

R T H =CH RP

R' I R'

H 'R3 H R4

(71) 71%

McLi t

( 7 2 ) - HzO 1

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46 Organophosphorus Chemistry

Miscellaneous.-Additional examples of the cage-like phosphoranes (70) have been obtained,62 including the first penta-alkylphosphorane (70; R1, R2, R3 = Me). The biphenylylenephosphonium salt (73) with methyl-lithium gave63 the phosphorane (71), but with (72) gave only the phosphorane (74) and not a six-co-ordinate anion analogous to that formed from the bisbiphenylylene salt and (72).

The order of reactivity MeOPCl, > (63) > (EtO)2PCl 9 (MeO),P has been found 64 for addition to isoprene. This diene and the phosphites (75) gave only the phospholens (76).65 If phosphoranes are intermediates in these reactions, then the fate of the aromatic nucleus is of some interest. The phospholens (77) with diethyl peroxide gave isoprene and diethyl phenylphosphoni te, presumably via the phosphorane.ll

0 + (EtO), ---+ + +

PhP(OEt), Ph

(77)

F3C CF3

F3C 0 CF3

From the multiplicity of its 19F n.m.r. spectrum, it seems unlikely that the compound obtained 66 from hexafluorobut-2-yne and the gold complex MeAuPPh, has the structure (78).

62 E. W. Turnblom and T. J. Katz, J . Amer. Chem. Soc., 1971, 93, 4065. E. W. Turnblom and D. Hellwinkel, J . C. S. Chern. Comm., 1972, 404.

64 L. I. Zubtsova, N. A. Razumova, and T. V. Yakovleva, J , Gen. Chern. (U.S.S.R.), 1971, 41, 2450.

66 B. A. Arbuzov, V. IS. Krupnov, and A. 0. Vizel, Bull. Acad. Sci., U.S.S.R., 1971, 20 1233.

66 C. M. Mitchell and F. G . A. Stone, J . C. S. Dalton, 1972, 102.

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Quinquecovalent Phosphorus Compounds 47

X-Ray analysis has shown6' that although the 31P chemical shift of the phosphorane (79) is + 66.9p.p.m. and the geometry around the phosphorus is approximately trigonal bipyramidal, the PO bond length is 2.14A. Contributions to the structure by the dipolar species (80) and (81) are suggested.

The 2:l adducts formed at low temperature from dimethylketen and phosphites or aminophosphines have now been shown 68 to

EtOAc Me,C=C=O 3- P X Y Z

Y

R' R2 M R1COCR2=NMe + P X Y Z 0 N M ~ \ /

X+Z Y

6' I. Kawamoto, T. Hata, Y. Kishida, and C. Tamura, Tetrahedron Letters, 1972, 1611. g8 W. G. Bentrude, W. D. Johnson, and W. A. Khan, J . Amer. Chern. Sac., 1972,94,3058.

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48 Organophosphorus Chemistry

be 1,3,5-dioxaphospholans (82) and not the previously suggested 69

1,3-oxap hosp holans. a-Imino-ketones have been condensed 70 with a range of phosphites

and related tervalent phosphorus compounds to give the 1,3,2-ox~a- phospholens (83). The imino-ketones are less reactive than the correspond- ing a-diketones. The isolation of the aminotetroxyphosphorane (86) in 50% yield from the reaction of the nitro-compound (84) with an excess of trimethyl phosphite 71 provides evidence for the formation of spirodienyl intermediates, e.g. (85), in deoxygenations of nitro-compounds involving rearrangements.

Although acyclic aminophosphines with amidoximes give the oxides (87), cyclic phosphoramidites, e.g. (88), yield isolable phosphoranes (89).72 With

I N W )

,PNMe, + R1C(:NOH).NHR2 ---+ RICH ' NHR2

\

\

(8 7)

R &

N' Reflux \ I .H

RCONHNH, + (Me,N),P - 69 W. G. Bentrude and W. D. Johnson, J. Amer. Chem. SOC., 1968,90,5924. 7 0 D. Bernard and R. Burgada, Compt. rend., 1971, 272, C, 2077. i 1 J. I. G. Cadogan, D. S. B. Grace, P. K. K. Lim, and B. S. Tait, J. C. S. Chem. Comm.,

1972, 520. i 2 L. Lopez and J. Barras, Cumpt. rend., 1971, 273, C, 1540.

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Quinquecovalent Phosphorus Compounds 49

benzamidoxime, exchange then occurs to give the phosphorane (go), which is also obtainable directly from benzamidoxime and phosphorus trichloride in the presence of triethylamine.

The compounds previously obtained from acyl hydrazides and phosphorus trihalides have now been obtained 73 using tris(dimethy1amino)- phosphine and shown to be the spirophosphoranes (91). The oxathia- phospholans (92) are less reactive towards a-diketones than are the corresponding dioxapho~pholans.~~ The phosphites (93) and (94) exist as such 74 and do not give the trioxythiopho~phoranes.~~

6 Six-co-ordinate Species The preparation of the salt (95) has been improved 76 by using phosphorus trichloride at room temperature instead of the pentachloride at - 70 "C. The spirophosphorane (96) with ethylene glycol and sodium methoxide gave the tris(ethy1enedioxy)phosphate (97).77 Attempts to prepare the six-membered-ring analogue failed. X-Ray analysis of the salt (98) confirmed the octahedral arrangement of oxygens around phosphorus.

78 A. Schmidpeter and J. Luber, Angew. Chem. Internat. Edn., 1972, 11, 306. 74 D. Bernard, P. Savignac, and R. Burgada, Bull. Soc. chim. France, 1972, 1657. 7 6 P. M. Zavlin, E. R. Rodnyanskaya, A. I. D'yakonov, and V. M. Al'bitskaya, J. Gen.

Chem. (U.S.S.R.), 1971, 41, 1883. '13 R. Rothius, T. K. J. Luderer, and H. M. Buck, Rec. Trau. chim., 1972, 91, 836. 77 €3 C. Chang, D. B. Denney, R. L. Powell, and D. W. White, Chem. Comm., 1971,

1070. H. R. Allcock and E. C. Bissell, J. C. S. Chem. Comm., 1972, 676.

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50 Organophosphorus Chemistry

0-P + HOCH,CH,OH ___j NaoMe Na' PE]]-

3

(97) alp +89 p.p.m.

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