Reactivity of yttrium quinoline-imine-phenoxide complexes towards interand intramolecular alkyl nucleophilic attacks

Article abstract of DOI:10.1002/ejic.200800493

Yttrium(III) chloride complexes [YCl²(NNO^H)] (1H) and [YCl₂(NNO^Me)] (1^Me) {NNO^H = 2-tert-butyl-6-(quinolin-8-yliminomethyl) phenoxide; NNO^Me = 2-tert-butyl-6-[(2-methylquinolin-8-ylimino)methyl]phenoxide} were synthesized by treating a thf solution of YCl₃ at room temperature with the NNO^H-H and NNO^Me-H ligands {NNO^H-H = 2-tert-butyl-6-(quinolin-8-yliminomethyl)phenol; NNO^Me-H = 2-tert-butyl-6-[(2-methylquinolin-8-ylimino)methyl]phenol}, which were previously deprotonated with potassium tert-butoxide or thallium ethoxide. Surprisingly, reaction of 1^H with the Grignard reagent MeMgBr to prepare the corresponding dialkyl derivative led to the formation of the tetranuclear magnesium dimer [Mg₂BrCl{NN(Me)O^H}(thf)] ₂ {NN(Me)O^H = 2-tert-butyl-6-[1-(quinolin-8-ylamido)ethyl] phenoxide} (2), whose structure was determined by single-crystal X-ray diffraction. By reacting the neutral ligand NNO^H-H with Y(CH ₂SiMe₃)₃·2thf in toluene at low temperature the alkyl complex [Y(CH₂SiMe₃){NN(CH ₂SiMe₃)O}(thf)] {NN(CH₂Si-Me₃)O = 2-tert-butyl-6-[1-(quinolin-8-ylamido)-2-trimethylsilanylethyl] phenoxide} (3) was isolated. The supposed reaction mechanism leading to the formation of 3 was simulated by using the PM6 Hamiltonian. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800493

FULL PAPER
DOI: 10.1002/ejic.200800493
Reactivity of Yttrium Quinoline–Imine–Phenoxide Complexes Towards Inter-
and Intramolecular Alkyl Nucleophilic Attacks
Gino Paolucci,*[a] Marco Bortoluzzi,[a] and Valerio Bertolasi[b]
Keywords: Yttrium / Magnesium / Chloride complexes / Imine Ligands
Yttrium(III) chloride complexes [YCl2(NNOH)] (1H) and sium dimer [Mg2BrCl{NN(Me)OH}(thf)]2 {NN(Me)OH
=
[YCl2(NNOMe)] (1Me) {NNOH = 2-tert-butyl-6-(quinolin-8-yl- 2-tert-butyl-6-[1-(quinolin-8-ylamido)ethyl]phenoxide} (2),
iminomethyl)phenoxide; NNOMe = 2-tert-butyl-6-[(2-methyl- whose structure was determined by single-crystal X-ray dif-
quinolin-8-ylimino)methyl]phenoxide} were synthesized by fraction. By reacting the neutral ligand NNOH-H with
treating a thf solution of YCl3 at room temperature with the Y(CH2SiMe3)3·2thf in toluene at low temperature the alkyl
NNOH-H and NNOMe-H ligands {NNOH-H = 2-tert-butyl-6- complex [Y(CH2SiMe3){NN(CH2SiMe3)O}(thf)] {NN(CH2Si-
(quinolin-8-yliminomethyl)phenol; NNOMe-H = 2-tert-butyl- Me3)O
=
2-tert-butyl-6-[1-(quinolin-8-ylamido)-2-trimeth-
6-[(2-methylquinolin-8-ylimino)methyl]phenol}, which were ylsilanylethyl]phenoxide} (3) was isolated. The supposed re-
previously deprotonated with potassium tert-butoxide or action mechanism leading to the formation of 3 was simu-
thallium ethoxide. Surprisingly, reaction of 1H with the Grig- lated by using the PM6 Hamiltonian.
nard reagent MeMgBr to prepare the corresponding dialkyl (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
derivative led to the formation of the tetranuclear magne- Germany, 2008)
isolation of reactive alkyl complexes bearing imine-based
ligands in their coordination sphere can be a demanding
Introduction
Group 3 and lanthanide alkyl and aryl complexes are an
objective.
attractive field of research, as the predominant ionic char-
acter of the Ln···C bond makes these derivatives reactive
precursors towards a wide range of inorganic and catalytic
During the last years our research group has been inter-
ested in the coordination chemistry of early d- and f-block
elements with polydentate imine-based ligands and in the
reactions.[1] In particular, recent literature shows a develop-
preparation of organometallic derivatives for olefin polyme-
ment of new neutral and cationic alkyl complexes of group
rization.[5–7] It was observed that the synthesized precata-
3 and rare-earth metals as catalysts for olefin polymeriza-
lysts, once activated with alkylating agents, often showed a
tion.[2] The organometallic active species in this type of re-
relatively low activity with formation of polymers with high
actions are often obtained in situ by reacting precatalysts
polydispersivity index (PDI), this suggesting the formation
such as chloride complexes with cocatalysts like MAO
of different catalytic sites. To better give insight into the
(methyl aluminoxane), Grignard reagents and lithium or al-
organometallic chemistry of group 3 and lanthanides com-
uminium alkyls, including also, for example, compounds
plexes with polydentate imine-based ancillary ligands, in
able to act as carbanion sources, even if several organome-
this paper the results of inter- and intramolecular nucleo-
tallic derivatives have been isolated and characterized.
philic attacks by carbanion sources on yttrium-coordinated
A great variety of ancillary ligands have been reported in
quinoline–imine–phenoxide ligands, leading to the isolation
the coordination chemistry of group 3 metals and lantha-
and characterization of unexpected products, are reported.
nides, mainly containing N-, O- or C-donor groups. Among
The ionic radius of YIII, 89.3 pm, intermediate among
all, imine–phenoxide-based ligands are usually able to
many Ln3+ ions, allows this element to be considered as a
strongly coordinate hard metal centers such as LnIII and
representative for several 4f-block metals, in particular thu-
analogous ions to give well-defined species.[3] Free and co-
lium (87.0 pm), erbium (88.1 pm), holmium (89.4 pm) and
ordinated imines are, however, susceptible to nucleophilic
dysprosium (90.8 pm).
attack or insertion into the Ln···C bond;[4] therefore, the
[a] Dipartimento di Chimica, Università Ca’ Foscari di Venezia,
Results and Discussion
Dorsoduro 2137, 30123 Venezia, Italy
Fax: +39-0412348684
Synthesis and Characterization of the Quinoline–Imine–
Phenoxide Complexes
[b] Dipartimento di Chimica e Centro di Strutturistica Diffratto-
metica, Università di Ferrara,
Via Borsari 46, 44100 Ferrara, Italy
The neutral quinoline–imine–phenoxide yttrium chloride
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
complexes YCl2(NNOH) (1H) and YCl2(NNOMe) (1Me
)
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Reactivity of Yttrium Quinoline–Imine–Phenoxide Complexes
{NNOH = 2-tert-butyl-6-(quinolin-8-yliminomethyl)phen- YCl2(NNOMe) (1Me) derivative is, as expected, quite similar
oxide; NNOMe = 2-tert-butyl-6-[(2-methylquinolin-8-yl- to the one previously described. The most downfield reso-
imino)methyl]phenoxide} were prepared in good yields by nance is attributed to the imine proton, whose coupling
reacting the YCl3 salt with the corresponding ancillary li- with the metal center is identical to that of compound 1H,
3
gands previously deprotonated with potassium tert-butox- that is, JYH = 1.2 Hz. The aromatic H atoms show signals
ide or thallium ethoxide, as depicted in Scheme 1. In the between 8.05 and 6.38 ppm, and the last triplet corresponds
case of thallium ethoxide as base, the thallium salts to the proton in the para position with respect to oxygen
Tl(NNOH) and Tl(NNOMe) were isolated before the subse- atom in the phenoxide ring, as for 1H. The aliphatic region
quent reaction with YCl3. Similar synthetic approaches shows, besides the tert-butyl singlet at δ = 1.31 ppm, the
were already successfully applied for the preparation of quinoline methyl group at δ = 2.77 ppm as a sharp singlet.
group 4 chloride complexes of the type MCl3(NNOH)
(M = Ti, Zr, Hf)[6] and the scandium(III) complex
ScCl2(NNOH)(thf).[7] The neutral ligands NNOH-H and
NNOMe-H were prepared on the basis of a reported pro-
cedure,[6] that is, by treating 8-aminoquinoline or 2-methyl-
8-aminoquinoline with 3-tert-butyl-2-hydroxybenzaldehyde
in refluxing methanol in the presence of anhydrous magne-
sium sulfate and molecular sieves. The commercially un-
available 2-methyl-8-aminoquinoline was synthesized from
2-methyl-8-nitroquinoline on the basis of a reported
method.[8]
Figure 1. 1H NMR signal of the hydrogen atom of the imine group
coupled to the metal center in compound 1H.
In both the mass spectra of 1H and 1Me it was possible
to detect the isotopic clusters of the molecular ions at m/z
= 462 and 477, respectively, in agreement with the theoreti-
cal ones. The other characterized fragments are attributable
to the loss of the molecular ion of chloride and/or methyl
groups: in the 1H spectrum the clusters at m/z = 447, 427
and 411 correspond to the [M·+ – CH3]+, [M·+ – Cl]+ and
Scheme 1. Synthesis of 1H and 1Me
.
[M·+ – Cl – Me]·+ ions, respectively, whereas in the 1Me spec-
trum the [M·+ – Cl]+ and [M·+ – Cl – Me]·+ ions show their
clusters at m/z = 442 and 425, respectively.
The two yttrium chloride compounds were characterized
by elemental analyses, 1D and 2D H NMR spectroscopic
1
experiments and mass spectrometry. All data strongly agree
with the proposed formulations. In particular, homonuclear
decoupling, 1H COSY and 1H NOESY, experiments al-
lowed all the resonances corresponding to the aromatic pro-
tons of the coordinated ligands to be assigned unambigu-
Reaction of 1H with MeMgBr and X-ray Structure
Determination of the Product
Once isolated and characterized, chloride complex 1H
ously. The most downfield signal of the 1H NMR spectrum was allowed to react in thf at low temperature with two
of YCl2(NNOH) 1H is a doublet of doublets at δ = 8.97 ppm equivalents of methylmagnesium bromide. The objective of
corresponding to the proton in the α position with respect this reaction was to prepare a yttrium dialkyl derivative
to the N atom of the quinoline group. A characteristic H with the NNOH ligand, that is, a species able to undergo
1
signal of the imine group falls at 8.88 ppm (Figure 1). The facile cation formation by reaction with Brønsted or Lewis
coupling between this hydrogen atom and the metal center acids like B(C6F5)3, [Ph3C][B(C6F5)4], [PhNMe2H]-
3
(100% 89Y, I = 1/2) is diagnostic, with a JYH constant of [B(C6F5)4], etc., with consequent formation of a charged
1.2 Hz, which is probably due to the presence of the imine π organometallic complex potentially active for olefin poly-
system and a favourable Karplus angle. The other aromatic merization. The crude product was separated from the by-
protons fall in the range 7.91–7.39 ppm, with the exception products by extraction with toluene and allowed to precipi-
of the quite strongly shielded hydrogen atom in the para tate by addition of n-hexane. Two classes of reactions were
position with respect to the oxygen atom, which corre- potentially expected: the nucleophilic attack of the Grig-
sponds to a triplet at δ = 6.69 ppm. In the aliphatic region, nard reagent on the coordinated imine group and/or the
only a sharp singlet due to the tert-butyl group is observ- substitution of the coordinated chloride ligands by a methyl
able. The complete H NMR spectrum of complex 1H and group.
1
1
1
the corresponding H COSY spectrum are reported in the
The H NMR spectrum of isolated product 2, reported
Supporting Information. The 1H NMR spectrum of the in the Supporting Information, shows the signals of the aro-
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4127

G. Paolucci, M. Bortoluzzi, V. Bertolasi
FULL PAPER
matic rings between 7.90 and 6.26 ppm. The corresponding atom of the symmetry-related ligand. Conversely, each pe-
13C{1H} singlets fall in the range 142.5–102.2 ppm. The as- ripheral Mg2 cation displays a distorted tetrahedral coordi-
signments of the aromatic hydrogen and carbon atoms were nation and is bound to Br1 and N2 bridging Mg1 and Mg2
carried out on the basis of 2D homo- and heteronuclear cations, forming two four-membered Mg1–Br1–Mg2–N2
experiments. The downfield region of the NMR spectra of rings. The remaining coordination sites are occupied by a
compound 2 show the absence of signals attributable to the Cl anion and the oxygen atom of a thf molecule. The OR-
R-CH=N-RЈ group. In the aliphatic region, besides the TEP[9] view is shown in Figure 2 and selected bond lengths
presence of the tert-butyl group and a molecule of coordi- and angles are given in Table 1.
1
nated thf, is diagnostic evidence for the presence of a H
quartet at δ = 4.54 ppm, which couples with a doublet at δ
= 0.65 ppm (3JHH = 6.6 Hz).The corresponding signals in
Table 1. Selected bond lengths and angles.
the 13C{1H} NMR spectrum fall at δ = 59.7 and 20.2 ppm.
Bond lengths [Å]
1
This H AB3 spin system allowed for the assumption that
Mg1–Br1
Mg1–O1
Mg1–N1
Mg1–N2
2.600(2)
1.996(5)
2.200(6)
2.106(6)
Mg2–Br1
Mg2–Cl1
Mg2–O2
Mg2–N2
2.452(2)
2.277(6)
2.052(6)
2.156(6)
nucleophilic attack of the MeMgBr reagent at the coordi-
nated imine occurred with subsequent formation of the cor-
responding coordinated amido group. No signal attribut-
able to alkyl group coordination was detected.
Bond angles [°]
The formation of a complex of the type YCl[NN(Me)-
OH](thf) {NN(Me)OH = 2-tert-butyl-6-[1-(quinolin-8-yl-
amido)ethyl]phenoxide} was therefore supposed, but ele-
mental analysis data for compound 2 showed a strong con-
trast with the proposed formulation. Crystals suitable for
X-ray structure analysis were thus obtained by slow cooling
of saturated toluene/n-hexane solutions: astonishingly, com-
pound 2 resulted to be the tetranuclear magnesium dimer
[Mg2BrCl{NN(Me)OH}(thf)]2 represented in Figure 2 and
not the expected yttrium quinoline–amide–phenoxide com-
plex. Compound 2 has C2 symmetry by virtue of a twofold
crystallographic axis passing in between the Mg1 cations.
The structure consists of two different Mg environments.
The central Mg1 cations are five-coordinate and are
bridged by two µ-O1 phenoxide oxygen atoms forming a
Mg1–O1–Mg1–O1 four-membered ring. They adopt a dis-
torted trigonal bipyramidal geometry with the ligand acting
in a tridentate mode where the O1 phenoxide oxygen atom
and the N1 quinoline nitrogen atom are in axial positions,
whereas the equatorial sites are occupied by the N2 amido
nitrogen atom, the Br1 anion and the O1 phenoxide oxygen
Br1–Mg1–O1
Br1–Mg1–O1Ј
Br1–Mg1–N1
Br1–Mg1–N2
O1–Mg1–O1Ј
O1–Mg1–N1
O1Ј–Mg1–N1
O1–Mg1–N2
O1Ј–Mg1–N2
N1–Mg1–N2
100.1(2)
132.5(2)
99.0(2)
90.3(2)
78.6(2)
157.4(2)
97.0(2)
90.1(2)
136.8(2)
77.9(2)
Br1–Mg2–Cl1
Br1–Mg2–O2
Br1–Mg2–N2
Cl1–Mg2–O2
Cl1–Mg2–N2
O2–Mg2–N2
Mg1–Br1–Mg2
Mg1–N2–Mg2
Mg1–O1–Mg1Ј
134.6(2)
95.8(2)
93.2(2)
105.5(2)
115.2(2)
110.1(2)
78.4(1)
97.1(2)
98.0(2)
The monomer unit of compound 2 is sketched in
Scheme 2 for the sake of clarity. Even if the suggestion of a
complete reaction mechanism for the formation of
[Mg2BrCl{NN(Me)OH}(thf)]2 from 1H is a demanding ob-
jective, it appears reasonable to consider the nucleophilic
attack of one equivalent of the Grignard reagent on the
coordinated imine bond of YCl2(NNOH) and the conse-
quent formation of the corresponding amide group as one
of the key steps of the reaction pathway leading to the for-
mation of 2. The substitution of the yttrium center by mag-
nesium does not find, instead, a simple explanation, espe-
cially on considering the polydentate nature of the ancillary
ligand used. From the mother liquor of 2 it was impossible
to separate pure yttrium compounds, and as a matter of
Figure 2. ORTEP view of complex 2 displaying the thermal ellip-
soids at 40% probability.
Scheme 2. Sketch of the monomer unit of complex 2.
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Reactivity of Yttrium Quinoline–Imine–Phenoxide Complexes
fact, any attempt to reduce the MeMgBr/1H ratio from the
original 2:1 led only to the formation of complex mixtures
of hardly separable products.
Synthesis and Characterization of
[Y(CH2SiMe3){NN(CH2SiMe3)O}(thf)] (3)
After the structural characterization of 2, we tried to im-
prove our knowledge about the reactivity of Y-coordinated
imine groups in the presence of carbanion sources by treat-
ing the neutral ligand NNOH-H with a stoichiometric
amount of the organometallic precursor Y(CH2SiMe3)3·
2thf[10] in toluene.
Isolated compound 3 was characterized by elemental
analysis and 1H and 13C NMR spectroscopy. The 1H NMR
spectrum, reported in the Supporting Information, shows
the characteristic signals of the phenoxide and quinoline
rings between 7.66 and 6.40 ppm, assigned on the basis of
COSY and NOESY experiments. The corresponding car-
bon atoms were identified in the 13C{1H} NMR spectrum
between 143.3 and 104.4 ppm by HMQC experiments. As
for compound 2, the NMR spectra of complex 3 do not
show any signal in the downfield region attributable to the
R-CH=N-RЈ group, whereas a molecule of coordinated thf
and the ancillary tert-butyl ligand can be detected. At
Scheme 3. Proposed mechanism for the formation of
[Y(CH2SiMe3){NN(CH2SiMe3)O}(thf)] (3).
A possible reaction mechanism leading to the formation
of complex 3 is outlined in Scheme 3. The first reaction step
is probably constituted by a fast acid–base reaction between
one of the CH2SiMe3 groups of the Y(CH2SiMe3)3·2thf or-
ganometallic precursor and the phenol group of the free
neutral ligand NNOH, with the elimination of tetramethyl-
silane and the formation of an intermediate quinoline–
imine–phenoxide yttrium dialkyl complex. Intermolecular
migration of a CH2SiMe3 ligand from the metal center to
the coordinated imine carbon atom can be supposed as the
second step of the reaction pathway leading the formation
of final product 3.
Intermolecular nucleophilic attack on the imine carbon
atom by the alkyl ligand was simulated by using the semi-
empirical PM6 Hamiltonian. Computed data are reported
in Table 2. Once optimized, the geometries of both the two
ground states and the transition state of the “CH2SiMe3
migration” pathway represented in Scheme 3, the computed
enthalpy difference between the supposed intermediate and
the product is about –13 kcal/mol, which, from a thermo-
dynamic point of view, justifies why we did not isolate the
expected quinoline–imine–phenoxide yttrium dialkyl com-
plex depicted in Scheme 3 (intermediate) after the hydro-
genolysis reaction between NNOH-H and Y(CH2SiMe3)3·
2thf. Moreover, the computed energy barrier between the
transition state and the intermediate for the proposed
4.54 ppm falls a doublet of doublets corresponding to a 13
C
singlet at δ = 61.4 ppm, which couples with two different
hydrogen atoms at δ = 1.80 and 1.42 ppm (3JHH = 10.0 and
1
4.8 Hz), as observable in the H COSY spectrum reported
in the Supporting Information. These two aliphatic protons
couple each other with a 2JHH coupling constant of 13.0 Hz
and give HMQC signals with a single carbon atom at δ =
31.2 ppm. The chemical shift of the most downfield reso-
nance of the described ABC spin system is attributable to
the N-bonded CH formed after nucleophilic attack at the
imine carbon atom of a CH2SiMe3 group, whereas the B
and C multiplets can be referred to the methylene group of
the nucleophile. Both the yttrium-coordinated nitrogen
atom and the carbon atom of the N-CH amido group are
stereocenters, and this justifies the nonequivalence of the
CH2 protons of the CH2SiMe3 chain. Finally, the most up-
field signals in the 1H NMR spectrum of 3 are a doublet at
δ = 0.20 ppm attributed to the CH2 group of a yttrium-
2
coordinated CH2SiMe3 ligand, with JYH = 2.7 Hz, and a
strong singlet centered at δ = 0.08 ppm attributed to the
SiMe3 groups of the isolated product. All the silicon-
bonded carbon atoms of 3 correspond to a single, slightly
broad 13C signal at δ = –1.8 ppm, which was partially re-
solved by means of sine-bell apodization. From its NMR
spectroscopic data, compound 3 can be formulated as the
Table 2. Computational results for the proposed intermolecular
alkyl migration leading to the formation of 3.
neutral
quinoline–amide–phenoxide
alkyl
complex
[Y(CH2SiMe3){NN(CH2SiMe3)O}(thf)] {NN(CH2SiMe3)O
= 2-tert-butyl-6-[1-(quinolin-8-ylamido)-2-trimethylsilanyl-
ethyl]phenoxide} sketched in Scheme 3. The heaviest frag-
ment observed in the mass spectrum (m/z = 536) corre-
sponds to the molecular ion after the loss of thf and two
methyl fragments.
Compound
Heat of formation
[kcal/mol]
Imaginary frequency
[cm–1]
Intermediate
Transition state
Final product
–236.5
–197.3
–249.4
–
I835
–
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G. Paolucci, M. Bortoluzzi, V. Bertolasi
FULL PAPER
was prepared by following a reported procedure.[6] The same
method was followed for the synthesis of the analogous ligand
NNOMe-H, 2-tert-butyl-6-[(2-methyl-quinolin-8-ylimino)methyl]-
phenol, that is, by treating 2-methyl-8-aminoquinoline and 3-tert-
butyl-2-hydroxybenzaldehyde in refluxing methanol in the presence
of anhydrous magnesium sulfate and molecular sieves (yield Ͼ
60%). 2-Methyl-8-aminoquinoline was obtained on the basis of a
reported procedure by reducing 2-methyl-8-nitroquinoline with
tin(II) chloride in acidic media.[8] Tl(NNOH) and Tl(NNOMe), that
is, the thallium(I) salts of the NNOH-H and NNOMe-H ligands,
were prepared by treating a stoichiometric amount of thallium
ethoxide with the free ligands in thf. The organometallic precursor
Y(CH2SiMe3)3·2thf was synthesized by following a literature
method by treating YCl3 with trimethylsilylmethyllithium.[10]
mechanism is about 39 kcal/mol, sufficiently low to kinet-
ically allow the intermolecular alkyl migration from the
metal center to the imine group. A picture of the optimized
transition-state geometry is reported in Figure 3. It is to
be noted that a similar reaction was already observed in a
previous work by following the reaction between the orga-
nometallic precursor Zr(CH2Ph)4 and the ligand NNOH-H
by NMR spectroscopy.[6]
Microanalyses were performed at the Istituto di Chimica Inor-
1
ganica e delle Superfici, CNR, Padova. H NMR, 13C{1H} NMR,
COSY, NOESY and 13C APT were recorded at 298 K with a
Bruker Avance 300 spectrometer operating at 300 MHz (1H) and
75 MHz (13C). NMR chemical shifts are internally referred to the
solvent resonance and are quoted relative to tetramethylsilane (δ =
0 ppm). The SwaN-MR and MestRe-C software packages were
used for NMR spectroscopic data treatment and spin systems simu-
lation.[11] NMR deuterated solvents (CDCl3, C6D6, CD2Cl2, [D8]-
thf) were purchased from Euriso-Top. Mass spectra (EI, 70 eV)
were recorded with a Finnigan Trace GC–MS equipped with a
probe controller for the sample direct inlet. Sample temperature
was varied between 80 and 280 °C. The assignments were done by
comparison between theoretical and experimental isotopic clusters
and the most intense signals of each characterized cluster are re-
ported.
Figure 3. PM6 optimized geometry of the transition state leading
to the formation of 3. Hydrogen atoms are omitted for the sake of
clarity.
Crystal data of compound 2 were collected with a Nonius Kappa
CCD diffractometer by using graphite monochromated Mo-Kα ra-
diation (λ = 0.7107 Å) at low temperature (120 K). Data sets were
integrated with the Denzo-SMN package[12] and corrected for Lo-
rentz-polarization and absorption[13] effects. The structure was
Conclusions
The described work was focused on the reactivity of the
imine group of a yttrium-coordinated quinoline–imine–
phenoxide ancillary ligand towards carbanion intra- and solved by direct methods (SIR97)[14] and refined by full-matrix least
square methods with all non-hydrogen atoms anisotropic and hy-
drogens included on calculated positions, riding on their carrier
atoms. The methyl groups C20H3 and C21H3 were found disor-
dered and refined over two positions with occupancy 0.5 each. The
correct absolute configuration, (R), of the C10 carbon atom
bonded to N2 was obtained by the value of the Flack parameter[15]
of 0.09(2), calculated after the last cycle of refinement. All calcula-
tions were performed by using SHELXL-97[16] and PARST[17] im-
plemented in WINGX system of programs.[18]
intermolecular nucleophilic attack. The nature of the iso-
lated products strongly highlighted the ease of inter- and
intramolecular reactions between the coordinated –CH=N–
fragment and alkyl nucleophile sources, with the formation
of new complexes such as tetranuclear magnesium dimer 2.
Also, the computed results for the proposed reaction
mechanism leading to quinoline–amide–phenoxide yttrium
alkyl complex 3 underline from both thermodynamic and
kinetic points of view that the obtainment of stable group 3
and lanthanide alkyl complexes with imine-based ancillary
ligands can be a demanding objective.
Semiempirical computational geometry optimizations were carried
out with the MOPAC2007 software package.[19] In all the calcula-
tions the PM6 Hamiltonian[20] was used. The singlet multiplicity
was always considered; thus, the “restricted” formalism was ap-
plied. Calculations were carried out without symmetry constrains
and all the resultant stationary points were characterized as true
minima (i.e. no imaginary frequencies) or transition state geome-
tries (i.e., one imaginary frequency).
Experimental Section
Materials and Methods: All inorganic manipulations were carried
out under oxygen- and moisture-free atmosphere in a Braun MB
200 G-II glove box. All reaction solvents were thoroughly deoxy-
genated and dehydrated under argon by refluxing over suitable dry-
ing agents, whereas NMR solvents were kept in the dark over mo-
lecular sieves. The salt YCl3 (Strem) was used as received, like 8-
aminoquinoline, 3-tert-butyl-2-hydroxybenzaldehyde (Aldrich) and
2-methyl-8-nitroquinoline (Lancaster). Also, potassium tert-butox-
ide, thallium ethoxide, anhydrous magnesium sulfate and tin(II)
chloride dihydrate were purchased from Aldrich. The neutral li-
gand NNOH-H, 2-tert-butyl-6-(quinolin-8-yliminomethyl)phenol,
NNOMe-H: Refer to Scheme 4 for numbering. 1H NMR (CDCl3,
298 K): δ = 14.58 (s, 1 H, OH), 9.03 (s, 1 H, CH=N), 8.07 (d, 3JHH
3
= 8.3 Hz, 1 H, H3), 7.67 (t, JHH = 4.8 Hz, 1 H, H5), 7.51, 7.50 (2
3
3
4
d, JHH = 4.8 Hz, 2 H, H4-H6), 7.44 (dd, JHH = 7.7 Hz, JHH
=
3
3
1.6 Hz, 1 H, H9), 7.35 (d, JHH = 8.3 H, 1 H, H2), 7.32 (dd, JHH
4
3
= 7.7 Hz, JHH = 1.6 Hz, 1 H, H7), 6.90 (t, JHH = 7.7 Hz, 1 H,
H8), 2.79 (s, 3 H, Me), 1.55 (s, 9 H, tBu) ppm. 13C{1H} NMR
(CDCl3, 298 K): 165.9 (CH=N); 136.4 (C3); 131.1 (C7); 130.6 (C9);
126.2 (C5); 126.0, 119.8 (C4–C6); 122.8 (C2); 118.3 (C8); 161.8,
4130
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4126–4132

Reactivity of Yttrium Quinoline–Imine–Phenoxide Complexes
159.6, 145.0, 142.2, 138.2, 127.8, 120.0 (quaternary aromatic car-
1H: Refer to Scheme 4 for numbering of aromatic H atoms. 1H
bon atoms), 35.5 (tBu); 29.8 (tBu); 26.2 (Me) ppm. C21H22N2O NMR (CD2Cl2 + 10% [D8]thf, 298 K): δ = 8.97 (dd, 3JHH = 4.5 Hz,
3
(318.41): calcd. C 79.2, H 6.96, N 8.80; found C 79.1, H 7.10, N
8.65.
4JHH = 1.5 Hz, 2 H, H1), 8.88 (d, JYH = 1.2 Hz, 2 H, CH=N),
3
4
3
8.36 (dd, JHH = 8.4 Hz, JHH = 1.5 Hz, 1 H, H3), 7.91 (dd, JHH
4
3
4
= 7.8 Hz, JHH = 1.3 Hz, 1 H, H6), 7.82 (dd, JHH = 7.8 Hz, JHH
3
= 1.3 Hz, 1 H, H4), 7.75 (t, JHH = 7.8 Hz, 1 H, H5), 7.53 (dd,
3JHH = 8.4 Hz, JHH = 4.5 Hz, 1 H, H2), 7.44 (dd, JHH = 7.5 Hz,
3
3
4JHH = 1.8 Hz, 1 H, H7), 7.39 (dd, JHH = 7.5 Hz, JHH = 1.8 Hz,
1 H, H9), 6.69 (t, 3JHH = 7.5 Hz, 1 H, H8), 1.19 (s, 9 H, tBu) ppm.
MS (EI, 70 eV): m/z = 462 [M]·+, 447 [M – CH3]+, 427 [M – Cl]+,
411 [M – Cl – Me]·+. C20H19Cl2N2OY (463.19): calcd C 51.86, H
4.13, N 6.05, Cl 15.3; found C 51.6, H 4.55, N 6.05, Cl 15.1.
3
4
1Me: Refer to Scheme 4 for numbering of aromatic H atoms. 1H
NMR (CD2Cl2 + 10% [D8]thf, 298 K): δ = 8.18 (d, 3JYH = 1.2 Hz,
3
3
1 H, CH=N), 8.05 (d, JYH = 8.4 Hz, 1 H, H3), 7.56 (dd, JHH
=
7.8 Hz, 4JHH = 1.4 Hz, 1 H, H6), 7.42 (t, 3JHH = 7.8 Hz, 1 H, H5),
7.31 (dd, 3JHH = 7.8 Hz, JHH = 1.4 Hz, 1 H, H4), 7.25 (d, JHH
=
4
3
3
4
8.4 Hz, 1 H, H2), 7.20 (dd, JHH = 7.6 Hz, JHH = 1.8 Hz, 1 H,
3
4
H9), 7.02 (dd, JHH = 7.6 Hz, JHH = 1.8 Hz, 1 H, H7), 6.38 (t,
3JHH = 7.6 Hz, 1 H, H8), 2.77 (s, 3 H, Me), 1.31 (s, 9 H, tBu) ppm.
MS (EI, 70 eV): m/z = 477 [M]·+, 442 [M – Cl]+, 425 [M – Cl –
Me]·+. C21H21Cl2N2OY (477.22): calcd. C 52.85, H 4.44, N 5.87,
Cl 14.9; found C 53.0, H 4.65, N 5.65, Cl 15.2.
Scheme 4. Numbering scheme for the aromatic atoms of the li-
gands.
Tl(NNOH): Refer to Scheme 4 for numbering. 1H NMR (C6D6,
[Mg2BrCl(NN(Me)OH)(thf)]2 (2): To a solution of 1H (0.667 g,
1.44 mmol) in thf (50 mL), cooled to –40 °C was dropwise added a
solution of MeMgBr (3  in Et2O, 0.96 mL, 2.88 mmol) diluted to
15 mL with thf. The color immediately turned from yellow to dark
red. The reaction mixture was allowed to stir at –40 °C for 2 h and
then allowed to slowly reach room temperature and left overnight
whilst stirring. The solvent was removed by evaporation at reduced
pressure and toluene (20 mL) was added. The solution was centri-
fuged to remove residual solids and concentrated to 5 mL. Ad-
dition of n-hexane allowed the product to separate as red micro-
crystals, which were filtered, washed with n-hexane and dried under
vacuum. Yield Ͼ 60%. Crystals suitable for X-ray structure diffrac-
tion were obtained by slow cooling of toluene/n-hexane solutions.
Refer to Scheme 4 for numbering scheme. 1H NMR (CD2Cl2,
298 K): δ = 7.90 (dd, 3JHH = 8.2 Hz, 4JHH = 1.4 Hz, 1 H, H3), 7.83
3
298 K): δ = 8.31 (s, 1 H, CH=N); 8.12 (dd, 3JHH = 4.2 Hz, JHH
=
3
4
1.6 Hz, 1 H), 7.70 (dd, JHH = 7.5 Hz, JHH = 1.9 Hz, 1 H), 7.48
3
4
(dd, JHH = 8.3 Hz, JHH = 1.6 Hz, 1 H), 7.22–7.13 (m, 3 H), 8.82
(t, 3JHH = 4.4 Hz, 1 H), 6.74 (dd, JHH = 8.3 Hz, JHH = 4.2 Hz, 1
3
4
3
H), 6.65 (t, JHH = 7.5 Hz, 1 H) aromatic protons; 1.89 (s, 9 H,
tBu) ppm. C20H19N2OTl (507.76): calcd. C 47.3, H 3.77, N 5.52;
found C 47.0, H 3.65, N 5.70.
Tl(NNOMe): Refer to Scheme 4 for numbering. 1H NMR (C6D6,
4
298 K): δ = 8.33 (s, 1 H, CH=N); 7.69 (dd, 3JHH = 7.3 Hz, JHH
=
3
1.9 Hz, 1 H), 7.45 (d, JHH = 8.4 Hz, 1 H), 7.25–6.80 (m, 3 H),
3
4
6.82 (dd, JHH = 6.6 Hz, JHH = 2.2 Hz, 1 H), 6.70–6.58 (m, 2
H) aromatic protons; 2.12 (s, 3 H, Me); 1.89 (s, 9 H, tBu) ppm.
C21H21N2OTl (521.79): calcd. C 48.3, H 4.06, N 5.37; C 48.5, H
4.15, N 5.25.
Synthesis of [YCl2(NNOH)] (1H) and [YCl2(NNOMe)] (1Me
)
3
4
3
(dd, JHH = 4.5 Hz, JHH = 1.4 Hz, 1 H, H1), 7.26 (dd, JHH
=
7.5 Hz, 4JHH = 1.7 Hz, 1 H, H9), 7.16 (t, 3JHH = 7.9 Hz, 1 H, H5),
Method a: To a solution of the ligand NNOH-H or NNOMe-H
(1.1 mmol) in thf (20 mL) was slowly added a stoichiometric
amount of potassium tert-butoxide (0.123 g, 1.1 mmol) at room
temperature. After 15 min under magnetic stirring, solid YCl3
(0.215 g, 1.1 mmol) was added, and the resulting mixture was al-
lowed to react at room temperature for 12 h. The solvent was re-
moved by evaporation under reduced pressure, and the solid resi-
due was extracted with CH2Cl2 (5ϫ20 mL). The resulting bright-
yellow solution was concentrated under reduced pressure to 5 mL.
By slow addition of ethyl ether (20 mL) a yellow microcrystalline
product precipitated, which was filtered, washed with ethyl ether
and dried under vacuum. Yield Ͼ 75%.
3
3
3
7.01 (dd, JHH = 8.2 Hz, JHH = 4.5 Hz, 1 H, H2), 6.87 (dd, JHH
4
3
= 7.5 Hz, JHH = 1.7 Hz, 1 H, H7), 6.64 (t, JHH = 7.5 Hz, 1 H,
3
3
H8), 6.26 (d, JHH = 7.9 Hz, 2 H, H4–H6), 4.54 (q, JHH = 6.6 Hz,
1 H, CH), 3.48 (m, 4 H, thf), 1.76 (s, 9 H, tBu), 1.49 (m, 4 H, thf),
0.65 (d, 3JHH = 6.6 Hz, Me) ppm. 13C{1H} NMR (CD2Cl2, 298 K):
δ = 142.5 (C1); 137.9 (C3); 130.7 (C5); 129.2 (C7); 125.8 (C9); 120.2
(C2); 117.5 (C8); 102.2, 102.1 (C4–C6); 154.2, 138.6, 135.3, 131.6,
122.3, 102.2 (non H-bonded aromatic carbon atoms); 69.6 (thf);
59.7 (CH); 34.0 (quaternary tBu); 32.5 (tBu); 22.3 (thf); 20.2 (Me)
ppm. C50H60Br2Cl2Mg4N4O4 (1108.97): calcd. C 54.1, H 5.45, N
5.05; found 53.9,
H 5.50, N 4.90. Crystal data: formula
C50H60Br2Cl2Mg4N4O4; M = 1108.98; System = Orthorhombic;
Space group = Fdd2; Space group number = 43; a = 26.4038(7) Å;
b = 38.9380(13) Å; c = 10.1479(2) Å; U = 10433.2(5) Å3; Z = 8; Dc
= 1.412 gcm–3; µ = 17.51 cm–1; T = 120 K; θ(min–max) = 3.26–
Method b: A suspension of YCl3 (0.198 g, 1.01 mmol) in thf
(50 mL) was heated under reflux for 1 h. After cooling to –50 °C,
a solution of Tl(NNOH) or Tl(NNOMe) (1.01 mmol) was added
drop by drop. The resulting reaction mixture was allowed to slowly
warm to room temperature and left overnight whilst stirring. The
solvent was removed by evaporation at reduced pressure, and the
product was extracted from the resulting solid by extraction with
CH2Cl2 by using a Soxhlet. The resulting yellow solution was con-
centrated at reduced pressure and, by addition of n-hexane, a yel-
low product precipitated, which was filtered, washed with n-hexane
and dried under vacuum. Yield Ͼ 85%.
27.50°; Measured reflns = 18770; Unique reflns = 3136; Rint
=
0.061; Obs. reflns [IϾ2σ(I)] = 2723; R (Obs. reflns) = 0.0672; RW
(all reflns) = 0.2054; GOF = 1.109; No. variables = 317; Flack
parameter = 0.09(2); ∆ρmax = 0.655 eÅ–3; ∆ρmin = –1.019 eÅ–3.
[Y(CH2SiMe3)(NN(CH2SiMe3)O)(thf)] (3): To a stirred solution of
Y(CH2SiMe3)3·2thf (1.147 g, 2.32 mmol) in toluene (70 mL) at
room temperature was very slowly added a solution of NNOH-H
Eur. J. Inorg. Chem. 2008, 4126–4132
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4131

G. Paolucci, M. Bortoluzzi, V. Bertolasi
FULL PAPER
Angew. Chem. Int. Ed. 2003, 42, 5075–5079; e) D. P. Long, P. A.
Baconi, J. Am. Chem. Soc. 1996, 118, 12453–12454; f) K. C.
Hultzsch, T. P. Spaniol, J. Okuda, Angew. Chem. Int. Ed. 1999,
38, 227–230; g) S. Arndt, J. Okuda, Adv. Synth. Catal. 2005,
347, 339–354; h) Z. Hou, Y. Luo, X. Li, J. Organomet. Chem.
2006, 691, 3114–3121.
(0.706 g, 2.32 mmol) in toluene (30 mL). The time required for the
addition of the ligand solution was about 30 min. The resulting
dark-red reaction mixture was allowed to react at room tempera-
ture for 2 h, then the solvent was reduced to about 15 mL by evapo-
ration at reduced pressure. Slow addition of n-hexane (about
100 mL) allowed a red solid to separate, which was filtered. The
crude product was purified by cooling a toluene/n-hexane saturated
solution at –25 °C. Yield after purification Ͼ 40%. Refer to
Scheme 4 for numbering scheme. 1H NMR (C6D6, 298 K): δ = 7.66
[3]
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M. N. Burnett, C. K. Johnson, ORTEP-III: Oak Ridge Ther-
mal Ellipsoids Plot Program for Crystal Structure Illustrations,
Oak Ridge National Laboratory Report ORNL-6895, TN,
1996.
3
4
3
(dd, JHH = 7.5 Hz, JHH = 1.5 Hz, 1 H, H1), 7.50 (dd, JHH
7.5 Hz, JHH = 1.5 Hz, 1 H, H3), 7.49 (dd, JHH = 7.8 Hz, JHH
=
=
4
3
4
3
3
1.8 Hz, 1 H, H9), 7.04 (t, JHH = 7.5 Hz, 1 H, H2), 6.94 (t, JHH
3
4
= 7.8 Hz, 1 H, H5), 6.64 (dd, JHH = 4.4 Hz, JHH = 1.8 Hz, 1 H,
3
3
H7), 6.63 (dd, JHH = 7.8 Hz, JHH = 4.4 Hz, 1 H, H8), 6.40 (d,
3JHH = 7.8 Hz, 1 H, H6), 6.30 (d, JHH = 7.8 Hz, 1 H, H4), 4.54
3
3
3
(dd, JHH = 4.8 Hz, JHH = 10.0 Hz, 1 H, N-CH-CH2SiMe3), 3.74
(br. m, 4 H, thf), 1.80 (dd, JHH = 13.0 Hz, JHH = 10.0 Hz, 1 H,
2
3
2
N-CH-CH2SiMe3), 1.60 (s, 9 H, tBu), 1.42 (dd, JHH = 13.0 Hz,
3JHH = 4.8 Hz, 1 H, N-CH-CH2SiMe3), 1.40 (br. m, 4 H, thf), 0.20
2
(d, JYH = 2.7 Hz, 2 H, Y-CH2), 0.08 (s, 18 H, SiMe3) ppm.
13C{1H} NMR (C6D6, 298 K): δ = 143.3 (C7); 136.0 (C9); 130.5
(C1); 129.3 (C5); 124.8 (C3); 119.2 (C8); 115.0 (C2); 105.2 (C4);
104.4 (C6); 163.2, 156.7, 142.3, 137.7, 136.9, 128.8 (non H-bonded
aromatic carbon atoms); 68.2 (thf); 61.4 (N-CH-CH2SiMe3); 34.1
(quaternary tBu); 31.2 (N-CH-CH2SiMe3); 30.4 (tBu); 24.5 (thf);
–1.8 (slightly br.; Y-CH2 + SiMe3) ppm. MS (EI, 70 eV): m/z = 536
[M – 2Me]·+. C32H49N2O2Si2Y (638.82): calcd. C 60.2, H 7.73, N
4.39; found C 60.3, H 7.65, N 4.50.
[5]
[6]
[7]
[8]
CCDC-687376 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[9]
Supporting Information (see footnote on the first page of this arti-
1
cle): Selected 1D and 2D H NMR spectra.
[10]
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K. C. Hultzsch, P. Voth, K. Beckerle, T.P. Spaniol, J. Okuda,
Organometallics 2000, 19, 228–243.
Acknowledgments
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The authors are indebted to MIUR (Italian Minister of Uni-
versity and Research) for financial support (PRIN 2004 prot.
2004030307_003).
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Received: May 19, 2008
[20]
Published Online: August 8, 2008
4132
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Eur. J. Inorg. Chem. 2008, 4126–4132