Bulky bis(alkylamidinate) complexes of group 4. Syntheses and characterization of M(CyNC(R′)NCy)2Cl2 and Zr(CyNC(Me)NCy)2Me2 (R′= Me, M = Ti, Zr, Hf; R′ = tBu, M = Zr)

Article abstract of DOI:10.1021/om9707533

Synthesis of a series of bis(alkylamidinate) group 4 compounds of the general formula M(CyNC(CH₃)NCy)₂Cl₂ (M = Ti (1), Zr (2), Hf (3); Cy = cyclohexyl), Zr(CyNC(CMe₃)NCy)₂-Cl₂ (4), and Zr(CyNC(CH₃)NCy)₂(CH₃)₂ (5) are reported. In the presence of methylaluminoxane (MAO) as a cocatalyst, compounds 1-5 are active ethylene polymerization catalysts.

Full text of DOI:10.1021/om9707533

446
Organometallics 1998, 17, 446-451
Bu lk y Bis(a lk yla m id in a te) Com p lexes of Gr ou p 4.
Syn th eses a n d Ch a r a cter iza tion of M(CyNC(R′)NCy)2Cl2
a n d Zr (CyNC(Me)NCy)2Me2 (R′) Me, M ) Ti, Zr , Hf; R′ )
tBu , M ) Zr )
Adam Littke, Nassrin Sleiman, Corinne Bensimon, and Darrin S. Richeson*
Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
Glenn P. A. Yap†
Department of Chemistry and Biochemistry, University of Windsor,
Windsor, Ontario, Canada N9B 3P4
Stephen J . Brown
Nova Research and Technology Corporation, 2928 16th Street Northeast,
Calgary, Alberta T2E 7K7
Received August 21, 1997
Synthesis of a series of bis(alkylamidinate) group 4 compounds of the general formula
M(CyNC(CH3)NCy)2Cl2 (M ) Ti (1), Zr (2), Hf (3); Cy ) cyclohexyl), Zr(CyNC(CMe3)NCy)2-
Cl2 (4), and Zr(CyNC(CH3)NCy)2(CH3)2 (5) are reported. In the presence of methylalumi-
noxane (MAO) as a cocatalyst, compounds 1-5 are active ethylene polymerization catalysts.
In tr od u ction
Steric analysis of this ligand system places it intermedi-
ate between the Cp and Cp* ligands.25-27 However,
substantial differences have been noted between the
electronic features of these two systems.26 Most notably,
bis(trimethylsilyl)benzamidinate anions are four-elec-
tron donors that are expected to have polarized M-N
bonds. These effects are anticipated to lead to more
electrophilic metal centers.
Our initial attraction to the amidinate ligand system
was motivated by the possibility of exploring the effects
of making rational modifications to both the steric bulk
and electronic properties of these ligands through
changes to the organic substituents on the nitrogen and
the bridging carbon positions. We wish to report a
portion of our systematic study of complexes of these
ligands with early transition metals. These efforts
compliment our work with these ligands and the main
group elements.28-32 Included in this report are the
syntheses and characterization of a novel family of bis-
The quest for alternatives to cyclopentadienyl-based
ligands in early transition metal chemistry has recently
generated a great deal of effort on preparing complexes
with N-centered donor ligands.1-10 Within this realm,
a variety of amidinato complexes of the group 4 metals
have been reported.11-24 However, they have been, by
and large, limited to the use of N,N′-bis(trimethylsilyl)-
benzamidinate-based ligands, [Me3SiNC(C6H4R)NSiMe3].
†Present address: Department of Chemistry, University of Ottawa,
Ottawa, Ontario, Canada K1N 6N5.
(1) Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994,
33, 497.
(2) Brand, H.; Arnold, J . A. Coord. Chem. Rev. 1995, 140, 137.
(3) Andersen, R. A. Inorg. Chem. 1979, 18, 2928.
(4) Housmekerides, C. E.; Ramage, D. L.; Kretz, C. M.; Shontz, J .
T.; Pilato, G. L.; Geoffroy, G. L.; Rheingold, A. L.; Haggerty, B. S. Inorg.
Chem. 1992, 31, 4453.
(5) J acoby, D.; Isoz, S.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J .
Am. Chem. Soc. 1995, 117, 5801.
(6) Schaller, C. P.; Cummins, C. C.; Wolczanski, P. T. J . Am. Chem.
Soc. 1996, 118, 591.
(7) Schrock, R. R.; Cummins, C. C.; Wilhelm, T.; Lin, S.; Reid, S.
M.; Kol, M.; Davis, W. M. Organometallics 1996, 15, 1470.
(8) Scollard, J . D.; McConville, D. H. J . Am. Chem. Soc. 1996, 118,
10008.
(9) Shapiro, P. J .; Cotter, W. D.; Schaefer, W. P.; Labinger, J . A.;
Bercaw, J . E. J . Am. Chem. Soc. 1994, 116, 4623.
(10) Uhrhammer, R.; Black, D. G.; Gardner, T. G.; Olsen, J . D.;
J ordan, R. F. J . Am. Chem. Soc. 1993, 115, 8493.
(11) Hagadorn, J . R.; Arnold, J . Organometallics 1994, 13, 4670.
(12) Hagadorn, J . R.; Arnold, J . J . Chem. Soc., Dalton Trans. 1997
3087.
(13) Hagadorn, J . R.; Arnold, J . J . Am. Chem. Soc. 1996, 118, 893.
(14) Dick, D. G.; Duchateau, R.; Edema, J . H.; Gambarotta, S. Inorg.
Chem. 1993, 32, 1959.
(17) Flores, J . C.; Chien, J . C. W.; Rausch, M. D. Organometallics
1995, 14, 1827.
(18) Flores, J . C.; Chien, J . C. W.; Rausch, M. D. Organometallics
1995, 14, 2106.
(19) Herskovics-Korine, D.; Eisen, M. J . Organomet. Chem. 1995,
503, 307.
(20) Roesky, H. W.; Meller, B.; Noltemeyer, M.; Schmidt, H.-G.;
Scholz, U.; Sheldrick, G. M. Chem. Ber. 1988, 121, 1403.
(21) Walther, D.; Fischer, R.; Gorls, H.; Koch, J .; Schweder, B. J .
Organomet. Chem. 1996, 508, 13.
(22) Edelmann, F. T. Coord. Chem. Rev. 1994, 137, 403.
(23) Barker, J .; Kilner, M. Coord. Chem. Rev. 1994, 133, 219.
(24) Dehnicke, K. Chem.-Ztg. 1990, 114,
(25) Wedler, M.; Knosel, F.; Noltemeyer, M.; Edelmann, F. T. J .
Organomet. Chem. 1990, 388, 21.
(15) Gomez, R.; Green, M. L. H.; Haggitt, J . L. J . Chem. Soc., Chem.
Commun. 1994, 2607.
(16) Gomez, R.; Duchateau, R.; Chernega, A. N.; Teuben, J . H.;
Edelmann, F. T.; Green, M. L. H. J . Organomet. Chem. 1995, 491, 153.
(26) Duchateau, R.; van Wee, C. T.; Meetsma, A.; van Duijnen, P.
T.; Teuben, J . H. Organometallics 1996, 15, 2279.
(27) Edelmann, F. T. J . Organomet. Chem. 1992, 426, 295.
(28) Zhou, Y.; Richeson, D. S. Inorg.Chem. 1996, 35, 1423.
S0276-7333(97)00753-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/16/1998

Bis(alkylamidinate) Complexes of Group 4
Organometallics, Vol. 17, No. 3, 1998 447
Sch em e 1
Ta ble 1. Cr ysta llogr a p h ic Da ta for 2 a n d 5
(alkylamidinate) group 4 compounds of the general
3
2
5
formula M(CyNC(CH )NCy)2Cl2 (M ) Ti (1), Zr (2), Hf
t
(3); Cy ) cyclohexyl), a Bu-substituted analog Zr(CyNC-
formula
fw
C
28H50N4Cl2Zr
C30H58N4Zr
566.02
(tBu)NCy)2Cl2 (4), and a dimethyl complex Zr(CyNC-
(CH3)NCy)2(CH3)2 (5). Furthermore, in the presence of
methylaluminoxane (MAO) as a cocatalyst, compounds
1-5 are capable of polymerizing ethylene.
604.86
cryst color and
habit
colorless block
colorless block
cryst size, mm
space group
a, Å
0.2 × 0.2 × 0.2
P21/n
0.3 × 0.3 × 0.3
P21/n
13.034(3)
13.693(2)
18.036(4)
106.49(5)
3086(5)
4
1.193
4.68
Rigaku AFC6S
10.491(3)
14.380(5)
21.516(7)
92.43(2)
3243(2)
b, Å
c, Å
Resu lts a n d Discu ssion
â, deg
Reaction of MeLi with 1,3-dicylohexylcarbodiimide
proceeded smoothly in ether at room temperature to
yield Li[CyNC(Me)NCy]. Subsequent addition of 0.5
equiv of MCl4(THF)2 (M ) Ti, Zr, Hf) followed by
recrystallization resulted in the isolation of a series of
bis(alkylamidinate) complexes M(CyNC(Me)NCy)2Cl2
(1-3) (Scheme 1) with isolated yields in the 60% range.
Spectroscopic characterization and microanalysis con-
firmed the formulas of these materials. Specifically, all
three compounds exhibited similar 1H and 13C NMR
spectra with the most notable features being the ap-
pearance of single resonances for the cyclohexyl R-H,
R-C, and the CH3 group on the methyne bridge. Spec-
troscopic equivalence of the Cy groups in 1-3 is further
supported by the 13C NMR spectroscopy. However, on
the basis of the NMR observations for 4 and the
molecular structure of 2 (vide infra), we provide the C2-
symmetric structures for these complexes shown in
Scheme 1. Furthermore, 1-3 gave similar NMR spectra
to those previously observed for the analogous Sn
complexes Sn(CyNC(Me)NCy)2Cl2.31
We have found that other alkylamidinate ligands are
also accessible through a similar reaction scheme.
Thus, reaction of tBuLi with 1,3-dicyclohexylcarbodiim-
ide in ether followed by addition of ZrCl4(THF)2 in a 2:1
ratio yielded the corresponding bis(amidinato)dichloro
complex [CyN(CMe3)NCy]2ZrCl2 (4) (Scheme 1). On the
basis of the 1H NMR, complex 4 appeared to exhibit
equivalent Cy groups, as indicated by a single resonance
for the cyclohexyl proton a to N at 3.85 ppm. However,
the greater dispersion provided by 13C NMR spectra
indicated otherwise. At room temperature, a single
broad resonance was observed at 56.3 ppm, which was
assigned to the R-C of the cyclohexyl groups. This
resonance sharpened upon warming the sample and
split into two signals upon cooling to 263 K. These
V, Å3
Z, Å3
4
F(calcd), g cm-3
µ, cm-1
diffractometer
λ, Å
1.159
3.61
Siemens SMART CCD
1.540 56 (Cu KR) 0.710 73 (Mo KR)
120
T, K
297
no. of reflns collected 3354
12 967
4226
4186 (I > 2σI)
5.84
[15.58]
13.25
no. of indep reflns
no. of obs reflns
R(F), %
3177
3067 (I > 2.5σI)
7.8
R(wF) or [Rw(F)2], % 11.4
data/parameter
10.02
observations are consistent with inequivalent cyclohexyl
groups that are part of a fluxional molecule.
The dimethyl derivative of 2 was easily prepared from
the metathesis reaction with MeLi. Isolated yields of
crystalline Zr(CyNC(Me)NCy)2Me2 (5) from this proce-
1
dure were in the range of 50%. New signals in the H
and 13C NMR spectra at 0.88 and 42.74 ppm, respec-
tively, are consistent with the formulation of this species
and comparable to those observed for bis(trimethylsilyl)-
benzamidinates.12,21
X-r a y Cr ysta llogr a p h ic An a lyses of 2 a n d 5.
Single-crystal X-ray diffraction analyses of 2 and 5 were
undertaken in order to establish the coordination ge-
ometry of the metal center and the connectivity of the
ligand for these compounds (Table 1).
Structural analysis revealed the molecular geometry
for 2 shown in Figure 1. The metal center is in a
distorted pseudo-octahedral environment consisting of
the four nitrogen atoms of the two amidinate anions
with cis-chloride ligands completing the coordination
sphere. Tables 2 and 3 present a summary of selected
bond distances and angles for 2. The bonding param-
eters within the two amidinate ligands are not dramati-
cally different, and the two nitrogens and bridging
carbon atoms for each of the individual amidinate
ligands lie in a plane which includes the Zr atom,
resulting in a solid-state molecular geometry with
approximately C2 symmetry. The termini of the amidi-
(29) Zhou, Y.; Richeson, D. S. Inorg.Chem. 1996, 35, 2448.
(30) Zhou, Y.; Richeson, D. S. J . Am. Chem. Soc. 1996, 118, 10850.
(31) Zhou, Y.; Richeson, D. S. Inorg. Chem. 1997, 36, 501.
(32) Foley, S. R.; Bensimon, C.; Richeson, D. S. J . Am. Chem. Soc.
1997, 119, 10359.

448 Organometallics, Vol. 17, No. 3, 1998
Littke et al.
Ta ble 3. Selected Atom ic Bon d An gles (d eg) for
Com p ou n d 2
Cl1-Zr-Cl2
Cl1-Zr-N1
Cl1-Zr-N2
Cl1-Zr-N3
Cl1-Zr-N4
N1-Zr-N2
N1-Zr-N3
N1-Zr-N4
N2-Zr-N3
N2-Zr-N4
N3-Zr-N4
Zr-N1-C1
Zr-N1-C7
93.11(11)
90.57(20)
105.90(21)
94.68(21)
101.92(22)
60.3(3)
104.8(3)
160.0(3)
94.0(3)
106.4(3)
59.2(3)
143.2(6)
92.6(5)
C1-N1-C7
Zr-N2-C7
Zr-N2-C8
C7-N2-C8
Zr-N3-C15
Zr-N3-C21
Zr-N4-C21
Zr-N4-C2
C21-N4-C22
C21-N4-C22
N3-C21-N4
N1-C7-N2
121.2(8)
93.6(5)
143.0(6)
121.7(8)
141.1(6)
94.9(6)
122.7(8)
92.7(6)
141.6(6)
121.7(8)
111.6(8)
111.8(8)
Ta ble 4. Selected Atom ic Bon d Dista n ces (Å) for
Com p ou n d 5
Zr-N1
Zr-N4
Zr-C30
Zr-C29
Zr-N2
Zr-N3
N1-C1
N1-C7
C13-C14
2.225(4)
2.231(4)
2.244(6)
2.245(6)
2.291(4)
2.284(4)
1.470(12)
1.325(12)
1.509(8)
C27-C28
N1-C13
N1-C6
N2-C13
N2-C12
N3-C27
N3-C20
N4-C27
N4-C26
1.523(7)
1.327(6)
1.463(7)
1.314(6)
1.473(6)
1.327(6)
1.460(7)
1.313(7)
1.467(7)
Figu r e 1. Molecular structure and atom-numbering scheme
for Zr[CyNC(Me)NCy]2Cl2 (2) (Cy ) cyclohexyl). Hydrogen
atoms have been omitted for clarity.
Ta ble 5. Selected Atom ic Bon d An gles (d eg) for
Com p ou n d 5
C30-Zr-C29
N1-Zr-N4
N1-Zr-N2
N1-Zr-N3
N4-Zr-N2
N4-Zr-N3
N2-Zr-N3
N1-Zr-C29
N4-Zr-C29
C29-Zr-N2
C29-Zr-N3
C13-N1-C6
C13-N1-Zr
92.4(3)
96.0(2)
58.2(2)
113.1(2)
107.3(2)
58.2(2)
163.8(2)
94.1(2)
145.9(2)
105.7(2)
87.9(2)
124.5(4)
96.0(3)
C6-N1-Zr
139.5(3)
121.4(4)
93.4(3)
144.7(3)
122.3(4)
92.2(3)
142.4(4)
123.6(5)
95.0(3)
139.6(4)
112.4(4)
112.7(5)
C13-N2-C12
C13-N2-Zr
C12-N2-Zr
C27-N3-C20
C27-N3-Zr
C20-N3-Zr
C27-N4-C26
C27-N4-Zr
C26-N4-Zr
N2-C13-N1
N4-C27-N3
amidinate) ligand set in 2 appears to be a good imitation
of the bis(Cp) ligand set. The longer Zr-Cl bonds for 2
compared to the bis(benzamidinate) complex perhaps
reflect to a lesser degree the ionic bonding for 2.
Figu r e 2. Molecular structure and atom-numbering scheme
for Zr[CyNC(Me)NCy]2(CH3)2 (5) (Cy ) cyclohexyl). Carbon
atoms were refined anisotropically but are depicted as
spheres due to high thermal activity. Hydrogen atoms have
been omitted for clarity.
Complex 5 crystallized in the monoclinic space group
P21/n with the molecular geometry shown in Figure 2.
Monomeric 5 displays a distorted pseudo-octahedral Zr-
(IV) center similar to that of 2 with methyl groups
replacing the chloride ligands. Again, the Zr atom lies
on an approximate 2-fold axis that bisects the C29-Zr-
C30 angle, resulting in an approximately C2-symmetric
solid-state molecular geometry. Tables 4 and 5 present
a summary of selected bond distances and angles for 5.
As with 2, the termini of the two planar amidinate
ligands in 5 can be divided into two types, the cis-NCy
groups (N1, N4) and trans-NCy groups (N2, N3), and
the Zr-N bond lengths are slightly longer than the
reported values for the bis(trimethylsilyl)benzamidinate
analog. In addition, the cis-ZrN bond lengths (2.225-
(4), 2.231(4) Å) are slightly longer than the trans-ZrN
distances (2.291(4), 2.284(4) Å). This feature is likely
due to the relative steric congestion experienced by the
two groups. Comparison of the structures of 5, [Me3-
SiNC(C6H5)NSiMe3]2ZrMe2,12,21 and Cp2ZrMe234 (Figure
3) shows a similar trend as that for the dichlorides.
Ta ble 2. Selected Atom ic Bon d Dista n ces (Å) for
Com p ou n d 2
Zr-Cl1
Zr-Cl2
Zr-N1
Zr-N2
Zr-N3
Zr-N4
N1-C1
N1-C7
2.426(3)
2.436(3)
2.228(70
2.186(8)
2.192(7)
2.234(8)
1.470(12)
1.325(12)
N2-C7
1.355(12)
1.466(12)
1.470(12)
1.317(12)
1.326(12)
1.466(13)
1.501(13)
1.495(13)
N2-C8
N3-C15
N3-C21
N4-C21
N4-C22
C7-C14
C21-C8
nate ligand can be divided roughly into two types, the
cis-NCy groups (N2, N3) with a N2-Zr-N3 angle of
94.0(3)° and trans-NCy groups (N1, N4) with a N1-Zr-
N4 angle of 160.0(3)°. The two cis-ZrN bond lengths
are slightly longer (2.186(8), 2.192(7) Å) than the trans-
ZrN values (2.228(7), 2.234(8) Å), and all four bond
lengths are only slightly shorter (approx 0.02 Å) than
for the benzamidinate complex [Me3SiNC(C6H5)NSiMe3]2-
ZrCl2.12,19,21 A further comparison of the structures of
33
2, [Me3SiNC(C6H5)NSiMe3]2ZrCl2, and Cp2ZrCl2 is
made in Figure 3. Both the Cl-Zr-Cl angles and Zr-
Cl bond lengths indicate that the bis(dicylohexylacet-
(33) Prout, K.; Cameron, T. S.; Forder, R. A.; Critchley, S. R.;
Denton, B.; Rees, G. V. Acta Crystallogr. 1974, B30, 2290.

Bis(alkylamidinate) Complexes of Group 4
Organometallics, Vol. 17, No. 3, 1998 449
33
F igu r e 3. Comparison of the structures of Zr[CyNC(Me)NCy]2Cl2 (2), [Me3SiNC(C6H5)NSiMe3]2ZrCl2,12,19,21 and Cp2ZrCl2
and the structures of Zr(CyNC(Me)NCy)2Me2 (5), [Me3SiNC(C6H5)NSiMe3]2ZrMe2,12,21 and Cp2ZrMe2.34 The values for the
benzamidiante complexes are averages for the values reported it the literature.
Ta ble 6. Rea ction Con d ition s a n d Molecu la r
Weigh t for P olyeth ylen e Usin g Com p ou n d s 1-5
a s Ca ta lysts
Sch em e 2
catalyst
Al:M
entry compound (mmol) mol ratio
Mw
361:1 503 900 12 700 40
0.00827 1322:1 695 100 14 300 49
Mn
Mw/Mn
1
2
3
4
5
6
7
1
2
2
2
3
4
5
0.0303
0.0347
0.0413
0.0318
346:1 790 100 9 060 87
106:1 754 600 20 100 38
385:1 754 900 49 300 15.3
However, in this case the Zr-Me bond lengths of the
two amidinate complexes are identical and both are
slightly shorter (approximately 0.03Å) than those of Cp2-
ZrMe2.
A comparison of the angles around the N atoms of 2
and [Me3SiNC(C6H5)NSiMe3]2ZrCl2 is provided in Scheme
2. In particular, the increase in the Cbridge-N-R (R )
Cy, SiMe3) angle and concomitant decrease in the Zr-
N-R angle for the benzamidinate relative to our alkyl-
amidinate is presumably due principally to steric in-
teractions of the SiMe3 and Ph substituents versus the
corresponding Me and Cy groups.
Eth ylen e P olym er iza tion Stu d ies. Olefin polym-
erization catalysts were generated from bis(alkylamidi-
nate) complexes (1-5) using MAO as a cocatalyst. The
results of this study are summarized in Table 6. The
most effective catalysts in this series are the Zr species
1 and 4. Entries 2, 3, and 4 indicated a slight improve-
ment in Mw with a decreasing ratio of Al:Zr. This result
is similar to what has been noted for [Me3SiNC-
(C6H5)NSiMe3]2ZrCl2.19 The activity of zirconium com-
plex 2 was also superior among the series of dichloro
complexes (1-3), exhibiting an activity of about twice
that of the Ti derivative (e.g., 16 × 103g (mol of Zr)-1
(atm of ethylene)-1 h-1 for 2 and 7 × 103 g (mol of Ti)-1
(atm of ethylene)-1 h-1 for 1). This is the same trend
as that for both metallocene and bis(benzamidinate)
0.00871 1254:1 865 200 42 900 20
0.00353 1238:1 448 700 14 400 31
compounds, and while the activities are comparable to
the bis(benzamidinate) systems, they are substantially
lower than those of the metallocene systems.19,35-38
In all cases, fairly high molecular weights of polyeth-
ylene (PE) were obtained but with a very broad weight
distribution (Mw/Mn). Our alkylamidinate complexes
gave comparable Mw values to the reported benzamidi-
nate systems.17,19 Unfortunately, there are no published
values for the weight distribution for comparison with
these systems. In contrast, a typical metallocene system
gives 106 g (mol of M)-1 (atm of ethylene)-1 h-1 with
ratios of Al/M of 102-104 and Mw/Mn values of about
2.35-38
Mixed cyclopentadienyl-amidinato Ti, Zr, and Hf
systems have been prepared and the activity of the Ti
and Zr compounds toward PE formation using MAO as
a cocatalyst have been investigated.15,16,39 These ma-
terials had activities that were similar to the benzam-
idinate and our alkylamidinate analogs but yielded low
molecular weight PE.
(35) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Reiger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
(36) Kaminsky, W.; Sinn, H. Transition Metals and Organometallics
for Catatlysts for Olefin Polymerization; Springer: New York, 1988.
(37) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325.
(38) Sinn, H.; Kaminsky, W. Adv. Organomet. Chem. 1980, 18, 99.
(39) Chernega, A.; Gomez, R.; Green, M. L. H. J . Chem. Soc., Chem.
Commun. 1993, 1415.
(34) Hunter, W. E.; Hrncir, D. C.; Bynum, R. V.; Pentilla, R. A.;
Atwood, J . L. Organometallics 1983, 2, 750.

450 Organometallics, Vol. 17, No. 3, 1998
Littke et al.
Following a procedure similar to the synthesis of 1, analyti-
cally pure yellow-green crystals of 2 were isolated from ether
at -30 °C (64%) and colorless crystals of 3 were isolated from
hexane/diethyl ether at -30 °C (68%).
Spectroscopic data for 2: 1H NMR (C6D6, ppm) 3.06 (br,
C6H11, 4H), 2.15-1.15 (m, C6H11, 40H), 1.51 (s, CH3, 6H). 13C
NMR (C6D6, ppm) 178.1 (s, NC(Me)N), 57.4, 35.0, 26.2, 25.8
(4s, C6H11), 10.7 (s, CH3); IR (KBr pellet, cm-1) 1655 (s, C-N
stretch). Anal. Calcd for C28H50N4Cl2Zr (2): C, 55.60; H, 8.33;
N, 9.26. Found: C, 55.54; H, 8.62; N, 9.10.
Spectroscopic data for 3: 1H NMR (C6D6, ppm) 3.30-3.10
(br, C6H11, 4H), 2.15-1.10 (m, C6H11, 40H), 1.52 (s, CH3, 6H);
13C NMR (C6D6, ppm) 177.6 (s, NC(Me)N), 57.1, 35.0, 26.2, 25.8
(4s, C6H11), 11.0 (s, CH3). Anal. Calcd for C28H50N4Cl2Hf (3):
C48.59; H 7.28; N 8.09. Found: C48.41; H 7.26; N 8.10.
A comparison of the two alkylamidinates in this
report and the effect of replacing the chlorides on Zr
with methyl groups is provided by entries 2, 6, and 7 of
t
Table 6. These results suggest that 4, which has a Bu
substituent on the amidinate ligand, may be superior
to 2 in terms of the Mw of the resultant PE. They also
indicate that the dichloro complex is a better catalyst
precursor than the corresponding dialkyl compound.
In summary, amidinate ligands have proven to be
useful in the preparation of a family of six-coordinate
group 4 complexes. A combination of X-ray crystal-
lographic and spectroscopic studies confirm the C2-
symmetric structures of these compounds and indicate
the fluxional nature of these species in solution. With
MAO as a cocatalyst, complexes 1-5 polymerize ethyl-
ene to yield relatively high Mw PE but very broad
polydispersities. Further experiments are underway to
investigate the effects of ligand and olefin variation,
cocatalyst, and ethylene pressure on this process. In
addition to these studies, our continuing investigations
are oriented at further revealing the steric and elec-
tronic features that influence the reactivity of transition
metal amidinate compounds.
P r ep a r a tion of Zr [C6H11NC(CMe3)NC6H11]2Cl2 (4). Fol-
t
lowing a procedure similar to the synthesis of 1, BuLi (3.1
mL, 5.3 mmol) and 1,3-dicyclohexylcarbodiimide (l.09 g, 5.3
mmol) were combined in diethyl ether (30 mL). This solution
was then added to a slurry of ZrCl4(THF)2 (1.0 g, 2.7 mmol) in
diethyl ether (l0 mL). The resulting solution was initially
bright orange in color, but after stirring overnight, it became
yellow. Filtration, evaporation of the solvent, and recrystal-
lization from toluene at -30 °C yielded l.06 g (58%) of yellow
microcrystalline 4.
Spectroscopic data: 1H NMR (C6D6, ppm) 3.85 (br, C6H11
,
4H), 2.50-1.10 (m, C6H11, 40H), 1.23 (s, CMe3, 18H); 13C NMR
(C7D8, ppm) 263 K 185.01(s), 57.97, 55.34 (2br s) 40.97 (s),
36.24, 35.24, 33.72 (3 br), 30.30 (s), 26.85 (br), 26.00 (br); 300
K 185.06 (s) 56.30 (br) 40.92 (s) 35.12 (br), 30.32 (s), 26.53 (s),
25.89 (s); 343 K 185.13 (s), 57.08 (s), 40.93 (s), 34.93 (s), 30.58
(s), 26.51 (s), 25.79 (s). Anal. Calcd for C34H62N4Cl2Zr: C,
59.27; H, 9.07; N, 8.13. Found: C, 59.29; H, 9.24: N, 7.98.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out in either a nitrogen-filled drybox or under nitrogen using
standard Schlenk-line techniques. Solvents were distilled
under nitrogen from Na/K alloy. Deuterated benzene was
distilled from potassium. MeLi (1.4 M in diethyl ether), tBuLi
(1.7 M in hexane), and 1,3-dicyclohexylcarbodiimide were
purchased from Aldrich and used without further purification.
Ethylene (CP grade) was purchased from Air Products and
used as received. Methylaluminoxane (6.7 wt % Al solution
in toluene, d ) 0.88g/mL) was purchased from Akzo Nobel and
used as received. TiCl4(THF)2, ZrCl4(THF)2, and HfCl4(THF)2
were prepared by literature procedures. Thermal analyses
were performed with a Polymer Laboratories STA1500HF. All
measurements were carried out with an alumina sample pan.
Molecular weight determinations of the polymers was per-
formed on a Waters 150C GPC with Shodex AT 103, 104, 105,
and 106 Å columns at 140 °C with 1,2,4-trichlorobenzene as
the mobile phase. 1H NMR spectra were run on a Gemini 200
MHz spectrometer with deuterated benzene as the solvent and
internal standard. All elemental analyses were run on a
Perkin-Elmer PE CHN 4000 elemental analysis system.
P r ep a r a tion of Zr [C6H11NC(Me)NC6H11]2Me2 (5). A 50
mL Schlenk flask was charged with 2 (0.17 g, 0.28 mmol),
diethyl ether (15 mL), and a stir bar. The solution was cooled
to -78 °C, and MeLi (0.40 mL, 0.56 mmol) was added dropwise
via syringe. After the mixture was warmed to room temper-
ature, the solvent was removed in vacuo and the residue was
extracted with 20 mL of hexane and filtered. Concentration
to approximately 10 mL and cooling to -30 °C gave clear,
colorless crystals (0.08 g, 0.14 mmol, 50%).
Spectroscopic data: 1H NMR (C6D6, ppm) 3.20-3.05 (br,
C6H11, 4H), 2.00-1.10 (m, C6H11, 40H), 1.66 (s, NC(CH3)N, 6H),
0.88 (s, Zr-CH3, 6H); 13C NMR (C6D6, ppm) 177.35 (s, NC-
(Me)N) 57.08, 35.45, 26.32, 26.18 (4s, C6H11), 42.74 (s, Zr-
CH3), 10.70 (s, NC(CH3)N). Anal. Calcd for C30H56N4Zr: C,
63.89; H, 10.01; N, 9.93. Found: C, 63.69; H, 9.93; N, 9.88.
Eth ylen e P olym er iza tion Exp er im en ts. In a glovebox,
a Schlenk flask equipped with a teflon stopcock was charged
with a weighed quantity of the bis(alkylamidinate) metal
complex, measured amounts of MAO and toluene, and a stir
bar. The flask was sealed, removed from the glovebox, and
attached to a high-vacuum line. Gaseous ethylene was admit-
ted to the vessel with rapid stirring, and the pressure was
maintained at 1 atm by means of a bubbler. After a measured
time interval (2 h), the reaction was quenched by addition of
acidified methanol. The polymeric product was collected by
filtration, washed and sonicated in 6 M HCl for 1 hr, filtered
and washed sequentially with methanol and hexane, then
dried overnight under vacuum.
P r ep a r a tion of Ti[C6H11NC(Me)NC6H11]2Cl2 (1), Zr [C6-
11NC(Me)NC6H11]2Cl2 (2), a n d Hf[C6H11NC(Me)NC6H12]2-
H
Cl2 (3). A 100 mL Schlenk flask was charged with 1,3-
dicyclohexylcarbodiimide (0.87g, 4.2 mmol), diethyl ether (30
mL), and a stir bar. To this solution was added MeLi (3 mL,
4.2 mmol, 1.4 M in diethyl ether) dropwise via syringe at room
temperature. The solution was stirred for 30 min and then
added dropwise via pipette to a yellow slurry of TiCl4(THF)2
(0.70 g, 2.1 mmol) in diethyl ether (10 mL). An immediate
color change to deep red-purple was observed. The resulting
solution was then stirred overnight and filtered to remove LiCl.
Evaporation of the solvent yielded 0.66 g (1.2 mmol, 56%) of a
very dark red-purple solid. Recrystallization from hexane-
diethyl ether at -30 °C afforded an analytically pure dark
purple microcrystalline solid.
Spectroscopic data for 1: 1H NMR (C6D6, ppm) 3.35-3.15
(br, C6H11, 4H), 2.40-1.10 (m, C6H11, 40H), 1.49 (s, CH3, 6H);
13C NMR (C6D6, ppm) 175.6 (s, NC(Me)N), 60.3, 33.9, 26.3,
25.9, (4s, C6H11), 10.3 (s, CH3). Anal. Calcd for C28H50N4Cl2-
Ti: C, 59.89; H, 8.97; N, 9.98. Found: C, 58.94; H, 9.09; N,
9.81.
Cr ysta llogr a p h ic Stu d y of 5. A suitable crystal of 5 was
mounted, under an inert atmosphere, in a thin-walled, glass
capillary. Systematic absences and the unit-cell parameters
are uniquely consistent for the reported space group. No
absorption correction was required (µ ) 3.6 cm -1). The
structure was solved by direct methods and refined by full-
2
matrix least-squares procedures based on |F| . All non-
hydrogen atoms were refined with anisotropic displacement
coefficients. Hydrogen atoms were treated as idealized con-

Bis(alkylamidinate) Complexes of Group 4
Organometallics, Vol. 17, No. 3, 1998 451
tributions. All computations used the SHELXTL (5.03) pro-
gram library (G. Sheldrick, Siemens XRD, Madison, WI).
Cr ysta llogr a p h ic Stu d y of 2. Data were collected on a
Rigaku AFC6S diffractometer with graphite-monochromated
Cu KR radiation at -153 °C using the ω-2θ scan technique
to a maximum 2θ value of 50° for crystals mounted on glass
fibers. Cell constants and orientation matrices were obtained
from the least-squares refinement of 24 carefully centered
high-angle reflections. Absorption corrections (ψ scan) were
made. The minimum and maximum transmission factors were
0.238 668 and 0.372 842. The structure was solved by direct
methods. The non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atom positions were located in the difference
Fourier maps and refined isotropically in the case of a
favorable observation/parameter ratio. The final cycle of full-
matrix least-squares refinement was based on the number of
observed reflections with [I > 2.5σ(I)]. All calculations were
performed using the NRCVAX package.
Ack n ow led gm en t. This work was supported by the
Natural Sciences and Engineering Research Council of
Canada.
Su p p or tin g In for m a tion Ava ila ble: Text providing a
description of the structural solutions, tables of atomic posi-
tions, thermal parameters, crystallographic data, and bond
distances and angles, ORTEP drawings for compound 2 and
5, and GPC traces for the polymers reported in Table 6 (27
pages). Ordering information is given on any current mast-
head page.
OM9707533