Cationic group 4 metal alkyl compounds containing o-arylphenoxide ligation

Article abstract of DOI:10.1021/om980287x

Treatment of the dibenzyl compounds [(ArO)₂M(CH₂Ph)₂] (ArO = 2,6-diphenyl-3,5-dimethylphenoxide, M = Ti, Zr; ArO = 2,6-diphenylphenoxide, M = Ti) with [B(C₆F₅)₃] gave the corresponding zwit

Full text of DOI:10.1021/om980287x

3636
Organometallics 1998, 17, 3636-3638
Ca tion ic Gr ou p 4 Meta l Alk yl Com p ou n d s Con ta in in g
o-Ar ylp h en oxid e Liga tion
Matthew G. Thorn, Zac C. Etheridge, Phillip E. Fanwick, and Ian P. Rothwell*
Department of Chemistry, 1393 Brown Building, Purdue University,
West Lafayette, Indiana 47907-1393
Received April 15, 1998
Sch em e 1
Summary: Treatment of the dibenzyl compounds
[(ArO)2M(CH2Ph)2] (ArO ) 2,6-diphenyl-3,5-dimeth-
ylphenoxide, M ) Ti, Zr; ArO ) 2,6-diphenylphenoxide,
M ) Ti) with [B(C6F5)3] gave the corresponding zwitter-
ionic species [(ArO)2M+(CH2Ph)(η6-C6H5CH2B-(C6F5)3)].
Addition of [B(C6F5)3] to the titanium dimethyl com-
pounds [(ArO)2TiMe2] gave unstable species which po-
lymerize ethene and propene.
The great success of group 4 metallocene olefin
polymerization catalysts1 has stimulated interest in the
development of related homogeneous catalysts sup-
ported by non-Cp ancillary ligation.2,3 We report here
on the synthesis and reactivity of cationic alkyl deriva-
tives of Zr and Ti that contain o-phenyl phenoxide
ligation.
Addition of [B(C6F5)3]4 to benzene solutions of the
zirconium and titanium dibenzyl compounds 1 and 35
leads to the rapid (1H NMR) formation of the corre-
sponding zwitterionic species 2 and 4 (Schemes 1 and
2).6 The molecular structures of 2a and 4a (Figure 1)7
show a three-legged piano-stool geometry about the
metal center with the titanium benzyl ligand η1-bound.
The M-O(aryloxide) distances in 2a and 4a are among
the shortest for aryloxide ligands bound to these met-
als.8 In solution NMR data show no evidence for
displacement of the η6-bound anion by the o-phenyl
substituents of the aryloxide ligands.6 Indeed, at ambi-
ent temperatures there is evidence in the 1H NMR
spectrum for restricted rotation of the η6-bound arene
ring in 4b. Specifically, the resonances for the protons
(1) (a) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255. (b)
Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (c) Mo¨hring, P. C.;
Coville, N. J . J . Organomet. Chem. 1994, 479, 1. (d) Kaminsky, W.;
Kulper, K.; Brintzinger, H. H. Angew. Chem., Int. Ed. Engl. 1985, 24,
507.
(2) (a) Scollard, J . D.; McConville, D. H. J . Am. Chem. Soc. 1996,
118, 10008. (b) Tsuie, B.; Swenson, D. C.; J ordan, R. F.; Petersen, J .
L. Organometallics 1997, 16, 1392. (c) Scollard, J . D.; McConville, D.
H.; Rettig, S. J . Organometallics 1997, 16, 1810. (d) Baumann, R.;
Davis, W. M.; Schrock, R. R. J . Am. Chem. Soc. 1997, 119, 3830. (e)
Go¨mez, R.; Green, M. L. H.; Haggitt, J . L. J . Chem. Soc., Chem.
Commun. 1994, 2607. (f) Friedrich, S.; Gade, L. H.; Edwards, A. J .;
McPartlin, M. J . Chem. Soc., Dalton Trans. 1993, 2861. (g) Brand, H.;
Capriotti, J . A.; Arnold, J . Organometallics 1994, 13, 4469. (h) Aoyagi,
K.; Gantzel, P. K.; Kalai, K.; Tilley, T. D. Organometallics 1996, 15,
923. (i) Cloke, F. G. N.; Geldbach, T. J .; Hitchcock, P. B.; Love, J . B. J .
Organomet. Chem. 1996, 506, 343. (j) Horton, A. D.; de With, J .; van
der Linden, A. J .; van de Weg, H. Organometallics 1996, 15, 2672. (k)
Shah, S. A. A.; Dorn, H.; Voigt, A.; Roesky, H. W.; Parisini, E.; Schmidt,
H.-G.; Noltemeyer, M. Organometallics 1996, 15, 3176. (l) Herskovics-
Korine, D.; Eisen, M. S. J . Organomet. Chem. 1995, 503, 307.
(3) For the polymerization of olefins by bidentate aryloxides see: (a)
van der Linden, A.; Schaverien, C. J .; Meijboom, N.; Grant, C.; Orpen,
A. G. J . Am. Chem. Soc. 1995, 117, 3008. (b) Fokken, S.; Spaniol, T.
P.; Kang, H.-C.; Massa, W.; Okuda, J . Organometallics 1996, 15, 5069.
For cationic zirconium alkyls supported by chelating phenoxides see:
(c) Cozzi, P. G.; Gallo, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.
Organometallics 1995, 14, 4994.
(4) (a) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015. (b) Ewen, J . A.; Elder, M. J . Chem. Abstr. 1991, 115,
136998g. (c) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2,
245. (d) Bochmann, M.; Lancaster, S. J .; Hursthouse, M. B.; Malik, K.
M. A. Organometallics 1994, 13, 2235. (e) Gillis, D. J .; Tudoret, M.-J .;
Baird, M. C. J . Am. Chem. Soc. 1993, 115, 2543. (f) Pellecchia, C.;
Pappalardo, D.; Oliva, L.; Zambelli, A. J . Am. Chem. Soc. 1995, 117,
6593.
(5) (a) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I.
P. Organometallics 1985, 4, 902. (b) Chesnut, R. W.; Durfee, L. D.;
Fanwick, P. E.; Rothwell, I. P.; Folting, K.; Huffman, J . C. Polyhedron
1987, 6, 2019.
(6) Full experimental details and product characterization are
contained in the Supporting Information. Representative synthesis of
a zwiterionic species, [Ti(OC6H3Ph2-2,6)2(CH2Ph)][η6-C6H5CH2B(C6F5)3]
(4a ): a sample of [Ti(OC6H3Ph2-2, 6)2(CH2Ph)2] (3a ; 1.00 g, 1.39 mmol)
was placed in a solvent-sealed flask along with 1.3 equiv of tris-
(pentafluorophenyl)boron (0.92 g, 1.80 mmol) and 5 mL of benzene.
The reaction solution immediately turned red. The flask was left
undisturbed for 12 h, and then the solution was evacuated to dryness.
The resulting red solid was redissolved in a minimum of benzene and
layered with hexane, affording [Ti(OC6H3Ph2-2,6)2(CH2Ph)][η6-C6H5-
CH2B(C6F5)3] (4a ) as dark red crystals in 63% yield (1.07 g). Anal. Calcd
for C68H40BF15O2Ti: C, 66.26; H, 3.27. Found: C, 66.32; H, 3.28. 1H
NMR (C6D6, 30 °C): δ 6.75-7.30 (aromatics); 6.65 [d, 3J (1H-1H) )
7.0 Hz, ortho Ti-CH2Ph]; 6.07 [d, 3J (1H-1H) ) 6.7 Hz, ortho Ti-η6-
C6H5]; 4.78 [t, 3J (1H-1H) ) 7.5 Hz, meta Ti-η6-C6H5]; 4.43 [t, 3J (1H-
1H) ) 7.3 Hz, para Ti-η6-C6H5]; 2.77 (br, B-CH2); 2.12 (s, Ti-CH2).
Selected 13C NMR (C6D6, 30 °C): δ 161.9 (Ti-O-C); 151.0 (br, B-CH2);
146.2 (ipso BCH2-Ph); 101.2 (TiCH2). Synthesis of [Ti(OC6H3Ph2-2,6)2-
(C{CH3}C{Ph}CH2{η6-C6H5})][PhCH2B(C6F5)3] (5a ):
A sample of
[Ti(OC6H3Ph2-2,6)2(CH2Ph)][η6-C6H5CH2B(C6F5)3] (4a ; 130 mg, 0.105
mmol) was dissolved in 2 mL of benzene in a round-bottomed flask.
To this solution was added 1.0 equiv of 1-phenylpropyne (13.2 µL, 0.105
mmol). The color of this solution slowly turned from red to orange over
the course of 1 h. This orange solution was evacuated to dryness,
affording [Ti(OC6H3Ph2-2,6)2(C{CH3}C{Ph}CH2{η6-C6H5})][B(C6F5)3(CH2-
Ph)] (5a ) as a red glassy solid in 64% yield (90 mg). 1H NMR (C6D6, 30
°C): δ 6.60-7.40 (aromatics); 6.29 [t, 3J (1H-1H) ) 7.6 Hz, meta Ti-
η6-C6H5]; 5.82 [d, 3J (1H-1H) ) 7.4 Hz, ortho Ti-η6-C6H5]; 4.29 [t,
3J (1H-1H) ) 7.4 Hz, para Ti-η6-C6H5]; 3.22 (s, CH2); 3.17 (s, B-CH2);
1.87 (s, CH3). Selected 13C NMR (C6D6, 30 °C): δ 231.6 (Ti-C{CH3});
163.8 (Ti-O-C); 45.7 (CH2); 34.3 (Ti-C{CH3}). Attempts to isolate
5a as a crystalline solid have thus far been unsuccessful.
S0276-7333(98)00287-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/30/1998

Communications
Organometallics, Vol. 17, No. 17, 1998 3637
Sch em e 2
F igu r e 1. Molecular structure of 2a showing the atomic
numbering scheme. The three C6F5 groups attached to
boron have been omitted for clarity. The titanium com-
pound 4a is isostructural, with an identical numbering
scheme. Selected bond lengths (Å) and angles (deg) for 2
{4a }: M-O(2), 1.893(3) {1.761(5)}; M-O(3), 1.900(3)
{1.795(4)}; M-C(40), 2.230(4) {2.159(9)}; M-C(1), 2.821(4)
{2.627(6)}; M-C(2), 2.653(4) {2.555(6)}; M-C(3), 2.662(4)
{2.543(7)}; M-C(4), 2.681(5) {2.566(7)}; M-C(5), 2.694(4)
{2.538(7)}; M-C(6), 2.764(4) {2.558(7)}; O(2)-M-O(3),
113.6(1) {110.0(2)}; O(2)-M-C(40), 99.4(2) {96.6(3)}; O(3)-
M-C(40),99.6(1){97.8(3)};M-O(2)-C(21),165.3(3){158.9(5)};
M-O(3)-C(31), 158.8(4) {170.5(3)}; M-C(40)-C(41), 117.4-
(3) {120.6(6)}.
(Scheme 2).6 The spectroscopic data for these com-
pounds are consistent with insertion of 1 equiv of
substrate into the Ti-benzyl bond being followed by
chelation via η6 binding to the benzyl arene ring. In
the 1H NMR spectra of 5 and 6 the free anion
[PhCH2B-(C6F5)3] was observed. Furthermore, the η6-
arene ring gives rise to three and five multiplets upfield
of the normal aromatic region for 5 and 6, respectively.
Although not conclusive, the regiochemistry of phenyl-
propyne insertion is assigned as shown (Scheme 2) on
the basis of the upfield shift of the methyl resonance
from δ 1.87 for 5a to δ 1.03 in 5b. Previous work has
shown that the introduction of m-methyl substituents
increases the upfield shifting of adjacent groups by the
diamagnetic anisotropy of the o-phenyl rings.9 The 1,2-
insertion of R-olefins is unequivocal from the NMR data.
Attempts to crystallize these insertion products led only
to the formation of hexane- or pentane-insoluble oils
that dried to glassy solids. The addition of propene or
1-hexene to solutions of 4 initially led to the analogous
insertion products 7 and 8, identified by 1H NMR
attached to the η6-bound arene ring in 4b are broadened
considerably compared to those of 4a . Further evidence
for restricted rotation is given in the 1H NMR of 2b,
where five distinct signals for the protons of the η6-
bound arene ring are observed. This implies that
bulkier aryloxides restrict rotation of the η6-bound arene
ring on the metal center with 2,6-di-tert-butyl phenoxide
(2b) completely locking the arene ring into one confor-
mation with nonequivalent ortho and meta protons.
The zirconium complexes 2 are stable in solution in
the presence of propene and phenylpropyne. In con-
trast, the titanium compounds 4 react with 1 equiv of
phenylpropyne or allylbenzene to produce salts 5 and 6
(7) Crystallographic data for 2a at 203 K: ZrF15O2C84BH55, Mr
)
1483.38, space group P1h (No. 2), a ) 13.358(2) Å, b ) 14.722(4) Å, c )
20.596(7) Å, R ) 71.45(2)°, â ) 77.55(2)°, γ ) 72.18(2)°, V ) 3624(2)
Å3, dcalc ) 1.359 g cm-3, Z ) 2. Of the 9594 unique reflections collected
2
(5.14 e 2θ e 45.34°) with Mo KR (λ ) 0.710 73 Å), 9594 with Fo
>
2σ(Fo2) were used in the final least-squares refinement to yield R(Fo)
) 0.055 and Rw(Fo2) ) 0.160. Crystallographic Data for 4a at 295 K:
TiF15O2C68BH40, Mw ) 1232.76, space group P1h (No. 2), a ) 12.917(2)
Å, b ) 13.045(2) Å, c ) 19.600(2) Å, R ) 84.757(12)°, â ) 77.580(12)°,
γ ) 61.871(13)°, V ) 2844.0(8) Å3, dcalc ) 1.444 g cm-3, Z ) 2. Of the
7524 unique reflections collected (5.78 e 2θ_ e 45.34°) with Mo KR (λ
) 0.710 73 Å), the 7523 with Fo2 > 2σ(Fo2) were used in the final least-
squares refinement to yield R(Fo) ) 0.069 and Rw(Fo2) ) 0.178.
(8) Based upon analysis of the Cambridge Structural Database.
(9) Vilardo, J . S.; Lockwood, M. A.; Hanson, L. G.; Clark, J . R.;
Parkin, B. C.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Dalton
Trans. 1997, 3353.

3638 Organometallics, Vol. 17, No. 17, 1998
Communications
Ta ble 1. P olyeth ylen e a n d P olyp r op ylen e
P r op er ties a n d Ca ta lyst Activitiesa
(Scheme 2). These species carry out the very slow
oligomerization of propene and isomerization of 1-hex-
ene into 2-hexene and 3-hexene.
cat.
10-3(activity),
precursor
10-3Mn
10-3Mw
Mw/Mn
g mol-1 h-1 atm-1
The dimethyl compounds 95b also react rapidly (1H
NMR) with 1 equiv of [B(C6F5)3] in C6D6 to initially
produce a solution containing the single component 10
(Scheme 2). The spectroscopic data for 10 are consistent
with the anion being bound to the cationic metal center,
as observed for related methyl species. Within 1 h at
ambient temperatures this solution converts to a mix-
ture of [(ArO)2Ti(Me)(C6F5)] (12), [MeB(C6F5)2] (13),4a
and a small amount of [(ArO)3TiMe],5b as identified by
1H NMR. This type of decomposition has precedence
in Zr-Cp chemistry.4a The Ti-Me resonance for 12
appears as a sharp triplet; 5J (19F-1H) ) 1.5 Hz.
Although broad, the B-Me resonance for 13 can be
resolved as a pentet; 5J (19F-1H) ) 1.8 Hz. The addition
of allylbenzene to the initially formed solution of 10
generated the salt 11, which contains the same cation
obtained by addition of propene to 4 (Scheme 2).
Polyethylene
9a
9b
9c
9d
2.59
2.61
8.23
12.5
5.64
4.91
11.8
23.5
2.2
3
4
3
2
1.9
1.4
1.9
Polypropylene
9a
9b
9c
9d
1.53
1.72
3.45
14.5
1.97
2.17
4.65
1.3
1.3
1.4
2.0
6
5
3
2
28.98
a
Conditions: 0.089 mmol of 9; 0.097 mmol of B(C6F5)3; 3 mL
of toluene; 0 °C; 1 atm; 15 min reaction time.
imposed upon the o-phenyl rings. Hence, the data in
Table 1 can be interpreted as a correlation between
ligand bulk and polymer molecular weight.
Ack n ow led gm en t. We thank the National Science
Foundation (Grant CHE-9700269) for financial support
of this research. We thank Dr. Dave Dockter and
Phillips Petroleum Co. for GPC characterization of
polymers.
Solutions of 10 will catalyze the polymerization of
ethene and propene (Table 1). Analysis of the polypro-
pylene by NMR showed an atactic polymer with pre-
dominantly vinylidene end groups consistent with 1,2-
insertion/â-hydrogen elimination pathways. It can be
seen (Table 1) that the molecular weight of both
polymers is strongly dependent on the nature of the
aryloxide. Although it is not possible at present to rule
out electronic effects, previously we have shown that
the most important influence of introducing meta sub-
stituents onto the 2,6-diphenylphenoxide nucleus is to
increase the steric properties of the ligand.9 This is a
consequence of a decrease in conformational flexibility
Su p p or tin g In for m a tion Ava ila ble: Figures giving NMR
spectra for 3a ,b and 5a , text giving experimental details and
product characterization, an ORTEP view of 4a , text giving a
description of the experimental procedures for X-ray diffraction
studies, and tables of thermal parameters, bond distances and
angles, intensity data, torsion angles, and mutiplicities for 2a
and 4a (55 pages). Ordering information is given on any
current masthead page.
OM980287X