Yttrium-amidopyridinate complexes: Synthesis and characterization of yttrium-alkyl and yttrium-hydrido derivatives

Article abstract of DOI:10.1002/ejic.200900934

Aryl- or heteroaryl-substituted aminopyridine ligands (N₂H ^Ar) react with an equimolar amount of [Y(CH₂SiMe ₃)₃(thf)₂] to give yttrium(III)-monoalkyl complexes. The process involves the deprotonation of N₂H^Ar by a yttrium alkyl followed by a rapid and quantitative intramolecular sp ²-CH bond activation of the aryl or heteroaryl pyridine substituents. As a result, new Y complexes distinguished by rare examples of CH bond activations have been isolated and completely characterized. Selective σ-bond metathesis reactions take place on the residual Y-alky1 bonds upon treatment with PhSiH₃. Unusual binuclear metallacyclic yttrium(III)hydrido complexes have been obtained and characterized by NMR spectroscopy and X-ray diffraction analysis.

Full text of DOI:10.1002/ejic.200900934

FULL PAPER
DOI: 10.1002/ejic.200900934
Yttrium-Amidopyridinate Complexes: Synthesis and Characterization of
Yttrium-Alkyl and Yttrium-Hydrido Derivatives
Lapo Luconi,[a] Dmitrii M. Lyubov,[b] Claudio Bianchini,[a] Andrea Rossin,[a]
Cristina Faggi,[c] Georgii K. Fukin,[b] Anton V. Cherkasov,[b] Andrei S. Shavyrin,[b]
Alexander A. Trifonov,*[b] and Giuliano Giambastiani*[a]
Keywords: Amidopyridinate / Yttrium / Hydrides / Metathesis / Ethylene / Polymerization
Aryl- or heteroaryl-substituted aminopyridine ligands
(N2HAr) react with an equimolar amount of [Y(CH2SiMe3)3-
(thf)2] to give yttrium(III)-monoalkyl complexes. The process
involves the deprotonation of N2HAr by a yttrium alkyl fol-
lowed by a rapid and quantitative intramolecular sp2-CH
bond activation of the aryl or heteroaryl pyridine substitu-
ents. As a result, new Y complexes distinguished by rare ex-
amples of CH bond activations have been isolated and com-
pletely characterized. Selective σ-bond metathesis reactions
take place on the residual Y–alkyl bonds upon treatment
with PhSiH3. Unusual binuclear metallacyclic yttrium(III)-
hydrido complexes have been obtained and characterized by
NMR spectroscopy and X-ray diffraction analysis.
A variety of bidentate or polydentate nitrogen-contain-
ing ligands (amide, imine) have been successfully employed
for the synthesis of discrete organo-rare-earth-metal com-
plexes, although the number of reported active catalysts re-
main still quite limited.[1f,7]
We have recently communicated on the synthesis of new
yttrium(III)-monoalkyl and yttrium(III)-hydrido complexes
stabilized by amidopyridinate ligands.[8] Interesting results
have been obtained from the reaction of the pyridylamine
ligands N2HPh and N2HXyl with [Y(CH2SiMe3)3(thf)2]. The
reactions have been found to proceed rapidly at 0 °C and
independently from the dilution conditions, with the elimi-
nation of 2 equiv. of tetramethylsilane, instead of the
1 equiv. expected and the concomitant formation of the
monoalkyl sp2 or sp3 ortho-metalated complexes of the type
shown in Scheme 1.
Introduction
Cyclopentadienyl-free rare-earth-metal alkyls or hydrides
are target compounds in organometallic chemistry due to
their unique properties and intriguing reactivity in poly-
merization catalysis.[1] To date, rare-earth-metal complexes
have been dominated by cyclopentadienyl moieties, includ-
ing mono-, bis- and ansa-systems.[2] Only recently, systems
such as bidentate amidinate,[3] guanidinate,[4] β-diketimin-
ate[5] and salicylaldiminates[6] have emerged as valuable an-
cillary ligands for lanthanide ions by virtue of their ability
to form strong metal–ligand bonds and to allow for an easy
tuning of the steric and electronic properties of the ligand.
Nevertheless, lanthanide-alkyl or -hydrido complexes stabi-
lized by these type of ligands are still fairly rare species,
largely because of their troublesome preparation. Indeed,
the rare-earth-metal centres in these complexes are gen-
erally both electronically and sterically less saturated than
those in metallocene or half-sandwich-type derivatives. As
a result, unusual reactivity paths are often observed for cy-
clopentadienyl-free lanthanide complexes, including dimer-
izations, intra- and intermolecular C–H bond activations or
ligand redistributions.[1g]
[a] Istituto di Chimica dei Composti Organometallici (ICCOM–
CNR),
via Madonna del Piano 10, 50019 Sesto Fiorentino (Firenze),
Italy
Fax: +39-055-5225203
E-mail: giuliano.giambastiani@iccom.cnr.it
[b] G. A. Razuvaev Institute of Organometallic Chemistry of Rus-
sian Academy of Sciences,
Tropinina 49, GSP-445, 603950 Nizhny Novgorod, Russia
E-mail: trif@iomc.ras.ru
[c] Dipartimento di Chimica Organica “U. Schiff”, Università
degli Studi di Firenze,
Scheme 1. Synthesis of yttrium(III)-alkyl-aryl and -alkyl-benzyl
complexes.
via della Lastruccia 13, 50019 Sesto Fiorentino (Firenze), Italy
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Yttrium-Alkyl and Yttrium-Hydrido Derivatives
Notably, both yttrium complexes undergo selective σ- free[4b,12] lanthanide-alkyl and -hydride complexes, they still
bond metathesis on the residual CH2SiMe3 bond upon attract considerable interest due to the intrinsic difficulty
treatment with PhSiH3. As a result, binuclear aryl-hydrido for organometallic fragments to activate inert chemical
and benzyl-hydrido complexes of the type shown in bonds. In this paper we provide a full account on the syn-
Scheme 2 have been isolated and characterized.
thesis, characterization and catalytic activity of a family of
novel yttrium(III)-alkyl and -hydrido complexes distin-
guished by stable Y–C(aryl) or Y–C(heteroaryl) bonds.
Results and Discussion
Synthesis and Characterization of the Aminopyridinate
Ligands 6–10
The 6-aryl-substituted ligands 6–10 were straightfor-
wardly prepared, in fairly good yields (70–93% of isolated
product) by reductive alkylation of the related iminopyr-
idines (1–5) with a slight excess amount of trimethylalumin-
ium in dry toluene at room temperature, followed by hy-
drolysis (Scheme 3).
Scheme 2. Synthesis of binuclear yttrium(III)-hydrido complexes
by selective σ-bond metathesis on the residual CH2SiMe3 group.
Much of the interest in group 4 and lanthanide-alkyl or
-hydrido complexes stabilized with amidopyridinate ligands
comes from their ability to undergo intramolecular C–H
bond activation, thus providing metal complexes with un-
conventional structures. A new family of strictly related
pyridylamido HfIV catalysts have been recently developed
by the group of Busico and researchers at Dow as effective
catalysts for the isotactic polymerization of propene in
high-temperature solution processes.[9]
One of the most notable features of these group 4 precat-
alysts is the ortho-metalation of the aryl substituent on the
pyridine ring, which results in the tridentate ligation of the
pyridylamido moiety and a distorted trigonal-bipyramidal
metal coordination (Figure 1a). The incorporation of sp3-C
donors into the imidopyridinate ligand framework has been
successfully achieved by Coates and co-workers through an
intramolecular migratory insertion of a cationic HfIV spe-
cies onto a facing vinyl moiety (Figure 1b).[10]
Scheme 3. Reductive alkylation of iminopyridines 1–5.
The imino precursors 1–5 were obtained on a multigram
scale according to procedures reported in the literature,[8,13]
in some cases with little modification.[14] All aminopyrid-
inate ligands appear as off-white/pale-yellow solids after ex-
tractive workup and solvent evaporation. Recrystallization
from hot MeOH gave the pure compounds as white/pale
yellow crystals with melting points ranging from 97 to
134 °C (see the Experimental Section).
The 1H NMR spectra of aminopyridines 6–10 confirmed
the formation of saturated –C(Me)2NH(2,6-iPr2C6H3) moi-
eties with the NH proton resonance appearing as a broad
singlet between 4.1 and 4.6 ppm and the related 13C{1H}
NMR spectra showing the expected number of independent
carbon atom signals.
Suitable crystals for X-ray diffraction studies of com-
pounds 6–10 were isolated by successive recrystallizations
from hot MeOH (Table 4). A perspective view of all ligand
structures is given in Figure 2, whereas selected bond
lengths and angles are listed in Table 1. All structures con-
sist of a central pyridine unit substituted at its 6-position by
an aryl (Figure 2, ligands 6 and 7) or a heteroaryl (Figure 2,
Figure 1. Group 4 metal complexes distinguished by amidopyrid-
inate ligands showing a) sp2 or b) sp3 C–H bond activation.
Although inter- and intramolecular metalations of sp2- ligands 8–10) group and at its 2-position by the same
and sp3-hybridized C–H bonds have been previously docu- amine-containing C(Me)2NH(2,6-iPr2C6H3) fragment. The
mented for cyclopentadienyl[3b,11] and cyclopentadienyl- aryl or heteroaryl moieties are almost coplanar with respect
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A. A. Trifonov, G. Giambastiani et al.
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Figure 2. Crystal structures of ligands N2HPh (6), N2HXyl (7), N2HTh (8), N2HEtTh (9) and N2HBFu (10). Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms, apart from those of the N–H moiety, are omitted for clarity.
to the pyridine unit [torsion angle (θ) N(1)–C(6)–C(22)– C(7)alk bond lengths are in the typical (sp2)–(sp3) range of
C(23): 6, 7.32(2)°; 8, 177.29(2)°; 9, 177.41(5)°; 10, –10.8(6)°] values.[15] The C(7)–N(2) vector is rotated closer to the pyr-
except for ligand 7, in which the more sterically demanding idine plane for all ligand structures, whereas the N(1)–C(2)–
xylyl group is nearly orthogonal to the pyridine plane, as C(7)–N(2) torsion angle brings the N(2)H hydrogen atom
expected [N(1)–C(6)–C(22)–C(23): –72.3(4)°]. The C(2)Py–
Table 1. Selected bond lengths [Å] and angles [°] for ligands 6–10.
6
7
8
9
10
1.492(4) 1.480(4) 1.497(9) 1.495(4) 1.493(4)
2.11(3) 2.61(4) 2.22(4)
N(2)–C(7)
N(1)–H(1)
–
–
N(2)–C(7)–C(2)
N(1)–C(2)–C(7)
110.5(3) 110.0(3) 109.8(6) 108.1(3) 109.9(3)
116.3(3) 115.9(3) 117.1(6) 113.9(4) 115.3(3)
N(1)–C(6)–C(22)–C(23) 7.32(2)
–72.3(4) 177.29(2) 177.41(5) –10.8(6)
Figure 3. N(1)–C(2)–C(7)–N(2) torsion angles on ligands 6–10.
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Yttrium-Alkyl and Yttrium-Hydrido Derivatives
into a position in which it is able to form a hydrogen bond step occurs immediately upon mixing of the ligands and
to the neighbouring pyridine nitrogen atom only for ligands metal precursor with no evidence for the formation of tran-
7, 9 and 10 (Figure 3) [calculated N(1)···HN(2) distances sient dialkyl intermediates.
[Å]: 7, 2.11(3); 9, 2.61(4); 10, 2.22(4)].
Apparently, the presence of a coordinating thien-2-yl sul-
fur atom on the ligand backbone does not compete with
the intramolecular sp2 C–H bond activation for the coordi-
nation to the metal centre, which occurs rapidly, even under
diluted reaction conditions, on the less acidic 3-position of
the heteroaryl group.[18] 1H NMR spectra for 13 and 14 are
consistent with six-coordinate yttrium complexes, each of
which contains a tridentate dianionic (L2–) amidopyridinate
ligand, a residual trimethylsilylmethylene fragment and two
thf molecules. Both complexes contain Y–C(alkyl) and Y–
C(aryl) bonds; clear doublets could be seen in the 1H NMR
spectrum centred at –0.77 ppm (2JY,H = 3.0 Hz) and
–0.69 ppm (2JY,H = 3.0 Hz), respectively, and are attributed
to the hydrogen atoms of each residual methylene group
attached to yttrium. The latter appears in the 13C{1H}
Synthesis and Characterization of the Yttrium-Alkyl-Aryl
and -Alkyl-Benzyl Complexes
The reaction of the neutral aminopyridines 6 and 7 with
[Y(CH2SiMe3)3(thf)2] (1 equiv.) in hexane at 0 °C have been
already discussed in our previous work[8] and are mentioned
here only for completeness. In both cases, the reaction is
almost instantaneous and gives the mono(alkyl) complexes
11 and 12, respectively (Scheme 1).
By following similar procedures as those reported for the
preparation of 11 and 12, the ligands containing either 2-
thienyl (8 and 9) or 2-benzofuryl (10) pendant groups have
been employed to study their coordination behaviour at the
metal centre.
Several cyclopentadienyl-based rare-earth-metal com-
plexes have previously been reported to yield ortho-met-
alation products in the presence of aromatic heterocycles
such as furan and thiophene (Th).[11b,16] To date, a few ex-
amples of cyclopentadienyl-free lanthanide complexes bear-
ing potentially coordinating sulfur or oxygen atoms have
been investigated,[17] whereas those containing thienyl or fu-
ranyl groups remain much less explored.[18]
NMR spectra as a doublet centred at 30.0 ppm (1JY,C
=
39.6 Hz) and 30.1 ppm (1JY,C = 39.6 Hz), for complexes 13
and 14, respectively, whereas further low-field doublets [13:
195.2 ppm (1JY,C = 38.9 Hz); 14: 198.6 ppm (1JY,C
=
38.9 Hz)] unambiguously indicate that the aryl rings are σ-
bonded to the metal centre.[18,19] Crystals of 14 suitable for
X-ray analysis were grown by cooling at –20 °C a concen-
trated solution in n-hexane (Table 5). The molecular struc-
ture of 14 is shown in Figure 4.
Unexpectedly, the reaction of the thienyl-containing li-
gands 8 and 9 with [Y(CH2SiMe3)3(thf)2] (1 equiv.) in hex-
ane at 0 °C resulted in the unique formation of 13 and 14
by means of alkane elimination and C–H bond activation
at the β position of the thienyl moiety (Scheme 4).
Figure 4. Crystal structure of [N2EtThY(CH2SiMe3)(thf)2] (14).
Thermal ellipsoids are drawn at the 30% probability level. Hydro-
gen atoms and methylene groups of the thf molecules are omitted
for clarity.
Scheme 4. Synthesis of yttrium(III)-alkyl-aryl complexes 13 and 14
by means of an alkyl elimination reaction.
The X-ray diffraction study has shown the monomeric
nature of 14. The coordination environment at the yttrium
Attempts to isolate yttrium-bis(alkyl) species by means centre is set up by two nitrogen atoms and one carbon atom
of monoalkane elimination always resulted in the quantita- from the dianionic tridentate amidopyridinate ligand, one
tive generation of the six-coordinate alkyl-heteroaryl com- carbon atom from the residual alkyl group and two oxygen
plexes, as a result of a deprotonation of the N–H moiety atoms from the two thf molecules. Overall, the coordination
followed by a rapid intramolecular sp2-CH bond activation can be considered to be a strongly distorted octahedron.
at the β position of the heteroaryl fragment (Scheme 4). The yttrium coordination number in 14 is 6. The Y–amido-
Further experiments conducted using different dilution pyridinate fragment is planar (average deviation from the
conditions never allowed the isolation of dialkyl species. Fi- plane is 0.0156 Å) and the Y–C(alkyl) bond length
1
nally, the reaction monitoring through H NMR spectro- [2.455(2) Å] is comparable to the values reported for related
scopic experiments has revealed that the cyclometalation six-coordinate yttrium-monoalkyl compounds.[18,20] The Y–
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Table 2. Selected bond lengths [Å] and angles [°] for complexes 12, 14, and 16–18.
12[a]
14
16[a]
17
18
Y–H
Y(1)–N(1)
Y(1)–N(2)
Y(1)–O(1)
Y(1)–O(2)
Y(1)–C(23)
Y(1)–C(28)
Y(1)–C(29)
–
–
2.15
2.4252(17)
2.2205(18)
2.3609(15)
2.44
2.472(7)
2.198(7)
2.346(6)
2.09(2)
2.450(2)
2.206(2)
2.42(14)
2.2015(14)
2.3422(13)
2.4616(17)
2.2543(17)
2.4035(14)
2.3816(14)
2.482(2)
2.455(2)
–
–
–
–
–
–
–
2.355(2)
2.514(3)
2.9421(17)
2.469(2)
–
–
–
–
–
2.4520(18)
2.462(9)
Y(1)–C(30)
Y(1)–Y(1)Ј
2.4139(17)
–
–
–
–
–
3.5780(4)
3.6917(14)
3.53(11)
C(28)–Y(1)–C(23)
C(29)–Y(1)–C(23)
C(30)–Y(1)–C(29)
N(1)–Y(1)–N(2)
N(1)–Y(1)–C(29)
N(1)–Y(1)–C(23)
N(2)–Y(1)–C(23)
N(2)–Y(1)–C(29)
N(1)–C(6)–C(22)–C(23)
–
98.04(7)
–
–
–
–
–
–
–
–
–
29.47(5)
117.20(6)
70.00(5)
–
–
67.44(6)
68.24(6)
–
68.43(7)
130.34(7)
–
69.1(3)
72.1(3)
–
66.39(8)
–
69.55(9)
131.49(9)
–
–
–
–
–
–
–
–
–
–
111.8(3)
50.5(15)
–52.57(6)
–4.13(2)
–7.52(3)
8.5(4)
[a] Selected data from the literature[20] listed here for completeness.
C(thien-2-yl) bond [2.482(2) Å] is slightly longer than that highly soluble in hydrocarbon solvents and a comparison
1
observed for related yttrium-monoalkyl thien-2-yl species of their H and 13C{1H} NMR spectra showed many simi-
featured by analogue intramolecular C–H bond activation larities. The 1H NMR spectrum of 15, which contains both
at the β position of the thienyl moiety [2.423(3) Å].[18] Re- Y–C(alkyl) and Y–C(aryl) bonds, shows one clear doublet
lated yttrium complexes that contain an amidopyridinate centred at –0.69 ppm (2JY,H = 3.0 Hz) attributed to the
ligand with a shorter ligand backbone[21] have shown a dra- hydrogen atoms of the residual methylene group bound to
matic perturbation of the ligand coordination mode once yttrium. The 13C{1H} NMR spectrum contains a doublet
an intramolecular C–H bond activation occurs {the Y–N for the sp3-carbon atom centred at 30.1 ppm (1JY,C
covalent bond [2.431(8) Å] becomes longer than the coordi- 37.6 Hz), whereas a further doublet at 158.6 ppm (1JY,C
=
=
native one [2.338(7) Å]}. In contrast to this, the presence of 38.9 Hz) is assigned to the sp2 carbon of the benzofuryl
an additional CMe2 group between the two nitrogen atoms moiety σ-bonded to the metal centre.
always results in a “classic” bonding mode (Y–N covalent
Recently Okuda and co-workers[16a,16d] have shown that
the introduction of a furan-2-yl group on the cyclopen-
bonds shorter than coordinative ones; Table 2).
In spite of the well-known oxophilic character of lantha- tadienyl ring of a half-sandwich lanthanide complex results
nide ions, the reaction of the 2-benzofuryl-substituted li- in a rapid intramolecular Cβ–H bond activation, thereby
gand 10 with [Y(CH2SiMe3)3(thf)2] in hexane at 0 °C yields triggering the formation of a thermally more stable yne-
the monoalkyl complex 15 (Scheme 5).
enolate yttrium product by means of furanyl ring open-
ing[22] (Scheme 6).
Scheme 5. Synthesis of the ytrrium(III)-alkyl-aryl complex 15.
As observed for the thienyl-containing systems, the 2-
benzofuryl group appended to the amidopyridinate ligand
10 rapidly undergoes metalation on the 3-position irrespec-
tive of the dilution conditions used, thus affording the first
example of stable cyclopentadienyl-free yttrium(III)-benzo-
furyl-amidopyridinate complex. Complex 15 could not be
Scheme 6. Furanyl ring opening in lanthanide-cyclopentadienyl
complexes.
In addition, in monitoring the intramolecular Cβ–H
obtained in the form of single crystals. The identification as bond activation and the subsequent yne-enolate formation
a six-coordinate yttrium complex with a tridentate dian- by 1H NMR spectroscopy, the same authors have found
ionic (L2–) aminopyridinate ligand, a residual trimethyl- first-order kinetics with respect to the complex concentra-
silylmethylene fragment and two thf molecules is based on tion as well as an increase of the reaction rate with increas-
several spectroscopic features (see the Experimental Sec- ing metal size.[16d] In our case, there is no evidence for the
tion). All the aforementioned monoalkyl complexes were formation of a dialkyl intermediate with the furanyl oxygen
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Yttrium-Alkyl and Yttrium-Hydrido Derivatives
occupying a coordinative position at the metal centre,
whereas a rapid metalation at the β position of the
heteroaryl substituent takes place to give 15. This complex
is very stable, with no appreciable decomposition even in
noncoordinating solvents for days. The close proximity of
the Y–alkyl and the Cβ–H bond in 15, due to the free rota-
tion of the pendant donor, is expected to affect the C–H
bond-activation rate strongly and make it predominant over
oxygen coordination.[16d]
Synthesis and Characterization of the Yttrium-Aryl-
Hydrido and -Benzyl-Hydrido Derivatives
The most common synthetic procedures for the prepara-
tion of rare-earth hydrido complexes from their M–alkyl
counterparts make use of either dihydrogen[2b,23] or phen-
ylsilane[8,24] as reagents. We have already reported on the
treatment of 11 and 12 with an equimolecular amount of
PhSiH3. In both cases the reaction proceeds rapidly in n-
hexane at 0 °C, thus resulting in the formation of binuclear
yttrium-aryl-hydrido and -benzyl-hydrido complexes 16 and
17 (Scheme 2). Although the crystallographic characteriza-
tion of 16 has already been reported previously,[8] orange
crystals of 17 suitable for X-ray diffraction have now been
prepared by the slow cooling of a benzene/n-hexane mixture
(1:3) down to 10 °C.
Figure 6. Crystal structure of [{N2BFuY(µ-H)(thf)}2] (18). Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms
(apart from yttrium hydrides), 2,6-diisopropylphenyl fragments,
methylene groups of the thf molecules and two molecules of ben-
zene (crystallization solvent) are omitted for clarity.
Unfortunately, all attempts to synthesize the hydrido
complexes supported by thiophenyl-substituted amidopyr-
idinate ligands by treating the monoalkyl complexes 13 and
14 with PhSiH3 failed and intractable materials were invari-
ably isolated.
The complexes adopt binuclear structures with two six-
coordinate yttrium atoms. The metal coordination spheres
are determined by the two nitrogen and one carbon atoms
from the tridentate amidopyridinate ligand, two bridging
hydrido ligands and one oxygen atom from a residual thf
molecule. Unlike the majority of binuclear hydrido species,
the tetranuclear Y2H2 cores are not planar. For complexes
16 and 18, the dihedral angles between the Y(1)H(1)H(1Ј)
and Y(1Ј)H(1)H(1Ј) planes have close values (20.1 and
21.0°), whereas for 17 this angle is much smaller (12.4°).
A similar trend is finally observed for the Y–H bonds. In
complexes 16 and 18, the Y–H bonds are significantly
shorter [2.15 and 2.09(2) Å, respectively] than that mea-
sured for 17 (2.44 Å). It should be noted that the coordi-
nated N and C atoms from the tridentate amidopyridinate
ligands in 16–18 lie in the same plane, although the chelat-
ing ligand is not wholly planar. The Y–C bond lengths in
16 [2.469(2) Å], 17 [2.462(9) Å] and 18 [2.514(4) Å] match
well the values previously reported for similar six-coordi-
nate yttrium-aryl species,[25] whereas the Y–Y distances [16:
3.5780(4) Å; 17: 3.6917(14) Å; 18: 3.53(11) Å] are noticeably
shorter than those measured in related binuclear yttrium
hydrides.[1i,6,26]
Complex 17 crystallizes as a solvate with one hexane
molecule per molecule of binuclear species. Its molecular
structure is illustrated in Figure 5.
Figure 5. Crystal structure of [{N2XylY(µ-H)(thf)}2] (17). Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms
(apart from yttrium hydrides), 2,6-diisopropylphenyl fragments and
methylene groups of the thf molecules and one molecule of hexane
(crystallization solvent) are omitted for clarity.
Notably, the Y–C(aryl) and Y–C(Bn) (Bn = benzyl)
By following the same chemistry, the treatment of 15 bonds do not react with PhSiH3 even in the presence of a
with an equimolecular amount of PhSiH3 resulted in the twofold excess amount of the reagent for prolonged reac-
formation of the binuclear heteroaryl-hydrido complex 18. tion times. Indeed, all of the binuclear hydrido complexes
Yellow-brown crystals of complex 18 were obtained by the can been recovered after stirring of the reagents for 24 h at
slow cooling of a benzene/n-hexane mixture (1:3) down to room temperature in the presence of an excess amount of
10 °C. The molecular structure of the benzene solvate com- PhSiH3, with no appreciable decomposition. Unlike
plex 18 is illustrated in Figure 6.
PhSiH3, the reaction of 11, 12 and 15 with H2 (1 bar) in
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Table 3. Ethylene polymerization with yttrium(III)-alkyl and -hydride precursors.[a]
Run
Precatalyst[a]
Cocatalyst (number of equiv.)
T
[°C]
Polymer yield
[g]
TOF
TOF
[kg of PE
[mol of C2H4 conv.
({mol of Y}barh)–1]
({mol of Y}barh)–1]
1
2
3
4
5
6
7
8
9
11
11
12
13
14
14
11
14
16
16
17
18
MAO (300)
MAO (300)
MAO (300)
MAO (300)
MAO (300)
22
50
22
22
22
50
65
65
22
65
22
65
0.144
0.096
0.018
0.132
0.186
0.162
0.048
0.024
traces
traces
traces
traces
2.4
1.6
0.3
2.2
3.1
2.7
0.8
0.4
–
85.7
57.1
10.7
78.6
110.7
96.4
28.6
14.3
–
MAO (300)
[Me2PhNH][B(C6F5)4]/AliBu3 (1.2)/(200)
[Me2PhNH][B(C6F5)4]/AliBu3 (1.2)/(200)
MAO (300)
[Me2PhNH][B(C6F5)4]/AliBu3 (1.2)/(200)
MAO (300)
10
11
12
–
–
–
–
–
–
[Me2PhNH][B(C6F5)4]/AliBu3 (1.2)/(200)
[a] Reaction conditions: toluene (final volume 50 mL), precatalyst 12 µmol, 30 min.
toluene at room temperature led to their complete decom- cal range of values for linear high-density polyethylene
position within a few minutes, followed by the precipitation (HDPE), and the absence of any type of branches has been
of insoluble off-white solid materials. This result proves the unambiguously confirmed by 13C{1H} NMR spectroscopy.
effectiveness of PhSiH3 as a reagent for the synthesis of the Finally, the thermogravimetric analysis (TGA) of all poly-
binuclear hydrido complexes 16–18 through a selective σ- olefin materials showed comparable thermal stability within
bond metathesis of the residual Y–CH2SiMe3 bond.
all the samples.
Ethylene Polymerization Tests
Conclusion
The catalytic performances of the mononuclear
We have shown in this paper that aminopyridinate li-
yttrium(III)-monoalkyl complexes and of their binuclear gands bearing aryl or heteroaryl substituents at the 6-posi-
hydride counterparts have been systematically scrutinized tion of the pyridine ring undergo fast intramolecular sp2 C–
for ethylene polymerization under different reaction condi- H bond activation upon treatment with an equimolecular
tions. Although all these complexes turned out to be com- amount of [Y(CH2SiMe3)3(thf)2], thereby leading to a novel
pletely inert in the absence of a proper activator, some of class of yttrium complexes with unusual Y–C bonds.
them have shown a moderate activity upon treatment with
Aminopyridinate systems that contain 2-thiophene or 2-
methylaluminoxane (MAO; see the Experimental Section benzofuryl moieties have been used to generate stable cyclo-
and Table 3). Particularly, complexes 11 and 14 have shown pentadienyl-free yttrium(III) complexes in which the intra-
activities at room temperature up to 2.4 and 3.1 kg of PE molecular C–H bond activation takes place at the less acidic
[(mol of Y)barh]–1, respectively. When the sp2-coordinative 3-position of the heteroaryl groups. The reaction of the
carbon atom from the aryl or heteroaryl substituent of the benzofuryl-containing ligand with the yttrium–tris(alkyl)
pyridine ring is replaced by an sp3 donor, as for complex complex gives the first example of a stable yttrium(III)-
12, a significant decrease in the catalytic activity is observed alkyl-aryl complex in which the C–H bond activation takes
{0.3 kg of PE [(mol of Y)barh]–1}. Finally, no polymeriza- place at the β position of the benzofuryl group with no
tion activity has been observed with the more sterically apparent decomposition of the heteroaromatic moiety (fu-
crowded Y–H dimers 16–18 under similar experimental ran ring opening), even upon standing in solution for days.
conditions. High-temperature polymerization tests (from 80
All monoalkyl complexes undergo selective σ-bond
to 90 °C) have resulted in the rapid deactivation of the cata- metathesis at the residual Y–CH2Si(CH3)3 bond upon treat-
lyst with the formation of traces of insoluble polyolefinic ment with phenylsilane. As a result, binuclear yttrium-
materials.
heteroaryl-hydrido and -benzyl-hydrido complexes have
Cationic active species are also generated from catalyst been synthesized and characterized by spectroscopic and
precursors 11 and 14 upon treatment with [Me2PhNH]- XRD methods. Selected complexes have been also scruti-
[B(C6F5)4] in combination with AliBu3 in toluene at 65 °C nized as catalyst precursors for ethylene polymerization and
(see the Experimental Section and Table 3) and were scre- show moderate HDPE production.
ened in the polymerization of ethylene.[27] Very modest ac-
tivity was observed with either catalyst precursor {0.8 and
0.4 kg of PE [(mol of Y)barh]–1, respectively}, which we
attribute to a rapid catalyst deactivation as indicated by the
drop in ethylene consumption in the first two minutes of
the reaction. The melting points (138–139 °C) of the PEs
Experimental Section
General: All air- and/or water-sensitive reactions were performed
under either nitrogen or argon in flame-dried flasks using standard
Schlenk-type techniques. thf was purified by distillation from so-
produced with catalyst precursors 11 and 14 are in the typi- dium/benzophenone ketyl after drying with KOH. Et2O, benzene,
614 Eur. J. Inorg. Chem. 2010, 608–620
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Yttrium-Alkyl and Yttrium-Hydrido Derivatives
n-hexane and toluene were purified by distillation from sodium/
triglyme benzophenone ketyl or were obtained by means of a
MBraun Solvent Purification Systems, whereas MeOH was distilled
from Mg prior to use. C6D6 was dried with sodium/benzophenone
ketyl and condensed in vacuo prior to use, whereas CD2Cl2 or
CDCl3 were dried with activated 4 Å molecular sieves. Literature
methods were used to synthesize both the iminopyridine ligands
amidopyridinate ligands (6–10) as crude off-white solids. The li-
gands were purified by crystallization from hot MeOH by cooling
the resulting solution at either 4 °C (6, 8, 10) or –20 °C (7, 9) over-
night to afford crystals. Suitable crystals for X-ray diffraction were
collected after successive recrystallization from hot MeOH. N2HPh
(6): 93% yield, white crystals;[8] N2HXyl (7): 89% yield, white crys-
tals;[8] N2HTh (8): 76% yield, pale yellow microcrystals; N2HEtTh
(9): 70% yield, white needles; N2HBFu (10): 83% yield, white crys-
EtTh [13]
BFu [14]
Xyl[8]
N2Ph, N2Th, N2
,
N2
,
N2
and the aminopyridine
systems N2HPh and N2HXyl [8]
.
[Y(CH2SiMe3)3(thf)2][2b,23,28] tals.
[N2PhY(CH2SiMe3)(thf)2] (11),[8] [N2XylY(CH2SiMe3)(thf)] (12),[8]
[{N2PhY(µ-H)(thf)}2] (16)[8] and [{N2XylY(µ-H)(thf)}2] (17)[8] were
prepared according to previously reported procedures. All the other
reagents and solvents were used as purchased from commercial
suppliers. 1H and 13C{1H} NMR spectra were obtained with either
a Bruker ACP 200 (200.13 and 50.32 MHz, respectively) or a
Bruker Avance DRX-400 (400.13 and 100.62 MHz, respectively).
Chemical shifts are reported in ppm (δ) relative to TMS, referenced
to the chemical shifts of residual solvent resonances (1H and 13C).
IR spectra were recorded as Nujol mulls or KBr plates with FSM
1201 and Bruker-Vertex 70 instruments. Lanthanide analyses were
carried out by complexometric titration. The C, H, N elemental
analyses were made in the microanalytical laboratory of IOMC or
at ICCOM–CNR with a Carlo Erba Model 1106 elemental ana-
lyzer with an accepted tolerance of Ϯ0.4 units on carbon (C),
hydrogen (H) and nitrogen (N). Melting points were ensured with
a Stuart Scientific Melting Point apparatus SMP3. Catalytic reac-
tions were performed with a 250 mL stainless steel reactor con-
structed at ICCOM–CNR (Firenze, Italy) and equipped with a me-
chanical stirrer, a Parr 4842 temperature and pressure controller, a
mass-flow meter equipped with a digital control for the connection
to the PC and an external jacket for the temperature control. The
reactor was connected to an ethylene reservoir to maintain a con-
stant pressure throughout the catalytic runs. Ethylene was purified
before use by passing it through two columns filled with activated
molecular sieves (4 Å) and BASF R3-11G catalysts, respectively.
The MAO solution was filtered through a D4 funnel and the sol-
vents evaporated to dryness at 50 °C under vacuum. The resulting
white residue was heated further to 50 °C under vacuum overnight.
A stock solution of MAO was prepared by dissolving solid MAO
in toluene (100 mgmL–1). The solution was used within three weeks
to avoid self-condensation effects of the MAO. Other activators/
cocatalysts were used as received from the providers. Melting tem-
peratures of the polymer materials were determined by differential
scanning calorimetry (DSC) with a Perkin–Elmer DSC-7 instru-
ment equipped with CCA-7 cooling device and calibrated with the
melting transition of indium and n-heptane as references (156.1 and
–90.61 °C, respectively). The polymer sample mass was 10 mg and
aluminium pans were used. Any thermal history in the polymers
was eliminated by first heating the specimen at a heating rate of
20 °Cmin–1 to 200 °C, cooling at 20 °Cmin–1 to –100 °C, and then
recording the second scan from –100 to 200 °C. Thermogravimetric
analysis (TGA) was obtained under nitrogen (60 mLmin–1) with a
TGA Mettler Toledo instrument at a heating rate of 10 °Cmin–1
from 50 to 700 °C.
N2HTh (8): 1H NMR (300 MHz, CD2Cl2, 293 K): δ = 1.10 [d, 3JH,H
= 6.8 Hz, 12 H, CH(CH3), H17,18,19,20], 1.48 [s, 6 H, C(CH3)2, H7,8],
3
3.39 [sept, JH,H = 6.8 Hz, 2 H, CH(CH3), H15,16], 4.52 (br. s, 1 H,
3
NH), 7.09 (m, 3 H, CH Ar, H11,12,13), 7.16 (dd, J = 3.7 Hz, 1 H,
3
3
CH Th, H23), 7.43 (dd, J = 7.7 Hz, 1 H, CH Ar, H2), 7.44 (dd, J
= 3.7 Hz, 1 H, CCH Th, H22), 7.60 (dd, J = 7.7 Hz, 1 H, CH Ar,
3
H4), 7.67 (dd, 3J = 3.7 Hz, 1 H, CCH Th, H24), 7.73 (t, 3J = 7.8 Hz,
1 H, CH Ar, H3) ppm. 13C{1H} NMR (100 MHz, CD2Cl2, 293 K):
δ = 23.8 [CH(CH3)2, C17,18,19,20], 28.1 [CH(CH3)2, C15,16], 28.7
[C(CH3)2, C7,8], 59.2 [C(CH3)2, C6], 116.1 (C4), 117.4 (C2), 122.9
(C11,13), 124.2 (C24), 124.4 (C12), 127.3 (C22), 127.8 (C23), 137.1
(C3), 140.3 (C21), 145.5 (C9), 146.9 (C14,10), 150.9 (C5), 167.8 (C1)
ppm. M.p. 99.3 °C. C24H30N2S (378.56 gmol–1): calcd. C 76.14, H
7.99, N 7.40, S 8.47; found C 76.71, H 7.85, N 7.24, S 8.20.
N2HEtTh (9): 1H NMR (300 MHz, CD2Cl2, 293 K): δ = 1.12 [d,
3
3JH,H = 6.8 Hz, 12 H, CH(CH3), H17,18,19,20], 1.37 (t, JH,H
=
7.5 Hz, 3 H, CH2CH3, H26), 1.47 [s, 6 H, C(CH3)2, H7,8], 2.91 (q,
3JH,H = 7.5 Hz, 2 H, CH2CH3, H25), 3.42 [sept, JH,H = 6.8 Hz, 2
3
H, CH(CH3), H15,16], 4.52 (br. s, 1 H, NH), 6.85–6.87 (m, 1 H,
3
CCH Th, H23), 7.10 (m, 3 H, CH Ar, H11,12,13), 7.37 (dd, J = 7.8,
4J = 0.87 Hz, 1 H, CH Ar, H2), 7.49 (d, 3J = 3.6 Hz, 1 H, CCH
Th, H22), 7.53 (dd, J = 7.8, J = 0.87 Hz, 1 H, CH Ar, H4), 7.70
3
4
(t, J = 7.8 Hz, 1 H, CH Ar, H3) ppm. 13C{1H} NMR (100 MHz,
3
CD2Cl2, 293 K): δ = 15.6 (CH2CH3, C26), 23.8 (CH2CH3, C25),
23.8 [CH(CH3)2, C17,18,19,20], 28.1 [CH(CH3)2, C15,16], 28.7
[C(CH3)2, C7,8], 59.2 [C(CH3)2, C6], 115.6 (C2), 116.8 (C4), 122.9
(C11,13), 124.1 (C22), 124.3 (C23), 124.4 (C12), 137.0 (C3), 140.3
(C24), 142.5 (C21), 146.9 (C10,14), 150.1 (C9), 151.2 (C5), 167.6 (C1)
ppm. M.p. 97.6 °C. C26H34N2S (406.63 gmol–1): calcd. C 76.80, H
8.43, N 6.89, S 7.89; found C 76.91, H 8.40, N 6.75, S 7.94.
General Procedure for the Synthesis of Aminopyridinate Ligands 6–
10: A solution of the appropriate iminopyridine ligand (1–5;
2 mmol) in toluene (20 mL) was cooled to 0 °C in an ice bath and
treated dropwise with a 2.0  solution of trimethylaluminium
(TMA) in toluene (1.5 mL, 3 mmol). The reaction mixture was al-
lowed to stir at room temperature for 12 h and then was quenched
with water (15 mL). The aqueous phase was extracted with AcOEt
(3ϫ20 mL) and the combined organic layers were dried with
Na2SO4. Removal of the solvent under reduced pressure gave the
N2HBFu (10): 1H NMR (300 MHz, CD2Cl2, 293 K): δ = 1.12 [d,
3JH,H = 6.8 Hz, 12 H, CH(CH3), H17,18,19,20], 1.52 [s, 6 H,
Eur. J. Inorg. Chem. 2010, 608–620
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
615

A. A. Trifonov, G. Giambastiani et al.
FULL PAPER
C(CH3)2, H7,8], 3.36 [sept, JH,H = 6.8 Hz, 2 H, CH(CH3), H15,16],
trated in vacuo to approximately one third of its initial volume and
3
4.58 (br. s, 1 H, NH), 7.10 (m, 3 H, CH Ar, H11,12,13), 7.30 (m, 1
was kept overnight at –20 °C. Complex 14 was isolated as a yellow
H, CH BFu, H25), 7.38 (m, 1 H, CH BFu, H26), 7.55–7.58 (2 H, microcrystalline solid in 84% yield (0.346 g). Crystals suitable for
CCH Th, H2,22), 7.61 (1 H, CH BFu, H27), 7.69 (m, 1 H, CH BFu,
H24), 7.84–7.85 (2 H, CH Ar, H3,4) ppm. 13C{1H} NMR (100 MHz,
CD2Cl2, 293 K): δ = 23.7 [CH(CH3)2, C17,18,19,20], 28.2 [CH-
X-ray analysis were obtained by slow evaporation of a solution of
1
complex 14 in toluene at room temperature. H NMR (400 MHz,
2
C6D6, 293 K): δ = –0.69 (d, JY,H = 3.0 Hz, 2 H, YCH2), 0.25 [s, 9
3
(CH3)2, C15,16], 28.9 [C(CH3)2, C7,8], 59.2 [C(CH3)2, C6], 104.4 H, Si(CH3)], 1.11 (m, 8 H, β-CH2 thf), 1.27 [d, JH,H = 6.8 Hz, 6
3
(C22), 111.2 (C27), 117.0 (C2), 118.9 (C4), 121.5 (C24), 122.9 (C11,13), H, CH(CH3)2, H17,18,19,20], 1.33 (t, JH,H = 7.5 Hz, 3 H, CH2CH3,
123.1 (C25), 124.5 (C12), 125.0 (C26), 128.9 (C24,27), 137.2 (C3), H26), 1.34 [d, JH,H = 6.8 Hz, 6 H, CH(CH3)2, H17,18,19,20], 1.36 [s,
3
140.5 (C9), 146.7 (C23), 147.4 (C21), 155.2 (C28), 155.8 (C5), 168.3 6 H, C(CH3)2, H7,8], 2.91 [qd, 3JH25
= 7.5, 4JH25
,H26
,H23
= 0.7 Hz
(C1) ppm. M.p. 133.7 °C. C27H29N2O (397.53 gmol–1): calcd. C (interaction between CH2 protons of ethyl group with aromatic
81.58, H 7.35, N 7.05, O 4.02; found C 76.71, H 7.85, N 7.24, O
8.20.
proton of the thiophene ring) 2 H, CH2CH3, H25], 3.63 (m, 8 H,
α-CH2 thf), 3.83 [sept, JH,H = 6.8 Hz, 2 H, CH(CH3)2, H15,16],
3
6.57 (d, JH,H = 7.8 Hz, 1 H, CH Ar, H2), 7.08 (t, JH,H = 7.8 Hz,
1 H, CH Ar, H3), 7.18–7.24 (compl. m, together 3 H, CH Ar,
H4,12,23), 7.31 (m, together 2 H, CH Ar, H11,13) ppm. 13C{H} NMR
(100 MHz, C6D6, 293 K): δ = 4.5 [s, Si(CH3)3], 17.0 (s, CH2CH3,
C26), 23.6 (s, CH2CH3, C25), 24.0 [s, CH(CH3)2, C17,18,19,20], 24.7
(s, β-CH2, thf), 27.6 [s, CH(CH3)2, C15,16], 27.8 [s, CH(CH3)2,
C17,18,19,20], 30.1 (d, 1JY,C = 39.6 Hz, YCH2), 31.7 [s, C(CH3)2, C7,8],
3
3
68.6 [d, JY,C = 2.2 Hz, C(CH3)2, C6], 70.0 (s, α-CH2 thf), 114.7 (s,
C4), 115.8 (s, C2), 123.8 (s, C11,13), 123.7 (s, C12), 135.0 (d, JY,C
=
2
2.9 Hz, C23), 139.2 (s, C3), 144.9 (s, C24), 145.2 (d, JY,C = 2.2 Hz,
2
C21), 149.3 (d, JY,C = 2.2 Hz, C9), 150.0 (s, C10,14), 158.8 (d, JY,C
2
2
= 1.7 Hz, C5), 174.8 (d, JY,C = 1.5 Hz, C1), 198.6 (d, JY,C
=
1
Synthesis of [N2ThY(CH2SiMe3)(thf)2] (13): A solution of N2ThH
(8) (0.152 g, 0.401 mmol) in n-hexane (15 mL) was added to a solu-
tion of [Y(CH2SiMe3)3(thf)2] (0.401 mmol, 0.198 g) in n-hexane
(10 mL) at 0 °C. The solution immediately became dark yellow. The
reaction mixture was stirred at the same temperature for 1 h. After
15 min, the precipitation of a yellow-brown microcrystalline solid
started. The solution was concentrated in vacuo to approximately
one third of its initial volume and was kept overnight at –20 °C.
Complex 13 was isolated as a dark yellow microcrystalline solid in
69% yield (0.193 g). 1H NMR (400 MHz, C6D6, 293 K): δ =
38.9 Hz, YC, C22) ppm. IR (Nujol, KBr): ν = 3040 (m), 1590 (s),
˜
1570 (s), 1420 (m), 1395 (m), 1260 (m), 1250 (m), 1230 (s), 1220
(m), 1180 (s), 1125 (m), 1105 (w), 1085 (s), 1030 (s), 1005 (s), 970
(w), 920 (w), 890 (m), 865 (s), 840 (s), 800 (s), 780 (m), 745 (m),
705 (m), 670 (m), 630 (w) cm–1. C38H59N2O2SSiY (724.9 gmol–1):
calcd. C 62.96, H 8.20, N 3.86, Y 12.26; found C 63.08, H 8.35, N
3.74, Y 12.17.
Synthesis of [N2BFuY(CH2SiMe3)(thf)2] (15): A solution of N2BFuH
(10) (0.190 g, 0.46 mmol) in n-hexane (15 mL) was added to a solu-
tion of [Y(Me3SiCH2)3(thf)2] (0.228 g, 0.46 mmol) in n-hexane
(10 mL) at 0 °C. The reaction mixture was stirred at 0 °C for 1 h.
The solution was concentrated in vacuo to approximately one third
of its initial volume and was kept overnight at –20 °C. Complex 15
was isolated as a yellow-orange microcrystalline solid in 69% yield
2
–0.77 (d, JY,H = 3.0 Hz, 2 H, YCH2), 0.22 [s, 9 H, Si(CH3)], 1.06
3
(m, 8 H, β-CH2 thf), 1.26 [d, JH,H = 6.8 Hz, 6 H, CH(CH3)2;
H17,18,19,20], 1.32 [compl. m., together 12 H, CH(CH3)2 and
C(CH3)2, H7,8,17,18,19,20], 3.60 (m, 8 H, α-CH2 thf), 3.80 [sept, 3JH,H
= 6.8 Hz, 2 H, CH(CH3)2, H15,16], 6.59 (d, JH,H = 7.8 Hz, 1 H,
3
3
CH Ar, H2), 7.00 (t, JH,H = 7.8 Hz, 1 H, CH Ar, H3), 7.13–7.23
1
2
(0.232 g). H NMR (400 MHz, C6D6, 293 K): δ = –0.69 (d, JY,H
= 3.0 Hz, 2 H, YCH2), 0.20 [s, 9 H, Si(CH3)], 0.95 (m, 8 H, β-CH2
(compl. m, together 3 H, CH Ar, H4,12,23), 7.29 (m, together 2 H,
3
CH Ar, H11,13), 7.47 (d, JH,H = 4.2 Hz, 1 H, H24) ppm. 13C{H}
3
thf), 1.27 [s, 6 H, C(CH3)2, H7,8], 1.30 [d, JH,H = 6.9 Hz, 6 H,
NMR (100 MHz, C6D6, 293 K): δ = 4.4 [s, Si(CH3)3], 23.9 [s,
3
CH(CH3)2; H17,18,19,20], 1.34 [d, JH,H = 6.9 Hz, 6 H, CH(CH3)2,
CH(CH3)2, C17,18,19,20], 24.6 (s, β-CH2, thf), 27.6 [s, CH(CH3)2,
H17,18,19,20], 3.65 (m, 8 H, α-CH2 thf), 3.79 [sept, 3JH,H = 6.8 Hz, 2
C15,16], 27.8 [s, CH(CH3)2, C17,18,19,20], 30.0 (d, JY,C = 39.6 Hz,
1
3
H, CH(CH3)2, H15,16], 6.63 (d, JH,H = 8.0 Hz, 1 H, CH Ar, H2),
YCH2), 31.5 [s, C(CH3)2, C7,8], 68.5 [d, JY,C = 2.0 Hz, C(CH3)2,
C6], 69.8 (s, α-CH2 thf), 115.0 (s, C4), 116.3 (s, C2), 123.7 (s, C11,13),
123.8 (s, C12), 125.6 (s, C24) 137.6 (s, C23), 139.1 (s, C3), 144.7 (s,
7.17–7.26 (compl. m, together 4 H, CH Ar, H3,12,25,26), 7.32 (m, 2
3
H, CH Ar, H11,13), 7.57 (d, JH,H = 8.0 Hz, 1 H, CH Ar, H4), 7.62
(dd, 3JH,H = 6.8, 4JH,H = 2.0 Hz, 1 H, CH Ar, H27), 8.12 (dd, 3JH,H
2
2
C21), 147.1 (d, JY,C = 2.2 Hz, C9), 149.8 (s, C10,14), 158.4 (d, JY,C
= 6.8, JH,H = 2.0 Hz, 1 H, CH Ar, H24) ppm. 13C{H} NMR
4
= 1.7 Hz, C5), 174.6 (d, JY,C = 1.5 Hz, C1), 195.2 (d, JY,C
=
1
(100 MHz, C6D6, 293 K): δ = 4.5 [s, Si(CH3)3], 23.8 [s, CH(CH3)2,
38.9 Hz, YC, C22) ppm. IR (Nujol, KBr): ν = 3045 (m), 1590 (s),
˜
C17,18,19,20], 24.7 (s, β-CH2, thf), 27.7 [s, CH(CH3)2, C15,16], 27.7 [s,
1570 (s), 1415 (s), 1300 (m), 1260 (m), 1245 (m), 1235 (m), 1220
(s), 1175 (s), 1130 (s), 1130 (s), 1105 (m), 1085 (s), 1070 (m), 1045
(w), 1035 (m), 1025 (s), 1000 (w), 970 (w), 915 (w), 890 (m), 865
(m), 840 (s), 805 (s), 800 (s), 780 (m), 745 (m), 705 (m), 670 (m),
630 (w) cm–1. C36H55N2O2SSiY (696.89 gmol–1): calcd. C 62.04, H
7.95, N 4.02, Y 12.76; found C 62.33, H 8.15, N 4.09, Y 12.54.
1
CH(CH3)2, C17,18,19,20], 30.1 (d, JY,C = 37.6 Hz, YCH2), 31.1 [s,
C(CH3)2, C7,8], 68.6 [d, JY,C = 2.6 Hz, C(CH3)2, C6], 70.2 (s, α-CH2
thf), 110.5 (s, C27) 113.5 (s, C4), 117.8 (s, C2), 122.1 (s, C26) 123.8
(s, C11,13), 124.1 (s, C12), 124.5 (s, C25), 126.7 (s, C24), 139.0 (s, C3),
140.0 (d, JY,C = 2.8 Hz, C23), 144.1 (s, C9), 149.7 (s, C10,14), 153.4
2
(br. s, C5), 156.6 (s, C28), 158.6 (d, 1JY,C = 38.9 Hz, YC, C22), 160.8
Synthesis of [N2EtThY(CH2SiMe3)(thf)2] (14):
A
solution of
(br. s, C21), 175.0 (br. s, C1) ppm. IR (Nujol, KBr): ν = 3075 (w),
˜
N2EtThH (9) (0.231 g, 0.57 mmol) in n-hexane (15 mL) was added
to a solution of [Y(CH2SiMe3)3(thf)2] (0.281 g, 0.57 mmol) in n-
hexane (10 mL) at 0 °C. The reaction mixture was stirred at the
same temperature for 1 h. After 15 min, the precipitation of a pale
yellow microcrystalline solid started. The solution was concen-
3045 (m), 1600 (s), 1585 (w), 1570 (s), 1500 (s), 1415 (s), 1350 (m),
1335 (w), 1325 (m), 1300 (m), 1255 (s), 1235 (m), 1220 (s), 1200
(w), 1175 (s), 1145 (s), 1120 (m), 1005 (m), 1080 (s), 1045 (w), 1025
(s), 1010 (m), 970 (w), 925 (s), 895 (w), 885 (m), 865 (s), 850 (s),
820 (m), 810 (s), 795 (m), 770 (m), 715 (m), 705 (m), 675 (s), 635
616
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 608–620

Yttrium-Alkyl and Yttrium-Hydrido Derivatives
(w), 620 (m) cm–1. C40H57N2O3SiY (730.88 gmol–1): calcd. C 65.73, 1320 (m), 1295 (m), 1230 (m), 1220 (s), 1200 (w), 1170 (s), 1140 (s),
H 7.68, N 3.83, Y 12.16; found C 65.32, H 7.93, N 3.71, Y 12.04.
1120 (m), 1010 (m), 1085 (s), 1040 (w), 1025 (s), 1015 (m), 975 (w),
935 (s), 895 (w), 880 (m), 820 (m), 810 (s), 790 (m), 770 (m),
710 (m), 675 (s), 635 (w), 615 (m) cm–1. C64H76N4O2Y2
(1145.14 gmol–1): calcd. C 67.13, H 6.87, N 4.89, Y 15.53; found
C 66.98, H 7.11, N 4.91, Y 15.44.
Synthesis of [{N2BFuY(µ-H)(thf)}2] (18): PhSiH3 (0.047 g,
0.431 mmol) was added to a solution of 12 (0.315 g, 0.431 mmol)
in n-hexane (25 mL) at 0 °C. The reaction mixture was stirred at
0 °C for 1 h and kept overnight at room temperature. The solution
was concentrated in vacuo and maintained overnight at –20 °C.
Complex 18 was isolated as a yellow-brown crystalline solid in 72%
General Procedure for Ethylene Polymerization: A 200 mL stainless
steel reactor was heated to 60 °C under vacuum overnight and then
cooled to room temperature under a nitrogen atmosphere.
1
yield (0.201 g). H NMR (400 MHz, C6D6, 293 K): δ = 0.72 [br. s,
6 H, CH(CH3)2; H17,18,19,20], 0.79 [s, 6 H, C(CH3)2, H7,8], 1.01 [m,
12 H, CH(CH3)2; H17,18,19,20], 1.24 (m, 8 H, β-CH2 thf), 1.33 [s, 6
H, CH(CH3)2; H17,18,19,20], 2.17 (s, 6 H, H7,8), 2.72 [m, 2 H,
CH(CH3)2, H15,16], 3.19 (m, 4 H, α-CH2 thf), 3.42 (m, 4 H, α-CH2
Activation with MAO: The solid precatalyst (12 µmol) was charged
into the reactor, which was sealed and placed under vacuum. A
solution of MAO in toluene (3600 µmol, 300 equiv.), prepared by
diluting a standard solution of MAO (2.4 mL, 10 wt% in toluene)
in toluene (47.6 mL), was then introduced by suction into the reac-
tor previously evacuated by a vacuum pump. The system was
heated to the desired temperature, pressurized with ethylene to the
final pressure (10 bar), and stirred at 1500 rpm for 30 min.
3
thf), 4.54 [m, 2 H, CH(CH3)2, H15,16], 6.75 (d, JH,H = 8.0 Hz, 1
H, CH Ar, H2), 6.92–7.18 (compl. m, together 8 H, CH Ar,
H3,11,12,13), 7.23 (t, 3JH,H = 7.2 Hz, 2 H, CH Ar, H26), 7.33 (t, 3JH,H
3
= 7.8 Hz, 2 H, CH Ar, H25), 7.61 (d, JH,H = 7.5 Hz, 2 H, CH Ar,
3
1
H4), 7.64 (d, JH,H = 7.5 Hz, 2 H, CH Ar, H27), 7.71 (t, JY,H
=
27.0 Hz, 2 H, YH) 7.99 (d, 3JH,H = 7.5 Hz, 2 H, CH Ar, H24) ppm.
Activation with [Me2PhNH][B(C6F5)4]/AliBu3: The reactor was
13C{H} NMR (100 MHz, C6D6, 293 K): δ = 23.0 [s, CH(CH3)2, charged with a suspension of the cocatalyst [Me2PhNH][B(C6F5)4]
C17,18,19,20], 23.9 (s, β-CH2, thf), 24.2 [s, CH(CH3)2, C17,18,19,20], (14.4 µmol) in toluene (35 mL) followed by the rapid addition of a
25.9 [s, CH(CH3)2, C17,18,19,20], 26.7 [s, CH(CH3)2, C17,18,19,20], 26.8 25 wt% solution of AliBu3 in toluene (2.4 mL, 2.4 mmol,
[s, CH(CH3)2, C15,16], 28.3 [s, C(CH3)2, C7,8], 29.1 [s, CH(CH3)2,
200 equiv.). After sealing the reactor, the system was pressurized
C15,16], 42.9 [s, C(CH3)2, C7,8], 66.2 [d, JY,C = 2.6 Hz, C(CH3)2, C6], with ethylene at 2 bar and heated at 65 °C for 10 min so as to dis-
70.3 (s, α-CH2 thf), 110.6 (s, C27), 114.3 (s, C4), 115.2 (s, C2), 121.2
solve the activator. The ethylene pressure was then released slowly
and a precatalyst solution (2.5 mL), prepared by dissolving the so-
lid precatalyst (12 µmol) in toluene (2.5 mL), was added into the
(s, C26), 122.8 (s, C11,13), 123.2 (s, C11,13), 124.0 (s, C12), 127.0 (s,
2
C25), 128.0 (s, C24), 138.9 (s, C3), 140.4 (d, JY,C = 2.8 Hz, C23),
147.1 (s, C9), 148.6 (s, C10,14), 150.2 (s, C10,14), 153.2 (br. s, C5), reactor with a syringe. The autoclave was then pressurized with
156.6 (s, C28), 160.1 (d, 1JY,C = 43.3 Hz, YC, C22), 162.6 (br. s, C21),
ethylene to the final pressure (10 bar) and stirred at 1500 rpm for
30 min. Irrespective of the procedure used, catalysts and cocatalyst
(activator) solutions were handled in the glove box and ethylene
175.8 (br. s, C1) ppm. IR (Nujol, KBr): ν = 3080 (w), 3050 (m),
˜
1605 (s), 1580 (w), 1560 (s), 1505 (s), 1425 (s), 1340 (m), 1330 (w),
Table 4. Crystal data and structure refinement for ligands 6–10.[a]
6
7
8
9
10
Empirical formula
Mr
C26H32N2
372.54
C28H36N2
400.59
C24H30N2S
378.56
C52H68N4S2
813.22
C28H32N2O
412.56
T [K]
λ [Å]
293(2)
1.54180
293(2)
0.71069
293(2)
0.71073
150(2)
0.71069
293(2)
0.71069
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
P21/n
8.9657(10)
22.814(4)
10.8298(10)
90
monoclinic
P21/n
12.087(1)
13.064(1)
15.807(1)
90
orthorhombic
Pc21n
8.8099(14)
10.711(4)
22.911(10)
90
orthorhombic
Pna21
14.551(1)
9.164(1)
35.733(2)
90(5)
monoclinic
P21c
15.321(17)
13.032(16)
12.129(12)
90(5)
α [°]
β [°]
95.554(10)
90
2204.7(5)
1.122
0.491
808
97.095(4)
90
2476.9(3)
1.074
0.062
872
90
90
90(4)
90(4)
4764.8(7)
1.134
0.150
102.738(11)
90(5)
2362(5)
1.160
0.070
γ [°]
V [Å3]
2162.0(10)
1.163
0.160
Dcalcd. [gm–3
]
Absorption coefficient [mm–1
F(000)
]
816
1760
888
Crystal size [mm]
θ range for data collection [°]
Limiting indices
0.52ϫ0.28ϫ0.15
3.88–60.06
–10 Յ h Յ 10,
–5 Յ k Յ 25,
0 Յ l Յ 12
3467/3275
1.028
0.1ϫ0.1ϫ0.2
3.71–25.70
–14 Յ h Յ 12,
–15 Յ k Յ 15,
–19 Յ l Յ 19
13804/4654
0.914
0.33ϫ0.30ϫ0.20
2.48–24.96
0 Յ h Յ 10,
0 Յ k Յ 12,
0 Յ l Յ 27
2013/2013
1.042
0.25ϫ0.3ϫ0.3
3.75–28.90
–19 Յ h Յ 18,
–7 Յ k Յ 12,
–39 Յ l Յ 47
15778/8366
0.776
0.01ϫ0.01ϫ0.01
3.75–24.36
–17 Յ h Յ 12,
–14 Յ k Յ 14,
–13 Յ l Յ 13
6754/2914
0.815
Reflections collected/unique
GOF on F2
Data/restraints/parameters
Final R indices
[IϾ2σ(I)]
3275/1/252
R1 = 0.0830,
wR2 = 0.2039
R1 = 0.1075,
wR2 = 0.2264
4654/0/275
R1 = 0.0717,
wR2 = 0.1748
R1 = 0.1809,
wR2 = 0.2169
2013/1/252
R1 = 0.0699,
wR2 = 0.1318
R1 = 0.1579,
wR2 = 0.1623
8366/1/539
R1 = 0.0456,
wR2 = 0.0804
R1 = 0.1354,
wR2 = 0.0987
2914/0/283
R1 = 0.0507,
wR2 = 0.0749
R1 = 0.1557,
wR2 = 0.0918
R indices (all data)
Largest diff. peak and hole [eÅ–3
[a] For all compounds, Z = 4.
]
0.2063 and –0.241 0.255 and –0.192 0.250 and –0.245
0.330 and –0.303 0.151 and –0.156
Eur. J. Inorg. Chem. 2010, 608–620
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
617

A. A. Trifonov, G. Giambastiani et al.
FULL PAPER
Table 5. Crystal data and structure refinement for complexes 12, 14, and 16–18.[a]
12[b]
14
16[a]
17
18
Empirical formula
Mr
T [K]
C36H53N2OSiY
646.80
100(2)
C38H59N2O2SiY
724.93
100(2)
C60H78N4O2Y2
1065.08
100(2)
C70H10N4O2Y2
1207.36
100(2)
C76H90N4O4Y2
1301.34
100(2)
λ [Å]
0.71073
monoclinic
P21/c
10.0924(5)
18.8418(9)
18.4703(9)
90
0.71073
monoclinic
P21/c
17.5740(7)
12.4289(5)
18.4721(7)
90
0.71073
tetragonal
P41212
12.9842(3)
12.9842(3)
33.0971(1)
90
0.71069
0.71069
orthorhombic
Pbcn
17.666(5)
17.642(9)
21.625(7)
90(5)
Crystal system
Space group
a [Å]
b [Å]
c [Å]
tetragonal
¯
P4n2
23.7470(6)
23.7470(6)
12.3501(4)
90
α [°]
β [°]
99.8130(10)
90
3460.9(3)
1.241
1.749
1376
110.97(10)
90
3767.5(3)
1.278
1.669
1544
90
90
5579.8(3)
1.268
2.113
90
90
6964.5(3)
1.151
1.701
90(5)
90(5)
6740(4)
1.283
1.765
2736
γ [°]
V [Å3]
Dcalcd. [gm–3
]
Absorption coefficient [mm–1
F(000)
]
2240
2568
Crystal size [mm]
θ range for data collection [°]
Limiting indices
0.30ϫ0.20ϫ0.15
2.43–26.00
–12 Յ h Յ 12,
–23 Յ k Յ 23,
22 Յ l Յ 22
29249/6787
1.032
0.35ϫ0.26ϫ0.13 0.15ϫ0.12ϫ0.06
0.2ϫ0.1ϫ0.1
3.82–26.45
–28 Յ h Յ 14,
–12 Յ k Յ 28,
–15 Յ l Յ 8
13954/5555
0.972
0.05ϫ0.01ϫ0.1
3.83–27.51
–21 Յ h Յ 21,
–15 Յ k Յ 20,
–27 Յ l Յ 14
18112/6035
0.903
2.75–26.00
2.42–26.00
–21 Յ h Յ 21,
–15 Յ k Յ 15,
–22 Յ l Յ 22
31546/7391
1.037
–16 Յ h Յ 15,
–16 Յ k Յ 16,
–40 Յ l Յ 40
48076/5466
1.079
Reflections collected/unique
GOF on F2
Data/restraints/parameters
Final R indices
[IϾ2σ(I)]
6787/3/380
R1 = 0.0349,
wR2 = 0.0761
R1 = 0.0523,
wR2 = 0.0806
7391/4/419
5466/0/316
5555/22/361
R1 = 0.0630,
wR2 = 0.1591
R1 = 0.1205,
wR2 = 0.1731
6035/0/391
R1 = 0.0363,
wR2 = 0.08
R1 = 0.0838,
wR2 = 0.0877
R1 = 0.0326,
wR2 = 0.0747
R1 = 0.0489,
wR2 = 0.0792
R1 = 0.0257,
wR2 = 0.0608
R1 = 0.0301,
wR2 = 0.0619
R indices (all data)
Largest diff. peak and hole
0.439 and –0.289
0.996 and –0.367
–0.190 and 0.389
0.941 and –0.349 0.470 and –0.471
[eÅ–3
]
[a] For all compounds, Z = 4. [b] Selected data in the literature[20] listed here for completeness.
was continuously fed to maintain the reactor pressure at the desired
value throughout the catalytic run. After 30 min, the reaction was
terminated by cooling the reactor to 0 °C, venting off the volatiles,
and introducing acidic MeOH (1 mL, 5% HCl v/v). The solid prod-
ucts were filtered off, washed with cold toluene and MeOH, and
dried in a vacuum oven at 50 °C. The filtrates were analyzed by
GC and GC–MS for detecting the presence of short oligomers.
disordered as well, even at 100 K; this disorder was not explicitly
treated since the final R1/wR2 values do not change significantly
when it is included in the refinement. CCDC-740105 (6), -740107
(7), -740106 (8), -740104 (9), -740103 (10), -740102 (14), -740100
(17) and -740101 (18) contain 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.
X-ray Diffraction Data: Crystallographic data of ligands 6–10 and
complexes 12, 14, 16–18 are reported in Tables 4 and 5, respectively.
X-ray diffraction intensity data were collected with either a
SMART APEX or Oxford Diffraction CCD diffractometer with
graphite monochromated Mo-Kα radiation (λ = 0.71073 Å) using
ω scans. Cell refinement, data reduction and empirical absorption
correction were carried out with the Oxford diffraction software
and SADABS.[29] All structure determination calculations were
performed with the WINGX package[30] with SIR-97,[31] SHELXL-
97[32] and ORTEP-3 programs.[33] Final refinements based on F2
were carried out with anisotropic thermal parameters for all non-
hydrogen atoms, which were included using a riding model with
isotropic U values depending on the Ueq of the adjacent carbon
atoms. In 9, a nonmerohedral twin is present; the twin component
was found to be 0.7(1). Two molecules are present in the asymmet-
ric unit, thus generating a “pseudochiral” helical lattice packing
[for this reason the space group found (Pna21) is noncentrosym-
metric]. The hydride ligand positions in complexes 16 and 17 were
determined from the residual density map during the refinement
and subsequently fixed at 2.15 and 2.44 Å from the Y atom, respec-
tively. The accessible voids of 273 Å3 found in the lattice of 17 are
probably occupied by disordered thf crystallization molecules that
could not be located precisely. The coordinated thf molecules are
Acknowledgments
The authors thank the Ministero dell’Istruzione, dell’Università e
della Ricerca of Italy (NANOPACK
- FIRB project no.
RBNE03R78E), the Russian Foundation for Basic Research (grant
no. 08-03-00391-a, 06-03-32728), FIRENZE HYDROLAB project
by Ente Cassa di Risparmio di Firenze (http://www.iccom.cnr.it/
hydrolab/) and the GDRE network “Homogeneous Catalysis for
Sustainable Development” for financial support of this work. G. G.
also thanks Dr. Andrea Meli and Dr. Andrea Ienco for fruitful
discussions.
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 608–620

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