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Activation of CH and CC bonds in ethylene and piperylene catalytic reactions
LO5
Journal of Moiecdcr Cataiysis, 14 (1962) 105 - 112 0 Eisevier Sequoie S.A. Lausznne -Printed in The Netherlands
ACTIVATION OF C-H AND C+Z BON-IX EN ETHYLENE PIE’ERYLENE CATALl?ITC REACTIONS
G. P. BELOV, T. S. DZHABIEV The Insfitufe of Chemical 142432 (Ij-.S.S.R.J (Received
Apti
AND
and I. M. KOLESNEKOV
Physics.
LES.S.iZ_
Academy
of
Sciences.
Chernogolovka.
14.1980)
Activation of C-H and C-C bonds ~JZ the dimerization of ethylene to butene-I by the T’i(OC4,4-9j4-MRB system and piperylene conversion into isoprene and cyclopenfene by homogeneous and heterogeneous catiysts have been considered. A new mechmism of ethylene dimerization and a general scheme for cyclopentene formation from piperylene have been proposed_
Introduction Remarkable progress in metal compiex catalysis has brought forward the problem of saturated hydrocarbon activation under mild conditions [I]. A solution would aUcw new reactions to be carried out and valuable new products to be obtained horn relatively cheap raw materi&. Olefin and diene activation by homogeneous and heterogeneous com-
plex catalysts is also very important. The present paper deals with possible C-H and C-C activation in the catalytic ethylene dimerization and cyclopentene formation fiorn piperylene.
&p&mental Tetrabutixytitanium, Ti(C,HsO)4, was repeatedly disti&d in oac~o. Trimethyialirminlurn, _4.1(CH3)3(50% solution in decalin), was used as received. Catalyst components were used as 5 - 10% soIutions in n-heptane or ndecane, the Latterhaving been puriEed by distillation [2l and kept under argon above sodium wire. EthyIene md tefzadeuteroethylene (>98% deuterium content) were p-urified by manifold distiUation irr OCTCLLO at low temperature. Piperylene (54.6% tins and 44.9% cis) contained ca. 0.5% isoprene aSa_nimpurity. A heterogeneous aluminium-tur;gsten c&y& was prepared by the impregpation of y-A&O, particles with ammonium tungstate followed by c&i-
136
nation in air at 500 “c for 6 h. The catalyst contained 85% w/w Al& and 15% w/w WOa. A homogeneous catalyst, (CH3)sSi,0sAlaCl, was prepared by the interaction of octamethyltetracyclosiloxane with AICEs at 126 % for 10 h. The fraction which separated had a boiling range of 130 - 190 %. After cooling this kaction, crystalline needles were isolated, m.p. 154 “C. ESR specks were recorded on a radiospectrometer EPR-2; mass-spectra of deuterobutenes were recorded on ma spectrometers MH-1302 and MI1305 (U.S.S.R.). Separation of dimerixation products before injection into the mass spectrometer was conducted on a Tsvet chromatograph (U.S.S.R.). Results and discussion Cablytic
_:fzylene
diwerization
TLe present s+ldy of ‘the catalytic Ziegler-Natta system involving Ti(3C4Hs)q and various aluminium trialkyls has shown ethylene dimerization to have some peculiarities. First of all, a considerable amount of s&urated hydrocarbon is evolved in the reaction of ethylene and 2 catdykic complex, thcugh the transition metal reduction is negligible in this case [S] . Similar results were obtained in the reaction of cyclopentadienyl-zircotium compounds with tiethylal uminium [4] . It has been proposed that an olefin formed together with an alkane via scheme (1) can oxidize iow-valence titanium species to produce binucle=Ti-CH,-CH2_Ti(ompounds \Ti/ /
[5].
R AR
-
Ti(II) f RH + R(-H)
Moreover, a further evolution of the akane in the presence of trialkylaluminium excess can proceed uic scheme (2): Y5L” Ti-CH2-CH2-Ti
+ RML,
-
Ti-CH-CH,-Ti
+ RH
(2)
Such mekllation may lead to the complete substitution of hydrogen atoms in the hydrocarbon bridge between two titanium atoms in the binuclear complex. This suggestion is confhmed by finding completely deuteriated alkanes in the hydrolyzate if DzO is added to the catalytic system [5]. In the hydrolyzate of the catalytic system, Ti(OC.& )4-Al(iso-C4H9 j3, the gaseous products contain methane up to 3% of ]Ti(OC,H,)4]0, besides isobutane and isobutene. This fact may be explained by the C< bond cleavage in a hydrocarbcn radical in the coordination sphere of a transition metal ion. The reaction mixture was found to contain propane, though the amount may differ greatly from that of evolved Cl&, which depends on the ~perimental conditions.
The titanate reduction by trhnethylduminium in the presence of C2De resuks in the formation of methane with significant deuterium content (up to 40% monodeuteromethane). This fact also supports the production of binuclear titanium derivatives Tf’i+ZDz-CDz+ with subsequent metahation by methyl-containing derivatives of duminium and titanium according to reaction (2). However, besides monodeuteromethane, this reaction ako gives CD& (1%). CDzH (1.5%) and CD4 (O-4%), thus indicating the subsequent activation of deuteriated methane, for example, by means of its oxidative addition to a low-valent Ti species [I] : m3 '\Ti' TqIE)+
CK‘$
,-
(3) /\ H
reported data contim the activation of the C-H and C-C bonds under mild conditions (room temperature, atmospheric pressure). The kinetic study of ethylene dimerization by ‘IX(OC&9)--AIRs, where R is arkakyl radical, has led us to conchxde that active centres include bititanium species with an ethane bridge between two Ti atoms [6,71. These compounds are readily formed in the catalytic system if X(CzHs)3 is used as a co-catiyst, since in tbk case ethylene is produced in reaction (1) to be used later as a bridge. With Al(CH3)s 2s a cocatalyst, bititanium ethylene-bridged complexes are producd, probably as a result of carbene compound recombinaTine
+’ ,Ti+ZH2-CH,-Ti~,
tion 131 Z;‘i=CH,
the carbene compIex being ob-
tained through the decomposition of dimethy titanium compounds accordingto: CH3 \Ti/ -
’
‘-ix
)mx,
f
CEI&
3
the other cases (when R is isoCzJ&, iso-C&I,, n-CeHzi, etc. ), for the bititanium Ti-CH,+X2-Ti complexes to be produced, ethylene is required in the reaction zone. Ethylene dimerization rate at the initial stage of the reaction increases with increasing bititanium compound content. Figure 1 gives the change in ethylene dimerization rate in the presence of Ti(OC,H,),-Ai(iso-C,&)3 catalyst together with the increasing content of mono-, di- and trideuteroethanes, obtained after deuterolysis. In addition, the formation of smti amouuk of tetideuteroethaue is aIso observed (not shown in Fig. I). The dimerization rate decreases after reaching a maximum with increasing amounts of dideuteroethane. To expIai.uthese rermlts, we propose that TiCH2CH2Ti compounds formed are converted in time, with the excess M-organic compound, into compounds of the Ti
108
Fig. 1. Kinetics of deuteroethane build-up in deuterolysis (by D,O) products of the reaction mixture Ti(OC~H~)4-Al(iso-C~&)~<~H~ and the change in dimerization rate with time. Experimental conditions: [Ti(OC;% )a] = 0.02 M; Ai/Ti = 7.2; Pc,H, = 255 Torr; heptane = 20 ml; T = 20 “C. Fig. 2. Dimerization kinetics of ethylene (l), tetradeuteroethylene (3) and their mixture (2) in the presence of catalyst Ti(OC4Hg)z-AI(CH3)3. [Ti(OC4Hg)a] = 0.01 M; Al/T3 dt.5; ethylene pressure = 1 bar.; decane = 4C ml; T = 20 “C.
=
To clarify the mechanism of butene-l formation, the composition of butenes produces in C2H, and C2D4 codimerization has been determined (Fig. 2). Figure 2 shows that the maximum rate of ethylene consumption is about 5 times that of tetradeuteroethylene [S] . The presence of such a kinetic isotopic effect indicates that C-H bond cleavage in the ethylene molecule is the limitig step in butene-i formation. A delayed attainment of :he dimerization rate maximum should be also noted when C,D, is used instead of C2H4. Such behavior suggests the existence of C-H bond cleavage also at the stage of active centre formation. Active centre formation is proposed to occur in the interaction of an ethylene molecule with a binuclezu paramagnetic complex via reaction (4):
CHn-CHs \I ,Ti-CH,-CH,-Ti
CH
(4)
Figure 3 represents a molecular model of the bititanium complex tith two ethylene molecules. It is noteworthy that the kinetics of ESR signal intensity change for this system (wide unresolved singlet mith g = 1.945) do not contradict reaction (4). ESR signal disappearance with time occurs in the presence of C*D, faster than it does in vacuum, and in ethylene atmosphere even faster, the latter being caused by partial oxidation of paramagnetic complexes by ethylene (eqn. 4). M-fZH=CHs ment formation in reaction (4) is confirmed by the presence of monodeuteroethylene and more fully deuteriated ethyienes in the products of D@ hydrolysis of the reaction mixture.
109
Fig. 3. A molecular model of the bititanium centre A.lR,OR with two coordinated ethylene molecules.
RzAlOR-
(RO),TiCH,CH~Ti(OR)~-
In an earlier paper [S] we assumed butene-1 formation to proceed via the mechanism of synchronous coupling [9]. In this case, CaH, and CaD, codimerizated butenes with molecular masses of 56 (C&is), 60 (C4H4D4) and 64 (C,Ds) should be obtained if no deuterium exchange between tetrade&ðylene and ethylene occurs in the presence of the catalyst system. Blank experiments have shown no deuterium exchange taking place between olefin molecules (ethylene and butenes). This shows the absence of active hydrogenoftheTi-Htype which causesbdene moleculeisomerization and deuterium exchange. Instead of the products expected for synchronous coupling, we found a number of butenes-l with molecular masses from 56 to 64 with relative content 1.07 : 1.07 : 0 : 0.91 : 2.24 : 1.03 : 0 : 1.06 : 1, respectively, of CzH4 co-dimerized with CzD+. The reaction was maintained at constant pressure by feeding the reaction vessel w-ith an equimolar mixture of C2Hl and CzD,-
To explain the results obtained, we assumed that in the limiting step of butene-l formation the insertion of coordinated ethylene in the C-H bond proceeds to give a butyl group:
F
4H 9
-
CH= CH,
)T-CHZ-CH2-Y$ CH=CH,
110
There then occurs a rapid chain transfer to the monomer [IO] in the non-limitling step with a return of the catalytically active centre to the i.niM step:
;ki-CH,XH,-Ti:
+ C,H,
AH=cH,
-
\I
,Ti-cH,-cH,--Til+ I’
C,H,
CH=CH2 (61
In this case, with equal opportunity for light and heavy monomers to enter into a dimer, the relative distribution of deuterobutenes with molecular massesfrom56ta64shouldcorrespondtol:I:O:l:2:1:O:1:P. This is confirmed by the experimental distribution data with an accuracy of i 10%. The proposed scheme for ethylene dimerization to butene-l in the presence of Ti(OCsHg),--AIR3 catalyst explains the observed kinetic isotopic effects and the deuterobutene distribution in the products of C,l& and C2De co&merization. If ethylene is not added to the Ti(OCbHg),-Al(CHs)s system, then monodeuteroethane molecules are practically absent in the products of hydrolysis of the catalytic mixture with D20. However, mere deuteriated ethane molecules are formed. This fact serves as additional confiiation for reaction (2). Otherwise, after prolonged ethylene dime&&ion, the monodeuteroethane content in the hydrolyzate (by D,O) exceeds by almost an order of magnitude that of the other deuteroethanes, in accordance with reaction (4). Thus, C-H bond activation in the coordination sphere of a transition metal is proposed to explain the dimerization of ethylene in the above homogeneous catalytic systems, involving 2 mechanism different horn those proposed earlier to explain olefm polymerization and oligomerization by ZieglerNatta catalysts. C-H bond activation by homogeneous and heterogeneous catalysts is very likely one of the main steps in the newlydiscovered intramolecular alkylation reaction [ 111.
Reactionofirr~~molecular4lky~tion
This alkylation reaction was observed in the catalytic conversion of piperylene to cyclopentene [ll] ~ Some experimental data are given in Table 1. Selectivity of the process in the presence of homogeneous catalyst was found to be very high, and under certain conditions might approach 100%. Pipe_ry!eneconversion in the presence of heterogeneous catalyst containing Al and W is less selective. The experimental results, given in Fig. 4, show the maximum yield of cyclopentene to be obtained at 65 33, of isoprene in the range of 63 - 75 93 and of amylenes at 75 “c. With increasing temperature coking increases appreciably, affecting the cztiyst activity even at the initial stages of the reaction.
111
TAELE
1
Cyclopentene catalyst Temperature
production
mme (h)
from
piperyIene
mixture
Liquid hydrocarbon/ piperylene ratio
(“C)
in the presence
Yield
92 90
1 3
89
5
(Bo mass)
ck
Cyclopentene
Piperylene
lmlzs
of homogeneous
Lsopre-e
2:l
64.3
33.3
1.7
0.6
2:l 2:l
55.8 58.7
40.5 35.2
3.2 5.3
0.5 0.6
of
heterogeneous
Fig. 4. Temperature effect catalyst_ (1) cyclopentene,
on piperylene
conversion
in the presence
(2) koprene, (3) amylenes.
The mechanism of cyclopentene formation fiorn piperylene is presently under study. Avoiding details of this complex reaction we may present its mechanism in a general scheme:
This sequence formally represents an intramolecular insertion reaction of the -CH=CH2 piperyIene fragment in the C-H bond of the methyl group with cyclization . Acknowkdgment We are grateful to Prof. F. S. Dyachkovskii
for helpfd
discussions.
References 1 A. E. Shilov and A. A Shteiqasn, Coo& CRem. Rev., 24 (1977) 97. 2 A. Weissberger, E. S. Proskauer, J. A. Raddick and E. noopsx Jr., Organic So[uents: Physical hoperties and Mr?fhorf.sof Ptification. Interscience, New York, 1955.
112 Zh. Obshch. KhimiI. 44 (1974) 332. 3 T. S. Dzbabiev and F. S. D‘jachkotiti, Chem.. 6 (1966) 373. 4 H. Sinn and E. KoLk, J. O~momet. 5 T. S. Dzhzbiev, F. S. Dy2chkovskii and A. E. Shilov, VysoRomoleR. Soed..
AI3 (1971) 2474. Symposium on the Mechmbm 6 G. P. Belov, T. S. Dzbabiev and F. S. Dyacbkov&i, gf Hydrocarbon Reactions, Siofok, Hungary, 1973. 7 G. P. Belov, Neftekhirniu. 17 (1977) 3. 16 s T. S. Dzhabiev, 2. M. Dzhabieva, G. P. BeIov and F. S. Dyachkonkii, Neftekhim& (1976) 706. of Homogeneous Cutulysis, 9 G. Lefebvre and Y. 0muvin, in R. Ugo (&I_), Aspects Milan, 1970. 10 G. HenriciUlivE snd S. Olivd. Am. Chem. Sm. Polym. Prepr., 15 (1974) 366. 11 I_ hl_ Kolesnikov and N_ N. Belov, Zh_ Fizhh_ Khimii. 52 (1978) 2712_
Journal of Moiecdcr Cataiysis, 14 (1962) 105 - 112 0 Eisevier Sequoie S.A. Lausznne -Printed in The Netherlands
ACTIVATION OF C-H AND C+Z BON-IX EN ETHYLENE PIE’ERYLENE CATALl?ITC REACTIONS
G. P. BELOV, T. S. DZHABIEV The Insfitufe of Chemical 142432 (Ij-.S.S.R.J (Received
Apti
AND
and I. M. KOLESNEKOV
Physics.
LES.S.iZ_
Academy
of
Sciences.
Chernogolovka.
14.1980)
Activation of C-H and C-C bonds ~JZ the dimerization of ethylene to butene-I by the T’i(OC4,4-9j4-MRB system and piperylene conversion into isoprene and cyclopenfene by homogeneous and heterogeneous catiysts have been considered. A new mechmism of ethylene dimerization and a general scheme for cyclopentene formation from piperylene have been proposed_
Introduction Remarkable progress in metal compiex catalysis has brought forward the problem of saturated hydrocarbon activation under mild conditions [I]. A solution would aUcw new reactions to be carried out and valuable new products to be obtained horn relatively cheap raw materi&. Olefin and diene activation by homogeneous and heterogeneous com-
plex catalysts is also very important. The present paper deals with possible C-H and C-C activation in the catalytic ethylene dimerization and cyclopentene formation fiorn piperylene.
&p&mental Tetrabutixytitanium, Ti(C,HsO)4, was repeatedly disti&d in oac~o. Trimethyialirminlurn, _4.1(CH3)3(50% solution in decalin), was used as received. Catalyst components were used as 5 - 10% soIutions in n-heptane or ndecane, the Latterhaving been puriEed by distillation [2l and kept under argon above sodium wire. EthyIene md tefzadeuteroethylene (>98% deuterium content) were p-urified by manifold distiUation irr OCTCLLO at low temperature. Piperylene (54.6% tins and 44.9% cis) contained ca. 0.5% isoprene aSa_nimpurity. A heterogeneous aluminium-tur;gsten c&y& was prepared by the impregpation of y-A&O, particles with ammonium tungstate followed by c&i-
136
nation in air at 500 “c for 6 h. The catalyst contained 85% w/w Al& and 15% w/w WOa. A homogeneous catalyst, (CH3)sSi,0sAlaCl, was prepared by the interaction of octamethyltetracyclosiloxane with AICEs at 126 % for 10 h. The fraction which separated had a boiling range of 130 - 190 %. After cooling this kaction, crystalline needles were isolated, m.p. 154 “C. ESR specks were recorded on a radiospectrometer EPR-2; mass-spectra of deuterobutenes were recorded on ma spectrometers MH-1302 and MI1305 (U.S.S.R.). Separation of dimerixation products before injection into the mass spectrometer was conducted on a Tsvet chromatograph (U.S.S.R.). Results and discussion Cablytic
_:fzylene
diwerization
TLe present s+ldy of ‘the catalytic Ziegler-Natta system involving Ti(3C4Hs)q and various aluminium trialkyls has shown ethylene dimerization to have some peculiarities. First of all, a considerable amount of s&urated hydrocarbon is evolved in the reaction of ethylene and 2 catdykic complex, thcugh the transition metal reduction is negligible in this case [S] . Similar results were obtained in the reaction of cyclopentadienyl-zircotium compounds with tiethylal uminium [4] . It has been proposed that an olefin formed together with an alkane via scheme (1) can oxidize iow-valence titanium species to produce binucle=Ti-CH,-CH2_Ti(ompounds \Ti/ /
[5].
R AR
-
Ti(II) f RH + R(-H)
Moreover, a further evolution of the akane in the presence of trialkylaluminium excess can proceed uic scheme (2): Y5L” Ti-CH2-CH2-Ti
+ RML,
-
Ti-CH-CH,-Ti
+ RH
(2)
Such mekllation may lead to the complete substitution of hydrogen atoms in the hydrocarbon bridge between two titanium atoms in the binuclear complex. This suggestion is confhmed by finding completely deuteriated alkanes in the hydrolyzate if DzO is added to the catalytic system [5]. In the hydrolyzate of the catalytic system, Ti(OC.& )4-Al(iso-C4H9 j3, the gaseous products contain methane up to 3% of ]Ti(OC,H,)4]0, besides isobutane and isobutene. This fact may be explained by the C< bond cleavage in a hydrocarbcn radical in the coordination sphere of a transition metal ion. The reaction mixture was found to contain propane, though the amount may differ greatly from that of evolved Cl&, which depends on the ~perimental conditions.
The titanate reduction by trhnethylduminium in the presence of C2De resuks in the formation of methane with significant deuterium content (up to 40% monodeuteromethane). This fact also supports the production of binuclear titanium derivatives Tf’i+ZDz-CDz+ with subsequent metahation by methyl-containing derivatives of duminium and titanium according to reaction (2). However, besides monodeuteromethane, this reaction ako gives CD& (1%). CDzH (1.5%) and CD4 (O-4%), thus indicating the subsequent activation of deuteriated methane, for example, by means of its oxidative addition to a low-valent Ti species [I] : m3 '\Ti' TqIE)+
CK‘$
,-
(3) /\ H
reported data contim the activation of the C-H and C-C bonds under mild conditions (room temperature, atmospheric pressure). The kinetic study of ethylene dimerization by ‘IX(OC&9)--AIRs, where R is arkakyl radical, has led us to conchxde that active centres include bititanium species with an ethane bridge between two Ti atoms [6,71. These compounds are readily formed in the catalytic system if X(CzHs)3 is used as a co-catiyst, since in tbk case ethylene is produced in reaction (1) to be used later as a bridge. With Al(CH3)s 2s a cocatalyst, bititanium ethylene-bridged complexes are producd, probably as a result of carbene compound recombinaTine
+’ ,Ti+ZH2-CH,-Ti~,
tion 131 Z;‘i=CH,
the carbene compIex being ob-
tained through the decomposition of dimethy titanium compounds accordingto: CH3 \Ti/ -
’
‘-ix
)mx,
f
CEI&
3
the other cases (when R is isoCzJ&, iso-C&I,, n-CeHzi, etc. ), for the bititanium Ti-CH,+X2-Ti complexes to be produced, ethylene is required in the reaction zone. Ethylene dimerization rate at the initial stage of the reaction increases with increasing bititanium compound content. Figure 1 gives the change in ethylene dimerization rate in the presence of Ti(OC,H,),-Ai(iso-C,&)3 catalyst together with the increasing content of mono-, di- and trideuteroethanes, obtained after deuterolysis. In addition, the formation of smti amouuk of tetideuteroethaue is aIso observed (not shown in Fig. I). The dimerization rate decreases after reaching a maximum with increasing amounts of dideuteroethane. To expIai.uthese rermlts, we propose that TiCH2CH2Ti compounds formed are converted in time, with the excess M-organic compound, into compounds of the Ti
108
Fig. 1. Kinetics of deuteroethane build-up in deuterolysis (by D,O) products of the reaction mixture Ti(OC~H~)4-Al(iso-C~&)~<~H~ and the change in dimerization rate with time. Experimental conditions: [Ti(OC;% )a] = 0.02 M; Ai/Ti = 7.2; Pc,H, = 255 Torr; heptane = 20 ml; T = 20 “C. Fig. 2. Dimerization kinetics of ethylene (l), tetradeuteroethylene (3) and their mixture (2) in the presence of catalyst Ti(OC4Hg)z-AI(CH3)3. [Ti(OC4Hg)a] = 0.01 M; Al/T3 dt.5; ethylene pressure = 1 bar.; decane = 4C ml; T = 20 “C.
=
To clarify the mechanism of butene-l formation, the composition of butenes produces in C2H, and C2D4 codimerization has been determined (Fig. 2). Figure 2 shows that the maximum rate of ethylene consumption is about 5 times that of tetradeuteroethylene [S] . The presence of such a kinetic isotopic effect indicates that C-H bond cleavage in the ethylene molecule is the limitig step in butene-i formation. A delayed attainment of :he dimerization rate maximum should be also noted when C,D, is used instead of C2H4. Such behavior suggests the existence of C-H bond cleavage also at the stage of active centre formation. Active centre formation is proposed to occur in the interaction of an ethylene molecule with a binuclezu paramagnetic complex via reaction (4):
CHn-CHs \I ,Ti-CH,-CH,-Ti
CH
(4)
Figure 3 represents a molecular model of the bititanium complex tith two ethylene molecules. It is noteworthy that the kinetics of ESR signal intensity change for this system (wide unresolved singlet mith g = 1.945) do not contradict reaction (4). ESR signal disappearance with time occurs in the presence of C*D, faster than it does in vacuum, and in ethylene atmosphere even faster, the latter being caused by partial oxidation of paramagnetic complexes by ethylene (eqn. 4). M-fZH=CHs ment formation in reaction (4) is confirmed by the presence of monodeuteroethylene and more fully deuteriated ethyienes in the products of D@ hydrolysis of the reaction mixture.
109
Fig. 3. A molecular model of the bititanium centre A.lR,OR with two coordinated ethylene molecules.
RzAlOR-
(RO),TiCH,CH~Ti(OR)~-
In an earlier paper [S] we assumed butene-1 formation to proceed via the mechanism of synchronous coupling [9]. In this case, CaH, and CaD, codimerizated butenes with molecular masses of 56 (C&is), 60 (C4H4D4) and 64 (C,Ds) should be obtained if no deuterium exchange between tetrade&ðylene and ethylene occurs in the presence of the catalyst system. Blank experiments have shown no deuterium exchange taking place between olefin molecules (ethylene and butenes). This shows the absence of active hydrogenoftheTi-Htype which causesbdene moleculeisomerization and deuterium exchange. Instead of the products expected for synchronous coupling, we found a number of butenes-l with molecular masses from 56 to 64 with relative content 1.07 : 1.07 : 0 : 0.91 : 2.24 : 1.03 : 0 : 1.06 : 1, respectively, of CzH4 co-dimerized with CzD+. The reaction was maintained at constant pressure by feeding the reaction vessel w-ith an equimolar mixture of C2Hl and CzD,-
To explain the results obtained, we assumed that in the limiting step of butene-l formation the insertion of coordinated ethylene in the C-H bond proceeds to give a butyl group:
F
4H 9
-
CH= CH,
)T-CHZ-CH2-Y$ CH=CH,
110
There then occurs a rapid chain transfer to the monomer [IO] in the non-limitling step with a return of the catalytically active centre to the i.niM step:
;ki-CH,XH,-Ti:
+ C,H,
AH=cH,
-
\I
,Ti-cH,-cH,--Til+ I’
C,H,
CH=CH2 (61
In this case, with equal opportunity for light and heavy monomers to enter into a dimer, the relative distribution of deuterobutenes with molecular massesfrom56ta64shouldcorrespondtol:I:O:l:2:1:O:1:P. This is confirmed by the experimental distribution data with an accuracy of i 10%. The proposed scheme for ethylene dimerization to butene-l in the presence of Ti(OCsHg),--AIR3 catalyst explains the observed kinetic isotopic effects and the deuterobutene distribution in the products of C,l& and C2De co&merization. If ethylene is not added to the Ti(OCbHg),-Al(CHs)s system, then monodeuteroethane molecules are practically absent in the products of hydrolysis of the catalytic mixture with D20. However, mere deuteriated ethane molecules are formed. This fact serves as additional confiiation for reaction (2). Otherwise, after prolonged ethylene dime&&ion, the monodeuteroethane content in the hydrolyzate (by D,O) exceeds by almost an order of magnitude that of the other deuteroethanes, in accordance with reaction (4). Thus, C-H bond activation in the coordination sphere of a transition metal is proposed to explain the dimerization of ethylene in the above homogeneous catalytic systems, involving 2 mechanism different horn those proposed earlier to explain olefm polymerization and oligomerization by ZieglerNatta catalysts. C-H bond activation by homogeneous and heterogeneous catalysts is very likely one of the main steps in the newlydiscovered intramolecular alkylation reaction [ 111.
Reactionofirr~~molecular4lky~tion
This alkylation reaction was observed in the catalytic conversion of piperylene to cyclopentene [ll] ~ Some experimental data are given in Table 1. Selectivity of the process in the presence of homogeneous catalyst was found to be very high, and under certain conditions might approach 100%. Pipe_ry!eneconversion in the presence of heterogeneous catalyst containing Al and W is less selective. The experimental results, given in Fig. 4, show the maximum yield of cyclopentene to be obtained at 65 33, of isoprene in the range of 63 - 75 93 and of amylenes at 75 “c. With increasing temperature coking increases appreciably, affecting the cztiyst activity even at the initial stages of the reaction.
111
TAELE
1
Cyclopentene catalyst Temperature
production
mme (h)
from
piperyIene
mixture
Liquid hydrocarbon/ piperylene ratio
(“C)
in the presence
Yield
92 90
1 3
89
5
(Bo mass)
ck
Cyclopentene
Piperylene
lmlzs
of homogeneous
Lsopre-e
2:l
64.3
33.3
1.7
0.6
2:l 2:l
55.8 58.7
40.5 35.2
3.2 5.3
0.5 0.6
of
heterogeneous
Fig. 4. Temperature effect catalyst_ (1) cyclopentene,
on piperylene
conversion
in the presence
(2) koprene, (3) amylenes.
The mechanism of cyclopentene formation fiorn piperylene is presently under study. Avoiding details of this complex reaction we may present its mechanism in a general scheme:
This sequence formally represents an intramolecular insertion reaction of the -CH=CH2 piperyIene fragment in the C-H bond of the methyl group with cyclization . Acknowkdgment We are grateful to Prof. F. S. Dyachkovskii
for helpfd
discussions.
References 1 A. E. Shilov and A. A Shteiqasn, Coo& CRem. Rev., 24 (1977) 97. 2 A. Weissberger, E. S. Proskauer, J. A. Raddick and E. noopsx Jr., Organic So[uents: Physical hoperties and Mr?fhorf.sof Ptification. Interscience, New York, 1955.
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