Indium complexes supported by 1, ω-dithiaalkanediyl-bridged bis(phenolato) ligands: Synthesis, structure, and controlled ring-opening polymerization of L-lactide

Article abstract of DOI:10.1021/ic900161w

Indium bis(phenolato) complexes [ln(L)R(THF)_n] (L = 1,4-dithiabutanedlylbis(4,6-di-tert-butylphenolato) (etbbp), R = Cl, n = 0, 1; L = 1,3-dithiapropanediylbis(6-tert-butyl-4-methylphenolato) (mtbmp), R = Me, n = 1, 2; L = 1, 4-dithiabutanediyl

Full text of DOI:10.1021/ic900161w

5526 Inorg. Chem. 2009, 48, 5526–5534
DOI: 10.1021/ic900161w
Indium Complexes Supported by 1,ω-Dithiaalkanediyl-Bridged Bis(phenolato)
Ligands: Synthesis, Structure, and Controlled Ring-Opening Polymerization
of -Lactide
L
Ilja Peckermann, Andreas Kapelski, Thomas P. Spaniol, and Jun Okuda*
Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany
Received January 25, 2009
Indium bis(phenolato) complexes [In(L)R(THF)n] (L = 1,4-dithiabutanediylbis(4,6-di-tert-butylphenolato) (etbbp), R =
Cl, n = 0, 1; L = 1,3-dithiapropanediylbis(6-tert-butyl-4-methylphenolato) (mtbmp), R = Me, n = 1, 2; L = 1,
4-dithiabutanediyl-bis(6-tert-butyl-4-methyl-phenolato) (etbmp), R = Me, n = 0, 3; L = etbbp, R = CH2SiMe3, n = 0, 4; L =
1,4-dithiabutanediylbis{4,6-di(2-phenyl-2-propyl)phenolato} (etccp), R = CH2SiMe3, n = 0, 5) were prepared from
indium trichloride or from the corresponding tris(alkyl) complexes and 1 equiv of tetradentate 1,ω-dithiaalkanediyl-
bridged bis(phenol) LH2. The monomeric nature of the alkyl indium complexes was shown by X-ray diffraction studies
of the complexes [In(mtbmp)Me(THF)] (2), [In(etbbp)(CH2SiMe3)] (4), and [In(etccp)(CH2SiMe3)] (5). Pseudo-
octahedral configuration was found for 2, while square pyramidal structure was observed for 4 and 5. The isopropoxy
complexes [In(L)(OiPr)] (L = etbbp, 6; etccp, 7) were synthesized starting with indium tris(isopropoxide). Complex 6
crystallized as homochiral dimer of pseudo-octahedral fragments with bridging μ2-alkoxide ligands, but in solution two
diastereomers were observed. The isopropoxy complexes efficiently initiated the ring-opening polymerization of
L-lactide in toluene to give isotactic poly(L-lactides) with narrow molecular weight distribution (Mw/Mn = 1.03-1.18).
Introduction
(ROP) a significant number of discrete initiators based on
Lewis acidic metals,1 including metal alkoxy complexes of
lithium,2 magnesium,3 tin,4 zinc,3,5,7d lanthanides,6 and alu-
minum7 have been introduced. Our interest in indium alk-
oxides as initiator for ROP of PLA stems from their
homologous relation to aluminum and certain analogy to
group 3 metal and lanthanide alkoxides6a,8 and from their
similarity to tin-based initiators,4 currently in commercial
For the production of biodegradable and biocompatible
polyester polylactide (PLA) by ring-opening polymerization
*To whom correspondence should be addressed. E-mail: jun.okuda@ac.
rwth-aachen.de. Fax: +49 241 8092644.
(1) Dechy-Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Chem. Rev. 2004,
104, 6147.
(2) (a) Chisholm, M. H. J. Organomet. Chem. 2008, 693, 808. (b) Yu,
T.-L.; Huang, B.-H.; Hung, W.-C.; Lin, C.-C.; Wang, T.-C.; Ho, R.-M.
Polymer 2007, 48, 4401. (c) Huang, B.-H.; Ko, B.-T.; Athar, T.; Lin, C.-C.
Inorg. Chem. 2006, 45, 7348. (d) Kricheldorf, H. R.; Boettcher, C. Makromol.
Chem. 1993, 194, 1665. (e) Ko, B.-T.; Lin, C.-C. J. Am. Chem. Soc. 2001, 123,
7973. (f) Bero, M.; Dobrzynski, P.; Kasperczyk, J. J. Polym. Sci., Part A:
Polym. Chem. 1999, 37, 4038. (g) Kasperczyk, J. E. Macromolecules 1995, 28,
3937. (h) Kricheldorf, H. R.; Boettcher, C. Makromol. Chem. 1993, 194,
1665.
(3) (a) Chisholm, M. H.; Gallucci, J. C.; Phomphrai, K. Inorg. Chem.
2005, 44, 8004. (b) Chisholm, M. H.; Eilerts, N. W.; Huffman, J. C.; Iyer, S.
S.; Pacold, M.; Phomphrai, K. J. Am. Chem. Soc. 2000, 122, 11845. (c)
Chisholm, M. H.; Huffman, J. C.; Phomphrai, K. J. Chem. Soc., Dalton
Trans. 2001, 3, 222. (d) Chamberlain, B. M.; Cheng, M.; Moore, D. R.; Ovitt,
T. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 3229.
(e) Chisholm, M. H.; Gallucci, J.; Phomphrai, K. Inorg. Chem. 2002, 41,
2785. (f) Wu, J.-C.; Huang, B.-H.; Hsueh, M.-L.; Lai, S.-L.; Lin, C.-C.
Polymer 2005, 46, 9784. (g) Tang, H.-Y.; Chen, H.-Y.; Huang, J.-H.; Lin, C.-
C. Macromolecules 2007, 40, 8855. (h) Sanchez-Barba, L. F.; Garces, A.;
Fajardo, M.; Alonso-Moreno, C.; Fernandez-Baeza, J.; Otero, A.; Antinolo,
A.; Tejeda, J.; Lara-Sanchez, A.; Lopez-Solera, M. I. Organometallics 2007,
26, 6403. (i) Lian, B.; Thomas, C. M.; Casagrande, O. L.Jr.; Roisnel, T.;
Carpentier, J.-F. Polyhedron 2007, 26, 3817. (j) Ovitt, T. M.; Coates, G. W. J.
Am. Chem. Soc. 1999, 121, 4072.
(4) (a) Kalmi, M.; Lahcini, M.; Castro, P.; Lehtonen, O.; Belfkira, A.;
Leskelae, M.; Repo, T. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 1901.
(b) Aubrecht, K. B.; Hillmyer, M. A.; Tolman, W. B. Macromolecules 2002,
35, 644. (c) Storey, R. F.; Mullen, B. D.; Melchert, K. M. J. Macromol. Sci.,
Part A: Pure Appl. Chem. 2001, A38, 897. (d) Kowalski, A.; Libiszowski, J.;
Duda, A.; Penczek, S. Macromolecules 2000, 33, 1964. (e) Abdel-Fattah, T.
M.; Pinnavaia, T. J. Chem. Commun. 1996, 5, 665. (f) Kricheldorf, H. R;
Fechner, B.; Shikanov, A.; Domb, A. Biomacromolecules 2003, 4, 950.
(5) Williams, C. K.; Breyfogle, L. E.; Choi, S. K.; Nam, W.; Young, V. G.,
Jr.; Hillmyer, M. A.; Tolman, W. B. J. Am. Chem. Soc. 2003, 125, 11350.
(6) (a) Ma, H. Y.; Spaniol, T. P.; Okuda J. Angew. Chem., Int. Ed. 2006,
45, 7818. (b) Amgoune, A.; Thomas, C. M.; Ilinca, S.; Roesnel, T.;
Carpentier, J. F. Angew. Chem., Int. Ed. 2006, 45, 2782. (c) Konkol, M.;
Kondracka, M.; Voth, P.; Spaniol, T. P.; Okuda, J. Organometallics 2008,
27, 3774. (d) Ma, H.; Okuda, J. Macromolecules 2005, 38, 2665.
(7) (a) Zhong, Z. Y.; Dijkstra, P. J.; Feijen, J. J. Am. Chem. Soc. 2003, 125,
11291. (b) Emig, N.; Nguyen, H.; Krautscheid, H.; Reau, R.; Cazaux, J. B.;
Bertrand, G. Organometallics 1998, 17, 3599. (c) Hormnirun, P.; Marshall,
E. L.; Gibson, V. C.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 2004,
126, 2688. (d) Zhang, C.; Wang, Z.-X. J. Organomet. Chem. 2008, 693, 3151.
(8) Arnold, P. L.; Buffet, J.-C.; Blaudeck, R. P.; Sujecki, S.; Blake, A. J.;
Wilson, C. Angew. Chem., Int. Ed. 2008, 47, 6033.
r
2009 American Chemical Society
pubs.acs.org/IC
Published on Web 05/08/2009

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5527
Chart 1
Scheme 1
Scheme 2
use. Important factors in the polymerization process such as
activity3b,3d,5 and stereoselectivity3b,3j still need to be ad-
dressed for indium-based initiators.9 Only one report on
structurally defined indium-based initiators has appeared
so far in the literature: Mehrkhodavandi et al.10a recently
introduced a highly active dimeric initiator featuring a chiral
diamine mono(phenolate) ligand of (NNO)-type. Indium
reagents are becoming increasingly important in organic
synthesis because of their new reactivity profile, low toxicity,
and water tolerance.11 We report here structurally well-
defined indium complexes with a tetradentate (OSSO)-type
ligand (Chart 1)12 and the suitability of some of them as
initiators for the controlled ROP of L-lactide.
(4,6-di-tert-butylphenol) (etbbpH2). The chloro complex
[In(etbbp)Cl] (1) was obtained in good yield as colorless
powder (Scheme 1). Because of its low solubility in
nonpolar solvents, we assume 1 to be dimeric.
Results and Discussion
Chloro and Alkyl Complexes. To test the coordination
behavior of the tetradentate (OSSO)-type ligand in in-
dium coordination chemistry, indium trichloride was first
reacted with the lithium salt of 1,4-dithiabutanediylbis
When trimethylindium [InMe3]13 was reacted with
1,3-dithiapropanediyl-bis(6-tert-butyl-4-methyl-phenol)
(mtbmpH2) in tetrahydrofuran (THF) at room tempera-
ture over a period of 2 days, the new methyl complex was
formed under methane elimination and isolated as a white
powder in 36% yield as mono(THF) adduct [In(mtbmp)
Me(THF)] (2) (Scheme 2). NMR spectroscopic and ana-
lytical data of 2 indicate a structure with a tetradentate bis
(phenolato) ligand, one methyl group, and one THF
ligand coordinated to the indium center. Single crystals
were grown from a THF/pentane solution. As shown in
Figure 1, the indium center in 2 is six-coordinated by the
tetradentate bis(phenolato) (OSSO)-type ligand, one
methyl group, and one THF molecule adopting a dis-
torted octahedral geometry (Tables 1 and 2). The methyl
ligand is located cis to the THF ligand and trans to one of
the sulfur atoms; both oxygen donors of the bis(pheno-
lato) ligand are in a trans arrangement, as indicated by the
corresponding angles C1-In-O3 102.82(6), C1-In-S1
103.33(5), and O1-In-O2 149.54(5)°.
(9) Cheng, M.; Attygalle, A. B.; Lobkovsky, E. B.; Coates, G. W. J. Am.
Chem. Soc. 1999, 121, 11583.
(10) (a) Douglas, A. F.; Patrick, B. O.; Mehrkhodavandi, P. Angew.
Chem., Int. Ed. 2008, 47, 2290. (b) For a report on the polymerization of ε-
caprolactone by an indium complex, see: Hsieh, I.-P.; Huang, C.-H.; Lee, H.
M.; Kuo, P.-C.; Huang, J.-H.; Lee, H.-I.; Cheng, J. T.; Lee, G. H. Inorg.
Chim. Acta 2006, 359, 497.
(11) (a) Chapin, R. E.; Harris, M. W.; Hunter, E. S.; Davis, B. J.; Collins,
B. J.; Lockhart, A. C. Fundam. Appl. Toxicol. 1995, 27, 140. (b) Cintas, P.
Synlett 1995, 11, 1087. (c) Pae, A. N.; Cho, Y. S. Curr. Org. Chem. 2002, 6,
715. (d) Podlech, J.; Maier, T. C. Synthesis 2003, 5, 633. (e) Araki, S.; Kamei,
T.; Hirashita, T.; Yamamura, H.; Kawai, M. Org. Lett. 2000, 2, 847. (f)
Babu, G.; Perumal, P. T. Aldrichimica Acta 2000, 33, 16. (g) Chauhan, K. K.;
Frost, C. G. J. Chem. Soc., Perkin Trans. 1 2000, 18, 3015. (h) Loh, T.-P.;
Chua, G. L. Chem. Commun. 2006, 2739. (i) Shanthi, G.; Perumal, P. T.
Synlett 2008, 18, 2791. (j) Shen, Z.-L.; Ji, S.-J.; Loh, T.-P. Tetrahedron 2008,
64, 8159. (k) Xiao, J.; Loh, T.-P. Synlett 2007, 5, 815. Song, J.; Hua, Z.-H.;
Qi, S.; Ji, S.-J.; Loh, T.-P. Synlett 2004, 5, 829. (l) Li, C.-J. Chem. Rev. 1993,
93, 2023. (m) Li, C.-J.; Chan, T.-H. Organic Reactions in Aqueous Media;
Wiley: New York, 1997.(n) Chen, D.-L.; Li, C.-J. Tetrahedron 1996, 52,
5643. (o) Li, C.-J.; Chan, T.-H. Tetrahedron 1999, 55, 11149.
The In-S1 and In-S2 distances are 2.8087(5) and
::
::
(12) (a) Capacchione, C.; Proto, A.; Ebeling, H.; Mulhaupt, R.; Moller,
K.; Spaniol, T. P.; Okuda, J. J. Am. Chem. Soc. 2003, 125, 4964. (b)
Capacchione, C.; Manivannan, R.; Barone, M.; Beckerle, K.; Centore, R.;
Oliva, L.; Proto, A.; Tuzi, A.; Spaniol, T. P.; Okuda, J. Organometallics
2005, 24, 2971. (c) Beckerle, K.; Manivannan, R.; Spaniol, T. P.; Okuda, J.
Organometallics 2006, 25, 3019. (d) Beckerle, K.; Manivannan, R.; Lian, B.;
˚
2.7920(5) A. The only structurally characterized com-
pound reported with coordinative In-S(thioether) bonds
is [InMe3(1,4-dithiane)] with bond lengths of 2.970(1) and
3.134(1) A.14 The In-O bond lengths of 2.1112(12) and
˚
˚
2.1498(12) A in the bis(phenolate) ligand and of 2.2455
Meppelder, G.-J. M.; Raabe, G.; Spaniol, T. P.; Ebeling, H.; Pelascini, F.;
˚
(12) A for the THF ligand in 2 fall into the range of
::
Mulhaupt, R.; Okuda, J. Angew. Chem., Int. Ed. 2007, 46, 4790. (e)
terminal In-O bond lengths in octahedral complexes.
Meppelder, G.-J. M.; Beckerle, K.; Manivannan, R.; Lian, B.; Raabe, G.;
Spaniol, T. P.; Okuda, J. Chem. Asian J. 2008, 3, 1312. (f) Gall, B.; Pelascini,
::
F.; Ebeling, H.; Beckerle, K.; Okuda, J.; Mulhaupt, R. Macromolecules 2008,
(13) Runge, F.; Zimmermann, W.; Pfeiffer, H.; Pfeiffer, I. Z. Anorg. Allg.
Chem. 1951, 267, 39.
(14) Blank, J.; Hausen, H.-D.; Schwarz, W.; Weidlein, J. J. Organomet.
41, 1627. (g) Lian, B.; Beckerle, K.; Spaniol, T. P.; Okuda, J. Angew. Chem.,
Int. Ed. 2007, 46, 8507. (h) Lian, B.; Spaniol, T. P.; Okuda, J. Organome-
tallics 2007, 26, 6653.
Chem. 1993, 443, 145.

5528 Inorganic Chemistry, Vol. 48, No. 12, 2009
Peckermann et al.
The methyl complex [In(etbmp)(Me)] (3) was prepared
in a similar manner from [InMe3] and etbmpH2 in hexane
under methane elimination. According to analytical and
NMR spectroscopic data, 3 does not contain a THF
molecule. When [In(CH2SiMe3)3]15 was reacted with
1,4-dithiabutanediylbis(4,6-di-tert-butylphenol)
(etbbpH2) complex [In(etbbp)(CH2SiMe3)] (4) was ob-
tained. Analogously, the reaction of [In(CH2SiMe3)3]
with 1,4-dithiabutanediylbis{4,6-di(2-phenyl-2-propyl)
phenolato} (etccp) gave the compound [In(etccp)
(CH2SiMe3)] (5) which were isolated as colorless crystals
in high yield (Scheme 3).
Complex [In(etbmp)(CH2SiMe3)] (4) crystallizes with
the indium center in a square pyramidal coordination
(Figure 2). The oxygen and sulfur atoms of the (OSSO)-
type ligand occupy the basal positions, and the trimethyl-
silylmethyl group is situated in the axial position. No
additional donor molecules such as THF coordinate to
the metal center, as found for 2. We ascribe this to the
more encumbered site, generated by the 1,4-dithiabuta-
nediyl-bridged ligand in 4 as compared to the shorter 1,3-
dithiapropanediyl-bridge in 2.20 The In-S distances are
˚
2.6372(6) and 2.8177(6) A and somewhat shorter than the
values found in 2. The In-O bond lengths of 2.0993(14)
and 2.0720(14) A are also shorter than the bond lengths
found in 2.
˚
Figure 3 shows the results of a single crystal X-ray
diffraction study of 5, confirming the square pyramidal
coordination geometry as in 4. The molecule is disordered
in the solid state and split positions were introduced in the
refinement. The distance between the metal center and the
sulfur atom S1 that is refined without split positions is
˚
2.7966(17) A and is similar to those in 4. In solution, the
introduction of cumyl substituents with diastereotopic
methyl groups, in addition to the methylene protons of
the trimethylsilylmethyl group, allow the study of config-
urational stability in solution (Figure 4). Variable-tem-
perature NMR spectra of 5 in THF-d8 over the
temperature range -60 °C to +55 °C are displayed in
Figure 5. Broad signals at 1.48 (6 H) and 1.57 (6 H) ppm
are observed for the methyl groups for the ortho-CMe2Ph
substituent groups and at 1.64 (12 H) ppm for the
resonances of the cumyl-groups in para position at
-60 °C. With increasing temperature, the ortho-signals
shift together to one broad signal at 1.56 (12 H) ppm at
55 °C, but no complete coalescence of the signals could be
observed within the measured temperature range. Mea-
surements up to +90 °C in toluene-d8 did not show any
significant shift of those signals. We explain this observa-
tion by a high barrier of the square pyramidal ground
state structure to any more symmetrical geometry in
which the diastereotopic groups become equivalent.
Isopropoxy Compounds. The chloro complex 1 did not
undergo clean nucleophilic substitution with alkali metal
isopropoxide. Alcoholysis experiments with isopropanol
Figure 1. ORTEP diagram of the molecular structure of [In(mtbmp)
(Me)(THF)] (2). Displacement ellipsoids are drawn at the 50% prob-
ability level. Hydrogen atoms, as well as the non coordinated solvent
molecule THF, are omitted for clarity.
Table 1. Crystallographic Data for Compounds 2, 4, 5, and 6
2
4
5
6
empirical formula
Mr (g mol-1
crystal size (mm)
crystal color and habit
crystal system
C28H41InO3S2 C4H8O
676.65
0.31 ꢀ 0.18 ꢀ 0.17
colorless block
triclinic
C34H55InO2S2Si
702.81
0.26 ꢀ 0.17 ꢀ 0.10
colorless plate
triclinic
C54H63InO2S2Si
951.07
0.24 ꢀ 0.17 ꢀ 0.08
colorless block
monoclinic
P21/n
11.5395(7)
21.0783(13)
20.0309(13)
90
96.922(12)
90
4836.7(5)
4
1.306
130(2)
0.639
1992
C66H102In2O6S4 4(C7H8)
1717.89
0.28 ꢀ 0.21 ꢀ 0.18
colorless block
triclinic
3
3
)
3
space group
˚
P1
P1
P1
a (A)
9.3348(8)
12.2093(11)
14.7162(13)
92.3820(12)
102.4243(12)
97.0638(12)
1621.5(2)
2
1.386
130(2)
0.891
708
9.4901(9)
13.7106(13)
14.8931(14)
75.9303(15)
74.9451(15)
79.3503(15)
1799.8(3)
2
1.297
130(2)
0.833
740
16.0249(17)
16.5918(18)
19.590(2)
111.8279(15)
108.6914(16)
90.3753(16)
4533.1(8)
2
1.259
130(2)
0.651
1816
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
Dcalc (g cm-3
T (K)
)
3
μ (mm-1
F(000)
)
θ range (deg)
2.3 - 30.9
24651
9325
2.2 - 30.4
27628
10390
2.2 - 24.9
50681
8351
2.2 - 29.8
66960
25242
no. of refl. collected
no. of independent refl.
Rint
0.0359
0.0566
0.0678
0.0591
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
goodness of fit on F2
0.0299, 0.0628
0.0357, 0.0642
0.948
0.0362, 0.0619
0.0533, 0.0655
0.768
0.0623, 0.1389
0.0900, 0.1553
1.034
0.0533, 0.1331
0.0857, 0.1462
0.952
-3
˚
ΔFmax, min/e A
0.926, -0.573
1.072, -0.651
1.090, -2.459
2.623, -0.899

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5529
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) of [In(mtbmp)Me(THF)]
(2) (R1 = C1, R2 = O3), [In(etbbp)(CH2SiMe3)] (4) (R1 = C31), [In(etccp)
(CH2SiMe3)] (5) (R1 = C51a), and [{In(etbbp)(OiPr)}2] (6) (R1 = O3, R2 = O4)a
2
4
5
6
In-O1
In-O2
In-S1
In-S2
In-R1
In-R2
2.1498(12)
2.1112(12)
2.8087(5)
2.7920(5)
2.1421(19)
2.2455(12)
2.0993(14)
2.0720(14)
2.6372(6)
2.8177(6)
2.127(2)
2.062(3)
2.070(4)
2.7966(17)
2.749(2)
2.144(13)
2.097(2)
2.103(2)
2.6734(10)
2.6828(10)
2.125(2)
2.110(2)
O1-In-O2
O1-In-R1
O2-In-R1
O1-In-S2
O2-In-S2
R1-In-S2
O1-In-S1
O2-In-S1
R1-In-S1
S1-In-S2
149.54(5)
101.98(6)
108.19(6)
75.91(3)
92.00(6)
110.92(7)
123.64(8)
149.65(4)
75.38(4)
98.91(6)
76.23(4)
97.58(4)
136.90(6)
78.215(19)
90.90(14)
113.9(4)
104.8(4)
109.55(11)
77.48(11)
136.4(4)
75.33(10)
140.03(10)
115.1(4)
157.56(10)
89.36(9)
111.53(10)
95.50(7)
76.42(7)
91.80(7)
76.55(7)
81.80(7)
164.97(7)
84.48(3)
73.68(4)
Figure 2. ORTEP diagram of the molecular structure of [In(etbmp)
(CH2SiMe3)] (4). Displacement ellipsoids are drawn at the 50% prob-
ability level. Hydrogen atoms are omitted for clarity. For tert-butyl
groups, only carbon atoms connected to the phenyl rings are shown.
168.71(5)
71.15(3)
97.38(4)
103.33(5)
65.421(14)
72.51(6)
a For 5, the values relate to the sulfur atom S2a.
Scheme 3
Figure 3. ORTEP diagram of the molecular structure of [In(etccp)
(CH2SiMe3)] (5). Displacement ellipsoids are drawn at the 50% prob-
ability level. Hydrogen atoms are omitted for clarity.
(Scheme 4). There was no change upon addition
of pyridine to the toluene solution of 6, indicating
that the dimer is stable toward Lewis bases at ambient
temperature.
using [In(L)(CH2SiMe3)] (4, 5) resulted in the release of
the bis(phenol) ligand. Thus, the isopropoxy complexes 6
and 7 were synthesized via the tris(isopropoxide) indium
complex,16,17 prepared by salt metathesis of indium tri-
halide with sodium isopropoxide, followed by protono-
lysis with etbbpH2 and etccpH2.
Figure 6 shows the homochiral indium alkoxide com-
plex 6 which crystallizes as a dimer with two bridging μ2-
oxygen atoms of the isopropoxide ligands. Both indium
centers are found in a distorted octahedral geometry, as
reflected in the values for the angles O1-In1-O2 157.56
(10)° and O5-In2-O6 153.99(10)° (cis-R configuration).
The 1H NMR spectrum in THF-d8 of 6 displays two full
sets of signals with a 1:1 ratio which does not vary in
intensity between +65 and -60 °C. The observation of
two septets at δ 4.59 and 4.77 ppm for the isopropoxy
methine protons in 6 over the whole temperature range
from -60 °C to +65 °C suggests the presence of two
dimers of this bis(phenolate) isopropoxide complex. One
signal set represents the meso (Λ,Δ); the second set, the
racemic mixture of Λ,Λ and Δ,Δ isomers. We assume that
the formation of dimer is irreversible and that the mono-
mer is not in a fast equilibrium in solution with the dimers
˚
The In-S bond lengths of 2.6734(10) and 2.6828(10) A,
˚
as well as 2.6591(9) and 2.6936(10) A, are shorter than
those in the previously mentioned complexes 2, 4, and 5.
˚
i
The In-O(O Pr) distances are 2.110(2), 2.125(2) A, 2.100
(2), and 2.123(2) A. With an average value of 2.11 A, the
˚
˚
˚
coordinative bonds are about 0.2 A shorter than those
in the oxygen centered cluster [In5(μ5-O)(μ3-OiPr)4(μ2-
OiPr)4(OiPr)5] reported by Bradley et al.17 Noteworthy is
the large angle of 57.48(2)° between the planes spanned by
S1-In1-S2 and S3-In2-S4.18
(15) (a) Beachley, O. T.Jr.; Rusinko, R. N. Inorg. Chem. 1979, 18, 1966.
(b) Kopasz, J. P.; Hallock, O. T.; Beachley, O. T.Jr. Inorg. Synth. 1986, 24,
89. (c) Peckermann, I.; Robert, D.; Englert, U.; Spaniol, T. P.; Okuda, J.
Organometallics 2008, 27, 4817.
(16) (a) Mehrotra, A.; Mehrotra, R. C. Inorg. Chem. 1972, 11, 2170. (b)
Chatterjee, S.; Bindal, S. R.; Mehrotra, R. C. J. Indian Chem. Soc. 1976, 53,
867.
The 1H NMR spectrum of complex 7 displays only one
set of signals in THF-d8, excluding the presence of
=
diastereomers. Two doublets at 1.01 and 1.17 (3JHH
6.0 Hz) ppm of equal intensity as well as one septet at 3.55
(17) (a) Bradley, D. C.; Chudzynska, H.; Frigo, D. M.; Hammond, M. E.;
::
Hursthouse, M. B.; Mazid, M. A. Polyhedron 1990, 9, 125. (b) Neumuller, B.;
(18) Meppelder, G.-J. M.; Spaniol, T. P.; Okuda, J. J. Organomet. Chem.
2006, 691, 3206.
Heravi, M. M.; Chamazi, N. N. Z. Anorg. Allg. Chem. 2006, 632, 2043.

5530 Inorganic Chemistry, Vol. 48, No. 12, 2009
Peckermann et al.
1
Figure 4. H NMR spectrum of 5 in THF-d8 at 25 °C. The right inset shows the AA0BB0 signal due to the methylene protons of the CH2SiMe3 group; the
left inset depicts that of the CH2CH2 backbone of the ligand.
Figure 5. Variable temperature 1H NMR spectra of complex 5 in THF-d8. The resonances for the CMe2Ph substituents are shown.
(3JHH = 6.0 Hz) ppm show the coordinated isopropoxy
ligand. The characteristic AA0BB0 pattern of the
SCH2CH2S bridge is found at 2.07 and 2.85 ppm. We
assume that compound 7 is monomeric in solution be-
cause of the steric hindrance caused by the etccp ligand or
exists as only one diastereomer.
different conditions. Both complexes are active in the
ROP of L-lactide. In reactions monitored to 90% conver-
sion by H NMR spectroscopy (toluene-d8, 20-70 °C),
100 equiv of L-lactide were converted to PLA by 7 at 50 °C
in 200 min. The polymerization proceeded in a controlled
fashion (Mw/Mn = 1.03-1.07) over the conversion range
(Table 3, Figure 7). However, inspection of the molecular
weights Mn as compared with calculated values show
1
ROP of L-lactide. The isopropoxy complexes 6 and 7
were tested as initiators for the ROP of L-lactide under

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5531
rather non-systematic deviations and no linear relation-
ship between Mn and conversion could be found.
Mw/Mn as low as 1.03. The polymerization experiments
with rac-lactide resulted in atactic polylactide.
Polymerizations carried out in the temperature range of
20 to 100 °C led to activation parameters from the Eyring
plot (ΔH‡ = 79(0) kJ mol-1, ΔS‡ =-41(6) J K-1 mol-1 for
6 and ΔH‡ = 62(3) kJ mol-1, ΔS‡ = -89(1) J K-1 mol-1
for 7). These values are comparable with values reported
for the indium phenolate initiator reported by Mehrkho-
davandi et al.10a (ΔH‡ = 49(2) kJ mol-1, ΔS‡ = -140(12)
J K-1 mol-1), and indicate an ordered transition state in a
coordination insertion mechanism.19 On the basis of these
results, we conclude that 7 is more active than 6. This might
be the result of the different position of the monomer-
dimer equilibrium for 6 or a initiation from the dinuclear
species.10a In comparison to previously reported aluminum
initiators with an (OSSO)-type ligand,20 which gave poly-
mers of molecular weights of up to 520,000 g mol-1 within
2 h at 24 °C, indium initiator 7 produced polylactide with
molecular weights of up to 30,000 g mol-1. The isolated
isotactic polymers are more uniform with a value for
Conclusions
Bis(phenolate) indium complexes featuring (OSSO)-type
ligand can be coordinated to trivalent indium centers. No-
tably, square pyramidal geometry with cis-O donors was
found for [In(etbbp)(CH2SiMe3)] (4) and [In(etccp)
(CH2SiMe3)] (5) according to crystal structure analysis, while
[In(mtbmp)Me(THF)] (2) with a 1,3-dithiapropanediyl-phe-
nolato ligand shows local C2-symmetry with trans-O donors
(cis-R configuration).21 Notably the isopropoxy complex [In
(etbbp)(OiPr)] (6) contains this type of coordination. In the
aluminum complex [Al(etbmp)(Et)], homologous to the alkyl
complexes 4 and 5, only one of the two sulfur donors is
coordinated, evidently because of the significantly smaller
metal center (ionic radius for Al3+ 0.535 A versus for In
˚
3+
20
˚
0.800 A, CN = 6). Both In-S interatomic distances are
comparable with related yttrium complexes [Y(etccp){N
˚
(SiHMe2)2}] which contain a larger central atom (0.900 A
for Y3+).22,23 Both indium isopropoxy complexes containing
a (OSSO)-type ligand 6 and 7 polymerized L-lactide in toluene
in a controlled ring-opening reaction to give isotactic poly-
mers with narrow Mw/Mn values. Compared to the recently
introduced chiral indium initiator with a monoanionic
(NNO)-type ligand by Mehrkhodavandi et al.10a complexes
6 and 7 require longer reaction time at elevated temperature
but give narrow polydispersities. When compared with re-
lated aluminum23 and rare-earth20 initiators containing an
(OSSO)-type ligand, the activity of the indium complexes 6
and 7 appears to be lower.
Experimental Part
Figure 6. ORTEP diagram of the molecular structure of homochiral
(Δ,Δ) dimer of [{In(etbbp)(OiPr)}2](6). Displacementellipsoidsare drawn
at the 50% probability level. Hydrogen atoms, as well as the non
coordinated solvent toluene molecules, are omitted for clarity. For tert-
butyl groups, only carbon atoms connected to the phenyl rings are shown.
General Considerations. All operations were performed
under an inert atmosphere of argon using standard Schlenk-
line or glovebox techniques. Toluene, hexane, and THF were
distilled under argon from sodium/benzophenone ketyl prior to
Scheme 4

5532 Inorganic Chemistry, Vol. 48, No. 12, 2009
Peckermann et al.
use. Pentane was purified by distillation from sodium/triglyme
benzophenone ketyl. Dichloromethane was distilled from cal-
cium hydride. Anhydrous indium trichloride (ABCR) was used
as received. Benzene-d6, chloroform-d1, THF-d8, and other
reagents were carefully dried and stored in a glovebox. The used
bis(phenols) 1,3-dithiapropanediyl-bis(6-tert-butyl-4-methyl-
phenol) (mtbmpH2),24 1,4-dithiabutanediyl-bis(6-tert-butyl-4-
methyl-phenolato), (etbmpH2),11b 1,4-dithiabutanediyl-bis
(4,6-di-tert-butylphenol), (etbbpH2),11g,20,25 and 1,4-dithiabu-
tanediylbis(4,6-dicumyl-phenol) (etccpH2)11a,11b were synthesized
according to reported methods, as were trimethylindium13 and tris
(trimethylsilylmethyl)indium.15 L-lactide (Aldrich) was recry-
stallized from dry toluene and sublimed twice under vacuum
at 50 °C. All other chemicals were commercially available and
used after appropriate purification. Glassware and vials used in
the polymerization were dried in an oven at 140 °C overnight and
exposed to vacuum-argon cycle three times.
NMR spectra were recorded on Bruker DRX 400, Varian 200
and 500 spectrometers at 25 °C (1H: 200, 400, 500 MHz; 13C: 50,
100, 125 MHz) unless otherwise stated. Chemical shifts for 1H
and 13C NMR spectra were referenced internally using residual
solvent resonances and reported relative to tetramethylsilane.
1
NMR assignments were confirmed by APT, H-1H (COSY),
1H-13C (HMQC) experiments where necessary. Elemental
analyses were performed by the microanalytical laboratory of
this department. Spectroscopic analysis of polymers was per-
formed in CDCl3. Molecular weights and polydispersities of
polymer samples were determined by size exclusion chromato-
graphy (GPC) in THF at 35 °C, at a flow rate of 1 mL/min
utilizing an Agilent 1100 Series HPLC, G1310A isocratic pump,
an Agilent 1100 Series refractive index detector and 8 ꢀ 600 mm,
8 ꢀ 300 mm, 8 ꢀ 50 mm PSS SDV linear M columns. Calibration
standards were commercially available narrowly distributed
linear polystyrene samples that cover a broad range of molar
masses (103 < Mn < 2 ꢀ 106 g mol-1).
Table 3. ROP of L-Lactide by Indium Complexes 4, 6, and 7
entry init. T (°C) (LA)0/(In)0 t (h) conv.d (%) Mn,exp (ꢀ103)e Mw/Mn
1
2
3
4
5
6
7
8
4
7
7
7
7
7
6
6
6
6
6
6
6
6
6
6
6
100
50
100
50
100
50
50
50
100a
100b
100b
100b
100b
100c
100c
100c
100c
100c
100c
100c
25c
4
4
4
2
2
2
4
6
8
2
4
6
4
4
4
4
4
27
35
99
96
99
66
65
75
61
60
67
86
30
22
66
95
99
7.54
1.12
1.08
1.06
1.07
1.07
1.06
1.03
1.06
1.09
1.15
1.10
1.18
1.12
1.09
1.05
1.08
1.10
28.88
12.41
6.03
12.30
8.87
11.54
14.56
11.43
14.44
12.24
15.83
2.44
9
50
10
11
12
13
14
15
16
17
100
100
100
50
50
50
(Chloro){1,4-dithiabutanediylbis(4,6-di-tert-butylpheno-
lato)}indium (1). To a cold suspension (-20 °C) of InCl3
(50 mg, 0.2 mmol) in 5 mL of toluene was added a cold
suspension of Li2(etbbp) (117 mg, 0.2 mmol) in 5 mL of toluene.
The mixture was allowed to warm to room temperature over-
night. After the removal of all volatiles, the residue was washed
with pentane (3 ꢀ 5 mL) to give a white powder; yield: 83 mg
50c
5.57
8.70
14.91
15.89
75c
50
50
150c
200c
1
(64%). H NMR (400 MHz, CDCl3): δ 1.26 (s, 2 ꢀ 9 H, C
(CH3)3), 1.27 (s, 2 ꢀ 9 H, C(CH3)3), 2.46 (AA0BB0, 1 ꢀ 2 H,
2JHH = 10.0 Hz, SCH2), 3.22 (AA0BB0, 1 ꢀ 2 H, 2JHH = 9.8 Hz,
CH2S), 7.16 (d, 1 ꢀ 2 H, 3JHH = 2.5 Hz, Ph-H), 7.18 (d, 1 ꢀ 2 H,
3JHH = 2.5 Hz, Ph-H). 13C{1H} NMR (128 MHz, CDCl3): δ
a (In)0 = 1.9 mmol/L. b (In)0 = 1.97 mmol/L. c (In)0 = 3.40 mmol/L.
d Monomer conversion determined by 1H NMR spectroscopy. e Deter-
mined by GPC using polystyrene standard and corrected using the
Mark-Houwink factor of 0.58.
Figure 7. Eyring plot for the polymerization of L-lactide using 6 and 7.

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5533
30.5 (4-C(CH3)3), 31.1 (6-C(CH3)3), 31.7 (4-C(CH3)3), 34.0
(6-C(CH3)3), 34.7 (SCH2CH2S), 115.5 (Ph-C2), 125.1 (Ph-C5),
129.7 (Ph-C3), 137.7 (Ph-C4), 138.1 (Ph-C6), 163.9 (Ph-C1).
Anal. Calcd for C30H44ClInO2S2: C, 55.34; H, 6.81. Found: C,
54.77; H, 6.61.
(4-C(CH3)3), 36.2 (6-C(CH3)3), 38.6 (SCH2CH2S), 113.7
(Ph-C2), 127.1 (Ph-C5), 127.9 (Ph-C3), 137.8 (Ph-C4), 140.0
(Ph-C6), 162.7 (Ph-C1). 1H NMR (400 MHz, CDCl3): δ 0.05 (s,
1 ꢀ 2 H, SiCH2), 0.11 (s, 3 ꢀ 3 H, Si(CH3)3), 1.30 (s, 2 ꢀ 9 H, 4-C
(CH3)3), 1.41 (s, 2 ꢀ 9 H, 6-C(CH3)3), 7.20 (s, 2 ꢀ 1 H, Ph-5),
7.26 (s, 2 ꢀ 1 H, Ph-3). 1H NMR (400 MHz, toluene-d8): δ 0.00
(s, 1 ꢀ 11 H, CH2Si(CH3)3), 1.11 (s, 2 ꢀ 9 H, 4- C(CH3)3), 1.46
(s, 2 ꢀ 9 H, 6-C(CH3)3), 2.03 (m, 1 ꢀ 2 H, SCH2), 2.25 (m, 1 ꢀ
2 H, CH2S), 7.11 (s, 2 ꢀ 1 H, Ph-3), 7.31 (s, 2 ꢀ 1 H, Ph-5). Anal.
Calcd for C34H55InO2S2Si: C, 58.10; H, 7.89. Found: C, 58.16;
H, 7.73.
{1,3-Dithiapropanediylbis(6-tert-butyl-4-methylpheno-
lato)}(methyl)indium (2). To a suspension of 1,3-dithiapro-
pandiyl-bis(6-tert-butyl-4-methylphenol) (253 mg, 6.25 mmol)
in 5 mL of THF was slowly added a solution of trimethylindium
(100 mg, 6.25 mmol) in 5 mL of THF. After 10 min the
suspension became clear with concomitant methane evolution.
The clear solution was stirred for 48 h at ambient temperature,
all volatiles were removed in vacuo, and the residue was washed
twice with pentane to give a white powder; yield 140 mg (36%).
Crystals were grown from a THF/pentane solution at -30 °C.
1H NMR (400 MHz, CDCl3): δ -0.09 (s, 1 ꢀ 3 H, InCH3), 0.89
(s, 1 ꢀ 9 H, 6-C(CH3)3), 1.42 (s, 1 ꢀ 9 H, 60-C(CH3)3), 2.12 (s, 1 ꢀ
[1,4-Dithiabutanediylbis{4,6-di(2-phenyl-2-propyl)phe-
nolato](trimethylsilylmethyl)indium (5). To a solution of [In
(CH2SiMe3)3] (200 mg, 0.531 mmol) in 8 mL of benzene was
added a solution of 1,4-dithiabutanediylbis{4,6-di(2-phenyl-2-
propyl)phenol} (399 mg, 0.531 mmol) in 8 mL of benzene. The
bright yellow solution was heated for 1 h at 70 °C. After removal
of all volatiles, the colorless precipitate was washed a few times
with pentane and dried under reduced pressure; yield: 298 mg
(59%); mp 189-191 °C. Crystals were grown from a saturated
THF/pentane solution over a period of one week. 1H NMR (400
MHz, THF-d8,): δ -0.79 (d, 2JHH = 12.1 Hz, 1 ꢀ 1 H, CH2Si),
-0.69 (d, 2JHH = 12.1 Hz, 1 ꢀ 1 H, CH2Si), -0.14 (s, 1 ꢀ 9 H,
SiCH3), 1.57 (s, 2 ꢀ 6 H, 6-cumyl-CH3), 1.64 (s, 2 ꢀ 6 H, 4-
cumyl-CH3), 2.07 (AA0BB0, 2JHH = 10.8 Hz, 1 ꢀ 2 H, SCH2),
2.85 (AA0BB0, 2JHH = 10.8 Hz, 1 ꢀ 2 H, SCH2), 6.95 (m, 4 H,
Ph-H), 7.04-7.10 (m, 10 H, Ph-H), 7.15-7.24 (m, 10 H, Ph-H).
13C{1H} NMR (128 MHz, THF-d8): δ -2.3 (CH2Si), 0.0
(SiCH3), 27.5, 27.8, 29.1, 29.2 ((CH3)2C), 33.2 (SCH2), 110.3
(Ph-C), 122.8 (Ph-C2), 123.8 (Ph-C), 124.2 (Ph-C), 125.2 (Ph-C),
125.8 (Ph-C), 126.2 (Ph-C), 127.2 (Ph-C), 128.7 (Ph-C5), 134.2
(Ph-C4), 136.1 (Ph-C6), 150.2 (Ph-C), 150.6 (Ph-C), 161.1 (Ph-
C1). Anal. Calcd for C54H63InO2S2Si: C, 68.19; H, 6.68. Found:
C, 67.37; H, 7.00.
3 H, 4-CH3), 2.36 (s, 1 ꢀ 3 H, 40-CH3), 3.28 (AA0BB0, 2JHH
=
2
13.2, 1 ꢀ 2 H, SCH2), 4.47 (AA0BB0, JHH = 13.2, 1 ꢀ 2 H,
CH2S), 6.93 (d, 3JHH = 4.0 Hz, 2 ꢀ 1 H, Ph-3, Ph-30), 7.19 (d,
3JHH = 4.0 Hz, 1 ꢀ 1 H, Ph-5), 7.24 (d, 3JHH = 4.0 Hz, 1 ꢀ 1 H,
13
Ph-50); C{1H} (128 MHz, CDCl3): δ 20.4 (InCH3), 25.6 (40-
CH3), 29.1 (4-CH3), 29.4 (60-C(CH3)3), 32.0 (60-C(CH3)3), 34.8
(6-C(CH3)3), 35.6 (6-C(CH3)3), 44.7 (SCH2CH2S), 120.0 (Ph-
C20), 123.9 (Ph-C2), 126.8 (Ph-C4), 130.2 (Ph-C50), 130.4 (Ph-
C5), 130.5 (Ph-C30), 131.0 (Ph-C3), 132.0 (Ph-C0), 132.7 (Ph-C),
140.7 (Ph-C60), 140.8 (Ph-C6), 161.8 (Ph-C10), 167.5 (Ph-C1).
Anal. Calcd for C28H41InO3S2: C, 55.63; H, 6.84. Found:
C, 55.53; H, 6.68.
{1,4-Dithiabutanediylbis(6-tert-butyl-4-methylphenola-
to)}(methyl)indium (3). To a suspension of 1,4-dithiabutane-
diylbis(6-tert-butyl-4-methylphenol) (131 mg, 3.1 mmol) in
5 mL of n-hexane was slowly added a solution of trimethylin-
dium (50 mg, 3.1 mmol) in 5 mL of hexane and stirred for 24 h at
ambient temperature. All volatiles were removed in vacuo to
give a white powder; yield 125 mg (84%). 1H NMR (400 MHz,
CDCl3): δ 0.46 (s, 1 ꢀ 3 H, InCH3), 1.36 (s, 2 ꢀ 9 H, 6-C(CH3)3),
2.19 (s, 2 ꢀ 3 H, 4-CH3), 3.04 (m, 1 ꢀ 2 H, SCH2), 3.13 (m, 1 ꢀ 2
H, CH2S), 7.03 (d, 3JHH = 2.3 Hz, 1 ꢀ 2 H, Ph-3, Ph-30), 7.11
(dd, 2JHH = 0.8 Hz, 3JHH = 1.5 Hz, 1 ꢀ 2 H, Ph-5, Ph-50). 13C
{1H} (128 MHz, toluene-d8): δ 20.7 (InCH3), 29.8 (4-CH3),
35.9 (6-C(CH3)3), 38.6 (SCH2SCH2), 114.0 (Ph-C2), 124.1
(Ph-C3), 130.9 (Ph-C5), 131.8 (Ph-C4), 140.4 (Ph-C6), 162.9
(Ph-C1). Anal. Calcd for C25H35InO2S2: C, 54.94; H, 6.46.
Found: C, 55.05; H, 6.23.
{1,4-Dithiabutanediylbis(4,6-di-tert-butylphenolato)}(iso-
propoxy)indium (6). A solution of “[In(OiPr)3]” (300 mg,
1.0 mmol) in 3 mL of toluene was added dropwise to a suspen-
sion of 1,4-dithiabutanediylbis(4,6-di-tert-butylphenol) (516
mg, 1.0 mmol) in 15 mL of toluene at -78 °C, and the reaction
mixture was stirred for 1.5 h at this temperature and for 16 h at
60 °C. After the removal of the volatiles the yellow residue was
dissolved in pentane and dried under reduced pressure to give a
colorless powder; yield 550 mg (82%). Crystals were grown from
saturated toluene solutions at -30 °C over a period of 4 months.
1H NMR (400 MHz, THF-d8): δ 1.06 (d, 2 ꢀ 3 H, 3JHH = 6.0
Hz, CH(CH3)2), 1.22, 1.25, 1.26, 1.50 (s, 4 ꢀ 9 H, C(CH)3), 1.38
(d, 2 ꢀ 3 H, 3JHH = 6.3 Hz, CH(CH03)2), 2.15 (AA0BB0, 1 ꢀ 2 H,
2JHH = 11.3 Hz, SCH2), 2.22 (AA0BB0, 1 ꢀ 2 H, 2JHH = 11.0
{1,4-Dithiabutanediylbis(4,6-di-tert-butylphenolato)}-
(trimethylsilylmethyl)indium(4). To a solution of 1,4-dithia-
butanediylbis(4,6-di-tert-butylphenol) (267 mg, 0.5 mmol) in 15
mL of toluene was added dropwise [In(CH2Si(CH3)3)3] (200 mg,
0.5 mmol) and stirred for 17 h at 60 °C. All volatiles were
removed in vacuo, and the residue washed twice with pentane to
give a white powder; yield 210 mg (60%); mp 139 °C. Crystals
2
Hz, SCH02), 2.97 (AA0BB0, 1 ꢀ 2 H, JHH = 11.3 Hz, CH2S),
3.09 (AA0BB0, 1 ꢀ 2 H, 2JHH = 11.3 Hz, CH02S), 4.59 (septet,
1 ꢀ 1 H, OCH), 4.77 (septet, 1 ꢀ 1 H, OCH0), 7.24 (d, 2 ꢀ
1 H, 3JHH = 2.5 Hz, Ph-50), 7.26 (d, 2 ꢀ 1 H, 3JHH = 2.5 Hz,
3
Ph-30), 7.28 (d, 2 ꢀ 1 H, JHH = 2.8 Hz, Ph-5), 7.36 (d, 2 ꢀ
1
were grown from a saturated toluene solution at -30 °C. H
1 H, 3JHH = 2.8 Hz, Ph-3). 13C{1H} NMR (100 MHz, THF-d8):
NMR: (400 MHz, C6D6): δ 0.20 (s, 1 ꢀ 11 H, CH2SiMe3), 1.31
(s, 2 ꢀ 9 H, 4-C(CH3)3), 1.69 (s, 2 ꢀ 9 H, 6-C(CH3)3), 2.12 (m, 1
ꢀ 2 H, SCH2), 2.36 (m, 1 ꢀ 2 H, CH2S), 7.31 (s, 2 ꢀ 1 H, Ph-3),
7.53 (s, 2 ꢀ 1 H, Ph-5). 13C{1H} NMR (128 MHz, C6D6):
δ 1.7 (Si(CH3)3), 29.8 (4-C(CH3)3), 31.7 (6-C(CH3)3), 34.2
0
δ 28.1 (CH(CH3)2), 28.3 (CH(CH3)2), 29.0 (CH(CH3 )2), 29.6
0
(CH(CH3 )2), 30.6 (C0(CH3)2), 30.9 (C(CH3)2), 31.3 (C0(CH3)2),
0
32.8 (C(CH3)2), 35.5 (SCH2), 35.6 (SCH2 ), 37.0 (SCH2),
37.2 (SCH2 ), 69.2 (OCH), 69.5 (OCH0), 127.3 (Ph-C3), 127.4
0
(Ph-C30), 128.3 (Ph-C5), 128.5 (Ph-C50), 128.9 (Ph-C2), 129.0
(Ph-C20), 138.5 (Ph-C4), 139.0 (Ph-C40), 139.7 (Ph-C6), 140.3
(Ph-C60), 163.6 (Ph-C1), 163.8 (Ph-C10). Anal. Calcd for
C33H51InO3S2: C, 58.74; H, 7.62. Found: C, 57.84; H, 7.43.
[1,4-Dithiabutanediylbis{4,6-di(2-phenyl-2-propyl)pheno-
lato}](isopropoxy)indium (7). A solution of “[In(OiPr)3]”
(300 mg, 1.027 mol) in 10 mL of benzene was treated with a
solution of 1,4-dithiabutanediylbis{4,6-di(2-phenyl-2-propyl)
phenol} (711 mg, 1.027 mol) in 10 mL of benzene. The red
solution was stirred at 70 °C for 1 h, and all volatiles were
removed under reduced pressure. The residue was washed
(19) (a) Chisholm, M. H.; Delbridge, E. E. New J. Chem. 2003, 27, 1167.
(b) Chisholm, M. H.; Eilerts, N. W. Chem. Commun. 1996, 853.
(20) Ma, H.; Spaniol, T. P.; Okuda, J. Inorg. Chem. 2008, 47, 3328.
(21) Knight, P. D.; Scott, P. Coord. Chem. Rev. 2003, 242, 125.
(22) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751.
(23) Ma, H.; Melillo, G.; Oliva, L.; Spaniol, T. P.; Englert, U.; Okuda, J.
J. Chem. Soc., Dalton Trans. 2005, 721.
(24) Centore, R.; Tuzi, A.; Capacchione, C.; Oliva, L. Acta Crystallogr.,
Sect. E 2006, 11, 2944.
::
(25) Okuda, J.; Moller, K.; Reimer, V. (BASF AG) DE 10309837 A1,
2004.

5534 Inorganic Chemistry, Vol. 48, No. 12, 2009
Peckermann et al.
several times with pentane to give a yellow powder (859 mg,
0.931 mmol, 91%); mp 212-214 °C. 1H NMR (400 MHz,
diffractometer with Mo KR radiation using ω-scans. Crystal
parameters and results of the structure refinements are given in
Table 1. Absorption corrections were carried out with the
multiscan method using Mulabs as implemented in the program
system PLATON.26 All structures were solved by direct meth-
ods (SIR-92)27 and refined (SHELXS-97)28 against all F2 data.
For the graphical representation, the Oak Ridge Thermal
Ellipsoid Plot (ORTEP) program was used as implied in the
program system WinGX.29 Crystallographic data (excluding
structure factors) have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
nos. CCDC 709983 (2), 709984 (4), 709985 (5), and 709986
(6). Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ,
U.K. (fax: (+44)1223-336-033. e-mail: deposit@ccdc.cam.ac.
uk or http://www.ccdc.cam.ac.uk).
3
C6H6): δ 1.01 (d, JHH = 6.0 Hz, 1 ꢀ 3 H, CH(CH3)2), 1.17
3
(d, JHH = 6.0 Hz, 1 ꢀ 3 H, CH(CH3)2), 1.49 (s, 1 ꢀ 6 H, 6-
cumyl-CH3), 1.58 (s, 2 ꢀ 6 H, 4-cumyl-CH3), 1.75 (s, 1 ꢀ 6 H, 4-
cumyl-CH3), 1.80 (AA0BB0, 2JHH = 11.3 Hz, 1 ꢀ 2 H, SCH2),
2
2.21 (AA0BB0, JHH = 11.3 Hz, 1 ꢀ 2 H, CH2S), 3.55 (septet,
3JHH = 6.0 Hz, 1 ꢀ 1 H, OCH), 6.93-7.03 (m, 12 H, Ph-H),
7.25-7.38 (m, 12 H, Ph-H). 13C{1H} NMR (128 MHz, toluene-
d8,): δ 25.4, 31.1, 31.2, 33.2 ((CH3)2Ph), 27.9, 29.3 (CH(CH3)2),
35.4 (SCH2), 124.9 (Ph-C2), 125.1 (Ph-C), 125.4 (Ph-C), 125.8
(Ph-C), 126.2 (Ph-C), 127.0 (Ph-C), 127.7 (Ph-C5), 127.8 (Ph-C),
128.0 (Ph-C), 128.2 (Ph-C), 128.6 (Ph-C), 128.8 (Ph-C5), 129.1
(Ph-C3), 129.5 (Ph-C4), 130.8 (Ph-C6), 151.4 (Ph-C), 151.9 (Ph-
C), 162.3 (Ph-C1). Anal. Calcd for C53H59InO3S2: C, 68.97; H,
6.44. Found: C, 68.71; H, 6.29.
Typical Polymerization Procedure. In a glovebox, 0.5 mL
of a stock solution of the initiator in toluene was injected
sequentially to an array of Schlenk tubes loaded with L-lactide
in 5.0 mL amount of dry solvent. After specified time inter-
vals, each solution was added via pipet to a cold methane
solution. All the volatiles were removed, and the residue
was subjected to monomer conversion determination which
was monitored by integration of monomer versus polymer
methine or methyl resonances in the 1H NMR spectra
(CDCl3, 200 MHz). The precipitates collected from the bulk
mixture were dried in air, dissolved in dichloromethane, and
sequentially precipitated into methanol. The obtained poly-
mer was further dried in a vacuum oven at 60 °C for 16 h and
analyzed by GPC.
Acknowledgment. We gratefully acknowledge the financial
support by the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie.
Supporting Information Available: Crystallographic data for
2, 4, 5, and 6 in a cif file; also, additional details are given in
Table S1 and Figures S1-S13. This material is available free of
charge via the Internet at http://pubs.acs.org
(26) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 1999.
(27) Altomare, A.; Burla, M. C.; Cavalli, M.; Cascarano, G. L.; Giacov-
azzo, C.; Gagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115.
(28) Sheldrick, G. M. SHELXL-97, A Program for Crystal Structure
::
::
Single Crystal X-ray Diffraction Studies. X-ray
diffraction measurements were performed on a Bruker AXS
Refinement; University of Gottingen: Gottingen, Germany, 1997.
(29) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.