Tantalum catalysts or catalyst precursors

Tantalum catalysts or catalyst precursors of the formula ##STR1## wherein X is a halide, or alkoxide and L is an alkene (CH.sub.2 .dbd.CHR) having from 2 to 20 carbon atoms, react with 1-olefins to give catalysts of the formula ##STR2## wherein R.sup.2 is hydrogen or a C.sub.1 to C.sub.18 alkyl such as methyl, ethyl, or propyl. The catalysts or catalyst precursors selectively dimerize 1-olefins to the two possible disubstituted .alpha.-olefin dimers, the ratio of which depends on the nature of R.

BACKGROUND OF THE INVENTION 
The invention relates to catalysts or catalyst precursors for forming 
disubstituted .alpha.-olefin dimers from a 1-olefin reactant. 
Prior to the present invention, there have been no known homegeneous 
catalysts for converting a terminal olefin selectively to a disubstituted 
.alpha.-olefin dimer at room temperature or above. Known homogeneous 
dimerization catalysts readily isomerize the initially formed dimer to the 
thermodynamically more stable internal olefin. It is also known that 
heterogeneous catalysts such as chromocene on alumina or silica produce 
1-butene from ethylene. In addition, other selected dimerization reactions 
are known. However, these reactions generally are successful for only one 
olefin, e.g., the use of KC.sub.8 to dimerize propylene selectively to 
4-methyl-1-pentene. 
Accordingly, it would be desirable to provide a homogeneous catalyst system 
for forming primarily one or both disubstituted .alpha.-olefin dimers 
which can be used with any one of a plurality of unsubstituted or 
substituted 1-olefin feed compositions. 
SUMMARY OF THE INVENTION 
This invention provides a class of tantalum catalysts or catalyst 
precursors for dimerizing 1-olefins primarily to disubstituted 
.alpha.-olefin dimers. The catalysts are useful with ethylene (to produce 
1-butene) or substituted C.sub.2 to C.sub.20 olefins, in particular 
propylene (to produce substantially pure 2,3-dimethyl-1-butene). The 
catalysts are homogeneous in that they are in the same phase as the 
reactants under the conditions utilized in the reaction and are 
represented by the formula: 
##STR3## 
wherein X is a halide, alkoxide, or an alkyl, and R.sup.2 is hydrogen or a 
C.sub.1 to C.sub.18 alkyl such as methyl, ethyl, or propyl. 
The precursors to the catalysts of this invention are represented by the 
formula: 
##STR4## 
wherein L is an alkene having from 2 to 20 carbon atoms and which which 
can be substituted with alkyl or aryl, and X is chloride, bromide, iodide, 
fluoride, or alkoxide. 
The catalysts of this invention are useful for forming disubstituted 
.alpha.-olefin dimers, either a mixture, or substantially one as shown in 
Table I. Ethylene gives solely 1-butene. Propylene gives 98% 
2,3-dimethyl-1-butene. 2,3-dimethyl-1-butene (or 2,3-dimethylbutane) is 
used as a gasoline additive to improve octane rating. 
The precursors I where L=ethylene or propylene can be prepared as follows. 
Tantalum pentahalide is treated with Zn(CH.sub.2 CMe.sub.3).sub.2 at a 
temperature between about 20.degree. and 40.degree. C. in toluene or 
pentane to form the compound Ta(CH.sub.2 CMe.sub.3).sub.2 X.sub.3. The 
latter compound is reacted with TlC.sub.5 Me.sub.5 or LiC.sub.5 Me.sub.5 
at a temperature of between about 20.degree. C. and 40.degree. C. in 
toluene or diethyl ether to give Ta(C.sub.5 Me.sub.5)(CH.sub.2 
CMe.sub.3)X.sub.3. Ta(C.sub.5 Me.sub.5)(CH.sub.2 CMe.sub.3)X.sub.3 reacts 
with one-half mole of Zn(CH.sub.2 CH.sub.3).sub.2 or Zn(CH.sub.2 CH.sub.2 
CH.sub.3).sub.2 to give I where L is ethylene or propylene, respectively. 
Table I 
______________________________________ 
Disubstituted .alpha.-olefin dimers made with a 
Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 catalyst in Hexane at 40.degree. 
C. 
Monomer Dimers 
______________________________________ 
CH.sub.3 CHCH.sub.2 
##STR5## 
##STR6## 
CH.sub.3 CH.sub.2 CH.sub.2 CHCH.sub.2 
##STR7## 
##STR8## 
CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 CHCH.sub.2 
##STR9## 
##STR10## 
(CH.sub.3).sub.3 CCH.sub.2 CHCH.sub.2 
##STR11## 
______________________________________ 
The precursors I where L is any other monosubstituted or cis-disubstituted 
linear or cyclic olefin can be prepared quantitatively by stirring same 
with Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 overnight at 25.degree. C. 
The catalysts are prepared by the following general reaction. Since this 
has been shown to be an equilibrium either I or II could be regarded as 
the catalyst. 
##STR12## 
They have been isolated when R.sup.2 is hydrogen, methyl, ethyl, or propyl 
and have been observed by .sup.13 C NMR when R.sup.2 is butyl or 
neopentyl. The Compounds II, in the presence of a C.sub.2 -C.sub.20 
olefin, catalytically effect dimerization of the olefin to disubstituted 
.alpha.-olefin dimers as shown in Table I. The reaction of compound I and 
the olefin is effected in a dry, oxygen-free, inert solvent such as 
pentane, benzene, decane or the like, at a temperature between about 
0.degree. C. and 200.degree. C., preferably between about 20.degree. C. 
and 100.degree. C. and at a pressure between about 15 psi and 1500 psi, 
preferably between about 45 psi and 60 psi. The olefin dimer is recovered 
by distillation after the reaction has been allowed to proceed to 
completion as indicated by gas chromatography. 
Representative compounds prepared by this invention include: 
##STR13##

SPECIFIC EMBODIMENTS OF THE INVENTION 
The following examples illustrate the present invention and are not 
intended to limit the same nor be construed as fully dilineating the scope 
of this discovery. 
In order to avoid the presence of molecular oxygen and moisture, all 
experiments below were carried out in an atmosphere of dry nitrogen gas. 
EXAMPLE I 
This example illustrates the method for making a compound of the formula 
##STR14## 
Ta(CH.sub.2 CMe.sub.3)Cl.sub.4 (7.92 g) and LiC.sub.5 Me.sub.5 (2.86 g) 
were stirred in 50 ml of ether for 2 hours. The mixture was filtered and 
the ether removed from the filtrate in vacuo. The residue was extracted 
into toluene and the solution filtered. The toluene was removed in vacuo 
and the crude product recrystallized from ether to give 5.54 g of 
red-orange crystals. The ether was removed from the filtrate in vacuo and 
the residue was again extracted into toluene. The solution was filtered 
and the toluene concentrated until crystals were noted. An equal volume of 
pentane was added and the solution was stored at -20.degree. C. for 24 h 
to give another 2.0 g of Ta(C.sub.5 Me.sub.5)(CH.sub.2 CMe.sub.3)Cl.sub.3 
(overall yield 76%). 
.sup.1 H NMR (.tau., C.sub.6 D.sub.6): 8.03 (s, 15, C.sub.5 Me.sub.5), 8.54 
(s, 9, CH.sub.2 CMe.sub.3), 8.62 (s, 2, CH.sub.2 CMe.sub.3). 
A solution of Zn(CH.sub.2 CH.sub.2 CH.sub.3).sub.2 (1.86 g, 12.29 mmol) in 
10 ml toluene was rapidly added to a solution of Ta(C.sub.5 
Me.sub.5)(CH.sub.2 CMe.sub.3)Cl.sub.3 (9.71 g, 19.61 mmol) in 140 ml of 
toluene at -78.degree. C. After stirring for 5 min at -78.degree. C. the 
cold bath was removed and the stirred solution was allowed to warm to room 
temperature. The color changed from orange to purple-red and a dark solid 
precipitated. The mixture was filtered and the precipitate was extracted 
with toluene until the filtrate was colorless. The toluene was removed in 
vacuo from the combined filtrates to give a dark solid which was 
recrystallized from pentane at -30.degree. C. to give 6.39 g of Ta(C.sub.5 
Me.sub.5)(propylene)Cl.sub.2 as dark purple crystals (two crops, 76% total 
yield). 
Anal. Calcd for TaC.sub.13 H.sub.21 Cl.sub.2 : C, 36.39, H, 4.93; Cl, 
16.52. Found: C, 36.58; H, 5.06; Cl, 16.66. .sup.1 H NMR (.tau., C.sub.6 
H.sub.6): 6.98-8.20 including a large peak at 7.12 (m, 6, CH.sub.3 
CH.dbd.CH.sub.2), 8.37(s, 15, C.sub.5 Me.sub.5). .sup.13 C NMR (ppm 
downfield from TMS, d.sub.8 -toluene, 0.degree. C., .sup.1 H gated 
decoupled): 11.6 (q, C.sub.5 Me.sub.5, J.sub.CH =128 Hz), 27.3 (q, 
CH.sub.3 CH.dbd.CH.sub.2, .sup.1 J.sub.CH =125 Hz), 72.3 (t, CH.sub.3 
CH.dbd.CH.sub.2, .sup.1 J.sub.CH =149 Hz), 80.0 (d,CH.sub.3 
CH.dbd.CH.sub.2, .sup.1 J.sub.CH =152 Hz), 117.2(s, C.sub.5 Me.sub.5). 
EXAMPLE II 
This example illustrates the method of making a compound with the formula 
##STR15## 
The procedure is virtually identical to that in Example I except 
Ta(CH.sub.2 CMe.sub.3)Br.sub.4 is used in place of Ta(CH.sub.2 
CMe.sub.3)Cl.sub.4. 
EXAMPLE III 
This example illustrates the method of making a compound with the formula 
##STR16## 
A 0.43 g (1 mmol) sample of Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 in 5 ml 
of tetrahydrofurm was treated with 3.0 g (20 mmol) of anhydrous NaI. Two 
mols of NaCl were filtered off after ten days and the solvent removed in 
vacuo. Ta(C.sub.5 Me.sub.5)(propylene)I.sub.2 was recrystallized from 
pentane as very dark red-purple crystals. The yield was essentially 
quantitative. 
EXAMPLE IV 
This example illustrates the method of making compounds the formula 
##STR17## 
A solution of Ta(C.sub.5 Me.sub.5)(C.sub.2 H.sub.4)Cl.sub.2 (0.42 g, 1.00 
mmol) in 2 ml C.sub.6 H.sub.6 was added to a solution of styrene (0.23 g, 
2.20 mmol) in 3 ml C.sub.6 H.sub.6. An .sup.1 H NMR spectrum recorded 
after 15 min showed a 1:1 mixture of Ta(C.sub.5 Me.sub.5)(C.sub.2 
H.sub.4)Cl.sub.2 and Ta(C.sub.5 Me.sub.5)(styrene)Cl.sub.2 along with 
excess free styrene. After 1 h at 25.degree. C. the .sup.1 H NMR spectrum 
showed no further change. The mixture was heated to 70.degree. C. for 1 h 
and the .sup.1 H NMR spectrum showed almost complete conversion to 
Ta(C.sub.5 Me.sub.5)(styrene)Cl.sub.2. The solvent was removed in vacuo 
and the solid was recrystallized from toluene/pentane (50/50) at 
-30.degree. C. to give 0.27 g (54%) dark purple crystals. A GLC analysis 
suggested there were no styrene/ethylene codimers in the final reaction 
mixture. 
Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 (0.86 g, 2.0 mmol) and styrene 
(0.62 g, 6.0 mmol) were stirred in 10 ml of benzene for 24 h. The benzene 
was removed in vacuo and the dark solid was extracted into pentane/toluene 
(50/50) and filtered. Cooling the filtrate to -30.degree. C. for 12 h 
produced 0.69 g of dark purple crystals. The filtrate was concentrated to 
a solid in vacuo and recrystallized from pentane/toluene (75/25) at 
-30.degree. C. to give an additional 0.07 g; overall yield 77% Ta(C.sub.5 
Me.sub.5)(styrene)Cl.sub.2. The only organic product observed in .sup.1 H 
NMR spectra of the reaction mixture was 2,3-dimethyl-1-butene. 
.sup.1 H NMR (.tau., C.sub.6 H.sub.6, 90 MHz): 6.56 (t, 1, C.sub.6 H.sub.5 
CH.dbd.CH.sub.2, .sup.3 J.sub.HH =12 Hz), 7.00-7.90 (m, 2, C.sub.6 H.sub.5 
CH.dbd.CH.sub.2), 8.33(s, 15, C.sub.5 Me.sub.5). .sup.13 C NMR(ppm 
downfield from TMS, C.sub.6 D.sub.6, .sup.1 H decoupled): 11.8 (C.sub.5 
Me.sub.5), 67.7 (C.sub.6 H.sub.5 CH.dbd.CH.sub.2), 85.2 (C.sub.6 H.sub.5 
CH.dbd.CH.sub.2), 118.5 (C.sub.5 Me.sub.5), 125.1, 126.1, 127.3, 149.9 
(C.sub.6 H.sub.5 CH.dbd.CH.sub.2). 
EXAMPLE V 
This example illustrates the method of preparing a compound with the 
formula 
##STR18## 
Ta(C.sub.5 Me.sub.5)(styrene)Cl.sub.2 (0.49 g, 1 mmol) in 5 ml of diethyl 
ether was treated with 50 mg of LiOCH.sub.3 (slight excess). After one 
hour the solvent was removed in vacuo and the residue was recrystalized 
from a mixture of toluene and pentane (1:2) to give deep red crystals of 
Ta(C.sub.5 Me.sub.5)(styrene)(Cl)(OCH.sub.3)(0.30 g, 60% yield). 
EXAMPLE VI 
This example illustrates the method of preparing a compound with the 
formula 
##STR19## 
Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 (3.43 g, 8.0 mmol) and 1-pentene 
(2.81 g, 40.0 mmol) were combined in 25 ml of toluene. After stirring for 
5 min. the color of the solution changed from red-purple (Ta(III) olefin 
complex) to orange (Ta(V) metallacycle). The color changed back to 
red-purple within 12 h and after 24 h the toluene was removed in vacuo to 
give a dark solid. Recrystallization of the crude product from pentane at 
-30.degree. C. yielded 3.16 g of dark purple crystalline Ta(C.sub.5 
Me.sub.5)(1-pentene)Cl.sub.2 (two crops, 86% total yield). 
.sup.1 H NMR (.tau., C.sub.6 H.sub.6): 7.00-9.20 including peaks at 
7.33(m), 8.90 (br s), 9.02 (s) and 9.13 (s)(m, b 1-pentene), 8.37 (s, 
C.sub.5 Me.sub.5). .sup.13 C NMR (ppm downfield from TMS, C.sub.6 D.sub.6, 
.sup.1 H gated decoupled): 11.8 (q, C.sub.5 Me.sub.5, .sup.1 J.sub.CH =129 
Hz), 14.4 (q, CH.sub.2 .dbd.CHCH.sub.2 CH.sub.2 CH.sub.3, .sup.1 J.sub.CH 
=125 Hz), 29.0, 43.3 (t, t, CH.sub.2 .dbd.CHCH.sub.2 CH.sub.2 CH.sub.3, 
.sup.1 J.sub.CH =125 Hz, 126 Hz), 72.9 (t, CH.sub.2 .dbd.CHCH.sub.2 
CH.sub.2 CH.sub.3, .sup.1 J.sub.CH =142 Hz), 87.0 (d, CH.sub.2 
.dbd.CHCH.sub.2 CH.sub.2 CH.sub.3, .sup.1 J.sub.CH =152 Hz), 117.6 (s, 
C.sub.5 Me.sub.5). 
EXAMPLE VII 
This example illustrates the method of preparing a compound with the 
formula 
##STR20## 
Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 (0.64 g, 1.5 mmol) and 
cis-2-pentene (0.32 g, 4.5 mmol) were stirred in 15 ml of benzene for 24 
h. The benzene was removed in vacuo and the dark solid was recrystallized 
from a minimal amount of pentane at -30.degree. C. to give 0.51 g of dark 
purple crystalline Ta(C.sub.5 Me.sub.5)(cis-2-pentene)Cl.sub.2 (two crops, 
74% total yield). 
Anal. Calcd. for TaC.sub.15 H.sub.25 Cl.sub.2 : C, 36.39; H, 4.93; Cl, 
15.51. Found: C, 36.58; H, 5.06; Cl, 15.77. .sup.1 H NMR (.tau., C.sub.6 
D.sub.6, 90 MHz): 6.30-7.97 including large peaks at 7.13 and 7.19 (m, 7, 
CH.sub.3 CH.dbd.CHCH.sub.2 CH.sub.3), 8.27 (s, 15, C.sub.5 Me.sub.5), 9.01 
(t, 3, CH.sub.3 CH.dbd.CHCH.sub.2 CH.sub.3, .sup.3 J.sub.HH =7 Hz). 
.sup.13 C NMR (ppm downfield from TMS, C.sub.6 D.sub.6, .sup.1 H gated 
decoupled): 11.8 (q, C.sub.5 Me.sub.5, .sup.1 J.sub.CH =128 Hz), 18.9, 
19.2 (q, q, CH.sub.3 CH.dbd.CHCH.sub.2 CH.sub.3, .sup.1 J.sub.CH =124 Hz), 
27.7 (t, CH.sub.3 CH.dbd.CHCH.sub.2 CH.sub.3, .sup.1 J.sub.CH =127 Hz) 
80.2, 87.3 (d, d, CH.sub.3 CH.dbd.CHCH.sub.2 CH.sub. 3, .sup.1 J.sub.CH 
=152 Hz, 148 Hz), 117.9 (s, C.sub.5 Me.sub.5). 
EXAMPLE VIII 
This example illustrates the method of preparing a compound with the 
formula 
##STR21## 
Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 (0.43 g, 1.00 mmol) and cyclooctene 
(0.33 g, 3.00 mmol) were combined in 6 ml benzene. After 12 h at 
25.degree. C. the benzene was removed in vacuo. The dark residue was 
recrystallized from toluene at -30.degree. C. to produce 0.16 g of dark 
purple crystals. The solvent was removed from the filtrate in vacuo and 
the solid was recrystallized from pentane/toluene (80/20) to give a second 
crop of 0.18 g (overall hield 68%) Ta(C.sub.5 
Me.sub.5)(cyclooctene)Cl.sub.2. The only organic product observed in 
.sup.1 H NMR spectra of the reaction mixture was 2,3-dimethyl-1-butene. 
.sup.1 H NMR (.tau., C.sub.6 D.sub.6): 6.90 to 9.20 with a broad singlet at 
7.33 (m, cyclooctene), 8.39 (s, C.sub.5 Me.sub.5). .sup.13 C NMR (ppm 
downfield of TMS, D.sub.8 -toluene, .sup.1 H decoupled): 11.6 (C.sub.5 
Me.sub.5), 17.9, 26.9, 33.8, 39.4 (aliphatic cyclooctene carbon atoms), 
86.0 (olefinic cyclooctene carbon atoms), 117.6 (C.sub.5 Me.sub.5). 
EXAMPLE IX 
This example illustrates the method of preparing a compound with the 
formula 
##STR22## 
Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 (0.43 g, 1.0 mmol) and 
4,4-dimethyl-1-pentene (0.35 g, 5.0 mmol) were stirred in 10 ml of toluene 
for 24 h. The toluene was removed in vacuo and the dark gummy solid was 
recrystallized from a minimal amount of pentane at -30.degree. C. to give 
0.38 g of dark purple crystalline Ta(C.sub.5 
Me.sub.5)(neopentylethylene)Cl.sub.2 (78%). 
.sup.1 H NMR (.tau., C.sub.6 D.sub.6): 6.80-8.50(m, 5, Me.sub.3 CCH.sub.2 
CH.dbd.CH.sub.2), 8.25 (s, 15, C.sub.5 Me.sub.5), 9.05 (s, 9, Me.sub.3 
CCH.sub.2 CH.dbd.CH.sub.2). .sup.13 C NMR (ppm downfield from TMS, C.sub.6 
D.sub.6, .sup.1 H gated decoupled): 11.6 (q, C.sub.5 Me.sub.5, .sup.1 
J.sub.CH =128 Hz), 29.7 (q, Me.sub.3 CCH.sub.2 CH.dbd.CH.sub.2, .sup.1 
J.sub.CH =124 Hz), 38.1 (s, Me.sub.3 CCH.sub.2 CH.dbd.CH.sub.2), 55.1 (t, 
Me.sub.3 CCH.sub.2 CH.dbd.CH.sub.2, .sup.1 J.sub.CH =126 Hz), 75.5 (t, 
Me.sub.3 CCH.sub.2 CH.dbd.CH.sub.2, .sup.1 J.sub.CH =150 Hz), 81.6 (d, 
Me.sub.3 CCH.sub.2 CH.dbd.CH.sub.2, .sup.1 J.sub.CH =150 Hz), 
117.4(s,C.sub.5 Me.sub.5). 
EXAMPLE X 
This example illustrates the method of a compound with the formula 
##STR23## 
A suspension of Ta(C.sub.5 Me.sub.5)(C.sub.2 H.sub.4)Cl.sub.2 (0.50 g, 1.20 
mmol) in 12 ml pentane was stirred under 40 psi ethylene in a glass 
pressure bottle. Over a period of 15 min the dark suspended solid 
disappeared and an orange crystalline solid precipitated. The mixture was 
filtered and the orange solid was rinsed with pentane and dried in vacuo; 
yield 0.43 g of 
##STR24## 
Samples for analysis were recrystallized at -30.degree. C. from 
methylcyclohexane or pentane/toluene (75/25). NMR spectra were recorded 
under 1 atmosphere of ethylene. 
Anal. Calcd for TaC.sub.14 H.sub.23 Cl.sub.2 : C, 37.94; H, 5.23; Cl, 
16.00. Found: C, 37.63; H, 5.35; Cl, 16.32. .sup.1 H NMR (.tau., C.sub.6 
H.sub.6): 
##STR25## 
8.20 (s, 15, C.sub.5 Me.sub.5), 
##STR26## 
.sup.1 H NMR (.tau., d.sub.8 -toluene, -60.degree. C., 270 MH.sub.z): 6.66 
(br s, H.sub..alpha.), 6.93 (br s, H.sub..alpha..sup.'), 8.33 (s, C.sub.5 
Me.sub.5), 8.78 (br s, H.sub..beta.), 8.90 (br s, H.sub..beta..sup.'). 
EXAMPLE XI 
This example illustrates the method of preparing a compound with the 
formula 
##STR27## 
A solution of Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 (0.65 g, 1.51 mmol) 
in 15 ml of pentane in a glass pressure bottle was stirred under 40 psi 
propene. Within 5 min orange crystals of the metallacycle formed in the 
solution. The propylene connection was shut off and the mixture was 
stirred for 1 h at 0.degree. C. The light orange supernatant solution was 
removed by syringe and the product was dried in vacuo for 30 min at 
0.degree. C. to give 0.56 g of 
##STR28## 
NMR samples were prepared and recorded at .ltoreq.10.degree. C. to prevent 
thermal decomposition. The solid can be handled at room temperature for 
short periods (.about.15 min) without significant decomposition. 
.sup.1 H NMR (.tau., d.sub.8 -toluene, 0.degree. C.): 7.05, 8.55, 8.64 and 
##STR29## 
8.17 (s, 15, C.sub.5 Me.sub.5). .sup.13 C NMR (ppm downfield from TMS, 
d.sub.8 -toluene, .sup.1 H decoupled, 0.degree. C.,): 12.1 (C.sub.5 
Me.sub.5), 
##STR30## 
122.9 (C.sub.5 Me.sub.5), the peaks for the .beta.-carbon atoms are close 
to the coalesence point. 
EXAMPLE XII 
This example illustrates the method of preparing a compound with the 
formula 
##STR31## 
Ta(C.sub.5 Me.sub.5)(1-pentene)Cl.sub.2 (0.54 g, 1.18 mmol) was dissolved 
in a minimal amount of pentane and 1-pentene (0.25 g, 3.54 mmol) was added 
with stirring. After 3 min the orange metallacycle began to crystallize 
from solution. Shortly thereafter the solution became too thick to stir. 
Enough pentane/toluene (80/20) was added to dissolve all of the 
metallacycle. The solution was filtered and cooled to -30.degree. C. for 
12 h to give 0.43 g orange crystalline 
##STR32## 
The solvent was removed from the filtrate in vacuo and the solid was 
redissolved in a minimal amount of pentane/toluene (80/20) with a few 
drops of 1-pentene. This solution was filtered and cooled to -30.degree. 
C. for 12 h to produce a second crop of 0.04 g (total yield 75%). 
.sup.1 H NMR (.tau., d.sub.8 -toluene, -40.degree. C.): 6.31(br m), 6.97 to 
9.81 (complex pattern including broad peak at 8.92), 8.18(C.sub.5 
Me.sub.5). 
EXAMPLE XIII 
This example illustrates the method of preparing a compound with the 
formula 
##STR33## 
A sample of Ta(C.sub.5 Me.sub.5)(styrene)(Cl)(OCH.sub.3)(0.50 g) was 
suspended in 10 ml pentane (in which it is slightly soluble) in a glass 
pressure vessel. The vessel was pressurized to 40 psi g and stirred for 1 
h to give a pale yellow homogeneous solution. Cooling this solution to 
-40.degree. for six hours produced pale yellow crystals of 
##STR34## 
(0.30 g) which were filtered off and dried in vacuo. 
EXAMPLE XIV 
This example illustrates the method of dimerizing propylene to primarily 
2,3-dimethyl-1-butene with Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 as the 
catalyst precursor. 
Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 (0.11 g, 0.25 mmol) was dissolved 
in 2.5 ml of hexane in a 20 ml glass pressure bottle containing a small 
teflon-coated magnetic stir bar. A pressure head equipped with a rubber 
system for sampling the mixture was clamped to the glass vessel and the 
vessel was pressurized to 40 psi with propylene and immersed in a stirred 
bath maintained at 32.degree. C. Samples were withdrawn by syringe at 
regular intervals, quenched with gaseous oxygen, and analyzed by gas 
chromatography. 2,3-dimethyl-1-butene and 2-methyl-1-pentene formed 
steadily in a 98:2 ratio at a rate of 0.0014 M min.sup.-1 or k.sub.1 
=0.014 min.sup.-1 since the catalyst concentration is 0.1 M. At 40.degree. 
k.sub.1 =0.039 min.sup.-1 which amounts to about 1 turnover per hour per 
Ta. The rate increases markedly at higher temperatures (.DELTA.H.sup.++ 
=19.+-.1 kcal mol.sup.-1, .DELTA.S.sup. ++ =14.+-.3 eu). 
The rate determining step of the catalytic reaction is the rate at which 
##STR35## 
which forms from Ta(C.sub.5 Me.sub.5)(propylene)C.sub.12 and propylene, 
decomposes to give the dimer and two moles of Ta(C.sub.5 
Me.sub.5)(propylene)Cl.sub.2 ; -dM/dt=2k.sub.1 M where M is the 
concentration of the metallacycle and k.sub.1 is the rate constant in the 
absence of propylene. This rate was measured by .sup.1 H NMR at four 
temperatures: k.sub.1 =0.0015 min.sup.-1 at 10.degree., 0.0044 min.sup.-1 
at 20.degree., 0.014 min.sup.-1 at 32.degree., and 0.039 min.sup.-1 at 
40.degree.. The values at 32.degree. and 40.degree. l are identical with 
those obtained by measuring the rate of the catalytic reaction. 
EXAMPLE XV 
This example illustrates the method of dimerizing propylene with Ta(C.sub.5 
Me.sub.5)(propylene)Br.sub.2 as the catalyst precursor. 
The procedure is identical to that in Example XIV using 0.11 g Ta(C.sub.5 
Me.sub.5)(propylene)Br.sub.2 instead of Ta(C.sub.5 
Me.sub.5)(propylene)Cl.sub.2 as the catalyst precursor. The products were 
2,3-dimethyl-1-butene (93%) and 2-methyl-1-pentene (7%) with k.sub.1 
=0.036 min.sup.-1. 
EXAMPLE XVI 
This example illustrates the method of dimerizing 1-pentene with Ta(C.sub.5 
Me.sub.5)(propylene)Cl.sub.2 as the catalyst precursor. 
Ta(C.sub.5 Me.sub.5)(propylene)Cl.sub.2 (0.11 g) was dissolved in 2.5 ml of 
hexane. 1-Pentene (1.0 ml) was added and the reaction was maintained at a 
temperature of 32.degree. C. The products were 2-butyl-3-methyl-1-heptene 
(85%) and 2-butyl-1-octene (15%) with k.sub.1 .apprxeq.0.01 min.sup.-1.