Scandium and yttrium complexes supported by NNCp heteroscorpionate ligands: Synthesis, structure, and polymerization of ∈-caprolactone

Article abstract of DOI:10.1021/om701033r

Mixtures of two scorpionate/cyclopentadiene regioisomers-bpzcpH (1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1 -diphenylethyl]-1,3-cyclopentadiene (la) and 2-[2,2-bis(3,5-dimethylpyrazol-1 -yl)-1,1 -diphenylethyl]-1,3- cyclopentadiene (1b)) and bpztcpH (1-[2,2

Full text of DOI:10.1021/om701033r

976
Organometallics 2008, 27, 976–983
Scandium and Yttrium Complexes Supported by NNCp
Heteroscorpionate Ligands: Synthesis, Structure, and
Polymerization of E-Caprolactone
Antonio Otero,*,† Juan Fernández-Baeza,*,† Antonio Antiñolo,† Agustín Lara-Sánchez,*,†
Emilia Martínez-Caballero,† Juan Tejeda,† Luis F. Sánchez-Barba,‡
Carlos Alonso-Moreno,‡ and Isabel López-Solera†
Departamento de Química Inorgánica, Orgánica y Bioquímica, UniVersidad de Castilla-La Mancha,
13071 Ciudad Real, Spain., and Departamento de Química Inorgánica y Analítica, UniVersidad Rey Juan
Carlos, 28933 Móstoles, Madrid, Spain
ReceiVed October 16, 2007
Mixtures of two scorpionate/cyclopentadiene regioisomerssbpzcpH (1-[2,2-bis(3,5-dimethylpyrazol-
1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene (1a) and 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphe-
nylethyl]-1,3-cyclopentadiene (1b)) and bpztcpH (1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl]-
1,3-cyclopentadiene (2a) and 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl]-1,3-cyclopentadiene
(2b))swere prepared by deprotonation of bis(3,5-dimethylpyrazol-1-yl)methane with BunLi followed
by reaction with 6,6-diphenylfulvene or 6-tert-butylfulvene and subsequent treatment with saturated
aqueous ammonium chloride. Reactions of hybrid scorpionate/cyclopentadiene compounds with
[M(CH2SiMe3)3(THF)3] (M ) Sc, Y) afford the dialkyl complexes [M(CH2SiMe3)2(bpzcp)] (M ) Sc
(3), Y (4)) and [M(CH2SiMe3)2(bpztcp)] (M ) Sc (5), Y (6)). The cationic alkyl complexes [M(CH2SiMe3)-
(bpzcp)]+ (M ) Sc (7), Y (8)) were also prepared by the reaction of complexes 3 and 4 with
[CPh3][B(C6F5)4] in THF. The structures of these compounds were determined by spectroscopic methods,
and the X-ray crystal structures of 2 and 3 were also established. The bis(alkyl) complexes 3 and 4 were
found to be active initiators for the ring-opening polymerization of ꢀ-caprolactone (up to 75% conversion
of 200 equiv in 10 min) and yielded polymers with narrow molecular weight distributions.
reports on the use of NNO, NNS, and NNN heteroscorpionates
in group 3 coordination or organometallic chemistry have been
published.4
Introduction
Poly(pyrazolyl)-based (“scorpionate”) ligands have been
widely exploited over a broad range of transition-metal applica-
tions, including organometallic, catalytic, bioinorganic, and
supramolecular contexts.1 Recently, anionic “heteroscorpionate”
ligands in which a neutral pyrazole ring has been formally
substituted by an arm (see Figure 1) bearing an anionic donor
“E”, such as carboxylate, dithiocarboxylate, aryloxide, alkoxide,
amide, cyclopentadienyl, and, more recently, acetamidate,
thioacetamidate, and amidinate functional groups have led to
considerable interest in the “post-metallocene” chemistry of the
transition metals.2 Although there is extensive literature con-
cerning transition metals and heteroscorpionate ligands, the
chemistry of group 3 and lanthanide metals with scorpionate
ligands has focused mainly on the very widely exploited
tris(pyrazolyl)hydroborate ligands.3 Only two (very recent)
(2) See for example: (a) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.;
Tejeda, J.; Carrillo-Hermosilla, F.; Diez-Barra, E.; Lara-Sánchez, A.;
Fernández-López, M.; Lanfranchi, M.; Pellinghelli, M. A. J. Chem. Soc.,
Dalton Trans. 1999, 3537. (b) Otero, A.; Fernández-Baeza, J.; Antiñolo,
A.; Tejeda, J.; Carrillo-Hermosilla, F.; Lara-Sánchez, A.; Sánchez-Barba,
L.; Fernández-López, M.; Rodríguez, A. M.; López-Solera, I. Inorg. Chem.
2002, 41, 5193. (c) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.; Tejeda,
J.; Lara-Sánchez, A.; Sánchez-Barba, L.; Rodríguez, A. M.; Maestro, M. A.
J. Am. Chem. Soc. 2004, 126, 1330. (d) Ghosh, P.; Parkin, G. J. Chem.
Commun. 1998, 37. (e) Adhikari, D.; Zhao, G.; Basuli, F.; Tomaszewski,
J.; Huffman, J. C.; Mindiola, D. J. Inorg. Chem. 2006, 45, 1604. (f) Hammes,
B. S.; Chohan, B. S.; Hoffman, J. T.; Einwächter, S.; Carrano, C. J. Inorg.
Chem. 2004, 43, 7800. (g) Smith, J. N.; Shirin, Z.; Carrano, C. J. J. Am.
Chem. Soc. 2003, 125, 868. (h) Kopf, H.; Pietraszuk, C.; Hübner, E.;
Burzlaff, N. Organometallics 2006, 25, 2533. (i) Otero, A.; Fernández-
Baeza, J.; Antiñolo, A.; Tejeda, J.; Lara-Sánchez, A.; Sánchez-Barba, L.;
Sánchez-Molina, M.; Franco, S.; López-Solera, I.; Rodríguez, A. M. Eur.
J. Inorg. Chem. 2006, 707. (j) Otero, A.; Fernández-Baeza, J.; Antiñolo,
A.; Tejeda, J.; Lara-Sánchez, A.; Sánchez-Barba, L.; Sánchez-Molina, M.;
Franco, S.; López-Solera, I., Rodríguez, A. M. Dalton Trans. 2006, 4359.
(k) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.; Tejeda, J.; Lara-Sánchez,
A.; Sánchez-Barba, L.; López-Solera, I.; Rodríguez, A. M. Inorg. Chem.
2007, 46, 1760–1770. (l) Milione, S.; Montefusco, S.; Cuenca, T.; Grassi,
A. Chem. Commun. 2003, 1176. (m) Milione, S.; Bertolasi, V.; Cuenca,
T.; Grassi, A. Organometallics 2005, 24, 4915.
* To whom correspondence should be addressed. E-mail: Antonio.Otero@
uclm.es (A.O.).
† Universidad de Castilla-La Mancha.
‡ Universidad Rey Juan Carlos.
(1) See for example: (a) Trofimenko, S., Scorpionates: The Coordination
Chemistry of Polypyrazolylborate Ligands; Imperial College Press: London,
1998. (b) Marques, N.; Sella, A.; Takats, J. Chem. ReV. 2002, 102, 2137.
(c) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.; Tejeda, J.; Lara-Sánchez,
A. Dalton Trans. 2004, 1499. (d) Parkin, G. Chem. ReV. 2004, 104, 699.
(e) Pettinari, C.; Pettinari, R. Coord. Chem. ReV. 2005, 249, 525. (f) Pettinari,
C.; Pettinari, R. Coord. Chem. ReV. 2005, 249, 663. (g) Bigmore, H. R.;
Lawrence, S. C.; Mountford, P.; Tredget, C. S. Dalton Trans. 2005, 635.
(3) See for example: (a) Marques, N.; Sella, A.; Takats, J. Chem. ReV.
2002, 102, 2137. (b) Stainer, M. V. R.; Takats, J. J. Am. Chem. Soc. 1983,
105, 410. (c) Long, D. P.; Bianconi, P. A. J. Am. Chem. Soc. 1996, 118,
12453. (d) Roitershtein, D.; Domingos, A.; Pereira, L. C. J.; Ascenso, J. R.;
Marques, N. Inorg. Chem. 2003, 42, 7666. (e) Blackwell, J.; Lehr, C.; Sun,
Y.; Piers, W. E.; Zaworotko, M. J.; Pearce-Batchilder, S. D.; Young, G.
Can. J. Chem. 1997, 75, 702.
10.1021/om701033r CCC: $40.75
2008 American Chemical Society
Publication on Web 02/14/2008

Sc and Y Complexes with Heteroscorpionate Ligands
Organometallics, Vol. 27, No. 5, 2008 977
protonolysis processes to prepare scorpionate/cyclopentadienyl
alkyl derivatives of scandium and yttrium. In addition, several
electron-deficient cationic alkyl complexes were also prepared.
Finally, the reactivity toward ring-opening polymerization of
ꢀ-caprolactone is reported for some of these complexes.
Results And Discussion
Ligand Syntheses. First, we prepared a series of new hybrid
Figure 1. Overall view of anionic heteroscorpionate ligands.
scorpionate/cyclopentadiene compounds. The one-pot reaction
of bis(3,5-dimethylpyrazol-1-yl)methane (bdmpzm)10 with Bun
-
Furthermore, cyclopentadienyl systems with an additional
donor function are attracting increased interest in the chemistry
of early transition metals because of their potential applications
as catalysts in polymerization processes.5 Ligands that possess
both a cyclopentadienyl ring and heteroatoms connected by an
appropriate spacer are receiving considerable attention in
synthesis and catalysis, as they lead to significant changes in
both steric and electronic effects on the metal centers.6 Bearing
in mind the development of donor-functionalized cyclopenta-
dienyl ligands and the emerging importance of the heteroscor-
pionate systems, it would be interesting to prepare hybrid
scorpionate/cyclopentadienyl compounds as precursors for the
introduction of these ligands into transition-metal complexes.
This type of ligand was unknown until we recently reported
the first hybrid scorpionate/cyclopentadienyl ligands.2c,7 The
preparation of this new class of tridentate ligand by a simple
and efficient synthetic route led us to develop and fully explore
the potential offered by this type of ligand in the organometallic
or coordination chemistry of group 3 metals, especially to
prepare scandium and yttrium derivatives that could have
potential interest as initiators in the ring-opening polymerization
(ROP) of cyclic esters such as lactones. These types of catalytic
processes are currently generating a great deal of interest because
of the biodegradability and biocompatibility of the resulting
polyesters.8,9
Li, followed by treatment with 6,6-diphenylfulvene or 6-tert-
butylfulvene11 and then with a saturated aqueous solution of
ammonium chloride, afforded the desired compounds as a
mixture of two regioisomers in a 3:1 ratio: bpzcpH (1-[2,2-
bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopen-
tadiene (1a), 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenyl-
ethyl]-1,3-cyclopentadiene (1b)) and bpztcpH (1-[2,2-bis(3,
5-dimethylpyrazol-1-yl)-1-tert-butylethyl]-1,3-cyclopentadi-
ene (2a), 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethyl]-
1,3-cyclopentadiene (2b)), which were isolated as white solids
in good yield (ca. 90%) after the appropriate workup. These
compounds can be stored indefinitely under an air atmosphere
(see Scheme 1).
For compounds 1 and 2 there are three possible tautomers
(see Figure 2), isomers a-c, in which the cyclopentadiene group
is bonded by C1, C2, or C5 to the bis(pyrazol-1-yl)methane
moiety, respectively. Two sets of 1H NMR signals are observed
for these mixtures, and this is consistent with the presence of
only two tautomers. Additionally, for both 1 and 2 the H5 signal
1
in the H NMR spectra is integrated for two protons, meaning
that the presence in the mixtures of tautomer c (in which the
cyclopentadiene group is bonded by C5 to the bis(pyrazol-1-
1
yl)methane unit) can be ruled out. Furthermore, the H and
13C{H} NMR spectra of both tautomers of 1 show only one
set of resonances for the pyrazole rings, indicating that the
pyrazoles are equivalent. However, the tautomers of 2, each of
which contains a stereogenic carbon center that makes the
pyrazole rings diastereotopic, show different signals for Me3,
Me5, and H4 in both rings in the 1H NMR spectra. 1H NOESY-
1D experiments were carried out in order to assign the signals
In this paper we describe the preparation, in a simple one-
pot procedure, of new scorpionate/cyclopentadiene compounds.
These compounds were subsequently employed in a series of
(4) See for example: (a) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.;
Tejeda, J.; Lara-Sánchez, A.; Sánchez-Barba, L.; Martínez-Caballero, E.;
Rodriguez, A. M.; López-Solera, I. Inorg. Chem. 2005, 44, 5336. (b) Howe,
R. G.; Tredget, C. S.; Lawrence, S. C.; Subongkoj, S.; Cowley, A. R.;
Mountford, P. Chem. Commun. 2006, 223.
1
of the two tautomers. The absence of a response in the H
NOESY-1D experiment from the methine proton on irradiating
the H5 protons of the major tautomer leads us to propose that
tautomer b is the major component. In addition, X-ray diffraction
studies were carried out on 2. Selected bond lengths and angles
are collected in Table 1. Only one tautomer was isolated in the
solid state (see Figure 3). The shorter distances for C(16)-C(17)
(1.396 (6) Å), C(16)-C(20) (1.396 (6) Å), and C(20)-C(19)
(1.405 (8) Å) are indicative of conjugated systems, whereas the
distances C(17)-C(18) (1.411 (7) Å) and C(18)-C(19) (1.451
(8) Å) are longer than those typically found for the classic
cyclopentadiene,12 which indicates single bonds between these
atoms. These results are consistent with the structural disposition
described for tautomer 2b. The pyrazole rings of this compound
are oriented in a quasi-antiparallel disposition with respect to
each other, presumably to minimize the intramolecular steric
interactions between the N(2) and N(4) atoms of the two rings.
(5) See for example: (a) Deng, D.; Qian, C.; Wu, G.; Zheng, P. J. Chem.
Soc., Chem. Commun. 1990, 880. (b) Qian, C.; Wang, B.; Wu, G.; Zheng,
P. J. J. Organomet. Chem. 1992, 427, C29. (c) Anwander, R.; Hermann,
W. A.; Scherer, W.; Munck, F. C. J. Organomet. Chem. 1993, 462, 163.
(d) Molander, G.; Schumann, H.; Rosenthal, E. C. E.; Demtschuk, J.
Organometallics 1996, 15, 3817. (e) Schumann, H.; Rosenthal, E. C. E.;
Demtschuk, J. Organometallics 1998, 17, 5324. (f) Britovsek, G. J. P.;
Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (g)
Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283.
(6) See for example: (a) McKnight, A. L.; Waymouth, R. M. Chem.
ReV. 1998, 98, 2587. (b) Siemeling, U. Chem. ReV. 2000, 100, 1495. (c)
Butenschön, H. Chem. ReV. 2000, 100, 1527. (d) Qian, Y.; Huang, J.; Bala,
M. D.; Lian, B.; Zhang, H.; Zhang, H. Chem. ReV. 2003, 103, 2633.
(7) (a) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.; Tejeda, J.; Lara-
Sánchez, A.; Sánchez-Barba, L.; Sanchez-Molina, M.; Rodríguez, A. M.;
Bo, C.; Urbano-Cuadrado, M. Organometallics 2007, 26, 4310. (b) Recently
the preparation of a new type of boron-containing cyclopentadienyl/
scorpionate hybrid ligand has been described: Kunz, K.; Vitze, H.; Botte,
M.; Lerner, H.-W.; Wagner, M. Organometallics 2007, 26, 4663.
(8) Selected reviews on aspects of biodegradable polymers: (a) Okada,
M. Prog. Polym. Sci. 2002, 27, 87. (b) Drumright, R. R.; Gruber, P. R.;
Henton, D. E. AdV. Mater. 2000, 12, 1841.
(10) (a) Sebastian, J.; Sala, P.; del Mazo, J.; Sancho, M.; Ochoa, C.;
Elguero, J.; Fayet, J.; Vertut, M. C. J. Heterocyclic Chem. 1982, 19, 1141.
(b) Diez-Barra, E.; de la Hoz, A.; Sanchez-Mingallon, A.; Tejeda, J. J. Chem.
Soc., Perkin Trans. 1 1993, 1079.
(9) Reviews addressing the polymerization of cyclic esters: (a) Dechy-
Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Chem. ReV. 2004, 104, 6147.
(b) Coates, G. W. Dalton Trans. 2002, 467. (c) Hou, A.; Wakatsuki, Y.
Coord. Chem. ReV. 2002, 231, 1.
(11) Stone, K. J.; Little, R. D. J. Org. Chem. 1984, 49, 1849.
(12) (a) Haumann, T.; Benet-Buchholz, J.; Boese, R. J. Mol. Struct. 1996,
374, 299. (b) Liebling, G.; Marsh, R. E. Acta Crystallogr. 1965, 19, 202.

978 Organometallics, Vol. 27, No. 5, 2008
Scheme 1. Summary of Reactions Leading to Compounds 1 and 2
Otero et al.
This conformation is similar to that found in the (2-hydroxy-
phenyl)bis(pyrazolyl)methane derivative.13
to consider bonding or interaction between N(3) and the
scandium atom, probably due to the steric hindrance caused by
the two bulky alkyl groups. The dihedral angle between the
N(1)-Sc(1)-Cp(cent) and C(13)-Sc(1)-C(17) planes (94.6°)
indicates a slightly distorted tetrahedral geometry. Furthermore,
the angles around the scandium atom show considerable
deviation from ideal values (range 99.7(2)-123.8°). The most
acute angle of 99.7(2)° is observed for C13-Sc1-C17, which
is constrained by the bite of the heteroscorpionate ligand. The
C5H4 ring is symmetrically bonded to the Sc atom with Sc-C
bond distances in the range 2.466(6)-2.491(6) Å. The
Sc(1)-N(1) bond distance of 2.279(4) Å is slightly shorter than
one would expect for a Sc/pyrazolyl complex.4,16 The Sc-
(1)-C(13) and Sc(1)-C(17) bond distances of 2.213(5) and
2.232(5) Å, respectively, and Sc-C-Si bond angles of 129.5(3)
and 131.0(3)°, respectively, are in good agreement with literature
data.16,17
Group 3 Alkyl Compounds. Having prepared this new class
of hybrid scorpionate/cyclopentadiene compound, we explored
their potential utility as ligands in the preparation of new group
3 metal complexes. It is well-known that the alkane elimination
reaction is frequently the route of choice to prepare early-
transition-metal organometallics, as the precursors are readily
available and “ate” complex formation is avoided. The depro-
tonation of the cyclopentadiene moiety is a well-known
procedure, and it normally proceeds by either acid–base or
protonolysis processes; for example, the reaction of scandium
or yttrium tris(alkyl) complexes and cyclopentadiene gives the
corresponding mono(cyclopentadienyl)metal-bis(alkyl) com-
plexes with elimination of alkane.14 In this way, the reaction
of the protio compounds 1 and 2 with [M(CH2SiMe3)3(THF)3]15
(M ) Sc, Y) in a 1:1 molar ratio in hexane at 0 °C yielded the
THF-free scandium and yttrium dialkyl complexes [M(CH2-
SiMe3)2(bpzcp)] (M ) Sc (3), Y (4)) and [M(CH2SiMe3)2-
(bpztcp)] (M ) Sc (5), Y (6)), after the appropriate workup
procedure, as pale yellow solids in good yield (Scheme 2). These
complexes are solvent-free and thermally stable. Complexes 3–6
constitute the first examples of group 3 metal complexes bearing
a hybrid scorpionate/cyclopentadienyl ligand.
The molecular structure of 3 was determined by X-ray
diffraction (Figure 4). Selected bond lengths and angles are
collected in Table 2. In this case, the heteroscorpionate ligand
is κ1NN-η5-Cp coordinated to the Sc atom, forming a pseudo-
four-coordinate tetrahedral complex with C1 symmetry. This
kind of coordination has never been observed before for these
hybrid scorpionate/cyclopentadienyl ligands. Recently, we
described the synthesis and reactivity of lithium and group 4
metal complexes containing these ligands, which in these cases
are in a facial, tripodal, κ2NN-η5-Cp coordination mode.2c,7a
The distance between N(3) and Sc(1) of 3.44(4) Å is too long
It is worth noting that, given the coordination mode of the
heteroscorpionate ligand, complex 3 is a chiral compound. This
complex crystallizes as a racemic mixture with both enantiomers
included in the unit cells belonging to a noncentrosymmetric
space group.
Solution NMR Characterization. In the present study, effort
has been focused on determining whether the κ1NN-η5-Cp bpzcp
ligand coordination mode observed in the solid-state structure
of 3 persists in solution and if complexes 3–6 exhibit flexible
structures in solution. The dynamic behavior of these complexes
1
was studied by VT NMR spectroscopy. The H NMR spectra
of the dialkyl complexes 3 and 4 at room temperature show a
singlet for each of the H4, Me3, and Me5 pyrazole protons,
indicating that the pyrazoles are equivalent, along with two
multiplets for the cyclopentadienyl protons and one methyl
resonance for the two equivalent CH2SiMe3 ligands. Further-
1
more, the room-temperature H NMR spectra of complexes 5
and 6, both of which have a stereogenic carbon, show two
singlets for each of the H4, Me3, and Me5 pyrazole protons,
four multiplets for the H2, H3, H4, and H5 cyclopentadienyl
(13) Higgs, T. C.; Carrano, C. J. Inorg. Chem. 1997, 36, 291.
(14) See for example: (a) Hultzsch, K. C.; Spaniol, T. P.; Okuda, J.
Angew. Chem., Int. Ed. 1999, 38, 227. (b) Li, X.; Baldamus, J.; Hou, Z.
Angew. Chem., Int. Ed. 2005, 44, 962. (c) Luo, Y.; Baldamus, J.; Hou, Z.
J. Am. Chem. Soc. 2004, 126, 13910.
(16) (a) Lawrence, S. C.; Ward, B. D.; Dubberley, S. R.; Kozak, C. M.;
Mountford, P. Chem. Commun. 2003, 2880. (b) Tredgdet, C. S.; Lawrence,
S. C.; Ward, B. D.; Howe, G. R.; Cowley, A. R.; Mountford, P.
Organometallics 2005, 24, 3136.
(15) (a) Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1973,
126. (b) Hultzsch, K. C.; Volh, P.; Beckerle, K.; Spaniol, T. P.; Okuda, J.
Organometallics 2000, 19, 228. (c) Ewans, J. W.; Brady, J. C.; Ziller, J. W.
J. Am. Chem. Soc. 2001, 123, 7711.
(17) (a) Allen, F. H.; Kennard, O. Chem. Des. Automation News 1993,
8 (1), 31. (b) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. J. Chem.
Inf. Comput. Sci. 1996, 36, 746.

Sc and Y Complexes with Heteroscorpionate Ligands
Organometallics, Vol. 27, No. 5, 2008 979
Figure 2. Proposed structures for the three isomers of compounds 1 and 2.
Table 1. Bond Lengths (Å) and Angles (deg) for 2b
in which the pyrazole ring that is outside the coordination sphere
of the metal center displaces the coordinated pyrazole ring
through a pentacoordinate transition state. The approach of the
free pyrazole ring is necessarily from the opposite side of the
coordinated pyrazole ring; therefore, inversion of configuration
at the metal center occurs (see Scheme 3). In the second possible
dissociative mechanism (SN1), the first step would involve the
pyrazole ring coordinated to the metal center leaving the
coordination sphere of the metal atom to produce a “three-
coordinate” transition state; in the second step, one of the two
free pyrazole rings would coordinate to the metal center to give
the final four-coordinate complex. In this step both stereoisomers
could be formed. It was not possible to distinguish between
these two mechanisms, as the exchange was too fast on the
NMR time scale. However, it is worth noting that a similar
exchange of coordinated and uncoordinated pyrazole groups has
already been observed in other complexes containing tridentate
scorpionate or heteroscorpionate ligands, with the conclusion
that the dynamic exchange process involves an intramolecular
associative displacement of one pyrazole group for the other.18
Bond Lengths
C(2)-C(3)
1.361(6) C(16)-C(20)
1.399(6) C(17)-C(18)
1.356(6) C(18)-C(19)
1.394(6) C(19)-C(20)
1.396(6)
1.396(6)
1.411(7)
1.451(8)
1.405(8)
C(3)-C(4)
C(7)-C(8)
C(8)-C(9)
C(16)-C(17)
Bond Angles
N(1)-C(1)-N(3)
N(1)-C(1)-C(21)
N(3)-C(1)-C(21)
110.4(3)
112.8(3)
115.3(3)
C(16)-C(17)-C(18) 109.5(5)
C(17)-C(18)-C(19) 106.6(5)
C(18)-C(19)-C(20) 106.4(5)
C(16)-C(20)-C(19) 109.9(5)
C(17)-C(16)-C(20) 107.5(4)
C(20)-C(16)-C(21) 124.6(4)
protons, and two methyl resonances for the two inequivalent
CH2SiMe3 ligands. Additionally, the methylene protons of
complex 6, YCH2SiMe3, are diastereotopic, giving rise to a pair
of doublet of doublets at -0.45 and -0.19 ppm (2JYH ) 2.9
2
Hz, JHH ) 11.2 Hz) due to coupling with the Y atom. On
lowering the temperature in the VT NMR study of 3 and 4, the
resonances of the alkyl groups bound to the metal center and
those due to the methyl groups and H4 of the pyrazole rings
broadened but did not resolve into two separate peaks. Even at
-90 °C the resonances did not become sharp and well resolved
and the NMR spectrum did not become consistent with the
observed solid-state structure for 3. These observations indicate
highly fluxional behavior (Scheme 3), thought to be due to an
exchange process between the coordinated and the noncoordi-
nated pyrazole rings, and this results in the interconversion from
one stereoisomer to the other (Scheme 3, a and c). At room
temperature the exchange is too fast to be detected on the NMR
time scale and, thus, the two pyrazole rings appear equivalent.
The same fluxional behavior was observed for complexes 5
and 6 in the corresponding VT NMR studies. Two different
mechanisms for the racemization of 3–6 can be envisaged. The
first involves an intramolecular associative displacement (SN2)
Cationic Group 3 Alkyl Compounds. Recently, rare-earth
alkyl cations have attracted considerable attention because of
their increased Lewis acidity/electrophilicity, and they should
have a great deal of potential as homogeneous catalysts in olefin
polymerization and organic transformations.19 The generation
of cationic derivatives of the heteroscorpionate scandium and
yttrium alkyl complexes was explored by reacting the neutral
complexes 3 and 4 with an alkyl-abstracting agent. Thus,
treatment of 3 and 4 with 1 equiv of [Ph3C][B(C6F5)4] afforded
the expected cationic mono(alkyl) species [Sc(CH2SiMe3)-
(bpzcp)]+ (7) and [Y(CH2SiMe3)(bpzcp)]+ (8) as borate salts
(Scheme 4) in good yield (70%).
The reaction was monitored by 1H NMR spectroscopy. It was
found that the reaction is fast (a few minutes) and quantitative.
The cationic complexes 7 and 8 are more stable in solvents
with coordinative capacity such as THF (t1/2(25 °C) ) 4 days
for 7; t1/2(25 °C) ) 7 days for 8), and they slowly decompose
to unknown species, thus hampering the crystallization.
The molecular structures of 7 and 8 were studied in solution
by NMR spectroscopy. The 1H NMR spectra of 7 and 8 in THF-
d8 show a high-field shift of the signal due to the methylene
protons to -0.22 and -0.76 ppm, respectively. In the 13C{1H}
NMR spectra the MCH2 resonances for the cations are found
downfield from those in the neutral dialkyl precursors, while
the JYC coupling constant increases by about 13.7 Hz, as
observed for other cationic alkyl complexes of Sc and Y.20 The
two pyrazole rings appear to be equivalent, and this fact suggests
(18) (a) Milione, S.; Grisi, F.; Centore, R.; Tuzi, A. Organometallics
2006, 25, 266. (b) Looney, A.; Parkin, G. Polyhedron 1990, 9, 265. (c)
Chisholm, M. H.; Eilerts, N. W.; Huffman, J. C. Inorg. Chem. 1996, 35,
445. (d) Jones, W. D.; Hessell, E. T. Inorg. Chem. 1991, 30, 778. (e) Eaves,
R.; Parkin, S.; Ladipo, F. T. Inorg. Chem. 2007, 46, 9495.
Figure 3. ORTEP view of 1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1-
tert-butylethyl]-1,3-cyclopentadiene (2b). Ellipsoids are given at
the 30% probability level.
(19) Arndt, S.; Okuda, J. AdV. Synth. Catal. 2005, 347, 339.

980 Organometallics, Vol. 27, No. 5, 2008
Scheme 2. Summary of Reactions Leading to Compounds 3–6
Otero et al.
Scheme 3. Mechanism Proposed for the Dynamic
a symmetrical disposition for both coordinated pyrazole rings,
as depicted in Scheme 4, in a pseudotetrahedral disposition in
which the ligand is in an “s-cis” conformation and κ2NN-η5-
Cp coordinated. A similar stabilizing effect by a pendant arm
was previously observed by Gibson et al.,21 who found that a
weakly bonding or nonbonding donor arm in the neutral
precursor becomes a strong ligand occupying the fourth
coordination position in the cation that stabilizes the electro-
positive metal center. The noncoordinating nature of the
[B(C6F5)4]- anion is further confirmed by the small chemical
Behavior of Complex 3 in Solution
shift difference (about ∆δ ) 3.9 ppm) between the m- and
p-fluorines in the 19F NMR spectra of 7 and 8.22
It is worth noting that proton resonances for both cationic
derivatives 7 and 8 are sharp and well-resolved even at low
temperatures (ca. -90 °C) in THF-d8, indicating the elevated
coordination energy of the ligand to the metal center and the
absence of any fluxional equilibrium involving the neutral
moiety of the ligand.
Preliminary Studies on Ring-Opening Polymerization
of E-Caprolactone Promoted by 3 and 4. Ring-opening
polymerization (ROP) of ꢀ-caprolactone (ꢀ-CL) has been well
established for a large number of lanthanide compounds and
so serves as an appropriate benchmark for the new compounds
described above. In general, the catalytic activities of the new
dialkyl complexes 3 and 4 toward ROP of ꢀ-CL (200 equiv per
metal center) were assessed in toluene solution at room
temperature. A rapid increase in the viscosity of the solution
was immediately observed and, after quenching with wet
toluene, the mixture was poured into ethanol or methanol/hexane
to precipitate poly(ꢀ-CL). The preliminary results are sum-
marized in Table 3. Complexes 3 and 4 exhibited remarkably
different behavior under rigorously identical polymerization
conditions. First, complex 3 yielded only traces of polymer after
1 min, while complex 4 was much more active and gave a
Figure 4. ORTEP view of 3. Ellipsoids are given at the 30%
probability level, and hydrogen atoms have been omitted for clarity.
Table 2. Bond Lengths (Å) and Angles (deg) for 3
Bond Lengths
Sc(1)-N(1)
Sc(1)-C(13)
Sc(1)-C(17)
Sc(1)-C(21)
2.279(4) Sc(1)-C(22)
2.213(5) Sc(1)-C(23)
2.232(5) Sc(1)-C(24)
2.482(5) Sc(1)-C(25)
2.466(6)
2.471(6)
2.491(6)
2.490(6)
(20) (a) Bambirra, S.; Meetsma, A.; Hessen, B.; Bruñís, A. P. Orga-
nometallics 2006, 25, 3486. (b) Bambirra, S.; Bouwkamp, M. W.; Meetsma,
A.; Hessen, B. J. Am. Chem. Soc. 2004, 126, 9182. (c) Elvidge, B. R.;
Arndt, S.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J. Inorg. Chem. 2005,
44, 6777.
Bond Angles
N(1)-Sc(1)-C(13)
N(1)-Sc(1)-C(17)
C(13)-Sc(1)-C(17)
C(2)-C(1)-C(21)
C(1)-C(2)-N(2)
103.1(2)
106.4(2)
99.7(2)
114.0(4)
115.7(4)
C(1)-C(2)-N(4)
N(2)-C(2)-N(4)
Sc(1)-C(13)-Si(2) 129.5(3)
Sc(1)-C(17)-Si(1) 131.0(3)
115.4(4)
107.5(4)
(21) Cameron, P.; Gibson, V. C.; Redshaw, C.; Segal, J. A.; Bruce, M.
D.; White, A. J. P.; Williams, D. J. Dalton Trans. 2002, 415.
(22) Blackwell, J. M.; Morrison, D. J.; Piers, W. E. Tetrahedron 2002,
58, 8247.

Sc and Y Complexes with Heteroscorpionate Ligands
Organometallics, Vol. 27, No. 5, 2008 981
Scheme 4. Preparation of Compounds 7 and 8
alkoxide propagating species.23 Thus, in addition to the main
Table 3. Ring-Opening Polymerization of E-Caprolactone initiated
by [Sc{CH2SiMe3}2(bpzcp)] (3) and [Y{CH2SiMe3}2(bpzcp)] (4)a
polymer chain peaks, a [C(O)CH2SiMe3] resonance was clearly
1
identified at δ 0.49 and 4.5 ppm in the H NMR and 13C{1H}
time
yieldb conversn
c
c
entry initiator (min)
(g)
(%)
Mn
Mw
PDIc
NMR spectra, respectively; additionally, the other end-group
1
2
3
4
5
6
7
8
9
3
3
3
3
4
4
4
4
4
5
10
30
60
1
0.338
0.389
0.352
0.212
0.175
0.251
0.312
0.281
0.116
65
75
68
40
33
47
59
53
22
20237 24134 1.19
25511 33291 1.30
22546 28977 1.28
7915 10014 1.26
(CH2OH) resonance was observed at δ 3.66 and 62.6 ppm in
1
the H NMR and 13C{1H} NMR spectra, respectively. This
suggests that both ends, P-CH2SiMe3 and P-CH2OH, of the
polymer chain result from a possible alkyl transfer in the
initiation stage and upon hydrolysis of the products, respectively.
5918
8068
7301 1.23
9980 1.23
5
10
30
60
9867 13077 1.32
8989 11456 1.27
Conclusion
3379
4269 1.26
a Polymerization conditions: 2.0 × 10-5 mol of complex 3 or 4, T )
25 °C; solvent toluene (4 mL); [ꢀ-CL]/[M] ) 200. b Isolated yield.
c Measured by GPC at 40 °C in THF relative to polystyrene standards.
An easy one-pot synthetic procedure based on the reaction
of bis(3,5-dimethylpyrazol-1-yl)methane with BunLi and ful-
venes and final hydrolysis with an aqueous solution of an
ammonium salt yielded the sterically encumbered scorpionate/
cyclopentadiene hybrid species 1 and 2. These compounds were
both isolated as a mixture of two tautomers. The potential utility
of these ligands as valuable scaffolds in organometallic chem-
istry has been verified through the preparation of new group 3
metal complexes. Thus, the series of neutral and cationic
scandium and yttrium complexes 3–8 were synthesized and
characterized by X-ray diffraction analysis and NMR spectro-
scopy.
Reaction of the neutral scandium and yttrium complexes 3
and 4 with the alkyl abstracting agent [Ph3C][B(C6F5)4]
produced the expected cationic derivatives 7 and 8 as borate
salts in which the bpzcp fragment was proposed to be
coordinated κ2NN-η5-Cp to the metal center.
Furthermore, the dialkyl complexes 3 and 4 proved to be
efficient initiators for the ring-opening polymerization (ROP)
of ꢀ-caprolactone, with the highest productivity being found for
the scandium complex 3. The polymerization takes place with
narrow molecular weight distributions and with a linear increase
of the peak molecular weight with conversion, which corre-
sponds to a living-polymerization. Work is currently under way
to increase the scope of this field.
Figure 5. Relationship between Mn and monomer conversion for
the polymerization of ꢀ-CL promoted by complex 4.
conversion of 33% after 1 min (entry 5). However, complex 3
showed a higher activity than complex 4 for longer reaction
times, with a conversion of 65% after 5 min and the highest
conversion of 75% after 10 min. Both complexes showed a
decrease in conversion with prolonged reaction times, and this
behavior may presumably be due to their high sensitivity toward
side reactions. Although the ꢀ-caprolactone used was exhaus-
tively dried (see Experimental Section), some deactivation of
the initiator could not be avoided.
Experimental Section
All reactions were performed using standard Schlenk-tube
techniques under an atmosphere of dry nitrogen. Solvents were
distilled from appropriate drying agents and degassed before use.
Microanalyses were carried out with a Perkin-Elmer 2400 CHN
analyzer. Mass spectra were recorded on a VG Autospec instrument
The polydispersity indexes (PDIs, evaluated by gel perme-
ation chromatography, GPC) of the polyesters formed with these
heteroscorpionate complexes (entry 1–9) range from 1.19 to 1.32
and the molecular weights (Mn) increase linearly in proportion
to the conversion (Figure 5), suggesting that the scandium (3)
and yttrium (4) dialkyl complex-initiated polymerization can
be considered to proceed in a living fashion.
1
using the FAB technique and nitrobenzyl alcohol as matrix. H,
13C, and 19F NMR spectra were recorded on a Varian Inova FT-
(23) (a) Yamashita, M.; Takemoto, Y.; Ihara, E.; Yasuda, H. Macro-
molecules 1996, 29, 1798. (b) Guillaume, S. M.; Schappacher, M.; Soum,
A. Macromolecules 2003, 36, 54. (c) Sarazin, Y.; Schormann, M.;
Bochmann, M. Organometallics 2004, 23, 3296. (d) Liu, X.; Shang, X.;
Tang, T.; Hu, N.; Pei, F.; Cui, D.; Chen, X.; Ping, X. Organometallics
2007, 26, 2747.
As expected, an end-group NMR study of various poly(ꢀ-
caprolactone) samples indicated that, in principle, polymerization
can be envisaged to occur by the transfer of the nucleophilic
alkyl ligands to the monomer with the formation of a metal

982 Organometallics, Vol. 27, No. 5, 2008
Otero et al.
500 (1H NMR 500 MHz, 13C NMR 125 MHz, and 19F NMR 470
MHz) spectrometer and referenced to the residual deuterated
solvent. The NOESY-1D spectra were recorded with the following
acquisition parameters: irradiation time 2 s and number of scans
256, using standard VARIAN-FT software. Two-dimensional NMR
spectra were acquired using standard VARIAN-FT software and
processed using an IPC-Sun computer. Gel permeation chroma-
tography (GPC) measurements were performed on a Polymer
Laboratories PL-GPC-220 instrument equipped with a PLgel 5 Å
Mixed-C column, a refractive index detector, and a PD2040 light-
scattering detector. The GPC column was eluted with THF at 40
°C at 1 mL/min and was calibrated using eight monodisperse
polystyrene standards in the range 580–483 000 Da.
Cp), 131.8 (C2-Cp), 133.4 (C3-Cp), 131.6 (C4-Cp), 40.9 (C5-Cp),
tautomer 2b, δ 74.1 (CH), 148.0, 146.3, 146.0, 139.6 (C3,3′ or 5,5′),
107.0, 106.1 (C4,4′), 14.3, 13.7 (Me3,3′), 11.5 (Me5,5′), 50.9 (Ca),
34.3 (C(CH3)3), 28.5 (C(CH3)3), 130.8 (C1-Cp), 128.3 (C2-Cp),
133.2 (C3-Cp), 131.4 (C4-Cp), 54.3 (C5-Cp).
Synthesis of [Sc(CH2SiMe3)2(bpzcp)] (3). A solution of bpzcpH
(1; 0.33 g, 0.76 mmol) in hexane (20 mL) was added dropwise to
a cooled (0 °C) solution of [Sc(CH2SiMe3)3(THF)3] (0.40 g, 0.76
mmol) in hexane (25 mL). The reaction mixture was stirred for
2 h at 0 °C, after which time a pale yellow precipitate had formed.
The solid was filtered off and dried under reduced pressure. This
material was recrystallized from toluene/hexane (10:1, 20 mL at
-20 °C) to give colorless crystals of the title compound. Yield:
72%. Anal. Calcd for C37H51N4ScSi2: C, 68.06; H, 7.87; N, 8.58.
Found: C, 68.45; H, 8.03; N, 8.21. 1H NMR (C6D6, 297 K): δ 6.45
(s, 1 H, CH), 5.24 (s, 2 H, H4), 2.55 (s, 6 H, Me3), 1.33 (s, 6 H,
Me5), 7.35–6.99 (m, 10 H, Ph), 5.86 (m, 2 H, H2,5-Cp), 6.96 (m,
2 H, H3,4-Cp), 0.52 (br s, 4 H, ScCH2SiMe3), 0.57 (s, 18 H,
ScCH2SiMe3). 13C{1H} NMR (C6D6, 297 K): δ 74.1 (CH), 144.2,
141.7 (C3 or 5), 108.0 (C4), 16.4 (Me3), 11.4 (Me5), 152.2–129.6
(Ph), 67.8 (Ca), 117.9 (C1-Cp), 120.1 (C2,5-Cp), 113.1 (C3,4-Cp),
41.8 (ScCH2SiMe3), 4.1 (ScCH2SiMe3).
Synthesis of [Y(CH2SiMe3)2(bpzcp)] (4). The synthetic proce-
dure was the same as for complex 3, using [Y(CH2SiMe3)3(THF)3]
(0.40 g, 0.70 mmol) and bpzcpH (1; 0.30 g, 0.70 mmol), to give 4
as a white solid. Yield: 75%. Anal. Calcd for C37H51N4Si2Y: C,
63.76; H, 7.37; N, 8.03. Found: C, 63.99; H, 7.62; N, 7.81. 1H
NMR (C6D6, 297 K): δ 6.90 (s, 1 H, CH), 5.19 (s, 2 H, H4), 2.40
(s, 6 H, Me3), 1.32 (s, 6 H, Me5), 7.10–6.95 (m, 10 H, Ph), 5.76
(m, 2 H, H2,5-Cp), 6.80 (m, 2 H, H3,4-Cp), -0.20 (d, JYH ) 2.9
Hz, 4 H, YCH2SiMe3), 0.48 (s, 18 H, YCH2SiMe3). 13C{1H} NMR
(C6D6, 297 K): δ 74.8 (CH), 145.2, 142.3 (C3 or 5), 108.0 (C4), 15.5
(Me3), 11.3 (Me5), 150.3–127.2 (Ph), 61.3 (Ca), 115.4 (C1-Cp),
118.3 (C2,5-Cp), 110.4 (C3,4-Cp), 30.5 (d, JYC ) 36.2 Hz,
YCH2SiMe3), 4.9 (YCH2SiMe3).
The compounds 6,6-diphenylfulvene and [Ph3C][B(C6F5)4] were
purchased from Aldrich. ꢀ-Caprolactone was purchased from
Aldrich, degassed and dried over CaH2 and over calcinated CaCl2,
and then freshly vacuum-distilled before use. The compounds
bdmpzm (bdmpzm ) bis(3,5-dimethylpyrazol-1-yl)methane),10
6-tert-butylfulvene,11 and [M(CH2SiMe3)3(THF)3]15 (M ) Sc, Y)
were prepared as reported previously.
Synthesis of a Mixture of Isomers 1a and 1b (bpzcpH). In a
250 mL Schlenk tube, bdmpzm (1.00 g, 4.89 mmol) was dissolved
in dry THF (70 mL) and cooled to -70 °C. A 1.6 M solution of
BunLi (3.06 mL, 4.89 mmol) in hexane was added, and the
suspension was stirred for 1 h. The reaction mixture was warmed
to 0 °C, and the resulting yellow suspension was treated with 6,6-
diphenylfulvene (0.75 g, 4.89 mmol). The solution was stirred for
40 min, and the product was hydrolyzed with 15 mL of saturated
aqueous NH4Cl (which was added dropwise). The organic layer
was extracted, dried over MgSO4 overnight, and filtered, and the
solvent was removed under vacuum to give the product as a yellow
oil. The oil was broken with a mixture of THF/hexane to give 1 as
a white solid. Yield: 92%. Anal. Calcd for C29H30N4: C, 80.15; H,
6.95; N, 12.89. Found: C, 80.31; H, 7.01; N, 12.75. 1H NMR (C6D6,
297 K): tautomer 1a, δ 7.92 (s, 1 H, CH), 5.57 (s, 2 H, H4), 2.07
(s, 6 H, Me3), 1.36 (s, 6 H, Me5), 7.53 (d, JHH ) 7.8 Hz, 4 H,
Ho-Ph), 7.25–7.04 (m, 6 H, Hm-Ph, Hp-Ph), 6.23 (m, 1 H, H2-Cp),
6.61 (m, 1 H, H3-Cp), 6.19 (m, 1 H, H4-Cp), 3.53 (brs, 2 H, H5-
Cp); tautomer 1b, δ 8.17 (s, 1 H, CH), 5.58 (s, 2 H, H4), 2.08 (s,
6 H, Me3), 1.46 (s, 6 H, Me5), 7.71 (d, JHH ) 7.5 Hz, 4 H, Ho-Ph),
7.25–7.04 (m, 6 H, Hm-Ph, Hp-Ph), 6.12 (m, 1 H, H1-Cp), 6.52
(m, 1 H, H3-Cp), 6.83 (m, 1 H, H4-Cp), 2.82 (brs, 2 H, H5-Cp).
13C{1H} NMR (C6D6, 297 K): tautomer 1a, δ 77.2 (CH), 149.9,
142.9 (C3 or 5), 106.1 (C4), 13.4 (Me3), 10.1 (Me5), 145.7, 131.7,
126.3, 125.7 (Ph), 60.9 (Ca), 141.5 (C1-Cp), 132.7 (C2-Cp), 131.1
(C3-Cp), 129.8 (C4-Cp), 42.6 (C5-Cp); tautomer 1b, δ 77.3 (CH),
153.9, 142.2 (C3 or 5), 106.1 (C4), 13.4 (Me3), 10.3 (Me5), 145.8,
131.4, 126.5, 125.9 (Ph), 62.1 (Ca), 135.3 (C1-Cp), 141.6 (C2-Cp),
131.2 (C3-Cp), 127.9 (C4-Cp), 40.8 (C5-Cp).
Synthesis of [Sc(CH2SiMe3)2(bpztcp)] (5). The synthetic pro-
cedure was the same as for complex 3, using [Sc(CH2SiMe3)3-
(THF)3] (0.40 g, 0.76 mmol) and bpztcpH (2; 0.25 g, 0.76 mmol),
to give 5 as a white solid. Yield: 68%. Anal. Calcd for
C29H51N4ScSi2: C, 62.54; H, 9.23; N, 10.06. Found: C, 62.84; H,
1
9.41; N, 9.79. H NMR (C6D6, 297 K): δ 6.33 (d, JHH ) 3.6 Hz,
1 H, CH), 5.27 (s, 2 H, H4,4′), 2.40, 2.30 (s, 3 H, 3 H, Me3,3′), 1.75
(s, 3 H, Me5′), 1.61 (s, 3 H, Me5), 2.91 (d, JHH ) 3.6 Hz, 1 H,
CHa), 0.96 (s, 9 H, C(CH3)3), 6.08 (m, 1 H, H2-Cp), 6.28 (m, 1 H,
H5-Cp), 6.95, 6.90 (m, 1 H, 1 H, H3,4-Cp), 0.30, 0.28 (br s, 2 H,
2 H, ScCH2SiMe3), 0.39 (s, 18 H, ScCH2SiMe3). 13C{1H} NMR
(C6D6, 297 K): δ 66.3 (CH), 151.5, 150.2, 140.6, 139.4 (C3,3′ or 5,5′),
107.4, 107.2 (C4,4′), 15.1, 15.0 (Me3,3′), 12.2 (Me5′), 11.2 (Me5),
58.2 (Ca), 35.2 (C(CH3)3), 28.8 (C(CH3)3), 112.4 (C1-Cp), 112.9
(C2-Cp), 115.8 (C3-Cp), 112.8, 110.3 (C4,5-Cp), 33.0, 30.6
(ScCH2SiMe3), 5.4 (ScCH2SiMe3).
Synthesis of a Mixture of Isomers 2a and 2b (bpztcpH). The
synthetic procedure was the same as for compound 1, using
bdmpzm (2.00 g, 9.79 mmol), a 1.6 M solution of BunLi (6.12
mL, 9.79 mmol) and 6-tert-butylfulvene (1.32 g, 9.79 mmol), to
give 2 as a white solid. Yield: 90%. Anal. Calcd for C21H30N4: C,
Synthesis of [Y(CH2SiMe3)2(bpztcp)] (6). The synthetic pro-
cedure was the same as for complex 3, using [Y(CH2-
SiMe3)3(THF)3] (0.40 g, 0.70 mmol) and bpztcpH (2; 0.23 g, 0.70
mmol), to give 6 as a white solid. Yield: 70%. Anal. Calcd for
C29H51N4Si2Y: C, 57.97; H, 8.55; N, 9.32. Found: C, 58.31; H,
1
74.51; H, 8.93; N, 16.55. Found: C, 74.62; H, 9.03; N, 16.43. H
NMR (C6D6, 297 K): tautomer 2a, δ 6.86 (d, JHH ) 11.2 Hz, 1 H,
CH), 5.57, 5.41 (s, 1 H, 1H, H4,4′), 2.19, 2.08 (s, 3 H, 3 H, Me3,3′),
2.40, 2.28 (s, 3 H, 3 H, Me5,5′), 4.44 (m, 1 H, CHa), 0.87 (s, 9 H,
C(CH3)3), 6.18 (m, 1 H, H2-Cp), 6.12 (m, 1 H, H3-Cp), 6.27 (m, 1
1
8.92; N, 9.10. H NMR (C6D6, 297 K): δ 6.27 (s, 1 H, CH), 5.33
(s, 2 H, H4,4′), 2.40, 2.26 (s, 3 H, 3 H, Me3,3′), 1.78 (s, 3 H, Me5′),
1.64 (s, 3 H, Me5), 2.59 (s, 1 H, CHa), 0.80 (s, 9 H, C(CH3)3), 5.67
(m, 1 H, H2-Cp), 6.16 (m, 1 H, H5-Cp), 6.95, 6.88 (m, 1 H, 1 H,
H3,4-Cp), -0.19 (dd, JHH ) 11.2 Hz, JYH ) 2.9 Hz, 2 H,
YCH2SiMe3), -0.45 (dd, JHH ) 10.7 Hz, JYH ) 2.9 Hz, 2 H,
YCH2SiMe3), 0.55 (s, 18 H, YCH2SiMe3). 13C{1H} NMR (C6D6,
297 K): δ 66.4 (CH), 151.9, 150.8, 140.5, 139.0 (C3,3′ or 5,5′), 107.9,
107.0 (C4,4′), 15.6, 15.3 (Me3,3′), 12.1 (Me5′), 11.1 (Me5), 57.9 (Ca),
34.9 (C(CH3)3), 28.5 (C(CH3)3), 112.2 (C1-Cp), 112.9 (C2-Cp),
116.0 (C5-Cp), 112,9, 110.1 (C3,4-Cp), 33.1, (d, JYC ) 37.4 Hz,
H, H4-Cp), 2.38 (br, 2 H, H5-Cp); tautomer 2b, δ 6.99 (d, JHH
)
10.2 Hz, 1 H, CH), 5.62, 5.45 (s, 1 H, 1 H, H4,4′), 2.21, 2.14 (s, 3
H, 3 H, Me3,3′), 2.40, (s, 6 H, Me5,5′), 4.64 (m, 1 H, CHa), 0.92 (s,
9 H, C(CH3)3), 5.96 (m, 1 H, H1-Cp), 6.50 (m, 1 H, H3-Cp), 6.05
(m, 1 H, H4-Cp), 5.56 (br, 2 H, H5-Cp). 13C{1H} NMR (C6D6,
297 K): tautomer 2a, δ 74.9 (CH), 146.7, 145.2, 140.0, 139.8
(C3,3 or 5,5′), 107.0, 106.1 (C4,4′), 13.8, 13.6 (Me3,3′), 12.0, 11.5
(Me5,5′), 51.3 (Ca), 34.7 (C(CH3)3), 28.6 (C(CH3)3), 130.5 (C1-

Sc and Y Complexes with Heteroscorpionate Ligands
Organometallics, Vol. 27, No. 5, 2008 983
Table 4. Crystal Data and Structure Refinement Details for 2b and 3
YCH2SiMe3), 28.6 (d, JYC ) 35.3 Hz, YCH2SiMe3), 5.2
(YCH2SiMe3).
2b
C21H30N4
338.49
180(2)
3
Synthesis of [Sc(CH2SiMe3)(bpzcp)][B(C6F5)4] (7). In a 100
mL Schlenk tube, [Sc(CH2SiMe3)2(bpzcp)] (3; 40.0 mg, 0.06 mmol)
and [PPh3][B(C6F5)4] (50.0 mg, 0.06 mmol) were dissolved in THF
(8.0 mL). The resulting bright yellow solution was stirred for 30
min at room temperature and then evaporated to dryness to yield a
yellow solid. The residue was washed with hexane (5.0 mL). The
solvent was filtered off by a short cannula and the resulting solid
dried under vacuum to afford complex 7 as a yellow solid. Yield:
65%. Anal. Calcd for C57H40BF20N4ScSi: C, 54.99; H, 3.24; N,
empirical formula
formula wt
temp (K)
C37H51N4ScSi2 · C6H14
739.13
200(2)
wavelength (Å)
crystal syst
space group
a (Å)
b (Å)
c (Å)
0.710 73
triclinic
P1
0.710 73
triclinic
j
j
P1
8.817(5)
10.720(5)
10.796(5)
90.095(9)
103.026(9)
99.885(8)
978.6(9)
2, 1.149
0.069
12.093(2)
12.191(2)
17.037(3)
83.874(3)
70.672(3)
67.402(2)
2187.4(7)
2, 1.122
0.255
R (deg)
1
4.50. Found: C, 55.51; H, 3.57; N, 4.05. H NMR (THF-d8, 297
ꢀ (deg)
K): δ 6.91 (s, 1 H, CH), 6.09 (s, 2 H, H4), 2.20 (s, 6 H, Me3), 2.15
(s, 6 H, Me5), 7.37–7.11 (m, 10 H, Ph), 5.69 (m, 2 H, H2,5-Cp),
6.96 (m, 2 H, H3,4-Cp), -0.22 (br, 2 H, ScCH2SiMe3), 0.07 (s, 9
H, ScCH2SiMe3). 13C{1H} NMR (THF-d8, 297 K): δ 75.2 (CH),
145.7, 144.9 (C3 or 5), 109.2 (C4), 14.6 (Me3), 11.5 (Me5), 150.3–128.3
(Ph), 62.0 (Ca), 116.8 (C1-Cp), 118.0 (C2,5-Cp), 111.5 (C3,4-Cp),
43.5 (ScCH2SiMe3), 4.8 (ScCH2SiMe3). 19F NMR (THF-d8, 297
K): δ -133.4 (s, 2 F, o-C6F5), -163.9 (t, 3JFF ) 21.4, 2 F, m-C6F5),
-167.8 (s, 1 F, p-C6F5).
γ (deg)
V (A3)
Z, calcd density (g/cm3)
abs coeff (mm-1
F(000)
)
368
800
cryst size (mm)
limiting indices
0.35 × 0.15 × 0.20 0.51 × 0.27 × 0.12
-7 e h e 8
-10 e k e 9
-10 e l e 9
-11 e h e 11
-11 e k e 11
-15 e l e 13
6581/3211
no. of collected/unique rflns 3409/1568
R(int) 0.0628
0.0411
Synthesis of [Y(CH2SiMe3)(bpzcp)][B(C6F5)4] (8). The syn-
thetic procedure was the same as for complex 7, using [Y(CH2-
SiMe3)2(bpzcp)] (4; 40.0 mg, 0.05 mmol) and [PPh3][B(C6F5)4](45.0
mg, 0.05 mmol), to give 8 as a bright yellow solid. Yield: 70%.
Anal. Calcd for C57H40BF20N4SiY: C, 53.12; H, 3.12; N, 4.34.
no. of data/restraints/params 1568/0/257
3211/0/474
1.023
goodness of fit on F2
0.947
final R indices (I > 2σ(I))
R1 ) 0.0615
wR2 ) 0.1564
R1 ) 0.0811
wR2 ) 0.1802
R1 ) 0.0475
wR2 ) 0.1166
R1 ) 0.0697
wR2 ) 0.1334
0.248, -0.262
R indices (all data)
1
Found: C, 53.69; H, 3.42; N, 4.09. H NMR (THF-d8, 297 K): δ
largest diff peak, hole (e Å-3) 0.207, -0.261
7.35 (s, 1 H, CH), 6.17 (s, 2 H, H4), 2.25 (s, 6 H, Me3), 2.17 (s, 6
H, Me5), 7.30–7.09 (m, 10 H, Ph), 5.71 (m, 2 H, H2,5-Cp), 6.98
(m, 2 H, H3,4-Cp), -0.76 (d, JYH ) 2.9 Hz, 2 H, YCH2SiMe3),
0.06 (s, 9 H, YCH2SiMe3). 13C{1H} NMR (THF-d8, 297 K): δ 74.4
(CH), 146.4, 145.0 (C3 or 5), 109.5 (C4), 14.4 (Me3), 11.8 (Me5),
150.1–128.2 (Ph), 61.2 (Ca), 117.1 (C1-Cp), 118.2 (C2,5-Cp), 111.2
(C3,4-Cp), 42.1 (d, JYC ) 59.9 Hz, YCH2SiMe3), 4.6 (YCH2SiMe3).
19F NMR (THF-d8, 297 K): δ -133.4 (s, 2 F, o-C6F5), -163.9 (t,
3JFF ) 21.4, 2 F, m-C6F5), -167.8 (s, 1 F, p-C6F5).
solved by direct methods using SHELXTL26 and refined by full-
matrix least-squares methods based on F2. All non-hydrogen atoms
were refined with anisotropic thermal parameters. Hydrogen atoms
were placed using a “riding model” and included in the refinement
at calculated positions. Complex 3 crystallizes with a hexane
molecule, which shows C55 in a disordered position (0.63 popula-
tion).
Typical Living Polymerization of E-Caprolactone by [Sc-
(CH2SiMe3)2(bpzcp)] (3) and [Y(CH2SiMe3)2(bpzcp)] (4). To a
stirred toluene solution (4–5 mL) of 3 or 4 (0.02 mmol) was added
ꢀ-caprolactone (4.0 mmol) by syringe. The mixture was magneti-
cally stirred at room temperature for different times. The viscous
mixture was quenched with wet toluene and poured into ethanol
or methanol/hexane. The white polymer was filtered off and dried
under vacuum to a constant weight.
X-ray Crystallography. Data for compounds 2b and 3 were
collected on a Bruker X8 APPEX II CCD-based diffractometer,
equipped with a graphite-monochromated Mo KR radiation source
(λ ) 0.710 73 Å). The crystal data, data collection, structural
solution, and refinement parameters are summarized in Table 4.
Data were integrated using SAINT,24 and an absorption correction
was performed with the program SADABS.25 The structure was
Acknowledgment. We gratefully acknowledge financial
support from the Ministerio de Educación y Ciencia (MEC)
of Spain (Grant Nos. CTQ2005-08123-CO2-01/BQU, Con-
solider-Ingenio 2010 CSD2007-00006) and the Junta de
Comunidades de Castilla-La Mancha (Grant No. PBI05-023).
Supporting Information Available: CIF files giving details of
data collection, refinement, atom coordinates, anisotropic displace-
ment parameters, and bond lengths and angles for complexes 2b
and 3. This material is available free of charge via the Internet at
http://pubs.acs.org.
OM701033R
(25) Sheldrick, G. M. SADABS version 2004/1. A Program for
Empirical Absorption Correction; University of Göttingen, Göttingen,
Germany, 2004.
(24) SAINT+v7.12a: Area-Detector Integration Program; Bruker-Nonius
AXS, Madison, WI, 2004.
(26) SHELXTL-NT version 6.12. Structure Determination Package;
Bruker-Nonius AXS, Madison, WI, 2001.