Yao et al.
thesis. Especially, some of these â-diketiminate metal
complexes exhibit exciting reactivity. For example, they
show high activity for the polymerization of ethylene1b and
lactide2c,3n and the copolymerization of carbon dioxide and
epoxide.1c,3l Although many rare earth metal complexes
supported by â-diketiminate anions have been synthesized
in recent years, their catalytic activity remains relatively
poorly explored.1a,2e,4-11 Piers et al. have developed the
chemistry of â-diketiminate scandium and yttrium complexes
and found that related scandium alkyls showed high catalytic
activity for the polymerization of ethylene in the presence
of cocatalysts.4b â-Diketiminate- neodymium borohydride
complex combining with MgnBu2 can catalyze the stereospe-
cific polymerization of isoprene.9 We previously reported
that some divalent â-diketiminate-ytterbium complexes as
single-component catalysts can catalyze the polymerization
of methyl methacrylate (MMA) with low activity,7b but the
mixed-ligand trivalent â-diketiminate-ytterbium amido com-
plexes, [(DIPPh)2nacnac](MeC5H4)YbNR2 (R ) Ph, Pri)
[(DIPPh)2nacnac ) N,N-2,6-diisopropylphenyl-2,4-pentane-
diimine anion], are inactive for this polymerization.7a Arnold
et al. also reported that â-diketiminate-samarium alkyls
[(DIPPh)2nacnac](C5Me5)SmR (R ) Me, CH2SiMe3) and
related cationic species are not active catalysts for ethylene
or MMA polymerization,10 and Hultzsch et al. reported very
recently that linked bis(â-diketiminate)-rare earth metal
complexes copolymerize cyclohexene oxide and CO2 with
low activity.11 Therefore, design and synthesis of new
â-diketiminate-lanthanide complexes, especially investiga-
tion of their catalytic activity, are still meaningful.12
(3) Recent examples for transition metals: (a) Cortright, S. B.; Huffman,
J. C.; Yoder, R. A.; Coalter J. N., III; Johnston, J. N. Organometallics
2004, 23, 2238. (b) Basuli, F.; Huffman, J. C.; Mindiola, D. J. Inorg.
Chem. 2003, 42, 8003. (c) Gregory, E. A.; Lachicotte, R. J.; Holland,
P. L. Organometallics 2005, 24, 1803. (d) Dai, X.; Kapoor, P.; Warren
T. H. J. Am. Chem. Soc. 2004, 126, 4798. (e) Kogut, E.; Zeller, A.;
Warren, T. H.; Strassner T. J. Am. Chem. Soc. 2004, 126, 11984. (f)
Gao, H. Y.; Guo, W. J.; Bao, F.; Gui, G. Q.; Zhang, J. K.; Zhu, F.
M.; Wu, Q. Organometallics 2004, 23, 6273. (g) Arom´ı, G.; Boldron,
C.; Gamez, P.; Roubeau, O.; Kooijman, H.; Spek, A. L.; Stoeckli-
Evans, H.; Ribas J.; Reedijk J. Dalton Trans. 2004, 3586. (h) Chai,
J.; Zhu, H.; Roesky, H. W.; Yang, Z.; Jancik, V.; Herbst-Irmer, R.;
Schmidt, H.-G.; Noltemeyer, M. Organometallics 2004, 23, 5003. (i)
Aboelella, N. W.; Kryatov, S. V.; Gherman, B. F.; Brennessel, W.
W.; Young, V. G., Jr.; Sarangi, R.; Rybak-Akimova, E. V.; Hodgson,
K. O.; Hedman, B.; Solomon, E. I.; Cramer, C. J.; Tolman, W. B. J.
Am. Chem. Soc. 2004, 126, 16896. (j) Reynolds, A. M.; Lewis, E. A.;
Aboelella, N. W.; Tolman, W. B. Chem. Commun. 2005, 2014. (k)
Shimokawa, C.; Itoh S. Inorg. Chem. 2005, 44, 3010. (l) Byrne, C.
M.; Allen, S. D.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc.
2004, 126, 11404. (m) Rieth, L. R.; Moore, D. R.; Lobkovsky, E. B.;
Coates, G. W. J. Am. Chem. Soc. 2002, 124, 15239. (n) Chen, H.-Y.;
Huang, B.-H.; Lin, C.-C. Macromolecules 2005, 38, 5400.
(4) Piers, W. E.; Emslie, D. J. H. Coord. Chem. ReV. 2002, 233-234,
131. (b) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc.
2002, 124, 2132. (c) Hayes, P. G.; Piers, W. E.; Parvez, M. J. Am.
Chem. Soc. 2003, 125, 5622. (d) Hayes, P. G.; Piers, W. E.; Parvez,
M. Organometallics 2005, 24, 1173. (e) Lauterwasser, F.; Hayes, P.
G.; Brase, S.; Piers, W. E.; Schafer, L. L. Organometallics 2004, 23,
2234. (f) Knight, L. K.; Piers, W. E.; Fleurat-Lessard, P.; Parvez, M.;
McDonald, R. Organometallics 2004, 23, 2087. (g) Hayes, P. G.;
Welch, G. C.; Emslie, D. J. H.; Noack, C. L.; Piers, W. E.; Parvez,
M. Organometallics 2003, 22, 1577. (h) Emslie, D. J. H.; Piers, W.
E.; Parvez, M.; McDonald, R. Organometallics 2002, 21, 4226.
(5) (a) Eisenstein, O.; Hitchcock, P. B.; Khvostov, A. V.; Lappert, M. F.;
Maron, L.; Perrin, L.; Protchenko, A. V. J. Am. Chem. Soc. 2003,
125, 10790. (b) Hitchcock, P. B.; Lappert, M. F.; Protchenko, A. V.
Chem. Commun. 2005, 951. (c) Avent, A. G.; Hitchcock, P. B.;
Khvostov, A. V.; Lappert, M. F.; Protchenko, A. V. Dalton Trans.
2004, 2272. (d) Avent, A. G.; Caro, C. F.; Hitchcock, P. B.; Lappert,
M. F.; Li, Z.; Wei, X.-H. Dalton Trans. 2004, 1567. (e) Avent, A. G.;
Hitchcock, P. B.; Khvostov, A. V.; Lappert, M. F.; Protchenko, A. V.
Dalton Trans. 2003, 1070.
We showed previously that lanthanocene amide (MeC5H4)2-
LnNPh2(THF) is a highly active initiator for the polymeri-
-
zation of MMA,13 while replacement one MeC5H4 group
by one [(DIPPh)2nacnac]- group caused a dramatic decrease
of the catalytic activity.7a The reasons might be that the
â-diketiminate is the more bulky and donative ligand,
-
compared with the MeC5H4 group; its coordination to
ytterbium atom increases the steric congestion around the
central metal and decreases the electrophilicity of the metal,
which makes the insertion of MMA into the Ln-N bond
difficult. If the steric congestion around the metal center plays
an important role in the decrease of the activity of
[(DIPPh)2nacnac](MeC5H4)YbNR2, it is to be expected that
less crowded â-diketiminate-lanthanide amides should
exhibit good catalytic activity. In this paper, we synthesized
new â-diketiminate-ytterbium monoamido complexes
[(DIPPh)2nacnac]Yb(NR2)Cl(THF)n (NR2 ) NPri2, NPh2,
NC5H10) and tested their catalytic activity for the polymer-
ization of some polar monomers. Indeed, these â-diketimi-
nate-ytterbium amido complexes can efficiently initiate the
polymerization of MMA and ꢀ-caprolactone. Here we report
these results.
(6) (a) Neculai, A. M.; Neculai, D.; Roesky, H. W.; Magull, J.; Baldus,
M.; Andronesi, O.; Jansen, M. Organometallics 2002, 21, 2590. (b)
Neculai, D.; Roesky, H. W.; Neculai, A. M.; Magull, J.; Herbst-Irmer,
R.; Walfort, B.; Stalke, D. Organometallics 2003, 22, 2279. (c)
Neculai, A.-M.; Cummins, C. C.; Neculai, D.; Roesky, H. W.;
Bunkoczi, G.; Walfort, B.; Stalke, D. Inorg. Chem. 2003, 42, 8803.
(d) Nikiforov, G. B.; Roesky, H. W.; Labahn, T.; Vidovic, D.; Neculai
D. Eur. J. Inorg. Chem. 2003, 433.
(7) (a) Yao, Y. M.; Zhang, Y.; Shen, Q.; Yu, K. B. Organometallics 2002,
21, 819. (b) Yao, Y. M.; Zhang, Y.; Zhang, Z. Q.; Shen, Q.; Yu, K.
B. Organometallics 2003, 22, 2876. (c) Yao, Y. M.; Xue, M. Q.; Luo,
Y. J.; Jiao, R.; Zhang, Z. Q.; Shen, Q.; Wong, W. T.; Yu, K. B.; Sun,
J. J. Organomet. Chem. 2003, 678, 108. (d) Yao, Y. M.; Luo, Y. J.;
Jiao, R.; Shen, Q.; Yu, K. B.; Weng, L. H. Polyhedron 2003, 22, 441.
(e) Zhang, Z. Q.; Yao, Y. M.; Zhang, Y.; Shen, Q.; Wong, W. T.
Inorg. Chim. Acta 2004, 357, 3173. (f) Xue, M. Q.; Yao, Y. M.; Shen,
Q.; Zhang, Y. J. Organomet. Chem. 2005, 690, 4685.
Results and Discussion
Synthesis and Characterization of â-Diketiminate-
Lanthanide Complexes. We previously reported the syn-
thesis and characterization of the dinuclear â-diketimi-
nate-ytterbium dichloride {[(DIPPh)2nacnac]YbCl(µ-Cl)3-
Yb[(DIPPh)2nacnac](THF)} (1), which has a rare triply
chloro-bridged structure.7a Further study revealed that the
bridged structure of complex 1 can be easily broken by DME
(8) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. Orga-
nometallics 2003, 22, 4705.
(9) Bonnet, F.; Visseaux, M.; Barbier-Baudry, D.; Vigier, E.; Kubicki,
M. M. Chem.sEur. J. 2004, 10, 2428.
(10) Cui, C.; Shafir, A.; Schmidt, J. A. R.; Oliver, A. G.; Arnold, J. Dalton
Trans. 2005, 1387.
(12) After we submitted this manuscript, Bochmann and co-workers
reported that (allyl â-diketiminato)lanthanide complexes are effective
initiators for the polymerization of ꢀ-caprolactone and lactide: Sanchez-
Barba, L. F.; Hughes, D. L.; Humphrey, S. M.; Bochmann, M.
Organometallics 2005, 24, 3792.
(11) Vitanova, D. V.; Hampel, F.; Hultzsch, K. C. Dalton Trans. 2005,
1565.
(13) Wang, Y. R.; Shen, Q.; Xue, F.; Yu, K. B. J. Organomet. Chem. 2000,
598, 359.
2176 Inorganic Chemistry, Vol. 45, No. 5, 2006