Isomerization and α-H elimination of dialkyltungsten complexes stabilized by a sulfur-bridged chelating diaryloxo ligand

Article abstract of DOI:10.1021/om9808965

Dichlorotungsten complexes bearing an O-S-O chelating dialkoxo and a diphenylacetylene ligand, W(η²-RC≡CR)[S(4-R′-6-R″C₆H ₂O)₂]Cl₂(R = Ph, R′ = Me, R″ = ^tBu (3a); R = Et; R′ = R″ = Me (3b)), were prepared by the reaction of W(η²-RC≡CR)Cl₄ and S(4-R′-6-R″C₆;H₂-OH)₂. Their C_s structures were confirmed by NMR study of these complexes and X-ray crystallography of 3b. Complex 3a reacted with Mg(CH₂SiMe₃)₂ in diethyl ether to give initially a Cs symmetric dialkyltungsten complex, W(η²-PhC≡CPh)[S(4-Me-6-^tBuC₆H ₂O)₂](CH₂-SiMe₃)₂ (5). In solution at room, temperature, 5 isomerizes to the C₁ symmetric isomer 6, whose structure was probed by the NMR spectroscopy. The thermodynamic parameters for the isomerization were determined to be G?(45 °C) = 23.8 ±0.4 kcal mol^-1 and S?(45 °C) = -3.3 ±t 0.7 cal K^-1 mol^-1. Upon heating to 60 °C, the generation of metal-alkylidene species occurs. A similar reaction of 3a with dimethyl- and dibenzylmagnesium directly gives C₁ symmetric dialkyltungsten complexes, W(η²-PhC≡CPh)[S(4-Me-6-^tBuC₆H ₂O)₂]R₂ (R = Me (7), CH₂Ph (8)), whose structures were determined by X-ray crystallography. The ring-opening metathesis polymerization (ROMP) of norbornene was initiated in the presence of these dialkyl complexes as catalyst precursors to give poly(norbornene) having high molecular weight (M_n = 1.7 ×10⁶) and high cis content (cis 93%) at the early stage of the reaction. At a polymerization temperature of 60 °C, the molecular weight and the cis content of the resulting poly(norbornene) are lowered due to the second metathesis reactions.

Full text of DOI:10.1021/om9808965

Organometallics 1999, 18, 3149-3158
3149
Isom er iza tion a n d r-H Elim in a tion of Dia lk yltu n gsten
Com p lexes Sta bilized by a Su lfu r -Br id ged Ch ela tin g
Dia r yloxo Liga n d
Yuushou Nakayama, Hideo Saito, Norikazu Ueyama, and Akira Nakamura*
Department of Macromolecular Science, Graduate School of Science, Osaka University,
Toyonaka, Osaka 560-0043, J apan
Received November 2, 1998
Dichlorotungsten complexes bearing an O-S-O chelating dialkoxo and a diphenylacetylene
t
ligand, W(η2-RCtCR)[S(4-R′-6-R′′C6H2O)2]Cl2 (R ) Ph, R′ ) Me, R′′ ) Bu (3a ); R ) Et; R′
) R′′ ) Me (3b)), were prepared by the reaction of W(η2-RCtCR)Cl4 and S(4-R′-6-R′′C6H2-
OH)2. Their Cs structures were confirmed by NMR study of these complexes and X-ray
crystallography of 3b. Complex 3a reacted with Mg(CH2SiMe3)2 in diethyl ether to give
initially a Cs symmetric dialkyltungsten complex, W(η2-PhCtCPh)[S(4-Me-6-tBuC6H2O)2](CH2-
SiMe3)2 (5). In solution at room temperature, 5 isomerizes to the C1 symmetric isomer 6,
whose structure was probed by the NMR spectroscopy. The thermodynamic parameters for
the isomerization were determined to be Gq(45 °C) ) 23.8 ( 0.4 kcal mol-1 and Sq(45 °C) )
-3.3 ( 0.7 cal K-1 mol-1. Upon heating to 60 °C, the generation of metal-alkylidene species
occurs. A similar reaction of 3a with dimethyl- and dibenzylmagnesium directly gives C1
symmetric dialkyltungsten complexes, W(η2-PhCtCPh)[S(4-Me-6-tBuC6H2O)2]R2 (R ) Me
(7), CH2Ph (8)), whose structures were determined by X-ray crystallography. The ring-opening
metathesis polymerization (ROMP) of norbornene was initiated in the presence of these
dialkyl complexes as catalyst precursors to give poly(norbornene) having high molecular
weight (Mn ) 1.7 × 106) and high cis content (cis 93%) at the early stage of the reaction. At
a polymerization temperature of 60 °C, the molecular weight and the cis content of the
resulting poly(norbornene) are lowered due to the second metathesis reactions.
In tr od u ction
A theoretical study suggested that the sulfur atom
coordination was essential to reduce the activation
energy for olefin insertion into a metal-carbon bond.17
We also introduced alkyne ligands as π-donors that can
be regarded as dianionic,18 such as imido or oxo ligands.
High-valent group 6 metal complexes are of much
interest as catalysts for the ring-opening metathesis
polymerization (ROMP) of the cyclic olefins to provide
polymers with unique functions.1-7 In particular, alkyli-
dene complexes having strong π-donor ligands such as
(8) (a) Schrock, R. R.; DePue, R. T.; Feldman, J .; Schaverien, C. J .;
Dewan, J . C.; Liu, A. H. J . Am. Chem. Soc. 1988, 110, 1423. (b) Schrock,
R. R.; Feldman, J .; Cannizzo, L. F.; Grubbs, R. H. Macromolecules 1987,
20, 1169. (c) Klavetter, F. L.; Grubbs, R. H. J . Am. Chem. Soc. 1988,
110, 7807. (d) Swager, T. M.; Dougherty, D. A.; Grubbs, R. H. J . Am.
Chem. Soc. 1988, 110, 2973. (e) Krouse, S. A.; Schrock, R. R.
Macromolecules 1988, 21, 1885. (f) Knoll, K.; Krouse, S. A.; Schrock,
R. R. J . Am. Chem. Soc. 1988, 110, 4424. (g) Schrock, R. R.; DePue, R.
T.; Feldman, J .; Yap, K. B.; Yang, D. C.; Davis, W. M.; Park, L.; DiMare,
M.; Schofield, M.; Anhaus, J .; Walborsky, E.; Evitt, E.; Kru¨ger, C.; Betz,
P. Organometallics 1990, 9, 2262. (h) Schrock, R. R.; Murdzek, J . S.;
Bazan, G. C.; Robbins, J .; DiMare, M.; O’Regan, M. J . Am. Chem. Soc.
1990, 112, 3875. (i) Bazan, G. C.; Khosravi, E.; Schrock, R. R.; Feast,
W. J .; Gibson, V. C.; O’Regan, M. B.; Thomas, J . K.; Dawis, W. M. J .
Am. Chem. Soc. 1990, 112, 8378. (j) Bazan, G. C.; Schrock, R. R.; Cho,
H.-N.; Gibson, V. C. Macromolecules 1991, 24, 4495. (k) Bazan, G. C.;
Oskam, J . H.; Cho, H.-N.; Park, L. Y.; Schrock, R. R. J . Am. Chem.
Soc. 1991, 113, 6899. (l) Bazan, G. C.; Schrock, R. R. Macromolecules
1991, 24, 817. (m) Oskam, J . H.; Schrock, R. R. J . Am. Chem. Soc.
1993, 115, 11831. (n) Oskam, J . H.; Fox, H. H.; Yap, K. B.; McConville,
D. H.; O’Dell, R.; Lichtenstein, B. J .; Schrock, R. R. J . Organomet.
Chem. 1993, 459, 185. (o) Fox, H. H.; Lee, J .-K.; Park, L. Y.; Schrock,
R. R. Organometallics 1993, 12, 759. (p) McConville, D. H.; Wolf, J .
R.; Schrock, R. R. J . Am. Chem. Soc. 1993, 115, 4413. (q) O’Dell, R.;
McConville, D. H.; Hofmeister, G. E.; Schrock, R. R. J . Am. Chem. Soc.
1994, 116, 3414. (r) Schrock, R. R. Polyhedron 1995, 14, 3177. (s)
Schrock, R. R.; Lee, J .-K.; O’Dell, R.; Oskam, J . H. Macromolecules
1995, 28, 5933. (t) Stanton, C. E.; Lee, T. R.; Grubbs, R. H.; Lewis, N.
S.; Pudelski, J . K.; Callstrom, M. R.; Erichson, M. S.; McLaughlin, M.
L. Macromolecules 1995, 28, 8713. (u) Fujimura, O.; de la Mata, F.;
Grubbs, R. H. Organometallics 1996, 15, 1865. (v) Pu, L.; Wagaman,
M. W.; Grubbs, R. H. Macromolecules 1996, 29, 1138.
i
imido, oxo, and alkoxo, M(dNC6H3 Pr2-2,6)(OR)2-
(dCHR′) (M ) Mo, W; R ) tBu, CMe2(CF3), CMe(CF3)2,
etc.),8 W(dNPh)(C6H4-2-CH2NMe2)(dCHSiMe3)(CH2-
SiMe3),9 and W(dO)(OR)2(dCHR′),10 are well-known to
be effective catalysts for ROMP.
We have been interested in the syntheses and reac-
tivities of tungsten complexes bearing chelating dialkoxo
ligands such as catecholate11 and 2,6-pyridinedietha-
nolate,12 both of which are effective for ROMP. The
tridentate ligand, 2,2′-thiobis(4-methyl-6-tert-butylphe-
noxo) (tBu2tbp), which was previously used as a ligand
in titanium complexes for olefin polymerization,13,14 was
found to coordinate to the metal ion in a fac fashion.15,16
(1) Ivin, K. J . Olefin Metathesis; Academic Press: New York, 1983.
(2) Dragutan, V.; Balaban, A. T.; Dimonie, M. Olefin Metathesis and
Ring Opening Polymerization of Cyclo-Olefins; J ohn Wiley & Sons:
New York, 1985.
(3) Olefin Metathesis and Polymerization Catalysts; Imamoglu, Y.,
Zu¨mreoglu-Karan, B., Amass, A. J ., Eds.; Kluwer Academic Publish-
ers: Dordrecht, 1990.
(4) Grubbs, R. H.; Tumas, W. Science 1989, 243, 907.
(5) Schrock, R. R. Acc. Chem. Res. 1990, 23, 158.
(6) Eilerts, N. W.; Heppert, J . A. Polyhedron 1995, 14, 3255.
(7) Schuster, M.; Blechert, S. Angew. Chem., Int. Ed. Engl. 1997,
36, 2036.
10.1021/om9808965 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/17/1999

3150 Organometallics, Vol. 18, No. 16, 1999
Nakayama et al.
Here we report the synthesis and reactivity of cis-
dialkyltungsten complexes having both tBu2tbp and
disubstituted acetylene ligands.
Resu lts a n d Discu ssion
Syn t h esis a n d St r u ct u r es of Dich lor o Com -
p lexes. The dichlorotungsten complexes W(η2-RCt
CR)(R′2tbp)Cl2 (R ) Ph, R′ ) tBu (3a ); R ) Et; R′ ) Me
(3b)) were prepared as red crystals by refluxing a
mixture of W(η2-RCtCR)Cl4 (R ) Ph (1a ), R ) Et (1b);
M ) Mo, R ) Ph (2)) and 1 equiv of (R′2tbp)H2 (R′2tbp
) 2,2′-thiobis(4-methyl-6-R′phenoxo)) in toluene-THF
(93:7). A molybdenum analogue, Mo(η2-PhCtCPh)(tBu2-
tbp)Cl2 (4), was obtained as black crystals in a similar
manner. The 1H NMR spectra of these complexes
suggest that they have symmetric structures, and the
X-ray crystallography of Me2tbp complex 3b confirmed
a Cs structure (vide infra). In the 13C NMR spectrum of
3 and 4, the alkyne carbon resonance appears at δ 230-
244 ppm, indicating that the diphenylacetylene donates
four electrons to the metal center.
F igu r e 1. ORTEP drawing of W(η2-EtCtCEt)(Me2tbp)-
Cl2 (3b) with a numbering scheme.
octahedral. The Me2tbp ligand coordinates to tungsten
in a facial fashion, and the alkyne ligand is located at
the trans position to the sulfur atom of the Me2tbp
ligand. The W-S bond distance (2.638(2) Å) of 3b is
slightly shorter than the Ti-S distances in [Ti(tBu2tbp)-
Cl2]2 (2.664(2) Å)19 and [Ti(tBu2tbp)(OiPr)2]2 (2.719(1)
Å)15,16 taking into account the similar ionic radii of W6+
(0.74 Å) and Ti4+ (0.745 Å).20 The bond angles O-W-
O, O-W-Cl, and Cl-W-Cl are 89.4(2)°, 89.0(1)°, and
86.65(7)°, respectively. The W-C distances, W-C17
(2.015(8) Å) and W-C18 (2.014(7) Å), are comparable
to those of [PPh4][WCl5(η2-PhCtCH)] (2.002(15) and
2.032(10) Å),21 [WCl3(µ-Cl)(η2-Me3SiCtCSiMe3)]2 (2.025-
(11) and 2.028(11) Å),22 and WCl2(OC6H3Ph2-2,6)2(η2-
EtCtCEt) (2.021(8) and 2.027(8) Å)23 but shorter than
the corresponding dialkyl complexes (vide infra).
P r ep a r a tion of Bis(tr im eth ylsilylm eth yl) Com -
p lexes. A bulky dialkyl complex, W(η2-PhCtCPh)(tBu2-
tbp)(CH2SiMe3)2 (5), was obtained as red crystals in 94%
yield from the reaction of 3a with 1 equiv of bis-
(trimethylsilylmethyl)magnesium in diethyl ether (eq
2). Complex 5 was characterized by elemental analysis
Cr ysta l Str u ctu r e of 3b. The Cs structure of 3b is
confirmed by the single-crystal X-ray analysis (Figure
1). Selected bond distances and angles are summarized
in Table 1. If the 1-hexyne ligand is considered to occupy
one coordination site, the coordination geometry around
the tungsten atom of 3b can be described as pseudo-
(9) (a) van der Schaaf, P. A.; Grove, D. M.; Smeets, W. J . J .; Spek,
A. L.; van Koten, G. Organometallics 1993, 12, 3955. (b) van der Schaaf,
P. A.; Smeets, W. J . J .; Spek, A. L.; van Koten, G. J . Chem. Soc., Chem.
Commun. 1992, 717. (c) van der Schaaf, P. A.; Abbenhuis, R. A. T. M.;
van der Noort, W. P. A.; de Graaf, R.; Grove, D. M.; Smeets, W. J . J .;
Spek, A. L.; van Koten, G. Organometallics 1994, 13, 1433.
(10) de la Mata, F. J .; Grubbs, R. H. Organometallics 1996, 15, 577.
(11) Nakayama, Y.; Saito, H.; Nakamura, A. Chem. Lett. 1996, 691.
(12) Nakayama, Y.; Ikushima, N.; Nakamura, A. Chem. Lett. 1997,
861.
(13) Miyatake, T.; Mizunuma, K.; Seki, Y.; Kakugo, M. Macromol.
Chem., Rapid Commun. 1989, 10, 349.
(14) van der Linden, A.; Schaverien, C. J .; Meijboom, N.; Ganter,
C.; Orpen, A. G. J . Am. Chem. Soc. 1995, 117, 3008.
(15) Fokken, S.; Spaniol, T. P.; Kang, H.-C.; Massa, W.; Okuda, J .
Organometallics 1996, 15, 5069.
(16) Porri, L.; Ripa, A.; Colombo, P.; Miano, E.; Capelli, S.; Meille,
S. V. J . Organomet. Chem. 1996, 514, 213.
(17) Froese, R. D. J .; Musaev, D. G.; Matsubara, T.; Morokuma, K.
J . Am. Chem. Soc. 1997, 119, 7190.
(18) Otsuka, S.; Nakamura, A. Adv. Organomet. Chem. 1976, 14,
245.
1
and NMR spectroscopy. In the H NMR spectrum of 5,
the proton signals of the trimethylsilylmethyl, tert-butyl,
and methyl groups appear as singlets at -0.11, 1.17,
and 2.03 ppm, respectively, indicating that 5 has a Cs
symmetric structure. The AB-type signals at 2.67 and

Isomerization of Dialkyltungsten Complexes
Organometallics, Vol. 18, No. 16, 1999 3151
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles (d eg) of 3b, 7, a n d 8
complex
W-O
3b
7
8
Bond Distances
1.931(5) (O1)
1.945(5) (O2)
2.638(2)
2.015(8) (C17)
2.014(7) (C18)
2.053(4) (O1)
1.912(4) (O2)
2.697(2)
2.060(6) (C7)
2.062(5) (C8)
2.148(7) (C50)
2.160(8) (C51)
2.019(5) (O1)
1.941(5) (O2)
2.637(2)
2.054(7) (C27)
2.053(7) (C28)
2.173(8) (C1)
2.15(1) (C11)
W-S
W-C(alkyne)
W-C(alkyl)
W-Cl
2.350(2) (Cl1)
2.394(2) (Cl2)
1.28(1)
C-C(alkyne)
1.319(8)
1.274(9)
Bond Angles
O-W-O
89.4(2)
102.7(3)
86.65(7) (X ) Cl)
89.6(2)
101.1(3)
100.2(3) (X ) Me)
89.9(2)
104.0(3)
C-S-C
X-W-X
W-C-C(alkyl)
111.3(4) (X ) CH2Ph)
125.4(6) (C1)
126.3(7) (C11)
128.5(5) (O1)
132.1(5) (O2)
W-O-C
130.3(4) (O1)
127.2(4) (O2)
128.4(4) (O1)
135.6(4) (O2)
1.80 ppm (2J HH ) 12.5 Hz) are assignable to the
R-methylene protons of W-CH2SiMe3. In the 13C NMR
spectrum, the R-methylene carbon signal is observed at
Ta ble 2. Obser ved Ra te Con sta n ts a n d Ha lf-Lives
a t Va r iou s Tem p er a tu r es for th e Isom er iza tion of
5 to Give 6
104kobs (s-1
)
t1/2 (m)
1
temp (°C)
57 ppm (t, J CH ) 112 Hz), and the alkyne carbon
resonance was observed at 240 ppm. The structure of 5
60
55
50
45
40
7.95
4.71
2.64
1.47
0.80
14.9
24.5
43.8
78.6
145
1
was confirmed by the 1H-1H COSY and H-1H NOESY
spectra, the latter showing a correlation between tri-
methylsilyl groups and o-, m-H of diphenylacetylene,
indicating that both trimethylsilylmethyl groups are cis
to the diphenylacetylene ligand. A correlation between
tert-butyl group and o-H of diphenylacetylene indicates
related with the signal of one of the two trimethylsilyl
protons at -0.06 ppm by a 13C-1H HMBC spectrum. A
1H-1H NOESY experiment revealed a close proximity
of the bis(trimethylsilyl)methyl group without agostic
interaction to both the two tert-butyl groups of the
tBu2tbp ligand, indicating that it is cis to the two oxygen
atoms of the tBu2tbp ligand. The resonance of the
diphenylacetylene alkyne carbons appears at 213.9 and
210.6 ppm, shifted more than 30 ppm upfield compared
to those of 5, indicating that the donation from diphe-
nylacetylene ligand was decreased in 6 compared with
the case of 5.24 This can be attributed to the increasing
electron density at the tungsten center due to the R-H
agostic interaction. The negative ESI-MS spectrum of
6 did not show any of the molecular ion peaks but a
signal assignable to [W(η2-PhCtCPh)(tBu2tbp)(CH2-
SiMe3)(O)]-. These results of MS came from decomposi-
tion of 6 during measurement operations. The structure
of 6 shown in eq 3 was also supported by the crystal
structures of the corresponding dibenzyl and dimethyl
complexes (vide infra).
The rate of the transformation of 5 to 6 in C6D6 was
measured in the temperature range 40-60 °C. The
decrease of 5 followed first-order kinetic behavior (Table
2); an Arrhenius plot afforded the activation data Gq-
(45 °C) ) 23.8 ( 0.4 kcal mol-1 and Sq(45 °C) ) -3.3 (
0.7 cal K-1 mol-1. The small Sq value indicates that the
isomerization is an intramolecular process.25
We speculate that this isomerization is controlled by
both electronic and steric effects. If the alkyne ligand
is located trans to the oxygen atom of the tBu2tbp ligand,
it would compete with the oxygen ligand for π-donation
to the same d orbital of the metal. Thus, the stereo-
t
that the alkyne is cis to the oxygen atoms of the Bu2-
tbp ligand.
Isom er iza tion of th e Bis(tr im eth ylsilylm eth yl)
Com p lex. When 5 was kept in C6D6 at 30 °C for 3 days,
the structure of 5 changed from a Cs structure to a C1
one (6: eq 3). Unfortunately, efforts to crystallize 6 were
not successful. The 1H NMR spectra of 6 revealed no
symmetry element at the metal ion. The diastereotopic
methylene protons of one of the trimethylsilylmethyl
groups were observed at 2.33 and 0.20 ppm. The large
upfield shift of one methylene proton suggests an
R-agostic interaction with the tungsten metal center.
The R-protons of the other trimethylsilylmethyl group
were observed at 3.56 and 3.48 ppm. In the 13C NMR
spectrum, the two R-carbon signals of trimethylsilyl-
1
methyl groups appear at 79.5 (t, J CH ) 112 Hz) and
1
82.3 ppm (dd, J CH ) 116, 107 Hz). The latter signal
can be assigned to the R-carbon of the trimethylsilyl-
methyl group with an R-agostic interaction and is
(19) Nakayama, Y.; Watanabe, K.; Ueyama, N.; Nakamura, A. To
be published.
(20) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
(21) Kersting, M.; Dehnick, K.; Fenske, D. J . Organomet. Chem.
1988, 346, 201.
(22) Hey, E.; Weller, F.; Dehnicke, K. Z. Anorg. Allg. Chem. 1984,
514, 18.
(23) Kriley, C. E.; Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1993, 12, 2051.
(24) Templeton, J . L. Adv. Organomet. Chem. 1989, 29, 1.
(25) Lee, D.; Suh, M. P.; Lee, J . W. J . Chem. Soc., Dalton Trans.
1997, 577.

3152 Organometallics, Vol. 18, No. 16, 1999
Nakayama et al.
Sch em e 1
chemistry having the alkyne ligand cis to the aryloxo
of the Bu2tbp ligand may be electronically more favor-
diphenylacetylene ligand followed by the rotation of the
acetylene moiety and â-alkyl elimination. Such an
exchange process of the metal-bound and the alkyne-
bound alkyl groups has been reported in Tp*NbCl-
(CH2R)(PhCtCR′) (Tp* ) hydrotris(3,5-dimethylpyra-
zolyl)borate).26 The last pathway (C) is based on the
simple rotation of the two alkyl groups and one diphe-
nylacetylene ligand around the axis through the center
of those three ligands and tungsten. In the case of path
A, the dissociation of diphenylacetylene is the rate-
determining step and ∆Gq should be larger than the
observed value. If path B is the case, the alkyl groups
should replace the phenyl group on diphenylacetylene
or should not react with diphenylacetylene ligand. Thus
we speculate that the path C is the most likely.
t
able especially for electron-deficient complexes such as
the Cs dichloro complex 3a . When the two chloro ligands
of 3a were replaced by two alkyl groups to increase
electron density around the metal center, π-donation
from the aryloxo decreases and the steric repulsion
t
between the diphenylacetylene and the Bu2tbp ligands
may overcome this electronic preference to result in the
isomerization. In the C1 isomer, π-donation from the
aryloxo oxygen trans to diphenylacetylene disturbs the
donation from diphenylacetylene to the same d orbital.
This reduced donation is clearly indicated by the change
of the 13C chemical shifts of the acetylenic carbons. Since
the steric bulk of the alkyl groups hinders the isomer-
ization of 5 (Cs isomer), the observed direct formation
of C1 isomers in the case of the methyl and the benzyl
complexes (vide infra) is rationalized.
Three plausible routes for the isomerization are
shown in Scheme 1. In route A, the diphenylacetylene
ligand is dissociated to generate a five-coordinated
square-pyramidal intermediate which changes to a
trigonal-bipyramidal structure, and then the diphenyl-
acetylene recoordinates to the metal ion. The next
pathway (B) includes an alkyl migratory insertion to the
At higher temperature (60 °C), complex 5 underwent
R-H elimination following the isomerization. The 1H
NMR spectra of 5 treated at 60 °C for 4 h showed the
absence of the signals for 5 and 6, and new signals
appeared at 9.76 and 10.69 ppm, which can be assigned
as the R-H protons of syn- or anti-alkylidenetungsten
(26) Etienne, M.; Mathieu, R.; Donnadieu, B. J . Am. Chem. Soc.
1997, 119, 3218.

Isomerization of Dialkyltungsten Complexes
Organometallics, Vol. 18, No. 16, 1999 3153
complexes. We have not succeeded in isolating an
alkylidene complex.
P r ep a r a tion of Dim eth yl (7) a n d Diben zyl (8)
Com p lexes. We synthesized the dimethyl and dibenzyl
complexes W(η2-PhCtCPh)(tBu2tbp)(R)2 [R ) CH3 (7),
CH2Ph (8)] from the reaction of 3a with dimethyl and
dibenzylmagnesium, respectively (see eq 4). In both
F igu r e 2. ORTEP drawing of W(η2-PhCtCPh)(tBu2tbp)-
Me2 (7) with a numbering scheme.
cases, the Cs complexes corresponding to 5 were not
detected, and the C1 complexes 7 and 8 were directly
produced as indicated by NMR spectroscopy and X-ray
analysis (vide infra). A signal for one of the four benzyl
R-protons in 8 appeared at significantly high field (1.52
ppm), indicating an R-agostic interaction with the
tungsten metal center as already observed in bis-
1
(trimethylsilylmethyl) complex 6. The H-1H NOESY
spectrum shows a correlation between the agostic
t
R-proton and the tert-butyl groups of Bu2tbp ligand.
This suggests that the agostic benzyl ligand is located
trans to sulfur. In the 13C NMR spectrum, a signal of
the benzyl R-carbon having the agostic proton was
1
observed at δ 96.9 ppm (dd, J CH ) 140, 120 Hz), and
the other benzyl R-carbon showed a resonance at δ 72.7
ppm (1J CH ) 125 Hz). The alkyne signals appeared at δ
208.1 and 205.8 ppm, suggesting that it can be regarded
as a 2-electron donor ligand. In the case of dimethyl
complex 7, the methyl protons were observed as two
1
singlets at 2.30 and 0.45 ppm in the H NMR spectra,
indicating a large difference in the magnetic shielding.
Cr ysta l Str u ctu r e of Dim eth yl (7) a n d Diben zyl
(8) Com p lexes. The X-ray analysis of complexes 7 and
8 confirmed their C1 symmetry as shown in Figures 2
and 3; the structural parameters 7 and 8 are included
in Table 1. If the diphenylacetylene ligand occupies one
coordination site around the metal, both 7 and 8 can be
best described as distorted octahedrons, in which the
tBu2tbp coordinates to tungsten in a facial fashion and
the diphenylacetylene ligand is located trans to the
oxygen atom of the tBu2tbp ligand. The distortion of the
dibenzyl complex 8 ( (C1-W-C11) ) 111.3(4)°) from
the octahedral geometry is larger than that of the
dimethyl complex 7 ( (C50-W-C51) ) 100.2(3)°). The
W-S bond distances of the dimethyl (7) and the dibenzyl
(8) complexes are 2.697(2) and 2.637(2) Å, respectively,
indicating weak coordination of sulfur to tungsten. The
W-C(alkyl) bond distances [7, 2.148(7) Å; 8, 2.15(1) Å,]
trans to sulfur are shorter by ca. 0.02 Å than those [7,
2.160(8) Å; 8, 2.173(8) Å,] trans to the phenoxo moiety
due to the weak trans influence of the thioether. The
W-O1 bond distances [7, 2.053(4) Å; 8, 2.019(5) Å] are
F igu r e 3. ORTEP drawing of W(η2-PhCtCPh)(tBu2tbp)-
(CH2Ph)2 (8) with a numbering scheme.
longer than the W-O2 ones [7, 1.912(4) Å; 8, 1.941(5)
Å] due to the trans influence of a π-donor diphenyl-
acetylene ligand. Although both the solution and the
solid-state 13C CP/MAS NMR spectrum of 8 indicate
that the R-methylene of the benzyl group trans to sulfur
participates in the R-agostic interaction, we could not
find any structural feature characteristic of the R-agostic
interaction such as wide M-CR-Câ and narrow M-
CR-H angles ( (W-CR-Câ) ) 125.4(6)° and 126.3(9)°).
In the solid state, the motion of the benzyl groups might
be constrained to a geometry preferable for the R-agostic
interaction.
Gen er a t ion of Alk ylid en e Sp ecies fr om t h e
Diben zyl Com p lex. When a C6D6 solution of 8 was
heated to 60 °C in an NMR tube, the generation of an
alkylidene species was not observed due to contamina-
tion by paramagnetic byproducts, while bis(trimethyl-
silylmethyl) complex 5 was observed to generate alky-

3154 Organometallics, Vol. 18, No. 16, 1999
Nakayama et al.
Ta ble 3. ROMP of Nor bor n en e by W(η2-P h CtCP h )(tBu 2tbp )R2 in Ben zen e for 1 h a
cis content
(%)c
b
b
run
catalyst
temp (°C)
time (h)
yield (%)
Mn/105
Mw/Mn
1
2
3
4
5
6
7
8
R ) CH2SiMe3 (5)d
30
30
30
30
30
60
60
30
60
30
60
1
6
12
24
48
1
24
1
1
1.6
19
65
82
87
62
89
6.4
22
<1
8.4
>20
19
19
6.9
3.4
4.9
0.2
17
1.7
1.7
1.8
2.6
2.6
3.4
2.8
1.8
93
93
77
79
75
83
54
83
81
R ) CH2Ph (8)
R ) CH3 (7)
9
10
11
bimodal
1
1
0.8
3.0
89
a
b
[Monomer]0 ) 1 M, [Catalyst] ) 10 mM. Determined by GPC analysis calibrated with standard poly(styrene)s. c Determined by 1H
d
NMR spectra. Heated to 60 °C for 1 h before addition of monomer.
lidene species by NMR (vide supra). When complex 8
was kept at room temperature in CD2Cl2 for several
months, new signals assignable to the R-protons of
1
alkylidene complexes appeared at 9.83 ppm in the H
NMR spectrum and at 281 ppm in the 13C NMR
spectrum. This encouraged us to isolate the alkylidene
complex.
When complex 8 was refluxed in toluene for 1 h
followed by extraction with hexane and recrystallization
from toluene-hexane (2:1), brown crystals were ob-
tained. The elemental analysis of the product indicates
that it has the same composition as the expected
benzylidene complex. However, 1H and 13C NMR spectra
of the product revealed it to be a mixture of tungstacy-
clobutene complex (9) and 1,2,3-triphenyl-2-prope-
nylidene complex (9′) (eq 5), and we could not separate
F igu r e 4. Time-conversion curve of the ROMP of nor-
bornene in the presence of W(η2-PhCtCPh)(tBu2tbp)(CH2-
SiMe3)2 (5) as catalyst in benzene at 30 °C.
these two species. In the 1H NMR spectrum of the
product, a signal of the R-H proton of 9 was observed
at 3.08 ppm, while the γ-H proton signals of 9′ appeared
at 8.57 and 9.67 ppm (syn and anti isomers). The 13C
NMR spectrum showed the signals of the metallacy-
clobutene of 9 at 102.3 (CHPh), 210.6 (R-CPh), and 160.6
(â-CPh) ppm and those of the γ-C of 9′ at 96.6 and 77.6
ppm. The signals for R- and â-carbons were not detected.
P olym er iza tion of Nor bor n en e Ca ta lyzed by th e
Dia lk yltu n gsten Com p lexes. The dialkyltungsten
complexes were found to initiate the polymerization of
norbornene without any cocatalysts, and the results are
summarized in Table 3. The catalytic activity at 60 °C
increased with increasing bulkiness of the alkyl groups
(run 6, run 9, run 11). This indicates that the R-H
abstraction occurs more easily with increasing steric
congestion. In the polymerization at 30 °C by 5, an
interesting time dependence of the molecular weight
F igu r e 5. Time-dependence of molecular weight and cis
content for the ROMP of norbornene in the presence of
W(η2-PhCtCPh)(tBu2tbp)(CH2SiMe3)2 (5) as a catalyst in
benzene at 30 °C.
and of the stereoregularity (Table 3 runs 1-5, Figure
5) was found. At the initial stage of the polymerization,
the produced polymer had extremely high molecular
weight (Mn > 106) and high stereoregularity (cis content
> 90%), although the polymer yield was low. With
longer reaction time, the polymer yield became higher,
but the molecular weight and stereoregularity of the
polymer were reduced. Such phenomena may result
from the second metathesis reaction.27 The isomeriza-
tion of the C-C double bonds in the polymer occurs prior
to the decrease of the molecular weights, as shown in
(27) Wallace, K. C.; Liu, A. H.; Dewan, J . C.; Schrock, R. R. J . Am.
Chem. Soc. 1988, 110, 4964.

Isomerization of Dialkyltungsten Complexes
Organometallics, Vol. 18, No. 16, 1999 3155
Ta ble 4. ROMP of Nor bor n en e by Usin g Mo(η2-P h CtCP h )(tBu 2tbp )Cl2 (4)/Coca ta lysta
cis content
(%)c
b
run
cocatalyst
none
Mg(CH2SiMe3)2
temp (°C)
time (min)
yield (%)
Mn/105 b
Mw/Mn
1
2
3
4
5
60
30
30
30
60
60
15
30
60
60
11
17
26
79
8.1
9.4
19
3.3
3.6
2.3
2.0
67
60
58
54
> 20
a
In benzene, [Monomer]0 ) 1 M, [Catalyst] ) 10 mM. b Determined by GPC analysis calibrated with standard poly(styrene). c Determined
by 1H NMR spectra.
Ta ble 5. Com p a r ison of Gr ou p 6 Meta l Com p lexes in th e ROMP of Nor bor n en e
cis content
catalyst system
temp (°C) time (h) yield (%) Mn/105 a Mw/Mn
(%)b
ref
a
5c
30
30
30
30
25
1
6
1.6
19
11
26
quant.
quant.
quant.
>20
>20
8.1
19
0.2
4
1.7
1.7
3.3
2.3
1.05
1.6
n.d.
93
93
67
58
40
>95
>90
this work
this work
this work
this work
8b
c
4/Mg(CH2SiMe3)2
0.25
1
0.16
2-3
0.16
W(CHtBu)(NAr)(OtBu)2
c
W(CHtBu)(NAr)[OCMe(CF3)2]2
-20
rt
8b
9a
d
W(dNPh)(C6H4-2-CH2NMe2)(dCHSiMe3)(CH2SiMe3)e
n.d.
a
b
Determined by GPC analysis calibrated with standard poly(styrene). Determined by 1H NMR spectra. c [Monomer]0/[Cat] ) 100.
[Monomer]0/[Cat] ) 288. e [Monomer]0/[Cat] ) 200.
d
Figures 4 and 5. The active species for cis-trans
isomerization are thus different from that for the
decrease of the molecular weight.
metallacycle-forming step, norbornene monomer may
coordinate to the metal ion to avoid steric hindrance,
resulting in the preferable formation of metallacycle 13
to give the cis polymer.
Unfortunately, we could not isolate the corresponding
dialkyl complexes of molybdenum, which is expected to
be more active than the corresponding tungsten cata-
lyst. Thus, we investigated the activity of a multicom-
ponent catalyst system, 4/Mg(CH2SiMe3)2, and the
results are summarized in Table 4. Indeed, the 4/Mg-
(CH2SiMe3)2 system showed a higher activity than that
of the tungsten systems. The molecular weight of the
resulting polymer increased with increasing the polymer
yield, indicating that the second metathesis reaction is
suppressed in the molybdenum system compared with
the corresponding tungsten systems. The molecular
weight distributions of the polymers were broader than
those in tungsten systems. This might be attributed to
the slow initiation step. The stereospecificity of the
molybdenum system was lower than that of the tung-
sten systems. We speculate that the lower stereospeci-
ficity of the molybdenum system can be attributed to
the higher Lewis acidity of dichloro complex 4 than
those of the dialkyl complexes 5-8, and the higher
Lewis acidity of 4 should promote isomerization.
Table 5 shows the comparison of the catalytic behav-
ior of the catalyst systems reported here with those of
the Schrock-type catalysts. Although the activity is low,
5 affords poly(norbornene) with extremely high molec-
ular weight and high stereoregularity compared to the
other catalyst systems.
Con clu sion
A series of new cis-dialkyltungsten complexes bearing
a bulky tridentate diaryloxo ligand was prepared. In the
case of the bis(trimethylsilylmethyl) complex, isomer-
ization from a Cs structure to a C1 structure proceeds
at 30 °C prior to R-H elimination, while the correspond-
ing dimethyl and dibenzyl complexes were directly
obtained as C1 complexes. At 60 °C, R-H elimination
occurs to generate reactive alkylidene species which
initiate the ROMP of norbornene. Under certain condi-
tions, these complexes yield polynorbornene with ex-
tremely high molecular weight and high cis content.
Exp er im en ta l Section
Gen er a l P r oced u r e. All manipulations involving air- and
moisture-sensitive compounds were carried out by use of the
standard Schlenk techniques under argon. Complexes, M(η2-
RCtCR)Cl4 [M ) W, R ) Ph (1a ); M ) W, R ) Et (1b); M )
Mo, R ) Ph (2)]28,29 and dialkylmagnesium30 were prepared
according to the literature. n-Hexane, THF, toluene, benzene,
and diethyl ether were purified by distillation under argon
after drying over sodium benzophenone ketyl. Dichloromethane
was distilled under argon after drying over phosphorus pent-
oxide. Dichloromethane-d2 and chloroform-d1 were distilled
from phosphorus pentoxide. Benzene-d6 was dried over sodium/
potassium alloy and thoroughly degassed by trap-to-trap
distillation prior to use. 2,2′-Thiobis(4-methyl-6-tert-butylphe-
nol) was supplied by Ciba-Geigy AG. 2,2′-Thiobis(4,6-dimeth-
ylphenol)31 was prepared according to the literature. Nor-
bornene (bicyclo[2.2.1]hept-2-ene) purchased from Aldrich
Chemical Co., Inc., was refluxed over sodium and distilled prior
to use.
Although the initiator efficiency was very low and the
active species were unidentified, we speculate a mech-
anism for the cis-specific polymerization of norbornene
as shown in Scheme 2. A key intermediate, metallacy-
clobutane, was assumed to be formed at the position of
the two alkyl groups in the X-ray structures of 7 and 8
t
without significant geometrical change of the Bu2tbp
(28) Hey, E.; Weller, F.; Dehnicke, K. Z. Anorg. Allg. Chem. 1984,
514, 25.
(29) Theopold, K. H.; Holmes, S. J .; Schrock, R. R. Angew. Chem.,
Int. Ed. Engl. 1983, 22, 1010.
(30) Andersen, R. A.; Wilkinson, G.; Lappert, M. F.; Pearce, R. Inorg.
Synth. 1979, 19, 262.
(31) Pastor, S. D.; Denney, D. Z. Phosphorus Sulfur 1987, 32, 105.
and diphenylacetylene ligands. The active alkylidene
species should consist of anti (10) and syn (11) isomers.
The anti isomer may be more favorable than the syn
isomer due to the smaller steric repulsion between the
polymer chain and the diphenylacetylene ligand. At the

3156 Organometallics, Vol. 18, No. 16, 1999
Nakayama et al.
Sch em e 2
The 1H (600, 500, and 400 MHz), and 13C (150, 125, and
100 MHz) NMR spectra in benzene-d6, dichloromethane-d2,
and chloroform-d1 were measured on a Varian-Unity-600, a
J EOL J NM-LA500, or a J EOL J NM-GSX400 spectrometer.
Assignments for 1H and 13C NMR peaks for some complexes
were aided by 2D 1H-1H NOESY, 2D 1H-1H COSY, and 2D
13C-1H COSY spectra. The solid-state NMR (CP/MAS) spectra
were measured on a Chemmagnetics CMX-300 spectrometer.
Elemental analysis was performed at Elemental Analysis
Center, Faculty of Science, Osaka University. All melting
points of complexes were measured in sealed tubes under an
argon atmosphere and were not corrected. ESI-MS measure-
ments were performed on a Perkin-Elmer/Sciex API III plus
spectrometer.
134.4 (3-C6H2O), 133.9, 130.8 (5-C6H2O), 129.3, 121.2, 32.5
(CH2CH3), 20.4 (4-Me), 16.8 (6-Me), 14.1 (CH2CH3). Anal. Calcd
for C22H26Cl2O2S1W1: C, 43.37; H, 4.30. Found: C, 43.52; H,
4.22.
P r ep a r a t ion of Mo(η2-P h CtCP h )[S(4-Me-6-tBu C6H 2-
O)2]Cl2(th f) (4). This complex was prepared and isolated in
a manner similar to that for 3a as black crystals in 54% yield,
1
mp 110-112 °C. H NMR (CD2Cl2, 30 °C, 400 MHz): δ 8.40
(dd, 4H, o-PhC), 7.69 (t, 4H, m-PhC), 7.65 (t, 2H, p-PhC), 7.48
(s, 2H, 3-C6H2O), 7.17 (s, 2H, 5-C6H2O), 3.67 (br, 4H, thf), 2.36
(s, 6H, Me), 1.80 (br, 4H, thf), 0.97 (s, 18H, tBu). 13C NMR (CD2-
Cl2, 30 °C, 100 MHz): 233.1 (PhC), 168.0 (4-C6H2O), 140.3,
135.4, 134.3 (6-C6H2O), 133.6 (o-PhC), 133.0 (p-PhC), 130.6 (3-
C6H2O), 130.0 (5-C6H2O), 128.3 (m-PhC), 121.1, 34.6 (CMe3),
29.4 (CMe3 ), 20.3 (Me). Analytically pure sample was obtained
as Mo(η2-PhCtCPh)[S(4-Me-6-tBuC6H2O)2]Cl2‚C7H8 upon re-
P r ep a r a tion of W(η2-P h CtCP h )[S(4-Me-6-tBu C6H2O)2]-
Cl2(th f) (3a ). A solution of 2,2′-S(4-Me-6-tBuC6H2OH)2 (0.31
g, 0.86 mmol) in toluene (5 mL) was added to a solution of
W(η2-PhCtCPh)Cl4 (1a ) (0.43 g, 0.86 mmol) in a mixture of
toluene (35 mL) and THF (2.5 mL) at -78 °C. The reaction
mixture was stirred for 10 min and then allowed to warm to
ambient temperature, followed by refluxing for 2 h. The color
of the solution was changed from red to dark red. All volatiles
were removed under reduced pressure to give microcrystals.
Recrystallization from a mixture of THF and n-hexane gave
W(η2-PhCtCPh)[S(4-Me-6-tBuC6H2O)2]Cl2(thf) (3a ) (0.22 g,
crystallization from toluene-hexane. Anal. Calcd for C43H46
Cl2MoO2S: C, 65.07; H, 5.84. Found: C, 65.09; H, 5.72.
-
P r ep a r a tion of W(η2-P h CtCP h )[S(4-Me-6-tBu C6H2O)2]-
(CH2SiMe3)2(th f) (5). A solution of Mg(CH2SiMe3)2 (0.22
mmol, 1 equiv) in diethyl ether was added to a solution of 3a
(0.17 g, 0.22 mmol) in diethyl ether (30 mL) via syringe at
-78 °C. After stirring for 20 min, the reaction mixture was
allowed to warm to ambient temperature and stirred for 4 h.
The color of the solution changed from dark purple to red. All
volatiles were removed under reduced pressure, followed by
extraction with n-hexane (25 mL) from the resulting residue.
After the extract was dried in vacuo, recrystallization from
THF (2 mL) and n-hexane (8 mL) at -20 °C afforded W(η2-
PhCtCPh)[S(4-Me-6-t BuC6H2O)2](CH2SiMe3)2(thf) (5) as red
1
33%) as red crystals, mp 128-130 °C. H NMR (C6D6, 30 °C,
400 MHz): δ 8.39 (dd, 4H, o-PhC), 7.33 (t, 4H, m-PhC), 7.30
(s, 2H, 3-C6H2O), 7.18 (t, 2H, p-PhC), 7.09 (s, 2H, 5-C6H2O),
3.62 (m, 4H, thf), 2.07 (s, 6H, Me), 1.46 (m,4H, thf), 1.17 (s,
1
t
18H, Bu). 13C NMR (C6D6, 30 °C, 100 MHz): 236.5 (PhC),
crystals in 36% yield, mp 122 °C. H NMR (C6D6, 30 °C, 400
MHz): δ 8.31 (dd, 4H, o-PhC), 7.43 (t, 4H, m-PhC), 7.39 (s,
2H, 3-C6H2O), 7.20 (t, 2H, p-PhC), 7.01 (s, 2H, 5-C6H2O), 3.62
167.1 (4-C6H2O), 142.6, 138.4 (6-C6H2O), 134.7 (o-PhC), 132.5
(p-PhC), 131.4 (3-C6H2O), 130.7 (5-C6H2O), 129.0 (m-PhC),
122.7, 35.3 (CMe3), 30.3 (CMe3), 20.7 (Me). Anal. Calcd for
2
(m, 4H, thf), 2.68 (d, 2H, 2J H
) 12.5 Hz, J WH ) 8.7 Hz,
A
B
H
CHA HBSi), 2.03 (s, 6H, Me), 1.80 (d, 2H, 2J H
) 12.6 Hz,
B A
H
C
40H46Cl2O3S1W1: C, 55.76; H, 5.38. Found: C, 55.66; H, 5.22.
2J WH ) 8.7 Hz, CHAHB Si), 1.47 (m, 4H, thf), 1.17 (s, 18H, tBu),
-0.11 (s, 18H, CH2SiMe3 ). 13C NMR (C6D6, 30 °C, 100 MHz):
244.1 (PhC), 167.2 (4-C6H2O), 141.6, 141.0 (6-C6H2O), 131.8
(o-PhC), 131.1 (p-PhC), 130.9 (3-C6H2O), 130.5 (5-C6H2O), 129.9
(m-PhC), 121.6, 67.8 (thf), 56.7 (t, 1J CH ) 112 Hz, CH2Si), 35.6
(CMe3), 30.5 (CMe3 ), 25.8 (thf), 20.8 (Me), 3.9 (SiMe3). Anal.
Calcd for C48H68O3S1Si2W1: C, 59.73; H, 7.10. Found: C, 59.37;
H, 7.08.
P r ep a r a t ion of W(η2-E t CtCE t )[S(4,6-Me2C6H 2O)2]Cl2
(3b). This complex was prepared and isolated in a manner
similar to that for 3a as black crystals in 73% yield, mp 261-
264 °C. 1H NMR (C6D6, 30 °C, 400 MHz): δ 7.09 (s, 2H,
3-C6H2O), 6.60 (s, 2H, 5-C6H2O), 4.21 (q, 4H, CH2CH3), 2.04
(s, 6H, 6-Me), 1.94 (s, 6H, 4-Me), 1.36 (t, 6H, CH2CH3). 13C
NMR (C6D6, 30 °C, 100 MHz): 244.5 (EtC), 166.3 (4-C6H2O),

Isomerization of Dialkyltungsten Complexes
Organometallics, Vol. 18, No. 16, 1999 3157
Ta ble 6. Cr ysta l Da ta a n d Da ta Collection P a r a m eter s of 3b, 7, a n d 8
3b
7
8
formula
fw
crystal system
space group
a, Å
C
22H26Cl2O2SW
C38H44O2SW
748.67
monoclinic
P21/n
10.587(6)
16.959(6)
19.427(5)
C50H52O2S1W1
900.87
triclinic
P1h
12.245(4)
16.728(4)
11.321(3)
100.19(2)
90.41(3)
110.60(2)
2
609.26
triclinic
P1h
11.280(4)
11.295(4)
9.596(2)
96.48(3)
100.32(4)
72.64(3)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
Z
98.65(3)
4
V, Å3
1145.7(8)
1.766
3448(2)
1.442
2130(1)
1.404
D
calcd, g/cm3
F(000)
596
1512
916
radiation
Mo KR
Mo KR
Mo KR
abs coeff, cm-1
scan mode
temp, °C
53.86
34.45
28.01
ω-2θ
23
ω-2θ
23
ω-2θ
23
scan speed, deg/min
scan width, deg
2θmax, deg
no. of unique data
no. of unique data
(I > 3σ (I))
no. of variables
R
16
16
8
1.63 + 0.35 tan θ
55.0
5275
3903
1.73 + 0.35 tan θ
55.0
8184
5282
1.52 + 0.35 tan θ
55.0
9760
5597
253
0.037
379
0.039
503
0.043
Rw
0.039
0.042
0.043
GOF
1.56
1.38, -1.57
2.12
1.53, -1.37
1.37
1.14, -0.92
∆, e Å-3
and kept at -20 °C until used. Reaction temperatures were
maintained within (0.1 °C by the GSX400 temperature
controller, and progress of isomerization was monitored by 1H
NMR. The value [5]t, which refers to the concentration of 5 at
the reaction time t, was determined by the sum of intensities
of areas assignable to 18 protons (SiMe3) in 5. Treatment of
the data is described in the text.
Ch a r t 1
P r ep a r a tion of W(η2-P h CtCP h )[S(4-Me-6-tBu C6H2O)2]-
(CH3)2 (7). This complex was prepared and isolated in a
manner similar to that for 5 as orange crystals in 46% yield,
1
mp 122 °C (dec 150 °C). H NMR (CD2Cl2, 30 °C, 500 MHz):
δ 7.64 (dd, 2H, o-PhC), 7.61 (dd, 2H, o′-PhC), 7.60 (t, 2H,
m-PhC), 7.44 (t, 2H, m′-PhC), 7.40 (t, 1H, p-PhC), 7.39 (s, 1H,
3-C6H2O), 7.32 (t, 1H, p′-PhC), 7.31 (s, 1H, 3′-C6H2O), 7.13 (s,
1H, 5-C6H2O), 6.91 (s, 1H, 5′-C6H2O), 2.30 (s, 3H, M-CH3),
Isom er iza tion of 5. Complex 5 was dissolved in C6D6 (0.6
mL) in a 5 mm NMR tube, which was sealed under argon and
placed for 3 days at room temperature. The color changed from
red to orange, and the 1H and 13C NMR spectra of the solution
were measured. A numbering scheme is shown in Chart 1. 1H
NMR (C6D6, 22.5 °C, 600 MHz): δ 7.83 (dd, 2H, o-PhC), 7.76
(dd, 2H, o′-PhC), 7.59 (s, 1H, 3-C6H2O), 7.40 (t, 2H, m-PhC),
7.33 (s, 1H, 3′-C6H2O), 7.23 (s, 1H, 5-C6H2O), 7.15 (t, 1H,
p-PhC), 7.12 (t, 2H, m′-PhC), 6.81 (s, 1H, 5′-C6H2O), 6.94 (t,
t
2.23 (s, 3H, Me), 2.07 (s, 3H, Me′), 1.48 (s, 9H, Bu), 1.05 (s,
9H, tBu′), 0.45 (s, 3H, M-CH3). 1H NMR (CD2Cl2, -90 °C, 500
MHz): δ 7.82 (dd, 2H, o-PhC), 7.72 (dd, 2H, o′-PhC), 7.61 (t,
2H, m-PhC), 7.47 (t, 2H, m′-PhC), 7.43 (t, 1H, p-PhC), 7.37 (s,
1H, 3-C6H2O), 7.36 (t, 1H, p′-PhC), 7.30 (s, 1H, 3′-C6H2O), 7.07
(s, 1H, 5-C6H2O), 6.84 (s, 1H, 5′-C6H2O), 2.23 (s, 3H, M-CH3),
2
3
4
1H, p′-PhC), 3.62 (m, 4H, thf), 3.56 (d, 1H, J H
) 7.69 Hz,
H
t
2.15 (s, 3H, Me), 1.86 (s, 3H, Me′), 1.37 (s, 9H, Bu), 0.96 (s,
CH3 H4Si), 3.48 (d, 1H, J H
) 7.69 Hz, CH4 H3Si), 2.33 (d,
2
4
3
H
t
9H, Bu′), 0.40 (s, 3H, M-CH3). 13C NMR (C6D6, 30 °C, 100
1H, 2J H
) 11.54 Hz, CH2 H1Si), 2.21 (s, 3H, Me), 1.95 (s,
2
1
H
MHz): 208.5 (PhC), 206.7 (PhC), 167.5 (4-C6H2O), 165.0 (4′-
C6H2O), 143.0, 142.0, 140.9 (6-C6H2O), 139.0 (6′-C6H2O), 132.2
(o-PhC), 131.1 (3-C6H2O), 130.6 (5-C6H2O), 130.1 (p′-PhC),
129.6 (5′-C6H2O), 129.0 (o′-PhC), 128.2 (3′-C6H2O), 121.8, 120.6,
66.4 (M-CH3), 60.7 (M-CH3), 35.6 (CMe3), 34.8 (CMe3′), 29.8
(CMe3), 29.4 (CMe3′), 20.8 (Me), 20.6 (Me′). Anal. Calcd for
3H, Me′), 1.80 (s, 9H, tBu), 1.46 (m, 4H, thf), 1.19 (s, 9H, tBu′),
0.31 (s, 9H, SiMe3 ), 0.20 (d, 1H, 2J H ) 11.54 Hz, CH H Si),
1
2
1
2
H
-0.07 (s, 9H, SiMe3′). 13C NMR (C6D6, 22.5 °C, 150 MHz):
213.9 (PhC), 210.6 (PhC), 167.4 (4-C6H2O), 165.6 (4′-C6H2O),
144.1, 142.8, 141.3 (6-C6H2O), 139.2 (6′-C6H2O), 131.0 (o-PhC),
130.84 (3-C6H2O), 130.76 (5-C6H2O), 130.0 (p′-PhC), 129.7 (5′-
C6H2O), 129.3 (o′-PhC), 129.2 (3′-C6H2O), 129.0 (m′-PhC), 128.9
C
38H44O2S1W1: C, 60.96; H, 5.92. Found: C, 61.10; H, 5.92.
P r ep a r a tion of W(η2-P h CtCP h )[S(4-Me-6-tBu C6H2O)2]-
(m-PhC), 128.5 (p-PhC), 122.2, 121.4, 82.3 (CH1H2Si, J CH
)
1
1
1
1
116 Hz, J CH ) 107 Hz), 79.5 (CH3H4Si, J CH ) 113 Hz), 67.8
(thf), 35.7 (CMe3), 35.0 (CMe3′), 30.5 (CMe3), 29.9 (CMe3′), 25.8
(thf), 20.7 (Me), 20.6 (Me′), 4.3 (SiMe3 ), 2.4 (SiMe3′). ESI-MS
for 184W m/z, 821 [(M - CH2SiMe3 + O)-]. All attempts to
isolate 6 failed because it was highly soluble even in hexane
at -78 °C.
2
(CH2P h )2 (8). This complex was prepared and isolated in a
manner similar to that for 5 as red crystals in 64% yield, mp
160 °C (dec). A numbering scheme of benzyl groups in 8 is
1
shown in Chart 2. H NMR (CD2Cl2, 30 °C, 500 MHz): δ 7.60
(s, 1H, 3-C6H2O), 7.44 (t, 2H, m-PhC), 7.40 (s, 1H, 3′-C6H2O),
7.33 (t, 1H, p-PhC), 7.30 (s, 1H, 5-C6H2O), 7.29-7.15 (m, 6H,
PhC + CH2Ph′), 7.07 (t, 2H, m-CH2Ph), 6.97 (s, 1H, 5′-C6H2O),
6.96-6.85 (m, 6H, PhC + CH2Ph′), 6.67 (d, 2H, o-CH2Ph), 6.65
Kin etic Stu d y for Isom er iza tion of 5 to 6. Complex 5
(0.063 g, 0.071 mmol) was dissolved in C6D6 (4.00 mL) at room
temperature, and the solution (0.018 M) was divided equally
among five NMR tubes. Each of them was sealed under argon
2
(t, 1H, p-PhC), 5.00 (d, 1H, J H ) 11.0 Hz, CH3 H4Ph), 4.72
3
4
H
4
3
2
(d, 1H, 2J H ) 11.2 Hz, CH H Ph), 4.11 (d, 1H, J H ) 10.1
4
3
2
1
H
H

3158 Organometallics, Vol. 18, No. 16, 1999
Nakayama et al.
available polystyrene standards (Aldrich). For polymers ob-
tained by using other complexes as catalysts, GPC analyses
were carried out using Tosoh TSKgel HXL-H and L columns
connected to a Tosoh UV-8010 absorbance detector. Samples
were prepared in THF (0.1-0.3% (w/v)) and were filtered
through an Advantec DISMIC-25J P filter in order to remove
particulates before injection. GPC columns were calibrated
versus commercially available polystyrene standards (Polymer
Laboratories Ltd.) whose molecular weight ranged from 500
to 2.15 × 106.
Ch a r t 2
Cr ysta llogr a p h ic Da ta Collection s a n d Str u ctu r e De-
ter m in a tion of 3b, 7, a n d 8. The crystals of 3b, 7, and 8
suitable for X-ray diffraction studies were sealed in glass
capillaries under argon and then mounted on a Rigaku AFC-
5R four-circle diffractometer for data collection using Mo KR
radiation. Relevant crystal and data statistics are summarized
in Table 6. The unit cell parameters at 23 °C were determined
by a least-squares fit to 2θ values of 25 strong higher
reflections for all complexes. Three standard reflections were
chosen and monitored every 150 reflections. Empirical absorp-
tion correction was carried out on the basis of an azimuthal
scan. Every sample showed no significant intensity decay
during the data collection. The structures of all complexes were
solved by direct methods (SHELXS 86)32 and refined by the
full-matrix least-squares method. Measured nonequivalent
reflections with I > 3.0σ(I) were used for the structure
determination. In the subsequent refinement the function
∑w(|Fo| - |Fc|)2 was minimized, where |Fo| and |Fc| are the
observed and calculated structure factor amplitudes, respec-
tively. The agreement indices are defined as R ) ∑||Fo| - |Fc||/
∑|Fo| and Rw ) [∑w(|Fo| - |Fc|)2/∑w(|Fo|)2]1/2, where w-1 ) σ2(Fo)
) [σc2(Fo) + p2/4(Fo2)]. The positions of all non-hydrogen atoms
for complexes 3b, 7, and 8 were found from a difference Fourier
electron density map and refined anisotropically. Hydrogen
atoms for each complex were placed as follows: for 8 hydrogen
atoms on the R-methylene carbons of the benzyl ligands were
found from a difference Fourier syntheses and were refined
isotropically, and the other hydrogen atoms were placed in
calculated positions (d(C-H) ) 0.95 Å) and constrained to ride
on their respective carbon atoms. For 3b and 7 all hydrogen
atoms were placed in calculated positions (d(C-H) ) 0.95 Å)
and kept fixed. All calculations were performed using the
TEXSAN crystallographic software package, and illustrations
were drawn with ORTEP.
Hz, CH2 H1Ph), 2.23 (s, 3H, Me), 1.93 (s, 3H, Me′), 1.83 (s, 9H,
1
2
t
tBu), 1.52 (d, 1H, 2J H ) 9.9 Hz, CH H Ph), 1.00 (s, 9H, Bu′).
1
2
H
13C NMR (CD2Cl2, 30 °C, 125 MHz): 208.1 (PhC), 205.8 (PhC),
165.4 (4-C6H2O), 164.3 (4′-C6H2O), 147.9-119.1 (PhC + CH2Ph
1
1
+ C6H2O), 96.9 (CH1H2Ph, J CH ) 140, J CH ) 120 Hz), 72.7
1
2
(CH3H4Ph, J CH ) 125 Hz), 34.6 (CMe3), 33.5 (CMe3′), 29.4
1
(CMe3), 28.1 (CMe3′),19.7 (Me), 19.6 (Me′). CP/MAS (rotating
7.3 kHz): δ 212.3 (PhC), 169.7-120.2 (aromatics), 103.5 (CH2-
Ph), 86.4 (CH2Ph), 35.7 (CMe3), 35.0 (CMe3′), 31.6 (CMe3), 30.6
(CMe3′), 23.4 (Me), 20.1 (Me′) Anal. Calcd for C50H52O2S1W1:
C, 66.66; H, 5.82. Found: C, 66.58; H, 5.89.
r-H Elim in a tion of 8. A solution of Mg(CH2Ph)2 (0.24
mmol, 1 equiv) in diethyl ether was added to a solution of W(η2-
PhCtCPh)[S(4-Me-6-t BuC6H2O)2]Cl2 (0.19 g, 0.24 mmol) in
diethyl ether (30 mL) via syringe at -78 °C. After stirring for
20 min, the reaction mixture was allowed to warm to ambient
temperature and stirred for 1 h. The color of the solution
changed from dark purple to orange. All volatiles were
removed under reduced pressure. The resulting residue was
extracted with n-hexane (30 mL). The extract was evaporated
to dryness and redissolved in toluene (25 mL). Heating the
solution to 80 °C for 3 h followed by refluxing for 1 h resulted
in a color change from red to dark brown. All volatiles were
removed under reduced pressure. The resulting residue was
extracted with n-hexane (30 mL). The solvent was removed
under reduced pressure, and recrystallization from toluene (1
mL) and n-hexane (2 mL) cooled to -20 °C gave 9 and 9′ as
brown microcrystals in 13% yield. Anal. Calcd for
C43H44O2S1W: C, 63.86; H, 5.48. Found: C, 63.53; H, 5.64. ESI-
MS for 184W m/z: 841 [(M + O2)- ].
P olym er iza tion of Nor bor n en e: Gen er a l P r oced u r es.
To a solution of W(η2-PhCtCPh)[S(4-Me-6-t BuC6H2O)2](CH2-
SiMe3)2 (18 mg, 0.02 mmol) in benzene (1.0 mL) was added a
solution of norbornene (100 equiv, 2 mmol) in benzene (2 M, 1
mL) at 30 °C. After the solution was stirred at 30 or 60 °C for
a prescribed period, methanol (15 mL) was added to the
resulting reddish viscous solution to precipitate a pale yellow
polymer. The polymer was washed with methanol and then
dried in vacuo.
Ack n ow led gm en t. Y.N. acknowledges the support
by the Grant-in-Aid for Scientific Research on Priority
Areas (No. 283, “Innovative Synthetic Reactions”) from
the Ministry of Education, Science, Sports and Culture,
J apan.
Su p p or tin g In for m a tion Ava ila ble: Tables of final
positional parameters, final thermal parameters, and bond
distances and angles for 3b, 7, and 8 together with their
drawings with all numbering schemes of nonhydrogen atoms,
and NMR spectra of 5 and 6. This material is available free of
charge via the Internet at http://pubs.acs.org.
GP C An a lysis of th e P oly(n or bor n en e). For polymers
obtained by using 6, 7, and 8 as catalysts, gel permeation
chromatographic (GPC) analyses were carried out at 40 °C
using a Shimadzu LC-10A liquid chromatograph system and
a RID-10A differential refractometer, equipped with a Shodex
KF-806L column. THF was used as the eluent at a flow rate
of 0.8 mL/min, and sample concentrations of 0.5 mg/mL were
applied. The GPC column was calibrated versus commercially
OM9808965
(32) Sheldrick, G. M. SHELXS86: Program for the Solution of
Crystal Structures; Universita¨t Go¨ttingen: Germany, 1986.