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Organic metals : studies related to the synthesis of acceptors derived from TCNQ 1979

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ORGANIC METALS: STUDIES RELATED TO THE SYNTHESIS OF ACCEPTORS DERIVED FROM TCNQ by Gerald Bruce Hammond B . S c , P o n t i f i c i a Universidad C a t o l i c a de Peru, 1975 A Thesis Submitted i n P a r t i a l F u l f i l l m e n t of the Requirements f o r the Degree of Master of Science i n The Fa c u l t y of Graduate Studies (Dept. of Chemistry) We accept t h i s t h e s i s as conforming to the required standard The U n i v e r s i t y of B r i t i s h Columbia A p r i l , 1979 © Gerald Bruce Hammond, 1979 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f Chemistry The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 H a t P May 16, 1979 ABSTRACT Since a report that the complex of TTF.TCNQ showed novel s o l i d s t a t e p r o p e r t i e s i n c l u d i n g high room temperature c o n d u c t i v i t y , there has been considerable i n t e r e s t i n the study of these so c a l l e d "organic metals." This t h e s i s describes the s y n t h e s i s of new acceptors derived from TCNQ. F i r s t the synthesis of 2-methoxycarbonyl-7,7,8,8-tetracyanoquino- dimethane (56) i s presented. Bromination of methyl 2,5-dimethylbenzoate followed by treatment w i t h sodium cyanide y i e l d e d the dicyano compound 60 which was converted to the dihydro-TCNQ 62_ v i a the corresponding phenylenetetracyanodiacetate intermediate. Oxidation of 6J2 a f f o r d e d 2- methoxycarbonyl-7,7,8,8-tetracyanoquinodimethane (56) , which was found to be unstable. The synthesis of 2,3-dimethoxycarbonyl-7,7,8,8-tetra- cyanoquinodimethane was attempted i n the f o l l o w i n g manner: the D i e l s - Alder c y c l i z a t i o n of trans,trans-2,4-hexadiene and dimethyl a c e t y l e n e d i - carboxylate followed by dehydrogenation of the adduct gave dimethyl 3,6- dimethylphthalate. B e n z y l i c bromination of t h i s m a t e r i a l followed by displacement of the bromines by cyanide y i e l d e d the dicyano compound 73. However, s e v e r a l attempts to convert _73 to the corresponding t e t r a e s t e r 78 were uns u c c e s s f u l . The s y n t h e s i s of 2,3-dimethyl-7,7,8,8-tetracyanoquinodimethane i s presented. The intermediate 2,3-dimethylcyclohexane-l,4-dione (87) was prepared from 2,3-dimethylphenol by standard means. I t was then condensed w i t h m a l o n o n i t r i l e , and the product was t r e a t e d w i t h bromine/pyridine to give the dihydro-DMTCNQ 89. When t h i s compound was treated w i t h a mixture of palladium and s u l f u r at 180°C the d e s i r e d 2,3-dimethyl-TCNQ 83 was obtained i n low y i e l d . - i i i — The second part of t h i s t h e s i s describes the preparation of 11,11, 12 ,12-tetracyano-4,5,9,10-tetrahydropyreno-2,7-quinodimethane (TCNTP) from mesitylene. This compound was bisbrominated to give 3,5-bis- (bromomethyl)toluene, which was then coupled with 3,5-bis(mercaptomethyl)- toluene to produce the dithia[3.3jmetacyclophane 98. This was converted to the dimethyl[2.2 jmetacyclophane 9_6 v i a W i t t i g rearrangement followed by r e d u c t i o n w i t h l i t h i u m i n l i q u i d ammonia. This cyclophane was then brominated and the r e s u l t i n g dibromo compound was converted to the corresponding dicyano-94. The l a t t e r compound was tr e a t e d w i t h bromine i n the presence of i r o n powder to produce 2,7-bis(cyanomethyl)-4,5,9,10- tetrahydropyrene. I n t r o d u c t i o n of the remaining two n i t r i l e groups was accomplished v i a use of the tetr a c y a n o d i a c e t a t e intermediate 9_2. H y d r o l y s i s and d e c a r b o x y l a t i o n of 9_2 followed by o x i d a t i o n w i t h NBS/triethylamine at -78°C furnished the des i r e d TCNTP (90). 7 £  —v- Table of Contents Page T i t l e Page i Abstract i i Table of Contents v L i s t of I l l u s t r a t i o n s v i L i s t of Schemes v i i Acknowledgements v i i i 1. I n t r o d u c t i o n 1 2. General Background 2.1 TCNQ Complexes and S a l t s 4 2.2 Extended TCNQ's 16 2.3 Su b s t i t u t e d TCNQ's 23 3. Results and D i s c u s s i o n 3.1 Synthesis of s u b s t i t u t e d TCNQ's 29 3.2 Synthesis of 11,11,12,12-tetracyano-4,5,9,10- 48 tetrahydropyreno-2,7-quinodimethane. 3.3 O v e r a l l r e s u l t s 64 Experimental 66 Bi b l i o g r a p h y 93 S p e c t r a l Appendix 97 - v i - L i s t of I l l u s t r a t i o n s Page 1. Scale of approximate c o n d u c t i v i t i e s . 2 2. Dimensions and r e l a t i v e c o n d u c t i v i t i e s of a 9 TTF.TCNQ c r y s t a l . 3. Temperature dependence of d.c. c o n d u c t i v i t y (o) 10 of TTF.TCNQ. 4. a) C r y s t a l s t r u c t u r e of TTF.TCNQ 11 b) Molecular overlap i n the columnar stacks of TTF and TCNQ. 5. Charge m i g r a t i o n using a hopping model. 13 6. UV-Vis spectrum of 2,7-bis(dicyanomethyl)-4,5,9,10- 60 tetrahydropyrene a f t e r treatment with aqueous bromine. 7. UV-Vis spectrum of TBA + TCNDQ~ and TBA + TCNTP~(114). 63-64 - v i i - L i s t of Schemes Page I. Synthesis of TCNQ. 5-6 I I . Synthesis of TTF. 9 I I I . Synthesis of TNAP (14). 17 IV. Improved synt h e s i s of TNAP (14). 18 V. Synthesis of the dihydro-TCNDQ 27. 20 VI. Oxidation s t a t e s of TCQQ (28). 22 V I I . Attempted syn t h e s i s of TCQQ (28). 23 V I I I . General method f o r the prep a r a t i o n of 24 s u b s t i t u t e d TCNQ's. IX. Synthesis of some p-xylylene d i h a l i d e s . 24 X. Synthesis of tetrafluoro-TCNQ (42) and 25 2,5-dicyano-TCNQ (43). XI. Synthesis of the polyurethane ^8_. 28 X I I . P r e p a r a t i o n of MTCNQ (49). 29 X I I I . Synthesis of 2-methoxycarbonyl-7,7,8,8-tetracyano- 33 quinodimethane (56). XIV. Synthesis of 3,6-bis(cyanomethyl)phthalic 39 anhydride (67). XV. Proposed synthesis of 2,3-dimethoxycarbonyl-7,7,8,8- 42 tetracyanoquinodimethane (115). XVI. Proposed route f o r the synth e s i s of 2,3-dimethyl- 45-46 TCNQ (83) . XVII. Proposed synthesis of TCNTP (90) from 5,13-dimethyl- 49-50 [2.2]-metacyclophane (96). XVI I I . A l t e r n a t e pathways to anti-5,13-dimethyl[2.2]meta- 52 cyclophane (96). XIX. Synthesis of 6,15-dimethyl-2,11-dithia[3.3]meta- 52 cyclophane (98) . - v i i i - Acknowledgements I am very g r a t e f u l to Dr. L a r r y Weiler f o r h i s guidance, kind encouragement and understanding throughout my period of research. I a l s o wish to express my g r a t i t u d e to a l l the members of the Organic Metals group, past and present, f o r t h e i r many h e l p f u l d i s - cussions. S p e c i a l thanks are due to Drs. Y. Hoyano and M. R. Bryce, and Ms. J . Lee. I a l s o thank Anna Wong f o r typing the manuscript. I f a man does not keep pace with h i s companions, perhaps i t i s because he hears a d i f f e r e n t drummer. Let him step to the music which he hears, however measured or f a r away... H. D. Thoreau A mis padres, con todo e l amor que s o l o e l l o s son capaces de i n s p i r a r -1- 1. INTRODUCTION In 1973 researchers at JohnsHopkins U n i v e r s i t y 1 d e t e c t e d signs of very high c o n d u c t i v i t y (around 1500 ohms *"cm 1 at room temperature) from a 1:1 organic complex of 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) (1_) , and t e t r a t h i a f u l v a l e n e (TTF) (2) . There q u i c k l y followed 2 an e x c i t i n g and c o n t r o v e r s i a l report from a group at U. of Pennsylvania who claimed that some c r y s t a l s of TTF.TCNQ showed "superconducting f l u c t u a t i o n s , " w i t h increases i n c o n d u c t i v i t y at 58°K of s e v e r a l hundred times the room temperature value. Research i n the f i e l d of organic conductors has been very a c t i v e ever s i n c e . VO S s - ^ 2 This new c l a s s of organic s o l i d s , t y p i f i e d by TTF.TCNQ, d i s p l a y s unexpected " m e t a l l i c l i k e " behavior over a wide temperature range. The ma t e r i a l s are composed s o l e l y of non-metallic atoms, such as carbon, n i t r o g e n , sulphur and oxygen; hence, the term "organic metal" has been used to describe these s o l i d s . These organic metals are part of a l a r g e r c l a s s of compounds known as charge-transfer s a l t s ; they are formed when an e l e c t r o n i s t r a n s f e r r e d from an organic donor to an acceptor molecule. The i n t e r e s t i n the novel transport p r o p e r t i e s of these organic metals can be f u l l y appreciated by comparing the c o n d u c t i v i t i e s of most organic compounds: t y p i c a l values are 10 1 1 to 10 7 ohm 1cm 1 ( i n s u l a t o r s ) -5 -3 -1 -1 and 10 to 10 ohm cm (semiconductors). However, the complex of hexamethylene-tetraselenafulvalene (HMTSF) and TCNQ has a room tem- the highest of any known 3 -1 -1 perature c o n d u c t i v i t y of 2 x 10 ohm cm organic substance. Organic Metals Nichrome S i l i c o n Most molecular c r y s t a l s l o g a |+ 6 Metals + 4 + 2 0 Molten s a l t s -2 -4 A l k a l i TCNQ s a l t s -10 Carbazole-iodine complex -12 Ferrocene 1-14 -16 Anthracene Figure 1. Scale of approximate c o n d u c t i v i t i e s The organic molecules which form these complexes are r e l a t i v e l y l a r g e and planar. They form stacks i n the s o l i d s t a t e w i t h t h e i r T T - molecular o r b i t a l s i n t e r a c t i n g s t r o n g l y along the sta c k s , and only weakly -3- between them, which gives them a quasi-one dimensional nature that i s r e f l e c t e d i n t h e i r p h y s i c a l and e l e c t r o n i c p r o p e r t i e s . TTF.TCNQ was i d e n t i f i e d as the f i r s t organic metal and has become the prototype organic conductor. The c r y s t a l s are h i g h l y a n i s o t r o p i c , and d i v e r s e s t u d i e s of t h e i r e l e c t r o n i c and p h y s i c a l p r o p e r t i e s are a l l c o n s i s t e n t w i t h a m e t a l l i c nature at room temperature. The d r i v i n g force behind the considerable amount of research done on one-dimensional metals has been the search f o r high temperature s u p e r c o n d u c t i v i t y . The quest f o r a t o t a l l y organic superconductor remains a major but unsuccessful goal. Nevertheless, a by-product of t h i s ambition has been the wealth of e x c i t i n g physics and chemistry which came as a r e s u l t of these endeavors, and that i s f i n d i n g p r a c t i c a l a p p l i c a t i o n s i n an ever growing number of areas, such as e l e c t r o l y t i c c a p a c i t o r s , s o l i d s t a t e b a t t e r i e s and p r i n t i n g systems. -4- 2. GENERAL BACKGROUND 2.1 TCNQ Complexes and S a l t s Research i n organic conductors has been progressing f o r some time and the published data have centered around charge-transfer complexes, f r e e r a d i c a l s and free r a d i c a l s a l t s , long chain compounds and polymers. Charge t r a n s f e r complexes have been studied e x t e n s i v e l y although i n many cases t h e i r s t r u c t u r e s were not w e l l c h a r a c t e r i z e d . I t was found that -3 a s u r p r i s i n g m i n o r i t y of these complexes had c o n d u c t i v i t i e s above 10 ohm "'"cm \ These types of complexes c o n t a i n i n g i o d i n e and aromatic hydrocarbons or aromatic amines provided the f i r s t examples of moderately high e l e c t r i c a l c o n d u c t i v i t y i n organic m a t e r i a l s ( g r a p h i t i z e d complexes are not i n c l u d e d ) . I t was found that tetracyanoethylene (TCNE) (_3) could polymerize with 4 5 some metal chelates ' forming charge t r a n s f e r complexes that had r e - l a t i v e l y low r e s i s t i v i t i e s (around 0.04 ohm cm). These r e s u l t s increased the e x p l o r a t i o n of the chemistry of other unsaturated systems c o n t a i n i n g the h i g h l y e l e c t r o n e g a t i v e n i t r i l e group, p a r t i c u l a r l y , s t r u c t u r e s i n which the double bond of TCNE i s replaced by a conjugated system. On the other hand, quinones are known to be good e l e c t r o n acceptors, a l s o forming s t a b l e complexes with some e l e c t r o n donors.^ C—C NC / \ CN 3 -5- NC •CN NC CN TCNQ (1) 1 In 1962, D. S. Acker and W. R. H e r t l e r ' synthesized a s u b s t i t u t e d quinodimethane , namely 7 ,7 ,8,8-tetracyanoquinodimethane (1_), a compound w i t h s e v e r a l e x c e p t i o n a l p r o p e r t i e s ; among them the formation of s t a b l e anion r a d i c a l d e r i v a t i v e s which have unusually low e l e c t r i c a l r e s i s t i - v i t i e s i n the s o l i d s t a t e . The synthesis of TCNQ i s i l l u s t r a t e d i n Scheme I. I t in v o l v e s the Knoevenagel condensation of 1,4-cyclohexane- dione (4) with m a l o n o n i t r i l e i n the presence of the Prout c a t a l y s t , 8- a l a n i n e , to give the tetrahydro intermediate 5̂ , i n 94% y i e l d ; t h i s compound i s then dehydrogenated e i t h e r w i t h bromine/pyridine at 0°C i n a c e t o n i t r i l e , or w i t h manganese d i o x i d e by b r i e f r e f l u x i n g i n g toluene. 4 5 -6- Vr id ine ^ T C N Q (1) Scheme I . Synthesis of TCNQ ( l ) 7 The unique c h a r a c t e r i s t i c s of t h i s molecule, namely, i t s high e l e c t r o n a f f i n i t y , i t s planar s t r u c t u r e and high symmetry, allowed the formation of e l e c t r i c a l l y conducting donor-acceptor complexes, w i t h TCNQ as the 9 acceptor. According to Melby et a l . these complexes could be sub- d i v i d e d i n t o three groups c h a r a c t e r i z e d by t h e i r composition and con- duction behavior: i ) TCNQ TT Complexes. These are c r y s t a l l i n e complexes formed w i t h aromatic hydrocarbons, amines, c h e l a t e s , and other n e u t r a l compounds, _3 u s u a l l y i n a r a t i o of 1:1. They have c o n d u c t i v i t i e s ranging from 10 -12 -1 -1 to 10 ohm cm . From these e a r l y s t u d i e s i t was c l e a r that there was no c o r r e l a t i o n between the b a s i c i t y of the donor and the e l e c t r i c a l c o n d u c t i v i t y of the complex. S t e r i c f a c t o r s and c r y s t a l packing seemed to play an important r o l e . i i ) TCNQ s a l t s of the composition M + n(TCNQ') . The c o n d u c t i v i t y of s a l t s of t h i s group ( M + n stands f o r a metal ion or an organic cation) i s u s u a l l y i n the range of 10 ^ to 10 ^ ohm "'"cm "*". The esr absorption i s very weak. U s u a l l y the c o n d u c t i v i t y i n these simple s a l t s i s i s o t r o p i c . i i i ) TCNQ S a l t Complexes of the composition M + n(TCNQ r)^ TCNQ°. These complex TCNQ s a l t s which, beside the TCNQ' r a d i c a l anion, contain -3 a n e u t r a l TCNQ molecule, d i s p l a y high c o n d u c t i v i t i e s ranging from 10 to +2 -1 -1 10 ohm cm . They show v a r i a b l e esr absorption. Furthermore, the -7- c o n d u c t i v i t y of s i n g l e c r y s t a l s d i s p l a y s strong anisotropy. Table I shows some examples of the d i f f e r e n t molecular complexes of TCNQ. Table I . C o n d u c t i v i t i e s of some TCNQ Complexes and S a l t s . Type Tr-complex H 2N Me2N Donor NH, NMe, Con d u c t i v i t y (ohm "'"cm L ) 3 x 10 -4 10 -6 Simple s a l t s Cs + 3 x 10 -5 Cu 5 x 10 -3 Complex s a l t s 100 ( C 2 H 5 ) 3 N 1.5 x 10 -1 During the mid 1960's the search f o r new and b e t t e r organic semi- conductors f a i l e d to y i e l d a true organic metal. Some of the d i f f e r e n t t h e o r i e s of organic c o n d u c t i v i t y i n organic s o l i d s that emerged were c o n t r o v e r s i a l and lacked experimental support. However, some f a c t s received a t t e n t i o n . I t was r e a l i z e d that i f a low r e s i s t i v i t y 1:1 complex i s to be formed, there should be con s i d e r a b l e , but not complete, charge t r a n s f e r . Acker and B l o m s t r o n ^ found that a c o n d i t i o n f o r high c o n d u c t i v i t y -8- i s that the c a t i o n be a planar, aromatic, h e t e r o c y c l i c molecule. Further- more, Le B l a n c 1 1 suggested the importance of having a p o l a r i z a b l e c a t i o n . 12 In 1965, Melby made a complex between N-methylphenazinium (NMP)(6) and TCNQ. I t s s i n g l e c r y s t a l c o n d u c t i v i t y reached 380 ohm "'"cm 1 at room temperature. This remained the most conductive organic s o l i d u n t i l 1973, when P e r l s t e i n , Cowan et^ a l 1 mixed TCNQ and TTF to produce a new compound with e x c i t i n g and novel s o l i d s t a t e p r o p e r t i e s , i n c l u d i n g a room tem- perature c o n d u c t i v i t y ranging from 600 to 1800 ohm 1cm 1 ( v a r i a b l e from sample to sample). The c o n d u c t i v i t y of t h i s 1:1 complex increases w i t h decreasing temperature down to 60°K ( m e t a l l i c region) where there i s a t r a n s i t i o n to an i n s u l a t i n g s t a t e (T<60°K). The peak c o n d u c t i v i t y at T=59°K i s comparable to the c o n d u c t i v i t y found i n some metals such as 4 -1 -1 lead and t i n (around 10 ohm cm ). The organic donor, TTF, i s a planar molecule w i t h an extensive TT e l e c t r o n system; i t i s h i g h l y symmetric and very s i m i l a r i n s i z e to TCNQ. This molecule i s a l s o h i g h l y p o l a r i z a b l e because of the presence of four s u l f u r atoms, and i t can be r e a d i l y o x i d i z e d to a r a d i c a l i o n , thereby number 14,15,16 13 forming conducting c a t i o n r a d i c a l s a l t s w i t h some h a l i d e s . A number of s y n t h e t i c pathways to TTF and i t s d e r i v a t i v e s are a v a i l a b l e . 16 One route to TTF developed by Melby et_ al_. (Scheme I I ) inv o l v e s depro- to n a t i o n of a 1 , 3 - d i t h i o l i u m i o n , synthesized from the commercially a v a i l a b l e dimethyl ac e t y l e n e d i c a r b o x y l a t e (_7_) and ethylene t r i t h i o - carbonate (8) . -9- c Me + C O M e -S" s- 2 Me 0 2 C • F 6 P H - ^ + 1) HOAc,A^ (T^Vc 2) p y r i d i n e , A ^ - ^ / 11 13 CH 3C0 3H ^ 2 N a P F * " 0 4 S H H - ^ S " 12 Scheme I I . Synthesis of TTF (2) 16 The 1:1 complex of TCNQ and TTF produces l u s t r o u s black p l a t e s when r e c r y s t a l l i z e d from a c e t o n i t r i l e . Figure 2 shows a diagramatic r e p r e s e n t a t i o n of a s i n g l e c r y s t a l , i n c l u d i n g approximate dimensions, along w i t h the corresponding room temperature conductivities."'" 7 This m a t e r i a l e x h i b i t s a h i g h l y a n i s o t r o p i c c o n d u c t i v i t y which reaches a 0.5 mm 5mm. -0.05mm. cr = 600-1800 ohm 1cm 1 b i o - = 150 Figure 2. Dimensions and r e l a t i v e c o n d u c t i v i t i e s of a TTF.TCNQ c r y s t a l . -10- maximum along the cry s t a l l o g r a p h i c b axis. The temperature dependence of the dc conductivity along the b axis is shown in Figure 3 . ^ The conductivity peaks at 59-60°K and begins to f a l l at lower temperatures,going through two t r a n s i t i o n s at 53°K and 38°K. The magnitude of oT /o300°K max is s t i l l a subject of controversy: i t i s found to be around 20 in most 2 cases, although a case was reported i n which the values for c e r t a i n c r y s t a l s reached as high as 150. o - ( T ) cr ( 3 0 0 K ) T ( K ) Figure 3. Temperature dependence of d.c. conductivity (a) of TTF.TCNQ 1 5 Insert shows the t r a n s i t i o n s at 53°K and 38°K. 18 The c r y s t a l structure of th i s material is shown in Figure 4. TTF.TCNQ consists of segregated, uniform columns of TTF and TCNQ molecules - l i - s t acked face-to-face along the h i g h l y conducting b a x i s . The molecular planes are t i l t e d w i t h respect to the b s t a c k i n g a x i s , and TTF and TCNQ have opposite t i l t s r e l a t i v e to each other. The i n t r a s t a c k distances are sh o r t e r than the van der Waals r a d i i of TTF or TCNQ, and permit a strong overlap of Tr-molecular o r b i t a l s along the s t a c k s . a ) \ W__x___y/ X___X_X X / X I7 " b ) X \ "A \ Figure 4. a) C r y s t a l s t r u c t u r e of TTF.TCNQ. b) molecular overlap i n the columnar stacks of TTF and TCNQ, showing the l a t e r a l displacements of t h e i r molecular centres (5). Above the t r a n s i t i o n temperature the TTF and TCNQ molecules are uniformly spaced w i t h i n the stack. As mentioned e a r l i e r , TTF i s a good e l e c t r o n donor, and TCNQ i s a 18 good e l e c t r o n acceptor. According to s e v e r a l recent i n v e s t i g a t i o n s , the charge t r a n s f e r i n the s o l i d s t a t e i n TTF.TCNQ amounts to 0.6±0.01 of one e l e c t r o n . In TCNQ r a d i c a l anion the HOMO i s a TT-MO. The i n t e r a c t i o n of these MO's on two adjacent TCNQ w i t h i n the same stack i s bonding, when each -12- uiolecule i s d i s p l a c e d l a t e r a l l y w i t h respect to the molecule below. This gives r i s e to the "ring-double bond" overlap shown i n Figure 4. In a d d i t i o n , c a l c u l a t i o n s of the energy surface f o r the dimer (TCNQ^ show a w e l l defined minimum when <S, d i s t a n c e between the molecular centres °19 ° (Figure 4 ) , i s 2.2A (observed v a l u e : 2.14A). S i m i l a r c a l c u l a t i o n s on TTF + ions show a strong i n t e r a c t i o n of the HOMO's, but the energy surface c a l c u l a t i o n s f o r TTF dimer show a minimum only f o r the case of two TTF's stacked d i r e c t l y over each other. The f a c t that t h i s type of TTF packing has been observed i n the h i g h l y conducting mixed valence h a l i d e s such as 13c TTF.I 7 1 , i n d i c a t e s that the i n t e r a c t i o n of HOMO's on the TCNQ stack and c r y s t a l forces are re s p o n s i b l e f o r the packing of the s o l i d i n TTF.TCNQ. The p i c t u r e f o r TTF.TCNQ that emerges at t h i s point i s one of segregated stacks c o n t a i n i n g p l a n a r , p a r t i a l l y charged molecules arranged so as to al l o w r e l a t i v e l y strong T r - o r b i t a l overlap w i t h i n the stack; thus p a r a l l e l conducting l i n e a r chains are formed which are only weakly coupled. There i s s t i l l controversy over which d e s c r i p t i o n best e x p l a i n s the c o n d u c t i v i t y i n these compounds. A u s e f u l model that describes the room temperature c o n d u c t i v i t y of TTF.TCNQ can be obtained by extending the MO approach of an i n d i v i d u a l TCNQ and TTF + to an i n f i n i t e array of l i n e a r chains. Thus the corresponding HOMO's of the r a d i c a l ions generate a conduction band c o n s i s t i n g of MO's d e l o c a l i z e d along the stack. C a l c u l a t i o n s ' using the extended Huckel Method of Hoffmann, showed that the l a r g e s t overlap occurs along the h i g h l y conducting b a x i s , and that the TCNQ band i s wider than the TTF band. There can be m e t a l l i c type c o n d u c t i v i t y i n the TCNQ or TTF band as long as i t i s p a r t i a l l y f i l l e d , as i n normal metals. These 1-D organic s o l i d s , however, are subject to l a t t i c e d i s - 21 t o r t i o n s ( P e i e r l s i n s t a b i l i t y ) that can create an energy gap i n the 20 -13- e l e c t r o n i c band. In the case of a h a l f - f i l l e d band t h i s w i l l cause the molecules w i t h i n a stack, to dimerize. This w i l l lead to a semiconducting 22 behavior. I t has been proposed that such a d i s t o r t i o n may be suppressing the m e t a l l i c c o n d u c t i v i t y at 59°K i n TTF.TCNQ. The p a r t i a l , as opposed to f u l l , charge t r a n s f e r i n TTF.TCNQ has two important consequences: i t provides c r y s t a l s t a b i l i z a t i o n by minimizing i n t r a s t a c k r e p u l s i v e i n t e r a c t i o n s , and i t lowers on s i t e e l e c t r o n - e l e c t r o n r e p u l s i v e i n t e r a c t i o n s i n both the donor and acceptor s t a c k s . This e f f e c t i s important i f we are to consider another approach to the c o n d u c t i v i t y i n these systems: that i s , a hopping model, i n which charge migrates along the donor and acceptor s t a c k s , w i t h some donors bearing two p o s i t i v e charges and some acceptors bearing two negative charges. This i s i l l u s t r a t e d i n Figure 5 . An a d d i t i o n a l requirement then, would be that these molecules D + D + D+. • D + D + D D + D + . . D+ D* A A A A ~ A ~ A = A" A : A" A (a) 2D D + D 2 A - ± A +• A Figure 5 . Charge migration using a hopping model; (a) stacked charge t r a n s f e r s a l t ; (b) the same s a l t under the e f f e c t of an e l e c t r i c f i e l d . -14- s h o u l d be a b l e to l o c a l i z e two c harges. A measurement of the redox p o t e n t i a l s o f the d i f f e r e n t s p e c i e s i n s o l u t i o n c o u l d be u s e f u l i n p r o v i d i n g some i n f o r m a t i o n and s u g g e s t i o n s f o r the d e s i g n of new o r g a n i c m e t a l s . The redox p o t e n t i a l s would p r o v i d e a measure of the e l e c t r o n a c c e p t i n g or d o n a t i n g a b i l i t y of the components i n the charge t r a n s f e r s a l t D+ + e" D° E 1 D A° -H e" A E 1 A D + A D + 4- A" E - E = AE 1A 1D F i n a l l y , an approach that r e g a r d s the o r g a n i c metals as r e s u l t i n g from the i n t e r m o l e c u l a r m i g r a t i o n of a r o m a t i e i t y was f i r s t proposed by 23 P e r l s t e i n . Under t h i s c o n c e p t , the most e f f i c i e n t c o n d u c t o r s should c o n t a i n m o l e c u l e s (a) whose r a d i c a l i o n s form a new a r o m a t i c s e x t e t upon o n e - e l e c t r o n o x i d a t i o n or r e d u c t i o n , and (b) whose a r o m a t i e i t y can m i g r a t e by mixed v a l e n c e i n t e r a c t i o n . S i n c e the i n i t i a l r e p o r t on TTF.TCNQ, an ever-growing number of new compounds have been added to t h i s c l a s s of m e t a l l i c - l i k e o r g a n i c s o l i d s . Much of t h i s e f f o r t has focused on p r e p a r i n g d e r i v a t i v e s of TTF, e i t h e r through replacement of the r i n g heteroatoms, or by a d d i t i o n of s u b s t i t u e n t s T a b l e I I c o n t a i n s the e l e c t r i c a l c o n d u c t i v i t y d a t a of TCNQ s a l t s of TTF and some of i t s d e r i v a t i v e s . From t h i s T nhle i t i s apparent t h a t s u b - s t i t u t i o n on the b a s i c s k e l e t o n of TTF may produce s o l i d s that have s i m i l a r -15- c o n d u c t i v i t i e s Co TTF.TCNQ. Indeed, the s u b s t i t u t i o n of selenium f o r s u l f u r i n TTF seems to improve the room temperature c o n d u c t i v i t y . This may r e s u l t from the greater o r b i t a l extent of selenium, which could lead to stronger overlap along the donor stack and, hence, to an increased band width. Nevertheless, the maximum c o n d u c t i v i t y f o r these new s a l t s i s s i m i l a r to that of TTF.TCNQ, although the m e t a l l i c s t a t e has been s t a b i l i z e d to higher temperatures. Table I I . E l e c t r i c a l c o n d u c t i v i t y data on the TCNQ s a l t s of TTF and d e r i v a t i v e s R C o n d u c t i v i t y data f o r TCNQ s a l t " 2 ^ * 2 a R T b a c T d R L . i a m a x ,a P Name ohm cm ohm~ icm - 1 (°K) T e t r a t h i a f u l v a l e n e X ,=S,R.. . =H 400-500 >10 4 58 (TTF) 1 - 4 D i s e l e n a d i t h i a - X =S, X =Se, 500 3 x l 0 3 64 fu l v a l e n e x' _ (DSDTF) R 1 - 4 _ H Tetraselena- X ^ ^ S e , RL_4=H 800 >10 4 '40 fu l v a l e n e (TSF) Hexamethylene- X 1 _ 4 = S ' R i 2 = R 3 4 5 0 0 2 x l 0 3 80 t e t r a t h i a f u l v a l e n e , r„ >. ' ' (HMTTF) -(CH 2; 3 -4 Ben z o - t e t r a t h i a - X.. . =S, R.. = 10 fu l v a l e n e , R3,4 ( C 4 H 4 ) Tetramethyl - TSF X, ,=Se, R, ,= 10 3 6 x l 0 3 71 1-4 1-4 C H 3 Hexamethylene - TSF X L_ 4=Se, ^ 2= 2 x l 0 3 7 x l 0 3 45-75 e R 3 > 4 = ( C H 2 ) 3 a b s i n g l e - c r y s t a l measurement. a = room temperature c o n d u c t i v i t y . RT , c d a = maximum c o n d u c t i v i t y at T . Temperature of maximum c o n d u c t i v i t y , max J p J e S t i l l h i g h l y conducting below T^. -16- Some of the chemical and structural features that may be required 2 15 2 A- for metallic behavior are summarized below: ' ' - the existence of unpaired electrons within molecular units. - a uniform crystal structure consisting of parallel and segregated stacked columns of planar molecules with delocalized T T - molecular orbitals. These ir-orbitals must have significant intermolecular overlap. - large Tr-systems in which the open shell cation and anion are of similar size. - a polarizable cation - a certain amount of disorder (including doping) in the one- dimensional system may prevent a uniform periodic distortion of the la t t i c e , and thus may stabilize the metallic state. A different approach to the design of organic metals has been 25 given by Torrance. According to him, the most important properties to consider are stacking, degree of charge transfer, and stoichiometry. Although most of the characteristic features of these organic metals are widely accepted, the relative importance of each of these parameters is s t i l l a matter of discussion. 2.2 Extended TCNQ's The unpaired electron in the anion radical salts of TCNQ is largely localized on the terminal dicyano methylene groups. It is the a b i l i t y of TCNQ to accommodate two electrons at opposite ends of the molecule which distinguishes i t from most other acceptors. Another potential quino- dimethane acceptor would be 11, 12, 11 , 12 - tetracyanonaphtho-2,6- quinodimethane (TNAP)(14), an extended, conjugated analog of TCNQ. The -17- 2 6 preparation of TNAP, f i r s t described by H e r t l e r et a l . , i s shown i n Scheme I I I . The sy n t h e s i s s t a r t e d w i t h 2,6-dimethylnaphthalene (15) which was brominated w i t h NBS (N-bromosuccinimide) to y i e l d the dibromide 16. Displacement of bromide w i t h cyanide gave 1_7_ i n poor y i e l d . This was then t r e a t e d w i t h d i e t h y l carbonate and base to give d i e t h y l 2,6- naphthalenedicyanoacetate (18). Treatment of the cyano ester 18 w i t h aqueous ammonia gave the corresponding amide 1_9 as a mixture of d i a s t e r e o - raers. A f t e r p u r i f i c a t i o n , 19 was dehydrated with POC£^ to give 2,6- napht h a l e n e d i m a l o n o n i t r i l e (20). F i n a l l y , o x i d a t i o n of the d i m a l o n o n i t r i l e (20) with N-iodosuccinimide gave TNAP i n 40% y i e l d . Scheme I I I . Synthesis of TNAP (14) 26 -18- 27 This s y n t h e t i c route was l a t e r improved by Sandman and Ga r i t o with a procedure that both avoided the stereochemical problem of the e a r l i e r s y n t h e s i s , and improved the o v e r a l l y i e l d . The r e a c t i o n of 17_ with sodium ethoxide and d i e t h y l carbonate i n toluene, followed by r e a c t i o n of the r e s u l t a n t d i a n i o n w i t h cyanogen c h l o r i d e , l e d to a 60% y i e l d of d i e t h y l 2,6-naphthalene a,a,a',a'-tetracyanodiacetate (21). H y d r o l y s i s and decarboxylation of 21_ gave 20_ which was o x i d i z e d i n s i t u w i t h aqueous bromine to a f f o r d TNAP i n e s s e n t i a l l y q u a n t i t a t i v e y i e l d (Scheme IV). The anion r a d i c a l s a l t s of TNAP have compaction r e s i s t i v i t i e s s i m i l a r -19- to those reported f o r s a l t s of TCNQ. 2 6 S i n g l e c r y s t a l s of TTF.TNAP. obtained 28 v i a a slow d i f f u s i o n process , show uniform, segregated stacks of c a t i o n and anion r a d i c a l s . However, the room temperature c o n d u c t i v i t y i s only 40 ohm "*"cm 1 and e x h i b i t s l i t t l e temperature dependence; a sharp "metal- i n s u l a t o r " t r a n s i t i o n occurs at 185°K. Next i n the s e r i e s i s 13,13,14,14-tetracyanodiphenoquinodimethane (TCNDQ)(22), which has not been i s o l a t e d as a n e u t r a l species. Attempts 27 29a b to prepare i t have l e d only to formation of polymeric m a t e r i a l . ' ' However, a number of s a l t s of the anions of TCNDQ have been prepared, and 29a t h e i r p h y s i c a l p r o p e r t i e s s t u d i e d . The preparation of the dihydro- 29a TCNDQ 27_ , the immediate precursor of TCNDQ, was accomplished using biphenyl (2_3) as the s t a r t i n g m a t e r i a l . Bisbromomethylation followed by displacement of the bromide with sodium cyanide afforded the dicyano-25 which was converted to the dihydro - TCNDQ _2_7 f o l l o w i n g the procedure of 27 24a Sandman and G a r i t o (Scheme V). G a r i t o and Heeger suggested that a strong T i-conjugation between the d i s t a n t withdrawing groups i s required to maintain the molecular s t a b i l i t y . I f the conjugation i s weakened, 22 -20- 23 22 Scheme V. 27_ 26 Synthesis of the dihydro - TCNDQ 2 7 . 2 7 ' 2 9 a ' b unwanted polymerization occurs. This could explain the d i f f i c u l t y in obtaining a neutral TCNDQ; the in t e r - r i n g hydrogen repulsions could 30 account for the weakening of the Tt-conjugation. As stated previously, an analysis of the redox potentials of the donors and acceptors i n solution could serve as an experimental approxi- 24a mat ion in the evaluation of the Coulombic repulsion energies , and -21- t h e r e f o r e , i t could be a p r a c t i c a l guide i n the search f o r new donors and acceptors. Table I I I l i s t s the redox p r o p e r t i e s of some of these acceptors. a29a,31b,c Acceptor AE TCNE TCNQ 0.15 0.13 0.52 0.21 0.08 •0.57 0.29 0.03 0.17 .08 0.72 0.42 0.49 0.38 0.16 F.-TCNQ TNAP TCNDQ a) reduction p o t e n t i a l s , i n v o l t s , vs SCE i n CH^CN reference e l e c t r o d e The experimental c o n d u c t i v i t i e s of the charge t r a n s f e r s a l t s obtained from some of these acceptors are i n agreement w i t h the observed trends i n AE ( d i f f e r e n c e between the f i r s t two polarographic r e d u c t i o n p o t e n t i a l s ) . A l l complexes of TCNE are i n s u l a t o r s , whereas complexes of TCNQ and TNAP are m e t a l l i c . A few complexes of F^-TCNQ are semi-con- ductors. In the case of TCNDQ, the proximity of the two r e d u c t i o n p o t e n t i a l s would i n d i c a t e a c l e a r r e d u c t i o n of the Coulombic r e p u l s i o n s i n the d i a n i o n . 30 The search f o r l a r g e r acceptors l e d Wudl et al_. to attempt the synthesis of 2,7-bisdicyanoquinomethano-2,7,H,H-quinazolino[6,5,4-def]- q u i n a z o l i n e (TCQQ)(28). This i s a pyrene analog of TCNDQ i n which four carbon atoms have been replaced by n i t r o g e n . This s u b s t i t u t i o n was expected to both enhance the e l e c t r o n a f f i n i t y of the acceptor,and to increase the number of a v a i l a b l e o x i d a t i o n s t a t e s (Scheme V I ) . The attempted preparation of TCQQ i s o u t l i n e d i n Scheme V I I . The tetrahydro intermediate 35 could not be p u r i f i e d and was treated d i r e c t l y w i t h base i n a c e t o n i t r i l e -22- Scheme VI. Oxidation states of TCQQ (28) in the presence of either tetrabutylammonium or tetraphenylarsonium chlo- ride to give the dianion 3_0 as the only characterizable product. Unfortunately, attempted oxidations of 3J3 to 29_ or 28_ were not successful. 2.3 S u b s t i t u t e d TCNQ's A systematic study of the s y n t h e s i s of s u b s t i t u t e d TCNQ's, together w i t h the observed conducting p r o p e r t i e s of t h e i r charge t r a n s f e r complexes 31 wit h a s e r i e s of donors, has been performed by Wheland. The reported TCNQ d e r i v a t i v e s have s u b s t i t u e n t s i n the r i n g ; these includ e a l k y l groups (e.g. Me, Et, i - P r ) , halogens (F, C£, Br, I ) , ethers and t h i o - ethers (e.g. OMe, O-i-Pr, O-i-Bu, SMe), and n i t r i l e s . These syntheses most fr e q u e n t l y s t a r t e d with the corresponding p- x y l y l e n e d i h a l i d e which i n most cases could be prepared by d i r e c t b i s - chioromethylation of an a p p r o p r i a t e l y s u b s t i t u t e d benzene 3_6 as shown i n Scheme V I I I . For some d i h a l i d e s and haloethers d e r i v a t i v e s , the p- x y l y l e n e d i h a l i d e was prepared according to Scheme IX, s t a r t i n g w i t h an -24- C0 2Me Scheme V I I I . General method f o r the preparation of s u b s t i t u t e d TCNQ's. 3 1 a a p p r o p r i a t e l y s u b s t i t u t e d p-xylene 37_. The corresponding t e r e p h t h a l i c a c i d 3_8_ was converted to the a c i d c h l o r i d e 39^ which was reduced to the g l y c o l 4CL This was then t r e a t e d w i t h hydrogen h a l i d e to give the p- x y l y l e n e d i h a l i d e 4_1. Once the p-xylylene d i h a l i d e s had been obtained, Scheme IX. Synthesis of some p-xylylene d i h a l i d e s . -25- the syntheses of a l l the s u b s t i t u t e d TCNQ's were s i m i l a r , as summarized i n Scheme V I I I . For the t e t r a f l u o r o d e r i v a t i v e 4_2 and the dicyano-TCNQ 43, the f i r s t step involved i n i t i a l n u c l e o p h i l i c displacement of aromatic halogen by the anion of t e r t - b u t y l m a l o n o n i t r i l e (44). Thermolysis of the r e s u l t i n g product w i t h the l o s s of i s o b u t y l e n e , followed by o x i d a t i o n w i t h aqueous-bromine, gave the TCNQ's 4_2 and 4_3 (Scheme X). Scheme X. Synthesis of tetrafluoro-TCNQ (42) and 2,5- dicyano-TCNQ ( 4 3 ) . 3 1 a -26- A c o r r e l a t i o n of the e l e c t r i c a l c o n d u c t i v i t y of d i f f e r e n t charge 31c t r a n s f e r complexes, w i t h the redox p o t e n t i a l s of each of the components, shows that strong acceptors, f o r which complete e l e c t r o n t r a n s f e r i s most l i k e l y , give poorly conductive complexes; whereas weaker e l e c t r o n acceptors give h i g h l y conductive complexes. On the other hand, lowering donor strength to the point where s i g n i f i c a n t e l e c t r o n t r a n s f e r i s u n l i k e l y , uniformly gives poorly conductive complexes. Therefore, i t can be speculated that the c o n d u c t i v i t y w i l l increase w i t h i n c r e a s i n g amounts of charge t r a n s f e r up to a maximum o c c u r r i n g at l e s s than f u l l e l e c t r o n t r a n s f e r ; and then c o n d u c t i v i t y w i l l decrease as one e l e c t r o n t r a n s f e r i s approached. For optimum charge t r a n s f e r , the redox p o t e n t i a l s of both donor and acceptor should be c l o s e l y matched (|E -E |< 0.25 V). However, regardless of how favourable these f a c t o r s are, c o n d u c t i v i t y w i l l be poor i f the requirements of c r y s t a l s t r u c t u r e are not met. In the c h a r a c t e r i s t i c segregated stacked s t r u c t u r e of TTF.TCNQ, the spacing of the molecules i n t h e i r stacks i s c l o s e r than t h e i r van der Waals r a d i i . The consequences of t h i s c l o s e encounter have been described i n previous s e c t i o n s . S t e r i c f a c t o r s may play a major r o l e i n the c r y s t a l packing. 31c The e f f e c t of s u b s t i t u t i o n on the TCNQ r i n g with i n c r e a s i n g l y l a r g e r groups appears to have minor e f f e c t s u n t i l f i v e or s i x side chain carbons or oxygens have been added. Beyond t h i s point there i s a sudden decrease i n c o n d u c t i v i t y of the complex, and i n some cases the complex does not form at a l l . Furthermore, the lowest r e s i s t i v i t i e s are found when the acceptor length/donor length r a t i o i s approximately equal to 1, suggesting that mismatching of donor and acceptor s i z e s upsets the c r y s t a l s t r u c t u r e . The need f o r h i g h l y p o l a r i z a b l e s u b s t i t u e n t s c l o s e to the conductive stack has been suggested i n s e v e r a l recent t h e o r i e s . " ' " ' 2 ' 2 4 3 In accord with -27- t h i s , the complex of TCNQ w i t h t e t r a s e l e n a f u l v a l e n e ( i n which the s u l f u r of TTF has been replaced by heavier selenium) shows a higher c o n d u c t i v i t y at room temperature than does TTF-TCNQ. The c o n d u c t i v i t y of the com- plexes of s u b s t i t u t e d TCNQ's increases when a c h l o r i n e s u b s t i t u e n t i s replaced by the heavier and more p o l a r i z a b l e bromine or i o d i n e atom. This e f f e c t i s cumulative i n that two bromines or i o d i n e s are more e f f e c t i v e than one. However, there i s only a s l i g h t increase i n con- d u c t i v i t y i n going from bromine to i o d i n e , suggesting that the l a r g e r s i z e of the i o d i n e might be a l t e r i n g other v a r i a b l e s . Some a l k y l d e r i v a t i v e s of TCNQ have been used to form charge t r a n s f e r s a l t s w i t h d e r i v a t i v e s of TTF and TSF. Results from these stu d i e s show that when sm a l l amounts of methyl-TCNQ 49_ are added as a dopant to TSF.TCNQ, the c h a r a c t e r i s t i c sharp phase t r a n s i t i o n i s broadened, 4 and the c o n d u c t i v i t y at low temperatures i s 10 times greater than f o r 32 the corresponding undoped system. I n t e r e s t i n s y n t h e s i z i n g on organic polymer having m e t a l l i c con- d u c t i v i t y l e d to the p r e p a r a t i o n of a polymer c o n t a i n i n g c o v a l e n t l y 33 bound TCNQ's. H e r t l e r synthesized 2,5-bis(2-hydroxyethoxy)-7,7,8,8- tetracyanoquinodimethane (45) s t a r t i n g from 1,4-bis(2-acetoxyethoxy) benzene (46) . A charge t r a n s f e r polymer was prepared by r e a c t i o n of 4_5 w i t h 1,1-di- isocyanatoferrocene (47) to give a b l a c k polyurethane 4_8, which contained e l e c t r o n acceptor TCNQ u n i t s a l t e r n a t i n g w i t h e l e c t r o n donating ferrocene u n i t s (Scheme X I ) . However, the c o n d u c t i v i t y of the compacted powder was -3 -1 -1 only 3x10 ohm cm heme XI. Synthesis of the polyurethane 48. -29- 3. RESULTS AND DISCUSSION 3.1 Studies r e l a t e d to the synthe s i s of s u b s t i t u t e d TCNQ's In view of the i n t e r e s t i n g p r o p e r t i e s observed i n TCNQ and i t s d e r i v a t i v e s , i t was decided to i n i t i a t e a s y n t h e t i c program l e a d i n g to various analogs of t h i s molecule. I t seemed p a r t i c u l a r l y a t t r a c t i v e to i n v e s t i g a t e the p o s s i b l e formation of d e r i v a t i v e s having C-substituents w i t h o x i d a t i o n l e v e l s d i f f e r e n t from that of saturated hydrocarbons. Furthermore, the c o n s t r u c t i o n of symmetrical or unsymmetrical dimers c o n t a i n i n g the TCNQ moiety could be f a c i l i t a t e d by the use of f u n c t i o n a l i z e d s u b s t i t u e n t s s e r v i n g as s y n t h e t i c handles to achieve d i m e r i z a t i o n . In the 31a past, work done i n t h i s area included the preparation of ethers, t h i o - e t h e r s , h a l i d e s , n i t r i l e s and a l k y l groups as s u b s t i t u e n t s on the TCNQ r i n g . Our i n i t i a l study involved the f u n c t i o n a l i z a t i o n of an a l k y l d e r i v a t i v e of TCNQ, i n p a r t i c u l a r , 2-methyl-7,7,8,8-tetracyanoquinodi- methane (MTCNQ) (49) . The synthesis of 49̂  i s o u t l i n e d i n Scheme X I I . The preparation of the intermediate 2-methyl-l,4^cyclohexanedione (52) was Scheme X I I . Synthesis of MTCNQ (49). -30- accomplished by a m o d i f i c a t i o n of the procedure reported by H e r t l e r et a l . shown below. The s t a r t i n g m a t e r i a l i n both cases was the r e a d i l y a v a i l a b l e OMe 50 52 methyl-p-hydroquinone (50). In our case i t was hydrogenated to the corresponding d i o l - 5 1 w i t h rhodium on powdered charcoal as a c a t a l y s t , i n 90% y i e l d . The crude mixture of stereoisomers was o x i d i z e d w i t h a 34 m o d i f i c a t i o n of Jones reagent to produce the dione-52 i n 54% y i e l d . 2 - Methylcyclohexane-1,4-dione (52) was condensed with m a l o n o n i t r i l e i n the presence of g-alanine to give 2-methyl-l,4-bis(dicyanomethylene)- cyclohexane (53)(85% y i e l d ) . This could be used without f u r t h e r p u r i - f i c a t i o n i n a r e a c t i o n w i t h bromine and p y r i d i n e to produce 49 i n 54% y i e l d a f t e r p u r i f i c a t i o n by s u b l i m a t i o n . The low y i e l d i n t h i s r e a c t i o n 2 6 i s a t t r i b u t e d to the simultaneous formation of a dimer of 4j}. The 26 p h y s i c a l and spectroscopic data of 49 were s i m i l a r w i t h those reported. I t s nmr spectrum showed two s i n g l e t s , at 62.70 (3H,-CH^) and 67.15 (IH, -r=CH) , and two doublets at 67.43 (2H,J«=4Rz, v i n y l ) . CH 3 I n i t i a l attempts to f u n c t i o n a l i z e the methyl group of 4_9 with NBS i n carbon t e t r a c h l o r i d e were unsuccessful. A change of solvent or i n i t i a t o r had no p o s i t i v e e f f e c t , and i n a l l cases s t a r t i n g , m a t e r i a l was recovered -31- unchanged. I t was hoped that the v i n y l methyl group of 4_9 could undergo an a l l y l i c o x i d a t i o n on treatment w i t h selenium d i o x i d e . However, when SeC^ was added to a s o l u t i o n of MTCNQ i n r e f l u x i n g e t h a n o l , s t a r t i n g m a t e r i a l was s t i l l present a f t e r 24 hours (by t i c a n a l y s i s ) . The re s i s t a n c e of _49_ to o x i d a t i o n might be due to i t s high o x i d a t i o n p o t e n t i a l , t h i s would make the o l e f i n i c bond l e s s a c c e s s i b l e f o r e l e c t r o p h i l i c a t t a c k 35 to form the intermediate a l l y l i c s e l e n i t e e s t e r 54. Treatment of MTCNQ wi t h sodium hydride i n THF (tetrahydrofuran) at room temperature, followed by a d d i t i o n of phenyl selenium c h l o r i d e at -78°C, y i e l d e d only s t a r t i n g m a t e r i a l . S i m i l a r r e s u l t s were obtained when potassium hydride i n DME (1,2-dimethoxyethane) was used, followed by a d d i t i o n of bromine. Warming the r e a c t i o n mixture to room temperature l e d , i n both cases, to complex mixtures of compounds (at l e a s t four by t i c ) , i n c l u d i n g s t a r t i n g m a t e r i a l . In l i g h t of the d i f f i c u l t y encountered with the above experiments, a d i f f e r e n t approach to s u b s t i t u t e d TCNQ's was taken. I t involved i n t r o d u c t i o n of an a l k y l h a l i d e group onto the r i n g of a dihydro d e r i v a t i v e of TCNQ, namely p-phenylenedimalononitrile (55). This compound was prepared by reduction of TCNQ wi t h t h i o g l y c o l i c a c i d i n g l a c i a l a c e t i c a c i d 7 ( 8 5 % y i e l d ) . H a l o a l k y l a t i o n was attempted with paraformaldehyde and hydrogen bromide f o l l o w i n g the procedure -32- developed by Reynolds and Durham. Hydrogen bromide was bubbled through a refluxing suspension of the dihydro-TCNQ 55 and paraformaldehyde in acetic acid. Analysis of the resulting gummy solid showed disappearance of the n i t r i l e band in the i r spectrum. In addition, strong bands at 3600-3200 cm L and 1710 cm * indicated that hydrolysis of the n i t r i l e s had taken place. It was decided at this point to introduce the functionalized carbon substituent at the beginning of the synthesis, prior to the construction of the TCNQ frame. An ester functionality seemed an appropriate choice, and the synthesis of 2-methoxycarbonyl-7,7,8,8-tetracyanoquinodimethane (56) was designed in the manner illustrated in Scheme XIII. 56 -33- fir 0 N C 56 C N Q „ M e Scheme X I I I . Synthesis of 2-methoxycarbonyl-7,7,8,8-tetracyano- quinodimethane (56). The commercially a v a i l a b l e 2,5-dimethyl benzoic a c i d (57) was e s t e r i - 37 f i e d under F i s c h e r c o n d i t i o n s to produce the corresponding methyl ester 58 i n 85% y i e l d . The next step involved bromination on the two methyl groups. When NBS i n carbon t e t r a c h l o r i d e was used with benzoyl peroxide ( r a d i c a l i n i t i a t o r ) , the desired dibromo compound _59_ was obtained i n 38% y i e l d . By-products included both monobromo isomers and the tribromo -34- d e r i v a t i v e . The amount of side products obtained, together w i t h the low y i e l d of 5_9 prompted the search f o r b e t t e r r e a c t i o n c o n d i t i o n s . Vogtle 38 et a l . reported that the use of methylene c h l o r i d e as solvent i n the b e n z y l i c bromination of 1,8-di-p-tolylnaphthalene (63) afforded the dibromo product Jp_4_ i n 80% y i e l d ; i n carbon t e t r a c h l o r i d e the y i e l d was around 50%. In our case best r e s u l t s were obtained when a s l i g h t excess 63 64 of NBS (2.2 equivalents) was added to a mixture of 58_ and AIBN ( a z o b i s - i s o b u t y r o n i t r i l e ) i n methylene c h l o r i d e , followed by r e f l u x i n g f o r 2.5 hours. The r e s u l t i n g dibromo ester 59_ was i s o l a t e d from the r e a c t i o n mixture by f r a c t i o n a l c r y s t a l l i z a t i o n i n methanol. The y i e l d was 70% a f t e r r e c r y s t a l l i z a t i o n . The nmr spectrum of t h i s compound showed absorptions at 63.93 (s,3H,-OCH ), 64.43(s,2H,-CH 2Br), 64.90(s,2H,-CH 2Br), 67.40(s,2H,aryl) and 67.93(s,IH,aryl), which were co n s i s t e n t w i t h s t r u c t u r e 59. 39 Reeves et a l . have reported the f a c i l e conversion of primary a l k y l bromides i n t o a l k y l cyanides under phase t r a n s f e r c o n d i t i o n s employing primary, secondary or t e r t i a r y amines as c a t a l y s t s . They noted that s e v e r a l r e q u i s i t e s are apparent f o r e f f i c i e n t c a t a l y s i s : i n p a r t i c u l a r , the use of long chain a l i p h a t i c amines, with a chain length of at l e a s t -35- s i x carbons. In a d d i t i o n , cyanide displacements are known to occur more r a p i d l y when a c e t o n i t r i l e i s used as s o l v e n t . Displacement of the bromines i n 59_ by cyanide took place when a s o l u t i o n of the dibromo e s t e r i n a c e t o n i t r i l e was s t i r r e d at room temperature f o r ten hours w i t h an excess of aqueous sodium cyanide. Tri-n-octylamine was used as c a t a l y s t ; the y i e l d i n t h i s r e a c t i o n was 70%. The absorption at 2290 cm 1 i n the i r spectrum of 60_ showed the presence of the n i t r i l e group, and the a r y l ester carbonyl has an absorption at 1720 cm The nmr spectrum of the dicyano product showed an u p f i e l d s h i f t f o r the methylene protons. I n t r o d u c t i o n of the remaining two n i t r i l e groups was accomplished v i a the phenylenetetracyanodiacetate intermediate 61_, according to the 29a procedure of Wheland and M a r t i n . Toluene instead of benzene was used as solvent f o r the r e a c t i o n . Treatment of ^0 w i t h sodium methoxide i n toluene-dimethyl carbonate e s t a b l i s h e s an e q u i l i b r i u m w i t h d i a n i o n _6_5 which may be d r i v e n to completion by d i s t i l l i n g o f f a toluene-methanol azeotrope. A d d i t i o n of cyanogen c h l o r i d e to the r e a c t i o n mixture at 0°C, i s followed by gradual warming of the mixture up to 80°C. The tetracyano- diacetatej61, i s obtained i n r e l a t i v e l y good y i e l d (59%). The i r spectrum -36- C ^ o ) 2 c o - M e O H f of the crude product showed a new absorption band at 1770 cm indicating the presence of a saturated ester. Its "*"H nmr spectrum had a new singlet at 64.00 corresponding to the new methoxycarbonyl groups at C-7 and C-8, and lacked the two singlets at 63.77 and 4.12 attributed to the cyano- methylene groups. The mass spectrum of the compound showed the expected parent peak at m/e 380. Attempted purification of the crude o i l by chromatography on s i l i c a gel, resulted in partial hydrolysis of the triester. The crude product could be used without further purification in the next reaction; this involved hydrolysis and decarboxylation of the 31a ester groups to produce the dihydro-TCNQ b2_. Wheland had used aqueous potassium hydroxide or sodium hydroxide, either hot (70°C) or at room temperature, to effect hydrolysis and decarboxylation of a number of TCNQ -37- d e r i v a t i v e s . In our case, milder conditions were desired i n order to avoid t o t a l or p a r t i a l hydrolysis of the a r y l ester group. Sodium carbonate, being a weaker base, served our purposes. Indeed, when a sol u t i o n of the t r i e s t e r J31_ in THF was s t i r r e d at room temperature with an excess of aqueous sodium carbonate, in the presence of small amounts of sodium borohydride, the dianion 66_ was formed. N e u t r a l i z a t i o n with hydrochloric acid gave the dihydro compound _62_. Its i r spectrum lacked the absorption band at 1770 cm but retained the a r y l ester band. P u r i f i c a t i o n of t h i s compound presented great d i f f i c u l t i e s . The crude material streaked on t i c ; attempted r e c r y s t a l l i z a t i o n proved unsuccessful; and sublimation i n vacuum only de- composed the product. However, the a c i d i t y of the methine protons in 62 permitted p u r i f i c a t i o n v i a acid-base extraction. After work-up the r e s u l t i n g greenish o i l p a r t i a l l y c r y s t a l l i z e d on standing. Gradual darkening of the s o l i d occurred on standing at room temperature a f t e r several days. The o v e r a l l y i e l d after p u r i f i c a t i o n was 32% (from the dicyano-60). -38- Oxidation to the de s i r e d ester-TCNQ _56 was c a r r i e d out w i t h aqueous 31a bromine at room temperature. Attempted p u r i f i c a t i o n of the r e s u l t i n g l i g h t green s o l i d proved d i f f i c u l t . Sublimation at 190°C/0.01 mm Hg y i e l d e d a green-yellow s o l i d ( 3 % ) , m.p. 220°-224° (decomp.), which darkened g r a d u a l l y on standing. The "̂H nmr spectrum of t h i s m a t e r i a l was of poor q u a l i t y and was u n r e l i a b l e ; t h i s was due to low s o l u b i l i t y , and to the presence of r a d i c a l anions formed by r e a c t i o n w i t h solvent i m p u r i t i e s . I t s i r spectrum showed a weak absorption band at 2220 cm 1 (conjugated C=N) and a strong band at 1725 cm 1 (unsaturated ester C=0). I t s mass spectrum f u r t h e r s u b s t a n t i a t e d the proposed s t r u c t u r e by having 262 (100) as the molecular ion peak. The product could not be p u r i f i e d f o r elemental a n a l y s i s . However, high r e s o l u t i o n mass spectrometry e s t a b l i s h e d the molecular formula of the product to be C,H,N,0„, as 14 6 4 2 required by s t r u c t u r e _56. I t s e l e c t r o n i c spectrum showed an absorption band at 396 nm (36,800) w i t h a shoulder at 375 nm. I f t h i s s o l u t i o n i s l e f t standing, i t s c o l o r darkens and the UV spectrum shows a s h i f t to 409 nm. Attempts to form a charge t r a n s f e r complex with TTF i n a c e t o n i t r i l e f a i l e d . A large planar molecule c o n t a i n i n g two i d e n t i c a l acceptor s i t e s at both ends could be of i n t e r e s t i n the study of new acceptors. I f one of the acceptor s i t e s was a TCNQ molecule, the r e s u l t i n g system could have a s t r u c t u r e such as: -39- I n o r d e r t o b u i l d t h i s s y m m e t r i c a l c a r b o n s k e l e t o n , a v i c i n a l d i s u b s t i t u t e d TCNQ was needed. I n i t i a l l y , i t was hoped t h a t t h e use o f a D i e l s - A l d e r r e a c t i o n between TCNQ and an a p p r o p r i a t e d i e n e would s e r v e our p u r p o s e s . However, i t has been r e p o r t e d 7 t h a t t h i s r e a c t i o n has not g i v e n any c h a r a c t e r i z a b l e a d d u c t s when v a r i o u s d i e n e s were u s e d , and i n some ca s e s TCNQ was r e c o v e r e d unchanged. I t was d e c i d e d t h a t the use of a d i s u b s t i t u t e d TCNQ w i t h a p p r o p r i a t e f u n c t i o n a l groups would be more c o n v e n i e n t . A c c o r d i n g l y , t h e s y n t h e s i s o f 3 , 6 - b i s ( c y a n o m e t h y l ) p h t h a l i c a n h y d r i d e (67) was plan n e d as f o l l o w s (Scheme X I V ) . I t was hoped t h a t t h i s compound c o u l d be c o n v e r t e d t o t h e c o r r e s p o n d i n g TCNQ d e r i v a t i v e . 68 69 • NC CN 67 Br 71 70 Scheme XIV. S y n t h e s i s o f 3 , 6 - b i s ( c y a n o m e t h y l ) p h t h a l i c a n h y d r i d e ( 6 7 ) . 3 , 6 - D i m e t h y l p h t h a l i c a n h y d r i d e (70) was p r e p a r e d by a D i e l s - A l d e r r e a c t i o n o f 2 , 5 - d i m e t h y l f u r a n (68) and m a l e i c a n h y d r i d e . The c o r r e s p o n d i n g -40- adduct was dehydrated d i r e c t l y by treatment w i t h concentrated s u l f u r i c 41 a c i d at -10°C to give 7_0 i n 24% o v e r a l l y i e l d . The low y i e l d obtained might be p a r t i a l l y explained by the occurrence of an a c i d c a t a l y z e d 42 reversal of the D i e l s - A l d e r r e a c t i o n , which competes w i t h the a c i d - c atalyzed dehydration to _7_0. When the p h t h a l i c anhydride was b i s b r o - 43 minated under Wohl-Ziegler c o n d i t i o n s , a mixture of mono and dibromo d e r i v a t i v e s was obtained. The dibromo-71 p r e c i p i t a t e d out from the mixture and was p u r i f i e d by r e c r y s t a l l i z a t i o n (26% y i e l d ) . I t s nmr spectrum showed resonances at 64.86 (s^Hj-CH^Br) and 67.82 ( s , 2 H , a r y l ) . I t s i r spectrum r e t a i n e d the three absorption bands at 1856, 1777 and 1260 cm 1 corresponding to the ac i d anhydride. Displacement of bromide by cyanide i n the presence of sodium i o d i d e 44 under anhydrous c o n d i t i o n s l e d to a mixture of compounds. Based on the ^H nmr spectrum of the crude mixture, the formation of a five-membered r i n g lactone was suspected. In a d d i t i o n , s i g n a l s at 64.72 and 64.96 were i n d i c a t i v e of cyanomethylene and bromomethylene groups, r e s p e c t i v e l y . The formation of a lactone was explained i n terms of an in t r a m o l e c u l a r displacement of bromide by a carboxylate from the anhydride. I t was hoped that s u b s t i t u t i o n of the anhydride by an ester group would permit a cleaner s u b s t i t u t i o n of bromine by n i t r i l e . However, an attempt to convert the anhydride 7_1 i n t o the d i e s t e r _76, using methanol and p - t o l u e n e s u l f o n i c 45 1 a c i d , produced only the bromolactone ester 7_2 i n 51% y i e l d . The H nmr spectrum of 72_ contained a three proton s i n g l e t at 64.01 a t t r i b u t e d -41- Br .Ci M e 2 O Br •O 71 72 to the methoxy group, while at 64.55 occurred a two proton s i n g l e t which was assigned to the methylene protons of the bromomethyl group. The si n g l e t at 65.24 corresponded to the two protons of the y lactone r i n g , while the aromatic protons gave r i s e to an AB-pattern (J=8Hz) centered at 67.55. Its i r spectrum showed sharp, strong absorptions at 1775 cm _ 1 (lactone C=0) and 1735 cm"1 ( a r y l ester C=0). It was decided at this point to try to synthesize the corresponding diester _73 as outlined in Scheme XV. The preparation of dimethyl 3,6- dimethylphthalate (75) v i a a Diels-Alder reaction of trans,trans-2,4- 46 hexadiene and dimethyl acetylenedicarboxylate has been reported. The Diels-Alder c y c l i z a t i o n took place in r e f l u x i n g benzene to give the adduct 74_ in e s s e n t i a l l y quantitative y i e l d . Dehydrogenation with DDQ (5,6-dichloro-2,3-dicyano-p-benzoquinone) in benzene overnight, led to the desired dimethylphthalate 7_5 in 80% o v e r a l l y i e l d . Its physical and 46 spectral data were in agreement with those reported in the l i t e r a t u r e . -42- 115 73 76 Scheme XV. Proposed s y n t h e s i s of 2,3-dimethoxycarbonyl-7,7,8,8- tetracyanoquinodimethane (115) 46 Gundermann et_ al_. have bisbrominated 7_5 under Wohl-Ziegler 43 co n d i t i o n s , i n 37% y i e l d , by using 1.7 equivalents of NBS. When a s t o i c h i o m e t r i c amount of NBS was used, the t r i b r o m o d e r i v a t i v e 7J7 was obtained. In our hands, the bromination of 7_5 was e f f e c t e d using the 77 co n d i t i o n s developed f o r the monoester _58_. In t h i s case, a mixture of d i - and tribromo compounds 7_6 and 7_7 was produced. The tribromo d e r i v a t i v e could be separated from the crude product by d i s s o l v i n g the s o l i d mixture -43- in minimum amounts of boiling ethanol followed by overnight cooling and selective crystallization by addition of methanol. The crude dibromo- 76 (64% yield) was treated directly with sodium cyanide, in a manner similar to that described for the monoester 5^. The yield of the desired dimethyl 3,6-bis(cyanomethyl)phthalate (73) was 44% after purification by preparative column chromatography. Analytical and spectroscopic data are consistent with structure 73_. Notably, the i r spectrum shows a weak band at 2290 cm 1 corresponding to n i t r i l e absorption, and again shows a sharp, strong band at 1730 cm 1 (aryl ester C=0). Attempts to introduce the remaining two n i t r i l e groups via use of a phenylenetetracyanodiacetate intermediate failed to give the desired tetraester 78. An unidentified mixture was obtained and no further charac- CC^Me terizations were made. Use of potassium hydride and methyl chloroformate in DME led to similar results. Treatment of _73 with base followed by direct alkylation with cyanogen chloride proved unsuccessful. In both 4 cases complex mixtures of compounds were obtained. It has been reported that intramolecular electrophilic cyclization of the acid chloride 79 leads to the isoquinolone derivative 80. In light of this fact, i t is -44- To our knowledge, the synthesis of a v i c i n a l d i a l k y l d e r i v a t i v e of 49 TCNQ has not been reported i n the l i t e r a t u r e . Studies of the t e t r a t h i a - and t e t r a s e l e n a f u l v a l e n e s a l t s of 2,5-dimethyl-7,7,8,8-tetracyanoquinodi- methane (82) have shown that the c o n d u c t i v i t i e s of these s a l t s are comparable -45- to that of other TCNQ analogs. However the m e t a l - i n s u l a t o r t r a n s i t i o n temperature i s lower i n the case of the d l a l k y l d e r i v a t i v e 8_2. This could a r i s e from di s o r d e r e f f e c t s i n the s o l i d , or these r e s u l t s might i n d i c a t e that s o l i d s t a t e p r o p e r t i e s are mainly dominated by the a c t u a l c r y s t a l s t r u c t u r e r a t h e r than by e l e c t r o n i c p r o p e r t i e s of donors and acceptors. 2,3-Dimethyl-7,7,8,8-tetracyanoquinodimethane (2,3-DMTCNQ) (83) i s l a r g e r than TCNQ and has a d i f f e r e n t molecular symmetry than TCNQ. A c h a r a c t e r i s t i c of the conducting s o l i d s formed by TCNQ i s the occurrence of separate stacks of acceptors and donors. The dimethyl-TCNQ J33 c a r r i e s the p o s s i b i l i t y of d i f f e r e n t s t a c k i n g p a t t e r n s . Stacks of 83 might be formed i n an a l t e r n a t i n g arrangement to f a c i l i t a t e minimum s t e r i c r e p u l s i o n of methyl groups of adjacent molecules. A l t e r n a t i v e l y , the methyl groups can be randomized causing d i s o r d e r i n the l a t t i c e . This l a t t e r p o s s i b i l i t y could cause a broadened phase t r a n s i t i o n and greater c o n d u c t i v i t i e s at low temperatures, as i s the case when small amounts of methyl-TCNQ 49_ are 32*15? added as a dopant to TSF-TCNQ. » In view of these i n t e r e s t i n g features o f f e r e d by 2,3-DMTCNO (83), a synth e s i s of t h i s molecule was attempted, as depicted i n Scheme XVI. Synthesis of the dione-87 was accomplished 85 -46- Scheme XVI. Proposed route for the synthesis of 2,3-DMTCNQ (S3). following Yamakawa's route. Oxidation of 2,3-dimethyl phenol (84) was readily achieved via the Teuber reaction"' 1, with two equivalents of potassium nitrosodisulfonate (Fremy's salt) to produce an intermediate p- benzoquinone. This quinone is reduced in situ during the work-up with aqueous sodium thiosulphate, giving the hydroquinone 85 in 75% yield; 48 i t s m.p. was 167-170°C ( l i t . m.p. 163-164°C). The hydrogenation step that follows was carried out using the same procedure as for the hydro- quinone _50. The crude o i l containing a mixture of isomers was isolated in 95% yield. Oxidation of the diol-86, in the manner described for 51, gave 2,3-dimethylcyclohexane-»l,4-dione (87) in 75% yield. Its i r and 1 48 H nmr spectra were identical to those supplied by Yamakawa. The dione-87 was condensed^ with malononitrile to produce the expected tetracyano-88 in 67% yield. The white solid thus obtained lacked a carbonyl absorption in i t s i r spectrum, but contained a new absorption band at 2250 cm 1 (conjugated C=N). Treatment of £38 with -47- bromine/pyridine f a i l e d to give the de s i r e d dimethyl-TCNQ 83. Instead, the p a r t i a l l y o x i d i z e d dihydro d e r i v a t i v e 89̂  was obtained i n 86% y i e l d . I t s 1H nmr spectrum showed a s i n g l e t at 67.06 corresponding to the two v i n y l protons, and i t included signals at 61.16 (d,J=7Hz,6H,CH^-CH) and 63.17 (m,2H,-CH-CH3). Further evidence for structure 89̂  came from i t s i r and mass spectra and microanalysis. Efforts to oxidize the a l l y l i c position i n 89_ with either NBS or NCS (N-chlorosuccinimide) were un- successful. In both cases starting material was recovered. The following conditions led to a similar r e s u l t : manganese dioxide i n refluxing toluene, or DDQ in refluxing dioxane. The search for stronger dehydrogenation conditions prompted the use of a mixture of sulfur and 52 palladium as dehydrogenating agents. Small amounts of th i s mixture were fi n e l y ground with 89 and the resulting powder was heated to 180°C for 3 hours. Analysis of the extract (by t i c ) showed several colored spots including s t a r t i n g material. The band at 0.5 (eluent methylene chloride) was collected and found to be the desired product 83. Its nmr spectrum showed two singlets at 62.35 (6H,-CH3) and 67.43 (2H, v i n y l ) . Its mass spectrum further substantiated this assignment by having 232 as the highest molecular ion recorded. Unfortunately, when -48- t h i s reaction was scaled up the r e s u l t s were d i f f e r e n t and 83_ could not be obtained. No further investigations were made. 3.2 Synthesis of -11,11 ,12,12-tetracyano-4,5,9,10-tetrahydropyreno-2,7- quinodimethane (TCNTP) (90). Among the extended conjugated analogs of TCNQ studied to date, TCNDQ (22) suggested some i n t e r e s t i n g p o s s i b i l i t i e s for further studies. Un- 27 29 fortunately, the neutral species has not been i s o l a t e d . ' It was hoped that the TCNDQ analog 90_, with i t s pyrene skeleton, would be more stable 30 because biphenyl i n t e r - r i n g hydrogen repulsions are eliminated. The N C \ / C N N C v ^ ^ C N -49- proposed syn t h e s i s of TCNTP (90) i s o u t l i n e d i n Scheme XVII. This scheme shows how a f i g u r a t i v e d i s s e c t i o n to simpler systems could help i n the search f o r an appropriate s t a r t i n g m a t e r i a l . TCNTP could be obtained from the dihydro precursor 91_ using m i l d o x i d a t i o n c o n d i t i o n s . In turn 91 could be prepared from the dicyano-93 v i a h y d r o l y s i s and decarboxylation of the phenylenetetracyanodiacetate intermediate 92_. Moving backwards i n stepwise f a s h i o n , obtention of 93_ r e q u i r e s a transannular r e a c t i o n of the dicyano[2.2]metacyclophane 94_- This compound can be formed from 95 by displacement of bromide w i t h cyanide. The dibromo metacyclophane 9_5 i s a v a i l a b l e from the corresponding dimethyl compound 96^ by treatment w i t h NBS." -50- Scheme XVII. Proposed synthesis of TCNTP (90) from 5,13-dimethyl- [2.2]metacyclophane (96). The metacyclophane _96_ contained a l l the necessary elements for the synthesis of 90; and i t has been prepared in the past by intermolecular coupling of 3,5-bis(bromomethyl)toluene (97), v i a use of the Wurtz 54 55 reaction, i n the presence of sodium (12% y i e l d ) , or phenyllithium (no y i e l d reported). The y i e l d s i n t h i s type of reaction are usually low 5 6 and the amounts of by-products large. On the other hand, the formation of the corresponding dithiacyclophane _98_ generally occurs in high y i e l d , -51- and so i t has been used as precursor f o r the s y n t h e s i s of 9_6 i n three ways: ( i ) the e x t r u s i o n of sulphur has been accomplished by conversion i n t o the corresponding bis-sulphone 9J9, followed by e l i m i n a t i o n of 53 sulphur d i o x i d e on p y r o l y s i s at 800°C (76%)(Scheme XVIII a ) ; ( i i ) the e x t r u s i o n of sulphur has been achieved i n one step by i r r a d i a t i o n of small amounts of 9_8_ i n the presence of t r i m e t h y l phosphite;"^ ( i i i ) 58 r e c e n t l y , M i t c h e l l _et_ a l . found that the W i t t i g rearrangement of 98, w i t h n - b u t y l l i t h i u m , followed by a l k y l a t i o n w i t h methyl i o d i d e , gave 100 as a mixture of isomers i n e x c e l l e n t y i e l d . This mixture was converted c l e a n l y to anti-5,13-dimethyl[2.2]metacyclophane (96) by reduction w i t h l i t h i u m i n l i q u i d ammonia (Scheme XVIII b ) . 58 I t was decided to use M i t c h e l l ' s route to £6 i n view of the f a c t that both steps could be c a r r i e d out on a l a r g e s c a l e and i n good y i e l d s . The s y n t h e s i s of 6,15-dimethyl-2,ll-dithio[3.3]metacyclophane (98) i s 59 depicted i n Scheme XIX. Bromination of mesitylene (101) w i t h NBS afforded 3,5-bis(bromomethyl)toluene (97) i n 50% y i e l d a f t e r r e c r y s t a l l i - z a t i o n . Conversion of the dibromo-97 to the d i t h i o l - 1 0 2 was achieved i n 95% y i e l d using the thiourea method. 5^'^ u This method i n v o l v e s the formation of the d i i s o t h i o u r o n i u m bromide 103, v i a n u c l e o p h i l i c a t t a c k on the h a l i d e by the s u l f u r . H y d r o l y s i s of t h i s s a l t i n r e f l u x i n g potassium Scheme XIX. Synthesis of 6,15-dimethyl-2,11-dithia[3.3]- metacyclophane (98). -53- hydroxide gave 102. I t s nmr spectrum showed s i g n a l s at 61.72 (t,J=8Hz, 2H.-SH), 62.31 (s,3H,-CH 3), 63.64 (d,J=8Hz,4H,-CH2-) and 66.97 (s,3H,aryl). Coupling of 97_ and 102 occurred i n an e t h a n o l i c s o l u t i o n of potassium hydroxide under high d i l u t i o n c o n d i t i o n s ^ 1 and over a period of 7 days. The crude product was p u r i f i e d by f i l t r a t i o n through s i l i c a g e l . Thus, the dit h i a c y c l o p h a n e 98 was obtained i n 85% y i e l d . A r e c r y s t a l l i z e d sample had a m e l t i n g point 101.5-103.5°C ( l i t . 5 3 mp 102-102.5°C). 59 S p e c t r a l data were i n agreement w i t h those reported p r e v i o u s l y Treatment of 98 with n - b u t y l l i t h i u m i n THF at -20°C, followed by methylation of the r e s u l t i n g t h i o l a t e afforded the mixture of isomers 100. The crude mixture was not p u r i f i e d but was used d i r e c t l y i n the reduction step that f o l l o w s . Cleavage of the carbon-sulfur bond was achieved by reduction of 100 w i t h l i t h i u m i n l i q u i d ammonia. The crude r e a c t i o n product was p u r i f i e d by p r e p a r a t i v e column chromatography; subsequent r e c r y s t a l l i z a t i o n from ethanol furnished 96 i n 30% o v e r a l l y i e l d , mp 145-146°C ( l i t . 5 3 m p 145-146°C). -54- It was found that NBS bromination of 96_ displayed a remarkable solvent dependence: in methylene chloride a transannular reaction occurred with the consequent formation of the tetrahydropyrene 104; while in carbon tetrachloride, the bisbromide 95 was formed exclusively, in 70% yield. The "*"H nmr spectrum of 9_5 showed the characteristic pattern o f 104 f2.2]metacyclophanes.°Z In particular, the intraannular protons exhibited an unusual high f i e l d shift at 64.25 (s) due to the ring current effect of the other benzene ring. Since the ten-membered ring system of _95 exists in a rigid chair conformation, the bridging ethyle signal appears as an A2B2~pattern arising from axial and equatorial protons: 6axial=2.14, 6 equatorial=3.13. Furthermore, the benzylic -55- methylene groups bearing bromine appear as a singlet at 64.56. In the case of 104, i t s ̂"H nmr spectrum consists of three singlets at 62.3b (methyl), 62.87 (methylene) and 66.96 (aryl) in a r a t i o of 3:4:2 respect i v e l y . It has been reported that in the NBS bromination of naphthaleno- 38 paracyclophane 105, when methylene chloride was used as solvent, bromination occurred exclusively in the aromatic ring to form the cyclo- phane 106 while i f carbon tetrachloride was used, the mono bromo-107 was formed alongside the gem-dibromo-108. 1 0 8 XzY = B r A similar solvent effect may be operating in the NBS bromination of 96. The tetrahydropyrene 104 now has six benzylic positions, and NBS bromination on this molecule would be expected to yie l d a mixture of -56- compounds. When 104 i s treated with NBS in carbon t e t r a c h l o r i d e , one of the major products of the mixture i s 2,7-diraethylpyrene (109). Its 1H nmr spectrum showed two s i n g l e t s at 62.80 (6H,-CH3) and 67.98 (8H,aryl) which are consistent with the l i t e r a t u r e v a l u e s . ^ Displacement of bromine i n dibromo-95 by cyanide was achieved i n a manner s i m i l a r to that described for the mono- and die s t e r ^9 and 7_6 resp e c t i v e l y . Due to s o l u b i l i t y problems, the reaction was car r i e d out in r e f l u x i n g THF. The r e s u l t i n g dicyano compound _94 was obtained i n 70% y i e l d . It exhibited an absorption band i n the i r , at 2300 cm 1 (C=N) , and i t s ̂ "H nmr spectrum showed an expected u p f i e l d s h i f t for the cyanomethyl groups to 63.80 (s,4H). Compound 9_4 could now be converted into the desired pyrene framework by transannular reaction between the 64 two rings. It has been reported that treatment of 110 with bromine in the presence of c a t a l y t i c amounts of iron powder, leads to the 53 formation of 111. More recently, Misumi e_t a l , have used these 109 104 conditions to achieve a transannular oxidation of 9 5 . The cyclophane 94 -57- was converted into the dicyanopyrene 93 by s t i r r i n g the mixture of 94, bromine in chloroform, and iron powder at 0°C for 1.5 hours. After work-up the crude reaction mixture i s chromatographed, and the dicyano- pyrene i s obtained in 70% y i e l d . Evidence for structure 93_ was supplied by i t s ''"H nmr spectrum which showed the disappearance of the signal at 64.24 (intraannular aromatic protons). In addition, since structure ^3 i s planar, the bridging ethylene protons are a l l equivalent, and the • ^ 2 ^ 2 ~ p a t t e r n c o H a P s e ^ t o a singlet at 62.83 (8H). Based on the 64 mechanistic studies on the transformation of 110 into 111, the following mechanism was suggested for the transannular reaction of 94. Intermediate 112 i s formed by the e l e c t r o p h i l i c attack of the bromonium ion on one r i n g , accompanied by a simultaneous transannular attack of the generated phenonium ion on the second ring. Regeneration of the aromatic character by loss of a proton followed by elimination of the elements of hydrogen bromide gave r i s e to the observed product. -58- -59- I n t r o d u c t i o n of the remaining two cyano groups was achieved v i a formation of the d i e s t e r 9_2, i n a manner s i m i l a r to that described p r e v i o u s l y f o r the synthesis of the t r i e s t e r 6̂ 1. The i r spectrum of 92 showed a strong absorption at 1745 cm 1 (saturated es t e r C=0). I t s nmr spectrum e x h i b i t e d a new s i g n a l at 63.91 (s,6H,-OCH^), and i t s mass spectrum showed the expected M~̂~ at 450. The crude product was not p u r i f i e d any f u r t h e r but was used d i r e c t l y i n the h y d r o l y s i s step that f o l l o w s . H y d r o l y s i s and dec a r b o x y l a t i o n of 92 afforded the dihydro-TCNTP 91. This r e a c t i o n was c a r r i e d out using the same procedure as f o r the t r i e s t e r 61. Disappearance of the s i g n a l corresponding to the methoxy carbonyl group i n the "'"H nmr spectrum of 91 i s accompanied by the appearance of a new s i n g l e t at 65.00 (2H,(CN)2CH-). P u r i f i c a t i o n methods such as chromato- graphy, r e c r y s t a l l i z a t i o n and s u b l i m a t i o n f a i l e d to give any p o s i t i v e r e s u l t s , and, as y e t , t h i s compound has not been obtained i n the pure s t a t e . I t was decided, however, to attempt the synthesis of TCNTP (90) usi n g crude compound 91_ i n view of the f a c t t h a t , from our past experience, TCNQ d e r i v a t i v e s have been more e a s i l y p u r i f i e d than the corresponding dihydro compounds. Oxidation of 91_ to the d e s i r e d TCNTP proved more d i f f i c u l t than g a n t i c i p a t e d . The use of manganese d i o x i d e i n r e f l u x i n g toluene led only to u n i d e n t i f i e d products; treatment w i t h aqueous bromine at room temperature produced a h i g h l y i n s o l u b l e green-brown s o l i d , mp 206-210°C (decomp.). I t s i r spectrum showed a band at 2220 cm 1 i n d i c a t i v e of a conjugated n i t r i l e , (TCNQ shows a band at 2220 cm ^ ) ^ . Furthermore i t s mass spectrum showed two peaks at 334 and 332 i n a 2:1 r a t i o , together w i t h small peaks at 412 and 414 (1:1 r a t i o ) . The l a t t e r peaks were b e l i e v e d -60- to be due to the presence of some bromine c o n t a i n i n g i m p u r i t i e s and w i l l be discussed l a t e r . I t was f e l t that the M + + 2 peak observed at 334 o r i - ginated from compound 91_, formed by arom a t i z a t i o n of TCNTP i n the probe (T=270°C). A small sample (5 mg) was r e c r y s t a l l i z e d from a c e t o n i t r i l e (ca. 400 ml), mp 210-212°C (decomp). This compound gave an intense purple c o l o r i n s o l u t i o n . Elemental a n a l y s i s , however, d i d not correspond w i t h the des i r e d values. I t s UV-Vis spectrum i s shown i n Figure 6. When t h i s compound was treated w i t h t h i o g l y c o l i c a c i d i n a c e t i c a c i d under the Figure 6. UV-Vis spectrum of 2,7-bis(dicyanomethyl)-4,5,9,10- tetrahydropyrene (91) a f t e r treatment w i t h aqueous bromine. same c o n d i t i o n s used for the red u c t i o n of TCNQ to the dihydro-TCNQ 55, the corresponding dihydropyrene 91 was the only m a t e r i a l i s o l a t e d from the r e a c t i o n mixture. -61- Other o x i d a t i o n c o n d i t i o n s were t r i e d , among them, the use of NCS and t r i e t h y l a m i n e i n methylene c h l o r i d e , at -20°C; i n t h i s r e a c t i o n a d r a s t i c c o l o r change took place when t r i e t h y l a m i n e was added, and the c o l o r of the r e a c t i o n mixture turned intense purple. A t i c examination of the product mixture revealed the presence of two main products; a n a l y s i s of the l e s s po l a r band i s o l a t e d by pr e p a r a t i v e t i c (eluent chloroform) y i e l d e d a blue s o l i d , mp 227-230°C, r e a d i l y s o l u b l e i n most organic s o l v e n t s . The presence of two c h l o r i n e atoms i n the molecule was evident by the c h a r a c t e r i s t i c i s o t o p i c d i s t r i b u t i o n e x h i b i t e d by the molecular ions at 402, 404, 406 (9:6:1) i n i t s mass spectrum. In a d d i t i o n , i t s "'"H nmr spectrum showed two s i n g l e t s at 63.50 and 67.56 i n a 4:1 r a t i o , perhaps suggesting c h l o r i n e s u b s t i t u t i o n on the benzene r i n g s . Treatment of 9_1_ with NBS i n methylene c h l o r i d e at -78°C followed by a d d i t i o n of t r i e t h y l a m i n e y i e l d e d a yellow-brown s o l i d . T i c a n a l y s i s showed one spot, Rf^0.5 (eluent chloroform); the s o l u t i o n i r spectrum of the crude r e a c t i o n product showed a weak absorption at 2228 cm 1 (conjugated CHN). P u r i f i c a t i o n of the crude product was attempted by f i l t r a t i o n through s i l i c a - g e l followed by r e c r y - s t a l l i z a t i o n from benzene; the green m i c r o c r y s t a l s so obtained melted at 206-208°C (decomposition). I t s i r spectrum (KBr p e l l e t ) showed two weak absorptions at 2225 and 2265 cm 1 ; the nmr spectrum showed s i g n a l s at 62.94 and 67.20, assigned to the methylene and v i n y l protons of 90 r e s p e c t i v e l y . However, due to the presence of u n i d e n t i f i e d products an accurate percentage y i e l d of 90 could not be c a l c u l a t e d . The mass spectrum of 9_0 contained peaks at 332 and 334 corresponding to TCNTP (90) and dihydro- TCNTP 91 r e s p e c t i v e l y , together w i t h two lower i n t e n s i t y peaks at 412 and 414 i n d i c a t i n g the presence of some bromine c o n t a i n i n g i m p u r i t i e s , as observed p r e v i o u s l y . The mass spectrum was then recorded at d i f f e r e n t -62- temperatures ranging from 280°C to 450°C. In t h i s i n t e r v a l , the r a t i o of the peaks at 334 and 332 decreased gradually with i n c r e a s i n g temperature, from a value of 3.1 at 280°C to a value of 1.8 at 450°C. At the same time the peaks at 412 and 414 disappeared g r a d u a l l y . These r e s u l t s seem to i n d i c a t e : (a) the peaks at 412 and 414 are derived from a compound other than 90; (b) the dihydro compound (m/e=334) i s probably formed from TCNTP (m/e=332) i n the mass spectrometer. The UV-Vis spectrum of 90 i s shown below. 700 - 6 3 - On treatment of _9_0 with excess tetrabutylammonium iodide i n benzene at room temperature, the color of the solu t i o n went' from purple to l i g h t red. After evaporation of the solvent, a mixture of TCNTP~ TBA + (114) (TEA"1": tetrabutylammonium cation) and unreacted tetrabutylammonium iodide was obtained. Its i r spectrum showed a strong sharp n i t r i l e absorption at 2180 cm and a smaller absorption at 2145 cm . Such a low absorption frequency for the n i t r i l e s i s consistent with the value of 2200-2175 cm 1 9 observed for the tetraethylammonium s a l t of TCNQ . Furthermore the UV-Vis spectrum of 114 in benzene i s si m i l a r to that observed for the r a d i c a l anion of TCNDQ (2_2) , as would be expected for the formation of TCNTP~. Both s p e c t r a are shown in F i g u r e 7. I + TCNTP -> - I + TCNTP € x lO" 3 -64- Figure 7. UV-Vis spectrum of ( i ) TBA TCNDQ and ( i i ) TBA TCNTP (114). 3.3 Overall Results In summary, the work done towards the synthesis of a pyrene analog of TCNDQ (22) has resulted in the preparation of 11,11,]2,12-tetracyano- 4,5,9,10-tetrahydropyreno-2,7-quinodimethane (TCNTP)(90). Pre]iminary r e s u l t s obtained from some exploratory experiments show that this molecule -65- could be p o t e n t i a l l y u s e f u l i n the study of new donors derived from extended TCNQ analogs. From the work described i n the f i r s t s e c t i o n of t h i s chapter i t can be concluded that the synthesis of new TCNQ d e r i - v a t i v e s c o n t a i n i n g f u n c t i o n a l i z e d carbon s u b s t i t u e n t s should s t a r t w i t h a p p r o p r i a t e l y s u b s t i t u t e d benzene or cyclohexane d e r i v a t i v e s as opposed to the rat h e r u n r e a c t i v e a l k y l s u b s t i t u t e d TCNQ's. This viewpoint r e s u l t e d i n the synthesis of 2-methoxycarbonyl-7,7,8,8-tetracyano- quinodimethane (56). F i n a l l y , the synthesis of 2,3-dimethyl-7,7,8,8- tetracyanoquinodimethane (83) has proved s u r p r i s i n g l y d i f f i c u l t because of the s t a b i l i t y of compound 89 to o x i d a t i o n . A new route should be devised, i n view of i n t e r e s t i n g s t r u c t u r a l features i n 83. -66- EXPERIMENTAL GENERAL S p e c t r a l Data A l l i n f r a r e d (IR) spectra were taken i n chloroform s o l u t i o n , unless otherwise s t a t e d . They were recorded on a Perkin-Elmer model 700 spectrophotometer and were c a l i b r a t e d w i t h the 1601 cm ^ band of poly- styrene. The assignment of each band i s noted i n parentheses a f t e r i t . ''"H NMR spectra were recorded on a Varian model T-60 or model XL-100 spectrometer. The solvent used i s reported i n parentheses at the beginning of each spectrum. Chemical s h i f t s ( 6 ) are quoted i n p.p.m. downfield from t e t r a m e t h y l s i l a n e , used as an i n t e r n a l standard. The m u l t i p l i c i t y , c oupling constants (quoted i n Hz), i n t e g r a t e d peak areas and proton assignments are i n d i c a t e d i n parentheses a f t e r each s i g n a l . U l t r a v i o l e t - v i s i b l e (UV-Vis) spectra were recorded on a Cary 17D spectrometer. The molar e x t i n c t i o n c o e f f i c i e n t s of the main bands are 2 l i s t e d i n parentheses a f t e r the absorptions and are expressed i n cm , -1 mole Mass spe c t r a were obtained using an A t l a s CH-4B mass spectrometer, and high r e s o l u t i o n determinations were obtained using an AEI MS-902 or MS-50 mass spectrometer. Both instruments were operated at an i o n i s i n g p o t e n t i a l of 70 eV. The value i n parentheses a f t e r each mass i s i t s r e l a t i v e i n t e n s i t y . P h y s i c a l Data. M e l t i n g points (mp) were determined on a K o f l e r hot stage microscope and are uncorrected. Elemental microanalyses were performed by Mr. Peter -67- Borda, U n i v e r s i t y of B r i t i s h Columbia. Chromatography Pr e p a r a t i v e t h i n l a y e r chromatography (TLC) was c a r r i e d out using 0.9 mm thickness s i l i c a g e l (E. Merck, grade PF-254 + 366) on e i t h e r 20 x 20 cm or 5 x 20 cm glass p l a t e s . Small a n a l y t i c a l p l a t e s were prepared by d i p p i n g microscopic s l i d e s i n t o a s t i r r e d s o l u t i o n of s i l i c a g e l i n chloroform. Column chromatography was done using s i l i c a g e l of grade f i n e r than 200 mesh. Solvents The term "dry" i n t h i s t h e s i s r e f e r s to solvents d r i e d i n the f o l l o w i n g ways: e t h y l ether and tetrahydrofuran (THF) were d r i e d by r e - f l u x i n g over l i t h i u m aluminium hydride. Toluene and benzene were d r i e d over sodium. Carbon t e t r a c h l o r i d e , methylene c h l o r i d e and a c e t o n i t r i l e were d i s t i l l e d from phosphorous pentoxide. Methanol was d r i e d by r e f l u x i n g over magnesium methoxide. Techniques Anhydrous magnesium s u l f a t e was used to dry organic s o l u t i o n s and was removed by f i l t r a t i o n . A l l s t i r r i n g , unless otherwise noted, was c a r r i e d out u s i n g t e f l o n - c o a t e d magnetic s t i r r i n g bars. 2-Hethyl-l,4-cyclohexanedione (52)* Methyl-p-hydroquinone (50) (8.8 g, 0.071 mole), rhodium (10%) on powdered charcoal (1.55 g) and a methanol-water mixture (198 ml, 10:1 V/V) were placed i n a hydrogenation b o t t l e which was then attached to a P a r r - low-pressure apparatus. A i r was evacuated and the f l a s k was flushed with hydrogen s e v e r a l times. The reduction was then c a r r i e d out at room -68- temperature at an i n i t i a l hydrogen pressure of 50-60 p s i . The r e a c t i o n was complete when a constant hydrogen pressure was reached (approximately 22 hours). The c a t a l y s t was removed by f i l t r a t i o n , washed w i t h methanol (50 ml ) , and d r i e d i n vacuo. The c a t a l y s t could be used again a f t e r i t had been r e a c t i v a t e d - two days i n the oven at 110°C. Solvents from the f i l t r a t e were removed under reduced pressure; traces of methanol and water were a z e o t r o p i c a l l y d i s t i l l e d w i t h chloroform (30 ml). The r e s u l t a n t o i l (8.3 g, 90%) was shown, by i r and "''H nmr s p e c t r a , to be 2-methyl-l,4- cyclohexanediol (51) which was not p u r i f i e d but was used d i r e c t l y i n the o x i d a t i o n step that f o l l o w s . A s o l u t i o n of chromium t r i o x i d e (26.72 g, 9.27 mole), water (77 m l ) , concentrated s u l f u r i c a c i d (23 ml), and manganese s u l f a t e (0.2 g) was prepared, and added slowly to a s t i r r e d s o l u t i o n of the crude d i o l - 5 1 (1.52 g, 0.012 mole) i n chloroform (50 ml) at 5°C. The a d d i t i o n was stopped a f t e r 3 equivalents (13 ml) of chromium t r i o x i d e had been introduced (30 minutes). S t i r r i n g was continued f o r 4 hours, and then the chloroform l a y e r was separated. The aqueous l a y e r was extracted wit h chloroform (3 x 50 ml) and the combined e x t r a c t s were washed with an aqueous s o l u t i o n of concentrated ammonium hydroxide (1 ml) i n saturated sodium c h l o r i d e (10 ml). A f t e r d r y i n g , the solvent was removed under reduced pressure to y i e l d 2-methyl-l,4-cyclohexanedione (52) (0.79 g, 54%) . IR v 1715 cm"1 (C=0). max 1H NMR(CDC£3)6 1.15(d,J=6,3H,-CH3>, 2.3-2.95(m,3H,-CH2-CH-) and 2.60 ppm(s,4H,-CH2-). Mass spectrum m/e 55(54) 56(100), 57(41), 68(58), 69(75), 71(32), 82(16), 83(19), 111(43) and 126(91). * Experiment f i r s t performed by Ms. J . Lee. -69- 2-Methyl-7,7,8,8-tetracyanoquinodimethane (49) The compound was prepared by the same procedure as that reported by 2 6 H e r t l e r et a_l. The reagents used were: 2-methyl-l,4-cyclohexanedione (52) (939 mg, 7.45 mmole), m a l o n o n i t r i l e (993 mg, 15.1 mmole) and a 2% aqueous s o l u t i o n of 8-alanine (1.68 ml), which gave 1.407 g (85%) of 2- methyl-l,4-bis(dicyanomethylene)cyclohexane (53) , i d e n t i f i e d by i t s i r and nmr spectra. Compound 52^ (440 mg, 1.98 mmole) was not p u r i f i e d but was trea t e d w i t h a 10% s o l u t i o n of bromine i n a c e t o n i t r i l e (2 ml) and p y r i d i n e (1 ml) to give 460 mg of 2-methyl-7,7,8,8-tetracyanoquino- dimethane (49). P u r i f i c a t i o n of compound 49 was achieved by su b l i m a t i o n at 150°C/0.01 mm (250 mg, 54%), mp 198-200°C ( l i t 2 6 mp 200-201°C). I t s i r , nmr and mass spectra were i n accord w i t h the proposed s t r u c t u r e . Methyl 2,5-dimethylbenzoate (58) The pr e p a r a t i o n of methyl 2,5-dimethylbenzoate (58) followed the 37 method described by F a l k and S c h l o g l . The reagents used were: 2,5- dimethylbenzoic a c i d (57) (16.82 g, 0.112 mole), methanol (46 ml) and concentrated s u l f u r i c a c i d (5 ml), which gave 15.20 g (82%) of methyl 2,5-dimethylbenzoate (58) a f t e r vacuum d i s t i l l a t i o n , bp 70-72°C/0.5 mm ( l i t 3 7 bp 106-107°C/13 mm). IR v 1715 cm _ 1 ( a r y l ester C=0). max J 1H NMR (CDC£3) 62.28 (s,3H,m-CH3), 2.48 (s,3H,o-CH 3) 3.77 (s,3H,-OCH 3); 6.97 (s,2H,aryl) and 7.55 ppm ( s , l H , a r y l ) . Mass spectrum m/e 77(21), 104(32), 105(58), 132(88), 133(100), 149(17) and 164(62). -70- Methyl 2,5-bis(bromomethyl)benzoate (59) An oven-dried 200-ml f l a s k was equipped with a condenser, magnetic s t i r r e r , and heating mantle. The condenser was stoppered with a septum cap, f i t t e d w i t h n i t r o g e n i n l e t and o u t l e t syringe needles, and flushed w i t h n i t r o g e n . The r e a c t i o n v e s s e l was then charged w i t h methyl 2,5-dimethyl benzoate (58) (5.53 g, 0.034 mole), NBS ( r e c r y s t a l l i z e d from water, 13.5 g, 0.075 mole), a z o b i s i s o b u t y r o n i t r i l e (0.3 g) and dry methylene c h l o r i d e (60 ml). The mixture was s t i r r e d and heated to r e f l u x f o r 2.5 hours, during which time i t turned yellow and then orange. The r e a c t i o n mixture was then cooled and f i l t e r e d . The f i l t r a t e was d i l u t e d w i t h 100 ml of methylene c h l o r i d e and washed s u c c e s s i v e l y w i t h saturated aqueous s o l u t i o n s of sodium b i s u l p h a t e (1 x 25 ml) and sodium bicarbonate (1 x 25 ml) to remove excess bromine and hydrobromic a c i d . A f t e r washing with water (2 x 30 m l ) , the organic l a y e r was d r i e d and the solvent r e - moved under reduced pressure. The r e s u l t i n g o i l y s o l i d was covered w i t h methanol and kept at -5°C overnight. The white s o l i d was c o l l e c t e d by vacuum f i l t r a t i o n and r e c r y s t a l l i z e d from methanol-pentane to y i e l d 7.66 g (70%) of pure compound (59) as white c r y s t a l s , mp 81.5-82.5°C. IR v 1720 cm"1 ( a r y l ester C=0). max 1H-NMR(CDC£3) 63.93(s,3H,-0CH 3), 4.43(s,2H,m-CH 2Br), 4.90(s,2H, o-CH 2Br), 7.40(s,2H,aryl) and 7.93 ppm(s,lH,aryl). Mass spectrum m/e 77(26), 119(25), 121(22), 122(17), 147(35), 162(67), 163(48), 209(17), 211(19), 241(100), 243(96), 291(13), 320(10), 321(17), 322(20) and 324(10). A n a l y s i s c a l c u l a t e d f o r C ^ H ^ B r ^ : C 37.30, H 3.13, Br 49.63; found: C 37.25, H 2.98, Br 49.40. -71- Methyl 2,5-bis(cyanomethyl)benzoate (60) Sodium cyanide (9.0 g, 0.183 mole) was weighed i n t o a 250-ml f l a s k and then d i s s o l v e d i n 30 ml of water. A s o l u t i o n of 59_ (9.15 g, 0.028 mole) i n a c e t o n i t r i l e (73 ml) was added, followed by 0.33 ml of t r i - n - o c t y l a m i n e (3% by weight of 59). The mixture was s t i r r e d f o r 10 hours at room temperature and poured i n t o water (200 ml). The mixture was extracted w i t h methylene c h l o r i d e (3 x 100 m l ) , and the e x t r a c t s were washed s u c c e s s i v e l y w i t h aqueous sodium b i s u l p h a t e (50 m l ) , d i l u t e h y d r o c h l o r i c a c i d (50 m l ) , and saturated sodium c h l o r i d e s o l u t i o n (50 ml). A f t e r d r y i n g , the solvents were evaporated under reduced pressure to give 6.1 g of a b u f f - c o l o r e d s o l i d . P u r i f i c a t i o n of 60_ was achieved by c a r e f u l r e c r y s t a l l i z a t i o n from methanol, followed by chromatography of the mother l i q u o r s using a carbon t e t r a c h l o r i d e - e t h y l ether mixture (9:1 V/V). Methyl 2,5-bis(cyanomethyl)benzoate (60) was i s o l a t e d as a white m i c r o c r y s t a l l i n e powder (4.19 g, 70%), mp 98-100°C. IR v 2290(C=N) and 1722 cm"1 ( a r y l ester C=0). max """H NMR(CDC£3) 63.77 (s,2H,m-CH2CN) , 3. 90 (s , 3H ,-0CH3) , 4.17(s,2H, o-CH 2CN), 7.50(s,2H,aryl) and 7.95 ppm(s,lH,aryl). Mass spectrum m/e 83(26), 101(18), 127(19), 128(26), 154(26), 155(33), 177(20), 172(19), 182(100), 183(68) and 214(84). A n a l y s i s c a l c u l a t e d f o r C 1 2 H 1 0 N 2 ° 2 : C 6 7 - 2 8 » H 4.71, N 13.08; found C 67.32, H 4.88, N 12.66. Dimethyl a,a, a",a^-tetracyano-2-methoxycarbonyl-l,4-phenylenediacetate (61). An oven-dried, three-neck, 250-ml round-bottom f l a s k was equipped w i t h a 2 i n magnetic s t i r r i n g bar, an o i l bath and d i s t i l l a t i o n head. The f l a s k was stoppered w i t h a ground glass bubbler and a septum cap f i t t e d -72- w i t h a n i t r o g e n i n l e t needle. The whole system was flamed and allowed to c o o l to room temperature under a n i t r o g e n flow. Fresh sodium methoxide was prepared i n s i t u by a d d i t i o n of sodium metal (0.8 g, 0.034 mole) to dry methanol (10 ml) followed by removal of the excess a l c o h o l under reduced pressure. The methoxide was suspended i n dry toluene (80 ml) and a s o l u t i o n of methyl 2,5-bis(cyanomethyl)benzoate (6QK2.632 g, 0.0123 mole) i n dry THF-toluene mixture (40 ml, 6:4 V/V) was syringed i n t o the f l a s k . The r e a c t i o n mixture was s t i r r e d f o r 15 minutes at room temperature; the mixture turned dark brown. Dimethyl carbonate ( f r e s h l y d i s t i l l e d from molecular s i e v e s , 10.3 ml, 0.123 mole) was syringed i n and the r e a c t i o n mixture was then heated to gentle b o i l i n g and r e f l u x e d f o r 4 hours. Then methanol was d i s t i l l e d o f f a z e o t r o p i c a l l y w i t h toluene. D i s t i l l a t i o n was continued u n t i l the temperature of the vapor reached 110°C (approximately one hour). A f t e r c o o l i n g the mixture to 0°C i n an i c e bath, an a d d i t i o n a l 95 ml of toluene was added. Cyanogen c h l o r i d e (2.7 ml, 0.052 mole) was condensed i n s i d e a graduated c y l i n d e r f i t t e d w i t h a septum cap and cooled i n an i c e bath. Then the cyanogen c h l o r i d e was d i s t i l l e d i n t o the r e a c t i o n f l a s k through a s t a i n l e s s s t e e l canulae, when the i c e bath was removed. The mixture loosened up and was s t i r r e d at 0°C f o r 1 hour. The f l a s k was then warmed to room temperature, g r a d u a l l y heated and kept at 80°C f o r 1 hour. A f t e r s t i r r i n g overnight at room temperature, the r e a c t i o n mixture was evaporated to dryness under reduced pressure. The crude s o l i d mixture of j>l_ and sodium c h l o r i d e was s t i r r e d w i t h c o l d water. The brown cake obtained by f i l t r a t i o n was d i s s o l v e d i n methylene c h l o r i d e , t r e a t e d w i t h N o r i t e and magnesium s u l f a t e , and f i l t e r e d using C e l i t e . -73- Evaporation of the solvent gave 2.68 g (58.6%) of 61 as a green t h i c k o i l . IR v 2280 (nonconjugated C=N) , 1770 (saturated ester C=0) and max 1720 cm _ 1 ( a r y l ester C=0). 1H NMR(CDC£3) 63.95(s,3H,-0CH 3), 4.00(s,6H,-(CN) 2C-C0 2CH 3), 8.02 (s,2H,aryl) and 8.40 ppm(s,1H,aryl). Mass spectrum: a) high r e s o l u t i o n c a l c u l a t e d f o r C. 0rL „N.0,:380.0757 l O 1/ 4 0 amu, found 380.0779 m/e; b) low r e s o l u t i o n m/e 59(68), 91(30), 92(21), 139(7), 175(11), 177(13), 193(15), 203(12), 247(14), 262(14), 277(100), 278(21), 303(24), 316(15), 336(25), 349(21) and 380(1). 2-Methoxycarbonyl-l,4-phenylenedimalononitrile (62) A s o l u t i o n of 61_ (450 mg, 1.18 mmole) i n THF (20 ml) was added i n t o a 100-ml f l a s k . The f l a s k was f i t t e d with a magnetic s t i r r i n g bar, septum cap and flushed w i t h n i t r o g e n . Sodium borohydride (2 mg) was added and the mixture was s t i r r e d at room temperature while a 5% aqueous s o l u t i o n of sodium carbonate (16 ml, 7.8 mmole) was syringed i n dropwise (8 minutes). A f t e r s t i r r i n g f o r 1 hour, the dark s o l u t i o n was acid i f i e d w i t h 1.5 N h y d r o c h l o r i c a c i d , extracted w i t h methylene c h l o r i d e (2 x 50 ml), and washed with water (2 x 25 ml). The e x t r a c t s were d r i e d and the solvents removed under reduced pressure to y i e l d 268 mg (86%) of compound 6̂2_. The crude product was p u r i f i e d as f o l l o w s . Crude product (120 mg) was d i s s o l v e d i n aqueous sodium carbonate (50 ml) and extracted w i t h e t h y l acetate (3 x 30 ml). The aqueous l a y e r was a c i d i f i e d w i t h 6 N hy d r o c h l o r i c a c i d and extracted w i t h e t h y l acetate (2 x 30 ml). A f t e r -74- d r y i n g , the solvent was evaporated under reduced pressure to give 72 mg of 62_ as a l i g h t green o i l which p a r t i a l l y c r y s t a l l i z e d on standing. A f t e r standing s e v e r a l days the c o l o r of t h i s product darkened gr a d u a l l y . IR v 2260 (nonconjugated C=N) and 1725 cm"1 ( a r y l e s t e r C=0). max 1H NMR (acetone-d 6) 63.93(s,3H-OCH 3), 6.0(bs,2H,(CN) 2CH-); 7.87(s, 2H,aryl) and 8 . 2 ( s , l H , a r y l ) . Mass spectrum m/e 59(28) 87(77) 85(52) 151(26) 152(26) 177(25), 178(37), 207(27), 208(22), 221(26), 222(26), 232(74), 233(100), 238(33), 249(33), 263(28), 264(93) and 265(22). 2-Methoxycarbonyl-7,7,8,8-tetracyanoquinodimethane (56) Ester 62 (0.38 g) was d i s s o l v e d i n 5% aqueous sodium carbonate (50 ml) and n e u t r a l i z e d w i t h 6 N h y d r o c h l o r i c a c i d . A s l i g h t excess of 0.1 M bromine s o l u t i o n i n water was added g r a d u a l l y at room temperature ( p o s i t i v e t e s t w i t h s t a r c h - i o d i n e paper). The r e s u l t i n g green s o l i d was f i l t e r e d , washed with water (50 ml), and d r i e d i n vacuo over phos- phorous pentoxide to y i e l d 0.38 g. A small s c a l e p u r i f i c a t i o n was achieved by sublimation of _56 (36 mg) at 190°C/0.01 mm overnight; the r e s u l t i n g green-yellow s o l i d (1 mg, 3%) had a mp 220-224°C (decomposition). IR(KBr)v 2220 (conjugated C=N) and 1725 (unsaturated ester C=0). max UV-Vis(CH 0CN) A 396 nm (36,800) and 375 nm (sh). 3 max 1H NMR(CDC£3) 6 4.4(s,3H,0CH3) and 7.4-8.6 ppm (m,3H,vinyl). Mass spectrum; high r e s o l u t i o n c a l c u l a t e d f o r C^^^^0^: 262.0491 amu found 262.0495 m/e; low r e s o l u t i o n m/e 55(72), 57(100), 69(64), 71(71), 111(44), 123(33), 125(39), 149(89), 203(37), 204(42), 231(97), 232(58), 262(100) and 263(26). -75- 3,6-Dimethylphthalic anhydride (70) To a w e l l - s t i r r e d suspension of maleic anhydride (24.3 g, 0.247 mole) i n dry e t h y l ether (40 ml) was added slowly 2,5-dimethylfuran (68) (26.4 ml, 0.247 mole). A f t e r s t i r r i n g a t room temperature f o r 20 hours, during which the maleic anhydride d i s s o l v e d and c r y s t a l s of the adduct began to separate, the mixture was cooled i n an i c e - s a l t bath f o r 1 hour. The c r y s t a l s of adduct 69_ (32.8 g, 69%) were c o l l e c t e d and d r i e d , 41 mp 57-59°C ( l i t mp 59-63°C). Compound 69_ was dehydrated d i r e c t l y by slow a d d i t i o n i n t o concentrated s u l f u r i c a c i d (322 ml) at -10°C The s o l u t i o n was s t i r r e d f o r 1 hour at -10°C before i t was allowed to r i s e to 10°C. A f t e r pouring onto 1 kg of crushed i c e the l i g h t brown p r e c i p i t a t e was c o l l e c t e d , washed w i t h i c e water and a i r - d r i e d . A f t e r successive r e - c r y s t a l l i z a t i o n s from benzene and toluene, the desired' 3,6-dimethylphthalic 41 anhydride (70) was obtained i n 24% y i e l d (9.96 g ) , mp 137-138°C ( l i t mp 142-143°C). IR v 1845 and 1765 cm 1 ( a r y l a c i d anhydride C=0) and 1260 cm 1 max J J (C-0 anhydride). hi NMR(CDC£3) 62.60 (s,6H,-CH 3) and 7.39 ppm (S,2H,aryl). Mass spectrum m/e 103(30), 104(68), 120(25), 132(55), 148(65) and 176(100). -76- 3,6-Bis(bromomethyl)phthalic anhydride (71) R e c r y s t a l l i z e d NBS (37 g, 0.208 mole) was weighed i n t o an oven- d r i e d 2-H f l a s k equipped w i t h a magnetic s t i r r i n g bar. The f l a s k was f i t t e d w i t h a r e f l u x condenser stoppered with a septum cap, and the whole system was flushed w i t h n i t r o g e n . A s o l u t i o n of 3,6-dimethyl- p h t h a l i c anhydride (70) (8.33 g, 0.047 mole) i n dry carbon t e t r a c h l o r i d e (710 ml) was added through the condenser followed by 0.1 g of benzoyl peroxide, and the mixture was heated at r e f l u x . A f t e r 8 hours, heating was stopped and the r e a c t i o n mixture was allowed to cool to room tem- perature. Succinimide and unreacted NBS were f i l t e r e d o f f and the f i l t r a t e was evaporated under reduced pressure. The r e s u l t i n g o i l c o n t a i n i n g a mixture of mono- and dibromo d e r i v a t i v e s was l e f t to stand at room temperature. The desired dibromo compound 7_1_ c r y s t a l l i z e d on standing (4.1 g, 26%) and was f u r t h e r p u r i f i e d by r e c r y s t a l l i z a t i o n from a carbon tetrachloride-hexanes mixture (3:7 V/V). The white c r y s t a l s obtained had a mp 121-125°C. IR v 1856 and 1777 cm" 1 (C=0, a r y l anhydride) and 1260 cm"1 max (C-0 anhydride). NMR(CDC£3) 64.86(s,4H,-CH^Br) and 7.82 ppm(s,2H,aryl). Mass Spectrum m/e 63(13), 74(12), 75(15), 76(16), 102(34), 117(13), . 129(9), 146(43), 173(24), 174(100), 175(40), 252(75), 253(87), 254(84), 255(87), 332(7), 334(12) and 336(6). A n a l y s i s c a l c u l a t e d f o r C,~H-Br~0_:C 36.85, H 1.85, Br 49.02; found: C 36.52, H 1.87, Br 49.20. 6-(Bromomethyl)-7-methoxycarbonylphthalide (72) A 50-ml f l a s k was equipped w i t h a magnetic s t i r r i n g bar, a heating -77- mantle, and a r e f l u x condenser protected by a calcium c h l o r i d e tube. The r e a c t i o n v e s s e l was charged w i t h 2,5-bis(bromomethyl)phthalic anhydride (71) (0.5 g, 1.5 mmole), methanol (25 ml) and p - t o l u e n e s u l f o n i c a c i d (10 mg). The mixture was r e f l u x e d f o r 2 hours and then cooled to room temperature. Methanol was evaporated under reduced pressure and the r e s u l t i n g s o l i d was d i s s o l v e d i n e t h y l ether (50 ml). The e t h e r e a l s o l u t i o n was extracted with a saturated s o l u t i o n of sodium bicarbonate (2 x 20 ml) and washed with saturated sodium c h l o r i d e s o l u t i o n (25 ml); a f t e r d r y i n g , the solvent was removed by evaporation under reduced pressure to y i e l d 0.216 g (50%) of crude compound _72_. A small sample was p u r i f i e d by p r e p a r a t i v e t i c (chloroform); the band between 0.6 and 0.8 was removed and extracted w i t h methylene c h l o r i d e . A f t e r evaporation of the solvent white c r y s t a l s of 72 were obtained, mp 125-128°C. IR v 1775 (lactone O O ) and 1735 cm 1 ( a r y l e s t e r C=0) . max J """H NMR(CDCi>3) 64.01(s,3H,-0CH 3) , 4 . 55 (s, 2H,-CH2Br) , 5. 24 (s, 2H ,-CH2" 0-CO) and 7.55 ppm (dd,J=8.0,2H,aryl). Mass spectrum: a) high r e s o l u t i o n c a l c u l a t e d f o r C^H^BrO^: 283.9684 amu, found 283.9685 m/e; b) low r e s o l u t i o n m/e 89(31), 90(18), 91(9), 117(17), 118(25), 129(12), 145(16), 146(24), 147(14), 149(15), 173(60), 174(75), 175(33), 176(18), 205(100), 206(23), 252(87), 253(28), 254(90), 255(28), 284(11) and 286(11). Dimethyl 3,6-dimethylphthalate (75) A 100-ml f l a s k was equipped w i t h a r e f l u x condenser and a calcium c h l o r i d e tube, a magnetic s t i r r i n g bar, and a heating mantle. Dimethyl a c e t y l e n e d i c a r b o x y l a t e (12.34 ml, 0.10 mole), trans ,trans-2,4-hexadiene -78- (13.88 ml, 0.12 mole) and dry benzene (25 ml) were added to the f l a s k and the mixture was s t i r r e d and r e f l u x e d f o r 24 hours. The l i g h t y e llow s o l u t i o n was cooled to room temperature and the solvent was removed under reduced pressure. The crude o i l obtained was d i s t i l l e d i n vacuo to a f f o r d the adduct 7_4; bp 101-103°C (0.4 mm). I t s spectroscopic data were i n agreement with s t r u c t u r e 7_4_. This compound (13.336 g, 0.0595 mole) was treated d i r e c t l y w i t h one equivalent of DDQ (13.97 g, 0.0615 mole) i n benzene (100 ml) and the mixture was s t i r r e d and r e f l u x e d f o r 20 hours. The r e a c t i o n mixture was then d i l u t e d w i t h two volumes of petroleum ether, bp 30-60°C, and the p r e c i p i t a t e of 2,3-dichloro-5,6-dicyano hydroquinone and unchanged DDQ was f i l t e r e d o f f . The f i l t r a t e was passed through a short (16 cm x 5 cm) alumina column which was washed with a d d i t i o n a l petroleum ether u n t i l no more 7_5 could be e l u t e d . The eluates were evaporated to give dimethyl 3,6-dimethylphthalate (10.5 g, 80% o v e r a l l 46 1 y i e l d ) , mp 74-77°C ( l i t . mp 72-75°C). I t s i r , H nmr and mass spectra • , 46 were i n agreement w i t h those reported. Dimethyl 3,6-bis(bromomethyl)phthalate (76) This compound was prepared by a s i m i l a r procedure as that employed i n the preparation of methyl 2,5-bis(bromomethyl)phthalate (59). The only d i f f e r e n c e was that the r e f l u x i n g time was 3 hours i n the case of 75. The reagents used were: dimethyl 3,6-dimethylphthalate (75) (10.5 g, 0.047 mole) i n 130 ml of dry methylene c h l o r i d e , NBS (19.3 g, 0.108 mole), and AIBN (0.5 g). The crude s o l i d obtained a f t e r work-up was d i s s o l v e d i n the minimum amount of b o i l i n g ethanol and the s o l u t i o n was l e f t to stand overnight. On a d d i t i o n of methanol white c r y s t a l s of dimethyl 6-bromo- methyl-3-dibromomethylphthalate (77) p r e c i p i t a t e d and were c o l l e c t e d by -79- f i l t r a t i o n (3.8 g ) , mp 118-126°C ( l i t . 4 7 mp 123°C). I t s i r , 1H nmr and mass spectra were c o n s i s t e n t w i t h s t r u c t u r e 7_7_. The f i l t r a t e was evaporated under reduced pressure to give 11.4 g (64%) of crude dimethyl 3,6-bis(bromomethyl)phthalate (76). A small sample (187 mg) was p u r i f i e d by t i c , using chloroform as eluent. The band at 0.6 was removed and eluted w i t h methylene c h l o r i d e . Evaporation of the solvent gave 115 mg (40%) of compound 7_6 as a c o l o r l e s s o i l . IR v 1730 cm"1 ( a r y l ester C=0) max J 1H NMR(CDC£3) 63.77(s,6H,-0CH 3),4.60(s,4H,-CH 2Br) and 7.38 ppm (s,2 H , a r y l ) . Mass spectrum a) high r e s o l u t i o n c a l c u l a t e d f o r C ^R^^Sr^0^: 377.9102 amu, found 377.9095 m/e; b) low r e s o l u t i o n m/e 77(31), 89(27), 90(21), 102(30), 103(26), 118(21), 129(22), 132(19), 145(67), 162(20), 174(19), 189(50), 205(86), 220(22), 267(40), 269(43), 299(64), 301(67), 347(53), 349(100), 350(44), 351(58), 378(5), 380(8) and 382(5). Dimethyl 3,6-bis(cyanomethyl)phthalate (73) The procedure used i n t h i s r e a c t i o n was the same to that employed i n the preparation of compound 60_. The f o l l o w i n g reagents were used: dimethyl 3,6-bis(bromomethyl)phthalate (76) (7.1 g, 0.0186 mole) i n a c e t o n i t r i l e (91 m l ) , 30% aqueous sodium cyanide (8.8 g, 0.18 mole), and t r i - n - o c t y l a m i n e (0.4 ml). A f t e r the work-up the crude mixture was p u r i f i e d u s i n g a 4 cm x 26 cm column of s i l i c a g e l e l u t e d w i t h carbon t e t r a c h l o r i d e - e t h y l ether (95:5 V/V). The band corresponding to a spot at R^ 0.65 on a n a l y t i c a l t i c was c o l l e c t e d and, a f t e r evaporation of the s o l v e n t s , gave 7_3 (2.2 g, 44%), mp 66-68°C. -80- I R V x 2 2 9 0 ( C E N ) a n d 1 7 3 0 c m 1 (ary! e s t e r C=0) max 1 "H NMR(CDC2.3) 63 .88 (s, 6H ,-0CH3) , 3.91 (s , 4H,-CH2CN) and 7.58 ppm (s,2H , a r y l ) . Mass Spectrum m/e 127(7), 128(8), 153(7), 154(10), 182(18), 213(4), 214(5), 225(5), 240(100), 241(59) and 272(1.2). A n a l y s i s c a l c u l a t e d f o r C ^ H ^ N ^ : C 61.76, H 4.44, Y. 10.29; found: c 61.89, H 4.34, N 10.17. 2,3-Dimethyl-l,4-cyclohexanedione (87) This compound was prepared by a s i m i l a r procedure to that employed i n the pre p a r a t i o n of 2-methyl-l,4-cyclohexanedione (52). The f o l l o w i n g reagents were used: 2,3-dimethylhydroquinone (85) (1.09 g, 0.0079 mole), rhodium c a t a l y s t (0.41 g) and methanol-water mixture (22 ml, 10:1 V/V), which gave 7.08 g (95%) of 2,3-dimethyl-l,4-cyclohexanediol (86), i d e n t i - f i e d by i t s i r and nmr spe c t r a . Compound 8_6 (0.94 g, 6.5 mmole) was not p u r i f i e d but was o x i d i z e d d i r e c t l y w i t h three equivalents of chromium t r i o x i d e s o l u t i o n (7.22 ml) i n chloroform (25 ml) at 5°C. A f t e r the a d d i t i o n of chromium t r i o x i d e (10 minutes), the r e a c t i o n mixture was s t i r r e d f o r 2 hours, and worked up as described p r e v i o u s l y f o r 51, to give 0.684 g (75%) of 2,3-dimethyl-l,4-cyclohexanedione (87). IR v 1710 cm"1 (C=0). max """H NMR (CDC£3) 61.08(d,J=7,6H,-CH 3), 2.70(s,4H,-CH 2-), and 2.2-3.0 ppm (m,2H,-CH-). Mass spectrum m/e 56(61), 69(21), 73(24), 125(87) and 140(100). -81- 2,3-Dimethy1-1,4-bis(dicyanomethylene)cyclohexane (88) To 2,3-dimethyl-l,4-cyclohexanedione (87) (335 mg, 2.39 mmole) i n a 50-ml f l a s k , was added a mixture of m a l o n o n i t r i l e (347 mg, 5.25 mmole) and a c a t a l y t i c amount of 8-alanine (30 mg) i n water (10 ml). The r e a c t i o n mixture was heated at r e f l u x f o r 3.5 hours. The product was i s o l a t e d by f i l t r a t i o n and was washed with water (40 ml). The y i e l d of crude 2,3-dimethyl-l,4-bis(dicyanomethylene)cyclohexane (88) was 379 mg (67%). A small sample, r e c r y s t a l l i z e d from a c e t o n i t r i l e , melted at 186-189°C. IR(KBr) v 2250 (C^N) and 1600 cm" 1 (C=C). max 1H NMR(acetone-d 6) 61.30(d,J=7,6H,-CH 3), 3.10(s,4H,-CH 2") and 3.33 ppm(q,2H,-CH-). Mass spectrum m/e 91(6), 92(6), 118(12), 119(18), 131(16), 145(100), 146(12), 194(18), 207(6), 208(9), 209(6), 219(8), 221(28), 222(5), 234(8), 235(6) and 236(14). A n a l y s i s c a l c u l a t e d f o r C ^ H ^ N ^ C 71.17, H 5.12, N 23.71; found: C 71.27, H 5.16, N 23.96. 5,6-Dimethylrl,4-bis(dicyanomethylene)-2-cyclohexene (89) An oven-dried, 50-ml f l a s k c o n t a i n i n g compound 8£5_ (304 mg, 1.29 mmol), a c e t o n i t r i l e (15 ml) and bromine (0.073 ml, 1.42 mmol) was stoppered w i t h a septum cap and f i t t e d w i t h a magnetic s t i r r i n g bar. I t was flushed with n i t r o g e n while cooled to 0-5°C i n an i c e bath. P y r i d i n e (0.42 ml, 5.16 mmol) was slowly syringed i n t o the r e a c t i o n f l a s k over a period of 15 minutes. A f t e r completion of the a d d i t i o n , the mixture was s t i r r e d at 0°C f o r 30 minutes and then f o r two more hours at room temperature. Cold -82- water was added and the mixture was s t i r r e d f o r about 15 minutes. The r e s u l t a n t s o l i d product was removed by f i l t r a t i o n , washed w i t h c o l d water (50 m l ) , and d r i e d over phosphorous pentoxide i n vacuo (258 mg, 86%). An a n a l y t i c a l sample was r e c r y s t a l l i z e d from a c e t o n i t r i l e , mp 203-205°C. I r v 2260 (C=N) and 1560 cm" 1 (conjugated C=C). max 1H NMR(CD3CN) 61.16(d,J=7,6H,-CH 3), 3.17(m,2H,-CH-) and 7.06 ppm ( s , 2 H , v i n y l ) . Mass Spectrum m/e 138(20), 139(20), 140(20), 142(33), 156(16), 165(26), 169(33), 192(22), 206(22), 207(32), 219(100), 233(33), 234(90) and 235(18). A n a l v s i s c a l c u l a t e d f o r C, .H., _N. :C 71.78, H 4.30, N 23.92; found: 14 10 4 C 71.96, H 4.40, N 24.02. 2,3-Dimethyl-7,7,8,8-tetracyanoquinodimethane (83) 5,6-Dimethyl-l,4-bis(dicyanomethylene)-2-cyclohexene (89) (64 mg, 0.27 mmole), 10% palladium on powdered charcoal (22 mg) and s u l f u r (32 mg) were ground i n a mortar. The homogeneous mixture was placed i n s i d e a small s u b l i m a t i o n apparatus and heated to 180°C f o r 3 hours. Some of the s u l f u r deposited on the c o l d f i n g e r , and the black residue was extracted with b o i l i n g a c e t o n i t r i l e . A f t e r f i l t r a t i o n , the a c e t o n i t r i l e was evaporated under reduced pressure. P u r i f i c a t i o n was achieved by t i c : 50 mg of the crude m a t e r i a l was chromatographed on a 5 cm x 20 cm s i l i c a coated p l a t e , using methylene c h l o r i d e as eluent. The two main components i s o l a t e d from t h i s chromatography were, i n order of e l u t i o n , s t a r t i n g m a t e r i a l and compound 83_ (20 mg, 32%). 2,3-Dimethyl-7,7,8,8-tetracyano- quinodimethane (83) was i d e n t i f i e d by i t s nmr and mass spe c t r a . -83- XH NMR(CD CN) 62.35(s,6H,-CH 3) and 7.43 ppm ( s , 2 H , v i n y l ) . Mass spectrum m/e 81(100), 100(61), 120(28), 132(43), 170(26), 182(78), 220(14) and 232(16). 3,5-Bis(bromomethyl)toluene (97) A 2-1 three neck f l a s k equipped w i t h two e f f i c i e n t condensers and a strong mechanical s t i r r e r was charged w i t h dry carbon t e t r a c h l o r i d e (400 m l ) , d i s t i l l e d mesitylene (138 ml, 1 mole), NBS ( r e c r y s t a l l i z e d from water, 356 g, 2 mole) and benzoyl peroxide (3 g). The mixture was s t i r r e d and heated at r e f l u x . A f t e r 15-30 minutes of r e f l u x , a vigorous r e a c t i o n took place and the heating mantle was then replaced by an acetone-dry i c e bath. Vigorous r e f l u x continued f o r about 15 minutes, a f t e r which time the r e a c t i o n was complete. The r e a c t i o n mixture was then cooled and f i l t e r e d and the f i l t r a t e was evaporated under reduced pressure. The product 96_ (128 g, 46%) was obtained by d i r e c t r e c r y s t a l - l i z a t i o n of the crude r e a c t i o n mixture from ethanol, mp 45-50°C ( l i t . ^ mp 60°C )• I t s spectroscopic data were i n agreement w i t h the proposed s t r u c t u r e . 3,5-Bis(mercaptomethyl)toluene (102) In a 250-ml f l a s k f i t t e d w i t h an e f f i c i e n t r e f l u x condenser and a heating mantle, were placed t h i o u r e a (10.9 g, 0.143 mole) and 95% ethanol (60 ml). The mixture was brought to the r e f l u x temperature and 3,5-bis(bromomethyl)toluene (97) (19.8 g, 0.071 mole) was added i n batches (ca 10 minutes), and the r e f l u x continued f o r 2 hours. A f t e r c o o l i n g , the white p r e c i p i t a t e was f i l t e r e d and d r i e d . The crude s a l t 103 so obtained was mixed w i t h potassium hydroxide (51 g, 0.92 mole) i n water (110 ml) and b o i l e d under r e f l u x f o r 6 hours. The r e a c t i o n mixture was -84- then cooled i n an i c e bath and a c i d i f i e d w i t h 9 M s u l f u r i c a c i d ; i t was extr a c t e d w i t h e t h y l ether (3 x 100 ml), and washed w i t h water (100 ml). A f t e r d r y i n g , the solvent was removed under reduced pressure to give 12.47 g (95%) of 3,5-bis(mercaptomethyl)toluene (102) as a c o l o r l e s s o i l . I t was not p u r i f i e d but was used d i r e c t l y i n the next r e a c t i o n . xll NMR(CDC£3) 61.72(t,J=8,2H,-SH), 2.31(s,3H,-CH 3), 3.64(d,J=8,4H, -CH 2-), and 6.97 ppm (s,3 H , a r y l ) . 6,15-Dimethyl-2,ll-dithia[3.3]metacyclophane. (98)* A 5-1 three neck f l a s k was f i t t e d with n i t r o g e n i n l e t and o u t l e t syringe needles, 3 i n magnetic s t i r r i n g bar and a Hershberg dropping fu n n e l . The r e a c t i o n v e s s e l was charged w i t h potassium hydroxide (9 g, 0.16 mole) d i s s o l v e d i n ethanol-water (9:1 V/V, 2£) and was s t i r r e d under argon at room temperature. A s o l u t i o n of 3,5-bis(bromomethyl)toluene (97) (19.02 g, 0.0684 mole) and 3,5-bis(mercaptomethyl)toluene (102)(12.47 g, 0.0677 mole) i n benzene (1.6£) was placed i n the funnel; i t was then added dropwise over a period of seven days. A f t e r the a d d i t i o n was complete, the r e a c t i o n mixture was f i l t e r e d ; the f i l t r a t e was evaporated under reduced pressure and the crude product was p u r i f i e d by column chromatography, using s i l i c a - g e l (10 cm x 20 cm) and a mixture of benzene and petroleum ether, bp 30-60°C, (2.5:7.5 V/V) to give compound 98_ i n 86% y i e l d (17.48 g). An a n a l y t i c a l sample, prepared by r e c r y s t a l l i z a t i o n 53 from cyclohexane, melted at 101.5-103.5°C ( l i t . mp 102-102.5C). IR v 1601 cm"*1 (C=C aromatic), max 1H NMR(CDC£3) 62.13(s,6H,-CH 3), 3.62(s,8H, -CH 2), 6.58(bs,2H, i n t e r n a l ArH) and 6.66(bs,4H,ArH). Mass spectrum m/e 119(68), 120(80), 149(27), 150(42), 151(52) and -85- 300(100). A n a l y s i s c a l c u l a t e d f o r C 1 8 H 2 u S 2 : C 71.95, H 6.71, S 21.34; found: C 72.15, H 6.74, S 21.22. 5,13-Dimethyl[2.2]metacyclophane (96)* An oven-dried, 1-1 f l a s k i n charged with 6,15-dimethyl-2,11- d i t h i a [3.3]metacyclophane (98) (17.48 g, 0.058 mole) d i s s o l v e d i n dry THF (290 ml), equipped with a magnetic s t i r r i n g bar and stoppered with a septum cap. The f l a s k was then f i t t e d w i t h a nit r o g e n i n l e t and o u t l e t needle, flushed with n i t r o g e n and cooled to -20°C (carbon t e t r a c h l o r i d e - dry i c e ) . n - B u t y l l i t h i u m , as a 1.55 M s o l u t i o n i n hexane, (94 ml, 0.145 mole) was added dropwise to the r e a c t i o n which was s t i r r e d f o r - a f u r t h e r 40 minutes before the a d d i t i o n of methyl i o d i d e (18 ml, 0.29 mole). The mixture turned yellow and a yellow p r e c i p i t a t e was formed. The r e a c t i o n mixture was s t i r r e d f o r an a d d i t i o n a l 30 minutes at -20°C and then warmed to room temperature. I t was quenched with c o l d water (200 ml), extracted w i t h e t h y l ether (2 x 100 ml) and washed with water (100 ml). The aqueous l a y e r was f u r t h e r extracted w i t h methylene c h l o r i d e (100 ml). The combined organic e x t r a c t s were washed with saturated sodium c h l o r i d e s o l u t i o n (100 ml), d r i e d , and the solvents were evaporated under reduced pressure to y i e l d 100 (17.72 g) , which was i d e n t i f i e d by i t s i r and nmr spect r a . Compound 100 was d i s s o l v e d i n dry THF-ether (200 ml, 6:4 V/V) and added to 250 ml of a blue s o l u t i o n of l i q u i d ammonia c o n t a i n i n g chips of l i t h i u m . The r e a c t i o n v e s s e l was kept at -78°C during the a d d i t i o n , and l i t h i u m chips were added whenever the blue c o l o r faded. A f t e r the a d d i t i o n was over, the r e a c t i o n mixture was s t i r r e d f o r 1.5 hours before ammonium c h l o r i d e was added to discharge the blue c o l o r . The f l a s k was -86- then warmed to room temperature and ammonia was allowed to evaporate overnight. Water (100 ml) was added to the r e s u l t i n g mixture which was then a c i d i f i e d w i t h 6 N h y d r o c h l o r i c a c i d . I t was extracted w i t h e t h y l ether (2 x 100 m l ) , washed with water (100 m l ) , and saturated sodium c h l o r i d e s o l u t i o n (100 ml). A f t e r d r y i n g , the sol v e n t s were evaporated under reduced pressure. The r e s u l t a n t l i g h t yellow s o l i d was p u r i f i e d by f i l t r a t i o n through s i l i c a g e l using petroleum ether, bp 30-60°C, subsequent r e c r y s t a l l i z a t i o n from ethanol afforded 96_ (3.8 g, 30%), as white c r y s t a l s , mp 145-146°C ( l i t . 5 3 mp 145-146°C). IR v 1600 cm"1 (aromatic C=C). max """H NMR(CDC£3) 62. 02 (d , J=8 ,4H,axial CH 2), 2 . 93 (d ,J=8, 4H .equatorial CH 2), 2.23(s,6H,-CH 3), 4.03(s,2H,aryl) and 6.67 ppm(s,4H,aryl). Mass spectrum m/e 118(21), 205(18), 206(28), 208(23), 219(20), 221(88), 222(24), 235(18), 236(100) and 237(26). A n a l y s i s c a l c u l a t e d f o r C ^ H ^ : C 91.47, B 8.53; Found: C 91.30, H 8.52. * Due to the p o s s i b l e t o x i c i t y of an intermediate or unknown by-products, t h i s r e a c t i o n should be t o t a l l y c a r r i e d out i n a w e l l vented hood. -87- 5,13-Bis(bromethyl)[2.2]metacyclophane (95) An oven-dried, 200-ml f l a s k was equipped with a magnetic s t i r r i n g bar, a r e f l u x condenser f i t t e d w i t h a n i t r o g e n i n l e t , and a heating- mantle. The r e a c t i o n v e s s e l was charged w i t h 5,13-dimethyl[2.2] metacyclophane (96) (580 mg, 2.46 mmole), NBS ( r e c r y s t a l l i z e d from water, 920 mg, 5.16 mmole), dry carbon t e t r a c h l o r i d e (83 ml) and benzoyl peroxide (40 mg). The r e a c t i o n mixture was then s t i r r e d and heated at r e f l u x f o r 1.5 hours under n i t r o g e n . Heating was discontinued and the mixture was s t i r r e d at room temperature overnight. I t was then f i l t e r e d and the solvent from the f i l t r a t e was removed by evaporation under reduced pressure. The residue was washed w i t h petroleum ether, bp 30-60°C, and d r i e d i n vacuo to give 686 mg (70%) of compound 95_. A small sample was r e c r y s t a l l i z e d from a c e t o n i t r i l e , mp 209-210°C ( l i t . 5 3 mp 205-206°C) IR v 1600 cm"1 (C=C aromatic) and 1780, 1755 cm"1 (1,3,5 t r i s u b -max s t i t u t e d benzene). 1H NMR(CDC£3) 2.14(d,J=8Hz,4H,axial-CH 2-), 3.13(d,J=8Hz,4H, e q u a t o r i a l - CH 2-), 4.25(s,2H,aromatic), 4.56(s,4H,-CH 2Br), 7.10(s,4H,aromatic). Mass spectrum m/e 101(14), 108(12), 109(11), 115(11), 116(25), 202(15), 203(18), 204(11), 217(11), 219(29), 220(15), 233(42), 234(69), 235(18), 299(11), 301(11), 313(100), 314(26), 315(95), 316(24), 392(24), 394(43) and 396(23). 5,13-Bis(cyanomethyl)[2.2]metacyclophane (94) A 200-ml f l a s k was equipped w i t h a magnetic s t i r r i n g bar, a r e f l u x condenser and a heating mantle. The r e a c t i o n v e s s e l was charged w i t h 5,13-bis(bromomethyl)[2.2]metacyclophane (95)(264 mg, 0.67 mmole), sodium cyanide (197 mg, 4.02 mmole) i n water (1 ml), THF (20 m l ) , and tri-n-octylamine(one drop). The mixture was s t i r r e d and heated at r e f l u x -88- overnight. I t was then allowed to co o l to room temperature, poured i n t o c o l d water (25 ml) and extracted w i t h methylene c h l o r i d e (3 x 30 ml). The organic l a y e r was washed with water (30 ml), saturated sodium c h l o r i d e (30 ml) and d r i e d . A f t e r evaporation of the solvents under reduced pressure a l i g h t y e l l o w s o l i d was obtained, t h i s was then r e c r y s t a l l i z e d from methanol (with c o o l i n g i n a carbon t e t r a c h l o r i d e - d r y i c e bath) to give compound 9Jt_ (135 mg, 70%). An a n a l y t i c a l sample, mp 190-195°C, was prepared by sublimation at 180°C/0.2 mm. IR v 2300 (C=N), 1600 (C=C aromatic), max 1H NMR(CDC£3) 62.14(d,J=8,4H,axial-CK^-), 3.13(d,J=8,4H,equatorial-CH 2"), 3.80(s,4H,-CH 2CN), 4.24(s,2H,aromatic) and 7.06 ppm(s,4H,aromatic). Mass spectrum m/e 203(12), 205(19), 206(100), 207(23), 245(13), 246(47), 247(11), 254(12), 286(59) and 287(13). A n a l y s i s c a l c u l a t e d f o r C„ nH 1 0N 0:C 83.88, H 6.34, N 9.78; found: C 83.49, H 6.30, N 9.62. 2,7-Bis(cyanomethyl)-4,5,9,10-tetrahydropyrene (93) 5,13-Bis(cyanomethyl)[2.2]metacyclophane (94)(0.28 g, 1 mmole) was d i s s o l v e d i n dry chloroform (passed through alumina, 15 ml) and added to an oven-dried 50 ml f l a s k . The r e a c t i o n v e s s e l was then charged with a c a t a l y t i c amount of i r o n powder (350 mesh), equipped w i t h a magnetic s t i r r i n g bar and flushed with n i t r o g e n . The mixture was s t i r r e d at 0°C i n an i c e bath f o r 5 minutes before a 10% s o l u t i o n of bromine i n chloroform (1.5 ml, 2.9 mmol) was added dropwise with a s y r i n g e ; then, the r e a c t i o n mixture was s t i r r e d v i g o r o u s l y f o r 1.5 hours at 0°C. The r e a c t i o n was quenched when saturated s o l u t i o n of sodium t h i o s u l f a t e (15 ml) was added followed by s t i r r i n g at room temperature f o r 15 minutes. The c o l o r of the -89- s o l u t i o n went from red-orange to l i g h t green. The r e a c t i o n mixture was then e x t r a c t e d w i t h methylene c h l o r i d e (2 x 25 m l ) , washed w i t h water (2 x 20 ml) and d r i e d . The solvents were evaporated under reduced pressure to give the crude compound 93_, which was p u r i f i e d by column chromatography, using chloroform as eluent, to give 199 mg (70%) of compound J93, mp 230-235°C. IR v 2300(CEN) and 1620 cm"1 (C=C aromatic), max 1H NMR(CDC£ 3): 2.84(s,8H,-CH 2~), 3.66(s,4H,-CH2CN) and 6.95 ppm (s ,4H,aromatic). Mass spectrum: a) high r e s o l u t i o n c a l c u l a t e d f o r C„.H., ,N0:284.1313 z U l o z amu, found 284.1317 m/e; b) low r e s o l u t i o n m/e 206(100), 246(40), 258(28), 284(97) and 285(23). 2.7-Bis(methyl a,a-dicyanoacetate)-4,5,9,10-tetrahydropyrene (92) This compound was prepared by a s i m i l a r procedure as that employed i n the preparation of dimethyl-a,a,a",a^-tetracyano-2-methoxycarbonyl- 1,4-phenylenediacetate(61). The only d i f f e r e n c e was that the r e f l u x i n g time was 1.5 hours i n t h i s case as opposed to 4 hours i n the case of the monoester 6J). The reagents used were: 2 ,7-bis (cyanomethyl)-4 ,5 ,9,10- tetrahydropyrene (93) (519 mg, 1.83 mmole), f r e s h sodium methoxide (5.13 mmole from 118 mg of sodium) dry toluene (30 ml + 25 ml) dry THF (10 m l ) , d i s t i l l e d dimethyl carbonate (2 ml, 24 mmol) and cyanogen c h l o r i d e (0.47 ml, 9.09 mmole). Work-up: solvents and v o l a t i l e components of the r e a c t i o n mixture were d i s t i l l e d o f f under reduced pressure and the r e s u l t i n g l i g h t brown s o l i d was s t i r r e d w i t h l . 5 N h y d r o c h l o r i c a c i d (40 ml) and extracted w i t h e t h y l acetate (3 x 50 ml). A f t e r d r y i n g , the solvent was evaporated under reduced pressure to y i e l d compound _92_ as a dark brown s o l i d , mp 110-115°C (662 mg). -90- IR v 2265 and 2210 cm 1 (C=N) and 1770 (saturated e s t e r C=0) max 1H NMR(CDC£3) 62.94(s,8H,-CH 2~), 3.91(s,6H,-0CH 3) and 7.33 ppm (s, 4 H , a r y l ) . Mass spectrum: a) high r e s o l u t i o n c a l c u l a t e d f or C^^-^s^^^1 450.1328 amu, found 450.1335 m/e; b) low r e s o l u t i o n m/e 59(100), 69(57), 91(36), 92(29), 202(25), 203(16), 206(20), 217(16), 219(15), 258(46), 282(17), 317(39), 341(31), 355(17), 400(15) and 450(5). -91- 2,7-Bis(dicyanomethyl)-4,5,9,10-tetrahydropyrene (91) A s o l u t i o n of 92 (250 mg, 0.55 mmole) i n THF (13 ml) was added i n t o a 50-ml f l a s k . The f l a s k was f i t t e d w i t h a magnetic s t i r r i n g bar, septum cap and flushed w i t h n i t r o g e n . Sodium borohydride (̂ 2 mg) was added and the mixture was s t i r r e d at room temperature w h i l e a 5% aqueous s o l u t i o n of sodium carbonate (8 ml, 4.0 mmol) was syringed i n dropwise (5 minutes). A f t e r s t i r r i n g f o r 1.5 hours, the dark s o l u t i o n was a c i d i f i e d w i t h 6 N h y d r o c h l o r i c a c i d , extracted w i t h e t h y l acetate (3x50 m l ) , and washed w i t h water (2x25 ml). The e x t r a c t s were d r i e d and the solve n t s removed under reduced pressure to y i e l d 162 mg of 2,7-bis(dicyanomethyl)- 4,5,9,10-tetrahydropyrene (91), mp 70-80°C. The crude product was i d e n t i f i e d by i t s i r and nmr sp e c t r a , and was used d i r e c t l y i n the r e a c t i o n that f o l l o w s . IR v 2260 and 2215 cm"1 (C=N) max 1H NMR (CDC£3) 62.93 (s,8H,-CH 2"), 5.00 (s,2H,-CH(CN) 2) and 7.14 ppm (s, 4 H , a r y l ) . 11,11,12,12-Tetracyano-4,5,9,10-tetrahydropyreno-2,7-quinodimethane (90) Compound _9_1 (116 mg, 0.34 mmol) was d i s s o l v e d i n dry methylene c h l o r i d e (25 ml) and placed i n an oven-dried 50-ml f l a s k . The f l a s k was f i t t e d w i t h a magnetic s t i r r i n g bar, septum cap and flushed w i t h n i t r o g e n . The s o l u t i o n was cooled to -78°C (dry ice-acetone bath) and NBS (26 mg, 0.15 mmole) was added followed by t r i e t h y l a m i n e (2 drops). The s o l u t i o n turned dark red instantaneously and i t was s t i r r e d f o r 5 minutes at -78°C before i t was warmed up to 0°C. Hydrochl o r i c a c i d was then added to a c i d i f y the r e a c t i o n mixture and t h i s was d i l u t e d w i t h methylene c h l o r i d e (25 ml). The mixture was washed with water (1x10 ml) and the solvent was d r i e d and evaporated under reduced pressure to y i e l d a dark brown s o l i d (99 mg). -92- The crude product was f i l t e r e d through a short s i l i c a g e l column (eluent: methylene c h l o r i d e ) ; evaporation of the solvent gave 24 mg of compound 90. This compound was f u r t h e r p u r i f i e d by r e c r y s t a l l i z a t i o n from benzene to give compound 90^ (19 mg) as green m i c r o c r y s t a l s , mp 206-208°C (decomposition). IR(KBr) v 2265 and 2225 cm"1 (C=N) max 1H NMR (CDC£3) 62.94 (s,8H,-CH 2") and 7.20 ppm (bs,4H,vinyl). 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