Synthesis of group 4 complexes that contain the diamidoamine ligands, [(2,4,6-Me3C6H2NCH2CH2)2NR]2- ([Mes2N2NR]2-; R = H or CH3), and polymerization of 1-hexene by activated [Mes2N2NR]ZrMe2 complexes

Full text of DOI:10.1021/ja983636n

J. Am. Chem. Soc. 1999, 121, 5797-5798
5797
using similar methods has been reported recently,3 as has arylation
of triethylenetetramine.4
Synthesis of Group 4 Complexes that Contain the
Diamidoamine Ligands,
The [Mes2N2NH]2- ligand was first attached to zirconium using
the now familiar Zr(NMe2)4 route shown in eq 2. Both [Mes2N2-
[(2,4,6-Me3C6H2NCH2CH2)2NR]2- ([Mes2N2NR]2-; R
) H or CH3), and Polymerization of 1-Hexene by
Activated [Mes2N2NR]ZrMe2 Complexes
Zr(NMe2)4 H [Mes N NH]8
2
2 2
-2Me2NH
Lan-Chang Liang,† Richard R. Schrock,*,†
2TMSCl
William M. Davis,† and David H. McConville‡
[Mes2N2NH]Zr(NMe2)2
8 [Mes2N2NH]ZrCl2 (2)
-2Me2NTMS
Department of Chemistry
Massachusetts Institute of Technology
Cambridge, Massachusetts 02139
Exxon Chemical Company
NH]Zr(NMe2)2 and [Mes2N2NH]ZrCl2 have mirror symmetry
according to NMR data, although it is likely (on the basis of a
dimeric structure observed for [(t-BuN-o-C6H4)2O]ZrCl2 ) that the
5
latter is a dimer containing two bridging chlorides in the solid
state. In [Mes2N2NH]Zr(NMe2)2 the two dimethylamido groups
are inequivalent (resonances at 3.05 and 2.28 ppm), consistent
with no rapid inversion of configuration at the central nitrogen
donor.6 The NH resonance is found as a broadened singlet at 1.80
ppm. The mesityl rings do not rotate rapidly on the NMR time
scale about the N-Cipso bonds in either [Mes2N2NH]Zr(NMe2)2
or [Mes2N2NH]ZrCl2.7 These data are consistent with either a fac
or a mer arrangement of the [Mes2N2NH]2- ligand in each
compound, as long as the central nitrogen donor remains bound.
The reaction between [Mes2N2NH]ZrCl2 and 2 (or more) equiv
of MeMgI in ether produces white crystalline [Mes2N2NH]ZrMe2
in high yield. The inequivalent ZrMe resonances are found at
0.24 and 0.07 ppm in the proton NMR spectrum of [Mes2N2NH]-
ZrMe2 in C6D6, and the NH proton resonance is found at 1.16
ppm. [Mes2N2NH]ZrMe2 is relatively stable in solution, although
it decomposes slowly to give a molecule that has yet to be
identified. It is interesting to note that the central NH proton is
not removed readily by MeMgI in ether at room temperature.
However, it is removed by LiMe to give what we formulate as
[(MesNCH2CH2)2NLi]ZrMe2. Addition of MeI to “[(MesNCH2-
CH2)2NLi]ZrMe2” then gives [Mes2N2NMe]ZrMe2 in high yield.
An X-ray study of [Mes2N2NMe]ZrMe2 reveals a structure
(Figure 1) in which the three nitrogens lie in a plane that bisects
the C(1)-Zr-C(2) angle, i.e., a mer structure. The donor amine
nitrogen nevertheless is virtually tetrahedral (C-N-C ) 109°,
109°, and 112°). The Zr-Namine bond length, Zr-Namido bond
lengths, Zr-Me bond lengths, and C-Zr-C, N-Zr-N, and Zr-
N-C angles are all typical of diamido/Ndonor complexes having
a mer geometry.1h,8 The mer structure of [Mes2N2NMe]ZrMe2
contrasts with the fac structures found for [(Me3SiNCH2CH2)2-
NSiMe3]ZrX2 (X ) halide or alkyl) complexes.1b,d
The apparent stability and ease of formation of [Mes2N2NH]-
ZrMe2 led us to attempt to form it “directly” from ZrCl4,
H2[Mes2N2NH], and MeMgI. Addition of ZrCl4 to H2[Mes2N2-
NH] in ether resulted in the formation of a precipitate in which
we assume the ligand has been at least partially attached to the
metal. Subsequent addition of 4 equiv of MeMgI followed by a
standard workup yielded [Mes2N2NH]ZrMe2 in ∼40% yield on
a scale of ∼0.6 g of product. A similar “direct” approach also
gave red [Mes2N2NH]TiMe2 in ∼35% yield and white [Mes2N2-
(3) Hong, Y.; Senanayake, C. H.; Xiang, T.; Vandenbossche, C. P.;
Tanoury, G. J.; Bakale, R. P.; Wald, S. A. Tetrahedron Lett. 1998, 39, 3121.
(4) Greco, G. E.; Popa, A. I.; Schrock, R. R. Organometallics 1998, 17,
5591.
(5) Baumann, R. Ph.D. Thesis, Massachusetts Institute of Technology, 1998.
(6) Inversion has been observed in titanium complexes that contain the
[(Me3SiNCH2CH2)2NSiMe3]2- ligand as a consequence of the relatively poor
basicity of the central nitrogen donor containing the bulkyl TMS substituent
and relatively weak Ti-N donor bond.1a
5200 Bayway Dr., Baytown, Texas 77522
ReceiVed October 16, 1998
Several types of “diamido/donor” ligands have been synthesized
in the last several years and attached to group 4 metal complexes,
often with the intent of preparing new group 4 olefin polymer-
ization catalysts.1 We have been interested in zirconium complexes
that contain diamido/ether ligands ([(t-BuN-o-C6H4)2O]2- or
[(ArylNCH2CH2)2O]2- 1e,f,k,m as catalysts for the polymerization
)
of R olefins, especially since in the first case the polymerization
of up to 500 equiv of 1-hexene has been found to take place in
a living manner at 0 °C via 1,2-insertion of the olefin into the
cationic alkyl complex.1e,f We became interested in diamido/donor
ligands in which the central donor cannot readily attain a planar
geometry. We report here zirconium complexes that contain the
[(2,4,6-Me3C6H2NCH2CH2)2NR]2- ([Mes2N2NR]2-; R ) H or
Me) ligand, along with [Mes2N2NH]TiMe2 and [Mes2N2NH]-
HfMe2 complexes, and the activation of zirconium dimethyl
complexes for the polymerization of 1-hexene at temperatures
up to 30 °C.
Many amines can now be arylated in a palladium-catalyzed
reaction.2 We have found that diethylenetriamine can be doubly
arylated readily using mesityl bromide in a procedure that is
analogous to that reported in one of several recent publications
by Buchwald.2c The yield of H2[Mes2N2NH] (eq 1) is virtually
Pd2(dba)3, rac-BINAP
HN(CH2CH2NH2)2 + 2MesBr 2NaO-t-Bu, toluene, heat8
HN(CH2CH2NHMes)2 (1)
quantitative and the reaction has been carried out without
complications on a 100 g scale. Synthesis of the analogous o-tolyl-
substituted diethylenetriamine (along with other arylated amines)
† Massachusetts Institute of Technology.
‡ Exxon Chemical Company.
(1) (a) Clark, H. C. S.; Cloke, F. G. N.; Hitchcock, P. B.; Love, J. B.;
Wainwright, A. P. J. Organomet. Chem. 1995, 501, 333. (b) Cloke, F. G. N.;
Hitchcock, P. B.; Love, J. B. J. Chem. Soc., Dalton Trans. 1995, 25. (c) Horton,
A. D.; de With, J. Chem. Commun. 1996, 1375. (d) Horton, A. D.; de With,
J.; van der Linden, A. J.; van de Weg, H. Organometallics 1996, 15, 2672.
(e) Baumann, R.; Davis, W. M.; Schrock, R. R. J. Am. Chem. Soc. 1997,
119, 3830. (f) Baumann, R.; Schrock, R. R. J. Organomet. Chem. 1998, 557,
69. (g) Gue´rin, F.; McConville, D. H.; Payne, N. C. Organometallics 1996,
15, 5085. (h) Gue´rin, F.; McConville, D. H.; Vittal, J. J. Organometallics
1996, 15, 5586. (i) Schattenmann, F. J.; Schrock, R. R.; Davis, W. M.
Organometallics 1998, 17, 989. (j) Friedrich, S.; Schubart, M.; Gade, L. H.;
Scowen, I. J.; Edwards, A. J.; McPartlin, M. Chem. Ber. Rec. 1997, 130, 1751.
(k) Aizenberg, M.; Turculet, L.; Davis, W. M.; Schattenmann, F. S.; Schrock,
R. R. Organometallics 1998, 17, 4795. (l) Male, N. A. H.; Thornton-Pett,
M.; Bochmann, M. J. Chem. Soc., Dalton Trans. 1997, 2487. (m) Schrock,
R. R.; Schattenmann, F.; Aizenberg, M.; Davis, W. M. Chem. Commun. 1998,
199.
(7) (a) Scollard, J. D.; McConville, D. H.; Vittal, J. J. Organometallics
1995, 14, 5478. (b) Scollard, J. D.; McConville, D. H.; Payne, N. C.; Vittal,
J. J. Macromolecules 1996, 29, 5241. (c) Scollard, J. D.; McConville, D. H.
J. Am. Chem. Soc. 1996, 118, 10008.
(8) Schrock, R. R.; Lee, J.; Liang, L.-C.; Davis, W. M. Inorg. Chim. Acta
1998, 270, 353.
(2) (a) Hartwig, J. F. Angew. Chem., Int. Ed. Engl. 1998, 37, 2046. (b)
Wolfe, J. P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc. Chem. Res.
1998, 31, 805. (c) Wolfe, J. P.; Wagaw, S.; Buchwald, S. L. J. Am. Chem.
Soc. 1996, 118, 7215.
10.1021/ja983636n CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/05/1999

5798 J. Am. Chem. Soc., Vol. 121, No. 24, 1999
Communications to the Editor
6, 8) is approximately double that found employing [Mes2N2-
NH]ZrMe2, consistent with less â elimination. When a 325 equiv
polymerization employing [Mes2N2NMe]ZrMe2 is begun at ∼20
°C (run 7) the results are essentially the same as those obtained
at 0 °C (run 6), even though the exotherm produces a rise in
temperature to ∼30 °C in ∼1 min under these conditions. Runs
9, 10, and 11 reveal that addition of the 1-hexene in two portions
with a 30 min pause between the two additions leads to polymer
with a higher PDI and a Mn corresponding approximately to the
number of equivalents of monomer added in the second step.
Therefore, it appears that a significant amount of â elimination
takes place within ∼30 min at 20-30 °C for oligomers that
contain between 20 and 100 monomer units in the absence of
excess monomer, but the product of â elimination is relatively
stable and can generate a second chain. However, heating a sample
to 65 °C for 10 min between the two additions of 1-hexene (run
12) leads to a less than quantitative yield (65%) of poly(1-hexene),
consistent with a significant amount of irreVersible decomposition
of the polymerization intermediate formed from 139 equiv of
monomer at 65 °C.
Figure 1. A Chem 3D drawing of the structure of [Mes2N2NMe]ZrMe2
(N(1)-Zr-N(2) ) 70.26(11)°; Zr-N(1)-C(11) ) 118.8(3)°; M-N(2)
) 2.373(5) Å; M-Nax ) 2.095(4) Å; N(1)-M-N(3) ) 140.5(2)°; M-C
) 2.240(7), 2.265(7) Å; C(1)-M-C(2) ) 103.2(3)°).
Table 1. Characterization of the Poly(1-hexene) Prepared with
[Mes2N2NR]ZrMe2 (R ) H (A), Me (B)) Initiatorsa
T (°C)/
no. precursor equiv min MW(calcd)b 10-2Mn 10-2Mw PDI
1
2
3
4
5
6
7
8
9
A
134
313
626
139
0/60
0/60
0/60
0/60
11300
26300
52700
11700
23400
27400
27400
54600
125c
170d
127d
167c
321
162
209
172
192
400
396
398
450
1.3
1.2
1.4
1.1
1.2
1.4
1.5
1.5
B
278 20/60e
So far no titanium diamido/donor complexes that we have
prepared in our laboratory have been found to be well-behaved
initiators for the polymerization of 1-hexene.
325
325 20/60e
649 0/60
0/60
287d
258d
291c
19 20/30e
259 20/60e
46 20/30e
232 20/60e
93 20/30e
185 20/60e
139 20/60,e
65/10
The results described here should be compared with those found
for Zr systems employing [(t-BuN-o-C6H4)2O]ZrMe2 as an
initiator, which yield poly(1-hexene) via primarily (>95%) a 1,2-
insertion process1f with little â elimination during synthesis of
up to a 500 mer.1e We now believe that the [(t-BuN-o-C6H4)2O]2-
system is successful in part as a consequence of the significant
steric hindrance afforded by tert-butyl substituents and the
formation of relatively crowded pseudo-tetrahedral monoalkyl
cations. It should be noted that a 2,1-insertion product would have
a different reactivity (presumably lower) and a different stability
(presumably also lower) than a 1,2-insertion product, as has been
proposed in propylene polymerization systems.10 Therefore we
hypothesize that {[Mes2N2NR]Zr(polymer)}+ intermediates be-
come more stable toward â elimination when R is a methyl group,
in part because of a lower percentage of sterically more difficult
2,1-insertions. We also propose that the pseudo-tetrahedral
configuration of the bound central nitrogen donor sharply
increases the tendency to form a pseudo-tetrahedral monoalkyl
cationic complex in which steric crowding is exacerbated by a
contraction of metal-ligand bond lengths, one in which the
strength of anion binding and 2,1 “misinsertions” therefore are
limited, although apparently not to the degree yet that is found
in the [(t-BuN-o-C6H4)2O]2- system. However, the steric bulk of
the amido and amine substituents should be adjustable to the point
where steric hindrance is maximized. Experiments aimed in this
direction are under way.
23400
23400
23400
265
207d
153
435
382
321
1.6
1.8
2.1
10
11
12f
139 20/60e
23400
174
213
1.4
a The initiator was prepared as described in the text and in the
Supporting Information; yields were quantitative except in run 12. Mw
and Mn were determined by a combination of light scattering and
refractometry. b Calculated on the basis of the number of monomers
added. c Average of three determinations for a single sample. d Average
of two determinations for a single sample. e Reactions were initiated
at ∼20 °C, but the temperature increased rapidly to as much as 30 °C
within ∼1 min. f The yield was ∼65% and the molecular weight
distribution was bimodal; the values for Mn, Mw, and PDI refer to the
higher molecular weight peak.
NH]HfMe2 in ∼35% yield on similar small scales (eq 3). The
1. MCl4 in ether
[Mes N NH]MMe
2
M ) Ti, Zr, Hf
H2[Mes2N2NH]
8
(3)
2
2
2. 4 MeMgI
preferred “direct” synthesis of [Mes2N2NH]ZrMe2 consists of
preparing the insoluble adduct in toluene (80 °C, 24 h, quantitative
yield), then treating the mixture with 4 equiv of MeMgBr in ether
(3.0 M). The magnesium salts were filtered off and [Mes2N2NH]-
ZrMe2 was isolated from the filtrate in 86% yield.
Acknowledgment. We thank Exxon Corporation and the Department
of Energy (DE-FG02-86ER13564) for supporting this research.
Addition of [Ph3C][B(C6F5)4] to [Mes2N2NH]ZrMe2 or [Mes2N2-
NMe]ZrMe2 in chlorobenzene at 0 °C yielded a yellow solution.
1-Hexene was added and the solution was kept at 0 °C for a period
of 1 h.9 The still yellow reaction mixture was then quenched with
ethereal HCl and the poly(1-hexene) isolated and analyzed as
described elsewhere.1k,m The results of analysis of the poly(1-
hexene) by gel permeation chromatography are shown in Table
1 (runs 1, 2, 3, 4, 6, 8). The number average molecular weight of
the poly(1-hexene) obtained was consistent with some chain
termination, presumably via â elimination. However, since the
yields were all quantitative, the presumed hydride product of â
elimination is stable enough to begin another chain. The maximum
molecular weight found employing [Mes2N2NMe]ZrMe2 (runs 4,
Supporting Information Available: Experimental procedures, fully
labeled ORTEP drawing, crystal data and structure refinement, atomic
coordinates, bond lengths and angles, and anisotropic displacement
parameters for [Mes2N2NMe]ZrMe2 (PDF). This material is available free
of charge via the Internet at http://pubs.acs.org.
JA983636N
(10) (a) Busico, V.; Cipullo, R.; Chadwick, J. C.; Modder, J. F.; Sudmeijer,
O. Macromolecules 1994, 27, 7538. (b) Busico, V.; Cipullo, R.; Talarico, G.
Macromolecules 1998, 31, 2387. (c) Busico, V.; Cipullo, R.; Talarico, G.;
Segre, A. L.; Caporaso, L. Macromolecules 1998, 31, 8720. (d) Resconi, L.;
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Organometallics 1996, 15, 5046. (e) Guerra, G.; Longo, P.; Cavallo, L.;
Corradini, P.; Resconi, L. J. Am. Chem. Soc. 1997, 119, 4394.
(9) The choice of 1-hexene (versus propylene) is based solely on the ease
of analyzing poly(1-hexene) by GPC and the relative convenience of the
polymerization procedure.