Complexes of zirconium with aryl substituted triamidoamines: Molecular structures of amide and alkyl derivatives

Article abstract of DOI:10.1016/S0022-328X(00)00310-7

Reactions of the arylated TREN derivatives N(CH₂CH₂NHAr)₃ [Ar = 2,4,6-C₆Me₃H₂ (H₃TMT), 3,5-C₆Bu^t₂H₃ (H₃TDT)] individually with Zr(NMe₂)₄ and Zr(CH₂Ph)₄ give the azazirconatranes [Zr(TMT)(NMe₂)], [Zr(TDT)(NMe₂)] and [Zr(TDT)(CH₂Ph)] and unexpectedly [Zr(HTMT)(CH₂Ph)₂]. The molecular structures of [Zr(TMT)(NMe₂)] and [Zr(TDT)(CH₂Ph)] show that the triamidoamine ligand is arranged with the usual three-fold symmetry about the metal and that the aryl substituents form a bowl cavity with the apical ligand at the base. The reactions of the alkyl with dihydrogen lead to decomposition, and a hydride species such as that proposed in earlier studies could not be detected.

Full text of DOI:10.1016/S0022-328X(00)00310-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 606 (2000) 141–146
Complexes of zirconium with aryl substituted triamidoamines:
molecular structures of amide and alkyl derivatives
Colin Morton, Kevin M. Gillespie, Christopher J. Sanders, Peter Scott *
Department of Chemistry, Uni6ersity of Warwick, Co6entry CV4 7AL, UK
Received 3 March 2000; accepted 9 May 2000
Abstract
Reactions of the arylated TREN derivatives N(CH2CH2NHAr)3 [Ar=2,4,6-C6Me3H2 (H3TMT), 3,5-C6But2H3 (H3TDT)]
individually with Zr(NMe2)4 and Zr(CH2Ph)4 give the azazirconatranes [Zr(TMT)(NMe2)], [Zr(TDT)(NMe2)] and
[Zr(TDT)(CH2Ph)] and unexpectedly [Zr(HTMT)(CH2Ph)2]. The molecular structures of [Zr(TMT)(NMe2)] and
[Zr(TDT)(CH2Ph)] show that the triamidoamine ligand is arranged with the usual three-fold symmetry about the metal and that
the aryl substituents form a bowl cavity with the apical ligand at the base. The reactions of the alkyl with dihydrogen lead to
decomposition, and a hydride species such as that proposed in earlier studies could not be detected. © 2000 Elsevier Science S.A.
All rights reserved.
Keywords: Zirconium; Azametallatrane; Amide; Alkyl; TREN; X-ray structure
SiMe2But groups to give II. This type of chemistry had
previously been observed in titanium [6c,d], molybde-
1. Introduction
num [2e], uranium and thorium [8] systems and is quite
commonplace for SiMe groups. We mentioned that
Schrock’s more recently introduced aryl substituted
triamidoamine ligands [2f] may be more resistant to this
type of reaction and we present here our investigations
in this area.
Synthetic and catalytic chemistry involving amido
R2N– complexes of the early transition metals and f
elements is currently an area of intense study [1]. The
triamidoamines constitute an important class of such
complexes [2]. These formally trianionic quadridentate
ligands are usually disposed in a symmetric (C3) orien-
tation leaving a sterically protected fifth coordination
site at the apex of an approximate trigonal bipyramid.
The geometric and electronic structure promotes the
formation of MꢀL multiple bonds at this site [3]. Also,
the (triamidoamine)lanthanide fragment is unusually
Lewis acidic [4].
Zirconium triamidoamines or azazirconatranes were
first reported by Verkade [5]. The titanium derivatives
have been more extensively studied [6]. Our recent
contribution [7] focussed on the synthesis of
organometallic derivatives such as [Zr(NN%)CH2Ph] (I)
3
and subsequent attempts to synthesise a hydride deriva-
tive [Zr(NN%)H] by hydrogenation. This reaction led
3
instead to clean metalation of the amide substituent
* Corresponding author. Fax: +44-203-572710.
E-mail address: peter.scott@warwick.ac.uk (P. Scott).
Scheme 1. Synthesis of complexes 1–4.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00310-7

142
C. Morton et al. / Journal of Organometallic Chemistry 606 (2000) 141–146
spectra show inequivalent benzyl groups (axial and
equatorial) in the presumed trigonal bipyramidal struc-
ture. The presence of five mesityl group methyl reso-
nances in the ratio 6:6:6:6:3 and an apparent mirror
plane through the amino nitrogen, Zr and bisecting the
two amido nitrogens would indicate inequivalence of
1
the ortho-methyl groups at the amide ligands on the H
Scheme 2.
chemical shift time-scale. We ascribe this to restricted
rotation about amido NꢀCipso bonds. This behaviour
has also been noted in a closely related diamidoamine
complex [10]. Unfortunately the thermal instability of 2
has impeded variable temperature NMR studies.
The amide complex 1 above is analogous to several
molybdenum complexes possessing various aryl N-sub-
stituents [2f]. Those without groups in the ortho posi-
tions of the aromatic ring readily form methyl
derivatives, whereas this was not achieved for com-
plexes of more sterically demanding ligands such as
TMT. As expected, ortho substituents have the most
significant steric influence about the metal. Nevertheless
the failure of H3TMT to be completely metalated by
Zr(CH2Ph)4 when it reacts cleanly and rapidly with
Zr(NMe2)4 is not explained. We conjectured however
that a ligand without ortho-methyl substituents but
with bulky groups in other positions, i.e. TDT would
be better suited to the formation of a zirconium alkyl
and perhaps also our target hydride.
Table 1
Experimental data for the X-ray diffraction studies of 1 and 4
[Zr(TMT)(NMe2)]
(1)
[Zr(TDT)(CH2Ph)]·
C5H12 (4)
Empirical formula
Formula weight
Crystal dimensions
(mm)
Colour
Crystal system
Space group
C35H51N5Zr
633.03
0.10×0.10×0.05
C60H82N4Zr
950.52
0.15×0.10×0.10
Colourless
Monoclinic
P21/c
11.9669(15)
15.755(2)
18.143(2)
102.6250(10)
3338.0(7)
4
1.260
1344
0.360
180(2)
Colourless
Monoclinic
P21/c
16.1683(9)
17.5095(3)
21.652
109.5200(10)
5777.4(3)
4
1.093
2040
0.228
180(2)
,
a (A)
,
b (A)
,
c (A)
,
i (A)
3
,
Cell volume (A )
Z
Dcalc (Mg m−3
F(000)
)
v (mm−1
)
Reaction of H3TDT with Zr(NMe2)4 gives the amido
complex [Zr(TDT)(NMe2)] (3) analogous to 1 (Scheme
1). A similar reaction with Zr(CH2Ph)4 gave the
monobenzyl complex [Zr(TDT)(CH2Ph)] (4) which was
characterised crystallographically (vide infra).
Temperature (K)
qmax (°)
Total reflections
Independent reflections
Rint
28.51
19 491
7736
0.0720
22.50
22 655
7555
0.0644
Parameters
403
604
Tmax, Tmin
0.928, 0.6934
1.083
0.928, 0.7151
1.079
2.2. Molecular structures
Goodness-of-fit on F2
Largest difference peak 0.660 and −0.504
1.556 and −0.491
−3
Single crystals of compounds 1 and 4 were readily
grown by slow cooling of saturated solutions in pen-
tane. Their molecular structures (Table 1) are shown in
Figs. 1 and 2. In both cases the triamidoamine ligand
has approximate three-fold symmetry about the metal
with the aryl substituents encircling the apical site and
forming a bowl- like cavity. This is analogous to the
structure of Schrock’s pentafluorophenyl derivative
[Mo(NNF3 )Cl] [11].
,
and hole (e A
R1, wR2 [I\2|(I)]
)
0.0623, 0.0985
0.0599, 0.1413
2. Results and discussion
2.1. Synthesis
It is instructional to compare the structures of the
aryl complexes 1 and 4 with the similar amido and
benzyl complexes containing the SiMe2But substituted
The triarylated proligands N(CH2CH2NHAr)3 [Ar=
2,4,6-C6H3Me3 (H3TMT) [2f], 3,5-C6H4But2 (H3TDT)]
were synthesised by palladium catalysed arylation of
TREN [9]. The triamine H3(TMT) reacted readily with
Zr(NMe2)4 to give the expected amido complex
[Zr(TMT)(NMe2)] (1) in 77% isolated yield (Schemes 1
and 2). This complex was characterised spectroscopi-
cally and by X-ray crystallography (vide infra).
triamidoamine ligand, i.e. [Zr(NN%)(NMe2)] and
3
[Zr(NN%)(CH2Ph)] which we reported recently [7]. A
3
summary of relevant data is given in Table 2. The
length of the ZrꢀNax bond has an inverse relationship
to both the dihedral angle NaxꢀZrꢀNeqꢀR and the antic-
ipated degree of steric compression in the apical site (X)
(Scheme 3). This can be rationalised as follows. A
complex suffering steric compression about the axial
site at X could relieve this by an increase in the
The reaction of H3(TMT) with Zr(CH2Ph)4 unexpect-
edly gave the dibenzyl complex [Zr(HTMT)(CH2Ph)2]
1
(2) together with two equivalents of toluene. H-NMR

C. Morton et al. / Journal of Organometallic Chemistry 606 (2000) 141–146
143
2.3. Reactions of the alkyls with dihydrogen
aforementioned dihedral angle. The resultant ‘upright’
conformation of the substituents R, which is more
usually associated with metals of smaller radii, leads to
compression of the ZrꢀNax bond.
We mentioned above that the benzyl complex
[Zr(NN%)(CH2Ph)] gives a metallacycle on reaction with
3
dihydrogen. The intermediacy of a hydride species in
this reaction is likely, and indeed a deuteride complex is
implicated in the mechanism of exhaustive deuteration
of the methylsilyl groups on exposure of the complex to
D2 [7]. The reactions of 2 and 4 with dihydrogen (1
atm) at room temperature however gave complex mix-
tures of products.
3. Conclusions
In an effort to synthesise a hydride derivative of
zirconium we used Schrock’s mesityl triamidoamine
ligand H3(TMT), but found that the ortho-substituents
of the aryl rings prevented complete metalation by
Zr(CH2Ph)2. The meta-substituted ligand H3(TDT) was
synthesised, and while this gave the target [Zr(TDT)X]
complexes, this ligand did not support the formation of
a stable hydride.
Fig. 1. Thermal ellipsoid plot of the molecular structure of
,
[Zr(TMT)(NMe2)] (5) (non-hydrogen atoms). Selected distances (A)
and angles (°): Zr(1)ꢀN(3) 2.108(3), Zr(1)ꢀN(1) 2.119(3), Zr(1)ꢀN(2)
2.124(3), Zr(1)ꢀN(5) 2.044(3), Zr(1)ꢀN(4) 2.393(3), N(3)ꢀZr(1)ꢀN(2)
109.42(13), N(3)ꢀZr(1)ꢀN(1) 109.53(13), N(2)ꢀZr(1)ꢀN(1) 118.23(13),
N(3)ꢀZr(1)ꢀN(5) 108.78(13), N(2)ꢀZr(1)ꢀN(5) 101.23(13), N(1)ꢀ
Zr(1)ꢀN(5) 109.09(13), N(3)ꢀZr(1)ꢀN(4) 74.81(12), N(2)ꢀZr(1)ꢀN(4)
73.64(12), N(1)ꢀZr(1)ꢀN(4) 72.72(11), N(5)ꢀZr(1)ꢀN(4) 174.65(13).
4. Experimental
4.1. General methods
All manipulations were carried out under an inert
atmosphere of argon using standard Schlenk techniques
and an MBraun dry-box. NMR samples were made up
in the dry box and the sample tubes were sealed in
vacuo or using Young type concentric stopcocks. Sol-
vents were pre-dried over sodium wire and then distilled
over sodium (toluene) and sodium–potassium alloy
(diethyl ether, pentane) under an atmosphere of dinitro-
gen. Deuterated hydrocarbons were dried by refluxing
over molten potassium in vacuo and then distilled
trap-to-trap also in vacuo. NMR spectra were recorded
at ca. 295 K on Bruker AC-250, AC-400 or DMX-300
spectrometers and the spectra referenced internally us-
ing residual protio solvent resonances relative to te-
tramethylsilane (l=0 ppm). EI mass spectra were
obtained on a VG Autospec mass spectrometer. Ele-
mental Analyses were performed by Warwick Analyti-
cal Services. H2 (Grade 6.0) was purchased from Air
Products. Zr(NMe2)4 [12] and Zr(CH2Ph)4 [13] and
H3TMT [2f] were synthesised by literature methods.
Fig. 2. Thermal ellipsoid plot of the molecular structure of
,
[Zr(TDT)(CH2Ph)] (8) (non-hydrogen atoms). Selected distances (A)
and angles (°): Zr(1)ꢀN(2) 2.070(4), Zr(1)ꢀN(3) 2.082(4), Zr(1)ꢀN(1)
2.114(4), Zr(1)ꢀC(49) 2.311(5), Zr(1)ꢀN(4) 2.455(5), N(3)ꢀZr(1)ꢀN(2)
117.23(18), N(3)ꢀZr(1)ꢀN(1) 106.71(16), N(2)ꢀZr(1)ꢀN(1) 111.05(17),
N(3)ꢀZr(1)ꢀC(49) 105.62(18), N(2)ꢀZr(1)ꢀC(49) 102.36(18), N(1)ꢀ
Zr(1)ꢀC(49) 113.97(18), N(3)ꢀZr(1)ꢀN(4) 71.87(15), N(2)ꢀZr(1)ꢀN(4)
71.60(16), N(1)ꢀZr(1)ꢀN(4) 75.43(15), C(49)ꢀZr(1)ꢀN(4) 170.46(17).
4.2. Crystallography
Crystals were coated with inert oil and transferred to
the cold N2 gas stream on the diffractometer (Siemens

144
C. Morton et al. / Journal of Organometallic Chemistry 606 (2000) 141–146
Table 2
A comparison of bond lengths and angles for 1 and 4 with related complexes
,
,
ZrꢀNax (A)
ZrꢀNeq (A)
Dihedral angles (°) NaxꢀZrꢀNeqꢀR
[Zr(TMT)(NMe2)] (1)
[Zr(TDT)(CH2Ph)] (4)
[Zr(NN3% )(CH2Ph)] (Ref. [7])
[Zr(NN3% )(NMe2)] (Ref. [7])
2.393(3)
2.455(4)
2.5484(15)
2.509(2)
2.108(3), 2.119(3), 2.124(3)
2.070(4), 2.082(4), 2.114(4)
2.0727(15), 2.0796(15), 2.0885(16)
2.096(2), 2.124(3), 2.130(2)
171.4, 160.9, 156.2
169.5, 165.3, 161.4
133.1, 131.0, 128.8
165.3, 131.0,123.8
for 18 h under static reduced pressure. After evapora-
tion of volatiles, the residue was dissolved in diethyl
ether–pentane (10 ml) and filtered. Cooling overnight
to −30°C afforded colourless crystals (0.19 g, 77%).
Anal. Calc. for C35H51N5Zr: C, 66.41; H, 8.12; N,
SMART three-circle with CCD area detector).
Graphite monochromated Mo–Ka radiation u=
,
0.71073 A was used. Absorption correction was per-
formed by multi-scan (SADAB). The structures were
solved by direct methods using SHELXS [14] with addi-
tional light atoms found by Fourier methods. Hydro-
gen atoms were added at calculated positions (except
the hydrogen atoms on C34 and C35 in 1 which were
found by Fourier methods) and refined using a riding
model with freely rotating methyl groups. Anisotropic
displacement parameters were used for all non-H atoms
except a solvent pentane molecule in 4 which was left
isotropic; H-atoms were given isotropic displacement
parameters Uiso(H)=1.2Ueq(C) or 1.5Ueq(C) for methyl
groups. The structures were refined using SHELXL-96
[15].
1
11.06. Found: C, 65.41; H, 7.99; N, 11.04%. H-NMR
(293 K, benzene-d6): l 6.94 (s, 6H, Ph), 3.49 (t, 6H,
CH2), 2.85 (t, 6H, CH2), 2.52 (s, 18H, Me), 2.20 (s, 9H,
Me), 2.04 (s, 6H, NMe2). 13C{1H}-NMR (293 K ben-
zene-d6): l 149.24 (s, Ph), 134.95 (s, Ph), 132.65 (s, Ph),
129.86 (s, Ph), 53.67 (s, CH2), 53.49 (s, CH2), 39.72 (s,
NMe2), 21.22 (s, Me), 20.66 (s, Me). MS (EI): m/z 632
(5%, M++1), 587 (11%, M+−NMe2).
4.3.3. [Zr(TMT)(CH2Ph)2] (2)
Toluene (20 ml) was added to
a mixture of
[H3(TMT)] (0.20 g, 0.40 mmol) and [Zr(CH2Ph)4] (0.19
g, 0.40 mmol) at r.t. The ampoule was wrapped in
aluminium foil and the solution was stirred at ambient
temperature for 3 days. After removal of volatiles, the
residue was extracted with diethyl ether (50 ml), filtered
and cooled to −30°C. Standing overnight afforded a
yellow microcrystalline precipitate (0.12 g, 39%).
4.3. Syntheses
4.3.1. [H3(TDT)]
Toluene (100 ml) was added to a large Schlenk vessel
charged with TREN (2.00 g, 13.7 mmol), 1-bromo-3,5-
di-tert-butylbenzene [16] (11.1 g, 41.1 mmol), Pd2(dba)3
(0.19 g, 0.20 mmol), rac-BINAP (0.34 g, 0.55 mmol)
and NaOBut (4.60 g, 47.5 mmol). The resulting deep-
orange mixture was heated over night at 90°C with
stirring. On cooling to room temperature (r.t.) the
cloudy solution was filtered and the toluene was re-
moved using a rotary evaporator. The crude yellow oil
was chromatographed with a 4:1 mixture of hexane–
ethyl acetate containing 5 vol% of MeOH saturated
with NH3 to give an off-white solid. Recrystallisation
from a 1:1 mixture of diethyl ether–pentane (40 ml)
afforded clear, colourless crystals (4.98 g, 51%).
1H-NMR (293 K, CDCl3): l 6.78 (s, 3H, Ph), 6.44 (s,
6H, Ph), 4.12 (s, 3H, NH), 3.25 (q, 6H, CH2), 2.86 (t,
6H, CH2), 1.24 (s, 54H, But). 13C{1H}-NMR (293 K,
CDCl3): l 152.06 (s, Ph), 148.05 (s, Ph), 112.75 (s, Ph),
107.99 (s, Ph), 54.02 (s, CH2), 42.45 (s, CH2), 35.16 (s,
CMe3), 31.85 (s, CMe3). MS (EI): m/z 712 (65%,
M++1)
Anal. Calc. for C47H60N4Zr: C, 73.10; H, 7.83; N,
1
7.26. Found: C, 72.67; H, 8.06; N, 7.03%. H-NMR
(293 K, benzene-d6): l 6.87 (m, 18H, Ph), 6.78 (d, 2H,
Ph), 6.43 (d, 2H, Ph), 3.44 (m, 2H, CH2), 3.34 (m, 2H,
CH2), 2.90 (m, 4H, CH2), 2.60 (m, 4H, CH2), 2.56 (s,
6H, CH3), 2.48 (s, 6H, CH3), 2.23 (s, 6H, CH3), 2.22
(bs, 9H, CH3), 1.91 (s, 2H, CH2Ph), 1.73 (s, 2H,
CH2Ph). 13C{1H}-NMR (293 K benzene-d6): l 147.97
(s, Ph), 145.16 (s, Ph), 143.70 (s, Ph), 135.38 (s, Ph),
135.02 (s, Ph), 134.79 (s, Ph), 132.47 (s, Ph), 130.92 (s,
Ph), 130.77 (s, Ph), 130.31 (s, Ph), 130.19 (s, Ph), 130.08
(s, Ph), 129.39 (s, Ph), 127.30 (s, Ph), 123.47 (s, Ph),
121.79 (s, Ph), 67.15 (s, CH2Ph), 63.56 (s, CH2Ph),
55.42 (s, CH2), 52.82 (s, CH2), 50.84 (s, CH2), 41.74
4.3.2. [Zr(TMT)(NMe2)] (1)
Toluene (20 ml) was added to
a mixture of
[H3(TMT)] (0.20 g, 0.40 mmol) and [Zr(NMe2)4] (0.11
g, 0.40 mmol). The reaction was then heated at 80°C
Scheme 3.

C. Morton et al. / Journal of Organometallic Chemistry 606 (2000) 141–146
145
(s, CH2), 21.32 (s, CH3), 20.55 (s, CH3), 19.67 (s, CH3),
Acknowledgements
18.91 (s, CH3). MS (EI): m/z 587 (28%, M+
−2CH2Ph).
P.S. wishes to thank EPSRC for Project Studentship
and Postdoctoral grants (C.M., C.J.S. and K.M.G.)
and SmithKline Beecham for a CASE award (C.J.S).
We thank EPSRC and Siemens Analytical Instruments
for grants in support of the diffractometer.
4.3.4. [Zr(TDT)(NMe2)] (3)
Toluene (20 ml) was added to
a mixture of
[H3(TDT)] (0.25 g, 0.35 mmol) and [Zr(NMe2)4] (94 mg,
0.35 mmol). The mixture was heated at 80°C for 2 days
under static reduced pressure. After removal of
volatiles, the residue was dissolved in pentane, filtered
and cooled to −30°C. Standing overnight afforded a
white microcrystalline precipitate (0.26 g, 88%).
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(293 K, benzene-d6): l 7.23 (t, 3H, Ph), 7.17 (d, 6H,
Ph), 3.78 (t, 6H, CH2), 2.68 (t, 6H, CH2), 2.34 (s, 6H,
NMe2), 1.44 (s, 54H, But). 13C{1H}-NMR (293 K ben-
zene-d6): l 155.01 (s, Ph), 151.50 (s, Ph), 117.31 (s, Ph),
115.81 (s, Ph), 55.32 (s, CH2), 53.30 (s, CH2), 40.61 (s,
NMe2), 35.38 (s, CMe3), 32.33 (s, CMe3).). MS (EI):
m/z 841 (6%, M+), 797 (18%, M+−NMe2).
4.3.5. [Zr(TDT)(CH2Ph)] (4)
Toluene (20 ml) was added to
a mixture of
[H3(TDT)] (0.25 g, 0.35 mmol) and [Zr(CH2Ph)4] (0.16
g, 0.35 mmol) at r.t. The ampoule was covered in
aluminium foil and the mixture was stirred at ambient
temperature for 3 days. After removal of volatiles, the
residue was redissolved in pentane (5 ml), filtered and
cooled to −30°C. Standing overnight afforded pale-or-
ange crystals (0.20 g, 64%).
Anal. Calc. for C55H82N4Zr: C, 74.18; H, 9.28; N,
1
6.29. Found: C, 70.41; H, 8.96; N, 6.20%. H-NMR
(293 K, benzene-d6): l 7.33 (t, 3H, Ph), 7.17 (d, 6H,
Ph), 7.01 (m, 3H, Ph), 5.86 (d, 2H, Ph), 3.55 (t, 6H,
CH2), 2.51 (s, 2H, CH2Ph), 2.31 (t, 6H, CH2), 1.48 (s,
54H, But). 13C{1H}-NMR (293 K benzene-d6): l 153.41
(s, Ph), 152.64 (s, Ph), 151.68 (s, Ph), 125.36 (s, Ph),
120.63 (s, Ph), 117.37 (s, Ph), 116.53 (s, Ph), 115.63
(s, Ph), 54.93 (s, CH2), 53.44 (s, CH2), 35.59 (s,
CMe3), 32.50 (s, CMe3). MS (EI): m/z 797 (42%,
M+−CH2Ph).
[7] C. Morton, I.J. Munslow, C.J. Sanders, N.W. Alcock, P. Scott,
Organometallics 18 (1999) 4608.
5. Supplementary material
[8] (a) R. Boaretto, P. Roussel, N.W. Alcock, A.J. Kingsley, I.J.
Munslow, C.J. Sanders, P. Scott, J. Organomet. Chem. 591
(1999) 174. (b) R. Boaretto, P. Roussel, A.J. Kingsley, I.J.
Munslow, C.J. Sanders, N.W. Alcock, P. Scott, Chem. Com-
mun. (1999) 1701.
[9] J.P. Wolfe, S. Wagaw, S.L. Buchwald, J. Am. Chem. Soc. 118
(1996) 7215.
[10] L.-C. Liang, R.R. Schrock, W.M. Davis, D.H. McConville, J.
Am. Chem. Soc. 121 (1999) 5797.
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC, nos. 141 097 (compound 1) and
141 098 (4). Copies of this information may be ob-
tained free of charge from: The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
[11] M. Kol, R.R. Schrock, R. Kempe, W.M. Davis, J. Am. Chem.
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[15] G.M. Sheldrick, SHELX-96 (beta-test, including SHELXS and
SHELXL), 1996.
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