Group 13 and lanthanide complexes supported by tridentate tripodal triamine ligands: Structural diversity and polymerization catalysis

Article abstract of DOI:10.1021/om700587w

Several different synthetic approaches to a total of 13 novel B, Al, and Sm complexes derived from the tridentate tripodal triamine ligand [N ₃]H₃ with a neopentane, trisilylmethane, or trisilylsilane backbone and different N-substituents, as well as applications of the selected complexes to polymerization catalysis, are reported. Salt metathesis between HC[SiMe₂N(CH₂Ph)]₃Li₃(THF) ₂ (THF = tetrahydrofuran) and AlCl₃ in Et ₂O/hexanes leads to complete elimination of LiCl and formation of the corresponding tripodal triamido alane HC[SiMe₂N(CH ₂Ph)]₃Al-(THF) (1). On the other hand, the reaction of {MeC[CHN(SiMe₃)]₃Li₃}₂ and AlCl ₃ in Et₂O/hexanes yields a LiCl-containing compound MeC[CH₂N(SiMe₃)]₃AlCl[Li(Et₂O)] (2). Alkane elimination involving [N₃]H₃ and 1 AlMe ₃ produces diamido-amino aluminum methyl HC[SiMe₂NHAr] [SiMe₂NAr]₂AlMe [Ar = 4-MeC₆H₄ (3), CH₂Ph (4)], while the reaction using ≥2 AlMe₃ gives amido-amino aluminum dimethyl [ArHNMe₂Si](H)C[SiMe ₂NAr]₂(AlMe₂)₂ (Ar = 4-MeC ₆H₄, 5) and [(Me₃Si)HNCH₂](Me) C[CH₂N(SiMe₂]₂(AlMe₂)₂ (6). The H₂-elimination route involves treatment of [N ₃]H₃ with LiAlH₄ and AlH₃, affording [{HC[SiMe₂N(4-MeC₆H₄)]₃AlH}Li] ₂ (7) and MeSi[SiMe₂N(4-MeC₆H ₄)]₃AlH(AlH₂) (8), respectively. There is no reaction between [N₃]H₃ and Al[N(SiMe₃) ₂]₃; however, the amine-elimination reaction using Sm[N(SiMe₃)₂]₃ produces tripodal triamido Sm complex {MeSi[SiMe₂N(4-MeC₆H₄)] ₃Sm}₂ (9). Ligand exchange between tripodal borane HC[SiMe₂N(4MeC₆H₄]₃B and AlR ₃ (R = Me, H) offers the first-step ligand exchange product HC[SiMe₂N(4-MeC₆H₄)]₃BMe(AlMe ₂) (10) or the second-step ligand:exchange product HC[SiMe ₂N(4-MeC₆H₄)]₃AlH(BH₂) (11). Activation of dimethyl metallocenes LZrMe₂ by HC[SiMe ₂N(4-MeC₆H₄)]₃B produces ligand redistribution products LZrMe[N(4-MeC₆H₄)SiMe ₂](H)C[SiMe₂N(4-MeC₆H₄)]2BMe [L = Cp₂ (12), rac-Et(Ind)₂ (13)]. Besides characterizations by NMR and elemental analysis of the above new complexes, six of them (2, 4, 5, 8, 9, and 13) have also been structurally characterized by X-ray single-crystal diffraction studies. "Activated" metallocene complexes 12 and 13 are inactive for ethylene or propylene polymerization. Complex 1 exhibits low activity for ring-opening polymerization (ROP) of propylene oxide, but high activity for ROP of ε-caprolactone (CL). Significantly, tripodal aluminum hydride 8 effects catalytic ROP of CL upon addition of benzyl alcohol as a chain-transfer reagent.

Full text of DOI:10.1021/om700587w

Organometallics 2007, 26, 5395-5405
5395
Group 13 and Lanthanide Complexes Supported by Tridentate
Tripodal Triamine Ligands: Structural Diversity and
Polymerization Catalysis
Hongping Zhu and Eugene Y.-X. Chen*
Department of Chemistry, Colorado State UniVersity, Fort Collins, Colorado 80523-1872
ReceiVed June 14, 2007
Several different synthetic approaches to a total of 13 novel B, Al, and Sm complexes derived from
the tridentate tripodal triamine ligand [N3]H3 with a neopentane, trisilylmethane, or trisilylsilane backbone
and different N-substituents, as well as applications of the selected complexes to polymerization catalysis,
are reported. Salt metathesis between HC[SiMe2N(CH2Ph)]3Li3(THF)2 (THF ) tetrahydrofuran) and AlCl3
in Et2O/hexanes leads to complete elimination of LiCl and formation of the corresponding tripodal triamido
alane HC[SiMe2N(CH2Ph)]3Al‚(THF) (1). On the other hand, the reaction of {MeC[CHN(SiMe3)]3Li3}2
and AlCl3 in Et2O/hexanes yields a LiCl-containing compound MeC[CH2N(SiMe3)]3AlCl[Li(Et2O)] (2).
Alkane elimination involving [N3]H3 and 1 AlMe3 produces diamido-amino aluminum methyl HC-
[SiMe2NHAr][SiMe2NAr]2AlMe [Ar ) 4-MeC6H4 (3), CH2Ph (4)], while the reaction using g2 AlMe3
gives amido-amino aluminum dimethyl [ArHNMe2Si](H)C[SiMe2NAr]2(AlMe2)2 (Ar ) 4-MeC6H4, 5)
and [(Me3Si)HNCH2](Me)C[CH2N(SiMe3)]2(AlMe2)2 (6). The H2-elimination route involves treatment
of [N3]H3 with LiAlH4 and AlH3, affording [{HC[SiMe2N(4-MeC6H4)]3AlH}Li]2 (7) and MeSi[SiMe2N-
(4-MeC6H4)]3AlH(AlH2) (8), respectively. There is no reaction between [N3]H3 and Al[N(SiMe3)2]3;
however, the amine-elimination reaction using Sm[N(SiMe3)2]3 produces tripodal triamido Sm complex
{MeSi[SiMe2N(4-MeC6H4)]3Sm}2 (9). Ligand exchange between tripodal borane HC[SiMe2N(4-
MeC6H4)]3B and AlR3 (R ) Me, H) offers the first-step ligand exchange product HC[SiMe2N(4-MeC6H4)]3-
BMe(AlMe2) (10) or the second-step ligand exchange product HC[SiMe2N(4-MeC6H4)]3AlH(BH2) (11).
Activation of dimethyl metallocenes LZrMe2 by HC[SiMe2N(4-MeC6H4)]3B produces ligand redistribution
products LZrMe[N(4-MeC6H4)SiMe2](H)C[SiMe2N(4-MeC6H4)]2BMe [L ) Cp2 (12), rac-Et(Ind)2 (13)].
Besides characterizations by NMR and elemental analysis of the above new complexes, six of them (2,
4, 5, 8, 9, and 13) have also been structurally characterized by X-ray single-crystal diffraction studies.
“Activated” metallocene complexes 12 and 13 are inactive for ethylene or propylene polymerization.
Complex 1 exhibits low activity for ring-opening polymerization (ROP) of propylene oxide, but high
activity for ROP of ꢀ-caprolactone (CL). Significantly, tripodal aluminum hydride 8 effects catalytic
ROP of CL upon addition of benzyl alcohol as a chain-transfer reagent.
double bonds between this center and its neighboring atoms
can significantly reduce or quench its Lewis acidity. On the
one hand, the incorporation of three strongly electron-withdraw-
ing perfluoroaryl ligands, e.g., E(C6F5)3 (E ) B, Al), further
enhances its Lewis acidity as well as the chemical robustness
of the resulting anion from the abstractive reaction between such
a LA and a transition-metal substrate carrying a basic or
nucleophilic ligand.2 A caveat for the activation process of
generating catalytically active ion pairs is the energy penalty
paid for the geometry reorganizationsfrom planar triangle to
monotrigonal pyramid at the LA center, excluding the abstracted
ligand. We viewed this situation as an opportunity for the design
of three-coordinate B and Al complexes adopting a preorganized
pyramidal geometry for enhanced Lewis acidity,4 based on the
reasoning that such a geometry not only provides a vacant sp3
orbital disposed ideally to accept a fourth donor ligand, but also
significantly suppresses the energy penalty for the geometry
reorganization during the LA-mediated chemical processes.
On the basis of the above working hypothesis, we4a recently
reported the synthesis and structure of such pyramidal B and
Introduction
There has been broad interest in organoboron and aluminum
Lewis acids (LAs) since they are essential as reagents, catalysts,
cocatalysts, initiators, and scavengers or stabilizers in organic
synthesis,1 olefin polymerization catalysis,2 and polymerization
of polar monomers.3 A three-coordinate, σ-bound boron or
aluminum center, in general, exhibits strong Lewis acidity due
to its electron deficiency; however, the formation of partial
* To whom correspondence should be addressed. E-mail: eychen@
lamar.colostate.edu.
(1) For reviews, see: (a) Ishihara, K. In Lewis Acids in Organic Synthesis,
Vol. 1; Yamamoto, H., Ed.; Wiley-VCH: Weinheim, Germany, 2000; pp
89-190. (b) Ooi, T.; Maruoka, K. In Lewis Acids in Organic Synthesis,
Vol. 1; Yamamoto, H., Ed.; Wiley-VCH: Weinheim, Germany, 2000; pp
191-282. (c) Wulff, W. D. In Lewis Acids in Organic Synthesis, Vol. 1;
Yamamoto, H., Ed.; Wiley-VCH: Weinheim, Germany, 2000; pp 283-
354.
(2) For reviews, see: (a) Piers, W. E. AdV. Organomet. Chem. 2005,
52, 1-76. (b) Erker, G. Dalton Trans. 2005, 1883-1890. (c) Pedeutour,
J.-N.; Radhakrishnan, K.; Cramail, H.; Deffieux, A. Macromol. Rapid
Commun. 2001, 22, 1095-1123. (d) Chen, E. Y.-X.; Marks, T. J. Chem.
ReV. 2000, 100, 1391-1434.
(3) For reviews, see: (a) Mecerreyes, D.; Jerome, R.; Dubois, P. AdV.
Polym. Sci. 1999, 147, 1-59. (b) Sugimoto, H.; Inoue, S. AdV. Polym. Sci.
1999, 146, 39-119. (c) Kuran, W. Prog. Polym. Sci. 1998, 23, 919-992.
(4) (a) Zhu, H.; Chen, E. Y.-X. Inorg. Chem. 2007, 46, 1481-1487. (b)
Jansen, G.; Schubart, M.; Findeis, B.; Gade, L. H.; Scowen, I. J.; McPartlin,
M. J. Am. Chem. Soc. 1998, 120, 7239-7251.
10.1021/om700587w CCC: $37.00 © 2007 American Chemical Society
Publication on Web 10/02/2007

5396 Organometallics, Vol. 26, No. 22, 2007
Zhu and Chen
Scheme 1
examine the reactivity and catalytic activity of the selected
tripodal amido borane and alane complexes. Accordingly, our
second goal of the current work was to investigate the
abstractive chemistry of the tripodal borane pertinent to olefin
polymerization catalysis as well as ROP of propylene oxide and
ꢀ-caprolactone (CL) by the tripodal alanes. For the CL polym-
erization, we emphasized the ROP of CL, employing an alcohol
as chain-transfer reagent (CTR)15 and a tripodal alane as catalyst
for the catalytic production of biodegradable poly(ꢀ-caprolac-
tone).
Al complexes (e.g., structures A and B shown in Scheme 1)
incorporating Gade’s tripodal triamido [N3]3- ligands5 having
the trisilylmethane or trisilylsilane backbone. A related ligand
system is the tetradentate tripodal triamidoamine N[N3]3- lig-
and; main-group (e.g., Verkade’s boron and aluminum aza-
tranes6) and transition-metal complexes bearing such a ligand
have been extensively studied by Verkade7 and Schrock.8
Another related ligand system is the tridentate diamidoamine
N[N2]2- ligand, main-group B and Al complexes of which are
also well-established.9 On the other hand, to the best of our
knowledge, B and Al complexes bearing the tridentate tripodal
triamido [N3]3- ligand were unknown prior to our recent report,4a
and this ligand system has not been employed for the synthesis
of relevant trivalent lanthanide (Ln) complexes, although its
complexes with the yttrium center10 and commonly the tetrava-
lent metal centers including those of group 4 metals11 are known.
The tripodal triamido borane [N3]B can now be readily prepared,
but the degree of pyramidalization in structure A is not
remarkable.4a The synthetic routes to the analogous alane
resulted in the formation of “[N3]Al” as a salt (LiCl) or donor-
solvent (tetrahydrofuran (THF)) adduct, implying a highly Lewis
acidic Al center in [N3]Al; however, the coordinated LiCl or
THF in structure B cannot be removed via various methods.
Hence, the first goal of the current work was to investigate
various synthetic approaches that could potentially lead to
isolation of the elusive salt- and solvent-free tripodal triamido
Al and Ln complexes, [N3]Al and [N3]Ln, with variations in
the peripheral N-substituents and ligand backbone framework
(including neopentane, trisilylmethane, and trisilylsilane back-
bones).
Experimental Section
Materials and Methods. All syntheses and manipulations of
air- and moisture-sensitive materials were carried out in flamed
Schlenk-type glassware on a dual-manifold Schlenk line, on a high-
vacuum line, or in an argon- or nitrogen-filled glovebox. HPLC
grade organic solvents were sparged extensively with nitrogen
during filling of the solvent reservoir and then dried by passage
through activated alumina (for THF, Et2O, and CH2Cl2) followed
by passage through Q-5-supported copper catalyst (for toluene and
hexanes) stainless steel columns. Benzene-d6 and toluene-d8 were
degassed, dried over sodium/potassium alloy, and filtered before
use, whereas CDCl3 and CD2Cl2 were degassed and dried over
activated Davison 4 Å molecular sieves. Propylene oxide and
ꢀ-caprolactone were degassed and dried over CaH2 overnight and
then vacuum-distilled before use. NMR spectra were recorded on
1
a Varian Inova 300 (FT 300 MHz, H; 96 MHz, 11B; 75 MHz,
13C) or a Varian Inova 400 spectrometer. Chemical shifts for H
1
(12) For selected recent examples, see: (a) Nomura, N.; Ishii, R.;
Yamamoto, Y.; Kondo, T. Chem. Eur. J. 2007, 13, 4433-4451. (b) Du,
H.; Pang, X.; Yu, H.; Zhuang, X.; Chen, X.; Cui, D.; Wang, X.; Jing, X.
Macromolecules 2007, 40, 1904-1913. (c) Chisholm, M. H.; Patmore, N.
J.; Zhou, Z. Chem. Commun. (Cambridge) 2005, 127-129. (d) Hormnirun,
P.; Marshall, E. L.; Gibson, V. C.; White, A. J. P.; Williams, D. J. J. Am.
Chem. Soc. 2004, 126, 2688-2689. (e) Dechy-Cabaret, O.; Martin-Vaca,
B.; Bourissou, D. Chem. ReV. 2004, 104, 6147-6176. (f) Zhong, Z.;
Dijkstra, P.; Feijen, J. J. Am. Chem. Soc. 2003, 125, 11291-11298. (g)
Nomura, N.; Ishii, R.; Akakura, M.; Aoi, K. J. Am. Chem. Soc. 2002, 124,
5938-5939. (h) Ovitt, T. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem.
Soc. 2002, 124, 1316-1326. (i) O’Keefe, B. J.; Hillmyer, M. A.; Tolman,
W. B. R. J. Chem. Soc., Dalton Trans. 2001, 2215-2224. (j) Jhurry, D.;
Bhaw-Luximon, A.; Spassky, N. Macromol. Symp. 2001, 175, 67-79. (k)
Radano, C. R.; Baker, G. L.; Smith, M. R. J. Am. Chem. Soc. 2000, 122,
1552-1553.
(13) For selected recent examples, see: (a) Milione, S.; Grisi, F.; Centore,
R.; Tuzi, A. Organometallics 2006, 25, 266-274. (b) Amgoune, A.;
Lavanant, L.; Thomas, C. M.; Chi, Y.; Welter, R.; Dagorne, S.; Carpentier,
J.-F. Organometallics 2005, 24, 6279-6282. (c) Lewin´ski, J.; Horeglad,
P.; Tratkiewicz, E.; Grzenda, W.; Lipkowski, J.; Kolodziejczyk, E.
Macromol. Rapid Commun. 2004, 25, 1939-1942. (d) Chen, C.-T.; Huang,
C.-A.; Huang, B.-H. Macromolecules 2004, 37, 7968-7973. (e) Alcazar-
Roman, L. M.; O’Keefe, B. J.; Hillmyer, M. A.; Tolman, W. B. Dalton
Trans. 2003, 3082-3087. (f) Liao, T.-C.; Huang, Y.-L.; Huang, B.-H.; Lin,
C.-C. Macromol. Chem. Phys. 2003, 204, 885-892. (g) Chakraborty, D.;
Chen, E. Y.-X. Organometallics 2003, 22, 769-774. (h) Chakraborty, D.;
Chen, E. Y.-X. Organometallics 2002, 21, 1438-1442. (i) Hsueh, M.-L.;
Huang, B.-H.; Lin, C.-C. Macromolecules 2002, 35, 5763-5768. (j) Yu,
R.-C.; Hung, C.-H.; Huang, J.-H.; Lee, H.-Y.; Chen, J.-T. Inorg. Chem.
2002, 41, 6450-6455. (k) Liu, Y.-C.; Ko, B.-T.; Lin, C.-C. Macromolecules
2001, 34, 6196-6201.
(14) For selected recent examples, see: (a) Wasserman, E. P.; Annis, I.;
Chopin, L. J., III; Price, P. C.; Petersen, J. L.; Abboud, K. A. Macromol-
ecules 2005, 38, 322-333. (b) Chisholm, M. H.; Zhou, Z. J. Am. Chem.
Soc. 2004, 126, 11030-11039. (c) Chakraborty, D.; Rodriguez, A.; Chen,
E. Y.-X. Macromolecules 2003, 36, 5470-5481. (d) Braune W.; Okuda, J.
Angew. Chem., Int. Ed. 2003, 42, 64-77468. (e) Chisholm, M. H.; Gallucci,
J.; Phomphrai, K. Inorg. Chem. 2002, 41, 2785-2794. (f) Munoz-
Hernandez, M.-A.; Mckee, M. L.; Keizer, T. S.; Yearwood, B. C.; Atwood,
D. A. J. Chem. Soc., Dalton Trans. 2002, 410-414. (g) Antelmann, B.;
Chisholm, M. H.; Iyer, S.; Huffman, J. C.; Navarro-Llobet, D.; Pagel, M.;
Simonsick, W. J.; Zhong, W. Macromolecules 2001, 34, 3159-3174.
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1530-1535. (b) Nomura, N.; Taira, A.; Tomioka, T.; Okada, M. Macro-
molecules 2000, 33, 1497-1499.
A wide range of organoaluminum and boron complexes have
been extensively used as potent olefin polymerization activators2
as well as efficient catalysts or initiators for ring-opening
polymerization (ROP) of heterocyclic monomers3 including
lactides,12 lactones,13 and epoxides.14 Thus, it is of interest to
(5) For reviews, see: (a) Gade, L. H. Acc. Chem. Res. 2002, 35, 575-
582. (b) Gade, L. H. Chem. Commun. (Cambridge) 2000, 173-181. (c)
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J. G. J. Am. Chem. Soc. 1993, 115, 3925-3931.
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Rhatigan, B. Organometallics 2000, 19, 963-965.

Tridentate Tripodal Triamine Ligand Complexes
Organometallics, Vol. 26, No. 22, 2007 5397
and 13C spectra were referenced to internal solvent resonances and
reported as parts per million relative to SiMe4, while chemical shifts
for 11B spectra were referenced to external standard BF3‚Et2O. IR
spectra were recorded on a Nicolet Magna-760 FT/IR instrument.
Elemental analyses were performed by Desert Analytics, Tucson,
AZ. Unless otherwise specified, all commercial reagents were
purchased from Aldrich Chemical Co. and used as received.
Literature procedures were employed for the preparation of the
following neutral tripodal amido ligands as well as Al, B, and Zr
complexes: HC[SiMe2NHAr]3 (Ar ) 4-MeC6H4, CH2Ph),16
MeSi[SiMe2NHAr]3 (Ar ) 4-MeC6H4),17 MeC[CH2NH(SiMe3)]3,18
AlH3,19 Al[N(SiMe3)2]3,20 Sm[N(SiMe3)2]3,21 HC[SiMe2NAr]3B (Ar
) 4-MeC6H4),4a Cp2ZrMe2,22 and rac-Et(Ind)2ZrMe2.23
slowly heated to reflux for 4 h. The solution was cooled to ambient
temperature and evaporated to dryness under vacuum. The residue
was extracted with hexanes (5 mL), and the hexanes extract was
kept at -30 °C for ca. 2 months, affording 0.15 g (25%) of 3 as an
1
off-white solid. H NMR (C6D6, 23 °C): δ 7.23 (d, 4H), 7.11 (d,
4H), 6.68 (br, 4H) (4-MeC6H4), 3.85 (s, 1H, NH), 2.21 (s, 6H),
1.93 (s, 3H) (4-MeC6H4), 0.45 (br, 12H), 0.21 (br, 6H) (SiMe2),
-0.69 (s, 3H, AlMe), -0.76 (s, 1H, HC). Complex 4 was
synthesized in a manner similar to that of 3. AlMe3 (0.55 mL, 2.0
M in hexanes, 1.10 mmol), HC[SiMe2NH(CH2Ph)]3 (0.56 g, 1.10
mmol), and toluene (30 mL) were used, producing 0.50 g (83%
yield) of 4 as a colorless crystalline solid. 1H NMR (C6D6, 23 °C):
δ 7.53 (d), 7.32 (t), 7.18 (br), 6.98-7.02 (br m), 6.78-6.83 (br m)
(15H, CH2Ph), 4.25-4.32 (m, 4H), 3.52-3.82 (m, 2H) (CH2Ph),
1.95 (dd, 1H, NH), 0.25 (s), 0.18 (s), 0.03 (br) (18H, SiMe2), -0.54
Synthesis of HC[SiMe2N(CH2Ph)]3Al‚(THF) (1). HC[SiMe2N-
(CH2Ph)]3Li3(THF)2 was first isolated from the reaction of HC-
n
1
[SiMe2NH(CH2Ph)]3 (0.61, 1.20 mmol) and BuLi (2.25 mL, 1.6
(s, 3H, AlMe), -0.95 (s, 1H, HC). Selected VT H NMR data in
M hexanes solution, 3.60 mmol) in Et2O (30 mL) and THF (0.5
mL). This solid was dissolved in 10 mL of Et2O and cooled to
-30 °C, and to this solution was slowly added AlCl3 (0.16 g, 1.20
mmol) in a solvent mixture (5 mL of hexanes and 10 mL of Et2O).
This mixture was warmed gradually to ambient temperature while
being stirred for 14 h, after which the resulting mixture was filtered
to remove LiCl precipitates. The filtrate was evaporated to dry-
ness under vacuum, and the residue was extracted with hexanes (8
mL). The extract was kept at -30 °C for 3 days, affording 0.32 g
C7D8 were listed as follows: -70 °C, δ 7.65 (d), 7.42 (t), 7.40 (t),
7.23 (t), 6.88-7.10 (m), 6.80-6.82 (br m), 6.35 (d) (15H, CH2Ph),
4.53 (d), 4.48 (d), 4.33 (d), 4.28 (d) (4H, CH2Ph), 3.68 (dd), 3.30
(dd) (2H, CH2Ph), 1.95 (dd, 1H, NH), 0.29 (s, 3H), 0.27 (s, 3H),
0.22 (s, 3H), 0.20 (s, 3H), 0.10 (s, 3H), -0.29 (s, 3H) (SiMe2),
-0.42 (s, 3H, AlMe), -1.29 (s, 1H, HC); 20 °C, δ 7.46 (d),
7.27 (t), 6.90-7.15 (m), 6. 86 (br) (15H, CH2Ph), 4.17-4.31 (m)
(4H, CH2Ph), 3.50-3.80 (m, 2H, CH2Ph), 1.94 (dd, 1H, NH), 0.17
(br s), 0.13 (br), -0.09 (br) (18H, SiMe2), -0.60 (s, 3H, AlMe),
-0.97 (s, 1H, HC); 60 °C, δ 7.43 (br), 7.22 (br), 6.80-7.20
(br m), (15H, CH2Ph), 4.21 (br, 4H, CH2Ph), 3.68 (br m, 2H,
CH2Ph), 1.96 (br, 1H, NH), 0.14 (br, 18H) (SiMe2), -0.66 (s, 3H,
AlMe), -0.90 (s, 1H, HC). 13C{1H} (C6D6, 23 °C): δ 147.2,
138.1, 127.6, 126.9, 126.1 (CH2Ph), 49.5, 47.4 (CH2Ph), 6.9 (HC),
4.52 (br), 2.88 (br) (SiMe2), -14.3 (br, AlMe). Anal. Calcd for
C29H44AlN3Si3: C, 63.80; H, 8.12; N, 7.70. Found: C, 63.42; H,
8.16; N, 7.53.
1
(53% yield) of 1 as a colorless crystalline solid. H NMR (C6D6,
23 °C): δ 7.66 (d, 6H), 7.28 (t, 6H), 7.09 (t, 3H) (CH2Ph), 4.39 (s,
6H, CH2Ph), 3.12 (br m, 4H, OCH2CH2), 0.52 (s, 18H, SiMe2),
0.28 (br m, 4H, OCH2CH2), -0.36 (s, 1H, HC). Anal. Calcd for
C32H48AlN3OSi3: C, 63.85; H, 8.04; N, 6.98. Found: C, 63.64; H,
7.78; N, 7.06.
Synthesis of MeC[CH2N(SiMe3)]3AlCl[Li(Et2O)] (2). To a
solution of AlCl3 (0.133 g, 1.00 mmol) in a hexanes (10 mL)/Et2O
(10 mL) solvent mixture at -30 °C was added slowly a solution
of {MeC[CH2N(SiMe3)]3Li3}2 (0.35 g, 1.00 mmol) in a solvent
mixture of hexanes (10 mL) and Et2O (10 mL). The mixture was
allowed to warm to room temperature and stirred for 12 h, after
which it was filtered to remove LiCl precipitates. The filtrate was
evaporated to dryness under vacuum, affording 0.27 g (57%
yield) of 2 as a colorless crystalline solid. 1H NMR (C6D6, 23 °C):
δ 3.31 (s, 2H), 3.29 (d, 2H) (CH2), 2.94 (q, 4H, OCH2CH3),
2.72 (d, 2H, CH2), 0.84 (t, 6H, OCH2CH3), 0.57 (s, 3H, MeC),
0.49 (s, 9H, SiMe3), 0.30 (s, 18H, SiMe3). Anal. Calcd for
C18H46AlClLiN3OSi3: C, 45.59; H, 9.78; N, 8.86. Found: C, 44.89;
H, 9.78; N, 9.27.
Syntheses of HC[SiMe2NHAr][SiMe2NAr]2AlMe (Ar )
4-MeC6H4, 3; Ar ) CH2Ph, 4). To a solution of HC[SiMe2NH-
(4-MeC6H4)]3 (0.536 g, 1.06 mmol) in 30 mL of toluene at -30
°C was added AlMe3 (0.53 mL, 2.0 M in hexanes, 1.06 mmol).
The mixture was allowed to warm gradually to ambient temperature
while being stirred for 12 h, after which the resulting solution was
Synthesis of [(4-MeC6H4)HNMe2Si](H)C[SiMe2N(4-MeC6H4)]2-
(AlMe2)2 (5). To a solution of HC[SiMe2NH(4-MeC6H4)]3 (0.254
g, 0.50 mmol) in 30 mL of toluene at -30 °C was added AlMe3
(1.60 mL, 1.0 M in toluene, 1.60 mmol). The resulting mixture
was allowed to warm gradually to ambient temperature while being
stirred for 20 h. The obtained solution was evaporated to dryness
under vacuum, and the residue was washed with hexanes (2 × 1
mL) to give, after drying in vacuo, 0.18 g (59%) of 5 as an off-
1
white solid. H NMR (C6D6, 23 °C): δ 6.84-6.98 (m, 6H), 6.85
(d, 4H), 6.53 (d, 2H) (4-MeC6H4), 3.10 (s, 1H, NH), 2.12 (s, 3H),
2.02 (s, 6H) (4-MeC6H4), 1.11 (s, 1H, HC), 0.45 (s, 6H), 0.36 (s,
6H), 0.26 (s, 6H) (SiMe2), 0.21 (s, 3H), 0.18 (s, 3H), -0.52 (s,
6H) (AlMe2). Anal. Calcd for C32H53Al2N3Si3: C, 62.19; H, 8.64;
N, 6.80. Found: C, 61.73; H, 8.42; N, 6.24.
Synthesis of [(Me3Si)HNCH2](Me)C[CH2N(SiMe3)]2(AlMe2)2
(6). To a solution of MeC[CH2NH(SiMe3)]3 (0.67 g, 2.00 mmol)
in 30 mL of toluene at ambient temperature was added AlMe3 (1.0
mL, 2.0 mmol, 2.0 M in toluene). The mixture was stirred at this
temperature for 2 h and then subjected to reflux for 12 h. After
being cooled to room temperature, the resulting solution was
evaporated to dryness under vacuum, affording an oily mixture (by
1H NMR). To this oil was added toluene (20 mL) and AlMe3 (2.0
mL, 4.0 mmol, 2.0 M in toluene). The mixture was stirred for
24 h, after which all volatiles were removed under vacuum and
the residue was extracted into hexanes (3 mL). The extract was
kept at -30 °C for 2 days, affording 0.32 g (36%) of 6 as color-
less crystals. 1H NMR (C6D6, 23 °C): δ 2.48-3.36 (m, 6H, CH2),
1.09 (t, 1H, NH), 0.18 (s, 3H, MeC), 0.12 (s, 12H, SiMe3, AlMe),
-0.10 (s, 9H), -0.27 (s, 9H) (SiMe3), -0.15 (s, 3H), -0.40 (s,
3H), -0.59 (s, 3H) (AlMe). 13C{1H} (C6D6, 23 °C): δ 57.8,
57.2, 54.9 (CH2), 34.5 (MeC), 23.8 (MeC), -0.01, -0.5, -0.8
(SiMe3), -3.8 (br), -6.9 (br), -10.1 (br) (AlMe). Anal. Calcd for
C18H49Al2N3Si3: C, 48.49; H, 11.08; N, 9.43. Found: C, 48.10;
H, 11.08; N, 9.21.
(16) Memmler, H.; Gade, L. H.; Lauher, J. W. Inorg. Chem. 1994, 33,
3064-3071.
(17) Schubart, M.; Findeis, B.; Gade, L. H.; Li, W.-S.; McPartlin, M.
Chem. Ber. 1995, 128, 329-334.
(18) Gade, L. H.; Mahr, N. J. Chem. Soc., Dalton Trans. 1993, 489-
494.
(19) (a) Brower, F.; Matzek, N. E.; Reigler, P. F.; Rinn, H. W.; Roberts,
C. B.; Schmidt, D. L.; Snover, J. A.; Terada, K. J. Am. Chem. Soc. 1976,
98, 2450-2453. (b) Yartys, V. A.; Denys, R. V.; Maehlen, J. P.; Frommen,
C.; Fichtner, M.; Bulychev, B. M.; Emerich, H. Inorg. Chem. 2007, 46,
1051-1055.
(20) Paciorek, K. J. L.; Nakahara, J. H.; Masuda, S. R. Inorg. Chem.
1990, 29, 4252-4255.
(21) Schueta, S.; Day, V. W.; Sommer, R. D.; Rheingold, A. L.; Belot,
J. A. Inorg. Chem. 2001, 40, 5292-5295.
(22) Samuel, E.; Rausch, M. D. J. Am. Chem. Soc. 1973, 95, 6263-
6267.
(23) Diamond, G. M.; Jordan, R. F.; Petersen, J. L. J. Am. Chem. Soc.
1996, 118, 8024-8033.

5398 Organometallics, Vol. 26, No. 22, 2007
Zhu and Chen
Synthesis of [{HC[SiMe2N(4-MeC6H4)]3AlH}Li]2 (7) and
7‚(OEt2)2. Precooled toluene (20 mL) was added to a mixture of
HC[SiMe2NH(4-MeC6H4)]3 (0.25 g, 0.50 mmol) and LiAlH4 (0.08
g, 2.10 mmol). The resulting suspension was stirred at ambient
temperature for 36 h, after which it was filtered and the filtrate
was evaporated to dryness under vacuum. The residue was extracted
with hexanes (2 mL), and the extract was kept at -30 °C for 3
days, affording 0.10 g (37%) of 7 as a colorless crystalline solid.
1H NMR (C6D6, 23 °C): δ 7.02 (qAB, 12H), (4-MeC6H4), 2.18 (s,
9H, 4-MeC6H4), 0.26 (s, 18H, SiMe2), -0.77 (s, 1H, HC). Mixing
of this compound with Et2O afforded its ether adduct 7‚(Et2O)2.
1H NMR (C6D6, 23 °C): δ 7.24 (d, 6H), 7.00 (d, 6H) (4-MeC6H4),
3.03 (q, 8H, OCH2CH3), 2.18 (s, 9H, 4-MeC6H4), 0.84 (t, 12H,
OCH2CH3), 0.44 (s, 18H, SiMe2), -0.57 (s, 1H, HC). IR (NaCl
plate, Nujol mull, cm-1): ν 1807 (w, AlH). Anal. Calcd for
C36H61AlLiN3O2Si3: C, 63.02; H, 8.96; N, 6.12. Found: C, 62.64;
H, 8.62; N, 6.13.
The resulting residue was extracted into hexanes (5 mL), and the
extract was kept at -30 °C overnight to give 46.0 mg (84%) of 11
1
as a crystalline solid. H NMR (C6D6, 23 °C): δ 7.15-7.34 (m,
8H), 6.83 (d, 4H) (4-MeC6H4), 2.22 (s, 3H), 1.99 (s, 6H)
(4-MeC6H4), 0.52 (s, 6H), 0.33 (s, 6H), 0.19 (s, 6H) (SiMe2), -0.93
(s, 1H, HC). 11B (C6D6, 23 °C): δ -6.23 (br). IR (NaCl plate,
Nujol mull, cm-1): ν 2401 (w), 2361 (w) (BH), 1900 (w, AlH).
Anal. Calcd for C28H43AlBN3Si3: C, 61.85; H, 7.97; N, 7.73.
Found: C, 61.73; H, 7.26; N, 7.18.
Reaction of HC[SiMe2N(4-MeC6H4)]3B with Cp2ZrMe2 and
Isolation of Cp2ZrMe[N(4-MeC6H4)SiMe2](H)C[SiMe2N(4-
MeC6H4)]2BMe (12). In an argon-filled glovebox, a 30 mL glass
reactor was equipped with a stir bar and charged with Cp2ZrMe2
(50.3 mg, 0.20 mmol), HC[SiMe2N(4-MeC6H4)]3B (103 mg, 0.20
mmol), and toluene (5 mL) at ambient temperature. The mixture
was stirred for 10 min to give a light yellow solution. The solution
was evaporated to dryness under vacuum, and the residue was
extracted with hexanes and filtered. The filtrate was evaporated to
dryness, affording 146 mg (95%) of 12 as a light yellow solid. 1H
NMR (C6D6, 23 °C): δ 6.87-6.97 (m, 10H), 6.68 (d, 2H)
(4-MeC6H4), 5.68 (s, 10H, CpH), 2.18 (s, 3H), 2.13 (s, 6H) (4-
MeC6H4), 0.50 (br, 7H, HC, SiMe2), 0.44 (s, 6H, SiMe2), 0.31 (s,
3H, BMe), 0.25 (s, 6H, SiMe2), 0.05 (s, 3H, ZrMe). 11B NMR (C6D6,
23 °C): δ 35.0 (br). Anal. Calcd for C40H56BN3Si3Zr: C, 62.78;
H, 7.38; N, 5.49. Found: C, 62.36; H, 7.06; N, 5.76.
Synthesis of MeSi[SiMe2N(4-MeC6H4)]3AlH(AlH2) (8). Tolu-
ene (30 mL) was added to a mixture of MeSi[SiMe2NH(4-
MeC6H4)]3 (0.36 g, 0.67 mmol) and AlH3 (0.02 g, 0.67 mmol) at
ambient temperature. The resulting suspension was stirred at this
temperature for 0.5 h and then heated to reflux for 3 h. After being
cooled to ambient temperature, all volatiles of the reaction mixture
were removed under vacuum to give a viscous oil. This oil was
dissolved in toluene (10 mL) and was added to a second portion of
AlH3 (0.04 g, 1.33 mmol). The mixture was stirred overnight and
then filtered; the filtrate was evaporated to dryness under vacuum,
and the residue was extracted with hexanes (5 mL). The extract
was kept at -30 °C for 24 h to produce 0.20 g (53% based on the
neutral ligand) of 8 as a crystalline solid. 1H NMR (C6D6, 23 °C):
δ 6.75-7.26 (m, 8H), 6.77 (d, 4H) (4-MeC6H4), 2.23 (s, 3H), 1.94
(s, 6H) (4-MeC6H4), 0.77 (s, 6H), 0.44 (6H), 0.27 (s, 6H) (SiMe2),
0.13 (s, 3H, MeSi). IR (NaCl plate, Nujol mull, cm-1): ν 1873 (s),
1844 (s) (AlH). Anal. Calcd for C28H45Al2N3Si4: C, 57.00; H, 7.69;
N, 7.12. Found: C, 57.17; H, 7.53; N, 6.90.
Reaction of HC[SiMe2N(4-MeC6H4)]3B with rac-Et(Ind)2ZrMe2
and Isolation of rac-Et(Ind)2ZrMe[N(4-MeC6H4)SiMe2](H)C-
[SiMe2N(4-MeC6H4)]2BMe (13). Isolation of 13 was carried out
in the same manner as that of 12. rac-Et(Ind)2ZrMe2 (75.5 mg,
0.20 mmol), HC[SiMe2N(4-MeC6H4)]3B (103 mg, 0.20 mmol), and
toluene (5 mL) were used to produce 169 mg (95%) of 13 as a
light yellow solid. 1H NMR (C6D6, 23 °C): δ 7.56 (dd, 2H), 7.33
(d, 1H), 6.87-7.14 (m, 17H) (C6H4), 6.19 (d, 1H), 5.70 (d, 1H),
5.63 (d, 1H), 5.60 (d, 1H) (C5H2), 2.99 (m, 1H), 2.85 (m, 3H)
(CH2CH2), 2.13 (s, 3H), 2.11 (s, 6H) (4-MeC6H4), 0.56 (s, 1H, HC),
0.48 (s, 3H), 0.43 (s, 3H), 0.42 (s, 3H), 0.20 (s, 6H), 0.07 (s, 3H)
(SiMe2), 0.21 (s, 3H, BMe), -0.67 (s, 3H, ZrMe). 11B NMR (C6D6,
23 °C): δ 37.1 (br). Anal. Calcd for C50H62BN3Si3Zr: C, 67.37;
H, 7.01; N, 4.71. Found: C, 67.05; H, 7.35; N, 4.43.
Synthesis of {MeSi[SiMe2N(4-MeC6H4)]3Sm}2 (9). A solution
of Sm[N(SiMe3)2]3 (0.107 g, 0.167 mmol) and MeSi[SiMe2NH(4-
MeC6H4)]3 (0.09 g, 0.167 mmol) in toluene (40 mL) was stirred
for 2 h at room temperature and then subjected to reflux for 12 h.
After being cooled to room temperature, the solution was evaporated
to dryness under vacuum. The residue was washed with hexanes
to afford 0.062 g (77%) of 9 as a light yellow solid. 1H NMR (C6D6,
23 °C): δ 11.7 (br, 6H), 6.13 (br, 6H) (4-MeC6H4), 1.16 (br, 9H,
4-MeC6H4), 0.31 (br, 18H, SiMe2), -3.50 (s, 3H, MeSi). Anal.
Calcd for C56H84N6Si6Sm2: C, 49.21; H, 6.19; N, 6.15. Found: C,
48.63; H, 6.13; N, 5.79.
Polymerization Procedures. Polymerizations of propylene oxide
(PO) and CL were carried out in a Schlenk line and in an argon-
filled glovebox, respectively, following literature procedures.13f,g,14c
In a typical experiment, 22.5 µmol of the tripodal amido aluminum
catalyst was dissolved in 1 mL of CH2Cl2 and then added to CL
(0.50 mL, [CL]/[cat.] ) 200) with or without BnOH in 4 mL of
CH2Cl2. The solution was stirred at ambient temperature. After a
measured time interval, the reactor was taken out of the box, and
methylene chloride was added to dissolve the polymer gel. The
solution was precipitated into cold methanol (50 mL), filtered,
washed with methanol, and dried in a vacuum oven at 50 °C
overnight to a constant weight.
Reaction of HC[SiMe2N(4-MeC6H4)]3B with AlMe3 and
Isolation of HC[SiMe2N(4-MeC6H4)]3BMe(AlMe2) (10). To a
solution of HC[SiMe2N(4-MeC6H4)]3B (51.3 mg, 0.10 mmol) in
toluene (10 mL) at -30 °C was added AlMe3 (4.8 µL, 0.10 mmol).
The mixture was stirred for 6 h, during which time it was freely
warmed to ambient temperature. The obtained solution was
evaporated to dryness, and the residue was extracted into hexanes
(5 mL). The hexanes extract was concentrated to ca. 1 mL and
kept at -30 °C for 4 days, affording 41.0 mg (70%) of 10 as
colorless crystals. 1H NMR (C6D6, 23 °C): δ 6.86-7.00 (m, 10H),
6.70 (d, 2H) (4-MeC6H4), 2.11 (s, 3H), 2.05 (s, 6H) (4-MeC6H4),
1.66 (s, 1H, HC), 0.46 (s, 6H), 0.44 (s, 6H) (SiMe2), 0.35 (s, 3H,
BMe), 0.29 (s, 3H), 0.08 (s, 3H) (SiMe2), -0.49 (s, 3H), -0.53 (s,
3H) (AlMe2). 11B (C6D6, 23 °C): δ 37.5 (br). Anal. Calcd for
C31H49AlBN3Si3: C, 63.56; H, 8.43; N, 7.17. Found: C, 63.08; H,
8.25; N, 6.61.
Gel permeation chromatography (GPC) analyses of the polymers
were carried out at 40 °C and a flow rate of 1.0 mL/min, with
CHCl3 as the eluent, on a Waters University 1500 GPC instrument
equipped with four 5 µm PL gel columns (Polymer Laboratories)
and calibrated using 10 poly(methyl methacrylate) (PMMA)
standards. Chromatograms were processed with Waters Empower
software (version 2002); number-average molecular weight and
polydispersity of polymers were given relative to PMMA standards.
X-ray Crystallographic Analyses of Complexes 2, 4, 5, 8, 9,
and 13‚1.2(Hexanes). Single crystals of all complexes suitable for
X-ray diffraction were grown from hexanes or hexanes/toluene
mixture at -30 °C inside the freezer of a glovebox. The crystals
were quickly covered with a layer of Paratone-N oil (Exxon, dried
and degassed at 120 °C/10-6 Torr for 24 h) after the mother liquors
were decanted and then mounted on a thin glass fiber and transferred
into the cold nitrogen stream of a Bruker SMART CCD diffrac-
Reaction of HC[SiMe2N(4-MeC6H4)]3B with AlH3 and Isola-
tion of HC[SiMe2N(4-MeC6H4)]3AlH(BH2) (11). The mixture of
HC[SiMe2N(4-MeC6H4)]3B (51.5 mg, 0.10 mmol) and AlH3 (3.0
mg, 0.10 mmol) in toluene (5 mL) was stirred for 3 h at ambient
temperature, after which all volatiles were removed under vacuum.

Tridentate Tripodal Triamine Ligand Complexes
Table 1. Crystal Data and Structure Refinements for 2, 4, 5, 8, 9, and 13‚1.2(Hexanes)a
compd 2 compd 4 compd 5 compd 8 compd 9
C18H46AlClLiN3OSi3 C29H44AlN3Si3 C32H53Al2N3Si3 C28H45Al2N3Si4 C56H84N6Si8Sm2
Organometallics, Vol. 26, No. 22, 2007 5399
compd 13‚1.2(hexanes)
57.20H78.80BN3Si3Zr
formula
Fw
C
474.22
545.92
618.00
589.99
1366.71
994.73
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
monoclinic
P21/n
11.5500(2)
16.0631(3)
15.9430(3)
triclinic
P1h
orthorhombic
Pca21
39.9056(13)
9.3888(3)
19.4839(9)
monoclinic
C2/c
36.5620(30)
9.5547(9)
19.4147(16)
triclinic
P1h
monoclinic
C2/c
43.7510(12)
12.7618(4)
26.9246(7)
9.8773(3)
11.8618(4)
13.7028(5)
105.722(2)
93.966(2)
96.701(2)
1526.3(1)
2
13.9744(6)
14.4704(6)
18.2232(8)
84.707(3)
80.305(3)
63.979(2)
3263.5(2)
2
92.407(1)
100.698(6)
127.374(2)
2955.3(1)
4
1.066
0.293
1032
0.41 0.32 0.09
1.80-32.58
-16 e h e 17
-24 e k e 24
-23 e l e 24
36 805
7299.9(5)
8b
1.125
0.203
2672
0.20 0.18 0.05
1.46-28.26
-53 e h e 53
-12 e k e 12
-24 e l e 25
78 291
6664.4(10)
8
1.176
0.253
2528
0.24 0.18 0.06
2.21-33.39
-56 e h e 55
-14 e k e 12
-29 e l e 29
54 156
11946.7(6)
8
1.106
0.279
4240
0.22 0.16 0.07
1.17-28.28
-57 e h e 58
-17 e k e 17
-35 e l e 35
175 125
Z
F
calcd/(g‚cm-3
)
1.188
0.207
588
0.35 0.12 0.08
1.55-30.53
-14 e h e 14
-16 e k e 16
-19 e l e 19
44 963
1.391
1.967
1396
0.39 0.08 0.06
1.64-33.19
-21 e h e 21
-22 e k e 22
-24 e l e 28
71 422
µ/mm-1
F(000)
cryst size/mm3
θ range/deg
index ranges
collecd data
unique data (Rint
)
10 684 (0.0421)
99.3
10684/62/313
0.994
9 305 (0.0510) 17 704 (0.0873) 12 328 (0.1652) 24 333 (0.0775)
14 811 (0.1306)
99.9
14811/20/632
1.022
completeness to θ/%
99.6
99.7
95.1
97.3
data/restraints/params
9305/0/336
1.015
17704/1/747
0.997
12328/0/356
1.052
24333/0/664
1.086
GOF on F2
final R indices [I > 2σ(I)]
R1
0.0446
0.1052
0.0394
0.0893
0.0508
0.0984
0.1117
0.2386
0.1160
0.2877
0.0699
0.1794
Rw2
R indices (all data)
R1
Rw2
0.0765
0.1209
0.0607
0.0990
0.0837
0.1113
0.2428
0.2942
0.1563
0.3050
0.1212
0.2172
a All data were collected at 173(2) K using Mo KR (λ ) 0.710 73 Å) radiation. R1 ) Σ(||Fo| - |Fc||)/Σ|Fo|, Rw2 ) {Σ[w(Fo - Fc )2/Σ[w(Fo )2]}2}1/2
,
2
2
2
2
2
GOF ) {Σ[w(Fo - Fc )2]/(No - Np)}1/2 b There were two solved independent molecules.
.
tometer. The structures were solved by direct methods and refined
using the Bruker SHELXTL program library by full-matrix least-
squares on F2 for all reflections.24 Unless otherwise indicated, all
non-hydrogen atoms were located by difference Fourier synthesis
and refined with anisotropic displacement parameters, whereas
hydrogen atoms were included in the structure factor calculations
at idealized positions. In 2, the coordinated Et2O solvent molecule
at Li atom was disordered and treated in part (O(1)C(6)C(7)C(8)-
C(9), 36%; O(1A)C(6A)C(7A)C(8A)C(9A), 64%). Due to the
significant vibration of these two groups which resulted in the
refining instability of atom positions, the suitable restriction was
employed, giving 62 least-squares restraints and one of carbon
atoms larger Ueq [C(7a), 0.166(4)Å2]. In 4 and 8, the NH and AlH
hydrogen atoms were located by difference Fourier synthesis but
refined isotropically. In 5, two independent molecules were
disclosed. In 9, C(53) was refined isotropically due to the
nonpositivity when treated aniostropically. The weak intensity X-ray
diffraction data of 8 and 9 resulted from the crystal quality.
Although the X-ray data of the two complexes was not of high
quality, the data led to reasonable structural determinations, allowing
for a brief discussion on their metric parameters. In 13‚1.2(hexanes),
the hexanes solvent molecules were disordered and treated in
part (C(71A)C(72A)C(73A)C(74A)C(75A)C(76A), 33%; C(71B)-
C(72B)C(73B)C(74B)C(75B)C(76B), 27%; C(81A)C(82A)C(83A)-
C(84A)C(85A)C(86A), 30%; C(81B)C(82B)C(83B)C(84B)C(85B)-
C(86B), 30%), in which the carbon atoms were refined isotropically.
Selected crystal data and structural refinement parameters are
collected in Table 1.
Et2O, or THF) gave rise to the formation of diverse adducts of
the transient [N3]Al with THF, LiCl, ClLi(Et2O)2, and Li(OCHd
CH2)(THF)2; the salt- or solvent-free [N3]Al cannot be isolated
from these adducts via a variety of methods. We reasoned that
two approaches could potentially solve this problem: the first
is to employ the N-benzyl substituent for providing stabilization
of the highly Lewis acidic Al center in [N3]Al via the proposed
η6-arene coordination of the benzyl group to Al, which could
facilitate the removal of the coordinated donor solvent or salt.
The second approach is to adjust the binding pocket size for Al
by changing the tripodal ligand backbone framework.
For the first approach, we carried out the reaction of HC-
[SiMe2N(CH2Ph)]3Li3(THF)2 with AlCl3, which led to the
corresponding tripodal triamido alane 1 as a THF adduct in 53%
yield (Scheme 2). The 1H NMR spectrum of 1 in C6D6 at room
temperature exhibits only one set of aromatic resonances, a
single benzyl-methylene peak, and a single SiMe2-methyl
peak, consistent with an apparent 3-fold symmetry in solution.
The resonances for the coordinated THF protons were observed
at 3.12 (m) and 0.28 (m) ppm. However, as in the case of the
N-4-MeC6H4 substituted derivative B (L ) THF), the coordi-
nated THF in 1 was not removed upon heating under high-
vacuum conditions.
For the second approach, we employed the tripodal triamido
ligand having the neopentane backbone. Accordingly, the
reaction of {MeC[CH2N(SiMe3)]3Li3}218 with AlCl3 in a Et2O/
hexanes solvent mixture gave an incomplete LiCl-elimination
product (2, Scheme 3), which was isolated as a crystalline solid
in 57% yield. This observation seems to reflect the donor solvent
effect (Et2O vs THF) more than the ligand framework effect
on the formation of different salt-metathesis products, as we
Results and Discussion
Salt Metathesis Route. We previously reported the synthesis
of tripodal triamido alane structure B via salt metathesis between
tripodal triamido lithium salt HC[SiMe2N(4-MeC6H4)]3Li3 and
AlCl3.4a Variations of the reaction medium (hexanes/toluene,
(24) SHELXTL, Version 6.12; Bruker Analytical X-ray Solutions: Madi-
son, WI, 2001.

5400 Organometallics, Vol. 26, No. 22, 2007
Zhu and Chen
Scheme 2
Scheme 3
The Al-Cl bond length in 2 [2.143(1) Å] is considerably shorter
than that in the dimeric {HC[SiMe2N(4-MeC6H4)]3Al‚ClLi}2
[2.227(1) Å] in which the Cl atom is also involved in the
Cl2Li2 ring coordination,4a but it compares well to the four-
coordinate terminal Al-Cl bond length of 2.153(1) Å found in
HC[(CMe)(NAr)]2AlClI (Ar ) 2,6-iPr2C6H3).25 The Li atom
keeps its original side coordination between two amido N
atoms18 and further links to one Et2O solvent molecule, forming
a triangular geometry (∆Li(1)N(1)N(2)O(1) ) 0.0422 Å) with the
Li-N bond distances of 2.049(3) and 2.057(3) Å as well as the
Li-O distance of 1.890(8) (av) Å. This bonding motif gives
rise to three nonequivalent tripodal arms and thus variations in
Al-N bond lengths [1.803(1); 1.870(1) and 1.881(1) Å] and in
N-Al-N angles [94.1(1); 108.4(1) and 108.4(1)°]. Similar
structural features have been observed in group 14 tripodal
triamido lithium adducts.26
previously observed the similar product, HC[Si(Me2)N(4-
MeC6H4)]3Al‚ClLi(Et2O)2,4a from the reaction using a different
ligand framework with the trisilyl methane backbone but the
same solvent (i.e., no THF in the reaction medium or without
the use of the preformed THF-solvated lithium salt).
The 1H NMR spectrum of 2 exhibits three sets of resonances
for the backbone methylene protons [3.31 (s, 2H), 3.29 (d, 2H),
and 2.70 (d, 2H) ppm] and two sets of resonances for the SiMe3
methyl protons [0.48 (s, 9H) and 0.30 (s, 18H) ppm], showing
a non-3-fold symmetry in solution. This NMR feature is in sharp
contrast to HC[SiMe2N(4-MeC6H4)]3Al‚ClLi(Et2O)2,4a which
presents a 3-fold symmetric 1H NMR feature because the ether-
solvated Li is coordinated to the terminal Cl, not to amido
nitrogen atoms as in 2. The molecular structure of 2 was
determined by X-ray single-crystal diffraction analysis (Figure
1), confirming the solution structure derived from the NMR
analysis. The remaining Al-Cl and three newly formed Al-N
bonds render the Al center to a distorted tetrahedral geometry.
Ligand Elimination Route. Verkade7 and Gade27 have
shown that reactions of the neutral tetradentate tripodal tris(2-
aminoethyl)amine ligand N[N3]H3 with AlR3 (R ) Me, NMe2)
readily generate the corresponding complete alkane or amine
elimination productssaluminum azatranes. On the other hand,
we found that reactions between the tridentate tripodal triamine
ligand [N3]H3 and AlMe3 show complexity.28 Monitoring of the
reaction between HC[SiMe2NH(4-MeC6H4)]3 and 1 equiv of
1
AlMe3 in C6D6 by H NMR revealed several NH resonances
from 4.00 to 3.00 ppm, indicative of the formation of incomplete
CH4-elimination products including the unreacted neutral ligand.
The scaled-up 1:1 ratio reaction in refluxing toluene gave
formally diamido-amino aluminum methyl 3 in low yield
(23%), but a similar reaction using the N-benzyl-substituted
ligand HC[SiMe2NH(CH2Ph)]3 afforded the analogous complex
4 in high yield (83%), Scheme 3. The VT NMR spectra from
-70 to +60 °C (see Experimental Section) indicated it is
fluxional in solution. Attempts to eliminate the third equivalent
of CH4 from either 3 or 4 under high-vacuum and -temperature
(100-200 °C) conditions were unsuccessful. Treatment of HC-
[SiMe2NH(4-MeC6H4)]3 with excess of AlMe3 afforded formally
amido-amino aluminum dimethyl 5 (Scheme 4); the same
strategy was utilized for the preparation of analogous complex
6 bearing the neopentane backboned ligand, MeC[CH2NH-
(SiMe3)]3, as its reaction with 1 equiv of AlMe3 in toluene led
to a complex mixture.
Besides NMR and analytical characterizations of these
aluminum complexes, one monomethyl Al complex (4, Figure
(25) Zhu, H.; Chai, J.; He, C.; Bai, G.; Roesky, H. W.; Jancik, V.;
Schmidt, H.-G.; Noltemeyer, M. Organometallics 2005, 24, 380-384.
(26) (a) Gade, L. H. Eur. J. Inorg. Chem. 2002, 1257-1268. (b)
Memmler, H.; Kauper, U.; Gade, L. H.; Stalke, D. Organometallics 1996,
15, 3637-3639. (c) Hellmann, K. W.; Gade, L. H.; Gevert, O.; Steinert,
P.; Lauher, J. W. Inorg. Chem. 1995, 34, 4069-4078.
Figure 1. X-ray crystal structure of 2 with thermal ellipsoids drawn
at the 50% probability and the disordered Et2O of 36% occupancy.
Selected bond lengths (Å) and angles (deg): Al-Cl(1), 2.143(1);
Al-N(1), 1.870(1); Al-N(2), 1.881(1); Al-N(3), 1.803(1);
Li(1)-N(1), 2.049(3); Li(1)-N(2), 2.057(3); Li(1)-O(1), 1.891-
(11); N(1)-Al(1)-N(2), 94.1(1); N(1)-Al(1)-N(3), 108.4(1);
N(2)-Al(1)-N(3), 108.4(1); Cl(1)-Al(1)-N(1), 112.5(1); Cl(1)-
Al(1)-N(2), 111.6(1); Cl(1)-Al(1)-N(3), 119.0(1); N(1)-Li(1)-
N(2), 83.9(1); N(1)-Li(1)-O(1), 138.6(4); N(2)-Li(1)-O(1),
136.3(4).
(27) Forcato, M.; Lake, F.; Blazquez, M. M.; Renner, P.; Crisma, M.;
Gade, L. H.; Licini, G.; Moberg, C. Eur. J. Inorg. Chem. 2006, 1032-
1040.
(28) The study of the reaction of triaminophosphines P(CH2NHAr)3 with
AlMe3 was reported: Han, H.; Johnson, S. A. Organometallics 2006, 25,
5594-5602.

Tridentate Tripodal Triamine Ligand Complexes
Organometallics, Vol. 26, No. 22, 2007 5401
Scheme 4
Scheme 5
2) and one dimethyl dinuclear Al complex (5, Figure 3) were
further characterized by X-ray crystallography. The undepro-
tonated donor amine arm is datively bonded to the Al center in
4, whereas in 5 it is resided alone. The Al-Me bond length in
4 [1.965(2) Å)] compares well to those in 5 [1.965(3)-1.976-
(3) Å], and they all are similar to those found in the other
four-coordinate aluminum methyl complexes {(()-trans-Cy-
(NSiMe3)2}Al2Me4 [1.954(4)-1.964(3) Å]13f and HC[(CMe)-
(NAr)]2AlMe2 [Ar ) 2,6-iPrC6H3, 1.955(4)-1.961(3) Å; Ar )
4-MeC6H4, 1.958(3)-1.970(3) Å].29 The dative Al-N bond in
4 [2.044(1) Å] is longer than those of σ-bonded ones [1.835-
(1), 1.840(1) Å]; however, all the Al-N bonds in 5 have similar
lengths [1.961(2)-1.988(3) Å)]. It can be seen from Figure 3
that in 5 the two side arrangements of the C-H bond and the
free C-SiMe2NH(4-MeC6H4) arm at the apical C atom toward
the chelating moiety C[SiMe2N(4-MeC6H4)]2(AlMe2)2 give rise
to nonequivalent steric environments for the two bridging AlMe2
moieties; this explains the observed well-separated AlMe2 1H
NMR resonances at -0.21 (s, 3H), -0.18 (s, 3H), and -0.52
(s, 6H) ppm for 5 as well as 0.12 (s, 3H), -0.15 (s, 3H), -0.40
(s, 3H), and -0.59 (s, 3H) ppm for 6.
Next, we investigated the H2-elimination approach using
reagents LiAlH4 and AlH3 to react with the neutral ligand
[N3]H3 and found that these reagents can completely deprotonate
all three amine arms, affording complexes 7 and 8, respectively
(Scheme 5). Addition of Et2O readily converted 7 to its ether
Figure 2. X-ray crystal structure of 4 with thermal ellipsoids drawn
at the 50% probability. Selected bond lengths (Å) and angles
(deg): Al(1)-C(8), 1.965(2); Al(1)-N(1), 1.840(1); Al(1)-N(2),
2.044(1); Al(1)-N(3), 1.835(1); N(1)-Al(1)-N(2), 98.5(1); N(1)-
Al(1)-N(3), 111.8(1); N(2)-Al(1)-N(3), 102.0(1); N(1)-Al(1)-
C(8), 114.4(1); N(2)-Al(1)-C(8), 108.1(1); N(3)-Al(1)-C(8),
119.0(1).
1
adduct. A 3-fold symmetric H NMR resonance profile was
observed for 7 and 7‚(Et2O)2 in C6D6 at room temperature, but
not for 8. The coordination of Et2O to Li in 7‚(Et2O)2 led to
the change of an AB spin splitting pattern for the Ar protons in
7 to a typical AX(M) pattern for the structures without Li-Ar
coordination, implying interaction between Li and Ar in 7 but
not in 7‚(Et2O)2. A similar observation has been discussed for
{HC[SiMe2N(4-MeC6H4)]3Al‚ClLi}2 vs its ether adduct HC-
[SiMe2N(4-MeC6H4)]3Al‚ClLi(Et2O)2.4a The reaction of [N3]H3
and AlH3 requires more than 1 equiv of AlH3 for obtaining a
clean product (8) as the 1:1 ratio led to an unidentifiable mixture
even under refluxing conditions, while excess AlH3 (>2) still
produced 8. Treatment of 8 under vacuum at elevated temper-
atures did not remove one molecule of AlH3 to the desired
[N3]Al.
The X-ray diffraction analysis of 8 confirms an unsymmetric
tripodal amido dinuclear aluminum hydride structure (Figure
4). One AlH moiety sits in the triamido binding pocket, while
the AlH2 moiety is bonded to two diamido N atoms. Both Al
centers adopt a distorted tetrahedral geometry with Al-H bond
lengths [1.41(5)-1.51(4) Å] within a range observed for
terminal aluminum hydrides [1.37-1.75) Å].30,31 The shortest
Figure 3. X-ray crystal structure of 5 with thermal ellipsoids drawn
at the 50% probability. Selected bond lengths (Å) and angles
(deg): Al(1)-N(1), 1.961(2); Al(1)-N(2), 1.980(2); Al(2)-N(1),
1.984(2); Al(2)-N(2), 1.988(3); Al(1)-C(41), 1.969(3); Al(1)-
C(42), 1.969(3); Al(2)-C(43), 1.976(3); Al(2)-C(44), 1.965(3);
N(1)-Al(1)-N(2), 84.4(1); N(1)-Al(2)-N(2), 83.6(1); C(41)-
Al(1)-C(42), 112.1(1); C(43)-Al(2)-C(44), 111.3(1).
(29) Qian, B.; Ward, D. L.; Smith, M. R., III. Organometallics 1998,
17, 3070-3076.
(30) Gardiner, M. G.; Lawrence, S. M.; Raston, C. L. J. Chem. Soc.,
Dalton Trans. 1996, 4163-4169.

5402 Organometallics, Vol. 26, No. 22, 2007
Zhu and Chen
Figure 4. X-ray crystal structure of 8 with thermal ellipsoids drawn
at the 50% probability. Selected bond lengths (Å) and angles
(deg): Al(1)-N(1), 1.997(3); Al(1)-N(2), 1.965(4); Al(1)-N(3),
1.842(4); Al(2)-N(1), 1.997(4); Al(2)-N(2), 1.955(4); Al(1)-H(1),
1.44(4); Al(2)-H(2), 1.41(5); Al(2)-H(3), 1.51(4); N(1)-Al(1)-
N(2), 86.3(2); N(1)-Al(1)-N(3), 120.5(2); N(2)-Al(1)-N(3),
113.8(2); H(1)-Al(1)-N(1), 103.0(16); H(1)-Al(1)-N(2), 116.0-
(15); H(1)-Al(1)-N(3), 114.2(15); N(1)-Al(2)-N(2), 86.6(2);
H(2)-Al(2)-H(3), 120.0(30).
Figure 5. X-ray crystal structure of 9 with thermal ellipsoids drawn
at the 40% probability. Selected bond lengths (Å) and angles
(deg): Sm(1)-N(2), 2.235(10); Sm(1)-N(3), 2.239(10); Sm(1)-
N(4), 2.506(9); Sm(1)-C(61), 2.855(11); Sm(1)-C(62), 2.880(11);
Sm(1)-C(63), 2.967(11); Sm(1)-C(64), 3.039(12); Sm(1)-C(65),
2.934(11); Sm(1)-C(66), 2.834(11); Sm(2)-N(4), 2.542(10);
Sm(2)-N(6), 2.344(10); Sm(2)-N(7), 2.243(11); Sm(2)-N(8),
2.264(10); Sm(2)-C(41), 2.801(10); Sm(2)-C(42), 2.883(12);
N(2)-Sm(1)-N(3), 106.4(4); N(2)-Sm(1)-N(4), 118.1(3); N(3)-
Sm(1)-N(4), 103.0(3); Sm(1)-N(4)-Sm(2), 113.9(3); N(6)-Sm-
(2)-N(7), 95.0(4); N(6)-Sm(2)-N(8), 118.5(4); N(7)-Sm(2)-
N(8), 103.4(4).
Scheme 6
refluxing toluene. However, this amine elimination route led
to the synthesis of the first lanthanide complex (9, Scheme 6)
incorporating the tripodal triamido ligand. Specifically, the
reaction of Sm[N(SiMe3)2]3 and MeSi[SiMe2NH(4-MeC6H4)]3
in toluene under refluxing conditions afforded 9 in 77% yield.
1
As expected, this paramagnetic species gives broad H NMR
resonances in C6D6 at ambient temperature.
The molecular structure of 9 was characterized by X-ray
diffraction, featuring an unsymmetric dinuclear structure (Figure
5). The complete elimination of 3 equiv of HN(SiMe3)2 settles
the Sm center nicely above the tripodal binding pocket σ-bound
to the three amido N atoms. Due to the low coordination number
environment provided by the tripodal triamido ligand and
high coordination nature of the 4f block Sm center, further
intermolecular interactions of the Sm center with donor groups
of another ligand moiety render a dinuclear structure. Sm(1)
sits above the [N3] plane by 0.7803 Å with the Sm-Nterminal
bonds [2.235(10) and 2.239(10) Å] being shorter than the
Sm-N(4)bridging bond [2.506(9) Å], both within a range found
for terminal [2.110(10)-2.371(5) Å] and bridging [2.430(10)-
2.574(3) Å] amido Sm(III) complexes.32 This Sm atom is
additionally coordinated to an aryl ring from the different
tripodal ligand in an η6-fashion, with the Sm(1)-C(Ar)N(6)
distances ranging from 2.834(11) to 3.039(12) Å (av. 2.924 Å),
which are compared with those found in complexes (η-C6Me6)-
Sm(AlCl4)3 (av. 2.89 Å),33 (η-C6H6)Sm(AlCl4)3 (av. 2.91 Å),34
(η-1,3-Me2C6H4)Sm(AlCl4)3 (av. 2.90 Å),35 and (ArO)6Sm2 [Ar
Al-N bond length of 1.842(4) Å is the bond between Al and
the only three-coordinate N(3), while the Al to other four-
coordinate N (edge-shared diamido N atoms) bonds are >0.1
Å longer [1.955(4)-1.997(4) Å] and still comparable to those
found in complexes 4 and 5. It can be argued that, in view of
this structure, the formation of 8 may go through an initial
elimination of 2 H2 by 1 equiv of AlH3 to give [N3H]AlH
analogous to complex 4, followed by further elimination of the
third H2 from [N3H]AlH by an additional equiv of AlH3.
In addition to the above-described CH4- and H2-eliminiation
routes, we also examined the amine elimination approach using
Al[N(SiMe3)2]3 to react with the neutral ligand MeSi[SiMe2-
NH(4-MeC6H4)]3, but we found no reaction took place even in
(31) (a) Zhu, H.; Yang, Z.; Magull, J.; Roesky, H. W.; Schmidt, H.-G.;
Noltemeyer, M. Organometallics 2005, 24, 6420-6425. (b) Zhu, H.; Chai,
J.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.; Vidovic, D.; Magull,
J. Eur. J. Inorg. Chem. 2003, 3113-3119. (c) Bauer, T.; Schulz, S.; Hupfer,
H.; Nieger, M. Organometallics 2002, 21, 2931-2939. (d) Wehmschulte,
R. J.; Power, P. P. Inorg. Chem. 1996, 35, 3262-3267. (e) Cowley, A. H.;
Isom. H. S.; Decke, A. Organometallics 1995, 14, 2589-2592. (f) Linti,
G.; No¨th, H.; Rahm, P. Z. Naturforsch., B: Chem. Sci. 1988, 43, 1101-
1112.
(32) For selected examples, see: (a) Sundermeyer, J.; Khvorost, A.;
Harms, K. Acta Crystallogr. 2004, E60, m1117-m1119. (b) Martin-Vaca,
B.; Dumitrescu, A.; Gornitzka, H.; Bourissou, D.; Bertrand, G. J. Orga-
nomet. Chem. 2003, 682, 263-266. (c) Click, D. R.; Scott, B. L.; Watkin,
J. G. Chem. Commun. (Cambridge) 1999, 633-634. (d) Minhas, R. K.;
Ma, Y.; Song, J.-I.; Gambarotta, S. Inorg. Chem. 1996, 35, 1866-1873.

Tridentate Tripodal Triamine Ligand Complexes
Organometallics, Vol. 26, No. 22, 2007 5403
) 2,6-iPr2C6H3, 2.847(8)-3.135(8) Å, 2.842(7)-3.160(8) Å].36
The Sm(2) center is located above the [N3] plane by 0.8822 Å
with Sm-Nterminal bond lengths of 2.243(11), 2.264(12), and
2.344(10) Å and further coordinated to N(4) and the N(4)-
substituted aryl group of the tripodal ligand moiety from another
molecule. The Sm(2)-N(4)bridging bond length is 2.542(10) Å,
while the Sm(2)-C(Ar)N(4) distances can be divided into two
groups: the distances of 2.801(10) and 2.883(12) Å for the
Sm(2)-C(41) and Sm(2)-C(42) bonds, respectively, are com-
parable to the Sm(1)-C(Ar)N(6) distances, while the separations
of the others are significantly larger (3.743-4.649 Å), clearly
indicating the Sm(2)-C(Ar)N(4) interaction in an η2-fashion. A
comparable case has been observed in compound [(C5Me5)2-
Sm]2(µ-η2:η4-CH2CHPh).37 Overall, complex 9 represents an
interesting structure model in which the holding of Sm3+ under
the [N3] binding pocket and tunable N-Ar substituents allow
for the presence of intermolecular metal-arene interactions via
different bonding modes. These structural features indicate a
highly unsaturated Sm center in “[N3]Sm” supported by the
tripodal triamido ligand and reflect the characteristics of the
highly electropositive, large Sm center being able to support
high coordination numbers.38
Ligand Exchange Route. While conventional routes have
failed to produce the strongly Lewis acidic alane Al(C6F5)3, the
facile Al/B alkyl/aryl ligand exchange reaction between AlMe3
and B(C6F5)3 has been successful in the high-yield synthesis of
this compound.39 Further studies showed that this ligand
exchange reaction proceeds via a stepwise fashion through
various boron and mono- or dinuclear aluminum intermediates,40
and additional procedures such as precipitation of the final
product Al(C6F5)3 by adjusting the solvent polarity (e.g., use a
1:3 toluene-hexane solvent mixture)41 are necessary to shift
the multiequilibria present in this reaction to the clean alane
product.
Scheme 7
1
10 (Scheme 7). A most useful, sensitive H NMR feature for
identifying if the tripodal triamido ligand framework is furnished
(i.e., all three amido nitrogen atoms are chelated to a central
atom as shown in structures A and B) or not is the chemical
shift of the apical CH for the complexes incorporating the
tripodal triamido ligand HC[SiMe2N(4-MeC6H4)]3: without
exception, we found that upon furnishing the tripodal geometry,
there is a significant upfield shift from the neutral ligand (0.88
ppm) to -0.23 in A, -0.46 in B, -0.36 in 1, -0.76 in 3, -0.95
in 4, and -0.77 ppm in 7, while this apical CH is located at a
downfield region when such a tripodal framework was not
established (e.g., 1.11 ppm in 5). The chemical shift of the apical
CH in 10 is 1.66 ppm, consistent with the nontripodal structure
10 depicted in Scheme 7.
Interestingly, the ligand exchange reaction between the
tripodal borane A and AlH3 produced a second-step ligand
exchange product (i.e., a BR2‚‚‚AlR type structure), complex
11 (Scheme 7). Using the same analysis as already discussed
above, complex 11 retains the tripodal triamido framework as
the chemical shift of its apical CH is -0.93 ppm. Moreover,
1
the H NMR profile of 11 is similar to that of the structurally
characterized 8, implying isostructure of each other. Further
treatment of 11 under high-vacuum and -temperature conditions
did not drive the reaction to form the third-step ligand exchange
product [N3]Al.
Ligand Redistribution Reaction. A potential application of
the preorganized pyramidal tripodal triamido borane [N3]B is
its use as a cocatalyst for metallocene-catalyzed olefin polym-
erization. To this end, we examined activation of prototypical
dimethyl metallocenes Cp2ZrMe2 and rac-Et(Ind)2ZrMe2 by HC-
[SiMe2N(4-MeC6H4)]3B (A: X ) C, Y ) H, Scheme 1).
Monitoring of the 1:1 molar ratio reactions of both metallocene
By analogy, we treated the tripodal borane A (X ) C, Y )
H, Scheme 1) with AlMe3 in hope of producing the correspond-
ing tripodal alane [N3]Al. However, this ligand exchange
reaction gave a species of non-3-fold symmetry in solution by
an observation of two sets of resonances for the 4-MeC6H4
methyl protons [2.11 (s, 3H) and 2.05 (s, 6H)] and four different
SiMe2 methyl resonances [0.46 (s, 6H), 0.44 (s, 6H), 0.29 (s,
3H), and 0.08 (s, 3H)]. There are still two methyl groups
attached to Al, indicating the exchange reaction took place only
for the first step, which is consistent with the observation of
one BMe group [0.35 (s, 3H)]. Furthermore, the observed
nonequivalency of these two AlMe2 methyl groups [-0.49 (s,
3H), -0.53 (s, 3H)] suggests that the AlMe2 is coordinated to
an additional N atom in the resulting ligand exchange product
1
dimethyls with A by H NMR in C6D6 at room temperature
revealed rapid reactions as indicated by the instantaneous
disappearance of precursory LZrMe2 methyl resonances [L )
Cp2, -0.12 ppm; rac-Et(Ind)2, -0.95 ppm] and the appearance
of resonances assigned to BMe and ZrMe (0.31 and 0.05 ppm
for 12; 0.21 and -0.67 ppm for 13, Scheme 8). These
spectroscopic features imply the rapid metallocene methide
abstraction by the borane. However, the resulting products (from
either the NMR-scale reaction or scaled-up isolation) exhibit
excellent solubility in hydrocarbons (hexanes, benzene, and
toluene), two types of the 4-MeC6H4 methyl groups [2.18 (s,
3H), 2.13 (s, 6H) for 12, 2.13 (s, 3H), 2.11 (s, 6H) for 13],
downfield apical HC protons (0.50 and 0.56 ppm for 12 and
13, respectively], and downfield BMe resonances in 11B NMR
(35.0 and 37.1 ppm for 12 and 13, respectively]. These lines of
evidence point to the neutral species structures with the
dismantled tripodal ligand, presumably derived from the initial
methide abstraction followed by the amido group transfer from
the transient anionic borate center to the cationic zirconocenium
center, giving rise to the final neutral species. On the other hand,
the weaker Lewis acid MeSi[SiMe2N(4-MeC6H4)]3B (A: X )
Si, Y ) Me, Scheme 1) showed no reaction with Cp2ZrMe2
and rac-Et(Ind)2ZrMe2. Overall, the facile ligand back-transfer
observed for the current tripodal borane system further highlights
(33) Cotton, F. A.; Schwotzer, W. J. Am. Chem. Soc. 1986, 108, 4657-
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(34) Fan, B.; Shen, Q.; Lin, Y. J. Organomet. Chem. 1989, 377, 51-
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Vincent, R. L.; Watkin, J. G.; Zwick, B. D. Inorg. Chem. 1994, 33, 3487-
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2002, 102, 1851-1896.
(39) (a) Lee, C. H.; Lee, S. J.; Park, J. W.; Kim, K. H.; Lee, B. Y.; Oh,
J. S. J. Mol. Catal., A: Chem. 1998, 132, 231-239. (b) Biagini, P.; Lugli,
G.; Abis, L.; Andreussi, P. U.S. Pat. 5,602,269, 1997.
(40) Klosin, J.; Roof, G.; Chen, E. Y.-X.; Abboud, K. A. Organometallics
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(41) Feng, S.; Roof, G. R.; Chen, E. Y.-X. Organometallics 2002, 21,
832-839.

5404 Organometallics, Vol. 26, No. 22, 2007
Zhu and Chen
Scheme 8
Table 2. Results of E-CL Polymerization by Tripodal Amido
the importance for having the chemical robustness (minimal
nucleophilicity or basicity) of the resulting anion when paired
with highly electrophilic metallocenium cations.2d
Aluminum Complexesa
run [N3]Al BnOH
no. complex (equiv)
solvent
(mL)
time yield
Mn
MWD b
b
(min) (%) (kg/mol) (Mw/Mn)
The molecular structure of 13 was confirmed by X-ray
diffraction analysis, featuring the neutral methyl zirconocene
amido species in which the original tripodal framework has been
dismantled to the dichelating bis(amido) boron methyl moiety
(Figure 6). The three-coordinate B center was formed in a
triangular geometry with a perfect plane [B(1)N(2)N(3)C(41)
(∆) 0.0054 Å) and 360.0(4)° peripheral angles around B]. The
B-N bonds [1.443(5) and 1.448(6) Å)] are slightly shorter than
those in [N3]B [1.459(2)-1.469(2) Å)],4a and the peripheral
angles around N(2) and N(3) are 359.6(3) and 358.6(3)°,
respectively. These metrical parameters indicate significant
π-interactions over the B-N bonds in comparison to those in
[N3]B. The Zr-C bond distance [2.282(4) Å] in 13 compares
well with a value of 2.270(7) Å found in another monomethyl
derivative rac-Et(Ind)2ZrMe[OC(NMe2)dCMe2].42 The Zr-N
bond [2.127(4) Å] is noticeably longer than those found in rac-
Et(Ind)2Zr(NMe2)2 [2.061(8) and 2.053(9) Å],23 while the
Zr-Ccentoid separations (2.289 and 2.311 Å) are comparable with
values of 2.307 and 2.319 Å observed in rac-Et(Ind)2Zr-
(NMe2)2.23
1
2
3
4
5
6
7
8
1
1
1
1
8
8
8
8
0
0
1
10
0
0
TOL (3)
DCM (5)
DCM (5)
DCM (5)
TOL (3)
DCM (5) 120
DCM (5)
DCM (5)
40c
60
60
60
46
9
48.6
30.4
7.12
2.59
1.99
1.12
34
0
5c >99
51.3
57.2
13.6
2.16
1.77
1.23
1.13
93
93
72
1
10
60
60
2.98
a Carried out in toluene (TOL) or CH2Cl2 (DCM) at 23 °C; 22.5 µmol
of the [N3]Al complex; 200 equiv of ꢀ-CL. b Number average molecular
weight (Mn) and molecular weight distribution (MWD) determined by GPC
relative to PMMA standards in CHCl3. c Gelation time.
insufficient Lewis acidity of this tripodal borane itself. We also
examined ROP of propylene oxide (PO) by selected tripodal
borane and alanes, including structures A, B, and 1, in the
absence and presence of the 1,4-butandiol initiator; however,
monomer conversions of these polymerizations were typically
below 5% in a 5000/1 [PO]/[catalyst] ratio for 2 h reactions at
ambient temperature, as compared to a quantitative PO conver-
sion when B(C6F5)3 was used as catalyst under identical
conditions.
Next, we investigated ROP of CL by tripodal triamido alane
1 and tripodal amido aluminum hydride 8, the results of which
were summarized in Table 2. As can be seen from this table
(runs 1, 2), in either toluene or CH2Cl2, alane 1 produced high
molecular weight (relative to the [CL]/[catalyst] ratio) PCL (Mn
) 4.86 × 104 or 3.04 × 104) but with relatively broad molecular
weight distributions (MWD ) 2.59 or 1.99), indicative of a
nonliving polymerization process. Upon addition of 1 equiv of
benzyl alcohol as initiator or chain-transfer reagent (CTR), the
same polymerization afforded PCL with considerably lower MW
(Mn ) 7.12 × 103) and much narrower MWD of 1.12 (run 3,
Figure 7). An increase in [BnOH] to 10 equiv shut down the
activity (run 4), suggesting this tripodal alane cannot tolerate
excess benzyl alcohol, thus failing to effect catalytic ROP of
CL. Consistent with these polymerization results, the reaction
of 1 and 1 equiv of BnOH showed negligible decomplexation
of the tripodal ligand, but the use of 10 equiv of BnOH caused
ca. 50% decomplexation of the ligand in a few minutes.
In the absence of BnOH or in the presence of 1 equiv of
BnOH, tripodal amido aluminum hydride 8 behaved similarly
to tripodal alane 1 in ROP of CL but with considerably higher
Polymerization Catalysis. Activation of Cp2ZrMe2 and rac-
Et(Ind)2ZrMe2 with tripodal borane HC[SiMe2N(4-MeC6H4)]3B
gave inactive species for ethylene or propylene polymerization.
The inactivity is due to the facile ligand redistribution reaction
leading to neutral complexes 12 and 13, rather than the suspected
Figure 6. X-ray crystal structure of 13 with thermal ellipsoids
drawn at the 30% probability. Selected bond lengths (Å) and angles
(deg): Zr(1)-CC5 ring, 2.606(4) (av) and 2.590(4) (av); Zr(1)-C(42),
2.282(4); Zr(1)-N(1), 2.127(4); B(1)-N(2), 1.443(5); B(1)-N(3),
1.448(6); B(1)-C(41), 1.574(6); N(1)-Zr(1)-C(42), 98.8(2);
N(2)-B(1)-N(3), 118.1(4); N(2)-B(1)-C(41), 120.9(4); N(3)-
B(1)-C(41), 121.0(4).
(42) Mariott, W. R.; Chen, E. Y.-X. Macromolecules 2005, 38, 6822-
6832.

Tridentate Tripodal Triamine Ligand Complexes
Organometallics, Vol. 26, No. 22, 2007 5405
) 4-MeC6H4,4a CH2Ph (1)]. Addition of a small amount of THF
to the reaction medium, instead of the use of the preformed
THF-solvated Li salt, renders the formation of the THF-ring-
opening byproduct HC[SiMe2N(4-MeC6H4)]3Al(OCHdCH2)‚
Li(THF)2.4a On the other hand, without using any THF the
reaction of [N3]Li3 in a Et2O/hexanes solvent mixture produces
LiCl-containing compounds such as HC[SiMe2N(4-MeC6H4)]3-
4a
Al‚ClLi(Et2O)2 and 2.
The products via the ligand elimination route are sensitive
to the reagent MR3 (M ) Al, R ) Me, H, N(SiMe3)2; M )
Sm, R ) N(SiMe3)2]. In general, the reaction of [N3]H3 with 1
equiv of AlMe3 leads to diamido-amino aluminum methyl
complexes such as 3 and 4, while the reaction with g2 AlMe3
affords amido-amino aluminum dimethyl complexes such as
5 and 6. However, none of these methyl aluminum complexes
can undergo further elimination of the third equivalent of CH4
to the still elusive product [N3]Al. The reaction of [N3]H3 with
1 equiv of AlH3 gives a complex mixture, but the use of g2
AlH3 leads cleanly to the formation of tripodal dinuclear
aluminum hydride 8. Although there is no reaction between
[N3]H3 and Al[N(SiMe3)2]3, this amine-elimination route pro-
duces tripodal triamido Sm complex 9 that exhibits a unique
dimeric structure in the solid state with intermolecular interac-
tions adopting different metal-arene bonding modes.
The ligand exchange route involves treatment of the tripodal
borane [N3]B with AlR3 (R ) Me, H). The products also depend
on AlR3; while the reaction using AlMe3 stops at the first-step
ligand exchange product (10), the AlH3 reagent drives the
reaction further to form the second-step ligand exchange product
(11). The third-step ligand exchange, which is required to occur
for obtaining the desired [N3]Al, did not proceed under the
present conditions.
The ligand redistribution products are observed when activat-
ing dimethyl metallocenes Cp2ZrMe2 and rac-Et(Ind)2ZrMe2
with tripodal borane [N3]B. Neutral complexes 12 and 13 are
formed presumably via the initial methide abstraction followed
by the amido group transfer from the transient anionic borate
center to the cationic zirconocenium center. As a result, the
“activated” species 12 and 13 exhibit no activity for ethylene
or propylene polymerization. This observation further highlights
the importance for having the chemically robust anion when
paired with highly electrophilic metallocenium cations.
The tripodal triamido alane 1 exhibits low activity for ROP
of PO, but moderate activity for ROP of CL. The tripodal
aluminum hydride 8 shows much higher activity for ROP of
CL than 1, but more important, 8 effects facile chain-transfer
ROP of CL in the presence of benzyl alcohol as CTR for the
catalytic production of biodegradable polymer.
Figure 7. Overlay of GPC traces of PCL produced by tripodal
alane 1. Broad trace: Mn ) 3.04 × 104, Mw/Mn ) 1.99 for run 2
in Table 2. Narrow trace: Mn ) 7.12 × 103, Mw/Mn ) 1.12 for run
3 in Table 2.
activity (runs 5-7 vs 1-3). More significantly, hydride 8 can
tolerate the benzyl alcohol CTR present in large excess (e.g.,
10 equiv, run 8), producing PCL with its Mn decreasing as the
amount of CTR added increases, characteristic of a chain-
transfer polymerization process. For example, when 10 equiv
of BnOH was employed (run 8), the resulting PCL exhibits a
Mn ) 2.98 × 103 and Mw/Mn ) 1.13, calculating to about six
polymer chains produced per catalyst center. Consistent with
these findings, the reaction of 1 and 1 equiv of BnOH showed
negligible decomplexation of the tripodal ligand and that the
use of 10 equiv of BnOH led to formation of the Al-OCH2Ph
moiety with the tripodal ligand remaining intact. Overall, these
results demonstrate that the aluminum hydride 8 can effect
catalytic ROP of CL in the presence of CTR.
Conclusions
Overall, by employing several different synthetic strategies
described herein we have synthesized a total of 13 new B, Al,
and Sm complexes derived from the tridentate tripodal triamine
ligand with a neopentane, trisilylmethane, or trisilylsilane
backbone and different N-substituents; six of these complexes
have been structurally characterized by X-ray diffraction studies.
We have also investigated the performances of some selected
complexes in polymerization of R-olefins, PO, and CL.
The salt-metathesis route involving a lithium salt of the
tripodal triamido ligand and AlCl3 requires the use of the
preformed THF-solvated Li salt such as HC[SiMe2N-
(CH2Ph)]3Li3(THF)2, and the reaction be carried out in a Et2O/
hexanes solvent mixture. Under these conditions, this route
readily leads to the formation of complete LiCl-elimination
products, tripodal triamido alanes HC[SiMe2NAr]3Al‚(THF) [Ar
Acknowledgment. This work was supported by unrestricted
research funds provided by Sumitomo Chemical Co. Ltd. We
thank Kazuo Takaoki for ethylene polymerization runs and
insightful discussions as well as Susie Miller for the X-ray
diffraction data collections.
Supporting Information Available: Crystallographic data for
complexes 2, 4, 5, 8, 9, and 13‚1.2(hexanes) (CIF). This material
is available free of charge via the Internet at http://pubs.acs.org.
OM700587W