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Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
Ethylene Oligomerization Reactions. Effect of A ux iliary Ligand on A ctiv ity and
Selectiv ity
Lucilene L. de Oliveira, Roberta R. Campedelli, Adão L. Bergamo, Ana H. D. P dos Santos and Osvaldo L. Casagrande*
Laboratório de Catálise Molecular, Instituto de Química, Univ ersidade F ederal do R io G rande do Sul, A v . Bento G onçalv es, 9 5 0 0 , 9 0 5 0 1 - 9 7 0 P orto A leg re- R S, Brazil
D ois nov os com p lex os de crom o( I I I ) contendo lig antes tridentados [ C rC l3( L ) ] (1 a, L = b is[ 2-(
3-f enil-1-p irazol) etil) ] am ina; 2 a, L = b is[ 2-( 3-m etil-5 -f enil-l-p irazol) etil] sulf eto) f oram p rep arados e caracterizados p or análise elem entar. A p ós ativ ação com m etilalum inox ano ( M A O ) , estes p ré-catalisadores m ostraram altas f req uências de rotação nas reações de olig om erização do etileno sob
condições otim izadas ( F R s = 22,9 -36 ,4 ×103 m ol C
2H4 ( m ol C r
I I I)-1 h-1, [ C r] = 10,0 µm ol, 80 °C ,
20 b ar de etileno, [ A l] / [ C r] = 300, tem p o de olig om erização = 20 m in) , p roduzindo oleinas-α no interv alo de C4-C14 + com alta seletiv idade ( 6 7,71-73,4 7% ) . O s desem p enhos catalíticos são af etados
sub stancialm ente p elos g rup os p resentes nos lig antes, esp ecialm ente os sub stituintes nas p osições 3 e 5 dos anéis p irazol. E m p aralelo, o em p reg o de com p lex os de níq uel( I I ) tais com o NiC l2{ b is[ 2-( 3,5 -dim etil-1-p irazol) m etil] b enzilam ina} 2-(3) e NiC l2{ b is[ 2-( 3,5 -dim etil-1-p irazol) etil) ] éter} (5) em reações de olig om erização conduzidas na p resença de trif enilf osina ( PPh3) resultou em sistem as catalíticos altam ente ativ os com f req uências de rotação ( F R s) v ariando de 36 ,4 a 15 4 ,2×103 m ol
C2H4 ( m ol NiI I)-1 h-1. A p resença deste lig ante aux iliar tem um im p acto sig niicativ o na p rodução
seletiv a de oleinas-α, dim inuindo sub stancialm ente a q uantidade de b uteno-1 com concom itante aum ento da q uantidade das f rações de b utenos-2. T entativ as de cristalização do com p lex o de níq uel 3 resultaram na f orm ação de um com p osto de níq uel tetram etálico [ { ( L ) (μ3-C l) NiC l}4]
(4, L = 1-anilinom etil-3,5 -dim etil-1-p irazol) o q ual f oi caracterizado p or dif ratom etria de raios X .
T w o new ch rom ium ( I I I ) com p lex es [ C rC l3( L ) ] b ased on tridentate lig ands (1 a, L = b is[ 2-( 3-p h eny l-1-3-p y razoly l) eth y l) ] am ine; 2 a, L = b is[ 2-( 3-m eth y l-5 -p h eny l-l-p y razoly l) eth y l] sulide) h av e
b een p rep ared and ch aracterized b y elem ental analy sis. U p on activ ation w ith m eth y lalum inox ane ( M A O ) , th ese p re-cataly sts sh ow ed h ig h turnov er f req uencies f or eth y lene olig om erization under op tim ized conditions ( T O F s = 22.9 -36 .4 ×103 m ol C
2H4 ( m ol C r
I I I)-1 h-1, [ C r] = 10.0 µm ol, 80 °C ,
20 b ar eth y lene, M A O : C r = 300, olig om erization tim e = 20 m in) , p roducing α-oleins in th e rang e C4-C14 + w ith h ig h selectiv ely ( 6 7.71-73.4 7% ) . T h e cataly tic p erf orm ances are sub stantially af f ected b y th e lig and env ironm ent, esp ecially th e sub stituents at th e 3- and 5 -p ositions of th e p y razoly l rings.
I n p arallel, th e use of nick el com p lex es such as NiC l2{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l) m eth y l] b enzy lam ine} (3) and NiC l2{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l) eth y l) ] eth er} (5) in olig om erization
reactions carried out in th e p resence of trip h eny lp h osp h ine ( PPh3) af f orded h ig h ly activ e cataly tic sy stem s w ith turnov er f req uencies ( T O F s) v ary ing f rom 36 .4 to 15 4 .2×103 m ol C
2H4 ( m ol Ni I I)-1 h-1.
T h e p resence of th is aux iliary lig and h as a strong im p act on th e selectiv ity tow ards th e p roduction of α-oleins, decreasing sub stantially th e am ount of 1-butene w ith a concom inat increase of
th e 2-b utene f ractions. A ttem p ts to cry stallize th e nick el com p lex 3 af f orded th e tetram etallic
[ { ( L ) (μ3-C l) NiC l}4] (4, L = 1-anilinom eth y l-3,5 -dim eth y lp y razole) w h ich w as ch aracterized b y X -ray dif f raction analy sis.
I ntroduction
T h e p ursuit of eth y lene olig om erization cataly sts cap ab le of p roducing selectiv ely α-oleins h as b een a m aj or f ocus of research in recent decades, due to th eir im p ortance in a v ariety of industrial p rocesses. D ep ending on th e ch ain
leng th of th e alk ene, th ey can b e used f or p roduction of v arious m aterials. T h e m ost im p ortant ones are linear low -density p oly eth y lene ( L L D PE ) ( C4-C10) , p oly -α-oleins
( C4, C10) , p lasticizers ( C6-C10) , lub ricants ( C8-C10) , lub e oil additiv es ( C12-C18) , and surf actants ( C12-C20) .1 F or th is p urp ose, sev eral olig om erization cataly st sy stem s hav e b een dev elop ed, m ost of w h ich are b ased on nick el2 and ch rom ium cataly sts3 b earing b i- and tridentate lig ands.
I n recent y ears w e h av e b een interested in study ing th e p otential ap p lications of tridentate lig ands in th e
olig om erization cataly sis ield. W e h av e th us p rev iously com m unicated new classes of NiI I 4 ,5 and C rI I I 6 ,7 com p lex es
b ased on th ese tridentate p y razoly l lig ands, w h ich act as h ig h ly selectiv e and h ig h ly activ e p re-cataly sts f or eth y lene olig om erization in th e p resence of m eth y lalum inox ane ( M A O ) as co-activ ator. M ore recently , w e h av e introduced a new set of NiI I com p lex es b ased on NZ N
lig ands th at f orm stab le 5 -m em b ered ch elate ring s and w h ich , in association w ith an alk y lalum inum ( M A O or A lE t2C l) , sh ow h ig h activ ity in eth y lene olig om erization ( T O F = 1.7-104 .5 ×103 m ol( eth y lene) m ol( Ni)−1 h−1) ,
g iv ing p redom inantly 1-b utene ( 70-9 4 % y ield) .8 H erein, w e rep ort th e sy nth esis and ch aracterization of tw o new C rI I I com p lex es, C rC l
3{ b is[ 2-( 3-p h eny l-1-p y razoly l) eth y l) ] am ine} (1 a) , and C rC l3{ b is[ 2-( 3-m eth y 5 -p h eny l-l-p y razoly l) eth y l] sulide} (2 a) , w h ich , in association w ith M A O , af f ord activ e cataly sts f or th e selectiv e p roduction of
α-oleins in th e rang e C4-C14 +. F urth erm ore, studies on th e inluence of th e aux iliary lig and trip h eny lp h osp h ine ( PPh3) on turnov er f req uency ( T O F ) , selectiv ity f or α-oleins, and p roduct distrib ution using 5 - and 6 -m em b ered ring nick el com p lex es NiC l2{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l) m eth y l] b enzy lam ine} (3) and NiC l2{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l) eth y l) ] eth er} (5) are also rep orted.
Ex p erimental
G eneral p rocedures
A ll m anip ulations w ere p erf orm ed using standard v acuum line and Sch lenk tech niq ues under a p uriied arg on
atm osp h ere. E t2O , th f and toluene w ere distilled f rom sodium -b enzop h enone k ety l under arg on and deg assed b y f reeze-th aw -v acuum cy cles p rior to use. 3-Ph eny lp y razole9 and [ C rC l3( th f )3]10 w ere p rep ared b y literature p rocedures.
NiC l2·6 H2O and trip h eny lp h osp h ine ( PPh3) , b oth f rom
A ldrich , w ere used as receiv ed. E th y lene ( W h ite M artins C o.) and arg on w ere deox y g enated and dried th roug h colum ns of BT S ( BA SF ) and activ ated m olecular siev es
( 3A ) p rior to use. PM A O -I P ( m eth y lalum inox ane, A k zo, 12.9 w t.% A l solution in toluene) and dieth y lalum inum
ch loride ( D E A C ) ( A ldrich , 1.8 m ol L-1, 25 w t.% toluene solution) w ere used as receiv ed. E lem ental analy ses w ere p erf orm ed b y th e A naly tical C entral Serv ice of th e I nstitute
of C h em istry -U F R G S ( Brazil) and are th e av erag e of tw o indep endent determ inations. 1H and 13C {1H } NM R sp ectra
w ere recorded on a Varian I nov a 300 sp ectrom eter operating at 25 °C . C h em ical sh if ts are rep orted in p p m v s. SiM e4 and w ere determ ined b y ref erence to th e residual solv ent p eak s.
I nf rared sp ectra w ere p erf orm ed on a F T I R Bruk er A lp h a Sp ectrom eter. Quantitativ e g as ch rom atog rap h ic analy sis of eth y lene olig om erization p roducts w as p erf orm ed on a Varian 34 00C X instrum ent w ith a Petrocol H D cap illary colum n ( m eth y l silicone, 100 m leng th , 0.25 m m i.d., and ilm th ick ness of 0.5 µm ) op erating at 36 °C f or 15 m in f ollow ed b y h eating at 5 °C m in-1 until 25 0 °C ; cy cloh ex ane w as used as internal standard.
Sy nthesis and characterization of tridentate p y razoly l lig ands
1 - ( 2 - hy drox y ethy l) - 3 - methy l- 5 - p heny lp y razole A solution of 2-h y drox y eth y lh y drazine ( 4 .6 4 g , 6 0.9 m m ol) in ab solute eth anol ( 10 m L ) w as added drop w ise
to a stirred solution of 1-p h eny l-1,3-b utanedione (10.01 g ,
6 1.7 m m ol) in ab solute eth anol ( 30 m L ) . T h e tem p erature of th e reaction m ix ture w as k ep t b elow 10 °C . A f ter th e addition of th e h y drazine, th e reaction m ix ture w as allow ed
to w arm to room tem p erature and stirred f or anoth er 2 h . T h e solv ent w as th en ev ap orated under reduced p ressure to g iv e a w h ite solid com p osed b y a m ix ture of tw o dif f erent isom ers:
1-( 2-h y drox y eth y l) -3-m eth y l-5 -p h eny lp y razole ( isom er A ) and 1-( 2-h y drox y eth y l) -3-p h eny l-5 -m eth y lp y razole ( isom er B) . T h e p ure f orm of isom er A w as ob tained af ter sev eral w ash ing s w ith dieth y l eth er ( 4 ×15 m L ) ( 6 .36 g , 5 2% ). 1H NM R ( C D C l3) : δ 2.4 7 ( s, 3 H , C H3) , 3.9 3 ( t, 2H , 3J
H H4 .8 H z, 2H ,C H2) , 4 .26 ( t, 3J
H H4 .7 H z, 2H , C H2) , 6 .22 ( s, 1H , C H ) , 7.24 -7.79 ( m , 5 H , C Har) . 13C NM R ( C D C l
3) : δ ( p p m ) 13.4 , 5 0.4 , 6 1.9 , 105 .6 , 128.5 , 130.5 , 14 4 .9 , 14 8.2. I R ( K Br) νm ax/ cm-1:
339 0s, 29 4 7m , 2813w 2788w , 19 5 5 w , 19 03w , 189 0w , 16 64 s, 16 20s, 15 9 5 s, 15 04 s, 14 6 0s, 14 27s, 1380s, 1307m , 1236 w ,
1070m , 9 29 w , 86 9 w , 781m and 707s. m p 9 1°C .
( 2.9 0 m L , 39 .9 m m ol) in ch lorof orm ( 25 m L ) w as allow ed to relux f or 4 h . T h e v olatiles w ere th en ev ap orated under
reduced p ressure, and th e resulting residue w as w ash ed
w ith sodium b icarb onate solution ( 5 % ) to g iv e a y ellow oil ( 3.87, 89 % ) . 1H NM R ( C D C l
3) : δ 2.6 1 ( s, 3H , C H3) , 4 .13 ( t, 3J
H H 6 .6 H z, 2H , C H2) , 4 .75 ( t, 3J
H H 6 .6 H z, 2H , C H2) , 6 .3 ( s, 1H , C H ) , 7.22-7.74 ( m , 5 H , C Har) . 13C NM R ( C D C l3) : d ( p p m ) 13.2, 4 2.1, 4 9 .8, 105 .8, 128.5 , 130.3, 14 4 .9 , 14 8.3. I R ( K Br) νm ax/ cm-1:306 0w , 29 6 0m , 29 28m ,
286 2w , 19 6 7w , 189 2w , 1824 w , 1770w , 16 02w , 15 4 8m , 14 9 4 s, 14 5 4 s, 14 25 m , 1384 m , 1307m , 1271m , 116 6 w , 1122w , 1072w , 1035 w , 9 9 7m , 9 16 w , 79 6 m , 76 3s, 6 9 8s and 6 6 3s.
Bis[ 2 - ( 3 - p heny l- 1 - p y razoly l) ethy l] amine (1)
U nder an arg on atm osp h ere, 3-p h eny lp y razole ( 2.71 g , 18.7 m m ol) w as slow ly added to a susp ension of NaH
( 1.2 g , 5 0 m m ol) in dry dm f ( 5 0 m L ) . T h e m ix ture w as stirred at room tem p erature f or 2 h . T o th e resulting solution,
a solution of b is( 2-ch loroeth y l) am ine ( 1.6 6 g , 9 .3 m m ol) in dry dm f ( 10 m L ) w as added drop w ise under stirring . T h e m ix ture w as allow ed to stir f or 2 h at 70 °C , cooled and treated cautiously w ith H2O ( 15 m L ) to decom p ose
ex cess NaH . T h e solv ents w ere th en ev ap orated under reduced p ressure. T h e residue w as ex tracted w ith eth y l acetate ( 4×4 0 m L ) , w ash ed w ith 10% NaO H ( 2×30 m L ) , H2O ( 2×30 m L ) , and th en dried ov er M g SO4. T h e solv ent w as ev ap orated to g iv e a y ellow oil ( 2.6 0 g , 77% ) . 1H NM R ( C D C l3) : δ 3.12 ( t, 3J
H H 5 .7 H z, 4 H , C H2) , 4 .36 ( t, 3J
H H 5 .7 H z, 4 H , C H2) , 6 .5 2 ( d, 2J
H H2.3 H z, 2H , C H ) , 7.4 0-7.85 ( m , 12 H , C Har) . 13C NM R ( C D C l
3) : δ ( p p m ) 4 8.2, 5 1.9 , 102.4 , 125 .3, 127.8, 128.3, 131.0, 133.3, 15 1.4 . I R ( K Br)
νm ax/ cm-1:29 4 8s, 285 2s, 19 5 7w , 1884 w , 1812w , 175 3w ,
16 6 4 w , 16 04 m , 15 25 m , 15 04 s, 14 6 1s, 14 09 s, 135 5 s, 1326 m , 1226 s, 1134 m , 1076 s, 104 9 m , 9 4 8m , 9 19 m , 84 6 w, 75 6 s, 6 9 8s) , 6 5 9 w , 6 26 w and 5 09 w .
Bis[ 2 - ( 3 - p heny l- 5 - methy l- 1 - p y razoly l) ethy l] sulide (2) A solution of l-( 2-ch loroeth y l) -3-m eth y l-5 -p h eny l p y razole h y droch loride ( 5 .07 g , 19 .8 m m ol) and sodium h y drox ide ( 0.5 g , 12.5 m m ol) in aq ueous eth anol ( 5 0% , 100 m L ) w as treated w ith Na2S·9 H2O ( 2.9 8 g , 12.4 m m ol) .
T h e solution w as allow ed to relux f or 3 h , cooled and ev ap orated under reduced p ressure. W ater w as added
( 20 m L ) , th e p roduct w as ex tracted w ith dich lorom eth ane ( 4 ×15 m L ) , and th e org anic ex tracts w ere dried ov er Na2SO4.
T h e v olatiles w ere ev ap orated under reduced p ressure to g iv e a y ellow oil ( 2.9 8 g , 75 % ) . 1H NM R ( C D C l
3) : δ 2.32 ( s, 6 H , C H3) , 3.84 ( t, 3J
H H7.2 H z, 4 H , C H2) , 4 .23 ( t, 3J
H H
7.2 H z, 4 H , C H2) , 6 .17 ( s, 2H , C H ) , 7.25 -7.6 7 ( m , 10 H , C Har) . 13C NM R ( C D C l
3) : δ ( p p m ) 13.5 , 31.8, 4 8.5 , 105 .9 ,
128.8, 129 .2, 129 .8, 130.7 14 4 .0, 14 8.5 . I R ( K Br) νm ax/ cm-1:
306 0m , 29 6 0m , 29 25 s, 286 4 m , 19 5 5 w , 189 2w , 1814 w , 176 4 w , 16 06 m , 15 4 8s, 14 9 6 s, 14 5 4 s, 14 23s, 1303s, 1278m ,
1218m , 1180w , 1118w , 1074 m , 1035 m , 9 9 3s, 9 5 4 w , 9 19 w, 79 4 m , 76 7s, 700s, 6 75 m , 6 35 w and 5 4 9 m .
CrCl3{ bis[ 2 - ( 3 - p heny l- 1 - p y razoly l) ethy l) ] amine} (1 a) T o a solution of b is[ 2-( 3-p h eny l-p y razol) eth y l) ] am ine ( 0.32 g , 0.9 0 m m ol) in th f ( 10 m L ) , a solution of [ C rC l3( th f )3] ( 0.30 m g , 0.80 m m ol) in th f ( 15 m L ) w as added, and th e resulting m ix ture w as stirred f or 30 m in at
room tem p erature. T h e solv ent w as rem ov ed until ca. 1/ 3 rem ained and 10 m L of p entane w as added to com p lete p recip itation. T h e p roduct w as collected b y iltration, w ash ed w ith p entane and dried in v acuo. C om p lex 1 a w as
ob tained as a g reen solid. Y ield: 0.38 g ( 9 2% ) . C om p ound 1 a, elem ental analy sis: F ound C , 5 0.71; H , 4 .33; N, 12.9 6 . C alc. f or C22H23C l3C rN5: C , 5 1.23; H , 4 .4 9 ; N, 13.5 8% .
CrCl3[ bis[ 2 - ( 3 - methy l- 5 - p heny l- l- p y razoly l) ethy l] sulide] (2 a)
T h is com p ound w as p rep ared according to th e m eth od describ ed f or 1 a using [ C rC l3( th f )3] ( 0.26 g , 0.70 m m ol) and b is[ 2-( 3-m eth y l-5 -p h eny l-1-p y razoly l) eth y l] sulide ( 0.33 g , 0.80 m m ol) . C om p lex 2 a w as ob tained as a lig h t
red w ine coloured solid ( 0.36 g , 9 0% ) . C om p ound 2 a, elem ental analy sis: F ound: C , 5 0.88; H , 4 .25 ; N, 9 .76 . C alc. f or C24H26C l3C rN4S: C , 5 1.39 ; H , 4 .6 7; N, 9 .9 9 % .
N i C l2{ b i s [ 2 - ( 3 , 5 - d i m e t h y l - 1 - p y ra z o l y l ) m e t h y l ] benzy lamine} (3)8
T o a solution of NiC l2·6 H2O ( 130 m g , 0.5 6 m m ol) in th f ( 10 m L ) , a solution of b is[ 2-( 3,5 -dim eth y l-1-p yrazoly l)
m eth y l) ] b enzy lam ine ( 200 m g , 0.6 2 m m ol) in th f ( 10 m L ) w as added, and th e resulting m ix ture w as stirred f or 24 h at
room tem p erature. Volatiles w ere rem ov ed under reduced p ressure, and th e resulting g reen solid residue w as w ash ed w ith E t2O ( 2×10 m L ) to af f ord 3 as a g reen solid ( 189 m g , 75 % ) . C om p ound 3, elem ental analy sis: F ound C , 4 6 .5 1; H , 5 .9 0; N, 14 .07. C alc. f or C19H25C l2N5Ni·2H2O : C , 4 6 .6 6 ; H , 5 .9 8; N, 14 .32% .
[ { ( 1 - anilinomethy l- 3 ,5 - dimethy lp y razole) ( μ3- Cl) N iCl}4] (4)
A solution of 3 ( 18 m g ) in C H2C l2 ( 7 m L ) w as k ep t at room tem p erature f or iv e day s, resulting in a f ew g reen cry stals of 4, w h ich w ere sep arated f rom th e solution and p rov ed suitab le f or X -ray dif f raction analy sis.
eth er ( 128 m g , 0.4 9 m m ol) in th f ( 10 m L ) w as added, and th e resulting m ix ture w as stirred f or 3 h at room tem p erature. Volatiles w ere rem ov ed under reduced p ressure, and th e resulting turq uoise solid residue w as w ash ed w ith Et2O
( 2×10 m L ) to af f ord a turq uoise b lue solid ( 175 m g , 9 1% ) . C om p ound 5, elem ental analy sis: F ound C , 39 .9 8; H , 6 .00; N, 12.83. C alc. f or C14H22C l2N4NiO ·2H2O : C , 39 .29 ; H , 6 .12; N, 13.09 % .
G eneral olig omerization p rocedure
A 100 m L doub le-w alled stainless Parr reactor eq uipp ed w ith m ech anical stirring and internal control of tem p erature
w as ev acuated and illed th ree tim es w ith arg on and tw ice w ith eth y lene. F resh ly distilled toluene ( 30 m L ) and th e p rop er am ount of M A O or D E A C w ere added into th e v essel under a stream of eth y lene. A f ter 15 m in, the toluene
cataly st solution ( 10 m L ) w as inj ected. T h e reactor p ressure
w as k ep t constant th roug h out th e olig om erization p rocess ( 20 b ar) b y m anually controlled addition of eth y lene. A f ter
th e desired tim e, th e reaction w as stop p ed b y cooling th e sy stem to −20 °C , dep ressurizing , and introducing 1 m L of eth anol. A n ex act am ount of cy cloh ex ane w as introduced ( as internal standard) and th e m ix ture w as analy zed b y q uantitativ e G L C .
X - ray cry stallog rap hic studies
A suitab le sing le cry stal of 2 w as m ounted onto a
g lass ib er using th e ‘‘oil-drop ’’ m eth od. D if f raction data
w ere collected at 100 K using an A PE X I I Bruk er-A X S dif f ractom eter w ith g rap h ite-m onoch rom atized Mα o-K radiation (λ = 0.71073 Å) . A com b ination of ο- and ϕ-scans
w as carried out to ob tain at least a uniq ue data set. T h e structure w as solv ed b y direct m eth ods using th e SI R 9 7 p rog ram ,11 and th en reined w ith f ull-m atrix least-sq uare m eth ods b ased on F2 ( SH E L X -9 7)12 w ith th e aid of th e W I NG X p rog ram .13 M any h y drog en atom s could b e f ound f rom th e F ourier dif f erence m ap . C arb on-b ound h y drog en atom s w ere p laced at calculated p ositions and f orced to
ride on th e attach ed carb on atom . T h e h y drog en atom contrib utions w ere calculated b ut not reined. A ll n
on-h y drog en atom s w ere reined w iton-h anisotrop ic disp lacem ent p aram eters.
Results and D iscussion
Sy nthesis, characterization of substituted bis( p y razoly l) -CrIII comp lex es and their use in olig omerization reactions
T h e s u b s t i t u t e d t r i d e n t a t e n i t r o g e n - b r i d g e d b is( p y razoly l) lig and (1) used in th is study w as readily p rep ared in h ig h y ield th roug h adap tation of literature p rocedures ( see E x p erim ental) . T h e sy nth esis of tridentate
lig and 2 w as ach iev ed starting f rom com m ercially av ailab le 1-p h eny l-1,3-b utanedione and 2-h y drox y eth y lh y drazine. T h e initial step p rocedure p rom otes th e f orm ation of tw o dif f erent isom ers ( Sch em e 1) w h ereas th e isom er A w as ob tained in p ure f orm ( 5 2% y ield) af ter w ork up . T h e identity of isom er A w as estab lish ed on th e b asis of m ultinuclear
O O
+ NH2
N
OH
ethanol
N N
OH
N N
OH +
H
CHCl3
SOCl2
N N
Cl HCl isomer A
(52 % of isolated product)
Na2S.9H2O
H2O/ethanol
NaOH S
N
N N
N
Ph Ph
2
isomer B
nuclear m ag netic resonance ( NM R ) and h eteronuclear m ultip le b ond correlation ( H M BC ) ex p erim ents ( see H M BC sp ectra in sup p orting inf orm ation) . C h lorination of th e isom er A w ith th iony l ch loride in C H C l3 g av e l-(
2-ch loroeth y l) -3-m eth y l-5 -p h eny l p y razole in 77% y ield. T h e latter com p ound reacted w ith Na2S·9 H2O in H2O / eth anol
to g iv e th e sub stituted sulf ur-b ridg ed tridentate lig and (2) in 75 % y ield.
T h e reaction of [ C rC l3( th f )3] w ith 1.1 eq uiv alent of tridentate nitrog en-, or sulf ur-b ridg ed b is( p y razoy l) lig ands (1 and 2) in th f at room tem p erature af f ords th e corresp onding [ C rC l3( NZ N) ] com p lex es 1 a and 2 a ( Sch em e
2) , w h ich w ere isolated, resp ectiv ely , as g reen or red w ine-colored solids in h ig h y ields ( ty p ically 9 0-9 2% ) . Th ese com p lex es sh ow m oderate solub ility at room tem p erature in dich lorom eth ane, th f and eth y l acetate, and are readily solub le in acetonitrile. D ue to th e p aram ag netic nature of th ese [ C rC l3( NZ N) ] com p lex es, 1H NM R sp ectra f eatured v ery b road resonances and p rov ed to b e uninf orm ative. T h e identity of 1 a and 2 a w as estab lish ed on th e b asis of elem ental analy sis.
T h e eth y lene olig om erization b eh av ior of ch rom ium com p lex es 1 a and 2 a h as b een ev aluated using op tim ized
conditions recently estab lish ed f or related 6 -m em b ered ch elate ch rom ium cataly sts,7 i.e., toluene as solv ent at
80 ºC under 20 b ar of eth y lene and A l: C r ratios of 300. R ep resentativ e results are sum m arized in T ab le 1.
W h en activ ated w ith M A O , all cataly tic sy stem s p roved to b e activ e f or olig om erization of eth y lene. A m oderate turnov er f req uency ( T O F ) of 22,9 00 m ol( eth y lene) m ol( C r)−1 h−1 w as ob tained w ith 1 a w h ile th e cataly st
sy stem deriv ed f rom 2 a, w h ich contains a sulf ur-b ridg ed lig and b earing m eth y l and p h eny l sub stituents at the 3-
and 5 -p ositions of th e p y razoly l ring s, g av e a h ig h T O F of 36 ,4 00 m ol( eth y lene) m ol( C r)−1 h−1. T h ese results are
consistent w ith th ose ob serv ed in 6 -m em b ered ring nick el and ch rom ium cataly sts b earing an analog ous tridentate sulf ur-b ridg ed lig and.4 ,6
T h e ch rom ium com p lex es 1 a and 2 a p roduce olig om ers rang ing f rom C4 to C14 + w ith a h ig h selectiv ity f or α-oleins attaining 6 7.71 and 73.4 7% , resp ectiv ely . Both cataly st
sy stem s sh ow sim ilar b eh av iour f or p roduction of α-oleins as sh ow n in F ig ure 1. T h is indicates th at th e central donor atom s and also th e p y razoly l R1 and R2 sub stituents p lay no sig niicant inluence in th is series on p roduct distrib ution. H ow ev er, enrich ed f ractions in α-C4 ( 16 .2 w t.% ) , α-C6
( 18.1 w t.% ) and α-C12 ( 9 .7 w t.% ) are ob tained using th e cataly st sy stem deriv ed f rom 2 a. T h is result is consistent w ith th ose ones f ound f or M A O -activ ated nick el and ch romium com p lex es b earing analog ous tridentate lig ands.4 ,6
I t is interesting to note th at th e p resence of p h eny l g roup s at 3-p osition of th e p y razoly l ring s in C rC l3{ b is[ 2-( 3-dip h eny l-1-p y razoly l) eth y l) ] am ine} (1 a) determ ines a dram atic ef f ect on activ ity and selectiv ity
as com p ared to th e sim ilar com p lex C rC l3{ b is[ 2( 3,5 -dim eth y l-1-p y razoly l) eth y l) ] am ine} (1 b)6 ( com p are entries 1 and 3, T ab le 1) . F or instance, cataly st 1 a ( 22,9 00 m ol( eth y lene) m ol( C r)−1 h−1) is 2.2 tim es m ore activ e th an 1 b ( 10,4 00 m ol( eth y lene) m ol( C r)−1 h−1) . F urth erm ore, th e am ount of PE p roduced b y 1 a rep resents only
3.2% of th e total am ount of p roducts ( olig om ers + PE ) , w h ile th e use of 1 b leads ex clusiv ely th e f orm ation of p oly eth y lene ( PE ) .
O n th e oth er h and, th e introduction of relativ ely bulk y p h eny l sub stituents at 5 -p osition of th e p y razoly l ring s in 2 a
Scheme 2 .
Z
N N
N N
R1 R1
R2 R2
Z
N N
N Cr N
Cl
Cl Cl
R1 R1
R2 R2
1a: Z = NH; R1 = Ph; R2 = H
2a: Z = S; R1 = Me; R2 = Ph
CrCl3(thf)3
thf, 30 min, RT
1-2
as com p ared to m eth y l g roup s in C rC l3{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l) eth y l) ] sulf ide} (2 b)6 leads to a noticeab le decrease in cataly tic activ ity in ( NSN) C rI I I sy stem s ( com p are entries 2 and 4 , T ab le 1) w h ich can b e associated to th e electronic ef f ects of th ese p h eny l g roup s to th e chrom ium m etal center. T h e selectiv ity f or C4-C12 f ractions rem ains alm ost unch ang ed ( com p are entries 2 and 4 ) .
Sy nthesis and structural characterization of the tetrametallic
nick el comp lex 4 deriv ed f rom N iCl2{ bis[ 2 - ( 3 ,5 - dimethy l-1 - p y razoly l) methy l] benzy lamine} (1)
T h e 5 -m em b ered-ring nick el cataly st NiC l2{ b is[
2-( 3,5 -dim eth y l-1-p y razoly l) m eth y l] b enzy lam ine} 2-(3) w as readily p rep ared in h ig h y ield v ia literature p rocedures.8
R ecry stallization of 3 in m eth y lene ch loride at room tem p erature af f orded a f ew g reen cry stals of an unex p ected tetram etallic nick el com p lex [ { ( L ) (μ3-C l) NiC l}4] (4, L = 1-anilinom eth y l-3,5 -dim eth y lp y razole) (ca. 8% y ield) ( Sch em e 3) , and a larg e am ount of unidentiied p roducts. T h e f orm ation of tetranuclear nick el com plex 4 can b e rationalized in term s of a lig and redistrib ution/ disp rop ortionation reaction.
C ry stal data and structure ref inem ent f or 4 are sum m arized in T ab le 2, and selected b ond distances and ang les are listed in T ab le 3. T h e m olecular g eom etry and atom -lab eling sch em e are sh ow n in F ig ure 2. C om p lex 4 h as a cub ane-ty p e { Ni4(µ3-C l)4} core w ith f our NiI I and
f our ch loro lig ands occup y ing alternate v ertices. Each
nick el center is cry stallog rap h ically distinct and p resents a slig h tly dif f erent distorted octah edral env ironm ent. T h e NiI I atom s are b ound to th ree µ
3-ch loro lig ands, a ch elating
anilinom eth y l-3,5 -dim eth y lp y razole and one term inal ch loride.
T h e Ni–Np y razoly l distances lie in th e rang e of 2.033-2.04 5 Å, w h ile Ni–Nanilino b onds are 2.105 -2.124 Å. T h e µ3-ch loro lig and in th e coordination sp h ere of each nick el atom y ields a Ni–C l b onding distance ly ing in th e rang e of 2.4 4 7-2.5 06 Å, w h ile th e Ni–C lterm inal b onds f all in
th e rang e of 2.34 4 9 ( 8) -2.379 9 ( 8) Å. A ll th ese v alues are in ag rem eent w ith th ose disclosed in th e literature.15
T h e C l–Ni–C l ang les inv olv ing th e b ridg ing ch lorine lig ands are sy stem atically low er th an 9 0°, rang ing f rom 82.73( 2) to 86 .4 ( 2) °. O n th e oth er h and, Ni–C l–Ni ang les are
sig niicantly h ig h er, tip ically in th e rang e of 9 3.17-9 7.4 0°. G eom etric constraints im p osed b y th e cub ane core reduce Ni–C l–Ni ang les f rom th e ideal tetrah edral v alue of 109 .5 °,
a reduction of ten associated w ith f errom ag netic coup ling of nick el centers.16 T h e distances v ary ing f rom 3.5 88 to 3.726 Å b etw een th e nick el atom s in th e cluster are b ey ond sig niicant interactions.
E f f ect of the aux iliary lig and on cataly st activ ity and selectiv ity using nick el( II) comp lex es bearing chelating N Z N lig ands
Prev ious studies on nick el-b ased cataly sts h av e dem onstrated th at th e incorp oration of PPh3 into cataly tic Table 1 . E th y lene olig om erization w ith com p lex es 1 a-b and 2 a-ba
E ntry C at. T O F
b
( 103)
O lig om er distrib ution ( w t.% )c
C14 + O lig om ers ( w t.% )
PE ( w t.% )
T otal p roduct ( m g ) C4 (α-C4) C6 (α-C6) C8 (α-C8) C10 (α-C10) C12 (α-C12)
1 1 a 22.9 15 .2 ( 9 3.5 ) 17.9 ( 9 2.9 ) 18.5 ( 88.0) 14 .9 ( 89 .1) 8.2 ( 89 .3) 19 .3 9 4 .0 6 .0 16 00 2 2 a 36 .4 16 .9 ( 9 6 .1) 19 .2 ( 9 4 .3) 17.6 ( 9 2.0) 14 .3 ( 9 2.3) 11.7 ( 83.3) 18.4 9 8.1 1.9 26 00
3d 1 b 10.4 - - - - - - - 100 2200
4d 2 b 6 6 .2 18.0 ( 9 4 .3) 18.8 ( 9 5 .8) 16 .4 ( 9 3.7) 12.8 ( 9 2.0) 10.4 ( 6 5 .5 ) 8.9 85 .3 14 .7 5 4 00 a R eaction conditions: toluene = 4 0 m L , olig om erization tim e = 15 m in, p ( eth y lene) = 20 b ar, T = 80 °C , [ C r] = 10 µm ol, [ A l] / [ C r] = 300. T h e results sh ow n
are rep resentativ e of at least dup licated ex p erim ents. b m ol of eth y lene conv erted ( m ol of C r)-1 h-1 as determ ined b y q uantitativ e G L C . c C
n, p ercentag e of olein w ith n carb on atom s in olig om ers; α-Cn, p ercentag e of term inal alk ene in th e Cn f raction, as determ ined b y q uantitativ e G L C .
d ref erence 6 .
N
N
N N
N Ni
Cl Cl
CH2Cl2, 25 °C
several days
Cl
LClNi
NiClL LClNi
Cl Cl
Cl NiClL
+ unidentified compounds
4 3
F igure 2 . M olecular structure of [ { ( L ) (μ3-C l) NiC l}4] (4) . T h erm al ellip soids are draw n at th e 30% p rob ab ility lev el; h y drog en atom s are om itted f or clarity .
Table 2 . C ry stal data and structure reinem ent f or 4
E m p irical f orm ula 5 2H6 8C lC8N12Ni4
F orm ula w eig h t / g m ol-1 1379 .6 2
T em p erature / K 100 ( 2)
W av eleng th / Å 0.71073
C ry stal sy stem T riclinic
Sp ace g roup P-1
U nit cell dim ensions
a / Å 13.5 35 5 ( 18)
b / Å 13.9 5 34 ( 19 )
c / Å 19 .208 ( 2)
α / ° 82.9 6 1( 6 )
β / ° 82.9 4 4 ( 7)
γ / ° 77.14 2( 6 )
Volum e / Å3 34 9 3.0( 8)
Z 2
calculated density / g cm-3 1.312
A b sorp tion coef icient / m m-1 1.4 07
F ( 000) 14 24
C ry stal size / m m 0.37×0.21×0.08
T h eta rang e f or data collection / ° 3.01 to 27.4 8 I ndex rang es −17 ≤ h ≤ 17, −18 ≤ k ≤ 18,
−24 ≤ l ≤ 24
R elections collected / uniq ue 5 076 5 / 15 824 [ R ( int) = 0.04 6 1]
C om p leteness to θ m ax 0.9 88
D ata / restraints / p aram eters 15 824 / 0 / 733
G oodness-of -it on F2 1.038
F inal R indices [ I > 2 σ( I ) ] 1 = 0.04 27, w RR 2 = 0.09 4 4
R indices ( all data) 1 = 0.06 85 , w RR 2 = 0.1021
L arg est dif f . p eak and h ole / e Å-3 0.85 6 and −0.4 31
sy stem s leads to h ig h er activ ity and long er cataly st lif etim e.17 W e w ere curious w h eth er such ef f ects w ould ap p ly to our nick el cataly st sy stem s. F or v erif y ing th at, w e h av e ch osen th e 5 - and 6 -m em b ered ring nick el com p lex es NiC l2{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l) m eth y l] b enzy lam ine} (3)8 and NiC l
2{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l) eth y l) ] eth er} (5)7 ( F ig ure 3) .
Table 3. Selected b ond leng th s ( Å) and ang les (°) f or 4
Ni( 1) -N( 14 ) 2.033( 2) Ni( 3) -N( 17) 2.037( 2) Ni( 1) -N( 24 ) 2.114 ( 2) Ni( 3) -N( 21) 2.105 ( 2) Ni( 1) -C l( 5 ) 2.379 9 ( 8) Ni( 3) -C l( 12) 2.34 4 9 ( 8) Ni( 1) -C l( 8) 2.4 4 71( 7) Ni( 3) -C l( 11) 2.4 5 08( 7) Ni( 1) -C l( 9 ) 2.4 6 83( 7) Ni( 3) -C l( 8) 2.4 89 7( 8) Ni( 1) -C l( 11) 2.4 9 5 0( 8) Ni( 3) -C l( 7) 2.4 9 26 ( 8) Ni( 2) -N( 15 ) 2.04 5 ( 2) Ni( 4 ) -N( 18) 2.034 ( 2) Ni( 2) -N( 22) 2.124 ( 2) Ni( 4 ) -N( 16 ) 2.123( 2) Ni( 2) -C l( 6 ) 2.35 30( 8) Ni( 4 ) -C l( 1) 2.34 5 7( 8) Ni( 2) -C l( 11) 2.4 6 4 0( 8) Ni( 4 ) -C l( 9 ) 2.4 6 36 ( 7) Ni( 2) -C l( 7) 2.4 6 76 ( 7) Ni( 4 ) -C l( 7) 2.4 6 6 1( 8) Ni( 2) -C l( 9 ) 2.5 05 7( 8)
Ni( 4 ) -C l( 7) -Ni( 2) 9 4 .05 ( 3) Ni( 4 ) -C l( 9 ) -Ni( 1) 9 3.9 8( 2) Ni( 4 ) -C l( 7) -Ni( 3) 9 7.4 1( 3) Ni( 4 ) -C l( 9 ) -Ni( 2) 9 3.17( 3) Ni( 2) -C l( 7) -Ni( 3) 9 2.6 7( 3) Ni( 1) -C l( 9 ) -Ni( 2) 9 7.01( 3) Ni( 1) -C l( 8) -Ni( 4 ) 9 3.88( 2) Ni( 3) -C l( 11) -Ni( 2) 9 3.78( 3) Ni( 1) -C l( 8) -Ni( 3) 9 3.4 4 ( 2) Ni( 3) -C l( 11) -Ni( 1) 9 3.21( 2)
T h e eth y lene olig om erization b eh av ior of com p lex es 3 and 5 w as inv estig ated in toluene w ith M A O activ ation. R ep resentativ e results are sum m arized in T ab le 4 . U nder op tim ized conditions ( toluene as solv ent at 30 ºC under 20 b ar of eth y lene, A l: Ni ratios of 25 0) th e nick el cataly sts 3 and 5 are activ e f or dim erization of eth y lene in th e ab sence of PPh3 (3, T O F = 11,300 m ol( eth y lene) m ol( Ni)−1 h−1; 5, T O F = 7,100 m ol( eth y lene) m ol( Ni)−1 h−1) w ith selectiv ity f or 1-b utene attaining 84 .4 and 87.5 % , resp ectiv ely ( T ab le 4 , entries 1 and 4 ) .
T h e olig om erization reactions p erf orm ed in th e p resence of 1 eq uiv of PPh3 resulted in m uch h ig h er T O F s m ainly in th e case of cataly st sy stem 5/ M A O ( com p are entries 4 and 6 ) . O ne reasonab le ex p lanation f or th is p h enom enon can b e associated to th e p artial sub stitution of the tridentate
NZ N lig and b y PPh3 to af f ord a b identate NZ / N-Ni-PPh3
com p lex . O n th e oth er h and, th e f act th at th e activ e nick el sp ecies are coordinated w ith aux iliary PPh3 on th e v acant
coordination sites w h en lack ing eth y lene m onom ers sh ould
b e also considered. H ow ev er, in b oth cases, th e p resence of PPh3 p rom otes th e f orm ation of m ore stab le cataly tic sp ecies and at th e sam e tim e p rev ents deactiv ation b y im p urities of activ e reactants in th e cataly tic sp ecies.18
T h e p resence of th is aux iliary lig and in th e olig om erization m edium p lay s no sig niicant inluence on th e total C4 p roduction w ith selectiv ities v ary ing f rom 9 9 .8 to 100% ( com p are entries 1/ 2, and 4 / 6 ) . O n th e oth er h and, th e PPh3 lig and h as a strong im p act in th e selectiv ity tow ards th e p roduction of α-oleins, decreasing
sub stantially th e am ount of 1-b utene ( 16 .2-20.0% ) w ith a concom itant increase of internal oleins f ractions (cis-C4:
25 .7-36 .0% ; trans-C4 f ractions: 5 4 .3-4 7.6 % ) as can b e b etter v isualized in F ig ure 4 . W e m ay reasonab ly assum e th at th e f av ored f orm ation of b utenes-2 rath er th an b utene-1
N N
N N
N Ni
Cl Cl
3
O N
N Ni NN
Cl Cl
5
F igure 3. Nick el com p lex es NiC l2{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l) m eth y l] b enzy lam ine} (3) , and NiC l2{ b is[ 2-( 3,5 -dim eth y l-1-p y razoly l)
eth y l) ] eth er} (5) used in eth y lene dim erization reactions in p resence of PPh3.
Table 4. E th y lene olig om erization w ith nick el com p lex es 3 and 5a
E ntry C at. (µm ol) PPh3 ( eq uiv .) O lig om ers ( m g ) T O F
b ( 103) Selectiv ity ( % )
c
C4 C4 (α-C4) C4 (cis-C4) C4 (trans-C4) C6 (α-C6)
1 3 ( 10.0) - 105 4 11.3 9 6 .3 84 .4 8.5 6 .5 3.7
2 3 ( 10.0) 1.0 3379 36 .4 100 20.0 25 .7 5 4 .3
-3 3 ( 3.0) 1.0 1301 4 5 .1 100 6 1.0 16 .2 22.8
4 5 ( 10.0) - 6 80 7.1 9 8.7 87.5 7.3 3.9 1.3
5 5 ( 10.0) 0.5 7770 81.4 9 9 .3 24 .1 23.7 5 1.6 0.7
6 5 ( 10.0) 1.0 124 20 113.4 9 9 .8 16 .2 36 .0 4 7.6 0.2
7 5 ( 3.0) 1.0 4 4 10 15 4 .2 100.0 24 .4 27.1 4 8.5
-8 5 ( 10.0) 10.0 79 5 0 83.5 9 9 .7 31.5 27.9 4 0.5 0.3
9d 5 ( 10.0) 1.0 186 0 77.9 9 9 .7 4 1.6 20.4 37.7 0.3
10e 5 ( 10.0) 1.0 8280 4 3.3 9 9 .7 20.4 26 .5 5 2.8 0.3
11f 5 ( 10.0) 1.0 119 4 0 125 .4 100.0 32.1 4 3.1 24 .8
-a R eaction conditions: toluene = 4 0 m L , p ( eth y lene) = 20 b ar, olig om erization tim e = 20 m in, M A O [ A l] / [ Ni] = 25 0. T he results are rep resentativ e of at
least dup licated ex p erim ents. b m ol of eth y lene conv erted ( m ol of Ni)−1 h−1, as determ ined b y q uantitativ e G L C . c C
n, am ount of olein w ith n carb on atom s in th e olig om ers; α-Cn, am ount of term inal alk ene in th e Cn f raction, as determ ined b y q uantitativ e G L C .
d O lig om erization tim e = 5 m in. e O lig om erization
tim e = 4 0 m in. f O lig om erization reaction using D E A C [ A l] / [ Ni] = 25 0.
F igure 4. I nluence of aux iliary lig and ( PPh3) on selectiv ity f or b utenes
is a conseq uence of th e p resence of PPh3 in th e m ilieu, w h ich w ould b lock coordination of incom ing eth y lene and lead to isom erisation rath er th an β-H elim ination of R .
W h en th e q uantity of p recataly sts 3 and 5 w as
decreased, v ery h ig h activ ities w ere ob serv ed. F or instance, w ith 3.0 µm ol of nick el com p lex es 3 and 5,
h ig h T O F s of 4 5 ,100 m ol( eth y lene) m ol( Ni)−1 h−1 and 15 4 ,200 m ol( eth y lene) m ol( Ni)−1 h−1 w ere ob tained,
resp ectiv ely ( entries 3 and 7) . T h is ef f ect can b e p rim arly associated to (i) an easier solub ilization of th e p recataly st
in toluene solution, and (ii) increase of m olar ratio [ eth y lene] /
[ Ni] ; h ow ev er, a decrease of ex cessiv e ex oth erm s during th e olig om erization reactions, w h ich w ould induce cataly st
decay , cannot b e ruled out.
Based on th ese p relim inary results, com p lex 5 w as selected f or f urth er op tim ization, inv estig ating the [ Ni] / [ PPh3] ratio, olig om erization reaction tim e, and cocataly st ty p e. A s dem onstrated in T ab le 4 , w h en a m inor q uantity of PPh3 w as used ( [ Ni] / [ PPh3] = 0.5 ) , com p lex 5 g av e a h ig h activ ity ( T O F = 81,4 00 m ol( eth y lene) m ol( Ni)−1 h−1, entry 5 ) , w h ich w as increased up on using 1.0 eq uiv alent of PPh3 ( T O F = 113,4 00 m ol( eth y lene) m ol( Ni)−1 h−1, entry 6 ) . A g reater loading of PPh3 ( 10 eq uiv alents) led to low er activ ity ( T O F = 83,5 00 m ol( eth y lene) m ol( Ni)−1 h−1, entry 8) . A t th e sam e tim e, increasing th e am ount of PPh3 f rom 0.5 to
10.0 eq uiv alents led to slig h tly im p rov ed selectiv ities f or 1-b utene ( 24 .1 to 31.5 % ) .
T h e reaction tim e can h av e a sig niicant ef f ect on TO F s,
and th e selectiv ity . I t w as f ound th at th e activ ity at 5 m in of reaction ( T ab le 4 , entry 9 ) w as ab out 1.5 tim es low er th an at 20 m in ( T ab le 4 , entry 6 ) , sug g esting th at th is ty p e of cataly st needs a long p re-activ ation tim e ( up to 5 m in) to p rom ote th e f orm ation of a h ig h er am ount of cataly tic sp ecies. I ncreasing th e reaction tim e to 4 0 m in led to a low er
T O F v alue ( 4 3,300 m ol( eth y lene) m ol( Ni)−1 h−1, entry 10) , indicating th at a p artial cataly st deactiv ation took p lace.
T h e reaction tim e af f ects sig niicantly th e selectivity f or 1-b utene. A s can b e seen in F ig ure 5 , th e selectiv ity f or C4 oleins rem ains h ig h and constant ov er tim e ( 9 9 .7-9 9 .8% ) . H ow ev er, v ary ing th e reaction tim e f rom 5 to 4 0 m in, a larg er am ount of 2-b utenes ( f rom 5 8.1 to 79 .3% ) is p roduced in conseq uence of th e isom erization p rocess
(i.e., ch ain isom erization transf er is f av ored relativ e to
ch ain p rop ag ation) . I t sh ould b e p ointed out th at th e ab ility of NiI I com p lex es to isom erize α-oleins is a w ell-k now n
p rocess.19 I n p articular, it w as f ound th at increasing th e reaction tim e results in h ig h er q uantity of trans-C4 ow ing to th e isom erization p rocess inv olv ing 1-b utene and cis-C4 ( Sch em e 4 ) .
A ctiv ation of nick el com p lex 5 w ith dieth y l alum inum -ch loride ( D E A C ) instead of M A O resulted in a m ore activ e sy stem ( T O F 125 ,4 00 m ol( eth y lene) m ol( Ni)−1 h−1) . T h is ob serv ation could relect a b etter stab ilization of activ e
sp ecies w ith D E A C th an w ith M A O , p ossib ly th ank s to th e ch lorine atom . A t th e sam e tim e, th e use of D E A C led to slig h tly im p rov ed selectiv ity f or 1-b utene ( 32.1 % ) , w ith p roduction of low er am ounts of 2-b utenes ( 6 7.9 % ) .
Conclusions
A new set of ch rom ium ( I I I ) com p lex es b ased on tridentate lig ands h as b een p rep ared and ev aluated f or eth y lene olig om erization under M A O activ ation. R ep lacem ent of th e O
N
N N
N Ni
Cl Cl 5
MAO, ethylene
+ + 5 min
40 min +
isomerization
time 5 min → 40 min
1 equiv PPh3
Scheme 4 .
F igure 5 . M onitoring of selectiv ities in th e eth y lene olig om erization reaction p rom oted b y th e 5/ M A O / PPh3 sy stem ( [ Ni] / [ PPh3] = 1.0, [ M A O ] / [ Ni] = 25 0; T = 30 ºC ; 20 atm eth y lene) : C4 p roducts, 1-b utene,
central b ridg ing nitrog en w ith a sulf ur donor atom af f ords a cataly st th at ex h ib its h ig h er T O F and h ig h er selectiv ity f or
α-C4, α-C6, and α-C8. T h e p resence of p h eny l g roup s at 3- or 5 -p osition of th e p y razoly l ring s determ ines a pronouced
ef f ect on activ ity and selectiv ity ow ing to th e steric/ electronic
ef f ects of th ese p h eny l g roup s on th e ch rom ium m etal center. I n p arallel, th e use of trip h eny lp h osp h ine ( PPh3) in th e olig om erization reactions using nick el cataly sts
(3 and 5) resulted in m uch h ig h er T O F s. H ow ev er, th e p resence of th is aux iliary lig and h as a strong im p act in th e selectiv ity tow ards th e p roduction of α-oleins,
decreasing sub stantially th e am ount of 1-b utene w ith a concom itant increase of th e 2-b utene f ractions. U nder op tim ized conditions ( [ Ni] / [ PPh3] = 1.0, [ Ni] = 3.0 µm ol,
30 °C , 20 b ar eth y lene, M A O -to-Ni = 25 0, olig om erization tim e = 20 m in) , p re-cataly st 5 leads to T O F = 15 4 .2×103 m ol( eth y lene) m ol( Ni)−1 h−1 and selectiv ities f or C
4 and
α-C4 are 100.0 and 24 .4 % , resp ectiv ely .
Sup p lementary I nformation
C C D C 74 6 5 6 9 contains th e sup p lem entary cry stallog rap h ic data f or 4. T h ese data can b e ob tained f ree of ch arg e v ia h ttp : / /
w w w .ccdc.cam .ac.uk / conts/ retriev ing .h tm l, or f rom th e C am b ridg e C ry stallog rap h ic D ata C entre, 12 U nion R oad,
C am b ridg e C B2 1E Z , U K ; f ax : ( + 4 4 ) 1223-336 -033; or e-m ail: dep osit@ ccdc.cam .ac.uk . H eteronuclear m ultip le b ond
correlation ( H M BC ) data f or 1-( 2-h y drox y eth y l) -3-m eth y l-5 -p h eny lp y razole ( isom er A ) are av ailab le f ree of ch arg e at h ttp : / / j b cs.sb q .org .b r, as PD F ile.
A cknow ledgments
T h is research w as inancially sup p orted b y C NPq , Petrob rás and I NC T -C atálise. L . L . de O liv eira, R . C am p adelli, A . L . Berg am o and A . H . D . P. dos Santos g ratef ully ack now ledg e C A PE S, C NPq and F A PE R G S f or f ellow sh ip s. T h e X -ray dif f raction analy sis of 4 w as
p erf orm ed b y T h ierry R oisnel at th e L ab oratoire de C h im ie du Solide et I norg aniq ue M oléculaire, I nstitut de C h im ie, U niv ersité de R ennes.
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Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
Ethylene Oligomerization Reactions. Effect of A ux iliary Ligand on A ctiv ity and
Selectiv ity
Lucilene L. de Oliveira, Roberta R. Campedelli, Adão L. Bergamo, Ana H. D. P dos Santos and Osvaldo L. Casagrande*
Laboratório de Catálise Molecular, Instituto de Química, Univ ersidade F ederal do R io G rande do Sul, A v . Bento G onçalv es, 9 5 0 0 , 9 0 5 0 1 - 9 7 0 P orto A leg re- R S, Brazil
