Chiral biarylamido/anisole complexes of yttrium in enantioselective aminoalkene hydaroamination/cyclisation

Article abstract of DOI:10.1039/b400799a

A group of chiral, dibasic, biaryl-bridged amido proligands containing peripheral methoxyphenyl (anisole) ligation are developed for the synthesis of new amide complexes of yttrium and lanthanum. A potentially tetradentate bis(amidoanisole) system L¹ gives, on reaction with [Y{N(SiMe ₂H)₂}₃(THF)] a crystallographically- characterised bis complex [YL¹(HL¹)] presumably as a result of low steric demand, since a more bulky version L² gives the target [L²Y{N(SiMe₂H)₂}(THF)]. The molecular structure of the latter reveals a similar cis-α structure to our recently reported Schiff-base analogue. Variable-temperature NMR studies are consistent with low rigidity in the molecular structure. A potentially tridentate, amidoanisolyl/amido proligand L³ gives complexes [L ³M{N(SiMe₂H)₂}(THF)_n] (M = Y, n = 1; M = La, n = 2). Chiral non-racemic versions of the above complexes were tested in the hydroamination/cyclisation of 2,2-dimethylaminopentane to the corresponding pyrrolidine. Activities were relatively low compared to recently reported examples, and ee values were in the range 20-40% despite the well-expressed chirality of the catalysts.

Full text of DOI:10.1039/b400799a

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F U L L P A P E R
Chiral biarylamido/anisole complexes of yttrium in
enantioselective aminoalkene hydaroamination/cyclisation
Paul N. O’Shaughnessy, Kevin M. Gillespie, Paul D. Knight, Ian J. Munslow and
Peter Scott*
Department of Chemistry, University of Warwick, Coventry, UK CV4 7AL.
E-mail: peter.scott@warwick.ac.uk; Fax: +024 7657 2710
Received 16th January 2004, Accepted 11th June 2004
First published as an Advance Article on the web 28th June 2004
A group of chiral, dibasic, biaryl-bridged amido proligands containing peripheral methoxyphenyl (anisole) ligation
are developed for the synthesis of new amide complexes of yttrium and lanthanum. A potentially tetradentate
bis(amidoanisole) system L1 gives, on reaction with [Y{N(SiMe2H)2}3(THF)] a crystallographically-characterised
bis complex [YL1(HL1)] presumably as a result of low steric demand, since a more bulky version L2 gives the target
[L2Y{N(SiMe2H)2}(THF)]. The molecular structure of the latter reveals a similar cis- structure to our recently reported
Schiff-base analogue. Variable-temperature NMR studies are consistent with low rigidity in the molecular structure. A
potentially tridentate, amidoanisolyl/amido proligand L3 gives complexes [L3M{N(SiMe2H)2}(THF)n] (M = Y, n = 1;
M = La, n = 2). Chiral non-racemic versions of the above complexes were tested in the hydroamination/cyclisation of
2,2′-dimethylaminopentane to the corresponding pyrrolidine. Activities were relatively low compared to recently reported
examples, and ee values were in the range 20–40% despite the well-expressed chirality of the catalysts.
it will be difficult using Schiff-base ligands to produce complexes as
durable and robust as the metallocenes.
Introduction
It is difficult to develop effective chiral ligand environments for
lanthanide-based enantioselective catalysts, essentially because the
ions have large radii and their coordination spheres are highly labile.1
The most significant progress has been made where the metal is act-
ing principally as a Lewis acid, and it would seem that the binol2 and
pybox3 ligands are the most generally efficient in this area. For reac-
tions such as hydrogenation and hydroamination (vide infra) where
the metal is required to mediate migratory insertion processes,
the first enantioselective systems were Marks’ C1-symmetric (S)-
menthylcyclopentadienyl ansa-metallocenes which, for example,
have been shown to catalyse the hydroamination/cyclisation of ami-
noalkenes with ee up to 74%.4 Last year saw a number of reports on
the first enantioselective non-metallocene catalysts for this process.
We have shown that chiral amino/phenoxide complexes of the lan-
thanides can catalyse such reactions with similar enantioselectivity
to the metallocene system but with lower activity.5 Marks and co-
workers reported a thorough study of efficient bis(oxazolinato) lan-
thanide catalysts.6 Collin et al.7 described a bis(binaphthyldiamido)
catalyst giving similar selectivity but rather higher activity than our
similar mono(biaryldiamido) system.8 Hultzsch has shown that yt-
trium binapholate complexes can also operate in this process.9 It
is striking that despite the efforts of these groups (and presumably
others10) that high enantioselectivities have never been obtained in
aminoalkene hydroamination/cyclisation.
In polymerisation catalysis research, diamido units (i.e. two R2N−
units) have been used as an alternative to bis(cyclopentadienyl). Re-
ports of chiral non-racemic diamido ligands are, however, rather rare.
A number of examples of 1,2-diaminocyclohexane based systems,
most notably the sulfonamides,11 have been found to catalyse the
addition of dialkylzinc reagents to aldehydes with high enantiose-
lectivity. Cloke et al. have reported a zirconium complex in which
two amido groups are linked by the atropisomeric 2,2′-diamino-
6,6′-dimethylbiphenyl backbone in 1.12 Gountchev and Tilley have
reported an yttrium complex containing a similar ligand system that
gave high enantioselectivity in the hydrosilation of norbornene.13
Our related tetradentate N2O2 Schiff-bases based on diamine 1, and
the binaphthyl systems of e.g. Che et al.14a give chiral-at-metal com-
plex structures,14b and while the middle and later transition metal
complexes give highly enantioselective catalyst systems,15 the early
metal complexes suffer from decomposition via 1,2-migratory inser-
tion reactions16 and radical processes.17 Although these reactions can
be avoided almost completely in some instances,18 we recognise that
In response to this problem we recently set out to synthesise a
range of new diamido ligands based on the diamine 119 with bulky
and heteroatom donor aryl substituents, and the subsequent zir-
conium complexes.20 In this contribution we outline our attempts
to prepare yttrium complexes of this type of ligand, and describe
their application to enantioselective hydroamination/cyclisation of
aminoalkenes.
Results and discussion
Ligand synthesis
The group of ligands used in this study (Fig. 1) were chosen to
explore the effects of varying denticity, steric demand and chelate
ring size on the catalytic hydroamination reaction. We recently
reported20 the preparation of a range of N-aryl substituted biaryl
diamine proligands including H2L1 and H2L3 from 119 and the ap-
propriate bromoarenes via palladium catalysed arylation.21 These
compounds are expected to act in their doubly deprotonated forms
as tetradentate and tridentate ligands, respectively. Attempts to
synthesise the more sterically demanding dianisole proligand H2L2
by a similar protocol using 2-bromo-4,6-di-tert-butylanisole was
unsuccessful, presumably because the bromoarene is too steri-
cally encumbered. Instead, H2L2 was synthesised efficiently using
the method outlined in Scheme 1, whereby 1 was arylated under
acid catalysed conditions using 2,4-di-tert-butylcatechol to give 2
which we found could be highly chemoselectively O-methylated.
The proligand H2L4 is similar to H2L2 in terms of functionality, with
the addition of methylene spacers between amino and anisole units.
This compound was synthesised via tetrahydroborate reduction of
the corresponding Schiff base16 and O-methylation as for H2L2.
Complex syntheses
We have previously shown that the reaction between H2L1 and
Zr(NMe2)4 gave exclusively the monomeric C2-symmetric N2O2
coordinated complex [L1Zr(NMe2)2].20 With the larger (and tri-
valent) yttrium metal, such a complex was rather more elusive.
The reactions between racemic† H2L1 and the homoleptic alkyl
† Racemic proligands were used for synthetic and structural studies. Opti-
cally-pure compounds were used in the subsequent catalytic studies.
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 , 2 2 5 1 – 2 2 5 6
2 2 5 1

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complex [L1Zr(NMe2)2] the longest such distance observed was
ca. 2.47 Å as a result of excessive ring-strain.20 The shorter Zr–O
distance was ca. 2.39 Å. In the yttrium compound, two of the ami-
doanisole chelate rings are essentially planar, and the associated
O-methyl groups lie approximately in these planes. The third
such chelate is significantly hinged however, with a torsion angle
C(30)–O(2)–Y(1)–N(2) of ca. 33.4°. Correspondingly the methyl
group at O(2) is oriented well out of the aryl plane. Nevertheless,
the three amidoanisole bite angles are very similar at 66.70(15),
66.93(16) and 67.36(15)°.
Fig. 1 Proligands used in this study.
Fig. 2 Thermal ellipsoid plot of the molecular structure of [YL1(HL1)].
In the hope of isolating complexes with only one chiral ligand
we turned to the more sterically demanding proligand H2L2.
While reactions of this compound with [Y{CH(SiMe3)2}3] and
[Y{N(SiMe3)2}3]gavemixturesthatappearedtocontainsomesortof
bis complex as with L1, the reaction with [Y{N(SiMe2H)2}3(THF)]
gave the target complex [L2Y{N(SiMe2H)2}(THF)] in good yield.A
corresponding lanthanum complex could not be isolated.
Scheme 1 Synthesis of the aminoanisole proligands H2L2,4. Reagents
and conditions (i) 2,4-di-tert-butylcatechol, acetic acid (cat.), hexane;5
(ii) KOH/THF, MeI, 82%; (iii) 3-tert-butyl-6-methyl-2-hydroxybenzalde-
hyde;18 (iv) NaBH4/EtOH.5
The asymmetric unit of [L2Y{N(SiMe2H)2}(THF)] contains two
independent molecules, but these have very similar geometries and
metrical parameters. Athermal ellipsoid plot of the molecular struc-
ture of one is shown in Fig. 3, and a structural diagram is also given
[Fig 4(a)]. The ligand L2 is disposed about the metal in the C2-sym-
metric fashion leaving two symmetry-related sites occupied by one
THF and one bis(dimethylsilyl)amido ligand. This cis- orientation
of the tetradentate chelate contrasts with the cis- structure found
for the related zirconium complex [L1Zr(NMe2)2],20 but since both
these complexes undergo dynamic processes in solution (vide infra)
a meaningful distinction is hard to draw.
[Y{CH(SiMe3)2}3] and amide [Y{N(SiMe3)2}3] gave mixtures
of the starting material and a species [YL1(HL1)] (vide infra).
Presumably, this results from the highly sterically shielded nature
of these starting materials which renders them less reactive than
the first-formed products e.g. [L1Y{CH(SiMe3)2}]. In any event
it is becoming clear that the less encumbered reagents such as
[Y{N(SiMe2H)2}3(THF)] are more synthetically useful, despite
the presence of ligated THF.5,8,22 Accordingly, the reaction of
H2L1 with [Y{N(SiMe2H)2}3(THF)] gave a mixture of what ap-
peared (by NMR) to be ca. 10% [YL1(HL1)] along with the target
[L1Y{N(SiMe2H)2}(THF)n]. Unfortunately, the latter complex was
found to be insufficiently stable for isolation.
A few crystals of the bis complex [YL1(HL1)] were isolated
from one of the above reactions and the structure of this species
(Fig. 2) was determined by X-ray crystallography. The complex
is homochiral in that both biaryl units have the same configura-
tion. The coordination number is seven, and the inner coordination
sphere is significantly distorted from the closest regular structure,
pentagonal bipyramidal, with best axial unit angle N(1)–Y(1)–N(3)
of 156.39(17)° and mean deviation of the remaining five atoms
from their least-squares plane of ca. 0.4 Å. One nitrogen atom
N(4) remains in its protonated form, with a correspondingly
long N(4)–Y(1) distance of 2.669(6) Å. Not surprisingly, given
the unfavourable geometry for ligation of the associated anisole
OMe unit, this oxygen atom is uncoordinated. The Y–N(amido)
distances of 2.28–2.30 Å are unremarkable. The three Y–O(anisole)
distances are in the range 2.42–2.45 Å. In the zirconium amide
We have recently reported the molecular structure of a biaryl
bridged salicylaldimine complex of yttrium i.e. Fig. 4(b).5 While
this complex has an essentially octahedral coordination sphere,
[L2Y{N(SiMe2H)2}(THF)] [Fig. 4(a)] with one less atom in each
of the NO chelates is significantly distorted from this ideal geom-
etry. Nevertheless, the chiral ligand environment as “seen” by the
auxiliary ligands is surprisingly similar for these two complexes
(Fig. 4, lower). The greatest distinction arises, not surprisingly, in
the presence of O-methyl groups in [L2Y{N(SiMe2H)2}(THF)]. The
distance Y(1)–O(2) of 2.444(6) Å is within the range observed in
[YL1 ] above, but the distance Y(1)–O(1) of 2.591(6) Å is signifi-
2
cantly longer.
1
The H NMR spectrum of [L2Y{N(SiMe2H)2}(THF)] at 233 K
indicates low symmetry, e.g. there are four sharp tert-butyl reso-
nances corresponding to 9H each. This slow exchange spectrum
may arise from the presence of the cis- structure, or perhaps more
likely one corresponding to the X-ray molecular structure above
2 2 5 2
D a l t o n T r a n s . , 2 0 0 4 , 2 2 5 1 – 2 2 5 6

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Table 1 Enantioslective hydroamination/ cyclisation of 2,2′-dimethylami-
nopent-4-ene
Entry Pre-catalyst
Temp/°C
Time/d
ee (%)
1
2
3
[L2Y{Y{N(SiMe2H)2}3(THF)2]
60
60
60
8
5
7
21
34
40
[L3La{N(SiMe2H)2}3(THF)2]
[L3Y{N(SiMe2H)2}3(THF)2]
of the THF ligand, which we have observed in similar systems,5
conversion between different tetradentate ligand orientations, or
perhaps both. Given the rather long Y–O bond measured above,
reversible decoordination of the anisole OMe group seems likely.
The reaction between H2L3 and [Y{N(SiMe2H)2}3(THF)]
gave a mixture containing largely [L3Y{N(SiMe2H)2}(THF)]
which was isolated is moderate yield after crystallisation from
pentane. A similar reaction with [La{N(SiMe2H)2}3(THF)2] gave
[L3La{N(SiMe2H)2}(THF)].
The proligand H2L4 undergoes very slow protonolysis with
[M{N(SiMe2H)2}3(THF)n] (M = Y, La) giving less than 10% con-
version after two weeks at 80 °C. Presumably this results from the
relatively weak proton acidity of the mono-aryl amino units com-
Fig. 3 Thermal ellipsoid plot of the molecular structure of
[L2Y{N(SiMe2H)2}(THF)].
pared to those in H2L1–3
.
Catalytic studies
The chiral non-racemic complexes from the above studies were
tested as catalysts for the enantioselective hydroamination/
cyclisation of 2,2′-dimethylaminopentene to the corresponding
pyrrolidine using an in-situ protocol. The di-anisole system L2
(Table 1, entry 1) is disappointingly unselective given the very
favourable catalyst structure. We propose that this is a result of
the fluxional nature of the coordination sphere. The lanthanum
complex of the unsymmetrical L3 (entry 2) was noticeably better.
Not surprisingly, given the more open coordination sphere the reac-
tion was faster, but the ee also improved; the molecular structure
of a related Zr complex of L3 displays well-expressed chirality.20
On moving to yttrium (entry 3), the rate fell and the ee improved
slightly, both commensurate with the smaller metal ion radius. Al-
though the enantiomeric excesses obtained were modest, it should
be noted that there are few catalysts for such a reaction that give a
significant ee at all.
Conclusions
Highly enantioselective catalysts for the hydroamination/cyclisation
of aminoalkenes have yet to be developed, and it would seem that
very precise control of the metal coordination sphere is required for
this to be a realistic prospect. In the attempts reported here using
peripheral anisole ligation in multidentate systems, it would seem
that the rigidity of the dative O-donor ligand is not sufficient for
this purpose.
Fig. 4 ChemDraw and chem3D diagrams of the molecular structures of
(a) [L2Y{N(SiMe2H)2}(THF)] and (b) a related salicylaldimine complex of
yttrium; the lower projections are viewed down the approximate C2 axes.
Experimental
All manipulations were carried out using standard Schlenk/glove-
box techniques under an atmosphere of dry argon, except for the
work-up procedures for the ligands, which were performed under
aerobic conditions. Solvents were distilled from Na/K alloy (pen-
tane, diethyl ether), potassium (THF) or sodium (toluene) under an
atmosphere of dinitrogen. Deuterated benzene and toluene were
heated to reflux in vacuo over potassium for three days, distilled
under vacuum, degassed by three freeze–pump–thaw cycles and
stored in a glove-box. The reagents [M{N(SiMe2H)2}3(THF)2]
(M = Y, La),23 2-methyl-4-tert-butylbromobenzene,24 and the
(the low symmetry arising from unsymmetrical coordination at the
two auxiliary sites).‡ At 298 K these peaks have coalesced and by
353 K two sharp resonances (each 18H) are observed. This fast
exchange regime spectrum could arise from reversible coordination
‡ Epimerisation of the stereogenic O-centres formed on coordination of the
methoxy groups to yttrium is a rather less likely source of symmetry disrup-
tion since we can see from the molecular structure that the configuration at O
is strongly directed by the helicity inherent in the ligand coordination mode.
D a l t o n T r a n s . , 2 0 0 4 , 2 2 5 1 – 2 2 5 6
2 2 5 3

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substrate 2,2-dimethylaminopent-4-ene25 were synthesised accord-
ing to literature procedures. The chiral-racemic and non-racemic
ligands HL1, HL3, were synthesised according to our own proce-
dures,20 as were 1,19 2 and 3.5
thoroughly in vacuo overnight to remove pentane of crystallisation
(see X-ray crystallography section). Combined yield 0.43 g, 74%.
Anal. Calc. for C52H80N3O3Si2Y: C, 66.42; H, 8.58; N, 4.47. Found:
1
C, 66.24; H, 8.71; N, 4.33%. H NMR (C6D6, 297 K, 400 MHz):
 0.14 (br d, 6H, SiHMe2), 0.19 (br d, 6H, SiHMe2), 1.31 (br, 18H,
CMe3), 1.41 (br, 18H, CMe3), 2.14 (br, 6H, Ar–Me), 3.57 (br, 4H,
THF), 3.79 (br, 6H, OMe), 4.70 (br, 2H, SiHMe2), 6.58 (br, 2H,
Ar–H), 6.9–7.25 (br, 8H, Ar–H).
Syntheses
(±)-HL2
To a stirred solution of aminophenol 2 (2.00 g, 3.22 mmol) in THF
(50 ml), was added an excess of KOH pellets (0.50 g, 8.91 mmol).
After stirring for ca. 24 h an excess of MeI (0.80 ml, 12.9 mmol)
was added to the dark green solution. After stirring for a further
24 h the red solution was washed with water and extracted with
diethyl ether. The solution was dried over MgSO4 and the solvent
was removed by rotary evaporation to yield a red oily material.
Pentane (2 × 10 ml) was added and removed in vacuo to yield a
pink solid. This solid was recrystallised from hot petroleum ether
(bp 40–60 °C) to give a white solid. The supernatant was kept at
5 °C overnight to yield a further crop. Combined yield 1.71 g, 82%.
Anal. Calc. for C44H60N2O2: C, 81.43; H, 9.32; N, 4.32. Found: C,
(±) [L3Y{N(SiHMe2)}(THF)]
H2L3 (0.31 g, 0.60 mmol) and [Y{N(SiMe2H)2}3(THF)2] (0.37 g,
0.59 mmol) were loaded into a Schlenk flask inside a glove-box.
Toluene (10 ml) was added and the reaction mixture was stirred
at 50 °C overnight. During this time the solution turned an amber
colour. The toluene was removed in vacuo to yield a brown foamy
material. Pentane (2 × 10 ml) was added and removed in vacuo
yielding a yellow powder. Pentane was carefully added until almost
all the solid had dissolved. The solution was filtered via cannula,
concentrated and placed in a refrigerator for 24 h yielding a crop
of small pale yellow crystals. The supernatant was separated, con-
centrated and cooled for a further 2 d yielding a second crop. The
crystalline material was dried in vacuo for 5 h. Combined yield
0.31 g, 64%. Anal. Calc. for C44H64N3O2Si2Y: C, 65.08; H, 7.94; N,
5.17. Found: C, 64.89; H, 8.47; N, 5.02%. 1H NMR (C6D6, 297 K,
400 MHz):  0.15 (d, 6H, SiHMe2), 0.16 (br, 6H, SiHMe2), 1.02 (br,
4H, THF), 1.45 (s, 18H, CMe3), 2.18 (br, 6H, Ar–Mebiaryl), 2.27 (s,
3H, Ar–Meanisyl), 3.48 (br, 4H, THF), 3.63 (s, 3H, OMe), 4.76 (br,
2H, SiHMe2), 6.52 (m, 2H, Ar–H), 6.81 (d, 1H, Ar–H), 6.88 (d,
1H, Ar–H), 6.91 (s, 1H, Ar–H), 7.12 (m, 3H, Ar–H), 7.22 (m, 1H,
Ar–H), 7.44 (m, 2H, Ar–H), 7.88 (d, 1H, Ar–H). 13C{1H} NMR
(C6D6, 297 K):  3.1 (SiHMe2), 21.2 (Ar–Me), 21.4 Ar–Me), 23.6
(THF), 32.2 (CMe3), 33.5 (CMe3) 56.1 (OMe), 71.0 (THF), 101.6,
101.9, 109.8, 110.5, 113.4, 116.6, 122.1, 123.8, 125.9, 127.77,
130.24, 133.5 139.8, 142.1 151.2 (Ar).
1
81.58; H, 9.25; N, 4.27%. H NMR (CDCl3, 297 K, 400 MHz): 
1.17 (s, 18H, CMe3), 1.24 (s, 18H, CMe3), 2.01 (s, 6H, Ar–Me),
3.32 (s, 6H, OMe), 5.29 (s, 2H, N–H), 6.76 (d, 2H, Ar–H), 7.85 (s,
2H, Ar–H), 7.00 (d, 2H, Ar–H), 7.11 (m, 4H, Ar–H). 13C{1H} NMR
(CDCl3, 297 K):  20.3 (Ar–Mebiaryl), 31.3 (CMe3), 31.9 (CMe3),
35.0 (CMe3), 35.6 (CMe3), 60.3 (OMe), 112.1, 117.7, 118.1, 121.7,
124.6, 128.9, 135.4, 138.6, 142.6, 142.9, 146.0, 149.7 (Ar). MS: m/z
648 (M+), 85, 78, 62.
S(−)-HL2
As for (±)-HL2 above. Combined yield 1.43 g, 69%. Anal. Calc. for
C44H60N2O2: C, 81.43; H, 9.32; N, 4.32. Found: C, 81.64; H, 9.59;
N, 4.15%. NMR Data as (±)-HL2 above.
(±)-HL4
(±) [L3La{N(SiHMe2)}(THF)2]
To a stirred solution of the aminophenol 3 (1.20 g, 2.12 mmol)
in THF (50 ml) was added an excess of KOH pellets (0.50 g,
8.91 mmol). After stirring for 3 d an excess of MeI (0.50 ml,
8.48 mmol) was added via syringe to the light green solution, and
the stirring was continued for a further 24 h. Water was added to the
solution. The combined diethyl ether extracts (3 × 50 ml) were dried
over MgSO4 and the solvent was removed by rotary evaporation
to yield a foamy material. A small quantity of petroleum ether (bp
40–60 °C) was added, followed by rotary evaporation to dryness.
This was repeated to yield a white solid. Yield 1.19 g, 95%. Anal.
Calc. for C40H52N2O2: C, 81.04; H, 8.84; N, 4.73. Found: C, 80.82;
H, 8.98; N, 4.62%. 1H NMR (CDCl3, 297 K, 400 MHz):  1.33 (s,
18H, CMe3), 1.86 (s, 6H, Ar–Me), 2.10 (s, 6H, Ar–Me), 3.52 (br,
2H, NH), 3.64 (s, 6H, OMe), 4.37 (m, 4H, NCH2), 6.64 (d, 2H, Ar),
6.71 (d, 2H, Ar), 6.78 (d, 2H, Ar), 7.11 (d, 2H, Ar), 7.16 (t, 2H, Ar).
13C{1H} NMR (CDCl3, 297 K):  18.8 (Ar–Me), 20.1 (Ar–Me), 31.3
(CMe3) 35.3 (CMe3), 41.5 (NCH2), 63.2 (OMe), 108.4, 119.6, 121.8,
125.9, 126.6, 129.2, 130.8, 137.9, 138.0, 142.5, 146.3 163.2 (Ar).
MS: m/z 592 (M+).
The racemic proligand H2L3 (0.33 g, 0.63 mmol) and
[La{N(SiMe2H)2}3(THF)2] (0.45 g, 0.66 mmol) were loaded into
a Schlenk flask inside a glove-box. Toluene (10 ml) was added
and the reaction mixture was stirred at 50 °C overnight during
which time the solution turned an amber colour. The product was
isolated as for the analogous Y compound above. Combined yield:
0.32 g, 59%. Anal. Calc. for C48H72LaN3O2Si2: C, 61.71; H, 7.77; N,
4.50. Found: C, 61.01; H, 7.42; N, 4.65%. 1H NMR (C6D6, 297 K,
400 MHz):  0.26 (br, 6H, SiHMe2), 0.35 (br, 6H, SiHMe2), 1.30 (br,
8H, THF), 1.57 (s, 18H, CMe3), 2.26 (br, 6H, Ar–Me), 2.43 (s, 3H,
Ar–Me), 3.45 (br, 4H, THF), 3.64 (br, 4H, THF), 3.83 (s, 3H, OMe),
4.95 (br m, 2H, SiHMe2), 6.45 (m, 1H, Ar–H), 6.57 (d, 1H, Ar–H),
6.67 (m, 2H, Ar–H), 7.04 (s, 1H, Ar–H), 7.19 (m, 3H, Ar–H), 7.36
(m, 2H, Ar–H), 7.49 (d, 1H, Ar–H), 7.75 (d, 1H, Ar–H). 13C{1H}
NMR (C6D6, 297 K):  5.4 (SiHMe2), 20.8 (Ar–Me), 21.1 (Ar–Me),
24.5 (THF), 32.2 (CMe3), 38.2 (CMe3) 54.8 (OMe), 69.0 (THF),
102.3, 105.4, 111.6, 111.9, 114.2, 119.8, 123.9, 124.4, 126.0, 128.5,
132.6, 137.1, 139.8, 146.3, 155.9 (Ar).
(±) [L2Y{N(SiHMe2)}(THF)]
Catalysis
The proligand H2L2 (0.40 g, 0.62 mmol) and [Y{N(SiMe2H)2}3-
(THF)2] (0.43 g, 0.68 mmol) were loaded into a Schlenk flask
inside a glove box. Toluene (10 ml) was added and the reaction was
stirred at 50 °C overnight during which time the solution turned yel-
low. The toluene was removed in vacuo to yield a foamy material.
Pentane (2 × 10 ml) was added and removed in vacuo [in an attempt
to remove residual toluene and HN(SiHMe2)2] yielding a yellow
powder. Pentane was added until most of the solid had dissolved.
The solution was filtered via cannula, concentrated and placed in
a refrigerator at 0 °C for two days. A crystalline yellow precipitate
formed. The supernatant was separated, concentrated and placed
in the fridge for a further two days yielding a second crop. The
combined material was crushed into a powder and was dried
In a typical reaction approximately 10 mg of the diamine ligand
under study and approximately 0.9 equivalents of the desired lan-
thanide amide starting material, (less than one equivalent is used to
ensure complete protonolysis of lanthanide amide starting material)
were loaded into a Young’s tap NMR tube in a glove-box. d8-Tol-
uene was added and the sample was heated at 50 °C until complete
1
protonolysis had occurred, as judged by H NMR spectroscopy.
The d8-toluene and the amine by-product were removed in vacuo
and d8-toluene and 2,2-dimethylaminopentene (25–30 equivalents)
were then added. The mixture was maintained at constant tempera-
ture (60 °C) until catalytic reaction was complete as judged by 1H
NMR spectroscopy.
2 2 5 4
D a l t o n T r a n s . , 2 0 0 4 , 2 2 5 1 – 2 2 5 6

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Table 2 Experimental data for the X-ray diffraction studies
Table 3 Selected bond lengths (Å) and angles (°) for [YL1(HL1)]·C5H12
and [L2Y{N(SiMe2H)2}(THF)]·0.5C5H12
[L2Y{N(SiMe2H)2}
[YL1(HL1)]·C5H12
(THF)]·0.5C5H12
[YL1(HL1)]·C5H12
[L2Y{N(SiMe2H)2}(THF)]·0.5C5H12
a
Molecular formula
Formula weight
Crystal system
Space group
a/Å
b/Å
c/Å
/°
C65H73N4O4Y
1063.18
Triclinic
P1
11.964(7)
14.017(10)
17.212(10)
91.90(4)
97.40(4)
100.67(5)
2808(3)
2
C54.5H86N3O3Si2Y
976.35
Triclinic
P1
11.5395(8)
20.6404(14)
26.6724(18)
111.4820(10)
91.202(2)
102.414(2)
5738.4
Y1–N1
Y1–N2
Y1–N3
Y1–N4
Y1–O1
Y1–O2
Y1–O3
2.295(5)
2.284(5)
2.302(5)
2.669(6)
2.445(4)
2.451(4)
2.418(4)
Y1–N3
Y1–N2
Y1–N1
Y1–O3
Y1–O2
Y1–O1
Y1–Si1
Si1–N3
Si2–N3
2.261(8)
2.265(8)
2.280(7)
2.352(6)
2.444(6)
2.591(6)
3.366(4)
1.696(9)
1.697(9)
/°
/°
N2–Y1–N1
N2–Y1–N3
N1–Y1–N3
N2–Y1–O3
N1–Y1–O3
N3–Y1–O3
N2–Y1–O1
N1–Y1–O1
N3–Y1–O1
O3–Y1–O1
N2–Y1–O2
N1–Y1–O2
N3–Y1–O2
O3–Y1–O2
O1–Y1–O2
N2–Y1–N4
N1–Y1–N4
N3–Y1–N4
O3–Y1–N4
O1–Y1–N4
O2–Y1–N4
86.52(17)
102.53(18)
156.39(17)
81.68(16)
93.39(16)
66.93(16)
139.10(16)
66.70(15)
93.40(16)
70.30(14)
67.36(15)
111.49(16)
92.10(16)
138.01(14)
150.16(13)
138.70(17)
102.40(18)
85.27(18)
136.63(16)
79.34(16)
71.91(15)
N3–Y1–N2
N3–Y1–N1
N2–Y1–N1
N3–Y1–O3
N2–Y1–O3
N1–Y1–O3
N3–Y1–O2
N2–Y1–O2
N1–Y1–O2
O3–Y1–O2
N3–Y1–O1
N2–Y1–O1
N1–Y1–O1
O3–Y1–O1
O2–Y1–O1
N3–Y1–Si1
N2–Y1–Si1
N1–Y1–Si1
O3–Y1–Si1
O2–Y1–Si1
O1–Y1–Si1
105.3(3)
145.1(3)
86.2(3)
104.1(3)
135.7(3)
88.2(2)
98.7(3)
66.9(2)
116.0(2)
76.5(2)
82.4(3)
121.0(2)
63.8(2)
95.1(2)
171.6(2)
27.0(2)
132.0(2)
133.9(2)
79.75(18)
104.18(16)
73.12(15)
V/Å3
Z
4
/mm−1
1.090
11893
4516
0.0891, 0.1595
1.098
36133
14947
0.0690, 0.1640
Total reflections
Independent reflections
R1, wR2 [I > 2(I)]
For the chiral non-racemic pre-catalysts, the volatile components
were vacuum transferred from NMR tube into a receiver flask and
the enantiomeric excesses were determined by diastereomeric
derivatization with (R)-(−)--methoxy--(trifluoromethyl)phenyl-
acetyl chloride (Mosher’s chloride).26 This was achieved by a
modification of the procedure of Hoye27 in which dichloromethane
(1–2 ml) was added to the distillate in the reciever flask followed
by addition of 1 equivalent of Mosher’s chloride and triethylamine.
The solution was stirred for 48 h and solvent removed in vacuo.
The enantiomeric excess was then determined from the relative
integration of the two resonances in the 19F NMR (CDCl3) spectra
recorded at 50 °C.
a Bond lengths and angles for only one independent molecule of [L2Y{N-
(SiMe2H)2}(THF)]2·C5H12 given. The other molecule is essentially the
same.
Crystallography
Crystals were coated in an inert oil prior to transfer to a cold
nitrogen gas stream on Bruker-AXS SMART three-circle area
detector diffractometer system equipped with Mo-K radiation
( = 0.71073 Å). Data were collected with narrow (0.3° in )
frame exposures. Intensities were corrected semi-empirically
for absorption, based on symmetry-equivalent and repeated
reflections (SADABS). Reflection data for [L2Y{N(SiMe2H)2}-
(THF)]·0.5C5H12, which contains two independent molecules
in the asymmetric unit, were weak and no significant data were
collected for 2 > 45°. Both structures were solved by direct
methods (SHELXS) with additional light atoms found by Fourier
methods. For [YL1(HL1)]·C5H12 the atoms of the slightly disor-
dered pentane molecule were subject to displacement parameter
restraints. Disordered tert-butyl groups were present in both in-
dependent molecules and were modelled and refined across two
alternative positions. Both structures were refined on F2 values
for all unique data. Table 2 gives further details. All non-hydro-
gen atoms were refined anisotropically. The atoms Si3, C47, C48,
C94, C98 and C100 of [L2Y{N(SiMe2H)2}(THF)]2·0.5C5H12 were
subject to additional displacement parameter restraints. All H
atoms were constrained with a riding model; U(H) was set at 1.2
(1.5 for methyl groups) times Ueq for the parent atom. Programs
used were Bruker AXS SMART (control), SAINT (integration)
and SHELXTL for structure solution, refinement, and molecular
graphics. Table 3 gives selected bond lengths and angles for the
two compounds.
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