Metallacyclopentane formation: A deactivation pathway for a tungsten(VI) alkylidene complex in olefin metathesis reactions

Article abstract of DOI:10.1021/om9708283

W(NPh)[o-(Me₃SiN)₂C₆H₄](CH ₂CMe₃)₂, 2h, is quantitatively converted to a new metalla-cyclopentane complex, W(CH₂CH₂CH₂CH₂)(NPh)[o-(Me ₃SiN)₂C₆H₄], 4, upon the addition of ethylene at T > 70 °C. The complex W(CH₂CH₂CH₂CH₂)(NPh)[o-(Me ₃SiN)₂C₆H₄], 4, was also formed by the transmetalation reaction of W(NPh)[o-(Me₃SiN)₂C₆H₄](Cl) ₂ with the corresponding Grignard reagent, BrMg(CH₂)₄MgBr, and also when W(NPh)[o-(Me₃SiN)₂C₆H₄]-(PMe ₃)(=C(H)t-Bu), 3, reacts with ethylene. Mechanistic studies suggest that 2h and 3 react with ethylene through a common base-free alkylidene intermediate which undergoes metathesis with ethylene and then generates a W(IV) intermediate which is converted to 4 by coupling two molecules of ethylene. This reaction is a deactivation pathway when 3 is used as an olefin metathesis catalyst for terminal olefins because ethylene is generated during the reaction. The tungsten(IV) complex W(NPh)[o-(Me₃SiN)₂C₆H₄](PMe ₃)₂(η²-C₂H₄), 5, was observed during the reaction between 3 and ethylene. Complex 5 can also be synthesized from the diethyl complex W(NPh)[o-(Me₃SiN)₂C₆H₄](CH ₂CH₄)₂, 2b, in the presence Of PMe₃. Addition of excess ethylene to 5 gives 4. The X-ray structure of 4 was determined.

Full text of DOI:10.1021/om9708283

2628
Organometallics 1998, 17, 2628-2635
Meta lla cyclop en ta n e F or m a tion : A Dea ctiva tion
P a th w a y for a Tu n gsten (VI) Alk ylid en e Com p lex in
Olefin Meta th esis Rea ction s
Shu-Yu S. Wang, Daniel D. VanderLende, Khalil A. Abboud, and
J ames M. Boncella*
Department of Chemistry and Center for Catalysis, University of Florida,
Gainesville, Florida 32611
Received September 22, 1997
W(NPh)[o-(Me3SiN)2C6H4](CH2CMe3)2, 2h , is quantitatively converted to a new metalla-
cyclopentane complex, W(CH2CH2CH2CH2)(NPh)[o-(Me3SiN)2C6H4], 4, upon the addition of
ethylene at T > 70 °C. The complex W(CH2CH2CH2CH2)(NPh)[o-(Me3SiN)2C6H4], 4, was
also formed by the transmetalation reaction of W(NPh)[o-(Me3SiN)2C6H4](Cl)2 with the
corresponding Grignard reagent, BrMg(CH2)4MgBr, and also when W(NPh)[o-(Me3SiN)2C6H4]-
(PMe3)(dC(H)t-Bu), 3, reacts with ethylene. Mechanistic studies suggest that 2h and 3 react
with ethylene through a common base-free alkylidene intermediate which undergoes
metathesis with ethylene and then generates a W(IV) intermediate which is converted to 4
by coupling two molecules of ethylene. This reaction is a deactivation pathway when 3 is
used as an olefin metathesis catalyst for terminal olefins because ethylene is generated during
the reaction. The tungsten(IV) complex W(NPh)[o-(Me3SiN)2C6H4](PMe3)2(η2-C2H4), 5, was
observed during the reaction between 3 and ethylene. Complex 5 can also be synthesized
from the diethyl complex W(NPh)[o-(Me3SiN)2C6H4](CH2CH3)2, 2b, in the presence of PMe3.
Addition of excess ethylene to 5 gives 4. The X-ray structure of 4 was determined.
In tr od u ction
of this class of d0 dialkyl complexes. For example, the
alkylidene complex W(NPh)[o-(Me3SiN)2C6H4](CHCMe3)-
(PMe3), 3, can be synthesized via an R-H abstraction
when 2h is heated in the presence of PMe3.1c,3
Recent work1,2 in our group has successfully used
N,N′-bis (trimethylsilyl)-o-phenylenediamide, [o-(Me3-
SiN)2C6H4]2-, TMS2pda, as an ancillary ligand for a
variety of tungsten(VI) complexes. The facile synthesis
of W(NPh)R2[o-(Me3SiN)2C6H4], 2(a -j), from W(NPh)-
Cl2[o-(Me3SiN)2C6H4], 1, (eq 1) for a wide range of alkyl
In this paper, we report that the reaction of 2h or 3
with ethylene results in the formation of a metallacy-
clopentane complex via an olefin metathesis initiated
pathway. Mechanistic aspects of the transformation of
3 into the metallacyclopentane complex W(CH2CH2CH2-
CH2)(NPh)[o-(Me3SiN)2C6H4], 4, are discussed, and the
reaction is shown to proceed through the W(IV) ethylene
complex W(C2H4)(NPh)[o-(Me3SiN)2C6H4](PMe3)2, 5. The
formation of a metallacyclopentane complex when 3
reacts with ethylene is the likely deactivation pathway
for 3 when 3 is used as a catalyst for the metathesis of
terminal olefins. Compounds 4 and 5 have been isolated
and structurally characterized by single-crystal X-ray
diffraction techniques.
Resu lts a n d Discu ssion
Rea ction of 2h w ith Eth ylen e. We have demon-
strated that the thermolysis reaction of complex 2h in
the presence of PMe3 at 80 °C affords the alkylidene
complex W(NPh)[o-(Me3SiN)2C6H4](CHCMe3)(PMe3), 3,
which has proven to be a catalyst precursor for ring-
opening metathesis polymerization (ROMP) of nor-
bornene and cyclooctene.1c,d In contrast, complex 2a
forms an adduct W(NPh)[o-(Me3SiN)2C6H4](Me)2(PMe3)
upon the addition of PMe3 but undergoes no further
reaction in the presence of PMe3 even under more
vigorous conditions. Although complex 2a does not
groups has allowed us to begin to explore the chemistry
(1) (a) Wang, S.-Y. S.; Abboud, K. A.; Boncella, J . Am. Chem. Soc.
1997, 119, 11990. (b) Huff, R. L.; Wang, S.-Y. S.; Abboud, K. A.;
Boncella, J . M. Organometallics 1997, 16, 1779. (c) VanderLende, D.
D.; Abboud, K. A.; Boncella, J . M. Organometallics 1994, 13, 3378. (d)
VanderLende, D. D.; Abboud, K. A.; Boncella, J . M. Polym. Prepr. 1994,
35, 691.
(2) Boncella, J . M.; Wang, S.-Y. S.; VanderLende, D. D.; Huff, R. L.;
Vaughan, W. M.; Abboud, K. A. J . Organomet. Chem. 1997, 530, 59.
(3) Vaughan, W. M.; Abboud, K. A.; Boncella, J . M. J . Am. Chem.
Soc. 1995, 117, 11015.
S0276-7333(97)00828-5 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/21/1998

Metallacyclopentane Formation
Organometallics, Vol. 17, No. 12, 1998 2629
Ta ble 1. Cr ysta llogr a p h ic a n d Da ta Collection
P a r a m eter s for W(NP h )[o- (Me3SiN)2C6H4]-
(CH2CH2CH2CH2), 4, a n d
react with ethylene, complex 2h reacts with ethylene
at 80 °C to form the metallacyclopentane complex
W(CH2CH2CH2CH2)(NPh)[o-(Me3SiN)2C6H4], 4, with
the loss of neopentane and tert-butylethylene (eq 2).
W(NP h )[o-(Me3SiN)2C6H4](P Me3)2(η2-C2H4), 5
5
4
A. Crystal Data (173 K)
36.2551(8)
13.5914(4)
13.9794(4)
90.0
a, Å
b, Å
c, Å
10.3249(1)
18.1030(2)
13.8308(2)
103.210(1)
2516.73(5)
1.535
â, deg
V, Å3
6888.5(3)
d
calc, g cm-3 (173 K) 1.450
empirical formula
fw
C
26H49N3P2Si2W‚1/2C7H8 C22H35N3Si2W
751.72
581.56
cryst system
space group
Z
orthorhombic
Pbcn
8
monoclinic
P21/n
4
1160
0.45 × 0.34 × 0.06
F(000), electrons
3064
cryst size (mm3)
0.44 × 0.38 × 0.10
B. Data Collection (173 K)
radiation, λ (Å)
mode
scan width and rate
2θ range, deg
range of hkl
Mo KR, 0.710 73
ω-scan
0.3 deg/frame and 30 s/frame
3-55
3-55
-24 e h e 50 -12 e h e 12
-11 e k e 18 0 e k e 23
-19 e l e7 0 e l e 17
12 840
tot. reflcns measd
unique reflcns
27 782
7881
Syn th esis of 4. The metallacyclopentane complex
4 was synthesized independently on a preparative scale
by allowing the dichloride complex W(NPh)[o-(Me3-
SiN)2C6H4](Cl)2, 1, to react with BrMg(CH2)4MgBr (eq
3).4 Compound 4 was characterized by NMR spectros-
5197
abs coeff, µ(Mo KR), 3.539
4.697
mm-1
C. Structure Refinement
refinement method
full-matrix least-squares on F2
S, goodness-of-fita
no. of variables
R1/reflcnsa
1.20
341
1.06
253
3.80/7180 > 2σ(I)
8.27/7784
3.34
3.49/4443 > 2σ(I)
8.11/5144
6.22
wR2/reflcnsa
Rint (%)
max shift/esd
min peak in diff
Four. map (e Å-3
max peak in diff
Four. map (e Å-3
0.001
-2.32
0.001
-1.38
)
)
1.19
0.92
R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]1/2
.
+
a
S ) [∑[w(Fo - Fc2)2]/(n - p)]1/2. w ) 1/[σ2(Fo2) + (0.0370p)2
2
0.31p], p ) [max(Fo2,0) + 2Fc2]/3.
copy and via a single-crystal X-ray diffraction study. The
1H NMR spectrum of 4 in benzene-d6 displays broad
resonances with unresolved fine structure that are
assigned to the CH2 protons of the metallacycle ring at
2.93, 2.91, 2.42, and 1.54 ppm, respectively, in a 2:2:2:2
ratio. The trimethylsilyl protons were observed as a
sharp singlet at 0.28 ppm, as is consistent with a square
pyramidal geometry in which a mirror plane contains
the imido ligand and tungsten atom and bisects the
N-W-N and C-W-C angles. The 13C{1H} NMR of 4
1
displays resonances at δ 61.25 (1J W-C ) 73.6 Hz, J C-H
) 122.9 Hz) and δ 35.23 (1J C-H ) 124.3 Hz) that are
assigned to CR and Câ of the metallacycle, respectively.
The 13C spectral parameters are similar to known
tungstacyclopentane complexes.5
A single crystal of 4 suitable for an X-ray structure
determination was grown by cooling a pentane solution
to -20 °C. General data collection and refinement data
are listed in Table 1. A thermal ellipsoid plot of complex
4 along with the atom-labeling scheme is given in Figure
1, while selected bond lengths and angles are presented
in Table 2. The coordination geometry around the W
atom is that of a slightly distorted square pyramid. In
this structure, the imido N occupies the axial site while
the N atoms of the TMS2pda ligand and the C atoms of
F igu r e 1. Molecular structure of W(NPh)[o-(Me3-
SiN)2C6H4](CH2CH2CH2CH2), 4, with 50% probability el-
lipsoids and showing the atom-numbering scheme. All
hydrogen atoms are omitted for clarity. The metallacyclo-
pentane ring is disordered by the flipping of the five-
membered ring, denoted by W-C(1)-C(2)-C(3)-C(4) and
W-C(1)-C(2′)-C(3′)-C(4).
(4) The Grignard reagent, BrMg(CH2)4MgBr, was obtained by
reacting Br(CH2)4Br (purchased from Aldrich) with Mg metal.
(5) Chisholm, M. H.; Huffman, J . C.; Hampden-Smith, M. J . J . Am.
Chem. Soc. 1989, 111, 5284.
the metallacyclopentane group form the basal plane.
The tungsten atom resides 0.717 Å above the plane
defined by N(1), N(2), C(1), and C(4) (mean deviation is

2630 Organometallics, Vol. 17, No. 12, 1998
Wang et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for W(NP h )[o-
(Me3SiN)2C6H4](CH2CH2CH2CH2), 4
W-N(1)
W-N(2)
W-N(3)
2.023(4)
2.004(4)
1.736(4)
W-C(1)
W-C(4)
2.182(5)
2.183(5)
N(1)-W-N(2)
N(1)-W-N(3)
N(1)-W-C(1)
N(1)-W-C(4)
N(2)-W-N(3)
N(2)-W-C(1)
84.1(2)
118.1(2)
86.3(2)
138.4(2)
119.5(2)
139.3(2)
N(2)-W-C(4)
N(3)-W-C(1)
N(3)-W-C(4)
C(1)-W-C(4)
C(11)-N(3)-W
85.5(2)
99.8(2)
102.0(2)
76.1(2)
174.0(3)
0.001 Å). The W-C(1) and W-C(4) bond lengths
(2.182(5), 2.183(5) Å, respectively) are within the range
expected for W(VI)-C distances.2,6 The W-Nimido bond
length is 1.736(4) Å and is consistent with a W-N triple
bond.7,8 The geometry about the N atoms of the [o-(Me3-
SiN)2C6H4]2- ligand is planar as is observed in silyl-
amines.9 The ligand is folded about the N-N vector
which causes the SiMe3 groups to be displaced above
the basal plane. The folding of the ligand also tilts the
N coordination planes by 60-65° relative to the basal
plane of the molecule.
The formal electron count at the metal center could
be as high as 18e- if both sets of nitrogen lone pairs of
the [o-(Me3SiN)2C6H4]2- ligand can be donated to the
metal center. Donation of both amide lone pairs is not
possible since there are only three d orbitals that are of
the proper symmetry to form π bonds with the ligands.
Given that the dxz and dyz orbitals form the π bonds with
the imido group, only the dxy orbital is available to
overlap with the N π electrons on the diamido ligand.
Thus, the maximum electron count at the metal center
is 16e-. Furthermore, the structure of 4 shows that the
folding of the diamide ligand brings the p orbitals on
the nitrogen atoms to within only ca. 25-30° of the xy
plane, preventing efficient overlap between the dxy
orbital and the N lone pairs. The structural constraints
imposed by the chelating nature of the [o-(Me3-
SiN)2C6H4]2- ligand lead us to suggest that 4 and the
other square pyramidal dialkyl complexes2 are best
described as 14e- or at most 16e- compounds.
ethylene protons, while the two equivalent PMe3 protons
are reasponsible for the resonance at 1.05 ppm. The
trimethylsilyl protons are observed as two broad peaks
at 0.28 and 0.61 ppm, indicating their chemical in-
equivalence. The gated, coupled, 13C NMR spectrum
reveals a triplet resonance at 36 ppm corresponding to
1
the ethylene carbon atoms with J C-H ) 156 Hz,
indicating some “metallacyclopropane” character.10
The structure of complex 5 was verified by a single-
crystal X-ray diffraction study. A thermal ellipsoid plot
of 5 with the atom-labeling scheme is given in Figure
2, while selected bond lengths and angles are presented
in Table 3. The coordination geometry around the W
atom is that of a slightly distorted octahedron. In this
structure, the imido nitrogen atom and one of the amide
nitrogen atoms occupy trans sites, while the phosphines
are also trans with respect to each other. The W-Nimido
bond length is 1.784(4) Å and is consistent with a W-N
triple bond making 5 an 18e- complex.7,8 The W-N(1)
and W-N(2) bond lengths (2.154(4), 2.160(3) Å) are
essentially the same which is surprising since this
implies that the imido group does not exert a significant
trans influence on the W-N(1) bond. It appears that
the steric bulk of the two trimethylphosphine ligands
prevents an asymmetric approach of the amido N atoms
to the W center causing an increase in the expected
W-N(2) bond length.
Syn th esis of 5. The W(IV) ethylene complex, 5, an
intermediate observed in the reaction of 3 with ethylene,
was synthesized independently on a preparative scale
by allowing the diethyl complex W(NPh)[o-(Me3-
SiN)2C6H4](CH2CH3)2, 2b, to react with trimethylphos-
A comparison of the W-Namide bond lengths in 5 with
the six coordinate dialkyl complex W(NPh)(CH3)2[o-
(Me3SiN)2C6H4](PMe3) reveals that W-N(2) in 5 is 0.1
Å longer that the W-Namide bonds (both cis to the imido
group) in W(NPh)(CH3)2[o-(Me3SiN)2C6H4](PMe3).2 The
related five coordinate complex, 2h , has a trigonal
bipyramidal structure with axial imido and amide
groups, while one amide and the two neopentyl groups
occupy the equatorial plane. The axial W-Namide and
equatorial W-Namide lengths2 are 1.98 and 2.13 Å,
respectively, and suggest that in the absence of other
steric influences, the strong trans influence of the imido
1
phine (eq 4).1a In the H NMR spectrum of 5, the two
multiplets at 1.96 and 2.19 ppm are assigned the
(6) (a) Churchill, M. R.; Youngs, W. J . Inorg. Chem. 1979, 18, 2454.
(b) Fischer, J .; Kress, J .; Osborn, J . A.; Ricard, L.; Wesolek, M.
Polyhedron 1987, 6, 1839. (c) Zhang, C.; Schlemper, E. O.; Schrauzer,
G. N. Organometallics 1990, 9, 1016. (d) Eagle, A. A.; Young, C. G.;
Tiekink, E. R. T. Organometallics 1992, 11, 2934. (e) 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.;
Kruger, C.; Betz, P. Organometallics 1990, 9, 2262. (f) Fletcher, S. R.;
Skapski, A. C. J . Organomet. Chem. 1973, 59, 299. (g) Faller, J . W.;
Kucharczyk, R. R.; Ma, Y. Inorg. Chem. 1990, 29, 1662. (h) Legzdins,
P.; Phillips, E. C.; Rettig, S. J .; Trotter, J .; Veltheer, J . E.; Yee, V. C.
Organometallics 1992, 11, 3104. (i) van der Schaaf, P. A.; Abbenhuis,
R. A. T. M.; Grove, D. M.; Smeets, W. J . J .; Spek, A. L.; van Koten, G.
J . Chem. Soc., Chem. Commun. 1993, 504.
group results in very different W-N
distances.
amide
The ethylene group coordinates cis to the imido
ligand, as observed in other d2 ethylene complexes that
have imido coligands reported by Schrock11 and Niel-
(7) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds;
Wiley: New York, 1988.
(8) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239.
(10) Visciglio, V. M.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc.,
Chem. Commun. 1992, 1505.
(11) Rocklage, S. M.; Schrock, R. R. J . Am. Chem. Soc. 1982, 104,
3077.
(9) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C.
Metal and Metalloid Amides; J ohn Wiley: New York, 1980; pp 244-
249.

Metallacyclopentane Formation
Organometallics, Vol. 17, No. 12, 1998 2631
F igu r e 3. Partial 1H NMR spectrum of W(NPh)[o-Me3-
SiN)2C6H4](CHtBuCH2CH2), 8 (300 MHz, room tempera-
ture, benzene-d6, *’s indicate five ring protons).
Figu r e 2. Molecular structure of W(NPh)[o-(Me3SiN)2C6H4]-
(η2-C2H4)(PMe3)2, 5, with 50% probability ellipsoids and
showing the atom-numbering scheme. All hydrogen atoms,
except those on the η2-ethylene, are omitted for clarity.
complexes that have been structurally character-
ized.12b,13c,e
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for W(NP h )[o-
Mech a n ism of th e F or m a tion of 4 fr om 2h a n d
3. The observation that the reaction between 2h and
ethylene produces neohexene and neopentane along
with 4 suggested to us that the formation of 4 is likely
to proceed through a metathetical pathway. This is
reasonable because neopentane is the product of R-H
abstraction to form a neopentylidene complex and
neohexene is the first product formed when a neopen-
tylidene complex undergoes productive metathesis with
ethylene. Previously,3 we had established that, upon
heating complex 2h , R-H abstraction to form the base
free neopentylidene complex is the predominant reaction
pathway. In the presence of PMe3, complex 3 is isolated,
while in the absence of PMe3 a reversible metalation of
one of the Me3Si groups of the o-(Me3SiN)2C6H4 ligand
occurs.3 Given that 3 is readily synthesized and isolated
and that dissociation of PMe3 from 3 in solution is a
rapid process, we examined the reaction between 3 and
ethylene in order to determine whether complex 4 would
be formed.
(Me3SiN)2C6H4](P Me3)2(η2-C2H4), 5
W-N(1)
W-N(2)
W-N(3)
W-P(1)
2.154(4)
2.160(3)
1.784(4)
2.562(1)
W-P(2)
W-C(1)
W-C(2)
C(1)-C(2)
2.564(1)
2.234(5)
2.223(5)
1.434(6)
N(1)-W-N(2)
N(1)-W-N(3)
N(1)-W-P(1)
N(1)-W-P(2)
N(1)-W-C(1)
N(1)-W-C(2)
N(2)-W-N(3)
N(2)-W-P(1)
N(2)-W-P(2)
N(2)-W-C(1)
N(2)-W-C(2)
78.60(14)
175.9(2)
89.66(10)
86.26(10)
87.7(2)
N(3)-W-P(1)
N(3)-W-P(2)
N(3)-W-C(1)
N(3)-W-C(2)
P(1)-W-P(2)
P(1)-W-C(1)
P(1)-W-C(2)
P(2)-W-C(1)
P(2)-W-C(2)
C(1)-W-C(2)
C(21)-N-W
94.40(12)
89.64(12)
91.2(2)
89.8(2)
170.27(4)
113.19(13)
75.92(13)
75.50(13)
113.00(13)
37.5(2)
91.8(2)
101.2(2)
84.42(10)
86.12(10)
157.8(2)
158.2(2)
170.3(3)
son.12 The ethylene ligand is oriented with the C atoms
in the W-P-N(2)-P plane in order to maximimize
back-donation from the dxy orbital to the ethylene π*
orbital. The observation of two resonances for the
1
ethylene protons in the H NMR spectrum of 5 at room
When 3 was allowed to react with ethylene at room
temperature in an NMR tube, an intermediate, W(CHt-
BuCH2CH2)(NPh)[o-(Me3SiN)2C6H4], 8, was observed
before any neohexene was produced. The 1H NMR
spectrum of 8 (Figure 3) shows five multiplet resonances
at 0.39, 0.71, 2.45, 2.61, and 3.75 ppm in a 1:1:1:1:1
ratio, which account for the five ring-protons of the
metallacycle. In the 13C{1H} NMR spectrum, three
singlets were observed at 77.6 (J W-C ) 56 Hz), 38.8
(J W-C ) 49.4 Hz), and 25.1 ppm which are assigned to
the metallacycle carbon atoms. Further investigation
by 2D NMR (1H-1H homonuclear and 13C-1H hetero-
nuclear correlation experiments) has allowed us to
assign all the proton and carbon resonances of 8. The
proton at 0.39 ppm is attached to CR (77.6 ppm, tert-
butyl-substituted carbon), the two multiplets at 0.71 and
2.45 ppm arise from the protons bonded to CR′ (38.8
ppm), and the most downfield protons at 2.61 and 3.75
ppm are assigned as the â-protons of the metallacy-
clobutane ring. The observation that the â-protons
appear at the most downfield chemical shifts is consis-
temperature is consistent with slow rotation of the
ethylene and indicates that a strong π bond exists
between W and ethylene. The C(1)-C(2) bond length,
1.434(6) Å, is in the middle of the range of C-C bond
lengths observed in other d2 olefin complexes,13 while
the W-C(1) and W-C(2) bond lengths of 2.234(5) and
2.223(5) Å are similar to those of other W(IV) olefin
(12) (a) Clark, G. R.; Nielson, A. J .; Richard, C. E. F.; Ware, D. C.
J . Chem. Soc., Dalton Trans. 1990, 1173. (b) Clark, G. R.; Nielson, A.
J .; Richard, C. E. F.; Ware, D. C. J . Chem. Soc., Chem. Commun. 1989,
1343.
(13) (a) Rietveld, M. H. P.; Teunissen, W.; Hagen, H.; ven de Water,
L.; Grove, D. M.; van der Schaaf, P. A.; Mu¨hlebach, A.; Kooijman, H.;
Smeets, W. J . J .; Veldman, N.; Spek, A. L.; van Koten, G. Organome-
tallics 1997, 16, 1674. (b) Ferna´ndez, F. J .; Go´mez-Sal, P.; Maneanero,
A.; Royo, P.; J acobson, H.; Berke, H. Organometallics 1997, 16, 1553.
(c) Fanwick, P. E.; Rothwell, I. P.; Kriley, C. E. Polyhedron 1996, 15,
2403. (d) Wehman-Ooyevaar, I. C. M.; Kapteijn, G. M.; Grove, D. M.;
Smeets, W. J . J .; Spek, A. L.; van Koten, G. J . J . Chem. Soc., Dalton
Trans. 1994, 703. (e) Su, F.-M.; Cooper, C.; Geib, S. J .; Rheingold, A.
L.; Mayer, J . M. J . Am. Chem. Soc. 1986, 108, 3545. (f) Cohen, S. A.;
Auburn, P. R.; Bercaw, J . E. J . Am. Chem. Soc. 1983, 105, 1136. (g)
Schultz, A. J .; Brown, R. K.; Williams, J . M.; Schrock, R. R. J . Am.
Chem. Soc. 1981, 103, 169. (h) Guggenberger, L. J .; Meakin, P.; Tebbe,
F. N. J . Am. Chem. Soc. 1974, 96, 5420.

2632 Organometallics, Vol. 17, No. 12, 1998
Wang et al.
Sch em e 1
tent with observations on similar metallacyclobutane
complexes.14
is an attractive mechanistic pathway. Thus, we have
not observed the formation of propene during the
reaction of 3 with ethylene under any conditions.
In the presence of excess ethylene, both 9 and 5 are
converted to the more stable metallacyclopentane com-
plex W(CH2CH2CH2CH2)(NPh)[(Me3SiN)2C6H4], 4 (>95%
by NMR). The formation of complex 4 arises from the
oxidative coupling of 2 equiv of ethylene to the tungsten-
(IV) complex.15 The relative concentrations of all the
intermediates as a function of time is shown in Figure
4. In a separate experiment, complex 5 was cleanly
converted to 4 within several days, upon the addition
of ethylene. This suggests that the formation of 4 from
3 is inevitable in the presence of ethylene.
To investigate the reversiblilty of the formation of 4
from 5, 4 was allowed to react with trimethylphosphine.
No reaction was observed within a few days at room
temperature. However, when the reaction mixture was
heated to 90 °C, 4 was slowly (60% conversion after 10
days; 91% after 30 days) converted to 5 with the loss of
ethylene (eq 5). This experiment clearly shows the
Attempts to synthesize and isolate complex 8 on a
preparative scale were thwarted by the instability of 8
in solution. While crude 8 could be isolated as a solid
by removing the solvent and PMe3 under reduced
1
pressure, the H NMR spectrum of this material (C6D6
solution) revealed that 8 readily loses ethylene or
neohexene to generate the metalated complex 6 or the
unsubstituted metallacyclobutane complex, 9, respec-
tively. Presumably, loss of ethylene gives the base free
neopentylidene complex which rapidly metalates (Scheme
1), while loss of neohexene leads to 9 via an intermediate
methylidene complex which is scavenged by the ethyl-
ene produced in the formation of 6.
When complex 3 was allowed to react with an excess
of ethylene at room temperature for 4 days, two products
were observed in a 44:56 ratio by 1H NMR spectroscopy.
One set of peaks (44%) were found at 3.89 (m, 2HR), 2.86
(m, 1Hâ), 2.90 (m, 1Hâ), and 2.59 (m, 2HR) ppm and were
assigned to the metallacyclobutane W(NPh)[(Me3-
SiN)2C6H4](CH2CH2CH2), 9. The structure of 9 is either
square pyramidal or the compound is undergoing a
rapid interconversion between square pyramidal and
trigonal bipyramidal geometries because only one sin-
glet was observed at 0.31 ppm for the trimethylsilyl
groups.
(5)
The other set of peaks (56%) were observed at 1.94
(2H) and 2.17 (2H) ppm. This product was shown to be
the tungsten(IV) complex W(NPh)[o-(Me3SiN)2C6H4]-
(PMe3)2(η2-C2H4), 5, by comparison with the spectrum
of an authentic sample which was obtained from the
reaction between 2b and excess PMe3 (as described
above). We propose that the unstable methylidene
complex undergoes bimolecular coupling of methylidene
ligands to give ethylene and a tungsten(IV) complex,
which then was trapped by phosphines and ethylene to
form compound 5 (Scheme 2). Formation of a W(IV)
intermediate from 9 via a â-H elimination/reductive
elimination process does not appear to occur though it
preferential formation of the W(VI) metallacyclopentane
product. The fact that compound 2a does not react with
ethylene even at elevated temperatures provides further
indirect evidence that the formation of 4 from 2h
proceeds through a neopentylidene intermediate.
Experiments using 3 as a metathesis catalyst for
1-pentene (40 equiv) show 90% conversion to 4-octene
after 8 h at 80 °C as well as the formation of neohexene
and 4 as the only observable metal-containing product.
This is to be expected since the productive metathesis
(14) (a) Feldman, J .; Davis, W. M.; Thomas, J . K.; Schrock, R. R.
Organometallics 1990, 9, 2535. (b) Schrock, R. R.; Murdzek, J . S.;
Bazan, G. C.; DiMare, M.; O’Regan, M. J . Am. Chem. Soc. 1990, 112,
3875.
(15) (a) McLain, S. J .; Wood, C. D.; Schrock, R. R. J . Am. Chem.
Soc. 1979, 101, 4558. (b) Grubbs, R. H.; Miyashita, A. J . Am. Chem.
Soc. 1978, 100, 7416.

Metallacyclopentane Formation
Organometallics, Vol. 17, No. 12, 1998 2633
Sch em e 2
pathway. Recently, we have demonstrated that the
mechanism of â-H transfer in the diethyl complex, 2b,
involves direct â-H abstraction,1a rather than â-H
elimination. It is possible that complex 4 does not
undergo decomposition via â-hydride transfer because
the geometric constraints of the metallacyclopentane
ring prevent the molecule from achieving the transition
state necessary to effect transfer of a â-H atom directly
to a carbon that is bound to the metal. As a result, the
reactivity of 4 is apparently limited to disruption of the
metallacyclopentane structure by expulsion of ethylene
and reduction of the metal center.
Con clu sion s
The observation that ethylene reacts with the bis-
(neopentyl) complex, 2h , at elevated temperatures to
give the metallacyclopentane complex, 4, is consistent
with the proposal that this reaction actually occurs
through a neopentylidene complex which is generated
in situ during the reaction. The formation of 4 in the
reaction of W(NPh)[o-(Me3SiN)2C6H4](CHCMe3)(PMe3),
3, with ethylene confirms this proposal because 3 is an
effective source of base free alkylidene through the
dissociation of PMe3. The conversion of the unsubsti-
tuted metallacyclobutane complex, 9, to the W(IV)
ethylene complex appears to proceed through the me-
thylidene complex, 10, and probably through a W(IV)
intermediate both of which are not observed.
F igu r e 4. Relative amounts of 3-5, 8, and 9 as a function
of time during thermolysis of 3 in the presence of ethylene.
of terminal olefins always gives ethylene as one of the
products. Thus, the ethylene that is produced reacts
with 3 or other alkylidene complexes that are formed
during the reaction and effectively deactivates the
catalyst system by converting all of the W complexes in
the system to 4 which is inactive for further metathesis.
It is worthwhile to note that the formation of 1-butene
was not observed when 4 was heated to its decomposi-
tion temperature (ca. 150 °C). The formation of 1-butene
from metallacyclopentanes of Pt,16 Ti,17 and Ta18 has
been reported to occur via a â-hydride elimination
In related chemistry, a dimeric Mo(IV) complex has
been isolated from the reaction of Mo[N(2,6-i-Pr2C6H3)]-
[OCMe3]2(C(H)CMe3) with ethylene.19 The precursor of
this Mo(IV) complex was proposed to be a Mo(VI)
methylidene which reductively coupled giving ethylene
(16) (a) McDermott, J . X.; White, J . F.; Whitesides, G. M. J . Am.
Chem. Soc. 1976, 98, 6521. (b) McDermott, J . X.; White, J . F.;
Whitesides, G. M. J . Am. Chem. Soc. 1973, 95, 4451.
(17) (a) McDermott, J . X.; Wilson, M. E.; Whitesides, G. M. J . Am.
Chem. Soc. 1976, 98, 6529. (b) McDermott, J . X.; Whitesides, G. M. J .
Am. Chem. Soc. 1974, 96, 947.
(18) McLain, S. J .; Sancho, J .; Schrock, R. R. J . Am. Chem. Soc.
1980, 102, 5610.
(19) Robbins, J .; Bazan, G. C.; Murdzek, J . S.; O’Regan, M. B.;
Schrock, R. R. Organometallics 1991, 10, 2902.

2634 Organometallics, Vol. 17, No. 12, 1998
Wang et al.
J C-H ) 121.4 Hz); 26.70 (-CH2CH2CH3, J C-H ) 132.2 Hz);
69.29 (-CH2CH2CH3, J C-H ) 113.1 Hz); 122.36, 124.08, 125.04,
125.77, 128.64, 134.48, 156.42 (aromatic).
and the observed dimeric Mo(IV) product. Changing the
alkoxide ligands to OCMe(CF3)2 allowed the observation
of an unstable metallacyclopentane complex, Mo(CH2-
CH2CH2CH2)[N(2,6-iPr2C6H3)][OCMe(CF3)2]2.19 A simi-
lar process is possible in the present case, only the
increased stability of W(VI) vs Mo(VI) facilitates the
formation and isolation of the metallacyclopentane
complex, 4, via the oxidative coupling of two molecules
of ethylene. Because PMe3 is present in the system
when 3 reacts with ethylene, the W(IV) PMe3-olefin
complex, 5, is also initially formed. The conversion of
5 to 4 is somewhat surprising since it involves loss of
PMe3 in favor of coordination of ethylene; however, it
is clear that stability of W(VI) relative to W(IV) is the
driving force for the formation of 4.
The formation of 4 from the alkylidene, 3, also
provides an explanation for the deactivation of 3 when
3 is used as an initiatior for the metathesis of terminal
olefins. When terminal olefins undergo metathesis,
ethylene is always produced. The presence of ethylene
thereby provides a facile path for the deactivation of 3
via the formation of 4. We would expect that metalla-
cyclopentane formation would be most likely to occur
when third-row transition metals are used as metath-
esis catalysts because of the propensity of these metals
to form stable, high oxidation state complexes.
P r ep a r a t ion of W(NP h )[o-(Me3SiN)2C6H 4](CH 2CH -
(CH3)2)2, 2d . W(NPh)[o-(Me3SiN)2C6H4](Cl)2 (1.2 g, 2.01 mmol)
was dissolved Et2O (100 mL) and cooled to -78 °C. Two
equivalents of i-BuMgCl (2.01 mL, 4.02 mmol; 2.0 M solution
in Et2O) were then added by a syringe. The reaction was
allowed to warm to room temperature and was stirred for 1
h, during which time a brown color appeared and salts
precipitated. The solvent was then removed under reduced
pressure, and the remaining brown-black oil was dried under
reduced pressure for 3 h. The oil was then extracted with
pentane and filtered by filter cannula until the filtrate was
almost clear. The solution was concentrated to about 10 mL
and cooled to -78 °C for 3 h. The resulting golden-brown solid
was isolated by filtration and was dried under reduced
pressure for 1 h to yield 0.78 g of 2d as a brown crystalline
solid. Yield: 63.7%. 1H NMR (C6D6, δ): 0.33 (s, 18H,
-Si(CH3)3); 0.93 (d, 6H, -CH2CH(CH3)2); 1.10 (d, 6H, -CH2-
CH(CH3)2); 1.72 (m, 2H, -CH2CH(CH3)2); 1.94 (m, 2H, -CH2-
CH(CH3)2); 2.55 (m, 2H, -CH2CH(CH3)2); 6.84 (t, 1H, p-NPh-
H); 7.01 (m, 2H, aromatic); 7.12 (t, 2H, m-NPh-H); 7.31 (d,
2H, o-NPh-H); 7.36 (m, 2H, aromatic). 13C{1H} NMR (C6D6,
δ): 2.20 (-Si(CH3)3, J C-H ) 119.3 Hz); 27.33 (-CH2CH(CH3)2,
J C-H ) 125.8 Hz); 29.15 (-CH2CH(CH3)2, J C-H ) 126.5 Hz);
33.73 (-CH2CH(CH3)2, J C-H ) 127.2 Hz); 80.01 (-CH2CH-
(CH3)2); 121.79, 123.60, 125.46, 126.65, 128.62, 133.12, 155.97
(aromatic). Anal. Calcd for C26H45N3Si2W: C, 48.82; H, 7.09;
N, 6.57. Found: C, 48.54; H, 7.11; N, 6.50.
P r epar ation of W(NP h )[o-(Me3SiN)2C6H4](P h )2, 2e. W(N-
Ph)[o-(Me3SiN)2C6H4](Cl)2 (1.0 g, 1.68 mmol) was dissolved in
Et2O (50 mL) and cooled to -78 °C. Two equivalents of
PhMgCl (1.12 mL, 3.36 mmol; 3.0 M solution in Et2O) were
then added by a syringe. The reaction was allowed to warm
to room temperature and was stirred for 2 h, during which
time a brown color appeared and salts precipitated. The
solvent was then removed under reduced pressure, and the
remaining brown-orange solid was dried in vacuo for 3 h. The
solid was then extracted with pentane and filtered by filter
cannula until filtrate was almost clear. The solution was
concentrated to about 10 mL and cooled to -78 °C for 3 h.
The resulting orange solid was isolated by filtration and dried
under reduced pressure for 1 h to yield 0.77 g of 2e as an
orange crystalline solid. Yield: 67.6%. 1H NMR (C6D6, δ):
0.12 (s, 18H, -Si(CH3)3); 6.80-7.66 (19 H overlapping aromatic
protons). Anal. Calcd for C30H37N3Si2W: C, 53.02; H, 5.49;
N, 6.18. Found: C, 52.83; H, 5.44; N, 6.13.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were conducted under
a dry argon atmosphere using standard Schlenk techniques
or were performed in a nitrogen-filled drybox. Diethyl ether
(Et2O) was distilled from sodium benzophenone ketyl. Tolu-
ene, pentane, and hexane were distilled from sodium. The
compounds 1 and 2a ,b,f,h ,j were prepared as described
previously.2 NMR solvents were stored over molecular sieves
and were degassed prior to use. 1H NMR spectra were
measured at 300 MHz on a Varian Gemini 300 or VXR 300
spectrometer with C6D6 and C7D8 as solvents. The chemical
shifts are reported in parts per million downfield from tet-
ramethylsilane (δ ) 0 ppm) and were referenced to residual
C6D5H (δ ) 7.15 ppm) and C7D7H (δ ) 2.09 ppm) as internal
standards. 13C NMR spectra were recorded at 300 MHz on a
Varian Gemini 300 or VXR 300 spectrometer with C6D6 and
C7D8 as solvents, referenced to the central line of the solvents,
and reported relative to tetramethylsilane. Elemental analy-
ses (C, H, N) were performed by Atlantic Microlab, Inc.,
Norcross, GA.
P r epar ation of W(NP h )[o-(Me3SiN)2C6H4](CH2CH2CH3)2,
2c. W(NPh)[o-(Me3SiN)2C6H4](Cl)2 (1.0 g, 1.68 mmol) was
dissolved in Et2O (100 mL) and cooled to -78 °C. Two
equivalents of n-PrMgCl (1.7 mL, 3.4 mmol; 2.0 M solution in
Et2O) were then added by a syringe. The reaction was allowed
to warm to room temperature and was stirred for 1 h, during
which time a brown color appeared and salts precipitated. The
solvent was then removed under reduced pressure, and the
remaining brown-black oil was dried under reduced pressure
for 3 h. The oil was then extracted with pentane and filtered
by filter cannula until the filtrate was almost clear. The
solvent was then removed under reduced pressure, and the
remaining brown oil was dried under reduced pressure for 2
h. Yield: 78%. 1H NMR (C6D6, δ): 0.53 (s, 18H, -Si(CH3)3,
2J Si-H ) 6.6 Hz); 1.30 (t, 6H, -CH2CH2CH3); 1.92 (m, 2H,
-CH2CH2CH3); 2.06 (dt, 2H, -CH2CH2CH3); 2.16 (m, 2H,
-CH2CH2CH3); 2.33 (dt, 2H, -CH2CH2CH3); 7.09 (t, 1H,
p-NPh-H); 7.27 (m, 2H, aromatic); 7.34 (t, 2H, m-NPh-H); 7.53
(d, 2H, o-NPh-H); 7.57 (m, 2H, aromatic). 13C{1H} NMR (C6D6,
δ): 1.49 (-Si(CH3)3, J C-H ) 119.3 Hz); 21.79 (-CH2CH2CH3,
P r ep a r a tion of W(NP h )[o-(Me3SiN)2C6H4](CH2CH2P h )2,
2g. W(NPh)[o-(Me3SiN)2C6H4](Cl)2 (2.0 g, 3.36 mmol) was
dissolved in Et2O (150 mL) and cooled to -78 °C. Two
equivalents of PhCH2CH2MgCl (3.4 mL, 3.4 mmol; 2.0 M
solution in Et2O) were then added by a syringe. The reaction
was allowed to warm to room temperature and was stirred
for 2 h, during which time a brown color appeared and salts
precipitated. The solvent was then removed under reduced
pressure, and the remaining brown-orange solid was dried in
vacuo for 3 h. The solid was then extracted with pentane and
filtered by filter cannula until the filtrate was almost clear.
The solution was concentrated to ca. 10 mL and cooled to -78
°C for 3 h. The resulting orange solid was isolated by filtration
and dried under reduced pressure for 1 h to yield 1.68 g of 2g
as a orange crystalline solid. Yield: 68.2%. 1H NMR (C6D6,
δ): 0.30 (s, 18H, -Si(CH3)3); 2.09 (dt, 2H, -CH2CH2Ph); 2.38
(dt, 2H, -CH2CH2Ph); 2.91 (dt, 2H, -CH2CH2Ph); 3.14 (dt,
2H, -CH2CH2Ph); 6.86 (t, 1H, p-NPh-H); 6.99 (m, 5H, aro-
matic); 7.02 (m, 2H, aromatic); 7.08 (t, 2H, m-NPh-H); 7.15
(m, 5H, aromatic); 7.22 (d, 2H, o-NPh-H); 7.39 (m, 2H,
aromatic). 13C{1H} NMR (C6D6, δ): 1.48 (-Si(CH3)3, J C-H
)
118.3 Hz); 39.65 (-CH2CH2Ph, J C-H ) 123.4 Hz); 65.61 (-CH2-
CH2Ph, J C-H ) 119.2 Hz, J W-C ) 77.2 Hz); 122.83, 125.01,

Metallacyclopentane Formation
Organometallics, Vol. 17, No. 12, 1998 2635
125.20, 125.43, 125.58, 128.14, 128.48, 128.62, 132.95, 149.20,
156.22 (aromatic). Anal. Calcd for C34H45N3Si2W: C, 55.50;
H, 6.17; N, 5.71. Found: C, 55.23; H, 6.09; N, 5.75.
isolated. The mother liquors were reduced in volume under
reduced pressure and cooled to -78 °C to give more solid. Total
yield: 1.44 g, 88.3%. 1H NMR (C6D6, δ): 0.31 (s, 9H, -Si-
(CH3)3); 0.60 (s, 9H, -Si′(CH3)3); 1.03 (s, 18H, -PMe3); 1.91
(m, C2H4); 2.09 (m, C2H4); 6.61-7.42 (aromatic). 13C{1H} NMR
(C6D6, δ): 2.67 (-Si(CH3)3); 6.34 (-Si′(CH3)3); 15.78 (s, -PMe3);
38.13 (s, C2H4, J C-H ) 156.2 Hz); 122.23, 123.13, 124.28,
125.51, 127.23, 128.91, 129.23, 129.78, 158.23 (aromatic).
Anal. Calcd for C26H49N3Si2P2W: C, 44.25; H, 7.00; N, 5.95.
Found: C, 43.91; H, 6.79; N, 5.78.
P r ep a r a tion of W(NP h )[o-(Me3SiN)2C6H4](CHt-Bu CH2-
CH2), 8. W(NPh)[o-(Me3SiN)2C6H4](CHCMe3)(PMe3), 3 (1 g,
1.49 mmol), was dissolved in hexane (50 mL) and allowed to
react with 16 psi of ethylene in the presence of excess
neohexene at room temperature for 30 min. The solvent was
removed under reduced pressure, and the resulting solid was
dried under reduced pressure for 1 h. The solid was then
extracted with pentane and filtered by cannula. The solution
was concentrated to ca. 10 mL and cooled to -78 °C for 1 h.
The resulting golden solid was isolated by filtration and dried
under reduced pressure for 1 h to yield red orange solid at
54% yield. 1H NMR (C6D6, δ): 0.24 (s, 9H, -Si(CH3)3); 0.26
(s, 9H, -Si′(CH3)3); 0.39 (m, 1H, -CHtBuCH2CH2); 0.71 (m,
1H, -CHtBuCH2CH2); 1.21 (s, 9H, t-Bu); 2.45 (m, 1H, -CHt-
BuCH2CH2); 2.61 (m, 1H, -CHtBuCH2CH2); 3.75 (m, 1H,
-CHtBuCH2CH2); 6.82-7.44 (m, 9H, aromatic). 13C{1H} NMR
(C6D6, δ): 1.35 (s, -Si(CH3)3); 1.54 (s, -Si′(CH3)3); 25.07 (-CHt-
BuCH2CH2); 38.80 (-CHtBuCH2CH2, 1J W-C ) 49.4 Hz); 77.58
(-CHtBuCH2CH2, J W-C ) 56.1 Hz).
P r epar ation of W(NP h )[o-(Me3SiN)2C6H4](CH2Si(CH3)3)2,
2j. W(NPh)[o-(Me3SiN)2C6H4](Cl)2, 1 (2.0 g, 3.35 mmol), was
dissolved in Et2O (30 mL) and cooled to -78 °C. Two
equivalents of ClMgCH2Si(CH3)3 (5.23 mL, 6.70 mmol, 1.28
M solution in Et2O) were then added. The reaction was
allowed to warm to room temperature after 30 min. After 1
h, solvent was removed under reduced pressure. The solid was
extracted with pentane until clear and filtered through a Celite
pad. The solution was concentrated to a total volume of about
10 mL and cooled in a -78 °C bath to yield 1.98 g dark crystals
of 2j. Yield: 84.2%. 1H NMR (C6D6, δ): 0.01 (s, 18H, -CH2-
Si(CH3)3); 0.49 (s, 18H, -NSi(CH3)3); 1.32 (d, 2H, -CH2-
Si(CH3)3); 1.96 (d, 2H, -CH2Si(CH3)3); 6.85 (t, 1H, p-NPh-H);
6.91 (m, 2H, aromatic); 7.19 (t, 2H, m-NPh-H); 7.23 (m, 2H,
aromatic); 7.52 (d, 2H, o-NPh-H). 13C{1H} NMR (C6D6, δ): 2.93
1
(-CH2Si(CH3)3); 3.96 (-NSi(CH3)3, J Si-C ) 56.8 Hz); 63.64
(-CH2Si(CH3)3); 119.91, 126.37, 127.92, 128.51, 128.58, 142.55,
155.59 (aromatic). Anal. Calcd for C28H47N3Si2W: C, 44.62;
H, 7.06; N, 6.00. Found: C, 44.63; H, 7.02; N, 6.10.
P r ep a r a tion of W(NP h )[o-(Me3SiN)2C6H4](CHCMe3)-
(P Me3), 3. In a 200 mL glass tube fitted with a Teflon J .
Young’s joint, W(NPh)[o-(Me3SiN)2C6H4] (CH2CMe3)2 (1.25 g,
1.87 mmol) was dissolved in toluene (25 mL). Five equivalents
of PMe3 (0.968 mL, 9.35 mmol) were then added, and the tube
was sealed. The reaction was then heated to 80 °C for 24 h.
The solution was transferred to a round-bottom Schlenk, and
the solvent was removed under reduced pressure. The brown
oil was extracted with pentane, and the volume of the filtrate
was concentrated to ca. 15 mL. The solution was cooled to
-10 °C to give 0.83 g of 3b as orange crystals. Yield: 66.0%.
1H NMR (C6D6, δ): 0.38 (s, 9H, -Si(CH3)3); 0.41 (s, 9H, -Si′-
X-r a y Cr ysta l Str u ctu r es. Data (Table 1) for both com-
pounds were collected at 173 K on a Siemens CCD SMART
PLATFORM equipped with
a CCD area detector and a
graphite monochromator utilizing Mo KR radiation (λ )
0.710 73 Å). Cell parameters were refined using 8173 and
8192 reflections for 4 and 5, respectively. A hemisphere of
data (1381 frames) was collected using the ω-scan method (0.3°
frame width). The first 50 frames were remeasured at the
end of data collection to monitor instrument and crystal
stability (maximum correction on I was <1%). Absorption
corrections were applied on the basis of the ψ scan using the
entire data set for 5 and on the basis of the measured crystal
faces for 4.
Both structures were solved by direct methods in SHELX-
TL520 and refined using full-matrix least squares on F2. The
non-H atoms were refined with anisotropic thermal param-
eters except for the disordered C atoms. All of the H atoms
were included in the final cycle of refinement and were riding
on the atoms to which they are bonded. The ethylene ligand
in 4 was found to be disordered in the 2 and 3 positions. Two
partial -CH2CH2- groups were refined with isotropic thermal
parameters and their occupation factors refined dependently
to 0.54(2) for one and consequently 0.46(2) for the other.
Atomic coordinates and equivalent isotropic displacement
parameters of 4 and 5 can be found in the Supporting
Information.
2
(CH3)3); 0.98 (d, 9H, -PMe3, J W-C ) 9 Hz); 1.39 (s, 9H,
-CMe3); 6.68-7.13 (m, 9H, aromatic). 13C{1H} NMR (C6D6,
δ): 3.41 (-Si(CH3)3); 4.11 (-Si′(CH3)3); 16.22 (d, -PMe3); 34.93
(-CMe3); 45.04 (-CMe3); 117.61, 119.32, 122.44, 123.56,
1
124.71, 128.71, 148.13 (aromatic); 277.41 (-CHCMe3, J C-H
) 110 Hz). Anal. Calcd for C26H46N3PSi2W: C, 46.49; H, 6.90;
N, 6.26. Found: C, 46.23; H, 6.81; N, 6.05.
P r ep a r a tion of W(CH2CH2CH2CH2)(NP h )[o-(Me3SiN)2-
C6H4], 4. W(NPh)[o-(Me3SiN)2C6H4](Cl)2 (1.05 g, 1.76 mmol)
was dissolved in Et2O (50 mL) and cooled to -78 °C. One
equivalent of BrMgCH2CH2CH2CH2MgBr (1.75 mL, 1.76 mmol;
0.99 M solution in Et2O) was then added by a syringe. The
reaction was allowed to warm to room temperature after 1 h
and was stirred for another 2 h. The solvent was removed
under reduced pressure, and the resulting solid was dried
under reduced pressure for 3 h. The solid was then extracted
with pentane and filtered through a Celite pad until the filtrate
was almost clear. The solution was concentrated to about 10
mL and cooled to -78 °C for 2 h. The resulting golden solid
was isolated by filtration and dried under reduced pressure
1
for 1 h to yield 0.77 g of 4 as a brown solid. Yield: 75.2%. H
NMR (C6D6, δ): 0.28 (s, 18H, -Si(CH3)3); 1.54 (m, 2H, R-CH);
2.42 (m, 2H, â-CH); 2.91 (m, 2H, â-CH′); 2.93 (m, 2H, R-CH′);
6.86-7.44 (m, 9H, aromatic). 13C{1H} NMR (C6D6, δ): 1.08
(-Si(CH3)3, 2J Si-H ) 6.6 Hz, J C-H ) 119.1 Hz); 35.23 (â-C, J C-H
) 124.3 Hz); 61.25 (R-C, J W-C ) 73.6 Hz, J C-H ) 122.9 Hz).
Anal. Calcd for C22H35N3Si2W: C, 45.43; H, 6.07; N, 7.23.
Found: C, 45.19; H, 5.97; N, 7.03.
Ack n ow led gm en t. We wish to acknowledge Na-
tional Science Foundation Grant CHE-9523279 for the
support of this work. K.A.A. wishes to acknowledge the
National Science Foundation for funding of the purchase
of the X-ray equipment.
P r ep a r a t ion of W(NP h )[o-(Me3SiN)2C6H 4](η2-C2H 4)-
(P Me3)2, 5. In a glass tube with a Teflon J . Young’s joint,
W(NPh)[o-(Me3SiN)2C6H4](CH2CH3)2 , 2b (1.35 g, 2.32 mmol),
was dissolved in pentane (50 mL). Five equivalents of PMe3
(1.19 mL, 11.56 mmol) were added by a syringe, and then the
flask was sealed. The reaction was stirred at room tempera-
ture for 4 h, during which time the brown solution turned
purple and purple crystals precipitated. The mixture was
transferred to a Schlenck tube, and the purple crystals were
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
lengths and angles and positional and thermal parameters (17
pages). Ordering information is given on any current mast-
head page.
OM9708283
(20) Sheldrick, G. M. SHELXTL5; Nicolet XRD Corp.: Madison, WI,
1995.