Neutral and cationic zirconium benzyl complexes containing bidentate pyridine-alkoxide ligands. Synthesis and olefin polymerization chemistry of (pyCR2O)2Zr(CH2Ph)2 and (pyCR2O)2Zr(CH2Ph)+ complexes

Article abstract of DOI:10.1021/om9702439

The reaction of Zr(CH₂Ph)₄ with the pyridine alcohols 6-pyCR¹R²OH (2a, R¹ = R² = CF₃; 2b, R¹ = R² = Me; 2c, R¹ = H, R² = CF₃) yields dibenzyl complexes (pyCR¹R²O)₂Zr(CH₂Ph)₂ (3a-c). These species adopt distorted octahedral structures with a trans-O, cis-N, cis-C ligand arrangement but undergo rapid inversion of configuration at Zr on the NMR time scale, with racemization barriers in the range from 8.6 (3b) to 10.1 (3c) kcal/mol. 3a and 3b react with B(C₆F₅)₃ to yield [(pyCR¹R²O)₂Zr(CH₂Ph)][PhCH ₂B(C₆F₅)₃] (6a,b) and with [HNMe₂Ph][B(C₆F₅)₄] to yield [(pyCR¹R²O)₂Zr(CH₂Ph)][B(C ₆F₅)₄] (7a,b). NMR spectra indicate that 6a,b and 7a,b are not strongly ion-paired in CD₂Cl₂. 6a polymerizes ethylene and 1-hexene to low molecular weight polymers. [{pyCH(CF₃)O}₂Zr(CH₂Ph)][PhCH ₂B(C₆F₅)₃] (6c, generated in situ) is much less active for ethylene polymerization than 6a, and 6b is inactive.

Full text of DOI:10.1021/om9702439

Organometallics 1997, 16, 3303-3313
3303
Neu tr a l a n d Ca tion ic Zir con iu m Ben zyl Com p lexes
Con ta in in g Bid en ta te P yr id in e-Alk oxid e Liga n d s.
Syn th esis a n d Olefin P olym er iza tion Ch em istr y of
(p yCR2O)2Zr (CH2P h )2 a n d (p yCR2O)2Zr (CH2P h )+
Com p lexes
Toru Tsukahara, Dale C. Swenson, and Richard F. J ordan*
Department of Chemistry, University of Iowa, Iowa City, Iowa 52242
Received March 24, 1997X
The reaction of Zr(CH2Ph)4 with the pyridine alcohols 6-pyCR1R2OH (2a , R1 ) R2 ) CF3;
2b, R1 ) R2 ) Me; 2c, R1 ) H, R2 ) CF3) yields dibenzyl complexes (pyCR1R2O)2Zr(CH2Ph)2
(3a -c). These species adopt distorted octahedral structures with a trans-O, cis-N, cis-C
ligand arrangement but undergo rapid inversion of configuration at Zr on the NMR time
scale, with racemization barriers in the range from 8.6 (3b) to 10.1 (3c) kcal/mol. 3a and
3b react with B(C6F5)3 to yield [(pyCR1R2O)2Zr(CH2Ph)][PhCH2B(C6F5)3] (6a ,b) and with
[HNMe2Ph][B(C6F5)4] to yield [(pyCR1R2O)2Zr(CH2Ph)][B(C6F5)4] (7a ,b). NMR spectra
indicate that 6a ,b and 7a ,b are not strongly ion-paired in CD2Cl2. 6a polymerizes ethylene
and 1-hexene to low molecular weight polymers. [{pyCH(CF3)O}2Zr(CH2Ph)][PhCH2B(C6F5)3]
(6c, generated in situ) is much less active for ethylene polymerization than 6a , and 6b is
inactive.
Ch a r t 1
In tr od u ction
We recently described the synthesis of a series of
zirconium alkyl complexes of the general type (Ox)2ZrR2
which contain methyl- and bromo-substituted quino-
linolato (Ox-) ancillary ligands (Chart 1).1 These spe-
cies adopt chiral C2-symmetric structures with a trans-
O, cis-N, cis-R ligand arrangement but undergo inver-
sion of configuration at the metal (Λ/∆ interconversion,
i.e., racemization) on the NMR time scale at elevated
+
temperatures. Protonolysis of (Ox)2ZrR2 with HNR3
reagents yields base-free (Ox)2ZrR+ cations, which are
of interest because of their relationship to Cp2Zr(R)+
cations, the active species in metallocene-based olefin
polymerization catalysts.2 The structures and reactivity
of (Ox)2Zr(CH2Ph)+ species are quite sensitive to the
quinolinolato ligand donor properties. (MeBr2Ox)2Zr-
(η2-CH2Ph)+ adopts a distorted square pyramidal struc-
ture with an η2-benzyl group in the apical position and
a trans-O, trans-N arrangement of basal ligands and is
an active ethylene polymerization catalyst. In contrast,
X Abstract published in Advance ACS Abstracts, J une 15, 1997.
(1) Bei, X.; Swenson, D. C.; J ordan, R. F. Organometallics 1997, 16,
3282.
(MeOx)2Zr(R)+ cations (R ) CH2Ph, CH2CMe3) adopt
distorted square pyramidal structures with a MeOx-
oxygen in the apical position and a cis-N arrangement
of basal ligands and are inactive for ethylene polymer-
ization. The analogous hafnium (Ox)2HfR2 and (Ox)2-
Hf(R)+ compounds exhibit similar behavior.
Here we describe initial studies of related zirconium
benzyl complexes of the general type (pyCR2O)2Zr(CH2-
Ph)2 (Chart 1) and (pyCR2O)2Zr(CH2Ph)+, which incor-
porate bidentate pyridine-alkoxide ancillary ligands.
The objectives of this study were to determine how the
increased flexibility of the pyCR2O- ligands (versus
MeOx- and MeBr2Ox-) influences the structures, dy-
namics, and olefin reactivity of the resulting metal
complexes. Of particular interest is the possibility of
tuning reactivity by variation of the substituents on the
(2) Metallocene catalysts and Cp2MR+ chemistry: (a) J ordan, R. F.
Adv. Organomet. Chem. 1991, 32, 325. (b) Marks, T. J . Acc. Chem.
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G. G.; Turner, H. W.; Eckman, R. R. J . Am. Chem. Soc. 1989, 111,
2728. (e) J ordan, R. F.; Bajgur, C. S.; Willett, R.; Scott, B. J . Am. Chem.
Soc. 1986, 109, 7410. (f) Giannetti, E.; Nicoletti, G. M.; Mazzocchi, R.
J . Polym. Sci., Part A: Polym. Chem. Ed. 1985, 23, 2117. (g)
Dyachkovskii, F. S.; Shilova, A. J .; Shilov, A. E. J . Polym. Sci. 1967,
16, 2333. (h) Thayer, A. M. Chem. Eng. News 1995, 73 (37), 15. (i)
Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (j) Sinclair, K. B.;
Wilson, R. B. Chem. Ind. 1994, 857. (k) Mo¨hring, P. C.; Coville, N. J .
J . Organomet. Chem. 1994, 479, 1. (l) Horton, A. D. Trends Polym.
Sci. 1994, 2, 158. (m) Bochmann, M. Nachr. Chem., Tech. Lab. 1993,
41, 1220. (n) Ewen, J . A.; Elder, M. J .; J ones, R. L.; Haspeslagh, L.;
Atwood, J . L.; Bott, S. G.; Robinson, K. Makromol. Chem., Macromol.
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Trans. 1996, 255.
S0276-7333(97)00243-4 CCC: $14.00 © 1997 American Chemical Society

3304 Organometallics, Vol. 16, No. 15, 1997
Tsukahara et al.
Ch a r t 2
alkoxide carbon and the pyridine ring. Pyridine-
alkoxide ligands have been used previously as ancillary
ligands in Mo(VI) oxo transfer systems, W(VI) olefin
metathesis catalysts, and other complexes.3-5
Resu lts
Liga n d Design a n d Syn t h esis. The pyCR2O-
ligands utilized in this work are listed in Chart 2.
Ligands 1a and 1b were chosen to probe the influence
of ligand electron-donating ability on the chemistry of
the target alkyl complexes. The pKa values of the
analogous alcohols (CF3)2HCOH (9.3) and Me3COH
(20.5) differ by more than 10 units. The chiral ligand
1c was used to study the stereochemistry and dynamic
behavior of metal complexes. Ligand 1d was designed
to suppress electron donation from the pyridine function
via front strain (i.e., steric crowding) due to the ortho-
SiMe3 substituent.
F igu r e 1. Molecular structure of (pyCMe2O)2Zr(CH2Ph)2
(3b).
and can be hydrolyzed to 2d . Compound 2c, pyCH-
(CF3)OH, was prepared by Wakselman’s method (eq 2).8
The reaction of 2-lithiopyridine reagents6 with alde-
hydes or ketones provides general access to pyCR2O-
ligands (eq 1).7 The reaction of 2-lithiopyridine (from
Syn th esis of (pyCR1R2O)2Zr (CH2P h )2 Com plexes.
The reactions of pyridine alcohols 2a -c with Zr(CH2-
Ph)4 in toluene or benzene solution result in toluene
elimination and yield orange solutions from which
(pyCR1R2O)2Zr(CH2Ph)2 (3a -c, eq 3) are isolated in
good yield as yellow to orange solids by precipitation
with hexane or pentane. The hexafluoro derivative 3a
2-bromopyridine and n-BuLi) with hexafluoroacetone or
acetone at -78 °C yields pyC(CF3)2OLi (1a ) or pyCMe2-
OLi (1b), which can be hydrolyzed to alcohols 2a and
2b. Deprotonation of 2a and 2b (n-BuLi) affords 1a and
1b as white solids of sufficient purity for use in further
reactions. Similarly, the reaction of 2-lithio-6-trimethyl-
silylpyridine with hexafluoroacetone yields 1d , which
is isolated as a white solid by recrystallization from Et2O
(3) Schultz, B. E.; Gheller, S. F.; Muetterties, M. C.; Scott, M. J .;
Holm, R. H. J . Am. Chem. Soc. 1993, 115, 2714.
(4) (a) van der Schaaf, P. A.; Abbenhuis, R. A. T. M.; van der Noort,
W. P. A.; de Graaf, R.; Grove, D. M.; Smeets, W. J . J .; Spek, A. L.; van
Koten, G. Organometallics 1994, 13, 1433. (b) van der Schaaf, P. A.;
Boersma, J .; Smeets, W. J . J .; Spek, A. L.; van Koten, G. Inorg. Chem.
1993, 32, 5108.
(5) (a) Nietlispach, D.; Veghini, D.; Berke, H. Helv. Chim. Acta 1994,
77, 2197. (b) van der Schaaf, P. A.; Wissing, E.; Boersma, J .; Smeets,
W. J . J .; Spek, A. L.; van Koten, G. Organometallics 1993, 12, 3624.
(c) Van der Zeijden, A. A. H.; Berke, H. Helv. Chim. Acta 1992, 75,
513. (d) Visalakshi, R.; J ain, V. K.; Kulshreshtha, S. K.; Rao, G. S.
Ind. J . Chem. 1989, 28A, 767. (e) Hiraki, K.; Katayama, R.; Yamaguchi,
K.; Honda, S. Inorg. Chim. Acta 1982, 59, 11. (f) Harrison, P. G.;
Phillips, R. C. J . Organomet. Chem. 1975, 99, 79.
(6) (a) Malmberg, H.; Nilsson, M. Tetrahedron 1986, 42, 3981. (b)
Parham, W. E.; Piccirilli, R. M. J . Org. Chem. 1977, 42, 257. (c) Gilman,
H.; Spatz, S. M. J . Am. Chem. Soc. 1940, 62, 446.
(7) (a) Taylor, S. L.; Lee, D. Y.; Martin, J . C. J . Org. Chem. 1983,
48, 4156. (b) Luz, W. D.; Fallab, S.; Erlenmeyer, H. Helv. Chim. Acta
1955, 38, 1114. (c) Wibaut, J . P.; DeJ onge, A. P.; Van der Voort, H. G.
P.; Otto, P. Ph. H. L. Recl. Trav. Chim. Pays-Bas 1951, 70, 1054.
is highly soluble in aromatic and chlorinated solvents,
whereas 3b and 3c are less soluble in aromatic solvents.
Solid Sta te Str u ctu r e of 3b. An X-ray diffraction
study was performed on 3b to determine the metal
geometry and the structure of the benzyl groups. Single
crystals were obtained from a CH2Cl2 solution at -35
°C. An ORTEP view is shown in Figure 1, and crystal-
lographic details and key bond distances and angles are
listed in Tables 1-2. Complex 3b adopts a distorted
octahedral structure in which the alkoxide ligands are
(8) Tordeux, M.; Francese, C.; Wakselman, C. J . Chem. Soc., Perkin
Trans. 1 1990, 1951.

Neutral and Cationic Zirconium Benzyl Complexes
Organometallics, Vol. 16, No. 15, 1997 3305
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for
(p yCMe2O)2Zr (CH2P h )2 (3b)
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for (p yCMe2O)2Zr (CH2P h )2 (3b)
compound
empirical formula
fw
cryst size (mm)
color/shape
space group
a (Å)
(pyCMe2O)2Zr(CH2Ph)2 (3b)
30H34N2O2Zr
545.8
Zr-O(30)
Zr-O(40)
Zr-N(21)
Zr-N(31)
Zr-C(1)
1.995(3)
2.004(3)
2.429(3)
2.391(3)
2.334(4)
2.307(5)
O(30)-C(27)
O(40)-C(37)
C(1)-C(2)
C(11)-C(12)
C(37)-C(38)
C(37)-C(39)
1.410(5)
1.410(5)
1.483(6)
1.461(6)
1.525(7)
1.528(6)
C
0.44 × 0.47 × 0.49
orange/irregular octahedron
P21/n
10.277(2)
21.958(5)
12.006(3)
93.48(2)
2704(2)
4
1.34
Zr-C(11)
O(30)-Zr-O(40)
O(30)-Zr-N(21)
O(30)-Zr-N(31)
O(30)-Zr-C(1)
O(30)-Zr-C(11)
O(40)-Zr-N(21)
O(40)-Zr-N(31)
O(40)-Zr-C(1)
O(40)-Zr-C(11)
N(21)-Zr-N(31)
N(21)-Zr-C(1)
N(21)-Zr-C(11)
N(31)-Zr-C(1)
149.9(1)
69.2(1)
94.6(1)
91.2(1)
104.5(2)
84.7(1)
70.1(1)
109.6(1)
98.9(1)
90.1(1)
156.1(1)
112.2(1)
77.6(1)
N(31)-Zr-C(11)
C(1)-Zr-C(11)
154.6(1)
85.2(2)
b (Å)
c (Å)
Zr-O(30)-C(27)
Zr-O(40)-C(37)
Zr-N(21)-C(22)
Zr-N(21)-C(26)
C(22)-N(21)-C(26)
Zr-N(31)-C(32)
Zr-N(31)-C(36)
C(32)-N(31)-C(36)
Zr-C(1)-C(2)
132.4(3)
130.9(2)
127.1(3)
114.8(3)
118.0(4)
125.9(3)
114.5(3)
119.3(4)
116.6(3)
96.1(3)
â (deg)
V (Å3)
Z
Dcalcd (g/cm3)
temperature (K)
diffractometer
diffraction geometry
radiation, λ
monochromator
2θ range (deg)
data collected h, k, l
total no. of reflns collected
no. of unique reflns
Rint
291
Enraf-Nonius CAD-4
bisecting
Mo KR, 0.710 73 Å
graphite
4 < 2θ < 50
-12 to 3, -1 to 26, -14 to 14
Zr-C(11)-C(12)
5754
4606
0.027
2575 > 3σ(I)
4.26
1.000/1.041
ψ scans
Å and appear not to be significantly strained.14 The Zr-
N(21)-C(26) angle (114.8(3)°) is 12° smaller than the
Zr-N(21)-C(22) angle (127.1(3)°); i.e., the Zr center is
displaced ca. 6° toward O(30) from the orientation which
would maximize the N-Zr donor interaction. A similar
effect is observed in the other chelate ring. The Zr-N
distances (2.429(3), 2.391(3) Å) are at the long end of
the range observed for Zr(IV) complexes of simple and
chelated pyridine ligands (2.3-2.4 Å),15 which may
reflect the constraints of the chelation and the trans
influence of the benzyl groups.
The C(1)-C(7) benzyl ligand of 3b has a normal
structure (Zr-C(1)-C(2) angle 116.6(3)°), while the
C(11)-C(17) benzyl ligand exhibits a small Zr-C(11)-
C(12) angle (96.1(3)°) and a nonbonded Zr-Cipso distance
of 2.86 Å. These features imply the presence of a weak
Zr‚‚‚Ph interaction (i.e., (η2-benzyl)), as commonly ob-
served for electron deficient metal benzyl complexes.16,17
The C(11)-C(17) benzyl is structurally similar to the
distorted benzyl in Zr(CH2Ph)4(dmpe) (Zr-C-C, 94.2(4)°;
Zr-Cipso 2.788(8) Å),16e but it is much less distorted than
obs reflns, criterion
µ (cm-1
)
abs corr factors (min/max)
abs corr method
structure solution
refinement
direct methodsa
FMLS on F; non-H, anisotropic;b
H bonded to sp3 C, isotropic; H
bonded to sp2 C, calculated
0.0327c
R
Rw
0.0433d
max residual density (e/Å3) 0.35
a
Main, P.; Fiske, S. J .; Hull, S. E.; Lessinger, L.; Germain, G.;
DeClercq, J . P.; Woolfson, M. M. Multan80; University of York:
York U.K., 1980. Data processing and refinement with MolEN.
b
Fair, C. K. An Interactive System for Crystal Structure Analysis;
Enraf Nonius: Delft, Netherlands, 1990. c R ) ∑(|Fo| - |Fc|)/∑Fo.
d
Rw ) {[∑(Fo - Fc)2]/[∑w(Fo)2]}1/2
.
trans and the pyridine and benzyl ligands are cis. The
cis L-M-L angles associated with the chelated pyri-
dine-alkoxide ligands are acute (69.2(1)° and 70.1(1)°),
while several cis angles involving the benzyl ligands are
obtuse (N(21)-Zr-C(11), 112.2(1)°; O(30)-Zr-C(11),
104.5(2)°; O(40)-Zr-C(1), 109.6(1)°). These effects can
be ascribed to the constraints imposed by the chelation
and to benzyl/pyridine-alkoxide steric interactions. The
trans L-M-L angles range from 149.9(1)° (O(30)-Zr-
O(40)) to 156.1(1)° (N(21)-Zr-C(1)).
The Zr-O-C units in 3b are bent (Zr-O-C angles
132.4(3)°, 130.9(2)°). The Zr-O distances (1.995(3),
2.004(3) Å) are in the range (ca. 1.95-2.08 Å) observed
for Cp2Zr(OR)2 and Cp2Zr(OAr)2 complexes,9,10 and are
longer than those in highly electron-deficient species
such as (tritox)2ZrCl3Li(OEt2)2,11 trans-1,2-{Cl3(THF)2-
ZrO}2-cyclohexane,12 and Zr(OtBu)3Si(SiMe3)3 (1.86-
1.9 Å).13 The Zr-O distances in 3b are slightly shorter
than those in (MeOx)2Zr(CH2Ph)2 (2.05 Å). It is reason-
able to describe the oxygens in 3b as sp2-hybridized and
to regard the alkoxides as four-electron (σ, π) donors.
The five-membered chelate rings are flat to within 0.05
(14) In systems of this type, chelate ring strain is expected to be
relieved by adjustment of the Zr-O-C angle. The potential surface
for Zr-O-C bending is probably quite flat.
(15) (a) Howard, W. A.; Parkin, G. J . Am. Chem. Soc. 1994, 116,
606. (b) Moore, E. J .; Straus, D. A.; Armantrout, J .; Santarsiero, B.
D.; Grubbs, R. H.; Bercaw, J . E. J . Am. Chem. Soc. 1983, 105, 2068.
(c) Arnold, J .; Woo, H.-G.; Tilley, T. D. Organometallics 1988, 7, 2045.
(d) J ordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organometallics 1990,
9, 1546.
(16) (a) Davies, G. R.; J arvis, J . A. J .; Kilbourn, B. T.; Pioli, A. J . P.
J . Chem. Soc., Chem. Commun. 1971, 677. (b) Davies, G. R.; J arvis, J .
A. J .; Kilbourn, B. T. J . Chem. Soc., Chem. Commun. 1971, 1511. (c)
Bassi, I. W.; Allegra, G.; Scordamaglia, R.; Chiccola, G. J . Am. Chem.
Soc. 1971, 93, 3787. (d) Mintz, E. A.; Moloy, K. G.; Marks, T. J .; Day,
V. W. J . Am. Chem. Soc. 1981, 104, 4692. (e) Girolami, G. S.; Wilkinson,
G.; Thornton-Pett, M.; Hursthouse, M. B. J . Chem. Soc., Dalton Trans.
1984, 2789. (f) Edwards, P. G.; Andersen, R. A.; Zalkin, A. Organo-
metallics 1984, 3, 293. (g) Latesky, S. L.; McMullen, A. K.; Niccolai,
G. P.; Rothwell, I. P.; Huffman, J . C. Organometallics 1985, 4, 902.
(h) J ordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.; Willet,
R. J . Am. Chem. Soc. 1987, 109, 4111. (i) Scholz, J .; Schlegel, M.;
Thiele, K. H. Chem. Ber. 1987, 120, 1369. (j) J ordan, R. F.; LaPointe,
R. E.; Baenziger, N.; Hinch, G. D. Organometallics 1990, 9, 1539. (k)
Alelyunas, Y. W.; J ordan, R. F.; Echols, S. F.; Borkowsky, S. L.;
Bradley, P. K. Organometallics 1991, 10, 1406. (l) Dryden, N. H.;
Legzdins, P.; Trotter, J .; Yee, V. C. Organometallics 1991, 10, 2857.
(m) Hughes, A. K.; Meetsma, A.; Teuben, J . H. Organometallics 1993,
12, 1936. (n) Pellecchia, C.; Immirzi, A.; Pappalardo, D.; Peluso, A.
Organometallics 1994, 13, 3773.
(9) Howard, W. A.; Trnka, T. M.; Parkin, G. Inorg. Chem. 1995, 34,
5900.
(10) Stephan, D. W. Organometallics 1990, 9, 2718.
(11) Lubben, T. V.; Wolczanski, P. T.; Van Duyne, G. D. Organo-
metallics 1984, 3, 977.
(12) Galeffi, B.; Simard, M.; Wuest, J . D. Inorg. Chem. 1990, 29,
955.
(13) Heyn, R. H.; Tilley, T. D. Inorg. Chem. 1989, 28, 1768.
(17) It is also possible that π-π stacking interactions between the
C(12)-C(17) phenyl ring and the C-C pyridine contribute to the small
Zr-C(11)-C(12) angle. There are several short inter-ring distances
(Å): C(13)-C(22), 3.55; C(14)-C(22), 3.52; C(17)-C(22), 3.95; C(17)-
C(23), 3.95.

3306 Organometallics, Vol. 16, No. 15, 1997
Tsukahara et al.
F igu r e 2. Schematic structures, stereochemical descrip-
tors, and interconversion of the stereoisomers of {pyCH-
(CF3)O}2Zr(CH2Ph)2 (3c).
those in cationic complexes such as Cp2Zr(CH2Ph)-
(CH3CN)+ (Zr-C-C, 84.9(4)°; Zr-Cipso, 2.648(6) Å) or
(C5Me5)Zr(CH2Ph)2+ (η7-benzyl, Zr-C-C, 62.1(2)°; Zr-
Cipso 2.349(3) Å).16n There are no close Zr-HR contacts
(Zr-HR > 2.67 Å).
Overall, 3b is best described as a 16-electron species
(counting the alkoxides as 4-electron donors), which may
be stabilized to some extent by the weak Zr‚‚‚Ph
interaction. The structure of 3b is very similar to that
of (MeOx)2Zr(CH2Ph)2, which was described in the
previous paper in this series.1
Solu tion Str u ctu r e a n d Dyn a m ics of 3c. (i)
Isom er P ossibilities. To elucidate the solution struc-
tures and dynamic properties of 3a -c, we first inves-
tigated the variable-temperature NMR spectra of 3c.
Neglecting for the moment the possibility of η2-benzyl
interactions, three diastereomers and with the same
metal geometry as that in the solid state structure of
3b are possible for 3c, as illustrated in Figure 2; these
isomers may be denoted by the descriptors (R, R, Λ),
(R, R, ∆), and (R, S, Λ) ) (S, R, Λ), where the first two
entries specify the configurations of the “top” and
“bottom” alkoxide carbons and the third specifies that
of the metal.
The C2 symmetric (R, R, Λ) and (R, R, ∆) diastereo-
mers differ in the orientation of the CF3 groups; in the
former both point toward the benzyl ligands, while in
the latter both point away from these groups.18 The
metal configurations of these isomers also differ. For
each of these isomers, two doublets for the ZrCH2
hydrogens (Ha and Hb; Hc and Hd) and a quartet for
the CHCF3 hydrogens (He; Hf, J CF) are expected in the
1H NMR spectrum.
F igu r e 3. Variable-temperature 1H NMR spectra of a
sample of {pyCH(CF3)O}2Zr(CH2Ph)2 (3c) enriched in the
(R, R, Λ) and (R, R, ∆) isomers. The resonances for these
species are labeled by asterisks and are noted in the text.
The remaining resonances are due to CHDCl2 (δ 5.32),
toluene (δ 2.30), and the (R, S, Λ) isomer of 3c.
eomers and racemization of the (R, S, Λ) isomer.
However, interconversion of the (R, R, Λ) and (R, R, ∆)
isomers with the (R, S, Λ) isomer requires intermolecu-
lar exchange of pyridine-alkoxide ligands, due to the
different alkoxide carbon configurations.
(ii) (R, R, Λ) a n d (R, R, ∆) Dia ster eom er s. The
sample of 3c isolated from eq 3 consists of a mixture of
the (R, R, Λ) and (R, R, ∆) diastereomers (93% total,
NMR) and a small amount of the (R, S, Λ) isomer (7%).
1
Variable-temperature H NMR spectra of this sample
(CD2Cl2) are shown in Figure 3. The 1H NMR spectrum
of the (R, R, Λ) and (R, R, ∆) isomers at -90 °C contains
four broad resonances (δ 2.73, 2.01, 1.65, 0.83) for the
ZrCH2 hydrogens (Ha, Hb, Hc, Hd in Figure 2) and two
broad resonances (δ 5.68, 4.95) for the CHCF3 hydrogens
(He, Hf). The ratio of the two isomers is 3/1 at -90 °C
based on integration of the ZrCH2 resonances. These
observations are consistent with the structures in
Figure 2; while the isomers cannot be assigned, it is
expected that the (R, R, Λ) isomer would be disfavored
by CF3/benzyl steric interactions. The broadness of
these resonances may be due to the incomplete freezing
out of the exchange process shown in Figure 2 or more
likely to rapid exchange of η2- and η1-benzyl groups. At
-60 °C, the ZrCH2 resonances collapse to two broad
signals (δ 1.79, 1.08) and the CHCF3 resonances coalesce
into a broad signal (δ 5.56). At 23 °C, two sharp
The (R, S, Λ) and (S, R, Λ) isomers are related by a
180° rotation about the axis which bisects the C-Zr-C
angle and are thus identical, as indicated in Figure 2.
The enantiomers, (S, R, ∆) and (R, S, ∆), are related in
1
the same way. The H NMR spectrum of the (R, S, Λ)
diastereomer should contain four doublets for the ZrCH2
hydrogens (Hg, Hh, Hi, Hj) and two quartets for the
CHCF3 hydrogens (Hk, Hl).
Inversion of the metal configuration would result in
interconversion of the (R, R, Λ) and (R, R, ∆) diaster-
(18) The enantiomer configurations are (S, S, ∆), (S, S, Λ).

Neutral and Cationic Zirconium Benzyl Complexes
Organometallics, Vol. 16, No. 15, 1997 3307
doublets (δ 1.94, 1.75; J ) 8.6 Hz) are observed for the
ZrCH2 hydrogens and a sharp quartet (δ 5.52, J CF
)
7.4 Hz) is observed for the CHCF3 hydrogens. These
observations are consistent with rapid (NMR time scale)
inversion of configuration at Zr above -60 °C (i.e., rapid
interconversion of the (R, R, Λ) and (R, R, ∆) isomers),
which exchanges Ha with Hc, Hb with Hd, and He with
Hf, as shown in Figure 2.19 The barrier estimated for
this exchange process from the coalescence of the
CHCF3 signals is ∆Gq (major to minor) ) 10.1(3) kcal/
mol.20
The presence of one weakly distorted and one normal
benzyl ligand in the solid state structure of 3b suggests
that distorted benzyl ligands are possible in 3c as well.
1
Distorted M-CH2Ph groups can be detected by H and
13C NMR spectroscopy; in particular, the reduction of
the M-C-C angle and concomitant increase in H-C-H
angle which result from M‚‚‚Ph interactions are mani-
fested by reduced J HH values (< ca. 10 Hz) and large
J CH values (> ca. 125 Hz).16 The J HH and J CH values
observed at 23 °C for the (R, R, Λ) and (R, R, ∆) isomers
of 3c are 8.6 and 130 Hz, respectively. These values,
which are averages for the four unique benzyl groups
in the two isomers, indicate that the benzyl groups are
distorted to some degree in solution. Given the struc-
ture of 3b, it is likely that the (R, R, Λ) and (R, R, ∆)
isomers of 3c each contain one distorted and one normal
benzyl group which undergo rapid exchange.
(iii) (R, S, Λ) Isom er . When the solution of 3c
described above, which was enriched in the (R, R, Λ)
and (R, R, ∆) isomers, was allowed to stand at 23 °C
for 9 h, the (R, S, Λ) ) (R, S, ∆) diastereomer grew in
at the expense of the (R, R, Λ) and (R, R, ∆) isomers.
The final isomer ratio {(R, R, Λ) + (R, R, ∆)}/(R, S, Λ)
was 46/54. As noted above, this isomer exchange
requires intermolecular exchange of the pyridine-
1
alkoxide ligands. The H NMR spectra of this mixture
(Figure 4) contain resonances for the (R, R, Λ) and (R,
R, ∆) isomers (for which the intensity ratio and tem-
perature dependence are identical to those observed for
the sample enriched in those isomers) and resonances
for the (R, S, Λ) isomer, which will be described here.21
At -90 °C, the spectrum of the (R, S, Λ) isomer contains
four doublets (δ 2.23, 2.02, J HH ) 6.8 Hz; 1.20, -0.30,
J HH ) 8.3 Hz) for the ZrCH2 hydrogens (Hg, Hh, Hi,
Hj) and two quartets (δ 5.92, 4.23) for the CHCF3
hydrogens (Hk, Hl), as expected from Figure 2. At -60
°C, the two low-field ZrCH2 resonances coalesce to a
broad signal (δ 2.13). As the temperature is raised, the
two high-field ZrCH2 resonances shift downfield, coa-
lesce to a broad signal at δ 1.03 at -40 °C, and sharpen
to a sharp singlet at δ 1.46 at 20 °C. The CHCF3
resonances coalesce to a sharp quartet (δ 5.49) as the
temperature is raised; however, this change is partially
masked by the temperature-dependent CHCF3 reso-
nances of the (R, R, Λ/∆) isomers. These results are
consistent with rapid (NMR time scale) racemization of
F igu r e 4. Variable-temperature 1H NMR spectra of a
sample of 3c enriched in the (R, S, Λ) isomer. The
resonances for this species are labeled by asterisks, and
the temperature dependence of these resonances is indi-
cated by the vertical lines. The remaining resonances are
due to the (R, R, Λ) and (R, R, ∆) isomers of 3c, CHDCl2,
toluene, and minor impurities.
the (R, S, Λ) isomer, which results in exchange of Hg
and Hh, exchange of Hi and Hj, and exchange of Hk
and Hl (Figure 2). A barrier ∆Gq (racemization) )
10.1(2) kcal/mol is estimated from the coalescence of the
low-field ZrCH2 doublets.
The ZrCH2 J HH (6.8, 8.3 Hz; -90 °C) and J CH (132,
127 Hz; 23 °C) values indicate that the two unique
benzyl ligands of the (R, S, Λ)/(R, S, ∆) isomer are both
distorted to some degree. These data can be accom-
modated by a structure which contains one normal and
one distorted benzyl (as observed for 3b in the solid
state) which undergo rapid exchange. The spread in the
J HH and J CH values indicates that the η2-interaction is
more favored for one benzyl than the other. Steric
crowding due to the proximal CF3 group may disfavor
a Zr‚‚‚Ph interaction involving the -CHiHjPh benzyl
(Figure 2). The origin of the large temperature de-
pendence of the chemical shifts of the high-field ZrCH2
resonances is unknown.22
(19) The downfield shift of the ZrCH2 resonances with increasing
temperature may be related to changes in the ZrCH2Ph conformation.
(20) (a) This barrier was estimated using the graphical method
described in Shanan-Atidi, H.; Bar-Eli, K. H. J . Phys. Chem 1970, 74,
961. (b) ∆Gq (minor to major) ) 9.6(3) kcal/mol.
(21) The 13C NMR spectrum of the (R, R, Λ), (R, R, ∆), (R, S, Λ)
mixture at 23 °C contains one set of pyridine and benzyl resonances
for the rapidly exchanging (R, R, Λ) and (R, R, ∆) isomers and one set
of pyridine resonances and two sets of benzyl resonances for the rapidly
racemizing (R, S, Λ) isomer.

3308 Organometallics, Vol. 16, No. 15, 1997
Tsukahara et al.
(iv) Su m m a r y. On the basis of these NMR results,
it is concluded that (i) the static structures for the three
isomers of 3c are similar to the solid state structure of
3b, i.e., the alkoxide groups are trans, the pyridine
ligands are cis, and the benzyl ligands are cis; (ii)
inversion of configuration at Zr occurs rapidly on the
NMR time scale at 23 °C, probably via a five-coordinate
intermediate formed by reversible pyridine dissociation;1
and (iii) intermolecular ligand exchange occurs slowly
(hours) on the lab time scale. Additionally, (iv) in the
static structure of 3c, one benzyl group is probably
distorted (η2); however, exchange of the distorted and
normal benzyl groups is rapid on the NMR time scale
even at -90 °C.
value for the two benzyl groups, is slightly higher than
that observed for 3b, which suggests that the degree of
benzyl group distortion may be higher.
Attem pted Syn th eses of {pyC(CF3)2O}2Zr Cl2. The
dichloride complex {pyC(CF3)2O}2ZrCl2 is a potential
general precursor to {pyC(CF3)2O}2ZrR2 complexes.
However, to date it has not been possible to synthesize
this species. The reaction of ZrCl4 or ZrCl4(THF)2 and
2 equiv of LiOC(CF3)2py (1a ) in toluene, hexane, or Et2O
under a variety of conditions yields mixtures in which
the tris(ligand) complex {pyC(CF3)2O}3ZrCl is a major
component. The reaction of ZrCl4 and 3 equiv of 1a in
Et2O yields {pyC(CF3)2O}3ZrCl cleanly. This species
was not studied further.
Syn t h esis of {6-SiMe3-p yC(CF 3)2O}2Zr Cl2 (5d ).
The reaction of ZrCl4(THF)2 and 2 equiv of 1d in hexane
yields {6-SiMe3-pyC(CF3)2O}2ZrCl2(THF)2 (4d ), which
is isolated as a white solid (eq 4). The 1H NMR
1
Solu tion Str u ctu r e a n d Dyn a m ics of 3b. The H
NMR spectrum of 3b at -100 °C contains a single set
of pyridine and benzyl aryl resonances (several of which
are broad), two broad singlets for the alkoxide methyl
groups, and two broad singlets for the benzyl methylene
hydrogens. This pattern is consistent with the metal
geometry observed for 3b in the solid state, in which
the Me groups are inequivalent and the ZrCH2 hydro-
gens are diastereotopic.23 At -90 °C, the Me resonances
and the ZrCH2 resonances collapse to singlets, and
above -20 °C, all of the resonances are sharp. These
observations establish that 3b undergoes rapid inver-
sion of the configuration at Zr. The barrier to this
process determined from the coalescence of the Me
signals is ∆Gq ) 8.6(2) kcal/mol. The bonding mode(s)
of the benzyl ligands for 3b in solution cannot be
unambiguously determined from the NMR data. How-
ever, in view of the solid state structure, the broadening
of the pyridine and benzyl aryl resonances at low
temperature may be ascribed to rapid exchange of one
normal and one weakly distorted benzyl ligand. The
ZrCH2 J CH value observed in the ambient-temperature
13C spectrum of 3b is normal (121 Hz). This value is
the average for the two benzyl groups, and little
deviation from the normal range is expected for a case
where one benzyl ligand is normal and one is only
slightly distorted.
spectrum of 4d contains resonances for coordinated
THF. The THF is removed from 4d at 95 °C (N2 flow,
toluene) to afford base-free {6-SiMe3-pyC(CF3)2O}2ZrCl2
(5d ), which is reconverted to 4d upon contact with THF.
The SiMe3 1H NMR resonance of THF adduct 4d (0.27,
C6D6) is not significantly shifted from those of 1d (δ
0.30, C6D6) or the parent alcohol 2d (δ 0.33, CDCl3)
while that of 5d is shifted ca. 0.3 ppm downfield (δ 0.64,
CD2Cl2). This suggests that the pyridine in 4d is not
coordinated. Due to the apparent lability of the bulky
ortho-disubstituted pyridine, this system was not stud-
ied further.
Solu tion Str u ctu r e a n d Dyn a m ics of 3a . The
variable-temperature NMR properties of 3a are similar
to those of 3b and 3c. The ambient-temperature 1H
NMR spectrum contains a single set of pyridine and
benzyl aryl resonances and a sharp singlet for the ZrCH2
hydrogens. As the temperature is lowered to -100 °C,
the benzyl aryl resonances broaden and the ZrCH2
resonance splits to two singlets. These observations are
consistent with a static structure analogous to the solid
state structure of 3b and rapid inversion of configura-
tion at Zr. The inversion barrier calculated from the
coalescence of the ZrCH2 signals (∆Gq ) 8.8(2) kcal/mol)
is very similar to that for 3b.24 The ZrCH2 J CH value
determined at 23 °C (125 Hz), which is the average
Gen er a t ion of (p yCR 2O)2Zr (CH 2P h )+ Sp ecies.
The reaction of 3a with B(C6F5)3 in benzene yields
[{pyC(CF3)2O}2Zr(CH2Ph)][(PhCH2)B(C6F5)3] (6a ), which
separates from the reaction solution as a yellow oil and
can be isolated as a yellow solid by washing and vacuum
drying (eq 5).25 Similarly, the reaction of 3a with
(22) The high-field ZrCH2 shifts may reflect R-agostic interactions.
For examples of early metal benzyl complexes with R-agostic interac-
tions, see: (a) Mena, M.; Pellinghelli, M. A.; Royo, P.; Serrano, R.;
Tiripicchio, A. J . Chem. Soc., Chem. Commun. 1986, 1118. (b) Booij,
M.; Meetsma, A.; Teuben, J . H. Organometallics 1991, 10, 3246.
(23) A minor isomer of 3b (15%) is observed at -60 °C and below;
NMR data for this species are consistent with a cis-O, cis-N, trans-
benzyl structure. 1H NMR (-90 °C, CD2Cl2): δ 8.66 (br d, 2H, 6-py),
7.91 (t, J ) 7.4 Hz, 2H, 4-py), 7.60 (br t, 2H, 5-py), 7.29 (d, J ) 8 Hz,
2H, 3-py), 6.62 (t, J ) 7.4 Hz, 4H, m-Ph), 5.92 (d, J ) 7.4 Hz, o-Ph),
1.73 (s, 4H, CH2), 0.97 (s, 6H, Me), p-Ph signal obscured.
(24) The two CF3 groups on a given pyC(CF3)2O- ligand of 3a are
inequivalent in the static structure. The ambient-temperature 13C and
19F NMR spectra contain single resonances for the CF3 groups. The
13C NMR CF3 resonance does not split as expected down to -80 °C.
Presumably, the 19F and 13C chemical shift differences for the in-
equivalent CF3 groups are small.
(25) For use of B(C6F5)3 in the generation of Cp2Zr(R)+ species, see
ref 2 and Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015 and references therein.

Neutral and Cationic Zirconium Benzyl Complexes
Organometallics, Vol. 16, No. 15, 1997 3309
Ch a r t 3
[HNMe2Ph][B(C6F5)4] in benzene yields the analogous
B(C6F5)4- salt [{pyC(CF3)2O}2Zr(CH2Ph)][B(C6F5)4] (7a )
in base-free form.26 These cationic species are soluble
in CD2Cl2 but decompose in several hours at ambient
temperature in this solvent.27 Similarly, the reaction
of 3b with B(C6F5)3 or [HNMe2Ph][B(C6F5)4] yields the
analogous salts [(pyCMe2O)2Zr(CH2Ph)][(PhCH2)B(C6F5)3]
(6b) and [(pyCMe2O)2Zr(CH2Ph)][B(C6F5)4] (7b). Com-
pound 6b is much more stable in CD2Cl2 than the
fluorinated analogue 6a , decomposing only slightly after
48 h at ambient temperature. Attempts to purify and
obtain crystalline samples of 6a ,b and 7a ,b were unsuc-
cessful due to poor solubility and thermal stability
properties, and therefore, these compounds were char-
acterized by NMR spectroscopy.
cation-anion interactions are not significant. The
(pyCMe2O)2Zr(CH2Ph)+ cation exists as a 3/2 mixture
of two isomers which are not fluxional on NMR time
1
scale at ambient temperature. For each isomer, the H
NMR spectrum contains four pyCMe2O resonances and
an AB pattern for the ZrCH2 unit, and the 13C NMR
spectrum contains four Me signals and two sets of
pyCMe2O signals. Thus, for each isomer, the two
pyCMe2O- ligands are inequivalent, the Me groups on
each are inequivalent, and the ZrCH2 hydrogens are
diastereotopic. The Zr-benzyl groups of the two iso-
mers are not significantly distorted by Zr‚‚‚Ph interac-
tions (major isomer J HH ) 10.7 Hz, J CH ) 126 Hz; minor
isomer J HH ) 11.2 Hz, J CH ) 119 Hz). We showed
previously by detailed 1- and 2-D NMR studies that
(MeOx)2Zr(R)+ cations (R ) CH2Ph, CH2CMe3) adopt
distorted square pyramidal structures with a MeOx-
oxygen in the apical position, the R group in a basal
position, and a cis-N arrangement of basal ligands
(Chart 1).1 The NMR data for the two isomers of
(pyCMe2O)2Zr(CH2Ph)+ are consistent with similar
distorted square pyramidal structures, with the benzyl
group in a basal position and either an alkoxide or a
pyridine ligand in the apical position (Chart 3).
The structural differences between the {pyC(CF3)2O}2-
Zr(η2-CH2Ph)+ and (pyCMe2O)2Zr(CH2Ph)+ cations may
be rationalized in terms of electronic effects similar to
those invoked in our earlier analysis of the (Ox)2M(R)+
system.1 Two key features of the proposed structure of
{pyC(CF3)2O}2Zr(η2-CH2Ph)+ are (i) the two alkoxide
ligands must share a single metal d orbital for p-d
π-bonding and (ii) the vacant coordination site is trans
to the benzyl ligand, which is the strongest trans-
influence ligand present. As O-Zr π-donation is ex-
tremely weak at best for the fluorinated alkoxide, the
latter feature controls the structure. In contrast, O-Zr
π-donation is more important for (pyCMe2O)2Zr(CH2-
Ph)+, and this species adopts structures in which the
alkoxides do not compete for the same d orbital.
Str u ctu r es of (pyCR2O)2Zr (CH2P h )+ Species. The
NMR spectra of 6a and 7a in CD2Cl2 are identical except
for the anion resonances, which indicates that cation-
anion interactions are absent or weak in this solvent.
The ambient-temperature 1H NMR spectrum of the
{pyC(CF3)2O}2Zr(CH2Ph)+ cation contains a single set
of pyridine resonances and a broad singlet for the ZrCH2
unit. However, the -80 °C spectrum contains two sets
of pyridine resonances and an AB pattern for the ZrCH2
unit and indicates that the sides of the benzyl Ph group
are inequivalent. These observations establish that the
static structure of {pyC(CF3)2O}2Zr(CH2Ph)+ is unsym-
metrical but that this species is fluxional. The ZrCH2
J HH value (8.2 Hz) and J CH value (142 Hz) indicate that
the benzyl ligand is distorted. X-ray crystallographic
studies establish that (MeBr2Ox)2Zr(η2-CH2Ph)+ (Chart
1)1 and {pyC(3,5-(CF3)2-C6H3)2O}2Ti(η2-CH2Ph)+,28 which
are both closely related to {pyC(CF3)2O}2Zr(η2-CH2Ph)+,
adopt distorted square pyramidal structures with an η2-
benzyl group in the apical position, the benzyl Ph group
aligned over a M-N bond, and a trans-O, trans-N
arrangement of basal ligands. The NMR data for the
{pyC(CF3)2O}2Zr(CH2Ph)+ cation are consistent with a
static structure of this type (Chart 3).
The NMR spectra of 6b and 7b in CD2Cl2 are identical
except for the anion resonances, again indicating that
Olefin P olym er iza t ion St u d ies. (i) E t h ylen e
P olym er ization with Discr ete Cation ic Com plexes.
The ethylene polymerization activities of (pyCR2O)2Zr-
(CH2Ph)+ cations 6a ,b and {pyCH(CF3)O}2Zr(CH2Ph)+
(6c)29 have been investigated. In an initial series of
experiments, 6a -c were generated in situ in benzene
via reaction of 3a -c with B(C6F5)3 and their activities
compared under standard conditions (benzene, 40 °C,
3 atm, 30 min polymerization time). The activity varies
(26) For use of HNR3 reagents in the generation of Cp2Zr(R)+
+
species, see ref 2 and (a) Bochmann, M.; Wilson, L. M. J . Chem. Soc.,
Chem. Commun. 1986, 1610. (b) Lin, Z.; Le Marechal, J .; Sabat, M.;
Marks, T. J . J . Am. Chem. Soc. 1987, 109, 4127. (c) Turner, H. W.;
Hlatky, G. G. Eur. Pat. Appl. 0 277 003, 1988. (d) Turner, H. W. Eur.
Pat. Appl. 0 277 004, 1988. (e) Hlatky, G. G.; Eckman, R. R.; Turner,
H. W. Organometallics 1992, 11, 1413. (f) Eshuis, J . J . W.; Tan, Y. Y.;
Meetsma, A.; Teuben, J . H.; Renkema, J .; Evens, G. G. Organometallics
1992, 11, 362. (g) Amorose, D. M.; Lee, R. P.; Petersen, J . L.
Organometallics 1991, 10, 2191. (h) Horton, A. D.; Orpen, A. G.
Organometallics 1991, 10, 3910. (i) Bochmann, M.; J agger, A. J .;
Nicholls, J . C. Angew. Chem., Int. Ed. Engl. 1990, 29, 780. (j) Horton,
A. G.; Frijins, J . H. G. Angew. Chem., Int. Ed. Engl. 1991, 30, 1152.
(k) Grossman, R. B.; Doyle, R. A.; Buchwald, S. L. Organometallics
1991, 10, 1501. (l) Bochmann, M.; Lancaster, S. J . J . Organomet. Chem.
1992, 434, C1. (n) Guo, Z.; Swenson, D. C.; J ordan, R. F. Organo-
metallics 1994, 13, 1424.
in the order 6a (32 (kg of PE)(mol of cat)-1 atm-1 h-1
)
> 6c (2.6) > 6b (no polymer). Thus, for this system,
the electron-withdrawing CF3 groups have a beneficial
effect on activity. The polymer produced by 6a under
these conditions is a low molecular weight (Mn ) 6,200),
linear polyethylene with one vinyl end group per chain;
i.e., a C400 R-olefin. The molecular weight distribution
(27) 1H NMR spectra of {pyC(CF3)2O}2ZrCH2Ph+ in CD2Cl2 following
decomposition are complicated, and the product(s) have not been
identified.
(28) (a) Lubben, T.; Nishihara, Y.; Young, V. G., J r.; J ordan, R. F.
Manuscript in preparation.
(29) Cation 6c was generated in situ only.

3310 Organometallics, Vol. 16, No. 15, 1997
Tsukahara et al.
(Mw/Mn ) 2.6) is somewhat broader than that expected
for a single site catalyst (Mw/Mn ) 2.0). Benzyl end
[B(C6F5)4] catalyst also may result from alkoxide trans-
fer to Al.
1
groups were also detected by H NMR, suggesting that
(iii) Hexen e P olym er iza tion by 6a . Complex 6a
catalyzes the polymerization of 1-hexene to low molec-
ular weight atactic polyhexene with moderate activity
(90 (kg PH)(mol of cat)-1 h-1) under mild conditions
(CD2Cl2, 23 °C). The 1H NMR spectrum of the poly-
hexene produced by 6a contains resonances for terminal
(H2CdCRR′; δ 4.72, 4.66) and internal (RHCdCR′H; δ
5.3) olefins in an intensity ratio of 7/4. These reso-
nances correspond to end groups resulting from â-H
elimination following 1,2 or 2,1 hexene insertions (eq
6). An Mn value of 840 (i.e., degree of polymerization
polymerization is initiated via insertion into the Zr-
CH2Ph bond of 6a or a Zr benzyl species derived
therefrom. These results are in accord with a normal
insertion mechanism and efficient chain transfer via â-H
elimination.
Activation of 3a by [HNMe2Ph][B(C6F5)4] (to generate
7a and NMe2Ph) resulted in decreased activity (13 (kg
of PE)(mol of cat)-1 atm-1 h-1)) under the standard
conditions noted above. While NMe2Ph does not coor-
dinate to 7a in CH2Cl2, it is possible that this Lewis
base may compete with ethylene for binding to
{pyC(CF3)2O}2Zr(R)+ species in benzene. Complex 3a
is also activated efficiently by [Ph3C][B(C6F5)4] (to
generate 7a ); in this case, the activity and polymer
properties are similar to those for the 3a /B(C5F5)3
catalyst (56 (kg of PE)(mol of cat)-1 atm-1 h-1; toluene,
45 °C, 8 atm, 60 min).30 The use of Al(iBu)3 as a
scavenger in conjunction with the [Ph3C][B(C6F5)4]
activator did not have a significant effect on activity but
did lower the molecular weight somewhat and broad-
ened the molecular weight distribution (Mw/Mn ) 3.7).
(ii) Eth ylen e P olym er iza tion w ith 3a /MAO. The
possibility of activating 3a with methylalumoxane
(MAO) was also briefly explored.31 Treatment of 3a
with MAO (Al/Zr ) 1000/1) yields a very low activity
catalyst (1.3 (kg of PE)(mol of cat)-1 h-1 atm-1; at 30
°C, 8 atm). Furthermore, the polyethylene produced by
the 3a /MAO catalyst at 30 °C has a low molecular
weight (Mn ) 13 400) and a very broad molecular weight
distribution (Mw/Mn ) 28). To probe the origin of the
difference in behavior of the 3a /B(C6F5)3 and 3a /MAO
catalysts, the reactivity of 3a with Al alkyls was
investigated. 1H NMR monitoring experiments estab-
lish that 3a reacts rapidly with AlMe3 to yield pyC(CF3)2-
OAlMe2 as a principal product (ca. 50% of the pyC-
(CF3)2O containing products).32 This species is also
produced by the reaction of alcohol 2a with AlMe3.
Thus, the alkoxide ligands of 3a are susceptible to
abstraction by Al reagents, and complicated chemistry
may be anticipated in the 3a /MAO catalyst system. The
broadening of the molecular weight distribution ob-
served upon addition of Al(iBu)3 to the 3a /[Ph3C]-
) 10) was determined by integration of these resonances
versus the major 12H polyhexene resonance (δ 0.8-1.2).
1H NMR monitoring of the hexene polymerization
reveals rapid disappearance of the 6a resonances and
simultaneous appearance of polyhexene resonances.
Discu ssion
Dibenzyl complexes of the type (pyCR2O)2Zr(CH2Ph)2
(3a -c) adopt distorted octahedral structures with a
trans-O, cis-N, cis-benzyl ligand arrangement. These
complexes have idealized C2 symmetry and are, thus,
chiral; however, inversion of configuration at the metal
is rapid on the NMR time scale at room temperature.
The racemization barriers (from 8.6 (3b) to 10.1 (3c)
kcal/mol) are significantly lower than those determined
for the 8-quinolinolato systems (Ox)2MR2 (M ) Zr, Hf;
∆Gq (racemization) ) 15-18 kcal/mol). Ambient tem-
perature NMR data reported by Holm for structurally
analogous (pyCAr2O)2Mo(dO)2 complexes establish that
these systems are also configurationally labile, although
racemization barriers were not determined.3 Some
years ago Serpone showed that the closely related
8-quinolinolato phenoxide complex (Ox)2Ti{O-2,6-(iPr)2-
C6H3}2, which adopts an analogous trans-O, cis-N, cis-
phenoxide structure, undergoes racemization via a
dissociative “bond rupture” mechanism.33 Serpone pro-
posed that racemization proceeds via a labile trigonal
bipyramidal intermediate formed by Ti-N bond dis-
sociation. It is likely that racemization of 3a -c and
(Ox)2MR2 complexes proceeds by the same mechanism.
The lower barriers observed for 3a -c reflect the fact
that pyCR2O- ligands are more flexible than Ox-
ligands, which allows Zr-N bond dissociation without
significant disruption of the Zr-O bond. Indeed, the
pyridine ligands of 5d , which albeit are ortho-disubsti-
tuted and thus very crowded, are easily displaced by
THF. It is also possible, especially for the fluorinated
system 3a , that alkoxide dissociation leads to a labile
intermediate and racemization. However, intermolecu-
lar exchange of the pyCH(CF3)2O- ligands of 3c occurs
only slowly (hours) on the laboratory time scale.
+
(30) For use of CPh3 in the generation of Cp2Zr(R)+ species, see:
(a) Chien, J . C. W.; Tsai, W.; Rausch, M. D. J . Am. Chem. Soc. 1991,
113, 8570. (b) Ewen, J . A.; Elder, M. J . Makromol. Chem., Macromol.
Symp. 1993, 66, 179. (c) Bochmann, M.; Lancaster, S. J . Organo-
metallics 1993, 12, 633. (d) Razavi, A.; Thewalt, U. J . Organomet.
Chem. 1993, 445, 111. See also (e) Straus, D. A.; Zhang, C.; Tilley, T.
D. J . Organomet. Chem. 1989, 369, C13.
(31) For discussions of the use, possible structures, and possible
mechanisms of the action of MAO, see (a) Sinn, H.; Kaminsky, W. Adv.
Organomet. Chem. 1980, 18, 99. (b) Sishta, C.; Hathorn, R. M.; Marks,
T. J . J . Am. Chem. Soc. 1992, 114, 1112. (c) Harlan, C. J .; Bott, S. G.;
Barron, A. R. J . Am. Chem. Soc. 1995, 117, 6465.
(32) (a) 1H NMR for pyC(CF3)2OAlMe2 (CD2Cl2): δ 8.60 (d, J ) 5.3
Hz, 1H, 6-py), 8.25 (td, J ) 7.9, 1.6 Hz, 1H, 4-py), 8.03 (d, J ) 8.2 Hz,
1H, 3-py), 7.86 (ddd, J ) 7.6, 5.5, 1.0 Hz, 1H, 5-py), -0.67 (s, 6H). (b)
A pentane solution (1 mL) of 2a (30 mg, 0.12 mmol) was added to AlMe3
(20 mg, 0.28 mmol) at 23 °C to give a white slurry. The volatiles were
removed under vacuum to give a white solid, which dissolved in CD2Cl2
to give a clear colorless solution. The 1H NMR spectrum revealed the
presence of pyC(CF3)2OAlMe2 (see ref 32a) and {pyC(CF3)2O}2AlMe
(ratio 8/2). 1H NMR of {pyC(CF3)2O}2AlMe (CD2Cl2): δ 8.76 (ddd, J )
5.3, 1.6, 1.0 Hz, 2H, 6-py), 8.13 (td, J ) 7.8, 1.8 Hz, 2H, 4-py), 7.91 (d,
J ) 8.3 Hz, 2H, 3-py), 7.77 (ddd, J ) 6.4, 5.3, 1.1 Hz, 2H, 5-py), -0.94
(5, 3H, Me). (c) Similar compounds have been described previously,
see: van Vliet, M. R. P.; van Koten, G.; de Keijser, M. S.; Vrieze, K.
Organometallics 1987, 6, 1652.
(33) Bickley, D. G.; Serpone, N. Inorg. Chem. 1979, 18, 2200.

Neutral and Cationic Zirconium Benzyl Complexes
Organometallics, Vol. 16, No. 15, 1997 3311
Cationic five-coordinate species (pyCR2O)2Zr(CH2Ph)+
6a -c are generated from 3a -c by alkyl abstraction or
Zr-R protonolysis reactions. These species most likely
adopt distorted square pyramidal structures (Chart 3)
in which the ligand arrangement is strongly influenced
by the π-donor properties of the alkoxide ligand. Cat-
ions 6a and 6c catalyze ethylene polymerization under
mild conditions, while 6b, which contains the relatively
electron-donating pyCMe2O- ligand, does not. This
trend is opposite to that reported for metallocene
catalysts, in which incorporation of electron-donating
substituents on the Cp ligands generally increases
activity in the absence of overriding steric factors.34 It
is reasonable to assume that the active species in these
polymerizations are (pyCR2O)2Zr(P)+ cations (P ) grow-
ing chains); however, at present, there is no definitive
evidence on this point. The presence of benzyl end
groups in, and the narrow molecular weight distribu-
tion of the polyethylene produced by 6a indicate that
polymerization is initiated by insertion into Zr-CH2Ph
bonds and that the catalyst is a single site catalyst.
Catalysts 6a and 6c exhibit much lower activity and
produce much lower molecular weight polymers than
metallocene catalysts under similar conditions (activity
typically >103 (kg of PE)(mol of cat)-1 h-1 atm-1).2 The
observed activity order 6a > 6c > 6b suggests that these
systems may be insufficiently electrophilic to efficiently
bind and activate olefins for insertion.35 This issue can
be addressed in greater detail when more is known
about the structures and reactivity of these cations.
This work provides an entry to neutral and cationic
group 4 metal alkyl complexes based on octahedral
geometries and tunable, bidentate pyridine-alkoxide
ligands. The chemistry of related (pyCAr2O)2MX2 and
(pyCAr2O)2M(R)+ complexes, as well as strategies to
increase the configurational stability and reactivity of
these systems, will be described in later papers in this
series.28,36
to an Et2O (20 mL) solution of pyC(CF3)2OH (2.41 g, 9.84
mmol), affording a yellow slurry. The slurry was stirred at
-78 °C for 2 h and allowed to warm to ambient temperature;
the color changed to red. The volatiles were removed under
vacuum, yielding a red solid. Benzene (20 mL) and then
pentane (20 mL) were added, and the off-white solid was
collected by filtration, washed with pentane (15 mL), and dried
under vacuum. Yield: 1.7 g, 70 %. 1H NMR (C6D6): δ 8.41
(d, J ) 4.2 Hz, 1H, 6-py), 7.54 (d, J ) 8.1 Hz, 1H, 3-py), 6.82
(td, J ) 8.0, 1.8 Hz, 1H, 4-py), 6.50 (ddd, J ) 7.5, 5.0, 1.0 Hz,
1H, 5-py). 13C{1H} NMR (C6D6): δ 156.7 (2-py), 148.9 (6-py),
137.1 (4-py), 125.6 (q, J CF ) 291 Hz, CF3), 124.3 (5-py), 123.2
(3-py); the CF3 and pyCO signals were not detected.
(6-SiMe3)p yC(CF 3)2OLi (1d ). A hexane solution of n-BuLi
(2.5 M, 6.8 mL, 17 mmol) was added dropwise at -25 °C over
1 h to an Et2O solution (50 mL) of 2-bromo-6-(trimethylsilyl)-
pyridine (3.97 g, 16.5 mmol), and the yellow solution was
stirred for 30 min. The temperature was increased to 4 °C,
and the reaction mixture was stirred for 40 min, resulting a
red solution. Hexafluoroacetone (17 mmol, 1.7 mL at -78 °C)
was condensed in over 10 min at -78 °C. The color changed
from red to yellow. The reaction mixture was allowed to warm
to and maintained at ambient temperature for 15 h. The
volatiles were removed at 60 °C under vacuum. The residue
was extracted with Et2O (30 mL), and the extract was
concentrated to 15 mL. Pentane (10 mL) was added to afford
a white slurry, which was cooled to -35 °C for 3 h. The white
solid was collected by filtration and dried under vacuum. Yield
1.92 g, 36.0%. 1H NMR (C6D6): δ 7.54 (d, J ) 8.1 Hz, 2H, 3 or
5-py), 7.09 (dd, J ) 7.5, 1.0 Hz, 2H, 3 or 5-py), 6.92 (t, J ) 7.9
Hz, 2H, 4-py), 0.30 (s, 9H, CH3). 13C{1H} NMR (C6D6): δ 170.1
(6-py), 156.3 (2-py), 135.3 (4-py), 130.8 (5-py), 122.8 (3-py), -1.1
(SiMe3); the CF3 and COLi signals were not detected.
p yC(CF 3)2OH (2a ). A hexane solution of n-BuLi (2.5 M,
54.4 mL, 136 mmol) was added dropwise at -78 °C over 15
min to an Et2O (200 mL) solution of 2-bromopyridine (13.0 mL,
136 mmol). The red solution was stirred for 10 min, and
hexafluoroacetone (15 mL at -78 °C, ca. 150 mmol) was added
over 1 h at -78 °C. The solution was allowed to warm to
ambient temperature and stirred for 15 h. The reaction
mixture was neutralized with aqueous [NH4]Cl, and the
organic layer was separated. The aqueous layer was extracted
with ether (2 × 50 mL), and the combined ether fractions were
dried over MgSO4 and evaporated to afford a brown oil, which
was vacuum distilled. The fraction boiling between 55 and
75 °C at 0.001 mmHg was collected (yellow oil, 3.2 g, 40%).
1H NMR (C6D6): δ 7.81 (d, J ) 4.0 Hz, 1H, 6-py), 7.50 (s, 1H,
OH), 7.32 (d, J ) 8.0 Hz, 1H, 3-py), 6.82 (m, 1H, 4-py), 6.3 (m,
1H, 5-py). 13C{1H} NMR (CD2Cl2): δ 148.2 (6-py), 139.1 (4-
py), 126.5 (5-py), 123.0 (br, 3-py), 122.9 (q, J CF ) 287 Hz, CF3);
the 2-py and pyCO signals were not detected.
p yCMe2OH (2b). A hexane solution of n-BuLi (2.5 M, 42
mL, 105 mmol) was added dropwise at -78 °C over 20 min to
an Et2O (50 mL) solution of 2-bromopyridine, and the resulting
red solution was stirred for 20 min. Acetone (7.7 mL, 105
mmol) was added via syringe over 20 min, and the dark green
slurry was allowed to warm to room temperature and stirred
for 12 h. Water (50 mL) was added, and the organic phase
was separated. The aqueous phase was extracted with ether,
and the combined ether fractions were dried over MgSO4 and
evaporated under vacuum to afford a brown oil. The oil was
sublimed twice (50 °C, 0.005 mmHg) yielding a white solid
(8.1 g, 56%). 1H NMR (CDCl3): δ 8.44 (d, J ) 4.9 Hz, 1H,
6-py), 7.63 (td, J ) 7.7, 1.7 Hz, 1H, 4-py), 7.32 (d, J ) 8.0 Hz,
1H, 3-py), 7.12 (m, 1H, 5-py), 5.09 (s, 1H, OH), 1.48 (s, 6H,
Me). 13C{1H} NMR (CDCl3): δ 165.9 (2-py), 147.3 (6-py), 136.8
(4-py), 121.7 (5-py), 118.6 (3-py), 71.6 (COH), 30.5 (Me).
(6-SiMe3)p yC(CF 3)OH (2d ). An Et2O solution (50 mL) of
(6-SiMe3)pyC(CF3)2OLi (0.82 g) was washed with water (20
mL) four times. The Et2O layer was dried over MgSO4, which
was filtered off. The volatiles were removed under vacuum,
yielding a colorless oil. Yield: 0.71 g, 88%. 1H NMR (C6D6):
Exp er im en ta l Section
Gen er a l Con sid er a tion s. The following compounds were
prepared by literature methods: 2-bromo-6-(trimethylsilyl)-
pyridine,37 pyCHCF3OH,38 Zr(CH2Ph)4,39 B(C6F5)3,40 and
[HNMe2Ph][B(C6F5)4].41 The lithium alkoxides were prepared
with n-BuLi in hexane. NMR spectra were recorded on Bruker
AMX-360 (1H, 13C) or AC-300 (19F) instruments in flame-sealed
or Teflon-valved tubes at 25 °C, unless otherwise indicated.
1H and 13C chemical shifts are reported versus Me4Si and were
determined by reference to the residual solvent peaks. 13C
NMR assignments and J CH values are based on gated-{1H}13C
spectra. The numbering system used for NMR assignments
is given in Chart 2. Representative ligand syntheses and olefin
polymerization experiments are described.
p yC(CF 3)2OLi (1a ). A hexane solution of n-BuLi (2.5 M,
3.9 mL, 9.8 mmol) was added dropwise at -78 °C over 25 min
(34) For example, see: Lee, I.-M.; Gauthier, W. J .; Ball, J . M.;
Iyengar, B.; Collins, S. Organometallics 1992, 11, 2115.
(35) For a discussion of the d0 metal olefin complexes, see: Wu, Z.;
J ordan, R. F.; Petersen, J . L. J . Am. Chem. Soc. 1995, 117, 5867.
(36) Kim, I.; Nishihara, Y.; Rogers, R. D.; Yap, G.; Rheingold, A. L.;
J ordan, R. F. Organometallics 1997, 16, 3314.
(37) J utzi, P.; Lorey, O. J . Organomet. Chem. 1976, 104, 153.
(38) Tordeaux, M.; Francese, C.; Wakselman, C. J . Chem. Soc.,
Perkin Trans. 1 1990, 1951.
(39) Zucchini, U.; Albizzati, E.; Giannini, U. J . Organomet. Chem.
1971, 26, 357.
(40) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2, 245.
(41) Tjaden, E. B.; Swenson, D. C.; J ordan, R. F. Organometallics
1995, 14, 371.

3312 Organometallics, Vol. 16, No. 15, 1997
Tsukahara et al.
δ 8.03 (s, 1H, OH), 7.41 (dm, J ) 8 Hz, 1H, 3-py), 7.06 (dd, J
) 7.4, 1.1 Hz, 1H, 5-py), 6.98 (t, J ) 8.0 Hz, 1H, 3-py), 0.06 (s,
9H, CH3). 13C{1H} NMR (CDCl3): δ 167.2 (2-py), 145.7 (6-
py), 136.3 (4- or 5-py), 130.8 (4- or 5-py), 122.4 (q, J CF ) 287
Hz, CF3), 121.6 (3-py), -2.1 (CH3); the pyCO signal was not
detected. Anal. Calcd for C11H13F6NOSi: C, 41.63; H, 4.14;
N, 4.41. Found: C, 41.42; H, 4.12; N, 4.32
2H, CH2), 0.83 (br, 2H, CH2); minor isomer δ 4.95 (br, 2H,
CHCF3), 2.73 (br, 2H, CH2), 2.01 (br, 2H, CH2). 1H NMR
(CD2Cl2, (R, S, Λ) isomer at 23 °C, rapid racemization): δ 8.14
(d, J ) 5.4 Hz, 2H, 6-py), 7.70 (td, J ) 8.0, 1.6 Hz, 2H, 4-py),
7.4 (3-py, partially obscured), 7.15 (t, J ) 6.6 Hz, 2H, 5-py),
6.33 (d, J ) 7.3 Hz, 2H, o-Ph), 5.47 (q, J ) 7.5 Hz, 2H, CHCF3),
2.20 (s, 2H, ZrCH2), 1.46 (s, 2H, ZrCH2), the other o-Ph signal
and the m- and p-Ph signals obscured). 1H NMR (CD2Cl2, (R,
S, Λ) isomer at -90 °C, slow racemization, aliphatic region
only): δ 5.92 (q, J ) 5.8 Hz, 1H, CHCF3), 4.23 (q, J ) 7.7 Hz,
1H, CHCF3), 2.23 (d, J ) 6.8 Hz, 1H, CH2), 2.02 (br d, 1H,
CH2), 1.20 (d, J ) 7.9 Hz, 1H, CH2), -0.30 (d, J ) 8.6 Hz, 1H,
CH2). 13C{1H} NMR (CD2Cl2, rapidly exchanging (R, R, Λ) and
(R, R, ∆) isomers): δ 158.7 (2-py), 148.4 (6-py), 145.7 (ipso-
Ph), 139.0 (4-py), 129.3 (o-Ph), 127.1 (m-Ph) , 124.5 (5-py),
{p yC(CF 3)2O}2Zr (CH2P h )2 (3a ). A toluene solution (20
mL) of pyC(CF3)2OH (0.545 g, 2.16 mmol) was added to a
toluene solution (20 mL) of Zr(CH2Ph)4 (0.492 g, 1.08 mmol)
at 23 °C. The orange solution was stirred for 1 h at 23 °C and
concentrated under vacuum until a precipitate appeared.
Pentane (10 mL) was added, and the slurry was cooled to -35
°C. The orange solid was collected by filtration, washed with
pentane, and dried under vacuum. Yield: 0.530 g, 65%. 1H
NMR (CD2Cl2): δ 7.92 (d, J ) 5.3 Hz, 2H, 6-py), 7.86 (td, J )
7.5, 1.6 Hz, 2H, 4-py), 7.77 (d, J ) 8.1 Hz, 2H, 3-py), 7.17 (ddd,
J ) 7.4, 5.5, 1.2 Hz, 2H, 5-py), 6.93 (t, J ) 7.7 Hz, 4H, m-Ph),
6.77 (t, J ) 7.3 Hz, 2H, p-Ph), 6.66 (d, J ) 7.2 Hz, 4H, o-Ph),
2.07 (s, 4H, CH2). 1H NMR (-90 °C, CD2Cl2): δ 7.90 (d, J )
4.8 Hz, 2H, 6-py), 7.82 (t, J ) 7.8 Hz, 2H, 4-py), 7.71 (d, J )
7.8 Hz, 2H, 3-py), 7.12 (t, J ) 6.3 Hz, 2H, 5-py), 6.86 (br, 3H,
m- and p-Ph), 6.42 (br, 2H, o-Ph), 1.65 (br s, 2H, CH2), 1.24
(br s, 2H, CH2). 13C{1H} NMR (CD2Cl2): δ 154.3 (br, 2-py),
150.0 (6-py), 146.8 (ipso-Ph), 140.1 (4-py), 128.9 (o-Ph), 127.3
(m-Ph), 125.9 (5-py or p-Ph), 123.6 (q, J CF ) 290 Hz, CF3), 123.1
(3-py), 121.8 (5-py or p-Ph), 89.1 (sept, J CF ) 30 Hz, pyCO),
68.3 (J CH ) 125 Hz, CH2). 19F NMR (CD2Cl2): δ -78.0. Anal.
4
2
122.1 (q, J CF ) 3 Hz, 3-py), 121.4 (p-Ph), 81.8 (q, J CF ) 31
Hz, CHCF3), 60.4 (CH2, J CH ) 130 Hz). 13C{1H} NMR (CD2Cl2,
(R, S, Λ) isomer, rapid racemization): δ 158.5 (2-py), 148.2
(6-py), 147.0 and 144.4 (ipso-Ph), 138.9 (4-py), 130.0 and 128.4
(o-Ph), 127.7 and 126.6 (m-Ph), 124.6 (5-py), 122.3 and 120.4
(p-Ph), 121.9 (q, J CF ) 3 Hz, 3-py), 81.8 (q, J CF ) 31 Hz,
CHCF3), 62.4 (CH2, J CH )132 Hz), 60.0 (CH2, J CH ) 127 Hz).
{p yC(CF 3)2O}3Zr Cl. Diethyl ether (30 mL) was added to
a mixture of solid ZrCl4 (116 mg, 0.500 mmol) and pyC(CF3)2-
OLi (374 mg, 1.49 mmol) at 23 °C. The white slurry was
stirred for 18 h. The volatiles were removed under vacuum
to afford a white solid, which was extracted with hot toluene
(50 mL). The extract was concentrated under vacuum and
cooled to -35 °C. The white solid was collected by filtration,
washed with pentane, and dried under vacuum (338 mg, 79%).
1H NMR (C6D6): δ 9.12 (d, J ) 5.3 Hz, 3H, 6-py), 7.30 (d, J )
8.0 Hz, 3H, 3-py), 6.74 (td, J ) 7.7, 1.6 Hz, 3H, 4-py), 6.54
(ddd, J ) 8.0, 5.6, 1.0 Hz, 3H, 5-py). 13C{1H} NMR (C6D6): δ
155.7 (2-py), 150.1 (6-py), 139.6 (4-py), 125.2 (5-py), 123.6 (q,
J CF ) 290 Hz, CF3), 122.8 (3-py); the COZr resonance was not
detected. 19F NMR (C6D6): δ -74.6 (s, CF3). Anal. Calcd for
Calcd for
C30H22F12N2O2Zr: C, 47.30; H, 2.92; N, 3.68.
Found: C, 47.12; H, 2.77; N, 3.79.
{p yCMe2O}2Zr (CH2P h )2 (3b). A toluene solution (5 mL)
of pyCMe2OH (284 mg, 2.07 mmol) was added to a toluene
solution (10 mL) of Zr(CH2Ph)4 (472 mg, 1.04 mmol) at 23 °C.
The orange solution was stirred for 2 h at 23 °C and
concentrated under vacuum until a precipitate formed. Hex-
ane (10 mL) was added, and the slurry was cooled to -35 °C.
The orange powder was collected by filtration, washed with
pentane, and dried under vacuum. Yield: 425 mg, 75%.
Single crystals suitable for X-ray diffraction were obtained by
crystallization at -35 °C from dichloromethane. 1H NMR
(CD2Cl2): δ 8.28 (d, J ) 5.3 Hz, 2H, 6-py), 7.73 (t, J ) 7.1 Hz,
2H, 4-py), 7.23 (d, J ) 8.0 Hz, 2H, 3-py), 7.14 (t, J ) 6.7 Hz,
2H, 5-py), 6.77 (t, J ) 7.5 Hz, 4H, m-Ph), 6.50 (t, J ) 7.3 Hz,
2H, p-Ph), 6.45 (d, J ) 7.4 Hz, 4H, o-Ph), 2.05 (s, 4H, CH2),
1.31 (s, 12H, CH3). 1H NMR (-100 °C, CD2Cl2): δ 8.42 (br s,
2H, 6-py), 7.74 (br t, 4-py), 7.19 (br d, J ) 5.3 Hz, 3-py), 7.13
(t, J ) 7.5 Hz, 5-py), 6.73 (br, 4H, m-Ph), 6.43 (br, 2H, p-Ph),
6.25 (br, 4H, o-Ph), 2.04 (br, 2H, CH2), 1.81 (br, 2H, CH2), 1.24
(br, 6H, CH3), 0.95 (br, 6H, CH3). 13C{1H} NMR (CD2Cl2): δ
173.7 (2-py), 149.9 (ipso-Ph), 147.8 (6-py), 138.9 (4-py), 128.0
(o-Ph), 125.7 (m-Ph), 122.3, 121.0, 119.1 (3-py, 5-py, and p-Ph),
84.3 (COZr), 61.4 (J CH ) 121 Hz, CH2), 31.65 (CH3). Anal.
Calcd for C30H34N2O2Zr: C, 66.00; H, 6.29; N, 5.13. Found:
C, 65.84; H, 6.44; N, 5.21.
{p yCH(CF 3)O}2Zr (CH2P h )2 (3c). A benzene solution (30
mL) of pyCH(CF3)OH (377 mg, 2.13 mmol) was added to a
benzene solution (30 mL) of Zr(CH2Ph)4 (489 mg, 1.07 mmol)
at 23 °C. The orange solution was stirred for 1 h at 23 °C.
The volatiles were removed under vacuum. The yellow solid
was slurried in a mixture of benzene (7 mL) and pentane (5
mL), collected by filtration, washed with pentane (15 mL), and
dried under vacuum. Yield: 425 mg, 63%. This compound
exists as a mixture of isomers as described in the text. 1H
NMR (CD2Cl2, (R, R, Λ) and (R, R, ∆) isomers at 23 °C, fast
exchange): δ 8.00 (d, J ) 5.3 Hz, 2H, 6-py), 7.68 (td, J ) 7.7,
1.6 Hz, 2H, 4-py), 7.41 (d, J ) 8.0 Hz, 2H, 3-py), 7.08 (t, J )
6.5 Hz, 2H, 5-py), 6.89 (t, J ) 7.5 Hz, 4H, m-Ph), 6.67 (t, J )
7.2 Hz, 2H, p-Ph), 6.50 (d, J ) 7.2 Hz, 4H, o-Ph), 5.52 (q, J CF
) 7.4 Hz, 2H, CHCF3), 1.94 (d, J ) 8.6 Hz, 1H, CH2), 1.75 (d,
J ) 8.6 Hz, 1H, CH2). 1H NMR (CD2Cl2, (R, R, Λ) and (R, R,
∆) isomers at -90 °C, 3/1 isomer ratio, aliphatic region only):
major isomer δ 5.68 (br q, J ) 6.5 Hz, 2H, CHCF3), 1.65 (br,
C
16H12ClF18N3O3Zr: C, 33.55; H, 1.41; N, 4.89; Cl, 4.13.
Found: C, 33.37; H, 1.30; N, 4.92; Cl, 3.95.
{(6-SiMe3)p yC(CF 3)2O}2Zr Cl2(THF )2 (4d ). Hexane (20
mL) was added to a mixture of solid ZrCl4(THF)2 (362 mg,
0.959 mmol) and (6-SiMe3)pyC(CF3)2OLi (620 mg, 1.92 mmol),
affording a white slurry, which was stirred for 18 h at 23 °C.
The volatiles were removed under vacuum to afford a white
solid, which was extracted with toluene (30 mL). The extract
was cooled to -35 °C. The white solid was collected by
filtration and dried under vacuum (604 mg, 59%). 1H NMR
(C6D6): δ 8.38 (d, J ) 7.7 Hz, 2H, 3 or 5-py), 7.10 (t, J ) 7.4
Hz, 2H, 4-py), 6.94 (d, J ) 7.4 Hz, 2H, 3- or 5-py), 4.08 (br,
8H, THF), 1.20 (br, 8H, THF), 0.27 (s, 18H, SiMe3).
{(6-SiMe3)p yC(CF 3)2O}2Zr Cl2 (5d ). A toluene solution (30
mL) of {(6-SiMe3)pyC(CF3)2O}2ZrCl2(THF)2 (315 mg, 0.295
mmol) was warmed at 95 °C under N2 flow for 3 h. The
volatiles were removed under vacuum to afford a colorless oil,
which was dried under vacuum (65 °C, 17 h) to give a white
solid. 1H NMR (CD2Cl2): δ 8.02 (dd, J ) 7.7, 1.1 Hz, 2H, 3- or
5-py), 7.94 (t, J ) 7.9 Hz, 2H, 4-py), 7.67 (d, J ) 8.0 Hz, 2H,
3- or 5-py), 0.64 (s, 18H, CH3). 13C{1H} NMR (CD2Cl2): δ 172.5
(6-py), 155.1 (2-py), 137.8 (4-py), 134.9 (5-py), 123.1 (3-py),
122.6 (q, J CF ) 290 Hz, CF3), 76.3 (COZr), 1.8 (SiMe3). 19F
NMR (CD2Cl2):
22H24Cl2F12N2O2Si2Zr: C, 33.24; H, 3.05; N, 3.53. Found: C,
33.50; H, 2.97; N, 3.38.
δ -74.4 (s, CF3). Anal. Calcd for
C
[{p yC(CF3)2O}2Zr (CH2P h )][P h CH2B(C6F5)3] (6a ). A ben-
zene solution (3 mL) of B(C6F5)3 (68.6 mg, 0.134 mmol) was
added to a benzene solution (5 mL) of {pyC(CF3)2O}2Zr(CH2-
Ph)2 (102.6 mg, 0.135 mmol) at 23 °C. A yellow oil separated.
The mixture was stirred for 25 min at 23 °C. The volatiles
were removed under vacuum. The yellow solid was washed
with pentane and dried under vacuum to afford a yellow solid
(97 mg, 57%). 1H NMR (CD2Cl2): δ 8.33 (m, 4H, 4- and 6-py),
7.98 (d, J ) 8 Hz, 2H, 3-py), 7.87 (t, J ) 6.5 Hz, 2H, 5-py),
7.57 (br, 2H, meta-ZrCH2Ph), 7.28 (t, J ) 7.4 Hz, 1H, para-

Neutral and Cationic Zirconium Benzyl Complexes
Organometallics, Vol. 16, No. 15, 1997 3313
ZrCH2Ph), 7.00 (d, J ) 7.3 Hz, 2H, ortho-ZrCH2Ph), 6.88 (t, J
) 7 Hz, 2H, meta-BCH2Ph), 6.79 (t, J ) 6.6 Hz, 1H, para-
BCH2Ph), 6.76 (d, J ) 7.3 Hz, 2H, ortho-BCH2Ph), 3.42 (s, 2H,
ZrCH2), 2.82 (s, 2H, BCH2). 1H NMR (-80 °C, CD2Cl2): δ 8.84
(d, J ) 4.8 Hz, 1H, 6-py), 8.35 (t, J ) 7.7 Hz, 1H), 8.13 (t, 1H),
8.04 (d, J ) 7.4 Hz, 1H, 3-py), 7.95 (t, J ) 6.3 Hz, 1H), 7.86 (t,
7.1 Hz, 1H), 7.73 (m, 3H), 7.63 (d, J ) 5.0 Hz, 1H, 6-py), 7.02
(d, 1H, ortho-ZrCH2Ph), 6.8 (m, 3H, meta- and para-BCH2Ph,
ortho-ZrCH2Ph), 6.61 (d, J ) 7.0 Hz, 2H, ortho-BCH2Ph), 3.49
(d, J ) 8.2 Hz, 1H, ZrCH2Ph), 3.20 (d, J ) 8.3 Hz, 1H, ZrCH2-
Ph), 2.68 (s, 2H, BCH2Ph); the para-ZrCH2Ph signal and one
two isomers (3/2 ratio). 1H NMR (CD2Cl2, aliphatic region
only): major isomer δ 3.18 (d, J ) 10.5 Hz, 1H, CH2), 2.93 (d,
J ) 10.7 Hz, 1H, CH2), 2.16 (s, 3H, Me), 1.71 (s, 3H, Me), 1.63
(s, 3H, Me), 1.43 (s, 3H, Me); minor isomer δ 2.88 (d, J ) 11
Hz, 1H, CH2), 2.68 (d, J ) 11 Hz, 1H, CH2), 2.35 (s, 3H, Me),
1.88 (s, 3H, Me), 1.83 (s, 3H, Me), 1.63 (s, 3H, Me).
Eth ylen e P olym er ization with 6a fr om 3a an d B(C6F5)3.
The following procedure is representative. Benzene (30 mL)
was added to a mixture of 3a (14 mg, 0.018 mmol) and B(C6F5)3
(9.1 mg, 0.018 mmol) in a Fischer-Porter bottle at 23 °C under
N2. The yellow solution was stirred for 10 min. The N2 was
replaced by ethylene (3.3 atm), and polymerization was carried
out for 30 min at 40 °C. Polyethylene precipitated im-
mediately. Methanol (80 mL) was added to quench the
polymerization, and the polymer was collected by filtration and
dried under vacuum. Polymer yield 0.96 g; activity 32 (kg of
PE)(mol of cat)-1 atm-1 h-1. Polymer analysis: Mn ) 6,200,
Mw/Mn ) 2.6, Tm ) 128 °C (DSC), 1 vinyl group/chain by 1H
NMR, PhCH2 end group by 1H NMR (25% of amount predicted
meta-ZrCH2Ph signal are obscured. 19F NMR (CD2Cl2):
δ
-76.2 (12F, CF3), -131.3 (d, J FF ) 21.5 Hz, 6F, o-C6F5), -164.9
(t, J FF ) 20.5 Hz, 3F, p-C6F5), -167.8 (t, J FF ) 18.9 Hz, 6F,
m-C6F5). 13C NMR (CD2Cl2): δ 78.9 (ZrCH2, J CH ) 142 Hz),
32 (br, BCH2). Anal. Calcd for C48H22BF27N2O2Zr: C, 45.26;
H, 1.74; N, 2.20. Found: C, 43.80; H, 2.03; N, 2.33. The low
C analysis may reflect thermal decomposition.
Gen er ation of [{pyC(CF3)2O}2Zr (CH2P h )][B(C6F5)4] (7a).
Benzene (0.5 mL) was added to a mixture of {pyC(CF3)2O}2-
Zr(CH2Ph)2 (23.5 mg, 0.031 mmol) and [HNMe2Ph][B(C6F5)4]
(25.2 mg, 0.031 mmol). A brown oil separated. The mixture
was shaken for 20 min at 23 °C. Pentane was added, and the
benzene/pentane layer was decanted. The yellow oil was
washed with pentane and dried under vacuum, yielding a
yellow solid. 1H NMR (CD2Cl2): δ 8.33 (m, 4H, 4- and 6-py),
8.00 (d, J ) 8 Hz, 2H, 3-py), 7.91 (t, 2H, J ) 6.7 Hz, 5-py), 7.5
(br, 2H, m-Ph), 7.30 (t, J ) 7.6 Hz, p-Ph), 7.02 (d, J ) 7.5 Hz,
o-Ph), 3.43 (s, 2H, ZrCH2Ph).
assuming all 3a is activated), 0.6 branches (>C5)/chain by 13
NMR.
C
Eth ylen e P olym er iza tion w ith 7a fr om 3a a n d [P h 3C]-
[B(C6F 5)4]. Conditions: 1 L autoclave, 500 mL of toluene, 44
µmol of 3a , 44 µmol of [Ph3C][B(C6F5)4], 45 °C, 8 atm, 60 min.
Activity: 56 (kg of PE)(mol of cat)-1 h-1 atm-1. Mn ) 10 400,
Mw/Mn ) 2.8. With added Al(iBu)3 (17 equiv vs 3a ), activity
) 60 (kg of PE)(mol of cat)-1 h-1 atm-1, Mn ) 5,900, Mw/Mn )
3.7.
E t h ylen e P olym er iza t ion w it h 7a fr om 3a a n d
[HNMe2P h ][B(C6F 5)4]. Conditions: Fischer-Porter bottle, 30
mL of benzene, 20 µmol of 3a , 19 µmol of [HNMe2Ph][B(C6F5)4],
42 °C, 3.3 atm, 30 min. Yield 0.42 g; activity 13 (kg of PE)-
[(p yCMe2O)2Zr (CH2P h )][P h CH2B(C6F 5)3] (6b). A ben-
zene solution (10 mL) of B(C6F5)3 (116 mg, 0.227 mmol) was
added dropwise to a benzene solution (20 mL) of (pyCMe2O)2-
Zr(CH2Ph)2 (124 mg, 0.228 mmol) over 10 min. A yellow oil
separated, and the mixture was stirred for 1.5 h at 23 °C. The
benzene layer was decanted, and the oil was washed with
benzene (2 × 10 ml) and dried under vacuum to afford a yellow
solid. Yield: 153 mg, 64%. The 1H NMR spectrum established
that this compound exists of two isomers (3/2 ratio). 1H NMR
(CD2Cl2, aliphatic region only): major isomer δ 3.15 (d, J )
10.7 Hz, 1H, CH2), 2.90 (d, J ) 10.7 Hz, 1H, CH2), 2.80 (s, 2H,
BCH2Ph), 2.13 (s, 3H, CH3), 1.69 (s, 3H, CH3), 1.61 (s, 3H,
CH3), 1.40 (s, 3H, CH3); minor isomer δ 2.82 (d, partially
obscured, CH2), 2.80 (s, 2H, BCH2Ph), 2.67 (d, J ) 11.2 Hz,
1H, CH2), 2.31 (s, 3H, CH3), 1.86 (s, 3H, CH3), 1.81 (s, 3H,
CH3), 1.58 (s, 3H, CH3); the aromatic region is complex. 13C
NMR (CD2Cl2, both isomers): δ 173.5 (2-py, major), 173.2 (2-
py, minor), 165.1 (2-py, major), 163.9 (2-py, minor), 148.9,
148.6 (dm, J CF ) 234 Hz, C6F5), 147.7, 146.1, 146.0, 145.0,
143.5, 143.3, 143.2, 142.3, 140.9, 137.8 (dm, J CF ) 244 Hz,
C6F5), 136.7 (dm, J CF ) 254 Hz, C6F5), 130.2, 129.5, 129.2,
129.0, 128.7, 128.4, 128.2, 127.1, 126.8, 125.5, 125.2, 125.2,
125.1, 123.5, 123.3, 122.8, 122.6, 122.2, 90.7 (CO, major), 90.5
(CO, minor), 90.0 (CO, minor), 89.2 (CO, major), 77.1 (minor
ZrCH2, J CH ) 119 Hz), 75.3 (major ZrCH2, J CH ) 126 Hz), 34.0
(Me, minor), 32.7 (2Me, major), 32.1 (Me, minor), 31.7 (Me and
BCH2 minor,), 31.3 (Me, major), 31.1 (Me, minor), 30.5 (Me,
major).
(mol of cat)-1 atm-1 h-1
.
Eth ylen e P olym er iza tion w ith 3c/B(C6F 5)3. Conditions:
Fischer-Porter bottle, 30 mL of toluene, 16 µmol of 3c, 16 µmol
of B(C6F5)3, 40 °C, 3.3 atm, 30 min. Yield 0.074 g; activity 2.6
(kg of PE)(mol of cat)-1 atm-1 h-1
.
Eth ylen e P olym er iza tion w ith 3a a n d MAO. Condi-
tions: 1 L autoclave, 500 mL of toluene, 44 µmol of 3a , 44
mmol of MAO (per Al basis), 45 °C, 8 atm, 60 min. Yield 0.46
g; activity: 1.3 (kg of PE)(mol of cat)-1 h-1 atm-1. Mn ) 13,000;
Mw/Mn ) 28.2.
Hexen e P olym er iza tion w ith 6a . Compound 6a (32 mg,
0.025 mmol) was dissolved in CD2Cl2 (0.5 mL) to give a yellow
solution. 1-Hexene (4.6 mmol) was added via vacuum transfer
at -78 °C, and the solution was warmed to 23 °C for 10 min.
1H NMR analysis of the reaction mixture showed that the
1-hexene was 98% converted to polyhexene, corresponding to
an activity of 90 (kg PH)(mol of cat)-1 h-1. The volatiles were
removed yielding a sticky solid, which was washed with
methanol and dried under vacuum. Mn ) 840 by 1H NMR;
microstructure atactic by 13C NMR.42
Ack n ow led gm en t. This work was supported by
DOE Grant No. DE-FG02-88ER13935 and the Mitsu-
bishi Chemical Corporation.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data, positional and thermal parameters, and
bond distances and angles for 3b (11 pages). Ordering
information is given on any current masthead page.
Gen er a tion of [(p yCMe2O)2Zr (CH2P h )][B(C6F 5)4] (7b).
Benzene (0.5 mL) was added to a mixture of (pyCMe2O)2Zr-
(CH2Ph)2 (18.4 mg, 0.034 mmol) and [HNMe2Ph][B(C6F5)4]
(27.3 mg, 0.034 mmol). A yellow oil separated. The mixture
was shaken for 15 min at 23 °C. The benzene layer was
decanted, and the oil was washed with benzene (3 × 0.5 ml).
The oil was dried under vacuum to afford a yellow solid. The
1H NMR spectrum established that this compound consists of
OM9702439
(42) (a) Babu, G. N.; Newmark, R. A.; Chien, J . C. W. Macromol-
ecules 1994, 27, 3383. (b) Asakura, T.; Demura, M.; Nishiyama, Y.
Macromolecules 1991, 24, 2334.