Synthesis, structure, and reactivity of C2-symmetric bis(phospholyl)zirconium and bis(phospholyl)hafnium complexes

Article abstract of DOI:10.1021/om010256t

Several C₂-symmetric bis(phospholyl) adducts of group 4 metals, including the first example of an η⁵-phospholyl complex of hafnium, have been synthesized and structurally characterized. These complexes undergo rac/meso isomerization in a process that is accelerated by Lewis bases. A C₂-symmetric bis(phospholyl)zirconium dichloride binds as a bidentate ligand to Mo(CO)₄. In the presence of methylalumoxane, bis(phospholyl)zirconium complexes serve as active catalysts for ethylene-hexene copolymerization reactions.

Full text of DOI:10.1021/om010256t

Organometallics 2001, 20, 3453-3458
3453
Syn th esis, Str u ctu r e, a n d Rea ctivity of C2-Sym m etr ic
Bis(p h osp h olyl)zir con iu m a n d Bis(p h osp h olyl)h a fn iu m
Com p lexes
Ste´phane Bellemin-Laponnaz,† Michael M.-C. Lo,†,1 Thomas H. Peterson,‡
J erry M. Allen,‡ and Gregory C. Fu*,†
Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, and Dow Chemical Company, Chemical Sciences Division,
South Charleston, West Virginia 25303
Received March 28, 2001
Several C2-symmetric bis(phospholyl) adducts of group 4 metals, including the first example
of an η5-phospholyl complex of hafnium, have been synthesized and structurally character-
ized. These complexes undergo rac/meso isomerization in a process that is accelerated by
Lewis bases. A C2-symmetric bis(phospholyl)zirconium dichloride binds as a bidentate ligand
to Mo(CO)4. In the presence of methylalumoxane, bis(phospholyl)zirconium complexes serve
as active catalysts for ethylene-hexene copolymerization reactions.
A few years ago, we initiated a program directed at
the development of applications of planar-chiral het-
erocycles as ligands for enantioselective transition
metal-catalyzed processes.2,3 As part of this effort, in
1998 we reported the synthesis and resolution of C2-
symmetric 1,1′-diphosphaferrocene 1, a potentially use-
ful chiral bidentate ligand.4,5 Of course, the essentially
parallel relationship between the two phospholyl rings
of complex 1 (6° deviation from coplanarity) is not the
ideal geometry for bidentate complexation to a transi-
tion metal.6 On the other hand, we felt that the bent
geometry of a bis(phospholyl) complex of a group 4 metal
(2) might be better predisposed for chelation.7 In 1999,
we therefore initiated an investigation of the chemistry
of such complexes, the results of which we describe in
this article.
methyl-substituted phospholyl complexes, because of the
ready accessibility of precursor phospholide 4 by the
procedure of Mathey.8 Treatment of ZrCl4 with 4
furnishes racemic bis(phospholyl)zirconium complex 5
in 39% yield after recrystallization from pentane (eq 1).9
The same procedure provides the corresponding C2-
symmetric bis(phospholyl)hafnium adduct (6) in 25%
yield after recrystallization from pentane/Et2O; to the
best of our knowledge, complex 6 is the first example of
an η5-phospholyl complex of hafnium. Attempts to apply
this route to the synthesis of the corresponding titanium
adduct instead afforded 3,3′,4,4′-tetramethyl-2,2′-diphen-
ylbiphosphole, which was fully characterized, including
an X-ray structure determination.10
Resu lts a n d Discu ssion
Syn th esis of Bis(ph osph olyl) Com plexes of Gr ou p
4 Met a ls. We chose to synthesize 2-phenyl-3,4-di-
† Massachusetts Institute of Technology.
‡ Dow Chemical Company.
(1) Correspondence concerning the X-ray crystal structures should
be directed to M.M.-C.L.
We have obtained an X-ray crystal structure of
zirconium complex rac-5, which is illustrated in Figure
(2) For ligands based on phosphorus heterocycles, see: (a) Shintani,
R.; Lo, M. M.-C.; Fu, G. C. Org. Lett. 2000, 2, 3695-3697. (b) Tanaka,
K.; Qiao, S.; Tobisu, M.; Lo, M. M.-C.; Fu, G. C. J . Am. Chem. Soc.
2000, 122, 9870-9871. (c) Qiao, S.; Fu, G. C. J . Org. Chem. 1998, 63,
4168-4169.
(3) For ligands based on nitrogen heterocycles, see: (a) Lo, M. M.-
C.; Fu, G. C. Tetrahedron 2001, 57, 2621-2634. (b) Rios, R.; Liang, J .;
Lo, M. M.-C.; Fu, G. C. Chem. Commun. 2000, 377-378. (c) Lo, M.
M.-C.; Fu, G. C. J . Am. Chem. Soc. 1998, 120, 10270-10271. (d) Dosa,
P. I.; Ruble, J . C.; Fu, G. C. J . Org. Chem. 1997, 62, 444-445.
(4) Qiao, S.; Hoic, D. A.; Fu, G. C. Organometallics 1998, 17, 773-
774.
(6) Chelation by
a 1,1′-diphosphaferrocene is rare. (a) For an
example of complexation of the phosphorus atoms to two different
metals, see: de Lauzon, G.; Deschamps, B.; Mathey, F. Nouv. J . Chim.
1980, 4, 683-685. (b) For an example of complexation to the same
metal, see: Atwood, D. A.; Cowley, A. H.; Dennis, S. M. Inorg. Chem.
1993, 32, 1527-1528.
(7) For a pioneering study with an achiral bis(phospholyl)zirconium
complex, see: Nief, F.; Mathey, F.; Ricard, L. J . Organomet. Chem.
1990, 384, 271-278.
(8) Holand, S.; J eanjean, M.; Mathey, F. Angew. Chem., Int. Ed.
Engl. 1997, 36, 98-100. Phosphole 3 can be synthesized in one step
from commercially available PhPCl2 and 2,3-dimethyl-1,3-butadiene:
Breque, A.; Mathey, F.; Savignac, P. Synthesis 1981, 983-985.
(5) For an overview of phospholyl chemistry, see: Mathey, F. Coord.
Chem. Rev. 1994, 137, 1-52.
10.1021/om010256t CCC: $20.00 © 2001 American Chemical Society
Publication on Web 06/30/2001

3454 Organometallics, Vol. 20, No. 16, 2001
Bellemin-Laponnaz et al.
F igu r e 1. ORTEP representation of rac-5, with thermal
ellipsoids drawn at the 35% probability level.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for r a c-5
F igu r e 3. Percentage of the meso isomer, as a function of
time, for bis(phospholyl) complexes 5 and 6 (benzene-d6 at
room temperature; c ) 0.010 mol/L).
Zr(1)-Cl(1)
Zr(1)-P(1)
Zr(1)-C(1)
Zr(1)-C(2)
Zr(1)-C(3)
Zr(1)-C(4)
P(1)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-P(1)
2.423(2)
2.728(2)
2.592(5)
2.655(5)
2.618(5)
2.550(5)
1.780(5)
1.421(7)
1.415(7)
1.402(8)
1.752(6)
Cl(1)-Zr(1)-Cl(2)
C(4)-P(1)-C(1)
P(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-P(1)
95.32(7)
88.8(3)
112.5(4)
112.1(5)
111.9(5)
114.4(4)
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for r a c-6
Hf(1)-Cl(1)
Hf(1)-P(1)
Hf(1)-C(1)
Hf(1)-C(2)
Hf(1)-C(3)
Hf(1)-C(4)
P(1)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-P(1)
2.409(3)
Cl(1)-Hf(1)-Cl(2)
C(4)-P(1)-C(1)
P(1)-C(1)-C(2)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-P(1)
94.08(10)
87.9(5)
112.9(9)
113.2(10)
110.4(10)
115.6(8)
2.690(3)
2.669(10)
2.697(10)
2.592(10)
2.508(9)
1.806(11)
1.382(15)
1.450(15)
1.387(14)
1.767(12)
The angle between the phospholyl planes is larger for
the hafnium adduct than for the zirconium complex (Hf,
57.5°; Zr, 46.8°).
Isom er iza tion of Bis(p h osp h olyl) Com p lexes of
Zir con iu m a n d Ha fn iu m . In the course of character-
izing zirconium complex rac-5, we discovered that, in
solution, diastereomerically pure rac-5 converts to a
mixture of racemic and meso isomers. A subsequent
study established that rac-5 equilibrates to a 1.9:1.0 rac/
meso ratio with a t1/2 of 12 h in benzene at room
temperature (Figure 3). This isomerization process
occurs much more rapidly with the hafnium complex,
rac-6, which reaches a 1.5:1.0 equilibrium mixture of
rac/meso with a t1/2 of 10 min (Figure 3).
We have determined that the isomerization of zirco-
nium complex rac-5 proceeds at a significantly faster
rate in THF than in benzene (t1/2 [THF] ) 30 min; t1/2
[benzene] ) 12 h).12 The addition of 1 equiv of PMe3
also markedly accelerates the equilibration process (in
benzene, t1/2 , 10 min). Polar, Lewis-basic species
probably facilitate isomerization by stabilizing ring-
slipped intermediates (e.g., see 7).13,14
F igu r e 2. ORTEP representation of rac-6, with thermal
ellipsoids drawn at the 35% probability level.
1 (for selected bond lengths and bond angles, see Table
1). The dihedral angle between the phospholyl planes
is 46.7°. The overall structure is similar to Cp2ZrCl2
(dihedral angle between Cp’s: 53.4°), with a centroid-
Zr-centroid angle of 135.4° (vs 129.2° for Cp2ZrCl2) and
a Cl-Zr-Cl angle of 95.3° (vs 97.0° for Cp2ZrCl2).11 The
phosphorus atoms of rac-5 are located at the back of
the wedge formed by the two rings, in good positions
for bidentate complexation to a metal.
The crystal structure of C2-symmetric hafnium com-
plex 6 (Figure 2; Table 2) reveals comparable values for
the centroid-metal-centroid angle (Hf, 132.1°; Zr,
135.4°) and the Cl-metal-Cl angle (Hf, 94.1°; Zr, 95.3°).
(9) For a crystal structure of Cp2ZrCl2, see: Repo, T.; Klinga, M.;
Mutikainen, I.; Su, Y.; Leskela¨, M.; Polamo, M. Acta Chem. Scand.
1996, 50, 1116-1120.
(10) For the first example of a bis(phospholyl) complex of a group 4
element, see: Meunier, P.; Gautheron, B. J . Organomet. Chem. 1980,
193, C13-C16. See also: Nief, F.; Mathey, F.; Ricard, L.; Robert, F.
Organometallics 1988, 7, 921-926.
(11) Bis(phospholyl)titanium complexes have been synthesized
through reaction of TiCl4 with a stannylated phosphole: Nief F.; Ricard
L.; Mathey F. Organometallics 1989, 8, 1473-1477.
(12) The rates of isomerization in DME and in acetonitrile are also
faster than in benzene.

C2-Symmetric Bis(phospholyl)zirconium Complexes
Organometallics, Vol. 20, No. 16, 2001 3455
olefin polymerization catalysts.18 We have synthesized
dimethylzirconocene derivative rac-9 in good yield
through the reaction of rac-5 with MeMgBr (85%; eq
3).19 The dimethyl derivative of bimetallic complex rac-8
can be generated by an analogous procedure (34%; eq
4).
F igu r e 4. ORTEP representation of rac-8, with thermal
ellipsoids drawn at the 35% probability level.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for r a c-8
Zr-Cl(1)
Zr-Cl(2)
Mo-P(1)
Mo-P(2)
Mo-C(25)
Mo-C(26)
Mo-C(27)
Mo-C(28)
2.423(2)
2.413(2)
2.501(2)
2.512(2)
2.053(7)
1.984(7)
1.987(7)
2.049(7)
Cl(2)-Zr-Cl(1)
P(1)-Mo-P(2)
P(1)-Mo-C(25)
P(1)-Mo-C(26)
P(1)-Mo-C(27)
P(1)-Mo-C(28)
96.15(7)
78.70(5)
91.5(2)
94.3(2)
176.8(2)
94.5(2)
Eth ylen e-Hexen e Copolym er ization s.18,20 We have
examined the activity of the rac form of complexes 5, 6,
8, 9, and 10 as ethylene-hexene copolymerization
catalyst precursors (hexane slurry in a 1 L stirred
autoclave reactor operated under a constant ethylene
pressure of 85 psi and maintained at 75 °C). The
polymerization experiments were conducted with me-
thylalumoxane (with 5, 6, 8, 9, and 10) and triphenyl-
carbenium tetrakis(pentafluorophenyl)borate (with 9) as
cocatalysts. Of the five catalyst precursors tested, only
rac-5 and rac-9 display polymerization activity.21
Polymerization data for rac-5 are presented in Table
4. The polymerization activities range between 5000 and
42 000 g PE (mmol Zr)-1 (h)-1 (100 psi C2H4)-1, with a
strong dependence on the Al/Zr ratio (entries 1-3) and
on the reaction temperature (entries 3-5). Using the
designations suggested by Gibson, rac-5 exhibits “very
high” activity for ethylene polymerization.18 The appar-
ent maximum in polymerization activity observed be-
tween 65 and 85 °C appears to be consistent with the
kinetic profile for ethylene consumption. Under poly-
merization conditions at 75 °C, the catalyst is short-
lived, with a half-life of ∼4-6 min. At higher temper-
ature, the rate of propagation and the rate of catalyst
decomposition both increase.
Zir con iu m Com p lex r a c-5 a s a Bid en ta te Liga n d .
Treatment of (CO)4Mo(nbd)15 with rac-5 in toluene at
75 °C for 5 h furnishes molybdenum complex 8 in nearly
quantitative yield (97%; eq 2).16 Although the rac and
the meso isomers of 5 are interconverting under these
conditions, only one diastereomeric complex is isolated.17
An X-ray crystallographic study established that it is
the C2-symmetric rac isomer of the metallocene that is
bound to molybdenum, in a bidentate mode (Figure 4;
Table 3). The geometry around molybdenum is pseudo-
octahedral.
Syn th esis of th e Cor r esp on d in g Dia lk yl Com -
p lexes. Alkylzirconium complexes have found wide-
spread application in organometallic chemistry, e.g., as
Analysis of the polymer samples by GPC, IR, and 13C
NMR reveals number average molecular weight (Mn)
values between 40 000 and 94 000, with polydispersity
indices (PDI) in the range 2.71-3.32, indicating normal
single-site behavior. The Mn shows a strong dependence
on the polymerization temperature, increasing with
decreasing temperature (entries 3-5), but it appears to
(18) For a recent review of the search for new olefin polymerization
catalysts, see: Britovsek G. J . P.; Gibson V. C.; Wass D. F. Angew.
Chem., Int. Ed. 1999, 38, 428-447.
(19) After 1 day in benzene-d6 at room temperature, rac-9 isomerizes
to an equilibrium mixture (1:1) of rac- and meso-9.
(13) For a review of ring slippage, see: O’Connor, J . M.; Casey, C.
P. Chem. Rev. 1987, 87, 307-318.
(14) For a study of the low barrier to inversion in phospholes, see:
Egan, W.; Tang, R.; Zon, G.; Mislow, K. J . Am. Chem. Soc. 1970, 92,
1442-1444.
(20) For previous studies of bis(phospholyl)zirconium complexes as
catalyts for Ziegler-Natta polymerization, see: (a) J aniak, C.; Lange,
K. C. H.; Versteeg, U.; Lentz, D.; Budzelaar, P. H. M. Chem. Ber. 1996,
129, 1517-1529. (b) de Boer, E. J . M.; Gilmore, I. J .; Korndorffer, F.
M.; Horton, A. D.; van der Linden, A.; Royan, B. W.; Ruisch, B. J .;
Schoon, L.; Shaw, R. W. J . Mol. Catal. A 1998, 128, 155-165. (c)
J aniak, C.; Versteeg, U.; Lange, K. C. H.; Weimann, R.; Hahn, E. J .
Organomet. Chem. 1995, 501, 219-234.
(15) Bennett, M. A.; Pratt, L.; Wilkinson, G. J . Chem. Soc. 1961,
2037-2044.
(16) For the first synthesis of a metal-bridged ansa-metallocene that
involves a bis(phospholyl)zirconium complex, see: Nief, F.; Mathey,
F.; Ricard, L. J . Organomet. Chem. 1990, 384, 271-278.
(17) Use of a mixture of rac- and meso-5 also furnishes rac-8 as a
single diastereomer in almost quantitative yield.
(21) We speculate that complexes 8 and 10 may decompose under
the polymerization conditions.

3456 Organometallics, Vol. 20, No. 16, 2001
Bellemin-Laponnaz et al.
Ta ble 4. Effect of Tem p er a tu r e a n d Al/Zr on th e P olym er iza tion P er for m a n ce of r a c-5
temp
(°C)
g PE (mmol Zr)-1 (h)-1
(100 psi C2H4)-1
BBF
(per 1000 C)
entry
Al/Zr
Mn
Mw
PDI
1
2
3
4
5
75
75
75
65
85
250
500
1000
1000
1000
5365
9682
41 964
23 647
13 624
51846
40050
49261
93773
41335
166 458
133 209
159 448
254 547
127 310
3.21
3.32
3.23
2.71
3.10
2.0
1.5
3.0
2.7
2.0
1
are referenced to an external standard (85% H3PO4, δ 0). H
data are reported as follows: chemical shift (in ppm), multi-
plicity (s ) singlet, d ) doublet, t ) triplet, q ) quartet, and
m ) multiplet), integration. All 13C and 31P spectra were
determined with complete proton decoupling. Infrared spectra
were obtained on a Perkin-Elmer Series 1600 FT-IR spectro-
photometer. High-resolution mass spectra were recorded on a
Finnegan MAT System 8200 spectrometer. All manipulations
were performed in a nitrogen-filled glovebox or with standard
Schlenk procedures under argon.
be insensitive to changes in the Al/Zr ratio (entries 1-3).
Interestingly, endgroup analysis of the samples by 13C
NMR reveals no detectable levels of unsaturation in the
polymer, suggesting that chain transfer to aluminum
(either the alumoxane or the triisobutylaluminum scav-
enger) is the dominant mechanism for chain termina-
tion. 1-Hexene comonomer incorporation into the poly-
mer is relatively low, with butyl branch frequencies
(BBF) in the range 1.5-3.0 per 1000 carbon atoms.
Changes in the polymerization temperature and alu-
moxane level have no significant effect on comonomer
incorporation.
3,3′,4,4′-Tet r a m et h yl-2,2′-d ip h en yl-1,1′-d ip h osp h a zir -
con ocen e Dich lor id e (r a c-5). A mixture of 3,4-dimethyl-1-
phenylphosphole (3)22 (0.66 g, 3.5 mmol) and t-BuOK (0.40 g,
4.2 mmol) in THF (3.5 mL) was heated (140 °C) with stirring
in a closed Schlenk tube for 12 h. The resulting yellow solution
was evaporated to dryness, and the yellow solid was then
dissolved in THF (4.5 mL) and added to a precooled (-30 °C)
suspension of ZrCl4 (0.37 g, 1.6 mmol) in THF (9 mL), resulting
in a deep green mixture. After 30 min, the reaction mixture,
which had turned orange, was evaporated to dryness and then
extracted with Et2O (30 mL). The Et2O extracts were filtered
through a glass frit and evaporated to dryness. The residue
was taken up in pentane (60 mL) and filtered through a bed
of Celite. The eluant was evaporated to a volume of 30-35
mL; crystallization furnished 150 mg of orange crystals that
were suitable for single-crystal X-ray diffraction. A second crop
(180 mg) was obtained after concentrating the filtrate to 25
mL. Total yield: 0.33 g (39%).
1H NMR (300 MHz, C6D6): 7.37 (d, 4H, J ) 7.2 Hz), 7.16-
7.05 (m, 6H), 6.25 (apparent dd, 2H, J ) 12.9 Hz, J ) 24.9
Hz), 2.22 (s, 6H), 2.06 (s, 6H). 13C (75 MHz, CD2Cl2): 153.7,
145.2, 144.4, 137.2 (apparent t, J C-P ) 9.1 Hz), 134.6 (m), 130.4
(apparent t, J C-P ) 5.2 Hz), 128.6, 128.4, 18.9, 16.2. 31P (122
MHz, C6D6): 83.3. IR (NaCl, Nujol): 3050, 3021, 2921, 2854,
1681, 1596, 1574, 1494, 1443, 1413, 1357, 1317, 1233, 1182,
1101, 1081, 1020, 1004, 986, 946, 920, 856, 842, 821, 758, 701,
663, 630 cm-1. HRMS calcd for C24H24Cl2P2Zr 534.9761, found
534.9770. Anal. Calcd: C, 53.73; H, 4.51. Found: C, 53.76; H,
4.49.
The dimethyl derivative rac-9 also exhibits high
polymerization activity when methylalumoxane is used
as a cocatalyst. At 75 °C with an Al/metal ratio of 1000,
activities in the range 38 000-41 000 g PE (mmol Zr)-1
(h)-1 (100 psi C2H4)-1 are observed. No polymerization
occurs when the reaction is carried out at 95 °C (see
above). As might be expected, the properties of the
polymers produced by rac-9 are essentially identical to
those furnished by rac-5. When the polymerization is
carried out in the absence of 1-hexene comonomer, the
catalytic activity decreases, as expected, to 15 000 g PE
(mmol Zr)-1 (h)-1 (100 psi C2H4)-1. Polymerization also
occurs when triphenylcarbenium tetrakis(pentafluo-
rophenyl)borate is employed as a cocatalyst; in two
separate experiments, activities were measured to be
4300 and 5200 g PE (mmol Zr)-1 (h)-1 (100 psi C2H4)-1
.
Su m m a r y
We have synthesized and structurally characterized
new bis(phospholyl) adducts of group 4 metals, including
the first example of an η5-phospholyl complex of hafni-
um. In addition, we have determined that these met-
allocenes undergo rac/meso isomerization in a process
that is accelerated by Lewis bases. Furthermore, we
have shown that a bis(phospholyl)zirconium complex
can serve as an effective bidentate ligand for Mo(CO)4
and that the C2-symmetric, rather than the meso,
isomer binds preferentially. Finally, we have converted
bis(phospholyl)zirconium dichloride complexes into the
corresponding dimethyl adducts through reaction with
MeMgBr, and we have established that, in the presence
of MAO, both bis(phospholyl)zirconium dichloride and
dimethyl complexes are active catalysts for ethylene-
hexene copolymerizations.
Data for the meso isomer: 1H NMR (300 MHz, C6D6): 7.53
(d, 4H, J ) 6.9 Hz), 7.16-7.05 (m, 6H), 6.67 (apparent dt, 2H,
J ) 39.0 Hz), 2.16 (s, 6H), 2.00 (s, 6H). 31P (122 MHz, C6D6):
85.3.
3,3′,4,4′-Tetr a m eth yl-2,2′-d ip h en yl-1,1′-d ip h osp h a h a f-
n ocen e Dich lor id e (r a c-6). A mixture of 3,4-dimethyl-1-
phenylphosphole (3)22 (0.66 g, 3.5 mmol) and t-BuOK (0.40 g,
4.2 mmol) in THF (3.5 mL) was heated (140 °C) with stirring
in a closed Schlenk tube for 12 h. The resulting yellow solution
was evaporated to dryness, and the yellow solid was then
dissolved in THF (4.5 mL) and added to a precooled (-30 °C)
suspension of HfCl4 (0.53 g, 1.65 mmol) in THF (9 mL),
resulting in a deep green mixture. After 1 h, the reaction
mixture was evaporated to dryness and then extracted with
Et2O (30 mL). The Et2O extracts were filtered through a glass
frit and evaporated to dryness. The residue was taken up in
pentane (80 mL) and filtered through a bed of Celite. The
eluant was evaporated to a volume of 40 mL, and Et2O (20
mL) was added; crystallization furnished 250 mg (25%) of
yellow crystals that were suitable for single-crystal X-ray
diffraction.
Exp er im en ta l Section
Gen er a l P r oced u r es. Solvents were distilled from the
indicated drying agents: CH2Cl2 (CaH2), Et2O (Na), THF (Na),
benzene (Na), and pentane (NaH). All other reagents were
used as received. 1H, 13C, and 31P nuclear magnetic resonance
spectra were recorded on a Varian XL-300 spectrometer at
ambient temperature. 1H NMR spectra are referenced to
solvent: 7.16 (C6D6), 7.27 (CDCl3), 5.32 (CD2Cl2). 13C NMR
spectra are referenced to solvent: 54.00 (CD2Cl2). 31P spectra
(22) Breque, A.; Mathey, F.; Savignac, P. Synthesis 1981, 983-985.

C2-Symmetric Bis(phospholyl)zirconium Complexes
Organometallics, Vol. 20, No. 16, 2001 3457
1H NMR (300 MHz, C6D6): 7.40 (d, 4H), 7.20-7.05 (m, 6H),
6.27 (apparent dd, 2H, J ) 12.6 Hz, J ) 24.8 Hz), 2.24 (s, 6H),
2.05 (s, 6H). 31P (122 MHz, C6D6): 73.7. IR (NaCl, Nujol): 3053,
2923, 2856, 1598, 1577, 1496, 1455, 1402, 1314, 1173, 1160,
1082, 1034, 1008, 990, 966, 939, 913, 890, 880, 840, 824, 756,
700, 694, 661, 637 cm-1. HRMS calcd for C24H24Cl2HfP2
624.0196, found 624.0209. Anal. Calcd: C, 46.21; H, 3.88.
Found: C, 46.42; H, 4.01.
Data for the meso isomer: 1H NMR (300 MHz, C6D6): 7.57
(d, 4H), 7.20-7.05 (m, 6H), 6.65 (apparent dt, 2H, J ) 38.9
Hz), 2.18 (s, 6H), 2.04 (s, 6H). 31P (122 MHz, C6D6): 72.2.
(3,3′,4,4′-Tetr a m eth yl-2,2′-d ip h en yl-1,1′-d ip h osp h a zir -
con ocen e d ich lor id e)m olybd en u m (CO)4 (r a c-8). A solu-
tion of rac-5 (260 mg, 0.48 mmol) in benzene (10 mL) was
added to (CO)4Mo(nbd)15 (145 mg, 0.48 mmol), resulting
immediately in a red solution. After 10 min at room temper-
ature, the solution was heated (75 °C) with stirring for 5.0 h
in a closed Schlenk tube. Then, CH2Cl2 (2 mL) was added (to
help dissolve the red solid), and the solution was filtered
through a bed of Celite. Evaporation of the solvents furnished
a deep red powder that was washed with cold pentane (2 × 1
mL). The solid was dried under vacuum overnight to provide
350 mg (97%) of rac-8. Crystals of rac-8 suitable for single-
crystal X-ray diffraction were obtained through crystallization
from a mixture of CH2Cl2 and acetonitrile.
1H NMR (300 MHz, C6D6): 7.38 (d, 4H, J ) 7.5 Hz), 7.22-
7.02 (m, 6H), 5.69 (app. dd, 2H, J ) 9.3 Hz, J ) 20.4 Hz), 2.01
(m, 12H). 13C (75 MHz, CD2Cl2): 213.1, 206.3 (m), 154.0 (m),
146.7, 143.3, 134.1 (apparent t, J C-P ) 7.1 Hz), 132.1 (m), 131.1
(apparent t, J C-P ) 5.2 Hz), 129.1, 129.0, 19.1, 16.1. 31P (122
MHz, C6D6): 65.0. IR (NaCl, Nujol): 3063, 2954, 2922, 2854,
2032, 1939, 1923, 1899, 1866, 1462, 1179, 1156, 1080, 1019,
915, 867, 842, 828, 754, 697, 605, 572, 537 cm-1. HRMS calcd
for C28H24Cl2MoO4P2Zr 743.8628, found 743.8612. Anal. Cal-
cd: C, 45.17; H, 3.25. Found: C, 45.48; H, 3.28.
3,3′,4,4′-Tet r a m et h yl-2,2′-d ip h en yl-1,1′-d ip h osp h a zir -
con ocen ed im eth yl (r a c-9). MeMgBr in Et2O (3.0 M; 0.27
mL, 0.81 mmol) was added to a precooled (-30 °C) solution of
rac-5 (195 mg, 0.36 mmol) in Et2O (10 mL). The solution
turned from orange to yellow and became cloudy. After 15 min,
1,4-dioxane (2 mL) was added. The suspension was filtered
through a bed of Celite, and the filtrate was evaporated to
dryness. Et2O (2 mL) was added to the resulting yellow oil,
followed by pentane (4 mL). The solution was concentrated
until precipitation occurred (∼3 mL). The resulting yellow
powder was collected, washed with cold pentane (2 mL), and
dried in vacuo to yield 150 mg of rac-9 (84%).
1H NMR (300 MHz, CD2Cl2): 7.45-7.27 (m, 10H), 5.92
(apparent dd, 2H), 2.35 (s, 6H), 2.32 (s, 6H), -0.27 (s, 6H). 31
P
(122 MHz, CD2Cl2): 31.0. IR (NaCl, Nujol): 3063, 2953, 2923,
2854, 2032, 1927, 1896, 1877, 1866, 1598, 1495, 1404, 1263,
1182, 1156, 1120, 1081, 1035, 986, 917, 872, 820, 758, 740,
702, 610, 572 cm-1. HRMS calcd for C30H30MoO4P2Zr 703.9720,
found 703.9708.
X-r a y Da ta Collection a n d Red u ction . X-ray quality
crystals of rac-5, rac-6, and rac-8 were obtained as described
above. The crystals were mounted under STP and transferred
to the diffractometer. A preliminary unit cell was determined
for each crystal by harvesting reflections I > 20σ(I) from three
sets of 15 10-s frames.
A hemisphere of data was then collected using ω scans of
0.30°. A measure of decay was obtained by re-collecting the
first 50 frames of each data set, and no statistically significant
changes in the intensities of the reflections were observed in
any case. The raw data frames were integrated using the
program SAINT23 with constant spot sizes of 1.6° in the
detector plane and 0.6° in ω. The data were corrected for
Lorentz and polarization effects, and absorption was corrected
as described in Table 5.
Str u ctu r e Solu tion a n d Refin em en t. All aspects of the
solution and refinement were handled by SHELXTL NT
version 5.10.24 The structure was solved by the Patterson
method for rac-6 and by direct methods for rac-5 and rac-8.
The refinement was carried out using standard difference
Fourier techniques. To distinguish between the centrosym-
metric space group C2/c and the non-centrosymmetric space
group Cc, rac-6 and rac-8 were solved under both space groups.
Subsequent refinement of the structures showed that C2/c gave
solutions with better statistics and well-behaved anisotropic
thermal parameters.
All non-hydrogen atoms were located and refined anisotro-
pically. All hydrogen atoms were included in calculated
positions and refined isotropically on a riding model. The
location of the largest peaks in the final difference Fourier map
calculation and the magnitude of the residual electron densi-
ties in each case were of no chemical significance.
The relevant crystallographic data are summarized in Table
5.
Gen er a l: P olym er iza tion s. Methylalumoxane (4.00 M in
Al in toluene) was purchased from Akzo Nobel. Triphenylcar-
benium tetrakis(pentafluorophenyl)borate was purchased from
Boulder Scientific and was used as received. All solvents were
purified by successive passage through a bed of activated
alumina and supported copper chromite deoxo catalyst (Q-5,
Engelhardt Corp.).
Rep r esen ta tive P r oced u r e for Activa tion of r a c-5 w ith
Meth yla lu m oxa n e (500:1 Al/Zr ). In a glovebox, a stock
solution of catalyst precursor was prepared by dissolving rac-5
(8.0 mg, 15 µmol) in toluene (10 mL). A 2.0 mL (3.0 µmol)
aliquot of the stock solution was removed and placed in a
scintillation vial, and 0.19 mL of a 4.00 M methylalumoxane
solution in toluene (760 µmol) was added via syringe. After
stirring at ambient temperature for 25 min, a 0.8 mL aliquot
of activated catalyst (1.0 µmol Zr) was removed via syringe
and injected into an autoclave reactor to which the remaining
methylalumoxane had already been added.
1H NMR (300 MHz, C6D6): 7.20-6.90 (m, 10H), 5.72 (app.
dd, 2H, J ) 12.3 Hz, J ) 24.9 Hz), 2.13 (s, 6H), 1.96 (s, 6H),
-0.37 (s, 6H). 13C (75 MHz, CD2Cl2): 150.1, 149.5, 139.9
(apparent t, J C-P ) 3.1 Hz), 138.6 (apparent t, J C-P ) 9.5 Hz),
135.5, 129.5 (apparent t, J C-P ) 5.2 Hz), 128.5, 127.4, 38.6
(ZrMe2), 18.6, 15.7. 31P (122 MHz, C6D6): 62.6. IR (NaCl,
Nujol): 3053, 2955, 2923, 2853, 1595, 1462, 1409, 1309, 1184,
1152, 1110, 1080, 1030, 986, 950, 912, 844, 827, 757, 699 cm-1
HRMS calcd for C26H30P2Zr 494.0870, found 494.0862.
.
Data for the meso isomer: 1H NMR (300 MHz, C6D6): 7.46
(d, 4H), 7.15-6.90 (m, 6H), 5.91 (apparent dt, 2H, J ) 39.0
Hz), 2.07 (s, 6H), 1.89 (s, 6H), -0.25 (s, 3H), -0.29 (s, 3H). 31
(122 MHz, C6D6): 71.4.
P
Rep r esen ta tive P r oced u r e for Activa tion of r a c-9 w ith
Tr ip h en ylca r b en iu m Tet r a k is(p en t a flu or op h en yl)b o-
r a te. Catalyst activation with triphenylcarbenium tetrakis-
(pentafluorophenyl)borate was carried out by dissolving a
mixture of rac-9 (5.0 mg, 10 µmol) and triphenylcarbenium
tetrakis(pentafluorophenyl)borate (9.3 mg, 10 µmol) in fluo-
robenzene (2 mL). A 0.50 mL aliquot of this solution (2.5 µmol)
(3,3′,4,4′-Tetr a m eth yl-2,2′-d ip h en yl-1,1′-d ip h osp h a zir -
con ocen ed im eth yl)m olybd en u m (CO)4 (r a c-10). MeMgBr
in Et2O (3.0 M; 0.22 mL, 0.66 mmol) was added to a precooled
(-30 °C) solution of rac-8 (219 mg, 0.29 mmol) in Et2O (10
mL). The solution turned from red to dark brown and became
cloudy. After 1 h, 1,4-dioxane (2 mL) was added. The suspen-
sion was filtered through a bed of Celite, and the resulting
brown solution was concentrated to ∼5 mL and cooled at -30
°C overnight. Orange-brown crystals were collected, washed
quickly with cold pentane, and dried in vacuo to yield 70 mg
of rac-10 (34%).
(23) SAINT; Siemens Industrial Automation, Inc.: Madison, WI,
1995.
(24) SHELXTL NT version 5.10; Bruker AXS, Inc.: Madison, WI,
1998.

3458 Organometallics, Vol. 20, No. 16, 2001
Bellemin-Laponnaz et al.
Ta ble 5. Cr ysta llogr a p h ic Da ta for Com p lexes r a c-5, r a c-6, a n d r a c-8a
rac-5
24H24Cl2P2Zr
rac-6
rac-8
empirical formula
fw
C
C24H24Cl2HfP2
623.76
C28H24Cl2MoO4P2Zr
744.47
536.49
cryst size (mm)
color/shape
cryst system
temp (K)
space group
a (Å)
0.33 × 0.24 × 0.24
orange/block
monoclinic
177(2)
0.33 × 0.09 × 0.06
yellow/plate
monoclinic
152(2)
0.24 × 0.12 × 0.09
red/block
monoclinic
177(2)
P21/c
C2/c
C2/c
25.573(6)
8.6736(13)
22.082(6)
104.594(14)
4739.9(18)
8
22.7285(4)
13.53160(10)
18.2118(4)
123.7610(10)
4656.54(14)
8
33.050(7)
11.214(2)
16.829(3)
109.98(3)
5861(2)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
8
µ (mm-1
abs corr
)
0.833
4.856
1.107
empirical
1.91-23.26
-24 e h e 26
-8 e k e 9
-17 e 1 e 24
14 535
SADABS25
1.85-23.28
-22 e h e 25
-13 e k e 15
-20 e l e 20
9327
empirical
2.19-23.26
-34 e h e 36
-12 e k e 11
-18 e l e 16
11 794
θ range (deg)
index ranges
no. of reflns
no. of indep reflns
6485
3343
4203
R indices (I > 2σ(I))b,c
R1 ) 0.0484
wR2 ) 0.1048
R1 ) 0.0716
wR2 ) 0.1169
1.128
R1 ) 0.0525
wR2 ) 0.0991
R1 ) 0.0778
wR2 ) 0.1085
1.096
R1 ) 0.0482
wR2 ) 0.0928
R1 ) 0.0525
wR2 ) 0.0941
1.351
R indices (all data)b,c
GooFd
a
All data were collected on a Bruker/AXS SMART/CCD three-circle diffractometer using graphite-monochromated Mo KR radiation (λ
) 0.71073 Å). R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
GooF ) [∑[w(Fo - Fc2)2]/(n - p)]1/2
.
b
2
d
2
was placed in a stainless steel bomb for transfer into the
pressurized reactor.
stainless steel bomb containing 2-5 µmol of activated catalyst
solution was pressurized to 250 psi with nitrogen, and the
solution was injected into the reactor through a dip tube.
Polymerization experiments were conducted with maintenance
of the set temperature (75 °C) and pressure (85 psi) for a period
of 30 min. Polymerization activities were calculated as PE
Gen er a l P r oced u r e for Slu r r y-P h a se Eth ylen e-1-Hex-
en e Cop olym er iza tion in a 1 L Stir r ed -Au tocla ve Rea c-
tor Usin g Meth yla lu m oxa n e a s a Coca ta lyst. Dry hexane
(600 mL) was added to a 1 L stirred autoclave reactor
(maintained at a temperature 10 °C below the run tempera-
ture) under a nitrogen purge. 1-Hexene (43 mL), triisobutyl-
aluminum (0.20 mL of 1.0 M solution in hexane, 200 µmol),
and one-half of the designated amount of alumoxane were
added successively via syringe. After stirring for approximately
10 min, a solution containing 1-10 µmol of activated catalyst
was injected into the reactor via syringe, and the reactor was
pressurized to 85 psi with ethylene and brought to the run
temperature. Polymerization experiments were conducted with
maintenance of the set temperature and pressure (85 psi) for
a period of 30 min. Polymerization activities were calculated
(mmol Zr)-1 (h)-1 (100 psi C2H4)-1
.
Note Ad d ed in P r oof: After we completed this work
(February 2000), in an independent study, Hollis discovered
the same isomerization reaction for zirconium complex 5 and
the same rate acceleration in the presence of Lewis bases.
Hollis cleverly exploited this isomerization process to effect a
dynamic resolution of 5 with (R-BINAP)Rh+.26
Ack n ow led gm en t. Support has been provided by
Bristol-Myers Squibb, Merck, the National Science
Foundation, Novartis, and Pfizer.
as g PE (mmol Zr)-1 (h)-1 (100 psi C2H4)-1
.
Su p p or tin g In for m a tion Ava ila ble: Molecular struc-
tures and numbering schemes for rac-5, rac-6, and rac-8.
Tables describing crystal data and structure refinement,
fractional atomic coordinates, bond distances and angles,
anisotropic displacement parameters, hydrogen coordinates,
and torsional angles. This material is available free of charge
via the Internet at http://pubs.acs.org.
Gen er a l P r oced u r e for Slu r r y-P h a se Eth ylen e-1-Hex-
en e Cop olym er iza tion in a 1 L Stir r ed -Au tocla ve Rea c-
tor Usin g Tr iph en ylcar ben iu m Tetr akis(pen taflu or oph e-
n yl)bor a te a s a Coca ta lyst. Dry hexane (600 mL) was added
to a 1 L stirred autoclave reactor (maintained at 75 °C) under
a nitrogen purge. 1-Hexene (43 mL) and triisobutylaluminum
(0.20 mL of 1.0 M solution in hexane, 200 µmol) were added
successively via syringe. After stirring for approximately 10
min, the reactor was pressurized to 85 psi with ethylene. A
OM010256T
(26) Hollis, T. K.; Wang, L.-S.; Tham, F. J . Am. Chem. Soc. 2000,
122, 11737-11738.
(25) SADABS: Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.