Yttrium complexes incorporating the chelating diamides {ArN(CH 2)xNAr}2- (Ar = C6H 3-2,6-iPr2, x = 2, 3) and their unusual reaction with phenylsilane

Article abstract of DOI:10.1039/b400149d

Novel yttrium chelating diamide complexes [(Y{ArN(CH₂) _xNAr}(Z)(THF)_n)_y,] (Z = I, CH(SiMe ₃)₂, CH₂Ph, H, N(SiMe₃)₂, OC₆H₃-2,6-^tBu₂-4-Me; x = 2, 3; n = 1 or 2; y = 1 or 2) were made via salt metathesis of the potassium diamides (x = 3 (3), x = 2 (4)) and yttrium triiodide in THF (5, 10), followed by salt metathesis with the appropriate potassium salt (6-9, 11-13, 15) and further reaction with molecular hydrogen (14). 6 and 11 (Z = CH(SiMe₃) ₂, x = 2, 3) underwent unprecedented exchange of yttrium for silicon on reaction with phenylsilane to yield (Si{ArN(CH₂) _xNAr}PhH) (x = 2 (16), 3) and (Si{CH(SiMe₃) ₂}PhH₂).

Full text of DOI:10.1039/b400149d

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Yttrium complexes incorporating the chelating diamides
{ArN(CH2)xNAr}2؊ (Ar ؍ C6H3-2,6-iPr2, x ؍ 2, 3) and their
unusual reaction with phenylsilane†
Anthony G. Avent, F. Geoffrey N. Cloke,* Benjamin R. Elvidge and Peter B. Hitchcock
Department of Chemistry, School of Life Sciences, University Of Sussex, Falmer, Brighton,
UK BN1 9QJ. E-mail: f.g.cloke@sussex.ac.uk; Fax: ϩ44 1273 677196; Tel: ϩ44 1273 678735
Received 6th January 2004, Accepted 19th February 2004
First published as an Advance Article on the web 10th March 2004
Novel yttrium chelating diamide complexes [(Y{ArN(CH2)xNAr}(Z)(THF)n)y] (Z = I, CH(SiMe3)2, CH2Ph, H,
N(SiMe3)2, OC6H3-2,6-tBu2-4-Me; x = 2, 3; n = 1 or 2; y = 1 or 2) were made via salt metathesis of the potassium
diamides (x = 3 (3), x = 2 (4)) and yttrium triiodide in THF (5, 10), followed by salt metathesis with the appropriate
potassium salt (6–9, 11–13, 15) and further reaction with molecular hydrogen (14). 6 and 11 (Z = CH(SiMe3)2,
x = 2, 3) underwent unprecedented exchange of yttrium for silicon on reaction with phenylsilane to yield
(Si{ArN(CH2)xNAr}PhH) (x = 2 (16), 3) and (Si{CH(SiMe3)2}PhH2).
Introduction
Since the pioneering work of Watson and Marks, considerable
research activity has been directed towards the synthesis and
characterisation of lanthanide and group 3 complexes that
might offer neutral, isolable, co-catalyst free alternatives to the
group 4 metallocene systems, which require activation by a
highly Lewis acidic species, often methylaluminoxane (MAO),
in order to polymerise olefins.1
Most of the seminal work on lanthanide and group 3 com-
plexes has relied on systems supported by permethylcyclo-
pentadienyl ligands.2 Lately, many research groups have studied
complexes incorporating ligand systems free of this ubiquitous
group, in an attempt to provide an alternative coordination
environment for the metal centre that might affect the structure
and reactivity of the complexes so-produced.3 Ligands
incorporating nitrogen donor atoms are especially versatile,
Fig. 1 Selected group 3 complexes supported by chelating diamide
ligands.
offering two valencies to the ligand framework that can be
tailored to kinetically stabilise the metal centre. In addition the
hard, anionic nitrogen atom is especially suited to the very hard,
the work already communicated, as well as similar studies on
cationic lanthanide centre.4
the less sterically encompassing congener {ArN(CH2)2NAr}2Ϫ
We recently reported the synthesis and characterisation of
yttrium iodide and bis(trimethylsilyl)methyl complexes sup-
(Ar = C6H3-2,6-iPr2) that was anticipated to offer a somewhat
different coordination environment at the metal centre,
ported by the chelating diamide {ArN(CH2)3NAr}2Ϫ (Ar =
especially with respect to donor solvent coordination and
C6H3-2,6-iPr2),5 previously reported by McConville and
reactivity towards olefinic monomers.
co-workers to effect ‘living’ polymerisation of α-olefins when
the dimethyl titanium derivative is activated by B(C6F5)3.6 A
number of structurally similar lanthanide and group 3 chelating
diamide complexes have been communicated by other groups,
Results and discussion
Synthesis of potassium salts
a representative sample of which includes [Y(NON){CH-
(SiMe3)2}(THF)] (i),7 [Y(DADMB){CH(SiMe3)2}(THF)] (ii),8
[Y(P2N2)(CH2SiMe3)] (iii),9 [Y(NPN)(CH2SiMe3)(THF)] (iv),10
We adopted a salt metathesis strategy in order to introduce the
organic frameworks to the yttrium centre, in contrast to the
σ-bond metathesis approach, using the tris-hydrocarbyl
[Y(CH2SiMe3)3(THF)2]13 or tris-amide [Y{N(SiMe3)2}3],14
preferred by a number of groups. It is now widely accepted that
potassium reagents are more effective at introducing organic
fragments to lanthanide centres than their lithium analogues.
Potassium salts are much more reactive and the co-product in
metathesis with lanthanide triiodides,15 potassium iodide, is
insoluble in all common organic solvents and is usually too
large to form an ate-complex with the lanthanide ion. Lithium
reagents by comparison often require forcing conditions
to react with the hard, Lewis-acidic lanthanides and give the
metathesis products LiX (X = Cl, Br, I), which are extremely
persistent as they have some solubility in organic solvents.16
The potassium reagents were prepared via transmetallation
of the in situ-generated lithium complex with a stoichio-
Mes
[Sc(BDPPyr)(CH2SiMe3)(THF)] (v)11 and [Sc(N2 Npy)-
(CH2SiMe3)(THF)] (vi)12 (Fig. 1). Many other lanthanide and
group 3 complexes supported by bi-, tri-, tetra- and polydentate
amide ligands have been reported and are detailed in a series of
excellent review articles.3
We report here the synthesis and characterisation of a
number of yttrium complexes incorporating the chelating
diamide {ArN(CH2)3NAr}2Ϫ (Ar = C6H3-2,6-iPr2), further to
† Electronic supplementary information (ESI) available: Molecular
structure
of
[Y{ArN(CH2)3NAr}(OC6H3-2,6-tBu2-4-Me)(THF)],
1
selected region of the variable-temperature H NMR spectrum of 6 in
d8-toluene, tables of selected bond lengths (Å), angles (Њ), selected crys-
tallographic data, full crystal data and structure refinements for 7–11
and 14–16, syntheses of YI3, potassium menthoxide, 4 and 10–13. See
http://www.rsc.org/suppdata/dt/b4/b400149d/
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 1 0 8 3 – 1 0 9 6
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metric amount of potassium menthoxide17 rather than direct
deprotonation of the parent diamine with potassium amide
or hydride.18 The reaction solvent was chosen such that the
potassium salt is insoluble, but the reagents and co-products
all soluble, allowing purification by filtration and repeated
washings with the reaction solvent. Reaction of ArNH(CH2)x-
under similar conditions, is base-free.20 The relatively low
yttrium coordination number in 6 and the proximal silylmethyl
groups lead to the possibility of agostic interactions between
yttrium and the latter in the solid state (as are found in the
structure of [NdCp*2CH(SiMe3)2]21 for instance). However, the
coordinated THF is likely to prevent any such interactions and
indeed no distortion of silylmethyl groups towards the metal
centre is found in this case, furthermore the sum of angles
about C(1) is only 344.76Њ.
n
NHAr (x = 3 (1), x = 2 (2)) with two equivalents of BuLi in
hexanes generated the lithium complex Li2{ArN(CH2)xNAr},
which was used in situ to yield K2{ArN(CH2)xNAr} (x = 3 (3),
x = 2 (4)) as a bright yellow, insoluble solid following addition
of a slight excess of potassium menthoxide. The product was
isolated in high yield from the lithium menthoxide solution by
successive washings with hexanes in the glove box. Both 3 and 4
are moderately soluble in aromatic solvents and highly soluble
in coordinating solvents such as diethyl ether or THF. 7Li NMR
studies (d6-benzene–d8-THF) indicated only trace residual
lithium-containing species.
In d6-benzene solution the yttrium-bound methine carbon of
6 gives rise to a doublet at δ 36.5 ppm (1JYC = 35 Hz) in the
13C{1H} NMR spectrum, whilst the attached protons display a
corresponding doublet at δ Ϫ1.09 ppm (2JYH = 2.2 Hz) in the 1H
NMR spectrum. The 89Y chemical shift is δ 801 ppm (d6-ben-
zene–d8-THF).22 These chemical shift values are very different
to those of the electron-rich permethylcyclopentadienyl-
supported complex [YCp*2CH(SiMe3)2] (δC: 25.2 ppm, 37.0 Hz;
δH: Ϫ0.10 ppm, 2.3 Hz; δY: 79 ppm), but similar to those in
compounds incorporating the harder, more electronegative
nitrogen-based co-ligands, such as [Y(DADMB){CH(SiMe3)2}-
(THF)] (δC: 39.4 ppm, 35.6 Hz; δH: Ϫ0.94 ppm, 2.1 Hz),8
[Y{PhC(NSiMe3)2}2{CH(SiMe3)2}] (δC: 43.5 ppm, 30.0 Hz; δH:
Ϫ0.94 ppm, 1.8 Hz; δY: 721 ppm)23 and [Y{Me2Si(NCMe3)-
(OtBu)}2{CH(SiMe3)2}] (δC: 33.8 ppm, 30.0 Hz; δH: Ϫ1.05 ppm,
2.0 Hz and Ϫ1.45 ppm, 1.5 Hz at Ϫ10 ЊC; δY 645 ppm).24
Synthesis of yttrium complexes supported by {ArN(CH2)3NAr}2؊
As we have previously communicated, reaction of 3 with a
stoichiometric amount of YI3 in THF overnight at room tem-
perature resulted in a precipitate of insoluble potassium iodide;
work-up yielded [Y{ArN(CH2)3NAr}I(THF)2] 5 as a white,
crystalline material in 18% yield after slow cooling of a toluene
solution to Ϫ40 ЊC.5 The co-product, a sticky brown solid, is
most likely a mixture of oligomeric species (addition of meth-
anol precipitates some white solid, thought to be {Y(OMe)3}x
and the free diamine 1). The previously reported structure of 5
gives an early indication of the steric bulk of the diamide
{ArN(CH2)3NAr}2Ϫ when compared with other known struc-
tures such as [Y{C5H3(SiMe3)2}2I(THF)]; the latter structure
incorporates only one THF unit whilst 5 includes two, strongly
suggesting that the diamide is less sterically encumbering than
1
The δ 1.0–4.0 ppm region of the H NMR spectrum of 6,
which unlike 5 has a prochiral yttrium centre, is broad and
poorly resolved in both d6-benzene and d8-toluene at room
temperature; the resonances arising from the diastereotopic
isopropylmethyl groups in particular coalesce to give a single,
broad signal (which is coincident with the peak arising from the
THF β-protons). These inequivalent groups resolve as four
poorly defined doublets below Ϫ35 ЊC (a poorly resolved
triplet, due to the THF β-protons, can also be seen).25 Elevation
of the temperature to 50 ЊC did not significantly change the
appearance of the spectrum compared to that at 20 ЊC. Thus
the motion of these diastereotopic ligand groups is sufficiently
rapid on the NMR timescale at room temperature for a single,
averaged signal to be observed, as the temperature is lowered
ligand movement becomes less energetic and these inequivalent
functional groups are resolved separately.
1
two {C5Me5}Ϫ or {C5H3(SiMe3)2}Ϫ units.19 The H NMR and
13C{1H} NMR spectra offer singly and sharply resolved peaks
for 5 alongside trace amounts of 1, which was retained during
the recrystallisation and could not be removed by washing with
pentane. Complex 5 provides an ideal route into yttrium
complexes supported by the diamide {ArN(CH2)3NAr}2Ϫ; salt
metathesis with appropriate potassium salts yields a range of
hydrocarbyl, amide and oxide derivatives of 5, as shown in
Scheme 1.
When three drops of d8-THF were added to a d6-benzene
1
solution of 6, the H NMR spectrum became sharply resolved
with no evidence of the inequivalence noted above (Fig. 2). The
Scheme 1
As we stated in our earlier communication the reaction of
5 with an equimolar amount of KCH(SiMe3)2 in benzene or
toluene at room temperature with overnight stirring and extrac-
tion into pentane yields [Y{ArN(CH2)3NAr}{CH(SiMe3)2}-
(THF)] 6 as a colourless, crystalline material after slow cooling
to Ϫ42 ЊC.5 We also reported the molecular structure of 6,
which shows the expected loss of one THF unit concomitant
with the exchange of iodide for the much bulkier bis(trimethyl-
silyl)methyl ligand. The stoichiometry further confirms the
notion that the diamide {ArN(CH2)3NAr}2Ϫ is not as sterically
bulky as two permethylcyclopentadienyl units; 6 has a co-
ordinated THF moiety whilst [YCp*2CH(SiMe3)2], isolated
1
Fig. 2 Selected region of the H NMR spectrum of 6 in d6-benzene
alone (above) and with three drops of d8-THF (below).
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appearance of free THF in this spectrum indicates that the
d8-THF added rapidly exchanged for the coordinated THF and,
since it is in vast excess, accounts for the majority of the
coordinated THF (and thus has the effect of masking any
exchange processes attributable to the labile THF co-ligand). It
is also possible that an extra equivalent of THF not seen in the
X-ray molecular structure becomes coordinated under these
conditions, which changes the symmetry about the yttrium
centre and thus removes the inequivalence of the diamide
functional groups, giving the simpler 1H NMR spectrum
observed. Experiments with olefins (vide infra) would
be expected to give further insight into the extent of THF
association and dissociation in solution.
The synthesis of a less sterically hindered hydrocarbyl, form-
ulated as the bis-THF adduct (Y{ArN(CH2)3NAr}(CH2SiMe3)-
(THF)2), was effected on a small scale in d6-benzene by reaction
of 5 with KCH2SiMe3 and confirmed unequivocally by a
characteristic doublet at δ Ϫ0.6 ppm (2JYH = 3.0 Hz) for the
yttrium-bound hydrocarbyl unit. However, all attempts to
repeat this reaction on a preparative scale resulted in the
formation of a complex mixture of this compound and others,
most likely to be thermal decomposition products (tetramethyl-
silane was noted in the 1H NMR spectrum). Whilst recrystallis-
ation of this crude mixture from pentane at low temperature
resulted in the deposition of colourless crystals from which
the stoichiometry of the product could be confirmed by X-ray
crystallography, it was not possible to isolate a pure sample for
further analysis. Such problems with the (trimethylsilyl)methyl
ligand have been encountered by other research groups, for
example Schrock and co-workers, when reporting their yttrium
complexes supported by the tridentate ‘NON’ ligand, noted
that [Y(NON){CH(SiMe3)2}(THF)] was much more stable
in vacuo than [Y(NON){CH2SiMe3}(THF)2].7
the ipso-carbon (Y–C(28)–C(29) bond angle = 121.2(3)Њ), in
contrast to the previously reported cerium complex
[Ce(Cp*)2(CH2C6H5)], in which the benzyl ligand coordinates
in an η3-mode.29 The Y–N bond lengths in 7 are significantly
longer than those in 5 or 6 (by 0.045 Å in the case of
Y–N(1) from 5), whilst the bite-angle of the ligand (N(1)–Y–
N(2)) is compressed by 1.47Њ from that in 5 and by 4.87Њ from 6,
presumably due to the different electronic requirements of the
co-ligand in the first instance and its steric bulk in the second.
As with 5 and 6, and typically for transition metal and lan-
thanide amides, the nitrogen centres in 7 are planar (sum of
angles at (N1) = 359.9Њ, (N2) = 359.1Њ), indicating sp2 hybridis-
ation, with the lone pair in the remaining
p orbital,
presumably in coordination with the yttrium centre.30 It is
worth noting that the homoleptic lanthanide bis(trimethyl-
silyl)amides have an unusual pyramidal rather than trigonal
planar lanthanide centre.31 The Y–THF separations are again
within the range of 2.35–2.45 Å typical of THF-solvated
yttrium complexes.32
1
The H NMR spectrum of 7 (d6-benzene) shows a doublet
due to coupling between yttrium and the two α-methylene
2
protons of the benzyl co-ligand (δH 2.29 ppm, JYH = 4 Hz);
corresponding resonances were seen in the 13C{1H} NMR
1
spectrum (δC 50.6 ppm, JYC = 38 Hz, d6-benzene) and the
89Y NMR spectrum (δY 608 ppm, d6-benzene–d8-THF). The 89
Y
chemical shift value is, as discussed for 6, typical of cyclo-
pentadienyl-free yttrium complexes within the broad chemical
shift range typical of this nucleus. The other resonances due to
7 are resolved in the 1H and 13C{1H} NMR spectra with much
greater clarity than seen for the mono-THF solvated hydro-
carbyl 6 (and the mono-THF solvated silylamide 8, vide infra),
the mirror plane that bisects 7 through the achiral yttrium
centre leading to single resonances with their associated
couplings for all functional groups.
Despite repeated attempts it was not possible to isolate 7 in
more than 10–15% yield. Furthermore, NMR studies of even
crystalline samples of 7 revealed some contamination with
small amounts of the diamine 1 and other unidentifiable
by-products. The elemental analysis consistently registered a
value some 3% too low in carbon content, also suggestive of a
certain amount of decomposition at room temperature.
Although not appropriate for olefin polymerisation studies,
heteroleptic lanthanide and group 3 amide complexes represent
excellent synthetic targets for polar monomer polymerisation as
well as offering interesting comparisons with the hitherto
reported hydrocarbyls. Reaction of 5 with KN(SiMe3)2 in
toluene gave a crystalline sample of [Y{ArN(CH2)3NAr}-
{N(SiMe3)2}(THF)] 8 in about 40% yield. X-Ray crystallo-
graphy confirmed the presence of a single THF unit at the
four-coordinate yttrium centre (Fig. 4). Both the diamide (sum
of angles at (N1) = 360Њ, (N2) = 359.4Њ) and the silylamide (sum
of angles at (N3) = 359.7Њ) nitrogen centres are planar,
indicating the expected sp2 hybridisation in each case. The lone
pair at each nitrogen resides in the remaining p orbital and is
presumably in coordination with the yttrium centre and in the
case of N(3) the vacant silicon d orbitals as well. The Y–N(1)
and Y–N(2) bond lengths are 0.084 and 0.079 Å respectively,
shorter than the Y–N(3) bonds, but essentially the same as
those in 7, due to this competition for lone-pair donation
between silicon and yttrium that occurs at N(3) but not at
the more basic, non-silylamide centres N(1) and N(2). The
Y–N(SiMe3)2 bond length of 2.272(3) Å is essentially the same
as those in the homoleptic complex [Y{N(SiMe3)2}3]33 (2.224(6)
Å) and in the heteroleptic complexes [YCp*2{N(SiMe3)2}]20
(two independent molecules in the unit cell; Y(1)–N(1)
2.274(5) Å, Y(2)–N(2) 2.253(5) Å) and [Y(C5Me4Et)2-
{NSiMe3)2}]34 (2.276(3) Å). As for 6, the relatively low yttrium
coordination number and the proximal silylmethyl groups
lead to the possibility of agostic interactions between these
functionalities in the solid state. For example, the permethyl-
It was also possible to synthesise another bis-THF solvated
complex [Y{ArN(CH2)3NAr}(CH2C6H5)(THF)2], 7, by reac-
tion of 5 with KCH2C6H5 in THF or diethyl ether. The molec-
ular structure (Fig. 3) confirms the presence of two THF
ligands at the five-coordinate yttrium centre and establishes 7
as a relatively rare example of a structurally characterised
yttrium benzyl complex; the only other examples known
are [Y(CH2C6H5)2(TMEDA)(µ-Br)2Li(TMEDA)],26 [Y(Cp*)2-
(CH2C6H5)(THF)],27 [Y{PhC(NSiMe3)N(CH2)2NMe2}2(CH2-
Ph)2Li] and [Y{PhC(NSiMe3)N(CH2)3NMe2}2(CH2Ph)].28 The
Y–C bond distance in 7 (2.458(4) Å) is very similar to those
reported for the above compounds (2.440(6)–2.490(8) Å) whilst
the coordinated THF units prevent any close approach of
Fig. 3 ORTEP representation of the molecular structure of 7.
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Y–N(1) 2.215(4), Y–N(2) 2.191(3), Y–O(1) 2.447(3), Y–O(2) 2.396(3),
Y–C(28) 2.458(4); N(2)–Y–N(1) 92.92(14), Y–C(28)–C(29) 121.2(3),
O(1)–Y–O(2) 74.12(12). Selected crystallographic data: crystal system:
monoclinic, space group: P21 (no. 4), a = 9.1530(2), b = 19.1733(4), c =
11.5265(3) Å, β = 99.595(1)Њ, U = 1994.52(8) Å3, Z = 2.
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Despite repeated attempts, the preparation of the highly ster-
ically congested complex [Y{ArN(CH2)3NAr}(OAr*)(THF)]
(OAr* = OC6H2-2,6-tBu2-4-Me) resulted in the deposition of
both colourless crystals of the target compound and other
unidentified white solids. The presence of the target compound
in this mixture and its stoichiometry were confirmed by X-ray
diffraction studies of a carefully selected single crystal, however
microanalysis revealed that this does not represent the bulk
composition of the sample, the carbon content in particular
being some ten percent too low.36 1H and 13C{1H} NMR studies
also indicated the presence of both the target compound and
other unidentifiable species.
The most active lanthanide complexes towards olefin poly-
merisation incorporate hydride co-ligands, those which adopt
the rare terminal hydride bonding mode being more active than
the more common hydride-bridged species.1 Unfortunately,
despite promising initial studies involving the reaction of 6 with
molecular hydrogen in d12-cyclohexane, it was not possible to
synthesise a hydride supported by the diamide {ArN(CH2)3-
NAr}2Ϫ on a preparative scale, the reaction repeatedly yielding
instead a pale yellow, highly viscous oil that did not show any
yttrium hydride resonances in the 1H NMR spectrum.
We commented in our earlier communication that the
unreactivity of 6 towards olefins is most likely caused by the
presence of coordinated THF. Consequently, we attempted to
synthesise complexes of the form (Y{ArN(CH2)3NAr}I) by
reacting YI3 with 3 in poorly coordinating solvents such as
tBuOMe or toluene.
Fig. 4 ORTEP representation of the molecular structure of 8.
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Y–N(1) 2.188(4), Y–N(2) 2.194(3), Y–N(3) 2.272(3), Y–O 2.320(3);
N(1)–Y–N(2) 95.43(14), N(1)–Y–N(3) 127.00(16), N(2)–Y–N(3)
126.24(13), N(1)–Y–O 104.09(15). Selected crystallographic data:
crystal system: monoclinic, space group: P21 (no. 4), a = 11.0609(4), b =
17.1207(6), c = 11.3288(4) Å, β = 106.524(2)Њ, U = 2056.74(13) Å3, Z = 2.
cyclopentadienyl complex [YCp*2{N(SiMe3)2}] has an essen-
tially planar Y–N–C–H unit that exhibits particularly promin-
ent γ-hydrogen agostic interactions with the yttrium centre.
There is a silylmethyl group aligned in a similar fashion in the
structure of 8, occupying the otherwise most vacant area of
the coordination sphere. Although there is no evidence for
γ-hydrogen agostic interactions in this case, this particular
silylmethyl group in 8 nevertheless describes a slightly more
acute angle than the others incorporating nitrogen–silicon
bonds in this structure (N(3)–Si(1)–C(28) 109.7(2)Њ, Av.
113.1(3)Њ), indicative of a certain amount of non-classical
interaction in the solid state.
tBuOMe is a more weakly basic solvent than THF yet still
offers reasonable solubility towards ionic systems such as 3.
Reaction between stoichiometric amounts of YI3 and 3 in
tBuOMe yielded exclusively the bis(ligand) ate-complex
[Y{ArN(CH2)3NAr}2K(PhMe)] 9 (Scheme 2) rather than the
target complex. This complex 9 can be isolated under ‘rational’
conditions in 28% yield by adding two equivalents of 3 to a
t
slurry of YI3 in BuOMe or in 15% yield if the reaction is
carried out in THF (no THF is retained after work-up).
The symmetry about yttrium in 8 is very similar to that in 6.
In both cases the yttrium centre is prochiral, however the
room-temperature 1H NMR spectrum of 8 is similar to the low-
temperature spectrum of 6, indicating that 8 has considerably
more structural rigidity in solution, due to delocalisation of the
silylamide nitrogen lone pair towards the yttrium centre, which
restricts the motion of the silylamide groups and in turn those
of the diamide co-ligand. The diastereotopic isopropylmethyl
groups in 8 resolve as two broad singlets and one (higher inten-
sity) broad singlet in the room-temperature 1H NMR spectrum;
the corresponding region of the 13C{1H} NMR spectrum also
exhibits the appropriate four signals for these methyl groups.
The inequivalent bridging methylene protons of the ligand
backbone also resolve separately. Heating the sample of 8 to
Scheme 2
Such an arrangement of ligands is revealing about the steric
nature of the diamide {ArN(CH2)3NAr}2Ϫ. Until the recent
work of Evans et al. it was thought that tris(permethylcyclo-
pentadienyl) complexes of lanthanide metals, particularly the
smaller late lanthanides and yttrium, could not be made.37
Indeed they cannot be made by simple salt metathesis of
the lanthanide trichlorides with LiCp* even under forcing con-
ditions, suggesting once again that the diamide {ArN(CH2)3-
NAr}2Ϫ is considerably less sterically demanding than two
permethylcyclopentadienyl units.
The molecular structure of 9 (Fig. 5) shows that the four
nitrogen atoms are distributed in a slightly distorted tetrahedral
array38 about each four-coordinate yttrium centre and confirms
the exclusion of any ethereal solvent molecules. The Y–N bond
lengths are slightly longer than those in the less sterically
congested heteroleptic complexes, by 0.095 Å in the case of
Y–N(1) (5) and Y–N(2) (9). There is a little variation in the
Y–N bond distances within the structure of 9 itself; the Y–N(1)
distance is the shortest (2.213(4) Å), but the discrepancies are
small. The sum of angles at each nitrogen centre is also very
similar; the greatest discrepancy from a planar arrangement is
at N(4) (358.3Њ), the other centres are essentially planar (N(1):
359.1Њ, N(2): 359.8Њ, N(3): 360.0Њ). These planar geometries and
similar Y–N bond lengths suggest that the lone pair at each
1
40 ЊC yields a H NMR spectrum very similar to the room-
temperature spectrum of 6, more rapid rotation causing the
resonances arising from the diastereotopic isopropylmethyl
groups in particular to coalesce; further heating to 60 and then
80 ЊC gives progressively better resolved spectra, but is accom-
panied by some decomposition after a few minutes at 80 ЊC,
noted by the appearance of bis(trimethysilyl)amine in the
spectrum.35 Despite the apparent intractability of much of the
1
ligand region in these spectra, H–13C COSY NMR spectro-
scopy made it possible to assign each of the broad resonances
1
in the room-temperature H NMR spectrum to one or more
particular functional groups (details are given in the Experi-
mental section). Excess d8-THF added to the sample of 8
rapidly exchanges with the original THF, chaging the symmetry
of the complex in the same manner discussed above for 6. Heat-
ing this sample to 50 ЊC made little difference to the appearance
of its 1H NMR spectrum.
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Recent work in our laboratory has shown that lanthanide
complexes can be prepared by the reaction of the lanthanide
triiodide and an appropriate potassium salt in toluene.42 In this
case, a stoichiometric mixture of YI3 and 3 in toluene was
heated to reflux for three days and yielded a mixture of highly
toluene soluble products, a small proportion of which was
recovered as a yellow powder from a highly concentrated
solution at Ϫ45 ЊC. 1H NMR studies revealed the presence of 9
and a compound that may be tentatively formulated as the
base-free yttrium complex (Y{ArN(CH2)3NAr}I), however the
poor yield and mixed nature of the products precluded any
meaningful microanalysis.
Synthesis of yttrium complexes supported by {ArN(CH2)2NAr}2؊
We were discouraged by a lack of success with preliminary
studies of yttrium complexes incorporating a more sterically
demanding diamide {ArN(CH2)4NAr}2Ϫ and consequently
turned to the less sterically demanding diamide {ArN(CH2)2-
NAr}2Ϫ in an attempt to discover whether the shortened bridge
between the two aniline centres would have an effect on the
structure and reactivity of the complexes so-produced. In doing
so, we carried out an identical set of reactions to those detailed
above and found strikingly similar behaviour in most cases,
although some of the structures and reactivities towards small
molecules were different.
Fig. 5 ORTEP representations of the molecular structure of 9: a
single unit (top) and the one-dimensional thread within the solid
(below). Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
angles (Њ): Y–N(1) 2.213(4), Y–N(2) 2.265(4), Y–N(3) 2.246(4), Y–N(4)
2.246(4); N(1)–Y–N(2) 92.80(16), N(1)–Y–N(3) 117.20(16), N(1)–Y–
N(4) 121.81(15). Selected crystallographic data: crystal system:
monoclinic, space group: P21/c (no. 14), a = 12.2379(2), b = 13.0294(2),
c = 36.6872(6) Å, β = 98.851(1)Њ, U = 5780.2(2) Å3, Z = 4.
The reaction of 4 with a stoichiometric amount of YI3 in
THF overnight at room temperature resulted in a precipitate
of insoluble potassium iodide; work-up gave [{Y{ArN(CH2)2-
NAr}I(THF)2}2] 10 as a white, crystalline material in 57% yield
after slow cooling of a toluene solution to Ϫ42 ЊC. The yield
is much higher than for 5, presumably because the shorter,
less flexible backbone disfavours any further reactions at the
yttrium centre, in particular bis-chelation, which yield
unwanted co-products.
An X-ray structure determination of 10 confirmed the
inclusion of two THF units per yttrium centre (Fig. 6). It is
interesting to note that 10 adopts a dimeric structure in the
solid state, whilst 5 is monomeric, yielding in the case of 10
six-coordinate yttrium centres. These observations are con-
sistent with the reduced steric demand of the two-carbon
backbone and a more open coordination environment around
the metal centre and give an early indication of the steric
properties of this diamide.
nitrogen interacts with the yttrium centre, yielding a formally
16-electron centre. The potassium counter-ion sits in a pocket
defined by two diamide aryl groups from separate yttrium
anions and a molecule of toluene; this structure is repeated in
one dimension throughout the lattice (Fig. 5).
There are two heteroleptic lanthanide anions incorporating
amide and cyclopentadienyl ligands that display non-planar
nitrogen centres. The bis(ligand) ate-complex [(Y{(C5Me4)-
SiMe2NCH2CH2OMe}2)Li] reported by Okuda and co-workers
for instance has a sum of nitrogen bond angles of 350.7(3) and
351.3(3)Њ, offering nitrogen centres somewhere in between
planar and tetrahedral.39 The similar bis(amide) anion
[LnCp2(NPh2)2]Ϫ (Ln = Y, Ln, Ce, Eu, Gd, Ho) offers structural
features more consistent with one formally sp2 and one sp3
centre, with an asymmetry in the Ln–N bond length across the
series,40 however both of these lanthanide centres have 18
electrons given the above configuration. The observation of
such a mixed hybridisation was rationalised by Lauher and
Hoffmann for the MCp2X2 unit by invoking a single empty a1
orbital at the metal centre into which only one lone pair of
electrons can be accommodated.41 In the case of 9 there are
fewer bonding electrons (two per amide nitrogen rather than the
six offered by the cyclopentadienyl anion) thus allowing
accommodation of all the non-bonding lone pair electrons into
empty metal orbitals via sp2 hybridisation at each nitrogen.
There are two distinct sets of ligand peaks of different
integral values in the 1H NMR spectrum. One set was assigned
to 9 and are all slightly broadened due to the motion of the
potassium cation within the coordination environment of the
bis-ligand anion partially, but not completely, equalising the
chemical shift of these protons. The other group, consisting of
sharp resonances of lower intensity slightly upfield from those
due to 9, was attributed to 1, formed during the reaction in
reproducibly similar proportions, which explains to an extent
the low yield of 9.
Fig. 6 ORTEP representation of the molecular structure of 10 (only
one of the two independent units shown). Thermal ellipsoids are drawn
at the 20% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (Њ): Y(1b)–N(1b) 2.212(10),
Y(1b)–N(2b) 2.198(11), Y(1b)–O(1b) 2.417(9), Y(1b)–O(2b) 2.394(8),
Y(1b)–I(1b) 3.122(2), Y(1b)–I(1b_2) 3.232(2); N(1b)–Y(1b)–N(1b)
78.7(4), I(1b)–Y(1b)–I(1b_2) 76.67(4), Y(1b)–I(1b)–Y(1b_2) 103.33(4).
¯
Selected crystallographic data: crystal system: triclinic, space group: P1
(no. 2), a = 12.2250(4), b = 14.2440(4), c = 25.3516(9) Å, α = 78.418(1),
β = 80.205(1), γ = 85.201(2)Њ, U = 4256.0(2) Å3, Z = 2.
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The structure of 10 consists of two independent units (only
one is shown in the diagram for clarity) and two-and-a-half
units of toluene (not shown either). Each yttrium centre has a
highly distorted octahedral arrangement of ligands: the axial
THF and amide centres O(1b) and N(2b) describe an angle
of 167.8(3)Њ whilst the ‘inner’ equatorial angles described by
I(1b)–Y(1b)–I(1b_2) and O(2b)–Y(1b)–N(1b) are 78.7(4) and
97.3(3)Њ, respectively. The only other dimeric yttrium iodide
known in the literature is the highly unusual halide-bridged
Ϫ
43
cation [Y2(µ-I)(NPPh3)4(THF)4]ϩI3 ؒ(THF)6.5
. The Y–I bond
lengths in 10 (3.112(2) and 3.239(2) Å) are shorter than in
this cation (3.2732(11) and 3.3011(13) Å). As expected, the
bridging Y–I bonds in both of these complexes are longer than
the terminal Y–I bond in 5 (2.997(2) Å).
Complex 10 is much more sparingly soluble in aromatic
hydrocarbons than 5; both are highly soluble in ethers. A
d6-benzene solution of 10 shows peaks for both 10 and the
highly soluble diamine 2. The 1H NMR spectrum is somewhat
deceptive; 2 is only present in trace amounts but appears to be a
major component due to its much higher solubility. Removal of
the d6-benzene and addition of a further quantity of the same
solvent yields a spectrum with a much smaller amount of
impurity and some concomitant loss of 10. Further washings
are impractical due to loss of 10, however washing with pentane
fails to remove 2.
Fig. 7 ORTEP representation of the molecular structure of 11.
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Y–N(1) 2.149(3), Y–N(2) 2.180(3), Y–C(27) 2.434(4), Y–O 2.327(3);
N(1)–Y–N(2) 80.32(12), N(1)–Y–C(27) 117.26(13), N(2)–Y–C(27)
127.08(13), O(1)–Y–C(27) 113.29(12). Selected crystallographic data:
crystal system: monoclinic, space group: P21/n (no. 14), a = 12.5573(2),
b = 17.9434(3), c = 19.4501(3) Å, β = 99.444(1)Њ, U = 4323.1(1) Å3, Z = 4.
In solution 10 may be dimeric, monomeric or an equilibrium
mixture of the two. Unfortunately the low solubility of 10 in
aromatic solvents prevented a study of its molecular weight in
solution via the depression of the freezing point of benzene.
Instead, NMR experiments were used to determine the
degree of aggregation in solution. Variable-temperature studies
showed that in the 20 to 60 ЊC range the degree of aggregation
does not change since the appearance of the spectrum remains
reasonably constant. The low solubility of 10 in aromatic
solvents precluded any meaningful low-temperature NMR
studies. Addition of five drops of d8-THF to a d6-benzene
solution of 10 vastly increases its solubility, thus increasing
the intensity of these peaks with respect to those of the highly
soluble trace impurity 2. However, since the chemical shift
values are not changed significantly by the addition of THF, a
strong Lewis base that would be expected to cleave the weak
iodide bridge, 10 is probably a monomer in both aromatic and
ethereal solvents.
yielding a substantially more exposed yttrium centre as a direct
result of the narrower bite of the chelate in this five-membered
ring system. The THF unit is rotated about 90Њ away from its
position in 6, whilst the yttrium amide bonding in 11 is more
asymmetric than in 6 (11: 2.149(3), 2.180(3) Å; 6: 2.170(5),
2.175(5) Å). The average Y–N bond length is slightly shorter in
11 (11: 2.165(3) Å, 6: 2.173(3) Å), as is the average Y–THF
contact (11: 2.327(3) Å, 6: 2.339(2) Å).
1
The H NMR spectrum of 11 (d6-benzene) is similar to that
obtained for 6, with overlapping peaks in the δ 3.5–4.0 ppm
region and a broad multiplet at δ 1.3 ppm as well as an upfield
doublet at δ Ϫ0.95 ppm (2JYH = 2.3 Hz). The 13C{1H} NMR
spectrum (d6-benzene) is clean and diagnostic, featuring all of
the expected peaks, with a doublet corresponding to the bis-
(trimethylsilyl)methyl α-carbon at δ 36.7 ppm (1JYC = 37 Hz).
The chemical shift values and coupling constants in both the
1H and 13C{1H} NMR spectra for this functionality are very
similar in both 6 and 11 (6: δ –1.09 ppm, 2JYH = 2.2 Hz; δ 36.5
1
1
The resonances assigned to 2 in these H NMR spectra are
ppm, JYC = 35 Hz). Additionally, excess d8-THF sharpens the
1
different to those appearing when 2 alone is examined in the
same solvent. Furthermore, the appearance of the THF peaks
in the spectrum of 10 changes as the impurity is removed by
successive washings with d6-benzene. In fact 2 behaves as a
chelating diamine, analogous to TMEDA, displacing THF
from the yttrium centres to yield a complex formulated
as (Y{ArN(CH2)2NAr}I{ArNH(CH2)2NHAr}(THF)x). The
coordination of 2 to the yttrium centre locks its conformation
such that the couplings between the amine protons and those in
diamide region of the H NMR spectrum of 11, in the same
manner and for the same series of reasons discussed and
demonstrated for 6. The 89Y chemical shift (d6-benzene–d8-
THF) for 11 is δ 606 ppm, somewhat different from that
observed for the three-carbon-backboned congener 6 (δ 801
ppm). This surprising result shows that the electronic environ-
ments of the two yttrium centres are slightly different and is
indicative of the different extent to which the excess d8-THF
added to each sample is coordinated, again symptomatic of the
more open coordination sphere at yttrium in 11, but must
be qualified by the large chemical shift range seen for the 89Y
nucleus (vide supra).
1
the methylene bridge are resolved the H NMR spectra, where
as the high degree of motional freedom on the NMR timescale
experienced by the diamine 2 alone leads to a well resolved
singlet for these protons. When a slight excess of {YCl3-
(THF)3.5} is suspended in a d6-benzene solution of 2 the
chemical shifts of the resonances arising from 2 change
markedly, demonstrating that 2 can also chelate around yttrium
trichloride in preference to THF, although the peaks are too
broad for coupling between the amine proton and those in the
methylene bridge to be seen in this case.
Reaction of 10 with KCH(SiMe3)2 in toluene for 3 h leads to
a deposit of insoluble potassium iodide; work-up with pentane
and recrystallisation at low-temperature gives [Y{ArN-
(CH2)2NAr}{CH(SiMe3)2}(THF)] 11 in about 50% yield. At
first glance the molecular structure (Fig. 7) is quite similar to
that of the congeneric species 6. However, the N(1)–Y–N(2)
bond angle in 11 is 80.32(12)Њ as opposed to 97.79(9)Њ in 6,
Complex 10 also reacts with KCH2SiMe3 in benzene or
toluene to give, in low yield, a complex mixture including a
species formulated as the thermally sensitive hydrocarbyl
(Y{ArN(CH2)2NAr}(CH2SiMe3)(THF)2). A diagnostic doublet
1
for the yttrium hydrocarbyl protons is found in the H NMR
spectrum (d6-benzene–d8-THF) at δ Ϫ0.41 ppm (2JYH = 3.4 Hz),
shifted slightly downfield from that offered by the earlier com-
pound (δ Ϫ0.60 ppm) but of a very similar coupling value. The
remainder of the spectrum and the 13C{1H} NMR spectrum
contain major resonances due to the hydrocarbyl along with a
number of unassigned peaks; the yttrium-bound silylmethylene
resonance could not be located in the 13C{1H} NMR spectrum.
The 89Y chemical shift is δ 656 ppm, similar to that for 11 (δ 606
ppm), but again shifted from that seen for 6 (δ 801 ppm).
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Unfortunately, the presence of aforementioned unidentified
species that could not be separated from the hydrocarbyl and its
high thermal sensitivity precluded any further characterisation
and confirm the problems associated with this co-ligand.
Further derivatives of 10 were made by reaction with
KCH2Ph in THF or diethyl ether to give [Y{ArN(CH2)2-
NAr}(CH2C6H5)(THF)2] 12 and with KN(SiMe3)2 to yield
[Y{ArN(CH2)2NAr}{N(SiMe3)2}(THF)] 13. Both can be
recovered from pentane as microcrystalline solids at low
temperature in moderate to good yields. In a similar manner to
the synthesis of 10, but in contrast to 11, a small amount of the
free diamine 2 co-crystallises with 12 and 13, the presence of
which can be diagnosed by its characteristic resonances in the
1H NMR spectrum. The high pentane solubility of 12 and 13
prevents the separation of these components; the proportion of
2 in the samples can be determined as a quarter and an eighth,
respectively, by integration of the 1H NMR spectra. Apart from
the presence of this diamine the 1H NMR spectra of 12 and 13
are very similar to those of the more sterically encumbered
complexes 7 and 8. There are four sets of benzylic resonances in
the 1H NMR spectrum of 12, three in the aromatic region and
one around δ 2 ppm with all associated couplings well resolved
2
(7: δ 2.29 ppm, JYH = 3.44 Hz, 12: δ 2.39 ppm, 2.09 Hz). The
remainder of this spectrum and the 13C{1H} NMR spectrum
both include the expected resonances at good resolution,
indicating rapid rotation of the diamide functional groups on
the NMR timescale and coordinative saturation of the yttrium
centre. The 1H NMR spectrum of 13 is broad and poorly
defined, the isopropyl methine, methylene bridge and THF
α-proton resonances appear together as a broad signal at δ 3.84
ppm whilst the diastereotopic isopropyl methyl groups gave a
single, broad peak at δ 1.41 ppm. Addition of d8-THF to the
sample resolves the peaks singly and sharply for reasons
detailed in the discussion of 8. Despite repeated attempts it was
not possible to grow X-ray quality crystals of either 12 or 13,
however the compositions were confirmed by microanalysis.
In contrast to the system supported by the more sterically
encompassing chelating diamide {ArN(CH2)3NAr}2Ϫ it was
possible to make a hydride complex supported by the ligand
{ArN(CH2)2NAr}2Ϫ via σ-bond metathesis of in situ generated
11 with molecular hydrogen. The colour of the reaction mixture
changed slightly from the pale, watery yellow of 11 to a yellow-
ish green over the 3 day reaction period, but there was no
deposition of solids. The hydride 14 was recovered from the
pentane solution at low temperature as a white, microcrystalline
solid in 9% yield.
Although most of the sample was microcrystalline, a single
crystal suitable for X-ray diffraction studies was isolated from a
concentrated sample of 14 at low temperature. The molecular
structure shows the highly unusual incorporation of super-
stoichiometric equivalents of molecular hydrogen that appear
to have added across one of the yttrium amide bonds at two
of the three yttrium centres to give [Y3{ArNH(CH2)2NAr}2-
{ArN(CH2)2NAr}(µ-H)3(µ3-H)2(THF)], in which all three
yttrium centres are different and there is an unusual mixture of
bridging and face-capping hydrides (Fig. 8). Three hydrides are
included in bridging positions at alternate apices of a hexagon
also defined by the positions of the three yttrium centres with
the remaining two capping opposite faces of the hexagon.
There is considerable asymmetry about the face-capping
hydrides H(4x) and H(5x), with the Y–H bond lengths varying
from 1.94(12) to 2.39(8) Å. The bond lengths for the other three
hydrides (H(1x)–H(3x)) range from 1.98(6) to 2.18(6) Å.
Fig.
8
ORTEP representation of the molecular structure of
14
[Y3{ArNH(CH2)2NAr}2{ArN(CH2)2NAr}(µ-H)3(µ3-H)2(THF)]
(above) and of the central hydride core only (below). Thermal ellipsoids
are drawn at the 20% probability level. Non-hydride hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and angles (Њ): Y(1)–
N(1) 2.184(7), Y(2)–N(4) 2.218(6), Y(2)–N(3) 2.589(7), Y(2)–O
2.375(5), Y(1)–H(1x) 2.18(6), Y(1)–H(4x) 2.30(8); N(1)–Y(1)–N(2)
81.4(2), H(1x)–Y(1)–H(3x) 122(2), H(4x)–Y(1)–H(5x) 49(3). Selected
crystallographic data: crystal system: monoclinic, space group: P21/c
(no. 14), a = 25.4497(7), b = 14.2389(3), c = 25.1449(5) Å, β =
105.140(1)Њ, U = 8795.6(4) Å3, Z = 4.
hydride [Y(C5H3-1,3-Me2)2H] determined by the crystallisation
solvent.46
Complex 14 is highly soluble in aromatic and ethereal
1
solvents. The H NMR spectrum of [Y3{ArNH(CH2)2NAr}2-
{ArN(CH2)2NAr}(µ-H)3(µ3-H)2(THF)] should contain five
complicated multiplets in the hydride region since all three
yttrium centres are different, rendering their associated
hydrides inequivalent, whilst even the face-capping hydrides are
different due to the absence of any mirror planes in the mole-
cule. In a similar manner, [{YCp2(µ-H)}3(µ3-H)][Li(THF)4] has
two complicated multiplets at δ 0.75 and Ϫ1.03 ppm in a 3 : 1
ratio, due to coupling between the inequivalent protons and the
yttrium centres. However, in d6-benzene solution at 20 ЊC a
single, slightly broadened triplet is found in a typical region for
yttrium hydrides with hard, electronegative co-ligands (δ 5.91
ppm, 1JYH = 28 Hz) whilst at 60 ЊC the same triplet is observed,
slightly shifted upfield and at much better resolution (δ 5.74
ppm, 1JYH = 28 Hz). Conversely at 8 ЊC only a very broad singlet
can be seen at δ 6.06 ppm. These values are similar to the
dimeric yttrium bis(benzamidinate) and bis(N,O-bis(tert-
butyl)(alkoxydimethysilyl)amide) hydrides, recently reported
1
by Teuben and co-workers (δ 8.28 ppm, JYH = 28 Hz and
δ 6.80 ppm, JYH = 31 Hz, respectively) and are much further
1
downfield than those arising from the previously reported
cyclopentadienyl-supported complexes.23,24 An NOE experi-
ment on a d6-benzene solution of 14, irradiating at the fre-
quency of the yttrium hydride at 60 ЊC in an attempt to see
whether other hydride resonances exist under the complicated
ligand region, produced a small enhancement at δ 4.14 ppm
(7.9%); selective irradiation at this frequency collapsed a peak
in the isopropylmethyl region (δ 1.36 ppm). The remainder
A mixture of bridging and face-capping hydrides is unusual
but by no means unprecedented in lanthanide chemistry. The
first trimetallic lanthanide hydrides were reported by Evans
et al., who synthesised [{ErCp2(µ-H)}3(µ3-Cl)][Li(THF)4] and
[{LuCp2(µ-H)}3(µ3-H)][Li(THF)4]44 and the analogous yttrium
complex [{YCp2(µ-H)}3(µ3-H)][Li(THF)4].45 Evans et al. later
reported two different coordination modes for the yttrium
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of the spectrum clearly has peaks attributable to the diamide
functional groups and THF but is generally broad and poorly
resolved. 89Y NMR spectroscopy also revealed just one reson-
ance, at δ 453 ppm (50 ЊC, 1JYH coupling was not resolved).
Although the environment at the hydride centre of 14 varies
slightly with temperature in solution, the basis of structure
remains that of doubly-bridging hydrides between two or more
equivalent yttrium centres throughout the temperature range
studied, suggesting the formulation [{Y{ArN(CH2)2NAr}-
(µ-H)(THF)}x] for 14, inconsistent with that obtained by X-ray
crystallography. The broadening of the signals at room tem-
perature compared to the higher temperature studies can be
attributed to fluxional processes within the coordination sphere,
such as the motion of THF or the associated isopropylmethyl
proton in close proximity to the hydrides, which are slow on the
NMR timescale at room temperature but more rapid at elevated
temperatures. The complex does not revert to this simple
dimeric form elucidated by NMR studies in solution from the
more unusual mixed amido–amine structure [Y3{ArNH-
(CH2)2NAr}2{ArN(CH2)2NAr}(µ-H)3(µ3-H)2(THF)] found by
X-ray crystallography, since no molecular hydrogen is seen in
Y–O bond length (2.066(4) Å) is very similar to that in
[Y{ArN(CH2)3NAr}(OAr*)(THF)] (2.092(3) Å) and in the
homoleptic, base free complex [Y(OAr)3]49 (OAr = OC6H3-2,6-
tBu2) (2.00(1) Å). It is also close to the values reported for the
heteroleptic complexes [YCp*{CH(SiMe3)2}(OAr*)]50 (2.090(3)
Å) and [Y{PhC(NSiMe3)2}2(OAr*)]51 (2.0750(19) Å). The Y–N
and Y–THF separations are essentially the same as those in
earlier complexes reported herein.
In a similar manner to many of the other yttrium compounds
1
reported herein, the room-temperature H NMR spectrum of
15, which again has a prochiral yttrium centre, has poorly
resolved, overlapping diamide and co-ligand resonances in the
δ 1.0–4.0 ppm region of the spectrum. Heating to 70 ЊC results
in coalesence of the three peaks, two of much lower intensity,
t
assigned to the Bu protons, and also gives better resolution
of the resonances arising from the diamide ligands due to
averaging of the chemical environments on the NMR timescale;
the THF peak is shifted downfield upon heating such that
it overlaps slightly with the sharpened isopropyl methine
resonance.
1
the H NMR spectrum. Neither does it revert to a ‘bridging-
Reaction of 6 and 11 with phenylsilane
only’ form of the hexagonal trimer described above, as the three
yttrium centres are still inequivalent, and would therefore give
rise to a much more complicated 1H NMR spectrum than that
observed. Microanalysis is consistent with both the form of the
hydride observed in solution and that seen in the solid state.47
It must be concluded that the very interesting and unusual
structure determined by X-ray crystallography only represents
a minor component of the mixture, which is predominantly
the more conventional hydride [{Y{ArN(CH2)2NAr}(µ-H)-
(THF)}x].48
In further contrast to the other diamide, it was possible to
isolate a pure sample of the phenoxide complex [Y{ArN-
(CH2)2NAr}(OAr*)(THF)] 15 from pentane following the
reaction of 10 with KOAr*(THF) in toluene. Crystals suitable
for X-ray diffraction studies were grown from a highly con-
centrated pentane solution at low temperature. The molecular
structure (Fig. 9) confirms the inclusion of a single THF unit
per yttrium centre; the structure itself is a distorted tetra-
hedron. The N(1)–Y–N(2) bond angle is narrower in 15 than in
the more sterically encompassing congener [Y{ArN(CH2)3-
NAr}(OAr*)(THF)]36 (82.53(15)Њ as opposed to 95.87(14)Њ),
consistent with the differences in angles found in the analogous
pairs of iodide and bis(trimethysilyl)methyl complexes. The
Lanthanide hydrocarbyl and hydride complexes have been
shown to be active towards both silane dehydrogenative
coupling52 and olefin hydrosilylation.53 Voskoboynikov et al.
later reported the systematic synthesis of a number of
lanthanide hydrides via the reaction of the hydrocarbyls with
various organosilicon, -germanium and -tin hydrides.54 Hydro-
silylation catalysis has since been extensively studied by Tilley
et al., in particular using chelating bis(silylamido)-supported
yttrium complexes.55 Phenylsilane was chosen in this context to
attempt to effect the synthesis of yttrium hydride complexes
incorporating both of the diamide ligands reported on herein.
Both 6 and 11 reacted with a slight excess of phenylsilane in
d6-benzene with complete consumption of the yttrium hydro-
carbyl; 11 took over five days at room temperature to react
completely whilst 6 required heating to 75 ЊC in order to do so
(Scheme 3). During both reactions, the pale yellow solutions
gradually turned a very dark orange. Neither 6 nor 11 reacted
with the more sterically hindered diphenylsilane under the same
conditions. Since reactions between lanthanide complexes and
phenylsilane involve a sigma-bond metathesis mechanism, the
difference in the N(1)–Y–N(2) bond angle and perhaps the way
in which THF is coordinated in solution between 6 and 11 must
be enough to change the reactive surface at yttrium. It turns out
that instead of yielding either of the expected metathesis
products (being an yttrium hydride or an yttrium phenyl) the
reaction produces silicon-based hydrocarbyl and diamide
complexes via the highly unusual substitution of yttrium for
silicon.
Scheme 3
1
The H and 13C{1H} NMR spectra of the in situ reaction of
Fig. 9 ORTEP representation of the molecular structure of 15.
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Y–N(1) 2.173(4), Y–N(2) 2.168(4), Y–O(1) 2.066(4), Y–O(2) 2.319(4);
N(1)–Y–N(2) 82.53(15), N(1)–Y–O(1) 126.86(16), N(1)–Y–O(2)
107.70(16), O(1)–Y–O(2) 98.99(15). Selected crystallographic data:
crystal system: monoclinic, space group: P21/n (no. 14), a = 10.2131(3),
b = 23.5543(6), c = 18.5374(7) Å, β = 101.190(1)Њ, U = 4374.6(2) Å3,
Z = 4.
6 with phenylsilane contain a great number of peaks and
therefore very little diagnostic information. By comparison, the
1H, 13C{1H}, 29Si and 29Si{1H} NMR spectra of the analogous
in situ reaction of 11 are clear and easily interpretable. None of
these spectra reveal any yttrium-coupled resonances. The 29Si
DEPT NMR spectrum has a doublet at δ Ϫ16.95 ppm (1JSiH
=
220.5 Hz), a triplet at δ Ϫ34.75 ppm (1JSiH = 193.8 Hz) and a
D a l t o n T r a n s . , 2 0 0 4 , 1 0 8 3 – 1 0 9 6
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1
quartet at δ Ϫ60.13 ppm (1JSiH = 200.7 Hz), which all resolve as
singlets in the 29Si{1H} NMR spectrum. The quartet is clearly
associated with excess PhSiH3; the other resonances correspond
to the highly soluble oils [Si{ArN(CH2)2NAr}PhH] 16 and
Si{CH(SiMe3)2}PhH2. These resonances are similar to those
observed by Schmidbaur and co-workers in their extensive
studies on the structure and reactivity of silylamines.56 In both
the reactions of 6 and of 11, EI mass spectrometry of small
aliquots taken from the NMR solutions revealed the existence
of two products in which the ligands {CH(SiMe3)2}Ϫ and
{ArN(CH2)xNAr}2Ϫ (x = 2, 3) had separately been transferred
to silicon, i.e. to give Si{CH(SiMe3)2}H2Ph and Si{ArN(CH2)x-
NAr}HPh. The latter is the highest molecular weight peak in
both spectra. All of these assignments have been confirmed by
high resolution EI mass spectroscopy.
silylmethyls. The inequivalence seen in the H NMR spectrum
arises, in an analogous manner to 6 and 8, from the prochiral
silicon centre, however the absence of a THF moiety that is
labile on the NMR timescale accounts for the clearer spectral
resolution in the case of 16.
X-Ray quality crystals were grown from a highly concen-
trated d6-benzene solution at room temperature thus allowing
final confirmation of the structure of 16. The molecular
structure (Fig. 11) clearly reveals the two equivalent sets of four
diastereotopic isopropylmethyl groups that give rise to the
1
four different resonances in the H NMR spectrum. The four-
coordinate silicon centre has a tetrahedral distribution of
ligands, whilst the two amine centres are essentially planar, with
slightly more distortion towards a tetrahedral arrangement at
N(2) than N(1) (sum of angles at N(1) = 359.22(12)Њ, at N(2) =
356.03(12)Њ). Such geometry, invoking sp2 hybridisation, has
already been discussed at length for early transition metal
amides and silylamides in this work and is also very common in
metal-free silylamine chemistry. Schmidbaur and co-workers
have noted the difference between the tetrahedral geometry
found at the non-silylated analogues of the planar trisilyl-
amines such as [N(SiH2Ph)3] and [N(SiH2Ph)(SiMe3)2] and
mono-silylamines, such as [N(SiH2Ph)(CH2Ph)2], [N{SiH2-
(C6H4-4-tBu)}(H)(C6H3-2,4-F2)] and [N(SiH2Ph)(H)(C6H2-
2,4,6-tBu3)].56 The Si–H bond length in 16 is 1.382(0.015) Å,
very similar to those in [N(SiH2Ph)3] (1.36(2), 1.35(2) Å), whilst
the Si–N contacts of 1.7098(13) Å (Si–N(1)) and 1.7196(13) Å
(Si–N(2)) are within the range of 1.70–1.75 Å found in the
above silylamines.
The reaction of 11 with phenylsilane was repeated on a pre-
parative scale in an attempt to separate the silicon-containing
products. This reaction was much slower, presumably due to
greater dilution (about half an equivalent of 11 remained after
five days), however over a 10-day period the reaction mixture
changed from yellow to dark orange. Removal of all volatiles
from the solution phase yielded a dark brown oil showing a 1H
NMR spectrum that was very similar to that of the earlier
in situ studies. The coloured component is insoluble in pentane
and can be removed by successive washings but displays only a
1
broad H NMR spectrum (d6-benzene) offering no diagnostic
information. The pentane fraction yielded a very pale yellow,
viscous oil, containing only Si{CH(SiMe3)2}H2Ph and 16.
Sublimation of this oily mixture (110 ЊC, 2 × 10Ϫ5 mbar) gave 16
as a colourless, viscous oil with concomitant decomposition of
Si{CH(SiMe3)2}H2Ph.
The 1H NMR spectrum of 16 (d6-benzene) has four doublets
and two septets (2JHH = 6.84 Hz), corresponding to four dia-
stereotopic isopropylmethyl protons and their associated
methine protons, in the δ 0.7–1.5 and δ 3.7–4.0 ppm regions
1
of the H NMR spectrum, respectively (Fig. 10). Two other
1
multiplets were found in the δ 3.3–3.6 ppm region of the H
NMR spectrum of 16, arising from the inequivalent backbone
methylene protons. Spin saturation transfer experiments
indicated that the isopropylmethyl protons exchange on the
NMR timescale at room temperature. The coupled silane
3
protons (δ 4.67 ppm, JHH = 3.57 Hz) and bis(trimethyl-
silyl)methine proton (δ Ϫ0.53 ppm, 3JHH = 3.57 Hz) in Si{CH-
1
(SiMe3)2}H2Ph are resolved cleanly in the H NMR spectrum
of the mixture of the two silicon-containing products, along
with a singlet (δ 0.12 ppm) corresponding to the associated
Fig. 11 ORTEP representation of the molecular structure of 16.
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles (Њ):
Si–N(1) 1.7098(13), Si–N(2) 1.7196(13), Si–H(1) 1.382(0.015), Si–C(27)
1.8557(16); N(1)–Si–N(2) 93.59(6), N(1)–Si–H(1) 110.7(0.6), N(2)–Si–
H(1) 117.7( 0.6), C(27)–Si–H(1) 103.7(0.6). Selected crystallographic
data: crystal system: monoclinic, space group: P21/n (no. 14), a =
16.7778(3), b = 9.6378(1), c = 19.7477(3) Å, β = 109.171(1)Њ, U =
3016.14(8) Å3, Z = 4.
Facile intermolecular ligand redistribution, a consequence
of the large size and predominantly ionic bonding mode
of lanthanide centres, has been employed in the synthesis of
lanthanide mixed amido–chloro complexes.57 However the
exchange of a lanthanide centre for a main group non-metal
is highly unusual and unexpected, especially for a chelating
dianionic fragment.
Ethene and 1-hexene studies
Two equivalents of 1-hexene failed to react with a solution
of any of the hydrocarbyl complexes in d6-benzene after 72 h
at room temperature. Addition of a further six equivalents of
1-hexene likewise failed to induce any reaction. Elevation of
the temperature in these experiments generally resulted in
thermal decomposition, although the bis(trimethylsilyl)methyl
and benzyl complexes were surprisingly thermally robust under
Fig. 10 Selected region of the 1H NMR spectrum of Si{CH-
(SiMe3)2}H2Ph and 16 in d6-benzene.
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these conditions. In all cases the THF unit blocks the active site
for olefin insertion; the steric bulk of the various co-ligands also
accounts for their unreactivity. Repeating these experiments
with an atmosphere of ethene on a preparative scale failed to
yield any insoluble poly(ethene). There is some evidence that
the THF ligand is labile; in all complexes THF exchanges for
d8-THF when a large excess of the latter is present and the
various chemical shift values arising from the THF co-ligands
show a small temperature dependency. However, were there to
be a significant base free ‘resting state’ in these equilibria, olefin
insertion would presumably take place. It was not possible to
activate these complexes towards olefin polymerisation by
the addition of the strong Lewis acid B(C6F5)3, which might
be expected to scavenge THF. This reagent instead caused
immediate degradation of the complexes.
and evacuated prior to use. Celite 545 filter aid was flame dried
in vacuo and filter cannulae equipped with Whatman® 25 mm
glass microfibre filters were dried in an oven at 120 ЊC prior
to use.
Reagents and materials
High purity nitrogen, argon, hydrogen and ethene gases were
used as supplied by BOC Gases. Toluene was dried by heating
to reflux over sodium, THF was heated to reflux over potassium
and hexanes and pentane were heated to reflux over sodium–
potassium alloy. Solvents were stored in an ampoule containing
a potassium mirror in all cases apart from THF, which was
stored over activated 4 Å molecular sieves. All solvents were
degassed prior to use. All deuterated solvents were purchased
from Goss Chemicals and were dried over potassium (d6-
benzene, d12-cyclohexane, d8-THF) or sodium (d8-toluene) then
vacuum transferred into ampoules and stored under nitrogen
prior to use. Yttrium chips, potassium metal, 1,3-dibromo-
propane, 1,8-diaminonaphthalene, sodium trifluoroacetate and
mercury() iodide were purchased from Aldrich and used as
supplied. 2,6-Diisopropylaniline was purchased from Aldrich,
stirred over decolourising charcoal overnight and filtered; zinc
powder was added and the mixture distilled to yield the pure
material as a clear, colourless, mobile oil (55 ЊC, 0.1 mbar).
nBuLi (2.5 M solution in hexanes) was purchased from Acros
Organics and used as supplied. KN(SiMe3)2 was purchased
from Fluka and recrystallised from toluene prior to use. KCH-
(SiMe3)2 was prepared via transmetallation of LiCH(SiMe3)2
with potassium menthoxide. KCH2SiMe3 was prepared via
transmetallation of LiCH2SiMe3 with potassium menthoxide.
By comparison the hydride complex 14, formulated in
solution as [{Y{ArN(CH2)2NAr}(µ-H)(THF)}x], does react
with 1-hexene and ethene in aromatic hydrocarbons. Addition
of three equivalents of 1-hexene to a d6-benzene solution of
14 gave rapid loss of the characteristic pale green colour, to give
a yellow solution, with concomitant loss of the hydride peak in
1
the H NMR spectrum. Integration of this spectrum revealed
that approximately one equivalent of 1-hexene had been
consumed; heating to 60 ЊC did not induce further monomer
consumption.58 Unfortunately, the complicated nature of the
resultant 1H NMR spectrum precluded any further in situ
characterisation of the reaction products and, despite repeated
attempts, it was not possible to isolate and characterise any of
these products on a preparative scale either, owing to their very
high solubility in pentane even at low temperatures. A toluene
solution of 14 also reacted with ethene (1.5 bar, 20 ЊC) with
rapid loss of the characteristic pale green colour, this time to
yield a colourless solution. After stirring for about 30 min at
room temperature a very small amount of highly floculant,
fibrous solid was deposited. Stirring for a further 30 min
at room temperature gave a little more solid, however an
additional 5 h stirring did not give a significantly increased
amount of solid and it was not possible to isolate and char-
acterise a measurable amount of this product.
ArNH(CH2)3NHAr,6
ArNH(CH3)NHAr,59
KCH2C6H5,
LiCH(SiMe3)2 and LiCH2SiMe3 were prepared according to
literature preparations.
Analytical techniques
7
1H, 13C{1H} and Li NMR spectra were recorded on a Bruker
Spectrospin AG 300DPX spectrometer operating at 300.13
1
MHz for H measurements, 75.47 MHz for 13C measurements
7
and 116.64 MHz for Li measurements and on a Bruker Spec-
trospin AG 500AMX spectrometer operating at 500.13 MHz
for 1H measurements. 29Si and 89Y NMR spectra were recorded
on a Bruker Spectrospin AG 500AMX spectrometer. 13C and
1H NMR spectra are referenced relative to the carbon or
residual proton chemical shifts of the internal deuterated
solvent set using external SiMe4 for 1H NMR and 13C{1H}
NMR. 29Si spectra were referenced to external SiMe4 and 89Y to
external YCl3 in D2O. Spectra were recorded at 20 ЊC unless
indicated otherwise.
Elemental analyses were carried out by Mikroanalytisches
Labor Pascher of Remagen-Bandorf, Germany (3–7) and
The University of North London (8–15). Extensive ligand
absorptions in the regions of the spectrum in which yttrium
organometallic functionalities generally come into resonance
precluded any meaningful IR studies.
Single crystal X-ray structural determinations were carried
out on a KappaCCD diffractometer. All structures were solved
by direct methods (SHELXS-86)60 and refined (SHELXS-97)61
against all F 2 data. Structures are drawn in the text throughout
as ORTEP representations derived from imported data
(ORTEP23 for windows).62 EI-TOF mass spectroscopy was
carried out on a VG autospec Fisons instrument (electron
ionisation at 70 eV).
Summary
Salt metathesis using first yttrium triiodide and the appropriate
potassium diamide, followed by further metathesis with
potassium hydrocarbyl, amide and phenoxide salts, provides a
reliable synthetic route into a range of yttrium complexes
incorporating the chelating diamides {ArN(CH2)xNAr}2Ϫ (x =
2, 3). These chelating diamides are not as sterically encom-
passing as the ubiquitous permethylcyclopentadienyl ligand,
leading to THF coordination or, in the absence of THF, ate-
complex formation. The bis(trimethylsilyl)methyl yttrium
chelating diamide complexes react with phenylsilane to yield
unprecedented ligand exchange products. In common with
many non-cyclopentadienyl lanthanide complexes the com-
pounds reported herein show at best very slight reactivity
towards olefins, however studies involving polar monomers
such as methyl methacrylate, rac-lactide and ε-caprolactone
have shown encouraging results and will be disclosed in due
course.
Experimental
General considerations
CCDC reference numbers 228144–228152.
See http://www.rsc.org/suppdata/dt/b4/b400149d/ for crystal-
lographic data in CIF or other electronic format.
All inorganic experimental procedures were carried out by
means of standard high-vacuum Schlenk-line techniques, under
an atmosphere of dry nitrogen or catalytically dried and
deoxygenated argon, or under catalytically dried and deoxygen-
ated nitrogen in an MBraun or a Miller-Howe glove box.
Glassware was dried in an oven at 120 ЊC, flame-dried in vacuo
and repeatedly purged with an inert gas (dry argon or nitrogen)
Syntheses
n
K2{ArN(CH2)3NAr} 3. BuLi (6.94 mL, 17.34 mmol, 2.5 M
solution in hexanes) was added dropwise over 15 min with
D a l t o n T r a n s . , 2 0 0 4 , 1 0 8 3 – 1 0 9 6
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1
stirring to a solution of 1 (3.42 g, 8.67 mmol, previously
dissolved in 40 : 60 petroleum ether and dried over anhydrous
Na2SO4) in 80 mL hexanes at Ϫ78 ЊC, then stirred for a further
2 h at room temperature. Potassium menthoxide (38.8 mL,
17.34 mmol, 0.447 M solution in heptane) was added dropwise
over 15 min with stirring to the resultant pale yellow solution at
Ϫ45 ЊC, which deposited a bright yellow precipitate. The result-
ant bright yellow suspension was stirred overnight at room
temperature, poured onto a glass frit in the glove box, washed
with hexanes (3 × 40 mL), dried on the frit for 2.5 h and
collected as a bright yellow powder (3.314 g, 7.06 mmol, 81%).
Characterising data for 3: 1H NMR (d6-benzene): broad and
poorly resolved; (d6-benzene with 3 drops d8-THF): δ 6.85
(s (br), 4H, C6H3(C3H7)2), 6.10 (m (br), 2H, C6H3(C3H7)2), 3.68
(m (br), 8H, CH(CH3)2, NCH2CH2CH2N), 1.98 (s (br), 2H,
NCH2CH2CH2N), 1.31 (s (br), 24H, CH(CH3)2); 13C{1H}
NMR (d6-benzene with 3 drops d8-THF): δ 141.2, 132.9,
124.4, 123.9 (C6H3(C3H7)2), 51.4 (NCH2CH2CH2N), 27.8
(CH(CH3)2), 24.5, 24.2 (CH(CH3)2, NCH2CH2CH2N); 7Li
NMR (d6-benzene): no resonances observed; 7Li NMR (d6-ben-
zene with 3 drops d8-THF): δ 2.19, 1.09 (both sharp and of low
intensity); elemental analysis: calc.: C: 68.88, H: 8.56, N: 5.95;
found: C: 69.90, H: 9.17, N: 5.69%.
CH2CH2N), 50.1 (NCH2CH2CH2N 1), 36.5 (d, JYC = 35 Hz,
YCH(SiMe3)2), 34.6 (NCH2CH2CH2N), 28.6 (CH(CH3)2),
25.9 (THF), 24.3 (CH(CH3)2), 5.0 (CH(SiMe3)2); 89Y NMR
(d6-benzene with 3 drops d8-THF): δ 801 ppm; elemental
analysis: calc.: C: 64.01, H: 9.47, N: 3.93; found: C: 63.89, H:
9.11, N: 4.29%.
[Y{ArN(CH2)3NAr}(CH2C6H5)(THF)2] 7. YI3 (0.408 g, 0.869
mmol) and 3 (0.408 g, 0.869 mmol) were slurried in THF
(40 mL, 0 ЊC). The resultant yellow suspension, on stirring,
rapidly turned to a white suspension, which was stirred over-
night at room temperature. A deep red solution of KCH2C6H5
(0.113 g, 0.869 mmol) in THF (20 mL) was added to the white
suspension at 0 ЊC. The resultant deep red suspension rapidly
changed to an off-white suspension, which was warmed to
room temperature and stirred for 3 h. The solvent was removed
under reduced pressure and the residue dried in vacuo for 1.5 h.
Pentane (30 mL) was added and the yellow suspension stirred
for 2 h and then filtered to yield a clear, very pale yellow
solution. The solvent volume was reduced to 10 mL and the
product recovered as a pale yellow microcrystalline solid (0.085
g, 0.119 mmol, 14%). Crystals suitable for X-ray diffraction
studies were grown from a highly concentrated pentane
solution at 4 ЊC.
K2{ArN(CH2)2NAr} 4. Complex 4 was prepared in an analo-
gous fashion to 3; full synthetic details can be found in the ESI.†
Characterising data for 7: 1H NMR (d6-benzene): δ 7.00–7.30
(m, residual protons from d6-benzene, C6H3(C3H7)2), 6.96 (m,
2H, m-CH2C6H5), 6.77 (d, 2H, o-CH2C6H5), 6.51 (t, 1H,
p-CH2C6H5), 4.00 (sept, 4H, CH(CH3)2), 3.68 (t, 4H, NCH2-
CH2CH2N), 3.12 (m, 10H, THF), 2.64 (m (br), 2H, NCH2-
[Y{ArN(CH2)3NAr}I(THF)2] 5. YI3 (1.000 g, 2.13 mmol) and
3 (1.000 g, 2.13 mmol) were slurried in THF (55 mL, 0 ЊC). The
resultant yellow suspension, on stirring, rapidly turned to a
white suspension, which was stirred overnight at room tem-
perature. The solvent was removed under reduced pressure and
the residue dried in vacuo for 1 h. Toluene (50 mL) was added
and the suspension filtered to yield a clear, pale yellow solution.
The solvent volume was reduced to 20 mL and the solution
cooled to Ϫ45 ЊC over three days to yield 5 as colourless
crystals (0.294 g, 0.391 mmol, 18%); a small amount of 1 was
retained.
2
CH2CH2N), 2.29 (d, JYH = 4 Hz, 2H, YCH2C6H5), 1.35 (d,
24H, CH(CH3)2), 1.00 (m, 10H, THF); 13C{1H} NMR (d6-
benzene): δ 154.3, 154.1, 146.0, 129.5, 123.7, 122.9, 116.7
(C6H3(C3H7)2, CH2C6H5), 69.4 (THF), 59.8 (NCH2CH2-
CH2N), 50.6 (d, 1JY-C = 38 Hz, YCH2C6H5), 34.5 (NCH2CH2-
CH2N), 28.0 (CH(CH3)2), 25.1 (THF), 22.7 (CH(CH3)2);
89Y NMR (d6-benzene): δ 608 ppm; elemental analysis: calc.: C:
70.07, H: 9.24, N: 3.89; found: C: 67.75, 67.54, H: 8.77, 8.69, N:
4.41, 4.42%.
Characterising data for 5: 1H NMR (d6-benzene): δ 7.00–7.20
(m, residual protons from d6-benzene, C6H3(C3H7)2), 4.17 (sept,
4H, CH(CH3)2), 3.74 (t, 4H, NCH2CH2CH2N), 3.35 (sept,
CH(CH3)2 1), 3.25 (s, 8H, THF), 3.05 (m, 2.5H, NCH2-
CH2CH2N; NCH2CH2CH2N, NH, 1), 1.41 (d, 24H, CH-
(CH3)2), 1.20 (d, 2.5H, CH(CH3)2 1), 0.98 (s, 8H, THF);
13C{1H} NMR (d6-benzene): δ 145.7, 143.8, 142.5, 124.2, 123.7,
123.4, 122.9 (C6H3(C3H7)2), 80.9 (low intensity), 70.1 (THF),
59.3 (NCH2CH2CH2N), 50.5 (NCH2CH2CH2N 1), 33.2
(NCH2CH2CH2N), 32.4 (NCH2CH2CH2N 1), 27.9 (CH-
(CH3)2), 26.8, 25.1 (low intensity), 24.5 (THF), 24.3
(CH(CH3)2); elemental analysis: calc.: C: 55.85, H: 7.50, N:
3.72; found: C: 55.25, H: 7.50, N: 3.71%.
[Y{ArN(CH2)3NAr}{N(SiMe3)2}(THF)] 8. 5 (0.200 g, 0.266
mmol) and KN(SiMe3)2 (0.053 g, 0.266 mmol) were dissolved
in toluene (50 mL, 0 ЊC). The resultant yellow suspension
was stirred overnight at room temperature. The solvent was
removed under reduced pressure and the residue dried in vacuo
for 1 h. Pentane (40 mL) was added, and the suspension filtered
to yield a clear, pale yellow solution. The solvent volume was
reduced to 20 mL and the solution cooled to Ϫ45 ЊC to yield
the product as colourless crystals (0.082 g, 0.115 mmol, 43%).
Characterising data for 8: 1H NMR (d6-benzene): δ 7.00–7.30
(m, residual protons from d6-benzene, C6H3(C3H7)2), 3.85 (m
(br), 8H: 4H, THF; 2H, CH(CH3)2; 2H, NCH2CH2CH2N), 3.47
(m (br), 4H: 2H, CH(CH3)2; 2H, NCH2CH2CH2N), 2.31 (m
(br), 2H, NCH2CH2CH2N), 1.60, 1.50 and 1.32 (s (br) 24H,
CH(CH3)2) 1.21 (m, 4H, THF), 0.04 (s, 18H, Si(CH3)2);
13C{1H} (d6-benzene): δ 153.1, 145.2, 144.4, 144.0, 142.7, 124.0,
123.8, 123.5 (C6H3(C3H7)2), 72.3 (THF), 59.8 (NCH2CH2-
CH2N), 34.6 (NCH2CH2CH2N), 28.9, 28.3 (CH(CH3)2), 27.4,
27.0, 24.5, 24.3 (CH(CH3)2), 25.1 (THF), 4.9 (N(SiMe3)2);
elemental analysis: calc.: C: 62.24, H: 9.32, N: 5.88; found: C:
61.63, 61.82 H: 8.95, 8.98 N: 5.68, 5.72%.
[Y{ArN(CH2)3NAr}{CH(SiMe3)2}(THF)] 6.
5 (0.200 g,
0.260 mmol) and KCH(SiMe3)2 (0.053 g, 0.260 mmol) were
dissolved in toluene (40 mL, 0 ЊC). The resultant pale yellow
suspension was stirred overnight at room temperature. The
solvent was removed under reduced pressure from the resultant
pale yellow suspension and the residue dried in vacuo for 1 h.
Pentane (30 mL) was added and the suspension filtered to yield
a clear, pale yellow solution. The solution was cooled to Ϫ45 ЊC
overnight to yield 6 as colourless crystals (0.042 g, 0.059 mmol,
22%).
[Y{ArN(CH2)3NAr}2K(PhMe)] 9. YI3 (0.250 g, 0.531 mmol)
Characterising data for 6: 1H NMR (d6-benzene): broad and
and 3 (0.500 g, 1.063 mmol) were slurried in BuOMe (50 mL,
t
1
poorly resolved; H NMR (d6-benzene with 3 drops d8-THF):
0 ЊC). The resultant yellow–green suspension was warmed to
room temperature and stirred overnight. The solvent was
removed under reduced pressure from the pale yellow–grey
suspension so-produced and the residue dried in vacuo at 40 ЊC
for 1 h. Toluene (50 mL) was added and the suspension filtered
to yield a clear, pale yellow solution. The solvent volume was
reduced to 25 mL and the sample cooled to 4 ЊC to yield 9 as
δ 7.20 (m, 6H, C6H3(C3H7)2), 3.77 (sept, 4H, CH(CH3)2), 3.58
(m, 8H, NCH2CH2CH2N and THF), 2.33 (m, 2H, NCH2CH2-
CH2N), 1.42 (m, 28H, CH(CH3)2 and THF), 0.06 (s, 18H,
2
SiMe3), Ϫ1.09 (d, JYH = 2.2 Hz, 1H, YCH(SiMe3)2); 13C{1H}
NMR (d6-benzene with 3 drops d8-THF): δ 151.8, 145.2, 142.9,
124.6, 124.3, 124.1 (C6H3(C3H7)2), 68.1 (THF), 60.0 (NCH2-
D a l t o n T r a n s . , 2 0 0 4 , 1 0 8 3 – 1 0 9 6
1093

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t
pale yellow crystals (0.150 g, 0.149 mmol, 28%). A directly
analogous procedure carried out in THF yields 9 as pale yellow
crystals (0.081 g, 0.08 mmol, 15%).
2.23 (s, 3H, C6H2 Bu2Me), 1.37 (d, 8.4H, CH(CH3)2 2), 1.29 (m,
t
72H, CH(CH3)2, C6H2 Bu2Me), 1.17 (s, 4H, THF), 13C{1H}
NMR (d6-benzene): δ 159.4, 152.8, 144.8, 143.8, 142.9, 137.0,
125.6, 124.5, 124.0, 123.4, 123.1 (C6H3(C3H7)2, C6H2 tBu2Me),
71.6 (THF), 58.8 (N(CH2)2N), 52.6 (N(CH2)2N 2), 34.4, 31.0
Characterising data for 9: 1H NMR (d6-benzene): δ 7.08,
6.89, 6.65 (m, C6H3(C3H7)2, PhMe), 3.88 (s (br), 4H, CH-
(CH3)2), 3.70 (s (br), 4H, NCH2CH2CH2N), 3.47 (s (br),
unidentified), 3.37 (sept, 4H, CH(CH3)2 1), 3.01 (m, 6H,
NCH2CH2CH2N, NH 1), 2.62 (s, 2H, NCH2CH2CH2N), 2.10
(s, PhMe), 1.75 (m, 2H, NCH2CH2CH2N 1), 1.24 (m, 48H,
CH(CH3)2, CH(CH3)2 1); 13C{1H} (d6-benzene): δ 157.5, 146.2,
144.0, 142.7, 125.6, 124.4, 124.0, 123.8, 120.8 (C6H3(C3H7)2,
PhMe), 58.5 (NCH2CH2CH2N), 50.8 (NCH2CH2CH2N 1),
36.1 (NCH2CH2CH2N), 32.7 (NCH2CH2CH2N 1), 28.3
(CH(CH3)2), 28.1 (CH(CH3)2 1), 24.7 (CH(CH3)2), 24.5
(CH(CH3)2 1); elemental analysis: calc.: C: 72.87, H: 8.82, N:
5.57; found: C: 72.69, 72.62 H: 8.67, 8.73 N: 5.46, 5.42%.
t
(C6H2 Bu2Me), 28.5 (CH(CH3)2), 28.1 (CH(CH3)2 2), 25.0
(CH(CH3)2), 25.8 (m, THF), 24.4, (CH(CH3)2 2); elemental
analysis: calc.: C: 71.22, H: 9.16, N: 3.69; found: C: 70.93,
71.06, H: 9.36, 9.24, N: 3.49, 3.58%.
Reaction of 6 with phenylsilane (NMR scale)
Complex 6 (0.010 g, 0.014 mmol) and PhSiH3 (3 µL, 2.6 mg,
0.024 mmol) were added t0 d6-benzene (0.5 mL) to yield a
watery yellow solution that was left at room temperature for
1
seven days; H NMR spectra taken at regular intervals, all of
which indicated that no reaction had taken place. The colour
did not change over the course of the week; no solid was
deposited. The reaction mixture was heated to 70 ЊC for two
days, during which time the colour darkened markedly, yielding
a brown solution.
[{Y{ArN(CH2)2NAr}I(THF)2}2] 10, [Y{ArN(CH2)2NAr}-
{CH(SiMe3)2}(THF)]
11,
[Y{ArN(CH2)2NAr}(CH2C6H5)-
(THF)2] 12, [Y{ArN(CH2)2NAr}{N(SiMe3)2}(THF)] 13. Com-
plexes 10, 11, 12 and 13 were prepared in analogous fashion to
5, 6, 7 and 8 respectively; full synthetic details can be found in
the ESI.†
1
Characterising data: H NMR: (d6-benzene): no diagnostic
information; EI mass spectrometry (high resolution): calc. for
[Si{ArN(CH2)3NAr}PhH]: m/z 498.343028, found: 498.339447
and calc. for {Si{CH(SiMe3)2}PhH2}: 266.134236, Found:
266.134790.
[{Y{ArN(CH2)2NAr}(ꢀ-H)(THF)}2] with trace amounts of
[Y3{ArNH(CH2)2NAr}2{ArN(CH2)2NAr}(ꢀ-H)3(ꢀ3-H)2(THF)]
14. 10 (0.200 g, 0.117 mmol) and KCH(SiMe3)2 (0.053 g, 0.260
mmol) were dissolved in toluene (40 mL, 0 ЊC). The resultant
yellow suspension was stirred for 3 h at room temperature. The
solvent was removed under reduced pressure from the resultant
pale yellow suspension and the residue dried in vacuo for 1 h.
Pentane (30 mL) was added, and the suspension filtered to yield
a clear, pale yellow solution, which was repeatedly frozen,
degassed and thawed before being exposed to an atmosphere of
H2 (1.5 bar, Ϫ210 ЊC) and stirred for 3 days at room temper-
ature. The resultant pale, watery-green suspension was cooled
to Ϫ45 ЊC overnight to yield 14 as a colourless microcrystalline
solid (0.035 g, 0.0236 mmol, 9% yield), which co-crystallises
with a small amount of 2.
Reaction of 11 with phenylsilane (NMR scale)
Complex 11 (0.010 g, 0.014 mmol) and PhSiH3 (3 µL, 2.6 mg,
0.024 mmol) were added to d6-benzene to yield a watery yellow
solution, which was left at room temperature for three days; 1H
NMR spectra taken at regular intervals. The colour deepened
markedly from a pale yellow to deep orange over the course of
the reaction.
Reaction of 11 with phenylsilane (preparative scale)
Complex 11 (0.200 g, 0.117 mmol) and KCH(SiMe3)2 (0.046 g,
0.234 mmol) were dissolved in toluene (50 mL, 0 ЊC). The
resultant pale yellow suspension was stirred for 3 h at room
temperature, the solvent removed under reduced pressure and
the residue dried in vacuo for 1 h. Pentane (50 mL) was added,
and the suspension filtered to yield a clear, pale yellow solution.
PhSiH3 (3 µL, 2.6 mg, 0.024 mmol) was added via microlitre
syringe and the mixture allowed to stand at room temperature
for 7 days, during which time the colour darkened markedly to
deep orange and a very small amount of microcrystalline solid
was deposited. The supernatant was separated from the solid,
the volatiles removed under reduced pressure and the resultant
orange oil dried in vacuo.
Characterising data for 14: 1H NMR (d6-benzene):63 δ 6.80–
7.45 (m, residual protons from d6-benzene, C6H3(C3H7)2), 5.75
1
(t, JYH = 27 Hz, YHY), 4.06 (sept, CH(CH3)2), 3.96 (s,
N(CH2)2N)), 3.54 (s (br), THF), 3.40 (m, N(CH2)2N 2, NH 2),
3.07 (m, 0.7H, CH(CH3)2 2), 1.00–1.80 (m (br), THF,
CH(CH3)2, other peaks), 0.53 (s (br), unassigned); 13C{1H}
NMR (d6-benzene): δ 155.5, 145.0, 144.2, 142.5, 124.3, 123.8,
123.3, 123.2, 122.4, 121.4, 120.8 (C6H3(C3H7)2), 69.7 (THF),
60.5, 60.2 (N(CH2)2N), 34.2, 28.8 (unassigned, low intensity),
28.2, 27.8 (low intensity; CH(CH3)2), 25.9, 25.5 (CH(CH3)2),
25.0 (THF), 24.2, 23.5, 22.5 (low intensity; CH(CH3)2), 14.0
(unassigned); 89Y NMR (d6-benzene, 323 K): δ 453 (s (br));
elemental analysis: calc.: C: 66.47, H: 8.78, N: 5.67; found: C:
66.59, 66.71, H: 8.58, 8.64, N: 5.25, 5.42%.
Characterising data for [Si{ArN(CH2)2NAr}PhH] 16: 1H
NMR (d6-benzene): δ 7.65 (m, 2H, SiC6H5), 7.00–7.15 (m,
residual protons from d6-benzene, C6H3(C3H7)2, SiC6H5), 5.55
(s, 1H, SiH ), 3.91, 3.78 (sept, 4H, CH(CH3)2), 3.68, 3.41 (m,
4H, N(CH2)2N), 0.73, 1.27, 1.37, 1.44 (d, 24H, CH(CH3)2);
13C{1H} NMR (d6-benzene): δ 149.3, 148.6, 139.7, 136.1,
135.6, 130.6, 126.9, 124.4, 124.3 (SiC6H5, C6H3(C3H7)2), 54.1
(N(CH2)2N), 28.7, 28.1 (CH(CH3)2), 25.8, 25.6, 25.0, 24.5
(CH(CH3)2); 29Si DEPT NMR (d6-benzene): δ Ϫ16.95 (d, 1JSiH
= 220.5 Hz); Accurate mass EI mass spectrometry: calc.: m/z
484.327378, found: 484.328691.
[Y{ArN(CH2)2NAr}(OAr*)(THF)] (OAr* ؍ OC6H2-2,6-tBu2-
4-Me) 15. 10 (0.200 g, 0.117 mmol) and KOAr* (0.061 g, 0.234
mmol) were dissolved in toluene (40 mL, 0 ЊC). The resultant
very pale yellow suspension was stirred overnight at room tem-
perature. The solvent was removed under reduced pressure
from the pale yellow suspension so-produced and the residue
dried in vacuo for 2 h. Pentane (50 mL) was added, and the
resultant pale yellow suspension filtered to yield a clear, pale
yellow solution. The solvent volume was reduced to 10 mL and
the solution was cooled to Ϫ45 ЊC to yield the product as
colourless crystals (0.020 g, 0.026 mmol, 23% yield), which co-
crystallises with approximately a quarter of an equivalent of 2.
Characterising data for mixture of [Si{ArN(CH2)2NAr}-
1
PhH] 16 and {Si{CH(SiMe3)2}PhH2}: H NMR (d6-benzene):
all above peaks plus δ 7.55 (m, 1H, SiC6H5), 4.67 (d, 2H, 3JHH
=
=
3
3.57 Hz, SiH2), 0.12 (s, 18H, SiCH(SiMe3)2), Ϫ0.53 (t, JHH
3.57 Hz, 1H, SiCH(SiMe3)2); 13C{1H} NMR (d6-benzene):
all above peaks plus δ 34.4, 22.7, 14.2, (unassigned) 1.8, 1.4
(SiCH(SiMe3)2), Ϫ2.4 (SiCH(SiMe3)2; 29Si NMR (d6-benzene):
1
Characterising data for 15: H NMR (d6-benzene): δ 7.00–
1
7.30 (m, residual protons from d6-benzene, C6H3(C3H7)2), 3.97
(m (br), 8H, CH(CH3)2, N(CH2)2N), 3.66 (s, 4H, THF), 3.44
(m, 2.1H, CH(CH3)2 2, NH 2), 3.07 (m, 1.6H, N(CH2)2N 2),
above peak plus δ Ϫ34.75 (t, JSiH = 193.8 Hz); EI mass
spectrometry: m/z 484 (37%, {Si{ArN(CH2)2NAr}PhH}ϩ), 266
(10%, {Si{CH(SiMe3)2}PhH2}ϩ).
D a l t o n T r a n s . , 2 0 0 4 , 1 0 8 3 – 1 0 9 6
1094

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18 Shortly after our initial disclosure an alternative synthesis of this
Polymerisation procedures
potassium salt along with synthetic data on certain yttrium and
lutetium complexes was published: P. W. Roesky, Organometallics,
2002, 21, 4756.
1-Hexene. In a typical experiment 10 µmol precatalyst and
30–40 µmol 1-hexene were dissolved in d6-benzene and the H
NMR spectra taken periodically to ascertain the extent of the
reaction.
1
19 Z. W. Xie, Z. X. Liu, F. Xue, Z. Y. Zhang and T. C. W. Mak,
J. Organomet. Chem., 1997, 542, 285.
20 K. H. Denhaan, J. L. Deboer, J. H. Teuben, A. L. Spek,
B. Kojicprodic, G. R. Hays and R. Huis, Organometallics, 1986, 5,
1726.
21 G. Jeske, H. Lauke, H. Mauermann, P. N. Swepston, H. Schumann
and T. J. Marks, J. Am. Chem. Soc., 1985, 107, 8091.
22 All of the 89Y chemical shift values reported herein were measured
with respect to external YCl3 in D2O and were obtained via a
1H observation shift correlation technique. The chemical shift
values were confirmed in every case by selective decoupling of the
89Y nucleus at the reported frequency during acquision of a
1H NMR spectrum.
Ethene. In a typical NMR-scale experiment a d6-benzene
solution of 10 µmol precatalyst was repeatedly frozen, degassed
and thawed before being exposed to an atmosphere of ethene
1
(1.5 bar, 20 ЊC). H NMR spectra were taken periodically to
ascertain the extent of the reaction. In a typical preparative-
scale experiment a toluene solution (30 mL) of 25 µmol pre-
catalyst was repeatedly frozen, degassed and thawed before
being exposed to an atmosphere of ethene (1.5 bar, 20 ЊC) and
stirred at room temperature.
23 R. Duchateau, C. T. vanWee, A. Meetsma, P. T. van Duijnen and
J. H. Teuben, Organometallics, 1996, 15, 2279.
24 R. Duchateau, T. Tuinstra, E. A. C. Brussee, A. Meetsma,
P. T. van Duijnen and J. H. Teuben, Organometallics, 1997, 16, 3511.
25 A figure depicting this variable-temperature NMR study can be
found in the ESI†.
26 A. Mandel and J. Magull, Z. Anorg. Allg. Chem., 1997, 623, 1542.
27 A. Mandel and J. Magull, Z. Anorg. Allg. Chem., 1996, 622, 1913.
28 S. Bambirra, M. J. R. Brandsma, E. A. C. Brussee, A. Meetsma,
B. Hessen and J. H. Teuben, Organometallics, 2000, 19, 3197.
29 M. Booij, A. Meetsma and J. H. Teuben, Organometallics, 1991, 10,
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30 M. F. Lappert, P. P. Power, A. R. Sanger and R. C. Srivastava, Metal
and Metalloid Amides, Ellis Horwood, Chichester, 1980.
31 M. Westerhausen, M. Hartmann, A. Pfitzner and W. Schwarz,
Z. Anorg. Allg. Chem., 1995, 621, 837.
32 Tables of selected bond lengths, angles and crystallographic data as
well as full details of all structure determinations and results of the
refinements for all of the molecular structures presented herein can
be found in the ESI†.
Acknowledgements
We would like to thank BP and EPSRC for financial support,
Dr Guy Clentsmith for support in the laboratory and Stefan
Arndt (RWTH, Aachen) for helpful discussions of the silane
chemistry.
Notes and References
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33 M. Westerhausen, M. Hartmann, A. Pfitzner and W. Schwarz,
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3 (a) F. T. Edelmann, Angew. Chem., Int. Ed. Engl., 1995, 34, 2466; (b)
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4 R. Kempe, Angew. Chem., Int. Ed. Engl., 2000, 39, 468.
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34 H. Schumann, E. C. E. Rosenthal, G. Kociok-köhn, G. A. Molander
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35 A diagram representing the variable-temperature 1H NMR study of
8 is included in the ESI†.
36 The structure and refinement of [Y{ArN(CH2)3NAr}(OAr*)(THF)]
(OAr* = OC6H2-2,6-tBu2-4-Me) can be found in the ESI†.
37 W. J. Evans and B. L. Davis, Chem. Rev., 2002, 102, 2119.
38 The dihedral angle defined by N(1)–N(2)–N(3)–N(4), for example, is
78.2Њ.
39 K. C. Hultzsch, T. P. Spaniol and J. Okuda, Organometallics, 1997,
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47 IR studies on 14 were complicated by ligand absorptions in the
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into resonance, and were thus inconclusive.
48 The value of x could have been found by depression of the freezing
point experiments in benzene, however it was not possible to
produce enough sample to carry out this experiment due to the low
yield of the reaction.
15 The lanthanide triiodides (except EuI3, SmI3 and YbI3) can
conveniently be prepared from the metal and mercury() iodide in a
sealed ampoule at high temperature. Full synthetic details can be
found in the ESI†.
16 F. T. Edelmann, in Synthetic Methods of Organometallic and
Inorganic Chemistry, ed. G. Brauer and W. A. Herrmann, Georg
Thieme Verlag, Stuttgart, 1997.
17 C. Callaghan, G. K. B. Clentsmith, F. G. N. Cloke, P. B. Hitchcock,
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synthetic details for potassium menthoxide can be found in the ESI†.
49 P. B. Hitchcock, M. F. Lappert and R. G. Smith, Inorg. Chim. Acta,
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50 W. T. Klooster, L. Brammer, C. J. Schaverien and P. H. M.
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51 K. B. Aubrecht, K. Chang, M. A. Hillmyer and W. B. Tolman,
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53 P. F. Fu, L. Brard, Y. W. Li and T. J. Marks, J. Am. Chem. Soc., 1995,
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D a l t o n T r a n s . , 2 0 0 4 , 1 0 8 3 – 1 0 9 6
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54 A. Z. Voskoboynikov, I. N. Parshina, A. K. Shestakova, K. P. Butin,
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55 T. I. Gountchev and T. D. Tilley, Organometallics, 1999, 18,
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lanthanide complexes. One possible explanation is the formation of
an yttrium allyl complex that is unreactive towards olefin insertion,
e.g.: (a) W. J. Evans, C. A. Seibel and J. W. Ziller, J. Am. Chem. Soc.,
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59 (a) L. Titcomb, Synth. Pages, 2001, 30; (b) L. Titcomb, Synth. Pages,
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60 G. M. Sheldrick, SHELXS-86, Program for Crystal Structure
Analysis, University of Göttingen, Germany, 1986.
61 G. M. Sheldrick, SHELXS-97, Program for Crystal Structure
Analysis, University of Göttingen, Germany, 1997.
62 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
63 The broad nature of this spectrum precluded any meaningful
integration.
58 Such behaviour towards higher olefins is well documented for
D a l t o n T r a n s . , 2 0 0 4 , 1 0 8 3 – 1 0 9 6
1096