N otizen 599
Phosphoranes w ith a Chiral Centre Containing the 1,2-O xaphosphetane R ing System
J a m e s A n d r e w G i b s o n , G e r d - V o l k e r R ö s c h e n t h a l e r ,
and R e i n h a r d S c h m u t z l e r
L eh rstu h l B für A norganische Chemie der Technischen U n iv ersität B raunschw eig
(Z. Naturforsch. 32 b, 599-600 [1977];
eingegangen am 17. J an u ar/7. Februar 1977)
H exafluoroacetone, T etra m eth y ld ip h o sp h in e, P h o sp h etan es, C hirality
H exafluoroacetone an d tetram eth y ld ip h o s- phine react readily a t low te m p eratu re s p ro ducing th re e 4,4-bis(trifluorom ethyl)-l,2- o x aphosphetanes (1), (2), an d (3). The com pounds have chiral ce n tres a t phosphorus producing doubling of resonances in th e N M R spectra.
Trialkylphosphines R 1 R 2 R 3 P react upon addition of hexafluoroacetone to give 1,3,2-dioxaphosphola- n es1. I f m ethyl and/or methylene groups are directly bonded to phosphorus in the resulting products rearrangement occurs to give 1,2-oxa- phosphetanes2. We report here the first reaction of a tetraalkyldiphosphine with hexafluoroacetone. At
— 50 °C a vigorous reaction was observed and from the resulting mixture the oxaphosphetanes 1 and 2 were isolated. In addition 3 was identified by comparison o f NMR spectra with those of an authentic sam ple3. Compound 3, because of its relative low yield and similar volatility to 2 could not be separated pure from the mixture. 1,3,2-4 and l,3 ,4 -5-6phospholanes were not observed. Similarly use of excess tetramethyldiphosphine does not give rise to a simple insertion into the P -P bond as has
R eq u ests for re p rin ts should be sent to D r. Ge r d- Vo l k e r Rö s c h e n t h a l e r, L e h rstu h l B für A norga
nische Chemie d e r T echnischen U niversität, Pockels- stra ß e 4, D -3300 Braunschweig.
been found in the reaction of hexafluoroacetone with tetrafluorodiphosphine7.
0^ c f3
JCF,
C,F3 I U
HC°ck I N Me
CF,-C-CF, 3 p J
'Me
H CO r t r » - P '" ^ H
.CF,
Cf3 HC 0
ck
___ P ' ' ” tH
It is difficult to rationalise the formation of 2 and 3 on the basis of the known reactions of hexa
fluoroacetone with phosphines, for examples see refs.1’2-4’5-6. The reactions involved in the forma
tion of 2 and 3 must occur by transfer of protons and/or hydrogen atoms (compound 2) or transfer of fluoride and/or fluorine atoms (compound 3). Phos
phines have been observed to abstract fluorine from hexafluoroacetone to give difluorophosphoranes but the reaction is slow and the mechanism is not known8. One possible reaction pathway could include homolytic cleavage of a P m -P v directly bonded intermediate to produce a reactive phos- phoranyl radical. Experiments are under way with related systems to elucidate the mechanism of this novel reaction. The compounds show, in the mass spectra, molecules ions and fragments such as [M-Me2PC(CF3)20]+ (1); [M-(CF3)2CHO]+ (2); and (M-F)+ (3) (m/e = 393) in high abundance.
The NMR data (Table) are entirely consistent with the structures indicated9’10. Compounds 1 and 3 are phosphoranes with five different substituents attached to phosphorus. In their 1H and 19F NMR spectra there are no coalescence phenomena observed. The chiral centre at phosphorus10 induces non-equivalence in the CF3 substituents in the freely rotating Me2PC(CF3) 2 0 (1) and (CF3)2CHO (1, 2) groups. The lack of a plane of symmetry in the phosphetane ring system, related of course to the chiral phosphorus centre, causes non-equivalences of CF3 groups and hydrogens in the four membered ring. Compound 2 exhibits observable fiuxional character with equivalent CF3 (phosphetane ring)
T able. A m b ient-tem perature NM R d a ta of 1, 2, a n d 3.
C om pounda (5Pb [ppm] <5h c
C h3
[ppm]
c h2 O CH Jp h [Hz]
CH z CH 2 O CH
f5pd [ppm]
(C-F3)2CP OCH(CjF3 ) 2 C(CF3 ) 2
1 + 6 . 8 (P 111)
+ 9 .4 (P V)
— 1.20 (P 111)
— 2 .1 0 (P V) - — 4.25e — 5.60
6 .0 (P IU)
16.5(PV) e 15.7f 67.0 67.7
72.4 73.1
76.5 78.3
2 + 1 0 . 0 — 1.90 - 3 .8 3 — 5.15 16.5 20.7 13.0e - 74.5 78.0
3k + 2 . 1 — 2.35 —4.30e — 5.50 17.6h e 15.61 - 72.9
73.5
76.4 77.0 a Solution in benzene. b M easured a t 2 4 . 3 M Hz to external 8 5 % H3P0 4 reference. c M easured a t 6 0 . 0 MHz relative to in te rn a l Me4Si reference. d M easured a t 5 6 . 4 and 9 4 . 1 3 MHz relativ e to in te rn al CC13F reference.
e A B X spin sy stem ; centered a t shift indicated. f D oublet of se p te ts; 3J h f = 6 . 0 H z. s 3 j H p — 50H z, m easured a t 5 0 °C. h D o u b let of d o u b le ts; 3J h f = 1 1-6H z. i 3 J H F — 5 . 6 H z. k dpF = 2 9 . 6 p p m ; Jp p = 8 3 2 Hz.
60 0 N otizen
and (CF3)2CHO groups at room temperature, probably involving an intermediate stereo isomer with two equatorial hexafluoroisopropoxy sub
stituents which eliminates the chiral centre at phosphorus10. At — 30 °C non-equivalent axial and equatorial hexafluoropropoxy groups and chirality phenomena (as in 1 and 3) were found. Compounds 1 and 3 m ay also be fluxional but intramolecular exchange may not destroy the chiral centre at phosphorus.
Experimental
Materials were handled throughout in thoroughly dried Pyrex-glass vacuum system, serviced with dry oxygen-free nitrogen.
if l, 19F and 31P NMR spectra were recorded at 60.0, 56.4 and 24.3 MHz on a Jeol JNM -C 60 HL spectrometer or at 100.06, 94.13 and 40.50 MHz on a Varian XL-100-12 spectrometer. The reference substances were TMS (internal), CCI3F (internal) and 85% H3P0 4 (external), respectively. CFCI3 was used as solvent for low-temperature studies. Mass spectra were obtained on an AEI MS 9 instrument.
Tetramethyldiphosphine (6.1 g, 0.005 mole) was condensed onto hexafluoroacetone (32.2 g, 0,2 mole) at — 196 °C. The reaction mixture was alloAved to warm over a period of three hours to — 50 °C when a vigorous reaction was observed. The yellow viscous liquid product was distilled under vacuum yielding two fractions at 30-52 °C/3 Torr and 61-63 °C/
0.01 Torr. The higher boiling fraction was pure 1:
1 F . Ra m i r e z, C. P . Sm i t h, J . F. Pi l o t, a n d A. S . Gu l a t i, J . Org. Chem. 33, 3787 [1968].
2 F . Ra m i r e z, C. P . Sm i t h, and J . F. Pi l o t, J . Amer.
Chem. S o c . 90, 6726 [1968].
3 T he a u th e n tic sam ple of 3 w as p rep a re d by fluorina- tio n o f th e chloro-phosphorane analog; J . A. Gi b s o n, G . - V . Rö s c h e n t h a l e r, K . Sa u e r b r e y, an d R . Sc h m u t z l e r, Chem. B er., su b m itte d for publication.
4 J . A. Gi b s o n, G.-V. Rö s c h e n t h a l e r, an d R . Sc h m u t z l e r, J . Chem. Soc. D alton T rans. 1975, 918.
5 V. N. Vo l k o v i t s k i i, I. L. Kn u n y a n t s, a n d E . G.
By k h o v s k a y a, Z h u r . V s e s o y u z . K h i m . o b s h c h . i m .
D. I. M e n d e l e e v a 18, 112 [1973].
2- (2-dimethylphosphino-l ,1,1,3,3,3-
hexafluoropropoxy)-2- (1,1,1,3,3,3-hexafluoro- propoxy )-2-methyl-4,4-bis( trifluoromethyl )-
1.2-oxaphosphetane,
an exceedingly air and moisture sensitive compound (9.3 g, 30% based on tetramethyldiphosphine).
Analysis (C13H12F18O3P2)
Calcd C 25.2 H 2.0 F 55.2 P 10.0, Found C 24.8 H 2.0 F 54.3 P 9.7.
The lower boiling fraction contained a mixture of 2 and 3 and other unidentified products 2:
2.2-bis (1,1,1,3,3,3-hexafluoropropoxy ) -2-methyl- 4,4-bis( trifluoromethyl) -1 ,2-oxaphosphetane, could be separated pure from the mixture by trap- to-trap fractionation under high vacuum. The crystalline material (m.p. 52 °C) was trapped at 0 °C/0.0001 Torr (8.4 g, 15% based on tetram ethyl
diphosphine).
Analysis (C1 1H7F18O3P)
Calcd C 23.6 H 1.3 F 6 1 .0 P 5.5, Found C 23.9 H 1.4 F 60.5 P 5.8.
W e th a n k D eutsche F orschungsgem einschaft for financial su p p o rt and A lexander von H u m b o ld t-S tif
tu n g for a research fellowship to J . A. G. Dr. V. Wr a y,
Gesellschaft für Biotechnologische F orschung, B ra u n schweig, an d D r. G. R. Co r a o r, Organic Chemicals D ep artm en t, E . I. du P o n t de N em ours & Co., Inc., W ilm ington, D elaware, U. S. A., are th a n k e d for NM R spectra an d a generous g ift of hexafluoroacetone, respectively.
6 E. Du f f, D . R . Ru s s e l l, a n d S. Tr i p p e t t. P h o s
phorus 4, 203 [1974].
7 G. N. Bo c k e r m a n and R . W . Pa r r y, J . F luorine Chem. 7, 1 [1976].
8 A. F. Ja n z e n and 0 . C. Va i d y a, Can. J . Chem. 51, 1136 [1973].
9 L. Ma i e r, in G. M . Ko s o l a p o f fa n d L. Ma i e r (ed s.):
O rganophosphorus Com pounds, 2nd ed. vol. 1, W iley-Interscience London, New Y ork, Sidney, Toronto 1972.
1 0 R. Lu c k e n b a c h, D ynam ic S tereochem istry of P en taco -o rd in ated P hosphorus a n d R e la te d E le m ents, Georg Thieme P ublishers, S tu ttg a rt 1973.
