Low temperature in situ UV irradiation of [(η5-C 5H5)Co(C2H4)2] in the NMR probe: Formation of Co(iii) silyl hydride complexes

Article abstract of DOI:10.1039/b705290a

Low temperature in situ UV irradiation of [(η⁵-C ₅H₅)Co(C₂H₄)₂] in the presence of silanes enables the characterisation of unstable fluxional Co(iii) silyl hydride complexes [(η⁵

Full text of DOI:10.1039/b705290a

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Low temperature in situ UV irradiation of [(g5-C5H5)Co(C2H4)2] in the
NMR probe: formation of Co(III) silyl hydride complexes
Kirsten A. M. Ampt, Simon B. Duckett* and Robin N. Perutz*
Received 10th April 2007, Accepted 10th May 2007
First published as an Advance Article on the web 31st May 2007
DOI: 10.1039/b705290a
5
Low temperature in situ UV irradiation of [(g -C5H5)Co-
complexes that interconvert on the NMR timescale as shown by
1H NMR spectroscopy at 400 MHz.
(C2H4)2] in the presence of silanes enables the characterisation
of unstable fluxional Co(III) silyl hydride complexes [(g -
5
An NMR tube, charged with [(g -C5H5)Co(C2H4)2],32 1, in
5
deuterated toluene and excess HSiEt3, was irradiated (He–Cd
laser, 325 nm) inside the NMR probe at 203 K. In the H NMR
C5H5)Co(SiR3)(H)(C2H4)] (SiR3 = SiEt3, SiMe3 or SiHEt2)
1
5
by NMR spectroscopy; the reaction of [Co(g -C5H5)(C2H4)2]
spectrum, a hydride resonance started to appear at d −20.25,
which grew in intensity during prolonged photolysis. After 3 h
photolysis, a photostationary state was reached at approximately
30% conversion. A new Cp resonance at d 4.28 and other proton
resonances could also be detected as well as 13C and 29Si resonances.
NMR characterisation with COSY, NOESY and HMQC methods
with HSiR3 proceeds thermally to reach an equilibrium when
SiR3 = Si(OMe)3 or SiClMePh.
The study of half sandwich complexes of cobalt, rhodium, and
iridium with ethene ligands has shown that there are substantial
5
differences in their chemical behaviour. [(g -C5H5)Co(C2H4)2] is
5
showed that these resonances belonged to the Co(III) complex, [(g -
very labile towards thermal loss of ethene,1–5 whereas the rhodium
and iridium analogues are much more thermally inert.6 It is a
rarity to find analogous reactions with all three metals.7 The
rhodium complex and its analogues lose ethene readily under
photochemical conditions,8–13 but the half sandwich iridium ethene
complexes are prone to photochemical isomerization to vinyl
hydride complexes in addition to photodissociation of ethene.14–17
Several studies have been carried out on the reactivity of
C5H5)Co(SiEt3)(H)(C2H4)], 2.† Four distinct proton resonances
could be distinguished for the ethene protons, indicating that the
ethene ligand does not rotate rapidly at 203 K, in accordance
with the failure to detect any exchange peaks connecting the four
resonances in the corresponding EXSY spectrum. There was no
sign of any other hydride resonances in the 1H spectrum suggesting
that double oxidative addition does not take place under these
5
conditions. This contrasts with [(g -C5H5)Rh(SiEt3)(H)(C2H4)]
5
5
[(g -C5H5)Rh(C2H4)2] and [(g -C5Me5)Rh(C2H4)2] towards silanes
5
which readily reacts further to form [(g -C5H5)Rh(SiEt3)2(H)2]
5
and species of the type [(g -C5H5)Rh(SiR3)(H)(C2H4)] have been
characterised following irradiation of [(g -C5H5)Rh(C2H4)2].8,18–24
2
under such conditions.20,21 The value of JSiH for the hydride
5
resonance of 2 was determined in a gradient-filtered 1H–29Si
Much less is known about the reactivity of their cobalt ana-
correlation as 30
3 Hz and is therefore substantially larger
5
logues. Heaton et al. isolated the Co(III) disilyl [(g -C5H5)Co{1,2-
than that in the corresponding Rh(III) analogue where it was
estimated as 12.2 Hz. When complex 2 was slowly warmed up,
its resonances started to disappear from the associated NMR
spectra above 223 K. At the same time, the free ethene in the
sample, produced during photolysis, was observed to react with
complex 2 to regenerate complex 1 (eqn (1)). A small amount of
decomposition also takes place. When the sample was cooled back
down and photolysed again, complex 2 was formed once more.
5
(SiMe2)2C6H4}(C2H4)] by reaction of [(g -C5H5)Co(C2H4)2] with
C6H4(1,2-SiMe2H)2.25 More recently, Brookhart et al. reported
5
the formation of the Co(V) complex [(g -C5Me5)Co(SiHPh2)2(H)2]
5
by reacting [(g -C5Me5)Co(C2H4)2] with diphenylsilane.26 It was
5
suggested that it was formed via the Co(III) silylhydride species [(g -
C5Me5)Co(SiHPh2)(H)(C2H4)], but no direct evidence was pre-
sented for this intermediate. The only half sandwich Co(III) silyl hy-
5
drides characterised so far, are [(g -C5H5)Co(SiR3)(H)(CO)] (R =
5
Cl, Et) formed by photochemical reaction of [(g -C5H5)Co(CO)2]
with HSiR3.27,28,29 In thermal reactions, [CpCo(C2H4)2] acts as
5
a very effective source of [(g -C5H5)Co],1–3 but such thermal
5
5
reactions rarely give (g -C5H5)Co(C2H4) products30 and [(g -
C5H5)Co(C2H4)2] is therefore normally unsuitable as a precursor
for detection of very labile species of this type. Presuming that the
corresponding Co(III) silyl hydride products would be very labile,
(1)
In order to establish the effect of the silicon substituents on the
reaction, complex 1 was photolysed in the presence of HSiMe3,
H2SiEt2 and HSiPh3. During photolysis in the presence of HSiMe3
at 203 K a hydride resonance at d −20.04 appeared after several
minutes, which grew in intensity during prolonged photolysis. The
corresponding value of 2JSiH was 35 3 Hz. A limiting conversion
of approximately 30% was again reached and the product was
5
we have investigated the photochemistry of [(g -C5H5)Co(C2H4)2]
at low temperatures using laser photolysis inside the NMR
5
probe head to generate [(g -C5H5)Co(C2H4)].31 We show that
photolysis of [CpCo(C2H4)2] in the presence of silanes does indeed
yield several silyl hydride complexes that react very readily with
ethene. Reaction with a chiral silane generates two diastereomeric
5
identified as [(g -C5H5)Co(SiMe3)(H)(C2H4)], 3 (Fig. 1).†Complex
3 proved to be stable until 253 K, a slightly higher temperature
than 2. When the corresponding reaction was carried out under
an ethene atmosphere, the formation of 3 was quenched entirely,
Department of Chemistry, University of York, Heslington, York, UK YO10
5DD. E-mail: sbd3@york.ac.uk, rnp1@york.ac.uk
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6.† Neither photolysis at room temperature, nor at 203 K,
increased the yield. When all the volatiles were removed, the
sample redissolved in toluene and further trimethoxysilane added,
the percentage conversioncould be increasedto15%. On repetition
of this process, the conversion progressed further to 21%. Clearly,
only a very small amount of ethene is necessary to affect the
position of equilibrium dramatically. The removal of the ethene
shifts the equilibrium towards complex 6, according to eqn (2).
The value of 2JSiH in 6 was 50 3 Hz and clearly lies outside the
range associated with classical oxidative addition products.35–37
2
We suggest that these Co species show substantial Co(I), g -SiH
character, decreasing in the order Si(OMe)3 > SiMe3 > SiEt3>
SiHEt2
295 K
−−−ꢀ
ꢁ−−−
CpCo(C2H4)2 + HSi(OMe)3
(2)
C
H
4
2
1
CpCo{Si(OMe)3}(H)(C2H4) + C2H4
6
When a sample containing a mixture of complexes 1 and 6,
ethene and trimethoxysilane, was heated for 10 min at 313 K,
1
Fig. 1 2D 1H–1H COSY NMR spectrum recorded at 203 K in toluene-d8
of complexes 1 and 3 with cross peaks due to the four inequivalent ethene
resonances of 3 indicated.
the H NMR spectrum, recorded at 295 K, showed three new
resonances at d 0.62, 1.05 and 3.43 consistent with the hydrosi-
lation product C2H5Si(OMe)3.38 The volatiles were transferred
into another NMR tube, and the 29Si resonance of the product
was detected at d −41.8 in agreement with the literature.39 In
suggesting a similar equilibrium to that shown in eqn (1). The
5
reaction between 1 and diethylsilane proceeded in a similar manner
previous studies [(g -C5H5)Rh(SiEt3)(H)(C2H4)] has been shown
5
to form [(g -C5H5)Co(SiHEt2)(H)(C2H4)], 4.† In the associated
to be involved in the hydrosilation process of C2H4 and HSiEt3,
forming both SiEt4 and CH2 CHSiEt3.21 It is suggested that [(g -
5
NMR spectra of 4, NOE’s could be measured from the Cp
resonance to the resonances of the ethyl groups indicating that
the two ethyl groups of the silane point towards the C5H5 ring. An
NOE connection could also be seen from the SiH proton resonance
to Hc of the ethene ligand, where the labelling is consistent with
that used in eqn (1).
=
C5H5)Co{Si(OMe)3}(H)(C2H4)] is the catalyst in the hydrosilation
of C2H4 and HSi(OMe)3. There was no evidence for the formation
=
of CH2 CHSi(OMe)3.
In previous studies, we have shown that the equivalence of
the two enantiomers of [(g -C5H5)Rh(SiR3)(H)(alkene)] in the
5
NMR spectra can be lifted by use of a mono-substituted alkene.
2
The resulting diastereomers undergo exchange via Rh(g -silane)
intermediates.40 A similar result was achieved by photolysis of
5
[(g -C5H5)Rh(C2H4)2] in the presence of a chiral silane.41 Upon
addition of racemic HSiClMePh to complex 1 (1 : HSiClMePh ≈
5
When 1 was left to react with triphenylsilane at 295 K, some
thermal reaction occurred resulting in detection of a hydride
resonance at d −18.95 and the resonance of free ethene (d 5.3).
With a ratio of 1 : Ph3SiH of 2.6, thermal conversion to the
product was less than 2% and the yield only increased to 8%
during photolysis at 203 K. Nevertheless, the product could be
5), two isomers of [(g -C5H5)Co(SiClMePh)(H)(C2H4)], 7a and
7b, are formed thermally at room temperature in almost equal
quantities.† The conversion of 44% is not altered by photolysis,
suggesting an equilibrium between 1 and 7 similar to that between
1 and 6. The hydride resonances sharpen and separate on cooling
reaching an optimum at 223 K, but on further cooling, they
broaden again. On heating, the resonances coalesce at 303 K
(Fig. 2), but further heating causes decomposition. The changes
in the spectrum between 223 and 303 K are consistent with
exchange between the two isomers, 7a and 7b. The broadening
of the resonances at lower temperatures probably arises from
restricted rotation of the silane ligand. Confirmation of free
rotation of the silyl ligand at higher temperatures comes from
NOE measurements which show connections between the hydride
5
identified as [(g -C5H5)Co(SiPh3)(H)(C2H4)], 5 (the integrals of
other hydride resonances were ca. fifty times smaller than that
of 5).† The small amount of conversion, even after photolysis,
suggests that the rate of oxidative addition is very slow compared
to the back reaction with ethene. The rapid back reaction can
probably be attributed to the bulk of the silane in agreement with
the observations made by Duczmal and co-workers who found
that for RhCl(cod)PPh3 the rate of oxidative addition of silanes is
reduced as the steric bulk of the silane increases.33,34 The percentage
conversion reverts to less than 1% if the sample is kept at 253 K
after photolysis, suggesting that the thermodynamic equilibrium
position lies in favour of complex 1.
resonance and the methyl and phenyl resonances in both isomers.
2
The value of JSiH was estimated to be 35
and 7b.
3 Hz in both 7a
Rates of exchange at the coalescence temperature were de-
termined using the method developed by Shanan-Atidi and
Bar-Eli for unequal populations (kAB = 382, kBA = 422 s−1).42
Activation barriers at 303 K could then be estimated from
The reaction of 1 and trimethoxysilane (1 : HSi(OMe)3 ≈ 2) also
proceeded thermally at room temperature and reached approx-
5
imately 10% conversion to [(g -C5H5)Co{Si(OMe)3}(H)(C2H4)],
2994 | Dalton Trans., 2007, 2993–2996
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5
[(g -C5H5)Co(SiMe3)(H)(C2H4)], 3 1H: −20.04 (s), 0.36 (s, Si(CH3)3), 1.00
(m, C2H4), 1.70 (m, C2H4), 2.14 (m, C2H4), 2.75 (m, C2H4), 4.21 (s, Cp),
1
13C{ H}: 7.1 (Si(CH3)3), 28.4 (C2H4), 31.9 (C2H4), 84.6 (Cp), 29Si: 24.0,
2JSiH = 35 Hz.
5
[(g -C5H5)Co(SiHEt2)(H)(C2H4)], 4 1H: −20.10 (s), 0.58 (q, 7 Hz,
SiCH2CH3), 1.08 (q, 7 Hz, SiCHꢀ2CHꢀ3), 1.09 (m, C2H4), 1.20 (t, 7 Hz,
SiCH2CH3), 1.32 (t, 7 Hz, SiCHꢀ2CHꢀ3), 1.77 (m, C2H4), 2.12 (m, C2H4),
1
2.77 (m, C2H4), 3.72 (s, SiH), 4.21 (s, Cp), 13C{ H}: 7.0 (SiCHꢀ2CHꢀ3),
7.1 (SiCH2CH3), 11.0 (SiCH2CH3), 11.6 (SiCHꢀ2CHꢀ3), 29.1 (C2H4), 32.4
(C2H4), 84.4 (Cp), 29Si: 28.7, 2JSiH = 25 Hz.
5
[(g -C5H5)Co(SiPh3)(H)(C2H4)], 5 1H: −18.95 (s), 1.23 (m, C2H4), 1.65 (m,
C2H4), 2.11 (m, C2H4), 2.79 (m, C2H4), 4.18 (s, Cp), 7.73 (m, Phm), 7.73
1
(m, Php), 7.97 (m, Pho), 13C{ H}: 31.9 (C2H4), 33.5 (C2H4), 86.1 (Cp), 29Si:
27.9.
5
[(g -C5H5)Co{Si(OMe)3}(H)(C2H4)], 6 1H: −20.14 (s), 1.86 (m, C2H4),
1.88 (m, C2H4), 2.09 (m, C2H4), 2.79 (m, C2H4), 3.57 (s, Si(OCH3)3), 4.45
1
(s, Cp), 13C{ H}: 30.7 (C2H4), 30.9 (C2H4), 50.1 (Si(OCH3)3), 86.1 (Cp),
29Si: −1.1, 2JSiH = 50 Hz.
5
[(g -C5H5)Co(SiClMePh)(H)(C2H4)], 7a (at 253 K): 1H: −18.95 (s), 0.69 (s,
Fig. 2 Variable temperature 1H NMR spectra of 7a and 7a in toluene-d8
in the hydride region.
CH3), 1.32 (m, C2H4), 1.65 (m, C2H4), 2.22 (m, C2H4), 2.79 (m, C2H4), 4.30
(s, Cp), 7.19 (m, Phm), 7.52 (m, Php), 7.68 (m, Pho), 13C{ H}: 9.2 (CH3),
1
32.0 (C2H4), 34.9 (C2H4), 86.3 (Cp), 128.0 (Phm), 128.4 (Php), 132.4 (Pho),
transition state theory; DG‡ = 59.3 kJ mol−1 for 7a to 7b
143.7 (Phi), 29Si: 57.8, 2JSiH = 35 Hz.
and DG‡ = 59.0 kJ mol−1303for 7b to 7a. These barriers are
5
1
[(g -C5H5)Co(SiClMePh)(H)(C2H4)], 7b (at 253 K): H: −19.26 (s), 0.77
303
(s, CH3), 1.44 (m, C2H4), 1.54 (m, C2H4), 2.26 (m, C2H4), 2.74 (m, C2H4),
similar to those determined previously for isomer interconversion
4.21 (s, Cp), 7.13 (m, Phm), 7.43 (m, Php), 7.65 (m, Pho), 13C { H}: 12.4
1
5
t
in [(g -C5H5)Rh(SiR3)(H)(C2H3CO2 Bu)] where the value of DG‡
(CH3), 32.9 (C2H4), 36.0 (C2H4), 85.8 (Cp), 128.1 (Phm), 128.8 (Php), 132.7
at 303 K is calculated to be 56.6 kJ mol−1.40 These experiments are
(Pho), 142.2 (Phi), 29Si: 59.7, 2JSiH = 35 Hz.
5
2
consistent with exchange between 7a and 7b via [(g -C5H5)Co(g -
HSiClMePh)(C2H4)] either as a transition state or an intermediate.
However, this mechanism is not the only one that could explain
the limited mechanistic data. We did not use line-shape analysis
because exchange is not the only factor contributing to the
variation of line shape with temperature in these cobalt complexes.
In conclusion, we have used NMR spectroscopy to study
1 K. Jonas, E. Deffense and D. Habermann, Angew. Chem., Int. Ed. Engl.,
1983, 22, 716.
2 A. Goswami, Y. Nie, T. Oeser and W. Siebert, Eur. J. Inorg. Chem.,
2006, 566.
3 J. K. Cammack, S. Jalisatgi, A. J. Matzger, A. Negron and K. P. C.
Vollhardt, J. Org. Chem., 1996, 61, 4798.
4 H. Wadepohl, W. Gulm, H. Pritzkow and A. Wolf, Chem.–Eur. J., 1996,
2, 1453.
5 W. A. Herrmann, C. E. Barnes, T. Zahn and M. L. Ziegler,
Organometallics, 1985, 4, 172.
6 W. D. Jones and R. M. Chin, J. Am. Chem. Soc., 1992, 114, 9851.
7 P. B. Hitchcock, M. J. Maah and J. F. Nixon, J. Chem. Soc., Chem.
Commun., 1986, 737.
8 S. B. Duckett, D. M. Haddleton, S. A. Jackson, R. N. Perutz, M.
Poliakoff and R. K. Upmacis, Organometallics, 1988, 7, 1526.
9 S. T. Belt, S. B. Duckett, D. M. Haddleton and R. N. Perutz,
Organometallics, 1989, 8, 748.
10 H. Wadepohl, A. Metz and H. Pritzkow, Chem.–Eur. J., 2002, 8, 1591.
11 J. Mu¨ller, C. Hirsch, A. L. Guo and K. Qiao, Z. Anorg. Allg. Chem.,
2000, 626, 2069.
12 J. Mu¨ller, P. E. Gaede, C. Hirsch and K. Qiao, J. Organomet. Chem.,
1994, 472, 329.
13 G. Kohl, R. Rudolph, H. Pritzkow and M. Enders, Organometallics,
2005, 24, 4774.
14 T. W. Bell, D. M. Haddleton, A. McCamley, M. G. Partridge, R. N.
Perutz and H. Willner, J. Am. Chem. Soc., 1990, 112, 9212.
15 T. W. Bell, M. Helliwell, M. G. Partridge and R. N. Perutz,
Organometallics, 1992, 11, 1911.
16 T. W. Bell, S. A. Brough, M. G. Partridge, R. N. Perutz and A. D.
Rooney, Organometallics, 1993, 12, 2933.
17 J. Mu¨ller, T. Akhnoukh, P. E. Gaede, A. L. Guo, P. Moran and K. Qiao,
J. Organomet. Chem., 1997, 541, 207.
18 D. M. Haddleton and R. N. Perutz, J. Chem. Soc., Chem. Commun.,
1985, 1372.
5
the formation of Co(III) silyl hydride complexes [(g -C5H5)-
5
Co(SiR3)(H)(C2H4)] by reaction of hydrosilanes with [(g -
C5H5)Co(C2H4)2] 1. The stability of these complexes is dependent
on the silane involved. When SiR3 is SiEt3, SiMe3 or SiHEt2, the
product can only be formed photochemically at low temperatures.
These species react very readily with the ethene released in the
initial reaction to regenerate 1. When SiR3 is SiPh3, the product is
formed thermally but the yield can be improved photochemically
at low temperature. When SiR3 is Si(OMe)3 or SiClMePh, the
reaction proceeds thermally at room temperature to yield 6 and 7,
respectively. Although 6 and 7 are observable at room temperature,
neither of them is stable for long periods, making it difficult to
isolate them as pure materials. The conversion can be improved
by removal of liberated ethene, as there is a clear equilibrium
5
between the products and [(g -C5H5)Co(C2H4)2]. Complex 7 exists
as two isomeric hydride species which interconvert with a free
energy of activation of ca. 59 kJ mol−1. In situ laser photolysis has
proved to be a valuable tool for the study of labile Co(III) silyl
hydrides. Contrary to our initial expectations some of the Co(III)
silyl hydrides are observable at room temperature.
19 S. T. Belt, D. M. Haddleton, R. N. Perutz, B. P. H. Smith and A. J.
Dixon, J. Chem. Soc., Chem. Commun., 1987, 1347.
20 S. B. Duckett and R. N. Perutz, J. Chem. Soc., Chem. Commun., 1991,
28.
21 S. B. Duckett and R. N. Perutz, Organometallics, 1992, 11, 90.
22 P. O. Bentz, J. Ruiz, B. E. Mann, C. M. Spencer and P. M. Maitlis,
J. Chem. Soc., Chem. Commun., 1985, 1374.
23 J. Ruiz and P. M. Maitlis, J. Chem. Soc., Chem. Commun., 1986, 862.
24 J. Ruiz, P. O. Bentz, B. E. Mann, C. M. Spencer, B. F. Taylor and P. M.
Maitlis, J. Chem. Soc., Dalton Trans., 1987, 2709.
25 Y. J. Kang, K. I. Kim, S. O. Kang, J. J. Ko, B. T. Heaton and J. V.
Barkley, J. Organomet. Chem., 1997, 532, 79.
Notes and references
† NMR data complexes 2–7 in toluene-d8 at 203 K (1H 400.13 MHz, 13
C
100.62 Hz, 29Si 79.49 MHz). 13C and 29Si NMR spectra were collected as
2D HMQC spectra with delays set both for short range and long range
coupling in the case of 13C spectra.
5
[(g -C5H5)Co(SiEt3)(H)(C2H4)],
2
1H: −20.25 (s), 0.68 (q,
7
Hz,
Si(CH2CH3)3), 1.10 (m, C2H4), 1.12 (t, 7 Hz, Si(CH2CH3)3), 1.61 (m,
C2H4), 2.02 (m, C2H4), 2.74 (m, C2H4), 4.28 (s, Cp), 13C{ H}: 9.8
1
(Si(CH2CH3)3), 10.3 (Si(CH2CH3)3), 28.7 (C2H4), 30.5 (C2H4), 84.2 (Cp),
29Si: 38.9, 2JSiH = 30 Hz.
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26 M. Brookhart, B. E. Grant, C. P. Lenges, M. H. Prosenc and P. S.
White, Angew. Chem., Int. Ed., 2000, 39, 1676.
27 W. Jetz and W. A. G. Graham, Inorg. Chem., 1971, 10, 4.
28 W. Jetz and W. A. G. Graham, J. Am. Chem. Soc., 1969, 91,
3375.
34 W. Duczmal, E. Sliwinska, B. Maciejewska, B. Marciniec and H.
Maciejewski, Transition Met. Chem., 1995, 20, 435.
35 J. Y. Corey and J. Braddock-Wilking, Chem. Rev., 1999, 99, 175.
36 S. K. Ignatov, N. H. Rees, S. R. Dubberley, A. G. Razuvaev, P.
Mountford and G. I. Nikonov, Chem. Commun., 2004, 952.
37 U. Schubert, Adv. Organomet. Chem., 1990, 30, 151.
38 F. Kakiuchi, S. Sekine, Y. Tanaka, A. Kamatani, M. Sonoda, N.
Chatani and S. Murai, Bull. Chem. Soc. Jpn., 1995, 68, 62.
39 P. Sormunen, E. Iiskola, E. Vahasarja, T. T. Pakkanen and T. A.
Pakkanen, J. Organomet. Chem., 1987, 319, 327.
29 P. T. Snee, C. K. Payne, K. T. Kotz, H. Yang and C. B. Harris, J. Am.
Chem. Soc., 2001, 123, 2255.
30 E. Fooladi, B. Dalhus and M. Tilset, Dalton Trans., 2004, 3909.
31 C. Godard, P. Callaghan, J. L. Cunningham, S. B. Duckett, J. A. B.
Lohman and R. N. Perutz, Chem. Commun., 2002, 2836.
32 K. Jonas, E. Deffense and D. Habermann, Angew. Chem. Suppl., 1983,
1005.
40 K. A. M. Ampt, S. B. Duckett and R. N. Perutz, Dalton Trans., 2004,
3331.
33 W. Duczmal, B. Maciejewska, E. Sliwinska and B. Marciniec, Transition
41 K. A. M. Ampt, PhD Thesis, University of York, 2005.
42 H. Shanan-Atidi and K. H. Bar-Eli, J. Phys. Chem., 1970, 74, 961.
Met. Chem., 1995, 20, 162.
2996 | Dalton Trans., 2007, 2993–2996
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