Molybdenum and tungsten mono-isodiazene complexes with alkyl ligands as ring-opening metathesis polymerisation procatalysts. Crystal and molecular structures of [Mo(CH2CMe2Ph)3-(NNPh2)(OC 6F5</su

Article abstract of DOI:10.1039/a903770e

Reaction of [M(NNPh₂)Cl₄] with RMgCl followed by addition of pentafluorophenol afforded the tris-alkyl complexes [MoR₃(NNPh₂)(OC₆F₅)] [M = Mo, R = CH₂CMe₂Ph 1; M = W,

Full text of DOI:10.1039/a903770e

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Molybdenum and tungsten mono-isodiazene complexes with alkyl
ligands as ring-opening metathesis polymerisation procatalysts.
Crystal and molecular structures of [Mo(CH2CMe2Ph)3-
(NNPh2)(OC6F5)], [W(CH2SiMe3)3(NNPh2)(OC6F5)] and
[WCl2(NNPh2)(OC6F5)2(thf)]
Jonathan R. Dilworth,*a Vernon C. Gibson,*b Carl Redshaw,b Andrew J. P. Whiteb and
David J. Williamsb
a Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR
b Department of Chemistry, Imperial College, South Kensington, London, UK SW7 2AY
Received 11th May 1999, Accepted 28th June 1999
Reaction of [M(NNPh2)Cl4] with RMgCl followed by addition of pentafluorophenol afforded the tris-alkyl
complexes [MoR3(NNPh2)(OC6F5)] [M = Mo, R = CH2CMe2Ph 1; M = W, R = CH2SiMe3 2] in moderate yields.
At ca. 80 ЊC in chlorobenzene 1 and 2 are active for the ring-opening metathesis polymerisation of norbornene;
intermediate alkylidene complexes are not observed. The crystal structures of 1 and 2 have been determined; the
metal centres adopt trigonal bipyramidal geometries in which the isodiazene and pentafluorophenoxide groups
are apical. The crystal structure of [WCl2(NNPh2)(OC6F5)2(thf)] 3 is also reported.
The role of ‘spectator’ ligands such as oxo or organoimido
groups in stabilising olefin metathesis catalysts is well estab-
lished. Imidoalkylidene complexes of the form [Mo(NAr)-
(CHCMe2Ph)(OR)2] [Ar = 2,6-iPr2C6H3; R = OBut, OC(CF3)-
Me2 or OC(CF3)2Me] developed by Schrock and co-workers1
are especially suited to the controlled polymerisation of a
variety of norbornene and norbornadiene monomers. However,
these four-co-ordinate imidoalkylidene initiators are quite
thermally sensitive, leading to difficulties with storage and
widespread applicability above ambient temperature.
We became interested in exploring the effect of replacing the
imido ligands in the above systems by isodiazene groups, since
in many cases isodiazene complexes are more thermally robust
than their imido analogues. In separate studies, we have investi-
gated the ring-opening metathesis polymerisation (ROMP)
activity of nitride, isodiazene and diazenide procatalysts and
have shown the first examples of such activity for these com-
plexes.2 Our previous attempts to prepare a new family of
catalysts based on the bis(isodiazene) Mo(NNPh2)2 core have
to-date met with little success.3 However, in the case of the
mono(isodiazene) M(NNPh2) systems, we believed that the
higher formal oxidation state of the metal would facilitate
alkylation. We now report the first examples of simple iso-
diazene complexes of the Group 6 metals with alkyl co-ligands
which can be used to generate in situ active ROMP catalysts.
The synthetic approach depends upon alkylation, followed by
treatment with a Brønsted acid source, viz. C6F5OH, a method-
ology that has successfully been exploited to access metathesis-
active imidoalkylidene complexes.4
Fig. 1 View of the molecular structure of complex 1 (hydrogen atoms
omitted for clarity in all Figures).
orange-red crystalline solid in ca. 40% yield. Crystals of 1
suitable for an X-ray analysis were grown from pentane at 0 ЊC;
a representation of the molecular structure is shown in Fig. 1.
Selected bond lengths and angles appear in Table 1.
The molecular geometry is trigonal bipyramidal with the iso-
diazene and pentafluorophenoxide ligands axial [N(1)–Mo–O
177.31(9)Њ]. For the isodiazene ligand the N–N distance [N(1)–
N(2) 1.333(4) Å], the Mo–N distance [1.746(2) Å] and the Mo–
N(1)–N(2) angle [174.5(2)Њ] lie within the range found for other
monoisodiazene complexes.6 The equatorial neophyl groups
are orientated in a “manx-like” arrangement with Mo–C bond
lengths in the range 2.126(3) to 2.152(3) Å and inter-ligand
C–Mo–C angles between 118.68(12) and 120.1(1)Њ. The associ-
ated Mo–C–C angles range between 120.2(2) and 130.5(2)Њ,
the largest angle being associated with the shortest Mo–C
Results and discussion
Attempts to alkylate [M(NNPh2)Cl4] (M = Mo or W) with
neophyllithium, PhMe2CCH2Li (>3 equivalents), afforded
mixtures of products that could not be purified. However, the
reaction of [Mo(NNPh2)Cl4]5 with neophylmagnesium chloride
(>3 equivalents) in diethyl ether followed by addition of penta-
fluorophenol readily afforded on work-up multigram quantities
of [Mo(CH2CMe2Ph)3(NNPh2)(OC6F5)] 1 as an air-stable
J. Chem. Soc., Dalton Trans., 1999, 2701–2704
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Table 1 Selected bond lengths (Å) and angles (Њ) for complex 1
Table 2 Selected bond lengths (Å) and angles (Њ) for complex 2
Mo–O
Mo–C(1)
Mo–C(3)
2.011(2)
2.152(3)
2.126(3)
Mo–N(1)
Mo–C(2)
N(1)–N(2)
1.746(2)
2.144(3)
1.333(4)
W–O
W–C(1)
W–C(3)
2.011(5)
2.095(8)
2.117(7)
W–N(1)
W–C(2)
N(1)–N(2)
1.741(6)
2.091(7)
1.337(8)
N(1)–Mo–O
O–Mo–C(3)
O–Mo–C(2)
N(1)–Mo–C(1)
C(3)–Mo–C(1)
C(21)–O–Mo
C(22)–C(1)–Mo
C(40)–C(3)–Mo
177.31(9)
85.5(1)
85.9(1)
N(1)–Mo–C(3)
N(1)–Mo–C(2)
C(3)–Mo–C(2)
O–Mo–C(1)
C(2)–Mo–C(1)
N(2)–N(1)–Mo
C(31)–C(2)–Mo
97.2(1)
92.6(1)
118.7(1)
86.1(1)
119.6(1)
174.5(2)
122.9(2)
N(1)–W–O
O–W–C(2)
O–W–C(1)
N(1)–W–C(3)
C(2)–W–C(3)
C(16)–O–W
Si(1)–C(1)–W
Si(3)–C(3)–W
177.3(3)
84.0(3)
88.0(3)
N(1)–W–C(2)
N(1)–W–C(1)
C(2)–W–C(1)
O–W–C(3)
C(1)–W–C(3)
N(2)–N(1)–W
Si(2)–C(2)–W
95.2(3)
94.6(3)
115.1(3)
83.9(3)
123.2(3)
174.8(5)
120.5(4)
92.7(1)
94.3(3)
120.1(1)
167.8(2)
120.2(2)
130.5(2)
119.8(3)
157.3(5)
124.5(4)
116.5(3)
Fig. 3 View of the molecular structure of complex 3.
between 115.1(3) and 123.2(3)Њ. The associated W–C–Si angles
range between 116.5(3) and 124.5(4)Њ. The isodiazene ligand is
again linear [174.8(5)Њ] with a W–N bond distance of 1.741(6)
Å and an N–N distance of 1.337(8) Å. Here, in 2, the W–O–
C6F5 angle is noticeably bent at 157.3(5)Њ, cf. 167.8(2)Њ for 1, the
reason for which is not immediately apparent. The packing of
the molecules is very different from that in 1 with here the
closest intermolecular contacts being T-type aromatic edge to
face interactions between Ci related pairs of diphenylisodiazene
ring systems, the centroid–centroid distance being 5.15 Å. Reac-
tion as for 1 with norbornene afforded polynorbornene but
only in 10% yield. Polymer characterising data were consistent
with ca. 45% cis-configurated double bonds, a molecular weight
(Mn) of 560 000 and a molecular weight distribution of 2.77.
Surprisingly, attempts at an analogous reaction with benzyl-
magnesium chloride afforded only [WCl2(NNPh2)(OC6F5)2-
(thf)] 3. The reasons for the failure of benzylmagnesium chlor-
ide to react at this stage are not clear; it is possible however that
an unisolable bis(benzyl) intermediate reacts in situ with penta-
fluorophenol to afford 3. Complex 3 can be accessed directly in
high yield via reaction of [WCl4(NNPh2)] and two equivalents
of NaOC6F5 in thf. The molecular structure is shown in Fig. 3
with selected bond lengths and angles given in Table 3.
The structure has crystallographic C2 symmetry about an
axis passing along the tungsten–isodiazene linkage. The geom-
etry at tungsten is distorted octahedral with cis angles in the
range 80.9(1) to 99.1(1)Њ and a noticeably bent trans O–W–O
angle of 161.8(3)Њ. There is a similar, but smaller, fold angle
associated with the trans chlorides [Cl–W–Cl 170.84(9)Њ] which,
coupled with the above distortion, results in the tungsten lying
0.26 Å out of the equatorial plane in the direction of the
isodiazene ligand, and away from the co-ordinated thf. The
equatorial W–O distance [1.934(5) Å] is as expected signifi-
cantly shorter than that to the axial furan oxygen [2.215(6) Å]
and also shorter than to the axial phenoxide in complex 2.
Interestingly, the W–N distance is unchanged [1.738(7) Å] from
Fig. 2 View of the molecular structure of complex 2.
distance. Conformational stabilisation is, in part, achieved by a
C–H ؒ ؒ ؒ π contact of 2.60 Å between one of the ortho iso-
diazene hydrogen atoms and the C(1) neophyl ring. The only
intermolecular feature of note is a partial stacking of Ci related
pentafluorophenoxy rings where F(19) in one ring overlays
C(20) [attached to F(20)] of the other at an internuclear dis-
tance of only 3.11 Å and at 3.07 Å from the plane of the ring.
The neophyl groups are located in cis positions which should
1
facilitate α-H abstraction via alkane elimination. Solution H
NMR data at ambient temperature are consistent with retention
of this structure. However, attempts to observe an alkylidene
intermediate by NMR upon warming the complex were unsuc-
cessful, only decomposition products being observed. Treat-
ment of 1 with 100 equivalents of norbornene in chlorobenzene
(80 ЊC, 12 h) yielded ring-opened polynorbornene in ca. 50%
isolated yield and with ca. 70% cis double bonds as indicated
by 13C NMR spectroscopy. Gel permeation chromatography
(GPC) data on the polymer gave a number average molecular
weight (Mn) of 55 100 [calc. 9416] and a PDI (polymer distri-
bution index) of 1.82. The Mn of the polymer and compar-
atively narrow molecular weight distribution are consistent with
efficient catalyst formation.
A similar reaction of [WCl4(NNPh2)] with trimethylsilyl-
methylmagnesium chloride, Me3SiCH2MgCl, gave, following
the addition of C6F5OH, the golden-yellow crystalline complex
[W(CH2SiMe3)3(NNPh2)(OC6F5)] 2 in ca. 30% yield. The
molecular structure of 2 is depicted in Fig. 2; selected bond
lengths and angles are given in Table 2. The gross structure
is very similar to that of 1 with the tungsten having trigonal
bipyramidal geometry.
As in complex 1, the alkyl groups are equatorial and orien-
tated in a “manx-like” arrangement with W–C distances in the
range 2.091(7) to 2.117(7) Å and interligand C–W–C angles
2702
J. Chem. Soc., Dalton Trans., 1999, 2701–2704

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Table 3 Selected bond lengths (Å) and angles (Њ) for complex 3
solution in thf) via a syringe. Stirring was continued for 3 h at
ambient temperature, the volatiles were removed in vacuo and
the residue was taken up in pentane (2 × 30 cm3). After fil-
tration, solid C6F5OH (2.87 g, 15.6 mmol) was added at Ϫ78 ЊC
and stirring was continued for 2 h. Filtration, concentration
(to ca. 30 cm3) and cooling to 0 ЊC afforded 1 as orange-red
blocks. Yield 2.6 g, 41%. Found: C, 65.7; H, 5.2; N, 3.5. C48H49-
F5MoN2O requires C, 66.0; H, 5.3; N, 3.4%. IR: 1649w, 1622w,
1588w, 1515s, 1504s, 1490s, 1324m, 1312m, 1275m, 1262s,
1207w, 1172s, 1157m, 1110m, 1090m, 1073m, 1024s, 980m,
921w, 893w, 850w, 801w, 758w, 749m, 738m, 723m, 702m,
W–N(1)
W–O(1Ј)
W–Cl
1.738(7)
1.934(5)
2.360(2)
1.317(10)
W–O(1)
W–O(2)
W–ClЈ
1.934(5)
2.215(6)
2.360(2)
N(1)–N(2)
N(1)–W–O(1Ј)
O(1Ј)–W–O(1)
O(1Ј)–W–O(2)
N(1)–W–Cl
99.1(1)
161.8(3)
80.9(1)
94.58(4)
90.1(2)
94.58(4)
88.4(2)
170.84(9)
180.0
N(1)–W–O(1)
N(1)–W–O(2)
O(1)–W–O(2)
O(1Ј)–W–Cl
O(2)–W–Cl
O(1Ј)–W–ClЈ
O(2)–W–ClЈ
C(7)–O(1)–W
99.1(1)
180.0
80.9(1)
88.4(2)
85.42(4)
90.1(2)
85.42(4)
132.8(5)
O(1)–W–Cl
N(1)–W–ClЈ
O(1)–W–ClЈ
Cl–W–ClЈ
1
692m, 660m and 647m cmϪ1. H NMR (500 MHz, C6D6):
δ 1.29 (s, 18 H, CMe2), 2.63 (s, 6 H, CH2) and 6.84–7.19 (over-
lapping multiplets, 15 H, aryl H). 13C NMR (400 MHz, C6D6):
δ 32.25 (CMe2), 42.23 (CMe2), 83.82 (CH2), 118.13, 122.63,
125.50, 125.82, 126.00, 126.20, 129.21, 129.37, 129.50, 129.81,
140.53 and 151.16. 19F NMR (400 MHz, C6D6): δ Ϫ162.48
(m, 2F, o-CF), Ϫ163.77 (m, 2F, m-CF) and Ϫ168.61 (m, 1F,
p-CF).
N(2)–N(1)–W
that observed in 2 where the co-ordination geometry is totally
different and the σ donation of the pentafluorophenoxide
group would be expected to be somewhat greater. The con-
formation is stabilised by pairs of intramolecular π–π stacking
interactions between the isodiazene rings and their penta-
fluorophenoxy neighbours, the mean interplanar and centriod–
centroid separations being 3.37 and 3.75 Å respectively. The
pattern of stacking extends to include the pentafluorophen-
oxide ring of an adjacent Ci related molecule [mean interplanar
and shortest internuclear F ؒ ؒ ؒ C separations 3.36 and 3.36 Å
respectively] resulting in the formation, via the C2 symmetry,
of zigzag chains of π–π linked molecules that extend in the
crystallographic c direction.
Complex 2. As for complex 1, but using [WCl4(NNPh2)] (1.0
g, 1.97 mmol), Me3SiCH2MgCl (7.88 cm3, 1.0 M) and C6F5OH
(0.73 g, 3.97 mmol) affording 2 as golden-yellow plates. Yield
0.48 g, 30%. Found: C, 43.9; H, 5.1; N, 3.5. C30H43F5N2OSi3W
requires C, 44.4; H, 5.3; N, 3.5%. IR: 1649w, 1623w, 1592m,
1505s, 1494s, 1407m, 1342m, 1331m, 1316m, 1286m, 1247s,
1176s, 1075m, 1028s, 989s, 962s, 930m, 906m, 833s, 744s, 721m,
1
697s, 667s, 649m, 626m and 612m cmϪ1. H NMR (400 MHz,
CDCl3): δ Ϫ0.07 (s, 27 H, SiMe3), 1.33 (s, 6 H, CH2) and 7.17–
7.48 (overlapping multiplets, 10 H, aryl H). 13C NMR (400
MHz, CDCl3): δ 1.62 (s, SiMe3), 66.41 (s, CH2), 121.81, 125.49,
129.41 and 141.16 (only observed aryl C). 19F NMR (400 MHz,
CDCl3): δ Ϫ157.37 (m, 2F, o-CF), Ϫ165.25 (m, 2F, m-CF) and
Ϫ172.40 (m, 1F, p-CF).
Conclusion
The successful synthesis of [Mo(CH2CMe2Ph)(NNPh2)-
(OC6F5)] and [W(CH2SiMe3)3(NNPh2)(OC6F5)] shows that
alkylation of the mono-isodiazene [M(NNPh2)] core is
much more favourable than for the related bis(isodiazene)
[M(NNPh2)2] core.4 Upon warming in chlorobenzene solution,
the air-stable five-co-ordinate trialkyl complex [Mo(CH2C-
Me2Ph)3(NNPh2)(OC6F5)] gives an effective catalyst for
metathesis polymerisation of norbornene in the absence of an
activator. The tungsten complex [W(CH2SiMe3)3(NNPh2)-
(OC6F5)] is somewhat less effective and gives broader molecular
weight distribution poly(norbornene). These results represent
the first indications that single-component isodiazene meta-
thesis catalysts are accessible, though additional work will be
required to improve the control features of the system.
Complex 3. As for complex 1, but using [WCl4(NNPh2)] (1.0
g, 1.97 mmol), PhCH2MgCl (7.88 cm3, 1.0 M solution) and
C6F5OH (0.73 g, 3.97 mmol) affording 3 as golden-yellow
plates. Yield 0.41 g, 24.3%. Found: C, 40.4; H, 2.4; N,
2.8. C28H18Cl2F10N2O3W requires C, 39.1; H, 2.1; N, 3.3%.
IR: 1590w, 1510s, 1308m, 1264w, 1192w, 1155m, 1063w,
1018s, 1000s, 987s, 917w, 881w, 844w, 753m, 721m, 692m
and 676m cmϪ1. 1H NMR (400 MHz, CDCl3): δ 2.19 (m,
4 H, thf), 4.69 (m, 4 H, thf) and 7.03–7.52 (overlapping
multiplets, 10 H, aryl H). 19F NMR (400 MHz, CDCl3):
δ Ϫ157.84 (m, 4F, o-CF), Ϫ163.55 (m, 4F, m-CF) and Ϫ165.45
(m, 2F, p-CF).
Experimental
General
X-Ray crystallography
Table 4 provides a summary of the crystal data, data collection
and refinement parameters for complexes 1, 2 and 3. The struc-
tures of 1 and 2 were solved by direct methods, that of 3 by the
heavy atom method, and the refinements were by full matrix
least squares based on F2. The pendant phenyl rings were
refined as idealised rigid bodies and all of the non-hydrogen
atoms were refined anisotropically. The C–H hydrogen atoms in
all three structures were placed in calculated positions, assigned
isotropic thermal parameters, U(H) = 1.2Ueq(C) [U(H) = 1.5Ueq-
(C–Me)], and allowed to ride on their parent atoms. Compu-
tations were carried out using the SHELXTL PC program
system.7
All manipulations were carried out under an atmosphere of
dinitrogen using standard Schlenk and cannula techniques or in
a conventional nitrogen-filled glove-box. Solvents were refluxed
over an appropriate drying agent, and distilled and degassed
prior to use. Elemental analyses were performed by the micro-
analytical services of the Department of Chemistry at Imperial
College. The NMR spectra were recorded on a Varian VXR 400
S spectrometer at 400.0 (1H), 75.0 (13C) and 376.3 MHz (19F)
with chemical shifts referenced to the residual protio impurity
of the deuteriated solvent, IR spectra (Nujol mulls, KBr
windows) on Perkin-Elmer 577 and 457 grating spectrophoto-
meters. The starting materials [MoCl4(NNPh2)] and [WCl4-
(NNPh2)] were prepared as described in the literature.5 All
other chemicals were obtained commercially and used as
received unless stated otherwise.
CCDC reference number 186/1540.
See http://www.rsc.org/suppdata/dt/1999/2701/ for crystallo-
graphic files in .cif format.
Preparations
Acknowledgements
Complex 1. To [MoCl4(NNPh2)] (3.0 g, 7.8 mmol) in diethyl
ether at Ϫ78 ЊC was added PhCMe2CH2MgCl (11.7 cm3, 2.0 M
The Engineering and Physical Sciences Research Council is
thanked for financial support.
J. Chem. Soc., Dalton Trans., 1999, 2701–2704
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Table 4 Crystal data, data collection and refinement parametersa for complexes 1–3
1
2
3
Formula
Formula weight
C48H49F5MoN2O
860.8
C30H43F5N2OSi3W
810.8
C28H18Cl2F10N2O3W
875.2
Crystal system
Space group
T/K
Triclinic
P1 (no. 2)
203
Triclinic
P1 (no. 2)
293
Monoclinic
C2/c (no. 15)
293
a/Å
b/Å
c/Å
α/Њ
11.809(3)
11.905(1)
16.348(3)
87.30(1)
81.01(2)
66.88(1)
2087.5(7)
2
9.997(1)
10.664(1)
18.101(1)
90.84(1)
90.34(1)
110.94(1)
1802.0(3)
2
10.908(2)
13.007(2)
21.660(4)
—
98.29(2)
—
β/Њ
γ/Њ
V/Å3
3041.0(9)
Z
4b
Dc/g cmϪ3
1.370
1.494
Cu-Kα
7.33
1.912
Mo-Kα
4.07
Radiation used
Cu-Kαc
3.07
µ/mmϪ1
No. unique reflections
measured
observed, |Fo| > 4σ(|Fo|)
R1
6537
6227
0.041
0.110
5327
4795
0.046
0.117
2412
2050
0.036
0.080
wR2
a Details in common: graphite monochromated radiation, ω scans, Siemens P4 diffractometer. b The complex has crystallographic C2 symmetry.
c Rotating anode source.
3 J. R. Dilworth, A. Desai and R. M. Thompson, J. Mol. Catal., 1997,
115, 73.
References
1 R. R. Schrock, Acc. Chem. Res., 1990, 23, 158; J. Feldman and
R. R. Schrock, Prog. Inorg. Chem., 1991, 1, 39; V. C. Gibson, Adv.
Mater., 1994, 6, 37; R. R. Schrock, J. S. Murdzek, G. C. Bazan,
J. Robbins, M. DiMare and M. O’Regan, J. Am. Chem. Soc., 1990,
112, 3875; G. C. Bazan, R. R. Schrock, H.-N. Cho and V. C. Gibson,
Macromolecules, 1991, 24, 4495; G. C. Bazan, E. Khosravi, R. R.
Schrock, W. J. Feast, V. C. Gibson, M. B. O’Regan, J. K. Thomas and
W. M. Davis, J. Am. Chem. Soc., 1990, 112, 8378.
4 J. R. Dilworth, J. R. Miller, Y. Zheng, V. C. Gibson and C. Redshaw,
J. Chem. Soc., Dalton Trans., 1997, 269.
5 J. R. Dilworth and S. A. Morton, Transition Met. Chem., 1987, 12,
41.
6 S. Kahlal, J.-Y. Saillard, J.-R. Harion, C. Mansur and D. Carillo,
J. Chem. Soc., Dalton Trans., 1998, 1229 and refs. therein.
7 SHELXTL PC, version 5.03, Siemens Analytical X-Ray Instruments,
Inc., Madison, WI, 1994.
2 A. Bell, W. Clegg, P. W. Dyer, M. R. J. Elsegood, V. C. Gibson and
E. L. Marshall, J. Chem. Soc., Chem. Commun., 1994, 2247; 2547.
Paper 9/03770E
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