4724
COMRIUKICATIONS TO T I I E EI)ITOR TABLE
\+ARIATION O F D I F F E R E S T I A L
COSCENTRATIOS A T -56';
"
I LISE BROADESISCIYITH DETERMIXATIOS OF k f
I
TI
=
kf.
aec
-1
[ r i . .ti
[ I I I , .ti'
0.125 0.167 0 084 0 063 0 083
0 125 0 084 0.167 0 . 063 0 042
From eq. 3.
From eq 7 .
9 9 8 8
L'ol. hli
1 1 8 8
8 %
1 'I
711.
sec.
i;f .ec.
-1
8.1 14.7 3 7 8 1 16 1
8 7 7 8 8
1
t'
1 4 4 1 2
Knowledge of t h e equilibrium constant (K,,, = kf l k r ) now makes k , accessible. Ultraviolet data,' using similar solutions of I as for the n.ni.r. experiments. = 2.S X a t -,j(io.$J Ysing yielded a value of K,,, an average value of k f = S.4 set.-', then 8 , = :3 X 1 0 4 set.-'. T h e conclusion t h a t exchange between I and I I occurs via an Sx1 process agrees with our preliniiriary observation t h a t factors which affect the exchange rates are those which modify kf. &Iccordingly, rate enhancements are observed with : (a) increasing solvent polarity, (b) increasing halogen polarizability, and (c) cation-stabilizing ring substituents. \Vork is continuing. Acknowledgment.-The authors thank Professors G . IVhiteside, C. G. Swain, and H . llorawetz for helpful discussions.
bands were fornied owing to the phenylation of the complexes under the last conditions. b u t no bands owing to free pyridine. \Then the decornpositiun of any complex was evidenced by either a decrease i n the intensity of the ligand infrared bands, or a color change. or the i!)rniation of a precipitate (silver metal by a n oxidation- reduction reaction with the silver complex) over a 3-clay period t h a t complex was discarded. The phenyl source used was N-nitroso-synz-diphenylurea which was completely decornposetl a t 23' over a :$day period under the reaction cuntlitions. This phenyl ( 8 ) \Ye t h a n k Dr I< W a a c k a n d 5 1 i s b SI D o r a n for t h e l i i w - t e m p e r a t u r e ultravi,,let d a t a . source was prepared by the known method4 ant1 also i Y ) T h i s c i i m p a r e s t o K , , = 2.1 X I O - ' for I in ClaCCHCIg a t 20' [ A G. bl- the reaction of diphenylurea with riitrosylsuliuric E v a n s A Price, a n d J. H. T h o m a * , 7 ' 7 a n s . F a r a d o 4 Soc., 62, X i 2 ( l < l X ) 1 . acid generated in sitir by the action o f water up(m THE Do\\- CHEMICAL COMPAXY 13. 1.1. FREEDMAS nitrosylsulfuric anhydride. EASTERSRESEARCH LABORATORY r\. E. V O L ~ S C The pure isomeric phenylpyridines were prepared b y FRAMINGHAM, MASSACHUSETTS 1.. R . SASDEL the phenylation of pyridine by- a standard method: RECEIVED .*UCUST 5, 1964 and separation of the three phenylpyridines by preparative thin layer chromatography. The picrates of the separated samples agreed with those reported previously.A llixtures oi the isomers, both prepare(1 and T h e Phenylation of Pyridine-Metal Complexes from the reactions, could be separated and their relative amounts measured by gas chromatography using Sir : specially prepared columns. The reliability of the T h e chemical reactions of coordinated ligands have method for isomer determination was checked and the been an area of recent interest to others,' and also results are : known mixture, : 3 9 I : :39.9: 2 1 . ( I : gas to us in terms of their iree-radical chemistry.2 T o chromatographic integration values, 11.5: :W.2 : 2 2 . 2 : further this inquiry, a set of experiments was designed column factor. 0.94: 1 . IO:0.95: and calculated values. whereby phenyl radicals were caused t o react with 3 S . 6 : :HO: Z3.2. I t was shown t h a t the isolation propyridine dissolved in S.N-dirnethylioritiaiiiide and in cedures were sufficiently efficient to begin with 0.4s g . separate experiments with a group of pyridine -metal of products in a 70.9: 1S.9: 1 0 . 1 ratio anti obtained coniplexes dissolved in the same solvent. 0.47g. in a 7 1. ( I : 19.6: 9.*5ratio. LVhcn these niethotls AIlarge number of complexes of pyridine were prewere applied to phenylation reaction mixtures involving pared, and the ones indicated in Table I were found to coniplrxes. the d a t a in Table I were obtained. be completely stable t o the reaction conditions (all .Itypical reaction involved dissolving I(;,; E. ( I ) . ( I ~ ! ) analyses were satisiactory) , This stability was ascermolej of tli~~~-ricliiiezinc~I I ) thiocyanate in SO ml. of tained by using the pyridine ligand bands in the intli~nethylfor~iia~iii~le, followed by the rapid additicin frared." The stable coriiplexes showed no change in of :N Ie. l s o n , .Valure, 196,,572 (1962). i i i J. C h a t t a n d I-, A . D u n c a n s u n , J . C h r m . SOL., 2939 ( 1 9 , 3 ) , see also sisting of arbitrary orientation about the i axis 13 1' C r a i g a n d G I l o g g e t t . i b r d . 1189 (1963). X very good approximation t o the molecular orienta1 8 ) I B L I R e s e a r c h L a b o r a t o r y . San J o s e . Calif.. t o w h o m inquiries should h e 5ent tion finally found was obtained by comparison of values R O YJ . G R I T T E R ~ of I< = ZliFo, - , F CZ L>EPARTMEST O F CHEMISTRY ~ Fo , computed for various ARTHURW'. GODFREY orientations from about 1 Oy0 of the observed diffracI-SIYERSITY O F COSSECTICUT S T O R R SCOSSECTICUT , tion maxima. The minimum value of li yielded a RECEIVED X U G ~ S 5, T 1961 structure which later comparison showed was very similar to the (PhAlN P h ) 4 structure, kindly communicated to us by XV. s. LIcDonald. However, the C Structure of the Dimer of Tetraphenylcyclobutadiene atoms of the previously assumed C, cube moved considerably, during the course of least-squares refinement, Sir: to the final positions shown in Fig. 1. Clearly, A three-dimensional X-ray diffraction study of Cs- this refinement has yielded the octaphenylcyclooctatetP h u , " ? where P h is C6H5,has yielded the octaphenylraene structure. The present value of /i is (1.12 for cyclooctatetraene structure. These results exclude the the 1627 observed reflections, 1.4 5 F l r k i 5 3336, and octaphenylcubane structure, as well as the tetrabithe thermal motion is highly anisotropic. Hence we phenylcyclooctane formula4 which had been rendered considered the possibility t h a t octaphenylcubane might improbable earlier on spectroscopic e ~ i d e n c e . ~ be transformed within the single crystul to octaphenylIi'e have confirmed the previously reported3 crystal cyclooctatetraene upon exposure to X-rays. Theresynimetry of I& a , the four molecules of CsPhqper unit fore, a sample previously unexposed to X-rays was cell, and the unit cell diniensions of a = 19.49 and c examined first by infrared and then by Kaman tech= 1 0 . ( 5 -4. The compound (PhXl?JPh)4, in which the niques, exposed to X-rays for a day. and then re-exA1 and X atoms are arranged a t the corners of a c ~ b e , ~ , ~ amined by infrared and Raman methods. N o evidence has the same space group and four molecules per unit of transformation of the molecule by X-ray irradiation cell; furthermore, its lattice dimensions of a = 20.0 could be detected. Hence, we conclude that the origiand r = 10.9 are increased over those for CbPhR nal sample as prepared is indeed octaphenylcycloocby an amount which seemed consistent with an initial tatetraene. The intermolecular contacts are, however, assumpt.ion of a slightly smaller cube for the Cn unit. primarily determined by the phenyl groups, which are Consequently, we chose a s a trial molecular structure a oriented within the molecule in such a way t h a t an a-H cube of eight C atoms to each of which was attached a atom of one phenyl group points toward the center of phenyl group having the C-Ph bond along a body the closest neighboring benzene ring. This suggestion diagonal of the cube, and having the C6H6plane oriented of a "dimple" toward the center of a benzene ring was , 1) H H F r e e d m a n , J A n i C h r m Coc , 83, 214.5 (1961). first noted in the intermolecular packing of the biphen2 ) fl H B r a y e . \T' H u h e l . a n d I C a p l i e r . tbid , 83, 1106 (1961) ylene crystal.* ~:i, Ii H F r e e i l n i a n and 1) R P e t r r s e n i b r d , 84, 2837 (1962). 1, R C C 0 u k 5 0 n a n d 1) IT' J o n e s , Z'roc ChPm. Soc , 11.5 (1963) The internal angles of the tub-shaped cyclooctatetH H F r e e d m a n a n d R S G o h l k e , tbiii , 249 (1963) raene (COT) ring are 1%0°, in agreement with pre-
I c l ) o n a l d . , b i d . . 366 (1962) K R X l c l ~ ~ ~ ann ~d U' l d S h1cl)onald. ibrd , 3 8 2 (1R6,'O
( 8 ) J \Vaqer a n d C S
1.11,
J A m ( - ' h i m ';or
6 6 , XO:{.i ( l ! r l l )
