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Studies on the mechanism of olefin metathesis promoted by a heterogeneous catalyst
Journat o f M d e c u h r C~talyWa, 8 (1'980)
8 5 - 90
85
ShOl~ Commt:._;cat~or~
S t u d / e s o n t h e M e c h ~ n k m o f OleFn~ M e t a t h ~ - - ~ P r o m o t e d b y a H e t e r o g e neous Catalyst
M I C H A E L F. F A R O N A and R O B E R T L. T U C K E R Department of Chemia,'ry, The University of Akron. Akron, Ohio 44325 (U.S.A.)
Whereas it has b e c o m e establkhed that the olefm metathesis reaction is Ln_i~ted and propagated by coorrI~nated carbenes, informal/on is ;.ncomplete o n the formation of the flrst cazbene. This is particularly true for heterogeneous cat~/ysts w~ich are active without the concurrent use of a cocatalysf~ This ind/ca,~s that the ini~IIy formed coordinated carbene m t u ~ c o m e from the oI~lqn. Depending on the m e t h o d of formation of the ~LrStformed carbene, the first-formed oleL~as can be d~f,%rent from the norm'~l metat/l~k products, lE.~m~nation of the nature of the _i~rst-formed products, which should be present in catalytic amotmts, e~n provide in.~ght into the m e c h a n i s m of metathesis. T h e catalyst chosen for this study was M o ( C O ) 6 on 7~[-r-ina (3.2 mr, pellets, surface area 2 0 0 m2/g) reported by several workers [I - 3]. T h e catalyst was activated in a 71 m/Parr pressure reactor hy ~-st electrically heating 30 g of 7 ~ / u m i n a at 5 0 0 ~C for 16 h under a v a c u u m of 0.2 Tort. A 40 ml solution of 1.5 g M o ( C O ) 6 in methylcyc/ohexane was injected at 90 5C, the so:vent r e m o v e d under vacunr-, and the c o m b i n e d al-minaM o ( C O ) 6 was heated at 2 0 0 ~ for 4 h under this ~r-e vacu,,m. T h e i~,al catalyst contained about 1.1% M o by weight. O n e problem using this catalyst is that, besides metathesis, olefin isomerization also occurs w h i c h can cause complications in makiz, g mecha~ c studies. With this problem in mind, olefins of structures were selected where the effects of isomer/zation would either be moot, or the extent could be minimized. Several processes for formation of the ini~l carbene have been suggested [ 4 , 5 ] . (a) Coordination followed ~'y a 2,i-hydrogen shift. For 2-pentene, the ini~l carbenes would be CHs~CHzCH2CH~ M
and CK-I3CHz~CHzCH~. M
86
T h e s e c o o r d i n a t e d c a x b e n e s r e a c t w i t h 2 @ e n t e n e t o give rise t o b r a n c h e d fLrst-formed ole-~ns 4 - n m t h y l . 3 J n e p t e n e , 3 ~ n e t h y l - 2 ~ n e x e n e , 3~ethyl-2p e n t e n e a n d 4 ~ t h y l ~ 3 4aexene. (b) Fission of ~lefi~..+q~nisprocess, which is unprecedented, would give rL~e to M = C H 2 C H 3 and M = C H C H 2 C H 3 . These would lead to normal metat h e s i s p r o d u c t s ~_s t h e f'wo't-formed o l ~ s .
(c) I-lydride transfer from the ~ p p o r t . I n t h e p r e p a r a t i o n o f t h e c a t a J y s t , h y d r o g e n c o u l d be ~ n ~ ' ~ tO t;he m e t a l giving rise t o M H as t h e active site [ 6 ] . H y d r i d e a d d i t i o n f o l l o w e d b y ~-H e l i m i n a t i o n gives r:~se t o t h e i n i t i a t i n g ca~benes: CH3CCH2CH2CH
3 and CHaCHaCI C H 2 C H a ,
M
M
w h i c h are t h e ~ r n e i n i t i a t o r s as s h o w n u n d e r (a). (d) Allyl and metaP~+yclobutane formation. Still a f o t a - ~ m e t h o d o f f o r m a t i o n o f t h e initial c a ~ b e n e c a n c o m e a b o u t b y a n ~ o g y t o t h e r e c e n t w o r k o n metL=llm~yclobu~nes r e p o r t e d b y G r e e n a n d c o w o r k e r s [7] a n d s u p p o r t i n g e v i d e n c e b y S h e r m a n a n d S c h r e i n e r [8] : CH CH /-\ / \ CH3CH=CHCH2CH3 ~ CH~ ",CH--CzH 5 + CH3CHf"xCH--CH I
3
I
M
M H
H
/CH2\ CH2\
/CH--CzHs M
/CH II -~ C H a C H \
M
/
~- CI-I2?CH 2
÷ CH2 ~_ CHz M= CHC2Hs ---II CHC2Hs
CHCH3 ~ C H 3 C H = C H z I M_~CHCH 3
Thus, this mechani~un p_,~lictsthe 15rst-fo_~nedolefins to be ethylene, propylene, and !&utene, whether isomeriz~-~ion to l~pentene occurs or not. The i~tlts of the study"~ are s h o w n Lu T~hle 1. Examination of the data in Table 1 shows that no branched olefins are d e t e c t e d , w h i c h s e e m s t o r u l e o u t prccesse¢. (a) a n d (c). F i r s t - f o r m e d oI~_6~s p r o p y l e n e amd i - b u t e n e c a n b e a c c o u n t e d f o r t h r o u g h o l e f i n ffzssion, ff
87
substantial/somerization t o l-pe_utene occtuTed. This is not supported, .~nce 1-butene grows to concen~zations c o m p a r a b l e t o t h a t of 1@entene. T h e data are handled quite adequately by p r o c e s s (d}, tha~ based o n Green's studies. T h e early presence of p r o p y I e n e a n d 1-butene are required, as t h e s e w o u l d be t h e f i r s t - f o r m e d p r o d u c t s . T o s h o w t h a t the~e, i n d e e d , are first f o r m e d , a p l o t o f t h e a p p e a r a n c e o f t h e n o n n ~ m e t a t h e s £ s p r o d u c t s (2-hutene and 3-hexene) and apparent first.formed oleXlus (propylene and l-butene) versu~ time shows thai;u p o n extrapolat/on to zero time, all four of these p r o d u c t s appear at about the smme %/me (exi~-apolation is in t h e 6.5 6.7 minute range).
TABLE
1
A n a l y s i s o~' t h e m e t a t h e s / s o f c i s - 2 - p e n t e c e Component
.~urea (%) Charge
10 mln
2 0 r,~,
30 r.÷.
cis-2-penteue
21.5
3-hex:ene (C&T} trans-2-hexene cis-2-heTene truns-3 -heptene c/s-3-heptene Methylcyclohex.ane b
78.5
0.005 0.01 0.13 0.07 0.02 -20.2 0.3 --0.0I 79_2
0.02 0.06 0.6 0_2 0.I 2.0 14.6 1.2 0.1 0.04 0.07 0.02 81.0
0.05 0.12 1.1 0.4 0_I 5.3 10.0 2.1 0.3 0.1 0.2 0.04 SO.1
Ethylene ~ Propylene l~u~ene trur~-2-hut~ne
cis-2-butene l-penCene truns-2-pent~ne
a E t h y l e n e detected +hroughout, b u t area ~ too l o w to b e deterr-~ned .q,,~- H~atively. l~Solvent.
c a r t e r c a t a l y s t acCi~-aCion, 1 1 m l o f 9 9 ~ c [ s - 2 - p e n C e n e i n 3 8 m l o f m e ~ h y l c y c l o h e T = r , e w a s a d d e d a n d t h e syb-te.z~ p r e s ~ z z ' i z e d t o 4 . 8 aerr~ w i f h d r y ni(;z'ogen. T h e L-e.ac~on s~,stemm w a s malmte/ned at 1 2 0 ± 3 5C..q~--ples were r e m o v e d pe~o
~8
A l s o r e q u i r e d is thai; t h e m o l a r r a t i o o f ~ ' s t - f o r m e d o I ~ n s t o M o be less t h a n u n i t y t h r o u g h o u t . T h e d a t a in t h e t a b l e s h o w t h a t a s l o w g r o w t h o f f i r s t - f o r m e d olef-ms o c c m ~ , b u t a t 3 0 r a i n r e a c t i o n t i m e , t h e 1 - b u t e n e : M o m o l a r r a t i o is a b o u t 0 . 0 5 ; a t o n e h o u r r e a c t i o n t~rne t h e r a t i o is a b o u t 0.1. A t e s t o f t h e m e c h ~ i ~ T n b a s e d o n G r e e n ' s s t u d i e s was c a r r i e d o u t o n the meta~hesis o f 2,4,4-i~Lmethyl-2-pentene; this hindered olefin w o u l d show a s l o w r a t e o f r e a c t i o n a n d c o u l d i s o m e r i z e t o t h e l ~ n e w h e r e t h e firstf o r m e d p r o d u c t s f r o m e i t h e r c a n be p~-~licted. T h e m e t a ~ a c y c l o b u t a n e s f r o m s t a r t i n g a n d i s o m e r i z e d p r o d u c t s w o u l d b e as f o U o ~ . / M\
CH2
\ /CI"ICH a ~ p r o p y l e n e + 4,4Mimethyl-9..-pentene
CH
+ M=CH2 + M=CHC(CHa)3
I
C(CH~)3 /CH2\
M
\ / CH2
C H C H 2 C ( C H a ) a -* 4 , 4 ~ i r n e f l a y l - l - p e n t e n e + M = CH2
M e t a t h e s i s o f t h e s t a r t i n g m a t e r i a l w i t h M = CH2 gives r~se t o i s o b u t y l e n e a n d / o r 3 , 3 ~ i r n e t h y l - l - b u t e n e as t h e F~rst-formed p r o d u c t s . A f t e r 4 rain r e a c t i o n ~ m e t h e f i r s t - f o r m e d olef'ms p r o p y l e n e , 4,4d h n e t h y l - l - p e n t e n e a n d c/~ a n d t r a n s 4 , 4 - d i m e t h y l - 2 - p e n t e n e w e r e i d e n t i , ~ e d as t h e o n l y c o m p o n e n t s p r e ~ n t in t h e r e a c t i o n m i x besides t h e s u b s t r a t e . T h e p r o d u c t m i x , a f t e r 2 0 h , is s h o w n in T a b l e 2. TABLE 2 l%IetathesLs o f 2 , 4 , 4 - t r L m e t h y l - 2 - p e n t e n e a Component Propylene Isobutylene 3,3 -dime thyl-1 -butene
4,4 ~lime thyl-l-pentene 4,4~iLmethyl-2-pentene 2,-'_,~_-i-"ime thyl-2-pen tene b
Area(%) 0.003 0.02 0.06
0.2 0.04 9 9.6
Comment FLrs~-formed olef'm F i r s t - f o r z n e d meLt.thesis p r o d u c t First-formed metathesis product First-formed olefin F i r ~ - f o r r n e d ole~m S t a r t i n g o l e t-m
aReaction c~-ried out o n neat olef'm, 1 2 0 ~C, 4.8 a r m N 2.
b s t a r t i n g purit-y a s ~ y e d a t 10C%.
T h e r e s u l t s o f t h e metatheais o f 2,4,4-trimethy1-2-pentene strongly ~,~pport t h e m e c h a p i ~ o f f o r m a t i o n o f t h e i~ki~l c o o ~ ! L r m t e d ¢a~bene a c c c r ,dSng t o G r e e n ' s s t u d i e s , since o n l y t h e p r e d i c t e d p r o d u c t s w e r e o b s e r v e d . The expected isomer 2,4,4-trimethyl-i-pentene was not observed, probably
89
because of the d ~ c u / t y of separation f l ~ m the IszKe s m o u n t of the starting material. T h e molar ratio of 4,4~imethyI-l~entene, the first-formed olefin found in largest amount, to that of [i~o in the caf~lyst wa~ 0.015 after 2 0 h. In order for a mech~nicr- based o n Green's studies to be o p e ~ / v e , an a/lyric hydrogen m u s t b e present in the o l e f i m . A cr~(/ca/test w a s cJ,.zzied out o n a 1 0 rain r~c(/on of an equa~ v o l - m e m~w~ure of C z D ¢ and CzH~, and the resudts were analyzed by mass spec(zometry e. N o C s H z D ~ was detected; the on/y products pre~ent, in addd~don to the starting m a ~ e r ~ , were propylene molecu/es c o n ~ - i n g the expected distrihu~/on of H and D. This is in accord with the stud/es of O qqeil~ and R o o n e y [9], w h o found that C z H 4 is slowly converted to propylene under metathesis condit/ons. I t s h o u l d be p o i n t e d out t h a t in t h e anaIysis o f t h e r e a c t i o n r - ~ r e a f t e r 2 0 m i n u t e s r e a c t i o n ~ m e , C~H-_Dz is d e t e c t e d , b u t a l s o f o u n d a t t h a t t~me is t h e p r e s e n c e o f b u t e n e s . O b v i o u d y , p r o p y l e n e s ~ r t s t o m e t a t h e s i z e , producing ethylene and 2-butene. Thence r e s u l t s a r e i n s u p p o r t o f t h e m e c h a - g c r - b a s e d o n G r e e n ' s s t u d d e s as t h e m e t h o d o f f o r m a t i o n o f t h e i n i t i a t i n g c a r b e n e . T h e y also r u / e o u t o I e f i n F u s i o n a s a v i a b l e m e t h o d o£ f o r m a t i o n o f m e t a l c a r b e n e s f r o m o I e ~ - ¢ . A l s o c o n c I u s i v e l y r u l e d o u t is a n y c o n s i d e r a t i o n o f a paicwL~e s c h e m e f o r metath~ by this heterogeneous cat2Jy~. O n e additional test of the ~nddcated m e c h s u , i ~ , was car~ed out o n the me~athesis of the m ~ r k e d olefins 4,4~mefhyl-1%uenfene and 4,4~mef/~yl-
2~entene. Isomerization of either of these oleR-s is of n o consequence cince the metaIIaeyclobutane f o r m e d f r o m both o|ef~-~ is identical Therefore, the results of f~he me~a~hesis of these olei~n~ m u s t be identic~/with re~-pect to ~-h-st-formed oie_C-msin the formation of the in~t~] caxbene. T h e ~rst-fonned o[eFms are predicted to be ethylene and 3,3~m6fhyl-l-bu~ene. In the actual studies the ~esu/ts were in fact identical, both predicted first-formed oleFms were observed in each case. T h e only d ~ e r e n c e between the t w o reactions was in their rates; first-formed olefins were observed after 5 ~ n of reac~on for 4,4~4imethyl-2~Den~ene and affer I 0 s i n for the l~ne. References 1" R. L. B a a l s ~ - d C-. C. ]~w.iley, I n d . Eng. Chem., Prod_ Re.s. Dec~top., 3 (1984) 179. 2 L . F . Heckelaherg, R. L. R=- -k.s sad G. C. Bailey, Ind. Ertg. C h e m . , Prod. Res. D e v e l o p . , 8 (1969) 9-59. 3 E . S . Dawie, D. A . W ~ - and C. K e m b a l l , J_ Catal.. 2 4 (1972) 2 7 2 . *A vacuum line was assembled with I I o f ethylene and I ! o f ethylene-d 4 . as well a.s a ~'adua~-=d cylinder, attached f;o the r-~-ifold. The gases were tz-an.~erred to the cylinder
and then to the reactorhy cooling to Hqu~clnitrogen ~emperatuze. In the ae~us/exper~memt. 1 r . I of eanh liquid ethylene was measured and t r a n s f ~ to the reactor and subjected to metatb~4~ conditions ( 1 2 0 ~, 4.8 atn~ N2). Sa.m~p[es were eo~feet.e¢:[[:~---~odfcaHy in special Was =~p~-~on Cubes which were used ~x~i n t r o d u c e the gases f o r ~ - = ~ s~met:rf.c
--~lysLs.
90
4 J. J. R o o n e y and A. Stew~It, Catalysis, 4oi. I, Spe~ml~t Periodical Report~, T h e C"he~nlic~_./S,ocie~"y. 1977, C'h~tp~,e!" S, p. Z77. 5 R. H. G r u b b s , in S. J. Lipp~-'d (ed.), Progress fn I n o r g a n i c Chem~tr-jp, Vol. 24, I n t e r scier, ce, New Y o r k , 197S, ~. I . 6 D . T . Laveety, J. J. Roone.v a n d A . Stew~-~t, J. C a ~ l . , 4 5 ( 1 9 7 6 ) 1 1 0 . 7 M. Ephr/C/~ne, M. L. H. Gzeen and R . M a c K e n z i e , C h e m . C o m m u n . , ( 1 9 7 6 ) 619. M. E p h r i t i k i n e a n d .-r'~I.L. H. G r e e n , C h e m . Cornmwr~_. ( 1 9 7 6 ) 926. 8 E. O. Sherman. and P. R . ,~hreine.r, C h e m . Commu.n_o ( 1 9 7 8 ) 2 2 3 . 9 P . P . O'Neill a n d J. J. R o o l t e y , J. A m . C h e m . ,.~,c~.. 9 4 ( 1 9 7 2 ) 4 383.
8 5 - 90
85
ShOl~ Commt:._;cat~or~
S t u d / e s o n t h e M e c h ~ n k m o f OleFn~ M e t a t h ~ - - ~ P r o m o t e d b y a H e t e r o g e neous Catalyst
M I C H A E L F. F A R O N A and R O B E R T L. T U C K E R Department of Chemia,'ry, The University of Akron. Akron, Ohio 44325 (U.S.A.)
Whereas it has b e c o m e establkhed that the olefm metathesis reaction is Ln_i~ted and propagated by coorrI~nated carbenes, informal/on is ;.ncomplete o n the formation of the flrst cazbene. This is particularly true for heterogeneous cat~/ysts w~ich are active without the concurrent use of a cocatalysf~ This ind/ca,~s that the ini~IIy formed coordinated carbene m t u ~ c o m e from the oI~lqn. Depending on the m e t h o d of formation of the ~LrStformed carbene, the first-formed oleL~as can be d~f,%rent from the norm'~l metat/l~k products, lE.~m~nation of the nature of the _i~rst-formed products, which should be present in catalytic amotmts, e~n provide in.~ght into the m e c h a n i s m of metathesis. T h e catalyst chosen for this study was M o ( C O ) 6 on 7~[-r-ina (3.2 mr, pellets, surface area 2 0 0 m2/g) reported by several workers [I - 3]. T h e catalyst was activated in a 71 m/Parr pressure reactor hy ~-st electrically heating 30 g of 7 ~ / u m i n a at 5 0 0 ~C for 16 h under a v a c u u m of 0.2 Tort. A 40 ml solution of 1.5 g M o ( C O ) 6 in methylcyc/ohexane was injected at 90 5C, the so:vent r e m o v e d under vacunr-, and the c o m b i n e d al-minaM o ( C O ) 6 was heated at 2 0 0 ~ for 4 h under this ~r-e vacu,,m. T h e i~,al catalyst contained about 1.1% M o by weight. O n e problem using this catalyst is that, besides metathesis, olefin isomerization also occurs w h i c h can cause complications in makiz, g mecha~ c studies. With this problem in mind, olefins of structures were selected where the effects of isomer/zation would either be moot, or the extent could be minimized. Several processes for formation of the ini~l carbene have been suggested [ 4 , 5 ] . (a) Coordination followed ~'y a 2,i-hydrogen shift. For 2-pentene, the ini~l carbenes would be CHs~CHzCH2CH~ M
and CK-I3CHz~CHzCH~. M
86
T h e s e c o o r d i n a t e d c a x b e n e s r e a c t w i t h 2 @ e n t e n e t o give rise t o b r a n c h e d fLrst-formed ole-~ns 4 - n m t h y l . 3 J n e p t e n e , 3 ~ n e t h y l - 2 ~ n e x e n e , 3~ethyl-2p e n t e n e a n d 4 ~ t h y l ~ 3 4aexene. (b) Fission of ~lefi~..+q~nisprocess, which is unprecedented, would give rL~e to M = C H 2 C H 3 and M = C H C H 2 C H 3 . These would lead to normal metat h e s i s p r o d u c t s ~_s t h e f'wo't-formed o l ~ s .
(c) I-lydride transfer from the ~ p p o r t . I n t h e p r e p a r a t i o n o f t h e c a t a J y s t , h y d r o g e n c o u l d be ~ n ~ ' ~ tO t;he m e t a l giving rise t o M H as t h e active site [ 6 ] . H y d r i d e a d d i t i o n f o l l o w e d b y ~-H e l i m i n a t i o n gives r:~se t o t h e i n i t i a t i n g ca~benes: CH3CCH2CH2CH
3 and CHaCHaCI C H 2 C H a ,
M
M
w h i c h are t h e ~ r n e i n i t i a t o r s as s h o w n u n d e r (a). (d) Allyl and metaP~+yclobutane formation. Still a f o t a - ~ m e t h o d o f f o r m a t i o n o f t h e initial c a ~ b e n e c a n c o m e a b o u t b y a n ~ o g y t o t h e r e c e n t w o r k o n metL=llm~yclobu~nes r e p o r t e d b y G r e e n a n d c o w o r k e r s [7] a n d s u p p o r t i n g e v i d e n c e b y S h e r m a n a n d S c h r e i n e r [8] : CH CH /-\ / \ CH3CH=CHCH2CH3 ~ CH~ ",CH--CzH 5 + CH3CHf"xCH--CH I
3
I
M
M H
H
/CH2\ CH2\
/CH--CzHs M
/CH II -~ C H a C H \
M
/
~- CI-I2?CH 2
÷ CH2 ~_ CHz M= CHC2Hs ---II CHC2Hs
CHCH3 ~ C H 3 C H = C H z I M_~CHCH 3
Thus, this mechani~un p_,~lictsthe 15rst-fo_~nedolefins to be ethylene, propylene, and !&utene, whether isomeriz~-~ion to l~pentene occurs or not. The i~tlts of the study"~ are s h o w n Lu T~hle 1. Examination of the data in Table 1 shows that no branched olefins are d e t e c t e d , w h i c h s e e m s t o r u l e o u t prccesse¢. (a) a n d (c). F i r s t - f o r m e d oI~_6~s p r o p y l e n e amd i - b u t e n e c a n b e a c c o u n t e d f o r t h r o u g h o l e f i n ffzssion, ff
87
substantial/somerization t o l-pe_utene occtuTed. This is not supported, .~nce 1-butene grows to concen~zations c o m p a r a b l e t o t h a t of 1@entene. T h e data are handled quite adequately by p r o c e s s (d}, tha~ based o n Green's studies. T h e early presence of p r o p y I e n e a n d 1-butene are required, as t h e s e w o u l d be t h e f i r s t - f o r m e d p r o d u c t s . T o s h o w t h a t the~e, i n d e e d , are first f o r m e d , a p l o t o f t h e a p p e a r a n c e o f t h e n o n n ~ m e t a t h e s £ s p r o d u c t s (2-hutene and 3-hexene) and apparent first.formed oleXlus (propylene and l-butene) versu~ time shows thai;u p o n extrapolat/on to zero time, all four of these p r o d u c t s appear at about the smme %/me (exi~-apolation is in t h e 6.5 6.7 minute range).
TABLE
1
A n a l y s i s o~' t h e m e t a t h e s / s o f c i s - 2 - p e n t e c e Component
.~urea (%) Charge
10 mln
2 0 r,~,
30 r.÷.
cis-2-penteue
21.5
3-hex:ene (C&T} trans-2-hexene cis-2-heTene truns-3 -heptene c/s-3-heptene Methylcyclohex.ane b
78.5
0.005 0.01 0.13 0.07 0.02 -20.2 0.3 --0.0I 79_2
0.02 0.06 0.6 0_2 0.I 2.0 14.6 1.2 0.1 0.04 0.07 0.02 81.0
0.05 0.12 1.1 0.4 0_I 5.3 10.0 2.1 0.3 0.1 0.2 0.04 SO.1
Ethylene ~ Propylene l~u~ene trur~-2-hut~ne
cis-2-butene l-penCene truns-2-pent~ne
a E t h y l e n e detected +hroughout, b u t area ~ too l o w to b e deterr-~ned .q,,~- H~atively. l~Solvent.
c a r t e r c a t a l y s t acCi~-aCion, 1 1 m l o f 9 9 ~ c [ s - 2 - p e n C e n e i n 3 8 m l o f m e ~ h y l c y c l o h e T = r , e w a s a d d e d a n d t h e syb-te.z~ p r e s ~ z z ' i z e d t o 4 . 8 aerr~ w i f h d r y ni(;z'ogen. T h e L-e.ac~on s~,stemm w a s malmte/ned at 1 2 0 ± 3 5C..q~--ples were r e m o v e d pe~o
~8
A l s o r e q u i r e d is thai; t h e m o l a r r a t i o o f ~ ' s t - f o r m e d o I ~ n s t o M o be less t h a n u n i t y t h r o u g h o u t . T h e d a t a in t h e t a b l e s h o w t h a t a s l o w g r o w t h o f f i r s t - f o r m e d olef-ms o c c m ~ , b u t a t 3 0 r a i n r e a c t i o n t i m e , t h e 1 - b u t e n e : M o m o l a r r a t i o is a b o u t 0 . 0 5 ; a t o n e h o u r r e a c t i o n t~rne t h e r a t i o is a b o u t 0.1. A t e s t o f t h e m e c h ~ i ~ T n b a s e d o n G r e e n ' s s t u d i e s was c a r r i e d o u t o n the meta~hesis o f 2,4,4-i~Lmethyl-2-pentene; this hindered olefin w o u l d show a s l o w r a t e o f r e a c t i o n a n d c o u l d i s o m e r i z e t o t h e l ~ n e w h e r e t h e firstf o r m e d p r o d u c t s f r o m e i t h e r c a n be p~-~licted. T h e m e t a ~ a c y c l o b u t a n e s f r o m s t a r t i n g a n d i s o m e r i z e d p r o d u c t s w o u l d b e as f o U o ~ . / M\
CH2
\ /CI"ICH a ~ p r o p y l e n e + 4,4Mimethyl-9..-pentene
CH
+ M=CH2 + M=CHC(CHa)3
I
C(CH~)3 /CH2\
M
\ / CH2
C H C H 2 C ( C H a ) a -* 4 , 4 ~ i r n e f l a y l - l - p e n t e n e + M = CH2
M e t a t h e s i s o f t h e s t a r t i n g m a t e r i a l w i t h M = CH2 gives r~se t o i s o b u t y l e n e a n d / o r 3 , 3 ~ i r n e t h y l - l - b u t e n e as t h e F~rst-formed p r o d u c t s . A f t e r 4 rain r e a c t i o n ~ m e t h e f i r s t - f o r m e d olef'ms p r o p y l e n e , 4,4d h n e t h y l - l - p e n t e n e a n d c/~ a n d t r a n s 4 , 4 - d i m e t h y l - 2 - p e n t e n e w e r e i d e n t i , ~ e d as t h e o n l y c o m p o n e n t s p r e ~ n t in t h e r e a c t i o n m i x besides t h e s u b s t r a t e . T h e p r o d u c t m i x , a f t e r 2 0 h , is s h o w n in T a b l e 2. TABLE 2 l%IetathesLs o f 2 , 4 , 4 - t r L m e t h y l - 2 - p e n t e n e a Component Propylene Isobutylene 3,3 -dime thyl-1 -butene
4,4 ~lime thyl-l-pentene 4,4~iLmethyl-2-pentene 2,-'_,~_-i-"ime thyl-2-pen tene b
Area(%) 0.003 0.02 0.06
0.2 0.04 9 9.6
Comment FLrs~-formed olef'm F i r s t - f o r z n e d meLt.thesis p r o d u c t First-formed metathesis product First-formed olefin F i r ~ - f o r r n e d ole~m S t a r t i n g o l e t-m
aReaction c~-ried out o n neat olef'm, 1 2 0 ~C, 4.8 a r m N 2.
b s t a r t i n g purit-y a s ~ y e d a t 10C%.
T h e r e s u l t s o f t h e metatheais o f 2,4,4-trimethy1-2-pentene strongly ~,~pport t h e m e c h a p i ~ o f f o r m a t i o n o f t h e i~ki~l c o o ~ ! L r m t e d ¢a~bene a c c c r ,dSng t o G r e e n ' s s t u d i e s , since o n l y t h e p r e d i c t e d p r o d u c t s w e r e o b s e r v e d . The expected isomer 2,4,4-trimethyl-i-pentene was not observed, probably
89
because of the d ~ c u / t y of separation f l ~ m the IszKe s m o u n t of the starting material. T h e molar ratio of 4,4~imethyI-l~entene, the first-formed olefin found in largest amount, to that of [i~o in the caf~lyst wa~ 0.015 after 2 0 h. In order for a mech~nicr- based o n Green's studies to be o p e ~ / v e , an a/lyric hydrogen m u s t b e present in the o l e f i m . A cr~(/ca/test w a s cJ,.zzied out o n a 1 0 rain r~c(/on of an equa~ v o l - m e m~w~ure of C z D ¢ and CzH~, and the resudts were analyzed by mass spec(zometry e. N o C s H z D ~ was detected; the on/y products pre~ent, in addd~don to the starting m a ~ e r ~ , were propylene molecu/es c o n ~ - i n g the expected distrihu~/on of H and D. This is in accord with the stud/es of O qqeil~ and R o o n e y [9], w h o found that C z H 4 is slowly converted to propylene under metathesis condit/ons. I t s h o u l d be p o i n t e d out t h a t in t h e anaIysis o f t h e r e a c t i o n r - ~ r e a f t e r 2 0 m i n u t e s r e a c t i o n ~ m e , C~H-_Dz is d e t e c t e d , b u t a l s o f o u n d a t t h a t t~me is t h e p r e s e n c e o f b u t e n e s . O b v i o u d y , p r o p y l e n e s ~ r t s t o m e t a t h e s i z e , producing ethylene and 2-butene. Thence r e s u l t s a r e i n s u p p o r t o f t h e m e c h a - g c r - b a s e d o n G r e e n ' s s t u d d e s as t h e m e t h o d o f f o r m a t i o n o f t h e i n i t i a t i n g c a r b e n e . T h e y also r u / e o u t o I e f i n F u s i o n a s a v i a b l e m e t h o d o£ f o r m a t i o n o f m e t a l c a r b e n e s f r o m o I e ~ - ¢ . A l s o c o n c I u s i v e l y r u l e d o u t is a n y c o n s i d e r a t i o n o f a paicwL~e s c h e m e f o r metath~ by this heterogeneous cat2Jy~. O n e additional test of the ~nddcated m e c h s u , i ~ , was car~ed out o n the me~athesis of the m ~ r k e d olefins 4,4~mefhyl-1%uenfene and 4,4~mef/~yl-
2~entene. Isomerization of either of these oleR-s is of n o consequence cince the metaIIaeyclobutane f o r m e d f r o m both o|ef~-~ is identical Therefore, the results of f~he me~a~hesis of these olei~n~ m u s t be identic~/with re~-pect to ~-h-st-formed oie_C-msin the formation of the in~t~] caxbene. T h e ~rst-fonned o[eFms are predicted to be ethylene and 3,3~m6fhyl-l-bu~ene. In the actual studies the ~esu/ts were in fact identical, both predicted first-formed oleFms were observed in each case. T h e only d ~ e r e n c e between the t w o reactions was in their rates; first-formed olefins were observed after 5 ~ n of reac~on for 4,4~4imethyl-2~Den~ene and affer I 0 s i n for the l~ne. References 1" R. L. B a a l s ~ - d C-. C. ]~w.iley, I n d . Eng. Chem., Prod_ Re.s. Dec~top., 3 (1984) 179. 2 L . F . Heckelaherg, R. L. R=- -k.s sad G. C. Bailey, Ind. Ertg. C h e m . , Prod. Res. D e v e l o p . , 8 (1969) 9-59. 3 E . S . Dawie, D. A . W ~ - and C. K e m b a l l , J_ Catal.. 2 4 (1972) 2 7 2 . *A vacuum line was assembled with I I o f ethylene and I ! o f ethylene-d 4 . as well a.s a ~'adua~-=d cylinder, attached f;o the r-~-ifold. The gases were tz-an.~erred to the cylinder
and then to the reactorhy cooling to Hqu~clnitrogen ~emperatuze. In the ae~us/exper~memt. 1 r . I of eanh liquid ethylene was measured and t r a n s f ~ to the reactor and subjected to metatb~4~ conditions ( 1 2 0 ~, 4.8 atn~ N2). Sa.m~p[es were eo~feet.e¢:[[:~---~odfcaHy in special Was =~p~-~on Cubes which were used ~x~i n t r o d u c e the gases f o r ~ - = ~ s~met:rf.c
--~lysLs.
90
4 J. J. R o o n e y and A. Stew~It, Catalysis, 4oi. I, Spe~ml~t Periodical Report~, T h e C"he~nlic~_./S,ocie~"y. 1977, C'h~tp~,e!" S, p. Z77. 5 R. H. G r u b b s , in S. J. Lipp~-'d (ed.), Progress fn I n o r g a n i c Chem~tr-jp, Vol. 24, I n t e r scier, ce, New Y o r k , 197S, ~. I . 6 D . T . Laveety, J. J. Roone.v a n d A . Stew~-~t, J. C a ~ l . , 4 5 ( 1 9 7 6 ) 1 1 0 . 7 M. Ephr/C/~ne, M. L. H. Gzeen and R . M a c K e n z i e , C h e m . C o m m u n . , ( 1 9 7 6 ) 619. M. E p h r i t i k i n e a n d .-r'~I.L. H. G r e e n , C h e m . Cornmwr~_. ( 1 9 7 6 ) 926. 8 E. O. Sherman. and P. R . ,~hreine.r, C h e m . Commu.n_o ( 1 9 7 8 ) 2 2 3 . 9 P . P . O'Neill a n d J. J. R o o l t e y , J. A m . C h e m . ,.~,c~.. 9 4 ( 1 9 7 2 ) 4 383.