Synthesis and reactivity of hydridotris(1-pyrazolyl)borate tungsten(VI) amido alkylidyne complexes

Article abstract of DOI:10.1016/S0020-1693(02)01350-6

The synthesis of a series of tungsten(VI) amido alkylidyne complexes containing the chelating ligands Tp (hydridotris(1-pyrazolyl)borate) and Tp′ (hydridotris(3,5-dimethyl-1-pyrazolyl)borate) is described. Complexes of general formula, TpW(CC(CH₃)₃)(Cl)(NHR) [R=C₆H₅, 4-Br-C₆H₄, 3,5-(CF₃)₂C₆H₃, H], (3-6), were formed by reaction of TpW(CC(CH₃)₃)(Cl)₂ with the appropriate amide [M][NHR] (M=Li, K). In presence of excess [Li][NHPh], TpW(CC(CH₃)₃)(NHPh)₂ (7) was isolated. Sub-stoichiometric quantities of H₂O or HCl were found to catalyze the tautomerization of 3 to the corresponding imido alkylidene. Reaction of excess H₂O with 3 produced significant amounts of TpW(O)(CHC(CH₃)₃)(Cl) (10) and TpW(O)(CC(CH₃)₃)(Cl) (11) along with tautomerization. Attempted acid catalyzed tautomerizations of 4 and 5 with HCl resulted in loss of the amido ligands and recovery of TpW(CC(CH₃)₃)(Cl)₂. The complex Tp′W(CC(CH₃)₃)(Cl)(NHPh) (8), was synthesized by reaction of (CH₃)₃SiN(H)Ph with (DME)W(CC(CH₃)₃)(Cl)₃ followed by addition of KTp′. X-ray crystal structures have been obtained for compounds 7 and 8 and show that the amido groups are syn with respect to the neopentylidyne ligand probably due to the steric demands of the chelating Tp and Tp′ ligands.

Full text of DOI:10.1016/S0020-1693(02)01350-6

Inorganica Chimica Acta 345 (2003) 103Á112
/
www.elsevier.com/locate/ica
Synthesis and reactivity of hydridotris(1-pyrazolyl)borate
tungsten(VI) amido alkylidyne complexes
Percy Doufou, Khalil A. Abboud, James M. Boncella *
Department of Chemistry, and Center for Catalysis, University of Florida, P.O. Box 117200, Gainesville, FL 32611-7200, USA
Received 15 May 2002; accepted 25 September 2002
Dedicated to Professor R.R. Schrock
Abstract
The synthesis of a series of tungsten(VI) amido alkylidyne complexes containing the chelating ligands Tp (hydridotris(1-
pyrazolyl)borate) and Tp? (hydridotris(3,5-dimethyl-1-pyrazolyl)borate) is described. Complexes of general formula,
TpW(CC(CH3)3)(Cl)(NHR) [Rꢀ
with the appropriate amide [M][NHR] (Mꢀ
/
C6H5, 4-BrÃ
/
C6H4, 3,5-(CF3)2C6H3, H], (3Á6), were formed by reaction of TpW(CC(CH3)3)(Cl)2
/
/
Li, K). In presence of excess [Li][NHPh], TpW(CC(CH3)3)(NHPh)2 (7) was isolated.
Sub-stoichiometric quantities of H2O or HCl were found to catalyze the tautomerization of 3 to the corresponding imido alkylidene.
Reaction of excess H2O with 3 produced significant amounts of TpW(O)(CHC(CH3)3)(Cl) (10) and TpW(O)(CC(CH3)3)(Cl) (11)
along with tautomerization. Attempted acid catalyzed tautomerizations of 4 and 5 with HCl resulted in loss of the amido ligands
and recovery of TpW(CC(CH3)3)(Cl)2. The complex Tp?W(CC(CH3)3)(Cl)(NHPh) (8), was synthesized by reaction of
(CH3)3SiN(H)Ph with (DME)W(CC(CH3)3)(Cl)3 followed by addition of KTp?. X-ray crystal structures have been obtained for
compounds 7 and 8 and show that the amido groups are syn with respect to the neopentylidyne ligand probably due to the steric
demands of the chelating Tp and Tp? ligands.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Tungsten(VI) complexes; Amido alkylidyne complexes; Alkylidyne complexes; Acid catalyzed tautomerization; Acid induced cleavage
1. Introduction
The chemistry of transition-metalÃ
molecular protonation of the metalÃ
/
carbon triple bond
[6].
/
ligand multiple
Our group has been investigating the chemistry of
W(VI) and Mo(VI) alkylidynes that contain tridentate
hydridotris(pyrazolyl)borate ancillary ligands [7]. The
complexes TpW(CC(CH3)3)Cl2 and Tp?W(CC(CH3)3)-
bonds is a subject of broad interest that crosses the
lines of inorganic and organometallic chemistry [1].
Complexes that contain double and triple bonds be-
tween a high-oxidation-state transition metal atom and
carbon are of special interest because many of these
complexes have demonstrated the ability to catalyze
olefin [2] or acetylene [3] metathesis, respectively.
Transition metal alkylidynes are also known to undergo
metathesis-like reactions with isocyanates [4], and Wit-
tig-type reactions with nitriles [5]. Additionally, alkyli-
dyne complexes have been frequently employed in the
preparation of alkylidene complexes via intra- or inter-
Cl2 (Tpꢀ
/
hydridotris(1-pyrazolyl)borate; Tp?ꢀhydri-
/
dotris(3,5-dimethyl-1-pyrazolyl)borate) have been con-
verted to oxo alkylidenes by stirring over neutral
alumina presumably via a mechanism that involves an
intra- or intermolecular proton transfer [7a,8]. These
complexes have proven to be remarkably inert to
protonation by either triflic acid, tetrafluoroboric acid,
or hydrochloric acid. In this paper, we report the
synthesis of several amido alkylidyne complexes as
well as studies of acid catalyzed proton transfer reac-
tions that can be used to convert the amido alkylidyne
complexes to imido alkylidene complexes.
* Corresponding author. Fax: ꢁ
/
1-352-392 8758.
E-mail address: boncella@chem.ufl.edu (J.M. Boncella).
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 3 5 0 - 6

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P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á112
/
2. Experimental
tallization from a minimum of Et2O/C5H12 at ꢂ78 8C
/
gave 3 as an orange powder. Typically, repeated
recrystallizations were necessary to remove traces of
TpW(CC(CH3)3)Cl2 still present due to incomplete
reaction. 1H NMR (25 8C in C6D6): d 1.2 (s, 9H,
C(CH3)3), 5.69, 5.78, 5.82 (t, 1H each, Tp ring H’s, 4-
position), 6.9 (t, 1H, p-Ph), 7.32, 7.35, 7.76, 7.79, 8.4 (d,
1H each, Tp ring H’s, 3,5-position, one overlaps with
solvent), 7.2 (t, 2H, m-Ph, other phenyl H’s overlap with
2.1. General details
All procedures were performed using standard
Schlenk techniques under argon, or were carried out in
a nitrogen filled dry box. Diethyl ether (Et2O), tetra-
hydrofuran (THF), C5H12, and hexanes were distilled
from sodium benzophenone ketyl. Toluene was deolefi-
nated by washing twice with cold H2SO4 followed by
water and bicarbonate. It was then dried by distillation
from potassium metal. Dichloromethane (CH2Cl2) was
distilled from CaH2. After collection, all solvents were
stored in an argon atmosphere over molecular sieves.
Glassware was oven dried before use. The compounds
(DME)W(CC(CH3)3)Cl3 [3e,9], potassium hydrido-
tris(1-pyrazolyl)borate (KTp) [10], potassium hydrido-
solvent), 10.5 (broad s, 1H, NÃ
H). 13C NMR (25 8C,
/
C6D6): d 32.4 (C(CH3)3), 49.43 (C(CH3)3), 105.92,
106.60, 123.38, 124.23, 128.74, 131.73, 135.44, 142.63,
144.99, 147.07, 157.08 (Tp, Ph), 306.80 (CC(CH3)3).
Anal. Calc. for: C20H26BClN7W: C, 40.4; H, 4.41; N,
16.5. Found: C, 39.9; H, 4.22; N, 16.3%. High Res. MS.
Calc. for: C20H26BClN7W, 594.154117. Found:
594.153641. The compound, TpW(15NHPh)(CC-
tris-(3,5-dimethyl-1-pyrazolyl)borate
(KTp?)
[10],
(CH3)3)Cl (1a) was prepared in a similar manner using
K15NHPh: H NMR (25 C in C6D6) d 10.5 (d, NÃ
1
TpW(CC(CH3)3)Cl2 (1) [8], and Tp?W(CC(CH3)3)Cl2
(2) [7a,8] were synthesized according to published
procedures. All NMR solvents were degassed and stored
over molecular sieves in an N2 filled drybox prior to use.
1H and 13C NMR spectra were measured using either
a General Electric QE 300 or a Varian VXR-300
spectrometer. Chemical shifts were referenced relative
to the residual protons in the deuterated solvents and
are reported relative to Me4Si. Elemental analyzes were
performed by either the University of Florida Analytical
Services or by Atlantic Microlabs, Norcross, Ga.
Repeated recrystallization of the samples were necessary
/H,
1J15NÃH
ꢀ
/
70 Hz).
2.4. TpW(CC(CH3)3)(NHÃ
/
4-BrÃ
/
C6H4)Cl (4)
A solution of p-bromoaniline (0.09 g, 0.75 mmol) in
10 ml THF was cooled to ꢂ78 8C and slowly added to a
78 8C THF suspension of KH (0.03 g, 0.75 mmol).
/
ꢂ
/
The reaction mixture was allowed to warm to r.t. and
stirred for approximately 40 min until the evolution of
H2 ceased. The color of the solution became yellow
upon warming to r.t. At this time, the solution was
to remove unreacted 2 from compounds 3Á
/7. High-
cooled to ꢂ
/
78 8C and was added slowly to a ꢂ78 8C
/
resolution mass spectra were obtained by the UF
Department of Chemistry Analytical Services and were
measured in FAB mode using p-nitrophenyloctyl ether
as the matrix material. Parent ions were calculated using
the most abundant isotopes for each element.
solution of TpW(CC(CH3)3)Cl2 (0.26 g, 0.5 mmol) in 20
ml THF. An immediate color change to green was
observed. As the reaction was left to stir and warm to
r.t. over the course of 10 h, the color changed to orange.
Recrystallization from a minimum volume of Et2O/
1
C5H12 at ꢂ
/
40 8C gave 4 as an orange solid. H NMR
2.2. Photolyses
(25 8C, C6D6): d 1.19 (s, 9H, C(CH3)3), 5.7, 5.75, 5.86 (t,
1H each, Tp H’s 4-position), 6.98, 7.32 (d, 2H each,
phenyl ring H’s), 7.2, 7.5, 7.79, 8.35 (d, 1H each, four
out six of Tp H’s 3,5-positions, the other two masked by
All photolyses were performed on solutions of the
compounds in NMR tubes with a teflon joint. A 275 W
tungsten lamp was used as broad band irradiation
source and the sample was cooled to ꢂ
CaCl2 bath that was refreshed every 5 min to maintain a
constant temperature.
solvent), 10.15 (broad s, 1H, NÃ
H). 13C NMR (25 8C,
/
/
10 8C in an ice/
C6D6): d 31.92 (C(CH3)3), 49.18 (C(CH3)3), 106.20,
106.80, 123.87, 124.38, 128.50, 128.87, 135.23, 143.10,
145.40, 148.10, 154.42, 156.08 (Tp, Ph), 297.15
(CC(CH3)3). Anal. Calc. for: C20H25BBrClN7W: C,
35.7; H, 3.74; N, 14.6. Found: C, 34.4; H, 3.65; N,
14.2%. High Res. MS. Calc. for: C20H25BBrClN7W,
672.064640. Found: 672.062891.
2.3. TpW(CC(CH3)3)(NHPh)Cl (3)
TpW(CC(CH3)3)Cl2 (0.15 g, 0.27 mmol) was dis-
solved in 20 ml Et2O and cooled to ꢂ78 8C. To this
/
solution was slowly added an Et2O solution of LiNHPh
(0.05 g, 0.54 mmol). An immediate color change from
purple to green was observed. The reaction mixture was
allowed to warm to room temperature (r.t.) and was
stirred for up to 12 h giving a dark orange solution.
After solvent removal, and dissolution in ether, recrys-
2.5. TpW(CC(CH3)3)(NH(3,5-(CF3)2C6H3))Cl (5)
The same procedure was followed as in 4. Immediate
color change of the reaction mixture from blue to brown
was observed which became lighter as the reaction was
allowed to warm to r.t. and stirred for 10 h. Recrys-

P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á
/
112
105
tallization from minimum Et2O/C5H12 at ꢂ
/
40 8C gave
(C(CH3)3), 50.71 (C(CH3)3), 105.88, 106.68, 120.61,
121.43, 128.76, 134.74, 135.31, 140.72, 144.96, 157.08
(Tp, Ph), 295.37 (CC(CH3)3). High Res. MS. Calc. for:
C26H31BN8W, 650.227463. Found: 650.228286.
1
an orange crystalline material. H NMR (25 8C, C6D6):
d 1.19 (s, 9H, C(CH3)3), 5.65, 5.67, 5.9 (t, 1H each, Tp
H’s 4-position), 7.1, 7.3, 7.56, 7.6, 7.79, 8.2 (d, 2H each,
Tp H’s 3,5-positions), 7.5 (s 2H, o-phenyl H’s, p-H
probably overlaps with solvent), 9.79 (broad s, 1H, NÃ
/
2.8. Tp?W(CC(CH3)3)(NHPh)Cl (8)
H). Anal. Calc. for: C22H24BClF6N7W: C, 36.2; H, 3.31;
N, 13.4. Found: C, 35.1; H, 3.15; N, 12.9%. High Res.
MS. Calc. for: C22H24BClF6N7W, 730.128885. Found:
730.128456.
(CH3)3SiÃ
/
N(H)Ph (0.19 ml, 1.1 mmol) in 10 ml THF
was added to a cold THF solution of (DME)W-
(CC(CH3)3)Cl3 (0.5 g, 1.1 mmol). An immediate color
change from purple to green was observed. The color of
the reaction mixture became lighter as it warmed to r.t.
After 30 min, the reaction mixture was cooled to
2.6. TpW(CC(CH3)3)(NH2)Cl (6)
TpW(CC(CH3)3)Cl2 (0.15 g, 0.3 mmol) was dissolved
in 20 ml THF and a suspension of NaNH2 (0.035 g, 1.5
mmol, 5 equiv.) in THF was added dropwise. No
immediate color change was observed. The reaction
mixture was left to stir and warm up to r.t. overnight. At
this point the reaction mixture had turned light green
and when the solvent was removed under reduced
pressure, a pale yellow solid was recovered. The solid
ꢂ78 8C and a solution of KTp? (0.37 g, 1.1 mmol) in
/
20 ml THF was slowly added. The color of the reaction
mixture continued becoming lighter until it was bright
orange. After stirring for 2 more hours at r.t., the
solvent was removed under reduced pressure. Recrys-
tallization from minimum Et2O at ꢂ40 8C gave bright
/
1
orange, X-ray quality crystals of 8. H NMR (25 8C,
C6D6): d 1.38 (s, 9H, C(CH3)3), 2.0, 2.12, 2.17, 2.28, 2.4,
3.1(s, 3H each, Tp? CH3, 3,5-positions), 5.57, 5.59, 6.1 (t,
1H each, Tp? H’s, 4-position), 6.9 (t, 1H, p-Ph), 7.2 (t,
was recrystallized from minimum Et2O/C5H12 at
1
ꢂ
/
40 8C giving a yellow crystalline material. H NMR
(25 8C, C6D6): d 1.3 (s, 9H, C(CH3)3), 5.7, 5.75, 5.8 (t,
1H each, Tp H’s 4-position), 7.29, 7.7.8, 7.86 [d, 1H
each, three out six of the Tp H’s at 3,5-position, (others
probably overlap with solvent)], 8.6, 8.9 (broad s, 1H
each, NH2 protons). 13C NMR (25 8C, C6D6): d 31.53
(C(CH3)3), 49.13 (C(CH3)3), 106.18, 106.37, 134.42,
134.61, 135.28, 142.02, 144.95, 147.14, 147.80 (Tp C’s),
303.53 (CC(CH3)3. Anal. Calc. For: C14H22BClN7W: C,
32.4; H, 4.27; N, 18.9. Found: C, 29.7; H, 4.21; N,
18.5%. High Res. MS. Calc. for: C14H22BClN7W,
518.122816. Found: 518.122091.
2H, m-Ph), 7.3 (d, 2H, o-Ph), 10.62 (broad s, 1H, NÃ
/
H).
13C NMR (25 8C, C6D6): d 12.09, 12.81, 13.47, 18.48,
18.77 (Tp? CH3’s, overlapping), 32.62 (CC(CH3)3),
49.66 (CC(CH3)3), 107.31, 107.65, 143.06, 144.78,
145.44, 152.46, 153.18, 153.84, 157.29 (Tp? ring C’s),
123.94, 124.55, 128.47 (Ph C’s). 310.17 (CC(CH3)3).
Anal. Calc. for C26H37ClN7W: C, 46.8; H, 5.55; N, 14.7.
Found: C, 46.5; H, 5.46; N, 14.4%.
2.9. X-ray experimental details
Compound 7: data were collected at 173 K on a
Siemens CCD SMART PLATFORM equipped with a
2.7. TpW(CC(CH3)3)(NHPh)2 (7)
CCD area detector and a graphite monochromator
˚
0.71073 A). Cell para-
To a cold Et2O solution of TpW(CC(CH3)3)Cl2 (0.2 g,
0.77 mmol) 3.3 equiv. of LiNHPh (0.25 g, 2.54 mmol) in
Et2O was slowly added. The reaction mixture was
allowed to warm to r.t. and changed from blue to bright
orange almost immediately. After stirring for 3 h, Et2O
was removed under reduced pressure and the orange
solid was extracted once with C6H5CH3 and once with
CH2Cl2. The solvent was removed from the combined
extracts and the resultant solid was recrystallized from a
r.t. CH2Cl2/C5H12 mixture to afford an orange crystal-
line solid. X-ray quality crystals were obtained by slow
diffusion of C5H12 into a r.t. saturated CH2Cl2 solution
utilizing Mo Ka radiation (lꢀ
/
meters were refined using the entire data set. A hemi-
sphere of data (1381 frames) was collected using the v-
scan method (0.38 frame width). The first 50 frames were
remeasured at the end of data collection to monitor
instrument and crystal stability (maximum correction on
I wasB1%). c-Scan absorption corrections were ap-
/
plied based on the entire data set. Compound 8: data
were collected at room temperature on a Siemens P3m/V
diffractometer equipped with a graphite monochroma-
˚
0.71073 A). Thirty-
tor utilizing Mo Ka radiation (lꢀ
/
two reflections with 20.0B
/
2u B22.08 were used to
/
1
of 7. H NMR (25 8C, C6D6): d 1.29 (s, 9H, C(CH3)3),
refine the cell parameters. The v-scan method was
used for data collection. Four reflections were measured
every 96 reflections to monitor instrument and crystal
5.73 (t, 2H, Tp H’s 4-position), 5.82 (t, 1H, Tp H, 4-
position), 6.90 (t, 2H, p-Ph), 7.23 (d, 2H, Tp H, 3,5-
position), 7.26 (t, 4H, m-Ph), 7.28 (d, 1H, Tp proton,
3,5-position), 7.31 (d, 1H, Tp proton 3,5,-position), 7.45
stability (maximum correction on I was B1%).
/
Both structures were solved by the Direct Method in
SHELXTL-5 [11], and refined using full-matrix least-
squares on F2. The non-H atoms were refined with
(d, 4H, o-Ph), 7.82 (s, 2H, NÃ
/
H), 7.99 (d, 2H, Tp H’s
3,5-positions). 13C NMR (25 8C, C6D6): d 32.47

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P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á112
/
anisotropic thermal parameters. The H atoms of 8 were
all refined in a riding mode on their parent atoms except
those bonded to boron, which were refined without
constraint. The structure also contains a disordered half
ether molecule. It was refined with isotropic thermal
parameters in three parts with site occupation factors of
0.25, 0.15 and 0.10, respectively. Compound 7 had all H
atoms riding on their parent atoms except the one on
Boron. For compound 8, 411 parameters were refined in
the final cycle of refinement using 4274 reflections with
to dark orange. Recrystallization of the reaction product
from an ether/pentane solution gave TpW(CC(CH3)3)-
(NHPh)Cl (3), Eq. (1), as a dark orange powder. The 1H
NMR spectrum is consistent with the formation of the
monoamide alkylidyne complex. The amido NÃ
/
H pro-
ton appears as a broad singlet at 10.50 ppm, while the
lack symmetry renders all the Tp ring protons inequi-
valent.
The compounds, TpW(CC(CH3)3)(N(H)4-Br(C6H3)-
Cl (4), and TpW(N(H)(3,5-(CF3)2C6H3)(CC(CH3)3)Cl
(5), were prepared from in situ generated K[anilide] and
a THF solution of 1. Removal of THF and subsequent
I ꢀ2s(I) to yield R1 and wR2 of 5.53 and 11.16,
/
respectively. For compound 7, 179 parameters were
refined in the final cycle of refinement using 2978
recrystallization from Et2O/pentane at ꢂ40 8C afforded
/
4 and 5 as orange solids. The 1H NMR spectra of 4 and
5 display inequivalent resonances arising from the
protons of the Tp rings confirming the asymmetric
structures of the compounds. The amide protons appear
as broad singlets at 10.15 ppm, 4, and 9.79 ppm, 5.
Compound 4 is moisture sensitive both in solution and
in the solid state and decomposes, forming a brown oil
after extended exposure to air. Complex 5 is also
relatively air and moisture sensitive and slowly decom-
poses forming a dark orange solid when exposed to air.
In both cases, the hydrolysis products were shown to be
mixtures of TpW(O)(C(H)C(CH3)3)Cl and TpW(O)2-
reflections with I ꢀ2s(I) to yield R1 and wR2 of 3.04
/
and 7.56, respectively. Refinement was done using F2.
3. Results and discussion
The coordinative saturation of the alkylidyne com-
pounds TpW(CC(CH3)3)Cl2 (1), and Tp?W(CC(CH3)3)-
Cl2 (2), render them somewhat unreactive with respect
to chemistry initiated at the metal center. Thus,
attempted acetylene metathesis with diphenyl acetylene
gave only unreacted starting materials. In order to
create a vacant site in the coordination sphere, we
added a Lewis acid (e.g. AlCl3, GaBr3) to these reaction
mixtures, with no observable change. Attempted sub-
stitution of one or both of the chloride ligands of 1 or 2
met with mixed results. While both of these compounds
react with lithium alkyls, Grignard or, other carbanion
sources, only intractable mixtures of alkyl substituted
products were observed. Reaction of 1 with lithiated
amines however, gives a number of amido complexes in
moderate yields.
1
(CH2C(CH3)3) by H NMR.
The reaction of 5 equiv. of NaNH2 with TpW(CC-
(CH3)3)Cl2 in THF, at ambient temperature overnight
gave pale yellowÁgreen TpW(NH2)(CC(CH3)3)-
/
1
Cl (6) upon recrystallization from ether. The H NMR
spectrum of 6 has inequivalent Tp proton resonances,
while the amido protons are inequivalent and appear as
broad singlets at 8.59 and 8.90 ppm, respectively. The
inequivalence of the two protons is consistent with slow
rotation about the WÃ
/
N bond on the NMR time scale.
When 3.3 equiv. of [Li][NHPh] was added to
Addition of 2Á/2.5 equiv. of Li[NHPh] to a THF
solution of 1 results in a slow color change from purple
TpW(CC(CH3)3)Cl2, extraction of the reaction mixture
ð1Þ

P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á
/
112
107
with toluene followed by recrystallization from CH2Cl2/
pentane gave bright orange, crystalline TpW(NHPh)2-
1
(CC(CH3)3) (7). The H NMR spectrum of the crude
also possible using the same method used to prepare 8
by substituting KTp for KTp?, but with no significant
improvement in yield or purity.
The room temperature 1H NMR spectrum of 8
displays six inequivalent methyl groups and three
inequivalent pyrazole ring protons. The amide peak
appears as a broad singlet at 10.62 ppm.
reaction mixture also shows formation of a small
amount of free aniline and an unidentified compound
that appears to arise from partial decomposition of the
1
Tp ligand. In the room temperature H NMR spectrum
Compound 8 is air and moisture stable and does not
decompose when heated in solution. The air and thermal
stability of this compound is comparable to that of other
of recrystallized 7, the protons of the pyrazole rings of
the Tp ligand appear in a 2:1 ratio indicating the
existence of a mirror plane in the molecule. The amide
protons appear as a broad singlet at 7.8 ppm indicating
either rapid rotation of the amide groups or possibly
hindered rotation that gives a single conformation that
retains the mirror plane in the molecule.
WÃTp? complexes [7a,8] and suggests that the increased
/
steric bulk of the Tp? ligand relative to the Tp ligand is
responsible for the enhanced kinetic stability of 8.
The presence of two distinct amido proton resonances
in the 1H NMR spectrum of 6 implies a rather rigid WÃ
/
The reaction of
1 equiv. of [K][NHPh] with
N bond. No change in the two amido proton resonances
of 6 was observed up to 120 8C (decomposition of 6
began at higher temperatures), indicating a very high
Tp?W(CC(CH3)3)Cl2 in THF gave intractable products.
An alternative route for the synthesis of the monoanilide
Tp? complex is shown in Eqs. (2) and (3). In this reaction
sequence, (CH3)3SiNHPh was allowed to react with
(DME)W(CC(CH3)3)Cl3 to generate the amide complex,
(DME)W(CC(CH3)3)Cl2(NHPh). Addition of 1 equiv.
of KTp? in THF to the resultant reaction mixture
completed the reaction. Removal of the solvent under
reduced pressure and recrystallization from Et2O at
activation barrier for rotation (DG%ꢀ
restricted rotation about the WÃN bond is a general
phenomenon for these compounds, two possible isomers
could exist for complexes 3Á5, 7, and 8 (The phenyl
/
26 kcal molꢂ1). If
/
/
group could be oriented syn or anti with respect to the
alkylidyne ligand). However, in the variable temperature
ꢂ
/
40 8C afforded bright orange crystals of Tp?W(CC-
proton NMR spectra of 3Á/5, 7, and 8 only one isomer
(CH3)3)(NHPh)Cl (8). The product of the reaction
between (CH3)3SiNHPh and (DME)W(CC(CH3)3)Cl3
has not been isolated, but we assume that it is the species
(DME)W(CC(CH3)3)Cl2(NHPh) since (DME)W(CC-
was observed between ꢂ100 and 100 8C. This observa-
/
tion can be explained if a single structure exists with
slow rotation on the NMR time scale, or if the amido
groups are undergoing rapid rotation on the NMR
timescale.
Further information on the orientation of the amide
groups in compounds 3 and 7 was obtained from proton
(CH3)3)Cl2(N(H)Ã
from the reaction between Me3SiN(H)Ã
and (DME)W(CC(CH3)3)Cl3 [6d]. Synthesis of 3 was
/
2,6-C6H3Ã
/
i-Pr2)) has been isolated
/2,6-i-Pr2C6H3
ð2Þ
difference nOe studies. Irradiation of the t-butyl peak in
3 produced positive enhancement of the meta and ortho
phenyl protons of the amido ligand, and of two Tp
resonances at 7.79 and 8.37 ppm. No enhancement of
the NÃ/H proton was observed. Alternatively, when the
amido proton was irradiated, positive enhancement was
measured for the ortho phenyl protons of the amido
ligands and for the Tp proton resonance at 7.76 ppm.
These results allow us to conclude that 3 is the syn
isomer in solution.
For complex 7 irradiation of the t-butyl peak
produced enhancement of the ortho phenyl protons
ð3Þ

108
P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á112
/
and the Tp resonance at 7.99 ppm whereas irradiation of
the NÃH proton resulted in a positive enhancement of
the ortho phenyl protons and of the Tp resonance at
7.28 ppm. These results suggest that the NÃH protons of
7 point away from the alkylidyne group, and we suggest
that only the syn isomer of 7 is present in the solution.
Although nOe studies were not carried out for the rest of
the aryl amido compounds we expect that they also
possess similar conformations in solution.
constraints of the Tp? ligand force the neopentylidyne,
amido, and chloride ligands to be mutually cis. Complex
8 is formally a 18-electron species with the neopentyli-
dyne ligand donating electron density into two metal d
orbitals of p symmetry. The hindrance imposed by the
size of the Tp? ligand forces the amido ligand to assume
the syn conformation with the phenyl ring tilted towards
the alkylidyne ligand. The syn orientation of the
phenylamido ligand allows the complex to achieve
/
/
We propose that in the amido alkylidyne complexes
maximum N-pp to W-dp-bonding [1], accounting for
˚
under discussion (where Rꢀ
the sterically demanding Tp and Tp? ligands together
with a strong WÃN bond disfavors the rotational
isomerization. Contrary to these observations, the
i-
/
Ph, Ar), a combination of
the short (1.946 A) length of the WÃ
/N(HPh) bond, and
bringing the electron count at W to 18 eꢂ. The pyrazole
˚
/
NÃ
/
W bonds range from 2.392 to 2.175 A showing that
the trans influence trend observed for 8 is alkylidyneꢀ
amideꢀchloride. The sp hybridization of the neopen-
tylidyne a-carbon is evident from the 1.766 A WÃ
C2 angle
/
related complex TpMo(CC(CH3)2Ph)(NH(2,6-C6H3Ã
/
/
˚
Pr2))(OCH3) exists as a mixture of two rotamers in
1
solution as observed in the room temperature H NMR
/C(1)
bond length and the nearly linear WÃ
/
C(1)Ã
/
spectrum [7d]. In the case of the Mo complex, p-
donation from the methoxy group competes with the
(174.58).
amido NÃ
/
Mo p interaction and lowers the barrier to
N bond enough to allow the
3.2. Tautomerization studies
rotation about the MoÃ
/
formation of syn and anti isomers.
There are a number of examples involving intramo-
lecular a-hydrogen transfers, in which the ultimate
proton acceptor is itself another multiply bonded ligand.
Such examples include proton transfers between amido/
imido [2c,12] amido/alkylidyne [6,13], hydroxo/oxo [14],
and alkylidene/oxo ligands [15]. In the tungsten and
molybdenum amido/alkylidyne systems, the transfer can
be thermal, and is usually catalyzed by bases. Although
not directly observed, a base induced proton transfer
may also be operative in the synthesis of
Tp?Ta(NPh)(CH2C(CH3)3)Cl (Eq. (4)) [16]. In the com-
plex, TpMo(NAr)(OCH3)(CHC(CH3)2Ph), a base cata-
lyzed proton transfer has been observed, in which the
alkylidene proton is transferred to the imido ligand in
the presence of excess methoxide (Eq. (5)) [7d].
3.1. Crystal structure determination of 7 and 8
A single crystal of 7 suitable for an X-ray diffraction
study was obtained by slow diffusion of pentane into a
saturated, CH2Cl2 solution of 7 at room temperature. A
thermal ellipsoid plot of 7 is found in Fig. 1. The data
collection parameters are summarized in Table 1, while
selected bond distances and angles are presented in
Table 2. The coordination geometry about the metal
center can best be described as a distorted octahedron
with the Tp ligand occupying facial sites. The structure
confirms the presence of a mirror plane that contains
one of the pyrazole rings and the neopentylidyne ligand.
The phenyl rings of the imido groups of 7 adopt a syn
conformation with respect to the alkylidyne ligand. The
˚
C(14) bond length (1.790 A) is within the expected
WÃ
/
range for d0 tungstenÃ
C(14)ÃC(10) angle is 166.68, which minimizes the
interaction between the t-butyl group and the two
/
carbon triple bonds [1]. The WÃ
/
ð4Þ
ð5Þ
/
phenyl rings, and is somewhat less than expected for
the sp hybridized a-carbon atom. The NÃ
/
W bond
lengths to the pyrazole rings range from 2.354 to 2.237
˚
A and are consistent with the decreasing trans influence
of the ligands alkylidyneꢀamido. The amido NÃ
/
/W
bonds are slightly longer than similar mono amido
compounds probably because of competition between
the nitrogen lone pairs for donation into the vacant
metal dp orbital.
The crystal structure of 8 was also determined by X-
ray diffraction, a thermal ellipsoid plot of is 8 is shown
in Fig. 2. Information on the data collection parameters
is presented in Table 1, and selected bond distances and
angles are summarized in Table 3. The geometric
Our initial studies of the tautomerization of
TpW(CC(CH3)3)(NHPh)Cl (3), to give the imido/alky-
lidene complex TpW(NPh)(CHC(CH3)3)Cl (9) [7c],
indicated that this reaction was possible, but was not
consistently reproducible. In some cases, conversion of
3Á9 was readily achieved at room temperature, while in
/

P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á
/
112
109
others no proton transfer was observed even upon
heating a sample of 3 at 70 8C for 2 days. Complexes
4 and 5 also displayed inconsistent behavior with respect
to proton transfer upon heating, while in no case was the
When H2O (approximately 0.05 equiv.) was added to
a sample of TpW(CC(CH3)3)(NH2)Cl (6), no compound
that could be identified as TpW(NH)(CHC(CH3)3)Cl
was detected even upon heating. Larger quantities of
H2O resulted in the formation of the oxo complexes, 10
and/or 11. This result implies that if TpW(NH)(CHC-
(CH3)3)Cl forms, it is rapidly hydrolyzed. Compounds 4
and 5 react very rapidly with H2O. Upon addition of
H2O to complex 4, complete hydrolysis to TpW(O)-
(CHC(CH3)3)Cl and TpW(O)2(CH2C(CH3)3) occurred
within minutes at room temperature. The addition of
even small quantities of water gives imido hydrolysis
products. Compound 5 reacts with water within minutes
corresponding imido alkylidene observed when 6Á8
/
were subjected to the same conditions. We suspected
that the inconsistent behavior was the result of an
impurity (most likely water) that might have been
present in varying amounts.
Because base catalyzed proton transfer between the
alkylidyne and amido ligands is well documented, we
attempted to catalyze the tautomerization by adding
base to the samples of 3 that did not thermally convert
to 9. Addition of up to 10 equiv. of NEt3 or PhNH2 to a
sample of 3 did not produce any change even upon
heating to 70 8C. The choice of PhNH2 was obvious
given the possibility of its presence as an impurity in
these samples. Moreover, since TpW(CC(CH3)3)
(NHPh)2 (7) instead of TpW(NPh)(CHC(CH3)3)Cl (9),
was isolated by addition of 3 or more equivalents of
[Li][NHPh] to 2, we concluded that the proton transfer
is not base promoted even in the presence of a strong
base such as anilide. A similar conclusion can be made
for the other Tp amido complexes as well, since an
excess of amide was also used in their synthesis with no
observable formation of imido/alkylidene complexes.
giving 11 as the major product along with TpW(ꢀ
/
N(3,5-(CF3)2C6H3)(CHC(CH3)3)Cl (12). After 3 days,
the only compounds evident in this sample were 10 and
11. Attempts to use HCl to catalyze the tautomerization
of complex TpW(CC(CH3)3)(NH2)Cl (6) were not
successful because even trace amounts of HCl displaced
the amido ligands giving the dichloride, 2.
The acid catalyzed proton transfer in 3 is unusual
because such proton transfer reactions (from amide to
alkylidyne) are typically base catalyzed [6,13]. Similar
acid catalyzed proton transfer has been observed in the
oxo/hydroxy species Re(O)(18OH)(RCCR)2 [17]. In this
rhenium complex, proton transfer between the oxo and
1
A close examination of the H NMR spectra of the
samples of TpW(CC(CH3)3)(NHPh)Cl (3) that under-
went tautomerization, revealed the presence of trace
hydroxy ligands is slow (half-life of Â11 h), but is rapid
/
in the presence of trifluoromethanesulfonic acid
(HOTf). The acid catalysis is believed to occur by initial
protonation of the oxo ligand and formation of a
symmetrical bis-hydroxide species. This mechanism
was proposed because HOTf was shown to protonate
the oxo ligand of the related complex [Re(O)Et-
(MeCCMe)2] [17].
amounts (approximately 1Á3%) of the oxo alkylidene
/
TpW(O)(CHC(CH3)3)Cl (10) and sometimes the dioxo
alkyl complex TpW(O)2(CHC(CH3)3) (11). The pre-
sence of these impurities suggests the presence of traces
of H2O in the reaction medium. Indeed, addition of
catalytic amounts of H2O (approximately 0.1 equiv.) to
a sample of 3 that had not tautomerized upon previous
heating at 80 8C for 10 h resulted in a slow color change
from orange to yellowish-olive, and the 1H NMR
spectrum showed the formation of 9. Heating this
sample accelerated the formation of 9. When larger
amounts of H2O were added, the hydrolysis products,
10 and 11 were also observed. This suggests that
hydrolysis competes with the tautomerization to form
9 (Scheme 1).
Since proton transfer in 3 is H2O catalyzed and not
base catalyzed, we suspected that H2O was behaving as
an acid, or generating an acid. To further test this
hypothesis, a trace amount of HCl (1.0 M in Et2O
approximately 0.05 equiv.) was added to a C6D6
solution of 3 at room temperature. A rapid color change
1
from orange to olive green ensued and the H NMR
spectrum showed complete conversion of 3Á9. Addition
/
of larger quantities of HCl resulted in complete proto-
nation of the amido ligand and formation of
TpW(CC(CH3)3)Cl2 (2) (Scheme 2).
Fig. 1. Thermal ellipsoid plot of compound 7.

110
P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á112
/
Table 1
Data collection parameters for compounds 7 and 8
7
8
Crystal parameters
Empirical formula
C
26H31BN8W
C26H37N7W×1/
/
2[C4H10O]
714.80
Formula weight
T (K)
650.25
173(2)
293(2)
monoclinic
P2(1)/c
Crystal system
Space group
monoclinic
P2(1)/m
7.6125(2)
16.3776(4)
10.5398(2)
98.705(1)
1298.91(5)
2
˚
a (A)
11.731(2)
17.315(3)
17.754(4)
108.56(2)
3418.7(11)
4
˚
b (A)
˚
c (A)
b (8)
3
V (A )
˚
Z
Crystal size (mm3)
0.24ꢃ
/
0.16ꢃ
/
0.24ꢃ
/
0.25ꢃ0.20
/
0.14
1.663
644
Dcalc (g cmꢂ3
F(000), electrons
Data collection
)
1.389
1436
˚
Radiation, l, (A)
Mo Ka,
0.71073
v-scan
Mo Ka, 0.71073
v-scan
Mode
Scan width and rate
2u Range (8)
Range of hkl
0.38/frame and 30 s/frame
1.95Á27.50 1.69Á25.00
65h 510, 05h 513,
185k 522, 05k 520,
145l 514 215l 520
/
/
Fig. 2. Thermal ellipsoid plot of compound 8.
ꢂ
/
/
/
/
/
ꢂ
/
/
/
/
/
suggests that the first step in these reactions is protona-
tion of the amide group. Furthermore, the qualitative
ꢂ/
/
/
ꢂ/
/
/
Total reflections measured
Unique reflections
9523
3087
6215
5911
3.485
reactivity of these complexes with water or HCl is 6ꢀ
5ꢀ4ꢀ3. It is possible that this reactivity trend reflects
/
Absolute coefficient, m(Mo Ka) 4.478
(mmꢂ1
/
/
)
the lability of the amine in the intermediate, 13. Thus,
the weaker donors (3,5-(CF3)2C6H3NH2, p-FC6H4NH2
and NH3) dissociate from the metal center before the
proton transfer to the alkylidyne ligand can occur giving
starting material with HCl or 10 and 11 with water.
Min/max transmission
Structure refinement
Refinement method
S, Goodness-of-fit
Variables
0.411Á
/
0.543
0.410Á
/
0.550
full-matrix least-squares on F2
1.111
179
1.152
411
5.53
R1/Reflections
3.04
7.56
3.38
0.001
wR2/Reflections
Rint (%)
Max. shift/esd
11.16
4.19
0.001
Table 2
˚
Bond lengths (A) and angles (8) for the Non-H atoms of compound 7
Minimum peak in difference
ꢂ3
ꢂ
/
2.44
ꢂ
/
0.77
˚
Fourier map (e A
)
Maximum peak in difference
1
2
3
1Ã/2
1Ã
/
2Ã3
/
1.387
0.97
ꢂ3
˚
Fourier map (e A
)
C(14)
C(14)
C(14)
C(14)
C(14)
N(1)
W
W
N(1)
1.789(5)
100.66(14)
100.66(14)
171.8(2)
N(1A)
N(2)
N(3)
R1ꢀ
a[w(Fo 2)2]]1/2.aꢀ
(0.0370*p)2ꢁ
0.31*p], pꢀ
/
a(jjFojꢂ
/
jFcjj)/ajFoj.
[a[w(Fo 2ꢂ
[max(Fo 2,0)ꢁ
wR2ꢀ
Fc 2)2]/(nꢂp)]1/2
2*Fc 2]/3.
/
[a[w(Fo 2ꢂ
/
Fc 2)2]/
W
W
/
/
/
.
wꢀ
/
1/[s2(Fo 2)ꢁ
/
93.2(2)
93.2(2)
102.7(2)
/
/
/
W
W
N(3A)
N(1A)
N(2)
2.034(3)
N(1)
N(1)
W
W
84.39(11)
88.65(13)
159.96(12)
84.39(11)
159.96(12)
88.65(13)
80.31(11)
80.31(11)
76.1(2)
For compound 3, two pathways could lead to 9
depending on where protonation occurs first (Scheme 3).
The first step in pathway A involves protonation of the
anilide ligand. Proton transfer to the alkylidyne from
the coordinated aniline in 13 followed by proton loss
from the amido group in 14 would complete the reaction
sequence. Pathway B involves direct protonation of the
neopentylidyne ligand 14. Subsequent loss of a proton
from the amido group would give 9.
N(3)
N(1)
W
W
N(3A)
N(2)
N(3)
N(1A)
N(1A)
N(1A)
N(2)
2.034(3)
2.356(4)
W
W
N(3A)
N(3)
W
W
N(2)
N(3)
N(3A)
N(3A)
W
W
2.239(3)
2.239(3)
1.353(5)
1.353(5)
1.512(7)
N(3A)
C(8)
N(1)
N(1A)
C(14)
W
W
W
140.5(3)
140.5(3)
166.5(4)
C(8A)
C(10)
The observation that higher concentrations of acid
result in loss of the amido groups from these complexes

P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á
/
112
111
4. Summary and conclusions
Table 3
Bond lengths (A) and angles (8) for the non-H atoms of compound 8
˚
The tungsten amido alkylidyne complexes reported
here tautomerize to the thermodynamically favored
imido alkylidene complexes only in the presence of a
source of protons. The nOe studies of complexes 3 and 7
suggest that the only isomer present in solution is the
syn isomer. This conformation orients the amide proton
away from the alkylidyne and renders the tautomeriza-
tion impossible without prior amide rotation or cata-
lysis. A similar argument has been proposed to explain
why the phosphide proton in the complex,
W(CC(CH3)3)(PHPh)(PEt3)Cl2, does not spontaneously
transfer to the alkylidyne carbon atom. In this case, the
proton, although pointing towards the alkylidyne car-
bon, is too far away to engage in direct transfer because
1
2
3
1Ã
/
2
1Ã
/
2Ã3
/
Cl
Cl
W
W
N(1)
N(2)
N(3)
N(4)
N(2)
N(3)
N(4)
C(1)
N(3)
N(4)
C(1)
N(4)
C(1)
C(1)
Cl
2.401(3)
97.6(2)
84.9(2)
87.4(2)
163.1(2)
80.7(3)
161.7(3)
91.0(3)
96.5(4)
82.2(3)
82.1(3)
176.6(3)
80.2(3)
100.7(4)
100.1(3)
93.5(3)
174.7(8)
139.5(6)
Cl
Cl
W
W
N(1)
N(1)
N(1)
N(1)
N(2)
N(2)
N(2)
N(3)
N(3)
N(4)
C(1)
C(2)
C(6)
W
W
1.943(7)
W
W
W
W
2.393(8)
2.223(8)
W
W
W
W
2.169(7)
W
1.773(10)
1.512(13)
1.407(11)
of the long WÃ/phosphido bond [6b].
C(1)
N(1)
W
W
Although the mechanism of the acid catalyzed proton
transfer in 3 has not been elucidated in detail, protona-
tion of the amido ligand followed by proton transfer
(Scheme 3, B) is a viable pathway. We also believe that
the electronics of the amido ligands account for some of
the observed differences in reactivity. Protonation of
amido ligands containing electron withdrawing groups
on the phenyl ring gives aniline complex intermediates
that lose the amine more readily. In this case, loss of the
aniline ligand can compete to a significant extent with
subsequent proton transfer and would explain the
observation that tautomerization is not observed with
these complexes. Finally, it is likely that the electron
donating nature of the Tp ligand systems used in these
complexes renders the amide nitrogen basic enough to
be protonated which causes the tautomerization to be
acid rather than base catalyzed.
5. Supplementary material
Tables of crystal data, thermal parameters, bond
distances, bond angles and atomic coordinates for
Scheme 1.
It is well known that photolysis of imido alkylidene
complexes can induce rotational isomerization of the
alkylidene ligand [18]. For example, the Schrock type
catalyst systems undergo the interconversion of syn and
anti isomers in this fashion. When a sample of 9, that
was generated by the proton catalyzed tautomerization
of 3, was photolyzed at ꢂ5 8C, a photostationary state
/
was established between 9 and 3. Experiments per-
formed with 9-15N, produced by acid addition to 3-15N,
confirmed that the compound generated from 9 was
indeed 3. Thus, while the photolysis of 9 probably
induces rotational isomerization of the alkylidene
ligand, proton transfer to the imido N atom also occurs.
Scheme 2.

112
P. Doufou et al. / Inorganica Chimica Acta 345 (2003) 103Á
/
112
Scheme 3.
(c) J.H. Freudenberger, R.R. Schrock, Organometallics 4 (1985)
1937;
compounds 7 and 8 (19 pages) are available from the
authors on request.
(d) C.J. Schaverien, J.C. Dewan, R.R. Schrock, J. Am. Chem.
Soc. 108 (1986) 2771.
[7] (a) L.L. Blosch, K.A. Abboud, J.M. Boncella, J. Am. Chem. Soc.
113 (1991) 7066;
Acknowledgements
(b) L.L. Blosch, A.S. Gamble, K.A. Abboud, J.M. Boncella,
Organometallics 11 (1992) 2342;
We wish to acknowledge the National Science Foun-
dation CHE-9523279 for the support of this work. KAA
wishes to acknowledge the National Science Foundation
for funding of the purchase of the X-ray equipment.
(c) A.S. Gamble, J.M. Boncella, Organometallics 12 (1993) 2814;
(d) W.M. Vaughan, K.A. Abboud, J.M. Boncella, Organometal-
lics 14 (1995) 1567.
[8] L.L. Blosch, A.S. Gamble, J.M. Boncella, J. Mol. Catal. 76 (1992)
229.
[9] D.N. Clark, J. Sancho, J.H. Wengrovius, S.M. Rocklage, S.F.
Pedersen, R.R. Schrock, Organometallics 1 (1982) 1645.
[10] S. Trofimenko, Acc. Chem. Res. (1971) 17.
[11] G.M. Sheldrick, SHELXTL-5, Siemens Analytical Instrumentation,
Madison, WI, USA, 1995.
References
[1] W.A. Nugent, J.M. Mayer, Metal-Ligand Multiple Bonds, Wiley
Interscience, New York, 1988.
[12] (a) T.E. Glassman, M.G. Vale, R.R. Schrock, Organometallics 10
(1991) 4046;
[2] (a) L.K. Johnson, S.C. Virgil, R.H. Grubbs, J. Am. Chem. Soc.
112 (1990) 5384;
(b) D.M.-T. Chan, W.C. Fultz, W.A. Nugent, C.D. Roe, T. Tulip,
J. Am. Chem. Soc. 107 (1985) 251;
(b) R.R. Schrock, R.T. De Pue, J. Feldman, K.B. Yap, D.C.
Yang, W.M. Davis, L. Park, M. DiMare, M. Schofield, J.
Anhaus, E. Walborsky, E. Evitt, C. Kruger, P. Betz, Organome-
tallics 9 (1990) 2262;
(c) W.A. Nugent, R.L. Harlow, Inorg. Chem. 19 (1980) 777.
[13] (a) R.R. Schrock, J. Organomet. Chem. 300 (1986) 249;
(b) R.R. Schrock, R.T. DePue, J. Feldman, C.J. Schaverien, J.C.
Dewan, A.H. Liu, J. Am. Chem. Soc. 110 (1988) 1423;
(c) R.R. Schrock, J.S. Murdzek, G.C. Bazan, J. Robbins, M.
DiMare, M. O’Regan, J. Am. Chem. Soc. (1990) 3875.
[14] H. Arzoumanian, H. Krentzien, H. Teruel, J. Chem. Soc., Chem.
Commun. (1991) 55.
(c) J. Kress, J.A. Osborn, R.M.E. Greene, K.J. Ivin, J.J. Rooney,
J. Am. Chem. Soc. 109 (1987) 899;
(d) J.C. Bryan, J.M. Mayer, J. Am. Chem. Soc. 112 (1990) 2298;
(e) P. Legzins, E.C. Phillips, L. Sanchez, Organometallics 8 (1989)
940.
[3] (a) J.H. Wengrovius, J. Sancho, R.R. Schrock, J. Am. Chem. Soc.
103 (1981) 3932;
[15] D.M. Hoffman, D.A. Wierda, J. Am. Chem. Soc. (1990) 7056.
[16] M.L. Cajigal, K.A. Abboud, J.M. Boncella, Organometallics 15
(1996) 1905.
(b) J. Sancho, R.R. Schrock, J. Mol. Catal. 15 (1982) 75;
(c) L.G. McCullough, R.R. Schrock, J. Am. Chem. Soc. 106
(1984) 4067;
[17] T.K.G. Erikson, J.M. Mayer, Angew. Chem., Int. Ed. Engl. 27
(1988) 1527.
(d) S.F. Pedersen, M.R. Churchill, H. Wasserman, R.R. Schrock,
J. Am. Chem. Soc. 104 (1982) 6808;
[18] (a) J.H. Oskam, R.R. Schrock, J. Am. Chem. Soc. 115 (1993) 11831;
(b) W.J. Feast, V.C. Gibson, K.J. Ivin, A.M. Kenwright, E.
Khosravi, J. Chem. Soc., Chem. Commun. (1994) 1399;
(c) J.H. Oskam, R.R. Schrock, J. Am. Chem. Soc. 114 (1992)
10680;
(e) L.G. McCullough, J.C. Dewan, J.C. Murdezk, R.R. Schrock,
J. Am. Chem. Soc. 107 (1985) 5987.
[4] K. Weiss, U. Schubert, R.R. Schrock, Organometallics 5 (1986)
397.
(d) J.H. Oskam, R.R. Schrock, J. Am. Chem. Soc. 114 (1992)
7588;
[5] J.H. Freudenberger, R.R. Schrock, Organometallics 5 (1986) 398.
[6] (a) R.R. Schrock, Acc. Chem. Res. 19 (1986) 342;
(b) S.M. Rocklage, M.R. Churchill, H.J. Wasserman, R.R.
Schrock, Organometallics 1 (1982) 1332;
(e) R. Toreki, R.R. Schrock, W.M. Davis, J. Am. Chem. Soc. 114
(1992) 3367.