and fellowships SFRH/BPD/73253/2010 and SFRH/BPD/
44262/2008. We also thank FCT-PHC for the PESSOA Program
2009-2010 (France-Portugal). F. H. is grateful to the ADEME
(French Agency for energy and sustainable development) and
the Région Alsace for a Ph. D. fellowship.
Notes and references
Scheme 3
1 (a) M. S. Lindblad, Y. Liu, A.-C. Albertsson, E. Ranucci and S. Karlsson,
Adv. Polym. Sci., 2002, 157, 139; (b) M. Vert, Biomacromolecules, 2005,
6, 538; (c) L. S. Nair and C. T. Laurencin, Prog. Polym. Sci., 2007, 32,
762.
2 Selected reviews: (a) B. J. O’Keefe, M. A. Hillmeyer and W. B. Tolman, J.
Chem. Soc., Dalton Trans., 2001, 2215; (b) O. Dechy-Cabaret, B. Martin-
Vaca and D. Bourissou, Chem. Rev., 2004, 104, 6147; (c) J. Wu, T.-L. Yu,
C.-T. Chen and C.-C. Lin, Coord. Chem. Rev., 2006, 205, 602;
(d) A. P. Dove, Chem. Commun., 2008, 6446; (e) R. H. Platel, L.
M. Hodgson and C. K. Williams, Polym. Rev., 2008, 48, 11;
(f) C. M. Thomas, Chem. Soc. Rev., 2010, 39, 165; (g) A. Arbaoui and
C. Redshaw, Polym. Chem., 2010, 1, 801.
3 For representative examples on the use of well-defined metal cations for
the ROP of cyclic esters, see: (a) M. D. Hannant, M. Schormann and
M. Bochmann, J. Chem. Soc., Dalton Trans., 2002, 4071; (b) Y. Sarazin,
M. Schormann and M. Bochmann, Organometallics, 2004, 23, 3296;
(c) S. Dagorne, F. Le Bideau, R. Welter, S. Bellemin-Laponnaz and
A. Maisse-François, Chem.–Eur. J., 2007, 13, 3202; (d) C. A. Wheaton, B.
J. Ireland and P. G. Hayes, Organometallics, 2009, 28, 1282; (e) J. Börner,
U. Flörke, K. Huber, A. Döring, D. Kuckling and S. Herres-Pawlis,
Chem.–Eur. J., 2009, 15, 2362; (f) M. Haddad, M. Laghzaoui, R. Welter
and S. Dagorne, Organometallics, 2009, 28, 4584; (g) J.-T. Issenhuth,
J. Pluvinage, R. Welter, S. Bellemin-Laponnaz and S. Dagorne,
Eur. J. Inorg. Chem., 2009, 4701; (h) Y. Sarazin, V. Poirier, T. Roisnel and
J.-F. Carpentier, Eur. J. Inorg. Chem., 2010, 3423; (i) B. J. Ireland, C.
A. Wheaton and P. G. Hayes, Organometallics, 2010, 29, 1079;
( j) H. Sun, J. S. Ritch and P. G. Hayes, Inorg. Chem., 2011, 50, 8063;
(k) C. A. Wheaton and P. G. Hayes, Chem. Commun., 2010, 46, 8404;
(l) E. Piedra-Arroni, P. Brignou, A. Amgoune, S. M. Guillaume, J.-
F. Carpentier and D. Bourissou, Chem. Commun., 2011, 47, 9828;
(m) Y. Sarazin, B. Lin, T. Roisnel, L. Maron and J.-F. Carpentier, J. Am.
Chem. Soc., 2011, 133, 9069.
Fig. 2 Molecular structure (ORTEP view) of the neutral Zn ethyl
complex 4a. Selected bond distances (Å) and angles (°): Zn(1)–N(1) =
2.212(2), Zn(1)–N(2) = 1.876(2), Zn(1)–C(33) = 1.947(2), C(1)–N(1) =
1.278(2), C(12)–N(2) = 1.462(2), N(1)–Zn(1)–N(2) = 83.13(6), N(2)–
Zn(1)–C(33) = 160.3(1), N(1)–Zn(1)–C(33) = 116.60(9).
supported by BIAN-derived amido-imino ligand, was prepared
for subsequent use in ROP of ε-CL. Complex 4a, readily pre-
pared in good yield upon mixing BIAN-Mes with one equiv. of
ZnEt2 (toluene, room temp.), thus arises from the insertion of a
BIAN-imine group into a Zn–Et bond (Scheme 3). Although
never reported in BIAN/organozinc chemistry, a similar reactiv-
ity has been once observed with a related-diimine Zn dialkyl
compound.9 The proposed formulation for complex 4a was
unambiguously established by single-crystal X-ray crystallogra-
phy, confirming the formation of a three-coordinate Zn ethyl
complex (Fig. 2). All bonding and geometrical parameters for 4a
are rather as expected, with a zinc metal centre adopting a dis-
torted planar trigonal geometry.
Compound 4a was found to exhibit a good activity in the bulk
ROP of ε-CL, yet inferior to that of cation 3a+ under identical
conditions (entry 4 vs. entry 7, Table 1). In addition, this lower
catalytic performance for 4a comes along with a broader PDI
(1.27) for the produced ε-PCL.
In conclusion, easily accessible cationic zinc alkyl species
were found to be highly active in the ROP of ε-PCL in the pres-
ence of alcohol sources such as BnOH and (−)-menthol.
Remarkably, these systems retain a high catalytic activity and an
excellent chain length control (of the resulting material) under
bulk polymerization conditions.
4 For a review on the coordination chemistry of BIAN ligands, see:
N. J. Hill, I. Vargas-Baca and A. H. Cowley, Dalton Trans., 2009, 240 and
references therein.
5 For selected examples of groups 12 to 16 metal species supported by
BIAN ligands, see: (a) H. Schumann, M. Hummert, A. N. Lukoyanov and
I. L. Fedushkin, Organometallics, 2005, 24, 3891; (b) I. L. Fedushkin,
A. A. Skatova, V. A. Chudakova and G. K. Kukin, Angew. Chem., Int. Ed.,
2007, 46, 4302; (c) V. Rosa, P. J. Gonzalez, T. Avilés, P. T. Gomes,
R. Welter, A. C. Rizzi, M. C. G. Passeggi and C. D. Brondino,
Eur. J. Inorg. Chem., 2006, 23, 4761; (d) I. L. Fedushkin,
A. N. Lukoyanov, S. Y. Ketkov, M. Hummert and H. Schumann, Chem.–
Eur. J., 2007, 13, 7050; (e) V. Rosa, S. A. Carabineiro, T. Avilés,
P. T. Gomes, R. Welter, J. M. Campos and M. R. Ribeiro, J. Organomet.
Chem., 2008, 693, 769; (f) V. Rosa, C. I. M. Santos, R. Welter, G. Aullón,
C. Lodeiro and T. Avilés, Inorg. Chem., 2010, 49, 8699; (g) P. de Frémont,
H. Clavier, V. Rosa, T. Avilés and P. Braunstein, Organometallics, 2011,
30, 2241.
6 For reviews on metal-based initiators for the immortal ROP of cyclic esters
and carbonates, see: (a) T. Aida and S. Inoue, Acc. Chem. Res., 1996, 29,
39; (b) N. Ajellal, J.-F. Carpentier, C. Guillaume, S. M. Guillaume,
M. Helou, V. Poirier, Y. Sarazin and A. Trifonov, Dalton Trans., 2010, 39,
8363.
7 While complex 2a was isolated in quantitative yield, its analogue 2b was
found to be unstable under vacuum and was thus in situ generated and sub-
sequently ionized.
Acknowledgements
8 A. D. Horton, Organometallics, 1996, 15, 2675.
9 E. Wissing, K. van Gorp, J. Boersma and G. van Koten, Inorg. Chim.
Acta, 1994, 220, 55.
We thank Fundação para a Ciência e Tecnologia (FCT), Portu-
gal for financial support (project PTDC/QUI-QUI/099873/2008
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 3377–3379 | 3379