Synthesis, structural investigation, and reactivity of neutral and cationic bis(guanidinato)zirconium(IV) complexes

Article abstract of DOI:10.1021/om000995u

The mono(guanidinato) complex Cp(guan)ZrCl₂ (1; guan = η²-(ⁱPrN)₂C(NMe₂)) was prepared by treatment of CpZrCl₃ (Cp = η⁵-C₅H₅) with the in situ generated lithium guanidinate salt 2. The dimethylamino group of 1 resists quaternization by alkylating and silylating reagents. Complex 1 undergoes ligand redistribution when treated with 2 equiv of MeLi, but reaction with 2 equiv of MeMgCl affords the dimethyl derivative Cp(guan)ZrMe₂ (3). Insertion of 2 equiv of diisopropylcarbodiimide into the Zr-N bonds of (Me₂N)₂ZrCl₂(THF)₂ produces the bis(guanidinato)zirconium dichloride complex (guan)₂ZrCl₂ (4). Alkylation of 4 with 2 equiv of MeLi or PhCH₂MgCl affords the dialkyl derivatives (guan)₂ZrMe₂ (5) and (guan)₂Zr(CH₂Ph)₂ (6), respectively. Variable-temperature NMR experiments on 6 reveal a limiting C₂-symmetric solution structure at 253 K. Complex 5 undergoes reaction with electrophiles (Me₃SiOTf(OTf = OSO₂CF₃), B(C₆F₅)₃, [Ph₃C][B(C₆F₅)₄]) to yield stable products of methide abstraction: neutral complexes (guan)₂Zr(OTf)₂ (7) and (guan)₂Zr(Me)OTf (8), base-free cationic alkyl salts [(guan)₂ZrMe][MeB(C₆ F₅)₃] (9) and [(guan)₂ZrMe][B(C₆ F₅)₄] (10), and the dinuclear methyl-bridged cation [((guan)₂ZrMe)₂-μ-Me][B(C₆ F₅)₄] (11). Complexes 1, 4-7, and 11 have been characterized by X-ray diffraction. Dinuclear cation 11 exhibits bridge-terminal methyl exchange on the NMR time scale at room temperature, with decoalescence observed at 224 K. Dibenzyl complex 6 undergoes reaction with [Ph₃C][B(C₆F₅)₄] in CH₂Cl₂, yielding the cationic benzyl complex [(guan)₂Zr(CH₂Ph)][B(C₆ F₅)₄] (15). Spectroscopic data imply that the benzyl ligand of 15 adopts an undistorted monodentate coordination mode. Complexes 4, 5, and 10 were found to have low to moderate activities for the polymerization of α-olefins.

Full text of DOI:10.1021/om000995u

1808
Organometallics 2001, 20, 1808-1819
Syn th esis, Str u ctu r a l In vestiga tion , a n d Rea ctivity of
Neu tr a l a n d Ca tion ic Bis(gu a n id in a to)zir con iu m (IV)
Com p lexes
Andrew P. Duncan, Sarah M. Mullins, J ohn Arnold,* and Robert G. Bergman*
Department of Chemistry and Center for New Directions in Organic Synthesis (CNDOS),
University of California, and Division of Chemical Sciences, Lawrence Berkeley
National Laboratory, Berkeley, California 94720-1460
Received November 21, 2000
The mono(guanidinato) complex Cp(guan)ZrCl2 (1; guan ) η2-(iPrN)2C(NMe2)) was prepared
by treatment of CpZrCl3 (Cp ) η5-C5H5) with the in situ generated lithium guanidinate salt
2. The dimethylamino group of 1 resists quaternization by alkylating and silylating reagents.
Complex 1 undergoes ligand redistribution when treated with 2 equiv of MeLi, but reaction
with 2 equiv of MeMgCl affords the dimethyl derivative Cp(guan)ZrMe2 (3). Insertion of 2
equiv of diisopropylcarbodiimide into the Zr-N bonds of (Me2N)2ZrCl2(THF)2 produces the
bis(guanidinato)zirconium dichloride complex (guan)2ZrCl2 (4). Alkylation of 4 with 2 equiv
of MeLi or PhCH2MgCl affords the dialkyl derivatives (guan)2ZrMe2 (5) and (guan)2Zr(CH2-
Ph)2 (6), respectively. Variable-temperature NMR experiments on 6 reveal a limiting C2-
symmetric solution structure at 253 K. Complex 5 undergoes reaction with electrophiles
(Me3SiOTf (OTf ) OSO2CF3), B(C6F5)3, [Ph3C][B(C6F5)4]) to yield stable products of methide
abstraction: neutral complexes (guan)2Zr(OTf)2 (7) and (guan)2Zr(Me)OTf (8), base-free
cationic alkyl salts [(guan)2ZrMe][MeB(C6F5)3] (9) and [(guan)2ZrMe][B(C6F5)4] (10), and the
dinuclear methyl-bridged cation [((guan)2ZrMe)2-µ-Me][B(C6F5)4] (11). Complexes 1, 4-7,
and 11 have been characterized by X-ray diffraction. Dinuclear cation 11 exhibits bridge-
terminal methyl exchange on the NMR time scale at room temperature, with decoalescence
observed at 224 K. Dibenzyl complex 6 undergoes reaction with [Ph3C][B(C6F5)4] in
CH2Cl2, yielding the cationic benzyl complex [(guan)2Zr(CH2Ph)][B(C6F5)4] (15). Spectroscopic
data imply that the benzyl ligand of 15 adopts an undistorted monodentate coordination
mode. Complexes 4, 5, and 10 were found to have low to moderate activities for the
polymerization of R-olefins.
In tr od u ction
sis, prompting intense synthetic and mechanistic in-
vestigations on these systems.9 Although olefin coordina-
tion and enchainment occur at the cationic metal center,
the nature of the cocatalyst/counteranion has also been
found to strongly affect catalyst productivity.10 Specif-
ically, it has been shown that attenuation of ion-pairing
interactions leads to higher catalyst activities.11-16 It
is not surprising, then, that some of the most active
homogeneous Ziegler-type catalysts reported to date
have utilized the extremely weakly coordinating tetra-
kis(pentafluorophenyl)borate (B(C6F5)4) counteranion.17-19
Although metallocenes and their derivatives have
provided stable platforms for many stoichiometric and
catalytic organometallic transformations, the need for
alternative ancillary ligands with diverse electronic and
steric properties has recently been emphasized.1-3 This
effort has been especially evident in the field of homo-
geneous Ziegler-Natta catalysis.2,4-8
Group 4 alkyl salts ([LnM(R)](X) (M ) Ti, Zr, Hf; R )
H, alkyl; X ) weakly coordinating anion) have been
implicated as the actively propagating species in homo-
geneous Ziegler-Natta R-olefin polymerization cataly-
(9) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325 and
references therein.
(1) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994,
33, 497.
(2) Gade, L. H. Chem. Commun. 2000, 173.
(10) Chen, E. Y.; Marks, T. J . Chem. Rev. 2000, 100, 1391.
(11) Chen, Y.; Metz, M. V.; Li, L.; Stern, C. L.; Marks, T. J . J . Am.
Chem. Soc. 1998, 120, 6287.
(3) Edelmann, F. T. Coord. Chem. Rev. 1994, 137, 403.
(4) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428. Because of the excellent coverage in this review,
we have not duplicated many of its citations explicitly in this paper.
References 5-8 provide examples of diverse ligand sets used recently
in Ziegler-Natta type polymerizations.
(5) Younkin, T. R.; Connor, E. F.; Henderson, J . I.; Friedrich, S. K.;
Grubbs, R. H.; Bansleben, D. A. Science 2000, 287, 460.
(6) Tshuva, E. Y.; Goldberg, I.; Kol, M.; Weitman, H.; Goldschmidt,
Z. Chem. Commun. 2000, 379.
(12) J ia, L.; Yang, X.; Stern, C.; Marks, T. J . Organometallics 1997,
16, 842.
(13) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015.
(14) Yang, X.; King, W. A.; Sabat, M.; Marks, T. J . Organometallics
1993, 12, 4254.
(15) Lancaster, S. J .; Walker, D. A.; Thornton-Pett, M.; Bochmann,
M. Chem. Commun. 1999, 1533.
(16) Bochmann, M. Angew. Chem., Int. Ed. Engl. 1992, 31, 1181.
(17) Stephan, D. W.; Guerin, F.; Spence, R. E. v. H.; Koch, L.; Gao,
X.; Brown, S. J .; Swabey, J . W.; Wang, Q.; Xu, W.; Zoricak, P.; Harrison,
D. G. Organometallics 1999, 18, 2046.
(7) Vollmerhaus, R.; Rahim, M.; Tomaszewski, R.; Xin, S.; Taylor,
N. J .; Collins, S. Organometallics 2000, 19, 2161.
(8) Shmulinson, M.; Galan-Fereres, M.; Lisovskii, A.; Nelkenbaum,
E.; Semiat, R.; Eisen, M. S. Organometallics 2000, 19, 1208.
(18) Giardello, M. A.; Eisen, M. S.; Stern, C. L.; Marks, T. J . J . Am.
Chem. Soc. 1995, 117, 12114.
10.1021/om000995u CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/30/2001

Bis(guanidinato)zirconium(IV) Complexes
Organometallics, Vol. 20, No. 9, 2001 1809
F igu r e 2. Resonance stabilization of a cationic metal
center by a guanidinato ligand.
Resu lts a n d Discu ssion
Syn th esis, Str u ctu r e, an d Reactivity of Cp(gu an )-
Zr X2 (X ) Cl, Me) Der iva tives. The synthesis of
cationic zirconium alkyl complexes is often accomplished
by alkide abstraction from neutral dialkylzirconium
complexes using a strong Lewis acid. An initial concern
about the (guanidinato)zirconium complexes was whether
the Lewis basic dialkylamino group of the ligand would
be inert under these conditions. Lone pair π-donation
to the chelate from the NR′2 group should lower its
basicity, thereby rendering the ligand resistant to
electrophilic attack at that site. Maximization of dialkyl-
amino lone pair donation requires, as stated above,
coplanarity of the NR′2 moiety and the metal chelate.
The ability of the ligand to achieve such a coplanar
arrangement is controlled to a large degree by the steric
demands of the ligand substituents. The choice of R′ )
Me and R ) iPr for the guanidinato ligand used in this
study represents a balance between minimization of
intraligand steric interactions and steric protection of
the metal center.
F igu r e 1. Resonance contributors for the guanidinate
monoanion.
While these catalysts are highly active, Lewis base free
[LnM-Me][B(C6F5)4] salts generally lack sufficient ther-
mal stability to be isolated in pure form.7,12,17,20,21 We
describe here the use of a bis(guanidinato) ancillary
ligand set in the synthesis and characterization of
neutral and cationic complexes of Zr, including the
isolated and fully characterized base-free methyl cation
[(guan)2Zr-Me][B(C6F5)4].
Several research groups have recently reported com-
plexes of both main group22,23 and transition metals24-32
with guanidinate monoanions ([(RN)2C(NR′2)]-). The
unique character of the chelating guanidinato (guan)
ligand arises from the ability of the NR′2 moiety to
donate lone pair electron density to the central carbon
atom of the chelate (provided that steric constraints
allow for coplanarity of the dialkylamino group and the
chelate ring) (Figure 1).22 The resulting zwitterionic
resonance structure places a formal negative charge on
both nitrogen atoms used for metal-ligand bonding,
thereby increasing their potential for electron donation
to the metal. In a case where the metal center bears a
positive charge, donation from the guanidinato ligand
is anticipated to stabilize that charge by delocalizing it
into the ligand framework (Figure 2). We anticipated
that this donor effect might provide stabilization to an
electronically unsaturated cationic Zr center sufficient
to allow isolation and characterization of Lewis base-
free B(C6F5)4 salts of [(guan)2Zr-R]+ cations.
The basicity of the dimethylamino moiety and the
extent of lone pair π-donation was assessed initially for
the mono(guanidinato) complex Cp(guan)ZrCl2 (1). Com-
plex 1 was synthesized in 67% yield by treatment of
CpZrCl3 with the lithium guanidinate salt 2 (generated
in situ from reaction of lithium dimethylamide and
diisopropylcarbodiimide) in Et2O (eq 1). Single crystals
(19) Chien, J . C. W.; Llinas, G. H.; Rausch, M. D.; Lin, G. Y.; Winter,
H. H. J . Am. Chem. Soc. 1991, 113, 8569.
(20) Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg,
H. Organometallics 1996, 15, 2672.
suitable for an X-ray diffraction study were obtained by
vapor diffusion of pentane into a toluene solution of 1.
An ORTEP diagram depicting the molecular structure
of 1 is shown in Figure 3. Representative bond lengths
and angles are given in Table 1, and selected crystal
and structure refinement data are shown in Table 2.
The shortened C(1)-N(3) bond length of 1.373(4) Å
(typical C-N single-bond length 1.42-1.45 Å) indicates
some double-bond character between these atoms. This
is likely the result of dimethylamino lone pair π-dona-
tion to the central carbon of the chelate ring and
suggests that the dimethylamino group will display
reduced Lewis basicity. Consistent with this hypothesis,
complex 1 is unreactive toward alkylating and silylating
agents (MeOTf, Me3SiOTf, CH3I) (Scheme 1). Thus,
quaternization at N(3) is not observed.
(21) The methyl(decamethylthorocene) cation reported by Marks
and co-workers is an important exception.11,43
(22) Aeilts, S. L.; Coles, M. P.; Swenson, D. C.; J ordan, R. F.; Young,
V. G. Organometallics 1998, 17, 3265.
(23) Giesbrecht, G. R.; Shafir, A.; Arnold, J . J . Chem. Soc., Dalton
Trans. 1999, 3601.
(24) (a) Wood, D.; Yap, G. P. A.; Richeson, D. S. Inorg. Chem. 1999,
38, 8. (b) Note added in proof: For
a very recent review of the
coordination chemistry of guanidines and guanidinates, see: Bailey,
P. J .; Pace, S. Coord. Chem. Rev. 2001, 91.
(25) Tin, M. K. T.; Yap, G. P. A.; Richeson, D. S. Inorg. Chem. 1999,
38, 998.
(26) Tin, M. K. T.; Thirupathi, N.; Yap, G. P. A.; Richeson, D. S. J .
Chem. Soc., Dalton Trans. 1999, 2947.
(27) Robinson, S. D.; Sahajpal, A. J . Chem. Soc., Dalton Trans. 1997,
3349.
(28) Holman, K. T.; Robinson, S. D.; Sahajpal, A.; Steed, J . W. J .
Chem. Soc., Dalton Trans. 1999, 15.
(29) Bailey, P. J .; Mitchell, L. A.; Parsons, S. J . Chem. Soc., Dalton
Trans. 1996, 2839.
(30) Thirupathi, N.; Yap, G. P. A.; Richeson, D. S. Chem. Commun.
1999, 2483.
(31) Okamoto, S.; Livinghouse, T. Organometallics 2000, 19, 1449.
(32) Thirupathi, N.; Yap, G. P. A.; Richeson, D. S. Organometallics
2000, 19, 2573.
Addition of 2 equiv of MeLi to 1 in Et2O solution
results in ligand redistribution: 0.5 equiv of Cp2ZrMe2
and 0.5 equiv of the bis(guanidinato) complex (guan)2-

1810 Organometallics, Vol. 20, No. 9, 2001
Duncan et al.
ligands of complex 4 are fluxional at room temperature,
as evidenced by observation (1H NMR spectroscopy) of
a single resonance for the eight isopropyl methyl groups
(doublet, 24H) and the four dimethylamino methyl
groups (singlet, 12H). Similar spectroscopic features are
observed for all (guan)2ZrX2 derivatives (vide infra).
Alkylation of 4 with 2 equiv of MeLi or 2 equiv of
PhCH2MgCl in Et2O gives (guan)2ZrMe2 (5) and (guan)2-
Zr(CH2Ph)2 (6) in 86 and 80% yields, respectively, after
recrystallization from pentane (Scheme 2). The isopropyl
(methyl and methine) and benzylic (methylene) reso-
nances of 6 are broad in the room-temperature 1H NMR
spectrum, presumably due to hindered rotation of the
benzyl and guanidinato ligands. The 1H NMR spectrum
of 6 at 220 K (toluene-d8) is consistent with a limiting
C2-symmetric structure: four distinct isopropyl methyl
resonances, as well as two doublets (2J HH ) 10.0 Hz)
for the diastereotopic benzylic protons, are observed.
ORTEP diagrams depicting the solid-state structures
of 5 and 6 are shown in Figures 5 and 6 along with
relevant bond lengths and angles in Tables 4 and 5,
respectively. Selected crystal and structure refinement
data are given in Tables 2 and 6. The X-ray diffraction
data for 6 are consistent with the structural assignment
F igu r e 3. ORTEP diagram of Cp(guan)ZrCl2 (1) showing
non-hydrogen atom-numbering scheme (50% thermal el-
lipsoids).
Ta ble 1. Metr ica l Da ta for Cp (gu a n )Zr Cl2 (1)
1
postulated from the low-temperature H NMR spectro-
Selected Bond Lengths (Å)
scopic data. Additionally, the solid-state structure of 6
reveals that both benzyl ligands adopt undistorted (η1)
coordination modes.
Zr-Cl(1)
2.4569(9)
2.166(3)
2.2120(3)
1.331(4)
Zr-Cl(2)
2.4247(9)
2.225(2)
1.349(4)
1.373(4)
Zr-N(1)
Zr-N(2)
Zr-Cpcentroid
N(2)-C(1)
N(1)-C(1)
N(3)-C(1)
Treatment of 5 with 2 equiv of Me3SiOTf in benzene
produces the bis(triflato) complex (guan)2Zr(OTf)2 (7) in
Selected Bond Angles (deg)
C(1)-Zr-Cl(2)
91.36(3) N(1)-Zr-N(2)
111.1(3)
44.78
60.43(9)
1
77% yield along with 2 equiv of Me4Si (detected by H
N(1)-C(1)-N(2)
[N(1)-C(1-N(2)]/
[C(8)-C(9)-N(3)]a
C(9)-N(3)-C(1) 121.0(3)
NMR spectroscopy) (Scheme 2). The isopropyl methyl
1
resonances are broadened in the room-temperature H
NMR spectrum of 7, again presumably due to hindered
rotation of the bulky triflato and guanidinato ligands.
Crystals of 7 suitable for X-ray diffraction were obtained
by allowing the reaction mixture to stand at room
temperature overnight. An ORTEP diagram showing
the solid-state structure of 7 is presented in Figure 7.
Representative bond lengths and angles are given in
Table 7; selected crystal and structure refinement data
are given in Table 6.
a
The angle between the planes of the chelate (N-C-N) and
its dimethylamino substituent.
1
ZrMe2 (vide infra), are observed by H NMR spectros-
copy (Scheme 1). However, alkylation with 2 equiv of
MeMgCl in Et2O affords the desired Cp(guan)ZrMe2
product (3) in 61% yield (Scheme 1).
Syn th esis a n d Str u ctu r es of (gu a n )2Zr X2 Com -
p lexes (X ) Cl, CH3, CH2P h , OTf). Synthesis of the
bis(guanidinato) complex (guan)2ZrCl2 (4) is accom-
plished by treatment of (Me2N)2ZrCl2(THF)2 with 2
equiv of diisopropylcarbodiimide (eq 2). Spectroscopi-
Com m en ts on th e Solid -Sta te Str u ctu r es of Neu -
tr a l (gu a n )2Zr X2 Der iva tives (X ) Cl, Me, CH2P h ,
OTf). The utility of the guanidinato ligand lies in its
ability to stabilize electron-deficient metal centers.
Although this effect is likely to be more pronounced in
highly electronically unsaturated systems (i.e., metal
cations), it is possible that the donor ability of the
guanidinato ligand may manifest itself in neutral
complexes as well. Analysis of the crystallographic data
for (guan)2ZrX2 (X ) Cl, Me, CH2Ph, OTf) derivatives
reveals that the relative electron-withdrawing or -re-
leasing ability of the X ligands affects the degree to
which π-donation from the dimethylamino group occurs.
Accordingly, 5 and 6, which bear electron-releasing alkyl
ligands and therefore possess more electron-rich metal
centers, exhibit Me2N-C bond lengths of 1.388(3) and
1.385(3) Å (for 5) and 1.394(4) and 1.385(4) Å (for 6):
slightly shorter than typical C-N single bonds. Com-
plexes 4 and 7, which bear electron-withdrawing chlo-
ride and triflato ligands, have electron-poor metal
centers relative to 5 and 6 and, hence, exhibit more
contracted Me2N-C bonds (1.365(5) and 1.360(5) Å for
cally pure 4 is obtained in >90% yield simply by removal
of solvent from the crude reaction mixture. Recrystal-
lization from Et2O gives analytically pure 4 in 54% yield.
Similar insertion of carbodiimides into metal-amide
bonds has been observed in related systems.25,33 An
ORTEP diagram depicting the molecular structure of 4
is shown in Figure 4. Relevant bond lengths and angles
are given in Table 3, and selected crystal and structure
refinement data are shown in Table 2. The guanidinato
(33) Chandra, G.; J enkins, A. D.; Lappert, M. F. J . Chem. Soc. A
1970, 2550.

Bis(guanidinato)zirconium(IV) Complexes
Organometallics, Vol. 20, No. 9, 2001 1811
Ta ble 2. Selected Cr ysta l Da ta a n d Da ta Collection P a r a m eter s for Cp (gu a n )Zr Cl2 (1), (gu a n )2Zr Cl2 (4), a n d
(gu a n )2Zr Me2 (5)
1
4
5
formula
fw
C
14H25N3Cl2Zr
C18H40Cl2N6Zr
502.68
C20H46N6Zr
461.84
397.50
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.20 × 0.21 × 0.30
monoclinic
P21/c
9.4940(2)
14.3186(4)
13.0843(4)
94.735(1)
1772.62(7)
4
1.489
9.16
-159
ω (0.30°/frame)
10
Mo KR (λ ) 0.710 69 Å)
graphite
3.0-45.0
8589 (unique 3281)
(Rint ) 0.025)
0.029
0.15 × 0.20 × 0.30
orthorhombic
Pbca
15.1279(3)
16.9122(1)
20.1017(4)
90.000
5142.9(3)
8
1.298
6.49
-103
ω (0.30°/frame)
10
Mo KR (λ ) 0.710 69 Å)
graphite
3.0-52.3
27 015 (unique 5583)
(Rint ) 0.044)
0.036
0.10 × 0.20 × 0.30
triclinic
P1h
8.6100(1)
9.0090(1)
18.3740(1)
94.280(1)
1271.51(3)
2
1.206
4.47
-99.0
ω (0.30°/frame)
15
Mo KR (λ ) 0.710 69 Å)
graphite
3.0-45.0
6130 (unique 4281)
(Rint ) 0.017)
0.030
â (deg)
V (Å3)
Z
dcalcd (g/cm3)
µ(Mo KR) (cm-1
T (°C)
)
scan type
scan rate (s/frame)
radiation
monochromator
2θ range (deg)
no. of rflns measd
R
Rw
0.033
0.040
0.036
Rall
0.029
0.036
0.030
GOF
2.22
1.36
1.26
p factor
no. of variables
0.030
181
0.031
244
0.030
244
Sch em e 1. Sa lt Meta th esis, Disp r op or tion a tion ,
a n d Attem p ted Qu a ter n iza tion of Cp (gu a n )Zr Cl2
(1)
4 and 1.364(3) and 1.356(3) Å for 7). These data imply
that the guanidinato ligand acts as a stronger donor
toward the more electron-poor metal centers of com-
plexes 4 and 7. Consistent with this argument, the mean
Zr-N distances of complexes 4 and 7 (2.206 and 2.167
Å, respectively) are slightly but significantly shorter
than those of 5 and 6 (2.257 and 2.252 Å, respectively).
The angle between the plane of the metal chelate and
that of the dimethylamino substituent varies between
39 and 49° for complexes 4-7. While not optimal for
delocalization, this does allow for some overlap of the
nitrogen p orbital with the π system of the chelate.
Although these effects are subtle, the data suggest
that the electronic environment at the metal center
dictates the extent of π-donation from the dimethyl-
amino group and, hence, the overall donor strength of
the guanidinato ligand. The ligand acts as a more
powerful electron donor toward the relatively electron-
poor metal centers of complexes 4 and 7 and as a less
powerful donor toward the electron-rich metal centers
of 5 and 6.
F igu r e 4. ORTEP diagram of (guan)2ZrCl2 (4) showing
atom-numbering scheme (50% thermal ellipsoids). Hydro-
gen atoms have been omitted for clarity.
ways to give stable (guan)2Zr(Me)X complexes. Treat-
ment of 5 with 1 equiv of Me3SiOTf affords (guan)2Zr-
(Me)OTf (8), along with 1 equiv of tetramethylsilane
(detected by 1H NMR spectroscopy) (Scheme 3). The
triflato ligand of 8 is formulated as inner sphere by
virtue of the solubility of the complex in aromatic
hydrocarbons and by analogy to other reported early-
metal triflato complexes.34-38 The lower molecular sym-
metry of 8 compared to that of (guan)2ZrX2 derivatives
(34) Luinstra, G. A. J . Organomet. Chem. 1996, 517, 209.
(35) Boutonnet, F.; Zablocka, M.; Igau, A.; Marjoral, J .-P.; J aud, J .;
Pietrusiewicz, K. M. J . Chem. Soc., Chem. Commun. 1993, 1487.
Met h id e Ab st r a ct ion fr om (gu a n )2Zr Me2 (5). A
methyl ligand may be abstracted from 5 in a variety of

1812 Organometallics, Vol. 20, No. 9, 2001
Duncan et al.
Ta ble 3. Metr ica l Da ta for (gu a n )2Zr Cl2 (4)
Selected Bond Lengths (Å)
Zr-Cl(1)
Zr-N(1)
2.441(1)
2.198(3)
2.218(3)
1.362(5)
1.322(5)
1.365(5)
Zr-Cl(2)
2.446(1)
2.198(3)
2.208(3)
1.338(5)
1.360(3)
1.360(5)
Zr-N(4)
Zr-N(2)
Zr-N(5)
N(1)-C(1)
N(2)-C(1)
N(3)-C(1)
N(4)-C(10)
N(5)-C(10)
N(6)-C(10)
Selected Bond Angles (deg)
60.4(1) Cl(1)-Zr-Cl(2)
60.1(1) N(1)-C(1)-N(2)
121.8(4) N(4)-C(10)-N(5)
N(4)-Zr-N(5)
91.46(4)
N(1)-Zr-N(2)
111.0(4)
110.5(4)
43.57
C(1)-N(3)-C(8)
[N(1)-C(1)-N(2)]/
[C(8)-N(3)-C(9)]a
41.04
[N(4)-C(10)-N(5)]/
[C(17)-N(6)-C(18)]a
a
The angle between the planes of the chelate (N-C-N) and
its dimethylamino substituent.
F igu r e 6. ORTEP diagram of (guan)2Zr(CH2Ph)2 (6)
showing atom-numbering scheme (50% thermal ellipsoids).
Hydrogen atoms have been omitted for clarity.
Ta ble 4. Metr ica l Da ta for (gu a n )2Zr Me2 (5)
Selected Bond Lengths (Å)
Zr-C(19)
Zr-N(1)
2.267(3)
2.230(2)
2.281(2)
1.352(3)
1.326(3)
1.385(3)
Zr-C(20)
2.264(3)
2.249(2)
2.269(2)
1.338(3)
1.338(3)
1.388(3)
Zr-N(4)
Zr-N(2)
Zr-N(5)
N(1)-C(1)
N(2)-C(1)
N(3)-C(1)
N(4)-C(10)
N(5)-C(10)
N(6)-C(10)
Selected Bond Angles (deg)
58.79(8) C(19)-Zr-C(20)
58.84(7) N(1)-C(1)-N(2)
122.3(2) N(4)-C(10)-N(5)
N(1)-Zr-N(2)
92.7(1)
N(4)-Zr-N(5)
111.6(2)
112.1(2)
39.36
F igu r e 5. ORTEP diagram of (guan)2ZrMe2 (5) showing
atom-numbering scheme (50% thermal ellipsoids). Hydro-
gen atoms have been omitted for clarity.
C(1)-N(3)-C(8)
[N(1)-C(1)-N(2)]/
[C(8)-N(3)-C(9)]a
40.57
[N(4)-C(10)-N(5)]/
[C(17)-N(6)-C(18)]a
a
The angle between the planes of the chelate (N-C-N) and
its dimethylamino substituent.
Sch em e 2. Syn th esis of (gu a n )2Zr X2 Der iva tives (X
) Me (5), CH2P h (6), OTf (7))
Ta ble 5. Metr ica l Da ta for (gu a n )2Zr (CH2P h )2 (6)
Selected Bond Lengths (Å)
Zr-C(19)
Zr-N(1)
2.310(3)
2.237(2)
2.271(2)
1.335(4)
1.341(4)
1.394(4)
Zr-C(26)
2.323(3)
2.260(2)
2.241(2)
1.347(3)
1.344(4)
1.385(4)
Zr-N(4)
Zr-N(2)
Zr-N(5)
N(1)-C(1)
N(2)-C(1)
N(3)-C(1)
N(4)-C(10)
N(5)-C(10)
N(6)-C(10)
Selected Bond Angles (deg)
59.24(9) N(1)-C(1)-N(2)
59.40(8) N(4)-C(10)-N(5)
89.7(1) C(1)-N(3)-C(8)
110.7(2) Zr-C(26)-C(27)
N(1)-Zr-N(2)
112.8(2)
N(4)-Zr-N(5)
112.0(2)
121.0(3)
110.5(2)
43.90
is evident in its 1H NMR spectrum; whereas (guan)2ZrX2
complexes exhibit a single resonance (doublet, 24H) for
the eight isopropyl methyl groups on the two guanidi-
C(19)-Zr-C(26)
Zr-C(19)-C(20)
[N(1)-C(1)-N(2)]/
[C(8)-N(3)-C(9)]a
49.46
[N(4)-C(10)-N(5)]/
[C(17)-N(6)-C(18)]a
1
nato ligands, the H NMR spectrum of 8 contains two
a
The angle between the planes of the chelate (N-C-N) and
its dimethylamino substituent.
resonances (doublets, 12H each) for the same groups.
Reaction of 5 with 1 equiv of tris(pentafluorophenyl)-
borane (B(C6F5)3) in pentane results in the formation
of [(guan)2ZrMe][MeB(C6F5)3] (9) as a pale yellow oil in
96% yield (Scheme 3). Room-temperature 1H NMR
analysis of 9 in CD2Cl2 reveals a sharp singlet for the
zirconium-bound methyl group (δ 0.86 ppm) and a broad
singlet for the boron-bound methyl group (δ 0.47 ppm).
derivatives) correlated to the 1H resonance at 0.86 ppm.
Additionally, a broadened 13C resonance at 9.5 ppm
1
correlates to the H resonance at 0.47 ppm. The methyl
carbon of the MeB(C6F5)3 anion is typically observed to
resonate at e30 ppm.13,20,39-41
Comparison of the 19F NMR spectra of 9 in CD2Cl2
and C6D5Cl reveals only a small difference in the
∆(m,p-F) values between the two solvents. In CD2Cl2
solution, the value of ∆(m,p-F) is 2.4 ppm, whereas in
1
These assignments are confirmed by a H-13C HMQC
experiment, which reveals a 13C resonance at 53 ppm
(typical for (guan)2Zr(CH3)X (X ) Me, OTf, B(C6F5)4)
(36) Baranger, A. M.; Bergman, R. G. J . Am. Chem. Soc. 1994, 116,
(39) Doerrer, L. H.; Green, M. L. H.; Ha¨ussinger, D.; Sassmann-
shausen, J . J . Chem. Soc., Dalton Trans. 1999, 2111.
(40) Gielens, E. E. C. G.; Dijkstra, T. W.; Berno, P.; Meetsma, A.;
Hessen, B.; Teuben, J . H. J . Organomet. Chem. 1999, 591, 88.
(41) Witte, P. T.; Meetsma, A.; Hessen, B. J . Am. Chem. Soc. 1997,
119, 10561.
3822.
(37) Feldman, J .; Calabrese, J . C. J . Chem. Soc., Chem. Commun.
1991, 134.
(38) Roddick, D. M.; Heyn, R. H.; Tilley, T. D. Organometallics 1989,
8, 324.

Bis(guanidinato)zirconium(IV) Complexes
Organometallics, Vol. 20, No. 9, 2001 1813
Ta ble 6. Selected Cr ysta l a n d Da ta Collection P a r a m eter s for (gu a n )2Zr (CH2P h )2 (6), (gu a n )2Zr (OTf)2 (7),
a n d [((gu a n )2Zr Me)2-µ-Me][B(C6F 5)4] (11)
6
7
11
formula
fw
C
32H54N6ZrO
H40C20ZrS2O6F6N6
729.90
C72H96.50Zr2F21.50N12
1731.85
B
630.04
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.25 × 0.20 × 0.38
monoclinic
P21/c
11.3795(2)
17.6096(2)
18.0488(3)
95.759(1)
3598.52(9)
4
1.163
3.36
-159
ω (0.30°/frame)
10
Mo KR (λ ) 0.710 69 Å)
graphite
3.0-52.2
17 209 (unique 6555)
(Rint ) 0.030)
0.029
0.30 × 0.15 × 0.27
monoclinic
P21/n
10.4422(2)
11.5751(2)
30.3803(4)
93.692(1)
3664.43(9)
4
1.323
4.81
-139
ω (0.30°/frame)
10
Mo KR (λ ) 0.710 69 Å)
graphite
3.0-49.4
16 382 (unique 6338)
(Rint ) 0.019)
0.024
0.07 × 0.27 × 0.33
monoclinic
P21/c
20.6187(3)
21.7004(2)
19.7608(4)
114.697(1)
8032.9(2)
4
1.432
30.89
-137
ω (0.30°/frame)
15
Mo KR (λ ) 0.710 69 Å)
graphite
3.0-49.4
37 506 (unique 13 968)
(Rint ) 0.036)
0.031
â (deg)
V (Å3)
Z
dcalcd (g/cm3)
µ(Mo KR) (cm-1
T (°C)
)
scan type
scan rate (s/frame)
radiation
monochromator
2θ range (deg)
no. of rflns measd
R
Rw
0.034
0.031
0.034
Rall
0.029
0.024
0.061
GOF
1.22
1.21
1.28
p factor
no. of variables
0.031
577
0.031
424
0.030
982
Sch em e 3. Meth id e Abstr a ction fr om
(gu a n )2Zr Me2 (5)
F igu r e 7. ORTEP diagram of (guan)2Zr(OTf)2 (7) showing
atom-numbering scheme (50% thermal ellipsoids). Hydro-
gen atoms have been omitted for clarity.
the oily nature of 9 and the observation that 9 is
insoluble in aromatic hydrocarbons (benzene, toluene),
indicate relatively loose ion pairing between the bis-
(guanidinato)zirconium methyl cation and the MeB-
(C6F5)3 anion.12,42 This may be due, in part, to delocal-
ization of positive charge by the guanidinato ligands (as
in Figure 2), resulting in a less electrophilic (i.e., “less
cationic”) metal center and hence weakening cation-
anion interactions.
The unique donor ability of the guanidinato ligand
allows for isolation and characterization of zirconium
methyl cations with the extremely weakly coordinating
B(C6F5)4 counteranion. Treatment of a pentane solution
of 5 with a suspension of [Ph3C][B(C6F5)4] (1 equiv) in
benzene results in the precipitation of a white solid.
Removal of the solvent followed by repeated pentane
washings gives base-free [(guan)2ZrMe][B(C6F5)4] (10)
as a spectroscopically and analytically pure powder in
92% yield (Scheme 3). The thermal stability of 10 is
Ta ble 7. Metr ica l Da ta for (gu a n )2Zr (OTf)2 (7)
Selected Bond Lengths (Å)
Zr-O(1)
2.129(2)
2.161(2)
2.168(2)
1.348(3)
1.353(3)
1.356(3)
Zr-O(4)
2.124(2)
2.149(2)
2.190(2)
1.348(3)
1.354(3)
1.364(3)
Zr-N(1)
Zr-N(4)
Zr-N(2)
Zr-N(5)
N(1)-C(1)
N(2)-C(1)
N(3)-C(1)
N(4)-C(10)
N(5)-C(10)
N(6)-C(10)
Selected Bond Angles (deg)
61.80(7) N(1)-C(1)-N(2)
61.75(7) N(4)-C(10)-N(5)
84.66(7) C(1)-N(3)-C(8)
N(1)-Zr-N(2)
110.8(2)
N(4)-Zr-N(5)
111.0(2)
123.1(3)
40.34
O(1)-Zr-O(4)
[N(1)-C(1)-N(2)]/
37.54
[N(4)-C(10)-N(5)]/
[C(8)-N(3)-C(9)]a
[C(17)-N(6)-C(18)]a
a
The angle between the planes of the chelate (N-C-N) and
its dimethylamino substituent.
C6D5Cl solution, ∆(m,p-F) is 2.6 ppm. These low (<3
ppm) values of ∆(m,p-F) imply that the MeB(C6F5)3
anion is not strongly associated with the Zr center in
these two solvents.20 The 19F NMR data, coupled with
(42) Sun, Y.; Metz, M. V.; Stern, C. L.; Marks, T. J . Organometallics
2000, 19, 1625.

1814 Organometallics, Vol. 20, No. 9, 2001
Duncan et al.
unusually high for a zirconium methyl cation with the
B(C6F5)4 counteranion.17,20,43,44 While 10 is sensitive to
air and moisture, it is stable indefinitely at room
temperature under an inert atmosphere and is stable
in CH2Cl2 solution for several hours. Because of the
increased electrophilicity of the cationic metal center,
the carbon atom of the methyl ligand of 10 resonates
at lower field (δ 51 ppm, chlorobenzene-d5) than the
methyl carbons of the neutral precursor 5 (δ 40 ppm,
1
chlorobenzene-d5).13,20 The room-temperature H NMR
spectrum of complex 10 is similar to those of neutral
(guan)2ZrX2 derivatives. A single sharp resonance (dou-
blet, 24H) is observed for the eight isopropyl methyl
1
groups. Observation of the H NMR spectrum of 10 at
188 K (CD2Cl2) reveals four inequivalent isopropyl
methyl resonances; while dynamic processes involving
the guanidinato ligands are slow on the NMR time scale
at 188 K, anion and/or solvent coordination to the
cationic metal center is still weak and rapid on the NMR
time scale at this temperature.
F igu r e 8. ORTEP diagram showing the cationic portion
of [((guan)2ZrMe)2-µ-Me][B(C6F5)4] (11) with atom-number-
ing scheme (50% thermal ellipsoids). Hydrogen atoms on
the bridging methyl group are shown in their refined
positions. All other hydrogen atoms have been omitted for
clarity.
Several workers have observed the formation of cat-
ionic methyl-bridged dinuclear complexes under varied
reaction conditions.7,11,20,45-51 Complexes of this type
have been implicated as inactive components in some
polymerization experiments.7 Treatment of 5 with 0.5
equiv of [Ph3C][B(C6F5)4] in pentane/benzene solution
results in the precipitation of the dinuclear cation
[((guan)2ZrMe)2-µ-Me][B(C6F5)4] (11) as a white powder
(Scheme 3). Alternatively, 11 may be generated and
observed upon mixing equimolar amounts of 5 and 10
at room temperature in chlorobenzene-d5 solution. This
indicates that neutral 5 is a better ligand for the cat-
ionic zirconium center than either the weakly coordinat-
ing B(C6F5)4 anion or the chlorinated solvent.47
The room-temperature 1H NMR spectrum of 11 shows
a single sharp resonance for the nine methyl protons of
the complex, indicating that bridge-terminal methyl
group exchange is fast on the NMR time scale. Decoa-
lescence of the bridging and terminal methyl groups is
observed by 1H NMR spectroscopy at 224.0 K in
CD2Cl2. In the low-temperature limit (188 K) bridge-
terminal exchange is slow on the NMR time scale and
sharp resonances corresponding to the two methyl
environments are observed. The resonance assigned to
the two terminal methyl groups (δ 0.33 ppm) can be
integrated and is found to correspond to six protons. The
bridging methyl resonance (δ 1.11 ppm) cannot be
accurately integrated, due to overlap with the multiple
isopropyl methyl resonances observed at 188 K. How-
ever, the peak is assigned as a Zr-bound methyl group
1
by a H-13C HMQC experiment, which shows that the
1
resonance at 1.11 ppm in the H spectrum correlates to
a
13C resonance at δ 46 ppm. The 13C shift of δ 46 ppm
falls into the observed range for (guan)2Zr(CH3)X com-
plexes (X ) Me, OTf, MeB(C6F5)3, B(C6F5)4).
Crystals of 11 suitable for X-ray diffraction were
grown from a concentrated fluorobenzene solution at -
30 °C. An ORTEP diagram of 11 is shown in Figure 8,
with relevant bond lengths and angles given in Table
8. Selected crystal and structure refinement data are
shown in Table 6. Dinuclear cation 11 crystallizes with
1.5 equiv of fluorobenzene in the crystal lattice. The
crystal structure revealed no close contacts between the
cation and the anion or fluorobenzene. The solid-state
structure of 11 is interesting in several respects. The
two terminal methyl groups are staggered by 33.0° with
respect to one another; similar arrangements have been
observed by Marks and co-workers11 and by Schrock and
co-workers.51 The Zr-CH3-Zr bridge of 11 is nearly
linear (170.84(13)°), but the two Zr-C bond lengths of
the bridge are significantly different (Zr(1)-C(1) )
2.397(3) Å; Zr(2)-C(1) ) 2.489(3) Å). The hydrogens on
the bridging methyl group were located and are directed
toward the longer Zr-C bond (sum of angles around
C(1) 351.0°). Apart from the distinct Zr-Cbridging bond
lengths, there are no significant differences between the
two sides of the cationic portion of 11. The Me2N-C
bond lengths of 11 vary between 1.362(4) and 1.382(4)
Å, in the same range observed for the (guan)2ZrX2
derivatives. The angles between the four metal chelates
of 11 and the dimethylamino groups attached to them
range from 36 to 45°.
(43) Baumann, R.; Davis, W. M.; Schrock, R. R. J . Am. Chem. Soc.
1997, 119, 3830.
(44) Schrock, R. R.; Liang, L. C.; Baumann, R.; Davis, W. R. J .
Organomet. Chem. 1999, 591, 163.
(45) Yang, X.; Stern, C. L.; Marks, T. J . Organometallics 1991, 10,
840.
(46) Beck, S.; Prosenc, M. H.; Brintzinger, H. H.; Goretzki, R.;
Herfert, N.; Fink, G. J . Mol. Catal. A 1996, 111, 67.
(47) Bochmann, M.; Lancaster, S. J . Angew. Chem., Int. Ed. Engl.
1994, 33, 1634.
(48) Wang, Q.; Gillis, D. J .; Quyoum, R.; J eremic, D.; Tudoret, M.
J .; Baird, M. C. J . Organomet. Chem. 1997, 527, 7.
(49) Ko¨hler, K.; Piers, W. E.; J arvis, A. P.; Xin, S.; Feng, Y.;
Bravakis, A. M.; Collins, S.; Clegg, W.; Yap, G. P. A.; Marder, T. B.
Organometallics 1998, 17, 3557.
Ben zyl An ion Abstr a ction fr om 6. In analogy to
the synthesis of the methyl cations, treatment of 6 with
[Ph3C][B(C6F5)4] in CH2Cl2 affords [(guan)2Zr(CH2Ph)]-
[B(C6F5)4] (15) as an analytically pure pale yellow
powder in 91% yield (eq 3). Several workers have
(50) Williams, V. C.; Dai, C.; Li, Z.; Collins, S.; Piers, W. E.; Clegg,
W.; Elsegood, M. R. J .; Marder, T. B. Angew. Chem., Int. Ed. 1999, 38,
3695.
(51) Schrock, R. R.; Casado, A. L.; Goodman, J . T.; Liang, L.-C.;
Bonitatebus, P. J .; Davis, W. M. Organometallics 2000, 19, 5325.
reported zirconium benzyl cations with weakly coordi-

Bis(guanidinato)zirconium(IV) Complexes
Organometallics, Vol. 20, No. 9, 2001 1815
Ta ble 8. Metr ica l Da ta for [(gu a n )2Zr Me)2-µ-Me][B(C6F 5)4] (11)
Selected Bond Lengths (Å)
Zr(1)-C(1)
Zr(2)-C(1)
Zr(1)-N(1)
Zr(1)-N(2)
Zr(2)-N(7)
Zr(2)-N(8)
N(1)-C(4)
N(2)-C(4)
N(3)-C(4)
N(7)-C(22)
N(8)-C(22)
N(9)-C(22)
2.397(3)
Zr(1)-C(2)
Zr(2)-C(3)
Zr(1)-N(4)
Zr(1)-N(5)
Zr(2)-N(10)
Zr(2)-N(11)
N(4)-C(13)
N(5)-C(13)
N(6)-C(13)
N(10)-C(31)
N(11)-C(31)
N(12)-C(31)
2.258(3)
2.251(3)
2.205(2)
2.248(2)
2.241(2)
2.226(2)
1.348(4)
1.346(4)
1.362(4)
1.343(4)
1.343(4)
1.363(4)
2.489(3)
2.234(2)
2.196(2)
2.260(2)
2.147(2)
1.329(4)
1.350(4)
1.382(4)
1.336(4)
1.358(4)
1.372(4)
Selected Bond Angles (deg)
C(1)-Zr(1)-C(2)
88.48(10)
90.11(11)
60.74(9)
59.42(8)
111.7(3)
111.1(3)
36.67
Zr(1)-C(1)-Zr(2)
170.84(13)
C(1)-Zr(2)-C(3)
N(1)-Zr(1)-N(2)
60.07(9)
59.69(8)
111.8(3)
110.7(3)
46.45
N(7)-Zr(2)-N(8)
N(4)-Zr(1)-N(5)
N(10)-Zr(2)-N(11)
N(1)-C(4)-N(2)
N(7)-C(22)-N(8)
N(4)-C(13)-N(4)
N(10)-C(31)-N(11)
[N(1)-C(4)-N(2)]/[C(11)-N(3)-C(12)]a
[N(7)-C(22)-N(8)]/[C(29)-N(9)-C(30)]a
[N(4)-C(13)-N(5)]/[C(20)-N(6)-C(21)]a
[N(10)-C(31)-N(11)]/[C(38)-N(12)-C(39)]a
39.95
41.16
a
The angle between the planes of the chelate (N-C-N) and its dimethylamino substituent.
nating anions.9,20,52-60 A common feature of these com-
pounds both in solution and in the solid state is a strong
interaction of the ipso carbon of the aryl ring with the
cationic metal center, resulting in a distorted, η2-coor-
dinated benzyl ligand. Spectroscopically, η2-benzyl lig-
Ta ble 9. P olym er iza tion Da ta for Com p lexes 4, 5,
a n d 10
amt
T
of
run catal cocatala (°C) [C2H4]b [Zr]c polymd Mw/Mn activitye
stdf MMAOg,h 75
106
106
106
85
1.0 52.3
3.2
24.8i
36.7i
49.7i
98 308
2350
160
1
1
2
3
4
ands typically exhibit high (>130 Hz) benzylic J CH
4
4
5
MMAOh
MMAOj
[Ph3C]-
[B(C6F5)4]
none
75
75
55
2.0
14.1
21.6
2.5
1.2
1.1
1
coupling constants and upfield-shifted ortho H reso-
nances.9,20,58,61-63 The spectroscopic data for 15 suggest
that the benzyl ligand adopts an undistorted (η1) coor-
dination mode. Evidence for this comes from the small
benzylic 1J CH coupling constant (127 Hz in CD2Cl2; 125
Hz in chlorobenzene-d5), which is only slightly higher
than the coupling constant measured for the neutral
dibenzyl derivative 6 (1J CH ) 123 Hz) which bears
undistorted benzyl ligands, as shown by X-ray diffrac-
tion (vide supra). Although the ortho protons of the
benzyl ligand could not be assigned, due to overlap with
the solvent (C6D5Cl), all aryl protons of 15 resonate at
g6.9 ppm, the expected range for an undistorted benzyl
ligand.61 Despite numerous attempts, crystals of 15
suitable for an X-ray diffraction study could not be
obtained. Monodentate coordination of a benzyl ligand
to a base-free cationic zirconium center is rare;64 it is
possible that the guanidinato ligand stabilizes the
120
5
6
7
10
10
10
85
50
50
75
130
130
130
85
4.4
8.9
13.3
13.3
0.4
0.9
0.2
2.0
ndl
nd
nd
nd
103
116
17
none
none
8k 10
none
354
a
100-200 µmol of triisobutylaluminum (TIBA) was used in all
the runs as a scrubbing agent. In units of psi. c In units of µmol.
b
In units of g. e Activity ) g of polymer (mmol of cat)-1 (100 psi
d
of C2H4)-1 h-1
.
f The standard used was (nBuCp)2ZrCl2. MMAO
g
h
i
) modified methylaluminoxane. [Al]:[Zr] ) 500. Polymer from
these runs showed broad and/or bimodal molecular weight distri-
butions. See the Supporting Information for a representative GPC
trace. [Al]:[Zr] ) 355. All runs except run 8 were carried out
with 10% 1-hexene comonomer. nd ) not determined.
j
k
l
electron-deficient metal center such that coordination
to the π-system of the aryl ring is unnecessary.
Olefin P olym er iza tion Exp er im en ts. Neutral bis-
(guanidinato)zirconium complexes 4 and 5 and alkyl salt
10 were screened for ethylene homopolymerization and
ethylene/1-hexene copolymerization. Results of the po-
lymerization experiments are shown in Table 9. All of
the compounds investigated are 1-3 orders of magni-
tude less active than (nBuCp)2ZrCl2. This is not surpris-
ing in light of the very modest ethylene polymerization
activities reported for structurally related3 bis(amidi-
nato)zirconium complexes.65-69 Differential scanning
calorimetry and size-exclusion chromatography assays
on the polymer obtained in runs 2-4 revealed broad
(52) Martin, A.; Uhrhammer, R.; Gardner, T. G.; J ordan, R. F.;
Rogers, R. D. Organometallics 1998, 17, 382.
(53) Tsukahara, T.; Swenson, D. C.; J ordan, R. F. Organometallics
1997, 16, 3303.
(54) Black, D. G.; Swenson, D. C.; J ordan, R. F.; Rogers, R. D.
Organometallics 1995, 14, 3539.
(55) Borkowsky, S. L.; Baenziger, N. C.; J ordan, R. F. Organome-
tallics 1993, 12, 486.
(56) Crowther, D. J .; Borkowsky, S. L.; Swenson, D. C.; Meyer, T.
Y.; J ordan, R. F. Organometallics 1993, 12, 2897.
(57) Bochmann, M.; Lancaster, S. J .; Hursthouse, M. B.; Abdul
Malik, K. M. Organometallics 1994, 13, 2235.
(58) Pellecchia, C.; Immirzi, A.; Grassi, A.; Zambelli, A. Organome-
tallics 1993, 12, 4473.
(59) Uhrhammer, R.; Black, D. G.; Gardner, T. G.; Olsen, J . D.;
J ordan, R. F. J . Am. Chem. Soc. 1993, 115, 8493.
(60) Bochmann, M.; Lancaster, S. J . Organometallics 1993, 12, 633.
(61) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I.
P.; Huffman, J . C. Organometallics 1985, 4, 902.
(62) Mintz, E. A.; Moloy, K. G.; Marks, T. J .; Day, V. W. J . Am.
Chem. Soc. 1982, 104, 4692.
(65) Littke, A.; Sleiman, N.; Bensimon, C.; Richeson, D. S.; Yap, G.
P. A.; Brown, S. J . Organometallics 1998, 17, 446.
(66) Hagadorn, J . R.; Arnold, J . J . Chem. Soc., Dalton Trans. 1997,
3087.
(67) Walther, D.; Fischer, R.; Gorls, H.; Koch, J .; Schweder, B. J .
Organomet. Chem. 1996, 508, 13.
(63) Giesbrecht, G. R.; Whitener, G. D.; Arnold, J . Organometallics
2000, 19, 2809.
(68) Flores, J . C.; Chien, J . C. W.; Rausch, M. D. Organometallics
1995, 14, 1827.
(64) Thorn, M. G.; Etheridge, Z. C.; Fanwick, P. E.; Rothwell, I. P.
J . Organomet. Chem. 1999, 591, 148.
(69) Herskovics-Korine, D.; Eisen, M. S. J . Organomet. Chem. 1995,
503, 307.

1816 Organometallics, Vol. 20, No. 9, 2001
Duncan et al.
and/or bimodal molecular weight distributions (see
Supporting Information). This is due, possibly, to ab-
straction of one or both of the guanidinato ligands by
excess aluminum present (as MMAO or triisobutylalu-
minum (TIBA)) to generate multiple active species.70
Analysis of the polymer obtained in runs 4 and 8 by
13C{1H} NMR spectroscopy revealed a preponderance
of saturated end groups, indicating that the dominant
mode of chain termination is chain transfer to alumi-
num.71 The 13C{1H} NMR spectrum of the ethylene/
1-hexene copolymer obtained in run 4 indicated low
1-hexene incorporation into the polymer (4.56 ( 0.53
butyl branches per 1000 carbons).72,73
it is clearly unwise to form conclusions about the nature
of the active catalyst(s) in these experiments. It is likely
that, although the guanidinato ligand resisted electro-
philic attack under stoichiometric conditions, the large
excess of Lewis acid present in the reactor (as MMAO
and/or TIBA) resulted in complex degradation via ligand
abstraction. Current work in this area is focused on the
interaction of bis(guanidinato)alkylzirconium cations
with olefins in the absence of aluminum-containing
additives.
Su m m a r y a n d Con clu sion s
We have shown that a variety of neutral and cationic
alkylzirconium complexes bearing guanidinato ancillary
ligands can be synthesized and isolated. Reactivity and
structural investigations have shown that π-donation
from the dimethylamino moiety of the guanidinato
ligand plays an important role in the chemistry of these
complexes. Most notable is the thermal stability of the
bis(guanidinato)methylzirconium cation when paired
with the extremely weakly coordinating tetrakis(pen-
tafluorophenyl)borate anion. We ascribe this stability
to the ability of the guanidinato ligands to act as strong
electron donors toward the cationic metal center, thereby
delocalizing the positive charge into the ligand frame-
work. The bis(guanidinato)benzylzirconium cation ex-
hibits (by 13C and 1H NMR spectroscopy) unusual η1
coordination of the benzyl ligand to the cationic zirco-
nium center. Although the bis(guanidinato)zirconium
complexes screened showed low to modest ethylene
polymerization activity, it is hoped that the stability of
the alkylzirconium cations responsible for the polym-
erization will permit detailed studies on the interactions
between the cationic metal center and olefin units.
The observed polymerization activities appear to be
sensitive to temperature, pressure, and catalyst con-
centration. For example, a 7-fold increase in the con-
centration of 4 resulted in a drop in activity of over an
order of magnitude (runs 2 and 3) at 75 °C and 106 psi
of C2H4. Simultaneously lowering the reactor temper-
ature from 85 to 50 °C and doubling the catalyst
concentration from 4.4 to 8.9 µmol had little effect on
the activity of 10 (runs 5 and 6), but a further increase
in catalyst concentration to 13.3 µmol caused a sub-
stantial decrease in activity (run 7) at 50 °C. The
attenuated activities observed at high concentrations of
4 and 10 (runs 3 and 7) are consistent with previous
reports that low zirconium concentrations lead to higher
polymerization activities, due to the suppression of
bimolecular deactivation pathways.70 Run 8 was per-
formed in the absence of 1-hexene and showed the
highest activity of any of the 10-derived catalysts,
indicating possible inhibition of the polymerization by
the R-olefin.71 Conversion of the activity figures for the
two most active catalysts (runs 2 and 8) to the units
proposed by Gibson4 gives activities of 342 and 53 g of
polymer (mmol of Zr)-1 h-1 bar-1, respectively. Accord-
ing to Gibson’s classification,4 complex 4 therefore rates
as “highly” active under these conditions (run 2),
whereas complex 10 is “moderately” active (run 8).
Activation of 5 with B(C6F5)3 under several sets of
conditions failed to yield an active polymerization
catalyst. Recent work by Marks,74,75 Brintzinger,76 and
Ziegler77 has shown that the MeB(C6F5)3 anion may
interact quite strongly with cationic zirconium centers,
especially in nonpolar media.74,75,77 Given that these
polymerization experiments were carried out in hex-
anes, it is likely that the MeB(C6F5)3 anions resulting
from activation by B(C6F5)3 were associated sufficiently
strongly with the metal to shut down polymerization
completely.
Exp er im en ta l Section
Gen er a l P r oced u r es. Unless otherwise noted, reactions
and manipulations were performed at ambient temperature
in an inert-atmosphere (N2) glovebox or using standard
Schlenk and high-vacuum-line techniques. Glassware was
dried overnight at 150 °C or flame-dried immediately prior to
use. All NMR spectra were obtained at ambient temperature
(except when noted) using Bruker AMX-300, AMX-400, or
DRX-500 spectrometers. 1H NMR chemical shifts (δ) are
reported in parts per million (ppm) relative to residual
protiated solvent. 13C{1H} NMR chemical shifts (δ) are re-
ported in ppm relative to the carbon resonance of the deuter-
ated solvent. 19F chemical shifts (δ) are reported relative to
external CFCl3 (0.00). 11B chemical shifts (δ) are reported
relative to external BF3‚OEt2 in C6D6 (0.00). In cases where
assignment of 13C{1H} resonances was ambiguous, standard
DEPT 45, 90, and/or 135° pulse sequences were utilized.
Unless otherwise noted, infrared (IR) spectra were recorded
as Nujol mulls between NaCl plates. Elemental analyses were
performed at the University of California, Berkeley Micro-
analytical Facility on a Perkin-Elmer 2400 Series II CHNO/S
analyzer.
Ma ter ia ls. Unless otherwise noted, reagents were pur-
chased from commercial suppliers and used without further
purification. Pentane, hexanes, benzene, and toluene (Fisher)
were passed through a column of activated alumina (type A2,
size 12 × 32, Purifry Co.) under nitrogen pressure and sparged
with N2 prior to use. Diethyl ether and tetrahydrofuran
(Fisher) were distilled from purple sodium/benzophenone ketyl
under N2 prior to use. Deuterated solvents (Cambridge Isotope
Laboratories) were purified by vacuum transfer from the
Given the broad, bimodal molecular weight distribu-
tions observed in the polymerization experiments, care
must be taken in the interpretation of the above data;
(70) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, R.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
(71) J aniak, C. In Metallocenes: Synthesis, Reactivity, and Applica-
tions; Togni, A., Halterman, R. L., Eds.; Wiley-VCH: New York, 1998;
Vol. 2, p 547.
(72) Soga, K.; Uozumi, T.; Nakamura, S.; Toneri, T.; Teranishi, T.;
Sano, T.; Arai, T. Macromol. Chem. Phys. 1996, 197, 4237.
(73) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587.
(74) Beswick, C. L.; Marks, T. J . J . Am. Chem. Soc. 2000, 122, 10358.
(75) Deck, P. A.; Beswick, C. L.; Marks, T. J . J . Am. Chem. Soc.
1998, 120, 1772.
(76) Beck, S.; Lieber, S.; Schaper, F.; Geyer, A.; Brintzinger, H. H.
J . Am. Chem. Soc. 2001, 123, 1483.
(77) Vanka, K.; Chan, M. S. W.; Pye, C. C.; Ziegler, T. Organome-
tallics 2000, 19, 1841.

Bis(guanidinato)zirconium(IV) Complexes
Organometallics, Vol. 20, No. 9, 2001 1817
appropriate drying agent (Na/Ph2CO or CaH2) prior to use.
Diisopropylcarbodiimide (Lancaster) was distilled from CaH2
and degassed prior to use. ZrCl4 and Zr(NMe2)4 were sublimed
prior to use. (Me2N)2ZrCl2(THF)2 was prepared according to a
literature procedure.78
solution of MeLi (22 mL, 1.4 M in Et2O, 31 mmol) was added
dropwise over 8 min via syringe. The reaction mixture was
stirred at -60 °C for 45 min and was then warmed to room
temperature over 3.5 h. Removal of the solvent under reduced
pressure and extraction into pentane (2 × 50 mL) followed by
filtration gave a clear, pale yellow solution. Concentration of
this solution to approximately 30 mL followed by cooling to
-78 °C for 2 days gave colorless crystals of 5 (5.73 g, 86%). 1H
NMR (300 MHz, C6D6): δ 3.68 (sept, 4H, CH(CH3)2 J ) 6.5
Hz), 2.44 (s, 12H, N(CH3)2), 1.36 (d, 24H, CH(CH3)2, J ) 6.5
Hz), 0.95 (s, 6H, ZrCH3) ppm. 13C{1H} NMR (125 MHz, C6D6):
δ 174.3 (s, N3C), 47.6 (s, CH(CH3)2), 42.9 (s, ZrCH3), 40.2 (s,
N(CH3)2), 25.4 (s, CH(CH3)2). FT-IR: 2614 (w), 1639 (w), 1515
(s), 1454 (s), 1279 (m), 1187 (s), 1122 (s), 1055 (s), 938 (w),
875 (w), 831 (w), 743 (s), 709 (m) cm -1. Anal. Calcd for
ZrC20H46N6: C, 52.01; H, 10.04; N, 18.20. Found: C, 52.20; H,
10.10; N, 18.11.
Cp (gu a n )Zr Cl2 (1). A 250 mL Schlenk tube was charged
with LiNMe2 (0.251 g, 4.9 mmol) and 100 mL of Et2O. The
resulting colorless suspension was cooled to 0 °C, at which
temperature diisopropylcarbodiimide (0.83 mL, 5.4 mmol) was
added dropwise via syringe. The reaction mixture was warmed
to room temperature over 2 h. The resulting cloudy solution
of lithium guanidinate reagent 2 was cannula-transferred into
a 250 mL Schlenk tube containing a solution of CpZrCl3 (1.291
g, 4.91 mmol) in THF (100 mL) at -78 °C. The reaction
mixture was stirred for 20 min at -78 °C and was warmed to
room temperature overnight. Removal of solvent in vacuo,
followed by extraction into Et2O (200 mL) and filtration, gave
a clear, yellow solution. Et2O was removed in vacuo to give
crude 1 as a yellow powder. Recrystallization from toluene at
-78 °C gave pure 1 as yellow-orange crystals (1.31 g, 67%).
1H NMR (500 MHz, C6D6): δ 6.40 (s, 5H, C5H5), 3.40 (sept,
2H, CH(CH3)2, J ) 6.5 Hz), 2.13 (s, 6H, N(CH3)2), 1.17 (d, 12H,
CH(CH3)2, J ) 6.5 Hz) ppm. 13C{1H} NMR (125 MHz, C6D6):
δ 170.1 (s, N3C), 115.8 (s, C5H5), 48.6 (s, CH(CH3)2), 40.2 (s,
N(CH3)2), 24.2 (s, CH(CH3)2) ppm. FT-IR: 1625 (w), 1522 (m),
1341 (m), 1198 (m), 1126 (m), 1058 (m), 1018 (m), 837 (m),
815 (s), 750 (w) cm -1. Anal. Calcd for ZrC14H25N3Cl2: C, 42.30;
H, 6.34; N, 10.57. Found: C, 42.60; H, 6.11; N, 10.36.
Cp (gu a n )Zr Me2 (3). A 250 mL Schlenk tube was charged
with 1 (0.407 g, 1.02 mmol), and Et2O (40 mL). The resulting
yellow suspension was cooled to -78 °C. At this temperature,
a MeMgCl solution (0. 72 mL, 3.0 M in THF, 2.15 mmol) was
added dropwise via syringe. The reaction mixture was stirred
at -78 °C for 30 min and was then warmed to room temper-
ature over 11 h. Removal of solvent under reduced pressure,
followed by extraction into pentane (2 × 25 mL) and filtration,
gave a clear, colorless solution. Concentration of this solution
to approximately 10 mL followed by cooling to -30 °C gave
pure 3 as colorless crystals (0.224 g, 61%). 1H NMR (300 MHz,
C6D6): δ 6.29 (s, 5H, C5H5), 3.41 (sept, 2H, CH(CH3)2, J ) 6.5
Hz), 2.33 (s, 6H, N(CH3)2), 1.03 (d, 12H, CH(CH3)2, J ) 6.5
Hz), 0.52 (s, 6H, Zr(CH3)2) ppm. 13C{1H} NMR (125 MHz,
C6D6): δ 172.9 (s, N3C), 111.5 (s, C5H5), 47.0 (s, CH(CH3)2), 42.7
(s, Zr(CH3)2), 39.7 (s, N(CH3)2), 24.4 (s, CH(CH3)2) ppm. FT-
IR: 1619 (w), 1514 (s), 1404 (s), 1375 (s), 1193 (s), 1170 (m),
1122 (s), 1054 (s), 1015 (m), 936 (w), 798 (s), 746 (m), 704 (w)
cm-1. Anal. Calcd for ZrC16H31N3: C, 53.88; H, 8.76; N, 11.78.
Found: C, 53.67; H, 8.63; N, 11.69.
(gu a n )2Zr (CH2P h )2 (6). A 500 mL Schlenk tube was
charged with 4 (2.11 g, 4.2 mmol) and Et2O (200 mL). The
resulting colorless suspension was cooled to -78 °C. At this
temperature, a solution of benzylmagnesium chloride (8.8 mL,
1.0 M in Et2O, 8.8 mmol) was added dropwise via syringe. The
resulting yellow heterogeneous reaction mixture was warmed
to room temperature with stirring over 15 h. Removal of
solvent under reduced pressure and extraction into pentane
(3 × 70 mL) followed by filtration gave a clear, bright yellow
solution. Concentration of this solution to approximately 40
mL, followed by storage at -30 °C overnight, gave yellow
needles of pure 6 (2.10 g, 80%). 1H NMR (500 MHz, C6D6, 300
K): δ 7.46 (d, 4 H, Ar o-H, J ) 7.5 Hz), 7.24 (t, 4H, Ar m-H,
J ) 7.5 Hz), 6.95 (t, 2H, Ar p-H, J ) 7.5 Hz), 3.54 (s (br), 4H,
CH(CH3)2), 2.76 (s (br), 2H, Zr(CH2Ph)2), 2.40 (s, 12H, N(CH3)2),
1.12 ppm (s (br), 24H, CH(CH3)2) ppm. 1H NMR (500 MHz,
C7D8, 220 K) 7.57 (d, 4H, Ar o-H, J ) 7.5 Hz), 7.32 (t, 4H, Ar
m-H, J ) 7.5 Hz), 3.51 (sept, 2H, CH(CH3)2, J ) 6.5 Hz), 3.44
(sept, 2H, CH(CH3)2, J ) 6.5 Hz), 3.01 (d, 2H, Zr(CH2Ph)2, J
) 10.0 Hz), 2.69 (d, 2H, Zr(CH2Ph)2, J ) 10.0 Hz), 2.38 (s, 6H,
N(CH3)2), 2.28 (s, 6H, N(CH3)2), 1.36 (d, 6H, CH(CH3)2, J )
6.0 Hz), 1.33 (d, 6H, CH(CH3)2, J ) 6.5 Hz), 1.03 (d, 6H, CH-
(CH3)2, J ) 6.5 Hz), 0.77 (d, 6H, CH(CH3)2, J ) 6.5 Hz) ppm
(para proton resonance of benzyl ligands could not be resolved
due to overlap with the solvent). 13C{1H} NMR (125 MHz,
C6D6): δ 175.3 (s, N3C), 149.9 (s, p-C6H5), 128.6 (s, m-C6H5),
120.7 (s, o-C6H5), 72.5 (s, ZrCH2Ph), 48.2 (s (br), CH(CH3)2),
40.0 (s, N(CH3)2), 25.2 (s (br), CH(CH3)2) ppm (ipso carbon
resonance of benzyl ligands was not detected). FT-IR: 1592
(m), 1514 (m), 1402 (s), 1186 (m), 1137 (w), 1054 (m), 956 (m),
875 (w), 793 (w), 744 (m), 695 (m) cm -1. Anal. Calcd for C32H54
(C5H12 0.5ZrN6 (complex 6 passed analysis with exactly 0.5
-
)
(gu a n )2Zr Cl2 (4). A 100 mL round-bottomed flask was
charged with (Me2N)2ZrCl2(THF)2 (0.738 g, 1.98 mmol) and
Et2O (50 mL). The resulting pale yellow solution was cooled
to -20 °C, and diisopropylcarbodiimide (0.70 mL, 4.5 mmol)
was added via syringe. The reaction mixture was warmed to
room temperature overnight. The pale yellow solution was
concentrated until crystals formed and then cooled to -30 °C
overnight. Pale yellow crystals were isolated by filtration
(0.540 g, two crops, 54%). 1H NMR (C6D6, 500 MHz): 3.56
(septet, J ) 6.5 Hz, 4H, CH(CH3)2), 2.33 (s, 12 H, N(CH3)2),
1.44 (d, J ) 6.4 Hz, 24H, CH(CH3)2). 13C{1H} NMR (C6D6, 500
MHz): 173.4 (s, N3C), 48.0 (s, NCH(CH3)2), 40.0 (s, N(CH3)2),
25.1 (s, NCH(CH3)2). FT-IR: 1620 (m), 1531 (m), 1455 (m),
1404 (m), 1378 (m), 1348 (m), 1318 (w), 1275 (w), 1191 (m),
equiv of pentane included in the crystal lattice, as was
1
confirmed by H NMR analysis of the analytical sample): C,
63.74; H, 9.30; N, 12.93. Found: C, 63.81; H, 9.31; N, 12.92.
(gu a n )2Zr (OTf)2 (7). A 200 mL Schlenk tube was charged
with 5 (0.504 g, 1.1 mmol) and benzene (6 mL) to give a clear,
colorless solution. Me3SiOTf (0.44 mL, 2.3 mmol) was added
dropwise via syringe at room temperature, resulting in forma-
tion of a white precipitate. The reaction mixture was stirred
for 20 h at ambient temperature. Removal of solvent in vacuo
gave a white powder, which was washed with pentane (1 ×
70 mL). Crystallization from a 1:3 THF/pentane mixture at
-30 °C gave pure 7 as colorless prisms (0.609 g, 77%). 1H NMR
(300 MHz, THF-d8): δ 3.80 (sept, 4H, (CH3)2CH, J ) 6.5 Hz),
2.94 (s, 12H, (CH3)2N), 1.31 (s (br), 24H, (CH3)2CH) ppm. 13C-
{1H} NMR (125 MHz, THF-d8): δ 174.6 (s, N3C), 120.4 (quart,
OSO2CF3, J C-F ) 316.3 Hz), 49.7 (s (br), CH(CH3)2), 48.8 (s
(br), CH(CH3)2), 40.5 (s, N(CH3)2), 25.0 (s (br), CH(CH3)2) ppm.
19F NMR (376.5 MHz, THF-d8): δ -73.1 (s, CF3) ppm. FT-IR:
1629 (w), 1535 (s), 1407 (s), 1355 (s), 1241 (s), 1187 (s), 1131
(m), 1063 (m), 1016 (s), 985 (s), 936 (w), 747 (m), 678 (w), 635
(s) cm-1. Anal. Calcd for ZrC20H40N6S2O6F6: C, 32.91; H, 5.52;
N, 11.51. Found: C, 32.82; H, 5.39; N, 11.39.
1128 (w), 1059 (m), 936 (w), 743 (w), 703 (w), 541 (w) cm-1
.
Anal. Calcd for C18H40N6Cl2Zr: C, 43.01; H, 8.02; N, 16.72.
Found C, 43.07; H, 8.29; N, 16.39.
(gu a n )2Zr Me2 (5). A 1 L Schlenk tube was charged with 4
(7.17 g, 14 mmol) and Et2O (400 mL). The resulting colorless
suspension was cooled to -60 °C. At this temperature, a
(78) Brenner, S.; Kempe, R.; Arndt, P. Z. Anorg. Allg. Chem. 1995,
621, 2021.

1818 Organometallics, Vol. 20, No. 9, 2001
Duncan et al.
(gu an )2Zr (Me)OTf (8). A 100 mL Schlenk tube was charged
with 5 (0.118 g, 0.026 mmol) and hexanes (10 mL). To the
resulting clear colorless solution was added via syringe a
solution of Me3SiOTf (0.057 g, 0.026 mmol) in hexanes (1.5
mL). The reaction mixture was stirred at room temperature
for 4 h. Removal of solvent under reduced pressure gave crude
8 (0.124 g, 82%). Crystallization from a concentrated Et2O
solution (5 mL) at -30 °C gave pure 8 (0.072 g, 47%). 1H NMR
(500 MHz, C6D6): δ 3.51 (sept, 4H, (CH3)2CH, J ) 6.5 Hz),
2.30 (s, 12H, (CH3)2N), 1.32 (d, 12H, (CH3)2CH, J ) 5.5 Hz),
1.27 (d, 12H, (CH3)2CH, J ) 5.5 Hz), 1.08 (s, 3H, ZrCH3) ppm.
13C{1H} NMR (125 MHz, C6D6): δ 174.4 (s, N3C), 121.0 (q,
OSO2CF3, J C-F ) 317.5 Hz), 47.9 (s, CH(CH3)2), 47.3 (s, ZrCH3),
40.0 (s, N(CH3)2), 25.2 (s, CH(CH3)2) ppm. 19F NMR (376.5
MHz, C6D6): δ -77.1 (s, CF3) ppm. FT-IR: 1531 (s), 1404 (s),
1345 (s), 1274 (m), 1237 (s), 1188 (s), 1124 (m), 1062 (s), 1002
(s), 938 (w), 747 (m), 712 (w), 6301 (s) cm-1. Anal. Calcd for
ZrC20H43N6F3O3S: C, 40.31; H, 7.27; N, 14.10. Found: C, 40.41;
H, 7.17; N, 14.34.
in toluene (4 mL). The reaction mixture was stirred at room
temperature for 1 h, over which time the red color of the trityl
reagent was bleached, and an off-white precipitate formed. The
solvent was decanted, and the precipitate was washed with
pentane (3 × 5 mL) and dried in vacuo to give crude 11 (0.393
g, 82%). Recrystallization of the crude product from a concen-
trated fluorobenzene solution at -30 °C overnight gave pure
11 (0.283 g, 56%) as colorless crystals containing 1 equiv of
fluorobenzene; this material was used for characterization. 1H
NMR (500 MHz, CD2Cl2): δ 7.36 (m, 2H, C6H5F), 7.15 (m, 1H,
C6H5F), 7.06 (m, 2H, C6H5F), 3.75 (sept, 8H, (CH3)2CH, J )
6.50 Hz), 2.86 (s, 24H, (CH3)2N), 1.20 (d, 48H, (CH3)2CH, J )
1
6.50 Hz), 0.71 (s, 9H, ZrCH3) ppm. H NMR (500 MHz, CD2-
Cl2, 190 K): δ 7.33 (m, 2H, o-C6H5F), 7.13 (t, 1H, p-C6H5F,
J HH ) 7.5 Hz), 7.04 (t, 2H, m-C6H5F, J HH ) 8 Hz), 3.77 (s (br),
4H, CH(CH3)2), 3.50 (s (br), 4H, CH(CH3)), 2.83 (s, 12H,
(CH3)2N), 2.68 (s, 12H, (CH3)2N), 1.26 (s, 6H, CH(CH3)2), 1.19
(s, 12H, CH(CH3)2), 1.13 (s, 6H, CH(CH3)2), 1.11 (s, 3H, Zr-
CH3-Zr), 1.02 (s, 6H, CH(CH3)2), 0.79 (s, 6H, CH(CH3)2), 0.76
(s, 6H, CH(CH3)2), 0.34 (s, 6H, Zr-CH3) ppm. 13C{1H} NMR
(125 MHz, CD2Cl2): δ 174.3 (s, N3C), 163.5 (d, ipso-C6H5F, J C-F
) 245 Hz), 148.8 (d, o-C6F5, J C-F ) 242.5 Hz), 138.8 (d, p-C6F5,
J C-F ) 246.3 Hz), 136.9 (d, m-C6F5, J C-F ) 241.3 Hz), 130.6
(d, C6H5F, J C-F ) 7.5 Hz), 124.7 (d, C6H5F, J C-F ) 3.8 Hz),
115.7 (d, C6H5F, J C-F ) 21.3 Hz), 48.2 (s, (CH3)2CH), 45.7 (s,
ZrCH3), 40.6 (s, (CH3)2N), 25.3 (s, (CH3)2CH) ppm (ipso carbons
of B(C6F5)4 were not detected). 19F NMR (376.5 MHz, C6D5-
Cl): δ -112.35 (s, 1F, C6H5F), -131.63 (s, 8F, o-C6F5), -162.44
(t, 4F, p-C6F5, J ) 21 Hz), -166.20 (m, 8F, m-C6F5) ppm. 11B
NMR (160.47 Hz, CD2Cl2): δ -17.3 (s, B(C6F5)4) ppm. FT-IR:
1642.3 (m), 1595 (w), 1514 (s), 1404(s), 1337 (s), 1274 (m), 1183
(m), 1122 (m), 1085 (m), 979 (s), 774 (m), 755 (m), 683 (w),
661 (w) cm-1. Anal. Calcd for Zr2C69H94N12F21B: C, 49.22; H,
5.63; N, 9.98. Found: C, 48.91; H, 5.37; N, 9.75.
[(gu a n )2Zr Me][MeB(C6F 5)3] (9). Pentane (2 mL) was
added with stirring to a mixture of 5 (0.046 g, 0.010 mmol)
and B(C6F5)3 (0.051 g, 0.010 mmol). The reaction mixture was
stirred at room temperature for 45 min. Removal of solvent
in vacuo gave pure 9 (0.094 g, 96%) as a pale yellow viscous
1
oil. H NMR (500 MHz, CD2Cl2): δ 3.77 (sept, 4H, (CH3)2CH,
J ) 6.5 Hz), 2.93 (s, 12 H, (CH3)2N), 1.27 (d, 24H, (CH3)2CH,
J ) 6.5 Hz), 0.86 (s, 3H, ZrCH3), 0.47 (br s, 3H, BCH3) ppm.
13C{1H} NMR (125 MHz, CD2Cl2): δ 170 (s, N3C), 147.9 (d,
o-C6F5, J C-F ) 238 Hz), 137.1 (d, p-C6F5, J C-F ) 238 Hz), 136.0
(d, m-C6F5, J C-F ) 238 Hz), 128.5 (br, ipso-C6F5), 53.1 (s, Zr-
CH3), 48.1 (s, CH(CH3)2), 39.4 (s, N(CH3)2), 24.0 (s, CH(CH3)2),
9.5 (br, B-CH3) ppm. 19F NMR (376.5 MHz, CD2Cl2): δ -131.7
(d, 6F, o-C6F5, J F-F ) 21.5 Hz), -164.3 (t, 3F, p-C6F5, J F-F
)
18.4 Hz), -166.8 (t, 6F, m-C6F5, J F-F ) 18.4 Hz) ppm. 19F NMR
(376.5 MHz, C6D5Cl): δ -131.3 (d, 6F, o-C6F5, J F-F ) 21.5 Hz),
-163.4 (t, 3F, p-C6F5, J F-F ) 18.1 Hz), -166.0 (t, 6F, m-C6F5,
J F-F ) 18.4 Hz) ppm. 11B NMR (160. 47 MHz, CD2Cl2): δ -15.6
(s, B-CH3) ppm. FT-IR (neat): 2973 (s), 2936 (s), 2878 (m),
2809 (w), 1640 (s), 1544 (s), 1511 (s), 1453 (s), 1402 (s), 1336
(s), 1266 (s), 1217 (w), 1177 (s), 1125 (s), 1087 (s), 1061 (s),
952 (s), 841 (m), 749 (s), 804 (m), 710 (m) cm -1. Anal. Calcd
for ZrC38H46N6F15B: C, 46.87; H, 4.76; N, 8.63. Found: C,
46.59; H, 4.81; N, 8.56.
[(gu a n )2Zr (CH2P h )][B(C6F 5)4] (15). To a stirred solution
of 6 (0.031 g, 0.05 mmol) in CH2Cl2 (1.5 mL) was added a
solution of [Ph3C][B(C6F5)4] (0.044 g, 0.05 mmol) in CH2Cl2 (1.5
mL). The reaction mixture was stirred at room temperature
for 35 min. The solvent was removed under reduced pressure
and the product washed with pentane (6 × 1.5 mL). Drying in
vacuo gave spectroscopically and analytically pure 15 as a
1
yellow powder (0.050 g, 88%). H NMR (300 MHz, C6D5Cl): δ
3.40 (sept. 4H, CH(CH3)2, J ) 6.5 Hz), 2.44 (s, 12H, N(CH3)2),
2.33 (s, 2H, ZrCH2Ph), 0.91 (d, 24H, CH(CH3)2, J ) 6.5 Hz)
ppm (aryl protons from benzyl ligand could not be resolved
due to overlap with resonances of the solvent). 13C{1H} NMR
[(gu a n )2Zr Me][B(C6F 5)4] (10). To a stirred solution of 5
(0.337 g, 0.07 mmol) in hexanes (6 mL) was added a suspension
of [Ph3C][B(C6F5)4] (0.673 g, 0.07 mmol) in benzene (6 mL).
The reaction mixture was stirred for 1.25 h, over which time
the orange color of the trityl reagent bleached, and a white
solid precipitated from solution. The solvent was decanted, and
the residual solid was washed with hexanes (2 × 5 mL) and
dried in vacuo to give 10 as a spectroscopically and analytically
(125 MHz, CD2Cl2): δ 171.2 (s, N3C), 148.8 (d, C6F5, J CF
243 Hz), 138.9 (d, C6F5, J CF ) 248 Hz), 136.9 (d, C6F5, J CF
)
)
244 Hz), 128.9 (s, C6H5), 128.5 (s, C6H5), 126.2 (s, C6H5), 77.3
(s, ZrCH2Ph), 49.3 (s, (CH(CH3)2), 40.6 (s, (CH3)2N), 25.4 (s,
(CH(CH3)2) ppm (ipso carbon resonances of C6F5 and C6H5 were
not detected). 19F NMR (376.5 MHz, C6D5Cl): δ -131.76 (s,
8F, o-C6F5), -162.49 (t, 4F, p-C6F5, J FF ) 21.5 Hz), -166.29
(m, 8F, m-C6F5) ppm. 11B NMR (160.47 Hz, CD2Cl2): δ -17.3
(s, B(C6F5)4) ppm. FT-IR: 1642.5 (m), 1541.0 (s), 1513.4 (s),
1410.4 (s), 1382.4 (s), 1336.2 (m), 1272.9 (m), 1176.4 (m), 1086.3
(s), 1059.1 (m), 979.1 (s), 773.9 (m), 754.5 (m), 686.2 (m), 661.7
(m) cm -1. Anal. Calcd for ZrC52H50F20N6B: C, 48.97; H, 3.94;
N, 6.99. Found: C, 49.10; H, 3.99; N, 6.89.
1
pure white powder (0.760 g, 92%). H NMR (300 MHz, C6D5-
Cl): δ 3.41 (sept, 4H, (CH3)2CH, J ) 6.5 Hz), 2.46 (s, 12H,
(CH3)2N), 1.02 (d, 24H, (CH3)2CH, J ) 6.5), 0.72 (s, 3H, ZrCH3)
ppm. 13C{1H} NMR (125 MHz, C6D5Cl): δ 167.7 (s, N3C), 146.3
(d, o-C6F5, J C-F ) 240 Hz), 136.1 (d, p-C6F5, J C-F ) 243 Hz),
134.2 (d, m-C6F5, J C-F ) 235 Hz), 51.3 (s, ZrCH3), 45.9 (s,
(CH3)2CH), 36.6 (s, (CH3)2N), 21.7 (s, (CH3)2CH) ppm (the ipso
carbon resonance of B(C6F5)4 was not detected). 19F NMR
(376.5 MHz, C6D5Cl): δ -131.7 (s, 8F, o-C6F5), -162.31 (t, 4F,
p-C6F5, J FF ) 18 Hz), -166.14 (m, 8F, m-C6F5) ppm. 11B NMR
(160.47 Hz, C6D5Cl) δ -16.6 (s, B(C6F5)4) ppm. FT-IR: 2727
(w), 1642 (m), 1545 (s), 1512 (s), 1412 (s), 1334 (m), 1313
(m), 1282 (m), 1176 (m), 1084 (s), 1060 (m), 981 (s), 929 (w),
842 (w), 755 (m), 683 (m), 661 (m) cm-1. Anal. Calcd for
ZrC43H43F20N6B: C, 45.87; H, 3.85; N, 7.46. Found: C, 46.18;
H, 4.02; N, 7.54.
Exp er im en ta l P r oced u r e for P olym er iza tion Exp er i-
m en ts. All polymerization runs were carried out according to
the following general procedure. The precatalyst (nBuCp2ZrCl2,
4, 5, or 10) and cocatalyst ([Ph3C][B(C6F5)4], run 4 only) were
dissolved in 0.50 mL of fluorobenzene. This solution was
injected into a preheated (50 °C) autoclave containing 600 mL
of hexane, 100-200 µmol of TIBA, 45 mL of 1-hexene (runs
1-7 only), and MMAO (runs 1-3 only). The autoclave was
sealed, pressurized with ethylene, and brought up to the
desired temperature. Runs 1-4 and 8 were 30 min in length;
runs 5-7 were 40 min. After completion of the run, the
resulting polymer was isolated by filtration and drying.
[((gu an )2Zr Me)2-µ-Me][B(C6F5)4](C6H5F) (11). To a stirred
solution of 5 (0.278 g, 0.06 mmol) in pentane (12 mL) was
added a suspension of [Ph3C][B(C6F5)4] (0.278 g, 0.03 mmol)

Bis(guanidinato)zirconium(IV) Complexes
Organometallics, Vol. 20, No. 9, 2001 1819
Gen er a l E xp er im en t a l Det a ils for X-r a y St r u ct u r e
Deter m in a tion s. Crystals were mounted onto glass fibers
using Paratone N hydrocarbon oil and were transferred to a
Siemens SMART diffractometer/CCD area detector,79 centered
in the beam, and cooled by a nitrogen-flow low-temperature
apparatus. Preliminary orientation matrix and cell constants
were determined by collection of 60 10 or 15 s frames, followed
by spot integration and least-squares refinement. A hemi-
sphere of data was collected using ω scans of 0.3° counted for
a total of 10.0 or 15.0 s per frame. The raw data were inte-
grated by the program SAINT. Data analysis was performed
using XPREP.80 An absorption correction was applied using
SADABS.81 The unit cell parameters and statistical analysis
of the intensity distribution were used for space group deter-
mination.82 The data were corrected for Lorentz and polariza-
tion effects, but no correction for crystal decay was applied.
Unique equivalent reflections were merged. The structures
were solved by direct methods83 and expanded using Fourier
techniques.84 Except as noted, all non-hydrogen atoms were
refined anisotropically and hydrogen atoms were included as
fixed contributions but not refined. The quantity minimized
by the least-squares program was ∑w(|Fo| - |Fc|)2, where w is
the weight of a given observation. The weighting scheme was
based on counting statistics and included a factor (p ) 0.030)
to downweight the intense reflections. The analytical forms
of the scattering factor tables for the neutral atoms were
used,85 and all scattering factors were corrected for both the
real and imaginary components of anomalous dispersion.86 All
calculations were performed using the teXsan87 crystallo-
graphic software package of Molecular Structure Corp.
The carbon atoms of the disordered solvent of compound 6,
C33-C38, were refined isotropically, whereas the remaining
non-hydrogen atoms were refined anisotropically. Some of the
hydrogen atoms of 6 were refined isotropically; the rest were
included in fixed positions. For compound 11, the hydrogen
atoms of the bridging methyl group (H1-H3) were refined
isotropically, whereas other hydrogen atoms were included as
fixed contributions but not refined.
Ack n ow led gm en t. We are grateful for financial
support of this work from the NSF (Grant No. CHE-
9633374 to R.G.B. and CHE-0072819 to J .A.). We wish
to acknowledge Dr. Fred Hollander of the UC Berkeley
CHEXRAY facility for determining the solid-state struc-
ture of complex 11. We also thank Dr. Timothy Wenzel
and Dr. Thomas Peterson of the Union Carbide Corp.
for performing ethylene polymerization experiments, the
Albemarle Corp. for generous gifts of [Ph3C][B(C6F5)4]
and B(C6F5)3, and Boulder Scientific Co. for the gener-
ous gift of [Li][B(C6F5)4(Et2O)2.5]. CNDOS is supported
by Bristol-Myers Squibb as Sponsoring Member.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data for compounds 1, 4-7, and 11, including ORTEP dia-
grams and tables of crystal data and data collection param-
eters, atomic coordinates, anisotropic displacement param-
eters, and all bond lengths and bond angles, as well as tables
summarizing 13C{1H} NMR and GPC data for the polymers
produced by compounds 4, 5, and 10. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM000995U
(84) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C.
DIRDIF: The DIRDIF Program System; Technical Report of the
Crystallography Laboratory, University of Nijmegen, Nijmegen, The
Netherlands, 1992.
(85) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. IV,
Table 2.2A.
(86) Creagh, D. C.; Hubbell, J . H. In International Tables for
Crystallography; Wilson, A. J . C., Ed.; Kluwer Academic: Boston, MA,
1992; Vol. C, Table 4.2.4.3, pp 200-206.
(87) teXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corp., The Woodlands, TX, 1985 & 1992.
(79) SMART: Area-Detector Software Package; Siemens Industrial
Automation, Inc., Madison, WI, 1995.
(80) XPREP (version 5.03): Part of the SHELXTL Crystal Structure
Determination Package; Siemens Industrial Automation, Inc., Madi-
son, WI, 1995.
(81) Sheldrick, G. M. SADABS: Siemens Area Detector ABSorption
correction program; Advance copy, private communication, 1996.
(82) International Tables for Crystallography, 2nd ed.; Kluwer
Academic: Boston, MA, 1989; Vol. A.
(83) Altomare, A.; Burla, M. C.; Camalli, Cascarano, M.; Giacovazzo,
C.; Guagliardi, A.; Polidori, G. SIR92. J . Appl. Crystallogr. 1993, 26,
343.