Isomerization in bent phosphametallocenes: Combining rotational barriers and the intramolecular slip-inversion-slip mechanism to control stereo-conformation

Article abstract of DOI:10.1016/j.jorganchem.2008.04.021

Four new phosphazirconocenes, [(4,5,6-trihydro-1-phosphapentalenyl)₂ZrCl₂] (8), [(4,5,6,7-tetrahydro-1-phosphindolyl)₂ZrCl₂] (9), [(4,5,6,7,8-pentahydro-1-phosphazulenyl)₂ZrCl₂] (10), (2,4-

Full text of DOI:10.1016/j.jorganchem.2008.04.021

Journal of Organometallic Chemistry 693 (2008) 2415–2423
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Isomerization in bent phosphametallocenes: Combining rotational barriers and
the intramolecular slip-inversion-slip mechanism to control stereo-conformation
a
b
William P. Freeman b,1, Yi Joon Ahn b, T. Keith Hollis a,b, , J. Andrew Whitaker , Victor C. Vargas ,
*
Ramel J. Rubio b, Karen D. Alingog b, Eike B. Bauer b,2, Fook S. Tham b
a Department of Chemistry and Biochemistry, 222 Coluter Hall, The University of Mississippi, MS 38677, USA
b Department of Chemistry, Physical Sciences 1, University of California, Riverside, CA 92521, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new phosphazirconocenes, [(4,5,6-trihydro-1-phosphapentalenyl)2ZrCl2] (8), [(4,5,6,7-tetrahydro-
1-phosphindolyl)2ZrCl2] (9), [(4,5,6,7,8-pentahydro-1-phosphazulenyl)2ZrCl2] (10), (2,4-dimethylphosp-
holyl)2ZrCl2 (11), were prepared and characterized. A crystal structure of [(4,5,6,7-tetrahydro-1-phosp-
hindolyl)2ZrCl2] (9), was obtained that revealed disorder (rac and meso isomers in the same crystal)
and demonstrates unambiguously the meso configuration in the bent early transition metal phosphamet-
allocenes. Lacking a spectroscopic probe of the rotational dynamics in phosphametallocenes, propylene
polymerization was chosen to provide a record of the stereoselective insertions and by inference insight
into the phosphametallocene dynamics. Phosphazirconocenes 8–11 were evaluated, and the rac/meso
mixture of [(4,5,6,7-tetrahydro-1-phosphindolyl)2ZrCl2] (9) was found to produce a mixture of isotactic
(iPP) and atactic (aPP) polypropylenes. 13C NMR spectral analysis of the stereo-errors contained in the
iPP fraction indicated enantiomorphic site control as the source of the stereoselectivity. The rotational
dynamics of the g5-phospholyl ligand of the parent phosphazirconocene, [(C4H4P)2ZrCl2], was examined
as a first order surrogate of reasonable computing complexity for the catalytically active species. The
phosphazirconocene was examined using a restricted Hartree–Fock method with a split basis set of 6-
311+G(d,p) for C, H, Cl, P and of LANL2DZ for Zr. The rotational potential energy surface was found to
be unsymmetrical with a maximum barrier of 8.8 kcal molꢀ1, which is about an order of magnitude
greater than that reported for Cp2ZrCl2. The projection of the calculated rotational dynamics onto a
1-phosphatetrahydroindenyl system is illustrated. This model leads to an interpretation of the polymeri-
zation results and the rotational dynamics in phosphametallocenes.
Received 9 January 2008
Received in revised form 11 April 2008
Accepted 11 April 2008
Available online 18 April 2008
Keywords:
Phospholyl ring dynamics
Phosphametallocenes
Phosphorus heterocycles
Propylene polymerization
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
cyclic p-ligands [3,4]. Metallocene dynamics have been the focus of
several groups with recent reports detailing other systems that
Having been engaged in the elucidation and applications of early
transition metal phosphametallocene dynamics [1], we sought to
understand the rotational issues involving the phospholyl ligand.
We report herein the synthesis of four new phosphazirconocenes,
preliminary polymerization experiments, an initial computational
study on the rotational barriers of bent phosphazirconocenes, and
a model for interpreting the results.
undergo face-to-face isomerization [5,6]. We have been engaged
in a detailed study of the dynamics of bent phosphametallocenes
investigating primarily Group 4 (Ti, Zr, Hf) [1,7,8]. In the course
of our studies we have reported the slip-inversion-slip mechanism
of intramolecular rac/meso phosphametallocene isomerization
and activation parameters associated with certain examples
(Scheme 1) [1b,1c].
Numerous studies have been reported describing the rotational
barriers of p-ligands in metal complexes [2], and more recently
there has been interest in these rotational issues for other hetero-
The slip-inversion-slip mechanism is illustrated in Scheme 2
[1b]. In this mechanism the p(g5)-bound heterocyclic ligand slips
to a r(g1)-bound ligand 1 that can then invert at P 2 and ring slip
back to the p(g5)-bound ligand resulting in inversion of the stereo-
chemistry. This process is distinct from the simple rotation around
the metal-centroid bond for isomer interconversion, which is also
present in phosphametallocenes.
Several groups have reported the use of bent phosphametalloc-
enes as catalysts for olefin polymerization [9]. The development of
single-site Ziegler–Natta catalysts for olefin polymerization has
* Corresponding author. Address: Department of Chemistry and Biochemistry,
222 Coluter Hall, The University of Mississippi, MS 38677, USA. Fax: +1 662 915
7301.
E-mail address: hollis@olemiss.edu (T.K. Hollis).
Present address: Nanosys Inc., 2625 Hanover Street, Palo Alto, CA 94304.
Present address: University of Missouri, St. Louis, Department of Chemistry and
1
2
Biochemistry, One University Boulevard, St. Louis, MO 63121.
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.04.021

2416
W.P. Freeman et al. / Journal of Organometallic Chemistry 693 (2008) 2415–2423
with the equilibrium position dictate the microstructure of the
Ph
R
polymer (Scheme 3, Keq, k1, kꢀ1, k2, kꢀ2 vs. kpM, kp (or kpm, kpr)).
P
Ph
P
P
P
Cl
Cl
solvent
solvent
Ph
If a catalyst system can be devised that will accomplish the
requirements outline in Scheme 3 a significant advance will be
made.
Zr
Cl
Cl
Cl
Cl
Ph
Zr
Zr
P
P
Ph
Ph
R
S
meso
2. Results and discussion
THF = rapid isomerization (sec)
CHCl3, CH2Cl2, Tol = slow isomerization (days)
2.1. Synthesis and characterization of phospholes and
phosphazirconocenes
Scheme 1. Isomerization of a phosphazirconocene.
The phospholes were synthesized through standard procedures
either from commercially-available dienes or easily synthesized
dienes (Eq. (1)). Cycloalkanones (3, cyclopentanone 3a, cyclohexa-
none 3b, and cycloheptanone 3c) were reacted with vinyl Grignard
[17]. The allylic alcohols obtained were dehydrated with KHSO4
yielding the desired dienes 4a–c on a gram-scale [18].
Ph
Ph
P
(S)
P
(R)
(S)
Ph
(R)
ZrCl2
P
P
ZrCl2
Ph
P
ZrCl2
(S)
P
ZrCl2
P
P
Ph
(S)
Ph
(S)
O
(S)
1. CH2CHMgBr
Ph
PhP
Ph
1. PhPBr2
2. 2-picoline
meso
CH2
CH2
1
2
2. KHSO4
CH2
n
n
n
Scheme 2. Slip-inversion-slip mechanism of phosphametallocene interconversion.
4
5
3
a, n = 1, 13%, 3.6 g
b, n = 2, 19%, 4.6 g
c, n = 3, 5%, 0.4 g
been a world-wide, industrial and academic effort [10,11]. A major
innovation in this area was the disclosure of ansa-metallocenes as
catalysts for the production of isotactic polypropylene (iPP) [11].
The introduction of the ‘‘oscillating catalyst” concept sparked con-
siderable work in the area of elastomeric polypropylene (ePP) syn-
thesis (Scheme 3a) [12]. Extensive efforts have been made to
manipulate the structures of metallocenes to control the cyclopen-
tadienyl (Cp) rotation rates (k1, kꢀ1) and thus control the ratio of
the stereoblocks [15].
ð1Þ
Phenyl dibromophosphine was prepared according to the liter-
ature procedure and employed in the McCormack reaction with
each diene to prepare the initial phosphenium heterocycle [9d].
Double dehydrohalogenation of the phosphonium salts with 2-pic-
oline provided the desired phospholes 5a–c (Eq. (1)) [19]. Commer-
cially obtained 2-methyl-1,3-pentadiene 6 was also subjected to
these conditions and produced the desired phosphole 7 (Eq. (2)).
Detailed characterization by high field 13C NMR spectroscopy of
the ePP produced by ‘‘oscillating catalysts” has revealed a micro-
structure that differs from that predicted by the Waymouth
hypothesis (Scheme 3a) [13]. Busico et al., interpreted the micro-
structure as a rac to rac interconversion of the catalyst conforma-
tions or a chain-end controlled mechanism, thus avoiding the
meso conformation and presented a new theory for ePP synthesis
(Scheme 3b). While the detailed mechanism of these catalysts is
still being debated, achieving a catalyst that fulfills the Waymouth
hypothesis will produce a highly-beneficial new class of polypro-
pylene catalysts [14]. As a thermoplastic elastomer, designer ePP
would offer many benefits due to its unique properties. Numerous
studies have been reported on the synthesis of ePP [15,16]. The key
feature of ‘‘oscillating catalysts” is control of the rate of catalyst
isomerization vs. monomer insertion. These relative rates along
Me
1. PhPBr2
10%, 1.7g
2. 2-picoline
PhP
ð2Þ
Me
6
7
Standard procedures were employed to prepare the phosphazir-
conocenes [9b,31]. The phosphole was reacted with Li to cleave the
P–Ph bond yielding PhLi and the phospholyl anion. PhLi was
quenched with t-BuCl, and ZrCl4(THF)2 was added as illustrated
in eq 3. Phosphazirconocenes 8–11 were prepared as outlined in
eq 3 and are illustrated below along with the yield of each com-
pound. Phosphazirconocenes 8–11 were obtained as mixtures of
rac and meso isomers as determined by 31P NMR spectroscopy in
a) Waymouth hypothesis for ePP synthesis.
b) BusicotheoryofWaymouth ePP synthesis-
chain-end control.
Ph
Cl
Ph
Cl
Ph
Ph
Cl
Ph
Cl
k1
k2
Cl
Ph
M
M
Cl
Cl
Ph
M
M
Cl
Ph
k-1
k-2
rac
meso
MAO
M
P
m
P
r
M
kp
kp
MAO kp
MAO kp
MAO
n
n
n
n
n= small number
iPP
aPP
"iPP"
"iPP"
Scheme 3. ‘‘Oscillating catalysts” for polypropylene synthesis.

W.P. Freeman et al. / Journal of Organometallic Chemistry 693 (2008) 2415–2423
2417
Table 1
the following ratios: 8 – ꢁ46:54, 9 – initially isolated product:
Crystal data and structure refinement for [(P6)2ZrCl2] (9)
ꢁ46:54; crystalline: ꢁ25:75, 10 – ꢁ50:50, 11 – ꢁ9:91 to ꢁ20:80.
Phosphametallocene 8, [(P5)2ZrCl2] (P5 = phosphapentalenyl),
was obtained in insufficient quantities for elemental analysis, but
the exact mass was found at 405.9137 for a calculated mass of
405.9151. Elemental analyses of phosphametallocenes 9,
[(P6)2ZrCl2] (P6 = tetrahydrophosphaindenyl), and 11 – the di-
methyl derivative – were consistent with residual ether present
as observed in the 1H NMR spectrum of the compound. Phosph-
ametallocene 10, [(P7)2ZrCl2] (P7 = pentahydrophosphazulenyl),
had an elemental composition consistent with that expected.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C16H20Cl2P2Zr
436.38
218(2)
0.71073
Monoclinic
P2(1)/n
7.4159(7)
24.722(3)
19.0722(17)
90
b (Å)
c (Å)
a(°)
b(°)
c (°)
92.647(2)
90
3492.8(6)
8
1.660
1.109
Rx
Rx
1. Li
2. t-BuLi
Volume (Å3)
Z
P
P
P
Ph
ZrCl2
ð3Þ
3. ZrCl4(THF)2
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
Rx
)
1760
Me
ZrCl2
Me
Crystal size (mm)
H range for data collection (°)
Index ranges
0.36 ꢂ 0.24 ꢂ 0.05
1.96–28.28
P
P
P
P
P
ZrCl2
P
P
P
ꢀ9 6 h 6 9, ꢀ32 6 k 6 32, ꢀ25 6 l 6 25
47689
ZrCl2
ZrCl2
Reflections collected
Independent reflections [Rint
Completeness to theta = 28.28°
Absorption correction
Maximum and minimum transmission
Refinement method
]
8661 [0.0411]
99.9%
Me
Me
28%
11
9%
16%
17%
10
SADABS
8
9
0.9466 and 0.6909
Full-matrix least-squares on F2
8661/1446/618
Fractional crystallization of bent phosphametallocenes has been
Data/restraints/parameters
Goodness-of-fit on F2
1.078
accomplished in several cases [1,7]. All attempts to fractionally
crystallize 9 have produced crystals containing a mixture of rac
and meso isomers [20]. An ORTEP plot of the molecular structure
in two different perspectives is presented in Fig. 1 along with key
metric data for the complex. Although it precluded independent
evaluation of the isomers in polymerization, these crystals provide
the first reported unambiguous proof of the meso isomer in bent
phosphametallocenes. Previous structural reports contained only
the rac isomer. An examination of the racemic isomer depicted in
Fig. 1b reveals a staggered array of the phosphazirconocene sub-
stituents sterically shields one chlorine (i.e. one site of olefin coor-
dination) more than the other as required for stereoselective
polymerization [21]. The details of refinement are included in
Table 1.
Final R indices [I > 2r(I)]
R1 = 0.0291, wR2 = 0.0715
R1 = 0.0410, wR2 = 0.0800
0.537 and ꢀ0.426
R indices (all data)
Largest difference peak and hole (e Åꢀ3
)
izations were performed employing MAO [Al]/[Zr] 2000:1 at
680 psi of propylene [9]. The polymers from the polymerizations
employing precatalysts 8, 10, and 11 were entirely soluble in
diethyl ether (see supporting information). In contrast, the poly-
mer obtained from precatalyst 9 contained an ether-insoluble
(EI) fraction (32%) and an ether-soluble (ES) fraction (68%). GPC
of the EI-polymer revealed a Mw/Mn ratio of 1.5. 13C NMR
(125 MHz) analysis of the EI fraction revealed an isotactic polymer
with 69% mmmm pentads and 91% m dyads (Fig. 2) [22]. The ob-
served stereo-errors are consistent with the isotactic polymer hav-
ing been produced by enantiomorphic site control since the mmmr,
mmrr, and mrrm pentads have an ꢁ2:2:1 ratio [11b,23]. This obser-
vation established the critical fact that the catalyst is responsible
for stereocontrol. While the stereoselectivity was modest, it is rare
for an unbridged, sterically-uncongested metallocene to have such
high levels of stereo-regularity [24,25]. Only complex 9,
[(P6)2ZrCl2], produced significant quantities of EI-polymer [26].
An explanation for the observed stereo-regularity is presented
below.
2.2. Polymerization of propylene with phosphazirconocenes
Phosphazirconocenes 8–11 were used as precatalysts for the
polymerization experiments. The initially isolated mixtures of dia-
stereomers were evaluated in the polymerization reactions. A sim-
ple Fischer–PorterÒ pressure bottle was employed to condense
propylene and conduct the polymerization experiments. Polymer-
Cl1
Cl2d
P2
P1
Cl2
Cl1d
Zr1
Zr1
P2d
Cl2
Cl1
P1
P2
(a) disordered rac/meso
(b) racemic
Fig. 1. (a) ORTEP plot at 50% thermal ellipsoids (hydrogens and centroids omitted
for clarity) of one of two disordered molecules in the asymmetric unit cell of ph-
osphazirconocene 9. The disordered site occupancy ratio is 72/28. (b) View perp-
endicular to Cl–Zr–Cl plane of the racemic isomer. Selected structural bond
distances (Å) and angles (°): Zr1–Ctr1, Ctr2 = 2.270, 2.289, Zr1–Cl1, Cl2 = 2.415(3),
2.443(2), P1–C1 = 1.767(3), P2–C9 = 1.753(5), C1–C2 = 1.384(4), C9–C10 = 1.399(5),
Ctr1–Zr1–Ctr2 = 133.55, Cl1–Zr1–Cl2 = 95.9(3), P–Ctr–Zr–Cl = 164.1, 176.4.
21.6 21.2 20.8
20.2
19.4
Fig. 2. 13C NMR(125 MHz) of the Me-pentad region of the EI polymer from catalysis
with [(P6)2ZrCl2] (9).

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W.P. Freeman et al. / Journal of Organometallic Chemistry 693 (2008) 2415–2423
2.3. Phosphametallocene rotational issues: computational study of
(C4H4P)2ZrCl2
monomer insertions in propylene polymerization [13c]. While
each rotamer may be accessible under ambient conditions, the
Boltzmann distribution predicts the global minimum to be favored
35:1 at 25 °C and ꢁ50:1 at 0 °C vs. the next lowest-energy local
minimum. It is well established in X-ray crystal structures that
the preferred location of the phosphorous in bent M(IV) phospha-
metallocenes is the narrow (closed) side of the wedge as illustrated
in D and 8–11, [1,31] and as may be seen for the structure illus-
trated in Fig. 1 (vide supra). Ring substituents will increase the bar-
rier to rotation and will enhance the preference for the global
minimum conformation.
The difference between the barriers in phosphametallocenes
and cyclopentadienyl complexes may be seen to arise from the
symmetry breaking that occurs upon incorporating the P-atom
and the presence of the lone pair on P. The calculated global and
local maximum energy conformations A and C (Fig. 3) occur when
the phosphorous and chlorine are eclipsing. The repulsions be-
tween the P lone pair and the Cl lone pairs account for the energy
increase in phosphametallocenes. Of course, the C–H bond of a
cyclopentadienyl ligand will have a significantly reduced repul-
The rotational barrier in a bent phosphazirconocene pertinent
to those in the catalysis reported was evaluated computationally.
Geometry optimization and conformational analysis were per-
formed using GAUSSIAN03 at the restricted Hartree–Fock level with
a split basis set of 6-311+G(d,p) for C, H, Cl, P and of LANL2DZ
for Zr [27]. The initial structure was prepared with the Gaussview
graphical interface in the conformation illustrated in Fig. 3, D,
which is found in most bent phosphametallocene crystal struc-
tures. An initial full minimization of the structure was completed
at 3-21G* level and used as input for the higher level calculations.
This initial conformation was eventually determined to be the glo-
bal minimum energy structure. This global minimum conforma-
tion was chosen to evaluate the rotational potential. One of the
phospholyl rings was rotated 10° and a single-point energy calcu-
lation was performed. The results of these computations are pre-
sented graphically in Fig. 3.
The global minimum-energy conformation is illustrated in Fig. 3
(molecule D) along with a plot of the energy vs. rotation angle (a).
The presence of two P-atoms produced an unsymmetrical energy
surface for rotation of a phospholyl ligand around the metal-cen-
troid axis. The global minimum occurred when the dihedral angle
P–Ctr–Zr–Cl angle is ꢁ180° with each P-atom opposite a different
Zr–Cl bond (D). The next lowest energy minimum has both P-
atoms with a dihedral angle of ꢁ180° from the same Cl (E) and is
2.1 kcal/mol higher in energy. The other local minimum (Fig. 3,
D) was 4.5 kcal/mol above the global minimum and occurred when
the P-atom bisected the Cl–Zr–Cl angle. The calculations revealed a
significant barrier to rotation for [(C4H4P)2ZrCl2] (Fig. 3). The max-
imum barrier to rotation of 8.8 kcal/mol occurs when the P eclipses
the Zr–Cl bond (a = 0). The predicted barrier for [(C4H4P)2ZrCl2] is
an order of magnitude greater than the 1.01 kcal/mol reported
for [Cp2ZrCl2] [28]. It is also higher than the value reported by
Waymouth for indenyl ligands [29], and it is comparable to the
neomenthyl-substituted indenyls reported by Erker [30]. Further-
more, the calculated barrier to rotation is on the same scale as
sion. The global energy minima represented by structure
D
(Fig. 3) may be explained by dipole minimization. In conformation
D, each P-lone pair vector, and, therefore, local dipole is ‘‘anti-par-
allel” to a Zr–Cl bond dipole vector thus producing a dipole mini-
mum for the molecule.
Phosphametallocene complexes were examined at low temper-
ature. Unsurprisingly, none displayed spectral characteristics that
revealed the dynamic nature found in the calculations. At the low-
est temperatures observable only one signal for the rapidly inter-
changing conformations was observed by 31P NMR spectroscopy.
It was reasoned that the polymerization studies (vide supra) would
provide indirect insight into the conformational issues calculated.
Propylene polymerizations contain a record of the stereoselectivity
of the catalyst [32]. Thus for reactions with enantiomorphic site
control the polymer reveals the structure of the catalyst. Therefore,
it was reasoned that the phosphametallocene with selectivity in
the polymerization provides an indirect record of the conforma-
tional structure of the catalyst during polymerization.
10
P
Zr
P
9
P
Cl
Cl
Zr
A
P
8
7
6
5
4
3
2
1
0
Cl
Cl
α
C
P
P
Zr
Cl
Cl
P
Zr
P
E
P
P
Zr
Cl
Cl
Cl
Cl
D
α
B
0
50
100
150
200
250
300
350
Dihedral angle (α)
Fig. 3. Energy vs dihedral angle plot for [(C4H4P)2ZrCl2] calculated at the RHF level with a split basis set with Gaussian03. The basis set for C, H, P, Cl was 6-311+G(d,p), and the
basis set for Zr was LANL2DZ. The conformation with the P-atom of the top ring eclipsing one of the Zr–Cl bonds is defined as a = 0 and rotation toward the other Cl
(counterclockwise) is defined as the positive direction.

W.P. Freeman et al. / Journal of Organometallic Chemistry 693 (2008) 2415–2423
2419
P
P
P
P
π-facial
P
P
isomerization
rotation
rotation
rotation
rotation
Cl
M
Cl
Cl
M
P
Cl
Cl
M
P
Cl
Cl
M
Cl
Cl
M
Cl
Cl
M
Cl
P
P
P
P
rac
meso-like
rac-
9
meso-9
rac-like
meso
stability:
R3
<<
<
>
> >
R2
R1
M1
M2
M3
MAO
MAO
aPP
iPP
Scheme 4. Rotational and configurational isomers of a chiral bent phosphametallocene.
2.4. Phosphametallocene rotational issues: implications for a
substituted phosphametallocene
duced the iPP, similar to that reported by Ewen for ansa-metallo-
cenes (Scheme 5) [23]. This is consistent with known
isomerization rates for phosphametallocenes in non-coordinating
solvents [1]. The greater proportion of ES-polymer (68%) is attrib-
uted to the meso-phosphametallocene 9 in the initially isolated
compound (meso:rac::54:46). These observations are consistent
with modest rotational stability and configurational stability of
the phosphametallocene on the time scale of monomer insertion
(Scheme 5).
The conformational analysis of the pre-catalysts, which is a
tractable calculation, provides insight into the dynamics of the ac-
tive form of the catalyst, a much more difficult computational is-
sue. The bent phosphametallocenes have an unsymmetrical
energy surface for rotation through 360° unlike Cp-based systems.
The consequences of this surface are illustrated for a substituted
phosphametallocene relevant to the current study in Scheme 4
[3]. The racemic isomer (R1) has two principal conformers of inter-
est at higher energy. There is a ‘‘meso-like” conformation (R2) with
one P bisecting the Cl–Zr–Cl angle and a much higher energy ‘‘rac”
conformation (R3) with both P atoms bisecting the Cl–Zr–Cl angle.
Likewise, the meso isomer (M1) has two higher energy conforma-
tions - a ‘‘rac-like” conformation M2 and a much higher energy
‘‘meso” conformation (M3) with both P atoms bisecting the
Cl–Zr–Cl angle. Thus R1 and M1 are expected to be the major con-
formation present in solution. It is worth noting that in the present
situation the barriers to interconversion of the isomers are ex-
pected to be greater than the barriers to monomer insertion and
polymer propagation, and thus Curtin–Hammett conditions are
not obtained [33].
These observations provide a preliminary model for the evalua-
tion of bent phosphametallocenes for polypropylene synthesis. The
calculated barrier and preliminary polymerization experiments re-
ported herein are consistent with the expectations of restricted
conformational rotation in certain bent phosphametallocenes and
a strong preference for the rac-conformation R1 in the chiral con-
figuration and for the meso conformation M1 in the achiral config-
uration. Simple p-ligand rotation does not produce degenerate
energy states as in Cp based systems.
3. Conclusions
In conclusion, the introduction of a phosphorous atom into a Cp
ring provides a new stereocontrol element for ligand rotation and
catalyst development. Several new phosphazirconocenes were
evaluated as catalysts for the polymerization of propylene catalysis
revealing a precatalyst, [(P6)2ZrCl2] (9), that produced EI-PP, which
upon 13C NMR spectral evaluation was isotactic with stereo-errors
indicative of enantiomorphic site control. The synthesis of iPP by
enantiomorphic site control was consistent with configurational
(rac/meso) stability and modest rotational stability of the phospha-
zirconocene on the time scale of multiple monomer insertions.
While configurational stability was expected based on known
isomerization rates [1,7], rotational stability has not been demon-
strated previously. A model incorporating configurational and rota-
tional issues is advanced to explain the observations. The
relationship between the phosphametallocene rac/meso isomeriza-
tion and that of the ‘‘oscillating catalysts” is notable. The phosph-
ametallocene ‘‘oscillates” (rac to meso) by
a fundamentally
different mechanism, which provides alternative methods of con-
trolling the rate (k1 vs. kꢀ1). These results are consistent with the
rac isomer 9 producing the iPP and the meso isomer 9 producing
the aPP. The combined rotational barriers and slip-inversion-slip
mechanism suggest an alternate route to achieving the ‘‘oscillating
catalyst hypothesis” for elastomeric polypropylene (ePP) synthesis.
These results suggest that phosphatitanocenes, which have signif-
icantly reduced inversion barriers near 11 kcal molꢀ1 may be
excellent candidates as catalysts for ePP synthesis [1b].
An Occam’s razor explanation of the observed polymer fractions
is that the meso isomer produced the aPP and the rac isomer pro-
π-facial
isomerization
P
P
Cl
Zr
Cl
Cl
Zr
Cl
P
P
4. Experimental
rac-9
meso-9
4.1. General considerations
MAO
MAO
All experiments were performed with Schlenk techniques under
an atmosphere of Ar or in an Ar filled glovebox. Toluene, THF,
CH2Cl2 and Et2O were dried by passing through activated alumina
[34]. Pentane was freshly distilled from Na. MAO (StremÒ),
2-methyl-1,3-pentadiene (AldrichÒ), 2-methylpyridine (AldrichÒ),
t-BuCl (AldrichÒ), MgSO4 (EMScienceÒ), HCL (1.0 M EMScienceÒ)
iPP
aPP
Scheme 5. Rationalization of polymer fractions. Polymerization from depicted
conformations was faster than slip-inversion-slip isomerization and rotational
interconversion.

2420
W.P. Freeman et al. / Journal of Organometallic Chemistry 693 (2008) 2415–2423
and ZrCl4 (StremÒ) were used as received. Propylene (MathesonÒ)
was passed through an O2 filter before condensation in the
polymerization experiments. Phenyl dibromophosphine [35], 1-vi-
nyl-1-cyclopentene [17], 1-vinyl-1-cyclohexene [17] and 1-vinyl-
1-cycloheptene [17] were prepared according to the literature
procedures. The 31P NMR spectra were calibrated with an external
standard 85% H3PO4 solution and recorded on VarianÒ Inova 300
and Inova 500 MHz instruments.
washed with degassed 1.0 M HCl (1 ꢂ 100 mL), washed with de-
gassed water (2 ꢂ 100 mL), dried over anhydrous magnesium sul-
fate and filtered. After removal of volatiles the viscous solution
was distilled trap to trap. The product was distilled again with a
short path distillation apparatus to produce a clear slightly yellow
oil (0.422 g, 1.85 mmol, 5%) with boiling point of 85 - 95 °C at
0.1 torr. 1H NMR (CDCl3, 300 MHz): d 7.33 (m, 5H), 6.78 (dd, 1H,
JHH = 7.2 Hz, JPH = 14.1 Hz), 6.59 (dd, 1H, JHH = 7.2 Hz, JPH = 37.5 Hz),
2.63 (br, 2H), 2.48 (br, 2H), 1.80 (br, 2H), 1.63 (br, 2H), 1.52 (br,
2H); 13C {1H} NMR (CDCl3, 75.5 MHz): d 150.9 (d, JPC = 13.6 Hz),
148.7 (d, JPC = 14.8 Hz), 147.1 (s), 143.7 (d, JPC = 6.7 Hz), 133.9 (d,
4.2. Preparation of phospholes
Phospholes were prepared according to variations on the litera-
ture methods [9d,19].
JPC = 18.7 Hz), 130.9 (d, JPC = 4.7 Hz), 129.4 (s), 128.6 (d, JPC = 8.0
Hz), 32.5 (s), 32.4 (s), 28.8 (d, JPC = 21.4 Hz), 28.4 (d, JPC = 5.3 Hz),
27.6 (s); 31P {1H} NMR (C6D6, 121.5 MHz): d 19 (s).
4.2.1. 1-Phenyl-4,5,6-trihydro-1-phosphapentalene (5a)
Phenyl dibromophosphine (38.0 g, 20.2 mL, 142 mmol) and
1-vinyl-1-cyclopentene (26.7 g, 284 mmol) were combined and
the flask was placed in the dark. The solution became cloudy after
15 min and after 1 h was opaque. After 2 weeks all volatile compo-
nents were removed by vacuum transfer. The residue was dis-
solved in CH2Cl2 (120 mL) and added dropwise over 1.5 h to a
solution of 2-methyl pyridine (26.4 g, 28.0 mL, 284 mmol) in tolu-
ene (200 mL) while the reaction flask was cooled in a water bath.
The organic layer was washed with degassed 1.0 M HCl (1 ꢂ
100 mL), washed with degassed water (2 ꢂ 100 mL), dried over
anhydrous magnesium sulfate and filtered. After removal of vola-
tiles the viscous solution was distilled trap to trap. The product
was distilled again with a short path distillation apparatus to pro-
duce a clear, colorless oil (3.58 g, 17.9 mmol, 13%) with boiling
point of 76–78 °C at 0.1 torr. 1H NMR (CDCl3, 300 MHz): d 7.42–
7.31 (m, 5H), 6.96 (dd, 1H, JHH = 7.5 Hz, JPH = 22.5 Hz), 6.88 (s,
1H), 2.77–2.65 (m, 4H), 2.41–2.32 (m, 2H); 13C {1H} NMR (CDCl3,
4.2.4. 2,4-Dimethyl-1-phenyl-phosphole (7)
Phenyl dibromophosphine (11.7 g, 43.7 mmol) and 2-methyl-
1,3-pentadiene (7.18 g, 87.4 mmol) were combined and the flask
placed in the dark. After 2 weeks all volatiles were removed under
reduced pressure. CH2Cl2 (50 mL) was added and the solution was
transferred drop-wise over 1.5 h to a solution of 2-methyl pyridine
(8.14 g, 8.60 mL, 87.4 mmol) in toluene (100 mL) while the reac-
tion flask was cooled in a water bath. The organic layer was
washed with degassed HCl (1.0 M, 50 mL), washed with degassed
water (2 ꢂ 50 mL), dried over anhydrous magnesium sulfate and
filtered. After removal of volatiles, the viscous liquid was vacuum
transferred under reduced pressure. Distillation yielded a pale
green oil (1.67 g, 8.88 mmol, 10%), bp = 75–85 °C, 0.1 torr). 1H
NMR (CDCl3, 300 MHz): d 7.32 (m, 5H), 6.46 (dt, 1H, JHH = 1.5 Hz,
JPH = 14.4 Hz), 6.23 (dt, 1H, JHH = 1.5 Hz, JPH = 40.2 Hz), 2.16 (dd,
3H, JHH = 1.2 Hz, JPH = 3.6 Hz), 2.09 (dd, 3H, JHH = 1.2 Hz, JPH
=
11.1 Hz); 13C {1H} NMR (CDCl3, 75.5 MHz): d 150.8, 149.6 (d,
JPC = 8.7 Hz), 136.5 (d, JPC = 10.6 Hz), 133.5 (d, JPC = 20.1 Hz), 132.5
(d, JPC = 9.7 Hz), 129.3, 128.8 (d, JPC = 8.1 Hz), 125.4, 19.3, 15.7 (d,
JPC = 20.0 Hz); 31P {1H} NMR (CDCl3, 121.5 MHz): d 13.3.
75.5 MHz): d 156.3 (d, JPC = 13.4 Hz), 148.4 (s), 138.0 (d, JPC
=
6.7 Hz), 134.1 (d, JPC = 5.3 Hz), 133.2 (d, JPC = 18.7 Hz), 131.8 (d,
JPC = 8.0 Hz), 128.9 (s), 128.7 (d, JPC = 6.7 Hz), 30.7 (s), 30.6 (d,
JPC = 6.6 Hz), 28.8 (d, JPC = 5.3 Hz); 31P {1H} NMR (C6D6, 121.5
MHz): d ꢀ6.9 (s).
4.3. Preparation of phospholyl complexes [31,9d]
4.2.2. 1-Phenyl-4,5,6,7-tetrahydro-1-phosphindole (5b) [36]
4.3.1. rac- and meso-Bis(4,5,6-trihydro-1-phosphapentalenyl)
zirconium dichloride (8)
Phenyl dibromophosphine (30.1 g, 16.0 mL, 112 mmol) and
1-vinyl-1-cyclohexene (24.3 g, 225 mmol) were combined and
the flask placed in the dark. The solution became cloudy after
15 min and after 1 h was opaque. After 2 weeks all volatile compo-
nents were removed. CH2Cl2 (125 mL) was added and the solution
was transferred to a solution of 2-methyl pyridine (26.1 g, 27.6 mL,
280 mmol) in 200 mL of toluene drop-wise over 1.5 h while the
reaction flask was cooled in a water bath. The organic layer was
washed with degassed 1.0 M HCl (1 ꢂ 100 mL) washed with de-
gassed water (2 ꢂ 100 mL) dried over anhydrous magnesium sul-
fate and filtered. After removal of volatiles the viscous solution
was distilled trap to trap. The product was distilled again with a
short path distillation apparatus to produce a clear colorless oil
(4.59 g, 21.4 mmol, 19%) with boiling point of 85–95 °C at 0.1 torr.
1H NMR (C6D6, 300 MHz): d 7.40–7.35 (m, 2 H), 7.16–7.02 (m, 3H),
6.69 (dd, 1H, JPH = 25.5 Hz, JHH = 7.2 Hz), 6.61 (s, 1H), 2.40–1.92 (m,
4H), 1.47–1.38 (m, 4H); 31P {1H} NMR (C6D6, 121.5 MHz): d 10.0 (s).
1-Phenyl-4,5,6-trihydro-1-phosphapentalene(1.87 g, 9.35 mmol)
was dissolved in THF (40 mL) and Li (0.324 g, 46.8 mmol) was added.
The clear, light-yellow–green reaction solution was stirred for 1.5 h
and turned opaque brown. The solution was filtered and t-BuCl
(4.33 g, 5.09 mL, 46.8 mmol) was added and the reaction solution
heated at 55 °C for 1 h. During this time the reaction solution
turned from opaque brown to clear, light brown. The volatiles were
removed and the orange–brown residue was dissolved in Et2O
(60 mL) and added over 15–20 min to ZrCl4(THF)2 (0.831 g,
2.20 mmol) [37] as a slurry in toluene (15 mL) cooled in a dry
ice/ethanol bath. The slurry turned from light-yellow to purple.
After 15 min the cooling bath was removed and the solution was
allowed to warm to room temperature while stirring overnight.
After stirring for 12–14 h at room temperature the solution was
cloudy light-yellow with some white precipitate. The volatiles
were removed by vacuum transfer and the slightly yellow residue
was extracted with Et2O (3 ꢂ 40 mL), the solution was filtered (to
remove the extracted portion) and the volatiles were removed by
vacuum transfer. The residue was recrystallized from Et2O/hex-
ane/(Me3Si)2O at ꢀ35 °C yielding 8 as a yellow solid (0.081 g,
4.2.3. 4,5,6,7,8-Pentahydro-1-phenyl-1-phosphazulene (5c)
Phenyl dibromophosphine (11.3 g, 6.0 mL, 42.1 mmol) and 1-vi-
nyl-1-cycloheptene (10.3 g, 84.3 mmol) were combined and the
flask placed in the dark. The solution became cloudy after 15 min
and after 1 h was opaque. After 2 weeks the volatile components
were removed. CH2Cl2 (60 mL) was added and the solution was
0.199 mmol, 9%). 1H NMR (C6D6, 300 MHz):
d 6.99 (ps dt,
J = 32.7 Hz, J = 12.0 Hz), 6.83 (ps dt, J = 31.8 Hz, J = 9.3 Hz), 6.30–
6.24 (m), 3.30-2.89 (m, 4H), 2.54-2.16 (m, 6H), 1.95–1.84 (m,
2H); 13C {1H} NMR (CDCl3, 125.774 MHz): 167.6 (d, J = 59.1 Hz),
166.0 (ps dt, J = 59.1, J = 29.0 Hz), 157.5 (s), 157.1 (s), 142.7 (dt,
J = 59.1 Hz, J = 27.0 Hz), 140.4 (ps dt, J = 57.1 Hz, J = 19.7 Hz),
added to
a solution of 2-methylpyridine (7.85 g, 8.33 mL,
84.3 mmol) in 100 mL of toluene drop-wise over 1.5 h while the
reaction flask was cooled in a water bath. The organic layer was

W.P. Freeman et al. / Journal of Organometallic Chemistry 693 (2008) 2415–2423
2421
125.2 (s), 124.3 (d, J = 4.2 Hz), 32.5 (t, J = 13.4 Hz), 32.2 (t,
J = 11.3 Hz), 30.2, 30.0, 29.1, 28.9; 31P {1H} NMR (C6D6,
121.5 MHz): d 67.0 (s, 46%), 65.3 (s, 54%). MS (LSIMS): Anal. Calc.
for C14H16Cl2P2Zr: 405.9151. Found: 405.9137. Insufficient sample
for elemental analysis.
(CDCl3, 125.774 MHz): d 165.4–164.4 (m), 148.8, 148.2, 136.3,
134.9, 132.5 (psuedo dt, J = 54.0 Hz, J = 33.2 Hz), 131.7 (psuedo
dt, J = 50.8 Hz, J = 19.7 Hz), 32.9–32.4 (m), 28.4, 28.3, 27.4; 31P
{1H} NMR (C6D6, 121.5 MHz): d 96.4 (s, 50%), 93.1 (s, 50%). Anal.
Calc. for C18H24Cl2P2Zr: C, 46.54; H, 5.22. Found: C, 46.46; H, 5.28%.
4.3.2. rac- and meso-Bis(4,5,6,7-tetrahydro-1-phosphindolyl)
zirconium dichloride (9)
4.3.4. rac- and meso-Bis(2,4-dimethylphospholyl) zirconium
dichloride (11)
1-Phenyl-4,5,6,7-tetrahydro-1-phosphindole (1.05 g, 4.40 mmol)
was dissolved in THF (40 mL) and Li (0.119 g, 17.2 mmol) was
added. The clear, light-yellow–green reaction solution was stirred
for 1.5 h and turned opaque brown. The solution was filtered to re-
move lithium. To this solution was added t-BuCl (0.952 g, 1.10 mL,
10.3 mmol), and it was heated at 55 °C for 1 h until the reaction
turned from opaque brown to clear, light- brown. The volatiles
were removed by vacuum transfer. The orange–brown residue
was dissolved in Et2O (60 mL) and added over 20 min to
ZrCl4(THF)2 (0.831 g, 2.20 mmol) [37] slurried in toluene (15 mL)
cooled to ꢀ78 °C (dry ice/ethanol). The slurry became red–orange.
After 15 min the cooling bath was removed, and the solution was
allowed to warm to room temperature while stirring overnight.
The solution was cloudy, light-yellow with a white precipitate.
The reaction was concentrated, and the slightly yellow residue
was extracted with Et2O (3 ꢂ 40 mL), which was filtered and con-
centrated. The residue was recrystallized in two crops from Et2O/
hexane/(Me3Si)2O at ꢀ35 °C yielding 9 as a yellow solid (0.305 g,
0.703 mmol, 16%). X-ray quality crystals were grown from Et2O
at ꢀ35 °C. 1H NMR (C6D6, 300 MHz): d 1H 6.97 (ps dt, J = 32.7 Hz,
J = 10.2 Hz, 2 H), 6.53 (ps dt, J = 31.2, J = 15.9 Hz, 2H), 6.28–6.25
(m, 4H), 3.40–3.06 (m, 8H), 2.58–2.48 (m, 4H), 2.39–2.29 (m,
4H), 1.72–1.62 (m, 8H), 1.43–1.30 (m, 8H); 13C {1H} NMR (C6D6,
125.774 MHz): 160.8 (d, J = 56.0 Hz), 159.0 (dt, J = 56.1 Hz,
J = 35.2 Hz), 145.6 (s), 144.9 (s), 134.3 (dt, J = 55.0 Hz, J = 31.1 Hz),
133.3 (dd, J = 51.8 Hz, J = 66.4 Hz), 131.9 (s), 130.3 (d, J = 3.1 Hz),
27.8 (t, J = 20.8 Hz), 27.5 (ps t, J = 18.7 Hz), 27.1 (s), 27.0 (s),
22.88 (s), 22.86 (s), 22.0 (s), 21.9 (s); 31P {1H} NMR (C6D6,
121.5 MHz): d 85.4 (s, 46%), 84.4 (s, 54%). MS (LSIMS): Anal. Calc.
for C16H20Cl2P2Zr: 433.9464. Found: 433.9476. Anal. Calc. for
[C16H20Cl2P2Zr ꢃ 0.33 C4H10O]: C, 45.17; H, 5.10. Found: C, 45.50;
H, 4.80%.
1-Phenyl-2,4-dimethyl-phosphole (1.01 g, 5.31 mmol) was dis-
solved in THF (40 mL) and Li (0.129 g, 18.6 mmol) was added.
The clear, light-yellow–green reaction solution was stirred for
1.5 h and turned opaque brown. The solution was filtered and to
the filtrate t-BuCl (1.48 g, 1.73 mL, 15.9 mmol) was added. The
reaction was heated at 55 °C for 30 min. During this time the reac-
tion solution turned from opaque brown to clear, light-brown. The
volatiles were removed. The orange–brown residue was dissolved
in Et2O (60 mL) and was added over 15–20 min to ZrCl4(THF)2
(1.00 g, 2.65 mmol) [37] as a slurry in toluene (15 mL) cooled to
ꢀ78 °C in a dry ice/ethanol bath. The toluene slurry turned from
light-yellow to purple. After 15 min the cooling bath was removed
and the solution was allowed to warm to room temperature while
stirring overnight. After stirring for 12–14 h at room temperature
the solution was cloudy, light green–yellow with a white precipi-
tate. The volatiles were removed by vacuum transfer, and the
slightly yellow residue was extracted with Et2O (3 ꢂ 30 mL), fil-
tered, and the volatiles removed by vacuum transfer. The residue
was recrystallized from Et2O/hexane/(Me3Si)2O at ꢀ35 °C yielding
11 as a yellow solid (0.283 g, 0.742 mmol, 28%). 1H NMR (CDCl3,
300 MHz): d 7.08–7.01 (m, 2H), 6.97–6.88 (m, 2H), 2.47 (d, 6H,
JPH = 9.6 Hz), 2.32 (s, 6H); 13C {1H} NMR (CDCl3, 75.5 MHz): d
164.3 (d, J = 54.6 Hz), 144.7, 136.6, 135.9, 133.5 (dd, J = 7.7 Hz,
J = 59.5 Hz), 19.7, 19.1 (psuedo t, J = 44.4 Hz); 31P {1H} NMR (CDCl3,
121.5 MHz): d 92.3 (s, 9%), 86.8 (s, 91%). MS (LSIMS): Anal. Calc. for
C12H16P2Cl2Zr: 381.9151. Found: 381.9146. Anal. Calc. for
[C12H16Cl2P2Zr ꢃ 0.25 C4H10O]: C, 38.76; H, 4.63. Found: C, 38.67;
H, 4.50%.
4.4. X-ray structure determination for compound 9
A yellow fragment of a prism (0.36 ꢂ 0.24 ꢂ 0.05 mm3) was
used for the single crystal X-ray diffraction study of C16H20Cl2P2Zr.
The crystal was coated with paratone oil and mounted on to a glass
fiber. X-ray intensity data were collected at 218(2) K on a Bruker
SMART 1000 [38] platform-CCD X-ray diffractometer system (Mo-
radiation, k = 0.71073 Å, 50 kV/45 mA power). The CCD detector
was placed at a distance of 4.1770 cm from the crystal. A total of
2424 frames were collected for a hemisphere of reflections (with
scan width of 0.3° in x and / angles of 0°, 90°, 180°, and 270° for
every 606, 606, 606, and 606 frames, respectively, 30 s/frame expo-
sure time). The frames were integrated using the Bruker SAINTPLUS
software package [39] and using a narrow-frame integration algo-
rithm. Based on a monoclinic crystal system, the integrated frames
yielded a total of 47689 reflections at a maximum 2h angle of
56.56° (0.75 Å resolution), of which 8661 were independent reflec-
tions (Rint = 0.0411, Rsig = 0.0266, redundancy = 5.5, complete-
ness = 99.9%) and 7160 (82.7%) reflections were greater than
2r(I). The unit cell parameters were, a = 7.4159(7) Å, b =
24.722(3) Å, c = 19.0722(17) Å, b = 92.647(2)°, V = 3492.8(6) Å3,
Z = 8, calculated density Dc = 1.109 g/cm3. Absorption corrections
were applied (absorption coefficient l = 1.109 mmꢀ1; max/min
transmission = 0.9466/0.6909) to the raw intensity data using the
SADABS program in the SAINTPLUS software [39]. The Bruker SHELXTL
(Version 6.10) software package [40] was used for phase determi-
nation and structure refinement. The distribution of intensities
(E2 ꢀ 1 = 0.957) and systematic absent reflections indicated one
possible space group; P2(1)/n. The space group P2(1)/n was later
4.3.3. rac- and meso-Bis(4,5,6,7,8-pentahydro-1-phosphazulenyl)
zirconium dichloride (10)
4,5,6,7,8-Pentahydro-1-phenyl-1-phosphazulene (0.422 g, 1.85
mmol) was dissolved in THF (40 mL) and Li (0.064 g, 9.2 mmol)
was added. The clear, light-yellow–green reaction solution was
stirred for 1.5 h and turned opaque brown. The solution was fil-
tered to remove the lithium. To this solution was added t-BuCl
(0.858 g, 1.01 mL, 9.24 mmol) and the reaction was heated at
55 °C for 1 h. The reaction solution turned from opaque brown to
clear, light-brown. The reaction was concentrated. The orange–
brown residue was dissolved in Et2O (20 mL) and added over
15–20 min to ZrCl4(THF)2 (0.349 g, 0.925 mmol) [37] as a slurry
in toluene (15 mL) cooled in a dry ice/ethanol bath. The toluene
slurry turned from light-yellow to purple. After 15 min the bath
was removed and the solution was allowed to warm to room tem-
perature while stirring overnight. After stirring for 12–14 h at
room temperature the solution was cloudy light-yellow with some
white precipitate. The volatiles were removed, and the slightly yel-
low residue was extracted with Et2O (3 ꢂ 40 mL). The solution was
filtered and the volatiles removed. The residue was recrystallized
from Et2O/hexane/(Me3Si)2O at ꢀ35 °C yielding 10 as a yellow solid
(0.063 g, 0.136 mmol, 17%). 1H NMR (C6D6, 300 MHz): d 6.83 (psu-
edo dt, J = 31.8 Hz, J = 9.6 Hz, 2 H), 6.59–6.57 (m, 2H), 6.55–6.52 (m,
2H), 6.40 (J = 29.7 Hz, J = 11.4 Hz, 2H), 3.05–2.63 (m, 8H), 1.72–1.57
(m, 6H), 1.39–1.24 (m, 2H), 1.14–0.94 (m, 4H); 13C {1H} NMR

2422
W.P. Freeman et al. / Journal of Organometallic Chemistry 693 (2008) 2415–2423
determined to be correct. Direct methods of phase determination
followed by two Fourier cycles of refinement led to an electron
density map from which most of the non-hydrogen atoms were
identified in the asymmetry unit of the unit cell. With subsequent
isotropic refinement, all of the non-hydrogen atoms were identi-
fied. There were two molecules of C16H20Cl2P2Zr present in the
asymmetry unit of the unit cell. One of the two C8H10P ligands
and the two Cl-atoms coordinated to Zr1 was disordered (disor-
dered site occupancy ratio was 72%/28%). Both the C16H20P ligands
coordinated to Zr10 were disordered (disordered site occupancy
ratio was 73%/27%).
as the Mark–Houwink coefficients. The numerical analyses were
performed using Waters ‘‘Millennium” software.
DSC melting points were determined on commercial DSC
instruments and are reported as the second melting point. The
polymer sample was heated to 200.0 °C for 10 min and then cooled
from 200 °C to 25 °C at 10 °C/min. The sample was held at 25 °C for
10 min. The second melt was then recorded as the sample was
heated from 25 °C to 200 °C at a rate of 10 °C/min. The peak tem-
perature was recorded as the second melting point.
Acknowledgements
Atomic coordinates, isotropic and anisotropic displacement
parameters of all the non-hydrogen atoms were refined by means
of a full matrix least-squares procedure on F2. The H-atoms were
included in the refinement in calculated positions riding on the
atoms to which they were attached. The refinement converged at
R1 = 0.0291, wR2 = 0.0715, with intensity, I > 2r(I). The largest
peak/hole in the final difference map was 0.537/ꢀ0.426 e/Å3.
This work was supported in part by NSF Grant CHE-0317089.
Acknowledgement is made to the donors of the American Chemical
Society Petroleum Research Foundation, the University of California,
Cancer Research Coordinating Committee, and the University of Cal-
ifornia Energy Institute and The University of Mississippi for partial
support of this work. Y.J.A. and R.J.R. acknowledge support from the
Department of Education, GAANN program. The authors thank Dr.
Richard Kondrat and Mr. Ron New for mass spectral analyses and
Dr. Dan Borchardt for assistance with NMR analyses. We gratefully
acknowledge Dr. Terry Burkhardt of ExxonMobil for performing
the GPC and DSC analyses of the polymers.
4.5. Polymerization
4.5.1. Representative example
A Fischer–PorterÒ pressure bottle was put under vacuum
(ꢁ0.1 torr) and back flushed with Ar twice before a final evacuation
and filled with propylene. The bottom of the glass bottle was
cooled with dry ice/ethanol and 1–2 mL of propylene was con-
densed as a liquid. The solid co-catalyst methylaluminoxane
(MAO) (fwt 58.02 for [MeAlO]n, 0.290 g, 5.0 mmol) was dissolved
in toluene (3.5 mL) to produce a clear, straw-yellow solution. The
catalyst (phospholyl)2ZrCl2 (0.0025 mmol) was added and the
solution stirred and its color turned to clear light-green–yellow.
The precatalyst/co-catalyst mixture was aged 10 min and was in-
jected into the propylene-containing Fischer–Porter bottle.
Once the precatalyst/co-catalyst mixture was added, the dry ice
bath was removed and rapid stirring was maintained. The pressure
increased and was maintained between 75 and 80 psi in the reac-
tion apparatus. At the desired time the polymerization was
stopped by release of the excess propylene and addition of 20 mL
of quench solution (3:1 mixture of methanol and 3 N HCl). Toluene
(10 mL) was added, the solution stirred in the reaction flask and
poured into a separatory funnel. After phase separation of the or-
ganic phase the aqueous/methanol phase was extracted with tolu-
ene (3 ꢂ 10 mL). The organic phases were combined and filtered
through a coarse porosity frit. The volatiles were removed and
the crude polypropylene was dried under high vacuum (0.1 torr)
for at least 8 h.
Appendix A. Supplementary material
CCDC 252898 contains the supplementary crystallographic data
for 9. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.jorganchem.
2008.04.021.
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[20] Crystal data for 9:
7.4159(7), b = 24.722(3), c = 19.0722(17) Å, V = 3492.8(6) Å3, Z = 8, d =
1.660 g cmꢀ3
T = 218(2) K, R = 0.0410, wR2 = 0.0800, GOF = 1.078. CCDC
C16H20Cl2P2Zr, Mw = 436.38, monoclinic, P2(1)/n, a =
,
252898 (1) contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data Centre, 12,
Union Road, Cambridge CB2 1EK, UK; fax: (+44) 1223-336-033; or
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