3830
J. Am. Chem. Soc. 1997, 119, 3830-3831
to that used to prepare NH(t-Bu)(C6H5)26 and NH(t-Bu-d6)(aryl)
Synthesis of Titanium and Zirconium Complexes
That Contain the Tridentate Diamido Ligand,
[((t-Bu-d6)N-o-C6H4)2O]2- ([NON]2-) and the Living
Polymerization of 1-Hexene by Activated
[NON]ZrMe2
derivatives.22 The yield of H2[NON], a yellow oil, is typically
Robert Baumann, William M. Davis, and
Richard R. Schrock*
Department of Chemistry 6-331,Massachusetts Institute of
Technology,Cambridge, Massachusetts 02139
55% on a scale of 10-15g. Addition of 2 equiv of butyllithium
to H2[NON] in ether at -35 °C followed by addition of TiCl2-
27
ReceiVed NoVember 4, 1996
(NMe2)2 yields Ti[NON](NMe2)2 in ∼55% yield, which can
be converted to Ti[NON]Cl2 with 2 equiv of Me3SiCl.28-30
Alkylation of Ti[NON]Cl2 with 2 equiv of MeMgCl affords
[NON]TiMe2 (1) in ∼75% yield. An X-ray study of 1 (Figure
1) shows that it has a trigonal bipyramidal structure in which
the Ti-O distance (2.402(4) Å) is much shorter than that
between Ti and the (essentially uncoordinated) donor nitrogen
in [(Me3SiNCH2CH2)2N(SiMe3)]TiMe2 (2.732(2) Å),12 although
it is still longer than one might expect for a “normal” Ti-Odonor
bond length (∼2.15-2.20 Å). The tert-butyl groups are
“tipped” (Oax-Ti-Neq-C ) 136-137°), in part as a conse-
quence of the enforced conformation of the [NON]2- ligand.
Proton and carbon NMR spectra of 1 suggest that it has C2V
symmetry on the NMR time scale. We propose that the methyl
groups equilibrate via an intermediate that contains a planar
form of the [NON]2- ligand in which the methyl groups occupy
two equatorial positions in a distorted trigonal bipyramid.
[NON]ZrI2 can be prepared as shown in eq 2.22 Alkylation
of [NON]ZrI2 with MeMgI in diethyl ether gives [NON]ZrMe2
(2) in 70% yield. NMR spectra of 2, even at -70 °C, suggest
that it has C2V symmetry on the NMR time scale. We assume
Enormous advances have been made in the last decade in
the design and synthesis of “well-defined” or “single-site”
catalysts for the polymerization of terminal olefins.1 The vast
majority of such catalysts are metallocene derivatives, although
some are known that contain one cyclopentadienyl ring and (for
example) a pendant amido ligand.2-8 Recently, however,
complexes that contain only a chelating dialkoxide9,10 or a
chelating diamido ligand11-19 have received attention as potential
Ziegler-Natta catalysts. An important recent result is the
finding that propylene-bridged aryl-substituted diamido titanium
complexes promote the living polymerization of neat R olefins.20
As a part of our program to investigate the utility of triami-
doamine ligands21 and new diamido15 ligands in early metal
chemistry, we were attracted to the [(t-BuN-o-C6H4)2O]2- ligand
for preparing new noncyclopentadienyl group 4 olefin polym-
erization catalysts for a variety of reasons, among them the likely
robust nature of the (tert-butyl)(phenyl)amide-metal linkage22-24
and the diphenyl ether linkage. We report here our preliminary
results for Ti and Zr.
The species [((t-Bu-d6)NH-o-C6H4)2O] (H2[NON], eq 1) can
be prepared from [(NH2-o-C6H4)2O]25 in a manner analogous
(1) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
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at this stage that the structure of 2 in the solid state is analogous
to that found for 1 and that C2V symmetry is achieved via a
distorted trigonal bipyramidal molecule containing a planar
[NON]2- ligand.
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Addition of B(C6F5)3 to 2 in bromobenzene-d5 or toluene-d8
at -35 °C yielded a bright yellow solution. NMR spectra
suggest that a product is formed quantitatively in which the
methyl groups are inequivalent. Addition of B(C6F5)3 to [NON]-
ZrMe2 in pentane at -35 °C yielded a bright yellow solution
from which some yellow oil precipitated immediately. The
pentane supernatant was filtered and cooled to -35 °C to afford
3a as yellow crystals (containing 0.5 equiv of pentane by NMR)
in 47% yield. Compound 3a is stable in the solid state at -35
°C, but decomposes in toluene, pentane, or bromobenzene over
a period of hours at 22 °C.
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“zwitterion” analogous to structurally-characterized compounds
obtained by adding B(C6F5)3 to group 4 methyl metallocenes31-34
in which the borane has partially abstracted the “apical” methyl
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Organometallics 1996, 15, 2672.
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S0002-7863(96)03823-1 CCC: $14.00 © 1997 American Chemical Society