Journal ofMotecu[ar Cctc/ysiz. 8 ( 1 9 8 0 ) 73 - 83 73 I~sevier S e q u o i a S .A. , L a u ~ - e - - P r in ted in t h e N e t h e r l a n d s

P I ~ . P A R A T I O N A N D C H A R A C T E R I Z A T I O N O F A C T I V E _NIOBIUM, T A N T A L U M A N D T U N G S T E N M E T A T H F ~ I S C A T A L Y S T S

RICHARD SCHROCK ~, SCOTT [~OCKLAGE, JEFFREY WENGROVI-US, GREGORY RUPPRECHT and/ERE FELL~',£ANN

_~assachusaett~ [natf~-~e o f T e c h n o l o g y , Dept. o f Chern~tr~, Cambridge, ~fass. 02139 (O:S.A.)

~ n ~ a r y

Octahedral complexes of the .t-~-pe t'r~n..,¢, met- and c/s. mer-_%[(C[-lCMe3)- (L)zXa (M = Nb or Ta , L = a ~ p h o s p h i n e , X = C1 o r Br) r e a c t w i th terminal o[efins to give only org~-~c products arlene from rearrangement of an intermediate metallacyclobutane complex, and o le fJn complexes ( o l ~ t q , = ethylene, propylene, styrene) of +,he type ~r~, mer-Ta(olef£n)(L)=X_~. Replacing two of the h-=lides with t-butoxide ligands yields complex~ of the type M(CHCMe~)(OCMe3)2(L)CI which are act£~e metathesis catalysts for c&s-2-pentene. We have extended the principles of Group V chemistry to tungs~n by tran~fe_,Ting a neopentyIidene Iigand from Ta(CHCIVIes}(PEt3)2- C13 t o W(O)(OCMe~)4 t o give W(O)(CHCI%{e3)(PEt3)2CI2 in high y ie ld . I t reac ts s lowly w i t h ~ t h y l e n e , b u t e n e , a n d s t y r e n e t o give t e r t ~ r y b u t ~ ' ! e t h T l e n e and ana logous c o m p l e x e s o f t h e t y p e W(O)(CHR)(PEt~)zC1 z ( I t = H, Pr, Ph) . I n t he p resence o f a t r ace o f ~dCl~ the.se r e a c t i o n s are r ap id a t 25 ~C a n d t h e so lu t ions are act ive f o r me ta thes i$ o f 1 -bu t ene a n d c~ -2 -pen t ene . We have

d e v e l o p e d a t e s t f o r m e t a t h e s i s o f 1 -bu tene wh ich tel ls us w h a t are s o m e o f t h e r eac t i ons o f i n t e r m e d i a t e m e t a l l a e y c l o b u t a n e a n d ~ ,~y l idene com- p lexes w h i c h t e r m i n a t e t h e m e t a t h e ~ cha in r eac t ion .

Introduction

To date, no one has prepared and s~'uc~u,-ally and chemically character- ized an acthre metathesis catalyst [I] *:~. Therefore, although the ali-ylidene

*C~miWe and H e n r y Drey£us T e a c h e r Scho la r G r a n t R e d p i e a t , 1978 . Addres s cor - r e s p o n d e n c e to £h~ author.

**We do not intend to slight the m~.y contributions by workers who model met~- thesis r eac t ions o r w h o have ohse_-wed s o m e me ta the s i s ac t iv i ty u n d e r foro~n~ c o n d i t i o a s employing compounds which possess a carhene-type H@~ancl. By "active" we mean at least seve_ral turnovers under mild conditions. We also wxU/not attempt Co adequately re£e=e--ce all inddvidual workers but simply refer ~.he reader to the m.ny e.~ceHent re~r[e~ in tb~

[z].

74

cha in mechani.~Tn is almost CeX~_ i~ |y correct, m~jor questions such as the following rem~n una-~wered: What ia the metal's oxidafdon stat~? Can the alky~dene ligand react directly with th~ olef_m or must the oletin first coordinate to the metal? What is (are) the chain termination step(s)? What is the role of co-cataly.~s? Is an alkylidene or a mefallacyclobutane complex t h e d o m i n a n t ac t ive i n t e r m e d i a t e ? Is t he c a t a l y s t a m o n o m e r ?

In t h e pas t f ew years , we have been s ~ d y i n g alk-ylidene c o m p l e x e s o , ~ niobium and tantalum (in the +5 oxida~on sgaf~ counl;ing the =]Icylidene ligand as a d{~nion) and how they react with olefins to give products result- ing ~-om the rearrangement of a pres~,med metallacyclobutane intermediate. We have now been able to slow this rearrangement with respect to metathesis by changing the ligands, and have isolated and characterized several catalysts which are active for the metathpc4= of internal olefins. We have also been able to extend these principles to tungsten.

~l~ne resul ts report~_=cl h e r e are p r e l i m i n a r y so we c a n n o t y e t p rov ide detailed experimental procedures. We will, however, ~e elomenfal analyc~s results and NMR data for several key compounds.

Resul t s a n d d iscuss ion

DineopentT1 (M = Nb or Ta) a n d d i b e n z y l (M = Ta) c o m p l e x e s o f t h e t 3 ~ e M(CH2R)2X3 (X = C1 or Br) r e a c t w i t h P o r N d o n o r l igands (L; e ~ . PRa) t o give m i x t u r e s o f c/s, mer- and t;',ans, m e r - M ( C H R ) L 2 X ~ (1) [ 2 ] . M o n o d e n t a t e phosphLnv IJgands are labile a n d a p p a r e n t l y t~exeby a l low a t e r m i n a l o le f in t o c o o r d i n a t e to t h e me ta l . We believe t w o met~ l lacyc lo - b u t a n e c o m p l e x e s t h e n f o r m a n d rea r range t o give a t o t a l o f f o u r organic p r o d u c t s as s h o w n in eqn. (1). We see n o s t o i c h i o m e t r i c m e t a t h e s i s p r o d u c t s o r c y c l o p r o p a n e s .

R

~=-C}"['~. 4- R 'C- . I=~. , , I 2 ~ M ~ - R ' +

/ \ R ~

R

R R

\ \ (1)

T h e o rganomet~ l l l c prodc:c ts are ole~-m c o m p l e x e s (ole_~n = e t h y l e n e , p ropy! - ene , s ty rene ) o f t h e t y p e / T a n s , mer-Ta(olpCln)L2X3 ( i f M = Ta) a n d olef in- f ree c o m p l e x e s o f t h e t y p e [NbL2X3] 2 ( i f M = Nb) [ 2 ] . I n t e r n a l o lef ins do n o t r e a c t r ead i ly w i t h I .

O n e ch lo r ide t igand in I can be rep lac~d b y a tez-t-butoxide t igand to give an o c t a h ~ c o m p l e ~ o f as y e t , m k n o w n con,~i~--at ion (2; eqn . (2); t h e PMea l igands are equ~-a len t a n d re la t ive ly t rans a n d 6 C~ = 282 p p m , 1JcH = 110 Hz, zJcp = 8.4 H_z).

75

Ta(CHzCMes)2(OCMes)X2 2 ~ e s M(CI-{CMes)(OCMe3)LzXz (2;) CHzClz 2

--L I + 2 L i O C ~ e s , M ( C ~ G ~ e s J ( O C M e s ) z L X (3)

3 O n replac ing a s e c o n d c ~ o r i d e I /gand wi th a t e r t - hu tox ide , o n e T. is los t give t-zve-coord~nate 3 (An~dysis: c ~ c . f o r TaCzeH3~CIPOz, C 37.".'7, H 7 .33; f o u n d , C 37 .84 , H 7.z~5). T h e c o , ~ r a ~ i o n s o f t he se c o m p ! e x e s are uncertain a t th is ~ n e ; the t w o ~ b u t o x i d e il~gands are inc-quivalent. The s~nal for the neopentylidene ~:arbon in 3 (IV[ = TR) is found at ~-7S ppm with *Jc~ = 114 Hz and ~Jc~ = ~ Hz. Both electzordc and static factors pro~rably are responsible for the loss of one L from M(CHCMea)(OCMe~)2- LzX to give 3; M(CHCMes)(OCMes)2LzX2 can be observed by NI~I~ at a b c u t --SO ~C (6 C~ = 275 ppm, ZJc~ = 128 PIz, 2Jc2 = 8 Hz). We attribute the progressive/y higher value for ~Jc~ in the series I -~ @ -~ (3 + L) to a lower ~fgniLT of the me~al for the electrons in the C[-I~ bond [S] and cor- r e~pondh lg ly less d i s t o r t i o n o f t h e M= ~ g e o m e t r y a w a y f r o m t h e "normal ' b o n d angles o n e w o u l d o t h e r w i s e p r e d i c t [ 4 ] . ~Ve a t t r i b u t e th i s r e su l t t o t h e fac£ t h a t an adkoxide l igand is p r o b a b l y a b e t t e r r . ~ l e c t r o n d o n o r f / , an a ch lo r ide l igand to an elec~xon-defic~ent m e t a l

T e r m i n a l olaf 'ms react with 3 s ign i f i can t ly d i f f e r e n t l y t h a n t h e y r e a c t w i t h 1. E x a m p l e s are s h o w n in eqns . (4) a n d (5).

__ /,m Ta(CHCMes)(OCMes)2(PMe3)CI + C2H4 -~ + + c~. 4~

L CI_.~ I / O ~ e 3

/ T a . ., l%,{eafX9 I \ ~---(D~,H.~)

L 4 (4)

( +l:r~e3 ) / Ta(CHCMe3)(OCMes)2(PMes)CI + PhCH=CH2 , > +

Ta(CHPh) (O C~Ie3)2(PMe3) 2Cl (5)

5

Note that we observe me~tlzesi~ products only_ The benzylidene complex (5) can be isolated as ]irne green crystals (5 C~ = 258 ppm). It loses one Pl~[e 3 in s o l u t i o n t o give an unstable ber~ylidene complex confairdng one P~%{e3 ligand (possibly [Ta(CHPh)(P~{e~)(OCMes)zCl]z; 5C~ = 957; el. [Ta- (CHC-%{es)(Pl%[e3) cI-~ ] 2 [3] ) which subsequently decomposes to give st,]benes, Therefore, a mef~hylene complex must be the init~l product of reaction 4, it mtLst react reach~y with ethylene to give (eventually) a rearrangement product, propylene.

In order to determine in more detail the course of s~ch reactions with various ~ylidene complexes, we have developed a test reaction u.~ng

76

S c h e m e I . R e a c t i o n p a t h w a y s i n t h e l - h u b e n e t e s t f o r m e ~ t h ~ - ' ~ a c t i v i t y

~ ~ " ~ 3 ÷ ~

" b 1 ~ . e 3 C'~e 3

.M=~2 .W~ ~ ~ olefin

I I

C5 - -

1-bu tene . T h e p o s t u l a t e d cou r se o f th is r e a c t i o n is s h o w n in S c h e m e I. M o s t o f t h e p r o d u c t s o f t h e possible r e a r r a n g e m e n t a n d m e t a t h e s i s r e~ r t i ons can be s epa ra t ed f r o m o n e a n o t h e r a n d i d e n t i f i e d by c o m p a r i s o n wi th a u t h e n t i c _~mples. We shou ld n o t e t h a t t h e s~,m o f t h e a m o u n t s o f all p r o d u c t s con- tai_nir.g a t e r ~ y b u t - y l g roup aq,,~l~ t h e e x t e n t :~f t he i_q.if':i~l r e a c t i o n whi le % ~ n - - E ( C s + ~-'7 + CMe3) equals t h e am__~,__~t o f a n y o t h e r t e r m i n a t i o n s tep (e.g. bimolec t f la r d e c o m p o s i t i o n o f Alk-y~idene co .~p lexes ) ; these f igures will p r o b a b l y va ry b y a t leas t -+ 5%. I f we a s sume tha.*. 3nly m e t h y l e n e c o m p l e x e s d e c o m p o s e bimolec,,1~r~y t o a n y ~ a n t e x t e m ~, .~nd t h a t all m e t h y l e n e c o m p l e x e s d o so, t h e n t h e m ~ i m u m a m o u n t o f 3&~exenes shou ld equa l t h e a m o u n t o f t e r t i a r y b u t y l e t h y l e n e f o r m e d in t h e ini t ia l r eac t ion . A n y excess is, th~_refore, p r o d u c t i v e me ta thes i s . We s h c u l d also n o t e t h a t we d o n o t see a n y ev idence t h a t a p r o p y l i d e n e c o m p l e x rear ranges t o a p r o p y l e n e c o m p l e x in th~s s y s t e m (eqn . (6)).

. : = / - - ,-,v- m_ +11"" (6 )

We f o u n d p rev ious ly t h a t such a r e a r r a n g e m e n t was n o t a d e c o m p o ~ t 2 o n p a t h w a y o f t h e 18 e l ec t ron e t h y I i d e n e c o m p l e x , T a ( q S ~ s H s ) ~ ( ~ e ) (CH3) [51.

T h e t~nzlts o f f ive mr.¢ are s h o w n in Tab le l . T h e f i r s t shows w h a t we a l ready m , ~ = ; ,.'niti~l met~ l lacyc les o n l y rearrange. T h e s e c o n d shows t h a t

%

m

L

° ° ° ? ~ 0

~ E

E ~ N 0 O ~

= N N E

N , - ~ 5

~ - ~ . ~ . ~

~,.~ o ~ _ ; . "

77

78

a b o u t 30% me t~ thes i s o c c u r s init~*ny i f o n e t e r t i a r y b u t o x i d e is s u b s t i t u t e d f o r a c,hloride l igand b u t t h e t w o m e t a H a c y c l e s f o r m e d f r o m t h e p r o p y l i d e n e c o m p l e x a n d Z-buCene rea r range exc lus ive ly t o l /near a n d b r a n c h e d C7 o le fms . T h e th i rd e x p e r i m e n t s h o w s t h a t t h e init ial m e ~ , a c y c l e s o n l y meLathes ize , b u t a n y m e t h y l e n e c o m p l e x e i t he r d e c o m p o s e s b i m o l e c u l a r l y ( ~ 50~o) o r gives a m e t a l l a c y c l e w h i c h rea r ranges t o a b r a n c h e d Cs. N o t e t h a t all 8 - h e x e n e c o m e s f r o m t h e r e a c t i o n o f t h e ini t ial p r o p y l i d e n e w i t h 1 -hu tene . T h e f o u r t h d e m o n s l ~ t e s t h a t a N b m e t h y l e n e c o m p l e x d e c o m p o s e s m u c h m o r e r ap id ly t h a n a T a m e t h y l e n e c o m p l e x ( t h e y n e e d n o t b e iden t ica l ) . T h e f i f t h s h o w s t h a t th is d e c o m p o s i i ~ o n can b e s l o w e d b y add ing m o r e L; the re - fo r e , i t s eems l ike ly t h a t m o s t i f n o t all o f this d e c o m p o s i t i o n c o n e ~ o f birnolecu/ar combination o f methylene ligands. By adding L, the ch~ i - can be .extended, Le. some of the methylene complex survives to produce a propylidene complex and ethylene (see footmote c) when it reac~ with 1-butene. It is the only run which yields productive metathesis (about 100% per Nb).

These experimen~ are the i-h-st attempts tow--~d understanding in detail how and x~ny these metatbesis catalysts work. We feel that these and similar experkcents will help establ,L~h the following:

(]) An olefin aimo.~t certainly must coordinate to the metal before a metallac'/clobutane complex can form.

(~-) Rearrangement of a me+L~II~cyclobutane complex must be slowed rela:ive to the rate of a n~etathesis reaction as more electron density is added to Lhe :z~._~l via ,7<lonor ligands. (The idea came from the observation that met~lhc :Tclopentane complexes also become more stable toward fl~lirnination i f :r-el_eztron d o n o r l igands are p r e s e n t [61 -) A similar a r g u m e n t c o u l d be i nvo lved t o he lp exp la in w h y the se a l k y l i d e n e l igands d o n o t r ea r range t o an o lef in . (The a l t e rna t ive e x p l a n a t i o n is t h a t t he p r o p y l i d e n e c o m p l e x ~ m p l y reacts with l-butene faster t h a n it rearranges; .~e later.)

(3) Rearrangement of (especially/3ethyl) me,~,acyclobutane inter- mediates and bimolec,,1~r decomposition of methylene complexes are impor~.:ant chain termination steps. We cannct yet say to ~'hat d ~ pro- pylidene complexes decompose bimoleoJ1~rly to 3-hexenes or when al- kylidene ligands rearrange to olefins.

(4) The initial metathesis products cannot he ra t ioD~l ized easily by invoking what is ~Imos£ certaiDJ.y a nucleophBic character of the ~l~-lidene ligand [4]. It is not yet clear what factors determine the m~.-mer in which an o.~efin adds to an alkylJdene ligand.

(5) %-he system is active in the presence of an electron donor (e.g. PMe3) and is also active in we~_Icly donor solvents such as diethyl ether. In fact, a donor ~¢ficient/y blocks some bimolec*,Isr decomposition of alkylidene complexes.

(6) Co~.atalysts such as AICI3_~R= are not neceemry and the in~ti~! alkyl groups on the me-~l serve as the ~il,-yIidene source by ~-abstraction [4].

Cis-P.-pentene does not react readily with M(CHCMe3)(PMes)zCI.~ since i~ evi_-dently canno~ compete effectively with PMe 3 for a coordination site.

7~

IC d o e s react rea,~-~y wif , h M ( C H C M e z ) ( O C I V [ o z ) z ( P M e z ) C I , h o w e v e r , t o g i v e m e t a t h e s i s p r o d u c t s i n a C-ypical f a s h i o n a s s h o w n i n F i g . Z. F i g u r e 2 s h o w s ~e r o t e of format/on of iniL-~ cleavage products along wi~h e~ylene and propylene: we believe the lacier arise by reazrangement of an intermediat~ eLhyl[dene and propylidene complex, respectively. We do not see any evi- dence ~J~at any im~ermediate ~'i~ubs~i~ted me~mllacyclobutane complex ~ e s du_~ing this time peridd. We want Co dr~w a~n~ion Co the follow- ing:

(I) P~opylidene and et~ylidene complexes mu~ not decompose bi- molecularly as readily as methylene complexes did in the former sys~m (as we proposed earlier) -~nce the meta~:hesis ch~f- length is long.

(2) Trisubsti~c~cl me~l~s~ydobut~ne rings probably do not r ~ e as rapidly (re~z~z've to me~athes~) compared wi~h di- or mono-subs~ituted rings (particularly the ~thyl derivative; see above).

(3) Rearrangement of et~ylidene and propylidene I/gands competes with other possible chain ~e_rm~na~ng steps because ~he ch~{- is longer and/ or because an internal ole~ cannot cap~t,~e an alkylidene complex as efficiently as 1-bu~ene (see above).

(4) Some chain carrying species is present in reasonable concentration between 2 5 m ~ n (when essen~lly ~ the/ni~ial neopenCylidene complex is

].*~,

I~,

]200.

7OO

T~

~ '- 0.~7

~ h 0.~

S I0 15 Z5 (s~

eeis~. '~ ¢~rae~l@ i n r.~ts ~rl~t ~ tO their ~lctlll~.

Fig. I . /~e tathe~ is o f c~s-~'-pent~ne by Nb(CHC'Mez XOCMe3)2(FMe~ ~L ~ in mer~'y!ene in the presenc~ o f PMe 3 at 25 ~C.

8 0

I

3 i

3~

27 '~* ~Yler*e*"

! - -

/ I t

T m

F:.g. 2. Cleavage and a]kylidene rean-dngement products in the met~t~zesis ot c/s-2-pen~ene with 1~rb(CHCC~e3XOC~Ie~ )2(P~Ie3 )CI.

gone ) a nd 1 2 0 mL,1 (at w h i c h ~ir~e a b o u t 60c7o o f t h e t o t a l poss ib le e t h y l e n e a n d p r o p y l e n e has appev_-~d).

M a n y o f t h e a b o v e fin'dings axe c lose ly a n a l o g o u s t o t h o .~e in m o l y b - d e n - m a nd t u n g s t e n c a t a l y z e d m e t a t h e s i s sys t ems . T h e r e f o r e , we se t o u t t o m a k e w h a t w e c o n s i d e 1 ~ l t o be t h e m o s t l ike ly t y p e o f t u n g s t e n ~ o n t a J n i n g ca t a ly s t , an i_~.- ' .ectronic W(VI) . I k y l i d e n e c o m p l e x .

An a~eml~: to e~change an oxo Iigancl on W(VI) with a naopentylidene ligand from t~_ntalum led to the ~mexkable re.cult shown m eqn. (7).

W(O)(OCMe3)4 + Ta(CH~--~I- ea)(PEt~)2CIa -~ Ta(OCMe3)~CI +

W(O)(CHCMea)(PEta)2C!2 (7)

6 Yellow W(O)(CHCMea)(PEt3)2CI2 is le~s soluble than Ta(OCMe3)~CI in pent~n'e and crystallizes out selectively (_Analysis: calc. for WCz ?H~oCI2OP2, C 35.37, H 6.98; found, C 35.40, H 7.01). The ~i~al for the C= atom in 6 is f o u n d a t 6 3 ! 3 in t h e ZaC N M R s p e c t r t t m wi th J ~ = 126 Hz c h a r a c t e r i s t i c of a 'normal' alkylidene (Table 2). This is reasonable ~ince an oxo ligand is -known to be a powerful ~lect~on donor [~/]. The PMe3 ligands are equival- ent b y 31p N I~R a n d t h e V w = o b a n d is f o u n d a t 9 7 0 c m -1 in t h e I R s p e c t r u m (Nujol ) . O [ t h e t w o poss ib l e s t ruc imres we p r e f e r t h e o n e w i t h c / $ ~ b l o r i d e Hgands ~,! ~ans-phosphine ligands by analogy ~dth the s~ue~u~e of oct~o

81

TABLE 2 Some ~ parameters for W(OKCHRk~Et~)2C~. z

R 6H_. zJ~e (Hz) 5C~ Zgc~ e (Hz) IJc~ (Hz) &P *JPw (Hz)

C M e ~ 1 2 . 0 3 3 . 3 3 . 3 . 3 ~ 1 0 . 3 1 2 6 1 9 . 5 3 1 9 P h 1 2 . 2 7 --4 2 9 1 . 6 11 .O 1 1 7 2 2 . 0 3 0 8 C H 2 C H ~ 1 2 . 1 . . . . . . [4 12.34 4~.0 281.1 12.1 -136 23.2 315

11.47 4 . 0 - - (J'cH A ~ ~CH B) - -

azJca w = 148 Hz.

hedral e~oxo ~ngsten d = complexes [7] ; Le. the alkyHdene and oxo also prefer to be ci~ relative to one another. Only in this manner can W form three =-bonds, o~..~ t o the alk-ylidene and two to the oxo I/gand, one of the two involving a lone pair on the oxo l/gand. (Note that vw= o is highly cha rac te r i s t i c of a ' t r ip l e ' W-O bond [ 7] .) Tbi~ be ing the caz-e, the ~Ik-yHdene l igand m u ~ lie in t h e O - W - C ~ p lane , i e . t_L.e s t r u c t u r e must be that s / low~ in eqn . (8) or t h e o n e in w h i c h t h e a l k y l i d e n e l igand is r o t a t e d b y 180 °.

T e r m i n a l o l e f i , ~ r e a c t s l owly w i t h 6 ( ~ I d). P re~yr -ab ly , L m u s t be los t t o a l l ow t h e o lef~ , t o c o o r d i n a t e t o t h e m e t a l s ince th is r e a c ~ o n is hnprac(/cally slow in the presence of PEt s. However, Lhese s~e reactions are comparatively fast (1 h) in the presence of a trace of AICI z. The products are analogous benzylidene, propylidene, and methylene complexes, 7 (R = Ph, Et, and H, r e spec t ive ly ; eqn. (8)).

--I d, 25 - 50 5C

or 1hat 25~C, trace of AICIs

MesCCH= CH2 + 6 + CH2=CHP~

L Cl~ I ~O

L A (8)

i% = Ph, Et, or H ; L = PE~

Their NMI% spec~ (Table 2) are all sinnqar to those of the neopen~-yHdene complex. The IH N-MR speck,r- of the methylene complex (Fig. 3) shows the expected AB pa~em for two inequivalent protons each coupled to ~-o phosphines. The methylene complex decomposes at 25 qC in several hours and is instantly destroyed when excess PEt~ is added; the organome~n~c products of these zeactions have not yet been identifiecL

When a r-~tre of 0.2 ramol W(O)(CHCMes}(PEt~)zClz and about 0.05 mmol ~CI s ill 5 I~- I chloroDenzene is stirred under 1-butene at 25 ~C, tertiarybutylethylene is formed steadily (quan~/tative after 44 h) along with 8.9 eq,,/valents of 3~exenes and about 0.9 equivalents of ethylene (no effort was made %0 measure ethylene accuraf~/y). Prr-Hm~.~ry resuIts s h o w that c/s-2-pentene is also metathesLzed by th~ ca t a ly s t , but more slowly.

8 2

!

I l ~

I'' ~ ii'~ i!! I, I ,i!ili

I

Fig. 3. The 90 ~ 1H NMI:{. s ~ o f W(O)(CH2XP]~{;3)2CI,7, in C6;D~ h-~ the re~ion (*re~idu~l W(O.~CHC~Me~}(PEtz)2CI2); chemical shifts in DPm.

_All t h e d a t a s o fro" b u ~ d a z t r o n g c a s e f o r d ° e J k y l i d e n e c o m p l e x e s ( a ] k y l i d e n e = d i ~ n i o n ) z s t h e m o s t c o m m o n t y p e o f m e t a t h e s i s c a t a l y s t . A t l e a s t o n e o x o l i g a n d m a y b e c r u c i a l f o r k e e p i n g a G r o u p V I m e f ~ in a d ° s t a t e . W e d o n o t t h i n k i t c i rc , m ~ s f ~ n ~ ] t h a t t r a c e s o f w a t e r a n d o x y g e n a r e b e n e f i c i a l t o m e t a t h e s i s a e G v l t y [ 1 ] ~nce t h ~ is a c l a ~ i c w a y ~o p r e p a r e o x o c o m p t e ~ e s [ 8 ] . T h e u s ~ _ o f e t h a n o l e.s a " ' c o ~ t ~ y s t ' " in t h e or~.ginal ~-~d s o m e of=her h o m o g e n e o t ~ ~ s t e m ~ m ~ y s e r v e p r i m z x f l y a s a s o u r c e o f ~ k o x i d e l i g a n d s . S ~ c e a n o x o l i ~ n d is n o t n e c e s s a r y in t h e N b a n d T a s y s t e m s , w e f e e l i t is u n n e c e s s a r y t o p o s ~ L ~ t e t h a t i t is m o r n d i r e c t l y i n v o l v e d in r a e t ~ - t h e s e , e ~ . t ~ a ~ a m e t ~ I l a o x o c y d o p e n t m ~ e c o m p l e x f o r m s w h e n t h e aUo~li- d e n e / o x o c o m p l e x r ~ c ~ s ~vith a n o l e f i n . F i n e l y , a l t h o u g h a co -ca~ /ys+~ s u c h a s AICI: R~_= is n o ~ n e c _ ~ a r y i t c a n c e r t a i n l y i n c r e a s e t h e r a t e o f m e f ~ t h e ~ s m a r k e d 3 y , p r o b a b l y b y c.xeat~ng a n e m p t y c o o r d i n a ~ o n s i t e ( a n d / o r f o x i n g -~ m o r e s o l u b l e c o m p l e x ) ; e x a c t l y w h a t is i t s ~ m c ~ i o n in t h e p a r t i c u l a r c a s e w e h a v e d i s c u s s e d hexe , h o w e v e r , is u n ~ x ~ ~ t h i s ~ m e .

A e k n o w i e d m ' n e n t s

W e th~nl¢ t h e N a t i o n a l S c O n c e F o u n d a t i o n f o r s u p p o r t ( C H E 7 9 - 5 0 3 0 7 ) a n d ( in p a r t ) t h e P e C r o l e , , m R~P~xc_h F u n d t ~ r o u g h a f e l l o w s h i p t o G . A . R .

R e f e r e n c e s

1 R . J . H ~ - e s and G. J. Leigh, ~L~.em. S~c. Rev. , 4 (1975) 155. N. Carrie.ton, E. A. Of-stead and ~ . _~_. Judy , A n g e w . Chem., Int. Ed. EngL, 15 (1976) 401. K. H. O_'ubhs, Prog. ~r.c, rg. CP.em., 24 (1978) I . T_ J. I~ tz , Adv_ Or-ganc,~et. Chem., 16 (1977) 283. N. Ca/devon, J. P. Lawr~nc~ and E. A. Ofmtead, Adv. Organor~et. Chem., 17 (1979) 4 4 9 . J. J. H o o n e y and A. Ste~wazt, Chem. Soc. Spec. Perfod. Rep . - - Coral., ! (1977) 277.

2 G. A. Rupprech¢, L. W. M e , e r i e , J. D. Fenm~nn and R. R . Schrock , J. A m . Chem. Soc., in the press.

8 3

3 A . J . Se.hulf;z, J. M. W'flfiams, R. R . Schrock , G. A_ R u p p r e c h t a n d J. D. Fe lTm~n, , J. A m . Cherry. Soc. , IOZ ( 1 9 7 9 ) 1 593 - 1 595 .

4 R. R . S c h r o e ~ , A c ~ . Chem. Re~., 12 ( 1 9 7 9 ) 98 - 104 . 5 P. R . Sharp and R . R . ~ , r Organomer. Chem. . 1 7 I ( 1 9 7 9 ) 43 - 51. 6 S . J . M c T - ~ , J. Sancho a.ncI 1:1. R . Sob.rock, ,r. A m . Chert . Soc. , i~t the press. 7 W. P. Gr~.ffith, Coord. Chern. Reu. , 5 ( 1 9 7 0 ) 459 - 517 . 8 D . L . Keper t , The Ear ly Transf t fon Meta/s, Ac~de-mic Press, L o n d o n a n d New York ,

1972 .