Late-Transition-Metal Complexes with Bisazaferrocene Ligands for Ethylene Oligomerization

Article abstract of DOI:10.1021/om034051r

The synthesis, characterization, and ethylene polymerization properties of bisazaferrocene complexes with late-transition-metal Ni(II) and Pd(II) were discussed. The Ni and Pd complexes were prepared and characterized by mass spectrometry (MS), nuclear ma

Full text of DOI:10.1021/om034051r

Organometallics 2003, 22, 5033-5046
5033
La te-Tr a n sition -Meta l Com p lexes w ith Bisa za fer r ocen e
Liga n d s for Eth ylen e Oligom er iza tion
Eric V. Salo and Zhibin Guan*
Department of Chemistry, University of California, Irvine, California 92697-2025.
Received J uly 17, 2003
Herein we report the synthesis, characterization, and ethylene polymerization properties
of novel C2-symmetric and unsymmetric bisazaferrocene complexes with late-transition-
metal Ni(II) and Pd(II). In the designed complexes, the two sp2-hybridized nitrogen atoms
in the azaferrocene rings coordinate to the transition metals with the azaferrocene
architecture presenting pentamethyl or pentaphenyl cyclopentadiene (Cp* or Cp°) rings above
and below the coordination plane for the purpose of preventing the associative chain transfer
processes of ethylene from the axial faces. The Ni(II) and Pd(II) complexes were prepared
and characterized by mass spectrometry (MS), 1H and 13C nuclear magnetic resonance (NMR)
spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Upon activation
with methylaluminoxane (MAO), the bisazaferrocene complexes with NiBr2 (2a ) and PdCl2
(2b) showed very low activities toward ethylene polymerization. Well-defined preactivated
bisazaferrocene-Pd(II) complexes (5 and 6) exhibited relatively high thermal stability for
ethylene oligomerization: for example, complex 5 remains active in ethylene oligomerization
at temperatures up to 120 °C. They have moderate activities in ethylene polymerizations to
form relatively low molecular weight oligomers. The polyethylene oligomers formed have
branching densities ranging from 20 to 60 branches/1000 carbons. To overcome the difficulty
encountered in the synthesis of complex 6, a novel route was developed to make Pd(Me)Cl
complexes with various dinitrogen ligands by in situ ligand substitution reaction. Finally,
to gain mechanistic insight into the low reactivity of the bisazaferrocene-PdII complexes (5
and 6) as compared to their R-diimine counterparts, kinetic studies were undertaken to
measure the energetic barriers for the first methyl migration and subsequent ethylene
consumption. It was found that the insertion barriers (∆Gq) for both the first methyl migration
and subsequent ethylene insertion for complex 5 were about 2-3 kcal/mol higher than the
values for the R-diimine counterparts, which corresponds to a 2-order difference in the rate
of polymerization. Variable-temperature experiments further revealed that the higher
ethylene insertion barrier for the bisazaferrocene-Pd(II) complexes arises from both higher
activation enthalpy (∆Hq) and smaller activation entropy (∆Sq).
In tr od u ction
incorporation of bulky substituents in the ortho-posi-
tions of the aryl rings, which block the axial faces of
the square plane and retard the rate of ethylene
associative chain transfer. Following Brookhart’s origi-
nal reports, considerable effort has been spent to
identify other Ni(II) and Pd(II) complexes bearing bulky
bidentate ligands for olefin polymerizations.6-25 One
The discovery by Brookhart and co-workers1,2 of
versatile, highly active Pd(II) and Ni(II) aryl-substituted
R-diimine catalysts 1 has sparked renewed interest in
developing late-transition-metal catalysts for olefin
polymerization.3-5 It was proposed that the key to
producing high molecular weight polymers by 1 is the
(6) Guan, Z.; Marshall, W. J . Organometallics 2002, 21, 3580-3586.
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A. L.; van Koten, G. Organometallics 1996, 15, 1405-1413.
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Eur. J . Inorg. Chem. 1998, 1811-1820.
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* Corresponding author. E-mail: zguan@uci.edu.
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1996, 118, 267-268.
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10.1021/om034051r CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/28/2003

5034 Organometallics, Vol. 22, No. 24, 2003
Salo and Guan
Ch a r t 1
unique feature of the polyolefins formed by the Ni(II)-
and Pd(II)-R-diimine catalysts is their branched topolo-
gies, which was proposed to be introduced by catalyst
isomerization or “walking” along the polyethylene back-
bone during the migratory insertion polymerization.1,2,26
By exploiting this chain-walking feature, it was shown
that polyethylenes with a broad spectrum of topology
ranging from linear to hyperbranched to dendritic can
be obtained from polymerization of ethylene by simply
varying ethylene pressure.27-31
The aim of this study is to explore a new family of
bisazaferrocene-based Ni(II) and Pd(II) complexes (2-6
in Chart 1) as potential catalysts for ethylene polym-
erization. In our plan, we want to explore a different
type of bidendate nitrogen donor ligand together with
a different type of molecular architecture for shielding
the axial faces of the coordination center. We chose
bisazaferrocene ligands on the basis of the following
three considerations: (1) The two sp2-hybridized nitro-
gen atoms in the azaferrocene rings can efficiently
chelate to Ni(II) and Pd(II). The relatively good σ-donat-
ing ability of azaferrocene nitrogen32 may result in an
improved thermal stability33 or better tolerance to polar
functional groups for the catalysts. (2) Upon coordina-
tion with metal ions, the bisazaferrocene molecular
architecture should present the bulky pentamethyl or
pentaphenyl cyclopentadiene (Cp* or Cp°) rings above
and below the coordination plane, which serves as an
alternative mode of blocking the associative chain
transfer processes of ethylene from the axial faces. (3)
The pseudo-C2 symmetry of the complexes may lead to
stereospecific polymerization for R-olefins. Whereas
planar-chiral azaferrocene ligands have been applied
extensively to asymmetric catalysis,34-38 to the best of
our knowledge, our work represents the first example
of exploring bisazaferrocene ligands in olefin polymer-
ization catalysis.
In this paper, we report the synthesis, characteriza-
tion, and ethylene polymerization properties of a series
of novel C2-symmetric and unsymmetric bisazaferrocene
complexes with late transition metals Ni(II) and Pd(II).
Resu lts a n d Discu ssion
A. Syn th esis of Sym m etr ic a n d Un sym m etr ica l
Bisa za fer r ocen e Liga n d s. Syn th esis of Sym m etr i-
ca l Bisa za fer r ocen e Liga n d s 7 a n d 8. Following
literature procedures, the bis(pentamethyl)azaferrocene
diastereomers 7 and 8 were prepared by the generation
of [Cp*FeCl] in situ followed by treatment with the
dilithiated di(2-pyrrole)methane (DPM, 9) and AgCN in
THF (Scheme 1).36 The reaction was quenched by
addition of methanol and 2,2′-dipyridyl (bpy). Purifica-
tion by flash chromatography with a solvent gradient
provided diastereomers 7 and 8 in 65% overall yield
with a diastereoselectivity ratio (dr) of 1.5:1.
Syn th esis of Un sym m etr ica l Bisa za fer r ocen e
Liga n d s 12 a n d 13. The synthesis of a bulkier bisaza-
ferrocene ligand was attempted with the purpose of fully
blocking the axial faces of the coordination center.1,2,39
However, the preparation of bis(pentaphenyl)azafer-
rocene ligand (10) was attempted at various conditions
without success. Instead of forming the anticipated
product 10, we only isolated the monosubstituted pen-
taphenylazaferrocenyl moiety, Cp°FeDPM-H (11), in
69% yield (Scheme 2). The failure to form complex 10
was attributed to the high sterics of the pentaphenyl
moiety.
(16) Ikeda, S.; Ohhata, F.; Miyoshi, M.; Tanaka, R.; Minami, T.;
Ozawa, F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2000, 39, 4512-4513.
(17) Rachita, M. J .; Huff, R. L.; Bennett, J . L.; Brookhart, M. J .
Polym. Sci., Part A: Polym. Chem. 2000, 38, 4627-4640.
(18) Lee, B. Y.; Bazan, G. C.; Vela, J .; Komon, Z. J . A.; Bu, X. J .
Am. Chem. Soc. 2001, 123, 5352-5353.
(19) Daugulis, O.; Brookhart, M. Organometallics 2002, 21, 5926-
5934.
(20) Daugulis, O.; Brookhart, M.; White, P. S. Organometallics 2002,
21, 5935-5943.
(21) J enkins, J . C.; Brookhart, M. Organometallics 2003, 22, 250-
256.
(22) Shen, H.; J ordan, R. F. Organometallics 2003, 22, 1878-1887.
(23) Foley, S. R.; Stockland, R. A., J r.; Shen, H.; J ordan, R. F. J .
Am. Chem. Soc. 2003, 125, 4350-4361.
(24) Gibson, V. C.; Tomov, A. Chem. Commun. 2001, 1964-1965.
(25) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskela, M.; Rieger, B.
Organometallics 2001, 20, 2321-2330.
Because of the difficulty in obtaining a bis(pentaphe-
nyl)azaferrocene ligand, a less sterically hindered Cp*Fe
group was subsequently introduced to the free pyrrole
ring of 11 to obtain an unsymmetrical Cp*Cp°Fe2DPM
(26) Moehring, V. M.; Fink, G. Angew. Chem. 1985, 97, 982-984.
(27) Guan, Z.; Cotts, P. M.; McCord, E. F.; McLain, S. J . Science
1999, 283, 2059-2062.
(28) Guan, Z. Chem.-Eur. J . 2002, 8, 3086-3092.
(29) Chen, G.; Ma, X. S.; Guan, Z. J . Am. Chem. Soc. 2003, 125,
6697-6704.
(34) Ruble, J . C.; Fu, G. C. J . Org. Chem. 1996, 61, 7230-7231.
(35) Dosa, P. I.; Ruble, J . C.; Fu, G. C. J . Org. Chem. 1997, 62, 444-
445.
(36) Lo, M. M. C.; Fu, G. C. J . Am. Chem. Soc. 1998, 120, 10270-
10271.
(37) Hodous, B. L.; Ruble, J . C.; Fu, G. C. J . Am. Chem. Soc. 1999,
121, 2637-2638.
(38) Fu, G. C. Acc. Chem. Res. 2000, 33, 412-420.
(39) Mecking, S.; J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am.
Chem. Soc. 1998, 120, 888-899.
(30) Guan, Z. J . Am. Chem. Soc. 2002, 124, 5616-5617.
(31) Cotts, P. M.; Guan, Z.; McCord, E.; McLain, S. Macromolecules
2000, 33, 6945-6952.
(32) Silver, J .; Zakrzewski, J .; Tosik, A.; BukowskaStrzyzewska, M.
J . Organomet. Chem. 1997, 540, 169-174.
(33) Moody, L. S.; MacKenzie, P. B.; Killian, C. M.; Lavoie, G. G.;
Ponasik, J . A., J r.; Smith, T. W.; Pearson, J . C.; Barrett, A. G. M. PCT
Int. Appl. WO 0222694, 2002.

Bisazaferrocene Polymerization Catalysis
Organometallics, Vol. 22, No. 24, 2003 5035
Sch em e 1
Sch em e 2
Sch em e 3
Sch em e 4
ligand (12, Scheme 3). The reaction gave two diastere-
omers 12 and 13 in equal amount. Previous reports have
shown that introduction of a silver reagent during the
course of a reaction improved the dr for a similar kind
of bisazaferrocene synthesis.36 It was postulated that
an energetically favorable semirigid six-membered sil-
vercyclic transition state was formed to promote a
favorable attack below the plane of pentamethylazafer-
rocene due to steric repulsion.40 Various metal ions
including ZnCl2, AgOAc, and AgCN were added to the
reaction solution after the lithiation of 11 (step 1 in
Scheme 3). However, the dr improvement was rather
modest with 1.3:1 as the highest obtained for 12 and
13. The two diastereomers were conveniently separated
by flash column chromatography. The syn- and anti-
stereoisomers are assigned on the basis of the charac-
teristic NMR features for the bridging methylene pro-
tons: the chemical shifts for the two diastereotopic
protons on the methylene bridge have larger chemical
shift differences for the syn-isomer 13 than for the anti-
isomer 12.
B. Syn th esis a n d Ch a r a cter iza tion of Ni(II) a n d
P d (II) Com p lexes w it h t h e Bisa za fer r ocen e
Liga n d s. Syn th esis of NiBr 2 a n d P d Cl2 Com p lexes
w ith th e Sym m etr ica l Bisa za fer r ocen e Liga n d a s
P r eca ta lysts. First, NiBr2 complexes with the sym-
metrical bisazaferrocene ligand 7 or 8 were prepared
according to modified literature procedures.1 The (DME)-
NiBr2 complex (14) was added to a solution of either 7
or 8 in dichloromethane (Scheme 4). Concentrated
solution of 2a or 15 was precipitated with hexanes to
afford 2a or 15 in 52% or 69% yields, respectively.
Due to the paramagnetic nature of the NiBr2 com-
plexes, satisfactory NMR spectra could not be obtained
for complexes 2a and 15, which were instead character-
ized by combustion analysis. Fortunately, good quality
single crystals of 2a were obtained from a concentrated
chloroform solution layered with hexanes. The X-ray
(40) O’Connor, J . M.; Casey, C. P. Chem. Rev. 1987, 87, 307-318.

5036 Organometallics, Vol. 22, No. 24, 2003
Salo and Guan
Sch em e 5
Sch em e 6
moieties is critical for preventing an associative chain
transfer process in order to form high molecular weight
polymers. Because of the exposed axial faces in the
bisazaferrocene complex, the metal center could be
susceptible to ethylene associative chain transfer pro-
cesses, which may contribute at least partially to the
formation of relatively low molecular weight PEs in the
ethylene polymerization catalyzed by the these com-
plexes (vide infra). Another notable difference between
the two complexes is the bite angle of the two nitrogens.
While the R-diimine NiBr2 complexes generally have
bite angles of 82.4-82.6°, the complex 2a has a bite
angle of 92.1°, which is almost 10° larger than the
R-diimine analogues.41,42
Complexes of PdCl2 with the symmetric bisazafer-
rocene, 2b and 16, were synthesized by combining and
modifying the procedures of Brookhart and Fu et al.1,36
The syntheses were accomplished by ligand substitution
of (COD)Pd(Me)Cl (17) with 7 or 8 (Scheme 5). After
recrystallization from hexanes, the complexes 2b and
16 were obtained in 70% and 77% yields, respectively.
Complexes 2b and 16 were characterized by 1H and 13C
NMR spectroscopy, high-resolution mass spectrometry
(HRMS), and combustion analyses.
Syn th esis of P r eactivated P d(II) Com plexes with
th e Sym m etr ic Bisa za fer r ocen e Liga n d 7. Because
of the low polymerization activities observed for the
NiBr2 and PdCl2 complexes (2a ,b, 15, 16) upon MAO
activation, in later studies we focused on the syntheses
and polymerization studies of Pd(II) complexes in pre-
activated forms. First, the Pd(Me)Cl-bisazaferrocene
complex 3 was prepared according to a modified litera-
ture procedure.43 The (COD)PdCl2 (18) was first con-
verted into (COD)Pd(Me)Cl (17), which was subse-
quently complexed to the C2-symmetrical bisazaferrocene
ligand 7 to afford 3 in 84% yield (Scheme 6).
F igu r e 1. ORTEP view of 2a showing important atoms
labeled. Selected interatomic distances (Å) and angles
(deg): Ni(1)-N(2) ) 1.986(4), Ni(1)-N(1) ) 1.990(5),
Ni(1)-Br(2) ) 2.3643(9), Ni(1)-Br(1) ) 2.3794(9), N(2)-
Ni(1)-N(1) ) 92.09(18), Br(2)-Ni(1)-Br(1) ) 121.25(3),
N(2)-Ni(1)-Br(2) ) 106.85(13), N(1)-Ni(1)-Br(2) )
116.15(14), N(2)-Ni(1)-Br(1) ) 117.92(13), N(1)-Ni(1)-
Br(1) ) 98.83(13), Cnt1-Fe(1)-Cnt2 ) 175.5, Cnt3-
Fe(2)-Cnt4 ) 176.2.
crystal structure of 2a was successfully solved as shown
in Figure 1 together with selected bond distances and
angles.
The bisazaferrocene-Ni(II) complex 2a is pseudo-C2
symmetrical, and the Ni coordination assumes a pseudo-
tetrahedral geometry with a boatlike conformation for
the six-membered coordination ring. The N-Ni and
Ni-Br bond distances of the complex 2a are very close
to the values observed in the R-diimine analogues.41,42
However, in contrast to the R-diimine NiBr2 complex
having bulky R substituents (1), the pentamethylaza-
ferrocene moieties may not sufficiently block the axial
faces of the coordination center for complex 2a . Instead
of being parallel to each other, the two Cp* rings are
titled with a torsion angle of 168.8° between them,
presumably caused by the steric repulsion between the
Br atoms with the Cp* rings. As shown by Brookhart
and co-workers in previous studies of Ni(II)- and Pd-
(II)-R-diimine complexes, blocking axial faces of the
coordination site with bulky substituents of the aniline
The complex 3 was then activated with sodium
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBAF,
19) in the presence of diethyl ether (Et2O) or acetonitrile
(41) Gates, D. P.; Svejda, S. K.; Onate, E.; Killian, C. M.; J ohnson,
L. K.; White, P. S.; Brookhart, M. Macromolecules 2000, 33, 2320-
2334.
(42) Maldanis, R. J .; Wood, J . S.; Chandrasekaran, W. A.; Rausch,
M. D.; Chien, J . C. W. J . Organomet. Chem. 2002, 645, 158-167.
(43) Rulke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .;
Vanleeuwen, P.; Vrieze, K. Inorg. Chem. 1993, 32, 5769-5778.

Bisazaferrocene Polymerization Catalysis
Organometallics, Vol. 22, No. 24, 2003 5037
Sch em e 7
Sch em e 8
Sch em e 9
Sch em e 10
activity of complex 2b toward SnMe4 may arise from a
destabilizing trans-ligand effect.45 Since the methyl
group is known to be an excellent σ-donor, the exchange
of a weaker σ-donating Cl atom with a methyl group
on the Pd(II) center should result in a destabilizing
trans-effect because the pentamethylazaferrocene ligand
has good σ-donating capability.32,45
To overcome the difficulty encountered in the syn-
thesis of the Pd(Me)Cl complexes 3 and 4, we developed
a new methodology for the synthesis of Pd(Me)Cl com-
plexes. In this approach, a Pd(II) precursor (PhCN)2PdCl2
(22), containing a more labile benzonitrile (PhCN)
ligand, was used to generate a transient [(PhCN)2Pd-
(Me)Cl] species as a reactive intermediate. Direct ligand
substitution in situ then leads to the formation of the
desired Pd(Me)Cl complexes. Because of its low stability,
the (PhCN)2Pd(Me)Cl species has to be generated at
low temperature under argon followed by in situ ligand
substitution within a short period of time. We first
employed R-diimine ligand 23 as a model to investigate
the feasibility and to optimize the reaction conditions
(Scheme 11).
As shown in Scheme 11, the product yield had a
strong dependence on the reaction time for the in situ
generation of the (PHCN)2Pd(Me)Cl species. High prod-
uct yield was obtained at shorter reaction times, which
suggests the decomposition of the (PhCN)2Pd(Me)Cl
species even at low temperatures.
Following successful model reaction studies, we ap-
plied this methodology to the synthesis of complex 4.
After optimization of reaction conditions, complex 4 was
(ACN) as stabilizers.1,2 While the ether-stabilized Pd
salt [Cp*2Fe2DPMPd(Me)OEt2]+BAF- (20) was unstable
as shown by 1H NMR, the ACN-stabilized Pd salt
[Cp*2Fe2DPMPd(Me)NCCH3]+BAF- (21) was suffi-
ciently stable to be isolated as brittle dark red crystals
in 91% yield (Scheme 7).1,44 Complex 21 was fully
1
characterized by HRMS, combustion analysis, and H
and 13C NMR.
Another preactivated Pd(II) complex, a palladacyclic
derivative [Cp*2Fe2DPMPd(CH2)3COOMe+]BAF- (5),
was synthesized by activating complex 3 with NaBAF
followed by the addition of methyl acrylate (MA).2 The
complex was characterized by 1H and 13C NMR, HRMS,
and combustion analysis.
Syn th esis of P r eactivated P d(II) Com plexes with
th e Un sym m etr ica l Bisa za fer r ocen e Liga n d 12. We
initially attempted to synthesize the unsymmetrical
Cp°Cp*Fe2DPM-Pd(Me)Cl complex 4 by following the
same route used in the synthesis of complex 3. Unfor-
tunately, the displacement of COD in 17 by the unsym-
metrical ligand 12 did not occur, which was presumably
caused by the steric hindrance of the bulky unsym-
metrical azaferrocene ligand 12 (Scheme 9).
An alternative route that involves a direct methyla-
tion of a PdCl2-bisazaferrocene complex with tetram-
ethyltin (SnMe4) to form the Pd(Me)Cl complex was
pursued next. The symmetric Cp*2Fe2DPMPdCl2 com-
plex (2b) was used as a model system to investigate the
1
feasibility of this route. Shown by MS and H NMR, the
transmetalation reaction to 2b did not occur at various
conditions (Scheme 10). We speculate that the nonre-
(45) J ames, P. C.; Hededus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry; 1987.
(44) Bahr, S. R.; Boudjouk, P. J . Org. Chem. 1992, 57, 5545-5547.

5038 Organometallics, Vol. 22, No. 24, 2003
Sch em e 11. Mod el Rea ction for in Situ Gen er a tion of P d (Me)Cl Com p lex (6)
Salo and Guan
Sch em e 12
Sch em e 13
obtained in 77% yield as pink crystals and was charac-
terized by 1H and 13C NMR, HRMS, and combustion
analysis. In complex 4, the regiochemistry of the methyl
group being trans to the Cp° azaferrocene was estab-
lished by Nuclear Overhausser Effects (NOE) on the
Pd-Me with the adjacent R-proton on the pyrrole ring
(Scheme 12). The regioselectivity of the reaction is
attributed to trans ligand effects.45 Because of inductive
and resonance stabilization of the phenyl groups, the
Cp° azaferrocene has significantly less σ-donating abil-
ity than the pentamethyl azaferrocene moiety. There-
fore, the strong σ-donating methyl group prefers to stay
trans to the Cp° azaferrocene moiety.
Polymerization reactions at various temperatures, eth-
ylene pressures, and varying Al/metal ratios afforded
only trace amount of polymers. For the PdCl2 complex,
black Pd dust was observed after terminating the
polymerization, indicating the decomposition of the Pd
species upon activation. For NiBr2 complexes, no direct
evidence of catalyst decomposition was observed. While
the reason for the very low activities of these complexes
activated by MAO is still unknown, we speculate the
highly reactive MAO may interact with the azaferrocene
ligand to cause the catalyst deactivation. To avoid the
use of MAO, we then focused on developing Pd(II)-
bisazaferrocene catalysts that are already in active form
with no need of further activation.
The preactivatived Pd(II) complexes 5 and 6 were
selected to test for ethylene polymerization at various
ethylene pressures and temperatures. The polymeriza-
tion data are summarized in Table 1. The pseudo-C2-
symmetric complex 5 polymerized ethylene to form
oligomers (number-averaged molecular weight, Mn,
about 200-600 g/mol) with moderate branching (20-
60 br./1000C) (Table 1). Both the polymerization activity
as measured by turnover frequency (TOF) and the PE
molecular weight are significantly lower than the values
obtained with the Pd(II)-R-diimine analogues.1,2,46
Ethylene polymerizations using complex 5 were first
run at different temperatures ranging from 20 to 120
°C while maintaining all other parameters constant
(entries 1-6). The catalyst productivity increases ini-
With complex 4 in hand, the synthesis of {Cp°Cp*Fe2-
DPM-Pd[(CH2)3COOMe]}+BAF- (6) was carried out by
following the same procedure as described previously
in the synthesis of complex 5. Immediately after the
addition of NaBAF into complex 4 in DCM, MA was
added and the solution was allowed to stir at room
temperature overnight to afford complex 6 in 89% yield
as dark red crystals (Scheme 13). The complex 6 was
1
characterized by H and 13C NMR, HRMS, and combus-
tion analysis.
C. Oligom er iza tion of Eth ylen e w ith th e P d II
a n d NiII Bisa za fer r ocen e Com p lexes. NiBr 2 a n d
P d Cl2 Com p lexes. The ethylene polymerization reac-
tions were carried out in a 600 mL Parr reactor using
toluene as the solvent. For all NiBr2 and PdCl2 com-
plexes (2a ,b, 15, and 16) methylaluminoxane (MAO)
was used to activate the catalyst precursors for polym-
erization of ethylene. Unfortunately, all these complexes
upon activation with MAO exhibited very low activities.
(46) Tempel, D. J .; J ohnson, L. K.; Huff, R. L.; White, P. S.;
Brookhart, M. J . Am. Chem. Soc. 2000, 122, 6686-6700.

Bisazaferrocene Polymerization Catalysis
Organometallics, Vol. 22, No. 24, 2003 5039
Ta ble 1. Eth ylen e Oligom er iza tion Da ta by Ca ta lysts 5 a n d 6a
loading
(µmol)
pressure
(psig)
temp
(°C)
time
(h)
yield of
branch/
1000 C
d
d
entry
catalyst
polymer (g) b
TOFc
Mn
1
2
3
4
5
6
7
8
5
5
5
5
5
5
5
5
5
6
6
6
13
13
13
13
13
13
14
14
12
6
100
100
100
100
100
100
50
200
500
100
100
100
20
40
60
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
24
0.055
0.152
0.423
1.89
60
167
465
2080
1615
992
855
1330
3110
13
598
424
318
235
233
230
226
242
236
270
186
247
50
45
41
29
38
36
43
28
27
33
19
60
80
100
120
80
80
80
20
40
80
1.47
0.903
0.838
1.30
9
2.61
10
11
12e
0.048
0.400
0.017
11
12
24
2.5
54
20
a
b
General polymerization procedure: 70 mL of toluene, 6-14 µmol of catalyst unless specified. Yield of PE may not accurately reflect
the true activity due to the removal of volatile oligomers during workup. c TOF ) turnover frequency per hour, i.e., moles of ethylene
consumed in formation of PE per mole of catalyst per hour. Mn and branching density were calculated on the basis of 1H NMR according
d
to Brookhart et al.47 e Polymerization was carried out in DCM.
Sch em e 14
tially with temperature and reaches a maximum around
80 °C. As the temperature was further raised, the
activity starts to drop, indicating catalyst deactivation
at higher temperature. Nevertheless, the catalyst re-
mains active even at 120 °C to polymerize ethylene for
many hours. This is in sharp contrast to the Pd(II)-R-
diimine counterparts, which is known to decompose
rapidly at about 50 °C.46 Increase of temperature
resulted in a decrease in Mn, which is typical for
transition-metal-catalyzed olefin polymerizations due to
increased rate of chain transfer reactions at elevated
temperatures. The molecular weights of the PEs ob-
tained with 5 are generally low compared to those
obtained with the Pd(II)-R-diimine catalysts. Whereas
the exact cause for this is yet to be understood, based
on the X-ray crystal structure of complex 2a (Figure 1),
we tentatively attributed this partially to the openness
of the axial faces of complex 5 (vide supra). The easy
access by ethylene from the axial faces makes the
catalyst susceptible to ethylene associative chain trans-
fer. The 1H NMR spectra of the PE products showed
that they contain a significant portion of internal olefins,
which could self-inhibit the catalyst and partially sup-
press the intrinsic catalytic activity of the catalyst.
Oligomerizations were then carried out at 80 °C with
three pressures (Table 1, entries 7-9). An increase in
pressure resulted in an increase in productivity (TOF)
but a decrease in branching density, both consistent
with the Pd(II)-R-diimine systems.46 The branches in the
PEs were presumably formed by the chain-walking
mechanism proposed by Brookhart and Fink for the Ni-
(II) and Pd(II) catalyst systems.1,2,26
than the symmetrical complex 5. In addition, the
unsymmetrical catalyst 6 appears to be less thermally
stable than the symmetrical analogue 5, as evident with
the drop of TOF at 40 °C and the observed formation of
Pd dust during polymerization. The significantly lower
activity for the unsymmetrical catalyst 6 than the
symmetric catalyst 5 is analogous to the comparison
between the reported unsymmetrical Pd(II)-phosphine-
imine (P∧N) complex 25 and its symmetrical Pd(II)-R-
diimine complexes.19 It was shown that the unsym-
metrical P∧N complexes with Ni(II) and Pd(II) were less
reactive than their symmetrical R-diimine or R-diphos-
phine counterparts. The migratory insertion barrier for
the unsymmetrical complex 25 was shown to be 7.4 kcal/
mol higher than the barrier for either the R-diimine or
R-diphosphine analogues. The lower reactivity of our
unsymmetrical complex 6 than the symmetrical one 5
can be explained by the same arguments used to explain
the low reactivity of other unsymmetrical complexes.19,45
As shown in Scheme 14, the situation is unfavorable
for migratory insertion for the unsymmetrical complex
in its more stable resting state 26a . In simple view, the
migratory insertion can be regarded as an attack of the
nucleophilic R group on the electrophilic ethylene
ligand. The R group in 26a (trans to Cp° azaferrocene)
is less nucleophilic than the R group in the symmetric
complex 26b (trans to Cp* azaferrocene). Therefore, the
nucleophilic addition of R to ethylene (equivalent to
migratory insertion) is slower for the unsymmetrical
complex 26a .19,45
D. Kin etic In vestiga tion of Meth yl Migr a tion
a n d Eth ylen e Con su m p tion . To understand why the
bisazaferrocene catalysts exhibit lower polymerization
activities than their R-diimine counterparts, kinetic
studies on methyl migration and subsequent ethylene
consumption for complex 27 were carried out and the
Oligomerization of ethylene with complex 6 was
carried out and compared to the symmetrical analogue,
5 (Table 1, entries 10-12). The unsymmetrical complex
6 was considerably less active in polymerizing ethylene

5040 Organometallics, Vol. 22, No. 24, 2003
Salo and Guan
Sch em e 15
Sch em e 16
F igu r e 2. Eyring plot for subsequent ethylene insertion
by complex 27.
data were compared to those of the bisimine ana-
logues.1,46,47 The complex 3 was activated in an NMR
tube with NaBAF at -78 °C and then complexed with
ethylene to form the Pd(Me)(H2CdCH2) complex (27).
After warming up to -14 °C, the first-order kinetics of
the first methyl migration was monitored by the de-
crease of the Pd-Me group with time (Scheme 15):
The first-order rate constant for the first methyl
migration was determined to be k ) 2.49 × 10-5 s-1 at
-14 °C, which corresponds to a ∆Gq of 20.6 kcal/mol
using the Eyring equation. This insertion barrier for the
first methyl migration of complex 27 is about 2-3 kcal/
mol higher than the values of the Pd(II)-R-diimine
analogues for which the ∆Gq is in the range 17.5-18.8
kcal/mol.1 The rate of subsequent insertions was mod-
eled by the zero-order kinetics of ethylene disappearance
at 9.5 °C, k ) 1.3 × 10-3 s-1, corresponding to a ∆Gq )
20.2 kcal/mol (Scheme 15). Again, this energetic barrier
is 2-3 kcal/mol higher than the values for the bisimine
analogues, for which the ∆Gq is usually in the range
16.9-17.6 kcal/mol.1 A ∆∆Gq of 2-3 kcal/mol corre-
sponds to about 2 orders of magnitude difference in rate
at room temperature, which agrees qualitatively with
the observed difference in polymerization activities
between the Pd(II)-bisazaferrocene complexes and the
Pd(II)-R-diimine counterparts. Furthermore, the ethyl-
ene consumption rates for complex 27 were measured
at various temperatures ranging from 255.7 to 282.7 K.
An Erying plot (Figure 2) gives ∆Hq ) 18.2 kcal/mol and
∆Sq ) -7.4 eu. This ∆Hq value is considerably higher
than the values for the Pd(II)-R-diimine counterparts
(14.2 kcal/mol), while the ∆Sq value is smaller than the
values for the Pd(II)-R-diimine counterparts (-11.2
eu).46 Therefore, the ethylene insertion by Pd(II)-bisaza-
ferrocene complex 27 is unfavorable from both enthalpic
and entropic considerations, which explains why the Pd-
(II)-bisazaferrocene complexes exhibit much lower re-
activity than the R-diimine counterparts. The higher
insertion barrier for the Pd(II)-bisazaferrocene complex
than for the R-diimine analogues could be the result of
a combination of both electronic and steric effects.
Electronically (Scheme 16), the better σ-donating ability
of bisazaferrocene should make the R group more
nucleophilic but the coordinated ethylene less electro-
philic for 26b than for R-diimine complex 29. The net
result of these two countereffects is not obvious, how-
ever. Sterically, both experimental46 and theoretical
calculation48 results have shown that bulkier R-diimine
complexes exhibit lower insertion barriers because steric
congestion causes ground state destabilization for the
resting complex 29. The rather open structure of the
bisazaferrocene complex 26b around the coordination
center makes the resting state relatively stable in the
ground state, which should lead to a larger activation
energy as it proceeds to its transition state.
Con clu sion s
A series of novel nickel and palladium complexes with
symmetrical and unsymmetrical bisazaferrocene cata-
lysts were successfully synthesized and characterized,
and some were tested for ethylene polymerization. The
X-ray crystal structure for the bisazaferrocene-NiBr2
complex (2a ) shows it as a pseudo-C2-symmetrical
complex with the Ni coordination center assuming a
pseudo-tetrahedral geometry. The titled Cp* rings leave
the coordination center susceptible to associative chain
transfer processes, which may partially contribute to the
low molecular weights in their ethylene polymerizations.
Because the bisazaferrocene complexes with simple
Ni(II) and Pd(II) halides (2a ,b, 15, and 16) gave only a
trace amount of PE upon activation with MAO, our
(47) Daugulis, A.; Brookhart, M.; White, P. S. Organometallics 2002,
21, 5935-5943.
(48) Deng, L.; Woo, T. K.; Cavallo, L.; Margl, P. M.; Ziegler, T. J .
Am. Chem. Soc. 1997, 119, 6177-6186.

Bisazaferrocene Polymerization Catalysis
Organometallics, Vol. 22, No. 24, 2003 5041
investigation then turned its focus on the development
and ethylene polymerization studies of preactivated
symmetrical and unsymmetrical Pd(II)-bisazaferrcoene
complexes (5, 6, and 21). Complex 5 and 21 were
synthesized in straightforward routes by first forming
the appropriate Pd(Me)Cl complexes through simple
ligand substitution followed by activation with NaBAF
in the presence of various stabilizers. However, signifi-
cant difficulty was encountered in the preparation of
the unsymmetrical bisazaferrocene complex 6 due to
steric and electronic factors, which prompted us to
investigate alternative routes to achieve the synthetic
goal. A novel route was successfully developed to make
Pd(Me)Cl complexes with various dinitrogen ligands by
generating a transient [(PhCN)2Pd(Me)Cl] species in
situ followed by ligand substitution reaction. Utilizing
this new methodology, the unsymmetrical azaferrocene
complex 6 was obtained in good yield.
Exp er im en ta l Section
Gen er a l P r oced u r e. All metal-related reactions were
initially weighed and carried out in a Vacuum Atmospheres
glovebox filled with nitrogen, unless otherwise noted. All other
moisture and air-sensitive reagents were carried out in either
oven-dried (180 °C) or flame-dried glassware using magnetic
stirring under positive pressure of argon or nitrogen. Flash
chromatography with unbound azaferrocene ligands was car-
ried out using forced flow under nitrogen with Silicycle 230-
400 mesh (pH 5.5-6.5) silica gel. All other flash chromatog-
raphy was performed using forced flow under nitrogen with
EM Science 230-400 mesh silica gel, unless otherwise noted.
NMR spectra were recorded on Bruker DRX400, Bruker
GN500, and Bruker Omega500 MHz FT-NMR instruments.
Proton and carbon NMR spectra were recorded in ppm and
were referenced to indicated solvents. Data were reported as
follows: chemical shift, multiplicity (s ) singlet, d ) doublet,
t ) triplet, q ) quartet, m ) multiplet), coupling constant(s)
in hertz (Hz), and integration. Multiplets (m) were reported
over the range (ppm) at which they appear at the indicated
field strength. Mass spectra were obtained on an ES/MS, a
VG Analysis 7070E, or a Fisons Autospec spectrometer and
were obtained by peak matching. Elemental analysis was
performed by Atlantic Microlabs in Marietta, GA. Number
average molecular weights (Mn) and degree of branching of
Preactivated complexes 5 and 6 were selected to test
for ethylene polymerization at various conditions. They
both gave oligomeric PEs with Mn in the range of 200-
600 g/mol and branching density from 20 to 60 br./1000
carbons. The symmetrical complex 5 has demonstrated
a higher productivity than the unsymmetrical complex
6, but both are significantly less productive than the
R-diimine counterparts. One unique feature is that their
thermal stability is considerably higher than the R-di-
imine counterparts: for example, complex 5 remained
active in ethylene polymerization at temperatures as high
as 120 °C. The formation of low molecular weight
oligomers may be partially due to the openness of the
axial faces of the coordination center, as shown by the
X-ray structure of the NiBr2 complex (2a ). The signifi-
cantly lower activity for the unsymmetrical catalyst 6
than the symmetric catalyst 5 is analogous to the
difference in activities between the reported unsym-
metrical Pd(II)-phosphine-imine (P∧N) complex 25 and
its symmetrical Pd(II)-R-diimine complex. The observa-
tion was explained by the same electronic arguments
(trans ligand effects) used to explain the low reactivity
of other unsymmetrical complexes.
1
the polymer samples were determined by H NMR spectra by
following literature procedures.47 THF, toluene, dichloromethane
(DCM), and diethyl ether were degassed under argon and
passed through an alumina-packed filtration system. Unless
otherwise stated, all reagents were purchased from commercial
suppliers and used as received. Pyrrole was distilled under
reduced pressure and stored over 4 Å molecular sieves in
glovebox at -35 °C. Di(2-pyrrole)methane (DPM) was synthe-
sized according to the procedure by Ka et al.49 NaBAF was
obtained from the procedure by Bahr et al.44 Ethylene polym-
erization is performed by using a 600 mL Parr high-pressure
reactor with an overhead mechanical stirrer and temperature
control.
Gen er a l P r oced u r e A: Syn th esis of Com p lexes w ith
Meta l Ha lid es.36,50-53 To a solution of (-(S,S)- and (R,R)-Cp*2-
Fe2DPM or meso-Cp*2Fe2DPM dissolved in THF or DCM (0.3
M relative to ligand) was added the metal halide (MX2) (the
ligand:M was typically in the range 1.05-1.15:1). The solution
was stirred at rt for at least 24 h in the glovebox. The solution
was filtered through Celite, concentrated, and precipitated by
layering with hexanes, unless otherwise noted. The metal
complex was washed with 3 × 2 mL of hexanes and dried in
vacuo overnight, unless otherwise noted.
Gen er a l P r oced u r e B: Syn th esis of P r ea ctiva ted P d II
Com p lexes.36,50-53 To a solution of Cp*2Fe2DPM-Pd(Me)Cl (3)
or Cp°Cp*Fe2DPM-Pd(Me)Cl (4) dissolved in DCM was added
an appropriate amount of NaBAF, which was followed im-
mediately by the addition of a stabilizer (Et2O, ACN, or MA).
The resulting solution was stirred at rt for at least 12 h in the
glovebox. The salt was filtered through a fine frit filter and
dried in vacuo overnight to give a preactivated PdII salt.
Gen er a l P r oced u r e C: Eth ylen e P olym er iza tion by
MAO-Activa ted Com p lexes. Approximately 10 mg of cata-
lyst was suspended or dissolved in 50 mL of toluene. The
resulting toluene suspension or solution was loaded into a 600
mL Parr reactor purged under nitrogen, followed by addition
of 20 mL of toluene. After the reactor was purged with 50 psi
To understand why the bisazaferrocene catalysts
exhibit much lower polymerization activities than their
R-diimine counterparts, kinetic studies on methyl mi-
gration and subsequent ethylene consumption for com-
plex 27 were carried out and the data were compared
to those of the R-diimine analogues. Low-temperature
NMR experiments revealed that the insertion barriers
for both the first methyl migration and subsequent
ethylene insertion by complex 27 are 2-3 kcal/mol
higher than the values obtained for the Pd(II)-R-diimine
analogues, which corresponds to about 2 orders of
magnitude difference in rate at room temperature. This
agrees qualitatively with the observed difference in
polymerization activities between the Pd(II)-bisazafer-
rocene complexes and the Pd(II)-R-diimine counterparts.
Further kinetic studies at various temperatures reveal
that ethylene insertion by Pd(II)-bisazaferrocene com-
plexes is unfavorable from both enthalpic and entropic
considerations. These kinetic data explain why the Pd-
(II)-bisazaferrocene complexes exhibit much lower re-
activity than the diimine counterparts.
(49) Ka, J . W.; Lee, C. H. Tetrahedron Lett. 2000, 41, 4609-4613.
(50) Killian, C. M.; J ohnson, L. K.; Brookhart, M. Organometallics
1997, 16, 2005-2007.
(51) Small, B. L.; Brookhart, M. J . Am. Chem. Soc. 1998, 120, 7143-
7144.
(52) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J . Am. Chem.
Soc. 1998, 120, 4049-4050.
(53) Gibson, V. C.; Tomov, A.; Wass, D. F.; White, A. J . P.; Williams,
D. J . J . Chem. Soc., Dalton Trans. 2002, 2261-2262.

5042 Organometallics, Vol. 22, No. 24, 2003
Salo and Guan
ethylene three times (5 min each) at rt, an appropriate amount
of MAO was loaded and the reactor was immediately charged
with ethylene to the desired pressure. The polymerization was
allowed to run for the allotted time at the desired temperature
and pressure. The reaction was stopped by the release of
ethylene and the addition of 2-propanol and hexanes. PE was
precipitated by the addition of MeOH containing a small
amount of HCl. PE was then filtered and washed with water,
methanol, acetone, and hexanes. The polymer was then dried
in vacuo overnight.
Gen er a l P r oced u r e D: E t h ylen e P olym er iza t ion b y
P r ea ctiva ted P d II Com p lexes 5 a n d 6. Approximately 10
µmol of catalyst was dissolved in 10 mL of toluene. Into a 600
mL Parr reactor purged under nitrogen, 55 mL of toluene
solvent was loaded followed by purging with 50 psi ethylene
three times (5 min each) at rt. After the catalyst solution was
introduced at rt, the reactor was immediately charged with
ethylene to the desired pressure. The polymerization was
allowed to run for the allotted time. The desired temperature
was reached within 5 min after the catalyst was loaded into
the reactor. The reaction was stopped by the release of
ethylene. Removal of solvent afforded PEs. To remove the
catalyst residue, the crude products were dissolved in hexanes,
decanted via pipet, and dried in vacuo for 1 h to afford clean
PEs.
Flash chromatography (under N2) was carried out with the
following gradient: 75:25:5 hexanes/EtOAc/Et3N f 60:40:5
hexanes/EtOAc/Et3N f 25:75:5 hexanes/EtOAc/Et3N. Deca-
methylferrocene eluted first as a yellow band, followed by an
orange-red band ((-(S,S)- and (R,R)-Cp*2Fe2DPM), a violet
band, and finally an orange-red band (meso-Cp*2Fe2DPM). The
solvent was then removed to obtain (-(S,S)- and (R,R)-Cp*2-
Fe2DPM (1.75 g, 38%, a dark red solid) and meso-Cp*2Fe2DPM
(1.17 g, 26%, a dark red solid) for an overall yield of 65%.
1H NMR of (-(S,S)- and (R,R)-Cp*2Fe2DPM (500 MHz,
C6D6): δ 1.89 (s, 30H), 3.73 (s, 2H), 3.87 (d, 2H, J ) 1.5 Hz),
4.04 (s, 2H), 4.82 (s, 2H). LRMS (ES/MS, m/z in MeOH): Anal.
1
Calcd for Fe2C29H38N2: 526.17 (M + H+). Found: 526.17. H
NMR and MS spectra are consistent with the authentic sample
as reported in Fu et al.36
1H NMR of meso-Cp*2Fe2DPM (500 MHz, C6D6): δ 1.84 (s,
30H), 3.79 (s, 2H), 4.01 (s, 2H), 4.02 (d, 1H, J ) 15.4 Hz), 4.09
(d, 1H, J ) 15.4 Hz), 4.81 (s, 2H). LRMS (ES/MS, m/z in
MeOH): Anal. Calcd for Fe2C29H38N2: 526.17 (M + H+).
1
Found: 526.17. H NMR and MS spectra are consistent with
the authentic sample as reported in Fu et al.36
Gen er a l P r oced u r e E: In Situ F or m a tion of P d (Me)-
Cl Com p lexes. After cooling a DCM solution of (PhCN)2PdCl2
(0.1 M) to -40 °C, tetramethyltin (3.0 equiv) was added. The
mixture was stirred for 1 h at -40 °C, then warmed to -30
°C and allowed to stir for the allotted time period, resulting
in the formation of a shiny silvery precipitate and a gray
solution. An appropriate ligand dissolved in DCM (0.3 M) was
added to the above solution at -30 °C. The resulting mixture
was allowed to stir at -30 °C for 30 min before slowly warming
to room temperature. The reaction was allowed to run for the
allotted time period. Using a small Celite plug, the solution
was filtered, concentrated, and precipitated with hexanes. The
resulting complex was washed with ether followed by drying
in vacuo overnight.
(-(S,S)- a n d (R,R)-Cp *2F e2DP M-Nick el(II) Br om id e
Com p lex (2a ). In a 5 mL scintillation vial, (-(S,S)- and (R,R)-
Cp*2Fe2DPM (34.6 mg, 0.0658 mmol) were dissolved in 2 mL
of DCM. To the red-orange solution, (DME)NiBr2 (18.1 mg,
0.0586 mmol) was added and allowed to stir for 48 h. The
brown solution was allowed to stir for 48 h, obtaining shiny
brown crystals (33.8 mg, 52%). Combustion (C, H, N): Anal.
Calcd for NiFe2C29H38N2Br2: C, 46.77; H, 5.14; N, 3.76.
Found: C, 44.22; H, 5.00; N, 3.54. Crystals suitable for X-ray
crystal determination were grown by layering a chloroform
solution of (-(S,S)- and (R,R)-Cp*2Fe2DPM-nickel(II) bromide
with hexanes.
Bis(1′,2′, 3′, 4′, 5′-pen tam eth ylazafer r ocen -2-yl)m eth an e
(Cp *2F e2DP M) (7 a n d 8). Following a literature procedure
by Fu and co-workers,36 di(2-pyrrole)methane (1.25 g, 8.55
mmol) was dissolved in 55 mL of THF. To the clear solution
at rt was added 1.6 M n-BuLi (11.3 mL, 18.1 mmol), affording
a light brown solution, and the mixture was allowed to stir
for 15 min. The solution was transferred via cannula to AgCN
(1.18 g, 8.82 mmol) slurry in THF (25 mL), and AgCN slowly
dissolved in approximately 10 min to form a black solution
(I).
m eso-Cp *2F e2DP M-Nick el(II) Br om id e Com p lex (15).
Following procedure A, meso-Cp*2Fe2DPM (87.0 mg, 0.165
mmol) was dissolved in 8 mL of DCM. To the red-orange
solution was added (DME)NiBr2 (43.7 mg, 0.142 mmol), and
the mixture was allowed to stir for 48 h. A brown powdery
solid was obtained (73.4 mg, 69%). Combustion (C, H, N):
Anal. Calcd for NiFe2C29H38N2Br2: C, 46.77; H, 5.14; N, 3.76.
Found: C, 44.21; H, 5.07; N, 3.79.
To a solution of Cp*H (4.66 g, 34.2 mmol) in THF (210 mL)
at rt was added 1.6 M n-BuLi (22.0 mL, 35.2 mmol). The
resulting tan slurry was allowed to stir at rt for 15 min and
transferred via cannula to a rapidly stirring FeCl2 (4.54 g, 35.8
mmol) slurry in THF (140 mL) at -20 °C. The resulting lime
green solution was stirred at -20 °C for 10 min. The black
solution (I) was transferred via cannula to the [Cp*FeCl]n
solution, affording a brown solution. The resulting solution was
allowed to react overnight (12 h). The reaction was quenched
by addition of 2,2′-dipyridyl (3.44 g, 22.0 mmol) dissolved in
MeOH (14 mL). The solution was passed through a silica plug
and washed with EtOAc and hexanes. The solvent was
removed, leaving a dark red oil that crystallized within a hour.
(Cycloocta-1,5-dien e)ch lor om eth ylpalladiu m (II), (COD-
)P d (Me)Cl (17). In a 25 mL RBF, (COD)PdCl2 (2.54 g, 8.88
mmol) was dissolved in 125 mL of DCM. To the resulting
yellow solution, tetramethyltin (2.22 mg, 12.4 mmol) was
added. The reaction was allowed to stir for 30 h, resulting in
a gray solution with dark gray precipitate. The solution was
filtered through Celite. The solvent was removed while the
temperature of the flask was strictly maintained at 0 °C, and
washed with diethyl ether (3 × 2 mL) to afford an off-white

Bisazaferrocene Polymerization Catalysis
Organometallics, Vol. 22, No. 24, 2003 5043
solid (2.00 g, 85%). 1H NMR (400 MHz, CDCl3): δ 1.19 (s, 3H),
2.45-2.70 (m, 8H), 5.16 (m, 2H), 5.93 (m, 2H). 13C NMR (100
MHz, CDCl3): δ 12.87, 28.11, 31.51, 101.27, 124.33.
91.13 (trans-Pd(Me)-R-pyrr-CH), 97.88 (trans-Pd(Me)-δ-pyrr-
C), 99.15 (cis-Pd(Me)-δ-pyrr-C). Combustion (C, H, N): Anal.
Calcd for PdFe2C30H41N2Cl: C, 52.74; H, 6.05; N, 4.18.
Found: C, 52.05; H, 5.93; N, 4.10. HRMS (ES/MS, m/z in
MeCN): Anal. Calcd for PdFe2C30H41N2Cl: 688.1285 (M - Cl-
+ MeCN). Found: 688.1276.
(-(S,S)- a n d (R,R)-Cp *2F e2DP M-P a lla d iu m (II) Ch lo-
r id e Com p lex (2b). Following procedure A, (-(S,S)- and
(R,R)-Cp*2Fe2DPM (49.0 mg, 0.0931 mmol) were dissolved in
2 mL of THF. To the red-orange solution was added (COD)-
PdCl2 (24.2 mg, 0.0848 mmol), and the mixture was allowed
to stir for 2 days, resulting in the formation of an orange
solution. An orange solid was obtained (45.9 mg, 70%). 1H
NMR (500 MHz, CDCl3): δ 1.92 (s, 30H), 3.93 (s, 2H), 4.27 (s,
2H), 4.34 (s, 2H), 6.31 (s, 2H). 13C NMR (125 MHz, CDCl3): δ
11.34, 25.26, 74.64, 75.30, 83.57, 91.78, 95.43. Combustion (C,
H, N): Anal. Calcd for PdFe2C29H38N2Cl2: C, 49.51; H, 5.44;
N, 3.98. Found: C, 50.25; H, 5.58; N, 4.17. HRMS (ES/MS,
m/z in MeOH): Anal. Calcd for PdFe2C29H38N2Cl + CH3OH:
699.0733 (M - Cl-). Found: 699.0736.
(S,S)- an d (R,R)-Cp*2Fe2DP M-P d(Me)NCCH3+BAF- (21).
Following procedure B, (-(S,S)- and (R,R)-Cp*2Fe2DPM-Pd-
(Me)Cl (75.3 mg, 0.11 mmol) were suspended in 2 mL of DCM.
To the red-orange suspension, NaBAF (97.5 mg, 0.11 mmol)
was added followed by the addition of ACN (0.5 mL). The
resulting solution was allowed to stir for 12 h. An orange-red
crystalline solid was obtained (167.7 mg, 98%). The structure
of 3 was fully assigned by various correlation NMR spectra
1
(see Supporting Information). H NMR (500 MHz, CDCl3): δ
0.77 (s, 3H), 1.80 (s, 30H), 2.36 (s, 3H), 3.85 (d, 1H, J ) 16.8
Hz), 3.89 (d, 1H, J ) 16.7 Hz), 4.30 (s, 1H), 4.31 (s, 1H), 4.39
(d, 1H, J ) 2.1 Hz), 4.42 (s, 1H), 4.87 (s, 1H), 5.20 (s, 1H),
7.61 (s, 4H), 7.79 (s, 8H). 13C NMR (125 MHz, CDCl3): δ 0.40
(Pd-CH3), 3.24 (Pd-NCCH3), 10.83 (trans-Pd(Me)-C5(CH3)5),
10.99 (cis-Pd(Me)-C5(CH3)5), 25.57 (pyrr-CH2-pyrr), 74.50 (cis-
Pd(Me)-γ-pyrr-CH), 75.70 (trans-Pd(Me)-â-pyrr-CH), 75.85 (cis-
Pd(Me)-â-pyrr-CH), 76.22 (trans-Pd(Me)-γ-pyrr-CH), 82.67
(trans-Pd(Me)-C5(CH3)5), 83.36 (cis-Pd(Me)-C5(CH3)5), 89.74
(cis- and trans-Pd(Me)-R-pyrr-CH), 97.64 (trans-Pd(Me)-δ-pyrr-
C), 98.29 (cis-Pd(Me)-δ-pyrr-C), 117.66 (Cp-BAF), 117.69 (Cp-
BAF), 120.14 (Pd-NCCH3), 124.81 (q, J CF3 ) 272.9 Hz), 129.15
(q, J Cm ) 32.7 Hz), 135.04 (Co-BAF), 161.96 (q, J B-C ) 50.3
Hz, Cipso). Combustion (C, H, N): Anal. Calcd for C64H56N3-
BF24Fe2Pd: C, 49.53; H, 3.64; N, 2.71. Found: C, 48.47; H,
3.58; N, 2.62. HRMS (ES/MS, m/z in DCM): Anal. Calcd for
C64H56N3BF24Fe2Pd: 688.1285 (M+ - BAF-). Found: 688.1299.
m eso-Cp *2F e2DP M-P a lla d iu m (II) Ch lor id e Com p lex
(16). Following procedure A, meso-Cp*2Fe2DPM (47.9 mg,
0.0910 mmol) was dissolved in 8 mL of DCM. To the red-orange
solution was added (COD)PdCl2 (23.6 mg, 0.0827 mmol),
affording an orange suspension. An orange powder was
1
obtained (44.6 mg, 77%). H NMR (500 MHz, CDCl3): δ 2.05
(s, 30H), 3.55 (d, 1H, J ) 14.5 Hz), 4.05 (s, 2H), 4.12 (s, 2H),
4.17 (d, 1H, J ) 14.9 Hz), 5.74 (s, 2H). 13C NMR (125 MHz,
CDCl3): δ 11.01, 26.74, 73.37, 74.72, 83.47, 91.76, 95.49.
Combustion (C, H, N): Anal. Calcd for PdFe2C29H38N2Cl2: C,
49.51; H, 5.44; N, 3.98. Found: C, 50.57; H, 5.74; N, 3.85.
HRMS (ES/MS, m/z in MeOH): Anal. Calcd for PdFe2C29H38N2-
Cl2: 667.0470 (M - Cl-). Found: 667.0441.
(S,S)- a n d (R,R)-Cp *2F e2DP M-P d (CH2)3COOMe+BAF -
(5). To the solution of DCM (2 mL) were added (-(S,S)- and
(R,R)-Cp*2Fe2DPM-Pd(Me)Cl (75.2 mg, 0.11 mmol). To the red-
orange suspension was added methyl acrylate (10.9 µL, 0.121
mmol) followed by addition of NaBAF (97.5 mg, 0.11 mmol).
The resulting deep red solution was allowed to stir for 12 h,
filtered, and dried in vacuo overnight. An red-orange crystal-
(S,S)- a n d (R,R)-Cp*2Fe2DP M-P a lla d iu m (m eth yl) Ch lo-
r id e(II) Com p lex (3). Following procedure A, (-(S,S)- and
(R,R)-Cp*2Fe2DPM (526 mg, 1.00 mmol) were dissolved in 16
mL of DCM. To the red-orange solution, (COD)Pd(Me)Cl (260
mg, 0.982 mmol) was added, and the mixture was allowed to
stir for 36 h, resulting in the formation of a peach-colored
suspension. After washing the solid with ether (3 × 3 mL) and
drying in vacuo for 30 min, an off-peach solid was obtained
(566 mg, 84%). The structure of 3 was fully assigned by various
correlation NMR spectra (see Supporting Information). 1H
NMR (500 MHz, CDCl3): δ 0.79 (s, 3H), 1.86 (s, 15H), 1.87 (s,
15H), 3.81 (d, 1H, J ) 16.4 Hz), 3.87 (d, 1H, J ) 16.4 Hz),
4.10 (s, 1H), 4.19 (s, 1H), 4.32 (d, 2H, J ) 2.9 Hz), 5.33 (s,
1H), 5.89 (s, 1H). 13C NMR (125 MHz, CDCl3): δ -3.06 (Pd-
CH3), 10.99 (cis-Pd(Me)-C5(CH3)5), 11.31 (trans-Pd(Me)-C5-
(CH3)5), 26.06 (pyrr-CH2-pyrr), 73.57 (trans-Pd(Me)-γ-pyrr-
CH), 74.67 (cis-Pd(Me)-γ-pyrr-CH), 74.85 (trans-Pd(Me)-â-pyrr-
CH), 75.61 (cis-Pd(Me)-â-pyrr-CH), 82.09 (cis-Pd(Me)-C5(CH3)5),
82.56 (trans-Pd(Me)-C5(CH3)5), 90.67 (cis-Pd(Me)-R-pyrr-CH),
1
line solid was obtained (175.7 mg, 90%). H NMR (500 MHz,
CDCl3): δ 0.88 (d, 3H, J ) 7.25 Hz), 0.90 (br s), 1.05 (m), 1.06
(br s), 1.33 (br s), 1.68-2.00 (m, 15H), 2.42 (s), 2.67 (br s, 2H),
3.3-3.4 (m, 1H), 3.7-4.6 (m, 9H), 4.9-5.2 (m, 1H), 7.61 (s,
4H, p-BAF-CH), 7.79 (o-BAF-CH). 13C NMR (125 MHz,
CDCl3): δ 1.47, 11.02 (C5CH3), 11.27 (C5CH3), 22.20, 23.12,
23.48, 25.03, 25.47, 25.83, 35.85, 46.32, 55.18 (COOCH31),
55.41 (COOCH32), 74.54, 74.83, 75.60, 75.80, 75.89, 75.96,
76.21, 76.76, 82.78, 82.84, 83.51, 83.79, 88.42, 89.64, 89.79,
90.22, 97.11, 98.73, 99.32, 117.89 (Cp-BAF), 124.81 (q, J CF3
)
272.9 Hz), 128.67, 129.35 (q, J Cm ) 31.4 Hz), 135.26 (Co-BAF),
161.77 (q, J B-C ) 50.3 Hz, Cipso), 183.25 (COOMe), 191.79
(COOMe). Combustion (C, H, N): Anal. Calcd for C66H59N2O2-
BF24Fe2Pd: C, 49.64; H, 3.72; N, 1.75. Found: C, 49.02; H,

5044 Organometallics, Vol. 22, No. 24, 2003
Salo and Guan
3.68; N, 1.83. HRMS (ES/MS, DCM, m/z): Anal. Calcd for
C66H59BF24Fe2N2O2Pd: 733.1389 (M+ -BAF-).Found: 733.1381
(100%).
(R,S)-Cp*Cp°Fe2DPM. The solvent was then removed to obtain
(S,S)- and (R,R)-Cp*Cp°Fe2DPM (114 mg, 43%, an orange-red
solid) and (S,R)- and (R,S)-Cp*Cp°Fe2DPM (113 mg, 43%, an
orange-red solid) for an overall yield of 86%.
1H NMR of (S,S)- and (R,R)-Cp*Cp°Fe2DPM (500 MHz,
CDCl3): δ 1.82 (s, 15H), 3.70 (d, 1H, J ) 14.5 Hz), 3.76 (d,
1H, J ) 14.5 Hz), 3.99 (s, 2H), 4.48 (d, 1H, J ) 1.9 Hz), 4.59
(d, 1H, J ) 1.9 Hz), 4.79 (s, 1H), 5.30 (s, 1H), 7.10-7.15 (m,
10H), 7.16-7.22 (m, 15H). 13C NMR (125 MHz, CDCl3): δ
11.22, 29.45, 72.77, 75.95, 76.02, 79.83, 81.15, 88.16, 92.15,
94.76, 105.14, 109.43, 126.94, 127.77, 132.81, 135.26. Combus-
tion (C, H, N): Anal. Calcd for C54H48N2Fe2: C, 77.52; H, 5.78;
N, 3.35. Found: C, 76.11; H, 6.20; N, 3.44. HRMS (ES/MS,
m/z): Anal. Calcd for C54H48N2Fe2: 837.2597 (M + H+).
Found: 837.2595 (100%).
Cp °F eDP M-H (11). To Cp°H in THF (50 mL) was added
1.6 M nBuLi (2.8 mL, 4.5 mmol), affording an orange-yellow
solution after stirring for 3 h at rt. The Cp°Li solution was
added via cannula to the rapidly stirring FeCl2 slurry, afford-
ing a purple solution that eventually changes to a transparent
brown-green solution after 3 h of stirring at rt.
To DPM in THF (20 mL) was added 1.6 M nBuLi (2.2 mL,
3.50 mmol), affording a yellow solution. The resulting DPM-
Li solution was allowed to stir for 15 min and was added via
cannula to the brown-green Cp°FeCl solution, immediately
forming an opaque brown solution. The brown solution was
heated at 65 °C for 2 h and cooled to rt overnight, obtaining
an off-red suspension. The reaction was quenched with MeOH
(10 mL), passed through a 1 in. Celite plug, and washed with
DCM to afford a red solution. The solvent was removed,
providing a red solid. Flash chromatography (100:0 DCM/Et3N
f 100:1 f 100:5) afforded two bands: Cp°H (light yellow) and
Cp°FeDPM-H (orange-red). A reddish-orange solid was ob-
tained and dried in vacuo overnight (1.55 g, 69%). 1H NMR
(500 MHz, CDCl3): δ 3.75 (d, 1H, J ) 16.3 Hz), 3.81 (d, 1H, J
) 16.3 Hz), 4.54 (d, 1H, J ) 2.1 Hz), 4.58 (d, 1H, J ) 1.6 Hz),
5.39 (s, 1H), 5.87 (s, 1H), 6.06 (m, 1H), 6.55 (m, 1H), 7.07-
7.20 (m, 25H), 8.16 (br s, 1H). 13C NMR (125 MHz, CDCl3): δ
27.19, 76.41, 79.53, 88.17, 95.21, 106.29, 108.48, 108.85,
117.41, 127.02, 127.81, 129.39, 132.73, 135.13. Combustion (C,
H, N): Anal. Calcd for C44H34N2Fe: C, 81.73; H, 5.30; N, 4.33.
Found: C, 80.00; H, 5.41; N, 4.20. HRMS (ES/MS, m/z in
DCM): Anal. Calcd for C44H34N2Fe: 647.2150 (M + H+).
Found: 647.2143 (100%).
1H NMR of diastereomer: (S,R)- and (R,S)- Cp*Cp°Fe2DPM
(500 MHz, CDCl3): δ 1.81 (s, 15H), 3.55 (d, 1H, J ) 1.8 Hz),
3.60 (d, 1H, J ) 15.5 Hz), 3.80 (d, 1H, J ) 15.5 Hz), 4.01 (s,
1H), 4.32 (d, 1H, J ) 1.8 Hz), 4.47 (d, 1H, J ) 1.7 Hz), 4.87 (s,
1H), 5.32 (s, 1H), 7.0-7.12 (m, 10H), 7.14-7.19 (m, 15H). 13C
NMR (125 MHz, CDCl3): δ 11.20, 28.55, 73.60, 75.22, 75.53,
79.12, 81.10, 88.06, 92.67, 95.28, 104.10, 109.69, 126.85,
127.73, 132.82, 135.38. Combustion (C, H, N): Anal. Calcd for
C
54H48N2Fe2: C, 77.52; H, 5.78; N, 3.35. Found: C, 75.75; H,
6.15; N, 3.37. HRMS (ES/MS, m/z): Anal. Calcd for C54H48N2-
Fe2: 837.2597 (M + H+). Found: 837.2580.
(Ar NdC(Me)-C(Me)CdNAr )P d (Me)Cl (Ar ) 2,6-C6H3-
(i-P r )2) (24). Using procedure E, (PhCN)2PdCl2 (203 mg, 0.528
mmol) was dissolved in DCM (5 mL). Tetramethyltin (0.22 mL,
1.62 mmol) was added and the mixture stirred for 2.5 h total
(1.5 h at -30 °C). Bisimine ligand 23 (211 mg, 0.521 mmol)
was dissolved in DCM (1.5 mL), affording an orange solution.
The solution stirred for 5 h and filtered through Celite, and
the solvent was removed. The orange solid was washed with
ether (3 × 1 mL), affording the title compound 23 in 97% yield
(285 mg). 1H NMR of (ArNdC(Me)-C(Me)CdNAr)Pd(Me)Cl
(Ar ) 2,6-C6H3(i-Pr)2) (400 MHz, CDCl3): δ 0.53 (s, 3H), 1.18
(d, 6H, J ) 2.1 Hz), 1.20 (d, 6H, J ) 2.1 Hz), 1.36 (d, 6H, J )
6.8 Hz), 1.45 (d, 6H, J ) 6.8 Hz), 2.04 (s, 3H), 2.07 (s, 3H),
3.06 (septet, 4H, J ) 6.9 Hz), 7.24-7.32 (m, arom. 6H). The
1H NMR spectra matched the authentic sample.29
(1,2,3,4,5-P en ta m eth yl-1′,2′,3′,4′,5′-p en ta p h en yla za fer -
r ocen -2-yl)m eth a n e, (12 a n d 13). The monosubstituted
complex Cp°FeDPM-H (204 mg, 0.316 mmol) was dissolved
in 2.0 mL of THF. To the clear red solution at rt was added
1.6 M n-BuLi (0.22 mL, 0.35 mmol). The resulting deep red
slurry was allowed to stir for 15 min (I).
To a solution of Cp*H (110 mg, 0.807 mmol) in THF (6.5
mL) at rt was added 1.6 M n-BuLi (0.55 mL, 0.88 mmol). The
resulting tan slurry was allowed to stir at -20 °C for 15 min
and transferred via cannula to a rapidly stirring FeCl2 (109
mg, 0.858 mmol) slurry in THF (4.5 mL) at -20 °C. The
[Cp*FeCl] solution stirred at -20 °C for 10 min. The deep red
slurry (I) was transferred via cannula to the lime green
[Cp*FeCl]n solution. The brown solution was allowed to stir
at rt for 15 h. The reaction was quenched by addition of 2,2′-
dipyridyl (50 mg, 0.32 mmol) dissolved in MeOH (1 mL). The
solution was passed through a Celite plug and washed with
hexanes and EtOAc. The dark red solvent was removed,
leaving a dark red solid. Flash chromatography (under N2) was
carried out with the following gradient: 20:80:1 hexanes/
EtOAc/Et3N f 40:60:1 hexanes/EtOAc/Et3N f 60:40:1 hex-
anes/EtOAc/Et3N. Decamethylferrocene eluted first as a yellow
band, followed by an orange-red band for (S,S)- and (R,R)-
Cp*Cp°Fe2DPM and finally an orange-red band for (S,R)- and
(S,S)- a n d (R,R)-Cp °Cp *F e2DP M-P a lla d iu m (m eth yl)
Ch lor id e(II) Com p lex (4). Following procedure E, (PhCN)2-
PdCl2 (181 mg, 0.472 mmol) was dissolved in DCM (4.8 mL).
Tetramethyltin (0.21 mL, 1.54 mmol) was added and stirred
for 2.0 h total (1 h at -30 °C). The unsymmetrical ligand (S,S)-
and (R,R)-Cp°Cp*Fe2DPM (306 mg, 0.365 mmol) dissolved in
3.0 mL of DCM was added to Pd(Me)Cl generated in situ (vide
infra). The resulting red solution slowly warmed to rt (-30
°C f rt over 5 h). The solution was filtered through Celite,
concentrated to ∼ 1 mL, and precipitated with hexanes. The
peach solid was washed with ether (4 × 2 mL) and dried in
vacuo for 30 min, affording the title Pd(Me)Cl complex as a
peach solid (363 mg, 77%). The structure of 4 was fully
assigned by various correlation NMR spectra, and the regio-
chemistry of the Pd-Me was established by nuclear Overhauser

Bisazaferrocene Polymerization Catalysis
Organometallics, Vol. 22, No. 24, 2003 5045
effect (NOE) (see Supporting Information). 1H NMR (500 MHz,
CDCl3): δ 0.92 (s, 3H), 1.83 (s, 15H), 3.40 (d, 1H, J ) 2.1 Hz),
3.77 (s, 2H), 4.09 (s, 1H), 4.64 (s, 1H), 4.74 (s, 1H), 5.32 (s,
1H), 6.43 (s, 1H), 7.12 - 7.17 (m, 20H), 7.18-7.22 (m, 5H).
13C NMR (125 MHz, CDCl3): δ -2.19 (Pd-CH3), 11.17 (cis-Pd-
(Me)-C5(CH3)5), 26.37 (pyrr-CH2-pyrr), 75.37 (cis-Pd(Me)-γ-
pyrr-CH), 76.36 (cis-Pd(Me)-â-pyrr-CH), 77.54 (trans-Pd(Me)-
γ-pyrr-CH), 79.76 (trans-Pd(Me)-â-pyrr-CH), 82.65 (cis-Pd(Me)-
C5(CH3)5), 90.94 (trans-Pd(Me)-C5(Ph)5), 94.42 (trans-Pd(Me)-
R-pyrr-CH), 97.40 (cis-Pd(Me)-δ-pyrr-C), 102.61 (trans-Pd(Me)-
δ-pyrr-C), 127.01 (Cp), 127.16 (Cp), 127.81 (Co), 128.00 (Co),
132.73 (Cp), 132.95 (Cp), 134.23 (C5-Cipso), 135.14 (C5-Cipso).
Combustion (C, H, N): Anal. Calcd for C55H51N2Fe2PdCl: C,
66.49; H, 5.17; N, 2.82. Found: C, 64.47; H, 5.31; N, 2.87.
HRMS (ES/MS, m/z in CH3CN/DCM (1:1 v/v)): Anal. Calcd
for C55H51N2Fe2PdCl: 957.1809 (M - Cl). Found: 957.1827.
TL56 program. The diffraction symmetry was mmm, and the
systematic absences were consistent with the orthorhombic
space group P212121, which was later determined to be correct.
The structure was solved by direct methods and refined on
F by full-matrix least-squares techniques. The analytical
scattering factors57 for neutral atoms were used throughout
the analysis. Hydrogen atoms were included using a riding
model. At convergence, wR2 ) 0.1054 and Goof ) 1.144 for
326 variables refined against 7226 data. As a comparison for
refinement on F, R1 ) 0.0441 for those 6392 data with I >
2.0σ(I). The absolute structure could not be assigned by
inversion of the model or by refinement of the Flack param-
eter.58
Low -Tem p er a tu r e NMR Kin etic Stu d ies. Meth yl Mi-
gr a tor y Ra te. An NMR tube with a screwcap was charged
with 0.01 mmol of Pd(Me)Cl and 0.014 mmol of NaBAF in the
glovebox. The NMR tube was wrapped with Teflon and capped
followed by wrapping with electric tape. For the generation of
the Pd(Me)(H2CdCH2) species, 1.0 equiv of ethylene (0.24 mL)
was added at -78 °C, which is immediately followed by
addition of CD2Cl2 (0.65 mL). The tube was shaken briefly for
15 min, and data points were collected at 30 min intervals to
record the change in methyl peak at δ ) 0.66 ppm with time
at -14 °C.
Eth ylen e Con su m p tion Ra tes. An NMR tube with a
screwcap was charged with 0.01 mmol of Pd(Me)Cl and 0.014
mmol of NaBAF in the glovebox. The NMR tube was wrapped
with Teflon and capped followed by wrapping with electric
tape. For the generation of the Pd(Me)(H2CdCH2) species, 1
equiv of ethylene (0.24 mL) was added at -78 °C, which is
immediately followed by addition of CD2Cl2 (0.65 mL). The
tube was shaken briefly for 15 min, and excess ethylene (10
equiv, 2.4 mL volume) was added. Acquisition collection times
were optimized at 6 s along with 7 scans to give an NMR
spectrum. Data points were collected at 5-30 min intervals
to record the change of free ethylene concentration with time
at various temperatures.
(S,S)- an d (R,R)-Cp*Cp°Fe2DP M-P d(CH2)3COOMe+BAF-
(6). To the solution of DCM (2 mL) was added (-(S,S)- and
(R,R)-Cp°Cp*Fe2DPM-Pd(Me)Cl (110 mg, 0.111 mmol). To the
red-orange suspension was added methyl methacrylate (11.0
µL, 0.122 mmol) followed by addition of NaBAF (98.4 mg, 0.111
mmol). The resulting deep red solution was allowed to stir for
24 h, filtered, and dried in vacuo overnight. An orange-red
1
crystalline solid was obtained (187.2 mg, 89%). H NMR (500
MHz, CDCl3): δ 0.66 (d, 3H, J ) 7.28 Hz), 0.68 (br m), 0.95
(d, J ) 7.09 Hz), 1.32 (br s), 1.55 (m), 1.65-1.76 (m, 15H),
1.83 (s), 1.91 (s), 1.95 (s), 2.01 (br m, 2H), 2.42 (s), 2.48 (m,
2H), 2.7 (m, 2H), 3.2 (m, 1H), 3.47 (s, 1H), 3.61 (s, 3H, OMe),
3.73 (s, 1H), 3.76 (s, 3H OMe1), 3.82 (s, 1H), 3.85 (s, 1H), 4.05
(d, 1H, J ) 2.43 Hz), 4.08 (d, 1H, J ) 2.54 Hz), 4.13 (d, 1H, J
) 6.21 Hz), 4.17 (d, 1H, J ) 5.82 Hz), 4.33 (d, 1H, J ) 1.40
Hz), 4.39 (d, 1H, J ) 1.48 Hz), 4.95 (s, 1H), 4.99 (s, 1H), 5.02
(s, 1H), 5.05 (s, 2H), 5.57 (s, 1H), 5.65 (s, 1H), 5.9 (s, 1H), 7.00-
7.30 (m, 25 H), 7.59 (s, 4H, p-BAF-CH), 7.78 (p-BAF-CH). 13C
NMR (125 MHz, CDCl3): δ 1.24, 10.84 (C5(CH3)5), 10.87 (C5-
(CH3)5), 15.49, 22.80, 23.21, 23.35, 25.30, 25.43, 25.50, 35.51,
45.82, 55.15 (COOMe), 55.24 (COOMe′), 66.06, 75.04, 75.44,
75.80, 76.22, 78.66, 79.52, 79.72, 79.83, 83.56, 83.70, 87.84,
88.44, 88.51, 89.13, 91.68, 92.68, 100.49, 117.66 (Cp-BAF),
124.79 (q, J CF3 ) 271.5 Hz), 127.67, 127.73, 127.80, 129.12 (q,
J Cm ) 31.4 Hz), 132.14, 132.32, 132.60, 133.09, 133.12, 135.03,
161.93 (q, J B-C ) 50.3 Hz, Cipso), 182.92 (COOMe), 191
Gen er a t ion of Cp *2F e2DP M-P d (Me)H2CdCH 2+BAF -
(27). The complexes (S,S)- and (R,R)-Cp*2Fe2DPM-Pd(Me)Cl
(3, 0.01 mmol, 1.0 equiv) and NaBAF (0.014 mmol, 1.4 equiv)
were added to an NMR tube in the glovebox. The NMR tube
was wrapped with Teflon and capped with a screwcap. The
cap was further sealed with electric tape. The tube was cooled
to -78 °C, and ethylene (0.24 mL, 1 equiv) was added, followed
by addition of CD2Cl2 (0.65 mL). The methyl migratory
(COOMe). Combustion (C, H, N): Anal. Calcd for C91H69BF24
-
Fe2N2O2Pd: C, 57.30; H, 3.65; N, 1.47. Found: C, 57.56; H,
3.63; N, 1.53. LRMS (ES/MS, DCM, m/z): Anal. Calcd for
1
insertion rate was followed by H NMR overnight at 259.1 K.
C
91H69BF24Fe2N2O2Pd: 1043.22 (M+ - BAF-). Found: 1043.22
1H NMR (500 MHz, CD2Cl2, 259.1 K): δ 0.66 (s, 3H, Pd-Me),
1.68 (s, 15H), 1.84 (s, 15H), 3.82 (d, 1H, J ) 16.8 Hz), 3.93 (d,
1H, J ) 16.8 Hz), 4.27 (s, 1H), 4.37 (s, 1H), 4.57 (s, 1H), 4.65
(s, 1H), 4.69 (s, 1H), 4.70 (br s, 4H, bound H2CdCH2), 5.27 (s,
1H), 7.60 (s, 4H), 7.77 (s, 8H). Unbound ethylene appears at
5.43 ppm.
(100%).
X-r a y Da ta Collection , Str u ctu r e Solu tion , a n d Re-
fin em en t for (-(S,S)- a n d (R,R)-Cp *2F e2DP M-Nick el (II)
Br om id e (2a ). A maroon crystal of approximate dimensions
0.12 × 0.13 × 0.25 mm was mounted on a glass fiber and
transferred to a Bruker CCD platform diffractometer. The
SMART program package was used to determine the unit-cell
parameters and for data collection (25 s/frame scan time for a
sphere of diffraction data). The raw frame data were processed
using SAINT54 and SADABS55 to yield the reflection data file.
Subsequent calculations were carried out using the SHELX-
The rate data reported are based on one run with an
automated integration of the peaks. The para-hydrogen of BAF
(δ ) 7.60 ppm) was used as an internal standard, and the
following peaks were monitored for disappearance: δ ) 5.43
(unbound ethylene) and 0.66 ppm (Pd-Me).
(56) Sheldrick, G. M. SHELXTL, Version 5.10; Bruker Analytical
X-Ray Systems, Inc.: Madison, WI, 1999.
(57) International Tables for X-Ray Crystallography; Kluwer Aca-
demic Publishers: Dordrecht, 1992; Vol. C.
(54) SMART Software Users Guide, Version 5.1; Bruker Analytical
X-Ray Systems, Inc.: Madison, WI, 1999.
(55) Sheldrick, G. M. SADABS, Version 2.03; Bruker Analytical
X-Ray Systems, Inc.: Madison, WI, 2000.
(58) Flack, H. D. Acta Crystallogr. 1983, A39, 876-881.

5046 Organometallics, Vol. 22, No. 24, 2003
Salo and Guan
(1) F ir st Meth yl Migr a tion . The first-order rate constant
for the first olefin insertion was monitored by the disappear-
ance of the Pd-Me group at 0.66 ppm over time. First methyl
migratory insertion of ethylene by complex 27: k ) 2.49 ×
10-5 s-1, 259.1 K, ∆Gq ) 20.6 kcal/mol.
(2) Su bsequ en t Olefin In ser tion s. The zero-order ethyl-
ene consumption rates were measured by monitoring the
disappearance of the unbound ethylene at 5.43 ppm over time.
Dr. J oseph Ziller for solving the X-ray crystal structure
for complex 2a , Dr. Phillip Dennison for help on NMR
studies, Professors William J . Evans, Larry E. Overman,
Scott D. Rychnovsky, Kenneth J . Shea, and Keith A.
Woerpel for various help on lab instrumentation and
chemicals, and the Evans group for helpful discussions
on organometallic chemistry. Z.G. gratefully acknowl-
edges an NSF CAREER Award, a Beckman Young
Investigator Award, a DuPont Young Professor Award,
and a 3M Non-Tenured Faculty Award.
The subsequent ethylene insertion by 27: k ) 4.18 × 10-5 s-1
,
255.7 K; k ) 1.08 × 10-4 s-1, 264.7 K, ∆Gq ) 20.2 kcal/mol; k
) 4.39 × 10-4 s-1, 273.7 K; k ) 4.18 × 10-5 s-1, 282.7 K; k )
1.31 × 10-3 s-1. An Eyring plot of the rates at different
temperatures gives ∆Hq ) 18.2 kcal/mol, ∆Sq ) - 7.4 eu.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystal struc-
ture data for complex 2a , low-temperature NMR kinetic data,
and NMR spectra (including correlation spectra) for charac-
terization of various complexes and polymers. This material
is available free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. We thank the Petroleum Re-
search Fund administered by the American Chemical
Society, the National Science Foundation, the Army
Research Office, and the University of California
at Irvine for partial financial support. We thank
OM034051R