Oligomerization of olefins catalyzed by new cationic palladium(II) complexes containing an unsymmetrical α-diimine ligand

Article abstract of DOI:10.1021/om990165k

The palladium complexes [(Py-2-CMe=NAr)-PdMe(MeCN)]⁺BAr′₄- (2⁺BAr′₄-) and [Pd(Py-2-CMe=NAr)₂]²⁺(BAr′₄ ^-)₂ [Ar = 2,6-(i-Pr)₂-C₆H_3<

Full text of DOI:10.1021/om990165k

2734
Organometallics 1999, 18, 2734-2737
Oligom er iza tion of Olefin s Ca ta lyzed by New Ca tion ic
P a lla d iu m (II) Com p lexes Con ta in in g a n Un sym m etr ica l
r-Diim in e Liga n d
Simoni Plentz Meneghetti,†,‡ Pierre J . Lutz,† and J acky Kress*,‡
Institut Charles Sadron, UPR 22 du CNRS, 6 rue Boussingault, and Laboratoire de Chimie
des Me´taux de Transition et de Catalyse, UMR 7513 du CNRS, Institut Le Bel,
4 rue Blaise Pascal. Universite´ Louis Pasteur, 67000 Strasbourg, France
Received March 8, 1999
Sch em e 1
Summary: The palladium complexes [(Py-2-CMedNAr)-
PdMe(MeCN)]+BAr′4
(2+BAr′4
)
and [Pd(Py-2-
-
-
CMedNAr)2]2+(BAr′4-)2 [Ar ) 2,6-(i-Pr)2-C6H3, Ar′ )
3,5-(CF3)2-C6H3)] have been synthesized from (Py-2-
CMedNAr)PdMeCl, and their crystal and molecular
structure has been determined by X-ray analysis. 2+BAr′4
-
is an efficient catalyst for the oligomerization of ethylene,
propylene, and 1-hexene, as well as for the cooligomer-
ization of ethylene with alkyl acrylates.
Palladium(II) complexes containing symmetrical 1,4-
diazabutadiene ligands with bulky substituents such as
the 2,6-diisopropylphenyl group at the nitrogen atoms
were shown recently to behave as efficient catalysts for
the polymerization of ethylene and R-olefins.1 On the
other hand, related complexes with sterically less
demanding ligands such as 2,2′-dipyridyl or 1,10-
phenanthroline can activate the dimerization of ethyl-
ene.2 We now report our studies on neutral and cationic
palladium(II) complexes of 2-(acetyl-2,6-diisopropyl-
phenylimine)pyridine, an unsymmetrical bidentate ligand
possessing both the pyridyl and the bulky 2,6-diisopro-
pylphenylimine functions.
The pyridinimine Py-2-CMedNAr [Ar ) 2,6-(i-Pr)2-
C6H3] was synthesized following classical condensation
methods1 and reacted with (COD)PdMeCl3 in diethyl
ether to yield a yellow precipitate of air-stable (Py-2-
CMedNAr)PdMeCl (1, yield 96%), which can be recrys-
tallized from CH2Cl2/hexane (Scheme 1). This compound
is analogous to previously synthesized derivatives pos-
sessing a different substituent at the imino nitrogen.4
A single isomer is detected for 1 on the 1H and 13C NMR
spectra,5 most probably adopting the expected square-
planar geometry. A NOESY experiment7 established
that the methyl ligand is cis to the imino function. This
configuration was also found to be the most favorable
for the majority of methyl(chloro)palladium complexes
of this type.4,8
Treatment of 1 with 1 equiv of NaBAr′4 (Ar′ ) 3,5-
(CF3)2-C6H3)9 in acetonitrile1b leads to slow forma-
tion of the cationic complex [(Py-2-CMedNAr)PdMe-
(MeCN)]+BAr′4 (2+BAr′4-) as an air-stable yellow-
-
brown solid (yield 80%). Recrystallization from cold
CH2Cl2 affords orange crystals which were suitable for
X-ray analysis (vide infra). The 1H and 13C NMR spectra
of 2+ in CD2Cl2 show two sets of resonances in an
approximate ratio 2/1, arising from the presence of the
two isomers 2a + (major isomer) and 2b+ (minor isomer),
depicted in Scheme 1, in which the methyl ligand is
respectively trans and cis to the imino nitrogen, as
deduced from NOESY correlation measurements.10
Hence, replacement in 1 of the chloro ligand by an
(5) 1H NMR for 1 (CDCl3): δ 9.32 (dd, 1H, py H-6), 8.07 (dt, 1H, py
H-4), 7.90 (dd, 1H, py H-3), 7.75 (ddd, 1H, py H-5), 7.3-7.2 (m, 3H, m-
and p-Ar), 3.08 (sept, 2H, CHMe2), 2.21 (s, 3H, MeCdN-), 1.29 (d,
6H, CHMeMe′), 1.10 (d, 6H, CHMeMe′), 0.48 (s, 3H, Me-Pd). 13C{1H}
NMR (CDCl3): δ 174.13 (CdN-), 152.70 (py C-2), 149.59 (py C-6),
141.87 (ipso-Ar), 139.22 (o-Ar), 138.80 (py C-4), 128.58 (p-Ar), 127.68
(py C-3), 124.92 (py C-5), 124.03 (m-Ar), 28.23 (CHMe2), 23.95, 23.39
(CHMeMe′, CHMeMe′), 19.13 (MeCdN-), 0.90 (Me-Pd).6
(6) The 13C NMR assignments were ascertained by DEPT experi-
ments.
* E-mail: jkress@chimie.u-strasbg.fr.
† Institut Charles Sadron.
‡ Laboratoire de Chimie des Me´taux de Transition et de Catalyse.
(1) (a) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem.
Soc. 1995, 117, 6414. (b) Mecking, S.; J ohnson, L. K.; Wang, L.;
Brookhart, M. J . Am. Chem. Soc. 1998, 120, 888. (c) Feldman, J .;
McLain, S. J .; Parthasarathy, A.; Marshall, W. J .; Calabrese, J . C.;
Arthur, S. D. Organometallics 1997, 16, 1514.
(7) Selected 1H-1H NOESY correlations: δ 9.32 (py H-6) with δ 7.75
(py H-5) and no other signal, δ 0.48 (Me-Pd) with δ 3.08 (CHMe2)
and 1.29 (CHMeMe′).
(2) (a) Drent, E. Pure Appl. Chem. 1990, 62, 661. (b) Brookhart, M.;
Rix, F. C.; DeSimone, J . M.; Barborak, J . C. J . Am. Chem. Soc. 1992,
114, 5894. (c) Rix, F. C.; Brookhart, M. J . Am. Chem. Soc. 1995, 117,
1137.
(3) Ru¨lke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier: C. J .; Van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(4) Ru¨lke, R. E.; Delis, J . G. P.; Groot, A. M.; Elsevier, C. J .; Van
Leeuwen, P. W. N. M.; Vrieze, K.; Goubitz, K.; Schenk, H. J .
Organomet. Chem. 1996, 508, 109.
(8) With the present ligand, a significant shielding effect of the Ar
group on the protons of the neighbouring ligand gives rise to remark-
able low 1H NMR chemical shifts: δ 0.48 for Me in 1, 1.78 for MeCN
in 2a +, 0.51 for Me in 2b+, and 6.22 for py H-6 in 32+. The unusually
high frequency of the IR ν(C-H) absorption observed at 3140 cm-1 for
32+ (BAr′4
) probably has the same origin.
2
-
(9) Bahr, S. R.; Boudjouk, P. J . Org. Chem. 1992, 57, 5545.
10.1021/om990165k CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/22/1999

Communications
Organometallics, Vol. 18, No. 15, 1999 2735
Sch em e 2
found for 2a + in solution. On dissolution of 2a +BAr′4
-
-
in CD2Cl2, its isomerization into 2b+BAr′4 could be
followed by 1H NMR, the equilibrium mixture of 2/1
being reached after ca. 15 min.
A further complex could be detected in the reaction
mixture when 1 was treated with more than 1 equiv of
NaBAr′4. This is best obtained by addition of 2 equiv of
NaBAr′4 to (COD)PdCl2,14 in the presence of 2 equiv of
Py-2-CMedNAr (Et2O, 24 h), and was identified as the
-
dicationic complex [Pd(Py-2-CMedNAr)2]2+(BAr′4
)
F igu r e 1. ORTEP diagram of 2a +BAr′4-. The counteran-
ion and all hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Pd-N(1) ) 2.038(5),
Pd-N(2) ) 2.093(5), Pd-N(3) ) 1.971(7), Pd-C(22) )
2.015(6), N(1)-Pd-N(2) ) 78.8(2), N(3)-Pd-C(22) ) 90.3-
(3), Pd-N(3)-C(20) ) 163.6(7).
2
[32+(BAr′4-)2, Scheme 2].15 Pale green single crystals of
2+(BAr′4-)2 were obtained by recrystallization from cold
3
methylene chloride and analyzed by X-ray diffraction
(Figure 2).13,16 Besides the expected square-planar
geometry, 32+ shows a mutually trans arrangement of
the two imino and of the two pyridyl nitrogens, the
palladium atom lying on a crystallographic symmetry
center. The other structural parameters are similar to
those of 2a +BAr′4-, the differences between the Pd-
N(1) or Pd-N(2) bond distances of 2a + (Figure 1) and
acetonitrile molecule inverts the relative stability of the
two expected configurations.8
The isomer present in the solid state is 2a +, as shown
by a single-crystal X-ray structure determination (Fig-
ure 1).12,13 As expected, the geometry about palladium
is nearly ideally square-planar, and the chelating angle
N(1)-Pd-N(2) is less than 90°. The MeCN ligand is
slightly twisted toward the facing Ar group, whose plane
is perpendicular to the plane of the complex. This
confirms for the solid state the main structural features
3
2+ (Figure 2) reflecting the trans effect of the opposite
ligands. The 1H and 13C NMR data15 for 32+ are
consistent with the molecular structure found for the
solid state.8
-
Complex 2+BAr′4 is an efficient long-lived catalyst
for the oligomerization of ethylene (Figure 3).17 The
catalytic reaction was carried out under various condi-
tions of temperature (10-60 °C) and pressure (2-6 bar),
which showed that its rate increases markedly at higher
temperatures (the average activity reaches for instance
(10) Data for 2+ BAr′4-: Anal. Calcd for C54H43N3BF24Pd: C, 49.61;
H, 3.29; N, 3.21. Found: C, 49.09; H, 3.26; N, 2.97. 1H NMR (CD2Cl2)
for 2a +: δ 8.60 (dd, 1H, py H-6), 8.21 (dt, 1H, py H-4), 8.00 (dd, 1H,
py H-3), 7.76 (dt, 1H, py H-5), 7.32 (s, 3H, m- and p-Ar), 2.92 (sept,
2H, CHMe2), 2.31 (s, 3H, MeCdN-), 1.78 (s, 3H, MeCN), 1.30 (d, 6H,
CHMeMe′), 1.16 (d, 6H, CHMeMe′), 1.03 (s, 3H, Me-Pd). 2b+: δ 8.54
(dd, 1H, py H-6), 8.17 (dt, 1H, py H-4), 8.00 (dd, 1H, py H-3), 7.76 (dt,
1H, py H-5), 7.32 (s, 3H, m- and p-Ar), 2.87 (sept, 2H, CHMe2), 2.41
(s, 3H, MeCN), 2.31 (s, 3H, MeCdN-), 1.27 (d, 6H, CHMeMe′), 1.11
(d, 6H, CHMeMe′), 0.51 (s, 3H, Me-Pd).11 Selected 1H-1H NOESY
(14) Chatt, L.; Vallarino, L. M.; Venanzi, L. M. J . Chem. Soc. 1957,
34.
(15) Yield: 65%. Anal. Calcd for C102H72N4B2F48Pd: C, 51.10; H,
3.00; N, 2.34. Found: C, 51.16; H, 3.11; N, 2.36. 1H NMR (CD2Cl2): δ
8.21 (dt, 2H, py H-4), 8.06 (dd, 2H, py H-3), 7.74 (t, 2H, p-Ar), 7.49 (d,
4H, m-Ar), 7.42 (dt, 2H, py H-5), 6.22 (dd, 2H, py H-6), 3.01 (sept, 4H,
CHMe2), 2.54 (s, 6H, MeCdN-), 1.21 (d, 12H, CHMeMe′), 1.02 (d, 12H,
CHMeMe′).11 13C{1H} NMR (CD2Cl2): δ 184.71 (CdN-), 155.22 (py
C-2), 149.89 (py C-6), 144.60 (py C-4), 141.72 (o-Ar), 137.65 (ipso-Ar),
133.12 (py C-3), 130.39, 129.99 (py C-5 and p-Ar), 127.26 (m-Ar), 29.83
correlations for 2a +
: δ 8.60 (py H-6) with δ 1.03 (Me-Pd) and 7.76
(py H-5), δ 1.78 (MeCN) with δ 1.30 CHMeMe′) and 7.32 (Ar), δ 1.03
(Me-Pd) with δ 8.60 (py H-6). 2b+: δ 8.54 (py H-6) with δ 7.76 (py
H-5), δ 2.41 (MeCN) with no other signal, δ 0.51 (Me-Pd) with δ 2.87
(CHMe2) and 1.27 (CHMeMe′). A chemical exchange process between
the acetonitrile ligands of the two isomers (δ 1.78 and 2.41) is moreover
revealed by this method. 13C{1H} NMR (CD2Cl2) for 2a +: δ 171.92 (Cd
N-), 156.88 (py C-2), 149.96 (py C-6), 141.09 (py C-4), 140.41 (ipso-
Ar), 138.58 (o-Ar), 129.35, 128.07 (py C-3 and p-Ar), 127.56 (py C-5),
124.31 (m-Ar), 28.79 (CHMe2), 23.63, 23.49 (CHMeMe′, CHMeMe′),
18.16 (MeCdN-), 3.22, 2.03 (MeCN, Me-Pd). 2b+: δ 179.20 (CdN-),
152.08 (py C-2), 148.84 (py C-6), 140.72 (py C-4), 140.60 (ipso-Ar),
139.13 (o-Ar), 129.97, 128.77 (py C-3 and p-Ar), 126.82 (py C-5), 124.59
(m-Ar), 28.56 (CHMe2), 23.77, 23.04 (CHMeMe′, CHMeMe′), 19.62
(MeCdN-), 6.09, 3.60 (MeCN, Me-Pd);6,11 the MeCN signals of 2a +
and 2b+ could not be detected.
(CHMe2), 23.53, 23.09 (CHMeMe′, CHMeMe′), 20.83 (MeCdN-).6,11
(16) Selected crystal and X-ray experimental data for 32+(BAr′4
)
2
-
(full data are reported in the Supporting Information): C102H72B2F48N4-
Pd, MW ) 2393.68, orthorhombic, space group Pbca, a (Å) ) 20.3950-
(6), b (Å) ) 20.3970(6), c (Å) ) 24.8420(6), Z ) 4, 173 K. The structure
was solved using direct methods and the Enraf-Nonius Molen package
for all calculations; R ) 0.049, Rw ) 0.069.
(17) In a typical experiment, 0.04 mmol of 2+BAr′4 was dissolved
-
in 60 mL of 1,2-dichloroethane, before ethylene was introduced into
the thermostated (30 °C) glass reactor. The ethylene pressure was
maintained at 6 atm, while the solution was vigorously stirred at a
controlled rate (450 rpm). After 18 h, the volume of the clear solution
had reached 83 mL, allowing us to estimate that 23 mL of oligomers
had been obtained at this stage. The catalytic reaction was then
quenched by addition of methanol, and the crude reaction mixture was
analyzed by GC. Evaporation of the volatiles under reduced pressure
(1 mmHg) was then followed by renewed GC analysis of the resulting
liquid (this showed that only the C4-C8 fractions initially present were
significantly lost during evaporation), which was further characterized
by size extrusion chromatography (SEC) and 1H NMR.
(11) The 1H and 13C NMR data for BAr′4 are identical to those
-
reported previously.1b
(12) Selected crystal and X-ray experimental data for 2a +BAr′4- (full
data are reported in the Supporting Information): C54H42BF24N3Pd,
MW ) 1306.13, monoclinic, space group P121/n1, a (Å) ) 12.3620(4),
b (Å) ) 24.9100(7), c (Å) ) 18.6450(6), â (deg) ) 100.234(2), Z ) 4, 173
K. The structure was solved using direct methods and the Enraf-
Nonius Molen package for all calculations; R ) 0.070, Rw ) 0.084.
(13) The X-ray structure determination was carried out by the
Service Commun de Rayons X de la Faculte´ de Chimie de Strasbourg.

2736 Organometallics, Vol. 18, No. 15, 1999
Communications
carbons, among which ca. 1.6 should correspond to chain
end methyl groups,21 and the other 0.55 to methyl or
longer branches. This confirms a certain degree of
branching already suspected on the basis of the numer-
ous isomers detected by GC. About 0.4 of the terminal
methyl groups belong to MeCHdCH- functions, and the
other type of internal carbon-carbon double bonds,
-CHdCH-, is present in approximately equal propor-
tions (0.4/10C). The high amount of such internal double
bonds contrasts with the surprising rarity of the vinyl
end groups which represent less than 1% of the total
number of double bonds.22,23 One can assume that each
oligomer contains one carbon-carbon double bond since
this leads to Mn ) 180 ((20), a value which is near to
that found by GC.
-
Catalyst 2+BAr′4 remains active in the presence of
1500 equiv of methyl or benzyl acrylates, although only
respectively 3 and 5 mL of oligomers were obtained from
ethylene under otherwise identical reaction conditions.17
The GC and SEC patterns of the products, the resultant
Mn values, and the main features of their 1H NMR
spectra are only slightly different from those obtained
in the absence of acrylates. However, the 1H NMR
spectra exhibit additional and relatively intense sig-
nals,24 indicating that the acrylates have cooligomerized
with ethylene. The acrylate incorporation25 reaches 9.3
and 8.2%, respectively. The initial acrylate insertion
products appear to have subsequently isomerized as in
preceding cases,1b suggesting that analogous mecha-
nisms1b are involved.
F igu r e 2. ORTEP diagram of 32+(BAr′4-)2. The counter-
anions and all hydrogen atoms are omitted for clarity.
Selected bond distances (Å) and angles (deg): Pd-N(1) )
2.054(4), Pd-N(2) ) 2.052(4), N(1)-Pd-N(2) ) 78.3(2),
N(1)-Pd-N(1′) ) N(2)-Pd-N(2′) ) 180.00.
Also R-olefins such as propylene (6 bar) and 1-hexene
(30 mL) are oligomerized in the presence of 2+BAr′4
-
(0.04 mmol) at 30 °C, affording respectively 12 and 1
mL of products after 18 h reaction time. The GC and
SEC profiles for these oligomers are similar to those of
the ethylene oligomers, the successive oligomerization
degrees being even better distinguished by both meth-
ods. They show that the average oligomerization degrees
are lowered (DP ) 3.5 and 2.9, respectively) and lead
to respective Mn values of 146 and 242 (by GC) or 237
and 333 (by SEC).19a The occurrence of slower olefin
insertion steps, with respect to ethylene, is hence clearly
indicated. Interestingly, three isomers of hexene are
(18) In the case of initial insertion of ethylene into palladium-
hydride bonds.
(19) (a) The SEC values were measured vs polystyrene standards
and are probably overestimated. (b) Each plot exhibits six maxima
corresponding to the shortest well-separated C2n (n ) 2-7) fractions.
(20) Beside the main chain CH2 and the Me resonances at δ 1.28
and δ 0.90, respectively, several more or less broad multiplets are
characteristic of three types of unsaturations: CH2dCH- (δ 5.81 and
4.96), cis and trans MeCHdCH- (δ 1.65, 1.60, and 5.41), and cis and
trans -CHdCH- (δ 5.41). The methylene protons adjacent to these
three double bonds give rise to a further signal at δ 1.98.
(21) This number is based on the value of Mn and on the fact that
each oligomer should possess almost exclusively methyl groups at both
chain ends, almost no terminal carbon-carbon double bonds being
detected (vide infra).
(22) Except at 60 °C, where up to 4% of vinyl end groups were found,
or at very long reaction times.
(23) The fact that the -CHdCH- bonds may occupy diverse
positions in the oligomer chains certainly contributes further to the
large number of isomers.
(24) These signals show up at δ 3.67 (s) and 2.29 (t) for methyl
acrylate and at δ 5.12 (s) and 2.36 (t) for benzyl acrylate and are
assigned respectively to -CH2CH2CO2Me, -CH2CH2CO2Me, -CH2-
CH2CO2CH2Ph, and -CH2CH2CO2CH2Ph groups.
(25) Actual insertion of benzyl acrylate into all C2n fractions of the
ethylene oligomer has been proven by determining that UV detection
(benzyl acrylate shows an absorption maximum at 254 nm, at which
wavelength the UV detector was set) affords the same SEC trace as
the refractive index detection.
F igu r e 3. Ethylene oligomerization (30 °C, 6 bar) in the
presence of 2+BAr′4 (0.04 mmol in 1,2-dichloroethane).
-
105 kg oligomer mol-1 h-1 after 6 h at 60 °C and 6 bar),
but is only slightly sensitive to pressure at 30 °C. The
nature of the oligomeric products does not change
significantly with the reaction conditions. GC and GC/
MS analysis of the crude reaction mixtures shows that
hydrocarbons containing as expected18 even numbers of
carbon atoms have been obtained. A large number of
isomers is distinguished for each C2n (n ) 2-10) fraction
(for instance 9 isomers for the C10 fraction), the integra-
tion of which yields Mn ) 155 ((5). These values
increase to Mn ) 190 ((15) after evaporation of the
volatiles,17 whereas SEC analysis of the resultant
liquids leads to higher values (Mn ) 275 ( 20).19
1
In the H NMR spectra of these liquids, five distinct
chemical groups can be distinguished,20 whose integra-
tion leads to overall 2.15 ((0.1) Me groups for 10

Communications
Organometallics, Vol. 18, No. 15, 1999 2737
found in comparable proportions in the crude reaction
mixture obtained from 1-hexene, suggesting the partial
conversion of 1-hexene into 2- and 3-hexene and the
existence of double bond shift reactions in the present
catalytic systems.26 The 1H NMR spectra lead to a
methyl content of 3.6 Me/10C for oligopropylene and 1.9
Me/10C for oligohexene, which is lower than expected
for these monomers (ca. 4.3 and 2.2, respectively),21 as
reported for analogous catalysts as a result of chain
isomerization reactions1a,b occurring also in the present
case.
chain-end analysis and allowed us to determine in
particular that the expected vinyl groups CH2dCR- (R
) H, R′) are present in only very low amount. We
suggest that 2+BAr′4- readily isomerizes the R-olefinic
oligomers into internal olefins, although less frequent
chain transfer after an olefin insertion step than after
one or several isomerization steps may also seem a
plausible explanation. Such a conclusion can probably
be extended to the higher molecular weight polymers
obtained in the presence of similar palladium(II) diimine
catalysts.1
Overall, these results can be reconciled with conven-
tional mechanistic assumptions.1,27 â-H transfer from
the growing oligomer chains to the palladium catalytic
centers would be followed either by the reverse but
regioselectively different reaction (leading to chain
branching) or by displacement of the olefin of the
resultant palladium-olefin-hydride complex (leading
to chain transfer and to the formation of one double
bond per oligomer molecule). The significant branch
content (which results also, however, from the reincor-
poration into further growing chains of the R-olefinic
oligomers produced in the early stage of the reactions)28
and the low molecular weight of the oligomeric products
show that these three steps are all relatively fast with
respect to the olefin insertion step. This enables easy
Ack n ow led gm en t. We thank the CNRS for finan-
cial support (Program Catalyse et Catalyseurs pour
l’industrie et l’environnement), N. Gruber and A. De
Cian for solving the X-ray structures, J . D. Sauer for
running the NOESY experiments, A. Rameau and R.
Meens for the GPC measurements, and R. F. de Souza
for the GC/MS analyses. S.P.M. is indebted to the
Brazilian Government (CAPES) for a fellowship.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
and X-ray experimental data, positional parameters, general
displacement parameter expressions, and bond distances and
bond angles for 2a +BAr′4 and 32+(BAr′4-)2. This material is
-
available free of charge via the Internet at http://pubs.acs.org.
OM990165K
(26) These are further confirmed by the detection on the 1H NMR
spectra of oligopropylene and oligohexene of a broad multiplet assigned
to RR′CdCHR′′ groups (δ 5.13, respectively 20% and 4% of the total
amount of double bonds), besides the weak signals due to the expected
RR′CdCH2 groups (δ 4.70, 10% of the total amount of double bonds in
the oligopropylene). The other 1H NMR resonances of both oligomers
were already found for oligoethylenes.
(27) Desjardin, S. Y.; Way, A. A.; Murray, M. C.; Adirim, D.; Baird,
M. C. Organometallics 1998, 17, 2382.
(28) This could be clearly proven by running ethylene oligomeriza-
tion (25 °C, 4 atm, 18 h)17 in the presence of 1-pentene (20 mL), which
led to the GC observation of approximately equal proportions of even-
and odd-carbon (in particular C7 to C13) oligomers.