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Vol. 85
COMMUNICATIONS TO THE EDITOR
the antiperiplanar position, essentially as in the concerted E2 elimination. Thus, the difference between E2 and E l in basic solvents may only be a matter of degree
//,yHs -pTs
Hac /
H
CHZ
/C H3
/c=c
H.,
'Solvent
B
D \ H
of polarization of the bond between the leaving group and the a-carbon. A41though it is not possible completely to rule out gegcnion free carbonium ions in each of the solvents, it is clear that they do not play a major role in these solvolytic eliminations. Streitwieser and Walsh' have demonstrated that the solvolytic displacement of tosylate by acetate group in the 2-octyl system occurs with 100% inversion in glacial acetic acid. .-I11 of these resiilts are best accommodated by rejjection of the idea that in these soholytic processes the fate of the carbonium ion is independent of i f s origin. Acknowledgment.-This work was supported by the U. S. Xrmy Research Office (Durham). 17) A Streitwieser, J r . . a n d
T 11. W a l i h , T e l r a h e d t o n L e t t e r s , 27 (1963).
DEPARTMENT O F CHEMISTRY T H E PENSSYLVASIA STATELXIVERSITY PARK,PENNSYLVANIA USIYERSITY RECEIVED J U L Y3, 1963
P. S.SKELL M' L. HALL
The Cyclononatetraenyl Anion Sir : The cyclononatetraenyl anion I should have a closed shell configuration of 10 T electrons and should be highly resonance stabilized. I T h a t i t should be aromatic is, however, questionable for two reasons: (1) The energy required to distort the angles of its bonds might be excessively large? and (2) the nine-membered ring might valence tautomerize3 spontaneously to form a single bond a t the expense of a double Nevertheless, t h e cyclononatetraenyl anion does appear to be aromatic. Its synthesis is the subject of this report.
Ia, h l T b,hlt
= =
Li+
RC
IIa, S = C1 b, X = OCHa c , S = H
I I I a , S = Cl b, S = OCHs c , X = H
Cold chloroform reacts with dipotassium cyclooctatetraenide4in tetrahydrofuran ( T H F ) to yield, after aqueous work-up, 9-chlorobicyclo [6.1.O]nonatriene ( I I a ) , b.p. 28-32' (0.2 mm.), in 3 2 7 , yield; ": :A: 218 mp (log E 3 . 5 7 ) . *lnal. Calcd. for CsH9C1: C. ; H . j . 9 4 ; C1, 2 3 . 2 3 Found: C, i l . 0 6 ; H , C1, 2,'3.42. Similarly, dichloromethyl methyl ether reacts to yield 9-methoxybicyclo [6.1.O]nonatriene ( I I b ) in 267' yield; b.p. 54-56 (1.1 m m . ) ; X":;lf 233 mp (log E 3.69). .Inal. Calcd. for CIoH110: C , S l . O 9 ; H,S.11. Found: C , 8 0 . 8 0 ; H , 8 . 1 8 . SIethylene chloride yields bicyclo [6.1.0]nonatriene5 (IIc) in 4ijT; yield. IIa was identified by its ultraviolet spectrum and by its n.in.r. spectrum. The latter exhibited a multiplet 11 I t - Huckel mulecular orbital delocalization energy is i3 5 3 (21 'The ccimpressiona! harrier i huwever, overcome b y its next lower homolog. Lhr cyclr,,xtatetraenyI d nion IT. J K a t z , W H R e i n m u t h , a n d D i t h . J . A m ( ' h e m Soc. 84, 02 i 1 9 l i 2 ) , a n d references t h e r e i n ]
J . K a t z . J A m ( h e m . .Sof , 83, :3781 ( 1 9 0 0 ) Yogel. A u ~ e mC'hem . , 73,A - I R ( I O i i l ) , a n d private c < , m m u n i c a t i m
a t 4.1 (rel. int. 6 ) and a coupled ( J = 4 c.P.s.) triplet a t 7.54 (rel. int. 1) and doublet a't 8.14 T (rel. int. 2). I I b exhibited a similar n.m.r. spectrum: a multiplet a t 4.2 (rel. int. Ci), a singlet a t 6.70 (rel. int. 3 ) , and a coupled ( J = 4 c.P.s.) triplet a t 7.40 (rel. int. 1) and doublet a t 8.40 T (rel. int. 2). Only the anti isomers appear to be found, in striking contrast to the formation of mixtures of comparable amounts of syn and anti isomers, the former predominating, when chloro-6 and methoxycarbene' are added to other olefins? Heating I Ia to 70' yields l-chloro-X,9-dihydroindene ( I I I a ; z'lnal. Found: C, 71.03; H , 6.01; C1, 23.24), identified by its ultraviolet spectrum [AX:,::' 2(j2 ( 3 . 5 2 ) , 270 mp (log E 3.14)]and its n.m.r. spectrum (4.2, 5.27, (5.6 T. rel. int. 6 : 1 : 2 ,all multiplets). Lithium aluminum hydride reduces I I I a to S.9-dihydroindeney (IIIc) [XXr);:" 262 ( 3 . 3 7 ) , 271 mp (log E X S I ) , maleic anhydride adduct, m.p. 141,5"J, which was identical with that obtained by heating IIc." IIa reacts with lithium in THF to give lithium cyclononatetraenide ( I a ) . On quenching with H 2 0 , I I I c is formed, and on quenching with DzO, i t is formed (24y6.yield) with the incorporation of 1 atom of deuterium.'" Similarly, I I b reacts with potassium to give potassium cyclononatetraenide ( I Ib), which, on quenching with DQ yields monodeuterated IIIc. I 1 The n.m.r. spectra of potassium and of lithium cyclononatetraenide in completely deuterated T H F consist of only one single very sharp peak at 2.96 and 33.15 7 , respectively.12 These spectra show t h a t the cyclononatetraenyl anion is aromatic.'3 If the cyclononatetraenyl anion and the cyclooctatetraenyl dianion are compared, their ring currentsL4should be sirnilar, but the protons in the former should be less shielded that in the latter because the negative charge density associated with each carbon atom is rather than z,g, T h a t is, the cyclononatetraenyl anion's proton n.m.r. should'6,Liappear (I '4 - y ) X 10 = l . 1 p . p . m .to lower fields than the resonance (4.3 T ) of the cyclooctatetraenyl d i a n i ~ n . ~ The agreement with the observed chemical shift is excellent. The ultraviolet spectra of l a 252 mp (5,0), :318 mp (3,9),325 mp (log t .'3.9)]and I b are similar.18 I t is remarkable that the cyclononatetraenyl anion has the all-cis stereochemistry.
[XzT
(13) (a) G I > Clriss a n d L E Closs. J . A m . ( ' h e w . Soc.. 83, .-,72:3 i l 9 0 0 ) ; ( b ) G . 1,. Closs, R A Sloss, a n d J . J . Coyle, ibiif , 84, 1985 ( I S H ? ) . ( 7 ) V , Schollkopf, A Lercn, a n d W . Pitteroff, Tetrahedron L e t l e r s , 241 (19ii2); L!. Y Schhllkopf a n d G J I.ehman, i b i d . , !&> ( 1 9 i i P ) ; V . Schiillkopf a n d H. Kuppers. t b i , I , , 102 ( I Q l i 3 ) . ( 8 ) T h e stereochemical assignment is based on t h e assumption t h a t t h e small size of t h e spin-spin coupling c o n s t a n t implies t h e nizti stereochemistry T h e presence of a trace of t h e o t h e r is. E. Closs, J . A m . Chem. S o c . , 82, 5723 (1960).
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analysis. Anal. Calcd. for CgHgC1: C, 70.82; H , 5.94; mol. wt., 152.6. Found: C, 70.76; H , 6.14; mol. wt., 152 (mass spec.)]. Upon treating the isomeric mixture I a and I b in tetrahydrofuran with a lithium dispersion for 2 hr. at room temperature, the multiplet a t 6.0 p.p.m. in the n.m.r. disappeared and a sharp line (width a t half height no greater than 0.8 c.P.s.) was observed a t 6.72 p,p.m. The lithium cyclononatetraenide (111) thus formed in 63Tc yield (n.m.r.) was stable in an inert a t mosphere, The C13 n.m.r. of the lithium salt 111 in T H F consisted of a doublet a t 19.0 p.p.m. ( J = 137 c.p.s.)to highfield from benzene.I3 hIetathesis of the lithium salt 111 with tetraethylammonium chloride produces tetraethylammonium cyclononatetraenide (IV, 97yc) as a stable (inert atmosphere) white solid which was purified by recrystallization from anhydrous acetonitrile, dec. pt. 818" (Anal. Calcd. for CIiH2gN: C, 82.5%; H , 11.81; N , 5.66. Found: C, 82.30; H , 11.55; K, 3.75); H1 n.m.r. (dfidimethyl sulfoxide) : 6.82 (aromatic H , width a t half height no greater than 0.0 c.P.s.), quartet a t 3.03 (CH2, J = 7 c.P.s.), triplet of triplets a t 1.05 (CH3, J = 7 c.p.s. and ca. 1.3 c.P.s.). The ultraviolet absorption spectrum is very simple, as expected for a molecule having a ninefold rotational axis: 250 m p (E >61,700) anddoubletat 3 1 i a n d 3 2 2 m p (E > 6 , l 7 0 ) . l 4 Polarographic analysis of the tetraethylammonium salt IV in acetonitrile containing LiC104 (0.1 :If) as the supporting electrolyte with a rotating platinum electrode shows what appears to be an irreversible oneelectron oxidation a t E o , 5= -0.03 v. (os. s.c.e.). As expected from this result, the tetraethylammonium salt I V can be oxidized by either tetracyanoethylerie or 7,7 ,8,8-tetracyanoquinodimethan.Attempts to detect the resulting radical'j in l ,%dirnethoxyethane solution via e.p.r. a t ambient temperature or a t -80' have been unsuccessful although the spectrum of TCNE:is observed. Lithium cyclononatetraenide (111) does not undergo detectable electron exchange over a period of 45 days with cyclooctatetraene to give cyclooctatetraene dianion. However, the salt I11 reacts with cyclopentadiene to give lithium cyclopentadienide. On the basis of the H ' and C13 n.ni.r. data and the strong absorption in the ultraviolet, it is concluded that cyclononatetracnide has aromatic character, Further studies are in progress. ( 1 2 ) J. Afeinwald, A Lewis, and P G. Gassman, i b i d , 84, 977 t1962), a n d references therein (13) We are grateful t o Dr. H Foster f o r t h e C11 N . m . r . studies I'he C L achemical shift is in excellent agreement with t h e simple linear correlation between chemical shift a n d r-electron density a s f o u n d recently f o r t h e a r o ~ matic series C7H7-, CsHs, CsHa- a n d CsHs*- [ H . Spiesecke a n d V,' G. Schneider, Telvohedron Letleis, No 14, 408 f1YO1) 1. Calculations using t h e least-squares method f o r their published d a t a together with t h a t found Although t h e value f o r CsHs- gives t h e equation 6C.S = l ( i 7 . 8 0 - Iti9.9 reported f o r CaHs- appears t o be anomalous, i t has been confirmed hy I>r. Foster. As previously noted [T Schaefer a n d V,' G . Schneider. C a n . J Chem , 41, 906 (19A3)1 t h e prediction of t h e H ' chemical shift f r o m t h e a-electron density is less satisfying f o r larger ring aromatic compounds d u e t o the diffic u l t y of applying ring size corrections. T h e HI chemical shift for 1,iCsHa f r o m internal benzene was found t o increase Upon dilution ( 2 7 :ic 11.5 a t ( a . 3 mole lo t o 30.5 C . P . S . a t ca 0 1 mole (,To) as expected f i x decreasiny ion association (11) Some difficulty was experienced in determining t h e exact value of the extinction coefficients since Beer'? law was n o t followed upon carrying o u t t h e necessary dilutions, presumably because of reaction with trace impurities in t h e solvent. (1.5) %'e are indebted t o l>r, 11.T. Jones f o r this experiment.
COSTRIBUTION S o . 909 E . .\. LALASCETTE CESTRALRESEARCH DEPARTYEST R.E . BENSON EXPERIMEYTAL STATION E. I . DU POSTDE SEXOL-RS ASD COMPANY WILMISGTOK, DELAWARE RECEIVED AUGUST2. 1963
